The present invention relates to a shoe press belt used for improving the capability of water squeezing from a wet paper web, and a felt in the press part of a papermaking machine or another similar machine and in particular relates to the groove shape provided along the felt side surface of the shoe press belt.
In papermaking, in order to improve productivity, it is a major issue how to increase the dewatering amount from the wet paper web in the press part in which moisture from the wet paper web is removed. As means for increasing the dewatering amount during pressing in order to achieve the object of reducing the moisture in the wet paper web as much as possible, methods such as increasing the pressure applied by the press rolls, increasing the hardness of the press rolls, or extending the time during which the pressure is applied by interposing a shoe press belt and the like are adopted; in recent years, in order to improve the dewatering effect by extending the time during which pressure is applied between the rolls and the felt in the course of pressing, a method in which a shoe press belt is interposed has increasingly come into use.
Moreover, recently examples have increased in which a plurality of grooves is provided along the felt side surface of the shoe press belt in order to efficiently drain the squeezed water. For example, according to Patent document 1, the water squeezing capability of the wet paper web is improved by providing a plurality of water drain grooves in the external peripheral surface of a belt used in a wide-width nip press (the so-called shoe press).
Most grooves in the prior art have a rectangular shape for reasons of productivity, cost and because they can be easily manufactured, but grooves with a curved groove bottom (Patent documents 2 and 3) and grooves with a concave curved top surface at the land part (Patent document 4) have also been proposed. Specifically, Patent document 2 provides a belt with good strength durability and good dewatering capability (water squeezing capability) of the shoe press by forming the groove section in the shape of the letter U, wherein the end parts of the land part of the water drain grooves are chamfered, the groove width is 0.5 to 4 mm, the depth is 0.5 to 5 mm and the space between adjacent water drain grooves is 1 to 4 mm. In Patent document 3, besides the curved groove bottom, the side walls of the grooves also curve towards the outside. The press jacket (press belt) according to Patent document 4 has a plurality of webs (land parts) at its external surface, grooves are interposed between these webs, and each web has a concave curved top surface. Patent document 5, moreover, shows a shoe press belt having a plurality of grooves that are substantially discontinued in the machine direction.
The groove shapes of the shoe press belts in the above-mentioned Patent documents have all been fixed at a single shape (groove width, groove depth, land part width, groove number); and the present situation is that, in view of cracks occurring in the internal groove part, damage, wear, transfer marks of the land part, water squeezing capability and the like, a satisfactory shoe press belt cannot necessarily be obtained.
The present inventors, having extensively studied the technology in the present field, confronted a situation in which, when a belt with a single shape in which the void volume has been increased is used, there is the tendency that cracks in the internal groove part and damage and wear of the land part easily occur and that the paper quality and the smoothness of the wet paper web surface degrade as a result of the pressing (there is an increase in the rate of transfer marks of the groove shape appearing in the wet paper web), and if, on the other hand, the groove width and the groove depth are reduced, the water squeezing capability is deteriorated, which results in an increase of the energy consumption for drying the wet paper after pressing.
In consideration of the above-mentioned problems, it is the object of the present invention to provide a belt (a shoe press belt) for a paper manufacturing machine which has good capability of water squeezing from wet paper web and wherein damage (cracks and wear) of the external peripheral belt surface during use is small.
The present inventors have discovered that the above problems can be solved by providing the water drain grooves in the above-mentioned shoe press belt as discontinuous grooves wherein the groove width and/or groove depth continuously change(s) in the same groove, and have completed the present invention.
The present invention basically relates to a shoe press belt for making paper having water drain grooves with a groove shape wherein the groove width and/or the groove depth change(s) continuously in the running direction (MD direction) and is based on the technologies described hereinafter.
(1) A shoe press belt for making paper carrying a felt which absorbs the water squeezed from the wet paper web, wherein said shoe press belt for making paper has water drain grooves in the surface of the felt side extending in the machine running direction (MD direction) and wherein said grooves are discontinuous grooves with a groove shape wherein the groove width and/or groove depth change(s) continuously.
(2) A shoe press belt for making paper according to (1), wherein the groove width at the central part of the discontinuous grooves is wider than the groove width of at least one of the running direction (MD direction) end parts.
(3) A shoe press belt for making paper according to (1), wherein the groove width at the central part of the discontinuous grooves is narrower than the groove width of at least one of the running direction (MD direction) end parts.
(4) A shoe press belt for making paper according to (1) or (2), wherein the groove shape is tapered towards both end parts of the discontinuous grooves.
(5) A shoe press belt for making paper according to any one of (1) to (4), wherein the groove shape of the discontinuous grooves is left/right unsymmetrical along the MD direction as axis.
(6) A shoe press belt for making paper according to any one of (1) to (4), wherein the groove shape of the discontinuous grooves is left/right symmetrical along the MD direction as axis.
(7) A shoe press belt for making paper according to any one of (1) to (6), wherein the groove depth at one end part of the discontinuous grooves is greater than the groove depth at the other end part.
(8) A shoe press belt for making paper according to any one of (1) to (6), wherein the groove depth at the central part of the discontinuous grooves is greater than the groove depth of at least one end part.
(9) A shoe press belt for making paper according to any one of (1) to (8), wherein the groove length of the discontinuous grooves is shorter than the width of the press shoe.
(10) A shoe press belt for making paper according to any one of (1) to (8), wherein the groove length of the discontinuous grooves is equal to the width of the press shoe or in a range of up to two times the width of the press shoe.
In the present specification, the term discontinuous grooves signifies water drain grooves wherein land parts where grooves are not formed and groove bottom parts where grooves are formed are alternately arranged in the MD direction. Moreover, in the present specification, the term central part of the discontinuous grooves signifies the central part of said groove bottom part in the MD direction, the term end part of the discontinuous grooves signifies the end parts in the MD direction of the same groove bottom part, and the term groove length of the discontinuous grooves signifies the groove length in the MD direction of the groove bottom part. Furthermore, in the present specification, in the case of one end part of the discontinuous grooves and the other end part of the discontinuous grooves as well as in the case of both end parts, respectively, the term end part(s) signifies the end part(s) in the same groove bottom part of the discontinuous grooves.
According to the present invention, it is possible to prevent the reverse flow of water at the nip entrance by configuring the water drain grooves as discontinuous grooves in the above-mentioned shoe press belt, the water is received below the nip and can be forcibly ejected by the action of the pressure at the exit, therefore, backwater does not occur in the low speed region and normal dewatering is possible during pressing.
Moreover, by configuring the same groove so that the groove width and groove depth are bigger at the central part than at the end parts, water enters the groove under the nip more easily and the water in the groove is drained more easily at the nip exit, therefore, it is possible to obtain advantageous water squeezing capabilities and to provide a shoe press belt for making paper wherein the water drainage is improved and, at the same time, the paper quality and surface smoothness of the wet paper web are also improved.
The embodiments of the present invention will now be explained with reference to the figures.
Firstly, an endless substrate 2 is placed around two rolls 3, 3 and stretched with a prescribed force. This roll 3 can rotate and the substrate 2 travels in the direction of rotation of the roll 3. Under such conditions liquid polyurethane is applied from above the substrate 2, which hardens and forms a polyurethane layer 4 over the entire periphery of the substrate 2. Then, a groove cutting device 6 is used to form discontinuous water drain grooves 7 on the external peripheral surface 5 of the substrate 2 on which the polyurethane layer 4 has been provided.
As shown in
In the embossing, as shown in the schematic diagram of
Regarding the groove shapes of the present invention, to start with, examples of the first embodiment are shown in
When the discontinuous groove passes the press nip, the elastic resin layer of the press belt is compressed and deformed so that the groove width becomes narrower. The further away from the land part, the bigger the degree of this deformation; therefore, the whole of the discontinuous groove is deformed so that the central part becomes narrower. Consequently, in order to maintain the water holding capacity of the groove, the width of the central part of the discontinuous groove, where the amount of deformation is big, is made bigger than the width of at least one of the MD direction end parts. Since the deformation force acting on the groove is left/right identical, the groove shape is preferably left/right symmetrical.
Furthermore, the groove shapes of
Examples of the second embodiment of the groove shapes according to the present invention are shown in
In a discontinuous groove having an MD direction groove length shorter than the width of the press shoe, the greatest force is obtained at the press center (the greatest force occurs in a water volume retained in a closed groove); therefore, in order to reduce the flow resistance at the press exit and to eject the retained water easily, the width of the central part of the discontinuous grooves is made narrower than the width of at least one of the MD direction end parts. At the press exit, it is preferred that the MD direction end part that opens first is wider than the central part of the discontinuous groove.
In the examples of the third embodiment of the groove shapes according to the present invention shown in
When the discontinuous groove passes the press nip, the elastic resin layer of the press belt is compressed and deformed so that the groove becomes shallower. The further away from the land part, the bigger the degree of this deformation; therefore, the central part of the discontinuous groove section is most deformed. Consequently, in order to maintain the water holding capacity of the groove, the central part of the discontinuous groove, where the deformation is big, is made deeper than at least one of the MD direction end parts. And since the deformation force acting on the groove is identical in front-back, the groove shape is preferably symmetrical in front-back.
Moreover, in order to reduce the flow resistance at the press exit and easily eject the retained water, the front end part in the MD direction is preferably deeper than the central part of the discontinuous groove, or it is curved at an inclination.
Groove dimensions in the following ranges can be adopted: groove width=0.5 to 2 mm, groove depth=0.5 to 2 mm and the space of the land part between adjacent water drain grooves=1 to 5 mm; with configurations in these ranges, the distance (clearance) between the external peripheral surface 5 of the belt and the groove cutting device 6 (embossing blades 8) is suitably adjusted.
As mentioned above, the MD direction groove length of the discontinuous grooves according to the present invention is preferably shorter than the width of the press shoe (the MD direction length of the shoe) because the greatest force, which is very strong, occurs due to a water volume retained in a closed groove. Shoe presses for the press part of a papermaking machine come in many different widths; however, most are in the range of about 50 to 400 mm; therefore, the MD direction groove length of the discontinuous grooves according to the present invention is set, shorter than the press shoe width, within the range of 40 to 390 mm; while the width of long discontinuous grooves equal to the width of the press shoe or in a range of up to two times the width of the press shoe can be set in the range of 50 to 800 mm.
By chamfering the end parts of the land part where no grooves are formed, damage and broken edges of the end parts are avoided.
By suitably adjusting the distance between the external peripheral surface of the belt and the cutting blades, it is possible to form continuous or discontinuous grooves in the MD direction. In the case of discontinuous grooves, it is possible to mechanically pull and push the embossing blades by the pulling and pushing action, and the like, at a fixed time interval with a thickness adjusting motor. It is also possible to rotate fixed blades in an elliptical orbit.
Moreover, in the case of a discontinuous groove, an embodiment of a tapered shape is preferred in which the depth inside the groove changes continuously in the MD direction and the thickness of the border part thereof is gradually reduced.
The performance of the shoe press belts produced was evaluated by the tests hereinafter, and the overall evaluation was performed by attributing a ranking.
The device shown in
Evaluation score A: 260,000 times or more, Evaluation score B: in the range between 120,000 and 260,000 times,
Evaluation score C: 120,000 times or less.
The water squeezing test of wet paper web was performed by using the device shown in
Evaluation score A: 45% or less,
Evaluation score B: in the range between 45% and 53%,
Evaluation score C: 53% or more.
Regarding the test results, the overall evaluation was performed based on the respective evaluation scores of the above tests, and the ranking was attributed as follows:
All evaluation scores were A: Ranking 1
One evaluation score was A and the others were B: Ranking 2
All evaluation scores were B: Ranking 3
One of the evaluation scores was C: Ranking 4
Regarding the shoe press belts of the above-mentioned constitution, specifically, the shoe press belts of Examples 1 to 9 and the Comparative Example 1 were produced by the processes described hereinafter.
Moreover, the groove shapes were adjusted in the ranges given hereinafter.
In order to form the grooves in the external peripheral surface of the belt, the distance between the external peripheral surface 5 of the belt and the embossing blades 8 was suitably adjusted during operation so as to form discontinuous grooves in the MD direction.
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
Embossing blades for embossing are installed so as to form the groove shape of
The groove shape in this Example is identical to the one in Example 7; in Example 8, the length of the discontinuous grooves in the MD direction is adjusted to 50 mm, which is identical to the press shoe width (50 mm) of the present test device.
The groove shape in this Example is identical to the one in Example 7; in Example 9, the length of the discontinuous grooves in the MD direction is adjusted to 80 mm, which is longer than the press shoe width (50 mm) of the present test device.
Embossing blades for embossing are installed so as to form a general rectangular groove shape. These blades are configured so that the central part of the grooves and both end parts in the MD direction have a fixed width. By machining with these blades, the groove shape at both end parts in the MD direction becomes rectangular. This is used for Comparative Example 1, the groove shape of which is shown in the three-dimensional view of
Regarding the shoe press belts relating to Examples 1 to 9 and Comparative Example 1, crack tests and water squeezing tests were performed and the performance was evaluated. The results thereof are shown in Table 1.
According to the results of Table 1, good evaluations were obtained in two evaluation tests with the groove shapes of Example 2 and Example 7, which are the groove shapes with the best balance.
Moreover, in Examples 8 and 9, in which the length of the discontinuous grooves in the MD direction was, respectively, identical and longer than the width of the press shoe, the evaluation of the water squeezing tests showed results inferior to those of the comparable Example 7; however, the ranking was by no means inferior.
The shoe press belt according to the present invention is most useful for improving the water squeezing capability of a wet paper web and a felt in the press part of a papermaking machine or another similar machine because it can improve the water drainage and, at the same time, improve the paper quality and the surface smoothness of the wet paper web.
Number | Date | Country | Kind |
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2007-062154 | Mar 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP08/54457 | 3/12/2008 | WO | 00 | 9/11/2009 |