ROTOMOLDING COMPOSITION

Abstract

A rotomolded composition comprises a mixture of two polyethylenes: 1) a well-stabilized polyethylene; and 2) a poorly stabilized polyethylene with a very low flow rate. The poorly stabilized polyethylene is further characterized by its large particle size (500 to 3000 microns). Rotomolded parts prepared from this composition have a rough inner surface. Polyurethane foam adheres well to this rough surface.

Claims

1. A polyethylene composition, characterized in that it comprises: 1) from 85 to 99% by weight of a stabilized polyethylene having a melt index I2, measured by ASTM D 1238 at 190°C using a 2.16 kg core, of 0.5 to 10 grams / 10 minutes; a density measured by ASTM D792 of 0.920 to 0.950 g / cc; and 2) from 15 to 1% by weight of a substantially unstabilized polyethylene having (i) a high load melt index, I2i, measured by ASTM D1238 at 190°C using a 21.6 kg load, from 2 to 20 grams / 10 minutes; (ii) a density of 0.950 to 0.965 g / cc measured by ASTM D792; and (iii) an average particle size of 500 to 3000 microns.

2. The polyethylene composition according to claim 1, characterized in that the particle size is from 500 to 1000 microns.

3. The polyethylene composition according to claim 1, characterized in that the average particle size of the stabilized polyethylene is less than the average particle size of the substantially unstabilized polyethylene.

4. The polyethylene composition according to claim 1, characterized in that the substantially unstabilized polyethylene has a high load melt index, I21, as measured by ASTM D1238 at 190°C using a load of 21.6 kg, from 3 to 6 grams per 10 minutes.

5. The polyethylene composition according to claim 1, characterized in that the stabilized polyethylene contains a stabilizing package comprising: 1.1) a primary antioxidant in an amount of 250 to 1500 parts per million by weight, and 1.2) a secondary antioxidant in an amount of 250 to 1500 parts per million by weight.

6. A process for preparing a rotomolded part, characterized in that it comprises a) preparing a polymer composition according to any of the preceding claims; and b) subjecting the mixture to rotomolding.

7. The process according to claim 6, characterized in that the rotational molding is carried out at a temperature of 250°C to 400°C.

8. The process according to claim 6 or 7, characterized in that it produces a rotomolded part having an inner surface with a surface roughness of 10 microns to 30 microns. 9.The polyethylene process according to claim 8, characterized in that the surface roughness is from 12 to 20 microns.

10. The process according to claim 8, characterized in that the inner surface is further characterized by having carbonyl functional groups that are detectable by a Fourier transform infrared instrument.