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Method for preparing polyolefin microporous membrane with symmetrical upper and lower surface structures

A polyolefin microporous film and surface structure technology, applied in flat products, household components, applications, etc., can solve the problems of asymmetrical micropore size, poor air permeability, and different degrees of phase separation, and achieve a symmetrical microporous structure on the upper and lower surfaces Uniform and breathable effect

Active Publication Date: 2010-06-09
SHENZHEN SENIOR TECH MATERIAL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In this way, the casting method causes the upper and lower surfaces of the thick sheet to be heated asymmetrically. During the cooling-induced phase separation process, the phase separation degree is different, and the size of the micropores formed after the subsequent extraction is asymmetrical. The structure of the microporous membrane is uneven and the air permeability is not good.
Moreover, due to the asymmetric shrinkage of the upper and lower surfaces, the microporous membrane is warped and deformed.
When the prepared microporous membrane is used as a lithium-ion battery separator, it has poor air permeability, low lithium ion penetration ability, and poor battery performance.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0025] 10% (weight) of high-density polyethylene (melting point 133° C.) is dropped into a twin-screw extruder (78 mm in diameter, L / D=50, strong mixing type), and 90 % (weight) of liquid paraffin (kinematic viscosity 90cst / 40°C), melted and kneaded under the conditions of 200°C and 150 rpm to form a solution, and passed the solution through a T-type die (die lip opening 0.8mm , die head temperature 180 ℃) and two rollers with symmetrical diameters to obtain thick sheets after casting, the diameter of the rollers is 200 mm, and the temperature of the rollers is 15 ℃. On the basis of preheating the thick sheet, it is stretched by biaxial stretching equipment, the preheating time is 10S, the preheating temperature is 100°C, and the stretching ratio is 3×3 times (that is, the longitudinal stretching ratio is 3 times, and the transverse stretching ratio is 3 times); Then do the setting treatment, the treatment temperature is 100°C, and the treatment time is 10s; finally, the liqui...

Embodiment 2

[0027]60% (weight) of polypropylene (melting point 167° C.) is dropped into a twin-screw extruder (78 mm in diameter, L / D=50, strong mixing type), and 40% ( weight) of liquid paraffin (kinematic viscosity 90cst / 40°C), melted and kneaded at 200°C and 150 rpm to prepare a solution, and passed the solution through a T-shaped die (die lip opening 0.8mm, die Head temperature 240 ℃) and two diametrically symmetrical rollers to obtain a slab, the diameter of the roller is 1000mm, and the roller temperature is 50 ℃. On the basis of preheating the thick sheet, it is stretched by biaxial stretching equipment, the preheating temperature is 150°C, and the stretching ratio is 5×9 times (that is, the longitudinal stretching ratio is 5 times, and the transverse stretching ratio is 9 times); The treatment temperature is 150°C, and the treatment time is 100s; finally, the liquid paraffin in the film is extracted with methyl ethyl ketone, and after drying, it is subjected to transverse stretchi...

Embodiment 3

[0029] Put 20% (weight) polyethylene (melting point 133°C) into the internal mixer with a preset temperature of 180°C, and add 80% (weight) dioctyl phthalate through the side feeding port with a metering pump Esters were melted and kneaded at 200°C and 150 rpm to prepare a solution, and the solution was cast through a hanger-type die (the opening of the die lip was 0.8mm, and the temperature of the die head was 200°C) and two rollers with symmetrical diameters. Thick sheets were obtained after sheeting, the diameter of the roller was 800mm, and the temperature of the roller was 15°C. The thick sheet is preheated on the basis of biaxial stretching, the preheating temperature is 125°C, and the stretching ratio is 3×3 times (that is, the longitudinal stretching ratio is 3 times, and the transverse stretching ratio is 3 times); then the setting treatment is performed, and the processing temperature is 125°C , the processing time is 10s; finally, the dioctyl phthalate in the film i...

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Abstract

The invention provides a method for preparing a polyolefin microporous membrane with symmetrical upper and lower surface structures. The method comprises the following steps of: 1) mixing polyolefin resin with a diluting agent in a weight ratio of 1-6:4-9; 2) extruding the mixture by a neck ring mold in an extrusion flow-casting mode and performing cold rolling and strip casting to obtain a thick sheet; 3) preheating the thick sheet and stretching the preheated thick sheet longitudinally and transversely; 4) shaping the stretched thick sheet; 5) extracting the diluting agent and drying the thick sheet; 6) stretching the thick sheet transversely and shaping the stretched thick sheet; and 7) winding the shaped thick sheet. For the polyolefin microporous membrane prepared by the process steps, the upper and lower two surfaces of the thick sheet are particularly provided with a set of rollers with the same diameter respectively, or one side of an air knife is provided with a set of the rollers on a conventional cold roller and an air knife auxiliary patch device to obtain the thick sheet in an auxiliary cooling mode, and then, the thick sheet is stretched and extracted to finally obtain a product with symmetrical and uniform upper and lower surface microporous structures and good ventilation property. Furthermore, warping deformation phenomenon is prevented.

Description

technical field [0001] The invention relates to a preparation method of a polyolefin microporous membrane, in particular to a preparation method of a polyolefin microporous membrane with symmetrical upper and lower surface structures. Background technique [0002] Polyolefin microporous film is a plastic film with numerous interconnecting micropores with a pore size in the range of 0.01-10 μm. It has been widely used in separators for lithium-ion batteries. The industrial production methods of this kind of microporous membrane at home and abroad mainly include melt stretching method and thermally induced phase separation method. [0003] The melt stretching method (that is, the dry method) is to extrude a crystalline polymer (such as polypropylene) into a film under the condition of increasing the stress of the molten polymer, and then anneal the film under no tension or low tension to obtain the necessary crystallization. structure, and then longitudinally stretched to pro...

Claims

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Application Information

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IPC IPC(8): C08J9/00C08J9/26C08J9/28C08L23/00C08L23/06C08L23/12C08L23/08C08L23/16C08L23/20C08K13/02B29C55/12B29C47/14B29C47/88B29C48/305
CPCC08L2203/16C08J2323/02B29C47/0057B29C47/8805B29C47/0042B29L2007/002C08L23/04B29C47/0019B29C47/0021B29C55/12B29C55/08B29K2023/00B29C55/18B29L2031/755C08J5/18B29K2105/04C08L23/02B29C47/14B29C48/0012B29C48/0018B29C48/07B29C48/08B29C48/305B29C48/91B29C48/914B29C48/917C08L2666/06
Inventor 陈秀蜂高东波陈勇
Owner SHENZHEN SENIOR TECH MATERIAL
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