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United States Patent |
6,214,270
|
Branum
|
April 10, 2001
|
Method of preparing polyethylene glycol modified polyester filaments
Abstract
Disclosed is a method of copolymerizing polyethylene glycol (PEG) into
polyethylene terephthalate (PET) to achieve a polyethylene glycol-modified
polyester composition that can be spun into filaments. The method includes
the steps of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase to form a copolyester composition, then
polymerizing the copolyester composition in the solid phase until the
copolyester is capable of achieving a melt viscosity that facilitates the
spinning of filaments, and thereafter spinning filaments from the
copolyester. A copolyester composition comprised of polyethylene glycol
and polyethylene terephthalate is also disclosed. Fabrics made from fibers
formed from the copolyester composition possess wetting, wicking, drying,
flame-retardancy, static-dissipation, and soft hand properties that are
superior to those of fabrics formed from conventional polyethylene
terephthalate fibers of the same yarn and fabric construction.
Inventors:
|
Branum; James Burch (Fort Mill, SC)
|
Assignee:
|
Wellman, Inc. (Shrewsbury, NJ)
|
Appl. No.:
|
444192 |
Filed:
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November 19, 1999 |
Intern'l Class: |
B28B 003/20; C08F 020/00 |
Field of Search: |
528/300,308,308.6,503
525/437
264/176.1,211.12,211.14
428/364,373
|
References Cited
U.S. Patent Documents
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4113704 | Sep., 1978 | MacLean et al.
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4167395 | Sep., 1979 | Engelhardt et al.
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4587154 | May., 1986 | Hotchkiss et al.
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4666454 | May., 1987 | DeMartino et al.
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4705525 | Nov., 1987 | Abel et al.
| |
4785060 | Nov., 1988 | Nagler.
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4827999 | May., 1989 | Yabuki et al.
| |
4975233 | Dec., 1990 | Blaeser et al.
| |
5089533 | Feb., 1992 | Park.
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5091504 | Feb., 1992 | Blaeser et al.
| |
5097004 | Mar., 1992 | Gallagher et al.
| |
5223317 | Jun., 1993 | Corbin et al.
| |
5709940 | Jan., 1998 | George et al.
| |
5902539 | May., 1999 | Schmidt et al.
| |
Foreign Patent Documents |
2932614 | Feb., 1992 | JP.
| |
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Philip Summa, P.A.
Claims
That which is claimed is:
1. A method of preparing polyethylene glycol modified copolyester
filaments, comprising:
copolymerizing polyethylene glycol into polyethylene terephthalate in the
melt phase to form a copolyester composition;
then polymerizing the copolyester composition in the solid phase until the
copolyester composition is capable of achieving a melt viscosity that
facilitates the spinning of filaments; and
thereafter spinning filaments from the copolyester.
2. A method of preparing copolyester filaments according to claim 1,
wherein the weight fraction of polyethylene glycol in the copolyester
composition is greater than about 4 percent.
3. A method of preparing copolyester filaments according to claim 1,
wherein the weight fraction of polyethylene glycol in the copolyester
composition is between about 4 percent and 20 percent.
4. A method of preparing copolyester filaments according to claim 1,
wherein the weight fraction of polyethylene glycol in the copolyester
composition is between about 8 percent and 14 percent.
5. A method of preparing copolyester filaments according to claim 1,
wherein the weight fraction of polyethylene glycol in the copolyester
composition is between about 10 percent and 12 percent.
6. A method of preparing copolyester filaments according to claim 1,
wherein the step of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase comprises copolymerizing polyethylene
glycol into polyethylene terephthalate in the melt phase, the polyethylene
glycol having an average molecular weight of between about 200 g/mol and
5000 g/mol.
7. A method of preparing copolyester filaments according to claim 6,
wherein the step of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase comprises copolymerizing polyethylene
glycol into polyethylene terephthalate in the melt phase, the polyethylene
glycol having an average molecular weight of between about 300 g/mol and
1000 g/mol.
8. A method of preparing copolyester filaments according to claim 1,
wherein the step of polymerizing the copolyester in the solid phase
comprises solid state polymerizing the copolyester composition until the
copolyester is capable of achieving a melt viscosity of at least about
2000 poise when heated to 260.degree. C.
9. A method of preparing copolyester filaments according to claim 8,
wherein:
the weight fraction of polyethylene glycol in the copolyester composition
is between about 10 percent and 12 percent; and
the step of solid state polymerizing the copolyester composition comprises
solid state polymerizing the copolyester composition until the copolyester
is capable of achieving a melt viscosity of between about 2500 and 3000
poise when heated to 260.degree. C.
10. A method of preparing copolyester filaments according to claim 1,
wherein the step of spinning filaments from the copolyester comprises
spinning copolyester filaments at a temperature between about 260.degree.
C. and 300.degree. C.
11. A method of preparing copolyester filaments according to claim 1,
wherein the weight fraction of polyethylene glycol in the copolyester
composition and the intrinsic viscosity of the copolyester after solid
state polymerization are defined by the shaded region of FIG. 1.
12. A method of preparing copolyester filaments according to claim 1,
wherein:
the step of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase comprises copolymerizing polyethylene
glycol into polyethylene terephthalate in the melt phase to an intrinsic
viscosity of less than about 0.65 dl/g; and
the step of polymerizing the copolyester composition in the solid phase
comprises further polymerizing the copolyester composition in the solid
phase to an intrinsic viscosity greater than the intrinsic viscosity
achieved via the melt polymerization.
13. A method of preparing copolyester filaments according to claim 12,
wherein the step of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase to an intrinsic viscosity of less than
about 0.65 dl/g comprises copolymerizing polyethylene glycol into
polyethylene terephthalate in the melt phase to an intrinsic viscosity of
less than about 0.60 dl/g.
14. A method of preparing copolyester filaments according to claim 12
wherein:
the weight fraction of polyethylene glycol in the copolyester composition
is about 5 percent; and
the copolyester composition is further polymerized in the solid phase to an
intrinsic viscosity of between about 0.67 and 0.78 dl/g.
15. A method of preparing copolyester filaments according to claim 12,
wherein:
the weight fraction of polyethylene glycol in the copolyester composition
is about 10 percent; and
the copolyester composition is further polymerized in the solid phase to an
intrinsic viscosity of between about 0.73 and 0.85 dl/g.
16. A method of preparing copolyester filaments according to claim 12
wherein:
the weight fraction of polyethylene glycol in the copolyester composition
is about 15 percent; and
the copolyester composition is further polymerized in the solid phase to an
intrinsic viscosity of between about 0.80 and 0.93 dl/g.
17. A method of preparing copolyester filaments according to claim 12,
wherein the weight fraction of polyethylene glycol in the copolyester
composition and the intrinsic viscosity of the copolyester after solid
state polymerization are defined by the shaded region of FIG. 1.
18. A method of preparing copolyester filaments according to claim 1,
further comprising the step of forming the copolyester into chips after
the step of copolymerizing polyethylene glycol into polyethylene
terephthalate in the melt phase and before the step of polymerizing the
copolyester composition in the solid phase.
19. A method of preparing polyethylene glycol modified copolyester
filaments, comprising:
reacting in the melt phase ethylene glycol and a reactant selected from the
group consisting of terephthalic acid and dimethyl terephthalate in the
presence of polyethylene glycol to form a copolyester composition having
an intrinsic viscosity of less than about 0.65 dl/g, wherein the weight
fraction of polyethylene glycol in the resulting copolyester composition
is between about 4 percent and 20 percent;
thereafter polymerizing the copolyester composition in the solid phase
until the copolyester is capable of achieving a melt viscosity of at least
about 2000 poise when heated to 260.degree. C.; and
thereafter spinning filaments from the copolyester.
20. A method for producing copolyester filaments according to claim 19,
further comprising dyeing the copolyester filaments at a temperature of
less than about 240.degree. F.
Description
FIELD OF THE INVENTION
The present invention relates to the production of polyethylene glycol
modified polyester fibers. The present invention also relates to the
manufacture of yarns and fabrics from these copolyester fibers.
BACKGROUND OF THE INVENTION
Polyester filament is strong, yet lightweight, and has excellent elastic
memory characteristics. Polyester fabric resists wrinkles and creases,
retains its shape in garments, resists abrasions, dries quickly, and
requires minimal care. Because it is synthetic, however, polyester is
often considered to have an unacceptable appearance for garment purposes
when initially formed as a filament. Accordingly, polyester filaments
require texturing to produce acceptable characteristics of appearance,
hand, and comfort in yarns and fabrics. Even then, polyester is often
viewed unfavorably in garments.
In pursuit of improved polyesters, various chemical modifications have been
attempted to obtain desirable textile features. Unfortunately, some such
treatments can produce unexpected or unwanted characteristics in the
modified polyester. For example, polyethylene glycol enhances certain
polyester properties, such as dye uptake, but diminishes other properties,
especially those melt phase characteristics that are critical to filament
spinning. Consequently, manufacturers have found that significant
fractions of polyethylene glycol in copolyester can complicate--and even
preclude--the commercial production of acceptable copolyester filaments.
To gain commercial acceptance, modified polyesters must be compatible with
commercial equipment with respect to melt-spinning, texturing, yarn
spinning, fabric forming (e.g., weaving and knitting), and fabric
finishing. This need for processing compatibility through conventional
equipment has constrained the development of innovative polyester
compositions.
To overcome the limitations of polyester compositions, polyester fibers are
often blended with other kinds of fibers, both synthetic and natural.
Perhaps most widely used in clothing are blended yarns and fabrics made of
polyester and cotton. In general, blended fabrics of polyester and cotton
are formed by spinning blended yarn from cotton fibers and polyester
staple fibers. The blended yarns can then be woven or knitted into
fabrics.
Cotton, like polyester, has certain advantages and disadvantages. Cotton is
formed almost entirely of pure cellulose. Cotton fibers are typically
about one inch long, but can vary from about one half inch to more than
two inches. Mature cotton fibers are characterized by their convolutions.
Under a microscope, cotton appears as a twisted ribbon with thickened
edges. Cotton is lightweight, absorbs moisture quickly and easily, and has
a generally favorable texture (i.e., hand) when woven into fabrics.
Cotton, however, lacks strength characteristics and elastic memory.
Consequently, garments formed entirely of cotton require frequent
laundering and pressing.
Blends of cotton and polyester fibers have found wide-ranging acceptance as
they combine the desirable characteristics of each. Even so, there are
continuing efforts to develop polyester filament, yarns, and fabrics that
more closely resemble those of cotton, silk, rayon, or other natural
fibers. One example is polyester microfibers, which are characterized by
extremely fine filaments that offer exceptionally good aesthetics and
hand, while retaining the benefits of polyester.
A need continues to exist, however, for enhanced polyester compositions
that have properties similar to those of cotton and other natural fibers,
while retaining the advantages of polyester. One such composition and
method for producing the same is disclosed by Nichols and Humelsine in
pending U.S. patent application Ser. No. 09/141,665 (Polyester Modified
with Polyethylene Glycol and Pentaerythritol), which is commonly assigned
with this application. U.S. patent application Ser. No. 09/141,665, which
is incorporated entirely herein by reference, discloses a polyester
composition that includes polyethylene terephthalate, polyethylene glycol
in an amount sufficient to increase the wetting and wicking properties of
a filament made from the composition to a level substantially similar to
the properties of cotton, but less than the amount that would reduce the
favorable elastic memory properties of the polyester composition, and
chain branching agent in an amount that raises the melt viscosity of the
polyester composition to a level that permits filament manufacture under
substantially normal spinning conditions. Including significant
concentrations of branching agents to increase melt viscosity, however, is
sometimes undesirable because branching agents promote cross-linking. This
reduces filament strength, which can lead to processing failures.
OBJECT AND SUMMARY OF THE INVENTION
Therefore, it is an object of this invention to provide polyethylene glycol
modified polyester filaments that possess favorable characteristics
similar to natural fibers, yet retain the advantages of polyester. It is a
further object of the present invention to provide a method of
copolymerizing polyethylene glycol (PEG) into polyethylene terephthalate
(PET) to achieve a PEG-modified polyester composition that is readily spun
into filaments, wherein the presence of branching agents is nonessential.
As is understood by those of ordinary skill in the art, modifying
conventional polyesters with polyethylene glycol can improve certain
polyester characteristics, yet can adversely affect others. For example,
adding polyethylene glycol to polyethylene terephthalate improves wetting
and wicking, but slows melt-phase polymerization kinetics. It also
depresses melt viscosity and renders the processing of such PEG-modified
polyesters somewhat impractical in commercial polyester spinning
operations.
Accordingly, in one aspect, the invention is a method of copolymerizing
polyethylene glycol into polyethylene terephthalate in a way that retains
the favorable properties of polyethylene glycol while attaining a high
intrinsic viscosity. This facilitates the commercial spinning of the
PEG-modified polyester using conventional spinning equipment. As will be
understood by those having ordinary skill in the art, copolymerizing
polyethylene glycol into polyethylene terephthalate is conventionally
achieved by reacting ethylene glycol and either terephthalic acid or
dimethyl terephthalate in the presence of polyethylene glycol.
In brief, polyethylene glycol, which typically makes up between about 4
percent and 20 percent by weight of the resulting copolyester, is
copolymerized into polyethylene terephthalate in the melt-phase to a
relatively low intrinsic viscosity (i.e., a viscosity that will not
support filament spinning). The resulting PEG-modified polyester is then
further polymerized in the solid phase until the copolyester is capable of
achieving a melt viscosity sufficient to spin filaments. Although
polyesters having lower intrinsic viscosities can be spun by employing
lower temperatures, this is often impractical using conventional spinning
equipment.
By introducing a solid state polymerization (SSP) step, the invention
reduces the need to add branching agents, such as pentaerythritol, to
increase the melt-phase polymerization rate and thereby achieve an
intrinsic viscosity that facilitates the spinning of filaments. Although
effective at increasing polymer viscosity, branching agents promote
cross-linking. Cross-linking leads to relatively weaker textiles. In
contrast, the present method achieves a copolyester that contains a
significant proportion of polyethylene glycol without relying on branching
agents to achieve a melt viscosity that is suitable for spinning
filaments.
In another aspect, the invention is a method of spinning the modified
polyester composition to form partially oriented yarns (POY). The
resulting copolyester POY is particularly suitable for yarns and fabrics,
either alone or in a blend with one or more other kinds of fibers. In yet
another aspect, the invention is a method of spinning the modified
polyester composition to form staple filaments, which can be drawn (and
perhaps crimped), and cut into staple fiber. Staple fiber, in turn, can be
formed into polyester yarns by employing conventional spinning techniques.
In addition, textured and spun yarns can then be formed into fabrics,
preferably by knitting or weaving, either alone or in a blend with one or
more other kinds of fibers.
The foregoing, as well as other objectives and advantages of the invention
and the manner in which the same are accomplished, is further specified
within the following detailed description and its accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 describes the post-SSP intrinsic viscosity of PEG-modified
copolyester versus the weight fraction of polyethylene glycol when
branching agent is employed in an amount of less than about 0.0014
mole-equivalent branches per mole of standardized polymer.
FIG. 2 describes the wicking properties of fabrics formed from copolyester
filaments produced according to the invention as compared to the wicking
properties of fabrics formed from conventional, unmodified polyethylene
terephthalate filaments.
FIG. 3 describes the drying properties of fabrics formed from copolyester
filaments produced according to the present invention as compared to the
drying properties of fabrics formed from conventional, unmodified
polyethylene terephthalate filaments.
FIG. 4 describes the flame-retardancy properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the flame-retardancy properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments.
FIG. 5 describes the static-dissipation properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the static-dissipation properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments.
FIG. 6 describes the abrasion resistance properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the abrasion resistance properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments.
FIG. 7 describes the strength properties of fabrics woven from copolyester
filaments produced according to the present invention as compared to the
strength properties of fabrics woven from conventional, unmodified
polyethylene terephthalate filaments.
FIG. 8 describes the improved properties of fabrics formed from copolyester
filaments produced according to the invention as compared to the
properties of fabrics formed from conventional, unmodified polyethylene
terephthalate filaments.
DETAILED DESCRIPTION
In its broadest aspect, the present invention is a method of preparing
PEG-modified copolyester filaments by copolymerizing polyethylene glycol
into polyethylene terephthalate in the melt phase to form a copolyester
composition, then polymerizing the copolyester composition in the solid
phase until the copolyester is capable of achieving a melt viscosity that
facilitates the spinning of filaments, and thereafter spinning filaments
from the copolyester.
In another aspect, the method of preparing PEG-modified copolyester
filaments includes copolymerizing polyethylene glycol and chain branching
agent into polyethylene terephthalate in the melt phase to form a
copolyester composition. The polyethylene terephthalate is present in the
copolyester composition in an amount sufficient for a filament made from
the copolyester composition to possess dimensional stability properties
substantially similar to those of conventional polyethylene terephthalate
filaments. The polyethylene glycol, which has an average molecular weight
less than about 5000 g/mol, is present in an amount sufficient for a
filament made from the copolyester composition to possess wicking, drying,
and static-dissipation properties that are superior to those of
conventional polyethylene terephthalate filaments. If used, the total
amount of chain branching agent is present in the copolyester composition
in an amount of less than about 0.0014 mole-equivalent branches per mole
of standardized polymer. (As discussed herein, to describe the molar
fraction of branching agent consistently, mole-equivalent branches are
referenced to unmodified polyethylene terephthalate.) The resulting
copolyester composition is further polymerized in the solid phase until
the copolyester is capable of achieving a melt viscosity that facilitates
the spinning of filaments. Finally, filaments are spun from the
copolyester.
The terms "melt viscosity" and "intrinsic viscosity" are used herein in
their conventional sense. Melt viscosity represents the resistance of
molten polymer to shear deformation or flow as measured at specified
conditions. Melt viscosity is primarily a factor of intrinsic viscosity,
shear, and temperature. As used herein, the term "melt viscosity" refers
to "zero-shear melt viscosity" unless indicated otherwise.
Intrinsic viscosity is the ratio of the specific viscosity of a polymer
solution of known concentration to the concentration of solute,
extrapolated to zero concentration. Intrinsic viscosity is directly
proportional to average polymer molecular weight. See, e.g., Dictionary of
Fiber and Textile Technology, Hoechst Celanese Corporation (1990); Tortora
& Merkel, Fairchild's Dictionary of Textiles (7.sup.th Edition 1996). As
used herein, average molecular weight refers to number-average molecular
weight, rather than weight-average molecular weight.
Both melt viscosity and intrinsic viscosity, which are widely recognized as
standard measurements of polymer characteristics, can be measured and
determined without undue experimentation by those of ordinary skill in
this art. For the intrinsic viscosity values described herein, the
intrinsic viscosity is determined by dissolving the copolyester in
orthochlorophenol (OCP), measuring the relative viscosity of the solution
using a Schott Autoviscometer (AVS Schott and AVS 500 Viscosystem), and
then calculating the intrinsic viscosity based on the relative viscosity.
See, e.g., Dictionary of Fiber and Textile Technology ("intrinsic
viscosity").
In particular, a 0.6-gram sample (.+-.0.005 g) of dried polymer sample is
dissolved in about 50 ml (61.0-63.5 grams) of orthochlorophenol at a
temperature of about 105.degree. C. Fiber and yarn samples are typically
cut into small pieces, whereas chip samples are ground. After cooling to
room temperature, the solution is placed in the viscometer and the
relative viscosity is measured. As noted, intrinsic viscosity is
calculated from relative viscosity.
In accordance with the invention, copolyester characteristics can be
tailored for specific applications by altering the polyethylene glycol
content. This permits choice in designing fabrics made with copolyester or
copolyester blends according to the present invention. In this sense, the
invention establishes a technology family. For example, the weight
fraction and the molecular weight of the polyethylene glycol can be
adjusted to produce specific effects, such as wetting, drying, dye rates,
and softness. Similarly, such modifications can improve the dye strike
rate and reduce the dye usage. In particular, higher polyethylene glycol
fractions, (e.g., greater than about 4 weight percent), result in softer
fabrics that wick faster, dry quicker, and dye darker.
In preferred embodiments, the polyethylene glycol is present in the
copolyester composition in an amount between about 4 weight percent and 20
weight percent. When amounts of polyethylene glycol greater than about 20
weight percent are present, the resulting copolyester does not polymerize
efficiently. Moreover, at such elevated polyethylene glycol fractions, the
copolyester composition is difficult to store and transport for it tends
to crystallize, causing undesirable sticking and clumping. Consequently,
polyethylene glycol amounts between about 8 weight percent and 14 weight
percent are more preferred, and amounts between about 10 weight percent
and 12 weight percent are most preferred. Furthermore, while polyethylene
glycol with molecular weights between about 200 and 5000 g/mol may be
effectively employed, the preferred average molecular weight for
polyethylene glycol is between about 300 and 1000 g/mol, most preferably
400 g/mol.
As known to those familiar with the manufacture of polyester, the equipment
used to spin polyester into filaments is designed, built, and adjusted to
process polymers whose melt viscosity falls within a certain range,
typically between about 1500 and 4000 poise. Thus, such equipment runs
most satisfactorily when the melt viscosity of the copolyester, which is
directly proportional to the intrinsic viscosity as discussed herein, is
within this viscosity range. If polyethylene glycol is included in
relatively significant amounts (i.e., more than about 4 weight percent), a
number of spinning failures are likely to occur when conventional
polymerization methods are followed. In other words, high polyethylene
glycol fractions can suppress melt viscosity, which in turn can hinder
spinning productivity.
The present invention provides a method for incorporating into polyester
the favorable properties of polyethylene glycol, particularly its
outstanding wetting and wicking properties. The invention accomplishes
this by employing a higher intrinsic viscosity to compensate for the
tendency of higher fractions of polyethylene glycol to lower the melt
viscosity of the copolyester. Consequently, the present method virtually
eliminates the need for significant amounts of branching agent. As will be
understood by those of skill in the art, a low melt viscosity hinders the
processing of copolyester through conventional spinning equipment.
Initially, polyethylene glycol is polymerized into polyethylene
terephthalate in the melt phase to form a copolyester composition. Except
for its premature termination, the melt polymerization otherwise follows
conventional techniques that are well known in the art. This melt
polymerization of the copolyester composition, however, is followed by a
solid state polymerization step. Conventional wisdom has held that an SSP
step is unnecessary and even undesirable with respect to forming
copolyester filaments.
In particular, the copolyester composition is polymerized in the solid
phase until the copolyester is capable of achieving a zero-shear melt
viscosity of at least about 2000 poise at 260.degree. C. It will be
understood by those having ordinary skill in the art that, as used herein,
the description of polymerizing the copolyester composition in the solid
phase until the copolyester is capable of achieving a certain melt
viscosity simply means that the solid copolyester would have that
particular melt viscosity if it were melted without further solid state
polymerization.
In a preferred embodiment of the method, when the weight fraction of
polyethylene glycol in the copolyester composition is between about 10
percent and 12 percent, the copolyester composition is polymerized in the
solid phase until the copolyester is capable of achieving a melt viscosity
of between about 2500 and 3000 poise at a temperature of 260.degree. C. As
will be understood by those having ordinary skill in this art, the
copolyester need not be spun immediately after undergoing solid state
polymerization. In fact, in preferred embodiments, the copolyester is
formed into chips after the step of copolymerizing polyethylene glycol
into polyethylene terephthalate in the melt phase and before the step of
polymerizing the copolyester composition in the solid phase.
According to the present method, copolyester filaments are preferably spun
at a temperature between about 260.degree. C. and 300.degree. C. This
temperature range comports with that employed in conventional spinning
equipment that uses Dowtherm A vapor heat transfer media, which is
available from Dow Chemical Co.
As discussed previously, in its broadest aspects, the method includes
forming polyethylene glycol modified copolyester filaments by
copolymerizing polyethylene glycol into polyethylene terephthalate in the
melt phase to form a copolyester composition, then polymerizing the
copolyester composition in the solid phase until the copolyester
composition is capable of achieving a melt viscosity that facilitates the
spinning of filaments, and thereafter spinning filaments from the
copolyester. FIG. 1 defines the preferred intrinsic viscosity of the
copolyester after solid state polymerization as a function of the weight
fraction of polyethylene glycol when low levels of branching agent are
employed (e.g., less than 500 ppm of pentaerythritol).
In preferred embodiments, polyethylene glycol is copolymerized into
polyethylene terephthalate in the melt phase to an intrinsic viscosity of
less than about 0.65 dl/g. In one preferred embodiment, the melt phase
copolymerization is terminated before the copolyester composition reaches
an intrinsic viscosity of about 0.60 dl/g. In another preferred
embodiment, the melt phase copolymerization is terminated before the
copolyester composition reaches an intrinsic viscosity of about 0.55 dl/g.
As will be understood by those having ordinary skill in the art, modified
polyethylene terephthalate having an intrinsic viscosity of less than 0.65
dl/g, more than about 4 weight percent polyethylene glycol, and low levels
of branching agent is not readily spun into filaments. Consequently, after
the melt polymerization step, the PEG-modified copolyester composition is
polymerized in the solid phase to an intrinsic viscosity greater than the
intrinsic viscosity achieved via the melt polymerization. For example,
when the weight fraction of polyethylene glycol in the copolyester
composition is about 5 percent, the copolyester composition is preferably
polymerized in the solid phase to an intrinsic viscosity of between about
0.67 and 0.78 dl/g. Similarly, when the weight fraction of polyethylene
glycol in the copolyester composition is about 10 percent, the copolyester
composition is preferably polymerized in the solid phase to an intrinsic
viscosity of between about 0.73 and 0.85 dl/g. Finally, when the weight
fraction of polyethylene glycol in the copolyester composition is about 15
percent, the copolyester composition is preferably polymerized in the
solid phase to an intrinsic viscosity of between about 0.80 and 0.93 dl/g.
More generally, the target intrinsic viscosity for any polyethylene glycol
weight fraction between about 5 percent and 15 percent is defined by the
shaded region in FIG. 1.
It will be understood to those of skill in the art that the polyethylene
glycol reduces melt temperature (T.sub.m) and glass transition temperature
(T.sub.g). Consequently, the temperature at which dyes will penetrate the
modified polyester structure is lowered. Accordingly, the present method
further comprises dyeing the copolyester filaments at a temperature of
less than about 240.degree. F. In one preferred embodiment, the method
includes dyeing the copolyester filaments at a temperature of less than
about 230.degree. F. In yet another preferred embodiment, the method
includes dyeing the copolyester filaments at a temperature of less than
about 220.degree. F. In fact, the copolyester filaments can be dyed at or
below the temperature defined by the boiling point of water at atmospheric
pressure (i.e., 212.degree. F. or 100.degree. C.). In fact, the
copolyester fibers have achieved excellent color depth when dyed at
200.degree. F.
As used herein, the concept of dyeing copolyester filaments includes dyeing
not only filaments (e.g., partially oriented yarn filaments), but also
staple fibers cut from filaments. Moreover, this concept further includes
dyeing copolyester fibers that are formed into yams or fabrics, either
alone or in blends with one or more other kinds of fiber (e.g., cotton or
spandex fibers).
In one particular embodiment, the method of preparing PEG-modified
copolyester filaments includes reacting in the melt phase ethylene glycol
and either terephthalic acid and dimethyl terephthalate in the presence of
polyethylene glycol to form a copolyester composition having an intrinsic
viscosity of less than about 0.65 dl/g. Preferably, the weight fraction of
polyethylene glycol in the resulting copolyester composition is between
about 4 percent and 20 percent. The copolyester composition is thereafter
polymerized in the solid phase until the copolyester is capable of
achieving a melt viscosity of at least about 2000 poise when heated to
260.degree. C. Finally, filaments are spun from the copolyester.
Additionally, the resulting copolyester filaments may be dyed at a
temperature of less than about 240.degree. F.
As noted, in one aspect the method of preparing PEG-modified copolyester
filaments includes copolymerizing polyethylene glycol and chain branching
agent into polyethylene terephthalate in the melt phase to form a
copolyester composition. The polyethylene terephthalate is present in an
amount sufficient for a filament made from the copolyester composition to
possess dimensional stability properties (e.g., shrinkage during home
laundering) substantially similar to those of conventional polyethylene
terephthalate filaments. The polyethylene glycol, which has an average
molecular weight less than about 5000 g/mol, is present in an amount
sufficient for filaments made from the copolyester composition to possess
wetting, wicking, drying, flame-retardancy, and static-dissipation
properties that are superior to those of conventional polyethylene
terephthalate filaments. It has been further observed that fabrics formed
according to the present invention possess significantly improved hand
(i.e., tactile qualities) as compared to conventional polyester fabrics
made of fibers having similar denier per filament (DPF).
As discussed previously, at least about 4 weight percent polyethylene
glycol is necessary to achieve these improved filament characteristics.
When used, chain branching agent is present in the copolyester composition
in an amount of less than about 0.0014 mole-equivalent branches per mole
of standardized polymer. The resulting copolyester composition is further
polymerized in the solid phase until the copolyester is capable of
achieving a melt viscosity that facilitates the spinning of filaments.
Finally, filaments are spun from the copolyester.
FIG. 2 describes the wicking properties of fabrics formed from copolyester
filaments produced according to the invention as compared to the wicking
properties of fabrics formed from conventional, unmodified polyethylene
terephthalate filaments. Wicking properties were measured using
1".times.7" strips that were suspended vertically above water-filled
beakers and then submersed one inch below the water surface. After one
minute, the water migration up the test strips was measured. The fabrics
were tested in both fabric directions and averaged. The test strip fabrics
were laundered once before testing. The room conditions were ASTM standard
21.degree. C. and 65 percent relative humidity.
FIG. 3 describes the drying properties of fabrics formed from copolyester
filaments produced according to the present invention as compared to the
drying properties of fabrics formed from conventional, unmodified
polyethylene terephthalate filaments. Drying rate was determined using a
Sartorius MA30-000V3 at 40.degree. C. Two or three drops of water were
placed on the fabrics. Then, the evaporation time was measured and an
evaporation rate was calculated. The room conditions were ASTM standard
21.degree. C. and 65 percent relative humidity.
FIG. 4 describes the flame-retardancy properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the flame-retardancy properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments. The testing was performed
in accordance with the NFPA 701 Method small-scale-after-flame test. FIG.
4 merely shows that fabrics formed from copolyester filaments produced
according to the invention have better flame-retardancy properties as
compared to those of fabrics formed from conventional, unmodified
polyethylene terephthalate filaments. FIG. 4 is not intended to imply that
fabrics formed from copolyester filaments produced according to the
invention will meet any particular government flammability standards.
FIG. 5 describes the static-dissipation properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the static-dissipation properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments. Static dissipation was
determined using a Rothschild Static-Voltmeter R-4021. In brief, fabric
was mounted between the electrodes, and then the time for the voltage
across the fabric to reduce from 150 volts to 75 volts was measured. The
room conditions were ASTM standard 21.degree. C. and 65 percent relative
humidity. As will be understood by those having ordinary skill in the art,
a shorter charge half-life is desirable in fabrics because it means fabric
static is dissipated faster.
FIG. 6 describes the abrasion resistance properties of fabrics formed from
copolyester filaments produced according to the invention as compared to
the abrasion resistance properties of fabrics formed from conventional,
unmodified polyethylene terephthalate filaments. The fabrics each had a
TiO.sub.2 level of 3000 ppm. Abrasion resistance was determined using
Stoll flat (knits) ASTM D 3886 method and Taber (wovens) ASTM D 3884
method.
FIG. 7 describes the strength properties of fabrics woven from copolyester
filaments produced according to the present invention as compared to the
strength properties of fabrics woven from conventional, unmodified
polyethylene terephthalate filaments. The somewhat weaker strength of
fabrics formed from the filaments prepared according to the invention
reduces undesirable pilling. Fabric strength was determined by strip test
(wovens) ASTM D 1682-64 method or by Ball Burst (knits) ASTM D3787-80A.
FIG. 8 summarizes on a percentage basis the improved properties of fabrics
formed from copolyester filaments produced according to the invention as
compared to the properties of fabrics formed from conventional, unmodified
polyethylene terephthalate filaments.
Preparing PEG-modified copolyester filaments according to the invention not
only yields certain improved textile characteristics, but also retains the
desirable dimensional stability of ordinary polyester. Despite the
significant concentration of polyethylene glycol, copolyester filaments
prepared according to the invention have dimensional stability properties,
especially shrinkage during home laundering, that are substantially
similar to those of conventional polyethylene terephthalate filaments. For
example, conventional polyester fabric exhibits less than about five
percent shrinkage in home laundering if finished at a fabric temperature
at or above 350.degree. F. Similarly, copolyester fabric of the invention
exhibits less than about five percent shrinkage in home laundering if
finished at a fabric temperature at or above only 330.degree. F.
It is also expected that fabrics formed from the filaments spun according
to the invention will possess better elastic-memory properties (i.e.,
stretch and recovery) as compared to fabrics formed from conventional
polyethylene terephthalate filaments.
The commonly-assigned patent application Ser. No. 09/141,665 discloses that
chain branching agents can raise the melt viscosity of PEG-modified
copolymer melt to within the range of normal, unmodified polyethylene
terephthalate. In contrast, the present invention introduces an
alternative method of producing filament from PEG-modified copolyester
without resorting to significant fractions of branching agent.
In accordance with this aspect of the invention, the total amount of chain
branching agent in the copolyester is insufficient to raise the melt
viscosity of the copolyester composition to a level that would permit the
manufacture of copolyester filament under conditions (e.g., spinning
temperature) that are substantially the same as those under which filament
can be formed from unmodified polyethylene terephthalate. More
specifically, chain branching agent is present in the copolyester
composition in an amount of less than about 0.0014 mole-equivalent
branches per mole of standardized polymer.
As used herein, the term "mole-equivalent branches" refers to the reactive
sites available for chain branching on a molar basis (i.e., the number of
reactive sites in excess of the two required to form a linear molecule).
For example, pentaerythritol is a tetrafunctional branching agent, so it
possesses two available chain branching reactive sites.
In addition, as used herein, the term "standardized polymer" refers to the
repeat unit of unmodified polyethylene terephthalate, which has a
molecular weight of 192 g/mol. In this regard, it will be understood by
those of skill in the art that, for a given total weight of polyethylene
terephthalate, polyethylene glycol, and branching agent, increasing the
relative weight fraction of polyethylene glycol, which preferably has a
molecular weight of between about 200 g/mol and 5000 g/mol, will decrease
total moles. (This is so because the molecular weight of polyethylene
terephthalate is less than the molecular weight of the polyethylene
glycol.) Consequently, to maintain uniformity across various
concentrations and molecular weights of polyethylene glycol, the chain
branching agent concentration of preferably less than about 0.0014
mole-equivalent branches per mole of standardized polymer is based on the
repeat unit of unmodified polyethylene terephthalate. In other words, the
weight fraction of branching agent should be calculated as if the polymer
is made of only unmodified polyethylene terephthalate. Consequently, the
weight fraction of polyethylene glycol (e.g., preferably between about 4
weight percent and 20 weight percent) and the molecular weight of the
polyethylene glycol (e.g., preferably between about 200 g/mol and 5000
g/mol) can be disregarded in calculating mole-equivalent branches per mole
of standardized polymer.
For example, an amount of pentaerythritol less than about 0.0014
mole-equivalent branches per mole of the copolyester composition is
equivalent to a weight fraction of less than about 500 ppm when based on
the standardized polymer of unmodified polyethylene terephthalate, whose
repeat unit has a molecular weight of about 192 g/mol. To further
illustrate this relationship, assume 1000 grams of starting materials--500
ppm pentaerythritol, which has a molecular weight of 136.15 g/mol, and the
remainder polyethylene terephthalate. This is equivalent to 0.5 gram
pentaerythritol, or 0.00367 moles of pentaerythritol, and 999.5 grams
polyethylene terephthalate, or 5.21 moles polyethylene terephthalate
repeat units. The mole fraction of pentaerythritol relative to the
polyethylene terephthalate is, therefore, 0.0705 mole percent (i.e.,
0.00367 moles of pentaerythritol.div.5.21 moles polyethylene
terephthalate). As noted, pentaerythritol has two available chain
branching reactive sites. Thus, the mole-equivalent branches per mole of
unmodified polyethylene terephthalate is 0.14 percent (i.e., 0.0014
mole-equivalent branches per mole of standardized polymer.)
The weight fraction corresponding to 0.0014 mole-equivalent branches per
mole of standardized polymer can be estimated for any branching agent
using the following equation:
branching agent
(ppm)=(MEB.div.CBRS).multidot.(BAMW.div.SPMW).multidot.10.sup.6,
wherein
MEB=0.0014 mole-equivalent branches per mole of standardized polymer
CBRS=number of available chain branching reactive sites
BAMW=molecular weight of the branching agent (g/mol)
SPMW=192 g/mol--molecular weight of the standardized polymer (i.e.,
unmodified polyethylene terephthalate)
It will be appreciated by those of skill in the chemical arts that if the
mole-equivalent branches were not referenced to a mole of standardized
polymer, a branching agent concentration of 0.0014 mole-equivalent
branches per mole of polymer (i.e., the copolyester composition) would
translate to a slightly lower weight fraction, (i.e., ppm), when a greater
polyethylene glycol weight fraction is used, or when polyethylene glycol
having a higher average molecular weight is employed. For example, if
mole-equivalent branches per mole of polymer were not related to a common
standard, but rather to the actual components of the copolyester
composition, an amount of pentaerythritol less than about 0.0014
mole-equivalent branches per mole of the copolyester composition would be
equivalent to a weight fraction of less than about 450 ppm when based on
polyethylene terephthalate that is modified by 20 weight percent
polyethylene glycol having an average molecular weight of about 400 g/mol.
Likewise, an amount of pentaerythritol less than about 0.0014
mole-equivalent branches per mole of the copolyester composition would be
equivalent to a weight fraction of less than about 400 ppm when based on
polyethylene terephthalate that is modified by 20 weight percent
polyethylene glycol having an average molecular weight of about 5000
g/mol. By employing unmodified polyethylene terephthalate as the
standardized polymer, however, an amount of pentaerythritol less than
about 0.0014 mole-equivalent branches per mole of standardized polymer is
equivalent to a weight fraction of less than about 500 ppm regardless of
the weight fraction or molecular weight of the polyethylene glycol.
To the extent a chain branching agent is employed, the chain branching
agent is preferably a trifunctional or tetrafunctional alcohol or acid
that will copolymerize with polyethylene terephthalate. As will be
understood by those skilled in the art, a trifunctional branching agent
has one reactive site available for branching and a tetrafunctional
branching agent has two reactive sites available for branching. Acceptable
chain branching agents include, but are not limited to, trimesic acid
(C.sub.6 H3 (COOH).sub.3), pyromellitic acid (C.sub.6 H.sub.2
(COOH).sub.4), pryomellitic dianhydride, trimellitic acid, trimellitic
anhydride, trimethylol propane (C.sub.3 H.sub.5 C(CH.sub.2 OH).sub.3) and
preferably pentaerythritol (C(CH.sub.2 OH).sub.4), If the total number of
reactive sites exceeds four per branching agent molecule, steric hindrance
may prevent full polymerization at the available reactive sites such that
more branching agent may be required to achieve the desired
mole-equivalent branches. See, e.g., U.S. Pat. Nos. 4,092,299 and
4,113,704 by MacLean and Estes.
Accordingly, in one particular embodiment, the method of preparing
PEG-modified copolyester filaments includes copolymerizing polyethylene
glycol and chain branching agent into polyethylene terephthalate in the
melt phase to form a copolyester composition having an intrinsic viscosity
of less than about 0.65 dl/g. As will be understood by those having
ordinary skill in the art, copolymerizing polyethylene glycol and
branching agent into polyethylene terephthalate is conventionally achieved
by reacting ethylene glycol and either terephthalic acid or dimethyl
terephthalate in the presence of polyethylene glycol and branching agent.
The polyethylene terephthalate is present in an amount sufficient for a
filament made from the copolyester composition to possess elastic memory
and dimensional stability properties substantially similar to those of
conventional polyethylene terephthalate filaments. The polyethylene
glycol, which has an average molecular weight less than about 5000 g/mol,
is present in an amount sufficient for a filament made from the
copolyester composition to possess wicking, drying, and static-dissipation
properties that are superior to those of conventional polyethylene
terephthalate filaments. Moreover, the total amount of chain branching
agent that is present in the copolyester composition is less than about
0.0014 mole-equivalent branches per mole of standardized polymer.
After the melt polymerization step, the copolyester composition is solid
state polymerized until the copolyester is capable of achieving a melt
viscosity of at least about 2000 poise when heated to 260.degree. C.
Finally, filaments are spun from the copolyester composition. In addition,
the resulting copolyester filaments may be dyed at a temperature of less
than about 240.degree. F.
In brief, the solid phase polymerization step following the melt
polymerization step produces a melt viscosity for the PEG-modified
polyester sufficient for practical processing, and sufficient spinning
tensions for a stable and high-throughput commercial process. This is so
despite the presence of only insignificant amounts of branching agent
(i.e., less than about 0.14 percent mole-equivalent branches per mole of
standardized polymer).
A distinct advantage of the present method is that it produces a
copolyester filament that, while possessing wetting, wicking, drying, soft
hand, flame-retardancy, abrasion-resistance, and static-dissipation
properties that are superior to those of conventional polyethylene
terephthalate filaments, can be processed using conventional textile
equipment. For example, in one broad aspect, the PET-modified copolyester
can be spun into partially oriented yarns (POY). As will be understood by
those having ordinary skill in the art, POY is often comprised of from
tens to hundreds of intermingled filaments (e.g., between 30 and 200) that
are extruded from a spinneret at speeds typically between about 2000 and
4000 meters per minute. The POY is then typically drawn to form a drawn
yarn, (e.g., by draw texturing, flat drawing, or warp drawing).
Thereafter, the drawn yarn is formed into fabric, which is typically
finished as well. As will be known by those skilled in the art, texturing
can be effected in numerous ways, such as air jet, gear crimping, and
false-twist techniques.
It should be noted that flat drawn POY produced according to the invention
results in yarns having dyeing characteristics similar to those of
cellulose acetate yarns. These copolyester yarns are especially suitable
for producing suit linings. As will be known to those having ordinary
skill in the art, suit linings are conventionally jig dyed using
low-energy dyes, which have poor fastness properties. The yarns and fabric
formed according to the invention, however, can be dyed on conventional
jig dyeing equipment using high-energy dyes, which have better fastness.
Because of the characteristic advantages that the invention brings to the
polyester compositions described herein, the resulting polyester filaments
are particularly useful in blended yarns and blended fabrics. Accordingly,
copolyester POY can be blended with at least one other kind of fiber
(i.e., a fiber having a different chemical composition or having been
differently processed) to form a blended yarn. As will be understood by
those familiar with textile processes, the copolyester POY is typically
either draw textured to form a draw-textured yarn (DTY) or flat drawn to
form a flat-drawn yarn (i.e., a hard yarn) before blending. The drawn
copolyester yarn is especially suitable for blending with cotton fibers,
rayon fibers, polypropylene fibers, acetate fibers, nylon fibers, spandex
fibers, and conventional polyester fibers.
Furthermore, the drawn copolyester yarn (e.g., DTY or hard yarn) can also
be blended with a least one other kind of fiber to form blended fabric. In
this regard, the drawn copolyester yarn is especially suitable for
blending with cotton fibers, rayon fibers, polypropylene fibers, acetate
fibers, nylon fibers, spandex fibers, conventional polyester fibers, and
even copolyester staple fibers of the present invention. It will be
understood that, as used herein, the concept of forming a blended fabric
from the drawn copolyester yarn and at least one other kind of fiber not
only includes directly forming a fabric from the drawn copolyester yarn
and a second kind of fiber, but also includes first forming a blended yarn
before forming the blended fabric. In either case, however, the blended
fabric is formed from a drawn copolyester yarn and a second kind of fiber.
As will be known to those skilled in the art, two different kinds of
filaments are not usually textured together unless they can use the same
temperature and draw ratio. Consequently, it is desirable to form a
blended fabric without first forming a blended yarn when the second kind
of fiber has different texturing requirements than those of the
copolyester POY.
It has been observed, however, that the copolyester POY and nylon yarn
require similar texturing temperatures. Accordingly, in a preferred
embodiment, the copolyester POY and a nylon yarn are formed into a blended
yarn. Thereafter, the blended yarn is textured. Interestingly, because of
dye selectivity, the resulting blended yarn may be dyed with disperse dye,
which preferentially dyes the copolyester component, and acid-based dye,
which preferentially dyes the nylon component. In this way, a heather yarn
(or a two-colored yam) can be produced, which may then be formed into an
attractive, heather fabric (or a two-colored fabric).
In another broad aspect, the invention further includes cutting the
copolyester filaments into staple fibers. As will be understood by those
having ordinary skill in the art, perhaps thousands of filaments can be
spun from a single spinneret, typically at speeds of between about 500 and
2000 meters per minute. The filaments, often from numerous spinneret
positions, are combined into a tow. The tow is often crimped before the
filaments are cut into staple fibers.
The staple fibers can be formed into yarn using any conventional spinning
technique, such as ring spinning, open-end spinning, and air jet spinning.
In this regard, open end and air jet spinning are becoming increasingly
more preferred for polyester yarns, as well as for blended yarns
containing polyester. The yarns formed from the copolyester filaments of
the invention, in turn, can be woven or knitted into fabrics that have the
advantageous characteristics referred to herein. Alternatively, the staple
fibers can be formed directly into a non-woven fabric. As used herein, the
concept of forming staple fibers into fabric includes first forming a
yarn, (e.g., knitting and weaving), in addition to forming the staple
fibers directly into fabric, (e.g., non-woven fabric).
In another aspect, the method includes blending the staple copolyester
fibers with at least a second kind of fiber, such as cotton fibers, rayon
fibers, polypropylene fibers, acetate fibers, nylon fibers, spandex
fibers, and conventional unmodified polyester fibers. In this regard,
acetate fibers and spandex fibers are usually in filament form.
Thereafter, the staple fibers and the second kind of fiber can be spun
into yam, and the yarn formed into fabric using conventional techniques.
Alternatively, the staple fibers and the second kind of fiber can be
formed directly into a non-woven fabric.
In yet another aspect, the invention includes forming copolyester fibers
from the copolyester composition, and then blending the copolyester fibers
with spandex fibers. As used herein, the term "copolyester fiber" broadly
refers to uncut filament (e.g., POY) and cut fiber (e.g., staple fiber).
For example, the copolyester fibers and the spandex fibers can be blended
into yarn. In one preferred embodiment, this comprises core spinning
copolyester staple fibers around a core of spandex filaments. Likewise, in
another preferred embodiment, the copolyester filaments--preferably in the
form of POY--are wrapped around spandex filaments.
The copolyester fibers and the spandex fibers may also be formed into
fabric using conventional techniques. For example, the fabric may be
formed, (e.g., woven or knitted), from a blended yarn that is spun from
the copolyester fibers and the spandex fibers. Alternatively, the
copolyester fibers and spandex fibers may be directly formed into a
fabric, preferably a knit fabric. To accomplish this, the spandex is laid
into a copolyester knit by employing an appropriate knitting machine
attachment.
As noted previously, the invention can include dyeing the copolyester
fibers at a temperature of less than about 240.degree. F. In particular,
this reduction in dyeing temperature not only reduces energy usage, but
also permits copolyester fibers that are produced according to this
embodiment of the invention to be more effectively combined with spandex
filaments. Blended yarns and fabrics that are made from PEG-modified
copolyester fibers--preferably staple fibers or POY--and spandex fibers
can be dyed at temperatures of less than about 240.degree. F., and yet can
achieve excellent fastness and depth of color. In one preferred
embodiment, the spandex fibers and the copolyester fibers may be dyed at a
temperature of less than about 230.degree. F. In another preferred
embodiment, the spandex fibers and the copolyester fibers may be dyed at a
temperature of less than about 220.degree. F. In yet another preferred
embodiment, the spandex fibers and the copolyester fibers may be dyed at
or below a temperature of less than the boiling point of water at
atmospheric pressure (i.e., 212.degree. F. or 100.degree. C.). In this
regard, it should be understood that the concept of dyeing copolyester
fibers and spandex fibers includes dyeing the blend in the form of blended
yarns and blended fabrics. It is emphasized that, as used herein, the term
"copolyester fibers" broadly refers to cut copolyester fibers, (e.g.,
staple fibers), and uncut copolyester filaments, (e.g., POY).
Dyeing copolyester fibers and spandex fibers at reduced temperatures
prevents the degradation of the stretch properties possessed by spandex.
In conventional polyester-spandex blended textiles, dyeing temperatures of
about 265.degree. F. are required to adequately dye the conventional
polyester fibers. Unfortunately, such high temperatures weaken such
high-power stretch polyurethane filaments. Consequently, dyeing blends of
copolyester and spandex at lower temperatures is advantageous.
In other embodiments of the method, copolyester fibers, whether staple
fibers or POY, are blended with cotton fibers. The preferred
copolyester/cotton blends include between about 5 percent and 95 weight
percent cotton fibers with the remainder comprising the copolyester
fibers. Most preferably, the blend includes between about 30 weight
percent and 70 weight percent cotton fibers with the remainder comprising
the polyester fibers. In this regard, the invention provides the
opportunity to increase the synthetic content of blended cotton and
polyester yarns to take advantage of the desirable characteristics of the
copolyester in the resulting yarns and fabrics. For example, unlike
conventional unmodified polyester filaments, the copolyester filaments
formed according to the present method possess static-dissipation
properties that are substantially similar to cotton. Moreover, the present
copolyester filaments retain the desirable dimensional stability
characteristics of conventional polyesters.
Those familiar with textile terminology will understand that "spinning"
refers to two different processes. In one sense, the term "spinning"
refers to the production of synthetic polymer filaments from a polymer
melt. In its older, conventional use, the term "spinning" refers to the
process of twisting a plurality of individual fibers into yarns. The use
of both of these terms is widespread and well understood in this art such
that the particular use herein should be easily recognized by those of
ordinary skill in the art.
Conventional techniques of polymerizing polyester and spinning filaments
are well known by those having ordinary skill in the art. Accordingly, the
following example highlights the inventor's modifications to conventional
process steps to achieve an especially desirable fabric.
EXAMPLE
Melt Polymerization--The copolyester composition was polymerized like
standard polyethylene terephthalate, except that the polymerization
temperature was 10.degree. C. lower than normal. Polyethylene glycol,
having an average molecular weight of 400 g/mole, was injected into the
process before the initiation of the polymerization at a rate sufficient
to yield 10 weight percent polyethylene glycol in the copolyester
composition. Likewise, pentaerthyritol was added before polymerization at
a rate that would yield 500 ppm in the copolyester composition. The
copolyester was then extruded, quenched, and cut. The quench water was
10.degree. C. colder than normal. The copolyester was crystallized
10.degree. C. lower than normal. The copolyester was melt polymerized to
an intrinsic viscosity of 0.62 dl/g.
Solid State Polymerization--The copolyester chip was solid state
polymerized like a normal polyethylene terephthalate bottle resin chip
except that the chip was maintained at 190.degree. C. for five hours. The
intrinsic viscosity of the copolyester chip was increased in the solid
phase to about 0.77 dl/g.
Filament Spinning--The copolyester formed POY like a conventional
polyethylene terephthalate product having the same filament count, except
that the spinning speed was reduced by seven percent and the spinning
temperature was reduced by 15.degree. C.
Texturing--The POY was textured on a contact heater false twist texturing
machine with polyurethane disks. The POY processed like standard
polyethylene terephthalate POY except that the 100-filament product used a
2-5-1 stainless-polyurethane-stainless disk stack. Moreover, the
temperature was about 50.degree. C. to 60.degree. C. below normal
primary-heater temperatures. Finally, the secondary heater was not used,
yielding a stretch textured yarn.
Fabric Formation--Fabric formation was identical to conventional
techniques.
Dyeing--Dyeing was the same as conventional techniques except that no
carrier was used and the batch was held at a dye temperature of
220.degree. F. for 30 minutes
Finishing--Finishing was the same as conventional techniques except that
the zone temperature was reduced 10.degree. C. and no finish was used in
the pad.
In the drawings and the specification, typical embodiments of the invention
have been disclosed. Specific terms have been used only in a generic and
descriptive sense, and not for purposes of limitation. The scope of the
invention is set forth in the following claims.
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