Multi-layered papermakers fabric for thru-dryer application

Abstract: A multi-layer fabric (10) for carrying and forming an embossed paper web is provided which comprises two separate woven fabric layers (12,14) which are joined together, preferably during weaving. The top fabric layer (12) is a very coarse mesh open fabric which supports the web and assists in forming the embossed characteristic of the web. The top layer is connected to a base fabric layer (14) which is a substantially finer mesh. The layers are preferably interconnected by binder strands (25) which interweave as structural warps or shutes of the finer mesh fabric layer.

Description: The present invention relates to a papermaking apparatus according to the preamble of claim 1 and to a method of using a papermaker's fabric according to the preamble of claim 11 for forming nonwoven paper products. The nonwoven paper products are intended to have the softness and feel associated with cloth products but have improved strength in comparison with similar nonwoven products. In general, products produced with fabrics in accordance with the invention may be classified as embossed nonwoven paper products. In the typical process for producing embossed nonwoven paper products, the papermaking equipment has a formation area, a thru-drying area and a final drying area. Such a process is described in U.S. Patent 4,528,239 which is incorporated herein by reference as if fully set forth. In the forming area, an initial embryonic web is formed on a formation fabric and is transferred to a second formation fabric which subsequently rearranges and further dewaters the web. The present invention of thru-dryer fabric is concerned with the second formation position. U.S. Patent 3,322,617 discloses the use of two formation fabrics in the forming position for the purpose of producing simulated grain on a nonwoven product. The upper or primary formation fabric is of a large open area with a very coarse weave and the second, fiber retention fabric is of a much finer weave. The fabrics run simultaneously but are not interconnected. U.S. Patent 3,885,603 discloses a formation fabric having a fine upper fabric and a coarse lower fabric which are interconnected by binder yarns. This dual layer fabric is used as a formation belt with the fine ply operating in contact with the paper web. As a result of the binder yarns, the two fabrics operate as one unit. U.S. Patent No. 4,515,853 discloses a similar use of binder yarns. French Patent 2,122,596 discloses a papermaker's apparatus having a metal mesh and a metal grid which are used in conjunction with, and may be attached to, one another. The metal mesh is of a substantially finer mesh than the metal grid, the exposed surface of which defines a paper carrying surface. This document also discloses that the metal mesh and grid may be woven, and later attached to each other by stitching. It does not, however, teach that the two meshes may be integrally woven together to form an integrally woven, two layer, unitary fabric. European patent application No. EP-A-0232715 discloses a papermaker's apparatus having a first and second forming area with first and second forming fabrics respectively. The second forming area has thru-dryer means and the second forming fabric is a thru-dryer fabric comprised of a first and a second layer integrally woven together into a unitary fabric; the second layer is woven in a substantially coarser mesh than the first layer. The first layer defines a paper-carrying surface for supporting the paper web through the second forming area of the papermaker's apparatus. The present invention relates to a fabric for use in a secondary formation process. Accordingly, the initial web is formed on a generally planar formation fabric and then is transferred to the thru-dryer fabric of the present invention. It is an object of the present invention to create a pillow effect on the wet-laid web to improve bulk, softness, and flexibility while at the same time allowing up to 40% reduction in basis weight over conventional fabrics. It is also an object of the invention to provide a relatively large cross machine direction to a machine direction stretch ratio which improves the total tensile strength. Further objects of the invention are to simplify the manufacturing of the thru-air drying fabric, provide substantially longer fabric service life, and improve the ability to clean the fabric in use. These objectives are accomplished through the apparatus and method according to claims 1 and 11 respectively. Further features of the apparatus are defined in dependent claim 2 to 10. A multilayer fabric is provided which comprises two separate fabric layers which are joined together, preferably during weaving. The top fabric layer is a very coarse mesh open fabric which supports the web and assists in forming the embossed characteristic of the web. The top layer is connected to a base fabric layer which is a substantially finer mesh. The layers are preferably interconnected by binder strands which interweave as structural warps or shutes of the finer mesh fabric layer. The coarse mesh top layer may be woven in a 2-shed, 3-shed, 4-shed or even higher harness construction, either in twill or a broken weave constructions. The base fabric is preferably woven in a plain weave, but also may be woven in a 3, 4 or 5-shed construction. Preferably, the top fabric layer is a 5-shed which is most advantageous for the pillow areas and the base fabric is preferably a plain weave to provide maximum stability for the upper layer. The fine mesh bottom layer in a plain weave offers substantial support to the coarse mesh upper layer. All material, both warp and shute, in addition to the binder, are preferably, hydrolysis resistant material to improve service life. Further objects and advantages are apparent from the following description of a presently preferred embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a partial cross section in the machine direction of a multi-layer fabric made in accordance with the teachings of the present invention; Figure 2 is a cross section of the fabric depicted in Figure 1 along the binding yarns which interweave the fabric layers; Figure 3 is a schematic cross section of the fabric depicted in Figures 1 and 2 in the cross machine direction; Figure 4 is a bottom plan view of the fabric depicted in Figure 1; and Figure 5 is a top plan view of the fabric depicted in Figure 1. Referring to Figures 1 and 2, a multi-layer fabric 10 according to the present invention is shown having an upper layer 12 and base layer 14. Yarns 16 and 18 are interwoven to produce a coarse upper fabric layer 12, and yarns 20 and 22 are interwoven to produce a finer bottom fabric layer 14. The two layers 12, 14 are connected by binder yarns 25. The layers are woven simultaneously with the binder strands which hold the two fabrics together. Preferably, yarns 16, 20, 25 are strung as warp on the loom and yarns 18, 22 are interwoven therewith. In the preferred embodiment the weave construction of the top coarser fabric is a 5-shed broken weave and the lower fabric is a plain weave. The 5-shed top layer is approximately 13.79 by 12.61 yarns per cm (35 and 32 yarns per inch) and can be as low as 5.52 by 4.73 yarns per cm (14 by 12 yarns per inch). The plain weave bottom is approximately 27.58 by 25.22 yarns per cm (70 by 64 yarns per inch) and which can be as low as 11.03 by 9.46 yarns per cm (28 by 24 yarns per inch). Preferably, the yarns of the top layer are between .025 and .064 cm (.010 and .025 inches) in diameter, and the base layer and binder yarn are smaller in diameter being between .013 and .043 cm (.005 and .017 inches). The mesh counts and yarn size in both the top and bottom fabrics can be varied in accordance with the above parameters and in view of the end product desired. Preferably the ratio of yarn count between the bottom and top layers is at least 2:1 and the size ratio is between 3:1 and 5:4. With reference to Figures 2-5, the binder yarns 25 interweave in pairs 25a, 25b with the top and bottom layers 12, 14. Each pair of binder yarns interweaves at a single warp location within the bottom fabric layer weave structure. For example, binder yarn 25a interweaves with five bottom layer yarns 22 then passes over seven bottom layer yarns while it interweaves with the top layer 12 before it returns to interweave with five more bottom layer yarns. Binder yarn 25b interweaves with five of the seven bottom layer yarns over which binder yarn 25a passes. When binder yarn 25b interweaves with the top layer 12, binder yarn 25b passes over seven bottom layer yarns which seven yarns include the five yarns with which binder yarn 25a interweaves. The binder yarns are preferably the same size as the bottom layer warp yarns. Accordingly, they blend into the weave of the bottom layer 14 and form a structural part of that layer. Although the binder yarns occupy discernibly more space than a single warp yarn 20 within the bottom layer 14, they occupy significantly less than the space occupied by two adjacent warp yarns 22 in the bottom layer 14. Thus the binding yarns do not have any substantial effect on the permeability and open area of the bottom layer. As best seen in Figures 2 and 5, the binder yarn pairs 25a, 25b preferably interweave with every third top layer yarn 18. In practice, the binder yarns 25a, 25b tend to weave along side warp yarns 16 when weaving over shute yarns 18, in lieu of weaving substantially in the middle between adjacent warp yarns 16. Due to the smaller size of the binder yarns and their tendencies in weaving, the open area and uniformity of surface and formation characteristics of the upper layer are substantially unaffected by the binder yarns. The use of a higher mesh count in the lower or bottom fabric prevents the fibres of the aqueous paper web from blowing through the fabric during the thru-dryer processing. The use of a coarser fabric having a lower mesh count in the upper or top layer permits formation of pillows on the web in the thru-dryer position. The binding yarns 25 lock the fabric layers 12, 14 to each other to avoid irregularities which may result from shifting of the fabric layers relative to each other. In addition the use of binder strands results in a bottom fabric layer which is a carrier for the forming ply. Example 1. The fabric is woven from monofilament, hydrolysis resistant, polyester yarns. A top fabric layer is woven 5.52 warp by 4.73 shute yarns per cm (14 warp by 12 shute yarns per inch). The weave pattern is a 5-shed broken weave with a warp of .051 cm (.020 inches) and a shute of .051 cm (.020 inches). Accordingly, the top layer hole size is .1608 cm (.0633 inches) by .1305 cm (.0514 inches) with a hole diagonal of .2073 cm (.0816 inches), open area 54.7%, air permeability 0.6254 CMM (per square metre at 1 N/m²) (1085 CFM (per square foot at 1/2 inch pressure drop)), and calliper .175 cm (.069 inches). The bottom fabric layer is woven 11.03 warp by 9.46 shute yarns per cm (28 warp by 24 shute yarns per inch) having warp yarns of .0401 cm (.0158 inches) and shute yarns of .0401 cm (.0158 inches) in a plain weave. The hole size in the bottom fabric is approximately .0658 cm (.0259 inches) by .0505 cm (.0199 inches) with a hole diagonal of .0828 cm (.0326 inches), open area 31.7%, and air permeability 0.403 CMM (700 CFM). The binder pairs define every tenth warp on the bottom layer and are disposed after every fifth warp layer of the top layer binding every third top shute as shown in Figures 2 - 5. Example 2. A top fabric layer is woven 13.79 warp by 12.61 shute yarns per cm (35 warp by 32 shute yarns per inch). The weave pattern is a 5-shed broken weave with a warp of .0401 cm (.0158 inches) and a shute of .0401 cm (.0158 inches). Accordingly, the top layer hole size is .0393 cm (.0155 inches) by .0325 cm (.0128 inches) with a hole diagonal of .051 cm (.020 inches), open area 22.1%, and air permeability .461 CMM (800 CFM). The bottom fabric layer is woven 27.58 warp by 25.22 shute yarns per cm (70 warp by 64 shute yarns per inch) having warp yarns of .0170 cm (.0067 inches) and shute yarns of .0170 cm (.0067 inches) in a plain weave. The hole size in the bottom fabric is approximately .0226 cm (.0089 inches) by .0193 cm (.0076 inches) with a hole diagonal of .0297 cm (.0117 inches), open area 30.3%, and air permeability .375 CMM (650 CFM). The binder pairs define every tenth warp on the bottom layer and are disposed after every fifth warp layer of the top layer binding every third top shute as shown in Figures 2 - 5. In both examples, the fabrics provide a uniform pattern of depressions or dimples with the lower fabric helping to increase the density of the paper web in the dimple area while its density is dramatically reduced on the top surface. The multilayer thru-dryer fabric may be surfaced by abrading the top layer yarns to provide from 15% to as high as 40% contact area. The contact area assists in the moving the fibre into the dimpled areas for basis weight reduction. In addition, through heatsetting processes, theratio of warp to shute contact areas may be varied in order to have a direct effect on the tensile strength of the sheet. The present thru-dryer fabric avoids the costly prior art techniques of creating an embossing layer on a substrate while producing a machine applications and the necessary paper contact characteristics to produce the desired nonwoven product.

Claims: A papermaking apparatus having a first forming area in which the web is transported by a first support fabric, and in which an initial embryonic web is formed, and a second forming area including thru-dryer means, the preformed paper web being transported in the second forming area by a second support woven fabric (10) comprising a first woven layer (14) defining a first fabric surface, and a second woven layer (12) defining a second fabric surface, the second layer (12) being woven in a substantially coarser mesh than the first layer (14) from yarns (16,18) having a significantly larger size than the first layer yarns (20,22), the first and second layers being integrally woven into a unitary fabric having means (25a, 25b) for interconnecting the first and second layers, said apparatus being characterised in that said second support fabric (10) is installed such that the paper web is carried on said second fabric surface, the interconnection of the first layer with the second layer providing structural support and stability to the second layer, said thru-dryer means further forming said web by forcing the web into the relatively coarse mesh of the second layer of said second support fabric (10) as the fabric transports the web, thereby creating a pillow effect on the web. A papermaker's apparatus according to claim 1 wherein said interconnecting means comprises pairs of binding yarns (25a and 25b) of substantially the same size as the first layer warp yarns (20 and 22), interwoven with said first layer (14) substantially within the repeat of the first layer (14) in a single warp yarn location and interweaving with selected individual yarns (18) of said second layer (12). A papermaker's apparatus according to claim 2 wherein said first fabric layer (14) is woven with at least twice the number of warp (20) and shute (22) yarns per cm than the warp (16) and shute (18) yarns per cm of said second fabric layer (12). A papermaker's apparatus according to claim 3 wherein said first fabric layer (14) is woven in a plain weave and said second fabric layer (12) is woven in a 5-shed broken weave. A papermaker's apparatus according to claim 4 wherein said first fabric layer (14) is woven between 27.6 and 11.0 warp yarns (20) per cm (70 and 28 warp yarns per inch) and between 25.2 and 9.5 shute yarns (22) per cm (64 and 24 shute yarns per inch and said second fabric layer (12) is woven between 13.8 and 5.5 warp yarns (16) per cm (35 and 14 warp yarns per inch) and between 12.6 and 4.7 shute yarns (18) per cm (32 and 12 shute yarns per inch). A papermaker's apparatus according to claim 5 wherein said binding yarn pairs (25a and 25b) define every tenth warp yarn (20) on said first layer (14) and are disposed after every fifth warp yarn (16) of said second layer (12), binding every third shute yarn (18) of said second fabric layer. Papermaker's apparatus according to claim 1 wherein said first fabric layer (14) is woven with approximately twice the number of warp (20) and shute (22) yarns per cm than the warp (16) and shute (18) yarns per cm of said second fabric layer (12). A papermaker's apparatus according to claim 1 wherein said first fabric layer (14) is woven in a plain weave and said second fabric layer (12) is woven in a 4-shed broken weave. A papermaker's apparatus according to claim 1 wherein said first fabric layer (14) is woven between 27.6 and 11.0 warp yarns (20) per cm (70 and 28 warp yarns per inch) and between 25.2 and 9.5 shute yarns (22) per cm (64 and 24 shute yarns per inch) and said second fabric layer is woven between 13.8 and 5.5 warp yarns (16) per cm (35 and 14 warp yarns per inch) and between 12.6 and 4.7 shute yarns (18) per cm (32 and 12 shute yarns per inch). A papermaker's apparatus according to claim 1 wherein said fabric (10) is surfaced by abrading the yarns (16, 18) of said second layer to provide from 15% to 40% contact area. Method of using in a papermaking apparatus a papermaker's fabric (10) of the type comprising a first woven layer (14) defining a first fabric surface, and a second woven layer (12) defining a second fabric surface, the second layer being woven in a substantially coarser mesh than the first layer (14) from yarns (16,18) having a significantly larger size than the first layer yarns (20,22), the first and second layers being integrally woven into a unitary fabric having means (25a, 25b) for interconnecting the first and second layers, whereby said fabric (10) forms a second support fabric to transport a pre-formed paper web in a second forming area of the papermaking apparatus provided with thru-dryer means, said paper web being initially formed in a first forming area of said papermaking apparatus in which it is transported by a first support fabric, the method being characterised in that the second support fabric (10) is installed such that the paper web is carried on said second fabric surface,the thru-dryer means thus forcing the paper web into the relatively coarse mesh of the second layer of said second support fabric as the fabric transports the web, thereby creating a pillow effect on the web, the interconnection of the first layer with the second layer providing structural support and stability to the second layer.

Inventors: BIASONE FRANK, DURKIN THOMAS B, BIASONE, FRANK, DURKIN, THOMAS B.
Applicants: ASTEN INC, ASTEN, INC.
Application year: 1990
Main classification: D21F1
IPC codes: D21F11, D21F1