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 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 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 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 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 schematic 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 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 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 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 |
| MD1 | PET monofilament yarn | PET monofilament yarn | PET twisted yarn | PET twisted yarn | PET twisted yarn | PET twisted yarn |
| MD2 | PET monofilament yarn | PET monofilament yarn | PET monofilament yarn | PET monofilament yarn | PET twisted yarn | PET twisted yarn |
| MD3 | PET monofilament yarn | Nylon yarn | Nylon yarn | Nylon yarn | PET twisted yarn | Nylon yarn |
| CD1 | PET monofilament yarn | PET monofilament yarn | PET monofilament yarn | PET twisted yarn | PET twisted yarn | PET twisted yarn |
| CD2 | PET monofilament yarn | PET monofilament yarn | PET monofilament yarn | PET monofilament yarn | PET twisted yarn | PET monofilament 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 CD1 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 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 (MD1) 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 (CD1) 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/cm
2 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.
[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 MD1 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 MD1 and the CD1 are the twisted yarns and the others are the monofilament yarns, and according to the sample 6 in which the MD1 and MD2 and CD1 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, the size of the crack was measured. The result is shown in table 3 as a crack progress length.
[Table 3] | Crack progress |
| | MD direction | CD direction | Determination |
| Sample |
| 1 | 0.5mm | 1mm | NG NG |
| Sample |
| 2 | 0.5mm | 1mm | NG NG |
| Sample |
| 3 | 0.5mm | 0.1mm | NG OK |
| Sample |
| 4 | 0.05mm | 0.1mm | OK OK |
| Sample |
| 5 | 0.05mm | 0.1mm | 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 MD1 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 MD1, the MD2 and the CD1 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.
[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 5 in which all the yarns are the twisted yarns is not set up vertically and its shape fixity is low. According to the samples 1 to 4 containing the MD monofilament 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.
