Definitions

• the invention relates to coatings and in particular to a method of coating and to coating compositions.
• Commonly used coatings are composed of resins or polymers, and one or more of solvents (except in the case of powder coating) together with pigments or filler components and other additives to provide stability or other desirable properties.
• the traditionally used coatings are classified into thermoplastic and thermosettable coatings and more recently radiation curable coatings have been used in some applications.
• a coating composition should allow quick curing, have good film forming properties and provide good adhesion to the substrate.
• Thermoplastic, thermosetting and radiation curable compositions require the presence of solvent or diluent to reduce the viscosity and provide film formation.
• the diluent is generally in the form of a monomer which on curing is incorporated into the polymer network.
• Thermosetting and radiation curable compositions require less solvent or diluent however higher solids contents reduce storage stability, film forming properties and produce less efficient curing. These problems are further exacerbated when significant proportions of filler or pigment are present.
• a method of preparing a coated substrate comprising: providing a radiation curable composition comprising a resin component including an unsaturated monomer and at least one of an unsaturated prepolymer and binder or mixture thereof; applying the radiation curable composition at a temperature above ambient temperature, preferably from 35°C to 150°C to the substrate; and curing the coating by subjecting the coating to radiation.
• the radiation curable composition is applied to the substrate at a temperature above ambient temperature and preferably in the range of from 35 to 150°C. More preferably the temperature is from 50 to 120°C and most preferably from 60 to 80°C.
• the composition is preferably curable by electron beam or ultraviolet radiation.
• UV curable compositions are preferred due to convenience and the cost advantage provided by UV-curing techniques.
• UV curable compositions may include a photoinitiator.
• the method of the invention provides considerable advantages in application of coatings containing pigment.
• the use of significant quantities of fillers or pigments tends to mask penetration of UV light significantly reducing the quality of resultant coating. Radiation curing of pigmented systems in air especially for exterior use, has proved to be particularly difficult. The presence of air results in surface inhibition reducing the quality, adhesion and durability of the cured coating. Although curing under nitrogen reduces these difficulties the use of nitrogen is inconvenient and increases the expense of forming coatings.
• previous attempts to coat substrates using UV curable coatings have generally required the use of relatively thin coatings of for example 10 microns. The formation of thicker coatings has therefore required the application of a number of layers.
• radiation curable coating composition comprising: a resin composition including a monomer and at least one of a prepolymer and binder polymer or mixture thereof; a pigment or filler preferably present in an amount of at least 40 parts of the total of the filler and pigment per 100 parts by weight of resin component; and a photoinitiator component comprising a combination of an acyl phosphine oxide initiator and an ⁇ -hydroxy- ⁇ , ⁇ -di-substituted acetophenone initiator.
• the total of the filler and pigment components may in some cases be up to about 1000 parts based on 100 parts by weight of the resin component.
• the coating composition will contain in the range of from 50 to 400 parts by weight of total of pigments and fillers per 100 parts by weight of resin component.
• the radiation curable coating composition will generally comprise an ethylenically unsaturated monomer.
• ethylenically unsaturated monomers include: unsaturated carboxylic acids and esters particularly acrylate and methacrylate esters; acrylamides, allyl compounds such as diallyl phthalate; maleic acid, maleic anhydride, maleimide and derivatives, fumaric acid, and their esters and amides; and other, unsaturated compounds such as vinyl toluene, divinyl benzene, N-vinylcarbazole and N-vinylpyrrolidone.
• the preferred monomers are monomers comprising a plurality of acrylate or methacrylate functional groups which may be formed, for example, from polyols or the like.
• multifunctional acrylates include trimethylolpropane triacrylate (TMPTA) and its ethoxylated derivative, neopentyl glyol diacrylate, tripropyleneglycol diacrylate (TPGDA), hexanediol diacrylate (HDDA) and polyethyleneglycol diacrylates such as that formed from PEG 200.
• TMPTA trimethylolpropane triacrylate
• TPGDA tripropyleneglycol diacrylate
• HDDA hexanediol diacrylate
• the molecular weight of the monomer will typically be less than 2000.
• the radiation curable coating compositions will generally contain a prepolymer or binder polymer or mixtures thereof.
• the prepolymer may, for example, comprise one or more oligomer selected from ethylenically unsaturated polyesters, ethylenically unsaturated polyethers, ethylenically unsaturated polyurethanes, ethylenically unsaturated epoxy, oligo-ester (meth)acrylates and ethylenically unsaturated poly(meth)acrylates and modified products thereof.
• Typical of prepolymers which may be used are acrylated oligomers selected from polyurethane, epoxy, polyesters, polyethers and copolymers and block copolymers thereof. Such prepolymers are described in the text UV Curing: Science and
• Binder polymers are generally of higher molecular weight than prepolymers and include polymers such as polystryrene, polyesters such as those used in the manufacture of fibre glass sheeting and formed by reaction of unsaturated acids and polyols, polyacrylamides, polyvinyl acetate, polyvinylpyrrolidones, acrylonitrile butadiene styrene (ABS) and cellulose derivatives.
• the binder polymer be soluble in the monomer component or the mixture of the monomer component, oligomer and other additives at the temperature of application.
• the molecular weight of the prepolymer and binder polymer is typically in the range of from 2000 to 200,000 and preferably from 5000 to 100,000.
• the weight ratio of monomer to the prepolymer and binder will generally be in the range of from 97.5:2.5 to 2.5:97.5.
• a high proportion of oligomer for example a monomer: oligomer weight ratio of 1:1 to 1 :40.
• monomer: oligomer and binder weight ratio of 1:1 to 40:1 it may be more economical to use a higher proportion of monomer for example a monomer: oligomer and binder weight ratio of 1:1 to 40:1.
• UV ultra violet light
• photoinitiators include benzoin ethers such as ⁇ , ⁇ -dimethoxy- ⁇ -phenylacetophenone (DMPA), ⁇ , ⁇ -diethoxyacetophenone; ⁇ -hydroxy- ⁇ , ⁇ -dialkylacetophenones such as ⁇ -hydroxy- ⁇ , ⁇ -dimethyl aceto- phenone and 1-benzoylcyclohexanol; acyl phosphine oxides such 2,4,6- trimethylbenzolyl diphenyl phosphine oxide and bis-(2,6-dimethoxybenzoyl)-2,4,4- trimethylphenyl phosphine; cyclic photoinitiators such as cyclic benzoin methyl ethers and benzil ketals; cyclic benzils; intermolecular hydrogen abstraction photoinitiators such as benzophenone, Michler's ketone, thioxanthones, benzil and quinones; and 3-ketocoumarins.
• the photoinitiator component may also be used in combination with an amine coinitiator particularly a tertiary amine coinitiator. This is particularly preferred in the case of the intermolecular hydrogen abstraction photoinitiators such as benzophenone.
• the amine is generally triethanolamine or an unsaturated tertiary amine such as dimethylaminoethyl acrylate, diethylaminoethylacrylate or the corresponding methacrylates.
• An amine/acrylate adduct such as that sold under the trade name Uvecryl 115 by Tollchem Pty. Ltd. Australia is also useful as a coinitiator. Where the unsaturated amine is used it will of course contribute to the monomer or prepolymer component.
• the amount of initiator is typically in the range of from 0 to 60 parts by weight based on 100 parts by weight of the resin component and when used amounts in the range of 0.1 to 15 parts by weight are more preferred.
• compositions to be cured by electron beam radiation a photoinitiator is not necessary.
• the composition of the invention generally contains an ⁇ -hydroxy- ⁇ , ⁇ -disubstituted acetophenone and an acyl phosphine initiator.
• the most preferred ⁇ -hydroxy- ⁇ ,- ⁇ -disubstituted aceto ⁇ phenone is 1-hydroxycyclohexyl phenyl ketone and the most preferred acyl phosphine oxide is bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.
• the phosphine oxide and acetophenone component will be present in a weight ratio of from 1:10 to 10:1.
• the initiator is a mixture of bis-(2,6-dimethoxybenzoyl) and 1-hydroxycyclohexyl phenyl ketone in a weight ratio of 25:75 to 50:50.
• Ciba products IRGACURE 1800 and IRGACURE 1850 are examples of suitable commercially available initiators.
• the excellent performance of coatings formed according to the invention was unexpected as radiation curable compositions particularly those containing a significant proportion of oligomers and binders were not expected to be thermally stable enough for heated application particularly in the presence of free radical initiators and pigments and/or fillers. Application at above ambient temperature in combination with the particular photoinitiator allows excellent coverage and adhesion to be obtained even with substantial proportions of filler.
• fillers examples include talc, calcium carbonate, silica or any of the other conventional fillers used in coating compositions or mixtures of such fillers.
• the coating compositions used in the process of the invention may include water, solvents or other additives to control viscosity.
• solvents may allow spray application.
• Propylene glycol monomethyl ether acetate is a particularly useful solvent and may be used as a solvent alone or in addition to water. Where water compatibility is not necessary, solvents other than PGMA may be preferred.
• the solvent is used in an amount of from 0 to 100 parts by weight per
• wetting agents provide a particularly useful viscosity control when pigments or fillers are used. Suitable wetting agents are commercially available and include products sold under the brand names "Dysperbyk 110", Dysperbyk 161" and BYK 361". Other flow, slip and gloss improvers including silanes such as the Z6020 brand available from the Dow Chemical Company and fluorinated compounds such as the FC 430 brand available from The 3M Company may also be used.
• the flow additive when used will preferably be present in an amount of up to 10 parts by weight based on 100 parts by weight of the resin component.
• composition for use in accordance with the invention contains a water compatible prepolymer, particularly a urethane acrylate prepolymer; an unsaturated monomer; from 50 to 1000 parts based on 100 parts by weight of the resin components of one or more pigment and/or fillers; and water in an amount of from 5 to 100 parts by weight (preferably from 5 to 20 parts and most preferably 5 to 15 parts) based on 100 parts of the unsaturated resin component.
• This embodiment has the significant advantage, where high amounts of filler are used, that it enables the use without solvent and their associated health and environmental problems to be avoided.
• urethane acrylates such as those acrylated polyurethanes containing a plurality of polymer groups such as polyether and polyester group linked through urethane linking groups, is preferred.
• Acrylate or methacrylate groups will generally be present at each end of the prepolymer.
• composition used in the method of the invention may include a thermal polymerisation inhibitor such as di-t-butyl-p-cresol, hydroquinone, benzoquinone or their derivatives and the like.
• a thermal polymerisation inhibitor such as di-t-butyl-p-cresol, hydroquinone, benzoquinone or their derivatives and the like.
• Di-t-butyl-p-cresol is preferred.
• the amount of thermal polymerisation inhibitor is typically up to 10 parts by weight relative to 100 parts by weight of the resin component.
• the composition may contain an ultraviolet light stabiliser which may be a UV absorber or a hindered amine light stabiliser (HALS).
• UV absorbers include the benzotriaziols and hydroxybenzophenones.
• the most preferred UV stabilisers are the HALS such as bis-(1,2,2,6,6-pentamethyl-4- piperidyl) sebacate which is available from Ciba as TINUVIN 292 and a poly[6-1 ,- 1,3,3-tetramethylbutyl)imino-1 ,3,5-triazin-2,4-diyl] [2,2,6,6-tetramethyl-4-piperidyl)- imino] hexamethylene [2,2,6,6-tetramethyl-4-piperidyl)imino] available from Ciba under the brand name TINUVIN 770.
• the amount of UV stabiliser which is effective will depend on the specific compounds chosen but typically up to 20 parts by weight relative to 100 parts by weight of resin component will be sufficient.
• the UV stabiliser may be used simply to provide UV protection to the coating applied in accordance with the invention in which case up to 10 parts by weight will generally be adequate and in the case of HALS 0.05 to 5 parts is preferred. In some embodiments however it may be desirable to use a high concentration of stabiliser particularly where UV protection is also to be provided for the substrate to which the coating is to be applied.
• composition used in the process of the invention preferably includes one or more flame retarding additives.
• Preferred examples of such additives may be selected from the following:
• L alkali metal and ammonium chromates and dichromates
• m alkali metal carbonates
• n alkali metal tungstate
• o boric acid and borax
• p organo phosphorus or organo boron compounds
• the preferred amount for each system may be determined by experiment.
• the finished product may be fire retarded in accordance with Australian Standard AS1530 Parts 2 and 3.
• Particularly preferred fire retarding additives are Fyrol 76, Fyrol 51 , PE-100 and W-2 and mixtures thereof.
• the other flame retardants in “a” to "p" are best used for specific applications and as with all the above retarding additions, their conditions of use are determined by the equivalent level of phosphorus present in the finish.
• the Fyrols or PE-100 or W-2 are used, the amounts are 1 to 50% based on the mass of resin solids with 2 to 20% preferred.
• the equivalent proportion of elemental phosphorus (and boron if used in combination) in the combination to a level of 4.0%P is needed to achieve the required flame retardancy.
• significantly less may be needed depending on the substrate material. For example some materials may need only 2.0% P.
• the invention therefore provides a method of coating a substrate comprising: providing a radiation curable coating composition comprising a resin component including an unsaturated monomer and an unsaturated oligomer or binder; providing a substrate having a wet surface; applying the radiation curable composition to the wet surface; and subjecting the coated substrate radiation to thereby cure the coating.
• the substrate used in this embodiment is wettable and may for example be a cementitious product or cellulosic product.
• products containing a cement or gypsum binder and reinforcing or filler materials such as compressed cellulose fibre, vermiculite, bagasse, crumbed rubber, corn stalks, rice husks and the like. Also the process provides particularly good results in coating paper and cardboard.
• the substrate may be wet by dipping in water or by spraying with water.
• Surfactants or wetting agents may also be used to improve wetting of the substrate surface.
• conventional wetting agent such as the "Teepol” may be used at the rate of up to 5% w/w, or more in water to improve wetting.
• the coating of wet products is particularly preferred in the recycling of paper products.
• wet reconstituted pulp is dried to produce the recycle paper products.
• the quantity of the recycled products and their acceptance is however reduced by the presence of colour variation and coloured contaminants in the recycled fibre pulp.
• the present invention provides a method by which the strength and appearance of the paper is significantly improved by coating the wet recycled paper with a radiation curable composition and curing the coated wet recycled paper by subjecting it to radiation. It is particularly preferred that a coating of high filler loading is used and is applied to the wet surface.
• the use of filler loadings of 10-200 parts of filler per 100 parts by weight of resin enables excellent coverage of the surface to provide colour uniformity and high quality finish.
• the present invention may be utilised in the application of clear finishes, pigmented finishes, undercoats and topcoat finishes.
• the clear finishes will contain a resin component comprising:
• a photopolymerization initiator 0.1 to 60 parts, (preferably 0.1 to 5 parts) by weight of a photopolymerization initiator; and optionally one or more components selected from the group consisting of:
• filler such as calcite or talc (preferably calcite and talc in a weight ratio of 2:1) in an amount of up to 1000 parts by weight and preferably up to 200 parts by weight (most preferably 50 to 200 parts);
• solvent such as PGMA and methylethylketone in an amount of up to 100 parts by weight and preferably up to 20 parts by weight.
• wetting agents and dispersant such as DYSPERBYK 110 or 161 in an amount of up to 100 parts by weight and preferably up to 20 parts by weight;
• thermal polymerisation inhibitor such as di-t-butyl-p-cresol (preferably 0.05 to 5 parts by weight);
• light stabiliser such as benzotriazoles included bis-benzotriazoles such as TINUVIN 384, triazines and HALS such as TINUVIN 292, TINUVIN 770 or TINUVIN 384 in an amount of up to 10 parts by weight (preferably 0.05 to
• the method of the invention in which the coating composition is heated has the significant advantage that it allows a higher proportion of oligomer to be iincorporated than would otherwise be possible. A higher proportion of oligomer allows the properties of the film to be precisely controlled.
• Pigmented finishes may comprise the same components as clear finishes described above but will contain a pigment such as titanium dioxide in an amount of up to 1000 parts by weight and preferably from 10 to 200 parts by weight.
• the formulations used in coating cementitious products will most preferably contain a pigment in an amount of up to 1000 parts by weight and preferably 10 to 200 parts by weight (most preferably 40 to 200 parts) and a filler in an amount of up to 1000 parts and preferably from 10 to 200 parts (most preferably 40 to 200 parts by weight.
• the composition may contain the components as described above for clear coatings.
• Some substrates after being treated by conventional processes on line are quite hot at the end of the treatment (for example in the range of from 100 to 150°C).
• UV coatings cure very efficiently and with excellent adhesion if applied at elevated temperatures i.e. immediately on line at the completion of the polymerisation process when the product emerges from the oven.
• the adhesion is generally far superior to room temperature application followed by UV cure on the same substrates.
• Materials particularly relevant to this process are plasterboard, styrene polyester resins (particularly those impregnated with glass fibres) plastics like the polyolefins and polystyrene in any form particularly as sheet or foam, and metals (either precoated with paint or bare).
• the substrate undergoes a prior, non-related thermal treatment or the like at the completion of which, whilst still on line a UV curable coating is applied hot and passed under the appropriate curing UV lamp system.
• the coating can be any of the preceding group of UV systems discussed in this patent. As previously discussed, the process is also applicable to EB systems.
• the invention therefore provides a method of coating as hereinbefore described wherein the substrate is also heated preferably to a temperature in the range of 50 to 200°C and more preferably 50 to 150°C and most preferably 70 to 150°C.
• the substrate is a styrene polymer resins particularly those incorporating glass fibre.
• Styrene polyester products may be formed by polymerisation in situ within a mould over shaping means such as an extruder. The reaction to form the polymer is exothermic so that the product after processing has a temperature of about 100 to 150°C. We have found that extremely good adhesion is provided if the coating composition is applied to the styrene polymer product before cooling.
• the strength of adhesion may be due to the presence of small amounts of unreacted monomers in the product on formation which may become involved in polymerization of the coating to provide a stronger bond with the surface than would otherwise occur.
• the minor amounts of unreacted monomer which may be about 1 per cent or less may become polymerised during cooling of the product.
• the invention in one preferred embodiment therefore provides a method of forming a coated styrene polymer or copolymer product, particularly styrene polyester, comprising forming the product by exothermic polymerisation to provide a hot formed product and applying a radiation curable coating to the hot formed product (preferably at a temperature the range of from 50 to 150°C (more preferably 70 to 150°C) and curing the coating by subjecting it to radiation.
• Example demonstrates the use of the invention in applying clear finishes.
• Tinuvin 292 1 The aliphatic urethane acrylate used was ULS 490 or 496 from Tollchem Australia. Other commercially available aliphatic urethane acrylates include CN 963B80 from Sartomer USA or "Ebecryl 284" from UCB Belgium.
• composition 1a to d Each of the composition 1a to d was heated to a temperature of 70 to 80° and applied to timber by spraying the hot composition onto the timber. Corresponding compositions were also prepared containing as an additional component the solvent PGMA in an amount of 5 parts by weight.
• Example 2 Each of the composition 1a to d was heated to a temperature of 70 to 80° and applied to timber by spraying the hot composition onto the timber. Corresponding compositions were also prepared containing as an additional component the solvent PGMA in an amount of 5 parts by weight.
• This example demonstrates the process of the invention and undercoat formulations.
• the undercoat formulation was prepared by combining the following components in the parts by weight listed:
• Urethane acrylate (aromatic) was used because it is cheaper than the aliphatic equivalent and dries faster.
• the composition is compatible with water to certain levels, so in a further example 10 parts by weight of water or solvent PGMA was added to the above formula.
• Epoxy acrylate like Sartomer CNS124A80 or Monocure Sydney product can be used in place of the urethane acrylate, however water compatibility with epoxy acrylates is not as good. Epoxy acrylates are cheaper.
• polyether acrylates, polyester acrylates and polyesters can be used.
• TPGDA may be used without prepolymer but that curing is significantly slower.
• the undercoat was dispersed in a roll mill (tripple roll mill) then heated to 70°C and sprayed onto the substrate. Curing was carried out using a
• the coating may be sanded if necessary.
• Example 1 and Example 2 were used in coating a number of substitutes at a temperature of 70 to 80°C.
• the coatings provided excellent adhesions to each of the substrate tests which included:
• Timber for flooring and panelling including penius radiata, huon pine, blackbutt, jarra, US redwood, cypress pine, kauri, reconstituted timbers and substrates include particle board, exterior grade MDF and standard MDF, bagasse, corn stalks, rice husks, gypsum, vermiculite mineral fibre board (US Gypsium Interiors) and masonite.
• cementitious products including cement panels, blocks, tiles, cement products modified with other materials, particularly fibres such as cellulose and wood, com stalks, rubber especially recycled car and truck tyres, plastic fibres like polypropylene and polyethylene.
• Plastics in all forms such as sheet, blocks, film and foams especially the polyolefins like polyethylene and polypropylene, polystyrene, PVC, ABS, polyacrylonitrile, polyester, polycarbonate, cellulose acetate, polymethylmethacrylate, nylon, polyacetal, PET.
• a composition was prepared by combining the following components in the parts by weight listed.
• the composition described was heated to 70 to 75°C and applied at a temperature of 70 to 75°C to a compressed cellulose fibrous cement board available under the brand name "Hardiplank” from James Hardie Pty. Ltd. of Sydney Australia at a thickness of about 30-40 microns. After application the coating was cured on the surface of the board at the rate of 20 metres/minute using a 300 watt per inch Fusion lamp. After curing the coating is ready for field installation. The coating was over reacted with a decorative top coat using water based acrylic paint sold under the brand name "Weathershield” by Dulux Australia Limited although any other solvent or exterior pigmented finish may be used.
• Example 3a Two further compositions corresponding to the above description were prepared with the addition in one case (Example 3a) 10 parts by weight of PGMA and in the other case (Example 3b) 10 parts by weight of water.
• the difference between process (a) with PGMA and (b) with water was after curing a trace of solvent is retained by the film on the board. This gradually evaporates but can leave a slightly softer film than when water is used or no solvent is used. This softer film may lead to subsequent "blocking" between sheets if they are stacked immediately after curing. Water did not lead to this problem since it is absorbed by the porous substrate and not the film. In non porous substrates the water is repelled by the highly cross-linked film.
• Tinuvin 292 1 b A further composition was prepared containing the components in the parts by weight listed in part (a) with the addition of 10 parts by weight of water.
• the mixture is ground in a triple roll mill or the like then is sprayed at 70 - 75°C or above, coated on to CFC Hardiboard which had previously been undercoated by UV process already discussed or by conventional solvent based undercoat which coatings had been sanded and cleaned of dust.
• Product is then cured at 20 metres/minute under Fusion lamp of 300 Watts/inch to give a high gloss finish.
• these topcoats are for use either alone (i.e. direct on to untreated or unprimed board) or over undercoat or primer which is the more frequently used method. Coatings of 75 microns or more can readily be achieved in one coat.
• This Example demonstrates the use of the method of the invention in coating cementitious products to provide low gloss durable finish.
• Tinuvin 292 1 Dysperbyk 110 4 The coating was applied in accordance with the procedure in Example 4 Part C.
• the lower gloss properties of the composition are achieved by the use of a increased ratio of whiting plus talc to the resin in the formulation.
• the required level of gloss can be achieved by adjusting this ratio.
• FC 430 and Z6020 may be added.
• the topcoat can be applied to board which has been previously undercoated with UV cured material (or conventional materials) then sanded or on unfilled board. The former is preferred. Coatings of 75 microns or more can readily be achieved in one application
• PGMA or the like
• 10 parts by weight of water may be added to reduce the viscosity of the formulation if needed.
• This example demonstrates the use of the invention in coating mixed polyester resin.
• a mixture of polyester resin typically supplier, An3ol paint Co., Sydney
• styrene monomer Heuntsman Chemicals, Melbourne
• glass fibre with catalyst are poured onto "Melinex" fibre (ICI Australia, Melbourne) containing UV stabiliser held in a conveyor belt and passed into an oven initially at approximately 40°C then with the heat gradually increased to sustain the exothermicity of the polymerisation to approximately 130°C.
• the sheet of fibre glass or "Melinex" emerges from the oven and, as soon as practical (usually several metres), a coating of the urethane acrylate/TPGDA resin formulation of Example 1 preheated to 70-80°C is sprayed or brushed onto the hot fibre glass sheet ( « 80-90°C).
• This coated sheet is then passed under a UV lamp as previously described (Fusion, 300 watts/inch) at typical line speeds of 10 metres/min. The coating is cured immediately with excellent adhesion. If the above urethane acrylate/TPGDA coating is applied hot (70-80°C) to the fibre glass sheet off line ie.
• the ability to flame retard the coating could be very valuable.
• a piece of cotton (4cm/15cm) is sprayed with the pigmented high gloss durable finish (at 70-80°C) in Example 2.
• Fyrol 51 flame retardant ex AK20, 15% by weight of resin component
• the coating is cured under a UV lamp (Fusion 300 W/inch) at 5 metres/minute.
• the resulting fibre is then subjected tot he standard AS 1530 Parts 2 and 3 test which it passes by sustaining a 12 second burn test with "standard flame”.
• This example demonstrates the use of the method of the invention in which the radiation curable composition is applied to a wet substrate.
• UV cured materials such as are described in this patent can be directly applied to the board whilst wet with water and then UV cured at line speeds relevant to the lamp intensity e.g. 20 metres/minute with a 300 Watts/inch Fusion lamp.
• a major advantage of the pre-wet process is that the amount of coating required is usually lower in the presence of water since absorption of coating into the substrate is minimised.
• composition of each of Examples 3 and 4 were applied to "Hardiplank" board which had been sprayed with water.
• the water pre-treatment is particularly useful since no undercoat is needed if the board is wet and direct coating (clear or pigmented finishes) on to pre-wet board, such as Hardiboard, gives a gloss finish if required.
• a conventional wetting agent e.g. Teepol 1% by weight of total coating materials
• Teepol 1% by weight of total coating materials

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