Flame retardant rotomolded polyolefin

1. A flame-retardant plastic article comprising a polyolefin substrate and additives incorporated in the polyolefin substrate, the polyolefin substrate comprising a low density polyethylene, the additives comprising:

i) a phosphonate ester;

ii) an N-alkoxy hindered amine;

iii) melamine cyanurate; and

iv) a base stabilization combination comprising pentaerythritol tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite and N,N-di(C 16 -C 18 alkyl)hydroxylamine,

wherein the plastic article contains a hollow portion therein, and

wherein the article has an average wall thickness of from about 1.50 mm to about 6.00 mm.

2. The plastic article according to claim 1 , wherein the phosphonate ester is of formula

wherein R 1 and R 2 are independently alkyl, substituted alkyl, aralkyl, substituted aralkyl, aryl or substituted aryl.

3. The plastic article according to claim 1 , wherein the N-alkoxy hindered amine contains one or more moieties of formula

wherein R 1 , R 2 , R 3 and R 4 are each independently C 1 -C 8 alkyl or R 1 and R 2 together and/or R 3 and R 4 together with the linking carbon form cyclohexyl and R 5 is a hydrocarbyl group.

4. The plastic article according to claim 1 , wherein the N-alkoxy hindered amine is selected from a group consisting of formula (1) through (9):

wherein n is an integer from 1 to 15 or is an integer from 1 to 10 or from 1 to 5,

wherein R 6 is a group of formula,

wherein * is the point of attachment,

wherein R 7 is C 1 -C 18 alkyl or C 1 -C 18 hydroxyalkyl,

wherein R 8 and R 8 ′ are independently C 1 -C 30 alkyl,

wherein R 9 and R 9 ′ are independently C 1 -C 30 alkyl or cylclohexyl,

wherein

n is an integer of from any of 1, 2, 3 or 4 to any of 5, 6, 7, 8, 9 or 10,

R 10 is C 1 -C 40 alkyl and

W is a hydrocarbyl containing from 50 to 1000 carbon atoms, and

wherein

n is an integer from any of 1, 2, 3, 4, 5, 6, 7 or 8 to any of 9, 10, 11, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 47 or 50 and

W is a hydrocarbyl containing from 50 to 1000 carbon atoms.

5. The plastic article according to claim 1 , wherein the melamine cyanurate has an average particle size of from about 1 micron to about 50 microns.

6. The plastic article according to claim 1 , wherein the article comprises from about 50 wt % to about 95 wt % polyolefin, based on the total weight of the article.

7. The plastic article according to claim 1 , wherein the article comprises from about 4 wt % to about 20 wt % phosphonate ester, based on the total weight of the article.

8. The plastic article according to claim 1 , wherein the article comprises from about 0.1 wt % to about 5.0 wt % N-alkoxy hindered amine, based on the total weight of the article.

9. The plastic article according to claim 1 , wherein the article comprises from about 1.0 wt % to about 10.0 wt % melamine cyanurate, based on the total weight of the article.

10. The plastic article according to claim 1 , wherein the article further comprises one or more additives selected from a group consisting of ultraviolet light absorbers, further hindered amines and antioxidants.

11. The plastic article according to claim 1 , wherein the article comprises from about 0.1 wt % to about 50 wt % of one or more fillers, based on the total weight of the article.

12. The plastic article according to claim 1 , wherein the article exhibits a UL-94 rating of V-0 wherein an average wall thickness is about 3.2 mm.

13. The plastic article according to claim 1 , wherein a weight/weight ratio of i) phosphonate ester to iii) melamine cyanurate is from 1/1 to 7/1 and a weight/weight ratio of iii) melamine cyanurate to ii) N-alkoxy hindered amine is from 1/1 to 8/1.