JPS61195133A - Finely porous membrane of ultra-high-molecular-weight alpha-olefin polymer - Google Patents

Abstract

PURPOSE:A finely porous, uniform, thin, and high-strength film having a large number of fine through holes with a narrow distribution, by drawing ultra-high- molecular-weight olefin gel in a high draw ratio. CONSTITUTION:A finely porous membrane consisting of an alpha-olefin polymer having >=5X10<5>, preferably 1X10<6>-15X10<6> alpha-olefin polymer, having through holes with 0.01-1mum average pore diameter and 30-90% void, stretched twice, preferably 5-20 times, drawn <=10 times, preferably 25-200 times in face draw ratio. Polypropylene is used as the alpha-olefin. Gel molded from a solution of the alpha-olefin polymer is subjected to solvent removal treatment, the alpha-olefin polymer carried in the gelatinous molded article is adjusted to a fixed amount and the molded article is drawn, to remove the remaining solvent. The amount of the solvent removed from the gelatinous molded article is at least 10wt%, and the amount of the alpha-olefin polymer contained in the gelatinous molded article is 10-90wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microporous membrane incorporating one ultra-high molecular weight α-olefin.

Conventional technologyPorous membranes are used in a variety of applications, such as battery separators, electrolytic capacitor diaphragms, various filters, and moisture-permeable waterproof clothing.Recently, however, porous membranes have been used to reduce the size and weight of equipment and improve sexual performance. Therefore, there is a demand for thinner and improved strength.

As a method for producing a porous membrane of polypropylene, which is a typical example of an a-olefin polymer, for example, polypropylene is blended with an inorganic compound, cast under high shear force in an area with a temperature gradient, and the cast film is t-stretched. There is a method (Japanese Unexamined Patent Publication No. 74327/1983). but,
Since the porous membrane obtained by this method uses polypropylene with a molecular weight of less than 500,000, there is a limit to how thin the membrane can be made and the strength can be increased by stretching.

In addition, ultra-high molecular weight polypropylene, which is expected to have high strength and high elastic modulus, has significantly entangled molecular chains compared to normal polypropylene having a tt molecule, making it difficult to stretch into a thin film using conventional extrusion molding.

On the other hand, a method for producing a molded article of ultra-high molecular weight polypropylene includes, for example, dissolving an ultra-high molecular weight thermoplastic crystalline polymer that is essentially polyethylene or polypropylene in a non-volatile solvent, and molding a gel from this solution. A method for producing a thermoplastic article that is substantially a fiber by heating and stretching a gel containing a non-volatile solvent or a dry gel obtained by extracting and removing the solvent contained in the gel with a volatile solvent 52
No. 28) has been proposed. However, with this method, it is not possible to obtain a microporous membrane having a large number of fine and narrowly distributed through holes from an ultra-high molecular weight α-olefin polymer, and which can be stretched uniformly and at a high magnification.

The present invention produces a thin, high-strength, microporous ultra-high molecular weight α-olefin polymer having a large number of fine and narrowly distributed through-holes by stretching a gel of an ultra-high molecular weight α-olefin polymer at a high magnification. The purpose is to obtain a membrane.

The present inventors conducted various studies on methods for obtaining ultra-high molecular weight α-olefin polymer microporous S, and found that a gel-like material formed from a solution of ultra-high molecular weight α-olefin polymer was subjected to solvent removal treatment. It was discovered that the object of the present invention could be achieved by removing the remaining solvent by stretching within a specific range of the amount of σ-olefin polymer contained in the gel-like molded product, but the present invention was completely defeated.

That is, the gA of the present invention has a weight average molecular weight of 5 x 105
Made of the above a-olefin polymer, the average pore size is 0.
It has a through hole of 01 to 1μ, a porosity of 30 to 90%,
This is a microporous layer of a HilII molecule Jla-olefin polymer, which is characterized by being stretched 2 times or more in the uniaxial direction and IO times or more in terms of area magnification.

The ultra-high molecular weight α-olefin polymer used in the present invention has a weight average molecular weight of 5×10 or more, preferably
It is in the range of 106 to 15X10'. If the weight average molecular weight is less than 5×10 5 , an ultrathin and high-strength microporous membrane cannot be obtained.

-10,000, although the upper limit is not particularly limited, if it exceeds f5XlO', it is recommended to thin the film by stretching. Such an ultra-high molecular weight α-olefin 1 polymer is a crystalline monopolymer of propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, etc.
Copolymers of -olefins and 10 mol% or less of ethylene or other α-olefins can be mentioned.

Among these, ultra-high molecular weight polypropylene mainly composed of propylene is preferred. In addition, the above-mentioned ultra-high molecular weight α-
S additives such as antioxidants, ultraviolet absorbers, lubricants, anti-blocking agents, pigments, dyes, and inorganic fillers may be added to the olefin polymer as necessary to the extent that the purpose of the present invention is not impaired. I can do it.

The ultrahigh molecular weight lα-olefin polymer microporous membrane of the present invention has an average pore diameter in the range of 0.01 to I μm, and has a narrow pore size distribution, which provides excellent permeability such as high water permeability and high air permeability. It has excellent selective permeability while retaining its properties. If the average pore diameter is less than 0.01 .mu.m, the permeation rate will be slow, while if it exceeds 1 .mu.m/Ii, the permselectivity will decrease, which is not preferable. In addition, the porosity is 30 to 90
%. If the porosity is less than 30%, the permeation rate will be slow, while if it exceeds 90%, the mechanical strength of the membrane will be low, making it difficult to put it to practical use. Furthermore, the microporous membrane is one that has been stretched uniaxially by a factor of 2 or more and by an area magnification of 10 times or more.

Such stretching makes it possible to put into practical use an ultra-thin microporous membrane having a large porosity and high strength, for example, a breaking strength of 100 ky/cm' or more. Those without grooves at the above-mentioned stretching ratio are undesirable because the porosity and mechanical strength are insufficient.

In the present invention, the solution of the ultra-high molecular weight α-olefin polymer used as a raw material has the above-mentioned weight average molecular weight of 3l-5×105
It is prepared by heating and melting the above α-olefin polymer in a solvent. This solvent is not limited to % as long as it can sufficiently dissolve the α-olefin polymer. Examples include aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, decalin, and paraffin oil, or mineral oil fractions with boiling points corresponding to these, and gel-like molded products that are stable in a solvent-containing state. A non-volatile solvent such as paraffin oil is preferred. The heating and dissolving is performed while stirring at a temperature at which the α-olefin polymer is completely dissolved in the solvent. The temperature varies depending on the polymer and solvent used, but for example, in the case of polypropylene, it is in the range of 160 to 250C. In addition, although the concentration of the α-olefin polymer solution varies depending on the molecular weight,
~10% by weight is preferred. If the concentration is too high, it will be difficult to produce a uniform solution of PT. In addition, it is preferable to add an antioxidant in order to prevent oxidative deterioration of the α-olefin polymer during heating and melting.

Next, 1. this a-olefin polymer heated solution is extruded into a sheet or tube shape from an appropriately selected die, or cast onto a support, and heated to a temperature below the gelling temperature in a water bath, air bath, solvent, etc., preferably at 15 Gell by cooling to a temperature of ~25C at a rate of at least 50C/min. The thickness of the gel-like molded product is usually about 0.1 to 5 nm.

This gel-like molded product is swollen with the solvent used to dissolve the α-olefin polymer, and requires removal of the solvent.

Examples of solvent removal treatment include immersing the gel-like molded product in a volatile solvent, extracting it, and drying it, compressing it, heating it, or a combination of these methods. Extractive removal using a readily volatile solvent is preferred since the solvent can be removed without significant changes. Examples of this easily volatile solvent include pentane, hexane, heptane,
, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, ethers such as diethyl ether and dioxane, and other alcohols such as methanol, ethanol, propatool, etc. can be given. These solvents are appropriately selected depending on the solvent used to dissolve the α-olefin polymer, and are used alone or in combination.

Further, the amount of solvent removed from the gel-like molded product is at least 10% by weight based on the solvent contained, and the amount of the ultra-high molecular weight α-olefin polymer contained in the gel-like molded product is 10 to 90% by weight. , preferably 20 to 60% by weight. Removal of solvent from gel-like molded product If the amount of the α-olefin polymer contained in the gel-like molded product is less than 10% by weight, the network shape of the gel-like molded product is Since the structure is highly swollen by the solvent, gel dissolution is likely to occur during heating and stretching. In addition, uneven stretching tends to occur locally, making it difficult to obtain a stretched product with a uniform thickness, and the pore size distribution of pores formed in the stretched product becomes undesirable. Furthermore, it is unfavorable from the viewpoint of handling, such as oozing of solvent during stretching. On the other hand, excessive desolvation treatment in which the α-olefin polymer contained in the gel molded product exceeds 901jL amount %,
The network structure of the gel-like molded product becomes too dense, making it difficult to stretch at a high magnification, making it difficult to obtain a thin and high-strength stretched product, and reducing the pore size and porosity of the micropores formed in the stretched product. Both decrease, which is not desirable.

The removal amount of the solvent contained in the gel-like molded product can be adjusted by the amount of contact of the easily volatile solvent with the gel-like molded product, the time, the compression pressure of the gel-like molded product, etc.

In addition, when desolventizing a gel-like molded product using a readily volatile solvent, the gel-like molded product shrinks or bends in three axes as the easily volatile solvent substituted in the gel-like molded product evaporates. Therefore, in order to prevent this and obtain a smooth original fabric with small shrinkage in the biaxial (longitudinal and horizontal) directions, which enables uniform and high stretching, the gel-like molded material is selectively stretched in the thickness direction. It is preferable that it shrinks to . Its shrinkage rate is 50% or more in the thickness direction, preferably 70% or more, and #″i20 in the biaxial direction.
%i is preferably 20% or less. Selective shrinkage of the gel-like molded product in the thickness direction can be achieved by, for example, applying a highly volatile solvent to the gel-formed molded product while adhering it to a completely smooth support, gripping it from two axes, or sandwiching it between porous plates. One method is to evaporate it.

Stretching is performed by heating the original fabric of the gel-like molded product that has been subjected to solvent removal treatment, and using the usual tenter method, roll method, inflation method,
Biaxial stretching is carried out at a predetermined magnification by the pressing method or a combination of these methods.

Biaxial stretching may be carried out simultaneously or sequentially.

The stretching temperature is the melting point of the ultra-high molecular weight α-olefin polymer +
The range is below the IOC, preferably from the crystal dispersion temperature to below the melting point. For example, in the case of polypropylene, 90 to 18
0C, more preferably in the range of 130 to 17QC. If the stretching temperature exceeds the melting point +10C1-, the resin will melt excessively and orientation cannot be achieved by stretching. Also.

If the stretching temperature is lower than the crystal dispersion temperature, the resin will not be sufficiently softened and the film will easily break during stretching, making it impossible to stretch at a high magnification.

(9) The stretching ratio varies depending on the thickness of the original fabric, or is at least 2 times or more in one axis direction, preferably 5 to 20 times, and 10 times or more in area magnification, preferably 25 to 400 times. If the areal magnification is less than 10 times, it is not preferable because the stretching is insufficient and a thin film with high porosity cannot be obtained. On the other hand, the area magnification is 4
If it exceeds 00 times, it is not preferable because restrictions will arise in terms of stretching equipment, stretching operations, etc.

The microporous membrane after stretching is immersed in the above-mentioned easily volatile solvent to extract and remove the remaining solvent, and then the solvent is evaporated and dried.

The solvent extraction requires removing the solvent in the microporous membrane to less than 1% by weight.

The thickness of the microporous ultrahigh molecular weight α-olefin polymer of the present invention can be appropriately selected depending on the application, but is usually 0.0
It ranges from 5 to 50 microns, preferably from 0.1 to 10 microns.

That’s it for the original F! AK twist and the average pore diameter of the fine through holes are 0.
．． It is possible to obtain an extremely thin ultra-high molecular weight a-olefin polymer microporous membrane having an OI of 1 μm, a porosity of 30 to 90%, and a breaking strength of *ooip/i or more.

The ultra-high molecular weight α-olefin polymer microporous membrane of the present invention is
It is extremely thin and has high strength that cannot be obtained with conventional α-olefin polymer microporous membranes having a normal molecular weight, has through-pores with a finer average pore diameter, and has a narrow pore size distribution.

The ultra-high molecular weight α-olefin polymer microporous membrane of the present invention is
Due to the above-mentioned excellent properties, it is suitable for battery separators, diaphragms for electrolytic capacitors, various filters, porous membranes for moisture-permeable and waterproof clothing, etc., and can be made smaller and lighter and have improved performance.

Examples Examples of the present invention are shown below. In addition, the test method in Examples is as follows.

(1) Film thickness: Measured in cross section a using a scanning electron microscope.

(2) Breaking strength: Based on ASTM D 882.

(3) Elongation at break: Based on ASTM n a 82.

(4) Average pore size, pore size distribution: The field of view observed with a scanning electron microscope after vacuum-depositing gold on the surface of a microporous membrane is statistically processed using an image analyzer to determine the area average pore diameter φS and number average pore diameter φK.

The pore size distribution (φS/φN) was determined. Let the value of the number average pore diameter be the average pore diameter.

(5) Porosity: Measured using a mercury porosimeter.

Example: Liquid paraffin (64
sat / 40 C') 2, to 100 parts by weight of the mixed solution
0.125 parts by weight of 6-di-t-butyl-P-cresol and tetrakis [methylene-S-(S,S-di-t-)]
? 0.25 parts by weight of cometaf (4-hydroxyphenyl)-propionate and an antioxidant were added and mixed.

Fill this mixed solution into an autoclave equipped with a stirrer, and
Heated to 0C and stirred for 90 minutes to obtain a homogeneous solution.

This solution was filled into a heated mold and rapidly cooled to 15C to form a gel-like sheet with a thickness of 2) Eml.

After immersing this gel-like sheet in methylene chloride for 60 minutes, the methylene chloride was evaporated and dried while it was attached to a smooth plate, and the amount of polypropylene was 19.4% by weight, and the shrinkage rate in the thickness direction was 79.4. % original fabric sheet was obtained.

The obtained raw sheet was set in a biaxial stretching machine and heated at
s Simultaneous biaxial stretching was performed at an OC1 speed of 50 cm for 1 minute and a magnification of aXa. The obtained stretched membrane was washed with methylene chloride to extract and remove residual liquid paraffin, and then dried to obtain a microporous polypropylene membrane. Table out its characteristics.
Good IK display.

Examples 2 to 6 Polypropylene microporous ilK was obtained in the same manner as in Example, except that the gel-like sheet molded in Example 1 was pleuralized under the conditions shown in Table IK. These characteristics are also listed in Table-1.

Example 7 A microporous polypropylene membrane was obtained in the same manner as in Example 1, except that the gel-like sheet molded in Example 1 was stretched at various times under the conditions shown in Table 1.

This characteristic is also listed in Table 1.

Comparative Example: The gel-like sheet formed in Example 1 was set in a biaxial stretching machine without removing the solvent, and # film was formed under the conditions shown in Table IK. Microporous mt- was obtained. Its characteristics are also listed in Table IK. The obtained nine-microporous membrane had a wide average pore size distribution and was non-uniformly stretched, as shown in Table 1. In addition, the surface of the film immediately after stretching was covered with excess solvent that oozed out, causing accumulations and drips in some places, and a large amount of solvent was required to clean them.

Example 8 In Example 1, a liquid paraffin solution t-vI4 containing 2.0% by weight of voliptetrapyrene was prepared, and Table-I
A microporous polypropylene membrane was obtained by forming a film under the conditions shown in K and following the same procedures as in the examples except for the following. These characteristics are also listed in Table IK.

Example 9 Mw x 4,7 x 10' used in Example 1
Instead of polypropylene, Mw= 2,5 x 10
Polypropylene microporous a was obtained in the same manner as in Example, except that polypropylene was used in a 6.0% by weight liquid paraffin solution 'twin' and a film was formed under the conditions shown in Table 1. This characteristic is also listed in Table 1.

Comparative Example 2 Same as Example 2 except that 9.0% by weight of the liquid paraffin in the gel sheet formed from the polypropylene solution prepared in Example 9 was removed and the film was formed under the conditions shown in Table 1. Polypropylene microporous a was obtained. These characteristics are also listed in Table-1. The resulting nine-microporous membrane is
The average pore size distribution is wide and the stretching is non-uniform.

In addition, the surface of the film immediately after stretching was covered with excess solvent that oozed out, causing pooling and sag in some places.

Comparative Example 3 Polypropylene was prepared in the same manner as in Example 1, except that 50% by weight of the liquid paraffin in the gel-like sheet formed from the polypropylene solution prepared in Example 8 was removed and # film was formed under the conditions shown in Table 1. A microporous membrane was obtained. The obtained microporous membrane had a wide average pore size distribution and was non-uniformly stretched. In addition, the entire surface of the film immediately after stretching was covered with excess solvent that oozed out, resulting in pooling and sag in some places.

Comparative Example 4 A gel-like sheet formed in Example 1 was immersed in a large amount of methylene chloride for 60 minutes, and then attached to a smooth plate and then evaporated and dried to dry the methylene chloride. Set the gel-like sheet in a biaxial stretching machine, stretch at a temperature of 110 to 70C, and at a speed of 30C.
Stretching was attempted at a rate of rII/min, but stretching at a magnification of 3x3 or more was not possible due to uneven stretching and breakage.

Claims (2)

[Claims] (1) Made of α-olefin polymer with a weight average molecular weight of 5 x 10^5 or more, has through pores with an average pore diameter of 0.01 to 1 μm, a porosity of 30 to 90%, and doubles in the uniaxial direction. that's all,
1. A microporous membrane of an ultra-high molecular weight α-olefin polymer, which is formed by stretching an area magnification of 10 times or more. (2) The microporous membrane according to claim 1, wherein the α-olefin polymer is polypropylene.