Melamine resins, a process for their preparation and their use a

Details Melamine resins, a process for their preparation and their use a Melamine resins, a process for their preparation and their use a

1982-09-30

1984-02-07

Phynes, Lucille M.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From aldehyde or derivative thereof as reactant

524593, 525398, 528265, C08G 1230

Patent

active

044304943

DESCRIPTION:

BRIEF SUMMARY
The invention relates to melamine resins which have a molar ratio of melamine to formaldehyde of 1:(1.27 to 0.7), which have been modified with glycol ethers and/or p-toluenesulfonamide and which can be diluted with water to a limited extent, to a process for their preparation and to their use for the production of molding compositions, and also to the molding compositions produced from the resins.
Melamine resins are prepared by reacting melamine and formaldehyde. Owing to the property of curing irreversibly, they have a wide industrial use, for example for the production of curable molding compositions, decorative laminates, textile finishing agents, lacquers and glues.
Moldings of a very wide variety of types, such as, for example, kitchen crockery, trays, casings for telephones, radios, clocks and television sets, buttons, valves, electrical insulation components and the like are prepared from curable molding compositions by the action of mechanical forces with a certain temperature range. Low values of shrinkage during processing and after-shrinkage must be maintained in the production of fairly large moldings, in order to enable the moldings to be processed satisfactorily and to prevent the moldings subsequently cracking. Requirements of this type are met, for example by phenolic resin molding compositions, but particularly by polyester resin and epoxide resin molding compositions. In some cases the resins required for their production are extensive and the moldings produced therefrom in some cases still have undesirable thermoplastic properties or are not adequately resistant to solvents or heat. Moldings which are used in the electrical industry, such as, for example, switches, knobs, fuse holders, chassis components, mountings for transistors, integrated circuits and the like must, in addition, be track-resistant to an adequate extent.
Molding compositions which have been prepared on the basis of customary melamine resins display higher figures of after-shrinkage during curing than do, for example, molding compositions based on phenolic resins and particularly on polyester or epoxy resins. Hitherto, therefore, it has only been possible to use customary melamine resins for the production of molding compositions or moldings in cases where the tolerances to be maintained have been large and the heating slight. Although it has been known that subsequent shrinkage can be decreased in the production of molding compositions by using high proportions of special inorganic fillers for example hydrated aluminum oxide (compare German Offenlegungsschrift No. 2,356,298), ground minerals and the like, in most cases it has then been necessary to accept poorer flow properties when processing the molding compositions.
Electrolyte-free melamine resins from which moldings having a high electrical resistance and a high electrical tracking resistance can be produced, are known from German Offenlegungsschriften Nos. 2,603,767 and 2,603,768. However, the shrinkage during processing and after-shrinkage of the molding compositions produced using these known melamine resins is still too great for the production of fairly large moldings.
British Patent Specification No. 673,742 discloses melamine resins which are prepared by subjecting melamine and formaldehyde to a condensation reaction in a molar ratio of 1:(1 to 1.7) in aqueous solution at a pH value of 7 to 11, and from which compression molding compounds having shrinkage during processing of only 0.69% can be produced.
German Offenlegungsschrift No. 2,824,473 discloses partially etherified liquid melamine resins having a molar ratio of melamine to formaldehyde of 1:(1.25 to 1.0), from which it is possible to prepare molding compositions which exhibit only a very small shrinkage during processing and after-shrinkage. Glycols and glycol ethers are employed in amounts of more than 26% by weight, for example 34 to 43% by weight, relative to the solids content of the resin, in the preparation of these resins. From their preparation, therefore, the finished liquid resins stil

REFERENCES:
patent: 4183832 (1980-01-01), Meunier et al.
patent: 4271286 (1981-06-01), Michel et al.
patent: 4303561 (1981-12-01), Piesch et al.
patent: 4369286 (1983-01-01), Czepel et al.

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