Flameproof styrenic resin composition

1. A flame retardant styrenic resin composition comprising:

(A) 70 to 99.5 parts by weight of a rubber-modified polystyrene resin; and

(B) 0.5 to 2 parts by weight of a ring-shaped alkyl phosphonic acid ester compound represented by the following formula (I):

wherein R 1 and R 2 are independently of each other C 1 -C 4 alkyl and x is 0 or 1 and wherein the concentration of polyphenylene ether in the composition is 0.

2. The flame retardant styrenic resin composition as defined in claim 1 , which further comprises up to 50 parts by weight of an additive selected from the group consisting of plasticizers, heat stabilizers, anti-oxidants, light stabilizers, compatibilizers, pigment, dye and/or inorganic filler per 100 parts by weight of rubber modified styrenic resin (A).

3. A flame retardant styrenic resin composition comprising:

(A) 70 to 99.5 parts by weight of a base resin prepared by blending a rubber, and styrene monomer and polymerizing the blend, and

(B) 0.5 to 2 parts by weight of a ring-shaped alkyl phosphonic acid ester compound represented by the following formula (I):

wherein R 1 and R 2 are independently of each other C 1 -C 4 alkyl and x is 0 or 1 and wherein the concentration of polynbenylene ether in the composition is 0.

4. A flame retardant styrenic resin composition according to claim 1 wherein (B) is methyl-bis (5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5y1) methyl methyl phosphonic acid ester P-oxide or methyl-bis(5-ethyl-2-methyl-1,3,2-dioxaphosphorinan-5yl) phosphonic acid ester P, P′-dioxide or a mixture thereof.

5. A flame retardant styrenic resin composition according to claim 1 wherein the particle size of the rubber is from 0.5 to 2.0 μm.

6. A flame retardant styrenic resin composition according to claim 3 herein the particle size of the rubber is from 0.5 to 2.0 μm.