JP2003003007A - Manufacturing method of thermoplastic resin-based microporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyolefin-based microporous film which is excellent in balance of porosity, permeability and mechanical strengths, and has good dimensional stability. SOLUTION: The manufacturing method of the thermoplastic resin-based microporous film includes some processes in which a solution obtained by melt- kneading a thermoplastic resin and a solvent is extruded, the residual solvent is removed from the gel molded article obtained by cooling with a washing solvent, two steps or more heat treatments are performed after drying. In this method, a washing solvent (A) of which the surface tension is 24 mN/m or less at 25 deg.C is used as the washing solvent, the heat treatment process includes a heating process (1) with contracting 0-10% in machine direction(MD) and/or transverse direction(TD) and a final heating process (2) with contracting in MD and/or TD while both MD and TD are fixed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic resin microporous film, and more particularly to a thermoplastic resin microporous film having an excellent balance of porosity, permeability and mechanical strength and excellent dimensional stability. The present invention relates to a method for manufacturing a membrane.

[0002]

2. Description of the Related Art Microporous polyolefin membranes include separators for batteries, diaphragms for electrolytic capacitors, various filters, moisture-permeable waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes and microfiltration membranes. Is used for various purposes. When the polyolefin microporous membrane is used as a battery separator, particularly as a lithium ion battery separator, its performance is deeply related to battery characteristics, battery productivity and battery safety. Therefore, excellent permeability, mechanical properties, dimensional stability, shutdown properties, meltdown properties, etc. are required.

In order to improve the battery characteristics, it is desired to improve the discharge characteristics in a low temperature range and to increase the output. Therefore, it is required to optimize the pore diameter, porosity and permeability of the separator used in various battery systems. To be done. Further, in terms of battery productivity, high mechanical strength is required because it is desired to improve the efficiency of the battery assembly process. Furthermore, regarding battery safety, it is desirable to reduce defects such as voltage drop caused by the pressure of impurities mixed on the electrodes and to improve cycle characteristics and high temperature storage stability. Therefore, permeability, mechanical strength and dimensional stability are required. Is required to improve.

The method for producing a microporous thermoplastic resin membrane includes a solvent method, a dry method, an open-pore stretching method and the like. Among them, the solvent method is generally used. The solvent method is a method including a drying step for volatilizing the washing solvent after adding a non-volatile solvent (solvent) to the thermoplastic resin, melt-kneading, and then washing the solvent with a volatile solvent (washing solvent). . However, in the washing treatment step and the drying step, the fine pores are crushed and the fibril structure is buckled, whereby the network structure is contracted and densified, so that the porosity / permeability is reduced.

On the other hand, as a method for improving the permeability of the thermoplastic resin microporous membrane produced by the solvent method, conventionally, there have been proposed changes of raw materials and improvement of stretching / rolling methods.
For example, as a polyolefin microporous membrane having high permeability, a composition containing an ultrahigh molecular weight component and blending a nucleating agent with a polyolefin having a value of (weight average molecular weight / number average molecular weight) within a specific range. There has been proposed a manufacturing method using the above (JP-A-5-222236, JP-A-5-222237 and JP-A-8-12799). However, there is a limit to improving the dimensional stability while maintaining the balance of porosity, permeability and mechanical strength.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing a polyolefin microporous membrane which is excellent in the balance of porosity, permeability and mechanical strength and is excellent in dimensional stability. Is to provide.

[0007]

As a result of earnest research in view of the above-mentioned problems, the present inventors have extruded a solution obtained by melt-kneading a thermoplastic resin and a solvent, and cooled it to obtain a gel form. The residual solvent from the molded product is removed by a washing solvent, and in a method for producing a thermoplastic resin microporous membrane that includes a step of performing heat treatment in two or more steps after drying, the surface tension at 25 ° C as a washing solvent is 24 mN / m or less. While using a certain washing solvent (A), the heat treatment process fixes both the machine direction (MD) and the transverse direction (TD; the direction orthogonal to the machine direction) and shrinks the MD and / or TD by 0 to 10%. Heat treatment process
It was found that the above problems can be solved by including (a) and the final heat treatment step (b) performed while shrinking to MD and / or TD, and arrived at the present invention.

That is, in the method for producing a thermoplastic resin microporous membrane of the present invention, the washing solvent (A) whose surface tension at 25 ° C. is 24 mN / m or less is used in the step of removing the solvent, and in the heat treatment step, After fixing both MD and TD, and performing heat treatment step (a) while shrinking MD and / or TD by 0 to 10%, as the final heat treatment step, heat treatment step while shrinking to MD and / or TD ( B) is performed.

The removal of the solvent is preferably carried out in two or more washing steps using a washing solvent, and at this time, the washing solvent (A) is preferably used in at least the final washing step. This improves the cleaning effect and improves the porosity, permeability and dimensional stability of the microporous polyolefin membrane. The washing solvent (A) is preferably used within a temperature range where the surface tension is 24 mN / m or less.

In order for the microporous polyolefin membrane to obtain more excellent properties, the thermoplastic resin preferably satisfies the following conditions (1) to (5). (1) At least one selected from the group consisting of polyolefin, polyester, polyamide, and polyarylene sulfide, and these thermoplastic resins may be used alone or in combination of two or more. . Of these, more preferred is polyolefin. (2) The polyolefin described in (1) above is at least one selected from the group consisting of polyethylene, polypropylene and polybutene-1, and more preferably polyethylene and / or polypropylene. (3) The polyolefin described in (1) or (2) above is a polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, more preferably a weight average molecular weight of 1 × 10 ⁶ to 15 × 10 ⁶ . Further, the thermoplastic resin is a composition containing a polyolefin having such a weight average molecular weight, and it is an ultra high molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more and a high density of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ More preferably, it is a composition comprising polyethylene. (4) The polyolefin according to any one of (1) to (3) above or the polyolefin composition according to (3) above has a weight average molecular weight / number average molecular weight (Mw / Mn) of 5 to 300. (5) The polyolefin composition according to the above (3) or (4) is an ultrahigh molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more and a high density polyethylene having a weight average molecular weight of 1 × 10 ⁴ or more and less than 5 × 10 ^5. And a shutdown function (polyolefin that melts the microporous membrane and blocks the micropores to block the current flow to prevent accidents such as ignition when the temperature inside the battery rises). The polyolefin that gives the function is low-density polyethylene, linear low-density polyethylene, low-molecular-weight polyethylene having a molecular weight of 1 × 10 ³ to 4 × 10 ³ , and an ethylene / α-olefin copolymer produced using a single-site catalyst. At least one selected from the group consisting of.

The polyolefin microporous membrane has more excellent characteristics
In order to obtain the cleaning solvent (A), the following conditions (6) to (12) must be satisfied.
It is preferable to add it. (6) The surface tension becomes 20 mN / m or less at 25 ° C. (7) Hydrofluorocarbon, hydrofluoroace
Tell, cyclic hydrofluorocarbon, perfluorocarbon
Carbon, perfluoroether, carbon number 5-10
Paraffin, isoparaffin with 6 to 10 carbon atoms, carbon number
Cyclopa such as aliphatic ether of 6 or less and cyclopentane
Raffin, 2-pentanone, methanol, ethanol, 1-
Propanol, 2-propanol, tertiary butano
, Isobutanol, 2-pentanol, propyl acetate,
Tertiary butyl acetate, secondary butyl acetate, vinegar
Ethyl acid, isopropyl acetate, isobutyl acetate, methyl formate
Chill, ethyl formate, isopropyl formate, isobutyrate
Less, selected from the group consisting of ethyl propionate
Both are a kind. (8) C_FiveH₂F_TenChain hydrofluoro represented by the composition formula
Carbon, C_FourF₉OCH₃And C _FourF₉OC₂H_FiveShown by the composition formula
Hydrofluoroether, C_FiveH₃F₇Shown by the composition formula
Cyclic hydrofluorocarbon, C₆F₁₄And C₇F₁₆Set of
Perfluorocarbon represented by the formula, and C_FourF₉OCF₃
And C_FourF₉OC₂F_FivePerfluoroete represented by the composition formula of
At least one fluorine-based compound selected from the group consisting of
It is a combination. (9) Normal pentane, normal hexane, normal he
Putane, Normal Octane, Normal Nonane, Normal
At least one norma selected from the group consisting of decane
Leparaffin. (10) 2-methylpentane, 3-methylpentane, 2,2-dib
Tilbutane, 2,3-dibutylbutane, 2-methylhexane,
3-methylhexane, 3-ethylpentane, 2,2-dimethyl
Ethane, 2,3-dimethylpentane, 2,4-dimethylpentane
1,3,3-dimethylpentane, 2,2,3-trimethylbutane,
2-methylheptane, 3-methylheptane, 2,2-dimethylheptane
Xane, 2,3-dimethylhexane, 2,5-dimethylhexa
1,3,4-dimethylhexane, 2,2,3-trimethylpenta
2,2,4-Trimethylpentane, 2,3,3-Trimethylpentane
Tan, 2,3,4-trimethylpentane, 2-methyloctane,
2,2,5-Trimethylhexane, 2,3,5-Trimethylhexa
From 2-methylnonane and 2,3,5-trimethylheptane
At least one isoparaffin selected from the group
It (11) Diethyl ether, butyl ethyl ether, dip
Is it a group consisting of ropyl ether and diisopropyl ether?
It is at least one ether selected from (12) Keep the surface tension below 24mN / m at 25 ℃.
Mixing blended C3 or less aliphatic alcohol with water
At least one selected from the group consisting of things.

The washing is preferably carried out by two or more washing steps, in which case a step of using a washing solvent (washing solvent (B)) other than the washing solvent (A) may be included. At this time, it is preferable to use the washing solvent (A) in the final washing step. As the washing solvent (B), it is preferable to use at least one selected from the group consisting of a readily volatile solvent and a non-aqueous solvent having a boiling point of 100 ° C. or higher and a flash point of 0 ° C. or higher.

In order for the microporous polyolefin membrane to obtain more excellent properties, the washing solvent (B) preferably satisfies the following conditions (13) to (25). (13) At least one selected from the group consisting of methylene chloride, carbon tetrachloride, ethane trifluoride, methyl ethyl ketone, pentane, hexane, heptane, diethyl ether and dioxane. (14) Normal paraffins having 8 or more carbon atoms, normal paraffins having 5 or more carbon atoms in which at least a part of hydrogen atoms are substituted with halogen atoms, isoparaffins having 8 or more carbon atoms, cycloparaffins having 7 or more carbon atoms, and hydrogen atoms Cycloparaffins having 5 or more carbon atoms, at least some of which are substituted with halogen atoms, aromatic hydrocarbons of 7 or more carbon atoms, aromatic hydrocarbons having 6 or more carbon atoms, in which at least some hydrogen atoms are substituted with halogen atoms , An alcohol having 5 to 10 carbon atoms in which a part of hydrogen atoms may be replaced with a halogen atom, an ester and an ether having 7 to 14 carbon atoms in which a part of hydrogen atoms may be replaced with a halogen atom, carbon Number 5 to 1
It is at least one selected from the group consisting of 0 ketones. (15) The normal paraffin having 8 or more carbon atoms has a carbon number of 8 to 12, more preferably at least one selected from the group consisting of normal octane, normal nonane, normal decane, normal undecane, and normal dodecane. is there. (16) Normal paraffins having 5 or more carbon atoms in which at least a part of the hydrogen atoms are substituted with halogen atoms are 1-chloropentane, 1-chlorohexane, 1-chloroheptane,
1-chlorooctane, 1-bromopentane, 1-bromohexane, 1-bromoheptane, 1-bromooctane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane It is at least one kind. (17) The above isoparaffins having 8 or more carbon atoms are 2,3,4-trimethylpentane, 2,2,3-trimethylpentane and 2,2,5-
Trimethylhexane, 2,3,5-trimethylhexane, 2,3,
At least one selected from the group consisting of 5-trimethylheptane and 2,5,6-trimethyloctane. (18) The cycloparaffins having 7 or more carbon atoms are cycloheptane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexane, cis-
And trans-1,3-dimethylcyclohexane, and at least one selected from the group consisting of cis- and trans-1,4-dimethylcyclohexane. (19) The cycloparaffin having 5 or more carbon atoms in which a part of the hydrogen atoms is substituted with a halogen atom is at least one selected from the group consisting of chlorocyclopentane and chlorocyclohexane. (20) The aromatic hydrocarbon having 7 or more carbon atoms is at least one selected from the group consisting of toluene, orthoxylene, metaxylene, and paraxylene. (21) Aromatic hydrocarbons having 6 or more carbon atoms in which some of the hydrogen atoms have been replaced by halogen atoms are chlorobenzene, 2-
Chlorotoluene, 3-chlorotoluene, 4-chlorotoluene, 3-chloroorthoxylene, 4-chloroorthoxylene, 2-chlorometaxylene, 4-chlorometaxylene, 5-
At least one selected from the group consisting of chlorometaxylene and 2-chloroparaxylene. (22) Alcohol having 5 to 10 carbon atoms in which a part of the hydrogen atoms may be replaced with a halogen atom is isopentyl alcohol, tertiary pentyl alcohol, cyclopentanol, cyclohexanol, 3-methoxy-1- Butanol, 3-methoxy-3-methyl-1-butanol, propylene glycol normal butyl ether, 5-chloro-1-
At least one selected from the group consisting of pentanol. (23) An ester having 7 to 14 carbon atoms in which a part of the hydrogen atoms may be replaced by a halogen atom is diethyl carbonate,
Selected from the group consisting of diethyl maleate, normal propyl acetate, normal butyl acetate, isopentyl acetate, 3-methoxybutyl acetate, 3-methoxy-3-methylbutyl acetate, ethyl normal butyrate, ethyl normal valerate, 2-chloroethyl acetate. At least one. (24) The ether having 7 to 14 carbon atoms in which a part of the hydrogen atoms may be replaced with a halogen atom is at least one selected from the group consisting of normal butyl ether, diisobutyl ether and bischloroethyl ether. (25) The above-mentioned ketone having 5 to 10 carbon atoms is 2-pentanone, 3-
It is at least one selected from the group consisting of pentanone, 2-hexanone, 3-hexanone, cyclopentanone, and cyclohexanone.

In the washing, the washing solvent (A) alone or the washing solvent (A) and the washing solvent (B) may be used to perform a multi-step treatment of three or more steps. It is preferable to carry out.

C as an optional component (C) in the washing solvent (B)_FiveH₂F_Ten
A chain hydrofluorocarbon represented by the composition formula of C,_Four
F₉OCH₃And C_FourF₉OC₂H_FiveHydroful represented by the composition formula
Oroether, C_FiveH₃F₇Cyclic hydro represented by the composition formula
Fluorocarbon, C₆F₁₄And C₇F₁₆The composition formula of
Perfluorocarbon, and C_FourF₉OCF₃And C_FourF₉OC ₂F
_FiveA group consisting of perfluoroethers represented by the composition formula
Use a mixture of at least one solvent selected from
May be used.

In order for the microporous polyolefin membrane to obtain more excellent properties, the heat treatment step preferably satisfies the following conditions (26) to (30). (26) The heat treatment process is performed in three steps. (27) The heat treatment step (a) is performed at 90 to 150 ° C. (28) 0.1-50% of MD and / or TD in the above heat treatment step (b)
While shrinking in the range of 60 ° C. or higher to the melting point of the thermoplastic resin or lower. (29) The heat treatment step (b) is performed by a belt conveyor method, a mesh drum method, or a floating method. (30) In the above heat treatment process, MD and / or TD are 0-2.
A heat treatment step (C) is performed while shrinking by 0%.

Regarding the physical properties of the polyolefin microporous membrane produced by the method of the present invention, the membrane thickness is usually 0.1 to 100 μm, and the air permeability is 1200 seconds / 100 cc or less, preferably 900.
Seconds / 100cc or less (film thickness 25μm conversion), porosity 30 ~ 9
0%, puncture strength is 5500 mN / 25 μm or more, tensile breaking strength is 100 MPa or more, tensile breaking elongation is 150% or more, thermal shrinkage is 3.7% or less in both MD and TD directions and MD Or 1.4% or less in either TD (105 ° C / 8h
r) is satisfied.

The porosity / permeability is improved by using the washing solvent (A) having a surface tension at 25 ° C. of 24 mN / m or less. It is considered that this is because the network structure can be prevented from shrinking and densifying due to the surface tension of the washing solvent in the washing step and / or the drying step. After the heat treatment step (a), the final heat treatment step (b) stabilizes the crystal, resulting in improved tensile strength, puncture strength, and heat shrinkage, and It is possible to produce a polyolefin fine porous film having an excellent balance between strength, puncture strength and heat shrinkage ratio and porosity / permeability.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION [1] Thermoplastic Resin As the thermoplastic resin used for producing the thermoplastic resin microporous membrane of the present invention, polyolefin, polyester, polyamide, and polyarylene sulfide are preferable. More preferably, it is polyolefin.

The polyolefin has a weight average molecular weight of 5 × 10 ⁵
The above is preferable, and 1 × 10 ⁶ to 15 × 10 ⁶ is more preferable. When the weight average molecular weight is less than 5 × 10 ^5, it is difficult to obtain a suitable microporous membrane because breakage easily occurs during stretching.

As the polyolefin, ultrahigh molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more is preferable. The ultra high molecular weight polyethylene may be not only a homopolymer of ethylene but also a copolymer containing a small amount of other α-olefin. Other α-olefins other than ethylene include propylene, butene-1, hexene-1, pentene.
-1,4-Methylpentene-1, octene, vinyl acetate, methyl methacrylate, and styrene are preferred.

As a thermoplastic resin, a weight average molecular weight of 5 × 10 ⁵
It is also possible to use a polyolefin composition containing the above polyolefin. The polyolefin composition is preferably a composition comprising a polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more and a polyolefin having a weight average molecular weight of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ . With a composition containing no polyolefin having a weight average molecular weight of less than 5 × 10 ^5, it is difficult to obtain a suitable microporous membrane because breakage easily occurs during stretching. Further, by setting the upper limit of the weight average molecular weight of the polyolefin and the polyolefin composition to be 15 × 10 ⁶ or less, melt extrusion can be facilitated.

In the polyolefin composition, ultrahigh molecular weight polyethylene is preferable as the polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, but the ultrahigh molecular weight polyethylene may be a copolymer containing a small amount of another α-olefin. Good.

In the polyolefin composition, polyethylene is preferable as the polyolefin having a weight average molecular weight of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ . As polyethylene, high-density polyethylene, low-density polyethylene, medium-density polyethylene, and ultra-high-molecular-weight polyethylene are preferable, and high-density polyethylene is more preferable. These may be not only ethylene homopolymers but also copolymers containing a small amount of other α-olefins. Other α-olefins other than ethylene include propylene, butene-1, hexene-1, pentene-1,4-methylpentene-1, octene, vinyl acetate,
Methyl methacrylate and styrene are preferred.

When used as a battery separator, it is preferable to add polypropylene in order to improve the meltdown temperature (breaking temperature of the thermoplastic microporous film). As the polypropylene, a block copolymer and / or a random copolymer can be used in addition to the homopolymer. The block copolymer and the random copolymer may contain a copolymerization component with an α-olefin other than propylene, and ethylene is preferable as the other α-olefin.

In order to improve the characteristics as a battery separator application, the above-mentioned low density polyethylene can be used as the polyolefin imparting the shutdown function. Low density polyethylene is branched low density polyethylene (LDPE), linear low density polyethylene (LLDPE),
At least one selected from the group consisting of ethylene / α-olefin copolymers produced by a single-site catalyst is preferable. Further, as the polyolefin imparting the shutdown function, low molecular weight polyethylene having a weight average molecular weight of 1 × 10 ³ to 4 × 10 ³ may be added. However, if the addition amount is large, breakage easily occurs when stretching, so that the addition amount is 20% with respect to 100 parts by weight of the entire thermoplastic resin.
It is preferably less than or equal to parts by weight.

The Mw / Mn of the above-mentioned polyolefin or polyolefin composition is preferably 5 to 300, more preferably 10 to 100. When Mw / Mn is less than 5, the amount of high molecular weight components is too large to make melt extrusion difficult, and when Mw / Mn is more than 300, the amount of low molecular weight components is too large, resulting in lower strength.

[2] Method for producing thermoplastic resin microporous membrane The method for producing a thermoplastic resin microporous membrane comprises: (a) adding a solvent to the above thermoplastic resin, melt-kneading, and dissolving the thermoplastic resin solution. A step of (b) extruding the thermoplastic resin solution from the die lip and cooling to form a gel-like molded article, (c) a step of removing the solvent from the gel-like molded article, (d) the obtained film It includes a drying step and (e) a heat treatment step. Further, after the steps (a) to (d), if necessary, (f) crosslinking treatment by ionizing radiation, (g) hydrophilic treatment and the like may be performed.

(A) Step of Preparing Thermoplastic Resin Solution First, a suitable solvent is added to the thermoplastic resin and melt-kneaded,
Prepare a thermoplastic resin solution. If necessary, various additives such as an antioxidant, an ultraviolet absorber, an anti-blocking agent, a pigment, a dye and an inorganic filler may be added to the thermoplastic resin solution within a range that does not impair the object of the present invention. .
For example, finely divided silicic acid can be added as a pore-forming agent.

As the solvent, nonane, decane, decalin,
Aliphatic or cyclic hydrocarbons such as paraxylene, undecane, dodecane and liquid paraffin, or a mineral oil fraction having a boiling point corresponding to these can be used. In order to obtain a gel-like molded product having a stable solvent content, it is preferable to use a non-volatile solvent such as liquid paraffin.

The viscosity of the solvent at 25 ° C. is preferably 30 to 500 cSt, more preferably 50 to 200 cSt.
If the viscosity at 25 ° C. is less than 30 cSt, uneven discharge from the die lip occurs and kneading is difficult, and if it exceeds 500 cSt, solvent removal becomes difficult.

The melt kneading method is not particularly limited, but it is usually carried out by uniformly kneading in an extruder. This method is suitable for preparing concentrated solutions of thermoplastics.
Since the melting temperature is preferably the melting point of the thermoplastic resin + 30 ° C to + 100 ° C, it is preferably 160 to 230 ° C, 170 to 200 ° C.
Is more preferable. Here, the melting point refers to a value obtained by differential scanning calorimetry (DSC) based on JIS K7121. The solvent may be added before the start of the kneading or may be added during the kneading in the middle of the extruder, but it is preferable to add the solvent before the start of the kneading to form a solution in advance. In melt-kneading, it is preferable to add an antioxidant to prevent the thermoplastic resin from being oxidized.

The mixing ratio of the thermoplastic resin and the solvent in the thermoplastic resin solution is 1 to 50% by weight, preferably 20 to 40% by weight, based on 100% by weight of both. If the amount of the thermoplastic resin is less than 1% by weight, swell and neck-in increase at the die outlet when forming the gel-like molded product, and the moldability and self-supporting property of the gel-like molded product deteriorate. On the other hand, if it exceeds 50% by weight, the moldability of the gel-like molded article is deteriorated.

(B) Step of forming gel-like molded product The melt-kneaded thermoplastic resin solution is extruded from the die lip directly or through another extruder, or once cooled and pelletized, then again through the extruder. . As the die lip, a sheet die lip having a rectangular mouthpiece shape is usually used, but a double cylindrical hollow die lip, an inflation die lip and the like can also be used. For sheet die lips, the die lip gap is typically 0.1.
~ 5 mm, heated to 140-250 ° C during extrusion.
The extrusion rate of the heated solution is preferably 0.2 to 15 m / min.

A gel-like molded product is formed by cooling the heated solution thus extruded from the die lip. Cooling is preferably performed at a rate of 50 ° C./min or more up to at least the gelation temperature. Generally, if the cooling rate is slow, the higher-order structure of the obtained gel-like molded article becomes coarse and the pseudo-cell units forming it become large, but if the cooling rate is fast, the cell units become dense. If the cooling rate is less than 50 ° C./minute, the crystallinity increases and it is difficult to form a gel-like molded product suitable for stretching. As a cooling method, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled with a refrigerant, or the like can be used.

(C) Stretching / solvent removal step of gel-like molded product Depending on the purpose for which the microporous polyolefin membrane is used,
If necessary, the gel-like molded product is stretched. In the case of stretching, after heating the gel-like molded product, it is stretched at a predetermined ratio by a normal tenter method, roll method, inflation method, rolling method or a combination of these methods. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either longitudinal / transverse simultaneous stretching or sequential stretching may be used, but simultaneous biaxial stretching is particularly preferable. Stretching improves the mechanical strength.

The stretching ratio varies depending on the thickness of the gel-like molded product, but in uniaxial stretching, it is preferably 2 times or more, more preferably 3 to 30 times. In biaxial stretching, it is at least 2 times or more in any direction, and the area magnification is preferably 10 times or more.
0 times is more preferable. If the areal magnification is less than 10 times, the stretching is insufficient and a thermoplastic resin microporous membrane having high elasticity and high strength cannot be obtained. On the other hand, if the areal magnification exceeds 400 times, there are restrictions on the stretching device, stretching operation and the like.

The stretching temperature is preferably below the melting point of the thermoplastic resin + 10 ° C., more preferably within the range from the crystal dispersion temperature to below the crystal melting point. If the stretching temperature exceeds the melting point + 10 ° C, the resin melts and the molecular chains cannot be oriented by stretching. Further, if the stretching temperature is lower than the crystal dispersion temperature, the resin is not sufficiently softened, and the film is easily broken during stretching, so that high-stretching cannot be performed. In the present invention, the stretching temperature is usually 100 to 140 ° C, preferably 110 to 120 ° C. Here, the crystal dispersion temperature is
The value obtained by measuring the temperature characteristics of dynamic viscoelasticity based on ASTM D 4065. When the stretching is carried out, the solvent can be removed before and / or after the stretching, but it is preferably carried out after the stretching.

For removing (washing) the solvent, a washing solvent (A) having a surface tension at 25 ° C. of 24 mN / m or less, preferably 20 mN / m or less is used. The washing solvent (A) is preferably one that is incompatible with the thermoplastic resin. By using such a washing solvent (A), it is possible to suppress the shrinkage and densification of the network structure caused by the surface tension of the gas-liquid interface generated inside the micropores during drying after washing. As a result, the porosity / permeability of the microporous membrane can be improved. The surface tension of the washing solvent can be lowered as the use temperature is raised, but the usable temperature range is limited to the boiling point or lower.
In the specification of the present application, "surface tension" refers to the tension generated at the interface between gas and liquid, and is measured based on JIS K 3362.

As the washing solvent (A), a fluorine compound such as hydrofluorocarbon, hydrofluoroether, cyclic hydrofluorocarbon, perfluorocarbon, perfluoroether, normal paraffin having 5 to 10 carbon atoms, isoparaffin having 6 to 10 carbon atoms, Such as aliphatic ethers having 6 or less carbon atoms, cycloparaffins such as cyclopentane, aliphatic ketones such as 2-pentanone, methanol, ethanol, 1-propanol, 2-propanol, tertiary butanol, isobutanol, 2-pentanol, etc. Aliphatic alcohol, propyl acetate, tertiary butyl acetate, secondary butyl acetate, ethyl acetate, isopropyl acetate, isobutyl acetate, methyl formate, ethyl formate,
Examples thereof include isopropyl formate, isobutyl formate, and ethyl propionate aliphatic ester.

As the fluorine compound, a chain hydrofluorocarbon represented by a composition formula of C ₅ H ₂ F ₁₀ , C ₄ F ₉ OCH ₃
And C ₄ F ₉ OC ₂ hydrofluoroether represented by the composition formula H _5, C ₅ H ₃ cyclic hydrofluorocarbons represented by the composition formula of F _7, represented by a composition formula of C ₆ F ₁₄ and C ₇ F _{1 6} And at least one selected from the group consisting of perfluorocarbons represented by the composition formula of C ₄ F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F ₅ . Since the surface tension of these fluorine compounds is 24 mN / m or less at 20 ° C., the effect of suppressing shrinkage and densification of the network structure due to the surface tension is high. Further, since the boiling point is 100 ° C or lower, it is easy to dry. Furthermore, because it has no ozone depletion, it can reduce the load on the environment, and its flash point is 40 ° C or higher (some compounds have no flash point), so the risk of flammable explosion during the drying process is low.

As the normal paraffin having 5 to 10 carbon atoms, normal pentane, normal hexane, normal heptane, normal octane, normal nonane, and normal decane are preferable. These have a surface tension of 24 mN at 20 ° C.
/ m or less. Among them, the boiling point is 100 ℃ or less,
Normal pentane, normal hexane, and normal heptane, which are easily dried, are more preferable.

As the isoparaffin having 6 to 10 carbon atoms, 2-
Methylpentane, 3-methylpentane, 2,2-dibutylbutane, 2,3-dibutylbutane, 2-methylhexane, 3-methylhexane, 3-ethylpentane, 2,2-dimethylpentane,
2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 2,2,3-trimethylbutane, 2-methylheptane, 3-methylheptane, 2,2-dimethylhexane, 2,
3-dimethylhexane, 2,5-dimethylhexane, 3,4-dimethylhexane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 2,3,3-trimethylpentane, 2,3, 4-trimethylpentane, 2-methyloctane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2-methylnonane and 2,3,5-trimethylheptane are preferred. Among them, the surface tension is 20 mN / m or less at 20 ° C, and the boiling point is
2-methylpentane, which is 100 ° C or less, 3-methylpentane, 2,2-dibutylbutane, 2,3-dibutylbutane, 2-methylhexane, 3-methylhexane, 3-ethylpentane, 2,
2-Dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane and 3,3-dimethylpentane are more preferable.

The ether having 6 or less carbon atoms is preferably diethyl ether, butyl ethyl ether, dipropyl ether or diisopropyl ether. These have a surface tension of 24 mN / m or less at 20 ° C. and a boiling point.
It is below 100 ℃.

Cyclopentane, methanol, ethanol, 1-propanol and 2-propanol have a surface tension of 24 mN / m or less at 20 ° C. and a boiling point of 100 ° C.
The following is preferable.

Among the above aliphatic esters, the surface tension is
Tertiary butyl acetate, secondary butyl acetate, isopropyl acetate, isobutyl acetate, ethyl formate, isopropyl formate, and isobutyl formate, which are 24 mN / m or less at 20 ° C., are preferable. Further, the boiling point is 100 ° C. or lower, but tertiary butyl acetate, ethyl formate, and isopropyl formate are more preferable.

As the washing solvent (A), it is also possible to use a mixture of water and an aliphatic alcohol having 3 or less carbon atoms, which is blended so as to have a surface tension of 24 mN / m or less at 25 ° C.

The above-mentioned washing solvent (A) can be used as a mixture with other solvents. In this case, the mixing ratio is such that the surface tension at 25 ° C is 24 mN / m or less. For example, a chain hydrofluorocarbon represented by the composition formula of C ₅ H ₂ F _10, a hydrofluoroether represented by the composition formula of C ₄ F ₉ OCH ₃ and C ₄ F ₉ OC ₂ H ₅ , and C ₅ H ₃ F ₇ Cyclic hydrofluorocarbons represented by composition formula, C ₆ F ₁₄ and C ₇ F
Perfluorocarbon represented by the composition formula of ₁₆ and C ₄
It is possible to use a mixture of at least one solvent selected from the group consisting of perfluoroethers represented by the composition formula of F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F ₅ and a hydrocarbon solvent such as paraffin. .

The washing is preferably performed in two or more washing steps, and a step of using a washing solvent (washing solvent (B)) other than the washing solvent (A) may be included. In this case, the washing solvent (A) may be used in at least one step. Washing solvent
As (B), those not compatible with the thermoplastic resin are preferable, for example, pentane, hexane, heptane and other known hydrocarbons as washing solvents, methylene chloride, chlorinated hydrocarbons such as carbon tetrachloride, and three, Fluorinated hydrocarbons such as fluorinated ethane, ethers such as diethyl ether and dioxane,
A readily volatile solvent such as methyl ethyl ketone can be used. It is also possible to use a non-aqueous solvent having a boiling point of 100 ° C or higher and a flash point of 0 ° C or higher. The above-mentioned washing solvent (B) is appropriately selected according to the solvent used for dissolving the polyolefin composition, and is used alone or as a mixture.

By such a washing process of two or more stages,
Sufficient cleaning can be performed while suppressing shrinkage and densification of the network structure caused by the surface tension of the cleaning solvent. Preferably, a washing solvent is used at least in the final washing step.
Process with (A). As a result, when the washing solvent (B) is used, the washing solvent (B) can be removed (hereinafter referred to as “rinsing treatment”), and shrinkage and densification of the network that occurs during drying after washing can be prevented. As a result, it is effective in improving the porosity / permeability of the microporous polyolefin membrane.

In the final washing step, the washing solvent (A)
When the treatment is performed with a washing solvent (A) having a boiling point of 100 ° C. or less, the efficiency of the drying step is improved. Furthermore, the above-mentioned C ₅ H ₂ F ₁₀
A chain hydrofluorocarbon represented by the composition formula of C ₄
Hydrofluoroether represented by the composition formula of F ₉ OCH ₃ and C ₄ F ₉ OC ₂ H ₅ , cyclic hydrofluorocarbon represented by the composition formula of C ₅ H ₃ F ₇ , composition of C ₆ F ₁₄ and C ₇ F ₁₆ Perfluorocarbon represented by the formula, and C ₄ F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F
_The use of a fluorine-based compound such as perfluoroether represented by the composition formula ₅ also has the effect of further reducing the environmental load in the manufacturing process as described above. Especially washing solvent
When a solvent having a boiling point of 150 ° C. or higher is used as (B), it takes time to dry simply by drying with hot air, and the porosity / air permeability may decrease in the subsequent heat treatment due to the influence, but the boiling point is 100%. The problem can be solved by using the washing solvent (A) at a temperature of not higher than ° C.

The non-aqueous solvent having a boiling point of 100 ° C. or higher and a flash point of 0 ° C. or higher, which can be used as the washing solvent (B), is hardly volatile, has a low load on the environment, and has a risk of ignition and explosion in the drying process. Since it is low, it is safe to use. In addition, since it has a high boiling point, it is easy to condense, easy to collect, and easy to recycle. In the present specification, "boiling point" refers to a boiling point at 1.01 x 10 ⁵ Pa, and "flash point" refers to a value measured based on JIS K 2265.

As the non-aqueous solvent, for example, a boiling point of 100 ° C.
Examples thereof include paraffin compounds having a flash point of 0 ° C. or higher, aromatic compounds, alcohols, esters, ethers and ketones. The flash point thereof is preferably 5 ° C or higher, more preferably 40 ° C or higher. However, it is not preferable to make the non-aqueous solvent into an aqueous solution because the solvent cannot be sufficiently removed.

As the non-aqueous solvent, normal paraffins having 8 or more carbon atoms, normal paraffins having 5 or more carbon atoms in which at least a part of hydrogen atoms are substituted with halogen atoms,
Isoparaffins having 8 or more carbon atoms, cycloparaffins having 7 or more carbon atoms, cycloparaffins having 5 or more carbon atoms in which at least a part of hydrogen atoms are replaced with halogen atoms, aromatic hydrocarbons having 7 or more carbon atoms, and at least hydrogen atoms Aromatic hydrocarbons having 6 or more carbon atoms partially substituted with halogen atoms, alcohols having 5 to 10 carbon atoms in which some hydrogen atoms may be substituted with halogen atoms, some hydrogen atoms being halogen atoms At least one selected from the group consisting of esters and ethers having 7 to 14 carbon atoms and ketones having 5 to 10 carbon atoms that may be substituted with is preferable.

As the normal paraffin having 8 or more carbon atoms, normal octane, normal nonane, normal decane, normal undecane and normal dodecane are preferable, and normal octane, normal nonane and normal decane are more preferable.

Examples of normal paraffins having 5 or more carbon atoms in which at least a part of hydrogen atoms are replaced by halogen atoms include 1-chloropentane, 1-chlorohexane, 1-chloroheptane, 1-chlorooctane and 1-bromopentane. , 1-bromohexane, 1-bromoheptane, 1-bromooctane, 1,
5-dichloropentane, 1,6-dichlorohexane and 1,7-dichloroheptane are preferable, and 1-chloropentane, 1-chlorohexane, 1-bromopentane and 1-bromohexane are more preferable.

2, as an isoparaffin having 8 or more carbon atoms,
3,4-trimethylpentane, 2,2,3-trimethylpentane,
2,2,5-Trimethylhexane, 2,3,5-trimethylhexane, 2,3,5-trimethylheptane and 2,5,6-trimethyloctane are preferable, and 2,3,4-trimethylpentane and 2,2 , 3-Trimethylpentane, 2,2,5-Trimethylhexane, 2,3,5-
Trimethylhexane is more preferred.

Cycloparaffins having 7 or more carbon atoms include cycloheptane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,3-dimethylcyclohexane,
Cis- and trans-1,4-dimethylcyclohexane are preferred, and cyclohexane is more preferred.

As the cycloparaffin having 5 or more carbon atoms in which at least a part of hydrogen atoms are substituted with halogen atoms, chlorocyclopentane and chlorocyclohexane are preferable, and chlorocyclopentane is more preferable.

As the aromatic hydrocarbon having 7 or more carbon atoms,
Toluene, ortho-xylene, meta-xylene and para-xylene are preferable, and toluene is more preferable.

Aromatic hydrocarbons having 6 or more carbon atoms in which at least a part of hydrogen atoms are replaced with halogen atoms include chlorobenzene, 2-chlorotoluene, 3-chlorotoluene,
4-chlorotoluene, 3-chloroorthoxylene, 4-chloroorthoxylene, 2-chlorometaxylene, 4-chlorometaxylene, 5-chlorometaxylene, 2-chloroparaxylene are preferred, chlorobenzene, 2-chlorotoluene, 3-
Chlorotoluene and 4-chlorotoluene are more preferable.

Alcohols having 5 to 10 carbon atoms in which a part of hydrogen atoms may be replaced with halogen atoms include isopentyl alcohol, tertiary pentyl alcohol, cyclopentanol, cyclohexanol, and 3-methoxy-1-. Butanol, 3-methoxy-3-methyl-1-butanol, propylene glycol normal butyl ether, 5-
Chloro-1-pentanol is preferable, and 3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butanol, propylene glycol normal butyl ether, and 5-chloro-1-pentanol are more preferable.

Esters having 7 to 14 carbon atoms in which a part of hydrogen atoms may be replaced with halogen atoms include diethyl carbonate, diethyl maleate, normal propyl acetate, normal butyl acetate, isopentyl acetate, 3-methoxybutyl acetate. , 3-methoxy-3-methylbutyl acetate, ethyl normal butyrate, ethyl normal valerate, 2-chloroethyl acetate is preferred, isopentyl acetate, 3-methoxybutyl acetate, 3-methoxy-3-methylbutyl acetate, ethyl normal butyrate, acetic acid 2 -Chloroethyl is more preferred.

Diether glycol dimethyl ether, normal butyl ether, diisobutyl ether and bischloroethyl ether are preferable as the ether having 7 to 14 carbon atoms in which a part of hydrogen atoms may be replaced by a halogen atom, and dipropylene glycol dimethyl ether, Bischloroethyl ether is more preferred.

As the ketone having 5 to 10 carbon atoms, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclopentanone and cyclohexanone are preferable, and 2-pentanone and 3-pentanone are more preferable.

The washing solvent (B) as described above may be used as a mixture, but the washing solvent (B) may be used as an optional component (C).
Chain hydrofluorocarbons represented by the composition formula of C ₅ H ₂ F ₁₀ listed as the cleaning solvent (A), C ₄ F ₉ OCH ₃ and C ₄ F ₉ OC ₂ H ₅
Hydrofluoroether represented by the composition formula of C ₅ H ₃ F ₇
A cyclic hydrofluorocarbon represented by the composition formula of C ₆
Perfluorocarbon represented by the composition formula of F ₁₄ or C ₇ F ₁₆ , at least from the group consisting of fluorine compounds such as perfluoroether represented by the composition formula of C ₄ F ₉ OCF ₃ and C ₄ F ₉ OC ₂ F _5. A mixture of one kind of solvent may be used. In this case, the washing solvent (B) and the optional component (C) are preferably mixed in a ratio such that the surface tension is 24 mN / m or less at any temperature of 20 to 80 ° C., specifically, the mixed solvent. Ten
The amount of the optional component (C) is 2 to 98 parts by weight, preferably 5 to 50 parts by weight in 0 part by weight. By including 2 to 98 parts by weight of the optional component (C), sufficient washing can be performed while suppressing shrinkage and densification of the network caused by the surface tension of the washing solvent.

The washing solvent (B) has a surface tension of 20 to 80 ° C.
It is preferable to use one having a temperature of 24 mN / m or less at any of the temperatures. For example, normal pentane, hexane, heptane, ethane trifluoride, diethyl ether, 2-
Methyl pentane, 3-methyl pentane, cyclohexane,
Cyclopentane, acetone, methyl ethyl ketone and the like.

Washing solvent used in the first step of washing here
Preferred combinations of (B) and the washing solvent (A) used in the second step are shown below. However, as described below, the washing solvent (A)
Since the washing with the washing solvent (B) can be performed in three or more steps, these are not intended to be limited to two steps. For example, washing solvent (B) / washing solvent (A) =
Methylene chloride / C ₄ F ₉ OCH ₃ , methylene chloride / C ₆ F ₁₄ , methylene chloride / C ₇ F ₁₆ , methylene chloride / normal heptane,
Methylene chloride / normal hexane, methylene chloride / diethyl ether, ether / hydrofluoroether,
Ether / cyclic hydrofluorocarbon, ether /
Alcohol, ether / alcohol / water mixture, normal paraffin / hydrofluoroether, normal paraffin / cyclic hydrofluorocarbon, normal paraffin / alcohol, normal paraffin / alcohol / water mixture, isoparaffin / hydrofluoroether, isoparaffin / cyclic hydro Fluorocarbon, isoparaffin / alcohol, mixture of isoparaffin / alcohol and water, cycloparaffin / hydrofluoroether, cycloparaffin / cyclic hydrofluorocarbon, cycloparaffin / alcohol, mixture of cycloparaffin / alcohol and water, ketone / hydrofluoroether, Ketone / Cyclic hydrofluorocarbon, Ketone / Alcohol, Mixture of Ketone / Alcohol with water Thing, and the like. More preferably, the washing solvent (B) / the washing solvent (A) = methylene chloride / C ₄ F ₉ OC
H ₃ , methylene chloride / C ₆ F ₁₄ , methylene chloride / C ₇ F ₁₆ , methylene chloride / normal heptane, methylene chloride / normal hexane, methylene chloride / diethyl ether, normal heptane / C ₄ F ₉ OCF ₃ , normal heptane / It is C ₆ F ₁₄ . By using such a combination, the porosity / permeability of the microporous membrane can be improved while effectively removing the solvent.

The washing solvent (A) alone or the washing solvent (A) and the washing solvent (B) may be washed in three or more steps. The one-step or two-step treatment is effective when the solvent cannot be sufficiently removed and the physical properties of the obtained thermoplastic resin microporous membrane are deteriorated. In this case, at least in the final washing step, the washing solvent (A) may be used, and the number of washings is not particularly limited, but it is usually 3 to 5 steps, preferably 3 to 4 steps. In addition, even if treated with the same washing solvent in each stage, the manufacturing process simply becomes long, the space of the thermoplastic resin microporous membrane manufacturing equipment is expanded, and the efficiency of solvent removal is reduced. It is preferred to use different wash solvents. However, it is not limited to using different cleaning solvents. Therefore, for example, in the case of three-step treatment, it is possible to use the same washing solvent in the first step and the second step, and to use a washing solvent different from the first and second steps in the third step.

The washing method may be a method of immersing in the washing solvent (A) and / or the washing solvent (B) for extraction, a method of showering the washing solvent (A) and / or the washing solvent (B), or a combination thereof. It can be performed by a method or the like. Also the washing solvent (A)
The washing solvent (B) is preferably used in an amount of 300 to 30,000 parts by weight per 100 parts by weight of the gel-like molded product. When the washing solvent (A) and the washing solvent (B) are used for washing in two or more steps, the amount of the washing solvent (A) is 100 parts by weight of the washing solvent (B). It is preferably 50 to 200 parts by weight. The washing with the washing solvent (A) alone or with the washing solvent (A) and the washing solvent (B) is preferably performed until the residual solvent is less than 1% by weight based on the amount added.

The washing temperature with the washing solvent (B) is the washing solvent (B).
Depends on the boiling point of. When the boiling point of the washing solvent (B) is 150 ° C. or less, washing can be performed at room temperature, and heating washing may be performed as necessary, and washing at 20 to 80 ° C. is generally preferable.
Further, when the boiling point of the washing solvent (B) is 150 ° C. or higher, the penetrability into the inside of the membrane is poor at room temperature, so it is preferable to wash by heating.

The washing temperature and / or the rinsing temperature with the washing solvent (A) depend on the surface tension of the washing solvent (A). Specifically, it is preferable to perform the washing and / or rinsing treatment at a temperature or higher at which the surface tension of the washing solvent (A) becomes 24 mN / m or less.
If the ambient temperature is lower than the temperature at which the surface tension of the washing solvent (A) becomes 24 mN / m or less, the surface tension is heated to a temperature at which the surface tension becomes 24 mN / m or less, if necessary. Washing solvent (A)
Has a surface tension of 24 mN / m or less at a temperature of at most 25 ° C., so that it does not require heating in most cases and can be washed and / or rinsed at ordinary room temperature.

(D) Drying Step of Membrane The membrane obtained by stretching and solvent removal can be dried by a heat drying method or an air drying method. The drying temperature is preferably a temperature not higher than the crystal dispersion temperature of the thermoplastic resin, and particularly preferably a temperature lower than the crystal dispersion temperature by 5 ° C. or more.

By the drying treatment, the content of the washing solvent (B) remaining in the thermoplastic resin microporous film is preferably 5% by weight or less (the film weight after drying is 100% by weight), 3
It is more preferable that the content be less than or equal to weight%. If the washing solvent (B) remains in the film in a large amount due to insufficient drying, the porosity decreases in the subsequent heat treatment and the air permeability deteriorates, which is not preferable.

(E) Heat Treatment Step The microporous membrane obtained by drying needs to be further heat-treated in two or more steps. In the heat treatment step, both MD and TD are fixed, and the heat treatment step (a) (hereinafter referred to as step (a)) is performed while shrinking MD and / or TD by 0 to 10%, and then the final heat treatment step. As a result, it is necessary to perform the heat treatment step (b) (hereinafter referred to as step (b)) while shrinking to MD and / or TD.

(1) Step (a) By fixing both MD and TD and performing 0 to 10% shrinkage in MD and / or TD, a microporous membrane having high tensile strength and puncture strength can be obtained. can get. Here, performing under 0% shrinkage means that the dimensions are not changed in both MD and TD directions. It is preferably contracted by 3 to 8%. By performing the heat treatment under the shrinkage of 10% or less, it is possible to improve the heat shrinkage while suppressing the deterioration of the air permeability. In the step (a), it is preferable to fix both the MD and TD directions of the film by a tenter method, a roll method or a rolling method.
If step (a) is performed by a free method using a belt conveyor method, a mesh drum (rotary drum) method, a floating method, etc., the heat shrinkage can be reduced, but the air permeability deteriorates and the physical properties become extremely poor. Not preferable.

The temperature of step (a) varies depending on the thermoplastic resin used, but is preferably 90 to 150 ° C. If it is less than 90 ° C, the effect of reducing the heat shrinkage is not sufficient, and if it exceeds 150 ° C, the air permeability deteriorates. The time is not particularly limited, but is usually 1 second or more and 10 minutes or less, preferably 3 seconds or more and 2 minutes or less. The step (a) may be performed in two or more steps, but it is preferably performed in one step or two steps in consideration of complication of the step.

(2) Step (b) (Final heat treatment step) As the final heat treatment step, by performing the step (b) while shrinking to MD and / or TD, microporous material having an excellent heat shrinkage ratio is obtained. A film is obtained. The step (b) may be performed by a fixed method such as a tenter method, a roll method, a rolling method, or a free method using a belt conveyor method, a mesh drum (rotating drum) method, a floating method, or the like. The free method is preferable from the viewpoint of uniform physical properties in the width direction and lengthening of the winding length. It is preferable that step (b) is performed under MD to MD and / or TD of the microporous membrane at a shrinkage of 0.1 to 50%.
More preferably, it is performed under a contraction of%. When the shrinkage is less than 0.1%, the heat shrinkage is not improved, and when it exceeds 50%, the air permeability is deteriorated. By shrinking MD, the thermal shrinkage rates of both MD and TD can be improved.

The temperature of the step (b) varies depending on the kind of the thermoplastic resin used, but is preferably in the range of 60 ° C. or higher to the melting point of the thermoplastic resin or lower, more preferably 110 to 125 ° C. The time is not particularly limited, but is usually 1 second or more and 10 minutes or less, preferably 3 seconds or more and 2 minutes or less. The process (b)
The step may be carried out in two or more steps, but it is preferably carried out in one step or two steps in consideration of complication of the step.

In the present invention, the step (b) needs to be performed in the final heat treatment step after the step (a). This stabilizes the crystals, and as a result, it is possible to produce a polyolefin fine porous film having an excellent balance of tensile strength, puncture strength, and air permeability and an excellent heat shrinkage rate. If the step (a) is performed after the step (b), the air permeability of the obtained polyolefin fine microporous membrane deteriorates.

(3) Step (c) When the heat treatment is performed in three or more steps, the heat treatment step (c) is performed while shrinking MD and / or TD by 0 to 20% (hereinafter referred to as step (c)). ) Is preferably provided. The air permeability deteriorates when the shrinkage exceeds 20%. In this case, step (c) may be provided before or after step (a). The heat shrinkage rate can be reduced without causing a large deterioration of air permeability in the step (c).

The step (c) is a tenter system, a roll system,
A fixed method such as a rolling method or a free method using a belt conveyor method, a mesh drum (rotary drum) method, a floating method, or the like may be used. The free method is preferable from the viewpoint of uniform physical properties in the width direction and lengthening of the winding length. The temperature of step (c) is preferably 90 to 150 ° C. The time is not particularly limited, but is usually 1 second or more and 10 minutes or less, preferably 3 seconds or more and 2 minutes or less.

(F) Crosslinking Treatment Step of Membrane It is preferable that the membrane obtained by stretching and solvent removal is dried by a heat drying method, an air drying method or the like and then subjected to a crosslinking treatment by ionizing radiation. Α-rays, β-rays, γ-rays, and electron beams are used as ionizing radiation, with an electron dose of 0.1 to 100 Mrad and an acceleration voltage of 100.
It can be done at ~ 300kV. This can improve the meltdown temperature. The crosslinking treatment is preferably performed before the heat treatment.

(G) Hydrophilization treatment step The obtained microporous membrane can be used after being hydrophilized. As the hydrophilic treatment, a monomer graft, a surfactant treatment, a corona discharge treatment or the like is used. The hydrophilic treatment is preferably performed after ionizing radiation.

When a surfactant is used, any of nonionic surfactants, cationic surfactants, anionic surfactants and amphoteric surfactants can be used, but nonionic surfactants are also usable. Is preferred. In this case, the surfactant is made into an aqueous solution or a solution of a lower alcohol such as methanol, ethanol or isopropyl alcohol, and is hydrophilized by a method such as dipping and a doctor blade.

The obtained hydrophilized microporous membrane is dried. At this time, in order to improve the permeability, it is preferable to perform heat treatment at a temperature equal to or lower than the melting point of the thermoplastic resin microporous film while preventing or stretching the shrinkage.

[3] Thermoplastic resin microporous membrane The physical properties of the polyolefin microporous membrane produced as described above are usually 0.1-100 μm in thickness and 1 in air permeability.
200 seconds / 100 cc or less, preferably 900 seconds / 100 cc or less (film thickness 25 μm conversion), porosity is 30 to 90%,
Puncture strength is 5500mN / 25μm or more, tensile breaking strength is 10
0 MPa or more, tensile elongation at break is 150% or more, thermal shrinkage is 3.7% or less in both MD and TD and MD or TD
In either case, the property of 1.4% or less (105 ° C / 8 hr) is satisfied.

As described above, the polyethylene microporous membrane obtained by the production method of the present invention has an excellent balance of porosity, permeability and mechanical strength and excellent dimensional stability. And the like can be preferably used.

[0089]

EXAMPLES The present invention will be explained in more detail by the following examples, but the present invention is not limited to these examples.

Example 1 20% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2.0 × 10 ⁶ and 80% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 3.5 × 10 ⁵ were used. Mn ＝
A polyethylene composition (melting point: 135 ° C, crystal dispersion temperature: 90 ° C) of 16.0 was added with tetrakis [methylene-
3- (3,5-ditert-butyl-4-hydroxyphenyl)-
Propionate] Methane was added at 0.375 parts by weight per 100 parts by weight of the polyethylene composition to obtain a polyethylene composition.
30 parts by weight of the obtained polyethylene composition was added to a twin-screw extruder (58
mmφ, L / D = 42, strong kneading type), 70 parts by weight of liquid paraffin is supplied from the side feeder of this twin-screw extruder, melt-kneaded at 200 ° C. and 200 rpm, and polyethylene in the extruder. A solution was prepared.

The obtained polyethylene solution was extruded from a T-die installed at the tip of the extruder at 190 ° C. so that the biaxially stretched film had a thickness of about 50 μm, and was taken up by a cooling roll controlled at 50 ° C. Sheet was formed. About the obtained gel-like sheet, 5 × at 114 ℃ using a batch stretching machine
Biaxial stretching was performed to obtain a stretched film of 5 times. The obtained membrane was fixed on a 20 cm x 20 cm aluminum fixing frame, and the temperature of the methylene chloride was adjusted to 25 ° C (surface tension 27.3 mN / m
(25 ℃), boiling point 40.0 ℃) in the first cleaning tank and the second cleaning tank while shaking at 100 rpm for 30 seconds each impregnation cleaning, liquid paraffin was extracted and removed (hereinafter, the first
The cleaning tank and the second cleaning tank are collectively referred to as "cleaning tank", and the processing in the first cleaning tank and the second cleaning tank is referred to as "cleaning processing"). After that, methyl perfluorobutyl ether ((C ₄ F ₉ OCH ₃ ), temperature controlled to 25 ° C, HFE-7100 manufactured by Sumitomo 3M Limited, surface tension 13.6mN / m (25 ° C), boiling point 61
Impregnation was performed for 30 seconds in each of the third and fourth cleaning tanks at ℃ and no flash point (the same applies below), and the methylene chloride contained in the membrane was replaced (hereinafter, the third cleaning tank and the fourth cleaning tank).
The cleaning tanks are collectively referred to as a "rinsing tank", and the replacement processing in the third cleaning tank and the fourth cleaning tank is called "rinsing processing"). After the rinse treatment, the film was dried by blowing hot air (70 ° C) on a roll heated to 60 ° C.

With respect to the film after drying, (1) the film was held in a tenter and heat-treated at 126 ° C. for 3 seconds under 0% shrinkage, and (2) the film was held in a tenter under 0% shrinkage. Heat treatment was performed at 126 ° C. for 3 seconds, and (3) the film was held in a tenter, and heat treated at 126 ° C. for 3 seconds while shrinking only 10% in TD.

Example 2 Normal pentane (surface tension: 15.5 mN / m, temperature controlled at 25 ° C.)
(25 ° C., boiling point 36.1 ° C.) Rinsing treatment in a rinsing bath, the same as in Example 1 except that the final heat treatment step was performed at 126 ° C. for 3 seconds while shrinking MD by 5% and TD by 10%. To produce a polyethylene microporous membrane.

Example 3 Washing treatment in a washing tank of 3-methoxy-3-methylbutyl ester (surface tension 28.8 mN / m (20 ° C.), boiling point 188 ° C.) temperature-controlled at 60 ° C., heat treatment in the final stage In the process, put the film on the belt conveyor and shrink it by 5% in MD and TD to 100.
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the treatment was carried out at 3 ° C for 3 seconds.

Example 4 Normal decane (surface tension 23.4 mN / m (2
5 ° C), boiling point 174 ° C) / HFE-7100 = 90/10 (wt / wt) in a washing tank, and after drying, (1) sandwich the film in a roll and shrink it to 0%. Heat treatment at 126 ° C for 3 seconds, (2) sandwich the membrane between rolls, heat treatment at 126 ° C for 3 seconds under 0% shrinkage, (3) place the membrane on a belt conveyor, and add 5% to MD and TD.
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the heat treatment was performed at 100 ° C. for 3 seconds while shrinking.

Example 5 With respect to the film after drying, (1) the film was sandwiched between rolling rolls, heat-treated at 126 ° C. for 3 seconds under 0% shrinkage, and (2) the film was sandwiched between rolling rolls and 0% Heat treated at 126 ℃ for 3 seconds under shrinkage (3)
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the membrane was placed on a belt conveyor and heat-treated at 100 ° C. for 3 seconds while shrinking 5% in MD and TD.

Example 6 With respect to the film after drying, (1) the film was held in a tenter, and heat-treated at 126 ° C. for 3 seconds under 0% shrinkage, and (2) the film was held in the tenter, MD and TD Heat treatment at 126 ℃ for 3 seconds while shrinking by 5%, (3) Hold the film on the tenter, and apply 5 to MD and TD.
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the heat treatment was performed at 126 ° C. for 3 seconds while shrinking by 100%.

Example 7 3-methoxy-3-methylbutyl ester (surface tension 28.8 mN / m (20 ° C.), boiling point 188 ° C.) whose temperature was controlled at 60 ° C. in the washing treatment
After cleaning in the washing tank of (1), the film is sandwiched between (1) rolls and heat-treated at 126 ° C for 3 seconds under 0% shrinkage. (2) The film is sandwiched between rolls and MD and TD 126 ℃ while shrinking
Heat treatment for 3 seconds at (3) Place the film on the belt conveyor,
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the heat treatment was performed at 100 ° C. for 3 seconds while shrinking MD and TD by 5%.

Example 8 Normal decane (surface tension adjusted to a temperature of 50 ° C. in the washing treatment)
23.4mN / m (25 ℃), boiling point 174 ℃) / HFE-7100 = 90/10 (wt /
(1) Hold the film in the tenter, and shrink it to TD only 8% for 3% at 126 ° C.
Heat treatment for 2 seconds, (2) Hold the film in the tenter, heat it at 126 ° C for 3 seconds under 0% shrinkage, and heat it for 3 seconds (3) Put the film on the belt conveyor and shrink it by 5% on MD and TD at 100 ° C. A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the heat treatment was performed for 3 seconds.

Comparative Example 1 Methylene chloride (surface tension adjusted to 25 ° C. by rinsing)
27.3mN / m (25 ℃), boiling point 40.0 ℃), and perform 0% shrinkage on the dried film while holding the film on the tenter.
A polyethylene microporous membrane was produced in the same manner as in Example 1 except that the heat treatment at 124 ° C for 3 seconds was repeated 3 times.

Comparative Example 2 A washing treatment was carried out with normal pentane (surface tension: 15.5 mN / m (25 ° C.), boiling point: 36.1 ° C.) temperature-controlled at 25 ° C., and a rinsing treatment was performed at a temperature of 25 ° C. methylene chloride ( Surface tension 27.3mN / m
(25 ℃), boiling point 40.0 ℃), the film after drying, the film is placed on a belt conveyor under 0% shrinkage 12
Example 1 except that the heat treatment at 4 ° C. for 3 seconds was repeated 3 times
A polyethylene microporous membrane was prepared in the same manner as in.

The physical properties of the thermoplastic resin microporous membranes obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were measured by the following methods. -Film thickness: Measured with a contact thickness meter. -Air permeability: Measured according to JIS P8117 (converted to a film thickness of 30 μm). -Porosity: Measured by a gravimetric method.・ Puncture strength: 25 μm thick microporous membrane with a diameter of 1 mm (0.5 mm R)
The maximum load was measured when the needle was pierced at a speed of 2 mm / sec.・ Tensile breaking strength: Tensile breaking strength of 10 mm wide strip
Measured according to ASTM D882.・ Tensile rupture elongation: Tensile rupture elongation of 10 mm wide strip test piece
Measured according to ASTM D882.・ Heat shrinkage ratio: M when the microporous membrane is exposed at 105 ° C for 8 hours
The shrinkage rates of D and TD were measured respectively.

[0103]

[Table 1]

As shown in Table 1, the polyethylene microporous membranes of Examples 1 to 8 produced by the method of the present invention have porosity,
It can be seen that the balance of air permeability and mechanical strength is excellent, and the heat shrinkage rate is also excellent. On the other hand, the microporous membranes of Comparative Examples 1 and 2 were rinsed and dried with a washing solvent having a surface tension of more than 24 mN / m at 25 ° C., and were treated only under 0% shrinkage in the heat treatment step. Therefore, in Comparative Example 1, the thermal contraction rate is significantly inferior, and in Comparative Example 2, the air permeability is significantly inferior, as compared with Examples 1 to 8.

[0105]

As described in detail above, the method for producing a thermoplastic resin microporous membrane of the present invention is a washing solvent having a surface tension of 24 mN / m or less at 25 ° C. in the step of removing the solvent.
In addition to treating with (A), in the heat treatment process, MD and T
After fixing both D and shrinking MD and / or TD by 0 to 10%, perform the heat treatment step (a), and then shrinking MD and / or TD as the final heat treatment step.
Since the step (b) is carried out, it is possible to produce a thermoplastic resin microporous film having an excellent balance of porosity, air permeability and mechanical strength, and an excellent thermal shrinkage. In particular, when a fluorine-based compound is used as the washing solvent (A), it has no ozone depletion property and is useful in terms of environmental problems. The obtained thermoplastic resin microporous membrane is useful for battery separators, filters and the like.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 101: 00 C08L 101: 00 (72) Inventor Koichi Kono 3-29-10-404 F-term, Mihara, Asaka City, Saitama Prefecture (Reference) 4D006 GA03 GA06 GA07 GA50 MA03 MA23 MA31 MB09 MB15 MB16 MC22X MC23 MC24 MC35 MC37 MC54 MC61 NA23 NA25 NA36 NA42 NA54 NA58 NA62 NA64 NA68 NA73 PA10 PC01 PC80 4F074 AA17 AA24 AA26 AA65 AA71 AA87 CA03 CC03 CA04 CC05 CC02 CA04 CC07 CC04 CA07 CC02 CC04 CA07 CC02 CC04 CA07 CC02 CC04 CA07 CC02 CC04 CA07 CC02 CA04 CC07 CA02 CC02 CA04 CC02 CC22X CC27Z CC28Z CC29Y CC42Y CC45Y CC61Y DA08 DA10 DA22 DA23 DA43 DA49 5H021 BB01 BB02 BB05 BB13 EE02 EE04 EE07 EE08 HH00 HH01 HH06

Claims (5)

[Claims] 1. A solution obtained by melt-kneading a thermoplastic resin and a solvent is extruded, and the remaining solvent is removed from a gel-like molded article obtained by cooling with a washing solvent, and after drying, two or more steps are carried out. In the method for producing a thermoplastic resin microporous membrane including a step of performing a heat treatment, a surface tension at 25 ° C. of a cleaning solvent (A) of 24 mN / m or less is used as the cleaning solvent, and the heat treatment step is performed in the machine direction. (MD) and transverse direction (TD) are both fixed and heat treatment process is performed while shrinking in the machine direction (MD) and / or transverse direction (TD) by 0-10%.
A method for producing a thermoplastic resin microporous membrane, comprising: (a) and a final heat treatment step (b) performed while shrinking in the machine direction (MD) and / or the transverse direction (TD). 2. The method for producing a thermoplastic resin microporous membrane according to claim 1, wherein the solvent is removed by two or more washing steps with the washing solvent, and the washing is performed at least in the final washing step. 1. A method for producing a thermoplastic resin microporous membrane, which comprises using a solvent (A). 3. The method for producing a thermoplastic resin microporous membrane according to claim 1, wherein the remaining solvent is removed before and / or after stretching the gel-like molded article. And a method for producing a thermoplastic resin microporous film. 4. The method for producing a thermoplastic resin microporous film according to claim 1, wherein the step (b) is performed by any one of a belt conveyor system, a mesh drum system and a floating system. A method for producing a microporous thermoplastic resin film, which is characterized. 5. The method for producing a thermoplastic resin microporous film according to claim 1, wherein the heat treatment step is 0 to 20% in a machine direction (MD) and / or a transverse direction (TD).
A method for producing a microporous thermoplastic resin film, comprising a heat treatment step (C) performed while shrinking.