JP2004330535A - Image forming method and aqueous ink set used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous ink set having a high concentration and capable of forming a uniform black image in using a cyan ink, a magenta ink and a yellow ink to form a color image by CM separation. <P>SOLUTION: The aqueous ink set used for the ink jet recording method by the CM separation comprises the cyan ink having an additive, a water-soluble cyan pigment and a first water-soluble organic solvent high in the solubility of the water-soluble cyan pigment and less volatile than water, the magenta ink having an additive, a water-soluble magenta pigment and a first water-soluble organic solvent high in the solubility of the water soluble magenta pigment and less volatile than water, and the yellow ink having a water-soluble yellow pigment and a first water-soluble organic solvent low in the solubility of the water-soluble yellow pigment but containing no additive. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２８】
（上記一般式（Ｉ）中、Ｒ_１は、置換若しくは未置換のアルコキシ基、又は置換若しくは未置換のアリール基を表し、Ｒ_２及びＲ_４は、各々独立に、水素原子又は置換若しくは未置換のアルキル基を表し、Ｒ_３は、水素原子、置換若しくは未置換のアルキル基、置換若しくは未置換のアルコキシ基、置換若しくは未置換のアリールオキシ基又はハロゲン原子を表す。Ｘ_１は、カルボキシル基若しくはその塩、又はスルホン酸基若しくはその塩を表す。ｎは１又は２を表す。）
【００２９】
【化２】

【００３０】
（上記一般式（ＩＩ）中、Ａｒ１は置換若しくは未置換のフェニル基、又は置換若しくは未置換のナフチル基を表し、Ａｒ２は、アセチル基、ベンゾイル基、１，３，５−トリアジニル基、ＳＯ_２−Ｃ_６Ｈ_５基又はＳＯ_２−Ｃ_６Ｈ_４−ＣＨ_３基のいずれかを表す。Ｍは、スルホン酸基の対イオンであり、水素原子、アルカリ金属、アンモニウム及び有機アンモニウムのいずれかを表す。）
（シアンインク）
一般式（ＩＩＩ）で表される水溶性色材を４．５質量％、グリセリン５．０質量％、エチレングリコール６．０質量％、ジエチレングリコール２．０質量％、２−ピロリドン５．０質量％、尿素１０．０質量％、アセチレノールＥ１００（川研ファインケミカル社製）０．２質量％、２−プロパノール２．５質量％、水６４．８質量％
【００３１】
【化３】

【００３２】
（上記一般式（ＩＩＩ）中ＣｕＰｃは、銅フタロシアニン残基を表し、Ｍはアルカリ金属又はアンモニウムであり、ｘは１、２、３または４であり、ｙは１、２または３である。）
シアンインク中の水溶性シアン色材の含量は０．１質量％以上、１０質量％以下が好ましく、０．５質量％以上、６質量％以下がより好ましい。マゼンタインク中の水溶性マゼンタ色材の含量は０．１質量％以上、１０質量％以下が好ましく、０．５質量％以上、６質量％以下がより好ましい。イエローインク中の水溶性イエロー色材の含量は０．１質量％以上、１０質量％以下が好ましく、０．５質量％以上、６質量％以下がより好ましい。インク中の水溶性色材含量がこれらの範囲内にあることによって、画像濃度が高く、均一な黒色画像を形成することができる。
【００３３】
その結果、画像に均一性があり、濃度が高い黒色画像が形成されるようになる。また、本発明のインクセットは、シアンインク、マゼンタインク及びイエローインクからなる群から選択された少なくとも一種のインクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であることが好ましい。３５℃での表面張力は３５ｍＮ／ｍ以上、４８ｍＮ／ｍ以下であることがより好ましく、３６ｍＮ／ｍ以上、４２ｍＮ／ｍ以下であることが更に好ましい。表面張力がこれらの範囲内にあることによって、被記録媒体へのインクの浸透速度が調整され、より黒色の画像濃度と画像均一性が向上する。
【００３４】
また、本発明のインクセットは、水溶性イエロー色材に対する溶解度が１質量％未満で、第１水溶性有機溶媒との相溶性の無い界面活性剤を用いると、上記第１溶剤との複合効果で被記録媒体中での水溶性イエロー色材の析出効果が更に促進される。
【００３５】
界面活性剤としては非イオン性界面活性剤を用いることができる。例えば、アセチレノールＥシリーズ（川研ファインケミカル社製）等のアセチレングリコール系界面活性剤を使用することが好ましく、特に、アセチレノールＥ１００（川研ファインケミカル社製）を使用することが好ましい。ここで「相溶性がない」とは、２つの物質を混合後、一定時間放置した後に、目視で層分離が観察されるか、または一方の物質が他方の物質中に分散していることを表す。
【００３６】
イエローインク中の界面活性剤の含量は、０．０５質量％以上、０．４５質量％以下であることが好ましく、０．１質量％以上、０．３質量％以下であることがより好ましい。水溶性イエロー色材の界面活性剤への溶解度は、１．０質量％未満であることが好ましい。界面活性剤の含量及び水溶性イエロー色材の界面活性剤への溶解度が、これらの範囲内にあることによって、画像濃度が高く、均一な黒色画像を形成することができる。
【００３７】
また、イエローインクに、水溶性イエロー色材が２５℃において１０質量％以上の範囲で溶解し、第１水溶性有機溶媒より揮発性である第２水溶性有機溶媒、を更に有することで、黒色画像のイエロー部の画像均一性を向上させるとともに、この第２水溶性有機溶媒への水溶性シアン色材、水溶性マゼンタ色材の溶解性も高いため、シアン部、マゼンタ部の画像均一性も向上させる。更に、イエローインクの記録ヘッドのノズル目詰まりや、イエローインクを収納するタンクの大気連通部の色材析出を抑制する効果も付与する。
【００３８】
シアンインク中の第１水溶性有機溶媒の含量は１質量％以上、２０質量％以下が好ましく、３質量％以上、１０質量％以下がより好ましい。マゼンタインク中の第１水溶性有機溶媒の含量は１質量％以上、２０質量％以下が好ましく、３質量％以上、１０質量％以下がより好ましい。イエローインク中の第１水溶性有機溶媒の含量は１質量％以上、１０質量％以下が好ましく、２質量％以上、５質量％以下がより好ましい。インク中の第１水溶性有機溶媒の含量が、これらの範囲内にあることによって、画像濃度が高く、均一な黒色画像を形成することができる。
【００３９】
また、シアン色材の第１水溶性有機溶媒への溶解度は１０質量％以上であることが好ましい。イエロー色材の第１水溶性有機溶媒への溶解度は３質量％未満であることが好ましく、２．５質量％未満であることがより好ましい。これらの色材の第１水溶性有機溶媒の溶解度が、これらの範囲内にあることによって、画像濃度が高く、均一な黒色画像を形成することができる。
【００４０】
また、第２水溶性有機溶媒にはジエチレングリコールと、テトラエチレングリコールが含まれていることが望ましい。更には、エチレングリコールと、ジエチレングリコールと、トリエチレングリコールと、テトラエチレングリコールと、が含まれていることがより望ましい。
【００４１】
ここで、揮発性の大小は、日本工業規格（ＪＩＳ）Ｒ３５０３に記載の平圧蒸発皿６０×３０ｍｍに所定量の各溶媒を添加し、６０℃２０％Ｒ．Ｈ．のオーブンに放置したときの各溶媒の揮発度合いを測定することによって評価した。
【００４２】
本発明の上記第１色材（以下、水溶性色材と単に呼ぶ）またはこれを有するインクに加えて好ましい技術課題は、画像自体の特徴を解析すると、高濃度である程、記録媒体表面側に色材が多く存在したり、視覚的に形状がばらついたドットを形成していたり、また、記録媒体中においては、所望の色材を有効に利用できずに無駄に使用していたりすることが判明した点にある。本発明はさらに、これらの少なくとも１つを解決することで、従来よりも優れた黒色系画像を形成できることを見出した。本発明が見出した課題を以下に挙げるが、本発明は以下の課題の少なくとも１つを解決することで上記発明をいっそう優れたものにするものである。
【００４３】
（１）低表面張力のインクを用いた場合には、インクの記録媒体の厚み方向への浸透性が高く、記録媒体内の表面近傍に高濃度で色材を分布させることができず、高画像濃度を達成できないという第１の課題。
（２）画像自体の視覚的な形状因子を作用するもの、すなわち、記録媒体の面方向の色材分布を均一化することができず、十分な画像均一性が達成できない。例えば、従来のインクではインクドットの真円性が悪いという第２の課題。
（３）更に、微細多孔質体を有する記録媒体は普通紙（サイズ紙）よりも微細な細孔を有するため、記録媒体中でのインク挙動が異なり、従来のインクでは高画像濃度化について十分な検討がなされていないという第３の課題。
【００４４】
本発明の更なる課題は以下の説明で明らかとなる。
【００４５】
そこで、本発明者達は主として上記第１、２、３課題について検討した結果、
第１課題は、相溶性のない２種の溶媒を含む高表面張力のインクを用いること、
第２課題は、相溶性のない２種の溶媒と、これらの溶媒を全て溶解させる更にもう一つの溶媒を含むインクを用いること、
第３課題は、インクは界面活性剤含量を所定範囲内とし、界面活性剤と相溶性のない溶媒を有すること、
によって上記課題が解決できることが判明した。
【００４６】
すなわち、前記第１課題を解決する第１水溶性色材関連第１発明のインクは高表面張力で、揮発性が低い溶媒と、この溶媒と相溶性のない溶媒を有することによって、高画像濃度及び画像均一性を図ることができる。
前記第２課題を解決する第１水溶性色材関連第２発明のインクは、上記２種の溶媒に加えて、これらの溶媒を全て溶解させる溶媒を含むことによって、画像均一性を図ることができる。
また、前記第３課題を解決する第１水溶性色材関連第３発明のインクは、界面活性剤の含量を所定範囲内とし、界面活性剤と相溶性のない溶媒を有することによって、微細多孔質体を有する記録媒体にインクを用いた場合にも更に高画像濃度化を図ることができる。
【００４７】
具体的には、
第１水溶性色材関連第１発明は、水溶性色材と、第１溶媒としての水と、
該水溶性色材が２５℃において３質量％未満の範囲で溶解し、該水よりも揮発性の低い第２水溶性有機溶媒と、
該水溶性色材が２５℃において１質量％未満の範囲で溶解する界面活性剤と、を含有し、
常温において該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、
該水系インクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であることを特徴とする水系インクに関する。
【００４８】
また、前記第１水溶性色材関連第３発明は、平均細孔直径が１０ｎｍ以上、３０ｎｍ以下である、微細な多孔質層を有している記録媒体に用いられる水系インクであって、
水溶性色材と、第１溶媒としての水と、
該水溶性色材が２５℃において３質量％未満の範囲で溶解し、該水よりも揮発性の低い第２水溶性有機溶媒と、
該水溶性色材が２５℃において１質量％未満の範囲で溶解する界面活性剤と、を含有し、
常温において該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、
該水系インク中の該第２水溶性有機溶媒の量が５質量％以下であって、
該水系インク中の該界面活性剤の量が０．４５質量％以下であることを特徴とする水系インクに関する。
【００４９】
前記第１水溶性色材関連第２発明は、インクジェットヘッドに使用される水系インクであって、
水溶性色材と、第１溶媒としての水と、
該水溶性色材が２５℃において３質量％未満の範囲で溶解し、該水よりも揮発性の低い第２水溶性有機溶媒と、
該水溶性色材が２５℃において１質量％未満の範囲で溶解する界面活性剤と、を含有し、
常温において該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、
該水系インクが更に、前記水溶性色材が２５℃において１０質量％以上溶解し、かつ、前記水よりも揮発性が低く、該界面活性剤及び第２水溶性有機溶媒を溶解させる第４水溶性有機溶媒を含有し、
該水系インクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であることを特徴とする水系インクに関する。
【００５０】
本発明は、インクジェットヘッドに使用される水系インクであって、
水溶性色材と、第１溶媒としての水と、
該水溶性色材が２５℃において３質量％未満の範囲で溶解し、該水よりも揮発性の低い第２水溶性有機溶媒と、
該水溶性色材が２５℃において１質量％未満の範囲で溶解する界面活性剤と、を含有し、
常温において該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、
該水系インクが更に、前記水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、前記水よりも揮発性の低い水溶性有機溶媒を含み、
該水系インクが更に、前記水溶性色材が２５℃において１０質量％以上溶解し、かつ、前記水よりも揮発性が低く、該界面活性剤及び第２水溶性有機溶媒の全てを溶解させる第３水溶性有機溶媒を含有し、
該水溶性色材が尿素結合を有し、
該水系インクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であって、
平均細孔直径１０ｎｍ以上、３０ｎｍ以下の微細多孔質体を有する記録媒体に用いられることを特徴とする水系インクに関する。
【００５１】
なお、各成分における水溶性色材の溶解率（溶解度）は、以下のようにして行った。
色材が液状の場合には、各成分単独にビーカー１００ｍｌ（ＪＩＳ Ｒ３５０３）に、色材が溶解した水溶液５０グラムを入れ、６０℃、２０Ｒ．Ｈ．％の恒温槽に放置し、３時間当たりの重量変化が０．０１グラム以下になるまで蒸発乾固したものを乳鉢ですりつぶし、粉体にした。これを再び、目的の溶媒に対して飽和状態になるまで溶解させ、この溶解に要した粉体色材の重量を溶媒と粉体色材の総重量で割ったものを溶解率（溶解度）とした。
【００５２】
また、色材がもともと粉体の場合には、目的の溶媒に対して飽和状態になるまで溶解させ、この溶解に要した粉体色材の重量を溶媒と粉体色材の総重量で割ったものを溶解率（溶解度）とした。
【００５３】
また、本発明においては、インクとして使用する溶媒は液体溶媒であるが、簡略のため溶媒と称して以下、説明する。また、インクが記録される媒体は記録媒体と称して説明する。
【００５４】
本明細書において分解性のある尿素結合を有する化合物には、色材は含まない。
【００５５】
次に、好ましい実施の形態を挙げて、本発明をより詳細に説明する。
【００５６】
（第１水溶性色材関連第１発明）
前記第１課題を解決する第１水溶性色材関連第１発明は、水溶性色材と、第１溶媒の水と、水溶性色材を３質量％未満の範囲で溶解し、かつ水よりも揮発性の低い第２水溶性有機溶媒と、水溶性色材を１質量％未満の範囲で溶解する界面活性剤と、を含有し、該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、該水性インクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下である、インク、を記録ヘッドを用いて印刷すると、インクドットが真円に近く、しかも濃度が高い上に、高耐湿性である画像を形成できることが明らかとなった。
ここで「相溶性がない」とは、２つの物質を混合後、一定時間放置した後に、目視で層分離が観察されるか、または一方の物質が他方の物質中に分散していることを表す。
【００５７】
また、揮発性の大小は、日本工業規格（ＪＩＳ）Ｒ３５０３に記載の平圧蒸発皿６０×３０ｍｍに所定量の各溶媒を添加し、６０℃２０％Ｒ．Ｈ．のオーブンに放置したときの各溶媒の揮発度合いを測定することによって評価した。
【００５８】
これらの効果が発生するメカニズムを従来のインクと対比しつつ説明する。
【００５９】
従来のインクでは比較的、界面活性剤の量が多い所謂、浸透型インクであると、着弾後も多くの界面活性剤がインク滴に存在するので、液体の表面張力が低いままである結果、インク的の部分の形状が、球状からゆがんでいく。従って、記録媒体へ着弾されたインク液滴の真円性が低くなってしまう。
【００６０】
従来のインクでは、溶媒及び界面活性剤への水溶性色材の溶解性を調節していないので、水の蒸発により濃縮、会合した水溶性色材は、再び溶媒及び界面活性剤中に溶解するなどして、記録媒体内を浸透してしまう。また、界面活性剤と第２水溶性有機溶媒は相溶性を調節していないため、溶媒が記録媒体内へ浸透しても、析出して壁を形成することもなく、記録媒体内を浸透してしまう。このように第２水溶性有機溶媒が水溶性色材の浸透の際に障害となるような壁構造が記録媒体内に形成されないため、水溶性色材は記録媒体表面に析出せずに奥深くまで浸透してしまう、このため、画像濃度が低くなってしまう。
【００６１】
これに対して、第１水溶性色材関連第１発明のインクは以下のメカニズムによる。
【００６２】
（１）記録媒体へ定着前のインク液滴
インク液滴の表面近傍には界面活性剤が存在し、その内側に水溶性色材、第１溶媒（水）、第２水溶性有機溶媒及び界面活性剤が存在する（図３（ａ））。
【００６３】
（２）インク液滴の記録媒体への着弾
記録媒体に液滴が着弾すると、インク液滴の表面近傍に界面活性剤が存在するため、記録媒体に接触した部位の近傍に存在する界面活性剤が、いち早く記録媒体内に浸透し始める。次に、液滴表面近傍で生じた界面活性剤の濃度差を是正し、インク液滴全体の表面張力を均一に保つように、インク液滴中の残りの界面活性剤が、インク滴表面全体広がる。そして、再び、記録媒体に接触した部位の近傍に存在する界面活性剤が、記録媒体内に浸透する。この過程を繰り返すことにより、液的中の界面活性剤量が次第に減少していく。
【００６４】
しかし、本発明の界面活性剤量であると、インク滴中の界面活性剤濃度が臨界ミセル濃度以下なので、界面活性剤が気−液界面であるインク滴に留まるのではなく、固−液界面である記録媒体に移動する。一方で、界面活性剤が少ない、残ったインク滴の表面張力が上昇するので、インク滴がより球状になる。つまり、画像に高い真円性が付与される（図３（ｂ））。
【００６５】
（３）浸透過程
界面活性剤が記録媒体中に浸透して行く過程で、記録媒体中の疎水性のサイズ剤と吸着する。しかし、界面活性剤の量が少ないので、比較的上面でしか界面活性剤が存在できない。
【００６６】
界面活性剤の浸透とほぼ同じタイミングで、小さい分子の水が浸透していく。水が浸透していき、更に水が蒸発していくと、インク滴内に、水溶性色材を溶解させる溶媒が少なくなり、水溶性色材が濃縮、会合してゆく。
【００６７】
その後、第２水溶性有機溶媒が浸透してゆく。界面活性剤と第２水溶性有機溶媒は相溶性がないため、界面活性剤よりも表面に近い位置に存在することにより、水溶性色材析出の２段階の壁を形成することになる（図３（ｃ））。
【００６８】
濃縮、会合した水溶性色材が浸透していく過程で、先ずは水溶性色材への溶解性が低い第２水溶性有機溶媒の作用により、多くの水溶性色材が析出すると同時に、水よりも揮発性の低い第２水溶性有機溶媒を用いることで、記録媒体中での色材の析出効果を発揮させることが可能となる（図３（ｄ））。また、第２水溶性有機溶媒を通過しても、同様に、水溶性溶媒への溶解性が低い界面活性剤の析出作用により水溶性色材が析出する（図３（ｅ））。
【００６９】
この第２水溶性有機溶媒と界面活性剤の、２段階の水溶性色材の析出作用により、より表面層で多くの水溶性色材が析出する（図３（ｆ））。その結果、高い画像濃度が得られるようになる。
【００７０】
上記の説明の様に、画像濃度の向上の観点で、上記のメカニズムを達成する上において、水溶性色材が３質量％未満の範囲で溶解する第２水溶性有機溶媒と、水溶性色材が１質量％未満の範囲で溶解する界面活性剤の双方の特性と、第２水溶性有機溶媒と界面活性剤の量のバランスと、が重要である。良好な画像濃度を得るには、第２水溶性有機溶媒と界面活性剤の量のバランスを考慮することが好ましい。
【００７１】
例えば、第２水溶性有機溶媒の量が多すぎる場合、第１溶媒の水が蒸発すると、インクが記録媒体に染み込む前に水溶性色材が析出する現象が発生する場合があった。すなわち、ブロンズ現象が発生したり、耐水性が低下したりする場合があった。反対に、第２水溶性有機溶媒の量が少なすぎる場合、第１溶媒の水が蒸発しつつ、第２水溶性有機溶媒インクが記録媒体に染み込こんでも、なかなか水溶性色材が析出せず、低い画像濃度しか得られなかった。
【００７２】
第２水溶性有機溶媒と界面活性剤の量は、本発明のインクに必要とされる表面張力を満たす範囲内で、上記のような観点から調製すればよい。
【００７３】
例えばインク中の第２水溶性有機溶媒量は５質量％以下であることが好ましく、２質量％以上、４．５質量％以下であることがより好ましい。第２水溶性有機溶媒量がこれらの範囲にあることによって、ブロンズ現象の発生や耐水性の低下が起こらず、高い画像濃度を達成できる。
【００７４】
また、第１溶媒である水はインク中に５０質量％以上、８５質量％以下、好ましくは６０質量％以上、８０質量％以下含有される。
【００７５】
一方で、界面活性剤の量が多すぎる場合、記録媒体への浸透速度が速すぎるため、記録媒体の比較的内部で析出現象が発生し、十分な画像濃度が得られない場合があった。反対に、界面活性剤の量が少なすぎる場合、インクが記録媒体中に染み込まず、画像品位が低下する場合があった。インク中の界面活性剤の量は０．４５質量％以下であることが好ましく、０．０７質量％以上、０．３質量％以下であることがより好ましく、０．１質量％以上、０．２質量％以下であることが更に好ましい。界面活性剤濃度がこれらの範囲内にあることによって、高い画像濃度を達成することができる。
【００７６】
また、上記の現象が、吐出量が３ピコリットル以下の小液滴インクであると、インクの２５℃での表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であると最適なバランスとなり、良好な画像が得られる、新しい事実を見出すに至った。インクの表面張力は、３５ｍＮ／ｍ以上、４５ｍＮ／ｍ以下であることが好ましく、３６ｍＮ／ｍ以上、４２ｍＮ／ｍ以下であることがより好ましい。インクの表面張力がこれらの範囲にあるとき、より真円性に優れ、良好な画像を得ることができる。
【００７７】
第１水溶性色材関連第１発明のインクは更に、水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、水よりも揮発性の低い第３水溶性有機溶媒を含み、第３水溶性有機溶媒が２５℃において液体であって、水系インク中の界面活性剤と、第２水溶性有機溶媒と、第３水溶性有機溶媒と、の総含量が、水系インク中の水溶性色材の含量よりも多く、且つ、水溶性色材の含量の４倍以下含まれるのが好ましい。総含量は、水溶性色材の含量よりも１．５倍以上、３．５倍以下がより好ましい。総含量がこれらの範囲内にあることによって、これらの溶媒への色材の溶解性の違いから、水溶性色材が被記録媒体の表面で大量に析出し、高画像濃度を達成することができる。
【００７８】
また、第１水溶性色材関連第１発明のインクは更に、水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、水よりも揮発性の低い第３水溶性有機溶媒を含み、第３水溶性有機溶媒が２５℃において液体であって、炭素数が５または６であり、かつ水酸基の数が２または３であるアルコールを有していることが好ましい。アルコールとしては、１，２，６−ヘキサントリオールを用いることがより好ましい。これらのアルコールは相溶性のない第２水溶性有機溶媒及び界面活性剤の記録媒体中への浸透速度に対して浸透速度が低いが、単独では粘度が高いため、水溶性色材の保全化と真円化を図ることができる。また、印字デューティー全般にわたって高濃度化を図ることができる。
【００７９】
本発明に用いる水溶性色材としては、例えば、従来より公知の水溶性染料、例えば水溶性のアニオン性染料や、直接染料、酸性染料、反応染料等を用いることができるが、特に、尿素結合を有するアゾ系直接染料を使用することが好ましい。
【００８０】
水溶性色材のインク中での含有量は、０．１質量％以上、６．０質量％以下、好ましくは０．５質量％以上、４．５質量％以下とすることができる。
【００８１】
また、第２水溶性有機溶媒としては、例えば、グリセリン等を使用することができる。
【００８２】
また、界面活性剤としては非イオン性界面活性剤を使用することができる。例えば、アセチレノールＥシリーズ（川研ファインケミカル社製）等のアセチレングリコール系界面活性剤を使用することが好ましく、特に、アセチレノールＥ１００（川研ファインケミカル社製）を使用することが好ましい。
【００８３】
（第１水溶性色材関連第３発明）
また、上記第３課題を解決する第１水溶性色材関連第３発明のインクは、微細多孔質体を有する記録媒体に用いるのが好ましい。微細多孔質体の平均細孔直径は１０ｎｍ以上、３０ｎｍ以下である必要があり、１５ｎｍ以上、２５ｎｍ以下が好ましい。また、微細多孔質体の比表面積は６０ｍ^２／ｇ以上、１３０ｍ^２／ｇ以下であることが好ましく、６５ｍ^２／ｇ以上、１２５ｍ^２／ｇ以下であることがより好ましい。微細多孔質体が、このような細孔直径及び比表面積を有することによって、とりわけ良好な、インクドットが真円に近く、濃度が高い上に、高耐湿性である画像を形成できる。
【００８４】
微細多孔質体を有する記録媒体には本発明の水溶性色材と、第１溶媒としての水と、該水溶性色材が２５℃において３質量％未満の範囲で溶解し、該水よりも揮発性の低い第２水溶性有機溶媒と、該水溶性色材が２５℃において１質量％未満の範囲で溶解する界面活性剤と、を含有し、常温において該第２水溶性有機溶媒と該界面活性剤の相溶性がなく、該インク中の該第２水溶性有機溶媒の含量が１質量％以上、５質量％以下であり、かつ、該インク中の界面活性剤の量が０．０５質量％以上、０．４５質量％以下であるこことを特徴とする水系インクを用いることによって、高画像濃度及び画像均一性を達成することができる。
【００８５】
本発明者達は、このような効果の発現にはインク中の界面活性剤含量が大きく影響しており、以下のメカニズムが起きていると考えている。
【００８６】
（１）記録媒体へ定着前のインク液滴及び（２）インク液滴の記録媒体への着弾は、水溶性色材、第１溶媒としての水、第２水溶性有機溶媒、及び界面活性剤を含有するインクを使用した時と同様の過程により、十分な速度で界面活性剤の記録媒体の浸透が進行する（図４（ａ））。
【００８７】
（２）浸透過程
多孔質の記録媒体を用いると、界面活性剤が記録媒体中に浸透して行く過程で、記録媒体中の細孔内で吸着される。しかし、界面活性剤含の量が少ない場合（０．４５質量％以下）には記録媒体内での浸透量が小さく、微細多孔質体に吸着する量も少ない。
【００８８】
界面活性剤の浸透とほぼ同じタイミングで、小さい分子の水が記録媒体内に浸透していく。水が浸透していき、更に水が蒸発していくと、インク滴内に、水溶性色材を溶解させる溶媒が少なくなり、水溶性色材が濃縮、会合してゆく。
【００８９】
その後、第２水溶性有機溶媒が細孔内に浸透してゆく過程で、先ずは水溶性色材への溶解性が低い第２水溶性有機溶媒の作用により、多くの水溶性色材が析出する（図４（ｂ））。このとき、細孔への界面活性剤の吸着量は少ないため、細孔内への色材の吸着時間をかせぐことができると共に、記録媒体の表面近傍の細孔には未吸着サイトが大量にあるため、この水及び第２水溶性有機溶媒中に溶解していた水溶性色材が色材が析出し、表面近傍の細孔に吸着する（図４（ｃ））。この結果、記録媒体の表面近傍に大量の色材が分布し、高画像濃度を達成することができる。
【００９０】
これに対して、界面活性剤の含量が多いインクを用いると、界面活性剤が記録媒体中に浸透して行く過程で、多孔質内の表面近傍で大量に吸着する（図４（ｅ））。界面活性剤の浸透とほぼ同じタイミングで小さい分子の水、またその後に第２水溶性有機溶媒が多孔質内に浸透していくが、すでに、多孔質内の表面近傍の吸着サイトには大量の界面活性剤が吸着しているため、第２水溶性有機溶媒中に溶解していた水溶性色材は析出し、表面近傍の細孔に吸着することができない（図４（ｆ））。第２水溶性有機溶媒は多孔質体の表面近傍を通り抜け、記録媒体の厚み方向のより内部にまで浸透していく。この結果、記録媒体の表面近傍に大量の色材が分布することができず、高画像濃度を達成することができない。
【００９１】
更に、インク中の第２水溶性有機溶媒量の量が５質量％以下であり、界面活性剤の量が０．４５質量％以下であると、より好ましい画像濃度がえら得ることが明らかとなった。
特に、本発明に好適に用い得る記録媒体は、平均粒子径が１μｍ以下の微粒子を主体として、インク受容層を形成したものが好ましい。上記の微粒子として、特に好ましいものは、例えばシリカ及び酸化アルミニウム微粒子等が挙げられる。シリカ微粒子として好ましいものは、コロイダルシリカに代表されるシリカ微粒子である。コロイダルシリカ自体も市場より入手可能なものであるが、特に好ましいものとして、例えば、特許文献１及び２に掲載されたものを挙げることができる。酸化アルミ微粒子として好ましいものとしては、アルミナ水和物微粒子を挙げることができる。このようなアルミナ系顔料の一つとして下記一般式（ＶＩ）により表されるアルミナ水和物を好適なものとして挙げることができる。
【００９２】
【化４】

【００９３】
上記式（ＶＩ）中、ｎは１、２または３の整数のいずれかを表し、ｍは０〜１０、好ましくは０〜５の値を表す。但し、ｍとｎは同時には０にはならない。ｍＨ_２Ｏは、多くの場合ｍＨ_２Ｏ結晶格子の形成に関与しない脱離可能な水相をも表すものである為、ｍは整数または整数でない値を取ることもできる。またこの種の材料を加熱するとｍは０の値に達することがありうる。アルミナ水和物は一般的には、特許文献２及び３に記載されているようなアルミニウムアルコキシドの加水分解やアルミン酸ナトリウムの加水分解のような、また特許文献４に記載されているアルミン酸ナトリウム等の水溶液に硫酸ナトリウム、塩化アルミニウム等の水溶液を加えて中和を行う方法などの公知の方法で製造されたものを使用したものが好適である。本発明においては、特許文献５に記載されたアルミナ水和物を用いることが特に好ましい。
【００９４】
更に、これらのアルミナ水和物を使用したインクジェット用記録媒体は、写真画質を実現するために必要とされる透明性、光沢、水溶性色材等、記録液中水溶性色材の定着性等の特性が得られることより、本発明を適用するのには最も好適である。インク受容層を、酸化アルミニウム微粒子及びシリカ微粒子などの無機顔料微粒子を用いて形成する場合、必要に応じてポリビニルアルコール等の水溶性樹脂などからなるバインダーを用いることができる。バインダーを用いる場合の無機顔料微粒子とバインダーの混合比は、質量比で、好ましくは１：１〜１００：１の範囲とすることができる。酸化アルミニウム微粒子またはシリカ微粒子のインク受容層中の好ましい含有量としては、５０質量％以上、より好ましくは７０質量％以上、更に好ましくは、８０質量％以上であり、上限についていえば９９質量％以下であることが最も好適である。インク受容層の塗工量としては、画像堅牢性向上剤の含浸性を良好とするために乾燥固形分換算で１０ｇ／ｍ^２以上であることが好ましく、１０〜３０ｇ／ｍ^２が最も好適である。
【００９５】
記録媒体の支持体としては、特段の制限がなく、上記したような微粒子を含むインク受容層の形成が可能であって、且つインクジェットプリンタ等の搬送機構によって搬送可能な剛度を与えるものであれば、いずれのものでも使用できる。そして、少なくともインク受容層が形成される側の面に、適度なサイジングを施した紙や、繊維状の基材の上に例えば硫酸バリウム等の無機顔料等をバインダーと共に塗工して形成した緻密な多孔性の層（いわゆる、バライタ層）の表面を有するもの（例えばバライタ紙等）は、支持体として特に好適に用いることができる。
【００９６】
本発明に適用できる記録媒体としては、表層に多孔質層を有している形態としては、基材上に多孔質のインク受容層を形成したものに限らず、アルマイト等も使用できる。
【００９７】
第１水溶性色材関連第３発明のインクは更に、水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、水よりも揮発性の低い水溶性有機溶媒を含み、水溶性有機溶媒が２５℃において液体であって、水系インク中の界面活性剤と、第２水溶性有機溶媒と、水溶性有機溶媒と、の総含量が、水系インク中の水溶性色材の含量よりも多く、且つ、水溶性色材の含量の４倍以下含まれるのが好ましい。総含量は、水溶性色材の含量よりも１．５倍以上、３．５倍以下がより好ましい。総含量がこれらの範囲内にあることによって、これらの溶媒への色材の溶解性の違いから、水溶性色材が被記録媒体の表面で大量に析出し、高画像濃度を達成することができる。
【００９８】
また、第１水溶性色材関連第３発明のインクは更に、水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、水よりも揮発性の低い水溶性有機溶媒を含み、水溶性有機溶媒が２５℃において液体であって、炭素数が５または６であり、かつ水酸基の数が２または３であるアルコールを有していることが好ましい。アルコールとしては、１，２，６−ヘキサントリオールを用いることがより好ましい。これらのアルコールは相溶性のない第２水溶性有機溶媒及び界面活性剤の記録媒体中への浸透速度に対して浸透速度が低いが、単独では粘度が高いため、水溶性色材の保全化と真円化を図ることができる。また、印字デューティー全般にわたって高濃度化を図ることができる。
【００９９】
本発明に用いる水溶性色材としては、例えば、従来より公知の水溶性染料、例えば水溶性のアニオン性染料や、直接染料、酸性染料、反応染料等を用いることができるが、特に、尿素結合を有するアゾ系直接染料を使用することが好ましい。
【０１００】
水溶性色材のインク中での含有量は、０．１質量％以上、６．０質量％以下、好ましくは０．５質量％以上、４．５質量％以下とすることができる。
【０１０１】
また、第２水溶性有機溶媒としては、例えば、グリセリン等を使用することができる。
【０１０２】
また、界面活性剤としては非イオン性界面活性剤を使用することができる。例えば、アセチレノールＥシリーズ（川研ファインケミカル社製）等のアセチレングリコール系界面活性剤を使用することが好ましく、特に、アセチレノールＥ１００（川研ファインケミカル社製）を使用することが好ましい。
【０１０３】
また、本発明のインクは、吐出量が３ピコリットル以下の小液滴インクを吐出させる記録ヘッドに用いられるのに好適である。
【０１０４】
（第１水溶性色材関連第２発明）
上記第２課題を解決する第１水溶性色材関連第２発明のインクは、更に水溶性色材を１０質量％以上溶解させ、かつ水よりも揮発性が低く、該界面活性剤及び該第２水溶性有機溶媒を溶解させると共に、第４水溶性有機溶媒を有する事によってより均一な記録画像が得られることが明らかとなった。
この現象について、本発明者らは以下のメカニズムが起きていると考えている。
【０１０５】
（１）記録媒体へ定着前のインク液滴及び（２）インク液滴の記録媒体への着弾は、水溶性色材、第１溶媒としての水、第２水溶性有機溶媒、及び界面活性剤を含有するインクを使用した時と同様の過程により進行する（図５（ａ）、（ｂ））。
（３）浸透過程
界面活性剤が記録媒体中に浸透して行く過程で、記録媒体中の疎水性のサイズ剤と吸着する。しかし、界面活性剤の量が少ないので、比較的上面でしか界面活性剤が存在しない。
【０１０６】
界面活性剤の浸透とほぼ同じタイミングで、小さい分子の水が浸透していく。水が浸透していき、更に水が蒸発していくと、インク滴内に、水溶性色材を溶解させる溶媒が少なくなり、水溶性色材への溶解性が高い第４水溶性有機溶媒へ移動、溶解し、濃縮、会合していく。第４水溶性有機溶媒による水溶性色材の高濃度溶液が、記録媒体の表面で真円状に、かつほぼ均一に存在するようになる。
【０１０７】
その後、第２水溶性有機溶媒、第４水溶性有機溶媒が記録媒体内へ浸透してゆく。界面活性剤と第２水溶性有機溶媒は相溶性がないため、第２水溶性有機溶媒は記録媒体において界面活性剤よりも表面に近い位置に存在することにより、水溶性色材析出の２段階の壁を形成する（図５（ｃ））。一方で、第４水溶性有機溶媒は第２水溶性有機溶媒よりも揮発性が高いので徐々に揮発してゆきながら、かつ、第２水溶性有機溶媒と界面活性剤の双方に対して相溶性があるため、２段階の壁をすり抜けつつ、ゆっくりと浸透してゆく（図５（ｄ））。その際には、第４水溶性有機溶媒に溶解している水溶性色材は、上記２段階の壁でその多くが析出してしまうため、第４水溶性有機溶媒が比較的表面に近い位置で、析出するようになる（図５（ｅ））。
【０１０８】
また、上で述べたように、水溶性色材は、第４水溶性有機溶媒の影響により、記録媒体上では、ほぼ均一に存在していたため、その析出現象も均一に発生し、結果として濃度が均一な画像が得られるようになる（図５（ｆ））。
【０１０９】
ここで、インク中に更に水溶性色材を１０質量％以上溶解させ、界面活性剤及び第２水溶性有機溶媒を溶解し、かつ第２水溶性有機溶媒より揮発性である第４水溶性有機溶媒を用いることによって、高濃度化、均一化を達成し、画像堅牢性の劣化を抑制するインクとすることができる。第３の溶媒を用いた場合には、以下のメカニズムによりこれらの効果が得られるものと考えられる。
【０１１０】
更に、第４水溶性有機溶媒を用いることにより、インク中の水分が蒸発しても、記録ヘッドなどの微細ノズルの目詰まり抑制などにも効果がある。
【０１１１】
第４水溶性有機溶媒は、界面活性剤、第２水溶性有機溶媒を溶解すると共に、水溶性の溶解性が１０質量％以上あり、第２水溶性有機溶媒より揮発性であれば、どれを使用してもよいが、第４水溶性有機溶媒は、ジエチレングリコール及びテトラエチレングリコールを有することが好ましい。また、エチレングリコール、ジエチレングリコール、トリエチレングリコール、及びテトラエチレングリコールを有することが更に好ましい。例えば、ポリエチレングリコール２００を使用することができる。
【０１１２】
また、第４水溶性有機溶媒は、水溶性色材を１０質量％以上、溶解させることが好ましく、１０．５質量％以上、溶解させることがより好ましい。第４水溶性有機溶媒に対して水溶性色材がこれらの溶解性を有することによって、より優れた画像濃度を得ることができる。また、インク中の第４水溶性有機溶媒の含量は５質量％以上、２０質量％以下であることが好ましく、６質量％以上、１５質量％以下であることがより好ましい。第３水溶性有機溶媒がこれらの含有量だけ存在することによって、より優れた画像濃度を得ることができる。
【０１１３】
また、インク中の前記界面活性剤、第２水溶性有機溶媒及び水溶性色材が２５℃において３質量％未満の範囲で溶解し、かつ、水よりも揮発性の低い第３水溶性有機溶媒の総含量が、インク中の水溶性色材の含量よりも多く、水溶性色材の含量の４倍以下であることが好ましい。総含量は水溶性色材の含量よりも１．５倍以上、３．５倍以下がより好ましい。総含量がこれらの範囲内にあることによって、これらの溶媒への色材の溶解性の違いから、色材が記録媒体の表面で大量に析出し、高画像濃度を達成することができる。
【０１１４】
これらのインク及び記録媒体を使用することにより、画像濃度、画像均一性が良好になり、更に、記録ヘッドなどの微細ノズルの目詰まり抑制などにも効果がある。特に、本発明のインクは、吐出量が３ピコリットル以下の小液滴インクを吐出させる記録ヘッドに用いられるのに好適である。
【０１１５】
また、第４水溶性有機溶媒としてジエチレングリコール及びテトラエチレングリコールを有する、水系インクであることが好ましく、エチレングリコール、ジエチレングリコール、トリエチレングリコール及びテトラエチレングリコールを有する水系インクであることがより好ましい。
また、微細な多孔質層として、シリカ、アルミナを有する記録媒体に使用されると、より好ましくなる。
【０１１６】
また、本発明のインクを用いると、紙面内で水溶性色材が析出するため、湿度の影響による水溶性色材分子の移動（マイグレーション）も発生しにくくなる。水系インク中に、水溶性色材以外に、分解性のある尿素結合を有する化合物を実質的に含まないことが好ましい。従来の尿素が含まれるインクでは、高温で長期間保存した後、低温で放置すると、水溶性色材の種類によっては、水溶性色材が沈殿する場合があった。この現象は、尿素がアンモニウムイオン、炭酸イオンなどに分解し、イオン強度が増大する事で塩析効果を生じ、水溶性色材が沈殿すると考えられている。従って、インク中に分解性のある尿素結合を有する化合物を実質的に含まないとこのような問題が生じない。
【０１１７】
（第１水溶性色材にかかわる第１水溶性色材関連実施例）
以下、第１水溶性色材関連実施例によって本発明を具体的に説明するが、これらは本発明の範囲を限定するものではない。尚、文中、部及び％とあるのは特に断りのない限り質量基準である。
【０１１８】
（第１水溶性色材関連第１発明）
下記表１の各成分を充分混合溶解した後、ポアサイズ０．２μｍのフィルター（富士フィルム製）で加圧濾過し、インクを調製した。
【０１１９】
（第１水溶性色材関連実施例１）
【０１２０】
【表１】

【０１２１】
□：１質量％未満、×：１質量％以上３質量％未満、△：３質量％以上１０質量％未満、○：１０質量部以上
第２水溶性有機溶媒と界面活性剤との相溶性：なし
第１溶媒の揮発性は水の揮発性より低い
第４水溶性有機溶媒は、界面活性剤及び第２水溶性有機溶媒を溶解
第３水溶性有機溶媒の１，２，６−ヘキサントリオールは水溶性色材を２５℃において３質量％未満の範囲で溶解し、かつ、前記水よりも揮発性の低く、２５℃において液体である
（第１水溶性色材関連実施例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．４５質量％、水を７４．０５質量％（表面張力３５．４ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２２】
（第１水溶性色材関連実施例３）
第３水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成において１，２，６−ヘキサントリオールを０質量％、ジエチレングリコールを１２．００質量％（表面張力３９．９ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２３】
（第１水溶性色材関連実施例４）
第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてテトラエチレングリコールと、ジエチレングリコールと、を０質量％、水を８６．３５質量％（表面張力３９．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２４】
（第１水溶性色材関連比較例１）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．８０質量％、水を７３．７０質量％（表面張力３３．７ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２５】
（第１水溶性色材関連比較例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を１．１５質量％、水を７３．３５質量％（表面張力３２．９ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２６】
（第１水溶性色材関連比較例３）
第２水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてグリセリンを０質量％、ジエチレングリコールを１２．００質量％（表面張力３９．９ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２７】
（第１水溶性色材関連比較例４）
第２水溶性有機溶剤及び第３水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてグリセリンと、１，２，６−ヘキサントリオールと、を０質量％、ジエチレングリコールを１６．００質量％（表面張力３９．８ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２８】
（第１水溶性色材関連比較例５）
界面活性剤、第３水溶性有機溶剤及び第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてアセチレノールＥ１００と、１，２，６−ヘキサントリオールと、テトラエチレングリコールと、ジエチレングリコールと、を０質量％、水を９０．５質量％（表面張力６５．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１２９】
また、各溶媒間の揮発性の度合いをシミュレートするため、日本工業規格（ＪＩＳ）Ｒ３５０３に記載の平圧蒸発皿６０×３０ｍｍに所定量の各溶媒を添加し、６０℃２０％Ｒ．Ｈ．のオーブンに放置したときの各溶媒の揮発度合いを測定した。
【０１３０】
結果を図２に示す。第４水溶性有機溶媒のジエチレングリコール、トリエチレングリコール、テトラエチレングリコールの揮発性はグリセリンよりも高いことがわかる。また、エチレングリコールはジエチレングリコールよりも揮発性が高い（図示せず）。なお、図示していないが、水は本第１水溶性色材関連実施例における、第２水溶性有機溶媒、第３水溶性有機溶媒や第４水溶性有機溶媒（エチレングリコール、ジエチレングリコール、トリエチレングリコール、テトラエチレングリコール、グリセリン、１，２，６−ヘキサントリオール等）と比較すると非常に揮発性が高い。一方、本第１水溶性色材関連実施例中に記載の２−プロパノールは水よりも揮発性が高い（例えば、２０℃における水の蒸気圧が１７．５ｍｍＨｇに対して２−プロパノールは３２．４ｍｍＨｇ（溶剤ハンドブック 講談社サイエンティフィク １９７６年））ため、第２水溶性有機溶媒、第３水溶性有機溶媒や第４水溶性有機溶媒には含まれないことは明らかである。
【０１３１】
（評価方法）
上記の様にして得られたインクを用いて、インクジェット記録装置として発熱素子をインクの吐出エネルギー源として利用したインクジェットプリンタＰｉｘｕｓ９５０ｉ（商品名：キヤノン製）を使用し、印字（８パス双方向）した後に下記に示す画像評価を行った。測定方法を以下に示す。また、この結果を表２に示す。
【０１３２】
（１）画像濃度
プリンタにインクを充填し、記録密度２４００ｄｐｉ×１２００ｄｐｉで、吐出量を２．５ｐｌとして、１００％までの種々のデューティ（階調）でインクを打ち込んだ記録をＰＢペーパー（普通紙）（商品名：キヤノン製）に行った。
【０１３３】
このようにして記録した画像をＧＲＥＴＡＧスペクトロリノで光源：Ｄ５０、視野：２°の条件で測定し、光学濃度Ｏ．Ｄ．を測定した。Ｏ．Ｄ．が高い程、画像濃度が高い。
◎：Ｏ．Ｄ．が非常に高い画像が得られた。
○：Ｏ．Ｄ．が高い画像が得られた。
△：Ｏ．Ｄ．が若干低い画像が得られた。
×：Ｏ．Ｄ．が低く画像として好ましくない
（２）画像ブロンズ性
前記（１）画像濃度測定で得られた画像を用いて、画像ブロンズ性を判断した。
○：画像がブロンズしていない。非常に良好な画像均一性が得られた。
×：画像のブロンズが認められた。
【０１３４】
（３）ドット新円性
前記（１）画像濃度測定で得られた画像を用いて、ドット真円性を判断した。
◎：非常に良好なドット真円性が得られた。
○：良好なドット真円性が得られた。
△：一部、ドット真円性が劣る箇所がある。
×：全体としてドット真円性に劣る。
【０１３５】
（４）画像裏向け性
前記（１）画像濃度測定で得られた画像で、記録媒体の印刷面とは反対の面で、画像裏向け性を判断した。
◎：画像の裏抜けが完全にない。
○：画像の裏抜けが目立たない。
△：画像の裏抜けが若干存在する。
×：画像の裏抜けが多く存在する。
【０１３６】
（評価結果）
表２に第１水溶性色材関連実施例１、２、３、４、及び、第１水溶性色材関連比較例１、２、３、４、５の画像濃度、画像ブロンズ性、ドット真円性、画像裏抜け性の評価結果を示す。
【０１３７】
表２の結果より、画像濃度については、第１水溶性色材関連実施例１から４のすべてのインクにおいて、表面張力が低かったり、第２水溶性有機溶媒が存在しないかったりする、第１水溶性色材関連比較例のインクよりも高い結果が得られた。従って、高画像濃度を達成するためには、第２水溶性有機溶媒が存在し、かつ、インクの表面張力が３５ｍＮ／ｍ以上のものが必要であることがわかる。また、第１水溶性色材関連実施例の中でも、より表面張力が高いインクや、第３溶媒が存在するインクに関しては、更に、画像濃度が高いものが得られた。従って、更なる高画質画像を達成するためには、本発明の範囲内で表面張力がより高いインクや、第３溶媒が更に含まれるインクであるのが好ましい。
【０１３８】
画像ブロンズ性については、表面張力が６５．２ｍＮ／ｍと高い第１水溶性色材関連比較例５のインクは悪い結果となった。従って、ブロンズのない高画質を達成するには表面張力が低い、具体的には５０ｍＮ／ｍ以下のインクが必要となることがわかる。
【０１３９】
ドット真円性については、表面張力が３５ｍＮ／ｍ以下のインク（第１水溶性色材関連比較例１、及び、２）が悪いことがわかった。従って、ドット真円性のある高画質を達成するには表面張力が３５ｍＮ／ｍ以上のインクが必要となることがわかる。第１水溶性色材関連実施例の中でも、より表面張力が高いものに関しては、更に、ドット真円性の良好なものが得られた。従って、更なる高画質画像を達成するためには、本発明の範囲内で表面張力がより高いインクであることが好ましい。
【０１４０】
画像裏抜け性については、表面張力が３５ｍＮ／ｍ以下のインク（第１水溶性色材関連比較例１、及び、２）が悪いことがわかった。従って、裏抜けのない画像を達成するには表面張力が３５ｍＮ／ｍ以上のインクが必要となることがわかる。第１水溶性色材関連実施例の中でも、より表面張力が高いものに関しては、更に、画像裏抜け性の良好なものが得られた。従って、更なる裏抜けのない画像を達成するためには、本発明の範囲内で表面張力がより高いインクであることが好ましい。
【０１４１】
【表２】

【０１４２】
（第１水溶性色材関連第３発明）
（第１水溶性色材関連実施例１）
上記表１の各成分を充分混合溶解した後、ポアサイズ０．２μｍのフィルター（富士フィルム製）で加圧濾過し、インクを調製した。
【０１４３】
第１水溶性色材関連実施例１のインク組成：表面張力３９．９ｍＮ／ｍ
（第１水溶性色材関連実施例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．４５質量％、水を７４．０５質量％（表面張力３５．４ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４４】
（第１水溶性色材関連実施例３）
第３水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成において１，２，６−ヘキサントリオール４．００質量％をジエチレングリコール４．００質量％（第１水溶性色材関連実施例３のジエチレングリコールの総量は１２．００質量％となる）に置き換えた（表面張力３９．９ｍＮ／ｍ）以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４５】
（第１水溶性色材関連実施例４）
第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてテトラエチレングリコール４．０質量％と、ジエチレングリコール８．００質量％を抜き、水を８６．３５質量％（表面張力３９．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４６】
（第１水溶性色材関連比較例１）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．８０質量％、水を７３．７０質量％（表面張力３３．７ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４７】
（第１水溶性色材関連比較例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を１．１５質量％、水を７３．３５質量％（表面張力３２．９ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４８】
（第１水溶性色材関連比較例３）
第２水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてグリセリン４．０質量％をジエチレングリコール４．００質量％（第１水溶性色材関連比較例３のジエチレングリコールの総量は１２．００質量％となる）に置き換えた（表面張力３９．９ｍＮ／ｍ）以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１４９】
（第１水溶性色材関連比較例４）
第２水溶性有機溶剤及び第３水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてグリセリン４．００質量％と１，２，６−ヘキサントリオール４．０質量％をジエチレングリコール８．００質量％（第１水溶性色材関連比較例４のジエチレングリコールの総量は１６．００質量％となる）に置き換えた（表面張力３９．８ｍＮ／ｍ）以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１５０】
（第１水溶性色材関連比較例５）
界面活性剤、第３水溶性有機溶剤及び第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてアセチレノールＥ１００と、１，２，６−ヘキサントリオールと、テトラエチレングリコールと、ジエチレングリコールと、を０質量％、水を９０．５質量％（表面張力６５．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１５１】
（評価方法）
上記の様にして得られたインクを用いて、インクジェット記録装置として発熱素子をインクの吐出エネルギー源として利用したインクジェットプリンタＰｉｘｕｓ９５０ｉ（商品名：キヤノン製）を使用し、印字（８パス双方向）した後に下記に示す画像評価を行った。測定方法を以下に示す。また、この結果を表４に示す。
【０１５２】
（１）画像濃度測定
プリンタにインクを充填し、記録密度２４００ｄｐｉ×１２００ｄｐｉで、吐出量を２．５ｐｌとして、１００％までの種々のデューティ（階調）でインクを打ち込んだ記録をＳＰ−１０１（商品名：キヤノン製）に行った。
【０１５３】
このようにして記録した画像をＧＲＥＴＡＧスペクトロリノで光源：Ｄ５０、視野：２°の条件で測定し、光学濃度Ｏ．Ｄ．を測定した。Ｏ．Ｄ．が高い程、画像濃度が高い。
◎：Ｏ．Ｄ．が非常に高い画像が得られた。
○：Ｏ．Ｄ．が高い画像が得られた。
△：Ｏ．Ｄ．が若干低い画像が得られた。
×：Ｏ．Ｄ．が低く画像として好ましくない
（２）画像ブロンズ性
前記（１）画像濃度測定で得られた画像を用いて、画像ブロンズ性を判断した。
◎：非常に良好な画像均一性が得られた。
○：良好な画像均一性が得られた。
△：一部、画像均一性が劣る箇所がある。
×：画像全体が均一性に劣る。
【０１５４】
（３）ドット新円性
前記（１）画像濃度測定で得られた画像を用いて、ドット真円性を判断した。
◎：非常に良好なドット真円性が得られた。
○：良好なドット真円性が得られた。
△：一部、ドット真円性が劣る箇所がある。
×：全体としてドット真円性に劣る。
【０１５５】
（評価結果）
表３に第１水溶性色材関連実施例１、２、３、４、及び、第１水溶性色材関連比較例１、２、３、４、５の画像濃度、画像ブロンズ性、ドット真円性の評価結果を示す。
【０１５６】
表３の結果より、画像濃度については、第１水溶性色材関連実施例１から４のすべてのインクにおいて、界面活性量が多かったり、第２水溶性溶媒が存在しなかったりする第１水溶性色材関連比較例のインクよりも高い結果が得られた。従って、高画像濃度を達成するためには、第２溶媒が存在し、かつ、界面活性剤の量が０．４５質量％以下のインクが必要であることがわかる。また、第１水溶性色材関連実施例の中でも、より界面活性剤量の少ないインクや、第３溶媒が存在するインクに関しては、更に、画像濃度が高いものが得られた。従って、更なる高画質画像を達成するためには、界面活性剤量がより少ないインクや、第３溶媒が更に含まれるインクであるのが好ましい。
【０１５７】
画像ブロンズ性については、界面活性剤が存在しない第１水溶性色材関連比較例５のインクは悪い結果となった。従って、ブロンズのない高画質を達成するには少なくとも界面活性剤が含まれるインクが必要となることがわかる。
【０１５８】
ドット真円性については、界面活性剤量が０．４５質量％を超えるインク（第１水溶性色材関連比較例１、及び、２）が悪いことがわかった。従って、ドット真円性のある高画質を達成するには界面活性剤量が０．４５質量％以下のインクが必要となることがわかる。第１水溶性色材関連実施例の中でも、より界面活性剤量の少ないインクに関しては、更に、ドット真円性の良好なものが得られた。従って、更なる高画質画像を達成するためには、より界面活性剤量の少ないインクであることが好ましい。
【０１５９】
【表３】

【０１６０】
（第１水溶性色材関連第２発明）
（第１水溶性色材関連実施例１）
上記表１の各成分を充分混合溶解した後、ポアサイズ０．２μｍのフィルター（富士フィルム製）で加圧濾過し、インクを調製した。
【０１６１】
第１水溶性色材関連実施例１のインク組成：表面張力３９．９ｍＮ／ｍ
（第１水溶性色材関連実施例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．４５質量％、水を７４．０５質量％（表面張力３５．４ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１６２】
（第１水溶性色材関連実施例４）
第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてテトラエチレングリコール４．０質量％と、ジエチレングリコール８．００質量％を抜き、水を８６．３５質量％（表面張力３９．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１６３】
（第１水溶性色材関連比較例１）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を０．８０質量％、水を７３．７０質量％（表面張力３３．７ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１６４】
（第１水溶性色材関連比較例２）
第１水溶性色材関連実施例１のインク組成において界面活性剤のアセチレノールＥ１００を１．１５質量％、水を７３．３５質量％（表面張力３２．９ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１６５】
（第１水溶性色材関連比較例５）
界面活性剤、第３水溶性有機溶剤及び第４水溶性有機溶剤をなくす目的で、第１水溶性色材関連実施例１のインク組成においてアセチレノールＥ１００と、１，２，６−ヘキサントリオールと、テトラエチレングリコールと、ジエチレングリコールと、を０質量％、水を９０．５質量％（表面張力６５．２ｍＮ／ｍ）とした以外は第１水溶性色材関連実施例１と同様にインクを調製した。
【０１６６】
（評価方法）
（１）画像均一性
上記の様にして得られたインクを用いて、インクジェット記録装置として発熱素子をインクの吐出エネルギー源として利用したインクジェットプリンタＰｉｘｕｓ９５０ｉ（商品名：キヤノン製）を使用し、吐出量を２．５ｐｌ、記録密度２４００ｄｐｉ×１２００ｄｐｉで、印字（８パス双方向）し、１００％までの種々のデューティ（階調）でインクを打ち込んだ記録をＰＢペーパー（キヤノン製）、および、ＳＰ−１０１（商品名：キヤノン製）に行った。
このようにして記録した画像を用いて、画像均一性を判断した。
◎：非常に良好な画像均一性が得られた。
○：良好な画像均一性が得られた。
△：一部、画像均一性が劣る箇所がある。
×：画像全体が均一性に劣る。
【０１６７】
（評価結果）
表４に、記録媒体としてＳＰ−１０１を用いた時の、第１水溶性色材関連実施例１、２、４、及び、第１水溶性色材関連比較例１、２、５の画像均一性、ノズル目詰まり特性の評価結果を示す。
【０１６８】
表４の結果より、画像均一性については、第１水溶性色材関連実施例１、２、４のすべてのインクにおいて、本発明の範囲から外れる表面張力のインクよりも良好な結果が得られた。従って、高画像濃度を達成するためには、表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下の範囲であることが必要である。また、第１水溶性色材関連実施例の中でも、第３溶媒が含有するインク関しては、更に、画像均一性の濃度が高いものが得られた。従って、更なる高画質画像を達成するためには、第３溶媒が更に含まれるインクであるのが好ましい。
【０１６９】
【表４】

【０１７０】
なお、この結果は普通紙のＰＢペーパーにおいても同様であった。
【０１７１】
（２）インク目詰まり特性
また、前記第１水溶性色材関連実施例１、および、第１水溶性色材関連比較例５について、インクジェットプリンタＰｉｘｕｓ９５０ｉに各々インクを充填し、所定の回復動作を行ない、印字チェック用のパターンを印字後、インクジェットプリンタ本体から取り出し、インクタンクを外した記録ヘッドを、６０℃（湿度５〜２０％ＲＨ）環境下に裸状態で１５日間放置後、２５℃にて２４時間放置した記録ヘッドのノズルを観察した。
○：ノズル目詰まりを発生させるような析出物が殆ど観察されない。
×：ノズル目詰まりを発生させるような析出物が多く観察された。
【０１７２】
（評価結果）
表５に、第１水溶性色材関連実施例１及び、第１水溶性色材関連比較例５のインク目詰まり特性の評価結果を示す。表５の結果より、表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下の範囲内であり、かつ、第４水溶性有機溶媒を有する第１水溶性色材関連実施例１は記録ヘッドの目詰まりは認められなかった。従って、インク目詰まり特性を良好にするには、表面張力が３５ｍＮ／ｍ以上、５０ｍＮ／ｍ以下の範囲内であり、かつ、第４水溶性有機溶媒を有することが必要であることがわかる。
【０１７３】
【表５】

【０１７４】
【実施例】
以下、実施例によって本発明を具体的に説明するが、これらは本発明の範囲を限定するものではない。尚、文中、部及び％とあるのは特に断りのない限り質量基準である。
【０１７５】
［実施例１］
下記表６の各成分を充分混合溶解した後、ポアサイズ０．２μｍのフィルター（富士フィルム製）で加圧濾過し、インクを調製した。
【０１７６】
【表６】

【０１７７】
□：１質量％未満、△：１質量％以上３質量％未満、○：１０質量％以上
ここで、表６中のマゼンタ色材１は下記一般式（Ｉ）、マゼンタ色材２は下記一般式（ＩＩ）、シアン色材１は下記一般式（ＩＩＩ）を使用した。
【０１７８】
（マゼンタ色材）
【０１７９】
【化５】

【０１８０】
（上記一般式（Ｉ）中、Ｒ_１は、置換若しくは未置換のアルコキシ基、又は置換若しくは未置換のアリール基を表し、Ｒ_２及びＲ_４は、各々独立に、水素原子又は置換若しくは未置換のアルキル基を表し、Ｒ_３は、水素原子、置換若しくは未置換のアルキル基、置換若しくは未置換のアルコキシ基、置換若しくは未置換のアリールオキシ基又はハロゲン原子を表す。Ｘ_１は、カルボキシル基若しくはその塩、又はスルホン酸基若しくはその塩を表す。ｎは１又は２を表す。）
【０１８１】
【化６】

【０１８２】
（上記一般式（ＩＩ）中、Ａｒ１は置換若しくは未置換のフェニル基、又は置換若しくは未置換のナフチル基を表し、Ａｒ２は、アセチル基、ベンゾイル基、１，３，５−トリアジニル基、ＳＯ_２−Ｃ_６Ｈ_５基又はＳＯ_２−Ｃ_６Ｈ_４−ＣＨ_３基のいずれかを表す。Ｍは、スルホン酸基の対イオンであり、水素原子、アルカリ金属、アンモニウム及び有機アンモニウムのいずれかを表す。）
（シアン色材）
【０１８３】
【化７】

【０１８４】
（上記一般式（ＩＩＩ）中ＣｕＰｃは、銅フタロシアニン残基を表し、Ｍはアルカリ金属又はアンモニウムであり、ｘは１、２、３または４であり、ｙは１、２または３である。）
また、各溶媒間の揮発性の度合いをシミュレートするため、日本工業規格（ＪＩＳ）Ｒ３５０３に記載の平圧蒸発皿６０×３０ｍｍに所定量の各溶媒を添加し、６０℃２０％Ｒ．Ｈ．のオーブンに放置したときの各溶媒の揮発度合いを測定した。
【０１８５】
結果を図２に示す。第２水溶性有機溶媒のジエチレングリコール、トリエチレングリコール、テトラエチレングリコールの揮発性はグリセリンよりも高いことがわかる。また、エチレングリコールはジエチレングリコールよりも揮発性が高い（図示せず）。なお、図示していないが、水は本実施例における、第１水溶性有機溶媒や第２水溶性有機溶媒（エチレングリコール、ジエチレングリコール、トリエチレングリコール、テトラエチレングリコール、グリセリン、１，２，６−ヘキサントリオール等）と比較すると非常に揮発性が高い。一方、本実施例中に記載の２−プロパノールは水よりも揮発性が高い（例えば、２０℃における水の蒸気圧が１７．５ｍｍＨｇに対して２−プロパノールは３２．４ｍｍＨｇ（溶剤ハンドブック 講談社サイエンティフィク １９７６年））ため、第２水溶性有機溶媒や第３水溶性有機溶媒には含まれないことは明らかである。
【０１８６】
なお、実施例１のインクセットの各インクを各々密閉容器に充填し、６０℃で３ヶ月間保存した後、５℃に２４時間放置しても、色材の析出は生じなかった。
【０１８７】
［比較例１］
実施例１のマゼンタインク、及びシアンインクから尿素を省いたインクセットを用いた。
【０１８８】
［比較例２］
なお、実施例１のイエローインクに尿素を１０％添加したものを、密閉容器に充填し、６０℃で３ヶ月間保存した後、５℃に２４時間放置すると、イエロー色材が析出した。
【０１８９】
（評価）
上記の様にして得られたインクを用いて、インクジェット記録装置として発熱素子をインクの吐出エネルギー源として利用したインクジェットプリンタＰｉｘｕｓ８５０ｉ（商品名：キヤノン製）を使用し、ＣＭ分離の画像処理が入った状態で、イエローインク、マゼンタインク、シアンインクの順で印刷が行えるように、アウエー側からホームポジションへの複印刷のみを行った。被記録媒体として、ＳＰ−１０１（商品名：キヤノン製）を用いて、種々のデューティ（階調）でブラック画像を形成した。
【０１９０】
得られた画像で、ＧＲＥＴＡＧスペクトロリノで光源：Ｄ５０、視野：２°の条件で、ブラックの光学濃度Ｏ．Ｄ．を測定した。Ｏ．Ｄ．が高い程、ブラックの画像濃度が高い。図１に実施例１と比較例１の各インク打ち込み量の黒色画像のＯ．Ｄ．値を示す。この結果より、打ち込み量によらず、比較例１の画像濃度よりも、実施例１の画像濃度が高いことが分かる。
【０１９１】
【発明の効果】
シアンインク、マゼンタインク及びイエローインクを用いて、ＣＭ分離によりカラー画像を形成する場合に、濃度が高く、均一な黒色画像を形成するような水系インクセットを提供する。
【図面の簡単な説明】
【図１】実施例１と比較例１の各インクセットを種々のデューティ（階調）打ち込むことで得られたブラック画像のＯ．Ｄ．値を表す図である。
【図２】本発明のインクに使用する溶媒の揮発性を測定した結果である。
【図３】図３（ａ）は、記録媒体へ着弾前の本発明のインク液滴を表す概念図である。図３（ｂ）は、本発明のインク液滴が記録媒体へ着弾した状態を表す概念図である。図３（ｃ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図３（ｄ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図３（ｅ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図３（ｆ）は、本発明のインクが記録媒体へ定着した状態を表す概念図である。
【図４】図４（ａ）は、記録媒体へ着弾前の本発明のインク液滴を表す概念図である。図４（ｂ）は、本発明のインク液滴が記録媒体へ着弾した状態を表す概念図である。図４（ｃ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図４（ｄ）は、界面活性剤濃度が高いインク成分が記録媒体へ浸透する状態を表す概念図である。図４（ｅ）は、界面活性剤濃度が高いインク成分が記録媒体へ浸透する状態を表す概念図である。図４（ｆ）は、界面活性剤濃度が高いインクが記録媒体へ定着した状態を表す概念図である。
【図５】図５（ａ）は、記録媒体へ着弾前の本発明のインク液滴を表す概念図である。図５（ｂ）は、本発明のインク液滴が記録媒体へ着弾した状態を表す概念図である。図５（ｃ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図５（ｄ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図５（ｅ）は、本発明のインク成分が記録媒体へ浸透する状態を表す概念図である。図５（ｆ）は、本発明のインクが記録媒体へ定着した状態を表す概念図である。
【符号の説明】
× 界面活性剤
○ 第１溶媒（水）
◇ 第２水溶性有機溶媒
● 水溶性色材
☆ 第３水溶性有機溶媒[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a water-based ink set used for ink-jet recording, in particular, an image forming method and a water-based ink which form a uniform black image with high density of each color, particularly black, obtained by a combination of cyan ink, magenta ink and yellow ink. It is about sets.
[0002]
[Prior art]
In the inkjet recording, an image is formed by discharging ink droplets from fine nozzles in a recording head and fixing the ink droplets on a recording material.
[0003]
As the recording ink, oil-based ink or ink which is solid at normal temperature may be used, but water-based ink is most widely used for consumer use. The water-based ink is generally composed of water, a water-soluble organic solvent, and an additive which is solid at room temperature, and further contains a dye or a pigment as a coloring material.
[0004]
One of the roles of the additive is to provide ink moisturizing properties for suppressing ink evaporation from a location that is open to the atmosphere, such as a nozzle of a recording head.
In recent years, images obtained by inkjet recording have become higher definition, and are now comparable to the image quality of silver halide photography, which is a synonym for high image quality.
A recording head used for such high-quality recording needs to stably eject small droplets from finer nozzles than before. Therefore, the moisturizing property of the ink becomes more important than ever.
[0005]
In addition, as a requirement necessary for high-quality recording, improvement in image density is given. Needless to say, a single color is used, but various techniques are used to improve the density of each color, particularly a black image formed by combining a cyan ink, a magenta ink, and a yellow ink.
As one of techniques for improving image density, there is a printer system using an ink set including black ink of a cationic pigment and color ink of an anionic dye. In this system, when the black ink dot and the color ink dot overlap on the medium, the color materials of both inks are deposited, and a high black image density is generated.
[0006]
Conventionally, when a multi-valued image is output using cyan, magenta, and yellow inks, pseudo gradation processing is performed independently using an error diffusion method or the like for each color. However, when two or more colors overlap, good visual characteristics are not always obtained. In order to reduce the granularity of a medium-density region of a color image, Japanese Patent Application Laid-Open No. H11-163,873 discloses an image forming method in which dots of a cyan component and a magenta component do not overlap each other (hereinafter, referred to as CM separation). An image is formed such that the yellow component is adjacent to the cyan component and the magenta component, or at least partially overlaps the yellow component, and further discharges the yellow ink before the cyan ink and the magenta ink to form a black image. Are described. By using this method, a high-quality image can be formed by high-speed processing.
[0007]
Alumina hydrate is generally used for the hydrolysis of aluminum alkoxide and sodium aluminate as described in Patent Documents 2 and 3, and for sodium aluminate described in Patent Document 4 It is preferable to use an aqueous solution prepared by a known method such as a method of adding an aqueous solution of sodium sulfate, aluminum chloride or the like to an aqueous solution of the above to neutralize the aqueous solution. In the present invention, it is particularly preferable to use the alumina hydrate described in Patent Document 5.
[0008]
[Patent Document 1]
JP-A-2002-171407
[Patent Document 2]
U.S. Pat. No. 4,242,271
[Patent Document 3]
U.S. Pat. No. 4,202,870
[Patent Document 4]
JP-B-57-44605
[Patent Document 5]
Japanese Patent No. 2714352
[0009]
[Problems to be solved by the invention]
The present invention is a study on an ink set for CM separation, and forms a color image including a color obtained by combining at least two types of a cyan ink, a magenta ink, and a yellow ink by using the CM separation. In this case, the present invention provides an ink set that forms a uniform black image with a high density.
[0010]
[Means for Solving the Problems]
Then, the present inventors conducted intensive research and completed the present invention.
That is, the present invention provides a first water-soluble coloring material that is promoted by a predetermined additive,
A second water-soluble coloring material that is not promoted by the additive, and a third water-soluble coloring material;
A first water-soluble organic solvent having low solubility in the first water-soluble coloring material, a high solubility in the second water-soluble coloring material, and a high solubility in the third water-soluble coloring material;
A water-based first ink having the first water-soluble coloring material and the first water-soluble organic solvent, and not having the additive;
A water-based second ink having the second water-soluble coloring material, the first water-soluble organic solvent, and the additive,
An aqueous third ink having the third water-soluble coloring material, the first water-soluble organic solvent, and the additive;
The present invention relates to an image forming method, wherein a black image is formed by bringing each of the second ink and the third ink into contact with the first ink.
[0011]
The present invention comprises at least a water-based first ink, a second ink, and a third ink,
A black image is formed by bringing the second ink and the third ink into contact with the first ink, respectively.
Water-based ink set for
A first additive having a predetermined additive, a first water-soluble colorant whose deposition is promoted by the additive, and a first water-soluble organic solvent having low solubility in the first water-soluble colorant. Ink and
A second ink having the additive, a second water-soluble coloring material that is not promoted by the additive, and a first water-soluble organic solvent that is highly soluble in the second water-soluble coloring material; ,
A third ink having the additive, a third water-soluble coloring material that is not accelerated by the additive, and a first water-soluble organic solvent that is highly soluble in the third water-soluble coloring material; ,
A water-based ink set comprising:
[0012]
The present invention comprises at least a water-based, cyan ink, a magenta ink, and a yellow ink,
When the yellow ink dot and the cyan ink dot or the magenta ink dot are adjacent to each other, the yellow ink dot at least partially overlaps the cyan ink dot or the magenta ink dot, and
Neither the cyan ink dot nor the magenta ink dot is adjacent or overlapped,
Further, the yellow ink is ejected before the cyan ink and the magenta ink to form a black image.
Water-based ink set for
An additive that improves the moisturizing properties of the ink, a water-soluble cyan coloring material whose deposition is not promoted by a decomposition product of the additive, and a water-soluble cyan coloring material that dissolves in a range of 10% by mass or more at 25 ° C. A first water-soluble organic solvent having a low volatility, and the cyan ink,
The additive, a water-soluble magenta colorant whose precipitation is not promoted by a decomposition product of the additive, and the water-soluble magenta colorant is dissolved at 25 ° C. in a range of 10% by mass or more and has lower volatility than water. The magenta ink, comprising: the first water-soluble organic solvent;
A water-soluble yellow coloring material whose precipitation is promoted by a decomposition product of the additive, and the first water-soluble organic solvent in which the water-soluble yellow coloring material dissolves in a range of less than 3% by mass at 25 ° C. And not containing the additive, the yellow ink,
A water-based ink set comprising:
[0013]
In the present invention, it is preferable that the surface tension of at least the yellow ink at 25 ° C. in the aqueous ink set is 35 mN / m or more and 50 mN / m or less.
The present invention further provides that the yellow ink contains at least one surfactant, and the solubility of the water-soluble yellow coloring material in the surfactant is less than 1% by mass at 25 ° C.
At 25 ° C., the surfactant is preferably not compatible with the first water-soluble organic solvent.
The present invention is further preferably characterized in that the cyan ink and the magenta ink have a surface tension at 25 ° C. of 35 mN / m or more and 50 mN / m or less.
[0014]
The present invention further provides the aqueous ink set, wherein the yellow ink is:
The solubility of the water-soluble yellow color material, the water-soluble cyan color material, and the water-soluble magenta color material is 10% by mass or more at 25 ° C, and
More volatile than the first water-soluble organic solvent,
It is preferable to further include a second water-soluble organic solvent.
[0015]
In the present invention, it is preferable that in the aqueous ink set, the second water-soluble organic solvent includes diethylene glycol and tetraethylene glycol.
In the present invention, it is preferable that in the aqueous ink set, the second water-soluble organic solvent includes ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in more detail with reference to preferred embodiments.
The present invention forms a color image having a density gradation from a high image density region to a low image density region using CM separation, and discharges yellow ink before cyan ink and magenta ink. This is a water-based ink set effective for improving the image density when forming a black image.
It is presumed that the following mechanism causes the black image density to increase when the ink set of the present invention is used.
[0017]
When the yellow ink lands on the recording medium first, the water, the first water-soluble organic solvent, the additive, and the water-soluble yellow coloring material in the yellow ink permeate into the recording medium. At this time, since water evaporates or permeates relatively quickly, the ratio of the first water-soluble organic solvent increases near the water-soluble yellow colorant. As a result, the water-soluble yellow coloring material is in a state where it is easily deposited.
[0018]
Subsequently, when the cyan ink or the magenta ink lands on the recording medium and penetrates, similarly to the yellow ink, a first water-soluble organic solvent other than water and an additive are added near the water-soluble cyan coloring material and the water-soluble magenta coloring material. Ratio increases.
[0019]
In the present invention, the dots of the yellow ink at least partially overlap the dots of the cyan ink and the dots of the magenta ink. At this time, since the first water-soluble organic solvent in which the cyan and magenta inks have high solubility is also present in the yellow ink, the dots of the cyan ink and the magenta ink are not adjacent to each other due to the CM separation, and are not overlapped. Also, the water-soluble cyan coloring material and the water-soluble magenta coloring material are precipitated while being mixed in the recording medium. As a result, uniformity is generated in the image.
[0020]
In addition, although yellow ink does not contain additives, it is not only due to the deposition effect due to the decomposition products of the additives contained in the cyan ink and magenta ink, but also to the deposition effects due to the decomposition products of the additives that exist partially. The precipitation occurs earlier than in the prior art.
[0021]
The additive must have ink moisturizing properties, and its decomposition product does not promote the precipitation of the water-soluble cyan coloring material and the water-soluble magenta coloring material, but must promote the deposition of the water-soluble yellow coloring material. It is preferable to use a compound having a decomposable urea bond, and it is more preferable to use urea. The mechanism by which the decomposition products of these additives promote the precipitation of the water-soluble yellow coloring material is that ions generated by the decomposition of the additives dissolve in the yellow ink, and the water-soluble yellow coloring material precipitates due to the salting-out effect. It is. For example, when urea is used as an additive, a water-soluble yellow color material precipitates due to the presence of ammonium ions, carbonate ions, and the like generated by the decomposition of urea in the ink.
[0022]
The content of the additive in the ink is preferably 0.1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less in the cyan ink. The content is preferably 0.1% by mass or more and 20% by mass or less in the magenta ink, and more preferably 3% by mass or more and 15% by mass or less. When the additive content in the ink is within these ranges, a black image having a high density can be formed.
[0023]
Further, the precipitation of the water-soluble cyan coloring material and the water-soluble magenta coloring material is promoted not only by the effect of the additive decomposed product but also by the water-soluble yellow coloring material precipitated in a short time.
[0024]
Further, since the first water-soluble organic solvent contained in the ink has lower volatility than water, it is possible to exhibit the effect of depositing the yellow coloring material in the recording medium.
As the ink set of the present invention, for example, those having the following composition can be used.
[0025]
(Yellow ink)
C. I. 3.0% by mass of Direct Yellow 132, 4.5% by mass of glycerin, 0.5% by mass of ethylene glycol, 7.5% by mass of diethylene glycol, 1.0% by mass of triethylene glycol, 3.0% by mass of tetraethylene glycol, 1,2,6-hexanetriol 3.0% by mass, acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.) 0.2% by mass, 2-propanol 2.5% by mass, water 74.8% by mass.
[0026]
(Magenta ink)
2.5% by mass of a water-soluble coloring material represented by the general formula (I), 1.6% by mass of a water-soluble coloring material represented by the general formula (II), I. Acid Red 289, 0.4% by mass, glycerin 7.0% by mass, ethylene glycol 6.0% by mass, triethylene glycol 1.0% by mass, tetraethylene glycol 2.0% by mass, urea 10.0% by mass, Acetyleneol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.) 0.2% by mass, 2-propanol 2.5% by mass, water 66.9% by mass
[0027]
Embedded image

[0028]
(In the above general formula (I), R ₁ Represents a substituted or unsubstituted alkoxy group or a substituted or unsubstituted aryl group; ₂ And R ₄ Each independently represents a hydrogen atom or a substituted or unsubstituted alkyl group; ₃ Represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, or a halogen atom. X ₁ Represents a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof. n represents 1 or 2. )
[0029]
Embedded image

[0030]
(In the general formula (II), Ar1 represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group, and Ar2 represents an acetyl group, a benzoyl group, a 1,3,5-triazinyl group, a SO ₂ -C ₆ H ₅ Group or SO ₂ -C ₆ H ₄ -CH ₃ Represents any of the groups. M is a counter ion of a sulfonic acid group, and represents any one of a hydrogen atom, an alkali metal, ammonium and organic ammonium. )
(Cyan ink)
4.5% by mass of a water-soluble coloring material represented by the general formula (III), 5.0% by mass of glycerin, 6.0% by mass of ethylene glycol, 2.0% by mass of diethylene glycol, 5.0% by mass of 2-pyrrolidone Urea 10.0% by mass, acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.) 0.2% by mass, 2-propanol 2.5% by mass, water 64.8% by mass
[0031]
Embedded image

[0032]
(In the general formula (III), CuPc represents a copper phthalocyanine residue, M is an alkali metal or ammonium, x is 1, 2, 3, or 4, and y is 1, 2, or 3.)
The content of the water-soluble cyan coloring material in the cyan ink is preferably from 0.1% by mass to 10% by mass, more preferably from 0.5% by mass to 6% by mass. The content of the water-soluble magenta coloring material in the magenta ink is preferably from 0.1% by mass to 10% by mass, more preferably from 0.5% by mass to 6% by mass. The content of the water-soluble yellow colorant in the yellow ink is preferably from 0.1% by mass to 10% by mass, more preferably from 0.5% by mass to 6% by mass. When the content of the water-soluble coloring material in the ink is within these ranges, a high image density and a uniform black image can be formed.
[0033]
As a result, a black image having uniformity and high density is formed. In the ink set of the present invention, the surface tension at 25 ° C. of at least one ink selected from the group consisting of cyan ink, magenta ink and yellow ink is preferably 35 mN / m or more and 50 mN / m or less. . The surface tension at 35 ° C. is more preferably 35 mN / m or more and 48 mN / m or less, further preferably 36 mN / m or more and 42 mN / m or less. When the surface tension is within these ranges, the permeation speed of the ink into the recording medium is adjusted, and the image density and image uniformity of black are improved.
[0034]
Further, in the ink set of the present invention, when a surfactant having a solubility in a water-soluble yellow colorant of less than 1% by mass and having no compatibility with the first water-soluble organic solvent is used, the composite effect with the first solvent can be obtained. Thus, the effect of depositing the water-soluble yellow colorant in the recording medium is further promoted.
[0035]
As the surfactant, a nonionic surfactant can be used. For example, it is preferable to use an acetylene glycol-based surfactant such as acetylenol E series (manufactured by Kawaken Fine Chemical Co., Ltd.), and particularly preferable to use acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.). Here, “incompatible” means that two substances are mixed and then left for a certain period of time, after which layer separation is visually observed or one substance is dispersed in the other substance. Represent.
[0036]
The content of the surfactant in the yellow ink is preferably 0.05% by mass or more and 0.45% by mass or less, and more preferably 0.1% by mass or more and 0.3% by mass or less. The solubility of the water-soluble yellow colorant in the surfactant is preferably less than 1.0% by mass. When the content of the surfactant and the solubility of the water-soluble yellow coloring material in the surfactant are within these ranges, a high image density and a uniform black image can be formed.
[0037]
In addition, the water-soluble yellow coloring material is dissolved in the yellow ink in a range of 10% by mass or more at 25 ° C., and further has a second water-soluble organic solvent that is more volatile than the first water-soluble organic solvent, so that the black ink is black. In addition to improving the image uniformity of the yellow portion of the image and the high solubility of the water-soluble cyan coloring material and the water-soluble magenta coloring material in the second water-soluble organic solvent, the image uniformity of the cyan portion and the magenta portion is also improved. Improve. Further, the present invention also has an effect of suppressing nozzle nozzle clogging of a recording head for yellow ink and precipitation of a coloring material in an air communication portion of a tank storing the yellow ink.
[0038]
The content of the first water-soluble organic solvent in the cyan ink is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 10% by mass or less. The content of the first water-soluble organic solvent in the magenta ink is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 10% by mass or less. The content of the first water-soluble organic solvent in the yellow ink is preferably from 1% by mass to 10% by mass, more preferably from 2% by mass to 5% by mass. When the content of the first water-soluble organic solvent in the ink is within these ranges, a high image density and a uniform black image can be formed.
[0039]
Further, the solubility of the cyan coloring material in the first water-soluble organic solvent is preferably 10% by mass or more. The solubility of the yellow coloring material in the first water-soluble organic solvent is preferably less than 3% by mass, more preferably less than 2.5% by mass. When the solubility of the first water-soluble organic solvent of these coloring materials is within these ranges, a high image density and a uniform black image can be formed.
[0040]
It is desirable that the second water-soluble organic solvent contains diethylene glycol and tetraethylene glycol. More preferably, ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol are more preferably contained.
[0041]
Here, the magnitude of the volatility is determined by adding a predetermined amount of each solvent to a flat pressure evaporating dish 60 × 30 mm described in Japanese Industrial Standards (JIS) R3503, at 60 ° C., 20% R.F. H. Was evaluated by measuring the degree of volatilization of each solvent when left in an oven.
[0042]
In addition to the first color material of the present invention (hereinafter simply referred to as a water-soluble color material) or an ink having the same, a preferable technical problem is that when the characteristics of an image itself are analyzed, the higher the density, the more the recording medium surface side A large amount of color material, forming dots with visually varying shapes, or using wastefully in a recording medium because the desired color material cannot be used effectively Has been found. The present invention has further found that, by solving at least one of these problems, a black image superior to the related art can be formed. The problems found by the present invention will be described below, and the present invention makes the above-mentioned invention even more excellent by solving at least one of the following problems.
[0043]
(1) When an ink having a low surface tension is used, the ink has high permeability in the thickness direction of the recording medium, and the coloring material cannot be distributed at a high density near the surface of the recording medium. The first problem is that image density cannot be achieved.
(2) Those which exert a visual form factor of the image itself, that is, the color material distribution in the surface direction of the recording medium cannot be made uniform, and sufficient image uniformity cannot be achieved. For example, the second problem is that the roundness of the ink dots is poor in the conventional ink.
(3) Further, since the recording medium having a fine porous body has finer pores than plain paper (size paper), the ink behavior in the recording medium is different, and the conventional ink is not sufficient for high image density. The third issue is that no serious consideration has been made.
[0044]
Further objects of the present invention will become clear from the description below.
[0045]
Therefore, the present inventors have mainly studied the first, second, and third problems, and as a result,
The first problem is to use a high surface tension ink containing two types of incompatible solvents,
The second problem is to use an ink containing two kinds of incompatible solvents and another solvent that dissolves all of these solvents,
The third problem is that the ink has a surfactant content within a predetermined range and has a solvent that is incompatible with the surfactant,
It was found that the above problem could be solved.
[0046]
In other words, the first water-soluble coloring material-related ink of the first invention which solves the first problem has a high surface tension, a solvent having low volatility, and a solvent which is incompatible with this solvent, thereby achieving high image density. Further, image uniformity can be achieved.
The ink of the second invention relating to the first water-soluble coloring material that solves the second problem includes, in addition to the above two solvents, a solvent that dissolves all these solvents, thereby achieving image uniformity. it can.
In addition, the ink of the first invention relating to the first water-soluble coloring material that solves the third problem has a surfactant content within a predetermined range, and has a solvent that is incompatible with the surfactant, thereby providing a fine porous ink. Even when ink is used for a recording medium having a solid body, higher image density can be achieved.
[0047]
In particular,
A first invention relating to a first water-soluble colorant, a water-soluble colorant, water as a first solvent,
A second water-soluble organic solvent in which the water-soluble coloring material dissolves in a range of less than 3% by mass at 25 ° C. and is less volatile than the water;
A surfactant in which the water-soluble coloring material dissolves in a range of less than 1% by mass at 25 ° C.,
At room temperature, the second water-soluble organic solvent is not compatible with the surfactant,
The present invention relates to a water-based ink, wherein the water-based ink has a surface tension at 25 ° C. of 35 mN / m or more and 50 mN / m or less.
[0048]
The third water-soluble coloring material-related third invention is an aqueous ink used for a recording medium having a fine porous layer having an average pore diameter of 10 nm or more and 30 nm or less,
A water-soluble coloring material, water as a first solvent,
A second water-soluble organic solvent in which the water-soluble coloring material dissolves in a range of less than 3% by mass at 25 ° C. and is less volatile than the water;
A surfactant in which the water-soluble coloring material dissolves in a range of less than 1% by mass at 25 ° C.,
At room temperature, the second water-soluble organic solvent is not compatible with the surfactant,
An amount of the second water-soluble organic solvent in the aqueous ink is 5% by mass or less,
The present invention relates to a water-based ink, wherein the amount of the surfactant in the water-based ink is 0.45% by mass or less.
[0049]
The first water-soluble coloring material-related second invention is a water-based ink used for an inkjet head,
A water-soluble coloring material, water as a first solvent,
A second water-soluble organic solvent in which the water-soluble coloring material dissolves in a range of less than 3% by mass at 25 ° C. and is less volatile than the water;
A surfactant in which the water-soluble coloring material dissolves in a range of less than 1% by mass at 25 ° C.,
At room temperature, the second water-soluble organic solvent is not compatible with the surfactant,
The aqueous ink further dissolves at least 10% by mass of the water-soluble coloring material at 25 ° C. and has a lower volatility than the water, and a fourth aqueous solution dissolving the surfactant and the second water-soluble organic solvent. Containing an organic solvent,
The present invention relates to a water-based ink, wherein the water-based ink has a surface tension at 25 ° C. of 35 mN / m or more and 50 mN / m or less.
[0050]
The present invention is a water-based ink used for an inkjet head,
A water-soluble coloring material, water as a first solvent,
A second water-soluble organic solvent in which the water-soluble coloring material dissolves in a range of less than 3% by mass at 25 ° C. and is less volatile than the water;
A surfactant in which the water-soluble coloring material dissolves in a range of less than 1% by mass at 25 ° C.,
At room temperature, the second water-soluble organic solvent is not compatible with the surfactant,
The water-based ink further contains a water-soluble organic solvent in which the water-soluble coloring material is dissolved at 25 ° C. in a range of less than 3% by mass, and has a lower volatility than the water.
The aqueous ink further dissolves at least 10% by mass of the water-soluble coloring material at 25 ° C. and has a lower volatility than the water, and dissolves all of the surfactant and the second water-soluble organic solvent. Containing 3 water-soluble organic solvents,
The water-soluble coloring material has a urea bond,
The aqueous ink has a surface tension at 25 ° C. of 35 mN / m or more and 50 mN / m or less,
The present invention relates to an aqueous ink used for a recording medium having a fine porous material having an average pore diameter of 10 nm or more and 30 nm or less.
[0051]
The solubility (solubility) of the water-soluble coloring material in each component was determined as follows.
When the coloring material is in a liquid state, 50 g of an aqueous solution in which the coloring material is dissolved is placed in a beaker (100 ml, JIS R3503) for each component alone at 60 ° C. and 20R. H. %, And the mixture was evaporated to dryness until the weight change per 3 hours became 0.01 g or less, and ground in a mortar to obtain powder. This is again dissolved in the target solvent until it becomes saturated, and the weight of the powder coloring material required for this dissolution divided by the total weight of the solvent and the powder coloring material is referred to as the dissolution rate (solubility). did.
[0052]
When the coloring material is originally a powder, the coloring material is dissolved until it becomes saturated with the target solvent, and the weight of the powder coloring material required for the dissolution is divided by the total weight of the solvent and the powder coloring material. The dissolution rate was taken as the dissolution rate (solubility).
[0053]
In the present invention, the solvent used as the ink is a liquid solvent. A medium on which ink is recorded will be described as a recording medium.
[0054]
In the present specification, the compound having a decomposable urea bond does not include a coloring material.
[0055]
Next, the present invention will be described in more detail with reference to preferred embodiments.
[0056]
(First water-soluble coloring material first invention)
A first invention relating to a first water-soluble coloring material that solves the first problem is to dissolve a water-soluble coloring material, water as a first solvent, and a water-soluble coloring material in a range of less than 3% by mass, and to dissolve the water-soluble coloring material in less than 3% by mass. Contains a second water-soluble organic solvent having low volatility and a surfactant that dissolves a water-soluble coloring material in a range of less than 1% by mass, and a phase of the second water-soluble organic solvent and the surfactant. When an ink having no solubility and having a surface tension at 25 ° C. of 35 mN / m or more and 50 mN / m or less at 25 ° C. is printed using a recording head, the ink dots are close to a perfect circle and the density is high. Above, it became clear that an image having high moisture resistance can be formed.
Here, “incompatible” means that two substances are mixed and then left for a certain period of time, after which layer separation is visually observed or one substance is dispersed in the other substance. Represent.
[0057]
The degree of volatility is determined by adding a predetermined amount of each solvent to a flat pressure evaporating dish 60 × 30 mm described in Japanese Industrial Standards (JIS) R3503, and heating at 60 ° C. and 20% R.F. H. Was evaluated by measuring the degree of volatilization of each solvent when left in an oven.
[0058]
The mechanism by which these effects occur will be described in comparison with a conventional ink.
[0059]
In a conventional ink, a so-called penetrating ink having a relatively large amount of surfactant is a so-called penetrating ink, so that many surfactants are present in the ink droplets even after landing, so that the surface tension of the liquid remains low, The shape of the ink-like portion is distorted from a spherical shape. Therefore, the roundness of the ink droplet landed on the recording medium is reduced.
[0060]
In the conventional ink, the solubility of the water-soluble coloring material in the solvent and the surfactant is not adjusted, so that the water-soluble coloring material concentrated and associated by evaporation of water is dissolved in the solvent and the surfactant again. For example, it penetrates the recording medium. Further, since the compatibility between the surfactant and the second water-soluble organic solvent is not adjusted, even if the solvent permeates into the recording medium, it does not precipitate and form a wall, but penetrates into the recording medium. Would. As described above, since the second water-soluble organic solvent does not form a wall structure in the recording medium that hinders the penetration of the water-soluble coloring material, the water-soluble coloring material does not precipitate on the surface of the recording medium and goes deep. Infiltration, which results in low image density.
[0061]
On the other hand, the ink of the first invention relating to the first water-soluble coloring material is based on the following mechanism.
[0062]
(1) Ink droplets before fixing to recording medium
A surfactant is present near the surface of the ink droplet, and a water-soluble colorant, a first solvent (water), a second water-soluble organic solvent, and a surfactant are present inside the surfactant (FIG. 3A). .
[0063]
(2) Landing of ink droplets on a recording medium
When the droplet lands on the recording medium, the surfactant is present near the surface of the ink droplet, so that the surfactant existing near the portion in contact with the recording medium starts to quickly penetrate into the recording medium. Next, the remaining surfactant in the ink droplet is removed from the entire surface of the ink droplet so as to correct the difference in the concentration of the surfactant generated near the surface of the droplet and keep the surface tension of the entire ink droplet uniform. spread. Then, the surfactant present in the vicinity of the portion in contact with the recording medium again permeates into the recording medium. By repeating this process, the amount of the surfactant in the liquid gradually decreases.
[0064]
However, with the surfactant amount of the present invention, the surfactant concentration in the ink droplet is not more than the critical micelle concentration, so that the surfactant does not stay in the ink droplet which is the gas-liquid interface, but the solid-liquid interface. Is moved to the recording medium. On the other hand, since the surface tension of the remaining ink droplets containing less surfactant is increased, the ink droplets become more spherical. That is, high roundness is given to the image (FIG. 3B).
[0065]
(3) Penetration process
While the surfactant permeates into the recording medium, it adsorbs to the hydrophobic sizing agent in the recording medium. However, since the amount of the surfactant is small, the surfactant can be present only on the relatively upper surface.
[0066]
At about the same time as the penetration of the surfactant, water of small molecules permeates. As the water permeates and further evaporates, the amount of the solvent that dissolves the water-soluble coloring material in the ink droplets decreases, and the water-soluble coloring material concentrates and associates.
[0067]
Then, the second water-soluble organic solvent permeates. Since the surfactant and the second water-soluble organic solvent are not compatible with each other, if they are present at a position closer to the surface than the surfactant, a two-stage wall of water-soluble colorant deposition is formed (see FIG. 3 (c)).
[0068]
In the process of concentrating and associating the water-soluble coloring material, first, by the action of the second water-soluble organic solvent having low solubility in the water-soluble coloring material, many water-soluble coloring materials are precipitated, By using the second water-soluble organic solvent having a lower volatility, it is possible to exhibit the effect of depositing the coloring material in the recording medium (FIG. 3D). Further, even when the solution passes through the second water-soluble organic solvent, the water-soluble coloring material is similarly precipitated by the precipitation effect of the surfactant having low solubility in the water-soluble solvent (FIG. 3E).
[0069]
Due to the two-step precipitation action of the water-soluble coloring material of the second water-soluble organic solvent and the surfactant, more water-soluble coloring material is deposited on the surface layer (FIG. 3 (f)). As a result, a high image density can be obtained.
[0070]
As described above, from the viewpoint of improving the image density, in achieving the above mechanism, the second water-soluble organic solvent in which the water-soluble coloring material is dissolved in a range of less than 3% by mass, and the water-soluble coloring material Is important, the balance between the properties of both surfactants, which dissolve in a range of less than 1% by mass, and the amounts of the second water-soluble organic solvent and the surfactant. In order to obtain a good image density, it is preferable to consider the balance between the amounts of the second water-soluble organic solvent and the surfactant.
[0071]
For example, when the amount of the second water-soluble organic solvent is too large, when the water of the first solvent evaporates, a phenomenon that a water-soluble coloring material precipitates before the ink permeates the recording medium may occur. That is, the bronze phenomenon may occur or the water resistance may decrease. Conversely, when the amount of the second water-soluble organic solvent is too small, the water of the first solvent evaporates and the water-soluble coloring material easily precipitates even if the second water-soluble organic solvent ink permeates the recording medium. And only a low image density was obtained.
[0072]
The amounts of the second water-soluble organic solvent and the surfactant may be adjusted within the range satisfying the surface tension required for the ink of the present invention from the above viewpoint.
[0073]
For example, the amount of the second water-soluble organic solvent in the ink is preferably 5% by mass or less, more preferably 2% by mass or more and 4.5% by mass or less. When the amount of the second water-soluble organic solvent is within these ranges, a high image density can be achieved without occurrence of a bronze phenomenon or reduction in water resistance.
[0074]
Further, water as the first solvent is contained in the ink in an amount of 50% by mass or more and 85% by mass or less, preferably 60% by mass or more and 80% by mass or less.
[0075]
On the other hand, when the amount of the surfactant is too large, the permeation speed into the recording medium is too high, so that a precipitation phenomenon occurs relatively inside the recording medium, and a sufficient image density may not be obtained. On the contrary, when the amount of the surfactant is too small, the ink does not permeate into the recording medium, and the image quality may be reduced. The amount of the surfactant in the ink is preferably 0.45% by mass or less, more preferably 0.07% by mass or more and 0.3% by mass or less, and 0.1% by mass or more and 0.1% by mass or less. More preferably, it is at most 2% by mass. When the surfactant concentration is within these ranges, a high image density can be achieved.
[0076]
In addition, the above-mentioned phenomenon shows that when the ejection amount is a small droplet ink of 3 picoliter or less, an optimal balance is obtained when the surface tension of the ink at 25 ° C. is 35 mN / m or more and 50 mN / m or less. Have come up with new facts that will give you a great image. The surface tension of the ink is preferably 35 mN / m or more and 45 mN / m or less, more preferably 36 mN / m or more and 42 mN / m or less. When the surface tension of the ink is in these ranges, the ink is more excellent in roundness and a good image can be obtained.
[0077]
First Water-Soluble Coloring Material Related The ink of the first invention further comprises a third water-soluble organic solvent in which the water-soluble coloring material is dissolved at 25 ° C. in a range of less than 3% by mass and is less volatile than water. The third water-soluble organic solvent is liquid at 25 ° C., and the total content of the surfactant, the second water-soluble organic solvent, and the third water-soluble organic solvent in the water-based ink is It is preferable that the content is larger than the content of the water-soluble coloring material and is not more than four times the content of the water-soluble coloring material. The total content is more preferably 1.5 times or more and 3.5 times or less than the content of the water-soluble coloring material. When the total content is within these ranges, due to the difference in solubility of the coloring material in these solvents, a large amount of the water-soluble coloring material can be precipitated on the surface of the recording medium to achieve a high image density. it can.
[0078]
Further, the ink of the first invention relating to the first water-soluble coloring material further includes a third water-soluble organic solvent in which the water-soluble coloring material is dissolved at 25 ° C. in a range of less than 3% by mass and is less volatile than water. And the third water-soluble organic solvent is a liquid at 25 ° C., and preferably has an alcohol having 5 or 6 carbon atoms and 2 or 3 hydroxyl groups. It is more preferable to use 1,2,6-hexanetriol as the alcohol. These alcohols have a low permeation rate with respect to the permeation rate of the incompatible second water-soluble organic solvent and the surfactant into the recording medium, but have a high viscosity by themselves, so that the water-soluble coloring material can be preserved. Roundness can be achieved. In addition, high density can be achieved over the entire printing duty.
[0079]
As the water-soluble coloring material used in the present invention, for example, conventionally known water-soluble dyes, for example, water-soluble anionic dyes, direct dyes, acid dyes, reactive dyes and the like can be used. It is preferable to use an azo-based direct dye having the following formula:
[0080]
The content of the water-soluble coloring material in the ink can be 0.1% by mass or more and 6.0% by mass or less, preferably 0.5% by mass or more and 4.5% by mass or less.
[0081]
Further, as the second water-soluble organic solvent, for example, glycerin or the like can be used.
[0082]
In addition, a nonionic surfactant can be used as the surfactant. For example, it is preferable to use an acetylene glycol-based surfactant such as acetylenol E series (manufactured by Kawaken Fine Chemical Co., Ltd.), and particularly preferable to use acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.).
[0083]
(Third invention relating to the first water-soluble coloring material)
Further, the ink of the third invention relating to the first water-soluble coloring material that solves the third problem is preferably used for a recording medium having a fine porous body. The average pore diameter of the microporous body needs to be 10 nm or more and 30 nm or less, and is preferably 15 nm or more and 25 nm or less. The specific surface area of the microporous body is 60 m ² / G or more, 130m ² / G or less, preferably 65 m ² / G or more, 125m ² / G or less. When the microporous body has such a pore diameter and a specific surface area, it is possible to form a particularly good image in which the ink dots are close to a perfect circle, have a high density, and have high moisture resistance.
[0084]
The water-soluble coloring material of the present invention, water as a first solvent, and the water-soluble coloring material are dissolved in a recording medium having a microporous body in a range of less than 3% by mass at 25 ° C. A second water-soluble organic solvent having low volatility, and a surfactant in which the water-soluble coloring material dissolves in a range of less than 1% by mass at 25 ° C., and at room temperature, the second water-soluble organic solvent and The surfactant is not compatible, the content of the second water-soluble organic solvent in the ink is 1% by mass or more and 5% by mass or less, and the amount of the surfactant in the ink is 0.05% by mass. High image density and image uniformity can be achieved by using a water-based ink characterized by being not less than 0.4% by mass and not more than 0.45% by mass.
[0085]
The present inventors believe that the expression of such an effect is greatly affected by the surfactant content in the ink, and that the following mechanism occurs.
[0086]
(1) The ink droplets before being fixed on the recording medium and (2) the landing of the ink droplets on the recording medium are formed by a water-soluble coloring material, water as a first solvent, a second water-soluble organic solvent, and a surfactant. The permeation of the surfactant into the recording medium proceeds at a sufficient speed by the same process as when the ink containing is used (FIG. 4A).
[0087]
(2) Penetration process
When a porous recording medium is used, the surfactant is adsorbed in the pores of the recording medium in the process of permeating into the recording medium. However, when the content of the surfactant is small (0.45% by mass or less), the permeation amount in the recording medium is small, and the amount adsorbed on the microporous body is also small.
[0088]
At substantially the same timing as the penetration of the surfactant, water of small molecules permeates into the recording medium. As the water permeates and further evaporates, the amount of the solvent that dissolves the water-soluble coloring material in the ink droplets decreases, and the water-soluble coloring material concentrates and associates.
[0089]
Thereafter, in the process of the second water-soluble organic solvent penetrating into the pores, first, a large amount of the water-soluble colorant is deposited by the action of the second water-soluble organic solvent having low solubility in the water-soluble colorant. (FIG. 4B). At this time, since the amount of the surfactant adsorbed on the pores is small, it is possible to increase the time for adsorbing the coloring material into the pores, and the pores near the surface of the recording medium have a large amount of unadsorbed sites. For this reason, the water-soluble coloring material dissolved in the water and the second water-soluble organic solvent precipitates the coloring material and is adsorbed on the pores near the surface (FIG. 4C). As a result, a large amount of color material is distributed near the surface of the recording medium, and high image density can be achieved.
[0090]
On the other hand, when an ink containing a large amount of surfactant is used, a large amount of the surfactant is adsorbed in the vicinity of the surface in the porous medium in the process of penetrating into the recording medium (FIG. 4E). . At the same timing as the penetration of the surfactant, water of small molecules and then the second water-soluble organic solvent penetrate into the porous material. Since the surfactant is adsorbed, the water-soluble coloring material dissolved in the second water-soluble organic solvent precipitates and cannot be adsorbed on pores near the surface (FIG. 4 (f)). The second water-soluble organic solvent passes through the vicinity of the surface of the porous body and penetrates deeper into the recording medium in the thickness direction. As a result, a large amount of color material cannot be distributed near the surface of the recording medium, and a high image density cannot be achieved.
[0091]
Further, when the amount of the second water-soluble organic solvent in the ink is 5% by mass or less and the amount of the surfactant is 0.45% by mass or less, it becomes clear that more preferable image density can be obtained. Was.
In particular, a recording medium that can be suitably used in the present invention is preferably a medium in which an ink receiving layer is formed mainly of fine particles having an average particle diameter of 1 μm or less. Particularly preferred examples of the fine particles include silica and aluminum oxide fine particles. Preferred as silica fine particles are silica fine particles represented by colloidal silica. Colloidal silica itself is also available from the market, but particularly preferred examples include those described in Patent Documents 1 and 2. Preferred examples of the aluminum oxide fine particles include alumina hydrate fine particles. As one of such alumina-based pigments, alumina hydrate represented by the following general formula (VI) can be preferably mentioned.
[0092]
Embedded image

[0093]
In the above formula (VI), n represents an integer of 1, 2 or 3, and m represents a value of 0 to 10, preferably 0 to 5. However, m and n do not become 0 at the same time. mH ₂ O is often mH ₂ M can also be an integer or a non-integer value, since it also represents a detachable aqueous phase that does not participate in the formation of the O crystal lattice. In addition, m can reach a value of 0 when this type of material is heated. Alumina hydrate is generally used for the hydrolysis of aluminum alkoxide and sodium aluminate as described in Patent Documents 2 and 3, and for sodium aluminate described in Patent Document 4 It is preferable to use an aqueous solution prepared by a known method such as a method of adding an aqueous solution of sodium sulfate, aluminum chloride or the like to an aqueous solution of the above to neutralize the aqueous solution. In the present invention, it is particularly preferable to use the alumina hydrate described in Patent Document 5.
[0094]
Further, the recording medium for inkjet using these alumina hydrates has transparency, glossiness, fixing property of water-soluble coloring material in a recording liquid, etc., required for realizing photographic image quality. Is most suitable for applying the present invention. When the ink receiving layer is formed using inorganic pigment fine particles such as aluminum oxide fine particles and silica fine particles, a binder made of a water-soluble resin such as polyvinyl alcohol can be used as necessary. When a binder is used, the mixing ratio of the inorganic pigment fine particles and the binder can be in the range of preferably 1: 1 to 100: 1 by mass ratio. The content of the aluminum oxide fine particles or the silica fine particles in the ink receiving layer is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. Is most preferred. The coating amount of the ink receiving layer is 10 g / m 2 in terms of dry solid content in order to improve the impregnation of the image fastness improver. ² It is preferably at least 10 g / m ² Is most preferred.
[0095]
The support of the recording medium is not particularly limited as long as it can form the ink receiving layer containing the fine particles as described above and has a rigidity that can be transported by a transport mechanism such as an inkjet printer. , Any of which can be used. Then, at least the surface on the side on which the ink receiving layer is formed, a densely sized paper formed by applying an inorganic pigment such as barium sulfate together with a binder onto a fibrous base material or a fibrous base material. Those having a surface of a highly porous layer (so-called baryta layer) (for example, baryta paper) can be particularly suitably used as a support.
[0096]
As a recording medium applicable to the present invention, the form having a porous layer on the surface layer is not limited to a recording medium having a porous ink receiving layer formed on a substrate, and alumite or the like can also be used.
[0097]
The ink of the third invention related to the first water-soluble coloring material further contains a water-soluble organic solvent in which the water-soluble coloring material is dissolved at 25 ° C. in a range of less than 3% by mass and is less volatile than water. The water-soluble organic solvent is liquid at 25 ° C., and the total content of the surfactant, the second water-soluble organic solvent, and the water-soluble organic solvent in the water-based ink is the content of the water-soluble colorant in the water-based ink More preferably, the content of the water-soluble coloring material is 4 times or less. The total content is more preferably 1.5 times or more and 3.5 times or less than the content of the water-soluble coloring material. When the total content is within these ranges, due to the difference in solubility of the coloring material in these solvents, a large amount of the water-soluble coloring material can be precipitated on the surface of the recording medium to achieve a high image density. it can.
[0098]
Further, the ink of the third invention related to the first water-soluble coloring material further contains a water-soluble organic solvent in which the water-soluble coloring material is dissolved at 25 ° C. in a range of less than 3% by mass and which is less volatile than water. Preferably, the water-soluble organic solvent is liquid at 25 ° C., and has an alcohol having 5 or 6 carbon atoms and 2 or 3 hydroxyl groups. It is more preferable to use 1,2,6-hexanetriol as the alcohol. These alcohols have a low permeation rate with respect to the permeation rate of the incompatible second water-soluble organic solvent and the surfactant into the recording medium, but have a high viscosity by themselves, so that the water-soluble coloring material can be preserved. Roundness can be achieved. In addition, high density can be achieved over the entire printing duty.
[0099]
As the water-soluble coloring material used in the present invention, for example, conventionally known water-soluble dyes, for example, water-soluble anionic dyes, direct dyes, acid dyes, reactive dyes and the like can be used. It is preferable to use an azo-based direct dye having the following formula:
[0100]
The content of the water-soluble coloring material in the ink can be 0.1% by mass or more and 6.0% by mass or less, preferably 0.5% by mass or more and 4.5% by mass or less.
[0101]
Further, as the second water-soluble organic solvent, for example, glycerin or the like can be used.
[0102]
In addition, a nonionic surfactant can be used as the surfactant. For example, it is preferable to use an acetylene glycol-based surfactant such as acetylenol E series (manufactured by Kawaken Fine Chemical Co., Ltd.), and particularly preferable to use acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.).
[0103]
Further, the ink of the present invention is suitable for use in a recording head that ejects small droplet ink having an ejection amount of 3 picoliters or less.
[0104]
(Second invention related to the first water-soluble coloring material)
The ink of the second invention relating to the first water-soluble coloring material that solves the second problem further dissolves the water-soluble coloring material by 10% by mass or more and has a lower volatility than water. (2) It became clear that a more uniform recorded image could be obtained by dissolving the water-soluble organic solvent and having the fourth water-soluble organic solvent.
Regarding this phenomenon, the present inventors believe that the following mechanism has occurred.
[0105]
(1) The ink droplets before being fixed on the recording medium and (2) the landing of the ink droplets on the recording medium are formed by a water-soluble coloring material, water as a first solvent, a second water-soluble organic solvent, and a surfactant. (A) and (b) proceed in the same manner as when an ink containing is used.
(3) Penetration process
While the surfactant permeates into the recording medium, it adsorbs to the hydrophobic sizing agent in the recording medium. However, since the amount of the surfactant is small, the surfactant is present only on the relatively upper surface.
[0106]
At about the same time as the penetration of the surfactant, water of small molecules permeates. As the water penetrates and evaporates further, the solvent that dissolves the water-soluble coloring material in the ink droplets decreases, and the water-soluble coloring material becomes highly soluble in the fourth water-soluble organic solvent. Move, dissolve, concentrate and associate. The high-concentration solution of the water-soluble coloring material in the fourth water-soluble organic solvent is present on the surface of the recording medium in a perfect circle and almost uniformly.
[0107]
Thereafter, the second water-soluble organic solvent and the fourth water-soluble organic solvent permeate into the recording medium. Since the surfactant and the second water-soluble organic solvent are not compatible with each other, the second water-soluble organic solvent is located closer to the surface of the recording medium than the surface of the recording medium. Is formed (FIG. 5C). On the other hand, since the fourth water-soluble organic solvent has higher volatility than the second water-soluble organic solvent, it gradually evaporates and is compatible with both the second water-soluble organic solvent and the surfactant. Therefore, it penetrates slowly while penetrating the two-stage wall (FIG. 5D). At that time, most of the water-soluble coloring material dissolved in the fourth water-soluble organic solvent is deposited on the two-stage wall, so that the fourth water-soluble organic solvent is relatively close to the surface. Then, precipitation occurs (FIG. 5E).
[0108]
Further, as described above, since the water-soluble coloring material was almost uniformly present on the recording medium due to the influence of the fourth water-soluble organic solvent, the precipitation phenomenon also occurred uniformly, and as a result, the density Is obtained (FIG. 5F).
[0109]
Here, the water-soluble coloring material is further dissolved in the ink by 10% by mass or more, the surfactant and the second water-soluble organic solvent are dissolved, and the fourth water-soluble organic solvent which is more volatile than the second water-soluble organic solvent is used. By using a solvent, it is possible to obtain an ink that achieves high concentration and uniformity and suppresses deterioration of image fastness. It is considered that when the third solvent is used, these effects are obtained by the following mechanism.
[0110]
Further, by using the fourth water-soluble organic solvent, even if moisture in the ink evaporates, it is effective in suppressing clogging of fine nozzles such as a recording head.
[0111]
The fourth water-soluble organic solvent dissolves the surfactant and the second water-soluble organic solvent, and has a water-soluble solubility of 10% by mass or more and is more volatile than the second water-soluble organic solvent. Although it may be used, the fourth water-soluble organic solvent preferably has diethylene glycol and tetraethylene glycol. Further, it is more preferable to have ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. For example, polyethylene glycol 200 can be used.
[0112]
The fourth water-soluble organic solvent preferably dissolves the water-soluble coloring material in an amount of 10% by mass or more, more preferably 10.5% by mass or more. When the water-soluble coloring material has such solubility in the fourth water-soluble organic solvent, more excellent image density can be obtained. The content of the fourth water-soluble organic solvent in the ink is preferably 5% by mass or more and 20% by mass or less, more preferably 6% by mass or more and 15% by mass or less. When the third water-soluble organic solvent is present only in these contents, more excellent image density can be obtained.
[0113]
A third water-soluble organic solvent in which the surfactant, the second water-soluble organic solvent, and the water-soluble colorant in the ink are dissolved at 25 ° C. in a range of less than 3% by mass, and are less volatile than water; Is preferably greater than the content of the water-soluble coloring material in the ink, and not more than four times the content of the water-soluble coloring material. The total content is more preferably 1.5 times or more and 3.5 times or less than the content of the water-soluble coloring material. When the total content is within these ranges, the coloring material precipitates in large quantities on the surface of the recording medium due to the difference in solubility of the coloring material in these solvents, and a high image density can be achieved.
[0114]
By using these inks and recording media, image density and image uniformity are improved, and further, there is an effect of suppressing clogging of fine nozzles of a recording head and the like. In particular, the ink of the present invention is suitable for use in a recording head that ejects small droplet ink having an ejection amount of 3 picoliters or less.
[0115]
Further, it is preferably an aqueous ink having diethylene glycol and tetraethylene glycol as the fourth water-soluble organic solvent, and more preferably an aqueous ink having ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol.
Further, it is more preferable to use a recording medium containing silica or alumina as a fine porous layer.
[0116]
In addition, when the ink of the present invention is used, the water-soluble coloring material precipitates in the paper surface, so that the migration (migration) of the water-soluble coloring material molecules due to the influence of humidity hardly occurs. It is preferable that the water-based ink does not substantially contain a compound having a decomposable urea bond other than the water-soluble coloring material. When a conventional ink containing urea is stored at a high temperature for a long time and then left at a low temperature, the water-soluble coloring material may precipitate depending on the type of the water-soluble coloring material. This phenomenon is considered that urea is decomposed into ammonium ions, carbonate ions, and the like, and a salting-out effect occurs due to an increase in ionic strength, whereby a water-soluble coloring material precipitates. Therefore, such a problem does not occur unless a compound having a decomposable urea bond is substantially contained in the ink.
[0117]
(Examples Related to First Water-Soluble Coloring Material Related to First Water-Soluble Coloring Material)
Hereinafter, the present invention will be specifically described with reference to first water-soluble coloring material-related examples, but these do not limit the scope of the present invention. In the following description, parts and% are based on mass unless otherwise specified.
[0118]
(First water-soluble coloring material first invention)
After sufficiently mixing and dissolving each of the components shown in Table 1 below, pressure filtration was carried out through a filter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare an ink.
[0119]
(First Water-Soluble Coloring Material Related Example 1)
[0120]
[Table 1]

[0121]
□: less than 1% by mass, ×: 1% by mass or more and less than 3% by mass, Δ: 3% by mass or more and less than 10% by mass, ○: 10% by mass or more
Compatibility between second water-soluble organic solvent and surfactant: none
Volatility of the first solvent is lower than that of water
The fourth water-soluble organic solvent dissolves the surfactant and the second water-soluble organic solvent.
The third water-soluble organic solvent, 1,2,6-hexanetriol, dissolves a water-soluble coloring material in a range of less than 3% by mass at 25 ° C., is less volatile than the water, and is a liquid at 25 ° C. is there
(First Water-Soluble Coloring Material Related Example 2)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the amount of the surfactant acetylenol E100 was 0.45% by mass and the amount of water was 74.05% by mass (surface tension: 35.4 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0122]
(First Water-Soluble Coloring Material Related Example 3)
In order to eliminate the third water-soluble organic solvent, 0% by mass of 1,2,6-hexanetriol and 12.00% by mass of diethylene glycol in the ink composition of Example 1 relating to the first water-soluble coloring material (surface tension: 39. An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material, except that the ink composition was 9 mN / m).
[0123]
(First Water-soluble Coloring Material Related Example 4)
In order to eliminate the fourth water-soluble organic solvent, in the ink composition of the first water-soluble coloring material-related Example 1, 0% by mass of tetraethylene glycol and diethylene glycol and 86.35% by mass of water (surface tension of 39. An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material except that the pressure was 2 mN / m).
[0124]
(1st water-soluble coloring material-related comparative example 1)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the surfactant acetylenol E100 was 0.80% by mass and water was 73.70% by mass (surface tension: 33.7 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0125]
(1st water-soluble coloring material-related comparative example 2)
First Water-Soluble Coloring Material Related to the ink composition of Example 1, except that the amount of surfactant acetylenol E100 was 1.15% by mass and the amount of water was 73.35% by mass (surface tension of 32.9 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0126]
(Comparative Example 3 Related to First Water-Soluble Coloring Material)
In order to eliminate the second water-soluble organic solvent, the ink composition of Example 1 related to the first water-soluble coloring material was replaced with 0% by mass of glycerin and 12.00% by mass of diethylene glycol (surface tension: 39.9 mN / m). Prepared an ink in the same manner as in Example 1 for the first water-soluble coloring material.
[0127]
(1st water-soluble coloring material-related comparative example 4)
In order to eliminate the second water-soluble organic solvent and the third water-soluble organic solvent, 0% by mass of glycerin and 1,2,6-hexanetriol in the ink composition of the first water-soluble coloring material-related Example 1 was used. An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material, except that diethylene glycol was changed to 16.00% by mass (surface tension: 39.8 mN / m).
[0128]
(1st water-soluble coloring material-related comparative example 5)
In order to eliminate the surfactant, the third water-soluble organic solvent and the fourth water-soluble organic solvent, the acetylenol E100, 1,2,6-hexanetriol, An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material, except that tetraethylene glycol and diethylene glycol were 0% by mass and water was 90.5% by mass (surface tension: 65.2 mN / m). .
[0129]
Further, in order to simulate the degree of volatility between the solvents, a predetermined amount of each solvent was added to a flat pressure evaporating dish 60 × 30 mm described in Japanese Industrial Standards (JIS) R3503, and the mixture was heated at 60 ° C. and 20% R.V. H. The degree of volatilization of each solvent when left in the oven was measured.
[0130]
FIG. 2 shows the results. It can be seen that the volatility of diethylene glycol, triethylene glycol and tetraethylene glycol as the fourth water-soluble organic solvents is higher than that of glycerin. Ethylene glycol is more volatile than diethylene glycol (not shown). Although not shown, water is the second water-soluble organic solvent, the third water-soluble organic solvent, or the fourth water-soluble organic solvent (ethylene glycol, diethylene glycol, triethylene) in the first water-soluble coloring material-related embodiment. Glycol, tetraethylene glycol, glycerin, 1,2,6-hexanetriol, etc.). On the other hand, 2-propanol described in the first water-soluble coloring material-related example is more volatile than water (for example, the vapor pressure of water at 20 ° C. is 17.5 mmHg and 2-propanol is 32.Hg). Since it is 4 mmHg (Solvent Handbook, Kodansha Scientific, 1976), it is clear that it is not included in the second water-soluble organic solvent, the third water-soluble organic solvent, or the fourth water-soluble organic solvent.
[0131]
(Evaluation method)
Using the ink obtained as described above, printing (8-pass bidirectional) was performed using an inkjet printer Pixus 950i (trade name: manufactured by Canon Inc.) using a heating element as an ink ejection energy source as an inkjet recording apparatus. The image evaluation shown below was performed later. The measuring method is described below. Table 2 shows the results.
[0132]
(1) Image density
A printer is filled with ink, a recording density of 2400 dpi × 1200 dpi, an ejection amount of 2.5 pl, and a recording in which ink is ejected at various duties (gradations) up to 100% is printed on PB paper (plain paper) (trade name: (Canon).
[0133]
The image recorded in this manner was measured with GRETAG Spectrolino under the conditions of a light source: D50 and a visual field: 2 °. D. Was measured. O. D. Is higher, the image density is higher.
A: O. D. But very high images were obtained.
：: O. D. Was high.
Δ: O. D. Was slightly lower.
×: O. D. Is not desirable as an image
(2) Image bronze properties
Using the image obtained in the above (1) image density measurement, the image bronze property was determined.
：: The image is not bronze. Very good image uniformity was obtained.
X: Bronze of the image was recognized.
[0134]
(3) New dot circularity
The dot roundness was determined using the image obtained in the above (1) image density measurement.
A: Very good dot roundness was obtained.
：: Good dot roundness was obtained.
Δ: Some portions have poor dot roundness.
×: The dot roundness is poor as a whole.
[0135]
(4) Image back-facing
In the image obtained by the above (1) image density measurement, the image turning property was determined on the surface opposite to the printing surface of the recording medium.
：: Image strikethrough is completely absent.
：: Image strikethrough is not conspicuous.
Δ: Image strikethrough is slightly present.
×: There are many strikethroughs in the image.
[0136]
(Evaluation results)
Table 2 shows the image density, image bronze properties, and dot trueness of the first water-soluble colorant-related Examples 1, 2, 3, 4, and the first water-soluble colorant-related Comparative Examples 1, 2, 3, 4, and 5. The evaluation results of circularity and image strike-through are shown.
[0137]
From the results shown in Table 2, regarding the image density, in all the inks of Examples 1 to 4 relating to the first water-soluble coloring material, the surface tension was low or the second water-soluble organic solvent was not present. Higher results were obtained than the water-soluble colorant-related comparative inks. Accordingly, it can be seen that in order to achieve a high image density, it is necessary that the second water-soluble organic solvent is present and the ink has a surface tension of 35 mN / m or more. Further, among the first water-soluble coloring material-related examples, with respect to inks having a higher surface tension and inks having a third solvent, those having higher image densities were obtained. Therefore, in order to achieve higher quality images, it is preferable to use an ink having a higher surface tension or an ink further containing a third solvent within the scope of the present invention.
[0138]
Regarding the image bronze property, the ink of Comparative Example 5 relating to the first water-soluble coloring material having a high surface tension of 65.2 mN / m gave a bad result. Therefore, it is understood that an ink having a low surface tension, specifically, an ink of 50 mN / m or less is required to achieve high image quality without bronzing.
[0139]
With respect to dot roundness, it was found that inks having a surface tension of 35 mN / m or less (Comparative Examples 1 and 2 relating to the first water-soluble coloring material) were poor. Therefore, it can be seen that an ink having a surface tension of 35 mN / m or more is required to achieve high image quality with dot roundness. Among the first water-soluble colorant-related examples, those having higher dot tension were obtained with higher dot tension. Therefore, in order to achieve higher quality images, it is preferable that the ink has a higher surface tension within the scope of the present invention.
[0140]
Regarding the image strike-through property, it was found that inks having a surface tension of 35 mN / m or less (Comparative Examples 1 and 2 relating to the first water-soluble coloring material) were poor. Therefore, it is understood that an ink having a surface tension of 35 mN / m or more is required to achieve an image without strike-through. Among the examples relating to the first water-soluble coloring material, those having higher surface tension were more excellent in image strike-through. Therefore, in order to achieve an image without further strikethrough, it is preferable that the ink has a higher surface tension within the scope of the present invention.
[0141]
[Table 2]

[0142]
(Third invention relating to the first water-soluble coloring material)
(First Water-Soluble Coloring Material Related Example 1)
After sufficiently mixing and dissolving each of the components shown in Table 1 above, the mixture was filtered under pressure through a filter having a pore size of 0.2 μm (manufactured by Fuji Film) to prepare an ink.
[0143]
Ink composition of Example 1 relating to first water-soluble coloring material: surface tension 39.9 mN / m
(First Water-Soluble Coloring Material Related Example 2)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the amount of the surfactant acetylenol E100 was 0.45% by mass and the amount of water was 74.05% by mass (surface tension: 35.4 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0144]
(First Water-Soluble Coloring Material Related Example 3)
In order to eliminate the third water-soluble organic solvent, 4.00% by mass of 1,2,6-hexanetriol was added to 4.00% by mass of diethylene glycol (first water-soluble An ink was prepared in the same manner as in the first water-soluble coloring material-related example 1 except that the total amount of diethylene glycol in the coloring material-related example 3 was changed to 12.00% by mass (surface tension: 39.9 mN / m). .
[0145]
(First Water-soluble Coloring Material Related Example 4)
In order to eliminate the fourth water-soluble organic solvent, 4.0% by mass of tetraethylene glycol and 8.00% by mass of diethylene glycol in the ink composition of the first water-soluble coloring material-related Example 1 were extracted, and 86.35% of water was removed. % (Surface tension: 39.2 mN / m), an ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material.
[0146]
(1st water-soluble coloring material-related comparative example 1)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the surfactant acetylenol E100 was 0.80% by mass and water was 73.70% by mass (surface tension: 33.7 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0147]
(1st water-soluble coloring material-related comparative example 2)
First Water-Soluble Coloring Material Related to the ink composition of Example 1, except that the amount of surfactant acetylenol E100 was 1.15% by mass and the amount of water was 73.35% by mass (surface tension of 32.9 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0148]
(Comparative Example 3 Related to First Water-Soluble Coloring Material)
In order to eliminate the second water-soluble organic solvent, 4.0% by mass of glycerin was added to 4.00% by mass of diethylene glycol in the ink composition of the first water-soluble colorant-related example 1 (the first water-soluble colorant-related comparative example 3). An ink was prepared in the same manner as in Example 1 for the first water-soluble coloring material, except that the total amount of diethylene glycol was changed to 12.00% by mass (surface tension: 39.9 mN / m).
[0149]
(1st water-soluble coloring material-related comparative example 4)
In order to eliminate the second water-soluble organic solvent and the third water-soluble organic solvent, 4.00% by mass of glycerin and 4.0 of 1,2,6-hexanetriol in the ink composition of the first water-soluble coloring material-related embodiment 1 were used. The first aqueous solution was replaced by 8.00% by mass of diethylene glycol (the total amount of diethylene glycol in Comparative Example 4 related to the first water-soluble coloring material was 16.00% by mass) (surface tension: 39.8 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0150]
(1st water-soluble coloring material-related comparative example 5)
In order to eliminate the surfactant, the third water-soluble organic solvent and the fourth water-soluble organic solvent, the acetylenol E100, 1,2,6-hexanetriol, An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material, except that tetraethylene glycol and diethylene glycol were 0% by mass and water was 90.5% by mass (surface tension: 65.2 mN / m). .
[0151]
(Evaluation method)
Using the ink obtained as described above, printing (8-pass bidirectional) was performed using an inkjet printer Pixus 950i (trade name: manufactured by Canon Inc.) using a heating element as an ink ejection energy source as an inkjet recording apparatus. The image evaluation shown below was performed later. The measuring method is described below. Table 4 shows the results.
[0152]
(1) Image density measurement
SP-101 (trade name: manufactured by Canon) is a printer in which ink is filled, and a recording density of 2400 dpi × 1200 dpi, an ejection amount of 2.5 pl, and ink ejection with various duties (gradations) up to 100% are applied. I went to.
[0153]
The image recorded in this manner was measured with GRETAG Spectrolino under the conditions of a light source: D50 and a visual field: 2 °. D. Was measured. O. D. Is higher, the image density is higher.
A: O. D. But very high images were obtained.
：: O. D. Was high.
Δ: O. D. Was slightly lower.
×: O. D. Is not desirable as an image
(2) Image bronze properties
Using the image obtained in the above (1) image density measurement, the image bronze property was determined.
A: Very good image uniformity was obtained.
：: Good image uniformity was obtained.
Δ: Some portions have poor image uniformity.
X: The whole image is inferior in uniformity.
[0154]
(3) New dot circularity
The dot roundness was determined using the image obtained in the above (1) image density measurement.
A: Very good dot roundness was obtained.
：: Good dot roundness was obtained.
Δ: Some portions have poor dot roundness.
×: The dot roundness is poor as a whole.
[0155]
(Evaluation results)
Table 3 shows the image densities, image bronze properties, and dot trueness of the first water-soluble colorant-related examples 1, 2, 3, 4, and the first water-soluble colorant-related comparative examples 1, 2, 3, 4, and 5. The evaluation results of circularity are shown.
[0156]
From the results shown in Table 3, regarding the image density, in all the inks of Examples 1 to 4 relating to the first water-soluble coloring material, the first aqueous solution having a large amount of surface activity or the absence of the second water-soluble solvent was used. Higher results were obtained than the inks of the comparative examples related to the coloring material. Therefore, it can be seen that in order to achieve a high image density, an ink in which the second solvent is present and the amount of the surfactant is 0.45% by mass or less is required. Further, among the first water-soluble coloring material-related examples, with respect to the ink having a smaller amount of the surfactant and the ink in which the third solvent was present, those having higher image density were obtained. Therefore, in order to achieve a higher quality image, it is preferable that the ink has a smaller amount of the surfactant or an ink further containing the third solvent.
[0157]
Regarding the image bronzing property, the ink of Comparative Example 5 related to the first water-soluble coloring material in which no surfactant was present gave a poor result. Therefore, it can be seen that an ink containing at least a surfactant is required to achieve bronze-free high image quality.
[0158]
Regarding the dot roundness, it was found that the inks (the first water-soluble coloring material-related comparative examples 1 and 2) in which the amount of the surfactant exceeded 0.45% by mass were poor. Therefore, it is understood that an ink having a surfactant amount of 0.45% by mass or less is required to achieve high image quality with dot roundness. Among the first water-soluble colorant-related examples, with respect to the ink having a smaller amount of the surfactant, an ink having better dot roundness was obtained. Therefore, in order to achieve higher quality images, it is preferable that the ink has a smaller amount of surfactant.
[0159]
[Table 3]

[0160]
(Second invention related to the first water-soluble coloring material)
(First Water-Soluble Coloring Material Related Example 1)
After sufficiently mixing and dissolving each of the components shown in Table 1 above, the mixture was filtered under pressure through a filter having a pore size of 0.2 μm (manufactured by Fuji Film) to prepare an ink.
[0161]
Ink composition of Example 1 relating to first water-soluble coloring material: surface tension 39.9 mN / m
(First Water-Soluble Coloring Material Related Example 2)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the amount of the surfactant acetylenol E100 was 0.45% by mass and the amount of water was 74.05% by mass (surface tension: 35.4 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0162]
(First Water-soluble Coloring Material Related Example 4)
In order to eliminate the fourth water-soluble organic solvent, 4.0% by mass of tetraethylene glycol and 8.00% by mass of diethylene glycol in the ink composition of the first water-soluble coloring material-related Example 1 were extracted, and 86.35% of water was removed. % (Surface tension: 39.2 mN / m), an ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material.
[0163]
(1st water-soluble coloring material-related comparative example 1)
First water-soluble coloring material The first water-soluble coloring material was the same as the ink composition of Example 1, except that the surfactant acetylenol E100 was 0.80% by mass and water was 73.70% by mass (surface tension: 33.7 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0164]
(1st water-soluble coloring material-related comparative example 2)
First Water-Soluble Coloring Material Related to the ink composition of Example 1, except that the amount of surfactant acetylenol E100 was 1.15% by mass and the amount of water was 73.35% by mass (surface tension of 32.9 mN / m). An ink was prepared in the same manner as in Example 1 relating to the coloring material.
[0165]
(1st water-soluble coloring material-related comparative example 5)
In order to eliminate the surfactant, the third water-soluble organic solvent and the fourth water-soluble organic solvent, the acetylenol E100, 1,2,6-hexanetriol, An ink was prepared in the same manner as in Example 1 relating to the first water-soluble coloring material, except that tetraethylene glycol and diethylene glycol were 0% by mass and water was 90.5% by mass (surface tension: 65.2 mN / m). .
[0166]
(Evaluation method)
(1) Image uniformity
Using the ink obtained as described above, an inkjet printer Pixus950i (trade name: manufactured by Canon Inc.) using a heating element as an ink ejection energy source was used as an inkjet recording apparatus, and the ejection amount was 2.5 pl. Printing at a density of 2400 dpi × 1200 dpi (8-pass bidirectional) and recording with ink at various duties (gradations) up to 100% was performed using PB paper (manufactured by Canon) and SP-101 (trade name: Canon). Made).
Using the images recorded in this way, image uniformity was determined.
A: Very good image uniformity was obtained.
：: Good image uniformity was obtained.
Δ: Some portions have poor image uniformity.
X: The whole image is inferior in uniformity.
[0167]
(Evaluation results)
Table 4 shows image uniformity of the first water-soluble colorant-related examples 1, 2, and 4, and the first water-soluble colorant-related comparative examples 1, 2, and 5 when SP-101 was used as a recording medium. The evaluation results of the performance and nozzle clogging characteristics are shown.
[0168]
From the results in Table 4, with respect to the image uniformity, in all the inks of Examples 1, 2, and 4 related to the first water-soluble coloring material, a better result was obtained than the ink having a surface tension outside the range of the present invention. Was. Therefore, in order to achieve a high image density, the surface tension needs to be in the range of 35 mN / m or more and 50 mN / m or less. Further, among the first water-soluble coloring material-related examples, with respect to the ink containing the third solvent, those having a higher image uniformity concentration were obtained. Therefore, in order to achieve higher quality images, it is preferable that the ink further includes the third solvent.
[0169]
[Table 4]

[0170]
This result was the same for plain PB paper.
[0171]
(2) Ink clogging characteristics
Further, for the first water-soluble colorant-related example 1 and the first water-soluble colorant-related comparative example 5, each of the ink jet printers Pixus 950i was filled with ink, a predetermined recovery operation was performed, and a print check pattern was obtained. After printing, the recording head with the ink tank removed from the main body of the ink jet printer, left in a 60 ° C. (5 to 20% RH) environment in a naked state for 15 days, and then left at 25 ° C. for 24 hours. Was observed.
：: Almost no precipitate that causes nozzle clogging is observed.
×: Many precipitates that cause nozzle clogging were observed.
[0172]
(Evaluation results)
Table 5 shows the evaluation results of the ink clogging characteristics of the first water-soluble coloring material related example 1 and the first water-soluble coloring material related comparative example 5. From the results in Table 5, it is found that the recording head is clogged in Example 1 relating to the first water-soluble coloring material having a surface tension in the range of 35 mN / m or more and 50 mN / m or less and having the fourth water-soluble organic solvent. Was not found. Therefore, in order to improve the ink clogging characteristics, it is understood that the surface tension needs to be in the range of 35 mN / m or more and 50 mN / m or less and it is necessary to have the fourth water-soluble organic solvent.
[0173]
[Table 5]

[0174]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but these do not limit the scope of the present invention. In the following description, parts and% are based on mass unless otherwise specified.
[0175]
[Example 1]
After sufficiently mixing and dissolving each of the components shown in Table 6 below, the mixture was filtered under pressure with a filter having a pore size of 0.2 μm (manufactured by Fuji Film) to prepare an ink.
[0176]
[Table 6]

[0177]
□: less than 1% by mass, Δ: 1% by mass or more and less than 3% by mass, ○: 10% by mass or more
Here, in Table 6, magenta color material 1 used the following general formula (I), magenta color material 2 used the following general formula (II), and cyan color material 1 used the following general formula (III).
[0178]
(Magenta color material)
[0179]
Embedded image

[0180]
(In the above general formula (I), R ₁ Represents a substituted or unsubstituted alkoxy group or a substituted or unsubstituted aryl group; ₂ And R ₄ Each independently represents a hydrogen atom or a substituted or unsubstituted alkyl group; ₃ Represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, or a halogen atom. X ₁ Represents a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof. n represents 1 or 2. )
[0181]
Embedded image

[0182]
(In the general formula (II), Ar1 represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group, and Ar2 represents an acetyl group, a benzoyl group, a 1,3,5-triazinyl group, a SO ₂ -C ₆ H ₅ Group or SO ₂ -C ₆ H ₄ -CH ₃ Represents any of the groups. M is a counter ion of a sulfonic acid group, and represents any one of a hydrogen atom, an alkali metal, ammonium and organic ammonium. )
(Cyan color material)
[0183]
Embedded image

[0184]
(In the general formula (III), CuPc represents a copper phthalocyanine residue, M is an alkali metal or ammonium, x is 1, 2, 3, or 4, and y is 1, 2, or 3.)
Further, in order to simulate the degree of volatility between the solvents, a predetermined amount of each solvent was added to a flat pressure evaporating dish 60 × 30 mm described in Japanese Industrial Standards (JIS) R3503, and the mixture was heated at 60 ° C. and 20% R.V. H. The degree of volatilization of each solvent when left in the oven was measured.
[0185]
FIG. 2 shows the results. It can be seen that the volatility of diethylene glycol, triethylene glycol and tetraethylene glycol as the second water-soluble organic solvents is higher than that of glycerin. Ethylene glycol is more volatile than diethylene glycol (not shown). Although not shown, water is the first water-soluble organic solvent or the second water-soluble organic solvent (ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerin, 1,2,6- Hexanetriol, etc.). On the other hand, 2-propanol described in the present example is more volatile than water (for example, the vapor pressure of water at 20 ° C. is 17.5 mmHg, whereas 2-propanol is 32.4 mmHg (Solvent Handbook Kodansha Scientific) FIG. 1976)), it is apparent that the organic solvent is not included in the second water-soluble organic solvent or the third water-soluble organic solvent.
[0186]
In addition, each ink of the ink set of Example 1 was filled in a closed container, stored at 60 ° C. for 3 months, and then left at 5 ° C. for 24 hours.
[0187]
[Comparative Example 1]
The ink set of Example 1 in which urea was omitted from the magenta ink and the cyan ink was used.
[0188]
[Comparative Example 2]
The yellow ink of Example 1 to which 10% of urea was added was filled in a closed container, stored at 60 ° C. for 3 months, and then left at 5 ° C. for 24 hours to deposit a yellow colorant.
[0189]
(Evaluation)
Using the ink obtained as described above, an inkjet printer Pixus850i (trade name: manufactured by Canon) using a heating element as an ink ejection energy source was used as an inkjet recording apparatus, and image processing for CM separation was performed. In this state, only double printing from the outer side to the home position was performed so that printing could be performed in the order of yellow ink, magenta ink, and cyan ink. Black images were formed at various duties (gradations) using SP-101 (trade name: manufactured by Canon Inc.) as a recording medium.
[0190]
In the obtained image, a black optical density O.D. D. Was measured. O. D. Is higher, the black image density is higher. FIG. 1 shows the O.D. of black images of the ink ejection amounts of Example 1 and Comparative Example 1. D. Indicates a value. From this result, it can be seen that the image density of Example 1 is higher than that of Comparative Example 1 regardless of the amount of shot.
[0191]
【The invention's effect】
Provided is an aqueous ink set that forms a high-density and uniform black image when a color image is formed by CM separation using cyan ink, magenta ink, and yellow ink.
[Brief description of the drawings]
FIG. 1 shows the O.D. of black images obtained by applying various duties (gradations) to each of the ink sets of Example 1 and Comparative Example 1. D. It is a figure showing a value.
FIG. 2 shows the results of measuring the volatility of a solvent used in the ink of the present invention.
FIG. 3A is a conceptual diagram illustrating an ink droplet of the present invention before landing on a recording medium. FIG. 3B is a conceptual diagram illustrating a state where the ink droplet of the present invention has landed on a recording medium. FIG. 3C is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 3D is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 3E is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 3F is a conceptual diagram illustrating a state where the ink of the present invention is fixed on a recording medium.
FIG. 4A is a conceptual diagram illustrating an ink droplet of the present invention before landing on a recording medium. FIG. 4B is a conceptual diagram illustrating a state where the ink droplet of the present invention has landed on a recording medium. FIG. 4C is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 4D is a conceptual diagram illustrating a state in which an ink component having a high surfactant concentration permeates into a recording medium. FIG. 4E is a conceptual diagram illustrating a state in which an ink component having a high surfactant concentration permeates into a recording medium. FIG. 4F is a conceptual diagram illustrating a state in which the ink having a high surfactant concentration is fixed on the recording medium.
FIG. 5A is a conceptual diagram illustrating an ink droplet of the present invention before landing on a recording medium. FIG. 5B is a conceptual diagram illustrating a state where the ink droplet of the present invention has landed on a recording medium. FIG. 5C is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 5D is a conceptual diagram illustrating a state where the ink component of the present invention permeates a recording medium. FIG. 5E is a conceptual diagram illustrating a state in which the ink component of the present invention permeates a recording medium. FIG. 5F is a conceptual diagram illustrating a state where the ink of the present invention is fixed on a recording medium.
[Explanation of symbols]
× Surfactant
○ 1st solvent (water)
◇ Second water-soluble organic solvent
● Water-soluble coloring materials
☆ Third water-soluble organic solvent

Claims (9)

A first water-soluble coloring material whose deposition is promoted by a predetermined additive,
A second water-soluble coloring material that is not promoted by the additive, and a third water-soluble coloring material;
A first water-soluble organic solvent having low solubility in the first water-soluble coloring material, a high solubility in the second water-soluble coloring material, and a high solubility in the third water-soluble coloring material;
A water-based first ink having the first water-soluble coloring material and the first water-soluble organic solvent, and not having the additive;
A water-based second ink having the second water-soluble coloring material, the first water-soluble organic solvent, and the additive,
An aqueous third ink having the third water-soluble coloring material, the first water-soluble organic solvent, and the additive;
An image forming method, wherein a black image is formed by bringing each of the second ink and the third ink into contact with the first ink. At least a water-based first ink, a second ink, and a third ink,
A water-based ink set for forming a black image by contacting each of the second ink and the third ink with the first ink,
A first additive having a predetermined additive, a first water-soluble colorant whose deposition is promoted by the additive, and a first water-soluble organic solvent having low solubility in the first water-soluble colorant. Ink and
A second ink having the additive, a second water-soluble coloring material that is not promoted by the additive, and a first water-soluble organic solvent that is highly soluble in the second water-soluble coloring material; ,
A third ink having the additive, a third water-soluble coloring material that is not accelerated by the additive, and a first water-soluble organic solvent that is highly soluble in the third water-soluble coloring material; ,
Aqueous ink set consisting of At least water-based, consisting of cyan ink, magenta ink, and yellow ink,
When the yellow ink dot and the cyan ink dot or the magenta ink dot are adjacent to each other, the yellow ink dot at least partially overlaps the cyan ink dot or the magenta ink dot, and
Neither the cyan ink dot nor the magenta ink dot is adjacent or overlapped,
A water-based ink set for forming a black image by discharging the yellow ink before the cyan ink and the magenta ink,
An additive that improves the moisturizing properties of the ink, a water-soluble cyan coloring material whose deposition is not promoted by a decomposition product of the additive, and a water-soluble cyan coloring material that dissolves in a range of 10% by mass or more at 25 ° C. A first water-soluble organic solvent having a low volatility, and the cyan ink,
The additive, a water-soluble magenta colorant whose precipitation is not promoted by a decomposition product of the additive, and the water-soluble magenta colorant is dissolved at 25 ° C. in a range of 10% by mass or more and has lower volatility than water. The magenta ink, comprising: the first water-soluble organic solvent;
A water-soluble yellow coloring material whose precipitation is promoted by a decomposition product of the additive, and the first water-soluble organic solvent in which the water-soluble yellow coloring material dissolves in a range of less than 3% by mass at 25 ° C. And not containing the additive, the yellow ink,
Aqueous ink set consisting of The water-based ink set according to claim 3, wherein at least the surface tension of the yellow ink at 25 ° C is 35 mN / m or more and 50 mN / m or less. The yellow ink contains at least one surfactant, and the solubility of the water-soluble yellow coloring material in the surfactant is less than 1% by mass at 25 ° C;
The aqueous ink set according to claim 3, wherein the surfactant is not compatible with the first water-soluble organic solvent at 25 ° C. The aqueous ink set according to any one of claims 3 to 5, wherein the cyan ink and the magenta ink have a surface tension at 25 ° C of 35 mN / m or more and 50 mN / m or less. The yellow ink is
The solubility of the water-soluble yellow color material, the water-soluble cyan color material, and the water-soluble magenta color material is 10% by mass or more at 25 ° C, and
More volatile than the first water-soluble organic solvent,
The aqueous ink set according to any one of claims 3 to 6, further comprising a second water-soluble organic solvent. The aqueous ink set according to any one of claims 3 to 7, wherein the second water-soluble organic solvent includes diethylene glycol and tetraethylene glycol. 9. The water-based ink set according to claim 3, wherein the second water-soluble organic solvent includes ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

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