MICROPOROUS POLYETHYLENE FILM MANUFACTURED ACCORDING TO LIQUID-LIQUID PHASE SEPARATION AND METHODS OF PRODUCING THE SAME

• US 20070232709A1
• Filed: 05/24/2007
• Published: 10/04/2007
• Est. Priority Date: 05/16/2005
• Status: Active Grant

• Current Assignee: SK IE Technology Co., Ltd. (SK Innovation Company Limited), SK Innovation Company Limited
• Original Assignee: SK Corporation (Kimberly-Clark Corporation)
• Inventors: RHEE, Jang-Weon, LEE, Young-Keun, JO, Byoung-Cheon, SUNG, Jung-Moon, LEE, Je-An, KANG, Gwi-Gwon, LEE, Chol-Ho, JUNG, In-Hwa
• Granted Patent: US 8,323,547 B2
• Time in Patent Office: Days
• US Class Current: 521/80
• CPC Class Codes: C08J 2323/04 Homopolymers or copolymers of ethene
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: C08K 5/04 Oxygen-containing compounds C08K5/0091 takes precedence
• CPC Class Codes: H01M 50/417 Polyolefins
• CPC Class Codes: H01M 50/489 Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Disclosed in the present invention are a microporous polyethylene film and a method of manufacture thereof. The polyethylene microporous film manufactured according to the present invention may contribute to an increased productivity of stable products as its extrusion and stretching may be done readily. And thus manufactured product may be used for battery separators and various filters owing to its high gas permeability, superior puncture strength, and small ratio of shrinkage.

Claims

1. A method of manufacture of a microporous polyethylene film comprising the steps of:

melt-mixing a resin mixture, containing 20-55 weight % of polyethylene (component I) and 80-45 weight % of a diluent (component II) characterized by liquid-liquid phase separation from the above component I at 160-280°

C., at a temperature higher than the temperature of liquid-liquid phase separation to make a thermodynamic single phase in an extruder;

separating liquid-liquid phase, by after making the mixture to a single phase molten material, then passing it through a phase separating zone in an extruder, controlled to be in a temperature range of liquid-liquid phase separation;

molding the molten material extruded as liquid-liquid phase separation is progressed in the form of a sheet;

stretching the above sheet to have a ratio of stretching of 4 times or greater each in the machine and traverse directions and the total ratio of stretching of 25-50 times in the sequential or simultaneous stretching method including the roll or tenter method;

extracting component II from the stretched film and drying it; and

heat-setting the dried film by removing its residual stress to have a ratio of shrinkage of the film in each of the machine and transverse directions of 5% or less.

2. The method of manufacture of said microporous polyethylene film of claim 1, characterized by the phase separation zone, in the extruder, regulates the phase separation rate by means of either modulating residence time in the separating zone by controlling melt-mixing zone and phase separation length or productivity;

or controlling temperature of the phase separation

3. The method of manufacture of said microporous polyethylene film of claim 1, characterized by that said component I is polyethylene having a weight average molecular weight in the range of from 2×

10⁵ to 4.5×

10⁵.

4. The method of manufacture of said microporous polyethylene film of claim 1, characterized by that said component II is one or more components selected from phthalic acid esters such as dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, etc.;

aromatic ethers such as diphenyl ether, benzyl ether, etc.;

aliphatic acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc.;

aliphatic alcohols having 10 to 20 carbon atoms such as palmitic acid alcohol, stearic acid alcohol, oleic acid alcohol, etc.; and

among saturated and unsaturated fatty acids having 4 to 26 carbon atoms in the fatty acid group, fatty acid esters in which one or more fatty acids are combined through esterification with alcohols having 1 to 8 hydroxy radicals and 1 to 10 carbon atoms, such as palmitic acid mono-, di-, or triester;

stearic acid mono-, di-, or triester;

oleic acid mono-, di-, or triester;

l linoleic acid mono-, di-, or triester.

5. The method of manufacture of said microporous polyethylene film of claim 4, characterized by that said component II further contains one or more components selected from a paraffin oil, mineral oil, and wax.

6. The method of manufacture of said microporous polyethylene film of claim 1, characterized by that the temperature of extrusion is lower than the temperature of liquid-liquid phase separation −

10°

C. in the liquid-liquid phase separation state, and the residence time in the extruder in the liquid-liquid phase separation is loner than 30 seconds

7. The method of manufacture of said microporous polyethylene film of claim 1, characterized by that molding of said sheet is done in the casting or calendering method using a water-cooling and air-cooling method.

8. The method of manufacture of said microporous polyethylene film of claim 1, characterized by that said heat-setting is done within a temperature range within which 10-30 weight % of the crystalline portion of the extracted and dried film is molten in the tenter method in which the time for heat-setting is for 15 seconds to 2 minutes.

9. The microporous polyethylene film manufactured according to a method in claim 1.

10. The microporous polyethylene film of claim 9, characterized by that said microporous polyethylene film has a gas permeability (Darcy'"'"'s permeability constant) of 2.0×

10<sup>−

5</sup> or greater, puncture strength of 0.17 N/μ

m or greater, multiplication of said gas permeability and said puncture strength of 0.45×

10<sup>−

5</sup> Darcy. N/μ

m or greater, and ratio of shrinkage in each of machine and traverse directions of 5% or less.

11. The microporous polyethylene film manufactured according to a method in claim 2.

12. The microporous polyethylene film manufactured according to a method in claim 3.

13. The microporous polyethylene film manufactured according to a method in claim 4.

14. The microporous polyethylene film manufactured according to a method in claim 5.

15. The microporous polyethylene film manufactured according to a method in claim 6.

16. The microporous polyethylene film manufactured according to a method in claim 7.

17. The microporous polyethylene film manufactured according to a method in claim 8.