JP2007160694A - Porous body and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a porous body in a laminated state constituted so that continuity is provided in the thickness direction of the porous body by eliminating a surface skin layer being a problem when a subcritical or supercritical fluid is utilized. <P>SOLUTION: The manufacturing method of the porous body includes a process for manufacturing a laminate having at least a three-layered structure which contains at least one intermediate layer and is constituted so that both outer layers are laminated on both sides of the intermediate layer, a process for impregnating the obtained laminate with a fluid in a supercritical or subcritical state and subsequently releasing the impregnated laminate from the supercritical or subcritical state to evaporate the fluid to form micropores to the laminate and a process for forming micropores to both outer layers by removing at least one component from the thermoplastic resin composition constituting both outer layers to allow them to communicate with the micropores formed in the previous process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a porous body and a porous body obtained by the production method, and the porous body is a packaging product, sanitary product, livestock product, agricultural product, building product, medical product, separation membrane, light diffusion plate, and reflective sheet. Or it can utilize as a separator for batteries, and it is used suitably as a separator for nonaqueous electrolyte batteries, such as a lithium ion secondary battery especially utilized as power supplies, such as various electronic devices.

  A porous body made of a polymer having a large number of fine communication holes is a separation membrane used for production of ultrapure water, purification of chemicals, water treatment, etc., a waterproof and moisture-permeable film used for clothing and sanitary materials, batteries, etc. It is used in various fields such as battery separators.

Various techniques as described below have been proposed as techniques for creating a large number of fine communication holes in this type of polymer.
For example, Japanese Patent Application Laid-Open No. 5-25305 (Patent Document 1) proposes that a porous film can be obtained by kneading and sheeting ultrahigh molecular weight polyethylene and a solvent, extracting the solvent after stretching.
However, in this method, as described in paragraph 0045 and the like, the solvent contained in the entire porous membrane is removed by washing with an organic solvent for washing, so a large amount of organic solvent is required. This is not preferable from an environmental point of view.

In Japanese Patent No. 3166279 (Patent Document 2), a porous film having communication properties is obtained by inflation-molding a resin composition containing a polyolefin resin and a filler, and uniaxially stretching the obtained film or sheet in the take-off direction. It has been proposed that a sheet be obtained.
Similarly, in Japanese Patent Application Laid-Open No. 2004-95550 (Patent Document 3), a porous film used as a separator for a lithium secondary battery is stretched at least in a uniaxial direction from a sheet formed from a resin composition containing a thermoplastic resin and a filler. It is obtained by doing.
However, in the porous film or sheet obtained by these methods, since the mass (basis weight) per unit area is increased due to the presence of the filler in all layers, there is room for improvement for weight reduction. is there.

In Japanese Patent Application Laid-Open No. 10-50286 (Patent Document 4), a high melting point polyolefin film and a low melting point polyolefin film are heat-treated to adjust birefringence and elastic recovery, respectively, and then subjected to thermocompression bonding to three or more layers. It is proposed to produce a porous film to be used as a battery separator by stretching the porous film in two stages, making it porous, and then heat setting.
In this method, which is generally referred to as an open-hole stretching method using a single polymer, an organic solvent is not required in the production process, and since no filler is present, the mass per unit area (basis weight) is also Don't get big. However, this method is very difficult to control crystals, and the conditions under which a preferred porous structure can be obtained under stretching conditions such as stretching temperature, stretching ratio, and multi-stage stretching are very narrow (columns 0025 to 0028, etc.). It is not preferable when considering process control when producing on a scale.

  As described above, although the porous films described in Patent Documents 1 to 4 have their respective characteristics, there are not sufficient in terms of environmental aspects, light weight, and productivity particularly with respect to the production method.

In addition, foaming techniques using subcritical or supercritical fluids are also known. Specifically, a polymer is impregnated with a subcritical or supercritical fluid to be saturated, and then a supersaturated state is created by a rapid pressure drop or the like, and supersaturated gas is foamed.
This method has the advantage that fine and uniform foaming can be obtained, and if an inert gas subcritical or supercritical fluid such as carbon dioxide or nitrogen is used, the load on the environment is extremely small.
However, in the vicinity of the surface, when a sudden pressure drop or the like occurs, the state is not supersaturated, and gas is immediately released from the surface by diffusion / evaporation. . For this reason, it has not been possible to make a porous body having micropores having communication properties in the thickness direction.

JP-A-5-25305 Japanese Patent No. 3166279 JP 2004-95550 A Japanese Patent Laid-Open No. 10-50286

The present invention has been made in view of the above problems, and can eliminate the skin layer on the surface, which has been a problem when using a subcritical or supercritical fluid, and can be connected in the thickness direction, and By using a subcritical or supercritical fluid, it is not necessary to use a large amount of an organic solvent to reduce the burden on the environment, and a porous body made of a laminate having a wide range of manufacturing conditions and excellent productivity. It is an object to provide a manufacturing method.
Furthermore, an object of the present invention is to provide a porous body having uniform communication holes as a whole and having a small mass per unit area. In particular, when used as a battery separator, it is possible to provide a separator and a battery that can provide a non-aqueous electrolyte secondary battery that has good electrolyte retention and high safety without greatly increasing the battery weight. Is an issue.

In order to solve the above-mentioned problem, the present invention provides, as a first invention, a method for producing a porous body having a large number of micropores having communication in the thickness direction,
At least one intermediate layer composed of a hard segment and a thermoplastic resin composition having a soft segment is included, and both outer layers composed of a thermoplastic resin composition including at least a thermoplastic resin and a micropore forming material are laminated on both sides of the intermediate layer. Producing a laminated body having at least a three-layer structure,
The obtained laminate is impregnated with a fluid in a supercritical state or a subcritical state, and then released from the supercritical state or the subcritical state to vaporize the fluid. Leaving the skin layer to form micropores in the laminate;
After forming the micropores, the micropores are formed in the skin layer by removing at least the micropore forming material from the thermoplastic resin composition constituting the both-side outer layer, and communicated with the micropores formed in the step. 3 steps
The manufacturing method of the porous body characterized by providing is provided.

Before or after the step of removing the micropore forming material, it is preferable to include a stretching step of stretching the micropores formed in the step by stretching in at least a uniaxial direction.
An organic solvent extractable plasticizer is used as the micropore forming material, and both outer layers include at least a thermoplastic resin and the organic solvent extractable plasticizer, and the organic solvent extractable plasticizer is removed from the micropore forming material. In the process, it is removed by extraction with an organic solvent.

The present invention has been made on the basis of results obtained by the inventors through repeated studies and experiments.
That is, the present inventors first made various studies by conducting research and experiments for making porous using a subcritical or supercritical fluid. However, the problem that a skin layer is formed on the surface cannot be avoided. It was.
Therefore, the present inventors provide a non-porous layer (skin layer) on the outermost surface of the layer that is made porous by using a subcritical or supercritical fluid, and so-called a lid, so that the outermost surfaces of both outer layers are formed. It was found that it is possible to obtain a porous body having an intermediate layer and a micropore communicating with both outer layers while leaving the non-porous layer alone.
That is, when the laminate is impregnated with a subcritical or supercritical fluid and then a sudden pressure drop is generated, the outermost surfaces of both outer layers are covered with non-porous layers. As a result, it was possible to create a supersaturated state without vaporization of gas from the surface, and succeeded in producing micropores in the intermediate layer and both outer layers except for the outermost surface of both outer layers.
After that, when micropores are provided in the nonporous layer by removing at least one component from the resin composition constituting the nonporous layer (skin layer) on the surface serving as the lid of the outer layers on both sides, the intermediate layer and the outer layers on both sides are already provided. It was possible to obtain a laminated porous body having micropores that communicate with the formed micropores in the thickness direction.

  In the manufacturing method of the present invention, first, in the first step, at least one intermediate layer made of a thermoplastic resin having a hard segment and a soft segment is included, and at least the thermoplastic resin and the micropore forming material are included on both sides of the intermediate layer. A laminated body having at least a three-layer structure in which outer side layers made of a thermoplastic resin composition are laminated is produced.

As the thermoplastic resin constituting the intermediate layer, a known thermoplastic resin can be used as long as it has a hard segment and a soft segment.
The hard segment serves to maintain the strength of the layer, and the soft segment serves to impregnate the subcritical or supercritical fluid. In order to ensure that each segment plays the role, it is preferable that the hard segment ratio is 5 to 95 mass% and the soft segment ratio is 95 to 5 mass%. If the hard segment ratio is less than 5% by mass, the intermediate layer is too soft to maintain the strength, and the subcritical or supercritical fluid cannot remain in the intermediate layer and is degassed. There is a possibility that it cannot be made porous. On the other hand, when the soft segment ratio is less than 5% by mass, the amount of subcritical or supercritical fluid impregnated decreases, making it difficult to obtain sufficient communication.
The soft segment is preferably 90 to 10% by mass, more preferably 70 to 20% by mass.

  The thermoplastic resin constituting the intermediate layer may contain a filler, but preferably does not contain a filler. This is because the present invention aims to provide a porous body having a small mass per unit area.

  As the soft segment of the thermoplastic resin constituting the intermediate layer, for example, polyisoprene, polybutadiene, hydrogenated polybutadiene, hydrogenated polyisoprene, amorphous polyethylene, polyvinyl chloride, polyether, ethylene-propylene rubber, isobutene-isoprene rubber , Fluorine rubber or silicone rubber. Examples of the hard segment include polystyrene, polyethylene, polypropylene, polyurethane, polyester, polyamide, polybutylene terephthalate, or a fluororesin.

More specifically, examples of the thermoplastic resin constituting the intermediate layer include a styrene-based thermoplastic resin, a polyester-based thermoplastic resin, a polyamide-based thermoplastic resin, and an olefin-based thermoplastic resin.
As the styrene-based thermoplastic resin, as a hard segment, a styrene derivative such as styrene or methylstyrene, indene or vinylnaphthalene, etc., preferably polystyrene is used, and a conjugated diene polymer such as polybutadiene or polyisoprene as a soft segment, or ethylene Styrene thermoplastic resins using polyolefin elastomers such as / butylene copolymer, ethylene / propylene copolymer or polyisobutene.

As the polyester-based thermoplastic resin, an aromatic polyester, an alicyclic polyester or a derivative thereof, or a mixture thereof is used as a hard segment, and a polytetramethylene glycol or poly (ethylene / propylene) block poly is used as a soft segment. And polyester-based thermoplastic resins using polyalkylene glycols such as glycols.
As the polyamide-based thermoplastic resin, polyamides such as polyamide 6, polyamide 66, polyamide 610, polyamide 612, polyamide 11 and polyamide 12 or copolymers thereof are used as hard segments, and polytetramethylene glycol or the like as soft segments. Examples thereof include polyamide-based thermoplastic resins using polyalkylene glycol such as poly (ethylene / propylene) block polyglycol.

As a hard segment constituting the olefin thermoplastic resin,
A homopolymer resin of ethylene, a copolymer resin having ethylene as a main component and an α-olefin having 3 or more carbon atoms as a minor component;
A homopolymer resin of propylene, a copolymer resin of propylene as a main component and ethylene or an α-olefin having 4 or more carbon atoms;
1-butene homopolymer resin, a copolymer resin of 1-butene as a main component and ethylene, propylene or an α-olefin having 5 or more carbon atoms;
· Homopolymer resin of 4-methyl-1-pentene, copolymer resin of 4-methyl-1-pentene as a main component and ethylene, propylene, 1-butene or α-olefin having 6 or more carbon atoms ;
・ Modified products of the above resins. Two or more of these may be mixed.

Examples of the soft segment constituting the olefin-based thermoplastic resin include diene rubber, hydrogenated diene rubber, olefin elastomer, and the like.
Examples of the diene rubber include isoprene rubber, butadiene rubber, butyl rubber, propylene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-isoprene rubber, and styrene-butadiene rubber.
The hydrogenated diene rubber is obtained by adding a hydrogen atom to at least a part of a double bond of a diene rubber molecule.
The olefin elastomer is an elastic copolymer obtained by adding at least one polyene copolymerizable with two or three or more olefins. As the olefin, an α-olefin such as ethylene or propylene is used. 1,4-hexadiene, cyclic diene, norbornene and the like are used. Preferred olefin elastomers include, for example, ethylene-propylene copolymer rubber, ethylene-propylene-diene rubber, ethylene-butadiene copolymer rubber and the like.
Of these, olefin-based thermoplastic resins using polyethylene or polypropylene as the hard segment and ethylene-propylene rubber or ethylene-propylene-diene rubber, hydrogenated polybutadiene or hydrogenated polyisoprene as the soft segment are preferable.

In particular, an olefin-based thermoplastic resin having a propylene-based resin as a hard segment and an ethylene-propylene rubber in a proportion of 5 to 95% by mass as a soft segment is preferable.
The propylene resin as the hard segment includes homopolymers and copolymers, and the copolymers include random copolymers and block copolymers. Homopolymers are propylene homopolymers, which are isotactic or syndiotactic and polypropylene exhibiting various degrees of stereoregularity. On the other hand, as a copolymer, propylene is a main component, and this and α such as ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene or 1-decene. -Copolymers with olefins are used. This copolymer may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer.
The propylene resin may be mixed with a resin having a lower melting point than that of the propylene homopolymer. Examples of such a resin having a low melting point include high-density or low-density polyethylene. It is preferable that the compounding quantity is 2-50 mass%.

The ethylene-propylene rubber as a soft segment includes a binary copolymer of ethylene and propylene and a terpolymer containing a small amount of a non-conjugated diene monomer as a third component. It may be used. Examples of the non-conjugated diene monomer include dicyclopentadiene, ethylidene norbornene, and hexadiene. As the ethylene-propylene rubber, an ethylene-propylene rubber having an ethylene content of 7 to 80% by mass relative to the whole rubber is preferable, and an ethylene-propylene rubber having 10 to 60% by mass is more preferable.
By adjusting the ethylene-propylene rubber content or the ethylene content in the ethylene-propylene rubber, the ethylene content relative to the entire resin composition constituting the intermediate layer is preferably 5 to 95 mass%.

As a classification by the method for producing the thermoplastic resin constituting the intermediate layer, a soft component such as ethylene-propylene rubber constituting a soft segment is mixed with a propylene-based resin constituting a hard segment into a kneader such as a twin-screw extruder. There are compound-type polymers that are blended using a polymer and polymer-type polymers that directly polymerize ethylene and propylene.
From the viewpoint of dispersibility of soft components such as ethylene-propylene rubber constituting the soft segment, it is preferable to use a polymerization type polymer.

Further, as a method for increasing the content of the soft segment, there is a method of blending a commercially available propylene copolymer with a soft component such as ethylene propylene rubber. In this case, the content of the soft segment can be easily increased by using a kneader such as a twin screw extruder.
Similarly, an olefinic thermoplastic resin having a preferable soft segment content can be obtained by blending propylene homopolymer with ethylene propylene rubber or polyethylene using a kneader such as a twin screw extruder.

  Furthermore, additives that are generally blended into the resin composition in the thermoplastic resin constituting the intermediate layer, such as antioxidants and thermal stabilizers, are within a range that does not impair the purpose of the present invention and the properties of the intermediate layer. , A light stabilizer, an ultraviolet absorber, a neutralizing agent, an antifogging agent, an antiblocking agent, an antistatic agent, a slipping agent or a coloring agent may be blended.

  Both side outer layers positioned on the outermost surfaces on both sides with the intermediate layer interposed therebetween are layers made of a non-porous resin composition having no holes. Here, “non-porous” in the present invention means that the hole is not open to the extent that it can serve as a lid so as not to cause a skin layer on the surface of the intermediate layer. That is, when a sudden pressure drop occurs after impregnation with a subcritical or supercritical fluid, the surface of the intermediate layer does not become supersaturated, and gas is immediately released from the surface of the intermediate layer by diffusion and evaporation. This means that the hole is not opened to such an extent that a region that does not foam is not formed.

The outer side layers include at least a thermoplastic resin and a micropore forming material that can be removed in order to make the non-porous skin layer formed on the outermost surfaces of the outer side layers.
The micropore forming material can be removed in a later step, and micropores can be formed by removing the micropore forming material. Further, when mixed with the thermoplastic resin constituting the outer layers on both sides, a uniform solution is formed above the melting point of the resin. Any known material can be used as long as it has a boiling point higher than the melting temperature of the thermoplastic resin constituting the outer layers on both sides so that it does not evaporate during melt kneading or molding.

The micropore forming material is appropriately selected according to the type of the thermoplastic resin constituting the outer layers on both sides, and specifically, hydrocarbons, esters, higher alcohols, ketones, nitrogen-containing organic compounds, ethers, etc. Is mentioned.
Examples of the hydrocarbons include n-decane, n-dodecane, liquid paraffin, and paraffin wax.
Examples of the esters include long-chain alkyl esters such as stearates; di-n-butyl phthalate, di (2-ethylhexyl) phthalate, diisodecyl phthalate, di-n-octyl phthalate, diheptyl phthalate, or dihexyl phthalate. Phthalates; trimellitic esters such as tri (2-ethylhexyl) trimellitate or tri-n-octyl trimellitate; pyromellitic acids such as tetra (2-ethylhexyl) pyromellitate or tetra-n-octylpyromellitate Examples include esters; sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate, or phosphoric acid esters.
Examples of the higher alcohol include oleyl alcohol and stearyl alcohol.

  One kind of the micropore forming material may be used alone, or two or more kinds may be used in combination. When two or more kinds are used in combination, it is possible to use a combination in which only a part thereof is melted by utilizing the difference in the melting points. In this way, the pore diameter of the micropores can be controlled.

As the micropore forming material, an organic solvent extractable plasticizer is preferably used.
Of these, hydrocarbons such as liquid paraffin and paraffin wax, esters such as dioctyl phthalate and dibutyl phthalate, and higher alcohols such as oleyl alcohol and stearyl alcohol are preferable. In particular, when the polyolefin resin is polyethylene, liquid paraffin is preferable because it is highly compatible with polyethylene and the resin and the plasticizer are not easily peeled during stretching, so that uniform stretching can be easily performed.

The mixing ratio of the thermoplastic resin and micropore forming material used in the outer layers on both sides is a ratio that enables uniform melt-kneading, is a ratio sufficient to form a sheet-like laminate, and is productive. As long as it does not spoil.
Specifically, the mass fraction of the thermoplastic resin in the resin composition containing the thermoplastic resin and the micropore forming material is preferably 10 to 95 mass%, and more preferably 20 to 70 mass%. preferable. When the mass fraction of the thermoplastic resin is smaller than 10% by mass, the melt tension at the time of melt molding tends to be insufficient, and the moldability tends to be lowered. Moreover, the stretching stress applied during stretching may be reduced, and uniform stretching may be insufficient. On the other hand, when the mass fraction of the thermoplastic resin exceeds 90% by mass, it is difficult to obtain a hole having communication properties.

  The method of melt kneading the thermoplastic resin and the micropore forming material in the outer layers on both sides is not particularly limited, and a kneading method generally used for resin mixing such as dry blending and melt kneading can be applied.

  For example, a thermoplastic resin is put into a resin kneading apparatus such as an extruder or kneader, a micropore forming material is introduced at an arbitrary ratio while the resin is heated and melted, and a composition comprising the resin and the micropore forming material is kneaded. Thus, a method of obtaining a uniform solution is preferable. Further, a kneaded resin and micropore forming material may be added in advance. The form of the resin to be charged may be any of powder, granule, and pellet. Further, the form and properties of the micropore forming material to be added are not particularly limited.

More preferably, the thermoplastic resin that constitutes the outer layers on both sides is compatible with the thermoplastic resin that constitutes the intermediate layer.
If the thermoplastic resin constituting the outer layer on both sides and the thermoplastic resin constituting the intermediate layer do not have compatibility, the subcritical or supercritical fluid is impregnated, and then a sudden pressure drop occurs. However, it is difficult to form a supersaturated state at the interface between the outer layers on both sides and the intermediate layer, and gas is released from the interface by diffusion / evaporation, which may make it impossible to form a hole communicating with the outer layer and the intermediate layer.

Specific examples of the thermoplastic resin constituting the both outer layers include thermoplastic resins such as polyolefin resin, fluororesin, polystyrene, ABS resin, vinyl chloride resin, vinyl acetate resin, acrylic resin, polyamide resin, acetal resin, and polycarbonate. Is mentioned.
As the thermoplastic resin, a polyolefin resin is preferably used. When used as a battery separator, it is particularly preferable to use a polyolefin resin from the viewpoint of stability with the electrolytic solution. As a polyolefin resin, you may use the well-known polyolefin resin used for normal extrusion, injection, inflation, and blow molding.

More specifically, examples of the polyolefin resin include homopolymers or copolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene or 1-decene, Or a copolymer mainly composed of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, or a copolymer of 1-decene and another monomer such as vinyl acetate. It is done.
Among them, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, polybutene, propylene ethylene block copolymer, propylene ethylene random copolymer Ethylene propylene rubber and the like are preferable.

Of the thermoplastic resins, it is more preferable to use a polyethylene resin. That is, it is preferable that at least one layer of the outer layers is made of a thermoplastic resin composition containing a polyethylene resin.
The polyethylene resin may be either a polyethylene homopolymer or a polyethylene copolymer, but is preferably a polyethylene homopolymer. The polyethylene copolymer is preferably a polyethylene copolymer having an α-olefin comonomer content of 2 mol% or less. The kind of the α-olefin comonomer is not particularly limited.

For the both outer layers, the above-described polyethylene resin is preferably used alone, but a general thermoplastic resin may be mixed with the polyethylene resin.
Specific examples of the thermoplastic resin that can be mixed with polyethylene include thermoplastic resins such as polyolefin resins other than polyethylene, fluorine resins, polystyrene, vinyl acetate resins, acrylic resins, polyamide resins, acetal resins, and polycarbonates. Preferably, polypropylene, polybutene, propylene ethylene block copolymer, propylene ethylene random copolymer and the like can be mentioned. The thermoplastic resin that can be mixed with polyethylene preferably has a melting point of 140 ° C. or higher.
Thus, when mixing other thermoplastic resin with polyethylene, the compounding quantity of the said other thermoplastic resin is 1-100 mass parts with respect to 100 mass parts of polyethylene, Preferably it is 1-50 mass parts, More Preferably it is 1-25 mass parts, More preferably, you may be 1-10 mass parts.

  Further, when it is desired to provide shutdown characteristics, it is particularly preferable to use a resin mainly composed of high-density polyethylene because the thermoplastic resin constituting the outer layers on both sides is a low melting point resin and high strength required performance. . It is also particularly preferable to use ultra high molecular weight polyethylene.

  In the present invention, the thermoplastic resin constituting the outer layers on both sides preferably has a viscosity average molecular weight of 50,000 or more and less than 12 million, more preferably 100,000 or more and less than 4 million, and most preferably 200,000 or more and less than 2 million. When the viscosity average molecular weight is less than 50,000, the melt tension at the time of melt molding becomes small and the moldability tends to be lowered, and it is difficult to impart sufficient entanglement and the strength tends to be low. When the viscosity average molecular weight exceeds 12 million, it tends to be difficult to obtain uniform melt-kneading and tends to be inferior in moldability, particularly thickness stability.

Furthermore, it is preferable that the polyethylene resin constituting the outer layers on both sides has a density of 0.92 g / cm ³ or more. The reason why the density is 0.92 g / cm ³ or more is to provide required strength and rigidity that do not easily tear even when the layer thickness is about 5 to 40 μm. The density of polyethylene is more preferably 0.93 g / cm ³ or more, and the upper limit is not particularly limited, but a density of about 0.97 g / cm ³ is suitable.

It should be noted that the resin composition constituting the outer layers on both sides includes, as necessary, an antioxidant such as phenol, phosphorus or sulfur, or a metal such as calcium stearate or zinc stearate within a range not impairing the advantages of the present invention. Known additives such as soaps, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments can be mixed and used.
It is preferable that the compounding quantity of these additives is about 1-30 mass parts with respect to 100 mass parts of thermoplastic resins which comprise a both-sides outer layer.

The thermoplastic resin composition constituting the both outer layers and the intermediate layer may contain a filler, but a porous body having a smaller mass per unit area can be provided if the intermediate layer does not contain a filler.
When using a filler, any filler of an inorganic filler and an organic filler can be used, and it can be used 1 type or in combination of 2 or more types.
Examples of inorganic fillers include carbonates such as calcium carbonate, magnesium carbonate and barium carbonate; sulfates such as calcium sulfate, magnesium sulfate and barium sulfate; chlorides such as sodium chloride, calcium chloride and magnesium chloride; calcium oxide, magnesium oxide, Examples thereof include oxides such as zinc oxide, titanium oxide and silica; silicates such as talc, clay and mica. Among these, calcium carbonate or barium sulfate is preferable.
In order to improve the dispersibility in the resin, the inorganic filler may be hydrophobized by coating the surface of the inorganic filler with a surface treatment agent. Examples of the surface treatment agent include higher fatty acids such as stearic acid or lauric acid, or metal salts thereof.

As the organic filler, resin particles having a melting point higher than the melting point of the thermoplastic resin constituting the both-side outer layers are preferable so that the filler does not melt under the temperature condition of the treatment involving heating such as stretching treatment, and the gel content is 4 to 4 More preferably, about 10% crosslinked resin particles.
Examples of the organic filler include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide. , Thermoplastic resins such as melamine and benzoguanamine, and thermosetting resins. Among these, cross-linked polystyrene and the like are particularly preferable.

  The average particle size of the filler is about 0.01 to 25 μm, preferably 0.05 to 7 μm, and more preferably 0.1 to 5 μm. When the average particle size is less than 0.01 μm, the dispersibility decreases due to the aggregation of fillers. Further, when the average particle diameter exceeds 25 μm, it is difficult to mix uniformly. When using a filler, you may add additives, such as a plasticizer, as needed.

The laminated body produced in the laminating process of the present invention has at least three layers of the above-described intermediate layer and two non-porous outer layers located on the outermost surfaces on both sides with the intermediate layer interposed therebetween. It is not limited.
For example, the intermediate layer may be composed of a plurality of layers having different compositions, and one or both of the outer side layers may be composed of a plurality of layers having different compositions. Further, a five-layer structure in which a nonporous layer having the same composition as the outer layers on both sides is sandwiched between intermediate layers may be adopted.

  Furthermore, the composition or structure of each of the two outer layers may be the same or different. For example, when each of the two outer layers is in contact with a different substance, it is necessary to select a thermoplastic resin that matches the respective characteristics. For example, when one layer is in contact with water and the other layer is in contact with an organic solvent, the thermoplastic resin constituting the outer layer in contact with water is water-resistant polystyrene, and the outer layer in contact with the organic solvent is formed. The thermoplastic resin can be polypropylene having high organic solvent resistance.

In the laminate, the ratio tr (= to / t) of the total thickness of the outer layers on both sides to the thickness t of all layers is 0.05 to 0.95, preferably 0.10 to 0.90, more preferably 0. It is adjusted to be 15 to 0.80.
If tr is smaller than 0.05, the substantial thickness of the outer layers on both sides becomes extremely thin, and as a result, the porous structure on the surface of the outer layers on both sides tends to become extremely uneven. Also, if the thickness of the outer layers on both sides is extremely thin, it does not serve as a lid. That is, when impregnated with a fluid in the supercritical state or subcritical state and then deviated from the supercritical state or subcritical state, gas is released from the surface of the intermediate layer by diffusion / evaporation through the thin outer layers on both sides. For this reason, there is a possibility that a region where foaming does not occur in the intermediate layer, that is, a so-called skin layer, is not preferable.
On the other hand, if tr is larger than 0.95, the intermediate layer becomes extremely thin, and the connectivity in the thickness direction may be deteriorated. In addition, when the outer layers on both sides include a plasticizer that can be extracted with an organic solvent as a micropore forming material, the amount of the organic solvent for extracting the plasticizer contained in the outer layers on both sides increases when the outer layers on both sides become extremely thick. The burden on the environment increases.
In the present invention, when the stretching treatment is performed in any step, the ratio tr (= to / t) of the total thickness of the outer layers on both sides to the thickness t of all layers is calculated from the measured value after the stretching treatment. Is.

A known technique may be used as a method for producing a laminate composed of at least three layers of the outer side layers and the intermediate layer. For example, it can be created by the following method.
First, the components constituting each layer may be mixed and granulated once using a powder mixer such as a Henschel mixer or a kneader such as a uniaxial or biaxial kneader or a kneader.
The said laminated body is produced using the resin composition or granulated material which comprises a both-sides outer layer, and the resin composition or granulated material which comprises an intermediate | middle layer.
Examples of the method for producing the laminate include a thermal bonding method, an extrusion lamination method, a dry lamination method, and a coextrusion method. Among these, a co-extrusion method using a T-die molding method or an inflation molding method is particularly preferably used. This is because the method in which the intermediate layer and the outer layers on both sides are separately formed and then fused with a hot roll or the like is difficult to adhere with uniform adhesive strength, and defects such as wrinkles are likely to occur. In particular, when the thickness of a film or the like is thin, since this tendency is remarkable, a coextrusion method is usually used.

As described above, after the laminate is manufactured, the laminate is impregnated with a fluid in a supercritical state or a subcritical state, and then released from the supercritical state or the subcritical state to vaporize the fluid. The non-porous skin layer is left on the outermost surface of the outer layers on both sides to form micropores in the laminate.
Thus, in this step, micropores are formed when the fluid impregnated in the supercritical state or subcritical state is released from the intermediate layer together with the intermediate layer in the supercritical state or subcritical state. The skin layer of the pores remains, and the skin layer can act as a so-called lid, creating a supersaturated state, and communicating with the intermediate layer and both outer layers in the thickness direction without causing a skin layer on the surface of the intermediate layer The micropore which has can be formed.

The gas that can be used as the subcritical or supercritical fluid is not limited to the following, but examples include carbon dioxide, nitrogen, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, and tetrafluoromethane. , Trifluoromethane, 1,1-difluoroethylene, trifluoroamide oxide, cis-difluorodiazine, trans-difluorodiazine, nitrogen difluoride, phosphorus deuteride, dinitrogen tetrafluoride, ozone, phosphine, Nitrosyl fluoride, nitrogen trifluoride, deuterium chloride, hydrogen chloride, xenon, sulfur hexafluoride, fluoromethane, perfluoroethane, tetrafluoroethane, pentafluoroethane, tetrafluoromethane, trifluoromethane, 1,1-difluoro Ethene, ethyne, diborane, water, te La fluoro hydrazine, silane, silicon tetrafluoride, four germanium hydride, boron trifluoride, carbonyl fluoride, chlorotrifluoromethane, bromotrifluoromethane and vinyl fluoride, and the like.
Among them, preferable gases include carbon dioxide, nitrogen, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, tetrafluoromethane, trifluoromethane, and 1,1-difluoroethylene. Of these, carbon dioxide and nitrogen, which are inert gases, are particularly preferred in that they are non-flammable and non-toxic, are fairly inexpensive, and are non-reactive with most polymers.

  The “supercritical state” refers to a state where the temperature (critical temperature) and pressure (critical pressure) at which gas and liquid can coexist are exceeded. “Subcritical state” means a state where the pressure or temperature is in the vicinity of the critical pressure or temperature. Preferably, assuming that the critical temperature is Tc and the critical pressure is Pc, the temperature is 0.5 Tc or higher and / or the pressure is 0.5 Pc or higher (except when the temperature is Tc or higher and the pressure is Pc or higher. ). In particular, it is more preferable that either the pressure or the temperature exceeds the critical pressure or the critical temperature.

A fluid in a supercritical state or a subcritical state is a special fluid having properties different from those of ordinary gases and liquids, and has a very high impregnation property. Therefore, when the supercritical or subcritical fluid is brought into contact with the laminate obtained in the first step, the laminate is impregnated with the fluid.
A specific method for impregnating the laminate with a fluid in a supercritical state or a subcritical state may be a known method.
For example, the laminate is placed in a pressure-resistant container such as an autoclave, and a gaseous or liquid substance to be impregnated into the laminate is made into a fluid as exemplified above. Next, the temperature or / and pressure in the pressure vessel is increased to create a supercritical state or a subcritical state. That is, the temperature in the pressure vessel is raised to 0.5 Tc or higher, preferably higher than the critical temperature, or / and the pressure in the pressure vessel is raised to 0.5 Pc or higher, preferably higher than the critical pressure. In particular, it is more preferable to raise the temperature in the pressure vessel to a critical temperature or higher and raise the pressure to a critical pressure or higher.

Specifically, for example, when carbon dioxide is used, the critical temperature of carbon dioxide is 304.3 K and the critical pressure is 7.38 MPa.
When nitrogen is used, the critical temperature of nitrogen is 126.2 K and the critical pressure is 3.40 MPa. Therefore, it is preferable that the pressure is 3 MPa or more while maintaining the temperature at room temperature.
When nitrous oxide is used, since the critical temperature of nitrous oxide is 309.6K and the critical pressure is 7.24 MPa, it is preferable that the pressure is 7 MPa or more while keeping the temperature at room temperature.
When ethylene is used, since the critical temperature of ethylene is 282.4 K and the critical pressure is 5.04 MPa, it is preferable that the temperature is 10 ° C. or higher and the pressure is 5 MPa or higher.
When ethane is used, since the critical temperature of ethane is 305.2K and the critical pressure is 4.88 MPa, it is preferable that the pressure is 4.5 MPa or more while maintaining the temperature at room temperature.

  The time for impregnating the fluid in the supercritical state or subcritical state varies depending on the composition of the resin constituting the intermediate layer, the target air permeability, porosity, etc. It is preferable. This is because when the time is less than 1 minute, the intermediate layer cannot be sufficiently impregnated with the fluid. The upper limit value is 10 hours or less, preferably 5 hours or less, more preferably 2 hours or less from the viewpoint of production efficiency.

Next, the micropores are formed except for the outermost surfaces of the outer layers on both sides by releasing (deviating) from the supercritical state or the subcritical state to vaporize the fluid.
At this time, the temperature or pressure may be rapidly returned to normal temperature or normal pressure, or may be gradually decreased. Alternatively, the temperature may be lowered to a temperature below normal temperature or a pressure below normal pressure and then returned to normal temperature or normal pressure.

  After the step, in order to make the non-porous skin layer remaining on the outermost surfaces of the outer layers on both sides, the micropore forming material made of an organic solvent extractable plasticizer is removed, and the micropores formed in the step Communicating with In that case, it is preferable that the residual amount of the micropore forming material in the porous body after removal is less than 1% by mass.

In this step, the method for removing the micropore forming material is appropriately selected from known methods according to the type of micropore forming material.
When the micropore forming material is an organic solvent extractable plasticizer, the plasticizer is substantially removed from the porous material by immersing the porous material obtained in the above step in the extraction solvent and then thoroughly drying it. can do. The method of extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous body, it is preferable to restrain the end portion during a series of steps of immersion and drying.

  The extraction solvent is a poor solvent for the thermoplastic resin contained in the thermoplastic resin composition that constitutes the outer layers on both sides, and a good solvent for the plasticizer, and has a boiling point that constitutes the outer layers on both sides. It is desirable that the temperature be lower than the melting point of the thermoplastic resin contained in the resin composition. When the thermoplastic resin contained in the thermoplastic resin composition constituting the outer layers on both sides is a polyolefin resin, examples of the extraction solvent include hydrocarbons such as n-hexane and cyclohexane, methylene chloride and 1,1,1- Examples thereof include halogenated hydrocarbons such as trichloroethane, alcohols such as ethanol and isopropanol, ethers such as diethyl ether and tetrahydrofuran, and ketones such as acetone and 2-butanone.

As described above, the method for producing a porous body having a step of extracting a plasticizer as described in JP-A-5-25305 (Patent Document 1) uses a large amount of an organic solvent from the environmental aspect. It is not preferable. The reason why a large amount of an organic solvent is used in Patent Document 1 is that it is necessary to reliably achieve the extraction of the plasticizer present in the central portion of the porous body, which is considered to be the most difficult, and to reduce the remaining amount of the plasticizer. .
However, in the case of the present invention, the intermediate layer does not contain a plasticizer, and the plasticizer is present only in the outer layers on both sides of the surface layer, and there is no plasticizer in the center where extraction is difficult. Since the extraction efficiency is high and the amount of the extraction solvent used is extremely small, the environmental load is not significantly increased as in Patent Document 1.

  In the method for producing a porous body of the present invention, it is preferable to perform a stretching treatment before or after the step of removing the micropore forming material from the outer layers on both sides, and in particular, the laminate is stretched before removing the micropore forming material. Is preferred. By performing the stretching treatment, it is possible to more reliably ensure the connectivity of the micropores formed in the previous step.

The stretching treatment may be either uniaxial stretching or biaxial stretching, but biaxial stretching is preferred from the viewpoint of isotropic property. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching in which the film is stretched in the longitudinal direction (longitudinal direction) and then in the transverse direction. As a stretching method, a method using a general apparatus such as a roll stretching machine or a tenter stretching machine may be used. As a draw ratio, it is at least 2 times by area magnification, Preferably it is 4 times or more, More preferably, it is 4-16 times.
The stretching temperature is not particularly limited, but stretching is preferably performed at a temperature lower than the melting point of the thermoplastic resin constituting the outer layers on both sides, preferably 30 ° C. or less from the melting point. If the stretching temperature is too close to the melting point, it will be difficult to develop communication between the two outer layers.

Further, if necessary, measures such as heat shrinkage and dimensional stability may be taken by performing heat fixation near the melting point or relaxation after stretching.
These treatments can be performed by known methods. For example, the heat treatment can be performed by any known method such as contact heating with a heating roll or heating in air in an oven. Moreover, it is also possible to divert the above-mentioned extending | stretching apparatus. The heat treatment temperature can be any temperature below the melting point of the thermoplastic resin constituting the intermediate layer and both outer layers, but is preferably 100 ° C. or higher and lower than the melting point of the resin, more preferably 110 ° C. or higher and 130 ° C. or lower. It is said.

  In the production method of the present invention, post-treatment may be performed within a range that does not impair the advantages of the present invention. Examples of the post-treatment include a hydrophilic treatment with a surfactant or the like, or a cross-linking treatment with ionizing radiation.

As a second invention, a porous body made of a laminate comprising the above production method is provided.
The physical properties of the porous body of the present invention include the type of resin constituting both the outer layer and the intermediate layer, the type and amount of the micropore forming material, conditions for impregnating the subcritical or supercritical fluid, stretching conditions (stretching ratio, stretching temperature, etc. ) Etc. can be adjusted freely.

The porous body of the present invention preferably has an air permeability, which is an index of communication, in the range of 1 to 10,000 seconds / 100 ml.
This means that if the air permeability is greater than 10,000 seconds / 100 ml, the numerical value of the air permeability will be obtained in the measurement, but it means that the structure is quite poorly connected. It may be equal to nothing. The air permeability is preferably 1 to 5,000 seconds / 100 ml, more preferably 50 to 4,000 seconds / 100 ml, and particularly preferably 100 to 2,000 seconds / 100 ml. . The air permeability is measured in accordance with JIS P 8117.

  In the porous body of the present invention, the porosity is also an important factor for limiting the porous structure. Although the measuring method of a porosity is mentioned later, it is preferable to make the porosity of the porous body of this invention into the range of 5 to 80%. If the porosity is less than 5%, it is difficult to substantially obtain communication. Moreover, if the porosity is higher than 80%, handling becomes difficult from the viewpoint of strength, which is not preferable. The porosity is more preferably 20 to 70%, and particularly preferably 40 to 60%.

Since the range required for the air permeability and the porosity differs depending on the application, the air permeability and the porosity are appropriately adjusted according to the application.
For example, when used for sanitary products such as diapers and sanitary products, the air permeability is preferably 1 to 2,000 seconds / 100 ml.
When used as a battery separator, the air permeability is preferably 1 to 500 seconds / 100 ml.

The air permeability and porosity are, for example, the content of the soft segment in the thermoplastic resin constituting the intermediate layer, the time for impregnating the fluid in the supercritical state or subcritical state, the fluid in the supercritical state or subcritical state. It can be controlled by adjusting the temperature or pressure at the time of impregnation.
If the content of the soft segment in the thermoplastic resin constituting the intermediate layer is increased, the fluid in the supercritical state or the subcritical state is easily impregnated, so that the permeability and the porosity are increased. Further, the time for impregnating the fluid in the supercritical state or the subcritical state can be lengthened, and the permeability and the porosity can be increased.

The porous body of the present invention preferably has a mass per unit area (referred to as a weight) of 10 to 30 g / m ² and more preferably 10 to 25 g / m ² when converted to a thickness per 25 μm. . By reducing the weighing, it is possible to reduce the weight of the device on which the porous body of the present invention is mounted. In order to show a certain range of weighing, no filler is blended in the intermediate layer and both outer layers, or even when filler is blended, the ratio of the filler mass to the total mass of the porous body of the present invention, that is, the filler content It is suppressed to 40% by mass or less, more preferably 30% by mass or less.

In the porous body of the present invention, when the intermediate layer is composed of a polypropylene resin composition, higher heat resistance can be exhibited than a conventional porous film made of only a polyethylene resin. That is, the shape can be maintained even when exposed to high temperatures.
As an index of heat resistance, the porous body of the present invention preferably has a thermal shrinkage of 25% or less, more preferably 15% or less, and particularly preferably 10% or less. When the thermal shrinkage rate is larger than 25%, when the porous body of the present invention is used as a battery separator, there is a concern that the positive electrode and the negative electrode come into contact with each other at the end of the porous body, causing a short circuit.

The thickness or shape of the porous body of the present invention is not particularly limited. For example, the porous body of the present invention may be any of a film shape having an average thickness of 1 μm or more and less than 250 μm, a sheet shape having a thickness of 250 μm or more and less than several mm, and a molded product having a thickness of several mm or more. It can be appropriately selected depending on the situation.
Especially, it is preferable that the porous body of this invention exhibits a film form. That is, the average thickness of the porous body is 1 to 250 μm, preferably 10 to 200 μm, and more preferably 10 to 150 μm.
Note that the average thickness is a value obtained by measuring five in-plane positions in an unspecified manner with a 1/1000 mm dial gauge and calculating the average.

The porous body of the present invention having the above characteristics can be applied to various uses that require air permeability. Battery separators; Sanitary materials such as disposable paper diapers and sanitary items such as pads or bed sheets for absorbing body fluids; Medical materials such as surgical clothing or base materials for warm compresses; Materials for clothing such as jumpers, sportswear or rainwear ; Building materials such as wallpaper, roof waterproofing material, heat insulating material, sound absorbing material; desiccant; moisture-proofing agent; oxygen scavenger; disposable body warmer; can be used very suitably as a material for packaging materials such as freshness preservation packaging or food packaging .
Especially, the porous body of this invention is used suitably as a separator for nonaqueous electrolyte batteries, such as a lithium ion secondary battery utilized as power supplies, such as various electronic devices.

The method for producing a porous body of the present invention eliminates the skin layer on the surface, which has been a problem when using a subcritical or supercritical fluid, and can ensure connectivity in the thickness direction. In particular, if a non-toxic inert gas such as carbon dioxide or nitrogen is used as a subcritical or supercritical fluid, the burden on the environment can be reduced.
Furthermore, the method for producing a porous body having a laminated structure according to the present invention has an advantage that the production conditions are wide and process management is easy.

  The porous body of the present invention obtained by the above production method is characterized by having uniform communication holes throughout and having a small mass per unit area. Therefore, the porous body of the present invention can be particularly suitably used as a battery separator, and in this case, a non-aqueous electrolyte secondary battery having good electrolyte retention and high safety without greatly increasing the battery weight is provided. can do.

Hereinafter, embodiments of the present invention will be described.
First, FIG. 1 and FIG. 2 show the first and second embodiments of a film-like porous body made of a laminate produced by the production method of the present invention described later, respectively.
Although the porous body of 1st and 2nd embodiment consists of the porous body 1 (1-1, 1-2) which made the number of lamination | stacking differ, all are manufactured with the same manufacturing method mentioned later.

  The porous body 1 (1-1) according to the first embodiment shown in FIG. 1 has a three-layer structure, in which an intermediate layer 2 and a pair of outer layers 3 and 4 positioned on both outer surfaces thereof are laminated and integrated in the thickness direction. Yes. The intermediate layer 2 and the outer layers 3 and 4 on both sides have a large number of minute holes 2a, 3a and 4a, respectively, and these minute holes 2a, 3a and 4a communicate with each other in the thickness direction. The outer side layers 3 and 4 are made of the same resin composition, and the intermediate layer 2 is made of a resin composition different from the outer side layers 3 and 4. The resin compositions of the outer side layers 3 and 4 may be different.

  The porous body 1 (1-2) of the second embodiment shown in FIG. 2 has a four-layer structure, two intermediate layers 2 (2A, 2B), and both outer layers 3 on both outer surfaces of the two intermediate layers 2. 4, as in the first embodiment, each of these layers has micropores 2a to 4a, which are communicated in the thickness direction.

  In any aspect, the porous body 1 of the first and second embodiments is such that the intermediate layer 2 is made of a thermoplastic resin having a hard segment and a soft segment not containing a filler, and both outer layers 3 and 4 are made of a filler. It does not contain and consists of the thermoplastic resin which contains a thermoplastic resin and a micropore formation agent at least. The micropores 2a present in the intermediate layer 2 are formed by impregnation of supercritical or subcritical fluid, and the micropores 3a, 4a present in both outer layers 3 and 4 are impregnated with supercritical or subcritical fluid and micropore formation. It is formed by extracting and removing the agent.

Below, the manufacturing method of the porous body 1 of 1st Embodiment of 3 layer structure is demonstrated.
As described above, the method for manufacturing the porous body according to the second embodiment includes the following steps similar to those in the first embodiment.

The manufacturing method of the porous body 1 is as follows:
A three-layer structure in which an intermediate layer 2 made of a polypropylene resin composition and both outer layers 3 and 4 made of a thermoplastic resin composition containing at least a polyethylene resin and an organic solvent extractable plasticizer are laminated on both sides of the intermediate layer 2. A first step of producing a laminate;
The obtained laminate is impregnated with a fluid in a supercritical state or a subcritical state, and then released from the supercritical state or the subcritical state to vaporize the fluid, whereby the outermost surfaces of the both outer layers 3 and 4 are formed. A second step of forming micropores in the intermediate layer 2 and the outer layers 3 and 4 on both sides while leaving the non-porous skin layers 3b and 4b;
In the second outer layer 3, 4 by extracting a plasticizer with an organic solvent from the thermoplastic resin composition constituting the second outer layer and the second ′ step in which the laminate obtained in the second step is stretched. This includes a third step of forming micropores including the skin layers 3b and 4b and communicating the micropores with the micropores formed in the third step.

As the polypropylene resin composition constituting the intermediate layer 2, a resin composition in which an ethylene-propylene rubber is blended with a polypropylene homopolymer is used.
The ethylene-propylene rubber content is preferably 5 to 95% by mass, more preferably 15 to 75% by mass, and further preferably 30 to 60% by mass.
As the ethylene-propylene rubber, an ethylene-propylene rubber having an ethylene content of 30 to 55% by mass based on the whole rubber is particularly preferable.
By adjusting the ethylene-propylene rubber content and the ethylene content in the ethylene-propylene rubber, the ethylene content relative to the entire polypropylene resin composition constituting the intermediate layer is preferably 5 to 70% by mass. It is more preferably ˜50 mass%, and particularly preferably 10 to 30 mass%.
Thus, by using a polypropylene resin for the intermediate layer 2, there is an advantage that higher heat resistance can be exhibited than a conventional porous film made of only a polyethylene resin. That is, the shape can be maintained even when exposed to high temperatures.

The polyethylene resin constituting the both outer layers 3 and 4, density of 0.94 g / cm ³ or more, preferably a molecular weight high-density polyethylene or ASTM method, the 0.95~0.97g / cm ³ is 50 to 600 Ultra high molecular weight polyethylene is preferred.
As an organic solvent extractable plasticizer blended in the polyethylene resin, hydrocarbons such as liquid paraffin and paraffin wax are preferably used, and paraffin wax is more preferably used. The content of the plasticizer is preferably 30 to 90 parts by mass, and more preferably 40 to 80 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition constituting the both outer layers 3 and 4. .

The following method is used as a method of producing a laminate composed of the intermediate layer 2 and the three outer side layers 3 and 4 disposed so as to sandwich the intermediate layer 2 therebetween.
First, with respect to the outer layers 3 and 4 on both sides, a thermoplastic resin and a plasticizer are mixed with a powder mixer such as a Henschel mixer, and heated and kneaded with a uniaxial or biaxial kneader, a kneader, etc., and pellets are formed beforehand . In view of the dispersion state of the plasticizer, it is more preferable to use a biaxial kneader.
The moisture content of the pellets is controlled to 1000 ppm or less, preferably 700 ppm or less. This is because if the moisture content of the pellet is larger than 1000 ppm, gel and pinball are extremely generated, which is not preferable.

A film in which the pellets for both outer layers prepared as described above and the polypropylene resin composition for the intermediate layer are co-extruded and laminated into three layers is extruded. More specifically, lamination is performed under a temperature condition of 150 to 250 ° C, preferably 190 to 220 ° C, using an inflation die or T die for multilayer molding.
In the laminated body thus obtained, the ratio tr (= to / t) of the total thickness of the outer layers on both sides to the thickness t of all layers is 0.4 to 0.80, preferably 0.5 to 0.7. It is adjusted so that.

The laminate obtained in the first step is placed in a pressure vessel, and carbon dioxide gas or nitrogen gas is sealed in the pressure vessel. The pressure in the pressure vessel is increased, and carbon dioxide gas or nitrogen gas is brought into a supercritical state or a subcritical state.
More specifically, when carbon dioxide is used, the pressure is increased to 7 Mpa or more, preferably 15 Mpa or more. When nitrogen is used, the pressure is increased to 3 Mpa or more, preferably 10 Mpa or more. The temperature in the pressure vessel may be room temperature, but can be heated.

By maintaining the pressure and temperature in the pressure vessel, carbon dioxide or nitrogen in a supercritical state or a subcritical state is impregnated into the laminate. The impregnation time is 10 minutes to 2 hours, preferably 30 minutes to 1.5 hours.
Thereafter, the impregnated carbon dioxide or nitrogen is vaporized by returning the pressure or temperature in the pressure vessel to normal pressure or normal temperature. The pressure or temperature in the pressure vessel may be gradually decreased, or may be returned to normal pressure or room temperature at once.

The laminate obtained in the second step is stretched in the second ′ step. Although this stretching process is not an essential process, the stretching process can widen the micropores generated by the subcritical or supercritical fluid, and can ensure the communication in the thickness direction.
The stretching method in the 2 ′ step is preferably sequential biaxial stretching in which the film is stretched in the longitudinal direction (longitudinal direction) and then in the transverse direction. The draw ratio is 4 to 16 times, preferably 4 to 12 times in terms of area magnification. The stretching temperature is preferably 30 to 80 ° C.

  Further, after the second 'step, heat treatment may be performed on the porous body obtained as necessary to impart thermal dimensional stability. The heat treatment can be performed by any known method such as contact heating with a heating roll or heating in the air in an oven. The heat treatment temperature can be any temperature lower than the melting point of the thermoplastic resin constituting the intermediate layer 2 and both outer layers 3 and 4, preferably 100 ° C. or higher and lower than the melting point of the resin, more preferably 110 ° C. or higher. It is 130 degrees C or less.

Next, in the third step, the plasticizer is extracted with an organic solvent from the thermoplastic resin composition constituting the both outer layers. More specifically, the plasticizer can be substantially removed from the porous body by immersing the porous body obtained in the second 'step in the extraction solvent and then sufficiently drying it.
What is necessary is just to select an extraction solvent suitably according to the kind of plasticizer. When using hydrocarbons such as liquid paraffin and paraffin wax as the plasticizer, it is preferable to use alcohols such as ethanol and isopropanol as the extraction solvent.
By extracting the plasticizer in this manner, micropores are formed in the entire outer layers 3 and 4 including the skin layers 3a and 4a, and the micropores communicate with the micropores formed in the second step. Thus, a porous body having a large number of micropores having communication in the thickness direction can be obtained.

The porous body 1 produced as described above has an air permeability as an index of communication of 100 to 5,000 seconds / 100 ml, preferably 100 to 2,000 seconds / 100 ml. The porosity is 30 to 70%, preferably 35 to 60%.
Since the porous body 1 contains no filler in the intermediate layer 2 and the outer outer layers 3 and 4, the mass per unit area (referred to as “weighed”) when converted to a thickness per 25 μm is 10 to 30 g / m ^2. The porous body 1 is reduced in weight, preferably 10 to ²⁰ g / m ² , more preferably 10 to 15 g / m ² .
The porous body 1 has a film shape and has an average thickness of 1 to 250 μm, preferably 10 to 200 μm, more preferably 10 to 100 μm, and is prepared according to the use of the porous body.

The porous body 1 described above can be used for various applications that require air permeability, and among these, it is preferable to use it as a battery separator.
When the porous body 1 of the present invention is used as a battery separator, the air permeability is 50 to 500 seconds / 100 ml. This is because when the air permeability is less than 50 seconds / 100 ml, the electrolyte solution retainability is lowered and the capacity of the secondary battery is lowered or the cycle performance is lowered. On the other hand, if the air permeability exceeds 500 seconds / 100 ml, the ion conductivity is lowered and sufficient battery characteristics cannot be obtained. Preferably, it is 100 to 300 seconds / 100 ml.
Moreover, the porosity is set to 30 to 70%. This is because if the porosity is less than 30%, the ion permeability is low and it is difficult to obtain sufficient battery performance, whereas if the porosity exceeds 70%, it is not preferable from the viewpoint of battery safety. More preferably, it is 35 to 65%.

  As a battery separator, a porous film composed mainly of a polyethylene resin is used because of the necessity of shutdown characteristics. However, by using a polypropylene resin composition for the intermediate layer, the dimensional stability after shutdown is improved and the battery is not suitable. It can be made difficult to fall into a stable state.

Next, a non-aqueous electrolyte battery containing the porous body 1 of the present invention as a battery separator 10 will be described with reference to FIG.
Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the separator 10, and the outside is stopped with a winding tape to form a wound body. When winding in this spiral shape, the separator 10 preferably has a thickness of 5 to 40 μm, and more preferably 5 to 30 μm. This is because when the thickness is less than 5 μm, the separator is easily broken, and when it exceeds 40 μm, the battery area is reduced and the battery capacity is reduced when wound in a predetermined battery can as a battery separator.

  A wound body in which the positive electrode plate 21, the separator 10 and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. Next, the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the separator 10 or the like, the positive electrode lid 27 is sealed to the periphery of the opening of the battery can via the gasket 26, and precharging and aging are performed. Type non-aqueous electrolyte battery.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used. The organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile. 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more.
Among them, an electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.4 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

As the negative electrode, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like.
When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  In this embodiment, as a negative electrode, a carbon material having an average particle size of 10 μm is mixed with a solution in which vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a 70-mesh net. After removing the large particles, uniformly apply to both sides of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm and dry, and then compression-molded with a roll press machine, cut, and strip-shaped negative electrode plate What is used.

  As the positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

In the present embodiment, a strip-like positive electrode plate produced as follows is used as the positive electrode. In other words, lithium graphite oxide (LiCoO ₂ ) was added with phosphorous graphite as a conductive additive at a mass ratio of 90: 5 and mixed, and this mixture was mixed with a solution in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone. To make a slurry. The positive electrode mixture slurry is passed through a 70 mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm and dried. After compression molding, it is cut into a strip-like positive electrode plate.

Hereinafter, examples of the porous body of the present invention will be described.
Example 1
As a preparation of the resin composition constituting the outer layers on both sides, 25 parts by mass of ultra high molecular weight polyethylene (“Hi-Zex Million 240M” manufactured by Mitsui Chemicals, Inc.) and 75 parts by mass of paraffin wax (“135” manufactured by Nippon Seiwa Co., Ltd.) Were mixed and pelletized with a twin screw extruder. Next, the thermoplastic resin composition is used as both outer layers, and a thermoplastic elastomer (“Zelas 5053” manufactured by Mitsubishi Chemical Co., Ltd.) containing polypropylene and ethylene propylene rubber is used as the thermoplastic resin composition constituting the intermediate layer. Then, while adjusting the layer ratio so that the outer layer / intermediate layer / outer layer = 30/40/30, it was molded at a temperature of 200 ° C. using a T-die for multilayer molding, and a two-layer / three-layer laminate Got.
The obtained laminate was charged into a pressure vessel, and carbon dioxide as an inert gas was sealed in the pressure vessel at room temperature. Next, the pressure was increased to 15 MPa to bring carbon dioxide into a subcritical state or supercritical state, and this state was maintained for 1 hour, and the laminate was impregnated with carbon dioxide in the subcritical state or supercritical state. Thereafter, the pressure vessel valve was fully opened to release the pressure in the vessel.
The laminate impregnated with carbon dioxide is stretched by a stretcher at a stretching temperature of 70 ° C. at a stretching ratio of 2 times in the longitudinal direction (longitudinal direction) and 2.5 times in the transverse direction, and then heated at 123 ° C. Fixing was performed.
Thereafter, paraffin wax was extracted using isopropyl alcohol at 80 ° C. to form micropores in both outer layers, and a porous body of Example 1 having connectivity in the film thickness direction was obtained.

(Examples 2 to 5)
A porous body of the present invention was obtained in the same manner as in Example 1 except that the resin used, the layer ratio, the fluid impregnation conditions, and the stretching conditions were changed as shown in Table 1.

The detail of the component described in the table | surface is shown below.
“240M”; ultra high molecular weight polyethylene (“Hi-Zex Million 240M” manufactured by Mitsui Chemicals, density: 0.95 g / cm ³ )
“7000FP”; high density polyethylene (“HI-ZEX7000FP” manufactured by Prime Polymer Co., Ltd., density: 0.954 g / cm ³ , melt flow rate: 0.04 g / 10 min)
“135”: Paraffin wax (Nippon Seiwa Co., Ltd., density: 0.91 g / cm ³ )
“150”: Paraffin wax (Nippon Seiwa Co., Ltd., density: 0.93 g / cm ³ )
“Zelas 5053”; a polymerization type polypropylene resin composition containing ethylene-propylene rubber in a polypropylene homopolymer (“Zelas 5053” manufactured by Mitsubishi Chemical Corporation, density 0.88 g / cm ³ , melt flow rate 0.8 g / 10 minutes)
"Zelas 7053": a polymerization type polypropylene resin composition containing ethylene-propylene rubber in a polypropylene homopolymer ("Zelas 7053" manufactured by Mitsubishi Chemical Corporation), density 0.88 g / cm ³ , melt flow rate 0.8 g / 10 minutes)

(Comparative Example 1)
In Comparative Example 1, a porous film was prepared by the method described in Example 1 of JP-A-5-25305 of Patent Document 1.
That is, 20% by mass of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2.0 × 10 ⁶ , 66.7% by mass of high density polyethylene (HDPE) having a weight average molecular weight of 3.9 × 10 ⁵ , 15 parts by mass of a raw material resin mixed with 13.3% by mass of low density polyethylene (LDPE) 2.0 g / 10 min of an index (190 ° C., 2.16 kg load) and 85 parts by mass of liquid paraffin (64 cst / 40 ° C.) Were mixed to prepare a polyethylene composition solution. Next, 100 parts by mass of this polyethylene composition solution was added 0.125 parts by mass of 2,5-di-t-butyl-p-cresol (“BHT”, manufactured by Sumitomo Chemical Co., Ltd.) and tetrakis [methylene -3- (3,5-di-t-butyl-4-hydroxylphenyl) -propionate] methane ("Irganox 1010", Ciba Geigy) 0.25 part by mass was added as an antioxidant. This mixed solution was filled in an autoclave equipped with a stirrer and stirred at 200 ° C. for 90 minutes to obtain a uniform solution. This solution was extruded from a T die by an extruder having a diameter of 45 mm, and a gel-like sheet was formed while being taken up by a cooling roll.
The obtained sheet was set in a biaxial stretching machine and the temperature was 115 ° C. and the stretching speed was 5 m / min.
Simultaneous biaxial stretching was performed 5 times. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, and then heat-set at 100 ° C. for 30 seconds to obtain a polyethylene microporous membrane.

(Comparative Example 2)
In Comparative Example 2, a porous film was prepared by the method described in Example 1 of JP-A-2004-95550 of Patent Document 3.
High density polyethylene (“HI-ZEX7000FP” manufactured by Prime Polymer Co., Ltd., density: 0.956 g / cm ³ , melt flow rate: 0.04 g / 10 min) 100 parts by mass, soft polypropylene (“PER R110E manufactured by Idemitsu Petrochemical Co., Ltd.) 15.6 parts by mass, hardened castor oil (“HY-CASTOR OIL” manufactured by Toyokuni Seiyaku Co., Ltd., molecular weight 938) 9.4 parts by mass, barium sulfate (“B-55” manufactured by Sakai Chemical Co., Ltd.) 187.5 parts by mass Were blended and compounded. Next, inflation molding was performed at a temperature of 210 ° C. using the obtained compound to obtain a raw sheet.
Next, the obtained raw fabric sheet was sequentially stretched at 70 ° C. in the longitudinal direction (MD) of the sheet at 1.23 times, and then at 11.5 ° C. in the transverse direction (TD) at 2.86 times to obtain a porous film. It was.

The following physical properties of the porous bodies obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were measured.
(Measurement 1; thickness)
With a 1/1000 mm dial gauge, five in-plane measurements were made unspecified, and the average was taken as the thickness.
(Measurement 2: Air permeability (Gurley value))
The air permeability (second / 100 ml) was measured according to JIS P 8117.
(Measurement 3: Porosity)
The porosity is a numerical value indicating the proportion of the space portion in the porous body. The porosity is calculated by measuring the substantial amount W1 of the porous body, calculating the mass W0 when the porosity is 0% from the density and thickness of the resin composition, and calculating the following from the difference from the substantial amount of the porous body: The porosity is calculated based on the formula.
Porosity Pv (%) = {(W0−W1) / W0} × 100
(Measurement 4; basis weight)
The basis weight is a numerical value representing the mass per unit area. The measuring method cuts a porous body into 10 cm square, and measures the mass. Since the dependence on the thickness is large, this time was converted to a thickness per 25 μm, this operation was repeated three times, and the average was defined as the basis weight.

The results of the above measurements are shown in the following table.

From Examples 1 to 5, using a subcritical or supercritical fluid, a porous body having physical properties comparable to those of the conventional porous film represented by Comparative Example 1 can be produced.
Furthermore, in the invention described in Comparative Example 1, a large amount of an organic solvent such as methylene chloride is required to remove the plasticizer contained in the entire porous film. However, in the production method of the present invention, it is contained in both outer layers. Since the organic solvent is used only for removing the plasticizer to be used, the amount of the organic solvent used may be remarkably small, and it is not necessary to place a heavy load on the environment as in the invention described in Comparative Example 1. .
In the porous film of Comparative Example 2, since the filler is present in all layers, the basis weight becomes as heavy as 33 g / m ^2. However, in the porous films of Examples 1 to 5, the basis weight is 11 to 15 g / m ^2. It was as small as m ² and it was found that weight saving was possible.

  The porous body of the present invention can be suitably used as a sanitary article such as a diaper, a packaging material, an agricultural / livestock article, a building article, a medical article, a separation membrane, a light diffusing plate, a reflecting sheet, etc., in addition to a battery separator.

(A) (B) is a schematic sectional drawing of the porous body of 1st embodiment. It is a schematic sectional drawing of the porous body of 2nd embodiment. It is a partially broken perspective view of the nonaqueous electrolyte battery which has accommodated the porous body of the present invention as a nonaqueous electrolyte battery separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous body 2 Intermediate | middle layer 3, 4 Both-sides outer layer 2a, 3a, 4a Micropore 10 Separator 20 Nonaqueous electrolyte battery 21 Positive electrode plate 22 Negative electrode plate

Claims (10)

A method for producing a porous body having a large number of micropores having connectivity in the thickness direction,
At least one intermediate layer composed of a hard segment and a thermoplastic resin composition having a soft segment is included, and both outer layers composed of a thermoplastic resin composition including at least a thermoplastic resin and a micropore forming material are laminated on both sides of the intermediate layer. Producing a laminated body having at least a three-layer structure,
The obtained laminate is impregnated with a fluid in a supercritical state or a subcritical state, and then released from the supercritical state or the subcritical state to vaporize the fluid. Leaving the skin layer to form micropores in the laminate;
After forming the micropores, the micropores are formed in the skin layer by removing at least the micropore forming material from the thermoplastic resin composition constituting the both-side outer layer, and communicated with the micropores formed in the step. 3 steps
A method for producing a porous body, comprising:   2. The method for producing a porous body according to claim 1, comprising a stretching step in which the micropores formed in the step are communicated with each other before or after the step of removing the micropore forming material.   The micropore forming material is made of an organic solvent extractable plasticizer, and the outer side layers include at least a thermoplastic resin and the organic solvent extractable plasticizer, and the organic solvent extractable plasticizer is removed from the microporous material. The method for producing a porous body according to claim 1, wherein in the step, the organic material is extracted and removed.   The method for producing a porous body according to any one of claims 1 to 3, wherein the fluid impregnated in the supercritical state or the subcritical state is carbon dioxide or nitrogen.   The porous body manufactured by the method of any one of Claims 1 thru | or 4.   The porous body according to claim 5, wherein at least one of the outer layers is made of a thermoplastic resin composition containing a polyethylene resin.   The porous body according to claim 5 or 6, wherein the thermoplastic resin composition constituting the intermediate layer contains at least ethylene-propylene rubber as a soft segment and a polypropylene resin as a hard segment.   The porous body according to any one of claims 4 to 7, which has an air permeability of 1 to 10,000 seconds / 100 ml.   A battery separator comprising the porous body according to any one of claims 4 to 8.   A battery comprising the battery separator according to claim 9.

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