Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties

a polyolefin film, microporous technology, applied in sustainable manufacturing/processing, battery technology, cell components, etc., can solve the problems of irregular and large pore size, low mechanical strength, and difficulty in securing quality uniformity

Inactive Publication Date: 2014-11-27
SK INNOVATION CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This approach results in high-quality microporous films with improved mechanical strength, uniformity, and production stability, enabling the production of films with enhanced puncture strength and permeability while maintaining excellent quality and productivity.

Problems solved by technology

Three of the methods have favorable features such as formation of pores, which proposes desired permeability and reduced production costs to achieve economical benefits, but also have disadvantages such as low mechanical strength, irregular and large pore size, and difficulties in securing quality uniformity.
However, overall examples recited, in the above patents are particularly restricted to the simultaneous biaxial stretching or simply describe a biaxial stretching, however, have not specifically defined about stretching temperature in each of the machine and transverse directions.
The former has pores formed while extracting the diluent, which are prone to be deformed during stretching, therefore, the stretching process could hardly improve physical properties.
Further, since flexibility of the polyolefin free from the diluent is not proper, the stretching process is not easily conducted.
Such a non-gripped area has a lower actual stretching ratio than that of a gripped area, to cause non-uniformity in qualities between the gripped area and the non-gripped area.
The above tendency is more serious in the case where a stretching ratio is increased, a stretching temperature is decreased for enhancing a mechanical strength, and a sheet before stretching has a relatively large thickness, or the like.
For this reason, when a thick film, having a high strength is fabricated by the simultaneously biaxial stretching process, a problem of deteriorated uniformity in quality may be encountered.
However, the simultaneous biaxial drawing process has disadvantages in that quality uniformity is reduced when the sheet is thick and rigid, which can be easily disengaged from the grip chuck, thus causing a decrease in productivity stability.
Further, as for the simultaneously biaxial stretching process, due to difficulties in designing a machine and limitation in equipment costs, it is difficult to design the machine having a variable stretching ratio and apply tints in commercial production lines.
That is, it is not easy to manufacture commercial products having different characteristics by controlling the stretching ratio.
However, this method has a limitation in improving the mechanical strength via stretching.
Accordingly, the separator with high strength cannot be fabricated via this method.
That is, since a size of the pore and permeability of the film tend to excessively increase whereas the mechanical strength is slightly enhanced, an increase in a stretching ratio above a critical level is restricted.
In other words, it is difficult to manufacture products having a wide range of mechanical strengths (in particular, a product having puncture strength of not less than 0.25N / μm); and, when a pore size is excessively increased, quality uniformity is seldom secured.
However, it is difficult to overcome limitations of a battery separator fabricated by the dry process such as low mechanical strength and reduced quality uniformity.

Method used

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  • Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties
  • Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties
  • Method for preparing microporous polyolefin film with improved productivity and easy control of physical properties

Examples

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Effect test

example 1

[0083]A resin composition included 97 wt % of a high density polyethylene having a weight-average molecular weight of 3.0×105 and a melting temperature of 135° C. and 3 wt % of a homopolypropylene having a weight-average molecular weight of 5.7×105 and a melting temperature of 163° C. A diluent was a paraffin oil having a kinetic viscosity of 100 cSt at 40° C. A sheet composition was prepared by mixing the resin composition and the diluent in a ratio by weight of 35:65; mixing, extruding and molding through a twin screw compounder equipped with T-die at 250° C.; and using a casting roll set at 40° C. to prepare a sheet having a width of 300 mm and an average thickness of 1100 μm.

[0084]The prepared sheet was introduced into a machine direction stretcher while applying a tensile strength of 10.6N / cm2 in the machine direction, and preheated in a preheating roll having six (6) rolls and set at 115° C. for 76 seconds. A stretching roll which consists of four (4) rolls and is set at 118° ...

example 2

[0088]A sheet composition was prepared by using a high density polyethylene having a weight-average molecular weight of 3.0×105 and a melting temperature of 135° C., and a paraffin oil having a kinetic viscosity of 100 cSt at 40° C. as a diluent in a ratio by weight of 30:70. The prepared sheet composition was subjected to mixing, extruding and molding through a twin screw compounder equipped with T-die at 250° C. and treated by using a casting roll set at 40° C., thereby resulting in a sheet having a width of 600 mm and an average thickness of 2000 μm.

[0089]The prepared sheet was introduced into a machine direction stretcher while applying a tensile strength of 16.7N / cm2 in the machine direction and preheated in a preheating roll having eight (8) rolls and set at 110° C. for 50 seconds. A stretching roll which consists of six (6) rolls and is set at 108° C., and in which each of the rolls has a roll, contact coefficient of 13.5 degree (of angle)×m, was used. Also, these rolls have ...

example 3

[0093]A resin composition included 90 wt % of a high density polyethylene having a weight-average molecular weight of 3.0×105 and a melting temperature of 135° C. and 10 wt % of calcium carbonate having an average particle size of 0.8 / μm. A diluent was a paraffin oil having a kinetic viscosity of 100 cSt at 40° C. A sheet composition was prepared by mixing the resin composition and the diluent in a ratio by weight of 40:60; mixing, extruding and molding through a twin screw compounder equipped with T-die at 250° C.; and using a casting roll set at 40° C. to prepare a sheet having a width of 800 mm and an average thickness of 640 μm.

[0094]The prepared sheet was introduced into a machine direction stretcher while applying a tensile strength of 19.5N / cm2 in the machine direction, and preheated in a preheating roll having nine (9) rolls and set at 110° C. for 91 seconds. A stretching roll which consists of four (4) rolls and is set at 95° C., and in which each of the rolls has a roll co...

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Abstract

Provided is a method of manufacturing a microporous polyolefin film useable as a battery separator, which is easy to control strength, permeability and shrinking properties of the microporous film and embodies excellent quality uniformity and production stability in fabricating the microporous film.

Description

CROSS-REFERENCE TO BELATED APPLICATIONS[0001]This is a division of application Ser. No. 13 / 642,072 (allowed), which is a national phase application of International Application No. PCT / KR2011 / 002808, filed on Apr. 20, 2011, which claims the benefit of Korean Patent Application No, 10-2010-0036339 filed Apr. 20, 2010, the content of all of which are incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to a method for preparing a microporous polyolefin film capable of being used as a separator for a battery, with beneficial characteristics such as ease of controlling mechanical strength, permeability and thermal-shrinking properties of the microporous film, and excellent uniform quality, production stability, productivity, or the like, compared to existing production methods. More particularly, a stretching process involved in the method for preparing a microporous polyolefin film, which significantly influences determination of shrinkable properties as ...

Claims

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Application Information

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Patent Type & AuthorityApplications(United States)
IPC IPC(8): B29C67/20H01M2/16B29C55/14H01M2/14B29C47/00B29C47/88H01M50/406H01M50/417
CPCB29C67/202H01M2220/20B29C47/0021B29C47/8845B29C55/143H01M2/145B29C47/8805H01M2/1653B29L2031/3468B29K2023/065B29K2105/0088B29K2105/0005B29K2995/0088H01M2220/30B29C47/0057C08L23/06H01M10/0525C08K3/26C08L91/00B29C48/08B29C48/0012B29C48/0018B29C48/91B29C48/914Y02E60/10H01M50/446Y02P70/50H01M50/417H01M50/406H01M50/403H01M50/491
InventorKANG, GWI GWONRHEE, JANG-WEONJUNG, IN HWA
OwnerSK INNOVATION CO LTD