JP2004143624A

JP2004143624A - Bulky coated paper for printing use

Info

Publication number: JP2004143624A
Application number: JP2002309929A
Authority: JP
Inventors: Koji Kazumori; 数森　康二; Kosaku Kobayashi; 小林　耕作; Masayoshi Sakuma; 佐久間　雅義
Original assignee: Hokuetsu Paper Mills Ltd
Current assignee: Hokuetsu Paper Mills Ltd
Priority date: 2002-10-24
Filing date: 2002-10-24
Publication date: 2004-05-20
Anticipated expiration: 2022-10-24
Also published as: JP4210507B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bulky and flexible printing coated paper either usable for sheet-fed printing and rotary offset printing and excellent in printing workability and ink-receiving uniformity. <P>SOLUTION: The coated paper is obtained by providing both sides of a base paper sheet consisting mainly of wood pulp and essentially containing a bulk agent, a paper strengthening agent and a filler with pigment coating layers respectively, wherein the modulus of the pigment coating layer is ≥20% lower than that of the base paper sheet. The binder for the pigment coating layer consists of a SBR latex comprising ≥35wt.% of butadiene, ≤40wt.% of styrene and ≤20wt.% of acrylonitrile, and the amount of the SBR latex used is preferably ≥8pts.wt. based on 100pts.wt. of the pigment. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は印刷用嵩高塗工紙に関し、特に柔軟性があり枚葉オフセット、輪転オフセットいずれにも使用でき、印刷作業性、インキ受理均一性の優れた塗工紙に関する。
【０００２】
【従来の技術】
近年印刷用紙の分野、特に書籍用紙の分野において従来品にくらべ同一厚みで重量の低いいわゆる嵩高紙が脚光をあびている。嵩高紙あるいは紙の軽量化といった概念は決して新しいものではないが、嵩高紙がもてはやされる理由としては軽量化と結びついた省資源の観点、さらには本にした場合の持ち運びにおける利便性、ボリューム感、嵩高でありながら従来品とかわらぬ印刷適性の維持が大幅の価格アップをともなわずにできる技術面の進歩等各種の理由が挙げられる。
【０００３】
嵩高化とともに書籍用紙では紙の柔軟性も要求されている。すなわち、本を開いた場合に自然に閉じたり、ページをめくる場合に抵抗があったりしないように紙にしなやかさが要求される。非塗工紙では柔軟性を付与するために厚みと強度が若干犠牲にはなるが、柔軟剤の使用や填料の使用量を増やすことで比較的容易に達成できる。
【０００４】
一方、塗工紙においても嵩高紙への要求がたかまっているが、本来原紙よりも密度の高い塗工層をもうけることから密度も増加する方向であり、また単純に原紙の密度を下げてもその後の仕上げ工程によっては厚みが大幅に減少する危険性があることから、非塗工紙とは違った配慮が必要となる。厚みを重視するあまり、平滑度が犠牲になると、印刷品質面での劣化が問題となる。塗工紙は通常多色印刷されることから、印刷品質についても特段の注意が必要となる。
【０００５】
塗工紙の場合は非塗工紙と比べると、同一坪量では厚みが小さく、したがって剛度も低いのが通常である。したがって同一坪量では塗工紙は非塗工紙よりも柔軟であり、特に薄物においては柔軟化よりも剛度をあげることが従来の課題であった。ただ、嵩高塗工紙の登場による軽量化や厚み増に伴い従来の塗工紙よりも剛度が上がる方向であり、特に坪量が９０ｇ／ｍ^２以上の中厚物においては非塗工紙と同様、柔軟性の要求がでてきている。
【０００６】
嵩高紙を製造する方法としては各種の方法が提案されている。近年の特徴としては密度を減少させるために嵩高剤と称する界面活性剤を添加する例が多い（例えば特許文献１、特許文献２、特許文献３、特許文献４、特許文献５参照）。また嵩のでる特定の繊維を配合する技術も公知である（例えば特許文献６、特許文献７参照）。特別に処理した繊維を使用することで嵩をだす技術も公知である（例えば特許文献８、特許文献９、特許文献１０参照）。また特定の充填剤を使用する技術も公知である（例えば特許文献１１、特許文献１２）。
【０００７】
嵩と同時に柔軟性を付与した紙も公知である（例えば特許文献１３、特許文献１４、特許文献１５）。
【０００８】
一方塗工紙の分野では、特許文献１６に、緊度０．７ｇ／ｃｍ^３未満の原紙に、サチン、重質炭酸カルシウムを含有した塗料を塗工することで紙腰が強く嵩高な塗工紙を製造する技術が、また特許文献１７に機械パルプと無定形シリカを含有する原紙上に特定の粒径分布を有する顔料塗工層を設けた印刷用塗工紙がそれぞれ開示されている。
【０００９】
上記の如く、嵩高紙を製造する方法として多くの提案がなされているが、特に塗工紙において柔軟性があり印刷適性に優れた嵩高塗工紙についてはあまり提案がなされていない。
【００１０】
嵩高な塗工紙を製造する際には、非塗工紙において周知の技術が適用されるが、非塗工紙とは別の配慮も必要となる。前記したことに加え、以下のことを注意する必要がある。嵩高剤や嵩高なパルプの使用等嵩高にするための方法は強度、特に紙層の内部結合強度の低下を伴いやすい。非塗工紙においては、多少内部結合強度が低下してもそもそも透気性が良好なことから印刷インキの乾燥を熱によって行う輪転オフセット印刷においてもトラブルは発生しにくい。しかし塗工紙においては非塗工紙に比べ透気性が悪く、内部結合強度がある値を超えて低下すれば、輪転オフセット印刷においてブリスターと呼ばれる紙層破壊を伴う膨れが発生し、印刷品質を著しく損ね使用に耐えないものとなる。嵩高剤の使用は通常繊維間の結合を阻害することから、柔軟性も付与されるが、内部結合強度を補強するために紙力増強剤の使用を強化すると今度は剛度があがり柔軟性が犠牲になる。非塗工紙では填料を増加させることで柔軟性を上げることができるが、塗工紙においてこの方法を採用すると再び内部結合強度を低下させブリスタートラブルを発生しやすい。
【００１１】
特許文献１：特許第３１２８２４８号公報、
特許文献２：特開平１１−２００２８３号公報、
特許文献３：特開平１１−２００２８４号公報、
特許文献４：特開平１１−２００２８５号公報、
特許文献５：特開平１１−２６８７９９号公報、
特許文献６：特開２０００−２５６９８６号公報、
特許文献７：特開平１１−３０２９９１号公報、
特許文献８：特開平１０−１２１３９５号公報、
特許文献９：特開平７−１８９１６８号公報、
特許文献１０：特開平７−５４２９３号公報、
特許文献１１：　特開２００１−２１４３９５号公報、
特許文献１２：　特開２０００−２８２３９２号公報、
特許文献１３：特開２０００−２８８６９０号公報、
特許文献１４：特開２０００−２８８６９１号公報、
特許文献１５：特開２００１−２７１２９２号公報、
特許文献１６：特開平８−９２８９４号公報、
特許文献１７：特開２００１−２１４３９５号公報。
【００１２】
【発明が解決しようとする課題】
以上のような状況に鑑み、本発明の課題は嵩高でかつ柔軟性があり枚葉オフセット印刷、輪転オフセット印刷いずれにも使用でき、印刷作業性、インキ受理均一性の優れた印刷用塗工紙を提供することにある。
【００１３】
【課題を解決するための手段】
本発明者等は、原紙とともに塗料処方を最適化することで上記課題が一挙に解決されることを見出した。
【００１４】
すなわち，本発明は、木材パルプを主体とする、少なくとも嵩高剤、紙力向上剤、填料を含有した原紙の両面に顔料塗工層を設けた塗工紙において、該顔料塗工層の弾性率が原紙の弾性率よりも２０％以上低いことを特徴とする、印刷用嵩高塗工紙に関する。
【００１５】
本発明の有利な一つの実施態様においては、顔料塗工層のバインダーが顔料１００重量部当たり８重量部以上のＳＢＲラテックスと０〜２重量部の補助バインダーから構成され、該ＳＢＲラテックスはブタジエン含有量が３５重量％以上、スチレン含有量が４０重量％以下、アクリロニトリル含有量が２０重量％以下である。
【００１６】
本発明の有利な別の一つの実施態様においては、バインダーに補助バインダーが含まれ、該補助バインダーの使用量が顔料１００重量部当たり２重量部以下である。
【００１７】
本発明の他の有利な一つの実施態様においては、塗工紙の比容積が１．０以上で、下記の式で計算される剛度の厚さ補正値が１．７以下である：
【００１８】
【外２】

Ｓ_Ｔ：縦方向の剛度（ｍＮ）、Ｓ_Ｙ：横方向の剛度（ｍＮ）、ｔ：厚さ（ｍｍ）
本発明では特に塗工層と原紙の弾性率に注目している。一般にｎ層から構成される材料の曲げこわさ（以下剛度という）は下記の式で表現される。
【００１９】
Ｓ＝ΣＥｎＩｎ、Ｉｎ＝ｈｎＸｎ^２＋ｈｎ^３／１２
ここでＳは剛度、Ｅｎは第ｎ層の弾性率、Ｉｎは第ｎ層の断面２次モーメント、ｈｎは第ｎ層の厚さ、Ｘｎは第ｎ層中心の中立軸からの距離を示す。上式より全体の剛度は各層の弾性率と断面２次モーメントの積を足したものとして表現される。弾性率は材料の特性によって決まり、断面２次モーメントは断面の厚みと中立軸からの距離によって決定される。断面が中心線に対して対称構造になっている場合、中立軸は断面の中心線と一致する。上式は中立軸から離れた位置にある層程、全体の剛度への寄与が高いことを意味する。両面塗工紙は両面に塗工層、中央に原紙層から成る３層対称構造とみなすことができる。ここで塗工層は最外層に位置することから中立軸からの距離が長く、塗工層の弾性率と厚さによって塗工紙全体の剛度に大きく寄与し得る可能性があることを示している。すなわち原紙層の弾性率と比較して塗工層の弾性率が低い場合には同じ厚さの原紙からだけ構成される紙に比べ塗工紙の剛度は低下することがわかる。さらに、弾性率の差が大きいほど、低下の度合いは大きくなる。通常のオフセット印刷用塗工紙では剛度が高いことが好ましい特性であり、スターチやＣＭＣ等硬い天然バインダーを比較的硬いラテックスと併用することが多く、塗工層弾性率は原紙弾性率より高い場合が多い。一方嵩高剤を使用する原紙に従来の塗料をそのまま適用した塗工紙では嵩高剤により原紙の弾性率が低下する分塗工層弾性率は原紙弾性率よりさらに高い値となる。本発明では嵩高な原紙に塗工層を設ける際に原紙の弾性率と比較し弾性率が相対的に低くなるような塗工層を設けることを特徴としている。塗工層弾性率は低いほど塗工紙の剛度低下は大きくなるが、塗工層の厚みが原紙の厚みに比べ小さいために、塗工紙剛度として１０％程度下げるためには塗工層弾性率は原紙弾性率よりも最低でも２０％以上下げることが好ましい。剛度として１０％の差は触感として認知できる差である。さらに好ましくは４０％以上である。こうすることで単に嵩高な原紙を使用し、従来の塗工層を設けた場合に比べより柔軟な印刷用塗工紙を得ることができる。また塗工紙の柔軟性は塗工層で付与できることから嵩高剤添加で低下した原紙の内部結合強度は紙力増強剤の添加で補うことができる。
【００２０】
塗工層弾性率はＰＥＴフィルム等に塗料を所定量両面塗工し基材と塗工後の厚み、剛度を測定することで計算により求めることができる。原紙弾性率は原紙の厚みと剛度を測定することで直接求めることができる。塗工紙から原紙、塗工層の弾性率を簡便的に推定するにはまず塗工紙の剛度、厚さを測定し、ついで塗工層を剛度が無視できる程度に柔軟なポリエチレンフィルム等に熱融着させ原紙部分を銅エチレンジアミン溶液で溶解させる。得られた塗工層とフィルムの一体化物の剛度と厚さを測定することで塗工層弾性率を求め、その値をもとに原紙剛度を計算で求める。
【００２１】
本発明の顔料塗工層のバインダーは上述の組成のＳＢＲラテックスであり、その使用量は顔料１００重量部当たり８重量部以上である。バインダーの他に補助バインダーを使用してもよく、その場合には、顔料１００重量部当たり２重量部以下の量で使用するのが好ましい。バインダー使用量が８重量部に満たない場合には、枚葉オフセット印刷に耐える表面強度が得られない。上限は印刷適性を考慮して通常２０重量部以下、好ましくは１８重量部以下である。２０重量部を超えて使用すると印刷時のインキセットが遅くなり、また塗工層が柔軟であるために、塗工紙同士が加圧化で接着するブロッキングが発生する恐れがある。
【００２２】
ここで補助バインダーとは酸化澱粉、デキトリン、カチオン澱粉、尿素燐酸エステル化澱粉、ヒドロキシエチルエーテル化澱粉等の澱粉類、カゼイン、大豆蛋白、ポリビニールアルコール、カルボキシメチルセルロース、ヒドロキシエチルセルロース等の水溶性高分子であり、保水性とバインダー機能を有する薬品類を包含する。これら水溶性高分子を単独で使用した塗工層弾性率は通常原紙の弾性率よりも２〜５倍程度高い値となることから、その使用は極力少なくすることが必要であり、上限は上記の通り、２重量部である。２重量部を超えて使用すると柔軟なラテックスの使用による塗工層弾性率低下効果を阻害し十分な効果が得られない。好ましくは１．５重量部以下であり、保水性確保や操業性の悪化を来さない範囲で必要最小限の量にすべきである。使用するＳＢＲラテックスはブタジエン含有量が３５重量％以上、スチレン含有量が１０〜４０重量％、アクリロニトリル含有量が５〜２０重量％である。ブタジェンは弾性率が低く、スチレン、アクリロニトリルは弾性率の高い皮膜を造るために、このようなモノマー組成のラテックスを使用することで柔軟性に優れ印刷適性も良好な塗工層が得られる。このようにして得られる顔料塗工層の弾性率は通常の塗工原紙、上質紙、嵩高紙など、広い範囲の非塗工紙の弾性率にくらべてもはるかに低い弾性率を示す。但しブタジエン含有量の下限、スチレン、アクリロニトリル含有量の上限、いずれか一つでも範囲から外れると満足すべき塗工層弾性率が得られない可能性がある。その他、上記組成範囲を外さない範囲でメチルメタアクリレート等公知のモノマーを使用してもかまわない。本発明のバインダー組成は塗工層弾性率を低くする効果の他に、補助バインダーを極力減らした効果により、塗工層自体がよりポーラスになることで、インク受理性がより均一になる。何よりも低いキャレンダー線圧で平滑、光沢が出やすい効果があり、その結果塗工紙の柔軟化に加え嵩高剤を添加した効果との組み合わせ効果により、キャレンダー、ソフトキャレンダー、スーパーキャレンダー等の仕上げ工程後における塗工紙の嵩高化にも大いに寄与する。
【００２３】
本発明における塗工紙の比容積を１．０以上、剛度の厚さ補正値を１．７以下にすることで塗工紙の中で最も嵩があり、したがって剛度の高い範疇に属するマット紙分野で従来の一般オフセット印刷用塗工紙に比べすべての坪量範囲で従来品と明らかに区別ができる。剛度の厚さ補正値として縦、横の幾何平均値を規定したのは塗工層の弾性率を下げる方法がかならずしも塗工紙の剛度を縦、横均一に低下するようには作用しないためである。本発明の塗工紙では通常、横方向の剛度低下がより大きいが、縦と横の幾何平均で比較することで初めて塗工層弾性率を操作したことによる効果を定量的に評価することができる。特定方向の剛度をより低下させたい場合には、周知の抄紙技術上の方法で原紙の縦横比を制御することで可能である。また本発明では剛度調整を主として塗工層の弾性率で調整するため、原紙の強度を低下させる必要性が少なく、内部結合強度を２００ｍＪ以上に維持でき、枚葉オフセット印刷はもちろんとして輪転オフセット印刷にも耐え得る塗工紙が得られる。
【００２４】
本発明を構成する原紙の原料としては通常の漂白化学パルプ、機械パルプ、古紙パルプ等の木材パルプが主として使用される。嵩をだすためにはこれら原料パルプの選定も重要であるが、本発明で嵩高効果を確実のものとするために嵩高剤を使用する。本発明で使用する嵩高剤については特に限定するものではないが、非イオン性、アニオン性、カチオン性、両性いずれか単独または混合物からなる各種界面活性剤やそれ以外の有機性嵩高剤が使用できる。一例として高級アルコールのエチレンオキサイド、プロピレンオキサイド付加物、多価アルコールと脂肪酸のエステル化合物、脂肪族ポリアミドアミン等を例示できる。嵩高剤は嵩高効果と強度のバランスの中で適切なものを選定する。特に同一厚さすなわち同一比容積で比較した場合、内部結合強度の低下が少ない薬品が好ましい。しかしながら、嵩高剤の使用によって程度の差はあるものの内部結合強度の低下はさけられないことから、通常紙力向上剤を併用する。紙力向上剤としては公知の各種薬品が内添または外添で使用できる。通常使用される紙力向上剤としては、酸化澱粉、カチオン化澱粉、両性澱粉等の各種澱粉類、各種イオン性のポリアクリルアマイド、澱粉とアクリルアマイドのグラフト共重合物、メラミン樹脂、ポリアミドエピクロリン樹脂等を例示できる。また不透明度や白色度を高めるために各種填料が添加されるが、填料の添加は紙を柔軟にする効果はあるものの、反面内部結合強度を低下させるために、本発明では必要最低量にすることが好ましい。すなわち、原紙中において１０重量％以下にする必要がある。通常使用される填料としては、タルク、カオリンクレー、重質炭酸カルシウム、軽質炭酸カルシウム、酸化チタン等が挙げられる。嵩高剤、紙力向上剤、填料の添加量は、内部結合強度が２００ｍＪより低くならないようにそれぞれの添加量を調節する必要がある。
【００２５】
その他必要に応じて、製紙の際に一般的に使用されるサイズ剤、染料、蛍光染料、歩留向上剤、濾水促進剤等を紙料に添加し、抄紙する。抄紙方法は特に限定されるものではなく、公知の抄紙機、すなわち長網、丸網、ハイブリッドフォーマー、ギャップフォーマー等を使用し、プレス工程、乾燥工程を経て塗工原紙を作成する。途中の工程で、サイズプレス、フィルムトランスファーロールコーター、メタリングサイズプレスを使用して、澱粉、ポリビニールアルコール、ポリアクリルアマイド等単独または混合物、あるいは予備塗工として顔料とバインダーからなる塗料を原紙に塗工することができる。塗工原紙の坪量は特に限定するものではないが通常５０〜１５０ｇ／ｍ^２程度の範囲にあり、厚くなるほど本発明の優位性が発揮できる。
【００２６】
塗工原紙に塗料を塗工する装置としてはブレードコーター、バーコーター、エアナイフコーター、リバースロールコーター、カーテンコーター等が使用できるが、ファウンテンノズルタイプのブレードコーターが好ましい。また塗工方式はオンマシンまたはオフマシンどちらでも良い。塗工量は片面あたり乾燥重量として７〜１５ｇ／ｍ^２が好ましい。塗工量が７ｇ／ｍ^２より少ないと原紙の被覆が不十分であり、印刷時にざらつき感が発生する。一方、塗工量が１５ｇ／ｍ^２を超えると、原紙の嵩高性が打ち消され結果として塗工紙としての嵩高性が損なわれる。
【００２７】
原紙に塗工する塗料としては顔料、バインダー組成物、助剤から構成されるが本発明では特にバインダー組成物の構成が重要であり、これについては前述した通りである。使用する顔料については特に限定するものでは無く、従来から一般的に使用されている、カオリンクレー類、重質炭酸カルシウム、軽質炭酸カルシウム、酸化チタン、硫酸バリウム、サチンホワイト、シリカ等無機顔料、プラスチックピグメント等有機顔料が挙げられる。助剤としては分散剤、保水剤、増粘剤、潤滑剤、耐水化剤、着色剤、防腐剤等が適宜使用される。
【００２８】
塗工後の乾燥はシリンダードライヤー、熱風ドライヤー、赤外線ヒータードライヤー等公知のドライヤーで行われる。塗工後乾燥工程を経て得られた塗工紙は、必要に応じて仕上げ工程で加圧処理される。仕上げ工程はオンマシン、オフマシンいずれでも可能である。仕上げ工程を経ることで塗工紙に平滑性、光沢性を付与でき、印刷適性は向上するが、一方厚みが減少することから処理条件は注意する必要がある。仕上げ装置としてはキャレンダー、ソフトキャレンダー、スーパーキャレンダー、ラスタープレス等が使用できる。
【００２９】
【実施例】
以下に実施例をあげて本発明をさらに詳細に説明するが、本発明はこれに限定されるものではない。なお特に断らない限り、実施例中の部及び％はそれぞれ重量部、重量％を示す。
【００３０】
実施例１
［原紙の製造］
原料としてＬＢＫＰ（広葉樹晒クラフトパルプ）９０％、ＮＢＫＰ（針葉樹晒クラフトパルプ）１０％の配合からなるパルプをＣＳＦ５００ｍｌまで叩解し、対原料（乾燥重量）、填料として軽質炭酸カルシウム５％、カチオン澱粉１％、嵩高剤として花王（株）製ＫＢ１１５（商品名）を１．０％添加した。該紙料をハイブリッドフォーマーにより抄紙し、オンマシンゲートロールコーターで酸化澱粉２ｇ／ｍ^２（両面）を付与し、坪量７５ｇ／ｍ^２の塗工原紙を得た。
【００３１】
［塗料の調製］
カオリン（商品名ＵＷ９０：エンゲルハード社製）／湿式重質炭酸カルシウム（商品名カービタル９０：イメリス社製）＝５０重量部／５０重量部からなる顔料スラリーを調製し、表１に示すモノマー組成の異なるＳＢＲラテクッスＡ〜Ｇ（旭化成工業合成品）の７種を用い、添加部数、補助バインダーの種類、部数を変えて＃１〜＃１１の塗料（固形分６０％）を調製した。ラテックスＡはアルカリで増粘する増粘剤を含有し補助バインダーを必要としないいわゆるソールバインダーである。尚、補助バインダーとしては次の商品を使用した。
尿素燐酸エステル化澱粉（商品名ＭＳ＃４６００：日本食品化工製）
ＣＭＣ（商品名セロゲンＰＲ：第一工業製薬製）。
【００３２】
［弾性率の測定］
ガーレー剛度計を用い、ガーレー剛度と厚さから弾性率を求めた。原紙の弾性率は式（１）により求めた。＃１〜＃１１の塗料から形成される塗工層の弾性率はＰＥＴフィルム上に各塗料を片面あたり１０ｇ／ｍ^２で両面塗工し、塗工前後の剛度、厚さを測定し式（２）により算出した。
（１）式
Ｅｂ＝９．１４×１０^５×Ｇｂ／ｈ^３
Ｅｂ：原紙弾性率（ＧＰａ）
Ｇｂ：原紙の剛度（ｍＮ）
ｈ　：原紙の厚さ（μｍ）
（２）式
Ｅｓ＝４．５７×１０^５×（Ｇｔ−Ｇｃ）／（３ｈｓ×（ｈｃ＋ｈｓ）^２　＋ｈｓ^３）
Ｅｓ：塗工層弾性率（ＧＰａ）
Ｇｔ：塗工後の剛度（ｍＮ）
Ｇｃ：塗工前の剛度（ｍＮ）
ｈｓ：塗工層厚さ（片面あたり）（μｍ）
ｈｃ：塗工基材厚さ（μｍ）
［塗工紙の作製］
上記塗工原紙にブレードコーターを用い、＃１の塗料を塗工量が片面あたり１０ｇ／ｍ^２になるよう原紙Ｆ面次いでＷ面に塗工し、坪量９５ｇ／ｍ^２の両面塗工紙を作製した。次いで該塗工紙をソフトキャレンダーで１１０℃、線圧５０ｋＮ／ｍで処理し、印刷用塗工紙を得た。
【００３３】
実施例２〜５
実施例１において＃１の塗料のかわりに＃２〜＃５の塗料を用いた以外は実施例１と同様にして印刷用塗工紙を得た。
【００３４】
比較例１
［原紙の製造］
原料としてＬＢＫＰ９０％、ＮＢＫＰ１０％の配合からなるパルプをＣＳＦ５００ｍｌまで叩解し、対原料（乾燥重量）、填料として軽質炭酸カルシウム５％、カチオン澱粉１％、を添加した。該紙料をハイブリッドフォーマーにより抄紙し、オンマシンゲートロールコーターで酸化澱粉２ｇ／ｍ^２（両面）を付与し、坪量８５ｇ／ｍ^２の塗工原紙を得た。
【００３５】
［塗工紙の作製］
上記塗工原紙にブレードコーターを用い、＃１０の塗料を塗工量が片面あたり１０ｇ／ｍ^２になるよう両面塗工し、坪量１０５ｇ／ｍ^２の塗工紙を作製した。次いでソフトキャレンダーで１１０℃、線圧５０ｋＮ／ｍで処理し、印刷用塗工紙を得た。
【００３６】
比較例２〜７
実施例１において＃１の塗料にかわりに＃６〜＃１１の塗料を用いた以外は実施例１と同様にして塗工紙を得た。
【００３７】
比較例８
比較例１における［原紙の製造］において、填料として軽質炭酸カルシウムを１２％添加し、坪量７５ｇ／ｍ^２の原紙を製造した以外は比較例１と同様にして印刷用塗工紙を得た。
【００３８】
以上の実施例、比較例の塗工紙を下記の方法で評価して表２に結果をまとめた。
［塗工紙の評価］
坪量、厚さ、比容積：　ＪＩＳ　　Ｐ−８１２４に準拠し坪量を測定、次いでＪＩＳ　　Ｐ−８１１８に準拠し厚さを測定した。比容積は厚さを坪量で割ることで求めた。
【００３９】
ガーレー剛度：　Ｊａｐａｎ　Ｔａｐｐｉ　Ｎｏ．４０に従い、縦方向、横方向各々について測定し、両者の幾何平均をとり剛度とした。
【００４０】
ガーレー剛度の厚さ補正：　下記式で行った。
【００４１】
【外３】

Ｓ_Ｔ：縦方向の剛度（ｍＮ）、Ｓ_Ｙ：横方向の剛度（ｍＮ）、ｔ：厚さ（ｍｍ）
白紙光沢度：　ＪＩＳ　　Ｐ−８１４２に従い７５度条件で塗工紙のＦ面を測定した。
【００４２】
印刷強度　：　ＲＩ印刷試験機を用い、特殊インキ（ＳＭＸタックグレード１５；東洋インキ社製）を用い塗工紙のＦ面に印刷し、印刷面のピック状態を目視で評価した。◎：ピック無し、○：ピック極めて少ない、△：ピックが散見、×：ピックが非常に多い。
【００４３】
内部結合強度：　Ｊａｐａｎ　　Ｔａｐｐｉ　Ｎｏ．　１８−２に準拠して測定した。
【００４４】
インキ受理ムラ：　ＲＩ印刷試験機を用い、塗工紙Ｆ面についてプロセスインキ（ジオスＧ：ＤＩＣ社製）黄を印刷後、紅を印刷しトラッピングの均一性を目視で評価した。◎：極めて均一、○：均一、△：ややムラ、×：ムラが顕著
【００４５】
【表１】

【００４６】
【表２】

【００４７】
【発明の効果】
表２の結果から明らかなように、本発明による塗工紙（実施例１〜５）は、比較例１で代表されるような従来の一般的塗工紙に比べ、印刷強度、内部結合強度が同等で、嵩高かつ柔軟性のある塗工紙が得られる。加えて、塗料面での光沢発現性、インキ受理の均一性が優れることから、得られる塗工紙の白紙光沢度、印刷した場合のインキ受理均一性に優れた塗工紙が得られる。また本発明によらない比較例９のように、塗工紙の柔軟化を添加する填料の量を増加させて行うと、内部結合強度が著しく低下し、その結果耐ブリスター性が悪化し、オフ輪印刷に耐えられないものとなる。本実施例ではソフトキャレンダー処理を固定した条件で実施しているが、白紙光沢度を同一にするよう処理条件を変更して塗工紙を作製した場合には、本発明の塗工紙は仕上げ条件を軽減できることから、例えば比容積において差の無い比較例２〜４、６〜８に比べ比容積においても有意性が発揮されることから、同一厚さの塗工紙を製造する場合にはより少ない原料での生産が可能である。特に高光沢度品を製造する場合にはこの差が顕著になる。本発明は従来の塗工紙に比べ、品質のみならず、より少ない原料、より低いエネルギーで塗工紙を生産できることから、省資源、省エネルギーという観点からも優れた塗工紙を提供できるものである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bulky coated paper for printing, and more particularly to a coated paper which is flexible and can be used for both sheet-fed offset and rotary offset, and is excellent in printing workability and ink receiving uniformity.
[0002]
[Prior art]
In recent years, in the field of printing paper, especially in the field of book paper, so-called bulky paper having the same thickness and lower weight than conventional products has been spotlighted. The concept of bulky paper or paper weight reduction is not new at all, but the reason why bulky paper is touted is the viewpoint of resource saving linked to weight reduction, as well as the convenience of carrying in books, the feeling of volume, Various reasons can be cited, such as technical progress, which can maintain the printability that is bulky and does not differ from conventional products without a significant increase in price.
[0003]
With the increase in bulk, book paper is also required to have flexibility. That is, paper is required to be flexible so that it does not close naturally when a book is opened and does not have resistance when turning pages. In uncoated paper, thickness and strength are slightly sacrificed in order to impart flexibility, but it can be achieved relatively easily by using a softener or increasing the amount of filler.
[0004]
On the other hand, there is a growing demand for bulky paper in coated paper, but the density tends to increase from the fact that a coating layer with a higher density is originally provided than the base paper, and simply lowering the density of the base paper Depending on the subsequent finishing process, there is a risk that the thickness will be significantly reduced, so that consideration different from that of uncoated paper is required. If the smoothness is sacrificed so much as to emphasize the thickness, deterioration in print quality becomes a problem. Since coated paper is usually printed in multiple colors, special attention must be paid to print quality.
[0005]
In the case of coated paper, the thickness is smaller and the rigidity is generally lower at the same basis weight as compared with uncoated paper. Therefore, it has been a conventional problem that coated paper is more flexible than uncoated paper at the same basis weight, and that the rigidity of the thin paper is higher than that of the softened paper. However, a direction in which the stiffness increases than the conventional coated paper with the weight reduction and increase of the thickness by the appearance of bulky coated paper, especially in a basis weight of 90 g / m ² or more in thickness was a non-coated paper Similarly, there is a need for flexibility.
[0006]
Various methods have been proposed for producing bulky paper. In recent years, there has been a case in which a surfactant called a bulking agent is added in order to reduce the density (for example, see Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, and Patent Literature 5). In addition, a technique of blending specific fibers that are bulky is also known (for example, see Patent Documents 6 and 7). Techniques for producing bulk by using specially treated fibers are also known (for example, see Patent Literature 8, Patent Literature 9, and Patent Literature 10). Techniques using a specific filler are also known (for example, Patent Documents 11 and 12).
[0007]
Papers having flexibility as well as bulk are also known (for example, Patent Literature 13, Patent Literature 14, Patent Literature 15).
[0008]
On the other hand, in the field of coated paper, Patent Document 16 discloses that a paper containing satin and heavy calcium carbonate is coated on a base paper having a tensile strength of less than 0.7 g / cm ³ , thereby providing a strong and bulky coating. Patent Document 17 discloses a technique for manufacturing paper, and discloses a coated paper for printing in which a pigment coated layer having a specific particle size distribution is provided on base paper containing mechanical pulp and amorphous silica.
[0009]
As described above, many proposals have been made as a method for producing bulky paper. However, there have been few proposals regarding a bulky coated paper which is particularly flexible in coated paper and has excellent printability.
[0010]
When producing a bulky coated paper, a well-known technique is applied to uncoated paper, but another consideration is required for uncoated paper. In addition to the above, the following should be noted. A method for increasing the bulk, such as use of a bulking agent or bulky pulp, tends to be accompanied by a decrease in the strength, particularly the internal bonding strength of the paper layer. Even in the case of uncoated paper, even if the internal bonding strength is reduced to some extent, since air permeability is good in the first place, trouble hardly occurs even in rotary offset printing in which printing ink is dried by heat. However, coated paper has poor air permeability compared to uncoated paper, and if the internal bonding strength drops below a certain value, blisters called blisters occur in rotary offset printing that cause paper layer breakage, resulting in poor print quality. It is significantly damaged and cannot be used. Although the use of bulking agents usually hinders the bonding between fibers, it also provides flexibility, but when the use of a paper strength enhancer is used to reinforce the internal bond strength, the use of a bulking agent increases rigidity and sacrifices flexibility. become. For uncoated paper, flexibility can be increased by increasing the filler, but when this method is used for coated paper, the internal bonding strength is again reduced and blister troubles are likely to occur.
[0011]
Patent Document 1: Japanese Patent No. 3128248,
Patent Document 2: JP-A-11-200283,
Patent Document 3: JP-A-11-200284,
Patent Document 4: JP-A-11-200285,
Patent Document 5: JP-A-11-268799,
Patent Document 6: JP-A-2000-256986,
Patent Document 7: JP-A-11-302991,
Patent Document 8: JP-A-10-121395,
Patent Document 9: JP-A-7-189168,
Patent Document 10: JP-A-7-54293,
Patent Document 11: JP-A-2001-214395,
Patent Document 12: JP-A-2000-282392,
Patent Document 13: JP-A-2000-288690,
Patent Document 14: JP-A-2000-288691,
Patent Document 15: JP-A-2001-271292,
Patent Document 16: JP-A-8-92894,
Patent Document 17: JP-A-2001-214395.
[0012]
[Problems to be solved by the invention]
In view of the above situation, an object of the present invention is a bulky and flexible coated paper for printing that can be used for both sheet-fed offset printing and rotary offset printing, and has excellent printing workability and ink receiving uniformity. Is to provide.
[0013]
[Means for Solving the Problems]
The present inventors have found that the above problems can be solved at once by optimizing the paint formulation together with the base paper.
[0014]
That is, the present invention relates to a coated paper mainly composed of wood pulp, which is provided with a pigment coated layer on both sides of a base paper containing at least a bulking agent, a paper strength improver, and a filler, and an elastic modulus of the pigment coated layer. Is 20% or more lower than the modulus of elasticity of the base paper.
[0015]
In one advantageous embodiment of the invention, the binder of the pigment coating layer is composed of at least 8 parts by weight of SBR latex and 100 parts by weight of auxiliary binder per 100 parts by weight of pigment, said SBR latex containing butadiene containing The amount is 35% by weight or more, the styrene content is 40% by weight or less, and the acrylonitrile content is 20% by weight or less.
[0016]
In another advantageous embodiment of the invention, the binder comprises an auxiliary binder, the amount of which is less than 2 parts by weight per 100 parts by weight of pigment.
[0017]
In another advantageous embodiment of the invention, the specific volume of the coated paper is greater than or equal to 1.0 and the stiffness thickness correction calculated by the following formula is less than or equal to 1.7:
[0018]
[Outside 2]

S _T: vertical stiffness (mN), _{S Y:} lateral stiffness (mN), t: thickness (mm)
The present invention pays particular attention to the elasticity of the coating layer and the base paper. Generally, the bending stiffness (hereinafter referred to as rigidity) of a material composed of n layers is expressed by the following equation.
[0019]
^{^{S = ΣEnIn, In = hnXn 2}} + hn 3/12
Here, S is the rigidity, En is the elastic modulus of the n-th layer, In is the second moment of area of the n-th layer, hn is the thickness of the n-th layer, and Xn is the distance from the neutral axis of the center of the n-th layer. From the above equation, the overall stiffness is expressed as the product of the elastic modulus of each layer and the second moment of area. The modulus of elasticity is determined by the properties of the material, and the second moment of area is determined by the thickness of the section and the distance from the neutral axis. If the cross section is symmetrical with respect to the center line, the neutral axis coincides with the center line of the cross section. The above equation means that the layer located farther from the neutral axis has a higher contribution to the overall rigidity. The double-sided coated paper can be regarded as a three-layer symmetric structure having a coating layer on both sides and a base paper layer in the center. Here, since the coating layer is located at the outermost layer, the distance from the neutral axis is long, indicating that the elastic modulus and thickness of the coating layer may significantly contribute to the rigidity of the entire coated paper. I have. That is, when the elastic modulus of the coating layer is lower than the elastic modulus of the base paper layer, the stiffness of the coated paper is lower than that of paper consisting only of base paper of the same thickness. Furthermore, the greater the difference in elastic modulus, the greater the degree of reduction. In the case of coated paper for normal offset printing, high rigidity is a desirable property. A hard natural binder such as starch or CMC is often used in combination with a relatively hard latex, and the elastic modulus of the coating layer is higher than the base paper elastic modulus. There are many. On the other hand, in a coated paper in which a conventional paint is directly applied to a base paper using a bulking agent, the bulk coating layer elastic modulus at which the elasticity of the base paper is reduced by the bulking agent is a higher value than the base paper elastic modulus. The present invention is characterized in that when a coating layer is provided on a bulky base paper, the coating layer is provided such that the elastic modulus is relatively lower than the elastic modulus of the base paper. The lower the modulus of elasticity of the coated layer, the greater the decrease in stiffness of the coated paper. However, the thickness of the coated layer is smaller than the thickness of the base paper. Preferably, the modulus is at least 20% lower than the modulus of the base paper. A difference of 10% in stiffness is a difference that can be recognized as a tactile sensation. More preferably, it is at least 40%. This makes it possible to obtain a coated paper for printing that is more flexible than a case where a bulky base paper is simply used and a conventional coating layer is provided. Further, since the flexibility of the coated paper can be imparted by the coating layer, the internal bonding strength of the base paper, which has been reduced by the addition of the bulking agent, can be compensated for by the addition of a paper strength enhancer.
[0020]
The coating layer elastic modulus can be determined by calculation by applying a predetermined amount of a coating material to a PET film or the like on both sides, and measuring the thickness and rigidity of the base material and the coating. The base paper elastic modulus can be directly obtained by measuring the thickness and rigidity of the base paper. To easily estimate the modulus of elasticity of the base paper and coating layer from the coated paper, first measure the stiffness and thickness of the coated paper, and then convert the coated layer to a polyethylene film that is flexible enough to ignore the stiffness. The base paper portion is melted with a copper ethylenediamine solution by heat fusion. The elasticity of the coating layer is determined by measuring the stiffness and thickness of the integrated product of the obtained coating layer and film, and the stiffness of the base paper is calculated based on the value.
[0021]
The binder of the pigment coating layer of the present invention is the SBR latex having the above-mentioned composition, and the amount of the binder used is 8 parts by weight or more per 100 parts by weight of the pigment. An auxiliary binder may be used in addition to the binder. In this case, the auxiliary binder is preferably used in an amount of 2 parts by weight or less per 100 parts by weight of the pigment. If the amount of the binder used is less than 8 parts by weight, the surface strength sufficient for sheet-fed offset printing cannot be obtained. The upper limit is usually 20 parts by weight or less, preferably 18 parts by weight or less in consideration of printability. When used in an amount exceeding 20 parts by weight, the ink setting at the time of printing becomes slow, and since the coating layer is flexible, there is a possibility that blocking occurs in which the coated papers are adhered under pressure.
[0022]
Here, the auxiliary binder is a starch such as oxidized starch, dextrin, cationic starch, urea phosphate esterified starch, or hydroxyethyl etherified starch, or a water-soluble polymer such as casein, soybean protein, polyvinyl alcohol, carboxymethyl cellulose, or hydroxyethyl cellulose. And includes chemicals having a water retention property and a binder function. Since the elastic modulus of the coating layer using these water-soluble polymers alone is usually about 2 to 5 times higher than the elastic modulus of the base paper, it is necessary to minimize the use thereof, and the upper limit is as described above. 2 parts by weight. If it is used in excess of 2 parts by weight, the effect of lowering the elastic modulus of the coating layer due to the use of a soft latex is impaired, and a sufficient effect cannot be obtained. Preferably, the amount is 1.5 parts by weight or less, and the amount should be the minimum necessary within a range that does not cause deterioration of water retention or operability. The SBR latex used has a butadiene content of 35% by weight or more, a styrene content of 10 to 40% by weight, and an acrylonitrile content of 5 to 20% by weight. Butadiene has a low modulus of elasticity, and styrene and acrylonitrile form a film with a high modulus of elasticity. By using a latex having such a monomer composition, a coating layer having excellent flexibility and good printability can be obtained. The elastic modulus of the pigment-coated layer thus obtained is much lower than the elastic modulus of a wide range of uncoated papers such as ordinary coated base paper, high-quality paper, and bulky paper. However, if any one of the lower limit of the butadiene content and the upper limit of the styrene and acrylonitrile contents is out of the range, a satisfactory coating layer elastic modulus may not be obtained. In addition, a known monomer such as methyl methacrylate may be used without departing from the above composition range. In addition to the effect of lowering the elastic modulus of the coating layer, the binder composition of the present invention has the effect of reducing the auxiliary binder as much as possible, so that the coating layer itself becomes more porous and the ink receptivity becomes more uniform. Above all, the calendering line pressure has the effect of producing smoothness and luster easily. As a result, the calender, soft calender, and super calender are combined with the effect of adding a bulking agent in addition to the softening of the coated paper. Etc. greatly contributes to bulking of the coated paper after the finishing step.
[0023]
By setting the specific volume of the coated paper in the present invention to 1.0 or more and the thickness correction value of rigidity to 1.7 or less, the matte paper which is the bulkiest among the coated papers and therefore belongs to the category of high rigidity In the field, it can be clearly distinguished from the conventional product in all the basis weight ranges as compared with the conventional coated paper for general offset printing. The vertical and horizontal geometric mean values are specified as the thickness correction value of the stiffness because the method of lowering the elastic modulus of the coated layer does not necessarily act to reduce the stiffness of the coated paper vertically and horizontally uniformly. is there. In the coated paper of the present invention, the reduction in stiffness in the horizontal direction is generally larger, but it is possible to quantitatively evaluate the effect of operating the coating layer elastic modulus for the first time by comparing the vertical and horizontal geometric averages. it can. When it is desired to further reduce the rigidity in a specific direction, it is possible to control the aspect ratio of the base paper by a known papermaking technique. Further, in the present invention, since the stiffness adjustment is mainly adjusted by the elasticity of the coating layer, the necessity of lowering the strength of the base paper is small, the internal bonding strength can be maintained at 200 mJ or more, and the web offset printing as well as the sheet-fed offset printing can be maintained. A coated paper that can withstand the above is obtained.
[0024]
Wood pulp such as ordinary bleached chemical pulp, mechanical pulp, and waste paper pulp is mainly used as a raw material of the base paper constituting the present invention. The selection of these raw pulp is important in order to increase the bulk, but in the present invention, a bulking agent is used in order to ensure the bulking effect. The bulking agent used in the present invention is not particularly limited, but nonionic, anionic, cationic, amphoteric surfactants or other organic bulking agents comprising one or a mixture thereof can be used. . Examples thereof include ethylene oxide and propylene oxide adducts of higher alcohols, ester compounds of polyhydric alcohols and fatty acids, and aliphatic polyamidoamines. An appropriate bulking agent is selected in a balance between the bulking effect and the strength. Particularly, when compared at the same thickness, that is, at the same specific volume, a chemical with a small decrease in internal bonding strength is preferable. However, although the degree of internal bonding strength cannot be reduced although the degree varies depending on the use of a bulking agent, a paper strength improver is usually used in combination. Various known chemicals can be used internally or externally as the paper strength improver. Examples of commonly used paper strength improvers include various starches such as oxidized starch, cationized starch and amphoteric starch, various ionic polyacrylamides, graft copolymers of starch and acrylamide, melamine resins, polyamide epichlorin. Resins and the like can be exemplified. Various fillers are added to increase the opacity and whiteness, but the addition of the filler has the effect of softening the paper, but on the other hand, in order to reduce the internal bond strength, the present invention requires the minimum amount. Is preferred. That is, it is necessary to make it 10% by weight or less in the base paper. Examples of commonly used fillers include talc, kaolin clay, heavy calcium carbonate, light calcium carbonate, and titanium oxide. The addition amounts of the bulking agent, paper strength improver, and filler need to be adjusted so that the internal bond strength does not become lower than 200 mJ.
[0025]
In addition, if necessary, a sizing agent, a dye, a fluorescent dye, a retention aid, a drainage enhancer, and the like generally used in papermaking are added to the stock to make paper. The papermaking method is not particularly limited, and a known paper machine, that is, a long net, a round net, a hybrid former, a gap former, or the like is used, and a coated base paper is prepared through a pressing step and a drying step. In the middle of the process, using a size press, film transfer roll coater, metalling size press, starch, polyvinyl alcohol, polyacrylamide, etc. alone or as a mixture, or as a preliminary coating, paint containing pigment and binder as base paper Can be coated. Although the basis weight of the coating base paper is not particularly limited, it is usually in the range of about 50 to 150 g / m ^{2, and the} greater the thickness, the more the superiority of the present invention can be exhibited.
[0026]
As a device for coating the coating base paper with a coating material, a blade coater, a bar coater, an air knife coater, a reverse roll coater, a curtain coater and the like can be used, and a fountain nozzle type blade coater is preferable. The coating method may be either on-machine or off-machine. The coating amount is preferably 7 to 15 g / m ² as a dry weight per one side. If the coating amount is less than 7 g / m ² , the coating of the base paper is insufficient, and a rough feeling occurs during printing. On the other hand, when the coating amount exceeds 15 g / m ² , the bulkiness of the base paper is canceled, and as a result, the bulkiness of the coated paper is impaired.
[0027]
The coating applied to the base paper is composed of a pigment, a binder composition, and an auxiliary agent. In the present invention, the configuration of the binder composition is particularly important, and this is as described above. The pigment to be used is not particularly limited, and inorganic pigments such as kaolin clays, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, satin white, silica, and plastics generally used in the past are used. Pigment and other organic pigments. As the auxiliary agent, a dispersant, a water retention agent, a thickener, a lubricant, a waterproofing agent, a coloring agent, a preservative, and the like are appropriately used.
[0028]
Drying after coating is performed by a known dryer such as a cylinder dryer, a hot air dryer, and an infrared heater dryer. Coated paper obtained through a drying step after coating is subjected to a pressure treatment in a finishing step as necessary. The finishing process can be performed either on-machine or off-machine. Through the finishing step, smoothness and glossiness can be imparted to the coated paper, and the printability is improved. However, since the thickness is reduced, it is necessary to pay attention to the processing conditions. As a finishing device, a calender, a soft calender, a super calender, a raster press, etc. can be used.
[0029]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Unless otherwise specified, parts and% in the examples indicate parts by weight and% by weight, respectively.
[0030]
Example 1
[Manufacture of base paper]
Pulp composed of 90% LBKP (hardwood bleached kraft pulp) and 10% NBKP (softwood bleached kraft pulp) is beaten to 500 ml CSF, and the raw material (dry weight) is 5% light calcium carbonate and 5% cationic starch as filler. As a bulking agent, 1.0% of KB115 (trade name) manufactured by Kao Corporation was added. The stock was made by a hybrid former, and 2 g / m ² (both sides) of oxidized starch was applied by an on-machine gate roll coater to obtain a coated base paper having a basis weight of 75 g / m ² .
[0031]
[Preparation of paint]
A pigment slurry composed of kaolin (trade name UW90: manufactured by Engelhard Co.) / Wet heavy calcium carbonate (trade name: Carbital 90: manufactured by Imeris) = 50 parts by weight / 50 parts by weight was prepared. Coatings # 1 to # 11 (solid content 60%) were prepared using seven different SBR latexes A to G (Asahi Kasei Kogyo Kogyo Co., Ltd.) and changing the number of added parts, the kind of auxiliary binder, and the number of parts. Latex A is a so-called sole binder that contains a thickener that thickens with an alkali and does not require an auxiliary binder. The following products were used as auxiliary binders.
Urea phosphate esterified starch (trade name MS # 4600: manufactured by Nippon Shokuhin Kako)
CMC (trade name Cellogen PR: manufactured by Daiichi Kogyo Seiyaku).
[0032]
[Measurement of elastic modulus]
Using a Gurley stiffness meter, the elastic modulus was determined from the Gurley stiffness and the thickness. The modulus of elasticity of the base paper was determined by equation (1). The modulus of elasticity of the coating layer formed from the coating materials # 1 to # 11 is determined by applying each coating material on both sides of a PET film at 10 g / m ² per side, and measuring the rigidity and thickness before and after coating ( It was calculated by 2).
(1) Formula Eb = 9.14 × 10 ⁵ × Gb / h ³
Eb: base paper elastic modulus (GPa)
Gb: Stiffness of base paper (mN)
h: Thickness of base paper (μm)
(2) Formula Es = 4.57 × 10 ⁵ × (Gt−Gc) / (3hs × (hc + hs) ² + hs ³ )
Es: Coating layer elastic modulus (GPa)
Gt: Stiffness after coating (mN)
Gc: Stiffness before coating (mN)
hs: Coating layer thickness (per side) (μm)
hc: Coating substrate thickness (μm)
[Preparation of coated paper]
Using a blade coater on the coated base paper, apply # 1 paint to base paper F side and then W side so that the coating amount is 10 g / m ² per side, and double coated paper with basis weight 95 g / m ² Was prepared. Next, the coated paper was treated with a soft calender at 110 ° C. and a linear pressure of 50 kN / m to obtain a coated paper for printing.
[0033]
Examples 2 to 5
A coated paper for printing was obtained in the same manner as in Example 1 except that the paints of # 2 to # 5 were used instead of the paint of # 1.
[0034]
Comparative Example 1
[Manufacture of base paper]
Pulp composed of 90% LBKP and 10% NBKP as raw materials was beaten to a CSF of 500 ml, and the raw materials (dry weight), 5% light calcium carbonate and 1% cationic starch were added as fillers. The stock was made with a hybrid former, and oxidized starch was applied at 2 g / m ² (both sides) with an on-machine gate roll coater to obtain a coated base paper having a basis weight of 85 g / m ² .
[0035]
[Preparation of coated paper]
Using a blade coater, the coating base paper was coated on both sides with a coating of # 10 at a coating amount of 10 g / m ² on one side to prepare a coated paper having a basis weight of 105 g / m ² . Then, it was treated with a soft calender at 110 ° C. and a linear pressure of 50 kN / m to obtain a coated paper for printing.
[0036]
Comparative Examples 2 to 7
A coated paper was obtained in the same manner as in Example 1 except that the paints of # 6 to # 11 were used instead of the paint of # 1.
[0037]
Comparative Example 8
A coated paper for printing was obtained in the same manner as in Comparative Example 1 except that 12% of light calcium carbonate was added as a filler in [Production of base paper] in Comparative Example 1 to produce a base paper having a basis weight of 75 g / m ² . .
[0038]
The coated papers of the above Examples and Comparative Examples were evaluated by the following methods, and the results are summarized in Table 2.
[Evaluation of coated paper]
Basis weight, thickness, specific volume: The basis weight was measured according to JIS P-8124, and then the thickness was measured according to JIS P-8118. The specific volume was determined by dividing the thickness by the grammage.
[0039]
Gurley stiffness: Japan Tappi No. In accordance with No. 40, measurements were made in each of the vertical and horizontal directions, and the geometric average of the two was taken as the rigidity.
[0040]
Gurley stiffness thickness correction: Performed by the following equation.
[0041]
[Outside 3]

S _T: vertical stiffness (mN), _{S Y:} lateral stiffness (mN), t: thickness (mm)
Blank paper glossiness: The F side of the coated paper was measured under the condition of 75 degrees according to JIS P-8142.
[0042]
Printing strength: Using a RI printing tester, printing was performed on the F side of the coated paper using a special ink (SMX tack grade 15; manufactured by Toyo Ink Co., Ltd.), and the picking state of the printing surface was visually evaluated. ◎: no pick, ：: extremely few picks, Δ: scattered picks, ×: very many picks.
[0043]
Internal bond strength: Japan Tappi No. It measured according to 18-2.
[0044]
Ink Receiving Unevenness: Using a RI printing tester, process ink (Gios G: manufactured by DIC) yellow was printed on the coated paper F side, then red was printed, and the trapping uniformity was visually evaluated. ◎: extremely uniform, ：: uniform, Δ: slightly uneven, ×: marked unevenness
[Table 1]

[0046]
[Table 2]

[0047]
【The invention's effect】
As is clear from the results in Table 2, the coated paper according to the present invention (Examples 1 to 5) has a higher printing strength and inner bond strength than the conventional general coated paper represented by Comparative Example 1. And a bulky and flexible coated paper is obtained. In addition, since the gloss appearance on the paint surface and the uniformity of ink reception are excellent, a coated paper excellent in white paper glossiness of the obtained coated paper and uniformity of ink reception when printed can be obtained. Further, when the amount of the filler to be added for softening the coated paper is increased as in Comparative Example 9 not according to the present invention, the internal bond strength is significantly reduced, and as a result, the blister resistance deteriorates, and It will not be able to withstand ring printing. In the present embodiment, the soft calendering process is performed under a fixed condition.However, when a coated paper is manufactured by changing the processing conditions so that the blank glossiness is the same, the coated paper of the present invention is Since the finishing conditions can be reduced, for example, the significance is also exhibited in the specific volume as compared with Comparative Examples 2 to 4 and 6 to 8 having no difference in the specific volume. Can be produced with fewer raw materials. In particular, this difference is remarkable when a high gloss product is manufactured. The present invention can provide coated paper not only in quality but also in terms of resource saving and energy saving because it can produce coated paper with less raw materials and lower energy as well as quality compared to conventional coated paper. is there.

Claims

Based on wood pulp, at least a bulking agent, a paper strength improver, in a coated paper having a pigment coated layer on both sides of a base paper containing a filler, the elastic modulus of the pigment coated layer is greater than the elastic modulus of the base paper Bulky coated paper for printing, characterized in that it is also 20% or lower.

The binder of the pigment coating layer is an SBR latex having a butadiene content of 35% by weight or more, a styrene content of 40% by weight or less, and an acrylonitrile content of 20% by weight or less, and the amount of the SBR latex used is 100% by weight of the pigment. The bulky coated paper for printing according to claim 1, wherein the amount is 8 parts by weight or more per part.

The bulky coated paper for printing according to claim 2, wherein the binder contains an auxiliary binder, and the amount of the auxiliary binder used is 2 parts by weight or less per 100 parts by weight of the pigment.

The bulkiness for printing according to any one of claims 1 to 3, wherein the specific volume of the coated paper is 1.0 or more, and the thickness correction value of stiffness calculated by the following formula is 1.7 or less. Coated paper.
[Outside 1]

S _T: vertical stiffness (mN), _{S Y:} lateral stiffness (mN), t: thickness (mm)