Papermakers felt with a resin matrix surface

Abstract: A woven press felt base 20 (single or multiple layer) has a plastic, fibre reinforced, resinous matrix coating 25 comprising a resin 40, textile fibres 30 distributed throughout the resin and open air channels and voids 50 throughout the resin once it is hardened.

Description: This invention pertains to fabrics used in the papermaking industry. More particularly it relates to felts used in the wet section of a papermaking machine. During the papermaking process, felts are used to dewater the paper web. The felts undergo severe environmental stresses, ie changes in temperature, pressure, humidity, etc. Despite these changes, the felts must retain compaction resistance, resiliency, wear resistance, dimensional stability and ability to distribute pressure uniformly. Various felts have been developed to meet these demands, however none have been found to be completely satisfactory. One example of a prior art press felt is disclosed in International Patent Application Specification No. WO 86/05219 and comprises a belt made by casting a polymer on an endless mould. The mould is provided with nails that cause the formation of tapered channels in the finished belt, which channels permit the passage of fluid through the belt. European Patent Application Specification No. 0 196 045 discloses a further example of a prior art press felt comprising a woven base fabric on which is provided a resin coating containing a plurality of channels. The channels are formed by incorporating solvent-removable fibres or particles in the liquid coating, and, once the coating has been cured, removing such fibres or particles by means of an appropriate solvent. EP-0 248 182 A, which forms part of the state of the art under Art.54 (3) EPC in relation to the designated states BE, DE, FR, GB, IT, NL, SE, discloses a press felt comprising a needled felt on a base, with a plastic foam material embedded in the needled felt. It is an object of the present invention to provide a felt having improved characteristics compared with those at present available. The present invention provides a press felt for use in papermaking machines, comprising an endless, woven base and a plastic, fibre-reinforced, resinous matrix coating on the woven base, said resinous matrix coating comprising: a resin; a network of textile fibres distributed throughout said resin; and open channels and voids throughout said matrix to permit fluid flow therethrough and allow a paper web to dewater; in which press felt the fibres are not bonded to the woven base other than by the resin. The woven base is made endless either by being constructed endless, or by being seamed or joined to make it endless. The resin may be thermoplastic, for example polyurethane or polyvinyl chloride. The present invention further provides a method of manufacturing a press felt, which comprises: providing an endless, woven base; coating said woven base with fluid resin containing a network of textile fibres; curing said resin on said woven felt base; and grinding said resin coated woven felt base to open sealed voids and channels and to impart a smooth, highly uniform finished surface to said felt. The present invention also provides a method of manufacturing a press felt, which comprises: providing an endless, woven base, with a network of textile fibres on the woven base, said fibres not being bonded to the woven base; coating said woven base with a fluid resin; curing said resin on said woven base; and grinding said resin coated woven felt base to open sealed voids and channels and to impart a smooth, highly uniform finished surface to said felt. By way of example, a press felt constructed in accordance with the invention will now be described with reference to the accompanying drawings. In the drawings, like reference numerals indicate corresponding parts throughout both views: Fig. 1 is a pictorial plan view illustrating a papermakers felt in the form of an endless belt, and Fig. 2 is a cross-sectional view of the felt. As shown in Fig. 1 the woven press felt base 20 is made endless to obtain the papermakers felt 10. The press felt base may be either constructed endless, seamed or joined. The felt 10 may be mounted in the press section of a papermakers machine after being treated as will be described hereinafter. Fig. 2 is an enlarged cross-sectional view of the felt 10 shown in Fig. 1 and shows that the woven base 20 has a matrix coating 25 which is comprised of a thermoplastic resin 40, a network of fibres 30, and voids and open channels 50 throughout the matrix. The voids and channels permit fluid flow in the matrix. The resin 40 is applied to the woven base 20 by conventional techniques, such as by dipping, spraying and the like of the liquid pre-former of the resin. The method and rate of application of the resin, along with the fibre reinforcement structure and chemical additions, will control the volume of voids within the matrix. The pre-former of the resin may contain fibres 30 prior to its application on the base. An alternative method is to have the fibres 30 on the woven base 20 prior to application of the resin. Following application, the resin 40 is dried and cured, employing conventional drying and heating apparatus. The temperature of curing will be dependent on the type of resin employed. A wide variety of such resins is known and many are commercially available. Representative resins which may be used are polyurethane for workability, resiliency and cleanability and polyvinyl chloride for hardness and compaction resistance. Flexible coatings may also be formed from mixtures of polymeric resins. Following curing, the resin-coated woven base 20, 40 is ground to impart a smooth, highly uniform finished surface to the felt. The grinding will also open up sealed voids and channels 50. While the woven base 20 shown in Fig. 2 is a single layer, a greater number of layers in the woven base is also possible. In the press felt shown in the drawings, the plastic, fibre reinforced, resinous matrix surface replaces the normal needle-punched staple fibre surface of a conventional press felt. The distribution, composition and size of the network of textile fibres 30 is engineered to enhance the mechanical properties of the total matrix and it has been found that the matrix will maintain caliper longer than staple fibres when subjected to the successive loading/unloading cycles in a nip press of a papermaking machine. The matrix also has an ability to recover from deformation which is superior to staple fibres. This results in a longer operational life of the felt and cost savings from a reduced machine downtime associated with felt replacement. The felt also has increased wear resistance arising directly from the matrix material and also from its improved bonding characteristics (the thermomechanical and chemical adhesion being far better than the fibre entanglement used in prior art felts). The resinous materials used in the matrix also have an intrinsically low affinity for the contaminants found in the paper machine environment. In addition, the felt provides a uniform and complete pressure distribution between the paper web and felt surfaces in the nip, and this feature results in improved dewatering of the paper sheet.

Claims: A press felt to be used in papermaking machines, comprising an endless, woven base (20) and a plastic, fibre reinforced, resinous matrix coating (25) on the woven base, said resinous matrix coating comprising: a resin (40); a network of textile fibres (30) distributed throughout said resin; and open channels and voids (50) throughout said matrix to permit fluid flow therethrough and allow a paper web to dewater; in which press felt the fibres are not bonded to the woven base other than by the resin. A woven press felt according to claim 1, in which said resin is thermoplastic. A woven press felt according to claim 1 or claim 2, in which said resin is polyurethane. A woven press felt according to claim 1 or claim 2, in which said resin is polyvinyl chloride. A method of manufacturing a press felt, which comprises: providing an endless, woven base; coating said woven base with fluid resin containing a network of textile fibres; curing said resin on said woven felt base; and grinding said resin coated woven felt base to open sealed voids arid channels and to impart a smooth, highly uniform finished surface to said felt. A method of manufacturing a press felt, which comprises: providing an endless, woven base with a network of textile fibres on the woven base, said fibres not being bonded to the woven base; coating said woven base with a fluid resin; curing said resin on said woven base; and grinding said resin coated woven felt base to open sealed voids and channels and to impart a smooth, highly uniform finished surface to said felt.

Inventors: BOYER DONALD R, CROOK ROBERT L, BOYER, DONALD R., CROOK, ROBERT L.
Applicants: ALBANY INT CORP, ALBANY INTERNATIONAL CORP.
Application year: 1987
Main classification: D21F7
IPC codes: D21F1, D21F7