U.S. patent application number 14/562945 was filed with the patent office on 2016-06-09 for monofilament, spiral fabric and method of forming a spiral fabric.
The applicant listed for this patent is VOITH PATENT GMBH. Invention is credited to Vikram DHENDE, Brian GOOD.
Application Number | 20160160393 14/562945 |
Document ID | / |
Family ID | 55070985 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160160393 |
Kind Code |
A1 |
DHENDE; Vikram ; et
al. |
June 9, 2016 |
MONOFILAMENT, SPIRAL FABRIC AND METHOD OF FORMING A SPIRAL
FABRIC
Abstract
A monofilament is particularly suited for use as a component in
a spiral fabric. The monofilament is formed from a resin
composition including a thermoplastic polymer. The thermoplastic
polymer has an average molecular weight of less than 14200 g/mol.
Alternatively, the monofilament is formed from a resin composition
including a thermoplastic polymer, the thermoplastic polymer having
a free thermal shrinkage of less than 1%. According to yet another
embodiment, the monofilament is formed from a resin composition
including a thermoplastic polymer, the thermoplastic polymer having
an intrinsic viscosity of less than 0.72 dl/g. Yet alternatively,
the monofilament is formed from a resin composition including a
thermoplastic polymer, the thermoplastic polymer having a melt
viscosity of less than 3000 P.
Inventors: |
DHENDE; Vikram;
(Summerville, SC) ; GOOD; Brian; (Summerville,
SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOITH PATENT GMBH |
Heidenheim |
|
DE |
|
|
Family ID: |
55070985 |
Appl. No.: |
14/562945 |
Filed: |
December 8, 2014 |
Current U.S.
Class: |
428/222 ;
264/103; 28/100; 428/397; 428/401; 524/195; 524/605; 528/308.1 |
Current CPC
Class: |
D21F 1/0072 20130101;
D01F 6/84 20130101; D04H 1/06 20130101 |
International
Class: |
D01F 6/84 20060101
D01F006/84; D04H 1/06 20060101 D04H001/06; D21F 7/12 20060101
D21F007/12 |
Claims
1. A monofilament, comprising a resin composition formed into a
monofilament, said resin composition including a thermoplastic
polymer, the thermoplastic polymer having a number average
molecular weight of less than 14200 g/mol.
2. The monofilament according to claim 1, wherein said
thermoplastic polymer has a number average molecular weight ranging
from 5000 g/mol to 11000 g/mol.
3. The monofilament according to claim 1, wherein the monofilament
has a free thermal shrinkage of less than 1%, wherein the free
thermal shrinkage is determined as a percentage of a change in a
length of the monofilament after a heat treatment of the
monofilament in an oven at 177.degree. C. for 5 min compared to the
length of the monofilament before the heat treatment.
4. The monofilament according to claim 3, wherein the free thermal
shrinkage is less than 0.5%.
5. The monofilament according to claim 3, wherein the free thermal
shrinkage is less than 0.35%.
6. The monofilament according to claim 1, wherein said
thermoplastic polymer is a polymer selected from the group
consisting of polyethylene terephthalate, polyphenylene sulfide,
polyamide, and polyolefin.
7. The monofilament according to claim 1, wherein said
thermoplastic polymer is a homopolymer or a copolymer.
8. The monofilament according to claim 1, wherein said resin
composition includes a stabilizer selected from the group
consisting of hydrolytic stabilizers and heat stabilizers.
9. The monofilament according to claim 8, wherein said hydrolytic
stabilizer is a monomeric or polymeric carbodiimide.
10. The monofilament according to claim 1, wherein said
monofilament has a circular cross section, an oval cross section,
or a rectangular cross section.
11. The monofilament according to claim 1, wherein said
monofilament has a maximum diameter ranging from 0.005 mm to 5
mm.
12. A monofilament, comprising a resin composition formed into a
monofilament, said resin composition including a thermoplastic
polymer, the thermoplastic polymer having an intrinsic viscosity of
less than 0.72 dl/g.
13. The monofilament according to claim 12, wherein said
thermoplastic polymer has an intrinsic viscosity ranging from 0.35
dl/g to 0.6 dl/g.
14. A monofilament, comprising a resin composition formed into a
monofilament, said resin composition including a thermoplastic
polymer, the thermoplastic polymer having a melt viscosity of less
than 3000 P.
15. The monofilament according to claim 14, wherein said
thermoplastic polymer has a melt viscosity of less than 2000 P.
16. A spiral fabric, comprising: a plurality of coiled
monofilaments arranged side-by-side in intermeshing relationship; a
plurality of elongated pintles extending through intermeshed
portions of said coiled monofilaments; and a plurality of stuffer
yarns extending through central portions of said coiled
monofilaments between mutually adjacent pintles; said stuffer yarns
and/or said pintles being formed from a resin composition including
a thermoplastic polymer; and said thermoplastic polymer having a
number average molecular weight of less than 14200 g/mol.
17. The spiral fabric according to claim 16, wherein said
thermoplastic polymer has an average molecular weight ranging from
5000 g/mol to 11000 g/mol.
18. The spiral fabric according to claim 16, wherein said stuffer
yarns and/or said pintles have a free thermal shrinkage of less
than 1%, wherein the free thermal shrinkage is determined as
percentage of a change in a length of the stuffer yarn or pintle
after a heat treatment in an oven at 177.degree. C. for 5 min
compared to the length of the stuffer yarn or pintle before the
heat treatment.
19. The spiral fabric according to claim 18, wherein the free
thermal shrinkage is less than 0.5%.
20. The spiral fabric according to claim 18, wherein the free
thermal shrinkage is less than 0.35%.
21. The spiral fabric according to claim 16, configured to form an
endless belt.
22. The spiral fabric according to claim 16, configured with
sufficient mechanical and thermal stability to be used as a dryer
belt in a paper machine.
23. A method of forming a monofilament, the method comprising the
following steps: providing a resin composition including a
thermoplastic polymer, the thermoplastic polymer having a number
average molecular weight of less than 14200 g/mol; and extruding
the resin composition through a spinneret to form a monofilament;
and drawing the monofilament for one or more times.
24. The method according to claim 23, which comprises preparing the
resin composition at least in part from a recycled polymer.
25. The method according to claim 23, which comprises drawing the
monofilament for one or more times at an overall draw ratio ranging
from 3.0 to 6.0.
26. The method according to claim 23, which comprises drawing the
monofilament for one or more times in an oven at a temperature
ranging from 90.degree. C. to 250.degree. C.
27. A method of forming a spiral fabric, the method comprising the
following steps: providing a plurality of coiled monofilaments and
arranging the coiled monofilaments side-by-side in intermeshing
relationship; extending a plurality of elongated pintles through
intermeshed portions of the coiled monofilaments; extending stuffer
elements formed from monofilaments according to claim 1 through
central portions of the coiled monofilaments between mutually
adjacent pintles; and heat setting the arrangement of coiled
monofilaments and pintles at an elevated temperature, to thereby
release structural stresses of the monofilaments.
28. The method according to claim 27, wherein the stuffer elements
are drawn from a resin composition including a thermoplastic
polymer, the thermoplastic polymer having a number average
molecular weight of less than 14200 g/mol.
29. The method according to claim 27, wherein the stuffer elements
are drawn from a resin composition including a thermoplastic
polymer, the thermoplastic polymer having an intrinsic viscosity of
less than 0.72 dl/g.
30. The method according to claim 27, wherein the stuffer elements
are drawn from a resin composition including a thermoplastic
polymer, the thermoplastic polymer having a free thermal shrinkage
of less than 1%, the free thermal shrinkage being determined as a
percentage of a change in a length of the stuffer element after a
heat treatment of the stuffer element in an oven at 177.degree. C.
for 5 min compared to the length of the stuffer element before the
heat treatment.
31. The method according to claim 27, wherein the pintles are
equally formed from monofilaments having a free thermal shrinkage
of less than 1%, the free thermal shrinkage being determined as a
percentage of a change in a length of the monofilament after a heat
treatment of the monofilament in an oven at 177.degree. C. for 5
min compared to the length of the monofilament before the heat
treatment.
32. The method according to claim 27, which comprises extending the
stuffer elements through the central portions of the coiled
monofilaments between adjacent pintles before the step of heat
setting the arrangement of coiled monofilaments and pintles at an
elevated temperature.
33. The method according to claim 27, which comprises extending the
stuffer elements through the central portions of the coiled
monofilaments between adjacent pintles after the step of heat
setting the arrangement of coiled monofilaments and pintles at an
elevated temperature.
34. The method according to claim 27, which comprises not
subjecting the arrangement of coiled monofilaments and pintles to
any further thermal treatment after the step of heat setting.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a monofilament in
particular for use as a component in a spiral fabric, wherein the
monofilament is formed from a resin composition including a
thermoplastic polymer.
[0002] Spiral fabrics manufactured from coiled polymeric
monofilaments are widely used in dryers, conveyors and other
industrial applications. For example, endless belts of spiral
fabrics are important constituents of the dryer sections of paper
machines, which are also called paper machine clothings (PMC). Such
paper machine clothings are described, for example, in British
publication GB 2141749 A and in U.S. patent application publication
US 2008/0169039 A1.
[0003] A spiral fabric may comprise pintles extending through
intermeshed portions of the coiled monofilaments and linking the
individual monofilaments together. Furthermore, a spiral fabric may
be provided with stuffer elements or filler elements which extend
through central portions of the coiled monofilaments and which
serve to control the air permeability properties of the fabric as
well as to support the fabric's structural integrity. The pintles
and/or the stuffer elements may equally be formed from
monofilaments, preferably from elongated instead of coiled
monofilaments. The coiled monofilaments are usually converted into
shaped spiral products by means of a thermomechanical process, in
order to form a spiral fabric. Such a thermomechanical process for
manufacturing a spiral fabric usually comprises two heat-setting
steps, which are carried out at elevated temperatures of e.g. more
than 180.degree. C. While the first heat-setting step serves to
release structural stresses within the fabric and to stabilize the
spiral shapes of the monofilaments, the second heat-setting step is
necessary to stabilize the stuffier elements.
[0004] However, the heat-setting processes are energy-intensive and
time-consuming. On account of these reasons there is a need to
reduce the energy consumption and the production time required for
manufacturing spiral fabrics.
SUMMARY OF THE INVENTION
[0005] It is accordingly an object of the invention to provide a
monofilament, a spiral fabric, and a corresponding production
method which overcome the above-mentioned and other disadvantages
of the heretofore-known devices and methods of this general type
and which provides for a monofilament which has a low degree of
shrinkage.
[0006] With the foregoing and other objects in view there is
provided, in accordance with a first aspect of the invention, a
monofilament in particular for use as a component in a spiral
fabric, wherein the monofilament is formed from a resin composition
including a thermoplastic polymer, wherein the thermoplastic
polymer has a number average molecular weight of less than 14200
g/mol.
[0007] Surprisingly, it has been found that monofilaments formed
from a polymer having such a comparable low molecular weight are
characterized by and an extraordinarily low shrinkage.
Specifically, it has been determined that the shrinkage of a
monofilament formed from such a polymer composition is sufficiently
low to eliminate in the aforementioned fabric production process
one of the two heat-setting steps. This omission of one of the
heat-setting processes leads to a significant energy saving and
sustainability. Moreover, this leads to a significant reduction of
fabric processing time and production costs. Due to the low
shrinkage of the monofilaments in accordance with the present
invention, the monofilaments may even contain recycled polymer.
Thus, the invention enables a reduction of carbon footprint in
connection with fabric production.
[0008] In accordance with the present invention, the number average
molecular weight is measured by gel permeation chromatography
making use of polystyrene standards.
[0009] Particularly good results are achieved, when the
thermoplastic polymer has a number average molecular weight ranging
from 5000 g/mol to 11000 g/mol.
[0010] In accordance with another aspect of the present invention,
a monofilament in particular for use as a component in a spiral
fabric has a free thermal shrinkage of less than 1%, wherein the
free thermal shrinkage is determined as percentage of the change in
the length of the monofilament after incubating the monofilament in
an oven at 177.degree. C. for 5 min compared to the length of the
monofilament before the heat treatment, i.e. wherein the free
thermal shrinkage is (length of the monofilament before incubating
the monofilament in an oven at 177.degree. C. for 5 min minus
length of the monofilament after incubating the monofilament in an
oven at 177.degree. C. for 5 min)/(length of the monofilament
before incubating the monofilament in an oven at 177.degree. C. for
5 min). Monofilaments having such a low shrinkage, when used as
stuffier yarns and/or pintles in a spiral fabric, offer the
possibility to omit one heat-setting step during the production of
the spiral fabric.
[0011] Notably good results are achieved, when the monofilament has
a free thermal shrinkage of less than 0.5% and most preferably of
less than 0.35%.
[0012] According to a preferred embodiment of the present
invention, the thermoplastic polymer in both aforementioned aspects
of the present invention is a polyethylene terephthalate (PET). PET
has a high dimensional stability, a sufficient resistance to
abrasion and a low moisture absorption and is moreover available at
a moderate price. Furthermore, the tensile properties and the
processability of PET are excellent. Therefore, PET monofilaments
are especially suited for PMC applications.
[0013] In accordance with an alternative embodiment of the present
invention, the thermoplastic polymer is a polyphenylene sulfide, a
polyamide or a polyolefin. Such polymers may be advantageous in
certain applications.
[0014] The thermoplastic polymer may be a homopolymer or a
copolymer.
[0015] In a further development of the present invention, it is
proposed that the resin composition includes a hydrolytic
stabilizer, which is preferably a monomeric carbodiimide or a
polymeric carbodiimide. Preferably, the content of the hydrolytic
stabilizer with respect to the resin composition ranges from 1 to
2% by weight. Apart from a hydrolytic stabilizer, the resin
composition may, if necessary, include other additives, such as
e.g. one or more plasticizers.
[0016] The resin composition may include a heat stabilizer to
minimize thermal degradation.
[0017] According to yet another preferred embodiment of the present
invention, the monofilament has a circular, oval or rectangular
cross section. Specifically, the cross-sectional shape of the
monofilament may be selected depending on the type of spiral fabric
to produce for and depending on the application field of the
fabric.
[0018] In accordance with still another preferred embodiment of the
present invention, the monofilament has a maximum diameter ranging
from 0.005 mm to 5 mm, preferably from 0.05 mm to 4 mm. According
to the present invention, the term "maximum diameter" means the
maximum dimension in the cross-section of the monofilament.
Monofilaments having a dimension falling in this numeric value
range have been found to be specifically suited for PMC
applications.
[0019] Accordingly, it is preferred that the monofilament has a
linear mass density of at least 50 dtex.
[0020] A third aspect of the present invention relates to a
monofilament in particular for use as a component in a spiral
fabric, wherein the monofilament is formed from a resin composition
including a thermoplastic polymer, the thermoplastic polymer having
an intrinsic viscosity of less than 0.72 dl/g. In accordance with
the present invention, the intrinsic viscosity is measured
according to ASTM D4603 making use of a solvent containing 60%
phenol and 40% 1,1,2,2-tetrachloroethane. As the intrinsic
viscosity of a thermoplastic polymer is directly correlated to its
number average molecular weight, the monofilament in accordance
with this aspect of the present invention has the same advantages
as the aforementioned monofilaments according to the first and
second aspect of the present invention.
[0021] Notably good results are obtained, when the thermoplastic
polymer has an intrinsic viscosity ranging from 0.35 dl/g to 0.6
dl/g.
[0022] A fourth aspect of the invention relates to a monofilament
in particular for use as a component in a spiral fabric, wherein
the monofilament is formed from a resin composition including a
thermoplastic polymer, the thermoplastic polymer having a melt
viscosity of less than 3000 P, wherein P denotes Poise. Like the
intrinsic viscosity, the melt viscosity is a parameter which is
correlated with the number average molecular weight of the
thermoplastic polymer, wherefore the monofilament in accordance
with this aspect of the present invention has the same advantages
as the aforementioned monofilaments according to the first to third
aspect of the present invention.
[0023] In a further development of the present invention, it is
proposed that the thermoplastic polymer has a melt viscosity of
less than 2000 P. Such a polymer enables the forming of
specifically stable monofilaments.
[0024] Moreover, the present invention is directed to a spiral
fabric comprising: [0025] a plurality of coiled monofilaments
arranged side-by-side in intermeshing relationship, [0026] a
plurality of elongated pintles extending through intermeshed
portions of the coiled monofilaments, and [0027] a plurality of
stuffer yarns extending through central portions of the coiled
monofilaments between adjacent pintles, [0028] wherein the stuffer
yarns and/or the pintles are formed from a resin composition
including a thermoplastic polymer, and wherein the thermoplastic
polymer has a number average molecular weight of less than 14200
g/mol.
[0029] Such a spiral fabric is easy to produce, cost-effective and
sufficiently stable to be used as a dryer belt or conveyor belt in
a high temperature environment, such as the dryer section of a
paper machine. Surprisingly, it has been found that the use of
monofilaments formed from a comparable low molecular weight polymer
enables the omission of one of the two heat-setting steps in the
fabric production process. This omission of one of the heat-setting
processes leads to a significant energy saving and sustainability.
Moreover, this leads to a significant reduction of fabric
processing time and production costs. The low shrinkage of the
monofilaments in accordance with the present invention may even
contain recycled polymer. Thus, the invention enables a reduction
of carbon footprint in connection with fabric production.
[0030] According to a further preferred embodiment of the present
invention, the thermoplastic polymer has a number average molecular
weight ranging from 5000 g/mol to 11000 g/mol. This range of
molecular weight has turned out to provide especially good
results.
[0031] Alternatively or in addition, the thermoplastic polymer may
have an intrinsic viscosity of less than 0.72 dl/g and/or a melt
viscosity of less than 3000P.
[0032] Moreover, it is preferred that the stuffier yarns and/or the
pintles have a free thermal shrinkage of less than 1%, more
preferably of less than 0.5% and most preferably of less than
0.35%. Stuffer yarns and/or pintles having such a low shrinkage
offer the possibility to omit one heat-setting step during the
production of a spiral fabric.
[0033] According to a further preferred embodiment of the present
invention, the fabric forms an endless belt. Such an endless belt
can be used as a conveyor belt or, preferably, as a dryer belt in a
paper machine.
[0034] Therefore, according to still another embodiment of the
invention, the fabric has a sufficient mechanical and thermal
stability to be used as a dryer belt in a paper machine.
[0035] In addition, the present invention relates to a method for
forming a monofilament in particular for use as a component in a
spiral fabric, which comprises the steps of: [0036] providing a
resin composition including a thermoplastic polymer, the
thermoplastic polymer having a number average molecular weight of
less than 14200 g/mol, [0037] extruding the resin composition
through a spinneret to form a monofilament and [0038] drawing the
monofilament for one or more times.
[0039] Apart from using a low molecular weight polymer, the drawing
of the monofilament may be performed according to the principles
that are generally known in the field of monofilament production.
The provision of a low molecular weight polymeric resin enables the
drawing of monofilaments which are characterized by a high thermal
stability and by an extraordinarily low shrinkage.
[0040] Alternatively or in addition, the thermoplastic polymer may
have an intrinsic viscosity of less than 0.72 dl/g and/or a melt
viscosity of less than 3000 P.
[0041] Moreover, it is preferred that the monofilaments have a free
thermal shrinkage of less than 1%, more preferably of less than
0.5% and most preferably of less than 0.35%. Monofilaments having
such a low shrinkage, when used as stuffier yarns and/or pintles in
a spiral fabric, offer the possibility to omit one heat-setting
step during the production of the spiral fabric.
[0042] In a further development of the present invention, it is
proposed that the resin composition is prepared at least partially
from a recycled polymer. The use of a recycled polymer does not
only reduce the production costs, but reduces also the carbon
footprint.
[0043] According to yet another preferred embodiment of the present
invention, the monofilament is drawn for one or more times at an
overall draw ratio ranging from 3.0 to 6.0. Such draw ratios are
advantageous with respect to the mechanical properties of the
monofilament.
[0044] Notably good results are obtained, when the monofilament is
drawn for one or more times in an oven at a temperature ranging
from 90.degree. C. to 250.degree. C.
[0045] With the above and other objects in view there is also
provided, in accordance with the invention, a method for forming a
spiral fabric. The method comprises the following method steps:
[0046] providing a plurality of coiled monofilaments, [0047]
arranging the coiled monofilaments side-by-side in intermeshing
relationship, [0048] extending a plurality of elongated pintles
through intermeshed portions of the coiled monofilaments, [0049]
extending stuffier elements having a free thermal shrinkage,
measured in an oven at 177.degree. C. for 5 min, of less than 1%,
preferably of less than 0.5%, and most preferably of less than
0.3%, through central portions of the coiled monofilaments between
adjacent pintles, and [0050] heat-setting the arrangement of coiled
monofilaments and pintles at an elevated temperature, whereby
structural stresses of the monofilaments are released.
[0051] Manufacturing a spiral fabric using stuffer yarns having a
low shrinkage provides for a more efficient production process.
Specifically, it has been found that the use of low shrinkage
stuffer elements eliminates the need for a second heat-setting
step, thus contributing to energy saving and sustainability.
[0052] According to a further preferred embodiment of the present
invention, the stuffer elements are drawn from a resin composition
including a thermoplastic polymer, the thermoplastic polymer having
a number average molecular weight of less than 14,200 g/mol.
[0053] Alternatively or in addition thereto, the stuffer elements
may be drawn from a resin composition including a thermoplastic
polymer, wherein the thermoplastic polymer has an intrinsic
viscosity of less than 0.72 dl/g and/or a melt viscosity of less
than 3000 P.
[0054] Preferably, the pintles are equally formed from
monofilaments having a free thermal shrinkage of less than 1%,
preferably of less than 0.5%, and most preferably of less than
0.3%, wherein the free thermal shrinkage is determined as
percentage of the change in the length of the monofilament after
incubating the monofilament in an oven at 177.degree. C. for 5 min
compared to the length of the monofilament before the heat
treatment.
[0055] According to a further preferred embodiment of the present
invention, the stuffer elements are extended through the central
portions of the coiled monofilaments between adjacent pintles
before the step of heat setting the arrangement of coiled
monofilaments and pintles at an elevated temperature.
[0056] Alternatively, the stuffer elements may be extended through
the central portions of the coiled monofilaments between adjacent
pintles after the step of heat setting the arrangement of coiled
monofilaments and pintles at an elevated temperature.
[0057] Preferably, the arrangement of coiled monofilaments and
pintles is not subjected to any further thermal treatment after the
step of heat setting.
[0058] Furthermore, the present invention relates to the use of the
aforementioned monofilaments for forming a spiral fabric.
[0059] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0060] Although the invention is illustrated and described herein
as embodied in a monofilament, a spiral fabric, and a production
method, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0061] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0062] FIG. 1A is an enlarged side view of a spiral fabric made up
from coiled monofilaments, pintles and stuffier yarns;
[0063] FIG. 1B is an enlarged side view of a spiral fabric
according to an alternative embodiment;
[0064] FIG. 2 is a plan view of the spiral fabric of FIG. 1;
[0065] FIG. 3 is a perspective view of an endless belt formed from
the spiral fabric of FIGS. 1 and 2; and
[0066] FIG. 4 is a diagram showing the correlation between the
inherent viscosity of a PET solution and the number average
molecular weight of the PET.
DETAILED DESCRIPTION OF THE INVENTION
[0067] Referring now to the figures of the drawing in detail and
first, particularly, to FIGS. 1A, 1B, and 2, thereof, there is seen
a fabric 12 formed from a plurality of coiled monofilaments 14
intermeshing to form continuous loops in a machine direction
MD.
[0068] The fabric 12 is formed to provide an endless belt 20 as
shown in FIG. 3.
[0069] At the intersections 16 of the coiled monofilaments 14,
there are arranged pintles 18 which extend transverse to the
machine direction MD. After the coiled monofilaments 14 are
interweaved and the pintles 18 are inserted, stuffer elements 10
are inserted so as to extend transverse to the machine direction
MD. The stuffer elements 10 shown in FIG. 1A have a circular cross
section, whereas the stuffer elements 10' shown in FIG. 1B have an
essentially rectangular cross section with slightly rounded
corners. In order to stabilize the spiral form of the monofilaments
14 and to release thermal stresses within the monofilaments 14, the
fabric 12 is subjected to a thermal treatment called heat-setting,
carried out at a temperature of more than 180.degree. C.
[0070] The stuffer elements 10, 10' and the pintles 18 are formed
from a resin composition including a thermoplastic polymer and a
carbodiimide, as it is described above and for an exemplary
embodiment below.
Examples
[0071] Different samples of monofilaments were produced on the
basis of a recycled polyethylene terephthalate (PET). More
specifically, PET monofilament scrap was pelletized and a resin
composition was prepared from the pelletized PET monofilament
scrap. The intrinsic viscosity of the resin composition was
measured according to ASTM D4603, with 60% phenol and 40%
1,1,2,2-tetrachloroethane solvent combination. Monofilaments were
prepared by extrusion and then the monofilaments were drawn from
each resin composition at different draw ratios and at different
oven temperatures so as to have a length of one meter. The obtained
samples were kept in an enclosed hot air oven at 177.degree. C. for
5 minutes in an unrestrained condition. After this hot air
treatment, the change in the length of each samples was measured
and therefrom the free shrinkage percentage was calculated.
[0072] The intrinsic viscosity correlates with the average
molecular weight of the PET. The correlation between the inherent
viscosity of a PET solution and the corresponding molecular weight,
which is largely linear, is shown in FIG. 4. It has to be noted
that the inherent viscosity is the ratio of the natural logarithm
of the relative viscosity to the mass concentration of the polymer,
whereas the intrinsic viscosity is the limiting value of the
reduced viscosity or the inherent viscosity at infinite dilution of
the polymer.
[0073] Table 1 shows the properties of two monofilament samples 1
and 2 according to the present invention as well as of two control
examples. It can be deduced from table 1 that the use of a low
viscosity PET composition, which is equivalent to the use of a low
molecular weight PET, leads to a monofilament having a free
shrinkage of less than 1%. Such a low shrinkage eliminates the need
for a second heat-setting step in the production process of a
spiral fabric as shown in FIG. 1.
TABLE-US-00001 TABLE 1 Tensile properties of monofilaments Oven
Oven Oven Free Intrinsic Draw Draw Draw Temp 1 Temp 2 Temp 3 Shrink
Sample Size/mm viscosity ratio 1 ratio 2 ratio 3 (.degree. C.)
(.degree. C.) (.degree. C.) % Control 0.70 0.95 3.54 1.54 0.81 96
216 232 2.3 1 0.70 0.54 3.50 1.00 1.00 96 196 196 0.0 Control 0.55
0.72 4.35 1.16 0.89 96 243 243 1.0 2 0.55 0.54 4.35 1.16 0.89 96
243 243 0.3
[0074] The following is a summary list of reference numerals and
the corresponding structure used in the above description of the
invention: [0075] 10, 10' stuffier element [0076] 12 fabric [0077]
14 monofilament [0078] 16 intersection [0079] 18 pintle [0080] 20
endless belt [0081] MD machine direction
* * * * *