Pulverulent coating materials

#This invention relates to pulverulent coating materials, which cure at temperatures above the melting point, based on saponified ethylene-vinyl acetate copolymers and additives which cross-link, and also relates to the coatings which are prepared therefrom.

#Saponified ethylene-vinyl acetate copolymers which, before saponification, contain polymerised units of ethylene and vinyl acetate in molar ratios of from 2:1 to 20:1, and which are saponified to a hydrolysis level of more than 50%, are suitable for coating articles made of metal, ceramics, glass, plastics and wood according to various known methods for immersion and spray coating processes, e.g. whirl sintering, flame spraying or electrostatic powder spraying process (EPS). The use of these coating materials is admittedly restricted to the case where dimensional stability at temperatures above the softening or melting point of the coatings produced therefrom is unnecessary. In many cases, therefore, it is impossible to use the coating materials, e.g. for coating metal pipes which are exposed to hot liquids or through which materials of this type are conveyed, or for coating metal components which are located near hot objects or machine parts, or also for coating multipath glass bottles which have to endure being washed at relatively high temperatures (from 70.degree. to 90.degree. C.).

#It is known that generally by cross-linking copolymers of this type, but particularly by adding compounds which are able to react in a bi- or polyfunctional manner with the hydroxyl groups contained in the polymer, infusible polymer coatings may be obtained. Admittedly, there is a prerequisite that these compounds which cross-link only exhibit their effect at higher temperatures, i.e. substantially above the melting point of the polymer, that is that they may be worked into the polymer without becoming actively cross-linking. Also, during storage of the coating powder, they should not become ineffective in the presence of air or atmospheric moisture even after relatively long periods of time. The following have hitherto been suggested as cross-linking additives: di- and polyfunctional carboxylic acids, carboxylic acid anhydrides, carboxylic acid chlorides and isocyanates and also those compounds which release compounds containing isocyanate groups during thermal decomposition in the temperature range of from about 100.degree. to 250.degree. C.

#560 g of isophorone diisocyanate are reacted with 36 g of methanol with the addition of 0.1 g of tin di-2-ethyl-hexoate as the catalyst, in 2000 ml of xylene at 45.degree. C. within 2 hours. After adding 6.68 g of 1-methyl-phospholine oxide to the reaction mixture, it is heated to 137.degree. C. until an isocyanate band can no longer be detected in the infrared spectrum. After removing the solvent in a rotary evaporator in a water jet vacuum, a tough resin is obtained.

#2500 g of an ethylene-vinyl acetate copolymer, having a content of 32.0% by weight of vinyl acetate which corresponds to an ethylene-vinyl acetate molar ratio of 6.5:1, are dissolved in 250 g of dry toluene in a vessel equipped with a stirrer at approximately 80.degree. C., and a solution of 25 g of sodium methylate dissolved in 1300 g of methanol is added to the solution which is cooled to approximately 60.degree. C. The reaction mixture is boiled for 1 hour under reflux and a total of 1200 ml of distillate are then distilled off using a packed column at a rate of 24 parts by volume/hour. The transesterification catalyst is then decomposed by adding 2.5 parts by weight of water. The solution of 250 g of the cross-linker prepared in part A of this Example, dissolved in a three-fold weight of toluene, is added to the clear solution thus obtained. After homogeneously mixing the two solutions, the warm solution is suspended in water at approximately 55.degree. C. according to the process described in German Offenlegungsschrift No. 2,611,548 and the clinging organic solvent mixture is removed by means of steam distillation at a reduced pressure of approximately 100 mm Hg. The material obtained in the form of a coarse powder is filtered off and dried under reduced pressure at from 50.degree. to 60.degree. C. The product obtained in a quantity of 2190 g is ground and is divided up by sieving into grain fractions of <80 .mu.m, from 80 to 200 .mu.m and from 200 to 500 .mu.m grain size. The grain fraction of from 80 to 200 .mu.m in diameter of the obtained product is filled into a fluid bed and a one liter glass bottle which has been previously heated to 250.degree. C. in a heating chamber is immersed for seven seconds into the whirled powder. The powder now melts onto the bottle in the form of an approximately 400 .mu.m thick coating. The initially slightly cloudy and brittle layer, after being heated for 15 minutes at 190.degree. C. produces a glass-clear, smooth, firm and elastic coating which, even at temperatures above 100.degree. C. is not sticky and has a substantially improved flexibility and strength and also an improved adhesiveness to glass compared with the coating which was obtained by using the cross-linker-free coating powder of the same composition according to Comparative Example 1.

#222 g of 1-isocyanatomethyl-5-isocyanato-1,3,4-trimethyl-cyclohexane (isophorone diisocyanate) and 0.4 ml of a mixture 1-methyl-1-phospha-2-cyclopentene-1-oxide and 1-methyl-1-phospha-3-cyclopentene-1-oxide are heated under nitrogen at 160.degree. C. until 1 liter of carbon dioxide is produced within 2 hours. The liquid product is cast onto a metal sheet where it solidifies into a readily pulverisable composition at a temperature below 50.degree. C.