JP3641321B2 - Method for producing polyolefin microporous membrane - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、超高分子量ポリオレフィン又は該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、特に高強度のポリオレフィン微多孔膜を低コスト及び高い生産性で製造する方法に関する。
【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。
【０００３】
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６１−４９５３１２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。
【０００４】
【発明が解決しようとする課題】
しかしながら、上記発明においては、ゲル状シートを逐次または同時の二軸延伸法によって微細な孔を多数形成させており、高倍率の二軸延伸によらなければ、高強度で微細で孔径分布のシャープな孔を持つ微多孔膜が得られないためにコスト及び生産性に問題があった。
【０００５】
したがって、本発明は、従来知られている微多孔膜の製造方法のこのような問題点を改良するもので、微細孔を有する高強度のポリオレフィン微多孔膜を低コスト及び高い生産性で製造する方法を提供することである。
【０００６】
【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の溶液を特定の条件下で剪断結晶化を行いながらシート状に押し出して、特定の引取り比で得られたゲル状シートを、特定の範囲で少なくとも一軸方向に延伸することにより、低コストで、生産性が高く高強度の微多孔膜が得られることを見い出し、本発明に想到した。
【０００７】
すなわち、本発明は、重量平均分子量７×１０5 以上の超高分子量ポリオレフィン又は該超高分子量ポリオレフィンを１重量％以上含有するポリオレフィン組成物１０〜８０重量％と、溶媒９０〜２０重量％からなる溶液を調製し、前記溶液をダイギャップが０．５〜２．５ｍｍのダイから、ダイ温度が１２０〜２５０℃でシート状に押し出し、冷却しながら引取り比１１０〜１０００％で引取り、ゲル状成形物を形成し、ゲル状成形物を少なくとも一軸方向に５〜５０倍に加熱延伸し、しかる後残存する溶媒を除去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。
【０００８】
【発明の実施の形態】
本発明を以下に詳細に説明する。
【０００９】
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７×１０5 以上の超高分子量ポリオレフィン又は該超高分子量ポリオレフィンを１重量％以上含有す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に含有する重量平均分子量７×１０5 以上の成分が１重量％未満では、延伸性の向上に寄与する超高分子量ポリオレフィンの分子鎖の絡み合いが不十分となるので、強度を十分に向上させるのが困難となる。一方、超高分子量成分の含有率の上限は特に限定的ではないが、９０重量％を超えると目的とするポリオレフィン溶液の高濃度化の達成及び延伸が困難となるため好ましくない。なお、上記ポリオレフィンは分子量１×１０3 以下の成分を実質的に含有しないのが好ましい。また、上記ポリオレフィンの分子量分布（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を超えると、延伸時に低分子量成分の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。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。
【００１０】
このポリオレフィンは、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。
【００１１】
多段重合の場合、例えば、重量平均分子量が７×１０5 以上の超高分子量成分を１重量％以上含有し、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。
【００１２】
また、２種以上のポリオレフィンによる組成物の場合、前記オレフィンの単独重合体又は共重合体で重量平均分子量が７×１０5 以上の超高分子量ポリオレフィンと、重量平均分子量が７×１０5 未満のポリオレフィンとを分子量分布が上記範囲となるように、適量混合することによって得ることができる。
【００１３】
組成物の場合、ポリオレフィン組成物中の超高分子量ポリオレフィンの含有量は、ポリオレフィン組成物全体を１００重量％として、１重量％以上である。超高分子量ポリオレフィンの含有量が１重量％未満では、延伸性の向上に寄与するところが不十分である。一方、上限は特に限定的ではない。
【００１４】
また、ポリオレフィン組成物中の超高分子量ポリオレフィン以外のポリオレフィン（重量平均分子量が７×１０5 未満のポリオレフィン）の分子量の下限としては、１×１０4 以上のものが好ましい。重量平均分子量が１×１０4 未満のポリオレフィンを用いると、延伸時に破断が起こりやすく、目的の微多孔膜がえ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７×１０5 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。
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。
【００１５】
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。
【００１６】
加熱溶解は、ポリエチレン組成物を溶媒中で完全に溶解する温度で攪拌しながら行うか、又は押出機中で均一混合して溶解する方法で行う。溶媒中で攪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。
【００１７】
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に対して、液状の溶媒を押出機の途中から供給する。
【００１８】
ポリオレフィンと溶媒との配合割合は、ポリオレフィンと溶媒の合計を１００重量％として、ポリオレフィンが１０〜８０重量％、好ましくは１５〜７０重量％であり、溶媒が９０〜２０重量％、好ましくは８５〜３０重量％である。ポリオレフィンが１０重量％未満では（溶媒が９０重量％を超えると）、シート状に成形する際に、ダイ出口で、スウェルやネックインが大きくシートの成形が困難となる。一方、ポリオレフィンが８０重量％を超えると（溶媒が２０重量％未満では）、均一な溶液の調製が困難となる。
【００１９】
なお、上記溶媒は途中にサイドフィーダー等を有する押出機を用いて、押出機の途中から溶融状態のポリオレフィンに供給する必要がある。超高分子量ポリオレフィンを含むポリオレフィンと溶媒とを同時に供給すると、粘度差が大き過ぎるために混合ができず、ポリオレフィンと押出機のスクリューとが共回りを起こし溶液を調製できない。このようにして溶融状態のポリオレフィンに溶媒を添加し、押出機中で混練することにより、均一な濃度のポリオレフィンの高濃度溶液を短時間で調製することができる。
【００２０】
次に、このようにして溶融混練したポリオレフィン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。
【００２１】
ダイは、通常長方形の口金形状をしたシート用ダイが用いられる。剪断結晶化を行わせるためにダイギャップは０．５〜２．５ｍｍであり、好ましくは１．５〜２．５ｍｍである。０．５ｍｍ未満ではシェアーがかかりすぎて表面肌荒れを起こす。押し出し成形温度は１５０〜２５０℃であり、好ましくは１６０〜２３０℃である。２５０℃を超えると劣化が生じるため好ましくなく、１５０℃未満ではポリオレフィン溶液の移送が困難で、吐出が安定しなくなるため好ましくない。この際押し出し速度は、通常２０〜３０ｃｍ／分ないし２〜３ｍ／分である。
【００２２】
このようにしてダイから押し出された溶液は、冷却することによりゲル状成形物に形成される。冷却は少なくともゲル化温度以下までは５０℃／分以上の速度で行うのが好ましい。一般に冷却速度が遅いと、得られるゲル状組成物の高次構造が粗くなり、それを形成する疑似細胞単位も大きなものとなるが、冷却速度が速いと、密な細胞単位となる。冷却速度が５０℃／分未満では、結晶化度が上昇し、延伸に適したゲル状組成物となりにくい。冷却方法としては、冷風、冷却水、その他の冷却媒体に直接接触させる方法、冷媒で冷却したロールに接触させる方法などを用いることができる。
【００２３】
ダイから押し出されたゲル状シートは、１１０〜１０００％の高引取り比で引取りながら冷却固化し、剪断結晶化させる。引取り比が１０００％を超えるとネックインが大きくなり、また延伸時に破断を起こしやすくなり好ましくなく、１１０％未満では剪断結晶化が十分には起こらず、微多孔膜が得られない。引取る際には、バンク成形法を用いることも可能である。
【００２４】
次に、このゲル状成形物を少なくとも一軸方向に延伸を行う。延伸はゲル状成形物を加熱し、通常のテンター法で、５〜５０倍、好ましくは１０〜２０倍に延伸する。この延伸によって、結晶間の開裂が生じ、孔が形成される。倍率が５０倍を超えると、延伸操作などで制約が生じる。倍率が５倍未満では十分な結晶間の開裂が行われず、満足できる微多孔膜が得られない。
【００２５】
延伸温度はポリエチレンの融点＋１０℃以下、好ましくはポリエチレンの結晶分散温度から結晶融点未満の範囲である。
【００２６】
得られた延伸成形物は、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、溶剤に侵漬し抽出する方法、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。
【００２７】
上述のような洗浄は、延伸成形物中の残存溶媒が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。乾燥した延伸成形物は、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。
【００２８】
さらに、得られた微多孔膜を逐次または同時の二軸延伸機で４〜４９倍、好ましくは２５〜４９倍に延伸することにより孔径をコントロールすることができる。
【００２９】
以上のようにして製造したポリエチレン微多孔膜は、空孔率が３５〜９５％で平均貫通孔径が０．００１〜０．５μで、かつ破断強度が５００ｋｇ／ｃｍ2 以上である。また本発明のポリエチレン微多孔膜の厚さは、用途に応じて適宜選択しうるが、一般に０．１〜１００μであり、好ましくは２〜５０μにすることができる。
【００３０】
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。
【００３１】
【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）破断強度：ＡＳＴＭ Ｄ８８２に準拠して測定。
（４）平均孔径：オムニソープ３６０（日機装（株））によって測定。
【００３２】
実施例１
重量平均分子量が２×１０6 の超高分子量ポリエチレン５．５重量部、重量平均分子量が３．０×１０5 の高密度ポリエチレン２４．５重量部、酸化防止剤をポリエチレン１００重量部当たり０．３７５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７０重量部を供給し、溶融混練して押出機中にてポリエチレン溶液を調製した。
【００３３】
続いて、この押出機の先端に設置されたＴダイからダイギャップ１．５ｍｍ、温度１８０℃で押し出し、冷却ロールで引取り比５００％で引取りながらゲル状シートを成形した。続いてこのゲル状シートを、１１５℃で５倍に横一軸延伸を行い、延伸膜を得た。得られた延伸膜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。
【００３４】
実施例２
実施例１において、延伸倍率を横一軸方向に１０倍にした以外は、実施例１と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００３５】
実施例３
実施例２において、引き取り比を１０００％にする以外は実施例２と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００３６】
実施例４
実施例３において、ポリエチレンとして重量平均分子量が１×１０6 の超高分子量ポリエチレン３０重量部を用いる以外は実施例３と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００３７】
実施例５
実施例３において、ポリエチレンとして重量平均分子量が２．５×１０6 の超高分子量ポリエチレンを７重量部、重量平均分子量が３．０×１０5 の高密度ポリエチレン３３重量部、溶媒として流動パラフィンを６０重量部用いる以外は実施例３と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００３８】
実施例６
実施例１において、延伸倍率を二軸方向に面倍率で２５倍にする以外は実施例１と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００３９】
実施例７
実施例２において、ダイ温度を２００℃、ダイギャップを２．５ｍｍで、バンク成形により２００％引取りをする以外は実施例２と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表１の物性を有していた。
【００４０】
比較例１
実施例１において、シート成形条件で、ダイ温度を２００℃、ダイギャップを２．５ｍｍ、引取り比を１００％にし、延伸を横軸方向に１０倍にした以外は実施例１と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表２の物性を有していた。
【００４１】
比較例２
実施例１において、シート成形条件で、ダイ温度を２００℃、ダイギャップを０．３ｍｍ、引取り比を１００％にし、延伸を横軸方向に１０倍にした以外は実施例１と同様にして微多孔膜を得た。以上のようにして得られた微多孔膜は表２の物性を有していた。
【００４２】
【表１】
【表２】
【００４４】
【発明の効果】
以上詳述したように本発明の方法である、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溶液からゲル状シートを、特定のダイギャップ、特定のダイ温度、特定の引取り比で成形することにより、高強度の微多孔膜が容易に得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a microporous membrane comprising an ultrahigh molecular weight polyolefin or a polyolefin composition containing the ultrahigh molecular weight polyolefin, and in particular, a method for producing a high-strength polyolefin microporous membrane at low cost and high productivity. About.
[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.
[0003]
Various methods for producing high-strength microporous membranes using ultrahigh molecular weight polyolefins have been proposed. For example, JP-A-60-242035, JP-A-61-495312, JP-A-61-195133, JP-A-63-39602, JP-A-63-273651, etc. include ultrahigh molecular weight polyolefins. A method is described in which a gel-like sheet is formed from a solution obtained by heating and dissolving a polyolefin composition containing the solvent in a solvent, the gel-like sheet is heated and stretched, and a microporous film is produced by extracting and removing the solvent.
[0004]
[Problems to be solved by the invention]
However, in the above invention, a number of fine pores are formed in the gel sheet by sequential or simultaneous biaxial stretching, and if high-strength biaxial stretching is not used, the strength is fine and the pore size distribution is sharp. There was a problem in cost and productivity because a microporous film having various pores could not be obtained.
[0005]
Therefore, the present invention improves such a problem of a conventionally known method for producing a microporous membrane, and produces a high-strength polyolefin microporous membrane having micropores at low cost and high productivity. Is to provide a method.
[0006]
[Means for Solving the Problems]
The present inventors extrude a solution of ultra-high molecular weight polyolefin into a sheet while carrying out shear crystallization under specific conditions, and obtain a gel-like sheet obtained at a specific take-off ratio at least uniaxially within a specific range. It has been found that by stretching in the direction, a microporous membrane with high productivity and high strength can be obtained at low cost, and the present invention has been conceived.
[0007]
That is, the present invention comprises an ultrahigh molecular weight polyolefin having a weight average molecular weight of 7 × 10 5 or more or a polyolefin composition containing 1% by weight or more of the ultrahigh molecular weight polyolefin and a solvent of 90 to 20% by weight. A solution is prepared, and the solution is extruded from a die having a die gap of 0.5 to 2.5 mm into a sheet shape at a die temperature of 120 to 250 ° C., and taken out at a take-off ratio of 110 to 1000 % while cooling. A method for producing a microporous polyolefin membrane, comprising forming a shaped molded product, heating and stretching the gel shaped product at least 5 to 50 times in a uniaxial direction, and then removing the remaining solvent.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0009]
The polyolefin microporous membrane produced in the present invention comprises an ultrahigh molecular weight polyolefin having a weight average molecular weight of 7 × 10 5 or more or a polyolefin composition containing 1% by weight or more of the ultrahigh molecular weight polyolefin .
If the component having a weight average molecular weight of 7 × 10 5 or more contained in the polyolefin composition is less than 1% by weight, the entanglement of the molecular chains of the ultra-high molecular weight polyolefin that contributes to the improvement of the stretchability becomes insufficient, so that the strength is sufficient. It is difficult to improve it. On the other hand, the upper limit of the content of the ultrahigh molecular weight component is not particularly limited, but if it exceeds 90% by weight, it is not preferable because it is difficult to achieve high concentration of the polyolefin solution and stretching. The polyolefin preferably contains substantially no component having a molecular weight of 1 × 10 3 or less. The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin is preferably 300 or less, particularly preferably 5 to 50. If the molecular weight distribution exceeds 300, the low molecular weight component breaks during stretching and the strength of the entire film is lowered, which is not preferable. 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.
[0010]
As long as this polyolefin has the above-mentioned molecular weight and molecular weight distribution, it may be either multistage polymerization or a composition of two or more polyolefins.
[0011]
In the case of multi-stage polymerization, for example, it is produced by multi-stage polymerization of olefin so that it contains 1% by weight or more of an ultra-high molecular weight component having a weight average molecular weight of 7 × 10 5 or more and a molecular weight distribution of 300 or less. Can do. 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.
[0012]
In the case of a composition comprising two or more types of polyolefin, a homopolymer or copolymer of the olefin and a super high molecular weight polyolefin having a weight average molecular weight of 7 × 10 5 or more and a weight average molecular weight of less than 7 × 10 5 It can be obtained by mixing an appropriate amount of polyolefin so that the molecular weight distribution is in the above range.
[0013]
In the case of the composition, the content of the ultrahigh molecular weight polyolefin in the polyolefin composition is 1% by weight or more, based on 100% by weight of the entire polyolefin composition. When the content of the ultrahigh molecular weight polyolefin is less than 1% by weight, the portion contributing to the improvement of stretchability is insufficient. On the other hand, the upper limit is not particularly limited.
[0014]
In addition, the lower limit of the molecular weight of polyolefins other than the ultrahigh molecular weight polyolefin (polyolefin having a weight average molecular weight of less than 7 × 10 5 ) in the polyolefin composition is preferably 1 × 10 4 or more. If a polyolefin having a weight average molecular weight of less than 1 × 10 4 is used, it is not preferable because breakage tends to occur during stretching, 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 7 × 10 5 into the ultrahigh molecular weight polyolefin.
The polyolefin containing the ultra-high molecular weight component as described above may contain 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 be added as long as the purpose is not impaired.
[0015]
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.
[0016]
The dissolution by heating is performed with stirring at a temperature at which the polyethylene composition is completely dissolved in a solvent, or by uniformly mixing and dissolving in an extruder. When dissolving with stirring in a solvent, the temperature varies depending on the polymer and solvent used, but in the case of a polyethylene composition, for example, it is in the range of 140-250 ° C. When producing a microporous membrane from a high concentration solution of a polyolefin composition, it is preferable to dissolve in a extruder.
[0017]
When melt | dissolving in an extruder, the polyolefin mentioned above is first supplied to an extruder, and is melted. 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 to the molten polyolefin from the middle of the extruder.
[0018]
The blending ratio of the polyolefin and the solvent is 10 to 80% by weight, preferably 15 to 70% by weight, and 90 to 20% by weight, preferably 85 to 85% by weight, with the total of the polyolefin and the solvent being 100% by weight. 30% by weight. When the polyolefin is less than 10% by weight (when the solvent exceeds 90% by weight), when forming into a sheet, swell and neck-in are large at the die exit, making it difficult to form the sheet. On the other hand, when the amount of polyolefin exceeds 80% by weight (when the solvent is less than 20% by weight), it is difficult to prepare a uniform solution.
[0019]
In addition, it is necessary to supply the said solvent to the molten polyolefin from the middle of an extruder using the extruder which has a side feeder etc. in the middle. If a polyolefin containing ultra-high molecular weight polyolefin and a solvent are supplied simultaneously, the difference in viscosity is too large to be mixed, and the polyolefin and the screw of the extruder co-rotate and a solution cannot be prepared. Thus, a high concentration solution of polyolefin having a uniform concentration can be prepared in a short time by adding a solvent to polyolefin in a molten state and kneading in an extruder.
[0020]
Next, the polyolefin melt solution kneaded and kneaded in this way is directly or via another extruder, or once cooled and pelletized, and then extruded again from the die or the like via the extruder. Mold.
[0021]
As the die, a sheet die having a generally rectangular base shape is used. In order to perform shearing crystallization, the die gap is 0.5 to 2.5 mm, preferably 1.5 to 2.5 mm. If it is less than 0.5mm to Oko the surface roughening is too much shear. The extrusion molding temperature is 150 to 250 ° C, preferably 160 to 230 ° C. If it exceeds 250 ° C., it is not preferable because deterioration occurs, and if it is less than 150 ° C., it is not preferable because it is difficult to transfer the polyolefin solution and discharge becomes unstable. At this time, the extrusion speed is usually 20 to 30 cm / min to 2 to 3 m / min.
[0022]
The solution extruded from the die in this way is formed into a gel-like molded product by cooling. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. In general, when the cooling rate is low, the higher order structure of the resulting gel-like composition becomes coarse, and the pseudo cell units that form the gel composition become large. However, when the cooling rate is high, the cells become dense cell units. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases and it is difficult to obtain a gel composition suitable for stretching. As a cooling method, a method of directly contacting cold air, cooling water, or another cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used.
[0023]
The gel-like sheet extruded from the die is cooled and solidified while being drawn at a high take-off ratio of 110 to 1000%, and is sheared and crystallized. If the take-up ratio exceeds 1000 %, the neck-in becomes large and breakage is liable to occur at the time of stretching, which is not preferred. If it is less than 110%, shear crystallization does not occur sufficiently and a microporous film cannot be obtained. When taking over, it is also possible to use a bank forming method.
[0024]
Next, this gel-like molded product is stretched in at least a uniaxial direction. Stretching is performed by heating the gel-like molded product and stretching it 5 to 50 times, preferably 10 to 20 times, by a usual tenter method. This stretching causes cleavage between the crystals and forms pores. If the magnification exceeds 50 times, there will be restrictions in the stretching operation and the like. If the magnification is less than 5 times, sufficient cleavage between crystals is not performed, and a satisfactory microporous film cannot be obtained.
[0025]
The stretching temperature is the melting point of polyethylene + 10 ° C. or less, preferably in the range from the crystal dispersion temperature of polyethylene to below the crystal melting point.
[0026]
The obtained stretched molded product 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 washing method can be performed by a method of immersing and extracting in a solvent, a method of showering a solvent, or a method of a combination thereof.
[0027]
Washing as described above is performed until the residual solvent in the stretched 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 stretched molded product is preferably heat-set within the temperature range of the crystal dispersion temperature to the melting point.
[0028]
Further, the pore diameter can be controlled by stretching the obtained microporous membrane 4 to 49 times, preferably 25 to 49 times, with a sequential or simultaneous biaxial stretching machine.
[0029]
The polyethylene microporous membrane produced as described above has a porosity of 35 to 95%, an average through-hole diameter of 0.001 to 0.5 μm, and a breaking strength of 500 kg / cm 2 or more. The thickness of the polyethylene microporous membrane of the present invention can be appropriately selected according to the use, but is generally 0.1 to 100 μm, preferably 2 to 50 μm.
[0030]
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.
[0031]
【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) Breaking strength: measured in accordance with ASTM D882.
(4) Average pore diameter: Measured with Omni Soap 360 (Nikkiso Co., Ltd.).
[0032]
Example 1
5.5 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 × 10 6 , 24.5 parts by weight of high density polyethylene having a weight average molecular weight of 3.0 × 10 5 , and 0.1 parts by weight of antioxidant per 100 parts by weight of polyethylene. 375 parts by weight were charged into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Further, 70 parts by weight of liquid paraffin was supplied from the side feeder of this twin-screw extruder, melt kneaded, and a polyethylene solution was prepared in the extruder.
[0033]
Subsequently, a gel sheet was formed while being extruded from a T die installed at the tip of the extruder at a die gap of 1.5 mm and a temperature of 180 ° C., and being drawn with a cooling roll at a take-up ratio of 500%. Subsequently, the gel-like sheet was subjected to transverse uniaxial stretching at 115 ° C. five times to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a polyethylene microporous membrane. The results of the physical property evaluation of this polyethylene microporous membrane are shown in Table 1.
[0034]
Example 2
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that the draw ratio was 10 times in the transverse uniaxial direction. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0035]
Example 3
In Example 2, a microporous membrane was obtained in the same manner as in Example 2 except that the take-up ratio was 1000%. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0036]
Example 4
In Example 3, a microporous membrane was obtained in the same manner as in Example 3 except that 30 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1 × 10 6 was used as polyethylene. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0037]
Example 5
In Example 3, 7 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2.5 × 10 6 as polyethylene, 33 parts by weight of high density polyethylene having a weight average molecular weight of 3.0 × 10 5 , and liquid paraffin as a solvent. A microporous membrane was obtained in the same manner as in Example 3 except that 60 parts by weight was used. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0038]
Example 6
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that the stretching ratio was 25 times in the biaxial direction and the surface ratio. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0039]
Example 7
In Example 2, a microporous film was obtained in the same manner as in Example 2 except that the die temperature was 200 ° C., the die gap was 2.5 mm, and 200% drawing was performed by bank molding. The microporous membrane obtained as described above had the physical properties shown in Table 1.
[0040]
Comparative Example 1
In Example 1, the same conditions as in Example 1 except that the die temperature was 200 ° C., the die gap was 2.5 mm, the take-up ratio was 100%, and the stretching was 10 times in the horizontal axis direction under the sheet forming conditions. A microporous membrane was obtained. The microporous membrane obtained as described above had the physical properties shown in Table 2.
[0041]
Comparative Example 2
In Example 1, the same conditions as in Example 1 except that the die temperature was 200 ° C., the die gap was 0.3 mm, the take-up ratio was 100%, and the stretching was 10 times in the horizontal axis direction under the sheet forming conditions. A microporous membrane was obtained. The microporous membrane obtained as described above had the physical properties shown in Table 2.
[0042]
[Table 1]
[Table 2]
[0044]
【The invention's effect】
As described above in detail, by forming a gel-like sheet from a polyolefin composition solution containing an ultrahigh molecular weight polyolefin, with a specific die gap, a specific die temperature, and a specific take-off ratio, which is the method of the present invention. A high-strength microporous film can be easily obtained.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13745396A JP3641321B2 (en) | 1996-05-08 | 1996-05-08 | Method for producing polyolefin microporous membrane |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13745396A JP3641321B2 (en) | 1996-05-08 | 1996-05-08 | Method for producing polyolefin microporous membrane |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09302120A JPH09302120A (en) | 1997-11-25 |
| JP3641321B2 true JP3641321B2 (en) | 2005-04-20 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP13745396A Expired - Lifetime JP3641321B2 (en) | 1996-05-08 | 1996-05-08 | Method for producing polyolefin microporous membrane |
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| Country | Link |
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| JP (1) | JP3641321B2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5948557A (en) * | 1996-10-18 | 1999-09-07 | Ppg Industries, Inc. | Very thin microporous material |
| JP4925238B2 (en) * | 2004-08-17 | 2012-04-25 | 旭化成イーマテリアルズ株式会社 | Method for producing polyolefin microporous membrane |
| CN114128031A (en) * | 2019-07-25 | 2022-03-01 | 东丽株式会社 | Polyolefin microporous membrane, laminate, and nonaqueous electrolyte secondary battery using same |
| KR20230160224A (en) * | 2021-03-23 | 2023-11-23 | 도레이 카부시키가이샤 | Polyolefin microporous membrane, battery separator and secondary battery |
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1996
- 1996-05-08 JP JP13745396A patent/JP3641321B2/en not_active Expired - Lifetime
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| Publication number | Publication date |
|---|---|
| JPH09302120A (en) | 1997-11-25 |
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| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
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| EXPY | Cancellation because of completion of term |