A kind of polyolefin film and preparation method thereof

Abstract

The invention relates to a polyolefin film and a preparation method thereof. The polyolefin resin is placed in a solvent, and the temperature is controlled to perform swelling treatment at the swelling temperature of the polyolefin resin; after filtration, an antioxidant is added, and the polyolefin resin is processed through a twin-screw extruder. Extrude at 170°C-230°C, cool at room temperature-90°C, stretch, extract with extractant, stretch at 110°C-130°C, and set at 100°C-128°C to prepare a polyolefin film. Compared with the prior art, the invention can carry out continuous production, and the prepared film has the advantages of good solubility and the like.

Description

technical field [0001] The invention relates to the field of polymer material preparation, in particular to a polyolefin film and a preparation method thereof. Background technique [0002] Lithium-ion battery is a hot spot in the research of new power supply technology in recent years. One of its core components, the separator, melts and closes cells when overheating, short circuit and other accidents occur. The separator is usually made of polyethylene and polypropylene. The performance of ultra-high molecular weight polyethylene is superior to that of ordinary polyethylene and polypropylene, especially when the temperature is higher than the melting point, the melt can still maintain a gel state and melt without collapsing. However, due to the high molecular weight of ultra-high molecular weight polyethylene, the melt viscosity increases sharply during the melting process. In order to reduce the viscosity of the system and reduce the difficulty of processing, a solvent is...

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Problems solved by technology

[0005] Chinese patent CN101164677B discloses a method for preparing a high-performance ultra-high molecular weight polyethylene porous membrane by thermally induced phase separation. In this method, the mixture of resin and solvent is placed in a high-temperature stirring tank, heated to 180°C-280°C, and stirred to form The homogeneous solution is directly coated on the template to obtain a flat film. The Weissenberg phenomenon (that is, the rod climbing phenomenon) will occur in the kettle-type dissolution adopted in this method. In order to eliminate the rod climbing phenomenon, the heating time can only be prolonged, so the heating of polyethylene is inevitable. degradation

[0006] The swelling process of ultra-high molecular weight polyethylene resin is a slow endothermic process. It takes a certain amount of time to swell. The swelling of the resin is extremely sensitive to temperature. Dissolution also affects the uniform feeding of the extruder. Due to the limitation of the length-to-diameter ratio of the extruder screw, the residence time of the resin and solvent mixture in the extruder is limited, which affects the sufficient swelling and uniform dissolution of the resin.

If the polymer dissolves without sufficient swelling, a high-viscosity layer will be formed at the interface of the polymer, which will inhibit the penetration of the solvent into the interior, and local swelling will occur on the surface of the polymer, and the swelling phenomenon of fish-eye spots will appear. The continuous penetration and diffusion in the polymer hinders the diffusion of polymer macromolecules into the solvent during the dissolution process, which affects the uniformity of the solution and further affects the performance of the product

Chinese patent CN102136557B discloses a lithium-ion battery separator and its preparation method. In this method, a mixture of polyolefin and solvent is directly extruded in an extruder to form a flat film. There is no additional swelling process for polyolefin, and both swelling and dissolution Completed in the extruder, this method inevitably has some polyolefin resins that do not swell completely

Although the Chinese patent CN1067731C discloses a continuous preparation method for a homogeneous solution of ultra-high molecular weight polyethylene, in the ultra-high molecular weight polyethylene jelly spinning process, the ultra-high molecular weight polyethylene is moderately swollen in a swelling kettle, and then put into a storage kettle. Continue to stir and cool to a certain temperature for later use. Two storage tanks are used alternately, but this method is suitable for using one solvent, which is suitable for low-concentration spinning solutions, but not for high-concentration membrane-making solutions. When the concentration increases There is a possibility of insufficient swelling, and the feeding equipment in this method is relatively complicated, and it involves the matching problem of the swelling tank, storage tank and extruder

The above-mentioned method solves the problem that ultra-high polyethylene is difficult to process and form a film, but there are still the following defects: a homogeneous solution is prepared at a high temperature by a high-temperature stirred tank, and due to the rod-climbing phenomenon, it is necessary to reduce the concentration and reduce the stirring speed, prolonging the dissolution process, and it is difficult to produce a long-term solution. The problem of time-consuming industrialized continuous production; directly extruding the polyolefin mixture continuously, there is a problem that the high molecular weight polyolefin in the extruder is not fully swollen and difficult to completely and uniformly dissolve, which ultimately affects the performance of the film; The feeding method is suitable for low-concentration solutions. When the concentration increases to a certain extent, the swelling time of ultra-high molecular weight polyethylene in the swelling tank will be greatly prolonged. If the change of molecular weight, the mixing of different resins and the mixing of different solvents are considered , the swelling temperature and swelling time will become more complicated, and the matching of the corresponding feeding equipment and extruder will also become complicated

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