Polyacetals with improved resistance to bleach

1. A molding composition exhibiting bleach resistance comprising a polyoxymethylene matrix polymer, wherein the polyoxymethylene is selected from the group consisting of oxymethylene copolymers comprising about 90 to about 99.9 percent oxymethylene repeat units interspersed with repeat units derived from ethylene oxide or 1,3 dioxolane, wherein said molding composition further comprises from about 0.5 to about 10 weight percent of a bleach stabilizer selected from alkali metal or alkaline earth element carbonates or phosphates and mixtures thereof dispersed in the matrix resin and a bleach co-stabilizer selected from the group consisting of:

(a) a poly(alkoxy) stabilizer;

(b) a zinc oxide stabilizer;

(c) a color stabilizer consisting of a mixture of calcium citrate and calcium propionate, wherein the calcium citrate is the predominant component of the color stabilizer mixture, and wherein said calcium citrate is in an amount of about 0.05-0.1 weight % ; or

(d) mixtures of two or more of (a), (b) and (c); and

wherein the composition exhibits a bleach resistance index of at least 2.0.

2. The molding composition according to claim 1 , wherein the composition comprises from about 0.5 to about 2 weight percent of bleach stabilizer.

3. The molding composition according to claim 1 , wherein the composition comprises from about 0.5 to about 1.5 weight percent of bleach stabilizer.

4. The composition according to claim 1 , wherein said calcium propionate is in an amount of about 0.01-0.05 weight %.

5. The composition according to claim 1 , wherein the poly (alkoxy) stabilizer is polyethylene glycol.

6. The present composition according to claim 5 , wherein the polyethylene glycol is in an amount of about 0.25-5.0 weight %.

7. The composition according to claim 1 , wherein the bleach stabilizer is selected from the group consisting of: calcium carbonate, sodium carbonate, potassium carbonate and barium carbonate.

8. The composition according to claim 7 , wherein the bleach stabilizer is calcium carbonate.

9. The composition according to claim 8 , further comprising at least one hindered phenol selected from the group comprising: hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), 2,2′-methylenebis(4-methyl-6-t-butylphenol), hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydro-cinnamate), tetrabis[methylene(3,5-di-t-butyl-4-hydroxyhydro-cinnamate)]methane, triethyleneglycol-bis-3-(3-t-butyl-760 4-hydroxy-5-methylphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)-benzene, p-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butyl-phenol)propionate, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-butylidene-bis-(6-t-butyl-3-methylphenol), 2,2′-thiodiethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenol)propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate and 2-t-butyl-6-(3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenylacrylate, hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane and triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate.

10. The composition according to claim 9 , wherein the hindered phenol is at least one hindered phenol selected from the group consisting of: hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate) and triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate.

11. The according to according to claim 10 , wherein the hindered phenol is in an amount of about 0.25-1.0 weight %.

12. The composition according to claim 11 , comprising:

(a) at least about 94.0 weight percent of a polyoxymethylene copolymer; and

(b) from about 0.01 to 0.1 weight percent of color stabilizer.

13. The composition according to claim 1 , wherein the composition exhibits a bleach resistance index of at least 2.5.

14. The composition according to claim 1 , wherein the composition exhibits a bleach resistance index of at least 3.0.

15. An injection molded part adapted for interfacing aqueous bleach prepared from a composition comprising a polyoxymethylene matrix polymer, from about 0.5 to about 10 weight percent of calcium carbonate dispersed in the matrix polymer, and a bleach co-stabilizer selected from the group consisting of:

(a) a poly(alkoxy) stabilizer;

(b) a zinc oxide stabilizer;

(c) a color stabilizer consisting of a mixture of calcium citrate and calcium propionate, wherein the calcium citrate is the predominant component of the stabilizer mixture; or

(d) mixtures of two or more of (a), (b) and (c); and

wherein the composition exhibits a bleach resistance index of at least 2.0.

16. The injection molded part according to claim 15 , wherein the composition comprises from about 0.5 to about 2.0 weight percent of calcium carbonate.

17. The injection molded part according to claim 15 , wherein the composition comprises from about 0.5 to about 1.5 weight percent of calcium carbonate.

18. The injection molded part adapted for interfacing aqueous bleach according to claim 15 , further comprising at least one hindered phenol selected from the group comprising: hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnaniate), 2,2′-methylenebis(4-methyl-6-t-butylphenol), hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), tetrabis[methylene(3,5-di-t-butyl-4-hydroxyhydro-cinnamate)]methane, triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)-benzene, p-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butyl-phenol)propionate, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-butylidene-bis-(6-t-butyl-3-methylphenol), 2,2′-thiodiethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenol)propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate and 2-t-butyl-6-(3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenylacrylate, hexamethylene-glycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane and triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate.

19. The injection molded part adapted for interfacing aqueous bleach according to claim 18 , wherein the hindered phenol is at least one hindered henol selected from the group consisting of: hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate) and triethylene-glycol-bis-3-(3-t-butyl-4-hydroxy-5-methyiphenyl)propionate.

20. The injection molded part adapted for interfacing aqueous bleach compositions prepared according to claim 15 , wherein the part is selected from the group consisting of: housing components, washers, bearings, valves, gears, impellers, jets, fittings, nozzles, elbows, detergent baskets, grommets, flanges, tumblers, pump components, blades, shafts, conduits and the like.

21. The injection molded part according to claim 15 , wherein the composition exhibits a bleach resistance index of at least 2.5.

22. The injection molded part according to claim 15 , wherein the composition exhibits a bleach resistance index of at least 3.0.