JPH02296840A - Porous film and production thereof - Google Patents

Abstract

PURPOSE:To produce a porous film of a large surface opening by forming two resin compositions by mixing a polyolefin with a filler in two specified mixing ratios, melt-molding these two compositions into films to form a multilayer film and stretching this film. CONSTITUTION:A resin composition (A) is obtained by mixing a polyolefin resin (a) of an MI of 0.05-20g/10min (e.g. linear low-density PE) with a filler (b) (e.g. barium sulfate) of a mean particle diameter of 0.01-20mum, optionally surface-treated so that formula I (wherein X is the volume of component (b), and Y is the volume of component (a)) may be satisfied. Separately, component (a) is mixed with component (b) to obtain a resin composition (B). Component A and component B are laid in such a way that component A is laid on at least one side of component B and melt-molded into a film by coextrusion to obtain a film of an at least bilayer structure. This film is monoaxially or biaxially orientated to obtain the title film of a ratio of the thickness of the layer comprising component A to that of the layer comprising component B of 3.00-0.03.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a porous film and a method for producing the same, and more particularly to a porous film having a multilayer structure and a large surface porosity and a method for producing the same.

The porous film according to the present invention has a much larger surface porosity than conventional porous films, so it can be used for waterproof clothing,
It can also be used for packaging materials, sanitary materials, etc., but especially large iI! Ideal for filtration materials that require a large area, battery separators that require uniform ion conduction, electric double layer capacitor separators, etc.

[Conventional technology]

Conventionally, various methods have been proposed for producing porous films by melt-forming a resin composition containing a filler into a polyolefin resin and then subjecting it to stretching treatment. for example,
JP-A No. 57-47334 discloses a method in which a resin composition containing a filler and liquid polybutadiene is blended with a polyolefin resin is melt-formed into a film, and then stretched. A resin composition containing barium sulfate is melted into a film,
Examples include a method in which a porous film is produced by subsequent stretching treatment.

However, the porous film obtained by the above method is
A skin layer is formed on the surface, and although the inner layer has a large porosity, the surface porosity becomes small. Here, the surface porosity is the area ratio of the pores present per unit area. (Hereinafter, simply referred to as surface porosity.) If the surface porosity is small, the pores are sparsely opened, and the filtration efficiency of the filtration material decreases. However, the ion current concentrates, causing problems such as performance deterioration. Other packaging materials and sanitary materials may also cause uneven flow of fluids such as water vapor or air.
Problems such as insufficient permeation rate occur.

In order to solve the above problems, simply increasing the amount of filler will reduce the stretchability, increase the frequency of stretch breakage, make it difficult to stably stretch (and the surface porosity will not be sufficient). Furthermore, although there are differences depending on the filler and the surface treatment agent for the filler, if the volume ratio of the filler exceeds 35%, the elongation of the resin composition will become extremely small, resulting in extremely poor stretchability. It will drop to .

[Problem to be solved by the invention]

An object of the present invention is to provide a porous film with large surface pores that solves the above problems.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present inventors conducted extensive studies and finally arrived at the present invention.

That is, the present invention is a porous film obtained by forming a resin composition formed by blending a filler into a polyolefin resin into an i8 film, and then stretching it, as shown below (formula 11 and (
2) It has a multilayer structure of two or more layers composed of resin compositions A and B that satisfy the formula, and the thickness ratio of All and BJiJ is 3.00 to 0.03, and one side of layer B or The present invention provides a porous film and a method for producing the same, characterized in that layers A are formed on both sides.

32≦X/ (X0Y)X100≦70 (1) B layer 10≦X/ (X+Y) X100 <32- (2)
(In the above formula, X is the volume of the filler, and Y is the volume of the polyolefin resin.) Hereinafter, the value of X/(X-1-Y)X100O will be referred to as the blending ratio.

The thickness ratio between the A layer and the B layer is the value obtained by dividing the weight of the resin composition constituting the A layer by the weight of the resin composition constituting the B layer. (Hereinafter, simply referred to as A/B thickness ratio.) Examples of the polyolefin resin used in the present invention include high density polyethylene, linear low density polyethylene, low density polyethylene, propylene homopolymer, and ethylene-propylene. Polymer, ethylene-vinyl acetate copolymer, polybutene, poly-4-methylpentene-1
etc. These polyolefin resins may be used alone or as a mixture of two or more, and from the viewpoint of stretching stability and film properties, linear low-density polyethylene, high-density polyethylene, propylene homopolymers, ethylene-brobylene, etc. Preferred is the carbon copolymer IJ-4-methylpentene-1.

Here, linear low density polyethylene refers to ethylene and α-
It is a copolymer with an olefin, and as the α-olefin, butene, hexene-11octene-1,4-methylpentene-1, etc. can be preferably used. A known lubricant, dispersant, ultraviolet absorber,
Dyes, pigments, etc. may also be added.

The melt index of the polyolefin resin is 0.05 to 20 g/10 ain from the viewpoint of moldability and physical properties.

is preferable, and 0.1 to 8 g/10 m1n is more preferable.

If the melt index is less than 0.05 g/10 s+in, the melt viscosity will be large and productivity will decrease, and if it exceeds 20 g/10 m1n, the melt viscosity will be small and the workability of film forming will deteriorate. , the mechanical strength of the film also becomes low.

As fillers it is possible to use inorganic and organic fillers. Inorganic fillers include barium sulfate, calcium sulfate, magnesium sulfate, barium carbonate, calcium carbonate, magnesium hydroxide, aluminum hydroxide,
Zinc oxide, magnesium oxide, titanium oxide, silica, alumina, talc, zeolite, kaolin, glass powder, etc. can be used, and barium sulfate, calcium carbonate, magnesium hydroxide, zinc oxide, and silica are particularly preferably used. Nylon, polystyrene, etc. can be used as the organic filler. These inorganic and organic fillers may be used alone or in a mixture of two or more.

The average particle size of the filler is preferably 0.01 to 20 μm, more preferably 0.05 to 5 μm; if the average particle size exceeds 20 μm, the pore size of the porous film obtained by stretching becomes large. If the film thickness is made thinner, stretching breaks will easily occur and the stretching stability will deteriorate.If the film thickness is less than 0.01//m, the filler will cause secondary agglomeration and the resin will be damaged. The dispersion is poor, stretching tearing is likely to occur, the stretching stability is poor, and agglomerated lumps of filler are formed in the obtained film, resulting in a decrease in film quality.

In order to improve the dispersion of the filler into the resin, surface treatment of the filler with a fatty acid, a metal soap of a fatty acid, an oil or fat, a coupling agent, a surfactant, etc. can be preferably used.

The blending ratio of polyolefin resin and filler is preferably 32 to 70% in layer A, and more preferably 35 to 60%.
is preferable. If the blending ratio in layer A is less than 32%, the surface porosity will not be sufficient, and if it exceeds 70%, the surface porosity will increase, but the stretchability will decrease and the problem of stretch breakage will occur. This occurs more frequently, making it impossible to stably perform the stretching process.

In the B layer, it is preferably 10 to 32%, and further 15%.
~30% is preferable, the blending ratio in BJiJ is 10%
If it is less than 32%, there will be almost no communicating holes and there will be almost no fluid permeation, and if it is more than 32%, the stretchability will decrease and stretching breaks will occur more frequently, making it difficult to stretch stably. It becomes impossible to process.

The A/B thickness ratio is preferably 3.00 to 0.03, and further 2
It is preferably from 0.00 to 0.10. A/B thickness ratio is 3.00
If the A/B thickness ratio is less than 0.03, the stretchability will decrease, the frequency of stretch breakage will increase, and the stretching process cannot be performed stably.If the A/B thickness ratio is less than 0.03, the A layer will The film is not formed uniformly and the layer A is partially missing, making it impossible to obtain a film that is uniform and has a large surface porosity.

The polyolefin resin, filler, and various additives added as necessary are mixed by a known method such as a Henschel mixer tumbler mixer or a super mixer, and then the mixture is transferred to a single screw extruder, twin screw extruder, or Banbury extruder. The mixture is kneaded and pelletized by a known method such as a mixer, or the mixture is subjected to a film forming process as it is.

The film forming process can use known methods such as T-Guy, inflation silane, and calendering.The method for obtaining an unstretched film with a multilayer structure of layer A and layer B is to heat the film after forming each layer. It may be thermally bonded with a roll, or extrusion lamination may be performed after forming the A layer or BiJ in advance, but coextrusion is the most suitable method in terms of glabella adhesive strength, workability, and productivity. There is. Coextrusion may be performed by the T-Gouy method or by the inflation method.

The molten resin composition released from the goo is cooled and solidified using a chill roll, air, etc., and then subjected to a stretching process.

The unstretched film with a multilayer structure obtained by the above method has a weight of 10
A porous film is obtained by stretching in the temperature range from °C to the melting point of the resin composition -10"C.The stretching treatment may be uniaxial or biaxial stretching, and in the case of biaxial stretching, sequential two-wheel stretching is performed. However, simultaneous biaxial stretching may be used. As the stretching method, known methods such as roll stretching, tenter stretching, tubular stretching, and mandrel stretching can be used.

- The stretching ratio in the case of axial stretching is preferably 2.0 to 9.0 times, more preferably 2.5 to 7.0 times. Stretching ratio is 2
．． If it is less than 0 times, the film will be porous, but the fluid permeation rate will be low and the surface porosity will be insufficient.
If it exceeds 9.0 times, the fluid permeation rate and surface flowering rate are high, but the frequency of stretching breakage increases extremely, resulting in poor productivity.

The stretching ratio in the case of two-wheel stretching is 2.2 to 18 in terms of area ratio.
．． The area magnification is preferably 0 times, where the area magnification is the value obtained by multiplying the vertical stretching magnification by the horizontal stretching magnification.
If it is less than 18.0 times, it becomes a porous film, but the fluid permeation rate is low and the surface porosity is insufficient.
If it exceeds twice that, the fluid permeation rate and surface flowering rate will be high, but the frequency of stretch breakage will increase extremely, resulting in poor productivity.

It is preferable to heat set the porous film obtained by stretching with a hot roll or a hot air oven in order to improve the pores and the dimensional stability of the film.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the spirit thereof.

Evaluations in Examples were performed by the following method.

■Thickness (μm) Based on JIS C231B ■A/B thickness ratio (-) Measure the extrusion weights QA and QB (kg/hr,) of A resin composition and B resin composition, respectively, and calculate using the following formula. did.

■Tensile properties Based on JIS P 8113, the test conditions were as follows.

Test piece size 100+sm Length
D (direction perpendicular to MD) is measured.

Elongation at break (%) The elongation when the test piece breaks is measured in MD and TD, respectively.

■Air permeability (sec/100cc) JIS P
Based on 8117, ■ Moisture permeability (g/I 24h) Based on ASTM E 96-66 Temperature: 32.2°C Relative humidity: 50% 0Surface porosity (%) From a porous film surface image taken with a scanning electron microscope , calculated from the open pore area per unit area.

■Stretching stability The stretching stability was evaluated as follows based on observation during stretching.

very good lgood
2 Slightly unstable
3 Stretching breaks occur 4 Stretching breaks occur extremely frequently 5 Example 1 Density 0.920 g/cc, melt index 2°0
g/10 sin, 1 part by weight of calcium stearate was added to 100 parts by weight of a blend of barium sulfate with an average particle size of 0.9 μm at a blending ratio of 45%. The formulation was mixed in a Henschel mixer and then melt kneaded in a twin screw extruder and pelletized. The pellet of this resin composition was designated as A resin composition.

Density 0.920g/cc, melt index 2゜0
g/10m1n, barium sulfate with an average particle size of 0.9 μm was added to 100 parts by weight of a mixture with a blending ratio of 25%, and 1 part by weight of calcium stearate was added. The resulting mixture was mixed in a Henschel mixer, then melt-kneaded in a twin-screw extruder and pelletized. The pellet of this resin composition was designated as a B resin composition.

Beref) A and B of the obtained resin composition were
- The resin compositions of A and B were melted and formed into a film using a two-type, three-layer T-die coextruder with A/B/A, and then cooled and solidified using a 4-chill roll. The obtained unstretched film has layer A, layer B
It has a three-layer structure of layer A and layer A, and the A/B thickness ratio was measured to be 1.0. The unstretched film was stretched 6.0 times in the machine direction using a roll stretching machine at a preheating temperature of 75°C, and then heat-set with a hot roll at 95°C. Table 1 shows the physical properties of the porous film obtained.

Examples 2 to 4 A porous film was obtained in the same manner as in Example 1, except that the linear low-density polyethylene and barium sulfate of resin composition A in Example 1 were adjusted to the blending ratio shown in Table 1. . Table 1 shows the physical properties of the porous film obtained.

As the blending ratio of the filler in resin composition A increases, the physical properties of air permeability, moisture permeability, and surface porosity improve.

Comparative example 1 Density 0.920g/cc, melt index 2°0
g/login, 1 part by weight of calcium stearate was added to 100 parts by weight of a mixture containing barium sulfate with an average particle size of 0.9 μm at a blending ratio of 25%. The formulation was mixed in a Henschel mixer, then melt kneaded in a twin screw extruder and pelletized. The pellet of this resin composition was designated as a B resin composition.

The resulting resin composition Beref) B was heated to a diameter of 65-1.
- Using a Gui single-layer extruder, the resin composition of B was melted and formed into a film, cooled and solidified using a chill roll, and then stretched 6.0 times in the longitudinal direction using a roll stretching machine at a preheating temperature of 75°C. ,9
Heat fixation was carried out using a heat roll at 5°C. As shown in Table 1, the physical properties of the obtained porous film were such that the surface porosity was comparable to that of conventional porous films.

Comparative Example 2 Stretching was performed in the same manner as in Comparative Example 1, except that the linear low density polyethylene and barium sulfate of the B resin composition in Comparative Example 1 were adjusted to the blending ratio shown in Table 1.
Stretching breakage occurred and a porous film could not be obtained.

Comparative Example 3.4 Stretching was carried out in the same manner as in Example 1, except that the linear low density polyethylene and barium sulfate of resin composition A in Example 1 were mixed in the proportions shown in Table 1.
In Comparative Example 3, since the filler blending ratio of AM was high, stretching breakage occurred and a porous film could not be obtained. In Comparative Example 4, since the filler compounding ratio of layer A was small,
The surface porosity was comparable to that of conventional porous films.

Example 5.6 A porous film was obtained in the same manner as in Example 1, except that the stretching ratio in Example 1 was changed to the ratio shown in Table 1. The physical properties of the obtained porous film are shown in Table 1, and as the stretching ratio increases, the air permeability, moisture permeability,
Physical properties of surface porosity are improved.

Comparative Example 5.6 Stretching was performed in the same manner as in Example 1, except that the stretching ratio in Example 1 was changed to the ratio shown in Table 1. In Comparative Example 5, the stretching ratio was small and there was almost no air permeability. In Comparative Example 6, the stretching ratio was too high and stretching breakage occurred, making it impossible to obtain a porous film.

Examples 7 to 9 Porous films were obtained in the same manner as in Example 1, except that the linear low-density polyethylene and barium sulfate of the B resin composition in Example 1 were adjusted to the blending ratio shown in Table 2. . The physical properties of the obtained porous film are shown in Table 2. As the filler compounding ratio increases, the air permeability and moisture permeability improve, but the surface porosity increases depending on the filler compounding ratio of layer A. Since it is determined by , it is almost constant regardless of the filler blending ratio of the B layer.

Comparative Example 7.8 Stretching was carried out in the same manner as in Example 1, except that the linear low density polyethylene and barium sulfate of the resin composition B in Example 1 were mixed in the proportions shown in Table 2. In Comparative Example 7, the blending ratio of the filler was large and stretching breakage occurred, making it impossible to obtain a porous film. Comparative example 8
In this case, the blending ratio of filler was small, resulting in a film with almost no air permeability.

Examples 10 to 12 Stretching was performed in the same manner as in Example 1, except that the thickness ratio in Example 1 was changed to the ratio shown in Table 2. The physical properties of the obtained porous film are shown in Table 2, and as the thickness ratio increases, the air permeability and moisture permeability improve.

Comparative Example 9.10 Stretching was performed in the same manner as in Example 1, except that the thickness ratio in Example 1 was changed to the ratio shown in Table 2. In Comparative Example 9, the thickness ratio was too large and stretching breakage occurred, making it impossible to obtain a porous film. In Comparative Example 10, the thickness ratio was too small and a uniform layer A was not formed.

Example 13 The same procedure as in Example 1 was carried out, except that the linear low-density polyethylene of the A resin composition in Example 1 was changed to high-density polyethylene with a melt index of 2.0 g/10 m1n and a density of 0.959 g/cc. A porous film was obtained. Table 3 shows the physical properties of the porous film obtained.

Example 14 The linear low density polyethylene of the resin compositions A and B in Example 1 was prepared with a melt index of 2°0g/10si
A porous film was obtained in the same manner as in Example 1, except that high-density polyethylene with a density of 0.959 g/cc was used. Table 3 shows the physical properties of the porous film obtained.

Example 15 The linear low density polyethylene of the resin composition A in Example 1 had a melt index of 2.0 g/10 m1n.

A porous film was obtained in the same manner as in Example 1, except that a propylene homopolymer having a density of 0.890 g/cc was used. Table 3 shows the physical properties of the porous film obtained.

Example 16 The linear low-density polyethylene of resin compositions A and B in Example 1 was prepared with a melt index of 2°0 g/10v+
A porous film was obtained in the same manner as in Example 1, except that a propylene homopolymer having a density of 0.890 g/cc was used. Table 3 shows the physical properties of the porous film obtained.

Example 17 A porous film was prepared in the same manner as in Example 1, except that calcium carbonate with an average particle size of 1.2 μm surface-treated with stearic acid was used as the filler in the resin compositions A and B in Example 1. Obtained. The physical properties of the obtained porous film were
Shown in the table.

Example 18 The same procedure as in Example 1 was carried out, except that magnesium hydroxide having an average particle size of 0.6 μm and surface-treated with stearic acid was used as the filler in the resin compositions A and B in Example 1.
A porous film was obtained. Table 3 shows the physical properties of the porous film obtained.

Example 19 A porous film was obtained in the same manner as in Example 1, except that magnesium hydroxide having an average particle size of 0.6 μm and surface-treated with stearic acid was used as the filler in the A resin composition in Example 1. Ta. Table 3 shows the physical properties of the porous film obtained.

Example 20 Pellet A of resin composition obtained in the same manner as Example 1
The resin compositions of A and B were melted and formed into a film using a two-type, two-layer T-die coextruder (A/B) with a diameter of 65 m+m, and the resin compositions were cooled and solidified using a chill roll.

The obtained unstretched film had a two-layer structure of layer A and layer B, and the A/B thickness ratio was measured to be 1.0. The unstretched film was stretched 6.0 times in the machine direction using a roll stretching machine at a preheating temperature of 75"C, and then stretched at 95°
It was heat-fixed with a heat roll C. Table 3 shows the physical properties of the porous film obtained.

Examples 21 to 23 Using the A and B resin compositions in Example 1, the caliber was 6.
The resin compositions A and B were melted and formed into a film using a two-type, three-layer T-die coextruder with A/B/A configuration, and the resin compositions were cooled and solidified using a chill roll. The obtained unstretched film has layer A, layer B
It has a three-layer structure of layer A and layer A, and the A/B thickness ratio was measured to be 1.0. The unstretched film was sequentially stretched with two wheels to the stretching ratios shown in Table 4. The stretching conditions were as follows: stretching in the longitudinal direction using a roll stretching machine at a preheating temperature of 75°C, then stretching in the transverse direction using a tenter transverse stretching machine at a preheating temperature of 85°C, and heat setting with a hot roll at 95°C. . Table 4 shows the physical properties of the porous film obtained.

Comparative Example 11.12 In Example 21, sequential biaxial stretching treatment was performed in the same manner as in Example 20, except that the stretching ratio was changed to the ratio shown in Table 4. In Comparative Example 11, the stretching ratio was too small, resulting in almost no air permeability.

In Comparative Example 12, the stretching ratio was too high and stretching breakage occurred, making it impossible to obtain a porous film.

〔Effect of the invention〕

The porous film according to the present invention has a surface porosity so large that it cannot be obtained by simply increasing the amount of filler, and can be used for waterproof clothing, packaging materials, sanitary materials, etc. Filtration materials that require a large filtration area,
Ideal for battery separators and electric double layer capacitor separators that require uniform ion conduction.

Claims (1)

[Claims] 1. A porous film obtained by melt-forming a resin composition formed by blending a filler with a polyolefin resin and then stretching the film, which has the following formulas (1) and (2): It has a multilayer structure of two or more layers composed of resin compositions A and B that satisfy the following, the thickness ratio of layer A and layer B is 3.00 to 0.03, and A porous film characterized by having a layer A formed thereon. A layer 32≦X/(X+Y)×100≦70...(1) B layer 10≦X/(X+Y)×100<32...(2) (In the above formula, X is the volume of the filler, (Y is the volume of the polyolefin resin.) 2. In the method of manufacturing a porous film by melting and forming a resin composition formed by blending a filler into a polyolefin resin and then stretching it, the following method is used: Equation (1) and (
2) It has a multilayer structure of two or more layers composed of resin compositions A and B that satisfy the formula, and the thickness ratio of layer A and layer B is 3.0.
0 to 0.03, and which comprises stretching an unstretched film in which layer A is formed on one or both sides of layer B. A layer 32≦X/(X+Y)×100≦70...(1) B layer 10≦X/(X+Y)×100<32...(2) (In the above formula, X is the volume of the filler, Y is the volume of the polyolefin resin.)