Polyurethane shoe press belt

Abstract

A shoe press belt includes a body defining an endless loop and having an inner layer, a reinforcing yarn layer, and an outer layer. The inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material includes: poly-1,4-phenylene diisocyanate (PPDI) prepolymer; polycaprolactone diol; and an alkyl-diol chain extender.

Description

Attorney Docket No. 5690.234.WOPOLYURETHANE SHOE PRESS BELTRelated Application

[0001] The present application claims priority from and the benefit of U.S. Provisional Patent Application No. 63 / 692,858, filed September 10, 2024, the disclosure of which is hereby incorporated herein by reference in full.Field of the Invention

[0002] The present invention relates generally to industrial belts, and more particularly to belts for shoe presses for papermaking machines.Background of the Invention

[0003] In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper "stock") is fed onto the top of the upper run of an endless belt of woven wire and / or synthetic material that travels between two or more rolls. The belt, often referred to as a "forming fabric," provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity or vacuum located on the lower surface of the upper run (z.e., the "machine side") of the fabric.

[0004] After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more presses (often roller presses) covered with another fabric, typically referred to as a "press felt." Pressure from the presses removes additional moisture from the web; the moisture removal is often enhanced by the presence of a "batt" layerAttorney Docket No. 5690.234.WO of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.

[0005] Over the last few decades, a “shoe press” has been developed for the press section of the papermaking machine. A shoe press includes a roll or similar structure that mates with a “shoe” of an opposed roll or press structure; the surface of the shoe is somewhat concave and approximates in curvature the convex profile of the mating roll. This arrangement can increase the width of the nip in the direction of paper travel, thereby enabling greater amounts of water to be removed therein.

[0006] Endless belts or blankets have traditionally been used in shoe press operations. The belt overlies and contacts the shoe of the press; in turn, the press felt overlies the shoe press belt, and the paper web overlies the press felt. The shoe press belt and press felt travel through the nip and, in doing so, convey the paper web through the nip. The press felt is driven by a set of drive rollers arranged around the shoe. In older embodiments, shoe press belts were also driven by sets of drive rollers arranged around the shoe. In some newer configurations, however, the shoe press belt is clamped or otherwise fixed to the edges of circular head plates located on either end of the shoe, such that rotation of the head plates causes the shoe press belt to rotate and travel through the nip.

[0007] Given the performance requirements, a shoe press belt should be sufficiently flexible to pass around the drive rollers or head plates and through the shoe and sufficiently durable to withstand the repeated application of pressure within the nip. Because of these performance parameters, most endless belts are formed entirely or predominantly of a polymeric material (often polyurethane). Many shoe press belts also include reinforcing fibers or a reinforcing fabricAttorney Docket No. 5690.234.WO between or embedded in polymeric layers. Also, shoe press belts may be configured to encourage water to pass from the paper web. To this end, some shoe press belts have grooves or blind-drilled holes in the surface adjacent the press felt that serve to vent water from the paper that is exiting the press felt.

[0008] As can be gleaned from the foregoing, the material comprising a shoe press belt should be mechanically tough, and in addition should be resistant to both water (as the belt will be exposed to water as the paper web drains) and oil (as the belt will be exposed to lubricants and the like within the shoe press). Thus, it may be desirable to provide a material for a shoe press belt that has a balance of properties that enables the belt to withstand the rigors of shoe press operations.Summary

[0009] As a first aspect, embodiments of the invention are directed to a shoe press belt. The shoe press belt comprises a body defining an endless loop and having: an inner layer; a reinforcing yam layer; and an outer layer. The inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material comprises: poly-l,4-phenylene diisocyanate (PPD1) prepolymer; poly caprolactone diol; and an alkyl-diol chain extender.

[0010] As a second aspect, embodiments of the invention are directed to a shoe press belt comprising a body defining an endless loop and having: an inner layer; a reinforcing yarn layer; and an outer layer. The inner layer and outer layer are formed of a polyurethane material. The polyurethane material comprises: poly-l,4-phenylene diisocyanate (PPDI) prepolymer, wherein the PPDI prepolymer is present in the polyurethane in a weight percent of between about 60 and 90 percent; polycaprolactone diol, wherein the polycaprolactone diol is present in the polyurethane in a weight percent of between about 10 and 30 percent; a 1,4-Attorney Docket No. 5690.234.WO butanediol chain extender, wherein the 1 ,4-butanediol chain extender is present in the polyurethane in a weight percent of between about 1 and 5 percent; and an aromatic diamine curing agent.

[0011] As a third aspect, embodiments of the invention are directed to a method of making paper. The method comprises: a. determining at least one property of a shoe press belt on a paper machine, at least one property of the paper machine, or at least one property of the paper, wherein the shoe press belt includes a body defining an endless loop and having: an inner layer; a reinforcing yarn layer; and an outer layer; wherein the inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material comprises: poly-l,4-phenylene diisocyanate (PPDI) prepolymer; polycaprolactone long chain diol; and an alkyl-diol chain extender; and b. regulating at least one property of the shoe press belt, at least one operation behavior of the fabric, or replacing the shoe press belt.Brief Description of the Figures

[0012] FIG. 1 is an end view of a shoe press according to embodiments of the present invention.

[0013] FIG . 2 is a front section view of the lower roll and shoe press belt of the shoe press of FIG. 1.Attorney Docket No. 5690.234.WO

[0014] FIG. 3 is a perspective view of the shoe press belt of the shoe press of FIG. 1.

[0015] FIG. 4 is a greatly enlarged cross-section of the shoe press belt of FIG. 3 taken along lines 4 — 4 of FIG. 3.Detailed Description

[0016] The present invention will now be described more fully hereinafter, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.

[0017] In the figures, certain layers, components or features may be exaggerated for clarity, and broken lines illustrate optional features or operations unless specified otherwise. This invention may, however, be embodied in many different forms and should not be constmed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0018] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, aAttorney Docket No. 5690.234.WO first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. The sequence of operations (or steps) is not limited to the order presented in the claims or figures unless specifically indicated otherwise.

[0019] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0020] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0021] As used herein, phrases such as "between X and Y" and "between about X and Y" should be interpreted to include X and Y. As used herein, phrasesAttorney Docket No. 5690.234.WO such as "between about X and Y" mean "between about X and about Y." As used herein, phrases such as "from about X to Y" mean "from about X to about Y."

[0022] Referring now to FIGS. 1 and 2, a shoe press, designated broadly at 20, is illustrated therein. The shoe press 20 includes a lower roll 22 and a mating upper roll 24 that define therebetween a nip 25 through which a web or sheet, such as a paper web 37, can travel. Each of the lower and upper rolls 22, 24 defines a respective axis Al, A2; the axes Al, A2 are essentially parallel with one another and substantially perpendicular to the direction MD that the web 37 travels. As can be seen in Figure 1, illustratively press felts 35, 36 are positioned between the lower and upper rolls 22, 24; tire press felts 35, 36 are driven around respective sets of drive rollers 35a, 36a by the lower and upper rolls 22, 24. The web 37 is conveyed by and between the press felts 35, 36.

[0023] Referring again to FIGS. 1 and 2, the lower roll 22 includes a beam 26 that extends parallel to the axis Al . At either end, the beam 26 includes a round shaft 28 that engages and is supported by a bracket 30. A shoe 32 with a concave pressing surface 33 extends upwardly from the beam 26. The shoe 32 is mounted onto the beam 26 such that it can be controllably biased upwardly; the biasing of the shoe 32 can be accomplished with, for example, a hydraulic system (not shown). A circular head plate 34 is rotatably mounted on each shaft 28 spaced apart from the end of the shoe 26. Bearings 35 enable the head plates 34 to be rotated on the shaft 28.

[0024] A substantially cylindrical shoe press belt 40 is mounted about the perimeter of each head plate 34 such that its longitudinal axis is substantially parallel with the axis Al . The shoe press belt 40 is fixed to the head plates 34 (by clamping or the like) such that, as the head plates 34 rotate about the shafts 28, they cause the shoe press belt 40 to rotate also. Typically, the shoe press belt 40 is between aboutAttorney Docket No. 5690.234.WO1,000 and 2,150 mm inches in diameter and between about 3,000 and 12,500 mm in length.

[0025] As shown in FIG. 1, the lower and upper rolls 22, 24 are positioned relative to each other so that the upper roll 24 causes the shoe press belt 40 to deflect from a cylindrical configuration and confonn to the configuration of the pressing surface 33 of the shoe 32. The pressing surface 33 of the shoe 32 is shaped to be substantially complimentary to the convex profile of the upper roll 24, with the result that the nip 25 has significant width and is extended in the direction MD; this dimension is typically between about 150 and 320 mm. Both the shoe 32 and the upper roll 24 can be adjusted to control the magnitude and distribution of the pressure in the nip 25; in particular, the shoe 32 may be pivotable about an axis parallel to axis Al that enables the pressure to be adjusted along the direction of web travel MD. As the shoe press belt 40 rotates with the head plates 34, portions thereof are deflected by the contact surface 24a of the upper roll 24 to contact the contact surface 33 of the shoe 32.

[0026] Referring now to FIGS. 3 and 4, illustratively the shoe press belt 40 has a body 41 that defines an endless loop and includes an inner layer 42, a reinforcing yam layer 44, and an outer layer 46. Typically, the base polymer of the material comprising the inner and outer layers 42, 46 is the same, but it need not be. The inner layer 42 may have a thickness dimension of between about 2 and 4 mm, the outer layer 46 may have a thickness dimension of between about 2 and 6 mm, and / or the total thickness dimension of the shoe press belt 40 may be between about 4 and 8 mm. Also, it may also be desirable for the outer layer 46 to include grooves, blind-drilled holes, or other recesses to vent water from the paper web and press felt during operation; exemplary structures are illustrated in U.S. Patent Nos.Attorney Docket No. 5690.234.WO4,559,258 to Kiuchi and 6,030,503 to Matuschcyzk, the disclosures of which are hereby incorporated herein by reference in their entireties.

[0027] The reinforcing yarn layer 44 is included in the shoe press belt 40 to provide reinforcement in the machine and cross-machine directions. As used herein, the reinforcing yarn layer 44 is intended to encompass both woven fabrics (such as those illustrated in U.S. Patent No. 5,196,092 to Stigberg) and reinforcing structures having circumferentially-extending members and / or axially-extending members, such as the constructions described and illustrated in U.S. Patent No. 5,525,194 to Jermo and shown in FIG. 4. The disclosures of both patents are hereby incorporated herein in full.

[0028] In embodiments of the present invention, the shoe press belt 40 is formed of polyurethane. More specifically, the polyurethane of the shoe press belt 40 comprises a poly- 1 ,4-phenylene diisocyanate (PPDI) prepolymer, a polycaprolactone-based long chain polyol, and a chain extender comprising an alkyl-diol (e.g., a C4-C8-diol, such as 1,4 butanediol). This formulation can impart to shoe press belts the toughness and strength required to withstand the harsh conditions of continuous operation in a paper machine. In addition to these important properties, shoe press belt formed of this material exhibit high cracking resistance, as well as excellent oil and water resistance.

[0029] Generally speaking, polyurethane materials result from the interaction of diisocyanates with amines and polyols. Using a mixture of hydroxy-terminated and amine-terminated curing agents results in a polyurethane containing both urethane and urea linkages. Depending on the specific formulation and synthesis conditions, polyurethanes exhibit two main phases within their structure: a hard segment phase and a soft segment phase. The hard segment phase is formed by the reaction of diisocyanates with chain extenders, providing rigidity and strength toAttorney Docket No. 5690.234.WO the polymer. The soft segments are formed by the reaction of diisocyanates with long-chain polyols, contributing flexibility and elasticity to the polymer.

[0030] Often it is the case that the polyol chains in the hard and soft segments are of the same material group (e.g., ether, ester, carbonate). Hard and soft segments in polyurethane can be controlled by varying the hydrogen bonding, which is influenced by the different loading levels of ether and ester bonds.

[0031] PPDI has the structure shown in Formula I below:Formula I

[0032] Polycaprolactone diol has the structure shown in Formula II below:Formula II

[0033] 1,4 Butanediol has the structure shown in Formula III below:Formula III

[0034] In some embodiments, the PPDI prepolymer (which may have a molecular weight of between about 200 to 3,000 g / mol) is provided within theAttorney Docket No. 5690.234.WO formulation at a weight percent of between about 60 and 90 percent, and in certain embodiments between about 70 and 80 percent, with particular embodiments having a weight percent of PPDI prepolymer of between about 73 and 78 percent. In some embodiments, the poly caprolactone diol (which may have a molecular weight of between about 200 to 5,000 g / mol) is provided in the formulation at a weight percent of between about 10 and 30 percent, and in certain embodiments between about 17 and 23 percent, with particular embodiments having a weight percent of polycaprolactone diol of between about 18 and 21 percent. In some embodiments, 1 ,4-butanediol is the alkyl-diol, and is provided in the formulation at a weight percent of between about 1 and 5 percent, and in certain embodiments between about 3 and 4 percent, with particular embodiments having a weight percent of 1,4 butanediol of between about 3.25 and 3.9 percent.

[0035] In some embodiments, the formulation may benefit from the addition of a curing agent, such as 4,4 ’-m ethyl enebis(2-ethylbenzeneamine)(MBOEA), 3,5- diethyltoluene -2,4-diamine (DETDA), or another aromatic diamine, which can help to optimize the pot lifetime of the formulation during casting. The aromatic diamine curing agent may be provided in the formulation at a weight percent of between about 1 and 2 percent. In embodiments in which the shoe press belt 40 has multiple layers (e.g., an inner layer 42 and an outer layer 46), the polyurethane materials for each may be similar with the exception of the concentration of a curing agent, as it may be desired to have different pot life for each layer.

[0036] Other ingredients may also be added to the formulation. Exemplary ingredients include colorants, fillers and the like. For example, colorant may be added at a weight percent of between about 1 and 2 percent.

[0037] The process for forming the polyurethane described above may begin with the mixing of the components. In some embodiments the components areAttorney Docket No. 5690.234.WO pre-heated prior to mixing. For mixing, these components are typically injected into mixing tanks, which also may be heated.

[0038] In some embodiments, separate mixing tanks may be employed for the polyurethane of the inner layer 42 of the shoe press belt 40 and for the polyurethane of the outer layer 46. This separation enables the polyurethane of the inner layer 42 to have a different concentration of a curing agent in order to have a longer pot life than the polyurethane of the outer layer 46.

[0039] The mixture is then cast onto a mandrel or other casting device. The mandrel holds yams (monofilament or multifilament) in axial and circumferential directions as described in U.S. Patent No. 7,014,733 (the disclosure of which is hereby incorporated herein by reference in full). Also, in some embodiments the yarns of the reinforcing yam layer 44 may be pre-heated prior to application.

[0040] Once the polyurethane has been cast, the shoe press belt 40 is cured (typically via heating) for a suitable duration, then is removed from the mandrel. In some instances grooves, holes, and other recesses are formed on the outer surface of the outer layer 46 after curing.

[0041] Polyurethanes as described above can result in a material with a well- balanced ratio of hard and soft segments, which in turn exhibits high wear and tear resistance, excellent oil and water resistance, and outstanding mechanical and thermal properties. These characteristics make it particularly suitable for shoe press belts, offering significant potential performance advantages compared to prior formulations. In some embodiments, the hardness of the shoe press belt may be between about 88 and 98 Shore A, and in certain embodiments may be between about 94 and 96 Shore A.

[0042] Those of skill in this art will appreciate that shoe press belts according to embodiments of the present invention may include sensors, detectors, and otherAttorney Docket No. 5690.234.WO indicators of stress, temperature, wear and other operational parameters of shoe press belt usage. Such sensor arrangements are discussed in, for example, U.S. Patent No. 5,752,908 and PCT Patent Application No. PCT / US24 / 28089, the disclosures of which are hereby incorporated by reference herein in full. Such a belt may then enable the user (e.g., a technician at a paper mill) to monitor one or more of these operational parameters and make adjustments to the operating conditions. Such adjustments may include changing the processing conditions and / or replacing the shoe press belt.

[0043] Those skilled in this art will recognize that the present invention may be suitable for shoe presses of other configurations. For example, the lower roll 22 may include a fixed shaft and a hydraulic shoe (such as that available from Voith Sulzer Papiermachschinen GmbH, Heidenheim, Germany under the tradename FLEXONTP), or may be replaced with a shoe alone, wherein the shoe press belt is guided across the shoe by a set of drive rollers. The upper roll 24 may be hydraulically supported (as is the case with the FLEXONIP press mentioned above), may include an adjustable convex shoe (such as that available from Voith Sulzer, Heidenheim, Germany, under the tradename 1NTENSA), or may lack adjustability. Also, the lower and upper members may be oriented such that the concave pressing surface of the shoe is presented by the upper member of the shoe press and the convex pressing surface is presented by the lower member of the shoe press. These and other configurations of suitable shoe presses are described and illustrated in Joint Textbook Committee of the Paper Industry, Pulp and Paper Manufacture, Vol. 7, 267-70 (Third Edition, 1991). Alternative configurations should include a shoe with a concave pressure surface that is adjustable and a mating structure (such as a roll or opposed convex shoe) that form a nip through which a shoe press belt travels.Attorney Docket No. 5690.234.WO

[0044] Those skilled in this art will also appreciate that the polyurethane material described above may also be suitable for use in other applications. For example, the polyurethane material may be suitable for use in other components of a papermaking machine, such as covers for rolls that convey and / or press the paper web. Other utilizations and applications of the polyurethane material may also be contemplated.

[0045] The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

Attorney Docket No. 5690.234.WOWhat is Claimed is:

1. A shoe press belt, comprising: a body defining an endless loop and having: an inner layer; a reinforcing yarn layer; and an outer layer; wherein the inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material comprises: poly-l,4-phenylene diisocyanate (PPDI) prepolymer; poly caprolactone diol; and an alkyl-diol chain extender.

2. The shoe press belt defined in Claim 1, wherein the PPDI prepolymer is present in the polyurethane in a weight percent of between about 60 and 90 percent.

3. The shoe press belt defined in Claim 1 or Claim 2, wherein the polycaprolactone diol is present in the polyurethane in a weight percent of between about 10 and 30 percent.

4. The shoe press belt defined in Claim 1 or Claim 2, wherein the alkyldiol chain extender is present in the polyurethane in a weight percent of between about 1 and 5 percent.

5. The shoe press belt defined in Claim 1 or Claim 2, wherein the reinforcing layer includes axial and circumferential yarns.Attorney Docket No. 5690.234.WO6. The shoe press belt defined in any preceding claim, wherein the outer layer includes grooves and / or holes in an outer surface thereof.

7. The shoe press belt defined in Claim 1 or Claim 2, wherein the polyurethane material further comprises an aromatic diamine curing agent.

8. The shoe press belt defined in Claim 7, wherein the inner layer comprises the curing agent at a lower weight percentage than the outer layer.

9. The shoe press belt defined in any preceding claim, wherein the polyurethane material has a Shore A hardness of between about 88 and 98.

10. The shoe press belt defined in any preceding claim, wherein the body has a thickness of between about 4 and 8 mm.

11. The shoe press belt defined in Claim 1 , in combination with a shoe press.

12. A shoe press belt, comprising: a body defining an endless loop and having: an inner layer; a reinforcing yarn layer; and an outer layer; wherein the inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material comprises: poly-l,4-phenylene diisocyanate (PPDI) prepolymer, wherein the PPDI prepolymer is present in the polyurethane in a weight percent of between about 60 and 90 percent;Attorney Docket No. 5690.234.WO polycaprolactone diol, wherein the polycaprolactone diol is present in the polyurethane in a weight percent of between about 10 and 30 percent; a 1 ,4-butanediol chain extender, wherein the 1 ,4-butanediol chain extender is present in the polyurethane in a weight percent of between about 1 and 5 percent; and an aromatic diamine curing agent.

13. The shoe press belt defined in Claim 12, wherein the reinforcing layer includes axial and circumferential yarns.

14. The shoe press belt defined in Claim 12 or Claim 13, wherein the outer layer includes grooves and / or holes in an outer surface thereof.

15. The shoe press belt defined in Claim 12 or Claim 13, wherein the aromatic diamine curing agent is selected from MBOEA and DEDTA.

16. The shoe press belt defined in Claim 15, wherein the inner layer comprises the aromatic diamine curing agent at a lower weight percentage than the outer layer.

17. The shoe press belt defined in Claim 12 or Claim 13, wherein the polyurethane material has a Shore A hardness of between about 88 and 98.

18. The shoe press belt defined in Claim 12, in combination with a shoe press.

19. The shoe press belt defined in Claim 12, wherein the body has a thickness of between about 4 and 8 mm.Attorney Docket No. 5690.234.WO20. A method of making paper, the method comprising: a. determining at least one property of a shoe press belt on a paper machine, at least one property of the paper machine, or at least one property of the paper, wherein the shoe press belt includes a body defining an endless loop and having: an inner layer; a reinforcing yarn layer; and an outer layer; wherein the inner layer and outer layer are formed of a polyurethane material, wherein the polyurethane material comprises: poly-l ,4-phenylene diisocyanate (PPDI) prepolymer; polycaprolactone long chain diol; and an alkyl-diol chain extender; and b. regulating at least one property of the shoe press belt, at least one operation behavior of the fabric, or replacing the shoe press belt.

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