Polymers vary widely in their resistance to burning. Some, such as the polyolefins, polystyrene, polyalkyl acrylates and methacrylates, and the like, burn readily. Polytetrafluoroethylene, polyvinylidene chloride and polyvinyl chloride, on the other hand, have a rather high resistance to burning. In any event, it obviously is highly desirable that, for certain applications, a polymer should have a high degree of flame retardance so that it will meet the requirements of various building codes or that it will meet safety standards imposed on toys, carpeting, drapery materials, automotive applications, etc.
The treatment of these more flammable polymers to increase their resistance to burning is well known; such treatment generally has involved the incorporation in the polymer composition of substantial proportions of antimony oxide, halogenated hydrocarbons and low molecular weight phosphate esters. Ordinarily, though, the effective use of these and other additives has required their presence in such high concentrations as to adversely affect the desirable properties of the polymer. Thus, such desirable properties as hardness, clarity, strength, elasticity, etc., are diminished significantly by the presence of large amounts of a flame-retardant chemical.
An alternative approach is to incorporate char-forming additives which, in the presence of flame, form a thick, non-flammable insulating barrier to protect the substrate polymer. One such intumescent or char-forming system, disclosed in U.S. Pat. No. 3,936,416, employs a combination of melamine pyrophosphate and a polyol. This additive combination is effective in providing a non-burning, non-dripping polypropylene composition. Preparation and compounding with these materials can be difficult. During preparation, however, the additive combination must be degassed in order to avoid foaming during the compounding with polypropylene and/or in subsequent molding operations. In addition, the additive as obtained has a substantial tan or brown color which imparts an undesirable hue to the polypropylene compositions, and the additive is obtained as a hard, solid mass which is pulverized with some difficulty for compounding.
The pentate, i.e., pentaerythritol diphosphate, salts of amino-s-triazines are effective intumescent flame retardant additives for polyolefins, providing compositions that are self-extinguishing, intumescent and non-dripping. The additives are dry, white, powdery solids and are readily compounded with polyolefins to provide compositions which have excellent color and which are readily processed without apparent foaming or decomposition. The preparation of these compounds is disclosed in U.S. Pat. No. 4,154,930, and their use in polyolefin compositions is disclosed in U.S. Pat. No. 4,201,705 and U.S. Pat. No. 4,253,972.
The preparation of these pentate salts is accomplished by the reaction of dichloropentate, melamine and water. A mixture of these three is heated briefly to cause formation of the desired salt. The salt product is said to be particularly useful as a flame-retardant additive in polymers when used in combination with a polyol such as pentaerythritol.