JP2014091071A - Manufacturing method of laminated porous film, laminated porous film, separator for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention provides a laminated porous film having excellent powder resistance and heat resistance without deteriorating high air permeability and having excellent characteristics when used as a battery separator.
A coating layer is formed by applying a coating liquid containing a filler, a resin binder, and at least two solvents of a first solvent and a second solvent to at least one surface of a polyolefin-based resin porous film and drying it. comprising the step of forming a method for producing a laminated porous film, the coating solution, the first solvent is 60 mass% or more of the total solvent, SP value of the first solvent (SP _1), the second solvent The SP value (SP ₂ ) and the SP value (SP _B ) of the resin binder satisfy the following relational expressions (i) and (ii), and SP ₁ > SP _B (i) 10 <| SP ₁ -SP ₂ <30 (ii) A method for producing a laminated porous film, wherein the boiling point of the second solvent is higher than the boiling point of the first solvent, and the resin binder is completely dissolved in the solvent.
[Selection figure] None

Description

  The present invention relates to a laminated porous film and a method for producing the same, and can be used as a packaging, sanitary, livestock, agricultural, architectural, medical, separation membrane, light diffusion plate, battery separator, and in particular, non-aqueous electrolysis. It can be suitably used as a separator for a liquid secondary battery.

  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 a 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 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 closed when the temperature is about 100 to 150 ° C., and as a result, ion conduction inside the battery is cut off. 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 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 exceeds 130 ° C., the melting point of polyethylene, and further increases. There is a possibility that both electrodes are short-circuited due to 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 demand, a multilayer porous film (Patent Documents 1 to 3) is proposed in which a porous layer containing a metal oxide and a resin binder is provided on at least one surface of a polyolefin-based resin porous film. By providing a coating layer that is highly filled with inorganic fine particles such as α-alumina on the porous film, abnormal heating occurs, and even when the temperature continues to rise beyond the SD temperature, both electrodes are prevented from being short-circuited. It is possible to be a very safe method.

JP 2004-227972 A JP 2008-186721 A International Publication No. 2008/149986 Pamphlet

  However, in the methods described in Patent Documents 1 to 3, in order to ensure high air permeability, it is necessary to reduce the content of the resin binder and increase the particle size of the filler in the porous layer containing the metal oxide. However, on the other hand, there is a problem that the binding force between the fillers is reduced, and powder falling off due to the falling off of the fillers is likely to occur.

  The subject of this invention is solving the said problem. That is, an object of the present invention is to provide a laminated porous film that has excellent characteristics when used as a separator for a non-aqueous electrolyte secondary battery, with less dropout of filler, heat resistance and excellent air permeability. To do.

The first aspect of the present invention is to apply a coating liquid containing a filler, a resin binder, and at least two solvents, ie, a first solvent and a second solvent, to at least one surface of a polyolefin-based resin porous film, and then drying. comprising the step of forming the coating layer, a method for producing a laminated porous film, the coating solution, the first solvent is at least 60 wt% of the total solvent, SP value of the first solvent (SP ₁₎ The SP value (SP ₂ ) of the second solvent and the SP value (SP _B ) of the resin binder satisfy the following relational expressions (i) and (ii),
SP ₁ > SP _B (i)
_{10 <| SP 1 - SP 2} | <30 (ii)
In this method, the boiling point of the second solvent is higher than the boiling point of the first solvent, and the resin binder is completely dissolved in the solvent.

  Moreover, about 1st this invention, it is preferable in the said coating liquid that a 2nd solvent is 1 mass% or more and 40 mass% or less in all the solvents.

  Moreover, about 1st this invention, it is preferable that the boiling point of said 2nd solvent is 10 degreeC or more higher than the boiling point of said 1st solvent.

  In the first aspect of the present invention, the filler preferably comprises a metal oxide.

  Moreover, about 1st this invention, it is preferable in the said coating liquid that the content rate of the filler which occupies for the total amount of the said filler and the said resin binder is the range of 80 to 99 mass%.

  In the first aspect of the present invention, the polyolefin resin porous film preferably comprises polypropylene.

  In the first aspect of the present invention, the polyolefin resin porous film preferably has β crystal activity.

  In the first aspect of the present invention, water is preferably used for at least one of the first solvent and the second solvent.

  Furthermore, the laminated porous film produced by the method for producing a laminated porous film according to the first aspect of the present invention is also included in the present invention.

The second aspect of the present invention includes a coating layer containing a filler and a resin binder on at least one surface of a polyolefin resin porous film, and further containing at least 10 ppm of at least two solvents of a first solvent and a second solvent. The SP value (SP ₁ ) of the first solvent, the SP value (SP ₂ ) of the second solvent, and the SP value (SP _B ) of the resin binder are the following relational expressions (i) and (ii) )
SP ₁ > SP _B (i)
_{10 <| SP 1 - SP 2} | <30 (ii)
And it is a laminated porous film whose boiling point of a 2nd solvent is higher than the boiling point of a 1st solvent.

  Further, a separator for a non-aqueous electrolyte secondary battery using the laminated porous film according to the first or second invention, and a non-aqueous electrolyte secondary battery containing the separator are also included in the present invention. .

  According to the present invention, it is possible to obtain a laminated porous film having anti-powder resistance, heat resistance and excellent air permeability and having excellent characteristics when used as a separator for a non-aqueous electrolyte secondary battery. it can.

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 fixing method of the lamination | stacking porous film in a wide angle X-ray-diffraction measurement.

Hereinafter, the laminated porous film of this invention and embodiment of the manufacturing method are 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.

  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)
Examples of the polypropylene resin used in the present invention include homopropylene (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.

  Moreover, as a polypropylene resin, it is preferable that the isotactic pentad fraction (mmmm fraction) which shows stereoregularity is 80 to 99%. More preferably 83-98%, still more preferably 85-97%. If the isotactic pentad fraction is too low, the mechanical strength of the film may be reduced. 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. Signal assignment of the methyl group region is as follows. It conformed to Zambelli et al (Macromolecules 8,687, (1975)).

  Moreover, as a polypropylene resin, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution is 2.0-10.0. More preferably, 2.0 to 8.0, and still more preferably 2.0 to 6.0 is used. This means that the smaller the Mw / Mn is, the narrower the molecular weight distribution is. However, when the Mw / Mn is less than 2.0, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. . On the other hand, when Mw / Mn exceeds 10.0, low molecular weight components increase, and the mechanical strength of the laminated porous film tends to decrease. Mw / Mn is obtained by GPC (gel permeation chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene-based resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and 1.0 to 10 g / 10 minutes. It is more preferable. When the MFR is 0.5 g / 10 min or more, the resin has a high melt viscosity at the time of molding, 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. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

  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. Examples thereof include slurry polymerization, melt polymerization, bulk polymerization, gas phase polymerization, and bulk polymerization using a radical initiator.

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

(Polyethylene resin)
Polyethylene resins 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, that is, ethylene and propylene. , Butene-1, pentene-1, hexene-1, heptene-1, octene-1, etc., α-olefins having 3 to 10 carbon atoms; vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate Copolymer or multi-component copolymer with one or more comonomers selected from unsaturated carboxylic acid esters such as methyl methacrylate and ethyl methacrylate, and unsaturated compounds such as conjugated and non-conjugated dienes A coalescence or a mixed composition thereof may be mentioned. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, at least one polyethylene resin selected from low density polyethylene, linear low density polyethylene, and high density polyethylene is preferable, and high density polyethylene is more preferable.

Density of the polyethylene resin is preferably 0.910~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, 0.940~0.970g / cm ³ is more preferable. A density of 0.910 g / cm ³ or more is preferable because it can have appropriate SD characteristics. On the other hand, 0.970 g / cm ³ or less is preferable in that it can have an appropriate SD characteristic and can maintain stretchability.
The density can be measured according to JIS K7112 using a density gradient tube method.

Further, the melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.03 to 30 g / 10 minutes, and preferably 0.3 to 10 g / 10 minutes. It is more preferable. If the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, which is excellent in productivity and preferable. On the other hand, if it is 30 g / 10 minutes or less, since sufficient mechanical strength can be obtained, it is preferable.
MFR is measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 2.16 kg.

  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. As a polymerization method of the polyethylene resin, there are a one-stage polymerization, a two-stage polymerization, or a multistage polymerization more than that, and any method of the polyethylene resin can be used.

(Β crystal activity)
In the laminated porous film of the present invention, the polyolefin resin porous film preferably has β crystal activity. The β crystal activity can be regarded as an index indicating that β crystals were generated in the film-like material before stretching. If β crystals are generated in the film before stretching, even if no fillers or other additives are used, micropores can be easily formed by stretching, so a laminate with air permeability A porous film can be obtained.

  In the laminated porous film of the present invention, the presence or absence of “β crystal activity” is determined when the crystal melting peak temperature derived from the β crystal is detected by a differential scanning calorimeter described later and / or the X-ray diffractometer described later. When a diffraction peak derived from the β crystal is detected by the measurement using γ, it is judged to have “β crystal activity”.

  Hereinafter, the case where the polyolefin resin is the polypropylene resin will be specifically exemplified.

  Presence or absence of “β crystal activity” is determined by holding the laminated porous film with a differential scanning calorimeter from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min for 1 minute, and then cooling from 240 ° C. to 25 ° C. Crystal melting peak temperature (Tmβ) derived from β crystals of polypropylene resin when the temperature is lowered at 10 ° C / min and held for 1 minute and then heated again from 25 ° C to 240 ° C at a heating rate of 10 ° C / min. Is detected, it is determined to have β crystal activity.

Further, the β crystal activity of the laminated porous film is calculated by the following formula using the crystal heat of fusion derived from the α crystal of the polypropylene resin (ΔHmα) and the crystal heat of heat derived from the β crystal (ΔHmβ). Yes.
β crystal activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, when the polypropylene resin is homopolypropylene, the amount of heat of crystal melting derived from the β crystal (ΔHmβ) detected mainly in the range from 145 ° C. to less than 160 ° C. It can be calculated from the heat of crystal melting (ΔHmα) derived from the α crystal. Further, for example, in the case of random polypropylene copolymerized with 1 to 4 mol% of ethylene, the crystal melting heat amount (ΔHmβ) derived from the β crystal detected mainly in the range of 120 ° C. or more and less than 140 ° C., and mainly 140 It can be calculated from the crystal melting calorie (ΔHmα) derived from the α crystal detected in the range of from 0 ° C. to 165 ° C.

The polyolefin resin porous film preferably has a higher β crystal activity, specifically 20% or more, more preferably 40% or more, and particularly preferably 60% or more. . If the laminated porous film has a β crystal activity of 20% or more, it indicates that a large number of β crystals of polypropylene resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. As a result, a battery separator having high mechanical strength and excellent air permeability can be obtained.
The upper limit value of the β crystal activity is not particularly limited, but the higher the β crystal activity, the more effective the effect is obtained, so the closer it is to 100%, the better.

The presence or absence of the β crystal activity can also be determined by a diffraction profile obtained by wide-angle X-ray diffraction measurement of a laminated porous film subjected to a specific heat treatment.
Specifically, wide-angle X-ray measurement was performed on a laminated porous film that was subjected to heat treatment at 170 ° C. to 190 ° C., which is a temperature exceeding the melting point of the polypropylene resin, and was slowly cooled to generate and grow β crystals. When the diffraction peak derived from the (300) plane of β crystal is detected in the range of 2θ = 16.0 ° to 16.5 °, it is determined that there is β crystal activity.
Details on the β crystal structure and wide angle X-ray diffraction of polypropylene resins can be found in Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein. A detailed evaluation method of the β crystal activity using wide-angle X-ray diffraction will be described in Examples described later.

The β crystal activity can be measured in the state where the laminated porous film of the present invention is in the entire laminated porous film.
In addition, if a layer containing a polypropylene resin is laminated on a polyethylene resin, for example, in addition to a layer made of a polypropylene resin, both layers preferably have β crystal activity.

  As the method for obtaining the β crystal activity described above, there is a method in which a substance that promotes the generation of α crystal of the polypropylene resin is not added, or a treatment for generating a peroxide radical as described in Japanese Patent No. 3739481. Examples thereof include a method of adding the applied polypropylene and a method of adding a β crystal nucleating agent to the composition.

(Β crystal nucleating agent)
Examples of the β crystal nucleating agent used in the present invention include those shown below, but are not particularly limited as long as they increase the formation and growth of β crystals of polypropylene resin, and two or more types are mixed. May be used.
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: 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 IIA metal of the periodic table; a cyclic phosphorus compound; Made of magnesium compound Such as the formation thereof. In addition, specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A Nos. 06-228966, and JP-A Nos. 09-194650.

  As a commercial product of β crystal nucleating agent, β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., specific examples of polypropylene resin to which β crystal nucleating agent is added include polypropylene “Bepol” manufactured by Aristech. 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 to be added to the polyolefin resin needs to be appropriately adjusted depending on the type of the β crystal nucleating agent or the composition of the polyolefin resin. It is preferable that it is 0.0001-5 mass parts with respect to 100 mass parts of resin. Moreover, 0.001-3 mass parts is more preferable, and 0.01-1 mass part is still more preferable. If it is 0.0001 part by mass or more, β-crystals of polyolefin-based resin can be sufficiently generated and grown during production, and sufficient β-crystal activity can be secured even when used as a separator, and the desired air permeability performance. Is obtained. The addition of 5 parts by mass or less is preferable because it is economically advantageous and there is no bleeding of the β crystal nucleating agent on the surface of the laminated porous film.

(Other ingredients)
In the present invention, in addition to the components described above, additives generally added to the resin composition can be appropriately added to the polyolefin resin porous film within a range that does not significantly impair the effects of the present invention. As the additive, for the purpose of improving and adjusting the moldability, productivity and various physical properties of the polyolefin resin porous film, recycled resin generated from trimming loss such as ears, silica, talc, kaolin, Inorganic particles such as calcium carbonate, pigments such as carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, oxidation Examples thereof include additives such as an inhibitor, a light stabilizer, an ultraviolet absorber, a neutralizer, an antifogging agent, an antiblocking agent, a slip agent, and a colorant.
Further, in order to promote the opening and impart moldability, the modified polyolefin resin, the aliphatic saturated hydrocarbon resin or a modified product thereof, an ethylene polymer, as long as the effects of the present invention are not significantly impaired. Wax or low molecular weight polypropylene may be added.

(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. Among them, a single layer of the polyolefin resin-containing layer (hereinafter sometimes referred to as “A layer”), within a range that does not interfere with the function of the A layer, the A layer and other layers (hereinafter referred to as “B layer”) Is sometimes preferred). For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low melting point resin layer is provided to close the hole in a high temperature atmosphere as described in JP-A No. 04-181651 and to ensure the safety of the battery. Can be made.
Specific examples include a two-layer structure in which A layers / B layers are stacked, a three-layer structure in which A layers / B layers / A layers, or B layers / A layers / B layers are stacked. In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions. In this case, the order of stacking with layers 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.

  In addition, the physical property of the polyolefin resin porous film used for this invention can be freely adjusted with a layer structure, a lamination ratio, a composition of each layer, and a 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, using the polyolefin-based resin, a non-porous film-like product was produced by melt extrusion, and a number of fine pores having communication in the thickness direction were formed by stretching the non-porous film-like product. A porous film can be obtained.

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. Further, a method of cutting a film-like material manufactured by a tubular method into a flat shape can be applied.
The method for making the nonporous film-like material is not particularly limited, and a known method such as wet uniaxial stretching or porous uniaxial stretching or porous uniaxial stretching may be used. As the stretching method, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and these methods are used alone or in combination of two or more to perform uniaxial stretching or biaxial 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 the present invention, when the polyolefin-based resin porous film is laminated, the production method is roughly classified into the following four types depending on the order of porous formation 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 non-porous film to make it porous.
(Iv) A method of forming a laminated porous film by preparing a porous layer and then coating with inorganic / organic particles or depositing metal particles.
In the present invention, it is preferable to use the method (ii) from the viewpoint of simplification 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 detail of the manufacturing method of a polyolefin resin porous film is demonstrated.
First, a mixed resin composition of a polyolefin resin and, if necessary, a thermoplastic resin and additives is prepared. For example, raw materials such as polypropylene resin, β crystal nucleating agent, and other additives as required, preferably using Henschel mixer, super mixer, tumbler type mixer, etc., or by hand-blending all ingredients in a bag After mixing, the mixture is melt-kneaded with a single-screw or twin-screw extruder, a kneader or the like, preferably a twin-screw extruder, and then cut to obtain pellets.

The pellets are put into an extruder and extruded from a T-die extrusion die to form a 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 determined from the final required film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5. -1.0 mm. If it is 0.1 mm or more, it is preferable from a viewpoint of production speed, and if it is 3.0 mm or less, since the draft rate does not become too large, it is preferable from the viewpoint of production stability.

In 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 cooling and solidification temperature by the cast roll is very important in the present invention, and the ratio of the β crystal of the polyolefin resin in the film can be adjusted. The cooling and solidification temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. It is preferable to set the cooling and solidification temperature to 80 ° C. or higher because the ratio of β crystals in the film can be sufficiently increased. Further, it is preferable to set the temperature to 150 ° C. or lower because troubles such as the extruded molten resin sticking to and wrapping around the cast roll hardly occur and the film can be efficiently formed into a film.

It is preferable to adjust the β crystal ratio of the polyolefin resin of the film-like material before stretching to 30 to 100% by setting a cast roll in the temperature range. 40-100% is more preferable, 50-100% is still more preferable, and 60-100% is the most preferable. By setting the β crystal ratio in the film-like material before stretching to 30% or more, a polyolefin-based resin porous film having good gas permeability can be obtained because it is easily made porous by the subsequent stretching operation.
The β crystal ratio in the film before stretching is detected when the film is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. Calculation is made by the following formula using the heat of crystal melting (ΔHmα) derived from the α crystal and the heat of crystal melting derived from the β crystal (ΔHmβ) of the polyolefin resin.
β crystal ratio (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100

  Next, the obtained nonporous film-like material is stretched. The stretching step may be uniaxial stretching, but at least biaxial stretching is more preferable. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching, but the stretching conditions (magnification, temperature) can be easily selected in each stretching step, and the porous structure can be easily controlled. Biaxial stretching is more preferable. The longitudinal direction of the film and the 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 using sequential biaxial stretching, the stretching temperature needs to be changed from time to time depending on the composition of the resin composition to be used, the crystal melting peak temperature, the degree of crystallinity, etc., but the stretching temperature in the longitudinal stretching is preferably about 0 to 130 ° C. More preferably, it is controlled in the range of 10 to 120 ° C, and more preferably 20 to 110 ° C. Moreover, 2-10 times are preferable, More preferably, it is 3-8 times, More preferably, it is 4-7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while suppressing breakage during stretching.
On the other hand, the stretching temperature in transverse stretching is generally 100 to 160 ° C, preferably 110 to 150 ° C, and more preferably 120 to 140 ° C. Further, the preferred longitudinal 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 further 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. In this case, the effect of dimensional stability can be expected by setting the temperature to preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and still more preferably 140 ° C. or higher. 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. A heat treatment temperature of 170 ° C. or lower is preferable because the polyolefin resin hardly melts by the heat treatment and the porous structure can be maintained. Moreover, you may perform a 1-20% relaxation process as needed during the heat processing process. In addition, after heat processing, a polyolefin resin porous film is obtained by cooling uniformly and winding up.

<Coating layer>
In the present invention, at least one surface of the polyolefin resin porous film is coated with a coating liquid containing a filler, a resin binder, and at least two solvents of a first solvent and a second solvent and dried. Form.

(Filler)
Examples of the filler that can be used in the present invention include inorganic fillers and organic fillers, but are not particularly limited.

  Specific examples of inorganic fillers 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, barium sulfate, and magnesium sulfate, calcium oxide, Examples thereof include metal oxides such as magnesium oxide, zinc oxide, alumina, silica, and titanium oxide, metal chlorides such as sodium chloride, magnesium chloride, silver chloride, and calcium chloride, and clay minerals such as talc, clay, mica, and montmorillonite. Among these, when used as a battery separator, a metal oxide is more preferable and alumina is particularly preferable from the viewpoint of being chemically inert when incorporated in a battery.

  Examples of organic fillers that can be used in the present invention include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetra Thermoplastic resins and thermosetting resins such as fluoroethylene, polyimide, polyetherimide, melamine, and benzocamine are included. Among these, cross-linked polystyrene and the like are preferable from the viewpoint of resistance to electrolyte solution swelling when the laminated porous film of the present invention is used as a separator for nonaqueous electrolyte secondary batteries.

The lower limit of the average particle size of the filler is preferably 0.01 μm or more, more preferably 0.1 μm or more, and further 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. The average particle size of 0.01 μm or more is preferable because the laminated porous film of the present invention can exhibit sufficient heat resistance. Moreover, it is preferable from a viewpoint that the dispersibility of the filler in the said coating liquid and a coating layer improves that the said average particle diameter shall be 3.0 micrometers or less.
In the present embodiment, the “average particle diameter of the filler” is, for example, the short diameter of a two-dimensional projection image when the filler is projected from two directions in the vertical direction and the horizontal direction, for example, using an image analyzer. And the average value of the major axis are calculated as the average value after calculating for each direction.

The specific surface area of the filler is preferably 5 g / m ² or more and less than 30 g / m ² . A specific surface area of 5 g / m ² or more is preferable because the penetration of the electrolytic solution becomes faster and the productivity becomes better when the laminated porous film of the present invention is incorporated as a separator in a non-aqueous electrolyte secondary battery. Moreover, if a specific surface area is less than 30 g / m < ² >, when the laminated porous film of this invention is integrated in a nonaqueous electrolyte secondary battery as a separator, adsorption | suction of an electrolyte component is suppressed, and it is preferable.

(Resin binder)
As the resin binder used in the present invention, the filler and the polyolefin-based resin porous film can be favorably bonded, are electrochemically stable, and the laminated porous film is used as a separator for a nonaqueous electrolyte secondary battery. The case is not particularly limited as long as it is stable against the organic electrolyte. Specifically, polyethers, polyamides, polyimides, polyamideimides, polyaramides, ethylene-vinyl acetate copolymers (with a structural unit derived from vinyl acetate of 0 to 20 mol%), ethylene-ethyl acrylate copolymers, etc. Polyethylene vinylidene copolymers such as ethylene-acrylic acid copolymer, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polytetrafluoroethylene, fluorine-based rubber, styrene-butadiene rubber, nitrile butadiene Rubber, polybutadiene rubber, polyacrylonitrile, polyacrylic acid and its derivatives, polymethacrylic acid and its derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, cyanoethyl cellulose, polyvinyl Alcohol, cyanoethyl polyvinyl alcohol, polyvinyl butyral La tetrazole, polyvinyl pyrrolidone, N- vinyl acetamide, crosslinked acrylic resin, polyurethane, epoxy resins, maleic acid-modified polyolefin. These resin binders may be used alone or in combination of two or more. Among these resin binders, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride, polyvinyl pyrrolidone, polyacrylonitrile resin, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid and its derivatives, and maleic acid-modified polyolefin are relatively stable in water. This is more preferable.

  In the coating solution, the filler content in the total amount of the filler and the resin binder is preferably in the range of 80% by mass to 99% by mass. The content of the filler is more preferably 85% by mass or more, further preferably 87% by mass or more, and particularly preferably 90% by mass or more. When the filler content is in this range, the coating layer can maintain excellent air permeability and binding properties.

(solvent)
It is important that the coating liquid contains at least two solvents, ie, a first solvent and a second solvent. First, as a premise, in the present invention, the coating liquid is at least one side of the polyolefin resin porous film. Since the coating layer is formed by coating and drying, it is preferable to select a solvent suitable for the coating and drying method. More specifically, it is preferable to use a solvent in which the filler and the resin binder can be dissolved or dispersed in a reasonably uniform and stable manner. Examples of such a solvent include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, dioxane, acetone, acetonitrile, lower alcohol, glycols, glycerin, and lactic acid ester. As the first solvent and the second solvent, two kinds of solvents satisfying the following conditions can be appropriately selected from these. Among these, from the viewpoint of cost and environmental burden, it is preferable to use water for at least one of the first solvent and the second solvent, and it is particularly preferable to use water as the first solvent.

In the present invention, SP value of the first solvent _(SP 1), _SP value of the second solvent _(SP 2), _SP value of the resin binder (SP _B) satisfies the following relationship (i) and (ii) This is very important.
SP ₁ > SP _B (i)
_{10 <| SP 1 - SP 2} | <30 (ii)
Qualitatively speaking, the first solvent is higher in polarity than the resin binder, and the first solvent and the second solvent are significantly different in polarity.
That is, the combination of the first solvent and the second solvent satisfying such conditions can be changed depending on the type and properties (for example, hydrophilicity, hydrophobicity, etc.) of the resin binder. Regardless of the above, the present inventors have found an effect that the air permeability of the laminated porous film of the present invention is further improved by using at least two kinds of solvents in which the SP value of the resin binder is in a specific range.

The SP value (SP ₁ ) of the first solvent is preferably larger than the SP value (SP _B ) of the resin binder by 0.5 or more, particularly preferably 1 or more.
The SP value of each solvent and resin binder is, for example, that of PLYMER HANDBOOK THIRD EDITION (WILEY INTERSCIENCE Publishing, 1989). 526-P. 533 TABLE 3.1 and P.C. 551-P. Values described in known literature, such as the values described in 555 TABLE 3.5, can be used.

  Moreover, it is important that the first solvent in the coating solution is 60% by mass or more in the total solvent, more preferably 65% by mass or more, and particularly preferably 70% by mass or more. When the content ratio of the first solvent is 60% by mass or more, a coating solution having excellent coating stability can be obtained, and a coating layer having excellent air permeability can be formed. In addition, about an upper limit, it is 99 mass% or less normally from a viewpoint which makes a 2nd solvent essential.

  On the other hand, the second solvent in the coating solution is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more in the total solvent. When the content ratio of the second solvent is 1% by mass or more, a coating layer having excellent air permeability can be formed. In addition, about an upper limit, it is 40 mass% or less normally from a viewpoint which makes a 1st solvent essential.

  Furthermore, it is important that the boiling point of the second solvent in the coating liquid is higher than the boiling point of the first solvent. More specifically, the difference in boiling point between the second solvent and the first solvent is preferably 10 ° C. or higher, and more preferably 20 ° C. or higher. When the difference in boiling points is 10 ° C. or more, the laminated porous film of the present invention has an effect of expressing better air permeability. On the other hand, the upper limit is preferably 200 ° C. or lower, more preferably 150 ° C. or lower. When the difference in boiling points is 200 ° C. or less, it is possible to suppress the residual solvent after the coating layer is formed.

  More specifically, when the resin binder is dissolved in the solvent by the presence of the second solvent, which is a low polarity solvent, in the first solvent that is more polar than the resin binder, the first solvent and the second solvent The second solvent, which is a low polarity solvent, at the solvent interface causes a phase separation phenomenon. Then, when the coating liquid is applied onto the polyolefin resin porous film and dried to form the coating layer, the solvent is removed, and the higher order structure is formed in the resin binder due to the phase separation phenomenon. That is, since fine pores are formed, the laminated porous film of the present invention is particularly excellent in air permeability.

In order to express the above phenomenon, it is important that the resin binder is completely dissolved in the solvent in the coating solution. In addition, the state in which the resin binder is completely dissolved in the solvent specifically means “the solution is transparent (it may be colored)”, “the concentration is uniform regardless of which part of the solution is taken out. It meets the requirement of “some” and “cannot be centrifuged”. So-called emulsions are excluded because they do not meet this requirement.
As a method for completely dissolving the resin binder in the solvent, a method in which the SP value (SP ₁ ) of the first solvent and the SP value (SP _B ) of the resin binder are as close as possible is selected, or the coating described later Preferred examples include heating and stirring in the step of preparing the liquid. However, it is not limited to these methods.

  In addition, in the range which does not impair the said effect, you may add other solvents other than a 1st solvent and a 2nd solvent further as needed, such as a defoaming and paintability. At this time, the SP value of the resin binder with respect to another solvent is not particularly limited. On the other hand, the content ratio of the other solvent is usually preferably smaller than the content ratio of the second solvent.

  The coating liquid preferably 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 ppm or more and 10,000 ppm or less of the acid component. The content of the acid component is more preferably 100 ppm or more and 9000 ppm or less, and further preferably 1000 ppm or more and 8000 ppm or less.
If content is 10 ppm or more, since there exists an effect that the coating film excellent in coating-material stability and coating property is obtained, it is preferable. Moreover, if content is 10,000 ppm or less, since it does not have a bad influence on the performance of a nonaqueous electrolyte secondary battery, it is preferable.

About the coating layer of the laminated porous film of the present invention formed using the coating solution, not all of the solvent is necessarily removed in the drying step, and usually a trace amount of solvent remains. That is, the coating layer contains 10 ppm or more of at least two solvents of the first solvent and the second solvent.
On the other hand, the upper limit of the content ratio is preferably 10,000 ppm or less, and more preferably 5000 ppm or less. By being 5000 ppm or less, there is little risk of adverse effects on the electrolyte when the laminated porous film of the present invention is accommodated in a non-aqueous electrolyte secondary battery as a separator for a non-aqueous electrolyte secondary battery. .
The content ratio of such a solvent can be measured and calculated using various known analysis methods.

(Formation method of coating layer)
The coating layer in the laminated porous film of the present invention is formed by applying the coating liquid to at least one surface of the polyolefin resin porous film and drying it. By adopting this so-called coating drying method, the laminated porous film of the present invention is excellent in continuous productivity.

  In the step of preparing the coating liquid, as a method of dissolving or dispersing the filler and the resin binder in the solvent, for example, a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, Examples thereof include a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, a mechanical stirring method using a stirring blade, and the like.

  Also, when dispersing the filler and the resin binder in the solvent, a dispersion aid, a stabilizer, a thickener, etc. are added to improve the stability of the coating liquid and optimize the viscosity. May be.

  The step of applying the coating liquid to the surface of the polyolefin resin porous film may be after the extrusion molding step or after the longitudinal stretching step in the production process of the polyolefin resin porous film. It may be after the transverse stretching step. Among these, from the viewpoint of shortening the production line and improving productivity, it is preferable to be after the longitudinal stretching step.

  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.

  In addition, as a method of forming the coating layer by applying the coating solution to the polyolefin resin porous film and then drying to remove the solvent, the polyolefin resin porous film is fixed at a temperature equal to or lower than its melting point. Examples include a method of drying at a temperature and a method of drying at a low temperature under reduced pressure.

(Shape and physical properties of laminated porous film)
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. When it is used as a battery separator, if it is 5 μm or more, substantially necessary electrical insulation can be obtained. For example, even when a large force is applied to the protruding portion of the electrode, the battery separator is broken and short-circuited. It is difficult and safe. Moreover, if thickness is 100 micrometers or less, since the electrical resistance of a lamination | stacking porous film can be made small, 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, further 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.

The porosity in all layers of the laminated porous film of the present invention 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 further 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.

The air permeability of the laminated porous film of the present invention is preferably 500 seconds / 100 ml or less, more preferably 10 to 300 seconds / 100 ml, and further preferably 50 to 180 seconds / 100 ml. An air permeability of 500 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 difficulty in passing through the air in the film thickness direction, and is specifically expressed by the number necessary 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 battery separator, a low air permeability means that lithium ions can be easily transferred, and the 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.

  The shrinkage percentage at 130 ° C. of the laminated porous film of the present invention is preferably less than 5%, more preferably less than 4.5%, and even more preferably less than 4%. If the shrinkage rate at 130 ° C. is less than 5%, even when abnormal heat is generated exceeding the SD temperature, it is suggested that the dimensional stability is good and has heat resistance, preventing film breakage, and internal short circuit. The temperature can be improved. Although it does not specifically limit as a minimum, 0% or more is more preferable.

The anti-powder resistance of the coating layer of the laminated porous film of the present invention can be evaluated by a stone mill test described later. Reduction of the mass of the laminated porous film according millstone test is preferably 1 g / m ² or less, and more preferably 0.8 g / m ² or less. When the amount of decrease is 1 g / m ² or less, a laminated porous film excellent in heat resistance can be obtained with very little powder falling off due to falling off of the filler.

(battery)
Next, a nonaqueous electrolyte secondary battery containing the laminated porous film of the present invention as a battery separator 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 manufactured.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used. The organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile. 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more. Among them, an electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 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.

  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 polyvinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a mesh of 70 mesh. After removing the large particles, uniformly apply to both sides of the 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, strip-shaped negative electrode plate and We use what we did.

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

In the present embodiment, a strip-like positive electrode plate produced as follows is used as the positive electrode. That is, lithium graphite oxide (LiCoO ₂ ) is added with phosphorous graphite as a conductive additive at a mass ratio of 90: 5 (lithium cobalt oxide: phosphorous graphite) and mixed, and this mixture and polyvinylidene fluoride are mixed with N -Mix with a solution dissolved in methylpyrrolidone to make a slurry. This 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, dried, and then compressed by a roll press. After forming, it is cut into a strip-like positive electrode plate.

  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”.

(1) Filler content The ratio of the filler in the total amount of the filler and the resin binder in the coating liquid was defined as the filler content.

(2) Content ratio of resin binder The ratio of the resin binder in the total amount of the filler and the resin binder in the coating liquid was defined as the content ratio of the resin binder.

(3) Ratio of first solvent The mass ratio of the first solvent in the total solvent mass in the coating solution was defined as the ratio of the first solvent.

(4) Ratio of second solvent The mass ratio of the second solvent in the total solvent mass in the coating liquid was defined as the ratio of the second solvent.

(5) SP value The SP value (SP _B ) of the resin binder, the SP value (SP ₁ ) of the first solvent, and the SP value (SP ₂ ) of the second solvent are respectively POLYMER HANDBOOK THIRD EDITION (WILEY INTERSCIENCE publication, 1989). P.). 526-P. 533 TABLE 3.1 and P.C. 551-P. The value described in 555 TABLE 3.5 was used.

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

(7) Coating Layer Thickness The coating layer thickness was calculated by subtracting the thickness of the polyolefin resin porous film before forming the coating layer from the total thickness.

(8) Air permeability (Gurley value)
The air permeability was measured according to JIS P8117. A sample having an air permeability of 180 seconds / 100 mL or less was regarded as acceptable.

(9) Curl The curl amount is calculated by cutting out the sample after coating to A4 size, removing the electricity sufficiently by grounding, placing it on the SUS flat plate, and summing the height at which each vertex floats with respect to the SUS plate Then, the success or failure of the curl was determined according to the following criteria.
○: Curling amount is less than 15 mm ×: Curling amount is 15 mm or more

(10) Stone mill test (powder resistance)
The laminated porous film was cut into 50 mm × 50 mm squares, and one side was affixed to cardboard and fixed. Then, a weight of 40 mm and a weight of 600 g covered with a cotton cloth was placed on the coating layer side, and these were rubbed at a rotational speed of 60 rpm for 200 seconds. In addition, the amount of decrease in the mass of the contact portion was measured and evaluated.
○: The mass reduction amount of the contact portion (about 12.56 cm ² ) of the coating layer is less than 1 g / m ² .
×: weight reduction of the contact portion of the coating layer (approximately 12.56cm ²⁾ is 1 g / ^{m 2} or more

(11) Shrinkage rate at 130 ° C. A sample obtained by cutting a laminated porous film into a 150 mm × 10 mm square is marked so that the distance between chucks is 100 mm, and is set in an oven set at 130 ° C. (Tabai Gear Spec, Tabai Gear Oven GPH200). The sample was put and allowed to stand for 1 hour. After the sample is removed from the oven and cooled, the length is measured. The shrinkage rate 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.

(12) Heat resistance Heat resistance was evaluated according to the following evaluation criteria.
○: Shrinkage rate at 130 ° C. for 1 hour is less than 5% in both the vertical direction and the horizontal direction ×: Shrinkage rate at 130 ° C. for 1 hour in either the vertical direction or the horizontal direction is 5% or more

(13) Differential scanning calorimetry (DSC)
Using a differential scanning calorimeter (DSC-7) manufactured by PerkinElmer Co., Ltd., the resulting laminated porous film was heated from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then The temperature was lowered from 240 ° C. to 25 ° C. at a scanning rate of 10 ° C./min and held for 1 minute, and then the temperature was raised again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min. The presence or absence of β crystal activity was evaluated according to the following criteria depending on whether or not a peak was detected at 145 to 160 ° C., which is the crystal melting peak temperature (Tmβ) derived from the β crystal of the polypropylene resin at the time of reheating. .
○: When Tmβ is detected within the range of 145 ° C to 160 ° C (with β crystal activity)
X: When Tmβ is not detected within the range of 145 ° C to 160 ° C (no β crystal activity)
The β crystal activity was measured with a sample amount of 10 mg in a nitrogen atmosphere.

(14) Wide angle X-ray diffraction measurement (XRD)
The laminated porous film was cut into a 60 mm vertical and 60 mm horizontal square, and as shown in FIG. 2 (A), an aluminum plate having a circular hole with a central portion of 40 mmφ (material: JIS A5052, size: 60 mm vertical, 60 mm horizontal, (Thickness 1 mm) was sandwiched between two sheets, and the periphery was fixed with clips as shown in FIG. 2 (B).
In a state where the laminated porous film is constrained to two aluminum plates, put it in a constant temperature incubator (Yamato Scientific Co., Ltd., model: DKN602) having a set temperature of 180 ° C. and a display temperature of 180 ° C. The temperature was changed to 100 ° C. and gradually cooled to 100 ° C. over 10 minutes or more. When the display temperature reaches 100 ° C., the product obtained by cooling for 5 minutes in an atmosphere of 25 ° C. while being constrained by two aluminum plates is 40 mmφ at the center under the following measurement conditions. Wide angle X-ray diffraction measurement was performed on the circular portion.
-Wide-angle X-ray diffraction measurement device: manufactured by Mac Science Co., Ltd., model number: XMP18A
X-ray source: CuKα ray, output: 40 kV, 200 mA
Scanning method: 2θ / θ scan, 2θ range: 5 ° to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min
About the obtained diffraction profile, the presence or absence of β crystal activity was evaluated as follows from the peak derived from the (300) plane of β crystal of the polypropylene resin.
◯: When a peak is detected in the range of 2θ = 16.0 to 16.5 ° (with β crystal activity)
X: When a peak is not detected in the range of 2θ = 16.0 to 16.5 ° (no β crystal activity)
In addition, when a laminated porous film piece cannot be cut out to 60 mm length and 60 mm width, you may adjust so that a laminated porous film may be installed in the circular hole of 40 mmphi in the center part.

(Polyolefin resin porous film)
Polypropylene resin Novatec PP FY6HA (manufactured by Nippon Polypro Co., Ltd., MFR; 2.4 g / 10 min) and 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4 as β crystal nucleating agent 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 in a water bath, cut into strands with a pelletizer, and produced polypropylene resin pellets. The β-crystal activity of the polypropylene resin composition was 80%.

Using the raw material, the film was extruded from a die and cooled and solidified with a casting roll at 124 ° C. to produce a film-like material.
The film-like material is stretched 4.6 times in the longitudinal direction using a longitudinal stretching machine, and then stretched twice in the transverse direction at 100 ° C. by a transverse stretching machine, followed by heat setting / relaxation treatment, and the corona surface By performing the treatment, a polyolefin resin porous film was obtained.

[Example 1]
19.5 parts by mass of alumina (manufactured by Nippon Light Metal Co., Ltd., LS-410, average particle size: 0.5 μm, specific surface area: 7.3 m ² / g), 18.0 parts by mass of water, zirconia beads (φ = 0. 8 mm) 20.0 parts by mass were mixed and shaken for 30 minutes. Subsequently, the zirconia beads were removed with a polyethylene mesh sheet with a weight of # 50 to obtain an alumina slurry having a solid content of 52% by mass.
Subsequently, 2.5 parts by mass of N-methylpyrrolidone was added to 37.5 parts by mass of the alumina slurry and stirred well, and then 10 parts by mass of an aqueous polyvinyl alcohol (Kuraray Co .: PVA-124) solution having a solid content concentration of 5%. Added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Example 2]
After adding 2.5 parts by mass of ethyl lactate to 37.5 parts by mass of the alumina slurry obtained in Example 1 and stirring well, 10 parts by mass of an aqueous polyvinyl alcohol (PVA-124 manufactured by Kuraray Co., Ltd.) solution having a solid content concentration of 5%. Added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Example 3]
To 37.5 parts by mass of the alumina slurry obtained in Example 1, 0.5 part by mass of 1-butanol and 2.0 parts by mass of N-methylpyrrolidone were added and stirred well, and the solid content solid content concentration was 5%. 10 parts by mass of an aqueous polyvinyl alcohol solution was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Example 4]
After adding 0.5 parts by mass of isopropyl alcohol and 2.0 parts by mass of N-methylpyrrolidone to 37.5 parts by mass of the alumina slurry obtained in Example 1, and stirring well, polyvinyl having a solid content solid content concentration of 5% 10 parts by mass of an aqueous alcohol solution was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Comparative Example 1]
After adding 2.5 parts by mass of water to 37.5 parts by mass of the alumina slurry obtained in Example 1 and stirring well, 10 parts by mass of a polyvinyl alcohol aqueous solution having a solid content concentration of 5% was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Comparative Example 2]
To 37.5 parts by mass of the alumina slurry obtained in Example 1, 2.5 parts by mass of isopropyl alcohol was added and stirred well, and then 10 parts by mass of a polyvinyl alcohol aqueous solution having a solid content concentration of 5% was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Comparative Example 3]
To 37.5 parts by mass of the alumina slurry obtained in Example 1, 2.5 parts by mass of isopropyl alcohol was added and stirred well, and then 10 parts by mass of a polyvinyl alcohol aqueous solution having a solid content concentration of 3% was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Comparative Example 4]
After 2.5 parts by mass of n-decane was added to 37.5 parts by mass of the alumina slurry obtained in Example 1 and stirred well, 10% aqueous solution of polyvinyl alcohol (Kuraray Co., Ltd .: PVA-124) with a solid content concentration of 5% was added. Part by mass was added.
Hydrochloric acid was added to the obtained paint so as to have a concentration of 50 ppm, and the polyolefin-based resin porous film was applied using a bar coater having a basis weight of # 10 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 summarized in Table 1.

[Comparative Example 5]
The physical properties of the polyolefin resin porous film were evaluated, and the results are summarized in Table 1.

* Formal names of compound symbols in the table PVA: Polyvinyl alcohol NMP: N-methylpyrrolidone IPA: Isopropyl alcohol

  From Table 1, the laminated porous films obtained in Examples 1 to 4 could have excellent powder resistance, heat resistance, and air permeability. As described above, this is presumably because the second solvent builds a higher-order structure (fine vacancies) that exhibits excellent air permeability in the evaporation drying process.

On the other hand, since the laminated porous film obtained in Comparative Example 1 did not contain the second solvent, the gas permeability performance was slightly deteriorated.
In the laminated porous film obtained in Comparative Example 2, since the boiling point of the second solvent is lower than the boiling point of the first solvent, the second solvent evaporates first without forming a higher order structure. The air permeability performance was slightly deteriorated.
The laminated porous film obtained in Comparative Example 3 exhibited good air permeability because the amount of the resin binder was reduced, but on the other hand, there were many fillers falling off in the stone mill test, and the anti-powder resistance was insufficient. It was.
In Comparative Example 4, since the absolute value of the difference between the SP values of the first solvent and the second solvent was too large, the second solvent was separated on the surface layer of the obtained paint, and the resulting laminate after coating The porous film was slightly deteriorated in air permeability.
The polyolefin resin porous film of Comparative Example 5 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. Separators for lithium ion secondary batteries; sanitary materials such as disposable paper diapers and pads for absorbing body fluids such as sanitary items or bed sheets; medical materials such as surgical clothing or base materials for warm compresses; jumpers, sportswear or rainwear Material for clothing; Building materials such as wallpaper, roof waterproofing material, heat insulating material, sound absorbing material, etc .; Desiccant; Dampproofing agent; Deoxidant agent; Disposable body warmer; It can be suitably used.

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 lid 31 Aluminum plate 32 Sample 33 Clip 34 Film longitudinal direction 35 Film lateral direction

Claims (12)

A step of forming a coating layer by applying a coating liquid containing a filler, a resin binder, and at least two solvents of a first solvent and a second solvent to at least one surface of a polyolefin-based resin porous film and drying the coating solution. A method for producing a laminated porous film comprising:
In the coating solution, the first solvent is 60% by mass or more of the total solvent,
The SP value of the first solvent (SP ₁ ), the SP value of the second solvent (SP ₂ ), the SP value of the resin binder (SP _B ) satisfy the following relational expressions (i) and (ii),
SP ₁ > SP _B (i)
_{10 <| SP 1 - SP 2} | <30 (ii)
The boiling point of the second solvent is higher than the boiling point of the first solvent,
And the manufacturing method of a laminated porous film which dissolves a resin binder completely in a solvent.   2. The method for producing a laminated porous film according to claim 1, wherein in the coating solution, the second solvent is 1% by mass or more and 40% by mass or less in the total solvent.   The manufacturing method of the laminated porous film of Claim 1 or 2 whose boiling point of said 2nd solvent is 10 degreeC or more higher than the boiling point of said 1st solvent.   The manufacturing method of the laminated porous film of any one of Claims 1-3 in which the said filler comprises a metal oxide.   In the said coating liquid, the content rate of the filler which occupies for the total amount of the said filler and the said resin binder is the range of 80 mass% or more and 99 mass% or less of any one of Claims 1-4. A method for producing a laminated porous film.   The method for producing a laminated porous film according to any one of claims 1 to 5, wherein the polyolefin resin porous film comprises polypropylene.   The manufacturing method of the lamination | stacking porous film of any one of Claims 1-6 with which the said polyolefin resin porous film has (beta) crystal activity.   The method for producing a laminated porous film according to any one of claims 1 to 7, wherein water is used for at least one of the first solvent and the second solvent.   The laminated porous film produced by the manufacturing method of the laminated porous film of any one of Claims 1-8. A laminated porous film comprising a filler and a resin binder on at least one surface of a polyolefin resin porous film, and further having a coating layer containing at least 10 ppm of each of two kinds of solvents, a first solvent and a second solvent, The SP value of the first solvent (SP ₁ ), the SP value of the second solvent (SP ₂ ), and the SP value of the resin binder (SP _B ) satisfy the following relational expressions (i) and (ii):
SP ₁ > SP _B (i)
_{10 <| SP 1 - SP 2} | <30 (ii)
And the laminated porous film whose boiling point of a 2nd solvent is higher than the boiling point of a 1st solvent.   The separator for nonaqueous electrolyte secondary batteries using the lamination | stacking porous film of Claim 9 or 10.   A non-aqueous electrolyte secondary battery containing the non-aqueous electrolyte secondary battery separator according to claim 11.

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