Preparation method of polyolefin microporous membrane

Abstract

The invention provides a preparation method of polyolefin microporous membrane, comprising the following steps of: (1) mixing polyolefin resin and diluent according to the weight percent ratio of 10-60%:40-90%; (2) extruding and molding the mixture in an extrusion-blow molding manner to form bubble and cooling; (3) sizing the superposed and drawn membrane; (4) extracting diluent and drying; (5) performing transverse stretching and sizing treatment; and (6) rolling. By adopting the method of forming the bubble in a blow molding way, the invention avoids uneven structure caused by different cooling on the both surfaces in the casting process of general bidirectional stretching technique as well as uneven structure caused by slippage during longitudinal stretching, solves the problem of slippage of rollers during longitudinal stretching and ensures balanced longitudinal and transverse properties to finally obtain the polyolefin microporous membrane with even structure. Besides, the invention has the advantages of little investment, small occupation area, no slitter edge, easily-controlled production field, and the like.

Description

technical field [0001] The invention relates to a preparation method of a plastic film, in particular to a preparation of a polyolefin microporous film. Background technique [0002] Polyolefin microporous film is a plastic film with numerous interconnected micropores with a pore size of 0.01-10 μm. Its preparation methods mainly include: stretching high-filling plastic film method, melt stretching method, heat-induced phase separation method, hollow fiber method, physical and mechanical perforation method, etc. Among them, the industrialized methods mainly include melt stretching method and thermally induced phase separation method. [0003] The melt stretching 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 crystal structure, and then carry out longitudinal stretching. Stretching creates a netw...

AI Technical Summary

Problems solved by technology

In the step-by-step stretching process, due to the existence of a large amount of diluent in the formulation, after thermally induced phase separation, there is a large amount of diluent liquid on the surface of the cast sheet, and after entering the longitudinal stretching rollers, during the stretching process between the rollers due to Slipping leads to uneven structure and large thickness deviation of the final microporous membrane; and then in the process of horizontal stretching, due to the inherent tensile characteristics of horizontal stretching, the film is thicker on both sides and thinner in the middle, which also leads to uneven structure

In the process of synchronous stretching, although the slipping problem of longitudinal stretching is solved, on the one hand, it is the same as step stretching, and waste edges need to be cut off, resulting in low product yield; on the other hand, the investment in equipment is relatively large