U.S. patent application number 10/635261 was filed with the patent office on 2004-06-03 for low-shrink textile articles made from polypropylene fibers.
Invention is credited to Cowan, Martin E., Mehl, Nathan A., Morin, Brian G., Parks, William S..
Application Number | 20040105978 10/635261 |
Document ID | / |
Family ID | 25332541 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040105978 |
Kind Code |
A1 |
Morin, Brian G. ; et
al. |
June 3, 2004 |
Low-shrink textile articles made from polypropylene fibers
Abstract
Improved polypropylene fibers exhibiting greatly reduced heat-
and moisture-shrink problems are provided. Such fibers require the
presence of certain compounds that quickly and effectively provide
rigidity to the target polypropylene fiber after heat-setting.
Generally, these compounds include any structure that nucleates
polymer crystals within the target polypropyelene after exposure to
sufficient heat to melt the initial pelletized polymer and upon
allowing such a melt to cool. The compounds must nucleate polymer
crystals at a higher temperature than the target polypropylene
without the nucleating agent during cooling. In such a manner, the
"rigidifying" nucleator compounds provide nucleation sites for
polypropylene crystal growth. After drawing the nucleated
composition into fiber form, the fiber is then exposed to
sufficient heat to grow the crystalline network, thus holding the
fiber in a desired position. The preferred "rigidifying" compounds
include dibenzylidene sorbitol based compounds, as well as less
preferred compounds, such as sodium benzoate, certain sodium and
lithium phosphate salts (such as sodium
2,2'-methylene-bis-(4,6-di-tert-butylphenyl)phosphate, otherwise
known as NA-11). Specific methods of manufacture of such fibers, as
well as fabric articles made therefrom, are also encompassed within
this invention.
Inventors: |
Morin, Brian G.; (Greer,
SC) ; Mehl, Nathan A.; ( Moore, SC) ; Cowan,
Martin E.; (Moore, SC) ; Parks, William S.;
(Boiling Springs, SC) |
Correspondence
Address: |
Milliken & Company
P.O. Box 1927
Spartanburg
SC
29304
US
|
Family ID: |
25332541 |
Appl. No.: |
10/635261 |
Filed: |
August 6, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10635261 |
Aug 6, 2003 |
|
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09860130 |
May 17, 2001 |
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6656404 |
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Current U.S.
Class: |
428/372 ;
442/301; 442/304 |
Current CPC
Class: |
C08K 5/098 20130101;
C08K 5/49 20130101; Y10T 428/2927 20150115; C08K 5/0083 20130101;
C08K 5/1575 20130101; Y10T 442/40 20150401; C08K 5/49 20130101;
C08K 5/1575 20130101; C08K 5/098 20130101; Y10T 442/3976 20150401;
C08L 23/10 20130101; C08L 23/10 20130101; C08L 23/10 20130101 |
Class at
Publication: |
428/372 ;
442/301; 442/304 |
International
Class: |
D04B 001/00 |
Claims
What we claim is:
1. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 1 50.degree. C. hot air of at most 11%,
wherein said fiber further comprises at least one nucleating agent
selected from the group consisting of dibenzylidene sorbitols,
sodium and lithium phosphate salts, carboxylate salts of cyclic
organophosphoric esters, and any mixtures thereof.
2. The fabric article of claim 1 wherein said nucleating agent is a
dibenzylidene sorbitol selected from the group consisting of
monomethyl dibenzylidene sorbitols, dimethyl dibenzylidene
sorbitols, trimethyl dibenzylidene sorbitols, and any mixtures
thereof.
3. The fabric article of claim 2 wherein said nucleating agent is
selected from the group consisting of
1,3:2,4-bis(p-methylbenzylidene) sorbitol,
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol,
1,3:2,4-bis(2,4,5-trimethy- lbenzylidene) sorbitol, Liquid
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol, and any mixtures
thereof.
4. The fabric article of claim 1 wherein said article is
non-woven.
5. The fabric article of claim I wherein said article is woven.
6. The fabric article of Claim 1 wherein said article is knit.
7. The fabric article of claim 2 wherein said article is
non-woven.
8. The fabric article of claim 2 wherein said article is woven.
9. The fabric article of claim 2 wherein said article is knit.
10. The fabric article of claim 3 wherein said article is
non-woven.
11. The fabric article of claim 3 wherein said article is
woven.
12. The fabric article of claim 3 wherein said article is knit.
13. The fabric article of claim 1 wherein said at least one
polypropylene fiber possesses a denier per filament of at most
1,000, wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 9%, and wherein said at least one
nucleating agent is present in an amount of at least 100 ppm.
14. The fabric article of claim 13 wherein said at least one
polypropylene fiber possesses a denier per filament of at most 500,
wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%, and wherein said at least one
nucleating agent is present in an amount of at least 1250 ppm.
15. The fabric article of claim 14 wherein said at least one
polypropylene fiber possesses a denier per filament of at most 100
and wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%.
16. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 150.degree. C. hot air of at most 11%,
wherein said fiber further exhibits a fiber peak crystallization
temperature measurement of at least 115.degree. C. as measured by
differential scanning calorimetry in accordance with ASTM Test
Method D3417-99 at a cooling rate of 20.degree. C./min.
17. The fabric article of claim 16 wherein said article is
non-woven.
18. The fabric article of claim 16 wherein said article is
woven.
19. The fabric article of claim 16 wherein said article is
knit.
20. The fabric article of claim 16 wherein said at least one
polypropylene fiber possesses a denier per filament of at most
1,000, wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 9%, and wherein said fiber peak
crystallization temperature measurement is at least 116.degree.
C.
21. The fabric article of claim 20 wherein said at least one
polypropylene fiber possesses a denier per filament of at most 500,
wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%, and wherein said fiber peak
crystallization temperature measurement is at least 116.5.degree.
C.
22. The fabric article of claim 21, wherein said at least one
polypropylene fiber possesses a denier per filament of at most 100
and wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%.
23. The fabric article of claim 16 wherein said at least one
polypropylene fiber further comprises at least one nucleating agent
selected from the group consisting of dibenzylidene sorbitols,
sodium and lithium phosphate salts, carboxylate salts of cyclic
organophosphoric esters, and any mixtures thereof.
24. The fabric article of claim 23 wherein said nucleating agent is
a dibenzylidene sorbitol selected from the group consisting of
monomethyl dibenzylidene sorbitols, dimethyl dibenzylidene
sorbitols, trimethyl dibenzylidene sorbitols, and any mixtures
thereof.
25. The fabric article of claim 24 wherein said nucleating agent is
selected from the group consisting of
1,3:2,4-bis(p-methylbenzylidene) sorbitol,
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol,
1,3:2,4-bis(2,4,5-trimethylbenzylidene) sorbitol, Liquid
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol, and any mixtures
thereof.
26. The fabric article of claim 23 wherein said at least one
nucleating agent is present in an amount of at least 100 ppm.
27. The fabric article of claim 26 wherein said at least one
nucleating agent is present in an amount of at least 1250 ppm.
28. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 150.degree. C. hot air of at most 11%,
wherein said fiber further comprises at least one nucleating agent
selected from the group consisting of dibenzylidene sorbitols,
sodium and lithium phosphate salts, carboxylate salts of cyclic
organophosphoric esters, and any mixtures thereof, and wherein said
fiber further exhibits a long period of at least 20 nm as measured
by small-angle x-ray scattering.
29. The fabric article of claim 28 wherein said article is
non-woven.
30. The fabric article of claim 28 wherein said article is
woven.
31. The fabric article of claim 28 wherein said article is
knit.
32. The fabric article of claim 28 wherein said wherein said
nucleating agent is a dibenzylidene sorbitol selected from the
group consisting of monomethyl dibenzylidene sorbitols, dimethyl
dibenzylidene sorbitols, trimethyl dibenzylidene sorbitols, and any
mixtures thereof.
33. The fabric article of claim 32 wherein said nucleating agent is
selected from the group consisting of
1,3:2,4-bis(p-methylbenzylidene) sorbitol,
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol,
1,3:2,4-bis(2,4,5-trimethylbenzylidene) sorbitol, Liquid
1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol, and any mixtures
thereof.
34. The fabric article of 28 wherein said at least one
polypropylene fiber possesses a denier per filament of at most
1,000, wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 9%, wherein said at least one
nucleating agent is present in an amount of at least 100 ppm, and
wherein said fiber exhibits a long period of at least 22 nm.
35. The fabric article of claim 34 where said at least one
polypropylene fiber possesses a denier per filament of at most 500,
wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%, and wherein said at least one
nucleating agent is present in an amount of at least 1250 ppm.
36. The fabric article of claim 35, wherein said at least one
propylene fiber possesses a denier per filament of at most 100 and
wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%.
37. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 1 50.degree. C. hot air of at most 11%,
wherein said fiber further exhibits a fiber peak crystallization
temperature measurement of at least 115.degree. C. as measured by
differential scanning calorimetry in accordance with ASTM Test
Method D3417-99 at a cooling rate of 20.degree. C./min, and wherein
said fiber further exhibits a long period of at least 20 nm as
measured by small-angle x-ray scattering.
38. The fabric article of claim 37 wherein said article is
non-woven.
39. The fabric article of claim 37 wherein said article is
woven.
40. The fabric article of claim 37 wherein said article is
knit.
41. The fabric article of claim 37, wherein said at least one
polypropylene fiber possesses a denier per filament of at most
1,000, wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 9%, wherein said peak
crystallization temperature is at least 116.degree. C., and wherein
said fiber exhibits a long period of at least 22 nm.
42. The fabric article of claim 41, wherein said at least one
polypropylene fiber possesses a denier per filament of at most 500,
wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%, and wherein said peak
crystallization temperature is at least 116.5.degree. C.
43. The fabric article of claim 42, wherein said at least one
polypropylene fiber possesses a denier per filament of at most 100
and wherein said fiber exhibits a heat shrinkage in at least
150.degree. C. hot air of at most 8%.
44. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 150.degree. C. hot air of at most 11%,
wherein said fiber further comprises at least one nucleating agent
present in an amount of at least 1250 ppm.
45. A fabric article comprising at least one polypropylene fiber
possessing at most 5,000 denier per filament and comprising at
least one nucleating agent present in an amount of at least 1250
ppm, and wherein said fiber further exhibits a long period of at
least 20 nm as measured by small-angle x-ray scattering.
46. The fabric article of claim 45 wherein said fiber possesses a
denier per filament of at most 1,000, wherein said at least one
nucleating agent is present in an amount of at least 100 ppm, and
wherein said fiber exhibits a long period of at least 22 nmn.
47. A woven fabric having a length and a width and comprising at
least 90% by weight of polypropylene fibers containing a nucleating
agent at a concentration of greater than 1250 ppm wherein the area
shrinkage of said fabric in after five home washings at a
temperature of 60.degree. C. and 5 home dryings at a temperature of
75.degree. C. is less than 6%.
48. The woven fabric of claim 47 wherein the shrinkage is less than
4%.
49. A knit fabric having a length and a width and comprising at
least 90% by weight of polypropylene fibers comprising
polypropylene fibers containing a nucleating agent at a
concentration of greater than 1250 ppm wherein the area shrinkage
after exposure to hot air at 150.degree. C. for five minutes is
less than 12%.
50. A knit fabric having a length and width and comprising at least
90% by weight of polypropylene fibers containing a nucleating agent
selected from the group consisting of dibenzylidene sorbitols,
sodium and lithium phosphate salts, carboxylate salts of cyclic
organophosphoric esters, and any mixtures thereof, at a
concentration of greater than 100 ppm wherein the area shrinkage
after five home washings at a temperature of 60.degree. C. and five
home dryings at a temperature of 75.degree. C. is less than
10%.
51. A molded non-woven fabric comprising at least 90% by weight of
polypropylene fibers wherein said molded non-woven fabric exhibits
a shrinkage amount of at most 12% as compared with the same
non-woven fabric prior to molding.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending application
Ser. No. 09/860,130, filed on May 17, 2001. This parent application
is herein entirely incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to improvements in preventing heat-
and moisture-shrink problems in specific polypropylene fibers. Such
fibers require the presence of certain compounds that quickly and
effectively provide rigidity to the target polypropylene fiber
after heat-setting. Generally, these compounds include any
structure that nucleates polymer crystals within the target
polypropylene after exposure to sufficient heat to melt the initial
pelletized polymer and upon allowing such a melt to cool. The
compounds must nucleate polymer crystals at a higher temperature
than the target polypropylene without the nucleating agent during
cooling. In such a manner, the "rigidifying" nucleator compounds
provide nucleation sites for polypropylene crystal growth. After
drawing the nucleated composition into fiber form, the fiber is
then exposed to sufficient heat to grow the crystalline network,
thus holding the fiber in a desired position. The preferred
"rigidifying" compounds include dibenzylidene sorbitol based
compounds, as well as less preferred compounds, such as sodium
benzoate, certain sodium and lithium phosphate salts (such as
sodium 2,2'-methylene-bis-(4,6-di-tert-butylphenyl)phospha- te,
otherwise known as NA-11), and carboxylate salts of cyclic
organophosphoric esters (such as NA-21). Specific methods of
manufacture of such fibers, as well as fabric articles made
therefrom, are also encompassed within this invention.
DISCUSSION OF THE PRIOR ART
[0003] There has been a continued desire to utilize polypropylene
fibers in various different products, ranging from apparel to
carpet backings (as well as carpet pile fabrics) to reinforcement
fabrics, and so on. Polypropylene fibers exhibit excellent strength
characteristics, highly desirable hand and feel, and do not easily
degrade or erode when exposed to certain "destructive" chemicals.
However, even with such impressive and beneficial properties and an
abundance of polypropylene, which is relatively inexpensive to
manufacture and readily available as a petroleum refinery
byproduct, such fibers are not widely utilized in products that are
exposed to relatively high temperatures during use, cleaning, and
the like. This is due primarily to the high and generally
non-uniform heat- and moisture-shrink characteristics exhibited by
typical polypropylene fibers. Such fibers are not heat stable and
when exposed to standard temperatures (such as 150.degree. C. and
130.degree. C. temperatures), the shrinkage range from about 5% (in
boiling water) to about 7-8% (for hot air exposure) to 12-13% (for
higher temperature hot air). These extremely high and varied shrink
rates thus render the utilization and processability of highly
desirable polypropylene fibers very low, particularly for end-uses
that require heat stability (such as apparel, carpet pile, carpet
backings, molded pieces, and the like). To date, there has been no
simple solution to such a problem. Some ideas have included
narrowing and controlling the molecular weight distribution of the
polypropylene components themselves in each fiber or mechanically
working the target fibers prior to and during heat-setting.
Unfortunately, molecular weight control is extremely difficult to
accomplish initially, and has only provided the above-listed shrink
rates (which are still too high for widespread utilization within
the fabric industry). Furthermore, the utilization of very high
heat-setting temperatures during mechanical treatment has, in most
instances, resulted in the loss of good hand and feel to the
subject fibers. Another solution to this problem is preshrinking
the fibers, which involves winding the fiber on a crushable paper
package, allowing the fiber to sit in the oven and shrink for long
times, (crushing the paper package), and then rewinding on a
package acceptable for further processing. This process, while
yielding an acceptable yarn, is expensive, making the resulting
fiber uncompetitive as compared to polyester and nylon fibers. As a
result, there has not been any teaching or disclosure within the
pertinent prior art providing any heat- and/or moisture-shrink
improvements in polypropylene fiber technology.
DESCRIPTION OF THE INVENTION
[0004] It is thus an object of the invention to provide improved
shrink rates for standard polypropylene fibers. A further object of
the invention is to provide a class of additives that, in a range
of concentrations, will give low shrinkage. A further object of the
invention is to provide a specific method for the production of
nucleator-containing polypropylene fibers permitting the ultimate
production of such low-shrink fabrics therewith.
[0005] Accordingly, this invention encompasses a polypropylene
fiber possessing at most 5,000 denier per filament and exhibiting a
heat-shrinkage in at least 150.degree. C. hot air of at most 11%,
wherein said fiber further comprises at least one nucleating agent.
Also, this invention encompasses a polypropylene fiber possessing
at most 5,000 denier per filament and exhibiting a heat-shrinkage
in at least 150.degree. C. hot air of at most 11%, wherein said
fiber further comprises at least one nucleating agent, and wherein
said fiber further exhibits a long period of at least 20 nm as
measured by small-angle x-ray scattering. Furthermore, this
invention encompasses a polypropylene fiber possessing at most
5,000 denier per filament and comprising at least one nucleating
agent, and wherein said fiber further exhibits a long period of at
least 20 nm as measured by small-angle x-ray diffraction
spectroscopy. Additionally, this invention encompasses a
polypropylene fiber possessing at most 5,000 denier per filament
and exhibiting a peak crystallization temperature of at least
115.degree. C. as measured by differential scanning calorimetry in
accordance with a modified ASTM Test Method D3417-99 at a cooling
rate of 20.degree. C./min, and wherein said fiber further exhibits
a long period of at least 20 nm as measured by small-angle x-ray
scattering. Certain yarns and fabric articles comprising such
inventive fibers are also encompassed within this invention.
[0006] Furthermore, this invention also concerns a method of
producing such fibers comprising the sequential steps of a)
providing a polypropylene composition in pellet or liquid form
comprising at least 100 ppm by weight of a nucleator compound; b)
melting and mixing said polypropylene composition of step "a" to
form a substantially homogeneous molten plastic formulation; c)
extruding said plastic formulation to form a fiber structure; d)
mechanically drawing said extruded fiber (optionally while exposing
said fiber to a temperature of at most 105.degree. C.); and e)
exposing said drawn fiber of step "d" to a subsequent heat-setting
temperature of at least 110.degree. C. Preferably, step "b" will be
performed at a temperature sufficient to effectuate the melting of
all polymer constituent (e.g., polypropylene), and possibly the
remaining compounds, including the nucleating agent, as well
(melting of the nucleating agent is not a requirement since some
nucleating agents do not melt upon exposure to such high
temperatures). Thus, temperatures within the range of from about
175 to about 300.degree. C., as an example (preferably from about
200 to about 275.degree., and most preferably from about 220 to
about 250.degree. C., are proper for this purpose. The extrusion
step ("c") should be performed while exposing the polypropylene
formulation to a temperature of from about 185 to about 300.degree.
C., preferably from about 210 to about 275.degree. C., and most
preferably from about 230 to about 250.degree. C., basically
sufficient to perform the extrusion of a liquefied polymer without
permitting breaking of any of the fibers themselves during such an
extrusion procedure. The drawing step may be performed at a
temperature which is cooler than normal for a standard
polypropylene (or other polymer) fiber drawing process. Thus, if a
cold-drawing step is followed, such a temperature should be below
about 105.degree. C., more preferably below about 100.degree. C.,
and most preferably below about 90.degree. C. Of course, higher
temperatures may be used if no such cold drawing step is followed.
The final heat-setting temperature is necessary to "lock" the
polypropylene crystalline structure in place after extruding and
drawing. Such a heat-setting step generally lasts for a portion of
a second, up to potentially a couple of minutes (i.e., from about
{fraction (1/10)}th of a second, preferably about {fraction
(1/2)}of a second, up to about 3 minutes, preferably greater than
{fraction (1/2)} of a second). The heat-setting temperature must be
greater than the drawing temperature and must be at least
110.degree. C., more preferably at least about 115.degree., and
most preferably at least about 125.degree. C. The term
"mechanically drawing" is intended to encompass any number of
procedures which basically involve placing an extensional force on
fibers in order to elongate the polymer therein. Such a procedure
may be accomplished with any number of apparatus, including,
without limitation, godet rolls, nip rolls, steam cans, hot or cold
gaseous jets (air or steam), and other like mechanical means.
[0007] In another embodiment of the method of making such inventive
fibers, step "c" noted above may be further separated into two
distinct steps. A first during which the polymer is extruded as a
sheet or tube, and a second during which the sheet or tube is slit
into narrow fibers of less than 5000 deniers per filament
(dpf).
[0008] All shrinkage values discussed as they pertain to the
inventive fibers and methods of making thereof correspond to
exposure times for each test (hot air and boiling water) of about 5
minutes. The heat-shrinkage at about 150.degree. C. in hot air is,
as noted above, at most 11% for the inventive fiber; preferably,
this heat-shrinkage is at most 9%; more preferably at most 8%; and
most preferably at most 7%. Also, the amount of nucleating agent
present within the inventive fiber is at least 10 ppm; preferably
this amount is at least 100 ppm; and most preferably is at least
1250 ppm. Any amount of such a nucleating agent should suffice to
provide the desired shrinkage rates after heat-setting of the fiber
itself; however, excessive amounts (e.g., above about 10,000 ppm
and even as low as about 6,000 ppm) should be avoided, primarily
due to costs, but also due to potential processing problems with
greater amounts of additives present within the target fibers.
[0009] The term "polypropylene" is intended to encompass any
polymeric composition comprising propylene monomers, either alone
or in mixture or copolymer with other randomly selected and
oriented polyolefins, dienes, or other monomers (such as ethylene,
butylene, and the like). Such a term also encompasses any different
configuration and arrangement of the constituent monomers (such as
syndiotactic, isotactic, and the like). Thus, the term as applied
to fibers is intended to encompass actual long strands, tapes,
threads, and the like, of drawn polymer. The polypropylene may be
of any standard melt flow (by testing); however, standard fiber
grade polypropylene resins possess ranges of Melt Flow Indices
between about 2 and 50. Contrary to standard plaques, containers,
sheets, and the like (such as taught within U.S. Pat. No. 4,016,118
to Hamada et al., for example), fibers clearly differ in structure
since they must exhibit a length that far exceeds its
cross-sectional area (such, for example, its diameter for round
fibers). Fibers are extruded and drawn; articles are blow-molded or
injection molded, to name two alternative production methods. Also,
the crystalline morphology of polypropylene within fibers is
different than that of standard articles, plaques, sheets, and the
like. For instance, the dpf of such polypropylene fibers is at most
about 5000; whereas the dpf of these other articles is much
greater. Polypropylene articles generally exhibit spherulitic
crystals while fibers exhibit elongated, extended crystal
structures. Thus, there is a great difference in structure between
fibers and polypropylene articles such that any predictions made
for spherulitic particles (crystals) of nucleated polypropylene do
not provide any basis for determining the effectiveness of such
nucleators as additives within polypropylene fibers.
[0010] Another class of nucleating agents, alluded to above, was
suggested by Nakahara et al. in U.S. Pat. No. 4,463,113, in which
cyclic bis-phenol phosphates was disclosed as nucleating and
clarifying agents for polyolefin resins. Kimura et al. then
suggests in U.S. Pat. No. 5,342,868 that the addition of an alkali
metal carboxylate to basic polyvalent metal salt of cyclic
organophosphoric ester can further improve the clarification
effects of such additives. Compounds that are based upon these
technologies are marketed under the trade name NA-11 and NA-21,
respectively, by Asahi Denka, again as mentioned above.
[0011] The terms "nucleators", "nucleator compound(s)", "nucleating
agent", and "nucleating agents" are intended to generally
encompass, singularly or in combination, any additive to
polypropylene that produces nucleation sites for polypropylene
crystals from transition from its molten state to a solid, cooled
structure. Hence, since the polypropylene composition (including
nucleator compounds) must be molten to eventually extrude the fiber
itself, the nucleator compound will provide such nucleation sites
upon cooling of the polypropylene from its molten state. The only
way in which such compounds provide the necessary nucleation sites
is if such sites form prior to polypropylene recrystallization
itself. Thus, any compound that exhibits such a beneficial effect
and property is included within this definition. Such nucleator
compounds more specifically include dibenzylidene sorbitol types,
including, without limitation, dibenzylidene sorbitol (DBS),
mono-methyldibenzyliden- e sorbitol, such as
1,3:2,4-bis(p-methylbenzylidene) sorbitol (p-MDBS), dimethyl
dibenzylidene sorbitol, such as 1,3:2,4-bis(3,4-dimethylbenzylid-
ene) sorbitol (3,4-DMDBS); other compounds of this type include,
again, without limitation, sodium benzoate, NA-11, and the like.
The concentration of such nucleating agents (in total) within the
target polypropylene fiber is at least 100 ppm, preferably at least
1250 ppm. Thus, from about 100 to about 5000 ppm, preferably from
about 500 ppm to about 4000 ppm, more preferably from about 1000
ppm to about 3500 ppm, still more preferably from about 1500 ppm to
about 3000 ppm, even more preferably from about 2000 ppm to about
3000 ppm, and most preferably from about 2500 to about 3000 ppm.
Furthermore, fibers may be produced by the extrusion and drawing of
a single strand of polypropylene as described above, or also by
extrusion of a sheet, then cutting the sheet into fibers, then
following the steps as described above to draw, heat-set, and
collect the resultant fibers. In addition, other methods to make
fibers, such as fibrillation, and the like, are envisioned for the
same purpose.
[0012] Also, without being limited by any specific scientific
theory, it appears that the shrink-reducing nucleators which
perform the best are those which exhibit relatively high solubility
within the propylene itself. Thus, compounds which are readily
soluble, such as 1,3:2,4-bis(p-methylbenzylidene) sorbitol provides
the lowest shrinkage rate for the desired polypropylene fibers. The
DBS derivative compounds are considered the best shrink-reducing
nucleators within this invention due to the low crystalline sizes
produced by such compounds. Other nucleators, such as NA-11, also
provide good low-shrink characteristics to the target polypropylene
fiber; however, apparently due to poor dispersion of NA-11 in
polypropylene and the large and varied crystal sizes of NA-11
within the fiber itself, the shrink rates are noticeably higher
than for the highly soluble, low crystal-size polypropylene
produced by well-dispersed MDBS.
[0013] One manner of testing for the presence of a nucleating agent
within the target fibers is preferably through differential
scanning calorimetry to determine the peak crystallization
temperature exhibited by the resultant polypropylene. The fiber is
melted and placed between two plates under high temperature and
pressure to form a sheet of sample plastic. A sample of this
plastic is then melted and subjected to a differential scanning
calorimetry analytical procedure in accordance with modified ASTM
Test Method D3417-99 at a cooling rate of 20.degree. C./minute. A
sufficiently high peak crystallization temperature (above about
115.degree. C., more preferably above about 116.degree. C., and
most preferably above about 116.5.degree. C.), well above that
exhibited by the unnucleated polypropylene itself, shall indicate
the presence of a nucleating agent since attaining such a high peak
crystallization without a nucleating agent is not generally
possible.
[0014] It has been determined that the nucleator compounds that
exhibit good solubility in the target molten polypropylene resins
(and thus are liquid in nature during that stage in the
fiber-production process) provide more effective low-shrink
characteristics. Thus, low substituted DBS compounds (including
DBS, p-MDBS) appear to provide fewer manufacturing issues as well
as lower shrink properties within the finished polypropylene fibers
themselves. Although p-MDBS is preferred, however, any of the
above-mentioned nucleators may be utilized within this invention as
long as the long period (SAXS) measurements are met or the low
shrink requirements are achieved through utilization of such
compounds. Mixtures of such nucleators may also be used during
processing in order to provide such low-shrink properties as well
as possible organoleptic improvements, facilitation of processing,
or cost.
[0015] In addition to those compounds noted above, sodium benzoate
and NA-11 are well known as nucleating agents for standard
polypropylene compositions (such as the aforementioned plaques,
containers, films, sheets, and the like) and exhibit excellent
recrystallization temperatures and very quick injection molding
cycle times for those purposes. The dibenzylidene sorbitol types
exhibit the same types of properties as well as excellent clarity
within such standard polypropylene forms (plaques, sheets, etc.).
For the purposes of this invention, it has been found that the
dibenzylidene sorbitol types are preferred as nucleator compounds
within the target polypropylene fibers. Of interest, as well, is
the ability to provide a purely liquid formulation of the
dibenzylidene sorbitol compounds for introduction within the target
polypropylene compositions. Such liquid DBS formulations comprise
certain nonionic surfactants that can be selected both for their
liquefying and stability-providing benefits to the DBS compounds
themselves, but also potentially for their lubricating properties
for the eventual fiber. In such a manner, the amount of lubricant
generally required for and added to the target fiber may be reduced
or eliminated, thus reducing costs associated with such additives.
Thus, the surfactants required for such a liquid nucleator
composition of 3,4-DMDBS (or other types of nucleating agents),
include those which are nonionic and which are ethoxylated to the
extent that their hydrophilic-lipophilic balance (HLB) is greater
than about 8.5. HLB is a measure of the solubility of a surfactant
both in oil and in water and is approximated as one-fifth
({fraction (1/5)}) the weight percent of ethoxy groups present on
the particular surfactant backbone. More specifically, such
surfactants exhibit a HLB value of more preferably greater than
about 12, and most preferably greater than about 13, and must
possess at least some degree of ethoxylation, more preferably
greater than about 4 molar equivalents of ethylene oxide (EO) per
molecule, and most preferably greater than about 9.5 molar
equivalents of EO per molecule.
[0016] Of these preferred surfactants, the most preferred for
utilization within the potential fluid nucleating agent dispersion
for purposes of this invention include, in tabulated form:
1 SURFACTANT TABLE Preferred Diluent Surfactants (with Tradenames)
Ex. Surfactant Available as and From HLB # 1 sorbitan monooleate
(20 EO) Tween 80 .RTM.; Imperial Chemical (ICI) 15.0 2 sorbitan
monostearate (20 EO) Tween 60 .RTM.; ICI 14.9 3 sorbitan
monopalmitate (20 EO) Tween 40 .RTM.; ICI 15.6 4 sorbitan
monolaurate (20 EO) Tween 20 .RTM.; ICI 16.7 5 dinonylphenol ether
(7 EO) Igepal .RTM. DM 430; Rhone-Poulenc (RP) 9.5 6 nonylphenol
ether (6 EO) Igepal .RTM. CO 530; RP 10.8 7 nonylphenol ether (12
EO) Igepal .RTM. CO 720; RP 14.2 8 dinonylphenol ether (9 EO)
Igepal .RTM. DM 530; RP 10.6 9 nonylphenol ether (9 EO) Igepal
.RTM. CO 630; RP 13.0 10 nonylphenol ether (4 EO) Igepal .RTM. CO
430; RP 8.8 11 dodecylphenol ether (5.5 EO) Igepal .RTM. CO 520; RP
430 9.6 12 dodecylphenol ether (9.5 EO) Igepal .RTM. RC 620; RP
12.3 13 dodecylphenol ether (11 EO) Igepal .RTM. RC 630; RP 13.0 14
nonylphenol ether (9.5 EO) Syn Fac .RTM. 905; Milliken &
Company .about.13 15 octylphenol ether (10 EO) Triton .RTM. X-100;
Rohm & Haas 13.5
[0017] This list is not exhaustive as these are merely the
preferred surfactants for use within the potential fluid nucleating
agent dispersion for utilization within this invention. In such a
fluid dispersion, then, the nucleating agent, such as preferably
3,4-DMDBS, comprises at most 40% by weight, preferably about 30% by
weight, of the entire inventive fluid dispersion. Any higher amount
will deleteriously affect the viscosity of the dispersion.
Preferably the amount of surfactant is from about 70% to about
99.9%, more preferably from about 70% to about 85%; and most
preferably, from about 70% to about 75% of the entire inventive
fluid dispersion. A certain amount of water may also be present in
order to effectively lower the viscosity of the overall liquid
dispersion. Optional additives may include plasticizers, antistatic
agents, stabilizers, ultraviolet absorbers, and other similar
standard polyolefin thermoplastic additives. Other additives may
also be present within this composition, most notably antioxidants,
antistatic compounds, perfumes, chlorine scavengers, and the like.
As noted above, this type of fluid dispersion is disclosed in
greater detail within U.S. Pat. Nos. 6,102,999 and 6,127,440, both
herein entirely incorporated by reference. Most preferred is a
composition of 30% by weight of 3,4-DMDBS and 70% by weight of
Tween.RTM. 80. This mixture is listed in the Preferred Embodiments
section below as "Liquid 3,4-DMDBS".
[0018] The closest prior art references teach the addition of
nucleator compounds to general polypropylene compositions (such as
in U.S. Pat. No. 4,016,118, referenced above). However, some
teachings include the utilization of certain DBS compounds within
limited portions of fibers in a multicomponent polypropylene
textile structure. For example, U.S. Pat. Nos. 5,798,167 to Connor
et al. and 5,811,045 to Pike, both teach the addition of DBS
compounds to polypropylene in fiber form; however, there are vital
differences between those disclosures and the present invention.
For example, both patents require the aforementioned multicomponent
structures of fibers. Thus, even with DBS compounds in some
polypropylene fiber components within each fiber type, the shrink
rate for each is dominated by the other polypropylene fiber
components which do not have the benefit of the nucleating agent.
Also, there are no lamellae that give a long period (as measured by
small-angle X-ray scattering) thicker than 20 nm formed within the
polypropylene fibers due to the lack of a post-heatsetting step
being performed. Again, these thick lamellae provide the desired
inventive higher heat-shrink fiber. Also of importance is the fact
that, for instance, Connor et al. require a nonwoven polypropylene
fabric laminate containing a DBS additive situated around a
polypropylene internal fabric layer which contained no nucleating
agent additive. The internal layer, being polypropylene without the
aid of a nucleating agent additive, dictates the shrink rate for
this structure. Furthermore, the patentees do not expose their
yarns and fibers to heat-setting procedures in order to permanently
configure the crystalline fiber structures of the yarns themselves
as low-shrink is not their objective.
[0019] In addition, Spruiell, et al, Journal of Applied Polvmer
Science, Vol. 62, pp. 1965-75 (1996), reveal using a nucleating
agent, MDBS, at 0.1%, to increase the nucleation rate during
spinning. However, after crystallizing and drawing the fiber,
Spruiell et al. do not expose the nucleated fiber to any heat,
which is necessary to impart the very best shrinkage properties,
therefore the shrinkage of their fibers was similar to conventional
polypropylene fibers without a nucleating agent additive. In the
examples below, yarn made with similar levels of nucleating agent
additives included and no further heat exposure showed worse
shrinkage (at all measured temperatures after the standard 5 minute
exposure time) than commercial fibers, and fibers which contained
no additive and were exposed to the same conditions. Thus, in
addition to the presence of the nucleating agent additive, exposure
to heat after mechanical drawing is a crucial step in the
invention.
[0020] Of particular interest and which has been determined to be
of primary importance in the production of such inventive
low-shrink polypropylene fibers, is the discovery that, at the very
least, the presence of nucleating agent within heat-set
polypropylene fibers (as discussed herein), provides high long
period measurements for the crystalline lamellae of the
polypropylene itself. This discovery is best explained by the
following:
[0021] Polymers, when crystallized from a melt under dynamic
temperature and stress conditions, first supercool and then
crystallize with the crystallization rate dependent on the number
of nucleation sites, and the growth rate of the polymer, which are
both in turn related to the thermal and mechanical working that the
polymer is subjected to as it cools. These processes are
particularly complex in a normal fiber drawing line. The results of
this complex crystallization, however, can be measured using small
angle x-ray scattering (SAXS), with the measured SAXS long period
representative of an average crystallization temperature. A higher
SAXS long period corresponds to thicker lamellae (which are the
plate-like polymer crystals characteristic of semi-crystalline
polymers like PP). The higher the crystallization temperature of
the average crystal, the thicker the measured SAXS long period will
be. Further, higher SAXS long periods are characteristic of more
thermally stable polymeric crystals. Crystals with shorter SAXS
long periods will "melt", or relax and recrystallize into new,
thicker crystals, at a lower temperature than those with higher
SAXS long periods. Crystals with higher SAXS long periods remain
stable to higher temperatures, requiring more heat to destabilize
the crystalline structure.
[0022] In highly oriented polymeric samples such as fibers, those
with higher SAXS long periods will remain stable to higher
temperatures. Thus the shrinkage, which is a normal effect of the
relaxation of the highly oriented polymeric samples, remains low to
higher temperatures than in those highly oriented polymeric samples
with lower SAXS long periods. In this invention, as is evident from
these measurements, the nucleating additive is used in conjunction
with a thermal treatment to create fibers with extremely high SAXS
long periods of at least 20 nm, or preferably at least 22 nm, which
in turn are very stable and exhibit low shrinkage up to very high
temperatures.
[0023] Furthermore, such fibers may also be colored to provide
other aesthetic features for the end user. Thus, the fibers may
also comprise coloring agents, such as, for example, pigments, with
fixing agents for lightfastness purposes. For this reason, it is
desirable to utilize nucleating agents that do not impart visible
color or colors to the target fibers. Other additives may also be
present, including antistatic agents, brightening compounds,
clarifying agents, antioxidants, antimicrobials (preferably
silver-based ion-exchange compounds, such as ALPHASAN.RTM.
antimicrobials available from Milliken & Company), UV
stabilizers, fillers, and the like. Furthermore, any fabrics made
from such inventive fibers may be, without limitation, woven, knit,
non-woven, in-laid scrim, any combination thereof, and the like.
Additionally, such fabrics may include fibers other than the
inventive polypropylene fibers, including, without limitation,
natural fibers, such as cotton, wool, abaca, hemp, ramie, and the
like; synthetic fibers, such as polyesters, polyamides,
polyaramids, other polyolefins (including non-low-shrink
polypropylene), polylactic acids, and the like; inorganic fibers
such as glass, boron-containing fibers, and the like; and any
blends thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate a potentially
preferred embodiment of producing the inventive low-shrink
polypropylene fibers and together with the description serve to
explain the principles of the invention wherein:
[0025] FIG. 1 is a schematic of the potentially preferred method of
producing low-shrink polypropylene.
[0026] FIG. 2 is described in greater detail below with regard to
small angle X-ray scattering and is a graphical representation of
the integrated intensity data I(q) as a function of 74 in order to
determine the long period spacing of the target fibers.
[0027] FIG. 3 is also described in greater detail below with regard
to small angle X-ray scattering and is a graphical representation
of the K(z) function to aid in the ultimate determination of long
period spacing.
DETAILED DESCRIPTION OF THE DRAWING AND OF THE PREFERRED
EMBODIMENT
[0028] FIG. 1 depicts the non-limiting preferred procedure followed
in producing the inventive low-shrink polypropylene fibers. The
entire fiber production assembly 10 comprises an extruder 11
comprising four different zones 12, 14, 16, 18 through which the
polymer (not illustrated) passes at different, increasing
temperatures. The molten polymer is mixed with the nucleator
compound (also molten) within a mixer zone 20. Basically, the
polymer (not illustrated) is introduced within the fiber production
assembly 10, in particular within the extruder 11. The
temperatures, as noted above, of the individual extruder zones 12,
14, 16, 18 and the mixing zone 20 are as follows: first extruder
zone 12 at 205.degree. C., second extruder zone 14 at 215.degree.
C., third extruder zone 16 at 225.degree. C., fourth extruder zone
18 at 235.degree. C., and mixing zone 20 at 245.degree. C. The
molten polymer (not illustrated) then moves into a spin head area
22 set at a temperature of 250.degree. C. which is then moved into
the spinneret 24 (also set at a temperature of 250.degree. C.) for
strand extrusion. The fibrous strands 28 then pass through a heated
shroud 26 having an exposure temperature of 180.degree. C. The
speed at which the polymer strands (not illustrated) pass through
the extruder 11, spin pack 22, and spinneret 24 is relatively slow
until the fibrous strands 28 are pulled through by the draw rolls
32, 34, 38. The fibrous strands 28 extend in length due to a
greater pulling speed in excess of the initial extrusion speed
within the extruder 11. The fibrous strands 28 are thus collected
after such extension by a take-up roll 32 (set at a speed of 370
meters per minute) into a larger bundle 30 which is drawn by the
aforementioned draw rolls 34, 38 into a single yarn 33. The draw
rolls are heated to a very low level as follows: first draw roll 34
68.degree. C. and second draw roll 38 88.degree. C., as compared
with the remaining areas of high temperature exposure as well as
comparative fiber drawing processes. The first draw roll 34 rotates
at a speed of about 377 meters per minute and is able to hold
fifteen wraps of the polypropylene fiber 33 through the utilization
of a casting angle between the draw roll 34 and the idle roll 36.
The second draw roll 38 rotates at a higher speed of about 785
meters per minute and holds eight wraps of fiber 33, and thus
requires its own idle roll 40. After drawing by these cold
temperature rolls 34, 38, the fiber is then heat-set by a
combination of two different heat-set rolls 42, 44 configured in a
return scheme such that eighteen wraps of fiber 33 are permitted to
reside on the rolls 42, 44 at any one time. The time of such
heat-setting is very low due to a low amount of time in contact
with either of the actual rolls 42, 44, so a total time of about
0.5 seconds is standard. The temperatures of such rolls 42, 44 are
varied below to determine the best overall temperature selection
for such a purpose. The speed of the combination of rolls 42, 44 is
about 1290 meters per minute. The fiber 33 then moves to a relax
roll 46 holding up to eight wraps of fiber 33 and thus also having
its own feed roll 48. The speed of the relax roll 46 is lower than
the heat-set roll (1280 meters per minute) in order to release some
tension on the heat-set fiber 33. From there, the fiber 33 moves to
a winder 50 and is placed on a spool (not illustrated).
Inventive Fiber and Yarn Production
[0029] The following non-limiting examples are indicative of the
preferred embodiment of this invention:
[0030] Yarn Production
[0031] Yarn was made by compounding Amoco 7550 fiber grade
polypropylene resin (melt flow of 18) with a nucleator additive and
a standard polymer stabilization package consisting of 500 ppm of
Irganox.RTM. 1010, 1000 ppm of Irgafos.RTM. 168 (both antioxidants
available from Ciba), and 800 ppm of calcium stearate. The base
mixture was compounded at 2500 ppm in a twin screw extruder (at
220.degree. C. in all zones) and made into pellets. The additive
was selected from the group of three polypropylene clarifiers
commercially available from Milliken & Company, Millad.RTM.
3905 (DBS), Millad.RTM. 3940 (P-MDBS sorbitol), Millad.RTM. 3988
(3,4-DMDBS), two polypropylene nucleators commercially available
from Asahi-Denka Chemical Company (NA-11 and NA-21), sodium
benzoate, Liquid 3,4-DMDBS, and
1,3:2,4-bis(2,4,5-trimethylbenzylidene) sorbitol (2,4,5-TMDBS).
[0032] The pellets were then fed into the extruder on an Alex James
& Associates fiber extrusion line as noted above in FIG. 1.
Yarn was spun with the extrusion line conditions shown in Table 1
using a 68 hole spinneret, giving a yarn of nominally 150 denier.
For each additive, four yarns were spun with heat-set temperatures
of 100.degree., 110.degree., 120.degree., and 130.degree. C.
respectively. These temperatures are the set temperatures for the
controller for the rolls 42, 44. In practice, a variation is found
to exist over the surface of the rolls 42, 44, up to as much as
10.degree. C. Pellets with no nucleator additive were used to make
control fibers. The yarns were tested for shrinkage in boiling
water by cutting a length of yarn, marking the ends of a 10"
section with tape, placing the yarn in boiling water for 5 minutes,
then taking the yarn out and measuring the length of the section
between the tape marks. Measurements were taken on five pieces of
each yarn, and the average change in dimension is divided by the
initial length (10 inches) to give % shrinkage. Also, the
measurements below have a statistical error of +/-0.4 percentage
units.
[0033] The yarns were similarly tested for shrinkage in hot air at
150.degree. C. and 130.degree. C. by marking a 10" section of yarn,
placing it in an oven for five minutes at the measurement
temperature, and similarly measuring the % shrinkage after removing
the yarn from the oven. Again, five samples were measured, and the
average shrinkage results are reported for each sample in Table 1.
The shrink measurements are listed below the tested nucleators for
each yarn sample. The yarn samples were as follows:
2 POLYPROPYLENE YARN COMPOSITION TABLE Yarn Samples with Specific
Nucleators Added Yarn Sample Nucleator Added A NA-11 B NA-21 C
Sodium Benzoate D DBS E p-MDBS F 3,4-DMDBS G Liquid 3,4-DMDBS H
2,4,5-TMDBS I(Comparative) None (Control)
Fiber and Yarn Physical Analyses
[0034] These sample yarns were then tested for shrink
characteristics with a number of different variables including
heat-set temperatures differences (on the heat-set rolls) during
manufacture and different heat-exposure conditions (hot air at
various temperatures and boiling water exposure at temperatures in
excess of 100.degree. C.). The results are tabulated below:
3 EXPERIMENTAL TABLE 1 Experimental Shrink Measurements for Sample
Yarns Shrinkage Test Sample Yarn Heatset Temp.(.degree. C.) and
Temp..(.degree. C.) Shrinkage A 100 150 Hot air 9.5% A 110 150 Hot
air 9.4% A 120 150 Hot air 8.1% A 130 150 Hot air 6.7% A 100 130
Hot air 7.4% A 110 130 Hot air 5.9% A 120 130 Hot air 4.9% A 130
130 Hot air 4.0% A 100 Boiling water 4.9% A 110 Boiling water 4.1%
A 120 Boiling water 3.6% A 130 Boiling water 2.7% B 100 150 Hot air
11.1% B 110 150 Hot air 10.1% B 120 150 Hot air 9.3% B 130 150 Hot
air 6.7% B 100 130 Hot air 8.1% B 110 130 Hot air 7.3% B 120 130
Hot air 6.3% B 130 130 Hot air 3.4% B 100 Boiling water 5.6% B 110
Boiling water 4.7% B 120 Boiling water 2.7% B 130 Boiling water
2.3% C 100 150 Hot air 10.9% C 110 150 Hot air 11.2% C 120 150 Hot
air 9.5% C 130 150 Hot air 7.1% C 100 130 Hot air 7.8% C 110 130
Hot air 7.4% C 120 130 Hot air 6.2% C 130 130 Hot air 4.5% C 100
Boiling water 6.0% C 110 Boiling water 5.0% C 120 Boiling water
3.9% C 130 Boiling water 2.6% D 100 150 Hot air 9.8% D 110 150 Hot
air 9.7% D 120 150 Hot air 9.5% D 130 150 Hot air 5.8% D 100 130
Hot air 7.4% D 110 130 Hot air 6.9% D 120 130 Hot air 6.2% D 130
130 Hot air 2.9% D 100 Boiling water 5.6% D 110 Boiling water 4.5%
D 120 Boiling water 3.1% D 130 Boiling water 2.1% E 100 150 Hot air
10.9% E 110 150 Hot air 9.2% E 120 150 Hot air 8.0% E 130 150 Hot
air 4.0% E 100 130 Hot air 7.5% E 110 130 Hot air 6.1% E 120 130
Hot air 4.5% E 130 130 Hot air 2.7% E 100 Boiling water 4.6% E 110
Boiling water 4.0% E 120 Boiling water 2.4% E 130 Boiling water
1.9% F 100 150 Hot air 13.6% F 110 150 Hot air 12.4% F 120 150 Hot
air 7.3% F 130 150 Hot air 7.2% F 100 130 Hot air 9.2% F 110 130
Hot air 8.0% F 120 130 Hot air 3.7% F 130 130 Hot air 3.4% F 100
Boiling water 6.5% F 110 Boiling water 4.0% F 120 Boiling water
2.6% F 130 Boiling water 2.7% G 100 150 Hot air 12.9% G 110 150 Hot
air 11.7% G 120 150 Hot air 9.3% G 130 150 Hot air 7.6% G 100 130
Hot air 9.2% G 110 130 Hot air 8.8% G 120 130 Hot air 6.5% G 130
130 Hot air 4.3% G 100 Boiling water 6.0% G 110 Boiling water 5.3%
G 120 Boiling water 3.9% G 130 Boiling water 2.8% H 100 150 Hot air
12.2% H 110 150 Hot air 10.9% H 120 150 Hot air 9.6% H 130 150 Hot
air 6.8% H 100 130 Hot air 8.9% H 110 130 Hot air 8.0% H 120 130
Hot air 6.3% H 130 130 Hot air 3.0% H 100 Boiling water 5.5% H 110
Boiling water 4.7% H 120 Boiling water 3.3% H 130 Boiling water
2.1% I 100 150 Hot air 21.3% I 110 150 Hot air 19.3% I 120 150 Hot
air 17.4% I 130 150 Hot air 13.4% 1 100 130 Hot air 12.5% I 110 130
Hot air 10.7% I 120 130 Hot air 8.6% I 130 130 Hot air 5.3% I 100
Boiling water 6.8% I 110 Boiling water 5.2% I 120 Boiling water
3.2% I 130 Boiling water 3.2%
[0035] In addition, two commercial yarns were obtained from
Filament Fiber Technology and tested in each of the three tests,
with the results shown in Table 3. Commercial Yarn #1 is an air jet
textured yarn with a black pigment. Commercial Yarn #2 is an air
jet textured yarn with a white pigment.
4 EXPERIMENTAL TABLE 2 Experimental Data for Comparative Commercial
Polypropylene Yarns Test Comm. Yarn #1 Comm. Yarn #2 150.degree. C.
Hot air shrinkage 13.0% 12.1% 130.degree. C. Hot air shrinkage 7.8%
7.0% Boiling water shrinkage 4.8% 5.5%
[0036] It is evident from these two TABLEs that the inventive
polypropylene yarns (including those made from the inventive method
described above) exhibit vastly improved shrinkage rates for all
three test methods and thus are clearly improvements over the
commercially available prior art yarns as well as those yarns
lacking nucleating agent and heat-set.
[0037] Additive Level Dependence
[0038] To test the dependence on nucleator additive level,
additional yarns were spun in accordance with the method described
above with varying levels of additive using Amoco 7550 resin. The
additive was compounded into the resin and the fibers spun under
the same conditions as in the previous examples. The yarns were
similarly tested, with the results shown in Table 5.
5 POLYPROPYLENE YARN SAMPLE TABLE Yarn Samples with Specific
Nucleators Added Yarn Sample Nucleator Added (Amount ppm) J NA-11
(1000) K 3,4-DMDBS (1250) L 2,4,5-TMDBS (1250)
[0039]
6 EXPERIMENTAL TABLE 3 Experimental Data for Different Nucleator
Levels in Polypropylene Yarns Shrinkage Test Sample Yarn Heatset
Temp.(.degree. C.) and Temp..(.degree. C.) Shrinkage J 100 150 Hot
air 18.1% J 110 150 Hot air 16.6% J 120 150 Hot air 16.7% J 130 150
Hot air 9.0% J 100 130 Hot air 10.4% J 110 130 Hot air 9.0% J 120
130 Hot air 6.8% J 130 130 Hot air 4.5% J 100 Boiling water 5.4% J
110 Boiling water 4.8% J 120 Boiling water 3.3% J 130 Boiling water
2.6% K 100 150 Hot air 15.7% K 110 150 Hot air 17.1% K 120 150 Hot
air 13.0% K 130 150 Hot air 8.8% K 100 130 Hot air 9.3% K 110 130
Hot air 8.6% K 120 130 Hot air 5.5% K 130 130 Hot air 4.0% K 100
Boiling water 6.8% K 110 Boiling water 4.5% K 120 Boiling water
3.3% K 130 Boiling water 2.5% L 100 150 Hot air 16.9% L 110 150 Hot
air 15.8% L 120 150 Hot air 13.2% L 130 150 Hot air 8.7% L 100 130
Hot air 11.1% L 110 130 Hot air 9.2% L 120 130 Hot air 6.8% L 130
130 Hot air 4.5% L 100 Boiling water 6.8% L 110 Boiling water 4.3%
L 120 Boiling water 3.3% L 130 Boiling water 2.3%
[0040] Thus, additive levels are important to providing overall
good low shrinkage characteristics for the target polypropylene
yarns. Higher levels appear to provide better shrinkage
properties.
[0041] X-Ray Scattering Analysis
[0042] The long period spacing of several of the above yarns was
tested by small angle x-ray scattering (SAXS). The small angle
x-ray scattering data was collected on a Bruker AXS (Madison, WI)
Hi-Star multi-wire detector placed at a distance of 105 cm from the
sample in an Anton-Paar vacuum chamber where the chamber was
evacuated to a pressure of not more than 100 mTorr. X-rays
(.lambda.=1.54178 .ANG.) were generated with a MacScience rotating
anode (40 kV, 40 mA) and focused through three pinholes to a size
of 0.2 mm. The entire system (generator, detector, beampath, sample
holder, and software) is commercially available as a single unit
from Bruker AXS. The detector was calibrated per manufacturer
recommendation using a sample of silver behenate.
[0043] A typical data collection was conducted as follows. To
prepare the sample, the yarn was wrapped around a 3 mm brass tube
with a 2 mm hole drilled in it, and then the tube was placed in an
Anton-Paar vacuum sample chamber on the x-ray equipment such that
the yarn was exposed to the x-ray beam through the hole. The path
length of the x-ray beam through the sample was between 2-3 mm. The
sample chamber and beam path was evacuated to less than 100 mTorr
and the sample was exposed to the X-ray beam for one hour.
Two-dimensional data frames were collected by the detector and
unwarped automatically by the system software. The data were
smoothed within the system software using a 2-pixel convolution
prior to integration. To obtain the intensity scattering data
[I(q)] as a function of scattering angle [2.theta.] the data were
integrated over .phi. with the manufacturer's software set to give
a 2.theta. range of 0.2.degree.-2.5.degree. in increments of
0.01.degree. using the method of bin summation. These raw
scattering data were then transformed into a real space correlation
function K(z) using a FORTRAN program written in house to evaluate
the integral: 1 K ( z ) = 0 .infin. 4 q 2 I ( q ) cos ( 2 q z ) q
where q = 4 sin ( ) / .
[0044] The integral was evaluated by direct summation over all
values 2 in the data range (0.2.degree.-2.5.degree.) and over the
real space values from 0 nm-50 nm. This follows the method of G.
Strobl (Strobl G. The Physics of Polymers; Springer: Berlin 1997,
pp. 408-14), entirely incorporated by reference. From the
one-dimensional correlation function, K(z), one can extract the
morphological data of interest, in this case long period spacing
(L). The integrated intensity data I(q) as a function of 20.theta.
demonstrates a broad hump corresponding to the long period spacing
(FIG. 2). The K(z) function has a characteristic shape (FIG. 3).
The relevant extractable data points are indicated. Long-period
spacing is extracted from K(z) data as the global maximum of the
function occurring at a higher z value than the global minimum.
[0045] These data are collected in Table 6. Also included in Table
6 are the measurements as a result of 150.degree. C. hot air
exposure (to test for shrinkage). As can be clearly seen, a longer
SAXS long period corresponds to a lower shrinkage. In addition,
samples prepared with the additive, but without sufficient heat in
the process (represented in this case by a 130.degree. C. heatset),
gave a smaller SAXS long period and a correspondingly higher
150.degree. C. hot air shrinkage. The following TABLE thus shows
the correlation between SAXS long period measurements with
150.degree. C. hot air exposure (for shrinkage of the target
yarns), as well as the correlation between heat-set temperatures
with such characteristics.
7 EXPERIMENTAL TABLE 4 SAXS and 150.degree. C. Hot Air Shrinkage
Data For Yarn Samples Sample Yarn Heat-set Temp. (.degree. C.)
Shrinkage SAXS Long Period A 130 6.7% 26.45 B 130 6.7% 22.35 C 130
7.1% 21 D 130 5.8% 23.2 E 130 4.0% 26.4 E 120 8.0% 21 E 110 9.2%
18.4 F 130 7.2% 21.55 H 130 6.8% 22.4 Comm. Yarn 1 -- 12.1% 16.95
Comm. Yarn 2 -- 13.0% 15.6
[0046] It is thus evident that the higher the long period as
measured by small-angle X-ray scattering, the lower the shrinkage
exhibited by the target polypropylene yarn.
[0047] Peak Crystallization Temperatures
[0048] As noted above, in order to provide the desired low-shrink
characteristics to the target yarns and/or fibers, a nucleating
agent should be added. Although the presence of a nucleating agent
or agents is necessary to accord such low-shrink properties in
tandem with a proper heat-setting of the fiber and/or yarn, it is
not a requirement that all nucleating agents present within the
target yarn and/or fiber exhibit a relatively high peak
crystallization temperature. There are certain instances, however,
wherein the nucleating agent does induce such high peak
crystallization temperatures and thus their presence may be
determined through differential scanning calorimetry analysis. For
those nucleating agents that do not induce the target polymer to
exhibit such high peak crystallization temperatures, other methods
of analysis (gas chromatography/mass spectroscopy, as one example)
may be utilized to determine their presence. For example, although
sodium benzoate is well known as a polyolefin nucleating agent (as
defined above), peak crystallization results within polypropylene
yarns and/or fibers are not consistent with accepted results for
sodium benzoate within other types of polypropylene articles (such
as plaques, containers, and the like). Some peak crystallization
measurements for sodium benzoate within polypropylene fibers have
been nearly as low as the measurements for the polypropylene
itself. Again, since sodium benzoate provides effective low-shrink
characteristics for such fibers and/or yarns, the lack of high peak
crystallization temperatures for such sodium benzoate-containing
polypropylene fiber samples does not remove sodium benzoate from
the definition of nucleating agent for the purposes of this
invention.
[0049] Thus, for the polypropylene samples including the remaining
types of nucleating agents, peak crystallization was measured by
the following method (a modified version of ASTM D3417-99 including
a manner of creating a proper measurable sample of the test fibers
themselves): A Perkin-Elmer DSC7 calibrated with an indium metal
standard at a heating rate of 20.degree. C./min was used to measure
the peak crystallization temperature of the polypropylene fibers.
Bundles of polypropylene fibers were heated to 220.degree. C. for 1
minute and then compressed into thin disks approximately 250
{circle over (3 )} m thick. The specific polyolefin/DBS mixture
composition was heated from 60.degree. C. to 220.degree. C. at a
rate of 20.degree. C. per minute to produce a molten formulation
and held at the peak temperature for 2 minutes. At that time, the
temperature was then lowered at a rate of 20.degree. C. per minute
until it reached the starting temperature of 60.degree. C. The peak
crystallization temperature of the polymer was thus measured as the
peak maximum during the crystallization exotherm. This entire
procedure of first preparing fibers into plaques followed by DSC
analysis in accordance with the modified ASTM D-3417-99 test is
herein referred to as "fiber peak crystallization temperature
measurement(s)" for the purposes of this invention. The results for
the fiber peak crystallization temperature measurements for the
samples from Table 1, above, are tabulated below (with a standard
deviation of +/-0.5.degree. C.):
8 EXPERIMENTAL TABLE 5 Peak Crystallization Temperatures For Yarn
Samples Peak Crystallization Sample Yarn Heat-set Temp. (.degree.
C.) Temperature (Tc)(.degree. C.) A 120 124.3 B 130 124.6 D 130
117.0 E 130 123.7 F 130 124.5 H 130 122.2 I(Comparative) 130
109.9
[0050] Thus, the presence of certain nucleating agents provided
relatively high peak crystallization temperatures for the sample
yarns (at least above 115.degree. C., and as high as a low level of
about 117.0.degree. C.).
Fabric Article Production and Analyses
[0051] Woven Fabric Comprising the Inventive Yarn
[0052] Fabric was woven using the inventive yarns and a 150 denier,
34 filament polyester warp, and weaving a square weave with 84
picks/inch using five yarns: a control made as above with no
additive with final draw roll 3A and 3B temperatures of 110.degree.
C. and 130.degree. C. Three experimental yarns were made having
2500 ppm 3,4-DMDBS (Sample yarns F, from above) and a final draw
roll 3A and 3B temperature of 110.degree. C., 130.degree. C., and
140.degree. C. respectively. These sample fabrics were separated
into 18 inch squares. A 12" box was drawn in the center of the
piece of fabric, and the fabric was washed five times in either hot
(60.degree. C.) or cold (20.degree. C.) water, and dried for 30
minutes in a conventional dryer (at about 70.degree. C. for 20
minutes). The dimensional change of the 12" box was measured, and
is reported in Table 6 as % shrinkage.
9 EXPERIMENTAL TABLE 6 Fabric Sample Shrinkage Data Sample Fabric
(corresponding Yarn Heat-set Cold Wash Hot Wash to TABLE 1, above)
Roll Temp. (.degree. C.) Shrinkage Shrinkage F 110 2.4% 5.8% F 130
2.9% 3.7% F 140 2.4% 3.7% I(Comparative) 110 8.9% 14.9%
I(Comparative) 130 5.0% 6.8%
[0053] Thus, it is evident that the fabric samples comprising the
inventive yarns exhibit lower shrinkage rates as well.
[0054] Knit Fabric Construction Comprising the Inventive Yarn
[0055] Yarns from TABLE 1 were produced with a heat-set roll
temperature of 130.degree. C. and were subsequently knit into socks
on a Lawson Hemphill FAK Knitter 36 gage knitting machine using 160
needles (needle no. 71.70) at speed setting 4 using 40 PSI of air
pressure. The fabric was laid flat, and a 2.75".times.10" section
of sock was marked (10" in the course direction, 2.75" in the wales
direction). The socks were placed in an oven at 150.degree. C. (hot
air) for five minutes, and then the dimensions of the marked
section were measured. The shrinkage in each direction and the area
shrinkage are reported in TABLE 8, below. The area shrinkage is the
product of the measured dimensions (the area) divided by 27.5 sq.
inches (the original area), reported as a percentage.
10 EXPERIMENTAL TABLE 7 150.degree. C. Hot Air Shrinkage Data For
Knit Fabric Samples Sample Yarn Course Shrinkage Wales Shrinkage
Area Shrinkage A 5.3% 2.8% 8.0% B 7.2% 2.8% 9.8% C 8.8% 2.2% 10.8%
D 0.6% 3.4% 4.0% E 1.6% 1.6% 3.2% F 5.6% 2.8% 8.2% H 7.2% 2.2% 9.2%
I(Comparative) 11.3% 4.4% 15.2% Comm. Yarn 1 20.6% 5.3% 24.8% Comm.
Yarn 2 20.0% 3.8% 23.0%
[0056] Therefore, it is evident that the inventive knit fabrics
exhibit far better shrinkage characteristics than the commercial
yarn-containing fabric samples as well as the control without any
nucleator compound present. The control yarn gave very high area
shrinkage, which was eclipsed by the air jet textured commercial
yarns. Yarns with DBS and p-MDBS gave very low shrinkage, easily
acceptable within the apparel industry.
[0057] Non-Woven Fabric Construction Comprising the Inventive
Yarn
[0058] Yarns from Sample E of TABLE 1 were produced with a heat-set
roll temperature of 130.degree. C. and were extruded at a pump rate
of 87.6 cc/min with a 68 hole spinneret, to give a total yarn
denier of 680 and a denier per filament of 10. The fibers were
combined by plying such into 5 yarns of 2720 denier, which were
then combined into a single tow of 13600 denier, which was heated
at .about.90.degree. C. in steam, crimped in a stuffer box, and
then cut to a staple length of 3.25 inches. The staple was then
carded, lapped using a Fiber Locker manufactured by James Hunter
Machine Company, and then needled with a Di-Lour-6 manufactured by
Dilo, Inc. into a bat approximately 12.times.24 inches. Boxes of
130.3 cm.sup.2 were marked on the bat. The bat was then molded by
heating with an IR lamp for 60 seconds to temperatures reaching
120-150.degree. C. and then compressing in a 10.degree. C. mold.
The boxes showed average shrinkage of 3.2%.
[0059] A control yarn of 10 DPF with no additive was obtained. It
was then crimped and cut into staple, carded, lapped, and needled
in the same manner. Boxes were again marked prior to molding. When
molded under the same conditions, the boxes showed an average
shrinkage of 11.7%.
[0060] It is thus evident that the non-woven fabrics made from the
inventive low-shrink propylene yarns also exhibit excellent
low-shrink characteristics in comparison with control samples.
[0061] There are, of course, many alternative embodiments and
modifications of the present invention which are intended to be
included within the spirit and scope of the following claims.
* * * * *