JPH082983B2 - Method for manufacturing porous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Fields of Industrial Application) The present invention is excellent in air permeability, ion permeability, mechanical strength, etc., and is preferably used as a material for battery separators, condenser films, filtration membranes and the like. The present invention relates to a method for producing a porous film that can be manufactured. Generally, the maximum pore size is 1 for battery separators and condenser films.
Those having a large number of fine pores having an average pore diameter of about 0.005 to 0.6 μm and having a diameter of not more than μm are used. Therefore, also in this invention, it aims at obtaining such a microporous film.

(Prior Art and Problems to be Solved by the Invention) As a conventional method for producing a porous film, a method of uniaxially or biaxially stretching a film-like material obtained by mixing a polyolefin resin such as polyethylene or polypropylene and a filler is used. Are known. In such a method, in order to obtain a porous film having a practical air permeability, it was necessary to mix a large amount of 25 parts by volume or more of filler with 100 parts by volume of the polyolefin resin. This is because when the amount of the filler is less than 25 parts by volume, pore formation due to interfacial peeling between the polyolefin resin and the filler becomes insufficient.

On the other hand, it is proposed that a film-like material composed of a polyolefin-based resin and a filler be cold-stretched at a low magnification in advance to cause interfacial peeling between the polyolefin-based resin and the filler, and then uniaxially or biaxially stretched by a known method. (Japanese Patent Publication No. 58-7449). However, in this method, when the filling amount of the filler is small, the necking phenomenon due to stretching causes the interface peeling between the polyolefin-based resin and the filler, and where it does not occur. It is practically difficult to raise it, and even if it is possible to make it porous in the subsequent stretching, there is a problem that thickness accuracy is poor and only those having large variations in physical properties such as air permeability can be obtained.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present inventors have earnestly conducted research on a method for producing a porous film. As a result, the surface of the membranous material composed of the polyolefin resin and the filler,
By cold stretching while rubbing with a blade, good stretching can be performed even in a range of a small amount of filler, and further by performing ordinary stretching, it was found that a porous film having good air permeability can be obtained, The invention was completed.

That is, according to the present invention, after the surface of a membranous material consisting of 100 parts by volume of a polyolefin resin and 3 to 100 parts by volume of a filler is cold stretched 1.05 to 1.8 times while rubbing with a blade having a radius of curvature of 0.05 to 1.5 mm, And a uniaxially or biaxially stretched film without further rubbing.

The polyolefin resin used in the present invention,
Α-olefin homopolymers such as polyethylene, polypropylene, polybutene-1 or polymethylpentene, α
-Copolymers of olefins with other copolymerizable monomers and mixtures thereof. Of these, a homopolymer of propylene, a copolymer of propylene and another copolymerizable monomer, and a mixture thereof are preferable in consideration of heat resistance and moldability of the obtained porous film. Especially, the melt flow index measured at 230 ℃ is 0.01
-50 g / 10 min, preferably 0.1-30 g / 10 min propylene homopolymer, copolymer of propylene and other copolymerizable monomer, or a mixture thereof, has a moldability when molded into a film. Is favorable, and therefore, it is preferably used in the present invention.

The above-mentioned copolymer of α-olefin and other copolymerizable monomer is generally a copolymer containing α-olefin, particularly propylene in an amount of 90% by weight or more, and another copolymerizable monomer in an amount of 10% by weight or less. Is preferred. The copolymerizable monomer is not particularly limited, and known ones can be used. Generally, α-olefins having 2 to 8 carbon atoms, particularly ethylene and butene are preferable.

Next, as the filler used in the present invention, known fillers such as an inorganic filler and a synthetic resin filler made of a synthetic resin are adopted without any limitation. As the inorganic filler, an oxide, hydroxide, carbonate or sulfate of one kind of metal selected from the group consisting of Group IIA, Group IIIA and Group IVB of the Periodic Table is preferably used. . For example, Periodic Table IIA
Group IIIA metals are alkaline earth metals such as calcium, magnesium and barium, Group IIIA metals are metals such as boron and aluminum, and Group IV
As the group B metal, metals such as titanium, zirconium and hafnium are suitable. Oxides, hydroxides, carbonates or sulfates of these metals can be used without particular limitation. In particular, inorganic fillers that are preferably used are more specifically illustrated. Calcium oxide, magnesium oxide, barium oxide, aluminum oxide, boron oxide, titanium oxide, oxides such as zirconium oxide; calcium carbonate, magnesium carbonate, Carbonates such as barium carbonate; hydroxides such as magnesium hydroxide, calcium hydroxide and aluminum hydroxide; sulfates such as calcium sulfate, barium sulfate and aluminum sulfate.

A synthetic resin filler is also suitably used as the filler used in the present invention. The above-mentioned synthetic resin filler, if the softening temperature or decomposition temperature is higher than the molding temperature of the polyolefin-based resin, preferably 10 ° C. or higher, a known synthetic resin regardless of thermosetting resin and thermoplastic resin. Can be used. When the softening temperature or the decomposition temperature is lower than the molding temperature of the polyolefin resin, the synthetic resin filler is softened or decomposed to generate a gas when the mixture of the polyolefin resin and the filler is molded into a film. However, it cannot be made porous. The molding temperature of the polyolefin resin is usually in the range of 200 to 230 ° C.

Specific examples of synthetic resin fillers that can be preferably used in the present invention include polyamides such as 6-nylon and 6,6-nylon; polytetrafluoroethylene, tetrafluoroethylene-hexafluoride. Fluorine-based resins such as propylene copolymers; polyimides; silicone resins; phenol resins; benzoguanamine resins; or copolymers of styrene, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, etc. with a cross-linking agent such as divinylbenzene. Is preferred. Above all, a silicone resin is preferably used in the present invention because it has a good interfacial peeling property from a polyolefin and can be easily made porous by stretching.

The filler used in the present invention preferably has an average particle diameter of 20 μm or less, preferably 0.01 to 5.0 μm, in order to use the obtained porous film for the above-mentioned uses.

The blending ratio of the polyolefin resin and the filler in the present invention should be selected so that the filler is 3 to 100 parts by volume, preferably 5 to 80 parts by volume, based on 100 parts by volume of the polyolefin resin. In particular, the compounding ratio in which the curing of the present invention remarkably appears is 3 to 25 parts by volume of the filler with respect to 100 parts by volume of the polyolefin resin. In the range where the amount of the filler exceeds 25 parts by volume, it is possible to make it porous by a known stretching method without cold stretching while rubbing it with a blade, but if it is used in the method of the present invention, the subsequent stretching operation is easy. In addition, it is possible to obtain those having excellent physical properties such as thickness accuracy. Filler amount is 3 ~
In the range of 25 parts by volume, it is extremely difficult to form a porous film by a known stretching method, and a porous film having desired physical properties cannot be obtained. It is possible to easily obtain a porous film. When the amount of the filler is less than 3 parts by volume, the ratio of the interfacial peeling between the polyolefin resin and the filler due to cold stretching is small, and the desired physical properties cannot be obtained.
If the amount is more than the capacity part, a molding failure may occur during molding into a film or the stretchability may be deteriorated, and a desired porous film cannot be obtained.

In the present invention, the method for mixing the polyolefin resin and the filler is not particularly limited, and a known method can be adopted. For example, it can be mixed with a super mixer, a Henschel mixer, or the like. Further, upon mixing, an antioxidant, within a range that does not deteriorate the performance of the target porous film,
It is a desirable mode to add known additives such as deterioration inhibitors and lubricants, and further known dispersants in order to enhance the dispersing effect of the filler.

The method of shaping the mixture into a film is not particularly limited, but generally an inflation molding method or a melt molding method using a T die is preferable. The thickness of the film is 0.03-3.
Those having a diameter of 0 mm, preferably 0.05 to 1.5 mm are used.

In the present invention, the surface of the above-mentioned membranous material is
It is particularly important to cold draw at a time of 1.05 to 1.8 times, preferably 1.1 to 1.7 times while rubbing with a blade of 0.05 to 1.5 mm, preferably 0.1 to 1.2 mm. If any of these requirements are lacking, the porous film aimed at by the present invention cannot be obtained. When the radius of curvature of the blade is smaller than 0.05 mm, the film-like material breaks, which is not practical, and when it exceeds 1.5 mm, the blade has no effect and interfacial peeling hardly occurs uniformly.

Next, regarding the cold stretching ratio, if it is less than 1.05 times, interfacial peeling does not occur especially when the amount of the filler is small, and a porous film cannot be obtained even by performing the known stretching in the next step. On the other hand, when it exceeds 1.8 times, it becomes difficult to obtain a porous film having performance suitable for the purpose of the present invention. Cold stretching is preferably performed in the range of 0 to 50 ° C. The rubbing with a blade may be performed on both sides of the film-like material, but the purpose can be sufficiently achieved with only one side. Further, rubbing with a blade can be usually achieved by pressing the blade against a film-like material. The angle formed by the film and the blade at that time is 25 to 85 °, and preferably 30 to 75 ° in order to achieve good interfacial separation between the polyolefin resin and the filler.

In this way, a film-like material having fine pores between the polyolefin resin and the filler can be obtained. This film-like material can be made into a porous film by stretching by a usual stretching method. As a usual stretching method, generally, uniaxial stretching by a roll stretching method, or after uniaxial stretching, successively biaxially stretching in the transverse direction by a tenter stretching machine, an air inflation stretching machine or the like, or simultaneously in the longitudinal and transverse directions. A stretching method is adopted. The stretching temperature is generally 60 ° C. or higher to the melting point of the polyolefin resin or lower, and particularly preferably 10 to 80 ° C. lower than the melting point.

The area draw ratio is preferably in the range of 1.5 to 30 times. The above area stretching ratio does not necessarily need to be biaxially stretched, and may be uniaxially stretched. When the film is stretched only in the uniaxial direction (longitudinal direction), it is preferably stretched 1.5 to 12 times, preferably 3 to 7 times. When stretching in the biaxial direction,
Stretching is preferably 1.2 times or more in the uniaxial direction (longitudinal direction), preferably 1.5 times or more, and 1.2 times or more in the biaxial direction (transverse direction), preferably 1.5 times or more, and most preferably 2 to 1 axis direction.
Those stretched 5 times and 2 to 7 times in the biaxial direction are preferable.

When uniaxially or biaxially stretched as described above, the resulting porous film has a porosity of 58 to 77% and an air permeability of 100 to 420 seconds.
It is a porous film suitable for the purpose of the present invention including the range of / 100 cc.

The thus-obtained porous film has pores formed by further expanding fine pores due to interfacial separation between the polyolefin-based resin and the filler due to stretching of the polyolefin-based resin film containing the above-mentioned filler. .

It is preferable that the porous film obtained by stretching is further heat-treated under tension, for example, heat-set at a temperature of 100 to 160 ° C., and then cooled to room temperature to obtain a target product. In addition, it is a preferred embodiment to perform surface treatment by corona discharge treatment for the purpose of improving printability and adhesiveness.

(Operations and Effects) As described above, according to the present invention, the interfacial peeling between the polyolefin-based resin and the filler can be uniformly generated on the entire surface of the film-like material even with a small amount of the filler. Then, in the next step, by uniaxially or biaxially stretching this film-like material, interfacial delamination is expanded and thickness accuracy is good, and furthermore, a porous film having excellent physical properties such as air permeability and ion permeability is obtained. You can In addition, when the amount of the filler contained in the film is small, the porous film can be uniaxially or biaxially stretched to have excellent molecular orientation of the polyolefin resin and excellent mechanical strength.

Since the porous film obtained by the present invention has the above-mentioned excellent physical properties, it is extremely useful particularly for applications such as battery separators, condenser films, and filtration membranes.

(Examples) Examples are shown below to more specifically describe the present invention, but the present invention is not limited to these examples.

The film physical properties shown in Examples and Comparative Examples are
It was measured by the following method.

(1) Porosity Measured by a specific gravity measuring method.

(2) Air permeability Measured according to JIS-P-8117 (Gurley air permeability).

(3) Tensile strength Measured according to ASTM-882.

In Table 1, MD represents the film winding direction, and TD represents the direction perpendicular to the film winding direction.

(4) Ion permeability Propylene carbonate / 1,2 dimethoxyethane = 1/1
A solution obtained by dissolving lithium perchlorate in a solvent (volume ratio) so that the amount of lithium perchlorate becomes 1 mol and a solution that does not dissolve are partitioned by a film, and a change in electric conductivity due to permeation of lithium ions is measured by a conductivity meter.

(5) Thickness accuracy The thickness was measured at 50 locations at 5 cm intervals in the film winding direction and expressed as the difference between the maximum value and the minimum value.

The following were used as the polyolefin resin.

(1) Polypropylene; PN120 (trade name) manufactured by Tokuyama Soda Co., Ltd., melt flow index 1.7 g / 10 minutes measured at 230 ° C. (2) Propylene-ethylene copolymer; Tokuyama Soda Co., Ltd. MS624 ( (Trade name), melt flow index 1.7 g / 10 minutes measured at 230 ° C., ethylene content 4.7 g wt% (3) polyethylene; Mitsui Petrochemical Co., Ltd., Hi-Zex 6100M (trade name), measured at 190 ° C. Melt flow index 0.18g
/ 10 min The capacity of the polyolefin resin and the filler was the weight of the polyolefin resin and the filler divided by the respective densities.

Example-1 100 parts by weight of polypropylene (PN120 manufactured by Tokuyama Soda Co., Ltd.), 8 parts by volume of calcium carbonate having an average particle size of 0.09 μm, and 0.8 parts by volume of zinc stearate were mixed with a super mixer, and then 210 by a twin-screw extruder. Pellets were made at ° C.

The obtained pellets are extruded at 215 ° C. with an extruder having a screw diameter of 40 mmφ and L / D = 28 equipped with a T-die,
It is brought into contact with a 70 ° C chill roll and taken at 3.0 m / min, 0.1 mm
A thick film was obtained. A radius of curvature of 0.2 m on one side of the film
While rubbing against the blade of m so that the angle formed by the film and the blade was 45 °, it was stretched 1.4 times at normal temperature between two pairs of rolls having different rotation speeds.

Further, the cold-stretched film is stretched 4.0 times at 100 ° C. between two pairs of heating rolls having different rotation speeds, and stretched by a tenter at a temperature of 152 ° C. at 2.0 times in a direction perpendicular to the uniaxial stretching direction. Then
A porous film was obtained. The physical properties of the obtained porous film are shown in Table 1.

In Table 1, regarding the uniform whitening property, "good" indicates that the entire surface of the film has been uniformly whitened, and "bad" indicates that the part is partially whitened.

Comparative Examples-1 to 3 As Comparative Examples-1, 2 and 3, the films were prepared by cold drawing, rubbing with a blade but not cold drawing, and 1.4 times cold drawing without rubbing with a blade. Then, a film was obtained and then biaxially stretched in the same manner as in Example-1 to obtain a stretched film.

The physical properties of the stretched films obtained in Comparative Examples-1 to 3 are shown in Table-1.

Example-2 100 parts by volume of polypropylene (PN120 manufactured by Tokuyama Soda) and 30 parts by volume of a silicone resin having an average particle size of 2.0 μm were used in Example-
A film-like material having a thickness of 0.1 mm was obtained in the same manner as in 1.

While rubbing one side of the film with a blade with a radius of curvature of 1.2 mm so that the angle between the film and the blade is 30 °, 1.1 times at room temperature between two pairs of rolls with different rotation speeds. It was stretched.

Further, the cold-stretched membranous material was biaxially stretched by the same method as in Example-1 to obtain a porous film.

 The physical properties of the obtained porous film are shown in Table 1.

Comparative Example-4 Without cold-drawing the film-like material molded in Example-2,
In the same manner as in Example-1, the film was stretched 4.4 times in the uniaxial direction and 2.0 times in the direction perpendicular to the uniaxial stretching direction to obtain a porous film.

 The physical properties of the obtained porous film are shown in Table 1.

Example-3 A film-like material having a thickness of 0.1 mm was obtained from the polyolefin resin, the filler, and 0.4 volume part of aluminum stearate shown in Table 1 by the same method as in Example-1.

One side of the membranous material, on a blade having a radius of curvature shown in Table-1,
While rubbing so that the angle formed by the blade of the film-like object is 45 °, at the room temperature between two pairs of rolls with different rotation speeds, see Table-1.
It was stretched at the magnification shown in.

Further, the cold-stretched film-like material was uniaxially stretched 4.0 times by the same method as in Example-1, and uniaxially stretched in the direction perpendicular to
It was stretched 4.0 times to obtain a porous film.

 The physical properties of the obtained porous film are shown in Table 1.

Example-4 High-density polyethylene (Hi-Z 61 manufactured by Mitsui Petrochemical Co., Ltd.
00M) 100 parts by volume, calcium carbonate with an average particle size of 1.2 μm 10
A 0.1 mm film-like material was obtained from the capacity part by the same method as in Example-1.

Stretch one side of the film with a blade with a radius of curvature of 1.0 mm so that the angle between the film and the blade is 60 °, while stretching 1.3 times at normal temperature between two pairs of rolls with different rotation speeds. did.

Further, the cold-stretched membranous material was uniaxially stretched 3.0 times at 80 ° C. in the same manner as in Example-1 and stretched 2.0 times at 140 ° C. in the direction perpendicular to the uniaxial stretching direction to obtain a porous film. It was

 The physical properties of the obtained porous film are shown in Table 1.

Comparative Example-5 The film-like material molded in Example 1 was cold stretched 1.04 times while rubbing with a blade, and then biaxially stretched in the same manner as in Example-1.
A stretched film was obtained.

 The physical properties of the obtained stretched film are shown in Table 1.

Claims (1)

[Claims] 1. A surface of a film-like material comprising 100 parts by volume of a polyolefin resin and 3 to 100 parts by volume of a filler has a curvature radius of 0.05.
A method for producing a porous film, which comprises cold-stretching 1.1 to 1.7 times while rubbing with a blade of ~ 1.5 mm, and then stretching uniaxially or biaxially without further rubbing.