ABS product with improved fire retardancy

1. A process for the preparation of a graft polymer A) having bimodal particle size distribution made from, based on A),

a1) from 40 to 90% by weight of an elastomeric particulate graft base a1), obtained by polymerization of, based on a1),

a11) from 75.5 to 89.5% by weight of at least one conjugated diene,

a12) from 10.5 to 24.5% by weight of at least one vinylaromatic monomer and

a2) from 10 to 60% by weight of a graft a2) made from, based on a2),

a21) from 65 to 95% by weight of at least one vinylaromatic monomer,

a22) from 5 to 35% by weight of acrylonitrile, and

a23) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer, the process comprising steps (i), (ii) and (iii):

(i) emulsion polymerization of monomers a11) and a12) to obtain a graft base a1),

(ii) partial agglomerization of the graft base a1), and

(iii) emulsion polymerization of graft monomers a21), a22) and optionally a23) onto the graft base obtained in step (i) or (ii),

wherein in step (i) the graft base a1) is obtained by emulsion polymerization of an initial seed of from 3 to 8% by weight of vinylaromatic monomer a12),—each based on a1)—followed by addition and statistical copolymerization of the remaining vinylaromatic monomer a12) together with the entire amount of conjugated diene a11).

2. A process according to claim 1 , wherein from 5 to 8% by weight of vinylaromatic monomer a12) is used in the initial seed.

3. A graft copolymer A) obtained by the process according to claim 1 .

4. A thermoplastic molding composition comprising components A) to G):

A) from 5 to 80% by weight of a graft polymer A) according to claim 3 ,

B) from 20 to 95% by weight of a thermoplastic polymer B) having a viscosity number VN (determined according to DIN 53726 at 25° C., 0.5% by weight in dimethylformamide) of from 50 to 120 ml/g, made from, based on B),

b1) from 69 to 81% by weight of at least one vinylaromatic monomer,

b2) from 19 to 31% by weight of acrylonitrile, and

b3) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer and

C) from 0 to 50% by weight of a thermoplastic polymer C) having a viscosity number VN of from 50 to 120 ml/g made from, based on C),

c1) from 69 to 81% by weight of at least one vinylaromatic monomer,

c2) from 19 to 31% by weight of acrylonitrile and

c3) from 0 to 30% by weight of at least one other monoethylenically unsaturated monomer,

where components B) and C) differ in their viscosity numbers VN by at least 5 units [ml/g], or in their acrylonitrile content by at least 5 units [% by weight], or in both characteristics, viscosity number VN and acrylonitrile content, by at least 5 units and

D) from 0 to 75% by weight of a thermoplastic polymer D) made from, based on D),

d1) from 63 to less than 69% by weight of at least one vinylaromatic monomer,

d2) from more than 31 to 37% by weight of acrylonitrile,

d3) from 0 to 40% by weight of at least one other monoethylenically unsaturated monomer and

E) from 0 to 50% by weight of a thermoplastic polymer E) made from, based on E),

e1) from 4 to 96% by weight of at least one vinylaromatic monomer,

e2) from 4 to 96% by weight of at least one monomer selected from the group consisting of methyl methacrylate, maleic anhydride and maleimides, and

e3) from 0 to 50% by weight of acrylonitrile,

where the polymer E) is different from the polymers B) and from C) and D) if they are present

F) from 0 to 50% by weight of additives F, and

G) from 0 to 75% by weight of polymer G) selected from the group of polycarbonates, polyesters, polyester carbonates and polyamides, and

wherein the entire components A) to G) give 100% by weight.

5. A thermoplastic molding composition according to claim 4 wherein based on a1) the vinylaromatic monomer a12) is used in an amount of from 12 to 22% by weight.

6. A thermoplastic molding composition according to claim 4 comprising components A), B) and if present C) to G) in the following amounts, based on the total weight of the molding composition:

A) 10 to 70% by weight,

B) 30 to 90% by weight,

C) 0 to 40% by weight,

D) 0 to 40% by weight,

E) 0 to 40% by weight,

F) 0 to 45% by weight, and

G) 0 to 70% by weight,

where the entire components A) to G) give 100% by weight.

7. A thermoplastic molding composition according to claim 4 comprising component G) in an amount of from 0.1 to 75% by weight, based on the total weight of the molding composition.

8. A molding or a shaped article produced from thermoplastic molding composition according to claim 4 .

9. A method of producing a molded article, comprising the step of molding composition according to claim 4 to form a molded article selected from the group of a sheet, a semifinished product, a foil, a fiber, or a foam.

10. A graft copolymer A) according to claim 3 , wherein based on a1) the vinylaromatic monomer a12) is used in an amount of from 14 to 21% by weight.