Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/417—Polyolefins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/491—Porosity
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/494—Tensile strength
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
  • C08J2323/04—Homopolymers or copolymers of ethene
  • C08J2323/06—Polyethene
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a separation membrane used for separating substances, selective permeation, etc., and a polyolefin microporous membrane widely used as a separating material for an electrochemical reaction device such as an alkaline battery, a lithium secondary battery, a fuel cell, and a capacitor. ..
• the present invention is a polyolefin microporous membrane preferably used as a separator for a lithium ion battery, which exhibits superior battery characteristics as compared with a conventional polyolefin microporous membrane, and is used as a separator having high safety.
• Polyolefin microporous membranes are used as filters, fuel cell separators, condenser separators, etc. In particular, it is suitably used as a separator for lithium ion batteries widely used in notebook personal computers, mobile phones, digital cameras and the like. The reason for this is that the polyolefin microporous membrane has excellent mechanical strength, shutdown characteristics, and lithium ion permeation performance.
• lithium-ion secondary batteries have been used in vehicles in recent years, it is necessary to shorten the charging time and improve acceleration, and the characteristics of batteries include rapid charging (large current charging) and increased power consumption (large current discharge). ) Is required. Along with this, further improvements in output characteristics are required for separators.
• Patent Documents 1 and 2 As a method for improving output characteristics, in Patent Documents 1 and 2, polyethylene (PE) and polypropylene (PP) are blended to increase the pore ratio, control the number of pores, the pore diameter, and the curvature ratio, and improve ionic conductivity. ing.
• PE polyethylene
• PP polypropylene
• Patent Documents 3 and 4 describe a method for improving ionic conductivity by controlling the fibril diameter, pore diameter, and surface aperture ratio of the microporous membrane and reducing the membrane resistance. ing.
• Patent Document 5 the pore structure on the surface and the inside is controlled to improve the electrolyte impregnation property and the output characteristics.
• Patent Document 6 in order to improve film rupture resistance, polyethylene having a molecular weight of 280,000 and polyethylene having a molecular weight of 2 million are blended, and under the condition of a resin concentration of 32 wt%, 7.0 times in the MD direction and 6. in the TD direction. A method of stretching 4 times, washing and drying, and then stretching 1.2 times (area magnification 54 times) is described.
• Patent Documents 7 and 8 describe a method of stretching Hi-Zex Million 145M to 6.4 ⁇ 6.0 times (area magnification 38.4 times) under the condition of a resin concentration of 18%. Since polyethylene with a relatively high molecular weight is stretched 38.4 times, a pore ratio of 30 to 60% and a puncture strength of 6.0 N / 20 ⁇ m are obtained, and a microporous membrane having excellent output characteristics and safety can be obtained. ing.
• Japanese Patent Application Laid-Open No. 2017-140840 Japanese Patent Application Laid-Open No. 2003-231772 Japanese Patent Application Laid-Open No. 2011-192529 Japanese Patent Application Laid-Open No. 2003-86162 Japanese Patent Application Laid-Open No. 2012-48987 Japanese Patent Application Laid-Open No. 2006-124652 Japanese Patent Application Laid-Open No. 2018-147858 Japanese Patent Application Laid-Open No. 2018-147690
• microporous membranes described in Patent Documents 3 and 4 are microporous membranes having a large pore diameter, a high porosity, and relatively thick fibrils, and good strength has not been obtained.
• Patent Document 5 it is considered that the permeation path of lithium ions tends to be non-uniform because the pore structures on the surface and the inside are different. Therefore, the conventional microporous membrane is insufficient to achieve both high output characteristics and strength required for in-vehicle applications.
• the microporous membrane obtained in Patent Document 6 has a relatively high puncture strength of 5.5 to 5.9 N / 20 ⁇ m and good film rupture resistance, but has a porosity of 35 to 40%. It is a relatively low value, and the porosity ratio close to that of the high output separator as shown in Patent Documents 1 and 2 has not been obtained, and there is room for improvement in the output characteristics.
• Patent Documents 7 and 8 since the separator is required to be thinned as the capacity of the battery is increased, there is room for improvement in safety improvement due to the thinning.
• an object of the present invention is to provide a polyolefin microporous membrane having superior output characteristics and strength as compared with the conventional one.
• the present inventors have made the pores finer and more uniform by improving the pore-opening property in the drawing step in the first embodiment of the present invention.
• the ion permeation path is increased and the output characteristics are improved, and the resin layer is uniformly stressed to form a fine and uniform fibril structure. Therefore, it has been found that the strength and the heat shrinkage rate are improved, and high safety and output characteristics that cannot be achieved by the prior art can be realized.
• the present inventors in the second embodiment of the present invention, improve the pore-opening property in the drawing step to make the pores fine and uniform. Therefore, by increasing the number of surface pores per unit area as compared with the conventional polyolefin microporous membrane, the ion transmission path is increased and the output characteristics are improved, and the resin layer is uniformly stressed to form a fine and uniform fibril structure. It has been found that the strength and the heat shrinkage rate are improved due to the formation of the resin, and high safety and output characteristics that could not be achieved by the prior art can be realized.
• the present inventors in the third embodiment of the present invention, improve the pore opening property in the drawing step to make the pores fine and uniform.
• the surface aperture ratio as compared with the conventional polyolefin microporous film, the ion permeation path is increased and the output characteristics are improved, and the resin layer is uniformly stressed to form a fine and uniform fibril structure. Therefore, it has been found that the strength and the heat shrinkage ratio are improved, and high safety and output characteristics that cannot be achieved by the conventional technology can be realized.
• the present invention adopts the following configuration. ⁇ 1>
• the puncture strength Y (N) converted to a film thickness of 10 ⁇ m and the number of holes X (pieces / ⁇ m 3 ) per unit volume satisfy the relationship of the following formula (1), and the number of holes X is 40 holes / ⁇ m 3
• the above is the polyolefin microporous film.
• ⁇ 5> The polyolefin microporous membrane according to any one of ⁇ 1> to ⁇ 4>, which has an average pore diameter of less than 40 nm.
• ⁇ 6> The microporous polyolefin membrane according to any one of ⁇ 1> to ⁇ 5>, wherein both the tensile breaking strength in the MD direction and the tensile breaking strength in the TD direction are 180 MPa or more.
• ⁇ 8> The polyolefin microporous membrane according to any one of ⁇ 1> to ⁇ 7>, wherein the porosity is 40% or more and less than 60%.
• ⁇ 9> The polyolefin microporous membrane according to any one of ⁇ 1> to ⁇ 8>, wherein the piercing strength Y is 3.0 N or more.
• ⁇ 10> The microporous polyolefin membrane according to any one of ⁇ 1> to ⁇ 9>, wherein the heat shrinkage rate at 120 ° C. in the MD direction measured by thermomechanical analysis is 15% or less.
• ⁇ 11> The polyolefin microporous membrane according to any one of ⁇ 1> to ⁇ 10>, wherein the polyolefin that is the microporous membrane is polyethylene.
• a battery separator comprising the polyolefin microporous membrane according to any one of ⁇ 1> to ⁇ 11>.
• a secondary battery including the battery separator according to ⁇ 12>.
• ⁇ 14> The method for producing a microporous polyolefin membrane according to any one of ⁇ 1> to ⁇ 11>.
• the content ratio of the ultra-high molecular weight polyethylene having a weight average molecular weight of 1 million or more is 5 to 30% by mass, and the content ratio of the polyolefin resin is less than 30% by mass.
• It has a step of extracting a plasticizer from the stretched film and drying the stretched film, and a step of performing at least one of heat treatment of the stretched film after drying and re-stretching of the stretched film after drying.
• a method for producing a microporous polyolefin membrane is a method for producing a microporous polyolefin membrane.
• the present invention can provide a polyolefin microporous membrane having excellent safety, output characteristics, and strength as compared with a conventional polyolefin microporous membrane.
• the polyolefin microporous membrane of the present invention (hereinafter, may be simply referred to as “microporous membrane”) relates to the polyolefin microporous membrane according to the first embodiment of the present invention described later, and the second embodiment of the present invention. Includes a polyolefin microporous membrane and the polyolefin microporous membrane according to the third embodiment of the present invention.
• the polyolefin microporous membrane according to the first embodiment of the present invention has a relationship between the puncture strength Y (N) in terms of film thickness of 10 ⁇ m and the number of holes X (pieces / ⁇ m 3 ) per unit volume according to the following formula (1). It is filled and the number of holes X is 40 / ⁇ m 3 or more.
• Y (N) ⁇ ⁇ 6.7 ⁇ 10 -3 ⁇ X (pieces / ⁇ m 3 ) +4.5 ⁇ ⁇ ⁇ Equation (1)
• the relationship between the puncture strength Y (N) in terms of film thickness of 10 ⁇ m and the number of surface holes Z (pieces / ⁇ m 2 ) per unit area is the following formula (2).
• the puncture strength Y (N) in terms of film thickness of 10 ⁇ m and the surface aperture ratio W (%) satisfy the relationship of the following formula (3), and the surface aperture ratio W is 5% or more and 45% or less.
• the raw material such as the resin in the microporous polyolefin membrane of the present invention does not have to have a single composition, and may be a composition in which a main raw material and an auxiliary raw material are combined.
• the resin is preferably a polyolefin resin, and may be a polyolefin resin mixture (polyolefin resin composition) composed of two or more kinds of polyolefin resins.
• the raw material form of the polyolefin microporous membrane is preferably a polyolefin resin, and examples of the polyolefin resin include polyethylene and polypropylene, and a single composition is more preferable.
• the polyolefin resin is preferably a homopolymer such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and particularly preferably an ethylene homopolymer (polyethylene).
• Polyethylene may be a copolymer containing a homopolymer of ethylene and another ⁇ -olefin.
• ⁇ -olefins include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, or alkene having a carbon number of more than that, vinyl acetate, methyl methacrylate, styrene, and the like. Can be mentioned.
• the polyolefin resin mixture for example, a mixture of two or more types of ultra-high molecular weight polyethylene having different weight average molecular weights (Mw), a mixture of high density polyethylene, a mixture of medium density polyethylene, or a mixture of low density polyethylene may be used. Alternatively, a mixture of two or more polyethylenes selected from the group consisting of ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene may be used.
• Mw may be a mixture 1 ⁇ 10 6 or more ultra-high molecular weight polyethylene and Mw consists 1 ⁇ 10 5 or more 9 ⁇ 10 5 less than polyethylene.
• the weight average molecular weight of the ultrahigh-molecular-weight polyethylene used 1.0 ⁇ 10 6 or more, preferably 1.0 ⁇ 10 7 or less.
• the weight average molecular weight is more preferably 1.1 ⁇ 10 6 or more, more preferably 1.2 ⁇ 10 6 or more, particularly preferably 1.4 ⁇ 10 6 or more, more preferably 1.7 ⁇ 10 6 or more, most preferably 2.0 ⁇ 10 6 or more.
• the weight average molecular weight is more preferably 8.0 ⁇ 10 6 or less, more preferably 6.0 ⁇ 10 6 or less, more preferably 5.0 ⁇ 10 6 or less, and most preferably 4.0 ⁇ 10 6 or less Is.
• the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of ultra-high molecular weight polyethylene is preferably in the range of 3.0 to 100 from the viewpoint of mechanical strength.
• the lower limit of the molecular weight distribution is more preferably 4.0 or more, still more preferably 5.0 or more, more preferably 6.0 or more, and most preferably 8.0 or more.
• the upper limit of the molecular weight distribution is more preferably 80 or less, further preferably 50 or less, still more preferably 20 or less, and most preferably 17 or less.
• Ultra-high molecular weight polyethylene may be used as the above-mentioned polyolefin resin mixture, but when used alone, the workability is inferior when the molecular weight distribution is less than 3.0, and the low molecular weight component increases when the molecular weight distribution exceeds 100. Therefore, there is a high possibility that defects and the like are likely to occur during processing.
• ultra-high-molecular-weight polyethylene for example, 1.0 ⁇ 10 5 or more 1.0 ⁇ 10 than 6, preferably such a range of 2 ⁇ 10 5 ⁇ 9.5 ⁇ 10 5, the weight-average of less than 1.0 ⁇ 10 6
• Polyethylene having a molecular weight may be used as an auxiliary material.
• the molding processability is improved, the mixing ratio of the polyolefin resin and the plasticizer can be easily selected, and the overlapping density of the molecular chains can be adjusted.
• the most preferred form of the polyolefin resin has a weight average molecular weight (Mw) of preferably 1.0 ⁇ 10 6 or more polyolefin resins, Mw is more preferably 1.4 ⁇ 10 6 or more polyolefin resins, Mw of 2.0 ⁇ 10 6 or more polyolefin resins is more preferred. If the Mw of the polyolefin resin is 1.0 ⁇ 10 6 or more to increase the number of entanglement of molecular chains, openability and uniform stress propagation in the stretching step can be improved.
• the pores are finely and uniformly opened, and at least one of the number of pores per unit volume, the surface aperture ratio, and the number of surface pores per unit area of the polyolefin microporous membrane is increased, and good output characteristics are obtained.
• Mw is Thailand number of molecules is increased by use of 1.0 ⁇ 10 6 or more polyolefin resins, to increase the strength of the fibrils, the balance of the surface pore number and intensity of the hole number and per unit area per unit volume Can be improved.
• Mw is hard to stress propagation in the stretching step is less than 1.0 ⁇ 10 6, there is a case where the opening is lowered.
• the type of polyolefin resin high density polyethylene such as density exceeding 0.94 g / cm 3, density polyethylene in the range density of 0.93 ⁇ 0.94g / cm 3, density of 0.93g / lower cm 3 low-density polyethylene, include linear low density polyethylene, high density polyethylene having a weight-average molecular weight of 1,000,000 or more ultra-high molecular weight in terms of uniformity and film strength of the opening alone It is preferable to use it.
• the blending ratio of the polyolefin resin and the plasticizer may be appropriately selected as long as the molding processability is not impaired, but the ratio of the polyolefin resin is 10 to 50% by mass, where the total of the polyolefin resin and the plasticizer is 100% by mass. It is preferable to have.
• the proportion of polyolefin resin is 10% by mass or more (the proportion of plasticizer is 90% by mass or less)
• swell and neck-in can be suppressed at the outlet of the base when molding into a sheet, and the formability and film forming property of the sheet can be suppressed. Is improved.
• the proportion of the polyolefin resin is less than 50% by mass (the proportion of the plasticizer exceeds 50% by mass), the pressure increase in the film forming process can be suppressed and good molding processability can be obtained.
• the proportion of the polyolefin resin is preferably 12% by mass or more, more preferably 14% by mass or more, further preferably 16% by mass or more, still more preferably 20% by mass or more.
• the ratio used differs depending on the raw material used, but when a polyolefin resin with an Mw of 1 million or more is used, the ratio of the polyolefin resin is different from that of the polyolefin resin from the viewpoint of pressure and stretching stress in the film forming process.
• the total with the agent is 100% by mass, 40% by mass or less is preferable, 30% by mass or less is more preferable, and 25% by mass or less is further preferable.
• antioxidants various additions of antioxidants, heat stabilizers, antistatic agents, ultraviolet absorbers, blocking inhibitors, fillers, etc. are added to the microporous polyolefin membrane of the present invention as long as the effects of the present invention are not impaired.
• the agent may be contained.
• antioxidants examples include 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6-tris (3,5-tris).
• Di-t-butyl-4-hydroxybenzyl) benzene for example, BASF "Irganox” (registered trademark) 1330: molecular weight 775.2
• tetrakis [methylene-3 (3,5-di-t-butyl-4) -Hydroxyphenyl) propionate]
• methane for example, "Irganox" (registered trademark) 1010: molecular weight 1177.7 manufactured by BASF).
• Appropriate selection of the type and amount of antioxidant and heat stabilizer added is important for adjusting or enhancing the characteristics of the polyolefin microporous membrane.
• the layer structure of the microporous polyolefin membrane of the present invention may be single layer or laminated, and lamination is preferable from the viewpoint of physical property balance.
• the raw material, the raw material ratio, and the raw material composition may be within the above ranges.
• the high output characteristic layer contains 50% by mass or more in the total film thickness.
• the polyolefin microporous membrane according to the first embodiment of the present invention has a puncture strength Y (N) equivalent to a film thickness of 10 ⁇ m and a number of holes X (pieces / ⁇ m 3 ) per unit volume. It is characterized in that the relationship (1) is satisfied and the number of holes per unit volume is 40 holes / ⁇ m 3 or more.
• Y (N) ⁇ ⁇ 6.7 ⁇ 10 -3 ⁇ X (pieces / ⁇ m 3 ) +4.5 ⁇ ⁇ ⁇ Equation (1)
• the number of holes X (pieces / ⁇ m 3 ) per unit volume can be calculated by the following formula (1a).
• Number of holes X (pieces / ⁇ m 3 ) 4 ⁇ ( ⁇ /100) / ( ⁇ ⁇ d 2 ⁇ ⁇ a / L) ⁇ ⁇ ⁇ Equation (1a) [ ⁇ : Pore ratio (%), d: Average pore diameter ( ⁇ m), ⁇ a : Curvature ratio calculated by equation (1b), L: Film thickness ( ⁇ m)]
• Curve rate ⁇ a ⁇ d ⁇ ( ⁇ /100) ⁇ v / (3L ⁇ P s ⁇ R gas ) ⁇ 0.5 ... Equation (1b)
• R gas Gas permeation constant calculated by equation (1c) (m 3 / (m 2 ⁇ sec ⁇ Pa)]
• the resin layer is uniformly stressed and stretched to form a fine and uniform fibril structure, the number of fibrils is increased, the strength is increased, and the pores are uniformly opened.
• the number of holes per unit volume is increased, and the relationship of the above equation (1) is satisfied. Therefore, the strength of fibrils is increased and safety such as foreign matter resistance is improved, the number of pores per unit volume is increased and uniform micropore formation is promoted, the permeation path of Li + ions is increased, and the polyolefin is microporous. The output characteristics and safety of the film are improved.
• the puncture strength affects the safety of the battery such as foreign matter resistance, and the number of holes per unit volume affects the output characteristics of the battery.
• the piercing strength is an index showing the strength in the depth direction of the film, and as the number of holes per unit volume increases, the voids increase and the piercing strength decreases. In other words, they are in a trade-off relationship. Therefore, it is important to improve the balance between the number of holes per unit volume and the puncture strength in order to achieve both safety and output characteristics.
• the present inventors have focused on the puncture strength (N) in terms of film thickness of 10 ⁇ m and the number of holes per unit volume (pieces / ⁇ m 3 ).
• the present inventors have derived the relationship of the above equation (1) as follows. First, the puncture strength (N) in terms of film thickness of 10 ⁇ m was defined as the y-axis, and the number of holes per unit volume (pieces / ⁇ m 3 ) was defined as the x-axis, and the examples and comparative examples described later were plotted. Then, it was found that the existence range is clearly different between the plot of the polyolefin microporous membrane in which the puncture strength and the number of pores are increased and the output characteristics and the safety are compatible, and the plot of the polyolefin microporous membrane in which the output characteristics and safety are not compatible. ..
• a method for establishing the relationship of the above formula (1) for example, a method of quenching in a gel-like sheet forming step described later to obtain a fine and uniform crystal structure, or a method of overlapping molecular chains in the presence of a plasticizer can be used. Examples thereof include a method of increasing and improving the uniformity of stretching, and a method of stretching at a high stretching ratio. By using these methods alone or in combination, the output characteristics can be improved without increasing the porosity, and it is possible to achieve both safety and output characteristics, which have been in a trade-off relationship in the past.
• the polyolefin microporous membrane according to the second embodiment of the present invention has Z and Y when the number of surface pores per unit area is Z (pieces / ⁇ m 2 ) and the puncture strength in terms of film thickness 10 ⁇ m is Y (N). Is characterized by satisfying the relationship of the following equation (2). Y (N) ⁇ ⁇ 0.06 ⁇ Z (pieces / ⁇ m 2 ) + 9.4 ⁇ ⁇ ⁇ Equation (2)
• the present inventors have derived the relationship of the above equation (2) as follows. First, the puncture strength (N) in terms of film thickness of 10 ⁇ m was defined as the y-axis, and the number of surface holes per unit area (pieces / ⁇ m 2 ) was defined as the x-axis, and the examples and comparative examples described later were plotted. Then, they found that the existence range is different between the plot of the polyolefin microporous membrane in which the output characteristics and the safety are compatible and the plot of the polyolefin microporous membrane in which the output characteristics and the safety are not compatible.
• the number of surface holes correlates with the porosity rate, and the strength decreases as the number of surface holes increases.
• the number of entangled molecular chains is increased, stress is uniformly applied to the resin layer and the resin layer is stretched, so that stress propagation in the stretching step is uniform.
• the openness is improved and a uniform and fine pore structure is formed.
• the number of surface holes measured by SEM observation increases and the number of fibrils per unit area increases, so that both good ion permeability and strength can be achieved at the same time. It was found that the relationship between the number of surface holes and the puncture strength, which had been in a trade-off relationship in the past, is improved.
• the surface pore number of the microporous membrane can be measured by SEM (scanning electron microscope) observation, the surface pore number is preferably 40 / [mu] m 2 or more, more preferably 60 / [mu] m 2 or more, 80 / [mu] m 2 The above is more preferable, 90 pieces / ⁇ m 2 or more is most preferable, and 100 pieces / ⁇ m 2 or more is remarkably preferable.
• surface pore number is preferably 135 pieces / [mu] m 2 or less, more preferably 120 / [mu] m 2 or less.
• W and Y when the surface aperture ratio is W (%) and the puncture strength in terms of film thickness of 10 ⁇ m is Y (N) are as follows. It is characterized in that the relationship of 3) is satisfied and the surface aperture ratio W is 5% or more and 45% or less.
• the present inventors have derived the relationship of the above equation (3) as follows. First, the puncture strength (N) in terms of film thickness of 10 ⁇ m was defined as the y-axis, and the surface aperture ratio (%) was defined as the x-axis, and the examples and comparative examples described later were plotted. Then, they found that the existence range is different between the plot of the polyolefin microporous membrane in which the output characteristics and the safety are compatible and the plot of the polyolefin microporous membrane in which the output characteristics and the safety are not compatible.
• the surface aperture ratio correlates with the pore ratio. Since an increase in the surface aperture ratio leads to a decrease in the amount of resin in the depth direction of the microporous membrane, an increase in the surface aperture ratio reduces the puncture strength.
• the improved pore-opening property of the microporous membrane according to the third embodiment of the present invention stress propagation in the stretching step becomes uniform, the strength of the formed fibrils increases, and high puncture strength can be obtained. Therefore, if the relationship between the surface aperture ratio and the puncture strength, which has been in a trade-off relationship in the past, is improved and the relationship of the above equation (3) is satisfied, it is possible to achieve both excellent battery safety and output characteristics.
• the surface aperture ratio W of the microporous membrane is measured from SEM (scanning electron microscope) observation by a method described later, and the surface aperture ratio is preferably 5% or more, more preferably 8% or more, and 10% or more. More preferably, 12% or more is even more preferable. Further, if the surface aperture ratio is too high, dendrites are likely to be generated and the safety is lowered. Therefore, the surface aperture ratio is preferably 45% or less, more preferably 40% or less, further preferably 38% or less, and more preferably 35% or less. More preferred.
• Examples of the method of increasing the porosity include a method of increasing the proportion of the plasticizer in the kneading process and the sheeting process, and a method of increasing the stretching ratio in the dry re-stretching process.
• the proportion of the plasticizer is increased (the resin concentration is lowered)
• the plasticizer layer in the sheet is large and the polyolefin resin layer is not subjected to stretching stress, and the uniformity of the opening is lowered.
• the amount of resin decreases due to the increase in the pore ratio, and the stiffness of the film decreases, so that the draw ratio increases and "crushing of pores" occurs in the washing and drying process.
• the draw ratio increases in the dry re-stretching step, voids are likely to be formed in the polyolefin microporous film, and it becomes difficult to obtain the uniformity of the film.
• the viscosity increases by using a polyolefin resin having an Mw of 1 million or more, good film-forming property can be obtained even at a relatively low resin concentration, and a good porosity can be obtained. Further, since the polyolefin resin having Mw of 1 million or more has a long molecular chain, the number of entanglements increases, the stress applied to the resin layer in the drawing step is easily propagated, and the pore opening property is improved. Therefore, at least one of the number of pores per unit volume, the aperture ratio of the surface, and the number of surface pores per unit area in the polyolefin microporous membrane is increased as compared with the conventional polyolefin microporous membrane, and the ion permeation path is increased. To increase.
• the porosity of the microporous polyolefin membrane of the present invention is preferably 40% or more, more preferably 41% or more, still more preferably 42% or more, from the viewpoint of permeation performance and electrolyte content.
• the porosity is 40% or more, the balance between permeability, strength and electric field liquid content is improved, and the non-uniformity of the battery reaction is eliminated.
• the generation of dendrites is suppressed and the battery can be used without impairing the performance of the conventional battery, and can be suitably used as a separator for a secondary battery.
• the porosity is preferably less than 60%, more preferably 58% or less, still more preferably 55% or less.
• the puncture strength of the polyolefin microporous film in which the film thickness is converted to 10 ⁇ m is preferably 3.0 N or more, more preferably 3.2 N or more, still more preferably 3.5 N or more. 3.8N or more is even more preferable, and 4.0N or more is most preferable.
• the piercing strength is 3.0 N or more, short circuit due to foreign matter in the battery is suppressed, and good battery safety can be obtained. From the viewpoint of improving safety, the higher the piercing strength is, the more preferable it is, and in order to increase the piercing strength, a method of increasing the resin concentration or increasing the draw ratio is taken.
• an increase in the resin concentration means a decrease in the porosity, and the output characteristics decrease. Further, when the draw ratio is increased, the polyolefin microporous film is crushed in the film thickness direction, so that "pore crushing” and voids (defects) are formed, so that the uniformity of the battery reaction is lowered and the output characteristics are deteriorated.
• the raw material composition of the polyolefin microporous film is within the above range, and the stretching conditions at the time of forming the polyolefin microporous film are within the range described later.
• the term "piercing strength” is used to mean “piercing strength when the film thickness is converted to 10 ⁇ m”.
• the electrolytic solution is electrochemically decomposed inside the battery to generate solid products such as organic substances and gases such as ethylene and hydrogen. These products clog the pores in the microporous polyolefin membrane, degrading battery characteristics. Further, since the decomposition reaction is likely to proceed due to the bias of the ion permeation path, it is preferable that the number of ion permeation paths is large.
• the number of holes per unit volume obtained in Examples described later is preferably 40 / [mu] m 3 or more, more preferably 50 / [mu] m 3 or more, more preferably 60 / [mu] m 3 or more, 70 / [mu] m 3
• the above is even more preferable, 80 pieces / ⁇ m 3 or more is even more preferable, 100 pieces / ⁇ m 3 or more is particularly preferable, and 120 pieces / ⁇ m 3 or more is most preferable.
• the number of pores per unit volume and the number of surface pores correlate with the porosity, and the strength decreases as the number of pores per unit volume and the number of surface pores increase.
• Mw is by using a 1.0 ⁇ 10 6 or more of the polyolefin resin of a large molecular weight, increased number entanglement of molecular chains, has improved stress propagation is uniform openness in the stretching step, conventional polyolefin microporous
• the number of pores per unit volume and the number of surface pores are increasing while maintaining the same porosity as the film.
• the polyolefin microporous membrane of the present invention has excellent piercing strength by using a polyolefin resin having a large molecular weight and increasing the number of tie molecules, and has output characteristics and safety that have been in a trade-off relationship in the past. It is excellent in that it is compatible with.
• the piercing strength depends on the amount of resin per unit volume, an increase in piercing strength leads to a decrease in the porosity. Therefore, there is a trade-off between piercing strength and output characteristics.
• the direction parallel to the film-forming direction of the polyolefin microporous film is referred to as the film-forming direction, the longitudinal direction or the MD direction, and the direction orthogonal to the film-forming direction within the polyolefin microporous film surface is the width direction or TD. Called direction.
• the shrinkage rate obtained by TMA thermomechanical analysis
• the heat shrinkage rate in the MD direction at 120 ° C. measured by TMA is preferably 15% or less, more preferably 12% or less, further preferably 10% or less, and 8% or less. Is more preferable.
• the heat shrinkage rate in the TD direction at 120 ° C. measured by TMA is preferably 15% or less, more preferably 12% or less, further preferably 10% or less, and 7% or less. Is more preferable.
• the heat shrinkage rate is within the above range, even if abnormal heat is generated locally, the expansion of the internal short circuit can be prevented and the effect can be minimized.
• the heat shrinkage has a trade-off relationship with the aperture ratio, the number of pores per unit volume, the number of surface pores, and the puncture strength.
• the polyolefin microporous membrane of the present invention makes the stress propagation uniform in the stretching process, the polyolefin The stress applied to the resin is even. Therefore, strain is unlikely to remain, a low heat shrinkage rate is achieved, and an excellent heat shrinkage rate and strength balance are obtained.
• the tensile breaking strength in the MD direction and the TD direction (hereinafter, also simply referred to as "MD strength” and "TD strength”) is preferably 180 MPa or more, more preferably 190 MPa or more, further preferably 200 MPa or more, and more preferably 210 MPa or more. More preferably, 250 MPa or more is more preferable, 260 MPa or more is even more preferable, and 270 MPa or more is most preferable.
• the MD strength and TD strength are less than 180 MPa, a short circuit due to foreign matter in the battery is likely to occur, and the safety of the battery may be lowered.
• the improvement of the tensile breaking strength is often a trade-off between the porosity and aperture ratio, the number of holes per unit volume and the number of surface holes, and MD.
• Both the strength and the TD strength are preferably 350 MPa or less, more preferably 300 MPa or less.
• the raw material composition of the polyolefin microporous film is in the above range, and the stretching conditions at the time of forming the polyolefin microporous film are in the range described later.
• Toughness which is a measure of impact resistance obtained from tensile breaking strength and tensile breaking elongation, is calculated by the following formula using each of tensile breaking strength and tensile breaking elongation in the MD direction and the TD direction.
• Toughness (MPa x%) MD tensile breaking strength x MD tensile breaking elongation + TD tensile breaking strength x TD tensile breaking elongation
• the toughness which is a measure of impact resistance, is preferably 20,000 (MPa ⁇ %) or more, more preferably 25,000 (MPa ⁇ %) or more, still more preferably 30,000 (MPa ⁇ %) or more, most preferably from the viewpoint of impact resistance. Is 35,000 (MPa ⁇ %) or more, particularly preferably 40,000 (MPa ⁇ %) or more.
• the upper limit of toughness is preferably 500,000 (MPa ⁇ %) or less, more preferably 400,000 (MPa ⁇ %) or less, still more preferably 300,000 (MPa ⁇ %) or less, because other physical properties, for example, ion permeability deteriorate. Most preferably, it is 200,000 (MPa ⁇ %) or less.
• the average pore size measured by the poromometer is preferably 10 nm or more from the viewpoint of ion permeability.
• the average pore diameter is 10 nm or more, a good aperture ratio, the number of holes per unit volume and the number of surface holes can be obtained, and excellent battery characteristics can be obtained. Further, since the preferable pore ratio is determined from the viewpoint of battery characteristics, fine and uniform pores are effective for increasing the ion transmission path.
• the average pore size is preferably less than 40 nm, more preferably less than 35 nm, further preferably less than 30 nm, even more preferably less than 28 nm, and most preferably less than 25 nm.
• the surface pore diameter obtained from the SEM image taken by the method described in the examples is preferably 20 nm or more and 70 nm or less, more preferably 20 nm or more and 60 nm or less, and further preferably 20 nm or more and 50 nm or less from the viewpoint of puncture strength and ion permeability. is there.
• the surface hole diameter is within the above range, the number of holes per unit volume and the number of surface holes can easily be within the above range, and good safety and output characteristics can be obtained.
• the air permeability is a value measured in accordance with JIS P 8117 (2009). Unless otherwise specified, the term "air permeability” is used in the present specification to mean “air permeability when the film thickness is 10 ⁇ m".
• the air permeability measured in the polyolefin microporous membrane having a film thickness of T1 ( ⁇ m) is P1
• the air permeability (Gurley value) is of 1,000 sec / 100 cm 3 or less, more preferably 700sec / 100cm 3 or less, still more preferably 500 sec / 100 cm 3 or less, it is 350sec / 100cm 3 or less Is more preferable.
• the air permeability is 1000 sec / 100 cm 3 or less, good ion permeability can be obtained and the electrical resistance can be reduced.
• the production method of the present invention preferably has the following steps (a) to (e).
• Step of melt-kneading a polymer material containing one or more kinds of polyolefin resins and, if necessary, a solvent to prepare a polyolefin resin solution (b) Extruding the solution and molding it into a sheet. Step of cooling and solidifying (c) Step of stretching the obtained sheet by a roll method or a tenter method (d) Then, a step of extracting a plasticizer from the obtained stretched film and drying the film (e) Heat treatment / re-stretching Process to do
• Step of preparing a polyolefin resin solution The above polymer material is heated and dissolved in a plasticizer to prepare a polyolefin resin solution.
• the plasticizer is not particularly limited as long as it is a solvent capable of sufficiently dissolving the polyolefin resin, but the solvent is preferably a liquid at room temperature in order to enable stretching at a relatively high magnification.
• the content ratio of the ultra-high molecular weight polyethylene having a weight average molecular weight of 1 million or more in the solution is, for example, 5 to 30% by mass, preferably 9 to 30% by mass, when the total of the solvent and the polyolefin resin is 100% by mass. , 16 to 30% by mass is more preferable, 17 to 30% by mass is further preferable, and 19 to 30% by mass is particularly preferable. Further, the content ratio of the polyolefin resin in the solution is, for example, less than 30% by mass, preferably 10 to 29% by mass, more preferably 15 to 29% by mass, when the total of the solvent and the polyolefin resin is 100% by mass. It is preferable, and 17 to 29% by mass is more preferable.
• Solvents include aliphatic, cyclic aliphatic or aromatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin, mineral oil distillates having corresponding boiling points, and dibutylphthalate. Examples thereof include phthalates that are liquid at room temperature, such as dioctyl phthalates.
• a non-volatile liquid solvent such as liquid paraffin
• a solid solvent may be mixed with the liquid solvent.
• a solid solvent include stearyl alcohol, ceryl alcohol, paraffin wax and the like. However, if only a solid solvent is used, uneven stretching may occur.
• the viscosity of the liquid solvent is preferably 20 to 200 cSt at 40 ° C.
• the viscosity of the liquid solvent is the viscosity measured at 40 ° C. using an Ubbelohde viscometer.
• the uniform melt-kneading method of the polyolefin resin solution is not particularly limited, but when a high-concentration polyolefin resin solution is desired to be prepared, the solution is extruded from a die (for example, The method (using a twin-screw extruder) is preferable. If necessary, various additives such as antioxidants may be added as long as the effects of the present invention are not impaired. In particular, it is preferable to add an antioxidant in order to prevent oxidation of the polyolefin resin.
• the polyolefin resin solution is uniformly mixed at a temperature at which the polyolefin resin completely melts.
• the melt-kneading temperature varies depending on the polyolefin resin used, but is preferably (melting point of the polyolefin resin + 10 ° C.) to (melting point of the polyolefin resin + 120 ° C.). More preferably, it is (melting point of polyolefin resin + 20 ° C.) to (melting point of polyolefin resin + 100 ° C.).
• the melting point means a value measured by DSC (Differential Scanning Calorimetry) based on JIS K7121 (1987) (hereinafter, the same applies).
• the melt-kneading temperature is preferably in the range of 140 to 250 ° C, more preferably 160 to 230 ° C, and most preferably 170 to 200 ° C.
• the melt-kneading temperature is preferably 140 to 250 ° C., most preferably 180 to 230 ° C.
• the melt-kneading temperature is low from the viewpoint of suppressing deterioration of the polyolefin resin, but if the melt-kneading temperature is lower than the above-mentioned temperature, unmelted matter is generated in the extruded product extruded from the die, and in the subsequent stretching step. It may cause film rupture. Further, when the melt-kneading temperature is higher than the above-mentioned temperature, the thermal decomposition of the polyolefin resin becomes intense, and the physical properties of the obtained polyolefin microporous film, for example, the strength and the porosity may deteriorate.
• the decomposed product precipitates on a chill roll, a roll in the stretching process, or the like and adheres to the sheet, which leads to deterioration of the appearance. Therefore, it is preferable that the melt-kneading temperature is within the above range.
• a gel-like sheet is obtained by cooling the obtained extruded product, and the microphase of the polyolefin resin separated by the solvent can be immobilized by cooling.
• the cooling step it is preferable to cool the gel sheet to 10 to 50 ° C. This is because the final cooling temperature is preferably set to be equal to or lower than the crystallization end temperature, and by making the higher-order structure finer, uniform stretching can be easily performed in the subsequent stretching. Therefore, cooling is preferably performed at a rate of 30 ° C./min or higher at least up to the gelation temperature or lower.
• Examples of the cooling method include a method of directly contacting the extruded product with cold air, cooling water, and other cooling media, a method of contacting the extruded product with a roll cooled with a refrigerant, a method using a casting drum, and the like. is there.
• the polyolefin microporous membrane of the present invention is not limited to a single layer and may be a laminated body.
• the number of layers is not particularly limited, and may be two layers or three or more layers.
• the laminated portion may contain a desired resin in addition to the polyolefin resin to the extent that the effects of the present invention are not impaired.
• a conventional method can be used as a method for forming a polyolefin microporous film as a laminate.
• desired resins are prepared as needed, these resins are separately fed to an extruder to melt at the desired temperature and merge in a polymer tube or die to achieve the desired stacking thickness.
• (C) Stretching Step The obtained gel-like (including laminated sheet) sheet is stretched to obtain a stretched film.
• MD uniaxial stretching by a roll stretching machine TD uniaxial stretching by a tenter, sequential biaxial stretching by a roll stretching machine and a tenter, or a combination of a tenter and a tenter, simultaneous biaxial stretching by a simultaneous biaxial tenter, etc.
• MD uniaxial stretching by a roll stretching machine TD uniaxial stretching by a tenter
• sequential biaxial stretching by a roll stretching machine and a tenter sequential biaxial stretching by a roll stretching machine and a tenter, or a combination of a tenter and a tenter, simultaneous biaxial stretching by a simultaneous biaxial tenter, etc.
• the stretching ratio varies depending on the thickness of the gel-like sheet from the viewpoint of uniformity of film thickness, but it is preferable to stretch 7 times or more in any direction.
• the area magnification is 40 times or more, preferably 49 times or more, more preferably 60 times or more, further preferably 80 times or more, and particularly preferably 100 times or more. If the area magnification is less than 40 times, the stretching is insufficient and the uniformity of the film is likely to be impaired, and a good number of holes per unit volume and a good number of surface holes cannot be obtained.
• the area magnification is preferably 150 times or less. When the area magnification is large, tearing is likely to occur frequently during the production of the polyolefin microporous film, and the productivity is lowered.
• a preferable form of the stretching ratio and the raw material composition is to wet-stretch a raw material having an Mw of 1 million or more to 8 ⁇ 8 times or more, more preferably 10 ⁇ 10 times or more. It is to stretch in a wet manner.
• a more preferable form is to wet-stretch a raw material having an Mw of 2 million or more by 8 ⁇ 8 times or more, and most preferably to stretch it by wet-water at 10 ⁇ 10 times or more.
• the stretching temperature is in the range of (crystal dispersion temperature Tcd of the gel sheet) to (melting point of the gel sheet + 10 ° C.) and (crystal dispersion temperature Tcd of the gel sheet) to (melting point of the gel sheet + 5 ° C.). Is preferable. Specifically, since the polyethylene composition has a crystal dispersion temperature of about 90 to 110 ° C., the stretching temperature is preferably 90 to 130 ° C., more preferably 90 to 120 ° C.
• the crystal dispersion temperature Tcd is obtained from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D 4065 (2012).
• the stretching temperature is less than 90 ° C., the pores are insufficiently opened due to the low temperature stretching, it is difficult to obtain the uniformity of the film thickness, and the pore ratio is also low. If the stretching temperature is higher than 130 ° C., the sheet melts and the pores are likely to be closed.
• the polyolefin microporous membrane of the present invention is suitable for a battery separator.
• the polyolefin resin is sufficiently plasticized and softened, so that the higher-order structure can be cleaved smoothly and the crystal phase can be uniformly refined. it can. Further, by stretching before removing the plasticizer, cleavage is facilitated, so that strain during stretching is less likely to remain, and the heat shrinkage rate can be lowered as compared with the case of stretching after removing the plasticizer. it can.
• cleaning solvent examples include saturated hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, ethers such as diethyl ether and dioxane, ketones such as methyl ethyl ketone, and ethane trifluoride. Chain fluorocarbon and the like can be mentioned.
• These cleaning solvents have low surface tension (eg, 24 mN / m or less at 25 ° C.).
• a cleaning solvent with a low surface tension By using a cleaning solvent with a low surface tension, the reticulated structure forming microporous material is suppressed from shrinking due to the surface tension of the gas-liquid interface during drying after cleaning, and a polyolefin microporous membrane with excellent porosity and permeability. Is obtained.
• These cleaning solvents are appropriately selected depending on the plasticizer and used alone or in combination.
• Examples of the cleaning method include a method of immersing the stretched film in a cleaning solvent for extraction, a method of showering the stretching film with the cleaning solvent, and a method using a combination thereof.
• the amount of the cleaning solvent used varies depending on the cleaning method, but is generally preferably 300 parts by mass or more with respect to 100 parts by mass of the stretched film.
• the cleaning temperature may be 15 to 30 ° C, and if necessary, heat to 80 ° C or less.
• the mechanical property of the polyolefin microporous film From the viewpoint of improving physical properties and electrical properties, the longer the stretched film is immersed in the washing solvent, the better.
• the above-mentioned washing is preferably carried out until the residual solvent in the stretched film after washing, that is, the polyolefin microporous film becomes less than 1% by mass.
• the solvent in the stretched film is dried and removed in the drying step.
• the drying method is not particularly limited, and a method using a metal heating roll, a method using hot air, or the like can be selected.
• the drying temperature is preferably 40 to 100 ° C, more preferably 40 to 80 ° C. If the drying is insufficient, the porosity of the polyolefin microporous membrane will decrease in the subsequent heat treatment, and the permeability will deteriorate.
• Heat treatment / re-stretching step At least one of heat treatment and re-stretching (stretching in at least one axial direction) is performed on the dried stretched film.
• the heat treatment can be performed using, for example, a heat treatment in the MD direction using a roll, a heat treatment in the TD direction using a tenter, a roll and a tenter, or a combination of a tenter and a tenter.
• the temperature of the heat treatment is preferably 120 to 140 ° C, more preferably 125 to 135 ° C.
• Re-stretching can be performed by the tenter method or the like in the same manner as the above-mentioned stretching while heating the stretched film.
• the re-stretching may be uniaxial stretching or biaxial stretching. In the case of multi-stage stretching, simultaneous biaxial or sequential stretching is performed in combination.
• the re-stretching temperature is preferably equal to or lower than the melting point of the stretched film, and more preferably within the range of (Tcd-20 ° C. of the stretched film) to the melting point of the stretched film.
• the re-stretching temperature is preferably 70 to 135 ° C, more preferably 110 to 132 ° C.
• the re-stretching temperature is most preferably 120-130 ° C.
• the re-stretching ratio is preferably 1.01 to 2.0 times, particularly preferably 1.1 to 1.6 times, more preferably 1.2 to 1.4 times in the TD direction. ..
• biaxial stretching it is preferable to stretch 1.01 to 2.0 times in the MD direction and the TD direction, respectively.
• the re-stretching magnification may be different in the MD direction and the TD direction.
• the relaxation rate from the maximum re-stretching ratio is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less.
• the relaxation rate is 20% or less, a uniform fibril structure can be obtained.
• the polyolefin microporous membrane can be hydrophilized.
• the hydrophilization treatment can be performed by a monomer graft, a surfactant treatment, a corona discharge, or the like.
• the monomer graft is preferably carried out after the cross-linking treatment.
• the polyolefin microporous membrane is crosslinked by irradiation with ionizing radiation such as ⁇ -ray, ⁇ -ray, ⁇ -ray, and electron beam.
• ionizing radiation such as ⁇ -ray, ⁇ -ray, ⁇ -ray, and electron beam.
• electron beam irradiation an electron dose of 0.1 to 100 Mrad is preferable, and an accelerating voltage of 100 to 300 kV is preferable.
• the cross-linking treatment raises the meltdown temperature of the microporous polyolefin membrane.
• any of nonionic surfactant, cationic surfactant, anionic surfactant or amphoteric surfactant can be used, but nonionic surfactant is preferable.
• the polyolefin microporous membrane is immersed in water or a solution prepared by dissolving a surfactant in a lower alcohol such as methanol, ethanol, or isopropyl alcohol, or the solution is applied to the polyolefin microporous membrane by the doctor blade method.
• the porous polyethylene film of the present invention is a fluororesin porous body such as polyvinylidene fluoride or polytetrafluoroethylene, or polyimide or polyphenylene for the purpose of improving meltdown characteristics and heat resistance when used as a battery separator.
• Surface coating such as a porous body such as sulfide or inorganic coating such as ceramic may be applied.
• the polyolefin microporous membrane obtained as described above can be used for various purposes such as a filter, a separator for a fuel cell, and a separator for a capacitor, and is particularly excellent in safety and output characteristics when used as a separator for a battery. .. Therefore, the separator can be preferably used as a battery separator for a secondary battery that requires high energy density, high capacity, and high output for electric vehicles and the like.
• Weight average molecular weight (Mw) The weight average molecular weights of ultra-high molecular weight polyethylene and high density polyethylene were determined by gel permeation chromatography (GPC) under the following conditions.
• -Measuring device GPC-150C manufactured by WATERS CORPORATION -Column: SHODEX UT806M manufactured by Showa Denko KK ⁇
• -Injection amount 500 ⁇ L -Detector: WATERS CORPORATION differential refractometer (RI detector)
• RI detector differential refractometer
• Air permeability (sec / 100 cm 3 )
• Puncture strength in terms of film thickness of 10 ⁇ m Using a piercing meter manufactured by MARUBISHI, a needle with a spherical tip (radius of curvature R: 0.5 mm) and a diameter of 1 mm has a film thickness of T1 ( ⁇ m) and a polyolefin microporous film of 2 mm. The maximum load when piercing at a speed of / sec was measured and used as the piercing strength.
• the above measurement was performed at 3 points at different random sampling points in the same polyolefin microporous membrane, and the average value of the puncture strength at 3 points and the puncture strength converted to a film thickness of 10 ⁇ m was obtained.
• Toughness (MPa x%) MD tensile breaking strength x MD tensile breaking elongation + TD tensile breaking strength x TD tensile breaking elongation
• the shrinkage rate is measured in the same manner, and the TD shrinkage at 120 ° C. in TMA. It was a rate.
• the average pore diameter was converted from the pressure at the intersection of the pressure and the half slope of the flow rate curve in the Dry-up measurement and the pressure at the intersection of the Wet-up measurement curve. The following formula was used to convert the pressure and the average pore size.
• d C ⁇ ⁇ / P (In the above formula, “d ( ⁇ m)” is the average pore size of the polyolefin microporous membrane, “ ⁇ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant. .)
• the binarization process was carried out using an accelerating voltage of 2 kV, a magnification of 10000 times, an image of 11.7 ⁇ m ⁇ 9.4 ⁇ m (1280 pixels ⁇ 1024 pixels), and an 8-bit (256 gradations) gray scale image.
• an image processing method after removing noise from the above SEM image by averaging 3 pixels x 3 pixels, a dynamic binary value is set to -30 gradations from the image averaged by 21 pixels x 21 pixels. By performing the conversion process, the dark part was extracted and the binarization process was performed.
• the ratio of the area occupied by the total dark part in the entire original SEM image was defined as the surface aperture ratio (SEM) (%).
• SEM surface aperture ratio
• the number of surface holes existing per 1 ⁇ m 2 was calculated from the extracted independent dark areas and used as the number of surface holes (SEM) (pieces / ⁇ m 2 ).
• A The amount of transfer (mm) / separator thickness ( ⁇ m) was 0.030 or more.
• B The amount of transfer (mm) / separator thickness ( ⁇ m) was 0.025 or more and less than 0.030.
• C The transfer amount (mm) / separator thickness ( ⁇ m) was 0.020 or more and less than 0.025.
• D The amount of transfer (mm) / separator thickness ( ⁇ m) was 0.015 or more and less than 0.020.
• E The amount of transfer (mm) / separator thickness ( ⁇ m) was less than 0.015.
• the polyolefin microporous membrane is incorporated into a non-aqueous electrolyte secondary battery composed of a positive electrode, a negative electrode, a separator and an electrolyte as a separator and charged. A discharge test was performed.
• NMC532 Lithium Nickel Manganese Cobalt Composite Oxide (Li 1.05 Ni 0.50 Mn 0.29 Co 0.21) at 9.5 mg / cm 2 on an aluminum foil with a width of 38 mm, a length of 33 mm and a thickness of 20 ⁇ m. O 2 )) is laminated on a cathode, and natural graphite with a density of 1.45 g / cm 3 is laminated on a copper foil having a width of 40 mm, a length of 35 mm, and a thickness of 10 ⁇ m at a unit area mass of 5.5 mg / cm 2.
• the positive electrode and the negative electrode were dried and used in a vacuum oven at 120 ° C.
• a microporous polyolefin membrane having a length of 50 mm and a width of 50 mm was dried in a vacuum oven at room temperature and used.
• the electrolytic solution is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (30/35/35, volume ratio) in which vinylene carbonate (VC) and LiPF 6 are dissolved, and the VC concentration is 0.5% by mass, LiPF 6.
• a solution of concentration: 1 mol / L was prepared.
• a non-aqueous electrolyte secondary battery is formed by stacking a positive electrode, a separator, and a negative electrode, arranging the obtained laminate in a laminate pouch, injecting an electrolytic solution into the laminate pouch, and vacuum-sealing the laminate pouch. Made.
• the prepared non-aqueous electrolyte secondary battery was charged for 10 to 15% at a temperature of 35 ° C. and 0.1 C, and left at 35 ° C. overnight (12 hours or more) for degassing.
• CC-CV charging with a temperature of 35 ° C., a voltage range of 2.75 to 4.2 V, a charging current value of 0.1 C (termination current condition 0.02 C), and CC discharge with a discharge current value of 0.1 C were performed. ..
• the time point at which this was performed was defined as the initial stage of the non-aqueous electrolyte secondary battery.
• CC-CV charging with a temperature of 35 ° C., a voltage range of 2.75 to 4.2 V, a charging current value of 0.2 C (termination current condition of 0.05 C), and CC discharge with a discharge current value of 0.2 C are performed.
• the discharge capacity at that time was set to 0.2 C capacity.
• CC-CV charging (termination current condition 0.05C) at a temperature of 35 ° C., a voltage range: 2.75 to 4.2V, and a charging current value of 0.5C
• a rate test was performed at 17C (306mA, 24.48mA / cm 2 ). From this result, the ratio of 17C capacity to 0.2C capacity ⁇ (17C capacity / 0.2C capacity) ⁇ 100 ⁇ (%) was defined as the capacity retention rate (%).
• Example 1 Mw as the starting material was used an ultra-high molecular weight polyethylene of 20 ⁇ 10 5. 90 parts by mass of liquid paraffin is added to 10 parts by mass of ultra-high molecular weight polyethylene, and 0.5 parts by mass of 2,6-di-t-butyl-p-cresol and 0.7 mass by mass based on the mass of ultra-high molecular weight polyethylene.
• a polyethylene resin solution was prepared by adding tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant and mixing them.
• the obtained polyethylene resin solution was put into a twin-screw extruder, kneaded at 180 ° C., supplied to a T-die, and the extruded product was cooled with a cooling roll controlled at 15 ° C. to form a gel-like sheet.
• the obtained gel-like sheet was simultaneously biaxially stretched 8 times in both the longitudinal direction and the width direction at 115 ° C. by a tenter stretching machine, the sheet width was fixed as it was in the tenter stretching machine, and the sheet was held at a temperature of 115 ° C. for 10 seconds. ..
• the stretched gel-like sheet was immersed in a methylene chloride bath in a washing tank, and after removing liquid paraffin, it was dried to obtain a polyolefin microporous membrane.
• an oven composed of a plurality of zones divided in the longitudinal direction was used as the oven of the tenter stretching machine, and heat fixing was carried out at a temperature of 120 ° C. for 10 minutes without stretching.
• Table 1 shows the raw material formulation and film forming conditions for the polyolefin microporous membrane
• Table 3 shows the evaluation results for the polyolefin microporous membrane.
• Examples 2 to 11, Comparative Examples 1 to 11 A polyolefin microporous film was prepared in the same manner as in Example 1 except that the raw material formulation and the film forming conditions were changed as shown in Tables 1 and 2.

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• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
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• 2020
  • 2020-03-27 JP JP2020536697A patent/JP7380570B2/ja active Active
  • 2020-03-27 CN CN202080022113.5A patent/CN113631644A/zh active Pending
  • 2020-03-27 WO PCT/JP2020/014348 patent/WO2020203901A1/ja not_active Ceased
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