The production of products pet preform manufacturers of this type is however expensive, and difficulties are frequently involved in that precise production conditions have to be maintained; and,furthermore, certain properties, for instance, crystallisability, can be impaired. There have already been used for specific thermoplastic materials additives which for many purposes are satisfactory. The flame resistant agent is added to the polymer at any suitable stage of production by a simple mixing together of the constituents, whereby this flame-resistant agent must not react chemically with the polymer. 3,997,510 noninflammable thermoplastic polyesters formedfrom terephthalic acid, isophthalic acid or aliphatic dicarboxylic acids and aliphatic diols, which contain halogenated benzimidazolones incorporated by condensation.Other products effective in small amounts by virtue of a high halogen content, such as hexabromobenzene, pentabromotoluene and hexabromobiphenyl, as well as decabromobiphenyl known from the British Pat.

As areinforcing filler are used especially glass fibres, for example in an amount of 5 to 60 percent by weight, particularly 10 to 40 percent by weight, relative to the total amount of material. 3,403,036, have an excellent flame-resistant action with only slight impairment of the physicalproperties of the polymer. The demands made of such substances having a fire-retarding action are however high. The polyesters thus obtained have a surprisingly high level of heat resistance. The adding of non-reactive, monomeric or polymeric substances having a fire-retarding action to plastic mould materials is known. Substances which satisfy all these requirements are not known, for the reason in particular that relatively large amounts of substances of this kind have to be added to the polymer for the flame retarding action to be extended to the whole of theplastics material. The plastic mould materials according to the invention are either already shaped articles, for example when duroplasts are concerned, or materials which are to be moulded by customary methods, such as by casting, injection moulding, and soforth.

In order to avoid the stated disadvantages, reactive flameproofing agents are incorporated into the polymers during their production. No. For example, the addition of polyvinyl chloride to acrylonitrile-butadiene-styrene terpolymers enables a noninflammableplastics materials having high impact strength and good dimensional stability under heat to be obtained. It has now been shown that the addition of halogenated benzimidazolones to plastics materials to form a purely mechanical mixture leads to the obtainment of products which have properties as good as those of products made from plastics materialswithout an additive, and which at the same time are flame-resistant. The substances need to becolourless, easy to mix in, compatible with the polymer, and stable to heat and to light, and should moreover have no unfavourable effect on the physical properties of the plastics material; furthermore, they must not migrate and have to be nontoxic. 1,298,880, are indeed sufficientlythermostable, but they tend to migrate at high temperatures.

Also additions of low-molecular halogenated compounds of cycloaliphatic structure, such as the endocyclic compounds known from the U.S.S. Pat. No. The plastic mould materials can moreover contain other customary fillers, in particular also reinforcing fillers, for example pigments, optical brighteners, crystallisation-promoting agents, lubricants, plasticisers, and so forth. These compounds too however have inadequate heat stability for the production of plastics requiring the application of high temperatures.Flame resistant plastic mould material formed from a polymer, preferably a thermoplast, and a halogenated benzimidazolone or halogenated benzimidazolone derivative. There are known for example from the U. The impairment of the physical properties can in this way be reduced to a minimum. On the other hand, the instability to heat limits the use of this mixture in the injection moulding process.