JP5685039B2 - Multilayer porous film, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a laminated porous film, which can be used as a packaging, sanitary, livestock, agricultural, architectural, medical, separation membrane, light diffusion plate, battery separator, and particularly as a separator for non-aqueous electrolytic batteries. It can be used suitably.

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

  In particular, 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 safety of the separator for a non-aqueous electrolyte secondary battery, 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 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 laminated porous film are blocked is referred to as a shutdown temperature (hereinafter referred to as “SD temperature”). In addition, with the recent increase in capacity of batteries, the temperature inside the battery rises rapidly, so that it is necessary to quickly block ion conduction. For this reason, the range between the temperature at which the SD characteristic starts and the SD temperature at which the micropores are blocked and ion conduction is blocked is required to be a narrow range. Especially, when using as a separator for nonaqueous electrolyte secondary batteries, it is necessary to have these SD characteristics.

  In response to the demand, a method has been proposed in which a thermoplastic resin is coated on a porous film having no SD characteristics to impart SD characteristics. In Patent Document 1, a shutdown layer made of an adhesive resin is formed on a PTFE porous film by coating a shutdown resin particle containing ethylene copolymer as a main component and a unitary copolymer containing acrylic ester acid and maleic anhydride. Has been. In Patent Document 2, a shutdown layer including a shutdown resin particle made of polyethylene particles and an adhesive resin made of polyolefin is formed by coating on a polypropylene porous film.

  On the other hand, in Patent Document 3, polyethylene particles are provided on a polyethylene porous film by coating for the purpose of improving film strength and providing safety at high temperatures.

JP-A-9-219185 JP 2009-19118 A Japanese Patent No. 2955323

However, in the method described in Patent Document 1, since the melting point temperature of the shutdown resin particles and the adhesive resin is as low as 100 ° C. or less, there is a problem that air permeability is lost even in a temperature range used as a normal battery.
Further, in Patent Document 2, since the softening temperature of the polyolefin adhesive resin used is lower than that of the resin particles for SD, the SD start temperature and the temperature range in which the micropores are closed and the shutdown is completed are widened. There was a problem of lacking.
In addition, the method described in Patent Document 3 is not only intended for imparting SD characteristics, but also because the melting point of the polyethylene particles used is as low as 100 ° C. or less. There was a problem of losing.

  The subject of this invention is solving the said problem. That is, it aims at providing the laminated porous film which was excellent in the SD characteristic, and had the outstanding characteristic, when used as a separator for nonaqueous electrolyte batteries.

  The present invention provides a resin binder having a melting point or glass transition temperature of 100 ° C. or more and less than 150 ° C. and a melting point or glass transition temperature of 150 ° C. or more on at least one surface of a polyolefin resin porous film (I layer). The laminated porous film is characterized in that a coating layer (II layer) containing (b) is laminated, and the air permeability at 25 ° C. is 2000 sec / 100 ml or less.

  In the present invention, the resin binder (b) is preferably a thermoplastic resin selected from at least one selected from polyvinyl alcohol, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid.

  In the present invention, the ratio of the particles (a) to the total amount of the particles (a) and the resin binder (b) is preferably 96% by mass or more.

  Further, the present invention preferably has β crystal activity.

  According to the present invention, it is possible to obtain a laminated porous film having excellent air permeability and having excellent SD characteristics as a separator for a nonaqueous electrolyte secondary battery.

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 laminated porous film in the air permeability at high temperature and a wide angle X-ray diffraction measurement.

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.

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

(Polyolefin resin porous film (I layer))
Examples of the polyolefin resin used in the polyolefin resin porous film include homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexane, and the like. Among these, a polypropylene resin is preferable.

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

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 polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. And a polymerization method using a single site catalyst.

  Examples of the polypropylene resin include trade names “Novatech PP” “WINTEC” (manufactured by Nippon Polypro), “Versify” “Notio” “Tafmer XR” (manufactured by Mitsui Chemicals), “Zeras” “Thermolan” (Mitsubishi Chemical) Manufactured by Sumitomo Chemical Co., Ltd.), “Sumitomo Noblen” “Tufselen” (manufactured by Sumitomo Chemical Co., Ltd.), “Prime TPO” (manufactured by Prime Polymer Co., Ltd.), “Adflex”, “Adsyl”, “HMS-PP (PF814)” (manufactured by Sun Aroma) Commercially available products such as “Inspire” (Dow Chemical) can be used.

The laminated porous film of the present invention preferably has the β crystal activity.
The β crystal activity can be regarded as an index indicating that the polypropylene resin produced β crystals in the film-like material before stretching. If the polypropylene resin in the film-like material before stretching produces β crystals, fine pores can be easily formed by stretching even when additives such as fillers are not used. A laminated porous film having characteristics 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 measurement using, it is determined that the crystal has “β crystal activity”.
Specifically, the laminated porous film is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min for 1 minute with a differential scanning calorimeter, and then cooled from 240 ° C. to 25 ° C. at a cooling rate of 10 ° C./min. Was maintained for 1 minute after the temperature was lowered, and when the temperature was raised again from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min, a crystal melting peak temperature (Tmβ) derived from the β crystal of the polypropylene resin was detected. In this case, it is determined that it has β crystal activity.

In addition, the β crystal activity of the laminated porous film is calculated by the following formula using the detected heat of crystal melting (ΔHmα) and the heat of crystal melting (ΔHmβ) derived from the β crystal of the polypropylene tree. 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 of 145 ° C. or higher and lower than 160 ° C., and mainly detected at 160 ° C. or higher and 170 ° C. or lower. 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 laminated porous film preferably has a higher β crystal activity, and the β crystal activity is preferably 20% or more. More preferably, it is 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 amount of β crystals of polyolefin resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. As a result, a separator for a lithium ion lithium battery 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 of the entire laminated porous film even when the laminated porous film of the present invention has a single layer structure or when other porous layers are laminated. .
Further, if a layer containing a polypropylene resin other than the layer made of polypropylene resin is laminated, it is preferable that both layers have β crystal activity.

  As a method for obtaining the β crystal activity described above, a method of adding polypropylene subjected to a treatment for generating a peroxide radical as described in Japanese Patent No. 3739481, and a method of adding a β crystal nucleating agent to the composition Etc.

(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., as a specific example of polypropylene resin to which β crystal nucleating agent is added, polypropylene manufactured by Aristech “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 polypropylene-based resin. The agent is preferably 0.0001 to 5.0 parts by mass. 0.001-3.0 mass parts is more preferable, and 0.01-1.0 mass part is still more preferable. If it is 0.0001 part by mass or more, β-crystals of polypropylene resin can be sufficiently produced and grown during production, and sufficient β-crystal activity can be secured even when used as a separator, and desired air permeability performance. Is obtained. Addition of 5.0 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.
Further, when a layer containing a polypropylene resin other than the layer made of polypropylene resin is laminated, the amount of β crystal nucleating agent added to each layer may be the same or different. The porous structure of each layer can be appropriately adjusted by changing the addition amount of the β crystal nucleating agent.

(Other ingredients)
In the present invention, in addition to the components described above, additives generally added to the resin composition can be added as appropriate within a range that does not significantly impair the effects of the present invention. Examples of the additive include recycling resin, silica, talc, kaolin, calcium carbonate, and the like, which are added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, Examples thereof include additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents. Specifically, the interfaces as antioxidants described in P154 to P158 of PLASTICS compounding agents, UV absorbers described in P178 to P182, and antistatic agents described in P271 to P275 Activators, lubricants described in P283 to P294, and the like.

(Method for producing polyolefin resin porous film (I layer))
Next, although the manufacturing method of the polyolefin resin porous film (I layer) of this invention is demonstrated, this invention is not limited only to the lamination | stacking porous film manufactured by this manufacturing method.

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 film-like thing manufactured by the tubular method and making it planar is also applicable.
There are methods for stretching the nonporous film-like material, 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.

In the present invention, when the polyolefin-based resin porous film (I layer) is laminated, the production method is roughly classified into the following four types depending on the order of the 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 a nonporous film to make it porous.
(IV) A method of forming a laminated porous film by preparing a porous layer and then applying a coating such as inorganic / organic particles or depositing metal particles.
In the present invention, it is preferable to use the method (II) from the viewpoint of 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 detail of a manufacturing method 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 laminated 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 less than 0.1 mm, it is not preferable from the viewpoint of production speed, and if it is more than 3.0 mm, it is not preferable from the viewpoint of production stability because the draft rate increases.

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

In the stretching step, uniaxial stretching may be performed in the longitudinal direction or the transverse direction, or biaxial stretching may be performed. Moreover, when performing biaxial stretching, simultaneous biaxial stretching may be sufficient and sequential biaxial stretching may be sufficient. When producing the polyolefin resin porous film of the present invention, sequential biaxial stretching is more preferable because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled.
Next, it is more preferable to stretch the obtained nonporous film-like material at least biaxially. 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 sequential biaxial stretching is used, the stretching temperature needs to be appropriately selected depending on the composition of the resin composition to be used and the crystallization state, but is preferably selected within the range of the following conditions.

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 laminated 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 preferred because the polyolefin hardly melts by the heat treatment and can maintain a porous structure. Moreover, you may perform a 1-20% relaxation process as needed during the heat processing process. In addition, a laminated porous film is obtained by cooling uniformly and winding up after heat processing.

(Coating layer (II layer))
The present invention provides a resin binder having a melting point or glass transition temperature of 100 ° C. or more and less than 150 ° C. and a melting point or glass transition temperature of 150 ° C. or more on at least one surface of a polyolefin resin porous film (I layer). It is characterized in that a coating layer (II layer) containing (b) is laminated.

(Particle (a))
It is important that the coating layer (II layer) of the present invention contains particles (a) having a melting point or glass transition temperature of 100 ° C. or higher and lower than 150 ° C. Due to the melting point or glass transition temperature of the particles (a) being 100 ° C. or higher and lower than 150 ° C., when used as a separator for a non-aqueous electrolyte secondary battery, the micropores are blocked when a high temperature of about 100 to 150 ° C. is reached. In addition, ion conduction inside the battery can be blocked.

  Examples of the particles (a) are not particularly limited as long as they are particles composed of a thermoplastic resin whose melting point or glass transition temperature falls within the range of 100 ° C. or higher and lower than 150 ° C. Specific examples include thermoplastic resins such as polyolefin resins, polystyrene resins, polyester resins, vinyl resins, polycarbonate resins, polyamide resins, polyimide resins, and polyurethane resins. Among these, particles composed of a polyolefin resin are preferable from the viewpoint of electrochemical stability.

The average particle diameter of the particles (a) is preferably 0.1 μm or more, more preferably 1 μm or more, still more preferably 3 μm or more, and the upper limit is preferably 10 μm or less, more preferably 6 μm or less. When the average particle diameter is within the specified range, sufficient SD characteristics can be expressed. Moreover, when it uses as a separator for nonaqueous electrolyte secondary batteries by making an average particle diameter into 0.1 micrometer or more, it is more preferable from a viewpoint of an air permeability characteristic and SD characteristic.
In the present embodiment, the “average particle diameter” is a value measured according to a method using SEM.

(Resin binder (b))
It is important that the coating layer (II layer) of the present invention contains a resin binder (b) having a melting point or glass transition temperature of 150 ° C. or higher. By using the resin binder (b), since the resin binder (b) does not melt in the temperature range in which the particles (a) melt and develop SD characteristics, from the start temperature of the SD characteristics to the SD temperature. This is preferable because the temperature range can be narrowed and excellent SD characteristics can be obtained.

  Examples of the resin binder (b) are not particularly limited as long as it is a thermoplastic resin having a melting point or glass transition temperature of 150 ° C. or higher, and the particles (a) and the polyolefin resin porous film are good. If it can adhere | attach and can be electrochemically stable, there will be no restriction | limiting. Specifically, ethylene-vinyl acetate copolymer (EVA, structural unit derived from vinyl acetate is 20 to 35 mol%), fluorine resin (polyvinylidene fluoride (PVDF), etc.), fluorine-based rubber, styrene-butadiene Rubber (SBR), nitrile butadiene rubber (NBR), polybutadiene rubber (BR), polyacrylonitrile (PAN), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl Examples include butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, cross-linked acrylic resin, polyurethane, and epoxy resin. These resin binders may be used alone or in combination of two or more. Among these, from the viewpoint of electrochemical stability, a thermoplastic resin selected from at least one selected from polyvinyl alcohol, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid is preferable.

  In the coating layer (II layer), the proportion of the particles (a) in the total amount of the particles (a) and the resin binder (b) is preferably 96% by mass or more, and more preferably 98% by mass or more. When the proportion of the particles (a) is 96% by mass or more, a laminated porous film having communication properties can be produced, and excellent air permeability and SD characteristics can be exhibited.

(Manufacturing method of coating layer (II layer))
The laminated porous film of the present invention dissolves or disperses the particles (a) having a melting point or glass transition temperature of 100 ° C. or higher and lower than 150 ° C. and the resin binder (b) having a melting point or glass transition temperature of 150 ° C. or higher in a solvent. The coated dispersion is applied to at least one surface of the polyolefin resin porous film (I layer) to form a coating layer (II layer) on the surface of the polyolefin resin porous film (I layer). be able to. The particles (a) having a melting point or glass transition temperature of 100 ° C. or higher and lower than 150 ° C. may be a solution dispersed in an emulsion.

  As the solvent, it is preferable to use a solvent in which the particles (a) and the resin binder (b) can be dissolved or dispersed uniformly and stably. Examples of such a solvent include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, hexane, and the like. Further, in order to stabilize the dispersion or improve the coating property to the polyolefin resin porous film, the dispersion includes a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent. Various additives such as an agent, a pH adjusting agent including an acid and an alkali may be added. The additive is preferably one that can be removed upon solvent removal or plasticizer extraction, but is electrochemically stable in the range of use of the nonaqueous electrolyte secondary battery, does not inhibit the battery reaction, and is about 200 ° C. If it is stable, it may remain in the battery (in the laminated porous film).

  Examples of a method for dissolving or dispersing the particles (a) and the resin binder (b) in a solvent include, 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, a high-speed impeller dispersion, Examples thereof include a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a mechanical stirring method using stirring blades.

  In the coating step, the coating method is not particularly limited as long as it can realize a required layer thickness and coating area. 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 dispersion liquid may be apply | coated to only one side of the polyolefin resin porous film in light of the use, and may be applied to both surfaces.

  The solvent is preferably a solvent that can be removed from the dispersion applied to the polyolefin resin porous film. As a method for removing the solvent, any method that does not adversely affect the polyolefin resin porous film can be adopted without any particular limitation. As a method for removing the solvent, for example, a method of drying a polyolefin resin porous film while fixing it at a temperature below its melting point, a method of drying at a low temperature under reduced pressure, or immersing in a poor solvent for the resin binder (b). And a method of extracting the solvent simultaneously with coagulation.

  In addition, the laminated porous film of this invention can also be manufactured using the method different from the manufacturing method mentioned above. For example, a raw material for polyolefin resin porous film (I layer) is introduced into one extruder, a raw material for a coating layer (II layer) is introduced into the other extruder, and integrated with one die to form a laminated film It is also possible to adopt a method of forming a porous material after forming the product.

(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 used as a separator for a non-aqueous electrolyte secondary battery, 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, Breaks through the separator for the electrolyte secondary battery and is not easily short-circuited. 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 (II layer) is preferably 0.5 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more, and particularly preferably 4 μm or more from the viewpoint of SD characteristics. 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.

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 is hardly lowered, which is preferable from the viewpoint of handling. The porosity is measured by the method described in the examples.

Regarding the laminated porous film of the present invention, the air permeability at 25 ° C. is important to be 2000 seconds / 100 ml or less, preferably 10 to 10,000 seconds / 100 ml, more preferably 50 to 800 seconds / 100 ml. If the air permeability at 25 ° C. is 2000 sec / 100 ml or less, it 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 thickness direction of the film. 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, which is preferable because battery performance is excellent.

  The laminated porous film of the present invention preferably has SD characteristics when used as a separator for a nonaqueous electrolyte secondary battery. Specifically, any of the air permeability after heating for 30 seconds in a temperature range of 100 to 150 ° C. is preferably 10000 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 to 10000 seconds / 100 ml or more, the holes are quickly closed and the current is interrupted during abnormal heat generation, so that troubles such as battery rupture can be avoided. Here, the SD temperature is the first one in which the air permeability after heating the laminated porous film at 100 ° C., 110 ° C., 120 ° C., 130 ° C., 140 ° C., and 150 ° C. for 30 seconds becomes 50000 seconds / 100 ml or more. The air permeability at that time is defined as the SD air permeability.

The laminated porous film of the present invention has an air permeability increase rate ΔPa ₁ of 100% obtained from the air permeability at 25 ° C. (Pa ₀ ) and the air permeability at a temperature 20 ° C. lower than the SD temperature (Pa ₁ ). Is preferably less than 30%, more preferably less than 30%. The air permeability increase rate ΔPa ₁ is calculated from the following equation.
ΔPa ₁ (%) = [(Pa ₁ −Pa ₀ ) / Pa ₀ ] × 100
As the battery capacity increases in recent years, the temperature inside the battery rises rapidly, so that it is necessary to quickly cut off ion conduction. Therefore, the range between the temperature at which the SD characteristic starts and the SD temperature at which the micropores are blocked and the ionic conduction is blocked is preferably a narrow range.
If the air permeability increase rate ΔPa ₁ is less than 100%, the SD characteristic does not appear within the temperature range from 25 ° C. to 20 ° C. lower than the SD temperature, and from the temperature lower by 20 ° C. than the SD temperature. This suggests that the SD characteristics are rapidly developed within the temperature range up to. That is, it is preferable for rapidly interrupting ionic conduction in a temperature range from a temperature 20 ° C. lower than the SD temperature to the SD temperature and calming the heating leading to ignition. On the other hand, if the ΔPa ₁ is 100% or more, ion conduction is slowly cut off, and therefore, Joule heat generation occurs, heating is accelerated, and ignition may occur, which is not preferable.

Further, the laminated porous film of the present invention has an increase in air permeability determined from the air permeability (Pa ₁ ) at a temperature 20 ° C. lower than the SD temperature and the air permeability (Pa ₂ ) at a temperature 10 ° C. lower than the SD temperature. The rate ΔPa ₂ is preferably less than 300%, more preferably less than 200%, and even more preferably less than 100%. The air permeability increase rate Pa ₂ is calculated from the following equation.
ΔPa ₂ (%) = [(Pa ₁ −Pa ₂ ) / Pa ₂ ] × 100
If the ΔPa ₂ is less than 300%, the SD characteristics are not yet fully developed within the temperature range from a temperature 10 ° C. lower than the SD temperature to a temperature 20 ° C. lower than the SD temperature, and a temperature 10 ° C. lower than the SD temperature. This suggests that the SD characteristics are rapidly developed within the temperature range from to the SD temperature. That is, it is preferable for rapidly interrupting ionic conduction within a temperature range from a temperature 10 ° C. lower than the SD temperature to the SD temperature to calm the heating leading to ignition. On the other hand, if the ΔPa ₂ is not less than 300%, the ion conduction is slowly interrupted as in the ΔPa ₁ , so that Joule heat generation occurs and heating is promoted, which may lead to ignition. Absent.

(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.

  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 vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a 70-mesh net. After removing the large particles, uniformly apply to both sides of 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. In other words, lithium graphite oxide (LiCoO ₂ ) was 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 were 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) Thickness With a 1/1000 mm dial gauge, 30 in-plane measurements were made unspecified, and the average value was taken as the thickness.

(2) Air permeability at 25 ° C (Gurley value)
In accordance with JIS P8117, the air permeability (second / 100 ml) was measured at 25 ° C.

(3) Air permeability at high temperature The obtained laminated porous film was cut into a 60 mm long × 60 mm wide 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 long, 60 mm wide, 1 mm thick) and sandwiched between two sheets, and the periphery was fixed with clips as shown in FIG.
A sample in which the laminated porous film was constrained to two aluminum plates was placed in a blowing constant temperature incubator (Tabai Espec Corp., Tabai Gear Oven GPH200) as a set temperature, and held for 30 seconds after the display temperature reached the set temperature. Then, the sample was taken out and the air permeability (second / 100 ml) at high temperature was measured according to JIS P8117.

(4) SD temperature, SD air permeability According to the measurement method of (3), the obtained laminated porous film is held at 100 ° C, 110 ° C, 120 ° C, 130 ° C, 140 ° C, 150 ° C for 30 seconds. After that, the air permeability was measured, and the first temperature at which the air permeability reached 50000 (seconds / 100 ml) or more was defined as the SD temperature. The air permeability at the SD temperature was defined as SD air permeability.

(5) Air permeability increase rate (ΔPa ₁ )
Air permeability increase rate Delta] Pa ₁ is calculated Delta] Pa ₁ from the following equation from air permeability at 25 ℃ (Pa ₀₎ and air permeability at 20 ° C. lower temperature than the SD temperature (Pa _1). Evaluation was made according to the following criteria.
ΔPa ₁ (%) = [(Pa ₁ −Pa ₀ ) / Pa ₀ ] × 100
A: ΔPa ₁ is 0% or more and less than 30%
Δ: ΔPa ₁ is 30% or more and less than 100% ×: ΔPa ₁ is 100% or more

(6) Air permeability increase rate (ΔPa ₂ )
Air permeability increase rate Delta] Pa ₂ has a Delta] Pa ₂ from the following formula from the air permeability of the SD temperature below 20 ° C. lower temperature (Pa ₁₎ and air permeability at 20 ° C. lower temperature than the SD temperature (Pa ₂₎ Calculation. Evaluation was made according to the following criteria.
ΔPa ₂ (%) = [(Pa ₁ −Pa ₂ ) / Pa ₂ ] × 100
A: ΔPa ₂ is 0% or more and less than 100%
○: ΔPa ₂ is 100% or more and less than 200% Δ: ΔPa ₂ is 200% or more and less than 300% ×: ΔPa ₂ is 300% or more

(7) SD characteristics The SD characteristics were evaluated according to the following criteria.
A: SD air permeability is 50000 seconds / 100 ml or more, and
ΔPa ₁ and ΔPa ₂ are both judged Δ or more ×: SD air permeability is 50000 seconds / 100 ml or more, and
Which of the determinations of ΔPa ₁ and ΔPa ₂ is ×

Further, the obtained laminated porous film was evaluated for β crystal activity as follows.
(8) Differential scanning calorimetry (DSC)
The obtained laminated porous film was heated from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min for 1 minute using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, and then held for 240 minutes. The temperature was lowered from 10 ° C. to 25 ° C. at a scanning speed of 10 ° C./min and held for 1 minute, and then heated again from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min. Based 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 re-heating, the presence or absence of β-crystal activity was evaluated according to what criteria. .
○: 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.

(9) Wide angle X-ray diffraction measurement (XRD)
The obtained laminated porous film was cut into a 60 mm long × 60 mm wide square, and as shown in FIG. 2 (A), an aluminum plate (material: JIS A5052, size: 60 mm long, with a central hole of 40 mmφ). The sheet was sandwiched between two sheets (60 mm in width and 1 mm in thickness), and the periphery was fixed with clips as shown in FIG.
A sample in which the laminated porous film is constrained to two aluminum plates is placed in a ventilation constant temperature thermostat (Yamato Scientific Co., Ltd., model: DKN602) having a set temperature of 180 ° C. and a display temperature of 180 ° C., and then set for 3 minutes. The temperature was changed to 100 ° C., and the mixture was gradually cooled to 100 ° C. over 10 minutes or more. When the display temperature reaches 100 ° C., the sample is taken out and cooled for 5 minutes in an atmosphere of 25 ° C. while being restrained by two aluminum plates. Wide-angle X-ray diffraction measurement was performed on a 40 mmφ circular portion.
-Wide-angle X-ray diffraction measurement device: manufactured by Mac Science, 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 a 60 mm x 60 mm square, it may adjust so that a laminated porous film may be installed in the circular hole of 40 mmphi in the center part, and may produce a sample.

[Production Example 1]
With respect to 100 parts by mass of polypropylene resin (manufactured by Prime Polymer Co., Ltd., Prime Polypro F300SV, density: 0.90 g / cm ³ , MFR: 3.0 g / 10 min), 3,9-bis [ After adding 0.2 parts by mass of 4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, the same-direction twin screw extruder (manufactured by Toshiba Machine Co., Ltd.) , Diameter: 40 mmφ, L / D: 32), melt-kneaded at a set temperature of 300 ° C., extruded from a strand die, cooled and solidified in water, cut into strands with a cutter, and polypropylene resin composition Article pellets were made. The β-crystal activity of the polypropylene resin composition was 80%.

Using the polypropylene resin composition, it was extruded from a T-die and cooled and solidified with a casting roll at 124 ° C. to prepare a nonporous film-like material.
The nonporous membrane-like material is stretched 4.6 times in the longitudinal direction using a longitudinal stretching machine, stretched twice in the lateral direction at 100 ° C. with a transverse stretching machine, and then subjected to heat setting / relaxation treatment. Was a polyolefin-based resin porous film having an air permeability at 25 ° C. of 256 sec / 100 ml.

  The obtained polyolefin resin porous film was subjected to corona surface treatment with a corona treatment apparatus (manufactured by Kasuga Denki Co., Ltd., line speed: 50 m / min, treatment output: 2 kW).

[Example 1]
As particles (a) having a melting point or glass transition temperature of 100 ° C. or more and less than 150 ° C., 45.9 parts by mass of Chemipearl W300 (Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm), As a resin binder (b) having a melting point or glass transition temperature of 150 ° C. or higher, 0.4 part by mass of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA124, degree of saponification: 98.0 to 99.0, average degree of polymerization: 2400) is water. A dispersion liquid dispersed in 53.7 parts by mass was obtained. At this time, the ratio of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 98% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Example 2]
As the particles (a), Chemipearl W300 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm) 47.1 parts by mass, the resin binder (b) as polyvinyl alcohol (Kuraray) PVA124, degree of saponification: 98.0 to 99.0, average degree of polymerization: 2400), obtained by dispersing 0.2 parts by mass in 52.7 parts by mass of water. At this time, the ratio of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 99% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Example 3]
As the particles (a), Chemipearl W100 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 128 ° C., average particle size: 3 μm) 45.9 parts by mass, the resin binder (b) as polyvinyl alcohol (Kuraray) PVA124, degree of saponification: 98.0 to 99.0, average degree of polymerization: 2400), obtained by dispersing 0.4 parts by mass in 53.7 parts by mass of water. At this time, the ratio of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 98% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Comparative Example 1]
As the particles (a), Chemipearl W300 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm), 73.2 parts by mass, and as the resin binder (b), Chemipearl EP-150H (Mitsui Chemicals Co., Ltd. solid content: 45%, melting point: 115 ° C.) A dispersion in which 7.2 parts by mass was dispersed in 19.6 parts by mass of water was obtained. At this time, the proportion of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 90% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Comparative Example 2]
As the particles (a), Chemipearl W100 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 128 ° C., average particle size: 3 μm) 73.2 parts by mass, and as the resin binder (b), Chemipearl EP-150H (Mitsui Chemicals Co., Ltd. solid content: 45%, melting point: 115 ° C.) A dispersion in which 7.2 parts by mass was dispersed in 19.6 parts by mass of water was obtained. At this time, the proportion of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 90% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Comparative Example 3]
As the particles (a), Chemipearl W300 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm), 73.2 parts by mass, and as the resin binder (b), Chemipearl EP-150H (Mitsui Chemicals, solid content: 45%, melting point: 115 ° C.) A dispersion in which 3.4 parts by mass was dispersed in 23.4 parts by mass of water was obtained. At this time, the ratio of the particles (a) to the total amount of the particles (a) and the resin binder (b) was 95% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C. The coatability of the (II layer) was insufficient, and the adhesion with the polyolefin resin porous film (I layer) was also insufficient.

[Comparative Example 4]
As the particles (a), 42.4 parts by mass of Chemipearl W300 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm), polyvinyl alcohol (Kuraray) as the resin binder (b) PVA124, degree of saponification: 98.0 to 99.0, average degree of polymerization: 2400), obtained by dispersing 0.9 parts by mass in 56.7 parts by mass of water, was obtained. At this time, the ratio of the particles (a) to the total amount of the particles (a) and the resin binder (b) was 95% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

[Comparative Example 5]
As the particles (a), Chemipearl W300 (manufactured by Mitsui Chemicals, solid content: 40%, melting point: 132 ° C., average particle size: 3 μm) 37.3 parts by mass, the resin binder (b) as polyvinyl alcohol (Kuraray) PVA124, degree of saponification: 98.0 to 99.0, average degree of polymerization: 2400), 1.7 parts by mass in 61.0 parts by mass of water, was obtained. At this time, the proportion of the particles (a) in the total amount of the particles (a) and the resin binder (b) was 90% by mass.
The obtained dispersion was applied to the corona-treated surface of the polyolefin resin porous film produced in Production Example 1 using a gravure coater so that the thickness after drying was 4 μm, and then dried at 75 ° C.
The physical properties of the obtained laminated porous film were evaluated, and the results are summarized in Table 1.

The laminated porous film obtained in any of the examples had excellent air permeability characteristics and could have excellent SD characteristics as a separator for a non-aqueous electrolyte secondary battery.
On the other hand, when a resin binder having a melting point of less than 150 ° C. is used as in Comparative Examples 1 and ₂ , the values of ΔPa ₁ and ΔPa ₂ increase, and good SD characteristics are obtained as a separator for a nonaqueous electrolyte secondary battery. I couldn't.
Further, in Comparative Example 3, the particle (a) is excessive with respect to the resin binder (b), and a good coating solution cannot be prepared. Therefore, the coating property and adhesion of the coating layer (II layer) Sex was insufficient.
Moreover, when the ratio of the said particle | grain (a) resin binder (b) contained in a dispersion liquid like the comparative examples 4 and 5 increased, the air permeability characteristic was inadequate.
In Comparative Example 5, although the air permeability was insufficient, a resin binder having a melting point of 150 ° C. or higher was used, so that the SD characteristics were good.

  The laminated porous film of the present invention can be applied to various uses that require air permeability. Separators for lithium 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 hot compresses; for clothing such as jumpers, sportswear or rainwear Materials: Architectural materials such as wallpaper, roof waterproofing material, heat insulating material, sound absorbing material, etc .; Desiccant; Dampproofing agent; Deoxygenating agent; Disposable body warmer; Used as packaging materials such as freshness preservation packaging or food packaging, etc. it can.

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 31 Aluminum Plate 32 Separator 33 Clip 34 Film Vertical Direction 35 Film Horizontal Direction

Claims (5)

On at least one surface of the polyolefin resin porous film (I layer), the particles include only particles (a) having a melting point or glass transition temperature of 100 ° C. or higher and lower than 150 ° C., and having a melting point or glass transition temperature of 150 ° C. or higher. coating layer comprising a resin binder (b) (II layer) are stacked, Ri air permeability der less 2000 sec / 100ml at 25 ° C., wherein the particles (a) and the resin binder (b) and the laminated porous film wherein the ratio of particles (a) relative to the total amount is characterized by der Rukoto least 96 wt%.   The laminate according to claim 1, wherein the resin binder (b) is a thermoplastic resin selected from at least one selected from polyvinyl alcohol, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid. Perforated film. laminated porous film according to claim 1 or 2, characterized in that it has β-crystal activity. The separator for nonaqueous electrolyte secondary batteries using the lamination | stacking porous film of any one of Claims 1-3 . A nonaqueous electrolyte secondary battery using the separator for a nonaqueous electrolyte secondary battery according to claim 4 .

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