JP2005017844A - Recording sheet for wet electrophotography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording sheet for wet electrophotography which is excellent in coating suitability to a sheet-like base and excellent in toner fixing property and transferability by a wet electrophotographic system using wet toner. <P>SOLUTION: In the recording sheet for wet electrophotography in which one or more coating layers are provided on at least one side of the sheet-like base, 20% or more by mass of adhesive components in the coating layers is polyvinyl alcohol with a saponification degree of 80% or more and its average polymerization degree is 100 to 800. Preferably, the recording sheet for wet electrophotography is used for a printing system in which a blanket shell rotates for two rotations or more while an image by the wet toner is formed in the blanket shell and transferred to a sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３０】
また、ここで言う８０％以上の鹸化度とは、ポリビニルアルコールの高分子式量中の３０％以上が水酸基の式量であることと言い直すことができる。よって、上記で述べる量以上に水酸基が含有すれば、その製法によらず、すべて応用することができる。
【００３１】
しかし、ポリビニルアルコールは粘度が高く、２０質量％以上加えると塗工液の濃度を相当下げなければならず、塗工速度が下がる、必要塗工量が併せにくくなる、乾燥負荷が大きくなる、カレンダー不可が大きくなるなど、操業性に悪影響を及ぼす。しかし、重合度が１００〜８００の間のポリビニルアルコールを使用することでこれらの悪影響はほとんどなくなる。ポリビニルアルコールの接着剤に占める割合が６０質量％以上であると、わずかながら操業性や塗工面の面質に悪影響がでるために、最も効果的であるのは４０〜６０質量％である。ポリビニルアルコールの操業性に与える悪影響をより小さくするにはポリビニルアルコールの重合度を１８０〜５００の間にするとよい。
【００３２】
このようなポリビニルアルコールは、例えば、日本合成化学社製のＮＬ−０５、ＮＬ−０４、ＮＬ−０４Ｌなどが挙げられる。
【００３３】
しかし、いくらポリビニルアルコールが湿式トナーと相性がいいとはいえ、接着剤は顔料と湿式トナーの相互作用を妨害する存在には他ならないので、その含有量はできるだけ少ない方がよい。よって、接着剤全体の該塗工層中含有量を５〜９質量％の範囲内にすることにより、湿式トナーの定着性を向上させることができる。９質量％を超えたあたりから、湿式トナー定着性は比例的に下がっていく。また５質量％を下回ると塗工層に必要な強度を与えることが難しくなる。
【００３４】
顔料は湿式トナーとの相性が比較的良いが、顔料の中でも炭酸カルシウムが最も良い。カオリンやタルクなどは相性が比較的悪く、シリカ、アルミナ、サチンホワイトなどは相性がよいが操業性を非常に悪くする。よって、炭酸カルシウムを顔料成分の７０質量％以上にすることは効果的である。７０質量％以下では効果が低くなる。
【００３５】
さらに、炭酸カルシウムを微細化した方が湿式トナーと相互作用する面積が広がるのでよい。具体的には、炭酸カルシウムの９５質量％以上を２μｍ以下の粒子径とすることが効果的である。
【００３６】
ここで言う炭酸カルシウムは、重質炭酸カルシウム、軽質炭酸カルシウムなど主成分がＣａＣＯ_３であれば種類を問わない。例えば、白石カルシウム社製のセタカーブ−ＨＧ、イメリスミネラルズジャパン社製のカービタル９５、奥多摩工業社製のタマパールＴＰ−１２１などが代表的なものとして挙げられる。
【００３７】
ただし、このままでは炭酸カルシウムの含有量が多いので、顔料間に挟まる緩衝効果を示すものが少なく、ストリーク、石筍、凝集物によるフィルターの目詰まりなど、操業性に悪影響を及ぼす。よって、炭酸カルシウム以外の顔料成分に緩衝効果が高い有機顔料を顔料成分の３質量％以上加えることでこれらの悪影響を抑えることができる。ただし、有機顔料は、湿式トナーとほとんど相互作用を示さず、１５質量％より多く加えると定着性に悪影響がでる。
【００３８】
ここで言う有機顔料には、例えば、ロームアンドハース社製のＨＰ−９１、日本ゼオン社製のＶ１００５が効果的なものとして挙げられる。
【００３９】
泡立ちや潤滑効果などの目的で加える消泡剤や潤滑剤などの界面活性剤成分は顔料の表面に油膜を形成するので湿式トナーの定着に悪影響を及ぼす。よって、これらの総量での添加量は全体の１質量％以下にすることが好ましい。
【００４０】
これらの手段を用いて製造した湿式電子写真用シートは、湿式トナーがブランケット胴に画像を形成してからシートに転写するまでの間に、ブランケット胴が２回転以上する印刷方式に適用すると、適用しないものに比べてより高い印刷適性を発揮することができる。このような印刷方式には、ＨＰ−ｉｎｄｉｇｏ ｐｒｅｓｓ ｗ３２００などのロール給紙タイプの印刷機が挙げられる。
【００４１】
湿式トナー受理層の塗工量としては、５ｇ／ｍ^２以上塗工することによってシート状基材の表面を隙間なく覆うことができ、好ましくなる。しかし、４０ｇ／ｍ^２を超えると塗工層の強度の問題が生じる。また、５ｇ／ｍ^２未満では、湿式トナーの転写（受理）ムラが発生して好ましくない。
【００４２】
本発明における湿式電子写真用記録シートは、湿式電子写真用記録シートとしての使用に留まらず、乾式電子写真用記録シート、オフセット印刷用シート、インクジェット用シート、熱転写用シートなどの他の印刷方式に使用することもできる。
【００４３】
本発明に用いられる湿式電子写真用記録シートの基材としては、木材パルプ、綿、麻、竹、サトウキビ、トウモロコシ、ケナフなどの植物繊維、羊毛、絹などの動物繊維、レーヨン、キュプラ、リヨセルなどのセルロース再生繊維、アセテートなどの半合成繊維、ポリアミド系繊維、ポリエステル系繊維、ポリアクリロニトリル系繊維、ポリビニールアルコール系繊維、ポリプロピレン系繊維、ポリ塩化ビニリデン系繊維、ポリウレタン系繊維などの化学繊維、ガラス繊維、金属繊維、炭素繊維などの無機繊維をシート状にしたもの、またはその上に樹脂フィルム層を設けたものが使用される。
【００４４】
各繊維をシート状にする製法としては、一般的な抄紙工程、湿式法、乾式法、ケミカルボンド、サーマルボンド、スパンボンド、スパンレース、ウォータージェット、メルトブロー、ニードルパンチ、ステッチブロー、フラッシュ紡糸、トウ開維などの各工程から一つ以上が適宜選ばれる。
【００４５】
また、これらの繊維には、軽質炭酸カルシウム、重質炭酸カルシウム、タルク、クレー、カオリン、二酸化チタン、水酸化アルミなどの各種填料、バインダー、サイズ剤、定着剤、歩留り剤、紙力増強剤などの各種配合剤を各工程、各素材に合わせて好適に配合する。さらには、これらの繊維シートの上に樹脂コート層を設ける場合もある。
【００４６】
その他の基材としては、上質紙、中質紙、色上質、書籍用紙、キャスト用紙、微塗工紙、軽量コート紙、コート紙、アート紙、中質コート紙、グラビア用紙、インディア紙、コートアイボリー、ノーコートアイボリー、アートポスト、コートポスト、ノーコートカード、特板、コートボール、トレーシングペーパー、タイプ紙、ＰＰＣ用紙、ＮＩＰ用紙、連続伝票用紙、フォーム用紙、複写紙、ノーカーボン紙、感熱紙、インクジェット用紙、熱転写用紙、合成紙、などの紙や板紙、不織布、または各種樹脂やプラスチック、金属をフィルム状に成形したものも含まれる。
【００４７】
塗工する前の基材は、必要とする密度、平滑度、透気度を得るために各種表面処理やカレンダー処理を施す場合がある。
【００４８】
本発明において、塗工層に用いられる顔料は、特に限定されるものではなく、例えば、各種カオリン、タルク、重質炭酸カルシウム（粉砕炭酸カルシウム）などの精製した天然鉱物顔料、軽質炭酸カルシウム（合成炭酸カルシウム）、炭酸カルシウムと他の親水性有機化合物との複合合成顔料、サチンホワイト、リトポン、酸化チタン、シリカ、アルミナ、水酸化アルミニウム、酸化亜鉛、炭酸マグネシウム、焼成カオリン、プラスチック顔料などが挙げられる。
【００４９】
塗工液に用いられるバインダーとしては、天然植物から精製した澱紛、ヒドロキシエチル化澱粉、酸化澱紛、エーテル化澱紛、りん酸エステル化澱粉、酵素変性澱紛やそれらをフラッシュドライして得られる冷水可溶性澱粉、デキストリン、マンナン、キトサン、アラビノガラクタン、グリコーゲン、イヌリン、ペクチン、ヒアルロン酸、カルボキシメチルセルロース、ヒドロキシエチルセルロースなどの天然多糖類およびそのオリゴマーさらにはその変性体が挙げられる。
【００５０】
さらに、ガゼイン、ゼラチン、大豆蛋白、コラーゲンなどの天然タンパク質およびその変性体、ポリ乳酸、ペプチドなどの合成高分子やオリゴマーが挙げられる。
加えてスチレン−ブタジエン系、アクリル系、ポリ酢酸ビニル、エチレン酢酸ビニルなどの各種共重合体ラテックス、ポリビニルアルコール、変性ポリビニルアルコール、ポリアクリル酸ナトリウム、ポリエチレンオキシド、ポリアクリルアミド、ユリアまたはメラミン／ホルマリン樹脂、ポリエチレンイミン、ポリアミドポリアミン／エピクロルヒドリンなどの水溶性合成物などがあげれれる。これらは一種以上で使用することができる。この他、公知の天然、合成有機化合物を使用することは特に限定されない。
【００５１】
また、塗工液に用いられる増粘剤としては、カルボキシメチルセルロース、アルギン酸ソーダ、メチルセルロース、ヒドロキシエチルセルロース、カゼイン、ポリアクリル酸ソーダなどの水溶性高分子、ポリアクリル酸塩、スチレンマレイン酸無水共重合体などの合成重合体、珪酸塩などの無機重合体などが挙げられる。
【００５２】
また、必要に応じて、分散剤、消泡剤、耐水化剤、着色剤などの通常使用されている各種助剤、およびこれらの各種助剤をカチオン化したものが好適に用いられる。
【００５３】
本発明において、塗工層を塗工する方法は、特に限定されるものではなく、サイズプレス、ゲートロール、シムサイザーなどの各種フィルムトランスファーコーター、エアーナイフコーター、ロッドコーター、ブレードコーター、ダイレクトファウンテンコーター、スプレーコーター、キャストコーターなどの各方式を適宜使用する。
【００５４】
さらに、一連の操業で、塗工、乾燥された塗工シートは要求される、密度、平滑度、透気度、外観を得るために、必要に応じてカレンダー処理などの各種仕上げ処理が施される。
【００５５】
【実施例】
以下に、本発明の実施例を挙げて説明するが、本発明はこれらの実施例に限定されるものではない。また、実施例において示す「部」および「％」は、特に明示しない限り、質量部および質量％を示す。
【００５６】
実施例１〜３２および比較例１〜６
下記の配合にて、実施例１〜３２および比較例１〜６の湿式電子写真用記録シートを作製した。
【００５７】
＜原紙＞
ＬＢＫＰ（濾水度３３０〜４４０ｍｌｃｓｆ） ７０部
ＮＢＫＰ（濾水度３９０〜４９０ｍｌｃｓｆ） ３０部
軽質炭酸カルシウム（＊原紙中灰分で表示） ＊８部
市販カチオン化澱粉 １．０部
市販カチオン系ポリアクリルアミド歩留まり向上剤 ０．０３部
パルプ、内添薬品を上記の配合で調整し、坪量７０ｇ／ｍ^２の原紙を抄造した。
【００５８】
この原紙に対して、サイズプレスにより両面０．８０ｇ／ｍ^２の酸化澱粉を付着させ、塗工用原紙を得た。
【００５９】
＜塗工液＞
顔料の配合は表１に、接着剤の配合は表２に掲げた。その他の配合は以下のとおりである。
市販ポリアクリル酸系分散剤 適当量
市販カルボキシメチルセルロース系増粘剤（ＣＭＣ） ０．１部
水酸化ナトリウムにてｐＨ９．６に調整
なお、表１中の重カル、軽カル、中空、密実、表２中のＰＶＡ、ＳＢＲとは以下の材料を指す。
重カル：市販重質炭酸カルシウム
軽カル：市販軽質炭酸カルシウム
中空：市販中空有機顔料
密実：市販密実型有機顔料
ＰＶＡ：市販ポリビニルアルコール
ＳＢＲ：市販スチレンブタジエン系ラテックスバインダー
【００６０】
【表１】

【００６１】
【表２】

【００６２】
上記の各種塗工液を調整し、ファウンテン／ブレードコーターを用いて各面１５ｇ／ｍ^２の塗工量により上記塗工用原紙に両面塗工し、スーパーカレンダー処理を施して湿式電子写真用記録シートを得た。
【００６３】
上記実施例１〜３２および比較例１〜６により得られた湿式電子写真用記録シートについて、下記の測定方法により測定し、その評価結果を表３に掲げた。
【００６４】
１．印刷
湿式電子写真用枚葉転写機として、ＨＰ社製「Ｅ−ｐｒｉｎｔ１０００」、巻き取り式印刷機として、ＨＰ社製「ＨＰ−ｉｎｄｉｇｏ ｐｒｅｓｓ ｗ３２００」を用いて評価を行った。評価に使用するための印刷画像としては、ブラック、シアン、マゼンタ、イエローの各４色についてベタ印字部があるような画像を出力するようにした。ベタ印字部の印刷面積としては、最低でも一辺が３ｃｍ以上の四角形になるようにした。印刷したブラック、シアン、マゼンタ、イエローの各色のベタ印刷部について以下の２〜５のような定着評価を行った。なお、表の評価結果はこれらの評価結果を平均したものである。なお、平均評価結果の「△」以上を発明の対称とした。
【００６５】
２．テープ剥離
枚葉式、巻き取り式共に、印刷後２４時間経過した印刷サンプルに幅１８ｍｍのニチバン社製セロハン粘着テープ「セロテープ Ｎｏ．４０５」を各色の印刷部に貼りむらが無いように貼りつけ、１８０度剥離で約５ｍｍ／秒の速さでゆっくりとテープを剥がした。剥離後のトナーのシートへの定着度合いを目視により判定し、以下の基準で６段階評価を行った。
◎◎：各色全くトナーが剥離しない。
◎：各色共にトナーがシートの上に大部分残っている。
○：各色共にトナーが残っているが、テープ剥離後の印刷部の印刷濃度が下がるのがわかる。
△：一部の色でトナーがシートから剥がれ、印刷部に白く抜けた部分がある。
×：各色共にトナーがシートから剥がれ、印刷部の白く抜けた部分が目立つ。
××：印刷時にトナーがシートにきちんと転移しない（印刷サンプルが作成できない）。
【００６６】
３．こすれ
こすれ評価は、ＪＩＳ Ｐ８１４７「紙および板紙の摩擦係数試験方法」の水平法を応用した。各実施例および比較例について、水平板には、白紙の湿式電子写真用記録シートを取り付け、おもりには、上記の印刷機で印刷された印刷部がある該記録シートを取り付けた。そして、印刷部がある該記録シートをおもりに貼りつける場合、印刷部の印刷された面が、水平板に取り付けられた白紙の該記録シートと擦りあうようにした。
【００６７】
以上のように、試験片を水平板、おもりに貼りつけた後は、ＪＩＳ Ｐ８１４７に記載されている条件でおもりを水平板の上で滑らせる。「摩擦試験」においては、一つの試験片の組み合わせで一度だけ、水平板上でおもりを滑らせるが、本評価においては、一つの試験片の組み合わせで５０回、おもりを水平板の上で滑らせた。使用した試験片は印刷後２４時間経過したものを使用した。
【００６８】
その後、おもりに取り付けられた印刷部を観察し、シート同士の擦れによるトナーの脱落度合いを観察した。印刷部のトナーの残り具合いを目視により判定し、以下の基準で６段階評価を行った。
◎◎：各色共に印刷部の濃度低下が全く認められない。
◎：各色共に印刷部の濃度低下がほどんと認められない。
○：各色共にわずかながら印刷濃度が下がるのがわかる。
△：各色共に印刷濃度が下がるのがわかる。
×：各色共に印刷濃度が下がるのがわかり、部分的に白く抜けた部分がある。
××：印刷時にトナーがシートにきちんと転移しない（印刷サンプルが作成できない）。
【００６９】
４．消しゴム剥離
印刷後、２４時間後に各色の印刷部を未使用消しゴム「トンボ鉛筆、ＰＥー０１Ａ」の角を利用して、均一の力で５往復させた。往復後のトナーのシートへの定着度合いを目視により判定し、以下の基準で６段階評価を行った。
◎◎：各色共にトナーがシートから全く剥離しない。
◎：各色共にトナーがシートからほとんど剥離しない。
○：一部にシートから剥離するトナーが存在するが２割未満である。
△：５割未満でトナーがシートから剥がれ、一部に白く抜けた部分がある。
×：各色ともシートからトナーが容易に剥がれ、白く抜けた部分が目立つ。
××：印刷時にトナーがシートにきちんと転移しない（印刷サンプルが作成できない）。
【００７０】
５．転移性
各印刷機で５００部以上印刷を行った後、プリントクリーナーで掃除を行い、プリントクリーナーの汚れ方で転移性を判断した。
◎◎：全く汚れない。
◎：ほとんど汚れない。
○：ごく小さい汚れが付着する。
△：小さい汚れが付着する。
×：はっきりと汚れる。
××：印刷時にトナーがシートにきちんと転移しない（印刷サンプルが作成できない）。
【００７１】
６．塗工適性
先に述べた配合で調液した各塗液をブレードコーターで塗布したときに、面質の良いサンプルを製造できる条件に従い、以下の基準で６段階評価した。
◎◎：塗工速度８００ｍ／ｍｉｎ以上、ストリーク発生、１本／分以下。
◎：塗工速度８００ｍ／ｍｉｎ以上、ストリーク発生、１本〜３本／分。
○：塗工速度５００〜８００ｍ／ｍｉｎ、ストリーク発生、１本〜３ 本／分。
△：塗工速度３００〜５００ｍ／ｍｉｎ、ストリーク発生、１本〜３ 本／分。
×：塗工速度３００ｍ／ｍｉｎ以下。
××：塗工できない。
【００７２】
７．塗工層強度
作成した湿式電子写真シートをＴＶ２０のオフセットインキを用いてＲＩ印刷試験器で２回印刷し、剥け具合を目視で判断し、下記の基準で４段階評価した。
◎：塗工層がほとんど剥離しない。
○：塗工層が全体の５％以下の面積部分で剥離する。
△：塗工層が全体の５〜１０％の面積部分で剥離する。
×：塗工層が全体の１０％以上の面積部分で剥離する。
【００７３】
【表３】

【００７４】
＜評価結果＞
比較例１、４のようにポリビニルアルコールの鹸化度が８０％を下回ると、湿式印刷適性が出ない。比較例１、２、５のようにポリビニルアルコールが接着剤成分の２０質量％を下回る場合も同様である。一方、比較例１〜３のようにポリビニルアルコールの平均重合度が８００を上回ると、塗工適性が出ない。また、ポリビニルアルコールの平均重合度が１００を下回ると塗工層強度が出ない。それに対して、すべての実施例のように、鹸化度、平均重合度、対接着剤含有量が本発明の範囲に入ることによって、塗工適性、強度、印刷適性のすべてを満足させることができる。
【００７５】
実施例１、２のようにポリビニルアルコールの鹸化度が８０以上であれば印刷適性を満足する。実施例１、３〜７のように、ポリビニルアルコールの対接着剤含有量が２０質量％以上であれば印刷適性を満足するが、４０質量％以上である方がより高い印刷適性を得ることができる。ただ、６０質量％を超えると塗工適性が下がるので、最も良い範囲は４０〜６０質量％となる。
【００７６】
実施例１、８〜１２のようにポリビニルアルコールの平均重合度が１００〜８００の範囲であれば、塗工層強度を満足させながら、塗工適性を満足させることができるが、実施例９、１０のように塗工適性、強度のバランスを最も満足させる範囲は平均重合度１８０〜５００である。
【００７７】
実施例１３〜１５のように接着剤対塗工層含有量は５〜９質量％の範囲で印刷適性が最も高い。実施例１のようにこれを上回ると印刷適性が若干落ち、また実施例１６のようにこれを下回ると強度が若干落ちる。
【００７８】
実施例２０〜２２、２４、２５のように炭酸カルシウムの対顔料含有量が７０質量％を超え、かつ有機顔料が３〜１５質量％であると、印刷適性に悪影響を与えることなく、塗工適性を挙げることができる。実施例２１、２２のように有機顔料の種類は問わない。実施例１７のように炭酸カルシウムの条件を満たすだけでは、塗工適性は上がらず、実施例１８のように有機顔料の条件を満たすだけでは印刷適性が若干下がる。また、実施例２３のように中空粒子が規定量を超えると、印刷適性が若干下がり、実施例１９のように中空粒子が規定量以下では塗工適性が上がらない。実施例２４、２５のようにこれらの条件を満たしつつ、炭酸カルシウムの２μｍ以下の粒子の含有量が９５％を超えると、さらに印刷適性を上げることができる。実施例２６のようにこの効果は炭酸カルシウムの種類を問わないが、実施例２７のように炭酸カルシウム以外の顔料では印刷適性が下がる。
【００７９】
実施例２８〜３２のように本発明における好ましい条件を複合的にそろえることで塗工適性、印刷適性を非常に高いレベルで発揮することができる。
【００８０】
比較例、実施例を見るとわかるように巻き取り式印刷適性は枚葉適性に比べ高いレベルを要求される。よって、本発明を本実施例で使用した巻き取り印刷機のような、湿式トナーによる画像がブランケット胴に形成されシートに転写される間に２回転以上ブランケット胴が回転する印刷方式に利用することは非常に効果があるといえる。
【００８１】
【発明の効果】
以上の結果より、本発明の湿式電子写真用記録シートは、本発明で示す条件を満足させることで、シート状基材への塗工適性に優れ、湿式トナーを用いた湿式電子写真方式によるトナー定着性および転写性に優れた効果が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a recording sheet for wet electrophotography, and more specifically, excellent in suitability for coating on a sheet-like substrate, and excellent in toner fixability and transferability by a wet electrophotographic method using a wet toner. The present invention relates to a wet electrophotographic recording sheet.
[0002]
[Prior art]
Applications for printing using the electrophotographic method are not limited to terminal PC printers, fax machines, or copiers, but can also be put into practical use in the so-called on-demand printing field, which enables various types of small lot printing and variable information printing. Progress and technical progress is remarkable. In recent years, with the increase in printing speed, the number of printed copies has started to reach the area that has been covered by printing such as offset and gravure.
[0003]
Electrophotographic printing has the advantage of being able to handle variable information, but offset and gravure printing are inferior in terms of quality and price because they have achieved very high quality printing at a low price due to many years of accumulated technology. It was. For this reason, technological development for higher image quality, higher speed, lower power consumption, and lower costs is being promoted from both sides of printing machines and printing sheets. Printed materials are required to have higher definition and better color reproducibility, but this is in conflict with speeding up and cost reduction, as well as the performance of toner and printing machines, as well as electrophotography. As for recording sheets for printing, more stringent quality demands such as toner fixing property, transfer property, color reproducibility and running property are gathered.
[0004]
Among such electrophotographic printing methods, the dry electrophotographic method is a method typified by an office copying machine and the like, and a solid powder toner made of a pigment and a synthetic resin is used as a toner for forming an image. In the image forming method, printing is performed by a method in which toner is adsorbed to an electrostatic image generated by corona charging, and this toner is heat-pressed to a transfer object. However, in this method, if the toner is made finer, it is likely to be scattered to the surrounding environment, and if this is inhaled, a health problem is caused, so that the working environment is deteriorated and the printed matter is stained. For this reason, there is a limit to miniaturizing the solid powder toner, and it is difficult to obtain high resolution. Furthermore, since the thickness of the transfer object is not uniform, the charge density on the transfer object surface varies due to corona discharge, and an undesired image called fog occurs in the non-image area, or at a somewhat high temperature. There are many problems such as having to melt and solidify.
[0005]
On the other hand, another promising printing method that can handle variable information is an inkjet method. The ink jet method is a method in which fine ink droplets are ejected onto the surface of an object to be transferred to form an image. Recent technological advances have been tremendous, with extremely high image quality, and the weak weather resistance has been greatly improved with the advent of pigment-type inks. However, compared with offset printing or the like, there is a problem that the printing speed is slow and a relatively expensive dedicated sheet must be used to obtain high image quality.
[0006]
Therefore, when considering variable information in the on-demand printing area and satisfying conditions such as high image quality, high speed, and cost, the wet electrophotographic method is the most promising method among various printing methods. This is because the wet electrophotographic method disperses the toner in the liquid medium, so that the scattering of the powder is not a problem, and the toner can be reduced to 1/10 or more compared to the dry electrophotographic method. This is because the pigment can be used as a coloring material and there is no problem of weather resistance or water resistance.
[0007]
Wet toner does not use charge or the like when transferring an image from a blanket roll to a sheet. The image is transferred using the fact that the wet toner printing sheet has higher adhesiveness than the blanket roll. That is, the ability to remove the wet toner from the blanket roll is important, and the adhesion ability cannot be increased more than necessary.
[0008]
For this reason, in the case of wet electrophotographic printing, there are drawbacks that sufficient toner strength cannot be obtained even if printing is performed, and that toner particles are not sufficiently transferred to the sheet. In order to solve such problems, the amount of ash in the base paper is specified, and zirconium is applied to the surface (see, for example, Patent Document 1), or surface smoothness and sizing agent are devised ( For example, see Patent Document 2.) There is an example. These are effective for plain paper (non-coated) type printing paper.
[0009]
However, in the case of a coating sheet for printing, the above method cannot be applied, and there is no commercially available printing sheet that has sufficient toner suitability for the wet electrophotographic printing method. In order to solve this problem, there is an example that attempts to solve the problem by defining the type of pigment or binder and the blending amount of the binder (see, for example, Patent Document 3). In practice, however, the fixability and transferability of wet toners are greatly influenced by the physical and chemical properties of the sheet surface, which are complexly related to various substances. It can be said that it is difficult to sufficiently improve sex. In fact, there has been no coated sheet that is sufficiently applicable to a printing system in which the blanket cylinder rotates two or more times while an image of wet toner is formed on the blanket cylinder and transferred to the sheet.
[0010]
Also, in such a wet electrophotographic printing system, toner stains accumulate in non-image areas as long run printing is performed. The stain on the non-image area is a serious problem for reducing the operability of printing, but there has not been any coated sheet that is difficult to cause stain on the non-image area.
[0011]
As a means for imparting wet electrophotographic printing suitability regardless of the type of sheet, there is a generally known means called “sapphire treatment”, but this method requires a post-process in the preparation of the sheet. Therefore, it is not worth the cost. Further, there are disadvantages that the toner fixing property is lowered with time and the sheet becomes yellow.
[0012]
In order to solve these problems, there is an example in which creation of an electrophotographic recording sheet having wet toner suitability is achieved by controlling the area where the wet toner on the coating layer surface can interact (for example, patents) Reference 4). However, this method sometimes has insufficient coating suitability.
[0013]
[Patent Document 1]
JP-A-10-171146
[Patent Document 2]
Japanese Patent Laid-Open No. 10-171148
[Patent Document 3]
JP-A-9-281739
[Patent Document 4]
Japanese Patent Application No. 2002-343237
[0014]
[Problems to be solved by the invention]
In the future, when the quality of printed materials is increased, and high-speed printing and operability in subsequent processes are considered, there is a strong demand for recording sheets for wet electrophotography that have excellent fixability with wet toner. An object of the present invention is to provide a recording sheet for wet electrophotography that is excellent in application property to a sheet-like substrate and excellent in toner fixability and transferability by a wet electrophotographic method using a wet toner.
[0015]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have invented the following wet electrophotographic recording sheet.
[0016]
That is, the wet electrophotographic recording sheet of the present invention is a wet electrophotographic recording sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, and 20% by mass of the adhesive component in the coating layer. The above is polyvinyl alcohol having a saponification degree of 80% or more and an average polymerization degree of 100 to 800.
[0017]
In the present invention, 40 to 60% by mass of the adhesive component is preferably polyvinyl alcohol.
[0018]
Moreover, in this invention, it is preferable that the average degree of polymerization of polyvinyl alcohol is 180-500.
[0019]
Moreover, in this invention, it is preferable that an adhesive agent component is 5-9 mass% of the coating layer component total amount.
[0020]
Moreover, in this invention, it is preferable that a coating layer component contains 3-15 mass% organic pigment as a pigment component, and contains 70 weight% or more of calcium carbonate in addition.
[0021]
Furthermore, in this invention, it is preferable that 95 mass% or more of calcium carbonate has a particle diameter of 2 micrometers or less.
[0022]
In addition, in the present invention, the wet electrophotographic recording sheet is more preferably used in a printing system in which an image of a wet toner is formed on a blanket cylinder and the blanket cylinder rotates two or more times while the image is transferred to the sheet. preferable.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the wet electrophotographic recording sheet of the present invention will be described in detail.
[0024]
As a result of earnest research on the toner fixability of the wet electrophotographic recording sheet in the wet electrophotographic method, the present inventor has achieved the fixability and transferability of the wet toner while maintaining high coating suitability. It has been found that new coated sheet properties are required which are completely different from other coated sheets. That is, it has been found that these can be achieved by strictly controlling the materials used.
[0025]
The interaction between the wet toner and the pigment occurs only on the very surface of the coated sheet. An important factor for fixing the wet toner is the surface area of the pigment on the surface of the coating layer that can come into contact with the wet toner. The wet toner in contact with the pigment is adsorbed on the pigment surface by physical and chemical interaction with the pigment. Incidentally, an adhesive component is usually added to the coating layer. The adhesive component covers the surface of the pigment and interferes with the interaction between the wet toner and the pigment. A plastic binder has a particularly strong hindering action, which poses a serious problem in producing a wet electrophotographic recording sheet.
[0026]
Among the adhesive components, polyvinyl alcohol having a sufficiently large number of hydroxyl groups has a relatively good compatibility with the adhesive component of the wet toner, and therefore has a small hindrance to the adhesion between the pigment and the wet toner. However, the degree of saponification needs to be 80% or more in order to sufficiently reduce the disturbing action. This is because the hydroxyl group is compatible with the adhesive component of the wet toner.
[0027]
Therefore, the quality is improved by using polyvinyl alcohol having a saponification degree of 80% or more (hereinafter simply abbreviated as polyvinyl alcohol) for 20% by mass or more of the adhesive component in the coating layer. In order to further exert the effect, it may be 40% by mass or more. If it is 40% by mass or less, the effect is relatively small, and if it is 20% by mass or less, the effect does not correspond to the present invention.
[0028]
Polyvinyl alcohol as used herein is conventionally referred to as polyvinyl alcohol, but chemically represented as (-CH ₂ It refers to a polymer compound having a structure mainly containing an alcohol side chain in the CH-) group. The alcohol side chain may have a structure in which a linker is sandwiched therebetween, a hydroxyl group, or a mixture thereof. Further, any other structure may be used as long as the main structural unit is the above structure.
[0029]
[Chemical 1]

[0030]
Moreover, the saponification degree of 80% or more mentioned here can be rephrased that 30% or more of the polymer formula amount of polyvinyl alcohol is the formula amount of the hydroxyl group. Therefore, as long as the hydroxyl group is contained in an amount more than the amount described above, it can be applied regardless of the production method.
[0031]
However, polyvinyl alcohol has a high viscosity, and if it is added in an amount of 20% by mass or more, the concentration of the coating solution has to be considerably reduced, the coating speed decreases, the required coating amount becomes difficult to combine, the drying load increases, the calendar It will adversely affect operability, such as increasing impossibility. However, the use of polyvinyl alcohol having a polymerization degree of 100 to 800 almost eliminates these adverse effects. When the proportion of polyvinyl alcohol in the adhesive is 60% by mass or more, the operability and the surface quality of the coated surface are slightly adversely affected, so that the most effective amount is 40 to 60% by mass. In order to reduce the adverse effect on the operability of the polyvinyl alcohol, the degree of polymerization of the polyvinyl alcohol is preferably between 180 and 500.
[0032]
Examples of such polyvinyl alcohol include NL-05, NL-04, and NL-04L manufactured by Nippon Synthetic Chemical.
[0033]
However, although polyvinyl alcohol is compatible with the wet toner, the adhesive is nothing but the presence of interference with the interaction between the pigment and the wet toner, so the content should be as low as possible. Therefore, the fixability of the wet toner can be improved by setting the content of the entire adhesive in the coating layer within the range of 5 to 9% by mass. From around 9% by mass, the wet toner fixability decreases proportionally. On the other hand, if it is less than 5% by mass, it is difficult to give the coating layer the necessary strength.
[0034]
The pigment has a relatively good compatibility with the wet toner, but among the pigments, calcium carbonate is the best. Kaolin, talc, etc. have relatively poor compatibility, and silica, alumina, satin white, etc. have good compatibility, but the operability is very poor. Therefore, it is effective to make calcium carbonate 70 mass% or more of the pigment component. Below 70% by mass, the effect is low.
[0035]
Furthermore, the area where the calcium carbonate is made finer may increase the area interacting with the wet toner. Specifically, it is effective to set 95% by mass or more of calcium carbonate to a particle size of 2 μm or less.
[0036]
The calcium carbonate here is composed mainly of heavy calcium carbonate, light calcium carbonate, etc. ₃ Any type is acceptable. For example, Cetacurve-HG manufactured by Shiraishi Calcium Co., Carbital 95 manufactured by Imeris Minerals Japan Co., Ltd., Tama Pearl TP-121 manufactured by Okutama Kogyo Co., Ltd., and the like are typical examples.
[0037]
However, since the content of calcium carbonate is large as it is, there are few things showing a buffering effect sandwiched between the pigments, which adversely affects operability such as clogging of the filter due to streak, stone wall, and aggregates. Therefore, these adverse effects can be suppressed by adding an organic pigment having a high buffering effect to pigment components other than calcium carbonate in an amount of 3% by mass or more of the pigment component. However, the organic pigment hardly interacts with the wet toner, and if it is added in an amount of more than 15% by mass, the fixability is adversely affected.
[0038]
Examples of the organic pigment referred to herein include HP-91 manufactured by Rohm and Haas and V1005 manufactured by Nippon Zeon.
[0039]
Surfactant components such as antifoaming agents and lubricants added for the purpose of foaming and lubricating effect form an oil film on the surface of the pigment, and thus adversely affect the fixing of wet toner. Therefore, it is preferable that the total amount added is 1% by mass or less.
[0040]
Wet electrophotographic sheets manufactured using these means are applicable when applied to a printing method in which the blanket cylinder makes two or more revolutions after the wet toner forms an image on the blanket cylinder and is transferred to the sheet. Higher printability can be exhibited compared to those not. Examples of such a printing method include a roll paper feed type printing machine such as HP-indigo press w3200.
[0041]
The coating amount of the wet toner receiving layer is 5 g / m. ² By coating as described above, the surface of the sheet-like substrate can be covered without any gap, which is preferable. However, 40g / m ² If it exceeds 1, the problem of the strength of the coating layer occurs. 5g / m ² If it is less than the range, uneven transfer (acceptance) of wet toner occurs, which is not preferable.
[0042]
The wet electrophotographic recording sheet in the present invention is not limited to use as a wet electrophotographic recording sheet, but can be used in other printing systems such as a dry electrophotographic recording sheet, an offset printing sheet, an inkjet sheet, and a thermal transfer sheet. It can also be used.
[0043]
As the base material of the wet electrophotographic recording sheet used in the present invention, plant fibers such as wood pulp, cotton, hemp, bamboo, sugarcane, corn, kenaf, animal fibers such as wool, silk, rayon, cupra, lyocell, etc. Cellulose recycled fibers, semi-synthetic fibers such as acetate, polyamide fibers, polyester fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polypropylene fibers, polyvinylidene chloride fibers, polyurethane fibers, and other chemical fibers, glass A fiber, metal fiber, carbon fiber or other inorganic fiber in the form of a sheet or a resin film layer provided thereon is used.
[0044]
Production methods for making each fiber into a sheet form include general paper making processes, wet methods, dry methods, chemical bonds, thermal bonds, spun bonds, spun laces, water jets, melt blows, needle punches, stitch blows, flash spinning, tow One or more are appropriately selected from each process such as restoration.
[0045]
These fibers include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, titanium dioxide, aluminum hydroxide and other fillers, binders, sizing agents, fixing agents, retention agents, paper strength enhancers, etc. These various compounding agents are suitably blended according to each step and each material. Furthermore, a resin coat layer may be provided on these fiber sheets.
[0046]
Other base materials include fine paper, medium paper, color fine paper, book paper, cast paper, fine coated paper, lightweight coated paper, coated paper, art paper, medium coated paper, gravure paper, Indian paper, coated Ivory, uncoated ivory, art post, coated post, uncoated card, special board, coated ball, tracing paper, type paper, PPC paper, NIP paper, continuous slip paper, foam paper, copy paper, carbonless paper, heat sensitive Also included are paper, paperboard such as paper, inkjet paper, thermal transfer paper, synthetic paper, non-woven fabric, or various resins, plastics, and metals formed into a film.
[0047]
The substrate before coating may be subjected to various surface treatments and calendar treatments in order to obtain the required density, smoothness, and air permeability.
[0048]
In the present invention, the pigment used in the coating layer is not particularly limited. For example, various natural mineral pigments such as various kaolins, talc, and heavy calcium carbonate (ground calcium carbonate), light calcium carbonate (synthetic) Calcium carbonate), composite synthetic pigments of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium oxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined kaolin, plastic pigment, etc. .
[0049]
Binders used in coating liquids include starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, and flash dried. Cold water soluble starch, natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, oligomers thereof, and modified products thereof.
[0050]
Further, natural proteins such as casein, gelatin, soybean protein, collagen, and modified products thereof, and synthetic polymers and oligomers such as polylactic acid and peptides can be mentioned.
In addition, copolymer latex such as styrene-butadiene, acrylic, polyvinyl acetate, ethylene vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, urea, or melamine / formalin resin, Examples thereof include water-soluble synthetic compounds such as polyethyleneimine and polyamidepolyamine / epichlorohydrin. One or more of these can be used. In addition, the use of a known natural or synthetic organic compound is not particularly limited.
[0051]
Further, as a thickener used in the coating solution, water-soluble polymers such as carboxymethylcellulose, sodium alginate, methylcellulose, hydroxyethylcellulose, casein, sodium polyacrylate, polyacrylate, styrene maleic anhydride copolymer And synthetic polymers such as silicates and inorganic polymers such as silicates.
[0052]
In addition, various auxiliary agents that are usually used such as a dispersant, an antifoaming agent, a water-proofing agent, and a coloring agent, and those obtained by cationizing these auxiliary agents are suitably used as necessary.
[0053]
In the present invention, the method for coating the coating layer is not particularly limited, and various film transfer coaters such as size press, gate roll, shim sizer, air knife coater, rod coater, blade coater, direct fountain coater, Each system such as a spray coater or cast coater is appropriately used.
[0054]
Furthermore, in order to obtain the density, smoothness, air permeability, and appearance required for coated and dried coated sheets in a series of operations, various finishing processes such as calendering are performed as necessary. The
[0055]
【Example】
Examples of the present invention will be described below, but the present invention is not limited to these examples. Further, “parts” and “%” shown in the examples indicate parts by mass and mass% unless otherwise specified.
[0056]
Examples 1-32 and Comparative Examples 1-6
Wet electrophotographic recording sheets of Examples 1 to 32 and Comparative Examples 1 to 6 were prepared with the following composition.
[0057]
<Base paper>
70 parts of LBKP (freeness 330-440 mlcsf)
NBKP (freeness 390-490 mlcsf) 30 parts
Light calcium carbonate (* Indicated in ash content of base paper) * 8 parts
1.0 parts of commercially available cationized starch
Commercially available cationic polyacrylamide yield improver 0.03 parts
Pulp and internal chemicals are adjusted with the above composition, basis weight 70g / m ² Paper was made.
[0058]
0.80 g / m on both sides of this base paper by size press ² An oxidized starch was attached to obtain a base paper for coating.
[0059]
<Coating fluid>
The pigment composition is listed in Table 1, and the adhesive composition is listed in Table 2. Other blends are as follows.
Commercially available polyacrylic acid dispersant
0.1 parts of commercially available carboxymethylcellulose thickener (CMC)
Adjust to pH 9.6 with sodium hydroxide
In Table 1, heavy, light, hollow, solid, and PVA and SBR in Table 2 refer to the following materials.
Heavy Cal: Commercial heavy calcium carbonate
Light Cal: Commercially available light calcium carbonate
Hollow: Commercial hollow organic pigment
Dense: Commercially available dense organic pigment
PVA: Commercial polyvinyl alcohol
SBR: Commercial styrene butadiene latex binder
[0060]
[Table 1]

[0061]
[Table 2]

[0062]
Prepare various coating liquids as described above and use a fountain / blade coater for 15g / m on each side. ² The coating base paper was coated on both sides according to the coating amount and subjected to supercalendering to obtain a wet electrophotographic recording sheet.
[0063]
The wet electrophotographic recording sheets obtained in Examples 1 to 32 and Comparative Examples 1 to 6 were measured by the following measuring methods, and the evaluation results are listed in Table 3.
[0064]
1. printing
Evaluation was performed using “E-print 1000” manufactured by HP as a single-wafer transfer machine for wet electrophotography, and “HP-indigo press w3200” manufactured by HP as a take-up printing machine. As a print image to be used for evaluation, an image having a solid print portion for each of four colors of black, cyan, magenta, and yellow was output. As a printing area of the solid printing portion, at least a square with a side of 3 cm or more was used. Fixing evaluations such as the following 2 to 5 were performed on the printed solid portions of each color of black, cyan, magenta, and yellow. In addition, the evaluation result of a table | surface is an average of these evaluation results. The average evaluation result of “Δ” or more was regarded as the symmetry of the invention.
[0065]
2. Tape peeling
For both sheet-fed and take-up types, a cellophane adhesive tape “Cello Tape No. 405” with a width of 18 mm was applied to a print sample that had passed 24 hours after printing so that there would be no unevenness in the printing of each color, 180 degrees The tape was slowly peeled off at a speed of about 5 mm / sec. The degree of fixing of the toner after peeling to the sheet was visually determined, and a six-level evaluation was performed according to the following criteria.
A: The toner does not peel at all for each color.
A: Most of the toner remains on the sheet for each color.
○: The toner remains in each color, but it can be seen that the print density of the printing portion after the tape is peeled is lowered.
(Triangle | delta): The toner peeled off from the sheet | seat with one part color, and there exists a part from which the printing part fell white.
X: For each color, the toner is peeled off from the sheet, and a white portion of the printed portion is noticeable.
XX: The toner does not transfer properly to the sheet during printing (a print sample cannot be created).
[0066]
3. Rubbing
For the rubbing evaluation, the horizontal method of JIS P8147 “Test method for friction coefficient of paper and paperboard” was applied. For each of the examples and comparative examples, a blank wet electrophotographic recording sheet was attached to the horizontal plate, and the recording sheet having a printing portion printed by the printing machine was attached to the weight. Then, when the recording sheet having the printing portion was attached to the weight, the printed surface of the printing portion was rubbed against the blank recording sheet attached to the horizontal plate.
[0067]
As described above, after the test piece is attached to the horizontal plate and the weight, the weight is slid on the horizontal plate under the conditions described in JIS P8147. In the “friction test”, the weight is slid on the horizontal plate only once with one test piece combination. In this evaluation, the weight is slid on the horizontal plate 50 times with one test piece combination. Let The test piece used was 24 hours after printing.
[0068]
Thereafter, the printing portion attached to the weight was observed, and the degree of toner dropout due to rubbing between the sheets was observed. The remaining condition of the toner in the printed portion was visually determined, and a six-level evaluation was performed according to the following criteria.
A: No decrease in the density of the printed part is observed for each color.
A: A decrease in the density of the printed portion is hardly recognized for each color.
○: It can be seen that the print density decreases slightly for each color.
Δ: It can be seen that the print density decreases for each color.
X: It can be seen that the print density decreases for each color, and there is a part that is partially whitened.
XX: The toner does not transfer properly to the sheet during printing (a print sample cannot be created).
[0069]
4). Eraser peeling
After printing, 24 hours later, the printed portion of each color was reciprocated five times with a uniform force using the corner of an unused eraser “dragonfly pencil, PE-01A”. The degree of fixing of the toner on the sheet after the reciprocation was visually determined, and a six-level evaluation was performed according to the following criteria.
A: The toner does not peel from the sheet at all for each color.
A: The toner hardly peels from the sheet for each color.
○: Some toner is peeled from the sheet, but less than 20%.
Δ: Less than 50%, the toner is peeled off from the sheet, and a part of the toner is white.
X: For each color, the toner is easily peeled off from the sheet, and the white portions are conspicuous.
XX: The toner does not transfer properly to the sheet during printing (a print sample cannot be created).
[0070]
5. Metastatic
After printing 500 copies or more with each printing machine, cleaning was performed with a print cleaner, and transferability was judged based on how the print cleaner was stained.
◎◎: Not dirty at all.
A: Almost no dirt
○: Very small dirt adheres.
Δ: Small dirt adheres.
X: It becomes dirty clearly.
XX: The toner does not transfer properly to the sheet during printing (a print sample cannot be created).
[0071]
6). Coating suitability
When each coating liquid prepared with the above-mentioned formulation was applied with a blade coater, it was evaluated according to the following criteria based on the following criteria according to the conditions for producing a sample with good surface quality.
A: Coating speed of 800 m / min or more, streak generation, 1 line / min or less.
A: Coating speed of 800 m / min or more, streak generation, 1 to 3 / min.
○: Coating speed 500 to 800 m / min, streak generation, 1 to 3 / min.
Δ: Coating speed of 300 to 500 m / min, occurrence of streak, 1 to 3 / min.
X: Coating speed of 300 m / min or less.
XX: Cannot be applied.
[0072]
7. Coating layer strength
The prepared wet electrophotographic sheet was printed twice with an RI printing tester using the offset ink of TV20, the degree of peeling was judged visually, and was evaluated in four stages according to the following criteria.
A: The coating layer hardly peels off.
○: The coating layer peels at an area portion of 5% or less of the whole.
(Triangle | delta): A coating layer peels in the area part of 5-10% of the whole.
X: A coating layer peels in the area part of 10% or more of the whole.
[0073]
[Table 3]

[0074]
<Evaluation results>
When the saponification degree of polyvinyl alcohol is less than 80% as in Comparative Examples 1 and 4, wet printing suitability is not achieved. The same applies when the polyvinyl alcohol is less than 20% by mass of the adhesive component as in Comparative Examples 1, 2, and 5. On the other hand, when the average degree of polymerization of polyvinyl alcohol exceeds 800 as in Comparative Examples 1 to 3, the coating suitability is not achieved. Moreover, when the average degree of polymerization of polyvinyl alcohol is less than 100, the coating layer strength is not obtained. On the other hand, as in all the examples, when the degree of saponification, the average degree of polymerization, and the content of the adhesive are within the scope of the present invention, all of coating suitability, strength, and printability can be satisfied. .
[0075]
If the saponification degree of polyvinyl alcohol is 80 or more as in Examples 1 and 2, the printability is satisfied. As in Examples 1 and 3 to 7, the printability is satisfied when the content of the polyvinyl alcohol with respect to the adhesive is 20% by mass or more. However, when the content is 40% by mass or more, higher printability can be obtained. it can. However, if it exceeds 60% by mass, the coating suitability is lowered, so the best range is 40 to 60% by mass.
[0076]
If the average degree of polymerization of polyvinyl alcohol is in the range of 100 to 800 as in Examples 1 and 8 to 12, the coating suitability can be satisfied while satisfying the coating layer strength. As shown in FIG. 10, the average polymerization degree is 180 to 500 in the range where the balance of coating suitability and strength is most satisfied.
[0077]
As in Examples 13 to 15, the adhesiveness to the coating layer content is in the range of 5 to 9% by mass, and the printability is the highest. If it exceeds this as in Example 1, the printability is slightly lowered, and if it is below this as in Example 16, the strength is slightly lowered.
[0078]
As in Examples 20 to 22, 24, and 25, when the content of calcium carbonate with respect to the pigment exceeds 70% by mass and the organic pigment is 3 to 15% by mass, the coating performance is not adversely affected. The aptitude can be mentioned. As in Examples 21 and 22, the type of organic pigment is not limited. The coating suitability is not improved only by satisfying the conditions of calcium carbonate as in Example 17, and the printability is slightly lowered only by satisfying the conditions of the organic pigment as in Example 18. Further, when the hollow particles exceed the prescribed amount as in Example 23, the printability is slightly lowered, and when the hollow particles are less than the prescribed amount as in Example 19, the coating suitability is not improved. When these conditions are satisfied as in Examples 24 and 25 and the content of particles of 2 μm or less of calcium carbonate exceeds 95%, the printability can be further improved. Although this effect does not ask | require the kind of calcium carbonate like Example 26, printability falls with pigments other than calcium carbonate like Example 27. FIG.
[0079]
By combining preferable conditions in the present invention in a composite manner as in Examples 28 to 32, coating suitability and printability can be exhibited at a very high level.
[0080]
As can be seen from the comparative examples and examples, the winding-type print suitability is required to be higher than the sheet suitability. Therefore, the present invention is used for a printing system in which the blanket cylinder rotates more than two times while the image by the wet toner is formed on the blanket cylinder and transferred to the sheet, such as the winding printer used in this embodiment. Is very effective.
[0081]
【The invention's effect】
From the above results, the wet electrophotographic recording sheet of the present invention satisfies the conditions shown in the present invention, and is excellent in coating property to a sheet-like substrate, and is a toner by a wet electrophotographic method using a wet toner. An effect excellent in fixing property and transfer property can be obtained.

Claims (7)

In a recording sheet for wet electrophotography in which at least one coating layer is provided on at least one side of a sheet-like substrate, 20% by mass or more of the adhesive component in the coating layer is polyvinyl alcohol having a saponification degree of 80% or more. And the average degree of polymerization is 100-800, The recording sheet for wet electrophotography characterized by the above-mentioned. The recording sheet for wet electrophotography according to claim 1, wherein 40 to 60% by mass of the adhesive component is polyvinyl alcohol. 3. The wet electrophotographic recording sheet according to claim 1, wherein the average degree of polymerization of the polyvinyl alcohol is from 180 to 500. 4. The wet electrophotographic recording sheet according to any one of claims 1 to 3, wherein the adhesive component is 5 to 9 mass% of the total amount of the coating layer components. The wet coating composition according to any one of claims 1 to 4, wherein the coating layer component contains 3 to 15% by mass of an organic pigment as a pigment component, and additionally contains 70% by weight or more of calcium carbonate. Recording sheet for electrophotography. 6. The wet electrophotographic recording sheet according to claim 5, wherein 95% by mass or more of calcium carbonate has a particle size of 2 μm or less. 7. The wet electrophotographic recording sheet is used in a printing system in which the blanket cylinder rotates two or more times while an image of the wet toner is formed on the blanket cylinder and transferred to the sheet. A recording sheet for wet electrophotography according to claim 1.