[0001] The instant invention relates to unique polymeric bicomponent fibers and to the production
of various products from such fibers by thermal bonding. More specifically, this invention
is directed to the production and use of a novel sheath-core melt blown bicomponent
fiber wherein a core of a thermoplastic material is substantially fully covered with
a sheath of polyethylene terephthalate or a copolymer thereof.
[0002] The term "bicomponent" as used herein refers to the use of two polymers of different
chemical nature placed in discrete portions of a fiber structure. While other forms
of bicomponent fibers are possible, the more common techniques produce either "side-by-side"
or "sheath-core" relationships between the two polymers. The instant invention is
concerned with production of "sheath-core" bicomponent fibers wherein a sheath of
polyethylene terephthalate or a copolymer thereof is spun to completely cover and
encompass a core of relatively low cost, low shrinkage, high strength thermoplastic
polymeric material such as polypropylene or polybutylene terephthalate, preferably
using a "melt blown" fiber process to attenuate the extruded fiber.
[0003] The term "polyethylene terephthalate or a copolymer thereof" as used herein refers
to a homopolymer of polyethylene terephthalate or a copolymer thereof having a melting
point which is higher than the melting point of the thermoplastic core material in
the bicomponent fiber.
[0004] Conventional linear polyester used to make fibers is the product of reaction of ethylene
glycol (1,2 ethanediol) and terephthalic acid (benzene-para-dicarboxylic acid). Each
of these molecules has reactive sites at opposite ends. In this way, the larger molecule
resulting from an initial reaction can react again in the same manner, resulting in
long chains made of repeated units or "mers". The same polymer is also industrially
made with ethylene glycol and dimethyl terephthalate (dimethyl benzene-para-dicarboxylate).
It is believed that polyesters of a broad range of intrinsic viscosities are useful
according to this invention, although those with lower intrinsic viscosities are preferred.
[0005] By partially substituting another diol for the ethylene glycol or another diacid
for the terephthalic acid, a more irregular "copolymer" is obtained. The same effect
is achieved by the substitution of another dimethyl ester for the dimethyl terephthalate.
Thus, there is a wide choice of alternative reactants and of levels of substitution.
[0006] The deviation from a regularly repeating, linear polymer makes the crystallization
more difficult (less rapid) and less complete. This is reflected in a lower and wider
melting range. Excessive substitution will result in a totally amorphous polymer which
is unacceptable for use in this invention.
[0007] Crystar 1946 or 3946 made by DuPont has been successfully used as the sheath-forming
material in the production of the bicomponent fibers of this invention and products
made therefrom. This copolymer has substituted 17% of the dimethyl terephthalate with
dimethyl isophthalate (dimethyl benzyl-meta-dicarboxylate) lowering the peak melting
point from 258°C to 215°C. This melting point is still well above that of polypropylene
(166°C).
[0008] DuPont's Crystar 3991 with 40% dimethyl isocyanate has a melting point of 160°C,
i.e., slightly below the 166°C melting point of polypropylene. Thus, for bicomponent
fibers incorporating a polypropylene core, it is believed that copolymers of polyethylene
terephthalate containing up to about 35 weight percent of dimethyl isocyanate or isocyanic
acid will be commercially acceptable.
[0009] While a comprehensive list of alternate reactants is difficult to identify, other
likely substitutes for the diol are propylene glycol, polyethylene glycol and butylene
glycol, and other likely substitutes for the diacid are adipic acid and hydroxybenzene
acid.
[0010] The term "melt blown" as used herein refers to the use of a high pressure gas stream
at the exit of a fiber extrusion die to attenuate or thin out the fibers while they
are in their molten state. Melt blowing of single polymer component fibers was initiated
at the Naval Research Laboratory in 1951. The results of this investigation were published
in Industrial Engineering Chemistry 48, 1342 (1956). Seven years later Exxon completed
the first large semiworks melt blown unit demonstration. See, for example, Buntin
U.S. Patent Nos. 3,595,245, 3,615,995 and 3,972,759 (the '245, '995 and '759 patents,
the subject matters of which are incorporated herein in their entirety by reference)
for a comprehensive discussion of the melt-blowing process.
[0011] Melt blown polypropylene monocomponent fibers are presently used in the production
of a variety of products, including fine particle air and liquid filters, and high
absorbing body fluid media (diapers). However, such fibers have low stiffness and
very low recovery when compressed. Moreover, they are not susceptible to thermal bonding
and are difficult to bond by chemical means. Thus, while they have been successfully
used in making thin porous non-woven webs, they are not commercially acceptable for
the production of three-dimensional, self-supporting items such as ink reservoirs,
cigarette filters, wicks for chemical and medical test devices, and flat or corrugated
filter sheets.
[0012] Melt blown monocomponent fibers formed from polyesters such as polyethylene terephthalate
have found even less commercial acceptance. Such fibers, which are largely undrawn
and not crystallized, rapidly shrink and became extremely brittle upon heating above
approximately 70°C. A comprehensive discussion of this problem and a proposal for
treatment of melt blown polyester webs with volatile solvents such as acetone to stabilize
them, is found in Pruett et al., U.S. Patent No. 5,010,165 (the '165 patent, the subject
matter of which is also incorporated herein in its entirety by reference). The '165
patent provides a good definition of the type of melt blown polyesters which are recognized
by the industry as problematic, but the solution proposed in the '165 patent appears
environmentally questionable, or, at the very least, quite expensive when safely performed.
The instant invention overcomes the lack of stability with the polyesters iterated
in the '165 patent in a more commercially and ecologically acceptable manner.
[0013] The melt blowing of bicomponent fibers is a recent development and is described for
a very specific application in Krueger U.S. Patent No. 4,795,668 (the '668 patent,
the subject matter of which is incorporated herein in its entirety by reference).
Also relevant is Berger copending U.S. patent application Serial No. 08/166,009, filed
December 14, 1993 (the subject matter of which is also incorporated herein in its
entirety by reference), which describes the use of this process for the production
of very fine bicomponent fibers having a sheath of plasticized cellulose acetate,
ethylene vinyl acetate copolymer, polyvinyl alcohol, or ethylene vinyl alcohol copolymer,
over a core of a thermoplastic material such as polypropylene or the like, primarily
for the manufacture of tobacco smoke filter elements.
[0014] Notwithstanding the fairly extensive prior art on bicomponent fibers, and even the
limited prior art relating to melt blown bicomponent fibers, the sheath-core conjugates
of this invention, comprising a sheath of polyethylene terephthalate or a copolymer
thereof over a thermoplastic core such as polypropylene or polybutylene terephthalate,
are believed to be unique, whether melt blown or not, having attributes that would
not have been expected. This dearth of specifically relevant prior art is, however,
not surprising since bicomponent fibers have been commonly proposed heretofore primarily
for use as thermal bonding materials in the production of non-woven fabrics, for example,
in the molding of face masks or the like, as seen in the aforementioned '668 patent,
or in the production of filter products, such as cigarette filters or the like, as
seen, for example, in Tomioka et al. U.S. Patent No. 4,173,504 or Sugihara et al.
U.S. Patent No. 4,270,962 (the '504 and '962 patents, respectively, the subject matters
of which are incorporated herein in their entirety by reference). Such use requires,
however, that a significant circumferential portion of the fiber be formed of a polymer
having a lower melting point than the polymer conjugated therewith. Thus, during molding
or forming of products from such bicomponent fibers, they may be heated to a temperature
between the melting points of the polymers, enabling the lower melting point polymer
at the surface to function as the bonding agent without deleteriously affecting the
higher melting point polymer material. Obviously, in a sheath-core construction, according
to these prior art teachings, the sheath must be formed of the lower melting point
polymer or the conjugate will not have useful thermal bonding properties.
[0015] In contrast to the prior art bicomponent technology, the disposition of the polymers
in the sheath-core bicomponent fibers of this invention comprises a continuous covering
of a higher melting point polymer, namely polyethylene terephthalate or a copolymer
thereof, over a lower melting point, low shrinkage polymer core such as polypropylene
or polybutylene terephthalate. Such fibers, particularly when melt blown, are uniquely
adapted to the production of webs or rovings and elements therefrom useful for diverse
commercial applications. Yet, it is believed that early attempts to produce and then
attenuate melt spun polyester/polypropylene bicomponent fibers were abandoned because
of delamination at the fiber interface. The instant inventive techniques enables the
production of fine fibers from such diverse polymers by melt blowing the sheath-core
bicomponent structures.
[0016] A principal focus of the instant invention is the production of elongated highly
porous ink reservoir elements for marking and writing instruments. Ink reservoirs
have conventionally been formed of a fibrous bundle compacted together into a rod-shaped
unit having longitudinal capillary passageways which extend therethrough between the
fibers and which serve to hold the ink and release it at the required controlled rate.
For a number of years, the fibrous material generally employed for the production
of ink reservoirs was plasticized cellulose acetate fibers, which could readily be
heat-bonded into a unitary body, and which were compatible with all of the ink formulations
then in use.
[0017] For example, Bunzl et al. U.S. Patent No. 3,094,736 (the '736 patent, the subject
matter of which is incorporated herein in its entirety by reference), discloses a
marking device having as the adsorbent body thereof a tow or tow segment gathered
with its filaments randomly oriented primarily in a longitudinal direction and bonded
at a plurality of spaced locations by a heat-activated plasticizer for such filaments.
An impermeable overwrap was used to give rigidity to the body and facilitate handling
thereof.
[0018] The term "filamentary tow" is defined in the '736 patent, and such continuous filamentary
tows are also discussed in Berger U.S. Patent Nos. 3,095,343 and 3,111,702 (the '343
and '702 patents, respectively, the subject matters of which are also incorporated
herein in their entirety by reference). Such filamentary tows usually comprise at
least 50% cellulose acetate fibers. Such tow bodies, bound with plasticizers, provide
rigidity. The '702 patent shows an apparatus for handling and steam-treating the tow
material to form therefrom a continuous body of fibers randomly oriented primarily
in a longitudinal direction. The phrase, "randomly oriented primarily in a longitudinal
direction" is intended to describe the condition of a body of fibers which are, as
a whole, longitudinally aligned and which are, in the aggregate, in a parallel orientation,
but which have short portions running more or less at random in non-parallel diverging
and converging directions. The '702 patent teaches bonding, tensioning and impregnating
a raw tow into a plasticizer-impregnated layer of continuous uncrimped filaments,
and then curing the continuous filamentary tow simultaneously with, or immediately
after, gathering of such impregnated layer into a final raw shape. Apparatus is shown
for handling such raw tow. The raw tow is taken from a supply bale through a device
having jets to separate the tow, and a plasticizing device adds plasticizer to the
fibers. The fibers are simultaneously gathered together and heated, thereby comprising
a curing station. Some of the apparatus used for processing the cellulose acetate
tow in these prior Berger patents are useful with, perhaps, minor modifications, to
process the melt blown bicomponent fiber webs of the instant invention, as will be
discussed in some detail hereinbelow.
[0019] Over the years, ink formulations have been developed that are not compatible with,
and tend to degrade, cellulose acetate. Thus, various thermoplastic fibers, in particular,
fine denier polyester fibers, such as polyethylene terephthalate, replaced cellulose
acetate as the polymer of choice in the production of ink reservoir elements for disposable
writing and marking instruments. Unfortunately, such polyester fibers are practically
impossible to thermally bond due to the highly crystalline nature of conventional
polyethylene terephthalate fibers. Resin bonding is slow and expensive and greatly
reduces ink absorption. Undrawn polyethylene terephthalate fibers are not crystallized
and can be thermally bonded, but such amorphous polymers shrink excessively in normal
use and become brittle.
[0020] Therefore, techniques for forming unitary ink reservoirs from such materials have
generally required the incorporation of extraneous adhesives and/or have overwrapped
the porous rod with a covering or coating of plastic film to render the same relatively
self-sustaining. Polyester polymers are also relatively expensive. The requirement
for additional materials or processing techniques to commercially produce ink reservoir
elements from such materials exacerbated the high manufacturing costs.
[0021] Efforts to heat-bond polyester fibers to each other in the absence of additive adhesives
have not met with much success. Because of the narrow softening point of crystalline
polyester polymers, it has not been feasible to commercially bond drawn polyester
fibers such as tow with heat. As noted, undrawn or amorphous polyester fibers are
heat-bondable, but produce an unusable product which shrinks excessively during processing.
Moreover, such materials lack stability in the presence of commercial inks at the
temperatures required for storage of writing instruments.
[0022] Consequently, for some time, polyester fiber ink reservoir elements were commercially
produced in the form of an unbonded bundle of fibers compacted and held together in
a rod-shaped unit by means of a film overwrap. Depending upon the design of the writing
instrument in which such reservoirs were incorporated, they could be provided with
a small diameter plastic "breather" tube disposed between the fibrous bundle and the
overwrap to serve as an air release passage, if necessary.
[0023] Such film-overwrapped polyester fiber ink reservoir elements, when made with parallel
continuous-filament fibers, have had adequate ink holding capacity and ink release
properties for use with certain types of marking or writing instruments, primarily
those employing fiber tips or nibs. Yet, with the more recent development of roller
ball writing instruments which require a faster ink release, or "wetter" system, such
ink reservoir elements are commercially unacceptable. Attempts to increase the rate
of ink release by lowering the fiber density and/or changing the fiber size had limited
success because 1) the release was not uniform from start to finish; 2) the reduced
fiber density decreased the ink holding capacity of the reservoir; 3) the low density
polyester tow formed a very soft "rod" which was difficult to handle in the high speed
automated commercial production equipment; and (4) the ink was often held so loosely
that when writing instruments incorporating such reservoirs were dropped, "leakers"
occurred. To test for "leakers", a pen or the like is dropped point first onto a hard
surface. Should ink leak or spurt out, the product is unacceptable.
[0024] To overcome such "leakers", polyester sliver having random fibers has been used which
holds the ink better at lower densities. However, sliver-type polyester ink reservoir
elements still tend toward undesirable softness and often suffer from unacceptable
weight variation which makes it difficult to control ink flow to a roller marker.
[0025] Forming the reservoir from staple fibers randomly laid, rather than from continuous-filament
parallel fibers, has been found to increase the ink release properties of short-length
reservoirs, but at the longer lengths required for adequate ink holding capacity,
this construction lacks the capillarity to function effectively.
[0026] Some of these prior art problems were overcome by the techniques disclosed in Berger
U.S. Patent No. 4,286,005 (the '005 patent, the subject matter of which is incorporated
herein in its entirety by reference). The ink reservoir of the '005 patent provides
a combination of ink holding capacity and ink release properties useful with various
types of marking or writing instruments, including roller markers and plastic nibs.
Such ink reservoirs are formed from coherent sheets of flexible thermoplastic fibrous
material composed of an interconnecting network of randomly arranged, highly dispersed,
continuous-filament junctions which has been embossed with a multiplicity of longitudinally
extending parallel grooves and formed or compacted into a dimensionally stable rod-shaped
body whose longitudinal axis extends parallel to the embossed grooves. This ink reservoir
could be provided with a longitudinal slot extending continuously along the periphery
of the entire length of its body if a "breather" passage was required for the particular
barrel design. Unfortunately, the ink reservoir of the '005 patent, while overcoming
many problems with prior art products, required the use of relatively expensive materials,
having a complex shape, and, for this reason, has not found commercial acceptance.
[0027] Most commercially available polyester ink reservoirs are currently made by the process
described in Berger U.S. Patent No. 4,729,808 (the '808 patent, the subject matter
of which is incorporated herein in its entirety by reference) which utilizes a raw
material stretch yarn, often referred to as "false twist stretch yarn", which has
unusual properties including the ability to stretch and curl or twist. For the most
part, the product and process of the '808 patent overcame substantially all of the
aforementioned problems of the prior art and, thus, has achieved remarkable acceptance
in the marking and writing instrument market. However, false twist yarn requires the
use of melt spun fibers, generally averaging over 2 denier per filament (dpf) or about
12 microns in diameter. While larger fibers are useful in some wetter systems, since
larger fibers take up more volume, there is less interstitial space for holding ink
and, thus, less capacity in the reservoir. Small fiber size, less than about 12 microns,
which cannot be achieved with false twist yarn, provides better release pressure without
reducing capacity. Higher release pressure, which minimizes leakers, a particular
problem with some very low surface tension ink compositions, is difficult to realize
with false twist yarn. Increasing density to improve leakers, further reduces capacity.
[0028] As noted, polyesters such as polyethylene terephthalate, which are uniquely effective
in the production of ink reservoir elements because of their compatibility with ink
formulations currently in use, are expensive compared to other polymer materials.
Therefore, the ability to minimize the quantity of polyethylene terephthalate necessary
to the production of an ink reservoir having acceptable ink holding capacity, while
being capable of controllably releasing the ink in a marking or writing instrument,
would be highly desirable. The use of a bicomponent fiber which replaces a significant
portion of the polyethylene terephthalate with a lower cost polymer is problematic
because polyethylene terephthalate has a higher melting point that the common thermoplastic
polymers with which it might be conjugated, such as polypropylene or polybutylene
terephthalate. Thus, it would be expected that a sheath-core bicomponent fiber wherein
the sheath was effectively entirely polyethylene terephthalate as is necessary for
compatibility with the ink, would not be sufficiently bondable to produce a substantially
self-sustaining porous rod for commercial application as an ink reservoir. Moreover,
attenuation of such materials by conventional drawing or stretching techniques to
produce fine bicomponent fibers capable of forming a high capacity porous rod is limited
by the difference in processing properties of the conjugated polymers resulting in
delamination or separation of the core from the sheath during stretching. These and
other anticipated problems have discouraged the use of bicomponent fiber forming technology
heretofore in the production of ink servoir elements for marking and writing instruments.
Surprisingly, the instant invention has found that, with careful selection of the
processing techniques and materials, a bicomponent fiber having a complete polyethylene
terephthalate sheath can be commercially processed to produce a highly efficient,
low cost, ink reservoir element.
[0029] While the primary application of the instant inventive concepts are in the production
of ink reservoir elements for use in marking and writing instruments, the bicomponent
fibers of this invention can be effectively used in the production of many other commercially
important products. For example, sheets formed from such fibers have excellent filtration
properties making them particularly useful in high temperature filtration environments
because of the relatively high melting point of polyethylene terephthalate. Moreover,
the same porous rod which can be used as an ink reservoir element comprises a network
of continuous fibers which defines tortuous interstitial paths effective for capturing
fine particulate matter when a gas or liquid is passed therethrough as in a filtering
application. Filter rods made from such materials are substantially self-sustaining,
provide commercially acceptable hardness, pressure drop, resistance to draw, and filtration
characteristics when used, for example, as tobacco smoke filter elements in the production
of filtered cigarettes or the like. While the taste properties of the polyethylene
terephthalate polymer sheath in the bicomponent fibers of such a filter element may
not be acceptable to many smokers, it is believed possible to add a smoke-modifying
or taste-modifying material to the surface of the fiber or even to compound a material
such as tobacco extract, or even menthol, into the sheath-forming polymer to overcome
this problem. Moreover, the introduction of an additive, such as particles of activated
charcoal which enhances the gas phase filtration efficiency of a tobacco smoke filter
element, into the highly turbulent environment produced at the exit of the sheath-core
bicomponent extrusion die by the high pressure gas streams used in the melt blowing
attenuation techniques of this invention, results in surprisingly uniform incorporation
and bonding of the additive into the web or roving and, ultimately, the filter rod,
produced therefrom.
[0030] Thus, bicomponent fibers according to this invention have significant commercial
applications in the production of wick reservoirs, that is, materials designed to
take up a liquid and later controllably release the same as in an ink reservoir for
a marking and writing instrument. They are also particularly useful in the production
of filters, whether in sheet or rod form.
[0031] Additionally, because of their high capillarity, such materials function effectively
in the production of simple wicks for transporting liquid from one place to another.
The wicking properties of these materials may find use, for example, in the production
of the fibrous nibs found in certain marking and writing instruments. Wicks of this
nature are also useful in diverse medical applications, for example, to transport
a bodily fluid by capillary action to a test site in a diagnostic device.
[0032] Products made from the bicomponent fibers of the instant invention are not only useful
as wicks and wick reservoirs, they may also be used as absorption reservoirs, i.e.,
as a membrane to take up and simply hold a liquid as in a diaper or an incontinence
pad. Absorption reservoirs of this type are also useful in medical applications. For
example, a layer or pad of such material may be used in an enzyme immunoassay diagnostic
test device where they will draw a bodily fluid through the fine pores of a thin membrane
coated, for instance, with monoclonal antibodies that interact with antigens in the
bodily fluid which is pulled through the membrane and then held in the absorption
reservoir.
[0033] As mentioned, according to the preferred embodiments of this invention, the bicomponent
fibers are highly attenuated as they exit the bicomponent sheath-core extrusion die
using available melt blowing techniques to produce a web or roving wherein the fibers
have, on the average, a diameter of about 12 microns or less, down to 5 and even 1
micron. Melt spun fibers of a larger size or even larger melt blown fibers, on the
order of, perhaps, 20 microns, are useful in certain applications, for example, in
some wicking applications where strength is more important that capillarity; yet,
the finer melt blown fibers made possible by the instant inventive concepts have significant
advantages in most all of the applications mentioned above. For example, when used
in the production of ink reservoirs, these small diameter fibers provide high surface
area, and an increased holding capacity as compared to currently available conventional
ink reservoirs produced entirely of polyethylene terephthalate. Likewise, the fine
fiber size of the melt blown bicomponent continuous filaments of this invention produce
tobacco smoke filter elements of enhanced filtration efficiency, providing increased
fiber surface area at the same weight of fiber.
[0034] Thus, the bicomponent fibers according to this invention containing a polyethylene
terephthalate continuous sheath on a polypropylene or other crystalline polymer core,
particularly the melt blown bicomponent fibers, have unique and commercially important
properties. Contrary to melt blown monocomponent polyester fibers, the melt blown
bicomponent fibers of this invention are not brittle and evidence much less shrinkage
under heat. The melt blown bicomponent fibers of this invention shrink only about
6% in the amorphous stage and zero after heating to or above 90°C to crystallize the
polyethylene terephthalate. This compares with 40 to 60% shrinkage for conventional
melt blown polyethylene terephthalate.
[0035] The stiffness of the fibers of this invention is greater than that of conventional
melt blown polypropylene; this is reflected in higher and more resilient bulk. Moreover,
the stiffness of the bicomponent fibers and bonding of the product permits the use
of a less thick wrapping material than currently used in the production of ink reservoirs.
Likewise, the solvent resistance of the melt blown bicomponent fibers hereof, having
a continuous crystallized polyethylene terephthalate covering, is also much superior
to polypropylene fibers when exposed to aromatic, aliphatic and chlorinated solvents.
[0036] Webs or rovings formed from the fibers of the invention are thermally bondable with
heated fluids such as hot air, saturated steam, or other heating media because of
the unusual property of the polyethylene terephthalate sheath to undergo crystallization
at a temperature less than the melting temperature of the core material. Thus, the
polyethylene terephthalate sheath is still amorphous at up to 90°C or so in the collected
melt blown web or roving. As the web or roving is gathered and shaped in a steam treating
or other heating zone, the fibers are bonded at their points of contact and the polyethylene
terephthalate is crystallized. The higher melting temperature crystalline core material
supports the sheath during the heating step and minimizes shrinkage of the bicomponent
fiber as the polyethylene terephthalate is crystallized. Once heated to temperatures
above about 90°C, however, the shaped product is relatively self-sustaining and the
crystallized polyethylene terephthalate renders the sheath solvent resistant.
[0037] The unique method for forming the melt blown bicomponent fibers of the instant invention
enables the extrusion, melt blowing and conversion of the resultant fiber web into
an elongated, substantially self-sustaining, porous rod which may be subdivided for
use, for example, as ink reservoir elements or tobacco smoke filters, in a one-step
or continuous process. The porous rod can be continuously overwrapped or covered with
a film or coating, if desired, and an air passage can be continuously formed longitudinally
along the periphery of the porous rod in an obvious manner. Likewise, if the porous
rod is to be used as a cigarette filter, it can be continuously encased in an air
permeable or impermeable paper filter wrap, if desired, before the rod is cut into
discrete filter rods or filter plugs.
[0038] With the foregoing in mind, the primary object of the instant inventive concepts
is the production of bicomponent polymeric fibers comprising a continuous sheath of
polyethylene terephthalate or a copolymer thereof covering a core of a relatively
low cost, low shrinkage, high strength thermoplastic pclymeric material such as, preferably,
polypropylene or polybutylene terephthalate, and products made therefrom by thermal
bonding. As noted, such bicomponent fibers, particularly when melt blown, have a stiffness
greater than melt blown monocomponent fibers of a similar diameter, and yet they are
not brittle resulting in a fibrous mass with higher and more resilient bulk.
[0039] More specifically, the instant invention is directed to methods of making bicomponent
fibers having a complete sheath of polyethylene terephthalate or a copolymer thereof
on a thermoplastic core wherein, preferably, the fibers, on average, have a diameter
of about 12 microns or less, providing high surface area at low fiber weights.
[0040] A further important object of this invention is the provision of a substantially
self-sustaining three-dimensional porous element formed from a web of flexible thermoplastic
fibrous material comprising an interconnecting network of highly dispersed continuous
fibers randomly oriented primarily in a longitudinal direction and bonded to each
other at points of contact to provide high surface area and very high porosity, preferably
over 70%, with at least a major portion, and preferably all of the fibers being bicomponent
fibers comprising a continuous sheath of polyethylene terephthalate or a copolymer
thereof, and with the element being dimensionally stable at temperatures up to about
100°C and resistant to common organic ink solvents such as alcohols, ketones and xylene
up to at least about 60°C. Obviously, the products of this invention can be of various
sizes and shapes. In many instances, such as, for example, when used as an ink reservoir
or a cigarette filter, such elements will be generally elongated and substantially
cylindrical. Yet, when used, for example, for other applications, the three-dimensional
elements may be shaped, as by grinding or in any other conventional manner, depending
upon their particular application. Thus, while the term "elongated porous rod" is
used herein to describe many of these elements, it should be understood that this
term is not intended to be limited to a cylindrical shape except where such a configuration
would be appropriate.
[0041] Yet another object of this invention is the provision of a method for making such
substantially self-sustaining elongated elements combining bicomponent extrusion technology
with melt blown attenuation to produce a web or roving of highly entangled fine fibers
with a sheath of substantially amorphous polyethylene terephthalate or a copolymer
thereof which is bondable at a lower temperature than the melting point of the core
material, and then gathering the web or roving and heating the same by a heated fluid,
preferably saturated steam, or in a dielectric oven, to bond the fibers at their points
of contact and crystallize the polyethylene terephthalate at the same time.
[0042] A still further object of the instant inventive concepts is the provision of products
incorporating porous elements formed from the bicomponent fibers of the instant invention
useful commercially as 1) wick reservoirs, including ink reservoirs and marking and
writing instruments incorporating the same; 2) filtering materials, including tobacco
smoke filters and filtered cigarettes formed therefrom; 3) wicks for transporting
liquid from one place to another by capillary action, including fibrous nibs for marking
and writing instruments and capillary wicks in medical applications designed to transport
a bodily fluid to a test site in a diagnostic device; and 4) absorption reservoirs,
including membranes for taking up and holding a liquid as in a diaper or an incontinence
pad, or in medical applications such as enzyme immunoassay diagnostic test devices
wherein a pad of such material will draw a bodily fluid through a thin membrane and
hold the fluid pulled therethrough.
[0043] While the foregoing applications are all commercially important, a primary object
of this invention is the provision of a high capacity ink reservoir for a marking
or writing instrument defined by an elongated porous rod formed of a network of fine
bicomponent fibers having a continuous sheath of polyethylene terephthalate or a copolymer
thereof which is compatible with all currently available ink formulations and which
provides an adequate release pressure to minimize "leakers" even when used in a roller
ball pen or the like.
[0044] Upon further study of the specification and the appended claims, additional objects
and advantages of this invention will become apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] A better understanding of the present invention, as well as other objects, features
and advantages thereof, will become apparent upon consideration of the detailed description
herein, in connection with the accompanying drawings wherein like reference characters
refer to like parts:
Figure 1 is an enlarged perspective view of one form of a "sheath-core" bicomponent
fiber according to the instant invention;
Figure 2 is an enlarged end elevation view of a trilobal or "Y" shaped bicomponent
fiber according to this invention;
Figure 3 is a similar view of an "X" or cross-shaped embodiment of the bicomponent
fiber of this invention;
Figure 4 is an enlarged perspective view of a substantially self-sustaining elongated
element formed from a web of the bicomponent fibers of the instant invention;
Figure 5 is a cross-sectional view, partially broken away, of one form of a writing
instrument in the nature of a roller ball disposable pen incorporating an ink reservoir,
and possibly a roller ball wick made according to the instant inventive concepts;
Figure 6 is a side elevational view of an ink reservoir element according to this
invention, including a longitudinally continuous peripheral air passageway integrally
formed therein;
Figure 7 is an enlarged transverse cross-sectional view along lines 7-7 of Figure
6;
Figure 8 is a side elevational view, partially broken away, of a marking instrument
in the nature of what is commonly called a "felt tip" marker also incorporating an
ink reservoir and, in this instance, a fibrous nib, made according to the instant
inventive concepts;
Figure 9 is a perspective view of an overwrapped tobacco smoke filter rod produced
from bicomponent fibers according to the instant invention concepts;
Figure 10 is an enlarged perspective view of a cigarette including a filter element
according to this invention;
Figure 11 is a schematic elevational view of a diagnostic test device incorporating
a lateral flow wick according to the instant invention designed to transport a bodily
fluid to a test site;
Figure 12 is a schematic elevational view of a pipette tip or an intravenous solution
injection system incorporating a pad of material according to the instant inventive
concepts designed as an in-line filter for in vitro or in vivo treatment of a liquid sample;
Figure 13 is a schematic view of one form of a process line for producing porous rods
from the bicomponent fibers of this invention;
Figure 14 is an enlarged schematic view of the sheath-core melt blown die portion
of the process line of Figure 13;
Figure 15 is an enlarged schematic view of a split die element for forming bicomponent
fibers according to the instant invention;
Figure 16 is a schematic cross-sectional view of a steam-treating apparatus which
can be used for bonding and forming a continuous porous rod according to the instant
invention; and
Figure 17 is a schematic view of an alternate heating means in the nature of a dielectric
oven for bonding and forming the continuous porous rod of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] The instant inventive concepts are embodied in a bicomponent, sheath-core, preferably
melt blown, fiber where the core is a low cost, low shrinkage, high strength, thermoplastic
polymer, preferably polypropylene or polybutylene terephthalate, and the sheath is
polyethylene terephthalate or a copolymer thereof.
[0047] The method of manufacturing the specific polymers used in the production of the bicomponent
fibers is not part of the instant invention. Processes for making these polymers are
well known in the art and, as noted above, most commercially available polyethylene
terephthalate materials or copolymers thereof can be used. While it is not necessary
to utilize sheath and core materials having the same melt viscosity, as each polymer
is prepared separately in the bicomponent melt blown fiber process, it may be desirable
to select a core material, e.g. polypropylene or polybutylene terephthalate, of a
melt index similar to the melt index of the sheath polymer, or, if necessary, to modify
the viscosity of the sheath polymer to be similar to that of the core material to
insure compatibility in the melt extrusion process through the bicomponent die. Providing
sheath-core components with compatible melt indices is not a significant problem to
those skilled in this art with commercially available thermoplastic polymers and additives.
[0048] Additionally, while reference is made, for example, to a sheath formed of polyethylene
terephthalate or a copolymer thereof, additives may be incorporated or compounded
into the polymer prior to extrusion to provide the fibers and products produced therefrom
with unique properties, e.g., increased hydrophilicity or even increased hydrophobicity.
[0049] While polypropylene and polybutylene terephthalate are the preferred core materials
for the reasons iterated below, other highly crystalline thermoplastic polymers such
as high density polyethylene, as well as polyamides such as nylon 6 and nylon 66,
can be used. The main requirement of the core material is that it is crystallized
when extruded or crystallizable during the melt blowing process. Polyethylene terephthalate,
in contrast, normally requires a separate drawing stage for crystallization.
[0050] Polypropylene is a preferred core-forming material due to its low price and ease
of processability. Polypropylene has also been found to be particularly useful in
providing the core strength needed for production of fine fibers using melt blown
techniques. Various modified polypropylenes can be used as the core-forming material
to achieve even better adhesion to the sheath such as DuPont's BYNEL CXA Series 5000
anhydride-modified polypropylenes, other acid anhydride (preferably maleic acid anhydride)
polypropylenes, anhydride functionalized polypropylenes, adhesive polypropylenes such
as Quantum Chemical Corporation's PLEXAR extrudable adhesive polypropylenes, or other
reactive polypropylenes.
[0051] Unlike polyethylene terephthalate, polybutylene terephthalate crystallizes easily
and is not amorphous for any appreciable length of time. Thus, it is ineffective as
a sheath-forming material according to this invention in that the resultant bicomponent
fiber is not bondable. A polyethylene terephthalate sheath/polybutylene terephthalate
core bicomponent fiber has the advantage, however, of an especially effective bond
between the sheath and core due to the similar properties in these related polyester
polymers, and is stable to temperatures approaching 250°C, in contrast to the degradation
of product at substantially lower temperatures using a polypropylene core bicomponent
fiber.
[0052] Reference is now made generally to the drawings, and more particularly, to Figure
1, wherein a bicomponent fiber according to the preferred embodiments of the instant
inventive concepts is schematically shown at 20. Of course, the size of the fiber
and the relative proportion of the sheath-core portions thereof have been greatly
exaggerated for illustrative clarity. The fiber 20 is preferably comprised of a polyethylene
terephthalate or polyethylene terephthalate copolymer sheath 22 and a polypropylene
or polybutylene terephthalate core 24. The core material comprises at least about
30%, and up to about 90% by weight of the overall fiber content.
[0053] It is well known that capillary pressure and absorbency of porous media increases
in approximately direct proportion to the wettable fiber surface. One way to increase
the fiber surface is to modify the fiber cross-section to product trilobular or Y-shaped
fibers or other multi-branched cross-sections such as "X"- or "H"-shapes. Process
imperatives heretofore have produced non-round fibers which are relatively large resulting
in an absorbing medium of high surface area, but with a relatively low number of fibers
placed far from each other. Such media has large pores, and while retaining a liquid
at the fiber surface, the liquid is poorly held in the center of the pores. This is
particularly disadvantageous in the production of an ink reservoir for writing and
marking instruments which requires controlled release of sufficient ink to the writing
point or nib, while retaining the ink sufficiently to avoid leakage under shock, as
in the conventional drop test, or in the presence of rising temperatures, as in the
conventional transport and oven test.
[0054] With a constant fiber bulk density or weight, the surface increases with diminishing
fiber diameter. Absorbing media made of numerous small fibers has a more uniform retention
and can be better tailored for optimum performance. The bicomponent melt blown process
utilized according to the instant inventive concepts provides fine fibers with increased
surface area having improved capillary pressure and absorbency over ordinary fibers,
even those with non-round cross-sections. The rate of flow of a liquid can be controlled
through density changes only, when the smallest commercial fibers are used. With the
melt blown techniques of this invention, the flow can be controlled by simply changing
the size of the fiber.
[0055] If desired, however, even fine bicomponent fibers of non-round cross-section can
be produced according to this invention for particular applications. Thus, by selecting
openings in the sheath-core extrusion die of an appropriate shape, melt blown bicomponent
fibers with a non-round cross section having even further increased surface area can
be produced which may be advantageous, for example, if the product is to be used as
a filter. Moreover, the non-round fiber cross-section enhances the use of air when
the fiber is attenuated by melt blowing techniques. A trilobal or "Y" shaped fiber
20a is shown in Figure 2 comprising a sheath 22a and a core 24a. Similarly, a cross
or "X" shaped bicomponent fiber as seen at 20b in Figure 3, comprising a sheath 22b
and a core 24b, is illustrative of many multi-legged fiber core sections possible.
It will be seen that, in each instance, the sheath of polyethylene terephthalate completely
covers the core material. Failure to enclose any major portion of the core material
minimizes or obviates many of the advantages of the instant invention discussed herein.
[0056] Figures 13 through 17 schematically illustrate preferred equipment used in making
a bicomponent fiber according to the instant inventive concepts, and processing the
same into continuous, three-dimensional, porous elements, that can be subsequently
subdivided to form, for example, ink reservoir elements to be incorporated into marking
or writing instruments, or tobacco smoke filter elements to be incorporated into filtered
cigarettes or the like. The overall processing line is designated generally by the
reference numeral 30 in Figure 13. In the embodiment shown, the bicomponent fibers
themselves are made in-line with the equipment utilized to process the fibers into
the porous elements. Such an arrangement is practical with the melt blown techniques
of this invention because of the small footprint of the equipment required for this
procedure. While the in-line processing has obvious commercial advantages, it is to
be understood that, in their broadest sense, the instant inventive concepts are not
so limited, and bicomponent fibers and webs or rovings formed from such fibers according
to this invention may be separately made and processed into diverse products in separate
or sequential operations.
[0057] Whether in-line or separate, the fibers themselves can be made using standard fiber
spinning techniques for forming sheath-core bicomponent filaments as seen, for example,
in Powell U.S. Patent Nos. 3,176,345 or 3,192,562 or Hills U.S. Patent No. 4,406,850
(the '345, '562 and '850 patents, respectively, the subject matters of which are incorporated
herein in their entirety by reference). Likewise, methods and apparatus for melt blowing
of fibrous materials, whether they are bicomponent or not, are well known. For example,
reference is made to the aforementioned '245, '995 and '759 patents as well as Schwarz
U.S. Patent Nos. 4,380,570 and 4,731,215, and Lohkamp et al, U.S. Patent No. 3,825,379,
(the '570, '215 and '379 patents, respectively, the subject matters of which are incorporated
herein in their entirety by reference). The foregoing references are to be considered
to be illustrative of well known techniques and apparatus for forming of bicomponent
fibers and melt blowing for attenuation that may be used according to the instant
inventive concepts, and are not to be interpreted as limiting thereon.
[0058] In any event, one form of a sheath-core melt blown die is schematically shown enlarged
in Figures 14 and 15 at 35. Molten sheath-forming polymer 36, and molten core-forming
polymer 38 are fed into the die 35 and extruded therefrom through a pack of four split
polymer distribution plates shown schematically at 40, 42, 44 and 46 in Figure 15
which may be of the type discussed in the aforementioned '850 patent.
[0059] Using melt blown techniques and equipment as illustrated in the '759 patent, the
molten bicomponent sheath-core fibers 50 are extruded into a high velocity air stream
shown schematically at 52, which attenuates the fibers 50, enabling the production
of fine bicomponent fibers on the order of 12 microns or less. Preferably, a water
spray shown schematically at 54, is directed transversely to the direction of extrusion
and attenuation of the melt blown bicomponent fibers 50. The water spray cools the
fibers 50 to enhance entanglement of the fibers while minimizing bonding of the fibers
to each other at this point in the processing, thereby retaining the fluffy character
of the fibrous mass and increasing productivity.
[0060] If desired, a reactive finish may be incorporated into the water spray to make the
polyethylene terephthalate fiber surface more hydrophilic or "wettable". Even a lubricant
or surfactant can be added to the fibrous web in this manner, although unlike spun
fibers which require a lubricant to minimize friction and static in subsequent drawing
operations, melt blown fibers generally do not need such surface treatments. The ability
to avoid such additives is particularly important, for example, in medical diagnostic
devices where these extraneous materials may interfere or react with the materials
being tested.
[0061] On the other hand, even for certain medical applications, treatment of the fibers
or the three-dimensional elements, either as they are formed or subsequently, may
be necessary or desirable. Thus, while the resultant product may be a porous element
which readily passes a gas such as air, it is possible by surface treatment or the
use of a properly compounded sheath-forming polymer, to render the fibers hydrophobic
so that, in the absence of extremely high pressures, it may function to preclude the
passage of a selected liquid. Such a property is particularly desirable when a porous
element according to the instant invention is used, for example, as a vent filter
in a pipette tip or in an intravenous solution injection system. The materials to
so-treat the fiber are well known and the application of such materials to the fiber
or porous element as they are formed is well within the skill of the art.
[0062] Additionally, a stream of a particulate material such as granular activated charcoal
or the like (not shown) may be blown into the fibrous mass as it emanates from the
die, producing excellent uniformity as a result of the turbulence caused by the high
pressure air used in the melt blowing technique. Likewise, a liquid additive such
as a flavorant or the like may be sprayed onto the fibrous mass in the same manner.
[0063] The melt blown fibrous mass is continuously collected as a randomly dispersed entangled
web or roving 60 on a conveyor belt shown schematically at 61 in Figure 13 (or a conventional
screen covered vacuum collection drum as seen in the '759 patent, not shown herein)
which separates the fibrous web from entrained air to facilitate further processing.
This web or roving 60 of melt blown bicomponent fibers is in a form suitable for immediate
processing without subsequent attenuation or crimp-inducing processing.
[0064] The polyethylene terephthalate sheath material at this point in the processing is
still amorphous. In contrast, the core material, whether it be polypropylene, polybutylene
terephthalate or other appropriate polymers, is crystalline, providing strength to
the bicomponent fibers and precluding significant shrinkage of these materials.
[0065] The remainder of the processing line seen in Figure 13 may use apparatus known in
the production of plasticized cellulose acetate tobacco smoke filter elements, although
minor modifications may be required to individual elements thereof in order to facilitate
heat bonding of the fibers. Exemplary apparatus will be seen, for example, in Berger
U.S. Patent Nos. 4,869,275, 4,355,995, 3,637,447 and 3,095,343 (the '275, '995,'447
and '343 patents, the subject matters of which are incorporated herein in their entirety
by reference). The web or roving of melt blown sheath-core bicomponent fibers 60 is
not bonded or very lightly bonded at this point and is pulled by nip rolls 62 into
a stuffer jet 64 where it is bloomed as seen at 66 and gathered into a rod shape 68
in a heating means 70 which may comprise a heated air or steam die as shown at 70a
in Figure 16 (of the type disclosed in the '343 patent), or a dielectric oven as shown
at 70b in Figure 17. The heating means raises the temperature of the gathered web
or roving above about 90°C to cure the rod, first softening the sheath material to
bond the fibers to each other at their points of contact, and then crystallizing the
polyethylene terephthalate sheath material. The element 68 is then cooled by air or
the like in the die 72 to produce a stable and relatively self-sustaining, highly
porous fiber rod 75.
[0066] For ink reservoirs, the bonding of the fibers need only provide sufficient strength
to form the rod and maintain the pore structure. optionally, depending upon its ultimate
use, the porous rod 75 can be coated with a plastic material in a conventional manner
(not shown) or wrapped with a plastic film or a paper overwrap 76 as schematically
shown at 78 to produce a wrapped porous rod 80. The continuously produced porous fiber
rod 80, whether wrapped or not, may be passed through a standard cutter head 82 at
which point it is cut into preselected lengths and deposited into an automatic packaging
machine.
[0067] By subdividing the continuous porous rod in any well known manner, a multiplicity
of discrete porous elements are formed, one of which is illustrated schematically
in Figure 4 at 90. Each element 90 comprises an elongated air-permeable body of fine
melt blown bicomponent fibers such as shown at 20 in Figure 1, bonded at their contact
points to define a high surface area, highly porous, self-sustaining element having
excellent capillary properties when used as a reservoir or wick and providing a tortuous
interstitial path for passage of a gas or liquid when used as a filter.
[0068] It is to be understood that elements 90 produced in accordance with this invention
need not be of uniform construction throughout as illustrated in Figure 4. For example,
a continuous longitudinally extending peripheral groove such as seen at 92 in Figures
6 and 7 can be provided as an air passage in an ink reservoir 95 (which may or may
not include a coating or film wrap 96) if necessary for use in, for example, a writing
instrument as shown generally at 100 in Figure 5. The writing instrument 100 may include
a roller ball wick 102 which can also be produced by the techniques of this invention
which engages a roller ball writing tip 103 in a conventional manner. The ink reservoir
95 is contained within a barrel 104 in fluid communication with the roller ball wick
102 to controllably release a quantity of ink 106 to the roller ball 103 in the usual
way.
[0069] As is well known in the art, the roller ball wick 102 will generally have a higher
capillarity than the reservoir 95, with the fibers thereof being more longitudinally
oriented so as to draw the ink 106 from the reservoir 95 and feed the same to the
roller ball 103. It is well within the skill of the art to form the three-dimensional
porous elements of the instant invention with higher or lower capillarity depending
upon the particular application by controlling, for example, the speed with which
the fibrous mass is fed into the forming devices, the size and shape of the forming
devices and other such obvious processing parameters.
[0070] In Figure 8, a marking device is shown generally at 120, as including a conventional
barrel 122, containing an ink reservoir 95a in fluid communication with a fibrous
wick or nib 124, which may be of the type commonly referred to as a "felt tip". The
fibrous wick or nib 124 may be provided with the shape shown in Figure 8, or any other
desired shape, by conventional grinding techniques well known to those skilled in
this art. Again, the nib 124 is generally denser, with the fibers generally more longitudinally
oriented, than the fibers from which the reservoir 95a are made, in order to provide
the nib with the higher capillarity necessary to draw the ink from the reservoir in
use.
[0071] Elements 90 can also be provided with interior pockets, exterior grooves, crimped
portions or other modifications (not shown) as in the aforementioned prior patents
to Berger, or others, particularly if they are to be used as tobacco smoke filters.
A conventional filtered cigarette is illustrated at 110 in Figure 10 as comprising
a tobacco rod 112 covered by a conventional cigarette paper 114 and secured to a filter
means comprising a discrete filter element 115, such as would result from further
subdividing a filter rod 116 shown in Figure 9. The filter element 115 may be overwrapped
with an air permeable or air impermeable plugwrap 118 and secured to the tobacco rod
112 in a conventional manner as by standard tipping wrap 119.
[0072] To illustrate various other uses for three-dimensional porous elements made according
to the instant inventive concepts, reference is made to Figures 11 and 12. In Figure
11, a diagnostic test device is shown generally by reference numeral 130 as comprising
a shell or housing 132 encasing a test site 134 which may be, for example, a porous
membrane or the like, with an exposed wick element 136 which may be made according
to this invention, an internal wick 138 of a higher capillarity, also made by the
instant inventive concepts, and an absorptive reservoir 140, also a product of this
invention. A device of this type is capable, for example, of collecting a bodily fluid
with the exposed wick 136, carrying the same via the internal wick 138 to and through
the test site 134, and then absorbing and holding the liquid in the reservoir 140.
Thus, this device utilizes porous elements according to this invention as a lateral
flow wick designed to transport a liquid to a test site, and then also provides a
reservoir to draw the liquid past the test site and then to hold the liquid.
[0073] Figure 12 is a schematic showing of the use of a plug 152 of filtering material according
to this invention, as a vent filter in a pipette designated generally by the reference
numeral 150 (or as an in-line filter in, for example, an intravenous solution injection
system). The pad or plug of material 152 formed according to this invention may have
been pre-treated to render the fibers or the element in general hydrophobic so that
air may pass, but liquids will not. In-line filters are well known and are commonly
used
in vitro to remove undesirable materials from a sample prior to a diagnostic test, or
in vivo, for example, in flushing the kidneys prior to kidney dialysis, or to filter out
blood clots in open heart surgery.
[0074] Pads of material made according to this invention can also be used as capillaries
to absorb excess ink in a printing device, for example, as an "overshot pad" in an
ink jet printer. Likewise, such materials can be used as an absorptive device for
the removal of saliva and other bodily fluids from the oral cavity.
[0075] The foregoing illustrative applications of three-dimensional porous elements made
according to the instant invention are not to be considered as limiting, but are indicative
of the many uses of such materials which will be recognized by those skilled in this
art. Because of the bonded nature of such porous elements, they can be provided in
any shape, either by direct formation or by subsequent grinding or molding to any
desired configuration.
[0076] The following examples provide further information regarding the instant inventive
concepts and illustrate some of the advantages of the products of this invention particularly
when utilized as an ink reservoir for a marking or writing instrument. It is to be
understood, however, that these examples are illustrative and the various materials
and processing parameters may be varied within the skill of the art without departing
from the instant inventive concepts.
[0077] Dry polyethylene terephthalate with an intrinsic viscosity of 0.57 (measured in 60/40
phenol/tetrachlorethane) was extruded at about 290°C. Simultaneously, polypropylene
of a melt flow of 400 g/10 min was extruded from a second extruder into a common die
head. In the die head, the two polymers were separately distributed by multiple channels
into a triangular section "nose cone". The polymers exited at the tip of the nose
cone through spinneret type capillaries, each molten filament having an amorphous
polyethylene terephthalate sheath on a crystalline polypropylene core at approximately
a 50/50 weight ratio. The filaments were attenuated (drawn) by high velocity air,
flowing at both sides of the nose cone in a manner typical of melt blown processes.
[0078] The resulting melt blown webs were shaped into cylindrical rods by pulling them through
dies where the fibers were exposed to live steam. The steam heating not only shaped
and bonded the web, but also crystallized the fibers.
[0079] The crystallized fibers were dimensionally stable to subsequent heating and did not
swell when submerged in ink carrier solvents, such as low alcohols, ketones and xylene
and formic acid-containing inks.
[0080] Table 1, compares various properties of cylindrical ink reservoirs formed from the
novel melt blown bicomponent fibers of this invention with the more conventional monocomponent
polyethylene terephthalate fiber reservoirs of the prior art.
Sample |
Fiber |
Res, Dia. (mm) |
Fiber Dia. (microns) |
Fiber Wt. (gm) |
Porosity % |
Ink Abs. (gm) |
Relative Hardness |
Prior Art |
PET |
25.0 |
18 |
7.99 |
86.9 |
24.7 |
85.1 |
Invention |
PET/PP |
25.1 |
9 |
4.80 |
90.9 |
25.1 |
90.0 |
[PET = Polyethylene Terephthalate; PP = Polypropylene] |
Reservoirs 90 mm. long Alcohol based marker ink. Absorption measured in grams of ink
absorbed in 5 minutes per cm.2 of cross-sectional area. |
[0081] The novel polyethylene terephthalate/polypropylene fibers show a substantially equal
liquid absorption using about 40% less fiber weight. Raw material costs are reduced
not only because of lower overall polymer weights, but also because of the lower cost
of polypropylene as compared with polyethylene terephthalate, particularly on a volume
basis (the specific gravity of polyethylene terephthalate is 1.38 g/cm
3, while that of polypropylene is only 0.90 g/cm
3). The market price of polyethylene terephthalate per cubic inch, listed in the November
1995 issue of
Plastics Technology, is 3.6 cents for railcar quantities while the comparable price for polypropylene
is only 1.3 cents.
[0082] Additional cost savings are realized because of the manufacturing efficiencies of
the method of this invention. For example, the production of conventional polyester
ink reservoirs requires the melt spinning of polyethylene terephthalate yarn, followed
by a separate drawing and crimping step, and finally a further separate operation
to wrap the tow with plastic film. The bicomponent melt blowing process of this invention
effects all of the processing in a single step, since the fiber formation and reservoir
shaping is done in-line, while the drawing and crimping is not necessary. Even wrapping
can be minimized or avoided in many instances due to the relatively self-sustaining
nature of the porous rod. Labor costs, inventory costs and time savings are evident.
[0083] A similar comparison is shown in Table 2.
TABLE 2
Sample |
Fiber |
Fiber Dia. (microns) |
Fiber Wt. (gm) |
Porosity % |
Ink Abs. (gm) |
Relative Hardness |
Prior Art |
PET |
18 |
2.10 |
89.0 |
5.39 |
80.9 |
Sample 1 |
PET/PP |
9 |
1.50 |
89.6 |
5.39 |
95.8 |
Sample 2 |
PET/PP |
6 |
1.28 |
88.9 |
5.45 |
88.4 |
Sample 3 |
PET/PP |
3 |
1.20 |
91.7 |
5.83 |
86.2 |
[PET = Polyethylene Terephthalate; PP = Polypropylene] |
[0084] The melt blown bicomponent fibers in Samples 1-3 contain approximately 40% polyethylene
terephthalate by weight. Again, the higher absorption of the bicomponent fibers of
this invention is seen when compared to the same quantity of conventional polyethylene
terephthalate crimp yarn. Table 2 also illustrates the advantage of with increasingly
small fibers, which can only be provided with the melt blowing process of this invention.
[0085] While preferred embodiments and processing parameters have been shown and described,
it is to be understood that these examples are illustrative and can be varied within
the skill of the art without departing from the instant inventive concepts.
1. A substantially self-sustaining, three-dimensional, porous element formed of a web
of flexible thermoplastic fibrous material comprising an interconnecting network of
highly dispersed continuous fibers randomly oriented primarily in a longitudinal direction
and bonded to each other at points of contact, wherein at least a major part of said
continuous fibers are bicomponent fibers comprising a core of thermoplastic polymer
material substantially totally surrounded by a sheath of polymer material selected
from polyethylene terephthalate and copolymers thereof.
2. An element according to claim 1 wherein said bicomponent fibers, on average, have
a diameter of about 12 microns or less.
3. An element according to claim 2 wherein said bicomponent fibers are made by melt blowing
a continuous extrusion of said sheath-core materials.
4. An element according to claim 1 or 2 or 3 wherein said core material is polypropylene
or polybutylene terephthalate.
5. An element according to any of claims 1 to 4 wherein said core material comprises
between 30 and 90% by weight of the total bicomponent fiber.
6. An element according to any of claims 1 to 5 wherein said bicomponent fibers have
a "Y" shaped or "X" shaped or other non-round cross-section.
7. An element according to any of claims 1 to 6 which is an ink reservoir element, said
network of continuous fibers defining intercommunicating interstitial spaces capable
of holding and controllably releasing a quantity of ink.
8. An ink reservoir element according to claim 7 further including [a] an elongated passageway
extending the full length of said porous rod to define an air passage from one end
to the other thereof; and/or [b] a continuous film circumferentially enveloping said
porous rod.
9. A marking or writing instrument comprising an elongated hollow barrel member closed
at one end and carrying a marking or writing tip at the opposite end, an ink reservoir
element according to claim 6 or 7 contained within said barrel in contact with said
tip, and a quantity of ink held by said reservoir element for controlled release through
said tip.
10. An instrument according to claim 8 having an air passage defined by a longitudinal
recess formed in a continuous film circumferentially enveloping said porous rod, said
air passage extending continuously along the periphery of said porous element from
one end to the other.
11. An element according to claim 1 which is a tobacco smoke filter element, said network
of continuous fibers defining a tortuous interstitial path for passage of smoke therethrough.
12. A filter element according to claim 11 further including additive carried by the fibers
of said filter element, said additive preferably being selected from activated charcoal
and flavourant.
13. A filter rod comprising a multiplicity of filter elements according to claim 11 or
12 integrally connected to each other in end-to-end relationship.
14. A cigarette comprising a tobacco portion and a filter portion, wherein said filter
portion comprises a filter element according to claim 11 or 12, said tobacco and filter
portions preferably being connected to each other by tipping overwrap.
15. An element according to claim 1 which is [a] a wick for transporting liquid from one
place to another by capillary action, e.g. a lateral flow wick designed to transport
ink between an ink reservoir and a rolling ball in a writing instrument; or [b] a
nib for extracting and applying ink from a reservoir to a surface used in a marking
or writing instrument; or [c] a lateral flow wick designed to transport a bodily fluid
to a test site in a diagnostic test device; or [d] an absorptive reservoir for taking
up and holding of liquids; or [e] a reservoir used to collect and hold bodily fluids
which have passed through a test site in a diagnostic test device; or [f] a capillary
reservoir pad used to absorb excess ink in a printing device or [g] an absorptive
device for the removal of saliva or other bodily fluids from a bodily cavity; or [h]
a filtering material for filtering solid matter from bodily fluids in preparation
for diagnostic testing or for therapeutic purposes.
16. An element according to claim 1 wherein the surface of said bicomponent fibers is
hydrophobic and wherein said element is [a] a filter material for use as a vent filter
in a pipette tip; or [b] a filtering material for use as in an intravenous solution
injection system.
17. A method of making a substantially self -sustaining elongated porous element comprising:
a] providing separate sources of a molten core-forming thermoplastic material and
a molten sheath-forming material selected from amorphous polyethylene terephthalate
and copolymers thereof;
b] continuously extruding said molten core-forming and sheath-forming materials through
a multiplicity of openings in a conjugate sheath-core die to provide a multiplicity
of bicomponent fibers, each fiber comprising a continuous core of core-forming material
substantially totally surrounded by a sheath of sheath-forming material;
c] collecting said bicomponent fibers on a continuously moving surface to form a highly
entangled web of said bicomponent fibers in the form of an interconnecting network
of highly dispersed continuous fibers randomly oriented primarily in the direction
of movement of said moving surface;
d] gathering said web of bicomponent fibers;
e] heating said gathered web to bond said fibers to each other at their points of
contact and crystallize said polyethylene terephthalate;
f] cooling said gathered web to form a three-dimensional continuous porous element
comprising intercommunicating interstitial spaces; and
g] cutting said continuous porous element into discrete lengths.
18. A method according to claim 17 wherein said multiplicity of bicomponent fibers is
contacted with a gas under pressure as they exit the sheath-core die to attenuate
said bicomponent fibers while they are still in their molten state.
19. A method according to claim 17 or 18 wherein the bicomponent fibers are formed and
processed into said porous element in a continuous, in-line, manner.
20. A method according to any of claims 17 to 19 wherein said core-forming material is
polypropylene or polybutylene terephthalate.
21. A method according to any of claims 17 to 20 wherein said fibers are attenuated sufficiently
to produce a web or roving of fibers having an average diameter of about 12 microns
or less.
22. A method according to any of claims 17 to 21 wherein said openings of said sheath-core
die through which said bicomponent fibers are extruded are non-circular, thereby producing
bicomponent fibers of a non-round cross-section (e.g. a "Y" shaped or "X" shaped cross-section.).
23. A method according to any of claims 17 to 22 further including incorporating an additive
(e.g. activated charcoal or flavourant) into said web or roving as said bicomponent
fibers exit the sheath-core die.
24. A method according to any of claims 17 to 23 further including one or more of the
steps of [a] continuously forming a longitudinal recess in said porous element along
the periphery thereof; [b] continuously covering said porous element with an outer
sheath prior to cutting the same into discrete lengths; [c] continuous overwrapping
said porous element with a strip material to form said outer sheath; [d] wrapping
said porous rod with a filter tipping material prior to cutting the same into discrete
lengths.