JP4425595B2 - Electric double layer capacitor separator - Google Patents
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- 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
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Abstract
Description
本発明は、水溶液系電解液を用いた低自己放電タイプの電気二重層キャパシタ用セパレータに関する。 The present invention relates to a low self-discharge type electric double layer capacitor separator using an aqueous electrolyte.
電気二重層キャパシタは、電極と電解液との界面においてイオンの分極によりできる電気二重層を利用したキャパシタであり、従来のコンデンサに比較して大容量の静電容量を充放電可能である。大容量を急速充放電するためには、内部抵抗が低い電気二重層キャパシタが要求される。
また、長期間のバックアップを必要とする用途では、自己放電による電圧降下が少ない低自己放電タイプの電気二重層キャパシタが要求されている。
An electric double layer capacitor is a capacitor that uses an electric double layer formed by ion polarization at the interface between an electrode and an electrolyte, and can charge and discharge a larger capacitance than a conventional capacitor. In order to rapidly charge and discharge a large capacity, an electric double layer capacitor having a low internal resistance is required.
In applications that require long-term backup, a low self-discharge type electric double layer capacitor with a small voltage drop due to self-discharge is required.
従来、内部抵抗を低減する方法として、セパレータの細孔径を制御する方法や、かしめ板やバネ等を用いて集電体―分極性電極―セパレータ間をかしめることによって各層間の接触抵抗を小さくする方法等が検討されている。
例えば、特許文献１には、弾性体からなるセパレータを用い、該セパレータの厚みを圧縮せしめることにより、電気二重層キャパシタ内に適当なかしめ圧を付与し内部抵抗を低減できることが開示されている。
しかし、前記特許文献１に開示のものでは、かしめ圧を常に一定に制御することは困難であり、セパレータ内の細孔径がかしめ圧によって変動することから、セパレータ内の電解質の量が一定とならず電気二重層キャパシタの内部抵抗がばらつくという問題があるとともに、セパレータ内の細孔径が変動して大きくなると、電極中の電荷を帯び電極から脱離した活性炭微粒子が電気泳動によってセパレータ内を貫通し対極に到達し易くなり、自己放電による電圧降下が大きくなるという問題があった。
Conventionally, as a method for reducing the internal resistance, the contact resistance between each layer is reduced by controlling the pore diameter of the separator or by caulking the current collector-polarizable electrode-separator using a caulking plate or a spring. The method to do is examined.
For example, Patent Document 1 discloses that by using a separator made of an elastic material and compressing the thickness of the separator, an appropriate caulking pressure can be applied to the electric double layer capacitor to reduce the internal resistance.
However, with the one disclosed in Patent Document 1, it is difficult to always control the caulking pressure to be constant, and since the pore diameter in the separator varies depending on the caulking pressure, the amount of electrolyte in the separator is constant. In addition, there is a problem that the internal resistance of the electric double layer capacitor varies, and when the pore diameter in the separator fluctuates and becomes large, activated carbon particles charged with charges in the electrode and desorbed from the electrode penetrate through the separator by electrophoresis. There was a problem that the counter electrode was easily reached and the voltage drop due to self-discharge increased.
この問題を解決するため、特許文献２には、セパレータとして剛性の異なる複数の多孔質層の積層体を使用し、しかも、高剛性の多孔質層の細孔径を低剛性の多孔質層よりも小さくすることで、かしめ圧が変化してもセパレータの細孔径が変動しにくいようにすることができ、内部抵抗のばらつきや、自己放電による電圧降下を抑えることができることが開示されている。 In order to solve this problem, Patent Document 2 uses a laminate of a plurality of porous layers having different rigidity as a separator, and further, the pore diameter of the high-rigidity porous layer is smaller than that of the low-rigidity porous layer. It is disclosed that, by reducing the size, it is possible to prevent the pore diameter of the separator from fluctuating even if the caulking pressure changes, and to suppress variations in internal resistance and voltage drop due to self-discharge.
また、特許文献３には、実用上問題ない内部抵抗で、かつ自己放電の少ないキャパシタとするため、セパレータの空隙率Ｐ（％）と厚みｔ（ｃｍ）の関係（Ｐ／１００）／ｔの値が５〜３０であるセパレータを用いるようにしたものが開示されている。この特許文献３の実施例には、厚さ１００μｍ以上のセパレータで空隙率別のセパレータを試験した例が記載されている。
しかしながら、前記特許文献３には、セパレータの空隙率と厚さの関係について開示されているだけで、セパレータの具体的な製法の開示がなく、厚さや空隙率の適用範囲が明確でない。
また、前記特許文献２に開示のものでは、積層体からなるセパレータを使用するため、セパレータの厚さばらつきが大きくなったり、キャパシタの組立作業性が悪くなるという問題がある。
そこで、本発明は、水溶液系電解液を用いた低自己放電タイプの電気二重層キャパシタにおいて、内部抵抗が低く、かつ自己放電の少ない電気二重層キャパシタを得るためのセパレータを提供することを目的とする。
However, Patent Document 3 discloses only the relationship between the porosity and thickness of the separator, does not disclose a specific method for manufacturing the separator, and the application range of thickness and porosity is not clear.
Moreover, since the separator disclosed in Patent Document 2 uses a separator made of a laminated body, there are problems that the thickness variation of the separator becomes large and the assembling workability of the capacitor is deteriorated.
Accordingly, an object of the present invention is to provide a separator for obtaining an electric double layer capacitor having low internal resistance and low self-discharge in a low self-discharge type electric double layer capacitor using an aqueous electrolyte. To do.
本発明者等は、前記目的を達成するべく、微多孔質膜からなる電気二重層キャパシタ用セパレータについて、鋭意検討を重ね、実験を重ねた結果、以下のような知見を得るに至った。
つまり、電気二重層キャパシタにおける自己放電と内部抵抗の両特性を考えた場合に、この両特性に影響を与えるセパレータの主な要因としては、（１）空隙率、（２）孔構造（主に孔径）、（３）厚さがあると考えられる。
ここでは、前記微多孔質膜として、ポリオレフィン系樹脂と、無機粉体と、可塑剤とを混合した原料混合物を加熱溶融・混練しながら押し出したシート状物に対して、薄肉化処理を行った後、前記可塑剤を抽出除去して得られるような微多孔質膜を想定しており、この製法自体は基本的に不変であり、よって、出来上がる微多孔質膜の性状も基本的に不変となることを前提としている。
In order to achieve the above-mentioned object, the present inventors have made extensive studies and experiments on an electric double layer capacitor separator made of a microporous film. As a result, the inventors have obtained the following knowledge.
In other words, when considering both self-discharge and internal resistance characteristics in an electric double layer capacitor, the main factors affecting the separator are as follows: (1) porosity, (2) pore structure (mainly (Pore diameter), (3) It is considered that there is a thickness.
Here, as the microporous film, a thinning process was performed on a sheet-like material extruded while heating and melting and kneading a raw material mixture obtained by mixing a polyolefin resin, an inorganic powder, and a plasticizer. Thereafter, a microporous membrane obtained by extracting and removing the plasticizer is assumed, and the manufacturing method itself is basically unchanged, so that the properties of the resulting microporous membrane are basically unchanged. It is assumed that
自己放電は、前記したように、電荷を帯びた活性炭微粒子がセパレータ内を貫通することによって引き起こされる現象であるので、言い換えれば、活性炭微粒子の通過し易さであり、セパレータにとっては、主に空隙率および孔径の大小が大きく影響する。
一方、内部抵抗つまり電気抵抗は、言い換えれば、電解液イオンの通過し易さであり、セパレータにとっては、主に空隙率および厚さの大小が大きく影響する。孔径も影響がないとは言えないが、電解液イオンの大きさが、前記製法で作られる微多孔質膜の孔径の大きさに対して明らかに小さいため、影響としては軽微に留まる。
As described above, the self-discharge is a phenomenon caused by the charged activated carbon fine particles penetrating through the separator, in other words, it is easy for the activated carbon fine particles to pass through. The ratio and the size of the hole diameter have a great influence.
On the other hand, the internal resistance, that is, the electrical resistance is, in other words, the ease of passage of electrolyte ions, and for the separator, the porosity and the thickness are largely affected. Although the pore diameter cannot be said to have no influence, the influence of the electrolyte solution ion is slight because the size of the electrolyte ions is clearly smaller than the pore diameter of the microporous membrane produced by the above-mentioned manufacturing method.
本発明者等は、まず、低自己放電化の要求に対応するため、セパレータの空隙率を下げることで、低自己放電化を図るようにした。
ところが、同時に要求される低内部抵抗化（低電気抵抗化）の要求に対応するためには、単純にセパレータの空隙率を上げればよいが、空隙率を上げると低自己放電化が阻害されるので、空隙率を弄ることなく低内部抵抗化を図るため、セパレータをより薄肉化する必要が生じた。しかし、上記のような製法で作られる微多孔質膜において薄肉化を追求しようとする場合、押し出したシート状物に対して押し出し直後に行う一般的な薄肉化処理である圧延処理には技術的な限界、すなわち厚さ精度（厚さの均一性を含む）の限界があり、１００μｍ未満に薄肉化する場合には、前記薄肉化処理として、圧延処理に加え延伸処理を行う必要があった。
In order to meet the demand for low self-discharge, the present inventors first tried to reduce the self-discharge by reducing the porosity of the separator.
However, in order to meet the demand for low internal resistance (low electrical resistance) that is required at the same time, it is sufficient to simply increase the porosity of the separator. However, increasing the porosity inhibits low self-discharge. Therefore, it is necessary to make the separator thinner in order to reduce the internal resistance without changing the porosity. However, when pursuing thinning in a microporous membrane made by the above-described manufacturing method, it is technical to use a rolling process, which is a general thinning process performed immediately after extrusion on an extruded sheet. When the thickness is reduced to less than 100 μm, there is a need to perform a stretching process in addition to the rolling process.
ところが、低内部抵抗化に対応するために前記シート状物に延伸処理を施して薄肉化した微多孔質膜では、微多孔質膜の微細構造が歪みを起こすことにより、多孔質化後の孔構造も変形させられ孔径が大きくなってしまうことが分かった。つまり、空隙率を弄らないで、延伸処理を含んだ薄肉化処理によってセパレータを薄肉化する方法では、厚さ減少により低内部抵抗化（低電気抵抗化）は図れたが、孔径の拡大化により低自己放電化を阻害することになり、この方法では、低自己放電化と低内部抵抗化を同時に達成することができなかった。 However, in order to cope with the low internal resistance, in the microporous membrane that has been thinned by subjecting the sheet-like material to stretching, the fine structure of the microporous membrane is distorted, resulting in pores after being made porous. It was found that the structure was also deformed and the hole diameter was increased. In other words, in the method of thinning the separator by thinning processing including stretching, without reducing the porosity, low internal resistance (low electrical resistance) was achieved by reducing the thickness, but by increasing the hole diameter As a result, the low self-discharge is hindered, and this method cannot achieve low self-discharge and low internal resistance at the same time.
このため、前記圧延処理の厚さ精度を改善することにより、１００μｍ未満に薄肉化する場合でも、圧延処理のみでの薄肉化処理を可能とした上で、セパレータに低空隙率化（５５％以下）と同時に薄肉化（１００μｍ未満）を与えることによって、低空隙率化により、低内部抵抗化を阻害するものの低自己放電化を図り、薄肉化により、低自己放電化を阻害することなく低内部抵抗化を図るようにし、低自己放電化と低内部抵抗化の両立が図れるようになることを発見した。 For this reason, by improving the thickness accuracy of the rolling process, even when the thickness is reduced to less than 100 μm, the separator can be made thin by only the rolling process, and the separator has a low porosity (55% or less). ) At the same time, by reducing the thickness (less than 100 μm), by reducing the porosity, the internal resistance is reduced, but the self-discharge is reduced. By reducing the thickness, the internal is reduced without inhibiting the low self-discharge. It was discovered that resistance can be reduced, and both low self-discharge and low internal resistance can be achieved.
本発明の電気二重層キャパシタ用セパレータは、かかる知見に基づきなされた発明であって、請求項１記載の通り、水溶液系電解液を用いた低自己放電タイプの電気二重層キャパシタ用セパレータにおいて、前記セパレータは、ポリオレフィン系樹脂と、無機粉体と、可塑剤とを混合した原料混合物を加熱溶融・混練しながら押し出したシート状物に対して、近接して連続多段に配置した圧延ロール間を連続的に通すことにより行う圧延処理のみにより、薄肉化処理を行った後、前記可塑剤を抽出除去して得られる、厚さが８５μｍ以下で空隙率が５５％以下の微多孔質膜であり、前記薄肉化処理として延伸処理を実質的に含んでいないことを特徴とする。
また、請求項２記載の電気二重層キャパシタ用セパレータは、請求項１記載の電気二重層キャパシタ用セパレータにおいて、前記薄肉化処理は、前記シート状物の長さ方向及び幅方向に対する延伸率が３０％以下であることを特徴とする。
また、請求項３記載の電気二重層キャパシタ用セパレータは、請求項１又は２記載の電気二重層キャパシタ用セパレータにおいて、前記原料混合物に界面活性剤を更に混合したことを特徴とする。
また、請求項４記載の電気二重層キャパシタ用セパレータは、請求項１乃至３の何れか１項に記載の電気二重層キャパシタ用セパレータにおいて、前記ポリオレフィン系樹脂はポリエチレンであり、前記無機粉体はシリカであることを特徴とする。
The separator for an electric double layer capacitor of the present invention is an invention made based on such knowledge, and as described in claim 1, in the separator for an electric double layer capacitor of a low self-discharge type using an aqueous electrolyte, Separator is continuous between rolling rolls arranged in multi-stages in close proximity to a sheet-like product extruded while heating, melting and kneading a raw material mixture in which polyolefin resin, inorganic powder, and plasticizer are mixed. A microporous film having a thickness of 85 μm or less and a porosity of 55% or less , obtained by extracting and removing the plasticizer after performing a thinning process only by rolling treatment performed by passing through The thinning treatment is substantially free from a stretching treatment.
The separator for an electric double layer capacitor according to claim 2 is the separator for an electric double layer capacitor according to claim 1, wherein the thinning treatment is performed at a drawing ratio of 30 in the length direction and width direction of the sheet-like material. % Or less .
The electric double layer separator for capacitors as claimed in claim 3, wherein, in the electric double layer separator for capacitors as claimed in claim 1, characterized by being further mixed a surfactant to the raw material mixture.
The separator for an electric double layer capacitor according to claim 4 is the separator for an electric double layer capacitor according to any one of claims 1 to 3 , wherein the polyolefin resin is polyethylene, and the inorganic powder is It is characterized by being silica.
本発明の電気二重層キャパシタ用セパレータは、水溶液系電解液を用いた低自己放電タイプの電気二重層キャパシタ用セパレータとして、ポリオレフィン系樹脂と、無機粉体と、可塑剤とを混合した原料混合物を加熱溶融・混練しながら押し出したシート状物に対して、延伸処理を実質的に含まない形で薄肉化処理を行った後、前記可塑剤を抽出除去して得られる、厚さが８５μｍ以下で空隙率が５５％以下の微多孔質膜として構成するようにしたものであることから、前記薄肉化処理において微多孔質膜の孔構造を変形させ孔径を拡大化させてしまう延伸処理を実質的に含んでいないため、非常に薄肉でありながら孔構造が良好に保たれた微多孔質膜からなるセパレータとすることができるので、このようなセパレータを電気二重層キャパシタに用いれば、内部抵抗が低く、かつ自己放電による電圧低下が少ない電気二重層キャパシタを得ることができる効果をもたらす。 The separator for an electric double layer capacitor of the present invention is a low self-discharge type electric double layer capacitor separator using an aqueous electrolyte, and a raw material mixture obtained by mixing a polyolefin resin, an inorganic powder, and a plasticizer. The sheet-like material extruded while being heated and melted and kneaded is subjected to a thinning process in a form that does not substantially include a stretching process, and then is obtained by extracting and removing the plasticizer. The thickness is 85 μm or less . Since it is configured as a microporous film having a porosity of 55% or less, the stretching process that deforms the pore structure of the microporous film and enlarges the pore diameter in the thinning process is substantially performed. Therefore, it is possible to provide a separator made of a microporous membrane that has a very thin wall and maintains a good pore structure. By using the data, resulting in an effect by which the internal resistance is low, and to obtain an electric double layer capacitor is less voltage drop due to self-discharge.
本発明の水溶液系電解液を用いた低自己放電タイプの電気二重層キャパシタ用セパレータを構成するための混合物の主成分は、ポリオレフィン系樹脂、無機粉体、可塑剤及び、必要に応じ、界面活性剤である。 The main components of the mixture for constituting the low self-discharge type electric double layer capacitor separator using the aqueous electrolyte solution of the present invention are polyolefin resin, inorganic powder, plasticizer and, if necessary, surface active. It is an agent.
前記ポリオレフィン系樹脂としては、ポリエチレン、ポリプロピレン、ポリブテンおよびこれらの共重合物又はこれらの混合物から選択される１種又は２種以上が使用できるが、側鎖を持たず酸化劣化を生じ難い点から、ポリエチレンの単独使用が好ましい。特に、重量平均分子量１００万以上の高密度ポリエチレンを使用すれば、機械的強度の優れたセパレータを得ることができる。また、重量平均分子量の異なる樹脂を混合使用することも可能であり、例えば、重量平均分子量２００万以上の高密度ポリエチレンと重量平均分子量３０万未満の低密度ポリエチレンをブレンドして使用することもできる。 As the polyolefin-based resin, one or two or more selected from polyethylene, polypropylene, polybutene and copolymers thereof, or a mixture thereof can be used. The use of polyethylene alone is preferred. In particular, if high-density polyethylene having a weight average molecular weight of 1,000,000 or more is used, a separator having excellent mechanical strength can be obtained. It is also possible to use a mixture of resins having different weight average molecular weights. For example, a high density polyethylene having a weight average molecular weight of 2 million or more and a low density polyethylene having a weight average molecular weight of less than 300,000 can be blended and used. .
前記無機粉体としては、比表面積が１００〜４００ｍ2／ｇのシリカ、アルミナ、チタニア等の耐酸性無機粉体から選択される１種又は２種以上が使用できるが、比較的安価で不純物が少ない点から、シリカが好ましい。 As the inorganic powder, one or more selected from acid-resistant inorganic powders such as silica, alumina, and titania having a specific surface area of 100 to 400 m 2 / g can be used. Silica is preferred from the viewpoint of few.
前記可塑剤としては、パラフィン系、ナフテン系等の工業用潤滑油、あるいはフタル酸ジオクチル等のエステル系可塑剤が使用できる。 As the plasticizer, industrial plastic oils such as paraffinic and naphthenic or ester plasticizers such as dioctyl phthalate can be used.
前記界面活性剤としては、アルキルスルホコハク酸塩やナフタリンスルホン酸塩ホルマリン縮合物等のアニオン系、又はポリオキシエチレンアルキルエーテル等のノニオン系の単独又は混合物が使用できる。界面活性剤を混合することにより、セパレータの電解液濡れ性を向上させることができる。 As the surfactant, anionic compounds such as alkylsulfosuccinates and naphthalenesulfonate formalin condensates, or nonionic compounds such as polyoxyethylene alkyl ethers may be used alone or as a mixture. The electrolyte wettability of the separator can be improved by mixing the surfactant.
本発明の電気二重層キャパシタ用セパレータは、ポリオレフィン系樹脂と、無機粉体と、可塑剤とを混合した原料混合物を加熱溶融・混練しながら押し出したシート状物に対して、延伸処理を実質的に含まない形で薄肉化処理を行った後、前記可塑剤を抽出除去するようにして、厚さが８５μｍ以下で空隙率が５５％以下の微多孔質膜として構成するようにしたものであるが、ここで言う、延伸処理を実質的に含まない薄肉化処理とは、具体的には、前記シート状物の長さ方向及び幅方向に対する延伸率が３０％以下であるような薄肉化処理を指す。つまり、押し出し直後のシート状物に対して圧延処理を行う場合であっても、通常はラインを使った連続生産であるため、前記シート状物を工程間で連続的に受け渡しする際には、前記シート状物に一定の張力がかかっているため、意図せずとも延伸を施したような状況になり易く、前記延伸率を完全にゼロとすることは難しい。
前記薄肉化処理は、実質的に圧延処理のみである。
また、この場合、前記圧延処理が、押出直後のシート状物に対して、近接して連続多段に配置した圧延ロール間を連続的に通すことにより行う。
The separator for an electric double layer capacitor of the present invention substantially extends a sheet-like material extruded while heating, melting and kneading a raw material mixture obtained by mixing a polyolefin resin, an inorganic powder, and a plasticizer. The plasticizer is extracted and removed after being thinned in a form not included in the film, and is configured as a microporous film having a thickness of 85 μm or less and a porosity of 55% or less. However, the thinning treatment substantially free of the stretching treatment referred to here is specifically a thinning treatment in which the stretching ratio in the length direction and the width direction of the sheet-like material is 30% or less. Point to. In other words, even when the rolling process is performed on the sheet-like material immediately after extrusion, because it is usually continuous production using a line, when continuously transferring the sheet-like material between processes, Since a certain tension is applied to the sheet-like material, it is likely that the sheet is stretched unintentionally, and it is difficult to make the stretching ratio completely zero.
The thinning process, Ru der substantially only rolling treatment.
In this case, the rolling process for sheet immediately after extrusion, intends row by continuously passing rolling rolls disposed in the continuous multi-stage close to.
次に、本発明の実施例について比較例と共に詳細に説明する。尚、以下において、配合量を示す部とは質量部を意味するものとする。
（実施例１）
ポリオレフィン系樹脂として重量平均分子量２００万の高密度ポリエチレン樹脂粉体７０部と、無機粉体として比表面積が２００ｍ2／ｇのシリカ微粉体３０部と、可塑剤としてパラフィン系オイル１００部と、界面活性剤としてアルキルスルホコハク酸塩５部とを混合した原料混合物を、先端にＴダイを取り付けた二軸押出機にて加熱溶融混練しながらシート状に押し出し、続いて、該シート状物を、近接して連続多段に配置された圧延ロール間を連続的に通して薄肉化処理を行い、厚さ８５μｍのシートを得た。次に、該シート中の可塑剤を有機溶剤で抽出除去して加熱乾燥し、ポリエチレン樹脂６６．７質量％、シリカ微粉体２８．５質量％、アルキルスルホコハク酸塩４．８質量％で構成される、厚さ８５μｍの微多孔質膜からなる電気二重層キャパシタ用セパレータを得た。尚、前記圧延ロール及び圧延装置は高精度な厚さ精度が出せるように特別に設計された非常に精密なものを使用した。
Next, examples of the present invention will be described in detail together with comparative examples. In addition, below, the part which shows a compounding quantity shall mean a mass part.
Example 1
70 parts of a high density polyethylene resin powder having a weight average molecular weight of 2 million as a polyolefin resin, 30 parts of silica fine powder having a specific surface area of 200 m 2 / g as an inorganic powder, 100 parts of paraffinic oil as a plasticizer, an interface A raw material mixture obtained by mixing 5 parts of alkylsulfosuccinate as an activator was extruded into a sheet while being melted and kneaded with a twin screw extruder having a T-die attached to the tip, and the sheet was then brought into proximity. Then, the thinning process was performed by continuously passing between the rolling rolls arranged in a continuous multi-stage to obtain a sheet having a thickness of 85 μm. Next, the plasticizer in the sheet is extracted and removed with an organic solvent and dried by heating, and is composed of polyethylene resin 66.7% by mass, silica fine powder 28.5% by mass, and alkyl sulfosuccinate 4.8% by mass. An electric double layer capacitor separator made of a microporous film having a thickness of 85 μm was obtained. The rolling roll and rolling apparatus used were very precise ones specially designed so that high thickness accuracy can be obtained.
（実施例２）
ポリオレフィン系樹脂として重量平均分子量２００万の高密度ポリエチレン樹脂粉体７０部と、無機粉体として比表面積が２００ｍ2／ｇのシリカ微粉体３０部と、可塑剤としてパラフィン系オイル１００部と、界面活性剤としてアルキルスルホコハク酸塩５部とを混合した原料混合物を、先端にＴダイを取り付けた二軸押出機にて加熱溶融混練しながらシート状に押し出し、続いて、該シート状物を、近接して連続多段に配置された圧延ロール間を連続的に通して薄肉化処理を行い、厚さ５０μｍのシートを得た。次に、該シート中の可塑剤を有機溶剤で抽出除去して加熱乾燥し、ポリエチレン樹脂６６．７質量％、シリカ微粉体２８．５質量％、アルキルスルホコハク酸塩４．８質量％で構成される、厚さ５０μｍの微多孔質膜からなる電気二重層キャパシタ用セパレータを得た。尚、前記圧延ロール及び圧延装置は高精度な厚さ精度が出せるように特別に設計された非常に精密なものを使用した。
(Example 2)
70 parts of a high density polyethylene resin powder having a weight average molecular weight of 2 million as a polyolefin resin, 30 parts of silica fine powder having a specific surface area of 200 m 2 / g as an inorganic powder, 100 parts of paraffinic oil as a plasticizer, an interface A raw material mixture obtained by mixing 5 parts of alkylsulfosuccinate as an activator was extruded into a sheet while being melted and kneaded with a twin screw extruder having a T-die attached to the tip, and the sheet was then brought into proximity. Then, the thinning process was performed by continuously passing between the rolling rolls arranged in a continuous multi-stage to obtain a sheet having a thickness of 50 μm. Next, the plasticizer in the sheet is extracted and removed with an organic solvent and dried by heating, and is composed of polyethylene resin 66.7% by mass, silica fine powder 28.5% by mass, and alkyl sulfosuccinate 4.8% by mass. An electric double layer capacitor separator made of a microporous film having a thickness of 50 μm was obtained. The rolling roll and rolling apparatus used were very precise ones specially designed so that high thickness accuracy can be obtained.
（実施例３）
ポリオレフィン系樹脂として重量平均分子量２００万の高密度ポリエチレン樹脂粉体５０部と、無機粉体として比表面積が２００ｍ2／ｇのシリカ微粉体５０部と、可塑剤としてパラフィン系オイル１００部と、界面活性剤としてアルキルスルホコハク酸塩５部とを混合した原料混合物を、先端にＴダイを取り付けた二軸押出機にて加熱溶融混練しながらシート状に押し出し、続いて、該シート状物を、近接して連続多段に配置された圧延ロール間を連続的に通して薄肉化処理を行い、厚さ８５μｍのシートを得た。次に、該シート中の可塑剤を有機溶剤で抽出除去して加熱乾燥し、ポリエチレン樹脂４７．６質量％、シリカ微粉体４７．６質量％、アルキルスルホコハク酸塩４．８質量％で構成される、厚さ８５μｍの微多孔質膜からなる電気二重層キャパシタ用セパレータを得た。尚、前記圧延ロール及び圧延装置は高精度な厚さ精度が出せるように特別に設計された非常に精密なものを使用した。
(Example 3)
50 parts of a high density polyethylene resin powder having a weight average molecular weight of 2 million as a polyolefin resin, 50 parts of silica fine powder having a specific surface area of 200 m 2 / g as an inorganic powder, 100 parts of paraffinic oil as a plasticizer, an interface A raw material mixture obtained by mixing 5 parts of alkylsulfosuccinate as an activator was extruded into a sheet while being melted and kneaded with a twin screw extruder having a T-die attached to the tip, and the sheet was then brought into proximity. Then, the thinning process was performed by continuously passing between the rolling rolls arranged in a continuous multi-stage to obtain a sheet having a thickness of 85 μm. Next, the plasticizer in the sheet is extracted and removed with an organic solvent and dried by heating, and is composed of 47.6% by mass of polyethylene resin, 47.6% by mass of fine silica powder, and 4.8% by mass of alkylsulfosuccinate. An electric double layer capacitor separator made of a microporous film having a thickness of 85 μm was obtained. The rolling roll and rolling apparatus used were very precise ones specially designed so that high thickness accuracy can be obtained.
（比較例１）
ポリオレフィン系樹脂として重量平均分子量２００万の高密度ポリエチレン樹脂粉体７０部と、無機粉体として比表面積が２００ｍ2／ｇのシリカ微粉体３０部と、可塑剤としてパラフィン系オイル１００部と、界面活性剤としてアルキルスルホコハク酸塩５部とを混合した原料混合物を、先端にＴダイを取り付けた二軸押出機にて加熱溶融混練しながらシート状に押し出し、続いて、該シート状物を、圧延ロール間を通して薄肉化処理を行い、厚さ１１０μｍのシートを得た。次に、該シート中の可塑剤を有機溶剤で抽出除去して加熱乾燥し、ポリエチレン樹脂６６．７質量％、シリカ微粉体２８．５質量％、アルキルスルホコハク酸塩４．８質量％で構成される、厚さ１１０μｍの微多孔質膜からなる電気二重層キャパシタ用セパレータを得た。
(Comparative Example 1)
70 parts of a high density polyethylene resin powder having a weight average molecular weight of 2 million as a polyolefin resin, 30 parts of silica fine powder having a specific surface area of 200 m 2 / g as an inorganic powder, 100 parts of paraffinic oil as a plasticizer, an interface A raw material mixture obtained by mixing 5 parts of alkylsulfosuccinate as an activator is extruded into a sheet while being melted and kneaded with a twin screw extruder having a T-die attached to the tip, and the sheet is then rolled. A thinning process was performed between the rolls to obtain a sheet having a thickness of 110 μm. Next, the plasticizer in the sheet is extracted and removed with an organic solvent and dried by heating, and is composed of polyethylene resin 66.7% by mass, silica fine powder 28.5% by mass, and alkyl sulfosuccinate 4.8% by mass. An electric double layer capacitor separator comprising a microporous film having a thickness of 110 μm was obtained.
（比較例２）
ポリオレフィン系樹脂として重量平均分子量２００万の高密度ポリエチレン樹脂粉体７０部と、無機粉体として比表面積が２００ｍ2／ｇのシリカ微粉体３０部と、可塑剤としてパラフィン系オイル１００部と、界面活性剤としてアルキルスルホコハク酸塩５部とを混合した原料混合物を、先端にＴダイを取り付けた二軸押出機にて加熱溶融混練しながらシート状に押し出し、続いて、該シート状物を、圧延ロール間を通して薄肉化処理を行い、厚さ１１０μｍのシートを得た。次に、該シートを更に延伸機を用いて長さ方向に約２５０％延伸して薄肉化処理を行い、厚さ５０μｍのシートを得た。次に、該シート中の可塑剤を有機溶剤で抽出除去して加熱乾燥し、ポリエチレン樹脂６６．７質量％、シリカ微粉体２８．５質量％、アルキルスルホコハク酸塩４．８質量％で構成される、厚さ５０μｍの微多孔質膜からなる電気二重層キャパシタ用セパレータを得た。
(Comparative Example 2)
70 parts of a high density polyethylene resin powder having a weight average molecular weight of 2 million as a polyolefin resin, 30 parts of silica fine powder having a specific surface area of 200 m 2 / g as an inorganic powder, 100 parts of paraffinic oil as a plasticizer, an interface A raw material mixture obtained by mixing 5 parts of alkylsulfosuccinate as an activator is extruded into a sheet while being melted and kneaded with a twin screw extruder having a T-die attached to the tip, and the sheet is then rolled. A thinning process was performed between the rolls to obtain a sheet having a thickness of 110 μm. Next, the sheet was further stretched by about 250% in the length direction using a stretching machine and subjected to a thinning process to obtain a sheet having a thickness of 50 μm. Next, the plasticizer in the sheet is extracted and removed with an organic solvent and dried by heating, and is composed of polyethylene resin 66.7% by mass, silica fine powder 28.5% by mass, and alkyl sulfosuccinate 4.8% by mass. An electric double layer capacitor separator made of a microporous film having a thickness of 50 μm was obtained.
次に、上記実施例１〜３及び比較例１〜２の各セパレータを使用し、以下の方法により、電気二重層キャパシタを作製し、内部抵抗、電圧保持率をそれぞれ測定した。結果を表１に示す。
［電気二重層キャパシタの作製］
（１）３０質量％の硫酸と比表面積約１０００ｍ2／ｇの活性炭とを混合したカーボンペースト電極を作製し、外径約１４ｍｍで内径約８ｍｍのリング状に打抜いた非導電性の未加硫ブチルゴムシートの下面に、外径約１４ｍｍに打抜いた導電性の未加硫ブチルゴムシートを配置し、リング内にカーボンペーストを充填し、ペースト充填シートを得た。
（２）次に、外径約１２ｍｍに打抜いたセパレータをペースト充填シートに載せ、更にペースト面がセパレータと接するようにペースト充填シートを載せ、加圧保持した状態で加熱し、加硫接着させて電気二重層キャパシタの基本セルを得た。
（３）この基本セルを６枚積層し、積層体の上下端面から電極を取り出して、動作電圧５Ｖの電気二重層キャパシタを得た。
Next, using the separators of Examples 1 to 3 and Comparative Examples 1 and 2, an electric double layer capacitor was prepared by the following method, and the internal resistance and the voltage holding ratio were measured. The results are shown in Table 1.
[Production of electric double layer capacitor]
(1) A non-conductive non-added carbon paste electrode prepared by mixing 30% by mass of sulfuric acid and activated carbon having a specific surface area of about 1000 m 2 / g and punched into a ring shape having an outer diameter of about 14 mm and an inner diameter of about 8 mm. A conductive unvulcanized butyl rubber sheet punched to an outer diameter of about 14 mm was placed on the lower surface of the butyl butyl rubber sheet, and the paste was filled with carbon paste to obtain a paste-filled sheet.
(2) Next, a separator punched to an outer diameter of about 12 mm is placed on the paste-filled sheet, and the paste-filled sheet is placed so that the paste surface is in contact with the separator. Thus, a basic cell of an electric double layer capacitor was obtained.
(3) Six basic cells were stacked, and electrodes were taken out from the upper and lower end surfaces of the stacked body to obtain an electric double layer capacitor having an operating voltage of 5V.
表１から以下のようなことが分かった。
（１）実施例１〜３のセパレータでは、延伸処理を実質的に含まない薄肉化処理方法を適用して、厚さが８５μｍ以下で、空隙率が５５％以下の微多孔質膜を形成するようにしたので、電気二重層キャパシタにおける内部抵抗が低く、かつ電圧保持率が高い良好な結果が得られた。
（２）比較例１のセパレータでは、従来の圧延装置を使用して圧延処理のみによる薄肉化処理を行ったため、８５μｍ以下に薄肉化することができなかったことから、電気二重層キャパシタにおける電圧保持率は高かったが、内部抵抗が高い結果となった。
（３）比較例２のセパレータでは、圧延処理に延伸処理を加えた薄肉化処理を行ったため、８５μｍ以下に薄肉化することができたことから、電気二重層キャパシタにおける内部抵抗は低かったが、延伸処理により微多孔質膜の孔径が拡大されてしまったことにより、電圧保持率が低い結果となった。
Table 1 shows the following.
(1) In the separators of Examples 1 to 3, a thinning method that substantially does not include a stretching process is applied to form a microporous film having a thickness of 85 μm or less and a porosity of 55% or less. As a result, good results were obtained with low internal resistance and high voltage holding ratio in the electric double layer capacitor.
(2) In the separator of Comparative Example 1, since the thinning process was performed only by the rolling process using a conventional rolling device, the thickness could not be reduced to 85 μm or less. The rate was high, but the internal resistance was high.
(3) In the separator of Comparative Example 2, since the thinning process was performed by adding the stretching process to the rolling process, the internal resistance in the electric double layer capacitor was low because the thickness could be reduced to 85 μm or less . Since the pore diameter of the microporous membrane was expanded by the stretching treatment, the voltage holding ratio was low.
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