IE68774B1 - Powder thermoplastic compositions based on polyamide and/or polyetheresteramide process for their preparation and their use for coating metal substrates - Google Patents

Abstract

Thermoplastic powder compositions based on polyamide and / or polyetheresteramide, process for their preparation and their use for coating metal substrates. Powder compositions based on polyamide and / or polyetheresteramide, which additionally contain epoxy / sulfonamide resins and are suitable for coating metal substrates, are described.

Description

The present invention relates to powder thermoplastic compositions based on polyamide and/or polyetheresteramide, which can be employed especially for coating metal substrates without the need for an adhesion primer.

Polyamides are commonly employed for coating metal substrates, especially because of their good mechanical properties such as abrasion resistance, impact strength, etc. and chemical inertness towards many products such as hydrocarbons, bases, inorganic acids, etc.

It is known, however, that the adhesiveness of polyamides to metals is insufficient because of a poor wetting ability of the polyamides in the molten state, which does not allow them to enter well into the roughness and interstices of the metal in order to acquire strong mechanical adhesiveness. Furthermore, when a uniform deposit of polyamide powder is produced over a whole metal surface and when this deposit is heated until it melts at the appropriate temperature, the molten polyamide film shrinks and gathers together in droplets which can fall off the metal substrate.

To overcome this defect, the metal substrate is coated with an undercoat, called an adhesion primer, intended to ensure the bonding and the mechanical anchoring of the polyamide powder. The adhesion primer employed is generally based on thermosetting resins and is applied in the form of a powder or in solution or suspension in organic solvents.

Additional plant must therefore be provided for possible removal of the solvents and for curing the primer before the substrate thus coated is clad with the polyamide powder. Moreover, the curing and/or the drying of the primer lead to an appreciable increase in the duration of the coating operations and hence in their cost.

French Patent No. 72/41,484 discloses powder compositions based on polyamide containing blocked phenols, which do not require the use of an adhesion primer. However, the application conditions are tricky and do not make it possible to obtain high-performance adhesiveness, although they are improved.

The powder thermoplastic compositions according to the present invention comprise a mixture of polyamide and/or of polyetheresteramide and of epoxy/sulphonamide resins.

The powder thermoplastic compositions of the present invention have a good ability to wet metal substrates and high-performance adhesiveness results, this being so without the necessity for any adhesion primer.

The weight ratio of the epoxy/sulphonamide resins to the polyamide and/or the polyetheresteramide is generally from 0.5 to 20 %, preferably from 2 to 7 %.

The term polyamide, as used herein, means an aliphatic polyamide obtained from a lactam or from an amino acid with a hydrocarbon chain having 4 to 20 carbon atoms, such as caprolactam, oenantholactam, dodecalactam, undecanolactam, ll-aminoundecanoic acid, 12-aminododecanoic acid, the products of condensation of a dicarboxylic acid with a diamine such as polyamides 66, 69, 610, 612 and 96 (products of condensation of hexamethylenediamine with adipic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid and of nonamethylenediamine with adipic acid), a copolyamide resulting from the polymerization of one or more of the monomers mentioned above or a mixture of such polyamides.

Preferred polyamides include polyamide 11, obtained by polycondensation of ll-aminoundecanoic acid, polyamide 12, obtained by polycondensation of 12aminododecanoic acid or of dodecanolactam, and copolyamides obtained from such monomers.

In general, the inherent viscosity (measured at 20°C for a solution containing 0.5 g per 100 g of metacresol) of the polyamides is from 0.20 to 2.0, preferably 0.60 to 1.30 dl g”1.

A polyamide may also be a semiaromatic amorphous polyamide, especially those described in FR-A-1,588,130, 2,324,672 and 2,575,756, EP-A-53,876 and JP-59/015,447 and 60/217,237.

The term polyetheresteramide means both a random polyetheresteramide (i.e. one formed by random chain sequencing of the various monomeric constituents) and block polyetheresteramides, i.e. those made up of blocks of varying chain lengths of the various constituents.

Polyetheresteramides are products of the copolycondensation of polyamide blocks with reactive ends with polyether blocks with reactive ends, such as polyamide blocks with dicarboxylic chain ends with polyetherdiol blocks. Products of this kind have been described, for example, in FR-A-74/18,913 and 77/26,678.

The number-average molecular mass of these polyamide blocks is generally from 500 to 10,000, more particularly from 600 to 5,000. These blocks are preferably made up of polyamide 6, 66, 612, ll or 12 units or of copolyamides resulting from the polycondensation of their monomers.

The number-average molecular mass of the polyethers is generally from 200 to 6,000 and more particularly from 600 to 3,000.

The polyether blocks preferably consist of polytetramethylene glycol (PTMG), polypropylene glycol (PPG) or polyethylene glycol (PEG).

» The inherent viscosity (measured as above) of the polyetheresteramides is advantageously from 0.8 to 2.05, preferably from 0.80 to 1.20, dig”1.

The polyetheresteramides used are typically made up of 5 to 85 %, preferably 30 to 80 %, by weight of polyether and of 95 to 15 %, preferably 70 to 20 %, by weight of polyamide.

The epoxy resins are solid or liquid compounds which contain at least one epoxide functional group, which can be used singly or mixed. The mixtures may consist of compounds which have a different number of epoxide functional groups and which very frequently have an overall (epoxy) functionality which is not integral.

A very large number of examples of organic compounds corresponding to this definition and whose structures are very diverse exist. The most widely used compounds are those derived from the reaction of bisphenol A and epichlorohydrin, especially the compounds resulting from the addition of two molecules of epichlorohydrin to one molecule of bisphenol A (BADGE). However, a large number of other epoxy resins can be employed, such as those resulting from the attachment of an epoxide group to both ends of a paraffinic hydrocarbon chain (for example diepoxides derived from butanediol) or of a polyether chain, such as alpha,omega-diepoxy polypropylene glycol. More preferred diepoxy compounds include vinylcyclohexene dioxide, 3,4epoxycyclohexylmethy1 3,4-epoxycyclohexanemonocarboxylate, 3-(3,4-epoxycyclohexyl)-8,9-epoxy-2,4dioxaspiro[5.5]undecane, bis(2,3-epoxycyclopentyl) ether, bis(3,4-epoxy-6-methylcyclohexyl) adipate and resorcinol diglycidyl ether.

If the intention is to obtain a final material exhibiting a high crosslinking density then it may be advantageous to employ epoxy compounds containing more than two epoxide functional groups per molecule, such as epoxidized soya oils, polyglycidyl ethers of phenolic resins of the novolak type, p-aminophenoltriglycidyl ether or 1,1,2,2-tetra-(p-hydroxyphenyl)ethane tetraglycidyl ether.

The epoxy equivalent weight is generally from 43 to 5,000, preferably from 150 to 1,000.

Preferred epoxy resins are those whose overall functionality is from 1.9 to 2.1, advantageously about 2.

The aromatic sulphonamides may be monosulphonamide derivatives of benzene, halogenated or otherwise, such as benzenesulphonamide, nitrobenzenesulphonamide, ortho-, meta- or paratoluenesulphonamide, aminoalkylbenzene-sulphonamides, naphthalene or xylenesulphonamide.

The epoxy/sulphonamide resins according to the invention can be obtained by reaction of sulphonamide compounds with epoxy compounds.

The proportion of the epoxy and sulphonamide compounds should be such as to make the number of epoxide functional groups equal to the number of sulphonamide functional groups. However, for reasons of reaction kinetics and/or of final product quality it may be necessary to vary the stoichiometric ratio (number of sulphonamide functional groups/number of epoxide functional groups) from, say, 0.25:1 to 1:1, preferably 0.5:1 to 1:1.

The melting point of the epoxy/sulphonamide resins used is generally 50 to 180°C and their weightaverage molecular mass Mw 500 to 10,000.

Various other constituents may be incorporated 5 into the mixture described above, such as fillers, pigments, additives such as antipitting or reducing agents and antioxidants.

Suitable fillers include talc, calcium and manganese carbonates and potassium and aluminium silicates.

Suitable pigments include titanium dioxide, strontium chromate, zinc phosphate, lead silicochromate, carbon black and iron oxides.

As discussed, various constituents may be incorporated into the mixture of polyamide/ polyetheresteramide and epoxy/sulphonamide resins, in proportions which are within the limits usually encountered in such powder compositions for coating metal substrates. In general up to 100 % by weight of the said constituents can be incorporated.

The powder thermoplastic compositions of this invention can be obtained in a number of ways.

The first process consists in dissolving the epoxy/sulphonamide resin(s) in a suitable solvent, adding to the resulting solution the powdered polyamide and/or polyetheresteramide and drying and screening the mixture to produce a powder composition with the desired particle size range. All these stages can be carried out at room temperature.

The solvent in which the epoxy/sulphonamide resin is dissolved is advantageously a ketone such as acetone, an ester, or any other solvent in which the resin is highly soluble and which can be removed easily according to known techniques which are usually employed.

The second process for obtaining the powder compositions consists in melt-blending the epoxy/sulphonamide resin with the polyamide in a kneader of suitable type. The blending temperature is suitably from 150 to 300°C, preferably 170 to 230°C.

The mixture thus obtained is generally in the form of granules, which can be milled, according to the usual techniques, to the desired particle size range for coating metal substrates.

The third process consists in dry-mixing the epoxy/sulphonamide resin, finely milled beforehand, and the polyamide powder. This dry-mixing or dry-blending does not require any special apparatus; it can be carried out at room temperature and is therefore economical and fast.

The fourth process consists in performing a (co)polycondensation of the polyamide monomers in the presence of the epoxy/sulphonamide resin such as defined above. This is generally carried out at a temperature of 150 to 300°C, preferably 190 to 250°C.

Any kind of apparatus can be employed for the polycondensation e.g. a reactor fitted with a stirrer for stirring at, say, 50 revolutions/min, and capable of withstanding a pressure of 20 bars.

The polycondensation period is typically 5 to 5 15 hours, preferably 4 to 8 hours.

When the copolycondensation operations are finished the mixture is obtained in the form of granules which can be milled to the desired particle size range.

The particle size of the powders of this 10 invention is generally 5 μιη to 1 mm.

The powder thermoplastic compositions of this invention can be used for coating a wide range of metal substrates.

The substrates may be ordinary or galvanized 15 steel components or components made of aluminium or aluminium alloys. It can be of any thickness, for example about 0.1 mm or several times 0.1 cm.

The metal substrate, especially one made of ordinary steel, aluminium or aluminium alloy may have been subjected to one or more of the following surface treatments: rough degreasing, alkaline degreasing, brushing, fine degreasing, hot rinsing, phosphating degreasing, iron or zinc phosphating, chromating, cold rinsing and chromic rinsing.

Examples of metal substrates which can be coated with a composition according to the invention include degreased, smooth or shot-blasted steel, degreased, - 10 phosphated steel, iron or zinc phosphate-treated steel, Sendzimir galvanized steel, zinc-electroplated steel, dipgalvanized steel, electrophoresis steel, chromated steel, anodized steel, carborundum-sanded steel, degreased aluminium, smooth or shot-blasted aluminium, and Alodine 1200 aluminium.

The composition according to the invention can therefore be applied onto the metal substrate in the form of a powder, using conventional techniques.

The powder milling can be carried out in equipment cooled cryogenically or with high air intake (e.g. an impeller, hammer or disc mill). The powder particles obtained are classified in suitable equipment to remove the undesired particle size fractions: for example too coarse and/or too fine particles.

Among the preferred techniques for applying the powder there may be mentioned electrostatic spraying and fluidized bed dip-coating.

In electrostatic spraying the powder is introduced into a gun where it is conveyed by compressed air and runs through a nozzle raised to a high voltage, generally from 10 to 100 kilovolts. The applied voltage may be positive or negative in polarity. * The flow rate of the powder through the gun is generally from 10 to 200, preferably 50 to 120, g/min.

When it passes through the nozzle the powder becomes charged with a certain quantity of electricity and -lithe powder particles conveyed by the compressed air are applied onto the metal surface to be coated, the said surface being itself connected to earth, that is to say to a zero electrical potential. The powder particles are held onto this surface by their electrostatic charge; the electrostatic attraction forces are sufficient for the powder-treated object to be moved and heated in an oven to a temperature which causes the coating powders to melt or to crosslink.

The polarity of the electrostatic charge is generally chosen as a function of the nature of the powder which it is desired to apply; generally powders can give good results with a particular polarity and less good or even no results when the polarity is of opposite sign. In general, positive polarity gives better results for the application of polyamide 11 or 12 powder by electrostatic spraying.

However, we have noted that for the powder compositions of this invention, the adhesiveness and the final coating quality are practically independent of the polarity of application.

Electrostatic spraying of the polyamide-based compositions offers the advantage, regardless of the polarity of application, that it is possible to employ existing standard industrial plants which are designed for the electrostatic spraying of a powder coating with a single polarity. - 12 In electrostatic spraying the preferred weight ratio of epoxy/sulphonamide resin present in the polyamide mixture is from 1.5 to 7.5 %.

A powder with a mean particle size of 5 to 100, preferably 5 to 65, μη is generally employed.

Coatings produced with a composition according to the invention and applied by electrostatic spraying have good adhesive properties and a good quality final appearance, for a thickness of 40 to 400 μη. This is not the case with powder coatings based on polyamide alone, . which exhibit numerous faults in appearance with low (e.g. < 40 μη) and high thicknesses (e.g. > 400 μια). For example, with low thicknesses, a polyamide coating exhibits pitting; with high thicknesses there are considerable risks of coating delamination and bubbles and molehills appear in large numbers.

In the case of the fluidized bed dip-coating process, the metal substrate to be coated, carefully prepared, for example by being subjected to one or more of the surface treatments listed above and preferably to a shot-blasting operation, is heated in an oven to a specified temperature depending especially on the nature of the said substrate, its form and the desired coating thickness. Thus heated, the substrate is then immersed in a powder composition according to the invention which is kept in suspension by a gas circulating in a vessel with a porous bottom. The powder melts in contact with the hot metal - 13 surfaces and thus forms a deposit whose thickness is a function of the temperature of the substrate and of the length of its immersion in the powder.

In fluidized bed dip-coating the preferred 5 proportion of epoxy/sulphonamide resin relative to the weight of polyamide is from 1 to 5 %.

The particle size of the powders applied in a fluidized bed is typically from 10 to 1,000, preferably 80 to 200, μπι. The coating thickness is generally from 150 to 1,000, preferably 200 to 700, μα.

The following Examples further illustrate the present invention.

EXAMPLE 1 A - PREPARATION OF THE POWDER COMPOSITION; 6 parts of aromatic epoxy/sulphonamide resin with Mw = 1,200 and glass transition temperature Tg = 54°C are dissolved in 100 parts by weight of acetone.

The epoxy compound is a resin derived from the reaction of bisphenol A and epichlorohydrin.

The epoxy equivalent weight of this resin is 172 g and its hydroxyl content is 0.11 hydroxyl equivalents per kg of resin.

The sulphonamide compound consists of paratoluenesulphonamide. 200 parts of powder are then added, of polyamide ll with an inherent viscosity of 0.9 and containing 13 % by weight of various additives including 9.6 - 14 % of filler, 1.8 % of colorants and 1.6 % of antioxidant, antipitting and reducing agents. The mixture is stirred continuously for 4 min at room temperature. A paste is obtained, which is dried for 5 hours in an oven at 40°C to remove the acetone.

The dry residue is powdered and screened through a ΙΟΟ-μπι mesh sieve to remove the coarse particles which are not suitable for electrostatic deposition.

B - APPLICATION: The powder composition obtained in A is deposited at room temperature using (a) negative or (b) positive electrostatic spraying at 30 kV onto a steel panel which has previously been subjected to a degreasing operation followed by shot-blasting, the metal surface being at zero potential.

Thus coated, the substrate is moved to an oven maintained at 220 + 20°C, where it stays for 5 to 15 minutes and is then taken out of the oven and cooled in air.

C - CHARACTERISTICS OF THE MATERIAL 1) The material is a composite comprising successively: - a degreased and shot-blasted steel panel (1.5 mm thick) - a layer of powder composition such as 25 described under A, 100 gm thick. 2) The material described in C.l) is subjected to the following adhesiveness test, which we have developed: - 15 - 2 parallel grooves 10 nun apart are scribed into the coating and as far as the metal with a cutter. Another groove, perpendicular to the first 2 and intersecting them is then scribed.

- Using the same tool, whose cut width is mm, the latter groove is entered and a forward movement is applied between the 2 parallel grooves at the metal/coating interface to obtain a 10 mm coating flap.

The flap is pulled to try to part the coating 10 from the metal.

The results are classified as follows: - Class 4: the film cannot be parted from the metal, - Class 3: the film parts nonuniformly, the 15 bonding is complete over at least 50 % of the surface, - Class 2: the film parts uniformly, the force needed to pull it off is high and is at the strength limit of the coating, - Class 1: the film parts from the surface 20 easily, bonding is weak, - Class 0: the coating shows no bonding to the surface. 3) The spreading of the powder composition applied to a 100 100 1 mm steel panel is assessed visually when it is melted at 220°C, the panel being placed vertically in the oven.

A score from 0 to 4 is given according to the - 16 following observations: - Class 0: no coating left on the panel. All the molten coating has fallen off in the oven.

- Class 1: at least half of the coating has fallen off during the melting, leaving bare approximately half of the surface area of the metal panel.

- Class 2: there are a few points of coating separation (generally at the edges and the corners of the panels).

- Class 3: no separation. Faults due to poor wetting: bubbles, large craters, etc.

- Class 4: the coating is tight and shows no wetting or spreading fault.

The adhesiveness and spreading results obtained using the material described in C.l) are listed in Table I.

Note. The half-score values correspond to properties which are intermediate between the classifications between which they lie. For example: a score of 1.5 corresponds to properties which are intermediate between those of Class 1 and those of Class 2.

EXAMPLE 2 The test of Example l is repeated using a mixture comprising (by weight): - 100 parts of acetone, parts of epoxy/sulphonamide resin with the same characteristics as those described in Example l.A, - 17 - 200 parts of powder of polyamide 12 and of copolyamide 6/12 with an inherent viscosity of 0.96 and containing 12 % of various additives including 11.3 % of filler and 0.7 % of antioxidant and reducing agents.

A composite material is thus produced, comprising successively: - a zinc phosphate-treated steel panel 1.5 mm thick, - a layer of polyamide 12, 6/12, 120 μτα thick.

The material described above is subjected to an adhesiveness test as defined in 1.C.2) and to a spreading assessment as defined in 1.C.3).

The results are listed in Table I.

EXAMPLE 3 A - PREPARATION OF THE POWDER COMPOSITION parts by weight of epoxy-sulphonamide resin with characteristics which are identical to those of Example I.A., milled beforehand to an average particle size of between 5 and 40 /xm are added to 1,000 parts of PA 11 with an inherent viscosity of 0.90 and containing 13.8 % of additives including 11.3 % of fillers.

The whole is blended and homogenized at a temperature of between 200 and 220°C. The residence time in the blending apparatus is of the order of 45 s.

Once cooled in the open air, the product obtained is milled to obtain a powder particle size of between 10 and 80 gm. -Ιδιο Β - APPLICATION The powder composition obtained under A is sprayed electrostatically onto a steel panel under the same conditions as those described in Example l.B.

C ~ CHARACTERISTICS OF THE MATERIAL 1) The material is a composite comprising successively: - a degreased and shot-blasted steel panel (1.5 mm thick), - a layer of powder composition such as described under A, 100 pm thick. 2) The material described in C.l) is subjected to adhesiveness and spreading tests as defined in Example 1.C.2) and 1.C.3).

The results obtained using the material described in C.l) are listed in Table I.

EXAMPLE 4 The test of Example 3 is repeated using a mixture comprising: - 30 parts by weight of epoxy/sulphonamide resin with characteristics which are identical with those of Example l.A, milled beforehand to a particle size of between 5 and 40 gm, added to 1,000 parts of polyamide 12 with an inherent viscosity of 0.95.

The whole is blended and homogenized at a temperature of between 180°C and 230°C. The residence time in the blending apparatus is of the order of 45 s. - 19 Once cooled, the product obtained is milled cryogenically in order to obtain a powder particle size of between 10 and 80 gm.

A composite material is thus produced, comprising successively: - a degreased, shot-blasted steel panel, 1.5 mm thick, - a layer of polyamide 12, 100 Mm thick.

The material thus described is subjected to the adhesiveness and spreading tests specified in 1.C.2) and l.C.3).

The results are listed in Table 1.

EXAMPLE 5 A - PREPARATION OF THE POWDER COMPOSITION kg of PA 11 powder, 0.6 kg of epoxy/ sulphonamide resin milled to an average particle size of 10 μη and 0.02 kg of fluidization agent are charged into a Henschel-type fast blender.

The PA 11 employed has an inherent viscosity of 0.90 and contains 13.8 % of additives, including 11.3 % of pigments and fillers and 2.5 % of antioxidant, antipitting and reducing agents.

The epoxy/sulphonamide resin has a weightaverage molecular mass Mw = 1,200 and a glass transition temperature Tg = 54°C.

The mixture is s.tirred for 100 s at a speed of 830 rev/min. The powder obtained can be applied as such. - 20 Β - APPLICATION The powder composition obtained under A is sprayed electrostatically onto a steel plate under the same conditions as those described in Example l.B.

C - CHARACTERISTICS OF THE MATERIAL 1) The material is a composite comprising successively: - a degreased and shot-blasted steel panel (1.5 mm thick), - a layer of powder composition such as described under A, 100 gm thick. 2) The material described in C.l) is subjected to adhesiveness and spreading tests as defined in Example 1.C.2) and 1.C.3).

The results obtained using the material described in C.l) are listed in Table I.

EXAMPLE 6 A composition consisting of 1/3 by weight of polyamide 12 and 2/3 of copolyamide 6/12, the PA 12 being encapsulated in the PA 6/12, and of various additives including 11.3 % of pigments and fillers and 0.7 % of antioxidant and reducing agents and of 3 % of epoxy/sulphonamide resin milled according to the characteristics given in Example 5 is sprayed electrostatically onto a degreased and shot-blasted steel panel under the same conditions as those of Example 5B.

A composite material is thus produced. - 21 comprising successively: - a degreased and shot-blasted steel panel, 1.5 mm thick, - a layer of polyamide 12 and 6/12, 100 gm thick.

The material described above is subjected to the adhesiveness and spreading tests such as defined in 1.C.2) and 1.C.3).

The results obtained are combined in Table I.

EXAMPLE 7 (COMPARATIVE) 1, A PA 11 powder with the same characteristics as those described in Example 5.A and with an average particle size of 35 gm is sprayed electrostatically onto a smooth degreased steel panel under the same conditions as those of Example l.B. 2) The material obtained is a composite comprising successively: - a smooth degreased steel panel (1.5 mm thick), - a layer of PA 11 powder, 100 gm thick. 3) The material described in 2) is subjected to an adhesiveness test such as defined in Example 1.C.2).

The adhesiveness results are combined in Table I.

EXAMPLE 8 (COMPARATIVE) 1) A powder composition based on PA 11 whose characteristics are identical with those described in - 22 Example 5.A and containing 13.5 % by weight of blocked phenolic resins is sprayed electrostatically onto a smooth degreased steel panel under the same conditions as those of Example l.B. 2) The material obtained is a composite comprising successively: - a smooth degreased steel panel (1.5 mm thick), - a layer Of powder composition such as 10 defined in 1) , 100 μπι thick. 3) The material described in 2) is subjected to the adhesiveness and spreading tests as defined in Example l.C.2) and 1.C.3).

The results are combined in Table 1.

EXAMPLE 9 The test of Example 5 is repeated under the same conditions using PA 11 powder with the same characteristics but containing different additives: A - the powder employed contains: - 99.25 % by weight of PA 11 - 0.75 % of additives (antioxidant agents, antipitting agent and fluidization agent).

B - The white-coloured powder employed contains 68.8 % by weight of PA 11, 29.5 % of fillers and 1.7 % of additives (antioxidant agent and antipitting agent).

C - The black-coloured powder employed contains 58.5 % by weight of PA 11, 39 % of fillers, 0.5 % of black pigment, 2 % of additives (antioxidant agent, antipitting agent, adhesion promoter).

D - The grey-coloured powder employed contains 85.3 % by weight of PA 11, 13.5 % of pigments and fillers and 1.2 % of additives (antioxidant agent, antipitting agent).

E - The yellow-coloured powder employed contains 67.4 % by weight of PA 11, 28.9 % of fillers, 1.7 % of colorants and 2 % of additives (antioxidant agent, antipitting agent, reducing agent).

The adhesiveness and spreading results obtained for tests A to E are combined in Table II.

EXAMPLE 10 The test of Example 5 is repeated under operating conditions which are identical by using greycoloured PA 11 powder containing 13 % by weight of additives including 11.4 % of pigments and fillers and 1.6 % of antioxidant, antipitting and reducing agent (10.A).

The following compositions also contain 0.2 kg (10.B), 0.6 kg (10.C) and 1 kg (10.D) of epoxy/sulphonamide resin respectively per 20 kg of PA 11 powder described above.

The influence of the quantity of epoxy/ sulphonamide resin on the performance of the polyamide compositions can be assessed from Table III. - 24 EXAMPLE 11 A - The powder composition obtained in Example 10 (Sample 10.C) is applied electrostatically onto various metal substrates under operating conditions which are identical with those described in Example l.B.

B - The powder composition obtained in Example 6 is applied electrostatically under the same conditions as in A.

C - By way of comparison, PA 11 powder with an 10 inherent viscosity of 0.90 is applied electrostatically and under the same conditions.

D - By way of comparison, a powder composition based on PA 11 with an inherent viscosity of 0.90 and containing 13.5 % by weight of blocked phenolic resins is applied electrostatically and under the same conditions.

The adhesiveness and spreading results obtained for Tests A to D are combined in Table IV.

TABLE I 1 1 ex ! 1 1 Class of Epoxy/sulphonamide resin Powder preparation Application type andi polarity Adhesiveness Spreading PA + additives (X by weight) la 3 4 3 dissolving ESi-Y IV 3 4 i 3 dissolving EXC+) 2a 3 4 3 dissolving ESC-) 2b 3 4 3 dissolving Esm 3a 4 4 3 melt-blending ESC-) 3b 3 4 3 melt-blending ESC+) 4a 3 3 3 melt-blending ESC-) 4b 3 3 3 melt-blending ESC+) 5a 4 4 3 drv mixing ESC-) 5b 4 4 3 drv mixing ESC+) 6a 4 4 3 drv mixing ESC-) 6b 4 4 3 drv mixing ESC+) 74 0 1 0 ESC-) 7V I 0 1 0 ESC+) 8a 2 3 13.5 X of ohenolic resins dry mixing ES(-) 8b 2 4 13.5 X of phenolic resins dry mixing ES(+) ES — electrostatic spraying TABLE II ϊ 1 'ex Class of Epoxy/sulphonamide resin 1 1 X by weight of additives 1 Application type and polarity Adhesiveness Spreading PA + additives (X by weight) 9A 4 4 3 0.75 ESi-Y 9A 2 4 i 3 0.75 ES(+) 9β 4 4 3 31.2 ESi-1 9P 4 4 3 31.2 ESi+1 9C 4 4 3 41.5 ES(-) 9C 4 4 3 41.5 ES(+) 9P 3 4 3 14.7 ES(-) ?D 3 4 3 14.7 ES(+) ?E 4 4 3 32.6 ESf-1 9E 4 4 3 32..6 ES(+) TABLE III . EX1 ..... 1 | Class of Epoxy/sulphonamide resin Appli* cation type and polarity Adhesiveness Spreading PA + additives (X by weight) 10A Γ 0 1 0 ESf-1 J.OA 0 1 I 0 ESf+) 1OB 3 3 1 ESf-1 1OB 2 2 1 ESf+) IOC 4 4 3 ES(-) IOC 4 4 3 ESf+) XOD 4 4 5 ESf-1 XOD 4 4 5 ESi±L TABLE IV ί- ADHESIVENESS CLASS SUBSTRATE EX 11.A EX 11.B EX 11.c EX 11.D Application type and polarity 1 ES(+) 1 f ES(-) ES(+) ES(-) 1 ES(+) 1 ES(-) ES(+) ES(-) cf2-chf decreased steel 1.5 2.5 4 4 0 0 2 2 shot-blasted decreased steel 4 3.5 4 4 1 1 2 2.5 iron phosphatetreated steel 3 3.5 4 4 00 1 1 zinc phosphatetreated steel 3 4 4 4 0 0 I 1 J 1 chromated aluminium 2 2.5 3.5 3.5 0 0 f 1 1 1 EXAMPLE 12 Powder of an average particle size of between 80 and 200 pm is placed in a fluidized bed dip-coating vessel. f This powder is fluidized by a compressed gas delivery under the porous sole of the vessel.

The shot-blasted steel substrate to be coated is preheated in a ventilated oven until it reaches a temperature of approximately 240-260°C.

The substrate is immersed in the bath of fluidized powder for 4 to 6 s and it is then taken out and allowed to cool to room temperature.

The powder employed is PA 11, white-coloured PA 11 and PA 12 (Sample A, B and C respectively) containing 0 % or 3 % of epoxy/sulphonamide resin with I a weight-average molecular mass Mw = 1,200 and a glass transition temperature Tg = 54*C.

The adhesiveness of the coatings produced is measured after 15 days in open air according to the test described in Example l.C.2).

The results obtained are combined in Table V.

TABLE V Epoxy/sulphonamide resin ADHESIVENESS PA + additives (X by weight) EX 12. A EX 12.B EX 12.C 0 Class 1 Class 1 Class 2 2: Class 3 Class 3 Class 3

Claims (19)

1. A powder thermoplastic composition which comprises a polyamide and/or a polyetheresteramide, and an epoxy/sulphonamide resin.

2. A composition according to Claim 1, in which the weight ratio of the epoxy/sulphonamide resin to the polyamide and/or to polyetheresteramide is from 0.5:100 to 20:100.

3. A composition according to Claim 2 in which the said weight ratio is from 2:100 to 7:100.

4. A composition according to any one of Claims 1 to 3 in which the polyamide is polyamide ll, polyamide 12, alone or mixed, or a copolymer of the monomers of polyamide 11 and/or polyamide 12.

5. A composition according to any one of Claims 1 to 4 in which the ratio of the number of sulphonamide groups to the number'of epoxide groups is from 0.5:1 to 1:1.

6. A composition according to any one of Claims 1 to 5 in which the particles have a size from 5/tm to 1mm.

7. A composition according to Claim 1 substantially as described in any one of Examples l to 12.

8. Process for the preparation of a composition as claimed in any one of Claims 1 to 7 which comprises: dissolving the epoxy/sulphonamide resin in a suitable. solvent, adding the polyamide and/or polyetheresteramide as a powder, and evaporating off the solvent and screening or milling the mixture obtained to the desired particle size.

9. Process for the preparation of a composition as claimed in any one of Claims 1 to 7, in which the 5 constituents are melt-blended and are then milled to the desired particle size.

10. Process for the preparation of a composition as claimed in any one of Claims 1 to 7, in which the constituents of the composition, which are milled into powder 10 form beforehand, are mixed dry.

11. Process for the preparation of a composition as claimed in any one of Claims 1 to 7 which comprises polymerising the monomers of polyamide and/or of polyetheresteramide in the presence of the epoxy/sulphonamide 15 resin.

12. Process according to any one of Claims 8 to 11 substantially as described in any one of Examples 1 to 12.

13. A composition as defined in Claim 1 whenever prepared by a process as claimed in any one of Claims 8 to 20 12.

14. Use of a powder composition as claimed in any one of Claims 1 to 7 and 13 for coating a metal substrate.

15. Use according to Claim 14 in which the 25 composition is applied by electrostatic spraying.

16. Use according to Claim 15 in which the weight ratio of the epoxy/sulphonamide resin to the polyamide and/or polyetheresteramide is from 1.5:100 to 7.5:100.

17. Use according to Claim 14 in which the composition is applied by fluidized bed dip-coating.

18. Use according to Claim 17 in which the 5 weight ratio of the epoxy/sulphonamide resin to the polyamide and/or polyetheresteramide is from 1:100 to 5:100.

19. Use according to Claim 14, 17 or 18 substantially as described in any one of Examples 1 to 12.