WO1999023305A1

WO1999023305A1 - Soft nip calender

Info

Publication number: WO1999023305A1
Application number: PCT/US1998/018076
Authority: WO
Inventors: Philip W. Smith
Original assignee: Beloit Technologies Inc
Current assignee: Beloit Technologies Inc
Priority date: 1997-10-31
Filing date: 1998-08-31
Publication date: 1999-05-14
Anticipated expiration: 2000-04-30
Also published as: AU9127698A

Abstract

A calender apparatus (2) for a paper web (4) is disclosed which utilizes a rotating drum (28) having a smooth, hard circumferential surface (36) and a belt (30) comprising a material which is soft relative to the hard surface of the rotating drum. A roll or roller drive mechanism (32) supports and moves the belt along a path of travel opposite the rotating drum such that a soft, low pressure nip (60) is defined between the belt and the rotating drum. The belt and the rotating drum together move the paper web along the path of travel through the nip with one of the sides of the web in engagement with the circumferential surface of the rotating drum. The rotating drum, as the web passes through the nip, provides a surface smoothing action to the side of the web in engagement with the drum. However, due to the softness of the belt, the force applied by the nip through the thickness of the web is minimized such that the web is not significantly crushed and its bulk is substantially maintained.

Description

PATENT APPLICATION TITLE: SOFT NIP CALENDER

FIELD OF THE INVENTION The present invention relates to a calender for paper webs. In particular, the invention relates to a calender having a soft nip for providing a smooth finish on a paper web while at the same time preventing loss of bulk in the paper.

BACKGROUND OF THE INVENTION In general, calendering is a part of the papermaking process in which a continuous web of paper is passed through an array of rolls to provide the web with desired properties. The properties are determined by the surface character of the rolls and their temperature, nip pressures, nip length and rotational speed.

Where a smooth surface paper web is desired, the web is engaged in a nip with a smooth calender roll which is commonly a roll having a metallic shell, although other types of hard surface rolls may be used. To assist with obtaining a smooth surface, the roll may be heated and/or the paper web may be moistened prior to passing through the calender nip. Both the heating of the roll which increases the temperature of the web and the moistening of the web will have the affect on the web of softening it so that its surface is deformable to a relatively smooth character.

A problem in calendering the paper web to provide a smooth surface is that this calendering step may also tend to compress the web and reduce its bulk. This is particularly true where a pair of steel calender rolls are used to form the nip through which the web passes such that a relatively high level of pressure is applied to both sides of the web. As a solution to this problem, soft covered calender rolls have been used on at least one side of the nip to reduce the pressure. Thus, a smooth surface will result on the side of the web engaged by the steel roll as the web passes through the nip. However, the problems with soft covered rolls are that they are expensive and also tend to deteriorate due to the heat applied to assist with the deformation to provide the smooth surface. Also, it is difficult to effectively use a pair of steel rolls on- machine to calender the paper web as it is produced since the two steel rolls tend to apply stress levels to the web which may exceed its tensile limit.

SUMMARY OF THE INVENTION It is an object of the invention to provide a calender apparatus in which a smooth surface may be produced on one side of a paper web while minimizing loss of bulk in the paper web. The foregoing object includes providing a smooth surface while minimizing bulk loss in particular in a tissue web. It is also an object of the invention to provide a calender apparatus in which a smooth surface without significant loss in bulk is obtained using a hard, smooth surface drum and a counter drum along which a continuous relatively soft belt is run.

The calender apparatus of the invention utilizes a rotating drum having a smooth, hard circumferential surface and a belt comprising a material which is soft relative to the hard surface of the rotating drum. The belt may be made of a material such as a polyurethane in outer layers and a woven fiber base which may be interiorly of the polyurethane layers. Alternatively, the belt may comprise a felt material which will have a somewhat less smooth surface than that of the belt having the polyurethane outer layer. A roll or roller drive mechanism supports and moves the belt along a path of travel opposite the rotating drum such that a soft, low pressure nip is defined between the belt and the rotating drum. The belt and the rotating drum thus together move the paper web along the path of travel through the nip with one of the sides of the web in engagement with the circumferential surface of the rotating drum. The rotating drum, as the web passes through the nip, provides a surface smoothing action to the side of the web in engagement with the drum. However, due to the softness of the belt, the force applied by the nip through the thickness of the web is minimized such that the web is not significantly crushed and its bulk is substantially maintained. This type of calendering of the web is particularly important for tissue webs where retaining bulk for absorbency purposes is necessary.

The drive mechanism may be a calender roll having a rotational axis parallel to that of the rotating drum and a circumferential surface facing the drum. The belt is driven by and is in engagement with the roll along a portion of the circumferential surface of the roll to form the nip area with the rotating drum. Alternatively, the drive mechanism may comprise a pair of support rollers spaced from each other and from the rotating drum with each having an axis of rotation parallel to that of the rotating drum. Although spaced from the drum, the support rollers are sufficiently adjacent to the drum that the belt, which is wrapped partially around each of the rotating rollers, is held against the circumferential surface of the rotating drum to thereby cooperate with the rotating drum to define the nip between the drum and the belt in the space between the two support rollers. Further, the support rollers may be positioned such that the belt extends a distance along the surface of the rotating drum to form an extended nip with the rotating drum. Consequently, the smoothing action of the rotating drum will be increased due to the increased time of contact of the tissue web with the rotating drum.

The calender apparatus of the invention may incorporate components of a winder apparatus wherein the paper web being passed through the calender apparatus is wound into a roll by a winder apparatus subsequent to the calendering process. Thus, a winder drum may serve as the rotating drum which provides the surface smoothing the paper web during calendering. In such case, the belt will be driven along a path immediately adjacent the winder drum to form the nip with the winder drum through which the paper web travels.

The rotating drum, whether it is a separate drum or the winding drum of a winding apparatus, is typically heated to a selected temperature that will assist with the smoothing of the web surface. Thus, the calender roll will also be at a temperature near or at that of the rotating drum. Also, the belt will be at or near the temperature of the rotating drum especially in the area of the nip. Consequently, the belt material must be such that it will withstand the temperature operating range of the rotating drum.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description taken in conjunction with the accompanying drawings as follows:

Fig. 1 is a side elevation schematic view of the calender according to this invention;

Fig. 2 is a side elevation schematic view of an alternative embodiment of the invention;

Fig. 3 is a side elevation schematic view of another alternative embodiment of the invention; and

Fig. 4 is a side elevation schematic view of the invention utilized with a multi-ply winding apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to Figs. 1-4, wherein like numbers refer to similar parts, a soft nip calender apparatus 2 is shown in Fig. 1. The calender apparatus 2 receives a web of paper 4 from a paper machine, of which only a dryer 6 of a Yankee type is shown. The paper 4 travels along a path indicated by the arrow 8 to a winding apparatus 10 where it is wound into a paper roll 12 on a core 14. The winding of the web 4 on the roll 12 is accomplished in conjunction with a winding drum 16 in a well-known manner. The core 14 is shown both in solid lines within the roll 12 and in phantom lines at the initiation of the winding process. A guide roll 18 guides the movement of the web 4 along its path 8 to the winder apparatus 10. Scanners 20 and 22 provide an inspection of the web to determine whether its surfaces as produced by the paper machine and modified by the calender apparatus 2 are satisfactory. In moving the web 4 along its path 8 to the calender apparatus 2, a doctor 24 assists with the removal of the web 4 from the Yankee dryer 6 and a web guide 26 maintains a vacuum above a foraminous surface to hold the web stable.

With reference to Fig. 1, the calender apparatus 2 comprises a rotating drum 28, a belt 30 and a drive mechanism 32 for the belt 30. The rotating drum is rotatable about an axis 34 in the direction of arrow 25 and has a circumferential surface 36 which is preferably hardened and very smooth. The drum 28 may be of a steel material and frequently is heatable by means (not shown) to a temperature above the surrounding ambient temperature in the vicinity of the paper machine and calender apparatus to assist with the smoothing action of the drum.

The belt 30 is of a continuous or closed loop type and has an inner surface 40 and an outer surface 38 which may be relatively smooth and even although not necessarily as smooth as the surface 36 of the drum 28. The outer surface 38, with reference to Fig. 1A, is part of an outer layer 42 of the belt which comprises a material which is solid but relatively soft in comparison to the hard surface of the drum 28 and may be of a polymeric material such as polyurethane. The belt may also have an inner solid layer 44 which includes the inner surface 40 and also may be of a polymeric material. The belt further includes a base 46 comprising a woven fiber material impregnated with a polymeric material such as polyurethane. Alternatively, with reference to Fig. 1 B, the belt 30 may comprise a felt material which is also soft relative to the surface of the drum 28 and has outer and inner fibrous batt layers 78 and 80, respectively, both of which may be of a polymer such as nylon, and a base layer 82 of a woven polymer fiber. Whether the belt 30 is of a type having solid outer and inner polymeric layers or is a fibrous felt material, it will be at or near the higher temperature of the drum 28 if the latter is heated and accordingly must be able to withstand the higher temperature.

The drive mechanism 32 illustrated in Fig. 1 comprises a calender roll 48 and guide rolls 50, 52 and 54 for the belt 30. The calender roll 48 is rotatable about an axis 56 in the direction of arrow 26 and has a circumferential surface 58 engaging the inner surface 40 of the belt 30. The drive mechanism 32 drives the belt 30 in the direction of arrow 76 and at least one of the guide rolls 50, 52, 54 is moveable to adjust the tension in the belt 30. The calender roll 48 is positioned opposite the drum 28 so that the belt moves along a path indicated by arrow 76 opposite and adjacent to the circumferential surface of the drum 28 to define a soft nip 60 between the belt 30 and the circumferential surface 36 of the rotating drum 28. Due to its engagement with the belt 30 and its proximity to the drum 28, the roll 48 will be at or near the higher temperature of the drum 28 if the latter is heated. The belt 30 and the rotating drum 28 together move the web 4 through the nip 60 with the side 7 of the paper web engaging the belt 30 opposite the rotating drum 28 and the side 5 of the paper web engaging the circumferential surface 36 of the drum 28 so that the drum 28 imparts a smooth finish to the surface 5 of the web. At the same time, because the belt 30 is of a relatively soft material engaging side 7 of the web 4, the nip is relatively soft. Thus, the web will not be subjected to such pressure that it will be crushed in cross-section and therefore its bulk will be substantially maintained. This is of particular significance for tissue webs since the bulk of tissue is desirable to maintain for liquid absorbency purposes. With reference to Fig. 2, an alternate embodiment of the invention is shown in which the rotating drum 28 is identical to that shown in Fig. 1 , but the drive means differs and is identified in Fig. 2 as drive means 62. The drive means 62 comprises a group of guide rolls 64, 66, 68 and 70 rotatable about axes parallel to the axis 34 of drum 28 and which serve to drive the belt 30. The belt 30 of Fig. 2 is essentially identical to the belt 30 of Fig. 1 except that it may differ somewhat in length and it wraps partially about the rolls 64, 66, 68 and 70. Thus, the guide rolls 64, 66, 68 and 70 guide and drive the belt 30 in the embodiment of Fig. 2 along a path indicated by arrow 72 opposite and adjacent to the circumferential surface 36 of the rotating drum 28. Two of the guide rolls 64 and 70 are spaced apart from each other and from the drum 28 at positions such that the belt 30 extends along its path a distance and partially wraps about drum 28 to form an extended nip 74 with the rotating drum 28. The extended nip 74 has the benefit of enabling increased engagement of the rotating drum 28 and belt 30 to correspondingly increase the imparting of a smoother glossy surface to the web 4 by the drum 28 without substantially decreasing the bulk of the web 4. In its movement through the nip 74, the paper web 4 engages the belt 30 only adjacent to and along the nip 74. The embodiment of Fig. 2 also has the ability to provide a soft nip due to a softer surface than there might be on a calender roll 48.

Referring now to Fig. 3, an embodiment of the invention is illustrated in which the drive means 32 and belt 30 are identical to the drive means and belt illustrated in Fig. 1 with the exception that they are positioned above the web 4 to cooperate with the calender drum 16 rotating in the direction of arrow 76. The calender drum 16 has an axis 90 about which it rotates and a hard circumferential surface 92. The belt 30 is driven along a path indicated by arrow 94 opposite and adjacent to the circumferential surface 92 of the calender drum 16 to form a nip 96. The web 4 passes through the nip 96 and has its side 7 smoothened by the action of the hard, smooth surface 92 of the calender drum 16. However, the softness of the nip 96 due to the soft material belt 30 forming a part of the nip minimizes the reduction in bulk of the web 4 as it passes through the nip. The web 4 continues on along the surface 92 of the calender drum 16 to the roll 12 on which the web 4 is wound.

Considering Fig. 4, the embodiment of the calender apparatus 2 illustrated in Fig. 2 is utilized in conjunction with two paper webs 100, 102 that are unwound respectively, from rolls 104 and 106 and guided respectively, by rolls 108 and 110 to the calender apparatus 2. Further, both webs 100 and 102 pass around roll 110 and move toward calender 2 and, as they do, they become two ply web 112. The calender apparatus 2 includes the drum 28 rotating about axis 34 in the direction of arrow 25 and having a hard circumferential surface 36. Also, the calender 2 includes the belt 30 driven by drive means 62 in the direction of arrow 72 by guide rolls 64, 66, 68 and 70. At the calender apparatus 2, a side 114 of the web 112 engages the circumferential surface 36 of the rotating drum 28 at the nip 98 to thereby impart a smooth surface to the side 114. Similarly, to the embodiment of Fig. 2, the web 112 maintains its bulk as a result of the softness of the nip 98 due to the soft material belt 30. The calender apparatus of the invention is particularly suitable for providing a smooth surface to multiple layers of plies of webs as illustrated in Fig. 4 due to the increased caliper of multiple ply webs and their consequent susceptibility to crushing and reduction of bulk.

It is understood that the invention is not limited to the particular construction and arrangements of parts herein illustrated and described, but embraces such modified forms thereof that come within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A calender apparatus for imparting a smooth surface to a paper web having opposite sides, said apparatus comprising: a rotating drum having an axis of rotation and a smooth, hard circumferential surface; a belt comprising soft material relative to the surface hardness of the rotating drum; drive means for supporting and moving the belt along a path opposite the circumferential surface, the belt and the circumferential surface form a soft low pressure nip therebetween; and the belt and the rotating drum together move the paper web through the nip with one of the sides of the web engaging the surface of the drum such that the bulk of the web is maintained and the surface of the drum imparts a smooth surface to said one side of the web.

2. The calender apparatus according to claim 1 wherein the belt and the paper web are in engagement opposite the rotating drum.

3. The calender apparatus according to claim 1 wherein the belt has a relatively smooth surface in engagement with the web.

4. The calender apparatus according to claim 1 wherein: the drive means comprises a calender roll having a circumferential surface; and the belt moves in engagement with the roll along a portion of the latter's circumferential surface including along the nip.

5. The calender apparatus according to claim 4 wherein the belt and the paper web are in engagement only along the nip.

6. The calender apparatus according to claim 4 wherein the calender roll and the belt are at temperatures above ambient temperatures.

7. The calender apparatus according to claim 6 wherein the rotating drum is heated to a temperature above ambient temperature and the belt is substantially at a temperature determined by the temperature of the rotating drum.

8. The calender apparatus according to claim 4 wherein the belt comprises a polymeric material.

9. The calender apparatus according to claim 4 wherein the web comprises a tissue paper web.

10. The calender apparatus according to claim 9 wherein the web comprises a two ply tissue paper web.

11. The calender apparatus according to claim 1 wherein: the drive means includes a pair of rotating rolls spaced from each other and from the rotating drum and each having a circumferential surface and an axis of rotation parallel to that of the rotating drum; and the belt wraps partially around each of the rotating rolls and cooperates with the rotating drum to define the nip.

12. The calender apparatus according to claim 11 wherein the belt and the paper web are in engagement only adjacent to and along the nip.

13. The calender apparatus according to claim 11 wherein the rotating rolls are spaced from the rotating drum such that the belt extends a distance along said path sufficient to form an extended nip with the rotating drum through which the web passes.

14. The calender apparatus according to claim 11 wherein the web comprises a tissue paper web.

15. The calender apparatus according to claim 14 wherein the web comprises a two ply tissue paper web.

16. The calender apparatus according to claim 11 wherein the rotating drum is at a temperature above ambient temperature and the belt is also substantially at said temperature.

17. The calender apparatus according to claim 11 wherein the belt comprises a polymeric material.

18. A calender apparatus according to claim 1 further comprising: a winder apparatus for winding the paper web onto a roll, the winder apparatus including a rotating winder drum; the winder drum comprises the rotating drum; the belt moves in engagement with the winder drum along a portion of the circumferential surface of the winder drum to define the nip; and the belt and the winder drum move the web through the nip.

19. The apparatus according to claim 18 wherein the belt and the paper web are in engagement only along the nip.

20. A calender apparatus according to claim 18 wherein the winder drum carries the web to the roll on which the web is being wound simultaneously with the movement of the web through the nip.

21. The calender according to claim 18 wherein the winder drum is at a selected temperature and the belt is also at said temperature.

22. The calender according to claim 14 wherein the calender apparatus is part of a tissue papermaking machine.