Colour stabilised polyolefins

1. A polyolefin composition which comprises:

(a) a polyolefin containing transition metal catalyst residue (excluding metallic co-catalyst residues) at a level below 5 ppm based on the weight of the polyolefin;

(b) a first stabilising component consisting of a phenolic antioxidant or a mixture of phenolic antioxidants selected from the group consisting of:

1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione;

2,2′-methylenebis(6-t-butyl-4-methylphenol);

4,4′-bu-tylidenebis(2-t-butyl-5-methylphenol);

2,2′-isobutylidenebis(4,6-dimethylphenol);

1,1,3-tris(2′-methyl-4′-hydroxy-5′-t-butylphenyl)butane;

2,5-di-t-amylhydroquinone;

2,2′-methylene-bis(4-methyl)-6-(1-methyl cyclohexyl)phenol;

4,4′-thiobis(2-t-butyl-5-methylphenol);

2,2′-thiobis(6-t-butyl-4-methyl phenol);

triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate],

synthetic alpha-tocopherol,

and mixed tocopherols as found in Vitamin E;

(c) a second stabilising component consisting of a phosphite antioxidant or a mixture of phosphite antioxidants with the proviso that if the phosphite antioxidant is trilauryl phosphite it must be used in combination with another phosphite; and

(d) a third stabilising component which acts also as a colour suppressant and which is a polyfunctional alcohol selected from the group consisting of erythritol, pentaerythritol, dipentaerythritol, sorbitol, triisopropanolamine and polypentaerythritols wherein stabilising components (b) and (c) are present in a ratio of between 1/1 and 1/20.

2. The polyolefin composition according to claim 1 wherein the metallic element of the catalyst residue is titanium, zirconium, chromium or mixtures thereof.

3. The polyolefin composition as claimed in claim 1 , wherein stabilising component (b) is 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H, 3H, 5H)-trione or mixed tocopherols.

4. The polyolefin composition as claimed in claim 1 , wherein stabilising component (b) is present in an amount of 20 ppm to 1000 ppm based on the weight of the polyolefin.

5. The polyolefin composition as claimed in claim 1 , wherein stabilising component (c) is tris(mono-nonylphenyl)phosphite, tris(2,4-di-t-butylphenyl)phosphite or bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite.

6. The polyolefin composition as claimed in claim 1 , wherein stabilising component (c) is present in an amount of 50 to 2000 ppm based on the weight of the polyolefin.

7. The polyolefin composition as claimed in claim 1 , wherein stabilising component (d) dipentaerythritol or tri-isopropanol amine.

8. The polyolefin composition as claimed in claim 1 , wherein component (d) is present in an amount of 50 to 1500 ppm based on the weight of the polyolefin.

9. The polyolefin composition as claimed in claim 1 , which contains a fourth stabilising component (e) which is a hindered amine stabiliser.

10. The polyolefin composition as claimed in claim 9 wherein stabilising component (e) is selected from at least one of dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol, poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] or 1,3,5-triazine-2,4,6-triamine, N,N′″-1,2-ethanediylbis[N-[3-[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazin-2-yl]amino]propyl]-N′,N″dibutyl-N′,N″-bis-(1,2,2,6,6-pentamethyl-4-piperidinyl).

11. The polyolefin composition as claimed in claim 1 wherein stabilising component (e) is present in an amount of 50 to 3000 ppm based on the weight of the polyolefin.

12. The polyolefin composition as claimed in claim 1 , which contains an acid scavenger as component (f) selected from the group consisting of metal oxides, and light metal salts fatty acids.

13. The polyolefin composition as claimed in claim 12 wherein component acid scavenger component (f) is present in an amount of 50 to 3000 ppm based on the weight of the polyolefin.

14. The polyolefin composition as claimed in claim 10 wherein the total amount of components (b), (c), (d), (e) and (f) is present in an amount of 500 to 5000 ppm based on the weight of the polyolefin.

15. The polyolefin composition as claimed in claim 1 , wherein the polyolefin is polypropylene or polyethylene.

16. The polyolefin composition as claimed in claim 1 , wherein the polyolefin is polypropylene and the transition metal catalyst residue (excluding metallic cocatalyst residues) comprises less than 0.5 ppm vanadium.

17. Articles made from a polyolefin composition as claimed in claim 1 .

18. A process for producing a polyolefin composition according to claim 1 , comprising homogenising the additives into the polymer by melt extrusion or dispersing liquidized or powdered additives into the polymer.