U.S. Pat. No. 5,096,950 discloses the co-use of certain NOR (N-alkoxy) hindered amines with a brominated Sb2O3-containing flame retardant in polypropylene.
U.S. Pat. No. 5,393,812 discloses polyolefin compositions which are made flame retardant by a combination of a halogenated hydrocarbyl phosphate or phosphonate ester flame retardant in combination with a alkoxyamine functional hindered amine.
U.S. Pat. No. 5,844,026 discloses polyolefin compositions comprising certain NOR hindered amines and certain traditional flame retardants.
U.S. Pat. No. 6,117,995 discloses that certain N-alkoxy hindered amines may be used as flame retardants for organic polymers.
U.S. Pat. No. 6,271,377 discloses polyolefin compositions that comprise N-hydroxyalkoxy hindered amines and a halogenated flame retardant.
U.S. Pat. No. 6,309,987 and equivalent WO 99/54530 teach polyolefin non-woven flame retardant fabrics that comprise N-alkoxyamines.
A Revolutionary UV Stable Flame Retardant System for Polyolefins—R. Srinivasan, A. Gupta and D. Horsey, Int. Conf. Addit. Polyolefins 1998, 69-83, teaches polyolefins comprising certain NOR hindered amines with halogen and phosphorus containing traditional flame retardants.
Advances in a Revolutionary Flame Retardant System for Polyolefins—R. Srinivasan, B. Rotzinger, Polyolefins 2000, Int Conf Polyolefins 2000, 571-581, teaches polyolefins comprising certain NOR hindered amines with brominated and phosphorus containing flame retardants.
EP 0792911 A2, discloses polyolefin compositions that comprise alkoxyamine functional hindered amines and tris(trihalogenopentyl) phosphate flame retardants.
WO 99/00450, copending U.S. application Ser. Nos. 09/502,239, filed Nov. 3, 1999, and 09/714,717, filed Nov.16, 2000, disclose the use of certain N-alkoxy hindered amines as flame retardants.
EP 1104766 discloses cross-linked phenoxyphosphazene compounds as flame retardants for synthetic resins.
The flame retardant (FR) market today is comprised of products which function to interfere with the combustion process by chemical and/or physical means. Mechanistically these FRs have been proposed to function during combustion of an article in either the gas phase, the condensed phase or both. The organohalogens are proposed to generate halogen species (e.g. HX) which interferes in the gas phase with free radical organic “fuel” from the polymer substrate. Synergists are proposed to react with HX to form additional chemical species with interfere with combustion in the gas phase, such as reaction of antimony oxide with HX to form antimony halide and water vapor. Antimony compounds such as antimony trioxide also act as a radical scavenger forming antimony halides. Thus, it can inhibit the propagation of the fire.
Although antimony compounds are efficient in terms of cost performance, it recently raised a lot of concern because of the toxicity of the byproducts which are formed during combustion in the presence of a halogenated flame retardant. Antimony oxides often contain trace amounts of arsenic compounds which are suspected carcinogens. Because of these ecological concerns, there is a motion to replace antimony trioxide in the present commercial flame retardant applications. However, it is very difficult to find an effective synergist which is both enviromentally friendly and efficient as far as the cost performance is concerned.
Another reason to add flame retardant additives is to prevent dripping during the application of the fire. Dripping during combustion is the process of the separation of parts of the polymer from the matrix in the shape of droplets. Most often, the droplets are flaming and are imposing tremendous danger for fire spread. It is a common measure to add fillers such talc in large amounts to the polymer, with some negative consequences on the mechanical properties. Other fillers sometimes used include calcium carbonate, magnesium carbonate, zinc borate, silicates, silicones, glass fibres, glass bulbs, asbestos, kaolin, mica, barium sulfate, calcium sulfate, metal oxides, hydrates and hydroxides such as zinc oxide, magnesium hydroxide, alumina trihydrate, silica, calcium silicate, magnesium silicate.
It has been found that polymers with good flame retardant properties are prepared when a sterically hindered amine of the nitroxyl, hydroxylamine or alkoxyamine class is added thereto together with a phosphazene flame retardant. With this combination, antimony compounds and fillers may be largely reduced or replaced. As the instant nitroxyl, hydroxylamine and alkoxyamine compounds are active as stabilizers, the polymer compositions of the invention are efficiently protected from the deleterious effects of light, oxygen and/or heat.