【０００１】
【発明の属する技術分野】
本発明は、パルプを主原料とする紙に、親水性塗料を塗工するに当たり、紙内部へ塗料が浸透するのを抑制し、塗料を支持体に塗工層として効率よく形成することができる、あらたな浸透抑制剤とその使用法に関し、より詳しくは、多孔性の軽量嵩高な紙に適用して有利な効果を得る浸透抑制剤および浸透抑制方法に関するものである。
【０００２】
【従来の技術】
近年、印刷用紙においても輸送及び郵送コストの削減などのため軽量化に対する要求が非常に高くなってきている。しかし、単純に軽量化すなわち印刷用紙の坪量を下げると紙の厚さが低下し、冊子のボリューム感が損なわれるため好ましくない。求められている軽量化とは紙重量を低下させる一方で紙厚は低下させないこと、より好ましくは紙厚を増加させ嵩高化すること、即ち軽量嵩高化を意味している。一方、印刷物のビジュアル化やカラー化が進み、非塗工印刷用紙に比較し、紙表面に平滑な塗工層をインキ受理層とする印刷用塗工紙の需要も年々増加している。炭酸カルシウムやカオリンなどの無機顔料を主体とする塗工層は、パルプを主体とする塗工原紙に比較して比重が重く、塗工紙の軽量のためには塗工量を出来るだけ少なくする必要がある。また、嵩高化のためには、塗工原紙を嵩高化することが考えられる。しかし、原紙を嵩高化すると低密度となり細孔が多くなるので、塗工時に、塗料の原紙内部への浸透性が上がり、低塗工量で均一に原紙表面を被覆することが難しくなる。そこで、原紙の細孔量を減らすために塗工前に原紙をカレンダー処理すれば、紙厚が低下するため嵩高低密度紙は得られない。このように、塗工紙の軽量嵩高化のために、軽量嵩高な原紙を用いても、比重の高い無機顔料を主体とする塗料を単に塗布しただけでは塗料の浸透のため塗布量が多くなって軽量嵩高化を実現することは難しい。
【０００３】
原紙内部への塗料の浸透を抑制する方法としては、原紙と、塗料の溶媒である水との濡れ性を下げるために原紙にサイズ処理を施す方法が考えられる。しかしが、細孔量の多い低密度原紙にこのような処理を施してもその効果は小さいものであった。また、塗工用でんぷん、ポリビニルアルコール（ＰＶＡ）などの水溶性高分子を主成分とする表面処理剤を紙表面に塗工し、紙表面に塗膜を形成させ、その後に塗工される塗料の浸透を抑制する方法も考えられるが、軽量嵩高原紙ではその表面塗工剤も紙層に浸透してしまうため、紙表面に有効な浸透抑制塗膜を形成させることが難しかった。また、親水性塗料ではないが、剥離紙用基材にシリコーン等の離型剤の浸透を抑制するため、水溶性高分子であるカルボキシルメチルセルロース（ＣＭＣ）を含有する水溶液で表面処理し、さらにＰＶＡを含有する水溶液を２〜７ｇ／ｍ２塗工する方法が開示されている（特許文献１参照）が、２度の塗工が必要な上、塗布量が多くなり低密度嵩高原紙への処理方法には適さない。このように軽量嵩高原紙表面に、親水性塗料の浸透を効果的に抑制し、塗工層の塗膜を効率良く形成させることは非常に困難であった。
【０００４】
【特許文献１】特開平６−２８０１９９９号公報
【発明が解決しようとする課題】
本発明は、上記のような従来技術の問題を解決するために創案されたものであり、低密度嵩高紙表面に効率良く浸透抑制効果を発現させる浸透抑制剤、及びそれを用いた塗料の浸透抑制方法、更にそれにより軽量嵩高な塗工原紙及びその塗工紙を提供するものである。
【０００５】
【課題を解決するための手段】
本発明者等は、低密度嵩高紙への塗料の浸透抑制方法について鋭意検討を重ねた結果、表面塗工剤として水溶性が小さく、水膨潤性または実質的に水不溶性のカルボキシメチルセルロースナトリウム塩を利用することで、上記課題を解決できることを見い出し、この知見に基づいて本発明をなすに至った。本発明において、水膨潤性または実質的に水不溶性とは、ＣＭＣを常温で２重量％濃度に水に撹拌溶解操作をしたときの状態を目視で観察したとき、均一な溶液とならず、全く溶解していないと見られるか、膨潤状態を示し一部は溶解していると見られる状態を示す。水膨潤性あるいは実質的に水不溶性のカルボキシメチルセルロースナトリウム塩を、以下単に不溶性ＣＭＣと略称する。
【０００６】
不溶性ＣＭＣを浸透抑制剤として、その希薄溶液を軽量嵩高紙表面に塗布したとき、上記課題が解決される理由は明らかではないが、軽度にカルボキシメチル化したＣＭＣは水膨潤性または実質的に水不溶性であって、水に分散させた際に、完全に溶解することなくある程度の形態を持ち、一方でＣＭＣ化により塗膜性能も付与されているため、細孔量の大きい低密度嵩高紙に塗工しても紙表面に留まり易く、紙表面に連続した塗膜を形成し、後に塗工される無機顔料を主体とした塗料の紙内部への浸透を抑制することが可能になったと推定される。
【０００７】
【発明の実施の形態】
本発明の浸透抑制剤である不溶性のＣＭＣは、セルロースを発底原料とし軽度にカルボキシメチル化反応を行うことで製造される。
【０００８】
セルロース原料としては、晒または未晒木材あるいは非木材パルプ、精製リンター、酢酸菌等の微生物によって生産されるセルロース等の天然セルロースや、セルロースを銅アンモニア溶液、モルホリン誘導体等何らかの溶媒に溶解し、改めて紡糸された再生セルロース、および上記セルロース系素材を酸加水分解、アルカリ加水分解、酵素分解、爆砕処理、振動ボールミル処理等によって解重合処理した微細セルロースまたは機械的に処理した微細セルロースが例示される。
【０００９】
不溶性のＣＭＣは、公知の方法、例えば、セルロース原料を水酸化ナトリウムなどのアルカリでマーセル化し、次いでカルボキシメチル化剤であるモノクロル酢酸またはモノクロル酢酸ナトリウムでエーテル化反応を行うという製法を適用する。
【００１０】
例えば、セルロースを発底原料とし、溶媒に３〜２０重量倍の低級アルコール、具体的にはメタノール、エタノール、ｎ−プロピルアルコール、イソプロピルアルコール、ｎ−ブタノール、イソブタノール、第３級ブタノール等の単独、または２種以上の混合物と水との混合媒体を使用する。尚、低級アルコールと水の合計に対する低級アルコールの割合は６０〜９５重量％である。マーセル化剤としては、発底原料のグルコース残基当たり０．５〜２０倍モルの水酸化アルカリ金属、具体的には水酸化ナトリウム、水酸化カリウムを使用する。発底原料と溶媒、マーセル化剤を混合し、反応温度０〜７０℃、好ましくは１０〜６０℃、かつ反応時間１５分〜８時間、好ましくは３０分〜７時間、マーセル化処理を行う。その後、カルボキシメチル化剤を発底原料のグルコース残基当たり０．０５〜２．０倍モル添加し、反応温度３０〜９０℃、好ましくは４０〜８０℃、かつ反応時間３０分〜１０時間、好ましくは１時間〜４時間、エーテル化反応させる。
【００１１】
尚、不溶性のＣＭＣは必要に応じて、洗浄工程、乾燥工程、粉砕工程、分級工程を経たものであっても問題はない。
【００１２】
本発明では、不溶性ＣＭＣは、置換度（グルコース残基の水酸基がカルボキシメチル基で置換された数、以下ＣＭ−ＤＳと略）が０．２５〜０．５０で、かつ１％水溶液粘度が５〜３００ｍＰａ・ｓの範囲にあるものが好ましい。ＣＭ−ＤＳが０．２５未満もしくは１％水溶液粘度が５ｍＰａ・ｓ未満であれば、塗膜形成能力が低く、また粘度が低いために浸透抑制効果が低い。また、ＣＭ−ＤＳが０．５０を越えた場合には水に対する溶解性が高まり、軽量嵩高で細孔量の多い嵩高原紙の紙表面に留まることが出来ず、塗料の浸透を抑制することが難しくなる。さらには１％水溶液粘度が３００ｍＰａ・ｓを越えた場合、粘性が高すぎるため表面塗工剤として紙表面に塗工するのが難しくなる。より好ましくは、ＣＭ−ＤＳが０．２５〜０．４０、かつ１％水溶液粘度が５〜２００ｍＰａ・ｓの範囲である。本発明における粘度とは、Ｂ型回転粘度計（ローターＮＯ．２、回転数３０ｒｐｍ）により、２５℃にて無水物換算１％水溶液を測定した値である。
【００１３】
なお、本発明の不溶性ＣＭＣを浸透抑制剤として使用するときは、不溶性のＣＭＣを５０重量％以上配合するものであり、その他の成分としては、従来使用されている表面サイズ剤、でんぷんやＰＶＡなどの水溶性高分子等を併用して使用することが出来る。
【００１４】
本発明においては、パルプを主原料とする紙に、浸透抑制剤を設けるための不溶性ＣＭＣの塗工量は、０．３〜３．５ｇ／ｍ２（片面あたり）塗布するのが好ましい。０．３ｇ／ｍ２より少ないと塗料浸透抑制効果が小さく、３．５ｇ／ｍ２より多いと両面では７ｇ／ｍ２になり軽量化に適さない。軽量嵩高を維持し、塗料浸透抑制を効果的に行うには特に０．５〜３ｇ／ｍ２塗布するのが好ましい。塗工方法としては公知の方法より適宜選択して行うことが出来るが、特にポンド式サイズプレス、ゲートロールコーター、シムサイザー等が好ましい。
【００１５】
本発明においては、紙に浸透抑制剤を塗工した原紙に、顔料や接着剤を含有する親水性塗料を設ける。親水性塗料に使用する顔料及び接着剤としては、通常の塗工紙用に用いられるものを使用することができ、必要に応じて分散剤、増粘剤、保水剤、消泡剤、耐水化剤等の通常使用される各種助剤を使用する。
【００１６】
親水性塗料の塗工方法としては、ブレードコーター、ゲートロールコーターなどの公知の方法を使用することができ、必要に応じて、スーパーカレンダー、ソフトカレンダーなどの平滑化処理を行う。本発明の効果をより発揮させるために塗工紙の密度は１．００ｇ／ｃｍ３以下が好ましい。
【００１７】
【実施例】
以下、本発明の実施の形態を実施例により説明するが、本発明はこれによって限定されるものではない。尚、配合量を示す「部」および「％」はすべて「固形分重量部」および「固形分重量％」を示した。
［製造例１］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール１０４５部と水酸化ナトリウム６８．８部を水１６０部に溶解したものとを加え、市販の溶解パルプ（ＮＤＰＴ、日本製紙ケミカル（株式会社）製）を絶乾で２００部仕込んだ。３０℃で９０分間撹拌、混合しアルカリセルロースを調製後、さらに、撹拌しつつ９０％イソプロピルアルコール１００部に溶解したモノクロル酢酸４０．０部を添加し、３０分で７０℃に昇温し、９０分間反応させた。反応終了後、８０％メタノールで２回洗浄、中和、脱液、乾燥し、ＣＭ−ＤＳ ０．２８、１％水溶液粘度３６ｍＰａ・ｓのＣＭＣ（１）を得た。
［製造例２］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール１０４５部と水酸化ナトリウム６８．８部を水１６０部に溶解したものとを加え、市販の溶解パルプ（ＮＤＰＳ、日本製紙ケミカル（株式会社）製）を絶乾で２００部仕込んだ。３０℃で９０分間撹拌、混合しアルカリセルロースを調製後、さらに、撹拌しつつ９０％イソプロピルアルコール１００部に溶解したモノクロル酢酸４０．０部を添加し、３０分で７０℃に昇温し、９０分間反応させた。反応終了後、８０％メタノールで２回洗浄、中和、脱液、乾燥し、ＣＭ−ＤＳ ０．２８、１％水溶液粘度１５５ｍＰａ・ｓのＣＭＣ（２）を得た。
［製造例３］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール１１５０部と水５０部を加え、ＣＭＣ（２）を絶乾で２００部仕込んだ。撹拌しつつ７０℃まで昇温後、３０％過酸化水素水（和光純薬工業（株式会社）製）２０．０部を添加し、更に９０分間撹拌を継続した。冷却後、脱液、乾燥し、ＣＭ−ＤＳ ０．２８、１％水溶液粘度８ｍＰａ・ｓのＣＭＣ（３）を得た。
［製造例４］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール９３２部と水酸化ナトリウム４７．２部を水１１８部に溶解したものとを加え、市販の溶解パルプ（ＮＤＰＳ、日本製紙ケミカル（株式会社）製）を絶乾で２００部仕込んだ。３０℃で９０分間撹拌、混合しアルカリセルロースを調製後、さらに、撹拌しつつ９０％イソプロピルアルコール８０部に溶解したモノクロル酢酸２０．１部を添加し、３０分で７０℃に昇温し、９０分間反応させた。反応終了後、中和、脱液、乾燥し、ＣＭ−ＤＳ ０．１３、１％水溶液粘度５ｍＰａ・ｓのＣＭＣ（４）を得た。
［製造例５］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール１０４５部と水酸化ナトリウム５１．７部を水１６０部に溶解したものとを加え、市販の溶解パルプ（ＬＤＰＴ、日本製紙ケミカル（株式会社）製）を絶乾で２００部仕込んだ。３０℃で９０分間撹拌、混合しアルカリセルロースを調製後、さらに、撹拌しつつ９０％イソプロピルアルコール９０部に溶解したモノクロル酢酸３２．５部を添加し、３０分で７０℃に昇温し、９０分間反応させた。反応終了後、中和、脱液、乾燥、粉砕し、ＣＭ−ＤＳ ０．２１、１％水溶液粘度５．４ｍＰａ・ｓのＣＭＣ（５）を得た。
［製造例６］
回転数を１００ｒｐｍに調節した二軸ニーダーに９９％イソプロピルアルコール１１５０部と水５０部を加え、ＣＭＣ（１）を絶乾で２００部仕込んだ。撹拌しつつ７０℃まで昇温後、３０％過酸化水素水（和光純薬工業（株式会社）製）１０．０部を添加し、更に９０分間撹拌を継続した。冷却後、脱液、乾燥し、ＣＭ−ＤＳ ０．２８、１％水溶液粘度４．５ｍＰａ・ｓのＣＭＣ（６）を得た。
【００１８】
製造例１〜６で得たＣＭＣの置換度（ＣＭ−ＤＳ）と、水溶性の試験法は下記の通りである。
＜ＣＭ−ＤＳの測定方法＞
試料約２．０ｇを精秤して、３００ｍｌ共栓付き三角フラスコに入れた。硝酸メタノール（無水メタノール１Ｌに特級濃硝酸１００ｍｌを加えた液）１００ｍｌを加え、３時間振とうして、ＣＭＣのナトリウムを酸型に変換しカルボキシメチルセルロース（以下Ｈ−ＣＭＣと略す）にした。その絶乾Ｈ−ＣＭＣを１．５〜２．０ｇ精秤し、３００ｍｌ共栓付き三角フラスコに入れた。８０％メタノール１５ｍｌでＨ−ＣＭＣを湿潤し、０．１Ｎ−ＮａＯＨ１００ｍｌを加え、室温で３時間振とうした。指示薬として、フェノールフタレインを用いて、０．１Ｎ−Ｈ２ＳＯ４で過剰のＮａＯＨを逆滴定した。ＣＭ−ＤＳは次式によって、算出した。
Ａ ＝（（１００×Ｆ´ − ０．１Ｎ− Ｈ２ＳＯ４ （ｍｌ）×Ｆ）×０．１）／ Ｈ−ＣＭＣの絶乾重量（ｇ）
ＣＭ−ＤＳ ＝ ０．１６２×Ａ ／ （１−０．０５８×Ａ）
Ａ：Ｈ−ＣＭＣ１ｇを中和するのに必要な１Ｎ−ＮａＯＨの量（ｍｌ）
Ｆ：０．１Ｎ− Ｈ２ＳＯ４のｆａｃｔｏｒ
Ｆ´：０．１Ｎ−ＮａＯＨのｆａｃｔｏｒ
＜水溶解性試験＞
得られたＣＭＣ試料２ｇを常温の水１００ｍｌ中に添加し、スターラーで１０分間撹拌後、その状態を目視で判断した。尚、評価は以下のように定めた。
○：不溶または膨潤して一部溶解
×：均一に溶解
［実施例１］
浸透抑制剤として、上記製造例１で製造したＣＭ−ＤＳが０．２８、１％濃度で水に分散した時の粘度が３６ｍＰａ・ｓのＣＭＣ（１）を用い、このものを３％濃度で水に分散し、ブレード式のラボ用塗工機（速度２ｍ／分）を使用して、密度０．４１ｇ／ｃｍ３、透気抵抗度は１５秒の中質紙（坪量６０．４ｇ／ｍ２）の片面に塗布量２．１ｇ／ｍ２塗工して塗工原紙を得た。この浸透抑制処理した塗工原紙の透気抵抗度は４６秒であった。炭酸カルシウムスラリー（ＦＭＴ９０ ファイマテック株式会社製）と微粒カオリン（アマゾンプラス，カデム株式会社製）を５０：５０の重量割合で配合、分散し、バインダーとして顔料１００部に対してラテックス１１部、澱粉３．５部にて塗料濃度６５％で塗料を調整し、この塗料を塗工原紙の浸透抑制剤塗工面に上記のブレード式ラボ用塗工機にて塗工した。その際の塗布量は３３．９ｇ／ｍ２であった。さらにテストスーパーカレンダーにて線圧５０ｋｇ／ｃｍ、２ニップ処理した。
［実施例２］
浸透抑制剤として、上記製造例２で製造したＣＭ‐ＤＳが０．２８、１％濃度で水で分散した時の粘度が１５５ｍＰａ・ｓのＣＭＣ（２）を２．５％濃度で水で分散し、片面塗工量を１．４ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制表面処理後の塗工原紙の透気抵抗度は２７７秒で、顔料含有塗料の塗工量は３１．３ｇ／ｍ２であった。
［実施例３］
浸透抑制剤として、上記製造例２で製造したＣＭ‐ＤＳが０．２８、１％濃度で水で分散した時の粘度が１５５ｍＰａ・ｓのＣＭＣ（２）を１．５％濃度で水で分散し、片面塗工量を０．９ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制処理した塗工原紙の透気抵抗度は３９秒で、顔料含有塗料の塗工量は３４．７ｇ／ｍ２であった。
［実施例４］
浸透抑制剤として、上記製造例３で製造したＣＭ‐ＤＳが０．２８、１％濃度で水で分散した時の粘度が８ｍＰａ・ｓのＣＭＣ（３）を４．０％濃度で水で分散し、片面塗工量を２．３ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制処理した塗工原紙の透気抵抗度は４４秒で、顔料含有塗料の塗工量は３４．３ｇ／ｍ２であった。
［比較例１］
実施例１と同じ密度０．４１ｇ／ｃｍ３、透気抵抗度が１５秒の中質紙（坪量６０．４ｇ／ｍ２）に、浸透抑制剤を塗布せずに、そのまま実施例１と同様にラボ用塗工機にて片面に顔料含有塗料を塗工した。
その際の塗工量は３７．３ｇ／ｍ２であった。
［比較例２］
市販のＰＶＡ（ＰＶＡ１１７、クラレ（株式会社））を浸透抑制剤として濃度５％で溶解し、片面塗工量を２．０ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお浸透抑制処理した塗工原紙の透気抵抗度は２７秒で、塗工量は３６．２ｇ／ｍ２であった。
［比較例３］
市販の酸化澱粉（ＳＫ２０、日本コーンスターチ（株式会社））を浸透抑制剤として濃度５％で溶解し、片面塗工量を４．０ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお浸透抑制処理後の塗工原紙の透気抵抗度は４６秒で、塗工量は３５．１ｇ／ｍ２であった。
［比較例４］
浸透抑制剤として、上記製造例４で製造したＣＭ−ＤＳが０．１３、１％濃度で水に分散した時の粘度が５ｍＰａ・ｓのＣＭＣ （４）を３％濃度で水に分散し、片面塗工量を１．９ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制処理後の塗工原紙の透気抵抗度は１４秒で、塗工量は３７．３ｇ／ｍ２であった。
［比較例５］
浸透抑制剤として、上記製造例５で製造したＣＭ−ＤＳが０．２１、１％濃度で水に分散した時の粘度が５．４ｍＰａ・ｓのＣＭＣ（５）を２％濃度で水に分散し、片面塗工量を２．８ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制処理後の塗工原紙の透気抵抗度は１８秒で、塗工量は３６．９ｇ／ｍ２であった。
［比較例６］
浸透抑制剤として、上記製造例６で製造したＣＭ−ＤＳが０．２８、１％濃度で水に分散した時の粘度が４．５ｍＰａ・ｓのＣＭＣ（６）を５．８％濃度で水に分散し、片面塗工量を１．８ｇ／ｍ２とした以外は実施例１と同様にし、さらに顔料含有塗料の塗工も実施例１と同条件にて実施した。なお、浸透抑制処理後の塗工原紙の透気抵抗度は２３秒で、塗工量は３６．６ｇ／ｍ２であった。
［比較例７］
実施例１と同じ密度０．４１ｇ／ｃｍ３、透気抵抗度は１５秒の中質紙に、浸透抑制剤を塗布せずに、さらにそのまま実施例１と同様にラボ用塗工機にて片面を顔料含有塗料を塗工した。ただし、塗工する際の塗料濃度を６０％として、実施例１と同程度の塗工量が得られるようにした。この時の塗布量は３３．５ｇ／ｍ２であった。これ以外は同様にした。
【００１９】
これらの実施例、比較例で得た印刷用紙の評価は、透気抵抗度、顔料含有塗料の塗工量（付着量）、密度、および紙質試験として平滑度と光沢度で行った。
【００２０】
それぞれの測定方法は下記の通りであり、結果は纏めて表１として示した。
＜透気抵抗度＞Ｊａｐａｎ Ｔａｐｐｉ 紙パルプ試験法Ｎｏ５−２ 王研法に準じて測定した。
＜密度＞ ＪＩＳ Ｐ８１１８の方法に準じて測定した。
＜平滑度＞ Ｊａｐａｎ Ｔａｐｐｉ 紙パルプ試験法Ｎｏ５−２ 王研法に準じて測定した。
＜光沢度＞ ＪＩＳ Ｐ８１４２の方法に準じて測定した。
【００２１】
【表１】
表１において、実施例と比較例を比べると、実施例１〜４のように、本発明のＣＭＣ（１）〜（３）を浸透抑制剤として表面塗工すると、塗工しない場合（比較例１）や、また一般的に被膜形成能が高いといわれるＰＶＡを塗工した場合（比較例２）より透気抵抗度が高く、すなわち原紙表面で塗膜が形成されて空気の透過を阻害し、この表面塗膜が塗料の浸透も抑制していることが明らかである。実際に顔料含有塗料の塗布量も実施例は低く、かつカレンダー処理した際の平滑性も大幅に高くなっており、比較例に比較して塗料中の顔料の浸透を抑制し、効率的に表面を被覆していることが分かる。一方、比較例３では澱粉を片面あたり４ｇ／ｍ２塗布すると実施例１並の透気抵抗度となるが、実施例１の塗布量の倍であり、このため密度が高くなるので好ましくない。
置換度が低いＣＭＣ（４）および（５）を用いた比較例４、５、また置換度は実施例１と同じでも減粘処理して粘度が低いＣＭＣ（６）を用いた比較例６は透気抵抗度の上昇が小さく、原紙表面での塗膜形成が不充分で、浸透抑制も不充分であった。さらに、塗料濃度を下げて塗布量を落とすと（比較例７）、密度は低下するが、塗工液の浸透がさらに大きくなり、顔料による紙表面の被覆が悪いため平滑性、光沢度が低下していることがわかる。
【００２２】
【発明の効果】
請求項１記載の特定の物性を有するＣＭＣからなる浸透抑制剤および請求項２あるいは３記載の浸透抑制方法によれば、嵩高な紙のような親水性かつ多孔性表層部を有する支持体の内部への親水性塗料の浸透が抑制され、少ない塗布量で有効な塗工層が得られた。
【００２３】
請求項４あるいは請求項５記載の塗工原紙、あるいは塗工紙によれば、軽量嵩高な塗工紙を得ることができた。
【００２４】
省資源省エネルギーの観点からも重要性を増しており、需要もあるが、従来製造が困難であった、低密度軽量で、嵩高な塗工紙を製造することができる手段を見出したことは、工業的価値が極めて高いものである。[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention, when a hydrophilic paint is applied to paper made of pulp as a main raw material, suppresses the penetration of the paint into the inside of the paper, and the paint can be efficiently formed as a coating layer on a support. The present invention relates to a new permeation inhibitor and a method for using the same, and more particularly to a permeation inhibitor and a permeation suppression method which can be applied to a porous lightweight and bulky paper to obtain an advantageous effect.
[0002]
[Prior art]
In recent years, the demand for weight reduction of printing paper has been increasing to reduce transportation and mailing costs. However, simply reducing the weight, that is, reducing the basis weight of the printing paper, is not preferable because the thickness of the paper is reduced and the volume feeling of the booklet is impaired. The required weight reduction means that the paper weight is reduced while the paper thickness is not reduced, and more preferably the paper thickness is increased to increase the bulk, that is, the weight is increased. On the other hand, the visualization and colorization of printed materials have been progressing, and the demand for coated paper for printing, which has a smooth coating layer on the paper surface as an ink receiving layer, has been increasing year by year as compared with uncoated printing paper. The coating layer mainly composed of inorganic pigments such as calcium carbonate and kaolin has a higher specific gravity than the base paper mainly composed of pulp, and the coating amount is reduced as much as possible to reduce the weight of the coated paper. There is a need. In order to increase the bulk, it is conceivable to increase the bulk of the coated base paper. However, when the base paper is made bulky, the density becomes low and the number of pores increases. Therefore, at the time of coating, the permeability of the paint into the base paper increases, and it becomes difficult to uniformly coat the base paper surface with a low coating amount. Therefore, if the base paper is calendered before coating in order to reduce the amount of pores in the base paper, the thickness of the base paper is reduced, so that bulky low density paper cannot be obtained. Thus, even if a lightweight and bulky base paper is used to increase the weight and bulk of the coated paper, simply applying a paint mainly composed of an inorganic pigment having a high specific gravity increases the amount of application due to penetration of the paint. It is difficult to realize lightweight and bulky.
[0003]
As a method for suppressing the penetration of the paint into the inside of the base paper, a method of sizing the base paper to reduce the wettability between the base paper and water as a solvent for the paint can be considered. However, even if such a treatment is applied to a low-density base paper having a large amount of pores, the effect is small. Also, a surface treating agent mainly containing a water-soluble polymer such as starch for coating and polyvinyl alcohol (PVA) is applied to the paper surface to form a coating film on the paper surface, and a coating material to be subsequently applied Although a method of suppressing permeation is also conceivable, it is difficult to form an effective permeation suppression coating on the paper surface because the surface coating agent of the lightweight bulky base paper also penetrates the paper layer. Although not a hydrophilic paint, it is surface-treated with an aqueous solution containing carboxymethylcellulose (CMC), which is a water-soluble polymer, in order to suppress the penetration of a release agent such as silicone into a release paper substrate, and furthermore, PVA. Discloses a method of applying 2 to 7 g / m 2 of an aqueous solution containing (i.e., Patent Document 1), but requires two coatings, increases the amount of application, and processes low density bulky base paper. Not suitable for the method. Thus, it was very difficult to effectively suppress the permeation of the hydrophilic paint on the surface of the lightweight bulky base paper and efficiently form the coating film of the coating layer.
[0004]
[Patent Document 1] Japanese Patent Application Laid-Open No. 6-2801999 [Problems to be Solved by the Invention]
The present invention has been conceived in order to solve the problems of the prior art as described above, and a permeation suppressant that efficiently exhibits a permeation suppression effect on a low-density bulky paper surface, and a permeation of a paint using the same. An object of the present invention is to provide a method for suppressing the occurrence of light, and thereby a light and bulky coated base paper and the coated paper.
[0005]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a method for suppressing the penetration of paint into low-density bulky paper.As a result, the water-soluble, water-swellable or substantially water-insoluble carboxymethylcellulose sodium salt is used as a surface coating agent. It has been found that the above problem can be solved by utilizing the present invention, and the present invention has been made based on this finding. In the present invention, the term “water swelling or substantially water-insoluble” means that when a CMC is stirred and dissolved in water to a concentration of 2% by weight at room temperature and visually observed, a uniform solution is not obtained. It is seen as not being dissolved or showing a swollen state and partly as being dissolved. Water-swellable or substantially water-insoluble carboxymethylcellulose sodium salt is hereinafter simply referred to as insoluble CMC.
[0006]
When insoluble CMC is used as a permeation inhibitor and a dilute solution is applied to the surface of a light bulky paper, it is not clear why the above problem is solved. However, lightly carboxymethylated CMC is water-swellable or substantially water-soluble. Insoluble, when dispersed in water, it has a certain form without completely dissolving it, and on the other hand, it has been given a coating performance by CMC conversion, so it can be used for low density bulky paper with a large amount of pores. It is presumed that it easily stayed on the paper surface even after coating, and a continuous coating film was formed on the paper surface, and it was possible to suppress the penetration of the paint mainly composed of inorganic pigments to be applied later inside the paper Is done.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The insoluble CMC, which is the permeation inhibitor of the present invention, is produced by performing a carboxymethylation reaction lightly using cellulose as a starting material.
[0008]
As a cellulose raw material, bleached or unbleached wood or non-wood pulp, refined linters, natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, and cellulose are dissolved in a solvent such as a copper ammonia solution, a morpholine derivative, and then renewed. Examples include spun regenerated cellulose, fine cellulose obtained by depolymerizing the above-mentioned cellulose-based material by acid hydrolysis, alkali hydrolysis, enzymatic decomposition, explosion treatment, vibrating ball mill treatment or the like, or mechanically treated fine cellulose.
[0009]
For the insoluble CMC, a known method, for example, a method of mercerizing a cellulose raw material with an alkali such as sodium hydroxide and then performing an etherification reaction with monochloroacetic acid or sodium monochloroacetate as a carboxymethylating agent is applied.
[0010]
For example, cellulose is used as the starting material, and the solvent is a lower alcohol of 3 to 20 times by weight, specifically methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, tertiary butanol or the like alone. Or a mixed medium of two or more mixtures and water. The ratio of the lower alcohol to the total of the lower alcohol and water is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 moles of an alkali metal hydroxide, specifically, sodium hydroxide or potassium hydroxide is used per 0.5 to 20 moles of the glucose residue of the starting material. The bottom starting material, the solvent and the mercerizing agent are mixed, and the mercerizing treatment is performed at a reaction temperature of 0 to 70 ° C, preferably 10 to 60 ° C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 2.0 times mol per glucose residue of the starting material, and the reaction temperature is 30 to 90 ° C, preferably 40 to 80 ° C, and the reaction time is 30 minutes to 10 hours. The etherification reaction is preferably performed for 1 to 4 hours.
[0011]
It should be noted that there is no problem even if the insoluble CMC has undergone a washing step, a drying step, a pulverizing step, and a classification step as necessary.
[0012]
In the present invention, the insoluble CMC has a degree of substitution (the number of hydroxyl groups of glucose residues substituted with carboxymethyl groups, hereinafter abbreviated as CM-DS) of 0.25 to 0.50, and a 1% aqueous solution viscosity of 5%. Those in the range of ~ 300 mPa · s are preferred. When the CM-DS is less than 0.25 or the 1% aqueous solution viscosity is less than 5 mPa · s, the ability to form a coating film is low, and the viscosity is low, so that the effect of suppressing permeation is low. On the other hand, when the CM-DS exceeds 0.50, the solubility in water increases, and it is not possible to remain on the paper surface of the bulky base paper having a light weight and a large amount of pores. It becomes difficult. Further, when the 1% aqueous solution viscosity exceeds 300 mPa · s, it is difficult to apply as a surface coating agent on the paper surface because the viscosity is too high. More preferably, the CM-DS ranges from 0.25 to 0.40, and the 1% aqueous solution viscosity ranges from 5 to 200 mPa · s. The viscosity in the present invention is a value obtained by measuring an anhydrous 1% aqueous solution at 25 ° C. with a B-type rotational viscometer (rotor No. 2, rotation speed 30 rpm).
[0013]
When the insoluble CMC of the present invention is used as a permeation suppressant, the insoluble CMC is blended in an amount of 50% by weight or more. Other components include conventionally used surface sizing agents, starch and PVA. Can be used in combination.
[0014]
In the present invention, it is preferable to apply 0.3 to 3.5 g / m 2 (per one side) of the insoluble CMC for providing the penetration inhibitor on paper made mainly of pulp. 0.3 g / m 2 less and less paint permeation suppressing effect than in the double-sided with more than 3.5 g / m 2 is not suitable for weight reduction becomes 7 g / m 2. In order to maintain the lightweight bulkiness and effectively control the penetration of the paint, it is particularly preferable to apply 0.5 to 3 g / m 2 . The coating method can be appropriately selected from known methods, but a pound size press, a gate roll coater, a shim sizer, and the like are particularly preferable.
[0015]
In the present invention, a hydrophilic paint containing a pigment or an adhesive is provided on a base paper obtained by applying a penetration inhibitor to paper. Pigments and adhesives used in hydrophilic paints can be those used for ordinary coated paper, and if necessary, dispersants, thickeners, water retention agents, defoamers, water resistance Various commonly used auxiliaries such as agents are used.
[0016]
As a method for applying the hydrophilic paint, a known method such as a blade coater or a gate roll coater can be used. If necessary, a smoothing treatment such as a super calender or a soft calender is performed. The density of the coated paper is preferably 1.00 g / cm 3 or less in order to further exert the effects of the present invention.
[0017]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, “parts” and “%” indicating the blending amounts all indicate “parts by weight of solid content” and “% by weight of solid content”.
[Production Example 1]
To a biaxial kneader whose rotation speed was adjusted to 100 rpm, 1045 parts of 99% isopropyl alcohol and 68.8 parts of sodium hydroxide dissolved in 160 parts of water were added, and commercially available dissolved pulp (NDPT, Nippon Paper Chemical Co., Ltd.) )) Was completely dried and 200 parts were charged. After stirring and mixing at 30 ° C. for 90 minutes to prepare alkali cellulose, 40.0 parts of monochloroacetic acid dissolved in 100 parts of 90% isopropyl alcohol was added with stirring, and the temperature was raised to 70 ° C. in 30 minutes. Allowed to react for minutes. After completion of the reaction, the resultant was washed twice with 80% methanol, neutralized, drained, and dried to obtain CMC (1) having a CM-DS of 0.28 and a 1% aqueous solution viscosity of 36 mPa · s.
[Production Example 2]
To a twin-screw kneader whose rotation speed was adjusted to 100 rpm, 1045 parts of 99% isopropyl alcohol and 68.8 parts of sodium hydroxide dissolved in 160 parts of water were added, and commercially available dissolved pulp (NDPS, Nippon Paper Chemical Co., Ltd.) )) Was completely dried and 200 parts were charged. After stirring and mixing at 30 ° C. for 90 minutes to prepare alkali cellulose, 40.0 parts of monochloroacetic acid dissolved in 100 parts of 90% isopropyl alcohol was added with stirring, and the temperature was raised to 70 ° C. in 30 minutes. Allowed to react for minutes. After completion of the reaction, the resultant was washed twice with 80% methanol, neutralized, drained, and dried to obtain CMC (2) having a CM-DS of 0.28 and a 1% aqueous solution viscosity of 155 mPa · s.
[Production Example 3]
1150 parts of 99% isopropyl alcohol and 50 parts of water were added to a twin-screw kneader whose rotation number was adjusted to 100 rpm, and 200 parts of CMC (2) were completely dried. After the temperature was raised to 70 ° C. while stirring, 20.0 parts of 30% hydrogen peroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and stirring was further continued for 90 minutes. After cooling, it was drained and dried to obtain CMC (3) having a CM-DS of 0.28 and a 1% aqueous solution viscosity of 8 mPa · s.
[Production Example 4]
932 parts of 99% isopropyl alcohol and 47.2 parts of sodium hydroxide dissolved in 118 parts of water were added to a biaxial kneader adjusted to a rotation speed of 100 rpm, and commercially available dissolved pulp (NDPS, Nippon Paper Chemical Co., Ltd. )) Was completely dried and 200 parts were charged. After stirring and mixing at 30 ° C. for 90 minutes to prepare alkali cellulose, 20.1 parts of monochloroacetic acid dissolved in 80 parts of 90% isopropyl alcohol was added with stirring, and the temperature was raised to 70 ° C. in 30 minutes. Allowed to react for minutes. After completion of the reaction, neutralization, deliquoring and drying were performed to obtain CMC (4) having a CM-DS of 0.13 and a 1% aqueous solution viscosity of 5 mPa · s.
[Production Example 5]
To a biaxial kneader whose rotation speed was adjusted to 100 rpm, 1045 parts of 99% isopropyl alcohol and 51.7 parts of sodium hydroxide dissolved in 160 parts of water were added, and commercially available dissolved pulp (LDPT, Nippon Paper Chemical Co., Ltd.) )) Was completely dried and 200 parts were charged. After stirring and mixing at 30 ° C. for 90 minutes to prepare alkali cellulose, 32.5 parts of monochloroacetic acid dissolved in 90 parts of 90% isopropyl alcohol were added with stirring, and the temperature was raised to 70 ° C. in 30 minutes. Allowed to react for minutes. After the completion of the reaction, neutralization, deliquoring, drying, and pulverization were performed to obtain CMC (5) having a CM-DS of 0.21, and a 1% aqueous solution viscosity of 5.4 mPa · s.
[Production Example 6]
1150 parts of 99% isopropyl alcohol and 50 parts of water were added to a twin-screw kneader whose rotation speed was adjusted to 100 rpm, and 200 parts of CMC (1) were completely dried. After the temperature was increased to 70 ° C. with stirring, 10.0 parts of 30% aqueous hydrogen peroxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and stirring was continued for another 90 minutes. After cooling, it was drained and dried to obtain CMC (6) having a CM-DS of 0.28 and a 1% aqueous solution viscosity of 4.5 mPa · s.
[0018]
The substitution degree (CM-DS) of the CMC obtained in Production Examples 1 to 6 and the water solubility test method are as follows.
<Measurement method of CM-DS>
About 2.0 g of the sample was precisely weighed and placed in a 300 ml Erlenmeyer flask with a stopper. 100 ml of methanol nitrate (1 L of anhydrous methanol to which 100 ml of special grade concentrated nitric acid was added) was added, and the mixture was shaken for 3 hours to convert sodium in CMC into an acid form to obtain carboxymethyl cellulose (hereinafter abbreviated as H-CMC). 1.5 to 2.0 g of the absolutely dried H-CMC was precisely weighed and placed in a 300 ml stoppered Erlenmeyer flask. H-CMC was wet with 15 ml of 80% methanol, 100 ml of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. As an indicator, using phenolphthalein was back titrated excess NaOH with 0.1N-H 2 SO 4. CM-DS was calculated by the following equation.
A = ((100 × F′−0.1N—H 2 SO 4 (ml) × F) × 0.1) / absolute dry weight of H-CMC (g)
CM-DS = 0.162 × A / (1-0.058 × A)
A: Amount of 1N-NaOH required to neutralize 1 g of H-CMC (ml)
F: 0.1N-of H 2 SO 4 factor
F ': 0.1N-NaOH factor
<Water solubility test>
2 g of the obtained CMC sample was added to 100 ml of water at normal temperature, and the mixture was stirred for 10 minutes with a stirrer, and the state was visually determined. The evaluation was determined as follows.
：: Insoluble or swollen and partially dissolved X: Uniformly dissolved [Example 1]
As the permeation suppressant, CMC (1) having a viscosity of 36 mPa · s when the CM-DS produced in Production Example 1 was dispersed in water at a concentration of 0.28 and 1% was used. Dispersed in water, using a blade-type lab coater (speed 2 m / min), a density of 0.41 g / cm 3 , and air resistance of 15 seconds for medium paper (basis weight 60.4 g / m 2 ) was coated on one side at a coating amount of 2.1 g / m 2 to obtain a coated base paper. The air permeability resistance of the coated base paper subjected to the permeation suppression treatment was 46 seconds. A calcium carbonate slurry (FMT90, manufactured by Fimatec Co., Ltd.) and fine kaolin (Amazon Plus, manufactured by Kadem Co., Ltd.) were mixed and dispersed in a weight ratio of 50:50, and 11 parts of latex and 100 parts of starch were used as a binder for 100 parts of pigment. The paint was adjusted at a paint concentration of 65% in 0.5 part, and this paint was applied to the surface of the base paper for coating with the penetration inhibitor using the above-mentioned blade-type lab coater. The coating amount at that time was 33.9 g / m 2 . Further, a linear pressure of 50 kg / cm and a 2-nip treatment were performed by a test super calendar.
[Example 2]
As a penetration inhibitor, CMC (2) having a viscosity of 155 mPa · s when the CM-DS produced in Production Example 2 was dispersed in water at a concentration of 0.28 and 1% was dispersed in water at a concentration of 2.5%. In the same manner as in Example 1 except that the amount of one-side coating was changed to 1.4 g / m 2 , coating of a pigment-containing paint was performed under the same conditions as in Example 1. The air permeability resistance of the coated base paper after the permeation suppression surface treatment was 277 seconds, and the coating amount of the pigment-containing paint was 31.3 g / m 2 .
[Example 3]
As a penetration inhibitor, CMC (2) having a viscosity of 155 mPa · s when the CM-DS produced in Production Example 2 was dispersed in water at a concentration of 0.28 and 1% was dispersed in water at a concentration of 1.5%. Then, the same procedure as in Example 1 was carried out except that the amount of one-side coating was 0.9 g / m 2, and the coating of the pigment-containing paint was also carried out under the same conditions as in Example 1. The air permeability resistance of the base paper subjected to the permeation suppression treatment was 39 seconds, and the coating amount of the pigment-containing paint was 34.7 g / m 2 .
[Example 4]
As a penetration inhibitor, CMC (3) having a viscosity of 8 mPa · s when the CM-DS produced in Production Example 3 was dispersed in water at a concentration of 0.28 and 1% was dispersed in water at a concentration of 4.0%. In the same manner as in Example 1 except that the amount of one-side coating was 2.3 g / m 2 , coating of a pigment-containing paint was performed under the same conditions as in Example 1. The air permeability resistance of the coated base paper subjected to the permeation suppression treatment was 44 seconds, and the coating amount of the pigment-containing paint was 34.3 g / m 2 .
[Comparative Example 1]
The same density as in Example 1 was applied to a medium paper (basic weight: 60.4 g / m 2 ) having a density of 0.41 g / cm 3 and an air resistance of 15 seconds, without applying a penetration inhibitor. Similarly, a pigment-containing paint was applied on one side by a laboratory coater.
The coating amount at that time was 37.3 g / m 2 .
[Comparative Example 2]
Commercially available PVA (PVA117, Kuraray Co., Ltd.) was dissolved at a concentration of 5% as a permeation suppressor, and the same procedure as in Example 1 was carried out except that the coating amount on one side was 2.0 g / m 2. Was carried out under the same conditions as in Example 1. The air permeability resistance of the coated base paper subjected to the permeation suppression treatment was 27 seconds, and the coated amount was 36.2 g / m 2 .
[Comparative Example 3]
A commercially available oxidized starch (SK20, Nippon Corn Starch (KK)) was dissolved at a concentration of 5% as a penetration inhibitor, and the same procedure as in Example 1 was carried out except that the coating amount on one side was 4.0 g / m 2. The coating of the contained paint was also performed under the same conditions as in Example 1. The air permeability resistance of the coated base paper after the permeation suppression treatment was 46 seconds, and the coated amount was 35.1 g / m 2 .
[Comparative Example 4]
As a penetration inhibitor, CMC (4) having a viscosity of 5 mPa · s when the CM-DS produced in Production Example 4 was dispersed in water at a concentration of 0.13 and 1% was dispersed in water at a concentration of 3%, The same procedures as in Example 1 were carried out except that the amount of one-side coating was 1.9 g / m 2, and the coating of a pigment-containing paint was also carried out under the same conditions as in Example 1. The air permeability resistance of the coated base paper after the permeation suppression treatment was 14 seconds, and the coated amount was 37.3 g / m 2 .
[Comparative Example 5]
As a penetration inhibitor, CMC (5) having a viscosity of 5.4 mPa · s when the CM-DS produced in Production Example 5 was dispersed in water at a concentration of 0.21 and 1% was dispersed in water at a concentration of 2%. In the same manner as in Example 1 except that the amount of one-side coating was changed to 2.8 g / m 2 , coating of a pigment-containing paint was performed under the same conditions as in Example 1. The air permeability resistance of the coated base paper after the permeation suppression treatment was 18 seconds, and the coated amount was 36.9 g / m 2 .
[Comparative Example 6]
As a penetration inhibitor, CMC (6) having a viscosity of 4.5 mPa · s when the CM-DS produced in Production Example 6 was dispersed in water at a concentration of 0.28 and 1% was used at a concentration of 5.8%. In the same manner as in Example 1 except that the amount of one-side coating was changed to 1.8 g / m 2, and the coating of a pigment-containing coating was performed under the same conditions as in Example 1. The air permeability resistance of the coated base paper after the permeation suppression treatment was 23 seconds, and the coated amount was 36.6 g / m 2 .
[Comparative Example 7]
The same density as in Example 1, 0.41 g / cm 3 , and air permeability of 15 seconds were applied to a medium paper without applying a permeation suppressant, and further as it was in Example 1, using a laboratory coating machine. One side was coated with a pigment-containing paint. However, the coating amount at the time of coating was set to 60% so that the same amount of coating as in Example 1 was obtained. The coating amount at this time was 33.5 g / m 2 . Other than this, it was the same.
[0019]
The evaluation of the printing papers obtained in these Examples and Comparative Examples was performed based on the air resistance, the coating amount (adhesion amount) of the pigment-containing paint, the density, and the smoothness and glossiness as paper quality tests.
[0020]
The respective measuring methods are as follows, and the results are collectively shown in Table 1.
<Air Permeability> Measured according to Japan Tappi paper pulp test method No. 5-2 Oken method.
<Density> It was measured according to the method of JIS P8118.
<Smoothness> Japan Tappi paper pulp test method No.5-2 was measured according to the Oken method.
<Glossiness> The glossiness was measured according to the method of JIS P8142.
[0021]
[Table 1]
In Table 1, when Examples and Comparative Examples are compared, as in Examples 1 to 4, when CMC (1) to (3) of the present invention is surface-coated as a permeation suppressant, no coating is performed (Comparative Example). 1) and the air permeability resistance is higher than when PVA, which is generally said to have a high film forming ability, is applied (Comparative Example 2), that is, a coating film is formed on the base paper surface to inhibit air permeation. It is clear that the surface coating also suppresses the penetration of the paint. Actually, the coating amount of the pigment-containing paint was low in the examples, and the smoothness when calendered was also significantly increased. Thus, compared to the comparative example, the penetration of the pigment in the paint was suppressed, and the surface efficiency was improved. It can be seen that is covered. On the other hand, in Comparative Example 3, when the starch was applied at 4 g / m 2 per one surface, the air permeability resistance was equivalent to that of Example 1. However, the amount of application was twice that of Example 1 and the density was increased, which is not preferable.
Comparative Examples 4 and 5 using CMCs (4) and (5) having a low degree of substitution, and Comparative Examples 6 using CMC (6) having a low viscosity by performing a viscosity reducing treatment even though the degree of substitution was the same as in Example 1 The rise in air permeability was small, the formation of a coating film on the base paper surface was insufficient, and the suppression of penetration was insufficient. Further, when the coating amount was lowered by lowering the coating concentration (Comparative Example 7), the density was lowered, but the penetration of the coating liquid was further increased, and the smoothness and glossiness were lowered due to poor coating of the paper surface with the pigment. You can see that it is doing.
[0022]
【The invention's effect】
According to the permeation suppressant comprising CMC having the specific physical properties described in claim 1 and the permeation suppression method according to claim 2 or 3, the inside of a support having a hydrophilic and porous surface layer such as bulky paper. The penetration of the hydrophilic paint into the coating was suppressed, and an effective coating layer was obtained with a small coating amount.
[0023]
According to the coated base paper or coated paper according to claim 4 or 5, a light and bulky coated paper could be obtained.
[0024]
From the viewpoint of resource saving and energy saving, the importance is increasing, and there is demand, but it has been difficult to manufacture conventionally, and it has been found that means for manufacturing low-density, lightweight, bulky coated paper has been found. It has an extremely high industrial value.
