JPH09157423A - Porous film having high strength and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-strength porous film having high face strength and proper air permeability. SOLUTION: This high strength porous film comprises a high-molecular weight polyethylene resin having >=300000 viscosity average molecular weight and has 5-50μm thickness, 200-1000sec-100cc air permeability, 10-50% porosity and >=600gf/25μm strength against stinging of pin. In melt-extrusion molding the resin composition containing the high-molecular weight polyethylene and a plasticizer, into a film, cooling, removing the plasticizer and drawing the film, total deformation ratio (DR×λMD)/(WD×λTD) of length and width (DR: draft ratio in extrusion molding; λMD: lengthwise draw ratio in drawing; WD: deformation ratio in width direction in extrusion molding; λTD: transverse draw ratio in drawing) is made to be 0.1-1. A porous film having high face strength while keeping general performances such as air permeability can be obtained by carrying out extrusion molding and drawing in the above total deformation ratio of length and width.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength porous film useful as a battery / separator, a separation membrane such as a microfiltration membrane, clothing such as an air-permeable jumper, sanitary articles such as diapers and sanitary articles, and the like. The present invention relates to a manufacturing method. More specifically, it relates to a high-strength porous film having a tough surface strength and an appropriate air permeability, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, porous films (including sheets) have been widely used for various purposes, and various methods for producing such porous films have been proposed. For example, a porous film for use as a battery separator is generally produced by melt-extruding a film from a resin composition containing ultra-high molecular weight polyethylene and a plasticizer, and then producing a plastic film contained in the film. It is manufactured by dissolving and removing the agent with an organic solvent such as isopropanol, ethanol and hexane.

The applicant of the present invention has previously proposed a porous film which provides a battery separator having excellent surface strength, particularly pin puncture strength (JP-A-7-29563).

[0004]

It is desired to further improve the strength of these porous films. For example, the demand for surface strength of a porous film as a battery separator is increasing with the increase in battery manufacturing speed.

However, it is difficult for the conventional manufacturing technique to satisfy such a required strength, and it is impossible to achieve both a particularly high surface strength and an appropriate air permeability. For example, when it is attempted to manufacture a film having a high surface strength such that the pin puncture strength exceeds 600 gf / 25 μm, the air permeability becomes 3000 seconds / 100 cc or more, and the air permeability, which is the basic performance of the porous film, is reduced. There was a problem of being damaged. On the contrary, in the case of a highly breathable porous film, only a film having weak surface strength was obtained.

The present invention solves the above-mentioned conventional problems and provides a high-strength porous film having a high surface strength and an appropriate air permeability, and a high-strength porous film such as this. The purpose is to provide a method.

[0007]

The high-strength porous film of the present invention is a porous film composed of a high molecular weight polyethylene resin having a viscosity average molecular weight of 300,000 or more, having a thickness of 5 to 50 μm and an air permeability. 200-1000 seconds / 100c
c, porosity 10 to 50%, pin puncture strength 600 gf / 25
It is characterized by having a characteristic of not less than μm.

The method for producing a high-strength porous film of the present invention comprises melt-extruding a resin composition containing a high-molecular-weight polyethylene resin having a viscosity average molecular weight of 300,000 and a plasticizer into a film, cooling the film, and then cooling the film. Is a method for producing a porous film in which the plasticizer contained in is removed and then stretched, wherein extrusion molding and stretching are performed so that the total longitudinal / lateral deformation ratio represented by the following formula is 0.1 to 1. And

Vertical / lateral total deformation ratio = (DR × λMD) / (WD × λTD) (where DR: draft ratio during extrusion molding λMD: longitudinal stretching ratio during stretching (1 if not longitudinal stretching) WD: Deformation ratio in the width direction during extrusion molding (blow ratio in the case of inflation molding) λTD: transverse stretching ratio during stretching (1 when not transversely stretched) That is, the present inventors have high surface strength and transparency. As a result of repeated intensive studies to realize a high-strength porous film with an appropriate degree of temper, when the aspect ratio of the deformation rate to the film is within a specific range through the manufacturing process, specifically high strength is expressed,
Moreover, they have realized that the air permeability is appropriate, and have accomplished the present invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In addition, in the present invention, the “film” includes “sheet”.

As the high molecular weight polyethylene resin constituting the film of the present invention, polyethylene having a viscosity average molecular weight of 300,000 or more is used, preferably a viscosity average molecular weight of 50.
Those having a viscosity of 1,000,000 to 4,000,000, particularly preferably 1.5,000,000 to 3,000,000, are used. Such high molecular weight polyethylene has a melting temperature of 110 to 110 from the viewpoint of easy melt deformation.
It is preferred to use 140 ° C. ethylene homopolymer.

In the present invention, if necessary,
Polybutene-1, polypropylene or polyethylene having a viscosity average molecular weight of less than 300,000 may be used in combination in an amount of 100% by weight or less, preferably 2 to 80% by weight, based on the high molecular weight polyethylene. Examples of such polyethylene include branched or linear low density polyethylene (molecular weight 5000 to 100,000), high density polyethylene (molecular weight 10,000 to 300,000), polyethylene wax (molecular weight 1000 to
5000). Polybutene-1 and polypropylene having a molecular weight of 4,000,000 or less can be used.

In the present invention, a raw material mixture obtained by mixing a high molecular weight polyethylene and a plasticizer is melt-extruded into a film, and then the plasticizer is removed and then stretched to obtain a porous film.

The plasticizer has good compatibility with the high molecular weight polyethylene, has a melting point lower than the melting point of the polyethylene and a boiling point higher than the melting temperature of the polyethylene, and is soluble in an organic solvent insoluble in polyethylene. Suitable substances are preferably used. For example, higher aliphatic alcohols such as stearyl alcohol and ceryl alcohol, n
-N-alkanes such as decane and n-dodecane, paraffin wax, liquid paraffin, and kerosene.

The proportion of the high molecular weight polyethylene and the plasticizer to be used depends on the porosity of the desired molded article, but is usually 5 to 60% by weight, preferably 10 to 50% by weight of polyethylene and 95 to 10% of the plasticizer. 40% by weight, preferably 90-5
It is selected from the range of 0% by weight. In the present invention, various known additives such as antioxidants are added to the raw material composition containing polyethylene and a plasticizer in such a proportion, and optionally the polybutene-1 and the like in an amount of 0.01
It may be added in the range of about 5% by weight.

Such a raw material composition is uniformly kneaded by a known uniaxial or biaxial extruder and melt-extruded. As the extruder, a twin-screw extruder is preferably used in terms of extrusion rate, extrusion stability, and kneading strength.

The extrusion molding is usually carried out at a temperature of 140 to 240 ° C., and it is usually a known method such as T-die or inflation molding, and usually 5 to 500 μm, especially 10 to 300 μm.
To form a film of thickness.

After cooling, the film is made porous by removing the plasticizer.

As a method of removing the plasticizer, for example, there is a so-called known organic solvent method in which the plasticizer in the film is dissolved in an organic solvent such as isopropanol, ethanol or hexane and the solvent is replaced to extract and remove.

The film made porous by removing the plasticizer as described above is uniaxially or biaxially stretched in order to improve its mechanical strength. For stretching, any known stretching device such as a roll stretching machine or a tenter can be used. Regarding uniaxial stretching, either longitudinal stretching or transverse stretching can be selected. As for the biaxial stretching, both sequential biaxial stretching and simultaneous biaxial stretching are possible.

In the extrusion molding and stretching steps in the manufacturing process, the MD (machine) direction and the T direction are applied to the film.
Mechanical deformation is applied in the D (width) direction. The mechanical deformation of the film is imparted in the form of melt deformation during extrusion molding and solid phase stretching during stretching after removing the plasticizer. In the method of the present invention, in these mechanical deformations, the vertical and horizontal total deformation ratio represented by the following formula is 0.1 to 1, preferably 0.
The extrusion molding conditions and the stretching conditions are set so as to be in the range of 2 to 0.8. If the total vertical / horizontal deformation ratio is less than 0.1 or more than 1, the air permeability of the obtained film deviates from the appropriate range, and the basic performance as a porous film, particularly as a battery separator, is not satisfied.

Vertical / lateral total deformation ratio = (DR × λMD) / (WD × λTD) (where DR: draft ratio during extrusion molding λMD: longitudinal stretching ratio during stretching (1 when not longitudinally stretched) WD: Width-direction deformation rate during extrusion molding (blow ratio in the case of inflation molding) λTD: transverse stretching ratio during stretching (1 when not transversely stretching)) The porous film of the present invention produced in this manner is 5
It has a thickness of ˜50 μm, preferably 15-35 μm. Further, the air permeability is a value measured according to JIS P8117 of 200 to 1000 sec / 100 cc, preferably 300 to 1000 sec / 100 cc, and more preferably 40.
It is about 0 to 900 seconds / 100 cc. For example, when the present porous film is used as a battery separator, when the air permeability value is less than 200 seconds / 100 cc, the resistance becomes small, while the air permeability value is 1000 seconds / 10.
If it exceeds 0 cc, the resistance increases, and in any case, the desired performance as a battery may not be obtained. The porosity of the present porous film is 10 to 50%, preferably 30 to 45%. The porosity is calculated by the following formula by punching 5 locations in the width direction of the film into a circle having a diameter of 3 cm, measuring the thickness and weight of the punched film at the center.

Porosity (%) = (Vρ−W) / (Vρ) × 100 (where V: volume of film (5 sheets) W: weight (5 sheets) ρ: density of material) The porous film of the present invention has extremely good mechanical strength, especially pin puncture strength, and the pin puncture strength is measured according to Japanese Agricultural Standards Notification No. 1019 (pin diameter 1 mmφ,
0.5R at tip, pin piercing speed of 300 mm / min), 600 gf / 25 μm or more film thickness, preferably 60
0 to 1000 gf / 25 μm film thickness, particularly preferably 60
It is about 0 to 800 gf (25 μm film thickness).

[0024]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

In Examples and Comparative Examples, the air permeability of the porous film was measured according to JIS P8117,
As described above, the porosity is the porosity (%) = (Vρ−W) /
It was calculated by the formula of (Vρ) × 100, and the pin puncture strength was measured according to Japanese Agriculture and Forestry Standards Notification No. 1019.

Example 1 A mixture of 25 parts by weight of ultra-high molecular weight polyethylene having a melting point of 135 ° C. and a viscosity average molecular weight of 2,000,000 and 75 parts by weight of stearyl alcohol was extruded at a temperature of 170 ° C. and an extruded amount of 10 kg using a 40 mmφ twin screw extruder. / Hr, and the film was formed by the inflation method. At this time, the draft rate DR was 12 and the blow ratio WD was 9.

The obtained film was immersed in ethanol at 60 ° C. for 10 minutes to extract and remove stearyl alcohol. Then, at 120 ° C. using a roll stretching machine, MD
2 times in the TD direction, and then 4 times in the TD direction at 128 ° C. using a tenter stretching device to obtain a porous film having a thickness of 25 μm. The total vertical and horizontal deformation ratios in this manufacturing process are as shown in Table 1.

The pin puncture strength, air permeability and porosity of the obtained molded product were measured, and the results are shown in Table 1.

Example 2 A mixture of 20 parts by weight of ultrahigh molecular weight polyethylene having a melting point of 135 ° C. and a viscosity average molecular weight of 2,000,000 and 80 parts by weight of paraffin wax (average molecular weight 389) was extruded at a extrusion temperature of 170 using a 40 mmφ twin-screw extruder. ℃, extrusion rate 10kg / hr
And extruded to form a film by the inflation method.
At this time, the draft rate DR was 12 and the blow ratio WD was 6.

The obtained film was immersed in hexane at 60 ° C. for 10 minutes to extract and remove paraffin wax.
Then, using a tenter stretching device at 130 ° C., TD
The film was stretched 7 times in the direction to obtain a porous film having a thickness of 26 μm. Table 1 shows the values of the total vertical and horizontal deformation ratios and the physical properties of the obtained porous film.

Example 3 A mixture of 25 parts by weight of ultrahigh molecular weight polyethylene having a melting point of 135 ° C. and a viscosity average molecular weight of 2,000,000 and 75 parts by weight of stearyl alcohol was extruded at a temperature of 170 ° C. and an extrusion amount of 10 kg using a 40 mmφ twin-screw extruder. / Hr, and the film was formed by the T-die method. At this time, the draft rate DR was 5 and the width direction deformation rate (WD) was 1.

The obtained film was immersed in ethanol at 60 ° C. for 10 minutes to extract and remove stearyl alcohol. Then, using a tenter stretching device at 128 ° C,
The film was stretched 6 times in the TD direction to obtain a porous film having a thickness of 25 μm. Table 1 shows the values of the total vertical and horizontal deformation ratios and the physical properties of the obtained porous film.

Comparative Example 1 A porous film was obtained in the same manner as in Example 1, except that the stretching ratio in the MD direction by the roll stretching machine was set to 3 times and the stretching ratio in the TD direction by the tenter stretching device was set to 3 times. It was Table 1 shows the vertical and horizontal total deformation ratios and the physical properties of the obtained porous film.

Comparative Example 2 In Example 1, 20 parts by weight of ultrahigh molecular weight polyethylene and 80 parts by weight of stearyl alcohol were mixed to give a draft ratio of 20 during inflation molding and a blow ratio of 4, and after stearyl alcohol was extracted and removed, Using a roll stretching machine at 125 ° C., stretching 5 times in the MD direction,
A porous film having a thickness of 27 μm was obtained in the same manner except that stretching in the D direction was not performed. Table 1 shows the vertical and horizontal total deformation ratios and the physical properties of the obtained porous film.

[0035]

[Table 1]

As is clear from Table 1, according to the present invention, it is possible to produce a porous film having a high surface strength and an appropriate air permeability.

[0037]

As described above in detail, the high-strength porous film of the present invention has a high surface strength and an appropriate air permeability which cannot be realized by the conventional method and which cannot be realized by the conventional method. According to the present invention, it is possible to provide a porous film having excellent surface strength while maintaining general performance. For example, when used as a battery separator, it is possible to assemble a battery at a higher speed than ever before. Becomes

The high-strength porous film of the present invention as described above can be easily and efficiently manufactured by the method of the present invention in which the aspect ratio of the deformation ratio of the film is within a specific range through the manufacturing process.

Claims (2)

[Claims] 1. A porous film composed of a high molecular weight polyethylene resin having a viscosity average molecular weight of 300,000 or more,
Thickness 5 to 50 μm, Air permeability 200 to 1000 seconds / 100
cc, porosity 10 to 50%, pin puncture strength 600 gf / 2
A high-strength porous film having characteristics of 5 μm or more. 2. A resin composition containing a high-molecular-weight polyethylene resin having a viscosity average molecular weight of 300,000 or more and a plasticizer is melt-extruded into a film, cooled, and then the plasticizer contained in the film is removed and then stretched. A method for producing a porous film, wherein a total longitudinal and lateral deformation ratio represented by the following formula is 0.1 to 0.1.
A method for producing a high-strength porous film, which comprises performing extrusion molding and stretching so as to be 1. Vertical / lateral total deformation ratio = (DR × λMD) / (WD × λTD) (where DR: draft ratio during extrusion molding λMD: longitudinal stretching ratio during stretching (1 when not longitudinal stretching) WD: during extrusion molding Deformation ratio in the width direction (blow ratio in the case of inflation molding) λTD: transverse stretching ratio during stretching (1 if not transversely stretched))