JP4746797B2 - Method for producing polyolefin microporous membrane - Google Patents

Description

【００９９】
表１に示すように、本発明の方法により製造した実施例１及び２の熱可塑性樹脂微多孔膜はその空孔率及び透気度において優れ、かつ乾燥後の膜幅変化が小さい。一方、比較例１〜４の微多孔膜は、吸引ロールを用いずに乾燥しているために、実施例１及び２と比較して物性が劣っている。
【０１００】
【発明の効果】
以上詳述したように、本発明の溶剤法による熱可塑性樹脂微多孔膜の製造において、溶剤を除去するために用いた洗浄溶媒を除去する工程で、吸引ロールを用いて吸引除去することにより、洗浄溶媒の拡散を抑制しながら高速に、かつ熱可塑性樹脂の収縮を抑制しつつ除去することができる。本発明の製造方法により、空孔率、透過性及び寸法安定性に優れた微多孔膜を製造することができる。得られた微多孔膜は電池用セパレーター、フィルター等に有用である。 [0001]
BACKGROUND OF THE INVENTION
  The present inventionPolyolefinRegarding the microporous membrane manufacturing method, in particular, the diffusion of the solvent and / or the washing solvent used to remove the plasticizer added during the film formation process.And shrinkage of microporous membraneHigh speed while suppressingRemovedPossible to leavePolyolefinManufacturing method of microporous membraneTo the lawRelated.
[0002]
[Prior art and problems to be solved by the invention]
Thermoplastic resin moldings are used in automobile interior and exterior materials, battery components, and the like, and have various forms including films and sheets. Among them, thermoplastic resin microporous membranes (microporous membranes) are widely used in various applications such as battery separators, diaphragms for electrolytic capacitors, various filters, moisture permeable and waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes. It is used.
[0003]
When manufacturing such a thermoplastic resin molded body, a solvent and a plasticizer are often added particularly during film formation during film production. However, in the case of a product such as a microporous film in which the solvent and plasticizer should not remain in the final product, it is necessary to remove the added solvent and plasticizer. When removing the solvent or plasticizer, it is usually washed with a volatile washing solvent and then dried with hot air. However, the thermoplastic resin contracts during hot air drying, and the desired physical properties cannot be obtained. In particular, in the case of a microporous film, there is a problem that the transmittance is lowered because the pores contract.
[0004]
For this reason, conventionally, a method has been employed in which a gel-like molded body after film formation is fixed to a tenter and then dried with hot air, or fixed to a small-diameter multistage heating roll and dried. However, the tenter method has a problem that the membrane cannot be sufficiently retained because it does not have a gripping force that can resist the shrinkage force of the membrane, particularly when a cleaning solvent such as methylene chloride having high volatility is dried. When a multi-stage heating roll is used, it is necessary to make the roll small in diameter in order to secure the gripping force of the film. For this reason, the effective dry area on the roll is small, and bending due to roll rigidity reduction occurs. There was a problem that the film contracted in the width direction in the gap. Therefore, these methods are not necessarily suitable methods for drying at high speed while suppressing shrinkage of the thermoplastic resin. There is also a method of combining small-diameter multi-stage heating rolls with hot air drying, but especially when hot air drying is performed at high speed, there is a problem that the recovery of the volatilized cleaning solvent becomes severe, making recovery difficult. There was a problem when using a cleaning solvent such as methylene chloride, which could cause environmental pollution.
[0005]
Accordingly, the object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to diffuse the solvent and / or the washing solvent used for removing the plasticizer during the film forming process.And shrinkage of microporous membraneHigh speed while suppressingRemovedPossible to leavePolyolefinIt is to provide a method for producing a microporous membrane.
[0006]
[Means for Solving the Problems]
  As a result of intensive studies in view of the above problems, the present inventors havePolyolefinThe solution obtained by melt-kneading the solvent and the solvent is extruded from a die and the remaining solvent is removed from the gel-like product obtained by cooling with a washing solvent.Washed polyolefin microporous membrane(Hereinafter, the removal of the solvent with the washing solvent is referred to as “washing”), and then the step of removing the washing solvent is included.PolyolefinIn the method for producing a microporous membrane, a suction force is applied,Washed polyolefin microporous membraneFrom the above, it was found that the above problem can be solved by removing the washing solvent by suction, and the present invention was conceived.
[0007]
  That is, the present inventionPolyolefinThe manufacturing method of the microporous membrane is:The solution obtained by melt-kneading the polyolefin and the solvent is extruded from a die, and the remaining solvent is removed from the gel-like molded product obtained by cooling with a washing solvent. A step of removing the cleaning solvent, wherein the cleaning solvent is suctioned and removed from the cleaning polyolefin microporous film using a suction roll having a nonwoven fabric on the outer peripheral surface of the roll in a poor solvent for the cleaning solvent.It is characterized by that.
[0008]
  By removing by suction, diffusion of the cleaning solvent during removal can be prevented, and therefore, when a cleaning solvent that may cause environmental pollution such as methylene chloride is used, there is an effect of preventing environmental pollution. As a suction meansHas non-woven fabric on the roll outer surfaceBy using a suction roll,Washed polyolefin microporous membraneIt is possible to suck and remove the washing solvent at high speed while suppressing the shrinkage of. BadThe woven fabric roll exhibits a uniform and effective suction function over the entire outer peripheral surface of the roll body, and has a high suction resistance, and therefore can be suitably used for suction removal of the cleaning solvent.The porosity of the nonwoven fabric is preferably 5 to 50%.By performing suction removal in a poor solvent for the cleaning solvent, the cleaning solvent is sucked together with the poor solvent, and the removal is effectively performed.It is preferable to use water as the poor solvent.At this time, by performing at a temperature equal to or higher than the boiling point of the cleaning solvent, the cleaning solvent is effectively removed by the action of vaporization.The upper limit of the temperature of the poor solvent is preferably not more than the crystal dispersion temperature of the polyolefin.
[0009]
  Thermoplastic resin microporous membraneHowever, it is preferable that the thermoplastic resin satisfies the following conditions (1) to (12).
(1) At least one selected from the group consisting of polyolefin, polyester, polyamide, polyarylene ether, and polyarylene sulfide.
(2) The polyolefin described in (1) above is polyethylene or a polyethylene composition.
(3) The polyethylene according to (2) above has a weight average molecular weight of 1 × 10^Four~ 5 × 10⁶It is.
(4) The polyethylene according to (2) above has a weight average molecular weight of 1 × 10^Five~ 4 × 10⁶It is.
(5) The polyethylene according to any one of the above (2) to (4) is at least one selected from the group consisting of ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene.
(6) The polyethylene according to any one of (2) to (5) above has a weight average molecular weight of 5 × 10.^FiveThe above ultra high molecular weight polyethylene.
(7) The weight average molecular weight / number average molecular weight (hereinafter referred to as “Mw / Mn”) of the polyethylene according to any one of (2) to (6) is 5 to 300.
(8) The polyethylene composition as described in (2) above comprises at least two selected from the group consisting of ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene.
(9) The polyethylene composition according to (2) or (8) above has a weight average molecular weight of 5 × 10^FiveUltra high molecular weight polyethylene and weight average molecular weight 1 × 10^Four5 × 10 or more^FiveLess than high density polyethylene.
(10) Mw / Mn of the polyethylene composition according to the above (2), (8), (9) is 5 to 300.
(11) The polyolefin described in (1) above has a shutdown function (inside of the battery) in the polyethylene described in (3) to (7) or the polyethylene composition described in any of (8) to (10). In order to prevent accidents such as ignition when the temperature rises, branched low-density polyethylene and linear low-density polyethylene as polyolefins that give the function of blocking the current by melting the microporous membrane and clogging the microporous Polyethylene, ethylene-α-olefin copolymer produced using a single site catalyst, and molecular weight 1 × 10^Three~ 4 × 10^ThreeA polyolefin composition to which at least one selected from the group consisting of low molecular weight polyethylenes is added.
(12) The polyolefin is added to the polyethylene described in (3) to (7) above or the polyethylene composition described in any of (8) to (11) above with a meltdown temperature (breakdown of a thermoplastic microporous membrane). It is a polyolefin composition to which polypropylene for improving the film temperature is added.
[0010]
A cleaning solvent is used to remove the solvent used in preparing the melt-kneaded product. At this time, it is preferable to use a cleaning solvent (A) having a surface tension at 25 ° C. of 24 mN / m or less, preferably 20 mN / m or less. This improves the porosity, permeability and dimensional stability, particularly when producing a thermoplastic microporous membrane. This is presumed to be because the use of the cleaning solvent (A) can suppress the shrinkage and densification of the network structure due to the surface tension of the cleaning solvent in the cleaning step and / or the cleaning solvent removal step.
Washing is preferably performed by two or more steps, and at this time, it is preferable to use the washing solvent (A) in at least the final step. This improves the cleaning effect. The washing solvent (A) is preferably used within a temperature range in which the surface tension is 24 mN / m or less.
[0011]
In order for the thermoplastic resin microporous membrane to obtain more excellent characteristics, the cleaning solvent (A) preferably satisfies the following conditions (13) to (19).
(13) The surface tension becomes 20 mN / m or less at 25 ° C.
(14) Hydrofluorocarbon, hydrofluoroether, cyclic hydrofluorocarbon, perfluorocarbon, perfluoroether, normal paraffin having 5 to 10 carbon atoms, isoparaffin having 6 to 10 carbon atoms, aliphatic ether having 6 or less carbon atoms, cyclopentane, etc. Cycloparaffin, 2-pentanone, methanol, ethanol, 1-propanol, 2-propanol, tertiary butanol, isobutanol, 2-pentanol, propyl acetate, tertiary butyl acetate, secondary butyl acetate, ethyl acetate, isopropyl acetate, It is at least one selected from the group consisting of isobutyl acetate, methyl formate, ethyl formate, isopropyl formate, isobutyl formate and ethyl propionate.
(15) C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula: C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula: C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by the composition formula: C₆F₁₄And C₇F₁₆Perfluorocarbon represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveAt least one fluorine-based compound selected from the group consisting of perfluoroethers represented by the composition formula:
(16) At least one normal paraffin selected from the group consisting of normal pentane, normal hexane, normal heptane, normal octane, normal nonane and normal decane.
(17) 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- At least one isoparaffin selected from the group consisting of trimethylpentane, 2-methyloctane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2-methylnonane and 2,3,5-trimethylheptane is there.
(18) At least one ether selected from the group consisting of diethyl ether, butyl ethyl ether, dipropyl ether and diisopropyl ether.
(19) At least one selected from the group consisting of a mixture of an aliphatic alcohol having 3 or less carbon atoms and water mixed at 25 ° C. so that the surface tension is 24 mN / m or less.
[0012]
Washing is preferably performed by two or more steps. In that 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 step. As the cleaning 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.
[0013]
In order for the thermoplastic resin microporous membrane to obtain more excellent characteristics, it is preferable that the cleaning solvent (B) satisfies the following conditions (20) to (32).
(20) 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.
(21) Normal paraffins having 8 or more carbon atoms, normal paraffins having 5 or more carbon atoms in which at least some of the hydrogen atoms are substituted with halogen atoms, isoparaffins having 8 or more carbon atoms, cycloparaffins having 7 or more carbon atoms, hydrogen atoms A cycloparaffin having 5 or more carbon atoms, at least a part of which is substituted with a halogen atom, an aromatic hydrocarbon having a carbon number of 7 or more, an aromatic hydrocarbon having 6 or more carbon atoms in which at least a part of the hydrogen atoms are substituted with a halogen atom An alcohol having 5 to 10 carbon atoms in which a part of hydrogen atoms may be substituted with a halogen atom, an ester and an ether having 7 to 14 carbon atoms in which a part of hydrogen atoms may be substituted with a halogen atom, and It is at least one selected from the group consisting of ketones having 5 to 10 carbon atoms.
(22) The normal paraffin having 8 or more carbon atoms has 8 to 12 carbon atoms, more preferably at least one selected from the group consisting of normal octane, normal nonane, normal decane, normal undecane and normal dodecane. is there.
(23) Normal paraffins having 5 or more carbon atoms in which at least some 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 and 1,7-dichloroheptane.
(24) The above-mentioned isoparaffin having 8 or more carbon atoms includes 2,3,4-trimethylpentane, 2,2,3-trimethylpentane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2, It is at least one selected from the group consisting of 3,5-trimethylheptane and 2,5,6-trimethyloctane.
(25) The cycloparaffin having 7 or more carbon atoms includes cycloheptane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,3-dimethylcyclohexane, and cis-and At least one selected from the group consisting of trans-1,4-dimethylcyclohexane.
(26) The cycloparaffin having 5 or more carbon atoms in which part of the hydrogen atoms is substituted with a halogen atom is at least one selected from the group consisting of chlorocyclopentane and chlorocyclohexane.
(27) The aromatic hydrocarbon having 7 or more carbon atoms is at least one selected from the group consisting of toluene, orthoxylene, metaxylene and paraxylene.
(28) The aromatic hydrocarbon having 6 or more carbon atoms in which a part of the hydrogen atoms is substituted with a halogen atom is chlorobenzene, 2-chlorotoluene, 3-chlorotoluene, 4-chlorotoluene, 3-chloroorthoxylene, It is at least one selected from the group consisting of 4-chloroorthoxylene, 2-chlorometaxylene, 4-chlorometaxylene, 5-chlorometaxylene and 2-chloroparaxylene.
(29) Alcohols having 5 to 10 carbon atoms in which part of the hydrogen atoms may be substituted with halogen atoms are isopentyl alcohol, tertiary pentyl alcohol, cyclopentanol, cyclohexanol, 3-methoxy-1- It is at least one selected from the group consisting of butanol, 3-methoxy-3-methyl-1-butanol, propylene glycol normal butyl ether and 5-chloro-1-pentanol.
(30) Esters having 7 to 14 carbon atoms in which part of the hydrogen atoms may be substituted with halogen atoms are diethyl carbonate, diethyl maleate, normal propyl acetate, normal butyl acetate, isopentyl acetate, 3-methoxy acetate It is at least one selected from the group consisting of butyl, 3-methoxy-3-methylbutyl acetate, ethyl normal butyrate, ethyl normal valerate, and 2-chloroethyl acetate.
(31) The ether having 7 to 14 carbon atoms in which a part of the hydrogen atoms may be substituted with a halogen atom is at least one selected from the group consisting of normal butyl ether, diisobutyl ether and bischloroethyl ether.
(32) The ketone having 5 to 10 carbon atoms is at least one selected from the group consisting of 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclopentanone and cyclohexanone.
[0014]
In washing, the washing solvent (A) alone or the washing solvent (A) and the washing solvent (B) may be used to carry out a multistage treatment of three or more stages, and in this case, it is preferably carried out in a three-stage to five-stage process. .
[0015]
As an optional component (C) in the washing solvent (B), for example, C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula of, for example, C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula of, for example, C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by a composition formula of, for example, C₆F₁₄And C₇F₁₆Perfluorocarbons represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveA mixture of at least one solvent selected from the group consisting of perfluoroethers represented by the composition formula:
[0016]
  Obtained by the production method of the present inventionPolyolefinThe physical properties of the microporous membrane are a porosity of 25 to 80% and an air permeability of 10 to 2000 seconds / 100 cc (converted to a film thickness of 30 μm).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
[1] thermoplastic resin
  Thermoplastic resinExamples thereof include polyolefins, polyesters, polyamides, polyarylene ethers and polyarylene sulfides. Of these, polyolefins are preferred. The polyolefin may be either a single polyolefin (not a mixture) or a polyolefin composition comprising two or more polyolefins.
[0018]
In the case of a single polyolefin, polyethylene is preferred. The weight average molecular weight of polyethylene is not particularly limited, but is usually 1 × 10^Four~ 1 × 10⁷Preferably 1 × 10^Four~ 5 × 10⁶And more preferably 1 × 10^Five~ 4 × 10⁶It is.
[0019]
Examples of polyethylene include ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene. Of these, ultra high molecular weight polyethylene is preferred. Ultra high molecular weight polyethylene has a weight average molecular weight of 5 x 10^FiveOr more, preferably 1 × 10⁶~ 15 × 10⁶Is more preferable, 1 × 10⁶~ 5 × 10⁶Is particularly preferred. Weight average molecular weight 15 × 10⁶By making it below, melt extrusion can be facilitated. The polyethylene may be not only a homopolymer of ethylene but also a copolymer containing a small amount of other α-olefin. Suitable α-olefins other than ethylene include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene, and the like.
[0020]
The molecular weight distribution Mw / Mn of polyethylene is not limited, but is preferably 5 to 300, more preferably 10 to 100. When Mw / Mn is less than 5, the high molecular weight component is excessively increased, making melt extrusion difficult, and when Mw / Mn exceeds 300, the low molecular weight component is excessively increased, leading to a decrease in strength. Mw / Mn is used as a measure of molecular weight distribution, and the larger the value, the wider the molecular weight distribution. That is, in the case of a single polyolefin, Mw / Mn shows the spread of its molecular weight distribution, and the larger the value, the wider the molecular weight distribution. Mw / Mn can be appropriately adjusted by preparing polyethylene by multistage polymerization. The multistage polymerization method is preferably a two-stage polymerization in which a high molecular weight component is polymerized in the first stage and then a low molecular weight component is polymerized in the second stage.
[0021]
As the polyolefin, a polyethylene composition in which two or more kinds of polyethylene are mixed may be used. That is, two or more kinds of ultrahigh molecular weight polyethylenes having different weight average molecular weights, two or more kinds of high density polyethylenes having different weight average molecular weights, two or more kinds of medium density polyethylenes having different weight average molecular weights, and two or more kinds of weights Low density polyethylenes with different average molecular weights may be used, or two or more types of polyethylene selected from the group consisting of ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene may be mixed. . Above all, weight average molecular weight 5 × 10^FiveUltra high molecular weight polyethylene above and weight average molecular weight 1 × 10^Four5 × 10 or more^FiveA polyethylene composition comprising less than polyethylene is preferred. Weight average molecular weight 1 × 10^Four5 × 10 or more^FiveAs the lower polyethylene, any of high-density polyethylene, medium-density polyethylene and low-density polyethylene can be used, but it is particularly preferable to use high-density polyethylene. Weight average molecular weight 1 × 10^Four5 × 10 or more^FiveTwo or more types of polyethylenes having different molecular weights may be used, or two or more types having different types (density) may be used. The upper limit of the weight average molecular weight of the polyolefin composition is 15 × 10⁶The melt extrusion can be facilitated by the following. Weight average molecular weight in polyolefin composition 5 × 10^FiveThe polyethylene content is preferably 21% by weight or more, more preferably 21 to 50% by weight, based on 100% by weight of the entire polyolefin composition.
[0022]
The Mw / Mn of the polyolefin composition is preferably 5 to 300, more preferably 10 to 100. When Mw / Mn is less than 5, the high molecular weight component is excessively increased and melt extrusion becomes difficult, and when Mw / Mn exceeds 300, the low molecular weight component is excessively increased and the strength is lowered. In the case of a polyolefin composition, the larger the Mw / Mn, the larger the difference in the weight average molecular weight of each polyolefin to be blended, and the smaller the Mw / Mn, the smaller the difference in the weight average molecular weight. Mw / Mn can be appropriately adjusted by adjusting the molecular weight and mixing ratio of each component in the polyolefin composition.
[0023]
When used for a battery separator, the polyolefin composition preferably contains polypropylene in order to improve the meltdown temperature (the membrane breaking temperature of the thermoplastic microporous membrane). The weight average molecular weight of polypropylene is 1 × 10^Four~ 4 × 10⁶Is preferred. 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 can contain a copolymer component with other α-olefin other than propylene, and ethylene is preferable as the other α-olefin. The amount of polypropylene added is preferably 80 parts by weight or less based on 100 parts by weight of the entire polyolefin composition.
[0024]
In order to improve the properties as a battery separator, the polyolefin composition preferably contains a polyolefin imparting a shutdown function. The aforementioned low-density polyethylene can be used as the polyolefin imparting the shutdown function. The low density polyethylene is preferably at least one selected from the group consisting of branched low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and an ethylene / α-olefin copolymer produced by a single site catalyst. . As a polyolefin that provides a shutdown function, the weight average molecular weight is 1 × 10^Three~ 4 × 10^ThreeThe low molecular weight polyethylene may be added. However, if the amount added is large, breakage is likely to occur when stretching, and therefore the amount added is preferably 20 parts by weight or less based on 100 parts by weight of the entire thermoplastic resin.
[0025]
As the polyolefin composition containing ultra high molecular weight polyethylene, the above weight average molecular weight 1 × 10^Four5 × 10 or more^FiveIn addition to less than polyethylene, the above-mentioned polypropylene for improving the meltdown temperature, and the above-mentioned polyolefin imparting a shutdown function, a weight average molecular weight of 1 × 10^Four~ 4 × 10⁶Polybutene-1, weight average molecular weight 1 × 10^Three~ 1 × 10^FourPolyethylene wax and weight average molecular weight 1 × 10^Four~ 4 × 10⁶A polyolefin composition to which at least one polyolefin selected from the group consisting of ethylene / α-olefin copolymers is added can also be used. Thus, when it is set as the polyolefin composition which added other polyolefin to ultra high molecular weight polyethylene, it is preferable that the addition amount of other polyolefin shall be 80 weight part or less by making the whole polyolefin composition into 100 weight part.
[0026]
[2] Process for producing thermoplastic resin microporous membrane
The method for producing a thermoplastic resin microporous membrane includes the steps of: (a) adding a solvent to the thermoplastic resin and melt-kneading to prepare a thermoplastic resin solution; (b) extruding the thermoplastic resin solution from a die lip and cooling. Forming a gel-like molded product, (c) removing the solvent from the gel-like molded product, and (d) removing the washing solvent from the obtained film. Furthermore, after the steps (a) to (d), (e) a crosslinking treatment by ionizing radiation, (f) a heat treatment, and (g) a hydrophilization treatment may be performed as necessary. Moreover, you may put the process extended | stretched before and after the (d) process as needed.
[0027]
(a) Preparation process of thermoplastic resin solution
First, an appropriate solvent is added to the thermoplastic resin and melt-kneaded to prepare a thermoplastic resin solution. Various additives such as an antioxidant, an ultraviolet absorber, an anti-blocking agent, a pigment, a dye, and an inorganic filler can be added to the thermoplastic resin solution as necessary 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.
[0028]
Either a liquid solvent or a solid solvent can be used as the solvent. Examples of the liquid solvent include nonane, decane, decalin, paraxylene, undecane, dodecane, aliphatic hydrocarbons such as liquid paraffin, and mineral oil fractions having boiling points corresponding to these. In order to obtain a gel-like molded product having a stable solvent content, it is preferable to use a non-volatile liquid solvent such as liquid paraffin. The solid solvent preferably has a melting point of 80 ° C. or lower. Examples of such a solid solvent include paraffin wax, ceryl alcohol, stearyl alcohol, dicyclohexyl phthalate, and the like. You may mix and use a liquid solvent and a solid solvent suitably.
[0029]
The viscosity of the liquid solvent is preferably 30 to 500 cSt at 25 ° C., and more preferably 50 to 200 cSt. If the viscosity at 25 ° C. is less than 30 cSt, non-uniform discharge from the die lip occurs, and kneading is difficult, and if it exceeds 500 cSt, solvent removal becomes difficult.
[0030]
The method of melt kneading is not particularly limited, but it is usually carried out by uniformly kneading in an extruder. This method is suitable for preparing a high concentration solution of a thermoplastic resin. Since the melting temperature is preferably the melting point of the thermoplastic resin + 10 ° C. to + 100 ° C., it is preferably 140 to 230 ° C., more preferably 170 to 200 ° C. 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 kneading, or may be added from the middle of the extruder during the kneading, but it is preferable to add the solvent before starting the kneading to make a solution in advance. In melt kneading, it is preferable to add an antioxidant in order to prevent oxidation of the thermoplastic resin.
[0031]
In the thermoplastic resin solution, the blending ratio of the thermoplastic resin and the solvent is 1 to 50% by weight, preferably 20 to 40% by weight with respect to 100% by weight of the total of both. When the thermoplastic resin is less than 1% by weight, swell and neck-in increase at the die outlet when forming a gel-like molded product, and the moldability and self-supporting property of the gel-like molded product are lowered. On the other hand, if it exceeds 50% by weight, the moldability of the gel-like molded product is lowered.
[0032]
(b) Formation process of gel-like molding
The melt-kneaded thermoplastic resin solution is directly or through another extruder, or once cooled and pelletized, and then extruded from the die lip through the extruder again. As the die lip, a sheet die lip having a rectangular base shape is usually used, but a double cylindrical hollow die lip, an inflation die lip, or the like can also be used. In the case of a sheet die lip, the gap of the die lip is usually 0.1 to 5 mm, and it is heated to 140 to 250 ° C. during extrusion. The extrusion rate of the heated solution is preferably 0.2 to 15 m / min.
[0033]
A gel-like molded product is formed by cooling the solution extruded from the die lip in this manner. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less, and is preferably cooled to 25 ° C. or less. In this way, the phase separation structure can be fixed. In general, when the cooling rate is low, the higher order structure of the gel-like molded product becomes coarse, and the pseudo cell unit forming it becomes large, but when the cooling rate is high, it becomes a dense cell unit. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases and it is difficult to obtain a gel-like product suitable for stretching. As a cooling method, a method of directly contacting cold air, cooling water, or other cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used.
[0034]
(c) Gel-formed product stretching and solvent removal process
Depending on the purpose for which the thermoplastic resin microporous membrane is used, the gel-like molded product is stretched as necessary. In the case of stretching, after heating the gel-like molded product, it is performed at a predetermined magnification 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 or lateral simultaneous stretching or sequential stretching may be used, but simultaneous biaxial stretching is particularly preferable. The mechanical strength is improved by stretching.
[0035]
Although the draw ratio varies depending on the thickness of the gel-like molded product, it is preferably 2 times or more and more preferably 3 to 30 times in uniaxial stretching. In biaxial stretching, it is preferable to set at least 3 times or more in any direction and 9 times or more in terms of surface magnification because the puncture strength can be improved. If the surface magnification is less than 9, the stretching is insufficient and a highly elastic and high strength thermoplastic resin microporous film cannot be obtained. On the other hand, when the surface magnification exceeds 400 times, there are restrictions in terms of stretching apparatus, stretching operation, and the like.
[0036]
The stretching temperature is preferably the melting point of the thermoplastic resin + 10 ° C. or less, and more preferably in the range from the crystal dispersion temperature to less than the crystal melting point. When the stretching temperature exceeds the melting point + 10 ° C., the resin melts and the molecular chain cannot be oriented by stretching. Further, if the stretching temperature is lower than the crystal dispersion temperature, the resin is not sufficiently softened, the film is easily broken during stretching, and 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 refers to a value obtained by measuring temperature characteristics of dynamic viscoelasticity based on ASTM D 4065. When stretching is performed, the solvent can be removed before stretching and / or after stretching, but is preferably performed after stretching.
[0037]
A cleaning solvent is used to remove (wash) the solvent. At this time, it is preferable to use a cleaning solvent (A) having a surface tension at 25 ° C. of 24 mN / m or less, preferably 20 mN / m or less. The washing solvent (A) is preferably one that is not compatible with the thermoplastic resin. By using such a washing solvent (A), it is possible to suppress the densification and densification of the network structure caused by the surface tension of the gas-liquid interface that occurs 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 cleaning solvent can be lowered as the use temperature is raised, but the usable temperature range is limited to the boiling point or less. In the present specification, “surface tension” means the tension generated at the interface between gas and liquid, and is measured based on JIS K 3362.
[0038]
As the cleaning solvent (A), fluorine compounds such as hydrofluorocarbon, hydrofluoroether, cyclic hydrofluorocarbon, perfluorocarbon, perfluoroether, normal paraffin having 5 to 10 carbon atoms, isoparaffin having 6 to 10 carbon atoms, carbon number 6 The following aliphatic ethers, cycloparaffins such as cyclopentane, aliphatic ketones such as 2-pentanone, aliphatic alcohols such as methanol, ethanol, 1-propanol, 2-propanol, tertiary butanol, isobutanol and 2-pentanol Propyl acetate, tertiary butyl acetate, secondary butyl acetate, ethyl acetate, isopropyl acetate, isobutyl acetate, methyl formate, ethyl formate, isopropyl formate, isobutyl formate, aliphatic propionate, etc. Kill.
[0039]
Examples of fluorine compounds include C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula of, for example, C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula of, for example, C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by a composition formula of, for example, C₆F₁₄And C₇F₁₆Perfluorocarbons represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveAt least one selected from the group consisting of perfluoroethers represented by the composition formula: Since these fluorine compounds have a surface tension of 24 mN / m or less at 20 ° C., the effect of suppressing the shrinkage and densification of the network structure due to the surface tension is high. Further, since the boiling point is 100 ° C. or less, it is easy to remove the cleaning solvent. Furthermore, since there is no ozone destructive effect, the load on the environment can be reduced, and the 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.
[0040]
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 / m or less at 20 ° C. Of these, normal pentane, normal hexane and normal heptane, which have a boiling point of 100 ° C. or less and are easily dried, are more preferable.
[0041]
The isoparaffin having 6 to 10 carbon atoms is 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-dimethyl Hexane, 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 these, 2-methylpentane, 3-methylpentane, 2,2-dibutylbutane, 2,3-dibutylbutane, 2-methylpentane, which has a surface tension of 24 mN / m or less at 20 ° C. and a boiling point of 100 ° C. or less, More preferred are methylhexane, 3-methylhexane, 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane and 3,3-dimethylpentane.
[0042]
Preferred ethers having 6 or less carbon atoms are diethyl ether, butyl ethyl ether, dipropyl ether and diisopropyl ether. These have a surface tension of 24 mN / m or less at 20 ° C. and a boiling point of 100 ° C. or less.
[0043]
Cyclopentane, methanol, ethanol, 1-propanol and 2-propanol are preferred because their surface tension is 24 mN / m or less at 20 ° C. and boiling point is 100 ° C. or less.
[0044]
Among the aliphatic esters, tertiary butyl acetate, secondary butyl acetate, isopropyl acetate, isobutyl acetate, ethyl formate, isopropyl formate, and isobutyl formate having a surface tension of 24 mN / m or less at 20 ° C. are preferable. Furthermore, although boiling point is 100 degrees C or less, tertiary butyl acetate, ethyl formate, and isopropyl formate are more preferable.
[0045]
As the cleaning solvent (A), a mixture of an aliphatic alcohol having 3 or less carbon atoms and water blended so that the surface tension at 25 ° C. is 24 mN / m or less can also be used.
[0046]
The above-mentioned washing solvent (A) can be used as a mixture with other solvents. In this case, the mixing ratio is set so that the surface tension is 24 mN / m or less at 25 ° C. For example C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula of, for example, C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula of, for example, C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by a composition formula of, for example, C₆F₁₄And C₇F₁₆Perfluorocarbons represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveIt is possible to use a mixture of at least one solvent selected from the group consisting of perfluoroethers represented by the composition formula: and a hydrocarbon-based solvent such as paraffin.
[0047]
The washing is preferably performed in two or more 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 stage. The washing solvent (B) is preferably one that is not compatible with the thermoplastic resin, for example, known washing solvents such as pentane, hexane, heptane, etc., chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride, etc. Fluorocarbons such as ethane trifluoride, ethers such as diethyl ether and dioxane, and easily volatile solvents such as methyl ethyl ketone can be used. A non-aqueous solvent having a boiling point of 100 ° C. or higher and a flash point of 0 ° C. or higher can also be used. The washing solvent (B) as described above is appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or in combination.
[0048]
By such two or more cleaning steps, sufficient cleaning can be performed while suppressing the shrinkage and densification of the network caused by the surface tension of the cleaning solvent. Preferably, the washing solvent (A) is treated at least in the final stage. As a result, when the washing solvent (B) is used, the washing solvent (B) can be removed (hereinafter referred to as “rinsing treatment”), and the shrinkage and densification of the network that occurs when the washing solvent is removed after washing can be prevented. . As a result, it is effective in improving the porosity / permeability of the thermoplastic microporous membrane.
[0049]
When treating with the cleaning solvent (A) in the final step, the efficiency of the cleaning solvent removal step is improved by treating with the cleaning solvent (A) having a boiling point of 100 ° C. or lower. Furthermore, for example, C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula of, for example, C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula of, for example, C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by a composition formula of, for example, C₆F₁₄And C₇F₁₆Perfluorocarbons represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveWhen a fluorine-based compound such as perfluoroether represented by the composition formula is used, there is also an effect that the environmental load in the production process can be further reduced as described above. In particular, when a solvent having a boiling point of 150 ° C. or higher is used as the cleaning solvent (B), the removal takes time, and the porosity / air permeability may be lowered due to the influence. However, a cleaning solvent having a boiling point of 100 ° C. or lower (A ) Can be used to solve the problem.
[0050]
Non-aqueous solvents that have a boiling point of 100 ° C or higher and a flash point of 0 ° C or higher that can be used as the cleaning solvent (B) are less volatile, have a low environmental impact, and have a low risk of flammable explosion in the cleaning solvent removal process. Therefore, it is safe to use. Moreover, since it has a high boiling point, it is easy to condense, recover easily, and is easy to recycle. In the present specification, “boiling point” means 1.01 × 10^FiveIt refers to the boiling point at Pa, and “flash point” refers to the value measured based on JIS K 2265.
[0051]
Examples of the non-aqueous solvent include paraffinic compounds having a boiling point of 100 ° C. or higher and a flash point of 0 ° C. or higher, aromatics, alcohols, esters, ethers, ketones, and the like. The flash point is preferably 5 ° C. or higher, more preferably 40 ° C. or higher. However, making the non-aqueous solvent into an aqueous solution is not preferable because the solvent cannot be removed sufficiently.
[0052]
Examples of the non-aqueous solvent include 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 some of the hydrogen atoms are substituted with halogen atoms, aromatic hydrocarbons having 7 or more carbon atoms, and aromatics having 6 or more carbon atoms in which at least some of the hydrogen atoms are substituted with halogen atoms Group hydrocarbons, alcohols having 5 to 1 carbon atoms in which some hydrogen atoms may be substituted with halogen atoms, esters having 7 to 14 carbon atoms in which some hydrogen atoms may be substituted with halogen atoms, and At least one selected from the group consisting of ethers and ketones having 5 to 10 carbon atoms is preferred.
[0053]
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.
[0054]
Examples of normal paraffins having 5 or more carbon atoms in which at least some of the hydrogen atoms are substituted with halogen atoms include 1-chloropentane, 1-chlorohexane, 1-chloroheptane, 1-chlorooctane, 1-bromopentane, 1-bromopentane, Bromohexane, 1-bromoheptane, 1-bromooctane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane are preferred, 1-chloropentane, 1-chlorohexane, 1-bromopentane And 1-bromohexane is more preferred.
[0055]
Isoparaffins having 8 or more carbon atoms include 2,3,4-trimethylpentane, 2,2,3-trimethylpentane, 2,2,5-trimethylhexane, 2,3,5-trimethylhexane, 2,3,5- Trimethylheptane and 2,5,6-trimethyloctane are preferred, and 2,3,4-trimethylpentane, 2,2,3-trimethylpentane, 2,2,5-trimethylhexane and 2,3,5-trimethylhexane are preferred. More preferred.
[0056]
Cycloparaffins having 7 or more carbon atoms include cycloheptane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,3-dimethylcyclohexane, and cis- and trans-1 1,4-dimethylcyclohexane is preferred, and cyclohexane is more preferred.
[0057]
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.
[0058]
As the aromatic hydrocarbon having 7 or more carbon atoms, toluene, orthoxylene, metaxylene and paraxylene are preferable, and toluene is more preferable.
[0059]
Aromatic hydrocarbons having 6 or more carbon atoms in which at least a part of hydrogen atoms are substituted with halogen atoms include chlorobenzene, 2-chlorotoluene, 3-chlorotoluene, 4-chlorotoluene, 3-chloroorthoxylene, 4-chloro Ortho-xylene, 2-chlorometaxylene, 4-chlorometaxylene, 5-chlorometaxylene and 2-chloroparaxylene are preferred, and chlorobenzene, 2-chlorotoluene, 3-chlorotoluene and 4-chlorotoluene are more preferred.
[0060]
Examples of the alcohol having 5 to 10 carbon atoms in which a part of hydrogen atoms may be substituted with a halogen atom include isopentyl alcohol, tertiary pentyl alcohol, cyclopentanol, cyclohexanol, 3-methoxy-1-butanol, 3 -Methoxy-3-methyl-1-butanol, propylene glycol normal butyl ether and 5-chloro-1-pentanol are preferred, 3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butanol, propylene glycol normal Butyl ether and 5-chloro-1-pentanol are more preferred.
[0061]
Examples of the ester having 7 to 14 carbon atoms in which a part of hydrogen atoms may be substituted with a halogen atom include diethyl carbonate, diethyl maleate, normal propyl acetate, normal butyl acetate, isopentyl acetate, 3-methoxybutyl acetate, acetic acid 3 -Methoxy-3-methylbutyl, ethyl normal butyrate, ethyl normal valerate, 2-chloroethyl acetate are preferred, and isopentyl acetate, 3-methoxybutyl acetate, 3-methoxy-3-methylbutyl acetate, ethyl normal butyrate and 2-chloroethyl acetate are preferred. More preferred.
[0062]
As the C7-14 ether in which a part of hydrogen atoms may be substituted with a halogen atom, dipropylene glycol dimethyl ether, normal butyl ether, diisobutyl ether, and bischloroethyl ether are preferable, and dipropylene glycol dimethyl ether and bischloroethyl are preferred. Ether is more preferred.
[0063]
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.
[0064]
The washing solvent (B) as described above may be used as a mixture, but as the washing solvent (B), the optional component (C), for example, the washing solvent (A) mentioned as C_FiveH₂F_TenA chain hydrofluorocarbon represented by the composition formula of, for example, C_FourF₉OCH_ThreeAnd C_FourF₉OC₂H_FiveHydrofluoroether represented by the composition formula of, for example, C_FiveH_ThreeF₇A cyclic hydrofluorocarbon represented by a composition formula of, for example, C₆F₁₄Or C₇F₁₆Perfluorocarbons represented by the composition formula of_FourF₉OCF_ThreeAnd C_FourF₉OC₂F_FiveA mixture of at least one solvent selected from the group consisting of perfluoroethers represented by the composition formula (1) may be used. In this case, the cleaning solvent (B) and the optional component (C) are preferably mixed at a ratio of the surface tension of 24 mN / m or less at any temperature of 20 to 80 ° C., specifically, the mixed solvent In 100 parts by weight, the optional component (C) is 2 to 98 parts by weight, preferably 5 to 50 parts by weight. By containing 2 to 98 parts by weight of the optional component (C), sufficient cleaning can be performed while suppressing shrinkage densification of the network caused by the surface tension of the cleaning solvent.
[0065]
As the cleaning solvent (B), a solvent having a surface tension of 24 mN / m or less at any temperature of 20 to 80 ° C. is preferably used. For example, normal pentane, hexane, heptane, trifluoroethane, diethyl ether, 2-methylpentane, 3-methylpentane, cyclohexane, cyclopentane, acetone, methyl ethyl ketone and the like.
[0066]
Here, preferred combinations of the washing solvent (B) used in the first stage of washing and the washing solvent (A) used in the second stage are shown. However, as will be described later, the cleaning using the cleaning solvent (A) and the cleaning solvent (B) can be performed in three or more stages. Therefore, these are not intended to be performed in two stages. For example, cleaning solvent (B) / cleaning solvent (A) = methylene chloride / C_FourF₉OCH_Three, Methylene chloride / C₆F₁₄, Methylene chloride / C₇F₁₆, Methylene chloride / normal heptane, methylene chloride / normal hexane, methylene chloride / diethyl ether, ether / hydrofluoroether, ether / cyclic hydrofluorocarbon, ether / alcohol, mixture of ether / alcohol and water, normal paraffin / hydrofluoroether Normal paraffin / cyclic hydrofluorocarbon, normal paraffin / alcohol, normal paraffin / alcohol and water mixture, isoparaffin / hydrofluoroether, isoparaffin / cyclic hydrofluorocarbon, isoparaffin / alcohol, isoparaffin / alcohol and water mixture, cycloparaffin / Hydrofluoroether, cycloparaffin / cyclic hydrofluorocarbon, cyclopara Fin / alcohol, a mixture of cycloparaffins / alcohol and water, ketone / hydrofluoroethers, ketone / cyclic hydrofluorocarbon, a mixture of a ketone / alcohol, and ketones / alcohols and water. More preferably, washing solvent (B) / washing solvent (A) = methylene chloride / C_FourF₉OCH_Three, Methylene chloride / C₆F₁₄, Methylene chloride / C₇F₁₆, Methylene chloride / normal heptane, methylene chloride / normal hexane, methylene chloride / diethyl ether, normal heptane / C_FourF₉OCF_Three, And normal heptane / C₆F₁₄It is. By using such a combination, it is possible to improve the porosity / transmittance of the microporous membrane while effectively removing the solvent.
[0067]
Washing with the washing solvent (A) alone or with the washing solvent (A) and the washing solvent (B) may be performed in three or more steps. One-step or two-step treatment is effective when the solvent cannot be sufficiently removed and the physical properties of the resulting thermoplastic resin microporous film are lowered. In this case, the cleaning solvent (A) may be used at least in the final step, and the number of times of cleaning is not particularly limited, but is usually 3 to 5 steps, preferably 3 to 4 steps. Also, even if each stage is treated with the same washing solvent, the manufacturing process is simply lengthened, so the space for the thermoplastic resin microporous membrane manufacturing facility is expanded and the efficiency of solvent removal is reduced. It is preferred to use a different cleaning solvent. However, it is not limited to using different cleaning solvents. Thus, for example, in the case of a three-stage treatment, the same washing solvent can be used in the first stage and the second stage, and a different washing solvent from the first and second stages can be used in the third stage.
[0068]
The cleaning method includes a method of immersing and extracting in the cleaning solvent (A) and / or the cleaning solvent (B), a method of showering the cleaning solvent (A) and / or the cleaning solvent (B), or a method using a combination thereof. It can be carried out. The washing solvent (A) and the washing solvent (B) are preferably used in an amount of 300 to 30000 parts by weight per 100 parts by weight of the gel-like molded product. Further, when washing is performed by two or more steps using the washing solvent (A) and the washing solvent (B), the amount of the washing solvent (A) used is 100 parts by weight of the amount of the washing solvent (B) used. The amount is preferably 50 to 200 parts by weight. Washing with the washing solvent (A) alone or with the washing solvent (A) and the washing solvent (B) is preferably carried out until the remaining solvent is less than 1% by weight based on the amount added.
[0069]
The washing temperature with the washing solvent (B) depends on the boiling point of the washing solvent (B). When the boiling point of the cleaning solvent (B) is 150 ° C. or lower, it can be cleaned at room temperature, and may be heated and cleaned as necessary, and it is generally preferable to wash at 20 to 80 ° C. When the boiling point of the cleaning solvent (B) is 150 ° C. or higher, the penetration into the membrane is poor at room temperature.
[0070]
The cleaning temperature and / or rinsing temperature with the cleaning solvent (A) depends on the surface tension of the cleaning solvent (A). Specifically, it is preferable to perform the cleaning and / or rinsing treatment at a temperature at which the surface tension of the cleaning solvent (A) is 24 mN / m or less. If the ambient air temperature is less than the temperature at which the surface tension of the cleaning solvent (A) is 24 mN / m or less, heating is performed as necessary to a temperature at which the surface tension is 24 mN / m or less. Since the surface tension of the cleaning solvent (A) is 24 mN / m 2 or less at 25 ° C. at most, heating is not necessary in most cases, and cleaning and / or rinsing treatment can be performed at normal room temperature.
[0071]
(d) Cleaning solvent removal process
By applying a suction force to the film obtained by stretching and solvent removal, the cleaning solvent is removed by suction. By removing by suction, diffusion of the cleaning solvent during removal can be prevented, and therefore, when a cleaning solvent that may cause environmental pollution such as methylene chloride is used, there is an effect of preventing environmental pollution. Examples of means for applying a suction force include a suction roll and a suction belt. Among these, it is preferable to use a suction roll. By using the suction roll, it is possible to remove the cleaning solvent while suppressing the shrinkage of the thermoplastic resin, and it is possible to perform suction removal in a poor solvent described later. The suction roll has a roll-shaped (cylindrical) outer shape, and has a hollow portion that can be subjected to vacuum loading in the longitudinal direction inside the shaft portion. A cylindrical shaft main body, a pair of side plates provided at both ends of the shaft main body and communicating with the cavity, and a pair of through holes communicating with the through holes of the side plates. A bearing portion is provided. The hollow portion is decompressed by being sucked by a vacuum pump communicating through a pipe from the through hole of the bearing portion, and the suction roll can suck liquid and gas on the outer peripheral surface of the roll while being driven and rotated by a motor. .
[0072]
Examples of the suction roll include a punching roll, a slit roll, and a wire roll, and a nonwoven fabric roll formed by superimposing a large number of nonwoven fabrics on the outer peripheral surface of these rolls is particularly preferable. A nonwoven fabric roll having a suction mechanism as described above (hereinafter simply referred to as “nonwoven fabric roll”) excites the capillary effect in the radial direction inside the nonwoven fabric portion in a liquid absorption state when the cleaning solvent is sucked, and the roll In addition to exerting a liquid-absorbing capillary effect in the direction of the outer peripheral surface, exhibiting a uniform and effective absorption function over the entire outer peripheral surface of the roll body, and having a high suction resistance, it can be suitably used for suction removal of the cleaning solvent. When there is no non-woven fabric on the outer peripheral surface of the roll, the suction resistance is low, especially the ratio of sucking air or a poor solvent to be described later from through holes (punched holes, slits, gaps between wires, etc.) not covered with a microporous film On the contrary, the suction efficiency of the cleaning solvent is lowered, which is not preferable. In addition, it is preferable that the shape, size, and arrangement of the through holes are set so that the suction force acts uniformly on the outer peripheral surface of the nonwoven fabric roll.
[0073]
As the nonwoven fabric used for the nonwoven fabric roll, not only polyolefins, polyamides, polyesters, polyacrylonitriles or copolymers thereof which are generally used, but also nonwoven fabrics such as fluorine resins and polyphenyl sulfide resins can be used. When sucking the microporous membrane, the non-woven fabric preferably has a porosity of 5 to 50%. If the porosity of the nonwoven fabric roll is less than 5%, the squeezing property of the liquid is deteriorated, and if it exceeds 50%, the nonwoven fabric becomes sponge-like and weak in strength, which is not preferable.
[0074]
When sucking the microporous membrane, the diameter of the nonwoven fabric roll is preferably 50 to 500 cm. The vacuum pump for suction is preferably one having the ability to make the pressure of the cavity inside the roll provided with the non-woven fabric layer as described above become -5 kPaG or less.
[0075]
The film obtained by stretching and solvent removal is transferred while the cleaning solvent is removed by suction on the outer peripheral surface of the suction roll. At this time, the membrane sticks to the roll by suction, and the cleaning solvent is suctioned and removed in a fixed state. Therefore, the cleaning solvent can be removed at high speed while suppressing shrinkage of the membrane. In particular, in the case of a microporous film, since it can be removed and dried while allowing air to pass through the holes by suction, there is an effect of suppressing the shrinkage of the holes. The transfer speed by the suction roll is preferably 1 to 50 m / min. At this time, the suction roll may be heated while improving the drying effect. However, the heating temperature is not higher than the crystal dispersion temperature of the thermoplastic resin, preferably 5 ° C. or more lower than the crystal dispersion temperature. In addition, since the diffusion of the cleaning solvent becomes intense due to heating, it is preferable to suck at room temperature when using a cleaning solvent that may cause environmental contamination such as methylene chloride.
[0076]
In order to further suppress the shrinkage of the pores of the microporous membrane, it is preferable to perform suction in a poor solvent with respect to the cleaning solvent. In this case, a tank for the poor solvent is installed so that the suction roll is immersed in the poor solvent. The membrane is transferred through the poor solvent tank while being sucked by a suction roll, and the cleaning solvent is sucked together with the poor solvent, so that the removal is performed effectively and the poor solvent passes through the pores. It is possible to perform cleaning while further suppressing the above. At this time, the poor solvent tank is preferably heated to a temperature of at least the boiling point of the cleaning solvent of −20 ° C. or higher, preferably the boiling point of the cleaning solvent or higher. However, it is performed at a temperature not higher than the crystal dispersion temperature of the thermoplastic resin, preferably 5 ° C. or more lower than the crystal dispersion temperature. As a result, the action of vaporization of the cleaning solvent is promoted and effectively removed. In this case, since suction is performed in a poor solvent, vaporization and diffusion of the cleaning solvent caused by heating can be suppressed. When heating, a poor solvent having a boiling point higher than that of the washing solvent is used. The poor solvent is not particularly limited as long as it is poorly compatible with the washing solvent. For example, when methylene chloride or hydrofluoroether is used as the washing solvent, water, ethylene glycol, or the like is suitable as the corresponding poor solvent. is there.
[0077]
The suction removal by the suction roll can usually remove the washing solvent sufficiently if one suction roll is used, but the two suction rolls may be made continuous so that both surfaces of the film come into contact with the suction roll. . Thereby, suction can be performed more effectively. At this time, it is preferable to immerse at least one suction roll in a poor solvent. Alternatively, the film may be sandwiched between two suction rolls so that the film passes between the two, and both surfaces of the film may be sucked simultaneously by both suction rolls.
[0078]
The film from which the washing solvent has been removed by suction can be further dried by a heat drying method or an air drying method. When the film is heated and dried, it is preferable to dry the film with hot air after fixing it to a tenter or the like because the film can be dried while suppressing shrinkage. When the poor solvent is not used at the time of suction, the cleaning solvent is sucked and removed, so that the time required for heat drying or air drying is shorter than conventional. On the other hand, when suction removal is performed using a poor solvent, heat drying or air drying may be performed continuously, but after removing the poor solvent using another suction roll, drying may be performed by heat drying or air drying. By drying with a suction roll for removing the poor solvent before heat drying or air drying, the time required for removal of the poor solvent is shortened, and pore shrinkage due to the poor solvent can be effectively suppressed. At this time, the poor solvent removing suction roll may be heated. The temperature at which the film is dried with hot air and the temperature at which the suction roll for removing the poor solvent is heated are preferably not more than the crystal dispersion temperature of the thermoplastic resin, and particularly 5 ° C. or more lower than the crystal dispersion temperature. preferable. Usually around 70 ° C.
[0079]
The content of the washing solvent remaining in the thermoplastic resin microporous membrane by suction removal is preferably 5% by weight or less (the weight of the dried film is 100% by weight), and 3% by weight or less. Is more preferable. If the suction removal is insufficient and a large amount of the cleaning solvent remains in the film, it is not preferable because the porosity decreases and the air permeability deteriorates in the subsequent heat treatment.
[0080]
(e) Film cross-linking process
It is preferable to remove the washing solvent by suction from the film obtained by stretching and solvent removal, and then perform a crosslinking treatment by ionizing radiation. As the ionizing radiation, α rays, β rays, γ rays, electron beams and the like are used, and can be performed with an electron dose of 0.1 to 100 Mrad and an acceleration voltage of 100 to 300 kV. Thereby, meltdown temperature can be improved.
[0081]
(f) Heat treatment process
Heat treatment may be performed after the cleaning solvent is removed. The crystal is stabilized by the heat treatment, and the lamellar layer is made uniform. As the heat treatment, any of a heat stretching process, a heat setting process, and a heat shrinking process can be used. These treatments are performed at a melting point of the thermoplastic resin microporous film or lower, preferably 60 ° C. or higher and melting point −10 ° C. or lower.
[0082]
The heat stretching treatment is performed by a commonly used tenter method, roll method, or rolling method, and is preferably performed at a stretching ratio of 1.01 to 2.0 times, more preferably 1.01 to 1.5 times in at least one direction.
[0083]
The heat setting treatment is performed by a tenter method, a roll method, or a rolling method. Moreover, you may perform a heat contraction process by a tenter system, a roll system, or a rolling system, or using a belt conveyor or a floating. The heat shrinkage treatment is preferably in the range of 50% or less in at least one direction, more preferably in the range of 30% or less.
[0084]
In addition, you may perform combining many above-mentioned heat | fever extending processes, heat setting processes, and heat shrink processes. In particular, it is preferable to perform a heat shrinkage treatment after the heat stretching treatment because a microporous membrane having a low shrinkage rate and a high strength can be obtained.
[0085]
(g) Hydrophilization treatment process
The microporous membrane obtained by removing the washing solvent can be used after being hydrophilized. As the hydrophilic treatment, monomer grafting, surfactant treatment, corona discharge treatment, or the like is used. The hydrophilic treatment is preferably performed after ionizing radiation.
[0086]
When using a surfactant, any of nonionic surfactants, cationic surfactants, anionic surfactants and amphoteric surfactants can be used, but nonionic surfactants are 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 or doctor blade.
[0087]
The obtained hydrophilic microporous membrane is dried. At this time, in order to improve permeability, it is preferable to perform heat treatment while preventing shrinkage or stretching at a temperature below the melting point of the thermoplastic resin microporous membrane.
[0088]
(h) Other processing steps
The microporous membrane obtained by washing solvent removal has a meltdown property by covering the surface with a porous resin porous material such as polyvinylidene fluoride and polytetrafluoroethylene, or a porous material such as polyimide and polyphenylene sulfide. Can also be improved.
[0089]
[3] Thermoplastic resin microporous membrane
The physical properties of the microporous membrane produced as described above usually have a porosity of 25 to 80% and an air permeability of 10 to 2000 seconds / 100 cc (converted to a film thickness of 30 μm). Since a film with a high porosity can be obtained, a thermoplastic resin having a porosity / air permeability equal to or higher than that of the prior art and excellent in dimensional stability even if the subsequent heat treatment is performed at a higher temperature than before. A microporous membrane is obtained. The film thickness of the thermoplastic resin microporous film can be appropriately selected depending on the application, but for example, when used as a battery separator, it is preferably 5 to 200 μm. Thus, since the thermoplastic resin microporous film obtained by the production method of the present invention exhibits excellent permeability, it can be suitably used as a battery separator, filter, or the like.
[0090]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
[0091]
Example 1
Weight average molecular weight is 2.0 × 10⁶Ultra high molecular weight polyethylene (UHMWPE) 20% by weight and weight average molecular weight 3.5 × 10^FiveA polyethylene composition (melting point: 135 ° C., crystal dispersion temperature: 90 ° C.) having an Mw / Mn of 16.8% and a tetrakis [methylene-3- (3, 5-Ditertiarybutyl-4-hydroxyphenyl) -propionate] methane was added to obtain a polyethylene composition with 0.375 parts by weight per 100 parts by weight of the polyethylene composition. 30 parts by weight of the obtained polyethylene composition was put into a twin screw extruder (inner diameter 58 mm, L / D = 42, strong kneading type), and 70 parts by weight of liquid paraffin was supplied from the side feeder of this twin screw extruder. The mixture was melt-kneaded at 200 ° C. and 200 rpm to prepare a polyethylene solution in an extruder. Subsequently, this polyethylene solution was extruded from a T-die installed at the tip of the extruder so that the biaxially stretched film was about 50 μm, and a gel-like sheet was formed while being drawn off with a cooling roll adjusted to 50 ° C. . The obtained gel-like sheet was biaxially stretched at 114 ° C. so as to be 5 × 5 times using a batch stretching machine to obtain a stretched film. The obtained film was fixed to a 20 cm x 20 cm aluminum frame and contained in a washing tank containing methylene chloride (surface tension 27.3 mN / m (25 ° C), boiling point 40.0 ° C) adjusted to 25 ° C. And washed with rocking at 100 rpm for 3 minutes. About the film after washing, methylene chloride was removed by suction in hot water at 60 ° C. using a nonwoven fabric roll (φ500 mm, porosity of nonwoven fabric 35%, cavity pressure inside the roll: −10 kPaG) (transfer speed: 20 m / min) ). Next, the membrane was dried with hot air at 70 ° C., and further heat-fixed at 124 ° C. for 10 minutes to produce a polyethylene microporous membrane.
[0092]
Example 2
After immersing in a washing tank containing methylene chloride temperature-controlled at 25 ° C. and shaking for 3 minutes at 100 rpm, methyl perfluorobutyl ether ((C_FourF₉OCH_Three), Immersed in a washing tank containing HFE-7100 manufactured by Sumitomo 3M Co., Ltd., surface tension of 13.6mN / m (25 ° C), boiling point of 61 ° C, no flash point (the same applies hereinafter)) and 100 rpm for 1 minute Rinse while oscillating, and the membrane after rinsing is treated with HFE-7100 in warm water at 85 ° C using a nonwoven fabric roll (φ500mm, porosity of nonwoven fabric 35%, cavity pressure inside the roll: -10kPaG). A polyethylene microporous membrane was prepared in the same manner as in Example 1 except that it was removed by suction.
[0093]
Comparative Example 1
A polyethylene microporous membrane was prepared in the same manner as in Example 1 except that methylene chloride was removed using a heating roll (φ100 mm, 3 stages) adjusted to 60 ° C.
[0094]
Comparative Example 2
A polyethylene microporous membrane was produced in the same manner as in Example 2 except that the removal of HFE-7100 was performed using a heated roll (φ100 mm, 3 stages) adjusted to 80 ° C.
[0095]
Comparative Example 3
To remove methylene chloride, 6m of dry air at 60 ° C on a heated roll (φ100mm, 3 steps) adjusted to 60 ° C^ThreeA polyethylene microporous membrane was prepared in the same manner as in Example 1 except that the blowing was performed with an air volume of / min.
[0096]
Comparative Example 4
Removal of HFE-7100, 6m of dry air at 80 ° C on a heated roll (φ100mm, 3 steps) adjusted to 80 ° C^ThreeA polyethylene microporous membrane was produced in the same manner as in Example 2 except that the blowing was performed with an air volume of / min.
[0097]
The physical properties of the thermoplastic resin microporous membranes obtained in Examples 1-2 and Comparative Examples 1-4 were measured by the following methods.
-Film thickness: measured with a contact thickness meter.
Air permeability: Measured according to JIS P8117 (film thickness 30 μm conversion).
-Porosity: measured by gravimetric method.
-Film width change rate: The film width before and after cleaning solvent removal was measured, and the change rate was examined.
[0098]
[Table 1]

[0099]
As shown in Table 1, the thermoplastic resin microporous membranes of Examples 1 and 2 produced by the method of the present invention are excellent in porosity and air permeability, and have little change in membrane width after drying. On the other hand, the microporous membranes of Comparative Examples 1 to 4 are inferior in physical properties as compared with Examples 1 and 2 because they are dried without using a suction roll.
[0100]
【The invention's effect】
  As detailed above, in the production of the thermoplastic resin microporous membrane by the solvent method of the present invention, in the step of removing the cleaning solvent used to remove the solvent, by suction removal using a suction roll, It can be removed at a high speed while suppressing the diffusion of the washing solvent and while suppressing the shrinkage of the thermoplastic resin. Of the present inventionDepending on the manufacturing methodA microporous membrane having excellent porosity, permeability and dimensional stability can be produced. The obtained microporous membrane is useful for battery separators, filters, etc.The

Claims (6)

A solution obtained by melt-kneading a polyolefin and a solvent extruded from a die, the said solvent remaining from the gel-like molding obtained by cooling was removed by washing the solvent from the resulting wash polyolefin microporous membrane In the manufacturing method of the polyolefin microporous film including the step of removing the cleaning solvent, the cleaning solvent is removed from the cleaning polyolefin microporous film using a suction roll having a nonwoven fabric on the outer peripheral surface of the roll in a poor solvent for the cleaning solvent. A method for producing a polyolefin microporous membrane, comprising removing by suction. 2. The method for producing a polyolefin microporous membrane according to claim 1, wherein water is used as the poor solvent. 3. The method for producing a microporous polyolefin membrane according to claim 1 or 2, wherein the nonwoven fabric has a porosity of 5 to 50%. The method for producing a polyolefin microporous membrane according to any one of claims 1 to 3, wherein (a) the polyolefin has (i) a weight average molecular weight of 5 × 10 ^Five Or (ii) the ultrahigh molecular weight polyethylene and the weight average molecular weight of 1 × 10 ^Four ~ 5 × 10 ^Five Less than high density polyethylene, and each weight average molecular weight is 1 × 10 ^Four ~ 4 × 10 ⁶ Polypropylene, polybutene-1 and ethylene / α-olefin copolymer within the range, and a weight average molecular weight of 1 × 10 ^Three ~ 1 × 10 ^Four A composition which may contain at least one selected from the group consisting of polyethylene waxes within the range of (b), wherein the temperature of the poor solvent is (boiling point-20 ° C. of the washing solvent) or more to (crystals of the polyolefin (Dispersion temperature) or lower. A method for producing a polyolefin microporous membrane. 5. The method for producing a microporous polyolefin membrane according to claim 1, wherein at least a cleaning solvent (A) having a surface tension at 25 ° C. of 24 mN / m or less is used as the cleaning solvent. A method for producing a polyolefin microporous membrane. The method for producing a microporous polyolefin membrane according to claim 5, wherein the solvent is removed by using a cleaning solvent (B) other than the cleaning solvent (A), and a final step using the cleaning solvent (A). In a combination of the washing solvent (B) and the washing solvent (A), methylene chloride / C _Four F ₉ OCH _Three , 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 _Four F ₉ OCF _Three And normal heptane / C ₆ F ₁₄ Any one of these is selected, The manufacturing method of the polyolefin microporous film characterized by the above-mentioned.