JP3583256B2

JP3583256B2 - Thin paper for hot stencil printing and method for producing the same

Info

Publication number: JP3583256B2
Application number: JP08091797A
Authority: JP
Inventors: 義幸安藤; 靖典村手; 義堅大野
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 1997-03-31
Filing date: 1997-03-31
Publication date: 2004-11-04
Anticipated expiration: 2017-03-31
Also published as: JPH10272857A

Description

【０００１】
【発明の属する技術分野】
本発明は、ハロゲンランプ、キセノンランプ、フラッシュバルブ等による閃光照射や赤外線照射、あるいはサーマルヘッド等によって穿孔製版される感熱性孔版印刷用原紙に使用する熱孔版印刷用薄葉紙及びその製造法に関する。さらに詳しくは、抄紙時の分散性が良好で、インクの保持性及び耐水強度に優れた熱孔版印刷用薄葉紙に関する。
【０００２】
【従来の技術】
従来、感熱孔版印刷用薄葉紙として、楮、三椏、マニラ麻などの天然繊維１００％からなる和紙、合成化学繊維１００％からなる不織布、または天然繊維と合成化学繊維を混抄した不織布等種々のものが知られていた。とくに合成繊維１００％からなる不織布としては、特開平３−８８９２号公報においてポリエステルまたはアクリルの０．１デニール以下の極細繊維を含む感熱孔版印刷用薄葉紙が提案されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、熱孔版印刷用薄葉紙にポリエステルフィルムをラミネート加工し感熱孔版印刷用原紙を作りサーマルヘッド等にて穿孔製版印刷すると、天然繊維１００％の和紙では結束繊維の存在によりインクの通過しない白抜け部分が発生したり、耐水強度不足による製版の短寿命が問題であった。
また、合成化学繊維１００％では耐水強度は向上するものの繊維自体の親水性不足からインクの保持性が悪く印字濃度が低くなるという欠点を有していた。
さらに、天然繊維と合成化学繊維を混抄した不織布においてはその双方の欠点が存在した。
ポリエステルまたはアクリルの極細繊維を含む薄葉紙はインク保持性及び耐水強度が向上するが、極細繊維は抄紙時の分散性が悪く繊維が絡み合うといった問題が生じ、目付斑のない薄葉紙を安定して得ることは工業的には実際上非常に難しいと言わざるを得ない。
【０００４】
本発明の目的は、抄紙時の分散性が良好であり、印刷時の白抜け部分がなく、且つ耐水強度及びインク保持性が良好な熱孔版印刷用薄葉紙を提供することであり、さらに、該薄葉紙を工業的に安定に製造する方法を提供することである。
【０００５】
【課題を解決するための手段】
すなわち、本発明は、アルカリ水溶液に難溶性の熱可塑性樹脂からなる単繊維繊度0.01〜0.2デニールの極細繊維Ａ１及びアルカリ水溶液に難溶性の熱可塑性樹脂からなり、該極細繊維Ａ１の平均繊度の1/5以下で且つ0.02デニール以下の単繊維繊度を有する極細繊維Ａ２とを合計で20重量％以上90重量％以下含む熱孔版印刷用薄葉紙であって、該極細繊維Ａ１と該極細繊維Ａ２の本数の比（Ａ１／Ａ２）が2／1〜1／2であり、該薄葉紙を構成する繊維間が、融点差30℃以上の２種以上のアルカリ水溶液に難溶性の熱接着性樹脂によって接着されている熱孔版印刷用薄葉紙及び、アルカリ水溶液に易溶性の熱可塑性樹脂Ｐ１（以下、単にアルカリ易溶性成分Ｐ１と称することもある。）によりアルカリ水溶液に難溶性の熱可塑性樹脂Ｐ２（以下、単にアルカリ難溶性成分Ｐ２と称することもある。）が複数個に分割された複合繊維であって、該複合繊維断面における熱可塑性樹脂Ｐ２からなる成分には2種類の大きさが存在し、その面積比が5倍以上である複合繊維Ｃを30重量％以上、及び融点差が30℃以上であるアルカリ難溶性の低融点成分Ｐ３とアルカリ難溶性の高融点成分Ｐ４とからなる熱接着性複合繊維Ｂを10重量％以上を含む紙料を湿式抄造法にて混抄する工程(i)、混抄物に熱処理を施して低融点成分Ｐ３により繊維間を熱接着させる工程(ii)、アルカリ水溶液により熱可塑性樹脂Ｐ１を溶解除去する工程(iii)、熱処理を施して高融点成分Ｐ４により繊維間を熱接着させる工程(iv)を含むことを特徴する熱孔版印刷用薄葉紙の製造方法である。
【０００６】
【発明の実施の形態】
前述のように、薄葉紙の原料として合成化学繊維を用いると耐水強度が向上することや単繊維繊度を０．１デニール以下とするとインクの保持性が良好となることは公知であるが、極細繊維は、抄紙時の初期分散性が悪く、特に０．１デニール以下の極細繊維は安定した抄紙が難しいため、本発明においては抄紙時には２デニール〜１０デニールという太繊度の複合繊維を用いて抄紙し、抄紙後に該複合繊維の一成分を除去することにより極細繊維を形成させ、極細繊維を含む薄葉紙を得ようとするものである。
【０００７】
さらに、本発明においては極細繊維として単繊維繊度０．０１〜０．２デニールの極細繊維Ａ１及び該極細繊維Ａ１の平均繊度の１／５以下で且つ０．０２デニール以下の単繊維繊度を有する極細繊維Ａ２とを併用することにより、１種類の極細繊維を単独で使用した場合よりも更なる分散安定性、インク保持性及び解像度の良好な薄葉紙を得ようとするものである。
【０００８】
本発明の特徴は、抄紙時の分散性が良好で且つ必要性能を満足する熱孔版印刷用薄葉紙が得られることであるが、特に、複合繊維Ｃのアルカリ易溶性成分Ｐ１を除去することにより、単繊維繊度の異なる極細繊維が混合された状態で形成され、その結果、薄葉紙内に微細な空隙構造が生じ、この空隙にインクが保持され、さらにインクの透過性、解像度が向上するという効果が得られる。
【０００９】
アルカリ難溶性成分Ｐ２からなる極細繊維Ａ１の単繊維繊度が０．２デニールを越えるとインクの保持性、解像度が悪くなり、０．０１デニール未満の繊維については繊維の製造が困難で、紡出時の糸切れ、不良断面の発生（断面均斉度の低下）といった問題が生じるので、０．０５〜０．１デニールであることが好ましい。
また、極細繊維Ａ２の単繊維繊度は、極細繊維Ａ１の平均繊度の１／５以下で且つ０．０２デニール以下である必要がある。極細繊維Ａ１とＡ２との繊度の比が１／５を超えたり、極細繊維Ａ２の単繊維繊度が０．０２デニールを超えると、極細繊維Ａ１との混入効果がなくなり、本発明の目的を達成することができない。
【００１０】
さらに、本発明においては、極細繊維Ａ１と極細繊維Ａ２との本数の比（Ａ１／Ａ２）が２／１〜１／２であることが必要であり、本数の比が２／１を超えると、インクの保持性や解像度が不良となる。一方、１／２未満となると、紡糸時に複合形状のコントロールが困難となり、例えば、海島型複合繊維とする場合、極細繊維の元となる島成分の島形状のコントロールができなくなる。
【００１１】
本発明の薄葉紙は、上記のような単繊維繊度の異なる２種の極細繊維が合計で２０重量％以上、好ましくは２２重量％以上含まれていることが必要である。２０重量％未満ではインクの保持性及び解像度が不良となる。
【００１２】
本発明の薄葉紙は、極細繊維Ａ１及び極細繊維Ａ２のみから構成されていてもよいが、１００％極細繊維から構成されると紙力が満足できない場合がある。そのため、本発明においては、少なくとも１０重量％以上、好ましくは２５重量％以上のバインダー樹脂により繊維間が熱接着され、シートとしての形態保持及び紙力を確保している。一方、バインダー樹脂は多すぎるとインク保持性が不良となるので、薄葉紙中に４０重量％以下、特に３５重量％以下含まれるようにすることが好ましい。
【００１３】
本発明においては、上記の分割性複合繊維Ｃを含む紙料から湿式抄造法により一旦シート状物を製造し、該シート状物にアルカリ処理を施して該複合繊維のアルカリ易溶性成分Ｐ１を除去し、最終的に極細繊維を含む薄葉紙とされるが、シート状物を形成するにあたっては、シートの形態を保つために繊維間を仮接着する必要があり、また、その後にアルカリ処理によって形成される多数の極細繊維同士を接着して紙力に優れた薄葉紙とする必要があり、最終的な薄葉紙となるまでに２回の接着処理を施すことが必要となる。
【００１４】
このような２段の接着を効率的に行なうために、本発明においては、それぞれの熱接着用樹脂を別々に準備することなく、低融点成分Ｐ３と高融点成分Ｐ４とからなる熱接着性複合繊維を用い、これを主体となる分割性複合繊維Ｃと混合して紙料スラリーを調整して、抄造に供することを特徴とするものである。この場合、熱接着性複合繊維の複合形態は、芯鞘型、サイドバイサイド型など適宜設定し得るが、芯鞘型にする場合は高融点成分を芯成分に配置することが必要である。
【００１５】
このような熱接着性複合繊維を使用し、抄造後の第１段の接着においては、低融点成分Ｐ３のみが溶融軟化する程度の加熱処理を行ない、成分Ｐ３のみにより繊維間を接着させ、アルカリ処理後の最終的な極細繊維間の接着においては、複合繊維の高融点成分Ｐ４が溶融軟化する程度の温度で加熱処理を行なうことにより、高融点成分Ｐ４と前記の低融点成分Ｐ３の両成分が繊維間の接着に寄与するのである。
【００１６】
さらに、本発明においては、複合繊維Ｃを構成するアルカリ易溶性成分Ｐ１のアルカリ除去処理の前後で熱処理（１段目、２段目）を施しているため、２段目の熱処理後は、薄葉紙において低融点及び高融点の２種の熱接着性樹脂Ｐ３及びＰ４成分によって繊維間が接着されており、１種の熱接着性樹脂で繊維間が接着されている薄葉紙に比して優れた紙力と耐熱性を有するものである。
本発明においては、２段階の熱処理を施すことが必須であるので、融点差の異なる最低２種の熱接着性樹脂の存在が必要であるが、目的に応じて、熱接着性樹脂の種類を３種類以上選択して用いても差支えない。
【００１７】
高融点成分と低融点成分との融点差は小さすぎると、第１段の熱処理時に低融点成分のみを溶融させるための温度コントロールが極めて困難となり、温度の若干の触れによって高融点成分が溶融した場合、製品に紙力の差が生じる場合があるので、好ましくは融点差が３０℃以上である組み合わせが好ましい。なお、熱可塑性樹脂のうち明確な融点を有さない物があるがその場合は、軟化点や熱接着開始温度として融点を読み替えて成分の組み合わせを決定すればよい。
【００１８】
高融点成分Ｐ４及び低融点成分Ｐ３の種類は、上記のような適切な融点差を持つ樹脂の組み合せであれば、特に限定されないが、薄葉紙の製造工程においてシートがアルカリ処理に供されるので、分割性複合繊維Ｃのアルカリ易溶性成分Ｐ１に比して相対的に十分にアルカリ難溶性の樹脂であることが必要である。
【００１９】
本発明の薄葉紙を製造するに際しては、抄紙時の分散性の問題が殆どないために、薄葉紙に極細繊維が均質に存在し、その緊度は任意の箇所を測定しても緊度が０．２０〜０．３０ｇ／ｃｍ３で、緊度のばらつきが０．０１ｇ／ｃｍ３以下という高品質のものが得られる。
【００２０】
本発明において、上記の極細繊維はＡ１とＡ２の合計で薄葉紙に２０〜９０重量％含まれていることが必要である。２０重量％未満ではインクの保持性や解像度が劣り、一方、９０重量％を超えると紙力が低下する。好ましくは、２０〜６５重量％含まれていることが望ましい。
【００２１】
上記のような本発明の薄葉紙とするためには、抄紙時に上記の分割性複合繊維Ｃを３０重量％以上及び熱接着性複合繊維Ｂを１０重量％以上となるように混抄することが必要であり、本発明においては、これらの繊維の他に天然繊維あるいは合成化学繊維を６０重量％以下含有しても必要性能を大きく損なうことなく熱孔版印刷用薄葉紙を得ることができる。
【００２２】
複合繊維Ｃの含有率は、成分Ｐ１と成分Ｐ２の複合比や最終的に成分Ｐ２で構成される極細繊維の単繊維繊度や本数（海島の島の数）にもよるが、３０重量％未満であるとインクの保持性、解像度が不良となり好ましくない。逆に９０重量％を越えると紙力が低下する場合があるので、少なくとも１０重量％の熱接着性複合繊維Ｂが必要となる。熱接着性複合繊維Ｂの含有率が４０重量％を越えると相対的に複合繊維Ｃの比率が低下するため、アルカリ処理後の繊維間空隙が大きくなりやすくインク保持性が低下する傾向がある。よって、熱接着性複合繊維Ｂは１０重量％〜３０重量％含有されることがより好ましい。
【００２３】
本発明における複合繊維Ｃの繊維断面形状は、アルカリ処理後に、アルカリ難溶性成分Ｐ２によって極細繊維が形成される断面形状であれば、海島型、貼り合せ型等の分割型等特に限定されないが、アルカリ処理後の極細繊維の断面が円形又は略円形となる複合形態の方がインク透過性に有効であるので、海島型断面が好ましく採用される。
【００２４】
また、複合繊維Ｃを構成するアルカリ易溶性成分Ｐ１は、例えば、金属スルホネート基含有エステル単位を共重合したポリエステル、金属スルホネート基を含有するイソフタル酸とポリアルキレングリコールを共重合したポリエステル、特開平６−２８０１５６号公報に開示された金属スルホネート基を含有するイソフタル酸、ポリアルキレングリコール及び側鎖型のポリオキシアルキレン基を特定の割合で有する共重合ポリエステル等が好ましく使用される。
【００２５】
複合繊維Ｃを構成するアルカリ難溶性成分Ｐ２としては、ポリエステル、アクリル、ナイロン、ポリオレフィン等アルカリ難溶性熱可塑性樹脂であればよいが、本発明においてはポリエステルが好ましく使用される。
尚、本発明において、アルカリ易溶性と難溶性の境界は、苛性ソーダの５ｇ／リットル水溶液中で１３０℃、４０分間処理したときに、減量率が３０重量％以上のものをアルカリ易溶性とし、３０％未満のものを難溶性とする。また、両者はアルカリ減量速度として２０倍以上の差を持つ組み合わせとすることが好ましい。
【００２６】
本発明における熱接着性複合繊維Ｂとしては、その繊維断面は特に制限されるものではないが、芯鞘型やサイドバイサイド型複合繊維、特に芯鞘型複合繊維が好ましい。バインダー繊維Ｂの低融点成分Ｐ３、高融点成分Ｐ４ともにアルカリ難溶性の熱可塑性樹脂であれば特に制限されないが、芯鞘型の場合、鞘に低融点成分Ｐ３、芯に高融点成分Ｐ４という組み合わせにしなければならない。
【００２７】
成分Ｐ３及び成分Ｐ４のポリマー種は特に限定されないが、良好な接着強度を得るために、薄葉紙を構成する極細繊維、即ち抄紙時の複合繊維を構成するポリマー種と類似したポリマーを使用することが好ましい。さらに、成分Ｐ３と成分Ｐ４との親和性が低いと両成分が剥離しやすいので成分Ｐ３及び成分Ｐ４とは親和性の良好な組み合わせとすることが望ましい。したがって、複合繊維Ｃの成分Ｐ１及び成分Ｐ２がポリエステルで構成される場合は、熱接着性複合繊維Ｂの成分Ｐ３及び成分Ｐ４ともにポリエステルであることが望ましい。
【００２８】
本発明の薄葉紙は基材として、その上に例えば熱可塑性ポリエステルフィルム、ポリエチレンフィルム、ポリアミドフィルム等のフィルムを酢酸ビニル系やアクリル系の接着剤で接着積層して熱孔版印刷用原紙とすることができ、本発明の薄葉紙を使用することにより、印字濃度が濃く、解像度に優れ、かつ耐刷枚数も大幅に改善されるものである。
【００２９】
【実施例】
以下、実施例により本発明を具体的に説明するが、本発明はそれらにより限定されない。尚、緊度、分散性、印字濃度、解像度及び耐刷枚数は以下のようにして評価した。
＜緊度＞
ＪＩＳＰ８１１８の紙及び板紙の厚さと密度の試験方法に基づき測定した。
＜分散性＞
抄紙筒内における繊維の分散性を視覚判定した。未分散繊維がなく均一に分散した状態のものを○とし、未分散繊維が存在する状態のものを×とした。
＜印字濃度＞
印刷物の印字の濃度を視覚判定した。文字や細線が濃くはっきり現れていれば○、文字や細線が薄くぼやけている場合は×とした。
＜解像度＞
印字濃度と同様印刷物を視覚判定した。文字や細線の太さ斑や黒ベタ部分での白抜けが全くないものを◎、殆どないものを○、文字や細線が部分的にとぎれたり太さ斑があるものを×とした。なお、○と×の中間的な場合は△とした。
＜耐刷枚数＞
全自動デジタル孔版印刷機を用いて印刷速度１３０枚／分で印刷し１枚目の印刷物の文字や細線が乱れるまでの枚数を測定した。
【００３０】
実施例１
複合繊維Ｃとして、５−ナトリウムスルホイソフタル酸２．５モル％、ポリエチレングリコール（分子量２０００）１０重量％、下記式（Ｉ）のポリオキシエチレングリコールから誘導される単位を１０重量％を共重合したポリエチレンテレフタレートＰ１を海成分とし、ポリエチレンテレフタレートＰ２（以後「ＰＥＴ」という）を島成分とし、島の数８０島（但し４０島ずつ島成分の面積が異なる）、海／島重量比４０／６０である単繊維繊度４デニール、カット長３ｍｍの海島型複合繊維を用い、熱接着性複合繊維Ｂとして、イソフタル酸を４５モル％共重合したアルカリ難溶性ポリエチレンテレフタレートＰ３（融点：１１０℃）を鞘成分とし、イソフタル酸を３０モル％共重合したアルカリ難溶性ポリエチレンテレフタレートＰ４（融点：１７０℃）を芯成分とした単繊維繊度２デニール、カット長５ｍｍの芯鞘型複合繊維を用いて、複合繊維Ｃ／熱接着性複合繊維Ｂ＝９０％／１０％の重量比率で、繊維濃度０．５％となるよう水中に分散し、この分散液を円網抄紙機に送り通常の方法で抄紙し、１１０℃熱処理（１段目）して坪量＝１２．５ｇ／ｍ^２の紙を得た。この際の初期分散性は良好であった。
【００３１】
【化１】

【００３２】
こうして得た紙を５ｇ／ｌ水酸化ナトリウム水溶液にてアルカリ処理した後、１７０℃で熱処理（２段目）して坪量＝８．３ｇ／ｍ^２、厚さ＝４０μｍ、緊度＝０．２０８ｇ／ｃｍ^３の薄葉紙を得た。この時、アルカリ難溶性成分Ｐ２からなる極細繊維Ａ１の単繊維繊度は、０．０５デニール、極細繊維Ａ２の単繊維繊度は０．０１デニールであった。また、極細繊維Ａ１とＡ２の本数比率（Ａ１／Ａ２）は４０／４０であった。
【００３３】
この薄葉紙を支持体とし、その上に厚さ３μｍの熱可塑性ポリエステルフィルムを酢酸ビニル系接着剤にて貼り合わせ、熱孔版印刷用原紙を得た。この熱孔版印刷用原紙をサーマルヘッドにて穿孔し製版した。この原紙の印刷結果は印字濃度が濃く、解像度も優れ、また耐刷枚数も大幅に改善できるものであった。
【００３４】
【表１】

【００３５】
比較例１
実施例１で使用した複合繊維Ｃにおいて極細繊維Ａ１とＡ２の本数比率が（４０／２０）と異なる繊維（海／島＝４５／５５）を紡糸し、実施例１と同様にして９．６ｇ／ｍ^２の薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、極細繊維Ａ２の本数比率が低く、極細繊維Ａ２を入れた効果が出ず印刷解像度が不十分であった。
【００３６】
実施例２
実施例１で使用した複合繊維Ｃにおいて極細繊維Ａ１とＡ２の本数比率が（４０／８０）と異なる繊維（海／島＝３０／７０）を紡糸し、実施例１と同様にして９．５ｇ／ｍ^２の薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、印字濃度、解像度、耐刷枚数にも優れていた。
【００３７】
実施例３
複合繊維Ｃにおいて極細繊維Ａ１とＡ２の本数比率が（４０／８０）となるようにし、該複合繊維Ｃ及び熱接着性複合繊維Ｂの比率（Ｃ／Ｂ）を７０％／３０％として実施例１と同様にして薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、印字濃度が高く、解像度にも優れ、また耐刷枚数も大幅に改善されたものであった。
【００３８】
実施例４
実施例２において、複合繊維Ｃ、熱接着性複合繊維Ｂに、さらにマニラ麻をそれぞれの比率が３０％／３０％／４０％となるようにして実施例１と同様にして薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、印字濃度が高く、解像度にも優れ、また耐刷枚数も大幅に改善されたものであった。
【００３９】
実施例５
実施例２で使用した複合繊維Ｃと熱接着性複合繊維Ｂの比率を７５％／２５％として実施例１と同様にして薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、印字濃度が高く、解像度にも優れ、また耐刷枚数も優れたものであった。
【００４０】
比較例２
実施例２で使用した複合繊維Ｃと熱接着性複合繊維Ｂの比率を９５％／５％として実施例１と同様にして薄葉紙を得た。しかしながら、熱接着性複合繊維Ｂの比率が少ないので紙力が低く、熱孔版印刷用薄葉紙として不適であった。
【００４１】
比較例３
実施例４における複合繊維Ｃ、熱接着性複合繊維Ｂ、マニラ麻のそれぞれの比率を１０％／３０％／６０％とし実施例１と同様にして薄葉紙を得た。この薄葉紙から得られた原紙の印刷結果は、印字濃度は高かったが、解像度が悪く、耐刷枚数も改善できなかった。
【００４２】
比較例４
単繊維繊度が０．１デニールであるポリエチレンテレフタレート繊維（カット長＝３ｍｍ）及び熱接着性複合繊維として、イソフタル酸を４５モル％共重合したアルカリ難溶性ポリエチレンテレフタレート（融点：１１０℃）を鞘成分とし、ポリエチレンテレフタレートを芯成分とした単繊維繊度２デニール、カット長３ｍｍの芯鞘型複合繊維を用いて、ポリエチレンテレフタレート繊維／熱接着性複合繊維＝７０％／３０％の重量比率で、実施例１と同様にして薄葉紙を製造したが、抄紙時の分散性が悪く均質な紙を得ることができなかった。
【００４３】
比較例５
複合繊維Ｃとして、５−ナトリウムスルホイソフタル酸２．５モル％、ポリエチレングリコール（分子量２０００）１０重量％、前記式（Ｉ）のポリオキシエチレングリコールから誘導される単位１０重量％を共重合したポリエチレンテレフタレートＰ１を海成分とし、ポリエチレンテレフタレートＰ２を島成分とし、島の数１２０島、海／島重量比３０／７０である単繊維繊度２０デニール、カット長５ｍｍの海島型複合繊維を用い、熱接着性複合繊維Ｂとして、イソフタル酸を４５モル％共重合したアルカリ難溶性ポリエチレンテレフタレート（融点：１１０℃）を鞘成分とし、イソフタル酸を４０モル％共重合したポリエチレンテレフタレート（融点：１５０ ℃）を芯成分とした単繊維繊度２デニール、カット長＝５ｍｍを用いて、複合繊維Ｃ／熱接着性複合繊維Ｂ＝９０％／１０％の重量比率で、繊維濃度０．５％となるよう水中に分散し、この分散液を円網抄紙機に送り通常の方法で抄紙し、１１０℃熱処理（１段目）して坪量＝１４．５ｇ／ｍ^２の紙を得た。この際の初期分散性は良好であった。
【００４４】
こうして得た紙を５ｇ／ｌ水酸化ナトリウム水溶液にてアルカリ処理した後、１７０℃で熱処理（２段目）して坪量＝１０．２ｇ／ｍ^２、厚さ＝４５μｍ、緊度＝０．２２７ｇ／ｃｍ^３の薄葉紙を得た。この時、主体繊維の繊度は０．２８デニールであった。
【００４５】
この薄葉紙を支持体とし、その上に厚さ３μｍの熱可塑性ポリエステルフィルムを酢酸ビニル系接着剤にて貼り合わせ、熱孔版印刷用原紙を得た。この熱孔版印刷用原紙をサーマルヘッドにて穿孔し製版した。しかしながら、この原紙の印刷結果は印字濃度は濃かったが、解像度が不良で、耐刷枚数も改善できなった。
【００４６】
比較例６
複合繊維Ｃを構成する海成分と島成分に用いる熱可塑性樹脂として、実施例１と同一の樹脂を使用し、アルカリ処理後に形成される極細繊維Ａ１と極細繊維Ａ２の単繊維繊度が前者が０．０５デニール、後者が０．０２デニールとなるように、また前者と後者の本数比率（Ａ１／Ａ２）が４０／８０となるように島成分を有する複合繊維Ｃ（海／島＝３０／７０，単繊維繊度５．１デニール、カット長＝５ｍｍ）を紡糸し、これと熱接着性複合繊維Ｂとして実施例１と同一の繊維を用い、それぞれの比率を１０％／９０％として実施例１と同様にして薄葉紙を得た。この薄葉紙を用いて得られた原紙の印刷結果は、印字濃度は高かったが、解像度は不十分であった。
【００４７】
【発明の効果】
本発明の薄葉紙は、抄紙時の初期分散性が良好で、この原紙の印刷結果は、印字濃度が高く、解像度及び耐刷枚数も大幅に改善されており、熱孔版印刷用に極めて有用である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thin paper for hot stencil printing used for a heat-sensitive stencil sheet used for flash irradiation or infrared irradiation by a halogen lamp, a xenon lamp, a flash bulb or the like, or perforated plate making by a thermal head or the like, and a method for producing the same. More specifically, the present invention relates to thin paper for hot stencil printing, which has good dispersibility during papermaking, and has excellent ink retention and water resistance.
[0002]
[Prior art]
Conventionally, various types of thin paper for heat-sensitive stencil printing, such as Japanese paper made of 100% natural fibers such as mulberry, mitsumata, and manila hemp, a nonwoven fabric made of 100% synthetic chemical fibers, and a nonwoven fabric made of a mixture of natural fibers and synthetic chemical fibers, are known. Had been. As a nonwoven fabric made of 100% synthetic fibers, a thin paper for heat-sensitive stencil printing containing ultra-fine fibers of 0.1 denier or less of polyester or acryl is proposed in JP-A-3-8892.
[0003]
[Problems to be solved by the invention]
However, when a polyester film is laminated on a thin paper for hot stencil printing to produce a heat sensitive stencil printing base paper and perforated stencil printing using a thermal head or the like, white portions where ink does not pass due to the presence of binding fibers in 100% natural fiber Japanese paper. And the short life of the plate making due to insufficient water resistance was a problem.
Further, when the synthetic chemical fiber is 100%, the water resistance is improved, but the ink itself is poor due to the insufficient hydrophilicity of the fiber itself, and the printing density is low.
Furthermore, nonwoven fabrics in which natural fibers and synthetic chemical fibers are mixed have both disadvantages.
Thin paper containing polyester or acrylic ultrafine fibers improves ink retention and water resistance.However, ultrafine fibers have poor dispersibility during papermaking, causing problems such as entanglement of fibers. Must be said to be extremely difficult in practice.
[0004]
An object of the present invention is to provide a thin paper for hot stencil printing, which has good dispersibility during papermaking, has no white spots during printing, and has good water resistance and ink retention. An object of the present invention is to provide a method for industrially stably producing thin paper.
[0005]
[Means for Solving the Problems]
That is, the present invention comprises a fine fiber A1 having a single fiber fineness of 0.01 to 0.2 denier made of a thermoplastic resin that is hardly soluble in an aqueous alkali solution and a thermoplastic resin hardly soluble in an alkali aqueous solution, and having an average fineness of 1 Stencil paper for hot stencil printing, comprising a total of 20% by weight to 90% by weight of ultrafine fibers A2 having a monofilament fineness of / 5 or less and 0.02 denier or less, wherein the number of the ultrafine fibers A1 and the number of the ultrafine fibers A2 The ratio (A1 / A2) is 2/1 to 1/2, and the fibers constituting the tissue paper are bonded by a thermo-adhesive resin which is hardly soluble in two or more kinds of alkaline aqueous solutions having a melting point difference of 30 ° C. or more. Thin paper for hot stencil printing and a thermoplastic resin P2 (hereinafter simply referred to as simply) which is hardly soluble in an aqueous alkali solution by a thermoplastic resin P1 (hereinafter sometimes simply referred to as an alkali easily soluble component P1) which is easily soluble in an aqueous alkali solution. A (Sometimes referred to as a hardly soluble potassium component P2) is a conjugate fiber divided into a plurality of components, and the component composed of the thermoplastic resin P2 in the cross section of the conjugate fiber has two types of sizes, and its area is different. A heat-adhesive conjugate fiber comprising a composite fiber C having a ratio of 5 times or more and 30% by weight or more, and a low-melting-point component P3 having a low melting point of 30 ° C. or more and a high-melting-point component P4 having a low alkali solubility. (I) mixing paper stock containing B in an amount of 10% by weight or more by wet papermaking, heat treating the mixed paper to thermally bond the fibers with the low melting point component P3 (ii), A method for producing thin paper for hot stencil printing, comprising: a step (iii) of dissolving and removing the plastic resin P1; and a step (iv) of performing a heat treatment to thermally bond the fibers with the high melting point component P4.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, it is known that the use of synthetic chemical fibers as the raw material of the tissue paper improves water resistance and that if the single fiber fineness is set to 0.1 denier or less, the ink retainability is improved. Is poor in initial dispersibility at the time of papermaking, and particularly, it is difficult to make stable papermaking with ultrafine fibers of 0.1 denier or less.In the present invention, papermaking is performed by using a composite fiber having a large fineness of 2 denier to 10 denier at the time of papermaking. An object of the present invention is to form an ultrafine fiber by removing one component of the conjugate fiber after papermaking, thereby obtaining a thin paper containing the ultrafine fiber.
[0007]
Further, in the present invention, as the ultrafine fibers, the ultrafine fibers A1 having a single fiber fineness of 0.01 to 0.2 denier and 1/5 or less of the average fineness of the ultrafine fibers A1 and 0. By using together with the ultrafine fiber A2 having a monofilament fineness of not more than 02 denier, it is possible to obtain a thin paper having better dispersion stability, ink holding property and resolution than when one type of ultrafine fiber is used alone. It is assumed that.
[0008]
A feature of the present invention is that a thin paper for hot stencil printing which has good dispersibility during papermaking and satisfies the required performance can be obtained. In particular, by removing the alkali-soluble component P1 of the composite fiber C, Ultrafine fibers of different single fiber fineness are formed in a mixed state, and as a result, a fine void structure is generated in the thin paper, the ink is retained in the void, and the effect of improving the permeability and resolution of the ink is further improved. can get.
[0009]
If the single fiber fineness of the ultrafine fiber A1 composed of the alkali-poorly soluble component P2 exceeds 0.2 denier, the ink retention and resolution deteriorate, and if the fiber is less than 0.01 denier, it is difficult to produce the fiber. Since problems such as breakage of the yarn at the time and occurrence of a defective cross section (reduction of the uniformity of the cross section) occur, the density is preferably 0.05 to 0.1 denier.
In addition, the single fiber fineness of the ultrafine fiber A2 needs to be 1/5 or less of the average fineness of the ultrafine fiber A1 and 0.02 denier or less. When the ratio of the fineness of the ultrafine fibers A1 and A2 exceeds 1/5, or when the fineness of the single fiber of the ultrafine fibers A2 exceeds 0.02 denier, the effect of mixing with the ultrafine fibers A1 is lost, and the object of the present invention is achieved. Can not do it.
[0010]
Furthermore, in the present invention, the ratio (A1 / A2) of the number of the ultrafine fibers A1 and the ultrafine fibers A2 needs to be 2/1 to 1/2, and when the ratio of the number exceeds 2/1. As a result, the ink retention and resolution become poor. On the other hand, if it is less than 1/2, it becomes difficult to control the composite shape during spinning. For example, in the case of a sea-island type composite fiber, it is impossible to control the island shape of the island component that is the origin of the ultrafine fiber.
[0011]
The thin paper of the present invention must contain a total of 20% by weight or more, preferably 22% by weight or more of the two types of ultrafine fibers having different single fiber finenesses as described above. If it is less than 20% by weight, the ink retention and resolution will be poor.
[0012]
The thin paper of the present invention may be composed of only the ultrafine fibers A1 and A2, but if it is composed of 100% ultrafine fibers, the paper strength may not be satisfactory. Therefore, in the present invention, the fibers are thermally bonded with at least 10% by weight or more, preferably 25% by weight or more of the binder resin, thereby maintaining the shape as a sheet and the paper strength. On the other hand, if the amount of the binder resin is too large, the ink retention becomes poor. Therefore, it is preferable that the content of the binder resin is 40% by weight or less, particularly 35% by weight or less in the thin paper.
[0013]
In the present invention, a sheet-like material is once produced from the stock containing the above-mentioned splittable conjugate fiber C by a wet papermaking method, and the sheet-like material is subjected to an alkali treatment to remove the alkali-soluble component P1 of the conjugate fiber. Finally, it is a thin paper containing microfibers.However, in forming a sheet-like material, it is necessary to temporarily bond between the fibers in order to maintain the form of the sheet, and thereafter, it is formed by an alkali treatment. It is necessary to bond a large number of ultrafine fibers to each other to obtain thin paper having excellent paper strength, and it is necessary to perform two bonding treatments until a final thin paper is obtained.
[0014]
In order to efficiently perform such two-stage bonding, in the present invention, a heat-adhesive composite composed of a low-melting component P3 and a high-melting component P4 is prepared without separately preparing each heat-bonding resin. The method is characterized in that fibers are used, mixed with the splittable composite fibers C as a main component to prepare a stock slurry, and supplied to papermaking. In this case, the composite form of the heat-adhesive conjugate fiber can be appropriately set such as a core-sheath type or a side-by-side type. However, in the case of a core-sheath type, it is necessary to arrange a high melting point component in the core component.
[0015]
In the first stage of bonding after papermaking using such a heat-adhesive conjugate fiber, a heat treatment is performed to the extent that only the low-melting-point component P3 melts and softens. In the final bonding between the ultrafine fibers after the treatment, the heat treatment is performed at a temperature at which the high melting point component P4 of the composite fiber melts and softens, so that both the high melting point component P4 and the low melting point component P3 are used. Contributes to the adhesion between the fibers.
[0016]
Further, in the present invention, the heat treatment (first and second stages) is performed before and after the alkali removal treatment of the alkali-soluble component P1 constituting the conjugate fiber C. The fibers are bonded by two kinds of thermo-adhesive resins P3 and P4 having a low melting point and a high melting point, and are superior to thin paper in which fibers are bonded by one kind of thermo-adhesive resin. It has strength and heat resistance.
In the present invention, since it is essential to perform a two-stage heat treatment, it is necessary to have at least two types of thermo-adhesive resins having different melting points, but depending on the purpose, the type of thermo-adhesive resin may be changed. Three or more types may be selected and used.
[0017]
If the melting point difference between the high melting point component and the low melting point component is too small, it is extremely difficult to control the temperature to melt only the low melting point component during the first heat treatment, and the slight melting of the high temperature melts the high melting point component. In such a case, a difference in paper strength may occur in the product, and therefore, a combination having a melting point difference of 30 ° C. or more is preferable. Some thermoplastic resins do not have a definite melting point. In such a case, the combination of components may be determined by reading the melting point as the softening point or the thermal bonding start temperature.
[0018]
The type of the high melting point component P4 and the type of the low melting point component P3 are not particularly limited as long as they are a combination of resins having an appropriate melting point difference as described above. However, since the sheet is subjected to an alkali treatment in the manufacturing process of the tissue paper, It is necessary that the resin be relatively insoluble in alkali relative to the alkali-soluble component P1 of the splittable composite fiber C.
[0019]
In producing the thin paper of the present invention, since there is almost no problem of dispersibility at the time of paper making, the ultrafine fibers are homogeneously present in the thin paper. A high-quality product having a strength of 20 to 0.30 g / cm3 and a variation of the tension of 0.01 g / cm3 or less can be obtained.
[0020]
In the present invention, the ultrafine fibers need to be contained in the thin paper in a total amount of 20 to 90% by weight in the total of A1 and A2. If it is less than 20% by weight, the ink retention and resolution are poor, while if it exceeds 90% by weight, the paper strength is reduced. Preferably, the content is 20 to 65% by weight.
[0021]
In order to make the thin paper of the present invention as described above, it is necessary to mix the splittable conjugate fiber C and the heat-adhesive conjugate fiber B at 30% by weight or more and 10% by weight or more at the time of papermaking. In addition, in the present invention, thin paper for hot stencil printing can be obtained without significantly impairing the required performance even if natural fibers or synthetic chemical fibers are contained in an amount of 60% by weight or less in addition to these fibers.
[0022]
The content of the composite fiber C is less than 30% by weight, although it depends on the composite ratio of the component P1 and the component P2, and finally on the fineness and the number of the fine fibers composed of the component P2 (the number of islands in the sea and islands). In this case, the ink retention and resolution are poor, which is not preferable. Conversely, if it exceeds 90% by weight, the paper strength may decrease, so that at least 10% by weight of the heat-adhesive conjugate fiber B is required. When the content of the heat-adhesive conjugate fiber B exceeds 40% by weight, the ratio of the conjugate fiber C relatively decreases, so that the inter-fiber voids after the alkali treatment tend to increase, and the ink retention tends to decrease. Therefore, it is more preferable that the heat-adhesive conjugate fiber B is contained in an amount of 10% by weight to 30% by weight.
[0023]
The fiber cross-sectional shape of the conjugate fiber C in the present invention is not particularly limited as long as it is a cross-sectional shape in which ultrafine fibers are formed by the alkali-insoluble component P2 after alkali treatment, such as a sea-island type, a split type such as a bonding type, etc. Since a composite form in which the cross section of the ultrafine fibers after the alkali treatment is circular or substantially circular is more effective for ink permeability, a sea-island cross section is preferably employed.
[0024]
Further, the alkali-soluble component P1 constituting the composite fiber C may be, for example, a polyester obtained by copolymerizing a metal sulfonate group-containing ester unit, a polyester obtained by copolymerizing a metal sulfonate group-containing isophthalic acid and a polyalkylene glycol, JP-A-280156 discloses isophthalic acid containing a metal sulfonate group, a polyalkylene glycol, and a copolymerized polyester having a side chain type polyoxyalkylene group at a specific ratio.
[0025]
As the poorly-soluble alkali component P2 constituting the conjugate fiber C, any alkali-soluble thermoplastic resin such as polyester, acryl, nylon, and polyolefin may be used. In the present invention, polyester is preferably used.
In the present invention, the boundary between the alkali-soluble property and the poorly-soluble property is determined such that a substance having a weight loss rate of 30% by weight or more when treated in a 5 g / liter aqueous solution of caustic soda at 130 ° C. for 40 minutes is made to be alkali-soluble. % Is made poorly soluble. Further, it is preferable that the two have a difference of at least 20 times in alkali weight loss rate.
[0026]
The fiber cross section of the heat-adhesive conjugate fiber B in the present invention is not particularly limited, but a core-sheath type or side-by-side type conjugate fiber, particularly a core-sheath type conjugate fiber, is preferable. Both the low melting point component P3 and the high melting point component P4 of the binder fiber B are not particularly limited as long as they are hardly alkali-soluble thermoplastic resins. In the case of a core-sheath type, a combination of a low melting point component P3 in the sheath and a high melting point component P4 in the core. Must be.
[0027]
Although the polymer type of the component P3 and the component P4 is not particularly limited, in order to obtain good adhesive strength, it is preferable to use a polymer similar to the polymer type forming the ultrafine fiber constituting the thin paper, that is, the composite fiber at the time of papermaking. preferable. Furthermore, if the affinity between the component P3 and the component P4 is low, the two components are likely to peel off. Therefore, it is desirable that the combination of the component P3 and the component P4 has a good affinity. Therefore, when the component P1 and the component P2 of the composite fiber C are composed of polyester, it is desirable that both the component P3 and the component P4 of the heat-adhesive composite fiber B are polyester.
[0028]
The thin paper of the present invention is used as a base material, and a film such as a thermoplastic polyester film, a polyethylene film, or a polyamide film is adhered and laminated with a vinyl acetate-based or acrylic-based adhesive on the base paper to form a stencil sheet. By using the thin paper of the present invention, the printing density is high, the resolution is excellent, and the number of printings is greatly improved.
[0029]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. The tension, dispersibility, print density, resolution and number of printings were evaluated as follows.
<Tension>
The thickness and density of paper and paperboard according to JIS P 8118 were measured based on the test method.
<Dispersibility>
The dispersibility of the fibers in the papermaking cylinder was visually determined. A sample in a state where there was no undispersed fiber and a state in which it was uniformly dispersed was evaluated as ○, and a sample in a state where undispersed fiber was present was evaluated as ×.
<Print density>
The print density of the printed matter was visually judged. When a character or a thin line appeared dark and clear, it was evaluated as O, and when a character or a thin line was lightly blurred, it was evaluated as X.
<Resolution>
The printed matter was visually judged similarly to the print density. ◎ indicates that there was no unevenness in the thickness of characters or thin lines or black spots, and ○ indicates that there was almost no character or thin lines, and X indicates that characters or thin lines were partially cut off or had uneven thickness. In the meantime, a case in the middle between “○” and “×” is indicated by “△”.
<Printable number>
Using a fully automatic digital stencil printing machine, printing was performed at a printing speed of 130 sheets / min, and the number of sheets of the first printed matter until characters and fine lines were disturbed was measured.
[0030]
Example 1
As the composite fiber C, 2.5 mol% of 5-sodium sulfoisophthalic acid, 10 wt% of polyethylene glycol (molecular weight 2000), and 10 wt% of a unit derived from polyoxyethylene glycol of the following formula (I) were copolymerized. Polyethylene terephthalate P1 is a sea component, polyethylene terephthalate P2 (hereinafter referred to as “PET”) is an island component, and the number of islands is 80 (however, the area of the island component is different for every 40 islands), and the sea / island weight ratio is 40/60. Using a sea-island composite fiber with a single fiber fineness of 4 denier and a cut length of 3 mm, as a heat-adhesive composite fiber B, a poorly alkali-soluble polyethylene terephthalate P3 (melting point: 110 ° C.) obtained by copolymerizing isophthalic acid at 45 mol% is used as a sheath component. Alkali-soluble polyethylene terephthalate P4 obtained by copolymerizing 30% by mole of isophthalic acid Melting point: 170 ° C.) Using a core-sheath type composite fiber having a denier of 2 denier and a cut length of 5 mm having a core component of a core component, a composite fiber C / heat-adhesive composite fiber B = 90% / 10% by weight, The fiber is dispersed in water so as to have a fiber concentration of 0.5%, and this dispersion is sent to a round paper machine to make paper by a usual method, and heat-treated at 110 ° C. (first stage) to obtain a basis weight of 12.5 g / m ^2. I got a piece of paper. The initial dispersibility at this time was good.
[0031]
Embedded image

[0032]
The paper thus obtained was alkali-treated with a 5 g / l sodium hydroxide aqueous solution, and then heat-treated (second stage) at 170 ° C., basis weight = 8.3 g / m ² , thickness = 40 μm, and tightness = 0. 208 g / cm ³ tissue paper was obtained. At this time, the fineness of single fiber of the ultrafine fiber A1 composed of the poorly alkali-soluble component P2 was 0.05 denier, and the fineness of single fiber of the ultrafine fiber A2 was 0.01 denier. The ratio (A1 / A2) of the number of the ultrafine fibers A1 and A2 was 40/40.
[0033]
The thin paper was used as a support, and a thermoplastic polyester film having a thickness of 3 μm was adhered on the thin paper with a vinyl acetate adhesive to obtain a base paper for stencil printing. The stencil sheet was perforated with a thermal head to make a plate. The printing result of this base paper was high in print density, excellent in resolution, and the number of printings could be greatly improved.
[0034]
[Table 1]

[0035]
Comparative Example 1
In the composite fiber C used in Example 1, a fiber (sea / island = 45/55) in which the number ratio of the ultrafine fibers A1 and A2 is different from (40/20) is spun. g / m ² tissue paper was obtained. In the printing result of the base paper obtained from the thin paper, the ratio of the number of the fine fibers A2 was low, and the effect of adding the fine fibers A2 was not obtained, and the printing resolution was insufficient.
[0036]
Example 2
In the composite fiber C used in Example 1, a fiber (sea / island = 30/70) in which the ratio of the number of the ultrafine fibers A1 and A2 is different from (40/80) is spun. g / m ² tissue paper was obtained. The printing result of the base paper obtained from this thin paper was excellent in print density, resolution and number of printings.
[0037]
Example 3
In the composite fiber C, the number ratio of the ultrafine fibers A1 and A2 was set to (40/80), and the ratio (C / B) of the composite fiber C and the heat-adhesive composite fiber B was set to 70% / 30%. Thin paper was obtained in the same manner as in Example 1. The printing result of the base paper obtained from the thin paper showed that the printing density was high, the resolution was excellent, and the number of printings was greatly improved.
[0038]
Example 4
In Example 2, tissue paper was obtained in the same manner as in Example 1 except that Manila hemp was further added to the composite fiber C and the heat-adhesive composite fiber B at a ratio of 30% / 30% / 40%. The printing result of the base paper obtained from the thin paper showed that the printing density was high, the resolution was excellent, and the number of printings was greatly improved.
[0039]
Example 5
Thin paper was obtained in the same manner as in Example 1 except that the ratio of the composite fiber C and the heat-adhesive composite fiber B used in Example 2 was 75% / 25%. The printing result of the base paper obtained from this thin paper was high in print density, excellent in resolution, and excellent in number of printings.
[0040]
Comparative Example 2
Thin paper was obtained in the same manner as in Example 1 except that the ratio of the conjugate fiber C and the heat-adhesive conjugate fiber B used in Example 2 was 95% / 5%. However, since the ratio of the heat-adhesive conjugate fiber B was small, the paper strength was low, and it was not suitable as thin paper for hot stencil printing.
[0041]
Comparative Example 3
Thin paper was obtained in the same manner as in Example 1 except that the ratio of each of the conjugate fiber C, the heat-adhesive conjugate fiber B, and Manila hemp was 10% / 30% / 60% in Example 4. The printing result of the base paper obtained from the thin paper showed a high print density, but the resolution was poor and the number of printings could not be improved.
[0042]
Comparative Example 4
Polyethylene terephthalate fiber having a single fiber fineness of 0.1 denier (cut length = 3 mm) and, as a heat-adhesive conjugate fiber, a poorly alkali-soluble polyethylene terephthalate copolymerized with 45 mol% of isophthalic acid (melting point: 110 ° C.) as a sheath component Using a core-sheath composite fiber having a denier of 2 denier and a cut length of 3 mm containing polyethylene terephthalate as a core component, polyethylene terephthalate fiber / heat-adhesive composite fiber = 70% / 30% by weight. Thin tissue paper was produced in the same manner as in Example 1, but the dispersibility during papermaking was poor and uniform paper could not be obtained.
[0043]
Comparative Example 5
As the composite fiber C, polyethylene obtained by copolymerizing 2.5 mol% of 5-sodium sulfoisophthalic acid, 10 wt% of polyethylene glycol (molecular weight: 2,000), and 10 wt% of a unit derived from the polyoxyethylene glycol of the formula (I) Using terephthalate P1 as a sea component and polyethylene terephthalate P2 as an island component, using a sea-island composite fiber having 120 islands, a monofilament fineness of 20 / denier with a sea / island weight ratio of 30/70, and a cut length of 5 mm, As the conductive composite fiber B, a core made of polyethylene terephthalate (melting point: 150 ° C.) obtained by copolymerizing isophthalic acid by 45 mol% (melting point: 110 ° C.) as a sheath component and 40 mol% of isophthalic acid is used as a core component. Using a single fiber fineness of 2 denier, cut length = 5 mm Disperse in water at a weight ratio of conjugate fiber C / heat-adhesive conjugate fiber B = 90% / 10% so as to have a fiber concentration of 0.5%, and send this dispersion to a round paper machine to make paper by a usual method. Then, the paper was heat-treated at 110 ° C. (first stage) to obtain paper having a basis weight of 14.5 g / m ² . The initial dispersibility at this time was good.
[0044]
The paper thus obtained was alkali-treated with a 5 g / l sodium hydroxide aqueous solution, and then heat-treated (second stage) at 170 ° C., basis weight = 10.2 g / m ² , thickness = 45 μm, and tightness = 0. A thin paper of 227 g / cm ³ was obtained. At this time, the fineness of the main fiber was 0.28 denier.
[0045]
This thin paper was used as a support, and a thermoplastic polyester film having a thickness of 3 μm was adhered thereon with a vinyl acetate adhesive to obtain a base paper for hot stencil printing. The stencil sheet was perforated with a thermal head to make a plate. However, although the printing density of this base paper was high, the resolution was poor, and the number of printings could not be improved.
[0046]
Comparative Example 6
As the thermoplastic resin used for the sea component and the island component constituting the conjugate fiber C, the same resin as in Example 1 was used, and the fineness of the fine fibers A1 and A2 formed after the alkali treatment was 0 in the single fiber. .05 denier, the latter being 0.02 denier, and the composite fiber C having the island component (sea / island = 30 /) so that the number ratio (A1 / A2) of the former and the latter is 40/8 0. 70, a single fiber fineness of 5.1 denier, cut length = 5 mm), and the same fiber as in Example 1 was used as the heat-adhesive conjugate fiber B, with the respective ratio being 10% / 90%. Thin paper was obtained in the same manner as in Example 1. The printing result of the base paper obtained using this thin paper had a high print density, but the resolution was insufficient.
[0047]
【The invention's effect】
The thin paper of the present invention has good initial dispersibility at the time of paper making, and the printing result of this base paper has a high print density, a greatly improved resolution and the number of printings, and is extremely useful for hot stencil printing. .

Claims

A single fiber fineness of a thermoplastic resin that is hardly soluble in an aqueous alkali solution, a fine fiber A1 having a fineness of 0.01 to 0.2 denier, and a thermoplastic resin that is hardly soluble in an aqueous alkali solution, wherein the average fineness of the fine fiber A1 is 1/5 or less and 0.02 or less. A thin paper for stencil printing containing a total of 20% by weight or more and 90% by weight or less of ultrafine fibers A2 having a single fiber fineness of not more than denier, wherein the ratio of the number of the ultrafine fibers A1 to the number of the ultrafine fibers A2 (A1 / A2 ) Is 2/1 to 1/2, and the fibers constituting the tissue paper are bonded by a thermo-adhesive resin which is hardly soluble in two or more kinds of alkaline aqueous solutions having a melting point difference of 30 ° C. or more. Thin paper for hot stencil printing.

The thin paper for hot stencil printing according to claim 1, wherein the cross-sectional shape of the ultrafine fibers is substantially circular.

The ultrafine fibers A1 and A2 are obtained by treating a composite fiber composed of a thermoplastic resin P1 easily soluble in an alkaline aqueous solution and a thermoplastic resin P2 hardly soluble in an alkaline aqueous solution with an alkaline aqueous solution and removing the thermoplastic resin P1. The thin paper for hot stencil printing according to claim 1 or 2, which is an ultrafine fiber made of the thermoplastic resin P2 obtained.

The two kinds of heat-adhesive resins for bonding fibers are derived from a composite fiber composed of a low melting point component P3 and a high melting point component P4 having a melting point difference of 30 ° C. or more. 2. The thin paper for hot stencil printing according to claim 1.

A composite fiber in which a thermoplastic resin P2 that is hardly soluble in an alkaline aqueous solution is divided into a plurality of thermoplastic resins P2 by a thermoplastic resin P1 that is easily soluble in an alkaline aqueous solution. 30% by weight or more of the composite fiber C having an area ratio of 5 times or more, and a low-melting-point component P3 having a low melting point difference of 30 ° C. or more and a high-melting-point component having a low melting point of alkali Step (i) of mixing paper stock containing 10% by weight or more of the heat-adhesive conjugate fiber B composed of P4 with a wet papermaking method, and subjecting the mixed paper to heat treatment to thermally bond the fibers with the low melting point component P3. Characterized by comprising a step (ii), a step (iii) of dissolving and removing the thermoplastic resin P1 with an alkaline aqueous solution, and a step (iv) of performing a heat treatment to thermally bond the fibers with the high melting point component P4. A method for producing thin paper.

The production method according to claim 5, wherein the composite fiber C is a sea-island type composite fiber containing the thermoplastic resin P1 as an island component.

The method according to claim 5 or 6, wherein the heat-adhesive conjugate fiber is a core-sheath conjugate fiber having a low-melting component P3 as a sheath component.

A stencil sheet based on the thin paper according to claim 1.