STRUCTURING FABRIC WITH SUBLAYER BEADS AND METHOD OF PRODUCING THE SAME

Abstract

A structuring fabric for use in a machine to produce a structured fiber web, such as a structured tissue fiber web, has a machine direction, a cross machine direction, and a thickness direction. The structuring fabric includes a woven base fabric with a web facing side and a machine side. A plurality of structuring beads of polymeric material are formed on the web facing side of the woven base fabric, the structuring beads being suitable to provide a visible structure to the fiber web that is produced on the structuring fabric. The structuring beads rest on an upper foundation surface of corresponding sublayer beads of polymeric material. The sublayer beads thereby provide a foundation for the structuring beads. There is also described a production method for producing such a structuring fabric.

Claims

1. A structuring fabric for use in a machine for producing a structured fiber web, the structuring fabric comprising: a woven base fabric having a web facing side and a machine side, and said woven base fabric defining a machine direction, a cross machine direction, and a thickness direction; a plurality of sublayer beads of polymeric material disposed in said woven base fabric; a plurality of structuring beads of polymeric material disposed on the web facing side of said woven base fabric, said structuring beads being configured to provide a visible structure to the fiber web produced on the structuring fabric; and said structuring beads resting on an upper foundation surface of respectively corresponding said sublayer beads, with said sublayer beads providing a foundation for said structuring beads.

2. The structuring fabric according to claim 1, wherein a shape of the upper foundation surface of said sublayer beads substantially corresponds to a shape of a lower surface of the corresponding said structuring beads resting thereon.

3. The structuring fabric according to claim 1, wherein the upper foundation surface of said sublayer beads is substantially flat.

4. The structuring fabric according to claim 1, wherein, in the thickness direction of the structuring fabric, said sublayer beads are disposed substantially within a volume of said woven base fabric.

5. The structuring fabric according to claim 1, wherein said woven base fabric comprises an upper layer defining the web facing side of said woven base fabric, said upper layer being formed from upper cross-machine direction yarns that are interwoven with upper machine direction yarns, and said sublayer beads extending so deeply into said woven base fabric to create a form-fit connection with at least some of said upper cross-machine direction yarns at deepest points thereof.

6. The structuring fabric according to claim 1, wherein said structuring beads have a substantially rectangular cross-sectional shape.

7. The structuring fabric according to claim 6, wherein said structuring beads are substantially square in cross-section.

8. The structuring fabric according to claim 1, wherein said structuring beads form continuous lines on a web-facing surface of said woven fabric.

9. The structuring fabric according to claim 8, wherein the continuous lines substantially extend in the machine direction of the structuring fabric.

10. The structuring fabric according to claim 1, wherein said structuring beads form straight lines on a web-facing surface of said woven fabric or said structuring beads have a wavy configuration.

11. The structuring fabric according to claim 1, wherein a polymeric material of said structuring beads is the same as a polymeric material of said sublayer beads.

12. The structuring fabric according to claim 1, wherein at least one of a polymeric material of said structuring beads or a polymeric material of said sublayer beads is a material selected from the group consisting of silicone and polyurethane.

13. The structuring fabric according to claim 1, wherein at least one of a polymeric material of said structuring beads or a polymeric material of said sublayer beads is an acrylic material.

14. The structuring fabric according to claim 13, wherein the acrylic material is a UV-curable acrylic material.

15. The structuring fabric according to claim 13, wherein the acrylic material comprises at least one component selected from the group consisting of: N,N-dimethylacrylamide; 2-propenoic acid, 2-hydroxyethyl ester, polymer with 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane; isobornyl acrylate; 2-(2-ethoxyethoxy)ethyl acrylate; diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; [3-(2,3-epoxypropoxy)propyl]trimethoxysilane; acrylic acid; 2-hydroxyethyl acrylate; and wherein none of said components contributes more than 50 wt-% to the composition of the acrylic material.

16. A method of producing a structuring fabric for use in a machine for producing a structured fiber web, the method comprising: providing a woven base fabric; extruding a sublayer bead of polymeric material through a first extrusion nozzle onto a web facing surface of the woven base fabric, the sublayer bead having an upper foundation surface; and extruding a structuring bead of polymeric material through a second extrusion nozzle onto a top of the upper foundation surface of the sublayer bead.

17. The production method according to claim 16, wherein the first extrusion nozzle and the second extrusion nozzle are integrally formed in one extrusion die.

18. The production method according to claim 16, which comprises, during an extrusion process, aligning a first surface of an extrusion die in which the first extrusion nozzle is formed substantially parallel to a web facing surface of the woven base fabric, and aligning a second surface of the extrusion die in which the second extrusion nozzle is formed inclined with respect to the web facing surface of the woven fabric.

19. The production method according to claim 18, wherein a spacing distance of the first extrusion nozzle to the web facing surface of the woven fabric is greater than a spacing distance of the second extrusion nozzle to the web facing surface of the woven fabric during the extrusion process.

20. The production method according to claim 16, which comprises extruding the structuring bead at a time when the sublayer bead has not yet been cured.

21. The production method according to claim 16, wherein the first nozzle is substantially rectangular-shaped and the second nozzle is substantially star-shaped.

22. The production method according to claim 21, wherein a width of the first, substantially rectangular-shaped nozzle is substantially equal to a smallest width of the second, substantially star-shaped nozzle, and/or a length of the first, substantially rectangular-shaped nozzle is substantially half a length of the second, substantially star-shaped nozzle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] FIG. 1 is a cross-sectional view through a portion of a structuring fabric according to the prior art;

[0044] FIG. 2 shows a cross-sectional view of a portion of a structuring fabric according to the present invention;

[0045] FIG. 3 shows a die with several pairs of first and second nozzles to extrude sublayer beads and corresponding structuring beads on top thereof; and

[0046] FIG. 4 shows the manufacturing process for producing the structuring fabric according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] Referring now once more to the figures of the drawing in detail, FIG. 2 shows a cross-section of a portion of a structuring fabric 10 according to the present invention. The structuring fabric may also be referred to as a structured fabric, a molding fabric, a papermaking belt or a clothing. The figure resembles FIG. 1 showing a corresponding portion of a structuring fabric known from the prior art, as described above. Therefore, the same reference signs are used for the same features, and it is referred to the description of FIG. 1 above regarding these features. In the following, only the differences between the embodiments of FIG. 1 and FIG. 2 will be explained.

[0048] In contrast with the prior-art embodiment of FIG. 1, in the embodiment of FIG. 2, which represents the invention, the structuring bead 14 does not only have a limited local contact with the yarn knuckles that characterize the web facing side 16 of the woven base fabric 12 but the structuring bead 14 rests with its lower surface on an upper foundation surface of a sublayer bead 20. The sublayer bead 20 is formed preferably completely within the volume of the woven base layer 12, thus having a strong bond to the woven base layer 12. Its upper foundation surface, i.e., its surface that is facing away from the machine side 18 of the woven base layer 12, is substantially flat, thereby providing a very good foundation for the structuring bead 14 resting thereon. In thickness direction TD of the structuring fabric 10, the dimension of the sublayer bead 20 may be smaller than the dimension of the structuring bead 14. In the present embodiment, the woven base fabric 12 is formed as a multi-layer woven fabric but it could also be a single-layer woven fabric. The upper layer, that defines the web facing side 16 of the woven base fabric 12 is preferably a plain weave. The upper layer is formed by upper machine direction yarns 32 interwoven with upper cross-machine direction yarns 34. The sublayer bead 20 extends so deep into the woven base fabric 12 as to create a form-fit connection (i.e., a positive or form-lock connection) with the upper cross-machine direction yarns 34 where these upper cross-machine direction yarns 34 pass under the machine direction yarns 34. In other words, the polymeric material of the sublayer bead 20 surrounds more than half of the diameter of the upper cross-machine direction yarns 34 at their lowest points. At the same time, the sublayer bead 20 does not extend deeper into the woven base fabric 12 than the thickness of the upper layer. In thickness direction, the sublayer bead 20 is almost as thick as the structuring bead 14 resting thereon.

[0049] In the present embodiment, the knuckles on the web facing side 16 of the woven fabric only slightly project above the substantially flat upper foundation surface of the sublayer bead 20. The sublayer bead 20 and the structuring bead 14 are preferably formed from the same polymeric material, such as a two component silicone. This results in a strong bond between the two beads, especially if the structuring bead 14 is applied on top of the sublayer bead 20 at a time when the material of the sublayer bead 20 has not yet been cured.

[0050] FIG. 3 shows an extrusion die 22 adapted to simultaneously apply several structuring beads 14 and corresponding sublayer beads 20 onto the web facing side 16 of the woven base fabric 12. More precisely, the extrusion die 22 comprises five pairs of first nozzles 24 and second nozzles 26, to extrude five pairs of sublayer beads 20 and structuring beads 14, respectively. For the sake of clarity, two pairs of first nozzles 24 and second nozzles 26 are shown in an enlarged view on the bottom of FIG. 3. The first nozzles 24 for extruding the sublayer beads 20 have a substantially rectangular form, whereas the second nozzles 26 for extruding the structuring beads 14 have a substantially star-shaped form. The term star-shaped form in this context refers to a form that resembles a square, wherein the lateral edges of the square are not straight but curved toward the center of the star-shaped form. The smallest distance between two opposite curved lateral edges is designated here with letter A. This smallest distance A is preferably between 0.3 mm and 1.0 mm, more preferably between 0.6 mm and 0.8 mm. The first, substantially rectangular shaped nozzle 24 has a width that substantially corresponds to the smallest distance A of the second, substantially star-shaped nozzle 26. The length of the first, substantially rectangular shaped nozzle 24 is significantly smaller than its width. It may be only half the width, i.e., half the smallest distance A of the second, substantially star-shaped nozzle 26.

[0051] The pitch of two directly neighboring pairs of first nozzles 24 and second nozzles 26 is B. The pitch B is measured as the distance from the center of one second nozzle 26 to the center of one of its directly neighboring second nozzles 26. The pitch B is preferably between 2 and 6 times the smallest distance A between two opposite curved lateral edges of the first, substantially rectangular shaped nozzle 24.

[0052] The first nozzles 24 are provided within a first surface 28, whereas the second nozzles 26 are provided within a second surface 30. The first surface 28 and the second surface 30 do not lie within the same plane. In other words, the second surface 30 is inclined with respect to the first surface 28. As shown in FIG. 4, during the manufacturing process of the structuring fabric 10 according to the present invention, the first surface 28 of the extrusion die 22 is placed close and substantially parallel to the web facing side 16 of the woven base fabric 12. This allows resinous material extruded through the first nozzles 24 to easily penetrate the volume of the woven base fabric 12, so as to form sublayer beads when the woven base fabric 12 is carried in moving direction v, preferably corresponding to the machine direction MD of the structuring fabric 10, below the extrusion die 22.

[0053] The resinous material extruded through the second nozzles 26 formed in the second surface 30 of the extrusion die 22 then forms the structuring beads 14 that rest upon the upper foundation surface of the corresponding sublayer beads 20. The inclination of the second surface 30 with respect to the first surface 28 and, thus, with respect to the web facing side 16 of the woven base fabric, helps to form substantially square shaped structuring beads 14.

[0054] During the manufacturing process of the structuring fabric 10, the extrusion die 22 may be stationary while the woven base fabric 12 moves in moving direction v, so as to form a pattern of structuring beads 14 that extend in parallel straight lines. However, if it is preferred to provide the structuring fabric 10 with another pattern of structuring beads 14, such as a zig-zag pattern or a wavy pattern, the extrusion die 22 may be moved, e.g. back and forth, orthogonally to the moving direction v during the manufacturing process, i.e., orthogonally to the image plane of FIG. 4.

[0055] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0056] 10 structuring fabric [0057] 12 woven base fabric [0058] 14 structuring bead [0059] 16 web facing side [0060] 18 machine side [0061] 20 sublayer bead [0062] 22 extrusion die [0063] 24 first nozzle [0064] 26 second nozzle [0065] 28 first surface [0066] 30 second surface [0067] 32 upper machine direction yarns [0068] 34 upper cross-machine direction yarns [0069] A smallest distance between two opposite curved lateral edges [0070] B pitch of two directly neighboring pairs of first and second nozzles [0071] MD machine direction [0072] TD thickness direction [0073] v moving direction