WO1999016964A1

WO1999016964A1 - Treatment of industrial fabrics

Info

Publication number: WO1999016964A1
Application number: PCT/GB1998/002785
Authority: WO
Inventors: Jan Ström
Original assignee: Scapa Group Plc
Priority date: 1997-09-30
Filing date: 1998-09-15
Publication date: 1999-04-08
Also published as: DE69810499T2; EP1019578A1; AU9088498A; DE69810499D1; EP1019578B1

Abstract

A method of treating industrial fabrics such as papermachine clothing, wherein at least one surface of the fabric, or of the yarns, fibres, strips or membranes from which such a fabric is made, is modified by using high energy electromagnetic radiation, from excimer or ablation lasers. This may be used to alter the hydrophilic/hydrophobic properties of the surface by etching on a micron scale. Selective masking at any desired scale may be used.

Description

TREATMEIMT OF INDUSTRIAL FABRICS

This invention relates to the treatment of industrial fabrics.

The term "industrial fabrics" includes within its scope all forms of

papermaking machine fabrics, including dryer fabrics, press felts (including

extended nip press belts), shoe press sleeves, corrugator machine press

belts, and also to conveyer belts, printing blankets, silicon wafer grinding

belts, and filter cloths.

As discussed in our co-pending British Patent Application No

971 5508.9, the surface characteristics of such fabrics may be influenced

by treatment, for example to adjust the wetting characteristics of the fabric,

or in a composite fabric of two or more layers, of at least one layer of the

fabric. The treatment may for example render at least one surface of the

fabric hydrophobic, or alternatively hydrophilic. Either of these alternatives

has advantages in particular circumstances for handling paper webs, filter

cakes, or drained or expressed water.

In the aforesaid co-pending application, we propose subjecting one

or more layers or surfaces of an industrial fabric to plasma treatment.

It has been found that the surface conditioning resulting from such

plasma treatment suffers from some disadvantages. For example the

conditioning may be insufficiently durable in certain conditions, especially

wet conditions, and most particularly where high temperatures are experienced.

In addition, plasma treatment requires the provision of expensive

apparatus for maintaining an atmosphere in the treatment area below

atmospheric pressure, as it has so far only been found to be possible to

carry out plasma treatment at atmospheric pressure on a restricted scale

under laboratory conditions. Also, all and the whole of any material

subjected to plasma treatment is treated during exposure to the plasma; it

is not possible to selectively expose certain surfaces or areas to treatment,

and leave other areas untreated.

In our co-pending Application No. PCT/GB97/63180 (WO 98/27277)

there is disclosed a method of making a papermakers fabric such as an

embossing felt wherein a batt of fibres is subjected to ultrasonic energy to

at least partially melt the surface fibres of the batt, and imprinting a pattern

into the molten or softened batt whilst the fibres are molten.

The process of the above application is relatively cumbersome, being

limited in machine speed by the time taken for absorbtion of ultrasonic

energy to cause the required degree of melting, in the fineness of the

patterns which can be produced, and the fact that a change of pattern

involves substituting one embossing roller for another in a time consuming

operation.

An object of the invention is to provide a method of treatment of industrial fabrics, as above defined, which enables at least some of the

mentioned limitations of plasma treatment to be overcome and can also be

applied to yarns, fibres, strips and membranes, etc.

Preferred objects are to enable treatment to be carried out at

atmospheric pressure, and to enable surfaces and areas of surfaces to be

selectively treated or untreated, including contiguous areas.

According to this invention, a method of treating an industrial fabric,

as hereinbefore defined, comprises modifying at least part of at least one

surface of such fabric or other material of the kinds suggested above, or of

a layer in or to form part of such a fabric, by treatment with high energy

electromagnetic radiation.

The invention also provides an industrial fabric, as hereinbefore

defined, wherein at least part of at least one surface of such fabric, or of a

layer in or to form part of such a fabric has been modified by treatment with

high energy electromagnetic radiation, and such a fabric including a least

some yarns, fibres, strips or membranes or the like which have been so

treated.

The high energy electromagnetic radiation is preferably UV excimer

radiation which may be applied using an excimer or an ablation laser, or a

UV excimer lamp.

The modification of the surface or part of a surface is preferably carried out at a submicron scale, by etching the surface using the laser.

The etching may effect pitting or scoring the surface to provide grooves,

hollows or protrusions at the selected scale or expose ionised material.

Such modification can alter the wetting characteristics of the surface, for

example by providing keying or electrostatic attraction for water adhesion

to render a surface hydrophilic; alternatively such modification can micro-

planarise a surface by removing small scale irregularities, removing such

keying points, to enhance the hydrophobic properties of the surface.

Such detailed modification can be carried out without charring of

polymeric materials used in the fabric, or incurring other thermal damage

to surrounding non-radiated regions.

The intensity of laser irradiation may be varied to thereby alter the

nature of the surface e.g. by making it more hydrophobic or hydrophilic

depending on the type of material being treated.

The process may be carried out in selected atmospheres, such as

those containing a silane, e.g. Si(CH₃)₄; a siloxane (Si (OCH ₃)₄) or a

perfluorocarbon (eg 1 -6C perfluoroalkane); or tetrafluoroethylene; ammonia,

or a combination of any one or more of the above.

Surface modification according to the invention may be used to

remove localised areas, on any required scale, of coatings to expose a

substrate surface. According to a further preferred embodiment of the invention there

is provided a method of treating an industrial fabric, as hereinbefore defined,

or of a yarn, comprising modifying at least part of at least one surface of

such a fabric or yarn, comprising exposing said part of said surface to

radiation from an excimer UV emitting device.

The UV emitting device is preferably one with a relatively wide beam

to enable simultaneous treatment of a substantial area of such fabric or

yarn.

A plurality of such UV emitting devices may be provided in an array

to direct their respective beams each over part of a greater area of the

fabric or yarns to be treated, e.g. subjecting the whole width, and a few

metres of the length of a papermachine fabric, to simultaneous treatment.

The fabric or a multiple yarn feed may be advanced at a preselected

speed through the zone effected by the UV emitting devices, to subject all

parts of the device to treatment for a dwell period governed by the advance

speed of the fabric or yarns and the length of the treatment zone in the

directions of advance.

As the UV radiation is propagated in direct linear paths, pattern

masks of any desired detail down to the limit imposed by diffraction effects

may be used to control the arrangement of areas exposed to and shielded

from the radiation. As the wavelength of UV radiation is typically around 200-250nm, details such as spots on a micron or submicron scale may be

created by using a mask with apertures of a suitable scale. The patterns

may of course be provided on any suitable scale, for example allowing

myriad pin-point, or full area exposures over certain areas and completely

masking others to provided patterns of hydrophilic or hydrophobic treated

areas to effect the properties of the paper web being produced.

The UV treatment need not be undertaken under a special

atmosphere, and thus may be carried out under standard pressure using

ambient air composition. Safety considerations may require provision of

shielding to prevent exposure of workers to excessive dosages of UV

radiation.

The UV treatment proceeds by way of dissociation of the molecules

of the surface, and provision may be needed for confinement or evacuation

of the radicals generated.

The UV excimer emitter or emitters can produce radiation in a narrow

waveband, and may typically be emitted at 222nm.

The treatment may for example create hydrophilic surfaces by

dissociating carboxylic bonds, leaving unsaturated carboxylic and/or ketone

bonds exposed at the surface.

The UV radiation may also or instead etch the surface in a submicron

scale due to molecular breakdown, and this can be used to produce micron or submicron scale pitting using a pin-hole mask.

Preferred examples of process and fabric according to the invention

will now be described by way of example with reference to the

accompanying drawings, wherein:-

Fig. 1 is a diagrammatic view of apparatus used

in the treatment method according to the

invention;

Fig. 2 is an enlarged diagrammatic cross-section

view of a first sample fabric of the invention

which has been treated by the method according

to the invention;

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

sample fabric of the invention, which has been

treated by the method according to the invention;

Fig. 4 is a diagrammatic view of apparatus used

in the treatment method according to the

invention;

Fig. 5 is a slightly enlarged view of a fragment of

a mask for partially covering a fabric being

treated to selectively expose some areas to

radiation, and mask other areas from the radiation;

Fig. 6 is a much enlarged view of a fragment of

an alternative mask, with pin-hole apertures, for

producing micron or submicron scale pitting in

the fabric surface; and

Fig. 7 is a view of a reflector device for enabling

yarns to be treated in both sides using only a

single bank of UV emitters.

Referring first to Fig. 1 , treatment apparatus for use in the method of

the invention comprises a fabric dispensing roll 10, and a fabric take up roll

1 1 . Untreated fabric 1 2 is unwound from roll 10, and passes through a

treatment station 1 3. After treatment in station 1 3, the treated fabric is

wound up on roll 1 1 .

Treatment station 13 is shown diagrammatically as comprising an

enclosure or cabinet through which the fabric is passed, with an inlet slot

1 and an outlet slot 15, which preferably have provision for sealing. This

enables an atmosphere to be maintained in the enclosure other than ordinary

air, and/or at below or above ambient atmospheric pressure or temperature,

as required by the particular treatment.

Laser means 16 are disposed at the treatment station 13, and may

comprise a bank of laser projectors directed towards at least the upper surface of the fabric 1 2. A further bank of lasers, not shown, may be

mounted below the fabric, to be directed at the underside of the fabric 12.

The lasers preferably comprise excimer lasers, but may be ablation

lasers, and are preferably fourth harmonic UV lasers with a beam wave

length of up to 320nm, typically 224-226nm, with a beam of size 20

microns minimum size 1 micron, preferably masked to be larger or smaller,

e.g. submicron dimensions; and may fire 10 pulses per second. If ablation

lasers are used, these may be a harmonic YAG laser apparatus, preferably

a Q-switched YAG laser used in conjunction with frequency tripling or

quadrupling crystals, e.g. Nd:YAG lasers. YAG lasers need no gas

environments and emit e.g. UV frequency light. Excimer lasers require a

gas environment in which to ablate.

The lasers operate in accordance with a predetermined program to

provide e.g. pitting or scoring of the fabric surface, in predefined areas or

over the entire surface, or localised removal of a coating over such areas.

As an alternative to programming of the lasers, areas where treatment

is not required may be masked e.g. by a foil cut-out pattern.

Fig. 2 shows a cross-section through a sample of treated fabric, the

fabric comprising a single woven layer made up of warp threads 20, and

interwoven weft threads 21 a, 21 b, 21 c in each repeat, each floated over

two warp threads and below one warp thread 20. Weft thread 21 a is shown in cross-section and is etched at 23, (scale exaggerated) by incident

laser beams 24. The other threads 21 b, 21 c etc. are similarly etched by the

incident laser beams.

This provides a surface of the fabric as a whole which is modified by

the pits 23 to provide a roughened surface at e.g. the submicron scale.

This can provide a key for adhesion of a water layer by surface tension, and

thus increase the hydrophilic properties of the surface.

Fig. 3 is a similar view of another sample of treated fabric, comprising

a single woven layer made up of warp threads 30 and interwoven weft

threads 31 a, 31 b, 31 c in each repeat. The woven layer is provided on its

upper surface with a coating 32. After treatment using lasers 1 6 in

accordance with the invention, localised areas 33 are removed by incident

laser beams 34 (the scale is again exaggerated) . This has the effect of

modifying the properties, e.g. the adhesion or water retaining properties of

the coating 32 by exposing the underlying fabric layer in treated areas of

the fabric. Fabrics treated by lasers in accordance with the method of the

invention may be used as filter fabrics, e.g. in belt filters, barrel-neck filters

and the like, and also as papermachine clothing, notably press felts, dryer

belts, shoe press sleeves, corrugator belts, and also conveyer belts and

silicon wafer grinding belts.

It is for example advantageous to provide hydrophilic surfaces for filter media to obtain improved cake release where moisture is present in the

material being filtered. This moisture will form a very thin film of water of

the surface of the filter which improves cake release. Conversely, in high

temperature gas filtration there will be little or no moisture, and the best

cake release is then achieved using a hydrophobic coating. Another use for

hydrophilic media is in papermachine forming fabrics or dryer fabrics to

improve adhesion between the paper web and the fabric.

For papermachine clothing a hydrophobic fabric conversely gives

improved pick-up or transfer of the paper, pulp or tissue web, since web

and contaminant release is improved. This is particularly important in high¬

speed machines for making fine paper grades (e.g. newsprint) or tissue.

These requirements can be met by a filter belt or papermachine

clothing appropriately treated by the method of the invention, wherein for

example the laser means etch away the top surface layer or coating, and

any contaminants, leaving a chemically activated or deactivated surface on

e.g. a polymer substrate which is either hydrophilic or hydrophobic, or

which can be rendered so by subsequent exposure to e.g. air, silanes,

ammonia or fluorocarbons.

The method according to the invention can also for example be used

to treat the underside of a papermachine forming fabric to render the

surface hydrophilic and thereby reduce rewetting of the paper web, particularly towards the end of the forming section prior to the pick-up

position where the web is transferred to the press section. This can

increase web dryness by 0.5-3.0%, which results in significant cost savings

for the papermaker as less energy has to be used in the dryer section to

remove water.

In a further example selected areas on the paper-contacting side of

a papermachine fabric may be laser treated by the method according to the

invention, to form a pattern of hydrophilic areas. This creates a

corresponding textured pattern in the paper or tissue product.

GB-A-2,233,334 describes the use of excimer lasers to ablate and

etch the surfaces of polymeric materials, and describes the physical effects

of laser treatment on a micron- and submicron- scale on the treated surface.

The present invention makes use of these effects to provide useful surface

treatment for industrial fabrics. The invention may also be used to laser

etch yarns, fibres, strips or membranes or he like which may subsequently

be made up into fabrics, or composite belt structures.

A further embodiment of the invention is illustrated in Figs. 4 to 6.

Referring first to Fig. 4, apparatus for UV excimer lamp treatment of

industrial fabrics, or yarns, is shown in extemely diagrammatic and

simplified form. The fabric 1 10 is payed out from a dispensing roll 1 1 1 , and

is passed through a treatment station 1 1 2, and wound up after treatment in a take-up roll 1 13.

Treatment station 1 12 comprises shielding 1 14, to prevent excessive

exposure of workers to ultra violet radiation reflected or diffuse from the

treatment station. The shielding encloses a first bank of UV excimer lamps

1 1 5 located above the path of the fabric 1 10. A second bank of UV

excimer lamps 1 16 is located below the part of the fabric 1 10 so that both

surfaces of the fabric may be treated in one pass of the fabric through the

treatment station 1 1 2.

An optional mask 1 17 is located over the fabric 1 10, and this is used

to provide for selective exposure and masking of areas of the fabric from

the lamps 1 15 so that only selected areas of the fabric are treated by the

excimer UV light. No corresponding mask is shown below the fabric, but

may be provided if desired. Further, either of the banks 1 1 5 or 1 16 of UV

excimer lamps may be deactivated if only one surface of the fabric 1 10 is

to be treated.

Instead of a web of fabric such as 1 10, the path may be occupied by

multiple yarns, dispensed from and taken up by banks of bobbins. Similarly

to the fabric 1 10, the yarns can be subjected to UV excimer radiation on

one or both sides.

Fig. 5 shows a small part of a mask 1 17, in the form of a net of

diamond shaped openings 1 1 8, and an interconnected grid of lands 1 19. The lands 1 19 serve to mask areas of the fabric from the UV radiation,

which is however admitted by the openings 1 18. This produces a patterned

array in the fabric surface of areas, in this case in a network, having

differing properties, for example hydrophilic properties in the exposed areas

and more hydrophobic properties in the unexposed areas. This pattern

influences the properties of any paper web processed in the fabric and

produces patterning in the paper or tissue produced.

Fig. 6 shows a fragment of a second mask 1 17, much enlarged. This

comprises a sheet 1 20 of e.g. metal foil provided with myriad of pin hole

apertures 121 . These allow UV excimer radiation to effect very small areas

of the fabric, producing micron and submicron scale pits due to dissociation

of molecules leading to erosion of the fabric surface.

This can effect the surface properties of fabrics or yarns by for

example improving mechanical keying for retention of surface water, thus

improving hydrophilic properties.

Fig. 7 suggests how a single bank of UV excimer lamps may be used

to treat both sides of yarns 1 22, using a reflector such as a silvered or

aluminised mirror 1 23 to reflect UV radiation passing between the yarns

back to the undersides of the yarns. The reflector may be formed with

flutings or channels on its reflective surface to direct reflected rays and

focus them on the yarns 1 22. The UV excimer lamps 1 15, 1 16 provide narrow band radiations, e.g.

centred on 222nm, this will dissociate surface molecules of e.g. PET, to

increase hydrophily of the surface, by generating unsaturated carboxylic

acid groups on the surface. Other materials which can be treated include

aramids, PEEK, etc.

The invention also provides an industrial fabric as defined

hereinbefore treated by the method of the invention, yarns when treated by

the method of the invention, and an industrial fabric made from such yarns.

Claims

1 . A method of treating an industrial fabric, comprising modifying at

least part of at least one surface of such fabric, or of yarns, fabric, strip,

membrane or the like in or to form part of such a fabric, by treatment with

high energy electromagnetic radiation.

2. A method according to claim 1 , wherein high energy electromagnetic

radiation is produced by a UV excimer or ablation laser.

3. A method according to claim 2, wherein the surface or surfaces are

etched using said laser.

4. A method according to claim 3, wherein the etching effects pitting or

scoring of said surface to provide grooves hollows or protrusions, or to

expose ionised material.

5. A method according to claim 3 wherein a coating is provided on said

surface, the coating being selectively removed to expose a substrate

surface, by the etching step.

6. A method according to claim 3 wherein the etching step effects

removal of surface irregularities.

7. A method according to any preceding claim wherein the treatment is

carried out in an atmosphere containing one or more of a silane, a siloxane,

a perfluorocarbon, tetrafluoroethylene or ammonia.

8. A method according to any proceeding claim wherein said etching is carried out at a micron-or submicron-scale.

9. A method according to any preceding claim wherein areas which are

not to be treated are masked by a shaped foil mask.

10. A method according to any preceding claim wherein the treatment

makes the said surface hydrophobic.

1 1 . A method according to any of claims 1 to 10, wherein the treatment

makes the said surface hydrophilic.

1 2. A method according to any preceding claim wherein a coating or

matrix material is applied to the treated fabric, yarns or fibres.

1 3. A method according to my preceding claim wherein said, yarns or

fibres comprise or include a polymer such as a polyester, polyamide, or

polyolefin.

14. An industrial fabric wherein at least part of at least one surface of

such fabric, or of a layer in or to form part of such a fabric has been

modified by treatment according to any one of claims 1 to 13.

15. A fabric according to claim 14 comprising a filter cloth, conveyor belt,

or papermachine clothing, or comprising a component thereof.

16. A method according to claim 1 wherein said high energy

electromagnetic radiation is produced by a UV excimer lamp.

17. A method according to claim 1 6 wherein said lamp has a relatively

wide beam to enable simultaneous treatment of a substantial area of said yarns or fabric.

18. A method according to claim 17 including a plurality of such lamps

provided is provided in an array to direct their respective beams each over

part of a greater area of the fabric or yarns to be treated.

19. A method according to claim 16, 17 or 18, wherein pattern masks are

used to control the arrangement of areas exposed to and shielded from the

radiation.

20. A method according to any one of claims 1 6 to 19, wherein said

radiation is produced in a narrow waveband centred on 222nm.