WO1992017643A1 - Papermachine clothing - Google Patents

Abstract

A base fabric for use in producing a papermakers fabric is proposed which includes superimposed layers (11, 12) of synthetic thermoplastics material in mesh form, the layers being secured together and at least one layer having load bearing yarns (16, 21) therein. Conveniently two of the superimposed layers (11, 12) have apertures of respective and different sizes, whilst one mesh layer (12) may be cut on the bias with respect to another layer (11) with which it is combined. The base fabric will provide support and reinforcement to a needled mat in producing a papermakers fabric.

Description

PAPERMACHINE CLOTHING

The invention concerns papermachine clothing, and has particular, though by no means exclusive, reference to clothing for use in the press section of the papermaking machine.

Conventionally, press felts comprise a woven base cloth providing adequate strength in the running direction of the felt and one or more compressible fibre layers applied thereto as, for example, by needling.

Base cloths of the conventional kind are expensive in manufacture and, furthermore, can give rise to the incidence of marking of the paper as it passes through the press section of the papermaking machine due to the presence of knuckles formed at the cross-over points of the warp and weft yarns which form the base cloth.

The primary object of the invention is to provide an alternative to the woven base cloth conventionally used in producing papermachine clothing which avoids, at least in part, the disadvantages inherent in known structures.

According to the present invention there is proposed a non-woven base cloth for use in producing papermachine clothing, the base cloth comprising plural superimposed layers of a synthetic thermoplastics material provided in mesh form, one at least of the mesh layers including load bearing yarns extending in the intended running directior. thereof. Preferably the base cloth includes two layers each of respective and different mesh size.

The invention also includes a papermakers fabric comprising a base fabric as aforesaid in combination with a fibrous batt and/or a finely woven fabric at one face at least thereof and secured thereto.

The invention will now be described further, by way of example only, with reference to the accompanying drawings illustrating several embodiments thereof and in which : -

Fig. 1 is a diagrammatic perspective view of one form of base fabric constructed in accordance with the invention;

Figs. 2 and 3 are enlarged sections taken on lines II-II and III-III, respectively of Fig. 1;

Fig. 4 is a view corresponding to Fig. 1 and shows an alternative relative alignment of the mesh layers of the base fabric; and

Fig. 5 shows, in diagrammatic manner, a typical cross-section through a press felt incorporating the base fabric of the invention.

Referring now to the drawings, and particularly to Fig. 1 thereof, a base fabric for use in the production of a press felt for a papermaking machine comprises a first mesh layer 11 and a second mesh layer 12 secured together in superimposed disposition.

Mesh layer 11 presents longitudinally extending land areas 13 and transversely extending land areas 14, to give rectangular mesh openings 15 of a first size, land areas 13 including yarns 16 to provide load bearing yarns in the intended running direction of the press felt.

Mesh layer 12 has longitudinally extending land areas 17 and transversely extending land areas 18, the mesh opening 19 also being of rectangular form but being of a second size ess than that of the openings 15 of mesh layer 11.

Whilst, in the embodiment under consideration, longitudinal land areas 17 also include reinforcing yarns 21, the presence of such yarns is not essential .

Typically the mesh openings 15 of mesh layer 11 will measure 5mm x 1mm, whilst those of mesh layer 12 will measure 2mm x 0.5 mm, the two layers being 1.5 mm and 1.0 mm thick, respectively, and the upper layer serving to diffuse water present in the fabric and thereby reduce the incidence of shadow marking of the paper sheet. The apertures need not, of course, be of rectangular configuration, and the mesh layer having the larger apertures may lie above or below the other mesh layer as preferred.

The preferred material for the matrix of the mesh layers is thermoplastic polyurethane (typically that sold by B.F. Goodrich under reference 58810) , whilst the reinforcing yarns of layers 11 and 12 may comprise any monofilament or multifilament yarn having good bonding characteristics ir. relation to the matrix material and physical characteristics appropriate to the context, and will typically be of 0.5 irur and 0.2 mm diameter, respectively.

The mesh layers are conveniently manufactured in accordance with the method described and claimed in GB-A-2202873, although other methods may be preferred, such as, for example, a powder dispersal technique.

The two mesh layers will ordinarily be secured together by thermal fusion of the abutting surfaces in conventional manner. However, it may be preferred, in some instances to join the fabrics by means of an adhesive or by ultrasonic welding or by applying a batt of fibres to the superimposed layers and needling such fibres into and through the layers.

It may be found desirable to provide localised protruberances on the land areas at one or both of the adjacent surfaces of the two mesh layers, to ensure the presence of a fluid flow path in the event that a land area of one mesh layer overlies, and thereby masks, an aperture in the other mesh layer.

In a second embodiment, see now Fig. 4, the longitudinal axis 22 of the mesh openings 19 is inclined with respect to the corresponding axis 23 of openings 15 of mesh 11, the individual mesh layers being of like kind to those shown in Figs. 1 to 3. The preferred angle of inclination shown is 45°as shown, but other bias angles may be used if desired.

The base fabrics as shown in the drawings will be provided with a fibrous batt of conventional form an materials. The batt may be subjected to pre-consolidation if desired, and is secured to the base fabric by thermal bonding, by an adhesive, ultrasonic welding or by needling. Ordinarily the fibres in the batt will be randomly orientated, but, in some circumstances length orientation may be preferred.

Alternatively, the batt may be built up in situ on the base fabric by means of a melt-blown technique wherein fibres are extruded onto the moving base fabric and, by virtue of their semi-molten state, adhere at their boundary surfaces to the base fabric and/or to any previously applied fibre layer. The degree of fineness of the fibres may be varied during batt build-up according to the specific requirements of the press felt. It is to be appreciated that spun laced, spun bonded or other non-woven web creating techniques may also be used to create the batt.

The press felt as above proposed is of open-ended form and the ends thereof may be joined, for example, by forming loops at the ends of the coarser mesh layer in accordance with the procedures proposed in GB-A-2231838, the loops being intended to receive a pintle wire on interdigitation of loops at the respective ends, the ends of the finer mesh layer being simply brought into abutment. The fibrous batt, whether previously formed or built-up in situ will extend across the line of join and, if necessary, can be cut transversely of the press felt in register or offset disposition with respect to the line of join, as is proposed, for example, in GB-A-223152 .

It is to be appreciated, however, that the felt may be of endless form.

As the base fabric as hereinbefore described is devoid of knuckles at the mesh/batt interface, the weight of batt applied may be reduced as compared with that necessary to avoid the incidence of marking in the context of a fabric embodying a woven base.

However, there are circumstances wherein controlled marking is desirable, and in these circumstances the surface of the overlying mesh could be of ribbed configuration, as would be the case if the base fabric were to be embodied in a marking felt. In the case of a felt for use in the fibre/ asbestos cement industry the overlying mesh would be formed with knuckles, (and if required ribs,) to provide localised pressure points to encourage bonding between the successive fibre cement layers.

Claims

Claims

1. A non-woven base cloth for use in producing papermachine clothing, the said base cloth comprising plural superimposed layers of a synthetic thermoplastics material provided in mesh form, one at least of the mesh layers including load bearing yarns extending in the intended running direction thereof.

2. A non-woven base cloth as claimed in claim 1, wherein said base cloth includes two layers each of respective and different mesh size.

3. A non-woven base cloth as claimed in claim 1 or 2, wherein each mesh layer includes load bearing yarns extending in the intended running direction thereof.

4. A non-woven base cloth as claimed in any one of the preceding claims, wherein the apertures in each mesh layer are of rectangular configuration.

5. A non-woven base cloth as claimed in any one of the preceding claims, wherein the apertures in one mesh layer define spaced parallel ribs extending in the intended running direction of the fabric, there being load bearing yarns encapsulated within said ribs.

6. A non-woven base cloth as claimed in claim 5, including a superimposed mesh layer wherein the apertures therein define spaced parallel ribs inclined with respect to the yarn carrying ribs of the said one mesh layer.

7. A non-woven base cloth as claimed in claim 6, wherein the ribs of the said one mesh layer and those of the said superimposed mesh layer are inclined at an angle of 45°.

8. A non-woven base cloth as claimed in any one of the preceding claims of endless form.

9. A non-woven base cloth as claimed in any one of claims 1 to 7, further including loops at the respective ends thereof, the said loops being provided at the ends of a mesh layer having load bearing yarns.

10. A non-woven base cloth as claimed in any one of the preceding claims, wherein the mesh layers are secured together in superimposed disposition.

11. A non-woven base cloth as claimed in claim 10, further including a batt of fibres needled to the layers thereby to secure said layers together.

12. A non-woven base cloth as claimed in any one of the preceding claims, in combination with a fibrous mat secured thereto at one face thereof.

13. A non-woven base cloth as claimed in claim 12, wherein the surface of that mesh layer adjacent the fibrous mat is of profiled form.

14. A non-woven base cloth as claimed in claim 13, wherein the profiled form of the surface of the mesh layer adjacent the fibrous mat includes upstanding ribs.

15. A papermakers fabric including a base cloth as claimed in any one of the preceding claims.