Background of the Invention
Field of the Invention
[0001] The field of art to which this invention pertains is shrinkable materials and, more
particularly, it is directed to processes for treating a tow of shrinkable fibers.
[0002] Specifically such invention is a process of treating a tow of aromatic polyamide
fibers by moving the tow in folds through a chamber having a plug section which is
operatively connected by a restricted opening to a treatment section and by heating
the tow with steam in the treatment section.
[0003] Sufficient steam migrates into the plug section to cause shrinkage of the tow in
this section. The cross-sectional area of the tow is substantially the same as the
cross-sectional area of the entrance opening of the plug section as it enters such
opening but it has a smaller cross-sectional area, due to shrinkage, as it leaves
this section and moves through the restricted entrance opening of the treatment section.
By making this opening smaller so that the cross-sectional area of the shrunken tow
as it enters such restricted opening is substantially the same as the cross-sectional
area of such opening, loss of steam through the entrance opening of the plug section
is minimized.
[0004] More specifically, this invention is a process for dyeing a fiber structure of poly(meta-phenylene
isophthalamide) fibers with a water-soluble dye by heating the amorphous, shrinkable
fibers, as spun and prior to drying, with steam, in a specifically designed chamber,
at a temperature from about 110°C. to about 140°C., and preferably at about 120°C.,
for a time sufficient to diffuse substantially all of the dye into the minute pores
in the fibers, throughout the fiber structure.
[0005] An organic water-insoluble material, such as an ultraviolet light screener, may
also be mixed with the water-soluble dye and padded onto the water-swollen fibers
prior to heating. While the dye is effectively diffused into the fiber structure at
temperatures between 110°C. and 140°C., such structure must also be heated with steam
at a sublimation temperature below the glass transition temperature of the fibers
in order to sublime the screener into the pores of the fibers. The fibers are then,
preferably, further heated with steam at about 165°C. for a time sufficient to collapse
the pores in the fibers and lock the dye therein. At this temperature the fibers also
will crystallize and the fiber structure is thereby stabilized against progressive
laundry shrinkage.
Description of the Related Art
[0006] Aromatic polyamide fibers are well known to the art. They have high tensile strength,
are flame and heat resistant, possess good flex life, and have high melting points
which make them particularly suited to be formed into fabrics usable as protective
clothing, and for many other uses.
[0007] It further is known that while aromatic polyamide fibers possess many desired properties
as manufactured they also require, for given uses, that various steps be taken to
improve a property or properties of the fibers to meet a specific end use. As an
example, various additives such as dyes, ultraviolet light screeners, flame retardants,
antistatic agents or water repellents, may be incorporated into the fibers during
basic manufacture or in subsequent processing steps to improve their performance levels.
[0008] This invention is specifically directed to aromatic polyamide fibers of a poly(meta-phenylene
isophthalamide) polymer, hereinafter referred to as "MPD-I fibers". Such fibers,
which are described in greater detail in U. S. patent 3,287,324 to Sweeny, for example,
possess many useful properties. It is well known to the art, however, that these fibers
are difficult to dye.
[0009] Various techniques have evolved to solve this dyeing problem. One such solution is
more fully described in copending EP-A-0 228 224, which application is incorporated
herein by reference.
[0010] The invention of this copending application solves various problems found in the
prior art by surprisingly finding that by heating as-spun, never-dried, water-swollen,
or still moist to the touch, MPD-I fibers with steam, heated within certain temperature
ranges, it is possible effectively to dye the fibers. Specifically, it has been found
that such fibers may be dyed, using a water-soluble dye, by heating the fibers with
steam heated at a temperature from about 110°C. to 140°C. for a time sufficient to
diffuse the dye into the pores of the fibers.
[0011] It further has been found that after this diffusion step has taken place that such
fibers may be subsequently heated, again with steam, at a temperature of about 165°C.
to collapse the fibers and lock the dye in place. This latter step will also crystallize
the fibers and stabilize them against progressive laundry shrinkage.
[0012] In practicing the invention just described, the treatment or dyeing of the fibers
is accomplished by moving such fibers, in tow form, through a treatment chamber having
one or more treatment sections. It has been found difficult to maintain the steam
temperatures at the critical limits required, within these sections, since the steam
tends to migrate toward the chamber openings. This problem is partially solved, as
described in the above-mentioned copending EP-A-0 228 224, by supplying the tow to
the chamber in folds. While this is an effective means of controlling the loss of
steam, the problem still remains troublesome, particularly in the case of shrinkable
tows because their cross-sections vary due to shrinkage as they move through the chamber.
The instant invention not only solves this shrinkage problem but also provides an
improved process for practicing the invention of copending EP-A-0 228 224.
[0013] Accordingly, this invention provides improved processes for treating aromatic polyamide
fibers, using steam to dye a water-swollen fiber structure of poly(meta-phenylene
isophthalamide) fibers with a water-soluble dye, before they are dried, or to add
an organic water-insoluble material to the fibers, either mixed with the dye or alone,
and to lock the dye and/or other impregnant into the pores of the fibers. This is
accomplished by maintaining the steam within certain critical temperature ranges (e.g.,
110°C. to 140°C.) in a specially designed chamber to diffuse the dye into the fiber
pores and up to 165°C. to sublime the water-insoluble material into such pores. At
this latter temperature the dye is also locked into the fibers, while stabilizing
such fibers against progressive laundry shrinkage.
Summary of the Invention
[0014] Briefly described, this invention is a process for treating synthetic fibers including
the steps of:
moving a tow of shrinkable fibers in folds through a treatment section having an entrance
opening and an exit opening smaller than the entrance opening and
heating the tow with steam in the treatment section.
[0015] In this process, the tow has a cross-sectional area substantially the same as the
cross-sectional area of the entrance opening as it enters that opening whereby loss
of steam through such opening is minimized and a smaller cross-sectional area as it
leaves the section, due to shrinkage. This latter area is only slightly smaller, or
substantially the same size as, the exit opening whereby loss of steam is minimized
through this opening as well.
[0016] In a more specific embodiment, this invention is a process of treating a tow of shrinkable
fibers which includes the steps of:
moving the tow in folds through a plug section operatively connected by a restricted
opening to a treatment section, with the plug section having an entrance opening
larger than the restricted opening of the treatment section, and
heating the tow with steam in the treatment section.
[0017] Sufficient steam migrates through the restricted opening from the treatment section
to the plug section to cause shrinkage of the tow in the plug section. The tow has
a cross-sectional area substantially the same as the cross-sectional area of the
entrance opening of the plug section as it moves through this opening and has a smaller
cross-sectional area as it leaves the plug section and moves through the entrance
opening of the treatment section, due to shrinkage. The cross-sectional area of
the shrunken tow as it enters the smaller entrance opening of the treatment section
is substantially the same as the cross-sectional area of this opening and, along with
the tow moving in folds in the plug section, this substanially prevents loss of steam
through the entrance opening of the plug section.
[0018] Preferably the tow is an amorphous aromatic polyamide and, more specifically the
aromatic polyamide is poly meta-phenylene isophthalamide). Such tow has a second order
glass transition temperature in steam of above about 150°C.
[0019] The processes just described further may include the steps of padding a water-soluble
dye onto the tow prior to the treatment section and heating the tow with steam in
the treatment section at a temperature of from about 110°C. to 140°C. for a time
sufficient to diffuse the dye into pores in the fibers of the tow. Still further steps
may include moving the tow into a second treatment section and heating the tow with
steam in this section at a temperature above its glass temperature from about 150°C.
to 165°C. for a time sufficient to collapse the pores and lock the dye within the
fibers and to crystallize such fibers and thereby stabilize the tow against progressive
laundry shrinkage.
[0020] In still another embodiment, the process of this invention includes the steps of:
moving the tow through first and second treatment sections,
contacting the fibers of the tow prior to the first treatment section with an aqueous
mixture containing a water-soluble dye and an organic water-insoluble material which
sublimes in steam at a temperature below the glass transition temperature of the fibers,
heating the water-swollen fibers with steam in the first treatment section at a temperature
from about 110°C. to 140°C. for a time sufficient to diffuse substantially all of
the water-soluble dye into the pores of such fibers throughout the fiber structure,
heating the water-swollen fibers with steam at a sublimation temperature below the
glass transition temperature of the fibers for a time sufficient to sublime the water-insoluble
material into the pores of such fibers throughout the fiber structure, and thereafter
heating the water-swollen fibers with steam in the second treatment section at a temperature
above the glass transition temperature of the fibers for a time sufficient to collapse
the pores and irreversibly lock the dye within the fibers and to stabilize the fibers
against progressive laundry shrinkage.
[0021] In this latter process, the fibers preferably are heated with steam at a sublimation
temperature from about 110°C. to 150°C. The water-insoluble material may be an ultraviolet
light screener and the water-insoluble material may be a disperse dye. Further the
fibers may be heated with steam in the second treatment section at a temperature of
about 165°C. to stabilize the fibers.
[0022] In more precise detail, this invention is a process of treating a tow of shrinkable
material including the steps of:
moving the tow at a first speed through an entrance opening at one end of a funnel-shaped,
fold-forming section having converging walls which define a discharge opening at
the other end of the section, with the entrance opening being larger than the discharge
opening;
moving the folded tow through a restricted entrance opening of a chamber defined by
walls and having a plurality of sections including a plug section and first and second
steam treatment sections, with the chamber being connected to the discharge opening
of the fold-forming section and the chamber entrance opening being smaller than the
entrance opening of fold-forming section, and the chamber further having a tow exit
opening
wherein the dual action of the converging walls of the fold-forming section and the
tow pushing through the restricted entrance opening of the chamber forms a plurality
of folds in the tow,
wherein steam is introduced into the second steam treatment section, which is positioned
between the entrance and exit openings of the chamber, whereby such steam flows,
in one direction into and through the second steam treatment section and into the
first steam treatment section, and from there into the plug section and toward the
entrance opening of the fold-forming section and
in the other direction into and through the second steam treatment section and toward
the exit opening of the chamber,
engaging the folds of the tow as it is moved in the fold-forming section and through
the entrance opening of the chamber with pins on an endless chain moving at a second
speed slower than the first speed
moving the tow in folds through the plug section at the second speed and
wherein the plurality of folds of the tow are in substantial contact with the walls
of chamber defining the plug section during a substantial portion of their movement
through this section whereby to help substantially eliminate loss of steam through
the entrance opening of the fold-forming section and
wherein the steam flowing into this plug section shrinks the tow so that it has a
cross-sectional area smaller than that at which it entered this section
moving the tow in folds through a restricted entrance opening of the first treatment
section, with such entrance opening being smaller than the entrance opening of the
chamber moving the tow through the first treatment section at the second speed and
wherein the plurality of folds of the tow, as shrunken in the first plug section,
are substantially in contact with the walls defining the first treatment section through
much of their movement through this section whereby to further help prevent any loss
of steam flowing though this section and through the plug section from escaping through
the entrance opening of the fold-forming section.
[0023] In such process, preferably, the chain engages two tows, one on each side, and moves
them at the second speed through the chamber and the entrance opening of the chamber
is connected to discharge opening of the fold-forming section by a tapered surface.
A tapered surface also preferably connects the plug section to the entrance opening
of the treatment section.
[0024] Finally, in its broadest terms, this invention matches the shrinking profile of the
tow with the profile of the chamber walls, during treatment of such tow in the chamber.
Brief Description of the Drawing
[0025]
Fig. 1 is a schematic view of an apparatus, including a treatment chamber suitable
for practicing the process of this invention.
Figs. 2 and 2A are schematic views showing the chamber in greater detail.
Fig. 3 is a cross-sectional view taken along lines A-A of Fig. 1, which highlights
a significant feature of this invention, in showing the substantial contact of the
tow with the walls defining the restricted opening of the treatment section of the
chamber as it is moved through that opening.
Description of the Preferred Embodiments
[0026] This invention is an improved process for treating shrinkable materials, such as
aromatic polyamide fibers.
[0027] More specifically,in the processes of this invention, a water-soluble material, and,
if desired, a water-insoluble material are diffused or sublimed into a fiber structure
of MPD-I amorphous synthetic fibers to improve their properties. During the diffusion
and sublimation steps, the fibers are water-swollen or damp to the touch, with open
pores. Steam controlled at critical temperatures in a chamber, is used to perfect
the process.
[0028] Briefly, the fibers of this invention are prepared from aromatic polyamide polymers
such as are disclosed in U. S. patent 3,063,966 to Kwolek, Morgan and Sorenson; 3,094,511
to Hill, Kwolek and Sweeny; and 3,287,324 to Sweeny, for example. These patents, and
their teachings, are incorporated by reference into this application.
[0029] In preparing the basic water-swollen MPD-I fibers which are treated by the process
of this invention, aromatic polyamides which have been prepared by procedures shown
in the above-mentioned patents are combined with various solvents to form a spinning
solution as shown, for example, in U. S. patent 3,063,966 and the fibers or filaments
are formed by extruding the spinning solution through orifices in a spinneret. Such
fibers may be dry-spun or wet-spun to form a water-swollen fiber structure. In either
case, the fibers as spun are substantially amorphous.
[0030] The fibers whether dry-spun or wet-spun contain a substantial amount of solvent after
having been solidified in a dry-spinning evaporation cell or coagulated in a wet-spinning
precipitation bath. To remove the solvent such fibers are brought into contact with
an aqueous extraction bath, as is known in the art. As a result the fibers become
"water-swollen" with a water content of around 35% or more.
[0031] The above-described steps of forming amorphous water-swollen fibers of an aromatic
polyamide polymer are known to the art and these fibers are all suitable for being
further treated or processed in accordance with the process of this invention.
[0032] Specifically, in a preferred process, these water-swollen fibers, which have not
been dried, are contacted with an aqueous solution containing a water-soluble material
and heated with steam at a temperature from about 110°C. to 140°C. for a time sufficient
to diffuse substantially all of the water-soluble material into the pores of the fibers
throughout such fiber structure. The material diffused into the fibers preferably
is a dye. It may also be a surfactant.
[0033] In another preferred embodiment, when the material is dyed, the water-swollen, dye-containing
fibers are then further heated with steam at a temperature above the glass transition
temperature of the fibers for a time sufficient to collapse the pores and irreversibly
lock the dye within the fibers and to crystallize such fibers and stabilize them against
progressive laundry shrinkage. Temperatures in the range from 150°C. to 165°C. will
accomplish these objectives.
[0034] In still another embodiment, never-dried, amorphous MPD-I fibers of the type described
are contacted with an aqueous mixture containing both a water-soluble material, such
as a dye, and an organic water-insoluble material which sublimes in steam at a temperature
below the glass transition temperature of the fibers. The water-swollen fibers are
then heated with steam at a temperature from about 110°C. to 140°C. for a time sufficient
to diffuse substantially all of the water-soluble dye into the pores of such fibers
and at a sublimation temperature below the glass transition temperature of the fibers
to sublime the water-insoluble material into the open pores of such fibers. After
the diffusion and sublimation steps have been completed, the fibers may be further
heated with steam at a temperature above the glass transition temperature of the fibers
for a time sufficient to collapse the pores and irreversibly lock the material within
the fibers and to stabilize the fibers against progressive laundry shrinkage.
[0035] The term "fiber", as used herein, includes both staple fibers and continuous filaments.
The continuous filaments may be in the form of a tow containing a large number of
filaments or in the form of a yarn.
[0036] Referring specifically to Figure 1 of the drawing, a fiber structure of never-dried,
shrinkable fibers, as spun, in large bundles called tow, as indicated by the reference
numeral 1, is supplied from a supply source 2 and passed over guide rolls 3 to nip
rolls 4 and 4′.
[0037] An aqueous bath 5 of constant level is maintained at the entrance to the nip rolls.
The tow 1 of moist to the touch fibers is brought into contact with the bath 5 which
contains the material (e.g., a water-soluble dye, or surfactant, or ultraviolet light
screener, for example) to be diffused or sublimed into the fibrous tow. The pick-up
of material on the never-dried tow may be adjusted by suitably controlling the speed
of the tow and the pressure applied between the nip rolls.
[0038] The tow 1 coated with the desired amount of material is then moved by feed rolls
6 into a treatment chamber 7, which is suitably an elongated tube having two or more
treatment sections to which steam under appropriate pressure can be supplied, as
will be explained in greater detail.
[0039] The tow is heated in these treatment sections at the required critical temperatures
to diffuse the water-soluble material and to sublime the insoluble material into the
fibers, after which such fibers may be further heated to stabilize the fiber structure
against progressive laundry shrinkage.
[0040] The processed tow is then moved out of the chamber 7 and onto a conveyor 8, and then
through squeeze rolls 9 to help remove water from the treated tow. The tow is then
fed by feed rolls 10 into a dryer 11, which includes upper and lower conveyors 12
and 13 which move the tow at a speed which is adapted to form folds in the tow in
the dryer. Such conveyors move the tow through the dryer 11 for a time sufficient
to remove substantially all of the water from the tow. The dried and processed tow
is then moved over transfer rolls 14 and into a storage container 15.
[0041] The treatment process will now be described in detail.
[0042] The tow 1 carrying the dye or other treatment material from the bath 5 is fed by
feed rolls 6 at a first speed through an entrance opening 17 at one end of a funnel-shaped,
fold-forming section 18 having converging walls 19 which define a discharge opening
20 at the other end of the section.
[0043] The tow is then moved through a restricted entrance opening 21 of the treatment chamber
7 defined by walls 22 and having a plurality of sections including a plug section
23 and first and second steam treatment sections 24 and 25. The chamber 7 is connected,
preferably by a sharply tapered surface 22′ to the discharge opening 20 of the fold-forming
section 18 and the chamber entrance opening 21 is smaller than the entrance opening
17 of the fold-forming section 18. The dual action of the converging walls of the
fold-forming section 18 and the tow 1 pushing through the restricted entrance opening
21 of the chamber 7 forms a plurality of folds in the tow. The chamber 7 further has
a tow exit opening 26.
[0044] Steam in introduced into the second steam treatment section 25 which is positioned
between the entrance and exit openings 21, 26 of the chamber 7. The steam flows in
one direction into the second steam treatment section 25, then through this section
and into the first steam treatment section 24, and from there into the plug section
23 and toward the entrance opening 17 of the fold-forming section 18 and in the other
direction into and through the second steam treatment section 25 and toward the exit
opening 26 of the chamber 7.
[0045] As best seen in Figure 3, the folds of the tow 1 are engaged by pins 27 on an endless
chain 28 as the tow is moving in fold-forming section 18 and through the entrance
opening 21 of the chamber 7. The chain 28 moves at a second speed slower than the
first speed at which the tow is fed into the fold-forming section 18, by feed rolls
6.
[0046] The tow is moved in folds through the plug section 23 at this second speed. In this
section 23 the plurality of folds of the tow are in substantial contact with the walls
of chamber 7 during a substantial portion of their movement through such section whereby
to help substantially eliminate loss of steam through the entrance opening 17 of the
fold-forming section 18. The steam flowing into this plug section 18 shrinks the tow
so that it has a cross-sectional area smaller than that at which it entered the section.
The tow is then moved from the plug section 23 and a restricted entrance opening 29
of the first treatment section 24. The restricted entrance opening 29 is smaller than
the restricted entrance opening 21 of the chamber 7.
[0047] The tow is moved through the first treatment section 24 at the second speed and the
plurality of folds of the tow, as shrunken in the plug section 23, are substantially
in contact with the walls defining the first treatment section 24 through much of
their movement through such section whereby to further help prevent any loss of steam
flowing through this section 24 and through the plug section 23 from escaping through
the entrance opening 17 of the fold-forming section 18. This invention provides better
control of steam temperatures in the critical treatment sections of the chamber.
[0048] The substantial contact of the folded tow with the walls of the chamber 7, pushing
through the restricted entrance opening 21 of the plug section 23 and hence through
the restricted opening 29 of the first treatment section 24, along the contact of
the folds with the walls 22 in these sections, substantially prevents escape of steam
through the entrance opening of the chamber.
[0049] In this same connection, it frequently is desirable to wash the treated fibers in
a wash section 30 of the chamber 7 prior to discharge of the tow from such chamber.
The wash water along with the folded tow, further combine to substantially prevent
loss of steam through the exit opening 26 of the chamber, as well.
[0050] By controlling loss of steam through the chamber openings, it is possible to maintain
better control of the critical temperatures required in the first and second treatment
sections, to effectively treat the fibers, as previously described.
[0051] The treatment of the tow in the manner just described provides MPD-I fibers having
the improved properties sought in the treatment.
[0052] The following example will further illustrate this invention.
Example
A. Preparation of Never-Dried Filaments of Poly(metaphenylene isophthalamide) (MPD-I).
[0053] Filaments of MPD-I having an inherent viscosity of 1.5 were dry spun from a filtered
solution containing 19% MPD-I, 70% dimethylacetamide (DMac), 9% calcium chloride,
and 2% water. On leaving the drying tower the as-spun filaments were given a preliminary
wash with water so that they contained about 60% DMac, 15% calcium chloride, and 100-150%
water, based on the weight of dry polymer. The filaments were washed and drawn 4X
at 90°C. in a counter-current extraction-draw process in which the calcium chloride
determined as chloride content and DMac content were reduced to about 0.1% and 0.5%,
respectively. The wet filaments were gathered together to form a tow, a conventional
antistatic finish was applied to the tow, and the tow was crimped in a stuffer box
crimper at a temperature of about 80°C. in the presence of steam. The tow was then
collected, still moist to the touch, in a plastic-lined cardboard box. The individual
filaments had a linear density of about 1.55 decitex (dtex) (1.7 dpf). The linear
density of the never-dried filaments here and elsewhere herein is based on the weight
of dry filaments.
B. Dyeing and Shrinkage Stabilization of Tows of Never-Dried MPD-I Filaments in a
Steam Chamber.
[0054] Two 120-kilotex (1,000,000 denier) tows of never-dried MPD-I filaments, prepared
as described in Part (A) above, were creeled through the guides of a continuous tow
dyeing apparatus equipped for high shrinkage tow. The tows were first fed between
nip rolls at a rate of 14 m/min. wherein an aqueous dye solution was padded onto the
tow so that the individual filaments in the tow were coated with the solution. The
solution contained 40 g/l of C.I. (Colour Index) No. Basic Yellow 28 dye (a water-soluble
dye), and 6 g/l of C.I. No. Basic Red 15 (a water-soluble dye), and 6 g/l cellulosic
thickner, and 58 g/l of anionic surfactant, adjusted to a pH of 7 (adding acetic acid
or caustic soda as needed until the desired pH was obtained). The pick-up of the
dye solution on the tow as 30 weight %.
[0055] After the tows were padded with the dye solution, they were then passed through the
entrance funnel of a chamber, such as that shown in Figure 2, the rectangular discharge
end of the funnel having a width of 95 mm and a depth of 115 mm. Within the funnel
the tows were turned and then gathered into folds as they were picked up by a chain
moving at 1 m/min., one tow on each side of the chain. The tows, carried by the chain,
were then passed into the entrance opening of a plug section of the chamber, which
had a rectangular cross section 90 mm in width and 110 mm in depth, the discharge
opening of the funnel and the entrance opening of the plug section being gently tapered
into one another to avoid a stair step transition. The plug section was 3 m in length,
and from it the tows were carried by the chain into a first treatment section, also
3 m in length, which had a rectangular cross section 88 mm in width and 107 mm in
depth, the transition from the plug section to the first treatment section being gently
tapered to avoid a stair-step transition. From the first treatment section the tows
were then carried by the chain into a second treatment section 6 m in length wherein
the tows of filaments coated with the solution were exposed to steam at a pressure
of 609 kPa (six bars) and a temperature of 165°C. the steam being introduced into
the chamber through holes in the walls of the chamber. The steam flowed from the
second steam section back into the first treatment section and then into the plug
section at progressively lower pressures and temperatures in the direction of the
entrance funnel, the folds of the tow effectively sealing the entrance to the plug
section so that substantially no steam flowed back into the entrance funnel. Within
a zone beginning at about the end of the plug section and extending well into the
first treatment section the filaments in the tows coated with the solution were exposed
to steam at a temperature of about 120°C. for a contact time of about two minutes.
The temperature of the tows at the end of the first treatment section, going into
the second steam treatment section, was about 165°C. and remained at about 165°C.
throughout the second treatment section. Upon leaving the treatment sections the
tows were passed into a final wash section, wherein they were washed with water. The
water and the wet tows acted together to condense the steam flowing from the second
treatment section and formed an effective seal to prevent any steam from flowing from
the exit end of the chamber.
[0056] After the tows were washed, they were fed into a forced air dryer, wherein their
moisture level was reduced to 7% moisture. Finish was not added to the tow. The tows
were dyed to a bright shade of orange. The shrinkage of the tows was measured and
determined to be 0.9%.
[0057] In other experiments with similar tows using apparatus having a steam chamber of
constant area, it was found to be difficult to maintain the steam at a pressure higher
than about 203 kPa (two bars). The shrinkage of the tow when heated with steam at
a pressure of only 203 kPa was 7%.
1. A process of treating a tow of shrinkable fibers including the steps of:
moving the tow in folds through a treatment section, said section having an entrance
opening and an exit opening smaller than the entrance opening and
heating the tow with steam in the treatment section,
said tow having a cross-sectional area substantially the same as the cross-sectional
area of the entrance opening as it enters the section whereby loss of steam through
that opening is minimized
said tow having a smaller cross-sectional area as it leaves the section, due to shrinkage,
and said area being substantially the same as the cross-sectional area of the exit
opening whereby loss of steam is minimized through that opening.
2. A process of treating a tow of shrinkable fibers including the steps of:
moving the tow in folds through a plug section operatively connected by a restricted
opening to a treatment section, said plug section having an entrance opening larger
than the restricted opening of the treatment section, and
heating the tow with steam in the treatment section
wherein sufficient steam migrates through the restricted opening from the treatment
section to the plug section to cause shrinkage of the tow in the plug section, and
wherein the tow has a cross-sectional area substantially the same as the cross-sectional
area of the entrance opening of the plug section as it moves through said opening
and
wherein the tow has a smaller cross-sectional area as it leaves the plug section and
moves through the entrance opening of the treatment section, due to shrinkage, and
wherein the cross-sectional area of the shrunken tow as it enters the smaller entrance
opening of the treatment section is substantially the same as the cross-sectional
area of this opening and
wherein the tow moving in folds in the plug section substantially prevents loss of
steam through the entrance opening of the plug section.
3. The method of claim 1 or claim 2 wherein the tow is an amorphous aromatic polyamide.
4. The method of claim 3 wherein the aromatic polyamide is poly(meta-phenylene isophthalamide).
5. The method of claim 3 or claim 4 wherein the aromatic polyamide has a second order
glass transition temperature in steam of above about 150°C.
6. The method of any one of claims 1 to 5 including the further step of:
padding a water-soluble dye onto the tow prior to the treatment section and wherein
the tow is heated with steam in such treatment section at a temperature of from about
110°C. to 140°C. for a time sufficient to diffuse the dye into pores in the fibers
of the tow.
7. The method of any one of claims 1 to 6 including the further step of:
moving the tow into a second treatment section wherein such tow is heated with steam
at a temperature above its glass temperature from about 150°C. to 165°C. for a time
sufficient to collapse the pores and lock the dye within the fibers and to crystallize
such fibers and thereby stabilize the tow against progressive laundry shrinkage.
8. The method of any one of claims 1 to 5 including the further steps of:
moving the tow through first and second treatment sections,
contacting the fibers of the tow prior to the first treatment section with an aqueous
mixture containing a water-soluble dye and an organic water-insoluble material which
sublimes in steam at a temperature below the glass transition temperature of the
fibers,
heating the fibers with steam in the first treatment section at a temperature from
about 110°C. to 140°C. for a time sufficient to diffuse substantially all of the water-soluble
dye into the pores of such fibers throughout the fiber structure,
heating the water-swollen fibers with steam at a sublimation temperature below the
glass transition temperature of the fibers for a time sufficient to sublime the water-insoluble
material into the pores of such fibers throughout the fiber structure, and thereafter
heating the water-swollen fibers with steam in the second treatment section at a temperature
above the glass transition temperature of the fibers for a time sufficient to collapse
the pores and irreversibly lock the dye within the fibers and to stabilize the fibers
against progressive laundry shrinkage.
9. The process of claim 8 wherein the fibers are heated with steam in the first treatment
section at a sublimation temperature of from about 110°C. to 150°C.
10. The process of claim 8 or claim 9 wherein the water-insoluble material is an ultraviolet
light screener.
11. The process of claim 8 or claim 9 wherein the water-insoluble material is a disperse
dye.
12. The process of any one of claims 8 to 11 wherein the fibers are heated with steam
in the second treatment section at a temperature of about 165°C.
13. A process of treating a tow of shrinkable material including the steps of:
moving the tow at a first speed through an entrance opening at one end of a funnel-shaped,
fold-forming section having converging walls which define a discharge opening at
the other end of the section, said entrance opening being larger than the discharge
opening;
moving the folded tow through a restricted entrance opening of a chamber defined by
walls and having a plurality of sections including a plug section and first and second
steam treatment sections, said chamber being connected to the discharge opening of
the fold-forming section and said chamber entrance opening being smaller than the
entrance opening of the fold-forming section, said chamber further having a tow exit
opening
wherein the dual action of the converging walls of the fold-forming section and the
tow pushing through said restricted entrance opening of the chamber forms a plurality
of folds in the tow,
wherein steam is introduced into the second steam treatment section, which is positioned
between the entrance and exit openings of the chamber, whereby such steam flows,
in one direction into the second steam treatment section, then through this section
and into the first steam treatment section, and from there into the plug section
and toward the entrance opening of the fold-forming section and
in the other direction into and through the second steam treatment section and toward
the exit opening of the chamber,
engaging the folds of the tow as it is moved in the fold-forming section and through
the entrance opening of the chamber with pins on an endless chain moving at a second
speed slower than the first speed
moving the tow in folds through the plug section at said second speed and
wherein the plurality of folds of the tow are in substantial contact with the walls
of chamber defining the plug section during a substantial portion of their movement
through this section whereby to help substantially eliminate loss of steam through
the entrance opening of the fold-forming section and
wherein the steam flowing into this plug section shrinks the tow so that it has a
cross-sectional area smaller than that at which it entered this section
moving the tow in folds through a restricted entrance opening of the first treatment
section, said entrance opening being smaller than the restricted entrance opening
of the chamber
moving the tow through the first treatment section at said second speed and wherein
the plurality of folds of the tow, as shrunken in the plug section, are substantially
in contact with the walls defining the first treatment section through much of their
movement through this section whereby to further help prevent any loss of steam flowing
through this section and through the plug section from escaping through the entrance
opening of the fold-forming section.
14. The process of claim 13 in which the chain engages two tows, one on each side,
and moves them at said second speed through the chamber.
15. The process of claim 13 or claim 14 in which the restricted entrance opening of
the chamber is connected to discharge opening of the fold-forming section by a tapered
surface.
16. The process of claim 13, 14 or 15 in which the restricted entrance opening of
the first treatment section is connected to the plug section by a tapered surface.
17. A process of treating a tow of shrinkable aromatic polyamide fibers by moving
the tow through a chamber defined by slanting walls which match the profile of the
shrunken tow as it moves through such chamber.