Document dYQnJa9nOEOOO8vD2e38O2GBG

United States Patent U9j Nield et al. US005141779A [ii] Patent Number: 5,141,779 [45] Date of Patent: Aug. 25, 1992 [54] PROCESS FOR FORMING A COATING FROM A CURABLE COMPOSITION CONTAINING CRYSTALLISABLE POLYMER P5] Inventors: Eric Nield, Beaconsfield; Daljit K Suemul, Birmingham; Denis M. H. Bovey, Berkshire, all of England [731 Assignee: Imperial Chemical Industries PLC, London, England [21] Appl. No.: 453,299 [22] Filed: Dec. 22, 1989 [30] Foreign Application Priority Data Dec 23. 1988 [GB] United Kingdom ................. 8830071 Jan. 4. 1989 [GB] United Kingdom ................. 8900077 [51] Int. Cl.' .............................. ............... B05D 3/02 [52] U.S. Cl................................. .. 427/385.5; 427/386; 427/388.5 [58] Field of Search ..................... 427/195. 375. 385.5, 427/398.1, 386. 388. 2. 388.5. 374.1, 374.2: 523/440 [56] References Cited U S. PATENT DOCUMENTS 3.766.109 3.959.209 3.969.430 4.133.916 4.206.096 4.552.932 4.622.368 4.833.026 4.919.992 10/1973 Pralt et al............................... 523/440 5/1976 Lake ......................................... 525/43 7/1976 Kalnin et al........................... 525/435 1/1979 McGinniis et al................. 427/385.5 6/1980 Takagi ................................... 525/233 11/1985 Schollenberger...................... 525/440 1 1/1986 Verbickv. Jr.et al................. 524/401 5/1989 Kausch ............................... 428/315.5 4/1990 Blundell et a)......................... 428/131 FOREIGN PATENT DOCUMENTS 701110 1/1965 Canada............... . 191224 10/1985 European Pat. Oft 1998846 11/1986 European Pat. Oft. 225792 6/1987 European Pat. Oft. 883123 11/1981 U.S.S.R. . 1155791 6/1969 United Kingdom . 1418701 12/1975 United Kingdom . 427/386 Primary Examiner--Shrive Beck Assistant Examiner--Terry J. Owens Attorney. Agent, or Firm--Cushman, Darby & Cushman [57] ABSTRACT A coating process in which a curable composition con taining crystallizable polymer is provided on a surface and subsequently cured to produce a cured coating on the surface, wherein the process comprises (a) making a curable composition comprising a disper sion in a curable non-permanent solvent system of solid crystallizable polymer comprising amorphous zones containing entrapped solvent by forming a solution of the polymer and non-permanent curable solvent system at an elevated temperature and cool ing the solution so obtained to cause liquid/solid phase separation of solid polymer, curable composi tion being made in situ on the surface or away from the surface, (b) introducing a curing agent reactable with the cur able solvent system so as to be able to cure the sys tem, (c) where the curable composition is made away from the surface, applying the curable composition to the surface and (d) subjecting the curable composition to conditions under which the solvent system cures to form the cured coating. 8 Claims, No Drawings 5,141,779 12 resistance and good adhesion to substrates. However, so PROCESS FOR FORMING A COATING FROM A far attempts to incorporate crystallisable thermoplastic CURABLE COMPOSITION CONTAINING polymers into cured coatings have led to highly in- CRYSTALLISABLE POLYMER homogenous structures which because of their inhomo- 5 geneitv have shown only minimal improvements in the This invention relates to coating processes in which a overall properties of the cured coating. An object of curable composition containing crystallisable polymer this invention is to provide a coating process which is provided on a surface and cured. It also relates to allows the production of cured coatings containing a curable compositions containing crystallisable thermo more uniform distribution of crystallisable thermoplas plastic polymers (including copolymers and polymers 10 tic polymer with consequent improvement of proper optionally modified by the presence of additives for ties. example other crystallisable or non-crystallisable poly This invention provides a coating process in which a mers or grafted moieties such as those containing car curable composition containing crystallisable polymer boxylic moieties), to methods for making such composi is provided on a surface and subsequently cured to tions and to the use of the compositions in coating pro 15 produce a cured coating on the surface wherein the cesses and formulations. process comprises Crystallisable polymers are well known to include a) making a curable composition comprising the crystal polyesters such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) which usually have a density of about 1.4 and 1.3 g/cm3 respectively, poly 20 carbonates. polyamides (often called nylons) and poly olefins. especially low, medium and high density polythevlenes and isotactic polypropylenes. A fuller de scription of the various types of polyester, polycarbon ate or nylon is given in the third edition of Kifk- 25 Othmer's "Encyclopaedia of Chemical Technology" published by John Wiley & Sons of New York in 1982: see Volume 18 pages 549 to 574 pages 479 to 494 or pages 406 to 425 for polyesters, polycarbonates and nylons respectively or Volume 16 pages 402 to 441 or 30 pages 453 to 467 for polyethyienes or polypropylenes respectively. These pages are herein incorporated by reference. Examples of useful polyester copolymers include polyethylene terephthalic and isophthalic acid and elastomeric polyesters having segments of a low- 35 glass transition temperature. Polyamides also include recently available nylon 4. 6 and so called partially crystalline aromatic nylons. Aromatic nylons are poly lisable polymer and curable non-permanent solvent system by alternatively i) forming a solution of the polymer and non-perma nent curable solvent system from which either solid/liquid phase separation of crystallisable poly mer can occur on cooling and/or solid/solid phase separation of crystallisable polymer can occur on curing of the solvent system or ii) forming a solution of the polymer and non-perma nent curable solvent system at an elevated tempera ture and cooling the solution so obtained to cause solid/liquid phase separation of crystallisable poly mer 7 or iii) forming a solution of the polymer and non-perma nent non-curable solvent system at an elevated temperature, cooling the solution so obtained to cause solid/liquid separation of polymer, removing the solvent from the polymer and adding the poly mer to the non-permanent curable solvent system at a temperature at which non-permanent solvent amides comprising condensates of aromatic diamines system becomes entrapped in the polymer such as l,3-di(aminomethyl) benzene. Examples of use 40 which curable composition when made as in (i) or (ii) ful copolymers of ethylene include copolymers of ethyl may be made in situ on the surface or away from the ene with up to 30 wt 9c of other alpha-olefins or olefinically unsaturated carboxylic acids or esters such as surface or which when made as in (iii) is made away from the surface vinyl acetate or lower (for example Ci to C4) alkyl b) where and when necessary, introducing a curing acrylates or methacrylates, and especially polyethyi 45 agent readable with the curable solvent system so as enes containing small amounts (for example a trace to to be able to cure the system, up to 1 wt 9i) of copolymerised or grafted carboxylic c) where the curable composition is made away from acid moiety. Useful propylene copolymers include co the surface, applying the curable composition to the polymers comprising up to 15 wt 9i of ethylene. Poly surface and olefins may be usefully blended with each other or up to 50 d) subjecting the curable composition to conditions 30 wt 9c of ethylene/propylene (optionally diene modi under which the solvent system cures to form the fied) rubbers or other rubbers. cured coating Other useful crystallisable polymers include polyvi whereby a cured coating is obtained which at ambient nyl fluorides, polyvinylidene fluorides polyurethanes temperature is enhanced by the presence of crystallisa and polyhydroxy butyrates. 55 ble polymer. A "non-permanent" solvent system for a Some of the above crystallisable polymers can ac crystallisable polymer is a solvent system which is able quire a crystalline form merely by solidifying from the to dissolve the polymer usually at elevated tempera molten state whilst some (notably the polycarbonates tures, that is to say temperatures above (and preferably and some polyesters) are amorphous as supplied but at least 40* C. above) ambient but which allows solid/- may be easily converted to partially crystalline form by 60 liquid phase separation of crystallisable polymer from exposure to solvents. It is for this reason that the poly the solvent to occur either mers are herein described generically as "crystallisable" 1) on cooling at rates of less than 100' C./min or rather than "crystalline". 2) on curing in those cases where the non-permanent In general crystallisable thermoplastic polymers have solvent is curable. many properties such as toughness, hardness, abrasion 65 Therefore the use of a non-permanent solvent means resistance and flexibility which make them useful as that at ambient temperature and/or in the cured system coating materials whereas conventional cured coating the polymer exists as a solid dispersed in the system. can have advantages such as corrosion and solvent Ambient temperatures are usually from 10 to 30 C. A 5,141,779 34 solution may comprise polymer dissolved in solvent Accordingly this invention provides either as a new system or solvent system dissolved in polymer. starting material or as a new intermediate in the coating Where the curable composition is obtained by dis process a curable composition comprising (optionally solving crystallisable polymer in non-permanent cur particles of) crystallisable polymer comprising amor able solvent system at elevated temperatures, the com 5 phous zones containing entrapped curable solvent sys position may be made either in situ on the surface by- tem whereby adjacent zones may be linked together by applying to the surface a dispersion of the polymer in curing of the entrapped system. the solvent system and then heating to dissolve the A practical difficulty concerning the use of particles polymer or alternatively it may be made away from the of crystallisable thermoplastic polymers arises from the surface and then applied to the surface usually as a hot 10 fact that many processes for their commercial manufac solution. In addition, it is sometimes possible to obtain ture produce pellets which have a maximum dimension metastable solutions of polymer in non-permanent sol of not less than 2 mm which means that the pellets need vent system by shock-cooling at a cooling rate of at to be converted into distinct fine particles, that is to say- least 100 C./min and preferably at least 300' C./min. particles having' a maximum dimension of below 500 Such metastable solutions may offer the opportunity to 15 pm. Hitherto this has been done by attritive methods apply the composition at temperatures lower than those such as grinding or milling. However attritive methods needed to dissolve the polymer (particularly ambient) produce particles of an unpredictable shape which are so reducing the risk of premature curing of heat-curable inconvenient to use in coating processes. It is therefore solvent systems or of thermal degradation of the poly another object of this invention to provide a non-attri- mer. If solid polymer can be caused to separate from the 20 tive process for making particles of crystallisable ther solvent system by curing the system, then cold metasta moplastic polymer containing entrapped curable sol ble solutions may also be applied to the surface. vent system and especially particles having a maximum Most solutions of polymer in curable solvent systems dimension of below 500 pm. are highly viscous at practicable concentrations of poly Accordingly this invention provides a non-attritive mer and so are less easily provided on surfaces, espe 25 method for making particles from crystallisable thermo cially surfaces which are not smooth or flat. plastic polymer which comprises Therefore it is preferred to employ compositions a) heating a mixture comprising a curable moderate (as which comprise a dispersion in curable solvent system hereinafter defined) solvent system and at least 5 of solid crystallisable polymer comprising amorphous (preferably 10 to 50) wt % of the polymer (the per zones containing entrapped curable solvent system. If 30 centage being based on the combined weights of the the polymer is required to dissolve or soften during moderate solvent and the polymer) to a temperature performance of the process, it is preferred that the poly above the crystalline melting point (Tm) of the poly mer be in the form of dispersed particles having a num mer when in the mixture and preferably to a tempera ber average maximum diameter of less than 500 pm (and ture in the range Tm+10' C. to Tm + 80` C. and preferably less than 30 pm, 1 pm being 10-6pm). Such 35 b) cooling the heated mixture (preferably to below Tm) particles not only facilitate dissolution but also offer an to cause separation preferably under conditions such alternative to complete dissolution of the polymer by that solid/liquid phase separation occurs the use of conditions (primarily less high temperatures whereby particles of crystallisable polymer are obtained and/or higher concentrations) which cause the particles which comprise crystalline zones and amorphous zones to soften rather than dissolve. By "soften" it is meant 40 containing entrapped curable solvent system. In a modi that the particles become less hard than they would be fication of the non-attritive method, a non-curable mod in the absence of solvent system at ambient temperature erate solvent system is used instead of the curable sol and preferably soft enough to enable contiguous parti vent system with the result that the particles obtained cles to coalesce. Softening is probably assisted by plas- have amorphous zones containing entrapped non-cura- ticisation by the entrapped solvent system. The use of 45 ble solvent system which is then replaced by curable softened particles as an alternative to dissolution re solvent system by removing the non-curable system duces the risk of premature curing of heat-curable sol from the particles, adding the particles to curable sol vent systems and/or of thermal degradation of the poly vent system and subjecting the particles and system to a mer. temperature at which the particles imbibe and entrap Curable compositions provided on a surface may be 50 curable solvent system. This modified method has the heated to form a solution of the polymer and the curable advantage of allowing particles to be made using non- solvent. Alternatively, if the composition comprises curable solvents so avoiding any risk of premature cur panicles, it may be heated to soften panicles of the ing during the heating which is necessary to form the polymer. Heating increased the ability of the polymer to solution. Non-curable solvents are also usually much flow which in turn gives coatings having better me 55 cheaper. Any non-permanent solvent system may be chanical properties and improved appearance, particu conveniently removed from the particles by first de larly better gloss and/or smoothness. Curing may be canting off any free liquid solvent system and then initialed whilst the polymer is still in a solution or soft washing the particles with a non-solvent for the poly ened state or alternatively the composition may be mer which is miscible with the non-curable solvent cooled towards (preferably to) ambient temperature 60 system. A "non-solvent'' is a liquid which has no signifi before any substantial curing is positively initiated. Cur cant dissolving effect on the polymer at the washing ing will then occur in the presence of solid polymer and temperature. will have the effect of linking together adjacent amor Particles obtained from the non-attritive method may phous zones of crystallisable polymer which generally sometimes be agglomerated. Where distinct particles improves homogeneity. Curing also similarly links to 65 are required, the agglomerate will need to be subjected gether amorphous zones of polymer particles which to a shearing operation. A shearing operation differs have not been heated after they have been provided on from an attritive operation in that shearing merely sepa the surface to be coated. rates particles which have already been formed whereas 5,141,779 56 attrition forms particles by fracturing polymer. Often obtained is defined to be the crystalline melting point of shearing can be achieved by forces no greater than the sample under test. those exertable between finger and thumb. More particularly for polyesters, polycarbonates The non-attritive methods employ a moderate sol polyamides and polyolefins a preferred moderate sol- vent system. In those cases where the solvent system 5 vent system is a system which depresses the crystalline does not react chemically with the polymer, "moder melting point Tm of the polymer by not more than 80' ate" can be defined as meaning a solvent system which C. when the polymer constitutes 20 wt % of a mixture when'used to make a mixture consisting of the solvent of dry moderate solvent system and dry polymer. Good system and 20 wt 9c of the crystallisable polymer solvents (for example orthochlorophenol for PET or a) is able to form a solution of the polymer and solvent 10 phenol for nylon for depress Tm by well in excess of 80' system when the mixture is heated to above the crys C. talline melting point Tm of the polymer when in the Examples of curable moderate solvent systems (espe mixture and the mixture is maintained at above Tmfor cially those suitable for use with polyesters) include S minutes and epoxy ethers based on various glycidyl derivatives and b) allows a solid/liquid separation and re-crystallisation 15 in particular derivatives of bisphenol A available from of the polymer to give distinct particles of polymer Shell Chemicals Limited as "EPIKOTES". Such epoxy when the mixture is cooled to a temperature below ethers have the general formula CH;--CH--CH-> \" / O o O--CH i--CH--CH i 1 ' \o/ ' CH;--C--CH; CH;--C--CH; where n is preferably from 0 to 9 and may be non-inte T,,, and preferably at least 30" C. below' Tm. 35 gral, eg. 1.2. Other useful epoxy compounds include For the purposes of the above definition insofar as it glycidyl derivatives of the following namely, bis(4-- relates to polyesters and polyamides, both the solvent hydroxy phenyl) methane, terephthalic acid, isocyanu- system and the polymer should be dry. A "dry solvent rate. sorbitol and NOVOLAC resins which are poly contains less than 0.005 wt 9c of water for polyesters phenol formaldehyde. The curable epoxy compounds and less than 0.05 wt 9c for polyamides and a "dry" 40 need to be used in combination with curing agents polymer is a polymer which has been heated in a vac which bring about curing when heated. Suitable curing uum oven for 16 h at 90' C. Crystalline melting point is agents include dodecanoic acid, phthalic anhydride, determined by differential scanning calorimetry per diaminodiphenylsulphone. dicyandiamide, triethylene formed in turn on the polymer alone and on the above tetramine. 1,6 hexamethylene diamine and melamine or mixture. The mixture must be contained in a sealed 45 urea formaldehydes. The curable NOVOLAC resins capsule to prevent loss of the moderate solvent during are particularly suitable for use with both polyesters heating. More particularly. 10 mg of polymer alone and and polyamides and need to be used in combination 10 mg of mixture are each in turn subjected to cycles of with curing agents such as hexamine and hexamethox- heating and cooling performed under nitrogen in the ymethylmelamine. Polyamides may also be used with calorimeter. Each heating/cooling cycle comprises 50 curable solvent systems such as glycerol or triethylene heating the sample under test, (which may be polymer glycol which cure by reacting with curing agents such alone or a mixture) at a rate of 20' C./min to cause as formaldehyde resins. crystalline melting which occurs at a temperature Tm, Unsaturated compounds such as long chain fatty subsequently holding the sample for two minutes at a acids (especially linseed oil) and dienes such as dicyclo- holding temperature T* which is above Tm, then cool- 55 pentadiene may be used as moderate curable solvent ing at a rate of 20' C./min to cause recrystallisation systems particularly with polyolefins. These cure by which occurs at a temperature Trand finally continuing autoxidation preferably in the presence of catalysts such cooling to a temperature of at least 10' C. below Tc. Tm as cobalt octoate or naphthenate and accordingly no and Tr are detected respectively as an endothermic added curing agent is needed since atmospheric oxygen trough and an exothermic peak in the graph of heat 60 will permeate the composition. absorbed or evolved versus temperature. Each cycle is The curable solvent system may consist solely of a repeated to discover whether a consistent value of Tr curable compound which is itself a non-permanent sol can be obtained. If consistency is not obtained, another vent for the polymer. Alternatively it may comprise a pair of heating/cooling cycles are performed using a curable compound present as a single phase mixture slightly higher T*. Further pairs of cycles with gradu- 65 with a non-curable solvent in which case the curable ally increasing T^are performed until consistent values compound need not necessarily be a solvent for the for Trare achieved whereupon the pair of cycles which crystallisable polymer or it may be a poor solvent in gave consistent values is repealed and the value for Tm which case the non-curable solvent may be regarded as 5,141,779 78 an auxiliary solvent. For example the single phase mix agent chosen should not react with the solvent system. ture may be a solution of curable compound in non-cur- In general higher cooling rates and also nucleating able solvent or a mixture of two miscible liquids one of agents favour smaller particles sizes. Typical nucleating which is the curable compound and one of which is agents for polyesters include talc, sodium benzoate or non-curable solvent. Any non-curable solvent either 5 the ionomeric copolymers of ethylene with minor should be tolerable in the cured coating (perhaps serv amounts of carboxylate comonomers, for example those ing as a plasticiser) or should be sufficiently volatile to known as "SURLYN" A available from El Dupont de be removable from the coating composition after the Nemours Inc. Typical nucleating agents for nylons composition has been provided on the surface being include talc, fluorspar and those disclosed in British coated. 10 patent specification GB 1 465 046 the contents of which It is essential when performing the non-attritive are herein incorporated by reference. Typical nucleat method for making particles of partially crystalline ing agents for polyolefins include talc, sodium benzoate polymers that the mixture be heated to above the melt or dibenzylidene sorbitol and its alkyl analogues. ing point (Tm) of the polymer when in the mixture for This invention also provides a partially attritive otherwise there will be obtained particles of unpredict 15 method for making particles of crystallisable polymer able shape comprising some undissolved polymer. Pref for use in a coating process according to this invention. erably the mixture should be heated at least to its clear The partially attritive method is a modification of the ing temperature "T/\ The "clearing temperature" (Tc/) non-attritive method wherein of any chosen mixture comprising moderate solvent a) any non-permanent solvent system may be used, system and polymer is the temperature at which the 20 b) the amount of polymer in the mixture is from 50 to 90 appearance of wt % (and preferably from 60 to 80 wt %), 15 the mixture becomes clear to the unaided eye. Tr/ c) the solvent system is chosen so as to cause solid/liq is determined by heating 2 g of a chosen mixture until uid phase separation of the polymer as a mass com the polymer dissolves and the initially turbid solution prising amorphous zones containing entrapped sol obtained turns clear for a first time, then cooling the 25 vent system, mixture to room temperature an Finally re-heating the d) the mass is ground into particles and mixture until it turns clear for the second time. The e) where the solvent is non-curable it is removed from temperature at which it turns clear for the second time the ground particles and the particles are added to is defined to be the clearing temperature (T<v) for that curable solvent system. mixture. Heating to Tf/and above (preferably to 10 to 30 The partially attritive method produces less uniform 30` C. above Tf/) leads to the formation of more uni particles than the wholly non-attritive method but has form particle sizes. Uniformity of particle size is also the advantage of giving a greater yield of particles than enhanced by heating the mixture to a holding tempera a method employing mixtures containing lower concen ture T/, which is above Tm for the polymer when in the trations of polymer. mixture (and preferably 10 to 40' C. or even 60 C. 35 It has further been discovered that a partially attritive above) and holding the mixture at temperature Th for method can be performed with any solvents or prefera from 1 to 60 minutes although holding for 1 to 5 minutes bly curable solvent systems which dissolve from 5 to 90 is usually sufficient. wt % of the polymer at elevated temperatures and It has been found that some large pellets of polymer which solidify at lower temperatures (preferably ambi available commercially can be inconveniently slow to 40 ent) so as to produce a solid mass of solvent system dissolve. Where time saving is important, this problem containing crystalline polymer dispersed as particles or can be alleviated by using a pre-heating and pre-cooling as a solid solution or alloy. The solid mass is then cycle as follows. The mixture is First pre-heated to a ground into particles. Such solidifiable solvent systems temperature well above (for example 60 C. above) the may comprise a solvent which by itself is solid at ambi melting point of the pure polymer. Such pre-heating 45 ent temperatures or which is caused to be solid at ambi causes a rapid dissolution of the polymer. The mixture is ent temperatures by the presence of the polymer. Gen then pre-cooled to at least a temperature at which the erally the solidified solvent system is more brittle than polymer re-solidiFies from the mixture. For example the the crystallisable polymer alone and so the polymer is in polymer is cooled to at least 30 to 80' C. below the contact with a more brittle material which makes the melting point of the pure polymer. Such re-solidifica- 50 polymer more easily fracturable during grinding. Ac tion produces polymer in a form which dissolves cordingly this invention further provides a modified quickly (usually within 2 minutes) on heating to Tm or partially attritive method for making particles of crys above so producing a mixture consisting of a solution of tallisable polymer for use in a coating process according polymer in solvent system which appears clear to the to this invention wherein unaided eye. 55 a) there is used a curable solvent system which is able to Also in performing the non-attritive method, it is dissolve the polymer at elevated temperature and essential to employ conditions which cause solid/liquid which solidifies at lower temperatures so producing a phase separation to occur from the mixture of dissolved solid mass of solvent system containing dispersed polymer and solvent system for otherwise a formless polymer, mass may be obtained. To achieve solid/liquid phase 60 b) the solid mass is ground into particles and separation, it is necessary to use a moderate solvent c) where the solvent system is non-curable, it is re system, to use a mixture containing at least 5 wt of moved from the particles and the particles are added polymer and to avoid shock cooling which usually to curable solvent system. means cooling at a rate of no faster than 300' C./min The crystallisable polymer may be mixed with the and preferably no faster than 100" C./min. 65 solvent system simply by adding the polymer to the The size of the polymer particles can be adjusted by system and then heating and stirring. However a conve varying the cooling rates employed or by incorporating nient way to mix polymer and solvent system at ele nucleating agents into the polymer. The nucleating vated temperatures comprises feeding both polymer 5,141,779 9 10 and solvent system to a closed shearing mixer and heat applied as a free flowing powder or as a paste or as a ing within the mixer to dissolve the polymer. The solu paste or dispersion comprising a non-solvent carrier tion can then be delivered directly to the surface to be liquid. The compositions may be applied to opposed coated. The solution may be cooled in or out of the surfaces in which case they serve as adhesives. mixer to cause particles to form which can be subse 5 The surfaces coated according to this invention may quently applied to the surface. The preferred mixer is an be metallic for example aluminium, stainless steel or extruder and the extrudate solution may be applied non-metallic. for example glass, wood, paper or textile. directly to a surface or cooled to form particles. Mixing In particular the panicles may be used to coat sheets in an extruder is particularly useful in performing the (especially sheets which are to be used in shaping pro heating steps in the non-attritive processes for making 10 cesses), and shaped anides such as cans. The composi particles containing entrapped solvent. Extruders offer tions may be used to impregnate continuous rovings of good control of temperature and so heating can be a wide variety of fibres including glass and carbon fibres performed with minimal risk of premature curing of by application to the surface of the fibres. The impreg heat-curable solvent systems. nated fibres, may be shaped during curing to produce a A shearing mixer can also be used to promote the 15 composite which on cooling comprises fibre consoli grafting of suitably reactive moieties onto the crystallis- dated in cured solvent. The compositions can be used as able polymer and in particular suitably reactive curable adhesives to provide laminates and especially laminates solvent systems may be so grafted with consequent for use in shaping processes. improvements in compatibility between crystallisable It also has been found that the particles of crystallisa polymer and cured coating. 20 ble polymer comprising amorphous zones containing Returning to the coating process according to this curable solvent disperse well in coating compositions invention, the curable composition is eventually sub (for example paints and varnishes) based on water or jected to conditions under which the solvent system organic solvents. Accordingly this invention provides a cures to form the cured coating. Conventional curing coating composition (which may be based on an organic techniques are employed. For example a heat-curable 25 solvent or water) comprising a binder of a type used in composition may be transferred to an oven heated to coating compositions and particles of polymer wherein the preferred temperatures for curing. An autoxidisable the particles of polymer comprise zones of amorphous composition may be allowed to stand in air. Other com polymer which contain the entrapped curable moderate positions ma> be exposed to curing vapours or liquids. solvent. The binder may be a curable resin which is Usually the weight ratio of crystallisable polymer to 30 co-curable with the solvent system. Typical binders for curable compound in the composition provided on the coating compositions are described in the third edition surface is from 1:0.1 to 19. Towards the higher ratios of of the book "Introduction to Paint Chemistry and Prin polymer to compound (often at ratios of above 1:4 espe ciples of Paint Technology" by G. P. A. Turner and cially 1:3 and above, the polymer may not always dis published by Chapman and Hall of London in 1988, the solve completely during coating but instead it becomes 35 contents of which are herein incorporated by reference. a mass (usually a paste) of polymer particles softened by The coating composition may also comprise pigments solvent system which later cohere for example if the and extenders and other conventional ingredients de composition is heated to a temperature at which soften scribed in the above book. ing or dissolution begins to take place. Most preferably Crystallisable polymer (preferably in particulate such healing will be to a temperature which is above the 40 form) comprising amorphous zones containing en temperature (Tm) at which crystalline melting occurs in trapped curable solvent system may also be used in a that composition. The composition will generally be wide variety of thermoforming operations such as ex held at these elevated temperatures for from 2 to 45 trusion, compression or injection moulding provided minutes. that conditions are chosen so as to avoid premature It has been found that when the weight ratio of crys 45 curing of the entrapped solvent. tallisable polymer to curable compound is from 1:0.25 The invention is further illustrated by the following to 4, the cured coating usually comprises a network of Examples in which the following tests are employed: cohering portions of crystallisable polymer interpene trated by a network of cohering portions of cured com The Rubbing Test pound. Where the amount of cured polymer is greater 50 In the Rubbing Test, each coating was rubbed back than 1:4, the tendency is for the cured coating to com and forth with a lambswool cloth soaked in methyl prise a homogenous dispersion of particles of crystallis ethyl ketone. After a number of back and forth rubs, the able polymer in and cohering to cured compound and coated surface became visible through the coating when vice versa if the amount of cured polymer is less than viewed through an optical microscope at ten fold mag 10.25. Interpenetrating networks confer optimum com 55 nification. The number of back and forth rubs needed binations of the properties of crystallisable polymers for this to happen is recorded. and cured resins. In particular they increase the ability of surfaces coated with cured resins to undergo shaping The Chisel Test operations. In the Chisel Test, the apex of an isoceles triangular The compositions may be applied to surfaces by a 60 blade was stood on the coating with the blade touching wide variety of conventional techniques such as doctor the coating and subtending an angle of 45* C. thereto. bar coating, roller coating, spray coating, extrusion The base of the triangle was 6.1 mm long and the dis coating, brushing and dip coating. Panicles may be tance from the base to the apex was also 6.1 mm. The applied as a dispersion in curable solvent system. Where chisel was loaded with a weight and then drawn once the panicles comprise amorphous zones containing 65 across the coating in a direction parallel to the 300 mm entrapped curable solvent system, they may contain edge of the sheet. The ioading weight was increased enough entrapped solvent to render the presence of until the apex of the blade caused the aluminium surface funher solvent unnecessary in which case they may be to become visible through the coating when viewed 5,141,779 11 12 through an optical microscope at ten fold magnifica the case of Examples 5 to 16 of 200' C. and in the case tion. The loading needed for this to happen is recorded. of Examples 1 to 4 and 17 to 20 of 230' C. The sheets The "T" Bend Test were then allowed to cool to room temperature where upon they were found to carry a smooth glossy tena The "T" Bend Test is performed according to the procedure of ASTM Test D 4145-83 the contents of 5 cious coating of cured synthetic material. These coat which are herein incorporated by reference. ings were then subjected to the rubbing and chisel tests and the results are shown in Table 2. The Corrosion Test TABLE 1 The Acetic Acid-salt Spray Corrosion Test is per- to formed according to the procedure of ASTM Test B 287-74 the contents of which are herein incorporated by reference. Eg Polymer Amount Polymer in Mixture. wt 9r Trf *C. Typical Panicle Dimension pm The Reverse Impact Test j1 The Reverse Impact Test is performed according to the procedure of ASTM Test D 4145-83 ("Resistance of 2 3 4 Organic Coatings to the Effects of Rapid Deforma ' 5 tion") the contents of which are herein incorporated by 6 reference. 20 7 Also in the Examples coatings are applied to flat 8 smooth sheets using a Meyer doctoring bar which com prises a cylindrical metal bar of diameter 9 mm around which is helically wound a single layer of a wire of diameter 0.8 mm with its adjacent helices contiguous ?.s throughout their length. In this way the bar is provided with a series of circumferential parallel grooves each 400 pm deep. To apply a coating, the bar sheet and the curvature of the bar combine to define a nip into which the composition to be applied is delivered. The bar is jq 9 10 n 12 13 14 15 16 17 18 then drawn across the sheet leaving a trail of parallel 19 ridges of the composition initially 400 pm high. 20 PET PET PET PET PET PET PET PET PET/I PET/I PET/1 PET/1 HYTREL 4056 HYTREL 7246 10 195-200 20 30 ** 40 200 10 170 20 170 30 170 40 170 10 135-140 20 30 40 10 95-100 20 30 40 10 195-200 20 30 40 10 5-10 5-10 2-5 2-5 EXAMPLES 1 TO 20 The pastes obtained could be converted to dry free Making and Use of Curable Compositions containing Polyester Particles 35 flowing particles by rinsing with acetone to remove moderate solvent system external of the particles. 10 g samples of various polyesters specified in Table In Table 1 the polymers used were as follows: The 1 were each mixed with a curable epoxy moderate sol vent system which was "EP1KOTE" 880 (which is bisphenol A diglycidyl ether) in amounts also specified 40 PET had an intrinsic viscosity of 0.64 to 0.66 cmVg in orthochlorophenol at 25 C. The PBT was CELANEX in Table 1. Each mixture was heated to a temperature 2002-2 from the Celanese Company. PET/I is a PET which was above the crystalline melting point Tmof the copolymer containing 18 wt % isophthalate. HY- polyester when in the mixture and also 50' C. above the TRELS are available from El DuPont de Nemours. clearing temperature Tc/of the mixture so as to dissolve the polyester whereupon the mixture existed as a clear 45 solution. Tf/for each mixture is given in Table 1. The mixture was held at this temperature for 2 minutes and then cooled to a temperature 50" C. below Tf/. A solid/liquid phase separation and re-crystallisation occurred. The heating and cooling cycle was repealed three times 50 except that the third cooling was allowed to proceed to room temperature thereby producing fine, distinct and approximately spherical partially plasticised particles comprising crystalline zones an amorphous zones con taining imbibed curable epoxy solvent system. A typical 55 Example l 2 3 4 5 6 7 TABLE 2 Wt of Curing Agent g No. of mbs to expose metal 3.0 >100 2.6 >100 2.3 >100 2.0 >100 3.0 >100 2.6 >100 2.3 >100 Chisel load to expose metal g 400 500 300 300 200 100 200 dimension of the particles as determined by optical 8 2.0 >100 200 microscopy is shown in Table 1. The particles com prised about 50 wt % of entrapped reactive solvent and were obtained as a paste consisting of particles and moderate solvent. 10 g of each of the above pastes were 60 in turn introduced to curing agent by thoroughly mix ing with (as shown in Table 2) the curing agent which was diaminodiphenylsulphone. The weight of curing 9 10 11 12 13 14 15 16 3.0 >100 300 2.6 >100 200 2.3 >100 200 2.0 >100 300 3.0 >100 200 2.6 >100 too 2.3 52 >100 2.0 6 200 agent used was equal to half the weight of EPILOTE 17 3.0 >100 400 880 used. Each paste in turn was then applied to a flat 65 smooth aluminum sheet 300 mm long by 100 mm wide using a Meyer doctoring plate. Next the sheets were 18 19 20 2.6 >100 2.3 >100 2.0 >100 300 300 300 heated in an oven for 45 minutes and at a temperature in 5,141,779 13 14 EXAMPLE 21 TABLE 3 Making and Use of Curable Composition containing Amount PE Polyamide Panicles in Mixture. 3 g of a nylon 6 polyamide available as "MARA- 5 NYL" B3 from Imperial Chemical Industries PLC was Eg 22 23 wt O 10 30 mixed with 5 g of a curable moderate solvent system Typical Panicle Dimension 2-6 2-6 which was a "NOVALAC" phenolic resin having a melting point 108' C. and available from Schenectady 10 Midland Chemicals Ltd and with 5 g of benzyl alcohol as auxiliary solvent. The mixture was heated to a tem perature of 200' C. which was above the crystalline melting point Tm of the nylon when in the mixture and also above its clearing temperature Tc/so as to dissolve 15 the nylon whereupon the mixture existed as a solution. The mixture was held at 200' C. for 2 minutes and then Amounl PE wt 10 30 TABLE 4 HEATING CYCLES 1st Pre-Heat to *C. Cool to c. 2nd Pre-heat to *C. Cool to c. 220 52 210 60 220 60 220 70 Heat to c. 210 210 cooled to 120' C. The mixture was heated to 200' C. for a second time and then allowed to cool to 50' C. Finally The pastes obtained can be mixed with a conven the mixture was heated to 200' C. for a third time and 20 tional amount of cobalt naphthenate to produce a cur then allowed to cool to room temperature and stood in able composition suitable for curing in a hot oven to iced water for 5 minutes whereupon a solid/liquid phase give smooth glossy tenacious coherent coatings on alu separation and re-crvstallisation occurred producing minium. fine, distinct and approximately spherical partially plas ticised particles comprising crystalline zones and amor 25 EXAMPLES 24 TO 27 phous zones containing entrapped solvent system. A Making and Use of Curable Compositions containing typical dimension of the particles as determined by Polypropylene Particles optical microscope was from 10 to 15 fxm. The particles comprised about 50 wt 95 of entrapped solvent system 10 g samples of a polypropylene (PP) were each and were obtained as a paste consisting of panicles and 30 mixed with a curable moderate solvent in amounts as moderate solvent system. specified in Table 5. The polypropylene was available The pastes obtained could be converted to dry free from Imperial Chemical Industries PLC as "PROPA- flowing particles by rinsing with acetone to remove THENE" GWE 26 and had a melt flow index of 3 as solvent system external of the particles. Rinsing determined by BS 2782720A using a 2.16 kg load at 230 amounted to placing the paste on filter paper in a funnel 35 C. Each mixture was subjected to a double pre- and pouring acetone through for 30 seconds at room heating/pre-cooling cycle and then heated to a temper temperature. The pastes were also suitable for mixing ature above the crystalline melting point of the polymer with hexamethoxymethyl melamine to produce a cur when in the solvent system and also above the clearing able composition which could be cured in a hot oven to give smooth glossy tenacious coherent coatings on alu minium. 40 temperature for the mixture. The mixture was finally allowed to cool to room temperature. The temperatures reached in these heating cycles are given in Table 6. EXAMPLES 22 AND 23 Heating caused the polymer to dissolve whereupon the Making and Use of Curable Compositions containing mixture existed as a solution. At least the last cooling Polyethylene Panicles 45 caused a solid/liquid phase separation and re-crystalli High density polyethylene available from BP Chemi cals Ltd as "RIG1DEX" HM 5590 EA was mixed with a curable moderate solvent system which was linseed sation which produced fine, distinct and approximately spherical partially plasticised panicles comprising crys talline zones and amorphous zones containing en oil in amounts as specified in Table 3. 10 g of each mix ture was subjected to a double pre-heating/pre-cooling 50 trapped curable solvent system. The panicles com prised about 50 wt % of entrapped solvent system and cycle and then heated to a temperature above the crys were obtained as a paste consisting of panicles and talline melting point of the polyethylene when in the solvent system. Typical particle sizes obtained as deter linseed oil and also above the clearing temperature for mined by optical microscopy are shown in Table 5. The the mixture. The mixture was finally allowed to cool to 55 particles were mixed with cobalt naphthenate to pro room temperature. The temperatures reached in these duce a curable composition which was suitable for cur heating cycles are given in Table 4. Heating caused the ing in an oven to produce smooth glossy tenacious polyethylene to dissolve whereupon the mixture existed coherent coatings on aluminium. as a solution. At least the last cooling caused a solid/liq uid phase separation and re-crystallisation which pro 60 TABLE 5 duced fine, distinct and partially plasticised particles Amount Polymer Typical comprising crystalline zones and amorphous zones con taining entrapped linseed oil. The particles were either Eg Solvent in Mixture. wt particle size pm spherical or oblate having a typical maximum dimen 24 Linseed oil 10 6-10 sion as determined by optical microscope as shown in 65 25 30 6-10 Table 3. The particles comprised about 50 wt 95 of 26 Dicyclopentadiene 10 12 imbibed linseed oil and were obtained as a paste consist 27 30 12 to 15 ing of panicles and linseed oil. 5,141,779 15 16 TABLE 6 HEATING CYCLES ture of 232 C. A smooth glossy tenacious coherent cured coating was obtained on the aluminium sheet. 1st Pre-Heat Cool to 2nd Pre-heat Coo! to Heat to EXAMPLES 30 TO 35 Eg to X 24 225 25 220 X to X RT 230 RT 230 X X. 5 Effect of Varying the Polyester content of Curable 78 210 72 210 Compositions 26 ISO 50 180 78 182 PBT similar to that used in Examples 5 to 8 but sup 27 180 52 180 70 180 plied by ATO Chemic as "ORGATOR" TMNO was RT mean* room temperature mixed with a moderate curable solvent system which 10 was "EPIKOTE" 880 bisphenol A diglycidyl ether to EXAMPLE 28 Making and Use of Curable Compositions containing give mixtures containing amounts of PBT as specified in Table 7. Each mixture was heated to a temperature which was above the crystalline melting point Tmof the Polyester and Curable Oligomeric Solvent System 2.2 g of PBT (available as "VALOX" 310) was mixed 15 polyester when in the mixture and also 50 C. above the clearing temperature Tr/of the mixture so as to dissolve with a curable oligomeric moderate solvent system the polyester whereupon the mixture existed as a clear which was 22 g of an oligomeric curable compound solution. Td for each mixture is given in Table 7. The which was a condensate of a mixture of terephthalic mixture was held at this temperature for 20 to 40 min acid, isophthalic acid, adipic acid trimethylylol propane 20 utes and then cooled to a temperature 50 C. below Tc/. and neopentaglycol in the molar ratios of A solid/liquid phase separation phase separation oc 0.51:0.09:0.4:0.12:0.98 having an weight average molec curred. The heating and cooling cycle was repeated and ular weight of about 1900. then cooling was allowed to proceed to room tempera The mixture was heated to 220 C., allowed to cool to ture. Examples 30 to 33 produced particles whereas 25 C. and then re-heated to 240 C. and allowed to cool 25 Examples 34 and 35 produced a hard mass which was to 100' C. whereupon re-crystallisation occurred. At ground into particles using the mill described in Exam 100" C.. the mixture was diluted by the addition of an ple 36. equal weight of an auxiliary solvent which was a 1:1 The cooled mixtures were mixed with curing agent mixture of "SOLVESSO" 150 and methyl propoxol which was diaminodiphenylsulphone. The amount of acetate. ("SOLVESSO" 150 is a mixture of aromatic 30 curing agent added was equal to half the weight of the C9 and C10 hydrocarbons having a boiling point range "EPIKOTE" used. The mixtures were then re-heated of 190 to 210" C. at 1 bar). The mixture then cooled to room temperature. to a temperature above their Tr/ and applied to smooth aluminium sheet 300 mm by 100 mm using the Meyer A curing agent system consisting of 1.85 g of hexame- doctoring bar. The sheets were heated in an oven at thoxymethyl melamine and 0.14 g of a sulphonic acid 35 230 C. for 30 minutes to cure the composition and then available as "NACURE" XP 253 was added to 23.35 g of the above mixture and the whole stirred. The stirred allowed to cool to ambient temperature (20 C.). Smooth glossy tenacious coherent coatings were ob mixture was then applied to a smooth aluminium sheet tained. using the Meyer doctoring bar and heated in an oven for 60 secs at a peak temperature of 232 C. A smooth 40 The above procedure was repeated except that coated sheets were forced cooled after curing the by glossy tenacious coherent cured coating was obtained on the aluminium. quenching in cold water at a temperature of 20 C. Again smooth glossy tenacious coherent coatings were obtained. EXAMPLE 29 Both quenched and unquenched coated sheets were Making and Use of curable Compositions containing Polyester Elastomer and Curable non-Solvent 45 subjected to various tests and the results are shown in Table 3 where the suffix "q" denotes the results ob tained from the quenched samples. A mixture of 72.3 g polyester curable elastomer avail The chisel test loading shown is the minimum loading able as "HYTREL" 4056 and 108.5 g of the oligomer needed to cause the aluminium sheet to become visible used in Example 28 was heated to 220 C., held for 10 50 through the coating. minutes at 220 C., then allowed to cool to 200 C. and The T bend result shows the minimum number of then 69.7 g of auxiliary solvent which was "SOL bends at which no fracture of the coating is visible to VESSO" 150 was added. The mixture was next allowed the unaided eye. For example a result of 0 (according to to cool to 150' C. when 50.8 g of a second auxiliary ASTM reporting practice) means that the coated sheet solvent which was methyl propoxol acetate was added. 55 can be bent back onto itself with no fracture occurring The mixture was allowed to cool to 50 C. and then at the bend. Bending back onto itself is the most severe re-heated to 90 C. and 100 g of a 1:1 mixture of "SOL test because the curvature at the bend is greatest. Re VESSO" 150 and methyl propoxol acetate was added. sults of 1,2 or more mean that the coated has to be bent The mixture was finally allowed to cool to room tem back onto 1,2 or more thicknesses of coated sheet in perature during which cooling re-crystallisation oc 60 order to escape fracture at the bend whereupon the curred. curvature is accordingly reduced by 50%, 33.33% or 50 g of the re-crystallised mixture was stirred with more respectively and so the test is less severe. 2.126 g of hexamethoxymethyl melamine curing agent, 0.28 g of the sulphonic acid curing agent used in Exam ple 28 and a further 25 g of "SOLVESSO" 150 to pro 65 duce a curable composition. The composition was ap plied to a smooth flat aluminium sheet as in Example 28 and heated in an oven for 60 seconds to a peak tempera Example A Aq Wt PBT in mixture 0 0 TABLE 7 Film Thickness Tr/ im -- 22 -- 16 Chisel Test Loading 200 200 T Bend 2 2 5,141,779 17 18 Example 30 30 31 31 32 32 33 33 34 34 35 35 TABLE 7-continued wi n PBT in mixture 10 10 20 20 30 30 40 40 50 50 75 75 Film Chisel Test Thickness T ci jim Loading g 210 20 210 23 208 20 208 20 218 23 218 19 218 27 218 20 220 20 220 17 225 lb 225 17 200 100 200 200 200 200 200 300 300 300 300 200 T Bend i 1 i 1 ). 0 0 0 0 0 0 0 amethoxymethyl melamine) supplied by CIBA-Geigy, the accelerator was a 1 wt 9fc solution of a blocked dinonyl naphthalene disulphonic acid (NACURE X 49-110) in butoxy ethanol and the carrier liquid was 5 methyl ethyl ketone. The paste contained 6.7 g of the ground particles, 1.07 g of "CYMEL" 303.0.54 g of the accelerator solution and sufficient ketone to give the paste a non-volatile content of 20 wt %. The paste was applied to a pair of aluminium sheets 10 300 mm by 100 mm, the sheets were heated to 225' C. for 10 minutes and then one was allowed to cool to ambient temperature (20* C.) and the other was forcecooled by quenching in cold water at a temperature of 20' C. The cooled sheets were subjected to various tests 15 and the results are shown in Table 8. The T-bend results show that compositions contain ing more that 20 wt 91 PBT are capable of being back onto themselves which indicates that they are highly suitable for use in forming processes. When such coat 20 For Comparative Example B, the above coating pro cedure was repeated but using "EPIROTE" 1001 which did not contain PBT. The results are also shown in Table 8. ings were etched with concentrated (959fc) sulphuric TABLE 8 acid for 1 to 2 minutes to remove the epoxy material and photographed at a magnification of 5000 using an elec Wl <Tr Film Chisel Test Reverse tron microscope, it could be seen that the particles of Ex- PBT in Thickness Loading T Impact PBT where contiguous and coalesced so forming a 25 largely continuous network of PBT which had perme ample B mixture 20 Td 20S jim lb g Bend kg m 200 i 0.4b ated the epoxy material. Provided that the amount of 3b 20 208 18 200 i 0.92 PBT did not exceed 75 wt %, the epoxy material like wise formed a network which permeated the PBT net works. A qualitative inspection of corrosion tests 30 show ed that coatings having interpenetrating networks Use of an extruder Equal weights of PET (as used in Examples 1 to 4) showed superior corrosion resistance. and "EPIROTE" 1004 (curable solvent) were simulta The photographs also showed that as the amount of neously fed to an extruder at a rate of 20 g each per PBT reached 30 wt 9r. the coalescence between parti minute. "EPIROTE" 1004 is a glycidyl derivative of cles increased giving the PBT network a structure re sembling a network of filaments. Increasing the amount 35 bisphenol A having the general formula shown earlier where n gives a number average molecular weight of of PBT further increases the degree of coalescence until about 1400. The extruder was a Werner Pfieiferer at amounts of 75 wt and above, the coating comprises ZSR30 twin screw machine operated with a screw particles of epoxy material dispersed in crystalline poly speed of 100 rpm. The barrel of the extruder was heated mer. 40 to 270 C. so that the PET dissolved in the "EPI The various coated sheets were subjected to the rub ROTE". On extrusion from the extruder, the mixture bing test and all were found to survive over 100 rubs. was allowed to cool to ambient temperature (20' C.) EXAMPLE 36 AND COMPARATIVE EXAMPLE B whereupon the "EPIROTE" solidified producing a solidified mass of "EPIROTE" containing uniform Use of Alternative Curable Solvent System 45 dispersion of particles of PET coalesced to form a net A mixture consisting of 20 wt 9 PBT and 80 wt 9i work. This mass was ground into particles using the "EPIROTE" 1001 (curable solvent) was made. "EPI technique of Example 36. ROTE" 1001 is a glycidy! derivative of bisphenol A The ground particles were mixed with the curing having the general formula shown earlier where n gives agent, accelerator and carrier liquid used in Example 36 a number average molecular weight of about 900. It has a melting point of from 64 to 76' C. and so is solid at 50 and converted to a paste containing 20 wt % of non volatile material. The amount of curing agent used was ambient temperatures and accordingly needs to be equal to 10 wt % of the "EPIROTE" present and the melted to permit mixing to occur. Mixing was in fact amount of accelerator was equal to 0.5 wt % of the performed at 80' C. curing agent. The molten mixture was heated to 260' C. (which is 55 The paste was applied to an aluminium sheet 300 mm 50' C. above its Tf/), cooled to 160' C., re-heated to 260' by 100 mm, heated to 255' C. for 10 minutes to cure the C. and then allowed to cool to ambient temperature (20' "EPIROTE" and then allowed to cool to ambient tem C.) producing a solid mass of "EPIROTE" containing perature (20* C.). A smooth glossy coating was ob a uniform dispersion of particles which had coalesced to tained. form a network. 60 EXAMPLE 38 The solidified mass was ground into particles using a Retsch ultracentrifugal mill as supplied by F Rurt Application of Curable Composition by Spray Coating Retsch of Haan in West Germany and as described in 40 g of PBT (as used in Examples 5 to 8) were added their brochure No 99.785.0002 of September 1987. to 60 g of a curable polyester solvent system which was The solid ground particles were mixed with curing 65 "ARAROTE" 3109 which is supplied by CIBA-Geigy. agent, curing accelerator and volatile carrier liquid to The PBT and resin were heated to 240 C., maintained form a curable paste which was convenient to apply to at that temperature for 30 minutes and then allowed to a surface. The curing agent was "CYMEL" 303 (hex- cool to room temperature whereupon a solid mass of 5,141,779 19 20 "ARAKOTE" was obtained containing a uniform dis amorphous zones containing entrapped solvent and had persion of panicles of PBT coalesced into a network. a particle size of from 2 to 10 fim. The solid mass w as ground into panicles as in Example The particles could be mixed with diaminodiphenyl- 36 and the panicles were mixed with a pre-ground sulphone curing agent and applied to aluminium sheets blocked isocyanate curing agent which was supplied as 5 as in Examples I to 4 to produce glossy smooth tena B 1530 by Chemische Werke Huls. The amount of cur cious coherent coatings. ing agent used was 16 wt % of the weight of the "ARA We claim: KOTE". 1. A coating process in which a curable composition The curable mixture so obtained was then electrostat containing crystaliisable polymer is provided on a sur ically sprayed onto aluminium panels 300 mm by 100 10 face and subsequently cured to produce a cured coating mm, heated to 230' C. for 20 minutes in an oven and on the surface, wherein the process comprises allowed to cool to ambient temperature (20* C.). Good (a) making a curable composition comprising a dis smooth coherent coatings were obtained. persion in a curable non-permanent solvent system EXAMPLE 39 Composition Curable at Ambient Temperature 15 of solid crystaliisable polymer comprising amor phous zones containing entrapped solvent by form ing a solution of the polymer and non-permanent 11 g of Nylon 66 was mixed with 25.6 g of glycerol, curable solvent system at an elevated temperature heated to 225 C. for 10 minutes and then allowed to and cooling the solution so obtained to cause li cool to ambient temperature (20* C.) whereupon a hard paste was obtained. The paste was ground in a pestel 20 quid/solid phase separation of solid polymer, cur able composition being made in situ on the surface and mortar with or away from the surface, a) 3 g of a copolymer consisting of 70 wt 9e hydroxy- (b) introducing a curing agent reactable with the ethyl acrylate copolymerised with 30 wt 9t of ethyl curable solvent system so as to be able to cure the acrylate b) 1 g of "CYMEL" 1172 which has the structure 25 system, (c) where the curable composition is made away from shown below and the surface, applying the curable composition to c) 1 g of para toluene sulphonic acid. the surface and The resultant mixed paste was applied to a glass and an (d) subjecting the curable composition to conditions aluminium panel each 300 mm by 100 mm using the Meyer bar. The panels were then allowed to stand at 30 under which the solvent system cures to form the cured coating. room temperature for 10 hours whereupon both ac 2. A process according to claim 1 wherein for a por quired smooth glossy tenacious coherent cured coat ings. tion of the time during which the curable composition is on the surface, the curable composition is at or reaches CHOH CH'OH I' I' N--CH--N / o=c \ c=o \/ N--CH --N II CH;OH CH;OH 35 a temperature at which the polymer is dissolved or is softened. 3. A process according to claim 1 wherein the curable composition cools toward room temperature before starting step (d). 40 4. A process according to claim 1 wherein the disper sion of solid polymer referred to in (a) is in the form of particles having a maximum diameter of less than 500 fim. EXAMPLE 40 Making and Use of Curable Composition containing Polycarbonate 5. A process according to claim 1 wherein the solu 45 tion of polymer and non-permanent solvent system in step (a) is formed in a closed shearing mixer. 6. A process according to claim 1 wherein the solu Amorphous bisphenol A polycarbonate available as tion of polymer and non-permanent solvent system in "SINVET" 251 from ENI Chem was mixed equal vol step (a) is formed in an extruder. umes of a curable solvent system which was "EPI- 50 7. A process according to claim 1 wherein the weight KOTE" 880 and of an auxiliary solvent which was ratio of crystaliisable polymer to curable solvent system dimethyl phthalate to produce a mixture consisting of is from 1:0.1 to 1:19. 40 wt 9t polycarbonate and 60 wt % of the solvents. 8. A process according to claim 7 wherein the weight The mixture was heated to 150' C. for two minutes and ratio is from 1:0.25 to 1:4 whereby the cured coating allowed to cool to ambient temperature (20' C.). A 55 comprises a network of cohering portions of crystaliisa portion of the cooled mixture was re-heated to 150" C. ble polymer interpenetrated by a network of cohering and again allowed to cool to ambient temperature portions of cured solvent system. whereupon particles were obtained which comprised 60 65