Foamed caps and closure seal comprising polyethylene foam

Abstract

The invention is directed to foamed caps and closure seals comprising as one of the layers polyethylene foam. The polyethylene foam is obtained by foaming of low density polyethylene copolymer obtained by a high pressure polymerization process in the presence of 1,4-butanediol dimethacrylate.

Claims

1. Foamed caps and closure seal comprising as one of the layers polyethylene foam wherein the foam is obtained by foaming of low density polyethylene copolymer obtained by a high pressure polymerisation process in the presence of 1,4-butanediol dimethacrylate.

2. The foamed caps and closure seal according to claim 1 wherein low density polyethylene obtained by the high pressure polymerisation process in the presence of 1,4-butanediol dimethacrylate has a density between 910 kg/m.sup.3 and 935 kg/m.sup.3 (according to ISO 1183) and a melt index between 0.10 and 100 dg/minute (according to ASTM D1133).

3. The foamed caps and closure seal according to claim 1, wherein the high pressure polymerisation process is a tubular polymerisation process.

4. The foamed caps and closure seal according to claim 1, wherein the foam is obtained by physically foaming of low density polyethylene.

5. The foamed caps and closure seal according to claim 1, comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.

6. The foamed caps and closure seal according to claim 2, wherein the high pressure polymerisation process is a tubular polymerisation process.

7. The foamed caps and closure seal according to claim 2, wherein the foam is obtained by physically foaming of low density polyethylene.

8. The foamed caps and closure seal according to claim 2, comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.

9. The foamed caps and closure seal according to claim 3, comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.

10. The foamed caps and closure seal according to claim 4, comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.

11. The foamed caps and closure seal according to claim 1, wherein the foam consist essentially of closed cells.

12. The foamed caps and closure seal according to claim 1, wherein at least 90% of the cells are closed.

13. The foamed caps and closure seal according to claim 1, wherein the foam has an open cell content of 10% to 90% of all cells.

14. The foamed caps and closure seal according to claim 8, wherein the foam consist essentially of closed cells.

15. The foamed caps and closure seal according to claim 8, wherein at least 90% of the cells are closed.

16. The foamed caps and closure seal according to claim 8, wherein the foam has an open cell content of 10% to 90% of all cells.

Description

EXAMPLES

Production of Foamed Seal for Caps and Closures

(1) Foamed seals for caps and closures were produced on a foam extruder (Aixfotec) using carbon dioxide as a blowing agent, LDPE as resin and 0.5% by weight relative to the total composition of Hydrocerol CF40 as nucleating agent.

(2) The melt temperature on the extruder was 108 degrees Celsius. With the dosing of carbon dioxide a foam density of 170 kg/m.sup.3 was obtained.

(3) The applied LDPE resins: LDPE resin I according to the invention (MFI 4.7; density 919 kg/m.sup.3) obtained by high pressure tubular polymerisation process in the presence of 1,4-butanediol dimethacrylate as co monomer. LDPE resin A (MFI 4.2; density 924 kg/m.sup.3) obtained by high pressure tubular polymerisation process.

(4) The above described process resulted in foamed seals: Example I: foam with a density of 170 kg/m.sup.3 and a thickness of 1 mm, produced with LDPE I. Comparative Example A: foam with a density of 170 kg/m.sup.3 and a thickness of 1 mm, produced with LDPE A.

(5) The foamed seals were analyzed via microscopy: Scanning electron microscopy (SEM) to investigate cell structure, Surface optical microscopy to validate the surface of the foam using image analysis AnalySIS auto from Olympus, a profilometer Veeco Dektak 6M Stylus to determine surface roughness parameters, and OTR-measurements to determine the oxygen transmission rate.
Description of Analysis of Foamed Seals:

(6) The samples for cross section analysis are cut out of the sheet (parallel to the length direction) using a razor blade, and fixed into a SEM sample holder.

(7) The samples for surface analysis are also cut out of the sheet and fixed with double sided adhesive tape to a SEM sample holder. All samples are coated with a conductive gold layer (150 s, 30 mA). Imaging of the cross sections is done using a Philips CP SEM XL 30 at an acceleration voltage of 15 kV.

(8) The samples for surface analysis are imaged with LM (reflected bright light) Leica MZFLIII.

(9) The image analysis is done using AnalySIS auto from Olympus. For each image a number of steps (in various combinations) have been taken to enhance the desired features: Resulting image contrast optimized and binarized. Features are analysed and put in Excel files. Conversion from 2D to 3D using Matlab tool.

(10) The pictures of the analysis are listed as FIGS. 1A, 1B, 2A, and 2B.

(11) FIGS. 1A, 1B, 2A, and 2B, are related to cell structure analysis.

(12) FIG. 1A: Foam produced with LDPE I (scale 500 mu)

(13) FIG. 1B: Foam produced with LDPE A (scale 500 mu)

(14) FIG. 2A: Foam produced with LDPE I (scale 1 mm)

(15) FIG. 2B: Foam produced with LDPE A (scale 1 mm)

(16) FIGS. 3A, 3B, 4A, and 4B, are related to surface structure analysis

(17) FIG. 3A: Foam produced with LDPE I (scale 5 mm)

(18) FIG. 3B: Foam produced with LDPE A (scale 5 mm)

(19) FIG. 4A: Foam produced with LDPE I (scale 5 mm)

(20) FIG. 4B: Foam produced with LDPE A (scale 5 mm)

(21) FIG. 5: Cell size distribution of foam produced with LDPE I and A, respectively.

(22) Table 1 contains the result of the digital analysis of the cell structure of the product of FIGS. 1A and 1B.

(23) TABLE-US-00001 TABLE 1 Description Number of cells FIG. 1A 578 FIG. 1B 462

(24) The cell size distribution is given in FIG. 5. Table 2 shows the derived numbers from the cell size distributions.

(25) TABLE-US-00002 TABLE 2 d.sub.50 Lower limit Upper limit Width Sample (m) (m) (m) (m) I 66 64 68 25 A 93 85 101 70

(26) The d.sub.50 indicates the location of the peak of the distribution at which 50% of the cell sizes is smaller and 50% is larger in case of a symmetric distribution which is valid here. The d.sub.50 of Sample A is about 30% smaller and the width is even a factor of three smaller. The cell sizes of Sample A are clearly smaller and exhibit a much narrower distribution.

(27) Table 3 shows the measured oxygen transmission rates (OTR) of foam produced with LDPE I and LDPE A, respectively.

(28) TABLE-US-00003 TABLE 3 Sample (cm.sup.3/m.sup.2 d bar) I 1315 A 2260

(29) The OTR has been measured according to method ISO 15105-2/DIN 53380-3 at a temperature of 23 C. and a relative humidity of 75%.

(30) The OTR of the foamed samples based on LDPE A is higher for all samples measured in comparison with the LDPE I according to the invention.

(31) Table 4 shows the roughness parameters Ra and Rq of the foam produced with LDPE I and LDPE A, respectively.

(32) TABLE-US-00004 TABLE 4 Roughness Parameters Estimated Surface Height (m) Distribution (m) Sample Ra Rq Max Min I - Side A - X 7.1 9.6 17.3 21.3 I - Side A - Y 8.1 11.0 16.0 38.3 I - Side B - X 7.4 9.8 38.7 26.0 I - Side B - Y 6.9 9.7 5.3 55.7 A - Side A - X 12.7 15.6 28.3 6.7 A - Side A - Y 11.3 14.4 12.7 20.7 A - Side B - X 8.9 12.8 16.0 24.3 A - Side B - Y 7.5 10.8 19.0 15.3

(33) X and Y indicate perpendicular directions in which the roughness profiles were measured. Measurements were repeated on both surfaces, called side A and Side B. Indicated are the maximum value and minimum values of the recorded roughness profile, as well.

(34) The roughness of the foamed samples based on LDPE A is higher for all samples measured in comparison with the LDPE I according to the invention.