Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
  • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
• • 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
• • 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 polyolefin microporous membrane, a polyolefin microporous membrane wound body, and a method for producing a microporous membrane.
• microporous membranes are used in various fields such as filters for filter membranes and dialysis membranes, separators for batteries and separators for electrolytic capacitors.
• microporous membranes made of polyolefin as a resin material are excellent in chemical resistance, insulating property, mechanical strength, etc., and have shutdown characteristics, and therefore have been widely used as separators for secondary batteries in recent years.
• lithium-ion secondary batteries are widely used in mobile phones, power tools, electric vehicles, etc.
• Higher output and higher capacity are progressing, and low resistance and low cost of microporous membranes are required for separator applications.
• the resistance of the microporous membrane is low, and the development of a microporous membrane having a high porosity is required.
• the roll diameter of the wound body is increased by increasing the length of the microporous membrane and increasing the number of turns in the wound body of the microporous membrane. It is expected that the diameter will increase.
• the large diameter referred to in this specification means a diameter of 280 mm or more.
• a microporous film wound body with a small difference in film thickness and pore ratio between the surface layer portion and the winding core portion will be required in the future. It is expected that.
• Patent Document 1 describes the rate of change in air permeation resistance when pressure compression treatment is performed under the conditions of a temperature of 60 ° C., a pressure of 4 MPa, and 10 minutes as a separator whose performance does not change much even under expansion and contraction of electrodes.
• a separator with a small pore size is disclosed, a hybrid structure having a ladder structure in the submicron region and a three-dimensional network structure in the micron region is formed, and the breakdown voltage including the portion having a large pore diameter is taken into consideration. It has not been.
• Patent Document 2 discloses a separator having a small rate of change in film thickness after pressure compression treatment at a temperature of 90 ° C. and a pressure of 5.0 MPa, but since the pore ratio is 40% or less, high output is performed. The resistance of the film was high and it was necessary to improve the performance.
• the present invention provides a microporous film having a high porosity and a high dielectric breakdown voltage, and having a small film thickness difference between the surface layer portion and the winding core portion even for a large-diameter wound body. ..
• the present invention was achieved by controlling the fibril structure of the microporous membrane by advanced film forming technology.
• the present invention has the following configuration.
• the thickness is 16 ⁇ m or more and 30 ⁇ m or less, the pore ratio is 40% or more and 60% or less, the bending ratio is 1.00 or more and 1.42 or less, and the dielectric breakdown voltage is 155 V / ⁇ m or more and 300 V.
• a microporous polyolefin membrane characterized by being / ⁇ m or less.
• a wound body characterized in that the microporous polyolefin membrane according to (1) or (2) is wound to an outer diameter of 280 mm or more.
• the method for producing a microporous polyolefin film according to (1) or (2) which comprises the steps (a) to (f).
• B A preheating step of preheating the unstretched gel sheet at 95 ° C. or higher and 115 ° C. or lower.
• the longitudinally stretched sheet is laterally stretched in the sheet width direction at a temperature higher than the temperature of the longitudinally stretching step in the range of 1 ° C. or more and 20 ° C. or less at a stretching ratio of the longitudinally stretching step or more to obtain a biaxially stretched sheet.
• Process (E) An extraction step of extracting a film-forming solvent from the biaxially stretched sheet.
• the polyolefin microporous film of the present invention has a small rate of change in film thickness and a high breakdown voltage even under pressure conditions such as the core of a wound body.
• a separator for an ion secondary battery can be provided.
• the polyolefin resin constituting the polyolefin microporous membrane of the present invention contains a polyethylene resin as a main component.
• the content of the polyethylene resin is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 100% by mass, assuming that the total mass of the polyolefin resin is 100% by mass.
• the polyethylene may be a single product, but is preferably a polyethylene mixture composed of two or more types of polyethylene.
• polyethylene mixture at least one selected from the group consisting of ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene, branched low density polyethylene and linear low density polyethylene can be used.
• polyethylene one type may be used alone, or two or more types may be used in combination. These can be appropriately selected according to the purpose of use.
• the polyethylene mixture, the weight average molecular weight (Mw) of 5 ⁇ 10 5 or more mixtures ultra high molecular weight polyethylene and Mw consists at least 1 ⁇ 10 4 5 ⁇ 10 5 or less of polyethylene.
• the content of ultra-high molecular weight polyethylene in the polyethylene mixture is preferably 25 to 50% by mass from the viewpoint of the change in film thickness during compression.
• the content of ultra-high molecular weight polyethylene in the polyethylene mixture is more preferably 28 to 45% by mass, still more preferably 30 to 40% by mass.
• the molecular weight distribution (Mw / Mn (number average molecular weight)) is preferably 1 or more and 20 or less, and more preferably 3 or more and 10 or less, from the viewpoint of extrusion moldability and physical property control by stable crystallization control.
• the film-forming solvent is not particularly limited as long as it is a substance that can be mixed with the polyolefin resin or a substance that can dissolve the polyolefin resin.
• a liquid solvent or a solid solvent can be used as the film-forming solvent.
• the liquid solvent include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin, and mineral oil distillates having corresponding boiling points.
• a non-volatile liquid solvent such as liquid paraffin.
• the solid solvent preferably has a melting point of 80 ° C. or lower, and examples of such a solid solvent include paraffin wax, ceryl alcohol, stearyl alcohol, dicyclohexylphthalate and the like.
• a liquid solvent and a solid solvent may be used in combination.
• a polyolefin resin and a solvent for film formation are heated, melted and kneaded, and the obtained resin solution is extruded from a die and cooled to form an unstretched gel-like sheet, and the obtained unstretched gel-like sheet is obtained.
• After preheating it is stretched in the vertical direction, which is the sheet transporting direction, and then stretched in the lateral direction, which is the direction perpendicular to the transporting direction, to obtain a biaxially stretched sheet, and the molding solvent is removed and dried to obtain a finely divided sheet.
• the sequential axial stretching method is used. Is preferable.
• the method for producing a microporous polyolefin membrane will be specifically described by taking the sequential stretching method as an example.
• a polyolefin solution containing a polyolefin resin containing ultra-high molecular weight polyethylene in a proportion of 20% by weight or more and 80% by mass or less and a solvent for film formation is melt-kneaded to prepare a polyolefin solution.
• the method of melt-kneading the polyolefin resin and the film-forming solvent is not particularly limited, but it is preferably performed in a twin-screw extruder.
• the preferred range of the temperature of the polyolefin solution in the twin-screw extruder varies depending on the resin.
• the temperature of the polyolefin solution in the polyethylene composition is 140 to 250 ° C.
• the temperature of the polyolefin solution in the extruder should be measured by installing a thermometer inside the extruder or in the cylinder. Indirectly grasp with, and adjust the heater temperature, rotation speed, and discharge amount of the cylinder part as appropriate so that the target temperature is reached.
• the film-forming solvent may be added before the start of kneading, or may be added during the kneading. In melt-kneading, it is preferable to add an antioxidant in order to prevent oxidation of the polyolefin resin.
• An unstretched gel-like sheet is formed by cooling the melted and kneaded polyolefin resin solution in the extruder.
• a method for forming the unstretched gel-like sheet for example, the methods disclosed in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used.
• Cooling is preferably performed at a rate of 50 ° C./min or higher, at least up to the gelation temperature. Cooling is preferably performed up to 35 ° C. or lower.
• the microphase of the polyolefin separated by the film-forming solvent can be immobilized.
• the cooling rate is within the above range, the crystallinity is maintained in an appropriate range, and an unstretched gel-like sheet suitable for stretching is obtained.
• a cooling method a method of contacting with a refrigerant such as cold air or cooling water, a method of contacting with a cooling roll, or the like can be used, but it is preferable to contact with a roll cooled with the refrigerant for cooling.
• an unstretched gel-like sheet containing a film-forming solvent is gradually heated by passing a plurality of metal rolls until it reaches the longitudinal stretching temperature.
• it is preheated by passing it through a plurality of metal rolls, but a roll coated with ceramic or Teflon (registered trademark) may be used.
• Teflon registered trademark
• the unstretched gel-like sheet can be stretched without temperature unevenness in the stretching step, and breakage due to physical characteristic spots and sudden temperature changes can be suppressed.
• the temperature immediately before entering the longitudinal stretching step in the preheating step is a temperature of ⁇ 15 ° C. or higher and -1 ° C.
• the temperature is -10 ° C or higher and -5 ° C or lower.
• the temperature obtained by subtracting the temperature of the longitudinal stretching step from the temperature immediately before entering the longitudinal stretching step may be abbreviated as the preheating temperature difference.
• the preheating temperature is in the range of 95 ° C to 115 ° C. It is important to provide a temperature difference between the inside and the surface of the gel-like sheet during longitudinal stretching.
• the pore diameter in the central portion in the film thickness direction can be made relatively smaller than that in the surface layer portion, and the dielectric breakdown voltage, which is difficult to achieve at the same time, can be improved while maintaining a small bending ratio. Can be done.
• (C) Longitudinal Stretching Step the polymer chains of polyolefin are oriented in the stretching direction by stretching the unstretched gel-like sheet in the longitudinal direction.
• the longitudinal stretching step is divided into a stretching step and a heat fixing step, and the temperature is adjusted for each.
• the longitudinal stretching is performed by passing a plurality of metal rolls having different peripheral speeds.
• the time for the gel-like sheet to come into contact with the stretched roll that comes into contact first from the preheating step is preferably 3 seconds or less. It is more preferably 2 seconds or less, still more preferably 1.5 seconds or less. Within this range, when a film-forming solvent having a low thermal conductivity such as liquid paraffin is used, vertical stretching can be performed while maintaining a constant difference between the temperature of the central portion and the temperature of the surface layer portion in the film thickness direction.
• the longitudinal stretching is performed in two or more steps from low magnification to high magnification in stages.
• the stretching ratio in the longitudinal stretching step if the temperature of the unstretched gel-like sheet is too low, the stretching stress during longitudinal stretching becomes extremely large and the stretching becomes unstable. Therefore, the initial stretching ratio is 1.1 times or more. It is preferably 2 times or less, more preferably 1.2 times or more and 2 times or less.
• the longitudinal stretching ratio of the second and subsequent stages is preferably 1.5 times or less of the longitudinal stretching ratio of the previous stage, and it is preferable to increase the number of stages to a desired stretching ratio. By doing so, breakage can be suppressed.
• the total longitudinal stretching ratio of the longitudinal stretching is preferably 5 times or more and 12 times or less, more preferably 5.5 times or more and 11 times or less.
• the total longitudinal stretching ratio is the sum of the stretching ratios of each stage. With such a longitudinal stretching ratio, it is easy to obtain a balance between strength and pore size.
• Pore opening is controlled by appropriately adjusting the stretching ratio while keeping the difference between the preheating temperature and the longitudinal stretching temperature of the longitudinal stretching within the above range, the curved path length of the microporous membrane is reduced, and the fine pore diameter is made uniform. Can be done. By doing so, a fibril structure having a relatively large pore diameter on the surface and a relatively small pore diameter in the central portion can be obtained, and both compressibility and high dielectric breakdown voltage can be achieved.
• (D) Step of obtaining biaxially stretched sheet The longitudinally stretched sheet obtained in the longitudinally stretching step is stretched in the width direction.
• the obtained transverse stretching sheet is stretched at a magnification higher than the total longitudinal stretching magnification by a tenter device while grasping both ends of the obtained transverse stretching sheet with clips. Specifically, it is preferably stretched 6 times or more and 13 times or less, and more preferably 6.5 times or more and 12 times or less.
• the transverse stretching temperature is the temperature inside the tenter, and stretching is performed at a temperature 1 ° C to 10 ° C higher than the longitudinal stretching temperature.
• the magnification and temperature of longitudinal stretching and transverse stretching preferably satisfy the following formulas (a) and (b).
• the transverse stretching step of stretching the polymer oriented in the longitudinal direction by longitudinal stretching in the width direction is higher than the longitudinal stretching temperature and the stretching ratio is increased. Therefore, a high breakdown voltage can be maintained by making the thicknesses of the fibrils in the vertical direction and the horizontal direction uniform.
• the difference between the transverse stretching temperature and the longitudinal stretching temperature of the formula (b) is represented by the transverse stretching temperature-longitudinal stretching temperature, preferably 1 ° C. or higher and 10 ° C. or lower, and more preferably 3 ° C. or higher and 6 ° C. or lower.
• the film from which the film-forming solvent is extracted is heat-treated in order to stabilize the crystals and make the lamella uniform.
• the heat fixing treatment is a heat treatment in which the film is heated while being held so that the dimensions of the film do not change.
• the heat relaxation treatment is a heat treatment in which the membrane is heat-shrinked in the vertical direction and the horizontal direction during heating.
• the heat fixing treatment is preferably performed by a tenter method or a roll method.
• a heat relaxation treatment method the method disclosed in JP-A-2002-256099 can be mentioned.
• the heat fixing treatment or the heat relaxation treatment is performed by stretching at least in the uniaxial direction at a magnification of 1.1 times or more and 2 times or less to increase the strength of the microporous film.
• the heat treatment of the microporous membrane is preferably performed at a temperature 1 ° C. or higher and 20 ° C. or lower higher than the transverse stretching temperature.
• the obtained microporous membrane was wound around a winding core made of ABS having an outer diameter of 150 mm to 450 mm with a winding tension of 10 N to 60 N, and jumbo rolls were collected.
• the tension of the jumbo roll is preferably 10 N or more and 60 N or less, and more preferably 15 N or more and 55 N or less. If the take-up tension is too low, winding misalignment is likely to occur, and if the take-up tension is too high, wrinkles and film deformation are likely to occur due to winding tightening.
• the microporous membrane wound around the jumbo roll is slit to the desired length and width.
• the slit may be performed from the jumbo roll to the required width and length with one slit, or the slit may be performed from the jumbo roll in two to four times.
• the number of slits is preferably 5 or less because the probability of foreign matter contamination increases.
• the slit tension is adjusted according to the film thickness and width, and is preferably 0.1 N or more and 50 N or less. More preferably 0.5N or more and 45N or less, still more preferably 1.0N or more and 40N or less. If the take-up tension is too low, winding misalignment is likely to occur, and if the take-up tension is too high, wrinkles and film deformation are likely to occur due to winding tightening.
• the obtained microporous membrane can be made into a laminated porous membrane by providing a layer other than the microporous layer, if necessary.
• the other layer include a porous layer formed by using a filler-containing resin solution containing a filler and a resin binder or a heat-resistant resin solution.
• the microporous polyolefin membrane of the present embodiment can have compressibility and high breakdown voltage while having a high porosity by satisfying the above conditions such as stretching temperature and stretching ratio.
• the film thickness can be measured with a measuring device having a display resolution of up to 0.01 ⁇ m.
• a measuring device having a display resolution of up to 0.01 ⁇ m.
• the contact type it is desirable to perform the measurement without crushing the pores of the microporous membrane, and the measuring force can be measured at 0.01 N or more and 0.15 N or less.
• the microporous polyolefin membrane is 16 ⁇ m or more and 30 ⁇ m or less, preferably 16 ⁇ m or more and 25 ⁇ m or less.
• the output of batteries has been increased, and some batteries use a thin microporous film of 16 ⁇ m or less.
• the output is less than 16 ⁇ m, the closer to the core in the manufacturing process, the closer the surface layer and the core are to the winding core.
• coating is often applied to ensure the safety of the battery, and by setting the thickness to 16 ⁇ m or more, a separator that ensures safety can be obtained without performing a coating process. Can be done. Further, by setting the film thickness to 30 ⁇ m or less, the battery capacity can be secured, and the amount of change in thickness between the surface layer portion and the winding core portion of the wound body can be reduced.
• the porosity is defined as the ratio of the volume of space to the total volume of the substance. Specifically, the film thickness and mass of the microporous film are measured, and the porosity is calculated using the value of the resin density. To do. The resin density can be measured according to JIS K 7112: 1999.
• the porosity of the polyolefin microporous membrane is preferably 40% or more and 60% or less. If the porosity is less than 40% when the output of the battery is increased, the resistance of the membrane increases, and when a microporous membrane is used as the battery separator, good output characteristics cannot be obtained.
• the pore ratio is 60% or more, the resistance of the film is small and good output characteristics can be obtained, but the amount of change in film thickness may be large, and when the amount of change in film thickness is large, the cycle characteristics deteriorate. There is a fear.
• the vacancy rate is more preferably 45% or more and 55% or less, and further preferably 48% or more and 53% or less.
• the amount of change in film thickness is the amount of change in core film thickness with respect to the surface layer film thickness, and is expressed by the following formula.
• Film thickness change (%) (surface film thickness-core film thickness) / surface film thickness x 100
• the amount of change in film thickness is preferably 0% or more and 0.8% or less, more preferably 0% or more and 0.7% or less, and further preferably 0% or more and 0.6% or less.
• the amount of change in film thickness is within the above range, the number of turns in the wound body of the microporous film can be increased in the microporous film manufacturing process.
• the bend ratio can be measured using a porosimeter.
• the porosimeter can be measured by either the non-mercury injection method or the mercury injection method, but it is desirable to use the non-mercury injection method that does not use harmful mercury.
• the curve rate is preferably 1.00 or more and 1.42 or less. Good compressibility can be obtained when the bend ratio is low. More preferably, it is 1.05 or more and 1.40 or less, and further preferably 1.10 or more and 1.38 or less. If the curvature ratio exceeds 1.42, the compressibility is likely to deteriorate. The closer the curve ratio is to 1.00, the better the output characteristics, while the higher the curve ratio is, the more advantageous it is in terms of safety. Therefore, the above range is good from the viewpoint of safety.
• the curve rate is based on the press-fitting method.
• the dielectric breakdown voltage can be measured according to JIS C2110-1: 2016.
• the dielectric breakdown voltage per 1 ⁇ m of the film thickness is preferably 155 V / ⁇ m or more and 300 V / ⁇ m or less, more preferably 160 V / ⁇ m or more and 290 V / ⁇ m or less, and further preferably 165 V / ⁇ m or more and 280 V / ⁇ m or less.
• the dielectric breakdown voltage is 155 V / ⁇ m or less, pinholes are less likely to open in the microporous membrane even if a discharge is generated by static electricity.
• the dielectric breakdown voltage exceeds 300 V / ⁇ m the average pore diameter of the microporous membrane becomes too small, and it becomes difficult for the electrolytic solution to permeate.
• the average pore size can be measured using a palm poromometer. Unlike the porosimeter, the palm poromometer can selectively measure the thinnest part of the pores.
• the average pore diameter determined from the palm poromometer of the polyolefin microporous membrane is preferably 20 nm or more and 30 nm or less, more preferably 22 nm or more and 28 nm or less, and further preferably 23 nm or more and 27 nm or less.
• the film thickness was cut out from an arbitrary position of the microporous membrane in a vertical direction of 110 cm and a horizontal direction of 6 cm to prepare a test piece. Twenty points of this test piece were measured in the vertical direction at intervals of 5 cm with a thickness contact thickness meter, and averaged to obtain the thickness of the test piece.
• a Mitutoyo Lightmatic VL-50B meter carbide spherical surface stylus ⁇ 9.5 mm
• the measurement environment was within the range of 23 ⁇ 2 ° C.
• a microporous polyolefin membrane slit to a width of 60 mm was wound around a core made of ABS having an outer diameter of 200 mm and an inner diameter of 76.2 mm until the outer diameter became 280 mm to obtain a wound body.
• the wound body of this polyolefin microporous film was stored at 23 ⁇ 2 ° C. for 2 weeks, and the film thickness was measured at 20 points in the winding direction at 50 mm intervals starting from a point 2 m from the surface layer, and the average value was the surface layer film thickness. And said.
• the wound body of the polyolefin microporous film was incised, the film thickness was measured at 20 points in the outer winding direction at intervals of 5 cm, starting from a point 10 m from the core, and the average value was taken as the core film thickness.
• the film thickness of the microporous polyolefin membrane was measured 5 minutes after being released from the wound state.
• Film thickness change rate (%) (surface film thickness-core film thickness) / surface film thickness x 100
• the tensile strength corresponding to each direction is cut into a shape conforming to JIS K7127 with a width of 10 mm and test piece type 2, and the microporous membrane is not marked, and the chuck gap is 20 mm and the test speed is 100 mm / min. It was measured. The measurement environment was within the range of 23 ⁇ 2 ° C.
• the pore specific volume, specific surface area, porosity, and permeability coefficient of the microporous membrane are measured using a pure water press-fit porosimeter, and the curvature ratio is obtained from the formula (a) using the film thickness with the above contact thickness meter. Be done.
• the film thickness was cut out from an arbitrary position of the microporous membrane into a square having a longitudinal direction of 5 cm and a width direction of 5 cm to prepare a test piece. Arbitrary 5 points of this test piece were measured with a thickness contact thickness meter and averaged to obtain the thickness of the test piece.
• a Mitutoyo Lightmatic VL-50B meter carbide spherical surface stylus ⁇ 9.5 mm having a measuring force of 0.01 N was used.
• the upper electrode used a 50 g brass cylinder with a diameter of 25 mm and a radius of 3 mm rounded at the edge, and the lower electrode used a copper flat plate.
• the microporous membrane was cut into 100 mm ⁇ 100 mm, and the lower electrode, the microporous membrane, and the upper electrode were arranged in this order for measurement.
• d ( ⁇ m) is the pore size of the microporous membrane
• ⁇ (mN / m) is the surface tension of the liquid
• P (Pa) is the pressure
• C is a constant.
• Example 1 Mw of 2.0 ⁇ 10 6 of the ultra high molecular weight polyethylene (UHPE) 30% by weight and Mw of 5.6 ⁇ 10 5 high density Porichiren (HDPE: density 0.955 g / cm 3, melting point 135 ° C.) 70 wt%
• a mixture was prepared by adding 0.2 parts by mass of tetrakis [methylene-3- (3,5-ditercious butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant to 100 parts by mass of a polyolefin resin composed of the above. ..
• the polyolefin resin solution was supplied from a twin-screw extruder to a T-die, and the extruded product was taken up by a cooling roll whose temperature was adjusted to 30 ° C. and cooled while being taken up to form an unstretched gel-like sheet.
• the unstretched gel-like sheet is passed through a preheating roll at 113 ° C., and a vertically stretched roll having a diameter of 200 mm is used at 119 ° C. where the surface temperature is 6 ° C. higher than the preheating temperature. It was divided into three stages of 1.3 times, 1.8 times, and 2.4 times in the direction, and stretched at a total longitudinal stretching ratio of 5.6 times. Then, three cooling rolls were passed and the sheet was cooled to 50 ° C. to form a vertically stretched sheet. At this time, the transport speed was adjusted so that the time during which the unstretched gel-like sheet was in contact with the vertically stretched roll that was first contacted from the preheating step was 2.0 seconds so that the temperature did not rise to the inside.
• Both ends of the obtained vertically stretched sheet were gripped with clips and stretched 8.9 times in the lateral direction with a tenter device set at 125 ° C. to obtain a biaxially stretched sheet.
• the obtained biaxially stretched sheet was washed with methylene chloride to extract and remove residual liquid paraffin, and dried.
• the obtained biaxially stretched sheet after drying is heated to 130 ° C. by a tenter type stretching machine, re-stretched so as to be 1.44 times the inlet width of the stretching machine, and then the entrance width of the re-stretching device.
• the heat treatment was carried out after adjusting the lateral magnification to 1.31 to obtain a polyolefin microporous film having a thickness of 19.5 ⁇ m.
• the winding tension of the slit was 4N to a width of 60 mm, and the slit was wound around a resin core having an outer diameter of 203 mm to obtain a wound body of a battery separator having an outer diameter of 303 mm.
• Example 2 Mw of 2.0 ⁇ 10 6 of the ultra high molecular weight polyethylene 25% by weight and Mw of 5.6 ⁇ 10 5 high density Porichiren (density 0.955 g / cm 3, melting point 135 ° C.) a polyolefin resin 100 consisting of 75 wt% A mixture was prepared by adding 0.2 parts by mass of tetrakis [methylene-3- (3,5-ditercious butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant to the parts by mass.
• Example 28.5 parts by mass of the obtained mixture was put into a strong kneading type twin-screw extruder, and 71.5 parts by mass of liquid paraffin [35 cSt (40 ° C.)] was supplied from the side feeder of the twin-screw extruder to 230 ° C.
• a polyolefin resin solution was prepared by melt-kneading under the conditions of 250 rpm and 250 rpm, a polyolefin microporous film having a thickness of 19.3 ⁇ m was obtained.
• a wound body was obtained in the same manner as in Example 1.
• Using this polyolefin microporous membrane a wound body was obtained in the same manner as in Example 1.
• a wound body was obtained in the same manner as in Example 1.
• Example 3 Mw of 2.0 ⁇ 10 6 of the ultra high molecular weight polyethylene 40% by weight and Mw of 5.6 ⁇ 10 5 high density Porichiren (density 0.955 g / cm 3, melting point 135 ° C.) a polyolefin resin 100 consisting of 60 wt% Example 1 except that 0.2 parts by mass of tetrakis [methylene-3- (3,5-ditersary butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant was added to the parts by mass to prepare a mixture.
• a polyolefin microporous film having a thickness of 19.5 ⁇ m was obtained.
• Using this polyolefin microporous membrane a wound body was obtained in the same manner as in Example 1. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 4 Example 1 except that the unstretched gel-like sheet of Example 1 was passed through a preheating roll at 115 ° C. and stretched in the longitudinal direction using a vertically stretched roll having a diameter of 200 mm at 119 ° C., the surface temperature of which is 4 ° C. higher than the preheating temperature.
• a polyolefin microporous film having a thickness of 19.5 ⁇ m was obtained.
• a wound body was obtained in the same manner as in Example 1.
• Example 5 Example 1 except that the unstretched gel-like sheet of Example 1 was passed through a preheating roll at 109 ° C. and stretched in the longitudinal direction using a vertically stretched roll having a diameter of 200 mm at 122 ° C. where the surface temperature was 13 ° C. higher than the preheating temperature.
• a polyolefin microporous film having a thickness of 19.6 ⁇ m was obtained.
• a wound body was obtained in the same manner as in Example 1.
• Example 6 A polyolefin microporous film having a thickness of 19.4 ⁇ m was obtained in the same manner as in Example 1 except that the vertically stretched sheet of Example 1 was stretched 8.9 times in the lateral direction by a tenter device set at 120 ° C. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 7 The unstretched gel sheet of Example 1 is passed through a preheating roll at 113 ° C., and a longitudinally stretched roll having a diameter of 150 mm at 119 ° C., whose surface temperature is 6 ° C. higher than the preheating temperature, is used to form a longitudinally stretched roll that comes into contact first from the preheating step.
• the transport speed is adjusted so that the contact time of the unstretched gel-like sheet is 1.0 second, and the total length is divided into three stages of 1.3 times, 1.8 times, and 2.4 times in the vertical direction. It was stretched at a stretching ratio of 5.62 times.
• a polyolefin microporous film having a thickness of 19.4 ⁇ m was obtained in the same manner as in Example 1 except for the above. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 8 The unstretched gel sheet of Example 1 is passed through a preheating roll at 113 ° C., and a longitudinally stretched roll having a diameter of 250 mm at 119 ° C., whose surface temperature is 6 ° C. higher than the preheating temperature, is used to form a longitudinally stretched roll that comes into contact first from the preheating step.
• the transport speed is adjusted so that the contact time of the unstretched gel-like sheet is 3.0 seconds, and the total length is divided into three stages of 1.3 times, 1.8 times, and 2.4 times in the vertical direction. It was stretched at a stretching ratio of 5.62 times.
• a polyolefin microporous film having a thickness of 19.5 ⁇ m was obtained in the same manner as in Example 1 except for the above. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 9 The same polyolefin resin solution as in Example 1 was supplied from a twin-screw extruder to a T-die, and the extrusion-formed body was taken up by a cooling roll whose temperature was adjusted to 30 ° C. and cooled while being taken up to form an unstretched gel-like sheet.
• the obtained unstretched gel-like sheet was divided into three stages of 1.8 times, 1.8 times, and 2.4 times in the longitudinal direction, and stretched at a total longitudinal stretching ratio of 7.8 times.
• a polyolefin microporous film having a thickness of 20.0 ⁇ m was obtained in the same manner as in Example 1 except that the unstretched gel-like sheet had a total longitudinal stretching ratio of 7.8 times. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 10 The polyolefin resin solution of Example 1 is supplied from a twin-screw extruder to a T-die, and the extruded body is taken up by a cooling roll whose temperature is adjusted to 30 ° C. and cooled while being taken up so that the thickness becomes 80% of that of Example 1.
• An unstretched gel-like sheet was formed in.
• a polyolefin microporous film having a thickness of 16.0 ⁇ m was obtained in the same manner as in Example 1 except for the thickness of the unstretched gel-like sheet. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 1 The polyolefin resin solution of Example 1 was supplied from a twin-screw extruder to a T-die, and the extruded product was taken up by a cooling roll whose temperature was adjusted to 30 ° C. and cooled while being taken up to form an unstretched gel-like sheet. The obtained unstretched gel-like sheet was simultaneously stretched 5 times in the vertical direction and 5 times in the horizontal direction with a tenter device set at 117 ° C. to obtain a biaxially stretched sheet. After obtaining the biaxially stretched sheet, the same procedure as in Example 1 was carried out to obtain a polyolefin microporous film having a thickness of 19.5 ⁇ m. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 1 30 parts by mass of the obtained mixture was put into a strong kneading type twin-screw dispenser, 70 parts by mass of liquid paraffin [35 cSt (40 ° C.)] was supplied from the side feeder of the twin-screw extruder, and the conditions were 230 ° C. and 250 rpm.
• a polyolefin resin solution was prepared
• a polyolefin microporous film having a thickness of 19.2 ⁇ m was obtained.
• a wound body was obtained in the same manner as in Example 1.
• a polyolefin microporous film having a thickness of 19.5 ⁇ m was obtained in the same manner as in Example 1 except for the above. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 4 The unstretched gel sheet of Example 1 was passed through a preheating roll at 113 ° C., and the surface temperature was 125 ° C., which is 12 ° C. higher than the preheating temperature, 1.3 times, 1.8 times, 2.4 times and 3 in the vertical direction. It was divided into stages and stretched at a total magnification of 5.62 times. Then, three cooling rolls were passed and the sheet was cooled to 50 ° C. to form a vertically stretched sheet.
• Both ends of the obtained longitudinally stretched sheet are gripped with clips and stretched 8.9 times in the transverse direction with a tenter device set to 113 ° C., which is 12 ° C. lower than the longitudinally stretched temperature so that the longitudinally stretched temperature ⁇ the transversely stretched temperature. Then, a biaxially stretched sheet was obtained.
• a polyolefin microporous film having a thickness of 19.4 ⁇ m was obtained in the same manner as in Example 1 except for the above. Using this polyolefin microporous membrane, a wound body was obtained in the same manner as in Example 1.
• Example 5 The unstretched gel-like sheet of Example 1 was preheated, and the magnification of stretching in the longitudinal direction was divided into three stages of 1.8 times, 1.8 times, and 2.4 times, and the total longitudinal stretching ratio was 7.8 times. A longitudinally stretched sheet was formed in the same manner as in Example 1 except that it was stretched.
• Both ends of the obtained vertically stretched sheet are gripped with clips and stretched 6.8 times in the lateral direction with a tenter device set at 125 ° C. so that the longitudinal stretching ratio ⁇ the transverse stretching ratio to obtain a biaxially stretched sheet. It was.
• a polyolefin microporous film having a thickness of 19.4 ⁇ m was obtained in the same manner as in Example 1.
• a wound body was obtained in the same manner as in Example 1.
• Example 6 The polyolefin resin solution of Example 1 is supplied from a twin-screw extruder to a T-die, and the extrusion-formed body is taken up by a cooling roll whose temperature is adjusted to 30 ° C. and cooled while being taken up so that the thickness becomes 60% of that of Example 1. An unstretched gel-like sheet was formed in.
• An unstretched gel sheet is passed through a preheating roll at 113 ° C., and a vertically stretched roll having a surface temperature of 120 ° C., which is 7 ° C. higher than the preheating temperature, and a diameter of 200 mm is used. It was divided into three stages of 1.8 times, 1.8 times, and 2.4 times in the direction, and stretched at a total longitudinal stretching ratio of 7.8 times. Then, three cooling rolls were passed and the sheet was cooled to 50 ° C. to form a vertically stretched sheet. At this time, the transport speed was adjusted so that the time for the unstretched gel-like sheet to contact the vertically stretched roll that was first contacted from the preheating step was 2.0 seconds.
• Both ends of the obtained vertically stretched sheet were gripped with clips and stretched 8.9 times in the lateral direction with a tenter device set at 115 ° C. to obtain a biaxially stretched sheet.
• the obtained biaxially stretched sheet was washed with methylene chloride to extract and remove residual liquid paraffin, and dried.
• the obtained biaxially stretched sheet after drying is heated to 130 ° C. by a tenter type stretching machine, re-stretched so as to be 1.44 times the inlet width of the stretching machine, and then the entrance width of the re-stretching device.
• the heat treatment was carried out after adjusting the lateral magnification to 1.31 to obtain a polyolefin microporous film having a thickness of 11.9 ⁇ m.
• the winding tension of the slit was 3.5 N to a width of 60 mm, and the slit was wound around a resin winding core having an outer diameter of 203 mm to obtain a wound body of a battery separator having an outer diameter of 268 mm.
• Tables 1 to 3 show the blending ratios, production conditions, evaluation results, etc. of each component of the polyolefin microporous membranes obtained in Examples 1 to 10 and Comparative Examples 1 to 6.

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