POLYETHYLENE FOAM COMPOSITION

Abstract

The present invention relates to a polyethylene composition comprising a) a polyethylene blend comprising from 95.5% to 99.5 wt % low density polyethylene (LDPE) and from 0.5% to 4.5 wt % high density polyethylene (HDPE), wherein the wt % (% by weight) is based the total amount of low density polyethylene and high density polyethylene in the blend, and b) a mixture of glycerol-mono-stearate and glycerol-mono-palmitate.

Claims

1. A polyethylene composition comprising a) a polyethylene blend comprising from 95.5 weight percent to 99.5 weight percent low density polyethylene and from 0.5% to 4.5 weight percent high density polyethylene, wherein the weight percent is based the total amount of low density polyethylene and high density polyethylene in the blend, and b) a mixture of glycerol-mono-stearate and glycerol-mono-palmitate.

2. The composition according to claim 1 characterised in that the weight percent of glycerol-mono-stearate is higher than the weight percent of glycerol-mono-palmitate in the mixture of glycerol-mono-stearate and glycerol-mono-palmitate.

3. The composition according to claims 1 characterized in that the weight ratio of glycerol-mono-stearate to glycerol-mono-palmitate in the mixture of glycerol-mono-stearate and glycerol-mono-palmitate ranges from 0.8 to 4.

4. The composition according to claim 1 characterized in that the mixture of glycerol-mono-stearate and glycerol-mono-palmitate was added to the composition as a masterbatch comprising glycerol-mono-stearate, glycerol-mono-palmitate and low density polyethylene.

5. The composition according to of claim 1 characterized in that the total amount of the polyethylene blend in the polyethylene composition ranges from 90.0 to 99.9 weight percent, based on the total amount of the polyethylene blend and the mixture of glycerol-mono-stearate and glycerol-mono-palmitate, and/or the amount of the mixture of glycerol-mono-stearate and glycerol-mono-palmitate ranges from 0.1 to 10.0 weight percent, based on the total amount of the polyethylene blend and the mixture of glycerol-mono-stearate and glycerol-mono-palmitate.

6. The composition according to claim 1 characterized in that the density of low density polyethylene ranges from 915 kg/m.sup.3 to 935 kg/m.sup.3, measured according to ISO 1183 and/or the melt flow rate of low density of polyethylene at 2.16 kg load and 190° C. measured according to ASTM D1133 ranges from 0.1 to 30 g/10 min.

7. The composition according to claim 1 characterized in that the density of high density polyethylene ranges from 940 kg/m.sup.3 to 970 kg/m.sup.3, measured according to ISO 1183 and/or the melt flow rate of high density polyethylene at 2.16 kg load and 190° C. measured according ASTM D1133 ranges from 0.1 to 20 g/10 min.

8. A foamed polyethylene composition obtained by foaming the polyethylene composition according to claim 1 in a physical foaming process in the presence of a physical blowing agent.

9. A process for physical foaming of the polyethylene composition according to claims 1 in the presence of a blowing agent selected from isobutane, CO.sub.2, pentane, butane, nitrogen or a fluorohydrocarbon.

10. An article comprising the composition according to claim 1.

11. A film, sheet, profile, rod, plank or tube comprising the composition according to claim 1.

12. (canceled)

13. (canceled)

14. The composition according to claim 1 characterized in that the weight ratio of glycerol-mono-stearate to glycerol-mono-palmitate in the mixture of glycerol-mono-stearate and glycerol-mono-palmitate ranges from 1.5 to 3.

15. The composition according to claim 1 characterized in that the weight ratio of glycerol-mono-stearate to glycerol-mono-palmitate in the mixture of glycerol-mono-stearate and glycerol-mono-palmitate ranges from 2.0 to 3.

16. The composition according to claim 1 characterized in that the total amount of the polyethylene blend in the polyethylene composition ranges from 95 to 99.9 weight percent, based on the total amount of the polyethylene blend and the mixture of glycerol-mono-stearate and glycerol-mono-palmitate, and/or the amount of the mixture of glycerol-mono-stearate and glycerol-mono-palmitate ranges from 0.1 to 5 weight percent, based on the total amount of the polyethylene blend and the mixture of glycerol-mono-stearate and glycerol-mono-palmitate.

17. An article comprising the foamed polyethylene composition according to claim 8.

18. An article comprising the foamed polyethylene composition obtained by the process according to claim 9.

19. A film, sheet, profile, rod, plank or tube comprising the foamed polyethylene composition according to claim 8.

20. A film, sheet, profile, rod, plank or tube comprising the foamed polyethylene composition obtainable by the process according to claim 9.

Description

EXAMPLES

Materials

Polyolefin 1 LDPE

[0096] Polyolefin 1 is LDPE with a density of 921 kg/m.sup.3 measured according to ISO 1183 and MFR of 1.9 g/10min measured at 190° C. and a load of 2.16 kg according to ASTM D1133.

Polyolefin 2 LDPE/HDPE Composition

[0097] Polyolefin 2 is a polyethylene blend of LDPE with a density of 921 kg/m.sup.3 measured according to ISO 1183 and MFR of 1.9 g/10 min measured at 190° C. and a load of 2.16kg according to ASTM D1133 and HDPE with a density of 964 kg/m.sup.3 measured according to ISO 1183 and a MFR of 8.0 g/10min measured at 190° C. and a load of 2.16 kg according to ASTM D1133. HDPE and LDPE were blended at 180 degrees Celsius in a ratio of 39:1 by using a compounding extruder.

[0098] The wt % of HDPE is 2.5% based on the total amount of LDPE and HDPE.

Cell Stabilizer 1

[0099] Glycerol-mono-stearate and glycerol-mono-palmitate were added via masterbatch. The masterbatch was comprising 50% by weight of a mixture of glycerol-mono-stearate and glycerol-mono-palmitate and 50% by weight of LDPE.

[0100] The weight ratio of glycerol-mono-stearate to glycerol-mono-palmitate in the masterbatch was 2.5.

Cell Stabilizer 2

[0101] Glycerol-mono-stearate and glycerol-mono-palmitate were added via masterbatch. The masterbatch was comprising 50% by weight of a mixture of glycerol-mono-stearate and glycerol-mono-palmitate and 50% by weight of LDPE.

[0102] The weight ratio of glycerol-mono-stearate to glycerol-mono-palmitate was 1.1.

Foaming Process and Measurements

[0103] The polyolefin (LDPE or LDPE/HDPE composition) was added to a physical foaming extruder.

[0104] The composition to be foamed was comprising [0105] 85.0% by weight of the polyolefin (LDPE or LDPE/HDPE composition), [0106] 11.5% by weight isobutane [0107] 1.75% by weight talcum masterbatch (50% masterbatch of talcum in LDPE) and [0108] 1.75% by weight of the masterbatch (cell stabilizer 1 or cell stabilizer 2).

[0109] The temperatures of the melting zones were set on a flat profile of 165 degrees Celsius. Cooling temperatures were set on 107 degrees Celsius.

[0110] A sheet (1.2 mm thickness) with a density of 31 kg/m.sup.3 was produced. The density was measured by water immersion method.

[0111] After producing the foam at 20 degrees Celsius via the regular physical extrusion process with isobutane, the time of a 50% reduction in concentration of isobutane was determined. The gas exchange in the foamed article was measured by monitoring the weight of the sheet during a certain time period. At the beginning the product was filled with isobutane and over time exchanged with air. Isobutane has a higher density (2, 44 kg/m.sup.3 at 25° C.) than air (1, 18 kg/m.sup.3 at 25° C.). By measuring the weight-loss of the product the isobutane degassing amount was calculated. 100% gas exchange took place when no weight change over time was observed anymore.

Composition of Samples and Measurement Results

[0112]

TABLE-US-00001 Time of 50% of degassing Cell of isobutane Sample Polyolefin stabilizer in hours Inv. 1 2 (LDPE/HDPE) 1 34 h Inv. 2 2 (LDPE/HDPE) 2 82 h Comp. 1 1 (LDPE) 1 115 h Comp. 2 1 (LDPE) 2 202 h

[0113] These experiments show that the use of the LDPE/HDPE mixture (compared to LDPE) in combination with the glycerol-mono-stearate and glycerol-mono-palmitate mixture improves the degassing of the foamed article.

[0114] In FIG. 1 the degassing process is shown as the weight change (%) of the foam over time (days). As one can see a much faster gas exchange is obtained for the inventive examples in comparison to the comparative examples.