The present invention relates primarily to industrial belts and particularly to such belts for use in environments of elevated temperatures. The invention has particular application in the field of phase separation apparatus, for example belts used in the field of papermaking. The invention has further application in relation to phase separation apparatus other than belts.

During the papermaking process, most particularly in the dryer section of the papermaking machine, it is essential that the cross-direction temperature profile of the paper web is monitored. An even temperature profile must be provided if differential drying of the paper web is to be avoided as this leads to paper web shrinkage, curling and streakiness resulting in the paper being written off as waste. Generally the temperature profile is monitored by means of infra red sensors and cameras which are expensive both to purchase and maintain as well as requiring continuous checks to ensure that they are kept free of dirt and other contaminates.

Similar problems are also encountered in monitoring the temperature profile across any other industrial belt such as tobacco suction tapes, tobacco garniture tapes, conveyor belts, printing blankets, fusing belts, laminating blankets or transfer blankets.

According to a first aspect of the present invention there is provided an industrial belt comprising a polymer matrix, said polymer matrix comprising at least one thermochromic material.

Similar problems are also encountered in monitoring the temperature profile across phase separation apparatus other than belts, such as filters.

According to a second aspect of the present invention there is provided phase separation apparatus comprising a polymer matrix, said matrix comprising at least one thermochromic compound.

Such problems are again encountered in industrial roll covers, for example, in the paper or printing industries. Thermal barring; that is vibrations in hard polyurethane roll covers (3-7 P & J Hardness) are sometimes caused by bars, i.e. lines in the axial direction of the roll, that have a higher temperature than the rest of the cover. This thermal barring is currently monitored by a complicated and expensive thermography analysis. A further problem with industrial roll covers is the generation of so-called "hot-spots" during use due to a non-uniform heating of the roll cover resulting from local overloading. This is particularly a problem with polyurethane roll covers.

According to a third aspect of the present invention there is provided an industrial roll cover comprising a polymer matrix, said polymer matrix comprising at least one thermochromic material.

The polymer matrix for the roll cover may comprise any of the following: polyurethane, synthetic or natural rubber or epoxy resins. The roll covers have many industrial applications, but will particularly be useful in papermaking machines.

The belting and phase separation apparatus ideally consists of a fabric. The said polymer matrix may be provided alone or in combination with a substrate. Thus the polymer matrix may be provided as a coating on a substrate or the polymer may encapsulate a reinforcing structure. For example, the coating substrate may comprise a base fabric and the reinforcement may comprise a reinforcement yarn and/or fabric which may be encapsulated in the polymer matrix. Reinforcement yarns would tend to run in the machine direction of the belt, although such yarns may also extend in the cross machine direction.

A thermochromic material is one which changes colour either reversibly or irreversibly due to the influence of heat changes. The thermochromic materials of the invention ideally provide a reversible colour change. The colour change is generally brought about by heat causing the colour-forming compound to melt and consequently come into contact with an electron accepting material.

The thermochromic materials preferably comprise an electron donating chromogenic material, an acidic substrate (i.e. an electron accepting material) and a binder.

Alternatively the thermochromic material may comprise an electron donating substance and acidic material. These materials tend to provide more intense colours. However, the colour change is generally slower and less distinct.

A further alternative is to use a combination of metal salt complexes and cholesteric liquid crystals. These materials tend to give a less intense colour, and frequently

need a black background for the colour change to be noticeable. Toxicity problems may also be associated with them.

The preferred thermochromic materials include so-called "lower temperature side colouring type materials", i.e. materials whose colour becomes deeper below the metachromatism (colour change) temperature.

A list of preferred electron donating materials is set out below.

A) substituted phenylmethane and fluoran derivatives, eg. 3,3'-dimethoxyfluoran, 3-chloro-6-phenylaminofluoran, 3- diethylamino-6-methyl-7-chlorofluoran, 3-diethyl-7,8- benzofluoran, 3,3' ,3' '-tris(p-dimethylaminophenyl) phthalide, 3-diethylamino-dibenzylaminofluoran

B) spiropyrans, eg. 2 ^, -(2-chloroanilino)-6'dibutylaminospiro [phthalide-3,9'-xanthene], 6' (cyclohexylmethylamino)-3'methyl- 2'-(phenylamino)-spiro[isobenzofuran-1(3H),9'-(9H)xanthen]-3 - one

C) indolyl phthalides, eg. 3-(4-diethylaminophenyl)-3-(l- ethyl-2-methylindol-3-yl) phthalide, 3-(4-diethylamino-2- methylphenyl)-3-(1 ,2-dimethylindol-3-yl) phthalide

D) leuco dyes, eg. phenylleucoauramine-n-bis- (dimethylaminophenyl)-2-amino-6-methylbenzothiazole

Examples of preferred electron accepting (acidic) substances are given below:

A' ) phenols or their salts or derivatives (eg. phenol, p- cresol, bisphenol A, 1,5-dihydroxynaphthalene, phenolic resins)

B' ) hydroxy aromatic carboxylic acids or their salts or derivatives (eg. salicylic acid, butyl gallate, tannic acid) C) carboxylic acids (eg. phthalic acid, benzoic acid, lauric acid, citric acid), sulphonic acid (eg. p-toluene sulphonic acid, lignin sulphonic acid)

D" ) azoles (eg. 5-chlorobenzotriazole, 5- hydroxybenzotriazole, triazole dicarboxylic acid) E ^• ) thiourea derivatives.

Examples of preferred solvents are given below: A' ' ) high boiling point alcohol (eg. 8-20C straight chain alkyl alcohol, olelyl alcohol)

B' ' ) fatty acid esters (eg. lauryl stearate, lanolin, lauric acid glyceride)

C') azomethines (eg. benzylidene aniline, p- methoxybenzylidene anisidine)

D' ¹ ) amides (eg. caprylic acid amide, acetanilide, benzoic acid amide)

E'') polymer binder (eg. polyester, polyamide, polyurethane, polphenylene sulphide)

Examples of cholesteric liquid crystals are as follows:-

Cholesterol acetate, cholesterol benzoate, cholesterol oleyl carbonate

Additional specific examples of colour changes are set out below: i) Malachite Green Lactone + tetrazole + 3,6- dimethoxyacetoaceta ide green to colourless at 70°C; ii) Indonine Blue + BLS-2700 phenol-formaldehyde resin blue to red at 120°C

o These materials are preferably microencapsulated to enable several thermochromic materials to be incorporated into a polymer matrix, preferably in separate capsules. The microcapsule diameter is preferably less than 50 microns and is ideally in the range from 5 to 15 microns. Thus for example a material A giving a colour transition at 90-100°C, a material B giving a transition at 105-115°C and a material C giving a transition at 120-130°C could all be added to the polymer matrix, which for a papermachine belt would be extruded to form a yarn. The microencapsulated nature of the material means that they retain the ability to exhibit metachromatism independently, as well as ensuring their protection from chemical degradation. Other additives may be incorporated into the microcapsules to enhance various properties. The microcapsules are readily blendable for extrusion into filaments and yarns.

The composition may contain a fluorescent brightening agent to ensure that the yarn has a white colour when the thermochromic material enters into a colourless state, thereby enhancing the colour contrast.

Rather than, as is preferred, incorporating the thermochromic materials into a polymer matrix for extrusion to form a yarn, it is possible to fix microencapsulated thermochromic dyestuffs onto the surface of a body made from the polymer, such as yarns of fibres, using a suitable, ideally cross-linked, resin. It is possible to fill hollow fibres with thermochromic dye, preferably in microencapsulated form.

As an alternative to the inclusion of several thermochromic materials into individual yarns or fibres would be to use multifilaments or braided yarns incorporating yarns, preferably with each containing a specific reversible thermochromic material. Thus different thermochromic materials may be incorporated into the different yarns or fabrics.

The thermochromic material may be provided in a so-called core-sheath yarn with the thermochromic material ideally being provided in the yarn sheath. In all applications the thermochromic material is to be concentrated in the surface regions so as to provide a visible colour change and also to ensure that the heat required to bring about colour change is not lost as a result of the insulating effect of the polymer material. Thermally conductive matter, such as metal and/or graphite particles may be added to the polymer matrix so as to reduce the insulation effect of the polymer which would reduce the temperature experienced by the thermochromic microcapsules.

The yarn polymer may include any of the following materials: polyester (PET, PBT, PPT, PTT, PEN, PBN, PCT, PCTA) , aliphatic polyamides (PA6, PA6.6, PA12), aromatic polyamides, (Kevlar, Twaron), partially aromatic polyamides (Amodel, HTN, MXD6), liquid crystal polymers (Suprex, Vectran), polyketones (Carilon), PEEK, PU, TPU, thermoplastic elastomers, PPS, PPO, PBO, polyimide, fluoropolymer (PTFE), polyolefin, (PP, PE), or blends or combinations of one or more of these materials.

As stated previously this invention is particularly useful when applied to papermakers dryer fabrics which are used in environments having an elevated temperature. However, the fabric could also feasibly be used in any of the following applications which are listed by way of example.

1) The lateral regions of papermakers fabrics are commonly coated with a polymer so as to provide edge sealing. The polymeric material in accordance with the invention could be used to achieve this.

2) It is common to resin treat one or more surfaces of papermakers fabrics, such as press felts. The polymeric material of the invention could be used for this surface treatment.

3) Extended nip press belts (ENP belts) usually comprise a base fabric coated on either side thereof with a polymeric material. The polymeric material in accordance with the invention could be used in the manufacture of ENP belts.

4) Rollers for use, for example, in the paper or printing industries often have polymeric roller covers. The polymeric material of the invention can be used in this application.