JP2007083549A - Perforated laminate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perforated laminate having communication properties provided thereto in its thickness direction. <P>SOLUTION: The manufacturing method of a perforated laminate having a large number of micropores includes a process for manufacturing a laminate having at least a three-layered structure wherein layers comprising a resin composition containing at least a filler and a thermoplastic resin are provided at both outer layers and an intermediate layer comprising a polypropylene resin composition and containing no filler is held between both the outer layers and the ratio tr(=to/t) of the sum total thickness of both the outer layers with respect to the thickness (t) of the whole layer is 0.5-0.95, a process for impregnating the obtained laminate with a fluid of a supercritical or sub-critical state and subsequently eliminating this state to evaporate the fluid to perforate the intermediate layer and a process for stretching the laminate at least in a uniaxial direction to peel the interface of the filler and the thermoplastic resin to perforate both the outer layers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a porous laminate and a porous laminate, and can be used as a packaging product, a sanitary product, a livestock product, an agricultural product, a building product, a medical product, a separation membrane, a light diffusion plate, a reflective sheet, or a battery separator, In particular, it is suitably used as a separator for a non-aqueous electrolyte battery such as a lithium ion secondary battery used as a power source for various electronic devices.

  The polymer porous body with many fine communication holes is used for separation membranes used for the production of ultrapure water, generation of chemicals, water treatment, waterproof and moisture permeable films used for clothing and sanitary materials, batteries, etc. It is used in various fields such as battery separators.

Conventionally, various techniques have been proposed as a technique for forming a large number of fine communication holes in a 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, since there is no filler on the surface of the porous film, the mass per unit area (basis weight) is small, but there is a drawback that the slipperiness of the porous film is low because there are no appropriate irregularities on the surface of the porous film. Furthermore, in this method, the solvent is extracted by washing with an organic solvent for washing (the column 0045, etc.). However, since a large amount of the organic solvent is required at this time, it is not preferable from the environmental viewpoint.

In Japanese Patent Laid-Open No. 10-50286 (Patent Document 2), 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. A porous film to be used as a battery separator is manufactured by stretching the porous film in two steps to make it porous and then heat-setting it.
Although the porous film has both communication properties and heat resistance, there is a drawback in that the film has low slipperiness because there is no filler on the surface as in Patent Document 1, and therefore there are no suitable irregularities on the film surface. Furthermore, in the method for producing a porous film, which is generally referred to as an open stretching method using a single polymer, there are conditions under which a preferred porous structure can be obtained under stretching conditions such as stretching temperature, stretch ratio, and multistage stretching. It is very narrow (such as columns 0025 to 0028), which is not preferable in view of process control when producing on an industrial scale.

In Japanese Patent No. 3166279 (Patent Document 3), a porous film or sheet 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
Similarly, in Japanese Patent Application Laid-Open No. 2004-95550 (Patent Document 4), 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. Is gained by.
In the porous film or sheet obtained by these methods, moderate irregularities exist due to the presence of filler on the surface, and the slipperiness of the film increases, but the presence of fillers in all layers results in a unit area per unit area. There is a disadvantage that the mass (basis weight) becomes large.

In order to reduce the weight while maintaining the surface roughness to some extent, Japanese Patent Application Laid-Open No. 11-060792 (Patent Document 5) discloses a porous structure made of polyethylene resin in which a fine particle roughening agent such as a filler is contained only on the surface. The film is described (claims 11, 12, 0018).
However, the porous film is based on polyethylene resin, and there is room for further improving heat resistance. In addition, in the production of the porous film, the pore formation is performed by removing the plasticizer (Claims 10 to 12 and the like). Similarly to the invention described in Patent Document 1, an organic solvent is used for removing the plasticizer. Since it is necessary in large quantities, there is room for further study to reduce the burden on the environment.

  Although the porous films described in Patent Documents 1 to 5 have their respective characteristics, there are not enough in all aspects of film slipperiness, weight reduction, heat resistance, and low load on the environment, and there is room for improvement. There is.

On the other hand, a foaming technique using a subcritical or supercritical fluid is known. Specifically, a polymer is impregnated with a subcritical or supercritical fluid to reach a saturated state, and then a supersaturated state is created by a rapid pressure drop or the like, and a 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, near the surface of the polymer, it does not become supersaturated when a sudden pressure drop occurs, and gas is immediately released from the surface by diffusion and evaporation, so there is always a region that does not cause foaming, a so-called skin layer. To do. For this reason, it has not been possible to produce a porous laminate having micropores that communicate in the thickness direction.

JP-A-5-025305 Japanese Patent Laid-Open No. 10-50286 Japanese Patent No. 3166279 JP 2004-95550 A JP-A-11-060792

The present invention eliminates the skin layer on the surface, which has been a problem when using a subcritical or supercritical fluid, and can provide communication in the thickness direction, and uses a subcritical or supercritical fluid. Therefore, an object of the present invention is to provide a method for producing a porous laminate having a small environmental load, a wide range of production conditions, and easy process management.
Furthermore, this invention makes it a subject to provide the porous laminated body which has all slidability, weight reduction, and heat resistance.

In order to solve the above problems, the present invention provides a first invention as follows:
A method for producing a porous laminate in which a large number of micropores having communication in the thickness direction exist,
It consists of at least three layers of a double-sided outer layer composed of a resin composition containing at least a filler and a thermoplastic resin, and an intermediate layer containing no filler and composed of a polypropylene resin composition disposed between the both-sided outer layers, A step of producing a laminate in which the ratio tr (= to / t) of the total thickness of the outer layers on both sides to the thickness t of the layer is 0.05 to 0.95;
After impregnating the supercritical or subcritical fluid in the laminate produced in the above step, micropores are formed in the intermediate layer by releasing the supercritical or subcritical fluid and vaporizing the fluid. And making it porous,
A method of producing a porous laminate comprising: forming a multilayer by stretching the intermediate layer in the step, and forming micropores to make the outer layers on both sides porous. providing.

The present invention has been made on the basis of results obtained by the inventors through repeated studies and experiments.
That is, the inventors first conducted research and experiments for making a porous structure using a subcritical or supercritical fluid, and made various studies, but avoiding the occurrence of a skin layer on the surface of the problem described above. could not.
Therefore, the present inventors provide a non-porous layer on the surface of the layer to be porous using a subcritical or supercritical fluid, and so-called a lid, so that the intermediate layer and the non-porous layers of both outer layers are formed. It has been found that a porous laminate having micropores communicating with can be obtained.
That is, when the laminate is impregnated with a subcritical or supercritical fluid and then a sudden drop in pressure or the like is generated, the intermediate layer is covered with the outer non-porous layer. It was possible to create a supersaturated state on the surface of the intermediate layer without vaporizing the gas, and as a result, succeeded in producing micropores in the intermediate layer.
Furthermore, the present inventors have also studied the composition of the outer layers on both sides serving as a lid, and as a result, if a filler is added to the outer layers on both sides, the intermediate layer can be made porous using a subcritical or supercritical fluid. Can be prevented from deaeration from the surface of the intermediate layer in the absence of pores, and thereafter, the outer layers on both sides can be easily made porous by simply performing a stretching process. It has been found that the porous laminated body can be produced without being restricted by strict production conditions. Furthermore, since a large amount of organic solvent is not used in the manufacturing process, the burden on the environment is reduced.

  Furthermore, in the porous laminate produced in this way, the filler is localized only on the surface, so that moderate unevenness exists and high slipperiness is ensured, but the mass per unit area is greatly increased. Furthermore, the present inventors have found that since the polypropylene resin composition is used for the intermediate layer, excellent heat resistance can be exhibited, and the above problems can be solved all at once.

The porous laminate of the present invention has at least a three-layer structure in which an intermediate layer is sandwiched between two outer layers on both sides, and a ratio tr (= to / t) is 0.05 to 0.95.
The value of tr is preferably in the range of 0.10 to 0.90, and more preferably in the range of 0.15 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 outermost surface becomes extremely nonuniform. 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 substantially does not differ greatly from the porous film containing filler in the entire layer, particularly the mass per unit area (basis weight). ) Will become large.

  In the production method of the present invention, as described above, first, in the first step, an intermediate layer made of a thermoplastic resin having a hard segment and a soft segment, and a non-porous both-side outer layer made of a resin composition located on both outer surfaces. And a laminate composed of at least three layers.

Specific examples of the thermoplastic resin constituting the outer layers on both sides of the porous laminate include polyolefin resin, fluororesin, polystyrene, ABS resin, vinyl chloride resin, vinyl acetate resin, acrylic resin, polyamide resin, acetal resin, polycarbonate, and the like. These thermoplastic resins can be mentioned.
A polyolefin resin is preferably used as the thermoplastic resin. When the porous laminate of the present invention is used as a battery separator, it is particularly preferable to use a polyolefin resin from the viewpoint of stability with an electrolytic solution. Examples of the polyolefin resin include monoolefin polymers such as ethylene, propylene, 1-butene, 1-hexene, 1-octene and 1-decene, or ethylene, propylene, 1-butene, 1-hexene and 1-octene. Or what has as a main component the copolymer of 1-decene, other monomers, such as 4-methyl- 1-pentene or vinyl acetate, etc. is mentioned. Among these, polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polybutene, propylene ethylene block copolymer, propylene ethylene random copolymer, and the like are preferable.

As the thermoplastic resin constituting the outer layers on both sides, it is particularly preferable to use a thermoplastic resin mainly containing polyethylene, specifically including at least 50% by mass, preferably including 80% by mass or more, and more preferably including 95% by mass or more. preferable.
The polyethylene 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.

The polyethylene preferably 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 0.94 g / cm ³ or more. The upper limit is not particularly limited, but is usually 0.97 g / cm ³ .
The polyethylene has a melt flow rate of 10 g / 10 min or less, preferably 1 g / 10 min or less. If the melt flow rate is greater than 10 g / 10 min, the strength of the porous laminate may be reduced.

  As a method for polymerizing polyethylene, there are one-stage polymerization, two-stage polymerization, or more multistage polymerization, and any method of polyethylene can be used. The polymerization catalyst for polyethylene is not particularly limited, and any of a Ziegler type catalyst, a Philips type catalyst, a Kaminsky type catalyst or the like may be used.

In the outer layers on both sides, the above-described polyethylene may be used alone, but a general thermoplastic resin may be mixed with polyethylene.
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 1 to 25 parts by mass, more preferably 1 to 5 parts by mass.

In the both-side outer layer, as a filler to be blended with the above-described thermoplastic resin, any of an inorganic filler and an organic filler can be used, and one or a combination of two or more can be used.
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 and oxidation Examples thereof include oxides such as magnesium, zinc oxide, titanium oxide and silica; silicates such as talc, clay and mica. Among these, 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 both outer layers are preferable so that the filler does not melt at the stretching temperature, and crosslinked resin particles having a gel content of about 4 to 10%. Further preferred.
Examples of organic fillers include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyether. Examples thereof include thermoplastic resins such as imide, 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 is reduced due to the aggregation of fillers to cause stretching unevenness, and the contact area of the interface between the thermoplastic resin and the filler is increased, resulting in interfacial peeling due to stretching. It is difficult to make it porous. On the other hand, if the average particle diameter exceeds 25 μm, it is possible to increase the surface irregularities, but at the same time, the possibility of generating large nonuniformities in the surface pore diameter increases, which is not preferable.

  Since the amount of filler varies depending on the type of filler, it cannot be generally stated, but it is preferably 50 to 400 parts by weight, preferably 50 to 300 parts by weight with respect to 100 parts by weight of the thermoplastic resin constituting the outer layers on both sides. Is more preferable. When the blending amount of the filler is less than 50 parts by mass with respect to 100 parts by mass of the resin, the desired good air permeability is hardly expressed, and the appearance and texture are liable to deteriorate. Moreover, when the compounding quantity of a filler exceeds 400 mass parts, it will become easy to raise | generate the malfunction on processes, such as resin baking, at the time of laminated body preparation, and the intensity | strength of a porous laminated body will also fall significantly.

The resin composition constituting the outer layers on both sides only needs to contain at least a filler and a thermoplastic resin, but a plasticizer is preferably added for the purpose of improving the dispersibility of the filler in the thermoplastic resin.
Examples of the plasticizer include ester compounds, amide compounds, alcohol compounds, amine salts, amine compounds (excluding amine salts), epoxy compounds, ether compounds, mineral oil, fats and oils, paraffin wax, liquid silicone, fluorine oil, and liquid polyether. , Liquid polybutenes, liquid polybutadienes, long chain fatty acids, carboxylates, carboxylic acid compounds (excluding carboxylates), sulfonates, sulfone compounds (excluding sulfonates), fluorine compounds, etc. Can be mentioned.
Specifically, plastic compounding agents (published by Taiseisha Co., Ltd., November 30, 1987, second edition) P31 to P64, P83, P97 to P100, P154 to P158, P178 to P182, P271 to P275, P283 to 294 And the like. More specifically, the plasticizers (TCP, TOP, PS, ESBO, etc.) described in the items of plasticizers P29 to P64 and listed in Tables 4 to 49 and P6 to P54 are listed. It can be used. Further, the surfactant compounds listed in the new introduction to surfactants (published by Sanyo Kasei Kogyo Co., Ltd., August 1992, third edition) can also be suitably used as plasticizers.

Examples of the ester compound include tetraglycerin tristearate, glycerin tristearate, stearyl stearate, glycerin monostearate, sorbitan monostearate, ethylene carbonate, distearyl carbonate or dioctyl naphthalate.
Examples of the amide compound include ethylene bis stearamide and hexamethylene bis stearamide.
Examples of the alcohol compound include stearyl alcohol, oleyl alcohol, and dodecylphenol.
Examples of the amine salt include stearyl dimethyl betaine or lauryl trimethyl ammonium chloride.
Examples of the amine compound include dihydrodiethyl stearylamine and laurylamine.
Examples of the epoxy compound include epoxy soybean oil.
Examples of the ether compound include triethylene glycol.
Examples of the mineral oil include kerosene and naphthenic oil.
Examples of the oil include castor oil, hardened castor oil, and derivatives thereof.
Examples of the fatty acid include stearic acid and caproic acid.
Examples of the carboxylate include calcium stearate and sodium oleate.
Examples of the carboxylic acid compound include stearic acid, oleic acid, and derivatives thereof (excluding salts).
Examples of the sulfonate include sodium dodecylbenzenesulfonate.
The sulfone compound may be a compound having a sulfone bond (excluding a salt), and examples thereof include sulfolane and dipropylsulfonic acid.

  Since the blending amount of the plasticizer varies depending on the type of the plasticizer and the like, it cannot be generally stated, but it is, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the thermoplastic resin constituting the outer layers on both sides. When the blending amount of the plasticizer is less than 1 part by mass, the desired good stretchability is hardly exhibited, and the appearance and texture are liable to deteriorate. Moreover, when the compounding quantity of a plasticizer exceeds 30 mass parts, it will become easy to raise | generate the malfunction on processes, such as resin burning, at the time of laminated body preparation.

  In addition to the plasticizers described above, additives generally blended in the resin composition are blended in the composition constituting the outer layers on both sides of the present invention within a range that does not impair the purpose of the present invention and the characteristics of the outer layers on both sides. May be. As an additive, for example, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a neutralizer, an antifogging agent, an antiblocking agent, an antistatic agent, a slip agent, or a coloring agent may be blended. . Specifically, as the antioxidant described in P154 to P158 of the “plastics compounding agent”, the ultraviolet absorber described in P178 to P182, and the antistatic agent described in P271 to P275. A surfactant and a lubricant described in P283 to 294 are appropriately blended as necessary.

The intermediate layer of the porous laminate of the present invention is molded from a polypropylene resin composition.
Polypropylene includes homopolymers and copolymers, and 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 the 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.

  In the polypropylene resin composition constituting the intermediate layer, other resin components other than polypropylene may be blended with polypropylene. As the other resin component, a resin having a melting point lower than that of the polypropylene homopolymer can be cited as a suitable example, and more specifically, high density or low density polyethylene can be exemplified. It is preferable that the compounding quantity of the said other resin component is 2-50 mass% with respect to the whole polypropylene resin composition.

In the intermediate layer, polypropylene copolymers such as block polypropylene and random polypropylene are preferable among various polypropylenes.
Among these, a polypropylene resin composition containing ethylene-propylene rubber in a proportion of 5 to 95% by mass is preferable. When the content of the ethylene-propylene rubber is less than 5% by mass, the impregnation amount of the subcritical or supercritical fluid decreases, and it becomes difficult to obtain sufficient communication. On the other hand, if the content of ethylene-propylene rubber exceeds 95% by mass, the polypropylene resin composition becomes too soft to maintain the strength, and the subcritical or supercritical fluid cannot remain in the intermediate layer and is removed. There is a risk that the intermediate layer may not be sufficiently porous.

Ethylene-propylene rubbers are roughly classified into two types: binary copolymers of ethylene and propylene, and terpolymers containing a small amount of a non-conjugated diene monomer as a third component. Also good. 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 content of ethylene-propylene rubber or the ethylene content in ethylene-propylene rubber, the ethylene content relative to the entire polypropylene resin composition constituting the intermediate layer is preferably 5 to 95% by mass.

According to the production method of the polypropylene resin composition constituting the intermediate layer, a compound type in which ethylene-propylene rubber is blended with polypropylene homopolymer using a kneader such as a twin screw extruder and ethylene and propylene are directly polymerized. There is a polymerization type to be caused. The polymerization type is preferred because the dispersibility of the ethylene-propylene rubber, which is a soft component, is good.
Further, as a method for increasing the content of the ethylene-propylene rubber component, there is a method in which ethylene propylene rubber is blended with a commercially available polypropylene copolymer. In this case, the content of the ethylene propylene rubber component can be easily increased by using a kneader such as a twin screw extruder.
Similarly, a polypropylene resin composition having a preferable ethylene-propylene rubber component content can be obtained by blending polypropylene-homopolymer with ethylene-propylene rubber, polyethylene or the like using a kneader such as a twin screw extruder. .

The thermoplastic resin constituting the intermediate layer does not contain a filler. This is because the object of the present invention is to prevent the mass per unit area from being greatly increased particularly when an inorganic filler is used while keeping the slipperiness of the porous laminate high by allowing the filler to be present in both outer layers. .
However, the thermoplastic resin constituting the intermediate layer of the present invention is blended with additives that are generally blended in the resin composition within a range that does not impair the purpose of the present invention and the characteristics of the intermediate layer as described above. be able to. Examples of the additive include the same additives as those that can be blended in the outer layers on both sides.

The structure of the porous laminate of the present invention is not particularly limited as long as it comprises at least three layers of the intermediate layer and two outer layers located so as to sandwich the intermediate layer. For example, the intermediate layer may be composed of a plurality of layers having different compositions, or one or both of the outer side layers may be composed of a plurality of layers having different compositions. Further, it may have a five-layer structure in which a resin layer containing a filler is sandwiched between intermediate layers. However, in the present invention, a structure consisting of three layers of both outer layers and an intermediate layer is simple and preferable.
The composition or structure of the outer layers on both sides 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 suitable for each characteristic. For example, when one side is in contact with water and the other side is in contact with an organic solvent, the thermoplastic resin constituting the outer layers on both sides in contact with water is, for example, water-resistant polystyrene, and both sides in contact with the organic solvent The thermoplastic resin constituting the outer layer can be made of polypropylene having a high organic solvent resistance. The same applies to the filler. For example, when the two outer layers are in contact with neutral and acidic liquids, calcium carbonate is added to the two outer layers in contact with the neutral liquid, and both outer layers are in contact with the acidic liquid. It is also possible to distinguish fillers to be blended, such as blending barium sulfate.

A known technique may be used as a method for producing a laminate composed of at least three layers of the both outer layers and the intermediate layer. For example, it can be produced by the following method.
The outer layers on both sides contain filler, so other components such as thermoplastic resin, filler and plasticizer are mixed in a powder mixer such as a Henschel mixer, and heated and kneaded in a single or twin screw kneader or kneader. And once pelletized. Considering the dispersion state of the filler, it is more preferable to use a biaxial kneader.
Regarding the intermediate layer, the resin composition obtained by mixing the constituent components may be used in the next lamination step as it is, or may be once pelletized in the same manner as the outermost layer.
The said laminated body is produced using the pellet of the resin composition which comprises a both-sides outer layer, the resin composition which comprises an intermediate | middle layer, or its pellet.

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 outermost layer 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. This tendency is particularly noticeable when the thickness of the film is thin. Furthermore, when laminating by the coextrusion method, due to the difference in the crystallization temperature of the intermediate layer and the outermost layer, the layer containing a resin having a low crystallization temperature relaxes the orientation in the machine direction and becomes porous by stretching. Since it becomes easy, air permeability tends to be higher than when each layer is formed as a single layer, which is preferable. In particular, the inflation method is more suitable than the T-die method because it tends to cause orientation relaxation due to the difference in crystallization temperature.
At that time, the thickness of the laminate composed of the intermediate layer and the two outer layers located on both sides of the intermediate layer is the sum of the thicknesses of the outer layers on both sides with respect to the total thickness t after the stretching treatment. The to ratio tr (= to / t) is adjusted to be 0.05 to 0.95, preferably 0.10 to 0.90, and more preferably 0.15 to 0.80.

  In the co-extrusion method, the resin composition constituting each layer or its pellets is melted and extruded at a temperature not lower than the melting point of the thermoplastic resin constituting each layer, preferably not lower than + 20 ° C. and lower than the decomposition temperature, by a separate extruder. And a laminated body is produced by laminating in a molten state at a joining portion in the die or before flowing into the die.

  In the method for producing a porous laminate of the present invention, as a second step, the laminate obtained in the first step is impregnated with a fluid in a supercritical state or a subcritical state, and then the supercritical state or the subcritical state. It is made porous by forming micropores in the intermediate layer by releasing the liquid from the gas and evaporating the fluid.

  Gases that can be used as subcritical or supercritical fluids are not limited to the following, but include, for example, carbon dioxide, nitrogen, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, tetrafluoromethane, Trifluoromethane, 1,1-difluoroethylene, trifluoroamide oxide, cis-difluorodiazine, trans-difluorodiazine, nitrogen chloride 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-difluoroethene , Ethin, diborane, water, tetra Le Oro hydrazine, silane, silicon tetrafluoride, four germanium hydride, boron trifluoride, carbonyl fluoride, chlorotrifluoromethane, bromotrifluoromethane and vinyl fluoride, and the like. Among these, preferred 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 0.7 Tc or higher and / or the pressure is 0.7 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 0.7 Tc or higher, preferably the critical temperature or higher, or the pressure in the pressure vessel is raised to 0.7 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 31.1 ° C. and the critical pressure is 7.38 MPa.
When nitrogen is used, since the critical temperature of nitrogen is −147 ° C. and the critical pressure is 3.40 MPa, it is preferable that the pressure is 3 MPa or more while keeping the temperature at room temperature.
When nitrous oxide is used, since the critical temperature of nitrous oxide is 36.4 ° C. and the critical pressure is 7.24 MPa, it is preferable that the pressure is 7 MPa or more with the temperature kept at room temperature.
When ethylene is used, since the critical temperature of ethylene is 9.2 ° C. and the critical pressure is 5.04 MPa, the temperature is preferably 10 ° C. or higher and the pressure is preferably 5 MPa or higher.
When ethane is used, since the critical temperature of ethane is 32 ° C. and the critical pressure is 4.88 MPa, it is preferable that the pressure is 4.5 MPa or more with the temperature kept 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 intermediate layer is made porous by releasing (deviating) from the supercritical state or 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.
In the present invention, the second step is not strictly limited to making only the intermediate layer porous, but the layer in contact with the intermediate layer is made porous on and near the surface in contact with the intermediate layer. There is no problem at all.

Next, the porous laminate obtained through the second step is stretched to peel the interface between the thermoplastic resin and the filler to make both outer layers porous, and there are many micropores having connectivity in the thickness direction. A porous laminate can be obtained.
The stretching method may be 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. 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 preferable that it is at least 2 times by area magnification, Preferably it is 4 times or more. The stretching temperature is not particularly limited, but the stretching is preferably performed at a temperature lower than the melting point of the thermoplastic resin constituting the both-side outer layer, 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 express the communication at the outer layer portions on both sides.
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.

As a second aspect of the present invention, there is provided a porous laminate produced by the above method, wherein the air permeability is 1 to 10,000 seconds / 100 ml.
Furthermore, as a third invention, not limited to the above production method, comprising a resin composition containing at least a filler and a thermoplastic resin, both side outer layers positioned on the outermost surface,
It is located between the outer layers on both sides, and is composed of a laminate of at least three layers including an intermediate layer made of a polypropylene resin composition that does not contain a filler, and
The ratio tr (= to / t) of the total to thickness of both outer layers to the thickness t of all layers of the laminate is 0.05 to 0.95, and
There are a large number of micropores communicating in the thickness direction in the outer layer and the intermediate layer on both sides,
A porous laminate having an air permeability of 1 to 10,000 seconds / 100 ml is provided.

  As described above, in the porous laminate of the present invention, the air permeability that is an index of communication is in the range of 1 to 10,000 seconds / 100 ml, preferably 1 to 5,000 seconds / 100 ml. If the air permeability is greater than 10,000 seconds / 100 ml, the value of air permeability will be obtained in the measurement, but it means that the structure is very poor in communication, so there is virtually no communication. You can think that it is equal to. The air permeability is measured according to JIS P 8117.

  The porosity is also an important factor for limiting the porous structure. Although the method for measuring the porosity will be described later, the porosity of the porous laminate of the present invention is preferably 5 to 80%, more preferably 20 to 70%, and particularly preferably 40 to 60%. 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.

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.

For example, the air permeability and the porosity are impregnated with the composition of the resin composition constituting the intermediate layer or both outer layers, the time for impregnating the fluid in the supercritical state or the subcritical state, the fluid in the supercritical state or the subcritical state. It can be controlled by adjusting the temperature or pressure.
For example, when the polypropylene resin composition constituting the intermediate layer contains ethylene-propylene rubber, if the content is increased, the fluid in the supercritical state or the subcritical state is easily impregnated. The porosity increases. Even if the time for impregnating the fluid in the supercritical state or subcritical state is lengthened, or the temperature or pressure at the time of impregnating the fluid in the supercritical state or subcritical state is increased, the air permeability and air The porosity can be increased.

  Moreover, when a polypropylene resin composition is used for an intermediate | middle layer, heat resistance higher than the porous film which consists only of the conventional polyethylene resin can be exhibited. That is, the shape can be maintained even when exposed to high temperatures. As a heat resistance index, the thermal shrinkage rate is preferably 20% or less, more preferably 15% or less, and particularly preferably 10% or less.

About the porous laminated body of this invention, thickness or a shape is not specifically limited. For example, any of a film shape having a 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 body having a thickness of several mm or more can be selected as appropriate.
Especially, it is preferable that the porous laminated body of this invention exhibits a film form. That is, the average thickness of the porous laminate is 1 to 250 μm, preferably 10 to 200 μm, and more preferably 50 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 laminate of the present invention preferably has a mass per unit area (referred to as a weight) of 10 to 30 g / m ² when converted to a thickness per 25 μm, and preferably 10 to 25 g / m ^2. Is more preferable. By reducing the weight, it is possible to reduce the weight of the device on which the porous laminate of the present invention is mounted.
In order to show the weight, the ratio of the mass of the filler to the total mass of the porous laminate of the present invention, that is, the filler content is 5 to 40 parts by mass, more preferably 5 to 30 parts by mass as described above. It is.

Furthermore, since the porous laminated body of the present invention contains fillers on the outer layers on both sides, it preferably has moderate irregularities on the surface and has a maximum height (Rmax) value of 2 μm or more. This is because if the thickness is 2 μm or more, moderate irregularities exist on the surface of the porous laminate, and the slipperiness of the porous laminate is enhanced. Preferably, it is 3 μm or more, preferably 5 μm or more, and the upper limit is not particularly limited, but is usually 7 μm or less.
The maximum height (Rmax) value is measured in accordance with the method described in JIS B 0601.

The porous laminate of the present invention having the above characteristics can be applied to various uses that require air permeability. Specifically, for example, battery separators; sanitary materials such as disposable paper diapers, sanitary and other body fluid absorbent pads or bed sheets; medical materials such as surgical clothing or hot compress substrates; Materials for clothing such as wallpaper, building materials such as waterproofing materials for roofs, heat insulating materials, and sound absorbing materials; desiccants; moisture-proofing agents; oxygen scavengers; disposable warmers; It can be used very suitably.
In particular, the porous laminate of the present invention is suitably used as a separator for a non-aqueous electrolyte battery such as a lithium ion secondary battery used as a power source for various electronic devices.

Especially, the porous laminated 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.
When used as the battery separator, the air permeability is preferably 50 to 500 seconds / 100 ml, more preferably 100 to 300 seconds / 100 ml. When the air permeability is less than 50 seconds / 100 ml, there is a possibility that the electrolyte retention will be reduced, the capacity of the secondary battery will be lowered, and the cycle performance will be reduced. On the other hand, if the air permeability exceeds 500 seconds / 100 ml, the ion conductivity becomes low and sufficient battery characteristics cannot be obtained.
When the porous laminate of the present invention is used as a battery separator, the porosity is preferably 30 to 70%, and more preferably 35 to 65%. If the porosity is less than 30%, the ion permeability is low and it is difficult to obtain sufficient battery performance. Further, if the porosity exceeds 70%, it is not preferable from the viewpoint of battery safety.
The heat resistance can be evaluated by the heat shrinkage rate. The heat shrinkage rate is preferably 0 to 25%, more preferably 0 to 10%. If the thermal shrinkage rate is greater than 25%, there is a concern that the positive electrode and the negative electrode come into contact with each other at the end of the porous laminate, causing a short circuit.

As described above, the method for producing a porous laminate of the present invention can reduce the burden on the environment because a large amount of an organic solvent is not used for porous formation. 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 further reduced.
Further, in the method of making porous by removing the plasticizer and the solvent, the plasticizer and the solvent may remain without being removed, but in the present invention, the subcritical or supercritical fluid is used. Such a problem of remaining does not occur, and a porous laminate with fewer impurities can be produced.
Furthermore, the manufacturing method of the porous laminate of the present invention has a wide range of manufacturing conditions, and process management is easy.

Since the porous laminated body of the present invention contains fillers in the outer layers on both sides, the surface has moderate irregularities. Therefore, it is suitably used for a porous body having a demand for roughening the surface of a battery separator or the like to some extent. In the battery separator, the sliding property of the porous laminate is improved, and the handling property at the time of winding the battery becomes suitable.
In the case of a conventional porous film for a battery separator, the maximum height (Rmax) value of the porous film surface measured by the method described in JIS-B-0601 was usually about 1 to 2 μm. In addition, when a known film roughening technique such as attaching fine particles or short fibers to the surface is applied to the porous film, physical property requirements essential for battery separators such as surface strength and shutdown characteristics are impaired. There is a problem.
On the other hand, the porous laminate of the present invention can have a maximum height (Rmax) value of 2 μm or more without impairing physical property requirements essential for a battery separator, such as surface strength and shutdown characteristics. This contributes to higher battery capacity and improved handling during battery winding.

  Although the porous laminate of the present invention has moderate unevenness due to the filler on the surface and can exhibit high slipperiness, there is no filler in all layers, so when using an inorganic filler in particular In addition, the mass per unit area is not greatly increased, and it is possible to contribute to the weight reduction of the apparatus for housing the porous laminate of the present invention.

  Since the porous laminate of the present invention uses a polypropylene resin composition for the intermediate layer, it is characterized by having higher heat resistance than a conventional porous film made only of polyethylene resin. That is, the shape is maintained even when exposed to high temperatures. As a result, for example, when the porous laminate of the present invention is used as a battery separator, dimensional stability after shutdown can be ensured and the battery can be prevented from becoming unstable.

Hereinafter, embodiments of the present invention will be described.
First, FIG. 1 to FIG. 3 show first to third embodiments of a film-like resin porous laminate produced by the production method of the present invention described later. The porous laminates of the first to third embodiments are composed of porous laminates 1 (1-1, 1-2, 1-3) with different numbers of layers, all of which are the same manufacturing method described later. Manufacture.

The porous laminate 1 of the first embodiment shown in FIG. 1 has a three-layer structure, in which an intermediate layer 2 and a pair of both outer layers 3 and 4 positioned on the outer surfaces on both sides are laminated and integrated in the thickness direction. The intermediate layer 2 and both outer layers 3 and 4 have a large number of micro holes 2a, 3a and 4a, respectively, and these micro 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 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 laminated body of the second embodiment shown in FIG. 2 has a four-layer structure 1 and two intermediate layers 2 (2A, 2B), and both outer layers 3, 4 on both outer surfaces of the two intermediate layers 2. In the same manner as in the first embodiment, the micro holes 2a to 4a are communicated with each of these layers in the thickness direction.

  The porous laminate 1 of the third embodiment shown in FIG. 3 has a five-layer structure, and includes a central intermediate layer 5 made of the same composition as the outer layers 3 and 4 on both sides between two intermediate layers 2 (2A and 2B). In addition, both exteriors 3 and 4 are provided outside the intermediate layers 2A and 2B, and the micro holes 2a to 5a are communicated with each of the layers in the thickness direction as in the first embodiment.

  In the porous laminates 1 of the first to third embodiments, the outer layers 3 and 4 on both sides and the central intermediate layer 5 of the third embodiment are made of a thermoplastic resin containing a filler 7, and the intermediate layer 2 is a filler. It consists of a thermoplastic resin having a hard segment and a soft segment that do not contain.

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

The method for producing the porous laminate 1 is as follows:
A first step of producing a laminate by disposing an intermediate layer 2 made of a polypropylene resin composition between non-porous outer layers 3 and 4 made of a polypropylene resin composition in which a filler is blended with polypropylene;
A second step in which the laminate obtained in the step is impregnated with a fluid in a supercritical state or a subcritical state, and then released from the state to vaporize the fluid to make the intermediate layer porous;
After making the intermediate layer 2 porous, the laminate is stretched at least in a uniaxial direction to peel the interface between the fillers of the both-side outer layers 3 and 4 and the thermoplastic resin, and the non-porous both-side outer layers 3 and 4 are made porous. The third step.

The thermoplastic resin contained in the resin composition constituting the outer layers 3 and 4 on both sides has a density of 0.94 g / cm ³ or more, preferably 0.95 to 0.97 g / cm ³ and a melt flow rate of 1 g / cm ^3. High-density polyethylene that is 10 minutes or less is used.

An inorganic filler is used as the filler 7 included in the resin composition constituting the both outer layers 3 and 4. As the inorganic filler, barium sulfate, calcium carbonate, titanium oxide, or a combination of two or more thereof is used. In this embodiment, barium sulfate is used. The filler has an average particle size of 0.1 to 5 μm, preferably 0.1 to 3 μm.
The filler content is 50 to 300 parts by mass, preferably 50 to 150 parts by mass, with respect to 100 parts by mass of the thermoplastic resin.

The resin composition constituting the outer layers 3 and 4 on both sides preferably further contains hardened castor oil as a plasticizer. Hardened castor oil is an ester of a fatty acid mixture containing 12-hydroxyoctadecanoic acid as a main component and hydrogenated at a double bond portion of ricinoleic acid to form a saturated fatty acid. These esters include monoesters, diesters and triesters, which may be used alone or as a mixture. Especially, what has triester as a main component is preferable. Examples of fatty acids other than 12-hydroxyoctadecanoic acid contained in the fatty acid mixture include hexadecanoic acid or octadecanoic acid having about 12 to 22 carbon atoms. Such hydrogenated castor oil is industrially produced by hydrogenating castor oil, which is a non-drying oil.
The compounding amount of the plasticizer is 1 to 15 parts by mass, preferably 2 to 10 parts by mass with respect to 100 parts by mass of the thermoplastic resin constituting both outer layers.

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 content of the ethylene-propylene rubber is 5 to 95 parts by mass, 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 with respect to the entire polypropylene resin composition constituting the intermediate layer 2 is preferably 5 to 70% by mass, It is more preferably 5 to 50% by mass, and particularly preferably 10 to 30% by mass.

In the manufacturing method of the porous laminate 1, first, a laminate having a three-layer structure in which the intermediate layer 2 and both outer layers 3 and 4 described above are sandwiched between the two outer layers 3 and 4 sandwich the intermediate layer 2 is prepared. Yes. At this time, the ratio tr (= to / t) of the total to of the thicknesses of both outer layers to the thickness t of all the layers after the stretching treatment is adjusted to be 0.2 to 0.7.
Specifically, first, for both outer layers 3, 4, thermoplastic resin, filler and plasticizer are mixed with a powder mixer such as a Henschel mixer, and heated and kneaded with a uniaxial or biaxial kneader, a kneader, Once in pellets. Considering the dispersion state of the filler, it is more preferable to use a biaxial kneader. It is preferable to control the moisture content of the pellets 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.
The pellet of the resin composition which comprises the both-side outer layers 3 and 4 prepared as described above and the polypropylene resin composition which constitutes the intermediate layer 2 are laminated by three-layer coextrusion. 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.

Next, the laminate obtained in the first step is put in a pressure vessel, and carbon dioxide gas or nitrogen gas is sealed in the pressure vessel. The pressure in the pressure vessel is raised, and the carbon dioxide gas or nitrogen gas is in a supercritical state or a subcritical state. More specifically, when carbon dioxide gas is used, the pressure is increased to 7 Mpa or more, preferably 20 Mpa or more. When nitrogen gas is used, the pressure is increased to 3 Mpa or more, preferably 15 Mpa or more.
The temperature in the pressure vessel may be normal temperature, but may be heated.

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

Next, the laminated body obtained through the second step is subjected to stretching treatment to form micropores to make both outer layers 3 and 4 porous, so that micropores having communication with the micropores 2a of the intermediate layer 2 in the thickness direction are formed. A large number of porous laminates 1 are obtained.
In the stretching method, successive biaxial stretching is performed by stretching in the longitudinal direction (longitudinal direction) and then stretching in the transverse direction. The stretching ratio is 4 to 25 times, preferably 9 to 16 times in terms of area ratio, and the stretching temperature is 40 to 80 ° C.

  Furthermore, you may heat-process in order to provide thermal dimensional stability with respect to the porous laminated body 1 obtained as mentioned above as needed. 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. Moreover, it is also possible to divert the above-mentioned extending | stretching apparatus. 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.

The porous laminate 1 produced by the above-described method has an air permeability that is an index of communication property in the range of 50 to 5,000 seconds / 100 ml, preferably 100 to 5,000 seconds / 100 ml. The porosity is 30 to 70%, preferably 40 to 60%.
Furthermore, it has excellent heat resistance, and its thermal shrinkage rate is 20% or less, preferably 10% or less as an index. The heat shrinkage rate can be measured by the method described in the examples.

Moreover, the said porous laminated body 1 is made into a film form, and the average thickness is 1-250 micrometers, Preferably it is 50-150 micrometers. 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.
Further, the porous laminate 1 has a surface maximum height (Rmax) value of 2 μm or more, preferably 5 μm or more. When the maximum height value of the surface is 2 μm or more, moderate irregularities are present on the surface of the porous laminate 1, and the slipperiness of the porous body is increased. Although there is no restriction | limiting in particular about an upper limit, Usually, it is 7 micrometers or less. The maximum height of the surface is measured according to the method described in JIS B 0601.

Further, the porous laminate 1 has a mass per unit area (referred to as a weight) of 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 the said measurement, the ratio of the mass of the filler 7 with respect to the total mass of a porous laminated body, ie, the filler content, is 5-40 mass parts, Preferably it is 5-35 mass%.

The porous laminate 1 of the present invention can be used for various applications that require air permeability, and among them, it is preferably used as a battery separator.
When the porous laminate of the present invention is used as a battery separator, the air permeability is 50 to 500 seconds / 100 ml, preferably 100 to 300 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 becomes low and sufficient battery characteristics cannot be obtained.
The porosity is 30 to 70%, preferably 35 to 65%. This is because if the porosity is less than 30%, the ion permeability is low and it is difficult to obtain sufficient battery performance, and if the porosity exceeds 65%, it is not preferable from the viewpoint of battery safety.

Conventionally, a porous film mainly composed of a polyethylene resin is used as a battery separator because of the necessity of shutdown characteristics, but by itself, the dimensional stability after shutdown is poor, and the battery tends to be unstable.
Therefore, the porous laminate of the present invention has a heat shrinkage ratio, which is an index of heat resistance, of 0 to 20%, preferably 0 to 10%. This is because if the thermal contraction rate is greater than 20%, the positive electrode and the negative electrode may come into contact with each other at the end of the porous body, causing a short circuit.

Next, a nonaqueous electrolyte battery containing the porous laminate of the present invention as a battery separator will be described.
In the non-aqueous electrolyte battery, for example, a wound electrode body obtained by laminating and winding a strip-shaped negative electrode, a positive electrode, and a separator is housed in a battery can, an electrolyte is injected into the battery can, and a necessary member such as a lid is assembled. Formed.

The structure of the nonaqueous electrolyte battery of the present invention will be described in more detail 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.

  The wound body in which the positive electrode plate 21, the separator 10 and the negative electrode plate 22 are integrally wound is accommodated 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, for example, 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 these, an electrolyte in which lithium hexafluorophosphate (LiPF ₆ ) is dissolved at a rate of 1.4 mol / L in a solvent in which 2 parts by mass of methyl ethyl carbonate is mixed with 1 part by mass of ethylene carbonate is preferable.

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 It is said.

  As the positive electrode, for example, a metal oxide such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, vanadium pentoxide or chromium oxide, or a metal sulfide such as molybdenum disulfide is used as an active material. A mixture obtained by appropriately adding a conductive additive or a binder such as polytetrafluoroethylene to these positive electrode active materials is formed into a molded body using a current collecting material such as a stainless steel net as a core material. Used.

In this 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 and mixed in a mass ratio of 90: 5 with phosphorus-like graphite as a conductive additive, 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 1 to 5 and Comparative Examples 1 to 3 will be described.

Example 1
As a preparation of the resin composition constituting the outer layers on both sides, 100 parts by mass of high density polyethylene and 100 parts by mass of barium sulfate were blended and compounded. Subsequently, the compound is used as both outer layers on both sides, and a thermoplastic resin composition containing ethylene propylene rubber in polypropylene is used as the intermediate layer polypropylene resin composition, and the layer ratio is both outer layers 1 / intermediate layer / both outer layers 2 = While adjusting to 25/50/25, molding was performed at a temperature of 200 ° C. using a T-die for multilayer molding to obtain a laminate of two types and three layers.
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. Subsequently, the pressure was increased to 24 MPa to bring carbon dioxide into a subcritical state or a supercritical state. This state was maintained for 1 hour, and the laminate was impregnated with carbon dioxide in the subcritical state or the supercritical state. Thereafter, the pressure vessel valve was fully opened to release the pressure in the vessel.
The obtained laminate was stretched at a stretching temperature of 70 ° C. with a stretcher at a stretching ratio of 3 times in the longitudinal direction (longitudinal direction) and 3 times in the transverse direction, and then heat-set at 125 ° C. A laminate was obtained.

(Examples 2 to 5)
A porous laminate was obtained in the same manner as in Example 1, except that the composition of the resin composition constituting the outer layers on both sides, the layer ratio between the both outer layers and the intermediate layer, and the stretching conditions were changed as shown in Table 1.

(Comparative Examples 1 and 2)
A porous laminate was obtained in the same manner as in Example 1 except that the layer ratio between the outer layers on both sides and the intermediate layer was changed as shown in Table 1.

(Comparative Example 3)
For comparison of basis weight, an intermediate layer made of a polypropylene resin composition was not laminated, and a layer structure consisting only of a layer containing a filler was used.
That is, 100 parts by mass of high density polyethylene and 100 parts by mass of barium sulfate were blended and compounded. Next, the compound was molded at a temperature of 200 ° C. using a T-die for multilayer molding to obtain a raw sheet.
The obtained raw sheet is stretched at a stretching temperature of 70 ° C. with a stretcher at a stretching ratio of 3 times in the longitudinal direction (longitudinal direction) and 3 times in the transverse direction, and then heat-set at 120 ° C., A porous body was obtained.

The detail of the component described in the table | surface is shown below.
“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)
“B55”; barium sulfate (“B-55” manufactured by Sakai Chemical Co., Ltd., average particle size 0.66 μm)
“B54”; barium sulfate (“B-54” manufactured by Sakai Chemical Co., Ltd., average particle size 1.2 μm)
“HCOP”; hardened castor oil (“HCOP” manufactured by Toyokuni Oil Co., Ltd., 0.88 g / cm 3)
“Zelas 5013”; a polymerization type polypropylene resin composition containing ethylene-propylene rubber in a polypropylene homopolymer (“Zelas 5013” manufactured by Mitsubishi Chemical Corporation, density 0.88 g / cm ³ , melt flow rate 0.8 g / 10 minutes)

The following physical properties were measured for the porous laminates obtained in Examples 1 to 5 and Comparative Examples 1 to 3.
(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: Filler content)
The mass Wa of the porous body is measured, the resin is completely carbonized at a high temperature in a crucible, and the mass Wb of the remaining filler is measured.
Filler content (%) = (Wb / Wa) × 100
(Measurement 5; 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.

(Measurement 6; Rmax (surface irregularity))
The maximum height (Rmax) value of the porous laminate surface was measured according to the method described in JIS B 0601.
(Measurement 7; heat shrinkage (heat resistance))
The porous laminate is cut into 100 mm × 200 mm, wound around a 150 mm square glass plate, and only two sides with a width of 100 mm are fixed. At this time, a mark is put in a direction parallel to the two sides fixed to a half position of the length of 150 mm of the glass plate. Next, after leaving in an oven at 120 ° C. for 2 minutes and taking out from the oven, the width H1 of the marked portion is measured. The shrinkage rate S due to heat obtained by the following formula was used as an index of heat resistance.
Thermal contraction rate S (%) = {(100−H1) / 100} × 100

The results are shown in the table below.

In the porous laminate of Comparative Example 1, since the thickness of the intermediate layer was very large, the air permeability was very large, and the porosity was also small. This level of air permeability is not suitable for practical use as a battery separator or the like.
In the porous laminate of Comparative Example 2, since the thickness of the outer layers on both sides was very large, the basis weight was large and heavy.
Since the porous body of Comparative Example 3 has no intermediate layer, the heat resistance is not sufficient.
In contrast to these comparative examples, the porous laminates of the examples show a reliable air permeability with an air permeability of 480 to 3,700 seconds / 100 ml and a porosity of 48 to 55%, and are sufficiently suitable for practical use. Furthermore, since the filler is localized only on the surface, the surface is uneven and can exhibit excellent slipperiness, but the weighing is small and the weight can be reduced. In addition, since a polypropylene composition is used for the intermediate layer, it has high heat resistance and can retain its shape even when exposed to high temperatures.

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

It is a schematic sectional drawing of the porous laminated body of 1st embodiment. It is a schematic sectional drawing of the porous laminated body of 2nd embodiment. It is a schematic sectional drawing of the porous laminated body of 3rd embodiment. It is a partially broken perspective view of the non-aqueous electrolyte battery which accommodates the porous laminated body of this invention as a non-aqueous electrolyte battery separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous laminated 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 (11)

A method for producing a porous laminate in which a large number of micropores having communication in the thickness direction exist,
It consists of at least three layers of a double-sided outer layer composed of a resin composition containing at least a filler and a thermoplastic resin, and an intermediate layer containing no filler and composed of a polypropylene resin composition disposed between the both-sided outer layers, A step of producing a laminate in which the ratio tr (= to / t) of the total thickness of the outer layers on both sides to the thickness t of the layer is 0.05 to 0.95;
After impregnating the supercritical or subcritical fluid in the laminate produced in the above step, micropores are formed in the intermediate layer by releasing the supercritical or subcritical fluid and vaporizing the fluid. And making it porous,
A method of producing a porous laminate, comprising: forming a multilayered intermediate layer in the step, and then stretching the laminate to make the outer layers on both sides porous.   The method for producing a porous laminate according to claim 1, wherein the fluid is carbon dioxide or nitrogen.   It is a porous laminated body manufactured by the method of Claim 1 or Claim 2, Comprising: Air permeability is 1 to 10,000 second / 100ml, The porous laminated body characterized by the above-mentioned. It consists of a resin composition containing at least a filler and a thermoplastic resin, and both outer layers positioned on the outermost surface,
It is located between the outer layers on both sides, and is composed of a laminate of at least three layers including an intermediate layer made of a polypropylene resin composition that does not contain a filler, and
The ratio tr (= to / t) of the total to thickness of both outer layers to the thickness t of all layers of the laminate is 0.05 to 0.95, and
There are a large number of micropores communicating in the thickness direction in the outer layer and the intermediate layer on both sides,
A porous laminate having an air permeability of 1 to 10,000 seconds / 100 ml.   The porous laminate according to claim 3 or 4, wherein the filler is an inorganic filler.   The porous laminate according to any one of claims 3 to 5, wherein a content of the filler with respect to the entire porous laminate is 5 to 40% by mass.   The porous laminate according to any one of claims 3 to 6, wherein the filler has an average particle size of 0.01 to 25 µm.   The porous laminate according to any one of claims 3 to 7, wherein a plasticizer is contained in the resin composition constituting the outer layers on both sides. The mass per unit area is 10 to 25 g / m ² when converted into a thickness per 25 µm, with a heat shrinkage of 20% or less, a maximum surface height (Rmax) value of 2 µm or more, and 3 to 25 g / m ^2. 9. The porous laminate according to any one of 8 above.   A battery separator comprising the porous laminate according to any one of claims 3 to 9.   A battery containing the battery separator according to claim 10.

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