Polymer membrane and preparation method thereof

Abstract

The invention discloses a polymer membrane, and a preparation method thereof. The polymer membrane is composed of a polypropylene composition; and the polypropylene composition contains, (a) 40 to 70wt% of a crystalline polypropylene A, wherein the crystalline polypropylene A is at least one selected from a propylene homopolymer and a propylene random copolymer, and (b) 30 to 60wt% of an ethylene-propylene elastic copolymer B. The molecular weight distribution indexes of the polypropylene composition and the crystalline polypropylene A are both larger than 4; melt mass-flow rate of the polypropylene composition at 230 DEG C under loading of 2.16kg ranges from 5 to 10g / 10min, and the ratio of the melt mass-flow rate ratio of the polypropylene composition to the melt mass-flow rate ratio of the crystalline polypropylene A ranges from 0.7 to 1.3; the polymer membrane contains a nucleating agent; and in 100 weight parts of the polypropylene composition, the content of the nucleating agent ranges from 200 to 2000ppm. The polymer membrane possesses relatively high transparency, excellent shock resistance, and excellent performance uniformity in the axial direction and the radial direction.

Description

technical field [0001] The invention relates to a polymer film and a preparation method of the polymer film. Background technique [0002] Polyolefin films are widely used in food packaging, refrigerated packaging, frozen packaging, medical equipment, daily necessities packaging, etc. These fields usually require films to have good transparency. Films made of propylene copolymers obtained by random copolymerization with monomers such as ethylene and butene generally have good transparency. Adding transparency aids to homopolypropylene can also produce high-transparency films. However, as a packaging film, it needs to have good impact resistance to prevent the film from being damaged under the impact of external force. Atactic polypropylene and homopolypropylene are limited by their molecular structure, and their impact resistance is not ideal. [0003] In order to improve the impact resistance of the film, it is mentioned in CN1675257A that 10-50% ultra-low density polyeth...

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Problems solved by technology

Atactic polypropylene and homopolypropylene are limited by their molecular structure, and their impact resistance is not ideal

[0003] In order to improve the impact resistance of the film, it is mentioned in CN1675257A that 10-50% ultra-low density polyethylene (ULDPE) is added to the syndiotactic polypropylene to improve the impact performance of the film. Although this method can improve the film while maintaining transparency Impact resistance, but the production method of syndiotactic polypropylene and ULDPE is more complicated, and the addition of ULDPE is high, resulting in a more complicated production process and prone to problems, and this method is more costly

In CN1861674A, it is mentioned that 80-95% of high crystalline random copolymer is blended with 5-20% of ethylene-propylene elastomeric copolymer, thereby improving the impact resistance and transparency of the product, but the first method needs to be blended Step, the second main body of the composition is a random copolymer, which will reduce the rigidity and heat resistance of the product, and for packaging films, better rigidity and stiffness are required to make it difficult to open during winding and packaging pleats

In the impact polypropylene produced by this method, the ethylene-propylene elastic copolymer and homopolypropylene will undergo phase separation, resulting in an increase in the haze of the final product. In addition, the binary ethylene- Propylene elastomeric copolymers usually have a very heterogeneous composition, so such copolymers are usually not transparent

This leads to the high haze of the film produced by ordinary impact polypropylene, which cannot meet the requirements of improving the impact resistance and transparency of the film at the same time.

[0006] Metallocene catalysts are used to produce impact polypropylene. Although products with better toughness and transparency can be obtained, metallocene catalysts are more expensive than Ziegler-Natta catalysts, and cannot be produced by most polyolefin plants.

Due to the narrow molecular weight distribution of the prepared polypropylene, the processing fluidity in the film making process is worse than that produced by Ziegler-Natta catalysts, so it cannot be widely used

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