JP2016087944A - Laminated porous film, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated porous film which is improved in adhesion between a polyolefin resin porous film and a coating layer and is excellent in heat resistance and air permeability, and when used as a separator for a nonaqueous electrolyte secondary battery, has excellent characteristics.SOLUTION: The laminated porous film has a coating layer containing inorganic particles and a resin binder on at least one surface of a polyolefin resin porous film. The resin binder is a water-soluble resin having a weight-average molecular weight of 110,000 to 500,000 inclusive. There are also provided a separator for a nonaqueous electrolyte secondary battery using the film, and a nonaqueous electrolyte secondary battery using the separator for a nonaqueous electrolyte secondary battery.SELECTED DRAWING: None

Description

  INDUSTRIAL APPLICABILITY The present invention can be used as packaging, hygiene, livestock, agriculture, building, medical, separation membrane, light diffusion plate, battery separator, and particularly suitable as a separator for non-aqueous electrolyte secondary batteries. The present invention relates to a laminated porous film that can be used.

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

Secondary batteries are widely used as power sources for portable devices such as OA, FA, household electric appliances and communication devices. In particular, portable devices using lithium ion secondary batteries are increasing because they have a high volumetric efficiency when mounted on devices, leading to a reduction in size and weight of the devices.
On the other hand, large-sized secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Therefore, the use of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary battery, is expanding.

  The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1V to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages. As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of allowing more lithium ions to be present is used, and organic carbonate compounds such as propylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. It is used. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage, and a function of diffusing and holding the electrolyte. In order to satisfy these requirements, a porous film is used as the separator.

  With the recent increase in battery capacity, the importance of battery safety has increased. As a characteristic that contributes to the safety of the battery separator, there is a shutdown characteristic (hereinafter also referred to as “SD characteristic”). This SD characteristic is a function that can prevent a subsequent increase in temperature inside the battery because the micropores are blocked when the temperature is about 100 to 150 ° C., and as a result, ion conduction inside the battery is blocked. At this time, the lowest temperature among the temperatures at which the micropores of the porous film are blocked is referred to as a shutdown temperature (hereinafter also referred to as “SD temperature”). When used as a battery separator, it is necessary to have this SD characteristic.

  However, with the recent increase in energy density and capacity of lithium ion secondary batteries, the normal shutdown function does not function sufficiently, and the temperature inside the battery is the melting point of polyethylene used as a material for conventional separators. There is a possibility that the temperature exceeds about 0 ° C. and further rises, and both electrodes are short-circuited by a film breakage accompanying thermal contraction of the separator. Therefore, in order to ensure safety, the separator is required to have higher heat resistance than the current SD characteristics.

  In response to the above requirement, multilayer porous films (Patent Documents 1 to 5) having a porous layer containing a metal oxide and a resin binder on at least one surface of a polyolefin-based resin porous film have been proposed. In these inventions, since a coating layer that is highly filled with inorganic fine particles such as α-alumina is provided on the porous film, abnormal heat generation occurs, and even when the temperature continues to rise beyond the SD temperature, It is a method that can prevent a short circuit and is extremely safe.

JP 2004-227972 A JP 2008-186721 A International Publication No. 2008/149986 JP 2008-305783 A International Publication No. 2012/023199

  However, in the step of providing a coating layer in which inorganic fine particles such as α-alumina are highly filled on the porous film, there is a problem that the adhesion between the coating layer and the porous film is reduced due to segregation on the surface of the resin binder.

  The subject of this invention is solving the said problem. That is, when a coating layer is formed on a polyolefin resin porous film, an object is to obtain a laminated porous film having excellent adhesion between the polyolefin resin porous film and the coating layer.

As a result of intensive studies in view of the above problems, the present inventors have identified the resin binder in a laminated porous film having a coating layer containing inorganic particles and a resin binder on at least one side of the polyolefin resin porous film. In the case of a water-soluble resin having a weight average molecular weight in the range, it has been found that such a problem can be solved, and the present invention has been completed.
That is, the present invention relates to the following [1] to [8].

[1] A laminated porous film having a coating layer containing inorganic particles and a resin binder on at least one surface of a polyolefin resin porous film, wherein the resin binder has a weight average molecular weight of 110,000 or more and 500,000 or less. A laminated porous film characterized by being:
[2] The laminated porous film according to the above [1], wherein in the coating layer, the content of the inorganic particles with respect to the total amount of the inorganic particles and the resin binder is 80 to 99.9% by mass.
[3] The laminated porous film according to the above [1] or [2], wherein the inorganic particles comprise alumina.
[4] The laminated porous film according to any one of [1] to [3], wherein the polyolefin resin used for the polyolefin resin porous film is a polypropylene resin.
[5] The coating layer is formed by applying a coating liquid containing inorganic particles, a resin binder, and a dispersion medium onto the polyolefin resin porous film, and then removing the dispersion medium. The laminated porous film according to any one of [1] to [4] above.
[6] The laminated porous film according to [5], wherein the dispersion medium in the coating solution contains 50% by mass or more of water.
[7] A separator for a non-aqueous electrolyte secondary battery using the laminated porous film according to any one of [1] to [6].
[8] A nonaqueous electrolyte secondary battery using the separator for a nonaqueous electrolyte secondary battery according to [7].

  The laminated porous film of the present invention has improved adhesion between the polyolefin-based resin porous film and the coating layer, and is excellent in heat resistance and air permeability, and is preferably used as a separator for a non-aqueous electrolyte secondary battery. Can do.

It is a schematic sectional drawing of the battery which accommodates the lamination | stacking porous film of this invention. It is a figure explaining the measuring method of peeling strength.

Hereinafter, embodiments of the laminated porous film of the present invention will be described in detail.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. The content ratio of the components is not specified, but the main component includes 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100%) in the composition. It is.
In addition, when described as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably smaller than Y” together with the meaning of “X to Y” unless otherwise specified. Is included. In the present specification, it is possible to arbitrarily adopt provisions that are preferable, and it can be said that a combination of preferable ones is more preferable.

[Laminated porous film]
Below, each component which comprises the laminated porous film of this invention is demonstrated.

<Polyolefin resin porous film>
Examples of the polyolefin resin used for the polyolefin resin porous film include homopolymers or copolymers obtained by polymerizing α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. . Also, two or more of these homopolymers or copolymers can be mixed. Among these, it is preferable to use a polypropylene-based resin or a polyethylene-based resin, and it is particularly preferable to use a polypropylene-based resin from the viewpoint of maintaining the mechanical strength, heat resistance, and the like of the laminated porous film of the present invention.

(Polypropylene resin)
As the polypropylene resin used in the present invention, homopolypropylene (propylene homopolymer), propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or Examples thereof include random copolymers or block copolymers with α-olefins such as 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of maintaining the mechanical strength and heat resistance of the laminated porous film of the present invention.

As said polypropylene resin, the isotactic pentad fraction (mmmm fraction) which shows stereoregularity becomes like this. Preferably it is 80 to 99%, More preferably, it is 83 to 98%, More preferably, it is 85 to 97%. Things can be used. When the isotactic pentad fraction is not less than the lower limit, the mechanical strength of the film is improved. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at the present time, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
The isotactic pentad fraction (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Means the three-dimensional structure located at or its proportion.
The isotactic pentad fraction (mmmm fraction) was calculated based on the measurement result of ¹³ C-NMR. It conforms to Zambelli et al (Macromolecules 8,687, (1975)).

  Mw / Mn, which is a parameter indicating the molecular weight distribution of the polypropylene resin, is preferably 2.0 to 10.0, more preferably 2.0 to 8.0, and further preferably 2.0 to 6.0. preferable. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, when the Mw / Mn is within this range, the extrusion moldability is improved and the mechanical strength of the laminated porous film is also improved. Mw / Mn of polypropylene resin is measured by GPC (gel permeation chromatography) method.

The density of the polypropylene resin is preferably 0.890 to 0.970 g / cm ³ ,
More preferably ^{0.895~0.970g / cm 3, 0.900~0.970g / cm} 3 is more preferred. If the density is 0.890 g / cm ³ or more, it can have appropriate SD characteristics. On the other hand, if it is 0.970 g / cm ³ or less, it can have appropriate SD characteristics and can maintain stretchability.
The density of the polypropylene resin is measured according to JIS K7112 (1999) using a density gradient tube method.

The melt flow rate (MFR) of the polypropylene resin is not particularly limited, but is preferably 0.5 to 15 g / 10 minutes, more preferably 1.0 to 10 g / 10 minutes, and 1.5 to 8. 0 g / 10 min is more preferable, and 2.0 to 6.0 g / 10 min is particularly preferable. By setting the MFR to 0.5 g / 10 min or more, the melt viscosity of the resin during the molding process is high, and sufficient productivity can be ensured. On the other hand, the mechanical strength of the obtained laminated porous film can be sufficiently maintained by setting it to 15 g / 10 min or less.
The MFR of the polypropylene resin is measured under conditions of a temperature of 230 ° C. and a load of 2.16 kg according to JIS K7210 (1999).

  The method for producing the polypropylene resin is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst or a metallocene catalyst represented by a Ziegler-Natta type catalyst. And suspension polymerization method, melt polymerization method, bulk polymerization method, gas phase polymerization method, and bulk polymerization method using a radical initiator.

  Examples of the polypropylene-based resin include trade names “Novatech PP”, “WINTEC” (manufactured by Nippon Polypro Co., Ltd.), “Notio”, “Toughmer XR” (manufactured by Mitsui Chemicals, Inc.), “Zeras”, “Thermo Run” (above, manufactured by Mitsubishi Chemical Corporation), “Sumitomo Noblen”, “Tough Selenium” (above, manufactured by Sumitomo Chemical Co., Ltd.), “Prime Polypro”, “Prime TPO” (above, manufactured by Prime Polymer Co., Ltd.), Commercial products such as “Adflex”, “Adsyl”, “HMS-PP (PF814)” (manufactured by Sun Allomer Co., Ltd.), “Versify”, “Inspire” (manufactured by Dow Chemical Co., Ltd.) can be used. .

(Polyethylene resin)
Examples of the polyethylene resin used in the present invention include low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and a copolymer mainly composed of ethylene.
As a copolymer having ethylene as a main component, that is, ethylene and propylene,
Α-olefins having 3 to 10 carbon atoms such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene; vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate, Unsaturated carboxylic acid esters such as methyl methacrylate and ethyl methacrylate; a copolymer or multi-component copolymer with one or more comonomers selected from unsaturated compounds such as conjugated dienes and non-conjugated dienes, or a mixed composition thereof Things. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, one or more polyethylene resins selected from low density polyethylene, linear low density polyethylene, and high density polyethylene are preferable, and high density polyethylene is more preferable.

Density of the polyethylene-based resin is preferably 0.910~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, more preferably 0.940 to 0.970 g / cm ^3. If the density is 0.910 g / cm ³ or more, appropriate SD characteristics can be obtained. On the other hand, if it is 0.970 g / cm ³ or less, it can have appropriate SD characteristics, and stretchability is maintained.
The density of the polyethylene resin is measured according to JIS K7112 (1999) using a density gradient tube method.

The melt flow rate (MFR) of the polyethylene resin is not particularly limited, but is preferably 0.03 to 30 g / 10 minutes, and more preferably 0.3 to 10 g / 10 minutes. When the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, so that productivity is excellent. On the other hand, if it is 30 g / 10 minutes or less, sufficient mechanical strength can be obtained.
The MFR of the polyethylene resin is measured under conditions of a temperature of 190 ° C. and a load of 2.16 kg according to JIS K7210 (1999).

  The production method of the polyethylene resin is not particularly limited, and is a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. A polymerization method using a single site catalyst may be mentioned. Examples of the polymerization method for the polyethylene resin include one-stage polymerization, two-stage polymerization, and higher multistage polymerization. A polyethylene resin polymerized by any method can be used.

(Other ingredients)
In the present invention, in addition to the above-described resins, additives that are generally blended in the resin composition can be appropriately added to the polyolefin-based resin porous film as long as the effects of the present invention are not impaired. As the additive, recycled resin generated from trimming loss such as ears, which is added for the purpose of improving and adjusting the moldability, productivity and various physical properties of the polyolefin resin porous film; silica, talc, kaolin, Inorganic particles such as calcium carbonate; pigments such as carbon black; flame retardants; weather resistance stabilizers; heat stabilizers; antistatic agents; melt viscosity improvers; cross-linking agents; Additives such as an inhibitor; a light stabilizer; an ultraviolet absorber; a neutralizer; an antifogging agent; an antiblocking agent; a slip agent;
In addition, various resins and low molecular weight compounds such as wax may be added within a range that does not hinder the effects of the present invention in order to promote opening and impart moldability.

(Layer structure of polyolefin resin porous film)
In the present invention, the polyolefin resin porous film may be a single layer or a laminate, and is not particularly limited. For example, a single layer of the polyolefin resin-containing layer (hereinafter also referred to as “P layer”), the P layer and another layer (hereinafter also referred to as “Q layer”) as long as the function of the P layer is not hindered. Can be laminated. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low-melting point resin layer is laminated to ensure the safety of the battery by closing holes in a high-temperature atmosphere as described in JP-A No. 04-181651. Can be made.
Specific examples include a two-layer structure in which a P layer and a Q layer are stacked, a P layer, a Q layer, and a P layer, or a three-layer structure in which the Q layer, the P layer, and the Q layer are stacked. In addition, it is possible to form three or three layers in combination with layers having other functions. In this case, the stacking order with the layer having other functions is not particularly limited. Further, the number of layers may be increased as necessary to 4 layers, 5 layers, 6 layers, and 7 layers.
The physical properties of the polyolefin-based resin porous film used in the present invention are the layer configuration and lamination ratio
It can be freely adjusted according to the composition of each layer and the manufacturing method.

(Manufacturing method of polyolefin resin porous film)
Next, although the manufacturing method of the polyolefin resin porous film used for this invention is demonstrated, this invention is not limited only to the polyolefin resin porous film manufactured by this manufacturing method.

  Specifically, a polyolefin resin nonporous film-like material (hereinafter also referred to as “nonporous film-like material”) is produced by melt extrusion using the polyolefin resin, and the nonporous film-like material is stretched. As a result, it is possible to obtain a porous film in which a large number of fine pores having communication in the thickness direction are formed.

  The method for producing the non-porous film is not particularly limited, and a known method may be used. For example, a method of melting a thermoplastic resin composition using an extruder, extruding from a T die, and cooling and solidifying with a cast roll. Is mentioned. Moreover, the method of cutting open the nonporous film-like thing manufactured by the tubular method and making it planar can also be applied.

The method for making the nonporous film-like material is not particularly limited, and a known method such as wet uniaxial or more stretched porous or dry uniaxial or more stretched porous may be used. As the stretching method, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, a simultaneous biaxial stretching method, and the like, and these are used alone or in combination of two or more to perform uniaxial stretching. Among these, sequential biaxial stretching is preferable from the viewpoint of controlling the porous structure.
Moreover, the method of extracting and drying the plasticizer contained in the polyolefin-type resin composition with a solvent before and behind extending | stretching as needed is also applied.

In addition, when using a polypropylene resin for a polyolefin resin porous film, it is preferable to produce what is called (beta) crystal in the said nonporous film-like thing. If β-crystals are generated in the non-porous film-like material, even if no filler or other additive is used, fine pores can be easily formed by stretching, so it has excellent air permeability. A polyolefin resin porous film can be obtained.
As a method of generating β crystals in a non-porous film of a polypropylene resin, a method in which a substance that promotes the formation of α crystals of the polypropylene resin is not added, or as described in Japanese Patent No. 3739481 And a method of adding polypropylene subjected to a treatment for generating peroxide radicals, a method of adding a β crystal nucleating agent to the composition, and the like.

(Β crystal nucleating agent)
Examples of the β crystal nucleating agent include those shown below, but the β crystal nucleating agent is not particularly limited as long as it increases the formation and growth of β crystals of the polypropylene resin, and a mixture of two or more types is used. Also good.
Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by, for example; a two-component compound comprising component A which is an organic dibasic acid and a component B which is an oxide, hydroxide or salt of a Group 2 metal in the periodic table; a cyclic phosphorus compound; Composition composed of magnesium compounds And the like. In addition, specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A No. 08-144122, and JP-A No. 09-194650.

  Examples of commercially available products of β crystal nucleating agent include β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of polypropylene resins to which β crystal nucleating agent is added include polypropylene “ Bepol B-022SP ”, polypropylene manufactured by Borealis“ Beta (β) -PP BE60-7032 ”, polypropylene manufactured by Mayzo“ BNX BETAPP-LN ”, and the like.

The ratio of the β crystal nucleating agent added to the polypropylene resin needs to be appropriately adjusted depending on the type of the β crystal nucleating agent or the composition of the polyolefin resin, but the polypropylene resin constituting the polyolefin resin porous film. It is preferable that it is 0.0001-5 mass parts with respect to 100 mass parts of resin, 0.001-3 mass parts is more preferable, 0.01-1 mass part is still more preferable, 0.1-0.8 mass Part is particularly preferred.
If the proportion of the β crystal nucleating agent is 0.0001 parts by mass or more with respect to 100 parts by mass of the polypropylene resin, the β crystals of the polyolefin resin can be sufficiently produced and grown at the time of production. Even when used as a separator for a secondary battery, sufficient β crystal activity can be secured, and desired air permeability can be obtained. Moreover, if the ratio of the β crystal nucleating agent is 5 parts by mass or less with respect to 100 parts by mass of the polypropylene resin, the balance between the production cost and the obtained effect is excellent, and the β crystal nucleating agent on the surface of the polyolefin resin porous film. No bleed or the like is preferable.

In the present invention, the polyolefin resin porous film is a two-layer structure in which the P layer and the Q layer are laminated as described above, a three-layer structure in which the P layer, the Q layer, the P layer, etc. are laminated, or a structure having four or more layers. In this case, the manufacturing method is roughly classified into the following three types according to the order of porosity and lamination.
(I) A method in which each layer is made porous, and then the layers made porous are laminated or bonded with an adhesive or the like.
(Ii) A method of laminating each layer to produce a laminated nonporous film-like material and then making the nonporous film-like material porous.
(Iii) A method in which one of the layers is made porous and then laminated with another layer of a non-porous film to make it porous.
In the present invention, it is preferable to use the method (ii) from the viewpoint of the simplicity of the process and productivity, and in particular, in order to ensure the interlayer adhesion between the two layers, a laminated nonporous film-like material is obtained by coextrusion. A method of forming a porous layer after preparing is particularly preferable.

Below, the suitable manufacturing method of a polyolefin resin porous film is demonstrated.
First, a resin composition containing a polyolefin resin and other thermoplastic resins and additives used as necessary is produced. For example, after mixing raw materials such as polypropylene resin, β crystal nucleating agent, and other additives as desired, preferably using a Henschel mixer, a super mixer, a tumbler mixer, etc., or in a container such as a bag. After mixing the ingredients and mixing by hand blending, after melt-kneading with a single-screw extruder, twin-screw extruder, kneader, etc., preferably a twin-screw extruder, the strand extruded in the molten state is cooled by water cooling, air cooling, etc. Cut with a pelletizer to obtain pellets. In this way, a pellet-shaped resin composition can be produced.

Next, the pellets are put into a film forming extruder and extruded from a T-die extrusion die to form a non-porous film. The type of T die is not particularly limited. For example, when the polyolefin resin porous film of the present invention has a laminated structure of two types and three layers, the T die may be a multi-manifold type for two types and three layers or a feed block type for two types and three layers.
The gap of the T die to be used is finally determined from the required film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, 0.5 -1.0 mm is preferred. The production speed can be improved by setting the gap of the T die to 0.1 mm or more. Moreover, since draft rate does not become large too much by setting it as 3.0 mm or less, production stability can be improved.

In the extrusion molding, the extrusion temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 180 to 350 ° C, more preferably 200 to 330 ° C, and further preferably 220 to 300 ° C. A temperature of 180 ° C. or higher is preferable because the viscosity of the molten resin is sufficiently low and the moldability is excellent and the productivity is improved. On the other hand, by setting the temperature to 350 ° C. or lower, it is possible to suppress the deterioration of the resin composition, and hence the mechanical strength of the laminated porous film obtained.
The β crystal ratio of the polypropylene resin in the nonporous film can also be adjusted by the cooling and solidification temperature by the cast roll. The cooling and solidifying temperature is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. By setting the cooling and solidification temperature to 80 ° C. or higher, the ratio of β crystals in the nonporous film can be sufficiently increased. Further, when the temperature is set to 150 ° C. or lower, troubles such as the molten resin extruded and sticking to the cast roll hardly occur, and it becomes possible to efficiently form a nonporous film-like film.

  Next, the obtained nonporous film-like film can be made porous by stretching. As the stretching step, it is more preferable to perform at least biaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching, but the stretching conditions (stretching ratio, stretching temperature) can be easily selected in each stretching step, and the porous structure is controlled. Easy sequential biaxial stretching is more preferable. In the present invention, the longitudinal direction of the nonporous film is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”. In addition, stretching in the longitudinal direction is referred to as “longitudinal stretching”, and stretching in the direction perpendicular to the longitudinal direction is referred to as “lateral stretching”.

When performing sequential biaxial stretching, the stretching temperature may be appropriately changed depending on the composition of the resin composition to be used, the crystal melting peak temperature, the crystallinity, etc., but the stretching temperature in the longitudinal stretching is preferably 0 to 130 ° C. 10-120 degreeC is more preferable, and 20-110 degreeC is still more preferable. In addition, the longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, and still more preferably 4 to 7 times.
By performing longitudinal stretching within the above range, an appropriate pore starting point can be expressed while suppressing breakage during stretching, and a nonporous film-like film can be made porous.
On the other hand, the stretching temperature in transverse stretching is preferably 100 to 170 ° C, more preferably 110 to 160 ° C, and still more preferably 120 to 155 ° C. Further, the transverse draw ratio is preferably 1.2 to 10 times, more preferably 1.5 to 8 times, and further preferably 2 to 7 times.
By transversely stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded, and a fine porous structure can be expressed.
The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and still more preferably 2500 to 8000% / min.

The polyolefin resin porous film thus obtained is preferably subjected to heat treatment for the purpose of improving dimensional stability. At this time, the heat treatment temperature is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and still more preferably 140 ° C. or higher. If the heat treatment temperature is 100 ° C. or higher, dimensional stability can be improved. On the other hand, the heat treatment temperature is preferably 170 ° C. or lower, more preferably 165 ° C. or lower, and further preferably 160 ° C. or lower. When the heat treatment temperature is 170 ° C. or lower, the polyolefin resin is hardly melted by the heat treatment, and the porous structure can be maintained well.
In the present invention, heat treatment for the purpose of improving dimensional stability may be referred to as “heat setting”.
Moreover, you may perform a 1-20% relaxation process as needed during the heat processing process. After the heat treatment, a polyolefin resin porous film is obtained by uniformly cooling and winding up.

  Moreover, for the purpose of improving interlayer adhesion, it is preferable to subject the surface of the polyolefin resin porous film to surface treatment such as corona treatment, plasma treatment, and chemical oxidation treatment. The surface treatment step may be after the extrusion molding step, after the longitudinal stretching step, or after the transverse stretching step in the production process of the polyolefin resin porous film. May be. Among these, from the viewpoint of shortening the production line and improving productivity, it is preferable to be after the transverse stretching step.

<Coating layer>
The laminated porous film of the present invention has a coating layer containing inorganic particles and a resin binder on at least one surface of a polyolefin resin porous film.

(Inorganic particles)
Examples of inorganic particles that can be used in the present invention include metal carbonates such as calcium carbonate, magnesium carbonate, and barium carbonate; metal sulfates such as calcium sulfate, magnesium sulfate, and barium sulfate; calcium fluoride, magnesium fluoride, and the like. Metal hydroxides such as aluminum hydroxide and magnesium hydroxide; metal oxides such as alumina, calcia, magnesia, titania, zinc oxide and silica; clay minerals such as talc, clay and mica; and titanium Examples include barium acid. Among these, it is preferable to contain barium sulfate or alumina from the viewpoint of being chemically inert when incorporated in a battery.

The lower limit of the average particle size of the inorganic particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, and still more preferably 0.2 μm or more. On the other hand, the upper limit is preferably 3.0 μm or less, more preferably 1.5 μm or less. By setting the average particle size to 0.01 μm or more, the laminated porous film of the present invention can exhibit sufficient heat resistance. Moreover, the dispersibility of the inorganic particle in the coating liquid used when forming the said coating layer and a coating layer improves by making the said average particle diameter into 3.0 micrometers or less.
In the present embodiment, the “average particle diameter of inorganic particles” refers to a two-dimensional projection image when the inorganic particles are projected from an arbitrary direction (direction Z) using, for example, an image analyzer. The average value of the minor axis and the major axis of the two-dimensional projection image when the inorganic particles are projected from an arbitrary direction orthogonal to the direction Z (referred to as direction X). Are calculated as an average value. The number of inorganic particles used for calculation may be 50 or more.

The specific surface area of the inorganic particles is preferably 5 m ² / g or more and less than 15 m ² / g. When the specific surface area is 5 m ² / g or more, when the laminated porous film of the present invention is incorporated as a separator in a non-aqueous electrolyte secondary battery, the penetration of the electrolyte solution becomes fast, and the productivity is improved. Moreover, if a specific surface area is less than 15 m < ² > / g, adsorption | suction of an electrolyte component will be suppressed when the laminated porous film of this invention is integrated in a nonaqueous electrolyte secondary battery as a separator.
In the present embodiment, “specific surface area of inorganic particles” is a value measured by a constant volume gas adsorption method.

  In the coating layer, the content of the inorganic particles with respect to the total amount of the inorganic particles and the resin binder is preferably 80 to 99.9% by mass. As for the content rate of an inorganic particle, 92 mass% or more is more preferable, 95 mass% or more is still more preferable, 98 mass% or more is especially preferable. When the content of the inorganic particles is within this range, the coating layer can maintain excellent air permeability, and while maintaining the adhesion between the polyolefin resin porous film and the coating layer, In this case, the heat resistance can be improved.

(Resin binder)
The resin binder used in the present invention can satisfactorily adhere the inorganic particles and the polyolefin resin porous film, is electrochemically stable, and uses the laminated porous film as a separator for a nonaqueous electrolyte secondary battery. In some cases, a water-soluble resin that is stable with respect to the organic electrolyte is used. Here, the water-soluble resin refers to a resin having a solubility in 100 g of water at 20 ° C. of 0.1 g or more. Specific examples of the water-soluble resin used in the present invention include (meth) acrylic acid derivatives such as polyacrylic acid, poly-2-hydroxyethyl acrylate, poly-2-hydroxyethyl methacrylate, and polyacrylamide; hydroxyethyl cellulose , Cellulose derivatives such as carboxymethyl cellulose; polyvinyl alcohol derivatives such as polyvinyl alcohol, polyvinyl formal, and polyvinyl butyral; polyvinyl amide derivatives such as polyvinyl pyrrolidone and polyvinyl acetamide; polyether derivatives such as polyethylene oxide and polypropylene oxide; and copolymers thereof Is mentioned. Among these, carboxymethyl cellulose and polyvinyl alcohol are more preferable because of their high stability with respect to organic electrolytes.

(Weight average molecular weight of resin binder)
The weight average molecular weight of the water-soluble resin used as the resin binder in the present invention needs to be 110,000 or more and 500,000 or less. The weight average molecular weight of the water-soluble resin is preferably 130,000 or more and 400,000 or less, and more preferably 150,000 or more and 300,000 or less. When the weight average molecular weight is 110,000 or more, a laminated porous film having good adhesion is obtained, and when the weight average molecular weight is 500,000 or less, the viscosity at the time of forming the coating layer is reduced, and film formation There is an effect of excellent stability.
The weight average molecular weight of the water-soluble resin can be determined by, for example, measurement by GPC method or calculation from the average degree of polymerization measured in advance.

<Method for forming coating layer>
Examples of the method for forming the coating layer in the laminated porous film of the present invention include a co-extrusion method, a laminating method, and a coating and drying method. In terms of continuous productivity, the coating layer is formed by a coating and drying method using a coating solution. It is preferable.

<Coating fluid>
In order to form the coating layer of the laminated porous film of the present invention, a coating liquid containing the inorganic particles, the resin binder and a dispersion medium is preferably used.

(Dispersion medium)
As the dispersion medium used in the coating liquid, it is preferable to use a dispersion medium in which the inorganic particles are dispersed in an appropriately uniform and stable manner and the resin binder can be dissolved or dispersed in an appropriately uniform and stable manner.
Examples of such a dispersion medium include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, dioxane, acetonitrile, alcohol having 1 to 4 carbon atoms, glycols, glycerin, and lactic acid ester. Etc. As C1-C4 alcohol, C1-C4 monohydric alcohol is preferable, and 1 or more types chosen from methanol, ethanol, and isopropyl alcohol are more preferable. In the present invention, when water is used as the dispersion medium, the content of water in the dispersion medium is preferably 50% by mass or more, more preferably 70% by mass or more from the viewpoint of improving the viscosity stability of the coating liquid. 80 mass% or more is more preferable, and 90 mass% or more is still more preferable.
Among these dispersion media, water or a mixed dispersion medium of water and an alcohol having 1 to 4 carbon atoms is preferable in terms of cost and environmental load, and mixed dispersion of water and a monovalent alcohol having 1 to 4 carbon atoms. A medium is more preferable, and a mixed dispersion medium of water and isopropyl alcohol is more preferable.

(Acid component)
It is desirable that the coating liquid used for forming the coating layer in the present invention contains an acid component. In the laminated porous film of the present invention, the acid component may remain in the coating layer as an acid itself, or may remain as a salt formed by reacting with an alkaline impurity in the coating layer.

The acid component preferably has a first acid dissociation constant (pK _a1 ) of 5 or less in a dilute aqueous solution at 25 ° C. and no second acid dissociation constant (pK _a2 ) or 7 or more. Examples of acid components having such characteristics include lower primary carboxylic acids such as formic acid, acetic acid, propionic acid, and acrylic acid; nitro acids such as nitric acid and nitrous acid; and halogens such as perchloric acid and hypochlorous acid. Oxo acids; Halogenated ions such as hydrochloric acid, hydrofluoric acid, hydrobromic acid; phosphoric acid, salicylic acid, glycolic acid, lactic acid, ascorbic acid, erythorbic acid, and the like. Among these, formic acid, acetic acid, nitric acid, hydrochloric acid, and phosphoric acid are preferable from the viewpoint that pH can be lowered by adding a small amount, availability, and acid stability are high.

The coating liquid preferably contains 10 to 10,000 ppm by mass of the acid component. As for content of the said acid component, it is more preferable that they are 100 mass ppm or more and 9000 mass ppm or less, and it is still more preferable that they are 150 mass ppm or more and 8000 mass ppm or less.
If content is 10 mass ppm or more, the aggregation of an alumina can be suppressed, the pot life of the coating liquid used for formation of a coating layer can be improved, and the coating film excellent in uniformity will be obtained. Moreover, if content is 10,000 mass ppm or less, it will not have a bad influence on the performance of a nonaqueous electrolyte secondary battery.

  In the method for forming a coating layer using a coating solution, the coating solution described above is used. In producing the coating liquid, it is necessary to uniformly disperse the inorganic particles in the dispersion medium. Examples of the method for dispersing the inorganic particles in the dispersion medium include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, and a sand mill. , Colloid mill, attritor, roll mill, high-speed impeller dispersion, disperser, homogenizer, high-speed impact mill, ultrasonic dispersion, mechanical stirring method using stirring blades, etc. to uniformly disperse inorganic particles in the dispersion medium Can do. The resin binder may be dissolved or dispersed at the same time when the inorganic particles are dispersed.

  In order to improve the suspension stability of the coating liquid and optimize the viscosity of the coating liquid when producing the coating liquid by dispersing the inorganic particles and the resin binder in a dispersion medium, a dispersion aid is used. Stabilizers, thickeners and the like may be added before and after that.

  The step of applying the coating liquid to the surface of the polyolefin resin porous film may be after extrusion of the nonporous film-like film and before stretching or after the longitudinal stretching step. However, it may be after the transverse stretching step, but is preferably applied after the transverse stretching step from the viewpoint of forming a more uniform coating layer.

(Method of forming a coating layer using a coating solution)
The coating layer is formed by applying a coating liquid containing inorganic particles, a resin binder, a dispersion medium, and an acid component used as necessary on the polyolefin resin porous film, and then removing the dispersion medium. It has been made.
The application method in the application step is not particularly limited as long as the required layer thickness and application area can be realized. Examples of such coating methods include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod Examples include a coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method. Moreover, the said coating liquid may be apply | coated only to the single side | surface of a polyolefin resin porous film in light of the use, and may be applied to both surfaces.

  After the coating liquid is applied to the surface of the polyolefin resin porous film, a coating layer can be formed on the surface of the polyolefin resin porous film by removing the dispersion medium in the applied coating liquid. . As a method for removing the dispersion medium in the coating liquid, any method that does not adversely affect the polyolefin resin porous film can be adopted without any particular limitation. For example, the polyolefin resin porous film is fixed. Examples thereof include a method of drying at a temperature below the melting point, a method of drying under reduced pressure at a low temperature, a method of immersing in a poor solvent for the resin binder to solidify the resin binder and simultaneously extracting the dispersion medium.

<Shape and physical properties of laminated porous film>
(Thickness)
The thickness of the laminated porous film of the present invention is preferably 5 to 100 μm. More preferably, it is 8-50 micrometers, More preferably, it is 10-30 micrometers. If the thickness is 5 μm or more, when used as a separator for a non-aqueous electrolyte secondary battery, substantially necessary electrical insulation can be obtained, for example, even when a large force is applied to the protruding portion of the electrode, It breaks through the separator for non-aqueous electrolyte secondary batteries and is not easily short-circuited, resulting in excellent safety. Moreover, since the electrical resistance of a laminated porous film can be made small if thickness is 100 micrometers or less, the performance of a battery can fully be ensured.

  The thickness of the coating layer is preferably 0.5 μm or more, more preferably 1 μm or more, still more preferably 2 μm or more, and particularly preferably 3 μm or more from the viewpoint of heat resistance. On the other hand, the upper limit is preferably 90 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, and particularly preferably 10 μm or less from the viewpoint of communication.

(Porosity)
In the laminated porous film of the present invention, the porosity is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more. If the porosity is 30% or more, it is possible to obtain a laminated porous film that ensures communication and has excellent air permeability.
On the other hand, the upper limit is preferably 70% or less, more preferably 65% or less, and still more preferably 60% or less. If the porosity is 70% or less, the strength of the laminated porous film can be sufficiently maintained, which is preferable from the viewpoint of handling.

(Air permeability)
The air permeability of the laminated porous film of the present invention is preferably 1000 seconds / 100 mL or less, more preferably 10 to 800 seconds / 100 mL, still more preferably 50 to 500 seconds / 100 mL. An air permeability of 1000 seconds / 100 mL or less is preferable because the laminated porous film can be communicated and can exhibit excellent air permeability.
The air permeability represents the ease of passage of air in the film thickness direction, and is specifically expressed as the time required for 100 mL of air to pass through the film. Therefore, it means that the smaller the numerical value is, the easier it is to pass through, and the higher numerical value is, the more difficult it is to pass. That is, a smaller value means better communication in the thickness direction of the film, and a larger value means poor communication in the film thickness direction. Communication is the degree of connection of holes in the film thickness direction. If the air permeability of the laminated porous film of the present invention is low, it can be used for various applications. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low air permeability means that lithium ions can be easily transferred, which is preferable because battery performance is excellent.

  The laminated porous film of the present invention preferably has SD characteristics when used as a battery separator. Specifically, the air permeability after heating at 135 ° C. for 5 seconds is preferably 10,000 seconds / 100 mL or more, more preferably 25000 seconds / 100 mL or more, and further preferably 50000 seconds / 100 mL or more. By setting the air permeability after heating at 135 ° C for 5 seconds to 10000 seconds / 100 mL or more, the holes are quickly closed and the current is interrupted during abnormal heat generation, thus avoiding problems such as battery rupture. be able to.

(Shrinkage factor)
The shrinkage rate at 130 ° C. of the laminated porous film of the present invention is preferably less than 10%, more preferably less than 9%, and even more preferably less than 8% in both the longitudinal direction and the transverse direction. If the shrinkage rate at 130 ° C. is less than 10%, even when abnormal heat is generated exceeding the SD temperature, it is suggested that the dimensional stability is good and the heat resistance is maintained, and the film breakage is prevented and the internal short circuit is prevented. The temperature can be improved. Although it does not specifically limit as a minimum, 0% or more is more preferable.
The shrinkage rate of the laminated porous film is measured by the method described in Examples described later.

(Adhesion)
The laminated porous film of the present invention is excellent in the adhesion between the polyolefin resin porous film and the coating layer. The adhesiveness of the coating layer can be evaluated by the peel strength measured by the method described in the examples below, and the higher the peel strength, the better the film.
The peel strength is preferably 3.5 N / 18 mm or more from the viewpoint of reducing film transportation troubles and appearance defects, and more preferably 3.7 N / 18 mm or more. The upper limit is not particularly limited and is ideally 20 N / 18 mm or less, but practically, it is preferably 10 N / 18 mm or less.

[Nonaqueous electrolyte secondary battery]
Next, a nonaqueous electrolyte secondary battery containing the laminated porous film of the present invention as a separator for a nonaqueous electrolyte secondary battery 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 battery separator 10, and the outside is stopped with a winding tape to form a wound body.
The winding process will be described in detail. One end of the battery separator is passed between the slit portions of the pin, and the pin is slightly rotated to wind one end of the battery separator around the pin. At this time, the surface of the pin is in contact with the coating layer of the battery separator. Thereafter, the positive electrode and the negative electrode are arranged so as to sandwich the battery separator, and the pins are rotated by a winding machine to wind the positive and negative electrodes and the battery separator. After winding, the pin is pulled out of the wound object.

  A wound body in which the positive electrode plate 21, the battery 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 battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed. A cylindrical non-aqueous electrolyte secondary battery is produced.

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, but 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 1.0 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.

  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.

  Examples and Comparative Examples are shown below, and the laminated porous film of the present invention will be described in more detail. However, the present invention is not limited to these. The longitudinal direction of the laminated porous film is referred to as “longitudinal direction”, and the direction perpendicular to the longitudinal direction is referred to as “lateral direction”.

<Evaluation method>
(1) Weight average molecular weight of resin binder For polyvinyl alcohol, the average degree of polymerization was measured and calculated based on JIS K6726 (1994).
For sodium carboxymethylcellulose, the intrinsic viscosity [η] was determined by an Ubbelohde viscometer using a 0.1 N normal NaCl aqueous solution as a solvent, and the average degree of polymerization was calculated by the following equation.
Average degree of polymerization = η / (16.6 × Km) Km: Degree of etherification Using this average degree of polymerization, the weight average molecular weight was calculated by the following conversion formula.
Weight average molecular weight = Average degree of polymerization × Molecular weight of repeating unit

(2) Total Thickness of Laminated Porous Film The total thickness of the laminated porous film was calculated as an average value of five in-plane measurements of the laminated porous film with a 1/1000 mm dial gauge.

(3) Coating Layer Thickness The coating layer thickness was calculated as the difference between the total thickness of the laminated porous film after the coating layer was formed and the polyolefin resin porous film thickness.

(4) Air permeability (Gurley value)
The air permeability was measured according to JIS P8117 (2009).

(5) Shrinkage at 130 ° C. First, the laminated porous films prepared in Examples and Comparative Examples were cut into a size of 150 mm in length × 10 mm in width, and a sample was prepared by placing two dots at 100 mm intervals in the length direction. did. Next, the sample was placed in an oven set at 130 ° C. (“Tabai Gear Oven GPH200” manufactured by Tabai Espec Co., Ltd.) and allowed to stand for 1 hour. After the sample was taken out of the oven and cooled, the length was measured, and the shrinkage was calculated by the following formula.
Shrinkage rate (%) = {(100−length after heating) / 100} × 100
The above measurements were performed for the longitudinal direction and the lateral direction of the laminated porous film, respectively.

(6) Heat resistance Heat resistance was evaluated according to the following evaluation criteria.
◯: When the shrinkage rate at 130 ° C. for 1 hour is less than 3% in both the vertical and horizontal directions.
X: When the shrinkage rate at 130 ° C. for 1 hour is 3% or more in either the vertical direction or the horizontal direction.

(7) Peel strength (adhesion)
About the produced laminated porous film, the peel strength between the polyolefin resin porous film and the coating layer was measured according to JIS Z0237 (2009).
First, the laminated porous film is cut into a width of 50 mm and a length of 150 mm to form a sample, and a cellophane tape (manufactured by Nichiban Co., Ltd., JIS Z1522, width: 18 mm) is attached as the tape 42 (FIG. 2) in the vertical direction of the sample. The cellophane tape was folded back at 180 ° so that the surfaces opposite to the adhesive surface overlapped, and the sample was peeled off by 25 mm.
Next, fix one end of the peeled portion of the sample to the lower chuck of a tensile tester (manufactured by Intesco Corporation, Intesco IM-20ST), fix the cellophane tape to the upper chuck, and pull at a test speed of 300 mm / min. The peel strength was measured (FIG. 2). After the measurement, the first measurement value of 25 mm length was ignored, and the 50 mm length peel strength measurement value peeled off from the test piece was averaged to give the peel strength. It shows that the adhesiveness of a polyolefin resin porous film and a coating layer is so high that this figure is large.

<Examples and comparative examples>
(Preparation of polyolefin resin porous film)
Polypropylene resin (“Novatec PP FY6HA” manufactured by Nippon Polypro Co., Ltd., density: 0.90 g / cm ³ , MFR: 2.4 g / 10 min) and 3,9-bis [4- ( N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane was prepared. Each raw material is blended at a ratio of 0.2 part by mass of β-crystal nucleating agent with respect to 100 parts by mass of this polypropylene resin, and the same direction twin screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber: 40 mmφ, L / D : 32), melted and mixed at a set temperature of 300 ° C., cooled and solidified the strands in a water tank, cut the strands with a pelletizer, and produced raw material pellets.

The raw material pellets were again put into an extruder, melted, extruded from a T die, and cooled and solidified with a 127 ° C. casting roll to produce a film-like material.
The film-like material was stretched 4.6 times in the longitudinal direction at 105 ° C. using a longitudinal stretching machine, then stretched twice in the transverse direction at 150 ° C. with a transverse stretching machine, and then heat-set / relaxed at 153 ° C. Processed. Subsequently, relaxation treatment was performed, and further, a generator CP1 manufactured by VETAPHONE was used to perform corona surface treatment at an output of 0.4 kW and a speed of 10 m / min, thereby obtaining a polyolefin resin porous film having a thickness of 20 μm.

[Example 1]
Alumina (“LS-410” manufactured by Nippon Light Metal Co., Ltd., specific surface area: 7.3 m ² / g, average particle diameter: 0.5 μm) 52.6 parts by mass, 5.3 parts by mass of isopropyl alcohol, 42.1 ion-exchanged water Mass parts were mixed and subjected to bead mill treatment to obtain an alumina slurry. The conditions of the used bead mill were as follows.
Apparatus: “NVM-1.5” manufactured by Imex Corporation
Beads: Diameter 0.5mm Made of zirconia Filling rate 85%
Peripheral speed: 10m / sec
Discharge rate: 350mL / min
After the obtained alumina slurry was allowed to stand for 1 week, 61.8 parts by mass of the alumina slurry, 5% by weight polyvinyl alcohol (“JC-40” manufactured by Nihon Acetate / Poval Co., Ltd., average degree of polymerization: 4000, weight average molecular weight) : 176,000) 9.9 parts by mass of an aqueous solution and 28.3 parts by mass of ion-exchanged water were mixed, and hydrochloric acid was added to a total mass of 170 mass ppm, whereby a coating solution with a solid content concentration of 33 mass% was added. Got.
The obtained coating solution was applied to the corona-treated surface of the polyolefin resin porous film using a # 12 number bar coater, and then dried in a drying furnace at 60 ° C. for 2 minutes. The physical property evaluation of the obtained laminated porous film was performed. The results are shown in Table 1.

[Example 2]
The alumina slurry obtained in the same manner as in Example 1 was allowed to stand for 1 week, and then an aqueous solution 9.9 of 61.8 parts by mass of alumina slurry and 5% by mass of sodium carboxymethyl cellulose (manufactured by Nacalai Tesque, Inc., molecular weight: 220,000). Mass parts, 23.3 parts by mass of ion-exchanged water, and 5 parts by mass of isopropyl alcohol were mixed to obtain a coating solution.
The obtained coating solution was applied to the corona-treated surface of the polyolefin resin porous film using a # 12 number bar coater, and then dried in a drying furnace at 60 ° C. for 2 minutes. The physical properties of the obtained laminated porous film were evaluated, and the results are shown in Table 1.

[Comparative Example 1]
A laminated porous film was obtained in the same manner as in Example 1 except that polyvinyl alcohol was changed to one having an average degree of polymerization of 2000 and a weight average molecular weight of 88,000 (manufactured by Nacalai Tesque).
The physical property evaluation of the obtained laminated porous film was performed. The results are shown in Table 1.

[Comparative Example 2]
A laminated porous film was obtained in the same manner as in Example 1 except that polyvinyl alcohol was changed to one having an average degree of polymerization of 200 and a weight average molecular weight of 8800 ("JMR-10HH" manufactured by Nippon Vinegar Poval Co., Ltd.). .
The physical property evaluation of the obtained laminated porous film was performed. The results are shown in Table 1.

[Comparative Example 3]
A laminated porous film was obtained in the same manner as in Example 2 except that sodium carboxymethylcellulose was changed to one having a weight average molecular weight of 69,000 (“Sunrose F01MC” manufactured by Nippon Paper Chemical Co., Ltd.).
The physical properties of the obtained laminated porous film were evaluated, and the results are shown in Table 1.

[Comparative Example 4]
The physical properties of the polyolefin resin porous film were evaluated, and the results are shown in Table 1.

As is clear from Table 1, the laminated porous film obtained in the examples had a high peel strength between the polyolefin resin porous film and the coating layer, and had high adhesion.
On the other hand, the laminated porous films obtained in Comparative Examples 1 to 3 were low in peel strength between the polyolefin resin porous film and the coating layer and low in adhesion.
The polyolefin resin porous film of Comparative Example 4 had insufficient heat resistance because the coating layer was not laminated.

  The laminated porous film of the present invention can be applied to various uses that require air permeability. Specifically, separators for lithium ion secondary batteries; sanitary materials such as disposable paper diapers and sanitary pads for absorbing body fluids or bed sheets; medical materials such as surgical clothing or base materials for hot compresses; jumpers, sports Materials for clothing such as clothes or rainwear; Building materials such as wallpaper, roof waterproofing materials, heat insulating materials, sound absorbing materials; desiccants; moisture-proofing agents; oxygen scavengers; disposable warmers; packaging materials such as freshness-keeping packaging or food packaging It can be used very suitably as a material such as.

DESCRIPTION OF SYMBOLS 10 Separator for nonaqueous electrolyte secondary battery 20 Secondary battery 21 Positive electrode plate 22 Negative electrode plate 24 Positive electrode lead body 25 Negative electrode lead body 26 Gasket 27 Positive electrode cover 41 Sample 42 Tape 43 Non-slip 44 Upper chuck 45 Lower chuck

Claims (8)

  A laminated porous film having a coating layer containing inorganic particles and a resin binder on at least one surface of a polyolefin resin porous film, wherein the resin binder is a water-soluble resin having a weight average molecular weight of 110,000 or more and 500,000 or less. A laminated porous film characterized by   2. The laminated porous film according to claim 1, wherein in the coating layer, the content of the inorganic particles with respect to the total amount of the inorganic particles and the resin binder is 80 to 99.9% by mass.   The laminated porous film according to claim 1 or 2, wherein the inorganic particles comprise alumina.   The laminated porous film according to any one of claims 1 to 3, wherein the polyolefin resin used for the polyolefin resin porous film is a polypropylene resin.   The coating layer is formed by applying a coating liquid containing inorganic particles, a resin binder and a dispersion medium onto the polyolefin resin porous film, and then removing the dispersion medium. The laminated porous film according to any one of 1 to 4.   The laminated porous film according to claim 5, wherein the dispersion medium in the coating liquid contains 50% by mass or more of water.   A separator for a non-aqueous electrolyte secondary battery using the laminated porous film according to claim 1.   A non-aqueous electrolyte secondary battery using the separator for a non-aqueous electrolyte secondary battery according to claim 7.