The invention relates to a powder paint binder composition and a powder paint composition for mat powder coatings.

As appears from 'Powder Paints' in Paintindia (February 1992, p. 50), from 'New developments in powder coatings' in Polymer Paint Colours Journal (December 1993, Vol. 183, pp. 590-591) and from the lecture 'Factors affecting the gloss reducing efficiency of ionomeric flatting agents for powder coatings' by Donald F. Loar at the Waterborne, Higher Solids and Powder Coatings

Symposium of 22-24 February 1995, it is very difficult to obtain mat powder coatings that also possess other desired properties. It is furthermore apparent from 'Grenzen und όglichkeiten in Sachen Pulverlack' in Metall-oberflache (43 (1989) 3, pp. 99-101) that powder coatings are usually matted with the aid of polyolefins and compounds containing silicon groups. However, such additives have an adverse effect on the mechanical properties and on the adhesion. It is the object of the present invention to provide powder paints, in particular thermosetting powder paints, which after curing result in (semi-)mat powder coatings having an excellent appearance and a gloss that can be adjusted depending on the desired application. Other desired properties of powder paint and the powder coating such as, for example, mechanical properties, corrosion resistance, weather resistance, hardness, flow properties, colour stability, scratch resistance and adhesion must be retained. The invention is characterised in that the binder composition for the powder paint or the powder paint composition contains melamine particles.

Preferably, these particles have a relatively small particle size. The particle size can be determined with a 'Malvern 2603 LC Particle Sizer'.

Preferably, the particle size distribution is such that d ₅₀ < 70 μm.

With the use of these melamine particles (semi-) mat powder coatings are obtained, that after curing of the powder paint composition show also the other desired properties. The gloss is generally measured according to

ASTM-D-523 at 60° and/or 20°.

In general, commercial powder coatings are high gloss coatings. The reflexion (gloss) at 60° generally is higher than or about 95%. When using conventional fillers as matting agents, a gloss at 60° of about 50% can be obtained without diminishing other properties. Unexpectedly it appears possible to obtain much lower gloss values with melamine, without deterioration of other paint properties. The definition of mat and satin-look (semi-mat or semi-gloss) is rather arbitrary. It has been found that the appearance of the powder coating improves considerably when use is made of melamine particle ^' s. It appears possible with the use of melamine particles, to obtain a wide range of mat and satin-look powder coatings. In particular, if relatively low amounts of melamine particles are used, coatings can be obtained with a gloss between for example 50-80% at 60°, whereas if relatively high amounts are used, mat coatings with a gloss lower than 20% at 60° can be obtained.

In particular favourable results are obtained when the particle size distribution is such that d ₅₀ < 20 μm. Excellent results are obtained when d ₅₀ < 10 μm. In general, d ₅₀ > 1 μm. The melamine particles preferably have a particle size distribution such that d ₉₀ < 150 μm, more preferably such that d ₉₀ < 40 μm, and very preferably, d ₉₀

< 20 μm. In general, d ₉₀ > 1 μm.

Preferably (d ₉₀ -d ₁₀ )/d ₅₀ < 1.9, more preferably < 1.6 and particularly < 1.1.

The percentage by weight of melamine is usually between 1 and 50 wt.% (relative to the percentage by weight of polymer plus crosslinker). Preferably it is more than 5 wt.%, preferably it is less than 40 wt.%.

The preparation of thermosetting powder coatings, the raw materials generally used and the chemical curing reactions for converting powder paints into cured powder coatings are described by Misev in Powder Coatings, Chemistry and Technology (1991, John Wiley) on pp. 42-54, p. 148 and pp. 224-226. A thermosetting binder composition is generally defined as the resinous part of the powder paint consisting of polymer and crosslinker.

Melamine can be added as an additive during the preparation of the polymer and/or to the polymer after the preparation of the polymer and/or to the crosslinker and/or to the binder composition and/or during the preparation of the powder paint.

In a preferred embodiment the melamine is added during the preparation of the powder paint in the extruder. This allows an easy preparation of a mat powder paint, and an easy adjustment of the gloss-value. In a further preferred embodiment of the invention the melamine is added to the polymer, or to the binder composition comprising the polymer and the crosslinker e.g. via an extruder after the polymer synthesis.

According to a further preferred embodiment of the invention the melamine is mixed with a crosslinker. The mixture obtained can be used as a masterbatch of the crosslinker. This mixture may optionally also contain fillers, or other components.

The present invention relates to a mixture " containing a polymer and melamine that is suitable for a

powder paint composition, to a melamine-containing crosslinker mixture (masterbatch) for powder paint systems, to a powder paint binder composition containing melamine, to a powder paint containing melamine and to a substrate that is coated with the cured powder paint according to the invention.

The powder paint comprising the binder composition according to the invention may contain a small, but effective amount of catalyst for the curing reaction between the polymer and the crosslinker.

The binder composition according to the invention can be supplied as a single-, two- or multi¬ component system, depending on the desired use.

Suitable individual components, to be combined in two- or a multi-component system are:

- [a (large) part of] the binder (polymer plus crosslinker)

- (a part of) the binder composition with melamine

- a polymer with the catalyst - (a part of) the polymer with melamine

- the crosslinker with melamine

- a catalyst, melamine, polymer and/or crosslinker as such

These components can be combined to obtain useful binder compositions in the paint preparation with appropriate amounts of polymer, crosslinker, catalyst (if needed) and melamine matting agent. A very convenient combination of components is: (1) a masterbatch of melamine in a binder composition; (2) a masterbatch of catalyst in a polymer and (3) a binder composition. If a composition with a large amount of melamine is to be made, more component (1) can be used at the expense of component (3). The reactivity of the system can be adjusted with the amount of component (2), irrespective of the degree of matting. In another embodiment, the melamine, catalyst and additives can be used as a masterbatch. Such a masterbatch may be a mixture of the polymer that is also

used for the binder composition or a different resin - whether or not reactive - containing melamine, the catalyst and optionally the total amount or a portion of the additives. In another embodiment, melamine can be used as plain powder, which is mixed with e.g. a masterbatch of catalyst in a polymer and with a binder composition during the paint preparation.

In addition to the melamine particles, other additives can be used to adjust the gloss. Suitable additives that may influence the gloss of the coating are in particular fillers such as aluminium trihydroxide, barium sulphate, silica powder or calcium carbonate.

The various components can be mixed with the aid of an extruder or a kneader mixer. In general, in this stage pigments, dyes, flow agent, degassing agent and other additives as required are added as well. In general, mixing is effected at temperatures above the binder 's melting point or within or above the binder 's melting range. Depending on the temperature used and the catalyst used it may be necessary to mix and cool rapidly. The average residence time in the mixing device is preferably less than half the system's gelling time at the mixing temperature. A two-component system for the preparation of a powder paint may contain a first component that consists substantially of the entire amount or a large proportion of the polymer and the crosslinker and a second component that consists substantially of a polymer as used in the first component or another (different) polymer and a catalyst for the curing reaction between the polymer (of the first component) and the crosslinker (masterbatch). Optionally, one of the two components or both components may contain melamine. A binder composition generally contains more than 50% by weight polymer and less than 50% by weight crosslinker.

Suitable polymers include for example a polymer containing carboxyl groups, epoxy groups, cyclic carbonate groups, anhydride groups, hydroxyl groups, acetoacetonate groups, α,J3-unsaturated carbonyls (acrylates and unsaturated polyesters), phosphoric acid groups, phosphorous acid groups, thiol groups or combinations thereof.

The polymer may be for example a polyester, a polyacrylate, a polyether (for example a polyether based on bisphenol or a phenol-aldehyde novolak), a polyurethane, a polycarbonate, a trifluoroethylene copolymer or a pentafluoropropylene copolymer, a polybutadiene, a polystyrene or a styrene-maleic anhydride copolymer. The polymer 's molecular weight (Mn) is usually higher than 800, but is preferably higher than 1500. The polymer has a molecular weight (Mn) that is lower than about 10,000, preferably lower than about 7000.

The polymer usually has a viscosity at 158°C that is lower than 8000 dPas. The viscosity will usually be higher than 100 dPas. It is advantageous for the viscosity to range from about 300 to about 5000 dPas. The viscosity as used here was measured by the Emila method, as described by Misev in Powder Coatings; Chemistry and Technology, pp. 287-288 (1991). The temperature (158°C) is the temperature actually measured in the sample.

The Tg of the polymer is usually higher than about 20°C, preferably higher than 30°C and may be higher than 40°C. The Tg of the polymer is usually lower than 120°C.

The polymer contains functional groups that are reactable with the reactive groups of the crosslinker. Such a polymer typically has a quantity of functional groups below about 2.7 meq/gram of resin (polymer). The quantity preferably is lower than 1.60 meq/gram of resin, and, in particular, it is preferably lower than about 1.25 meq/gram. The quantity of functional groups is generally

greater than about 0.09 meq/gram polymer, but preferably higher than 0.18 meq/gram polymer.

The acid or hydroxyl number of polymers with respectively acid or hydroxyl functional groups can be 5 calculated by multiplying the quantity given in meq/g by 56.1 (the molecular weight of KOH). Hence, a polymer with carboxyl reactive groups typically has an acid number below 150 mg KOH/gram of resin (polymer). The acid number preferably will be lower than 90 and, in particular is 0 lower than 70. The acid number is generally greater than 5, but preferably higher than 10.

Preferably polyesters, polyethers and polyacrylates are used as the polymer.

Preferably, the polymer is substantially non- 5 amino functional.

Polyacrylates useful herein as the polymer can be based on (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, propyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl 0 (meth)acrylate, decyl (meth)acrylate, isodecyl

(meth)acrylate, benzyl (meth)acrylate and hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate and/or glycidyl esters or glycidyl ethers of alkyl (meth)acrylates. By preference, 5 the polyacrylates are substantially vinyl chloride-free. The polyacrylates can be obtained by known methods. In these methods, comonomers such as, for example, styrene, maleic acid anhydride, as well as small amounts of ethylene, propylene and acrylonitrile, can be used. Other 30 vinyl or alkyl monomers, such as, for example octene, triallyl isocyanurate and diallyl phthalate can be added in small amounts.

A polyacrylate containing epoxy groups is obtained by using glycidyl (meth)acrylates in the 35. synthesis of the polyacrylate.

A polyacrylate containing acid groups is usually obtained by copolymerization of the desired amount of

acid, such as, for example, (meth)acrylic acid, maleic acid or fumaric acid.

A polyacrylate containing hydroxyl groups is obtained by copolymerization of the desired amount of monomers containing hydroxyl groups, such as, for example, hydroxyethyl (meth)acrylate and/or hydroxypropyl (meth)acrylate.

A polyacrylate containing thiol groups can be obtained by copolymerization of a sufficient amount of a monomer containing a preferably blocked thiol group.

Monomers containing a (blocked) thiol group include S- acetyl esters of thiol-ethyl (meth)acrylate, thiol-propyl (meth)acrylate and combinations thereof. After polymerisation, the acetyl group can be deblocked by hydrolysis.

A polyacrylate containing acetylacetonate groups can be obtained by copolymerising the acetoacetonate ester of 2-hydroxy ethylacrylate.

Suitable polyesters are generally based on the residues of aliphatic polyalcohols and polycarboxylic acids.

The polycarboxylic acids generally are selected from the group consisting of aromatic and cycloaliphatic polycarboxylic acids because these acids tends to have a Tg increasing effect on the polyester. In particular use is made of dibasic acids. Examplary polycarboxylic acids are isophthalic acid, terephthalic acid, hexahydroterephthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4-oxybisbenzoic acid and, where available, their anhydrides, acid chlorides or lower alkyl esters such as the dimethyl ester of naphthalenedicarboxylic acid. Although not required, the carboxylic acid component usually contains at least about 50 mol.%, preferably at least about 70 mol.%, isophthalic acid and/or terephthalic acid.

Other suitable aromatic cycloaliphatic and/or acyclic polycarboxylic acids useful herein include, for

example, 3,6-dichloro phthalic acid, tetrachloro phthalic acid, tetrahydro phthalic acid, hexahydro phthalic acid, hexachloro endomethylene tetrahydro phthalic acid, phthalic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, adipic acid, succinic acid, trimellitic acid and maleic acid. These other carboxylic acids can be used in amounts of at most 50 mol.% of the total amount of carboxylic acids. These acids can be used as such or, where available, in the form of their anhydrides, acid chlorides or lower alkyl esters.

Hydroxy carboxylic acids and/or optionally lactones can also be used, such as for example, 12- hydroxystearic acid, hydroxy pivalic acid and ε- caprolactone. Monocarboxylic acids, such as, for example, benzoic acid, tert.-butylbenzoic acid, hexahydrobenzoic acid and saturated aliphatic monocarboxylic acids can, if desired, be used in minor amounts.

Useful polyalcohols, in particular diols, reactable with the carboxylic acids to obtain the polyester include aliphatic diols such as, for example, ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-l,2-diol, butane-1,4-diol, butane-1,3-diol, 2,2- dimethylpropane diol-1,3 (=neopentyl glycol), hexane-2,5- diol, hexane-1,6-diol, 2,2-bis-(4-hydroxycyclohexyl)- propane (hydrogenated bisphenol A), 1,4- dimethylolcyclohexane, diethylene glycol, dipropylene glycol, 2,2-bis[4-2-hydroxylethoxy) phenyl] propane and the hydroxypivalic ester of neopentyl glycol.

Small amounts, for example less than about 4 wt.%, but preferably less than 2 wt.%, of trifunctional alcohols or acids may be used to obtain branched polyesters. Examples of suitable polyols and polyacids are glycerol, hexanetriol, trimethylolethane, trimethylolpropane, tris-(2-hydroxyethyl) isocyanurate and trimellitic acid.

The coating properties can e.g. be influenced by by diol selection. If, for example, good weather

resistance is desired, the alcohol component preferably contains at least 70 mol.% neopentyl glycol, 1,4- dimethylolhexane and/or hydrogenated bisphenol A. Caprolactone and hydroxypivalic acid are also useful if good weather resistance is required.

The polyester preferably contains from 5 wt.% to 30 wt.% aliphatic acids and/or cycloaliphatic alcohols. Examples of these compounds include adipic acid, cylcohexanedicarboxylic acid, succinic acid, cyclohexanedimethanol and hydrogenated bisphenol-A. The polyesters are prepared according to conventional procedures by esterification or transesterification, optionally in the presence of the usual esterification catalysts such as, for instance, dibutyl tin oxide or tetrabutyl titanate. The preparation conditions and the COOH/OH ratio can be chosen so that end products are obtained that have an acid value or a hydroxyl value that lies within targeted range of values. A carboxylic acid functional polyester is preferably prepared in a series of steps. In the last step of which an aromatic or, preferably, aliphatic acid is esterified so as to obtain an acid-functional polyester. As known to those skilled in the art in a first step, terephthalic acid is allowed to react in the presence of an excess of diol. Such reactions produce a mainly hydroxyl functional polyester. In a second or subsequent step an acid functional polyester is obtained by allowing further acid to react with the product of the first step. A further acid includes, for example, isophthalic acid, adipic acid, succinic anhydride, 1,4- cyclohexanedicarboxylic acid and trimellitic anhydride. If trimellitic anhydride is used at a temperature of 170- 200°C a polyester with a relatively large number of trimellitic acid end groups is obtained. The polyester can be a crystalline polyester, although amorphous polyesters are preferred.

Mixtures of crystalline and amorphous polyesters

can also be used.

Amorphous polyesters have a viscosity generally within a range of between 100 and 8000 dPas (measured at 158°C, Emila). Crystalline polyesters usually have a lower viscosity in the range of about 2 to about 200 dPas. If the polyester contains carboxylic-acid- reactive groups, the acid number of the polyester is selected so that the desired amount of crosslinker can be used. The acid number preferably is higher than 10, and preferably higher than 15 mg of KOH/gram of resin. The hydroxyl value is preferably lower than 10 mg of KOH/gram of resin.

Hydroxyl-functional polyesters can be prepared in a manner known per se by the use of a sufficient excess of glycol (polyalcohol) in the polymer synthesis.

Suitable polyesters for use in powder coatings are described in, for example, US-A-4,147,737 and US-A- 4,463,140 the disclosures of which are incorporated herein by this reference.

Polyethers useful as the polymer reactable with functional groups of the crosslinker can be based on cyclic compounds such as, for example, bisphenol. Examples of bisphenol based resins are resins containing bisphenol- A, hydrogenated bisphenol-A, bisphenol-S and bisphenyl. Polyethers containing epoxy functionality are usually bisphenol-A-based epoxy resins such as, for example, Epikote® resins with a Tg higher than 10°C. Epikote® 1003, 1004 and 1007, for example, are quite suitable. Bisphenol- terminated epoxy resins are an example of polyethers containing an hydroxyl group.

Examples of suitable crosslinkers include trisglycidyl isocyanurate (TGIC), (blocked) isocyanates, amino resins, polyanhydrides, dicyanediamides, polyhydroxy compounds, bisphenol A epoxy resins, compounds containing β-hydroxyalkylamide groups and crosslinkers containing epoxy groups and having at least one aliphatic chain

containing 5-26 carbon atoms carrying the epoxy groups, which are described in further detail in EP-A-600546, the disclosure herein by reference.

Carboxylic functional polymers are most often used in combination with crosslinkers having epoxy or β- hydroxyalkylamide functionality.

Aliphatic hydroxy functional polymers generally are cured with blocked-isocyanate functional crosslinkers, whereas aromatic-hydroxy functional polymers are cured with epoxy functional compounds.

Epoxy functional polymers can be cured amongst other with polyacids, polyacid anhydrides, (aromatic) hydroxy compounds and dicyanamide derivatives. These crosslinking agents are commonly available and well known by the skilled man.

With respect to mat powdercoatings very good results are obtained when melamine is combined with a polymer capable of reacting with epoxy groups and a crosslinker containing epoxy groups, wherein the crosslinker comprises at least one C ₅ -C ₂₆ lineair or branched aliphatic chain and the crosslinker has an epoxy functionallity greater than 1, with the proviso that the epoxy groups are carried on the at least one aliphatic chain. Suitable polymers include for example polymers having carboxyl groups, epoxy groups, anhydride groups, hydroxyl groups, acetoacetonate groups and phosphoric acid groups. Preferably, the polymers are carboxylic acid functional. The addition of the melamine reduces the gloss much more effectively than is possible using prior art matting techniques for exterior durable powder coatings. The exact desired reduced gloss level can be obtained by varying the amount of matting agent. The characteristics, such as, for example, whiteness stability, reproducibility, overbake, gas oven stability, QUV, salt spray, chemical, alkali and detergent resistance and

physical powder paint stability are good.

The aliphatic chains of this crosslinker can be linear or branched. The aliphatic chains carrying the epoxy functionality are preferably linear. The epoxy functional crosslinker can also comprise several aliphatic chains at least one of which carries epoxy functionality wherein the chains are linked via ester, amide, urethane or ether groups. As evident, it is not required that each chain carries an epoxy group. The epoxy functionality is, of course, greater than 1.

Preferably, the aliphatic chain contains 6 or more and in particular 12 or more carbon atoms. Preferably the aliphatic chain contains 22 or less carbon atoms.

The oxirane oxygen content of the crosslinker in general is higher than 1 wt.%, preferably higher than 2 wt.%. In general, the oxirane oxygen content of the crosslinker will be lower than 20 wt.%, in practice mostly lower than 15 wt.%.

The crosslinker preferably comprises an aliphatic ester carrying an epoxy group. When the crosslinker comprises aliphatic esters, the C ₅ to C ₂₆ aliphatic chains of the crosslinker are linked via ester groups. Exemplary crosslinkers include the epoxides of the methyl ester of linoleic acid and the ter.-butyl ester of linolenic acid, and epoxidized oil.

Preferably the epoxy group is not a terminal group. The epoxy groups in the crosslinker mainly comprise internal epoxy groups as shown in formula (I) 0 / \

- CH ₂ - CH - CH - CH ₂ - (I)

Although not required, the crosslinker usually contains more than one aliphatic chain, and can contain several chains, carrying an epoxy group. Unsaturated fatty acids with multiple unsaturations that are poly-epoxidized can for example also be used as alkyl ester, the alkyl

being, for example, methyl, ethyl, propyl, cycloehxyl or 2-ethylhexyl.

The average functionality of the crosslinker is usually higher than 1.2, preferably higher than 1.7, in particular higher than 2.1. In general the average functionality is lower than 8.

Examples of suitable crosslinkers containing aliphatic epoxy groups are epoxidised oils, wherein the oil is linseed oil, soybean oil, safflower oil, oiticica oil, caraway oil, rape seed oil, castor oil, dehydrated castor oil, cottonseed oil, wood oil, vernonia oil (a natural oil), sunflower oil, peanut oil, olive oil, soyleaf oil, maize oil, fish oil such as herring or sardine oil, or non-cyclic terpene oils. The epoxidised oil is preferably epoxidised soybean oil and/or epoxidised linseed oil.

This binder composition generally contains more than 50 wt.% polymer and less than 50 wt.% crosslinker. Generally, more than 2 wt.% crosslinker is used. Preferably more than 3 wt.%, relative to the binder composition, of crosslinker is used. It is also preferred, however, to use less than 30 wt.% of crosslinker. These amounts are defined as wt.% with respect to the amount of polymer and crosslinker. Examples of suitable catalysts for the curing reaction in particular acid/epoxy reactions are for example the salts of a carboxylic acid or an alcohol or a metal hydroxide. The acid may be a saturated aliphatic mono-or dicarboxylic acid or a saturated aromatic carboxylic acid such as decanoic acid, octanoic acid, stearic acid, lauric acid, linoleic acid, linolenic acid, decanedicarboxylic acid or benzoic acid. The salt may be based on any one of the elements lithium, sodium, potassium, cesium, magnesium, calcium, beryllium, copper or zinc. Examples of suitable catalysts include sodium stearate, lithium stearate, sodium benzoate, lithium benzoate, sodium laureate, lithium laureate, sodium

octanoate, lithium octanoate and lithium versatate.

Examples of suitable other classes of catalysts are N-dialkylamine pyridines, tertiary amines, imidazole derivatives, guanidines and cyclic amine compounds. If desired, the catalysts may be blocked.

Specific examples of catalysts include N-dimethylamino pyridine, benzotriazole, triethylamine or triphenylamine, 4,5-diphenyl imidazole, 1-ethyl imidazole, 2-methyl imidazole, 4-methyl imidazole, ethyl imidazole carboxylate, 5,6-dimethyl benzimidazole, 1-benzyl imidazole, imidazole or 1,1-carbonyl diimidazole, tetramethyl guanidine (TMG) , isocyanate-TMG adducts (e.g., isophorone diisocyanate-di-tetramethyl guanidine, tolonate-HDT-tetramethyl guanidine, or TMXDIdiTMG) , acetyl-TMG, 2-phenyl-l,1,3,3-tetramethyl guanidine, 1,5-diazabicyclo[4,3,0]non-5-ene and 1,5,7- triazabicyclo[4,4,0]dec-5-ene.

Other suitable catalysts include tetraalkyl phosphonium bromide, tetrabutyl ammonium fluoride, cetyl triethyl ammonium bromide and benzothiazole.

Melamine according to the invention may be added to said crosslinkers. This mixture may also contain fillers such as for example silicates, barium sulphate and aluminium-containing compounds. Mixture comprising a crosslinker, melamine and optionally a filler can be used as a crosslinker containing master batch during the preparation of the powder paint. The weight ratio of the crosslinker, melamine and the optional filler is preferably selected so that the mixture is well processable during the preparation of the powder paint. A very suitable crosslinker is obtained by mixing for example epoxidised linseed oil or soybean oil, melamine and silica powder and/or Ti0 ₂ .

Optionally, the usual additives, such as pigments, fillers, degassing agents, plasticisers and stabilisers, can be used in the powder coating systems according to the invention. Suitable pigments include

inorganic pigments, such as titanium dioxide, zinc sulphide, iron oxide and chromium oxide, and also organic pigments such as azo compounds. Examples of suitable fillers are metal oxides, silicates, carbonates and sulphates.

As additives use may be made of stabilisers such as primary and/or secondary antioxidants and UV stabilisers such as quinones, (sterically hindered) phenolic compounds, phosphonites, phosphites, thioethers and HALS compounds (hindered amine light stabilisers). Examples of degassing agents are benzoin and cyclohexanedimethanolbisbenzoate. The plasticisers include polyalkylacrylates, fluorocarbons and silicon oils. Other additives are for example additives for improving the tribo-chargeability, such as sterically hindered tertiary amines which are described in EP-B-371528.

Characteristic values for the particle size of powder paints are below about 90 to 100 μm; usually the average particle size is about 50 μm, although particle sizes of the order of 20 μm may also be used.

Powder paints according the invention can be applied in the usual manner, for example by means of electrostatic spraying of the powder onto an earthed substrate and curing the coating by subjecting it to heat for time a suitable temperature for a sufficient time. The applied powder can for example be heated in a gas oven or an electric oven or with the aid of infrared radiation.

Thermosetting coatings of powder paint (coating) compositions intended for industrial applications are described in further detail in a general sense in Misev, pp. 141-173 (1991).

Compositions according to the present invention can be used in powder coatings for use on metal, wooden and plastic substrates. Examples are general-purpose industrial coatings, coatings for machinery and for example for cans, household equipment, metal furniture, ceiling panels, computer housings and other small-scale

equipment. The coatings are also very suitable for use in the automotive industry, for coating external and/or internal components.

It is also possible to use the melamine according to the invention to obtain a mat thermoplastic powder coating.

The invention will be elucidated with reference to the following, non-limiting examples.

Examples

Determination of the particle size distribution of the melamine using a Malvern Laser.

The determination of the particle size distribution of melamine with the aid of the Malvern 2603 LC Particle Sizer is applied by dispersing the melamine particles in methanol (saturated with melamine) and pumped through a sample cell. A low power visible laser transmitter (He-Ne, 633 nm) illuminates the melamine particles. Next, the incident light is diffracted by the particles illuminated to give a stationary pattern of the mean size. This energy pattern is focused onto a multi element photo electric detector. Next, the size distribution by volume (weight) can be calculated.

The Malvern 2603 LC Particle Sizer comprises a recirculating small volume presentation unit provided with a sample cell and a lens type of 100 mm which is used to measure a particle size distribution ranging from 1.9-188 μm. The presentation unit has to be filled with 0.45 μm filtered methanol and next a blanc by measuring the back ground has to be determined. Next, as much sample (100 - 300 mg) to reach an optical density of 0.15 - 0.30 has to be added. After this the measurement can start.

Example I and Comparative Experiment A 480 parts by weight of polyester resin (Uralac

P5504 ^R , DSM Resins), 120 parts by weight of an isocyanate crosslinker (B1530 ^R ; Hills), 300 parts by weight of pigment

(titanium dioxide, Kronos 2160 ^R ) , 9 parts by weight of plasticising agent (Resiflow PV5 ^R , Worlee), 4.5 parts by weight of benzoin and (for example I) 100 parts by weight of melamine with d _so < 10 μm (as measured with a Malvern 2603 LC Laser diffraction technique) were introduced into an extruder (Buss, 100 rpm) at 130°C. For the comparative experiment, no melamine was used.

After extrusion, grinding, screening (to a particle size of < 90 μm) and electrostatic application to an aluminium substrate (0 panel S46) the composition was cured at 200°C for 10 minutes.

The gloss of the two coatings was measured according ASTM-D523. The results are as follows:

Example I 20°: 18 60°: 52

Experiment A 20°: 69 60°: 87

Example II and Comparative Experiment B

Example I and experiment A were repeated at an extrusion temperature of 120°C, using 420 parts by weight of Uralac P2450 ^R (DSM Resins) as the polyester, 180 parts by weight of epoxy resin (Araldit GT 7004 ^R ) as the crosslinker and 300 parts by weight of Kronos 2310 ^R as the titanium dioxide. The results of the gloss measurements were as follows:

Example II 20°: 16 60°: 46

Experiment B 20°: 79 60°: 93

Example III-V and Comparative Experiment C

Example I and Experiment A were repeated, using 558 parts b weight of Uralac P 5400 ^R (DSM Resins) as the polyester and 42 parts by weight of TGIC (Araldit PT 810 ^R ) as the crosslinker. For example III, 50 g melamine; example IV 100 g melamine and example V 150 g melamine was used.

The results of the gloss measurements were as

follows:

Example III 20°: 40 60°: 67

Example IV 20°: 19 60°: 48

Example V 20°: 11 60°: 37

Experiment C 20°: 85 60°: 94

Examples VI-VIII

Example III was repeated with for each example 100 g melamine, the type of melamine was for Example VI: d _so < 10 μm, d ₉₀ < 15 Example VII: d _s0 < 70 μm, d ₉₀ < 140 Example VIII: d ₅₀ < 20 μm, d ₉₀ < 30 The results of the gloss measurements were as follows:

Example VI 20°: 20 60°: 50

Example VII 20°: 20 60°: 46

Example VIII 20°: 19 60°: 47

Visual examination of the test panels showed that the finer type of melamine resulted in a more beautiful appearance.

Example IX-X

Example III was repeated, however, no Ti0 ₂ pigment was used. Example IX was a clear coat, and for Example X, use was made of 10 g % carbon black and 290 g

Blanc Fix Micro. The results of the gloss measurements were as follows

Example IX 20°: 28 60°: 59

Example X 20°: 12 60°: 41

Example XI

513 parts by weight of polyester resin (Uralac P

790 ^R ; DSM Resins) were mixed with 57 parts by weight of epoxidised linseed oil in a static mixer. This mixture was processed as described in Example I together with 30 parts by weight of a mixture of 80% of polyester resin (Uralac

790 ^R ) and 20% lithium versatate, 250 parts by weight of

titanium dioxide (Kronos 2160 ^R ) , 9 parts by weight of plasticiser (Resiflow PV 5 ^R ) and 200 parts by weight of melamine with d ₅₀ < 70 μm.

Example XII

Example I was repeated, with 506 parts by weight of Uralac P790 ^R and 64 parts by weight of epoxidised soybean oil being mixed in the extruder. This mixture was processed as described in Example I together with 30 parts by weight of a mixture of 80% of a polyester resin (Uralac 790 ^R ), with 20% lithium versatate, 250 parts by weight of titanium dioxide (Kronos 2160 ^R ) , 9 parts by weight of plasticiser (Resiflow PV 5 ^R ) and 200 parts by weight of melamine with d ₅₀ < 70 μm.

Example XIII

Example XII was repeated, with 513 parts by weight of polyester resin (Uralac P5900 ^R ) and 57 parts by weight of epoxidised linseed oil.

Example XIV

Preparation of a crosslinker containing masterbatch

200 parts by weight of an aluminium compound

(Micro Mica ^R ) and 200 parts by weight of melamine with d ₅₀ < 20 μm were mixed in a kneader mixer at 100°C, after which 54 parts by weight of epoxidised linseed oil were added. After 15 minutes' mixing a non sintering powder that was physically stable at room temperature was obtained.

Example XV

537 parts by weight of polyester resin (Uralac

P790 ^R ) , 454 parts by weight of crosslinker according to

Example XIV, 9 parts by weight of lithium versatate, 250 parts by weight of Kronos 2160 ^R and 9 parts by weight of

Resiflow PV5 ^R were further processed as described in

Example I.

Comparative Experiment D

In a static mixer 501 parts by weight of polyester resin (Uralac P790 ^R ; DSM Resins) were mixed with 54 parts by weight of epoxidised linseed oil. This mixture was processed as described in Example I together with 36 parts by weight of polyester resin (Uralac 790 ^R ), 9 parts by weight of lithium versatate, 250 parts by weight of titanium dioxide (Kronos 2160 ^R ) , 9 parts by weight of Resiflow PV 5 ^R and 150 parts by weight of barium sulphate. The gloss (ASTM-D-523) of the powder coatings according to Examples X, XII, XIII and XV and Comparative Experiment D was determined; the results were as follows:

TABLE 1

20° 60°

XI 6 30 XII 7 35

XIII 1 19

XV 1 10

D 65 88

Example XVI

A polyacrylate based on 2410 parts by weight of methylmethacrylate, 450 parts by weight of butylacrylate and 140 parts by weight of MA methacrylic acid was prepared via solution polymerisation by causing said mixture of monomers to polymerise in 1500 parts by weight of toluene in the presence of 222 parts by weight of initiator (Trigonox 21S ^R , Akzo Nobel). The monomers were mixed with the initiator and this mixture was added to the toluene solution in the reactor at 110°C in 3 hours' time. Then the solvent was removed through vacuum distillation. The obtained water-clear resin had an acid value of 29 mg

of KOH/gram of resin, a Tg of 70°C and a viscosity of 960 dPa.s.

547.5 parts by weight of the polyacrylate thus obtained were mixed according to Example I with 24 parts by weight of polyester resin (Uralac 790 ^R ) , 6 parts by weight of lithium versatate, 52.5 parts by weight of epoxidised linseed oil, 200 parts by weight of melamine with d ₅₀ < 70 μm, 250 parts by weight of titanium dioxide

(Kronos 2160 ^R ) and 9 parts by weight of plasticiser (Resiflow). The gloss of the cured coating was 2 at 20° amd 28 at 60°.

These examples show that the addition of melamine resulted in mat powder coatings, in white, clear and black coatings. Further, it is shown that the degree of matting can be adjusted while using various amounts of melamine. Further, it is shown that melamine is an effective matting agent with a large variety of powder coating binder compositions.