Process for producing polyolefin materials

• US 6,017,480 A
• Filed: 03/21/1997
• Issued: 01/25/2000
• Est. Priority Date: 03/22/1996
• Status: Expired due to Term

• Current Assignee: Nippon Mitsubishi Oil Corporation (ENEOS Holdings, Inc.)
• Original Assignee: Nippon Oil Corporation (ENEOS Holdings, Inc.)
• Inventors: Yoshida, Sumio, Otsu, Osamu
• Primary Examiner(s): Silbaugh, Jan H.
• Assistant Examiner(s): JONES, KENNETH MITCHELL
• Application Number:
  US08/823,031
• Time in Patent Office: 1,040 Days
• Field of Search: 264/289.6, 264/342 R, 264/342 RE, 264/230, 264/210.7, 264/290.2, 264/909, 264/DIG. 71, 264/164, 264/216
• US Class Current: 264/216
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B29C 55/065 in several stretching steps
• CPC Class Codes: B29C 55/18 by squeezing between surfaces, e.g. rollers
• CPC Class Codes: B29K 2023/0683 UHMWPE, i.e. ultra high molecular weight polyethylene
• CPC Class Codes: Y10S 264/71 Processes of shaping by shrinking

Abstract

A process for producing polyolefin materials is disclosed which comprises the steps of (a) preparing a molded article of an ultra-high-molecular-weight polyolefin having a viscosity-average molecular weight of more than 500,000; (b) stretching said article by more than thirty-fold; (c) contracting the thus stretched article to an extent ranging from 0.3 to 80% in the direction of stretch; and (d) re-stretching the thus contracted article. The resulting polyolefin materials are improved in mechanical strength and elasticity modulus.

Claims

1. A process for the production of polyolefinic materials which comprises the steps of (a) preparing a molded article of an ultra-high-molecular-weight polyolefin having a viscosity-average molecular weight of more than 500,000;

(b) stretching said molded article by more than thirty-fold in a direction of stretch;

(c) shrinking the thus stretched article to an extent ranging from 0.3 to 80% in the direction of stretch; and

(d) re-stretching the thus shrunken article.

2. The process according to claim 1 wherein said molded article in said step (a) is prepared without melting said ultra-high-molecular-weight polyolefin and/or dissolving the same in a solvent.

3. The process according to claim 1 wherein step (a) is performed using said ultra-high-molecular-weight polyolefin in a granular or powder form having a particle size not greater than 2,000 μ

m.

4. The process according to claim 1 further comprising the step of polymerizing an olefin monomer in the presence of a catalyst which comprises a compound containing transitional metal elements in groups IV to VI of the periodic table to form said ultra-high-molecular-weight polyolefin used in step (a).

5. The process according to claim 1 wherein said ultra-high-molecular-weight polyolefin is one selected from the group consisting of an ultra-high-molecular-weight polyethylene and an ultra-high-molecular-weight polypropylene.

6. The process according to claim 1 wherein said molded article in said step (a) is prepared by compression-molding.

7. The process according to claim 1 wherein said molded article in said step (a) is prepared by compression-molding, followed by rolling.

8. The process according to claim 6 wherein said compression-molding is conducted at a temperature below the melting point of said ultra-high-molecular-weight polyolefin.

9. The process according to claim 7 wherein said rolling is conducted at a temperature of higher than 20°

C.

10. The process according to claim 7 wherein said molded article has a deformation ratio in the range of 1.2 to 20 in terms of a length ratio after and before rolling.

11. The process according to claim 1 wherein the stretching in said step (b) is conducted at a temperature below the melting point of the ultra-high-molecular-weight polyolefin to be stretched.

12. The process according to claim 1 wherein the stretching in said step (b) is effected at a temperature of higher than 20°

C.

13. The process according to claim 1 wherein said stretching in said step (b) is conducted at a speed in the range of 0.1 to 500 m/min.

14. The process according to claim 1 wherein the contracting in said step (c) is conducted by heating said stretched article.

15. The process according to claim 1 wherein the contraction in said step (c) is effected at a temperature below the melting point of the ultra-high-molecular-weight polyolefin to be contracted.

16. The process according to claim 1 wherein the contraction in said step (c) is effected at least at a temperature of 50°

C. lower than the melting point of the ultra-high-molecular-weight polyolefin to be contracted.

17. The process according to claim 1 wherein the re-stretching in said step (d) is conducted at a temperature below the melting point of the ultra-high-molecular-weight polyolefin to be re-stretched.

18. The process according to claim 1 wherein the re-stretching in said step (d) is conducted at a temperature of higher than 20°

C.

19. The process according to claim 1 wherein the re-stretching is conducted at a speed in the range of 0.1 to 500 m/min.

20. The process according to claim 7 wherein said compression-molding is conducted at a temperature below the melting point of said ultra-high-molecular-weight polyolefin.