JP3561864B2 - Recording paper and its manufacturing method - Google Patents

Description

【００７１】
▲８▼不透明度：ＪＩＳ−Ｐ−８１３８に規定された方法で測定したときに５０％以上、特に９０％以上、最も好ましくは９４％以上が好ましい。
【００７２】
上記支持体と記録層の接着強度を大きくする等の目的で、記録層の塗布に先立って、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。
【００７３】
本発明においては、支持体上に親水性バインダーとしてポリビニルアルコールまたはその誘導体を含有し、かつ無機微粒子として平均粒径が０．０３〜０．００３μｍの平均１次粒子径を有する気相法により合成された微粒子シリカを含有し、更に親水性バインダーを架橋し得る硬膜剤を含有する空隙層を記録層として少なくとも１層有する。
【００７５】
シリカ微粒子は製造法により乾式法と湿式法に大別され、乾式法微粒子シリカとしてはハロゲン化珪素の高温での気相法加水分解による方法、およびケイ砂とコークスを電気炉でアーク法により加熱還元気化しこれを空気酸化する方法が知られている。また、湿式法シリカとしては珪酸塩の酸分解により活性シリカを生成した後、適度に重合させて凝集・沈殿させて得られる。
【００７６】
本発明においてはシリカ微粉末の中でも、特に気相法により合成された無水シリカが特に空隙率と強い皮膜強度が得られる点で好ましい。
【００７７】
上記無機微粒子の平均粒径は、その１次粒子として０．１μｍ以下のものが好ましい。
【００７８】
無機微粒子が気相法シリカである場合には１次粒子の平均粒径が０．００３〜０．０３μｍであり、特に０．００６〜０．０２μｍが最も好ましい。気相法シリカは塗布液中で２次凝集してより大きな粒子を形成することができるが、この場合、２次凝集粒子の平均粒径は０．０３〜０．２μｍが好ましい。
【００７９】
上記において無機微粒子の平均粒径は、粒子そのものあるいは空隙層の断面や表面を電子顕微鏡で観察し、１００個の任意の粒子の粒径を求めてその単純平均値（個数平均）として求められる。ここで個々の粒径はその投影面積に等しい円を仮定したときのその直径で表したものである。
【００８０】
本発明の記録用紙において、上記無機微粒子と組み合わせて用いられる親水性バインダーとしては、ポリビニルアルコールおよびその誘導体を用いるので、インクが含有する高沸点有機溶媒や水に対する膨潤性や溶解性が低く印字直後の皮膜強度の点から好ましい。
【００８１】
本発明で用いることができるポリビニルアルコールまたはその誘導体は、中でも平均重合度が１０００以上、最も好ましくは平均重合度が２０００以上のポリビニルアルコールまたはその誘導体である。また、ケン化度は７０〜１００％が好ましく、特に８０〜１００％が最も好ましい。
【００８２】
上記親水性バインダーは２種以上併用することもできるが、この場合であってもポリビニルアルコールまたはその誘導体を少なくとも５０重量％以上含有してるのが好ましい。
【００８３】
上記ポリビルアルコール誘導体としては、カチオン変性ポリビニルアルコール、アニオン変性ポリビニルアルコールまたはノニオン変性ポリビニルアルコールが上げられる。
【００８４】
カチオン変性ポリビニルアルコールは、カチオン性基を有するエチレン性不飽和単量体と酢酸ビニルとの共重合体をケン化することにより得られる。
【００８５】
カチオン性基を有するエチレン性不飽和単量体としては、例えばトリメチル−（２−アクリルアミド−２，２−ジメチルエチル）アンモニウムクロライド、トリメチル−（３−アクリルアミド−３，３−ジメチルプロピル）アンモニウムクロライド、Ｎ−ビニルイミダゾール、Ｎ−ビニル−２−メチルイミダゾール、Ｎ−（３−ジメチルアミノプロピル）メタクリルアミド、ヒドロキシルエチルトリメチルアンモニウムクロライド、トリメチル−（−メタクリルアミドプロピル）アンモニウムクロライド、Ｎ−（１，１−ジメチル−３−ジメチルアミノプロピル）アクリルアミド等が挙げられる。
【００８６】
カチオン変性ポリビニルアルコールのカチオン変性基含有単量体の比率は、酢酸ビニルに対して０．１〜１０モル％、好ましくは０．２〜５モル％である。
【００８７】
カチオン変性ポリビニルアルコールの重合度は通常５００〜４０００、好ましくは１０００〜４０００が好ましい。
【００８８】
また、酢酸ビニル基のケン化度は通常６０〜１００モル％、好ましくは７０〜９９モル％である。
【００８９】
アニオン変性ポリビニルアルコールは例えば、特開平１−２０６０８８号公報に記載されているようなアニオン性基を有するポリビニルアルコール、特開昭６１−２３７６８１号、および同６３−３０７９７９号公報に記載されているような、ビニルアルコールと水溶性基を有するビニル化合物との共重合体、及び特開平７−２８５２６５号公報に記載されているような水溶性基を有する変性ポリビニルアルコールが挙げられる。
【００９０】
また、ノニオン変性ポリビニルアルコールとしては、例えば、特開平７−９７５８号公報に記載されているようなポリアルキレンオキサイド基をビニルアルコールの一部に付加したポリビニルアルコール誘導体、特開平８−２５７９５号公報に記載された疎水性基を有するビニル化合物とビニルアルコールとのブロック共重合体等が挙げられる。
【００９１】
本発明の記録用紙の空隙層の親水性バインダーに対する無機微粒子の比率は重量比で５倍以上であることが、高い空隙率と高い皮膜強度を得る上で必要である。５倍未満である場合には、空隙率が低下して十分なインク吸収容量が得られにくくなり、また、インクジェット記録後に、親水性バインダー中に残存する高沸点有機溶媒により皮膜の強度が低下しやすい。好ましい無機微粒子の親水性バインダーに対する比率は６以上である。
【００９２】
親水性バインダーに対する無機微粒子の比率の上限は、皮膜のひび割れ性能から概ね２０以下である。
【００９３】
本発明の記録用紙の空隙層中には前記親水性バインダーと架橋し得る硬膜剤を添加するが空隙層の造膜性の改良、皮膜の耐水性、および本発明の目的である印字後の皮膜強度を改善する。そのような硬膜剤としてはエポキシ基、エチレンイミノ基、活性ビニル基等を含有する有機硬膜剤、クロムみょうばん、ほう酸、あるいはほう砂等の無機硬膜剤が挙げられる。
【００９４】
親水性バインダーがポリビニルアルコールであるので、分子中に少なくとも２個のエポキシ基を有するエポキシ系硬膜剤、ほう酸またはその塩、ほう砂が好ましい。ほう酸としてはオルトほう酸だけでなく、メタほう酸や次ほう酸等も使用出来る。
【００９５】
上記硬膜剤の添加量は上記親水性バインダー１ｇ当たり１〜２００ｍｇ、好ましくは２〜１００ｍｇである。
【００９６】
本発明のインクジェット記録用紙のインク受容性層側の任意の層中には、必要に応じて各種の添加剤を含有させることが出来る。
【００９７】
例えば、特開昭５７−７４１９３号公報、同５７−８７９８８号公報及び同６２−２６１４７６号公報に記載の紫外線吸収剤、特開昭５７−７４１９２号、同５７−８７９８９号公報、同６０−７２７８５号公報、同６１−１４６５９１号公報、特開平１−９５０９１号公報及び同３−１３３７６号公報等に記載されている退色防止剤、アニオン、カチオンまたはノニオンの各種界面活性剤、特開昭５９−４２９９３号公報、同５９−５２６８９号公報、同６２−２８００６９号公報、同６１−２４２８７１号公報および特開平４−２１９２６６号公報等に記載されている蛍光増白剤、硫酸、リン酸、酢酸、クエン酸、水酸化ナトリウム、水酸化カリウム、炭酸カリウム等のｐＨ調整剤、消泡剤、ジエチレングリコール等の潤滑剤、防腐剤、増粘剤、帯電防止剤、マット剤等の公知の各種添加剤を含有させることもできる。
【００９８】
本発明の記録用紙のインク吸収性側の任意の構成層中には、画像の耐水化剤として特開昭５６−８４９９２号公報のポリカチオン高分子電解質、特開昭５７−３６６９２号公報の塩基性ラテックスポリマー、特公平４−１５７４４号公報、特開昭６１−５８７８８号公報、同６２−１７４１８４号公報等記載のポリアリルアミン、特開昭６１−４７２９０号公報記載のアルカリ金属弱酸塩等を一種以上用いることができる。
【００９９】
本発明のインクジェット記録用紙におけるインク記録面側の塗布固形分の量は概ね５〜４０ｇ／ｍ^２が好ましく、１０〜３０ｇ／ｍ^２がより好ましい。
【０１００】
本発明の記録用紙をインクジェット用記録用紙として使用する場合には、空隙容量として記録用紙１ｍ^２当たり１０〜４０ｍｌ、好ましくは１５〜３０ｍｌになる範囲に調整されることが好ましい。
【０１０１】
但し、空隙容量はＪ．ＴＡＰＰＩ 紙パルプ試験方法 Ｎｏ．５１−８７紙及び板紙の液体吸収性試験方法（ブリストー法）に記載された方法で記録用紙のインク吸収性側を測定した時、吸収時間が２秒における液体転移量（ｍｌ／ｍ^２）で表される。なお、この時使用する液体は純水（イオン交換水）であるが、測定面積の判別を容易にするために２％未満の水溶性染料を含有していても良い。
【０１０２】
本発明の記録用紙は、前記した空隙層を有する記録層を２層以上有していても良く、この場合、２層以上の空隙層の無機微粒子の親水性バインダーに対する比率はお互いに異なっていてもよい。
【０１０３】
また、上記空隙層以外に、空隙層を有さず、インクに対して膨潤性の層を有していても良い。
【０１０４】
このような膨潤層は空隙層の下層（支持体に近い側）あるいは空隙層の上層（支持体から離れた側）に設けても良く、更には空隙層が２層以上有る場合には空隙層の間に設けられても良い。かかる膨潤性層には通常親水性バインダーが用いられ、ここに用いられる親水性バインダーの例としては、前記空隙層に用いられる親水性バインダーが挙げられる。
【０１０５】
本発明の記録用紙のインク吸収性層を有する側とは反対側にはカール防止や印字直後に重ね合わせた際のくっつきやインク転写を更に向上させるために種々の種類のバック層を設けることが好ましい。
【０１０６】
バック層の構成は支持体の種類や厚み、インク吸収性層の構成や厚みによっても変わるが一般には親水性バインダーや疎水性バインダーが用いられる。バック層の厚みは通常は０．１〜１０μｍの範囲である。
【０１０７】
また、バック層には他の記録用紙とのくっつき防止、筆記性改良、さらにはインクジェット記録装置内での搬送性改良のために表面を粗面化できる。この目的で好ましく用いられるのは粒径が２〜２０μｍの有機または無機の微粒子である。
【０１０８】
次に本発明の記録用紙を製造する方法について説明する。
【０１０９】
本発明の記録用紙は、支持体上に少なくとも空隙層を有する記録層を塗布乾燥して得られる。空隙層を形成する塗布液（親水性バインダー、無機微粒子および必要に応じて適宜添加される前記添加剤を含有する）を支持体上に塗布し、乾燥されるが、この際、塗布液の温度は通常は３０〜５０℃の範囲のものが用いられ、支持体上に塗布後にいったん冷却させてから乾燥させると乾燥時の点状故障が軽減される。
【０１１０】
塗布液をいったん冷却する事により、塗布液の粘度が著しく増大し、塗膜の流動性が低下して搬送時の振動や風の影響による塗膜のムラが大幅に減少する。塗膜のムラが有る場合には、膜厚が増大した箇所での点状故障が増大するだけでなく、部分的に空隙容量にムラが生じて画像品質に重大な影響を起こしかねない。
【０１１１】
塗膜の温度は塗布液の温度より１０℃以上、好ましくは２０℃以上低下させてその状態で水分や低沸点有機溶媒を一部蒸発させる。この状態に達すると塗膜の粘度はいっそう急速に増大しゲル化状態に近づくために、これを過ぎると乾燥温度を増加させても塗膜が動かなくなり高温の風を送り急速に乾燥してもムラや点状故障のない良好な塗膜面が得られる。
【０１１２】
いったん冷却する温度は塗布液の無機微粒子の粒径、濃度、親水性バインダーの種類や濃度、硬膜剤の種類や量、更には無機微粒子と親水性バインダーとの相互作用など種々の因子により変わりうるが、通常は０〜２０℃、好ましくは５〜１５℃である。
【０１１３】
冷却時間は冷却温度や湿潤膜厚などにより変わりうるが通常は５〜２００秒、好ましくは１０〜６０秒である。
【０１１４】
冷却後の乾燥は、通常は徐々に乾燥温度を挙げるのが好ましい。通常は室温付近の温度で一定時間乾燥後、最終的には４０〜６０℃の温風で乾燥される。
【０１１５】
上記の目的のために、塗布液の粘度特性は特に重要である。好ましくは塗布温度で５〜５００ｃｐ程度の塗布液であり、冷却時に１０００ｃｐ以上、特に好ましくはゲル化状態に成るように調整される。
【０１１６】
特に塗布液温度と冷却時の温度の粘度比が１００倍以上になるようにするのが好ましい。
【０１１７】
上記空隙層を支持体上に塗布する方法は公知の方法から適宜選択して行うことが出来る。塗布方式としては、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、カーテン塗布方法あるいは米国特許第２，６８１，２９４号公報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。
【０１１８】
次に本発明で用いることができる水性インクについて以下に説明する。
【０１１９】
水性インクは、通常は水溶性染料及び液媒体、その他の添加剤から成る記録液体である。水溶性染料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が使用できるが直接染料、または酸性染料が好ましい。
【０１２０】
水性インクの溶媒は水を主体としてなるが、インク液が乾燥した際に染料が析出してノズル先端やインク供給経路での目詰まりを防止するために、通常沸点が約１２０℃以上で室温で液状の高沸点有機溶媒が使用される。高沸点有機溶媒は水が蒸発した際に染料などの固形成分が析出して粗大析出物の発生を防止する作用を持つために水よりはるかに低い蒸気圧を有することが要求される一方、水に対して混和性が高い必要がある。
【０１２１】
そのような目的で高沸点有機溶媒としては高沸点の有機溶媒が通常多く使用されるが、具体例としては、エチレングリコール、プロピレングリコール、ジエチレングリコール、トリエチレングリコール、グリセリン、ジチレングリコールモノメチルエーテル、ジエチレングリコールモノブチルエーテル、トリエチレングリコールモノブチルエーテル、グリセリンモノメチルエーテル、１，２，３−ブタントリオール、１，２，４−ブタントリオール、１，２，４−ペンタントリオール、１，２，６−ヘキサントリオール、チオジグリコール、トリエタノールアミン、ポリエチレングリコール（平均分子量が約３００以下）等のアルコール類が挙げられる。また、上記した以外にも、ジメチルホルムアミド、Ｎ−メチルピロリドン等も使用できる。
【０１２２】
これらの多くの高沸点有機溶媒の中でも、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、トリエタノールアミ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。
【０１２３】
水性インクが含有するその他の添加剤としては、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。
【０１２４】
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及びインクジェットノズルからの吐出を安定化させる目的で、２５℃において、２５〜５０ｄｙｎｅ／ｃｍ、好ましくは２８〜４０ｄｙｎｅ／ｃｍの範囲内の表面張力を有するのが好ましい。
【０１２５】
また、水性インクの粘度は通常２５℃において２〜８ｃｐ、好ましくは２．５〜５ｃｐである。
【０１２６】
水性インクのｐＨは通常４〜１０の範囲である。
【０１２７】
インクノズルから吐出される最小インク液滴としては１〜３０×１０^−３ｎｌの容量の場合、記録紙上で約２０〜６０μｍの直径の最小ドット径が得られるので好ましい。このようなドット径で印字されたカラープリントは高画質画像を与える。好ましくは２〜２０×１０^−３ｎｌの容積を有する液滴が最小液滴として吐出される場合である。
【０１２８】
また、前記水性インクが、少なくともマゼンタおよびシアンについて、各々濃度が２倍以上異なる２種類のインクで記録する方式において、ハイライト部では低濃度のインクが使用されるためにドットの識別がしにくくなるが、本発明はかかる記録方式を採用した場合も適用できる。
【０１２９】
インクジェット記録方法において、記録方法としては、従来公知の各種の方式を用いることができ、その詳細はたとえば、インクジェット記録技術の動向（中村孝一編、平成７年３月３１日、日本科学情報株式会社発行）に記載されている。
【０１３０】
本発明のインクジェット記録方法において、最大インク量における高沸点有機溶媒量に対する空隙容量を３倍以上にする方法は高沸点有機溶媒のインク中の比率を下げる、最大吐出インク量を出来るだけ少なくする、記録用紙の空隙容量を膜厚を出来るだけ多くする等の方法を適宜組み合わせて最適な条件を設定し選択される。
【０１３２】
【実施例】
以下に本発明の実施例を挙げて説明するが、本発明はこれらの例に限定されるものではない。
【０１３３】
実施例１
１６０ｇ／ｍ^２の写真用原紙の両面をポリエチレンで被覆した紙支持体（記録面側の厚さ４０μｍのポリエチレン層中にアナターゼ型二酸化チタンを１３重量％含有。裏面側のポリエチレン層の厚みは２５μｍでポリエチレン層の上にＴｇ＝６５℃のアクリル径ラテックス樹脂を固形分として０．６ｇ／ｍ^２および平均粒径が約１３μｍのシリカをマット剤として０．３ｇ／ｍ^２含有するバック層を有する）を用意した。
【０１３４】
上記ポリエチレン被覆紙の特性として、光沢度、Ｗ_ＣＭ、最大高さ（ＪＩＳ−０６０１に従って求められる基準長さが２．５ｍｍ当たりの最大高さ、μｍ単位）を求め、表１に示した。
【０１３５】
次に平均粒径が約７ｎｍの１次微粒子シリカ粉末１５０ｇを純水１０００ｍｌ中に添加し、高速ホモジナイザーで分散して青白い澄明な分散液を得た。次にこのシリカ水分散液（Ｉ）中に、平均重合度が３５００でケン化度が８８％の２％ポリビニルアルコール水溶液（ＩＩ）（酢酸エチルを６重量％含有）１０００ｍｌを徐々に添加した。ついで硬膜剤として４％ほう砂水溶液４０ｍｌを添加し、高速ホモジナイザーにて分散して白色半透明状の塗布液を得た。この液はシリカをポリビニルアルコールに対して重量比で７．５倍含有している。また、上記塗布液の粘度はＢ型粘度計で測定したときに、４０℃で６０ｃｐ、１５℃で測定したとき５万ｃｐであった。
【０１３６】
ついで上記のようにして得られた４０℃の塗布液を、上記のポリエチレン被覆紙の記録面側に塗布し、塗布皮膜温度が１５℃以下に成るようにいったん冷却させた（２０秒間）。ついで２０℃の風を３０秒間、２５℃の風を３０秒間、３５℃の風を６０秒間、更に４５℃の風を１２０秒間順次吹き付けて乾燥し、さらに２５℃、相対湿度５０％の雰囲気を３０秒間通過させて調湿して記録用紙−１を作製した。
【０１３７】
次に、記録用紙−１において、支持体の原紙として平滑性の異なる種々の原紙を使用し記録用紙−１と同じポリエチレン層を表裏に被覆した記録用紙−２〜４を記録用紙−１と同様にして作製した。記録用紙−１〜４のポリエチレン被覆後の光学的特性および平滑性を表１に示した。
【０１３８】
記録用紙−１〜４は塗布乾燥後、ロール状に巻いた状態で３９℃で３日間保存した。
【０１３９】
得られた記録用紙について以下の項目について評価した。
【０１４０】
（１）空隙容量
熊谷理機工業株式会社製、Ｂｒｉｓｔｏｗ試験機ＩＩ型（加圧式）を使用し、接触時間２秒間における転移量（ｍｌ／ｍ^２）を空隙容量として求めた。
【０１４１】
（２）インク吸収性
空隙容量を測定したのと同じ試験機を用い、接触時間が０．５秒における転移量（ｍｌ／ｍ^２）からインク吸収性を求めた。
【０１４２】
（３）光沢度
日本電色工業株式会社製変角光度計（ＶＧＳ−１０１ＤＰ）で７５度鏡面光沢を測定した。
【０１４３】
（４）故障欠陥
１０×１０ｃｍの塗布試料について、表面の点状欠陥個数を調べた。
【０１４４】
（５）皮膜強度
セイコーエプソン株式会社製インクジェットプリンター、ＭＪ−５１００Ｃでベタ印字後、２３℃、相対湿度が８０％で２４時間保存してから同じ環境で引っ掻き強度試験機（ヘイドン・トライボギア、新東科学株式会社製）を用い、先端が０．３ｍｍφのサファイヤ針に、０〜１００ｇの連続荷重をかけて皮膜強度を試験し、皮膜が破壊される強度を皮膜強度とした。
【０１４５】
この評価方法で概ね３０ｇ以上であれば実用上十分高い皮膜強度を有していると言える。
【０１４６】
なお、（１）（２）において、使用したインクはジエチレングリコールを２０重量％、水溶性マゼンタ染料を１重量％含有するインクを使用した。結果を表１に示す。
【０１４７】
【表１】

【０１４８】
表１の結果から、原紙の種類を変えてポリエチレン樹脂で被覆後の表面特性を変化させた場合、Ｗ_ＣＭが４μｍ以下である記録用紙−１〜３は、Ｗ_ＣＭが４μｍを超える記録用紙−４に比べて故障欠陥が少ないことがわかる。
【０１４９】
特にＷ_ＣＭが２μｍ以下である支持体を使用した場合には故障欠陥が０で好ましい。
【０１５０】
また、支持体の差により、空隙容量や、インク吸収性は殆ど影響を受けず、乾燥膜厚が３０μｍ以上で、高い空隙率（大凡６３％）を有しているために通常のインクジェット記録でほぼ十分な空隙容量を保持している。
【０１５１】
実施例２
実施例１で作製した記録用紙−１において、記録面側のポリエチレン層の厚みを表２に示すように変化させたポリエチレン被覆紙支持体を用意し実施例１で作製した空隙層を形成する塗布液を実施例１と同様に塗布して記録用紙−２１〜２４を作製した。一方、実施例１で作製した記録用紙−１において、表側のポリエチレン層を原紙上に塗設直後に表面を種々の片づけ処理を行い、表面特性の異なる記録用紙−２５〜２７を記録用紙−１と同様にして作製した。
【０１５２】
記録用紙−２５の支持体はいわゆる絹目面と称されるようなピッチの長さが数百μｍ単位の片付けであり、記録用紙−２７の支持体は片づけはいわゆるマット面と称されるような微細な無光沢面である。記録用紙−２６はこれらの中間である。
【０１５３】
更に、記録用紙−２８の支持体は記録用紙−１の支持体表面を４０℃のアセトン溶液で処理して粗面化したものである。通常これらの粗面かは支持体と記録層の接着性の増大に効果がある。
【０１５４】
記録用紙−２１〜２８のポリエチレン被覆紙の表面特性および記録層を塗布後の特性を実施例１と同様にして評価した。結果を表２に示す。
【０１５５】
【表２】

【０１５６】
表２の結果から、Ｗ_ＣＭが４μｍ以下である本発明の記録用紙−２１、２２、および２３は、比較の記録用紙−２４に比較して故障欠陥が少ないことがわかる。また、実施例１と同様に特にＷ_ＣＭが２μｍ以下の記録用紙−２１が特に優れていることがわかる。
【０１５７】
一方、ポリエチレン樹脂層の表面を片付け処理したり粗面化して支持体の光沢性が低いものを使用した場合であっても、Ｗ_ＣＭが４μｍ以下である記録用紙−２７、２８は故障欠陥が少ないことがわかる。また片付け支持体の中でもＷ_ＣＭが４μｍを超える場合には故障欠陥が急速に増加することがわかる。
【０１５８】
比較例１
実施例１で作製した記録用紙−４用のポリエチレン被覆紙支持体上に、実施例１で作製した塗布液を湿潤膜厚を変化させて表３に示すような乾燥膜厚を有する記録用紙−３１〜３４を記録用紙−４と同様にして作製した。
【０１５９】
実施例１と同様に評価して表３に示す結果を得た。
【０１６０】
【表３】

【０１６１】
表３の結果から、Ｗ_ＣＭが４μｍを超える支持体を使用しても、乾燥膜厚を減少させていくと故障欠陥は低下してくるが、これに伴い空隙容量が徐々に低下してくるので、記録用紙−３１〜３４は実用的に使用する事は出来ない。
【０１６２】
実施例３
実施例１で作製した記録用紙−１〜４において、微粒子シリカを１次粒子の平均粒径が約２０ｎｍの気相法シリカに変えた以外は記録用紙−１〜４と同様にして記録用紙−４１〜４４を作製した。実施例１と同様に評価し、表４に示す結果を得た。
【０１６３】
【表４】

【０１６４】
表４の結果から、実施例１と同様の効果が得られることがわかる。但し、シリカの１次粒子の粒径の増大に伴い記録面の光沢性が実施例１より僅かに低下し、また、空隙容量は若干増加している。
【０１６５】
比較例２
平均粒径が約７ｎｍの１次微粒子シリカ粉末１５０ｇを純水１０００ｍｌ中に添加し、高速ホモジナイザーで分散して青白い澄明な分散液を得た。次にこのシリカ水分散液（Ｉ）中に、平均重合度が３５００でケン化度が８８％の２％ポリビニルアルコール水溶液（ＩＩ）（酢酸エチルを６重量％含有）２０００ｍｌを徐々に添加した。ついで硬膜剤として４％ほう砂水溶液４０ｍｌを添加し、高速ホモジナイザーにて分散して白色半透明状の塗布液を得た。この液はシリカをポリビニルアルコールに対して重量比で３．７５倍含有している。
【０１６６】
実施例１において使用した記録用紙−１〜４のポリエチレンで被覆紙上に上記の塗布液を乾燥膜厚が実施例１と同じ様になるように湿潤膜厚が１７０μｍになるように塗布し、実施例１に記載された方法で乾燥して記録用紙−５１〜５４を作製した。実施例１と同様に評価し、表５に示す結果を得た。
【０１６７】
【表５】

【０１６８】
表５に示す結果から、無機微粒子の親水性バインダーに対する比率を５以下にした場合には、故障欠陥は支持体としてＷ_ＣＭが４μｍを超えるものを使用してもほとんど生ぜず、記録面の光沢性も非常に高いが、空隙容量が低下し、また、皮膜の強度が大きく低下することがわかる。
【０１６９】
【発明の効果】
以上、本発明に従えば、高インク吸収性、高光沢性、高塗膜強度を有し、しかも点状故障を大きく減少させたインクジェット記録用紙が得られる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention,IHigh ink absorption, high gloss and high film strength in ink jet recording, with few film defectsInkjetThe present invention relates to a recording sheet and a method for manufacturing the recording sheet.
[0002]
[Prior art]
Ink-jet recording is the recording of images and characters by flying fine droplets of ink by various operating principles and attaching them to a recording sheet such as paper. Has an advantage that it is easy. With regard to nozzle clogging and maintenance, which has been a problem in the past, improvements have been made in both ink and equipment, and it is now rapidly spreading to various fields such as various printers, facsimile machines and computer terminals. .
[0003]
The details are described, for example, in the trend of inkjet recording technology (Koichi Nakamura, edited by Nihon Kagaku Information Co., Ltd., March 31, 1995).
[0004]
The recording paper used in this ink jet recording system has a high density of print dots, a bright and vivid color tone, and the ink does not flow out or bleed even when the print dots overlap with each other because of rapid ink absorption. Generally, it is generally required that the diffusion of print dots in the horizontal direction is not unnecessarily large and that the periphery is smooth and not blurred.
[0005]
Conventionally, various recording papers have been used as ink jet recording paper. For example, various types of coated paper (art paper, coated paper, cast coated paper, etc.) in which a layer composed of a hydrophilic binder and an inorganic pigment is coated on a plain paper or paper support, and further, these papers, transparent or opaque Recording paper in which an ink-absorbing layer is coated as a recording layer on various plastic film supports or various supports in which both sides of paper are coated with a plastic resin is used.
[0006]
The ink absorbing layer is roughly classified into a so-called swelling type ink absorbing layer mainly composed of a hydrophilic binder and a void type ink absorbing layer having a void layer in a recording layer.
[0007]
The advantage of the swellable ink absorbing layer is that after the ink solvent (water and high boiling point organic solvent) is completely evaporated, a very high gloss and a high maximum density can be obtained. Printing is slower than the gap-type recording paper, causing problems such as beading in the high ink area and the image quality is likely to be degraded due to the occurrence of roughness, and furthermore, the evaporation of the ink solvent, especially the high boiling point organic solvent, is extremely slow. For a while after that, there is a problem that the high-boiling organic solvent remains in the hydrophilic binder and the hydrophilic binder is swelled and placed in a wet state for a long time.
[0008]
Specifically, the printing surface cannot be strongly rubbed or paper cannot be overlapped for several hours after printing, and in some cases for several days.
[0009]
On the other hand, the void-type ink-absorbing layer exhibits high ink-absorbing properties due to the presence of voids in the recording layer. Therefore, beading of an image in a high ink region is less likely to occur than in a swelling type, and image quality is less deteriorated in a high density region.
[0010]
In addition, the void-type ink-absorbing layer, if the void volume is sufficient with respect to the amount of ink, even if the organic solvent remains in the void structure, at least the surface becomes apparently dry immediately after printing, It is also possible to touch the surface or overlap prints.
[0011]
Fine particles having a low refractive index (especially a refractive index of about 1.6 or less is preferable) and a small particle diameter (especially 200 nm or less) are used as the ink-absorbing layer of this type because a relatively transparent layer is formed. Is preferred), and among them, silica fine particles satisfying the above conditions are particularly preferably used since voids are efficiently formed, relatively high glossiness is obtained, and an image with high maximum density is obtained.
[0012]
Conventional techniques for using such inorganic fine particles having a small particle size in ink jet recording paper include, for example, JP-A-57-14091, JP-A-60-219083, JP-A-60-219084, JP-A-2-274857 and JP-A-2-274857. 4-93284, 5-51470, 7-179029, 7-137431, 8-25800, 8-67064 and 8-118790. JP-B-3-56552, JP-A-63-170074, JP-A-2-113986, JP-A-2-187383, JP-A-7-276789, JP-A-8-34160, JP-A-8-132728, and 8- Fine particle silica synthesized by a gas phase method described in each of JP-A Nos. 174992, for example, Japanese Patent Publication Nos. 3-24906 and 3-24. No. 07, No. 6-98844, No. 7-2430, No. 121609, JP-A-60-245588, JP-A-2-43083, JP-A-2-198889, JP-A-2-263683, JP-A-8-112964 And porous hydrates or hydrates thereof described in JP-A Nos. 8-197832 and 8-258397, for example, JP-A Nos. 57-120486, 57-129778, 58-55283, No. 61-20792, No. 63-57277, JP-A-4-25091, JP-A-3-251487, JP-A-4-2,50091, JP-A-4-260092, and fine-particle calcium carbonate described in JP-A-7-40648 and the like. And the like.
[0013]
The recording paper having the above-mentioned void-type ink absorbing layer on a support is particularly excellent in that high gloss, high porosity, and high maximum density can be obtained, and uses a support having relatively high flatness. In this case, a recording paper having a high glossy surface is obtained.
[0014]
As the weight ratio of the inorganic fine particles to the hydrophilic binder in the void layer increases, the porosity increases, and good ink absorbability can be easily achieved with a smaller coating amount, but the flexibility of the film decreases. However, minute cracks easily occur on the application surface. In particular, when the ratio of the inorganic fine particles to the hydrophilic binder exceeds 5 times in weight ratio, this problem tends to be remarkable.
[0015]
Although this cracking can be greatly improved by adding a hardener capable of crosslinking with a hydrophilic binder, there is a problem that a small number of spot-like defects on the coated surface still remain. As a result of various studies on the cause, it was found that this problem is related to the rigidity of the gap layer and the flatness of the support surface.
[0016]
In other words, in the process of shrinking during drying after application of the void layer, the film gradually becomes a hard film, but the rigidity of the film at this time is too high, so that minute undulations and irregularities on the support surface are obtained. As a result, it was found that minute cracks were locally formed in the film.
[0017]
The above problem is too large when the recording layer is substantially 5% by weight with respect to the hydrophilic binder, even when the recording layer is substantially composed of a hydrophilic binder or when inorganic fine particles are used. Less likely to be a problem.
[0018]
The above problem is more likely to occur when local unevenness in the drying speed of the coated surface is apt to occur during the drying process. In addition, high smoothness is obtained by mainly using fine particles having an average primary particle diameter of 100 nm or less as inorganic fine particles. It has also been found that recording paper having a high glossy recording surface is more likely to occur.
[0019]
JP-A-8-174992 discloses an ink jet recording paper which obtains high glossiness by using inorganic fine particles having an average particle size of 10 nm or less and a hydrophilic binder on a polyolefin-coated paper support having a mirror glossiness of 80% or more. Is described. However, simply defining the glossiness of the surface of the support does not necessarily solve the above problem.
[0020]
[Problems to be solved by the invention]
The present invention has been made in view of the above situation, and an object of the present invention is to have a void layer as a recording layer on a support.InkjetImproves point defects and cracks on the coated surface during the production of recording paper, and has high ink absorption, gloss, and film strengthInkjetAn object of the present invention is to provide a recording sheet and a method for manufacturing the recording sheet.
[0021]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitutions.
[0022]
(1)Paper coated on both sides with plastic resinOn a support, a hydrophilic binder andContaining polyvinyl alcohol or a derivative thereof, andInorganic fine particlesHardener containing fine-particle silica synthesized by a gas phase method having an average primary particle diameter of 0.03 to 0.003 μm as an average particle diameter, and further capable of crosslinking a hydrophilic binderHas at least one recording layer having a void containing the same, and the ratio of the inorganic fine particles to the hydrophilic binder in the recording layer is 5 times or more by weight.InkjetIn recording paper,Paper coated on both sides with plastic resinThe maximum waviness was measured with a reference length of 2.5 mm for a waviness curve derived from a cross-sectional curve measured in accordance with JIS-B-0610 with a cutoff value of 0.8 mm from the surface characteristics of the support on the recording layer side. The maximum undulation is 4 μm or lessInkjetRecording sheet.
[0023]
(2) The recording layer as described in (1) above, wherein a dry film thickness of the recording layer is 30 μm or more.InkjetRecording sheet.
[0024]
(3) The glossiness of the surface of the recording layer, wherein the 75-degree specular glossiness specified in JIS-Z-8741 is 50% or more.InkjetRecording sheet.
[0025]
(4)Inkjet recording paper that can record with water-soluble inkThe method according to any one of the above items 1 to 3, whereinInkjetRecording sheet.
[0029]
(5) On a paper support in which both sides of a base paper are coated with a plastic resin, polyvinyl alcohol or a derivative thereof is contained as a hydrophilic binder, and the average primary particle diameter is 0.03 to 0.003 μm as inorganic fine particles. Having at least one recording layer having voids containing a hardening agent capable of crosslinking a hydrophilic binder, which contains fine-particle silica synthesized by a gas phase method, wherein the recording layer has an inorganic property with respect to the hydrophilic binder. The ratio of the fine particles is 5 times or more by weight, and the surface characteristics of the recording medium side of the paper support in which both sides of the base paper are coated with the plastic resin are cut off from the cross-sectional curve measured according to JIS-B-0610. When the maximum swell of the filtered swell was measured with a reference length of 2.5 mm for the undulation curve derived under the condition of the value 0.8 mm, the maximum swell was 4 μm In the method for producing an ink jet recording paper, a coating liquid for forming the recording layer is applied on a paper support having both sides of the base paper coated with a plastic resin, and then cooled and dried once. Manufacturing method of ink jet recording paper.
[0031]
Hereinafter, the present invention will be described in detail. As the support used for the recording paper of the present invention,, BothPaper support coated on the surface with polyolefinBody is preferred.
[0035]
Further, as the paper support coated on both sides with polyolefin, a paper support coated on both sides with polyethylene, which is conventionally used in conventional color printing paper, is preferable. In this case, the polyethylene resin layer on the ink-absorbing layer side contains 7 to 15% by weight of anatase or rutile type titanium oxide with respect to polyethylene to improve the opacity and whiteness of the support, or It is preferable because the sharpness of the obtained image is not reduced.
[0036]
In the present invention, BothUses paper support coated on its surface with polyolefinBecauseThis is preferable from the viewpoint of the effects of the present invention, that is, the suppression of the occurrence of point-like defects on the coated surface in the manufacturing stage.
[0037]
After the coating solution for forming the recording layer is coated on the support, the drying process is usually performed by blowing air to the coated surface as necessary while passing the coated body through an area in a high temperature state. In this case, the coating surface temperature is usually lower than the ambient temperature due to the heat of evaporation of moisture, and the supply of heat energy for drying is performed by transferring heat from the back surface of the support to the recording layer rather than the front surface. Mainly done.
[0038]
When the support is made of a plastic film, since there is no porous layer, the distribution of heat energy caused by partial non-uniformity of various rollers and the like contacting the back surface of the support directly appears on the coating surface. As a result, uneven drying is likely to occur, and as a result, point-like defects are likely to occur.
[0039]
On the other hand, in the case of a paper support having a porous layer on both sides coated with a polyolefin resin, such defects are more likely to occur because heat variations are easily alleviated in the lateral direction in the paper layer. Hateful.
[0040]
The support used for the recording paper of the present invention has a surface length on the recording layer side, which is a reference length of a filter waviness curve derived from a cross-sectional curve measured according to JIS-B-0610 under a cutoff value of 0.8 mm. When the maximum undulation is measured at 2.5 mm, the maximum undulation is 4 μm or less.
[0041]
Here, the cross-sectional curve is a curve that appears at the cut end when cut on a plane perpendicular to the surface of the recording paper. It is a curve obtained by removing components. The cutoff value is a wavelength corresponding to a frequency at which the gain becomes 70% when a low-pass filter having an attenuation rate of -12 dB / oct is used to obtain a filtered undulation curve. Maximum wave height (W_CM) In μm unit.
[0042]
In the present invention, as the maximum undulation, a value obtained by measuring the maximum undulation at an arbitrary 10 locations and obtaining an average value thereof is used.
[0043]
In the present invention, the surface undulation was performed using a stylus type surface roughness meter (Surfcom 1500A, manufactured by Tokyo Seimitsu Co., Ltd.).
[0044]
In the above, representing the smoothness of the support by the filtered maximum swell is a method of representing the smoothness of the support, which is necessary for obtaining the effects of the present invention, depending on the unevenness of the shorter wavelength of the support surface. This is because it is hardly affected.
[0045]
The greater the dry film thickness of the recording layer having voids, the greater the influence of irregularities having longer wavelengths on point defects. In particular, when the dry film thickness exceeds 30 μm, the contribution of minute irregularities on the surface of the support is almost negligible, and the contribution of longer wave length undulation is generally remarkable.
[0046]
The lower limit of the dry film thickness is determined by the porosity of the film and the required amount of porosity, but is generally 15 μm or more, preferably 20 μm or more.
[0047]
The above W on the surface of the support_CMIs more than 4 μm, a point-like failure is likely to occur during coating and drying of the void layer. Preferably W_CMIs 3 μm or less, particularly preferably 2 μm or less.
[0048]
As a technique close to the constitution of the present invention, JP-A-8-174992 discloses that an inorganic fine particle having an average particle diameter of 10 nm or less and a hydrophilic binder are coated on a polyolefin-coated paper support having a specular gloss of 80% or more. Ink jet recording paper that uses and obtains a high gloss is described, but the flatness characteristics required for the high gloss are not the relatively long irregularities of the present invention but the short wavelength irregularities as in the present invention. Are distinctly different.
[0049]
In addition, the effect of the flatness of the support on the glossiness becomes less affected by the flatness of the support as the dry film thickness of the recording layer becomes larger, and the effect depends exclusively on the glossiness of the gap layer itself. However, the point-like failure, which is an effect of the present invention, generally increases with an increase in the dry film thickness, and the effect is more easily influenced by the support as the dry film thickness increases.
[0050]
The above-mentioned minute irregularities having a short wavelength can be obtained by measuring with the above-described measuring instrument under the conditions without performing high-frequency cutoff (for example, a method described in JIS-B-0601). Are also measured.
[0051]
The effect of the present invention can be obtained if the condition of the undulation is within the range of the present invention. However, when the measurement is performed with the above-described component having a short wavelength, the reference length obtained by JIS-B-0601. The maximum height per 5 mm is preferably 6 μm or less, and particularly preferably 4 μm or less.
[0052]
Next, a paper support coated on both sides with a polyolefin, which is particularly preferably used, will be described.
[0053]
The base paper used for the paper support is mainly made of wood pulp, and if necessary, is made of synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester in addition to wood pulp. As the wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, and NUKP can be used, but it is preferable to use LBKP, NBSP, LBSP, NDP, and LDP which contain a large amount of short fibers. However, the ratio of LBSP and / or LDP is preferably 10% by weight or more and 70% by weight or less.
[0054]
As the pulp, a chemical pulp containing less impurities (sulfate pulp or sulfite pulp) is preferably used, and pulp having improved whiteness by a bleaching treatment is also useful.
[0055]
Base paper contains sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc, and titanium oxide; paper strength agents such as starch, polyacrylamide, and polyvinyl alcohol; fluorescent whitening agents; and polyethylene glycols. , Etc., a water retention agent, a dispersing agent, a softening agent such as quaternary ammonium and the like can be appropriately added.
[0056]
The freeness of the pulp used for papermaking is preferably 200 to 500 cc according to the specification of CSF, and the fiber length after beating is 24 mesh residual weight% and 42 mesh residual weight specified in JIS-P-8207. % Is preferably 30 to 70%. In addition, it is preferable that the weight% of the remaining 4 mesh is 20% by weight or less.
[0057]
The basis weight of the base paper is preferably from 60 to 250 g, particularly preferably from 90 to 200 g. The thickness of the base paper is preferably 50 to 250 μm.
[0058]
The base paper may be calendered at the papermaking stage or after the papermaking to provide high smoothness. Base paper density is 0.7 to 1.2 g / m²(JIS-P-8118) is common. Further, the rigidity of the base paper is preferably from 20 to 200 g under the conditions specified in JIS-P-8143.
[0059]
A surface sizing agent may be applied to the base paper surface, and the same sizing agent as the sizing agent that can be added to the base paper can be used as the surface sizing agent.
[0060]
The pH of the base paper is preferably 5 to 9 when measured by the hot water extraction method specified in JIS-P-8113.
Polyethylene is particularly preferred as the polyolefin covering the front and back surfaces of the base paper, and is mainly low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE), but other LLDPE (linear low-density polyethylene) and polypropylene are also available. Some can be used.
[0061]
In particular, as the polyethylene layer on the ink receiving layer side, it is preferable to add rutile or anatase type titanium oxide to polyethylene to improve opacity and whiteness as widely used in photographic printing paper. The content of titanium oxide is about 3 to 20% by weight, preferably 5 to 15% by weight, based on polyethylene.
[0062]
The amount of polyethylene used on the front and back of the base paper is selected so as to optimize the curl in low humidity and high humidity conditions after providing the ink receiving layer and the back layer. The thickness is 50 μm, and the thickness on the back layer side is 10 to 40 μm.
[0063]
Further, the polyethylene-coated paper support preferably has the following characteristics.
[0064]
{Circle around (1)} Tensile strength: It is preferable that the tensile strength is specified by JIS-P-8113 and that the longitudinal direction is 2 to 30 kg and the horizontal direction is 1 to 20 kg.
[0065]
(2) The tear strength is preferably 10 to 300 g in the vertical direction and 20 to 400 g in the horizontal direction according to the method specified in JIS-P-8116.
[0066]
(3) Clark stiffness: 20 to 400 g / 100 is preferable.
[0067]
(4) Compression modulus ≧ 10³kgf / cm²
{Circle around (5)} Surface smoothness: Beck smoothness specified in JIS-P-8119 is preferably 500 seconds or more, particularly preferably 1000 seconds or more.
[0068]
{Circle around (6)} Surface gloss: 30% or more, preferably 70% or more, particularly preferably 90% or more when measured at a 75-degree angle by the method specified in JISZ-8741.
[0069]
{Circle around (7)} Surface whiteness: measured according to the method described in JIS-Z-8722 and displayed according to JIS-Z-8729,
[0070]
[Outside 1]

[0071]
{Circle around (8)} Opacity: When measured by the method specified in JIS-P-8138, it is preferably 50% or more, particularly 90% or more, and most preferably 94% or more.
[0072]
Prior to the application of the recording layer, the support is preferably subjected to a corona discharge treatment, an undercoating treatment, or the like, for the purpose of increasing the adhesive strength between the support and the recording layer.
[0073]
In the present invention, a hydrophilic binder on a supportContaining polyvinyl alcohol or a derivative thereof, andInorganic fine particlesHardener containing fine-particle silica synthesized by a gas phase method having an average primary particle diameter of 0.03 to 0.003 μm as an average particle diameter, and further capable of crosslinking a hydrophilic binderThe recording layer has at least one void layer containing
[0075]
Silica fine particles are roughly classified into a dry method and a wet method according to the manufacturing method.The dry method fine particle silica is a method by high-temperature gas phase hydrolysis of silicon halide, and a method in which silica sand and coke are heated by an electric furnace in an electric furnace. There is known a method of reducing and evaporating this gas in the air. The wet-process silica is obtained by generating active silica by acid decomposition of a silicate, and then polymerizing it appropriately to cause aggregation and precipitation.
[0076]
In the present invention, among the silica fine powders, anhydrous silica synthesized by a gas phase method is particularly preferable in that a porosity and a strong film strength can be obtained.
[0077]
The average particle size of the inorganic fine particles is preferably 0.1 μm or less as primary particles.
[0078]
When the inorganic fine particles are fumed silica, the average particle size of the primary particles is 0.003 to 0.03 μm, and most preferably 0.006 to 0.02 μm. The fumed silica can be secondary aggregated in the coating solution to form larger particles. In this case, the average particle diameter of the secondary aggregated particles is preferably 0.03 to 0.2 μm.
[0079]
In the above description, the average particle size of the inorganic fine particles can be obtained as a simple average value (number average) by observing the cross section or surface of the particle itself or the void layer with an electron microscope, obtaining the particle size of 100 arbitrary particles. Here, each particle size is represented by its diameter assuming a circle equal to its projected area.
[0080]
In the recording paper of the present invention, as the hydrophilic binder used in combination with the inorganic fine particles, polyvinyl alcohol and derivatives thereof are used.BodyUseBecauseLow swelling and solubility in high boiling organic solvents and water contained in inkKIt is preferable from the viewpoint of the film strength immediately after printing.
[0081]
In the present inventionCan be usedPolyvinyl alcohol or its derivativesIsAmong them, polyvinyl alcohol having an average degree of polymerization of 1000 or more, most preferably an average degree of polymerization of 2000 or more, or a derivative thereof. The saponification degree is preferably from 70 to 100%, and most preferably from 80 to 100%.
[0082]
The hydrophilic binder may be used in combination of two or more kinds, but even in this case, it is preferable that polyvinyl alcohol or a derivative thereof is contained in at least 50% by weight or more.
[0083]
Examples of the polyvinyl alcohol derivative include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol and nonion-modified polyvinyl alcohol.
[0084]
The cation-modified polyvinyl alcohol is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.
[0085]
Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamido-2,2-dimethylethyl) ammonium chloride, trimethyl- (3-acrylamido-3,3-dimethylpropyl) ammonium chloride, N-vinylimidazole, N-vinyl-2-methylimidazole, N- (3-dimethylaminopropyl) methacrylamide, hydroxylethyltrimethylammonium chloride, trimethyl-(-methacrylamidopropyl) ammonium chloride, N- (1,1- Dimethyl-3-dimethylaminopropyl) acrylamide and the like.
[0086]
The ratio of the cation-modified group-containing monomer in the cation-modified polyvinyl alcohol is 0.1 to 10 mol%, preferably 0.2 to 5 mol%, based on vinyl acetate.
[0087]
The polymerization degree of the cation-modified polyvinyl alcohol is usually 500 to 4000, preferably 1000 to 4000.
[0088]
The saponification degree of the vinyl acetate group is usually from 60 to 100 mol%, preferably from 70 to 99 mol%.
[0089]
Examples of the anion-modified polyvinyl alcohol include polyvinyl alcohol having an anionic group as described in JP-A-1-2060888, JP-A-61-237681, and JP-A-63-307979. Examples thereof include a copolymer of vinyl alcohol and a vinyl compound having a water-soluble group, and a modified polyvinyl alcohol having a water-soluble group as described in JP-A-7-285265.
[0090]
Examples of the nonion-modified polyvinyl alcohol include, for example, a polyvinyl alcohol derivative in which a polyalkylene oxide group is added to a part of vinyl alcohol as described in JP-A-7-9758, and JP-A-8-25795. A block copolymer of the described vinyl compound having a hydrophobic group and vinyl alcohol may, for example, be mentioned.
[0091]
The weight ratio of the inorganic fine particles to the hydrophilic binder in the void layer of the recording paper of the present invention is required to be 5 times or more in order to obtain a high void ratio and a high film strength. If the ratio is less than 5 times, the porosity decreases, and it is difficult to obtain a sufficient ink absorption capacity. In addition, after inkjet recording, the strength of the film decreases due to the high boiling organic solvent remaining in the hydrophilic binder. Cheap. A preferable ratio of the inorganic fine particles to the hydrophilic binder is 6 or more.
[0092]
The upper limit of the ratio of the inorganic fine particles to the hydrophilic binder is about 20 or less from the cracking performance of the coating.
[0093]
A hardener capable of crosslinking with the hydrophilic binder is added to the void layer of the recording paper of the present invention.ButImprove the film forming property of the void layer, improve the water resistance of the film, and improve the film strength after printing which is the object of the present invention.You.Examples of such a hardener include an organic hardener containing an epoxy group, an ethyleneimino group, an active vinyl group, and the like, and an inorganic hardener such as chrome alum, boric acid, or borax.
[0094]
The hydrophilic binder is polyvinyl alcoholBecauseAn epoxy hardener having at least two epoxy groups in a molecule, boric acid or a salt thereof, and borax are preferred. As boric acid, not only orthoboric acid but also metaboric acid and hypoboric acid can be used.
[0095]
The amount of the hardener to be added is 1 to 200 mg, preferably 2 to 100 mg, per 1 g of the hydrophilic binder.
[0096]
Various additives can be contained in any layer on the ink receiving layer side of the ink jet recording paper of the present invention, if necessary.
[0097]
For example, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988 and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, and JP-A-60-72785. JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376, etc., anti-fading agents, various anionic, cationic or nonionic surfactants, No. 42993, No. 59-52689, No. 62-280069, No. 61-242871 and JP-A-4-219266, etc., fluorescent brighteners, sulfuric acid, phosphoric acid, acetic acid, PH adjusters such as citric acid, sodium hydroxide, potassium hydroxide and potassium carbonate, defoamers, lubricants such as diethylene glycol, preservatives, Nebazai, antistatic agents, can also contain various known additives such as a matting agent.
[0098]
In any of the constituent layers on the ink-absorbing side of the recording paper of the present invention, a polycationic polymer electrolyte disclosed in JP-A-56-89992 and a base described in JP-A-57-36692 are used as a waterproofing agent for an image. A latex polymer, polyallylamine described in JP-B-4-15744, JP-A-61-58788, JP-A-62-174184, etc., alkali metal weak acid salt described in JP-A-61-47290, etc. The above can be used.
[0099]
The amount of the applied solid content on the ink recording surface side of the ink jet recording paper of the present invention is approximately 5 to 40 g / m²Is preferred, and 10 to 30 g / m²Is more preferred.
[0100]
When the recording paper of the present invention is used as an ink-jet recording paper, the space capacity is 1 m of the recording paper.²It is preferably adjusted to 10 to 40 ml, preferably 15 to 30 ml.
[0101]
However, the void volume is J. TAPPI Paper Pulp Test Method No. When the ink absorption side of the recording paper was measured by the method described in Liquid Absorbency Test Method for Paper and Paperboard (Bristow Method), the liquid transfer amount (ml / m2) at an absorption time of 2 seconds was measured.²). The liquid used at this time is pure water (ion-exchanged water), but may contain less than 2% of a water-soluble dye in order to easily determine the measurement area.
[0102]
The recording paper of the present invention may have two or more recording layers having the above-mentioned void layers, and in this case, the ratio of the inorganic fine particles of the two or more void layers to the hydrophilic binder is different from each other. Is also good.
[0103]
Further, in addition to the above-mentioned gap layer, the ink may not have the gap layer and may have a layer swellable with respect to the ink.
[0104]
Such a swelling layer may be provided below the gap layer (on the side close to the support) or above the gap layer (on the side away from the support). Further, when there are two or more gap layers, the gap layer may be provided. May be provided between them. A hydrophilic binder is usually used for such a swellable layer, and examples of the hydrophilic binder used here include the hydrophilic binder used for the void layer.
[0105]
On the side opposite to the side having the ink absorbing layer of the recording paper of the present invention, various types of back layers may be provided in order to prevent curling and further improve sticking and ink transfer when superimposed immediately after printing. preferable.
[0106]
Although the configuration of the back layer varies depending on the type and thickness of the support and the configuration and thickness of the ink absorbing layer, a hydrophilic binder or a hydrophobic binder is generally used. The thickness of the back layer is usually in the range of 0.1 to 10 μm.
[0107]
The surface of the back layer can be roughened in order to prevent sticking to other recording papers, improve writing properties, and further improve transportability in an ink jet recording apparatus. Organic or inorganic fine particles having a particle size of 2 to 20 μm are preferably used for this purpose.
[0108]
Next, a method for manufacturing the recording paper of the present invention will be described.
[0109]
The recording paper of the present invention is obtained by applying and drying a recording layer having at least a void layer on a support. A coating solution for forming the void layer (containing a hydrophilic binder, inorganic fine particles, and the above-mentioned additives which are added as needed) is coated on a support, and dried. Usually, a temperature in the range of 30 to 50 ° C. is used, and once coated on the support and then cooled and dried, the point failure at the time of drying is reduced.
[0110]
Once the coating solution is cooled, the viscosity of the coating solution is significantly increased, the fluidity of the coating film is reduced, and the unevenness of the coating film due to the influence of vibration and wind during transport is greatly reduced. When there is unevenness in the coating film, not only point-like failures at the place where the film thickness is increased are increased, but also unevenness is sometimes generated in the void volume, which may seriously affect image quality.
[0111]
The temperature of the coating film is lowered by at least 10 ° C., preferably at least 20 ° C. from the temperature of the coating solution, and in that state, water and the low-boiling organic solvent are partially evaporated. When this state is reached, the viscosity of the coating film increases more rapidly and approaches the gelled state, so after this, even if the drying temperature is increased, the coating film will not move even if the high temperature air is sent and the drying speed is increased. A good coating surface free of unevenness and point failure is obtained.
[0112]
The temperature once cooled depends on various factors such as the particle size and concentration of the inorganic fine particles in the coating solution, the type and concentration of the hydrophilic binder, the type and amount of the hardener, and the interaction between the inorganic fine particles and the hydrophilic binder. It is usually 0 to 20 ° C, preferably 5 to 15 ° C.
[0113]
The cooling time may vary depending on the cooling temperature, the wet film thickness and the like, but is usually 5 to 200 seconds, preferably 10 to 60 seconds.
[0114]
In the drying after cooling, it is usually preferable to gradually raise the drying temperature. Usually, after drying at a temperature around room temperature for a certain period of time, finally drying with warm air at 40 to 60 ° C.
[0115]
For the above purposes, the viscosity characteristics of the coating liquid are particularly important. It is preferably a coating solution having a coating temperature of about 5 to 500 cp, and is adjusted so as to be 1000 cp or more, particularly preferably a gelled state when cooled.
[0116]
In particular, it is preferable that the viscosity ratio between the temperature of the coating solution and the temperature at the time of cooling be 100 times or more.
[0117]
The method of applying the above-mentioned void layer on the support can be appropriately selected from known methods. As a coating method, a roll coating method, a rod bar coating method, an air knife coating method, a spray 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. .
[0118]
Next, the present inventionCan be used inThe aqueous ink will be described below.
[0119]
The water-based ink is a recording liquid usually composed of a water-soluble dye, a liquid medium, and other additives. As the water-soluble dye, a water-soluble dye such as a direct dye, an acid dye, a basic dye, a reactive dye or a food dye known in the ink jet can be used, but a direct dye or an acid dye is preferable.
[0120]
The solvent of the aqueous ink is mainly composed of water, but when the ink liquid dries, the dye precipitates to prevent clogging at the nozzle tip and the ink supply path. A liquid high boiling organic solvent is used. High boiling organic solvents are required to have a vapor pressure much lower than that of water in order to prevent solid components such as dyes from being precipitated when water evaporates and to prevent the formation of coarse precipitates. Must have high miscibility.
[0121]
As such a high-boiling organic solvent, a high-boiling organic solvent is usually used in many cases. Specific examples include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerin, dithylene glycol monomethyl ether, and diethylene glycol. Monobutyl ether, triethylene glycol monobutyl ether, glycerin monomethyl ether, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,4-pentanetriol, 1,2,6-hexanetriol, thiol Alcohols such as diglycol, triethanolamine, and polyethylene glycol (average molecular weight of about 300 or less) are exemplified. In addition to the above, dimethylformamide, N-methylpyrrolidone and the like can also be used.
[0122]
Among these many high-boiling organic solvents, polyhydric alcohols such as diethylene glycol, triethanolamine, glycerin and triethanolamine, and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monobutyl ether are preferred.
[0123]
Other additives contained in the aqueous ink include, for example, a pH adjuster, a metal-sequestering agent, a fungicide, a viscosity adjuster, a surface tension adjuster, a wetting agent, a surfactant, and a rust inhibitor. .
[0124]
The aqueous ink liquid has a surface tension in the range of 25 to 50 dyne / cm, preferably 28 to 40 dyne / cm at 25 ° C. for the purpose of improving the wettability to the recording paper and stabilizing the ejection from the inkjet nozzle. It is preferred to have
[0125]
The viscosity of the aqueous ink is usually 2 to 8 cp, preferably 2.5 to 5 cp at 25 ° C.
[0126]
The pH of the aqueous ink is usually in the range of 4 to 10.
[0127]
The minimum ink droplet ejected from the ink nozzle is 1 to 30 × 10^-3A capacity of nl is preferable because a minimum dot diameter of about 20 to 60 μm can be obtained on recording paper. A color print printed with such a dot diameter gives a high quality image. Preferably 2-20 × 10^-3This is a case where a droplet having a volume of nl is ejected as a minimum droplet.
[0128]
Further, in a method in which the aqueous ink is recorded with two types of inks, each of which differs in density at least twice for at least magenta and cyan, it is difficult to identify dots because a low density ink is used in a highlight portion. However, the present invention can be applied to a case where such a recording method is adopted.
[0129]
In the ink jet recording method, various conventionally known methods can be used as the recording method, and details thereof are described in, for example, the trend of the ink jet recording technology (Koichi Nakamura, edited by Koichi Nakamura, March 31, 1995, Japan Science Information Co., Ltd.). Issue).
[0130]
In the inkjet recording method of the present invention, the method of increasing the void volume to the amount of the high-boiling organic solvent in the maximum ink amount by 3 times or more reduces the ratio of the high-boiling organic solvent in the ink, and reduces the maximum ejected ink amount as much as possible. Optimal conditions are set and selected by appropriately combining methods such as increasing the void volume of the recording paper as much as possible.
[0132]
【Example】
Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.
[0133]
Example 1
160 g / m²A paper support in which both sides of the photographic base paper were coated with polyethylene (13% by weight of anatase type titanium dioxide was contained in a 40 μm thick polyethylene layer on the recording surface side. The thickness of the polyethylene layer on the back side was 25 μm and the polyethylene layer was An acrylic latex resin having a Tg of 65 ° C. and a solid content of 0.6 g / m.²And 0.3 g / m 2 of silica having an average particle size of about 13 μm as a matting agent.²Having a backing layer).
[0134]
Glossiness, W_CM, The maximum height (the maximum height per 2.5 mm of the reference length determined in accordance with JIS-0601, in μm units), and the results are shown in Table 1.
[0135]
Next, 150 g of primary fine particle silica powder having an average particle size of about 7 nm was added to 1000 ml of pure water, and dispersed with a high-speed homogenizer to obtain a pale and clear dispersion. Next, 1000 ml of a 2% aqueous polyvinyl alcohol solution (II) having an average degree of polymerization of 3500 and a saponification degree of 88% (containing 6% by weight of ethyl acetate) was gradually added to the aqueous silica dispersion (I). Then, 40 ml of a 4% aqueous solution of borax was added as a hardener, and the mixture was dispersed with a high-speed homogenizer to obtain a white translucent coating solution. This liquid contains 7.5 times the weight ratio of silica to polyvinyl alcohol. The viscosity of the coating solution was 60 cp at 40 ° C. when measured with a B-type viscometer, and 50,000 cp when measured at 15 ° C.
[0136]
Then, the coating solution of 40 ° C. obtained as described above was applied to the recording surface side of the polyethylene-coated paper, and cooled once (20 seconds) so that the coating film temperature became 15 ° C. or less. Then, a wind of 20 ° C. is blown for 30 seconds, a wind of 25 ° C. is blown for 30 seconds, a wind of 35 ° C. is blown for 60 seconds, and a wind of 45 ° C. is blown in order for 120 seconds to dry. After passing through for 30 seconds, the humidity was adjusted to prepare recording paper-1.
[0137]
Next, in the recording paper-1, various recording papers having different smoothness were used as the base paper of the support, and the recording paper-2 to 4 coated with the same polyethylene layers on both sides as the recording paper-1 were the same as the recording paper-1. It was produced. Table 1 shows the optical properties and smoothness of the recording papers 1 to 4 after being coated with polyethylene.
[0138]
After coating and drying, the recording papers 1 to 4 were stored in a rolled state at 39 ° C. for 3 days.
[0139]
The following items were evaluated with respect to the obtained recording paper.
[0140]
(1) Void volume
Using a Bristow tester type II (pressurized type) manufactured by Kumagai Riki Kogyo Co., Ltd., the transfer amount (ml / m²) Was determined as the void volume.
[0141]
(2) Ink absorption
Using the same tester for measuring the void volume, the transfer amount (ml / m²) Was determined for ink absorbency.
[0142]
(3) Glossiness
The specular gloss at 75 degrees was measured with a variable angle photometer (VGS-101DP) manufactured by Nippon Denshoku Industries Co., Ltd.
[0143]
(4) Failure defect
The number of point defects on the surface of a 10 × 10 cm coated sample was examined.
[0144]
(5) Film strength
After solid printing with an inkjet printer, MJ-5100C, manufactured by Seiko Epson Corporation, stored at 23 ° C. and a relative humidity of 80% for 24 hours, and then tested for scratching strength in the same environment (Haydon Tribogear, manufactured by Shinto Kagaku Co., Ltd.) , A continuous load of 0 to 100 g was applied to a sapphire needle having a tip of 0.3 mmφ to test the film strength, and the strength at which the film was broken was taken as the film strength.
[0145]
It can be said that the film has a practically sufficiently high film strength if it is approximately 30 g or more according to this evaluation method.
[0146]
In (1) and (2), the ink used was an ink containing 20% by weight of diethylene glycol and 1% by weight of a water-soluble magenta dye. Table 1 shows the results.
[0147]
[Table 1]

[0148]
From the results in Table 1, when the surface characteristics after coating with polyethylene resin were changed by changing the type of base paper, W_CMAre 4 μm or less,_CMIt can be seen that the number of failures is smaller than that of the recording paper-4 having a particle size exceeding 4 μm.
[0149]
Especially W_CMWhen a support having a particle size of 2 μm or less is used, the number of failure defects is preferably 0.
[0150]
In addition, the gap capacity and the ink absorbency are hardly affected by the difference between the supports. The dry film thickness is 30 μm or more and the porosity is high (about 63%). Almost sufficient void volume is maintained.
[0151]
Example 2
On the recording paper-1 prepared in Example 1, a polyethylene-coated paper support in which the thickness of the polyethylene layer on the recording surface side was changed as shown in Table 2 was prepared, and a coating for forming the void layer prepared in Example 1 was prepared. The liquid was applied in the same manner as in Example 1 to produce recording papers 21 to 24. On the other hand, in the recording paper-1 produced in Example 1, immediately after the front side polyethylene layer was applied on the base paper, various clearing treatments were performed on the surface, and recording papers 25 to 27 having different surface characteristics were recorded on the recording paper-1. It was produced in the same manner as described above.
[0152]
The support of the recording paper-25 has a pitch length of several hundreds of .mu.m which is called a so-called silk surface, and the support of the recording paper-27 has a so-called matte surface. It has a fine, matte surface. Recording paper-26 is intermediate between these.
[0153]
Further, the support of the recording paper-28 was obtained by treating the surface of the support of the recording paper-1 with a 40 ° C. acetone solution to roughen the surface. Usually, these rough surfaces are effective in increasing the adhesion between the support and the recording layer.
[0154]
The surface characteristics of the polyethylene-coated paper of the recording papers 21 to 28 and the characteristics after the application of the recording layer were evaluated in the same manner as in Example 1. Table 2 shows the results.
[0155]
[Table 2]

[0156]
From the results in Table 2, W_CMIt can be seen that the recording papers 21, 22, and 23 of the present invention having a particle size of 4 μm or less have fewer failures than the comparative recording paper-24. In particular, similarly to the first embodiment, W_CMIt can be seen that the recording paper 21 having a particle size of 2 μm or less is particularly excellent.
[0157]
On the other hand, even when the surface of the polyethylene resin layer is cleaned or roughened to use a substrate having low gloss,_CMIt can be seen that the recording papers -27 and 28 having a particle size of 4 μm or less have few failure defects. Also, W_CMIs larger than 4 μm, the number of faulty defects increases rapidly.
[0158]
Comparative Example 1
A recording paper having a dry film thickness as shown in Table 3 by changing the wet film thickness of the coating solution prepared in Example 1 on a polyethylene-coated paper support for recording paper-4 prepared in Example 1. 31 to 34 were produced in the same manner as in the case of the recording paper-4.
[0159]
Evaluation was performed in the same manner as in Example 1, and the results shown in Table 3 were obtained.
[0160]
[Table 3]

[0161]
From the results in Table 3, W_CMEven if a support having a thickness exceeding 4 μm is used, as the dry film thickness decreases, the number of defective defects decreases. However, the void volume gradually decreases. Cannot be used practically.
[0162]
Example 3
In the recording papers 1 to 4 prepared in Example 1, the recording papers were prepared in the same manner as the recording papers 1 to 4 except that the fine particle silica was changed to fumed silica having an average primary particle diameter of about 20 nm. 41 to 44 were produced. Evaluation was performed in the same manner as in Example 1, and the results shown in Table 4 were obtained.
[0163]
[Table 4]

[0164]
From the results in Table 4, it can be seen that the same effects as in Example 1 can be obtained. However, the glossiness of the recording surface was slightly reduced as compared with Example 1 as the particle size of the primary silica particles increased, and the void volume was slightly increased.
[0165]
Comparative Example 2
150 g of primary fine particle silica powder having an average particle size of about 7 nm was added to 1000 ml of pure water, and dispersed with a high-speed homogenizer to obtain a pale and clear dispersion. Next, 2000 ml of a 2% aqueous polyvinyl alcohol solution (II) having an average degree of polymerization of 3500 and a saponification degree of 88% (containing 6% by weight of ethyl acetate) was gradually added to the aqueous silica dispersion (I). Then, 40 ml of a 4% aqueous solution of borax was added as a hardener, and the mixture was dispersed with a high-speed homogenizer to obtain a white translucent coating solution. This liquid contains 3.75 times the weight ratio of silica to polyvinyl alcohol.
[0166]
The above coating solution was applied to the coated paper with the polyethylene of the recording paper-1 to 4 used in Example 1 so that the dry film thickness was the same as in Example 1 and the wet film thickness was 170 μm. It dried by the method described in Example 1 to produce recording papers 51-54. Evaluation was performed in the same manner as in Example 1, and the results shown in Table 5 were obtained.
[0167]
[Table 5]

[0168]
From the results shown in Table 5, when the ratio of the inorganic fine particles to the hydrophilic binder was set to 5 or less, the defect was regarded as W as a support._CMIt can be seen that even when a layer having a particle size of more than 4 μm is used, almost no gloss is produced and the glossiness of the recording surface is very high, but the void volume is reduced and the strength of the film is greatly reduced.
[0169]
【The invention's effect】
As described above, according to the present invention, it has high ink absorption, high gloss, high coating film strength, and greatly reduced point-like failure.InkjetA recording sheet is obtained.

Claims (5)

On a paper support having both surfaces of a base paper coated with a plastic resin, polyvinyl alcohol or a derivative thereof is contained as a hydrophilic binder, and an average primary particle diameter of 0.03 to 0.003 μm is contained as inorganic fine particles. Having at least one recording layer having voids containing a hardener capable of cross-linking a hydrophilic binder, the inorganic fine particles for the hydrophilic binder of the recording layer Is 5 times or more by weight, the surface characteristics of the recording paper side of a paper support in which both sides of the base paper are coated with a plastic resin are obtained from a cross-sectional curve measured according to JIS-B-0610. When the maximum swell of a filter was measured with a reference length of 2.5 mm for a swell curve derived under the condition of a cutoff value of 0.8 mm. The ink-jet recording sheet, wherein the maximum waviness is 4μm or less. 2. The ink jet recording paper according to claim 1, wherein the dry thickness of the recording layer is 30 [mu] m or more. The inkjet recording paper according to claim 1, wherein the glossiness of the surface of the recording layer is 75% specular glossiness specified by JIS-Z-8741 of 50% or more. The inkjet recording paper according to any one of claims 1 to 3, wherein the inkjet recording paper is an inkjet recording paper that can be recorded with a water-soluble ink. On a paper support having both surfaces of a base paper coated with a plastic resin, polyvinyl alcohol or a derivative thereof is contained as a hydrophilic binder, and an average primary particle diameter of 0.03-0.003 μm is contained as inorganic fine particles. Having at least one recording layer having voids containing a hardener capable of crosslinking a hydrophilic binder, the fine particles containing silica synthesized by a gas phase method , and inorganic fine particles for the hydrophilic binder of the recording layer a at ratio of 5 times or more in a weight ratio of the surface characteristics of the recording layer side of the paper support in which both sides of the base paper is coated with plastic resin, measured cut-off value from the sectional curve in accordance with JIS-B-0610 When the maximum undulation was measured with a reference length of 2.5 mm for the undulation curve derived under the condition of 0.8 mm, the maximum undulation was 4 μm or less. In a method for manufacturing an ink jet recording paper, the coating liquid for forming the recording layer is applied on a paper support having both sides of the base paper coated with a plastic resin, and then cooled and dried once. Manufacturing method of recording paper.