WO2016104791A1 - ポリオレフィン樹脂組成物およびポリオレフィン微多孔膜の製造方法 - Google Patents
ポリオレフィン樹脂組成物およびポリオレフィン微多孔膜の製造方法 Download PDFInfo
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- WO2016104791A1 WO2016104791A1 PCT/JP2015/086417 JP2015086417W WO2016104791A1 WO 2016104791 A1 WO2016104791 A1 WO 2016104791A1 JP 2015086417 W JP2015086417 W JP 2015086417W WO 2016104791 A1 WO2016104791 A1 WO 2016104791A1
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- polyolefin resin
- polyolefin
- film
- resin composition
- microporous membrane
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
- B29C48/07—Flat, e.g. panels
- B29C48/08—Flat, e.g. panels flexible, e.g. films
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/06—Polyethene
Definitions
- the present invention relates to a method for producing a polyolefin microporous membrane suitably used for a secondary battery separator, a coating separator substrate, and the like, and a polyolefin resin composition suitable for the production thereof.
- lithium ion secondary battery separators With the increase in capacity and output of lithium ion secondary batteries in recent years, from the viewpoint of safety, mechanical strength such as puncture strength of lithium ion secondary battery separators and withstand voltage characteristics such as dielectric breakdown voltage There is a need for improvement. Furthermore, in order to increase the capacity and output of a lithium ion secondary battery, it is preferable to shorten the distance between the electrodes. Therefore, the lithium ion secondary battery separator is becoming thinner. For this reason, higher mechanical strength and withstand voltage characteristics have been required for lithium ion secondary battery separators in order to prevent film breakage and short circuits.
- Patent Document 1 discloses a technique for improving withstand voltage characteristics and piercing strength by blending inorganic particles of a size in polyolefin.
- the fine particles are difficult to uniformly disperse, and after the film is formed, the porosity is excessively high and the withstand voltage characteristics are not sufficient.
- it is a microporous film formed by a process using a large amount of fine particles, it has problems in process, equipment, and maintenance.
- the present invention relates to a polyolefin resin composition
- a polyolefin resin composition comprising a polyolefin resin, a crystal nucleating agent and a film-forming solvent, and having a specific half-crystallization time t 1/2 , and a polyolefin microporous film using the same It relates to the manufacturing method.
- An object of the present invention is to provide a polyolefin microporous membrane excellent in mechanical strength such as puncture strength and withstand voltage characteristics such as dielectric breakdown voltage, and capable of efficiently producing a highly versatile and safe polyolefin microporous membrane. It is to provide a manufacturing method.
- the present invention is as follows.
- a first aspect of the present invention includes a polyolefin resin, a crystal nucleating agent, and a film-forming solvent, and has a half crystallization time t 1/2 at the isothermal crystallization at 117 ° C. of 8.0 minutes or less.
- a polyolefin resin composition includes a polyolefin resin, a crystal nucleating agent, and a film-forming solvent, and has a half crystallization time t 1/2 at the isothermal crystallization at 117 ° C. of 8.0 minutes or less.
- polyethylene resin As said polyolefin resin, it is preferable that 90 mass% or more is polyethylene resin, As said film-forming solvent, aliphatic or cyclic hydrocarbons, such as nonane, decane, decalin, and paraffin oil, and dibutyl phthalate And at least one selected from phthalate esters such as dioctyl phthalate.
- aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, and paraffin oil
- dibutyl phthalate At least one selected from phthalate esters such as dioctyl phthalate.
- a method for producing a polyolefin resin composition comprising a step of preparing a polyolefin resin composition by melt-kneading a polyolefin resin, a crystal nucleating agent and a film-forming solvent.
- a third aspect of the present invention is a method for producing a polyolefin microporous membrane, comprising the following steps. (1) Melting and kneading a polyolefin resin, a crystal nucleating agent and a film-forming solvent to prepare a polyolefin resin composition having a half-crystallization time t 1/2 of not more than 8.0 minutes at 117 ° C. isothermal crystallization. Step (2) Extruding the polyolefin resin composition and cooling to form a gel-like sheet (3) First stretching step for stretching the gel-like sheet (4) Film formation from the stretched gel-like sheet Step of removing solvent (5) Step of drying the sheet after removing the film-forming solvent
- the polyolefin microporous membrane preferably has a gas resistance of 100 to 500 seconds / 100 cc in terms of 20 ⁇ m, a porosity of 10% to 60%, and an average pore diameter of 100 ⁇ m or less.
- the dielectric breakdown voltage of the polyolefin microporous membrane is preferably 163 V / ⁇ m or more.
- the polyolefin resin composition of the present invention comprises a polyolefin resin, a crystal nucleating agent, and a film-forming solvent
- the polyolefin microporous film using this as a raw material has mechanical strength such as puncture strength and dielectric breakdown voltage. It becomes a microporous film excellent in withstand voltage characteristics such as.
- the polyolefin resin composition of the present invention can provide a microporous film having high strength and high withstand voltage characteristics even when having a lower viscosity.
- the microporous membrane obtained from the polyolefin resin composition of the present invention can be further thinned due to the characteristics of high strength and withstand voltage characteristics, and when used as a battery separator, improves the capacity of the battery.
- the method for producing a polyolefin microporous membrane of the present invention can efficiently produce a microporous membrane excellent in mechanical strength such as puncture strength and withstand voltage characteristics.
- FIG. 1 is a diagram showing the change over time in the amount of heat during 117 ° C. isothermal crystallization, measured using DSC of the polyolefin resin composition obtained in Example 1 and Comparative Example 1.
- Polyolefin resins include polyethylene, polypropylene, poly (4-methyl-pentene-1), ethylene-propylene copolymer, polytetrafluoroethylene, polytrifluoroethylene chloride, polyvinylidene fluoride, poly Examples include vinylidene chloride, polyvinyl fluoride, polyvinyl chloride, polysulfone, and polycarbonate.
- the MFR of the polyolefin resin is in the range of 2.0 g / 10 min or less, preferably in the range of 0.01 to 1.0 g / 10 min. This is because if the MFR exceeds 2.0 g / 10 min, the mechanical strength such as the piercing strength of the resulting polyolefin microporous membrane is lowered.
- the MFR was measured by extruding the molten polymer from a die (length 8 mm, outer diameter 9.5 mm, inner diameter 2.095 mm) at 190 ° C. and a load of 2.16 kg in accordance with JIS K6922-2. .
- the polyolefin resin may be a mixture of two or more polyolefins.
- the MFR as the mixture is preferably in the above range.
- the polyolefin resin preferably includes a polyethylene resin.
- the content of the polyethylene resin is preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 99% by mass or more in the polyolefin resin.
- the ratio of the polyethylene resin in the polyolefin resin is within the above range, the strength of the resulting polyolefin microporous film can be improved.
- polyethylene resin (i) an ethylene homopolymer, or (ii) a copolymer of ethylene and a comonomer such as propylene, butene-1, or hexene-1, or a mixture thereof can be used.
- ethylene homopolymer is preferable from the viewpoints of economy and film strength.
- the content of the comonomer in the copolymer as the polyethylene resin is preferably 10.0 mol% or less based on 100 mol% of the copolymer.
- Such copolymers can be made by any convenient polymerization process, such as a process using a Ziegler-Natta catalyst or a single site catalyst.
- the comonomer may be an ⁇ -olefin.
- the comonomer may be propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate. , One or more of styrene, or other monomers.
- the MFR of the polyethylene resin is preferably 2.0 g / 10 min or less, more preferably in the range of 0.01 to 1.0 g / 10 min.
- a microporous film having high mechanical strength can be obtained, which is preferable.
- the weight average molecular weight of the polyethylene resin is not particularly limited, but it is preferable to contain ultrahigh molecular weight polyethylene having a weight average molecular weight of 1.0 ⁇ 10 6 or more in a range of 1% by mass to 90% by mass, and more preferably 1% by mass. % To 80% by mass, more preferably 1% to 70% by mass.
- ultra high molecular weight polyethylene having a weight average molecular weight of 1.0 ⁇ 10 6 or more is contained within the above range, a high-strength microporous membrane can be obtained without impairing the productivity of the polyolefin microporous membrane.
- the polyethylene resin may be a single polyethylene or a mixture of two or more types of polyethylene.
- the MFR as the mixture is preferably 2.0 g / 10 min or less.
- the polyolefin resin may contain other resin components other than the polyethylene, if necessary.
- the other resin component is preferably a heat resistant resin.
- the heat resistant resin include crystalline resins having a melting point of 150 ° C. or higher (including partially crystalline resins) and / or glass.
- An amorphous resin having a point transfer (Tg) of 150 ° C. or higher is exemplified.
- Tg is a value measured according to JIS K7121.
- resin components include polyester, polymethylpentene [PMP or TPX (transparent polymer X), melting point: 230 to 245 ° C.], polyamide (PA, melting point: 215 to 265 ° C.), polyarylene sulfide ( Fluorine-containing resin such as PAS, polyvinylidene fluoride homopolymers such as polyvinylidene fluoride (PVDF), fluorinated olefins such as polytetrafluoroethylene (PTFE), and copolymers thereof; polystyrene (PS, melting point: 230 ° C.) ), Polyvinyl alcohol (PVA, melting point: 220-240 ° C.), polyimide (PI, Tg: 280 ° C.
- the resin component is not limited to one composed of a single resin component, and may be composed of a plurality of resin components.
- the preferred Mw of other resin components varies depending on the type of resin, but is generally 1 ⁇ 10 3 to 1 ⁇ 10 6 , more preferably 1 ⁇ 10 4 to 7 ⁇ 10 5 . Further, the content of other resin components in the polyolefin resin is appropriately adjusted within a range not departing from the gist of the present invention, but is contained in the range of approximately 10% by mass or less in the polyolefin resin.
- polyolefins other than the polyethylene may be included as required, and polybutene-1, polybutene-1, polypentene-1, polyhexene having Mw of 1 ⁇ 10 4 to 4 ⁇ 10 6 1. At least one selected from the group consisting of polyethylene wax having a polyoctene-1 and Mw of 1 ⁇ 10 3 to 1 ⁇ 10 4 may be used.
- the content of polyolefin other than polyethylene can be adjusted as appropriate within the range not impairing the effects of the present invention, but is preferably 10% by mass or less, and more preferably less than 5% by mass in the polyolefin resin.
- Crystal nucleating agent there are no particular limitations on the crystal nucleating agent that can be used in the polyolefin resin composition of the present embodiment, and general compound-based and fine particle-based crystal structuring used for polyolefin resins. Nucleating agents can be used.
- the crystal nucleating agent may be a master batch in which a crystal nucleating agent and fine particles are previously mixed and dispersed in a polyolefin resin.
- the compounding amount of the crystal nucleating agent is not particularly limited, but the upper limit thereof is preferably 10 parts by mass with respect to 100 parts by mass of the polyolefin resin, more preferably 5 parts by mass, and the lower limit thereof is 100 parts by mass of the polyolefin resin. 0.01 mass part is preferable and 0.1 mass part is more preferable.
- the blending amount of the crystal nucleating agent is within the above range, good dispersibility in the polyolefin resin, good handling workability and economical efficiency in the production process can be expected.
- Crystal nucleating agent accelerates the crystallization rate of polyolefin and refines the crystal.
- high density polyethylene is said to have a remarkably high crystallization rate and hardly obtain the effect of a crystal nucleating agent.
- the inventors have found that when the solvent for film formation is blended with polyolefin containing high-density polyethylene, the crystallization speed is delayed, while when a crystal nucleating agent is blended with the mixture of polyolefin and film-forming solvent. It was confirmed that the crystallization speed was promoted. From this, it is presumed that the blending of the crystal nucleating agent makes the pore structure of the resulting microporous polyolefin membrane more uniform and dense, and improves its mechanical strength and withstand voltage characteristics.
- Compound crystal nucleating agents include aromatic phosphate metal salt nucleating agents, sorbitol nucleating agents, carboxylic acid metal salt nucleating agents such as benzoic acid metal salt nucleating agents, and mixtures thereof. What is generally used as a nucleating agent for polyolefin resins can be used. Among them, from the viewpoint of dispersibility in a polyolefin resin solution described later, a carboxylic acid metal salt system such as an aromatic phosphate metal salt nucleating agent or a benzoic acid metal salt nucleating agent that basically does not contain a hydrosilyl group. A nucleating agent and a mixture thereof are preferred.
- Fine particle nucleating agent As the fine particle crystal nucleating agent, a fine particle crystal nucleating agent such as silica or alumina can be used.
- crystal nucleating agents “Gerol D” (manufactured by Shin Nippon Rika Co., Ltd .: sorbitol nucleating agent), “Adekastab” (manufactured by Adeka Corp .: aromatic phosphate metal salt nucleating agent), “ Hyperform ”(manufactured by Milliken Chemical Co .: carboxylic acid metal salt nucleating agent) or“ IRGACLEAR D ”(manufactured by Ciba Specialty Chemicals: sorbitol nucleating agent).
- “Rike Master” manufactured by Riken Vitamin Co., Ltd .: carboxylate metal salt nucleating agent
- the film-forming solvent contained in the polyolefin resin composition is nonane, decane, decalin, and aliphatic or cyclic hydrocarbons such as paraffin oil, and phthalic acid such as dibutyl phthalate and dioctyl phthalate. Examples include esters. Paraffin oil having a kinematic viscosity at 40 ° C. of 20 to 200 cst may be used.
- the blending amount of the film-forming solvent is preferably 50 to 90 parts by mass with respect to 10 to 50 parts by mass of the polyolefin resin, and 70 to 80 parts by mass with respect to 20 to 30 parts by mass of the polyolefin resin. Is more preferable. This is because when the blending amount of the film-forming solvent is within the above range, the melt viscosity of the polyolefin resin composition becomes an appropriate value, and the balance between extrudability and productivity is excellent.
- additives such as antioxidants, ultraviolet absorbers, pigments, dyes and the like are added to the polyolefin resin composition as described above as long as the purpose of the present invention is not impaired. Can be blended.
- the blending amount is preferably 0.01 parts by mass to less than 10 parts by mass with respect to 100 parts by mass of the polyolefin resin. If the amount is less than 0.01 parts by mass, a sufficient effect cannot be obtained, and it is difficult to control the blending amount during production. If the amount is 10 parts by mass or more, the economy is inferior.
- Half crystallization time t 1/2 at 117 ° C. isothermal crystallization of polyolefin resin composition is preferably 8.0 minutes or less, more preferably 6.0 minutes or less, and 5.0 minutes or less. It is more preferable that When the half crystallization time t 1/2 during the isothermal crystallization of 117 ° C. of the polyolefin resin composition exceeds the above range, the pore structure of the polyolefin microporous film obtained by stretching the polyolefin resin composition is more uniform. This is because it is difficult to improve the mechanical strength and withstand voltage characteristics.
- the pore structure of a microporous polyolefin membrane obtained by stretching the polyolefin resin composition when the half crystallization time t 1/2 of the polyolefin resin composition at the isothermal crystallization at 114 ° C. or 117 ° C. is within the above range. This is because it can be made more uniform and densified, and its mechanical strength and withstand voltage characteristics can be improved.
- the half crystallization time t1 / 2 at the time of 120 degreeC isothermal crystallization of the polyolefin resin composition of this invention can be observed within 60 minutes.
- melt-kneading After blending a polyolefin resin with a crystal nucleating agent and a suitable film-forming solvent, melt-kneading to prepare a polyolefin resin composition.
- melt-kneading method for example, a method using a twin-screw extruder described in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Since the melt-kneading method is known, the description thereof is omitted.
- the blending ratio of the crystal nucleating agent and the film-forming solvent in the polyolefin resin composition is as described above.
- the production method of the polyolefin microporous membrane of the present invention is not particularly limited except that it is produced using the above-described polyolefin resin composition, and a conventionally known method can be used.
- the methods described in Japanese Patent No. 2132327, Japanese Patent No. 3347835, International Publication No. 2006/137540, and the like can be used.
- it preferably includes the following steps (1) to (5), may further include the following step (6), and may further include the following steps (7) and / or (8). it can.
- Step of preparing the polyolefin resin composition (2) Step of extruding and cooling the polyolefin resin composition to form a gel sheet (3) First stretching step of stretching the gel sheet (4) The process of removing the film-forming solvent from the stretched gel-like sheet (5) The process of drying the sheet after removing the film-forming solvent (6) The second stretching process of stretching the dried sheet (7) ) Step of heat-treating the sheet after drying (8) Step of crosslinking and / or hydrophilizing the sheet after the stretching step
- each step will be described.
- a polyolefin resin composition is prepared by blending a polyolefin resin with a crystal nucleating agent and a suitable film-forming solvent and then melt-kneading. Details are as described above.
- the polyolefin resin composition is fed from an extruder to a die and extruded into a sheet form.
- a plurality of polyolefin resin compositions having the same or different compositions may be fed from an extruder to a single die, where they are laminated in layers and extruded into sheets.
- the extrusion method may be either a flat die method or an inflation method.
- the extrusion temperature is preferably 140 to 250 ° C.
- the extrusion speed is preferably 0.2 to 15 m / min.
- the film thickness can be adjusted by adjusting each extrusion amount of the polyolefin resin composition.
- a gel-like sheet is formed by cooling the obtained extrusion-molded body.
- a method for forming the gel-like sheet for example, methods disclosed in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature. Cooling is preferably performed to 25 ° C. or lower. (3) 1st extending
- the gel-like sheet is preferably stretched at a predetermined ratio after heating by a tenter method, a roll method, an inflation method, or a combination thereof.
- the stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred.
- biaxial stretching any of simultaneous biaxial stretching, sequential stretching and multistage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used.
- the stretching ratio (area stretching ratio) in this step is preferably 2 times or more, more preferably 3 to 30 times in the case of uniaxial stretching. In the case of biaxial stretching, 9 times or more is preferable, 16 times or more is more preferable, and 25 times or more is particularly preferable. Further, it is preferably 3 times or more in both the longitudinal direction and the transverse direction (MD and TD directions), and the draw ratios in the MD direction and the TD direction may be the same or different. When the draw ratio is 9 times or more, improvement in puncture strength can be expected.
- the draw ratio in this process means the area draw ratio of the microporous film immediately before being used for the next process on the basis of the microporous film immediately before this process.
- the stretching temperature in this step is preferably in the range of the crystal dispersion temperature (Tcd) to Tcd + 30 ° C. of the polyolefin resin, and in the range of crystal dispersion temperature (Tcd) + 5 ° C. to crystal dispersion temperature (Tcd) + 28 ° C. It is more preferable that the temperature be within the range of Tcd + 10 ° C. to Tcd + 26 ° C. When the stretching temperature is within the above range, film breakage due to stretching of the polyolefin resin is suppressed, and stretching at a high magnification can be performed.
- the crystal dispersion temperature (Tcd) is determined by measuring the dynamic viscoelastic temperature characteristics according to ASTM D4065. Since ultra high molecular weight polyethylene, polyethylene other than ultra high molecular weight polyethylene and polyethylene compositions have a crystal dispersion temperature of about 90-100 ° C., the stretching temperature is preferably 90-130 ° C., more preferably 110-120 ° C. And more preferably 114-117 ° C.
- the stretching as described above causes cleavage between polyethylene lamellae, the polyethylene phase becomes finer, and a large number of fibrils are formed. Fibrils form a three-dimensional irregularly connected network structure.
- the film-forming solvent is removed (washed) using a cleaning solvent. Since the polyolefin phase is phase-separated from the film-forming solvent phase, removing the film-forming solvent consists of fibrils that form a fine three-dimensional network structure, and pores (voids) that communicate irregularly in three dimensions. A porous membrane having the following is obtained. Since the cleaning solvent and the method for removing the film-forming solvent using the same are known, the description thereof is omitted. For example, the methods disclosed in Japanese Patent No. 2132327 and Japanese Patent Application Laid-Open No. 2002-256099 can be used.
- the microporous film from which the film-forming solvent has been removed is dried by a heat drying method or an air drying method.
- the drying temperature is preferably not higher than the crystal dispersion temperature (Tcd) of the polyolefin resin, and particularly preferably 5 ° C. or lower than Tcd. Drying is preferably carried out until the residual cleaning solvent is 5% by mass or less, more preferably 3% by mass or less, with the microporous membrane being 100% by mass (dry weight).
- Second stretching step It is preferable to stretch the dried microporous membrane in at least a uniaxial direction.
- the microporous membrane can be stretched by the tenter method or the like as described above while heating.
- the stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential stretching may be used.
- the stretching temperature in this step is not particularly limited, but is usually 90 to 135 ° C, more preferably 95 to 130 ° C.
- the upper limit is preferably 3.5 times or less, and 1.0 to 2.0 times in each of the MD direction and the TD direction, and the draw ratios in the MD direction and the TD direction may be the same or different.
- the draw ratio in this process means the draw ratio of the microporous film just before being provided to the next process on the basis of the microporous film immediately before this process.
- the microporous film after drying can be heat-treated.
- the crystal is stabilized by heat treatment, and the lamella is made uniform.
- heat setting treatment and / or heat relaxation treatment can be used.
- the heat setting treatment is a heat treatment in which heating is performed while keeping the dimensions of the film unchanged.
- the thermal relaxation treatment is a heat treatment that heat-shrinks the film in the MD direction or the TD direction during heating.
- the heat setting treatment is preferably performed by a tenter method or a roll method.
- a thermal relaxation treatment method a method disclosed in Japanese Patent Application Laid-Open No. 2002-256099 can be given.
- the heat treatment temperature is preferably within the range of Tcd to Tm of the polyolefin resin, more preferably within the range of the stretching temperature ⁇ 5 ° C. of the microporous membrane, and particularly preferably within the range of the second stretching temperature ⁇ 3 ° C. of the microporous membrane.
- a crosslinking treatment and a hydrophilization treatment can also be performed on the microporous membrane after bonding or stretching.
- the microporous membrane is subjected to a crosslinking treatment by irradiation with ionizing radiation such as ⁇ rays, ⁇ rays, ⁇ rays, and electron beams.
- ionizing radiation such as ⁇ rays, ⁇ rays, ⁇ rays, and electron beams.
- electron beam irradiation an electron dose of 0.1 to 100 Mrad is preferable, and an acceleration voltage of 100 to 300 kV is preferable.
- the meltdown temperature of the microporous membrane is increased by the crosslinking treatment.
- the hydrophilic treatment can be performed by monomer grafting, surfactant treatment, corona discharge, or the like. Monomer grafting is preferably performed after the crosslinking treatment.
- the upper limit of the porosity of the polyolefin microporous film of the present invention is 60% or less, preferably 50% or less, from the viewpoint of improving the film strength and voltage resistance characteristics.
- the lower limit of the porosity is preferably 20% or more, and more preferably 30% or more.
- the porosity of the polyolefin microporous membrane can be adjusted by a conventionally known method, but can be adjusted by using the polyolefin resin composition or by controlling the temperature and stretching conditions.
- the upper limit of the maximum pore size of the polyolefin microporous membrane of the present invention is 500 nm or less, preferably 300 nm or less, more preferably 80 nm or less, from the viewpoint of improving the film strength and voltage resistance.
- the lower limit of the maximum pore size of the polyolefin microporous membrane of the present invention is not particularly limited, but is preferably 1 nm or more, and more preferably 5 nm or more, from the relationship of air permeability resistance described later.
- the maximum pore diameter and average flow pore diameter of the polyolefin microporous membrane can be measured in the order of Dry-up and Wet-up using a palm porometer (PFP, CFP-1500A).
- PFP palm porometer
- the average flow pore size the pore size was converted from the pressure at the point where the curve showing the slope of 1/2 of the pressure / flow rate curve in the Dry-up measurement and the curve of the Wet-up measurement intersect. The following formula was used for conversion of pressure and pore diameter.
- d C ⁇ ⁇ / P (In the above formula, “d ( ⁇ m)” is the pore diameter of the microporous membrane, “ ⁇ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant.
- the air resistance when the film thickness is 20 ⁇ m is 100 to 1000 sec / 100 cc, preferably 100 to 800 sec / 100 cc, preferably 100 to 600 sec / 100 cc. It is particularly preferred. If the air permeability resistance exceeds 1000 sec / 100 cc, the ion permeability deteriorates and the electrical resistance increases, which is not preferable. On the other hand, when the air resistance is less than 100 sec / 100 cc, the membrane structure becomes excessively sparse, and when the temperature inside the battery rises, the shutdown before the meltdown is not sufficiently performed, or the dielectric breakdown voltage Is not preferable because of lowering.
- the air resistance when the film thickness is 20 ⁇ m means that the air resistance measured according to JIS P 8117 (2009) is P 1 in a microporous film having a film thickness T 1 ( ⁇ m).
- Is the air permeability resistance P 2 calculated by the formula: P 2 (P 1 ⁇ 20) / T 1 .
- the term “air permeability resistance” is used to mean “air resistance when the film thickness is 20 ⁇ m” unless otherwise specified.
- the air resistance of the polyolefin microporous membrane can be adjusted by using the polyolefin resin composition or by controlling the temperature and stretching conditions.
- the polyolefin microporous membrane of the present invention preferably has a dielectric breakdown voltage of 135 V / ⁇ m or more, more preferably 150 V / ⁇ m or more, and particularly preferably 164 V / ⁇ m or more.
- the upper limit of the dielectric breakdown voltage is not particularly limited, it is generally considered that the upper limit does not exceed 300 V / ⁇ m. This is because when the dielectric breakdown voltage of the polyolefin microporous membrane is within the above range, the battery can be expected to have good durability and withstand voltage performance when used as a battery separator.
- the dielectric breakdown voltage of the polyolefin microporous membrane of the present invention can be measured in accordance with, for example, a method defined in JIS C2110 or ASTM D149.
- the puncture strength is preferably 400 gf or more, and more preferably 550 gf or more. By setting it as such a range, even if it makes it thin, it will not break, and safety
- the puncture strength when the film thickness is 20 ⁇ m is a 1 mm diameter needle with a spherical tip (curvature radius R: 0.5 mm), and a microporous film with a film thickness T 1 ( ⁇ m) is 2 mm / mm.
- the puncture strength when the thickness of the polyolefin microporous film is 20 ⁇ m can be adjusted by using the polyolefin resin composition, or by controlling the temperature and stretching conditions.
- the film thickness of the microporous membrane of this embodiment is preferably 1 to 2000 ⁇ m, more preferably 1 to 1000 ⁇ m. A method for measuring the film thickness will be described later.
- the membrane structure can be densified, and the porosity, pore diameter, and air resistance can be made suitable. It is possible to achieve both desired film strength and withstand voltage characteristics.
- a porous layer may be provided on at least one surface of the polyolefin microporous membrane to form a laminated porous membrane.
- the porous layer formed using the filler containing resin solution and heat resistant resin solution containing a filler and a resin binder can be mentioned, for example.
- organic fillers such as inorganic fillers and cross-linked polymer fillers can be used. They have a melting point of 200 ° C. or higher, high electrical insulation, and electrochemical in the range of use of lithium ion secondary batteries. Stable ones are preferred. These can be used alone or in combination of two or more.
- the average particle diameter of the filler is not particularly limited, but is preferably 0.1 ⁇ m or more and 3.0 ⁇ m or less, for example.
- the proportion (mass fraction) of the filler in the porous layer is preferably 50% or more and 99.99% or less from the viewpoint of heat resistance.
- polyolefins and heat resistant resins described in the section of other resin components contained in the above-described polyolefin resin can be suitably used.
- the proportion of the resin binder in the total amount of the filler and the resin binder is preferably 0.5% or more and 8% or less in terms of volume fraction from the viewpoint of the binding property of both.
- heat resistant resin those similar to the heat resistant resin described in the section of other resin components contained in the polyolefin resin can be suitably used.
- the method for applying the filler-containing resin solution or the heat-resistant resin solution to the surface of the polyolefin microporous membrane is not particularly limited as long as it can achieve the required layer thickness and application area, such as a gravure coater method.
- the solvent for the filler-containing solution and the heat-resistant resin solution is preferably a solvent that can be removed from the solution applied to the polyolefin microporous membrane, and is not particularly limited. Specific examples include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride and hexane.
- the method for removing the solvent is not particularly limited as long as it does not adversely affect the polyolefin microporous membrane. Specifically, for example, a method of drying a polyolefin microporous film while fixing it at a temperature below its melting point, a method of drying under a reduced pressure, a resin binder and a poor solvent such as a heat-resistant resin, and simultaneously solidifying the resin The method of extracting is mentioned.
- the thickness of the porous layer is preferably from 0.5 ⁇ m to 100 ⁇ m from the viewpoint of improving heat resistance.
- porous layer may be formed on one surface of the laminated porous film or on both surfaces.
- the polyolefin microporous membrane obtained by the method for producing a polyolefin microporous membrane of the present invention can be suitably used for both a battery using an aqueous electrolyte and a battery using a non-aqueous electrolyte. Specifically, it can be preferably used as a separator for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries, and lithium polymer secondary batteries. Especially, it is preferable to use as a separator of a lithium ion secondary battery.
- the current collector, the positive electrode, the positive electrode active material, the negative electrode, the negative electrode active material, and the electrolyte used for the lithium ion secondary battery are not particularly limited, and conventionally known materials can be used in appropriate combination.
- Film thickness ( ⁇ m) The film thickness at 5 points in the range of 95 mm ⁇ 95 mm of the microporous film was measured with a contact thickness meter (Lightmatic manufactured by Mitutoyo Corporation), and the average value of the film thickness was determined.
- d C ⁇ ⁇ / P (In the above formula, “d ( ⁇ m)” is the pore diameter of the microporous membrane, “ ⁇ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant.
- Puncture strength (gf / 20 ⁇ m)
- the maximum load was measured when a microporous film having a film thickness T 1 ( ⁇ m) was pierced at a speed of 2 mm / second with a needle having a spherical surface (curvature radius R: 0.5 mm) and a diameter of 1 mm.
- Half crystallization time t 1/2 during isothermal crystallization was measured by the following method.
- the polyolefin resin composition was sealed in a measurement pan, heated to 230 ° C. using a PYRIS Diamond DSC manufactured by Parking Elmer, cooled to a predetermined temperature at 30 ° C./min, and held at the temperature.
- the time change of the amount of heat after entering the isothermal control at that temperature was recorded, and the time during which the peak area was halved was defined as the half crystallization time t 1/2 during isothermal crystallization at each temperature.
- “NA” was indicated as unobservable.
- Dielectric breakdown voltage A microporous film cut out in a circle having a diameter of 60 mm is placed on a square aluminum plate having a side of 150 mm, and a brass cylindrical electrode having a diameter of 50 mm, a height of 30 mm, and a weight of 500 g is placed thereon. Then, a TOS5051A dielectric breakdown resistance tester manufactured by Kikusui Electronics Industry was connected. A voltage was applied at a step-up rate of 0.2 kV / sec, and the voltage when dielectric breakdown occurred was read. The dielectric breakdown voltage was measured 15 times, and an average value was obtained.
- Tetrakis [methylene-3- (3,5-ditertiary) was added to 100 parts by mass of a polyethylene (PE) composition comprising 100 parts by mass of high density polyethylene (HDPE) having a weight average molecular weight (Mw) of 2.8 ⁇ 10 5.
- PE polyethylene
- HDPE high density polyethylene
- Mw weight average molecular weight
- butyl-4-hydroxyphenyl) -propionate 0.375 parts by mass of methane and 3 parts by mass of master batch Riquetmaster CN-002 (manufactured by Riken Vitamin) were dry blended to obtain a mixture.
- a polyethylene resin composition was prepared by melt-kneading at the temperature of
- Example 2 Masterbatch Polyolefin microporous membrane in the same manner as in Example 1 except that 3 parts by mass of sorbitol crystal nucleating agent Gelol D (manufactured by Nihon Rika) was used instead of Riquetmaster CN-002 (manufactured by Riken Vitamin). Got. The characteristics of the obtained microporous membrane are shown in Table 1.
- Example 2 Masterbatches A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that 3 parts by mass of calcium stearate was used instead of Riquemaster CN-002 (manufactured by Riken Vitamin). The characteristics of the obtained microporous membrane are shown in Table 1.
- Example 3 Polyethylene (PE) comprising 30 parts by mass of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight (Mw) of 1.0 ⁇ 10 6 and 70 parts by mass of high density polyethylene (HDPE) having an Mw of 2.8 ⁇ 10 5
- UHMWPE ultra high molecular weight polyethylene
- HDPE high density polyethylene
- Example 4 Polyethylene (PE) comprising 40 parts by mass of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight (Mw) of 1.0 ⁇ 10 6 and 60 parts by mass of high density polyethylene (HDPE) having an Mw of 2.8 ⁇ 10 5
- UHMWPE ultra high molecular weight polyethylene
- HDPE high density polyethylene
- a polyolefin microporous membrane was obtained in the same manner as in Example 1 except that 100 parts by mass of the composition was used. The characteristics of the obtained microporous membrane are shown in Table 3.
- the polyolefin resin composition according to the present invention can be used for producing a polyolefin microporous membrane suitable as a separator for a secondary battery. Moreover, the manufacturing method of the polyolefin microporous membrane which concerns on this invention can manufacture efficiently the polyolefin microporous membrane suitable as a separator for secondary batteries.
- the polyolefin microporous membrane obtained from the polyolefin resin composition according to the present invention and the method for producing a polyolefin microporous membrane according to the present invention can be suitably used as a separator for a secondary battery.
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Abstract
Description
(1)ポリオレフィン樹脂、結晶造核剤および成膜用溶剤を溶融混練して117℃等温結晶化時の半結晶化時間t1/2が8.0分以下であるポリオレフィン樹脂組成物を調製する工程
(2)前記ポリオレフィン樹脂組成物を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する第1の延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程
本発明のポリオレフィン樹脂組成物は、ポリオレフィン樹脂と結晶造核剤と成膜用溶剤とを配合した混合物からなる。以下、本発明について、各項目毎に説明する。
ポリオレフィン樹脂としては、ポリエチレン、ポリプロピレン、ポリ(4-メチル-ペンテン-1)、エチレン-プロピレン共重合体、ポリ四フッ化エチレン、ポリ三フッ化塩化エチレン、ポリフッ化ビニリデン、ポリ塩化ビニリデン、ポリフッ化ビニル、ポリ塩化ビニル、ポリスルホン、ポリカーボネートが例示される。
(i)ポリエチレン樹脂
前記ポリオレフィン樹脂は、必要に応じて、前記ポリエチレン以外のその他の樹脂成分を含むことができる。その他の樹脂成分としては、耐熱性樹脂であることが好ましく、耐熱性樹脂としては、例えば、融点が150℃以上の結晶性樹脂(部分的に結晶性である樹脂を含む)、及び/又はガラス点移転(Tg)が150℃以上の非晶性樹脂が挙げられる。ここでTgはJIS K7121に準拠して測定した値である。
本実施態様のポリオレフィン樹脂組成物に用いることができる結晶造核剤としては、特に限定はなく、ポリオレフィン樹脂用に使用されている一般的な化合物系、微粒子系結晶造核剤を使用できる。結晶造核剤としては、結晶造核剤および微粒子を予めポリオレフィン樹脂に混合、分散したマスターバッチであってもよい。
化合物系結晶造核剤としては、芳香族リン酸エステル金属塩系造核剤、ソルビトール系造核剤、安息香酸金属塩系造核剤等のカルボン酸金属塩系造核剤およびこれらの混合物などポリオレフィン樹脂用造核剤として一般的に使用されるものが使用できる。中でも、後述するポリオレフィン樹脂溶液への分散性の観点から、基本的にヒドロシリル基を含有しない芳香族リン酸エステル金属塩系造核剤、安息香酸金属塩系造核剤等のカルボン酸金属塩系造核剤およびこれらの混合物であることが好ましい。
微粒子系結晶造核剤としては、シリカ、アルミナ等の微粒子系結晶造核剤を用いることができる。
ポリオレフィン樹脂組成物に含まれる成膜用溶剤は、ノナン、デカン、デカリン、およびパラフィン油等の脂肪族または環状炭化水素、ならびにフタル酸ジブチルおよびフタル酸ジオクチル等のフタル酸エステルが挙げられる。40℃での動粘度が20~200cstであるパラフィン油を用いてもよい。
なお、上述したようなポリオレフィン樹脂組成物には、必要に応じて、酸化防止剤、紫外線吸収剤、顔料、染料、などの各種添加剤を本発明の目的を損なわない範囲で配合することができる。
ポリオレフィン樹脂組成物の117℃等温結晶化時の半結晶化時間t1/2は、8.0分以下であることが好ましく、6.0分以下であることがより好ましく、5.0分以下であることがより好ましい。ポリオレフィン樹脂組成物の117℃等温結晶化時の半結晶化時間t1/2が上記範囲内を超えると、前記ポリオレフィン樹脂組成物を延伸して得られるポリオレフィン微多孔膜の細孔構造をより均一化、緻密化することが困難になり、その機械的強度と耐電圧特性の向上が見込めないからである。
ポリオレフィン樹脂に、結晶造核剤および適当な成膜用溶剤を配合した後、溶融混練し、ポリオレフィン樹脂組成物を調製する。溶融混練方法として、例えば日本国特許第2132327号および日本国特許第3347835号公報に記載の二軸押出機を用いる方法を利用することができる。溶融混練方法は公知であるので説明を省略する。
本発明のポリオレフィン微多孔膜の製造方法としては、上述したポリオレフィン樹脂組成物を用いて製造する以外は、特に限定されず、従来公知の方法を用いることができ、例えば、日本国特許第2132327号および日本国特許第3347835号公報、国際公開2006/137540号等に記載された方法を用いることができる。具体的には、下記の工程(1)~(5)を含むことが好ましく、下記の工程(6)をさらに含んでもよく、さらに下記の工程(7)及び/又は(8)を含むこともできる。
(1)前記ポリオレフィン樹脂組成物を調製する工程
(2)前記ポリオレフィン樹脂組成物を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する第1の延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程
(6)前記乾燥後のシートを延伸する第2の延伸工程
(7)前記乾燥後のシートを熱処理する工程
(8)前記延伸工程後のシートに対して架橋処理及び/又は親水化処理する工程
以下、各工程についてそれぞれ説明する。
ポリオレフィン樹脂に、結晶造核剤および適当な成膜用溶剤を配合した後、溶融混練し、ポリオレフィン樹脂組成物を調製する。詳細は前記のとおりである。
前記ポリオレフィン樹脂組成物を押出機からダイに送給し、シート状に押し出す。同一または異なる組成の複数のポリオレフィン樹脂組成物を、押出機から一つのダイに送給し、そこで層状に積層し、シート状に押出してもよい。
(3)第1の延伸工程
次に、得られたゲル状シートを少なくとも一軸方向に延伸する。ゲル状シートは成膜用溶剤を含むので、均一に延伸できる。ゲル状シートは、加熱後、テンター法、ロール法、インフレーション法、又はこれらの組合せにより所定の倍率で延伸するのが好ましい。延伸は一軸延伸でも二軸延伸でもよいが、二軸延伸が好ましい。二軸延伸の場合、同時二軸延伸、逐次延伸及び多段延伸(例えば同時二軸延伸及び逐次延伸の組合せ)のいずれでもよい。
洗浄溶媒を用いて、成膜用溶剤の除去(洗浄)を行う。ポリオレフィン相は成膜用溶剤相と相分離しているので、成膜用溶剤を除去すると、微細な三次元網目構造を形成するフィブリルからなり、三次元的に不規則に連通する孔(空隙)を有する多孔質の膜が得られる。洗浄溶媒およびこれを用いた成膜用溶剤の除去方法は公知であるので説明を省略する。例えば日本国特許第2132327号公報や特開2002-256099号公報に開示の方法を利用することができる。
成膜用溶剤を除去した微多孔膜を、加熱乾燥法又は風乾法により乾燥する。乾燥温度はポリオレフィン樹脂の結晶分散温度(Tcd)以下であるのが好ましく、特にTcdより5℃以上低いのが好ましい。乾燥は、微多孔膜を100質量%(乾燥重量)として、残存洗浄溶媒が5質量%以下になるまで行うのが好ましく、3質量%以下になるまで行うのがより好ましい。
乾燥後の微多孔膜を、少なくとも一軸方向に延伸することが好ましい。微多孔膜の延伸は、加熱しながら前記と同様にテンター法等により行うことができる。延伸は一軸延伸でも二軸延伸でもよい。二軸延伸の場合、同時二軸延伸及び逐次延伸のいずれでもよい。
本工程における延伸温度は、特に限定されないが、通常90~135℃であり、より好ましくは95~130℃である。
また、乾燥後の微多孔膜は、熱処理を行うことができる。熱処理によって結晶が安定化し、ラメラが均一化される。熱処理方法としては、熱固定処理及び/又は熱緩和処理を用いることができる。熱固定処理とは、膜の寸法が変わらないように保持しながら加熱する熱処理である。熱緩和処理とは、膜を加熱中にMD方向やTD方向に熱収縮させる熱処理である。熱固定処理は、テンター方式又はロール方式により行うのが好ましい。例えば、熱緩和処理方法としては特開2002-256099号公報に開示の方法があげられる。熱処理温度はポリオレフィン樹脂のTcd~Tmの範囲内が好ましく、微多孔膜の延伸温度±5℃の範囲内がより好ましく、微多孔膜の第2の延伸温度±3℃の範囲内が特に好ましい。
また、接合後又は延伸後の微多孔膜に対して、さらに、架橋処理および親水化処理を行うこともできる。
例えば、微多孔膜に対して、α線、β線、γ線、電子線等の電離放射線の照射することに、架橋処理を行う。電子線の照射の場合、0.1~100Mradの電子線量が好ましく、100~300kVの加速電圧が好ましい。架橋処理により微多孔膜のメルトダウン温度が上昇する。
また、親水化処理は、モノマーグラフト、界面活性剤処理、コロナ放電等により行うことができる。モノマーグラフトは架橋処理後に行うのが好ましい。
上記したポリオレフィン微多孔膜の製造方法により得られたポリオレフィン微多孔膜の膜厚、空孔率、孔径、透気抵抗度などの物性は、特に制限されないが、以下の範囲に調整されることが好ましい。
本発明のポリオレフィン微多孔膜の空孔率の上限は、膜強度、耐電圧特性向上の観点から、60%以下であり、好ましくは50%以下である。また、リチウムイオン等のイオン透過性および電解液含有量の観点から、空孔率の下限は、20%以上であることが好ましく、より好ましくは30%以上である。空孔率を前記範囲内とすることにより、イオン透過性、膜強度および電界液含有量のバランスが好適となり、電池反応の不均一性が解消され、その結果、デンドライト発生が抑制される。また、膜構造の欠陥が少なくなることから耐電圧特性が向上する。すなわち、本発明のポリオレフィン微多孔膜を電池用セパレータとして用いたリチウムイオン二次電池には良好な安全性、強度、透過性が得られる。空孔率の測定方法は後述する。
本発明のポリオレフィン微多孔膜の平均孔径の上限は、膜強度、耐電圧特性向上の観点から、300nm以下であり、好ましくは100nm以下であり、さらに好ましくは50nm以下である。本発明のポリオレフィン微多孔膜の平均孔径の下限は特に限定されないが、後述する透気抵抗度の関係から1nm以上であることが好ましく、5nm以上であることがより好ましい。本発明のポリオレフィン微多孔膜の平均孔径が前記範囲であると、構造が緻密な膜となり、膜強度に優れ、高耐電圧特性な微多孔膜を得ることができる。
本発明のポリオレフィン微多孔膜の最大孔径の上限は、膜強度、耐電圧特性向上の観点から、500nm以下であり、好ましくは300nm以下であり、さらに好ましくは80nm以下である。本発明のポリオレフィン微多孔膜の最大孔径の下限は特に限定されないが、後述する透気抵抗度の関係から1nm以上であることが好ましく、5nm以上であることがより好ましい。本発明のポリオレフィン微多孔膜の最大孔径が前記範囲であると、構造が緻密な膜となり、膜強度に優れ、高耐電圧特性な微多孔膜を得ることができる。
平均流量孔径については、Dry-up測定で圧力、流量曲線の1/2の傾きを示す曲線と、Wet-up測定の曲線が交わる点の圧力から孔径を換算した。圧力と孔径の換算は下記の数式を用いた。
d=C・γ/P
(上記式中、「d(μm)」は微多孔膜の孔径、「γ(mN/m)」は液体の表面張力、「P(Pa)」は圧力、「C」は定数とした。
本実施態様において、イオン透過性の観点から、膜厚を20μmとしたときの透気抵抗度は100~1000sec/100ccであり、100~800sec/100ccであることが好ましく、100~600sec/100ccであることが特に好ましい。透気抵抗度が1000sec/100ccを超えると、イオン透過性が悪くなり、電気抵抗が増加するため好ましくない。一方、透気抵抗度が100sec/100cc未満の場合は、膜構造が過剰に疎になり、電池内部の温度が上昇した際、メルトダウンの前のシャットダウンが十分に行われなかったり、絶縁破壊電圧が低くなったりするため、好ましくない。
本発明のポリオレフィン微多孔膜は、絶縁破壊電圧が135V/μm以上であることが好ましく、150V/μm以上であることがより好ましく、164V/μm以上であることが特に好ましい。絶縁破壊電圧の上限は特に限定されないが、一般的にその上限は300V/μmを超えない程度と考えられる。ポリオレフィン微多孔膜の絶縁破壊電圧が上記範囲内であると、バッテリーセパレータとして使用した際、電池の耐久性、耐電圧性能が良好になることが期待できるからである。
ポリオレフィン微多孔膜の膜厚を20μmとしたときの突刺し強度は400gf以上であることが好ましく、550gf以上であることがより好ましい。このような範囲とすることで、薄膜化しても破膜することがなくなり、安全性が向上するからである。
本実施態様の微多孔膜の膜厚は、好ましくは1~2000μm、より好ましくは1~1000μmである。膜厚の測定方法は後述する。
また、前記ポリオレフィン微多孔膜の少なくとも一方の表面に、多孔層を設け、積層多孔膜としてもよい。多孔層としては、例えば、フィラーと樹脂バインダとを含むフィラー含有樹脂溶液や耐熱性樹脂溶液を用いて形成される多孔層を挙げることができる。
本発明のポリオレフィン微多孔膜の製造方法で得られたポリオレフィン微多孔膜は、水系電解液を使用する電池、非水系電解質を使用する電池のいずれにも好適に使用できる。具体的には、ニッケル-水素電池、ニッケル-カドミウム電池、ニッケル-亜鉛電池、銀-亜鉛電池、リチウム二次電池、リチウムポリマー二次電池等の二次電池のセパレータとして好ましく用いることができる。中でも、リチウムイオン二次電池のセパレータとして用いるのが好ましい。
なお、実施例で用いた評価法、分析の各法および材料は、以下の通りである。
微多孔膜の95mm×95mmの範囲内における5点の膜厚を接触厚み計(株式会社ミツトヨ製ライトマチック)により測定し、膜厚の平均値を求めた。
微多孔膜の重量w1とそれと等価な空孔のないポリマーの重量w2(幅、長さ、組成の同じポリマー)とを比較した、以下の式によって、空孔率を測定した。
空孔率(%)=(w2-w1)/w2×100
膜厚T1(μm)の微多孔膜に対して、JIS P 8117に準拠して、透気抵抗度計(旭精工株式会社製、EGO-1T)で測定した透気抵抗度P1(sec/100cm3)を、式:P2=(P1×20)/T1により、膜厚を20μmとしたときの透気抵抗度P2に換算した。
パームポロメーター(PMI社製、CFP-1500A)を用いて、Dry-up、Wet-upの順で、最大孔径及び平均流量孔径を測定した。Wet-upには表面張力が既知のPMI社製Galwick(商品名)で十分に浸した微多孔膜に圧力をかけ、空気が貫通し始める圧力から換算される孔径を最大孔径とした。
平均流量孔径については、Dry-up測定で圧力、流量曲線の1/2の傾きを示す曲線と、Wet-up測定の曲線が交わる点の圧力から孔径を換算した。圧力と孔径の換算は下記の数式を用いた。
d=C・γ/P
(上記式中、「d(μm)」は微多孔膜の孔径、「γ(mN/m)」は液体の表面張力、「P(Pa)」は圧力、「C」は定数とした。
先端が球面(曲率半径R:0.5mm)の直径1mmの針で、膜厚T1(μm)の微多孔膜を2mm/秒の速度で突刺したときの最大荷重を測定した。最大荷重の測定値L1(gf)を、式:L2=(L1×20)/T1により、膜厚を20μmとしたときの最大荷重L2に換算し、突刺し強度とした。
UHMWPE及びHDPEのMwは以下の条件でゲルパーミエーションクロマトグラフィー(GPC)法により求めた。
・測定装置:Waters Corporation製GPC-150C
・カラム:昭和電工株式会社製Shodex UT806M
・カラム温度:135℃
・溶媒(移動相):o-ジクロルベンゼン
・溶媒流速:1.0 ml/分
・試料濃度:0.1 wt%(溶解条件:135℃/1h)
・インジェクション量:500μl
・検出器:Waters Corporation製ディファレンシャルリフラクトメーター(RI検出器)
・検量線:単分散ポリスチレン標準試料を用いて得られた検量線から、所定の換算定数を用いて作成した。
JIS K6922-2に準拠して、190℃、2.16kg荷重の条件にて、測定した。
114℃~120℃における等温結晶化時の半結晶化時間t1/2は、以下の方法で測定した。ポリオレフィン樹脂組成物を測定パンに封入し、Parking Elmer製 PYRIS Diamond DSCを用いて、230℃まで昇温し、所定の温度まで30℃/minで降温させ、当該温度で保持した。当該温度での等温制御に入った後の熱量の時間変化を記録し、そのピーク面積が半分になる時間を各温度における等温結晶化時の半結晶化時間t1/2とした。なお、等温制御下60分経過してもピーク(極値)が認められなかった場合、観測不能として“NA”と表記した。
一辺150mmの正方形のアルミニウム板上に、直径60mmの円状に切り出した微多孔膜を置き、その上に真鍮製の直径50mm、高さ30mm、重さ500gの円柱電極を置いて、菊水電子工業製TOS5051A耐絶縁破壊特性試験器を接続した。0.2kV/秒の昇圧速度で電圧を加え、絶縁破壊したときの電圧を読み取った。絶縁破壊電圧の測定はそれぞれ15回行い、平均値を得た。
重量平均分子量(Mw)が2.8×105の高密度ポリエチレン(HDPE)100質量部からなるポリエチレン(PE)組成物100質量部にテトラキス[メチレン-3-(3,5-ジ-ターシャリーブチル-4-ヒドロキシフェニル)-プロピオネート]メタン0.375質量部、マスターバッチ リケマスターCN-002(理研ビタミン製)3質量部をドライブレンドし、混合物を得た。
マスターバッチ リケマスターCN-002(理研ビタミン製)に替えて、ソルビトール系結晶造核剤 ゲルオールD(新日本理化製)3質量部を使用した以外は実施例1と同様にして、ポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表1に示した。
マスターバッチ リケマスターCN-002(理研ビタミン製)を配合しなかった以外は、実施例1と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表1に示した。
マスターバッチ リケマスターCN-002(理研ビタミン製)に替えて、ステアリン酸カルシウム3質量部を使用した以外は実施例1と同様にして、ポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表1に示した。
重量平均分子量(Mw)が1.0×106の超高分子量ポリエチレン(UHMWPE)30質量部と、Mwが2.8×105の高密度ポリエチレン(HDPE)70質量部からなるポリエチレン(PE)組成物100質量部を使用した以外は、実施例1と同様にして、ポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
マスターバッチ リケマスターCN-002(理研ビタミン製)を配合しなかった以外は、実施例3と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表2に示した。
重量平均分子量(Mw)が1.0×106の超高分子量ポリエチレン(UHMWPE)40質量部と、Mwが2.8×105の高密度ポリエチレン(HDPE)60質量部からなるポリエチレン(PE)組成物100質量部を使用した以外は、実施例1と同様にして、ポリオレフィン微多孔膜を得た。 得られた微多孔膜の特性を表3に示した。
マスターバッチ リケマスターCN-002(理研ビタミン製)を配合しなかった以外は、実施例4と同様にしてポリオレフィン微多孔膜を得た。得られた微多孔膜の特性を表3に示した。
Claims (7)
- ポリオレフィン樹脂、結晶造核剤および成膜用溶剤を含み、117℃等温結晶化時の半結晶化時間t1/2が8.0分以下であることを特徴とするポリオレフィン樹脂組成物。
- ポリオレフィン樹脂の90質量%以上がポリエチレン樹脂であることを特徴とする請求項1に記載のポリオレフィン樹脂組成物。
- 成膜用溶剤がノナン、デカン、デカリン、およびパラフィン油等の脂肪族または環状炭化水素、ならびにフタル酸ジブチルおよびフタル酸ジオクチル等のフタル酸エステルから選ばれる少なくとも一つであることを特徴とする請求項1または請求項2に記載のポリオレフィン樹脂組成物。
- ポリオレフィン樹脂、結晶造核剤および成膜用溶剤を溶融混練してポリオレフィン樹脂組成物を調製することを特徴とする、請求項1~3のいずれか1項に記載のポリオレフィン樹脂組成物の製造方法。
- 下記工程を含むことを特徴とする、ポリオレフィン微多孔膜の製造方法。
(1)ポリオレフィン樹脂、結晶造核剤および成膜用溶剤を溶融混練して117℃等温結晶化時の半結晶化時間t1/2が8.0分以下であるポリオレフィン樹脂組成物を調製する工程
(2)前記ポリオレフィン樹脂組成物を押出し、冷却しゲル状シートを形成する工程
(3)前記ゲル状シートを延伸する第1の延伸工程
(4)前記延伸後のゲル状シートから成膜用溶剤を除去する工程
(5)前記成膜用溶剤除去後のシートを乾燥する工程 - ポリオレフィン微多孔膜の20μm換算の透気抵抗度が100~500秒/100ccであり、空孔率が10%~60%であり、平均孔径が100μm以下であることを特徴とする請求項5に記載のポリオレフィン微多孔膜の製造方法。
- ポリオレフィン微多孔膜の絶縁破壊電圧が163V/μm以上であることを特徴とする請求項5または請求項6に記載のポリオレフィン微多孔膜の製造方法。
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US11976177B2 (en) | 2020-07-01 | 2024-05-07 | Celanese International Corporation | Polymer composition and membranes made therefrom with improved mechanical strength |
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