JP4080558B2 - Porous high-density paper and method for producing the same - Google Patents

Description

【００２０】
表５に示すように、素材としてのセルロースは２３０℃までの耐熱性を有しており、セルロースを溶かす薬剤が今も探索されていることからも分るように薬品に対して安定であり、耐熱性も耐薬品性を合せ持っていると言える。一方、多孔質フィルムは本質的に耐熱性、耐薬品性に欠けている。そこで、叩解の程度を進めた原料で製造され、気密度が無限大となって測定不能となる高密度紙を多孔質のものとすることができれば、従来不可能とされていた高気密度であって低密度の紙を得ることができる。即ち、叩解を進めた原料を使用しても、空気が通過することのできる微細な貫通孔を有する紙を製造することができれば、高気密度であって低密度の紙を得ることができるのである。この高気密度であって低密度の紙によれば、気密度を高いレベルでコントロールすることができ、従来の気密度を上げると密度が高くなって電気特性が悪く、密度を下げて電気特性を良くすると気密度が下がり緻密性に欠けることとなり、気密度と電気特性を同時に満足させることが困難であった紙の欠点を解消することができる。更に、多孔質フィルムが耐熱性の不足により使用できなかった分野への利用や、従来使用されていた製品の安全性の向上に寄与することができ、同時に石油資源の利用から再生産可能な天然資源への利用へと転換を図ることができて望ましい。
【００２１】
そこで、本発明は上記従来の事情に基づき、耐熱性、耐薬品性に優れた再生産の可能な天然資源であるセルロースを原料として、微細な貫通孔を有する多孔質で低密度であるとともに、緻密性を有して気密度が高い新規な多孔質高気密度紙、具体的には厚さが１００μｍ以下、気密度が１０００秒／１００ｃｃ以上、密度が０．６ｇ／ｃｍ ^３ 以下の多孔質高気密度紙を提供することを課題とする。
【００２２】
【課題を解決するための手段】
本発明は上記課題を達成するために、平均繊維径が１μｍ以下の微細なセルロースを水に分散させて湿紙を製造し、該湿紙中の水分を水と相溶性のある表面張力の小さい溶媒と置換させて、該湿紙に存在する空隙構造を保持したまま乾燥させることにより、厚さが２４．６μｍ〜１００μｍ、気密度が１０００秒／１００ｃｃ〜１４０００秒／１００ｃｃ、密度が０．３７８ｇ／ｃｍ ^３ 〜０．６ｇ／ｃｍ^３ の紙とし、微細な貫通孔を有する多孔質と、高い気密度を同時に実現した多孔質高気密度紙及びその製造方法を基本として提供する。また、原料を水より表面張力の小さい有機溶媒に分散させて抄紙する。湿紙中の水分は凍結乾燥させ、或いは湿紙中の有機溶媒は揮発させることにより乾燥させる。
【００２３】
上記本発明によれば、湿紙の状態においてセルロース繊維間の空隙構造に保持された水を溶媒置換又は凍結乾燥によって乾燥し、或はセルロース繊維を有機溶媒に分散させて抄紙することにより湿紙を製造し、湿紙中の有機溶媒を揮発させることにより乾燥させるため、従来の抄紙法のように湿紙からの乾燥工程で水が蒸発するときに隣同志の繊維を強力に引き付けて水素結合により密着することがない。そのため、平均繊維径が１μｍ以下の微細なセルロース繊維を原料として、高気密度であって多孔質の紙を、厚さを厚くすることなく得ることができる。具体的には厚さが１００μｍ以下、気密度が１０００秒／１００ｃｃ以上、密度が０．６ｇ／ｃｍ ^３ 以下の多孔質高気密度紙を得ることができる。しかも、セルロース繊維を原料とするため、現在の工業紙に要求されている耐熱性、耐薬品性を大幅に向上させることができる。
【００２４】
【発明の実施の形態】
以下、本発明にかかる多孔質高気密度紙及びその製造方法の各実施形態を説明する。本発明は平均繊維径が１μｍ以下の微細なセルロースを原料として湿紙を製造し、該湿紙に存在する空隙構造を保持したまま乾燥させることにより、微細な貫通孔を有することに特徴を有する。
【００２５】
従来の抄紙法においても、原料としてのセルロース繊維の叩解を進めていくと得られる紙の気密度は高くなるが、前記したようにＪＩＳ法ＣＳＦの値で約２００ｍｌ以下に叩解を進めて抄紙をすると、繊維間の空隙なくなってしまい、紙には貫通孔がもはや存在しなくなり、気密度は無限大となって実際上測定できなくなってしまう。しかしながら、その場合であっても湿紙の状態においては空隙構造を有する。即ち、乾燥した紙には貫通孔が存在しなくても、乾燥前の湿紙には貫通孔が存在する。乾燥することによって、水分が蒸発し、セルロース繊維相互の水素結合によって空隙が癒されて貫通孔が存在しなくなるが、湿紙の状態ではどんなに叩解の程度を進めたとしても水分が保持されている空隙が存在するのである。例えば、ＪＩＳ法ＣＳＦの値で約２００ｍｌ以下まで叩解を進めて抄紙したとしても、湿紙の状態ではプレスすることにより脱水することができる。このことは湿紙中に連続した水の流路が存在することを示しているに他ならない。本発明は乾燥時における湿紙の空隙構造に与える水の影響を極力小さくすることによって、この湿紙状態の空隙構造、即ち水の流路を保持したまま乾燥させて、微細な貫通孔を有する多孔質高気密度紙を提供するものである。
【００２６】
先ず、本発明は高気密度の紙を得ることを目的とするため、平均繊維径が１μｍ以下の微細なセルロースを原料とする。繊維径が平均１μｍ以下の微細な繊維でなければ、厚さが２４．６μｍ〜１００μｍ、気密度が１０００秒／１００ｃｃ〜１４０００秒／１００ｃｃ、密度が０．３７８ｇ／ｃｍ ^３ 〜０．６ｇ／ｃｍ^３ の高気密度を実現する緻密性を得ることができないためである。具体的には高度に叩解したセルロース、或はマイクロフィブリル化セルロース（ＭＦＣ）を使用する。高度に叩解したセルロースは、基のセルロースの繊維の形状が破壊されて、外部フィブリル化が進み、直径０．４μｍ程度のフィブリルの占有率が高くなっているものであり、平均繊維径としては１μｍ以下のものである。なお、本発明でいう平均繊維径が１μｍ以下の微細なセルロースは、フィブリルの占有率が高いもの、即ちフィブリルが繊維の主たる要素となっていればよく、フィブリルだけのものと共に、一部にフィブリル化されていない繊維径１μｍを越える基の繊維が残存しているものであってもよい。
【００２７】
前記したようにセルロース繊維を叩解するとセルロース繊維は１／２や１／３に段階的に開裂して行くのではなく、直径０．４μｍ程度のフィブリルが繊維の外部から段階的にひげ状に発生して行く。従って、天然セルロース繊維を叩解或は他の手段によって、開裂させて平均繊維径を小さくすることはできないのである。叩解の程度は０．４μｍのフィブリルの発生状況のことであり、叩解が進むことはフィブリルの比率が増加することを示している。本発明ではこのフィブリルの占有率の高い微細な天然セルロースを原料とするものである。因に天然セルロース繊維で繊維径の小さいものとしてエスパルト繊維があるが、このエスパルト繊維でも繊維径は１０μｍ程度である。
【００２８】
使用するセルロースそのものには限定がなく、針葉樹木材パルプ、広葉樹木材パルプ、エスパルトパルプ、マニラ麻パルプ、サイザル麻パルプ、コットンパルプ等の天然セルロース繊維、或はこれら天然セルロース繊維を冷アルカリ処理して得たマーセル化パルプ、更には普通レーヨン繊維、ポリノジックレーヨン繊維、有機溶剤紡糸レーヨン繊維等の再生セルロース繊維などのいずれでもよい。なお、使用するセルロースは洗浄・脱水・除塵など公知の方法で不純物を除去しておく。
【００２９】
これらのセルロースを平均繊維径が１μｍ以下の微細なセルロースとするための手段の一つとして、ＪＩＳ法ＣＳＦの値で２００ｍｌ以下に、或は変法ＣＳＦの値で７００ｍｌ以下まで高度に叩解を行う。通常、叩解の程度はＪＩＳ法ＣＳＦ（ＪＩＳ Ｐ８１２１）の値で測定される。しかしながら、本発明ではより正確に気密度をコントロールするための叩解の程度の基準として、ＪＩＳ法ＣＳＦとともに、ＪＩＳ法ＣＳＦの変法として、変法ＣＳＦにより叩解の程度を特定する。そこで、ＪＩＳ法ＣＳＦの内容及び本発明で基準とする変法ＣＳＦの内容について以下に説明する。
【００３０】
〔ＪＩＳ法ＣＳＦ〕
ＪＩＳ Ｐ８１２１に規定されている測定手段である。先ず測定するパルプ３ｇを水で良く離解して正確に１０００ｍｌの試料液とし、この試料液を図７（Ａ）に示すカナダ標準型フリーネステスターのロ水筒３１に入れて上蓋３２を閉める。次に下蓋３３を開けて、上蓋のコック３４を開けると、ロ水筒３１の下部に配置された８０メッシュの網３５を通じてロ水が流れ出る。このとき８０メッシュの網３５上には繊維がマット状に堆積して行く。試料液はこのマット状の繊維間を通過して、ロ水としては図７（Ｂ）に示すロ水筒３１の下方に位置する漏斗３６に入り下部排出口３７から流出する。このとき漏斗３６へ一度に多くのロ水が入れば、ロ水は排出口３７だけでなく、漏斗３６の横に取付けた側管３８からも排水される。この側管３８からの排水をメスシリンダーに受け、この排水の量をもってＣＳＦの値とする。なお、図７（Ｃ）は架台３９を示すものであり、上台４０にロ水筒３１を載置し、下台４１に漏斗３６を載置して、ロ水筒３１と漏斗３６の高さと中心を合わせて測定するものである。
【００３１】
ＣＳＦの値は１０００ｍｌの試料液がロ水筒３１からロ水として漏斗３６に一度に流入する量によって決定される。漏斗３６に一度に多量のロ水が流入した場合は、下部排出口３７から全量を排出することができず、溜ったロ水が側管３８からあふれ出ることとなる。一方、ロ水が少しずつ流出すると全量が下部排出口３７から排出されることとなり、側管３８から流出することはない。この場合ＣＳＦは０ｍｌとなる。また、叩解の程度が浅いとマット状の繊維間を水が通過することができ、ロ水の量が多く流入速度も早いため、ＣＳＦの値が高くなる。一方、叩解の程度が高いとマット状の繊維間を水が通過しにくくなり、ロ水の量が減り流入速度も遅くなるため、ＣＳＦの値が低くなるのである。
【００３２】
ＪＩＳ法ＣＳＦではパルプの採取量を３ｇと規定している。この方法は叩解度の低いパルプを想定しており、低気密度紙を抄紙するには、ＪＩＳ法ＣＳＦは叩解の程度の変化が値として判り易くて都合が良い。しかしながら、高気密度の紙を抄紙するため叩解を進めていくと、ある時点からＪＩＳ法ＣＳＦの値が０ｍｌとなって、叩解の進行度を把握することができなくなる。本発明の課題とする多孔質高気密度紙を得るためにはＪＩＳ法ＣＳＦで規定する０ｍｌ前後からそれ以降の原料叩解が重要である。そこで、本発明では、高度に叩解を進めた原料の叩解の程度をより正確に測定するために、ＪＩＳ法ＣＳＦを基準として次のような変法を用いた。
【００３３】
〔変法ＣＳＦ〕
ＪＩＳ Ｐ８１２１に規定する方法を基本とし、パルプ量のみを３ｇから０．３ｇに変更して測定した。採取パルプの量以外は全てＪＩＳ法ＣＳＦと同様とした。
【００３４】
この変法ＣＳＦによれば、高度に叩解を進めた原料であっても叩解の程度の差をＣＳＦの値として捉えることができる。このＪＩＳ法ＣＳＦによる測定値と変法ＣＳＦによる測定値を比較検討するため、図１に叩解を進めたときのＪＩＳ法ＣＳＦと変法ＣＳＦの値の変化をグラフとして示すと共に、図２に縦軸に変法ＣＳＦの値を、横軸にＪＩＳ法ＣＳＦの値を取って、両者の関係をグラフとして示す。図１に示すように、変法ＣＳＦで７００ｍｌの値は、ＪＩＳ法ＣＳＦで略２００ｍｌの値となり、変法ＣＳＦで３００ｍｌの値はＪＩＳ法ＣＳＦでは０ｍｌとなって、もはや叩解の程度をＣＳＦの値として測定することができない。また、図２に示すように叩解の浅い初期の段階、即ちＪＩＳ法ＣＳＦの値で２００ｍｌ以上の状態（２００〜８００ｍｌ）ではＪＩＳ法ＣＳＦの測定値が大きく変化するのに対し変法ＣＳＦの値の測定値は変化が乏しい。この段階ではＪＩＳ法ＣＳＦの方が叩解の深浅の程度を把握しやすい。逆に、叩解が進んだ段階、即ちＪＩＳ法ＣＳＦで２００ｍｌ以下の値となると、変法ＣＳＦでの測定値の方が変化が大きくなって捉らえやすくなる。一方、ＪＩＳ法ＣＳＦの値では０ｍｌになった場合においても変法ＣＳＦの値では３００ｍｌであり、更に叩解を進めた場合ＪＩＳ法ＣＳＦでは測定不可能であるが、変法ＣＳＦでは叩解の程度を数値として測定することができる。
【００３５】
変法ＣＳＦの値は図２中の換算式を用いることにより、ＪＩＳ法ＣＳＦの値から換算することができる。なお、換算式は図２に示すように、ＪＩＳ法ＣＳＦの値で、２００ｍｌ以下の値、２００〜６００ｍｌの範囲の値、６００〜８００の範囲の値の３種類のゾーンにて係数を異にしている。なお、表３においてｒは相関係数であり、ＪＩＳ法ＣＳＦの値から換算式によって求めた変法ＣＳＦの値が実際の値と一致していることを示している。
【００３６】
変法ＣＳＦではパルプ量をＪＩＳ法ＣＳＦの１／１０である０．３ｇとすることによって、パルプの絶対量の減少と共に、料試料液の濃度が低下することとなり、ロ水の流入量が増加し流入速度も大きくなる。そのため、ＪＩＳ法ＣＳＦに比較してＣＳＦの値が高くなるのである。例えばＪＩＳ法ＣＳＦの値で０ｍｌまで叩解したパルプではＪＩＳ法ＣＳＦの測定方法である３ｇで測定すると、試料液の粘度が高くなり、８０メッシュの網３５の上に小量で緻密なマット状の繊維が形成されて、ロ水の流出が止まってしまうため、それ以上に叩解を進めたパルプのＣＳＦの測定を行うことができなくなる。これに対し、変法ＣＳＦの０．３ｇでは試料液の粘度が低く、８０メッシュの網３５の上にマット状の繊維が形成される前に一定量のロ水がロ水筒３１から漏斗３６に流入するため、側管３８からあふれ出たロ水の量を測定することができ、ＪＩＳ法ＣＳＦで０ｍｌ以下に更に叩解を進めたパルプのＣＳＦの値を変法ＣＳＦとして測定できるのである。
【００３７】
そこで、フィブリルを発生させて本発明における平均繊維径が１μｍ以下の微細なセルロースとするためには、ＪＩＳ法ＣＳＦの値で２００ｍｌ以下に、或は変法ＣＳＦの値で７００ｍｌ以下まで高度に叩解を行う必要があり、更に求める高気密度に応じて変法ＣＳＦの値で７００ｍｌ〜０ｍｌまでの叩解を行う。
【００３８】
また、叩解することなく、平均繊維径が１μｍ以下の微細なセルロースとしてセルロース繊維を高圧下剪断力で解繊したマイクロフィブリル化セルロース（ＭＦＣ）を使用することもできる。ＭＦＣとしては商品名：ダイセル化学株式会社製のセリッシュＫＹ−１１０Ｓが市販されている。更に、現在工業的に使用はされていないが、バクテリアセルロースを使用することもできる。バクテリアセルロースとはバクテリアが生産するセルロースのことで、繊維径が数ｎｍ（ナノメーター）〜数十ｎｍである。
【００３９】
これら所定の叩解を行った平均繊維径が１μｍ以下の微細なセルロース或はマイクロフィブリル化セルロース等からなる原料を水に分散させて、抄紙機上で抄紙を行うことにより、湿紙を製造する。抄紙機としては、平均繊維径が１μｍ以下の微細なセルロースであるため長網抄紙機を用いる。なお、製造した多孔質高気密度紙の強度向上のため叩解の浅い原料を用い円網抄紙機で抄紙したものを抄き合せる長網円網コンビネーションマシンで抄紙することも有効であるが、少なくとも１層は高度に叩解した原料を長網抄紙機で抄紙した湿紙が含まれていることが必要である。
【００４０】
更に、湿紙を製造する手段として抄紙機を使用することなく、平板上に原料としてのセルロース繊維の水系ドープ液をドクターブレード等でキャスティングして湿紙としての膜を形成することもできる。本発明における湿紙はキャスティング製膜による湿膜を含むものである。
【００４１】
このようにして製造した湿紙中には、変法ＣＳＦの値で７００ｍｌ〜０ｍｌに叩解した平均繊維径が１μｍ以下のフィブリル化した微細なセルロースを原料としていても、水の存在するセルロース繊維間の空隙構造を有している。本発明はこの湿紙中の空隙構造を保持したまま乾燥させるものである。そのために、湿紙中の空隙構造に保持された水を表面張力の小さい他の溶媒で置換して乾燥させる。この溶媒置換乾燥に用いる溶媒としては水と相溶性があり、表面張力の小さいものが適している。一般にはメチルアルコール、エチルアルコール、イソプロピルアルコールなどのアルコール類やアセトン、メチルエチルケトンなどのケトン類などが適している。また、置換は浸漬・プレス脱液あるいは噴霧・脱液等の方法で行う。目的とする気密度により、置換操作は１回もしくは複数回行う。溶媒置換は抄紙機上で行ってもよいし、湿紙のまま巻き取り別途行ってもよい。なお、製造された湿紙は溶媒置換の前に予め、プレスロールにより余分な水分を脱水しておくとよい。
【００４２】
上記した溶媒置換乾燥に代えて、凍結乾燥を採用することもできる。この凍結乾燥は湿紙を凍結させた後に、減圧下の条件で凍結した水分を昇華させて乾燥させる方法である。なお、本発明において凍結後、減圧下で凍結した氷を昇華させるのは、凍結した水分が再度融け、水の状態になった後に乾燥したのでは水の影響によるセルロース繊維相互の水素結合を防止して湿紙の空隙構造を維持できないためである。
【００４３】
溶媒置換された湿紙中、或は凍結乾燥した湿紙中に残っている溶媒及び水は乾燥することにより取り除く。乾燥は従来のドラム式ドライヤーでもよいし、送風や赤外線などを用いることもできる。
【００４４】
更に本発明では湿紙を製造するのに水を当初から使用せずに、平均繊維径が１μｍ以下の微細なセルロースを水より表面張力の小さい有機溶剤に分散させて、抄紙又はキャスティング製膜により湿紙を製造し、該湿紙中の有機溶剤を揮発・乾燥させることにより、湿紙に存在する空隙構造を保持したまま乾燥させるようにしてもよい。
【００４５】
また、本発明にかかる多孔質高気密度紙を電池用セパレータや、電解コンデンサ用セパレータ、各種フィルタとして使用する場合は、求められる電気特性、あるいはフィルタとして求められるロ過特性に応じてセルロース繊維に無機フィラーを添加することが有効である。これは無機フィラーとセルロースはもともと水が介在しても水素結合を形成せず、湿紙中の空隙が大きいため、電気特性やロ過特性が改善されるためと考えることができる。
【００４６】
以上説明した原料、湿紙製造方法、乾燥方法、紙の厚さ、密度等の組合わせにより気密度をコントロールして多孔質高気密度紙を製造することができる。得られた多孔質高気密度紙は湿紙の状態のときの空隙構造をそのまま維持しているため、微細な貫通孔を有しており、原料となるセルロース繊維の叩解の程度等に応じて高気密度を有する。また、原料としてのセルロース繊維の叩解の程度をＪＩＳ法ＣＳＦで２００ｍｌ以下、変法ＣＳＦの値で７００〜０ｍｌとしても、叩解の程度に応じて微細な貫通孔を維持しており、気密度が無限大となることはない。即ち、従来製造できなかった厚さが２４．６μｍ〜１００μｍ、気密度が１０００秒／１００ｃｃ〜１４０００秒／１００ｃｃ、密度が０．３７８ｇ／ｃｍ ^３ 〜０．６ｇ／ｃｍ^３ の多孔質高気密度紙を得ることができた。
【００４７】
次に本発明にかかる多孔質高気密度紙の製造方法について説明する。先ず、原料となるセルロース繊維をビーターあるいはダブルディスクリファイナー等の製紙用叩解機で所定のＪＩＳ法ＣＳＦ又は変法ＣＳＦの値まで叩解し、これを原料紙料２として図４に示すように長網インレット１に収納し、長網インレット１の下部で回転する長網ワイヤー３の表面に供給して、長網ワイヤー３の表面に連続した湿紙４を形成する。形成された湿紙４はウェットフェルト５に移送されて搬送され、プレスロール６にて過剰の水分が取り除かれる。その後所定の溶媒８を収納した第１の溶媒バット７に湿紙４を浸漬して、湿紙４中の水分と溶媒８を置換し、その後プレスロール９により余分な溶媒８を取り除いて、再び溶媒８が収納された第２の溶媒バット１０に湿紙４を浸漬して、湿紙４中に残存る水分と溶媒８を置換する。その後プレスロール１１により余分な溶媒８を取り除くと共に、ドライフェルト１２に移送されて搬送され、蒸気あるいは熱媒体によって加熱された円筒形状のドライヤー１３の外表面に接触して乾燥させて、巻取ロールに巻き取られて多孔質高気密度紙１４が製造される。この乾燥工程において、セルロース繊維を水素結合させて空隙構造を癒してしまう水分が存在せず、溶媒に置換されているため、乾燥後にも湿紙の空隙構造がそのまま維持された多孔質で高気密度の紙を製造することができる。この図４の例では長網抄紙機で抄紙後に抄紙機上で溶媒置換し、乾燥させて巻き取る例である。
【００４８】
図５は湿紙４を溶媒に浸漬することに代えて、湿紙４上に溶媒８を噴霧することによって、湿紙４中の水分と溶媒を置換するものである。前記図４と同一構成の部分については同一の符号を付して説明を省略する。なお、図５は図４と同様の長網抄紙機で抄紙された湿紙４を乾燥することなく巻き取り（ウエットワインディング）、長網抄紙機とは別の機械で溶媒置換する例を示している。即ち、ロール状に巻き取られた湿紙４はウェットフェルト５に移送されて搬送され、プレスロール６で過剰な水分が取り除かれ、その後湿紙４上に溶媒８が第１の溶媒噴霧器１６により噴霧されて、湿紙４中の水分と溶媒８が置換される。噴霧された溶媒８は吸引脱液装置１７によって吸引脱液されると共に、湿紙４から過剰な溶媒がプレスロール９にて取り除かれ、再び溶媒８が第２の溶媒噴霧器液１８により噴霧され、湿紙４中に残存する水分と溶媒８が置換される。噴霧された溶媒８は吸引脱液装置１９によって吸引脱液されると共に、その後湿紙４から過剰な溶媒がプレスロール１１にて取り除かれる。以後は図４の例と同様である。このように溶媒置換は抄紙機上で行ってもよいし、又別途行ってもよい。なお、図４における浸漬による溶媒置換、及び図５における噴霧による溶媒置換は２回行ったが、その回数は溶媒の種類や、原料、製造された湿紙等に必要に応じて選択するものである。
【００４９】
次に図６は溶媒置換に代えて、凍結乾燥によって湿紙中の空隙構造を保持したまま乾燥する例を示すものである。先ず湿紙４を冷凍庫２１内にて−７０℃の温度で凍結させて凍結湿紙４ａとする。次に凍結湿紙４ａを凍結乾燥器２２内に収納し、凍結乾燥器２２内の空気を脱気して減圧する。減圧によって凍結湿紙４ａ中の水分が凍結した氷が昇華して脱水されて、多孔質高気密度紙１４ａが製造される。尚、昇華を促進するために凍結乾燥器２２内に昇温棚２３を設置して、該昇温棚２３に凍結湿紙４ａを載置することが好ましい。なお、この際、凍結した氷が水に戻ることなく、氷から昇華することで乾燥することが肝要である。
【００５０】
従来の抄紙法では本発明に規定するほど叩解した原料を抄紙し乾燥する場合、多筒式のドライヤーが必要であるが、本発明のように湿紙中の水分を溶媒置換したものを乾燥する場合は、単筒式のドライヤーで十分である。これは従来の抄紙法では乾燥時の水分が蒸発する際、メニスカスの後退と同時に繊維を引きつけ合い、これがヒジワ（乾燥ジワ）となるため多筒式ドライヤーにより徐々に乾燥する必要があるからである。本発明の場合、乾燥時には、ヒジワ（乾燥ジワ）の原因となる水分がないため、又使用した溶媒が容易に飛散するため単筒式のドライヤーにより乾燥を行うことができる。更に、ドライヤーも従来のドラム式ドライヤーに限定することなく、赤外線ドライヤーや送風ドライヤーなど各種の乾燥方法が利用できる。
【００５１】
【実施例】
そこで、本発明にかかる多孔質高気密度紙の具体的な各種実施例と、比較のために製造した従来品の比較例を示す。各実施例および比較例の各測定値は次の方法で測定したものである。なお、ＪＩＳ法ＣＳＦ及び変法ＣＳＦの測定法法は前記した通りである。
【００５２】
（１）厚さ，密度
旧ＪＩＳ Ｃ２３０１（電解コンデンサ紙）に規定された方法で測定した。
【００５３】
（２）気密度
気密度に関してはＪＩＳ Ｃ２１１１（電気絶縁紙試験方法）に規定する“１２．１ 気密度”の項に従い、Ｂ型試験器（ガーレーデンソメータ）によって測定した。但し穴の部分の直径が６ｍｍであるアダプターを使用した。
【００５４】
［実施例１］
実施例１は木材パルプ（ＮＵＫＰ：針葉樹未晒クラフトパルプ）をダブルディスクリファイナーを用いて変法ＣＳＦの値で５０ｍｌまで高度に叩解したものを水に分散させて、長網抄紙機により湿紙を抄紙し、プレスロールにて過剰な水分を取り除いた後にロール状に巻き取った。このロール状の湿紙を繰り出して図４に示すように、エチルアルコールに浸漬して湿紙中の水分とエチルアルコールとを置換する作業を２度繰り返した後に、ドライヤーでエチルアルコール及び残渣としての水を乾燥させて、厚さ３０．３μｍ、密度０．５０８ｇ／ｃｍ³の多孔質高気密度紙を得た。
【００５５】
［比較例１，２］
実施例１における湿紙中の水分をエチルアルコールで溶媒置換することなく、通常の抄紙法におけるドライヤーで乾燥させてたものであり、厚さは２０．８μｍ、密度０．７４５ｇ／ｃｍ³となった。比較例２は実施例１と略同一厚さ、同一密度とするために、実施例１の原料の叩解の程度を変法ＣＳＦの値で７８０ｍｌとして、円網抄紙機で湿紙を製造し、該湿紙中の水分をエチルアルコールで溶媒置換することなく、通常の抄紙法におけるドライヤーで乾燥させたものであり、厚さは３０．２μｍ、密度０．５１３ｇ／ｃｍ³となった。これら実施例１と比較例１，２の気密度等を表１に示す。
【００５６】
【表１】

【００５７】
実施例１は原料セルロースとして未晒しクラフトパルプを使用しているため、本来ならば茶色の外観を呈するはずであるが、実際の外観は色目も白く、不透明感があった。このように白く不透明感があるのは溶媒置換乾燥を行っているために、湿紙中に存在した空隙構造がそのまま紙層内に残存しているため、光を乱反射するためである。実施例１の気密度は３２５０秒／１００ｃｃであって、極めて緻密ではあるが、空気が通り抜けることから貫通孔が存在していることが分る。従来製造できなかった１０００秒／１００ｃｃ以上の実現している。しかも、厚さは３０．３μｍであり、密度も０．５０８ｇ／ｃｍ³と変法ＣＳＦの値で５０ｍｌと高度に叩解しているにもかかわらず、比較例１より格段に低密度となっている。容較例１は溶媒置換を行っていないため、実施例１と同じ湿紙から製造したにもかかわらず、厚さが２０．８μｍであって、実施例１より薄くなり、密度も０．７４５ｇ／ｃｍ³と高くなって、色は茶色でフィルム状になっている。また、貫通孔が存在せず気密度も∞となって測定することができない。実施例１と比較例１は原料調成が同じ原料であるが、抄紙された紙の厚さ、密度には大きな差がある。これは溶媒置換を行わなかった比較例１が乾燥の際、表面張力の大きい水が蒸発し繊維同志をひき付け合い、繊維間に強固な結合ができたのに対し、溶媒置換した実施例１は水の蒸発に伴う繊維間のひき付け合いが無く、密度の低い紙となったためである。よって、実施例１によれば、叩解の程度を進めた原料を使用しても貫通孔を有する多孔質で低密度であるとともに、緻密性を有して高気密度の紙を得ることができている。
【００５８】
そこで、実施例１と略同じ厚さと密度である比較例２を実施例１を比較すると、比較例２の気密度は２．５秒／１００ｍｌであって、貫通孔は存在するが、緻密性がないことが判る。よって、目的とする気密度を達成することができない。これは表面張力の大きい水が乾燥時に蒸発することにより、繊維間を引合うが、原料叩解が浅いため繊維径が大きく、繊維同志の密着度が低いためである。
【００５９】
［実施例２〜６］
次に、叩解の程度を変法ＣＳＦの値で７００ｍｌ〜５０ｍｌまで段階的に変化させたマニラ麻パルプを原料として、長網抄紙機により湿紙を製造し、該湿紙にアセトンを噴霧して湿紙中の水分とアセトンとを置換する作業を２度繰り返した後に、ドライヤーでアセトン及び残渣としての水を乾燥させて、実施例２〜６の多孔質高気密度紙を得た。この実施例２〜６の厚さ、密度、気密度等を表２に、叩解の程度と気密度との関係をグラフ化したものを図３に示す。
【００６０】
【表２】

【００６１】
表２に示すように、実施例２〜６は厚さ５０μｍ前後、密度０．５００ｇ／ｃｍ³前後であって、いずれも１０００秒／１００ｃｃ以上の気密度を実現している。実施例２は変法ＣＳＦの値で７００ｍｌ（ＪＩＳ法ＣＳＦで２００ｍｌ）まで叩解した原料を使用したものであり、その気密度は１１００秒／１００ｃｃの気密度である。変法ＣＳＦの値７００ｍｌ（ＪＩＳ法ＣＳＦで２００ｍｌ）まで叩解を進めると基のセルロースの繊維の形状が破壊されて、外部フィブリル化が進み、直径０．４μｍ程度のフィブリルの占有率が高くなっているものであり、１０００秒／１００ｃｃ以上の気密度を実現するためには、基のセルロース繊維の形状が無くなるまで、即ち変法ＣＳＦの値７００ｍｌ（ＪＩＳ法ＣＳＦで２００ｍｌ）まで叩解する必要があることが判る。
【００６２】
また、実施例６は変法ＣＳＦの値で５０ｍｌ（ＪＩＳ法ＣＳＦでは測定不可）まで叩解しており、気密度は７０００秒／１００ｃｃである。よって、従来気密度が測定不可能な無限大となるＪＩＳ法ＣＳＦの値で２００ｍｌ以下まで叩解を進めても、貫通孔が存在していることが判る。このように本発明によれば、叩解の程度を進めても多孔質を維持することができて、気密度が無限大となることがないため、１０００秒／１００ｃｃ以上の気密度をコントロールすることができるのである。更に高気密度の紙が要求されれば原料叩解を進めたり、厚さを厚くしたり、密度を高くしたりすることで容易に製造することが可能である。なお、叩解が進むにつれ紙に不透明感が強く表れてくる。これは叩解が進むにつれ繊維間の空隙が小さくなり光の散乱が多くなり不透明感が強くなるからと考えられる。
【００６３】
図３は実施例２〜６の叩解の程度と気密度との関係をグラフ化したものであり、横軸が叩解の程度を、左軸が変法ＣＳＦの値を、右軸が気密度を示している。例えば、変法ＣＳＦの値のグラフにおいて、実施例２は左軸に示すように変法ＣＳＦの値が７００ｍｌであり、気密度を示すグラフにおいて実施例２は右軸に示すように１１００秒／１００ｃｃである。図に示すように、叩解が進むにつれ変法ＣＳＦの値が下がっている。一方、気密度は叩解が進むにつれ高くなることが判る。
【００６４】
［実施例７，８］
実施例７は実施例４と、実施例８は実施例６と同じ原料を使用して、厚さを厚くたしたものと、薄くしたものである。得られた多孔質高気密度紙の厚さ、密度、気密度等を表３に示す。
【００６５】
【表３】

【００６６】
表３に示すように実施例７は変法ＣＳＦの値が２１０ｍｌの原料を使用して、厚さ９５．８μｍと厚くすることにより、１４０００秒／１００ｃｃの気密度を実現している。実施例８は変法ＣＳＦの値が５０ｍｌと叩解を進めた原料を使用して、厚さを２４．６μｍとすることにより、３０００秒／１００ｃｃの気密度を実現している。このように、叩解の程度や厚さを調整することにより、１０００秒／１００ｃｃ以上の気密度をコントロールすることができるのである。
【００６７】
［実施例９，１０］
実施例９，１０は叩解したパルプあるいはＭＦＣを使用し、キャスティング法で湿膜を形成、凍結乾燥あるいは送風乾燥した例である。実施例９は変法ＣＳＦの値で３０ｍｌまで叩解したクラフトパルプ（ＮＵＫＰ）を水に分散させ、平板上にキャスティングして湿膜を形成して湿紙とし、該湿紙を冷凍庫で凍結した後（庫内温度 −７０℃、１時間）、凍結乾燥器内の昇温棚に凍結した湿紙を載置し、０．１ｍＢａｒに減圧し、湿紙中の水分が凍結した氷を昇華させて多孔質高気密度紙を得た。なお、昇華を速めるため、昇温棚を１０℃前後に昇温させたが、このとき氷が融け、液体の状態にならないように注意した。ほぼ１２時間で乾燥を終了した。実施例１０はセルロースを水に分散させるのではなく、ＭＦＣ（ダイセル化学のＭＦＣ・セリッシュＫＹ−１１０Ｓ）をエチルアルコールに分散させ、キャスティングにより湿膜を形成して湿紙とし、該湿紙中のエチルアルコールを送風乾燥させて多孔質高気密度紙を得た。なお、ＭＦＣをエチルアルコールに分散させるためホモジナイザーを使用した。得られた多孔質高気密度紙の厚さ、密度、気密度等を表４に示す。
【００６８】
【表４】

【００６９】
表４に示すように、実施例９は８０００秒／１００ｃｃの気密度を、実施例１０は６０００秒／１００ｃｃの気密度を実現している。よって、湿紙中の水分を溶媒置換ではなく凍結乾燥によって乾燥させ、或は水を使用することなく、有機溶媒中に分散させて湿紙を製造して、該湿紙中の有機溶媒を乾燥させることによっても本発明を実施できる。
【００７０】
【発明の効果】
以上詳細に説明した如く、本発明によればセルロース繊維を水もしくは水より表面張力の小さい有機溶媒に分散させて抄紙することにより湿紙を製造し、湿紙の状態においてセルロース繊維間の空隙構造に保持された水を溶媒置換又は凍結乾燥によって乾燥、或は湿紙中の有機溶媒を揮発させることにより乾燥させるため、従来の抄紙法のように湿紙からの乾燥工程で水が蒸発するときに隣同志の繊維を強力に引き付けて水素結合により密着することがない。そのため、平均繊維径が１μｍ以下となるように叩解された微細なセルロース繊維を原料として、高気密度であって多孔質の紙を、厚さを厚くすることなく得ることができる。具体的には厚さが２４．６μｍ〜１００μｍ、気密度が１０００秒／１００ｃｃ〜１４０００秒／１００ｃｃ、密度が０．３７８ｇ／ｃｍ ^３ 〜０．６ｇ／ｃｍ^３ の多孔質高気密度紙を得ることができる。即ち、本発明にかかる多孔質高気密度紙は叩解の程度を進めた原料を使用しても、貫通孔が存在するため、低密度であるとともに、緻密性を有して気密度が高いものである。外観的にも白色で不透明感があり、このことは紙中に多くの空隙を有していることを示している。このため電解液を含浸させた時、イオンの通過に対する抵抗も小さい。また、水、油やその他の溶媒に対する馴染みも良い。これは水などの親水性溶媒についてはセルロース中のＯＨ基により、非水溶媒に対しては微細な貫通孔へ浸入するためである。このような性質から電池用セパレータや電解コンデンサのセパレータとして広く応用が期待される。また、紙の表裏間に存在する貫通孔は小さく、低密度であり空隙率が高いため、フィルター用としての効果も大きい。特に従来のフィルターは厚くすることで微細な粒子を捕集していたが、本発明による多孔質高気密度紙によれば薄くても高捕集率のフィルタを実現することができる。
【００７１】
そのため、従来多孔質フィルムが使用されていた分野や、多孔質フィルムが耐熱性・耐薬品性で使用できなかった、あるいは、多孔質フィルムの利用が可能ではあるがコスト的に合わなかった分野において、再生産可能な天然資源であるセルロースを使い耐薬品性・耐熱性に優れた安価で緻密性をもった多孔質高気密度紙を提供することができる。
【図面の簡単な説明】
【図１】本発明における変法ＣＳＦとＪＩＳ法ＣＳＦとの関係を示すグラフ。
【図２】本発明における変法ＣＳＦとＪＩＳ法ＣＳＦとの関係を示すグラフ。
【図３】変法ＣＳＦの値と気密度との関係を示すグラフ。
【図４】本発明にかかる多孔質高気密度紙の溶媒置換による製造方法の一例を示す説明図。
【図５】本発明にかかる多孔質高気密度紙の溶媒置換による製造方法の他例を示す説明図。
【図６】本発明にかかる多孔質高気密度紙の凍結乾燥による製造方法を示す説明図。
【図７】叩解度の測定装置のロ水筒を示す説明図（Ａ）、漏斗を示す説明図（Ｂ）、架台を示す説明図（Ｃ）。
【符号の説明】
１…長網インレット
２…原料紙料
３…長網ワイヤー
４…湿紙
４ａ…凍結湿紙
５…ウェットフェルト
６，９，１１…プレスロール
７…第１の溶媒バット
８…溶媒
１０…第２の溶媒バット
１２…ドライフェルト
１３…ドライヤー
１４，１４ａ…多孔質高気密度紙
１６…第１の溶媒噴霧器
１７…第１の吸引脱液装置
１８…第２の溶媒噴霧器
１９…第２の吸引脱液装置
２１…冷凍庫
２２…凍結乾燥器
２３…昇温棚[0001]
BACKGROUND OF THE INVENTION
The present invention relates to porous high-density paper mainly used as industrial materials such as battery separators, electrolytic capacitor separators, and various filters, and in particular, is a natural resource that is excellent in heat resistance and chemical resistance and can be reproduced. The present invention relates to a novel paper having a fine through-hole, which is made of cellulose as a raw material, and is dense and has a high air density.
[0002]
[Prior art]
Paper is one of the most familiar items, not to mention newspapers and books, but also used for food and drink containers, home decoration, and as a versatile industrial material. It has become one of the research subjects. In general, this paper is produced by dispersing cellulose, which is obtained by digesting plant fibers with chemicals, in water, drawing it with a net to make a wet paper, and dehydrating and drying the wet paper.
[0003]
The cellulose fibers of the paper are bonded together mainly by hydrogen bonding of cellulose. That is, when water evaporates in the wet paper drying process, the surface tension of the water is large, so that the cellulose fibers adjacent to each other are strongly attracted. When the distance between the fibers becomes small, the Wander Walls force acts, and further attracts, and finally comes into close contact by hydrogen bonding. The degree of hydrogen bonding and the fiber diameter determine the gap between the fibers, that is, the air density of the paper.
[0004]
Cellulose, a raw material for paper, is a natural polymer, has heat resistance up to around 230 ° C, and has high chemical resistance to acids, alkalis, organic solvents, etc., so paper is a separator for batteries, separators for electrolytic capacitors, It is widely used as an inexpensive industrial material such as various filters.
[0005]
On the other hand, a porous film is used as an industrial material having the same application as paper in the above-described application. This porous film is as thin as 10 to 40 μm, and fine pores of about 0.1 μm are uniformly formed on the entire surface of the film, so it is impregnated with an electrolytic solution for filter applications and despite the high electrical insulation of the film itself. Because of its low electrical resistance when used, it is used as an industrial material, such as being used in various battery separators.
[0006]
For the porous film, a petroleum resin thermoplastic resin or cellulose acetate which is a cellulose derivative is used as a raw material. In order to produce a porous film using a thermoplastic resin, a thermoplastic resin melted by heating is formed, and an inorganic substance that has been stretched or premixed is dissolved with an acid. When a cellulose derivative is used, it is produced by dissolving in a solvent such as acetic acid or acetone to form a film and then stretching it.
[0007]
[Problems to be solved by the invention]
When paper is used as an industrial material such as a battery separator, it is important to control the air density of the paper. Battery separators for separating the anode active material and the cathode active material of the battery are strongly required to have a denseness for isolating the bipolar active material. In particular, a separator for a lithium ion battery has a high density of the separator. In order to ensure, it has become a standard of a necessary condition to have a gas density of 1000 seconds / 100 cc or more.
[0008]
Conventionally, the air density of paper has been controlled by the following two methods. One is a method for producing a paper having a higher density by increasing the degree of beating of cellulose fibers as a raw material, and the other is a method for thickening the paper.
[0009]
When controlling the air density by the degree of beating, the air density is low when making paper on low-density paper using cellulose fibers with shallow beating, and the air density is increasing when making paper using cellulose fibers that have been beaten. Can do. The degree of beating of the cellulose fiber is 770 ml of CSF (Canadian Standard Freeness, hereinafter referred to as JIS method CSF) defined by JIS P8121, and the density is 0. .3g / cm^ThreeIf the paper with a thickness of about 50 μm is made, the air density can be controlled to about 1 second / 100 cc. If the paper is made by beating up to about 400 ml with a JIS CSF value, the paper with the same thickness can be used. By proceeding with beating even if it exists, the density is 0.3 g / cm^ThreeTo 0.55 g / cm^ThreeThe airtightness can be controlled to several hundred seconds / 100 cc.
[0010]
Therefore, it is considered that if the beating is advanced to a high degree, the air density can be controlled from several thousand seconds / 100 cc to several tens of seconds / 100 cc or more. However, when raw materials that have been beaten to some extent are used, there are no through holes between the front and back of the paper, and the air density of 1000 seconds / 100 cc or more, which is required for battery separators in conventional paper, is controlled. I couldn't. This is a JIS CSF value, and when papermaking is performed from about 200 ml, the gap between fibers disappears, the paper no longer has through-holes, the air density is infinite, and it is actually measured. Because it becomes impossible. This is an unavoidable property due to the fact that paper is made of self-adhesive cellulose.
[0011]
Generally, the smaller the fiber diameter, the greater the force acting between the fibers in the wet paper due to the surface tension of water. This is known as the Campbell effect (Campbell effect). Campbell estimates that the attractive force between fibers with a fiber diameter of 30 μm is 6.1 kg / cm.²In contrast, when the fiber diameter is 2 μm, the attractive force between the fibers is 38 kg / cm.²When the fiber diameter is 0.2 μm, the attractive force between the fibers is 174 kg / cm.²become. Highly beaten plant fibers have a smaller fiber diameter than the original size, a greater force acting between the fibers, and a shorter distance between the fibers. Therefore, when the drying process starts from the wet paper state, the water evaporates, and at this time, the surface tension of the water is large, so that the fibers of neighboring neighbors are strongly attracted. When the distance between the fibers is reduced, the Wander Walls force acts, attracts the fibers, and finally comes into close contact by hydrogen bonding, thereby reducing the voids between the fibers. For this reason, when the beating is advanced to 200 ml or less with a JIS method CSF value, voids between the fibers of the obtained paper disappear, and the air density cannot be measured. On the other hand, when the degree of beating is shallow and the shape of a large fiber is maintained, even if hydrogen bonding occurs at the contact point of the fiber, there are many voids as a whole.
[0012]
Further, even if an attempt is made to finely adjust the value of the JIS method CSF before it reaches 200 ml as the value of the JIS method CSF, the air density of 1000 seconds / 100 cc or more cannot be controlled. As described above, as the fiber diameter decreases, the force acting between the fibers increases rapidly. Moreover, when the cellulose fiber is beaten, the cellulose fiber is not cleaved in steps of 1/2 or 1/3, but fibrils having a diameter of about 0.4 μm are generated in a whisker-like manner from the outside of the fiber. . That is, the degree of beating is the occurrence of 0.4 μm fibrils, and the progress of beating indicates that the fibril ratio increases. On the other hand, cellulose fibers as a base, for example, softwood pulp fibers are elliptical with a major axis of 40 μm and minor axis of 10 μm, and Manila hemp pulp fibers are approximately circular with a diameter of about 20 μm. Therefore, if the degree of beating is Manila hemp pulp, it can be grasped as a change in the ratio of fibers having a diameter of 20 μm and fibrils having a diameter of 0.4 μm. Therefore, the airtightness cannot be controlled by adjusting the subtle JIS method CSF value before the JIS method CSF value reaches 200 ml. Even if it is attempted, it is considered that variations of ± several thousands to tens of thousands of seconds / 100 cc occur with respect to the target value.
[0013]
Therefore, by adjusting the degree of beating, paper with a gas density of several hundred seconds / 100 cc can be manufactured, but it cannot be manufactured while controlling the gas density of 1000 to tens of thousands of seconds / 100 cc. It was.
[0014]
Another method for increasing the air density is to thicken the paper. Theoretically, the longer the distance that the air passes through, the higher the air density, and the thicker the paper, the higher the air density paper can be produced. However, it should be as thin as possible for use as an industrial material such as a battery separator. For example, a porous film used as a separator for a lithium ion battery is generally 25 μm, and a separator used for an electrolytic capacitor is mainly 15 to 90 μm, and a thicker one is actually used. I can't. In particular, at present, higher capacity and smaller size and weight are desired, and it is expected to be thinner than before. Therefore, in the range of thickness of 100 μm or less, which is required as an industrial material, the air density can be controlled at 1000 seconds / 100 cc or more by adjusting the thickness, or by combining the degree of beating and the thickness. I couldn't.
[0015]
Therefore, the porous film described above is currently used as an industrial material such as a battery separator and various filters that are porous and require a high air density. This porous film can have a gas density of several thousand seconds / 100 cc to tens of thousands of seconds / 100 cc.
[0016]
As a raw material for the porous film, a petroleum resin thermoplastic resin or a cellulose derivative such as cellulose acetate is used. Polyethylene (PE) and polypropylene (PP) are mainly used as thermoplastic resins for petroleum resins. Although these resins are excellent in chemical resistance, PE has a high heat resistance temperature of 120 ° C. and PP has a heat resistance temperature of 160 ° C., which is poor in heat resistance. On the other hand, although cellulose acetate, which is a cellulose derivative, has heat resistance up to around 230 ° C., it is poor in chemical resistance because it dissolves in chemicals such as acetic acid and acetone. For this reason, the porous film of a cellulose derivative cannot be used as a battery separator. As described above, the porous film has poor heat resistance if it has excellent chemical resistance, and has poor chemical resistance if it has excellent heat resistance. In addition, since the thermoplastic resin as the raw material is expensive and the manufacturing process is complicated, it is difficult to lower the manufacturing unit price.
[0017]
On the other hand, development of separators and the like having further heat resistance is expected from industrial products such as batteries that have become products to improve safety. For example, a lithium ion battery is required to have a separator that retains its form even at 190 ° C. or higher, which is the ignition temperature of lithium metal. Currently, there is no porous film having heat resistance that meets such requirements. In addition, both PE and PP are petroleum-based resources, and new materials are demanded from the recent environmental considerations.
[0018]
Table 5 shows the results of a comparative study of the characteristics of the paper produced by the conventional paper making method described above and the porous film produced from a petroleum resin thermoplastic resin.
[0019]
[Table 5]

[0020]
As shown in Table 5, cellulose as a raw material has heat resistance up to 230 ° C., and is stable against chemicals, as can be seen from the fact that drugs that dissolve cellulose are still being explored. It can be said that both heat resistance and chemical resistance are combined. On the other hand, porous films are essentially lacking in heat resistance and chemical resistance. Therefore, if the high density paper that is manufactured with raw materials with advanced beating and becomes impossible to measure due to infinite air density can be made porous, it will have a high air density that was previously impossible. Thus, low density paper can be obtained. That is, if a paper having fine through-holes through which air can pass can be produced even if a raw material that has been beaten is used, a high-density and low-density paper can be obtained. is there. With this high air density and low density paper, the air density can be controlled at a high level, and when the conventional air density is increased, the density increases and the electrical characteristics deteriorate, while the density decreases and the electrical characteristics decrease. If the air quality is improved, the air density is lowered and the denseness is lacking, so that it is possible to eliminate the drawbacks of paper which has been difficult to satisfy the air density and the electric characteristics at the same time. In addition, it can contribute to the use of porous films in areas where heat resistance is insufficient and to improve the safety of products that have been used in the past. This is desirable because it can be converted to resources.
[0021]
  Therefore, the present invention is based on the above-mentioned conventional circumstances, and is made of cellulose, which is a natural resource that is excellent in heat resistance and chemical resistance and can be reproduced, and is porous and low density having fine through holes, A new porous high-density paper having high density and high air density, specifically, a thickness of 100 μm or less and a gas density of 1000 seconds / 100 cc or moreThe density is 0.6 g / cm ³ Less thanAn object of the present invention is to provide a porous high-density paper.
[0022]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides fine cellulose having an average fiber diameter of 1 μm or less.Dispersed in waterManufacturing wet paper,Substituting the water in the wet paper with a solvent having a low surface tension compatible with water,The thickness is reduced by drying while maintaining the void structure present in the wet paper.24.6 μm ~100 μm,Airtightness is 1000 seconds / 100cc~ 14000 seconds / 100cc,Density0.378 g / cm ³ ~0.6 g / cm³ Paper andHas fine through holesRealized both porous and high air density at the same timeA porous high-density paper and a manufacturing method thereof are provided as a basis. Also,originalPaper is made by dispersing the material in an organic solvent having a surface tension smaller than that of water. The moisture in the wet paperFreeze-dried, orThe organic solvent in the wet paper is dried by volatilization..
[0023]
  According to the present invention, wet paper is made by drying the water retained in the void structure between the cellulose fibers in the wet paper state by solvent replacement or freeze drying, or by dispersing the cellulose fibers in an organic solvent and making paper. In order to dry by volatilizing the organic solvent in the wet paper, hydrogen bonds by strongly attracting the fibers of neighboring neighbors when water evaporates in the drying process from the wet paper as in the conventional papermaking method. It is not closely attached. for that reason,averageBy using fine cellulose fibers having a fiber diameter of 1 μm or less as a raw material, it is possible to obtain porous paper having a high air density without increasing the thickness. Specifically, the thickness is 100 μm or less, and the air density is 1000 seconds / 100 cc or more.The density is 0.6 g / cm ³ Less thanCan be obtained. Moreover, since cellulose fiber is used as a raw material, the heat resistance and chemical resistance required for current industrial paper can be greatly improved.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, each embodiment of the porous high-density paper concerning the present invention and its manufacturing method is described. The present inventionaverageA wet paper is produced using fine cellulose having a fiber diameter of 1 μm or less as a raw material, and is dried while retaining a void structure existing in the wet paper, thereby having a fine through hole.
[0025]
Even in the conventional papermaking method, the air density of the paper obtained increases as the cellulose fiber as the raw material is beaten. However, as described above, the beating is advanced to about 200 ml or less as the JIS method CSF value. As a result, voids between the fibers disappear, paper no longer has through-holes, and the air density becomes infinite, making it impossible to measure in practice. However, even in this case, the wet paper has a void structure. That is, even if there are no through holes in the dried paper, there are through holes in the wet paper before drying. By drying, moisture evaporates and the voids are healed by hydrogen bonds between cellulose fibers and there are no through-holes, but moisture is retained no matter how much beating is advanced in the wet paper state There are voids. For example, even if the paper is made by beating up to about 200 ml or less as the JIS CSF value, it can be dehydrated by pressing in the wet paper state. This is only an indication that there is a continuous water flow path in the wet paper. The present invention minimizes the influence of water on the gap structure of the wet paper during drying, so that it is dried while holding the gap structure in the wet paper state, that is, the water flow path, and has fine through holes. A porous high-density paper is provided.
[0026]
  First, since the present invention aims to obtain high-density paper, fine cellulose having an average fiber diameter of 1 μm or less is used as a raw material. If the fiber diameter is not fine fibers with an average of 1 μm or less, the thickness is24.6 μm ~100 μm,Airtightness is 1000 seconds / 100cc~ 14000 seconds / 100cc,Density0.378 g / cm ³ ~0.6 g / cm³ ofThis is because it is impossible to obtain denseness that achieves high air density. Specifically, highly beaten cellulose or microfibrillated cellulose (MFC) is used. Highly beaten cellulose is one in which the shape of the fiber of the base cellulose is destroyed and external fibrillation progresses, and the occupancy of fibrils having a diameter of about 0.4 μm is high, and the average fiber diameter is 1 μm. It is as follows. The fine cellulose having an average fiber diameter of 1 μm or less referred to in the present invention has a high fibril occupancy ratio, that is, fibrils only have to be the main element of the fiber, and some of the fibrils together with fibrils alone There may be fibers in which fibers having a diameter exceeding 1 μm are not left.
[0027]
  As described above, when the cellulose fiber is beaten, the cellulose fiber is not cleaved in steps of 1/2 or 1/3, but fibrils having a diameter of about 0.4 μm are generated stepwise from the outside of the fiber. Go. Therefore, natural cellulose fibers can be cleaved by beating or other means.averageThe fiber diameter cannot be reduced. The degree of beating is the occurrence of 0.4 μm fibrils, and the progress of beating indicates that the ratio of fibrils increases. In the present invention, fine natural cellulose having a high fibril occupancy is used as a raw material. Incidentally, there is an esparto fiber as a natural cellulose fiber having a small fiber diameter, and the fiber diameter of this esparto fiber is about 10 μm.
[0028]
The cellulose used is not limited, and natural cellulose fibers such as coniferous wood pulp, hardwood wood pulp, esparto pulp, manila hemp pulp, sisal hemp pulp, cotton pulp, etc., or these natural cellulose fibers are obtained by cold alkali treatment. Further, mercerized pulp, ordinary rayon fiber, polynosic rayon fiber, and regenerated cellulose fiber such as organic solvent-spun rayon fiber may be used. In addition, the cellulose used removes impurities by known methods such as washing, dehydration, and dust removal.
[0029]
  These celluloseaverageAs one of means for obtaining fine cellulose having a fiber diameter of 1 μm or less, beating is carried out to a high degree to a value of 200 ml or less in the JIS method CSF or 700 ml or less in the modified CSF value. Usually, the degree of beating is measured by the value of JIS method CSF (JIS P8121). However, in the present invention, the degree of beating is specified by the modified CSF as a modification of the JIS method CSF as well as the JIS method CSF as a standard of the degree of beating for controlling the air density more accurately. Accordingly, the contents of the JIS method CSF and the modified method CSF used as a reference in the present invention will be described below.
[0030]
[JIS method CSF]
This is a measuring means defined in JIS P8121. First, 3 g of the pulp to be measured is thoroughly disaggregated with water to make an exactly 1000 ml sample solution, and this sample solution is placed in a water canister 31 of a Canadian standard type freeness tester shown in FIG. Next, when the lower lid 33 is opened and the upper lid cock 34 is opened, the drainage water flows out through the 80-mesh net 35 disposed at the bottom of the drainage cylinder 31. At this time, the fibers accumulate in a mat shape on the 80-mesh net 35. The sample liquid passes between the mat-like fibers, enters the funnel 36 located below the water cylinder 31 shown in FIG. If a large amount of drainage water enters the funnel 36 at this time, the drainage water is drained not only from the discharge port 37 but also from the side pipe 38 attached to the side of the funnel 36. The waste water from the side pipe 38 is received by a measuring cylinder, and the amount of this waste water is taken as the CSF value. FIG. 7C shows a pedestal 39. The water bottle 31 is placed on the upper base 40, the funnel 36 is placed on the lower base 41, and the height and center of the water bottle 31 and funnel 36 are aligned. To measure.
[0031]
The value of CSF is determined by the amount of 1000 ml of the sample liquid that flows into the funnel 36 as low water from the low water tank 31 at a time. When a large amount of low water flows into the funnel 36 at a time, the entire amount cannot be discharged from the lower discharge port 37, and the accumulated low water overflows from the side pipe 38. On the other hand, when the low water flows out little by little, the entire amount is discharged from the lower discharge port 37 and does not flow out from the side pipe 38. In this case, the CSF is 0 ml. Also, if the degree of beating is shallow, water can pass between the mat-like fibers, and the amount of water is large and the inflow speed is high, so the CSF value is high. On the other hand, if the degree of beating is high, it becomes difficult for water to pass between the mat-like fibers, the amount of water is reduced, and the inflow speed is also slowed, so the CSF value is low.
[0032]
In JIS method CSF, the amount of pulp collected is defined as 3 g. This method assumes pulp with a low beating degree, and in order to make low-density paper, the JIS method CSF is convenient because the change in the degree of beating is easily understood as a value. However, if beating is advanced to make high-density paper, the value of the JIS method CSF becomes 0 ml from a certain point in time, and the progress of beating cannot be grasped. In order to obtain a porous high-density paper which is the subject of the present invention, it is important to beat the raw material from around 0 ml as defined in JIS method CSF. Therefore, in the present invention, in order to more accurately measure the degree of beating of a highly advanced raw material, the following variation is used with reference to the JIS method CSF.
[0033]
[Modified CSF]
Based on the method specified in JIS P8121, only the amount of pulp was changed from 3 g to 0.3 g and measured. Except for the amount of collected pulp, everything was the same as JIS CSF.
[0034]
According to this modified CSF, the difference in the degree of beating can be grasped as the value of CSF even if the raw material has advanced beating. In order to compare and compare the measured value by the JIS method CSF and the measured value by the modified CSF, FIG. 1 shows the change in the values of the JIS method CSF and the modified CSF as a graph, and FIG. Taking the value of modified CSF on the axis and the value of JIS method CSF on the horizontal axis, the relationship between them is shown as a graph. As shown in FIG. 1, the value of 700 ml in the modified CSF becomes approximately 200 ml in the JIS method CSF, and the value of 300 ml in the modified CSF becomes 0 ml in the JIS method CSF. It cannot be measured as a value. In addition, as shown in FIG. 2, in the initial stage of beating, that is, when the JIS method CSF value is 200 ml or more (200 to 800 ml), the measured value of the JIS method CSF greatly changes, whereas the value of the modified CSF The measured values of are not very variable. At this stage, JIS CSF is easier to grasp the depth of beating. On the contrary, when the beating progresses, that is, when the value is 200 ml or less in the JIS method CSF, the measurement value in the modified CSF becomes larger and easier to catch. On the other hand, even when the JIS CSF value reaches 0 ml, the modified CSF value is 300 ml, and when further beating is performed, the JIS method CSF cannot measure, but the modified CSF indicates the degree of beating. It can be measured as a numerical value.
[0035]
The value of the modified CSF can be converted from the value of the JIS method CSF by using the conversion formula in FIG. As shown in FIG. 2, the conversion formula is a JIS CSF value, and the coefficients are different in three types of zones: a value of 200 ml or less, a value in the range of 200 to 600 ml, and a value in the range of 600 to 800. ing. In Table 3, r is a correlation coefficient, which indicates that the value of the modified CSF obtained from the value of JIS method CSF by the conversion formula matches the actual value.
[0036]
In the modified CSF, by setting the pulp amount to 0.3 g, which is 1/10 of JIS method CSF, the concentration of the sample liquid decreases as the absolute amount of pulp decreases, and the inflow amount of water increases. The inflow speed is also increased. Therefore, the value of CSF is higher than that of JIS method CSF. For example, when the pulp is beaten to 0 ml with a JIS method CSF value, the viscosity of the sample liquid increases when measured with 3 g, which is the measurement method of JIS method CSF. Since the fibers are formed and the drainage of the water stops, it becomes impossible to measure the CSF of the pulp that has been further beaten. On the other hand, in the modified CSF of 0.3 g, the viscosity of the sample solution is low, and a certain amount of water is transferred from the water bottle 31 to the funnel 36 before mat-like fibers are formed on the 80-mesh net 35. Since it flows in, the amount of drainage overflowing from the side pipe 38 can be measured, and the CSF value of pulp that has been further beaten to 0 ml or less by JIS method CSF can be measured as modified CSF.
[0037]
  Therefore, fibrils are generated in the present invention.averageIn order to obtain fine cellulose with a fiber diameter of 1 μm or less, it is necessary to highly beat the JIS method CSF value to 200 ml or less, or the modified CSF value to 700 ml or less. Depending on the value, beating from 700 ml to 0 ml with the modified CSF value is performed.
[0038]
  Also, without beatingaverageAs fine cellulose having a fiber diameter of 1 μm or less, microfibrillated cellulose (MFC) obtained by defusing cellulose fibers with a shearing force under high pressure can also be used. As MFC, a trade name: SERISH KY-110S manufactured by Daicel Chemical Industries, Ltd. is commercially available. Furthermore, bacterial cellulose can be used although it is not currently used industrially. Bacterial cellulose is cellulose produced by bacteria and has a fiber diameter of several nanometers to several tens of nanometers.
[0039]
  These predetermined beatings were performedaverageA wet paper is manufactured by dispersing a raw material made of fine cellulose having a fiber diameter of 1 μm or less, microfibrillated cellulose, or the like in water and making paper on a paper machine. As a paper machine,averageSince it is a fine cellulose having a fiber diameter of 1 μm or less, a long net paper machine is used. In order to improve the strength of the produced porous high-density paper, it is also effective to make paper with a long-mesh net combination machine that combines raw paper made with a shallow beating machine with a circular net paper machine. One layer needs to contain wet paper made from a highly beaten raw material with a long paper machine.
[0040]
Furthermore, without using a paper machine as a means for producing wet paper, an aqueous dope solution of cellulose fiber as a raw material can be cast on a flat plate with a doctor blade or the like to form a film as wet paper. The wet paper in the present invention includes a wet film formed by casting film formation.
[0041]
  In the wet paper produced in this way, the modified CSF value was beaten to 700 ml to 0 ml.averageEven when fibrillated fine cellulose having a fiber diameter of 1 μm or less is used as a raw material, it has a void structure between cellulose fibers in which water exists. In the present invention, the wet structure is dried while maintaining the void structure. For this purpose, water held in the void structure in the wet paper is replaced with another solvent having a low surface tension and dried. As the solvent used for the solvent substitution drying, a solvent which is compatible with water and has a small surface tension is suitable. In general, alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol and ketones such as acetone and methyl ethyl ketone are suitable. Further, the substitution is performed by a method such as immersion / press draining or spraying / draining. The replacement operation is performed once or a plurality of times depending on the target air density. Solvent replacement may be performed on a paper machine, or may be performed separately with the wet paper wound. In addition, it is good to dehydrate the excess water | moisture content beforehand with the press roll before solvent substitution with the manufactured wet paper.
[0042]
Instead of the above-mentioned solvent substitution drying, freeze drying can be employed. This lyophilization is a method in which after wet paper is frozen, the frozen water is sublimated under reduced pressure conditions and dried. In the present invention, after freezing, the ice frozen under reduced pressure is sublimated because the frozen water is melted again and dried after becoming water, thereby preventing hydrogen bonding between cellulose fibers due to the influence of water. This is because the wet paper void structure cannot be maintained.
[0043]
Solvent and water remaining in the solvent-substituted wet paper or in the freeze-dried wet paper are removed by drying. For drying, a conventional drum dryer may be used, or air blowing or infrared rays may be used.
[0044]
  Furthermore, in the present invention, water is not used from the beginning to produce wet paper,averageMade of paper or casting by dispersing fine cellulose with a fiber diameter of 1 μm or less in an organic solvent having a surface tension smaller than that of water.filmThe wet paper may be manufactured by the above-described method, and the organic solvent in the wet paper may be volatilized and dried, and may be dried while maintaining the void structure existing in the wet paper.
[0045]
In addition, when the porous high-density paper according to the present invention is used as a battery separator, an electrolytic capacitor separator, or various filters, depending on the required electrical characteristics or filter characteristics required as a filter, It is effective to add an inorganic filler. It can be considered that this is because the inorganic filler and cellulose originally do not form hydrogen bonds even when water is present, and the voids in the wet paper are large, so that the electrical characteristics and the filtration characteristics are improved.
[0046]
  A porous high air density paper can be produced by controlling the air density by a combination of the raw material, wet paper manufacturing method, drying method, paper thickness, density and the like described above. Since the obtained porous high-density paper maintains the void structure in the wet paper state as it is, it has fine through-holes, depending on the degree of beating of the cellulose fiber that is the raw material, etc. Has high air density. In addition, even if the degree of beating of cellulose fiber as a raw material is 200 ml or less in JIS method CSF and 700 to 0 ml in modified CSF value, fine through holes are maintained according to the degree of beating, and the air density is It will never be infinite. That is, the thickness that could not be manufactured conventionally24.6 μm ~100 μm,Airtightness is 1000 seconds / 100cc~ 14000 seconds / 100cc,Density0.378 g / cm ³ ~0.6 g / cm³ ofA porous high-density paper could be obtained.
[0047]
Next, the manufacturing method of the porous high-density paper concerning this invention is demonstrated. First, cellulose fiber as a raw material is beaten to a predetermined JIS method CSF or modified CSF value with a paper making beating machine such as a beater or a double disc refiner, and this is used as a raw material stock 2 as shown in FIG. The wet web 4 is formed on the surface of the long mesh wire 3 by being stored in the inlet 1 and supplied to the surface of the long mesh wire 3 that rotates at the bottom of the long mesh inlet 1. The formed wet paper 4 is transferred to the wet felt 5 and conveyed, and excess water is removed by the press roll 6. Thereafter, the wet paper 4 is immersed in the first solvent vat 7 containing the predetermined solvent 8 to replace the water and the solvent 8 in the wet paper 4, and then the excess solvent 8 is removed by the press roll 9 and again. The wet paper 4 is dipped in the second solvent vat 10 in which the solvent 8 is stored, so that the water remaining in the wet paper 4 and the solvent 8 are replaced. Thereafter, the excess solvent 8 is removed by the press roll 11, transferred to the dry felt 12, transported, contacted with the outer surface of the cylindrical dryer 13 heated by steam or a heat medium, dried, and taken up. And the porous high-density paper 14 is manufactured. In this drying process, there is no water that hydrogen bonds the cellulose fibers and heals the void structure, and the solvent is replaced with a solvent. Density paper can be produced. The example of FIG. 4 is an example in which after making paper with a long paper machine, solvent substitution is performed on the paper machine, and the paper is dried and wound up.
[0048]
FIG. 5 replaces the water and the solvent in the wet paper 4 by spraying the solvent 8 on the wet paper 4 instead of immersing the wet paper 4 in the solvent. Parts having the same configurations as those in FIG. 4 are denoted by the same reference numerals and description thereof is omitted. FIG. 5 shows an example in which the wet paper web 4 made by the same long web paper machine as in FIG. 4 is wound without being dried (wet winding), and the solvent is replaced by a machine different from the long web paper machine. Yes. That is, the wet paper 4 wound up in a roll shape is transferred to the wet felt 5 and conveyed, and excess water is removed by the press roll 6, and then the solvent 8 is put on the wet paper 4 by the first solvent sprayer 16. The water in the wet paper 4 and the solvent 8 are replaced by spraying. The sprayed solvent 8 is sucked and drained by the suction and drainage device 17, excess solvent is removed from the wet paper 4 by the press roll 9, and the solvent 8 is sprayed again by the second solvent sprayer liquid 18. The water remaining in the wet paper 4 and the solvent 8 are replaced. The sprayed solvent 8 is sucked and drained by the suction and drainage device 19, and then excess solvent is removed from the wet paper 4 by the press roll 11. The subsequent steps are the same as in the example of FIG. Thus, the solvent replacement may be performed on a paper machine or separately. In addition, although the solvent substitution by immersion in FIG. 4 and the solvent substitution by spraying in FIG. 5 were performed twice, the number of times is selected according to the type of solvent, raw material, manufactured wet paper and the like. is there.
[0049]
Next, FIG. 6 shows an example of drying while retaining the void structure in the wet paper by lyophilization instead of solvent replacement. First, the wet paper 4 is frozen in the freezer 21 at a temperature of −70 ° C. to obtain a frozen wet paper 4 a. Next, the frozen wet paper web 4a is accommodated in the freeze dryer 22, and the air in the freeze dryer 22 is deaerated and decompressed. The ice in which the moisture in the frozen wet paper 4a is frozen by sublimation is sublimated and dehydrated to produce the porous high-density paper 14a. In order to promote sublimation, it is preferable to install a temperature rising shelf 23 in the freeze dryer 22 and place the frozen wet paper web 4 a on the temperature rising shelf 23. At this time, it is important that the frozen ice is dried by sublimating from the ice without returning to the water.
[0050]
In the conventional papermaking method, when the raw material beaten to the extent specified in the present invention is made and dried, a multi-cylinder dryer is necessary, but as in the present invention, the water-substituted wet paper is dried. In that case, a single-cylinder dryer is sufficient. This is because in the conventional paper making method, when moisture during drying evaporates, fibers are attracted at the same time as the meniscus retracts, and this becomes creases (dry creases), so it is necessary to gradually dry with a multi-cylinder dryer. . In the case of the present invention, at the time of drying, there is no moisture causing wrinkles (dry wrinkles), and since the solvent used is easily scattered, drying can be performed with a single cylinder dryer. Furthermore, the dryer is not limited to a conventional drum dryer, and various drying methods such as an infrared dryer and a blower dryer can be used.
[0051]
【Example】
Therefore, various specific examples of the porous high-density paper according to the present invention and comparative examples of conventional products manufactured for comparison are shown. Each measured value of each example and comparative example is measured by the following method. In addition, the measuring method of JIS method CSF and modified method CSF is as having mentioned above.
[0052]
(1) Thickness and density
It was measured by the method defined in the old JIS C2301 (electrolytic capacitor paper).
[0053]
(2) Air density
The air density was measured with a B-type tester (Gurley densometer) in accordance with the section “12.1 Air density” defined in JIS C2111 (electrical insulating paper test method). However, an adapter having a hole diameter of 6 mm was used.
[0054]
[Example 1]
In Example 1, wood pulp (NUKP: unbleached kraft pulp) was finely beaten to 50 ml with a modified CSF value using a double disc refiner and dispersed in water. Paper was made, and excess water was removed with a press roll, and then wound into a roll. As shown in FIG. 4, this roll-shaped wet paper web is dipped in ethyl alcohol and the operation of replacing water and ethyl alcohol in the wet paper paper is repeated twice. Water was dried, thickness 30.3μm, density 0.508g / cm^ThreeA porous high-density paper was obtained.
[0055]
[Comparative Examples 1 and 2]
The water in the wet paper in Example 1 was dried with a dryer in a normal paper making method without replacing the solvent with ethyl alcohol, the thickness was 20.8 μm, and the density was 0.745 g / cm.^ThreeIt became. In Comparative Example 2, in order to obtain substantially the same thickness and the same density as in Example 1, the degree of beating of the raw material in Example 1 was set to 780 ml with a modified CSF value, and wet paper was produced with a circular net paper machine. The moisture in the wet paper was dried with a drier in a normal papermaking method without replacing the solvent with ethyl alcohol. The thickness was 30.2 μm and the density was 0.513 g / cm.^ThreeIt became. Table 1 shows the air densities and the like of Example 1 and Comparative Examples 1 and 2.
[0056]
[Table 1]

[0057]
Since Example 1 uses unbleached kraft pulp as the raw material cellulose, it should originally have a brown appearance, but the actual appearance was white and opaque. The white and opaque feeling as described above is because the solvent substitution drying is performed, and the void structure existing in the wet paper remains in the paper layer as it is, so that the light is irregularly reflected. The air density of Example 1 is 3250 seconds / 100 cc, which is extremely dense, but it can be seen that through-holes exist because air passes through. Achieved 1000 seconds / 100 cc or more which could not be manufactured conventionally. Moreover, the thickness is 30.3 μm and the density is also 0.508 g / cm.^ThreeIn spite of being highly beaten with the modified CSF value of 50 ml, the density is much lower than that of Comparative Example 1. Since Comparative Example 1 was not subjected to solvent substitution, although it was manufactured from the same wet paper as Example 1, the thickness was 20.8 μm, which was thinner than Example 1, and the density was 0.745 g. / Cm^ThreeThe color is brown and film-like. Further, there is no through hole, and the air density becomes ∞, which cannot be measured. Example 1 and Comparative Example 1 are raw materials having the same raw material preparation, but there is a great difference in the thickness and density of the paper that was made. In Comparative Example 1 in which solvent substitution was not performed, water having a large surface tension evaporated upon drying, attracting fibers together, and strong bonds were formed between the fibers. This is because the paper has a low density because there is no tension between fibers due to water evaporation. Therefore, according to Example 1, it is possible to obtain a high-density paper having a porous and low-density structure having through-holes and a denseness even when using a raw material with advanced beating. ing.
[0058]
Therefore, when Comparative Example 2 having substantially the same thickness and density as Example 1 is compared with Example 1, the air density of Comparative Example 2 is 2.5 seconds / 100 ml, and through holes are present, but the denseness is high. It turns out that there is no. Therefore, the target air density cannot be achieved. This is because water having a high surface tension evaporates during drying and attracts the fibers, but because the raw material beating is shallow, the fiber diameter is large and the adhesion between the fibers is low.
[0059]
[Examples 2 to 6]
Next, wet paper is manufactured by a long net paper machine using Manila hemp pulp whose degree of beating is changed stepwise from 700 ml to 50 ml as a modified CSF value, and acetone is sprayed on the wet paper to wet the wet paper. After repeating the operation | work which substitutes the water | moisture content in paper and acetone twice, acetone and the water as a residue were dried with the dryer, and the porous high-density paper of Examples 2-6 was obtained. Table 2 shows the thickness, density, air density, etc. of Examples 2 to 6, and FIG. 3 shows the relationship between the degree of beating and air density.
[0060]
[Table 2]

[0061]
As shown in Table 2, Examples 2 to 6 have a thickness of around 50 μm and a density of 0.500 g / cm.^ThreeThe air density is about 1000 seconds / 100 cc or more. In Example 2, a raw material beaten to 700 ml (200 ml in JIS method CSF) was used as the modified CSF value, and the gas density was 1100 sec / 100 cc. When the beating is advanced to a modified CSF value of 700 ml (200 ml in JIS method CSF), the shape of the base cellulose fiber is destroyed, the external fibril formation proceeds, and the occupancy of fibrils having a diameter of about 0.4 μm increases. In order to realize a gas density of 1000 seconds / 100 cc or more, it is necessary to beat up until the shape of the base cellulose fiber disappears, that is, up to 700 ml of the modified CSF (200 ml in JIS CSF). I understand that.
[0062]
In Example 6, the modified CSF value was beaten to 50 ml (not measurable with JIS method CSF), and the air density was 7000 seconds / 100 cc. Therefore, it can be seen that through-holes exist even if the beating is advanced to 200 ml or less with a JIS method CSF value that is infinite where the air density cannot be measured in the past. As described above, according to the present invention, the porosity can be maintained even when the degree of beating is advanced, and the air density does not become infinite. Therefore, the air density of 1000 seconds / 100 cc or more can be controlled. Can do it. Furthermore, if a paper with a high air density is required, it can be easily manufactured by advancing the raw material, increasing the thickness, or increasing the density. As the beating progresses, the opacity of the paper becomes stronger. This is presumably because as the beating progresses, the gaps between the fibers become smaller, light scattering increases, and the opacity becomes stronger.
[0063]
FIG. 3 is a graph showing the relationship between the degree of beating and air density in Examples 2 to 6, with the horizontal axis indicating the degree of beating, the left axis indicating the value of the modified CSF, and the right axis indicating the air density. Show. For example, in the modified CSF value graph, Example 2 has a modified CSF value of 700 ml as shown on the left axis, and in the graph showing the airtightness, Example 2 shows 1100 seconds / as shown on the right axis. 100cc. As shown in the figure, as the beating progresses, the value of the modified CSF decreases. On the other hand, it can be seen that the airtightness increases as the beating progresses.
[0064]
[Examples 7 and 8]
Example 7 uses Example 4 and Example 8 uses the same raw material as Example 6, and increases and decreases the thickness. Table 3 shows the thickness, density, air density, and the like of the obtained porous high air density paper.
[0065]
[Table 3]

[0066]
As shown in Table 3, Example 7 achieves a gas density of 14000 seconds / 100 cc by using a raw material having a modified CSF value of 210 ml and increasing the thickness to 95.8 μm. Example 8 uses a raw material that has been beaten with a modified CSF value of 50 ml, and achieves an airtightness of 3000 seconds / 100 cc by setting the thickness to 24.6 μm. In this way, by adjusting the degree and thickness of beating, it is possible to control the air density of 1000 seconds / 100 cc or more.
[0067]
[Examples 9 and 10]
Examples 9 and 10 are examples in which a beaten pulp or MFC was used, a wet film was formed by a casting method, freeze-dried or air-dried. In Example 9, kraft pulp (NUKP) beaten to 30 ml with a modified CSF value was dispersed in water, cast on a flat plate to form a wet film, and the wet paper was frozen in a freezer. Place the frozen wet paper on the heating shelf in the freeze dryer (internal temperature -70 ° C, 1 hour), depressurize to 0.1 mBar, and sublimate the frozen ice in the wet paper. A porous high-density paper was obtained. In order to speed up the sublimation, the temperature raising shelf was raised to about 10 ° C., but care was taken so that the ice would not melt and become liquid. Drying was completed in about 12 hours. Example 10 does not disperse cellulose in water, but disperses MFC (MFC Selish KY-110S from Daicel Chemical) in ethyl alcohol and forms a wet film by casting to form a wet paper. Ethyl alcohol was blown and dried to obtain porous high-density paper. A homogenizer was used to disperse MFC in ethyl alcohol. Table 4 shows the thickness, density, air density, and the like of the obtained porous high air density paper.
[0068]
[Table 4]

[0069]
As shown in Table 4, Example 9 achieves a gas density of 8000 seconds / 100 cc, and Example 10 achieves a gas density of 6000 seconds / 100 cc. Therefore, moisture in the wet paper is dried by lyophilization instead of solvent replacement, or dispersed in an organic solvent without using water to produce wet paper, and the organic solvent in the wet paper is dried. The present invention can also be carried out.
[0070]
【The invention's effect】
  As explained in detail above, according to the present invention,Wet paper is produced by dispersing cellulose fiber in water or an organic solvent having a lower surface tension than water, and making paper.Water held in the void structure between cellulose fibers in the wet paper state is dried by solvent replacement or freeze-dryingOrIn order to dry by evaporating the organic solvent in the wet paper, when the water evaporates in the drying process from the wet paper as in the conventional papermaking method, the fibers of the neighbors are strongly attracted and adhered by hydrogen bonding. There is no. Therefore, the average fiber diameter is 1 μm or lessIt was beaten to becomeBy using fine cellulose fibers as a raw material, it is possible to obtain porous paper having a high air density without increasing the thickness. Specifically, the thickness24.6 μm ~100 μm,Airtightness is 1000 seconds / 100cc~ 14000 seconds / 100cc,Density0.378 g / cm ³ ~0.6 g / cm³ ofPorous high-density paper can be obtained. That is, the porous high-density paper according to the present invention has a low density and a high density with a high density because of the presence of through-holes even when a raw material with advanced beating is used. It is. The appearance is also white and opaque, indicating that there are many voids in the paper. For this reason, when impregnated with the electrolytic solution, the resistance to the passage of ions is also small. Also, familiarity with water, oil and other solvents is good. This is because a hydrophilic solvent such as water penetrates into a fine through-hole with respect to a non-aqueous solvent due to an OH group in cellulose. Such properties are expected to be widely applied as battery separators and electrolytic capacitor separators. Moreover, since the through-hole which exists between the front and back of paper is small, it is low density and the porosity is high, the effect for filters is also large. In particular, the conventional filter collects fine particles by increasing the thickness, but the porous high-air density paper according to the present invention can realize a filter having a high collection rate even if it is thin.
[0071]
Therefore, in the field where the porous film has been used in the past, the field where the porous film could not be used due to heat resistance and chemical resistance, or the use of the porous film was possible but the cost was not suitable. It is possible to provide a low-cost and dense porous high-density paper having excellent chemical resistance and heat resistance using cellulose, which is a natural resource that can be reproduced.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between a modified CSF and a JIS method CSF in the present invention.
FIG. 2 is a graph showing the relationship between modified CSF and JIS method CSF in the present invention.
FIG. 3 is a graph showing the relationship between the modified CSF value and the air density.
FIG. 4 is an explanatory view showing an example of a method for producing a porous high-density paper according to the present invention by solvent replacement.
FIG. 5 is an explanatory diagram showing another example of a method for producing a porous high-density paper according to the present invention by solvent replacement.
FIG. 6 is an explanatory view showing a method for producing a porous high-density paper according to the present invention by freeze drying.
FIG. 7 is an explanatory diagram (A) showing a water bottle of a beating degree measuring device, an explanatory diagram (B) showing a funnel, and an explanatory diagram (C) showing a gantry.
[Explanation of symbols]
1 ... Nagami inlet
2. Raw material stock
3 ... Long wire
4 ... wet paper
4a ... frozen wet paper
5 ... Wet felt
6,9,11 ... Press roll
7. First solvent bat
8 ... Solvent
10 ... Second solvent bat
12 ... Dry felt
13 ... Dryer
14, 14a ... porous high-density paper
16: First solvent sprayer
17 ... 1st suction drainage device
18 ... second solvent sprayer
19: Second suction dewatering device
21 ... Freezer
22 ... Freeze dryer
23 ... Temperature rising shelf

Claims (6)

A fine cellulose having an average fiber diameter of 1 μm or less is dispersed in water to produce a wet paper, and the water in the wet paper is replaced with a solvent having a low surface tension compatible with water and present in the wet paper. by drying while maintaining the void structure, the 24.6Myuemu～ 100 [mu] m thick, gas density 1000 seconds / 100cc ~14000 sec / 100 cc, a density of ^{0.378g / cm 3 ~ 0.6g / cm} 3 A porous high air density paper characterized in that it is made of paper and has a porous structure having fine through holes and a high air density at the same time . The average fiber diameter is less fine cellulose 1μm were dispersed in water to produce a wet paper web, the moisture in the wet paper web was lyophilized, and dried while maintaining the voids present in the wet paper A paper having a thickness of 24.6 μm to 100 μm, a gas density of 1000 seconds / 100 cc to 14000 seconds / 100 cc, and a density of 0.378 g / cm ^{3 to} 0.6 g / cm ³ , and having fine through holes And a porous high-density paper characterized by high air density. The average fiber diameter is less fine cellulose 1μm dispersed in a small organic solvent surface tension than water to produce a wet paper web, to volatilize the organic solvent in the wet paper, the void structure present in the wet paper by drying while maintaining, and thickness 24.6Myuemu～100myuemu, gas density 1000 seconds / 100Cc～14000 sec / 100 cc, density and paper ^{0.378g / cm 3 ~0.6g / cm 3} , a fine Porous high air density paper characterized by realizing a porous material having various through holes and a high air density at the same time . A wet paper is made using fine cellulose having an average fiber diameter of 1 μm or less dispersed in water as a raw material, and the water in the wet paper is replaced with a solvent having a low surface tension compatible with water. the Rukoto dried while maintaining the existing void structure, is 24.6Myuemu～ 100 [mu] m thick, gas density 1000 seconds / 100cc ~14000 sec / 100 cc, density of 0.378g ^/ cm 3 ~ 0.6g ^/ cm ^A method for producing a porous high-air-density paper, comprising producing a paper having a fine pore having ^three fine holes and a paper having a high air-density at the same time . The average fiber diameter was dispersed in water and paper wet paper less fine cellulose 1μm as a starting material, the moisture in the wet web and lyophilized, Ru dried while maintaining the voids present in the wet paper web by, is 24.6Myuemu～ 100 [mu] m thickness, a porous gas density 1000 seconds / 100cc ~14000 sec / 100 cc, the density has a fine through-hole of ^{0.378g / cm 3 ~ 0.6g / cm} 3 A method for producing a porous high air density paper, characterized in that a paper that simultaneously realizes a high air density is produced. A wet paper is made from fine cellulose having an average fiber diameter of 1 μm or less dispersed in an organic solvent having a surface tension smaller than that of water, and the organic solvent in the wet paper is volatilized to form a void structure existing in the wet paper. the benzalkonium dried while maintaining the, is 24.6Myuemu～ 100 [mu] m, the gas density 1000 seconds / 100cc ~14000 sec / 100 cc, a density of ^{0.378g / cm 3 ~ 0.6g / cm} 3 fine thickness A method for producing a porous high-air-density paper, characterized by producing a paper having a through-hole and a high air-density at the same time .

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