WO1999018282A1

WO1999018282A1 - Improved industrial fabrics

Info

Publication number: WO1999018282A1
Application number: PCT/GB1998/002832
Authority: WO
Inventors: Andrew Allum
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1997-10-08
Filing date: 1998-09-17
Publication date: 1999-04-15
Anticipated expiration: 2000-04-08
Also published as: EP1023484A1; AU9173198A; CA2305719A1

Abstract

An industrial fabric, suitable for use as papermachine clothing, belting or a filter cloth, comprises a permeable support (11) carrying a layer of sintered polymeric particles (15), and a layer (16) providing a smooth surface coating. The surface of layer (16) has an RzD value equal to or greater than 50.

Description

IMPROVED INDUSTRIAL FABRICS

This invention relates to industrial fabrics having improved surface

characteristics.

The term "industrial fabrics" is intended to include all forms of

papermachine clothing, filter cloths and filter belts, conveyer belts and roll

covers.

It is known, e.g. from GB 2,283,926 to form a filter from partially

fused particles, which may be polymeric or alternatively metal. The partially

fused particles may be located on a base structure, or a reinforcing

structure may be embedded within the partially fused particles. WO

95/21285 discloses a method of polymer coating an industrial fabric by

urging a release sheet coated with a polymer film against a textile substrate,

curing the polymer in contact with the substrate, and removing the release

sheet to leave the polymer on the substrate. The polymer coating is

preferably reticular comprising a network of two dimensional pores, thus

providing permeability.

Press felts for papermachines currently in use generally comprise one

or more fibrous batts, reinforced and carried by a woven or nonwoven

structure, including a foraminous membrane or a spiral-link fabric. Such

felts may be seamed or endless. If seamed, the seam structure, no matter

how carefully designed and made, has the potential to mark the paper web, as does the structure of the reinforcing or carrier layer, especially if woven

from yarns comprising relatively hard materials such as polyamide, and

spiral link fabrics, even through the fibrous batt(s).

An object of this invention is to provide an industrial fabric, in

particular for use as papermachine clothing, especially for example a press

felt, extended nip press belt, transfer belt or the like, wherein the potential

for marking of the paper web is further reduced beyond that obtainable by

careful design and manufacture of press felts etc. as presently used.

According to the invention, an industrial fabric, as hereinbefore

defined, comprises at least a paper-contacting layer comprising a layer of

sintered partially fused polymeric particles, coated on the paper-contacting

face with a smooth polymeric coating.

Preferably the coating surface has an R_ZD value greater than or equal

to 50 for the surface roughness.

The sintered polymeric particle layer may be carried upon a support

structure comprising a foraminous membrane, which may be reinforced by

yarns or filaments within its structure extending in the machine direction

and/or the cross-machine direction.

The support structure may merely carry the sintered layer, or be

wholly or partially encapsulated within the sintered layer.

The support structure may alternatively be a woven or nonwoven fabric, or a spiral link fabric.

The sintered layer may encapsulate one or more additional textile, or

membrane reinforcing layers.

The polymeric coating may be applied by any known method,

including by transfer as described in WO 95/21285 mentioned above. The

polymeric coating is preferably reticular, or at least porous according to

some pattern, sufficiently to allow passage of water expressed e.g. from a

paper web to pass through the layer into the particle layer.

The fabric, in a preferred embodiment, may comprise a porous

polymer layer over a layer of sintered polymeric particles, carried in turn

upon a foraminous membrane. Used as a press-felt in a papermachine, with

the polymeric layer contacting the paper web, a hierarchy of pore sizes may

be produced leading away from the paper, ensuring increasing void space,

and that flow away from the paper web will be encouraged whilst return

flow is restricted. The polymer layer provides an array of e.g. reticular

micro-pores, whilst the sintered layer provides larger voids between non-

contacting parts of the particles, and finally the foraminous membrane

provides apertures on a millimetre scale which are considerably larger than

the voids in the sintered layer.

The polymeric coating layer may be rendered porous by incorporating

a blowing agent which forms bubbles in the material, which are burst in application of the layer to provide pores passing through the layer.

In accordance with a preferred embodiment of the invention, an

industrial fabric is provided, substantially as set out above, save that the

polymeric coating is replaced by a layer of a nonwoven fabric. This is

preferably a melt-blown, spunbond, spunbond/meltblown/spunbond laminate

(SMS) or a thermally bonded nonwoven.

Preferably the nonwoven is bonded, directly or indirectly to the layer

of sintered particles by heat, chemicals (e.g. solvent or adhesive) or by

mechanical means such as ultrasonic welding.

The fibres of the nonwoven fabric may be of a material selected from

pol olefins (such as polypropylene or polyethylene) polyester (e.g. PET,

PBT, PPT, PEN, PBN) copolyesters (e.g. PCTA), polyamides (such as PA6,

PA6.6, PA6.10, PA1 1 , PA12) aramids, including meta or para-aramids;

fluoropolymers (e.g. PTFE or PVDF), elastomers (such as TPU); PPS; PPO:

PBO: glass, ceramics, basalt or carbon; or a blend of fibres of two or more

such materials.

The fineness, basis weight and thickness of the nonwoven material

forming said layer may be varied according to the intended use of the fabric.

In the case of a spunbond nonwoven, the fibres may be 0.1 -50 dtex and

form a nonwoven with a basis weight of 10-800 g/m², and thickness of 0.1 -

4.0mm. Meltblowns comprise much finer diameter fibres ( 1 -5 microns) and form very small pores less than 1 micron in size.

The fabric according to the invention may be used in papermaking

applications, such as press felts, etc. as set out in the patent application

mentioned above, but is particularly suitable for use as a filter medium.

Some embodiments of industrial fabric according to the invention will

now be described by way of example, with reference to the accompanying

drawings, wherein:-

Fig. 1 is a much enlarged sectional view of a

fragment of a papermachine press fabric

according to the invention;

Fig. 2 is an enlarged cross-section, of a second

embodiment of industrial fabric according to the

invention, which may for example be used as a

filter fabric;

Fig. 3 is a similar view to Fig 2 of a third

embodiment of industrial fabric according to the

invention; and

Fig. 4 is a similar view of a filter fabric according

to the invention.

Fig. 1 is a much enlarged fragmentary cross-section of a

papermachine press fabric 10 according to the invention, to replace conventional press felts, extended nip press belts and similar papermachine

fabrics. Fabric 10 comprises a membrane 1 1 of synthetic plastics material

comprising a sheet formed with a myriad of apertures or holes 1 2 there

through, thus providing a foraminous membrane. The membrane 1 1 is

reinforced by polyamide yarns 13 extending in the machine direction of the

fabric. Further yarns may extend in the cross-machine direction, but do not

appear in the drawing.

The upper (paper-side) surface of the membrane 1 1 carries a layer 14

of polymeric particles 15, which are sintered together , being partially fused

on contacting surfaces to provide a coherent structure, having a network

of interstices between the particles which renders the structure porous and

water permeable.

The sintered particle layer 1 4 in turn carries a layer or coating 1 6 of

polymeric material which is applied over the particle layer 14 by any suitable

coating technique, but may be applied by transfer from a release belt in the

process described in WO 95/21285 mentioned above.

The layer 16 is microporous, and preferably reticular, to allow

passage of water expressed from a paper web on layer 16 to pass through

the coating layer 16 into the lower layers of the fabric.

The coating layer 16 is microporous, whilst layer 14 has voids on a

submillimetre scale, and the membrane 1 1 , has apertures 12 which measure a few millimetres in diameter or width. A hierarchy of void sizes is thus

created leading away from the paper contacting surface of the coating layer

16, which encourages flow of water away from the paper web, but restricts

and impedes return flow, so that the fabric is effective in use in a

papermachine press drying stage in removing water from the paper web,

and preventing rewetting of the paper.

Fig. 2 illustrates an alternative embodiment of industrial fabric

according to the invention. This may be suitable for use for example as a

filter fabric. The fabric 20 comprises a woven substrate 21 (shown

diagrammatically by a conventionalised representation of warp and weft

yarns) which is encapsulated in a sintered layer 22 formed of partially fused

polymeric particles. Layer 22 carries a coating layer 23 of polymeric

material which has a reticular structure, applied thereto by any suitable

coating technique. The layer 23 may provide the upstream side of the filter

fabric, so that the filter cake collects on the coated face of the fabric, and

provides for improved release of the filter cake as compared with known

woven, felted or sintered filter fabrics without a coating.

Fig. 3 is a similar cross-section of an alternative embodiment of

papermachine clothing 30, for instance, and shows a woven substrate 31

encapsulated in a layer 32 of sintered partially fused polymeric particles.

Layer 32 carries a coating layer 33 of reticular polymeric material. The composite layer is supported on a spiral link fabric 34.

In Fig. 4 a filter fabric 40 is shown comprising a woven fabric support

layer 41 , carrying a layer 42 of sintered or partially fused polymeric particles

43, which is covered in turn by a layer 44 comprising a textile nonwoven

fabric. This is meltblown or spunbond, or thermally bonded, of fibres which

are 0.1-50 dtex, and form a nonwoven with a basis weight from 10-800

g/m², of 0.1 -4mm thickness.

In the case of a meltblown, fibres are from 1 -5 microns in diameter

and form pores less than 1 micron in size.

The nonwoven layer 44 is heat bonded to the sintered layer 42.

Other means such as chemicals (e.g. solvent or adhesive) or ultrasonic

welding may be used to effect this bond.

The nonwoven layer 44 is of spun polypropylene fibres, but may be

of any of a range of materials including polyesters, copolyesters,

polyamides, aramids, fluoropolymers, elastomers, polystyrene, or mineral

fibres, examples of which are set out above.

The nonwoven layer provides a coating or layer, which, whilst it

comprises a nonwoven fabric, provides a surface which is capable of being

sensibly smooth to the unaided eye and touch, and is therefore suitable for

use in place of the smooth polymeric coating specified in our

aforementioned application, and indeed is considered to provide such a coating.

The fabric according to Fig. 4 is described as a possibly endless filter

fabric, and may be suitable for use as a flexible cloth, or a rigid seam or

semi-rigid premoulded filter element, depending upon the nature of the

reinforcement support 41 , or the sintered layer 42. This type of structure,

within the scope of the invention, may also or instead be configured as a

papermachine belt, such as a dryer belt fabric, transfer belt, forming fabric,

tissue making belt or the like.

Preferred sinterable materials include EVA, polyethylene,

fluoropolymers (e.g. PTFE), thermoplastic elastomers, and thermoplastic

polyurethane, as these can provide flexible and tough sheets of material;

EVA is particularly preferred for this reason. Polyamides, polyacetals and

PEEK may also be sintered. The particles may be present as fibres rather

than granular particles.

The coating is an epoxy, silicone or fluoropolymer, (such as PTFE) for

good abrasion resistance. These materials are also suitable for use for high

temperature papermachine clothing applications, e. g. impingement dryers,

condebelt dryers, press dryers, or impulse dryer machines on account of

their resistance to thermal degradation and hydrolysis. The membrane is

preferably a thermoplastic elastomer, e. g. thermoplastic polyurethane for

good resilience and compaction resistance. Silicone may be used for higher temperature applications. Each coating provides a smooth coating, with an

R_ZD value greater than or equal to 50 for the surface roughness.

The uniformity of fabrics according to the invention reduces paper

sheet rewetting, provides improved sheet release control and improves the

uniformity of pressure transmission to the paper sheet, which all serve to

improve the uniformity and quality of the paper produced.

These embodiments are described by way of example only, and any

combination of encapsulated or separate support structures with the

sintered particle layer and coating layer may be provided. One or more

fibrous batt layers may be provided in the structure, between other layers,

or over the polymeric coating to e.g. provide mechanical cushioning of a

paper web carried by the fabric.

Claims

1 . An industrial fabric, at least an upper or paper-contacting layer of

which includes a layer of sintered partially fused polymeric particles and/or

fibres, coated on said upper paper-contacting face with a smooth polymeric

coating.

2. A fabric according to claim 1 , wherein said coating has a surface R₂D

value equal to or greater than 50.

3. A fabric according to claim 2 wherein said layer of sintered polymeric

material is carried upon a support structure comprising a foraminous

membrane.

4. A fabric according to claim 3 wherein said membrane is reinforced by

yarns or filaments within the structure of said membrane.

5. A fabric according to claim 3 or 4 wherein said support structure is

wholly or partially encapsulated within the layer of sintered polymeric

material.

6. A fabric according to claim 1 wherein said layer of sintered polymeric

material is carried upon a support structure comprising a woven or

nonwoven fabric, a needlefelt, or a spiral link fabric.

7. A fabric according to claim 5 wherein the sintered layer encapsulates

one or more additional layers.

8. A fabric according to claim 7 wherein the, or at least one of the, additional layers comprises a textile layer or a layer of chopped fibres.

9. A fabric according to claim 7 wherein the, or at least one of the,

additional layers comprises a membrane reinforcing layer.

10. A fabric according to any preceding claim wherein the polymeric

coating is applied by transfer.

1 1 . A fabric according to any preceding claim wherein the polymeric

coating is porous.

12. A fabric according to claim 1 1 wherein the polymeric coating is

reticular.

13. A fabric according to claim 1 comprising a porous polymer layer over

a layer of sintered polymeric particles carried in turn upon a foraminous

membrane.

14. A fabric according to claim 1 1 wherein the coating layer has been

rendered porous by incorporation of a blowing agent which forms bubbles

in the layer which are burst on application of the layer to the sintered layer.

15. A fabric according to claim 1 wherein the polymeric coating

comprises a layer of a nonwoven fabric.

16. A fabric according to claim 15 wherein said nonwoven fabric is any

one of a meltblown, a spunbond, a meltblown/spunbond laminate or a

thermally bonded nonwoven.

17. A fabric according to claim 15 wherein the nonwoven fabric is bonded to a layer of sintered particles.

18. A fabric according to claim 15 wherein the nonwoven fabric is

composed of fibres of a material selected from polyolefins, polyester,

copolyesters, polyamides, aramids, fluoropolymers, elastomers, PPS; PPO;

PBO; glass; ceramics, basalt or carbon, or a blend of fibres of two or more

such materials.

19. A fabric according to claim 15 wherein the fibres are 0.1 -50 dtex and

from a nonwoven with a basis weight of 10-800 g/m², and thickness of 0.1 -

4.0mm.

20. Papermachine clothing comprising a fabric as claimed in any

preceding claim.

21. Industrial belting comprising a fabric as claimed in any of claims 1 to

19.

22. An industrial filter medium comprising a fabric as claimed in any of

claims 1 to 19.