Polyolefin membrane and method for producing polyolefin membrane

Abstract

Provided is a polyolefin film containing polyolefin, said polyolefin containing polyethylene. The melting point of the polyolefin film is from 134ºC to 140ºC. The basis weight equivalent puncture strength Sm of the polyolefin film is from 70 gf / (g / m2) to 150 gf / (g / m2). Additionally, the shutdown temperature Ts of the polyolefin film and the Sm satisfy the following relational expression.　Ts < 0.13 × Sm + 130

Description

[Technical Field]

[0001] The present invention relates to a polyolefin membrane and a method for producing the polyolefin membrane. [Background technology]

[0002] In recent years, the development of energy storage devices, typified by lithium-ion secondary batteries (LiBs), has been actively pursued. Generally, an energy storage device is constructed by impregnating an electrolytic solution with a power generating element, which has a separator between a positive electrode and a negative electrode. This separator has minute pores that allow lithium ions to pass through during normal use of the energy storage device, but block the passage of lithium ions when the energy storage device generates abnormal heat, thereby preventing thermal runaway.

[0003] Various polyolefin materials have been considered for use as separator materials, and the specifications, such as the composition of the polyolefin, are typically adjusted appropriately depending on the desired balance of physical properties. For example, the trend toward higher capacity energy storage devices for both consumer and automotive applications has led to thinner separators. As separators become thinner, they require higher strength per unit area to maintain mechanical strength. Possible methods for achieving high thin-film strength include the use of high-molecular-weight polyethylene, low-temperature stretching, and sequential stretching. However, when achieving high thin-film strength using these methods, the trade-off is a higher shutdown temperature, which tends to reduce safety at high temperatures. To address this issue, a method of lowering the shutdown temperature using low-melting-point polyethylene has been used. As such a technique, for example, Patent Document 1 proposes the use of a high molecular weight polyethylene having a viscosity average molecular weight of 500,000 to 2,500,000 in combination with a polyolefin having a melt index of 2 g / 10 min to 50 g / 10 min and a melting point of 120° C. to 137° C. in a polyolefin microporous membrane from the viewpoint of a balance between low-temperature fuse function, sufficient mechanical strength, and good heat resistance. Also, Patent Document 2 proposes the use of a porous polyolefin film having a porosity Φ (%), a shutdown temperature T SD A porous polyolefin film has been proposed in which the Tm (°C) and the lowest melting point Tm (°C) of the melting points of each layer satisfy a predetermined relationship. Furthermore, Patent Document 3 proposes a polyolefin composite porous membrane having a first layer containing polypropylene (A), a first high-density polyethylene (B) having a melting point of 130°C or more, and a second high-density polyethylene (C) having a melting point of 120°C or more but less than 130°C, and a second layer containing polyethylene (D), in which the first layer and the second layer are laminated together integrally, from the viewpoint of a balance between external short-circuit resistance, high-temperature heat resistance, and impact resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-141029 [Patent Document 2] Japanese Patent Application Publication No. 2019-143142 [Patent Document 3] International Publication No. 2019 / 093184 Summary of the Invention [Problem to be solved by the invention]

[0005] When a low-melting-point resin such as those described in Patent Documents 1 to 3 is used, the shutdown temperature is lowered, but the temperature cannot be raised during the heat setting step of the film-forming process, which tends to deteriorate the heat shrinkage rate and permeability. Here, blending a low-melting-point resin with a high-molecular-weight polyethylene or the like may be considered to achieve strength, but in this case, the onset temperature of swelling by the plasticizer differs significantly between the low-melting-point resin and the high-molecular-weight polyethylene, which tends to result in the occurrence of unmelted gel defects due to insufficient swelling. As mentioned above, the techniques described in Patent Documents 1 to 3 still have room for improvement in terms of achieving both a low shutdown temperature and high strength while avoiding deterioration in heat shrinkage rate and permeability.

[0006] The present invention has been made in view of the problems inherent in the above-mentioned conventional techniques, and an object of the present invention is to provide a polyolefin membrane that has an excellent balance of heat shrinkage, permeability, shutdown temperature, and strength. [Means for solving the problem]

[0007] As a result of intensive research to solve the above-mentioned problem, the inventors discovered that the problem can be solved by configuring the melting point and basis weight equivalent strength of the polyolefin membrane to fall within a predetermined range, while also configuring the shutdown temperature and basis weight equivalent strength to satisfy a predetermined relationship, and thus completed the present invention.

[0008] That is, the present invention includes the following aspects. [1] A polyolefin membrane comprising a polyolefin, the polyolefin comprises polyethylene; The melting point of the polyolefin film is 134°C or higher and 140°C or lower, The polyolefin film has a puncture strength (Sm) converted to a basis weight of 70 gf / (g / m 2 ) or more 150gf / (g / m 2 ) or less, A polyolefin membrane, wherein the shutdown temperature Ts of the polyolefin membrane and the Sm satisfy the following relationship: Ts<0.13×Sm+130 [2] The polyolefin membrane according to [1], wherein the total amount of side chains having 3 carbon atoms and side chains having 4 carbon atoms measured on the polyolefin membrane is 0.1 mol % or less as a ratio to the total number of carbon atoms. [3] The polyethylene includes polyethylene A and polyethylene B different from polyethylene A, the polyethylene A is a homopolyethylene having a melting point of 134°C or higher and 138°C or lower and a melt index of 0.5 g / 10 min or higher and 50 g / 10 min or lower, The polyolefin film according to [1] or [2], wherein the content of the polyethylene A is 20 parts by mass or more and 80 parts by mass or less relative to 100 parts by mass of the total of the polyethylene A and the polyethylene B. [4] The polyethylene B is a homopolyethylene having a viscosity average molecular weight of 800,000 or more and 5,000,000 or less, The polyolefin film according to [3], wherein the content of the polyethylene B relative to 100 parts by mass of the total of the polyethylene A and the polyethylene B is 20 parts by mass or more and 80 parts by mass or less. [5] The polyolefin film according to any one of [1] to [4], which has a heat shrinkage rate of 10% or less at 120°C. [6] The polyolefin membrane according to any one of [1] to [5], wherein the thickness-equivalent air permeability Gt and the porosity P of the polyolefin membrane satisfy the following relationship: LN(Gt)≦-0.070×P+5.8 [7] The polyolefin film according to any one of [3] to [6], wherein the difference in swelling onset temperature between the polyethylene A and the polyethylene B, as determined by the following measurement, is 10°C or less. [Measurement of swelling onset temperature] (D 10 , D 50 and D 90 (measurement of The particle diameters of the polyethylene A and polyethylene B are measured using a laser particle size distribution analyzer with methanol as a dispersion medium. Based on the measurements, a cumulative particle size distribution is created from the small particle size side, and the particle sizes at 10%, 50%, and 90% of the cumulative size are designated as the D of each polyethylene. 10 , D 50 and D 90 Let's say. (Measurement of swelling starting temperature T) The particle size is determined as follows: 10 The swelling onset temperature T of polyethylene particles is 10 That is, from among the particle groups of each polyethylene, the particle whose major axis diameter and minor axis diameter (in the plan view of the particle observed using an optical microscope, the shortest distance between parallel lines is taken as the minor axis diameter of the particle, and the longest distance between parallel lines in the direction perpendicular to that is taken as the major axis diameter of the particle) is determined to be D 10 Polyethylene particles within a ±10% range are identified using an optical microscope, and one particle is randomly selected. The sampled polyethylene particle is placed on a glass slide, and 0.05 mL of liquid paraffin is dropped onto the polyethylene particle. A cover glass is then placed on top to sandwich the polyethylene particle. The slide glass is then placed on a heat stage and heated from room temperature to 150°C under the following heating conditions. Photographs of the appearance of the polyethylene particles during heating are taken every 6 seconds using an optical microscope equipped with a camera. The equivalent circle diameter of the polyethylene particles is calculated from each of the obtained images, and the minimum temperature at which the equivalent circle diameter of the polyethylene particles increases by 1% or more in the temperature range of 80°C to 150°C, based on the equivalent circle diameter of the polyethylene particles at 80°C, is taken as the swelling initiation temperature of the polyethylene particles. Measurements are taken at 10 points, and the average value of these measurements is taken as the swelling initiation temperature T 10 Let's say. (heating conditions) Heating rate from room temperature to 35°C: 5°C / min Heating rate in the range of 35℃ to 80℃: 8℃ / min Heating rate in the range of 80℃ to 150℃: 5℃ / min Next, the particle diameter is D 50 The swelling onset temperature T of polyethylene particles is 50 , and particle diameter is D 90 The swelling onset temperature T of polyethylene particles is 90 Regarding the swelling starting temperature T 10 The long and short axis diameters were D 50 Polyethylene particles within the range of ±10%, and the major and minor axis diameters are D 90 Calculate using polyethylene particles within a range of ±10%. Finally, the swelling initiation temperature T of each polyethylene is calculated as follows:

number

[0009] According to the present invention, it is possible to provide a polyolefin film that has an excellent balance of heat shrinkage, permeability, shutdown temperature, and strength. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the measurement results of the melting points of polyolefin films in Example 1 and Comparative Example 7. [Figure 2] 1 is a graph showing the measurement results of Tm1 of polyolefin films in Example 1 and Comparative Example 7. [Figure 3] FIG. 1 is an explanatory diagram relating to measurement of the shutdown temperature in an example. [Figure 4] FIG. 1 is an explanatory diagram relating to measurements in an impact test in an example. [Figure 5] FIG. 2 is an explanatory diagram of the relation between the pin puncture strength Sm converted into basis weight and the shutdown temperature Ts of the polyolefin films of Examples 1 to 20 and Comparative Examples 1 to 6, based on a graph plotting Sm and Ts. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below, but the present invention is not limited thereto and various modifications are possible without departing from the gist of the present invention. In this specification, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic". In addition, in this specification, "to" means that the numerical values ​​at both ends thereof are included as the upper and lower limits, unless otherwise specified.

[0012] [Polyolefin film] The polyolefin film of the present embodiment is a polyolefin film containing a polyolefin, wherein the polyolefin contains polyethylene, the melting point of the polyolefin film is 134°C or higher and 140°C or lower, and the polyolefin film has a basis weight equivalent pin puncture strength Sm of 70 gf / (g / m 2 ) or more 150gf / (g / m 2 ) or less, and the shutdown temperature Ts of the polyolefin membrane and the Sm satisfy the following relationship: Ts<0.13×Sm+130 The polyolefin film of the present embodiment has the above-described structure and therefore has an excellent balance of heat shrinkage, permeability, shutdown temperature, and strength. In this embodiment, when simply referring to "melting point," it refers to the second melting temperature Tm2 measured by differential scanning calorimetry (DSC) of the polyolefin (film) (see FIG. 1). The first melting temperature Tm1 is distinguished from the second melting temperature Tm2 by notation "melting point Tm1" (see FIG. 2).

[0013] (Polyolefin composition) Polyolefins include polyethylene. Polyolefins other than polyethylene are not particularly limited, but examples include homopolymers, copolymers, and multi-stage polymers obtained using monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. These polymers may be used alone or in combination of two or more. From the viewpoint of imparting melt viscosity and pin puncture strength, as well as shutdown and meltdown properties, suitable for use as a separator to the polyolefin membrane, the polyolefin preferably contains polyethylene and / or polypropylene, and the polyethylene more preferably contains a mixture of two or more polyethylenes.

[0014] Specific examples of polyethylene include, but are not limited to, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), high-molecular-weight polyethylene (HMWPE), and ultra-high-molecular-weight polyethylene (UHMWPE).

[0015] The form of the polyethylene is not particularly limited, and polyethylene in the form of powder, pellets, etc. can be used. However, from the viewpoint of suppressing the defects of unmelted material, the polyolefin film of this embodiment preferably contains powder-like polyethylene. The average particle size of the powder-like polyethylene is not particularly limited, and may be, for example, 50 to 300 μm. In this specification, when the term "powder" is used, it refers to particulate polyethylene that satisfies the above-mentioned average particle size range, unless otherwise specified. The above-mentioned average particle size is measured using a laser particle size distribution analyzer using methanol as a dispersion medium, and a cumulative particle size distribution from the small particle size side is created based on the measurement, and the particle diameter D at which the cumulative 50% is reached is determined. 50 can be determined by

[0016] In this embodiment, high molecular weight polyethylene (HMWPE) refers to polyethylene having a viscosity average molecular weight (Mv) of 100,000 or more. Generally, the Mv of ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more, and therefore, by definition, high molecular weight polyethylene (HMWPE) in this embodiment includes UHMWPE.

[0017] In this embodiment, high density polyethylene has a density of 0.942 to 0.970 g / cm 3 It refers to the following polyethylene: In the present embodiment, the density of polyethylene refers to a value measured in accordance with D) density gradient tube method described in JIS K7112 (1999).

[0018] Specific examples of polypropylene include, but are not limited to, isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

[0019] Specific examples of the copolymer of ethylene and propylene include, but are not limited to, ethylene-propylene random copolymers and ethylene-propylene rubber.

[0020] The polyolefin membrane may contain a resin other than the polyolefins listed above, including, but not limited to, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polyvinylidene fluoride, nylon, and polytetrafluoroethylene.

[0021] In this embodiment, from the viewpoint of achieving a better balance between heat shrinkage, shutdown temperature, and strength, the polyolefin film preferably contains polyethylene A and polyethylene B which is different from polyethylene A. In this embodiment, the polyethylene A is not particularly limited as long as it is a homopolyethylene having a melting point of 134.0°C or higher and 138.0°C or lower and a melt index of 0.5 g / 10 min or higher and 50 g / 10 min or higher, and one type may be used alone, or two or more types may be used in combination. From the same viewpoint as above, the melting point of the polyethylene A is preferably 134.0° C. or more and 138.0° C. or less, and more preferably 134.5° C. or more and 137.0° C. or less. From the same viewpoint as above, the melt index of the polyethylene A is preferably 0.5 g / 10 min or more and 50 g / 10 min or less, and more preferably 1.0 g / 10 min or more and 40 g / 10 min or less. The melting point and melt index can be measured based on the method described in the examples below. The melting point can be adjusted to fall within the above range by, for example, adjusting the hydrogen concentration during polymerization, the presence or absence of copolymerization components or their contents, or by appropriately selecting the type of catalyst used to adjust the molecular weight. The melt index can be adjusted to fall within the above range by, for example, adjusting the molecular weight by appropriately selecting the hydrogen concentration during polymerization, the presence or absence of copolymerization components or their contents, or the type of catalyst used.

[0022] The content of polyethylene A relative to 100 parts by mass of the total of polyethylene A and polyethylene B is preferably 20 parts by mass or more and 80 parts by mass or less, more preferably 25 parts by mass or more and 75 parts by mass or less, and even more preferably 30 parts by mass or more and 70 parts by mass or less, from the viewpoint of achieving a better balance between the heat shrinkage rate, the shutdown temperature, and the strength.

[0023] In the present embodiment, the polyethylene B is not particularly limited as long as it is different from the polyethylene A, and one type may be used alone, or two or more types may be used in combination. From the viewpoint of strength, the polyethylene B is preferably a homopolyethylene having a viscosity average molecular weight of 800,000 or more and 5,000,000 or less, more preferably a homopolyethylene having a viscosity average molecular weight of 850,000 or more and 2,500,000 or less, and even more preferably a homopolyethylene having a viscosity average molecular weight of 90 or more and 150 or less. From the same viewpoint as above, the melting point of polyethylene B is preferably 134.0°C or higher and 138.0°C or lower, and more preferably 134.5°C or higher and 137.0°C or lower. The viscosity average molecular weight can be measured based on the method described in the examples below. The viscosity average molecular weight can be adjusted to fall within the above range by, for example, appropriately selecting the hydrogen concentration during polymerization, the presence or absence of copolymerization components or their contents, and the type of catalyst used. The melting point of polyethylene B can be measured in the same manner as that of polyethylene A, and can be adjusted to fall within the above range in the same manner as that of polyethylene A.

[0024] In the present embodiment, from the viewpoints of extrusion stability and shutdown temperature, the viscosity average molecular weight of polyethylene A is preferably from 10,000 to 200,000, more preferably from 30,000 to 150,000, and even more preferably from 50,000 to 120,000. The viscosity average molecular weight of polyethylene A can be measured in the same manner as that of polyethylene B, and can be adjusted to fall within the above range in the same manner as that for the melting point of polyethylene B.

[0025] From the viewpoint of strength, the content of polyethylene B relative to 100 parts by mass of the total of polyethylene A and polyethylene B is preferably 20 parts by mass or more and 80 parts by mass or less, more preferably 25 parts by mass or more and 75 parts by mass or less, and even more preferably 30 parts by mass or more and 70 parts by mass or less.

[0026] (Swelling starting temperature) In this embodiment, it is preferable to select polyethylene A and polyethylene B from the viewpoint of the swelling initiation temperature. Here, "swelling" refers to the phenomenon in which, when polyethylene (polyethylene particles) and a plasticizer are mixed and heated, the plasticizer penetrates into the polyethylene particles, and the temperature at which swelling begins during the heating process is defined as the "swelling initiation temperature." The principle of swelling is as follows. When polyethylene particles are impregnated with a plasticizer, the plasticizer penetrates (dissolves) into the polyethylene particles, causing the polyethylene to swell. Because liquid paraffin cannot easily penetrate the crystalline portions of polyethylene, it is thought to penetrate into the amorphous portions of polyethylene. In fact, it has been confirmed that the crystalline long period of polyethylene extends with swelling. In other words, swelling is thought to be a phenomenon in which the plasticizer penetrates between the lamellar crystals of polyethylene and pushes the amorphous portions apart. Meanwhile, tie molecules exist between the lamellar crystals, connecting them. Because tie molecules play a role in connecting lamellar crystals, they are thought to provide resistance to swelling. In other words, the swelling onset temperature can be controlled by the number and / or tension of tie molecules. The fewer the number of tie molecules and / or the more relaxed the tie molecules, the easier it is for the plasticizer to penetrate into the amorphous portions, resulting in easier swelling. The number of tie molecules is highly dependent on molecular weight. In other words, polyethylene with a higher molecular weight generally tends to have a higher swelling onset temperature. Another factor that affects the swelling initiation temperature is the presence of copolymer components. In polyethylene, the parts derived from the copolymer components are amorphous (non-crystalline parts), so if such amorphous parts are scattered throughout the particles, plasticizers can easily penetrate, which tends to lower the swelling initiation temperature. Furthermore, specific methods for controlling the tension of tie molecules during the drying process include, but are not limited to, the drying temperature. When polyethylene is dried at high temperatures, the tie molecules become tense due to crystal rearrangement, and as a result, the swelling onset temperature tends to increase. For example, if the drying temperature is set to 70°C or below, the crystal rearrangement is suppressed, which suppresses the tension of tie molecules, and as a result, the swelling onset temperature tends to decrease. From the above, the factors that affect the swelling initiation temperature are mainly the number of tie molecules (correlated with molecular weight), the presence or absence of copolymerization components, and the drying temperature. In other words, the swelling initiation temperature tends to increase as the molecular weight increases, the number of copolymerization components decreases, and the drying temperature increases. Specifically, the swelling initiation temperature can be measured based on the method described in the examples below. In the present embodiment, from the viewpoint of preventing the occurrence of unmelted gel defects due to insufficient swelling of the polyethylene by the plasticizer, it is preferable that the difference in swelling onset temperature between polyethylene A and polyethylene B (hereinafter simply referred to as "swelling onset temperature difference") determined as described above is small. As described above, the swelling onset temperature is highly dependent on the molecular weight, and therefore polyethylene A tends to have a high swelling onset temperature, while polyethylene B tends to have a low swelling onset temperature. As a means for reducing this difference (i.e., swelling onset temperature difference), the difference can be reduced by using the above-mentioned means to reduce the swelling onset temperature of polyethylene A and increase the swelling onset temperature of polyethylene B. Specifically, the swelling onset temperature difference is preferably 10°C or less, more preferably 9°C or less, and even more preferably 8°C or less. Note that when two or more polyethylenes corresponding to polyethylene A and / or polyethylene B are contained, all of the conceivable "differences in swelling onset temperature between polyethylene A and polyethylene B" are calculated, and the largest of the calculated values ​​is adopted as the swelling onset temperature difference.

[0027] In this embodiment, from the viewpoint of ease of film formation and film stability at high temperatures, the viscosity average molecular weight of the polypropylene is preferably 100,000 or more and 2,000,000 or less, more preferably 200,000 or more and 1,500,000 or less, and even more preferably 300,000 or more and 1,000,000 or less. The viscosity average molecular weight can be measured based on the method described in the examples below. The viscosity average molecular weight can be adjusted to fall within the above range by, for example, adjusting the polymerization conditions.

[0028] In this embodiment, from the viewpoint of film stability at high temperatures, the melting point of the polypropylene is preferably 130°C or higher and 200°C or lower, more preferably 140°C or higher and 180°C or lower, and even more preferably 150°C or higher and 170°C or lower. The melting point can be measured based on the method described in the examples below. The melting point can be adjusted to fall within the above range by, for example, adjusting the polymerization conditions.

[0029] The polyethylene content based on the total mass of the resin components constituting the polyolefin film is preferably 50 parts by mass or more and 100 parts by mass or less, and more preferably 80 parts by mass or more and 100 parts by mass or less, from the viewpoint of shutdown characteristics or meltdown characteristics.

[0030] The polypropylene content based on the total mass of the resin components constituting the polyolefin film is preferably 0 parts by mass or more and less than 50 parts by mass, more preferably 0 parts by mass or more and 10 parts by mass or less, from the viewpoint of melt viscosity and shutdown characteristics.

[0031] (Melting point of polyolefin film) In this embodiment, from the viewpoint of reducing the thermal shrinkage rate due to the ability to perform heat fixation at high temperatures, the melting point of the polyolefin film is 134° C. or higher and 140° C. or lower, and the lower limit of the melting point may be 133.5° C., and the upper limit of the melting point may be 140.0° C. The melting point of the polyolefin film is preferably 134.0° C. or higher and 140.0° C. or lower, more preferably 134.0° C. or higher and 139.0° C. or lower, even more preferably 134.5° C. or higher and 139.0° C. or lower, still more preferably 134.5° C. or higher and 138.0° C. or lower, and even more preferably 135.0° C. or higher and 138.0° C. or lower. The melting point can be measured based on the method described in the examples below. The melting point can be adjusted to fall within the above range by, for example, adjusting the melting point of the polyethylene used, its mixing ratio, and the kneading conditions in the extruder.

[0032] (Melting point of polyolefin film Tm1) In this embodiment, from the viewpoint of realizing high strength due to the stretching orientation of the polyolefin, the melting point Tm1 of the polyolefin film is 135°C or higher and 145°C or lower, more preferably 136°C or higher and 143°C or lower, and even more preferably 137°C or higher and 141°C or lower. The melting point Tm1 can be measured based on the method described in the Examples below. The melting point Tm1 can be adjusted to fall within the above range by, for example, adjusting the weight-average molecular weight of a polyolefin resin composition containing a polyolefin (hereinafter also referred to simply as a "polyolefin resin composition." Note that the polyolefin resin composition and the plasticizer described below are separate entities), the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, etc.

[0033] (Total amount of side chains with 3 carbon atoms and side chains with 4 carbon atoms) In this embodiment, from the viewpoint of further reducing the heat shrinkage rate due to the ability to heat set at high temperatures and achieving higher strength due to the ease of forming extended chains during stretching and orientation, the total amount of C3 side chains and C4 side chains measured for the polyolefin film is preferably 0 mol% to 0.1 mol%, more preferably 0 mol% to 0.05 mol%, relative to the total number of carbon atoms. The total amount of C3 side chains and C4 side chains can be measured based on the method described in the Examples below. The total amount of C3 side chains and C4 side chains can be adjusted by, for example, adjusting the monomer components of the polyethylene used. For example, the total amount of C3 side chains and C4 side chains tends to decrease by reducing the amount of polyethylene copolymer containing 1-pentene, 1-hexene, or the like as a copolymerization component. Furthermore, the total amount of C3 side chains and C4 side chains tends to decrease by, for example, appropriately adjusting the polymerization conditions to reduce side reactions during monomer polymerization.

[0034] (Thickness of polyolefin film) In this embodiment, from the viewpoint of increasing the capacity of the electricity storage device, the thickness of the polyolefin film is preferably 1 μm or more and 18 μm or less, more preferably 1 μm or more and 14 μm or less, and even more preferably 1 μm or more and 12 μm or less. The film thickness can be measured based on the method described in the examples below. The film thickness can be adjusted to fall within the above range by controlling, for example, the die lip gap, the draw ratio in the drawing step, and the like.

[0035] (Polyolefin film puncture strength converted to basis weight Sm) In this embodiment, from the viewpoint of the strength of the polyolefin film, the puncture strength Sm (basis weight (g / m 2 The puncture strength when converted to 70gf / (g / m 2 ) or more 150gf / (g / m 2 ) or less. When the puncture strength Sm in terms of basis weight is in the above range, the strength is improved. From the same viewpoint, the puncture strength Sm in terms of basis weight is preferably 80 gf / (g / m 2 ) or more 150gf / (g / m 2 ) is as follows. The basis weight-equivalent pin puncture strength Sm can be measured by the method described in the Examples below. The basis weight-equivalent pin puncture strength Sm can be adjusted to fall within the above-mentioned range by, for example, appropriately adjusting the basis weight and pin puncture strength values ​​by the methods described below. More specifically, the basis weight-equivalent pin puncture strength Sm can be adjusted to fall within the above-mentioned range by, for example, adjusting the weight-average molecular weight of the polyolefin resin composition, the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, etc.

[0036] (Polyolefin film basis weight) The basis weight of the polyolefin film is preferably 1.0 g / m from the viewpoint of strength. 2 More preferably, it is 2.0 g / m or more. 2In addition, from the viewpoint of the capacity of the electricity storage device, the basis weight is preferably 10 g / m 2 More preferably, it is 8.0 g / m or less. 2 The following is the result. The basis weight can be measured by the method described in the examples below, and can be adjusted by controlling, for example, the die lip distance, the draw ratio in the drawing step, and the like.

[0037] (Puncture strength of polyolefin film) The pin puncture strength of the polyolefin film not converted into basis weight (hereinafter simply referred to as "pin puncture strength") is preferably 100 gf or more and 800 gf or less, more preferably 150 gf or more and 700 gf or less, from the viewpoints of strength and stability during film formation. The pin puncture strength can be measured by the method described in the examples described below, and can be adjusted to fall within the above range by adjusting, for example, the weight average molecular weight of the polyolefin resin composition, the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, etc.

[0038] (Shutdown temperature Ts of polyolefin membrane) From the viewpoint of ensuring safety in high temperature conditions, the shutdown temperature Ts of the polyolefin membrane is preferably 145°C or lower, more preferably 143°C or lower, and even more preferably 142°C or lower. The shutdown temperature Ts can be measured by the method described in the examples described later, and can be adjusted to fall within the above range by, for example, adjusting the weight average molecular weight of the polyolefin resin composition, the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, etc.

[0039] (Relationship between shutdown temperature Ts and puncture strength converted to basis weight Sm) Generally, the shutdown temperature Ts and the equivalent pin puncture strength Sm are proportional. As the equivalent pin puncture strength Sm increases, the amount of extended chain crystals (hexagonal crystals) oriented in the stretching direction increases in the polyolefin crystals. Since extended chain crystals have a higher melting point than lamellar crystals, the temperature required to melt the fibril crystals and seal the pores increases, and the shutdown temperature also rises. In this embodiment, from the viewpoint of a balance between strength and safety in a high-temperature state, it is preferable that the shutdown temperature Ts and the puncture strength Sm converted into basis weight satisfy the following relationship. Ts<0.13×Sm+130 Whether the above relationship is satisfied can be confirmed by the method described in the Examples below. That is, this can be confirmed by the value of "Ts-0.13×Sm-130" being negative, and from the same viewpoint as above, this value is preferably -10 or more and less than 0, more preferably -5 or more and less than 0. The above relationship tends to be satisfied by, for example, adjusting the weight average molecular weight of the polyolefin resin composition, the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, etc., as well as by employing the production method described below.

[0040] (Thermal shrinkage rate of polyolefin film at 120°C) From the viewpoint of expanding the range of applications of electrochemical devices, it is preferable that the polyolefin film has improved safety as evaluated by the crash test and rapid heating test described in the Examples below. In particular, it is believed that the heat shrinkage rate of the polyolefin film contributes to the safety as evaluated by the rapid heating test. That is, in this embodiment, from the viewpoint of ensuring a higher level of safety, the heat shrinkage rate of the polyolefin film at 120°C is preferably 10% or less. More specifically, the heat shrinkage rate in MD (the machine direction when the polyolefin film is continuously molded) and / or TD (the direction crossing the MD of the polyolefin film at an angle of 90°) is more preferably 10% or less. From the same viewpoint, the heat shrinkage rate in MD and / or TD is more preferably 8.0% or less, and even more preferably 7.0% or less. The MD and TD heat shrinkage rates can be measured based on the method described in the examples below. The MD and TD heat shrinkage rates can be adjusted to fall within the above ranges by adjusting, for example, the weight average molecular weight of the polyolefin resin composition, the mixing ratio of each polyolefin in the polyolefin resin composition, the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, the transverse stretching ratio during heat setting, the transverse stretching temperature, the relaxation ratio, the relaxation temperature, etc.

[0041] (Porosity P of polyolefin membrane) The porosity P of the polyolefin membrane is preferably 25% or more, more preferably 28% or more, from the viewpoint of permeability, and is preferably 65% ​​or less, more preferably 60% or less, from the viewpoint of membrane strength. The porosity P can be measured by the method described in the examples below. The porosity P can be adjusted by, for example, controlling the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting, or by combining these.

[0042] (Air permeability of polyolefin membrane) The air permeability of the polyolefin membrane is preferably 1 s / 100 cm from the viewpoint of preventing excessive current from flowing between the multiple electrodes through the polyolefin membrane. 3 More than 30s / 100cm 3 More preferably, 50s / 100cm 3 From the viewpoint of permeability, it is preferably 1000 s / 100 cm 3 More preferably, it is 300 s / 100 cm or less. 3 More preferably, it is 200 s / 100 cm or less. 3 The following is the result. The air permeability can be measured by the method described in the examples below. The air permeability can be adjusted by, for example, controlling the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting, or by combining these.

[0043] (Polyolefin membrane thickness equivalent air permeability Gt) In this embodiment, the thickness-equivalent air permeability Gt of the polyolefin membrane (air permeability when converted into thickness (μm)) may be any value calculated from the preferred ranges of thickness and air permeability described above. However, from the viewpoint of preventing excessive current from flowing between multiple electrodes through the polyolefin membrane and from the viewpoint of permeability, it is preferable that the thickness-equivalent air permeability Gt be 3s / 100cm. 3 More than 30s / 100cm 3 It is preferable that the value is equal to or less than 3s / 100cm. 3 More than 25s / 100cm 3 The following is the result. The membrane-thickness-equivalent air permeability Gt can be measured by the method described in the Examples below. The membrane-thickness-equivalent air permeability Gt can be adjusted to the above range by, for example, appropriately adjusting the membrane thickness and air permeability values ​​by the above-mentioned method. Generally, the membrane-thickness-equivalent air permeability tends to increase as the membrane thickness decreases. This is because pores near the membrane surface are easily crushed, and the effect of this increases as the membrane thickness decreases.

[0044] (Relationship between porosity P and membrane-converted air permeability Gt) In this embodiment, from the viewpoint of achieving a better balance between the heat shrinkage rate, permeability, shutdown temperature, and strength, it is preferable that the thickness-equivalent air permeability Gt and porosity P of the polyolefin membrane satisfy the following relationship. LN(Gt)≦-0.070×P+5.8 Whether the above relationship is satisfied can be confirmed by the method described in the Examples below. That is, it can be confirmed by the value of "LN(Gt)+0.070×P-5.8" being 0 or less, and from the same viewpoint as above, this value is preferably -2.0 or more and 0 or less, more preferably -2.0 or more and -0.2 or less. Generally, there is a trade-off between porosity P and membrane-thickness equivalent air permeability Gt. This is because as porosity decreases, that is, as the proportion of pores decreases, the number of paths for air to pass through decreases, resulting in a higher membrane-thickness equivalent air permeability. Furthermore, as mentioned above regarding membrane-thickness equivalent air permeability, the thinner the membrane, the higher the membrane-thickness equivalent air permeability value tends to be. The above relationship tends to be satisfied by, for example, controlling the mixing ratio of the polyolefin resin composition to the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, the relaxation rate during heat setting, and the like, or by combining these, as well as by employing the production method described below.

[0045] (Polyolefin film form) The form of the polyolefin film is not particularly limited, but examples thereof include a microporous polyolefin body. The microporous polyolefin body is also not particularly limited, but examples thereof include a polyolefin membrane, a woven fabric of polyolefin-based fibers, and a nonwoven fabric of polyolefin-based fibers.

[0046] [Polyolefin film manufacturing method] The method for producing the polyolefin film of this embodiment is not particularly limited as long as it can produce the polyolefin film of this embodiment, but from the viewpoint of preventing the occurrence of unmelted gel defects caused by insufficient swelling of polyethylene by a plasticizer, the following production method is preferred. That is, a preferred production method of this embodiment is a method for producing a polyolefin film containing a polyolefin, comprising: step A of feeding a polyolefin resin composition containing the polyolefin to a polyolefin feed port of an extruder; step B of feeding a portion of the plasticizer to a first plasticizer feed port of the extruder; and step C of feeding at least a portion of the remainder of the plasticizer to a second plasticizer feed port of the extruder, wherein the first plasticizer feed port is located downstream of the polyolefin feed port, the second plasticizer feed port is located downstream of the first plasticizer feed port, and the amount of the plasticizer fed in step B is 50 parts by mass or more and 90 parts by mass or less with respect to the total amount of the plasticizer. Since the polyolefin membrane manufacturing method of the present embodiment is configured as described above, it is possible to manufacture a polyolefin membrane that has an excellent balance of heat shrinkage rate, permeability, shutdown temperature, and strength while preventing the occurrence of unmelted gel defects. A preferred manufacturing method in this embodiment will be described in detail below.

[0047] The polyolefin resin composition that can be used in the polyolefin film production method of the present embodiment is not particularly limited as long as it contains a polyolefin, and the polyolefin may be any of the above-mentioned polyolefins. The above-mentioned polyolefins preferably include polyethylene A, polyethylene B, polypropylene, etc. In addition to the polyolefin resin composition, a plasticizer can be used. The plasticizer is not particularly limited, but examples thereof include non-volatile solvents capable of forming a homogeneous solution at or above the melting point of the polyolefin, such as hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among plasticizers, liquid paraffin is preferred because it has high compatibility with polyethylene, polypropylene, etc., and tends to prevent interfacial peeling between the resin and the plasticizer even when the molten mixture is stretched, making it easier to achieve uniform stretching.

[0048] The amount of plasticizer added in this embodiment is preferably 56 to 80 parts by mass, more preferably 60 to 76 parts by mass, and even more preferably 62 to 74 parts by mass, relative to 100 parts by mass of the polyolefin resin composition. By adjusting the amount of plasticizer added to 60 parts by mass or more, the balance between porosity and air permeability can be adjusted. The melt viscosity of the resin composition is reduced and melt fracture is suppressed, which tends to improve film formability during extrusion. On the other hand, by adjusting the amount of plasticizer added to 80 parts by mass or less, the strength development and the number of unmelted gel defects can be appropriately controlled. The amount of plasticizer added is appropriately selected depending on the molecular weight and target physical properties of the resin composition. Examples of the melt-kneading method include a method in which polyolefin and, if necessary, other additives are fed into a resin kneading device such as an extruder, feeder, Labo Plastomill, kneading roll, or Banbury mixer, and then a plasticizer is introduced at an arbitrary ratio while heating and melting the resin components, followed by kneading. Examples of additives include, but are not limited to, antioxidants, such as, but not limited to, pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate].

[0049] Next, the melt-kneaded material is molded into a sheet. Methods for producing a sheet-shaped product include, but are not limited to, extruding the melt-kneaded material into a sheet through a T-die or the like, contacting it with a thermal conductor, and cooling it to a temperature sufficiently lower than the crystallization temperature of the resin component to solidify it. Thermal conductors used for cooling and solidifying include, but are not limited to, metal, water, air, plasticizers, and the like. Among these, metal rolls are preferred because of their high thermal conductivity. Furthermore, sandwiching the extruded material between metal rolls when contacting them is more preferred because it further increases thermal conductivity, orients the sheet, increasing film strength, and tends to improve the surface smoothness of the sheet. When extruding the melt-kneaded material into a sheet through a T-die, the die lip spacing is preferably 200 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2,500 μm or less. When the die lip gap is 200 μm or more, the occurrence of scum and the like is reduced, and the impact on film quality such as streaks and defects is small, and the risk of film breakage in the subsequent stretching process tends to be reduced.On the other hand, when the die lip gap is 3,000 μm or less, the cooling rate is fast, preventing uneven cooling and tending to maintain the thickness stability of the sheet.

[0050] In sheet molding, the kneaded product obtained through the above kneading is extruded using an extruder such as a T-die or a circular die. This may be conventional extrusion or co-extrusion. In the case of co-extrusion, a polyolefin film can be obtained by extruding two or more different polyolefin resin compositions. The extrusion conditions are not particularly limited, and known methods can be used, for example. Furthermore, it is preferable to control the die lip clearance, etc., from the viewpoint of the thickness of the resulting polyolefin film.

[0051] A preferred production method of this embodiment includes step A of adding the polyolefin resin composition to a powder supply port of an extruder, step B of adding a plasticizer to a first plasticizer supply port of the extruder, and step C of adding at least a portion of the remaining resin composition to a second plasticizer supply port of the extruder, wherein the second plasticizer supply port is located downstream of the first plasticizer supply port. That is, the plasticizer is supplied in two or more separate batches from two or more supply ports located at different positions in the extruder. In this case, the amount of the plasticizer added in step B relative to the total amount of plasticizer used is set to be 50 parts by mass or more and 90 parts by mass or less. This tends to more effectively prevent the occurrence of unmelted gel defects caused by insufficient swelling of polyethylene by the plasticizer. From the same viewpoint, the amount of the plasticizer added in step B is more preferably 55 parts by mass or more and 85 parts by mass or less, and even more preferably 60 parts by mass or more and 80 parts by mass or less.

[0052] The sheet-like molded product may also be rolled. Rolling can be carried out, for example, by a pressing method using a double belt press or the like. Rolling tends to increase the orientation, particularly in the surface layer portion. The rolling areal ratio is preferably more than 1 and not more than 3, and more preferably more than 1 and not more than 2. If the rolling ratio exceeds 1, the planar orientation increases, and the membrane strength of the polyolefin membrane obtained as a result tends to increase. On the other hand, if the rolling ratio is 3 or less, the difference in orientation between the surface layer portion and the central interior is small, and a porous structure that is uniform in the thickness direction of the membrane tends to be formed.

[0053] Next, the plasticizer is removed from the sheet-like molded body. For example, the plasticizer can be removed by immersing the sheet-like molded body in an extraction solvent to extract the plasticizer, followed by thorough drying. The plasticizer extraction method may be either a batch method or a continuous method. To prevent shrinkage of the polyolefin film, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the polyolefin film be less than 1 part by mass relative to the total mass of the polyolefin film.

[0054] The extraction solvent used to extract the plasticizer is preferably a poor solvent for polyolefins and a good solvent for plasticizers, with a boiling point lower than the melting point of polyolefins. Examples of such extraction solvents include, but are not limited to, hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by distillation or other procedures. When an inorganic material is used as the plasticizer, an aqueous solution of sodium hydroxide, potassium hydroxide, or the like can be used as the extraction solvent.

[0055] It is preferable to perform stretching after obtaining the sheet-like molded body. Stretching may be performed before extracting the plasticizer from the sheet-like molded body. Stretching may also be performed after extracting the plasticizer from the sheet-like molded body. Furthermore, stretching may also be performed before and after extracting the plasticizer from the sheet-like molded body.

[0056] As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of improving the strength of the obtained polyolefin film, etc. When the sheet-like molded product is stretched in the biaxial direction at a high ratio, the molecules are oriented in the plane direction, and the finally obtained polyolefin film tends to be less likely to tear and has high puncture strength.

[0057] Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple stretching. From the viewpoints of improving puncture strength, uniformity of stretching, and shut-down property, simultaneous biaxial stretching is preferred. Furthermore, from the viewpoint of ease of control of plane orientation, sequential biaxial stretching is preferred.

[0058] Here, simultaneous biaxial stretching refers to a stretching method in which stretching in MD (the machine direction when continuously molding a polyolefin film) and stretching in TD (the direction crossing the MD of the polyolefin film at an angle of 90°) are carried out simultaneously, and the stretching ratios in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in MD and TD is carried out independently, and while stretching is carried out in MD or TD, the other direction is in an unconstrained state or fixed at a fixed length.

[0059] From the viewpoints of strength and productivity, the areal stretching ratio is preferably in the range of 20 to 100 times, and more preferably in the range of 25 to 70 times. From the same viewpoints as above, the stretching ratio in each axial direction is preferably 5 to 9 times, and more preferably 6 to 8 times, in MD. Also, from the same viewpoints as above, the stretching ratio in TD is preferably 5 to 9 times, and more preferably 6 to 8 times. Furthermore, from the same viewpoint as above, the temperature during stretching in each axial direction is preferably 112°C or more and 135°C or less in MD, more preferably 115°C or more and 130°C or less, and from the same viewpoint as above, the temperature is preferably 112°C or more and 135°C or less in TD, more preferably 115°C or more and 130°C or less.

[0060] The polyolefin film is preferably heat-treated for heat fixation in order to suppress shrinkage. Examples of heat-treatment methods include a stretching operation carried out at a predetermined temperature and a predetermined stretching ratio to adjust physical properties, and / or a relaxation operation carried out at a predetermined temperature and a predetermined relaxation ratio to reduce stretching stress. The relaxation operation may be carried out after the stretching operation. These heat treatments can be carried out using a tenter or roll stretching machine.

[0061] From the viewpoint of high strength and high porosity, the stretching operation in heat setting is preferably 1.6 to 2.3 times, more preferably 1.7 to 2.2 times, the MD and / or TD of the membrane. Furthermore, from the same viewpoint as above, the temperature during the MD and / or TD stretching operation is preferably 115°C to 140°C.

[0062] The relaxation operation is a shrinking operation of the membrane in the MD and / or TD. The relaxation rate is the value obtained by dividing the membrane dimension after the relaxation operation by the membrane dimension before the relaxation operation. When both the MD and TD are relaxed, the relaxation rate is the value obtained by multiplying the relaxation rate in MD by the relaxation rate in TD. The relaxation rate is preferably 0.95 or less. From the viewpoint of membrane quality, the relaxation rate is preferably 0.7 or more. From the same viewpoint as above, the temperature during the relaxation operation is preferably 128°C or more and 140°C or less, more preferably 130°C or more and 140°C or less. The relaxation operation may be performed in both MD and TD directions, or may be performed in only one of MD or TD.

[0063] From the viewpoint of process control, the stretching and relaxation operations after the plasticizer extraction are preferably carried out in TD. The temperature in the stretching and relaxation operations is preferably lower than the melting point (Tm) of the polyolefin, more preferably in the range of 1°C to 25°C lower than Tm. The temperature in the stretching and relaxation operations is preferably in the above range from the viewpoint of the balance between reduced heat shrinkage and porosity.

[0064] [Other steps] The method for producing a polyolefin film of this embodiment may include other steps in addition to the steps described above. The other steps are not particularly limited, but for example, in addition to the heat setting step, coextrusion may be performed as a step for obtaining a polyolefin film. Furthermore, after coextrusion, a peeling step may be included in which peeling is performed as necessary to obtain two or more polyolefin films. Furthermore, the method for producing a polyolefin film of this embodiment may include a surface treatment step in which the surface of the polyolefin film is subjected to surface treatment such as electron beam irradiation, plasma irradiation, surfactant application, chemical modification, etc. Furthermore, an inorganic component of inorganic particles may be applied to one or both sides of the polyolefin film to obtain a polyolefin film having an inorganic coating layer.

[0065] <Formation of inorganic coating layer> From the viewpoints of safety, dimensional stability, heat resistance, etc., an inorganic coating layer can be provided on the surface of the polyolefin film. The inorganic coating layer is a layer containing inorganic components such as inorganic particles, and may optionally contain a binder resin that binds the inorganic particles together, a dispersant that disperses the inorganic particles in a solvent, etc.

[0066] Examples of inorganic particle materials contained in the inorganic coating layer include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. The inorganic particles may be used alone or in combination. Examples of the binder resin include a conjugated diene polymer, an acrylic polymer, a polyvinyl alcohol resin, and a fluorine-containing resin. The binder resin may be in the form of a latex and may contain water or an aqueous solvent. The dispersant is adsorbed to the surface of inorganic particles in the slurry and stabilizes the inorganic particles by electrostatic repulsion or the like, and examples thereof include polycarboxylates, sulfonates, polyoxyethers, surfactants, and the like.

[0067] In the particle size distribution of the inorganic particles, the particle size D50 is preferably in the range of 0.05 μm to 1.2 μm, more preferably 0.05 μm to 0.8 μm, and even more preferably 0.05 μm to 0.5 μm. When D50 is 0.05 μm or more, migration of the inorganic particles from the inorganic coating layer into the pores of the polyolefin film is suppressed, which may improve the permeability of the polyolefin film equipped with the inorganic coating layer. Furthermore, when D50 is 1.2 μm or less, the heat resistance of the inorganic coating layer is easily obtained.

[0068] The inorganic coating layer can be formed, for example, by applying a slurry of the above-described components to the surface of the polyolefin film and drying it.

[0069] <Formation of adhesive layer> In order to prevent deformation or swelling due to gas generation in laminated batteries, which have recently been increasingly adopted in automotive batteries to increase energy density, an adhesive layer containing a thermoplastic resin can be provided on the surface of the polyolefin film. The thermoplastic resin contained in the adhesive layer is not particularly limited, and examples thereof include polyolefins such as polyethylene or polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, and acrylonitrile-butadiene-styrene copolymers. Examples of suitable resins include rubbers such as acrylate copolymers and their hydrogenated products, (meth)acrylate copolymers, styrene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins having a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0070] Furthermore, after the heat setting step (f), the coextrusion step, or the surface treatment step, the master roll on which the polyolefin film is wound can be subjected to an aging treatment under predetermined temperature conditions, and then the master roll can be rewound. This tends to make it easier to obtain a polyolefin film with higher thermal stability than the polyolefin film before rewinding. In this case, the temperature during the aging treatment of the master roll is not particularly limited, but is preferably 35°C or higher, more preferably 45°C or higher, and even more preferably 60°C or higher. Furthermore, from the viewpoint of maintaining the permeability of the polyolefin film, the temperature during the aging treatment of the master roll is preferably 120°C or lower. The time required for the aging treatment is not particularly limited, but is preferably 24 hours or longer, as this makes it easier to achieve the above-mentioned effects.

[0071] [Energy storage devices] The electricity storage device of this embodiment includes the separator for an electricity storage device of this embodiment. Typical examples of the configuration of the electricity storage device of this embodiment include, but are not limited to, a positive electrode, a separator for an electricity storage device, a negative electrode, and, if desired, an electrolyte solution. Specific examples of the power storage device include lithium batteries, lithium secondary batteries, lithium ion secondary batteries, sodium secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, calcium secondary batteries, calcium ion secondary batteries, aluminum secondary batteries, aluminum ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, zinc-air batteries, etc. Among these, from the viewpoint of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-metal hydride batteries, and lithium ion capacitors are preferred, and lithium ion secondary batteries are more preferred. As for the positive electrode, negative electrode, electrolyte, and other components of the electricity storage device, various known materials can be used appropriately depending on the type of electricity storage device. [Example]

[0072] The present embodiment will be described in more detail below using examples and comparative examples, but the present embodiment is not limited to the following examples. Various physical properties were measured and evaluated by the following measuring and evaluation methods.

[0073] [Viscosity average molecular weight Mv] The intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent was determined based on ASTM-D4020. For polyethylene, Mv was calculated using the following formula: [η]=6.77×10 -4 Mv 0.67 For polypropylene, Mv was calculated using the following formula: [η]=1.10×10 -4 Mv 0.80

[0074] [Melting point Tm (℃)] The melting points of the polyolefin raw materials (PE1 to PE14 and PP1 described below) were determined using a differential scanning calorimeter "DSC-60" (Shimadzu Corporation). Specifically, the temperature was raised from room temperature to 200°C at a rate of 10°C / min (first heating process), then lowered to 30°C at 10°C / min (first heating process), and then raised again to 200°C at a rate of 10°C / min. The temperature (Tm2) at the minimum of the endothermic peak during the second heating process was taken as the melting point of the polyolefin raw material. The value obtained was rounded to one decimal place to determine the melting point of the polyolefin raw material. Here, the temperature at the minimum of the endothermic peak during the first heating process is called Tm1, but Tm1 is easily affected by drying conditions during polymerization, etc. In this example, the melting point was determined by Tm2, ​​with the history of drying conditions, etc., reset. The melting points of polyolefin films (polyolefin films in each example described below) were determined using the DSC-60. Specifically, a folded polyolefin film sample was punched out to 4.5 mm diameter, placed in a 5-7 mg sample container, and crimped. The sample container was heated from room temperature to 200°C at a rate of 10°C / min (first heating process), cooled to 30°C at 10°C / min (first heating process), and then heated again to 200°C at a rate of 10°C / min. The temperature (Tm2) of the minimum point of the endothermic peak during the second heating process was determined as the melting point of the polyolefin film. Specifically, the value obtained was rounded to one decimal place to determine the melting point of the polyolefin film. The results of measuring Tm1 for the polyolefin films according to Example 1 and Comparative Example 7 are shown in Figure 1. The temperature Tm1 of the minimum point of the endothermic peak during the first heating process was also measured for the polyolefin film. The results of measuring Tm1 of the polyolefin membranes according to Example 1 and Comparative Example 7 are shown in Figure 2. Note that, since Tm1 of a polyolefin membrane is easily affected by the stretching conditions during membrane formation and the average molecular weight of the obtained membrane, we decided to focus on Tm2, ​​which contributes greatly to the effects of this embodiment.

[0075] [ 13 C-NMR] o-Dichlorobenzene-d4 was added to the sample taken from the polyolefin film and dissolved at 130°C. After returning to room temperature, 13 C-NMR measurement was carried out under the following conditions: Equipment:Bruker Avance NEO 600 Measurement probe: 5mm cryoprobe Pulse program: zgpg30 Pulse waiting time: 5 sec Window function: Exponential Accumulation count: 8000 times Measurement temperature: 130℃ Chemical shift reference: 29.9 ppm (-CH2-) Sample concentration: 10 wt% The total amount of side chains with 3 carbon atoms and side chains with 4 carbon atoms was calculated as a percentage of the total number of carbon atoms from the ratio of the peak integral value around 20 ppm for propylene and the peak integral value around 11 ppm for 1-butene to the peak integral value of 30 ppm carbon atoms.

[0076] [Melt Index MI] The MI was measured according to JIS K7210:1999 (Plastics - Melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics). Specifically, in the case of polyethylene, a load of 2.16 kgf was applied at 190°C, the amount of resin (g) that flowed out in 10 minutes was measured, and the value was rounded to the nearest tenth place to obtain the MI. In the case of polypropylene, a load of 2.16 kgf was applied at 230°C, the amount of resin (g) that flowed out in 10 minutes was measured, and the value was rounded to the nearest tenth place to obtain the MI.

[0077] [Swelling starting temperature] (D 10 , D 50 and D 90 (measurement of The particle sizes of polyethylenes PE1 to PE14 (all in powder form) described below were measured using a laser particle size distribution analyzer with methanol as a dispersion medium. Based on the measurements, a cumulative particle size distribution was created from the smallest particle size side, and the particle sizes at 10%, 50%, and 90% of the cumulative size were determined as the D of each polyethylene. 10 , D 50 and D 90 It was decided. (Swelling start temperature T B (measurement of The particle size is determined as follows: 10 The swelling onset temperature T of polyethylene particles is 10 That is, from among the particle groups of each polyethylene, the particle whose major axis diameter and minor axis diameter (in the plan view of the particle observed using an optical microscope, the shortest distance between parallel lines was taken as the minor axis diameter of the particle, and the longest distance between parallel lines in the direction perpendicular to that was taken as the major axis diameter of the particle) was determined to be D 10Polyethylene particles within ±10% were identified using an optical microscope, and one particle was randomly selected. One sampled polyethylene particle (hereinafter also referred to as the "measurement particle") was placed on a glass slide, and 0.05 mL of liquid paraffin was dropped onto the measurement particle using a 1 mL syringe, and then a cover glass was placed on top to sandwich the measurement particle. The slide glass was then set on a heat stage and heated from room temperature to 150°C under the following heating conditions. The appearance of the measured particles during the heating was photographed every 6 seconds using an optical microscope with a camera. The equivalent circle diameter of the measured particles was calculated from each of the obtained observation images, and the minimum temperature at which the equivalent circle diameter of the measured particles increased by 1% or more in the temperature range of 80°C to 150°C, based on the equivalent circle diameter of the measured particles at 80°C, was defined as the swelling initiation temperature of the measured particles. Measurements were made at 10 points, and the average value of these measurements was calculated as the swelling initiation temperature T 10 It was decided. (heating conditions) Heating rate from room temperature to 35°C: 5°C / min Heating rate in the range of 35℃ to 80℃: 8℃ / min Heating rate in the range of 80℃ to 150℃: 5℃ / min Next, the particle diameter is D 50 The swelling onset temperature T of polyethylene particles is 50 , and particle diameter is D 90 The swelling onset temperature T of polyethylene particles is 90 Regarding the swelling starting temperature T 10 The long and short axis diameters were D 50 Polyethylene particles within the range of ±10%, and the major and minor axis diameters are D 90 It was determined using polyethylene particles within a range of ±10%. Finally, the swelling initiation temperature T of each polyethylene was determined as follows.

number

[0078] [Swelling start temperature difference (℃)] The difference between the swelling initiation temperature of polyethylene corresponding to polyethylene A and the swelling initiation temperature of polyethylene corresponding to polyethylene B was calculated, and the absolute value was taken as the swelling initiation temperature difference.

[0079] [Thickness (μm)] The thickness of the polyolefin film was measured at room temperature of 23±2°C using a micro thickness measuring instrument "KBM (registered trademark)" manufactured by Toyo Seiki Co., Ltd.

[0080] [Porosity P (%)] A 10cm x 10cm square sample was cut from the polyolefin film and its volume (cm 3 ) and mass (g), and then calculate the density (g / cm 3 ) the porosity was calculated using the following formula: Porosity (%) = (volume - mass / density) / volume x 100

[0081] [Air permeability (s / 100cm 3 )] Measurement was carried out in accordance with JIS P-8117. That is, the air resistance of the polyolefin membrane was measured in an atmosphere of 23°C and 40% humidity using a Gurley air permeability meter "G-B2 (registered trademark)" manufactured by Toyo Seiki Co., Ltd., and this was taken as the air permeability.

[0082] [Air permeability converted to membrane thickness (s / 100cm 3 )] The value obtained by dividing the air permeability measured as above by the film thickness was taken as the film thickness equivalent air permeability.

[0083] [Piercing strength (gf)] Using a Kato Tech handy compression tester KES-G5 (registered trademark), the polyolefin film was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed polyolefin film at a needle tip curvature radius of 0.5 mm, a puncture speed of 2 mm / sec, and an atmosphere of 23°C and 40% humidity to obtain the puncture strength (gf) as the maximum puncture load.

[0084] [Weight (g / m 2 )] A 10 cm x 10 cm square sample was cut from the polyolefin film, and the mass was measured using an electronic balance AEL-200 (product name) manufactured by Shimadzu Corporation. The mass obtained was multiplied by 100 to obtain the mass of 1 m 2 Weight of sample per unit (g / m 2 ) was calculated.

[0085] [Piercing strength Sm(gf / (g / m) 2 ))] The value obtained by dividing the puncture strength measured as above by the basis weight was taken as the basis weight converted puncture strength.

[0086] [Shutdown temperature Ts (℃)] 3(A) shows a schematic diagram of the shutdown temperature measurement device. An electrical resistance measurement device 4 ("AG-4311" manufactured by Ando Electric Co., Ltd.) was connected to 10 μm-thick nickel foils 2A and 2B, a thermocouple 5 was connected to a thermometer 6, a data collector 7 was connected to the electrical resistance measurement device 4 and the thermometer 6, and the polyolefin film 1 was heated by an oven 8. More specifically, as shown in Figure 3(B), a polyolefin film 1 was placed on nickel foil 2A and fixed to the nickel foil 2A in the vertical direction with Teflon tape (the shaded area in the figure). The polyolefin film 1 was impregnated with a 1 mol / L lithium fluoroborate solution (solvent: a mixed solvent of propylene carbonate / ethylene carbonate / γ-butyl lactone in a volume ratio of 1 / 1 / 2) as an electrolyte. Teflon tape (the shaded area in the figure) was attached to nickel foil 2B as shown in Figure 3(C), and the center of foil 2B was masked, leaving a 15 mm x 10 mm window. Nickel foil 2A and nickel foil 2B were overlapped so as to sandwich polyolefin film 1, and the two nickel foils were then sandwiched between glass plates 3A and 3B on both sides. At this time, the window portion of foil 2B and polyolefin film 1 were positioned facing each other. Next, the two glass plates 3A and 3B were fixed in place by clamping them with clips. Thermocouple 5 was fixed to the glass plates with Teflon (registered trademark) tape. The temperature and electrical resistance of the polyolefin film 1 were continuously measured using this device. The temperature was raised from 25°C to 200°C at a rate of 15°C / min, and the electrical resistance was measured at 1V and 1kHz AC. The shutdown temperature was measured when the electrical resistance reached 10 3 The temperature value when the resistance reached Ω was rounded to one decimal place.

[0087] [120℃ heat shrinkage rate (%)] The polyolefin film was cut into a 100 mm strip in the MD direction and a 100 mm strip in the TD direction and left to stand in an oven at 120°C for 1 hour. The sample was sandwiched between two pieces of paper to prevent the hot air from directly hitting the sample. After removing the sample from the oven and cooling, the length (mm) was measured and the heat shrinkage was calculated using the following formula. Measurements were performed in the MD and TD directions, and the MD heat shrinkage and TD heat shrinkage were calculated, respectively. Heat shrinkage rate (%) = {(100 - length after heating) / 100} x 100

[0088] [Number of unmelted gel defects (pieces / 1000m 2 )] Resin aggregates (gel inclusions) in the polyolefin membrane were defined as regions having an area of ​​100 μm or more in length and 100 μm or more in width and through which light does not pass when the polyolefin membrane was observed under a transmission optical microscope. 2 The number of resin aggregates per unit area was measured and recorded as the number of unmelted gel defects. The number of unmelted gel defects was evaluated based on the following criteria. A: Number of unmelted gel defects is 0 to 5 B: Number of unmelted gel defects is 6 or more and 14 or less C: Number of unmelted gel defects is 15 or more

[0089] [Preparation of evaluation battery] A laminated lithium ion secondary battery was fabricated by the following steps a-1 to a-5. (a-1) Preparation of positive electrode The positive electrode active material was a lithium nickel, manganese, and cobalt composite oxide (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) as a conductive additive (90.4 parts by mass), graphite powder (TIMREX "KS6", density 2.26 g / cm 3 1.6 parts by mass of acetylene black powder (density 1.95 g / cm 3 3.8 parts by mass of polyvinylidene fluoride (density 1.75 g / cm 3) as a binder. 3 ) were mixed in a ratio of 4.2 parts by mass, and dispersed in N-methylpyrrolidone to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 109 g / m 2 It was. (a-2) Preparation of negative electrode Graphite powder A (density 2.23 g / cm) was used as the negative electrode active material. 3 87.6 parts by mass of graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7 parts by mass of ammonium salt of carboxymethylcellulose (number average particle diameter 6.5 μm) and 1.4 parts by mass (solids equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solids concentration of 1.83 parts by mass) and 1.7 parts by mass (solids equivalent) of diene rubber latex (aqueous solution with a solids concentration of 40 parts by mass) in purified water. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to prepare a negative electrode. The amount of negative electrode active material applied was 52 g / m 2 It was. (a-3) Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L. (a-4) Formation of adhesive layer An adhesive layer was formed on the polyolefin film of each example by the following procedure. A reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer was charged with 64 parts by mass of water and 0.25 parts by mass of sodium alkyldiphenyletherdisulfonate ("Pelex SS-L" manufactured by Kao Corporation, solid content 45%). Furthermore, while maintaining the temperature of the reaction vessel at 80°C, 0.15 parts by mass of ammonium persulfate (2% aqueous solution) was added to the reaction vessel. Separately, 24 parts by mass of methyl methacrylate (MMA), 34 parts by mass of butyl acrylate (BA), 1.5 parts by mass of acrylic acid (AA), 0.1 parts by mass of n-dodecyl mercaptan (nDDM), 1.5 parts by mass of Pelex SS-L, 0.15 parts by mass of ammonium persulfate, and 69 parts by mass of water were mixed in a homomixer at 6000 rpm for 5 minutes to prepare an emulsion. Five minutes after adding ammonium persulfate as described above, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes. After the emulsion was added dropwise, the temperature of the reaction vessel was maintained at 80°C for 60 minutes, and then cooled to room temperature. Next, a 25% aqueous ammonia solution was added to the reaction vessel to adjust the pH to 8.0, and water was added to adjust the solid content to 40 parts by mass, yielding an acrylic emulsion as an adhesive coating liquid. 7.5 parts by mass of the resulting acrylic emulsion was uniformly dispersed in 92.5 parts by mass of water to prepare a coating solution, which was then applied to the surface of the polyolefin membrane using a gravure coater. The coated surface was dried at 60°C to remove the water. The other side was similarly coated with the coating solution and dried to obtain a separator with an adhesive layer. (a-5) Battery production Using the positive electrode, negative electrode, and nonaqueous electrolyte obtained in a-1 to a-3 above, and the separator obtained in a-4 above, a laminate-type secondary battery having a size of 100 mm × 60 mm and a capacity of 3000 mAh was produced, which was charged at a constant current / constant voltage (CCCV) for 3 hours under conditions of a current value of 1 A (0.3 C) and an end-of-battery voltage of 4.2 V.

[0090] (a-6) Capacity measurement The laminated secondary battery assembled as described above was subjected to constant current constant voltage (CCCV) charging for 6 hours at a current of 1500 mA (0.5 C) and a final battery voltage of 4.2 V. The current value immediately before the end of charging was nearly 0. The battery was then left to stand (aged) for 1 week in an atmosphere at 25°C. Next, the batteries were cycled by constant current / constant voltage (CCCV) charging at a current of 3000 mA (1.0 C) and a final battery voltage of 4.2 V for 3 hours, followed by discharging at a constant current (CC) of 3000 mA down to a battery voltage of 3.0 V. The discharge capacity at this time was designated as the initial discharge capacity X. Batteries with an initial discharge capacity X within 3000±10 mAh were used as evaluation batteries and subjected to the evaluation described below.

[0091] [Rapid temperature rise test] The test battery was placed in a thermostatic chamber "PLM-73S" (manufactured by Futaba Scientific Co., Ltd.) set to 25°C and connected to a charge / discharge device "ACD-01" (manufactured by Asuka Electronics Co., Ltd.). The test battery was then charged at a constant current of 0.1 C until a voltage of 4.2 V was reached, then charged at a constant voltage of 4.2 V for one hour, and then discharged at a constant current of 0.1 C until a voltage of 3.0 V was reached. This charge / discharge cycle was repeated three times. The lithium-ion secondary battery was then fully charged by charging at a constant current of 0.1 C until a voltage of 4.2 V was reached. Note that 1 C represents the current value required to discharge the entire battery capacity in one hour, and 0.1 C represents one-tenth of that current value. An aluminum block heater was placed inside an explosion-proof thermostatic chamber, and the aluminum block was filled with nonflammable fluorinated paraffin oil. Fully charged lithium-ion secondary batteries were removed from the thermostatic chamber and immersed in the fluorinated paraffin oil inside the aluminum block heater. The aluminum block heater was then heated to 150°C at a rate of 15°C / min, and the behavior of the lithium-ion secondary batteries was observed. After 1 minute at 150°C, the batteries were checked for smoke generation or explosion. N=5 tests were performed, and the evaluation result was A (good) if all lithium-ion secondary batteries were normal, B (acceptable) if one or two batteries emitted smoke or exploded, and C (poor) if three or more batteries emitted smoke or exploded.

[0092] [Impact test] FIG. 4 is a schematic diagram of the impact test. In the impact test, a round bar (φ=15.8 mm) was placed on top of a battery sample (the aforementioned evaluation battery) placed on a test bench so that the battery sample and the round bar were roughly perpendicular to each other, and an 18.2 kg weight was dropped onto the top surface of the round bar from a position 61 cm above the round bar to observe the effect of the impact on the battery sample. The specific procedures for the impact tests in the examples and comparative examples were as follows. First, the above-mentioned evaluation battery was charged at a constant current and constant voltage (CCCV) for 3 hours under the conditions of a current value of 3000 mA (1.0 C) and a final battery voltage of 4.2 V. Next, in a 25°C environment, the test battery was placed horizontally on a flat surface, and a 15.8 mm diameter stainless steel rod was placed across the center of the test battery. The rod was positioned so that its long axis was parallel to the longitudinal direction of the test battery. An 18.2 kg weight was dropped from a height of 61 cm from the rod positioned in the center of the test battery, so that the impact was perpendicular to the longitudinal axis of the test battery. After the impact, the surface temperature of the test battery was measured. The above test was performed on five battery samples, and they were evaluated according to the following criteria. For this evaluation item, A (good) and B (acceptable) were used as the pass criteria. The surface temperature of the battery was measured using a thermocouple (K-type seal type) at a position 1 cm from the bottom of the battery's exterior. A (Good): The surface temperature of all battery samples was 60°C or less. B (Acceptable): There are battery samples with surface temperatures exceeding 60°C and up to 100°C, but the surface temperatures of all battery samples are 100°C or less. C (Not acceptable): The surface temperature of one or more battery samples exceeds 100°C or ignites.

[0093] [Output test (25℃)] The 1C discharge capacity and 5C discharge capacity of the evaluation battery were measured at a constant temperature of 25°C up to a discharge end voltage of 3V, and the 5C capacity / 1C capacity was used as the output characteristic value. The output characteristic value was evaluated based on the following criteria. A: Output characteristic value is 0.90 or more. B: Output characteristic value is 0.75 or more and less than 0.90. C: Output characteristic value is less than 0.75.

[0094] [Preparation of PE1 to PE14 and PP1] (Preparation of solid catalyst component [A]) (1) Synthesis of raw material (a-1) AlMg6(C4H9) was placed in an 8L stainless steel autoclave that had been thoroughly purged with nitrogen. 12 2,000 mL of a 1 mol / L hexane solution of an organomagnesium compound represented by (C2H5)3 (equivalent to 2,000 mmol of magnesium and aluminum) was charged, and 146 mL of a 5.47 mol / L n-butanol hexane solution was added dropwise over 3 hours while stirring at 50°C. After completion of the reaction, the line was washed with 300 mL of hexane. Stirring was continued for another 2 hours at 50°C. After the reaction was completed, the mixture was cooled to room temperature and used as raw material (a-1). The magnesium concentration of raw material (a-1) was 0.704 mol / L. (2) Synthesis of raw material (a-2) AlMg6(C4H9) was placed in an 8L stainless steel autoclave that had been thoroughly purged with nitrogen. 12 2,000 mL of a 1 mol / L hexane solution of an organomagnesium compound represented by (C2H5)3 (equivalent to 2,000 mmol of magnesium and aluminum) was charged, and while stirring at 80°C, 240 mL of a hexane solution of 8.33 mol / L methylhydrogenpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.) was pressure-fed, and stirring was continued at 80°C for another 2 hours. After the reaction was completed, the mixture was cooled to room temperature and used as raw material (a-2). The total concentration of magnesium and aluminum in raw material (a-2) was 0.786 mol / L. (3) (A-1) Synthesis of the carrier An 8L stainless steel autoclave, thoroughly purged with nitrogen, was charged with 1,000mL of a 1mol / L hydroxytrichlorosilane hexane solution, and 1,340mL of the hexane solution of the organomagnesium compound (a-1) (equivalent to 943mmol of magnesium) was added dropwise over 3 hours at 65°C. The reaction was continued for another 1 hour with stirring at 65°C. After the reaction was completed, the supernatant was removed and the mixture was washed four times with 1,800mL of hexane to obtain the (A-1) carrier. Analysis of this carrier revealed that the magnesium content per gram of solid was 7.5mmol. (4) Preparation of solid catalyst component [A] To 1,970 mL of hexane slurry containing 110 g of the above (A-1) carrier, 103 mL of a 1 mol / L hexane solution of titanium tetrachloride and 131 mL of raw material (a-2) were added simultaneously over 3 hours while stirring at 10°C. After the addition, the reaction was continued for 1 hour at 10°C. After the reaction was completed, the supernatant was removed, and the unreacted raw material components were removed by washing four times with hexane to prepare solid catalyst component [A]. (polymerization) Hexane, ethylene, hydrogen, and catalyst were continuously fed into a 300 L vessel-type polymerization reactor equipped with a stirrer. The polymerization pressure was 0.6 MPa. The polymerization temperature was maintained at 83°C by jacket cooling. Solid catalyst component [A] was used as the main catalyst, and a 9:1 mixture of triisobutylaluminum and diisobutylaluminum hydride was used as the cocatalyst. The cocatalyst was added to the polymerization reactor at a rate of 10 mmol / hr. The main catalyst was supplied so that the polyethylene production rate was 10 kg / hr and the slurry concentration in the polymerization reactor was 30 mass%. Hexane was supplied to maintain a constant liquid level. Hydrogen was continuously supplied by pump to maintain a hydrogen concentration of 45 mol% relative to the ethylene in the gas phase. The polymerization slurry was continuously discharged into a flash drum at a pressure of 0.05 MPa and a temperature of 70°C, and unreacted ethylene was separated. The separated polyethylene particles were dried at 90°C with nitrogen blowing. During this drying process, the particles after polymerization were sprayed with steam to deactivate the catalyst and cocatalyst. The resulting polyethylene particles were sieved through a 425 μm mesh sieve to remove any particles that did not pass through the sieve, yielding ethylene polymer particles of PE1. The molecular weight of PE1 was 7.0 × 10 4 It was. Based on the production conditions for PE1, PE2 to PE14 were produced by appropriately adjusting the polymerization pressure, polymerization temperature, hydrogen concentration and / or drying temperature as shown in Tables 1 and 2. All of PE1 to PE14 were in powder form. Here, copolymerization components were added to PE3, PE7, PE13, and PE14, and in the polymerization process, hexane, ethylene, hydrogen, a catalyst, and 1-butene were continuously fed by a pump so that the 1-butene concentration relative to the ethylene in the gas phase reached a predetermined concentration. The 1-butene concentration during the production of each PE is shown in Tables 1 and 2. The polypropylene (PP1) used was a commercially available homopolypropylene. The evaluation results of PE1 to PE14 and PP1 obtained as described above are shown in Tables 1 and 2.

[0095] [Example 1] 12.8 parts by mass of PE1 as the first polyethylene and 19.2 parts by mass of PE10 as the second polyethylene were mixed in a Henschel mixer, and 0.3 parts by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant was added and premixed. The resulting mixture was fed to the polyolefin feed port of a twin-screw co-rotating screw extruder using a feeder. Next, melt-kneading was carried out, and liquid paraffin (plasticizer; LP) was fed into the twin-screw extruder cylinder via side feed in two batches so that the total extruded mixture (100.3 parts by mass) contained 68.0 parts by mass of liquid paraffin. That is, 40.8 parts by mass (60% of the total amount added) was supplied from a first plasticizer supply port located downstream of the polyolefin supply port (step A) in the extruder (step B). Next, 27.2 parts by mass (40% of the total amount added) was supplied from a second plasticizer supply port located further downstream of the first plasticizer supply port (step C). The set temperatures were 160°C for the kneading section and 200°C for the T-die. Next, the molten kneaded product was extruded into a sheet from the T-die and cooled with a cooling roll whose surface temperature was controlled to 70°C, yielding a sheet-like molded product with a thickness of 2000 μm.

[0096] The obtained sheet-like molded product was introduced into a simultaneous biaxial stretching machine to obtain a primarily stretched membrane (primary stretching step). The set stretching conditions were an MD stretching ratio of 7 times, a TD stretching ratio of 6.38 times, and an MD and TD stretching temperature of 118°C. The obtained primarily stretched membrane was then introduced into a methylene chloride tank and thoroughly immersed to extract and remove the plasticizer, liquid paraffin, and then the methylene chloride was dried and removed to obtain an extracted membrane. The extracted membrane was then introduced into a TD uniaxial tenter for heat setting. In the heat setting step, the membrane was stretched at a TD stretching temperature of 130°C and a TD stretch ratio of 2.00, followed by relaxation at a relaxation temperature of 135°C and a relaxation ratio of 0.80. The polyolefin film obtained as described above was evaluated for various properties by the methods described above. The evaluation results are shown in Table 4.

[0097] [Examples 2 to 21 and Comparative Examples 1 to 9] Polyolefin membranes were obtained in the same manner as in Example 1, except that the raw material types, raw material composition ratios, extrusion conditions, sheet thickness, stretching process conditions, and heat setting process conditions were set as shown in Tables 3, 5, and 7, respectively. Here, the term "simultaneous" in the stretching method refers to a stretching method in which MD (the machine direction when continuously molding a polyolefin membrane) stretching and TD (the direction crossing the MD of the polyolefin membrane at an angle of 90°) stretching are performed simultaneously, and "sequential" refers to a stretching method in which MD and TD stretching are performed independently. The various properties of the obtained polyolefin membranes were evaluated by the above-mentioned methods. The evaluation results are shown in Tables 4, 6, and 8. In each table, the "swelling onset temperature difference" is indicated as "-" if polyethylene A in this embodiment is not used. The unit of "sheet thickness" in each table is μm.

[0098] [Table 1]

[0099] [Table 2]

[0100] [Table 3]

[0101] [Table 4]

[0102] [Table 5]

[0103] [Table 6]

[0104] [Table 7]

[0105] [Table 8]

[0106] Based on the results of Tables 3 to 8, the pin puncture strength Sm converted into basis weight and the shutdown temperature Ts of the polyolefin films of Examples 1 to 20 and Comparative Examples 1 to 6 are plotted in a graph shown in FIG.

[0107] This application is based on a Japanese patent application (Patent Application No. 2021-159432) filed on September 29, 2021, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0108] 1 Polyolefin membrane 2A, 2B Nickel foil 3A, 3B Glass plates 4. Electrical resistance measuring device 5 Thermocouples 6 thermometer 7. Data Collector 8. Oven

Claims

1. A polyolefin membrane comprising a polyolefin, the polyolefin comprises polyethylene; The polyethylene includes polyethylene A and polyethylene B different from polyethylene A, the polyethylene A is a homopolyethylene having a melting point of 134°C or higher and 138°C or lower and a melt index of 0.5 g / 10 min or higher and 50 g / 10 min or lower, the polyethylene B is a homopolyethylene having a melting point of 134°C or higher and 138°C or lower and a viscosity average molecular weight of 800,000 or higher and 5,000,000 or lower, the content of the polyethylene A is 20 parts by mass or more and 80 parts by mass or less relative to 100 parts by mass of the total of the polyethylene A and the polyethylene B, The melting point of the polyolefin film is 134°C or higher and 140°C or lower, The polyolefin film has a puncture strength (Sm) converted into a basis weight of 70 gf / (g / m 2 ) or more 150gf / (g / m 2 ) or less, The polyolefin membrane, wherein the shutdown temperature Ts and the Sm satisfy the following relationship: Ts<0.13×Sm+130

2. 2. The polyolefin membrane according to claim 1, wherein the total amount of side chains having 3 carbon atoms and side chains having 4 carbon atoms measured for the polyolefin membrane is 0.1 mol % or less, as a ratio to the total number of carbon atoms.

3. The polyolefin film according to claim 1 or 2, which has a heat shrinkage rate of 10% or less at 120°C.

4. The polyolefin membrane according to claim 1 or 2, wherein the thickness-equivalent air permeability Gt and the porosity P of the polyolefin membrane satisfy the following relationship: LN(Gt)≦-0.070×P+5.8

5. The polyolefin membrane according to claim 1 or 2, wherein the difference in swelling onset temperature between the polyethylene A and the polyethylene B, as determined by the following measurement, is 10°C or less. [Measurement of swelling onset temperature] (D 10 , D 50 and D 90 Measurement of The particle diameters of the polyethylene A and polyethylene B are measured using a laser particle size distribution analyzer with methanol as a dispersion medium. Based on the measurements, a cumulative particle size distribution is created from the small particle size side, and the particle sizes at 10%, 50%, and 90% of the cumulative size are designated as the D of each polyethylene. 10 , D 50 and D 90 Let's say. (Measurement of swelling initiation temperature T) The particle diameter D is calculated as follows: 10 The swelling starting temperature T of polyethylene particles is 10 That is, from among the particle groups of each polyethylene, the particle whose major axis diameter and minor axis diameter (in the plan view of the particle observed using an optical microscope, the shortest distance between parallel lines is taken as the minor axis diameter of the particle, and the longest distance between parallel lines in the direction perpendicular to that is taken as the major axis diameter of the particle) is determined to be D 10 Polyethylene particles within ±10% of the original particle size were identified using an optical microscope, and one particle was randomly selected. The sampled polyethylene particle was placed on a glass slide, and 0.05 mL of liquid paraffin was dropped onto the polyethylene particle. A cover glass was then placed on top to sandwich the polyethylene particle. The slide glass is then set on a heat stage and heated from room temperature to 150°C under the following heating conditions. The appearance of the polyethylene particles during heating is photographed every 6 seconds using an optical microscope equipped with a camera. The equivalent circle diameter of the polyethylene particles is calculated from each of the obtained observation images, and the minimum temperature at which the equivalent circle diameter of the polyethylene particles increases by 1% or more in the temperature range of 80°C to 150°C, based on the equivalent circle diameter of the polyethylene particles at 80°C, is defined as the swelling initiation temperature of the polyethylene particles. Measurements are made at 10 points, and the average value of these measurements is taken as the swelling initiation temperature T 10 Let's say. (Temperature increase conditions) Heating rate from room temperature to 35°C: 5°C / min Heating rate in the range of 35°C to 80°C: 8°C / min Heating rate in the range of 80°C to 150°C: 5°C / min Next, the particle diameter is D 50 The swelling starting temperature T of polyethylene particles is 50 , and the particle diameter is D 90 The swelling starting temperature T of polyethylene particles is 90 Regarding the swelling starting temperature T 10 The long and short axis diameters were D 50 Polyethylene particles having a major axis diameter and a minor axis diameter within a range of ±10%. 90 It is determined using polyethylene particles within a range of ±10%. Finally, the swelling initiation temperature T of each polyethylene is determined as follows: [Equation 1]

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