Improvements in papermaking fabrics

Abstract: A papermaking fabric comprises a base layer (10) which may be a woven or nonwoven textile, or a perforated plastics membrane. This supports a layer of partially fused layer (11) of metal or plastics particles or fibres, with a textile reinforcement structure (12). The layer (11) has a paper-contacting surface formed with raised areas (15) and/or recessed areas (16) provided by moulding or embossing the layer (11).

Description: This invention relates to improvements in papermaking fabrics. WO 96/35018 (Kimberly-Clark Corpn.) discloses a process of forming patterned or decorative markings on tissues including the use of a forming fabric with areas of relatively slow water drainage. Where a fibre slurry containing both relatively long and relatively short fibres is used, the provision of areas of different water drainage rates causes the markings to be delineated by areas of different fibre composition, or shorter fibre lengths, preferably avoiding areas of slower drainage. The areas of relatively slow water drainage are provided by providing additional filaments over or within the fabric weave pattern, or by a film or coating which blocks or fills void space within the fabric. The area does not necessarily protrude from the surface of the fabric. This arrangement however is somewhat restrictive in the possible variety of markings which may be imparted to a tissue or other fibrous web, for example it may be useful to include areas of enhanced drainage in the fabric as well as or instead of areas of slower drainage, or areas of the same drainage rate as the rest of the fabric which are perhaps distinguished in a different manner, e.g. by standing proud of the fabric surface or being recessed below the fabric surface, to emboss the tissue web. Such a variety of possible effects cannot be achieved by the forming fabric described in WO 96/35018 noted above. An object of this invention therefore is to provide a papermaking fabric which can enable such effects to be achieved. According to the invention, a papermaking fabric comprises a paper-contacting surface layer of partially fused particles, the paper-contacting layer having a surface which comprises areas which are proud of or recessed relative to the main plane of the paper-contacting surface. From another aspect, the invention provides a fabric comprising a base layer or substrate, having decoratively shaped areas on the web contacting surface, said areas comprising sintered particles which are fused or bonded to the substrate. The surface layer is normally supported by a base layer which may be a woven or nonwoven fabric, or a membrane (which may be perforated or in the form of a grid) of nonwoven material such as a sheet of a synthetic plastics material. The surface layer of partially fused particles may include a reinforcing textile structure which is fully or partially embedded in the layer of partially fused particles. The partially fused particles may form a sintered matrix, and be composed of sintered polymer or metal particles or fibres, or a mix of particles and fibres. The reinforcing textile structure may comprise a woven or nonwoven fabric, or a random but generally uniform dispersion of chopped fibres. The fibres or yarns of the reinforcing structure may be bicomponent structures incorporating materials of different melting point. The fibres or yarns may preferably have a higher melting point than the reinforcing structure. Both raised and recessed areas may be provided in the paper-contacting surface of the fabric. Raised areas may be provided by forming an additional thickness of the sintered matrix having the same density and thus the same drainage flow rate as the main body of the matrix. Similarly, recessed areas may be provided by omission of a thickness of the sintered matrix so that the matrix again has the same density and drainage flow rate as the main body of the matrix. On the other hand, the raised and/or recessed areas may be provided by moulding of the paper-contacting surface of the sintered matrix, e.g. using a patterned platten or roller to impress the surface. In this case recessed areas will have a greater density and thus reduced drainage flow rate than the main body of the matrix, and raised areas will have a lesser density and thus increased drainage flow rate with respect to the main body of the matrix. Where the fabric is to be used as a dryer fabric, for example in a through-air-dryer, it is to be noted that the air permeability is the relevant quality which is determined by the matrix density, rather than the drainage rate. The invention will be further described by way of example with reference to preferred embodiments of the invention as illustrated in the accompanying drawings wherein:- Figure 1 is a sectional view of a papermachine fabric according to the invention wherein raised and/or recessed areas of the paper-contacting surface have substantially the same density; Figure 2 is a sectional view of a papermachine fabric according to the invention wherein raised and/or recessed areas of the paper-contacting surface have reduced or increased density; and Figure 3 is a sectional view of a further embodiment of the invention. In Fig. 1, 10 is a support or base fabric which can be a woven fabric, a nonwoven fabric, a membrane or perforated or reticulated membrane or a composite of one or more layers of any of the said materials. A layer 11 is provided on at least the paper-contacting side of the base fabric 10 which is formed of a layer of sintered particles and/or fibres of a suitable plastics material such as polyethylene or polypropylene or other materials such as set out in EP-A-653512. This layer of sintered material has the fabric 10 embedded wholly within it to form a textile reinforcement structure which is shown diagrammatically as a conventional representation of a woven fabric. However, a nonwoven scrim or a dispersion of chopped fibres may be used instead or additionally. The paper-contacting surface 13 has a general or median level 14, to which most of the surface conforms. However, selected raised areas 15 stand proud of the surface level 14, whilst other areas 16 are recessed below the surface level 14. These proud and recessed areas preferably form a pattern which will have a decorative or a functional effect on a paper web formed or carried on the surface 13. The proud and recessed areas are formed by moulding of the layer 11 during the process of forming the layer, so that extra material is provided in the raised areas 15, whilst less material is provided in the recessed areas 16. Consequently, the sintered material has essentially the same density in the raised areas 15 and in the recessed areas 16 as elsewhere in the layer 11. The fabric according to Fig. 1 produces an embossing effect on any tissue or web formed or carried on the fabric due to the effect of the raised and/or lowered areas. Either the raised areas, or the recessed areas may be omitted. In Fig. 2, a papermachine fabric comprises a base layer 20, which may be any one of the options suggested in the description of Fig. 1 above. The base layer 20 carries a layer 21 which consists of a layer of sintered particles and/or fibres of a suitable plastics material, or of a sintered metal, as discussed in EP-A-653512. The base layer 10 comprises a reinforcing fabric 22 which is wholly embedded within the sintered layer 21 and may be a woven or nonwoven fabric, or a dispersion of chopped fibres, but is shown as a conventional representation of a woven fabric. Layer 21 has a paper-contacting surface 23 which has a general or median plane 24. The surface 23 carries raised areas 25, and recessed areas 26, as in Fig. 1. However, these areas are formed by embossing the layer 21 after formation using a roller or platten press. Consequently the parts of layer 21 below raised areas 25 are less densely compressed than the main part of the layer 21, and the parts of layer 21 below recessed areas 26 are more densely compressed than the main part of the layer 21. This is symbolised by less dense hatching of the raised parts and more dense hatching of the recessed parts. In this case, the air permeability and water drainage flow rate are differentially effected, so that the fabric not only embosses any tissue formed or carried thereon, but also introduces marking due to different fibre deposition patterns. Instead of using relatively complicated techniques such as silk screen printing or jacquard weaving to overlay patterns, a simple single step process is made available, and the fabric is not susceptible to wear or delamination of such patterns from the fabric. Fig. 3 illustrates a third embodiment, where discrete areas 30 of sintered particles and/or fibres of metal or plastics material are bonded direct to a base layer 31. The base layer 31 may again be a substrate comprised of a woven or nonwoven fabric, or a membrane, or a composite of such layers. The general or median level 32 of the paper-contacting face of the fabric is provided by the substrate, and raised areas are provided by the discrete areas 30. The present invention allows an embossing fabric to be made by a quick single step process and due to integral formation of the decoratively shaped areas from the material forming the web-contacting surface, the resistance of the areas to delamination is increased. The sintered areas offer greater resistance to wear than the materials used in the prior art referred to above, and thus the initial distinction of the embossed pattern is maintained over a much greater period. Drainage or permeability is varied in the decoratively shaped areas in a highly controlled manner by varying the density of the sintered material.

Claims: A papermaking fabric comprising a paper-contacting surface layer (11; 21) at least areas of which are formed from a layer of partially fused particles, the paper-contacting surface layer having a surface which comprises areas (15, 16; 25, 26) which are proud of or are recessed relative to a main plane (14; 26) of the paper-contacting surface. A papermaking fabric comprising a base layer (31) or substrate having discrete shaped areas (30) on the paper-contacting face of the fabric, said shaped areas comprising sintered particles which are joined to the substrate. A fabric according to claim 1 wherein said surface layer (11; 21) is supported by a base layer (10; 20). A fabric according to claim 3 wherein the base layer (10; 20) comprises a woven or nonwoven textile material. A fabric according to claim 3 wherein the base layer (10; 20) comprises a membrane of nonwoven sheet material. A fabric according to claim 5 wherein said membrane comprises a sheet of synthetic plastics material which is perforated or in the form of a grid. A fabric according to claim 1 wherein the layer of partially fused particles includes a reinforcing textile structure (22) which is fully or partially embedded in the layer of partially fused particles. A fabric according to claim 7 wherein the partially fused particles form a sintered matrix, and is composed of sintered particles and/or fibres of one or more polymeric materials, or a mix of such particles and fibres. A fabric according to claim 7 wherein the reinforcing textile structure comprises a woven or nonwoven fabric, or a random but generally uniform dispersion of chopped fibres. A fabric according to claim 9 wherein the reinforcing textile structure comprises fibres or yarns which are bicomponent structures incorporating materials of different melting point. A fabric according to any preceding claim wherein the reinforcing textile structure is provided by the base layer (10; 20; 31). A fabric according to claim 1 wherein both raised and recessed areas (15, 16; 25, 26) are provided in said surface layer (11; 21). A fabric according to claim 12 wherein said raised areas (15; 25) are provided by forming an additional thickness of a sintered matrix having the same density and drainage flow rate as the main body of said layer of partially fused particles, and said recessed areas (16; 26) are provided by omission of a thickness of the sintered matrix. A fabric according to claim 12 wherein said raised and/or recessed areas (15, 16; 25, 26) are provided by moulding of said paper-contacting surface (13; 23) of the layer of partially fused particles.

Inventors: SAYERS IAN CHRISTISON, SAYERS, IAN CHRISTISON
Applicants: VOITH FABRICS HEIDENHEIM GMBH, VOITH FABRICS HEIDENHEIM GMBH & CO.KG
Application year: 1999
Main classification: D21F1
IPC codes: D21F11, D21F1