JP5251193B2 - Porous polyolefin film - Google Patents

Description

  The present invention relates to a porous film excellent in easy slipping which is important as process handleability in addition to high air permeability and high porosity. Specifically, the present invention relates to a porous polyolefin film that improves slipperiness by providing a non-oriented polyolefin layer on a porous biaxially oriented polypropylene film and maintains high air permeability and porosity.

  Polypropylene films are used in various applications such as industrial materials, packaging materials, optical materials, and electrical materials due to their excellent mechanical, thermal, electrical, and optical properties. Since this porous polypropylene film is porous and porous, it has excellent properties such as permeability and low specific gravity in addition to the properties of a polypropylene film. Development of a wide range of applications, such as separation membranes, clothing, moisture-permeable waterproof membranes for medical applications, reflectors for flat panel displays, and thermal transfer recording sheets, is being considered.

  Various proposals have been made as methods for making a polypropylene film porous. Porous methods can be broadly classified into wet methods and dry methods. In the wet method, polypropylene is used as the matrix resin, the extractables to be extracted after sheeting are added and mixed, and only the additives are extracted using the good solvent of the extractables, creating voids in the matrix resin. Various methods have been proposed (for example, see Patent Document 1). On the other hand, as a dry method, for example, by adopting low-temperature extrusion and a high draft ratio at the time of melt extrusion, the lamella structure in the film before stretching formed into a sheet is controlled, and this is uniaxially stretched so that at the lamella interface There has been proposed a method (so-called lamellar stretching method) in which cleavage occurs to form voids (see, for example, Patent Document 2). Further, as a dry method, a large amount of incompatible resin is added as inorganic particles or polypropylene, which is a matrix resin, and a sheet is formed and stretched to cause cleavage at the interface between the particles and the polypropylene resin. A forming method has also been proposed (see, for example, Patent Document 3). Furthermore, there is a so-called β crystal method in which voids are formed in the film by utilizing the crystal density difference and crystal transition between α type crystal (α crystal) and β type crystal (β crystal), which are polymorphs of polypropylene. Many proposals of the called method are also made (for example, refer patent documents 4-6).

  When the porous polypropylene film produced by the various methods described above is used as a separator for an electricity storage device, particularly a lithium ion secondary battery, the β crystal method usually forms voids by biaxial stretching, so it is compared with other methods. Thus, a high porosity can be achieved. Therefore, the internal resistance of the battery can be lowered, and it is particularly suitable for a separator for a high-output power storage device that requires a large current (see, for example, Patent Document 7). However, since the β crystal method has a high porosity, the film surface has a high aperture ratio and a large number of fibrils, so that when the films are stacked, the fibrils tend to get caught, resulting in a coefficient of friction. As a result, there was a problem that the handling of the processing process was hindered.

In a porous film, as a proposal for improving the handleability resulting from a high friction coefficient and low slipperiness, a method of adding particles to the film (for example, see Patent Document 8) has been proposed. . However, in the method of adding particles to the film, when particles are dropped from the inside during handling of the film, or particles are released in the electrolyte during use as a separator and move onto the electrode. As a result, there is a possibility of insulation, which is insufficient as a countermeasure.
Japanese Patent Laid-Open No. 55-131028 Japanese Patent Publication No.55-32531 JP-A-57-203520 JP-A 63-199742 JP-A-6-100720 Japanese Patent Laid-Open No. 9-255804 International Publication No. 05/103127 Pamphlet JP 2005-171230 A

  An object of the present invention is to solve the above-described problems. That is, a porous polyolefin film that achieves excellent handling while maintaining high air permeability and porosity, and that hardly releases foreign matter into the electrolyte when used in a separator of an electricity storage device. It is to provide.

  The above-mentioned problem is that a non-oriented polyolefin resin layer is provided on at least one surface of a biaxially oriented polypropylene porous film, the film has a total thickness of 10 to 50 μm, and an air resistance of 10 to 500 seconds / 100 ml. This can be achieved with a conductive polyolefin film.

  The porous polyolefin film of the present invention has excellent ion conductivity suitable for a lithium ion battery separator and excellent processability, and can be suitably used as a separator.

  The biaxially oriented polypropylene porous film used in the present invention is a film having many fine through-holes penetrating both surfaces of the film and having air permeability. As a method for forming a through-hole in a film, it is preferable to use a β crystal method because it is necessary to make biaxial orientation to make the physical properties uniform and maintain high strength while being a thin film.

  In order to form through-holes in the film using the β crystal method, it is important to form a large amount of β crystals in the polypropylene resin. For this purpose, it is added to the polypropylene resin, which is called a β crystal nucleating agent. Thus, a crystallization nucleating agent that selectively forms β crystals is preferably used as an additive. Examples of the β crystal nucleating agent include various pigment compounds and amide compounds. In particular, amide compounds disclosed in JP-A-5-310665 can be preferably used. The addition amount of the β crystal nucleating agent is preferably 0.05 to 0.5 parts by mass, more preferably 0.1 to 0.3 parts by mass when the entire polypropylene resin is 100 parts by mass. .

  The polypropylene resin constituting the biaxially oriented polypropylene porous film used in the present invention has an isotactic range of 2-30 g / 10 min in melt flow rate (hereinafter referred to as MFR, measurement conditions are 230 ° C., 2.16 kg). A tic polypropylene resin is preferred. If the MFR is out of the above preferred range, it may be difficult to obtain a biaxially stretched film. More preferably, the MFR is 3 to 20 g / 10 minutes.

  The isotactic index of the isotactic polypropylene resin is preferably 90 to 99.9%. If the isotactic index is less than 90%, the crystallinity of the resin is low and high air permeability is achieved. May be difficult. A commercially available resin can be used as the isotactic polypropylene resin.

  A homopolypropylene resin can be used for the biaxially oriented polypropylene porous film used in the present invention, as well as an ethylene component in polypropylene from the viewpoint of stability in the film-forming process, film-forming properties, and uniformity of physical properties. Or α-olefin components such as butene, hexene and octene may be copolymerized within a range of 5% by mass or less. The form of the comonomer introduced into the polypropylene may be either random copolymerization or block copolymerization.

  Moreover, it is preferable that the above-mentioned polypropylene resin contains a high melt tension polypropylene in the range of 0.5 to 5% by mass in terms of improving the film forming property. High melt tension polypropylene is a polypropylene resin whose tension in the molten state is increased by mixing a high molecular weight component or a component having a branched structure into the polypropylene resin or by copolymerizing a long-chain branched component with polypropylene. However, among these, it is preferable to use a polypropylene resin copolymerized with a long chain branching component. This high melt tension polypropylene is commercially available, and for example, polypropylene resins PF814, PF633, and PF611 manufactured by Basel, polypropylene resin WB130HMS manufactured by Borealis, and polypropylene resins D114 and D206 manufactured by Dow can be used.

  The polypropylene resin constituting the biaxially oriented polypropylene porous film used in the present invention has improved void formation efficiency during stretching, and air permeability is improved by expanding the pore diameter. Therefore, 80 to 99% by mass of polypropylene and ethylene / α -It is preferable to set it as a mixture with 20-1 mass% of olefin copolymers. Here, examples of the ethylene / α-olefin copolymer include linear low density polyethylene and ultra-low density polyethylene. Among them, ethylene / octene-1 copolymer obtained by copolymerization of octene-1 is preferably used. be able to. Examples of the ethylene-octene-1 copolymer include commercially available resins such as “Engage (registered trademark)” (type names: 8411, 8452, 8100, etc.) manufactured by Dow Chemical.

  Since the biaxially oriented polypropylene porous film used in the present invention is preferably made porous by the β crystal method, the β crystal forming ability of the polypropylene resin constituting the film is preferably 40 to 80%. If the β-crystal forming ability is less than 40%, the amount of β-crystals is small at the time of film production, so the number of voids formed in the film is reduced by utilizing the transition to α-crystal, and as a result, only films with low permeability are obtained. It may not be possible. When the β crystal forming ability exceeds 80%, coarse pores may be formed, and the function as a separator for an electricity storage device may not be provided. In order to make the β crystal forming ability within the range of 40 to 80%, it is preferable to add the above-mentioned β crystal nucleating agent as well as using a polypropylene resin having a high isotactic index. The β crystal forming ability is more preferably 50 to 80%.

  In the porous polyolefin film of the present invention, a non-oriented polyolefin resin layer is provided on at least one surface of a biaxially oriented polypropylene porous film. As a method of providing a non-oriented polyolefin resin layer (hereinafter sometimes referred to as a non-oriented resin layer) on a biaxially oriented polypropylene porous film (hereinafter sometimes referred to as a biaxially oriented film), a biaxially oriented film is produced. After that, a coating liquid containing a resin that forms a non-oriented resin layer is applied in a later step, or a non-oriented resin layer is separately prepared and bonded, and a resin layer is provided during the manufacturing process of the biaxially oriented film An example is a method in which a process is incorporated and co-stretched at least in a uniaxial direction, and then only the resin layer is non-oriented by heat treatment or the like. However, in the former case, it is necessary to wind up after manufacturing the biaxially oriented film and unwind it in the processing step of providing the non-oriented resin layer. At that time, the slipperiness is bad, and the film may be wrinkled or the film may be torn. There are low yields, and the step of providing through-holes in the non-oriented resin layer is necessary for pasting in the latter process, so the non-oriented polyolefin is produced during the latter biaxially oriented film manufacturing process. A method of providing a resin layer is preferred.

  In the present invention, as the polyolefin resin constituting the non-oriented polyolefin resin layer, a resin made of a homopolymer or copolymer of polyethylene or polypropylene can be preferably used. In particular, in the present invention, it is preferable to incorporate a step of providing a polyolefin-based resin layer in the manufacturing process of the biaxially oriented film, and after co-stretching at least in a uniaxial direction, only the resin layer is non-oriented by heat treatment or the like. Therefore, it is preferable to use a resin having a softening temperature that softens and flows on the film surface to the extent that the through-holes are not blocked in the heat treatment step, and forms a non-oriented layer. Specifically, the softening temperature is biaxially oriented. It is preferably (melting point −75 ° C.) to (melting point −10 ° C.), more preferably (melting point −55 ° C.) to (melting point −15 ° C.). In the case of a polypropylene film having a melting point of 175 ° C., it is preferably 100 to 165 ° C., and particularly preferably 120 to 160 ° C.

  Since the porous polyolefin film of the present invention is suitably used for a separator for an electricity storage device, the air resistance is preferably 10 to 500 seconds / 100 ml. Here, the air permeation resistance is the air permeation resistance (Gurley) defined in JIS P8117 (1998), and is a value evaluated using the JIS B-type tester in the present invention. If the air permeability resistance is less than 10 seconds / 100 ml, the film strength is low, and pinholes are easily generated when used as a separator, causing a short circuit or tearing when wound for storage inside the battery. May be inferior in handleability. On the contrary, if the air resistance exceeds 500 seconds / 100 ml, the ion conductivity is poor. From the viewpoint of exhibiting excellent ionic conductivity as a separator, the air permeability resistance is more preferably 30 to 300 seconds / 100 ml, and particularly preferably 50 to 200 seconds / 100 ml.

  In the present invention, a non-oriented polyolefin resin layer is provided on at least one surface of a biaxially oriented polypropylene porous film. In order to achieve the above air resistance, the average thickness of the non-oriented polyolefin resin layer is 0.2 μm or less. Preferably there is. If the average thickness of the non-oriented polyolefin-based resin layer exceeds 0.2 μm, the number of through holes on the surface of the resin layer may be reduced, and air permeability may be reduced. The average thickness of the non-oriented polyolefin-based resin layer is preferably 0.001 to 0.2 μm, more preferably 0.005 to 0.17 μm, and 0.01 to 0.15 μm for the expression of slipperiness. It is particularly preferable in terms of both slipperiness and air permeability.

  The surface opening ratio of the non-oriented polyolefin resin layer surface of the porous polyolefin film of the present invention is preferably 10 to 50% from the viewpoint of film handling properties, particularly slipperiness. If the surface opening ratio is less than 10%, the air permeability may be inferior. If it exceeds 50%, the polypropylene fibrils forming the biaxially oriented polypropylene porous film are excessively exposed on the surface, so that the slipperiness is deteriorated and the film is handled. May inhibit sex. The surface aperture ratio is more preferably 10 to 40%, and particularly preferably 10 to 35%.

As a method for setting the surface opening ratio of the surface of the non-oriented polyolefin-based resin layer in such a preferable range, it can be realized by providing the resin layer with an average thickness of preferably 0.2 μm or less. Specifically, after uniaxially stretching an unstretched polypropylene sheet in the longitudinal direction, an aqueous dispersion of polyolefin resin is applied onto the uniaxially stretched polypropylene film at a solid content of 0.01 to 1 g / cm ^3. A method for obtaining the porous polyolefin film of the present invention by stretching in the width direction and heat setting at a temperature not lower than the softening point (or melting point) of the polyolefin resin and not higher than the melting point of the uniaxially stretched polypropylene film as the base. Is preferably adopted. By extending in the width direction in the above temperature range, the polyolefin resin layer can be non-oriented. In order to obtain a non-oriented polyolefin resin layer by coating in the manufacturing process of such a biaxially oriented film, commercially available water-dispersed polyolefin particles can be used as the polyolefin resin used, for example, Mitsui Chemicals ( Chemipearl (type: W100, WP100, etc.) of Co., Ltd. can be preferably used.

  The porous polyolefin film of the present invention preferably has a porosity of 60 to 90% from the viewpoint of ionic conductivity when used as a separator. When the porosity is less than 60%, the electric resistance increases when used as a separator, and when used for a high output, heat may be generated and energy may be lost. On the other hand, if the porosity exceeds 90%, the strength of the film is lowered and pinholes are easily generated, which may cause a short circuit or break when wound for storage inside the battery. It may be inferior in handleability. From the viewpoint of achieving both excellent battery characteristics and strength, the porosity of the film is more preferably 65 to 85%, and particularly preferably 70 to 82%.

  As a method for controlling the porosity of the film to such a preferable range, when the polypropylene film is made porous by the β crystal method, as described above, 80 to 99% by mass of polypropylene and 20 ethylene / α-olefin copolymer are added. It becomes easy to achieve by using a mixture of ˜1% by mass, and can be specifically achieved by adopting biaxial stretching conditions described later. In the extraction method or the lamellar stretching method, it is difficult to obtain a porous film having such a high porosity and strength that can be put into practical use.

  The porous polyolefin film of the present invention preferably has a total film thickness of 10 to 50 μm. If the total thickness is less than 10 μm, the film may break during use. If the total thickness exceeds 50 μm, the capacity of the porous film contained in the electricity storage device becomes too large, and a high energy density cannot be obtained. The total film thickness is more preferably 12 to 30 μm, and still more preferably 14 to 25 μm.

  In the porous polyolefin film of the present invention, an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, an anti-blocking agent, a filler, Various additives such as a compatible polymer may be contained. In particular, it is preferable to add 0.01 to 0.5 parts by mass of an antioxidant with respect to 100 parts by mass of the polypropylene resin in order to suppress oxidative degradation due to the thermal history of the polypropylene resin.

  Below, the manufacturing method of the porous polyolefin film of this invention is demonstrated concretely. In addition, the manufacturing method of the film of this invention is not limited to this.

  First, as a polypropylene resin constituting the biaxially oriented polypropylene porous film, 94 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 minutes, 1 part by mass of a high melt tension polypropylene resin having a commercially available MFR of 2.5 g / 10 minutes, and a melt index. Mix 5 parts by weight of ultra-low density polyethylene resin of 18 g / 10 minutes with 0.2 part by weight of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide, and use a twin screw extruder to obtain a predetermined ratio. Prepare the raw materials mixed in At this time, the melting temperature is preferably 270 to 300 ° C.

  Next, the mixed raw material is supplied to a single-screw melt extruder, and melt extrusion is performed at 200 to 230 ° C. And after removing a foreign material, a modified polymer, etc. with the filter installed in the middle of the polymer pipe | tube, it discharges on a cast drum from T-die, and an unstretched sheet is obtained. At this time, the surface temperature of the cast drum is preferably 105 to 130 ° C. from the viewpoint of controlling the β crystal fraction of the cast film to be high. At this time, in particular, since the forming of the end portion of the sheet affects the subsequent stretchability, it is preferable that the end portion is sprayed with spot air to be in close contact with the drum. Further, air may be blown over the entire surface using an air knife as necessary based on the state of close contact of the entire sheet on the drum.

  Next, the obtained unstretched sheet is biaxially oriented to form pores in the film. As a biaxial orientation method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method in that it is easy to obtain a highly air-permeable film, and in particular, it is possible to stretch in the width direction after stretching in the longitudinal direction. preferable.

  As specific stretching conditions, first, the temperature is controlled so that the unstretched sheet is stretched in the longitudinal direction. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. The stretching temperature in the longitudinal direction is preferably 90 to 120 ° C, more preferably 95 to 110 ° C. As a draw ratio, it is 3-6 times, More preferably, it is 3-5 times.

In order to provide a non-oriented polyolefin-based resin layer on at least one side of the biaxially oriented polypropylene porous film that is a feature of the present invention, after the film is stretched in the longitudinal direction, the film once cooled is improved by corona discharge treatment or the like. It is preferable to employ a method of applying an aqueous dispersion in which a polyolefin resin is dispersed on the wettability improving surface. As a coating method on the film, a generally used coater such as a Mayer bar, a die coater, or a gravure coater can be used. At this time, the coating amount on the film is preferably such that the resin solid content is 0.01 to 1 g / cm ³ . The polyolefin resin may be applied to both sides of the polypropylene film.

  Next, the polypropylene film coated with the aqueous dispersion is introduced by gripping the end of the film with a stenter type stretching machine. And it heats to 130-155 degreeC preferably, and extends 6 to 12 times in the width direction, More preferably, it extends 6 to 10 times. The transverse stretching speed at this time is preferably 100 to 5,000% / min, more preferably 1,000 to 4,000% / min. Subsequently, heat setting is performed in the stenter as it is, and the temperature is preferably from the transverse stretching temperature to 160 ° C. Furthermore, it may be carried out while relaxing in the longitudinal direction and / or the width direction of the film at the time of heat setting, and in particular, the relaxation rate in the width direction is preferably 7 to 12% from the viewpoint of thermal dimensional stability.

  The porous polyolefin film of the present invention is not only excellent in air permeability and mechanical properties, but also excellent in slipperiness, and thus is particularly preferable as a separator for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. Can be used.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) β-crystal forming ability 5 mg of resin or film was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 240 ° C. at 10 ° C./min (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 30 ° C. at 10 ° C./min. After holding for 5 minutes, the melting peak observed when the temperature is raised again at 10 ° C./min (second run) is the melting peak of the β crystal at 145 ° C. to 157 ° C., 158 ° C. The melting at which the peak is observed is defined as the melting peak of the α crystal, and the melting heat amount of the α crystal is obtained from the baseline and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. Is the ΔHα, and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. The heat of fusion was calibrated using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal in the same manner from the melting peak observed in the first run.

(2) Melt flow rate (MFR)
The MFR of polypropylene and thermoplastic elastomer is measured according to the condition M (230 ° C., 2.16 kg) of JIS K 7210 (1995). The polyethylene resin is measured in accordance with the condition D (190 ° C., 2.16 kg) of JIS K 7210 (1995).

(3) Melting point of polypropylene and polyolefin resin Polypropylene and solid polyolefin resin are used as samples, and in the case of polyolefin resin dispersed in water, an appropriate amount of water dispersion is sampled and heated at 70 ° C in a hot air oven. Dry and collect only the solid content as a sample.

  A solid content of 5 mg was taken as a sample in an aluminum pan and measured using a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi Kogyo). Regarding the melting peak observed when the temperature was raised from room temperature to 200 ° C. at 20 ° C./min under a nitrogen atmosphere, the peak temperature on the highest temperature side was taken as the melting point of the resin.

  When a melting point was observed in the polyolefin-based resin, the temperature was set as the softening temperature, and when it was amorphous and there was no melting point, the glass transition point was set as the softening temperature.

(4) Air permeability resistance A 100 mm long square was cut from the film and used as a sample. The permeation time of 100 ml of air was measured three times at 23 ° C. and relative humidity 65% using a JIS P 8117 (1998) type B Gurley tester. The average value of the permeation time was taken as the air resistance of the film.

(5) Porosity The film was cut into a size of 30 mm × 40 mm and used as a sample. Using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.), the specific gravity was measured in an atmosphere at a room temperature of 23 ° C. and a relative humidity of 65%. The measurement was performed three times, and the average value was defined as the specific gravity ρ of the film.

  Next, the measured film was hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C. to prepare a sheet from which pores were completely erased. The specific gravity of this sheet was measured in the same manner as described above, and the average value was defined as the specific gravity (d) of the resin. In the examples described later, the specific gravity d of the resin was 0.91 in any case. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.

Porosity (%) = [(d−ρ) / d] × 100
(6) Film total thickness The film total thickness measured the thickness about arbitrary 5 places in the state which piled up the film of 10 sheets according to JISK7130 (1992) A-2 method using the dial gauge. The average value of the five values was divided by 10 to calculate the total film thickness per sheet.

(7) Average thickness of non-oriented polyolefin-based resin layer A weight-average thickness calculated by the following formula from the mass of the film 50 m ² of the present invention provided with the non-oriented polyolefin-based resin layer and a non-oriented polyolefin-based resin layer are provided. Otherwise, the difference from the weight average thickness calculated by the following formula from the mass of the film 50 m2 prepared under the same conditions was taken as the average thickness of the polyolefin-based resin layer.

Weight average thickness (μm) = [(W / 50) / ρ] × 10 ³
Where W is the mass (kg) of the size of the film 50 m ² , ρ is the density of the film (g / cm ³ : the measurement method conforms to the specific gravity of (5) above, and the specific gravity = density)
(8) Surface opening ratio A scanning electron micrograph of the surface of the porous polyolefin film taken at a magnification of 1,500 is printed on a B4 size paper, and the open area is blackened in an arbitrary 100 mm square area. Filled. Imported into a computer with a scanner and converted to an electronic file. The image is processed with image processing software “Image-Pro Plus” (Media Cybernetics), and the area ratio of the unopened portion painted black and the other opening portions is obtained. did.

(9) Friction coefficient The dynamic friction coefficient when the non-oriented polyolefin resin layer surfaces of the film were brought into contact with each other was measured according to ASTM D-1894 (1995). The dynamic friction coefficient was measured using a surface property measuring machine HEIDON-14DR manufactured by Shinto Kagaku Co., Ltd. under the conditions of a sample moving speed of 200 mm / min, a load of 200 g, and a contact area of 63.5 mm × 63.5 mm. : Recorded and evaluated with HEIDON 3655E-99.

Class A: Dynamic friction coefficient is 0.2 or more and less than 0.6 Class B: Dynamic friction coefficient is 0.6 or more and less than 1.0 Class C: Dynamic friction coefficient is less than 0.2 or 1.0 or more Dynamic friction coefficient is less than 0.2 If this is the case, winding misalignment may occur. Conversely, if it exceeds 1.0, the surface may be damaged during conveyance. Practically, Class A and Class B were set as acceptable.

(10) Ionic conductivity An electrolytic solution was prepared by dissolving LiPF ₆ at a ratio of 1 mol / L in an equal volume mixed solvent of propylene carbonate and dimethyl carbonate. Nickel positive and negative electrodes and a porous polyolefin film between the positive and negative electrodes are placed in the electrolyte, and a Cole-Cole plot is measured by a complex impedance method using an LCR meter, and an impedance at 20,000 Hz is measured. The real part was obtained and used as an index of ion conductivity. The measurement was performed at 25 ° C. in a glove box in an argon atmosphere.

Class A: Impedance (real part) less than 0.12Ω Class B: Impedance (real part) 0.12Ω or more and less than 0.15Ω Class C: Impedance (real part) 0.15Ω or more (Example 1)
As a raw material resin for a polypropylene porous film, 94 parts by mass of homopolypropylene FSX80E4 (hereinafter referred to as PP-1; MFR = 5) manufactured by Sumitomo Chemical Co., Ltd., Basel polypropylene PF-814 (hereinafter referred to as a high melt tension polypropylene resin) , HMS-PP, MFR = 3) 1 part by mass, ethylene-octene-1 copolymer Dow Chemical Engage 8411 (melt index: 18 g / 10 min, hereinafter simply referred to as PE) 5 mass N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (manufactured by Shin Nippon Rika Co., Ltd., Nu-100, hereinafter simply referred to as β crystal nucleating agent) 0.2 parts by mass, and IRGANOX 1010, IRGAFO manufactured by Ciba Specialty Chemicals, which are antioxidants 168 are each 0.15, 0.1 parts by weight (hereinafter simply referred to as an acid inhibitor and used in a mass ratio of 3: 2 unless otherwise specified) from the weighing hopper to be mixed at this ratio. The raw material was supplied to a twin screw extruder, melt kneaded at 300 ° C., discharged from a die in a strand shape, cooled and solidified in a 25 ° C. water bath, cut into a chip shape, and used as a chip raw material.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 25 μm cut sintered filter, it is discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. Next, preheating was performed using a ceramic roll heated to 100 ° C., and the film was stretched 4.5 times in the longitudinal direction of the film. After cooling, the surface side in contact with the cast drum is subjected to corona discharge treatment to improve surface wettability, and there is an aqueous dispersion solution of polyolefin resin particles, Chemipearl (registered trademark) WP100 manufactured by Mitsui Chemicals, Inc. (Melting point: 145 ° C.) was diluted with a methanol aqueous solution (concentration: 50 mass%) to a solid content concentration of 2 mass%, and uniformly applied to the surface in contact with the cast drum using a Mayer bar (No. 6). Next, the end portion was introduced into a tenter-type stretching machine by holding a clip and stretched 6.5 times at 145 ° C. at a stretching speed of 1,300% / min. As it was, heat treatment was performed at 150 ° C. for 7 seconds while relaxing 8% in the width direction to obtain a porous polyolefin film having a total thickness of 20 μm.

(Example 2)
As a raw material resin for a polypropylene porous film, PP-1 is added to 96 parts by mass, HMS-PP is added to 1 part by mass, PE is added to 3 parts by mass, β-crystal nucleating agent is added to 0.2 part by mass, and an antioxidant 0. 25 parts by mass are fed to the twin screw extruder from the weighing hopper so as to be mixed at this ratio, melt kneaded at 300 ° C, discharged from the die in a strand shape, and cooled and solidified in a 25 ° C water bath Then, it was cut into a chip shape to obtain a chip raw material.

  This chip is supplied to a single screw extruder, melt extruded at 220 ° C., foreign matter is removed by a sintered filter of 25 μm cut, and then discharged from a T die to a cast drum whose surface temperature is controlled at 122 ° C. An unstretched sheet was obtained by casting for 15 seconds. Next, preheating was performed using a ceramic roll heated to 100 ° C., and the film was stretched 4.5 times in the longitudinal direction of the film. After cooling, the surface side that was in contact with the cast drum was subjected to corona discharge treatment to improve surface wettability, and there was an aqueous dispersion solution of polypropylene particles, Chemipearl (registered trademark) WP100 (manufactured by Mitsui Chemicals, Inc.). The melting point was 145 ° C.) was diluted with a methanol aqueous solution (concentration: 50 mass%) to a solid content concentration of 5 mass%, and uniformly applied to the surface in contact with the cast drum using a Mayer bar (No. 12). Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, and the film was stretched 6.5 times at 135 ° C. at a stretching speed of 1,300% / min. As it was, heat treatment was performed at 140 ° C. for 7 seconds while relaxing 7% in the width direction to obtain a porous polyolefin film having a total thickness of 18 μm.

(Example 3)
As a raw material resin for a polypropylene porous film, PP-1 is added to 94 parts by mass, HMS-PP is added to 3 parts by mass, PE is added to 3 parts by mass, β-crystal nucleating agent is added to 0.2 parts by mass, 25 parts by mass are fed to the twin screw extruder from the weighing hopper so as to be mixed at this ratio, melt kneaded at 300 ° C, discharged from the die in a strand shape, and cooled and solidified in a 25 ° C water bath Then, it was cut into a chip shape to obtain a chip raw material.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 25 μm cut sintered filter, it is discharged from a T-die onto a cast drum whose surface temperature is controlled at 120 ° C. The unstretched sheet was obtained by casting for 13 seconds. Next, preheating was performed using a ceramic roll heated to 105 ° C., and the film was stretched 3 times in the longitudinal direction of the film. After cooling, the surface side that was in contact with the cast drum was subjected to corona discharge treatment to improve surface wettability, and there was an aqueous dispersion of polyethylene particles, Chemipearl (registered trademark) W100 (manufactured by Mitsui Chemicals, Inc.). A melting point of 124 ° C. was diluted with a methanol aqueous solution (concentration: 50 mass%) to a solid concentration of 1 mass%, and uniformly applied to the surface in contact with the cast drum using a Mayer bar (No. 6). Next, the end portion was introduced into a tenter-type stretching machine by holding it with a clip, and stretched at 135 ° C. seven times at a stretching speed of 1,500% / min. As it was, heat treatment was performed at 145 ° C. for 7 seconds while relaxing 8% in the width direction to obtain a porous polyolefin film having a total thickness of 35 μm.

Example 4
As a raw material resin for a polypropylene porous film, PP-1 is added to 78 parts by mass, HMS-PP is added to 2 parts by mass, PE is added to 20 parts by mass, β-crystal nucleating agent is added to 0.2 parts by mass, and an antioxidant 0. 25 parts by mass are fed to the twin screw extruder from the weighing hopper so as to be mixed at this ratio, melt kneaded at 300 ° C, discharged from the die in a strand shape, and cooled and solidified in a 25 ° C water bath Then, it was cut into a chip shape to obtain a chip raw material.

  This chip is supplied to a single screw extruder and melt extruded at 220 ° C. After removing foreign matter with a 30 μm cut sintered filter, it is discharged from a T-die to a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. Subsequently, it preheated using the ceramic roll heated at 95 degreeC, and stretched 5 times in the longitudinal direction of the film. After cooling, the surface side that was in contact with the cast drum was subjected to corona discharge treatment to improve surface wettability, and there was an aqueous dispersion of polyethylene particles, Chemipearl (registered trademark) W100 (manufactured by Mitsui Chemicals, Inc.). A melting point of 124 ° C. was diluted with a methanol aqueous solution (concentration: 50 mass%) to a solid content concentration of 10 mass%, and uniformly applied to the surface in contact with the cast drum using a Mayer bar (No. 3). Next, the end portion was introduced into a tenter type stretching machine with a clip, and the film was stretched 7 times at 145 ° C. at a stretching speed of 1,500% / min. As it was, heat treatment was performed at 145 ° C. for 7 seconds while relaxing 8% in the width direction to obtain a porous polyolefin film having a total thickness of 25 μm.

(Example 5)
As a raw material resin for a polypropylene porous film, PP-1 is added to 97 parts by mass, HMS-PP is added to 3 parts by mass, β-crystal nucleating agent is added to 0.2 part by mass, and an antioxidant is added to 0.25 part by mass. The raw material is supplied from the weighing hopper to the twin screw extruder so that it is mixed at a ratio, melted and kneaded at 290 ° C, discharged from the die in a strand shape, cooled and solidified in a 25 ° C water tank, and cut into chips. And used as a raw material for chips.

  This chip is supplied to a single screw extruder and melt extruded at 230 ° C. After removing foreign matter with a 30 μm cut sintered filter, it is discharged from a T die to a cast drum whose surface temperature is controlled at 115 ° C. An unstretched sheet was obtained by casting for 15 seconds. Next, preheating was performed using a ceramic roll heated to 100 ° C., and the film was stretched 4 times in the longitudinal direction of the film. After cooling, both surfaces of the film were subjected to corona discharge treatment to improve wettability, and a water-based dispersion of polypropylene particles, Chemipearl (registered trademark) WP100 (melting point: 145 ° C.) made of methanol was added to methanol. It diluted to 5 mass% of solid content with aqueous solution (concentration 50 mass%), and it apply | coated uniformly on both surfaces using the Mayer bar (No. 6). Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, and stretched 6 times at 135 ° C. at a stretching rate of 1,300% / min. As it was, heat treatment was performed at 145 ° C. for 7 seconds while applying a relaxation of 7% in the width direction to obtain a porous polyolefin film having a total thickness of 20 μm.

(Comparative Example 1)
A polypropylene porous film was collected in the same manner as in Example 1 except that the polyolefin resin layer was not provided. The surface opening ratio on the cast drum surface side was 70%.

(Comparative Example 2)
In Example 2, the resin used for the polyolefin resin layer was a polypropylene aqueous particle Flowbrene (registered trademark) manufactured by Sumitomo Seika Co., Ltd. (melting point: 155 ° C.) in an aqueous methanol solution so that the solid concentration was 1% by mass. A film was formed in the same manner as in Example 2 except that the film was dispersed and coated. Since the melting point of the polypropylene-based particles was higher than that of the transverse stretching and heat setting temperature, the non-oriented layer was not formed and the particles existed. Therefore, the powder adhered to the roll of the winding device, and the film caused defects due to the powder. Therefore, it was judged that there was no practicality, and practical characteristics (friction coefficient, ion conductivity) were not evaluated.

  In Examples satisfying the requirements of the present invention, both excellent slipperiness and ionic conductivity can be achieved, and it is considered that it can be suitably used as a separator for an electricity storage device. On the other hand, in the comparative example, the ion conductivity is inferior or the slipperiness is inferior. Particularly, in the latter case, wrinkles and breakage are caused in the assembling process of the electricity storage device.

  The mixing ratio (mass%) of polypropylene and ethylene / α-olefin copolymer in the table indicates the mixing ratio when the entire polypropylene resin composed of polypropylene and ethylene / α-olefin copolymer is 100 mass%. ing.

  The porous polyolefin film of the present invention has excellent ion conductivity suitable for a lithium ion battery separator and excellent processability, and can be suitably used as a separator.

Claims (6)

A porous polyolefin film comprising a non-oriented polyolefin resin layer on at least one surface of a biaxially oriented polypropylene porous film, having a total film thickness of 10 to 50 μm and an air resistance of 10 to 500 seconds / 100 ml. The porous polyolefin film according to claim 1, wherein the surface opening ratio of the surface of the non-oriented polyolefin resin layer is 10 to 50%. The porous polyolefin film according to claim 1 or 2, wherein the porosity is 60 to 90%. The porous polyolefin film according to any one of claims 1 to 3, wherein a β-crystal forming ability of a polypropylene resin constituting the biaxially oriented polypropylene porous film is 40 to 80%. The polypropylene resin constituting the biaxially oriented polypropylene porous film is a mixture of 80 to 99% by mass of polypropylene and 20 to 1% by mass of an ethylene / α-olefin copolymer. Porous polyolefin film. The porous polyolefin film in any one of Claims 1-5 whose average thickness of a non-oriented polyolefin-type resin layer is 0.2 micrometer or less.