Patent Application
20240271364
The invention concerns a structuring fabric for use in a machine to produce a structured fiber web, preferably a structured tissue fiber web, the structuring fabric having a machine direction, a cross machine direction and a thickness direction, wherein the structuring fabric comprises a woven base fabric, the woven base fabric having a web facing side and a machine side, and wherein the structuring fabric further comprises a plurality of structuring beads of polymeric material 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. Furthermore, the invention concerns a method of producing such a structuring fabric.
Such structuring fabrics, sometimes also called “structured fabrics” or “molding fabrics”, are already known. They are often used in the production of bulky tissue webs. The structuring beads need to be of a certain minimum dimension to be suitable of imparting a visible structure into the fiber web produced thereon. For example, the structuring beads can have a substantially square cross-section of 0.5 mm×0.5 mm. The smallest dimension of the structuring beads should be at least 0.25 mm.
International published patent application WO 00/75424 A1 discloses such a fabric for making strong, soft, absorbent paper products. The content of WO 00/75424 A1 is incorporated herein by reference. The document teaches to extrude a fluid resinous material onto a reinforcing element, such as a woven fabric, according to a desired predetermined pattern and then solidifying the patterned resinous material. After solidification the resinous material is attached to the reinforcing element.
A portion of such a structuring fabric 10 known from the prior art is shown in a cross-sectional view along the machine direction MD in
Attempts to increase the contacting area by reducing the viscosity of the resinous material that form the structuring beads were not successful because the lower viscosity adversely affects the dimensional stability of the structuring beads. For obtaining a well visible pattern within the fiber web that is produced on the structuring fabric, the structuring beads should have a substantially rectangular cross-section, wherein the sidewalls of the structuring beads should be substantial perpendicular to the web facing surface of the woven fabric. However, this is difficult to achieve if the viscosity of the resinous material is reduced. The same is true if the still soft structuring beads are forced into the woven base fabric e.g. by a calendaring device as proposed in WO 00/75424 A1.
Thus, it is an object of the present invention to provide an improved structuring fabric with a strong bonding of the structuring beads to the web facing side of the woven base fabric, wherein at the same time the dimensional stability of the structuring beads should not be adversely affected. It is another object of the present invention to provide a manufacturing process for such a structuring fabric.
With the above and other objects in view there is provided, in accordance with the invention, a structuring fabric for use in a machine for producing a structured fiber web, the structuring fabric comprising:
In particular, the problem is solved by the generic structuring fabric as described at the beginning wherein the structuring beads are resting on an upper foundation surface of corresponding sublayer beads of polymeric material, the sublayer beads thereby providing a foundation for the structuring beads.
By providing sublayer beads below the structuring beads it is possible to significantly improve the strength of the bonding of the structuring beads to the web facing side of the woven base fabric, without adversely affecting the cross-sectional shape of the structuring beads. The sublayer beads can protrude deeper into the volume of the woven base fabric to have a larger contact area with the yarns of the woven base fabric, while providing a good foundation for the structuring beads that rest thereon. The polymeric material of the sublayer beads could be for example silicone, in particular a two-component silicone.
Preferably, the form of the upper foundation surface of the sublayer beads substantially corresponds to the form of a lower surface of the corresponding structuring beads that rest thereon. In other words, the dimensional extensions of the sublayer beads within the plane of the web facing side of the woven base fabric can be substantially the same as the dimensional extensions of the structuring beads. That way, the structuring beads can be fully supported by the sublayer beads while at the same time the sublayer beads do not or do hardly reduce permeability of the structuring fabric.
Furthermore, to provide a very good foundation for the structuring beads it is preferred that the upper foundation surface of the sublayer beads is substantially flat. At least the upper foundation surface of the sublayer beads shall be significantly smoother compared to the web facing surface of the woven base fabric, which is characterized by a plurality of individual yarn knuckles.
The woven base fabric can be a single layer weave or can comprise serval layers. Preferably, the layer defining the web facing side of the woven base fabric has a plain weave pattern. In a plain weave pattern, the warp and weft yarns cross at right angles, aligned so they form a simple criss-cross pattern. Each weft yarn crosses the warp yarns by going over one, then under the next, and so on. The next weft yarn goes under the warp yarns that its neighbor went over, and vice versa. With such a weave pattern, irregularities on the web facing side of the woven base structure can already be kept small.
In thickness direction of the structured fabric, the sublayer beads can be provided substantially within the volume of the woven base fabric. This maximizes their contact area with the yarns of the woven base fabric.
No matter if the woven base fabric is a single-layer woven fabric or a multi-layer woven fabric, it comprises an upper layer, that defines the web facing side of the woven base fabric. The upper layer is formed from upper cross-machine direction yarns that are interwoven with upper machine direction yarns. Preferably, the sublayer beads extend so deeply into the woven base fabric that they create a form-fit connection with at least some of the upper cross-machine direction yarns at their deepest points, that is where these upper cross-machine direction yarns pass under the upper machine direction yarns. In other words, the sublayer beads preferably surround the upper cross-machine direction yarns at their deepest points by more than half of their diameter to create such a form-fit connection. This leads to a very strong hold of the sublayer beads within the woven base fabric. At the same time, it is preferred that the sub-layer beads do not extend deeper than the thickness of the upper layer into the woven base fabric, so as not to reduce the void volume of the woven base fabric too much.
As mentioned above, to provide a highly visible pattern into the fiber web produced on the structuring fabric, it is preferred that structuring beads have a substantially rectangular cross-sectional shape. In particular, the structuring beads may have a substantially square cross-sectional shape. The term “substantially” shall mean here that the side-walls of the structuring beads do not necessarily have to be exactly flat and/or that the corners of the substantially rectangular cross-sectional shape are not allowed to be slightly rounded.
As shown and described in WO 00/75424 A1 the structuring beads can form continuous lines on the web facing surface of the woven fabric, wherein preferably the continuous lines substantially extend in machine direction of the structuring fabric. The term “substantially in machine direction” means in this context that their main extension is in machine direction and not in cross machine direction of the structuring fabric. However, the structuring beads do not have to extend precisely as straight lines in machine direction. For example, the structuring beads may have a wavy configuration or may form a zig-zag pattern. They also may have in total a small inclination angle with respect to the machine direction of the structuring fabric. Preferably, the structuring beads do not cross each other. Instead, they can extend substantially parallel to each other. If the structuring beads form continuous lines on the web facing surface of the woven fabric, this implies that they can not be formed by extruding the resinous material through a rotary screen. Instead, a method called “nozzle extrusion deposition” is preferably applied.
Of course, it is possible to use a polymeric material for forming the sublayer beads that differs from the polymeric material for forming the structuring beads. For example, the polymeric material for forming the sublayer beads may have a lower viscosity than the polymeric material for forming the structuring beads. A lower viscosity can be beneficial to enhance the penetration of the material into the volume of the woven base fabric. However, for the sake of simplicity and to achieve a very good bonding between the two beads, it is often preferred that the polymeric material of the structuring beads is the same as the polymeric material of the sublayer beads. A good bonding can be achieved especially achieved if the two beads are applied in a so-called “wet-in-wet” method.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing a structuring fabric of the present invention as described above. The method comprises the following steps:
The term “onto” in step a) might be read as “into” since the polymeric material forming the sublayer bead shall at least partly, preferably completely, penetrate into the woven base fabric.
The nozzles may be stationary while the woven base fabric is moved in machine direction of the structuring fabric to be produced. This will result in a pattern of straight lines extending in machine direction. If the pattern shall be a zig-zag configuration or a wavy configuration, the nozzles may be movable in cross machine direction during the manufacturing process. An example is illustrated in
To guarantee that the structuring bead is precisely located on top of the corresponding sublayer bead, the first extrusion nozzle and the second extrusion nozzle are preferably integrally formed in one extrusion die. Furthermore, it is advantageous if the distance between the two different nozzles is kept small. With respect to the moving direction of the woven base fabric during the production process of the structured fabric, the two nozzles are preferably located one behind the other so that first the sublayer bead is applied onto the web facing side of the woven base fabric and then, on top of the sublayer bead, the structuring bead is applied.
In a further preferred embodiment, a plurality of pairs of first extrusion nozzles and second extrusion nozzles are integrally formed in one extrusion die.
Preferably, the first extrusion nozzle is formed in a first surface of an extrusion die which first surface is substantially parallel to the web facing surface of the woven fabric during the extrusion process, wherein the second extrusion nozzle is formed in a second surface of an or the extrusion die which second surface is inclined with respect to the web facing surface of the woven fabric during the extrusion process. This allows to ensure that the resinous material extruded through the first extrusion nozzle to form the sublayer bead will penetrate deeper the volume of the woven base fabric.
Furthermore, the distance of the first extrusion nozzle to the web facing surface of the woven fabric is preferably larger than the distance of the second extrusion nozzle to the web facing surface of the woven fabric during the extrusion process.
To achieve a strong bonding between the sublayer bead and the structuring bead the structuring bead can be extruded in step b) at a time when the sublayer bead has not been cured yet, at least not completely. This is sometimes called “wet-in-wet” method. Even though the two beads may be formed from the same polymeric material, such as silicone, and may be cured substantially at the same time, it is still possible to clearly recognize, at least in a laboratory, the border between the two beads in the final product.
It has been found out that good results are achievable if the first nozzle is substantially rectangular shaped, whereas the second nozzle is substantially star-shaped. The star-shaped nozzle can lead to a structuring bead having a substantially rectangular, in particular substantially square, formed cross-section.
Furthermore, it has been found out that it is beneficial if the width of the first, substantially rectangular shaped nozzle is substantially the same as the smallest width of the second, substantially star-shaped nozzle and/or the length of the first, substantially rectangular shaped nozzle is substantially half the length of the second, substantially star-shaped nozzle. The term “width” of the first nozzle refers to its extension in cross machine direction of the structuring fabric during the production process, whereas the term “length” of the first nozzle refers to its extension in machine direction of the structuring fabric during the production process.
Good results as to the shape of the extruded beads and to the constitution of the structuring fabric are achievable if the polymeric material (extruded through the first extrusion nozzle) to form the sublayer-bead and/or the polymeric material (extruded through the second extrusion nozzle) to form the structuring-bead is a silicone, in particular a two-component silicone. Preferably, the same material is extruded through the first extrusion nozzle and the second extrusion nozzle to achieve a good bonding between the sublayer-bead and the structuring-bead.
However, it is also possible that the polymeric material forming the sublayer-bead and/or the polymeric material forming the structuring-bead is a polyurethane.
In another embodiment of the present invention, the polymeric material forming the sublayer-bead and/or the polymeric material forming the structuring-bead is an acrylic material, in particular a UV-curable acrylic material.
In that embodiment, the acrylic material, comprises at least one of the following components: 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.
In a preferred embodiment of the acrylic material composition, none of the mentioned components contributes more than 50% by weight to the composition of the acrylic material.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as being embodied in a structuring fabric with sublayer beads and a method of producing the same, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now once more to the figures of the drawing in detail,
In contrast with the prior-art embodiment of
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.
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.
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
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.
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
The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
| Number | Date | Country | Kind |
|---|---|---|---|
| 23166785.8 | Apr 2023 | EP | regional |
This application claims the benefit, under 35 U.S.C. § 119, of provisional patent application No. 63/485,060 filed Feb. 15, 2023, and of European patent application EP 23166785.8, filed Apr. 5, 2023; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63485060 | Feb 2023 | US |
