GB2108127A - Aqueous coating composition - Google Patents

Abstract

An aqueous coating composition comprising from 45 to 98 parts by weight (solids) of water-soluble (or water-dispersible) resin and from 2 to 55 parts by weight (solids) of finely- divided water-insoluble resin, in which the water-soluble resin has a water tolerance (as herein defined) of at least 4 and a surface tension, calculated for a 1% w/w aqueous solution, of less than 51 dyne/cm, and in which at least part of the water- soluble resin is a amine group- containing cationic resin whose amine nitrogen equivalent weight is from 40 to 2000. The resins may have mutually reactive functional groups.

Description

water-dispersible resin is an amine group-containing cationic resin in which the amine nitrogen equivalent weight is from 40 to 2000.

Examples of cationic resins having amine groups are the amine addition products of optionally modified epoxy resins, polymerisation-type resins having amine groups, polyester resins having amine groups, and polyethyleneimine resins. For the first of these four groups, the epoxy resin may be of any conventional type. Examples of such resins are bisphenol A-type epoxy resins and bisphenol F-type resins, and halogenated products thereof: polyalcohol-, dimer acid-, trimer acid-, and novolak-type phenol resins having epoxy groups introduced by reaction with epichlorhydrin; polyolefin resins having epoxy groups introduced by the reaction with peroxide; and alicyclic epoxy resins. Bisphenol A-type epoxy resins are preferred.

Examples of primary and secondary amines which can be used for the preparation of the given amine adducts are mono- and di-alkylamines (e.g. propylamine, butylamine, diethylamine and dipropylamine), mono- and di-alkanolamines (e.g. ethanolamine, propanolamine, diethanolamine and dipropanolamine), alicyclic monoamines (e.g. cyclohexylamine, pyrrolidine and morpholine) and polyamines (e.g. ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepenta mine, propylenediamine, dipropylenetriamine, butylenediamine, Naminoethanolamine, diethylethylenediamine, diethylaminopropylamine, piperazine, N-methylpiperazine and N-aminoethylpiperazine).Aromatic amines (e.g. aniline, N-methylaniline, toluidine, benzylamine, mxylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane) may be used together with aliphatic amines of the type exemplified above.

Modified epoxy resins may be any fatty acid-modified resins, polyamide-modified resins, the reaction products of such resins with partially blocked polyisocyanate compounds, and epoxy resins modified with partially blocked polyisocyanate compounds (free isocyante being less than l per molecule, on average). The fatty acids may be non-drying, semi-drying or drying oil fatty acids; examples are safflower, linseed, soy bean, tall, cotton seed, coconut, tung, oiticica and dehydrated castor oil fatty acids and Hidiene fatty acid (manufactured by Soken Kagaku-sha).

The polyamide resins used for the modification of epoxy resin are preferably amine groupbearing polymers obtained by the condensation of dibasic acids (e.g. phthalic, adipic, sebacic or dimerised fatty acid) and polyamines (e.g. ethylene diamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, propylenediamine or butylenediamine). However, other polyamides prepared, for example by condensation of such polyamines with oligomers obtained by the ring-opening polymerisation of lactams (e.g. E-caprotactam), and polyester-polyamides obtained by using, in place of such polyamines, an alkanolamine (e.g. ethanolamine or propanolamine) may be satisfactorily used.

These polyamide resins all contain amine or amide groups which are reactive with epoxy groups.

The polyisocyanate compounds may be aromatic or aliphatic diisocyanates (e.g. m- or pphenylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4- or 2,6-tolylenediisocyanate, hexamethylenediisocyanate, dimer acid diisocyanate or isophorone diisocyanate), addition products of excess amounts of such diisocyanates with polyols (e.g. ethylene glycol, propylene glycol, glycerol, trimethylol propane or pentaerythritol), or trimers of such diisocyanates. They may be blocked with volatile low molecular, active hydrogen-bearing compounds such as aliphatic or aromatic monoalcohols (e.g. methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, benzyl alcohol or ethylene glycol monoethyl or monobutyl ether), hydroxy-tertiary amines (e.g. dimethyl- or diethylaminoethanol), oximes (e.g. acetoxime or methyl ethyl ketone oxime), phenol, cresols and lactams (e.g. E-caprolactam).

Amine adducts of modified epoxy resins may be prepared by reacting modifying agents, as described above, with previously-made amine adducts of epoxy resins, or by first reacting the modifying agents with epoxy resins and then with primary or secondary amines. For example, in obtaining a fatty acid-modified resin, the epoxy may be first reacted with fatty acid at 80 to 1 300C and then with an amine, or the epoxy may be first reacted with an amine to obtain an amine adduct of epoxy resin, to which a fatty acid may be reacted in a later stage. In the latter case, it is preferred to use a secondary amine. The reaction between the hydroxy or amino group and the fatty acid may be carried out at 180 80 to 2300C for several hours.

Resins of polymerisation-type polymers containing amine groups can be prepared in conventional manner, by using a polymerisable monomer having amine group(s) as one of the monomers. The amount of the monomer may be from 3 to 60 weight % of the total monomers used. Examples of such monomers with amine groups are dimethylaminoethyl acrylate or methacrylate, diethylaminoethyl acrylate or methacrylate, N-(dimethylaminopropyl)acrylamide, N (dimethylaminopropyl)methacrylamide, 2-vinyl-pyridine and 4-vinylpyridine.Together with the amine bearing monomer, the following may be reacted and copolymerised: esters (e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, n-octyl, lauryl, stearyl, tridecyl, glycidyl, 2-butoxyethyl or benzyl esters) of acrylic or methacrylic acid, hydroxyalkyl (e.g. 2-hydroxyethyl, 2-hydroxypropyl, 3 hydroxypropyl or 4-hydroxybutyl) (meth)acrylates, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, styrene, vinyl acetate, vinyltoluene, ethylene, propylene, butadiene or vinyl chloride.

Polyester resins having amine groups include polymers obtained by the polycondensation of polybasic acids (e.g. phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride, methylcyclohexanetricarboxylic anhydride SPECIFICATION Aqueous coating compositions The present invention relates to aqueous coating compositions comprising resinous film-forming components.

Coating compositions comprising organic solvents are dangerous to use, being inflammable and liable to explode, and are physiologically and environmentally harmful. Aqueous coating compositions are therefore in increased demand. However, in order to dissolve or disperse a suitable resin in water, it is necessary that the resin should carry a number of hydrophilic groups, to use a neutralising agent capable of forming a water-soluble salt with the resin, and to use a resin of relatively low molecular weight. As a result, the performance of films applied using aqueous coating compositions, e.g. their durability and water-resistance tends to be iower than would be desirable. Further, aqueous coating compositions cannot have a high non-volatile content, and their working properties are therefore often unsatisfactory.Again, it is often difficult to disperse colouring matter in aqueous coating compositions, thereby limiting their use, and often excluding fields requiring a high order of finishing appearance, gloss and sharpness, properties which are required in, for example, the automobile industry.

In general, emulsion coating compositions, including a resin prepared by the so-called emulsion polymerisation tchnique, in an aqueous medium, can include relatively high molecular weight resins.

The polymerisation technique must, however, be very carefully controlled. However, the surfactant or emulsifier which is added can reduce the durability and water-resistance of the film which is ultimately obtained.

Powder coating compositions have been suggested as an alternative to coating compositions including an organic solvent, but again problems arise in their use. Blocking may occur if their glass transition point is too low, giving a coating of low performance properties, and the need to have a high baking temperature, and a special applicator, limits their field of use.

Coating compositions comprising a powder dispersed in water, as a slurry, are also known. Such compositions cannot have a high non-volatile content, making it difficult to obtain a thick coating and/or satisfactory film adhesion (which can lead to cracks in the film). Dispersed powder coating compositions are difficult to apply by spraying, and tend to have low gloss. The slurried powder tends to separate out during storage and, since a dispersing agent is usually present, the water-resistance of the films obtained on coating is often low. Slurry compositions have not generally been used in practice.

Many attempts have been made to overcome the problems associated with aqueous dispersiontype coating compositions. In particular, a water-soluble or water-dispersible resin has been added, for example, Japanese Patent Applications Nos. 127151/74, 25224/76 and 31636/76 disclose compositions comprising a water-insoluble, dispersed resin as the main ingredient, with a minor amount of a water-soluble or water-dispersible resin. Japanese Patent Applications Nos. 74606/79 and 170262/79 disclose coating compositions comprising a pulverised coating resin and a carboxyl groupbearing water-soluble resin in a weight ratio, as solids, of from 0.1 to 100:1; in the specific examples, however, the content of water-soluble resin is about 10 to 20% of the powdered resin and is thus no more than a dispersion stabiliser in a dispersion system.The same is true with respect to the disclosure of Japanese Patent Publication No, 4149/80, of an aqueous dispersion coating composition comprising at least two water insoluble resinous powders and one or more water-soluble resins.

In using an aqueous dispersion coating medium, the dispersion stability of the powder is always a problem. Various attempts have therefore been made to use finely pulverised resins or dispersion aids.

However, since the known systems have been developed on the assumption that, if the powder is surrounded by a water-soluble resin, dispersion stability is improved owing to the affinity of the watersoluble resin to the aqueous medium, it is not surprising that the known compositions comprise only a low content of the water-soluble resin with respect to the dispersed resin.

British Patent Application No. 8220927 (Serial No. ) discloses and claims an aqueous coating composition comprising from 45 to 98 parts by weight (solids) of a water-soluble (or waterdispersible) resin and from 2 to 55 parts by weight (solids) of a finely-divided water-insoluble resin, in which the water tolerance (as herein defined) of the water-soluble resin is greater than 4 and in which the surface tension of a 1% w/w aqueous solution of the water-soluble resin is less than 51 dyne/cm.

That invention is based on the discovery that, by using certain water-soluble resins, the content of such resins in an aqueous coating composition can be increased without increasing the viscosity of the composition, and that the composition can be stable, even in the absence of surfactant or dispersing agent, if particular rheological properties are observed. On storage and in use, therefore, such compositions can avoid sedimentation and separation of solid matter, and resin coagulation, thereby allowing the production of a good quality, thick coating which, on curing, can give a film having good durability and other properties. Such aqueous compositions comprise a finely-divided water-insoluble resin dispersed in a water-soluble or water dispersible resin system, and should not be confused with the known type of composition comprising water and a powdered resin to which a water-soluble resin has been added, as a modifier.

According to the present invention, in an aqueous coating composition of the type disclosed in British Patent Application No. 8220927 (Serial No. ), part at least of the water-soluble or or pyromellitic anhydride) with alkanolamines (e.g. monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine or dimethylethanolamine). Epoxy resins may be used in some cases.

Suitable polyethyleneimine resins are straight or branched polymer having repeating units of the formula -CH2-CH2-N-. Although such resins are freely available as, for example, Epomine (manufactured by Nippon Shokibai Kagaku K.K.) or Corcat (manufactured by Cordova Chemical Co.), preparation of these resins is very easy. If desired, ionene-type resins may be used; then can be obtained, for example, by the Menshutkin reaction of polyamines (preferably diamines) with polyhalogenides (perferably dihalogenides), having the basic repeating unit of [(N@(R)(R2)R)m]Xs wherein R1 and R2 are the same or different C18 alkyl groups, R is C,~,2 polyalkylene, X is halogen (F, Cl, Br, I), and m is an integer of 3 to 1000.

in preparing an aqueous coating composition of this invention, a cationic aqueous resin of the type described above is used, with or without neutralisation by an organic acid (e.g. formic, acetic, hydroxyacetic, propionic, butyric, lactic, valeric, heptanoic, caprioc, caprylic, pelargonic, capric, lauric, myristic, palmitic or stearic acid) or an inroganic acid (e.g. phosphoric, sulfuric or hydrochloric acid).

The water-soluble resin must have the characteristic that the amino-nitrogen equivalent weight is within the range of 40 to 2000. Otherwise, there is a marked tendency for the viscosity of the coating composition to increase and for the corrosion resistance and alkaline resistance of the coated film to be reduced.

When a water-soluble or water-dispersible resin having a viscosity within the range usually employed for the manufacture of coating compositions, in other words having a non-volatile content of as much es 20 to 50%, is progressively diluted with water, the solubility of the resin decreases rather than increases, after reaching a maximum solubilisation point, and the resin solution loses its transparency and becomes a turbid liquid. Water tolerance is a measure of this dilution limit for a watersoluble resin and is expressed herein as the water dilution factor, with respect to the stage at which exactly 5 g of the aqueous varnish or the resin are in a 100 ml beaker, at the stage, following progressive dilution with deionized water, when No. 1 type (26 point type) can no longer be correctly read through the beaker.

It has been found that there are certain correlations between the water tolerance and sruface tension of the aqueous resin varnish, the dispersion stability of the finely-divided resin and the fluid viscosity of a mixture thereof, and that a coating composition having good dispersion stability and working properties can be obtained with a water-soluble resin having a water tolerance more than 4 and a surface tension, for a 1% w/w aqueous solution, less than 51 dyne/cm. The rationale, whereby observance of the given requirements for the resin allow the desired properties to be obtained, is not yet clearly understood. However, when the watertolerance is under 4, the viscosity of the coating composition becomes too high and its dispersion stability is poor.Similar tendencies are clearly observed when the surface tension exceeds the limit of 51 dyne/cm.

It appears that the number average molecular weight of the water-soluble resin may have some influence on the properties of the coating composition and on the ultimate film performance, but this is not conclusive. The water-soluble resin preferably has a number average weight which is 500 to 30,000 and more preferably 700 to 15,000.

In addition to the or each water-soluble resin having the given characteristics, a coating composition of the invention may additionally comprise one or more water-soluble resins which do not meet the given criteria. When used, the amount of any such additional resin should not adversely affect the dispersion and storage stability of the coating composition. In general, the cationic-type resin used in the invention should comprise more than 50 weight % of the total water-soluble or water-dispersible resin content.

A water-soluble (or water-dispersible) resin used in the novel composition may carry, is desired, one or more functional groups which are mutually reactive, usually on heating, with groups present on another water-soluble and-or water-insoluble resin in the composition. Suitable such groups are hydroxyl, oxirane, active methylol and isocyanate (blocked or unblocked) groups, halogen atoms and unsaturated carbon-carbon bonds.

One or more water-insoluble resins may be used in a composition of the invention. In addition to their water-insolubility, such resins should be solid at ambient temperatures and, when heated, compatible with other resins in the composition. Such resins preferably have a glass transition point (Tg) of more than 400 C, since otherwise the composition can be difficult to prepare, and its storage stability may be impaired. Examples of such resins are acrylic, polyester, alkyd, epoxy, urethane, amino, phenol, polyolefin, vinyl, cellulose, polyalkadiene, polyamide, polycarbonate and fluorine resins.

The water-insoluble resin preferably has a particle size of from 0.5 to 100, more preferably 1 to 70 4. If the particle size exceeds 100 , the mechanical properties of the composition may be reduced; when less than 0.5 u, the viscosity of the composition may become undesirably high.

The water-insoluble resin may or may not carry functional groups capable of reacting, when heated, with those of other resins in the coating compositions. Since the presence or absence of functional groups on resins used in the invention is not critical, it may be understood that the resin composition used in the invention may be thermoplastic or thermosetting. Cross-linking between the resin components of the novel compositions may be achieved as the result of the presence of functional groups of the type described. Alternatively, cross-iinking agents such as blocked polyisocyanates, epoxy resins and amino resins may be added.

A composition of the present invention comprises from 45 to 98, preferably 50 to 80, parts by weight, of the water-soluble resin and from 2 to 55, preferably 20 to 50, parts by weight of waterinsoluble resin, as film-forming components. These amounts are calculated in terms of the solids content. When the weight ratio of resins is outside the given range, it is difficult or impossible to obtain a stable composition with optimum rheological properties. For example, if the content of water-soluble resin is too low, the dispersion stability of the water-insoluble resin is poor, with resultant damage on levelling the coated film; if the amount of water-soluble resin is too high, the viscosity of the composition may be too high, with the consequent possibility of pinhole formation and sagging of the coated film.

A composition of the invention may comprise, in addition to the aqueous medium, a hydrophilic, polar, organic solvent, if desired. Examples of such organic solvents are ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methanol, ethanol, isopropyl alcohol, n-butanoi, sec-butyl alcohol, t-butyl alcohol and dimethylformamide. In addition, the coating composition may comprise colouring matter.

The coating composition can be prepared in any conventional way. For example, in the preparation of a coloured coating composition, colouring matter is first added with a proportion of the water-soluble resin, to make a colour paste to which are added the remaining proportion of the water-soluble aqueous resin, water-insoluble resin and any other additives, and the whole is stirred well, using a known mixing device such as a gate mixer or high speed disperser. It is of course possible to add all components to a dispersing device at once, and effect formation of a uniform dispersion in a single operation.

The coating composition of the present invention may be applied, with or without dilution with water, by a conventional coating technique such as spraying, dipping or brushing, and then subjected to drying or heat-curing, as is conventional.

The following Examples illustrate the invention, by comparison with Comparative Examples.

Unless otherwise stated, all parts are by weight.

EXAMPLE 1 Preparation of white-coioured coating composition (1) aqueous resin (1) (solid) 109 parts resinous fine powder (1) 23 cross-linking agent (1) 11 rutile type titanium dioxide 50 deionized water 150 The above mixture was placed in 900 ml glass vessel and stirred well by using a paint conditioner for 1.5 hour to obtain a white coloured coating composition (1).

Aqueous resin (1) (as aqueous varnish) monomer composition (weight %) N-(dimethylaminopropyl)methacrylamide 1 5 styrene 22.5 methyl methacrylate 22.5 n-butyl acryiate 30 2-hydroxyethyl acrylate 10 neutralization with acetic acid nitrogen equivalent weight* 1040 water tolerance (as herein defined) more than 10 surface tension** 43 dyne/cm neutralization % 100% TABLE 2

aqueous resin resinous fine powder Cross-link deion (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (1) (2) (3) (4) (5) (6) (7) (8) (1) (2) TiO2 water Example 2 - 185 - - - - - - - - - - - 51 - - - - - 8 - 53 41 3 - - 215 - - - - - - - - - - - 39 - - - - - 11 71 60 4 - - - 234 - - - - - - - - 30 - - - - - - - - 45 27 5 - - - - 270 - - - - - - - - - - 22 - - - 11 - 57 18 6 - - - - - 102 - - - - - - - - - - 84 - - - - 41 117 7 - - - - - - 62 - - - - - 72 - - - - - - - - 60 144 8 - - - - - - - 223 - - - - - - - - - 70 - - - 43 22 9 - - - - - - - - 152 - - - - - - - - - 29 - 12 45 104 10 212 - - - - - - - - - - - - 47 - - - - - 11 - 41 23 Comp.

Example 1 - - - - - - - - - 225 - - - - - - - 50 - - 14 44 33 2 - - - - - - - - - - 282 - - 38 - - - - - - 18 100 45 3 - - 95 - - - - - - - - - 74 - - - - - - - 6 - 45 150 solid content 33 weight % number average molecular weight (Mn) 500 * molecular weight/number of nitrogen atoms per molecule ** measured by using CB-VP type surface tension balance, manufactured by Kyowa Kagaku-sha, with 1% w/w aqueous solution Resinous fine powder (1) Finedic M 6102, polyester resin manufactured by Dainippon Ink Co., Ltd.

Tm 100 C, hydroxyl value 30, acid value 9 Mn 4000 Cross-linking agent (1) Crelan, blocked isocyanate manufactured by Bayer A.G.

EXAMPLES 2-10 AND COMPARATIVE EXAMPLES 1-3 Coating compositions were prepared by the procedure given in Example 1. Various aqueous resins were used, whose properties are set in Table 1; (2) and (3) are nitrogen-containing acrylic resins, (4) and (5) are amine-modified epoxy resins, (6), (7) and (8) are polyethyleneimines, (9) and (10) are nitrogen-containing condensation resins and !11) is an alkyd resin.

With regard to the various finely-divided, water-insoluble resins, (2) is Finedic M 6107, a polyester resin manufactured by Dainippon Inc. Co. Ltd. (Tm 11 00C; hydroxyl value 0; acid value 55; Mn 3800), (3) is RD-6360, an epoxy containing acylic resin manufactured by Mitsui Toatsu Kagaku (epoxy equivalent 473), (4) is Nylon-i 2, manufactured by Unichika Co., (5) is UM-8400 a vinyl acetatemodified polyethylene manufactured by Ube Kosan, (6) is EP-1 004, an epoxy resin manufactured by Shell Chem. (epoxy equivalent 950), (7) is EP-1 007, an epoxy resin manufactured by Sheil Chem.

(epoxy equivalent 1 850) and (8) is Tafpren AP, a styrene-butadiene polymer manufactured by Asahi Kadei.

Cross-linking agent (2) is Cymel, a hexamethoxymethylol melamine manufactured by Mitsui Toatsu Kagaku. The results are shown in Table 2.

TABLE 1

Surface Neutrali Resin N Water tension sation Solids No. (eq. wt.) tolerance (dyne/cm) (%) (wt %) Mn (2) 1570 .> 10 47 100 33 4500 (3) 390 > 10 42 100 33 4600 (4) 1570 4 44 60 35 2500 (5) 1100 5 41 100 25 2200 (6) | 43 > 10 48 50 100 600 (7) 43 > 10 30 50 100 1800 (8) 43 > 10 35 30 30 15000 (9) 850 4 49 70 50 2500 (10) 2200 2 38 90 45 3500 (11) - 2 55 100 30 1400 Coating compositions prepared in the preceding Examples were applied onto a dull steel plate to a dry thickness of 30 y. After setting for 30 minutes, the coating was dried at 1 600C for 30 minutes, thereby effecting three-dimentional cross-linking. The film performance (water-resistance, corrosionresistance, alkaline-resistance) and working property were examined and the results are shown in Table 3. Evaluation standards are as follows:: working property film thickness showing film thickness showing mark no pinholes no sagging more than 50 y more than 55 # 40 to 50 40 to 55 A 35 to 40 y 30 to 40 x less than 35 y less than 30 y 0900 water resistance mark after dipping in water (400C) for 240 hours O no change A slight loss of gloss x severe loss of gloss - peeling corrosion-resistance mark cross-cutting, salt-spraying and tape peeling O tape-peeling width less than 3 mm each side (salt spraying 72 hours) A tape peeied width less than 3 mm each side (salt spraying 24 hours) and complete peeling (salt spraying 72 hours) x complete peeling (salt spraying for 24 hours) alkaline resistance mark after dipping in 2% NaOH for 24 hours O no change A slight loss of gloss x discolouring, or generation of blister or peeling TABLE 3

Example work property water resist. corrosion resist. alkaline resist.

1 ### # # # 2 ### 0 0 0 .3 # 0 0 0 4 0 0 0 0 5 # 0 0 0 6 0 0 0 0 7 # # # # # # 8 0 0 0 0 9 # 0 0 0 10 O ~ # O O O Comp. 1 x # # # Comp. 2 x # x x Comp. 3 # # # # EXAMPLE 11 To 110 parts of the coating composition of Example 1 were added 11 5 parts of deionised water, to obtain a uniform aqueous dispersion (solids content about 17 wt %, pH 6-7. Using this as an electrodeposition bath, a zinc phosphate-treated steel plate (cathode) was treated at 27 C, while applying 150V current, for 2 minutes. The plate was then baked at 1 800C for 30 minutes and a hard coating (35 thickness: pencil hardness 2H) was obtained.

Claims (9)

1. An aqueous coating composition comprising from 45 to 98 parts by weight (solids) of watersoluble (or water-dispersible) resin and from 2 to 55 parts by weight (solids) of finely-divided waterinsoluble resin, in which the water-soluble resin has a water tolerance (as herein defined) of at least 4 and a surface tension, calculated for a 1% w/w aqueous solution, of less than 51 dyne/cm, and in which at least part of the water-soluble resin is a amine group-containing cationic resin whose amine nitrogen equivalent weight is from 40 to 2000.

2. A composition according to claim 1, which comprises at least 2 resins having functional groups which are mutually reactive at elevated temperature.

3. A composition according to claim 1 or claim 2, wherein the cationic resin is selected from amine adducts of epoxy resins, amine adducts of modified epoxy resins, amine-bearing acrylic or polyester resins, and polyethyleneimine resins.

4. A composition according to any preceding claim, wherein the water-insoluble resin is selected from epoxy, polyester, acrylic, alkyd, phenol, urethane, amino, polyolefin, polyalkadiene, vinyl, cellulose, polyamide, polycarbonate and fluorine resins.

5. A composition according to any preceding claim, wherein the mean diameter of the particles of the finely-divided water-insoluble resin is from 0.5 to 100 CL.

6. A composition according to any preceding claim, wherein the water-insoluble resin has a glass transition point of more than 400C.

7. A composition according to any preceding claim, which comprises from 50 to 90 parts by weight (solids) of water-soluble resin and from 10 to 50 parts by weight (solids) of water-insoluble resin.

8. A composition according to any preceding claim, which additionally comprises a polar organic solvent.

9. A composition according to claim 1, substantially as described in any of the Examples.