JP2008201814A - Porous polypropylene film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous polypropylene film having high permeability while keeping the productivity and mechanical strength, etc., of a porous polypropylene film, and to provide a separator for a battery device capable of reducing the internal resistance. <P>SOLUTION: The porous polypropylene film contains 0.01-0.5 mass% amide-based compound based on the polypropylene resin and 0.01-0.1 mass% quinacridone-based compound based on the polypropylene resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a porous polypropylene film having through holes in the film thickness direction. More specifically, the present invention relates to a microporous biaxially oriented polypropylene film having low air permeability resistance, excellent permeability, and suitable for use as a moisture permeable waterproof material or a separator for an electricity storage device.

  Polypropylene films are used in various applications such as industrial material applications, packaging material applications, optical material applications, and electrical material applications because of their excellent mechanical properties, thermal properties, electrical properties, and optical properties. In addition to the properties of polypropylene film, porous polypropylene film with voids in this polypropylene film has excellent properties such as permeability and low specific gravity. It is used in a wide variety of applications such as separation membranes, clothing, moisture-permeable waterproof membranes in medical applications, flat panel display reflectors and thermal transfer recording sheets.

  A wide variety of proposals have been made as methods for making a polypropylene film porous. There are roughly two types of pore forming methods: a wet method and a dry method. In the wet method, when polypropylene is used as a matrix resin, the extractables to be extracted are added and mixed, and only the additive is extracted using the good solvent of the extractables. A method of forming a void can be mentioned, and various proposals have been made (for example, see Patent Document 1). On the other hand, as a dry method, for example, by adopting low temperature extrusion and high draft ratio at the time of melt extrusion, the lamellar structure in the pre-stretched film formed into a sheet is controlled, and this is uniaxially stretched to cleave at the lamellar interface. In other words, as a dry method, a large amount of resin that is incompatible with inorganic particles or polypropylene, which is a matrix resin, is added as a dry method. In addition, a method of forming a void by forming a sheet and stretching it to cause cleavage at the interface between the particle and the polypropylene resin has also been proposed (for example, see Patent Document 3). Furthermore, the so-called β crystal method, in which voids are formed in a film by utilizing the crystal density difference and crystal transition between α crystal (α crystal) and β crystal (β crystal), which are polymorphs of polypropylene. Many methods have been proposed (for example, Patent Documents 4 to 7). Furthermore, as a method for producing a porous polypropylene film using this β crystal method, in order to efficiently form β crystals of polypropylene resin and obtain a higher performance porous film, an additive called a β crystal nucleating agent is used. Proposals have also been made (for example, Patent Document 8). In particular, since the proposal of adding an amide compound related to the β crystal nucleating agent, the characteristics of the porous polypropylene film have been remarkably improved by the β crystal method, and various proposals have been made in conjunction therewith (for example, patent documents). 9). There has also been proposed a non-stretchable sheet that can be thermoformed using a quinacridone compound as a β crystal nucleating agent and having excellent impact resistance.

However, the permeability of the porous film obtained by these proposals is still insufficient. For example, considering the use of separators and various separation membranes for batteries and electrolytic capacitors, improving the permeability leads to a reduction in internal resistance in the case of batteries, and can improve the output density of the battery. At present, it is insufficient. Also, when used for a separation membrane, it leads to improvement of permeation efficiency and processing efficiency, so that the current level of permeability is still insufficient.
Japanese Patent Application 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 JP 2005-171230 A JP-A-7-33895 JP 2006-89727 A JP-A-7-126409

  An object of the present invention is to solve the above-described problems. That is, it is to provide a porous polypropylene film having good permeability while maintaining the productivity and mechanical strength of the porous polypropylene film, and for internal storage devices that can reduce internal resistance. To provide a separator.

  The above-described problem is solved by a porous polypropylene film containing 0.01 to 0.5% by mass of the amide compound with respect to the polypropylene resin and 0.01 to 0.1% by mass of the quinacridone compound with respect to the polypropylene resin. Can be achieved.

  The porous polypropylene film of the present invention is a film having excellent air permeability because a large number of through-holes penetrating through the pores formed in the film are formed. It can be preferably used.

  The porous polypropylene film of the present invention preferably contains a crystallization nucleating agent, particularly a β crystal nucleating agent, in the polypropylene resin. Among the β crystal nucleating agents, the amide compound is 0.01 to 0.00% relative to the polypropylene resin. It is preferable to contain 5 mass%. From the viewpoint of permeability in the film, it is more preferably 0.05 to 0.4% by mass, and particularly preferably 0.1 to 0.4% by mass. If the amide compound is less than 0.01% by mass, there may be cases where through holes cannot be formed in the polypropylene film. Conversely, the addition of more than 0.5% by mass not only saturates the effect, Nucleating agents may cause problems such as film pinholes as foreign matter. Here, as an amide compound which acts as a β crystal nucleating agent for polypropylene resin, an amide compound represented by the following general formula is preferable.

R ² —NHCO—R ¹ —CONH—R ³
Here, R ¹ represents an aromatic ring, an aliphatic ring, or an aliphatic hydrocarbon having 2 to 24 carbon atoms. R ² and R ³ represent an aromatic ring or an aliphatic ring.

  Specifically, adipic acid dianilide, terephthalic acid di (cyclohexylamide), terephthalic acid di (2-methylcyclohexylamide), N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide, N, N′-di (2-methylcyclohexyl) -2,6-naphthalenedicarboxamide and the like can be mentioned. Examples of the β crystal nucleating agent comprising such an amide compound include “NJ Star” (type name: Nu-100) manufactured by Shin Nippon Rika Co., Ltd., which can be preferably used.

  The porous polypropylene film of the present invention preferably contains 0.01 to 0.1% by mass of a quinacridone compound, which is a β crystal nucleating agent, based on the polypropylene resin. If the quinacridone-based compound is less than 0.01% by mass, the film has low permeability. On the other hand, even if added in an amount exceeding 0.1% by mass, the effect may be saturated or the effect of addition of the amide compound may be inhibited. The quinacridone compound is more preferably 0.02 to 0.1% by mass, and particularly preferably 0.03 to 0.08% by mass. Here, examples of the quinacridone compound which is a β crystal nucleating agent include γ-quinacridone and quinacridonequinone.

  In the present invention, as a β crystal nucleating agent, it has been found that by using an amide compound and a quinacridone compound in combination, high air permeability can be realized as compared with the case of using alone. is there. In addition, at that time, although the reason is unknown, the air permeability is improved with almost no change in the porosity indicating the ratio of the pores in the film and the average diameter of the pores. By using the compound and the quinacridone compound in combination, it is considered that the number of through holes penetrating between the pores increases. In addition, it is preferable that content in the film of a quinacridone type compound is 5-50 mass% with respect to content of an amide type compound. If the addition amount of the quinacridone compound is less than 5% by mass relative to the amide compound, the effect of adding the quinacridone compound may be difficult to be recognized. Conversely, if the addition amount exceeds 50% by mass, the function of the amide compound May be disturbed.

  The polypropylene resin constituting the porous polypropylene film of the present invention is not only homopolypropylene which is a homopolymer of propylene but also polypropylene containing a comonomer residue as long as it can form β crystals of polypropylene and form voids. A copolymer may also be used. The comonomer is preferably an unsaturated hydrocarbon, and examples thereof include 1-butene, 1-pentene, 4-methylpentene-1, 1-octene, which are ethylene and α-olefin. The copolymerization ratio of these ethylene and α-olefin to polypropylene is preferably 5% by mass or less.

  The polypropylene resin used in the present invention is preferably an isotactic polypropylene resin having a melt flow rate (MFR, condition 230 ° C., 2.16 kg) in the range of 2 to 30 g / 10 min. From the viewpoint of coexistence of high porosity, large pore diameter and film-forming stability, it is more preferable that MFR is in the range of 5 to 20 g / 10 min. Here, MFR is an index indicating the melt viscosity of a resin defined in JIS K 7210 (1995), and is widely used as a physical property value indicating the characteristics of a polyolefin resin. In the case of polypropylene resin, the measurement is performed under condition M of JIS K 7210, temperature 230 ° C., load 2.16 kg.

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

  The polypropylene film of the present invention can obtain a porous film having through-holes by forming voids in the film due to crystal transition from β-crystal to α-crystal in the stretching process during film formation. it can. In this case, the polypropylene resin constituting the polypropylene film is 99 to 95% by mass of the homopolypropylene resin and 5 to 1 mass of the ethylene / α-olefin copolymer in that the void formation efficiency can be improved and the restrictions on the film production conditions can be reduced. % Is preferable. 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. A commercially available resin can be used for the ethylene / α-copolymer.

  Moreover, it is preferable that the polypropylene resin of this invention contains a high melt tension polypropylene in the range of 1-5 mass% at the point of the film forming property improvement. High melt tension polypropylene is a polypropylene resin in which a high molecular weight component or a component having a branched structure is mixed with a polypropylene resin, a long chain branched component is copolymerized with polypropylene, or a tension in a molten state is increased. It is preferable to use a polypropylene resin obtained by copolymerizing a long-chain branching component. This high melt tension polypropylene is commercially available. For example, polypropylene resins PF814, PF633, and PF611 manufactured by Basell, polypropylene resin WB130HMS manufactured by Borealis, polypropylene resins D114 and D206 manufactured by Dow, and the like can be used.

  The polypropylene resin constituting the porous polypropylene film of the present invention and the amide compound and quinacridone compound to be contained in the polypropylene resin may be directly melt-extruded by mixing a predetermined amount at the time of film production. From the viewpoints of dispersibility in the resin, dispersibility when the resin itself is mixed, handling properties of the nucleating agent compound that is a powder, and uniformity of the physical properties of the film, a biaxial melt extruder is used in advance. It is preferable to produce a film by performing compounding. Alternatively, a commercially available resin obtained by adding a nucleating agent to a polypropylene resin, for example, a “NOPOL” polypropylene “BEPOL” (type name: B022-SP, etc.) manufactured by SUNOCO may be used.

  The polypropylene resin constituting the polypropylene film of the present invention preferably has a β-crystal forming ability of 50 to 100% from the viewpoint of producing a porous film. If the β-crystal forming ability is less than 50%, the amount of β-crystal 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 a film with low permeability is obtained. There may not be.

  Here, the β crystal-forming ability indicates the abundance ratio of β crystals in the polypropylene resin measured under the following conditions, and is a value indicating how much β crystals are formed. Define. In addition, the term “β crystal fraction” is sometimes used for the β crystal forming ability, but this term is a value indicating the abundance ratio of β crystals in the polypropylene resin at a certain point in time. That is, even if a film is produced using a resin having the same β-crystal forming ability, the β-crystal abundance ratio changes before and after the melt extrusion conditions and before and after stretching. The β crystal fraction will be used when indicated.

  The β crystal-forming ability was measured by heating 5 mg of polypropylene resin or polypropylene film at a rate of 10 ° C./min from room temperature to 240 ° C. in a nitrogen atmosphere using a differential scanning calorimeter and holding for 10 minutes. Cool to 30 ° C. at 10 ° C./min. About the melting peak observed when the temperature is raised (second run) again at 10 ° C./min after holding for 5 minutes, the melting having a peak in the temperature range of 145 to 157 ° C. is the melting peak of β crystal, 158 ° C. or more The melting at which the peak is observed is the melting peak of the α crystal, and the heat of fusion is determined. The heat of fusion of the α crystal is ΔHα and the heat of fusion of the β crystal is ΔHβ. Crystal formation ability.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, what computed the abundance ratio of (beta) crystal similarly from the melting peak observed by 1st run has shown the (beta) crystal fraction of the polypropylene.

  A method for bringing the β-crystal forming ability into a preferable range is not particularly limited, but can be adjusted depending on the composition of the polypropylene resin to be used and the addition amount of the β-crystal nucleating agent.

The porous polypropylene film of the present invention preferably has through holes in the thickness direction of the film, and the air permeation resistance (Gurley) by the through holes is preferably 1 to 250 seconds. Here, the air resistance (Gurley) is an index of air permeability measured based on JIS P 8117 (1998), and is the time required for 100 ml of air to pass through a film having an area of 642 mm ² . The smaller the air resistance, the better the film permeability and air permeability. If the film has almost the same pore diameter and porosity, and the air permeability is excellent, It is considered that more through holes are formed. The air permeability resistance (Gurley) is more preferably 1 to 200 seconds, and particularly preferably 1 to 160 seconds.

  The method for setting the air permeability resistance (Gurley) to a preferred range of 1 to 250 seconds is not particularly limited, but among the β crystal nucleating agent of the present invention, an amide compound and a quinacridone compound are used in combination. It is preferable from the viewpoint that more through holes can be formed in the film. Moreover, it is a preferable aspect for air permeability improvement that cleavage occurs uniformly in the film and the pore distribution is not biased. In order to realize such an aspect, it is preferable to set the stretching speed during biaxial stretching to a low speed as described later. In addition, it is desirable to keep stress during stretching low from the viewpoint of expanding pores by transverse stretching after forming cracks that cause pores in the film by longitudinal stretching. Specifically, it is preferable to set the temperature to 140 to 155 ° C.

  The porous polypropylene film of the present invention preferably has a film thickness of 10 to 100 μm from the viewpoint of achieving both excellent permeation performance and mechanical properties of the film. If the thickness is less than 10 μm, defects may occur when used for a separator or the like due to insufficient strength of the film. Further, if the thickness exceeds 100 μm, the permeability may be insufficient. The film thickness is preferably 15 to 80 μm, more preferably 20 to 50 μm.

  The porous polypropylene film of the present invention preferably has a porosity of 40 to 80% from the viewpoint of mechanical properties. From the viewpoint of air permeability, the porosity is preferably more than 80%, but the mechanical strength is lowered and defects may occur, so 80% or less is preferable. Moreover, if the porosity is less than 40%, the permeability may be insufficient. More preferably, it is 50 to 80%, and more preferably 60 to 80%. The method for setting the porosity to a preferred range is not particularly limited, but it can be controlled by controlling the β crystal fraction in the unstretched film at the time of film production, which will be described later, and the stretching temperature, speed, and the like. . Specifically, if the cast roll temperature is set to 105 to 130 ° C. so as to increase the β crystal fraction and an unstretched film is obtained, a film with a high porosity can be easily obtained. Further, when the stretching speed and temperature are set to a low stretching speed equivalent to the air resistance, it is easy to obtain a film having a high porosity.

  Below, the manufacturing method of the porous polypropylene film of this invention is demonstrated concretely. In addition, the manufacturing method of the film of this invention is not limited to this. As a polypropylene resin, 94 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 min, 3 parts by mass of a commercially available MFR of 2.5 g / 10 min, high melt tension polypropylene resin, and an ultra low density polyethylene resin 3 having a melt index of 18 g / 10 min. Mix 0.2 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide and 0.05 parts by mass of γ-quinacridone in a part by mass, and mix in advance at a predetermined ratio using a twin screw extruder. Prepare the raw materials. At this time, the melting temperature is preferably 200 to 230 ° C or 270 to 300 ° C. When this is melted in the temperature range of 230 to 270 ° C., N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide aggregates to form coarse crystals, and the β-crystal forming ability of the resin is significantly reduced. Because.

  Next, the mixed raw material is supplied to a single-screw melt extruder, and melt extrusion is performed at 220 ° 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, 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 adhere to the drum. Further, air may be blown over the entire surface using an air knife as necessary from 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. When the film is stretched in the longitudinal direction, a so-called neck-down phenomenon is observed in which the film width decreases. In order to achieve high air permeability, the neck-down ratio (film width after stretching / before stretching) The film width is preferably 30 to 70%. Considering stretching in the width direction, 40 to 65% is more preferable. Next, after cooling, the end of the film is gripped and introduced into a stenter type stretching machine. And it heats to 140-155 degreeC preferably, and extends 5 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 1,000% / minute, more preferably 100 to 600% / minute. Next, heat setting is performed in a stenter as it is, and the temperature is preferably a transverse stretching temperature or higher and 160 ° C. or lower. 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 polypropylene film of the present invention not only has excellent air permeability, but can retain sufficient mechanical properties, so that the anode and cathode of an electricity storage device such as a lithium ion secondary battery or an electric double layer capacitor are isolated, In addition, it can be preferably used as a separator in which ions, which are conductive substances, can move relatively freely.

  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 on an aluminum pan and measured using a differential scanning calorimeter (DSC) (Seiko Electronics Co., Ltd. RDC220). First, the temperature is raised (first run) from room temperature to 240 ° C. at 10 ° C./min in a nitrogen atmosphere, held for 10 minutes, and then cooled to 30 ° C. at 10 ° C./min. About the melting peak observed when the temperature is raised (second run) again at 10 ° C./min after holding for 5 minutes, the melting having a peak in the temperature range of 145 to 157 ° C. is the melting peak of β crystal, 158 ° C. or more The melting of the α crystal is taken as the melting peak of the α crystal, and the melting heat of the α crystal is obtained from the area of the region surrounded by the baseline and the peak drawn from the flat part on the high temperature side. When the heat of fusion of ΔHα and β crystals is ΔHβ, the value calculated by the following formula is β crystal forming ability. In addition, calibration of the heat of fusion was performed using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, what computed the existing ratio of (beta) crystal from the melting peak observed by 1st run has shown the (beta) crystal fraction in the state of the sample.

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

  Next, the measured film sample is hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C., and a sheet from which pores are completely erased is prepared. The specific gravity (d) of this sheet was measured in the same manner as described above, and the average value was taken as the specific gravity of the sheet. In Example 1 described later, the specific gravity d of the sheet was 0.91. When the specific gravity of the film was ρ, the porosity was calculated by the following formula.

Porosity (%) = [(d−ρ) / d] × 100
(3) Pore size The pore size of the film was measured by using an automatic pore size distribution meter (PERM-POROMETER manufactured by POROUS MATERIALS) according to the bubble point method (half dry method) of JIS K 3832 (1990). . Measurement conditions are as follows.

Test solution: 3M “Fluorinert” FC-40
Test temperature: 25 ° C
Test gas: Air Analysis software: Capwin
Measurement conditions: Automatic measurement under default conditions of Capillary Flow Porometry-Wet up, Dry down In the bubble point method, the following relational expression is established between the pore diameter (pore diameter) and the test pressure.

d = Cγ / P × 10 ³
However, d: pore diameter (nm), C: constant, γ: surface tension of fluorinate (16 mN / m), P: pressure (Pa).

  Here, based on the above, the average pore diameter was calculated from the 1/2 half-wetting curve using the data analysis software attached to the apparatus. This measurement is also described in detail in the manual attached to the device. The measurement was performed three times, and the average value was defined as the pore size of the film (unit: nm).

(4) Air permeability resistance (Gurley)
A square with a side length of 100 mm 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 defined as the air resistance (Gurley) of the film.

(5) Film thickness The film thickness measured the thickness about arbitrary 5 places in the state which piled up 10 sheets according to JISK7130 (1992) A-2 method using the dial gauge. The average value was divided by 10 to obtain the film thickness.

(6) Breaking strength The film was cut into a rectangle having a length of 150 mm and a width of 10 mm in the longitudinal direction and the width direction to obtain a sample. Using a tensile tester (Orientec Tensilon UCT-100), the tensile test was performed in the longitudinal direction and the width direction of the film at an initial tensile chuck distance of 50 mm and a tensile speed of 300 mm / min. Measurement atmosphere was 23 ° C. and relative humidity 65%. The load applied to the film when the film was broken was read, and the value obtained by dividing by the cross-sectional area (film thickness × 10 mm) of the sample before the test was taken as the breaking strength. In addition, the measurement was performed 5 times in each sample and in each direction, and evaluation was performed with an average value in each direction.

(7) Amide compound and quinacridone compound content in film The content of the amide compound or quinacridone compound contained in the film can be quantified as follows. The film can be dissolved in a good solvent, and the content compound and content can be quantified using each magnetic resonance spectrum (NMR). In the case of a quinacridone-based compound, quantification can be performed using excitation Raman spectroscopy. In the examples described later, the values measured when the amide compound and quinacridone compound in the film were added were used.

(8) Evaluation as a separator Evaluation as a film separator was carried out by producing a lithium ion battery as follows.

・ Positive electrode material LiCoO ₂ (C-012 manufactured by Seimi Chemical Co., Ltd.) ・ 89.5 parts by weight Acetylene black (75% press product manufactured by Denki Kagaku Kogyo Co., Ltd.) ・ 4.5 parts by weight polyvinylidene fluoride ( Kureha Chemical Industry Co., Ltd.) 6 parts by weight N-methyl-2-pyrrolidone 40 parts by weight The above materials were mixed to prepare a slurry. The obtained slurry was applied onto an aluminum foil as a current collector, dried and then punched.

・ Negative electrode material Mesocarbon microbeads (MCMB; manufactured by Osaka Gas Chemical Co., Ltd. 25-28) ・ 93 parts by weight acetylene black ・ 2 parts by weight polyvinylidene fluoride ・ 5 parts by weight N-methyl-2-pyrrolidone 50 parts by weight The above composition was mixed to prepare a slurry. The obtained slurry was applied onto a copper foil as a current collector, dried and then punched.

LiPF ₆ was dissolved in a solvent in which propylene carbonate and methyl ethyl carbonate were mixed at 3: 7 so as to have a concentration of 1 mol / L, and this was used as an electrolytic solution. The film was directly sandwiched between the positive electrode and the negative electrode produced as described above, and after punching, each terminal of the positive electrode and the negative electrode was taken out and inserted into an aluminum laminate type outer package. After sealing the three sides of the outer package, the electrolyte solution was injected, and the fourth side was sealed under reduced pressure to obtain an electricity storage device. For the lithium ion battery thus obtained, the internal resistance of the battery was measured with an electric resistance meter. Each film was measured three times, and the average value was evaluated. The internal resistance was set to a target level of 45 mΩ or less.

(Example 1)
As a polypropylene resin, 94 parts by mass of homopolypropylene WF836DG3 (MFR: 7 g / 10 min, isotactic index: 97%) manufactured by Sumitomo Chemical Co., Ltd., high melt tension homopolypropylene Pro-fax PF814 (MFR: 2) manufactured by Basell 0.5 g / 10 min, isotactic index: 97%) is added to 3 parts by mass of 3 parts by mass of Engage 8411 (melt index: 18 g / 10 min) manufactured by Dow Chemical Co., which is an ethylene / α-olefin copolymer. 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide (Shin Nippon Rika, Nu-100), which is a β crystal nucleating agent, and γ which is also a β crystal nucleating agent, -Add 0.05 parts by weight of quinacridone, mix, feed to twin screw extruder, melt blend at 290 ° C The kneading was performed, extruded into a strand shape, cooled and solidified in a water bath at 25 ° C., and cut into chips.

  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. 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, the ends were introduced into a stenter-type stretching machine by holding them with clips, and stretched 6 times at 145 ° C. at a stretching rate of 500% / min. As it was, heat treatment was performed at 160 ° C. for 5 seconds while relaxing 5% in the width direction to obtain a porous polypropylene film having a thickness of 25 μm.

(Example 2)
As a polypropylene resin, 95 parts by mass of homopolypropylene WF836DG3 manufactured by Sumitomo Chemical Co., Ltd. and 5 parts by mass of Basel's Pro-fax PF814, which is a high melt tension polypropylene, are added, and N, N′- which is a β crystal nucleating agent Add 0.5 parts by weight of dicyclohexyl-2,6-naphthalenedicarboxamide and 0.1 parts by weight of γ-quinacridone, mix, feed to twin screw extruder, melt knead at 290 ° C., and strand And solidified by cooling in a 25 ° C. water bath and cut into chips.

  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 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, the ends were introduced into a stenter-type stretching machine by gripping them with clips, and stretched 6 times at 135 ° C. at a stretching rate of 300% / min. As it was, heat treatment was performed at 155 ° C. for 5 seconds while relaxing 5% in the width direction to obtain a porous polypropylene film having a thickness of 25 μm.

(Example 3)
As a polypropylene resin, 97 parts by mass of Prime Polymer Homopolypropylene F107BV (MFR: 7 g / 10 min, isotactic index: 98%), manufactured by Dow Chemical Co., which is an ethylene / α-olefin copolymer Engage 8411 is added to 3 parts by mass, N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, which is a β crystal nucleating agent, and 0.4 part by mass of γ-quinacridone are added. The mixture was supplied to a twin screw extruder, melt kneaded at 220 ° C., extruded into a strand, cooled and solidified in a 25 ° C. water tank, and cut into chips.

    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. 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, the ends were then introduced into a stenter-type stretching machine by gripping them with clips, and stretched 6 times at 135 ° C. at a stretching rate of 500% / min. As it was, heat treatment was performed at 155 ° C. for 5 seconds while relaxing 5% in the width direction to obtain a porous polypropylene film having a thickness of 30 μm.

Example 4
As a polypropylene resin, 92 parts by mass of homopolypropylene WF836DG3 manufactured by Sumitomo Chemical Co., Ltd., 3 parts by mass of high melt tension homopolypropylene Pro-fax PF814 manufactured by Basell, Dow Chemical Company, which is an ethylene / α-olefin copolymer In addition to 5 parts by mass of Engage 8411 (melt index: 18 g / 10 min), N, N'-dicyclohexyl-2,6-naphthalenedicarboxyamide (Nippon Nippon Chemical Co., Ltd., Nu-100) which is a β crystal nucleating agent 0.15 parts by mass, and 0.02 parts by mass of γ-quinacridone, which is also a β-crystal nucleating agent, are mixed, supplied to a twin screw extruder, melt kneaded at 290 ° C., and extruded into a strand. Then, it was cooled and solidified in a water bath at 25 ° C. and cut into chips.

  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. 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 ends were then introduced into a stenter-type stretching machine by gripping them with clips, and stretched at 140 ° C. five times at a stretching rate of 400% / min. As it was, heat treatment was performed at 155 ° C. for 5 seconds while relaxing 5% in the width direction to obtain a porous polypropylene film having a thickness of 20 μm.

(Example 5)
As a polypropylene resin, N, N'-dicyclohexyl-2,6-naphthalenedicarboxyamide (Nunippon Rika Co., Ltd., Nu-100) as a β crystal nucleating agent is added to 100 parts by mass of homopolypropylene WF836DG3 manufactured by Sumitomo Chemical Co., Ltd. Add 0.25 part by mass, and 0.08 part by mass of γ-quinacridone, which is also a β-crystal nucleating agent, and supply to a twin-screw extruder, melt knead at 300 ° C., and extrude into a strand. Then, it was cooled and solidified in a water bath at 25 ° C. and cut into chips.
This chip is supplied to a single screw extruder and melt extruded at 225 ° C. After removing foreign matter with a 35 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 12 seconds. Next, preheating was performed using a ceramic roll heated to 120 ° C., and the film was stretched four times in the longitudinal direction of the film. After cooling, the end was introduced into a stenter-type stretching machine by holding the end with a clip and stretched 6 times at 135 ° C. at a stretching rate of 600% / min. As it was, heat treatment was performed at 155 ° C. for 5 seconds while relaxing 5% in the width direction to obtain a porous polypropylene film having a thickness of 30 μm.

(Comparative Example 1)
Except not adding γ-quinacridone which is a β crystal nucleating agent, a film was formed in the same manner as in Example 1 to obtain a porous polypropylene film having a thickness of 25 μm.

(Comparative Example 2)
Except not adding γ-quinacridone which is a β crystal nucleating agent, a film was formed in the same manner as in Example 2 to obtain a porous polypropylene film having a thickness of 25 μm.

(Comparative Example 3)
Film formation was performed in the same manner as in Example 3 except that N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, which is a β crystal nucleating agent, was not added and the amount of γ-quinacridone added was 0.3 parts by mass. And a 10 μm thick polypropylene film was obtained.

(Comparative Example 4)
A porous polypropylene film having a thickness of 22 μm was obtained in the same manner as in Example 1 except that the addition amount of γ-quinacridone, which is a β crystal nucleating agent, was 0.15 parts by mass.

  Comparing an example in which an amide compound and a quinacridone compound satisfying the requirements of the present invention were used in combination with a comparative example in which only one type was used, in the example, the air permeability resistance was maintained while maintaining the porosity, pore diameter, and breaking strength. The degree was small, that is, an improvement in air permeability was observed. Accordingly, the internal resistance, which is the evaluation of the separator, also showed a small value in the examples, and it was confirmed that the performance of the battery was improved.

  The porous polypropylene film according to the present invention is a film having excellent air permeability because a large number of through-holes passing through the pores formed in the film are formed, and is used as a separator for power storage devices and various separation membranes. It can be preferably used.

Claims (6)

A porous polypropylene film containing an amide compound in an amount of 0.01 to 0.5% by mass relative to the polypropylene resin and a quinacridone compound in an amount of 0.01 to 0.1% by mass with respect to the polypropylene resin. The porous polypropylene film according to claim 1, wherein the amide compound is a compound represented by the following general formula.
R ² —NHCO—R ¹ —CONH—R ³
Here, R ¹ represents an aromatic ring, an aliphatic ring, or an aliphatic hydrocarbon having 2 to 24 carbon atoms. R ² and R ³ represent an aromatic ring or an aliphatic ring. The porous polypropylene film according to claim 1 or 2, wherein the β crystal-forming ability of the polypropylene resin is 50 to 100%, and the air permeability resistance (Gurley) after biaxial stretching is 1 to 250 seconds. The porous polypropylene film according to any one of claims 1 to 3, wherein the polypropylene resin comprises 99 to 95% by mass of a homopolypropylene resin and 1 to 5% by mass of an ethylene / α-olefin copolymer. The porous polypropylene film according to any one of claims 1 to 4, wherein 1 to 5% by mass of the polypropylene resin is a high melt tension polypropylene. The separator for electrical storage devices which uses the porous polypropylene film of Claims 1-5.