WO1998007925A1

WO1998007925A1 - Permeable belts

Info

Publication number: WO1998007925A1
Application number: PCT/GB1997/002180
Authority: WO
Inventors: Ian Christison Sayers
Original assignee: Scapa Group Plc
Priority date: 1996-08-24
Filing date: 1997-08-15
Publication date: 1998-02-26
Also published as: GB2330844A; GB9902389D0; AU3948497A; GB2330844B; GB9617791D0

Abstract

A permeable belt comprises a woven or non-woven substrate encapsulated in synthetic plastics material and abraded on its major surfaces to expose hollow or soluble yarns, which may be weft yarns (11) of a woven fabric, needled fibres (22) of a needlefelt, or pile loops (31) of a tufted pile fabric. Soluble yarns are dissolved in, e.g., water and hollow yarns breached by abrasion to provide voids or passages extending through the belt.

Description

PFRMEABLE BELTS

This invention concerns permeable belts, suitable for use for example in

belts for paper making machines, and also for filter fabrics, conveyor and

corrugator belts, and belts for tobacco processing machines.

Permeable belts are used for such components generally to allow a liquid

fraction, usually water, to drain or be pressed, etc, from a suspension such as

a pulp of paper fibres on various stages of a process such as paper making,

e.g. at the forming, pressing or drying of the deposited fibres at respective

stages.

The permeability of such belts has generally been attained for example

by provision of a loose weave, or loosely matted fibres, through the interstices

between the yarns or fibres, weaving or needling of the fabric.

In order to control the porosity of papermakers belts, it is known, eg

from GB-A-2140836 to provide a fibrous non-woven batt supported on a

substrate, wherein one fibrous component of the batt is of fibres which are

soluble in eg alkali, and treating the fabric to dissolve the soluble fibres, leaving

a fibrous batt of lower density, with voids in the place of the dissolved fibres.

Also in EP-A-0123431 it is proposed to provide a papermakers felt wherein an

interior layer of machine direction yarns of soluble material is dissolved out to

leave a fabric with an increased internal void. Neither of these proposals

envisage a paper makers belt or fabric with voids or passages extending

between the opposite surfaces of the belt, i.e. from the paper contacting

surface to the opposite surface. An object of the invention is to provide a permeable belt which is

relatively inexpensive and simple to manufacture as compared with present

methods of making woven and nonwoven porous fabrics.

From a first aspect, the invention provides a permeable belt comprising

a woven or nonwoven substrate, at least partially encapsulated in a synthetic

plastics material and incorporating passages or voids therethrough which

extend between opposite faces of the belt, said voids being formed as part of

the weave or structure of the fabric, and exposed by grinding or abrading of

one or more faces of the fabric.

The invention provides as a second aspect, a method of manufacturing

a permeable belt, comprising:-

(a) providing a woven or nonwoven substrate incorporating yarns and/or

fibres which extend between opposite faces of the substrate, said yarns and/or

fibres being treatable to provide passages or voids through said substrate

which extend between opposite faces thereof;

(b) at least partially encapsulating said substrate in a synthetic plastics

material;

(c) curing said synthetic plastics material;

(d) grinding or abrading at least part of at least one face of said plastics

material to expose said treatable yarns and/or fibres;

(e) treating said yarns and/or fibres in order to create said passages or voids

through the completed belt.

The yarns may be of a material which is soluble in a readily available solvent such as water, so that after abrasion to expose the yarns, the

treatment step may comprise immersing the fabric in the solvent, to dissolve

away the yarns, leaving the desired passages or voids.

Alternatively, the yarns and/or fibres may contain continuous void

regions, or may be assembled from tubular fibres. For convenience these will

be referred to below as 'hollow' yarns or fibres and the treatment step may

comprise further abrasion to breach the walls of the yarns and/or fibres, to

expose the interior continuous void regions, thereby creating the desired

passages or voids.

The substrate may be a normal woven fabric, or may be in the form of

a velour needle felt in which the staple fibres are predominantly oriented in the

vertical position relative to the plane of the substrate fabric. In such a fabric,

the use of hollow and/or soluble staple fibres will produce a dense network of

near-perpendicular passages through the sheet.

Another possible form of substrate is a tufted-pile nonwoven fabric, such

as is commonly used for carpets. The tuft fibres may consist entirely of soluble

and/or hollow fibres.

The soluble or hollow fibres or yarns may take the form of reinforcing

pins, passed through a nonwoven layer, e.g. as disclosed in US 5,484,641.

One or both sides of the nonwoven layer may be encapsulated and ground.

In a normal woven fabric, abrading away the loops of the transverse

fibres where they over- and under-lie the longitudinal yarns and/or fibres will

produce oblique passages through the sheet. Wet-laid, air-laid, spun-bond and stitch-bonded nonwoven fabrics or felts

may also be used. In a stitch-bonded fabric, some stitch yarns or fibres may

be soluble and/or hollow to provide the passages. Impregnation of such fibres

on at least one surface with polymer ensures that integrity is retained despite

severing of stitching yarns or fibres.

A composite of two or more of the above fabric types or flocked textile

substrates may be used.

The invention will now be described, by way of example only, with

reference to the accompanying drawings, wherein:-

Fig.1 is a diagram of a woven fabric, in a first step of one method according to the invention;

Fig.2 shows the fabric of Fig.1 after encapsulation in synthetic plastics

material;

Fig.3 is a diagram showing the fabric of Figs. 1 and 2, after abrasion and

treatment; with soluble yarns;

Fig.4. is a similar diagram to Fig.3, showing hollow yarns;

Fig.5 diagrammatically shows a velour needlefelt fabric;

Fig.6 shows one fabric of Fig.5 after encapsulation, abrasion and

treatment-

Fig.? is a tufted pile nonwoven fabric; and

Fig.8 shows the belt resulting from Fig.7 after encapsulation, abrasion

and treatment.

Fig.1 shows a conventional woven fabric, with longitudinal yarns 10, and lateral yarns 1 1. In a first step of the process of this invention, the yarns 1 1

are either hollow, or dissoluble in a readily available solvent such as water.

Fig.2 shows the next step with the fabric of Fig .1 encapsulated in

synthetic plastics material.

Figs.3 and 4 show alternative finished belts. In Fig.3, the encapsulation

material of Fig.2 has been abraded down to break the loops of yarns 1 1 over-

and under- lying the yarns 10. In the treatment step, the fabric has then been

immersed in an appropriate solvent, and the remaining parts of the yarns 1 1

dissolved away to leave voids or passages 12 which pass obliquely, from one

face to the other of the resulting composite.

In Fig.4, the abrasion step has broken the loops of yarns 1 1 , and then

in the treatment step, the abrasion has been carried further to expose the

hollow interiors of tubular yarns 1 1 , which provide passages extending

obliquely between the faces of the composite fabric.

Fig.5 is a diagram of a velour needlefelt, wherein longitudinal yarns 20,

and transverse yarns 21 form a base fabric which is transfixed by a multitude

of vertical fibres 22. These fibres 22 are either soluble fibres, or hollow tubular

fibres, or a mixture of the same. After abrading and treatment, the

configuration of Fig.6 is achieved wherein the composite fabric is pierced by

a multitude of more or less vertically extending passages from one face to the

other.

Fig.7 is a similar diagram of a tufted pile fabric. A felt or mat 30 of

nonwoven fibres is pierced by loops of pile 31 , which are free to one side, and looped on the other. Both sides are encapsulated with plastics material as it

can be more easily ground in a controlled fashion than textile material. Both

surfaces are ground or abraded and treated to produce the finished belt of

Fig.8, the pile yarns 31 being either soluble fibres or hollow yarns, or a blend

thereof. In Fig.8, again a multitude of passages are provided between the

opposite surfaces of the belt.

The surface of the belt intended to contact e.g. a deposit of paper fibres may be provided with raised profiles for extra sheet support or to emboss the

resulting paper product. These profiles are achieved by selective grinding of

the encapsulating polymer to form e.g. grooves. These grooves preferably

extend in the machine direction of the belt so as to increase dewatering in the

case of a papermaking fabric. In the case of a pulp felt, these grooves mark

the pulp sheet to increase its surface area prior to drying. Void passages

extend from the base of the grooves to the other surface of the belt.

The surface of the belt may further be provided with coatings to improve

abrasion resistance non-stick properties, resistance to contamination etc. Such

coatings may include ormocers and fluoropolymers. UV-absorbent pigments,

photochromic dyes, and/or thermochromic materials can be incorporated into

one coating, polymer matrix or substrate yarns or fibres to detect premature

wear during use.

Examples of soluble yarn or fibre materials which may be used include

polyvinyl alcohols, and natural materials such as cellulose or alginate. The

substrate may also contain any type of natural or synthetic yarn or fibre, which may or may not be exposed at the fabric surfaces, as needed to attain desired

properties. The yarn or fibre material is preferably soluble in a cheap and

readily available solvent that does not present any problems in respect of

environmental or health and safety considerations, the best example of which

is water.

The dimensions of the yarns and/or fibres to be treated preferably

correspond to those of the interstices found in conventional papermachine clothing, filter fabrics, conveyor or corrugator belts or tobacco processing

machine belts, or other industrial fabrics. In the case of papermachine clothing

the dimensions are chosen so that the void passages are finer than the voids

in the paper web, thus a capillary effect is created which prevents rewet of the

paper by water in the belt.

The yarns and/or fibres of the substrate may be treated by chemical

and/or physical means to enhance adhesion between them and the polymer.

The encapsulating polymer is preferably an elastomer to give the fabric

a degree of resilience, most preferably polyurethane, thermoplastic

polyurethane, a silicone polymer or a synthetic rubber. Polyurethane is

preferred on account of its excellent abrasion resistance and the ease with

which it can be ground. Other suitable polymers include polyamides (eg. PA6,

or PA6.6), polyesters (eg. PET, PBT, PTT, PEN or PBN), copolyesters (eg.

PCTA), fluoropolymers (eg. PTFE or PVDF), polyetheretherketones (eg. PEEK),

polyketones, polyphenyiene sulphide or poiyphenylene oxide, or a combination

or blend of one or more of these polymers. Choice of polymer enables the resistance of the belt to wear, contamination, heat, hydrolysis, chemical attack

or compaction to be optimised, and in many cases the need for a textile resin

surface treatment is eliminated.

This polymer may encapsulate the substrate or act as a coating one or

both sides. The polymer may be applied in liquid and/or molten form, or

alternatively as a foam, or even as a powder, said powder then being melted

or sintered. The polymer layer is preferably of the same thickness as is found

with conventional polymer coatings for industrial fabrics, namely 2-5 mm.

The substrate according to the invention containing soluble yarns and/or

fibres only may be used in combination with a standard basecloth such as

woven or nonwoven fabric, composite membrane, needlefelt, spiral link fabric

or a spirally wound strip material (or a combination of one or more of these).

In this case the polymer encapsulation or coating is provided on one side of the

substrate according to the invention, opposite to the side adjacent to the

additional base.

Soluble yarns/and or fibres may be provided in the textile substrate and

the resin encapsulation or coating may take place on one side only.

Supplementary yarns may be incorporated into the belt structure to

provide strength and dimensional stability enhancing characteristics.

Claims

C AIMS

1 . A method of manufacturing a permeable belt, comprising:-

a) providing a woven or non woven substrate incorporating yarns

and/or fibres which extend between opposite faces of the substrate, said

yarns and/or fibres being treatable to provide passages or voids through said

substrate which extend between opposite faces thereof;

b) at least partially encapsulating said substrate in a synthetic plastics

material; c) curing said synthetic plastics material;

d) grinding or abrading at least part of at least one face of said

plastics material to expose said treatable yarns and/or fibres;

e) treating said yarns and/or fibres in order to create said passages

or voids through the completed belt.

2. A method according to claim 1 , wherein said yarns and/or fibres are

of a material which is soluble in a solvent and wherein after abrasion to

expose said yarns and/or fibres, said treatment step comprises immersing

the fabric in said solvent to dissolve away the yarns and/or fibres to leave

the desired passages or voids.

3. A method according to claim 1 , wherein said yarns and/or fibres

contain continuous void regions or comprise tubular yarns and/or fibres and

said treatment step comprises further abrasion to breach the walls of the

yarns and/or fibres to expose the interior continuous void regions, thereby

creating the desired passages or voids.

4. A method according to claim 1 , wherein the substrate comprises a

velour needle felt in which the staple fibres are predominantly oriented in

the vertical position relative to the plane of the substrate, at least some of

said staple fibres being hollow and/or soluble.

5. A method according to claim 1 , wherein the substrate is a tufted pile

non

woven fabric, wherein at least some of the tuft fibres comprise hollow and/or soluble fibres.

6. A method according to claim 1 , 2 or 3, wherein the substrate is a

woven fabric wherein at least some of the weft yarns are hollow or soluble or comprise hollow or soluble fibres.

7. A method according to claim 1 , wherein the substrate is a stitch-

bonded non woven fabric wherein at least some of the bonding stitches are

of hollow or soluble yarns or fibres.

8. A permeable fabric which has been made by a method according to

any of claims 1 to 7.

9. A permeable belt comprising a woven or non woven substrate which

is at least partially encapsulated in a synthetic plastics material and

incorporating passages or voids therethrough which extend between

opposite faces of the belt, said voids being formed as part of the weave or

structure of the fabric and being exposed by grinding or abrading one or

more faces of the fabric and subjecting the exposed yarns or fibres to

further treatment.