Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
PRESS BELT
TECHNICAL FIELD
The present invention relates to a press belt used to press an object to
be pressed in a papermaking industry, a magnetic recording medium
manufacturing industry and a fiber industry, and more particularly, to a
press belt having superior fatigue strength.
BACKGROUND ART
Various kinds of industries adopt a belt press in which a band-shaped
press object put on a press belt is pressed between one press member
positioned inside the circumference of the press belt and the other press
member positioned outside the circumference of the press belt. The press
member includes a press roll and a press shoe, for example.
The belt press includes a shoe press as a dehydrating press in a
papermaking industry. The shoe press is disclosed in Japanese
Unexamined Patent Publication No. 11-124788 and Japanese Unexamined
Patent Publication No. 2005-207000, for example.
According to the shoe press, in order to dehydrate a wet paper web
efficiently, a press treatment (dehydrating treatment) is performed such
that a surface pressure is applied to a press object (wet paper web) set on
the outer circumference of a press belt, between a press roll as press means
positioned outside the circumference of the press belt and a press shoe as
internal press means positioned inside the circumference of the press belt.
When the press shoe having a predetermined width in a running direction
is used, a nip width can be largely provided, so that the dehydrating
efficiency can be improved.
The operation of the shoe press will be described in detail with
reference to Fig. 1. Fig. 1 is a running-direction sectional view showing a
shoe press machine used in a press process of a paper machine.
The shoe press machine comprises a press roll 1 as press means, a
press belt 2 opposed to the press roll 1, and a press shoe 3 as internal press
means positioned inside the circumference of the press belt 2. In addition,
although the press shoe 3 is covered with the press belt 2 and the press belt
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2 is rolled in the form of an outer cylinder as a shoe press roll in the
machine shown in Fig. 1, the press roll is not necessarily rolled and it may
be used as an endless belt.
A wet paper web 5 as a press object is put on a felt 4 and passed
through the space between the press belt 2 and the press roll 1. The outer
circumferential surface of the press belt 2 is directly in contact with the
felt
4. Since lubricant oil is supplied between the press belt 2 and the press
shoe 3, the press belt 2 can slide on the press shoe 3. The press roll 1 is a
driving roll and the press belt 2 is driven by friction force with the running
felt 4 and slides on the press shoe 3.
The press shoe 3 is pressed from the inside of the circumference of the
press belt 2 toward the press roll 1, and the wet paper web is pressed by this
pressing force to be dehydrated. The surface of the press shoe 3 is dented
so as to correspond to the surface of the press roll 1. Therefore, a nip area
having a large width is formed along a belt running direction (MD : Machine
direction) between the press roll 1 and the press belt 2. This nip area
functions as a press part for dehydrating.
The press belt 2 is formed of an elastic material such as a resin and a
rubber and contains a reinforcement base material composed of a
multiply-woven cloth in general. As shown in Fig. 1, since the press belt 2
is dented inwardly at the nip area in the belt running direction during the
operation, bending stress and compressive stress are applied at the same
time to the nip area of the press belt constantly.
Fig. 2 is a schematic sectional view showing the shoe press machine in
a direction across the belt running direction (CD : cross direction). As
shown in Fig. 2, both ends of the press belt 4 in the width direction are
mounted on an engagement disk 6. The height of the press shoe 3 is lower
than that of the engagement disk 6 at the nip area in the CD. Therefore,
bending force in the CD is applied to both ends of the press belt 4 at the nip
area repeatedly in addition to the above bending stress and the compressive
stress.
Focusing on the reinforcement base material comprising the
multiply-woven cloth buried in the press belt 4, at the MD nip area, among
yarns extending along the belt running direction (MD), the yarn positioned
on the outermost surface is likely to be fatigued. In addition, at the CD nip
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area end, among yarns extending in the direction (CD) across the belt
running direction, the yarn positioned on the outermost surface is likely to
be fatigued.
As the yarn constituting the multiply-woven cloth, a monofilament
(monofilament yarn) formed of polyester is used in some cases. Although
this polyester monofilament is superior in dimensional stability, it is
vulnerable to repetitive compression. Therefore, when the polyester
monofilament is used on the outermost surface of reinforcement base
material of the multiply-woven cloth, a fatigue phenomenon is likely to
appear at the nip area in a comparatively short time.
When the reinforcement base material comprising the multiply-woven
cloth buried in the elastic material of the press belt is fatigued and
partially
broken, a crack is generated in the elastic material part positioned close to
the broken part. In addition, the fatigue of the reinforcement base
material affects the running property of the press belt and causes the press
belt to be twisted, which could generate the crack.
The crack generated in the press belt could spread in MD and CD of
the press belt due to repetitive bending stress, compressive stress and
bending curvature applied to the nip area, which could cause lubricant oil to
leak.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a press belt having
superior fatigue strength.
A press belt according to the present invention comprises a
reinforcement base material made of a multiply-woven cloth and buried in
an elastic material. The reinforcement base material comprises a first
yarn group extending along a belt running direction and a second yarn
group extending across the first yarn group. The first yarn group includes
a twisted yarn positioned on the outermost side of the belt and a
monofilament yarn positioned on the inner side of the belt. The second
yarn group includes a twisted yarn positioned on the outermost side of the
belt and a monofilament yarn positioned on the inner side of the belt.
The twisted yarn is flexible and shows superior tolerance against
bending stress and compressive stress. Therefore, when the twisted yarn
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is used for the yarn positioned on the outermost surface in the yarn groups
extending in the MD and CD, the reinforcement base material shows
superior tolerance against bending stress and compressive stress applied to
the nip area.
The monofilament yarn has high shape fixity. Especially, when the
monofilament yarn is used for the yarns extending in both MD and CD, the
nodal part at their intersection can be high in strength, so that the
reinforcement base material can be prevented from being twisted.
According to the above constitution of the present invention, since the
MD twisted yarn (extending in the MD) and the CD twisted yarn (extending
in the CD) positioned on the outermost side enhance the fatigue strength of
the reinforcement base material, and the MD monofilament yarn and the
CD monofilament yarn positioned on the inner side stabilize the shape of
the reinforcement base material, the press belt has superior fatigue
strength and a long life.
According to one embodiment, at least one of the first and second yarn
groups includes a multifilament between the twisted yarn and the
monofilament yarn. In this case, preferably, the multifilament is
impregnated with a sizing agent. Thus, when the reinforcement base
material containing the multifilament impregnated with the sizing agent is
used, a pinhole is prevented from being generated and the press belt is
superior in appearance and crack resistance.
In addition, according to one embodiment, a drainage groove
extending along the belt running direction is formed in the outermost
surface of the elastic material. The press belt is a shoe press belt, for
example.
As described above, according to the present invention, the press belt
has superior fatigue strength.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a view showing a running-direction section of a shoe press
machine used in a press process of a paper machine;
Fig. 2 is a view showing a width-direction section of the shoe press
machine,'
Fig. 3 is a schematic sectional view showing a reinforcement base
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material according to an embodiment of the present invention;
Fig. 4 is a schematic sectional view showing one example of a press
belt according to the embodiment of the present invention; and
Fig. 5 is a schematic sectional view showing a reinforcement base
material according to another embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The inventor of this application has evaluated the fatigue state, crack
progress and running performance of a press belt and found the following
things.
(1) When a reinforcement base material is a multiply-woven cloth
composed of all monofilament yarns, a MD monofilament yarn and a CD
monofilament yarn positioned on the side of an outermost surface are
fibrillated and likely to be crushed due to repetitive bending stress and
compression stress at a nip area.
(2) When a reinforcement base material is a multiply-woven cloth
composed of all twisted yarns, shape fixity is low and the press belt is
twisted and tilted at the time of running.
(3) When the MD yarn and the CD yarn positioned on the outermost side
of the reinforcement base material of the press belt are composed of the
twisted yarns, they are not fibrillated over a long period of time and
superior in fatigue strength and in addition, when the MD yarn and the CD
yarn positioned on the inner side of the reinforcement base material of the
press belt are composed of the monofilament yarns, the strength of a nodal
part between the MD monofilament yarn and the CD monofilament yarn is
increased and shape fixity is superior.
One embodiment of the present invention will be described with
reference to the drawings hereinafter.
Fig. 3 is a scheniatic view illustrating a reinforcement base material
made of a multiply-woven cloth, and Fig. 4 is a sectional view schematically
showing a press belt. The press belt according to this embodiment of the
present invention is used to press an object to be pressed in a paper
industry,
magnetic recording medium manufacturing industry, fiber industry and the
like, and its size is 2 to 15m in width, 1 to 30m in circumferential length,
and 2 to 10mm in thickness. In addition, the press belt is typically a shoe
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press belt.
As shown in Figs. 3 and 4, the press belt comprises an elastic material
20 and a reinforcement base material 10 buried in the elastic material 20.
The reinforcement base material 10 is a multiply-woven cloth including a
first yarn group 11, 12 and 13 extending along a belt running direction (MD)
and a second yarn group 14 and 15 extending across the first yarn group
(CD).
Preferably, an organic fiber is used as the material of the
reinforcement base material 10. As the press belt is required to be flexible,
when an inorganic fiber such as a glass fiber is used as the material of the
reinforcement base material, for example, the press belt is too hard to cause
a defect such as a crack. In this respect, as the material of the
reinforcement base material 10, an organic fiber such as a polyamide fiber,
aromatic polyamide fiber, polyester fiber, nylon fiber, and polyvinyl alcohol
fiber is preferably used. Especially, the reinforcement base material is
preferably formed of the polyester fiber in view of superior dimensional
stability.
Focusing on the specific structure of the reinforcement base material
10 made of the multiply-woven cloth, among the first yarn group extending
along the belt running direction, the yarn 11 positioned on the outermost
side of the belt is a twisted yarn (MD twisted yarn), and the yarns 12 and 13
positioned on the inner side of the belt are monofilament yarns (MD
monofilament yarns). Among the second yarn group extending along the
direction across the first yarn group 11, 12 and 13, the yarn 14 positioned on
the outermost side of the belt is a twisted yarn (CD twisted yarn) and the
yarn 15 positioned on the inner side of the belt is a monofilament yarn (CD
monofilament yarn).
As the elastic material 20, thermosetting polyurethane is used, for
example. The elastic material 20 comprises a back surface layer 20a
formed from the back side of the reinforcement base material 10, and a front
surface layer 20b formed from the front side of the reinforcement base
material 10. Many drainage grooves 21 extending along the belt running
direction are formed in the outermost surface of the elastic material 20.
Since these drainage grooves are not essential, they can be omitted.
The twisted yarn is flexible and strong and shows preferable fatigue
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strength against bending as compared with the monofilament yarn.
Meanwhile, since the monofilament yarn is harder than the twisted yarn,
and the strength at the nodal part of the monofilament yarn is high, the
reinforcement base material is prevented from being twisted there.
According to the embodiment of the present invention, among the yarn
groups constituting the reinforcement base material 10, the MD twisted
yarn 11 and the CD twisted yarn 14 positioned on the outermost side of the
belt show preferable tolerance against repetitive bending stress and
compressive stress at the nip area. Meanwhile, since the MD
monofilament yarns 12 and 13 and the CD monofilament yarn 15 on the
inner side of the belt enhance the strength at the nodal part, the
reinforcement base material is prevented from being twisted and the press
belt is prevented from being twisted at the time of running.
In the case of the polyester fiber, the twisted yarn is formed by
twisting two or three multifilaments each having a 200d to 1500d diameter.
In addition, the monofilament yarn has a 0.3 to 1.0mm diameter.
Fig. 5 is a schematic view showing a reinforcement base material 30 of
a press belt according to another embodiment of the present invention.
The reinforcement base material 30 is made of a multiply-woven cloth. A
first yarn group extending in a belt running direction includes a MD twisted
yarn 31 positioned on the outermost side, a MD monofilament yarn 32
positioned on the inner side, a MD multifilament 33 positioned on further
inner side, and a MD monofilament yarn 34 positioned on the innermost
side. A second yarn group extending across the first yarn group includes a
CD twisted yarn 35 positioned on the outermost side and a CD
monofilament yarn 36 positioned on the innermost side.
The MD multifilament 33 is not twisted. In addition, the
multifilament 33 is impregnated with a sizing agent. The sizing agent
enters between filaments constituting the multifilament to remove the air
in the multifilament. Therefore, when the press belt contains the
multifilament 33 impregnated with the sizing agent, since air bubble is
prevented from being generated, a pinhole is prevented from being
generated.
When the thermosetting polyurethane is used as the elastic material
of the press belt, it is preferable that the sizing agent contains an urethane
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resin or an epoxy resin as a main component in view of the adhesiveness to
the elastic material.
As described above, the elastic material typically comprises the back
surface layer formed from the back surface of the reinforcement base
material and the front surface layer formed from the front surface of the
reinforcement base material. In this case, since the multifilament 33
impregnated with the sizing agent prevents the resin from penetrating, it is
positioned at the boundary between the front surface layer and the back
surface layer.
Working Example 1
Six kinds of samples were prepared as the reinforcement base
material made of the multiply-woven cloth. The constitutions of the six
kinds of samples are shown in table 1.
[Table 1]
Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6
PET PET PET PET PET PET
MD1 monofilament monofilament twisted twisted twisted twisted
yarn yarn yarn yarn yarn yarn
PET PET PET PET PET PET
MD2 monofilament monofilament monofilament monofilament twisted twisted
yarn yarn yarn yarn yarn yarn
MD3 monofiEment Nylon Nylon Nylon twE ted Nylon
yarn yarn yarn yarn yarn yarn
PET PET PET PET PET PET
CD1 monofilament monofilament monofilament twisted twisted twisted
yarn yarn yarn yarn yarn yarn
PET PET PET PET PET PET
CD2 monofilament monofilament monofilament monofilament twisted monofilament
yarn yarn yarn yarn yarn yarn
* Resin stopper yarn is arranged between MD2 and MD3
In the table 1, reference "MD" designates a yarn extending in a belt
running direction and reference "CD" designates a yarn extending across
the belt running direction. In addition, MD1 and CD 1 designate yarns
positioned on the outermost side of the press belt, MD2 and CD2 designate
yarns positioned on the inner side, and MD3 designates a yarn positioned
on the innermost side of the press belt. In addition, in all of the samples, a
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multifilament as a resin stopper was arranged between the MD2 and MD3.
According to the reinforcement base material of a sample 1, all yarns
are monofilament yarns formed of polyester. According to the
reinforcement base material of a sample 2, a MD yarn (MD3) positioned on
the innermost side is a monofilament yarn formed of nylon and the others
are monofilament yarns formed of polyester. According to the
reinforcement base material of a sample 3, a MD yarn (MD1) positioned
outermost side is a twisted yarn formed of polyester, a MD yarn (MD3)
positioned innermost side is a monofilament yarn formed of nylon, and the
others are monofilament yarns formed of polyester. According to the
reinforcement base material of a sample 4 provided in the working example
of the present invention, a MD yarn (MD 1) positioned on the outermost side
is a twisted yarn formed of polyester, a CD yarn (CD1) positioned on the
outermost side is a twisted yarn formed of polyester, a MD yarn (MD3)
positioned innermost side is a monofilament yarn formed of nylon, and the
others are monofilament yarns formed of polyester. According to the
reinforcement base material of a sample 5, all yarns are twisted yarns
formed of polyester. According to the reinforcement base material of a
sample 6 provided in the working example of the present invention, a MD
yarn (MD1) positioned on the outermost surface and a MD yarn (MD2)
positioned on the inner side are twisted yarns formed of polyester, a MD
yarn (MD3) positioned on the innermost side is a monofilament yarn formed
of nylon, a CD yarn (CDl) positioned on the outermost side is a twisted yarn
formed of polyester, and a CD yarn (CD2) positioned on the innermost side
is a monofilament yarn formed of polyester.
Each reinforcement base material shown in the table 1 was buried in
a thermosetting polyurethane elastic material to produce an elastic band
and this elastic band was mounted on a roll having a diameter of 350mm
and a fatigue test was performed. More specifically, a pressure of 50kg/cm2
was applied to the elastic band mounted on the rotatable roll by a metal roll
rotating at a speed of 200m/min and this was continued for seven days.
After the above operation, the elastic material of the elastic band was
melted with a dimethylformamide solvent, and the reinforcement base
material was taken out and deterioration state of the MD yarn and the CD
yarn were checked with eyes. The result is shown in table 2.
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[Table 2]
Fatigue analysis
Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6
MD1 NG NG OK OK OK OK
MD2 OK OK OK OK OK OK
MD3 NG OK OK OK OK OK
CD1 NG NG NG OK OK OK
CD2 OK OK OK OK OK OK
NG: Crushed OK: Not changed
In the table 2, "NG " means that the yarn is fibrillated and crushed,
and "OK" means that the yarn remains unchanged (there is no particular
deterioration).
According to the samples 1 and 2 in which all yarns are the
monofilament yarns, the MD 1 and the CD1 on the outermost side are
fibrillated. According to the sample 3 in which the MD1 is the twisted
yarn and the others are the monofilament yarns, only the CD1 is fibrillated
and crushed.
According to the sample 4 in which the MD 1 and the CD 1 are the
twisted yarns and the others are the monofilament yarns, and according to
the sample 6 in which the MDl and MD2 and CDl are the twisted yarns
and the remaining yarns are monofilament yarns, there is no fibrillated
yarn. In addition, according to the sample 5 in which all yarns are the
twisted yarns, there is no fibrillated yarn.
The crack progress of the elastic band in which each of the samples 1
to 6 was buried was evaluated with the use of a de Mattia machine defined
by JIS K6260 under the following condition. In addition, the crack
progress in the MD and the crack progress in the CD were evaluated with
different test specimens. The test specimen was 20mm in width and
150mm in length. The distance of the reciprocating motion was 42.0mm.
A cut having a length of 5mm and a depth of 1.7mm was made at one end in
a width direction in the center in a length direction in an outer surface of
the test specimen.
After the test specimen was bent 1000 times under the above condition,
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the size of the crack was measured. The result is shown in table 3 as a
crack progress length.
[Table 31
Crack progress
MD direction CD direction Determination
Sample 1 0.5mm lmm NG NG
Sample 2 0.5mm lmm NG NG
Sample 3 0.5mm 0.lmm NG OK
Sample 4 0.05mm 0.lmm OK OK
Sample 5 0.05mm 0.lmm OK OK
Sample 6 0.05mm 0.1mm OK OK
As can be seen from the table 3, according to the elastic band having
the buried samples 1 and 2, a crack was progressed in both MD and CD.
According to the elastic band having the buried sample 3 in which the MD1
is the twisted yarn, there is no crack progress in CD but a crack was
progressed in MD. According to the elastic band having the buried
samples 4 and 5 in which the MDl and the CD1 are the twisted yarns, there
is no crack progress in both MD and CD. According to the elastic band
having the buried sample 6 in which the MDl, the MD2 and the CDl are
the twisted yarns, there is no crack progress in both MD and CD.
Next, each sample was cut to be a rectangle of 10cm x 30cm in order to
check the bending rigidity of the reinforcement base materials of the
samples 1 to 6. The sample was set up vertically with the longitudinal one
end of the rectangular sample held by a hand. The shape fixity of each
sample was evaluated depending on whether it could be set up vertically or
not. The result is shown in table 4.
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[Table 4]
Shape fixity
Determination
Sample 1 OK
Sample 2 OK
Sample 3 OK
Sample 4 OK
Sample 5 NG
Sample 6 OK
As can be seen from the table 4, it has been confirmed that the sample
in which all the yarns are the twisted yarns is not set up vertically and its
5 shape fixity is low. According to the samples 1 to 4 containing the MD
mono~ilament yarn and the CD monofilament yarn, it has been confirmed
that all of them can be set up vertically and their shape fixity is high.
Although the embodiments of the present invention have been
described with reference to the drawings in the above, the present invention
is not limited to the above-illustrated embodiments. Various kinds of
modifications and variations may be added to the illustrated embodiments
within the same or equal scope of the present invention.
INDUSTRIAL APPLICABILITY
The present invention can be advantageously used as a press belt
having superior fatigue strength and high shape fixity.
} 9,
