JP2005035006A - Inkjet recording paper and method for manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording paper and a method for manufacturing it in which even when a substrate is coated with a porous layer comprising a hydrophilic binder and fine particles in a thick film and at a high speed, a crazing is hardly generated during manufacturing, and a flexible coating film with a high ink absorbing properties, and an excellent image can be obtained. <P>SOLUTION: The inkjet recording paper with a porous layer comprising inorganic fine particles and a hydrophilic resin to be crosslinked by an ionizing radiation, is characterized in that the surface of the porous layer has a lightness index L<SP>*</SP>in a CIE color space of ≥85, a consciousness chromaticity index a<SP>*</SP>of -3 to +2 and a consciousness chromaticity index b<SP>*</SP>of -4 to +3 when it is displayed by a method for displaying a color prescribed by JIS-Z-8730 measured in accordance with a method prescribed by JIS-Z-8722. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４９】
で表される２−アジド−５−ニトロフェニルカルボニルオキシエチレン構造、又は、
【００５０】
【化２】

【００５１】
で表される４−アジド−３−ニトロフェニルカルボニルオキシエチレン構造を有する樹脂組成物である。
【００５２】
感光性樹脂の具体例は、該公報中の実施例１、２に、また感光性樹脂の構成成分及びその使用割合は該公報第２頁に記載されている。
【００５３】
また、特開昭６０−１２９７４２号公報には、感光性樹脂としてポリビニルアルコール構造体中に
【００５４】
【化３】

【００５５】
の構造を有する樹脂組成物が挙げられている。
本発明においては、電離放射線により架橋する親水性高分子化合物の中でも、光重合型の変性基としては、例えば、特開２０００−１８１０６２号公報に開示されている下記一般式（１）で示される構成単位を有するポリ酢酸ビニルケン化物が、反応性との観点から好ましい。
【００５６】
【化４】

【００５７】
一般式（１）において、Ｒ_１は水素原子またはメチル基を表し、Ｙは芳香族環または単なる結合手を表し、Ｘは、−（ＣＨ_２）_ｍ−ＣＯＯ−、−Ｏ−ＣＨ_２−ＣＯＯ−または−Ｏ−を表し、ｍは０〜６の整数、ｎは１または２を表す。
【００５８】
本発明に係る親水性の高分子化合物において、重合度や架橋密度は皮膜形成時の強度や柔軟性に影響し、重合度が低かったり架橋変性基が多すぎたりすると塗布乾燥時のひび割れや乾燥塗膜の折れ割れといった故障が生じてしまう。したがって、前記一般式（１）で示される構成単位を有するポリ酢酸ビニルケン化物を含む親水性の高分子化合物においては、重合度は４００〜５０００であることが好ましく、１０００〜４０００であることがより好ましい。また、セグメントに対する電離放射線反応架橋基の変性率が４ｍｏｌ％以下であることが好ましく、より好ましくは０．０１〜１ｍｏｌ％である。
【００５９】
なお、本発明においては、本発明の目的効果を損なわない範囲で、従来公知の親水性樹脂を併用しても良い。公知の親水性樹脂としては、例えば、ゼラチン、ポリビニルピロリドン、プルラン、ポリビニルアルコールまたはその誘導体、ポリエチレングリコール、ヒドロキシエチルセルロース、デキストラン、デキストリン、水溶性ポリビニルブチラール等を挙げることができる。
【００６０】
本発明においては、光重合開始剤や増感剤を添加するのも好ましい。これらの化合物は溶媒に溶解、または分散した状態か、もしくは感光性樹脂に対して化学的に結合されていてもよい。
【００６１】
適用される光重合開始剤、光増感剤について特に制限はなく、従来公知の物を用いることができ、例えば、ベンゾフェノン、ヒドロキシベンゾフェノン、ビス−Ｎ，Ｎ−ジメチルアミノベンゾフェノン、ビス−Ｎ，Ｎ−ジエチルアミノベンゾフェノン、４−メトキシ−４′−ジメチルアミノベンゾフェノン等のベンゾフェノン類。チオキサトン、２、４−ジエチルチオキサントン、イソプロピルチオキサントン、クロロチオキサントン、イソプロポキシクロロチオキサントン等のチオキサントン類。エチルアントラキノン、ベンズアントラキノン、アミノアントラキノン、クロロアントラキノン等のアントラキノン類。アセトフェノン類。ベンゾインメチルエーテル等のベンゾインエーテル類。２，４，６−トリハロメチルトリアジン類、１−ヒドロキシシクロヘキシルフェニルケトン、２−（ｏ−クロロフェニル）−４，５−ジフェニルイミダゾール２量体、２−（ｏ−クロロフェニル）−４，５−ジ（ｍ−メトキシフェニル）イミダゾール２量体、２−（ｏ−フルオロフェニル）−４，５−フェニルイミダゾール２量体、２−（ｏ−メトキシフェニル）−４，５−フェニルイミダゾール２量体、２−（ｐ−メトキシフェニル）−４，５−ジフェニルイミダゾール２量体、２，−ジ（ｐ−メトキシフェニル）−５−フェニルイミダゾール２量体、２−（２，４−ジメトキシフェニル）−４，５−ジフェニルイミダゾール２量体の２，４，５−トリアリールイミダゾール２量体、ベンジルジメチルケタール、２−ベンジル−２−ジメチルアミノ−１−（４−モルホリノフェニル）−ブタン−１−オン、２−メチル−１−［４−（メチルチオ）フェニル］−２−モルホリノ−１−プロパノン、２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オン、１−［４−（２−ヒドロキシエトキシ）−フェニル］−２−ヒドロキシ−２−メチル−１−プロパン−１−オン、フェナントレンキノン、９，１０−フェナンスレンキノン、メチルベンゾイン、エチルベンゾイン等ベンゾイン類、９−フェニルアクリジン、１，７−ビス（９，９′−アクリジニル）ヘプタン等のアクリジン誘導体、ビスアシルフォスフィンオキサイド、及びこれらの混合物等が挙げられ、上記は単独で使用しても混合して使用してもかまわない。
【００６２】
本発明のインクジェット記録用紙においては、特に、混合性等に優れ架橋効率の観点からも水溶性光重合開始剤を用いることが好ましく、例えば、水溶性の１−［４−（２−ヒドロキシエトキシ）−フェニル］−２−ヒドロキシ−２−メチル−１−プロパン−１−オン、４−（２−ヒドロキシエトキシ）−フェニル−（２−ヒドロキシ−２−プロピル）ケトン、チオキサントンアンモニウム塩、ベンゾフェノンアンモニウム塩等の水溶性光重合開始剤を挙げることができる。
【００６３】
これらの光重合開始剤に加え、重合促進剤等を添加することもできる。これらの例として、ｐ−ジメチルアミノ安息香酸エチル、ｐ−ジメチルアミノ安息香酸イソアミル、エタノールアミン、ジエタノールアミン、トリエタノールアミン等が挙げられる。
【００６４】
本発明に係る多孔質層において、親水性バインダー（Ｂ）（本発明に係る親水性樹脂及び公知の親水性樹脂の総量）に対する無機微粒子（Ｆ）の比率（Ｆ／Ｂ）は、質量比で２〜５０であることが好ましい。質量比が２以上であれば、多孔質層の空隙率は良好であり、充分な空隙容量が得やすく、過剰の親水性バインダーがインクジェット記録時に膨潤して空隙を塞ぐことをさけられる。一方、この比率が５０以下であれば、多孔質層を厚膜で塗布した際に、ひび割れが生じにくく好ましい。特に好ましい親水性バインダーに対する無機微粒子の比率（Ｆ／Ｂ）は、２．５〜２０である。更に、乾燥塗膜の折れ割れという観点からみると、Ｆ／Ｂが５〜１５であることがより好ましい。
【００６５】
本発明に係る空隙層は、塗膜の単位面積あたり１５〜４０ｍｌ／ｍ^２の容量を有することが好ましい。ここでいう容量とは、単位体積の塗膜を水に浸漬した際に発生した気泡の体積、塗膜が吸収しうる水の体積、または、最終的に得られる記録用紙を、Ｊ．ＴＡＰＰＩ ５１に規定される紙および板紙の液体吸収性試験方法（ブリストー法）で測定したときの、接触時間が２秒における液体転移量などで定義される。
【００６６】
本発明に係る無機微粒子と電離放射線により架橋された親水性樹脂を含有する塗布液を塗布してなる多孔質層の乾燥固形分量は１〜４０ｇ／ｍ^２が好ましい。１ｇ／ｍ^２より少ない場合、支持体自身が吸水性の場合においても、インク受容性が劣り、インク溢れが発生する。一方、４０ｇ／ｍ^２を超える場合においては、インクの沈み込みによる画像解像度の低下や、シートのカール等の課題が発生する。
【００６７】
本発明のインクジェット記録用紙においては、上記構成からなる多孔質層の表面が、ＪＩＳ−Ｚ−８７２２で規定される方法に準じて測定されたＪＩＳ−Ｚ−８７３０に規定された色の表示方法で表示したとき、ＣＩＥ色空間における明度指数Ｌ^＊が８５以上、知覚色度指数ａ^＊が−３以上、＋２以下で、かつ知覚色度指数ｂ^＊が−４以上、＋３以下であることが特徴であり、好ましくは明度指数Ｌ^＊が８５〜１００である。
【００６８】
明度指数Ｌの値が８５未満である場合には、白色が灰色がかり、色がくすんでしまうため好ましくない。また知覚色度指数ａの値が−３より小さい場合には、画像全体が緑味を帯びてしまい、また＋２より大きい場合には全体が赤みを帯びてしまうため好ましくない。また、知覚色度指数ｂはが−４より小さい場合には、全体が青みを帯びてしまい、＋３より大きな場合には黄色味を帯びてしまうため、いずれも好ましくない。
【００６９】
多孔質層表面のＬａｂの各値を、本発明で規定する範囲に調整する手段としては、特に制限はないが、多孔質層中に各種の着色剤を添加して適宜調整することが好ましい。添加しうる着色剤としては、公知の白色顔料、青色染料、赤色染料、蛍光染料等が挙げられ、塗工量に応じて添加量を適宜調整して使用することができる。
【００７０】
次いで、本発明に係る支持体について説明する。
本発明のインクジェット記録用紙に用いられる支持体としては、吸水性支持体（例えば、紙など）や非吸水性支持体を用いることができるが、より高品位なプリントが得られる観点から、非吸水性支持体を用いることが好ましい。
【００７１】
好ましく用いられる非吸水性支持体としては、例えば、ポリエステル系フィルム、ジアセテート系フィルム、トリアテセート系フィルム、ポリオレフィン系フィルム、アクリル系フィルム、ポリカーボネート系フィルム、ポリ塩化ビニル系フィルム、ポリイミド系フィルム、セロハン、セルロイド等の材料からなる透明または不透明のフィルム、あるいは基紙の両面をポリオレフィン樹脂被覆層で被覆した樹脂被覆紙、いわゆるＲＣペーパー等が用いられる。
【００７２】
上記支持体上に、前記の水溶性塗布液を塗布するに当たっては、表面と塗布層との間の接着強度を大きくする等の目的で、支持体にコロナ放電処理や下引処理等を行うことが好ましい。更に、本発明のインクジェット記録用紙では着色された支持体を用いても良い。
【００７３】
本発明で好ましく用いられ支持体は、透明ポリエステルフィルム、不透明ポリエステルフィルム、不透明ポリオレフィン樹脂フィルムおよび紙の両面をポリオレフィン樹脂でラミネートした紙支持体である。
【００７４】
以下、最も好ましいポリオレフィンの代表であるポリエチレンでラミネートした紙支持体について説明する。
【００７５】
紙支持体に用いられる原紙は、木材パルプを主原料とし、必要に応じて木材パルプに加えてポリプロピレンなどの合成パルプあるいはナイロンやポリエステルなどの合成繊維を用いて抄紙される。木材パルプとしては、例えば、ＬＢＫＰ、ＬＢＳＰ、ＮＢＫＰ、ＮＢＳＰ、ＬＤＰ、ＮＤＰ、ＬＵＫＰ、ＮＵＫＰのいずれも用いることができるが、短繊維分の多いＬＢＫＰ、ＮＢＳＰ、ＬＢＳＰ、ＮＤＰ、ＬＤＰをより多く用いることが好ましい。但し、ＬＢＳＰまたはＬＤＰの比率は１０質量％以上、７０質量％以下であることが好ましい。
【００７６】
上記パルプは、不純物の少ない化学パルプ（硫酸塩パルプや亜硫酸塩パルプ）が好ましく用いられ、又、漂白処理を行って白色度を向上させたパルプも有用である。
【００７７】
原紙中には、高級脂肪酸、アルキルケテンダイマー等のサイズ剤、炭酸カルシウム、タルク、酸化チタンなどの白色顔料、スターチ、ポリアクリルアミド、ポリビニルアルコール等の紙力増強剤、蛍光増白剤、ポリエチレングリコール類等の水分保持剤、分散剤、４級アンモニウム等の柔軟化剤などを適宜添加することができる。
【００７８】
抄紙に使用するパルプの濾水度は、ＣＳＦの規定で２００〜５００ｍｌであることが好ましく、また、叩解後の繊維長がＪＩＳ−Ｐ−８２０７に規定される２４メッシュ残分質量％と、４２メッシュ残分の質量％との和が３０〜７０質量％が好ましい。なお、４メッシュ残分の質量％は、２０質量％以下であることが好ましい。
【００７９】
原紙の坪量は３０〜２５０ｇが好ましく、特に５０〜２００ｇが好ましい。原紙の厚さは４０〜２５０μｍが好ましい。原紙は、抄紙段階または抄紙後にカレンダー処理を施して、高平滑性を与えることもできる。原紙密度は０．７〜１．２ｇ／ｃｍ^３（ＪＩＳ−Ｐ−８１１８に規定の方法に準ずる）が一般的である。更に、原紙剛度はＪＩＳ−Ｐ−８１４３に規定される条件で２０〜２００ｇが好ましい。原紙表面には表面サイズ剤を塗布しても良く、表面サイズ剤としては、前記原紙中添加できるサイズ剤と同様のものを使用することができる。原紙のｐＨは、ＪＩＳ−Ｐ−８１１３で規定された熱水抽出法ににより測定した場合、５〜９であることが好ましい。
【００８０】
原紙表面および裏面を被覆するポリエチレンは、主として低密度のポリエチレン（ＬＤＰＥ）または高密度のポリエチレン（ＨＤＰＥ）であるが、他のＬＬＤＰＥやポリプロピレン等も一部使用することができる。
【００８１】
また、多孔質層を塗設する面側のポリエチレン層には、写真用印画紙で広く行われているようにルチルまたはアナターゼ型の酸化チタンをポリエチレン中に添加し、不透明度および白色度を改良したものが好ましい。酸化チタン含有量は、ポリエチレンに対して、１〜２０質量％、好ましくは２〜１５質量％である。
【００８２】
ポリエチレン被覆紙は、光沢紙として用いることも、また、ポリエチレンを原紙表面上に溶融押し出してコーティングする際に、いわゆる型付け処理を行って通常の写真印画紙で得られるようなマット面や絹目等の微粒面を形成したものも本発明で使用することができる。
【００８３】
原紙の表裏のポリエチレンの使用量は、多孔質層塗布組成物の膜厚やバック層を設けた後での低湿および高湿下でのカールを最適化するように選択されるが、本発明に係る多孔質層用水系塗布組成物を塗布する面側のポリエチレン層としては２０〜４０μｍ、バック層側が１０〜３０μｍの範囲であることが好ましい。
【００８４】
更に、上記ポリエチレン被覆紙支持体は、以下の特性を有していることが好ましい。
【００８５】
１）引っ張り強さ：ＪＩＳ−Ｐ−８１１３で規定される強度で、縦方向が２０〜３００Ｎ、横方向が１０〜２００Ｎであることが好ましい
２）引き裂き強度：ＪＩＳ−Ｐ−８１１６による規定方法で、縦方向が０．１〜２Ｎ、横方向が０．２〜２Ｎが好ましい
３）圧縮弾性率：≧１０３０Ｎ／ｃｍ^２
４）表面ベック平滑度：ＪＩＳ−Ｐ−８１１９に規定される条件で、５００秒以上が光沢面としては好ましいが、いわゆる型付け品ではこれ以下であっても良い
５）裏面ベック平滑度：ＪＩＳ−Ｐ−８１１９に規定される条件で、１００〜８００秒が好ましい
６）不透明度：直線光入射／拡散光透過条件の測定条件で、可視域の光線での透過率が２０％以下、特に１５％以下が好ましい
７）白さ：ＪＩＳ−Ｐ−８１２３に規定されるハンター白色度で、９０％以上が好ましい。
【００８６】
本発明のインクジェット記録用紙においては、支持体の多孔質層を有する面側の表面が、ＪＩＳ−Ｚ−８７２２で規定される方法に準じて測定されたＪＩＳ−Ｚ−８７３０に規定された色の表示方法で表示したとき、ＣＩＥ色空間における明度指数Ｌ^＊が９０以上、知覚色度指数ａ^＊が−５以上、＋５以下で、かつ知覚色度指数ｂ^＊が−１０以上、＋５以下であることを特徴とし、好ましくは明度指数Ｌ^＊が９０〜１００である。
【００８７】
本発明に係る支持体表面の明度指数、各知覚色度指数を本発明で規定する範囲とすることにより、多孔質層の透明性を高めるため、支持体自身の白さが多孔質層表面に対して影響を与えるだけでなく、電離放射線を照射する際に、電離放射線が支持体により反射したハレーション光が、多孔質層中を往復することになり、照射効率の観点からも好ましい。
【００８８】
本発明に係る支持体の多孔質層を設けた面側表面のＬａｂの値を、本発明で規定した条件内に調整する方法としては、原紙層、中間層、または下引き層等に各種の着色剤を添加することで達成される。添加される着色剤は、耐光性、耐熱性に優れた従来公知の白色顔料、青色染料（顔料）、赤色染料（顔料）、黄色染料（顔料）、蛍光染料等、多孔質層の色調や塗設量に応じて添加量を適宜変更して使用することができる。
【００８９】
上記支持体のインク受容層を塗設する面側には、インク受容層との接着性を改良する目的で、下引き層を設けることが好ましい。下引き層のバインダーとしては、ゼラチンやポリビニルアルコール等の親水性ポリマーやＴｇが−３０〜６０℃のラテックスポリマーなどが好ましい。これらバインダーは、インクジェット記録用紙１ｍ^２当たり０．００１〜２ｇの範囲で用いられる。下引き層中には、帯電防止の目的で、従来公知のカチオン性ポリマーなどの帯電防止剤を少量含有させることができる。
【００９０】
上記支持体のインク受容層を有する面側とは反対側の面には、滑り性や帯電特性を改善する目的で、バック層を設けることもできる。バック層のバインダーとしては、ゼラチンやポリビニルアルコール等の親水性ポリマーやＴｇが−３０〜６０℃のラテックスポリマーなどが好ましく、またカチオン性ポリマーなどの帯電防止剤や各種の界面活性剤、更には平均粒径が０．５〜２０μｍ程度のマット剤を添加することもできる。バック層の厚みは、概ね０．１〜１μｍであるが、バック層がカール防止のために設けられる場合には、概ね１〜２０μｍの範囲である。また、バック層は２層以上から構成されていても良い。
【００９１】
下引き層やバック層の塗設に際しては、各々の層を塗設する支持体表面を、コロナ処理やプラズマ処理などの表面処理を施すこともできる。
【００９２】
本発明に係る多孔質層を形成する水溶性塗布液中には、上記説明した構成要素の他に、各種の添加剤を添加することができる。
【００９３】
そのような添加剤としては、例えば、カチオン性媒染剤、架橋剤、界面活性剤（カチオン、ノニオン、アニオン、両性）、白地色調調整剤、蛍光増白剤、防黴剤、粘度調整剤、低沸点有機溶媒、高沸点有機溶媒、ラテックスエマルジョン、退色防止剤、紫外線吸収剤、多価金属化合物（水溶性もしくは非水溶性）、マット剤、シリコンオイル等が挙げられるが、中でもカチオン媒染剤は、印字後の耐水性や耐湿性を改良するために好ましい。
【００９４】
カチオン媒染剤としては、第１級〜第３級アミノ基および第４級アンモニウム塩基を有するポリマー媒染剤が用いられるが、長期保存下での変色や耐光性の劣化が少ないこと、染料の媒染能が充分高いことなどから、第４級アンモニウム塩基を有するポリマー媒染剤が好ましい。
【００９５】
好ましいポリマー媒染剤は、上記第４級アンモニウム塩基を有するモノマーの単独重合体やその他のモノマーとの共重合体または縮重合体として得られる。
【００９６】
また、本発明で用いることのできる多価金属化合物としては、例えば、Ｍｇ^２＋、Ｃａ^２＋、Ｚｎ^２＋、Ｚｒ^２＋、Ｎｉ^２＋、Ａｌ^３＋などの硫酸塩、塩化物、硝酸塩、酢酸塩等で用いられる。なお、塩基性ポリ水酸化アルミニウムや酢酸ジルコニルなどの無機ポリマー化合物も、好ましい水溶性多価金属化合物の例に含まれる。これらの水溶性多価金属化合物は、一般に、耐光性を向上したり、滲みや耐水性を向上させる機能を有するものが多い。これらの水溶性多価金属イオンは、インクジェット記録用紙１ｍ^２当たり、概ね０．０５〜２０ミリモル、好ましくは０．１〜１０ミリモルの範囲で用いられる。
【００９７】
本発明のインクジェット記録用紙において、支持体上に各構成層を設けるための各塗布液の塗布方法としては、従来公知の方法から適宜選択して行うことができ、例えば、グラビアコーティング法、ロールコーティング法、ロッドバーコーティング法、エアナイフコーティング法、スプレーコーティング法、押し出し塗布方法、カーテン塗布方法あるいは米国特許第２，６８１，２９４号明細書に記載のホッパーを使用するエクストルージョンコート法が好ましく用いられる。
【００９８】
本発明の記録用紙に係る多孔質層は、単層であっても２層以上の複数の層で構成されたものであっても良く、複層構成である場合には、全ての構成層を同時に塗布することが、製造コスト低減の観点から好ましい。
【００９９】
本発明でいう電離放射線とは、例えば電子線、紫外線、α線、β線、γ線、エックス線等が上げられるが、人体への危険性や、取り扱いが容易で、工業的にもその利用が普及している電子線、紫外線が好ましい。
【０１００】
電子線の照射方法としては、例えば、スキャニング方式、カーテンビーム方式、ブロードビーム方式などがあるが、処理能力の観点からカーテンビーム方式が好ましい。
【０１０１】
電子線の加速電圧は、塗膜の比重と膜圧により適時変化させることができるが、２０ｋＶ〜３００ｋＶが適当である。電子線の照射量は０．１〜２０Ｍｒａｄの範囲が好ましい。
【０１０２】
紫外線照射の場合、光源として、例えば、数１００Ｐａから約１ＭＰａまでの動作圧力を有する低圧、中圧、高圧水銀ランプ、メタルハライドランプ等が用いられるが、光源の波長分布という観点で高圧水銀灯、メタルハライドランプが好ましく、メタルハライドランプがより好ましい。また、３００ｎｍ以下の波長光をカットするフィルターをもうけることが好ましい。ランプの出力としては４００Ｗ〜３０ｋＷ、発光主波長３５０ｎｍにおける照度が１ｍＷ／ｃｍ^２〜１Ｗ／ｃｍ^２、積算照射エネルギーが１ｍＪ／ｃｍ^２〜１Ｊ／ｃｍ^２がより好ましい。
【０１０３】
光源波長に３００ｎｍ以下の紫外線が含まれる場合や、照射エネルギーとして１Ｊ／ｃｍ^２を超える場合は、電離放射線架橋性樹脂の母核、または共存させる各種添加剤を電離放射線により分解する可能性があり、本発明の効果を得られないだけでなく、分解物に由来する臭気などの問題を起こす可能性があるので好ましくない。照射エネルギーが１ｍＪ／ｃｍ^２に満たない場合は、架橋効率が不足し、本発明の効果が十分にえられない。
【０１０４】
紫外線照射の際の照度は、１Ｗ／ｃｍ^２を超える場合、塗膜の表面硬化性は向上するが、深部硬化性が低下し表面のみ堅い膜が得られる。その場合は、膜の深度方向の堅さのバランスが崩れ、カールなどが起こり、好ましくない。また、照度が１ｍＷ／ｃｍ^２より低い場合は、膜中の散乱等により架橋が十分進まず、本発明の効果が得られないため好ましくない。
【０１０５】
同一積算光量（ｍＪ／ｃｍ^２）を与える場合、照度に好ましい範囲があることは、その光の透過率が変化することに起因する。紫外線の透過性により、発生した架橋反応種の濃度分布が異なり、紫外線照度が高い場合、表層に高濃度の架橋反応種が発生し、塗膜表層に堅い緻密な膜が形成されてしまう。
【０１０６】
照度が好ましい範囲にある場合には、表層の架橋度合いも低く、深部方向への光透過性が高いため緩やかな架橋が深部方向へ均一に形成される。
【０１０７】
照度が低すぎる場合には、必要積算照度を与える場合に照射時間がかかってしまい、設備導入等の面で不利であるばかりでなく、塗膜による紫外線の散乱による絶対光線量が不足するため好ましくない。
【０１０８】
本発明のインクジェット記録用紙を用いて画像記録する際には、水性インクを用いた記録方法が好ましく用いられる。
【０１０９】
上記水性インクとは、下記着色剤及び液媒体、その他の添加剤を有する記録液体である。着色剤としては、インクジェットで公知の直接染料、酸性染料、塩基性染料、反応性染料あるいは食品用色素等の水溶性染料あるいは水分散性顔料が使用できる。
【０１１０】
水性インクの溶媒としては、水及び水溶性の各種有機溶剤、例えば、メチルアルコール、イソプロピルアルコール、ブチルアルコール、ｔｅｒｔ−ブチルアルコール、イソブチルアルコール等のアルコール類；ジメチルホルムアミド、ジメチルアセトアミド等のアミド類；アセトン、ジアセトンアルコール等のケトンまたはケトンアルコール類；テトラヒドロフラン、ジオキサン等のエーテル類；ポリエチレングリコール、ポリプロピレングリコール等のポリアルキレングリコール類；エチレングリコール、プロピレングリコール、ブチレングリコール、トリエチレングリコール、１，２，６−ヘキサントリオール、チオジグリコール、ヘキシレングリコール、ジエチレングリコール、グリセリン、トリエタノールアミン等の多価アルコール類；エチレングリコールメチルエーテル、ジエチレングリコールメチル（又はエチル）エーテル、トリエチレングリコールモノブチルエーテル等の多価アルコールの低級アルキルエーテル類等が挙げられる。中でも、ジエチレングリコール、トリエタノールアミンやグリセリン等の多価アルコール類、トリエチレングリコールモノブチルエーテルの多価アルコールの低級アルキルエーテル等は好ましいものである。
【０１１１】
その他の水性インクの添加剤としては、例えば、ｐＨ調節剤、金属封鎖剤、防カビ剤、粘度調整剤、表面張力調整剤、湿潤剤、界面活性剤及び防錆剤、等が挙げられる。
【０１１２】
水性インク液は記録用紙に対する濡れ性を良好にするために、２０℃において、通常、２５〜６０ｍＮ／ｍ、好ましくは３０〜５０ｍＮ／ｍの範囲内の表面張力を有するのが好ましい。上記インクのｐＨは、好ましくは５〜１０であり、特に好ましくは６〜９である。
【０１１３】
【実施例】
以下、本発明の効果について実施例を挙げて説明するが、本発明はこれらの例に限定されるものではない。なお、実施例中に記載の「％」は、特に断りのない限り質量％を表す。
【０１１４】
実施例１
《シリカ分散液の調製》
〔シリカ分散液Ｓ−１の作製〕
予め均一に分散されている、一次粒子の平均粒径が約７ｎｍの気相法シリカ（日本アエロジル社製；アエロジル３００）を３０％含有するシリカ分散液（ｐＨ２．６、エタノール０．５％含有）の４００ｇを、１０％のカチオン性ポリマーＰ−１を含む水溶液（ｎ−プロパノールを１０％およびエタノールを２％含有）の１２０ｇに、室温で３０００ｒｐｍで攪拌しながら添加し、その後ｐＨを１モル／ＬのＮａＯＨ水溶液にて４．１に調整した。
【０１１５】
次いで、三和工業株式会社製の高圧ホモジナイザーで３ｋＮ／ｃｍ^２の圧力で分散し、全量を純水で仕上げて、シリカ含有量が２０％のほぼ透明なシリカ分散液Ｓ−１を得た。得られたシリカ分散液Ｓ−１を、アドバンテックス東洋社製のＴＣＰ−１０タイプのフィルターを用いてろ過を行った。シリカ粒子の二次平均粒径を測定したところ、３５ｎｍであった。
【０１１６】
二次平均粒径は、シリカ分散液Ｓ−１を５０倍に希釈し、動的光散乱方式の粒子径測定装置ゼータサイザー１０００ＨＳ（マルバーン社製）を用いて測定した値である。
【０１１７】
〔シリカ分散液Ｓ−２の調製〕
高速攪拌分散機を用いて、カチオン性ポリマーＰ−１を２．５ｇ含む１％エタノール水溶液中に、一次粒子の平均粒径が約１０ｎｍのゲル法湿式シリカ（日本シリカ工業社製；Ｎｉｐｇｅｌｌ ＡＺ２００）を徐々に加えながら攪拌分散し、ｐＨを４．０に調整した後、純水を加えて１００ｇに仕上げてシリカ固形分が２０％のシリカ分散液を得た。
【０１１８】
次いで、サンドミルにより分散時間を適宜調整して、ほぼ透明なシリカ分散液Ｓ−２を得た。得られたシリカ分散液Ｓ−２を、アドバンテックス東洋社製のＴＣＰ−１０タイプのフィルターを用いてろ過を行った。シリカ粒子の二次平均粒径を測定したところ、１８７ｎｍであった。
【０１１９】
二次平均粒径は、シリカ分散液Ｓ−２を５０倍に希釈し、動的光散乱方式の粒子径測定装置ゼータサイザー１０００ＨＳ（マルバーン社製）を用いて測定した値である。
【０１２０】
〔シリカ分散液Ｓ−３の調製〕
上記シリカ分散液Ｓ−２の調製において、サンドミルにより分散時間を適宜調整して、シリカ粒子の二次平均粒径を３４３ｎｍに変更した以外は同様にして、シリカ分散液Ｓ−３を調製した。
【０１２１】
《電離放射線により架橋される親水性樹脂の調製》
特開２０００−１８１０６２号公報の実施例に記載の方法に従って、重合度３０００、ケン化度８８％のポリビニルアルコールに、ｐ−（３−メタクリロキシ−２−ヒドロキシプロピルオキシ）ベンズアルデヒドを反応させ、下式の構造を有する紫外線重合型ポリビニルアルコール誘導体（架橋基変性率１ｍｏｌ％、固形分濃度８％）の親水性樹脂水溶液Ｖ−１を得た。
【０１２２】
【化５】

【０１２３】
《記録用紙の作製》
〔記録用紙１の作製〕
秤量１４２．５ｇ／ｍ^２のポリエチレンラミネート紙（インク受容層面側に０．０５ｇ／ｍ^２のゼラチン下引き層、反対側にＴｇが約８０℃のラテックス性ポリマーを有するバック層を０．２ｇ／ｍ^２として設けた）の表面に、ワイヤーバーを用いて下記多孔質層塗布液Ａ−１を、乾燥時塗設量が１８ｇ／ｍ^２となるように塗布した後、３６５ｎｍに主波長を持つメタルハライドランプで、波長３６５ｎｍにおける照度が６０ｍＷ／ｃｍ^２の紫外線を用い、エネルギー量で３０ｍＪ／ｃｍ^２の紫外線を照射し、次いで６０℃の熱風型オーブンで乾燥させて記録用紙１を作製した。
【０１２４】

〔記録用紙２の作製〕
上記記録用紙１の作製において、支持体を秤量８４．３ｇ／ｍ^２のコート紙に変更し、多孔質層塗布液Ａ−１を乾燥時塗設量が１０ｇ／ｍ^２となるように塗布した以外は同様にして、記録用紙２を作製した。
【０１２５】
〔記録用紙３の作製〕
上記記録用紙１の作製において、支持体を厚さ８０μｍの白色ポリエチレンテレフタラートフイルム（多孔質層塗設面側に０．０５ｇ／ｍ^２のゼラチン下引き層、反対側にＴｇが約８０℃のラテックス性ポリマーを有するバック層を０．２ｇ／ｍ^２として有する）に変更した以外は同様にして、記録用紙３を得た。
【０１２６】
〔記録用紙４の作製〕
上記記録用紙１の作製において、シリカ分散液Ｓ−１に代えて、シリカ分散液Ｓ−３を用いた以外は同様にして、記録用紙４を得た。
【０１２７】
〔記録用紙５の作製〕
上記記録用紙１の作製において、親水性樹脂水溶液Ｖ−１に代えて、重合度３５００、ケン化度８８％のポリビニルアルコールの１０％水溶液を同量用い、紫外線に代えて加速電圧２００ｋＶ、照射量２Ｍｒａｄの電子線を照射した以外は同様にして記録用紙５を得た。
【０１２８】
〔記録用紙６の作製〕
上記記録用紙１の作製において、親水性樹脂水溶液Ｖ−１の主鎖ＰＶＡ重合度を２５０に変更した樹脂を用いた以外は同様にして、記録用紙６を得た。
【０１２９】
〔記録用紙７の作製〕
上記記録用紙１の作製において、前記多孔質層塗布液Ａ−１に代えて、下記の多孔質層塗布液Ａ−２を用いた以外は同様にして、記録用紙７を得た。
【０１３０】

〔記録用紙８の作製〕
上記記録用紙１の作製において、前記多孔質層塗布液Ａ−１に代えて、下記の多孔質層塗布液Ａ−３を用いた以外は同様にして、記録用紙８を得た。
【０１３１】

〔記録用紙９の作製〕
上記記録用紙１の作製において、前記多孔質層塗布液Ａ−１に代えて、下記の多孔質層塗布液Ａ−４を用いた以外は同様にして、記録用紙９を得た。
【０１３２】

〔記録用紙１０の作製〕
上記記録用紙１の作製において、前記多孔質層塗布液Ａ−１に代えて、下記の多孔質層塗布液Ａ−５を用いた以外は同様にして、記録用紙１０を得た。
【０１３３】

〔記録用紙１１の作製〕
上記記録用紙１の作製において、親水性樹脂水溶液Ｖ−１に代えて、重合度３５００、ケン化度８８％のポリビニルアルコールの１０％水溶液を同量用い、ホウ酸を０．５部添加し、紫外線を照射しない以外は同様にして、記録用紙１１を得た。
【０１３４】
〔記録用紙１２の作製〕
上記記録用紙１の作製において、紫外線を照射しない以外は同様にして、記録用紙１２を得た。
【０１３５】
〔記録用紙１３の作製〕
上記記録用紙○○の作製において、親水性樹脂水溶液Ｖ−１の主鎖ＰＶＡ重合度を２５０に変更した樹脂を用いた以外は同様にして、記録用紙１３を得た。
【０１３６】
〔記録用紙１４の作製〕
上記記録用紙１の作製において、前記多孔質層塗布液Ａ−１に代えて、下記の多孔質層塗布液Ａ−６を用い、乾燥時塗設量を５ｇ／ｍ^２に変更した以外は同様にして、記録用紙１４を得た。
【０１３７】

《記録用紙の評価》
〔膜面性状の評価〕
上記作製した各記録用紙の多孔質塗設面を目視観察し、下記の方法に則りひび割れ耐性及び膜面平滑性の評価を行った。
【０１３８】
（ひび割れ耐性の評価）
１０ｃｍ^２中の膜面ひび割れ個数を測定した。
【０１３９】
（膜面平滑性の評価）
下記の基準に則り膜面平滑性を評価した。
【０１４０】
◎：全くうねりもみられず、平滑である
○：長周期の波打ちが若干認められるが、製品として問題ないレベル
△：一部膜面故障が見られ、明らかな膜面吹かれが確認できるが実用上許容範囲内である
×：短周期の膜面浪打が認められ、実技上許容されないレベル
××：吹き荒れにより短周期の波打ちと、膜面故障が多発し、全く許容されないレベル
（インク吸収性の評価）
上記作製した各記録用紙に、セイコーエプソン社製のインクジェットプリンターＰＭ９００Ｃを用い、反射濃度が約１．０のニュートラルグレー色を全面ベタ印字して、得られた画像のムラの発生状態を目視観察し、下記の基準に則りインク吸収性の評価を行った。
【０１４１】
１：ムラが全くなし
２：ムラが僅かに認められるがベタ印字しても実技上は問題ないレベル
３：ムラがベタ印字でははっきりわかる程度であるが、実際のプリントでは殆ど問題ないレベル
４：グレーの色ムラが認められ、実技上許容され得ないレベル
５：全く許容され得ないレベル
（折り割れ耐性の評価）
上記作製した各記録用紙を５×１０ｃｍの短冊状に断裁し、これをコア内径３ｃｍの紙管に多孔質層面が外側になる様に巻き付け、表面に発生する折れ割れ（ヒビ割れ）の状態を目視観察し、下記の基準に則り折り割れ耐性を評価した。
【０１４２】
◎：折り割れの発生が全くなし
○：折り割れの発生数が、１〜５本
△：折り割れの発生数が、６〜２０本
×：折り割れの発生数が、２１〜１００本
××：折り割れの発生数が、１０１本以上
（発色性の評価）
上記作製した各記録用紙に、セイコーエプソン社製のインクジェットプリンターＰＭ９００を用い、黒の最高濃度画像を印字して、得られた黒最高濃度画像の反射濃度を、反射濃度計を用いて測定した。
【０１４３】
（多孔質層面の明度指数Ｌ^＊、知覚色度指数ａ^＊、知覚色度指数ｂ^＊の測定）
上記作製した各記録用紙の多孔質層塗設面のＬ^＊、ａ^＊、ｂ^＊を、ミノルタ（株）製色彩色度計ＣＲ−１００により測定した。
【０１４４】
（白地性の感覚評価）
上記作製した各記録用紙の多孔質層塗設面を目視観察し、白地性（色相）について感覚評価を行った。
【０１４５】
以上により得られた結果を、表１に示す。
【０１４６】
【表１】

【０１４７】
表１より明らかな様に、無機微粒子と電離放射線により架橋される親水性樹脂とを含有する多孔質層を有し、多孔質層の表面の明度指数Ｌ^＊が８５以上、知覚色度指数ａ^＊が−３以上、＋２以下で、かつ知覚色度指数ｂ^＊が−４以上、＋３以下である本発明の記録用紙は、ひび割れ耐性、膜面平滑性、インク吸収性、折れ割れ耐性、発色性及び白地性の全ての特性に優れていることが分かる。
【０１４８】
実施例２
〔記録用紙１５の作製〕
（支持体の作製）
抄紙機を使用して下記の配合量からなる秤量１００ｇ／ｍ^２の原紙を作製した。
【０１４９】

次いで、サイズプレス装置を使用して、上記原紙に下記の配合からなる含浸液を乾燥質量が２．０ｇ／ｍ^２になるように含浸させた。
【０１５０】
〈含浸液〉
ポリビニルアルコール（クラレ製、ＰＶＡ１１０） ２．０部
蛍光染料（日本曹達製、Ｋａｙｃｏｌｌ ＢＵＬ） ０．２部
導電剤（三洋化成工業製、ケミスタット６１２０） １．０部
次いで、上記原紙の表面にコロナ放電処理を行った後、溶融押し出し塗工法により、厚さが２０μｍになるように、低密度ポリエチレン（密度０．９２ｇ／ｍ^３）３０部と高密度ポリエチレン（密度０．９６ｇ／ｍ^３）７０部からなる裏面樹脂被覆層を設けた。
【０１５１】
次いで、上記原紙の表面にコロナ放電処理を行った後、溶融押し出し塗工法により、厚さが２０μｍとなるように下記の構成からなる表面樹脂被覆層１を設けて、支持体を作製した。
【０１５２】
〈表面樹脂被覆層１〉
低密度ポリエチレン（密度０．９２ｇ／ｍ^３） ３０．０部
高密度ポリエチレン（密度０．９６ｇ／ｍ^３） ７０．０部
アナターゼ型二酸化チタン １０．０部
青色顔料（群青） ０．５部
次いで、上記支持体の表裏にコロナ放電処理を行い、多孔質層面側に０．０５ｇ／ｍ^２のゼラチン下引き層、反対側にＴｇが約８０℃のラテックス性ポリマーを含有するバック層を０．２ｇ／ｍ^２として設けて、支持体を作製した。
【０１５３】
（多孔質層の塗設）
上記作製した支持体上に、下記の多孔質層塗布液Ａ−７を乾燥時塗設量が１８ｇ／ｍ^２となるように塗布した後、３６５ｎｍに主波長を持つメタルハライドランプで、波長３６５ｎｍにおける照度が６０ｍＷ／ｃｍ^２の紫外線を用い、エネルギー量で３０ｍＪ／ｃｍ^２の紫外線を照射し、その後６０℃の熱風型オーブンで乾燥させて記録用紙１５を得た。
【０１５４】

〔記録用紙１６の作製〕
上記作製した記録用紙１５において、多孔質層塗布液Ａ−７の調製で用いたシリカ分散液Ｓ−１を、実施例１で調製したシリカ分散液Ｓ−２に変更した以外は同様にして、記録用紙１６を作製した。
【０１５５】
〔記録用紙１７の作製〕
上記作製した記録用紙１５において、多孔質層塗布液Ａ−７の調製で用いたシリカ分散液Ｓ−１を、実施例１で調製したシリカ分散液Ｓ−３に変更した以外は同様にして、記録用紙１７を作製した。
【０１５６】
〔記録用紙１８の作製〕
上記作製した記録用紙１５において、支持体を厚さ１００μｍの白色ポリエチレンテレフタラートフイルムに変更した以外は同様にして、記録用紙１８を得た。
【０１５７】
〔記録用紙１９の作製〕
上記作製した記録用紙１５において、支持体を秤量８４．９ｇ／ｍ^２のコート紙に変更した以外は同様にして、記録用紙１９を得た。
【０１５８】
〔記録用紙２０の作製〕
上記記録用紙１５の作製において、親水性樹脂水溶液Ｖ−１の主鎖ＰＶＡ重合度を２５０に変更した樹脂を用いた以外は同様にして、記録用紙２０を得た。
【０１５９】
〔記録用紙２１の作製〕
上記記録用紙１５の作製において、親水性樹脂水溶液Ｖ−１に代えて、重合度３５００、ケン化度８８％のポリビニルアルコールの１０％水溶液を同量用い、紫外線に代えて加速電圧２００ｋＶ、照射量２Ｍｒａｄの電子線を照射した以外は同様にして記録用紙２１を得た。
【０１６０】
〔記録用紙２２の作製〕
上記記録用紙１５の作製において、支持体の表面樹脂被覆層１を、以下の表面樹脂被覆層２に変更した以外は同様にして、記録用紙２２を得た。
【０１６１】
〈表面樹脂被覆層２〉
低密度ポリエチレン（密度０．９２ｇ／ｍ^３） ７０．０部
高密度ポリエチレン（密度０．９７ｇ／ｍ^３） ２０．０部
白色顔料（アナターゼ型二酸化チタン） ５．０部
黒色顔料（カーボンブラック） ０．００８部
青色顔料（群青） ０．５部
〔記録用紙２３の作製〕
上記記録用紙１５の作製において、支持体の表面樹脂被覆層１を、以下の表面樹脂被覆層３に変更した以外は同様にして、記録用紙２３を得た。
【０１６２】
〈表面樹脂被覆層３〉
低密度ポリエチレン（密度０．９２ｇ／ｍ^３） ７０．０部
高密度ポリエチレン（密度０．９７ｇ／ｍ^３） ２０．０部
白色顔料（アナターゼ型二酸化チタン） ５．０部
青色顔料（群青） １．０部
〔記録用紙２４の作製〕
上記記録用紙１５の作製において、支持体の作製に用いた原紙の配合量を以下のように変更した以外は同様にして、記録用紙２４を得た。
【０１６３】

〔記録用紙２５の作製〕
上記記録用紙１５の作製において、親水性樹脂水溶液Ｖ−１に代えて、重合度３５００、ケン化度８８％のポリビニルアルコールの１０％水溶液を同量用い、ホウ酸を０．５部添加し、紫外線を照射しない以外は同様にして、記録用紙２５を得た。
【０１６４】
〔記録用紙２６の作製〕
上記記録用紙１５の作製において、紫外線を照射しない以外は同様にして、記録用紙２６を得た。
【０１６５】
〔記録用紙２７の作製〕
上記記録用紙１５の作製において、前記多孔質層塗布液Ａ−７に代えて、下記の多孔質層塗布液Ａ−８を用いた以外は同様にして、記録用紙２７を得た。
【０１６６】

《記録用紙の評価》
以上の様にして作製した各記録用紙について、実施例１に記載の方法と同様にして、支持体表面の明度指数Ｌ^＊、知覚色度指数ａ^＊、知覚色度指数ｂ^＊の測定と、ひび割れ耐性、膜面平滑性、インク吸収性、折れ割れ耐性、発色性及び白地性の評価を行い、得られた結果を表２に示す。
【０１６７】
【表２】

【０１６８】
表２より明らかな様に、無機微粒子と電離放射線により架橋される親水性樹脂とを含有する多孔質層を有し、支持体表面の明度指数Ｌ^＊が９０以上、知覚色度指数ａ^＊が−５以上、＋５以下で、かつ知覚色度指数ｂ^＊が−１０以上、＋５以下である本発明の記録用紙は、ひび割れ耐性、膜面平滑性、インク吸収性、折れ割れ耐性、発色性及び白地性の全ての特性に優れていることが分かる。
【０１６９】
【発明の効果】
本発明により、支持体上に親水性バインダーと微粒子からなる多孔質層を厚膜で、かつ高速で塗布しても、製造時のひび割れが発生しにくく、高インク吸収性で柔軟な塗膜を有し、優れた画像が得られるインクジェット記録用紙及びその製造方法を提供することができた。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording paper (hereinafter, also simply referred to as recording paper) and a method for producing the same, and more specifically, has a good ink absorbability, a flexible coating film property, and a porous film capable of obtaining an excellent image. The present invention relates to an inkjet recording paper having a quality layer and a method for producing the same.
[0002]
[Prior art]
In recent years, image quality has been rapidly improved in the ink jet recording system, and the obtained image quality is approaching that of a silver salt photograph. As a means for achieving such photographic image quality by ink jet recording, rapid technical improvement is also being attempted in the ink jet recording paper to be used.
[0003]
Examples of the support used in the inkjet recording method include a water-absorbing support such as paper, a non-water-absorbing support coated with a polyester film or a resin, etc. Are known. The former has the advantage that the support itself can absorb ink, and thus has the advantage of having a high ink absorption ability, but on the other hand, there is a problem that wrinkles are generated after printing due to the water absorption of the support (also called cockling). There are problems such that it is difficult to obtain high-quality prints, and the print surface is easily rubbed by the head accompanying cockling during printing. On the other hand, when a non-water-absorbing support is used, there is an advantage that a high-quality print can be obtained without the above-described problems.
[0004]
On the other hand, as an ink receiving layer, for example, an ink jet recording sheet is known in which a hydrophilic binder such as gelatin or polyvinyl alcohol is applied as an ink absorbing layer on a support having high smoothness to form an ink receiving layer. . This type of ink jet recording paper absorbs ink by utilizing the swelling property of the binder.
[0005]
Since such a swelling ink receiving layer uses a water-soluble resin, it is difficult to dry the ink after printing, the image and film are weak against moisture and poor in water resistance. Since the printer has a high printing speed, there is a problem that the ink absorption ability due to the swelling of the binder cannot catch up with the ink discharge amount and the discharge speed, and the ink overflows and mottles and is not adaptable.
[0006]
On the other hand, Japanese Patent Application Laid-Open No. 63-18387 discloses an ink receiving layer composed of a modified polyvinyl alcohol and a water-resistant agent. Japanese Patent Application Laid-Open No. 1-286886 proposes a recording sheet for water-based ink having an ink receiving layer made of a hydrophilic resin crosslinked by ionizing radiation. By using a cured binder as the ink-receiving layer, the water resistance of the image and the film has been solved. However, since the ink is originally absorbed by the swelling property of the hydrophilic resin, the ink absorbability is improved. There is no current situation.
[0007]
For a swelling type ink jet recording paper that absorbs ink by utilizing the swellability of the water-soluble resin, a porous layer having minute voids described in JP-A-10-119423 is used as an ink absorbing layer. The provided ink jet recording paper has high ink absorbability and high-speed drying properties, and is becoming one of the methods for obtaining the image quality closest to the photographic image quality.
[0008]
This porous layer is mainly formed of a hydrophilic binder and fine particles. As the fine particles, inorganic fine particles or organic fine particles are known, but generally, the inorganic fine particles have a smaller particle size, It is preferably used because it has little scattered light, a high-density image can be obtained, and a highly glossy porous layer can be realized. By using a relatively small amount of a hydrophilic binder for such inorganic fine particles, voids are formed between the inorganic fine particles, and a porous layer having a high porosity can be obtained.
[0009]
Since the voids formed in this manner absorb ink by capillary action, the binder is cross-linked using a cross-linking agent or the like, so that the ink absorption speed is not impaired even if the water resistance is improved.
[0010]
The solvent in the ink after ink absorption is first held in the voids, and finally supported by swelling the binder or the like present around the inorganic fine particles. In this case, since the apparent particle size increases due to the swelling of the hydrophilic resin covering the inorganic fine particles, the film is devitrified due to the scattering caused thereby, and there is a problem that the sharpness of the obtained image is lowered. It was.
[0011]
On the other hand, the lightness index L defined by CIELAB on the surface of the ink receiving layer^*, Perceptual chromaticity index a^*And b^*In this case, an ink jet recording paper having excellent image sharpness and good color reproducibility has been proposed (see, for example, Patent Document 1).
[0012]
However, when pursuing a higher quality image because it approximates a photographic image, an ink jet recording paper having a porous layer of inorganic fine particles and a hydrophilic resin has a visually excellent white background alone. It has been found that the influence of the swelling of the hydrophilic resin due to the influence on the sharpness of the image and the image density cannot be eliminated.
[0013]
In order to solve the above problems, an inkjet recording paper is disclosed in which hydrophilic resin is crosslinked using boric acid and an isocyanate-based crosslinking agent to improve the water resistance of the film (for example, see Patent Document 2).
[0014]
However, in this method, even if the swelling of the hydrophilic resin due to the ink solvent is prevented, a film having a relatively high density and dense three-dimensional crosslinking is formed. There was a problem.
[0015]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-181194
[0016]
[Patent Document 2]
JP 2001-146068 A
[0017]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and its purpose is to provide a thick layer of a porous layer composed of a hydrophilic binder and fine particles on a support, and even when applied at high speed, cracks during production are not caused. It is an object of the present invention to provide an ink jet recording paper that is less likely to occur, has a high ink absorbability and a flexible coating film, and provides an excellent image, and a method for producing the same.
[0018]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitution.
[0019]
1. In an inkjet recording paper having a porous layer containing inorganic fine particles and a hydrophilic resin that is cross-linked by ionizing radiation on a support, the surface of the porous layer is a method defined by JIS-Z-8722. Lightness index L in the CIE color space when displayed in accordance with the color display method defined in JIS-Z-8730^*Is 85 or more, perceptual chromaticity index a^*Is -3 or more and +2 or less, and the perceptual chromaticity index b^*Is an ink jet recording paper, wherein -4 is -4 or more and +3 or less.
[0020]
2. In an inkjet recording paper having a porous layer containing inorganic fine particles and a hydrophilic resin that is cross-linked by ionizing radiation on a support, the surface of the support that has the porous layer is JIS-Z. Brightness index L in the CIE color space when displayed in the color display method specified in JIS-Z-8730 measured according to the method specified in -8722.^*Is 90 or more, perceptual chromaticity index a^*Is -5 or more and +5 or less, and the perceptual chromaticity index b^*Is an ink jet recording paper, characterized by being from −10 to +5.
[0021]
3. 3. The inkjet recording paper according to item 1 or 2, wherein the support is a non-water-absorbing support.
[0022]
4). 4. The inkjet recording paper according to any one of items 1 to 3, wherein the inorganic fine particles have an average particle size of 5 to 300 nm.
[0023]
5. The hydrophilic resin crosslinked by the ionizing radiation is a saponified product of polyvinyl acetate, polyvinyl acetal, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or their respective derivatives, And at least one selected from the group consisting of copolymers thereof, at least one selected from an ionizing radiation dimerization type, an ionizing radiation decomposition type, an ionizing radiation polymerization type, an ionizing radiation modified type, and an ionizing radiation depolymerization type The inkjet recording paper according to any one of 1 to 4 above, wherein the inkjet recording paper is modified with a modifying group.
[0024]
6). 6. The degree of polymerization of the hydrophilic resin modified with the modifying group is 300 or more and 4500 or less, and the modification rate by the modifying group is 0.1 mol% or more and 4 mol% or less. Inkjet recording paper.
[0025]
7). 7. The method for producing an inkjet recording paper according to any one of 1 to 6, wherein a porous layer containing a hydrophilic resin that is crosslinked by inorganic fine particles and ionizing radiation is applied on a support, A method for producing an inkjet recording paper, characterized by irradiating with ionizing radiation when the solid content concentration of the porous layer is in the range of 5 to 90% by mass and then drying.
[0026]
8). The ionizing radiation has an illuminance of 1 mW / cm at an emission main wavelength of 350 nm.²1 W / cm²And the integrated irradiation energy is 1 mJ / cm.²1J / cm²8. The method for producing an ink jet recording paper according to 7 above, wherein the ultraviolet rays are as follows.
[0027]
Hereinafter, the present invention will be described in detail.
The ink jet recording paper of the present invention is formed by applying a water-soluble coating solution that forms a porous layer mainly containing a hydrophilic resin crosslinked with ionizing radiation and inorganic fine particles on a support to form a porous layer having voids. It is a thing.
[0028]
First, the inorganic fine particles used in the porous layer according to the present invention will be described.
As the inorganic fine particles used in the present invention, fine inorganic fine particles having a large pore volume and a small average particle diameter are used. In particular, fine pigments such as silica, aluminum hydroxide, boehmite, pseudoboehmite, alumina and calcium carbonate are used.
[0029]
The silica used in the present invention is wet silica or vapor phase silica synthesized by precipitation or gel method using sodium silicate as a raw material.
[0030]
For example, as for wet silica, Tokuyama Fine Seal Co., Ltd. by the precipitation method, and as a silica by gel method, NIPGEL of Nippon Silica Kogyo Co., Ltd. is commercially available. Precipitated silica is generally characterized by 10-60 nm, and gel silica is characterized by silica particles having primary aggregates of approximately 3-10 nm forming secondary aggregates.
[0031]
Although there is no restriction | limiting in particular as a minimum regarding the primary particle diameter of wet silica, It is 3 nm or more from a viewpoint of the manufacture stability of a silica particle, and it is preferable that it is 50 nm or less from a viewpoint of the transparency of a film | membrane. In general, wet silica synthesized by the gel method is preferred because the primary particle size tends to be smaller than that of the precipitation method.
[0032]
Vapor phase silica is synthesized from silicon tetrachloride and hydrogen as raw materials by a combustion method or the like. For example, Aerosil series manufactured by Nippon Aerosil Co., Ltd. is commercially available.
[0033]
In order to obtain a high porosity ink absorbing layer, the specific surface area measured by the BET method is 400 m.²/ G or the isolated silanol group ratio is preferably 0.5 to 2.0.
[0034]
The lower limit of the specific surface area is 40 m from the viewpoint of obtaining a gloss similar to a photograph.²/ G. The BET method is a method for measuring the specific surface area by a method for obtaining the surface area per 1 g from the gas phase adsorption isotherm. In vapor phase silica having a specific surface area in this range, it is preferable from the viewpoint of porosity that the coefficient of variation in the primary particle size distribution is 0.4 or less. However, in wet silica, the primary particles themselves have a pore size, and this is not the case.
[0035]
Vapor phase silica is characterized in that secondary aggregates are formed by relatively weak interaction with wet silica and can therefore be dispersed with low energy in wet silica.
[0036]
The coefficient of variation in the primary particle size distribution of the vapor phase silica is determined by observing the cross section and surface of the void layer with an electron microscope, obtaining the particle size of 1000 arbitrary primary particles, and calculating the number average of the standard deviation of the particle size distribution. It is obtained as a value divided by the particle size value. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.
[0037]
The average particle size of the primary particles and secondary particles of the silica here is determined from the particle size of 100 arbitrary particles by observing the cross section and surface of the void layer with an electron microscope. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.
[0038]
In the present invention, the secondary average particle diameter is preferably 300 nm or less from the viewpoint of transmission of ionizing radiation.
[0039]
It is also preferable to adjust the water content of the vapor phase silica by storing the vapor phase silica in an environment of 20 to 60% humidity for 3 days or more.
[0040]
In the vapor phase method silica of the present invention, the isolated silanol group ratio is preferably 0.5 to 1.5, more preferably 0.5 to 1.1.
[0041]
Alumina that can be used in the ink jet recording paper of the present invention refers to aluminum oxide and hydrates thereof, which may be crystalline or amorphous, and have an amorphous, spherical, plate-like, or needle-like form. What you have is used. In particular, plate-like alumina hydrate and vapor phase method alumina having an aspect ratio of 2 or more and an average primary particle size of 5 to 30 nm are preferable.
[0042]
The content of the inorganic fine particles in the coating liquid for forming the porous layer is 5 to 40% by mass, and particularly preferably 7 to 30% by mass.
[0043]
Next, the hydrophilic resin that is cross-linked by ionizing radiation according to the present invention will be described.
[0044]
The hydrophilic resin (hereinafter also referred to as a polymer compound) that is cross-linked by water-soluble ionizing radiation used in the porous layer of the present invention is caused to react by irradiation with ionizing radiation such as ultraviolet rays and electron beams to cause a cross-linking reaction. It is a water-soluble polymer compound that is water-soluble before the cross-linking reaction but becomes substantially water-insoluble after the cross-linking reaction. This polymer compound is hydrophilic even after the cross-linking reaction. And maintain sufficient affinity for the ink.
[0045]
Such polymer compounds include saponified polyvinyl acetate, polyvinyl acetal, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose and other hydrophilic resins, or derivatives thereof. In addition, at least one selected from the group consisting of these copolymers may be modified with a modifying group such as a photodimerization type, a photolysis type, a photopolymerization type, a photomodification type, or a photodepolymerization type. preferable. Among these, a polymer compound modified with a photodimerization type or photopolymerization type modification group is preferable from the viewpoint of sensitivity or stability of the polymer compound itself.
[0046]
As the photodimerization-type modifying group, those having a diazo group, a cinnamoyl group, a stilbazonium group, or a stilquinolium group introduced are preferable, and a resin dyed with a water-soluble dye such as an anionic dye after photodimerization is preferable. Examples of such a resin include resins having a cationic group such as a primary amino group or a quaternary ammonium group, such as JP-A-62-283339, JP-A-1-198615, and JP-A-60-252341. No., JP-A 56-67309, JP-A 60-129742, etc., photosensitive resins (compositions), and after curing, become cationic after curing such as an azide group that becomes an amino group Resins, for example, photosensitive resins (compositions) described in JP-A-56-67309 and the like, and specific examples thereof include the following compounds.
[0047]
The photosensitive resin described in JP-A-56-67309 contains a polyvinyl alcohol structure,
[0048]
[Chemical 1]

[0049]
2-azido-5-nitrophenylcarbonyloxyethylene structure represented by:
[0050]
[Chemical formula 2]

[0051]
It is a resin composition which has 4-azido-3-nitrophenyl carbonyloxyethylene structure represented by these.
[0052]
Specific examples of the photosensitive resin are described in Examples 1 and 2 in the official gazette, and the constituent components and usage ratio of the photosensitive resin are described on page 2 of the official gazette.
[0053]
JP-A-60-129742 discloses a polyvinyl alcohol structure as a photosensitive resin.
[0054]
[Chemical Formula 3]

[0055]
The resin composition which has the following structure is mentioned.
In the present invention, among the hydrophilic polymer compounds that are cross-linked by ionizing radiation, the photopolymerizable modifying group is represented by, for example, the following general formula (1) disclosed in JP-A No. 2000-181062. A saponified polyvinyl acetate having a structural unit is preferred from the viewpoint of reactivity.
[0056]
[Formula 4]

[0057]
In the general formula (1), R₁Represents a hydrogen atom or a methyl group, Y represents an aromatic ring or a simple bond, and X represents — (CH₂)_m-COO-, -O-CH₂-COO- or -O- is represented, m is an integer of 0-6, n represents 1 or 2.
[0058]
In the hydrophilic polymer compound according to the present invention, the degree of polymerization and the crosslink density affect the strength and flexibility at the time of film formation. If the degree of polymerization is too low or there are too many crosslinkable groups, cracking and drying during coating and drying will occur. Failure such as breakage of the paint film will occur. Therefore, in the hydrophilic polymer compound containing the polyvinyl saponified product having the structural unit represented by the general formula (1), the degree of polymerization is preferably 400 to 5000, more preferably 1000 to 4000. preferable. Moreover, it is preferable that the modification | denaturation rate of the ionizing radiation reaction crosslinking group with respect to a segment is 4 mol% or less, More preferably, it is 0.01-1 mol%.
[0059]
In addition, in this invention, you may use together a conventionally well-known hydrophilic resin in the range which does not impair the objective effect of this invention. Examples of known hydrophilic resins include gelatin, polyvinyl pyrrolidone, pullulan, polyvinyl alcohol or derivatives thereof, polyethylene glycol, hydroxyethyl cellulose, dextran, dextrin, water-soluble polyvinyl butyral, and the like.
[0060]
In the present invention, it is also preferable to add a photopolymerization initiator or a sensitizer. These compounds may be dissolved or dispersed in a solvent, or may be chemically bonded to the photosensitive resin.
[0061]
There is no restriction | limiting in particular about the photoinitiator and photosensitizer which are applied, A conventionally well-known thing can be used, For example, a benzophenone, hydroxybenzophenone, bis-N, N-dimethylamino benzophenone, bis-N, N -Benzophenones such as diethylaminobenzophenone and 4-methoxy-4'-dimethylaminobenzophenone. Thioxanthones such as thioxatone, 2,4-diethylthioxanthone, isopropylthioxanthone, chlorothioxanthone, and isopropoxychlorothioxanthone. Anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone and chloroanthraquinone. Acetophenones. Benzoin ethers such as benzoin methyl ether. 2,4,6-trihalomethyltriazines, 1-hydroxycyclohexyl phenyl ketone, 2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di ( m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4,5-phenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-phenylimidazole dimer, 2- (P-methoxyphenyl) -4,5-diphenylimidazole dimer, 2, -di (p-methoxyphenyl) -5-phenylimidazole dimer, 2- (2,4-dimethoxyphenyl) -4,5 -2,4,5-triarylimidazole dimer of diphenylimidazole dimer, benzyldimethyl ketal, 2-benzyl-2-dimethyl Amino-1- (4-morpholinophenyl) -butan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-hydroxy-2-methyl-1- Phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, phenanthrenequinone, 9,10-phenanthrenequinone Benzoins such as methylbenzoin and ethylbenzoin, 9-phenylacridine, acridine derivatives such as 1,7-bis (9,9'-acridinyl) heptane, bisacylphosphine oxide, and mixtures thereof, etc. May be used alone or in combination.
[0062]
In the ink jet recording paper of the present invention, it is particularly preferable to use a water-soluble photopolymerization initiator from the viewpoint of excellent mixing property and crosslinking efficiency, for example, water-soluble 1- [4- (2-hydroxyethoxy). -Phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 4- (2-hydroxyethoxy) -phenyl- (2-hydroxy-2-propyl) ketone, thioxanthone ammonium salt, benzophenone ammonium salt, etc. And water-soluble photopolymerization initiators.
[0063]
In addition to these photopolymerization initiators, polymerization accelerators and the like can also be added. Examples of these include ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine and the like.
[0064]
In the porous layer according to the present invention, the ratio (F / B) of the inorganic fine particles (F) to the hydrophilic binder (B) (the total amount of the hydrophilic resin according to the present invention and the known hydrophilic resin) is expressed as a mass ratio. It is preferable that it is 2-50. If the mass ratio is 2 or more, the porosity of the porous layer is good, it is easy to obtain a sufficient void volume, and an excessive hydrophilic binder is prevented from swelling and closing the void during ink jet recording. On the other hand, if this ratio is 50 or less, it is preferable that cracking hardly occurs when the porous layer is applied as a thick film. The ratio (F / B) of the inorganic fine particles to the particularly preferred hydrophilic binder is 2.5-20. Furthermore, it is more preferable that F / B is 5 to 15 from the viewpoint of breakage of the dried coating film.
[0065]
The void layer according to the present invention is 15 to 40 ml / m per unit area of the coating film.²It is preferable to have a capacity of The capacity here means the volume of bubbles generated when a unit volume of the coating film is immersed in water, the volume of water that can be absorbed by the coating film, or the recording paper finally obtained. It is defined as the amount of liquid transfer when the contact time is 2 seconds as measured by the liquid absorbency test method (Bristow method) for paper and paperboard specified in TAPPI 51.
[0066]
The dry solid content of the porous layer formed by applying a coating solution containing the inorganic fine particles according to the present invention and a hydrophilic resin crosslinked by ionizing radiation is 1 to 40 g / m.²Is preferred. 1g / m²When the amount is less, even when the support itself absorbs water, the ink receptivity is poor and ink overflow occurs. On the other hand, 40 g / m²In the case of exceeding the above, problems such as a decrease in image resolution due to sinking of the ink and curling of the sheet occur.
[0067]
In the ink jet recording paper of the present invention, the surface of the porous layer having the above-described structure is a color display method specified in JIS-Z-8730 measured according to the method specified in JIS-Z-8722. When displayed, lightness index L in CIE color space^*Is 85 or more, perceptual chromaticity index a^*Is -3 or more and +2 or less, and the perceptual chromaticity index b^*Is not less than −4 and not more than +3, preferably a lightness index L^*Is 85-100.
[0068]
When the value of the lightness index L is less than 85, white is grayish and the color becomes dull. Further, when the value of the perceptual chromaticity index a is smaller than −3, the entire image is tinged with green, and when it is larger than +2, the whole is tinged with red. In addition, when the perceptual chromaticity index b is smaller than −4, the whole color is bluish, and when it is larger than +3, the color is yellowish.
[0069]
The means for adjusting each value of Lab on the surface of the porous layer to the range specified in the present invention is not particularly limited, but it is preferable to adjust various values by adding various colorants to the porous layer. Examples of the colorant that can be added include known white pigments, blue dyes, red dyes, fluorescent dyes, and the like, and the addition amount can be appropriately adjusted according to the coating amount.
[0070]
Next, the support according to the present invention will be described.
As the support used in the ink jet recording paper of the present invention, a water-absorbing support (for example, paper) or a non-water-absorbing support can be used. From the viewpoint of obtaining a higher-quality print, non-water-absorbing support. It is preferable to use a conductive support.
[0071]
As the non-water-absorbing support preferably used, for example, polyester film, diacetate film, triatesate film, polyolefin film, acrylic film, polycarbonate film, polyvinyl chloride film, polyimide film, cellophane, A transparent or opaque film made of a material such as celluloid, or a resin-coated paper in which both surfaces of a base paper are coated with a polyolefin resin coating layer, so-called RC paper, or the like is used.
[0072]
When applying the water-soluble coating solution on the support, the support is subjected to corona discharge treatment, subbing treatment or the like for the purpose of increasing the adhesive strength between the surface and the coating layer. Is preferred. Furthermore, a colored support may be used in the inkjet recording paper of the present invention.
[0073]
The support preferably used in the present invention is a transparent polyester film, an opaque polyester film, an opaque polyolefin resin film, and a paper support in which both sides of paper are laminated with a polyolefin resin.
[0074]
Hereinafter, a paper support laminated with polyethylene, which is the most preferred representative of polyolefin, will be described.
[0075]
The base paper used for the paper support is made from wood pulp as a main raw material, and if necessary, paper is made using synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester in addition to wood pulp. As wood pulp, for example, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, NUKP can be used, but more LBKP, NBSP, LBSP, NDP, LDP with more short fibers are used. Is preferred. However, the ratio of LBSP or LDP is preferably 10% by mass or more and 70% by mass or less.
[0076]
The pulp is preferably a chemical pulp (sulfate pulp or sulfite pulp) with few impurities, and a pulp having a whiteness improved by bleaching is also useful.
[0077]
In the base paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength enhancing agents such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, polyethylene glycols A water retaining agent such as a dispersant, a softening agent such as a quaternary ammonium, and the like can be appropriately added.
[0078]
The freeness of the pulp used for papermaking is preferably 200 to 500 ml as defined by CSF, and the fiber length after beating is a 24 mesh residual mass% defined by JIS-P-8207, and 42 30-70 mass% of sum with the mass% of a mesh remainder is preferable. In addition, it is preferable that the mass% of 4 mesh remainder is 20 mass% or less.
[0079]
The basis weight of the base paper is preferably 30 to 250 g, particularly preferably 50 to 200 g. The thickness of the base paper is preferably 40 to 250 μm. The base paper can be given a high smoothness by subjecting it to a calendar process at the paper making stage or after paper making. Base paper density is 0.7-1.2g / cm³(In accordance with the method prescribed in JIS-P-8118) is common. Furthermore, the base paper stiffness is preferably 20 to 200 g under the conditions specified in JIS-P-8143. A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, the same sizing agent that can be added to the base paper can be used. The pH of the base paper is preferably 5 to 9 when measured by a hot water extraction method defined in JIS-P-8113.
[0080]
The polyethylene covering the front and back surfaces of the base paper is mainly low-density polyethylene (LDPE) or high-density polyethylene (HDPE), but some other LLDPE, polypropylene, etc. can also be used.
[0081]
In addition, rutile or anatase type titanium oxide is added to the polyethylene layer on the side where the porous layer is to be coated, as is widely done in photographic paper, to improve opacity and whiteness. Is preferred. The titanium oxide content is 1 to 20% by mass, preferably 2 to 15% by mass, based on polyethylene.
[0082]
The polyethylene-coated paper can be used as glossy paper, or when the polyethylene is melt-extruded onto the surface of the base paper for coating, a matte surface or silky grain that can be obtained with ordinary photographic printing paper by performing a so-called molding process, etc. Those having a fine grain surface can also be used in the present invention.
[0083]
The amount of polyethylene used on the front and back of the base paper is selected so as to optimize the film thickness of the porous layer coating composition and the curl under low and high humidity after providing the back layer. The polyethylene layer on the surface side on which the aqueous coating composition for a porous layer is applied is preferably in the range of 20 to 40 μm and the back layer side in the range of 10 to 30 μm.
[0084]
Furthermore, the polyethylene-coated paper support preferably has the following characteristics.
[0085]
1) Tensile strength: strength specified in JIS-P-8113, preferably 20 to 300N in the vertical direction and 10 to 200N in the horizontal direction.
2) Tear strength: 0.1 to 2N in the vertical direction and 0.2 to 2N in the horizontal direction are preferred according to a method defined by JIS-P-8116.
3) Compression modulus: ≧ 1030 N / cm²
4) Surface Beck smoothness: 500 seconds or more is preferable as a glossy surface under the conditions specified in JIS-P-8119, but it may be less than this for so-called molded products.
5) Back surface Beck smoothness: 100 to 800 seconds are preferable under the conditions specified in JIS-P-8119.
6) Opacity: Under the measurement conditions of linear light incidence / diffuse light transmission conditions, the transmittance for light in the visible region is 20% or less, particularly preferably 15% or less.
7) Whiteness: Hunter whiteness specified in JIS-P-8123, preferably 90% or more.
[0086]
In the ink jet recording paper of the present invention, the surface of the support having the porous layer has a color specified in JIS-Z-8730 measured according to a method specified in JIS-Z-8722. Lightness index L in CIE color space when displayed in the display method^*Is 90 or more, perceptual chromaticity index a^*Is -5 or more and +5 or less, and the perceptual chromaticity index b^*Is not less than −10 and not more than +5, preferably a lightness index L^*Is 90-100.
[0087]
In order to increase the transparency of the porous layer by setting the lightness index and the perceived chromaticity index of the support surface according to the present invention within the ranges specified in the present invention, the whiteness of the support itself is formed on the porous layer surface. In addition to influencing the ionizing radiation, the halation light reflected by the support when the ionizing radiation is irradiated reciprocates in the porous layer, which is preferable from the viewpoint of irradiation efficiency.
[0088]
As a method of adjusting the value of Lab on the surface side surface provided with the porous layer of the support according to the present invention within the conditions defined in the present invention, various methods may be applied to the base paper layer, the intermediate layer, the undercoat layer, and the like. This is achieved by adding a colorant. The colorant to be added is a well-known white pigment, a blue dye (pigment), a red dye (pigment), a yellow dye (pigment), a fluorescent dye, or the like that is excellent in light resistance and heat resistance. The addition amount can be appropriately changed according to the amount of installation.
[0089]
An undercoat layer is preferably provided on the surface of the support on which the ink receiving layer is to be coated for the purpose of improving the adhesion to the ink receiving layer. The binder for the undercoat layer is preferably a hydrophilic polymer such as gelatin or polyvinyl alcohol, or a latex polymer having a Tg of −30 to 60 ° C. These binders are 1m of inkjet recording paper.²It is used in the range of 0.001 to 2 g per unit. In the undercoat layer, a small amount of a conventionally known antistatic agent such as a cationic polymer can be contained for the purpose of antistatic.
[0090]
A back layer can also be provided on the surface of the support opposite to the surface having the ink receiving layer for the purpose of improving slipperiness and charging characteristics. The binder for the back layer is preferably a hydrophilic polymer such as gelatin or polyvinyl alcohol, a latex polymer having a Tg of −30 to 60 ° C., an antistatic agent such as a cationic polymer, various surfactants, and an average. A matting agent having a particle size of about 0.5 to 20 μm can also be added. The thickness of the back layer is generally 0.1 to 1 μm, but in the case where the back layer is provided for preventing curling, it is generally in the range of 1 to 20 μm. Further, the back layer may be composed of two or more layers.
[0091]
When coating the undercoat layer or the back layer, the surface of the support on which each layer is coated can be subjected to a surface treatment such as corona treatment or plasma treatment.
[0092]
In the water-soluble coating liquid for forming the porous layer according to the present invention, various additives can be added in addition to the constituent elements described above.
[0093]
Such additives include, for example, cationic mordants, crosslinking agents, surfactants (cations, nonions, anions, amphoterics), white color tone adjusting agents, fluorescent whitening agents, antifungal agents, viscosity adjusting agents, low boiling points. Organic solvents, high-boiling organic solvents, latex emulsions, anti-fading agents, ultraviolet absorbers, polyvalent metal compounds (water-soluble or water-insoluble), matting agents, silicone oils, etc. It is preferable in order to improve the water resistance and moisture resistance.
[0094]
As the cationic mordant, a polymer mordant having a primary to tertiary amino group and a quaternary ammonium base is used, but there is little discoloration or deterioration of light resistance under long-term storage, and sufficient dye mordant ability. A polymer mordant having a quaternary ammonium base is preferred because it is expensive.
[0095]
A preferred polymer mordant is obtained as a homopolymer of a monomer having the quaternary ammonium base, a copolymer with another monomer, or a condensation polymer.
[0096]
Examples of the polyvalent metal compound that can be used in the present invention include Mg.²⁺, Ca²⁺, Zn²⁺, Zr²⁺, Ni²⁺, Al³⁺Used in sulfate, chloride, nitrate, acetate, etc. In addition, inorganic polymer compounds such as basic polyaluminum hydroxide and zirconyl acetate are also included as examples of preferable water-soluble polyvalent metal compounds. In general, many of these water-soluble polyvalent metal compounds have functions of improving light resistance and improving bleeding and water resistance. These water-soluble polyvalent metal ions are used in 1 m of inkjet recording paper.²It is generally used in the range of 0.05 to 20 mmol, preferably 0.1 to 10 mmol.
[0097]
In the ink jet recording paper of the present invention, the coating method of each coating liquid for providing each constituent layer on the support can be appropriately selected from conventionally known methods, for example, gravure coating method, roll coating A rod bar coating method, an air knife coating method, a spray coating method, an extrusion coating method, a curtain coating method, or an extrusion coating method using a hopper described in US Pat. No. 2,681,294 is preferably used.
[0098]
The porous layer according to the recording paper of the present invention may be a single layer or may be composed of a plurality of layers of two or more layers. It is preferable to apply simultaneously from the viewpoint of manufacturing cost reduction.
[0099]
Examples of the ionizing radiation in the present invention include electron beams, ultraviolet rays, α rays, β rays, γ rays, and X-rays. However, they are dangerous to the human body, easy to handle, and can be used industrially. Widely used electron beams and ultraviolet rays are preferable.
[0100]
Examples of the electron beam irradiation method include a scanning method, a curtain beam method, and a broad beam method. The curtain beam method is preferable from the viewpoint of processing capability.
[0101]
The acceleration voltage of the electron beam can be changed as appropriate depending on the specific gravity and film pressure of the coating film, but 20 kV to 300 kV is appropriate. The irradiation amount of the electron beam is preferably in the range of 0.1 to 20 Mrad.
[0102]
In the case of ultraviolet irradiation, as the light source, for example, a low pressure, medium pressure, high pressure mercury lamp, metal halide lamp or the like having an operating pressure of several hundred Pa to about 1 MPa is used. Is preferable, and a metal halide lamp is more preferable. Moreover, it is preferable to provide a filter that cuts light having a wavelength of 300 nm or less. The lamp output is 400 to 30 kW, and the illuminance at the emission main wavelength of 350 nm is 1 mW / cm.²~ 1W / cm², Integrated irradiation energy is 1mJ / cm²~ 1J / cm²Is more preferable.
[0103]
When the light source wavelength includes ultraviolet rays of 300 nm or less, or irradiation energy is 1 J / cm²In the case of exceeding the base of the ionizing radiation crosslinkable resin, or various coexisting additives may be decomposed by ionizing radiation, not only the effect of the present invention cannot be obtained, but also the odor derived from the decomposition product, etc. This is not preferable because it may cause problems. Irradiation energy is 1mJ / cm²If it is less than 1, the crosslinking efficiency is insufficient, and the effects of the present invention are not sufficiently obtained.
[0104]
Illuminance during UV irradiation is 1 W / cm²In the case where it exceeds 1, the surface curability of the coating film is improved, but the deep-curability is lowered and a film having only a hard surface can be obtained. In that case, the balance of the hardness in the depth direction of the film is lost, and curling or the like occurs, which is not preferable. Also, the illuminance is 1mW / cm²If it is lower, the crosslinking does not proceed sufficiently due to scattering in the film and the effect of the present invention cannot be obtained, which is not preferable.
[0105]
Same integrated light intensity (mJ / cm²), The preferable range of illuminance is due to the change in the light transmittance. When the concentration distribution of the generated cross-linking reactive species is different depending on the transmittance of ultraviolet rays, and the ultraviolet illuminance is high, a high concentration of cross-linking reactive species is generated on the surface layer, and a firm and dense film is formed on the surface of the coating film.
[0106]
When the illuminance is in a preferable range, the degree of cross-linking of the surface layer is low and light permeability in the deep direction is high, so that gentle cross-linking is uniformly formed in the deep direction.
[0107]
If the illuminance is too low, it takes a long time to give the required integrated illuminance, which is not only disadvantageous in terms of equipment introduction, etc., but also because the amount of absolute light due to scattering of ultraviolet rays by the coating film is insufficient. Absent.
[0108]
When recording an image using the ink jet recording paper of the present invention, a recording method using water-based ink is preferably used.
[0109]
The water-based ink is a recording liquid having the following colorant, liquid medium, and other additives. As the colorant, water-soluble dyes or water-dispersible pigments such as direct dyes, acid dyes, basic dyes, reactive dyes or food dyes known for inkjet can be used.
[0110]
Examples of water-based ink solvents include water and various water-soluble organic solvents, for example, alcohols such as methyl alcohol, isopropyl alcohol, butyl alcohol, tert-butyl alcohol, and isobutyl alcohol; amides such as dimethylformamide and dimethylacetamide; acetone , Ketones such as diacetone alcohol or ketone alcohols; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6 -Polyhydric alcohols such as hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, glycerin, triethanolamine , Ethylene glycol methyl ether, diethylene glycol methyl (or ethyl) ether, lower alkyl ethers of polyhydric alcohols such as triethylene glycol monobutyl ether. Of these, polyhydric alcohols such as diethylene glycol, triethanolamine and glycerin, and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monobutyl ether are preferable.
[0111]
Examples of other water-based ink additives include pH adjusters, metal sequestering agents, fungicides, viscosity modifiers, surface tension adjusters, wetting agents, surfactants and rust inhibitors.
[0112]
In order to improve the wettability with respect to the recording paper, the aqueous ink liquid preferably has a surface tension usually within a range of 25 to 60 mN / m, preferably 30 to 50 mN / m at 20 ° C. The pH of the ink is preferably 5 to 10, particularly preferably 6 to 9.
[0113]
【Example】
Hereinafter, although an example is given and the effect of the present invention is explained, the present invention is not limited to these examples. In the examples, “%” represents mass% unless otherwise specified.
[0114]
Example 1
<< Preparation of silica dispersion >>
[Preparation of Silica Dispersion S-1]
Silica dispersion (pH 2.6, containing 0.5% ethanol) containing 30% gas phase method silica (Nippon Aerosil Co., Ltd .; Aerosil 300) having an average primary particle size of about 7 nm and uniformly dispersed in advance ) Is added to 120 g of an aqueous solution containing 10% cationic polymer P-1 (containing 10% n-propanol and 2% ethanol) with stirring at 3000 rpm at room temperature, and then the pH is adjusted to 1 mol. Adjusted to 4.1 with / L NaOH aqueous solution.
[0115]
Next, 3 kN / cm with a high-pressure homogenizer manufactured by Sanwa Industry Co., Ltd.²And the whole amount was finished with pure water to obtain a substantially transparent silica dispersion S-1 having a silica content of 20%. The obtained silica dispersion S-1 was filtered using a TCP-10 type filter manufactured by Advantex Toyo. The secondary average particle diameter of the silica particles was measured and found to be 35 nm.
[0116]
The secondary average particle size is a value measured by diluting the silica dispersion S-1 50 times and using a dynamic light scattering type particle size measuring device Zeta Sizer 1000HS (manufactured by Malvern).
[0117]
[Preparation of silica dispersion S-2]
Using a high-speed stir disperser, gel method wet silica having an average primary particle size of about 10 nm in a 1% ethanol aqueous solution containing 2.5 g of the cationic polymer P-1 (manufactured by Nippon Silica Kogyo Co., Ltd .; Nippon AZ200) Was gradually dispersed while stirring, and the pH was adjusted to 4.0, and then pure water was added to make 100 g to obtain a silica dispersion having a silica solid content of 20%.
[0118]
Subsequently, the dispersion time was appropriately adjusted with a sand mill to obtain a substantially transparent silica dispersion S-2. The obtained silica dispersion S-2 was filtered using a TCP-10 type filter manufactured by Advantex Toyo. It was 187 nm when the secondary average particle diameter of the silica particle was measured.
[0119]
The secondary average particle size is a value measured by diluting the silica dispersion S-2 50 times and using a dynamic light scattering type particle size measuring device Zeta Sizer 1000HS (manufactured by Malvern).
[0120]
[Preparation of silica dispersion S-3]
A silica dispersion S-3 was prepared in the same manner as in the preparation of the silica dispersion S-2 except that the dispersion time was appropriately adjusted with a sand mill and the secondary average particle diameter of the silica particles was changed to 343 nm.
[0121]
<< Preparation of hydrophilic resin crosslinked by ionizing radiation >>
According to the method described in Examples of JP-A No. 2000-181062, p- (3-methacryloxy-2-hydroxypropyloxy) benzaldehyde is reacted with polyvinyl alcohol having a polymerization degree of 3000 and a saponification degree of 88%, A hydrophilic resin aqueous solution V-1 having an ultraviolet-polymerizable polyvinyl alcohol derivative (crosslinkable group modification rate: 1 mol%, solid content concentration: 8%) having the following structure was obtained.
[0122]
[Chemical formula 5]

[0123]
<Production of recording paper>
[Preparation of recording paper 1]
Weighing 142.5 g / m²Polyethylene laminated paper (0.05 g / m on the ink receiving layer side)²0.2 g / m of a gelatin subbing layer having a latex polymer having a Tg of about 80 ° C. on the opposite side.²The following porous layer coating solution A-1 was applied to the surface of the substrate) using a wire bar, and the coating amount during drying was 18 g / m.²After being applied so that the illuminance at a wavelength of 365 nm is 60 mW / cm, a metal halide lamp having a dominant wavelength at 365 nm²30mJ / cm in energy amount²Were then dried in a hot air oven at 60 ° C. to prepare a recording paper 1.
[0124]

[Preparation of recording paper 2]
In the production of the recording paper 1, the support was weighed 84.3 g / m.²The coated amount when the porous layer coating liquid A-1 is dried is 10 g / m.²A recording paper 2 was prepared in the same manner except that the coating was applied.
[0125]
[Preparation of recording paper 3]
In the production of the recording paper 1, a white polyethylene terephthalate film having a thickness of 80 μm (0.05 g / m on the porous layer coating surface side) was used as the support.²0.2 g / m of a gelatin subbing layer having a latex polymer having a Tg of about 80 ° C. on the opposite side²The recording paper 3 was obtained in the same manner except that the recording paper 3 was changed.
[0126]
[Preparation of recording paper 4]
A recording paper 4 was obtained in the same manner as in the production of the recording paper 1 except that the silica dispersion S-3 was used instead of the silica dispersion S-1.
[0127]
[Preparation of recording paper 5]
In the production of the recording paper 1, the same amount of 10% aqueous solution of polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 88% was used in place of the hydrophilic resin aqueous solution V-1, and an acceleration voltage of 200 kV and an irradiation amount were used instead of ultraviolet rays. A recording paper 5 was obtained in the same manner except that 2 Mrad electron beam was irradiated.
[0128]
[Preparation of recording paper 6]
A recording paper 6 was obtained in the same manner as in the production of the recording paper 1 except that a resin in which the main chain PVA polymerization degree of the hydrophilic resin aqueous solution V-1 was changed to 250 was used.
[0129]
[Preparation of recording paper 7]
In the production of the recording paper 1, a recording paper 7 was obtained in the same manner except that the following porous layer coating liquid A-2 was used instead of the porous layer coating liquid A-1.
[0130]

[Preparation of recording paper 8]
In the production of the recording paper 1, a recording paper 8 was obtained in the same manner except that the following porous layer coating liquid A-3 was used instead of the porous layer coating liquid A-1.
[0131]

[Preparation of recording paper 9]
In the production of the recording paper 1, a recording paper 9 was obtained in the same manner except that the following porous layer coating liquid A-4 was used instead of the porous layer coating liquid A-1.
[0132]

[Preparation of recording paper 10]
In the production of the recording paper 1, a recording paper 10 was obtained in the same manner except that the following porous layer coating liquid A-5 was used instead of the porous layer coating liquid A-1.
[0133]

[Preparation of recording paper 11]
In the production of the recording paper 1, in place of the hydrophilic resin aqueous solution V-1, the same amount of 10% aqueous solution of polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 88% was added, and 0.5 part of boric acid was added, Recording paper 11 was obtained in the same manner except that no ultraviolet rays were irradiated.
[0134]
[Preparation of recording paper 12]
A recording paper 12 was obtained in the same manner as in the production of the recording paper 1 except that ultraviolet rays were not irradiated.
[0135]
[Preparation of recording paper 13]
Recording paper 13 was obtained in the same manner except that a resin whose main chain PVA polymerization degree of hydrophilic resin aqueous solution V-1 was changed to 250 in the production of recording paper OO was used.
[0136]
[Preparation of recording paper 14]
In the production of the recording paper 1, the following porous layer coating solution A-6 was used instead of the porous layer coating solution A-1, and the coating amount during drying was 5 g / m.²The recording paper 14 was obtained in the same manner except that the recording paper 14 was changed.
[0137]

<Evaluation of recording paper>
(Evaluation of film surface properties)
The porous coated surface of each of the prepared recording sheets was visually observed, and crack resistance and film surface smoothness were evaluated according to the following methods.
[0138]
(Evaluation of crack resistance)
10cm²The number of cracks on the film surface was measured.
[0139]
(Evaluation of film surface smoothness)
The film surface smoothness was evaluated according to the following criteria.
[0140]
A: No swell is seen and smooth.
○: Slight long-period undulations are observed, but there is no problem as a product
Δ: Partial film surface failure is observed, and clear film surface blowing can be confirmed, but is within a practically acceptable range.
×: Level of short-period film surface hitting is recognized and is not allowed in practice
XX: Levels that are not allowed at all due to frequent short-circuit undulations and film surface failures due to blowing rough.
(Evaluation of ink absorbency)
Using the ink-jet printer PM900C manufactured by Seiko Epson, the neutral gray color having a reflection density of about 1.0 is printed on the entire surface of each of the recording papers produced above, and the resulting image unevenness is visually observed. The ink absorptivity was evaluated according to the following criteria.
[0141]
1: No unevenness at all
2: Slight unevenness is recognized, but there is no practical problem even if solid printing
3: Unevenness can be clearly seen with solid printing, but there is almost no problem with actual printing.
4: Level of gray color unevenness that is not acceptable in practice
5: Unacceptable level
(Evaluation of crack resistance)
Each of the recording sheets prepared above is cut into a strip of 5 × 10 cm, and this is wound around a paper tube having a core inner diameter of 3 cm so that the porous layer surface is on the outside, and the state of creases (cracks) generated on the surface Visual observation was made and the resistance to cracking was evaluated according to the following criteria.
[0142]
A: No cracking occurred
○: Number of occurrences of cracking is 1 to 5
Δ: The number of cracks generated is 6 to 20
X: Number of occurrences of folding is 21 to 100
XX: Number of occurrences of folding is 101 or more
(Evaluation of color development)
A black maximum density image was printed on each of the produced recording papers using an ink jet printer PM900 manufactured by Seiko Epson, and the reflection density of the obtained black maximum density image was measured using a reflection densitometer.
[0143]
(Lightness index L of porous layer surface^*, Perceptual chromaticity index a^*, Perceptual chromaticity index b^*Measurement)
L of the porous layer coating surface of each recording paper produced above^*, A^*, B^*Was measured with a color chromaticity meter CR-100 manufactured by Minolta Co., Ltd.
[0144]
(Evaluation of white background sensation)
The porous layer-coated surface of each of the recording papers prepared above was visually observed, and sensory evaluation was performed on the white background (hue).
[0145]
The results obtained as described above are shown in Table 1.
[0146]
[Table 1]

[0147]
As is clear from Table 1, it has a porous layer containing inorganic fine particles and a hydrophilic resin that is crosslinked by ionizing radiation, and has a lightness index L on the surface of the porous layer.^*Is 85 or more, perceptual chromaticity index a^*Is -3 or more and +2 or less, and the perceptual chromaticity index b^*It can be seen that the recording paper of the present invention having -4 or more and +3 or less is excellent in all the characteristics of crack resistance, film surface smoothness, ink absorbability, crack resistance, color development and white background.
[0148]
Example 2
[Preparation of recording paper 15]
(Production of support)
Weighing 100g / m consisting of the following blending amounts using a paper machine²A base paper was prepared.
[0149]

Then, using a size press apparatus, the impregnating liquid consisting of the following composition was added to the base paper with a dry mass of 2.0 g / m.²Impregnation was performed.
[0150]
<Impregnating liquid>
Polyvinyl alcohol (manufactured by Kuraray, PVA110) 2.0 parts
Fluorescent dye (Nippon Soda, Kaycoll BUL) 0.2 parts
Conductive agent (Sanyo Chemical Industries, Chemistat 6120) 1.0 part
Next, after the corona discharge treatment is performed on the surface of the base paper, low density polyethylene (density 0.92 g / m) is obtained by a melt extrusion coating method so that the thickness becomes 20 μm.³) 30 parts and high density polyethylene (density 0.96 g / m)³) A backside resin coating layer consisting of 70 parts was provided.
[0151]
Next, after the corona discharge treatment was performed on the surface of the base paper, the surface resin coating layer 1 having the following constitution was provided by a melt extrusion coating method so as to have a thickness of 20 μm, thereby preparing a support.
[0152]
<Surface resin coating layer 1>
Low density polyethylene (density 0.92 g / m³30.0 parts
High density polyethylene (density 0.96g / m³70.0 parts
Anatase type titanium dioxide 10.0 parts
Blue pigment (ultraviolet) 0.5 part
Next, corona discharge treatment is performed on the front and back of the support, and 0.05 g / m on the porous layer surface side.²Of a gelatin subbing layer, and 0.2 g / m of a back layer containing a latex polymer having a Tg of about 80 ° C. on the opposite side²To provide a support.
[0153]
(Coating of porous layer)
On the above-prepared support, the following porous layer coating solution A-7 was applied at a dry coating amount of 18 g / m.²After being applied so that the illuminance at a wavelength of 365 nm is 60 mW / cm, a metal halide lamp having a dominant wavelength at 365 nm²30mJ / cm in energy amount²The recording paper 15 was obtained by drying in a hot air oven at 60 ° C.
[0154]

[Preparation of recording paper 16]
In the recording sheet 15 produced above, the same applies except that the silica dispersion S-1 used in the preparation of the porous layer coating liquid A-7 was changed to the silica dispersion S-2 prepared in Example 1, Recording paper 16 was produced.
[0155]
[Preparation of recording paper 17]
In the recording paper 15 produced above, the same applies except that the silica dispersion S-1 used in the preparation of the porous layer coating liquid A-7 is changed to the silica dispersion S-3 prepared in Example 1. Recording paper 17 was produced.
[0156]
[Preparation of recording paper 18]
A recording paper 18 was obtained in the same manner as in the produced recording paper 15 except that the support was changed to a white polyethylene terephthalate film having a thickness of 100 μm.
[0157]
[Preparation of recording paper 19]
In the recording paper 15 produced above, the support was weighed 84.9 g / m.²The recording paper 19 was obtained in the same manner except that the coated paper was changed to the coated paper.
[0158]
[Preparation of recording paper 20]
A recording paper 20 was obtained in the same manner as in the production of the recording paper 15 except that a resin in which the main chain PVA polymerization degree of the hydrophilic resin aqueous solution V-1 was changed to 250 was used.
[0159]
[Preparation of recording paper 21]
In the production of the recording paper 15, the same amount of 10% aqueous solution of polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 88% was used in place of the hydrophilic resin aqueous solution V-1, and an acceleration voltage of 200 kV and an irradiation amount were used instead of ultraviolet rays. A recording paper 21 was obtained in the same manner except that 2 Mrad electron beam was irradiated.
[0160]
[Preparation of recording paper 22]
A recording paper 22 was obtained in the same manner as in the production of the recording paper 15 except that the surface resin coating layer 1 of the support was changed to the following surface resin coating layer 2.
[0161]
<Surface resin coating layer 2>
Low density polyethylene (density 0.92 g / m³70.0 parts
High density polyethylene (density 0.97 g / m³20.0 parts
White pigment (anatase type titanium dioxide) 5.0 parts
Black pigment (carbon black) 0.008 parts
Blue pigment (ultraviolet) 0.5 part
[Preparation of recording paper 23]
A recording paper 23 was obtained in the same manner as in the production of the recording paper 15 except that the surface resin coating layer 1 of the support was changed to the following surface resin coating layer 3.
[0162]
<Surface resin coating layer 3>
Low density polyethylene (density 0.92 g / m³70.0 parts
High density polyethylene (density 0.97 g / m³20.0 parts
White pigment (anatase type titanium dioxide) 5.0 parts
Blue pigment (ultraviolet) 1.0 part
[Preparation of recording paper 24]
In the production of the recording paper 15, the recording paper 24 was obtained in the same manner except that the amount of the base paper used for the production of the support was changed as follows.
[0163]

[Preparation of recording paper 25]
In the production of the recording paper 15, in place of the hydrophilic resin aqueous solution V-1, the same amount of a 10% aqueous solution of polyvinyl alcohol having a polymerization degree of 3500 and a saponification degree of 88% was added, and 0.5 part of boric acid was added. A recording paper 25 was obtained in the same manner except that the ultraviolet rays were not irradiated.
[0164]
[Preparation of recording paper 26]
A recording paper 26 was obtained in the same manner as in the production of the recording paper 15 except that ultraviolet rays were not irradiated.
[0165]
[Preparation of recording paper 27]
In the production of the recording paper 15, a recording paper 27 was obtained in the same manner except that the following porous layer coating liquid A-8 was used instead of the porous layer coating liquid A-7.
[0166]

<Evaluation of recording paper>
For each recording sheet produced as described above, the lightness index L of the support surface is the same as in the method described in Example 1.^*, Perceptual chromaticity index a^*, Perceptual chromaticity index b^*And the evaluation of crack resistance, film surface smoothness, ink absorptivity, crease resistance, color development and white background, and the results obtained are shown in Table 2.
[0167]
[Table 2]

[0168]
As is apparent from Table 2, it has a porous layer containing inorganic fine particles and a hydrophilic resin that is cross-linked by ionizing radiation, and has a lightness index L of the support surface.^*Is 90 or more, perceptual chromaticity index a^*Is -5 or more and +5 or less, and the perceptual chromaticity index b^*It can be seen that the recording paper of the present invention having -10 or more and +5 or less is excellent in all of the properties of crack resistance, film surface smoothness, ink absorbability, crack resistance, color development and white background.
[0169]
【The invention's effect】
According to the present invention, even when a porous layer composed of a hydrophilic binder and fine particles is applied on a support in a thick film and at a high speed, cracks during production are unlikely to occur, and a highly ink-absorbing and flexible coating film is formed. It was possible to provide an inkjet recording paper having a superior image and a method for producing the same.

Claims (8)

In an inkjet recording paper having a porous layer containing inorganic fine particles and a hydrophilic resin that is cross-linked by ionizing radiation on a support, the surface of the porous layer is a method defined by JIS-Z-8722. When displayed according to the color display method defined in JIS-Z-8730 measured according to the above, the lightness index L ^* in the CIE color space is 85 or more, the perceptual chromaticity index a ^* is −3 or more, and +2 or less. The perceptual chromaticity index b ^* is −4 or more and +3 or less. In an inkjet recording paper having a porous layer containing inorganic fine particles and a hydrophilic resin that is cross-linked by ionizing radiation on a support, the surface of the support that has the porous layer is JIS-Z. When displayed by the color display method specified in JIS-Z-8730 measured according to the method specified in -8722, the lightness index L ^* in the CIE color space is 90 or more, and the perceptual chromaticity index a ^* is An ink jet recording paper having −5 or more and +5 or less and a perceptual chromaticity index b ^* of −10 or more and +5 or less. The inkjet recording paper according to claim 1 or 2, wherein the support is a non-water-absorbing support. The inkjet recording paper according to any one of claims 1 to 3, wherein the inorganic fine particles have an average particle diameter of 5 to 300 nm. The hydrophilic resin crosslinked by the ionizing radiation is a saponified product of polyvinyl acetate, polyvinyl acetal, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or their respective derivatives, And at least one selected from the group consisting of copolymers thereof, at least one selected from an ionizing radiation dimerization type, an ionizing radiation decomposition type, an ionizing radiation polymerization type, an ionizing radiation modified type, and an ionizing radiation depolymerization type The inkjet recording paper according to any one of claims 1 to 4, wherein the inkjet recording paper is modified with a modifying group. The degree of polymerization of the hydrophilic resin modified with the modifying group is 300 or more and 4500 or less, and the modification rate by the modifying group is 0.1 mol% or more and 4 mol% or less. Inkjet recording paper. The method for producing an inkjet recording paper according to any one of claims 1 to 6, wherein a porous layer containing inorganic fine particles and a hydrophilic resin crosslinked by ionizing radiation is applied on a support, A method for producing an inkjet recording paper, characterized by irradiating with ionizing radiation when the solid content concentration of the porous layer is in the range of 5 to 90% by mass and then drying. The ionizing radiation is an ultraviolet ray having an illuminance at a main emission wavelength of 350 nm of 1 mW / cm ² or more and 1 W / cm ² or less and an integrated irradiation energy of 1 mJ / cm ² or more and 1 J / cm ² or less. The manufacturing method of the inkjet recording paper of Claim 7.