FIELD OF THE INVENTION
[0001] This invention relates to a tow or bundle of copper coated fibers, to a method for
producing such tows, and to composites produced from such fiber tows. The coated fibers
of this invention may be used in a number of ways. Tows or fibers can be chopped and
used as a radar obscuration chaff for example. Tows can also be incorporated into
composites with various matrices. Composites using copper coated fibers can have the
advantages of copper, such as high electrical and thermal conductivity, and can overcome
some of the deficient properties of copper such as its high density and high coefficient
of thermal expansion.
BACKGROUND OF THE INVENTION
[0002] The prior art describes fibers coated with metal and composites produced therefrom.
For example, in commonly assigned, U.S. Application of Morin, Serial No. 650,583,
filed September 12, 1984, and now allowed, graphite and other semimetallic fibers
coated with thin, uniform and firmly adherent electrically conductive layers of metals,
including nickel and copper are described. In Morin, Serial No. 507,603, filed June
24, 1986, now allowed, their use in metal composites is described. In Iwaskow and
Crum, Serial No. 358,549, filed March 16, 1982, their use in polymeric composites
is described. In Morin, Serial No. 630,709, filed July 13, 1984, now allowed, their
use in radar reflecting chaff is described. In Luxon, Serial No. 869,518, filed June
2, 1986, their use in elongated injection molding granules is described. However,
such coatings, while uniform and firmly adherent and electrically conductive, are
relatively thin being of the order of 0.25 to 1.0 microns, more normally 0.5 microns
in thickness. As such, they do not render themselves useful in certain applications,
particularly as starting materials for direct consolidation into composites. It would
be desirable to produce such fibers being uniformly and somewhat more relatively thickly.
[0003] Other prior art, however, which describes thicker coatings, do not have good uniformity
of coating thickness either around the fiber circumference, from fiber to fiber throughout
the tow, or along the length of the tow. Some prior art materials have heavily coated
fibers on the outside of the tow while inner fibers remain uncoated. Other prior art
materials contain fibers which are plated together in groups leaving a deficiency
of copper in the inside of each agglomerate.
[0004] Generally, such features are disadvantageous because they give uneven or irregular
properties to any material made from them. In particular, if copper coated fibers
are formed into copper matrix composites by consolidating under heat and pressure,
a lack of uniformity of the coating thickness will result in an irregular distribution
of the base fiber throughout the resulting copper matrix. The presence of uncoated
fibers and agglomerates of fibers leads to voids in the matrix in such a composite.
Such an uneven distribution of fibers and voids cause poor mechanical properties
as well as uneven thermal or electrical conductivity. Agglomerations of fibers can
also cause the tow of fibers to be difficult to spread and can thereby make difficult
the production of thin composites. In addition, the presence of agglomerations can
make the tow of fibers less flexible and so make production of filament wound or woven
materials difficult.
[0005] Among the prior art proposals to produce copper coated fibers, in particular copper
coated carbon fibers, electrolytic plating, electroless plating, a combination of
electroless followed by electrolytic plating, cementation, and ion plating have all
been tried.
[0006] As to electrolytic deposition, B.W. Howlett
et al. (
Proceedings of the International Conference organized by The Plastics Institute, Unwin Bros., Ltd., Surrey, February 1971, pp. 99-106) states that "a very satisfactory
method has been developed for the continuous electro-deposition...of copper ...onto
tows containing 1000 fibers". The method is only described as electrolytic deposition
via an "experimentally formulated cyanate solution". However, their photographs of
the fibers show very uneven thicknesses of coating from fiber to fiber, as well as
around the circumference of the fibers. Generally, the literature teaches that direct
electrolytic deposition of copper gives rough, uneven coatings. For example, M. Sakai
et al.,
Japan Institute of Metals Journal,
43 181-189, 1979 found "extremely severe hills and valleys in the surface of the electrocrystallized
copper" when a copper sulfate (200 g/l), sulfuric acid (60 g/l) plating solution was
used. An accompanying photograph shows that the coating thickness varies from fiber
to fiber as well. Japanese Patent Disclosure No. 1985-SHOWA 60-17,095 found that in
carbon fiber tows plated from a copper sulfate plating bath, that "knitting is difficult
because of poor slidability due to the roughness of the copper-plating layer". The
patent reports an improvement in slidability when a commercially prepared brightner,
UBAC-1, and chloride ions were added to the plating solution. However, no documentation
of the coating structure is provided, and when repeated herein, unsuitable coatings
were obtained as shown in the comparative examples to follow.
[0007] As to electroless deposition, attempts to coat carbon fibers with copper using an
electroless copper plating process is reported by several workers. Some reports are
vague and insufficiently detailed, for example U.S. Patent 3,550,247 states that "a
large bundle of fibers may be coated with metal substantially uniformly", but does
not give a specific procedure for plating copper. A report by N.C.W. Judd (
Composites, Dec. 1970, p.345) used a proprietary electroless solution to deposit copper onto
carbon fibers, but poor coating was obtained. It was stated that "coverage of the
fibers at the center of the tow was not achieved." Other reports have used electroless
plating to coat carbon fibers with copper. V.N. Sakovich
et al. (
Fiz. Khim. Obrab. Mater. 1975(2) 112-115 (1975)) precipitated copper by treating the fiber surfaces with boiling
water, stannous chloride solution, and palladous chloride solution. Then "a number
of electrolytes in which formaldehyde solution was used as a reducing agent were tested".
They report that "a bright coating, uniform in thickness on all fibers of the tow,
was obtained from the following electrolyte:
A:170 g/l Seignette salt (potassium sodium tartrate), 50 g/l sodium hydroxide, 30 g/l
sodium carbonate;
B: 40 percent formaldehyde solution;
A:
B = 5:1 (ph 12.3, temperature 20C)". It was reported that "the average precipitation
rate of the coating was 0.03 micron/minute for a charge density of the electrolyte
of 0.6 dm ²/l. When repeated herein, the coating produced was poor as will be shown.
German (Federal Republic of Germany) patent 2,658,234 describes a process "for coating
individual fibers of a bundle, in which the fiber bundle is exposed to a reaction
solution from which, by a currentless chemical means, a substance is deposited onto
the fiber." In order to assure individualization of the fibers of the tow, "a portion
of the fiber bundle is loosely suspended, and ... the reaction solution is fed along
the fibers of this portion". It is stated that "Because of the spreading of the fibers,
the reaction solution can reach the surfaces of all the fibers. The fibers can thus
be uniformly coated over both their length and their cross section". In one sample
embodiment, it is reported that "it is possible...to uniformly deposit a 1 micron
copper layer on the individual fibers of the bundle". However, when repeated herein,
unsuitable coatings were produced as will be shown in the comparative examples.
[0008] As to a cementation process, B.C. Pai
et al. (
Journal of Materials Science, Letters, 15 1860-1863 (1980)) reported on the use of a cementation process to deposit copper
and other metals on carbon fibers. It was disclosed that whereas nickel and cobalt
coat the fibers uniformly, "copper coating takes place by bridging...isolated precipitates".
Figures 3 through 7 in this reference show irregular thickness copper coatings.
[0009] As to ion plating or vacuum deposition, the prior art discloses the use of ion plating
or vacuum deposition to form "an assembly...of a plurality of carbon fibers each coated
with a matrix metal layer, the fibers having bonded points at the metal layers". This
process does not form individualized fibers. Japanese patent disclosure number 1982-SHOWA
57-57,851 discloses use of ion plating to coat fabrics of carbon fibers. However,
the goal of this process is not to form individualized fibers as the present invention
requires and forms.
[0010] As to electroless followed by electrolytic deposition, A.M. Kuz'min
et al. (USSR Patent No. 489,585, and
Fiz. Khim. Obrab. Mater.,
1975(5) 101-106) reported carbon fiber tows coated with copper prepared by depositing
a layer of copper using an electroless process and subsequently depositing further
copper electrolytically. It was stated that the process gives a material in which
"all elementary fibers are covered with a uniform layer of metal in the process of
chemical precipitation...the filling with metal during the electrolytic build-up of
the layer also proceeds uniformly". When repeated herein, however, uniform layers
were not obtained. U.S. Patent No. 3,495,940 discloses a process "comprising the
steps of (1) forming thin films of sensitizing and activating metals on the surface
of an organic fiber, (2) electrolessly plating a thin layer of copper on the activated
surface, (3) electrodepositing additional copper on top of said copper layer". The
process was used to form copper coatings comprising 10 to 50% by weight of said organic
fiber. This is a coating thickness of only 0.048 to 0.24 microns for an organic fiber
having a density of 1.25 g/cm², too thin to provide the advantages of the relatively
thick copper coatings required herein. The patentee, moreover, used this fiber to
electrically heat the organic fiber to the point that the fiber carbonizes and graphitizes
to a carbon fiber. Since such processes reduce the volume of the basic fiber, the
carbon fiber is not attached to the metal coating. No discussion was included concerning
the way in which the fiber tow was handled. Japanese Patent Publication No. 1984-59
SHOWA-53640 discloses "compound plating, which is a combination of electroless plating
and electroplating". In this method, the carbon fibers are held under tension on a
frame and then coated. The object of the process was to produce a "prepreg" of copper
and carbon fibers and not to produce individualized coated fibers. Composites produced
by hot pressing the prepregs were unsuitable because they had non-uniform distributions
of fibers as evidenced by photographs of cross sections presented therein. Kuz'min,
cited above, used a process of air oxidation or nitric acid etching, followed by electroless
plating, and then electrolytic plating. While the bath components are given, no specific
bath formulation is given. In addition, no fiber handling techniques are noted. EPO
0-156-432 discloses the coating of single optical fibers with a combination of electroless
followed by electrolytic plating. "In a favorable embodiment...the fiber...is electroless
plated continuously in a first step and is electroplated continuously with a metal
layer in a second step....the fiber is passed successively through a number of deposition
baths alternated by rinsing baths....In a particularly advantageous embodiment ...a
layer of metal is provided continuously by electrodeposition on the electrically
conductive layer in at least two successive steps, in which between the successive
steps the current density is increased and the metal-coated fiber is electrically
contacted". No plating of copper is actually exemplified.
[0011] Also disclosed in the prior art, are composites that have a copper matrix reinforced
with fibers, these having been formed by a number of techniques. For example, tows
of reinforcing fibers can be impregnated with a slurry of copper powder and then consolidated
under heat and pressure. Sometimes this process may involve sandwiching the fibers
between copper foils. Such methods, however, have several disadvantages. Since copper
does not spontaneously wet some fibers, especially carbon fibers, additives, for example,
titanium, must be provided in the copper to permit wetting. However, such additives
reduce the thermal and electrical conductivity of pure copper. Such composites also
have unevenly distributed reinforcing fibers.
[0012] To avoid having to wet the carbon fiber with liquid copper it is advantageous to
coat the fibers with copper individually and consolidate the coated fibers under heat
and pressure. This general procedure has been used by a number of workers. However,
since the ability to coat all the fibers of a tow uniformly has been limited, it has
not been possible until the present invention to create uniform distribution of reinforcing
fibers in a copper matrix composite. In addition, it is not uncommon for hot pressing
to be done at very high temperatures (around 900°C) which can cause dewetting of a
copper coating from a carbon fiber and lead to defects at the copper/carbon interface.
The present invention avoids this drawback, too.
SUMMARY OF THE INVENTION
[0013] An object of this invention is provide tows of fibers that are uniformly coated with
copper which are useful as reinforcing fibers or as fillers in composites that require
high thermal or electrical conductivity. Such tows of fibers can be used as "free"
fibers (as compared to fibers embedded in a matrix). For example, the fiber can be
chopped and used as chaff, or it can be used as conductive brushes.
[0014] Another object of this invention is to provide a process by which fibers may be coated
uniformly with copper.
[0015] A further object of this invention is provide copper matrix composite materials that
are useful as materials for low density radiators, low thermal expansion electrical
conductors, and other applications.
[0016] According to one aspect of this invention, there are provided yarns and tows comprising
composite fibers, which have a core and at least one relatively thick, uniform and
firmly adherent, electrically conductive layer comprising copper on said core.
[0017] According to another aspect of the invention, such tows of composite fibers are produced
by a process comprising (1) immersing at least a portion of the length of the fiber
in a bath of an aqueous solution of a wetting agent, (2) sensitizing the fiber surface
to the electroless deposition of a metal comprising copper by immersion in a bath
of a colloidal suspension of palladium and tin chloride, (3) immersion in a bath capable
of electrolessly plating the fibers with a metal comprising copper and depositing
an electrical conductive layer of metal on said fibers, (4) immersion in a bath capable
of electrolytically plating with a metal comprising copper, and (5) applying an external
voltage between the fibers and the bath sufficient to deposit a metal comprising
copper on the fibers, the voltage and resulting current to be applied for a time sufficient
to produce a relatively thick, uniform and firmly adherent coating comprising copper
on said core. These steps must be carried out under low tension and with spreading
of the tow.
[0018] Such fiber can be used as "free" fiber or, according to still another aspect of
the invention, it can be formed into composites comprising a continuous yarn or tow
of composite fibers, the majority of which have a core and at least one relatively
thick, uniform and firmly adherent electrically conductive layer comprising copper
on said core, disposed in a matrix comprising a metal or an organic poly mer. These
matrices can be formed by incorporation, by direct consolidation by hot pressing or
other methods. In the latter case, the composites obtained have a uniform distribution
of fibers throughout.
[0019] According to yet another aspect of the invention, an injection molding compound comprising
elongated granules containing a bundle of elongated composite fibers can be produced.
Said fibers have a core and at least one relatively thick, uniform and firmly adherent,
electrically conductive layer comprising copper on said core, such fibers extending
generally parallel to each other, lengthwise in the granule and uniformly dispersed
throughout the granule in a thermally stable, film forming thermoplastic adhesive.
DESCRIPTION OF THE DRAWINGS
[0020]
FIGURE 1 is a schematic view of the plating process in the present invention.
FIGURE 2 is a perspective view of the weired plating tank preferred for use in the
present invention.
FIGURE 3a is a top plan view of a beater bar arrangement preferred for use in the
present invention.
FIGURE 3b is an elevational plan view of the beater bar arrangement of FIGURE 3a.
FIGURE 4 is a schematic view of a hot press apparatus suitable for use in the present
invention.
FIGURE 5a is a semi-schematic view of a process for making the elongated molding pellets
of the present invention.
FIGURE 5b is a semi-schematic view of a way in which the elongated granules of the
present invention are mixed and molded into shaped articles.
FIGURE 6 is a cross-sectioned view of the copper coated fibers of the present invention
in a resin matrix, cut perpendicular to the length of the fibers.
FIGURE 7 is a schematic view of a fiber plating apparatus used in the electroless
deposition of metal under Schmitt, German Pat. No. 2,658,234.
FIGURE 8 is a cross-sectional view of an electro-plating tank commonly used in the
art.
FIGURE 9 is a schematic view of a hot press apparatus suitable for use in the present
invention.
FIGURE 10 is a cross-sectional view of copper coated fibers of Schmitt, German Pat.
No. 2,658,234, in a resin matrix, cut perpendicular to the length of the fibers.
FIGURE 11 is a cross-sectional view of copper coated fibers of Sakovich, et al.
FIGURE 12 is a cross-sectional view of copper coated fibers of Kuz'min, USSR Patent
No. 489,585 in a resin matrix, cut perpendicular to the fibers.
FIGURE 13 is a cross-sectional view of copper coated fibers of Yashioka et al., Japanese
Pat. No. 70-17095 in a resin matrix cut perpendicular to the fibers.
FIGURE 14 is a cross-sectional view of consolidated copper coated fibers of Schmitt,
German Pat. No. 2,658,234 cut perpendicular to the fiber length.
FIGURE 15 is a cross-sectional view of consolidated copper coated fibers of Sakovich
et al. cut perpendicular to the fiber length.
FIGURE 16 is a cross-sectional view of consolidated copper coated fibers of Kuz'min,
USSR Pat. No. 439,585, cut perpendicular to the fiber length.
FIGURE 17 is a cross-sectional view of consolidated copper coated fibers of the present
invention in a uniaxial configuration cut perpendicular to the fiber length.
FIGURE 18 is a cross-sectional view of consolidated copper coated fibers of the present
invention in a cross-plied configuration.
DETAILED DESCRIPTION OF THE INVENTION
[0021] With respect to the first two aspects of the invention, the fibers and processes
for their preparation, the fundamental improvement of the present invention over the
prior art is to provide tows of fibers containing as many as 12,000 (12K) fibers that
are coated with copper. The present invention provides tows in which the copper coating
is distributed very uniformly over the fibers of the tow. The fibers of this invention
may have a coating thickness of between about 0.5 microns and about 3.0 microns of
copper, preferably from about 0.6 microns to about 3.0 microns, especially preferably,
greater than at least about 0.8 microns, and most preferably, greater than at least
about 1.2 microns. The coating thickness is uniform around the circumference of the
fiber, having a standard deviation in thickness that is no more than 30% of the average
thickness. It is also uniform from fiber to fiber, having a standard deviation in
thicknesses that is less than 30% of the average thickness. In addition, the fibers
have a low degree of agglomeration. In the present invention, typically 80% of the
fibers of the tow are present as individually coated fibers. As a result of the low
agglomeration in the fiber tows of this invention, the tows are flexible and slidable.
Furthermore, the copper coating of this invention can be very pure. This means that
the highest thermal and electrical conductivities can be obtained.
[0022] The base fibers of this invention include carbon, graphite, polymeric, glass or ceramic
fibers. The choice of base fiber will depend on the nature of the application envisioned
for the coated fiber. Structural carbon fibers, such as those produced from polyacrylonitrile
(PAN), having moduli in the range of 30 to 50 x 10⁶ pounds per square inch (psi),
would be selected for applications where moderate strain to failure in the composite
were needed. Graphite fibers such as those produced from pitch that have moduli from
55 to 140 x 10⁶ psi might be used where very high thermal or electrical conductivity
or very low thermal expansion were required. Ceramic fibers having a high diameter
might be used in applications where compression strength were needed. Other criteria
will be evident to those familiar with the design of composite materials.
[0023] The process of this invention, as diagrammed in FIGURE 1, has several novel and useful
characteristics. The process of this invention employs a conventional composition
for the electroless bath, but includes preferred features to provide stability, speed
of plating and uniformity of coating on the individual fibers throughout the tow.
The coating process provides a uniform product in either a batch or continuous process,
with good rates of production and good stability of the component solutions.
[0024] The continuous version of the process uses features designed to give very little
tension to the fiber tow and spread the tow. Damage to the fiber is reduced preferably
by using a "straight through" design in which the fiber travels an essentially straight
path through the plating line. This enables very low strain-to-failure fibers such
as pitch based carbon fiber (e.g., Amoco Inc.'s P100 and P120 fibers) to survive the
rigors of a continuous plating process.
[0025] Preferably, and with reference to FIGURE 1, the copper coating process of the invention
comprises the following steps taken in order:
(i) Wet with an aqueous surfactant solution
(ii) Rinse
(iii) Sensitize in a colloidal suspension of tin and palladous chloride
(iv) Rinse
(v) Coat with a layer of electroless copper
(vi) Rinse
(vii) Coat with a layer or layers of electrolytic copper in baths having varying current
densities
(viii) Rinse
(ix) Dry
[0026] Rinsing steps (ii), (iv), (vi) and (viii) are optional.
[0027] As to step (i), the need for an electroless copper solution with high deposition
rates requires the use of a formaldehyde reduced bath. Although higher rates were
obtained with this bath, the tows had poor through-plating resulting in uncoated
inner filaments. To overcome this, a wetting agent suitable for carbon surfaces should
be used to allow for better penetration into the tow and adsorption of catalyst. Among
the suitable agents are Arquad® B-100, a surfactant made by Armak Chemicals (a division
of Akzo Chemie America, Chicago, Illinois). It can be used at concentrations of 0.1
to 1.0% in water, although higher and lower concentrations are also possible. When
used to wet carbon fiber bundles, uniform electroless plating of every filament in
a 12K tow can be obtained. Such fibers are then easily electroplated in an electrolytic
plating bath such as an acidic copper plating bath. Such copper coated carbon fibers
produced by a batch process are suitable for use to create copper matrix composites
as will be exemplified hereinafter. The electroless solution can also contain other
additives. For example, 1 ppm of mercaptobenzothiozole (MBT) can be included to provide
stability to the bath. In addition, the sensitizer solution (iii) can also be improved
in stability by omitting urea which is commonly used. These preferred features result
in more stable sensitizing and electroless baths with high deposition rates. Special
mention is made of the use of a combination of 2,2ʹ-dipyridyl and mercaptobenzothiazole.
This further improves stability of the electroless bath while maintaining a high
rate of deposition. Such solutions can be replenished with copper sulfate, formaldehyde
and NaOH and used over several days, which is a substantial advantage.
[0028] Although conventional acidic copper electroplating solutions deposit copper onto
the electroless copper layer in step (vii), the deposits can be dull, or rough or
tend to oxidize soon after plating. In a preferred feature of this invention, the
acidic copper solution will be replaced with a pyrophosphate copper plating solution,
which results in brighter deposits that do not oxidize as rapidly as those from the
more conventional acidic solutions. Acidic copper plating solutions also have a drawback
in the possible dissolution of the thin electroless copper layer on the fiber by the
presence of strong acid in the plating solution. If the fiber is made cathodic before
entering the solution, such difficulties are minimized.
[0029] In any event, unless careful attention is paid to tow tension, plating can be very
poor, especially on the central filaments of the fiber tow when high tension is placed
on the fiber. This is avoided if the fiber has little or no tension. In preferred
embodiments of a continuous coating process, all tension will be removed. This results
in all fibers being well plated. Further details of the preferred processes, both
batch and continuous, will be given in the Examples.
[0030] With respect to the solutions used, a preferred wetting agent bath (Bath 1) is preferably
1 ml. of Arquad® B-100 surfactant per liter of deionized water. Arquad® B-100 is a
cationic, surface active, water soluble benzylalkylammonium chloride. It is a 49%
solution of alkyl dimethyl ammonium chloride with alkyl groups derived from fatty
acids, with a typical molecular surfactant not only modifies the surface energy of
the fiber so that it is easily wet by aqueous solutions, but it also enhances the
adsorption of the tin and palladium used as sensitizers on the fiber surface.
[0031] A preferred sensitizing bath (Bath 2) comprises:
1 g. PdCl₂ dissolved in 500 ml. deionized H₂O;
300 ml. HCl - 35% hydrochloric acid carefully added to palladium chloride solution
while stirring;
1.5 g. SNCl₄ dissolved in 100 ml. of 35% HCl acid then added to the above solution
Heat to 80 deg. C then add
37.5 g. SnCl₂ and
Deionized water to 1 liter total volume then cool to room temperature and hold for
16 hours.
[0032] The catalyst is a mixed system and is similar to available commercial formulations.
It is preferred herein, however, not to use sodium chloride in the sensitizing bath,
although commercial catalysts containing large amounts of sodium chloride can be used.
A suitable electroless copper bath (Bath 3) comprises:
19 g. CuSO₄*5H₂O dissolved in 750 ml. deionized H₂O then add while stirring add the
following:
31.6 g EDTA disodium salt, dihydrate (ethylene diamine tetraacetic acid)
2 ml. MBT (mercaptobenzothiozole) solution at 0.5g of MBT per liter methanol
16 g. NaOH dissolved in 100 ml. of deionized H₂O heat copper solution to 45 deg C
and immediately before use add
15 ml. formaldehyde
Water to make one liter
[0033] Another suitable and especially preferred electroless copper bath (Bath 4) comprises:
10 g. CuSO₄*5H₂O dissolved in 750 ml. deionized H₂O then, while stirring, add the
following:
30 g. EDTA disodium salt , dihydrate (ethylene diamine tetraacetic acid)
0.5 ml. MBT (mercaptobenzothiozole) solution at 0.5 g of MBT per liter methanol
2 ml. of 2,2ʹ dipyridyl (DP) solution at 2g/100 ml methanol 10 g. NaOH dissolved in
100 ml. of deionized H₂O
Water to 0.990 liter
Heat to 45 deg C and immediately before use add: 10 ml. formaldehyde
Final pH should be 11.3
[0034] In the above electroless copper plating solutions the copper sulfate is the source
of the copper ions, EDTA salts act as a chelating agent, DP and MBT are stabilizers,
and sodium hydroxide is used to bring the solution a high pH, e.g., 11.3-12.2, formaldehyde
will act as a reducing agent at a good rate.
[0035] A suitable electroplating bath (Bath 5) comprises: UNICHROME® Pyrophosphate Copper
Plating Process; Technical Information Sheet No. P-C-10-Xb; and employs the following
to make 10 gals. of solution (M&T Chemicals Inc., Rahway, NJ): To 5 gal. of deionized
water, add in order the following while stirring:
0.35 gal. M&T Liquid C-11-Xb;
3.33 gal. M&T Liquid C-10-Xb copper pyrophosphate-containing solution; and
0.05 gal. Ammonium hydroxide, C.P.
Fill to total volume of 10 gal. with deionized water. Bath should be operated at 54.5°C
and a pH of 8.3 ± 0.2. A brightner M&T Addition Agent PY-61-H (0.9 ml/l) can be added
if additional brightness is desired.
[0036] Other suitable baths are in the literature (Lowenheim).
[0037] If a batch process is to be used, it is convenient to use 40 inch long cut sections
of tow and a glass weight placed halfway along the tow. The tow is then lowered into
suitable vessles, e.g., 1 liter graduate cylinders containing the various baths, to
provide that the weight rests on the bottom of the cylinder. In this way the fibers
in the tows remain aligned.
[0038] If a continuous process is to be used for the uniform plating of fibers with copper
it is convenient to operate as follows:
[0039] Referring to FIGURE 1, an apparatus for this process can be seen. The tanks of the
apparatus, which hold the various solutions, are designed to allow the fiber to be
treated with each solution without going over or under rollers which would increase
the amount of tension on the fiber. This method of plating is termed line-of-sight
plating. FIGURE 2 shows such tanks which use a "weired" design, so called because
a weir or overflow is created at the exits of the tank. Using such tanks, the fiber
can be passed through a series of baths without having to go around a series of rollers
or guides after the initial unspooling. It is possible to run several tows in parallel
through the apparatus. For example, eight tows can be plated at a time, or even more.
[0040] For feeding, spools of uncoated fiber (not shown) can be supported on bearings which
allow the fiber to be unspooled while creating very little tension. The fiber tows
are then threaded through eyelets (not shown) which guide the fiber into the first
bath (FIG. 2). As shown in FIGURE 1, the first bath contains a wetting agent, e.g.,
Arquad® B-100 in a 0.1 vol. % solution in the top tank, as shown in FIGURE 2. Filtration
of the solution, which is performed by in-line filters, is very desirable to keep
all solutions free of an accumulation of broken fibers.
[0041] Next, the fiber is then passed through an optional rinse station, desirably to remove
any excess surfactant or "drag-through" which can influence the chemistry of succeeding
baths. A suitable rinse station consists of a table over which the fiber runs, and
a water spray directed downward onto this table. The force of the water spray and
subsequent run-off the edges of the "table" help to spread the fiber.
[0042] The second tank in the series contains a catalyst bath, such as an emulsion of palladous
chloride and stannous chloride in a hydrochloric acid solution (Bath 2). This solution
serves to activate the surface of the fiber for the electroless deposition of copper.
The bath is circulated with a resevoir tank to maintain the concentration of the components.
The fiber is again optionally, but preferably, rinsed after leaving this tank. This
rinse is very desirable because drag-out to the following electroless plating tank
may severely limit the life and efficiency of the electroless plating solution.
[0043] As is shown in FIGURE 1, the third bath is in a long tank, to provide a sufficient
residence time for elec- for electroless plating. The bath contains an electroless
copper plating solution, such as given for Bath 3 or 4, above. The bath temperature
is maintained in a resevoir tank from which the solution is pumped, as shown in FIGURE
2. The heated solution is then pumped into the inner tank of the weired plating tank
arrangement. Preferably, the pH of the solution is maintained at 11.3, ± 0.5. In accordance
with known techniques, stability of the bath is increased by aerating the bath by
rapid pumping, stirring or sparging with a gas dispersion tube. Rapid solution flow
also helps in replenishing solution near the fiber in order to increase the depostion
rate of the copper. The fiber optionally is again rinsed as before.
[0044] Electrolytic plating next is performed in a series of weired tanks all of which are
of suitable length, e.g., 20 inches. The plating line may have multiple tanks, e.g.,
2, 3, 4, or more, and these many have different current densities. For example, the
initial electroplating tank can be run with a current of 8 amperes using 8 tows of
2K fiber. Using a low current in the first tanks permits an initial deposition of
an electrolytic layer of copper over the electroless copper. The remaining tanks can
be operated at currents of 20 to 30 amperes. This facilitates more rapid plating in
any of the remaining tanks. As will be described, spreading the tow of fibers apart
in each of these tanks is crucial to the even plating of the fiber and avoiding the
creation of agglomerates. Solution agitation, such as by pumping from a resevoir,
and oscillation resulting from the use a fiber spreading device permits the current
to be increased without evidence of hydrogen evolution, a symptom of overvoltages
in the plating operation, demonstrating that such agitation results in more efficient
plating.
[0045] Spreading of the fiber in the electrolytic tanks in accordance with this invention
can be carried out in many ways, for example, by use of ultrasonic vibration, agitation
of the solution or by physically spreading the fiber. A preferred method uses physically
spreading the fibers. Especially preferred is to use beater bars to spread the fibers.
A suitable beater bar arrangement can be seen in FIGURE 3. The "L"-shaped bar is oscillated
vertically. This agitates the solution, forces fresh solution into the tow of fibers,
and spreads the fibers of the tow. The movement of fresh solution into the filaments
of the tow increases the deposition rate and ensures uniformity of plating. The stationary
bars at either end of the tank help to keep the fiber under solution and also keep
the fiber spread out when leaving the plating tank. A 12K tow of IM-6 fiber can spread
to almost 1 inch wide by the time it reaches the final plating tank. This spreading
keeps the fibers from plating together at neighboring filaments and increases the
rate of plating by increasing the mass transfer of solution into the tow.
[0046] After the fiber has been plated to a sufficient volume fraction of copper, the fiber
optionally but preferably is rinsed as described above and then dried by means of
an air knife, heat gun or rotary drum drier. In this case a heat gun is attached to
a heating chamber (not shown). The fiber is then spooled, either onto a spool with
other tows or preferably individually onto separate spools by a fiber winder (e.g.,
graphite fiber winders made by Leesona Corp., South Carolina) (not shown).
[0047] Chaff according to the present invention is prepared by chopping strands of copper
coated composite fibers as described above into lengths designed to effectively reflect
impinging radar waves. Preferably, the fibers are cut to a length roughly one-half
the wavelength of the radar frequency the chaff is intended to be used against or,
where very high radar frequencies are encountered, full wavelengths.
[0048] In practice, a radar operator may be monitoring several frequencies, currently in
the 2-20 GHz range. In the future, radars may be developed using much higher frequencies.
An advantage of the chaff of the present invention is that it can be adapted to the
present and contemplated radar frequencies. Therefore, while present strategic chaffs
may contain different lengths of filament ranging from several centimeters and shorter
(e.g.,0.01-10 cm), corresponding to the half wavelengths (or full wavelengths) over
an entire bandwidth, the range that may be achieved with the chaff of this invention
is from 100 microns to hundreds of meters, depending on the specific use contemplated.
However, if the particular impinging frequency to be defended against is known, the
chaff may be "tuned" by increasing the proportion of chaff dipoles reflecting that
particular frequency, and many more dipoles per unit volume of chaff may be dispersed.
[0049] Chaff prepared in accordance with the present invention is highly efficient in comparison
with previously known chaff materials because the coating is continuous and of high
purity.
[0050] In addition, due to the core material, the chaff fibers are much stiffer than prior
materials, which facilitates dispersion. This ensures that the dipole length will
remain tuned to the object radar frequency.
[0051] The dispersibility of the chaff may be assisted by further treatment of the fibers
before chopping into strands to make them mutually repellant, or at least non-adhesive.
For example, rinsing the coated fiber with a solution to change the surface qualities
of the chaff dipoles is a typical method. In the case of the preferred embodiments
of this invention, e.g., copper coated carbon fibers, sizing the coated fiber with
a solution of oleamide in 1,1,1-trichloroethane (e.g., about 10 g/l) should provide
a hydrophobic and slippery surface and greatly aid dispersion of the chaff. After
the sizing dries and fuses, the plated, sized tow of fibers is typically pulled through
a series of rollers or rods ("breaker bars") to break apart fibers stuck together
by the sizing. This also is a means of maintaining collimation of the fibers. Other
rinses or sizings, as well as other treatments to aid chaff dispersion, will be readily
apparent to persons skilled in the art and are fully contemplated herein.
[0052] When broad band reflection is desired a certain amount of contact between individual
chaff dipoles may be advantageous. Because contact between two chaff dipoles according
to the present invention creates an effective longer dipole, controlled contact provides
larger dipoles that respond at different frequencies as the chaff disperses and the
individual dipoles separate. This is another method of "tuning" the chaff to the radar,
made possible by the present invention. Also, core fibers such as graphite fiber are
available in various shapes, e.g., X or Y shapes, permitting multilobal radar reflection.
A further advantage of the composite fiber chaff herein is its low bulk density.
[0053] The small comparative diameters of fibers contemplated herein permit chopping to
very short lengths, e.g., 100 microns, so as to be effective against super high frequency
radars. Also, broad band reflection is within the scope of the present invention.
[0054] A variety of types of composites of the invention can be produced using the fibers
having a copper coating thereon as described above. Methods for incorporating such
fibers into polymeric and metallic matrices are contemplated. The methods include
directly consolidating the copper coated fiber of this invention so that the coating
becomes the matrix. Simply by hot pressing, for example, between 600°C and 900°C,
most preferably between 725°C and 750°C, in a reducing atmosphere or a vacuum the
fibers of this invention can be consolidated to form substantially void-free, uniform
composites.
[0055] The fibers of this invention can be fabricated into composites by direct consolidation
also by "laying up" the fibers. To do so, the fibers are aligned into single layer
tow, which optionally may be held together by a fugitive binder or merely the capillary
action of water. These layers are then stacked by either keeping the layers aligned
in parallel or by changing the angle between adjacent layers to obtain a "cross-plied"
laminate. Since the physical properties of the composite and fiber are anisotropic,
a range of properties can be achieved by changing the orientation of the various layers
of the composite.
[0056] Because the coated fibers of this invention have few agglomerations, it is possible
to spread the fiber into very thin plies, as low as 3 mils. Thin plies are an advantage
when large area structures are to be built, such as radiator structures. In such an
application, the composite should be as thin as possible, yet to obtain sufficient
stiffness in all directions, several layers, having several orientations, are required.
Therefore, the thinner each ply is, the thinner the final, multi-layered composite
can be. By making thinner structures, substantial weight savings can be effected which
is crucial in any aerospace or transportation application.
[0057] Composites produced by direct consolidation of the fibers of this invention have
the advantage that the copper remains in intimate contact with the fibers during hot
pressing. This is possible because the carbon fibers are coated with copper by the
plating process and are consolidated at relatively low temperatures (e.g, 750°C).
This assures that dewetting does not occur during consolidation of the fibers into
the composite. The composites of this invention also have the advantage that they
have a very uniform distribution of the base fiber throughout the thickness without
undesirable matrix-rich regions. In addition, the void content of the composites
is low because of the uniformity of coatings and low agglomeration rate of the starting
coated fiber. Also, the purity of the copper matrix can be very high. The very low
agglomeration of the fibers of this invention makes possible thin copper matrix composites,
filament wound composites, braided composites and woven composites. The composites
of this invention have good mechanical properties due to their uniformity, and good
thermal and electrical properties due to the purity of the copper component of the
composite.
[0058] As the comparative examples will show, none of the fibers produced in the closest
prior art, in spite of their descriptions, will meet the characteristics of the fibers
herein or produce composites like those provided herein.
[0059] The organic polymeric materials for use as matrices in the composites of the invention
are numerous and generally any known polymeric material may find application. By way
of illustration, some of the known polymeric materials useful in the invention include:
polyesters, polyethers, polycarbonates, epoxies, phenolics, epoxy-novolacs, epoxy-polyurethanes,
urea-type resins, phenol-formaldehyde resins, melamine resins, melamine thiourea
resins, urea-aldehyde resins, alkyd resins, polysulfide resins, vinyl organic prepolymers,
multifunctional vinyl ethers, cyclic ethers, cyclic esters, polycarbonate-co-esters,
polycarbonate-co-silicones, polyetheresters, polyimides, bismalemides, polyamides,
polyetherimides, polyamideimides, polyetherimides, and polyvinyl chlorides. The polymeric
material may be present alone or in combination with copolymers, and compatible polymeric
blends may also be used. In short, any conventional polymeric material may be selected
and the particular polymer chosen is generally not critical to the invention. The
polymeric material should, when combined with the composite fibers, be convertible
by heat or light, alone or in combination with catalysts, accelerators, cross-linking
agents, etc., to form the components of the invention.
[0060] The electrically conductive composite fibers used in the invention are shown in Fig.
6 in a cross-section of composite fibers in an epoxy resin matrix. Each composite
fiber comprises a core shown in black circles and at least one relatively thick, uniform
and firmly adherent, electrically and/or thermally conductive layer of copper, shown
in white rings. The core may be made of carbon, graphite, a polymer, glass, a ceramic,
or other fibers although carbon and graphite fibrils or filaments are commercially
available from a number of sources.
[0061] Such composite fibers are well-suited for incorporation with polymeric materials
to provide electrically conductive components. The composite fibers have a very high
aspect ratio, i.e., length to diameter ratio, so that intimate contact between the
fibers to provide conductive pathways through the polymer matrix is achieved at relatively
low loading levels of fibers, and more particularly at much lower levels than the
metal coated spheres and metal flakes utilized in prior art attempts to provide electrically
conductive polymer compositions. This ability to provide electrical, and/or thermal
conductivity at low concentrations of fiber, significantly reduces any undesirable
degradation or modification of the physical properties of the polymer.
[0062] The copper coated fibers may be present in the composites as single strands, or
bundles of fibers or yarn. The fibers or bundles may be woven into fabrics or sheets.
In addition, the fibers, or bundles may be comminuted and dis persed within the polymeric
material, may be made into nonwoven mats and the like, all in accordance with conventional
techniques well-known to those skilled in this art.
[0063] The composites of the invention are convertible to many components. In one embodiment
of the invention, a composite is prepared by immersing and wetting a nonwoven mat
of the composite fibers, such as into a polymeric resin solution, such as one formed
by dissolving an epoxy resin or a phenolic resin in an alcohol solvent. Other forms
such as unidirectional fibers, woven fabrics, braided fabrics and knitted fabrics
can be used, too. This composition may then be converted to an electrically conductive
component in the form of a resin impregnated prepreg useful for forming electrically
conductive laminates. More particularly, the polymer resin solution wetted mat may
be heated to drive off the alcohol solvent. When the solvent removal is complete,
a component is formed comprising a layer of randomly oriented and over-lapping composite
fibers or bundles of fibers having a polymeric resin layer, and in this case epoxy
or phenolic resin layer, coating said fibers and filling any voids or interstices
within the mat. The resin impregnated prepreg so formed may be cut to standard dimensions,
and several of the prepregs may be aligned one on top of the other, to form a conventional
lay up. The lay up is then heated under pressure in a conventional laminating machine
which causes the polymer resin to flow and then cure, thereby fusing the layers of
the lay up together to form a hardened, unified laminate. The impregnating, drying,
lay up, and bonding steps for preparing these laminates are conventional and well-known
in the art. Further references as to materials, handling and processing may be had
from the
Encyclopedia of Polymer Science and Technology, Volume 8, pages 121-162, Interscience, New York, 1969.
[0064] The laminates prepared in accordance with the invention may be cut, molded, or otherwise
shaped to form many useful articles. For example, the laminate could be made to form
a structural base or housing for an electrical part or device, such as a motor, and
because the housing is electrically conductive, effectively ground the device.
[0065] In an alternate embodiment, the composition of the invention comprises a thin, normally
non-conductive polymer film or sheet and a woven, nonwoven unidirectional sheet, etc.,
formed of the composite fiber. The polymeric film or sheet may be formed by conventional
film forming methods such as by extruding the polymer into the nip formed between
the heated rolls of a calender machine, or by dissolving the polymeric material in
a suitable solvent, thereafter coating the polymer solution onto a release sheet,
such as a release kraft paper with for example a "knife over roll" coater, and heating
to remove the solvent. The polymer film or sheet is then heated to between 100° and
200°F and laminated with the nonwoven mat of composite fibers by passing the two layers
between the heated nip of a calender. The resulting component in the form of a fused
polymer film supported with a conductive mat is useful, for example as a surface ply
for laminates.
[0066] Air foil structures made with such laminated composites provide an effective lightning
strike dissipation system for aircraft. In the past, if lightning struck aircraft,
the non-metallic parts would be subject to significant damage because of their non-conductive
nature. With such a laminate forming the outer surface of air foil, should lightning
strike the craft, the resulting current will be conducted and dissipated through
the conductive fiber mat and conductive base laminate, thereby reducing the risk and
occurrence of damage to the airfoil.
[0067] In still another embodiment of the invention, the composites are made from a molding
composition wherein the polymeric material is, for example, a polyester, polycarbonate,
polystyrene, nylon, etc., resin molding composition having the chopped or comminuted
copper coated fibers, or woven mats, in contact therewith. The copper coated fibers
are dispersed in the resin by conventional means, and the composition is extruded
to form pellets. The pellets may then be injection molded in accordance with customary
procedures to produce shaped electrically conductive molded articles. The molded polyester
resin articles exhibit good physical properties as well as conductivity.
[0068] The elongated granules of this invention each contain a bundle of elongated reinforcing
copper coated fibers as defined above extending generally parallel to each other longitudinally
of the granule and substantially uniformly dispersed throughout the granule in a thermally
stable, film forming thermoplastic adhesive comprising
(a) a poly(C₂-C₆ alkyoxazoline) in combination with
(b) a poly (vinylpyrrolidone), said adhesive substantially surrounding each filament.
[0069] The injection molding compositions comprise:
(i) thermoplastic resin molding granules; and
(ii) elongated granules comprising 67.5-97.5% by volume of reinforcing copper coated
fibers extending generally parallel to each other longitudinally of each of the granules
and substantially uniformly dispersed throughout the granule in from 2.5 to 32.5%
by volume of a thermally stable, film forming thermoplastic adhesive comprising
(a) a poly(C₂-C₆ alkyoxazoline) in combination with
(b) a poly (vinylpyrrolidone), the amount of component (ii) in the composition being
sufficient to provide 1-60% by weight of the filaments per 100% by weight of (i) plus
(ii).
[0070] In still another aspect, the present invention contemplates, as an improvement in
the process of injection molding, the step of forcing into a mold an injection molding
composition comprising a blend of:
(i) thermoplastic molding granules; and
(ii) an amount effective to provide reinforcement of elongated granules as above defined.
[0071] Each filament contained in the injection molding granule is surrounded by and the
bundle is impregnated by the thermally stable, film-forming thermoplastic adhesive
combination. The pellet itself may be of cylindrical or rectangular or any other
cross-sectional configuration, but preferably is cylindrical. The length of the granules
can vary, but for most uses, 1/8 inch - 3/4 inch will be acceptable and 1/8 inch -
1/4 inch will be preferred. Unlike the prior art, the pellets of this invention have
close-packed filaments and the thermoplastic adhesive jacket is substantially dispersed
upon contact with hot molten thermoplastic in the present invention. On the other
hand, the prior art pellets will not readily separate into reinforcing filaments because
of interference by the relatively thick jacket of thermoplastic resin.
[0072] Instead of using a lot of resin to impregnate the fiber bundle and surround it, as
is done in the prior art, it is essential to use an adhesive efficient for the purposes
of the invention, and that is to bind a high proportion of filaments into each elongated
granule and maintain them throughout the chopping process and any subsequent blending
steps in high speed, high throughput machines. The adhesive preferably will be used
also in an amount which is not substantially in excess of that which maintains the
fiber bundle integrity during chopping. This amount will vary depending on the nature
of the fibers, the number of fibers in the bundle, the fiber surface area, and the
efficiency of the adhesive, but generally will vary from 2.5 to 32.5% and preferably
from 5 to 15% by volume of the granule.
[0073] For uniform adhesive pick up on the fibers in the bundle it is preferred to use a
small, but effective amount of a conventional surface active agent, which facilitates
wetting and bonding to numerous different substrates. Anion ic, cationic and non-ionic
surfactants are suitable for this purpose, the only requirement being that they be
miscible with any solvent system used for impregnation and compatible with the thermoplastic
film forming adhesive combination. Preferred surfactants, especially when graphite,
or metal coated carbon fiber substrates are used, comprise anionic surfactants especially
sodium salts of alkyl sulfuric acids. Particularly useful is sodium hepadecyl sulfate,
sold by Union Carbide Co., under the Trademark NIACET® No. 7.
[0074] Careful consideration should be given to selection of the film forming thermoplastic
adhesive combination, subject to the above-mentioned parameters. Some adhesives are
more efficient than others, and some, which are suggested for use as fiber sizings
in the prior art will not work. For example, poly(vinyl acetate) and poly(vinyl alcohol),
the former being suggested by Bradt in U.S. 2,877,501, as a sizing, do not work herein
because, it is believed, thermosetting or cross linking occurs and this operates
to prevent rapid melting and complete dispersion in the injection molding machine.
While such materials are suitable for the resin rich compounded granules used in the
Bradt patent, they are unsuitable herein.
[0075] Much preferred for use herein is a combination comprising poly (C₂-C₆ alkyl oxazolines)
and poly (vinylpyrrolidone). The former is somewhat structurally related to N,N-dimethylformamide
(DMF) and have many of its miscibility properties. A readily available such polymer
is poly(2-ethyl oxazoline), Dow Chemical Co. PEOx. This can also be made by techniques
known to those skilled in this art. Poly(2-ethyl oxazoline) is thermoplastic, low
viscosity, water-soluble adhesive. It can be used in the form of amber-colored and
transparent pellets 3/16" long and 1/8" diameter. Typical molecular weights are 50,000
(low); 200,000 (medium) and 500,000 (high). Being water soluble, it is environmentally
acceptable for deposition from aqueous media. It also wets the fibers well because
of low viscosity. It is thermally stable up to 380°C. (680°F.) in air at 500,000 molecular
weight. Poly(vinylpyrrolidone) is an item of commerce, being widely available from
a number of sources, and varying in molecular weight, as desired. While the poly(oxazoline)
appears to provide dispersibility to the elongated bundles the poly(vinylpyrrolidone)
is useful for high temperature resistance. Like the oxazoline, poly(vinylpyrrolidone)
works well in water based impregnation media. Typical molecular weight ranges readily
availabe can be used, for example 10,000; 24,000; 40,000; and 220,000. The higher
molecular weight material tends to provide bundles which are more difficult to disperse.
On the other hand, the lowest molecular weight causes some loss in heat resistance.
However, within the foregoing parameters, the adhesive combination on fiber bundles
does not fracture appreciably during chopping to minimize free filaments from flying
about, which can be a safety hazard. When blended with pellets of a thermoplastic
resin system, the adhesive combination will melt readily allowing complete dispersion
of the fibers throughout the resin melt while in a molding machine. However, pellets
bound with this thermoplastic adhesive combination are indefinitely stable with the
resin pellets during blending, and don't break apart prematurely.
[0076] As a result of a number of trials, this aspect of the invention as currently practiced
provides optimum results when the following guidelines are adhered to:
[0077] The fiber type can vary, any fiber being known to be useful as a filler or reinforcement
in a resin system can be used. Preferred fibers are carbon or graphite fibers, glass
fibers, aramid fibers, ceramic, e.g., alumina or silica carbide, fibers, metal coated
graphite fibers, or a mixture of any of the foregoing.
[0078] The preferred thermoplastic adhesive component (a) comprises poly(ethyloxazoline),
having a molecular weight in the range of about 25,000 to about 1,000,000, preferably
50,000-500,000, most preferably about 50,000.
[0079] The preferred thermoplastic adhesive component (b) comprises polyI(vinylpyrrolidone),
having a molecular weight in the range of from about 10,000 to about 220,000, preferably
from about 24,000 to about 40,000 and most preferably about 24,000.
[0080] It is preferred that the adhesive be deposited onto the filaments from a solvent
system which can comprise any polar organic solvent, e.g., methanol, or mixture of
such solvents, or water, alone, or in admixture. Acceptable bath concentrations for
the thermoplastic adhesive can vary but is generally for component (a) it is in the
range of 2.5-12% by weight, preferably 2.5-8%, and especially preferably 4-8% by weight
and, for component (b), in the range of 1-8% by weight, preferably 1-6% by weight,
and, especially preferably, 1-4% by weight.
[0081] If a surface active agent is used, this too can vary in type and amount, but generally
if an anionic alkyl sulfate is used, such as sodium heptadecyl sulfate, bath concentrations
can range from 0.0005-0.5% by weight, preferably from 0.0005 to 0.05%, and most preferably,
0.0005-0.005%, by weight.
[0082] The amount of non-filament material in the filament-containing granules of the invention
will vary, but, in general, will range from 2.5 to 32.5% by volume with any fiber,
preferably from 5 to 15% by volume.
[0083] The amount of component (b) will be from about 7.5 to about 75% by weight based on
the combined weights of (a) and (b) preferably from about 15% to about 50%.
[0084] The length of the elongated granule will generally range from 1/8 to 3/4 inch, preferably
from 1/8 to 1/4 inch. The diameters of each elongated granule can vary, depending
primarily on the number of filaments and the thicknesses will vary from about one-forty
eighth to about three-sixteenths inch in diameter. Preferably, the diameter will be
in the range of from about one-thirty-second to about one-eighth inches.
[0085] Numerous thermoplastic resins can be employed with the elongated granules of the
present invention. In general any resin that can be injection molded and that can
benefit from a uniform dispersion of fibers can by used. For example polystyrene,
styrene/acrylic acid copolymer, styrene/acrylonitrile copolymer, polycarbonate, poly
(methyl methacrylate) poly(acrylonitrile/butadiene/styrene), polyphenylene ether,
nylon, poly(1,4-butylene terephthalate), mixtures of any of the foregoing, and the
like, can be used.
[0086] It is preferred to manufacture the injection molding composition of this invention
by a continuous process. A suitable apparatus is shown in FIG. 5a. Typically, bundles
of filaments, such as graphite fiber tows or metal coated graphite fiber tows, 3,000
to 12,000 filaments per bundle, glass yarns, 240 filaments to a strand, or stainless
steel tow, 1159 filaments per bundle, are drawn from storage roller 2 and passed through
one or more baths 4, containing the thermally stable, film forming thermoplastic adhesive
in a solvent medium, e.g., water, to impregnate the filaments, then through means
such as die 6, to control pick up. The impregnated filaments thereafter are passed
into a heating zone, e.g., oven 8, to evaporate the solvent, e.g., water and then
to flux the thermoplastic adhesive. The treated filaments 10 are withdrawn from the
heated zone, transported to chopper 12 and cut into fiber pellets illustratively varying
beteen 1/8-1/4" according to the requirements of the particular apparatus. The pellets
are then stored in a suitable container 14 for subsequent use. Any surfactant conveniently
is included in a single bath with the adhesive. It will be observed that this procedure
results in the orientation of the reinforcing fibers along one axis of the granule.
[0087] To carry out the molding method of the present invention, a flow diagram in the
general form illustrated in FIG. 5b is preferably employed. Fiber pellets 16 are mixed
with resin pellets 18 to produce a blended mixture 20. This is added to conventional
hopper 22 on molding press 24. When passing through cylinder 26, prior to being forced
into mold 28 a uniform dispersion of the fibers is accomplished. Removal of molded
article 30 provides a fiber reinforced item produced according to this invention.
[0088] It is understood that other plasticizers, mold lubricants, coloring agents, and
the like, can be included, and that the amount of reinforcement in the components
can be varied according to well understood techniques in this art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0089] The following examples illustrate the present invention. They are not to be construed
to limit the claims in any manner whatsoever.
EXAMPLES 1-7
[0090] A batch process of this invention was used for the following examples. By first electrolessly
depositing copper for predetermined times then electrodepositing for a variety of
residence times, a variety of copper coating thicknesses could be produced on the
fibers. The carbon fiber used was Magnamite® IM-6, 12K, no size, no twist, supplied
by Hercules, Inc., Magma, Utah. The fibers were prepared for coating using above-described
wetting Bath 1 and sensitizing Bath 2, and separate samples of fiber tows were immersed
in the electroless plating Bath 3 for 0, 1, 3 or 5 minutes. These samples were then
electroplated, using above-described Bath 5 for various times as given in the chart
below. The thickness of a fiber's coating was measured and is included below.

[0091] Control sample A did not electroplate due to the lack of an electroless copper layer.
Coating thickness in Example 6 is anomously low, it may have been that an unrepresentative
fiber was measured.
EXAMPLE 8
[0092] Using the continuous plating line described in the specification above, and diagrammed
in Figs. 1-3, three tows of graphite fiber IM-6 (12K) were copper coated at a rate
of three inches a minute using above-described Baths 1, 2, 4 and 5. The temperature
of the electroless bath was 45°C and the temperature of the electrolytic baths were
53°C. The current in the first tank was 5 amperes, the second tank current was 30
amperes and the final tank was 12.5 amperes. The coating continuity, thickness, and
degree of fiber agglomeration were measured by scanning, electron microscopy (SEM)
of cross sections of the tows imbedded in epoxy resin and polished in accordance with
standard procedures. The results are summarized in the following table.

EXAMPLES 9 and 10
[0093] A batch process of this invention used Baths 1, 2, 4 and 5 described above to successively
coat 12 K tows of IM-6 graphite fiber with copper. Both tows were held in Bath 4 for
5 minutes. Example 9 was electroplated for 5 minutes at 2.5 amperes. Example 10 was
electroplated for 10 minutes at 2.5 amperes. A photomicrograph of Example 9 appears
herein as FIG. 6. SEM analysis of cross sections of the two tows showed the following:

EXAMPLES 11 and 12
[0094] Copper coated carbon fibers were prepared using the continuous process described
in Example 8 using Baths 1, 2, 4 and 5. Two base fibers were used: 12K IM-6 graphite
fiber (Hercules Co., Magma, Utah), and 2K P100 graphite fiber (Union Carbide Co.,
Danbury, CT). Coatings were applied in thicknesses sufficient to yield approximately
50% by volume of copper. The coated fiber tows were then aligned by hand into layers
to form unidirectionally aligned samples 1 x 8 inches. Hot pressing was performed
in a large hot press, FIG. 4, by heating to between 750° and 775°C under a pressure
of 1000 psi. Composite panels were measured for electrical resistivity, thermal conductivity
and coefficient of thermal expansion. Thermal expansion was measured using push rod
dilatometry. An axial rod technique, corrected for radial temperature loss, was used
to measure thermal conductivity. A four point bend technique was used to measure the
electrical resistivity. All measurements were made parallel to the fiber axis. All
of the hot pressed samples appeared to be well consolidated. High fiber volume fractions,
with low void contents, were obtained with both IM-6 and P100 carbon fibers. Individual
ply thicknesses were as low as 5 mils in these samples. The results of the tests are
given below:

[0095] These values are what would be predicted by rule-of-mixture calculations, demonstrating
uniformity, a low void content, and a high purity coating.
EXAMPLE 13
[0096] A composite is prepared by chopping the fibers of Example 8 into short lengths, 1/8"
to 1/4", then thoroughly mixing with thermoplastic nylon polyamide in an extruder,
and chopping the extrudate into molding pellets in accordance with conventional procedures.
The pellets are injection molded into plaques 4" x 8" x 1/8" in size. The plaque is
reinforced by the copper coated fibers. By virtue of the metal content, it also does
not build up static charge, and it can act as an electrical shield in electronic assemblies.
EXAMPLE 14
[0097] Bundles of copper plated graphite fibers of about one inch in length prepared according
to the procedure of Example 8 are mixed 1:9 with uncoated graphite fibers and laid
up into a non woven mat, at 1 oz./1 sq. yard. The mat has a metal content of about
10% by weight of copper and can be impregnated with thermosetting resin varnishes
and consolided under heat and pressure into reinforced laminates having high strength
and excellent electrical dissipation properties.
EXAMPLE 15
[0098] Long, copper coated graphite yarns prepared by the general procedure of Example 8
are pultruded at a high rate with molten lead in an apparatus from which a 1/8" diameter
rod issues in solidified form, down through the center of which runs the copper coated
graphite fibers. A reinforced composite having a lead matrix according to this invention
will be obtained.
EXAMPLE 16
[0099] The following example illustrates the preparation of a comminuted copper coated graphite
fiber filled epoxy resin film as a conductive surface ply for laminates. A solution
of catalyzed formulated epoxy resin system (American Cyanamid FM® 300) dissolved in
50/50 v/v mixture of ethylene dichloride and methyl ethyl ketone at 78-80% solids
is prepared in a 1 gallon capacity Ross Planetary mixture. 30% by weight of copper
plated graphite fiber prepared in accordance with Example 8 herein and chopped into
1/64 inch lengths is added to the mixer and the composition mixed until the copper
fibers are uniformly dispersed throughout. The composition is degassed by stirring
at a reduced pressure of 20 mm Hg for 15 minutes. The epoxy resin-chopped fiber composition
is coated onto a sheet of silicone treated kraft paper with the "knife over roll"
coater to a thickness of approximately 12 mils. The coated kraft paper sheet is dried
in an oven by gradually heating to about 190°F and the 190°F temperature was maintained
for approximately 40 minutes. A dry, filled polymer film according to this invention
is produced. The laminate is prepared with the polymer film prepared above as surface
ply following standard procedures. The lay-up contains 12 layers of a commercial prepreg
which is bagged and cured in the cured in the autoclave at 350°F for 120 minutes at
20-50 psi. The finished laminate has a uniform smooth surface suitable for final application
without further finishing operations. When tested in accordance with ASTM 0257-78,
the surface ply has a very low surface resistivity.
EXAMPLE 17
[0100] The following illustrates the use of the composition of the invention as a conductive
molding compound.
[0101] A polyester molding compound is prepared by charging the following reactants to
a sigma mixer:
10.5 parts styrenated, thermosettable polyester resin (USS Chemical MR 13017);
12.3 parts styrenated thermosettable polyester resin (USS Chemical MR 13018);
0.6 parts calcium stearate;
40.3 parts calcium carbonate;
0.5 parts t-butyl perbenzoate; and
0.06 parts inhibitor (35% hydroquinone in dibutylphthalate).
[0102] After mixing for 15 minutes, 25.7 parts of copper plated graphite fibers (Example
8) chopped to 1/4 inch length are blended into the mix for 10 minutes. The resulting
polyester premix is molded into 4 inch circular plaques in a molding press at 150°C.
The plaques have a very low surface restivity due to their content of metal coated
fiber. Because of the excellent thermal conductivity of the compositions like those
of Examples 16 and 17, they find utility also for constructing tools for use in molding.
Such tools, because of their unique characteristics, permit shorter cycle times as
a result of their more rapid heat build up and cool down. In contrast, tools made
with conventional materials require much longer cycle times.
EXAMPLE 18
[0103] Chaff according to the present invention is prepared by chopping strands of composite
fibers metal coated as described in Example 8 into lengths designed to effectively
reflect impinging radar waves. Preferably, the fibers are cut to a length roughly
one-half the wavelength of the radar frequency the chaff is intended to be used against
or, where very high radar frequencies are encountered, full wavelengths. In practice,
a radar operator may be monitoring several frequencies, typically in the 2-20 GHz
range. Therefore, strategic chaffs according to this invention are made to contain
different lengths of filament ranging from several centimeters and shorter (e.g.,
01-10 cm), corresponding to the halfwave lengths (or full wavelengths) over an entire
bandwidth, the range that may be achieved with the chaff of this invention is from
100 microns to hundreds of meters, depending on the specific use contemplated.
EXAMPLE 19
[0104] Using an apparatus of the type generally shown in FIG. 5a a bath comprising the following
is formulated:

[0105] With reference to FIG. 5a, a tow of continuous graphite fibers 2 (12,000 count) each
of which has a copper coating thereon is led through bath 4. The graphite filaments
each average about 7 microns in diameter. The copper-coating thereon is approximately
1.0 microns in thickness. The copper coated graphite tows are prepared by continuous
electroless plating followed by electroplating in accordance with the procedure described
in Example 8. After passing through coating bath 4 the treated fibers are passed over
grooved rollers 6 to remove excess adhesive then passed through oven 8 at about 300°F.
The impregnated filaments then are chopped to 1/4" lengths in chopper 12 and there
are produced elongated granules of approximately 1/16" in diameter of cylindrical
shape and form. The non-filament material content is 9% by volume.
EXAMPLE 20
[0106] Using the process generally shown in FIG. 5b, sufficient amounts of the elongated
pellets 16 produced in Example 19 are blended with pellets 18 of a thermoplastic molding
resin composition comprising poly(bisphenol A carbonate) (Mobay Co. MERLON® 6560)
to provide 5 weight percent of copper-coated graphite filaments in blend 20. The blended
mixture is molded in injection molding press 28 into work pieces 30 suitable for physical
and electrical testing. The electromagnetic shielding effectiveness (SE) and EMI attenuation
are measured and show high dispersion efficiency.
EXAMPLE 21
[0107] The procedure of Example 20 is repeated substituting for the thermoplastic resin
pellets, pellets comprising poly(acrylonitrile/butadiene/styrene) (Borg Warner CYCOLAC®
KJB) resin and plaques suitable for measuring SE effect are molded.
EXAMPLE 22
[0108] The procedure of Example 20 is repeated but poly(2,6-dimethyl-1,4-phenylene ether)-high
impact strength rubber modified polystyrene resin pellets (General Electric NORYL®
N-190) are substituted, and plaques suitable for measuring SE are prepared.
EXAMPLES 23 and 24
[0109] The general procedure of Examples 9 and 10 was repeated using IM-6 for Example 23
and P-55 for Example 24. The IM-6 fiber was coated to contain 50 vol. % of copper;
and the P-55 was coated to contain 40 vol. % of copper. The respective fibers were
hot pressed for 10 min. at 900°C., 1000 psi under a purge of 3% hydrogen and 97% nitrogen
gas. FIG. 18 is a photomicrograph of the IM-6 coated with 50 volume percent copper
that has been consolidated into a "cross-plied" laminate, that is, the fibers in the
center layer are at approximately a 60 degree angle to the polish plane, while in
the top and bottom layers, the fibers are perpendicular to the polish plane. FIG.
17 is a higher magnification photo of P-55 coated with about 40% copper. In this
laminate all the fibers shown are oriented perpendicular to the polish plane.
[0110] For comparison purposes, a number of copper plated graphite fibers are prepared by
techniques of the prior art and compared with those produced according to the present
invention.
COMPARATIVE EXAMPLE 1A
[0111] Direct electroplating of an untreated tow of graphite fibers was attempted using
a commercially available copper electroplating bath. The plating solution used was
Bath 5, described above. The graphite fiber used was P100 from Union Carbide (2,000
filament, no size, no twist). This graphite fiber was believed to have sufficient
electrical conductivity to allow the electrodeposition of copper. A 1 liter graduated
cylinder was filled with 1 liter of Bath 5. The bath was heated to 45°C by means of
a heating tape wrapped around the cylinder. The tape was plugged into a variable voltage
controller and then monitored by a thermometer hung on the inside of the cylinder.
Two long rectangles of OFHC grade copper sheet stock (high purity copper) were hung
in the bath by bending one end of the sheet over the side of the cylinder. The sheets
were connected to a power supply to serve as cathodes. The P100 fiber was wrapped
around a piece of copper bar stock which rested on the top of the graduated cylinder.
The fiber was then clamped to the bar and connected to the power supply as the anode.
Using a current of 1 ampere, plating was carried out for five minutes. The fiber was
then rinsed with deionized water and dried in a vacuum oven for 15 min. at 120°F at
a vacuum of 25 mm of Hg. Visual inspection of the fiber showed plating to be sporadic
and uneven. The material was considered to be unsuitable for hot pressing.
COMPARATIVE EXAMPLE 2A
[0112] Sizing was removed from commercially available P100 graphite fiber (2,000 filaments,
no twist, sized) using a procedure specified by the fiber's manufacturer, Union Carbide,
by heating at 400°C for 30 sec. in air. One liter of each solution was placed in a
graduate cylinder. The following solutions were used: Bath 1 was a wetting agent solution
as described above at room temperature, Bath 2 was a catalyst solution, described
above, at room temperature, and Bath 3 was an electroless copper plating solution,
described above, at 45°C. The last bath was aerated by means of a gas dispersion tube
which was connected to a compressed air line. Six bundles of fibers, each 2.5 inches
long, were immersed in Bath 1 for 2 min., agitated manually, and rinsed using deionized
water. The fibers were then agitated in Bath 2 for 2 min., and again rinsed. Rinsing
was continued until the run-off from the fibers was clear and colorless. The individual
bundles were then separately electrolessly plated in Bath 3 for 1, 5, 10, 15 and 30
minutes. An attempt was made to plate the sixth tow for one hour, however the plating
bath became unstable and began to precipitate out and the experiment was discontinued.
The fibers were then dried in a vacuum oven. The resulting fibers were mounted for
Scanning Electron Microscopy (SEM) and the coating thicknesses were measured. The
thicknesses ranged from 0.3 microns for the 1 min. residence time to 3.0 microns for
the 30 min. residence time. It was noted that the coating began to have nodular growths
after 10 min. in the plating solution. At 10 minutes the coating thickness was 1.8
microns.
COMPARATIVE EXAMPLE 3A
[0113] The process described in German Pat. No. 2,658,234 is said to guarantee the uniform
coating of individual very thin fibers with a metallic coating, such as copper. The
patent diagrams an apparatus which is comprised of a funnel through which a tow of
graphite fiber is suspended. Various solutions are then pumped into the funnel and
flow down the tow and causing it to be spread. The principal requirements of the apparatus
are: a pump, capable of attaining a flow of 1 liter/min., and a funnel having an inner
diameter of between 3 and 12 times the outer diameter of the tow to be coated. The
height of the liquid in the funnel must be 2 cm or more. The advantage of this particular
method is stated to lie in the fact that the individual fibers spread out from one
another in the stream of the reaction fluid flowing along them. The patent teaches
that this will produce fibers which will be uniformly coated over both the length
and the cross section. The rate of flow along the fiber length is stated as being
important along with keeping the turbulence in the flow to a minimum. Detailed instructions
as to the pumping times for each component and water rinses are given. Unfortunately,
the commercial electroless plating solution used by the German patentee, Schmidt,
made by the Shipley company is no longer available. Therefore, substitute solutions
recommended by the same manufacturer were used. A diagram of the apparatus is given
in Figure 7. A magnetically driven plastic pump (Teel) was used to pump solution into
a plastic funnel. The pump's flow was restricted by an adjustable hose clamp. Flow
was adjusted to 1 liter per minute. The i.d. of the bottom opening of the funnel was
0.5 cm. With a pumping rate of 1 liter/min., and this funnel, it was possible to maintain
a solution level height of 5 cm in the funnel when a tow of fibers was suspended through
the funnel opening. One meter of carbon fiber (12,000 filament tow of IM-6 fiber from
Hercules, no size, no twist) was hung from the top of a ring stand. The fiber used
by Schmidt had five twists per meter. Therefore, five twists were made in the fiber
tow. The bottom of the tow was run through a 5 cm. long glass tube. The glass tube
did not create tension in the tow, but gently rested on the bottom of the catch basin
to keep the fiber from untwisting. All of the water used was deionized water, including
the water which was used to rinse the fiber. The treatment of the fiber was as follows:
10 min. using Shipley Conditioner 1160B;
5 min. rinse with deionized water;
1.5 min. with 25 vol. % HCl in deionized water;
3.5 min. with Shipley Catalyst 9F;
5 min. rinse with deionized water;
5 min. with Shipley Accelerator 19;
5 min. rinse with deionized water;
12 min. using a Shipley electroless copper plating solution which was prepared by
combining 79 vol. % deionized water, 11 vol. % Shipley CP-78M, 4.5 vol. % Shipley
CP-78R, heating to 115°F then adding 5.5 vol. % Shipley CP-78B; and
5 min. rinse with deionized water.
[0114] When using the heated solution, a small glass evaporation dish was substituted for
the polypropylene tank and a heating plate was beneath it to maintain the temperature
of the solution. The fiber was dried using a vacuum drying oven at 120°C for 15 min.
at a vacuum of 25 mm of Hg. The apparatus caused the loosely suspended fiber to fill
with solution and spread. The twists induced into the fiber in order to duplicate
Schmidt's example remained in the tow during the experiment until the glass dish and
hot plate were substituted for the polypropylene tank. At that point the fiber was
allowed to untwist. The final solution was pumped through the fiber without twists.
This allowed the fiber to fill with solution more completely, however, one area about
20 cm from the bottom of the tow showed some evidence of constraint. Visual analysis
later showed the presence of a "wrapper" or errant fiber (or several fibers) which
wrapped around the tow and bound it together. The passive nature of the spreading
of the fibers by the solution flow in this technique does not overcome such a constraint.
When circulating the final solution, evidence of copper deposition was seen almost
immediately. Copper deposition was evidenced by an immediate color change as well
as considerable hydrogen evolution in the tow. After completion of the final rinse
the fiber was dried and visually inspected. Evidence was seen of one black section
in the center of the fiber approx. 20 cm. from the bottom of the tow. This area corresponded
to the section which was believed to contain a "wrapper". The tow appeared very bright
and copper colored and felt soft to the touch, although the fiber did not seem completely
free. This could indicate some evidence of "overplating" or the plating together of
neighboring fibers (agglomeration). On examination by Scanning Electron Microscopy
(SEM) it was found that fibers in the tow had coatings that were uneven in thickness
around the circumference, varying from 0.8 to 3.5 microns on the same fiber. A typical
view is shown in FIG. 10. Thickness variations were also seen from fiber to fiber
in the tow. Near the outside of the tow fibers were coated to a thickness of 2.5 microns
while in the center of the tow coatings as thin as 0.2 microns were seen. The tows
were also highly agglomerated having only 43% of the fibers in a cross section individualized.
The agglomeration was characterized by counting the number of agglomerates containing
1, 2, 3, 4, 5, 6, or greater than 6 fibers. The percentage of all fiber contained
in agglomerates of each size was then calculated. The results are shown below:

COMPARATIVE EXAMPLE 4A
[0115] In Sakovich et al., referred to above, a method is given of electrolessly plating
carbon fibers. Both nickel and copper coatings were applied to tows of graphite fiber
with between 1,500 and 10,000 filaments. The diameter of the fibers were between 6.5
and 10 microns. The fibers were first treated with boiling water, a stannous chloride
bath, then a palladous chloride bath before electroless plating. No residence times
or concentrations were given for the solutions. No apparatus was described. For copper
plated fibers, the authors state that a bright coating, uniform in thickness on all
fibers of the tow, was obtained from the following electrolyte:
A: 170 g/L Seignette salt [potassium sodium tartrate], 50 g/L sodium hydroxide, 30
g/L sodium carbonate;
B: 40 percent formaldehyde solution;
A:
B = 5:1 (pH 12.3, Temp. 20°C). The average precipitation rate was 0.03 microns/min.
It should be noted that the above solution for the electroless deposition of copper
does not include any chemical which contains copper in any form. It was therefore
assumed that this ommission was a typographical error or omission. To determine a
copper source and concentration that Sakovich might have been familiar with, a reference
text edited by F.A. Lowenheim was consulted (
Modern Electroplating, Third Edition, ed. F.A. Lowenheim, John Wiley & Sons, Inc., New York, 1974, pp.
734-739). A bath which is very similar to the one used by Sakovich is described on
p. 736, Bath 4. When compared it was seen that if the components were multiplied by
a factor of 6/5 the proportions of the given components were identical to those Sakovich
used.

[0116] The Lowenheim solution also included 17 g/L of Versene-T (EDTA + triethanolamine),
however, since this compound was not indicated by Sakovich it was not used in the
preparation of the electroless plating bath of this example. The exact compositions
and concentrations for the stannous and palladous chloride baths were not given so
commercially available solutions for the chemical deposition of copper were used.
These solutions are commonly used in the printed circuit board industry.
[0117] A tow of graphite fibers (12,000 filament IM-6 from Hercules, no size, no twist)
was used to perform the experiment. A loop of fiber, 40 in. long, was taped to a
frame made by bending a glass rod to form a rectangle. This frame held the fiber and
kept it from floating to the surface when immersing it in solution. This is especially
important when the fiber is placed in the copper containing solution since the production
of hydrogen gas on the fiber forces it to the surface of the bath. Four 1 liter graduated
cylinders were obtained to hold the reaction solutions. Water was heated to boiling
in an Erlenmeyer flask on a hot plate. The water was then poured into the first graduated
cylinder. This cylinder was warmed by means of a heating tape wrapped around the cylinder.
The fiber was immersed in the hot water for five minutes. In this time period the
water temperature fell to 92°C. The fiber was then transferred to the second cylinder
containing a stannous chloride solution (Shipley Accelerator 19) for 5 min. The fiber
was then rinsed with deionized water for 2 min. After rinsing, the fiber was placed
in a palladous chloride solution (Shipley Catalyst 9F) for 5 min. The fiber was again
rinsed for 2 min. with deionized water. At the end of the two min. rinse, the run-off
from the fiber appeared colorless and free of catalyst. The fiber was then placed
in the cylinder containing the electroless plating solution. This solution was made
in the following manner (as outlined in Lowenheim):
35 g of copper sulfate pentahydrate (CuSO₄*5H₂O) was dissolved in 600 mls. of dionized
H₂O;
170 g of potassium sodium tartrate was added while stirring;
50 g of sodium carbonate was added to the above solution while stirring;
50 g of sodium hydroxide pellets were dissolved in 100 mls. of water and this solution
was then slowly added to the stirred copper solution;
Deionized water was then added to bring the total volume of solution to 810 mls; and
Immediately before plating, 191 mls. of 37% formal dehyde was added to the solution.
[0118] The solution was at room temperature and the pH was measured to be 12.2. Immediately
after placing the fiber and frame into solution, evidence of gas evolution was seen.
Bubbling continued during the entire reaction time which was 33 min. This time period
was indicated to be long enough to produce a copper coating of 1 micron in thickness.
A color change in the solution was apparent after approximately 15 min. The solution
changed from a clear blue to a cloudy, dark blue green. At the end of the reaction
time, the fiber was rinsed and dried in a vacuum oven at 120°C for 15 min. at a vacuum
of 25 ml of Hg. The fibers were inspected visually and then a section was provided
for SEM analysis. Three one and one-half inch sections were cut from the tow of fibers
for consolidation into a composite.
[0119] The visual inspection of the fibers showed an excess of copper agglomerated on the
tow. The color of the metallic plating was dark reddish brown. The inside of the tow
was not easy to see since the outside of the bundle was covered in a dark powdery
copper. On examining a polished cross section of the tow by scanning electron microscopy,
the following was observed: the coating thickness was relatively uniform around the
fiber circumference, however, the thickness varied from fiber to fiber. A typical
view is shown in FIG. 11. The minimum thickness seen was 0.32 microns, and the maximum
was 1.54 microns. The average thickness was 0.98 microns with a standard deviation
of 0.43 microns. Only 43% of the fibers were individualized. The agglomeration was
characterized as in Example 3A; the results are given below:

COMPARATIVE EXAMPLE
[0120] USSR Patent No. 489,585, by Kuz'min teaches that to improve the physical and mechanical
properties of a copper- graphite composite, the copper coating of the fibers is initially
carried out by chemical precipitation and then by an electrolytic one, while the hot
pressing is performed at a temperature of 920-980°C under a pressure of 35-250 kg/cm².
In a paper published by the same experimenter, it is written that all elementary fibers
are covered with a uniform layer of metal in the process of chemical precipitation.
Although the experiment is not fully described in either the patent or the paper,
it is possible to piece together a procedure between the two articles. The experiment
in the literature was carried out on a carbon fiber produced in the form of a twisted
tow, of 7,200 elementary fibers with a bean-shaped cross-section, with a diameter
of 5.9 microns. Fibers were oxidized by holding them in 65% nitric acid for 5 min.
The following step was to activate the surface using an acidified palladous chloride
bath. The patent specifies a pH of 3-4 but no concentrations were given. Treatment
in stannous chloride solution was then carried out for ten minutes. No specific concentration
or pH was given. Careful washing of the fiber with running water between treatments
was recommended. The electroless copper plating solution, which is described in both
the paper and the patent, is an alkaline solution containing copper sulfate, formaldehyde
solution, sodium hydroxide, potassium-sodium tartrate, and sodium diethyldithiocarbonate.
Two commercial sources did not carry any chemical named sodium diethyldithiocarbonate,
but sodium diethyldithiocarbamate is listed and is known to be used as a chelating
agent. Thus the use of carbonate was taken to be a typographical error. Neither the
patent nor the journal article give concentrations for the components of the plating
bath. However, comparison to the text by Lowenheim, abovementioned, does suggest
a possible bath make-up. The coating thickness is given as between 0.1 to 0.4 microns
for a residence time between 3 to 6 minutes. The electrolytic deposition of copper
onto the graphite fibers is more fully described. The solution to be used is made
from combining 260 g/L copper sulfate pentahydrate and 60 ml/L sulfuric acid and plating
at a current density of 2-5 A/100 cm² and a pH of 1-2 in four hours. They report that
consolidation into a composite is performed in a vacuum for 30 minutes at a temperature
of 940°C under pressure of 50 kg/cm². This method should produce a composite with
a 5% weight fraction of fibers. The paper explains that in some of the composites
scanning microscopy showed some defects in the composite, including "clusters of fibers,
pores in the matrix".
[0121] Four 1-liter graduated cylinders were filled with the recommended solutions. A frame,
made from a glass rod bent into a rectangular shape, was used to hold the fiber. The
fiber used was a 40 in. long segment of 12,000 filament IM-6 graphite fiber (Hercules,
7 micron fiber), which was attached to the frame and ten twists were introduced into
the fiber, then the second end was taped to the top of the frame. The fiber and frame
were submersed into 65% nitric acid for 5 minutes then thoroughly rinsed with deionized
water. The fiber was then held in a commercially available palladous chloride solution
(Shipley Catalyst 9F) for 5 min. and carefully rinsed with deionized water. The fiber
and frame was then treated in a stannous chloride bath (Shipley Accelerator 19) for
ten minutes. Following the stannous chloride bath the fiber was thoroughly rinsed.
A solution for the electroless deposition of copper was made by the following method:
13 g of copper sulfate pentahydrate (CuSO₄.5H₂O) were dissolved in 800 ml of deionized
water;
66 g of potassium sodium tartrate was added to this solution while stirring;
0.018 g of sodium diethylydithiocarbamate was added to the above solution while stirring;
19.3 g of sodium hydroxide was dissolved in 100 mls of deionized water and this solution
was slowly added to the stirred copper solution;
Deionized water was added to this solution to bring the volume to 960 ml total volume;
and
Immediately before plating, 38 mls of 37% formaldehyde was added to the solution.
[0122] The solution was at room temperature for the treatment of the fibers. The fiber
and frame was immersed in the plating solution for a total of five minutes. The fiber
surface showed evidence of gas evolution upon immersion in the solution. At the end
of the electroless plating period the fiber was washed carefully. An electroplating
solution was prepared by dissolving 1040 g of CuSO₄.5H₂O in 3.5 liters of deionized
water while stirring. The solution was heated slightly in order to dissolve all the
copper sulfate into this volume of water. The solution was then allowed to cool to
room temperature. After cooling, 240 ml of sulfuric acid was carefully added to this
solution. Deionized water was then added to bring the total volume of solution to
4 liters. Electroplating was performed in a tank (FIG. 8) which contained an OFHC
grade copper bar stock anode. The cathodes were two sections of copper tubing which
were both supplied with current. Each end of the fiber was wrapped around a cathode
roller. A section of fiber approximately 125 cm in length was held below the surface
of the solution by two bent glass rods. The power supply was turned on and current
controlled. The current was slowly increased to 5 Amps. The cathodes and the section
of fiber between the cathode and solution surface was kept cool by spraying this section
with water from a plastic rinse bottle. After approximately 20 min. the fiber began
to spark near the intersection of the fiber and the solution interface. At this point
the experiment was discontinued. The fiber was removed from the bath, rinsed and
then dried in a vacuum drying oven for 15 min. at a vacuum of 25 mm of Hg. A small
section of fiber was cut out of the tow and provided for scanning electron microscopy.
Visual inspection of the tow showed some areas of incomplete coverage. The fibers
did not spread easily, suggesting that neighboring fibers were plated together. Three
small sections of fiber were removed and used to prepare a composite sample. Visual
inspection had further shown that coverage of the fiber was incomplete. This was documented
by the SEM analysis. Cross sections of the fiber tows showed relatively good evenness
of coating thickness around the circumference of the fibers, but very large variations
from fiber to fiber in the tow. Many of the fibers in the center of the tow were uncoated
and near the surface of the tow coatings as thick as 20 microns were found. A typical
view is shown in FIG. 12. Agglomeration was severe, only 7% of the fiber was individualized.
Agglomeration was as follows:

In addition, 36% of the fibers were uncoated.
COMPARATIVE EXAMPLE 6A
[0123] Japanese Patent No. 70-17095 (1985) by Yashioka
et al., teaches that electroplating graphite fibers in copper electroplating baths without
a brightener creates a non-bright coating with poor slidability during knitting into
a cloth due to the roughness of the coating. The patent states that its objective
is to produce copper coated carbon fibers with an improved discoloration resistance
and slidability. A number of copper electroplating baths are discussed and the availability
of suitable brighteners is assured. For example, UBAC-1 (trade name OMI Corp.) is
used for a copper sulfate bath, and copper ryumu (trade name MKT Co.) is used for
a cyanide bath. In Actual Example 1: a bundle of carbon fibers consisting of 3,000
single fibers having an average diameter of about 7 (microns) was pretreated by calcining
at ca. 500°C and plated in a copper sulfate plating bath containing a brightener
(composition: copper sulfate 100 g/l, sulfuric acid 100 g/l, brightener UBAC-1 10
ml/l,Cl- 10 ppm) at an average current density of 6 A/dm 2, yielding a ca 2(micron)
thick bright copper-plated layer. This was compared to a sample which did not contain
a brightener as to the brightness and slidability.
[0124] For comparison purposes, a section of 12K IM-6 graphite fiber 1.5 meters in length
was pulled into a tube furnace which had been heated to 500°C. The fiber was treated
in air at this temperature for 5 minutes. The center of the length of this tow, approximately
30 in., was marked and used for the electrolytic plating according to the patent description.
A total volume of 8 liters of solution was made in two 4-liter Erlenmeyer flasks.
The procedure for preparing the solution was as follows:
Stir together:
3 liters of deionized water;
400 g. of CuSO₄.5H₂O;
400 ml. of sulfuric acid;
40 ml. of UBAC-1 brightener; and
0.33 ml. 35% HCl acid solution.
[0125] Electroplating was performed in a tank (FIG. 8) which contained an OFHC grade copper
bar stock anode. The cathodes were two sections of copper tubing which were both supplied
with current. Each end of the fiber was wrapped around a cathode roller. A section
of fiber approximately 20 inches in length was held below the surface of the solution
by two bent glass rods. The power supply was turned on and current controlled. The
current was slowly increased to 5 Amps. The cathodes and the section of fiber between
the cathode and solution surface was kept cool by spraying this section with water
from a plastic rinse bottle. After approximately 20 minutes the fiber began to spark
near the intersection of the fiber and the solution interface. At this point the experiment
was discontinued. The fiber was removed from the bath, rinsed and then dried in a
vacuum drying oven for 15 minutes at a vacuum of 25 mm of Hg. A small section of fiber
was cut out of the tow and submitted for evaluation by scanning electron microscopy.
Visual inspection of the tow showed some areas of incomplete coverage. The quality
was not suitable for hot-pressing. A typical view is shown in FIG. 13. The fibers
did not spread apart easily, suggesting some evidence of plating together of neighboring
fibers.
[0126] SEM analysis of cross sections of the two tows showed the following:
Sample A
[0127] Evenness around circumference: Extremely poor, e.g., 14.7 to 3.5 micron thickness
on a single fiber.
Evenness from fiber to fiber:
Minimum thickness: 0 microns (uncoated)
Maximum thickness: 38 microns
Agglomeration:

[0128] In addition, 15% of the fibers were either not coated or only partially coated.
COMPARATIVE EXAMPLES 7A-9A
[0129] Using fiber prepared in Comparative Examples 3A-5A composites were formed according
to the hot pressing techniques described in the literature of 1975. Processing was
performed by laying the section of fibers together between two pieces of flexible
graphite sheets (POCO Graphite, Decature, TX) and then consolidating at 920°C for
30 minutes at a pressure between 600 and 750 psi under an atmosphere of 3% hydrogen,
97% nitrogen. The heat up time for the hot press (FIG. 9) was one hour and 35 minutes.
Once the furnace was cooled to 250°C the samples were removed. They were then potted
in epoxy for metallographic sectioning and polishing for microscopic analysis. Each
of the composites had voids, delaminations, matrix rich regions and, in the case of
the fiber of Example 5A, large unconsolidated sections due to the uncoated fiber in
the coated tow. Photomicrographs of the composites of comparative Examples 7A-9A appear
herein as FIGS. 14-16, respectively.
[0130] The foregoing comparative data demonstrate that relatively thick, uniform and firmly
adherent layers of copper are not deposited on carbon cores if the teachings of the
prior art are followed, in spite of allegations to the contrary. Moreover, the results
demonstrate that uniform, substantially void free composites are not obtained by hot
pressing fibers prepared according to the prior art.
[0131] The above-mentioned patents, publications, patent applications, technical information
sheets and test methods are incorporated herein by reference.
[0132] Many variations of the present invention will suggest themselves to those skilled
in this art in light of the above, detailed description. For example, instead of carbon
fibers, alumina fibers can be used. All such obvious variations are within the full
intended scope of the invention defined by the appended claims.
1. A continuous yarn or tow comprising composite fibers, which have a semimetallic
core and at least one relatively thick, uniform and firmly adherent, electrically
conductive layer comprising copper on said core.
2. A continuous yarn or tow as defined in Claim 1 wherein the thickness of said metal
layer or layers ranges from about 0.6 to about 3.0 microns.
3. A continuous yarn or tow as defined in Claim 2 wherein the thickness is at least
about 0.8 microns.
4. A continuous yarn or tow as defined in Claim 3 wherein the thickness is at least
about 1.2 microns.
5. A continuous yarn or tow as defined in Claim 1 wherein the standard deviation of
the coating thickness is less than 30% of the average coating thickness, both around
the circumference of each fiber and from fiber to fiber.
6. A continuous yarn or tow as defined in Claim 1 wherein the majority of the fibers
are individualized and non-aggregated.
7. A continuous yarn or tow as defined in Claim 1 wherein more than about 70% of the
fibers are individualized and non-aggregated.
8. A continuous yarn or tow as defined in Claim 7 wherein more than about 80% of the
fibers are individualized and non-aggregated.
9. A continuous yarn or tow as defined in Claim 1 wherein said core comprises carbon,
graphite, a polymer glass, a ceramic, or a combination of any of the foregoing.
10. A continuous yarn or tow as defined in Claim 1 wherein said core comprises a carbon.
11. A fabric woven, braided or knitted from yarns as defined in Claim 1, alone, or
in combination with yarns which are of different material.
12. A non-woven sheet laid up from lengths of yarns as defined in Claim 1, alone,
or in combination with yarns of different material.
13. A three-dimensional article of manufacture produced by weaving, braiding, knitting
or laying up a mat comprised of yarns as defined in Claim 1, alone, or in combination
with yarns of different material.
14. A composition of matter comprising chopped yarns or tows as defined in Claim 1.
15. A composition of matter as defined in Claim 14 adapted for use to reflect radar
wherein the yarns or tows have been chopped into lengths relative to the wavelengths
of one or more radar frequencies.
16. A continuous yarn or tow as defined in Claim 1 wherein said layer comprising copper
has been deposited on said core by a two stage process, the first stage comprising
electroless deposition and the second stage comprising electrolytic deposition.
17. A single fiber recovered from a continuous yarn or tow as defined in Claim 1.
18. A process for the production of yarns or tows of composite fibers, said process
comprising:
(a) providing a continuous length of a plurality of semimetallic core fibers,
(b) immersing at least a portion of the length of said fibers in a bath comprising
a wetting agent in an aqueous medium,
(c) immersing at least a portion of the length of said fibers in a bath capable of
sensitizing them to the electroless deposition of a metal comprising copper,
(d) immersing at least a portion of the length of said fibers in a bath capable of
electrolessly plating said fibers with a metal comprising copper and depositing an
electrically-conductive layer of said metal on said fibers,
(e) immersing at least a portion of the length of said fibers in a bath capable of
electrolytically depositing a metal comprising copper, and
(f) applying an external voltage between the fibers and the bath sufficient to deposit
a metal comprising copper on said fibers and maintaining said voltage and resulting
current for a time sufficient to produce at least one relatively thick, uniform and
firmly adherent, electrically conductive layer comprising copper on said core and
including carrying out steps (b) to (f), inclusive, under low tension on the yarn
or tow and with spreading of the fibers.
19. A process as defined in Claim 18 carried out continuously.
20. A process as defined in Claim 18 wherein the thickness of said metal layer or
layers on said yarn or tow ranges from about 0.6 to about 3.0 microns.
21. A process as defined in Claim 19 wherein the thickness is at least about 0.8 microns.
22. A process as defined in Claim 21 wherein the thickness is at least about 1.2 microns.
23. A process as defined in Claim 18 wherein the standard deviation of the coating
thickness is less than 30% of the average coating thickness, both around the circumference
of each fiber and from fiber to fiber.
24. A process as defined in Claim 18 wherein the majority of the fibers are individualized
and non-aggregated.
25. A process as defined in Claim 24 wherein more than about 70% of the fibers are
individualized and non-aggregated.
26. A process as defined in Claim 25 wherein more than about 80% of the fibers are
individualized and non-aggregated.
27. A process as defined in Claim 18 wherein said core comprises carbon, graphite,
a polymer, glass, a ceramic, or a combination of any of the foregoing.
28. A process as defined in Claim 18 wherein said core comprises carbon.
29. A process as defined in Claim 18 including the step of weaving, braiding or knitting
yarns produced by the process alone, or in combination with yarns of a different material,
into a fabric.
30. A process as defined in Claim 18 including the step of laying up the yarns produced
by the process alone, or in combination with yarns or a different material into a
non-woven sheet.
31. A process as defined in either of Claim 25 or 26 including weaving, knitting or
laying up the material into a three-dimensional article of manufacture.
32. A process as defined in Claim 18 including the step of chopping the yarns produced
by the process into shortened lengths.
33. A process as defined in Claim 32 including chopping the yarns or tows produced
into lengths relative to the wavelength of one or more radar frequencies.
34. A process as defined in Claim 18 wherein sensitizing bath (c) comprises a colloidal
suspension of palladium and tin chloride.
35. A process as defined in Claim 18 wherein electroplating bath (e) comprises a pyrophosphate
copper plating solution.
36. A process as defined in Claim 31 wherein said bath (e) also includes a stabilizing
amount of mercaptobenzothiozole, alone, or in combination with 2,2-bipyridyl.
37. Yarns or tows of composite fibers produced by the process of Claim 18.
38. A single fiber recovered from a continuous yarn or tow prepared by the process
defined in Claim 18.
39. A composition of matter comprising:
(a) a continuous yarn or tow comprising composite fibers, which have a semimetallic
core and at least one relatively thick, uniform and firmly adherent, electrically
conductive layer comprising copper on said core, said fibers being disposed in,
(b) a matrix comprising (i) a metal or (ii) an organic polymeric material.
40. A composition as defined in Claim 39 wherein the thickness of said metal layer
or layers ranges from about 0.6 to about 3.0 microns.
41. A composition as defined in Claim 40 wherein the thickness is at least about 0.8
microns.
42. A composition as defined in Claim 41 wherein the thickness is at least about 1.2
microns.
43. A composition as defined in Claim 39 wherein the standard deviation of the coating
thickness is less than 30% of the average coating thickness, both around the circumference
of each fiber and from fiber to fiber.
44. A composition as defined in Claim 39 wherein a majority of the fibers are individualized
and non-aggregated.
45. A composition as defined in Claim 44 wherein more than about 70% of the fibers
are individualized and non-aggregated.
46. A composition as defined in Claim 45 wherein more than about 80% of the fibers
are individualized and non-aggregated.
47. A composition as defined in Claim 39 wherein said core comprises carbon, graphite,
a polymer, glass, a ceramic, or a combination of any of the foregoing.
48. A composition as defined in Claim 39 wherein said core comprises carbon.
49. A composition of matter as defined in Claim 39 wherein said yarns or tows (a)
are chopped.
50. A composition as defined in Claim 39 wherein said layer comprising copper has
been deposited on said core by a two stage process, the first stage comprising electroless
deposition and the second stage comprising electrolytic deposition.
51. A composition as defined in Claim 39 wherein said composite fibers (a) are arranged
in a side-by-side, substantially parallel relationship, woven, or knitted into a reinforcing
structure.
52. A composition as defined in Claim 39 wherein said metal matrix (b) comprises copper,
aluminum, lead, zinc, silver, gold, magnesium, tin, titanium, iron, nickel alloys,
or a mixture of any of the foregoing.
53. A composition as defined in Claim 52 wherein said metal matrix comprises copper.
54. A composition as defined in Claim 39 wherein the core comprises graphite, the
metal layer comprises copper, the thickness of the copper layer is about 0.6 to 3.0
microns, the metal matrix comprises copper, and the graphite fibers are arranged in
a side-by-side, substantially parallel relationship.
55. A process for the production of an article of manufacture, said process comprising:
(a) providing a continuous metal coated yarn or tow as defined in Claim 39; and
(b) building up a metal matrix around the metal coated fibers to form a composite
material.
56. A process as defined in Claim 55 wherein the metal matrix is built up around the
coated filaments by powder technology techniques, casting or pultrusion.
57. An article of manufacture comprising:
(a) semimetallic core fibers uniformly distributed throughout its thickness in,
(b) a metal matrix comprising copper, said article being substantially free of voids
and having substantially no matrix-rich regions.
58. An article as defined in Claim 57 produced by direct consolidation under heat
and pressure of a continuous yarn or tow comprising composite fibers, the majority
of which have a core and at least one relatively thick, uniform and firmly adherent,
electrically conductive layer comprising copper on said core.
59. An article as defined in Claim 58 wherein the thickness of the metal layer or
layers ranges from about 0.6 to about 3.0 microns.
60. An article as defined in Claim 59 wherein the thickness is at least about 0.8
microns.
61. An article as defined in Claim 60 wherein the thickness is at least about 1.2
microns.
62. An article as defined in Claim 58 wherein the standard deviation of the coating
thickness is less than 30% of the average coating thickness, both around the circumference
of each fiber and from fiber to fiber.
63. An article as defined in Claim 58 wherein a majority of the fibers are individualized
and non-aggregated.
64. An article as defined in Claim 63 wherein more than about 70% of the fibers are
individualized and non-aggregated.
65. An article as defined in Claim 64 wherein more than about 80% of the fibers are
individualized and non-aggregated.
66. A composition as defined in Claim 39 wherein said matrix (b) comprises an organic
polymeric material.
67. A composition as defined in Claim 66 wherein said organic polymeric material is
substantially non-conductive.
68. A composition as defined in Claim 66 wherein said organic polymeric material is
selected from the group comprising polyesters, polyethers, polycarbonates, epoxies,
epoxy-novolacs, epoxy-polyurethanes, urea-type resins, phenol-formaldehyde resins,
thiourea resins, melamine resins, urea-aldehyde resins, alkyd resins, polysulfide
resins, vinyl organic prepolymers, multifunctional vinyl ethers, cyclic ethers, cyclic
esters, polycarbonate-co-esters, polycarbonate-co-silicones, polyetheresters, polyimides,
polyamides, polyesterimides, polyamideimides, polyetherimides and polyvinylchlorides.
69. An article of manufacture comprising a composition as defined in Claim 66 wherein
said organic polymeric material (i) is present with a woven, braided, knitted, or
non-woven fabric, sheet or mat comprising said composite fibers (a).
70. A shaped article of manufacture formed from a composition as defined in Claim
66 wherein the organic polymeric material (b) is reinforced with a woven, braided,
knitted or non-woven fabric, sheet or mat comprising said composite fibers (a).
71. A composition as defined in Claim 39 wherein the organic polymeric material (b)
is reinforced with composite fibers (a) in comminuted form.
72. A composition as defined in Claim 66 wherein the organic polymeric material (b)
is an epoxy, the electrically conductive core of said composite fibers (a) is carbon
and the electrically conductive metal layer is formed of copper.
73. An injection molding compound comprising elongated granules, each of said granules
containing a bundle of elongated composite fibers, which have a semimetallic core
and at least one relatively thick, uniform and firmly adherent, electrically conductive
layer comprising copper on said core, said fibers extending generally parallel to
each other longitudinally of the granule and substantially uniformly dispersed throughout
said granule in a thermally stable, film forming thermoplastic adhesive.
74. An injection molding compound as defined in Claim 73 wherein the thickness of
said metal layer or layers ranges from about 0.6 to about 3.0 microns.
75. An injection molding compound as defined in Claim 74 wherein the thickness is
at least about 0.8 microns.
76. An injection molding compound as defined in Claim 75 wherein the thickness is
at least about 1.2 microns.
77. An injection molding compound as defined in Claim 73 wherein standard deviation
of the coating thickness is less than 30% of the average coating thickness, both around
the circumference of each fiber and from fiber to fiber.
78. An injection molding compound as defined in Claim 73 wherein the majority of the
fibers are individualized and non-aggregated.
79. An injection molding compound as defined in Claim 78 wherein more than about 70%
of the fibers are individualized and non-aggregated.
80. An injection molding compound as defined in Claim 79 wherein more than about
80% of the fibers are individualized and non-aggregated.
81. An injection molding compound as defined in Claim 73 wherein said core comprises
carbon, graphite, a polymer, glass, a ceramic, or a combination of any of the foregoing.
82. An injection molding compound as defined in Claim 73 wherein said core comprises
carbon.
83. An injection molding compound as defined in Claim 73 wherein said adhesive comprises:
(a) a poly(C₂-C₆ alkyl oxazoline) in combination with
(b) a poly(vinylpyrrolidone), said adhesive substantially surrounding each said filament.
84. An injection molding compound as defined in Claim 83 wherein component (b) comprises
from about 7.5 to about 75 percent by weight of component (a) and component (b) combined.
85. An injection molding compound as defined in Claim 73 wherein said granules are
from about one-forty eighth to about three-sixteenths inches in diameter.
86. An injection molding compound as defined in Claim 85 wherein said granules are
from about one-thirty second to about one-eighth inches in diameter.
87. An injection molding compound as defined in Claim 73 wherein the amount of thermoplastic
adhesive is not substantially in excess of that which maintains fiber bundle integrity
during handling.
88. An injection molding compound as defined in Claim 73 wherein the reinforcing filaments
comprise from 67.5-97.5% by volume and the thermally stable, film forming adhesive
comprises correspondingly from 2.5-32.5% by volume.
89. An injection molding compound as defined in Claim 87 wherein the reinforcing filaments
comprise from 85 to 95% by volume and the thermally stable, film forming adhesive
comprises correspondingly from 5-15% by volume.
90. An injection molding compound as defined in Claim 74 wherein thermoplastic adhesive
comprises poly(ethyl oxazoline).
91. An injection molding compound as defined in Claim 90 wherein poly(ethyl oxazoline)
has a molecular weight in the range of from about 50,000 to about 500,000.
92. An injection molding compound as defined in Claim 74 wherein the thermoplastic
adhesive comprises poly(ethyl oxazoline) and poly(vinylpyrrolidone).
93. An injection molding compound as defined in Claim 92 wherein the poly(vinylpyrrolidone)
has a molecular weight in the range of from about 10,000 to about 220,000.
94. An injection molding composition comprising:
(i) thermoplastic resin molding granules; and
(ii) elongated granules as defined in Claim 1, the amount of component (ii) in said
composition being sufficient to provide 1-60% by weight of said filaments per 100%
by weight of (i) plus (ii).
95. In the process of injection molding, the step of forcing into a mold an injection
molding composition comprising a mixture of:
(i) thermoplastic molding granules; and
(ii) an amount of elongated granules as defined in Claim 1 effective to provide reinforcement.