CN-116507674-B - Polyolefin resin composition for porous film

Abstract

Disclosed are a polyolefin resin composition which can be used for the production of a single-layer dry porous film having excellent fusing characteristics and excellent closed cell characteristics, and a porous film using the same. The invention provides a polyolefin resin composition for porous films, which comprises 30-70 wt% of high-density polyethylene, wherein the melt flow index (190 ℃ C., 2.16kg load) of the high-density polyethylene is 0.1-5 g/10min, the crystallization temperature is 115-125 ℃ C., the crystallinity is more than 75%, and 30-70 wt% of high-crystalline polypropylene, and the melt flow index (230 ℃ C., 2.16kg load) of the high-crystalline polypropylene is 5-20 g/10min.

Inventors

• ZHENG SHANYING
• SUN CHANGKUI
• Zheng Menxi
• ZHAO XIYUAN
• JIN JINGXUN

Assignees

• 乐天化学株式会社

Dates

Publication Date

20260508

Application Date

20211105

Priority Date

20201118

Claims (3)

1. 1. A polyolefin resin composition for a porous film, comprising: 20 to 70 wt% of a high-density polyethylene having a melt flow index of 0.5 to 1.5g/10min at 190 ℃ under a load of 2.16kg, a crystallization temperature of 115 to 125 ℃ and a crystallinity of 75% or more, and 30-80 Wt% of high-crystalline polypropylene, wherein the high-crystalline polypropylene has a melt flow index of 6-10 g/10min at 230 ℃ under a load of 2.16kg, a crystallinity of 53% or more and a tacticity of 95% or more.
2. 2. The polyolefin resin composition for a porous film according to claim 1, wherein, The resin composition has a closed cell temperature of 140 ℃ or less, a fusing temperature of 160 ℃ or more, a perforation strength of 520gf or more, [ Measurement method ] After the sheet is molded by extruding the resin composition by a T-die method at 220 to 250 ℃ using a twin-screw extruder, a single-layer porous film having a thickness of 15 μm is prepared by sequentially stretching in MD and TD directions inside a stretching machine, a sample of the porous film having a size of 50×50mm is placed on a plate having holes having a diameter of 10mm, a penetrating force at the time of pressing by a 1mm probe is set as a perforation strength, and a lithium ion secondary battery prepared using the porous film is heated at a speed of 2 ℃ per minute in an oven while measuring a resistance in real time, a temperature at a time when the resistance exceeds 10,000 Ω is set as a closed-cell temperature, and a temperature at a time when the resistance is suddenly reduced after the closed-cell temperature is set as a fusing temperature.
3. 3. A porous film formed into a single layer using the resin composition according to claim 1 or 2.

Description

Polyolefin resin composition for porous film Technical Field The present invention relates to a polyolefin resin composition for a porous film, and more particularly, to a polyolefin resin composition for a porous film which is excellent in fusing characteristics and closed cell characteristics. The present application claims priority and benefit from korean patent application No. 10-2020-0154902, which was filed on 18/11/2020, the entire contents of which are incorporated herein by reference. Background Porous membranes are widely used in secondary battery separators, filters, and other applications where specific components need to be distinguished. In recent years, polyolefin is used for a porous film in a film form, which has been in demand, and the amount of raw materials used is gradually increasing with the demand. Among them, polyethylene, which can satisfy desired physical properties even with a small thickness, shows a remarkable trend of increasing demand. Recently, in response to the increase in capacity and power of secondary batteries, the safety problem of the batteries has been highlighted, and polyolefin porous films are not used alone due to the fusing property and the pore closing property, and are generally produced by laminating polypropylene microporous films and polyethylene microporous films. The battery preferably has a relatively low closed cell temperature and has a relatively high fusing temperature, and for low closed cell characteristics, a polyethylene-based resin is applied, and for high fusing temperature (film damage temperature) characteristics, a polypropylene-based resin is applied. As described above, the conventional battery film has a two-layer structure of a polypropylene porous layer/a polyethylene porous layer or a three-layer structure of a polypropylene porous layer/a polyethylene porous layer/a polypropylene porous layer, and thus has problems in that the production process is complicated, the control variables are large, and the production cost is also increased. Korean patent No. 1305264 only mentions a conventional multi-layer film, which is a polyolefin multi-layer micro-porous film formed by stacking a porous layer a formed of polypropylene and a porous layer B formed of polyethylene-based resin in the order of porous layer B/porous layer a/porous layer B. Disclosure of Invention The invention provides a polyolefin resin composition and a porous film using the same, wherein the polyolefin resin composition can be used for preparing a single-layer dry porous film with excellent fusing property and closed pore property. In order to solve the above-mentioned problems, the present invention provides a polyolefin resin composition for a porous film, comprising 20 to 70% by weight of a high-density polyethylene having a melt flow index (190 ℃ C., 2.16kg load) of 0.1 to 5g/10min, a crystallization temperature of 115 to 125 ℃ C., a crystallinity of 75% or more, and 30 to 80% by weight of a high-crystalline polypropylene having a melt flow index (230 ℃ C., 2.16kg load) of 5 to 20g/10min. Further, a polyolefin resin composition for a porous film is provided, which is characterized in that the resin composition has a closed cell temperature of 140 ℃ or less, a fusing temperature of 160 ℃ or more, and a perforation strength of 520gf or more, measured by the following method. [ Measurement method ] After the sheet is molded by extruding the resin composition by a T-die method at 220 to 250 ℃ using a twin-screw extruder, a single-layer porous film having a thickness of 15 μm is prepared by sequentially stretching in MD and TD directions inside a stretching machine, a sample of the porous film having a size of 50×50mm is placed on a plate having holes having a diameter of 10mm, a penetrating force at the time of pressing by a 1mm probe is set as a perforation strength, and a lithium ion secondary battery prepared using the porous film is heated at a speed of 2 ℃ per minute in an oven while measuring a resistance in real time, a temperature at a time when the resistance exceeds 10,000 Ω is set as a closed-cell temperature, and a temperature at a time when the resistance is suddenly reduced after the closed-cell temperature is set as a fusing temperature. Further, a porous film formed as a single layer using the above resin composition is provided. According to the present invention, in the preparation of a porous film using a polyolefin resin, a conventional complicated multilayer structure is eliminated by mixing a high-density polyethylene having a specific fluidity and a specific crystallization property and a high-crystallization polypropylene having a specific fluidity in a specific ratio, whereby a polyolefin resin composition for a porous film and a porous film using the same, which can realize excellent closed cell properties and fusing properties with a simple process, can be provided by single-layer molding. Detailed Description The present application will be de