Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BELT FOR SHOE PRESS
FIELD OF THE INVENTION
The invention relates to a belt used for a shoe press
mechanism such as a shoe press for papermaking, and especially
to a belt used for a closed type shoe press (referred to as "belt"
or "shoe press belt" hereinafter.).
BACKGROUND OF THE INVENTION
In the field of a press for papermaking, the use of shoe
presses is on the increase because they contribute to a reduction
in the total manufacturing costs. Above all, there is a trend
toward the use of a closed type shoe press because it requires
less space for setting and avoids scattering of oil.
Compared to conventional belts used in open type shoe presses,
belts used in a closed type shoe press are subject to more severe
conditions in terms of papermaking speed and nip pressure during
papermaking process. Accordingly, there has been a strong
demand by users for improvement in belt durability.
Among typical technologies used for producing belts for
closed type shoe presses, various manufacturing technologies
using mandrels are known. For example, Examined Japanese Patent
Publication No. 57236/1991 and Unexainined Japanese Patent
Publication No. 45888/1989 disclose a manufacturing method using
an endless woven fabric as a core member. In addition, Japanese
Patent No. 3213589 discloses a manufacturing method using an
endless mesh for a core member. However, these manufacturing
methods have deficiencies, especially difficulties encountered
in adjusting machine direction dimension of a belt.
In addition, PCT Patent application No. 503315/1989 and
Unexamined Japanese Patent Publication No. 209578/1996 disclose
a manufacturing method wherein a woven fabric is not used. These
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manufacturing methods form threads in the axial direction of a
mandrel at regular intervals around the entire circumference of
the mandrel. However, it is difficult to position threads
substantially parallel to the axial direction of a mandrel and
without threads being loosen under even tensile force. With these
methods, excessive time is required for forming threads.
Unexamined Japanese Patent Publication No. 298292/1989 and
PCT Patent application No. 505428/1993 disclose a manufacturing
method wherein a mat-shaped fiber band or a woven fabric
impregnated with uncured resin is wound in helix and then cured.
However, with these manufacturing methods, exfoliation can
easily occur at joints of the helix.
Figure 10 shows a manufacturing method for a conventional
shoe press belt.
An endless woven fabric (a woven fabric, which was woven
endlessly) C is arranged on two rolls A and B. After a shoe side
layer E is impregnated and coated on an external surface of the
woven fabric C by a coating apparatus D and is then cured, the
endless woven fabric C is removed from the rolls A and B, turned
inside-out, and reset on the rolls with its original inner surface
facing outward. After a wet paper web side layer F is impregnated
and coated on the external surface of the fabric and is cured
with its entire thickness adjusted, concave grooves G are formed,
and a belt 1 is produced.
The above-described conventional method had the following
two deficiencies: 1) in order to impregnate and coat the shoe
side layer E on one surface of the endless woven fabric and the
wet paper web side layer F on the other side, the belt needed
to be reversed, and reversal caused distortion to occur inside
the belt; 2) the distortion that existed when weaving the endless
woven fabric is released as the resin is cured, which results
in instability of the form of the belt due to flapping of the
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belt.
Japanese Patent No. 3408416 and Unexamined Japanese Patent
Publication No. 303377/2000 disclose a manufacturing method
wherein a resin layer is firstly formed on a mandrel followed
by formation of a base body, i.e., a substrate, around the
external circumference of the resin layer, and formation of
another resin layer, which is connected with first resin layer
through the base body.
According to this manufacturing method, after forming the
first resin layer, there is no need to grind or reverse the resin
layer, and therefore manufacturing efficiency and productivity
can be improved.
DISCLOSURE OF THE INVENTION
However, the shoe press belt manufactured according to the
manufacturing method disclosed in the Japanese Patent No.
3408416 has relatively large undulations at the joints of warp
yarns and weft yarns in the woven fabric because a woven fabric
piece is used as a base body. In the use of the belt, these
undulations result in large stress concentration at the joints
of warp yarns and weft yarns, which can result in cracking of
a resin layer, and impairment of the durability of the belt.
In the case of a manufacturing method disclosed in the
Unexamined Japanese Patent Publication No. 303377/2000,
similarly to the methods disclosed in the PCT Patent application
No. 503315/1989 and Unexamined Japanese Patent Publication No.
209578/1996, threads have to be formed in the axial direction
of the mandrel at regular intervals, and be distributed around
the entire circumference of the mandrel. The need for this
arrangement causes manufacture of the belt to be very time
consuming and labor intensive.
In the light of above, prior Japanese Patent Application No.
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76216/2005 proposed a shoe press belt comprising a base body
having a lattice material made by joining the crossing points
of warp yarns and weft yarns crossing one another at crossing
points and joined at the crossing points and a layer comprising
thread wound in helix, a wet paper web side layer; and a shoe
side layer formed on a mandrel having a polished surface.
However, since compressed air indwells in press rolls wearing
the above shoe press belt, it is employed in the condition that
tensile force is loaded on the entire belt. The shoe press belt
runs in the MD direction with drive at a roll axis and said tensile
force increases at a position immediately before the press and
decreases at the press exit.
Therefore, as the tensile force on the warp yarns of the
lattice material varies before and after the press, the warp yarns
move back and forward while the weft yarns remain almost still,
and the warp yarns and the weft yarns rub against each other.
If the warp yarns and the weft yarns of the lattice material
are made of same material, the problems are that the strength
of the belt in the CMD direction be deteriorated or that the belt
is subject to dilatation in the CMD direction since the weft yarns
are more easily worn than the warp yarns.
Crossing points of the warp yarns and the weft yarns are
joined. However, joints are so simple that they easily come off
by running and inflection of the lattice material. It is,
therefore, inevitable that the friction occurs between the warp
yarns and the weft yarns.
Thus, it is the object of the invention to provide a belt
for a shoe press that overcomes the above problems.
The invention solved above problems by a shoe press belt to
be disposed between press rolls and a shoe of a shoe press
apparatus, comprising a base body consisting of a lattice
material made by joining the crossing points of warp yarns and
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weft yarns and a thread layer wound in a helix, a wet paper web
side layer and a shoe side layer formed on a mandrel having a
polished surface, characterized in that said warp yarns are so
formed as to wear earlier than said weft yarns.
In the invention, since the warp yarns of the lattice
material are more likely to be worn than the weft yarns, the weft
yarns do not wear off early as before. As a result, strength
and dimensional stability of the belt are improved.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional view of a part of a shoe press belt
of the invention.
Figure 2 shows a mandrel in a process of forming a shoe side
layer; Figure 2 (a) is a side view of a mandrel and a coating
apparatus and Figure 2(b) is a perspective view of a mandrel.
Figure 3 is a perspective view of a shoe press mechanism.
Figure 4 is an enlarged view of a feature. of a lattice
material.
Figure 5 is a perspective view showing the process of
positioning a lattice material on a mandrel.
Figure 6 is a perspective view showing the process of winding
a thread layer.
Figure 7 is a perspective view showing the process of joining
after forming a thread layer.
Figure 8 is a side view showing the process of separating
a shoe press belt from a mandrel.
Figure 9 is a schematic view of an apparatus used for
examining abrasion resistance.
Figure 10(a) is a sectional view showing a conventional
manufacturing process of a shoe press belt; and Figure 10 (b) is
a partial sectional view of a shoe press belt produced by the
conventional method.
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BEST MODES FOR CARRYING OUT THE INVENTION
An embodiment of the invention is explained referring to
Figures 1 to 7.
Figure 1 is a sectional view of a part of a belt 10 for shoe
press of the invention. Figure 2 shows a mandrel M in a process
of forming a shoe side layer; Figure 2(a) is a side view of a
mandrel M and a coating apparatus T and Figure 2(b) is a
perspective view of a mandrel M. Figure 3 is a perspective view
of a shoe press mechanism 100 applying the belt 10 for shoe press
of the invention. Figure 4 is a partial enlarged view of a lattice
material used for a base body. Figure 5 is a perspective view
showing the process of positioning a lattice material 40 as a
base body on the external surface of a shoe side layer 20 formed
on the surface of the mandrel M, Figure 6 is a perspective view
showing the process of winding a wound layer 50 and Figure 7 is
a perspective view showing the process of joining after winding
the wound layer 50.
As shown in Figure 1, the belt 10 for shoe press of the
invention comprises a shoe side layer 20, a base body 30 formed
on the external circumference of the shoe side layer 20 and a
wet paper web side layer 60 formed on the external circumference
of the base body 30.
The shoe side layer 20 is formed on the mandrel M having a
polished surface.
The base body 30 comprises a lattice material 40, composed
of warp yarns 40A and weft yarns 40B, joined at their crossing
points, and a wound layer 50 composed of a thread 50A wound in
a helix.
As shown in Figure 2(b), the shoe side layer 20 is formed
on the surface of the mandrel M. Preferably, the mandrel M is
pre-coated with a remover material (not shown) , or a removing
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sheet (not shown) is applied to the surface of the mandrel M.
Afterwards, as shown in Figure 2(a), the shoe side layer 20 is
formed to a thickness in the range from about 0. 5mm to 2.0mm by
using a coating apparatus (a doctor bar, a coater bar, or the
like.) T.
Polishing the surface of the mandrel M not only ensures
smoothness of the shoe side layer 20 of the shoe press belt running
constantly in close sliding contact with a shoe 104, but also
facilitates removal of the belt 10 for shoe press from the mandrel
M after the manufacturing process. The mandrel M may include
a heating apparatus (not shown) , which facilitates curing of the
resin including the shoe side layer 20.
Next, the base body 30 is formed on the external
circumference of the shoe side layer 20.
The base body 30 comprises a lattice material 40 which is
composed of warp yarns 40A and weft yarns 40B, joined at their
crossing points, and a wound layer composed of a thread 50A wound
in a helix toward the mandrel M.
As shown in Figure 4, the lattice material 40 is composed
of warp yarns 40A and weft yarns 40B, joined and latticed at their
crossing points. As for the lattice material 40, a material such
as disclosed in the Unexamined Japanese Patent Publication No.
194855/2002 may be used. The warp yarns 40A and the weft yarns
40B may be joined at their crossing points by adhesion or gluing
by resin, by thermal bonding, or by other means.
The warp yarns 40A of the lattice material 40 are made to
wear earlier than the weft yarns 40B. As for warp yarns 40A,
for example, various kinds of yarns such as twisted yarns or spun
yarns made of various kinds of materials including inorganic
f ibe r such as carbon f iber or f iberglas s, natural f iber such as
cotton; or synthetic fiber such as polyester cotton,
multi-filament of polyester, acryl cotton, multi-filament of
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acryl or the like may be used.
As for weft yarns 40B, for example, synthetic fiber having
high modulus and high elastic modulus such as nylon, PET, aromatic
polyamide, aromatic polyimide or high strength polyethylene;
twisted yarns of multi-filament of polyester; or spun yarns made
of polyester cotton may be used, though it is not limited to these.
It is preferable that the strength of the lattice of the
lattice material 40 is in the range of 50-250kg/cm and 1 o modulus
is in the range of 5-40kg/cm.
As shown in Figure 5, one or more lattice materials 40 are
positioned on the external circumference of the shoe side layer
placed on the mandrel M in such a way that the weft yarns 40B
are along the axial direction of the mandrel M.
In order to improve the strength of the belt, it is preferable
15 to position the lattice material 40 so that their edges of
widthwise direction overlap one another along the axial
direction of the mandrel M.
The lattice material 40 can also be positioned, for example,
in a way that it is wound in a helix towards the shoe side layer
20 20. Also in this case, it is preferable to position the lattice
material 40 so that both edges of widthwise direction overlap
one another.
By turning the mandrel M gradually before the shoe side layer
20 stiffens completely, the lattice material 40 is positioned
on the external circumference of the shoe side layer 20 so that
the weft yarns 40B are along the axial direction of the mandrel
M.
Next, the wound layer 50 is formed by winding a thread 50A
in helix onto the lattice material 40.
In figure 6, wound layer 50 is formed by winding a thread
SOA led out from a bobbin Bo installed in a thread supplier, which
is not shown, in a helix about the lattice material 40 with
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rotating the mandrel M. At this time, plural bobbins Bo may be
used for winding the thread 50A on the lattice material 40. The
thread supplier also comprises a mobile unit which moves parallel
to the axial direction of the mandrel M interlocking with
formation of the wound layer 50, which is composed of the thread
50A wound in a helix.
This wound layer 50 provides the belt 10 for shoe press
especially with strength in the machine direction.
For the material of thread 50A of the wound layer 50,
monofilament yarn, multifilament yarn or twisted yarn thereof
comprising synthetic fiber having high strength, high modulus
and high elastic modulus, such as nylon, PET, aromatic polyamide,
aromatic polyimide and high strength polyethylene etc. may be
used; however, it is not limited to these.
It is preferable that the thread 50A be wound in the range
from 10 pieces/5cm to 50 pieces/5cm when the thread 50A is
multifilament comprising nylon or PET (7000 dtex) ; and from 10
pieces/Scm to 30 pieces/5cm when the thread 50A is multifilament
comprising aromatic polyamide (3000 dtex). The strength of the
thread 50A preferably is in the range from 100kg/cm to 300kg/cm.
After forming the wound layer 50, as shown in Figure 7, the
base body 30 is joined by coating it with resin while rotating
the mandrel M so that resin covers the lattice material 40 and
the wound layer 50. The resin in this case preferably has a
viscosity which facilitates impregnation of the resin into gaps
between the lattice material 40 and the wound layer 50.
Described above is an example of the base body 30 formed by
positioning one layer of the lattice material 40 on the external
surface of the shoe side layer 20, and forming the wound layer
50 on the external surface thereof. However, it is needless to
say that how the lattice material 40 and the wound layer 50 are
arranged is not limited to above example. For example, following
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ways may be possible other than above example: (1) the wound layer
50 is formed first, and then the lattice material 40 is
positioned; (2) plural layers of the lattice material 40 are
positioned; (3) the wound layer 50 is formed first, and then,
after positioning the lattice material 40, the wound layer 50
is further formed; and (4) the lattice material 40 is positioned
first, and then after forming the wound layer 50, the wound layer
50 is further formed with positioning the lattice material 40.
When applying plural layers of the lattice material 40, it
is preferable to position the layers in a way that the sections
where the edges of widthwise direction overlap one another are
not positioned at the same region through the plural layers, in
order that unnecessary undulations do not occur on the base body
30.
Next, an endless wet paper web side layer 60 is further formed
on the external circumference of the wound layer 50.
Resin forming the wet paper web side layer 60 impregnates
through the base body 30 and connects and integrates with the
base body 30 side surface of the shoe side layer 20. The extent
of integration between the shoe side layer 20 and the wet paper
web side layer 60 may be improved using a primer or an adhesive
agent if necessary.
Polyurethane resin is preferable as the resin for the shoe
side layer 20 and the wet paper web side layer 60, and rubbers
or other elastomer can be used other than it.
As a polyurethane resin, considering its physical property,
thermosetting urethane resin is desirable, preferably having a
hardness in the range from 80 to 98 degree (JIS-A) . Needless
to say, the hardness of the shoe side layer 20 and the wet paper
web side layer 60 can either be the same or different.
After the wet paper web side layer 60 is formed by heat-curing
the resin, its surface is polished to achieve a predetermined
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thickness and, if necessary, grooves 70 are formed on the surface
of the wet paper web side layer 60.
After that, the belt 10 for shoe press is removed from the
mandrel M.
As described above, it is preferable that a remover (not
shown) or a removing sheet (not shown) etc. be applied to a
position between the surface of the mandrel M and the shoe press
belt 10, so that the belt 10 for shoe press can easily be removed
from the mandrel M.
As shown in Figure 8, one end of the belt 10 is fixed to a
ring R which has a larger diameter than that of the mandrel M
and which can be removed from the mandrel M. Removal of the belt
10 for shoe press from the mandrel M can be achieved easily by
above structure.
(EMBODIMENT)
Examples 1 to 3 and a comparative example 1 of a shoe press
belt of the invention according to the above structure were
produced in the following process.
(EXAMPLE 1)
PROCESS 1: An appropriate amount of a remover (KS-61:
Shin-Etsu Chemical Co., Ltd.) was applied onto the polished
surface of the rotatable mandrel having a diameter of 1S00mm,
using a driving means. Thermosetting urethane resin
(prepolymer: Takenate L2395 from Takeda Chemicals Co., Ltd.,
curing agent: 3, 31 -dichloro-4, 4'-Diaminodiphenylmethane) was
applied to the surface of the mandrel to a thickness of imm using
a doctor bar, and it was left for 10 minutes.
PROCESS 2: Spun yarns of 500 dtex comprising polyester cotton
of 6.7 dtex were applied as the warp of the lattice material and
twisted yarns of 500 dtex multifilament yarns of polyester (75
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filament) were used as the weft of the lattice material. A
lattice material made by sandwiching the warp yarns in the weft
yarns, and joining the crossing points of the weft yarns and the
warp yarns with a urethane type resin adhesive (the mesh (pitch)
of the warp is the same 1 piece/cm in all embodiments from example
1 to example 3 and a comparative example 1, and the mesh (pitch)
of the weft is the same 4 pieces/cm in all embodiments from example
1 to example 3 and a comparative example 1) was prepared. Plural
layers of the lattice material comprising plural sheets were
positioned on the external circumference of the shoe side layer
in such a way that the weft yarns extended axially along the
mandrel and that the edges in the widthwise direction overlapped
one another. After that, a wound layer was formed by winding
a 4500 dtex multifilament yarn of polyester (50 filaments) in
a helix with a pitch of 30 pieces/5cm onto the external
circumference of the lattice material. Then, the lattice
material and the wound layer were joined to form the base body
by coating resin to the extent that the gaps of the two were
covered.
PROCESS 3: The shoe press belt of the invention was obtained
by first impregnating and coating the same thermosetting
urethane resin as used for said shoe side layer onto the wound
layer to a thickness of 5.5mm, secondly curing it with heat at
100 degrees Celsius for 5 hours, and thirdly polishing the surface
of the wet paper web side layer until the overall thickness of
the wet paper web side layer was brought to 5.2mm.
(EXAMPLE 2)
In the process 2, spun yarns of 500 dtex comprising cotton
of 6.7 dtex were used as the warps of the lattice material. Spun
yarns of 500 dtex comprising polyester cotton of 6.7dtex were
used as the wefts of the lattice material. A lattice material
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was prepared by sandwiching the warp yarns in the weft yarns,
and joining the crossing points of the weft yarns and the warp
yarns with a urethane type resin adhesive.
(EXAMPLE 3)
In the process 2, twisted yarns of 500 dtex multifilament
yarn of polyester (75 filaments) were used as the warps of the
lattice material. Twisted yarns of 1000 dtex multif ilament yarn
of polyester (150 filaments) were used as the wefts of the lattice
material. A lattice material was prepared by sandwiching the
warp yarns in the weft yarns, and joining the crossing points
of the weft yarns and the warp yarns with a urethane type resin
adhesive.
(COMPARATIVE EXAMPLE 1)
In the process 2, twisted yarns of 1000dtex multifilament
yarn of polyester (150 filaments) were used as the warps of
lattice material. Twisted yarns of 1000dtex multifilament yarn
of polyester (150 filaments) were used as the wefts of the lattice
material. A lattice material was prepared by sandwiching the
warp yarns in the weft yarns, and joining the crossing points
of the weft yarns and the warp yarns with a urethane type resin
adhesive.
Abrasion resistance of the lattice material was examined
about above examples 1 to 3 and comparative example 1.
The apparatus employed to examine abrasion resistance is
shown in Figure 9. In this test apparatus, both edges of the
experimental piece 13 are pinched by clamp hands CH, CH, which
are interlocked with one another and reciprocally movable in the
same direction as the arrow A. An evaluation surface of the
experimental piece 13 faces the rotating roll RR1. The
experimental piece 13 is compressed by moving the press shoe PS
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toward the roll RR1.
With this apparatus, since strong inflection is applied to
the shoe side of the experimental piece 13, stress from the
inflection occurs at the crossing points of the weft yarns and
the warp yarns of the lattice material.
On the other hand, the lattice material and the thread layer
wound in a helix are on the rotating roll side of the experimental
piece 13, and stress from the inflection therein is not so much
high. By means of this apparatus, therefore, abrasion degree
at the crossing points of the warp yarns and the weft yarns of
the lattice material can be examined.
Using this apparatus, the test was continued until the number
of reciprocation reaches 500000 times, and by measuring breaking
strengths of the experimental piece 13 both in the warp direction
and the weft direction after the test, abrasion property of the
lattice material of the experiment piece 13 was observed.
In addition, the tensile force applied to the experimental
piece 13 was 3kg/cm, the pressure was 36kg/cm2 and the speed of
reciprocation was 40cm/second.
Breaking strengths of examples 1 to 3 and a comparative
example 1 and abrasion property of the lattice material are shown
in Table 1.
(TABLE 1)
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The breaking strength and the abrasion property of the
lattice material in Table 1 are the results of the measurement
of breaking strengths of the warp yarns and the weft yarns of
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the lattice material by digesting the belt of the invention after
the test in an organic solvent of dimethyl formamide, dissolving
polyurethane covering the lattice material, taking out the
lattice material which remains without being dissolved; and
measuring breaking strengths of the warp yarn and the weft yarns
of the lattice material and observing the condition of the
crossing points of the lattice material.
As shown in Table 1, for all embodiments of examples from
1 to 3 of the invention, it is found that abrasion resistance
of the weft yarns is superior in particular in comparison with
that of the comparative example.
It is understood that abrasion resistance of the weft yarns
is superior in all the embodiments is because the warp yarns
crossing the weft yarns are made by threads that have more
tendency to be worn, so that when friction occurs in the crossing
points of the weft yarns and the warp yarns along with the
experimental piece 13 under the experiment curves, the warp yarns
are torn prior to the weft yarns. As a result, damage to the
weft yarns was reduced. Therefore, since less abrasion occurs
to the weft yarns of the invention, breaking strength in the
latitudinal direction is held and dimensional stability is also
maintained.
In addition, spun yarns of polyester cotton are formed by
making and twisting a carding web using short fibers of polyester,
and in general, crimps (curl) are formed in the short fibers in
a manufacturing process thereof. Therefore, the spun yarns
obtained in such a way have a convexo-concave surface. On the
other hand, since the twisted yarns of multi-filament have smooth
surfaces, polyester cotton having a convexo-concave surface is
more likely to be worn than the twisted yarns of multi-filament.
The above are verified by example 1.
Cotton as a material has a greater tendency to be worn than
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polyester cotton. This can be drawn from example 2.
From example 3, it is found out that thinner thread is more
likely to be worn if the same materials are used.
As thus, in order to make the warp yarns have more tendency
to be worn, the forms of the fibers (including the thickness)
or the combination of the materials may be selected
appropriately.
In the invention, since the thread-wound layer of polyester
having high-strength is formed on the external circumference of
the lattice material, strength of the belt as a whole is not so
much reduced even though the warp yarns of the lattice material
are worn while using the belt. In other words, a thread 50A of
the wound layer has a strength of 100 to 300kg/cm, so that the
strength of the warp yarns of the belt can be kept sufficiently
by the wound layer.
INDUSTRIAL APPLICABILITY
As described above, the invention reduced the abrasion of
the weft yarns when the belt is in use, by applying the lattice
material comprising the warp yarns being more likely to be worn
than the weft yarns. As a result, the dimensional stability in
the CMD direction of the belt is improved and accordingly the
strength and the durability of the belt are also improved.
