JP3638401B2 - Method for producing polyolefin microporous membrane - Google Patents
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- JP3638401B2 JP3638401B2 JP12025297A JP12025297A JP3638401B2 JP 3638401 B2 JP3638401 B2 JP 3638401B2 JP 12025297 A JP12025297 A JP 12025297A JP 12025297 A JP12025297 A JP 12025297A JP 3638401 B2 JP3638401 B2 JP 3638401B2
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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
- 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
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Description
【０００１】
【産業上の利用分野】
本発明は、超高分子量ポリオレフィンを含有するポリオレフィン組成物からなる微多孔膜を製造する方法に関し、特に高透過性ポリオレフィン微多孔膜に関する。
【０００２】
【従来の技術】
微多孔膜は、電池用セパレーター、電解コンデンサー用隔膜、各種フィルター、透湿防水衣料、逆浸透濾過膜、限外濾過膜、精密濾過膜等の各種用途に用いられている。
従来から、ポリオレフィンに有機媒体及び微粉末シリカ等の無機粉体を混合し溶融成形後、有機媒体及び無機粉体を抽出して微多孔膜を得る方法は知られているが、無機物の抽出する工程が必要であり、得られた膜の透過性は無機分体の粒径によるところが大きく、その制御は難しかった。
また、超高分子量ポリオレフィンを用いた高強度の微多孔膜の製造法が種々提案されている。例えば、特開昭６０−２４２０３５号、特開昭６１−１９５１３２号、特開昭６１−１９５１３３号、特開昭６３−３９６０２号、特開昭６３−２７３６５１号等には、超高分子量ポリオレフィンを含むポリオレフィン組成物を溶媒に加熱溶解した溶液からゲル状シートを成形し、前記ゲル状シートを加熱延伸、溶媒の抽出除去による微多孔膜を製造する方法が記載されているが、これらの技術によるポリオレフィン微多孔膜は孔径が小さく、孔径分布が狭いことが特徴で、電池用セパレーター等には好適であったが大孔径の微多孔膜は得られていなかった。
【０００３】
【発明が解決しようとする課題】
最近では各用途ごとに種々の透過性の微多孔膜がのぞまれており、それぞれの用途にあった特性を向上させるために膜の透過性の制御が望まれていた。しかしながら、先行発明においては、延伸法によって微細な孔を多数形成させており、孔径が小さく、孔径分布がせまいため、水処理、精密濾過膜等の用途に用いられる大孔径の微多孔膜は得られておらず、その開発が望まれていた。
【０００４】
【課題を解決するための手段】
本発明者らは、超高分子量ポリオレフィンを特定量含有する組成物を用い、その溶媒との特定濃度の溶液を押し出して、冷却することにより微多孔膜を得る際、冷却条件をコントロールすることにより、高透過性の膜を得ることが出来ることを見い出し、本発明に想到した。
すなわち、本発明は、重量平均分子量５×１０５以上の超高分子量ポリオレフィン（Ａ）と重量平均分子量５×１０５未満のポリオレフィン（Ｂ）の混合物で、（Ｂ）／（Ａ）の重量比が０．２〜２０であるポリオレフィン組成物５〜４０重量％と、溶媒９５〜６０重量％からなる溶液を調製し、前記溶液をダイより押し出し、冷却ロールにより引き取りフィルムを成形後、無延伸フィルム中の残存溶媒を除去し、乾燥してポリオレフィン微多孔膜を製造する方法において、ダイと冷却ロールの間隔（エアーギャップ）を５〜１００ｍｍ、冷却ロールの温度を３０℃〜１００℃（ポリオレフィンの結晶化温度）及び引き取り速度を１〜２０ｍ／分とすることにより冷却条件を調整することを特徴とするポリオレフィン微多孔膜の製造方法である。
【０００５】
【発明の実施の形態】
本発明を以下に詳細に説明する。
本発明において製造するポリオレフィン微多孔膜は、重量平均分子量５×１０5以上の超高分子量ポリオレフィン（Ａ）と重量平均分子量５×１０5未満のポリオレフィン（Ｂ）の混合物で、（Ｂ）／（Ａ）の重量比が０.２〜２０、好ましくは０.５〜１０であるポリオレフィン組成物からなる。
ポリオレフィン組成物中の（Ｂ）／（Ａ）の重量比が０.２未満では、得られるゲル状シートの厚み方向の収縮が起きやすく透過性が低下し、また溶液粘度が高くなり成形加工性が低下する。また、（Ｂ）／（Ａ）の重量比が２０を超えると低分子量成分が多くなり、ゲル構造が緻密化し、得られる微多孔膜の透過性が低下する。
【０００６】
本発明で用いる超高分子量ポリオレフィンは、重量平均分子量が５×１０5以上であり、好ましくは１×１０6〜１５×１０6である。また、重量平均分子量が５×１０5未満のポリオレフィンの分子量の下限としては、１×１０5以上のものが好ましい。重量平均分子量が１×１０5未満のポリオレフィンを用いると、破断が起こりやすく、目的の微多孔膜が得られないので好ましくない。したがって重量平均分子量が１×１０5以上５×１０5未満のポリオレフィンを超高分子量ポリオレフィンに配合するのが好ましい。
【０００７】
上記ポリオレフィンとしては、エチレン、プロピレン、１−ブテン、４−メチル−ペンテン−１、１−ヘキセンなどを重合した結晶性の単独重合体、２段重合体、又は共重合体及びこれらのブレンド物等が挙げられる。これらのうちではポリプロピレン、ポリエチレン（特に高密度ポリエチレン）及びこれらの組成物等が好ましい。
なお、上記ポリオレフィン組成物の分子量分布（重量平均分子量／数平均分子量）は３００以下、特に５〜５０であるのが好ましい。分子量分布が３００をこえると、低分子量成分による破断が起こり膜全体の強度が低下するため好ましくない。
【０００８】
このポリオレフィン組成物は、上記分子量及び分子量分布を有していれば、多段重合によるものであっても、２種以上のポリオレフィンによる組成物であっても、いずれでもよい。
多段重合の場合、例えば、重量平均分子量が５×１０５以上の超高分子量ポリオレフィン成分（Ａ）と重量平均分子量が５×１０５未満のポリオレフィン成分（Ｂ）を（Ｂ）／（Ａ）の重量比が０．２〜２０で、かつ分子量分布が３００以下となるように、オレフィンを多段重合することにより製造することができる。多段重合法としては、二段重合により、高分子量部分と低分子量部分とを製造する方法を採用するのが好ましい。
なお、上述したような超高分子量成分を含有するポリオレフィン組成物には、必要に応じて、酸化防止剤、紫外線吸収剤、アンチブロッキング剤、顔料、染料、無機充填材などの各種添加剤を本発明の目的を損なわない範囲で添加することができる。
【０００９】
本発明の微多孔膜の製造方法は、上述のポリオレフィン組成物を溶媒に加熱溶解することにより、溶液を調製する。この溶媒としては、ノナン、デカン、デカリン、ｐ−キシレン、ウンデカン、ドデカン、流動パラフィンなどの脂肪族または環式の炭化水素、あるいは沸点がこれらに対応する鉱油留分などを用いることができる。またこの溶媒の粘度としては、２５℃における粘度が３０〜５００ｃＳｔ、特に５０〜２００ｃＳｔであるのが好ましい。２５℃における粘度が３０ｃＳｔ未満では、不均一吐出を生じ、混練が困難であり、一方５００ｃＳｔを超えると、後工程での脱溶媒が容易でなくなる。
【００１０】
加熱溶解は、ポリオレフィン組成物を溶媒中で完全に溶解する温度で撹拌しながら行うか、又は押出機中で均一混合して溶解する方法で行う。溶媒中で撹拌しながら溶解する場合は、温度は使用する重合体及び溶媒により異なるが、例えばポリエチレン組成物の場合には１４０〜２５０℃の範囲である。ポリオレフィン組成物の高濃度溶液から微多孔膜を製造する場合は、押出機中で溶解するのが好ましい。
【００１１】
押出機中で溶解する場合は、まず押出機に上述したポリオレフィン組成物を供給し、溶融する。溶融温度は、使用するポリオレフィンの種類によって異なるが、ポリオレフィンの融点＋３０〜１００℃が好ましい。例えば、ポリエチレンの場合は１６０〜２３０℃、特に１７０〜２００℃であるのが好ましく、ポリプロピレンの場合は１９０〜２７０℃、特に１９０〜２５０℃であるのが好ましい。次に、この溶融状態のポリオレフィン組成物に対して、液状の溶媒を押出機の途中から供給する。
【００１２】
ポリオレフィン組成物と溶媒との配合割合は、ポリオレフィン組成物と溶媒の合計を１００重量％として、ポリオレフィン組成物が５〜４０重量％、好ましくは１０〜３０重量％であり、溶媒が９５〜６０重量％、好ましくは９０〜７０重量％である。ポリオレフィン組成物が５重量％未満では（溶媒が９５重量％を超えると）、シート状に成形する際に、ダイ出口で、スウエルやネックインが大きくシートの成形性、自己支持性が困難となる。一方、ポリオレフィン組成物が４０重量％を超えると（溶媒が６０重量％未満では）、厚み方向の収縮が大きくなり、空孔率が低下し、大孔径を有する微多孔膜が得られず、また成形加工性も低下する。この範囲において濃度を変えることにより、膜の透過性をコントロールすることができる。
【００１３】
次に、このようにして溶融混練したポリオレフィン組成物の加熱溶液を直接に、あるいはさらに別の押出機を介して、または一旦冷却してペレット化した後、再度押出機を介して、ダイ等から押し出して成形する。
ダイは、通常長方形の口金形状をしたシートダイが用いられるが、２重円筒状の中空糸ダイ、インフレーションダイ等も用いることができる。シートダイを用いた場合のダイギャップは通常０．１〜５ｍｍである。押し出し成形時には１４０〜２５０℃に加熱して押し出す。
【００１４】
ダイから押し出された溶液は、冷却ロールにより引き取られることによりゲル状物に成形されるが、この冷却条件をコントロールすることにより孔径等を制御できる。ダイから冷却ロールの間隔（エアーギャップ）は、５ｍｍ〜１００ｍｍ、好ましくは１０ｍｍ〜５０ｍｍにする必要がある。樹脂溶液の粘度が低い場合は、ダイから冷却ロールの間隔（エアーギャップ）が長いと得られたシートはネックインを起こしやすく短いほうが好ましい。
【００１５】
冷却ロールの温度は、３０℃〜１００℃（ポリオレフィンの結晶化温度）、好ましくは４０〜９０℃にする必要がある。冷却ロール温度が高すぎると、ゲル状シートは徐冷されてゲル構造を形成するポリオレフィンのラメラ構造を構成する壁が厚くなり、微多孔は独立泡になり易いため、脱溶媒性が低下し透過性が低下する。冷却ロール温度が低すぎると、ゲル状シートは急冷されてゲル構造が緻密になり過ぎるため、孔径が小さくなり、透過性が低下する。
引き取り速度は、１〜２０ｍ／分、好ましくは３〜１０ｍ／分である。引き取り速度が速過ぎるとシートがネックインを起こし、延伸されやすいため、遅いほうが好ましい。
【００１６】
ダイから押し出された溶液は、冷却ロールを通すことにより得られたゲル状成形物は、溶剤で洗浄し残留する溶媒を除去する。洗浄溶剤としては、ペンタン、ヘキサン、ヘプタンなどの炭化水素、塩化メチレン、四塩炭素などの塩素化炭化水素、三フッ化エタンなどのフッ化炭化水素、ジエチルエーテル、ジオキサンなどのエーテル類などの易揮発性のものを用いることができる。これらの溶剤はポリオレフィン組成物の溶解に用いた溶媒に応じて適宜選択し、単独もしくは混合して用いる。洗浄方法は、溶剤に浸漬し抽出する方法、溶剤をシャワーする方法、またはこれらの組合せによる方法などにより行うことができる。
上述のような洗浄は、成形物中の残留溶媒が１重量％未満になるまで行う。その後洗浄溶剤を乾燥するが、洗浄溶剤の乾燥方法は加熱乾燥、風乾などの方法で行うことができる。乾燥した成形物は、結晶分散温度〜融点の温度範囲で熱固定することが望ましい。
【００１７】
以上のようにして製造したポリエチレン微多孔膜は、透気度が５〜１００秒／１００ｃｃ、空孔率が３５〜９５％、平均貫通孔径が０.０５〜１．０μｍの高透過性膜である。
なお、得られたポリエチレン微多孔膜は、必要に応じてさらに、プラズマ照射、界面活性剤含浸、表面グラフト等の親水化処理などの表面修飾を施すことができる。
【００１８】
【実施例】
以下に本発明について実施例を挙げてさらに詳細に説明するが、本発明は実施例に特に限定されるものではない。なお、実施例における試験方法は次の通りである。
（１）膜厚：断面を走査型電子顕微鏡により測定。
（２）透気度：ＪＩＳ Ｐ８１１７に準拠して測定。
（３）平均孔径：コールターポロメーターＩＩ（コールター社製）にて測定。
（４）シートの成形性：メルトフラクチャー、ネックイン、シート表面性及び厚薄ムラを目視でチェックし、成形のしやすさを○△×で評価。
（５）シートの脱溶媒性：膜を四角の枠に固定し、室温において塩化メチレン中に５分間含浸させた時の膜の白色度により判定。溶媒が除去されているほど膜は白く、残っている場合は透明となる。
【００１９】
実施例１
重量平均分子量が３．０×１０5の高密度ポリエチレン（ＨＤＰＥ）８０重量％と重量平均分子量が２．５×１０6の超高分子量ポリエチレン（ＵＨＭＷＰＥ）２０重量％からなるポリエチレン組成物に、酸化防止剤をポリエチレン組成物１００重量部当たり０．３７５重量部を加えたポリエチレン組成物を得た。このポリエチレン組成物２０重量部を二軸押出機（５８ｍｍφ、Ｌ／Ｄ＝４２、強混練タイプ）に投入した。また、この二軸押出機のサイドフィーダーから流動パラフィン８０重量部を供給し、２００℃、２００ｒｐｍで溶融混練して、押出機にてポリエチレン溶液を調製し、押出機の先端に設置されたＴダイから押し出し、ダイとロールの間隔を２０ｍｍ、冷却ロール温度を６０℃、引き取り速度を５ｍ／分の条件でゲル状シートを押し出した。得られたシートを塩化メチレンで洗浄して残留する流動パラフィンを抽出除去した後、乾燥および１１５℃で熱処理を行いポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第１表に示す。
【００２０】
実施例２〜４
実施例１において、成形条件を表１に示すように変更した以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第１表に示す。
【００２１】
実施例５〜６
実施例１において、ポリエチレン組成物の割合を表１に示すように変更した以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第１表に示す。
【００２２】
実施例８〜９
実施例１において、ポリエチレン組成物と溶媒の割合を表１に示すように変更した以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第１表に示す。
【００２３】
比較例１〜４
実施例１において、成形条件を表２に示すように変更した以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第２表に示す。
【００２４】
比較例５
実施例１において、超高分子量ポリエチレンのみを使用する以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第２表に示す。
【００２５】
比較例６
実施例１において、ポリエチレン組成物の割合を表１に示すように変更した以外は、実施例１と同様の方法で、ポリエチレン微多孔膜を得た。このポリエチレン微多孔膜の物性評価の結果を第２表に示す。
【００２６】
【表１】
【表２】
表１及び表２から明らかなように、冷却時の成形条件を本発明の範囲内で行うと、得られる微多孔膜は、平均孔径が大きく高透過性の膜であることが解る。また、超高分子量ポリエチレンのみを用いて製造した微多孔膜はシート成形性が悪く、樹脂溶液濃度を高くして製造した微多孔膜は透気性が悪いことが解る。
【００２９】
【発明の効果】
以上詳述したように本発明の方法により得られるポリオレフィン微多孔膜は、孔径が大きく、高透過性であり、液体フィルター等として好適に用いることができる。[0001]
[Industrial application fields]
The present invention relates to a method for producing a microporous membrane comprising a polyolefin composition containing ultrahigh molecular weight polyolefin, and more particularly to a highly permeable polyolefin microporous membrane.
[0002]
[Prior art]
Microporous membranes are used in various applications such as battery separators, electrolytic capacitor membranes, various filters, moisture permeable and waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes.
Conventionally, a method for obtaining a microporous film by mixing an organic medium and inorganic powder such as fine powdered silica into polyolefin and melt-molding and then extracting the organic medium and inorganic powder is known. A process was required, and the permeability of the obtained membrane was largely dependent on the particle size of the inorganic fraction, and its control was difficult.
Various methods for producing a high-strength microporous film using ultrahigh molecular weight polyolefin have been proposed. For example, JP-A-60-242035, JP-A-61-195132, JP-A-61-195133, JP-A-63-39602, JP-A-63-273651, etc. include ultrahigh molecular weight polyolefins. A method for producing a microporous membrane by forming a gel-like sheet from a solution obtained by heating and dissolving a polyolefin composition containing the solvent in a solvent, heating and stretching the gel-like sheet, and extracting and removing the solvent is described. The polyolefin microporous membrane is characterized by a small pore size and a narrow pore size distribution, and was suitable for battery separators and the like, but a microporous membrane with a large pore size was not obtained.
[0003]
[Problems to be solved by the invention]
Recently, various permeable microporous membranes are desired for each application, and it has been desired to control the permeability of the membrane in order to improve the properties suitable for each application. However, in the prior invention, a large number of fine pores are formed by the stretching method, and the pore size is small and the pore size distribution is small. Therefore, a microporous membrane having a large pore size used for water treatment, microfiltration membranes, etc. is obtained. The development was desired.
[0004]
[Means for Solving the Problems]
The present inventors use a composition containing a specific amount of ultrahigh molecular weight polyolefin, extrude a solution having a specific concentration with the solvent, and cool it to obtain a microporous film by cooling, by controlling the cooling conditions. The present inventors have found that a highly permeable membrane can be obtained and have arrived at the present invention.
That is, the present invention is a mixture of an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 5 × 10 5 or more and a polyolefin (B) having a weight average molecular weight of less than 5 × 10 5 , and a weight ratio of (B) / (A). A solution comprising 5 to 40% by weight of a polyolefin composition having a weight of 0.2 to 20 and 95 to 60% by weight of a solvent is prepared, the solution is extruded from a die, a take-up film is formed by a cooling roll, and an unstretched film is formed. In the method for producing a polyolefin microporous membrane by removing the residual solvent in the substrate and drying it, the distance between the die and the cooling roll (air gap) is 5 to 100 mm, and the temperature of the cooling roll is 30 ° C. to 100 ° C. (polyolefin crystals) The cooling conditions are adjusted by adjusting the temperature of the reaction and the take-up speed to 1 to 20 m / min. .
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The microporous polyolefin membrane produced in the present invention is a mixture of an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 5 × 10 5 or more and a polyolefin (B) having a weight average molecular weight of less than 5 × 10 5 , and is (B) / ( It consists of a polyolefin composition having a weight ratio of A) of 0.2 to 20, preferably 0.5 to 10.
When the weight ratio of (B) / (A) in the polyolefin composition is less than 0.2, the resulting gel-like sheet tends to shrink in the thickness direction, the permeability is lowered, and the solution viscosity is increased, resulting in moldability. Decreases. On the other hand, when the weight ratio (B) / (A) exceeds 20, low molecular weight components increase, the gel structure becomes dense, and the permeability of the resulting microporous membrane decreases.
[0006]
The ultrahigh molecular weight polyolefin used in the present invention has a weight average molecular weight of 5 × 10 5 or more, preferably 1 × 10 6 to 15 × 10 6 . Further, the lower limit of the molecular weight of the polyolefin having a weight average molecular weight of less than 5 × 10 5 is preferably 1 × 10 5 or more. Use of a polyolefin having a weight average molecular weight of less than 1 × 10 5 is not preferable because breakage tends to occur and the desired microporous film cannot be obtained. Therefore, it is preferable to blend a polyolefin having a weight average molecular weight of 1 × 10 5 or more and less than 5 × 10 5 into the ultrahigh molecular weight polyolefin.
[0007]
Examples of the polyolefin include a crystalline homopolymer, a two-stage polymer, a copolymer and a blend thereof obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-pentene-1, 1-hexene, and the like. Is mentioned. Of these, polypropylene, polyethylene (particularly high-density polyethylene) and compositions thereof are preferred.
In addition, it is preferable that the molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin composition is 300 or less, particularly 5 to 50. A molecular weight distribution exceeding 300 is not preferable because breakage due to a low molecular weight component occurs and the strength of the entire film decreases.
[0008]
As long as this polyolefin composition has the above molecular weight and molecular weight distribution, it may be either multistage polymerization or a composition of two or more types of polyolefin.
In the case of multistage polymerization, for example, an ultrahigh molecular weight polyolefin component (A) having a weight average molecular weight of 5 × 10 5 or more and a polyolefin component (B) having a weight average molecular weight of less than 5 × 10 5 are represented by (B) / (A). It can be produced by multistage polymerization of olefins so that the weight ratio is 0.2 to 20 and the molecular weight distribution is 300 or less. As the multistage polymerization method, it is preferable to employ a method of producing a high molecular weight portion and a low molecular weight portion by two-stage polymerization.
The polyolefin composition containing the ultra-high molecular weight component as described above contains various additives such as an antioxidant, an ultraviolet absorber, an anti-blocking agent, a pigment, a dye, and an inorganic filler as necessary. It can add in the range which does not impair the objective of invention.
[0009]
In the method for producing a microporous membrane of the present invention, a solution is prepared by heating and dissolving the above-described polyolefin composition in a solvent. Examples of the solvent include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, p-xylene, undecane, dodecane, and liquid paraffin, or mineral oil fractions having boiling points corresponding to these. The viscosity of this solvent is preferably 30 to 500 cSt, particularly 50 to 200 cSt at 25 ° C. When the viscosity at 25 ° C. is less than 30 cSt, non-uniform discharge occurs and kneading is difficult. On the other hand, when the viscosity exceeds 500 cSt, solvent removal in the subsequent process becomes difficult.
[0010]
The dissolution by heating is performed with stirring at a temperature at which the polyolefin composition is completely dissolved in a solvent, or by uniformly mixing and dissolving in an extruder. When dissolving in a solvent while stirring, the temperature varies depending on the polymer and solvent used, but for example, in the case of a polyethylene composition, it is in the range of 140 to 250 ° C. When producing a microporous membrane from a high concentration solution of a polyolefin composition, it is preferable to dissolve in a extruder.
[0011]
When melt | dissolving in an extruder, the polyolefin composition mentioned above is first supplied to an extruder, and it melts. Although melting temperature changes with kinds of polyolefin to be used, melting | fusing point of polyolefin + 30-100 degreeC is preferable. For example, in the case of polyethylene, it is preferably 160 to 230 ° C., particularly 170 to 200 ° C., and in the case of polypropylene, it is preferably 190 to 270 ° C., particularly preferably 190 to 250 ° C. Next, a liquid solvent is supplied from the middle of the extruder to the molten polyolefin composition.
[0012]
The blending ratio of the polyolefin composition and the solvent is 5 to 40% by weight, preferably 10 to 30% by weight of the polyolefin composition, and 95 to 60% by weight of the solvent, with the total of the polyolefin composition and the solvent being 100% by weight. %, Preferably 90 to 70% by weight. When the polyolefin composition is less than 5% by weight (when the solvent exceeds 95% by weight), when forming into a sheet, swell and neck-in are large at the die exit, making it difficult to form and self-support the sheet. . On the other hand, when the polyolefin composition exceeds 40% by weight (when the solvent is less than 60% by weight), shrinkage in the thickness direction increases, the porosity decreases, and a microporous film having a large pore diameter cannot be obtained. Molding processability also decreases. By changing the concentration within this range, the permeability of the membrane can be controlled.
[0013]
Next, the heated solution of the polyolefin composition melt-kneaded in this way is directly or through another extruder, or once cooled and pelletized, and then again through the extruder and from a die or the like. Extrude and mold.
As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical hollow fiber die, an inflation die, or the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm. At the time of extrusion molding, it is heated to 140 to 250 ° C. and extruded.
[0014]
The solution extruded from the die is formed into a gel-like material by being taken up by a cooling roll, and the pore diameter and the like can be controlled by controlling this cooling condition. The distance between the die and the cooling roll (air gap) needs to be 5 mm to 100 mm, preferably 10 mm to 50 mm. When the viscosity of the resin solution is low, the sheet obtained when the distance between the die and the cooling roll (air gap) is long is likely to cause neck-in and is preferably short.
[0015]
Temperature of the cooling roll is (crystallization temperature of the polyolefin) 30 ℃ ~ 100 ℃, preferably it is necessary to 40 to 90 ° C.. If the chill roll temperature is too high, the gel sheet is gradually cooled to thicken the walls of the polyolefin lamellar structure that forms the gel structure, and the micropores tend to become closed-cell foams. Sex is reduced. If the cooling roll temperature is too low, the gel sheet is rapidly cooled and the gel structure becomes too dense, so that the pore diameter is reduced and the permeability is lowered.
The take-up speed is 1 to 20 m / min, preferably 3 to 10 m / min. If the take-up speed is too fast, the sheet will be necked in and easily stretched.
[0016]
The gel extruded product obtained by passing the solution extruded from the die through a cooling roll is washed with a solvent to remove the remaining solvent. Cleaning solvents include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and tetrasalt carbon, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Volatile ones can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or in combination. The cleaning method can be performed by a method of immersing and extracting in a solvent, a method of showering a solvent, or a method using a combination thereof.
Washing as described above is performed until the residual solvent in the molded product is less than 1% by weight. Thereafter, the cleaning solvent is dried. The cleaning solvent can be dried by heat drying, air drying, or the like. The dried molded product is preferably heat-set in the temperature range of the crystal dispersion temperature to the melting point.
[0017]
The polyethylene microporous membrane produced as described above is a highly permeable membrane having an air permeability of 5 to 100 sec / 100 cc, a porosity of 35 to 95%, and an average through hole diameter of 0.05 to 1.0 μm. is there.
The obtained polyethylene microporous membrane may be further subjected to surface modification such as plasma irradiation, surfactant impregnation, and hydrophilic treatment such as surface grafting, if necessary.
[0018]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not particularly limited to the examples. In addition, the test method in an Example is as follows.
(1) Film thickness: The cross section was measured with a scanning electron microscope.
(2) Air permeability: Measured according to JIS P8117.
(3) Average pore diameter: Measured with Coulter Porometer II (manufactured by Coulter).
(4) Sheet moldability: Melt fracture, neck-in, sheet surface property, and thickness unevenness were visually checked, and the ease of molding was evaluated by ○ △ ×.
(5) Solvent removal property of sheet: Judged by the whiteness of the membrane when the membrane is fixed to a square frame and impregnated in methylene chloride for 5 minutes at room temperature. The more the solvent is removed, the whiter the film is, and the remaining is transparent.
[0019]
Example 1
A polyethylene composition comprising 80% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 3.0 × 10 5 and 20% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2.5 × 10 6 was oxidized. The polyethylene composition which added 0.375 weight part of inhibitor with respect to 100 weight part of polyethylene compositions was obtained. 20 parts by weight of this polyethylene composition was put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). In addition, 80 parts by weight of liquid paraffin is supplied from the side feeder of this twin screw extruder, melt kneaded at 200 ° C. and 200 rpm, a polyethylene solution is prepared by the extruder, and a T-die installed at the tip of the extruder The gel sheet was extruded under the conditions that the distance between the die and the roll was 20 mm, the cooling roll temperature was 60 ° C., and the take-up speed was 5 m / min. The obtained sheet was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment at 115 ° C. to obtain a polyethylene microporous membrane. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 1.
[0020]
Examples 2-4
A polyethylene microporous membrane was obtained in the same manner as in Example 1 except that the molding conditions were changed as shown in Table 1 in Example 1. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 1.
[0021]
Examples 5-6
A polyethylene microporous membrane was obtained in the same manner as in Example 1 except that the ratio of the polyethylene composition was changed as shown in Table 1 in Example 1. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 1.
[0022]
Examples 8-9
A polyethylene microporous membrane was obtained in the same manner as in Example 1 except that the ratio of the polyethylene composition and the solvent was changed as shown in Table 1 in Example 1. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 1.
[0023]
Comparative Examples 1-4
A polyethylene microporous membrane was obtained in the same manner as in Example 1 except that the molding conditions were changed as shown in Table 2 in Example 1. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 2.
[0024]
Comparative Example 5
In Example 1, a polyethylene microporous membrane was obtained in the same manner as in Example 1 except that only ultrahigh molecular weight polyethylene was used. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 2.
[0025]
Comparative Example 6
A polyethylene microporous membrane was obtained in the same manner as in Example 1 except that the ratio of the polyethylene composition was changed as shown in Table 1 in Example 1. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 2.
[0026]
[Table 1]
[Table 2]
As is apparent from Tables 1 and 2, when the molding conditions during cooling are performed within the scope of the present invention, it can be seen that the obtained microporous film is a highly permeable film having a large average pore diameter. Moreover, it turns out that the microporous membrane manufactured using only ultra high molecular weight polyethylene has poor sheet moldability, and the microporous membrane manufactured by increasing the resin solution concentration has poor air permeability.
[0029]
【The invention's effect】
As described in detail above, the polyolefin microporous membrane obtained by the method of the present invention has a large pore size and high permeability, and can be suitably used as a liquid filter or the like.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12025297A JP3638401B2 (en) | 1997-04-23 | 1997-04-23 | Method for producing polyolefin microporous membrane |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12025297A JP3638401B2 (en) | 1997-04-23 | 1997-04-23 | Method for producing polyolefin microporous membrane |
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| JPH10296839A JPH10296839A (en) | 1998-11-10 |
| JP3638401B2 true JP3638401B2 (en) | 2005-04-13 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4877881B2 (en) * | 2000-08-07 | 2012-02-15 | 旭化成イーマテリアルズ株式会社 | Zinc halogen battery separator |
| JP2005193200A (en) * | 2004-01-09 | 2005-07-21 | Kuraray Co Ltd | Hollow fiber membrane having excellent mechanical strength and its production method |
| JP5191113B2 (en) * | 2005-09-27 | 2013-04-24 | 旭化成ケミカルズ株式会社 | Ethylene polymer composition powder |
| KR101243070B1 (en) | 2005-09-28 | 2013-03-13 | 도레이 배터리 세퍼레이터 필름 주식회사 | Process for producing microporous polyethylene film and separator for cell |
| WO2007046226A1 (en) * | 2005-10-18 | 2007-04-26 | Toray Industries, Inc. | Microporous film for power storage device separator and power storage device separator making use of the same |
| JP5202816B2 (en) * | 2006-04-07 | 2013-06-05 | 東レバッテリーセパレータフィルム株式会社 | Polyolefin microporous membrane and method for producing the same |
| JP4979824B1 (en) * | 2011-03-29 | 2012-07-18 | 株式会社アストム | Ion exchange membrane |
| WO2018078698A1 (en) * | 2016-10-24 | 2018-05-03 | 住友化学株式会社 | Separator, and secondary battery containing separator |
| CN106393646B (en) * | 2016-11-28 | 2018-08-21 | 中国科学院宁波材料技术与工程研究所 | A kind of 3D printing high temperature consumptive material wire-drawing equipment |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS60242035A (en) * | 1984-04-27 | 1985-12-02 | Toa Nenryo Kogyo Kk | Microporous polyethylene film and production thereof |
| JPS61195133A (en) * | 1985-02-25 | 1986-08-29 | Toa Nenryo Kogyo Kk | Finely porous membrane of ultra-high-molecular-weight alpha-olefin polymer |
| JPS61195132A (en) * | 1985-02-25 | 1986-08-29 | Toa Nenryo Kogyo Kk | Production of finely porous membrane of ultra-high-molecular-weight alpha-olefin polymer |
| JPH0679658B2 (en) * | 1986-08-05 | 1994-10-12 | 東燃株式会社 | Method for producing polyethylene microporous membrane |
| JPS63273651A (en) * | 1987-04-30 | 1988-11-10 | Toa Nenryo Kogyo Kk | Production of fine porous membrane of polyolefin having ultra-high molecular weight |
| JPH06104736B2 (en) * | 1989-08-03 | 1994-12-21 | 東燃株式会社 | Polyolefin microporous membrane |
| JP3307027B2 (en) * | 1992-12-21 | 2002-07-24 | 三菱化学株式会社 | Method for producing porous resin molded article |
| JP3050021B2 (en) * | 1993-05-11 | 2000-06-05 | 三菱化学株式会社 | Battery separator and lithium battery using the same |
| JPH07195487A (en) * | 1993-12-28 | 1995-08-01 | Johoku Seikosho:Kk | Resin film molder |
| JPH08300440A (en) * | 1995-05-11 | 1996-11-19 | Mitsubishi Chem Corp | Production of porous polyethylene molding |
| JP3351940B2 (en) * | 1995-09-26 | 2002-12-03 | 東燃化学株式会社 | Method for producing microporous polyolefin membrane |
| JP3055470B2 (en) * | 1995-10-05 | 2000-06-26 | 三菱化学株式会社 | High strength porous film and method for producing the same |
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