NL8400921A - PROCESS FOR MANUFACTURING MOLDING MOLDINGS FROM THERMO-CURING MATERIAL WITH AN IMPROVED FINISH. - Google Patents

Description

GL / WP / ag DSM RESINS B.V.

Inventors: Andreas N. J. Verwer of Beek (1.) -1- PN 3545

METHOD FOR MANUFACTURING FORMS FROM THERMQ-CURING MATERIAL WITH AN IMPROVED AE COATING

The invention relates to a method for manufacturing molded parts from thermosetting material with an improved finishing layer, in particular with a finishing layer containing melamine resin.

It is known, for example from Japanese patent publication 5 Sho 57-39925, to produce moldings from thermosetting material with a scratch-resistant finishing layer by applying and curing a melamine resin-containing layer on the surface of a press mold, and curing -pressing and curing a polyester material in the press mold thus coated.

However, the process has the disadvantage that reaction water is released when the resin cures. As a result, the thickness of the layer to be applied is considerably limited, so that various operations are necessary to obtain a desired layer thickness.

The object of the invention is to obviate the drawback of this known method by adding a water-binding agent to the melamine-containing resin which is applied to the surface of the press mold.

The melamine resins to be used according to the invention are in particular aldehyde-melamine resins with a molar ratio of aldehyde: melamine between 1.5: 1 and 5: 1, preferably between 1.5: 1 and 3.5: 1.

The aldehyde is preferably formaldehyde, but other aldehydes can also be used, such as acetaldehyde, furfural, trimethylolacetaldehyde, acrolene, benzaldehyde, glyoxal, phthalaldehyde, terephthalaldehyde.

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The melamine resins can be prepared in the usual manner, for example, by reaction of melamine and aldehyde in an aqueous alkaline medium, at a concentration of 50-70% by weight of solutes, in molar ratios as indicated above.

The pH of the reaction mixture is preferably adjusted between 8 and 10 and the temperature of the reaction mixture is preferably between 85 ° and the boiling point.

It is further also possible to add one or more compounds to the resin as a modifier before, during or after the reaction in order to improve the properties of the resin and / or the final product. Suitable modifiers are compounds such as caprolactam, diethylene glycol and other glycols, glycol ethers, sugars, sorbitol, polysaccharides, alcohols, acid amides, sulfamides such as toluene sulfonamide, urea, thioreum, polyureas, guanidine, silicates, urethanes, aliphatic amines, benzol, amines, amines -amide and other compounds used by experts in this field. Modification can also take place in such a form that the resin is reacted with alcohols such as e.g. methanol or butanol is partially etherified.

The method according to the invention is preferably applied by applying the melamine resin together with the water binding agent in powder form.

A resin solution obtained as described above is therefore preferably powdered, in particular by spray drying. This produces a fine powder suitable for mixing with the water binding agent.

The water binding agent is preferably used in an amount of 0-50 wt% relative to the melamine resin, most preferably in an amount of 5-30 wt%. The water-binding agent can for instance be selected from various gypsum and cement types, in particular aluminum cement, cement clinker, etc., from other fast-water-binding products such as C3A (mixture of calcium oxide and aluminum trioxide), anhydrides, molecular sieves, etc.

The method according to the invention is very suitably applicable in the so-called powder or pre-in-mold coating method, in which 84 0 0 9 2 t - ·· - *

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The powder composition is applied to a mold surface at such a temperature that the powder melts and. cured, after which a thermosetting press composition (such as DSM, SMC, BMC, etc.) is pressed into the coated mold, optionally after the application of an intermediate layer, and this is cured, in particular a press composition of unsaturated polyester material.

Example 1

1096 grams of melamine, 319 10 grams of water and 38.4 grams of caprolactam are added to 1480 grams of 30% formalin with a pH of 9.3 in a reactor provided with a heating jacket. This mixture is heated with stirring using hot water or steam and the reaction takes place at 94 ° C. After a reaction time of more than 2 hours, the cloud point is reached and the reaction is continued for more than half an hour while observing the water tolerance (number of grams of water which cause permanent turbidity in one gram of resin at 15 20 ° C) until a water tolerance of about 1.3 is reached. The resin is then cooled and during cooling 54.8 grams of diethylene glycol and 21.9 grams of thiourea are added. The resin solution now obtained is spray dried and then mixed with pigment 20 and 20 weight percent aluminum cement. The powder obtained can can be sprayed electrostatically as a powder in mold coating in a mold heated to 150 ° C without bubbles being formed by evaporation of the eluding reaction water.

EXAMPLE 2 882 g of melamine and 35 g of p-toluenesulfonamide are added to 1400 g of 30% formalin with a pH of 9.5 in a reactor provided with a heating jacket. After a reaction time of more than 2 hours, the cloud point is reached and the reaction is continued for more than half an hour while observing the water tolerance (number of grams of water that cause permanent turbidity in one 30 grams of resin at 20 ° C) until a water tolerance of about 1.3 has been reached. The resin is then cooled and 42 g of trioxytol is added during cooling. The resin solution now obtained is spray dried and then mixed with pigment and 20% by weight ground Portland cement clinker. The powder obtained can be electrostatically sprayed as a powder in mold coating in a mold heated to 150 ° C without blowing being formed by evaporation of the decomposing reaction water.

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Claims (6)

1. A method for manufacturing molded parts from thermosetting material with a melamine resin-containing finishing layer, by applying and curing at least one melamine resin-containing layer on at least a part of the surface of a press mold, and subsequently to press and harden a thermosetting material in the press mold thus coated, characterized in that the melamine resin is used together with a water-binding agent · 2. Process according to claim 1, characterized in that the melamine resin is applied to the mold surface together with the water-binding agent in powder form. 3. Process according to claim 2, characterized in that the powder composition is applied to a mold surface at a temperature such that the powder melts and hardens. 4. A method according to any one of claims 1-3, characterized in that a pressed composition of unsaturated polyester is pressed and cured in the coated mold, optionally after the application of an intermediate layer. A method according to any one of claims 1-4, characterized in that the water binding agent is selected from gypsum, cement, C3A (calcium 20 oxide / aluminum trioxide mixture) and molecular sieves. A method according to any one of claims 3-5, characterized in that the powder composition consists of a mixture of a melamine resin powder and water binding agent in powder form. 8400921