JP4074116B2 - Method for producing microporous membrane - Google Patents
Method for producing microporous membraneInfo
- Publication number
- JP4074116B2 JP4074116B2 JP2002095002A JP2002095002A JP4074116B2 JP 4074116 B2 JP4074116 B2 JP 4074116B2 JP 2002095002 A JP2002095002 A JP 2002095002A JP 2002095002 A JP2002095002 A JP 2002095002A JP 4074116 B2 JP4074116 B2 JP 4074116B2
- Authority
- JP
- Japan
- Prior art keywords
- microporous membrane
- weight
- polyolefin
- less
- producing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000012982 microporous membrane Substances 0.000 title claims description 59
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 229920000098 polyolefin Polymers 0.000 claims description 48
- 239000002245 particle Substances 0.000 claims description 46
- 239000002904 solvent Substances 0.000 claims description 27
- 239000000203 mixture Substances 0.000 claims description 15
- 239000010954 inorganic particle Substances 0.000 claims description 12
- 229920001903 high density polyethylene Polymers 0.000 claims description 11
- 239000004700 high-density polyethylene Substances 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 11
- -1 dioctyl ester Chemical class 0.000 claims description 9
- 229940057995 liquid paraffin Drugs 0.000 claims description 9
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 7
- 229910001416 lithium ion Inorganic materials 0.000 claims description 7
- 239000000155 melt Substances 0.000 claims description 6
- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 claims description 3
- 238000000638 solvent extraction Methods 0.000 claims description 3
- 238000000465 moulding Methods 0.000 claims description 2
- WNLRTRBMVRJNCN-UHFFFAOYSA-N adipic acid Chemical compound OC(=O)CCCCC(O)=O WNLRTRBMVRJNCN-UHFFFAOYSA-N 0.000 claims 2
- MQIUGAXCHLFZKX-UHFFFAOYSA-N Di-n-octyl phthalate Natural products CCCCCCCCOC(=O)C1=CC=CC=C1C(=O)OCCCCCCCC MQIUGAXCHLFZKX-UHFFFAOYSA-N 0.000 claims 1
- 235000011037 adipic acid Nutrition 0.000 claims 1
- 239000001361 adipic acid Substances 0.000 claims 1
- 229910010272 inorganic material Inorganic materials 0.000 claims 1
- 239000011147 inorganic material Substances 0.000 claims 1
- 239000000843 powder Substances 0.000 description 20
- 238000000034 method Methods 0.000 description 13
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 12
- 239000012528 membrane Substances 0.000 description 12
- 239000011888 foil Substances 0.000 description 10
- 230000035699 permeability Effects 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- 238000004898 kneading Methods 0.000 description 7
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 6
- 239000004698 Polyethylene Substances 0.000 description 6
- 235000014113 dietary fatty acids Nutrition 0.000 description 6
- 239000000194 fatty acid Substances 0.000 description 6
- 229930195729 fatty acid Natural products 0.000 description 6
- 150000004665 fatty acids Chemical class 0.000 description 6
- 229920000573 polyethylene Polymers 0.000 description 6
- 239000011521 glass Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 3
- 239000005977 Ethylene Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 3
- 229910052814 silicon oxide Inorganic materials 0.000 description 3
- VXNZUUAINFGPBY-UHFFFAOYSA-N 1-Butene Chemical compound CCC=C VXNZUUAINFGPBY-UHFFFAOYSA-N 0.000 description 2
- LIKMAJRDDDTEIG-UHFFFAOYSA-N 1-hexene Chemical compound CCCCC=C LIKMAJRDDDTEIG-UHFFFAOYSA-N 0.000 description 2
- WSSSPWUEQFSQQG-UHFFFAOYSA-N 4-methyl-1-pentene Chemical compound CC(C)CC=C WSSSPWUEQFSQQG-UHFFFAOYSA-N 0.000 description 2
- NEHDRDVHPTWWFG-UHFFFAOYSA-N Dioctyl hexanedioate Chemical compound CCCCCCCCOC(=O)CCCCC(=O)OCCCCCCCC NEHDRDVHPTWWFG-UHFFFAOYSA-N 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 239000004809 Teflon Substances 0.000 description 2
- 229920006362 Teflon® Polymers 0.000 description 2
- 150000001336 alkenes Chemical class 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- NNBZCPXTIHJBJL-UHFFFAOYSA-N decalin Chemical compound C1CCCC2CCCCC21 NNBZCPXTIHJBJL-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229920001519 homopolymer Polymers 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000002480 mineral oil Substances 0.000 description 2
- 235000010446 mineral oil Nutrition 0.000 description 2
- 229920005672 polyolefin resin Polymers 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 2
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000004438 BET method Methods 0.000 description 1
- DPUOLQHDNGRHBS-UHFFFAOYSA-N Brassidinsaeure Natural products CCCCCCCCC=CCCCCCCCCCCCC(O)=O DPUOLQHDNGRHBS-UHFFFAOYSA-N 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- URXZXNYJPAJJOQ-UHFFFAOYSA-N Erucic acid Natural products CCCCCCC=CCCCCCCCCCCCC(O)=O URXZXNYJPAJJOQ-UHFFFAOYSA-N 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- 235000021355 Stearic acid Nutrition 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 239000012615 aggregate Substances 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 125000000217 alkyl group Chemical group 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- CJZGTCYPCWQAJB-UHFFFAOYSA-L calcium stearate Chemical compound [Ca+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O CJZGTCYPCWQAJB-UHFFFAOYSA-L 0.000 description 1
- 239000008116 calcium stearate Substances 0.000 description 1
- 235000013539 calcium stearate Nutrition 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- NJLLQSBAHIKGKF-UHFFFAOYSA-N dipotassium dioxido(oxo)titanium Chemical compound [K+].[K+].[O-][Ti]([O-])=O NJLLQSBAHIKGKF-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- UAUDZVJPLUQNMU-KTKRTIGZSA-N erucamide Chemical compound CCCCCCCC\C=C/CCCCCCCCCCCC(N)=O UAUDZVJPLUQNMU-KTKRTIGZSA-N 0.000 description 1
- DPUOLQHDNGRHBS-KTKRTIGZSA-N erucic acid Chemical compound CCCCCCCC\C=C/CCCCCCCCCCCC(O)=O DPUOLQHDNGRHBS-KTKRTIGZSA-N 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 150000002576 ketones Chemical class 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
- 239000011976 maleic acid Substances 0.000 description 1
- 239000002667 nucleating agent Substances 0.000 description 1
- LYRFLYHAGKPMFH-UHFFFAOYSA-N octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(N)=O LYRFLYHAGKPMFH-UHFFFAOYSA-N 0.000 description 1
- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 description 1
- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 description 1
- 150000007524 organic acids Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 229920001955 polyphenylene ether Polymers 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000008117 stearic acid Substances 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
- PXXNTAGJWPJAGM-UHFFFAOYSA-N vertaline Natural products C1C2C=3C=C(OC)C(OC)=CC=3OC(C=C3)=CC=C3CCC(=O)OC1CC1N2CCCC1 PXXNTAGJWPJAGM-UHFFFAOYSA-N 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- XOOUIPVCVHRTMJ-UHFFFAOYSA-L zinc stearate Chemical compound [Zn+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O XOOUIPVCVHRTMJ-UHFFFAOYSA-L 0.000 description 1
Images
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Cell Separators (AREA)
- Secondary Cells (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は微多孔膜に関するものであり、特にリチウムイオン二次電池等の電池用セパレータとして好適に用いられる微多孔膜に関する。
【０００２】
【従来の技術】
近年、携帯電話や携帯情報端末やノート型パーソナルコンピューターなどの機器の電池として、軽量で高エネルギーが得られるリチウムイオン二次電池が広汎に用いられている。このリチウムイオン二次電池の正極と負極の間に、正負極間の短絡を防止すると同時にリチウムイオンが透過するセパレータが設けられているが、このセパレータとしてはポリオレフィンからなる微多孔膜が使用されている。ポリオレフィンからなる微多孔膜は低い温度で微多孔が閉塞するという特性を有しており、過充電などの原因によって電池の温度が上昇した場合に、電池内部の電流をより低い温度で遮断できる特徴を有するが、微多孔膜の微多孔が閉塞したあとも電池の温度が上昇した場合には、破膜して正負極間が短絡しやすい傾向がある。
【０００３】
ポリオレフィンからなる微多孔膜の高温での耐短絡性を向上させる方法として、無機粉体を含有するポリオレフィンからなる微多孔膜が提案されている。
たとえば、特開平１０−５０２８７号公報では、ポリオレフィン系樹脂に無機粉体として酸化チタン、酸化アルミニウム、チタン酸カリウム等を２０重量％〜８０重量％含有させたポリオレフィン系樹脂のセパレータが提案されている。
特開平１０−５０２８７号公報の実施例には、平均粒径が２ｎｍのアルミナ粉体３０重量部と高密度ポリエチレン１５重量部と鉱物オイル５５重量部とを混合した膜から鉱物オイルを抽出除去して得られるアルミナ粉体を６７重量％含有する微多孔膜が開示されている。
【０００４】
このように無機粉体を大量に含有する微多孔膜は、これを製造するときに、無機粉体とポリエチレンと溶媒を混練する工程で無機粉体同士が凝集してしまい凝集物が生成しやすくなる傾向がみられる。大量に添加された無機粉体の凝集物を防止するには、無機粉体とポリエチレンと溶媒の混練時間を長くとるなどの対応策が必要となりやすい。
また、アルミナなどの無機粉体は密度が高密度ポリエチレンの２倍以上と重いために、無機粉体を大量に添加したポリオレフィン微多孔膜の重量は、ポリオレフィン単体からなる微多孔膜の重量と比べて大きくなる。このため取り扱いや運搬を行う時の負荷が大きくなり、生産や輸送が煩雑となりやすい。
【０００５】
【発明が解決しようとする課題】
本発明は、破膜温度が高い微多孔膜であって、含有する無機粉体の量が少ない微多孔膜を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者は、前記課題を解決するため鋭意研究を行った結果、平均粒子径が１００ｎｍ以下である粒子を１重量％以上２０重量％未満含有するポリエチレンをポリエチレンの溶媒と混合したあと溶媒を抽出して多孔化した微多孔膜が、充填材粒子が少量であっても破膜温度が高く耐短絡性に優れる微多孔膜となることを見出し本発明をなすに至った。
即ち、本発明は下記の通りである。
１．平均粒子径が１００ｎｍ以下である無機物粒子を１重量％以上２０重量％未満含有するポリオレフィンからなる微多孔膜の製造方法であって、ポリオレフィンと無機物粒子の混合物１００重量％に対して、平均粒子径が１００ｎｍ以下である無機物粒子を１重量％以上２０重量％未満の割合で混合したものを、流動パラフィン、フタル酸ジオクチルエステルまたはアジピン酸ジオクチルエステルの単独、あるいはこれらの組み合わせからなる溶媒と混合して成形物を成形した後、溶媒の抽出工程前に延伸を行い、ポリオレフィンと無機物粒子の混合物１００重量％に対して、ポリオレフィン中の無機物粒子が１重量％以上２０重量％未満となるように溶媒を抽出することにより多孔化することを特徴とする微多孔膜の製造方法。
２．延伸が同時二軸延伸であることを特徴とする１．に記載の微多孔膜の製造方法。
３．ポリオレフィンがメルトフローレート１ｇ／１０分以下の高密度ポリエチレンであることを特徴とする１．に記載の微多孔膜の製造方法。
４．微多孔膜の膜厚が１０〜３０μｍであることを特徴とする１．に記載の微多孔膜の製造方法。
５．微多孔膜がリチウムイオン二次電池用セパレータである１．〜４．のいずれかに記載の微多孔膜の製造方法、
である。
本願発明によって得られる膜は、平均粒子径が１００ｎｍ以下である粒子を１重量％以上２０重量％未満含有するポリオレフィンからなる微多孔膜である。
【０００７】
【発明の実施の形態】
本発明の好ましい態様について、以下具体的に説明する。
本発明に用いる粒子は、平均粒子径が１００ｎｍ以下である粒子であり、平均粒子径が１００ｎｍ以下である無機物粒子を用いることが好ましい。さらに、無機物粒子は絶縁性であることが望ましい。さらには、粒子の表面をアルキル基で疎水化処理を行った酸化珪素やアルミナの粒子を用いることがより好ましい。粒子はポリオレフィン中で凝集していないことがさらに好ましい。粒子径の下限は好ましくは１ｎｍ以上、さらに好ましくは３ｎｍ以上である。微多孔膜中の粒子の濃度が従来技術より少ない濃度であるにもかかわらず、本発明の微多孔膜の破膜温度が高いのは、確認されたわけではないが、ポリオレフィン分子の広がりに近い大きさの粒子がポリオレフィン分子の間に分散し、ポリオレフィン分子の動きを抑制しているためと考えられる。
【０００８】
平均粒子径が１００ｎｍを越えると、無機物粒子を添加したポリオレフィン系微多孔膜の強度が小さくなりやすい。また、平均粒子径が１００ｎｍを越える粒子をポリオレフィンに混合したあと延伸して多孔化すると、孔径が大きくなり過ぎ、電池セパレータとして使用する場合には、不適なものとなりやすい。
本発明の平均粒子径とは、一般に比表面積測定法と呼ばれる平均粒子径測定法によって求められる平均粒子径の値であって、一般にＢＥＴ法とよばれている気体吸着法により測定された粒子の比表面積（Ｓ）と粒子の密度（ρ）を用いて、計算式６／（Ｓρ）により求められる平均粒子径の値のことである。微多孔膜中の粒子径を測定するための方法は、例えば、ポリオレフィンを溶解するが粒子を溶解しない溶媒を用いてポリオレフィンを溶解する事によって粒子を分離して取り出し上記の方法で測定することにより確認することができる。ポリエチレンが主体の場合は、熱溶媒としては、１３０℃〜１４０℃のデカリンを用いることが好ましい。
【０００９】
微多孔膜中に含有される粒子の割合は、微多孔膜総量に対して１重量％以上２０重量％未満であることが好ましく、更には１重量％以上１５重量％以下であることがより好ましい。粒子の含有割合が１重量％を下回る微多孔膜の場合は、粒子を含まない微多孔膜と比べて破膜温度の上昇効果が得られにくく、一方、粒子の含有割合が２０重量％以上の微多孔膜の場合は、微多孔膜の強度が小さくなったり、微多孔膜中に粒子の凝集物が生成しやすくなる。
【００１０】
本発明においてポリオレフィンとは、エチレンやプロピレンなどのオレフィンの単独重合体及びこれらのブレンド物、エチレンとプロピレン、1−ブテン、４−メチル−１−ペンテン、１−ヘキセンなどのオレフィンとの共重合体及びこれらの共重合体とエチレン単独重合体とのブレンド物、ポリオレフィンとポリアミドや変性ポリフェニレンエーテルなどとのブレンド物などをいう。
ポリオレフィン微多孔膜の強度を確保する観点から、これらのポリオレフィンの中から、ＪＩＳのＫ７２１０に記載された方法で測定したメルトフローレートが２ｇ／１０分以下のポリオレフィンを用いることが好ましく、より好ましくはメルトフローレートが１ｇ／１０分以下のポリオレフィン、更に好ましくはメルトフローレートが１ｇ／１０分以下の高密度ポリエチレンを用いることである。
【００１１】
本発明のポリオレフィン微多孔膜には、ポリオレフィンに粒子を均一に分散させるために、ステアリン酸やエルカ酸などの脂肪酸、ステアリン酸アミドやエルカ酸アミドなどの脂肪酸アミド化合物、ステアリン酸カルシウムやステアリン酸亜鉛などの脂肪酸金属塩、マレイン酸などの有機酸とポリオレフィンを反応させた酸変性ポリオレフィンなどを添加してもよい。
脂肪酸や脂肪酸アミド化合物や脂肪酸金属塩を用いる場合は、ポリオレフィンに対する添加割合は０．０５〜５重量％、好ましくは０．１〜４重量％である。酸変性ポリオレフィンを用いる場合は、ポリオレフィンに対する添加割合は５〜３０重量％、好ましくは５〜２０重量％である。
【００１２】
本発明で用いるポリオレフィンには、必要に応じて酸化防止剤、造核剤などの各種添加剤を添加してもよい。
本発明の微多孔膜は、厚みは電池用セパレータとしての強度を確保する点から５〜１００μｍが好ましく更には１０〜３０μｍがより好ましく、気孔率は電池用セパレータとしての強度確保や電池内部での短絡の防止や適度な電気抵抗を確保するなどの点から３０〜６０％であることが好ましく更には３５〜５０％がより好ましく、透気度は電池の性能確保の点から５０から１０００秒／１００ｃｃであることが好ましく更には７０〜６００秒／１００ｃｃがより好ましい。
【００１３】
微多孔膜の破膜温度は、高温で短絡して電気抵抗が低下する温度が１６０℃以上であることが好ましく、更には１７０℃以上がより好ましい。
本発明の微多孔膜は、平均粒径が１００ｎｍ以下である粒子を１重量％以上２０重量％未満の割合でポリオレフィンに混合したものを、ポリオレフィンの溶媒と溶融混練し、得られた溶液を冷却して固化させたあと溶媒を抽出して多孔化構造とする方法により製造することができる。
本発明で用いる溶媒は、ポリオレフィンと混合して加熱した場合に、均一な溶液を形成する溶媒であって、たとえば流動パラフィンやフタル酸ジオクチルエステルやアジピン酸ジオクチルエステルなどの溶媒を単独あるいは組み合わせて用いることができる。
【００１４】
ポリオレフィンと粒子と溶媒が溶融混練された溶液は、ニーダ−や二軸押出機などの混合装置を用いて、ポリオレフィンと粒子と溶媒をポリオレフィンの融点以上の温度に加熱して混練することにより製造することができる。溶液総量に対する溶媒の割合は、混合装置を用いた混練過程のトルクを軽減する観点や溶媒を抽出したあとの微多孔膜の気孔率を適度な値にする観点から２０重量％〜７０重量％であることが好ましく、更には３５重量％〜６５重量％であることがより好ましい。
【００１５】
ポリオレフィンと粒子と溶媒を加熱混練して得られた溶液を冷却してシート状や管状に成形することができる。たとえば、加熱混練した溶液を冷却した金属板に挟み込んで急冷してシート状に成形したり、シート成形ダイを先端に取り付けた押出機を用いて加熱混練した溶液をシート成形ダイから押出したものを冷却ロールで引き取ってシート状に成形したり、管状ダイを先端に取り付けた押出機を用いて溶液を押出して管状に成形することができる。
シート状あるいは管状に成形されたポリオレフィンと粒子と溶媒の混合物から溶媒を抽出することにより多孔構造を有する成形物を得ることができる。溶媒の抽出は、溶媒と相溶性であってポリオレフィンを溶解しない溶剤で成形物を洗浄するなどの方法で行うことができる。抽出溶剤としては、ヘキサンなどの低沸点炭化水素やメチルエチルケトンなどのケトンやハイドロフロロエーテルやハイドロフロロカーボンなどの非塩素含有フッ素系有機溶剤などの溶剤を用いることができる。
【００１６】
なお、本発明においては、溶媒抽出工程の前後のいずれか、或いは両方で成形物の延伸を行うことができる。シート状成形物の場合は、ロール延伸機やテンターなどを用いる一軸延伸あるいは同時二軸テンターを用いる同時二軸延伸あるいはロール延伸機とテンターを組み合わせた逐次二軸延伸を単独で或いは組み合わせて、シート状成形物の延伸を行うことができる。管状成形物の場合は、管状成形物の内部に圧縮空気を封入してチューブ状に延伸する方法で行うことができ、またチューブ状の延伸とシート状の延伸を組み合わせて行ってもよい。
【００１７】
本発明を実施例に基づいて説明する。
実施例における微多孔膜の物性の評価方法は次の通りである。
（ａ）厚み
尾崎製作所製ダイアルゲージＰＥＡＣＯＫ Ｎｏ．２５を用いて測定した。
（ｂ）気孔率
厚みと面積からサンプルの体積を求め、質量を測定して、次の式を用いて気孔率を求めた。
気孔率（％）＝（１−（質量／混合組成物の密度）／体積）×１００
なお、混合組成物の密度は、用いたポリオレフィンと粒子の各々の密度と混合割合とから計算で求められる値を用いた。
（ｃ）突刺強度
カトーテック製圧縮試験機ＫＥＳ−Ｇ５に、先端の曲率半径が０．５ｍｍの針をとりつけ、突刺速度２ｍｍ／秒で突刺試験を行い、最大突刺荷重を突刺強度（Ｎ）とした。
【００１８】
（ｄ）透気度
ＪＩＳ Ｐ−８１１７に準拠したガーレー式透気度計を用いて測定した。
（ｅ）孔閉塞温度及び破膜温度
図１（Ａ）〜（Ｃ）に孔閉塞温度及び破膜温度の測定装置の概略図を示す。図１（Ａ）は測定装置の構成図である。１は微多孔膜であり、２Ａ及び２Ｂは厚さ１０μのＮｉ箔、３Ａ及び３Ｂはガラス板である。４は電気抵抗測定装置（安藤電気ＬＣＲメーター ＡＧ４３１１）であり、Ｎｉ箔（２Ａ、２Ｂ）と接続されている。５は熱電対であり温度計６と接続されている。７はデーターコレクターであり、電気抵抗測定装置４及び温度計６と接続されている。８はオーブンであり、微多孔膜を加熱する。
【００１９】
さらに詳細に説明すると、微多孔膜１には規定の電解液が含浸されており、図１（Ｂ）に示すようにＮｉ箔２Ａ上にＭＤのみテフロン（登録商標）テープ（斜線部分）で止められた形で固定されている。Ｎｉ箔２Ｂは図１（Ｃ）に示すように１５ｍｍ×１０ｍｍの部分を残してテフロン（登録商標）テープ（斜線部分）でマスキングされている。Ｎｉ箔２ＡとＮｉ箔２Ｂを微多孔膜１を挟むような形で重ね合わせ、さらにその両側からガラス板３Ａ、３Ｂによって２枚のＮｉ箔を挟み込む。２枚のガラス板は市販のクリップではさむことにより固定する。図１（Ａ）に示した装置を用い、連続的に温度と電気抵抗を測定する。なお、温度は２℃／ｍｉｎの速度にて昇温させ、電気抵抗値は１ｋＨｚの交流にて測定する。孔閉塞温度とは微多孔膜１の電気抵抗値が１０3Ωに達する時の温度と定義する。破膜温度とは更に温度を昇温させたときに微多孔膜１の電気抵抗値が低下して再び１０3Ω以下に達する時の温度と定義する。
【００２０】
なお、規定の電解液組成とは下記の通りである。
溶媒：炭酸プロピレン／炭酸エチレン／ブチルラクトン＝１／１／２ 体積％溶質：上記溶媒にてホウフッ化リチウムを１ｍｏｌ／リットルの濃度になるように溶かした。
【００２１】
【実施例１】
メルトフローレートが０．０８ｇ／分、密度が０．９６ｇ／ｃｍ3の高密度ポリエチレンを９５重量％、平均粒子径が３０ｎｍであるアルミナ粉体を５重量％の割合で混合し、この混合物４０重量部を流動パラフィン６０重量部と東洋精機製作所製プラストミルＣ型を用いて加熱混合した。加熱混合は、プラストミルの温度を２００℃、回転数を５０ｒｐｍに設定して１０分間行った。溶融した混合物をプラストミルから取り出して冷却し、得られた固化物を２枚の金属板の間に挟んで、温度を２００℃に設定した熱プレス機を用いて圧力１０ＭＰａで圧縮し、厚さ１ｍｍのシートを作成した。
得られたシートを二軸延伸機（岩本製作所製）を用いて、温度１１５℃で縦方向に７倍、横方向に７倍延伸したあと、メチルエチルケトンの中に２４時間浸漬して流動パラフィンを除去したあと常温常圧で２４時間乾燥した。
乾燥して得られた微多孔膜は、厚みが２０μｍ、気孔率が４９％、透気度が３５０秒／１００ｃｃ、突刺強度が５．１Ｎ、破膜温度が１９０℃であった。
【００２２】
【実施例２】
実施例１のアルミナ粉体の混合割合を１５重量％に、高密度ポリエチレンの混合割合を８５重量％に変えたことのほかは実施例１と同じ条件で微多孔膜を作成した。
得られた微多孔膜は、厚みが２１μｍ、気孔率が５０％、透気度が３２０秒、突刺強度が４．９Ｎ、破膜温度が１９０℃であった。
【００２３】
【実施例３】
実施例１のアルミナ粉体を平均粒子径が７ｎｍである酸化珪素粒子に変えて、酸化珪素の混合割合を１５重量％、高密度ポリエチレンの混合割合を８５重量％の割合で混合したものを、実施例１と同じ条件で流動パラフィンと溶融混合した。溶融混合した混合物から実施例１と同じ条件でシートを作成し、延伸したあと流動パラフィンを抽出除去して微多孔膜を作成した。
得られた微多孔膜は、厚みが１９μｍ、気孔率が４９％、透気度が２６０秒、突刺強度が３．９Ｎ、破膜温度が１９０℃であった。
【００２４】
【比較例１】
実施例１で用いた高密度ポリエチレン４０重量部と流動パラフィン６０重量部を、実施例１と同じく温度２００℃、回転数５０ｒｐｍに設定したプラストミルを用いて１０分間混練し、実施例１と同じ方法で流動パラフィンを抽出して微多孔膜を作成した。
得られた微多孔膜は、厚みが２５μｍ、気孔率が４４％、透気度が４１０秒、突刺強度が５．６Ｎ、破膜温度が１５０℃であった。
【００２５】
【比較例２】
実施例１のアルミナ粉末の混合割合を０．５重量％に減らし、アルミナ粉末の減少分だけ高密度ポリエチレンをふやしたことのほかは実施例１と同じ条件で微多孔膜を作成した。
得られた微多孔膜は、厚みが２５μｍ、気孔率が４４％、透気度が４００秒、突刺強度が５．７Ｎ、破膜温度が１５０℃であった。
【００２６】
【比較例３】
実施例１のアルミナ粉末の混合割合を３０重量％に増やし、アルミナ粉末の増加分だけ高密度ポリエチレンを減らしたことのほかは実施例１と同じ条件で微多孔膜を作成することを試みた。
得られた微多孔膜には、アルミナの凝集物が多数見られ、延伸過程で破膜してしまった。
【００２７】
【発明の効果】
本発明の微多孔膜は、無機粉体の含有量が小さく、かつ破膜温度が高いポリエチレン微多孔膜であって、特にリチウムイオン二次電池に用いるセパレータとして極めて有用な微多孔膜である。
【図面の簡単な説明】
【図１】孔閉塞温度を測定する装置の構成を示す全体概略図であり、（Ａ）は孔閉塞温度を測定する装置、（Ｂ）は（Ａ）のＮｉ箔（２Ａ）面での断面図、（Ｃ）は（Ａ）のＮｉ箔（２Ｂ）面での断面図である。
【符号の説明】
１ ：微多孔膜
２Ａ、２Ｂ：Ｎｉ箔
３Ａ、３Ｂ：ガラス板
４ ：電気抵抗測定装置
５ ：熱電対
６ ：温度計
７ ：データーコレクター
８ ：オーブン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microporous membrane, and more particularly to a microporous membrane suitably used as a battery separator such as a lithium ion secondary battery.
[0002]
[Prior art]
In recent years, lithium ion secondary batteries that are lightweight and obtain high energy have been widely used as batteries for devices such as mobile phones, personal digital assistants, and notebook personal computers. Between the positive electrode and the negative electrode of this lithium ion secondary battery, a separator that prevents lithium short circuit between positive and negative electrodes and at the same time transmits lithium ions is provided. As this separator, a microporous film made of polyolefin is used. Yes. The microporous membrane made of polyolefin has the property that the micropores close at a low temperature, and when the temperature of the battery rises due to overcharge, etc., the current inside the battery can be cut off at a lower temperature However, when the temperature of the battery rises even after the micropores of the microporous membrane are blocked, the membrane tends to break and the positive and negative electrodes are likely to be short-circuited.
[0003]
As a method for improving the short circuit resistance at high temperatures of a microporous membrane made of polyolefin, a microporous membrane made of polyolefin containing inorganic powder has been proposed.
For example, Japanese Patent Laid-Open No. 10-50287 proposes a polyolefin resin separator in which 20 wt% to 80 wt% of titanium oxide, aluminum oxide, potassium titanate or the like is contained as an inorganic powder in a polyolefin resin. .
In an example of Japanese Patent Application Laid-Open No. 10-50287, mineral oil is extracted and removed from a film in which 30 parts by weight of alumina powder having an average particle diameter of 2 nm, 15 parts by weight of high-density polyethylene, and 55 parts by weight of mineral oil are mixed. A microporous membrane containing 67% by weight of alumina powder obtained in this manner is disclosed.
[0004]
As described above, when a microporous membrane containing a large amount of inorganic powder is produced, the inorganic powder is agglomerated in the process of kneading the inorganic powder, polyethylene and solvent, and aggregates are easily generated. There is a tendency to become. In order to prevent agglomeration of inorganic powder added in a large amount, measures such as increasing the kneading time of the inorganic powder, polyethylene and solvent are likely to be required.
In addition, since inorganic powders such as alumina are twice as heavy as high-density polyethylene, the weight of the polyolefin microporous membrane to which a large amount of inorganic powder is added is compared to the weight of the microporous membrane made of a single polyolefin. Become bigger. For this reason, the load at the time of handling and conveyance becomes large, and production and transportation tend to be complicated.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a microporous membrane having a high membrane breaking temperature and containing a small amount of inorganic powder.
[0006]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, the present inventor mixed polyethylene containing 1 wt% or more and less than 20 wt% of particles having an average particle diameter of 100 nm or less with a polyethylene solvent and then extracted the solvent. Thus, the present inventors have found that the porous microporous film becomes a microporous film having a high film breaking temperature and excellent short-circuit resistance even when the amount of filler particles is small.
That is, the present invention is as follows.
1. A method for producing a microporous membrane comprising a polyolefin containing 1% by weight or more and less than 20% by weight of inorganic particles having an average particle size of 100 nm or less, wherein the average particle size is 100 % by weight with respect to 100% by weight of a mixture of polyolefin and inorganic particles. A mixture of inorganic particles having a particle size of not more than 100% and less than 20% by weight mixed with a liquid paraffin, phthalic acid dioctyl ester or adipic acid dioctyl ester alone or a combination thereof. After molding the molded product, stretching is performed before the solvent extraction step, and the solvent is added so that the inorganic particles in the polyolefin are 1 wt% or more and less than 20 wt% with respect to 100 wt% of the mixture of polyolefin and inorganic particles. A method for producing a microporous membrane, which is made porous by extraction.
2. 1. Stretching is simultaneous biaxial stretching. The manufacturing method of the microporous film as described in 1 ..
3. 1. The polyolefin is a high-density polyethylene having a melt flow rate of 1 g / 10 min or less. The manufacturing method of the microporous film as described in 1 ..
4). 1. The microporous membrane has a thickness of 10 to 30 μm. The manufacturing method of the microporous film as described in 1 ..
5. 1. A microporous membrane is a separator for a lithium ion secondary battery. ~ 4. A method for producing a microporous membrane according to any one of
It is.
The film obtained by the present invention is a microporous film made of polyolefin containing 1% by weight or more and less than 20% by weight of particles having an average particle diameter of 100 nm or less.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be specifically described below.
The particles used in the present invention are particles having an average particle diameter of 100 nm or less, and inorganic particles having an average particle diameter of 100 nm or less are preferably used. Furthermore, the inorganic particles are desirably insulative. Furthermore, it is more preferable to use particles of silicon oxide or alumina whose surface has been subjected to a hydrophobic treatment with an alkyl group. More preferably, the particles are not agglomerated in the polyolefin. The lower limit of the particle diameter is preferably 1 nm or more, more preferably 3 nm or more. Although the concentration of particles in the microporous membrane is lower than that of the prior art, the membrane breaking temperature of the microporous membrane of the present invention is not confirmed to be high, but it is close to the extent of the polyolefin molecule spread. This is probably because the particles are dispersed between the polyolefin molecules to suppress the movement of the polyolefin molecules.
[0008]
When the average particle diameter exceeds 100 nm, the strength of the polyolefin microporous film to which inorganic particles are added tends to be small. Moreover, when particles having an average particle diameter exceeding 100 nm are mixed with polyolefin and then stretched to make porous, the pore diameter becomes too large, and it tends to be unsuitable when used as a battery separator.
The average particle size of the present invention is a value of an average particle size generally determined by an average particle size measuring method called a specific surface area measuring method, and is generally measured by a gas adsorption method called a BET method. Using the specific surface area (S) and the particle density (ρ), it is the value of the average particle diameter determined by the
[0009]
The proportion of the particles contained in the microporous membrane is preferably 1% by weight or more and less than 20% by weight, more preferably 1% by weight or more and 15% by weight or less with respect to the total amount of the microporous membrane. . In the case of a microporous membrane having a particle content of less than 1% by weight, the effect of increasing the membrane breaking temperature is less likely to be obtained compared to a microporous membrane not containing particles, whereas the particle content is 20% by weight or more. In the case of a microporous membrane, the strength of the microporous membrane is reduced, and aggregates of particles are easily generated in the microporous membrane.
[0010]
In the present invention, polyolefin refers to homopolymers of olefins such as ethylene and propylene and blends thereof, and copolymers of olefins such as ethylene and propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. And blends of these copolymers with ethylene homopolymers, blends of polyolefins with polyamides, modified polyphenylene ethers, and the like.
From the viewpoint of ensuring the strength of the polyolefin microporous membrane, among these polyolefins, it is preferable to use a polyolefin having a melt flow rate measured by the method described in JIS K7210 of 2 g / 10 min or less. Polyolefin having a melt flow rate of 1 g / 10 min or less, more preferably high density polyethylene having a melt flow rate of 1 g / 10 min or less is used.
[0011]
In the polyolefin microporous membrane of the present invention, a fatty acid such as stearic acid and erucic acid, a fatty acid amide compound such as stearic acid amide and erucic acid amide, calcium stearate, zinc stearate, etc. A fatty acid metal salt, an acid-modified polyolefin obtained by reacting an organic acid such as maleic acid with a polyolefin, or the like may be added.
When a fatty acid, a fatty acid amide compound or a fatty acid metal salt is used, the addition ratio to the polyolefin is 0.05 to 5% by weight, preferably 0.1 to 4% by weight. When acid-modified polyolefin is used, the addition ratio to the polyolefin is 5 to 30% by weight, preferably 5 to 20% by weight.
[0012]
Various additives such as antioxidants and nucleating agents may be added to the polyolefin used in the present invention, if necessary.
The thickness of the microporous membrane of the present invention is preferably 5 to 100 μm, more preferably 10 to 30 μm, from the viewpoint of securing the strength as a battery separator, and the porosity is the strength ensuring as a battery separator or inside the battery. It is preferably 30 to 60% from the standpoint of preventing short circuit and ensuring appropriate electrical resistance, and more preferably 35 to 50%, and the air permeability is 50 to 1000 seconds / sec from the standpoint of securing the performance of the battery. It is preferably 100 cc, more preferably 70 to 600 seconds / 100 cc.
[0013]
The breaking temperature of the microporous membrane is preferably 160 ° C. or higher, more preferably 170 ° C. or higher, at which the electrical resistance is reduced by short-circuiting at a high temperature.
The microporous membrane of the present invention is prepared by melting and kneading a polyolefin having a mean particle size of 100 nm or less mixed with polyolefin at a ratio of 1 wt% or more and less than 20 wt%, and cooling the resulting solution. Then, after solidifying, the solvent can be extracted to obtain a porous structure.
The solvent used in the present invention is a solvent that forms a uniform solution when mixed with polyolefin and heated. For example, a solvent such as liquid paraffin, phthalic acid dioctyl ester, or adipic acid dioctyl ester is used alone or in combination. be able to.
[0014]
The solution in which the polyolefin, particles and solvent are melt-kneaded is produced by heating and kneading the polyolefin, particles and solvent to a temperature equal to or higher than the melting point of the polyolefin using a kneader or a twin screw extruder. be able to. The ratio of the solvent to the total amount of the solution is 20% by weight to 70% by weight from the viewpoint of reducing the torque of the kneading process using the mixing apparatus and from the viewpoint of setting the porosity of the microporous film after extracting the solvent to an appropriate value. It is preferable that the content is 35% by weight to 65% by weight.
[0015]
A solution obtained by heating and kneading polyolefin, particles and a solvent can be cooled to be formed into a sheet or a tube. For example, a heat-kneaded solution is sandwiched between cooled metal plates and rapidly cooled to form a sheet, or a solution obtained by heating and kneading using an extruder with a sheet-forming die attached to the tip is extruded from the sheet-forming die. It can be formed into a sheet by taking it up with a cooling roll, or can be formed into a tube by extruding the solution using an extruder having a tubular die attached to the tip.
A molded product having a porous structure can be obtained by extracting a solvent from a mixture of polyolefin, particles, and a solvent molded into a sheet or tube. The extraction of the solvent can be performed by a method such as washing the molded article with a solvent that is compatible with the solvent and does not dissolve the polyolefin. As the extraction solvent, solvents such as low-boiling hydrocarbons such as hexane, ketones such as methyl ethyl ketone, and non-chlorine-containing fluorine-based organic solvents such as hydrofluoroether and hydrofluorocarbon can be used.
[0016]
In the present invention, the molded product can be stretched either before or after the solvent extraction step, or both. In the case of a sheet-like molded product, a sheet is formed by uniaxial stretching using a roll stretching machine or a tenter or simultaneous biaxial stretching using a simultaneous biaxial tenter or sequential biaxial stretching combining a roll stretching machine and a tenter alone or in combination. The shaped molded product can be stretched. In the case of a tubular molded product, it can be performed by a method in which compressed air is enclosed in the tubular molded product and stretched into a tube shape, or tube-shaped stretching and sheet-shaped stretching may be combined.
[0017]
The present invention will be described based on examples.
The evaluation method of the physical properties of the microporous membrane in the examples is as follows.
(A) Dial gauge PEACOK No. 25.
(B) The volume of the sample was determined from the porosity thickness and area, the mass was measured, and the porosity was determined using the following equation.
Porosity (%) = (1− (mass / density of mixed composition) / volume) × 100
In addition, the value calculated | required by calculation from the density of each used polyolefin and particle | grains, and the mixing ratio was used for the density of the mixed composition.
(C) Puncture strength A needle having a radius of curvature of 0.5 mm is attached to a compression tester KES-G5 manufactured by Kato Tech, and a puncture test is performed at a puncture speed of 2 mm / sec. did.
[0018]
(D) Air permeability It measured using the Gurley type air permeability meter based on JIS P-8117.
(E) Hole blockage temperature and rupture temperature FIG. 1A to FIG. FIG. 1A is a configuration diagram of a measuring apparatus. 1 is a microporous film, 2A and 2B are Ni foils having a thickness of 10 μm, and 3A and 3B are glass plates. 4 is an electrical resistance measuring device (Ando Electric LCR meter AG4311), which is connected to Ni foils (2A, 2B). A thermocouple 5 is connected to the
[0019]
More specifically, the microporous membrane 1 is impregnated with a prescribed electrolytic solution, and only the MD is stopped on the
[0020]
The prescribed electrolyte composition is as follows.
Solvent: Propylene carbonate / ethylene carbonate / butyl lactone = 1/1/2 volume% Solute: Lithium borofluoride was dissolved in the above solvent to a concentration of 1 mol / liter.
[0021]
[Example 1]
95% by weight of high density polyethylene having a melt flow rate of 0.08 g / min and a density of 0.96 g / cm 3 and 5% by weight of alumina powder having an average particle diameter of 30 nm were mixed. 60 parts by weight of liquid paraffin and plastmill C type manufactured by Toyo Seiki Seisakusho were mixed with heat. The heating and mixing were performed for 10 minutes with the temperature of the plastmill set to 200 ° C. and the rotation speed set to 50 rpm. The molten mixture is taken out from the plastmill, cooled, the obtained solidified product is sandwiched between two metal plates, and compressed at a pressure of 10 MPa using a hot press set at a temperature of 200 ° C., and a 1 mm thick sheet It was created.
Using a biaxial stretching machine (manufactured by Iwamoto Seisakusho), the obtained sheet was stretched 7 times in the longitudinal direction and 7 times in the transverse direction at 115 ° C, and then immersed in methyl ethyl ketone for 24 hours to remove liquid paraffin. And then dried at room temperature and normal pressure for 24 hours.
The microporous membrane obtained by drying had a thickness of 20 μm, a porosity of 49%, an air permeability of 350 seconds / 100 cc, a puncture strength of 5.1 N, and a membrane breaking temperature of 190 ° C.
[0022]
[Example 2]
A microporous membrane was prepared under the same conditions as in Example 1 except that the mixing ratio of the alumina powder in Example 1 was changed to 15 wt% and the mixing ratio of the high density polyethylene was changed to 85 wt%.
The obtained microporous membrane had a thickness of 21 μm, a porosity of 50%, an air permeability of 320 seconds, a puncture strength of 4.9 N, and a membrane breaking temperature of 190 ° C.
[0023]
[Example 3]
The alumina powder of Example 1 was changed to silicon oxide particles having an average particle diameter of 7 nm, and the mixing ratio of silicon oxide was 15% by weight, and the mixing ratio of high-density polyethylene was 85% by weight. It was melt mixed with liquid paraffin under the same conditions as in Example 1. A sheet was prepared from the melt-mixed mixture under the same conditions as in Example 1, and after stretching, liquid paraffin was extracted and removed to form a microporous membrane.
The obtained microporous membrane had a thickness of 19 μm, a porosity of 49%, an air permeability of 260 seconds, a puncture strength of 3.9 N, and a membrane breaking temperature of 190 ° C.
[0024]
[Comparative Example 1]
The same method as in Example 1 except that 40 parts by weight of high-density polyethylene and 60 parts by weight of liquid paraffin used in Example 1 were kneaded for 10 minutes using a plastmill set at a temperature of 200 ° C. and a rotation speed of 50 rpm as in Example 1. The liquid paraffin was extracted with a microporous membrane.
The obtained microporous membrane had a thickness of 25 μm, a porosity of 44%, an air permeability of 410 seconds, a puncture strength of 5.6 N, and a membrane breaking temperature of 150 ° C.
[0025]
[Comparative Example 2]
A microporous membrane was prepared under the same conditions as in Example 1 except that the mixing ratio of the alumina powder of Example 1 was reduced to 0.5% by weight and the high-density polyethylene was increased by the reduced amount of the alumina powder.
The obtained microporous membrane had a thickness of 25 μm, a porosity of 44%, an air permeability of 400 seconds, a puncture strength of 5.7 N, and a membrane breaking temperature of 150 ° C.
[0026]
[Comparative Example 3]
An attempt was made to create a microporous membrane under the same conditions as in Example 1 except that the mixing ratio of the alumina powder of Example 1 was increased to 30% by weight and the high-density polyethylene was reduced by the increased amount of the alumina powder.
In the obtained microporous membrane, many aggregates of alumina were observed, and the membrane was broken during the stretching process.
[0027]
【The invention's effect】
The microporous membrane of the present invention is a polyethylene microporous membrane having a low content of inorganic powder and a high membrane breaking temperature, and is particularly useful as a separator used in lithium ion secondary batteries.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an overall schematic diagram showing the configuration of an apparatus for measuring hole closing temperature, (A) is an apparatus for measuring hole closing temperature, and (B) is a cross section of Ni foil (2A) in (A). FIG. 4C is a cross-sectional view of the Ni foil (2B) in FIG.
[Explanation of symbols]
1:
Claims (5)
ポリオレフィンと無機物粒子の混合物１００重量％に対して、平均粒子径が１００ｎｍ以下である無機物粒子を１重量％以上２０重量％未満の割合で混合したものを、流動パラフィン、フタル酸ジオクチルエステルまたはアジピン酸ジオクチルエステルの単独、あるいはこれらの組み合わせからなる溶媒と混合して成形物を成形した後、溶媒の抽出工程前に延伸を行い、ポリオレフィンと無機物粒子の混合物１００重量％に対して、ポリオレフィン中の無機物粒子が１重量％以上２０重量％未満となるように溶媒を抽出することにより多孔化することを特徴とする微多孔膜の製造方法。 A method for producing a microporous membrane comprising a polyolefin containing 1% by weight or more and less than 20% by weight of inorganic particles having an average particle size of 100 nm or less,
Liquid paraffin, dioctyl phthalate or adipic acid prepared by mixing inorganic particles having an average particle diameter of 100 nm or less with a ratio of 1% by weight to less than 20% by weight with respect to 100% by weight of a mixture of polyolefin and inorganic particles. After molding a molded product by mixing with a solvent composed of dioctyl ester alone or a combination thereof, the mixture is stretched before the solvent extraction step, and the inorganic material in the polyolefin is 100% by weight of the mixture of polyolefin and inorganic particles. A method for producing a microporous membrane, wherein the porous layer is formed by extracting a solvent so that the particles are 1% by weight or more and less than 20% by weight .
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| JP2005322517A (en) * | 2004-05-10 | 2005-11-17 | Toshiba Corp | Nonaqueous electrolyte secondary battery |
| TWI305215B (en) | 2004-08-30 | 2009-01-11 | Asahi Kasei Chemicals Corp | Polyolefin microporous membrane and separator for battery |
| KR100943697B1 (en) * | 2005-04-06 | 2010-02-23 | 에스케이에너지 주식회사 | Microporous polyethylene film having excellent physical properties, productivity and quality consistency, and method for preparing the same |
| ATE533197T1 (en) † | 2006-09-20 | 2011-11-15 | Asahi Kasei Chemicals Corp | MICROPOROUS POLYOLEFIN MEMBRANE AND SEPARATOR FOR NON-AQUEOUS ELECTROLYTE BATTERY |
| JP5235487B2 (en) * | 2008-05-08 | 2013-07-10 | 旭化成イーマテリアルズ株式会社 | Method for producing inorganic particle-containing microporous membrane |
| KR101705563B1 (en) * | 2015-04-28 | 2017-02-13 | 더블유스코프코리아 주식회사 | Ion-exchange membrane for water treatment and manufacturing method the same |
| JP7235486B2 (en) | 2018-11-28 | 2023-03-08 | 旭化成株式会社 | Polyolefin microporous membrane |
| CN109860473B (en) * | 2018-12-03 | 2023-05-23 | 银隆新能源股份有限公司 | Preparation method of lithium ion battery diaphragm |
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