JP4174160B2

JP4174160B2 - Nonwoven fabric excellent in puncture resistance, method for producing the same, and battery separator

Info

Publication number: JP4174160B2
Application number: JP2000015293A
Authority: JP
Inventors: 博之山本; 豊彦佐野; 修二堀; 智文田中; 達宣木田
Original assignee: Daiwabo Co Ltd; Daiwabo Holdings Co Ltd
Current assignee: Daiwabo Co Ltd; Daiwabo Holdings Co Ltd
Priority date: 2000-01-25
Filing date: 2000-01-25
Publication date: 2008-10-29
Anticipated expiration: 2020-01-25
Also published as: JP2001207362A

Description

【０００１】
【発明の属する技術分野】
本発明は、異物などが不織布を貫通したり、突き破って破損したりするのを抑制し、包装材、ワイパー、壁紙などの化粧シート、防草シートなどの農業用、土木用資材に好適な不織布であって、特に、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物による破損を抑制するのに好適な電池用セパレータに関するものである。
【０００２】
【従来の技術】
従来より、包装材、ワイパー、壁紙などの化粧シート、防草シートなどの農業用、土木用資材などの用途において様々な不織布が商品化されており、通常不織布の形態として、サーマルボンドタイプ不織布、スパンボンド不織布、あるいはスパンレース不織布が好ましく利用されている。サーマルボンドタイプ不織布やスパンボンド不織布は繊維同士を接着させることにより不織布強力を維持しているが一般に空隙が大きく、容易に異物などが不織布を貫通したり、突き破って破損したりする。また、スパンレース不織布であっても、異物が不織布内部に入り込み易く、異物が尖った形状のものであれば容易に不織布を貫通したり、突き破って破損させたりしてしまう。それを解消するために、不織布の密度を高密度にする、あるいは目付や厚みを大きくする方法が採られているが、使用できる用途が限られていた。
【０００３】
また、電解液の保液性向上を目的として、異形断面繊維を用いた電池用セパレータが提案されている。例えば、特開昭５９−３７６４８号公報には、繊維断面形状に凹部と凸部を有するガラス繊維を使用した電池用セパレータが開示され、特開昭６０−６５４４９号公報には、異形断面を有しかつ多孔性のポリプロピレン繊維を用いた電池用セパレータが開示され、特開昭６３−１４８５３９号公報には、厚さ方向に密度差を有する２層以上の積層体からなり、構成繊維として異形断面繊維を用いた電池用セパレータが開示され、特開平９−８２３０３号公報には、平均繊維径２μm以下のガラス繊維と繊維長２〜３０mmの異形断面繊維を含有する電池用セパレータが開示されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、上記の電池用セパレータは、電解液の保液性向上を目的とし、不織布内部に空間を多くするために、表面積の大きい異形断面繊維を採用しているが、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物による破損を防止することについて検討されておらず、例えば、特開昭６０−６５４４９号公報では、発泡剤を添加して多孔性を付与しているため、繊維強度が部分的に弱く、突き刺し強力に劣る。特開昭５９−３７６４８号公報では、繊維径の細いガラス繊維を使用しておりコスト高である。特開昭６３−１４８５３９号公報では、厚さ方向に密度差を有しているため、低密度層から異物が不織布内部に入り込み易く、短絡を生じやすい。さらに、特開平９−８２３０３号公報でも、ガラス繊維主体であるためコスト高であるとともに、異形断面繊維が繊維間の空間を作り、嵩高性を持たせる目的で用いられるため、異物が不織布内部に入り込み易く、短絡を生じやすいという問題がある。
【０００５】
本発明はこれらの実情に鑑み、異物などが不織布を貫通したり、突き破って破損したりするのを抑制し、耐突き刺し強力に優れた不織布を得ることを目的としてなされたものである。
【０００６】
【課題を解決するための手段】
上記課題を解決するため、繊維断面が非円形形状からなり、該繊維断面の輪郭が丸みを帯びた十字形またはＨ字形であり、該繊維断面において断面の差し渡し長さの最も大きい部分を長辺としたとき、該長辺から延びる２以上の突起部を有し、前記長辺と直交する断面の差し渡し長さで最も大きくなる部分を短辺としたとき、扁平比（長辺の長さ／短辺の長さ）が少なくとも１．２である異形断面合成繊維を少なくとも１０ mass ％含有し、該異形断面合成繊維の他に熱接着性鞘芯型複合繊維を３０〜６０ mass ％含有し、湿式抄紙して鞘成分を溶融し熱接着された湿式不織布であり、かつ後述する単位不織布密度当りの突き刺し強力を少なくとも２０Ｎ／(g/cm³)とすることにより、異物などが不織布を貫通したり、突き破って破損したりするのを抑制し、耐突き刺し強力に優れた電池用セパレータを得ることを知り本発明に至った。
【０００７】
前記異形断面合成繊維における長辺の長さは、５〜６０μmであることが望ましい。また、前記異形断面合成繊維の繊維強度が７．０cN/dtex以上であることが望ましい。
【０００８】
前記異形断面合成繊維は、２以上の突起部を有していること望ましい。また、異形断面合成繊維は、繊維断面において２成分が交互に隣接して配置され、２成分のうち少なくとも１成分が２個以上に分割されてなる異形断面発生型複合繊維を各々の成分に分割した単繊維であることが望ましい。
【０００９】
前記不織布は、親水化処理を施されることが望ましい。
【００１０】
前記電池用セパレータは、繊維断面が非円形形状からなり、該繊維断面の輪郭が丸みを帯びた十字形またはＨ字形であり、繊維断面において断面の差し渡し長さの最も大きい部分を長辺としたとき、該長辺から延びる２以上の突起部を有し、長辺と直交する断面の差し渡し長さで最も大きくなる部分を短辺としたとき、扁平比（長辺の長さ／短辺の長さ）が少なくとも１．２である異形断面合成繊維を全繊維に対して少なくとも１０mass％となるように、該異形断面合成繊維の他に熱接着性鞘芯型複合繊維を３０〜６０ mass ％となるように水に分散させ、スラリーを調製し、抄紙機を用いて湿式抄紙して鞘成分を溶融し熱接着することにより製造できる。さらに、湿式抄紙後、最高水圧３MPa 以下で高圧水流を噴射し、繊維の分散を向上させることができる。
【００１１】
また、前記不織布は、異形断面発生型複合繊維を水に分散させるとともに全繊維に対して少なくとも１０mass％の異形断面合成繊維となるように各々の成分に分割してスラリーを調製し、抄紙機を用いて湿式抄紙することにより製造できる。さらに、湿式抄紙後、最高水圧３MPa 以下で高圧水流を噴射すると、繊維の分散を向上させることができる。
【００１２】
前記不織布を用いた電池用セパレータは、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物による破損を抑制する点で望ましい。
以下、本発明の内容を具体的に説明する。
【００１３】
【発明の実施の形態】
本発明に用いられる異形断面合成繊維は、繊維断面が非円形形状からなり、例えば、十字形、Ｉ字形、Ｈ字形、Ｌ字形、Ｔ字形、Ｘ字形、Ｙ字形、三角形以上の多角形、扇形、楕円形などの断面が用いられ、その一例を図１に示す。なかでも、図１（ａ）あるいは（ｂ）に示すような繊維断面の輪郭が丸みを帯びた十字形やＨ字形など断面の差し渡し長さの最も大きい部分を長辺としたとき、長辺から延びる２以上の突起部４を有する異形断面合成繊維、あるいは図２に示すような繊維断面において２成分が交互に隣接して配置され、２成分のうち少なくとも１成分が２個以上に分割されてなる異形断面発生型複合繊維を各々の成分に分割した単繊維を用いることが好ましい。
【００１４】
そして、繊維断面において断面の差し渡し長さの最も大きい部分を長辺とし、長辺と直交する断面の差し渡し長さで最も大きくなる部分を短辺としたとき、扁平比（長辺の長さ／短辺の長さ）を少なくとも１．２となる異形断面合成繊維が用いられる。より好ましくは、少なくとも２である。例えば、図１（ａ）〜（ｃ）に示す異形断面合成繊維であれば、断面の差し渡し長さの最も大きい部分が長辺２、長辺２と直交する断面の差し渡し長さで最も大きくなる部分が短辺３となり、図２に示す異形断面発生型複合繊維を各々の成分に分割した扇形断面繊維であれば、断面の差し渡し長さの最も大きい部分が長辺２、長辺２と直交する断面の差し渡し長さで最も大きくなる部分が短辺３となる。扁平比が少なくとも１．２であると、異物が不織布を突き刺したときに繊維が異物の押圧に対して逃げにくく、貫通するのを抑制することができ、例えば、電池用セパレータであれば、異物が対極に到達するのを防止することができるからである。
【００１５】
このとき、異形断面合成繊維における長辺の長さは、５〜６０μmであることが好ましい。より好ましくは８〜４０μmである。長辺の長さが５μm未満であると、繊維が異物の押圧に対して逃げてしまい、耐突き刺し性の効果が十分に得られず、長辺の長さが６０μmを超えると、繊維間の空隙が大きくなりすぎるため、逆に突き刺し性に劣る。
【００１６】
本発明に用いる異形断面合成繊維の素材としては、特に限定されるものではないが、ポリエステル系樹脂、ポリアミド系樹脂、ポリオレフィン系樹脂などが用いられ、特に、電池用セパレータに用いるのであれば、ポリエチレン、ポリプロピレン、ポリブテン−１、ポリ（４−メチルペンテン−１）、エチレン−ビニルアルコール共重合体などのポリオレフィン系樹脂が好ましい。繊維形態も単一繊維のみならず、異形断面であれば複合繊維であってもよい。
【００１７】
また、本発明においては、各々の成分に分割した単繊維が異形断面繊維であれば、繊維断面において２成分が交互に隣接して配置され、２成分のうち少なくとも１成分が２個以上に分割されてなり、その構成単位は長さ方向に連続し、全構成単位の一部は必ず繊維表面に露出している断面形状を有する異形断面発生型複合繊維も包含される。異形断面発生型複合繊維としては、例えば、ポリエステル系樹脂／ポリオレフィン系樹脂、ポリエステル系樹脂／ポリアミド系樹脂、ポリオレフィン系樹脂／ポリアミド系樹脂などの異族系樹脂の組み合わせ、あるいはポリ（４−メチルペンテン−１）／ポリプロピレン、エチレン−ビニルアルコール共重合体／ポリプロピレン、ポリプロピレン／ポリエチレンなどの同族系樹脂の組み合わせからなるものが用いられる。その繊維形態は、分割後異形断面を有していれば特に限定はされず、分割前は円形であってもよい。そして、異形断面発生型複合繊維の分割数は、４〜２０であることが好ましい。
【００１８】
そして、前記異形断面合成繊維は全繊維に対して少なくとも１０mass％含有される。より好ましくは、１０〜６０mass％である。異形断面合成繊維の含有量が１０mass％未満であると、耐突き刺し性の効果が十分に得られないからである。他に用いられる繊維としては、特に限定はされず、例えば、コットン、シルク、ウールなどの天然繊維、レーヨンなどの再生繊維、アクリル系繊維、ポリエステル系繊維、ポリアミド系繊維、ポリオレフィン系繊維などの単一繊維、複合繊維が用途に応じて適宜用いられる。特に、電池用セパレータに用いる場合、ポリオレフィン系単一繊維、あるいは鞘成分をポリエチレン、エチレン−プロピレン共重合体、ポリブテン−１、エチレン−ビニルアルコール共重合体とし、芯成分をポリプロピレン、ポリ（４−メチルペンテン−１）、ポリエチレンテレフタレートなどの鞘成分の融点より１０℃以上高い樹脂とした熱接着性鞘芯型複合繊維を用いるとよい。このとき、熱接着性鞘芯型複合繊維は３０〜６０mass％含有すると、各繊維間の自由度を抑制することができ、不織布の突き刺し性がさらに向上するので好ましい。
【００１９】
次に、本発明の耐突き刺し性に優れた不織布を製造方法に沿って説明する。前記異形断面合成繊維を含有してなる繊維ウェブの形態は、カード法、エアレイ法などにより得た乾式ウェブ、湿式抄紙法により得た湿式抄紙ウェブ、あるいはメルトブロー法やスパンボンド法などの直接法により得た長繊維ウェブが用いられるが、なかでも構成繊維の繊維長が３〜２５mmからなる湿式抄紙ウェブが均質なウェブを得て、異形断面合成繊維が繊維ウェブの長手方向（厚み方向と直交する方向）に整列し易い点で好ましい。より好ましい繊維長は５〜１５mmである。繊維長が３mm未満では、耐突き刺し性の効果が十分に得られず、後述する高圧水流処理時に繊維が飛散し、地合斑となり突き刺し強力が低下し、２５mmを超えると特に湿式抄紙法によって不織布を製造する場合、スラリー中における繊維の分散性が悪くなり均一な不織布を得ることができないからである。
【００２０】
上記繊維ウェブは、熱カレンダー処理、熱風加工処理、高圧水流処理等、あるいはそれらの組み合わせの方法により処理することができる。このとき、高圧水流処理を用いる場合、できるだけ構成繊維を厚み方向に配向させないような条件で処理することが好ましい。具体的には、高圧水流処理の最高水圧を３MPa 以下で噴射すると、厚み方向への配向を抑制することができる。構成繊維が厚み方向に配向していると、尖った異物が繊維を避けて不織布内部に進入し易く、例えば、電池用セパレータの場合、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物が対極に到達したり、または破損したりして、短絡する比率が増大するからである。
【００２１】
そして、前記不織布は、親水化処理されていることが好ましい。親水化処理としては、界面活性剤処理、ビニルモノマーのグラフト共重合処理、フッ素ガス処理、スルホン化処理、コロナ放電処理、プラズマ処理などが挙げられる。その後必要に応じて厚み等を調整して本発明の不織布となす。
【００２２】
例えば、本発明の電池用セパレータの製造方法の１例としては、まず、扁平比（長辺の長さ／短辺の長さ）が少なくとも１．２である異形断面合成繊維を１０mass％以上と、熱接着性鞘芯型複合繊維および／またはポリオレフィン系繊維を混合して、０．０１〜０．６％の濃度になるように水に分散させ、スラリーを調製する。このとき少量の分散剤を加えてもよい。スラリーは短網式、円網式、あるいは両者を組み合わせた抄紙機等を用いて抄紙される。次いで、熱接着性鞘芯型複合繊維を溶融させて繊維間を接着させる。この後、必要に応じて高圧水流処理を施してもよい。しかるのちに不織布には、前記親水化処理が施され、親水化不織布となす。その後、熱カレンダー処理して、所定の厚みに調整され、本発明の電池用セパレータが得られる。
【００２３】
また、本発明の電池用セパレータの製造方法の別の１例としては、まず異形断面発生型複合繊維と、熱接着性鞘芯型複合繊維および／またはポリオレフィン系繊維を混合して、０．０１〜０．６％の濃度になるように水に分散させ、スラリーを調製する。このとき、水に分散させる際にパルパーでの解離時間を長くしたり、事前に水または湯に浸漬したりして、全繊維に対して少なくとも１０mass％の異形断面合成繊維となるように各々の成分に分割させると、後述する高圧水流処理時の水圧を低く抑制できる点で特に好ましい。そして、抄紙機を用いて湿式抄紙され、不織布の取り扱い性を高めるために、熱接着性鞘芯型複合繊維を溶融させて繊維間を軽く接着させておく。さらに、湿式抄紙後、高圧水流を噴射し、未分割の異形断面発生型複合繊維を分割させる。このとき全ての異形断面発生型複合繊維が分割しなくても少なくとも１０mass％の異形断面合成繊維が得られていれば、本発明の目的は達成される。前述したように湿式抄紙前に異形断面発生型複合繊維を分割させた場合、最高水圧３MPa 以下で処理すると、厚み方向への繊維の絡合が抑制され、突き刺し強力が向上する点で好ましい。得られた不織布は、乾燥と同時に熱接着性鞘芯型複合繊維の低融点成分で構成繊維同士を熱融着させ、その後は上記方法と同様にして電池用セパレータが得られる。
【００２４】
本発明の不織布の目付は、用途に応じて適宜設定すればよいが、電池用セパレータに用いる場合であれば、３０〜１００g/m²にすることが好ましい。３０g/m²未満であると、突き刺し強力に劣るだけでなく、不織布の引張強力が弱すぎる為、電池の作製に問題が生じ、１００g/m²を超えると、突き刺し強力は向上するものの、ガスの通過性が悪化し、寿命面で不利となるからである。
【００２５】
さらに、本発明の不織布の密度は、１７５kPa荷重時（ＪＩＳ−Ｂ−７５０２に準じたマイクロメーターによる測定）で０．６g/cm³以下あることが好ましい。より好ましくは、０．３〜０．５g/cm³である。不織布密度が０．６g/cm³を超えると、ガスの通過性が悪化し、寿命面で不利となるからである。
【００２６】
このようにして、下記に示す単位不織布密度当りの突き刺し強力が少なくとも２０Ｎ／(g/cm³)である耐突き刺し性に優れた不織布が得られる。
（突き刺し強力）
カトーテック（株）製「ＫＥＳ−Ｇ５ハンディー圧縮試験機」を用いて、縦３０mm、横１００mmの大きさに裁断した不織布を準備し、試料の上に縦４６mm、横８６mm、厚み７mmのアルミ板の中央部に直径１１mmの孔を有する押さえ板を載置した後、先端部が１mmφの球状部、軸の部分が底面直径２．２mm、高さ１８．７mmの円錐状になった針を、２mm／秒の速度で押さえ板の孔の中央に垂直に突き刺した時の最大荷重（Ｎ）を測定し、１７５kPa荷重（ＪＩＳ−Ｂ−７５０２に準じたマイクロメーターによる測定）での不織布密度で除して突き刺し強力Ｎ／(g/cm³)とした。
単位不織布密度当りの突き刺し強力が２０Ｎ／(g/cm³)未満であると、異物などが不織布を容易に貫通したり、突き破って破損させたりし、特に、電池用セパレータの場合、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物が対極へ容易に到達したり、破損したりして、短絡の比率が増大してしまうからである。
【００２７】
また、得られた不織布は、親水化処理されていることが好ましい。親水化処理としては、ビニルモノマーのグラフト共重合処理、フッ素ガス処理、スルホン化処理、コロナ放電処理、プラズマ処理などが挙げられるが、なかでもスルホン化処理が電池の自己放電性を改良する点で優れており、スルホン化処理としては、濃硫酸処理、発煙硫酸処理、クロロスルホン酸処理、無水硫酸処理などが挙げられる。親水化処理を施すことにより、例えば、ワイパーとして用いる場合、水分のある対象物を払拭したり、ウェットワイパーとして利用することができ、電池用セパレータとして用いる場合、容量保存率やサイクル寿命の向上に寄与するからである。
【００２８】
【実施例】
以下、本発明の内容を実施例を挙げて説明する。なお、繊維断面における長辺および短辺の長さ、単繊維強度、不織布の引張強力、およびショート率は、以下の方法により測定した。
【００２９】
［長辺、短辺の長さ］
繊維を約１０００本に束ねて孔径０．５mmの開孔を有するアルミ板に通し、板表面に沿うようにカットし、電子顕微鏡を用いて４０倍に拡大し、１cm×１cm四方中に存在する異形断面合成繊維において断面の差し渡し長さの最も大きい部分を長辺、長辺と直交する断面の差し渡し長さで最も大きくなる部分を短辺として長さを各々測定し、その平均値を長辺および短辺の長さとした。
【００３０】
［単繊維強度］
ＪＩＳ−Ｌ−１０１５に準じ、引張試験機を用いて、試料のつかみ間隔を２０mmとしたときの荷重値を測定し、単位繊度あたりの荷重値を単繊維強度とした。
【００３１】
［不織布の引張強力］
ＪＩＳ−Ｌ−１０９６に準じ、不織布のタテ方向に対して、幅５cm、長さ１５cmの試料片をつかみ間隔１０cmで把持し、定速伸長型引張試験機を用いて引張速度３０cm／分で伸長し、切断時の荷重値を引張強力とした。
【００３２】
［ショート率］
負極を水素吸蔵合金、カルボニルニッケル、カルボキシメチルセルロース（ＣＭＣ）、ポリテトラフルオロエチレン（ＰＴＦＥ）に水を加え混練りしスラリーを調整し、このスラリーをニッケルメッキしたパンチングメタルに浸漬塗りした後８０℃で乾燥し、加圧成型して水素吸蔵合金負極とし、正極を公知の焼結式ニッケル極として、負極、正極の間に各セパレーターを挟み電槽缶に挿入し、電解液を注液することで、円筒形密閉ニッケル水素電池を作製した。作製した円筒形密閉ニッケル水素電池を、充電０．１Ｃ率で１２時間、休止０．５時間、放電０．１Ｃ率で終止電圧１．０Ｖとし、１０サイクル充放電を繰り返し、電池初期活性を行った。このとき、短絡が起きた割合をショート率とした。
【００３３】
［実施例１］
図１（ａ）に示す繊維断面を有し、融点１６３℃のポリプロピレン（日本ポリケム（株）製）からなる繊度２．２dtex、繊維長１０mmのポリプロピレン繊維を６０mass％と、鞘成分を融点１３２℃の高密度ポリエチレン（日本ポリケム（株）製）とし、芯成分を融点１６３℃のポリプロピレン（日本ポリケム（株）製）として複合比が５０：５０、繊度１．７dtex、繊維長１０mmの同心円鞘芯型複合繊維を４０mass％とを混合して、パルパーでの解離時間を１５分とし、０．５％の濃度になるようにスラリーを調製し、湿式抄紙したあと、ヤンキードライヤーを用い１３５℃で乾燥と同時に鞘芯型複合繊維の鞘成分を溶融し熱融着させて目付５０g/m²の湿式不織布を得た。
【００３４】
得られた湿式不織布の両面をそれぞれ４回ずつ、総放電量が、０．４６２KW・分／m²となるようにコロナ放電処理を施し、熱カレンダー処理して、目付５０g/m²、厚み１２０μmの電池用セパレータを得た。
【００３５】
［実施例２］
第１成分をエチレン−ビニルアルコール共重合体（エチレン含有量３８モル％）とし、第２成分をポリプロピレンとして、複合比が５０：５０、図２に示す２つの突起部からなる繊維断面を有する繊度３．３dtex、繊維長６mmの異形断面発生型複合繊維を５０mass％と、実施例１の同心円鞘芯型複合繊維を３０mass％と、融点１６３℃のポリプロピレン（日本ポリケム（株）製）からなり、繊維断面が円形形状を有する繊度０．８dtex、繊維長１０mmのポリプロピレン繊維を２０mass％とを混合して、パルパーでの解離時間を１５分とし、０．５％の濃度になるようにスラリーを調製し、湿式抄紙したあと、表裏面より３MPaの圧力で高圧柱状水流を噴射することによって、異形断面発生型複合繊維を分割させて扇形の繊維断面を有する極細繊維を形成させるとともに繊維間を交絡させ、１３５℃で乾燥と同時に熱融着させて目付５０g/m²の湿式不織布を得た。
【００３６】
得られた湿式不織布の両面をそれぞれ４回ずつ、総放電量が、０．４６２KW・分／m²となるようにコロナ放電処理を施し、熱カレンダー処理して、目付５０g/m²、厚み１２０μmの電池用セパレータを得た。
【００３７】
［比較例１］
実施例２の円形形状ポリプロピレン繊維を６０mass％と、実施例１の同心円鞘芯型複合繊維を４０mass％とした以外は、実施例１と同様の方法で目付５０g/m²、厚み１２０μmの電池用セパレータを得た。
【００３８】
［比較例２］
第１成分をエチレン−ビニルアルコール共重合体（エチレン含有量３８モル％）とし、第２成分をポリプロピレンとして、複合比が５０：５０、図２に示す繊維断面を有する繊度３．３dtex、繊維長４５mmの異形断面発生型複合繊維を５０mass％と、実施例１の同心円鞘芯型複合繊維を３０mass％と、融点１６３℃のポリプロピレン（日本ポリケム（株）製）からなり、繊維断面が円形形状を有する繊度０．８dtex、繊維長３８mmのポリプロピレン繊維を２０mass％とを混合し、セミランダムカード機により繊維ウェブを作製し、表裏面より１５MPaの圧力で高圧柱状水流を噴射することによって、異形断面発生型複合繊維を分割させて扇形の繊維断面を有する極細繊維を形成させるとともに繊維間を交絡させ、１３５℃で乾燥と同時に熱融着させて目付５０g/m²の乾式不織布を得た。得られた乾式不織布を実施例１と同様の方法で親水化処理を施し、目付５０g/m²、厚み１２０μｍの電池用セパレータを得た。
以下、実施例１〜２、比較例１〜２の物性を表１に示す。
【００３９】
【表１】

【００４０】
実施例１〜２においては、所定の異形断面を有しているので、突き刺し強力が大きく、得られた不織布を電池用セパレータとして用いると、ショート率が格段に低減され、さらに親水化処理を施したことによって、電池特性に優れたニッケル水素電池を得ることができた。一方、比較例１では、全てが円形形状の繊維断面からなる繊維を用いたため、突き刺し強力が小さく、ショート率が大きくなった。比較例２では、所定の異形断面を有しているものの、異形断面発生型複合繊維を分割させるのに、１５MPaの高圧水流で処理したため、不織布の厚み方向に構成繊維が配向してしまっただけでなく、水流痕も形成され密度斑が生じたため突き刺し強力が不十分であった。
【００４１】
【発明の効果】
本発明の不織布は、繊維断面が非円形形状からなり、所望の扁平比（長辺の長さ／短辺の長さ）を有する異形断面合成繊維を少なくとも１０mass％含有することにより、高い突き刺し強力を得ることができる。また、異形断面合成繊維が２以上の突起部を有する繊維、あるいは繊維断面において２成分が交互に隣接して配置され、２成分のうち少なくとも１成分が２個以上に分割されてなる異形断面発生型複合繊維を各々の成分に分割した単繊維であると、高い突き刺し強力とともに高い保液性を得ることができる。
そして、本発明の不織布は、湿式抄紙法を用いて、あるいは湿式抄紙した後、３MPa以下のような低水圧下での水流絡合処理法を用いて製造することにより、所望の突き刺し強力を有する不織布を得ることができる。
本発明の耐突き刺し性に優れた不織布は、包装材、ワイパー、壁紙などの化粧シート、防草シートなどの農業用、土木用資材に好適であり、特に、電極等のバリや充放電の繰り返しにより発生するデンドライドなど異物による破損を抑制する電池用セパレータとして好適である。
【図面の簡単な説明】
【図１】本発明に使用する異形断面合成繊維の繊維断面図の一例を示す。
【図２】本発明に使用する異形断面発生型複合繊維および発生後の異形断面合成繊維の繊維断面図の一例を示す。
【符号の説明】
１．異形断面合成繊維
２．長辺
３．短辺
４．突起部[0001]
BACKGROUND OF THE INVENTION
The present invention suppresses foreign matter or the like from penetrating or breaking through the nonwoven fabric, and is suitable for agricultural and civil engineering materials such as packaging materials, wipers, decorative sheets such as wallpaper, and herbicidal sheets. In particular, the present invention relates to a battery separator suitable for suppressing damage caused by foreign matters such as burrs of electrodes and the like and dendrites generated by repeated charge and discharge.
[0002]
[Prior art]
Conventionally, various nonwoven fabrics have been commercialized in applications such as packaging materials, wipers, decorative sheets such as wallpaper, agricultural materials such as grass protection sheets, and civil engineering materials. A spunbond nonwoven fabric or a spunlace nonwoven fabric is preferably used. Thermal bond type nonwoven fabric and spun bond nonwoven fabric maintain the strength of the nonwoven fabric by bonding the fibers together, but generally the voids are large, and foreign materials easily penetrate or break through the nonwoven fabric. Moreover, even if it is a spunlace nonwoven fabric, a foreign material will easily enter the nonwoven fabric, and if the foreign material has a pointed shape, the nonwoven fabric can be easily penetrated or broken and broken. In order to solve this problem, a method of increasing the density of the nonwoven fabric or increasing the basis weight or thickness has been adopted, but the usable applications are limited.
[0003]
In addition, a battery separator using a modified cross-section fiber has been proposed for the purpose of improving the liquid retention of the electrolytic solution. For example, Japanese Patent Laid-Open No. 59-37648 discloses a battery separator using glass fibers having concave and convex portions in a fiber cross-sectional shape, and Japanese Patent Laid-Open No. 60-65449 has a modified cross-section. In addition, a battery separator using porous polypropylene fibers is disclosed, and Japanese Patent Application Laid-Open No. 63-148539 comprises a laminate of two or more layers having a density difference in the thickness direction, and has a modified cross section as a constituent fiber. A battery separator using fibers is disclosed, and Japanese Patent Application Laid-Open No. 9-82303 discloses a battery separator containing glass fibers having an average fiber diameter of 2 μm or less and irregular cross-section fibers having a fiber length of 2 to 30 mm. .
[0004]
[Problems to be solved by the invention]
However, the above-mentioned battery separator is intended to improve the retention of the electrolyte solution, and has adopted a modified cross-section fiber having a large surface area in order to increase the space inside the nonwoven fabric. For example, in Japanese Patent Laid-Open No. 60-65449, a foaming agent is added to impart porosity to prevent damage caused by foreign matters such as dendrites generated by repetition of the above. Is partially weak and poorly pierced. In Japanese Patent Laid-Open No. 59-37648, glass fibers having a small fiber diameter are used, which is expensive. In JP-A-63-148539, since there is a density difference in the thickness direction, foreign substances are likely to enter the nonwoven fabric from the low-density layer, and a short circuit is likely to occur. Further, in Japanese Patent Laid-Open No. 9-82303, since the glass fiber is mainly used, the cost is high, and the modified cross-section fiber is used for the purpose of creating a space between the fibers and imparting bulkiness. There is a problem that it is easy to enter and easily cause a short circuit.
[0005]
In view of these circumstances, the present invention has been made with the object of obtaining a nonwoven fabric excellent in puncture resistance and puncture resistance by preventing foreign matter from penetrating the nonwoven fabric or breaking through and breaking.
[0006]
[Means for Solving the Problems]
To solve the above problem, the fiber cross section Ri Do from the non-circular shape, a cross or H-shaped contour with rounded of the fiber cross-section, the length of the largest part of the diametral length of the cross section in the fiber cross-section When a side has two or more protrusions extending from the long side, and the shortest part is the largest length in the cross-sectional length perpendicular to the long side, the flatness ratio (the length of the long side) / The length of the short side) contains at least 10 mass % of deformed cross-section synthetic fibers, and contains 30-60 mass % of heat-bondable sheath-core composite fibers in addition to the deformed cross-section synthetic fibers. This is a wet nonwoven fabric made by wet papermaking and melted with a sheath component and heat-bonded , and the penetration strength per unit nonwoven fabric density described later is at least 20 N / (g / cm ³ ), so that foreign matter penetrates the nonwoven fabric. Or break through and break Suppressing, leading to the present invention know that obtaining a separator strongly superior battery piercing resistance.
[0007]
The long side of the modified cross-section synthetic fiber is preferably 5 to 60 μm. Moreover, it is desirable that the fiber strength of the modified cross-section synthetic fiber is 7.0 cN / dtex or more.
[0008]
It is desirable that the modified cross-section synthetic fiber has two or more protrusions. In addition, the modified cross-section synthetic fiber is divided into two components, each of which is formed by dividing two-component alternately adjacent fibers in the fiber cross-section, and dividing at least one of the two components into two or more. Desirable monofilament.
[0009]
The nonwoven fabric is desirably subjected to a hydrophilic treatment.
[0010]
The battery separator has a non-circular cross section of the fiber, the cross section of the fiber has a rounded cross shape or an H shape, and the longest portion of the cross section of the cross section of the fiber is the longest crossing length . When the short side is the portion having the two or more protrusions extending from the long side and the largest cross-sectional length perpendicular to the long side is defined as the flatness ratio (long side length / short side length) In addition to the modified cross-section synthetic fiber, 30-60 mass % of the heat- bondable sheath-core composite fiber is used so that the modified cross-section synthetic fiber having a length) of at least 1.2 is at least 10 mass% with respect to the total fiber. The slurry can be dispersed in water to prepare a slurry, wet papermaking is performed using a paper machine, and the sheath component is melted and thermally bonded . Furthermore, after wet papermaking, a high-pressure water stream can be jetted at a maximum water pressure of 3 MPa or less to improve fiber dispersion.
[0011]
In addition, the nonwoven fabric is prepared by dispersing the irregular shaped cross-section type composite fiber in water and preparing a slurry by dividing into each component so as to be at least 10 mass% of the irregular shaped synthetic fiber. It can be produced by wet paper making. Furthermore, after wet papermaking, the dispersion of fibers can be improved by spraying a high-pressure water flow at a maximum water pressure of 3 MPa or less.
[0012]
The battery separator using the non-woven fabric is desirable in that it suppresses damage caused by foreign matters such as burrs of electrodes and the like and dendrites generated by repeated charge and discharge.
The contents of the present invention will be specifically described below.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The modified cross-section synthetic fiber used in the present invention has a non-circular cross section, for example, a cross shape, an I shape, an H shape, an L shape, a T shape, an X shape, a Y shape, a polygon more than a triangle, a sector shape. An elliptical cross section is used, an example of which is shown in FIG. In particular, when the longest part of the cross-sectional length of the cross section, such as a cross-shaped or H-shaped round cross-section as shown in FIG. 1 (a) or (b), is taken from the long side. In the modified cross-section synthetic fiber having two or more protrusions 4 extending, or in the fiber cross section as shown in FIG. 2, two components are alternately arranged adjacently, and at least one of the two components is divided into two or more. It is preferable to use a single fiber obtained by dividing the modified cross-section generating composite fiber into each component.
[0014]
Then, in the fiber cross section, when the longest portion of the cross-section passing length is the long side and the longest portion of the cross-section crossing length orthogonal to the long side is the short side, the flatness ratio (long side length / A modified synthetic fiber having a short side length of at least 1.2 is used. More preferably, it is at least 2. For example, in the case of the modified cross-section synthetic fibers shown in FIGS. 1A to 1C, the longest cross-sectional length of the cross section is the longest side 2 and the cross-sectional length perpendicular to the long side 2 is the longest. If the section is a short side 3 and the fan-shaped cross-section fiber is obtained by dividing the modified cross-section generating composite fiber shown in FIG. 2 into the respective components, the longest cross-sectional length is perpendicular to the long side 2 and the long side 2 The shortest side 3 is the largest portion of the crossing length of the cross section. When the flatness ratio is at least 1.2 , the fibers are less likely to escape against the pressing of the foreign matter when the foreign matter pierces the non-woven fabric, and can be prevented from penetrating. This is because it can be prevented from reaching the counter electrode.
[0015]
At this time, it is preferable that the length of the long side in a modified cross-section synthetic fiber is 5-60 micrometers. More preferably, it is 8-40 micrometers. When the length of the long side is less than 5 μm, the fiber escapes against the pressing of the foreign matter, and the effect of puncture resistance is not sufficiently obtained. When the length of the long side exceeds 60 μm, Since the gap becomes too large, the piercing property is inferior.
[0016]
The raw material of the modified cross-section synthetic fiber used in the present invention is not particularly limited, and polyester resins, polyamide resins, polyolefin resins, etc. are used. In particular, if used for battery separators, polyethylene Polyolefin resins such as polypropylene, polybutene-1, poly (4-methylpentene-1), and ethylene-vinyl alcohol copolymer are preferable. The fiber form is not limited to a single fiber, but may be a composite fiber as long as it has an irregular cross section.
[0017]
Moreover, in this invention, if the single fiber divided | segmented into each component is a modified cross-section fiber, two components will be alternately arrange | positioned adjacently in a fiber cross section, and at least 1 component of 2 components will be divided | segmented into 2 or more. The structural unit is continuous in the length direction, and a modified cross-section generating composite fiber having a cross-sectional shape in which a part of all the structural units is always exposed on the fiber surface is also included. Examples of the deformed cross-section generating composite fiber include polyester resins / polyolefin resins, polyester resins / polyamide resins, combinations of different resins such as polyolefin resins / polyamide resins, or poly (4-methylpentene- 1) A combination of homologous resins such as polypropylene, ethylene-vinyl alcohol copolymer / polypropylene, and polypropylene / polyethylene is used. The fiber form is not particularly limited as long as it has an irregular cross section after division, and may be circular before division. And it is preferable that the division | segmentation number of an irregular cross-section generation | occurrence | production composite fiber is 4-20.
[0018]
And the said odd-shaped cross-section synthetic fiber is contained at least 10 mass% with respect to all the fibers. More preferably, it is 10-60 mass%. This is because the puncture resistance effect cannot be sufficiently obtained when the content of the modified cross-section synthetic fiber is less than 10 mass%. Other fibers used are not particularly limited. For example, natural fibers such as cotton, silk, and wool, recycled fibers such as rayon, acrylic fibers, polyester fibers, polyamide fibers, polyolefin fibers, and the like. One fiber or composite fiber is appropriately used depending on the application. In particular, when used as a battery separator, the polyolefin single fiber or sheath component is polyethylene, ethylene-propylene copolymer, polybutene-1, ethylene-vinyl alcohol copolymer, and the core component is polypropylene, poly (4- It is preferable to use a heat-adhesive sheath-core composite fiber that is a resin that is higher by 10 ° C. or more than the melting point of the sheath component such as methylpentene-1) or polyethylene terephthalate. At this time, when the heat-adhesive sheath-core type composite fiber is contained in an amount of 30 to 60 mass%, the degree of freedom between the fibers can be suppressed, and the piercing property of the nonwoven fabric is further improved.
[0019]
Next, the nonwoven fabric excellent in puncture resistance of the present invention will be described along the manufacturing method. The form of the fiber web containing the modified cross-section synthetic fiber is a dry web obtained by a card method, an airlay method, a wet paper web obtained by a wet papermaking method, or a direct method such as a melt blow method or a spunbond method. The obtained long fiber web is used. In particular, a wet papermaking web having a fiber length of 3 to 25 mm is obtained as a homogeneous web, and the modified cross-section synthetic fiber is in the longitudinal direction of the fiber web (perpendicular to the thickness direction). It is preferable in that it can be easily aligned in the direction). A more preferable fiber length is 5 to 15 mm. If the fiber length is less than 3 mm, the effect of puncture resistance is not sufficiently obtained, the fibers are scattered during high-pressure water treatment described later, and the puncture strength is reduced when it exceeds 25 mm. This is because the dispersibility of the fibers in the slurry deteriorates and a uniform nonwoven fabric cannot be obtained.
[0020]
The fiber web can be processed by a method such as a heat calendar process, a hot air process, a high-pressure water flow process, or a combination thereof. At this time, when the high-pressure water flow treatment is used, it is preferable to perform the treatment under conditions that prevent the constituent fibers from being oriented in the thickness direction as much as possible. Specifically, when the maximum water pressure of the high-pressure water treatment is injected at 3 MPa or less, the orientation in the thickness direction can be suppressed. When the constituent fibers are oriented in the thickness direction, the sharp foreign matter can easily enter the nonwoven fabric while avoiding the fibers. For example, in the case of a battery separator, foreign matters such as dendrites that are generated due to burrs on electrodes and the like and repeated charge and discharge This is because the ratio of short-circuiting increases when the counter electrode reaches the counter electrode or breaks.
[0021]
And it is preferable that the said nonwoven fabric is hydrophilized. Examples of the hydrophilic treatment include surfactant treatment, vinyl monomer graft copolymerization treatment, fluorine gas treatment, sulfonation treatment, corona discharge treatment, and plasma treatment. Thereafter, the thickness and the like are adjusted as necessary to obtain the nonwoven fabric of the present invention.
[0022]
For example, as one example of the method for producing a battery separator of the present invention, first, a deformed cross-section synthetic fiber having a flatness ratio (long side length / short side length) of at least 1.2 is 10 mass% or more. Then, a heat-adhesive sheath-core type composite fiber and / or a polyolefin fiber are mixed and dispersed in water to a concentration of 0.01 to 0.6% to prepare a slurry. At this time, a small amount of a dispersant may be added. The slurry is made using a short net type, a circular net type, or a paper machine using a combination of both. Next, the heat-adhesive sheath-core composite fiber is melted to bond the fibers. Thereafter, a high-pressure water flow treatment may be performed as necessary. Thereafter, the nonwoven fabric is subjected to the hydrophilization treatment to obtain a hydrophilic nonwoven fabric. Then, it heat-calenders and is adjusted to predetermined thickness, The battery separator of this invention is obtained.
[0023]
As another example of the method for producing a battery separator of the present invention, first, a modified cross-section generating composite fiber, a heat-adhesive sheath-core composite fiber and / or a polyolefin fiber are mixed, and 0.01 Disperse in water to a concentration of ~ 0.6% to prepare a slurry. At this time, when disperse in water, the dissociation time in the pulper is lengthened, or pre-immersed in water or hot water, so that each cross-section synthetic fiber becomes at least 10 mass% with respect to the total fiber. Dividing into components is particularly preferable in that the water pressure during the high-pressure water treatment described later can be suppressed low. And in order to improve the handleability of a nonwoven fabric by wet papermaking using a paper machine, the heat-adhesive sheath-core type composite fiber is melted and lightly bonded between the fibers. Furthermore, after wet papermaking, a high-pressure water stream is jetted to divide the undivided modified cross-section generating composite fiber. At this time, the object of the present invention can be achieved as long as at least 10 mass% of a modified cross-section synthetic fiber is obtained even if all of the modified cross-section generating composite fibers are not divided. As described above, when the irregular cross-section generating composite fiber is divided before wet papermaking, treatment at a maximum water pressure of 3 MPa or less is preferable in terms of suppressing fiber entanglement in the thickness direction and improving piercing strength. The obtained non-woven fabric is heat-bonded with the low melting point component of the heat-adhesive sheath-core composite fiber simultaneously with drying, and then a battery separator is obtained in the same manner as described above.
[0024]
The basis weight of the nonwoven fabric of the present invention may be appropriately set according to the use, but is preferably 30 to 100 g / m ² when used for a battery separator. If it is less than 30 g / m ^2, not only inferior in strength piercing, because tension of the nonwoven fabric strength is too weak, there is a problem in the production of the battery, if it exceeds 100 g / m ^2, although powerful is improved piercing, gas This is because the passability of the resin deteriorates and becomes disadvantageous in terms of life.
[0025]
Furthermore, the density of the nonwoven fabric of the present invention is preferably 0.6 g / cm ³ or less at a load of 175 kPa (measured by a micrometer according to JIS-B-7502). More preferably, it is 0.3 to 0.5 g / cm ³ . This is because if the density of the nonwoven fabric exceeds 0.6 g / cm ³ , the gas permeability deteriorates and the life becomes disadvantageous.
[0026]
In this way, a nonwoven fabric excellent in piercing resistance having a piercing strength per unit nonwoven fabric density of at least 20 N / (g / cm ³ ) shown below can be obtained.
(Strong piercing)
Using a KES-G5 Handy Compression Tester manufactured by Kato Tech Co., Ltd., prepare a non-woven fabric cut to a size of 30 mm in length and 100 mm in width, and an aluminum plate of 46 mm in length, 86 mm in width and 7 mm in thickness on the sample After placing a holding plate having a hole with a diameter of 11 mm in the center of the tip, a spherical portion with a tip of 1 mmφ, a needle with a conical shape with a shaft having a bottom diameter of 2.2 mm and a height of 18.7 mm, Measure the maximum load (N) when pierced perpendicularly to the center of the hole in the press plate at a speed of 2 mm / second, and divide by the nonwoven fabric density at 175 kPa load (measured with a micrometer according to JIS-B-7502). The piercing strength was N / (g / cm ³ ).
When powerful piercing per unit nonwoven density is less than ^{20N / (g / cm 3)} , a foreign substance or easily penetrate the nonwoven, or to damage by breaking through, especially in the case of a battery separator, such as electrodes This is because foreign matters such as dendrites generated by repeated burrs and charging / discharging easily reach the counter electrode or break, increasing the ratio of short circuits.
[0027]
Moreover, it is preferable that the obtained nonwoven fabric is hydrophilized. Hydrophilic treatment includes vinyl monomer graft copolymerization treatment, fluorine gas treatment, sulfonation treatment, corona discharge treatment, plasma treatment, etc. Among them, sulfonation treatment improves the self-discharge property of the battery. Examples of the sulfonation treatment include concentrated sulfuric acid treatment, fuming sulfuric acid treatment, chlorosulfonic acid treatment, and sulfuric anhydride treatment. By applying a hydrophilization treatment, for example, when used as a wiper, it can wipe off an object with moisture, or can be used as a wet wiper, and when used as a battery separator, it improves capacity storage rate and cycle life. This is because it contributes.
[0028]
【Example】
Hereinafter, the contents of the present invention will be described with reference to examples. In addition, the length of the long side and short side in a fiber cross section, single fiber strength, the tensile strength of a nonwoven fabric, and the short rate were measured with the following method.
[0029]
[Length of long side, short side]
About 1000 fibers are bundled and passed through an aluminum plate having a hole diameter of 0.5 mm, cut along the plate surface, magnified 40 times using an electron microscope, and present in 1 cm × 1 cm square. In the modified cross-section synthetic fiber, the length is measured with the longest part of the cross-section length as the long side and the longest part of the cross-section length perpendicular to the long side as the short side, and the average value is the long side. And the length of the short side.
[0030]
[Single fiber strength]
According to JIS-L-1015, using a tensile tester, the load value when the holding distance of the sample was 20 mm was measured, and the load value per unit fineness was defined as the single fiber strength.
[0031]
[Tensile strength of nonwoven fabric]
In accordance with JIS-L-1096, a sample piece having a width of 5 cm and a length of 15 cm is gripped at a spacing of 10 cm with respect to the longitudinal direction of the nonwoven fabric, and stretched at a tensile speed of 30 cm / min using a constant speed extension type tensile tester. The load value at the time of cutting was taken as the tensile strength.
[0032]
[Short rate]
The negative electrode was kneaded by adding water to hydrogen storage alloy, carbonyl nickel, carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE) to prepare a slurry, and this slurry was dip-coated on nickel-plated punching metal at 80 ° C. By drying and pressure molding to form a hydrogen storage alloy negative electrode, the positive electrode is a known sintered nickel electrode, each separator is sandwiched between the negative electrode and the positive electrode, inserted into a battery case, and the electrolyte is injected. A cylindrical sealed nickel metal hydride battery was produced. The produced cylindrical sealed nickel-metal hydride battery was charged for 12 hours at a charging rate of 0.1 C, 0.5 hours at rest, and at a discharging voltage of 0.1 C, a final voltage of 1.0 V, and 10 cycles of charge and discharge were repeated for initial battery activation. It was. At this time, the ratio at which a short circuit occurred was defined as the short ratio.
[0033]
[Example 1]
The fiber cross section shown in FIG. 1 (a) has a fineness of 2.2 dtex made of polypropylene having a melting point of 163 ° C. (manufactured by Nippon Polychem Co., Ltd.), a polypropylene fiber having a fiber length of 10 mm is 60 mass%, and the sheath component is a melting point of 132 ° C. High-density polyethylene (manufactured by Nippon Polychem Co., Ltd.), core component of polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point of 163 ° C., a composite ratio of 50:50, fineness of 1.7 dtex, and fiber length of 10 mm. 40 mass% is mixed with mold composite fiber, the dissociation time in the pulper is 15 minutes, slurry is prepared to a concentration of 0.5%, wet papermaking is performed, and then dried at 135 ° C. using a Yankee dryer At the same time, the sheath component of the sheath-core composite fiber was melted and heat-sealed to obtain a wet nonwoven fabric with a basis weight of 50 g / m ² .
[0034]
Each side of the resulting wet nonwoven fabric is subjected to corona discharge treatment so that the total discharge amount is 0.462 KW · min / m ² , four times each, and heat calendering is performed, and the basis weight is 50 g / m ² and the thickness is 120 μm. A battery separator was obtained.
[0035]
[Example 2]
The first component is an ethylene-vinyl alcohol copolymer (ethylene content 38 mol%), the second component is polypropylene, the composite ratio is 50:50, and the fineness having a fiber cross section composed of two protrusions shown in FIG. 3.3 dtex, 50 mass% of the modified cross-section generating composite fiber having a fiber length of 6 mm, 30 mass% of the concentric sheath-core composite fiber of Example 1, and a polypropylene having a melting point of 163 ° C. (manufactured by Nippon Polychem Co., Ltd.) A slurry is prepared by mixing 20 mass% of polypropylene fiber with a fineness of 0.8 dtex and a fiber length of 10 mm having a circular cross section, and a dissociation time of 15 minutes with a pulper. After wet paper making, high-pressure columnar water flow is jetted from the front and back surfaces at a pressure of 3 MPa to divide the deformed cross-section generating composite fibers to form ultrafine fibers with fan-shaped fiber cross sections. Entangling between fibers causes to obtain by simultaneously thermally fused and dried at 135 ° C. and basis weight 50 g / m ² of wet-laid nonwoven fabric.
[0036]
Each side of the resulting wet nonwoven fabric is subjected to corona discharge treatment so that the total discharge amount is 0.462 KW · min / m ² , four times each, and heat calendering is performed, and the basis weight is 50 g / m ² and the thickness is 120 μm. A battery separator was obtained.
[0037]
[Comparative Example 1]
For batteries having a basis weight of 50 g / m ² and a thickness of 120 μm in the same manner as in Example 1, except that the circular-shaped polypropylene fiber of Example 2 is 60 mass% and the concentric sheath-core composite fiber of Example 1 is 40 mass%. A separator was obtained.
[0038]
[Comparative Example 2]
The first component is an ethylene-vinyl alcohol copolymer (ethylene content 38 mol%), the second component is polypropylene, the composite ratio is 50:50, the fineness of the fiber cross section shown in FIG. 2 is 3.3 dtex, the fiber length It consists of 45 mass% of the irregular cross-section generating composite fiber of 45 mm, 30 mass% of the concentric sheath-core type composite fiber of Example 1, and a polypropylene having a melting point of 163 ° C. (manufactured by Nippon Polychem Co., Ltd.). Polypropylene fiber with a fineness of 0.8dtex and fiber length of 38mm is mixed with 20mass%, a fiber web is produced by a semi-random card machine, and a high-pressure columnar water stream is injected from the front and back surfaces at a pressure of 15MPa, thereby generating a deformed cross section. The composite fiber is divided to form ultrafine fibers having a fan-shaped fiber cross section, and the fibers are entangled and thermally fused simultaneously with drying at 135 ° C. To obtain a dry nonwoven fabric of 50 g / m ^2. The obtained dry nonwoven fabric was hydrophilized in the same manner as in Example 1 to obtain a battery separator having a basis weight of 50 g / m ² and a thickness of 120 μm.
The physical properties of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1 below.
[0039]
[Table 1]

[0040]
In Examples 1 and 2, since it has a predetermined irregular cross section, the piercing strength is large. When the obtained nonwoven fabric is used as a battery separator, the short-circuit rate is remarkably reduced, and a hydrophilic treatment is performed. As a result, a nickel metal hydride battery excellent in battery characteristics could be obtained. On the other hand, in Comparative Example 1, since all fibers having a circular fiber cross section were used, the piercing strength was small and the short rate was large. In Comparative Example 2, although it has a predetermined irregular cross section, since the irregular cross-section generating composite fiber was treated with a high-pressure water flow of 15 MPa, the constituent fibers were only oriented in the thickness direction of the nonwoven fabric. In addition, since water marks were formed and density spots were generated, the piercing strength was insufficient.
[0041]
【The invention's effect】
The nonwoven fabric of the present invention has a high piercing strength by containing at least 10 mass% of a modified cross-section synthetic fiber having a non-circular fiber cross section and a desired flatness ratio (long side length / short side length). Can be obtained. Also, a modified cross-section synthetic fiber is a fiber having two or more protrusions, or a modified cross-section generated by arranging two components alternately adjacent to each other in the fiber cross section and dividing at least one of the two components into two or more. When the fiber is a single fiber obtained by dividing the mold composite fiber into each component, high stab strength and high liquid retention can be obtained.
And the nonwoven fabric of this invention has desired piercing strength by manufacturing using the hydroentanglement method under the low water pressure of 3MPa or less after using wet papermaking or wet papermaking. A nonwoven fabric can be obtained.
The nonwoven fabric excellent in puncture resistance of the present invention is suitable for agricultural and civil engineering materials such as packaging materials, wipers, wallpaper and other decorative sheets, grass protection sheets, etc. It is suitable as a battery separator that suppresses damage due to foreign matters such as dendrites generated by the above.
[Brief description of the drawings]
FIG. 1 shows an example of a fiber cross-sectional view of a modified cross-section synthetic fiber used in the present invention.
FIG. 2 shows an example of a fiber cross-sectional view of a modified cross-section generating composite fiber used in the present invention and a modified cross-section synthetic fiber after generation.
[Explanation of symbols]
1. 1. Modified cross-section synthetic fiber Long side 3. 3. Short side protrusion

Claims

Fiber cross section is Ri Do from the non-circular shape, a cross or H-shaped contour with rounded of the fiber cross-section, when the largest part of the diametral length of the cross section and long sides in the fiber cross-section, the long The flat ratio (long side length / short side length) is defined as a short side having a portion having two or more protrusions extending from the side and having the largest cross-sectional length perpendicular to the long side. sheath but it contains at least 10 mass% of at least 1.2 der Ru modified cross-section synthetic fiber, a heat-adhesive sheath-core type composite fibers containing 30 to 60 mass% in addition to said different-section synthetic fibers by a wet paper making for Ri wet nonwoven der melting the components are heat-bonded, and powerful puncture per unit nonwoven density shown below is excellent in penetration resistance, characterized in that at least 20N / (g / cm ³⁾ battery Separator .
(Strong piercing)
Using a KES-G5 Handy Compression Tester manufactured by Kato Tech Co., Ltd., prepare a non-woven fabric cut to a size of 30 mm in length and 100 mm in width, and an aluminum plate of 46 mm in length, 86 mm in width and 7 mm in thickness on the sample After placing a holding plate having a hole with a diameter of 11 mm in the center of the tip, a spherical portion with a tip of 1 mmφ, a needle with a conical shape with a shaft having a bottom diameter of 2.2 mm and a height of 18.7 mm, Measure the maximum load (N) when pierced perpendicularly to the center of the hole in the press plate at a speed of 2 mm / second, and divide by the nonwoven fabric density at 175 kPa load (measured with a micrometer according to JIS-B-7502). The piercing strength was N / (g / cm ³ ).

Penetration resistance excellent battery separator of claim 1, wherein the length of the long side of the modified cross-section synthetic fiber is 5 to 60 m.

3. The battery separator having excellent puncture resistance according to claim 1, wherein the fiber strength of the modified cross-section synthetic fiber is 7.0 cN / dtex or more.

A battery separator having excellent puncture resistance, wherein the nonwoven fabric according to any one of claims 1 to 3 is subjected to a hydrophilic treatment.

Fiber cross section is of a non-circular shape, a cross or H-shaped contour with rounded of the fiber cross-section, when the largest part of the diametral length of the cross section in the fiber cross section is a long side, the long side When the portion having the two or more extending protrusions and having the largest cross-sectional length perpendicular to the long side as the short side is the short side, the flatness ratio (long side length / short side length) is at least 1.2 so that the cross-section synthetic fiber of 1.2 is at least 10 mass% with respect to the total fiber, and the heat- bondable sheath-core composite fiber is 30 to 60 mass % in addition to the cross-section synthetic fiber. A method for producing a battery separator having excellent puncture resistance, characterized in that a slurry is prepared, wet paper is made using a paper machine, and the sheath component is melted and thermally bonded .

6. The method for producing a battery separator having excellent puncture resistance according to claim 5 , wherein a high-pressure water flow is jetted at a maximum water pressure of 3 MPa or less after wet papermaking.