GB2226820A - Curable polymer compositions - Google Patents

Abstract

Curable partially plasticised (optionally particulate) compositions comprising partially crystalline polymers are made by heating a mixture of the polymer in a moderate curable solvent for the polymer to a temperature above the melting point of the polymer when in the solvent and then cooling whereupon the polymer recrystallises from the mixture. Alternatively a non-curable solvent may be used and subsequently extracted, and the resulting porous crystalline polymer soaked in curable liquid. Such compositions may be used in coating formulation.

Description

CURABLE POLYMER COMPOSITIONS AND THEIR MANUFACTURE AND USE This invention relates to curable compositions comprising partially crystalline polymers (including copolymers and polymers modified by the presence of additives for example rubbers or grafted moieties such as those containing carboxylic moieties) to a method for making such compositions and to the use of the compositions, especially in coating processes and formulations. The invention also relates to the compositions when in fine particulate form.

Partially crystalline polymers are well known as thermoplastics. They include 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, polyamides (often called nylons) and polyolefins, especially low, medium and high density polyethylenes and isotactic polypropylenes. A fuller description of the various types of nylon is given in the third edition of Kirk-Othmers "Encyclopaedia of Chemical Technology" published by John Wiley & Sons of New York in 1982 see Volume 18 pages 549 to 574 or pages 406 to 425 for polyesters or nylons respectively or Volume 16 pages 402 to 441 or pages 453 to 467 for polyethylenes or polypropylenes respectively. These pages are herein incorporated by reference.Examples of useful polyester copolymers include copolymers comprising both terephthalic and with isophthalic acid and elastomeric polyesters having segments of a low glass transition temperature. Polyamides also include recently available nylon 4, 6 and so called partially crystalline aromatic nylons. Aromatic nylons are polyamides comprising condensates of aromatic diamines such as 1,3-di(aminomethyl) benzene.

Examples of useful copolymers of ethylene include copolymers of ethylene with up to 30 wt% of other alpha-olefins or olefinically unsaturated carboxylic acids or esters such as vinyl acetate or lower (for 'example C1 to C4) alkyl acrylates or methacrylates.

and especially polyethylenes containing small amounts (for example a trace to up to 1 wt%) of copolymerised or grafted carboxylic acid moiety. Useful propylene copolymers include copolymers comprising up to 15 wt% of ethylene. Polyolefins may be usefully blended with each other or up to 30 wt% of ethylene/propylene (optionally diene modified) rubbers or other rubbers.

Conventional curable systems involving partially crystalline polymers usually comprise a curable fluid in which are dispersed totally solid fine particles of the partially crystalline polymer. These systems are curable to produce a solid synthetic resin in which the particles of partially crystalline polymer have remained distinct and are in no way coalesced with each other. In addition, many processes for the commercial manufacture of partially crystalline polymers produces pellets which usually have a maximum dimension of at least about 2mm. For some purposes such as powder coating or addition to coating compositions, the pellets need to be converted into distinct fine particles, that is to say particles having a maximum dimension of below 500;m. Hitherto this has been done by attritive methods such as grinding or milling.However attritive methods produce particles of an unpredictable shape which are therefore inconvenient to use in coating processes and formulations and the particles are also totally solid which is sometimes a disadvantage.

An object of this invention is to provide a preferably non-attritive method for making curable compositions comprising partially crystalline polymer which usually permit the particles of polymer to fuse 'and coalesce during the curing operation so as to form a continuous layer of the composition. Another object is to provide a novel curable composition comprising partially crystalline polymer which is partially plasticised and which is amongst other things especially suitable for use in coating processes. Optionally the composition is in the form of distinct fine particles. A further object is to provide a process for coating surfaces in which such a novel composition is used.

Accordingly this invention provides a (preferably non-attritive) method for making a curable composition comprising partially crystalline polymer wherein the method comprises a) heating a mixture comprising a curable solvent for the polymer and at least 5 (preferably 10 to 60) wt% of the polymer (the percentage being based on the combined weights of the moderate solvent and the polymer) to a temperature above the crystalline melting point (Tm) of the polymer when in mixture and preferably to a temperature in the range Tm + 10 C to Tm + 40 C and b) cooling the heated mixture to below Tm, preferably under conditions such that solid/liquid phase separation occurs whereby the curable composition is produced.The composition contains imbibed curable solvent and may be in the form of a continuous solid (for example a solid composed of agglomerated particles), a paste or a paste or slurry of particles which are usually fine particles having a maximum dimension of from 0.1 to 200cm. Sometimes it may be necessary to subject the composition obtained to a light shearing action (for example by rolling it between finger and thumb) in order to convert an agglomerated solid into its component particles.

It is preferred to use a moderate solvent for if a good solvent is used with the concentrations of polymer employed in the performance of this invention, then the polymer may not be easily obtainable in particulate form merely by cooling the solution. A "moderate solvent" is a solvent which when used to make a mixture consisting of the solvent and 20 wt% of the partially crystalline polymer a) is able to dissolve the polymer when the mixture is heated to above the crystalline melting point Tm of the polymer and the mixture is maintained at above Tm for 5 minutes and b) causes a solid/liquid separation and re-crystallisation of the polymer to give distinct particles of polymer when the mixture is cooled to a temperature below Tm and preferably at least 30 C below Tm.

For polyesters and polyamides, both the solvent and the polymer should be dry. A "dry solvent" contains less than 0.005 wt % of water for polyesters and less than 0.05 wt% for polyamides and a "dry polymer" is a polymer which has been heated in a vacuum oven for 16h at 90"C. Crystalline melting point is determined by differential scanning calorimetry performed in turn on the polymer alone and on the above mixture.

The mixture must be contained in a sealed capsule to prevent loss of the moderate solvent during heating.

More particularly, 10mg of polymer alone and 10mug of mixture are each in turn subjected to cycles of heating and cooling performed under nitrogen in the calorimeter. Each heating/cooling cycle comprises heating the sample under test (which may be polymer alone or a mixture) at a rate of 200C/min to cause crystalline melting which occurs at a temperature Tm, subsequently holding the sample for two minutes at a holding temperature Th which is above Tm, then cooling at a rate of 200cumin to cause recrystallisation which occurs at a temperature Tc and finally continuing cooling to a temperature of at least 10 C below Tc. Tm and Tc are detected respectively as an endothermic trough and an exothermic peak in the graph of heat absorbed or evolved versus temperature.Each cycle is repeated to discover whether a consistent value for Tc can be obtained. If consistency is not obtained, another pair of heating/cooling cycles are performed using a slightly higher Th . Further pairs of cycles with gradually increasing Th are performed until consistent values for Tc are achieved whereupon the pair of cycles which gave consistent values is repeated and the value for Tm obtained is defined to be the crystalline melting point of the sample under test.

More particularly for polyesters, polyamides and polyolefins a "moderate solvent" is a solvent which depresses the crystalline melting point Tm of the polymer by not more than the amounts specified below when the polymer constitutes 20 wt% of a'mixture of dry moderate solvent and dry polymer: a) Polyesters: Tm should be depressed by not more than 600C. A good solvent for PET such as orthochlorophenol depresses Tm by well in excess of 60"C.

b) Polyamides: Tm should be depressed by not more than 800C. A good solvent for nylon 6 such as phenol depresses Tm by well in excess of 80"C.

c) Polyethylene: Tm should be depressed by not more than 80"C. A good solvent for low density polyethylene depresses Tm by well in excess of 80"C.

d) Polypropylene: Tm should be depressed by not more than 800C. A good solvent for propylene homopolymer such as decahydronaphthalene depresses Tm by well in excess of 800C.

Examples of curable moderate solvents suitable for use with polyesters include epoxide ethers such as the diglycidyl ether of dihydroxydiphenyl methane or triglycidyl isocyanurate or phenolic resins such as the so-called "Novalacs". These phenolic resins are also suitable for use with polyamides as moderate curable solvents. Compounds containing unsaturation such as linseed oil or dicyclopentadiene may be used as moderate curable solvents with polyolefins. The epoxide ethers are curable by mixing with curing agents and then heating. Suitable curing agents include dodecanoic acid, phthalic anhydride, diaminodiphenylsulphone, dicyandiamide, triethylene tetramine and 1,6 hexamethylene diamine. The phenolics are curable by mixing and heating with curing agents such as hexamine and hexamethoxy methylmelamine.Linseed oil cures by undergoing autoxidation in the presence of accelerators which are usually cobalt compounds such as cobalt naphthenate.

It is also important when performing the method of this invention to make particles that the mixture be heated to above the melting point of the polymer when in the mixture (Tm) for otherwise there will be obtained particles of unpredictable shape comprising some undissolved polymer and some re-crystallised polymer agglomerated onto the undissolved polymer.

Preferably the mixture should be heated at least: to its clearing temperature "Tc1,, The "clearing temperature" (TCl) of any chosen mixture comprising moderate solvent and polymer (both being dry when the polymer is a polyester or polyamide) is the temperature at which the appearance of the mixture becomes clear to the unaided eye. T,1 is determined by heating 2g of a chosen mixture until the polymer dissolves and the initially turbid solution obtained turns clear for a first time, then cooling the mixture to room temperature an finally re-heating the mixture until it turns clear for the second time. The temperature at which it turns clear for the second time is defined to be the clearing temperature (TCl) for that mixture.Heating to T and above (preferably to 10 to 30"C above Tcl) leads to the formation of more uniform particle sizes.

Uniformity of particle size is also enhanced by heating the mixture to a holding temperature Th which is above Tm for the polymer when in the mixture (and preferably 10 to 40CC above) and holding the mixture at temperature Th for from 1 to 30 minutes although holding for 1 to 5 minutes is usually sufficient.

It has been found that some large pellets of polymer available commercially can be inconveniently slow to dissolve. Where time saving is important, this problem can be alleviated by using 'a pre-heating and pre-cooling cycle as follows. The mixture is first pre-heated to a temperature above the melting point of the pure polymer, for example to 250 CC. Such pre-heating causes a rapid dissolution of the polymer. The mixture is then pre-cooled to at least a temperature (for example 30 to 800C below the melting point of the pure polymer or lower) so that polymer re-solidifies from the mixture. Such re-solidification produces polymer in a form which dissolves quickly (usually within 2 minutes) on heating to Tm or above so producing a mixture consisting of a solution of polymer in moderate curable solvent which appears clear to the unaided eye.

In performing the process of this invention to make particles it is essential to employ conditions which cause solid/liquid phase separation to occur from the mixture when it is in its solution state for otherwise an agglomerated mass will be obtained. To achieve solid/liquid phase separation, it is necessary to use a moderate curable solvent, to use a mixture containing at least 5 wt% of polymer and to avoid shock cooling which usually means cooling at a rate of no faster than 300"C/min. The preferred cooling rates are from 100C/min to 50 C/min. It is also preferred to stir the mixture during cooling.

Stirring promotes greater uniformity of particle size.

The moderate curable solvent may comprise a curable compound alone (for example pure linseed oil) or it may comprise a mixture of curable and non-curable compounds. If the non-curable compound is a moderate solvent for the polymer, it may be used as an auxiliary moderate solvent permitting the use 'of curable solvents which would otherwise be too poor a solvent for the polymer to be used conveniently by themselves. In extreme cases the use of an auxiliary moderate solvent can permit the use of curable compounds which have no dissolving effect on the polymer when used alone. However such non-dissolving curable compounds must be miscible with or soluble in the auxiliary moderate solvent to produce a combination which as a whole behaves as a moderate solvent for the polymer.

This invention also provides curable compositions (optionally as distinct fine particles) comprising partially crystalline polymer wherein the composition comprises zones of crystalline polymer and the composition is partially plasticised in that it also comprise zones of amorphous polymer containing imbibed moderate curable solvent.

Generally the composition will comprise from 10 to 90 (more usually from 40 to 75) wt% of imbibed curable moderate solvent. Usually large proportions of imbibed curable solvent and amorphous polymer are favoured by performing the method of this invention using high cooling rates (say 100 to 300"C/min).

Particles obtainable by the method of this invention are usually obtained as a slurry or paste in the moderate curable solvent but may occur as particles comprised in a solid mass particularly if the moderate solvent is solid at room temperature.

Alternatively the particles can be obtained in a free flowable condition by removal of the solvent external of the particles by for example rinsing with a liquid miscible with the moderate curable solvent but which does not dissolve the polymer. In particular, when an anxiliary moderate solvent has been used, rinsing 'liquid may be chosen so as to remove the auxiliary solvent whilst leaving the curable compound in the composition.

The size of the particles obtained by this invention can be adjusted by varying the cooling rates employed in the method or by incorporating nucleating agents into the polymer. In general higher cooling rates and also nucleating agents favour smaller particles sizes. Typical nucleating agents for polyesters include talc, sodium benzoate or the ionomeric copolymers of ethylene with minor amounts of carboxylate comonomers, for example those known as "Surlyn" A available from EI Dupont de Nemours Inc. Typical nucleating agents for nylons include talc, fluorspar and those disclosed in British patent specification GB 1 465 046 the contents of which are herein incorporated by reference. Typical nucleating agents for polyolefins include talc, sodium benzoate or benzylidene sorbitol.The uniformity of particle size increases as the temperature to which the mixture is heated is increased towards Tm + 400C. No advantage is generally gained by using temperatures above T + m 400C and of course temperatures high enough to cause thermal degradation of the polymer should be avoided.

Use of nucleating agents also improves uniformity of particle size.

The presence of a nucleating agent may cause a residual turbidity to persist at TCl. However the skilled eye is able to distinguish between turbidity caused by the polymer and that caused by a nucleating agent and so the determination of TCl and clearing are not unduly hindered.

The shape of the particles obtained varies with 'the concentration of polymer in the mixture. Lower concentrations favour flaky or rod-like particles whilst higher concentrations favour approximately spherical or oblate particles. Usually concentrations of at least 20 wt % should be used to obtain spherical or oblate particles with the best results being obtained with concentrations above 30 wt %. Good solvents may give non-particulate masses.

It has been discovered that the presence of imbibed solvent in the compositions of this invention enhances their ability to flow and/or form continuous layers of polymer when heated. In addition, particles of the composition show an improved ability to coalesce and form continuous layers. Curing is also evenly distributed through out the system. Accordingly this invention also provides a process for coating a surface with polymer which process comprises a) applying a covering of composition (optionally as particles) across the surface and b) heating the composition to cause it to become flowable and to cause the curable solvent to cure wherein the composition comprises zones of crystalline polymer and the compositions employed are partially plasticised in that they also comprise zones of amorphous polymer containing imbibed (preferably moderate) curable solvent.Preferably the composition when in particulate form is applied to the surface as a dispersion of usually 5 to 35 (especially 10 to 25) wt % of particles in either (preferably moderate) curable solvent or a liquid which is not a solvent for the polymer, for example methyl or ethyl alcohol or preferably water provided the polymer is not harmed by water. The surfaces may be metal for example aluminium, stainless steel or non-metallic, for example glass. In particular the composition may be used to coat sheets and shaped articles such as cans for example in conventional powder coating operations. Particles of the composition (especially the flaky or rod-like particles) may also be used to impregnate continuous rovings of a wide variety of fibres including glass and carbon fibres.If the impregnated fibres are heated to soften or melt the particles, they may be compressed to produce a composite which on cooling comprises fibre consolidated in cured polymer. The compositions may also be used as moulding materials especially when containing fibres or particulate materials (usually inorganic materials).

It also has been found that the particles according to this invention disperse well in coating compositions (for example paints and varnishes) based on both water or organic solvents. Accordingly this invention provides a coating composition (which may be based on an organic solvent or water) and comprising a binder of a type used in coating compositions and (from for example 0.5 to 50 wt % of) particles of polymer wherein the particles of polymer comprise zones of crystalline polymer and the particles are partially plasticised in that they also comprise zones of amorphous polymer containing imbibed (preferably moderate) curable solvent.

Typical binders for coating compositions are described in the third edition of the book "Introduction to Paint Chemistry and Principles of 'Paint Technology" by G P A Turner and published by Chapman and Hall of London in 1988, the contents of which are herein incorporated by reference. The coating composition may also comprise pigments and extenders and other conventional ingredients described in the above book.

The invention is further illustrated by the following Examples. In cases where the polymer was a polyester or polyamide the curable solvent used had been dried over molecular sieves to reduce its water content to not more than 0.005 wt% (polyester) or 0.05 wt% polyamide and where a dry polymer is specified, the polymer had been dried by heating it in a vacuum (lm bar) for 16h at 900C.

EXAMPLES 1 TO 20 Making and Use of Polyester Particles: 10g samples of various polyesters specifided in Table 1 were each mixed with a moderate curable epoxy solvent which was bisphenol A diglycidyl ether in amounts also specified in Table 1. Each mixture was heated to a temperature which was above the crystalline melting point Tm of the polyester when in the mixture and also 500C above the clearing temperature TCl of the mixture so as to dissolve the polyester whereupon the mixture existed as a clear solution. Tcl for each mixture is given in Table 1.

The mixture was held at this temperature for 2 minutes and then cooled to a temperature 500C below Tcl A solid/liquid phase separation and re-crystallisation occurred. The heating and cooling cycle was repeated three times 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 TABLE 1

I I I I I I Eg Polymer Amount TCl Typical Polymer Particle in Mix- C Dimension ture, m wt% 1 PET 10 195-200 10 2 PET 20 " " 3 PET 30 " " 4 PET 40 200 " 5 PBT 10 170 5-10 6 PBT 20 170 " 7 PBT 30 170 " 8 PBT 40 170 " 9 PET/I 10 135-140 " |10|PET/I 1 20 1 " 1 5-10 | 11 PET/I 30 " " 12 PET/I 40 " " 13 Hytrel 4056 1 10 1 95-1001 2-5 | 14 " " 20 " " 15 " " 30 " " 16 " " 40 " " 17 Hytrel 7246 10 195-200 2-5 18 " " 20 " " 19 " " 30 " " 20 " " 40 " " and amorphous zones containing imbibed curable epoxy solvent. A typical dimension of the particles as determined by optical microscopy is shown in Table 1.

The particles comprised about 50 wt % of imbibed curable solvent and were obtained as a paste consisting of particles and moderate solvent.

The pastes obtained could be converted to dry free flowing particles by rinsing with acetone.

10g of each of the above pastes were in turn thoroughly mixed with various amounts of curing agent which was diaminodiphenylsulphone as shown in Table 2. Each paste in turn was then applied to a flat smooth aluminium sheet 300mm long by 100mm wide using a Meyer doctoring plate containing a series of parallel ridges each 12m deep and spaced apart. The plates therefore become covered with a series of parallel ridges of paste. Next the sheets were heated in an oven for 45 minutes and at a temperature in the-case of Examples 5 to 16 of 2000C and in the case of Examples 1 to 4 and 17 to 20 of 230"C. The plates were then allowed to cool to room temperature whereupon they were found to carry a smooth glossy tenacious coating of cured synthetic material.These coatings were then subjected to rubbing and chisel 'tests.

In the rubbing test, each coating was rubbed back and forth with a lambswool pad soaked in methyl ethyl ketone. After a number of back and forth rubs, the aluminium surface became visible through the coating when viewed through an optical microscope at ten fold magnification. The number of back and forth rubs needed for this to happen is shown in Table 2.

In the chisel test, the apex of an isoceles triangular blade was stood on the coating with the blade touching the coating and subtending an angle of 450 thereto. The base of the triangle was 6.lmm long and the distance from the base to the apex was also 6.lmm. The chisel was loaded with a weight and then drawn once across the coating in a direction parallel to the 300mm edge of the sheet. The loading weight was increased until the apex of the blade caused the aluminium surface to become visible through the coating when viewed through an optical microscope at ten fold magnification. The loading needed for this to happen is shown in Table 2.

TABLE 2

I I I Example Wt of No. of rubs Chisel Curing to expose load Agent metal to expose g metal I I I g I I I I I 1 1 1 3.0 1 > 100 1 400 2 2 1 2.6 1 > 100 1 500 3 3 | 2.3 1 > 100 1 300 1 4 1 2.0 1 > 100 1 300 5 5 1 3.0 1 > 100 1 200 6 1 | 2.6 1 > 100 1 100 7 1 | 2.3 1 > 100 1 200 8 8 1 2.0 1 > 100 1 200 t I-- |-| 1 9 | 3.0 1 > 100 1 300 I 10 1 2.6 1 > 100 1 200 11 2.3 1 > 100 1 200 12 1 2.0 1 > 100 1 300 13 1 3.0 1 > 100 1 200 14 1 2.6 1 > 100 1 100 | 15 1 2.3 1 52 1 > 100 | 16 1 2.0 1 6 1 200 |-|-|-| 17 1 3.0 1 > 100 1 400 18 1 2.6 1 > 100 1 300 | 19 1 2.3 1 > 100 1 300 20 1 2.0 1 > 100 1 300 EXAMPLE 21 Making Polyamide Particles: 3g of a nylon 6 polyamide available as "Maranyl" B3 from Imperial Chemical Industries PLC was mixed with 5g of a moderate solvent which was a "Novalac" phenolic resin having a melting point 108 CC and available from Schenectady Midland Chemicals Ltd and with 5g of benzyl alcohol.The mixture was heated to a temperature of 2000C which was above the crystalline melting point Tm of the nylon when in the mixture and also above its clearing temperature TCl so as to dissolve the nylon whereupon the mixture exists as a solution. The mixture was held at 2000C for 2 minutes and then cooled to 1200C. The mixture was heated to 2000C for a second time and then allowed to cool to 500C. Finally the mixture was heated to 2000C for a third time and then allowed to cool to room temperature and stood in iced water for 5 minutes whereupon a solid/liquid phase separation and re-crystallisation occurred producing fine, distinct and approximately spherical partially plasticised particles comprising crystalline zones and amorphous zones containing imbibed solvent.A typical dimension of the particles as determined by optical microscope was from 10 to 15cm. The particles comprised about 50 wt% of imbibed solvent and were obtained as a paste consisting of particles and moderate curable solvent.

The pastes obtained could be converted to dry free flowing particles by rinsing with acetone.

Rinsing amounted to placing the paste on filter paper in a funnel and pouring acetone through for 30 seconds at room temperature. They were also suitable for curing in a hot oven to give smooth glossy tenacious coatings on aluminium.

EXAMPLES 22 AND 23 Making Polyethylene Particles: High density polyethylene available from BP Chemicals Ltd as "Rigidex" HM 5590 EA was mixed with a moderate curable solvent which was linseed oil in amounts as specified in Table 3. 10g of each mixture was subjected to a double pre-heating/pre-cooling cycle and then heated to a temperature above the crystalline melting point of the polyethylene when in linseed oil and also above the clearing 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 2.

Heating caused the polyethylene to dissolve whereupon 'the mixture existed as a solution. At least the last cooling caused a solid/liquid phase separation and re-crystallisation which produced fine, distinct and partially plasticised particles comprising crystalline zones TABLE 3

I I I I |Eg| Amount |Typical I I PE Particle I in Mix- Dimension! ture, m wt% 1221 10 1 2-6 1 23 30 2-6 TABLE 4 HEATING CYCLES

I I I I I I I Amount lst Cool to 2nd Cool to Heat to PE Pre-Heat C Pre-heat C C wt% to C to C I I I I 10 1 220 1 52 1 210 1 60 | 210 30 220 60 220 70 210 and amorphous zones containing imbibed linseed oil.

The particles were either spherical or oblate having a typical maximum dimension as determined by optical microscope as shown in Table 1. The particles comprised about 50 wt % of imbibed linseed oil and were obtained as a paste consisting of particles and moderate solvent.

The pastes obtained can be mixed with a conventional amount of cobalt naphthanate to produce a coating composition suitable for curing in a hot oven to give smooth glossy tenacious coatings on aluminium.

EXAMPLES 24 TO 28 Making Polypropylene Particles: 10g samples of a polypropylene (PP) were each mixed with a moderate curable solvent in amounts all as specified in Table 5. The polypropylene was available from Imperial Chemical Industries PLC as "Propathene" GWE 26 and had a melt flow index as determined by BS 2782720A using a 2.16kg load at 230"C of 3. Each mixture was subjected to a double pre-heating/pre-cooling cycle and then heated to a temperature above the crystalline melting point of the polymer when in the curable solvent and also above the clearing 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. Heating caused the polymer to dissolve whereupon the mixture existed as a solution.At least the last cooling caused a solid/liquid phase separation and re-crystallisation which produced fine, distinct and approximately spherical partially plasticised particles comprising crystalline zones TABLE 5

I I I I Eg Solvent Amount Typical Polymer particle in Mix- size ture, wt % m II I | 1|Linseed oil | 10 | 6-10 | 2| " " 30 1 6-10 3 Dicyclopentadiene 10 12 4 " 30 12 to 15 TABLE 6 HEATING CYCLES

lst Cool to 2nd Cool to Heat to Eg Pre-Heat C Pre-heat C C to C to C 24 225 RT 230 78 210 25 220 RT 230 72 210 26 180 50 180 78 182 27 180 52 180 70 180 RT means room temperature.

and amorphous zones containing imbibed curable solvent. The particles comprised about 50 wt % of imbibed solvent and were obtained as a paste consisting of particles and moderate curable solvent.

Typical particle sizes obtained as determined by optical microscopy are shown in Table 5. The particles were suitable for curing in an oven to produce smooth glossy tenacious coatings on aluminium.

EXAMPLE 29 Use of Polyester and Oligomer 2.2g of PBT (available as "Valox" 310) was mixed with 22g of an oligomer which was a condensate of a mixture of terephthalic acid, isophthalic acid and adipic acid in the molar ratios of 0.51 : 0.09 : 0.4 with a mixture of trimethylyl propane and neopentaglycol in the molar ratio of 0.12 to 0.98 and having an weight average molecular weight of about 1900. The mixture was heated to 220"C, allowed to cool to 250C and then re-heated to 2400C and allowed to cool to 1000C whereupon re-crystallisation occurred. At 1000C, the mixture was diluted by the addition of an equal weight of a 1:1 mixture of "Solvesso" 150 and methyl propoxol acetate.

("Solvesso" 150 is a mixture of aromatic Cg and C10 hydrocarbons having a boiling point range of 190 to 2100C at 1 bar. The mixture then cooled to room temperature.

1.85g of hexamethoxymethyl melamine curing agent and 0.14g of a sulphonic acid curing agent available as "Nacure" XP 253 were added to 23.35g of the above mixture and the whole stirred. The stirred mixture was then applied to a smooth aluminium sheet by the technique used in Examples 1 to 20 and heated in an oven for 60 secs at a peak temperature of 232"C. A smooth glossy cured coating was obtained on the aluminium.

EXAMPLE 30 Use of Polyester Elastomer and Oligomer: A mixture of 72.3g polyester elastomer available as "Hytrel" 4056 and 108.5g of the oligomer used in Example 29 was heated to 220"C, held for 10 minutes at 2200C and then allowed to cool to 2000C when 69.7g of "Solvesso" 150 was added. The mixture was then allowed to cool to 1500C when 50.8g of methyl propoxol acetate was added. The mixture was allowed to cool to 500C and then re-heated to 90CC whereupon 100g of a 1:1 mixture of "Solvesso" 150 and methyl propoxol acetate was added. The mixture was finally allowed to cool to room temeprature during which cooling re-crystallisation occurred.

50g of the re-crystallised mixture was stirred with 2.126g of hexamethoxymethyl melamine curing agent, 0.28g of the sulphonic acid curing agent used in Example 29 and a further 25g of "Solvesso" 150.

The stirred mixture was then applied to a smooth flat aluminium sheet as in Example 29 and heated in an oven for 60 seconds to a peak temperature of 2320C.

A smooth glossy cured coating was obtained on the aluminium sheet.

It is also possible to make useful curable compositions by using a totally non-curable moderate solvent to obtain a partially plasticised composition and then removing the non-curable solvent by extraction (preferably total or near total extraction) so as to create a porous composition and then soaking the porous composition in a curable liquid (preferably a moderate curable solvent) whereupon the porous composition imbibes the curable liquid.

Claims (1)

1. CLAIM

   1. A method for making a curable composition comprising partially crystalline polymer wherein the method comprises a) heating a mixture comprising a curable solvent for the polymer and at least 5 (preferably 10 to 60) wt% of the polymer (the percentage being based on the combined weights of the moderate solvent and the polymer) to a temperature above the crystalline melting point (Tm) of the polymer when in mixture and preferably to a temperature in the range Tm + 10 C to Tm + 40 C and b) cooling the heated mixture to below Tm, preferably under conditions such that solid/liquid phase separation occurs whereby the curable composition is produced.