Low-emission, tribologically modified polyoxymethylene molding compositions and moldings produced therefrom

1. A molding or molding composition composed of polyoxymethylene, comprising

(A) from 0.1 to 50% by weight of a tribological modifier selected from the group consisting of polytetrafluoroethylenes, molybdenum sulfides, calcium carbonates, graft copolymers containing an olefin polymer graft base and at least one polymer grafted to the graft base selected from polyvinyls and polyesters, graft copolymers containing an elastomeric polydiene-based core and a hard graft envelope comprising a (meth)acrylate and/or (meth)acrylonitrile, ultrahigh-molecular-weight polyethylene powders, stearyl stearates, ester waxes composed of a fatty acid and of a monohydric alcohol, polyethylene waxes, amide waxes; and mixtures thereof,

(B) from 0.01-0.5% by weight of a cyclic stabilizer which contains at least one nitrogen atom in the ring, and

(C) from 0.05 to 1% by weight of at least one ester composed of a polyhydric alcohol and of at least one (C 24 -C 32 ) fatty acid;

wherein the molding or a molding produced from the molding composition comprises a formaldehyde emission of less than 30 mg/kg, measured according to VDA 275 testing standard.

2. The molding or molding composition as claimed in claim 1 , which further comprises up to 0.5% by weight of a metal salt of a (C 10 -C 32 ) fatty acid (component D).

3. The molding or molding composition as claimed in claim 1 , wherein component (C) is a mixture comprising

(C1) x % by weight of an unsaponified ether composed of a polyhydric alcohol and of at least one (C 24 -C 32 ) fatty acid, and

(C2) y % by weight of a partially saponified ester composed of a polyhydric alcohol and of at least one (C 24 -C 32 ) fatty acid,

where x is greater than 0.01% by weight, y is smaller than 0.99% by weight and the total of x and y is smaller than 1.0% by weight.

4. The molding or molding composition as claimed in claim 3 , wherein the value of x and y, independently of the other, is from 0.03% by weight to 0.5% by weight.

5. The molding or molding composition as claimed in claim 1 , which comprises up to 1.0% by weight of an antioxidant.

6. The molding or molding composition as claimed in claim 1 , which comprises from 0 to 1% by weight of a metal salt of a (C 1 -C 9 ) carboxylic acid, from 0 to 1.0% by weight of at least one other stabilizer from the group of the benzotriazole derivatives or benzophenone derivatives or aromatic benzoate derivatives, and from 0 to 0.5% by weight of a sterically hindered amine (HALS).

7. A process for production of molding compositions and of molding composed of polyoxymethylene, where a tribological modifier selected from the group consisting of polytetrafluoroethylenes, molybdenum sulfides, calcium carbonates, graft copolymers containing an olefin polymer graft base and at least one polymer grafted to the graft base selected from polyvinyls and polyesters, graft copolymers containing an elastomeric polydiene-based core and a hard graft envelope comprising a (meth)acrylate and/or (meth)acrylonitrile, ultrahigh-molecular-weight polyethylene powders, stearyl stearates, ester waxes composed of a fatty acid and of a monohydric alcohol, polyethylene waxes, amide waxes; and mixtures thereof, and a stabilizer system comprising

from 0.01-0.5% by weight of a cyclic stabilizer which contains at least one nitrogen atom in the ring, and

from 0.05 to 1% by weight of at least one ester compound of a polyhydric alcohol and of at least one (C 24 -C 32 ) fatty acid is admixed with the polyoxymethylene;

wherein the molding or a molding produced from the molding composition comprises a formaldehyde emission of less than 30 mg/kg, measured according to VDA 275 testing standard.

8. A process for reduction of formaldehyde emission from polyoxymethylene molding compositions or from polyoxymethylene moldings, comprising treating the polyoxymethylene molding compositions or the polyoxymethylene moldings with a tribological modifier selected from the group consisting of polytetrafluoroethylenes, molybdenum sulfides, calcium carbonates, graft copolymers containing an olefin polymer graft base and at least one polymer grafted to the graft base selected from polyvinyls and polyesters, graft copolymers containing an elastomeric polydiene-based core and a hard graft envelope comprising a (meth)acrylate and/or (meth)acrylonitrile, ultrahigh-molecular-weight polyethylene powders, stearyl stearates, ester waxes composed of a fatty acid and of a monohydric alcohol, polyethylene waxes, amide waxes; and mixtures thereof, and a stabilizer system comprising

from 0.01-0.5% by weight of a cyclic stabilizer which contains at least one nitrogen atom in the ring, and

from 0.05 to 1% by weight of at least one ester compound of a polyhydric alcohol and of at least one (C 24 -C 32 ) fatty acid is admixed with the polyoxymethylene;

wherein the molding or a molding produced from the molding composition comprises a formaldehyde emission of less than 30 mg/kg, measured according to VDA 275 testing standard.

9. The process as claimed in claim 8 , wherein the molding or the molding produced from the molding composition has a formaldehyde emission of less than 20 mg/kg, measured according to VDA 275 testing standard.

10. The molding or molding composition as claimed in claim 1 , wherein the molding or a molding produced from the molding composition comprises a formaldehyde emission of less than 20 mg/kg, measured according to VDA 275 testing standard.

11. The process as claimed in claim 7 , wherein the molding or a molding produced from the molding composition comprises a formaldehyde emission of less than 20 mg/kg, measured according to VDA 275 testing standard.