Press fabric for a textured product

Abstract

Disclosed is a press fabric and related method to impart a texture to a cellulose product by having macro-voids in a complementary pattern on a sheet-contact side surface of the press fabric.

Claims

1. A press fabric for imparting a texture to a cellulose product, comprising: a papermaker's fabric having a sheet-contact side and a machine side, wherein the papermaker's fabric comprises macro-voids on the sheet-contact side, a depth of the macro-voids being less than a width of the papermaker's fabric, wherein the sheet-contact side is adapted to contact the cellulose product and the macro-voids are a topographical feature of the sheet-contact side that is complementary to a desired texture of the cellulose product, and wherein the percent dryness of the cellulose product exiting a press section is decreased compared to a press fabric without macro-voids.

2. The press fabric according to claim 1, wherein the macro-voids have a surface opening area sufficient to enable entry of fibers of the cellulose product.

3. The press fabric according to claim 1, wherein the macro-voids have a surface opening area in the range of 0.45 to 20 mm.sup.2.

4. The press fabric according to claim 1, wherein the macro-voids have a void volume in the range of 0.04 to 2.5 mm.sup.3.

5. The press fabric according to claim 1, wherein the macro-voids have a depth in the range of 0.3 to 1.5 mm.

6. The press fabric according to claim 1, wherein the machine side has voids.

7. The press fabric according to claim 6, wherein the machine-side voids have a void volume less than the void volume of some or all of the void volume of the macro-voids.

8. The press fabric according to claim 6, wherein the machine-side voids have a void volume greater than or equal to the void volume of the macro-voids.

9. The press fabric according to claim 1, wherein the machine side has no voids.

10. The press fabric according to claim 1, wherein the cellulose product is a paper product.

11. The press fabric according to claim 10, wherein the paper product is selected from the group consisting of: tissue, towel, and toilet paper.

12. A method of imparting a texture to a cellulose product, comprising: acquiring a press fabric according to claim 1; using the press fabric on nip rollers in the press section of a papermaking process; and compressing the cellulose product between the nip rollers and the press fabric, wherein fibers of the cellulose product are urged into void volumes of the macro-voids.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification. The drawings presented herein illustrate different embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

(2) FIGS. 1A-1C illustrate a top view, cross-sectional view, and bottom view of a portion of a press fabric according to the present disclosure.

(3) FIG. 2 illustrates a press section employing a press fabric of the present disclosure to impart a texture to a cellulose product.

(4) FIG. 3 is a graphical representation of the dewatering of a cellulose product produced with a press fabric of the present disclosure compared with a prior art press fabric at a speed of 800 meters/minute.

(5) FIG. 4 is a graphical representation of the dewatering of a cellulose product produced with a press fabric of the present disclosure compared with a prior art press fabric at a speed of 1000 meters/minute.

(6) FIGS. 5A-5B illustrate a cellulose product resulting from a press section having a prior art press fabric (FIG. 5A) and a cellulose product having a texture resulting from a press section having a press fabric of the present disclosure (FIG. 5B).

(7) FIG. 6 illustrates a cross-sectional view of a press fabric according to the present disclosure having batt material on a sheet side.

(8) FIG. 7 illustrates a cross-sectional view of a textured press fabric according to the present disclosure.

(9) FIG. 8 illustrates a representation of a three-dimensional profile of a textured sheet side surface according to the present disclosure.

(10) FIG. 9 is a photographic image of an embodiment of a textured surface exiting a press section having a press fabric according to the present disclosure.

DETAILED DESCRIPTION

(11) Terms “comprising” and “comprises” in this disclosure can mean “including” and “includes” or can have the meaning commonly given to the term “comprising” or “comprises” in U.S. Patent Law. Terms “consisting essentially of” or “consists essentially of” if used in the claims have the meaning ascribed to them in U.S. Patent Law. Other aspects of the invention are described in or are obvious from (and within the ambit of the invention) the following disclosure.

(12) The terms “threads”, “fibers”, “tows”, and “yarns” are used interchangeably in the following description. “Threads”, “fibers”, “tows”, and “yarns” as used herein can refer to monofilaments, multifilament yarns, twisted yarns, multifilament tows, textured yarns, braided yarns, coated yarns, bicomponent yarns, as well as yarns made of any material known to those skilled in the art. Yarns can be made of polyamide, fiberglass, cotton, aramid, polyester, metal, polyethylene, and/or other materials that exhibit desired physical, thermal, chemical or other properties.

(13) “Macro-voids” as used herein means a topographical feature of a sheet-contact side surface and is a volume that is below a nominal surface of a press fabric. The term “void volume” means the volume of space in an area of a fabric. For example, “void volume” of a macro-void that extends into a press fabric is the volume of empty space in the macro-void below a nominal surface of the press fabric.

(14) For a better understanding of the invention, its advantages and objects attained by its uses, reference is made to the accompanying descriptive matter in which non-limiting embodiments of the invention are illustrated in the accompanying drawings and in which corresponding components are identified by the same reference numerals.

(15) The present disclosure relates to the fabrics used in the press section, generally known as press fabrics, but it may also find application in the fabrics used in other paper industry processes.

(16) This disclosure relates to texturing an endless or seamed press fabric with the use of a laser or other mechanism to remove batt or other excess fiber in a desired pattern. The press fabric is textured by removing the sheet side batt fiber. The amount of batt fiber removed can be varied to achieve the amount and form of texturing desired. The depth and diameter or width of the removed batt fiber area can be altered. The pattern can also be altered. The pattern can contain any combination of shapes and depths. Shapes include, but are not limited to, circles, lines, dots, waves, drawings, logos, trademarks, or any random or ordered pattern desired.

(17) The disclosed technique is advantageous because the technique allows an existing conventional tissue or towel machine to be used in its current configuration to make higher bulk grades that previously required machine rebuilds or a new machine installation. The ability to use specific and custom patterns is also advantageous. For example, some tissues, paper towels, and toilet papers may have surface texture for purposes including ornamentation, bulk, or enhanced absorbency, or some other desired characteristic.

(18) FIGS. 1A-1C illustrate a top view, cross-sectional view, and bottom view of a portion of a press fabric 100 according to the present disclosure. The press fabric has a sheet-contact-side surface 104 and a machine side surface 106. The press fabric is often water permeable to enable passage of water from a cellulose product through the fabric as the product passes through the press section. However, some areas of the press fabric can be impermeable to water. Faceside or sheet-contact side surface 104 includes macro-voids 102. The sheet-contact surface is adapted to contact a cellulose product and impart a texture to that product as a result of the macro-voids and as will be described later. The opposite side of the belt is the machine or roller side 106, which is adapted to contact nip rollers of the press section. The machine side can have features distinguishable from the sheet-contact side to provide for such characteristics, for example, as adhesion to the nip rollers, water removal, wear resistance, etc.

(19) Macro-voids 102 are illustrated as an array of circular voids—a volume where press fabric is removed or missing—for convenience. The shape of the macro-voids is not limited to a circular shape or to an ordered array. Macro-voids 102 can be a negative (complementary) image of the texture desired for the cellulose product. Macro-voids below a nominal top surface 104 of a press fabric are described herein. Designs of the macro-voids include, for example, circular/hemispherical, square/pyramidal, rectangular/cuboid, hexagonal, elliptical, annular/semi-toroidal, and grooved. Other void array patterns may include, for instance, hexagonal, pseudo random, triangular, and linear/spiral (for example, grooved). Moreover, the macro-voids need not be in an ordered array and can have differing void volumes dependent on the desired texture imparted to the cellulose product. Macro-voids 102 may have a breadth L (surface opening area) and a depth D sufficient to enable fibers of a cellulose product to enter into the void volume. Macro-voids can have a void volume in the range of approximately 0.04 to 2.5 mm.sup.3, a surface opening area in the range of 0.45 to 20 mm.sup.2, and a depth in the range of 0.3 to 1.5 mm.

(20) Press fabric 100 may be water permeable and comprised of more than one layer (not shown). For example, sheet-contact side surface with macro-voids 102 may be one layer attached to a base fabric later. Attachment of layers may be accomplished by any method known to those of ordinary skill in the art and includes hydroentangling layers and laminating layers. Machine side 106 of the press fabric may have no voids, voids having void volumes less than that of the macro-voids, or voids with void volumes equal to or greater than the macro-voids 102 on the sheet-contact side of the press fabric.

(21) The macro-voids can be produced by any method known to those of ordinary skill in the art and includes laser etching, chemical etching, photo etching, drilling, pressing, and such. Laser etching can produce definition of the geometry of the macro-voids by control of laser parameters. However, the present disclosure is not limited by the method of producing the macro-voids.

(22) FIG. 2 illustrates press fabric 100 as may be used to impart a texture to a cellulose product 200, such as a paper sheet. The texture may be imparted during the press section and, in particular, when the belt and cellulose product are pressed together between nip rollers during dewatering of the cellulose product. Press fabric 100 and cellulose product 200 are shown separated for clarity and may be in contact during the texture imparting process.

(23) Cellulose product 200 can be conveyed by press fabric 100 to a nip section 212 between nip rollers 208, 210. The distance D3 between nip rollers 208, 210 is less than the sum of the width D1 of the cellulose product and the width D4 of the press fabric entering the nip section 212. As such, the cellulose product is compressed against the press fabric. The cellulose product will be compressed a greater amount in areas not having macro-voids 216 than in areas of the macro-voids 218 due to a depth of the void volume in the press fabric. Some of the fibers of the cellulose product can enter into macro-voids 102 of the press fabric. Compression between the nip rollers can result in compaction of the cellulose fibers and decrease width of the cellulose product to width D2. However, the lesser compaction and fiber entry in the macro-void areas can result in a surface texture 214.

(24) The cellulose product may be a slurry of cellulose fibers and water entering the press section where the product is compressed and dewatered. Dewatering results from compression of the cellulose slurry between nip rollers and the press fabric in the press section.

(25) As discussed above, a press fabric having macro-voids on the sheet-contact side surface 104 that contacts the cellulose slurry surface 206 applies less pressure in areas of the press fabric having macro-voids 218 than in areas of the press fabric not having macro-voids 216. Accordingly, there may be less dewatering using a press fabric having macro-voids according to the present disclosure than when using a comparable press fabric without the voids.

EXPERIMENTAL RESULTS

(26) Less dewatering using a press fabric with macro-voids was tested by comparing dryness of cellulose paper using a press fabric with macro-voids with paper dryness using a press fabric without macro-voids in a press section. The paper dryness trials were run at differing paper speeds.

(27) FIGS. 3 and 4 are graphical results of paper dryness ingoing and outgoing from the press section at a paper speed of 800 meters/minute (FIG. 3) and 1000 meters/minute (FIG. 4) as discussed in more detail below. Percent dryness, m, is calculated according to the formula:

(28) $\begin{array}{cc}m=100*\left(\frac{\mathrm{mass}\mathrm{of}\mathrm{cellulose}\mathrm{product}}{\mathrm{mass}\mathrm{of}\mathrm{water}+\mathrm{mass}\mathrm{of}\mathrm{cellulose}\mathrm{product}}\right)& \mathrm{Eqn}.1\end{array}$

Example 1

(29) Paper was processed using press fabric having a textured sheet side contacting the paper through the press section under the following conditions:

(30) TABLE-US-00001 Paper Grammage 27 grams/m.sup.2 (Tissue Pulp) Linear Load 30 kN/m~2.3 MPa Speed 800 m/min Uhle box vacuum −20 kPa Showers 2 liter/min uhle box lubrication

(31) FIG. 3 shows a comparison of the percent dryness for a cellulose product (sheet) at a speed of 800 meters/minute ingoing (entering) and outgoing (exiting) a press section having a press fabric with macro-voids on the sheet side 302, 306 and a press fabric without macro-voids on the sheet side 304, 308. The percent dryness of the cellulose product ingoing (entering) the press section with macro-voids 302 is 16.2% and the cellulose product entering the press section without macro-voids 304 is 16.6%. The ingoing values of percent dryness are close in value to one another. That is, the cellulose products are about the same percent dryness entering the press section.

(32) However, for cellulose product moving at 800 meters/minute, the percent dryness of the cellulose product outgoing (exiting) the press section having a press fabric with macro-voids on the paper contact surface 306 is 31.1%, which is substantially less dry than the 38.0% dryness of the cellulose product outgoing (exiting) the press section having a press fabric without macro-voids on the paper contact surface 308, In other words, the cellulose product has less dewatering from the press fabric with macro-voids as compared to the press fabric without macro-voids.

Example 2

(33) Paper was processed using press fabric having a textured sheet side contacting the paper through the press section under the following conditions:

(34) TABLE-US-00002 Paper Grammage 27 grams/m.sup.2 (Tissue Pulp) Linear Load 30 kN/m~2.3 MPa Speed 1000 m/min Uhle box vacuum −20 kPa Showers 2 liter/min uhle box lubrication

(35) FIG. 4 shows a comparison of the percent dryness for a cellulose product (sheet) at a speed of 1000 meters/minute ingoing (entering) and outgoing (exiting) a press section having a press fabric with macro-voids on the sheet side 402, 406 and a press fabric without macro-voids on the sheet side 404, 408. The percent dryness of the cellulose product ingoing (entering) the press section with macro-voids 402 is 16.3% and the cellulose product entering the press section without macro-voids 404 is 16.4%. The ingoing values of percent dryness are close in value to one another. That is the cellulose products are about the same percent dryness entering the press section.

(36) However, for cellulose product moving at 1000 meters/minute, the percent dryness of the cellulose product outgoing (exiting) the press section having a press fabric with macro-voids on the paper contact surface 406 is 30.3%, which is substantially less dry than the 37.6 percent dryness of the cellulose product outgoing (exiting) the press section having a press fabric without macro-voids on the paper contact surface 408. In other words, the cellulose product has less dewatering from the press fabric with macro-voids as compared to the press fabric without macro-voids.

(37) In summary, the experimental results confirm that macro-voids on a sheet-contact (or face) side of a press fabric results in less dewatering in a press section than with a press fabric without macro-voids on the sheet-contact side of the press fabric.

Example 3

(38) FIGS. 5A and 5B is an illustration of a portion of a resultant cellulose product produced with a press section having a press fabric without macro-voids on the sheet-contact surface 502 and a cellulose product produced with a press section having a press fabric with macro-voids on the sheet-contact surface 504. Cellulose product 502 has a surface 508 with a smooth or random texture of compressed cellulose fibers. In contrast, cellulose product 504 produced with a press fabric such as illustrated in FIGS. 1A-1C has a surface 506 with a textured surface having raised portions 510, which are a negative image of the press fabric. That is, depressed areas of the press fabric result in raised portions of the cellulose product.

(39) FIG. 6 illustrates a cross-sectional view of one embodiment of a press fabric 600. The press fabric can include a support layer 604 with a batt layer 602 disposed thereon on the sheet side 610 of the press fabric. Press fabric texturing is achieved by removing selected portions of sheet side batt in a pattern between the dashed line 606 and the solid line 608, provided for explanation purposes.

(40) FIG. 7 illustrates a cross-sectional view of a press fabric 700 having portions 706 of a batt layer 702 removed on a sheet side 710. The batt layer is disposed on a support layer 704. The removed portions 706 can impart a texture to a cellulose product produced using the press fabric 700 in the press section.

(41) FIG. 8 illustrates a representation of a textured surface of a press fabric of the present disclosure having a three-dimensional (3D) profile. Note that the surface profile could contain any combination of shapes and depths. Shapes include, but are not limited to, circles, lines, dots, waves, drawings, logos, trademarks, or any random or ordered pattern desired.

(42) FIG. 9 is a photographic image of a textured sheet side surface of a press fabric of the present disclosure as seen through a microscope. As discussed herein above, the surface profile could contain any combination of shapes and depths. Shapes include, but are not limited to, circles, lines, dots, waves, drawings, logos, trademarks, or any random or ordered pattern desired.

(43) Other embodiments are within the scope of the following claims.