The present invention relates to industrial fabrics and, in particular, to such fabrics for use in papermachine clothing such as in a press dryer or impulse dryer of a

papeπriaking machine.

The invention seeks to address the problem of resistance to wear, deformation and chemical attack encountered by a papermachine clothing, such a as press felt, and in particular a press dryer or impulse dryer fabric, where an environment of combined

high temperature (250°F) and pressure are experienced. A typical press dryer section

of a papermaking machine is described for example in Canadian Patent 1,299,863

(Beloit).

In general, a press dryer fabric must combine all the characteristics of a

standard press felt, such as high void volume (for water handling capacity) and good

resilience (to avoid felt compaction), both of which are offered by the standard batt-

on-base press felt designs. Yet, unlike conventional press felts, the press dryer fabric

must also possess a good resistance to hydrolytic and thermal degradation due to the

hot roll surface and the generation of steam in the press drying roll nip. The combination of pressure, heat and steam can lead to a deformation and/or wear as well

as undesirable plasticisation or glazing over of both the paper contacting batt staple

fibres and the basecloth support. The latter may be woven, or nonwoven such as a

membrane as described in GB 2235705B, a knitted fabric, or a fabric comprising

intermeshed and interconnected spirals such as that described in EP 0028630. A

polyester staple tends to fibrillate easily when subjected to repeated mechanical

pressure forces, whilst the polyamide staple normally used shows poor resistance to

thermal degradation. Aramids are susceptible to hydrolysis at elevated temperatures.

Polyolefins show very poor dry heat stability. Many of the high performance materials such as fluoropolymer or polyetheretherketone (PEEK) are prohibitively expensive and still suffer from glazing.

An object of the present invention is to overcome the abovementioned

disadvantages with known industrial fabrics for papermaking machines, particularly

press dryer fabrics, by providing a simple and inexpensive industrial fabric such as a press dryer fabric with an increased working life due to improved resistance to wear, thermal degradation, glazing and hydrolytic or chemical attack.

According to a first aspect of the invention there is provided an industrial fabric

comprising layer silicate material. The fabric is particularly for use as industrial belting, such as papermachine clothing.

The term layer silicate material used herein relates to silicate materials having a

micaceous, i.e. layered, structure which is similar to that of graphite. Preferred silicate

materials include hydrated silicate clays. The materials of the invention exhibit good

abrasion resistance and good lubricating properties and are readily dispersed in

aqueous formulations. These materials further have a high aspect ratio of particles,

typically in the order of 20,000. Thus the materials form very uniform films. The

materials of the invention exhibit high chemical inertness and high thermal resistance.

For example, the hydrated silicate clays retain their physical form up to temperatures in

the order of 1100°C with heat being dissipated to a much greater extent in the

horizontal plane, rather than the vertical plane, yielding better insulating properties.

The combination of the high aspect ratio and charge heterogeneity (-VE at the

layer surface and +VE at the particle edge) gives very good overlapping of particles

following evaporation of water, which are strongly attracted by electrostatic forces,

resulting in very flexible films or coatings.

The layer silicate material preferably comprises vermiculite in powder or dispersion form. The general molecular formula for vermiculite is as follows:-

(Mg, Ca, Fe ⁿ ),.(Si, Al, Fe ^m ) ₄ .(OH) _l0 .4H_O

The vermiculite preferably comprises "Microlite" which is marketed by W.R. Grace & Co. "Microlite" has the following general formula:

(Li,K (Mg, Ca, Fe ⁿ ) ₃ .(Si, Al,Fe ^m ) ₄ .O ₁₀ .(OH) ₂ .4H ₂ O.

The "Microlite" typically comprises: 40.50 wt% SiO^ 18.50 MgO, 9.30 Al ₂ O ₃ ,

11.00 FβjOj + FeO, 5.70 K ₂ O, 0.40 CaO, 2.10 TiO* 0.15 MnO, 0.25 Cr ₂ O _3» 0.15 Na_O, 0.41 Li ₂ O and 11.74 impurities water.

Other preferred layer silicate materials include any of the following:

montmorillonite, kaolinite or sepiolite. Each layer silicate material may be used alone

or in combination with other layer silicate material.

The layer silicate material dispersion may be applied as a coating at a surface of

a base fabric, which may be woven, partly woven or nonwoven. Such a coating would

be sufficiently flexible so as not to be brittle under dynamic conditions. Part or all of

the base fabric may be coated with the layer silicate material, preferably as a dispersion.

The coating dispersion preferably contains up to 15 wt.% of silicate, and more

preferably from 0.1 to 3 wt.% for the thin coatings usually required for industrial

fabrics. Alternatively, the layer silicate material may be incorporated into the fabric,

for example by incorporating the material, preferably a dispersion, into the organic

polymer melt for production of yarns or fibres to be incoφorated into the fabric. A

typical ratio of layer silicate material to melt would be less than 20wt% clay. The

fabric of the invention has particular application for use in a press dryer or impulse

dryer of a papermaking machine. Preferably the paper contacting side of the fabric is coated. The fabric or base fabric may comprise one or more layers and typically will comprise a basecloth support, which may be woven or non-woven preferably having a staple batt needled thereto so as to provide a felt. In this case the coating may be applied to the staple batt surface. Alternatively the layer silicate material may be

incoφorated into the yarns or fibres used to form one or more of the layers such as the basecloth support and/or the staple batt.

Preferably for a base fabric having a thickness in the range of 1.1 to 3.5mm, a

coating having a thickness in the range lOμm to 0.1mm is used.

The excellent heat resistance of these layer silicate materials confers thermal

insulation properties that protect the fabric, both staple and basecloth, from excessive

heat. Hence materials with relatively poor thermal stability may be used in the press

dryer fabric. The layered structure of these silicate materials gives them good lubricating properties. Thus resistance to wear is increased. The high aspect ratio

(ratio of width to depth) of the flakes makes them ideal for film formation. This aspect

ratio of the flakes is preferably in the range from 10 to 10000. The layer silicate

materials are also highly chemically inert, possess a low density and are inexpensive.

The layer silicate material is preferably present in exfoliated, that is flaked form.

The layer silicate material is preferably applied as an aqueous dispersion.

Examples include those marketed under the trade names of "Microlite 903", "Microlite

923" and "Microlite 963" marketed by W.R. Grace & Co., which have a viscosity in

the range of 100 - !2000cP and a solids content of 5 - 20% by weight.

One or more stabilising agents may be added to the coating mixture for

improving the stability of the mineral coating when in contact with water. Suitable

stabilising agents include any of the following: saturated magnesium salt solution (eg MgClj), urea-formaldehyde, condensation polymer resins, melamiπe-formaidehyde, condensation polymer resins or basic, sparingly soluble particulate compounds (eg CaO or MgO). Up to I5wt% of stabilising agent, with respect to the layer silicate material, would usually be added to the coating material. An additional or alternative stabilising method would involve the treatment of the coating with ammonic or alkyl

amine vapour.

A further possible additive would be silicone polymer. This would provide non-stick properties.

Optional additives include standard adhesion promoting agents, viscosity

modifiers and colourants.

The coatings can be applied by conventional methods such as the knife-on-roll,

reverse roll, dip-and-squeeze or dip-and-wipe techniques or by any other suitable method.

The knife-on-roll technique involves feeding the aqueous dispersion from a

trough onto the fabric substrate, the gap between the knife and the roll over which the

fabric passes being used to control the thickness of the coating. The reverse roll

technique involves feeding the fabric past an applicator roll which transfers the

dispersion from a trough to the fabric. The dip and squeeze technique involves feeding

the fabric through a coating trough and then passing it through nip rolls which may be

pressure or gap controlled to remove any excess coating. The dip and wipe technique

involves feeding the fabric through a coating trough and then removing the excess

coating by means of wiper bars. The dip and squeeze and the dip and wipe are the

preferred coating methods for the present invention; the former being preferred for

heavy weight texturised textiles and the latter for medium and low weight woven non- texturised textiles requiring low permeability. The coated fabric may be dried by

passing through an oven. Heat cleaning of the fabric prior to coating may improve the coating adhesion in certain cases.

Thus, the invention provides an improved fabric for use in a press dryer. The

invention may have application in other fields and in particular will provide an

improved fabric for use as a fusing belt such as described in GB 2250696 and as a laminating blanket such as described in EP 0375369.

Thus according to a second aspect of the invention there is provided a press or

impulse dryer fabric, a fusing belt or a laminating blanket comprising an industrial

fabric according to the invention.

Thus, the layer silicate material may be applied as a coating to a fabric as described in GB 2250696 or EP 0375369. Incoφoration of the layer silicate material

into the polymer melt for the preparation of yarns or staple fibres for fabrics such as

press dryer fabrics, fusing belts or laminating blankets, achieves the same properties as

the coating since the material tends to migrate towards the fabric surfaces.

Thus according to a third aspect of the present invention there is provided

yarns or fibres comprising a polymer matrix incoφorating layer silicate material.

The polymer may comprise any of the following: polyamides such as Nylon, for

example type PA6, PA6.6, PA6.10, PA6.12, polyesters, copolyesters,

polyetheretherketone or polyphenylene sulphide.

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

reference to the accompanying drawings in which:-

Fig.1 is a perspective view of a first embodiment of industrial fabric of the

invention; and

Fig.2 is a diagrammatic cross-sectional view of a second embodiment of industrial fabric of the invention.

Referring to the drawings, an industrial fabric, such as a press dryer fabric, comprises a base fabric 2 having a coating 4 of hydrated silicate clay applied to the paper-contacting surface thereof. In the first embodiment shown, the base fabric

comprises a non-woven membrane 6, comprising an array of parallel yarns 8 encapsulated within a polymeric plastic matrix material 10, and a fibrous layer 12 bound to the matrix material. The coating 4 is applied to the exposed surface of the fibrous layer 12.

In the second embodiment shown in fig.2, the base fabric comprises a non¬ woven base cloth 14 having two superimposed layers (16,18) of a synthetic thermoplastics material provided in mesh form and a fibrous batt 20 such as a needled mat. The coating is applied to the exposed surface of the fibrous batt 20.

It will be appreciated that the present invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

In particular the clay coating may be applied to any suitable fabric structure by any suitable means and/or the clay may be incoφorated into the yams or fibres used to

form any part of the fabric stmcture.