BACKGROUND OF THE INVENTION
[0001] This invention relates to papermaker's fabrics and more particularly to a papermaker's
fabric having high wear resistant cross machine direction monofilament yarns on the
machine side or wear side of the fabric.
[0002] Forming fabrics for use in papermaking machines usually are in the form of a fine
mesh cloth which has been woven endless or otherwise joined into an endless web. As
a very basis of good quality paper resides in the web formation itself, the structure
of the forming wire is of vital and decisive importance. At one time, all forming
wires were manufactured from metal wires. These metal-wire cloths were useful in all
kinds of papermaking machines and for all paper qualities.
[0003] Eventually, metal-wire cloths were replaced by single-layer cloths or wires of synthetic
fiber threads. The advantage of synthetic threads beyond metal-wire threads primarily
resides in their improved wear resistance. Single layer synthetic wires do, however,
suffer from the disadvantage of having considerably higher elasticity and less stability
than cloths made from metal-wires of corresponding coarseness.
[0004] With such synthetic materials, and in the case where the liquid suspension contains
in addition to the cellulosic fibers, an abrasive filler material such as calcium
carbonate, the problem arises that the mesh may become rapidly worn, and the working
life thereof consequently appreciably reduced, due to abrasion occurring as the mesh
moves against the rollers and suction devices.
[0005] The initial synthetic yarns used in papermaker's fabrics were multifilament yarns.
These yarns which frequently were made out of nylon were chemically treated in order
to improve the wear resistance of the fabric. (See U.S. Patent No. 3,032,441 issued
to Beaumont et al.) The introduction of all monofilament fabrics further improved
the wear resistance of forming fabrics by virtue of the higher apparent density of
the monofilament yarns compared to the multifilament yarns.
[0006] Efforts to improve the wear resistance of the monofilament yarns have so far had
only limited success. Attempts to improve the wear resistance of the monofilament
yarns are taught by U.S. Patent No. 4,289,173 issued to Miller and West German Patent
Application No. 25 02 466 in the name of Wandel. These patents disclose the use of
alternative nylon and polyester yarns in the cross machine direction for improving
the wear resistance of the fabric. The papermaking performance of such prior art fabrics
has been reduced by a pronounced wire mark on the sheet side. Furthermore, the combining
of nylon and polyester yarns have proven to be rather difficult due to the different
bending stiffnesses exhibited by the two types of synthetic yarns. Such yarns will
also tend to exhibit different crimp when used in the same fabric.
[0007] Attempts to improve the wear resistance by coating the fabric with an abrasion-resistant
film as taught by U.S. Patent No. 4,421,819 issued to Baker have also met with limited
success. The normal wear rates of the fabric will resume as soon as the thin wear
resistant coating has worn through. In addition, if the coating applied to the fabric
is too thick, the drainage passage through the coated fabrics is reduced by the thickness
of the coating up to the point where the drainage passages become completely blocked.
[0008] The problem of reduced drainage capacity due to the coating of monofilament fabrics
is a particularly serious problem with fine mesh fabrics used for fine paper applications
and with dual layer---fabrrcs where the distance between surfaces of adjacent machine
direction monofilament yarns is extremely small.
[0009] It is therefore a principal object of the present invention to provide a papermaker's
fabric having improved abrasion resistance and therefore working life without appreciable
adverse modification of texture and drainage characteristics of the fabric.
[0010] A further object of the present invention is to provide a papermakers fabric in which
the abrasion resistance of the fabric is improved without applying a coating to the
fabric.
SUMMARY OF THE INVENTION
[0011] The papermaker's fabric of the present invention is woven from monofilament yarns
manufactured from a high wear resistant polyester. The high-wear resistant yarns are
produced from a very high viscosity polymer having an intrinsic viscosity higher than
the intrinsic viscosity of the manufactured yarns which must be 0.84 or higher.
[0012] The high-wear resistant yarns are produced using normal extrusion conditions with
the polymer temperature increased by about 10°F in order to handle the high viscosity
polymer.
[0013] These and other features and objects of the present invention will be more fully
understood from the following detailed description which should be read in light of
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
Fig. 1 is a plan view of a single layer papermaker's fabric according to the present
invention which diagrammatically shows the wear area of the fabric;
Fig. 2 is a plan view of a double layer papermaker's fabric according to the present
invention which diagrammatically shows the wear area of the fabric;
Fig. 3 is a schematic representation of a yarn wire abrasion test;
Fig. 4 is a schematic representation of a wet roll abrasion test;
Figs. 5a and 5b are schematic diagrammatic representations of a double layer papermaker's
fabric, as shown in Fig. 2, containing regular polyester yarns, before and after wet
roll abrasion tests respectively;
Figs. 5c and 5d are schematic diagrammatic representations of a double layer papermaker's
fabric, as shown in Fig. 2, incorporating the high-wear resistant polyester yarns
of the present invention, before and after abrasion resistance tests respectively;
and
Figs. 5e and 5f are schematic diagrammatic representations of a double layer papermaker's
fabric, as shown in Fig. 2, containing alternating regular and nylon 6.6 cross machine
direction yarns, before and after abrasion resistance tests respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The papermakers fabric of the present invention, which may be a single (Fig. I),
double (Fig. 2) or multi-layer fabric, includes high wear resistant polyester yarns
in the bottom layer of the fabric. Preferably all or substantially all of the cross-machine
direction yarns are composed of or formed of a high viscosity polyester monofilament.
The high wear resistant yarns incorporated in the papermaker's fabrics of the present
invention are produced from a very high viscosity polyester of intrinsic viscosity
over 0.95 with the intrinsic viscosity of the yarns being 0.84 or higher, depending
on the extrusion rates. A suitable high viscosity polyester is that marketed by the
Goodyear Tire and Rubber Co. The polyester may be mixed with an imide stabilizer and/or
Ti0
2 and extruded into a monofilament.
[0016] The high wear resistant yarns of the present invention may be produced under the
same extrusion conditions as regular cross machine direction polyester yarns. The
only small adjustment needed is to use a polymer temperature about 10°F higher than
normal to handle the high viscosity polymer. Productivities from such production are
normal, and the high viscosity polymer costs only a few cents more per pound than
regular, normal viscosity polyester polymer.
[0017] Many other features and aspects of the present invention will become apparent from
the following non-limiting examples.
[0018] The fabrics in the following examples underwent two types of tests: the yarn wire
abrasion test and the wet roll abrasion test. In the yarn wire abrasion test, schematically
shown in Fig. 3, fifteen piano wires are distributed uniformally around a circle having
a 7 1/2-inch diameter. The yarn or monofil to be tested is in contact with 90° of
the "Squirrel Cage." The yarns are tensioned with a 1/2 pound weight, and the wires
comprising the squirrel cage are rotated at 34 r.p.m. towards the weight. There are
five positions on the wire tester and each has a counter which records the number
of revolutions or cycles of the squirrel cage required to break or fracture the yarn.
When the yarn breaks, the counter automatically stops. In the device of Fig. 3, the
yarn is stationary and the wires rub along the length of the yarn.
[0019] To perform the wet roll abrasion test, shown in Fig. 4, a rectangular fabric sample,
4 inches by 1/4 inch, is held stationary on a wet rotating papermaker's roll with
a 14-inch diameter. The water is added via a spray, and the fabric holder keeps the
fabric strip tangential to the roll and provides a controlled pressure on the fabric.
The surface speed of the roll is 1000 feet per minute. The test lasts for 10 or 20
minutes depending on fabric weight. The degree of abrasion is determined by the percent
lost in tensile strength of the abraded fabric strip compared to the strength of the
fabric before abrasion.
EXAMPLE 1
[0020] A 0.19 diameter high wear resistant (HWR) yarn of 0.87 Intrinsic Viscosity was produced
from Goodyear polymer 1005A of Intrinsic Viscosity (I.V.) 1.0. The yarn was drawn
4.0 x and heat set in an oven at 420°F. on the extrusion line. This yarn had a low
modulus of 0.65 gm/decitex for 1% extension and a free shrinkage of 12% in an oven
at 392°F.
[0021] The abrasion of this 0.19mm HWR yarn was compared with a regular polyester 0.19mm
yarn of I.V. 0.65 produced from Goodyear polymer 7201A with similar modulus of 0.63
and free shrinkage of 9%. The results of the yarn wire abrasion and wet roll abrasion
tests were as follows:

[0022] The regular and HWR 0.19mm yarns were woven as cross machine direction yarns in a
single layer fabric of the type shown in Fig. 1. The strength losses in the fabrics
after the same number of revolutions of the wet roll were:

EXAMPLE 2
[0023] The 0.19mm HWR yarn of Example 1 was evaluated as the cross machine direction yarns
in a double layer fabric of the type illustrated in Fig. 2. The strength losses in
the fabrics after an identical number of revolutions of the wet roll were:

EXAMPLE 3
[0024] In additional tests, 0.17mm HWR and regular yarns were produced using the following
conditions

[0025] These two yarns were evaluated in a double layer fabric similar but not identical
to that shown in Fig. 2. In addition, a pick and pick fabric with alternating regular
polyester and nylon 6.6 monofils on the bottom layer of the double fabric was woven
across the same warp.

[0026] The worn areas on each of these three double layer fabrics both before and after
wet roll abrasion are shown in Figs. 5a and 5b, 5c and 5d, 5e and 5f.
EXAMPLE 4
[0027] A 0.23mm HWR yarn of 0.87 I.V. was produced from Goodyear polymer 1005A using similar
extrusion draws and oven temperature as the yarn of Example 1. This 0.23mm yarn had
a modulus of 0.64 and a free shrinkage of 13%.
[0028] This 0.23 HWR yarn, along with regular 0.23mm polyester was woven as cross machine
direction yarn in a monoplane fabric similar to the fabric of Fig. 1. The abrasion
results were:

EXAMPLE 5
[0029] A coarse 0.36mm HWR yarn was obtained from a Goodyear polymer 9501A of I.V. 0.95.
The 0.36mm HWR monofil had an I.V. of 0.84, a modulus of 0.61, and a free shrinkage
of 15%. The yarn wire abrasion test results for this 0.36mm HWR monofil as compared
to a regular 0.36mm monofil were:

[0030] Many features and aspects of the present invention can be seen from examples 1-5
set forth above. These examples show that the high-wear resistant yarns can withstand
75% to 125% more wire abrasion revolutions than similar regular polyester monofils
of the same diameter. In addition, the fabrics composed of regular polyester yarns
have strength losses on the wet roll from 25% to 50% more than fabrics utilizing the
high-wear resistant yarns of the present invention. As seen in Fig. 5b a double layer
fabric having regular polyester yarns in the machine direction shows some wear on
these machine direction yarns. Figs. 5d and 5f, however, show that the use of high-wear
resistant yarns or pick and pick regular polyester/nylon 6.6 yarns results in little
or no wear of the machine direction yarns when the fabrics are subjected to the same
number of revolutions of the wet roll. Finally, most of the physical properties of
the high-wear resistant yarns are similar to regular polyester yarns so that few if
any changes in winding, weaving or finishing are required to process the fabrics incorporating
the high-wear resistant yarns. These high-wear resistant monofils do have slightly
more free shrinkage then regular polyester monofils. Most importantly, however, as
seen above, the main difference between regular and high-wear resistant yarns is that
the high-wear resistant yarns have significantly higher abrasion resistance than the
regular polyester yarns.
[0031] The foregoing invention has been described with reference to its preferred embodiments
and a number of non-limiting examples. Although variations and modifications will
occur to those skilled in the art, it is intended that such variations and modifications
fall within the scope of the appended claims.
[0032] What is claimed is:
1. A papermaker's fabric comprising high wear resistant polyester yarns on a wear
side of the fabric, said polyester yarns having an intrinsic viscosity of at least
0.84.
2. The papermaker's fabric of claim 1 wherein said high wear resistant polyester yarns
are monofilament yarns.
3. The papermaker's fabric of claim 1 wherein said polyester yarns include an imide
stabilizer and TiO2.
4. An open mesh band for use as a papermaker's fabric comprising high wear resistant
polyester yarns, on a wear side of the fabric, said polyester yarns having an intrinsic
viscosity of at least 0.84.
5. An open mesh band of claim 4 wherein said high wear resistant polyester yarns are
monofilament yarns.
6. An open mesh band of claim 4 wherein said polyester yarns include an imide stabilizer
and TiO2.