JP4235329B2 - Ink, ink container, ink set, ink jet recording apparatus and ink jet printing method - Google Patents

Description

上記式中、Ｒは例えば炭素数１〜１２の直鎖状もしくは分岐鎖状のアルキル基、置換もしくは未置換のフェニル基又は置換もしくは未置換のナフチル基を示す。ここでフェニル基やナフチル基の置換基としては例えば炭素数１〜６の直鎖状または分岐鎖状のアルキル基等が挙げられる。ここでＲが置換基を有するフェニル基又は置換基を有するナフチル基である場合の置換基としては、例えばＣ₁〜Ｃ₆の直鎖状もしくは分岐鎖状のアルキル基等が挙げられる。上記したような親水性基が結合されてカチオン性に帯電している自己分散型カーボンブラックを製造する方法としては、例えば、下記に示す構造のＮ−エチルピリジル基：
【００３７】
【化２】

を結合させる方法を例にとって説明すると、カーボンブラックを3-アミノ-N-エチルピリジウムブロマイドで処理する方法が挙げられる。この様にカーボンブラック表面への親水性基の導入によってアニオン性若しくはカチオン性に帯電させたカーボンブラックは、イオンの反発によって優れた水分散性を有する為、水性インク中に含有させた場合にも分散剤等を添加しなくても安定した分散状態を維持する。
【００３８】
ところで上記した様な種々の親水性基は、カーボンブラックの表面に直接結合させてもよい。或いは他の原子団をカーボンブラック表面と該親水性基との間に介在させ、該親水性基をカーボンブラック表面に間接的に結合させても良い。ここで他の原子団の具体例としては例えば炭素原子数１〜12の直鎖状若しくは分岐鎖状のアルキレン基、置換もしくは未置換のフェニレン基、置換もしくは未置換のナフチレン基が挙げられる。ここでフェニレン基及びナフチレン基の置換基としては例えば炭素数１〜６の直鎖状または分岐鎖状のアルキル基が挙げられる。また他の原子団と親水性基の組合わせの具体例としては、例えば−C₂H₄-COOM、−Ph-SO₃M、−Ph-COOM 等(但し、Phはフェニル基を表す)が挙げられる。
【００３９】
ところで、本実施形態に係るインクに含有させる自己分散型の顔料はその８０％以上が０．０５〜０．３μｍ、特には０．１〜０．２５μｍの粒径のものであるものとすることが好ましい。このようなインクの調整方法は後述する実施例に詳述した通りである。
（第２の顔料）
本実施形態のインクに用いることのできる第２の顔料は、インクの分散媒、具体的には例えば水性媒体に対して高分子分散剤の作用によって分散させることができる顔料が挙げられる。即ち、顔料粒子の表面に高分子分散剤が吸着した結果として初めて水性媒体に対して安定に分散させ得るような顔料が好適に用いられる。そしてそのような顔料としては、例えば黒色顔料としては、例えばファーネスブラック、ランプブラック、アセチレンブラック、チャンネルブラック等のカーボンブラック顔料が挙げられる。このようなカーボンブラック顔料の具体例としては、例えば下記のものを単独で、あるいは適宜組合わせて用いることができる。
・レイヴァン（Ｒａｖｅｎ）７０００、レイヴァン５７５０、レイヴァン５２５０、レイヴァン５０００ＵＬＴＲＡ、レイヴァン３５００、レイヴァン２０００、レイヴァン１５００、レイヴァン１２５０、レイヴァン１２００、レイヴァン１１９０ＵＬＴＲＡ−ＩＩ、レイヴァン１１７０、レイヴァン１２５５（以上コロンビア社製）、
・ブラックパールズ（Black Pearls）Ｌ、リーガル（Regal）４００Ｒ、リーガル３３０Ｒ、リーガル６６０Ｒ、モウグル（Mogul）Ｌ、モナク（Monarch）７００、モナク８００、モナク８８０、モナク９００、モナク１０００、モナク１１００、モナク１３００、モナク１４００、ヴァルカン（Ｖａｌｃａｎ）ＸＣ−７２Ｒ（以上キヤボット社製）
・カラーブラック（Color Black）FW1、カラーブラックFW2、カラーブラックFW2V、カラーブラック１８、カラーブラックFW200、カラーブラックS150、カラーブラックS160、カラーブラックS170、プリンテックス（Printex）35、プリンテックスＵ、プリンテックスＶ、プリンテックス１４０Ｕ、プリンテックス１４０Ｖ、スペシヤルブラック（Special Black）６、スペシヤルブラック５、スペシヤルブラック４Ａ、スペシヤルブラック４（以上デグッサ社製）
・No.２５、No.３３、No,４０、No.４７、No.５２、No.９００、No.２３００、ＭＣＦ−８８、ＭＡ６００、ＭＡ７、ＭＡ８、ＭＡ１００（以上三菱化学社製）
他の黒色顔料としてはマグネタイト、フェライト等の磁性体微粒子やチタンブラック等を挙げることができる。
【００４０】
また以上で述べた黒色顔料以外に青色顔料、赤色顔料等も用いることができる。
【００４１】
該第１及び第２の顔料を合わせた色材の量は、インク全量に対し、０．１〜１５重量％、より好ましくは、１〜１０重量％である。第１の顔料と第２の顔料の比率は、５／９５〜９７／３、より好ましくは１０／９０〜９５／５の範囲が好ましい。さらに好ましくは、第１の顔料／第２の顔料＝９／１〜４／６である。さらに好しい別の範囲は第１の顔料が多い範囲である。このような第１の顔料が多い場合においては、インクとしての分散安定性はもちろん、ヘッドの吐出安定性、特に吐出効率や吐出口面の濡れが少ないことによる信頼性を含めた安定性が発揮される。
【００４２】
また紙上でのインクの挙動として、高分子分散剤の吸着した第２の顔料が少ないインクで効果的に紙の表面にインクが拡がるため、高分子分散剤による均一な薄膜が表面に形成されると推定され、その効果により画像の耐擦過性も向上する。
（高分子分散剤）
上記第２の顔料を水性媒体に分散させる為の高分子分散剤は、例えば該第２の顔料の表面に吸着して該第２の顔料を水性媒体に安定して分散させる機能を有するものが好適に用いられる。このような高分子分散剤の例としてはアニオン性高分子分散剤、カチオン性高分子分散剤及びノニオン性高分子分散剤が挙げられる。
（アニオン性高分子分散剤）
親水性基としてのモノマーと疎水性基としてのモノマーの重合体及びその塩等が挙げられる。親水性基としてのモノマーの具体例としては、例えば、スチレンスルホン酸、α,β−エチレン性不飽和カルボン酸、α,β−エチレン性不飽和カルボン酸誘導体、アクリル酸、アクリル酸誘導体、メタクリル酸、メタクリル酸誘導体、マレイン酸、マレイン酸誘導体、イタコン酸、イタコン酸誘導体、フマル酸及びフマル酸誘導体等が挙げられる。
【００４３】
また疎水性成分としてのモノマーの具体例としては、例えばスチレン、スチレン誘導体、ビニルトルエン、ビニルトルエン誘導体、ビニルナフタレン、ビニルナフタレン誘導体、ブタジエン、ブタジエン誘導体、イソプレン、イソプレン誘導体、エチレン、エチレン誘導体、プロピレン、プロピレン誘導体、アクリル酸のアルキルエステル、メタクリル酸のアルキルエステル等が挙げられる。
【００４４】
なおここで塩とは具体的には水素、アルカリ金属、アンモニウムイオン、有機アンモニウムイオン、ホスホニウムイオン、スルホニウムイオン、オキソニウムイオン、スチボニウムイオン、スタンノニウム、ヨードニウム等のオニウム化合物等が挙げられるが、これらに限定されるものではない。また上記重合体やその塩に、ポリオキシエチレン基、水酸基、アクリルアミド、アクリルアミド誘導体、ジメチルアミノエチルメタクリレート、エトキシエチルメタクリレート、ブトキシエチルメタクリレート、エトキシトリエチレンメタクリレート、メトキシポリエチレングリコールメタクリレート、ビニルピロリドン、ビニルピリジン、ビニルアルコール及びアルキルエーテル等を適宜付加してもよい。
（カチオン性高分子分散剤）
カチオン性分散剤としては、三級アミンモノマー、及びこれらを４級化したものと疎水性モノマーとの共重合物等が用いられる。三級アミンモノマーとしては、例えばN,N-ジメチルアミノエチルメタクリレート、N,N-ジメチルアクリルアミド等が用いられる。疎水性モノマーとしては、スチレン、スチレン誘導体、ビニルナフタレン等が用いられる。また、３級アミンの場合において、塩を形成するための化合物としては、硫酸、酢酸、硝酸等が用いられる。また、塩化メチル、ジメチル硫酸等で４級化したものも用いることができる。
（ノニオン性高分子分散剤）
ノニオン性高分子分散剤の例は、ポリビニルピロリドン、ポリプロピレングリコール、ビニルピロリドンー酢酸ビニル共重合体等を含む。
【００４５】
上記した第１の顔料、第２の顔料及び高分子分散剤は、適宜その組合わせを選択し、水性媒体に分散、溶解せしめることによって本態様のインクを得ることができるが、第１の顔料として、少なくとも１つのアニオン性の基が直接もしくは他の原子団を介して顔料の表面に結合されている自己分散型の顔料を用いる場合には、高分子分散剤としてアニオン性の高分子分散剤を組合わせることは、インクの安定性の観点から好ましく、同じ理由により第１の顔料として少なくとも１つのカチオン性の基が直接もしくは他の原子団を介して顔料の表面に結合されている自己分散型の顔料を用いる場合には、高分子分散剤としてカチオン性の高分子分散剤を該第１の顔料と組合わせる。
【００４６】
例えば、メチルアルコール、エチルアルコール、ｎ−プロピルアルコール、イソプロピルアルコール、ｎ−ブチルアルコール、ｓｅｃ−ブチルアルコール、ｔｅｒｔ−ブチルアルコール、イソブチルアルコール、ｎ−ペンタノール等の炭素数１〜５のアルキルアルコール類；ジメチルホルムアミド、ジメチルアセトアミド等のアミド類；アセトン、ジアセトンアルコール等のケトン又はケトアルコール類；テトラヒドロフラン、ジオキサン等のエーテル類；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、ジプロピレングリコール、トリプロピレングリコール、ポリエチレングリコール、ポリプロピレングリコール等のオキシエチレン又はオキシプロピレン共重合体；エチレングリコール、プロピレングリコール、トリメチレングリコール、トリエチレングリコール、１，２，６−ヘキサントリオール等のアルキレン基が２〜６個の炭素原子を含むアルキレングリコール類；グリセリン；エチレングリコールモノメチル（又はエチル）エーテル、ジエチレングリコールモノメチル（又はエチル）エーテル、トリエチレングリコールモノメチル（又はエチル）エーテル等の低級アルキルエーテル類；トリエチレングリコールジメチル（又はエチル）エーテル、テトラエチレングリコールジメチル（又はエチル）エーテル等の多価アルコールの低級ジアルキルエーテル類；モノエタノールアミン、ジエタノールアミン、トリエタノールアミン等のアルカノールアミン類；スルホラン、Ｎ−メチル−２−ピロリドン、２−ピロリドン、１，３−ジメチル−２−イミダゾリジノン等が挙げられる。上記のごとき水溶性有機溶剤は、単独でも或いは混合物としても使用することができる。
（インクの記録媒体への浸透性）
以上説明してきた各種成分を含んでいる本実施態様のインクは、プリント媒体に対する浸透性に着目して、例えばＫａ値を１（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）未満に調整した場合、極めて均一な濃度の画像ドットを得ることができる。以下にインクのプリント媒体に対する浸透性について説明する。
【００４７】
インクの浸透性を１ｍ² 当たりのインク量Ｖで表すと、インク滴を吐出してからの時間ｔにおけるインク浸透量Ｖ（単位はミリリットル／ｍ² ＝μｍ）は、次に示すようなブリストウ方式により表されることが知られている。
【００４８】
【数１】
Ｖ＝Ｖｒ＋Ｋａ（ｔ−ｔｗ）^1/2
（ただし、ｔ＞ｔｗ）
インク滴がプリント媒体表面に滴下した直後は、インク滴は表面の凹凸部分（プリント媒体の表面の粗さの部分）において吸収されるのが殆どで、プリント媒体内部へは殆ど浸透していない。その間の時間がｔｗ（ウェットタイム）、その間の凹凸部への吸収量がＶｒである。インク滴の滴下後の経過時間がｔｗを超えると、超えた時間（ｔ−ｔｗ）の２分の１乗に比例した分だけ浸透量Ｖが増加する。Ｋａはこの増加分の比例係数であり、浸透速度に応じた値を示す。
【００４９】
Ｋａ値は、ブリストウ法による液体の動的浸透性試験装置Ｓ（東洋精機製作所製）を用いて測定した。本実験では、本出願人であるキヤノン株式会社のＰＢ用紙をプリント媒体（記録紙）として用いた。このＰＢ用紙は、電子写真方式を用いた複写機やＬＢＰと、インクジェット記録方式を用いたプリントの双方に使える記録紙である。
【００５０】
また、キヤノン株式会社の電子写真用紙であるＰＰＣ用紙に対しても、同様の結果を得ることができた。
【００５１】
Ｋａ値は界面活性剤の種類、添加量などによって決まってくる。例えば、エチレンオキサイド−２，４，７，９−テトラメチル−５−デシン−４，７−ジオール(ethylene oxide-2,4,7,9-tetramethyl-5-decyen-4,7-diol （以下、商品名「アセチレノール」；川研ファインケミカル社製）という非イオン性界面活性剤を添加することにより、浸透性は高くなる。
【００５２】
また、アセチレノールが混合されていない（含有割合が０％）インクの場合は浸透性が低く、後に規定する上乗せ系インクとしての性質を持つ。また、アセチレノールが１％の含有割合で混合されている場合は短時間で記録紙１０３内部に浸透する性質を持ち、後に規定する高浸透性インクとしての性質を持つ。そして、アセチレノールが０．３５％の含有割合で混合されているインクは、両者の中間の半浸透性インクとしての性質を持つ。
【００５３】
【表１】

上記の表１は、「上乗せ系インク」、「半浸透性インク」、「高浸透性インク」のそれぞれについて、Ｋａ値、アセチレノール含有量（％）、表面張力（ｄｙｎｅ／ｃｍ）を示している。プリント媒体である記録紙に対する各インクの浸透性は、Ｋａ値が大きいものほど高くなる。つまり、表面張力が小さいものほど高くなる。
【００５４】
表１におけるＫａ値は、前述の如くブリストウ法による液体の動的浸透性試験装置Ｓ（東洋精機製作所製）を用いて測定したものである。実験には、前述のキヤノン株式会社のＰＢ用紙を記録用紙として用いた。また、前述のキヤノン株式会社のＰＰＣ用紙に対しても、同様の結果を得ることができた。
【００５５】
ここで、「高浸透性インク」として規定される系のインクはアセチレノール含有割合が０．７％以上であり、浸透性に関して良好な結果が得られた範囲のものである。そして本実施態様のインクに担持させる浸透性の基準としては、「上乗せ系インク」のＫａ値、即ち１．０（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）未満とすることが好ましく、特には０．４（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）以下が好ましい。
（染料の添加）
上記した態様のインクに染料を更に添加してもよい。即ち第１の顔料、第２の顔料及び第２の顔料を水性媒体に分散させるための分散剤を含むインクに対して更に染料を添加したインクは、記録媒体として表面にコート層として樹脂層を備えたプリント媒体に図１に示したような顔料の凝集物の固まり１００１の間に「ひび割れ」１００３等のない、高品位な画像を形成することができる。染料を更に添加したインクによる樹脂層を備えたプリント媒体上の画像の「ひび割れ」が有効に防止できる理由は明らかでないが、染料を更に添加したインクを用いてプリント媒体上に画像を形成した場合に、プリント媒体上に形成される顔料の凝集物は図２に２００１として示した様に細かい粒子となって存在し、その周囲を染料が取り囲み、また凝集物が存在しない部分を染料が埋めた状態となる。また第２の顔料の凝集力が第１の顔料の存在によって緩和されることは先に述べた通りであるが、染料の添加によって第２の顔料の凝集力がもう１段緩和され、インクの吸収性が普通紙等と比較して悪い記録媒体において生じ易い「ひび割れ」等のプリント画像の不均一を有効に抑えることができるものと考えられる。ここで用いることのできる染料としては例えばアニオン染料やカチオン染料が挙げられ、好ましくは第１の顔料の表面に結合している基の極性と同極性の染料を採用することが好ましい。
（アニオン、カチオン染料）
上記した様な本実施形態で使用できる水性媒体に対して可溶なアニオン染料としては、公知の酸性染料、直接性染料、反応性染料等が好適に使用される。また、カチオン染料としては公知の塩基性染料が好適に使用される。また、特に好ましくは、両者の染料とも骨格構造として、ジスアゾ、または、トリスアゾ構造を有する染料を用いることが良い。またさらに、骨格構造の異なる２種以上の染料をもちいることも好ましい。使用する染料として、黒色の染料以外で、色調が大きく異ならない範囲で、シアン、マゼンタ、イエロー等の染料を用いてもかまわない。
（染料の添加量）
また染料の添加量としては、色材全体の５重量％〜６０重量％でよいが、第１及び第２の顔料を混合したことの効果を有効に活用することを考慮すると、５０重量％未満とすることが好ましい。更に普通紙上での印字特性を重視したインクとする場合には５重量％〜３０重量％とすることが好ましい。。
（記録方法）
本実施態様にかかるインクは、プリント媒体に対して公知のインク付与手段を用いて付与して画像を形成する。
【００５６】
本発明の好しい実施形態におけるインク付与方式は、公知のインクジェットプリント方式である。すなわち、プリントヘッドからプリント媒体にインクを吐出してプリントを行う形態に、本発明のインクが好適に用いられる。プリントヘッドにおける吐出方式は、ピエゾ方式等の公知の方式を採用できるが、好しい実施形態としては、インクに熱エネルギーを作用させ、これによってインク中に気泡を生じさせこの気泡の圧力によりインクを吐出する方式である。
【００５７】
なお、プリントヘッドから吐出されるインクがプリント媒体において打ち込まれる量は、単位面積当り０．０１４ピコリットル（ｐｌ）／μｍ² 以下であることが好しい。より具体的には、３６０ｄｐｉで７０ｐｌ／μｍ² 以下、６００ｄｐｉで２５ｐｌ／μｍ²以下であることが好ましい。これは、色材として１種類の顔料のみのインクを用いた場合、特に普通紙ではエリアファクターが不足しＯＤを低下させる場合があるが、本実施形態のインクによれば先に述べた様に エリアファクターを大きくできるため、それ程の打ち込み量を必要としないためである。
【００５８】
また、上述した本実施形態のインクを収納したインクカートリッジやインクを収容したインク収納部とそのインクを吐出させる手段とが一体化され、インクジェットプリンターに着脱可能に構成された記録ヘッド等のインク収納容器も本発明の一実施形態に含まれる。
【００５９】
更には前述した自己分散型カーボンブラックを色材として含む、本実施態様にかかるブラックインクと他のカラーインク、例えばイエローインク、マゼンタインク及びシアンインクから選ばれる少なくとも１つのカラーインクとが各々独立したインク収納部に収容されたインクセット等も又本発明の一実施形態に含まれる。
【００６０】
先に述べた、本発明者らの知見に基づく第１の顔料と第２の顔料及び高分子分散剤との相互作用がもたらす顔料の凝集力の緩和、そしてそれがもたらすプリント媒体上に優れた画像を形成できるという効果は、これらの成分を含む単一のインクによってももちろん達成されるものであるが、例えば、記録媒体上にてこれらの成分を液体の状態で接触させることによっても同様の効果が奏せられるものである。具体的には例えは図７に示す様に、第１の顔料を含む第１のインクを第１のインクジェットヘッド７０１から吐出させてプリント媒体の所定の位置に付着せしめる工程と、該第１の顔料の表面に結合している基と同一の極性を有する高分子分散剤と第２の顔料を含む第２のインクを第２のインクジェットヘッド７０２から吐出させて該プリント媒体７０３の、該第１のインクが付与された箇所もしくは該第１のインクが付与される箇所に付与する工程とを、該第１のインクと第２のインクとが該プリント媒体上で互いが液体の状態で混合される様なタイミングで行なうことによっても、エリアファクタが大きく、外形形状に優れ、またドット内で画像濃度が高くまた均一なインクドットを形成することができる。
【００６１】
更には図８に示す様に、一方では第１のインクジェットヘッド８０１から第１の顔料を含む第１のインクを吐出させ（８０４）、他方では第２のインクジェットヘッド８０２から該第１の顔料の表面に結合している基と同一の極性を有する高分子分散剤と第２の顔料を含む第２のインクを吐出させ（８０５）、各々のインクジェットヘッドから吐出させたインク同士（８０４、８０５）をプリント媒体８０３への付着前に合体させ、該第１のインクと第２のインクとを混合せしめたインク８０６をプリント媒体８０３の所定の部位に付着させる方法によっても、プリント媒体８０３上で第１のインクと第２のインクとが液体の状態で接触してなる状態を実現することができる。なおここで各々のインクを付与するプリント媒体８０３上の位置は、これらのインクが液体状態で接触しさえすれば、各々の付与位置が多少ずれていてもよいことは言うまでもない。
【００６２】
なおここで第１のインクと第２のインクとを混合せしめたインクのブリストウ法におけるKa値は１ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2未満となるように各インクを調製しておくことが好ましい。
【００６３】
同様に第１の顔料、第２の顔料、高分子分散剤及び染料との相互作用によってもたらされる顔料の凝集力の緩和効果、そしてそれがプリント媒体上、特に樹脂コート層を備えたプリント媒体上に優れた画像を形成できるという効果は、形成した画像が示す優れた効果もまた上記の４つの成分を含む単一のインクばかりでなく、記録媒体上にてこれらの成分を液体の状態で接触させることによっても同様の効果が奏せられるものである。即ち図９に示す様に、第１の顔料を含む第１のインクを第１のインクジェットヘッド９０１から吐出させてプリント媒体の所定の位置に付着せしめるステップと、該第１の顔料の表面に結合している基と同一の極性を有する高分子分散剤と第２の顔料を含む第２のインクを第２のインクジェットヘッド９０２から吐出させて該プリント媒体９０４の該所定の位置に付与するステップと、該第１の顔料の表面に結合している基と同極性の染料を含む第３のインクを第３のインクジェットヘッド９０３から吐出させて該プリント媒体９０４の該所定の位置に付与するステップとを、該第１のインクと第２のインクと該第３のインクとが該プリント媒体上で互いが液体の状態で混合される様なタイミングで行なうことによっても、エリアファクタが大きく、外形形状に優れ、またドット内で画像濃度が高くまた均一なインクドットを形成することができる。なおここで各々のインクを付与するプリント媒体９０４上の位置は、これらのインクが液体状態で接触しさえすれば、各々の付与位置が多少ずれていてもよいことは言うまでもない。
【００６４】
更には図１０に示す様に、第１のインクジェットヘッド１００１から第１の顔料を含む第１のインクを吐出させ（１００２）、第２のインクジェットヘッド１００３から該第１の顔料の表面に結合している基と同一の極性を有する高分子分散剤と第２の顔料を含む第２のインクを吐出させ（１００４）、第３のインクジェットヘッド１００５から該第１の顔料の表面に結合している基と同極性の染料を含む第３のインクを吐出させ（１００６）、各々のインクジェットヘッドから吐出させたインク同士をプリント媒体８０３への付着前に合体させ、該第１のインクと第２のインクと第３のインクとを混合せしめたインク（１００７）をプリント媒体１００８の所定の部位に付着させる方法によっても、プリント媒体１００８上で第１のインクと第２のインクと第３のインクとが液体の状態で接触してなる状態を実現することができる。この場合にもまた第１のインク、第２のインク及び第３のインクとが混合せしめられたインクのブリストウ法におけるＫａ値は１ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2未満となるように各インクを調製しておくことが好ましい。
【００６５】
コート層として樹脂層を備えたプリント媒体の例としては、例えば紙またはポリエステル等のプラスチックフィルム上に樹脂層を設けたものが知られている。コート層を構成する材料としては、水溶性樹脂、水分散樹脂等を主成分としたもので、この他カチオン性の化合物、界面活性剤、充填剤等を適宜使用してもよい。
【００６６】
水溶性樹脂としては、例えば、ポリビニルアルコール、及びアニオン変性ポリビニルアルコール、カチオン変性ポリビニルアルコール、アセタール変性ポリビニルアルコール等のポリビニルアルコールの変性物；水系ポリウレタン；ポリビニルピロリドン、及びビニルピロリドンと酢酸ビニル共重合体、ビニルピロリドンとジメチルアミノエチル・メタクリル酸の共重合体、４級化したビニルピロリドンとジメチルアミノエチル・メタクリル酸の共重合体、ビニルピロリドンとメタクリルアミドプロピル塩化トリメチルアンモニウム共重合体等のポリビニルピロリドンの変性物；カルボキシメチルセルロース、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース等のセルロース系水溶性樹脂、及びカチオン化ヒドロキシエチルセルロース等のセルロースの変性物；ポリエステル、ポリアクリル酸（エステル）、メラミン樹脂、或いはこれらの変性物、少なくともポリエステルとポリウレタンとを含むグラフト共重合体等の合成樹脂、又、アルブミン、ゼラチン、カゼイン、でんぷん、カチオン化でんぷん、アラビアゴム、アルギン酸ソーダ等の天然樹脂を挙げることができる。
【００６７】
又、水分散性樹脂としては、例えば、ポリ酢酸ビニル、エチレン−酢酸ビニル共重合体、ポリスチレン、スチレン−（メタ）アクリル酸エステル共重合体、（メタ）アクリル酸エステル系重合体、酢酸ビニル−（メタ）アクリル酸（エステル）共重合体、ポリ（メタ）アクリルアミド、（メタ）アクリルアミド系共重合体、スチレン−イソプレン共重合体、スチレン−ブタジエン共重合体、スチレン−プロピレン共重合体、ポリビニルエーテル、シリコン−アクリル系共重合体等、多数列挙することができるが、勿論これらに限定されるものではない。
【００６８】
また、以上の他、プリント媒体のコート層の材料として、カチオン性化合物も好適に使用される。このカチオン性化合物は、分子内にカチオン性部分を含むものであれば特に限定されるものではなく、例えば、モノアルキルアンモニウムクロライド、ジアルキルアンモニウムクロライド、テトラメチルアンモニウムクロライド、トリメチルフェニルアンモニウムクロライド、エチレンオキサイド付加アンモニウムクロライド、などの４級アンモニウム塩型のカチオン性界面活性剤、あるいは、アミン塩型のカチオン性界面活性剤、さらには、カチオン性部分を含むアルキルベタイン、イミダゾリウムベタイン、アラニン系などの両性界面活性剤でもよい。また、ポリマーあるいはオリゴマーとしては、ポリアクリルアミドのカチオン変性物、あるいは、アクリルアミドとカチオン性モノマーの共重合体、ポリアリルアミン、ポリアミンスルホン、ポリビニルアミン、ポリエチレンイミン、ポリアミド−エピクロルヒドリン樹脂、ポリビニルピリジニウムハライドなどが挙げられる。
【００６９】
さらに、ビニルオキサゾリドン系モノマーの単独、あるいは、他の一般的なモノマーとの共重合体、ビニルイミダゾール系モノマーの単独、あるいは、他のモノマーとの共重合体などが挙げられる。
【００７０】
上記の他のモノマーとしては、メタクリレート、アクリレート、アクリロニトリル、ビニルエーテル、酢酸ビニル、エチレン、スチレンなどが挙げられる。また、カチオン変性したセルロースなどでも良い。
【００７１】
以上のようなカチオン変性化合物が好適に用いられるが、もちろん、カチオン性化合物はこれらに限定されるものではない。
【００７２】
また、コート層の厚みに関しては、乾燥重量で０．１ｇ／ｍ² 〜１００ｇ／ｍ²の範囲で塗工されたものが好ましく、また、コート層を１層で構成したものの他、２層，３層構成等の多層構成で形成されたものでもよい。
【００７３】
以上のようなコート層が形成されたプリント媒体は、本実施形態のインクを用いることにより、特に「ひび割れ」を防止する点で有効であることは上述の通りであるが、このような効果に加え、顔料自体、コート層に対する濡れ性が良く、これにより、コート層に対する濡れ性が劣る染料の欠点を補なうことができるという効果を得ることもできる。すなわち、本実施形態の顔料および染料の混合インクを用いることにより、色材として染料のみが含まれるインクを用いる場合に生ずるビーディングの発生を抑制することもできる。
【００７４】
【実施例】
以下、上記実施形態の具体的実施例について以下に説明する。
（実施例１）
図３は第１実施例に係るフルラインタイプのプリント装置の概略構成を示す側面図である。
【００７５】
このプリント装置１は、プリント媒体としての記録媒体の搬送方向（同図中矢印Ａ方向）に沿って所定位置に配置された複数のフルラインタイプのプリントヘッドよりインクを吐出してプリントを行うインクジェットプリント方式を採用するものであり、不図示の制御回路に制御されて動作する。
【００７６】
ヘッド群１０１ｇの各プリントヘッド１０１Ｂｋ、１０１Ｃ、１０１Ｍおよび１０１Ｙのそれぞれは、図中Ａ方向に搬送される記録紙の幅方向（図の紙面に垂直な方向）に約７２００個のインク吐出口を配列し、最大Ａ３サイズの記録紙に対しプリントを行うことができる。
【００７７】
記録紙１０３は、搬送用モータにより駆動される一対のレジストローラ１１４の回転によってＡ方向に搬送され、一対のガイド板１１５により案内されてその先端レジ合わせが行われた後、搬送ベルト１１１上に搬送される。エンドレスベルトである搬送ベルト１１１は２個のローラ１１２、１１３により保持されている。ローラ１１３が回転駆動されることで、記録紙１０３が搬送される。なお、搬送ベルト１１１に対する記録紙１１３の吸着は静電吸着によって行われる。ローラ１１３は不図示のモータ等の駆動源により記録紙１０３を矢印Ａ方向に搬送する方向に回転駆動される。搬送ベルト１１１上を搬送されこの間に記録ヘッド群１０１ｇによって記録が行われた記録紙１０３は、ストッカ１１６上へ排出される。
【００７８】
記録ヘッド群１０１ｇの各プリントヘッドは、本発明の実施形態について上記で説明した第１の顔料としてブラックの顔料（自己分散型カーボンブラック）、高分子分散剤によって水性媒体中に分散させられる第２の顔料及び該高分子分散剤を含有したインクを収容したヘッド１０１Ｂｋ、カラーインクを各々収容した各ヘッド（シアンヘッド１０１Ｃ、マゼンタヘッド１０１Ｍ、イエローヘッド１０１Ｙ）が、記録紙１０３の搬送方向Ａに沿って図示の通りに配置されている。そして、各プリントヘッドにより各色のインクを吐出することでブラックの文字やカラー画像のプリントが可能になる。
【００７９】
本実施例で用いるＢｋインクの組成は次の通りである。なお以下で示す各成分の量は重量部を表わすものとする。
【００８０】
顔料分散液１ ２５部
顔料分散液４ ２５部
グリセリン ６部
ジエチレングリコール ７部
アセチレノールＥＨ ０．２部
（川研ファインケミカル製）
水 残部
尚、上記顔料分散液１は次のようにして調製したものである。酸性カーボンブラック（商品名：ＭＡ−７７（ｐＨ３．０、三菱化成社製））３００ｇを水１０００ｍｌによく混合した後、これに次亜塩素酸ソーダ（有効塩素濃度１２％）４５０ｇを滴下して、１００〜１０５℃で１０時間撹拌した。得られたスラリーを東洋濾紙Ｎｏ．２（アドバンティス社製）で濾過し、顔料粒子を充分に水洗した。この顔料ウェットケーキを水３０００ｍｌに再分散し、電導度０．２μｓまで逆浸透膜で脱塩した。更に、この顔料分散液（ｐＨ＝８〜１０）を顔料濃度１０重量％に濃縮した。以上の方法により、表面に、親水性の−ＣＯＯ- 基が直接結合したアニオン性に帯電した自己分散型カーボンブラックが分散された顔料分散液１を得た。
【００８１】
また上記した顔料分散液４は次のようにして調整したものである。分散剤としてスチレン−アクリル酸−アクリル酸エチル共重合体（酸価１８０ 平均分子量１２０００）１４部と、モノエタノールアミン４部と水７２部を混合し、ウォーターバスで７０℃に加温し、樹脂分を完全に溶解させる。この際溶解させる樹脂の濃度が低いと完全に溶解しないことがあるため、樹脂を溶解する際は、高濃度溶液をあらかじめ作成しておき、希釈して希望の樹脂溶液を調整してもよい。この溶液に、分散剤の作用によって初めて水性媒体に分散可能なカーボンブラック（商品名：ＭＣＦ−８８、ｐＨ８．０、三菱化学製）１０部を加え、３０分間プレミキシングを行った。次いで以下の操作を行ない、カーボンブラック（ＭＣＦ−８８）が分散剤によって水性媒体に分散された顔料分散液４を得た。
【００８２】
分散機：サイドグラインダー（五十嵐機械製）
粉砕メディア：ジルコニアビーズ１ｍｍ径
粉砕メディアの充填率：５０％（体積）
粉砕時間：３時間
遠心分離処理（１２０００ＲＰＭ、２０分間）
この様にして調製したＢｋインクのＫａ値は０．４０（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）であった。
（実施例２）
Ｂｋインクの他の実施例として、以下の成分のものを用いることもできる。
【００８３】
顔料分散液２ ４５部
顔料分散液４ ５部
グリセリン ６部
トリエチレングリコール ５部
アセチレノールＥＨ ０．２部
（川研ファインケミカル製）
水 残部
尚、上記顔料分散液２は次のようにして調製した。表面積が２３０ｍ² ／ｇでＤＢＰ吸油量が７０ｍｌ／１００ｇのカーボンブラック１０ｇと、ｐ−アミノ−Ｎ−安息香酸３．４１ｇとを水７２ｇによく混合した後、これに硝酸１．６２ｇを滴下して７０℃で撹拌した。数分後、５ｇの水に１．０７ｇの亜硝酸ナトリウムを溶かした溶液を加え、更に１時間撹拌した。得られたスラリーを東洋濾紙Ｎｏ．２（アドバンティス社製）で濾過し、顔料粒子を十分に水洗し、９０℃のオーブンで乾燥させた後、この顔料に水を足して顔料濃度１０重量％の顔料水溶液を作成した。以上の方法により、下記式で表したように、表面にフェニル基を介して親水性基が結合したアニオン性に帯電した自己分散型カーボンブラックが分散された顔料分散液２を得た。
【００８４】
【化３】

また顔料分散液４は実施例１と同様に調製したものである。こうして得たＢｋインクのＫａ値は0.３５（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）であった。
（実施例３）
Ｂｋインクのさらに他の実施例として、以下の成分のものを用いることもできる。
【００８５】
顔料分散液３ ４５部
顔料分散液４ ２．５部
Ｃ．Ｉ．ダイレクトブルー１９９ ０．２５部
グリセリン ６部
ジエチレングリコール ５部
アセチレノールEH ０.１部
水 残部
上記顔料分散液３は、次のようにして調製した。
【００８６】
水５．３ｇに濃塩酸５ｇを溶かした溶液に、５℃においてアントラニル酸１．５８ｇを加えた。この溶液を、アイスバスで撹拌することにより常に１０℃以下に保ち、５℃の水８．７ｇに亜硝酸ナトリウム１．７８ｇを加えた溶液を加えた。更に、１５分撹拌した後、表面積が３２０ｍ²／ｇでＤＢＰ吸油量が１２０ｍｌ／１００ｇのカーボンブラック２０ｇを混合した状態のまま加えた。その後、更に１５分撹拌した。得られたスラリーを東洋濾紙Ｎｏ．２（アドバンティス社製）で濾過し、顔料分子を充分に水洗し、１１０℃のオーブンで乾燥させた後、この顔料に水を足して顔料濃度１０重量％の顔料水溶液を作製した。以上の方法により、下記式で表したように、表面に、フェニル基を介して親水性基が結合したアニオン性に帯電した自己分散型カーボンブラックが分散した顔料分散液３を得た。また顔料分散液４は実施例１と同様にして調製したものである。
【００８７】
【化４】

こうして得たＢｋインクのＫａ値は０．３３（ｍｌ・ｍ^-2・ｍｓｅｃ^-1/2）であった。
（比較例１）
以上示した実施例１〜３に対する比較例として、実施例１と同様に調製した顔料分散体４のみを用いて以下の成分のインクを作成した。
【００８８】
顔料分散液４ ５０部
エチレングリコール ８部
グリセリン ５部
イソプロピルアルコール ４部
水 ３３部
（評価）
上記実施例１〜３及び比較例１のインクを用い、360dpiの解像度の記録ヘッドを備えたインクジェットプリンタを用いて吐出周波数７．２ｋＨｚで主走査方向に720dpiの間隔で印字を行なった。ここでは記録ヘッドからのインク１滴当たりの吐出量は約２５ピコリットルとして360dpi×720dpiの解像度で形成されるところの１画素にインクを１滴打ち込んで記録を行なった。そしてベタ画像及び文字パターン等を印字して画像のＯＤ、ドット周囲形状、ベタ均一性、裏抜け性、スムージング性及び真円度を評価した。なおプリント媒体としてはキヤノン（株）社製ＰＢ用紙を用いた。
【００８９】
ここで、
・ＯＤは、５ｍｍ角のベタパターンの部分を測定したものである。
・ドット周囲形状は、線画像のエッジ部分のシャープネスをルーペによって目視にて確認した。
◎：線のエッジがきれいに直線状につながっている。
○：線のエッジの直線性が若干失われているものの、実用上問題はない。
×：線のエッジの直線性が失われている。
・ベタ均一性は５ｍｍ角のベタパターンにおける濃度の均一性を目視て確認した。
◎：白く抜けている部分が認められない。
○：白く抜けている部分が認められるものの目立たず、実用上問題がない。
×：白く抜けている部分が目立ち、画像品質に影響を与えている。
・裏抜け性はベタパターンを印字した部分を、裏面から目視にて観察しパターンが透けて見える否かを確認し、またマクベス濃度計を用いて裏面の対応部部の光学濃度を測定した。
◎：殆ど透けて見えず、またマクベス濃度計による光学濃度が0.２未満である。
○：やや透けて見えるが、殆んど気にならず、またマクベス濃度計による光学濃度が0.２以上0.25未満である。
・真円度は、１滴のインクによってプリント媒体上に形成したインクドットの形状をルーペにて観察した。
◎：統計的に見て、殆どのドットが真円に近い。
○：統計的に見て、ドットの真円性が崩れているが、画像形成には支障が無い。
△：統計的に見て、かなりの数のドットの真円性が崩れ、いびつな形状のドットが形成されている。
【００９０】
以上の結果を下記表２に示す。
【００９１】
【表２】

なお第１の顔料のみを含むインクを調製し、上記実施例と同様にして記録を行なって評価したところ、上記評価基準に照らせば、全て○に該当する結果を得、実用上問題の無いインクであったが、本態様にかかるインクはそれを更に越える性能を示すものであり、本発明の有用性、優位性は明らかである。
【００９２】
次に実施例３のインクを用いて、実施例１の装置を用いて、本出願人であるキヤノン社製のコート層が形成されたトランスペアレンシィーフィルム（商品名；ＣＦ１０２）に対し、所定サイズのベタ画像をプリントし、「ひび割れ」の有無で評価したところ、「ひび割れ」は確認されなかった。これに対し、比較例１のインクを用いた場合にあっては、「ひび割れ」の現象が確認できた。
【００９３】
同様のインクを用いてキヤノン社製の、コート層が形成されたトランスペアレンシィーフィルム（商品名；ＣＦ１０１）に対してプリントし、「ひび割れ」の有無で評価したところ、比較例１のインクを用いた場合、「ひび割れ」の現象がＣＦ１０２にプリントしたときよりも、より顕著に認められた。しかし実施例３のインクを用いた場合には「ひび割れ」は認められなかった。
（他の実施例）
図４は本発明の上記各実施例に係るインクを用いることができる他の装置を示すものであり、シリアルタイプのプリント装置５の構成を示す概略斜視図である。なお図４において、図３に示した要素と同様の要素には同一の符号を付しその説明の詳細は省略する。
【００９４】
プリント媒体である記録紙１０３は、給紙１０５から挿入されプリント部１２６を経て排紙される。プリント部１２６において、キャリッジ１０７は、プリントヘッド１０１Ｂｋ、１０１Ｃ、１０１Ｍおよび１０１Ｙを搭載し、不図示のモータの駆動力によってガイドレール１０９に沿って往復移動可能に構成されている。プリントヘッド１０１Ｂｋは、本実施態様にかかるブラックインクを吐出する。また、プリントヘッド１０１Ｃ、１０１Ｍ、１０１Ｙはそれぞれシアンインク、マゼンタインク、イエローインクをそれぞれ吐出するものであり、この順序で記録紙１０３にインクを吐出するよう駆動される。
【００９５】
各ヘッドにはそれぞれ対応する吐出されるべきインクを収容したインクタンク１０８Ｂｋ、１０８Ｃ、１０８Ｍ、１０８Ｙからインクが供給され、インク吐出時には各ヘッドの吐出口毎に設けられている電気熱変換体（ヒータ）に駆動信号が供給され、これにより、インクに熱エネルギを作用させて気泡を発生させ、この発泡時の圧力を利用してインクの吐出が行われる。各ヘッドには、それぞれ３６０ｄｐｉの密度で６４個の吐出口が設けられ、これらは、記録紙１０３の搬送方向Ｙとほぼ同方向、つまり、各ヘッドによる走査方向とほぼ垂直方向に配列されている。そして、各吐出口毎の吐出量は２３ｐｌである。
【００９６】
以上の構成において、各カラーインク用のヘッド間距離は１／２インチであって、ヘッド１０１Ｂｋと１０１Cとの距離Ｄｉは１インチとなり、また、走査方向のプリント密度が７２０ｄｐｉ、各ヘッドの吐出周波数は７．２ｋＨｚである。
【００９７】
図５は、図４に示したシリアルタイプのプリント装置によるプリントプロセスを説明する図であり、プリント部１２６を上から見た状態を模式的に示している。図５において、キャリッジ１０７は、搬送される記録紙１０３の上方を搬送方向Ｙとほぼ垂直なＸ方向に往復移動する。キャリッジ１０７に搭載されたブラック吐出部１０１Ｂｋ、カラー吐出部（１０１Ｃ、１０１Ｍ、１０１Ｙ）の吐出口（図中、ドットで示す）は、記録紙１０３に対してインクを吐出する向き開口している。
【００９８】
各吐出部は、一回の走査により記録紙１０３の搬送方向Ｙに沿って幅ｄの記録が可能なように吐出口が配列されている。また、ブラック吐出部１０１Ｂｋによるインクの吐出とカラーインクの吐出に時間差を設けるため、ブラック吐出部１０１Ｂｋとカラーインク吐出部とは、プリント幅ｄの距離だけ搬送方向に沿ってずれた位置に配置されている。この吐出時間差は、ブラックインクが記録紙の厚さ方向の所定範囲への浸透をほぼ完了する時間である。このように構成することにより、記録紙１０３の所定位置に対するブラック吐出部１０１Ｂｋのインクの吐出とカラーインクの吐出が、キャリッジ１０７の一走査分（走査周期は１．５秒とした）ずれて、上記した所定の時間差で行われ、これによりＢｋの画像とカラー画像との境界におけるにじみの問題を解消できる。
【００９９】
図６はさらに他の実施例に係るインクジェットプリンタの他の例を示す斜視図であり、図３および図４に示した要素と同様の要素には同一の符号を付し、その説明は省略する。図６に示すように、本発明の一実施形態に係るインクは、ブラックインクとして、モノカラープリンタに用いることもできる。
【０１００】
【発明の効果】
以上の説明から明らかなように、本発明によれば自己分散性の顔料（第１の顔料）と分散剤の作用によって初めて水性媒体に分散させることができる顔料（第２の顔料）及び該分散剤を含有したインクは、該第１の顔料自体が該第２の顔料の分散剤として機能するためか、分散剤の含有量が少なくても該第２の顔料はインク中で安定に分散しており、保存性の優れたインクを得られる。一方このインクを例えばプリントに用いた場合、記録媒体上で生じる第２の顔料と分散剤との相互作用によって生じる顔料の凝集が第１の顔料によって緩和されるためか、顔料の凝集物は細かい粒子状になってインクドット内に均一に分散し、適切な広がりを持つドット径を有し、且つドット内の画像濃度分布が均一で、またフェザリング等が殆どない、周囲や外形形状の優れたインクドットを得ることができる。
【０１０１】
更に本発明の別の態様にかかる、第１の顔料、第２の顔料、分散剤及び染料を含むインクは、染料によって顔料の凝集力がより緩和されるためか、記録媒体上では顔料の凝集物は細かい粒子状となる。一方、染料はこの粒子状の顔料の回りを取込み、全体としてプリント画像は凝集による不均一が抑制されたものとなる。そしてその効果は、このインクをインク吸収性の悪いプリント媒体に対してインクジェット記録した場合にもインクドットへの「ひび割れ」の発生を極めて有効に抑制でき、或いは防止することができる点において最も顕著に観察することができる。
【０１０２】
尚、本明細書中、「部」又は「％」とある場合、特に断りのない限り重量基準である。
【図面の簡単な説明】
【図１】本発明が解決すべき課題である顔料インクの「ひび割れ」現象を模式的に示す図である。
【図２】本発明の一実施形態に係るインクを用いてプリントした結果を説明する図である。
【図３】本発明の一実施形態に係るインクジェットプリント装置の概略構成を示す側面図である。
【図４】本発明の他の実施例に係るインクジェットプリンタを示す斜視図である。
【図５】図４に示すプリンタにおけるプリント動作を説明する図である。
【図６】本発明のさらに他の実施例に係るインクジェットプリンタを示す斜視図である。
【図７】本発明の一実施態様にかかる画像形成方法の概略説明図である。
【図８】本発明の他の実施態様にかかる画像形成方法の概略説明図である。
【図９】本発明の一実施態様にかかる画像形成方法の概略説明図である。
【図１０】本発明の他の実施態様にかかる画像形成方法の概略説明図である。
【符号の説明】
１０１ｇ ヘッド群
１０１Ｂｋ、１０１Ｃ、１０１Ｍ、１０１Ｙ プリントヘッド
１０３ 記録紙
１１１ 搬送ベルト
１１２ ローラ
１１３ ローラ
１１４ レジストローラ
１１５ ガイド板
１１６ ストッカ
７０１、８０１ 第１のインク吐出用のインクジェットヘッド
７０２、８０２ 第２のインク吐出用のインクジェットヘッド
７０３、８０３ プリント媒体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink, particularly an ink used in ink jet printing and an ink jet printing method. The present invention also relates to an ink container, an ink set, and an ink jet recording apparatus. The present invention is applicable to all devices capable of recording on various recording media such as paper, cloth, leather, nonwoven fabric and OHP paper, for example, office equipment such as printers, copiers, facsimiles, etc., to which an ink jet recording system is applied. Is possible.
[0002]
[Prior art]
The inkjet printing method has various advantages such as low noise, low running cost, high-speed printing, easy downsizing of the apparatus, and easy colorization, and is widely used in printers and copiers. It is a method. In such a printer or the like, in general, an ink to be used is selected from the viewpoints of print characteristics such as ejection characteristics and fixability, print image bleeding, optical reflection density, and color quality.
[0003]
By the way, it is widely known that inks are roughly classified into two types, dye inks and pigment inks, depending on the color materials contained therein. Among these, the pigment ink has advantages such as excellent water resistance and light resistance as compared with the dye ink, and enables clear character quality. The pigment contained in the pigment ink is normally stably dispersed in the ink using a dispersant such as a polymer dispersant. Specifically, as the action, the pigment particles are adsorbed on the polymer dispersant, and the intermolecular molecules acting between the pigment particles mainly causing the aggregation of the pigment particles by utilizing the electric repulsive force of the polymer dispersant. The power is overcome and stably dispersed in the ink. Therefore, it is necessary to add a polymer dispersant in the ink according to the amount of the pigment. When such ink is printed on plain paper using the ink jet recording method, pigments aggregate due to penetration of ink such as moisture into the paper and evaporation into the air. At this time, as the behavior on paper, the larger the amount of the polymer dispersant, the stronger the cohesive force. Therefore, the diameter of the ink dots formed on the print medium by the ink having a certain volume ejected from the inkjet head is small, and the dot shape remains close to the re-distorted shape that collided with the paper. Therefore, in order to obtain ink dots having a dot diameter necessary for recording that has a recording density sufficient to form an image and that does not generate white streaks, the ink ejection volume from the inkjet head is large. It is necessary to adjust to. However, this is combined with a decrease in the permeability to the paper due to the strong cohesion of the pigment particles adsorbed by the polymer dispersant, leading to a delay in fixing the ink on the print medium or reducing the scratch resistance of the recorded image. It was sometimes reduced.
[0004]
In order to increase the dot diameter and improve the fixability, it is also considered that the ink contains a penetrant for the purpose of improving the penetrability of the ink into the print medium. However, this is accompanied by phenomena that are undesirable in aiming for high-quality recorded images, such as dot shape deterioration (deterioration of dot surroundings such as feathering) and ink penetration (so-called back-through) on the back side of paper. There is a case. In addition, since the color material penetrates into the print medium, the OD of the ink dot is not so high even if the dot diameter is relatively large.
[0005]
Furthermore, an ink using a self-dispersion type pigment has been proposed. In this ink, the cohesive force of the pigment on paper is weaker than that of the ink containing the pigment dispersed by the above-described dispersant. Can be expanded, but it is not enough.
[0006]
In this way, various factors that influence the quality of the recorded image, such as ink fixability, ink dot diameter expansion, density uniformity within the ink dots, high optical density of the ink dots themselves, etc. are satisfied at a high level, In addition, an ink and a printing method that satisfy the stability as an ink, in particular, a characteristic that can be stably ejected as an inkjet ink, are still under investigation with the aim of further improvement.
[0007]
[Problems to be solved by the invention]
One of the objects of the present invention is that the ink droplets applied to the recording medium spread appropriately in the lateral direction of the recording medium, and the penetration of the recording medium in the thickness direction is suppressed, resulting in appropriate spreading. It is an object of the present invention to provide an ink having a dot diameter having a high density, uniform image density in the dots, and having excellent outer shapes in which almost no feathering is observed. Another object of the present invention is to provide an inkjet printing method capable of forming a high-quality image with a high image density while suppressing the amount of ink applied to a recording medium. Another object of the present invention is to provide an ink jet recording apparatus capable of stably recording a high-quality image, and an ink container and an ink set used therefor.
[0008]
Furthermore, another object of the present invention is to provide ink that forms one dot and ink that forms one pixel (a pixel including an overlapped dot portion of a dot matrix of 3 × 3, 4 × 4, etc.). Therefore, it is an object of the present invention to provide an image forming ink and an image forming method capable of providing an image density and an image quality that can satisfy the above.
[0009]
[Means for Solving the Problems]
  An ink according to an embodiment of the present invention that can achieve the above object is an ink containing a first pigment and a second pigment as a coloring material dispersed in an aqueous medium, The first pigment is a self-dispersing pigment in which at least one anionic group is bonded to the surface of the first pigment directly or through another atomic group, or at least one cationic group is directly or A self-dispersing pigment bonded to the surface of the first pigment through another atomic group, and the second pigment can be dispersed in the aqueous medium by a polymer dispersant. The ink further has the same polarity as the group bonded to the surface of the first pigment.Polymer dispersantIt is characterized by including.
[0010]
  An ink according to another embodiment of the present invention that can achieve the above object is an image that is ejected from an orifice using an ink jet recording method and applied onto a print medium to form an element of the image. An ink for use in a recording method, comprising a first pigment and a second pigment dispersed in an aqueous medium as a coloring material, wherein the first pigment has at least one anionic group directly or other atom A self-dispersing pigment or at least one cationic group bonded to the surface of the first pigment through a group is bonded to the surface of the first pigment directly or through another atomic group A self-dispersing pigment, wherein the second pigment is a pigment that can be dispersed in an aqueous medium by a polymeric dispersant, and the ink further comprises a group bonded to the surface of the first pigment; Of polarityPolymer dispersantIt is characterized by including.
[0011]
  In addition, an inkjet printing method as one embodiment of the present invention that can achieve the above-described object is a method in which an ink is ejected toward a print medium using the inkjet recording method, and an image is recorded on the print medium. In the ink-jet printing method, the ink comprises a first pigment and a second pigment dispersed in an aqueous medium, and the first pigment has at least one anionic group directly or other atom. A self-dispersing pigment or at least one cationic group bonded to the surface of the first pigment through a group is bonded to the surface of the first pigment directly or through another atomic group A self-dispersing pigment, wherein the second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink further comprises the first face Groups of the same polarity being coupled to the surface of thePolymer dispersantIt is the ink which contains.
[0012]
  In addition, the image forming method as one embodiment of the present invention capable of achieving the above object is characterized in that at least one anionic group is directly or via other atomic groups on the surface of the first pigment. First ink comprising a self-dispersing pigment bonded or a self-dispersing pigment in which at least one cationic group is bonded to the surface of the first pigment directly or through other atomic groups And having the same polarity as the group bonded to the surface of the self-dispersing pigment in the first inkWith polymeric dispersantsA second ink containing a pigment that can be dispersed in an aqueous medium by the polymer dispersant is printed so that the first ink and the second ink are in liquid contact with each other on the surface of the print medium. The method includes a step of forming an image by applying to a medium.
[0013]
  Furthermore, the image forming method as one of the embodiments of the present invention capable of achieving the above-described object is provided such that at least one anionic group is directly or via other atomic groups on the surface of the first pigment. A self-dispersing pigment that is bound to or a self-dispersing pigment in which at least one cationic group is bound to the surface of the first pigment, either directly or through other atomic groups An ink, a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and a group having the same polarity as the group bonded to the surface of the self-dispersing pigment in the first inkPolymer dispersantA second ink containing and a third ink containing a dye of the same polarity as the group bonded to the surface of the self-dispersing pigment on the surface of the print medium, the first ink, the second ink, and It includes a step of applying to the print medium such that the third ink contacts with the third ink in a liquid state.
[0014]
As described above, the present invention provides a pigment and a polymer dispersion that can be dispersed in an aqueous medium by a self-dispersing pigment and a polymer dispersant in the course of research aimed at further improving the quality of inkjet recording images. This is based on the finding that the ink mixed with the agent satisfies various elements required for high image quality at a very high level and has excellent ink stability. .
[0015]
In other words, as an ink in a form until it is ejected from the recording head, a dispersant of a pigment (second pigment) in which a self-dispersing pigment (first pigment) can be dispersed in an aqueous medium by a polymer dispersant. The pigment in the ink could be stably maintained in a dispersed state even if the polymer dispersant as a whole of the ink was reduced. On the other hand, when printing on paper using this ink, the dot diameter is the dot diameter of the second pigment and the ink containing only the first pigment (self-dispersing pigment) or the ink containing the polymer dispersant for dispersing the second pigment. Compared to the above, it spreads uniformly on the paper surface, has a high OD, and has a relatively fast fixability.
[0016]
The reason why such a phenomenon is observed is not clear, but is presumed to be due to the following mechanism. That is, the second pigment and the first pigment on which the polymer dispersant is adsorbed are electrically repelled in the ink, and the cohesive force of the pigment is weaker than that of at least the polymer-dispersed pigment-only ink. Yes. When such ink is printed on the paper surface, since the polymer dispersant is adsorbed to the second pigment, the color material in the ink hardly penetrates in the thickness direction of the paper. On the other hand, with respect to the paper (lateral) direction, in the case of the ink containing the second pigment and the polymer dispersant, the polymers are rapidly entangled with the penetration of the ink solvent into the paper and the reduction of moisture due to evaporation. Or the polymer is strongly agglomerated by cross-linking between the pigments, whereas the ink of the present embodiment causes the entanglement or cross-linking of the polymer due to the mixing of the first pigment. The strong intermolecular force between the pigments in the ink is relieved by the repulsion between the first pigment and the polymer dispersant, and as a result, the ink easily diffuses in the lateral direction of the paper surface. Moreover, although the diffusion is moderated, it is considered that the diffusion is not disordered due to the influence of the cohesive force between the pigments. It is considered that this appears as securing a large dot diameter and dot roundness with a small discharge amount, and adaptability when a plurality of dots are connected, that is, good smoothing property. The phenomenon on the paper surface is that the Ka value in the Bristow method of the ink is 1 ml · m^-2・ Msec^-1/2If it is less than that, that is, it is designed to have a relatively low permeability with respect to the print medium, it becomes particularly prominent, and this is advantageous for improving the image quality.
[0017]
As described above, the ink of this embodiment is good in terms of dispersion stability in the ink tank, and also has a large dot diameter, high OD, good scratch resistance, and good printing characteristics as described above. Has great effects such as good roundness.
[0018]
This ink is also good when ejected by an ink jet recording head. That is, since the viscosity is small and the refill characteristics with respect to the nozzle are good, high speed driving is possible. In addition, with regard to discharge by a discharge method using bubble formation due to film boiling, the discharge speed and discharge amount are relatively large due to moderate wetting on the discharge heater surface and / or low viscosity resistance against sudden foaming. It ’s not too fluctuating. That is, the discharge efficiency and discharge stability are good.
[0019]
By the way, even when an experiment is performed by controlling the discharge amount so as to be the same for various inks in consideration of the improvement in the discharge efficiency, the dot diameter of the ink of this embodiment is sufficiently large. Therefore, the enlargement of the ink dot diameter by the ink of this embodiment cannot be explained simply because of the improvement of the ejection efficiency. When printing is performed with a conventional BJ recording head, by using the ink of this aspect, the discharge amount, the discharge speed, and the spreading property of the ink itself work as a synergistic effect, and ink dots with a larger diameter can be formed. The fact that ink dots with a sufficiently large diameter can be obtained even with a small discharge amount means that the ink is thin and spread over a wide area on the surface of the recording medium, resulting in rapid drying of the ink and consequently the time required for fixing the ink. Can be shortened.
[0020]
Furthermore, by adding a dye having the same polarity as the group bonded to the surface of the first pigment to the ink including the first pigment, the second pigment, and the polymer dispersant, It is possible to further reduce the cohesive strength of the pigment, which contributes to further expansion of the area factor and effectively causes “cracking” to occur in the recorded image of a print medium having a resin coating layer. A further preferable effect of suppressing is obtained.
[0021]
  An ink container according to an embodiment of the present invention capable of achieving the above object is an ink container containing ink, wherein the ink contains the first pigment and the second pigment as a coloring material in an aqueous medium. In a dispersed state, wherein the first pigment has at least one anionic group bonded to the surface of the first pigment directly or through other atomic groups, or at least one A self-dispersing pigment in which a cationic group is bonded to the surface of the first pigment directly or through another atomic group, and the second pigment is dispersed in the aqueous medium by a polymer dispersant A pigment of the same polarity as the group bonded to the surface of the first pigment.Polymer dispersantIt is characterized by including.
[0022]
  An ink set according to an embodiment of the present invention capable of achieving the above object includes a first pigment and a second pigment as a colorant in a dispersed state in an aqueous medium, wherein the first pigment is Self-dispersing carbon black or at least one cationic group having at least one anionic group bonded to the surface of the first pigment directly or through another atomic group, directly or through another atomic group A self-dispersing carbon black bonded to the surface of the first pigment through the second pigment, and the second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink Further of the same polarity as the group bonded to the surface of the first pigmentPolymer dispersantIt is characterized in that the black ink is combined with a known or various yellow ink, magenta ink, and cyan ink.
[0023]
  Furthermore, an ink jet recording apparatus according to an embodiment of the present invention capable of achieving the above object includes a first pigment and a second pigment as a coloring material dispersed in an aqueous medium, and the first pigment Is a self-dispersing carbon black in which at least one anionic group is bonded directly or via other atomic groups to the surface of the first pigment or at least one cationic group is directly or other atom A self-dispersing carbon black bonded to the surface of the first pigment through a group, and the second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, The ink further has the same polarity as the group bonded to the surface of the first pigment.Polymer dispersantAn ink storage section storing black ink, yellow ink, magenta ink, and cyan ink, respectively, and means for individually ejecting the black ink, yellow ink, magenta ink, and cyan ink by an inkjet printing method It is characterized by having. The yellow, cyan, and magenta inks used here can be known or can be appropriately improved. In particular, the Ka value in the Bristow method is 1 ml · m.^-2・ Msec^-1/2The above is preferable. According to the ink container, the ink set, and the ink jet recording apparatus, it is possible to record a more excellent image than the conventional one for the reasons described above.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail based on ink as one of the embodiments that can achieve the object of the present invention.
[0025]
  An example of an ink that can be used in the present invention is an ink containing a first pigment and a second pigment as a coloring material in a dispersed state in an aqueous medium, wherein the first pigment is at least one anionic property. A self-dispersing pigment or at least one cationic group bonded directly or via other atomic groups to the surface of the first pigment. A self-dispersing pigment bonded to the surface of the pigment, and the second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant or a nonionic polymer dispersant, The ink further has the same polarity as the group bonded to the surface of the first pigment.Polymer dispersantInk to be included.
[0026]
Hereinafter, the ink will be sequentially described.
(First pigment)
Self-dispersing pigments are ink-jet recording technologies that maintain stable dispersion in water, water-soluble organic solvents, or liquids mixed with these without the use of dispersants such as water-soluble polymer compounds. It refers to a pigment that does not cause agglomerates of pigments in the liquid to interfere with normal ink ejection from the orifice used.
(Anionic self-dispersing CB)
As such a pigment, for example, a pigment in which at least one anionic group is bonded to the pigment surface directly or via another atomic group is suitably used. Specific examples include at least one anionic group. It includes carbon black bonded to the surface directly or through other atomic groups.
[0027]
Examples of anionic groups bonded to such carbon black include, for example, —COOM, —SO_ThreeM, -PO_ThreeHM, -PO_ThreeM₂Etc. (wherein M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium).
[0028]
Examples of the “M” alkali metal include lithium, sodium, potassium, and the like, and examples of the “M” organic ammonium include mono to trimethyl ammonium, mono to triethyl ammonium, and mono to trimethanol ammonium. It is done.
[0029]
Among these anionic groups, especially -COOM and -SO_ThreeM is preferable because it has a large effect of stabilizing the dispersion state of carbon black.
[0030]
By the way, it is preferable to use the above-mentioned various anionic groups bonded to the surface of carbon black through other atomic groups. Examples of the other atomic group include a linear or unsubstituted alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted naphthylene group. Here, examples of the substituent which may be bonded to the phenylene group or naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms.
[0031]
Specific examples of the anionic group bonded to the surface of carbon black through other atomic groups include, for example, —C₂H_FourCOOM, -PhSO_ThreeExamples include M, -PhCOOM, etc. (where M is defined in the same manner as described above, and Ph represents a phenyl group), but is not limited thereto.
[0032]
Carbon black in which an anionic group is bonded to the surface directly or through another atomic group as described above can be produced, for example, by the following method.
[0033]
That is, as a method for introducing —COONa into the carbon black surface, for example, a method of oxidizing a commercially available carbon black with sodium hypochlorite can be mentioned.
[0034]
Further, for example, as a method of bonding an —Ar—COONa group (where Ar represents an aryl group) to the surface of carbon black, NH₂ A method of forming a diazonium salt in which nitrous acid is allowed to act on the —Ar—COONa group and bonding it to the surface of carbon black can be mentioned, but the present invention is of course not limited thereto.
(Cationic self-dispersing CB)
(Cationically charged CB)
Examples of the cationically charged carbon black include those in which at least one selected from the following quaternary ammonium groups is bonded to the surface of carbon black.
[0035]
-N⁺H_Three, -N⁺R_Three, -SO₂NH₂, -SO₂NHCOR,
[0036]
[Chemical 1]

In the above formula, R represents, for example, a linear or branched alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted naphthyl group. Here, examples of the substituent of the phenyl group or naphthyl group include linear or branched alkyl groups having 1 to 6 carbon atoms. Examples of the substituent when R is a phenyl group having a substituent or a naphthyl group having a substituent include, for example, C₁~ C₆And a linear or branched alkyl group. Examples of a method for producing a self-dispersing carbon black having a hydrophilic group bonded thereto and charged cationically include, for example, an N-ethylpyridyl group having the structure shown below:
[0037]
[Chemical formula 2]

As an example, a method of bonding carbon black is a method of treating carbon black with 3-amino-N-ethylpyridinium bromide. In this way, carbon black charged anionic or cationic by introducing a hydrophilic group to the surface of carbon black has excellent water dispersibility due to repulsion of ions, so even when it is contained in aqueous ink. A stable dispersion state is maintained without adding a dispersant or the like.
[0038]
By the way, various hydrophilic groups as described above may be directly bonded to the surface of carbon black. Alternatively, other atomic groups may be interposed between the carbon black surface and the hydrophilic group, and the hydrophilic group may be indirectly bonded to the carbon black surface. Here, specific examples of the other atomic groups include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Here, examples of the substituent of the phenylene group and the naphthylene group include linear or branched alkyl groups having 1 to 6 carbon atoms. Specific examples of combinations of other atomic groups and hydrophilic groups include, for example, -C₂H_Four-COOM, -Ph-SO_ThreeM, -Ph-COOM and the like (where Ph represents a phenyl group).
[0039]
By the way, 80% or more of the self-dispersing pigment contained in the ink according to the present embodiment has a particle diameter of 0.05 to 0.3 μm, particularly 0.1 to 0.25 μm. Is preferred. Such an ink adjustment method is as described in detail in the embodiments described later.
(Second pigment)
Examples of the second pigment that can be used in the ink of the present embodiment include a pigment that can be dispersed in an ink dispersion medium, specifically, an aqueous medium by the action of a polymer dispersant. That is, a pigment that can be stably dispersed in an aqueous medium for the first time as a result of the polymer dispersant adsorbing on the surface of the pigment particles is preferably used. Examples of such pigments include, for example, black pigments such as carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. As specific examples of such carbon black pigments, for example, the following can be used alone or in appropriate combination.
・ Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000ULTRA, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190ULTRA-II, Ray Van 1170, Ray Van 1255 (manufactured by Columbia)
Black Pearls L, Regal 400R, Regal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100, Monak 1300 , Monak 1400, Vulcan XC-72R (above manufactured by Cabot Corporation)
-Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa)
・ No.25, No.33, No.40, No.47, No.52, No.900, No.2300, MCF-88, MA600, MA7, MA8, MA100 (Mitsubishi Chemical Corporation)
Examples of other black pigments include magnetic fine particles such as magnetite and ferrite, and titanium black.
[0040]
In addition to the black pigments described above, blue pigments, red pigments, and the like can also be used.
[0041]
The amount of the color material combining the first and second pigments is 0.1 to 15% by weight, more preferably 1 to 10% by weight, based on the total amount of ink. The ratio of the first pigment to the second pigment is preferably 5/95 to 97/3, more preferably 10/90 to 95/5. More preferably, the first pigment / second pigment = 9/1 to 4/6. Another more preferable range is a range in which the first pigment is high. In the case of such a large amount of the first pigment, not only the dispersion stability as an ink, but also the stability including the ejection stability of the head, especially the reliability due to less ejection efficiency and less wetting of the ejection port surface is exhibited. Is done.
[0042]
In addition, as the behavior of the ink on the paper, since the ink spreads effectively on the surface of the paper with an ink with a small amount of the second pigment adsorbed by the polymer dispersant, a uniform thin film is formed on the surface by the polymer dispersant. It is estimated that, and the effect of this also improves the scratch resistance of the image.
(Polymer dispersant)
The polymer dispersant for dispersing the second pigment in an aqueous medium has, for example, a function of adsorbing on the surface of the second pigment and stably dispersing the second pigment in the aqueous medium. Preferably used. Examples of such polymer dispersants include anionic polymer dispersants, cationic polymer dispersants, and nonionic polymer dispersants.
(Anionic polymer dispersant)
Examples thereof include a polymer of a monomer as a hydrophilic group and a monomer as a hydrophobic group and a salt thereof. Specific examples of the monomer as the hydrophilic group include, for example, styrene sulfonic acid, α, β-ethylenically unsaturated carboxylic acid, α, β-ethylenically unsaturated carboxylic acid derivative, acrylic acid, acrylic acid derivative, and methacrylic acid. Methacrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives.
[0043]
Specific examples of the monomer as the hydrophobic component include styrene, styrene derivatives, vinyl toluene, vinyl toluene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, butadiene, butadiene derivatives, isoprene, isoprene derivatives, ethylene, ethylene derivatives, propylene, Examples include propylene derivatives, alkyl esters of acrylic acid, and alkyl esters of methacrylic acid.
[0044]
Specific examples of the salt include hydrogen, alkali metal, ammonium ion, organic ammonium ion, phosphonium ion, sulfonium ion, oxonium ion, stibonium ion, stannonium, iodonium and other onium compounds. It is not limited to. In addition, the above polymers and salts thereof include polyoxyethylene group, hydroxyl group, acrylamide, acrylamide derivative, dimethylaminoethyl methacrylate, ethoxyethyl methacrylate, butoxyethyl methacrylate, ethoxytriethylene methacrylate, methoxypolyethylene glycol methacrylate, vinylpyrrolidone, vinylpyridine, Vinyl alcohol and alkyl ether may be appropriately added.
(Cationic polymer dispersant)
As the cationic dispersant, a tertiary amine monomer, a copolymer obtained by quaternizing these with a hydrophobic monomer, or the like is used. As the tertiary amine monomer, for example, N, N-dimethylaminoethyl methacrylate, N, N-dimethylacrylamide and the like are used. As the hydrophobic monomer, styrene, a styrene derivative, vinyl naphthalene, or the like is used. In the case of a tertiary amine, sulfuric acid, acetic acid, nitric acid and the like are used as a compound for forming a salt. Further, those quaternized with methyl chloride, dimethyl sulfate or the like can also be used.
(Nonionic polymer dispersant)
Examples of nonionic polymer dispersants include polyvinyl pyrrolidone, polypropylene glycol, vinyl pyrrolidone-vinyl acetate copolymer, and the like.
[0045]
The first pigment, the second pigment, and the polymer dispersant described above can be appropriately selected in combination, and dispersed and dissolved in an aqueous medium to obtain the ink of this embodiment. When using a self-dispersing pigment in which at least one anionic group is bonded to the surface of the pigment directly or through another atomic group, an anionic group is used as the polymer dispersant.Polymer dispersantThe combination is preferable from the viewpoint of ink stability, and for the same reason, as the first pigment, at least one cationic group is bonded to the surface of the pigment directly or through another atomic group. In the case of using a pigment ofPolymer dispersantThe first pigment andCombine.
[0046]
For example, alkyl alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-pentanol; Amides such as dimethylformamide and dimethylacetamide; Ketones or ketoalcohols such as acetone and diacetone alcohol; Ethers such as tetrahydrofuran and dioxane; Diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene Oxyethylene or oxypropylene copolymers such as glycol and polypropylene glycol; ethylene glycol and propylene glycol Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as trimethylene glycol, triethylene glycol, 1,2,6-hexanetriol; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or Lower alkyl ethers such as ethyl) ether and triethylene glycol monomethyl (or ethyl) ether; lower dialkyl ethers of polyhydric alcohols such as triethylene glycol dimethyl (or ethyl) ether and tetraethylene glycol dimethyl (or ethyl) ether; Alkanolamines such as monoethanolamine, diethanolamine, triethanolamine; sulfolane, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2 Imidazolidinone. The water-soluble organic solvents as described above can be used alone or as a mixture.
(Penetration of ink into the recording medium)
The ink of the present embodiment containing the various components described above pays attention to the permeability to the print medium, for example, the Ka value is 1 (ml · m^-2・ Msec^-1/2), It is possible to obtain image dots with extremely uniform density. Hereinafter, the penetrability of the ink into the print medium will be described.
[0047]
1m ink permeability² The ink permeation amount V (unit: milliliter / m) at time t after ink droplet ejection² = Μm) is known to be expressed by the Bristow method as shown below.
[0048]
[Expression 1]
V = Vr + Ka (t−tw)^1/2
(However, t> tw)
Immediately after the ink droplets are dropped on the surface of the print medium, the ink droplets are mostly absorbed by the uneven portions of the surface (the roughness portion of the surface of the print medium) and hardly penetrate into the print medium. The time in the meantime is tw (wet time), and the amount of absorption in the concavo-convex portion in the meantime is Vr. When the elapsed time after the ink droplet is dropped exceeds tw, the penetration amount V increases by an amount proportional to the half power of the excess time (t-tw). Ka is a proportional coefficient of this increase, and shows a value corresponding to the penetration rate.
[0049]
The Ka value was measured using a liquid dynamic permeability test apparatus S (manufactured by Toyo Seiki Seisakusho) by the Bristow method. In this experiment, PB paper of Canon Inc., the present applicant, was used as a print medium (recording paper). This PB paper is a recording paper that can be used for both copying machines and LBPs using an electrophotographic system and printing using an inkjet recording system.
[0050]
Similar results were obtained for PPC paper, which is an electrophotographic paper manufactured by Canon Inc.
[0051]
The Ka value is determined by the type of surfactant and the amount added. For example, ethylene oxide-2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide-2,4,7,9-tetramethyl-5-decyen-4,7-diol (hereinafter referred to as “ethylene oxide-2,4,7,9-tetramethyl-5-decyen-4,7-diol”) By adding a nonionic surfactant called “Acetylenol” (manufactured by Kawaken Fine Chemical Co., Ltd.), the permeability is increased.
[0052]
In addition, in the case of an ink in which acetylenol is not mixed (content ratio is 0%), the permeability is low, and the ink has properties as an overlay ink specified later. Further, when acetylenol is mixed at a content rate of 1%, it has a property of penetrating into the recording paper 103 in a short time, and has a property as a highly penetrating ink specified later. An ink in which acetylenol is mixed at a content ratio of 0.35% has a property as a semi-permeable ink intermediate between the two.
[0053]
[Table 1]

Table 1 above shows the Ka value, the acetylenol content (%), and the surface tension (dyne / cm) for each of the “superposition ink”, “semi-permeable ink”, and “highly permeable ink”. . The permeability of each ink to the recording paper as a print medium increases as the Ka value increases. That is, the smaller the surface tension, the higher.
[0054]
The Ka values in Table 1 were measured using the liquid dynamic permeability test apparatus S (manufactured by Toyo Seiki Seisakusho) using the Bristow method as described above. In the experiment, the aforementioned PB paper from Canon Inc. was used as the recording paper. Similar results were obtained for the above-mentioned PPC paper from Canon Inc.
[0055]
Here, the ink of the system defined as “highly penetrating ink” has an acetylenol content ratio of 0.7% or more, and is in a range in which good results regarding penetrability are obtained. Further, as a standard of permeability to be carried on the ink of the present embodiment, the Ka value of “superimposed ink”, that is, 1.0 (ml · m^-2・ Msec^-1/2), Preferably 0.4 (ml · m^-2・ Msec^-1/2The following are preferred.
(Addition of dye)
A dye may be further added to the ink of the above embodiment. That is, an ink in which a dye is further added to an ink containing a dispersant for dispersing the first pigment, the second pigment, and the second pigment in an aqueous medium has a resin layer as a coating layer on the surface as a recording medium. A high-quality image without “cracks” 1003 or the like can be formed between the aggregates 1001 of pigment aggregates as shown in FIG. Although it is not clear why "cracking" of an image on a print medium provided with a resin layer with an ink further added with a dye can be effectively prevented, when an image is formed on the print medium with an ink further added with a dye In addition, the aggregates of the pigment formed on the print medium are present as fine particles as indicated by 2001 in FIG. 2, the dye surrounds the periphery, and the area where no aggregate is present is filled with the dye. It becomes a state. In addition, as described above, the cohesion of the second pigment is alleviated by the presence of the first pigment. However, the addition of the dye further reduces the cohesion of the second pigment by one step, and It is considered that non-uniformity in the printed image such as “cracking” that tends to occur in a recording medium having poor absorbency compared to plain paper or the like can be effectively suppressed. Examples of the dye that can be used here include an anionic dye and a cationic dye, and it is preferable to employ a dye having the same polarity as that of the group bonded to the surface of the first pigment.
(Anion, Cationic dye)
Known anionic dyes, direct dyes, reactive dyes and the like are suitably used as anionic dyes soluble in the aqueous medium that can be used in the present embodiment as described above. As the cationic dye, a known basic dye is preferably used. Particularly preferably, both dyes use a dye having a disazo or trisazo structure as a skeleton structure. It is also preferable to use two or more dyes having different skeleton structures. As the dye to be used, dyes such as cyan, magenta, and yellow may be used as long as the color tone is not significantly different from the black dye.
(Addition amount of dye)
The amount of the dye added may be 5% to 60% by weight of the entire coloring material, but is less than 50% by considering the effective use of the effect of mixing the first and second pigments. It is preferable that Further, in the case of using ink that emphasizes printing characteristics on plain paper, the content is preferably 5% by weight to 30% by weight. .
(Recording method)
The ink according to this embodiment is applied to the print medium using a known ink application unit to form an image.
[0056]
The ink application system in a preferred embodiment of the present invention is a known ink jet printing system. That is, the ink of the present invention is suitably used in a form in which printing is performed by ejecting ink from a print head onto a print medium. As a discharge method in the print head, a known method such as a piezo method can be adopted, but in a preferred embodiment, thermal energy is applied to the ink, thereby generating bubbles in the ink, and the pressure of the bubbles causes the ink to be discharged. This is a discharge method.
[0057]
Note that the amount of ink ejected from the print head on the print medium is 0.014 picoliter (pl) / μm per unit area.² It is preferable that: More specifically, it is 70 pl / μm at 360 dpi.² Below, 25 pl / μm at 600 dpi²The following is preferable. This is because when an ink of only one kind of pigment is used as a color material, the area factor is insufficient particularly on plain paper and the OD may be lowered. However, according to the ink of this embodiment, as described above. This is because the area factor can be increased, and so much driving amount is not required.
[0058]
Further, the ink cartridge such as the recording head configured to be detachable from the ink jet printer, in which the ink cartridge containing the ink of the present embodiment described above, the ink containing portion containing the ink, and the means for discharging the ink are integrated. Containers are also included in one embodiment of the present invention.
[0059]
Further, the black ink according to this embodiment containing the above-described self-dispersing carbon black as a color material and at least one color ink selected from other color inks such as yellow ink, magenta ink, and cyan ink are independent of each other. An ink set or the like stored in the ink storage unit is also included in one embodiment of the present invention.
[0060]
  The above-described reduction of the cohesive force of the pigment caused by the interaction between the first pigment, the second pigment and the polymer dispersant based on the knowledge of the present inventors, and the superiority on the print medium resulting from the relaxation. The effect of being able to form an image is of course also achieved by a single ink containing these components. For example, the same effect can be obtained by bringing these components into contact with each other in a liquid state on a recording medium. An effect is produced. Specifically, for exampleFIG.As shown in FIG. 3, the first ink containing the first pigment is ejected from the first inkjet head 701 and adhered to a predetermined position of the print medium, and is bonded to the surface of the first pigment. Has the same polarity as the groupWith polymeric dispersantsThe second ink containing the second pigment is ejected from the second inkjet head 702 and applied to the print medium 703 where the first ink is applied or where the first ink is applied. Is performed at a timing such that the first ink and the second ink are mixed in a liquid state on the print medium, the area factor is large, the outer shape is excellent, Also, it is possible to form ink dots with high image density and uniform within the dots.
[0061]
  Further, as shown in FIG. 8, on the one hand, the first ink containing the first pigment is ejected from the first ink jet head 801 (804), and on the other hand, the first ink of the first pigment is ejected from the second ink jet head 802. Has the same polarity as the group attached to the surfaceWith polymeric dispersantsThe second ink containing the second pigment is ejected (805), and the inks ejected from the respective inkjet heads (804, 805) are combined before adhering to the print medium 803, and the first ink and Also by the method of adhering the ink 806 mixed with the second ink to a predetermined portion of the print medium 803, the first ink and the second ink are in liquid contact on the print medium 803. A state can be realized. Here, it goes without saying that the positions on the print medium 803 to which the respective inks are applied may slightly deviate from each other as long as these inks come into contact with each other in a liquid state.
[0062]
Here, the Ka value in the Bristow method of the ink obtained by mixing the first ink and the second ink is 1 ml · m^-2・ Msec^-1/2It is preferable to prepare each ink so as to be less than
[0063]
  Similarly, the effect of reducing the cohesive strength of the pigment caused by the interaction with the first pigment, the second pigment, the polymeric dispersant and the dye, and on the print medium, in particular on the print medium with a resin coat layer In addition to the single ink containing the above four components, the excellent effect exhibited by the formed image is not limited to the single ink containing the above four components, and these components are contacted in a liquid state on the recording medium. The same effect can be achieved by making it. That is, as shown in FIG. 9, the step of ejecting the first ink containing the first pigment from the first inkjet head 901 and adhering it to a predetermined position of the print medium, and bonding to the surface of the first pigment Have the same polarity as the groupWith polymeric dispersantsEjecting a second ink containing a second pigment from a second inkjet head 902 and applying it to the predetermined position of the print medium 904; a group bonded to the surface of the first pigment; Ejecting a third ink containing a dye of the same polarity from the third inkjet head 903 and applying the third ink to the predetermined position of the print medium 904, the first ink, the second ink, and the second ink 3 is performed at a timing such that the three inks are mixed with each other in a liquid state on the print medium, the area factor is large, the outer shape is excellent, and the image density is high and uniform in the dots. Dots can be formed. Here, it goes without saying that the positions on the print medium 904 to which the respective inks are applied may slightly deviate from each other as long as these inks come into contact with each other in a liquid state.
[0064]
  Further, as shown in FIG. 10, the first ink containing the first pigment is ejected from the first ink jet head 1001 (1002), and the second ink jet head 1003 is bonded to the surface of the first pigment. Has the same polarity as the groupWith polymeric dispersantsThe second ink containing the second pigment is ejected (1004), and the third ink containing the dye having the same polarity as the group bonded to the surface of the first pigment is ejected from the third inkjet head 1005. (1006), the inks ejected from the respective inkjet heads are combined before adhering to the print medium 803, and the first ink, the second ink, and the third ink are mixed (1007). ) Is also attached to a predetermined portion of the print medium 1008 to realize a state in which the first ink, the second ink, and the third ink are in contact with each other on the print medium 1008. Can do. Also in this case, the Ka value in the Bristow method of the ink in which the first ink, the second ink, and the third ink are mixed is 1 ml · m^-2・ Msec^-1/2It is preferable to prepare each ink so as to be less than
[0065]
As an example of a print medium provided with a resin layer as a coat layer, for example, a print medium provided with a resin layer on a plastic film such as paper or polyester is known. The material constituting the coat layer is mainly composed of a water-soluble resin, a water-dispersed resin or the like, and other cationic compounds, surfactants, fillers, and the like may be used as appropriate.
[0066]
Examples of the water-soluble resin include polyvinyl alcohol and modified products of polyvinyl alcohol such as anion-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and acetal-modified polyvinyl alcohol; water-based polyurethane; polyvinyl pyrrolidone, and vinyl pyrrolidone and vinyl acetate copolymer Modification of polyvinylpyrrolidone such as vinylpyrrolidone and dimethylaminoethyl / methacrylic acid copolymer, quaternized vinylpyrrolidone / dimethylaminoethyl / methacrylic acid copolymer, vinylpyrrolidone and methacrylamidepropyltrimethylammonium chloride copolymer Products: Cellulose water-soluble resins such as carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and cationized hydroxyethyl cell Cellulose modified products such as cellulose; polyesters, polyacrylic acid (esters), melamine resins, or modified products thereof, synthetic resins such as graft copolymers containing at least polyester and polyurethane, albumin, gelatin, casein And natural resins such as starch, cationized starch, gum arabic, and sodium alginate.
[0067]
Examples of the water dispersible resin include polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene, styrene- (meth) acrylate copolymer, (meth) acrylate polymer, vinyl acetate- (Meth) acrylic acid (ester) copolymer, poly (meth) acrylamide, (meth) acrylamide copolymer, styrene-isoprene copolymer, styrene-butadiene copolymer, styrene-propylene copolymer, polyvinyl ether In addition, a large number of silicon-acrylic copolymers can be listed, but of course not limited thereto.
[0068]
In addition to the above, a cationic compound is also preferably used as a material for the coating layer of the print medium. The cationic compound is not particularly limited as long as it contains a cationic moiety in the molecule. For example, monoalkylammonium chloride, dialkylammonium chloride, tetramethylammonium chloride, trimethylphenylammonium chloride, ethylene oxide addition Quaternary ammonium salt type cationic surfactants such as ammonium chloride, or amine salt type cationic surfactants, and amphoteric interfaces such as alkylbetaines, imidazolium betaines and alanines containing cationic moieties It may be an activator. Examples of the polymer or oligomer include polyacrylamide cation-modified products, copolymers of acrylamide and cationic monomers, polyallylamine, polyaminesulfone, polyvinylamine, polyethyleneimine, polyamide-epichlorohydrin resin, polyvinylpyridinium halide, and the like. It is done.
[0069]
Furthermore, a vinyl oxazolidone monomer alone or a copolymer with another general monomer, a vinyl imidazole monomer alone, or a copolymer with another monomer may be mentioned.
[0070]
Examples of the other monomer include methacrylate, acrylate, acrylonitrile, vinyl ether, vinyl acetate, ethylene, and styrene. Also, cation-modified cellulose may be used.
[0071]
The cation-modified compounds as described above are preferably used, but of course, the cationic compounds are not limited to these.
[0072]
The thickness of the coat layer is 0.1 g / m in dry weight.² ~ 100g / m²Those coated in the above range are preferable, and the coating layer may be formed in a multilayer structure such as a two-layer or three-layer structure, in addition to the coating layer formed in one layer.
[0073]
As described above, the print medium on which the coating layer is formed as described above is particularly effective in preventing “cracking” by using the ink of the present embodiment. In addition, the pigment itself has good wettability with respect to the coating layer, whereby the defect of the dye having poor wettability with respect to the coating layer can be compensated. In other words, by using the pigment and dye mixed ink of this embodiment, it is possible to suppress the occurrence of beading that occurs when an ink containing only a dye is used as a color material.
[0074]
【Example】
Hereinafter, specific examples of the embodiment will be described below.
Example 1
FIG. 3 is a side view illustrating a schematic configuration of the full-line type printing apparatus according to the first embodiment.
[0075]
The printing apparatus 1 is an inkjet that performs printing by ejecting ink from a plurality of full-line type print heads arranged at predetermined positions along the conveyance direction of a recording medium as a print medium (the direction of arrow A in the figure). It employs a printing method and operates under the control of a control circuit (not shown).
[0076]
Each of the print heads 101Bk, 101C, 101M, and 101Y of the head group 101g has about 7200 ink ejection openings arranged in the width direction of the recording paper conveyed in the A direction in the drawing (a direction perpendicular to the drawing sheet). In addition, printing can be performed on recording paper having a maximum size of A3.
[0077]
The recording paper 103 is conveyed in the A direction by the rotation of a pair of registration rollers 114 driven by a conveyance motor, and is guided by a pair of guide plates 115 and aligned at the leading end thereof, and then is transferred onto the conveyance belt 111. Be transported. A conveyor belt 111 that is an endless belt is held by two rollers 112 and 113. The recording sheet 103 is transported by rotating the roller 113. Note that the recording paper 113 is attracted to the transport belt 111 by electrostatic attraction. The roller 113 is rotationally driven in a direction in which the recording paper 103 is conveyed in the direction of arrow A by a driving source such as a motor (not shown). The recording paper 103 conveyed on the conveying belt 111 and recorded during this time by the recording head group 101g is discharged onto the stocker 116.
[0078]
Each print head of the recording head group 101g is dispersed in an aqueous medium by a black pigment (self-dispersing carbon black) as the first pigment described above with respect to the embodiment of the present invention, and a polymer dispersant. The head 101Bk containing the ink containing the pigment and the polymer dispersant, and the respective heads (cyan head 101C, magenta head 101M, yellow head 101Y) containing the color ink are arranged along the conveyance direction A of the recording paper 103. Are arranged as shown. Then, black characters and color images can be printed by ejecting ink of each color from each print head.
[0079]
The composition of the Bk ink used in this example is as follows. In addition, the quantity of each component shown below represents a weight part.
[0080]
25 parts of pigment dispersion 1
25 parts of pigment dispersion 4
6 parts glycerin
7 parts of diethylene glycol
Acetylenol EH 0.2 parts
(Made by Kawaken Fine Chemicals)
Water balance
The pigment dispersion 1 was prepared as follows. After 300 g of acidic carbon black (trade name: MA-77 (pH 3.0, manufactured by Mitsubishi Kasei Co., Ltd.)) was mixed well with 1000 ml of water, 450 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise thereto. The mixture was stirred at 100 to 105 ° C. for 10 hours. The obtained slurry was Toyo Filter Paper No. 2 (manufactured by Advantis) and sufficiently washed the pigment particles with water. This pigment wet cake was redispersed in 3000 ml of water and desalted with a reverse osmosis membrane until the conductivity reached 0.2 μs. Further, this pigment dispersion (pH = 8 to 10) was concentrated to a pigment concentration of 10% by weight. By the above method, a pigment dispersion 1 was obtained in which an anionic charged self-dispersing carbon black having a hydrophilic -COO- group directly bonded thereto was dispersed on the surface.
[0081]
The pigment dispersion 4 described above is prepared as follows. As a dispersant, 14 parts of a styrene-acrylic acid-ethyl acrylate copolymer (acid value 180, average molecular weight 12000), 4 parts of monoethanolamine and 72 parts of water are mixed, heated to 70 ° C. in a water bath, and resin Dissolve the minutes completely. At this time, if the concentration of the resin to be dissolved is low, the resin may not be completely dissolved. Therefore, when the resin is dissolved, a high concentration solution may be prepared in advance and diluted to prepare a desired resin solution. To this solution, 10 parts of carbon black (trade name: MCF-88, pH 8.0, manufactured by Mitsubishi Chemical), which can be dispersed in an aqueous medium for the first time by the action of a dispersant, was added and premixed for 30 minutes. Subsequently, the following operation was performed to obtain a pigment dispersion 4 in which carbon black (MCF-88) was dispersed in an aqueous medium using a dispersant.
[0082]
Dispersing machine: Side grinder (Igarashi Machine)
Grinding media: Zirconia beads 1mm diameter
Filling rate of grinding media: 50% (volume)
Grinding time: 3 hours
Centrifugation (12000 RPM, 20 minutes)
The Ka value of the Bk ink prepared in this way is 0.40 (ml · m^-2・ Msec^-1/2)Met.
(Example 2)
As other examples of the Bk ink, the following components may be used.
[0083]
45 parts of pigment dispersion 2
5 parts of pigment dispersion 4
6 parts glycerin
5 parts of triethylene glycol
Acetylenol EH 0.2 parts
(Made by Kawaken Fine Chemicals)
Water balance
The pigment dispersion 2 was prepared as follows. Surface area is 230m² 10 g of carbon black having a DBP oil absorption of 70 ml / 100 g and 3.41 g of p-amino-N-benzoic acid were mixed well with 72 g of water, and 1.62 g of nitric acid was added dropwise thereto at 70 ° C. Stir. Several minutes later, a solution of 1.07 g of sodium nitrite dissolved in 5 g of water was added, and the mixture was further stirred for 1 hour. The obtained slurry was Toyo Filter Paper No. 2 (manufactured by Advantis), the pigment particles were sufficiently washed with water and dried in an oven at 90 ° C., and water was added to the pigment to prepare a pigment aqueous solution having a pigment concentration of 10% by weight. By the above method, as shown by the following formula, Pigment Dispersion Liquid 2 in which an anionically charged self-dispersing carbon black having a hydrophilic group bonded to the surface via a phenyl group was dispersed was obtained.
[0084]
[Chemical 3]

The pigment dispersion 4 was prepared in the same manner as in Example 1. The Ka value of the Bk ink thus obtained was 0.35 (ml · m^-2・ Msec^-1/2)Met.
(Example 3)
As other examples of the Bk ink, those having the following components may be used.
[0085]
45 parts of pigment dispersion 3
Pigment dispersion 4 2.5 parts
C. I. Direct Blue 199 0.25 part
6 parts glycerin
Diethylene glycol 5 parts
0.1 parts of acetylenol EH
Water balance
The pigment dispersion 3 was prepared as follows.
[0086]
To a solution of 5 g of concentrated hydrochloric acid dissolved in 5.3 g of water, 1.58 g of anthranilic acid was added at 5 ° C. This solution was always kept at 10 ° C. or lower by stirring with an ice bath, and a solution obtained by adding 1.78 g of sodium nitrite to 8.7 g of water at 5 ° C. was added. Furthermore, after stirring for 15 minutes, the surface area is 320 m.²/ G of carbon black with a DBP oil absorption of 120 ml / 100 g was added in a mixed state. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was Toyo Filter Paper No. After filtering through 2 (manufactured by Advantis), the pigment molecules were sufficiently washed with water and dried in an oven at 110 ° C., water was added to the pigment to prepare a pigment aqueous solution having a pigment concentration of 10% by weight. By the above method, as shown by the following formula, Pigment Dispersion Liquid 3 was obtained in which an anionically charged self-dispersing carbon black having a hydrophilic group bonded thereto via a phenyl group was dispersed on the surface. The pigment dispersion 4 was prepared in the same manner as in Example 1.
[0087]
[Formula 4]

The Ka value of the Bk ink thus obtained was 0.33 (ml · m^-2・ Msec^-1/2)Met.
(Comparative Example 1)
As comparative examples for Examples 1 to 3 described above, inks having the following components were prepared using only the pigment dispersion 4 prepared in the same manner as in Example 1.
[0088]
50 parts of pigment dispersion 4
8 parts of ethylene glycol
Glycerin 5 parts
Isopropyl alcohol 4 parts
33 parts of water
(Evaluation)
Using the inks of Examples 1 to 3 and Comparative Example 1, printing was performed at an interval of 720 dpi in the main scanning direction at an ejection frequency of 7.2 kHz using an inkjet printer equipped with a recording head having a resolution of 360 dpi. Here, the discharge amount per one drop of ink from the recording head was about 25 picoliters, and recording was performed by ejecting one drop of ink into one pixel formed at a resolution of 360 dpi × 720 dpi. Then, a solid image, a character pattern, and the like were printed, and the OD of the image, the dot peripheral shape, the solid uniformity, the back-through property, the smoothing property and the roundness were evaluated. As a print medium, PB paper manufactured by Canon Inc. was used.
[0089]
here,
-OD is obtained by measuring a portion of a solid pattern of 5 mm square.
-The shape around the dots was confirmed visually with a loupe for the sharpness of the edge of the line image.
A: The edge of the line is connected in a straight line.
○: Although the linearity of the edge of the line is slightly lost, there is no practical problem.
X: The linearity of the edge of a line is lost.
-Solid uniformity was confirmed by visual observation of density uniformity in a solid pattern of 5 mm square.
A: No white portion is recognized.
○: A white missing portion is recognized, but it is not noticeable, and there is no practical problem.
X: The white missing part is conspicuous and affects the image quality.
-The through-through property was determined by visually observing the portion where the solid pattern was printed from the back side to see if the pattern was seen through, and measuring the optical density of the corresponding part on the back side using a Macbeth densitometer.
A: Almost no see-through and optical density measured by Macbeth densitometer is less than 0.2.
○: Slightly transparent but hardly noticed, and optical density measured by Macbeth densitometer is 0.2 or more and less than 0.25.
-For roundness, the shape of the ink dots formed on the print medium with one drop of ink was observed with a loupe.
A: From a statistical point of view, most dots are close to a perfect circle.
○: Statistically, the roundness of the dots is broken, but there is no problem in image formation.
Δ: From a statistical viewpoint, the roundness of a considerable number of dots is broken, and irregularly shaped dots are formed.
[0090]
The above results are shown in Table 2 below.
[0091]
[Table 2]

An ink containing only the first pigment was prepared and recorded and evaluated in the same manner as in the above examples. In light of the above evaluation criteria, all results corresponding to ○ were obtained, and there was no practical problem. However, the ink according to this embodiment exhibits performance exceeding that, and the usefulness and superiority of the present invention are clear.
[0092]
Next, using the ink of Example 3, using the apparatus of Example 1, a transparency film (trade name; CF102) having a coat layer manufactured by Canon, which is the present applicant, was applied to a predetermined size. When a solid image was printed and evaluated by the presence or absence of “crack”, “crack” was not confirmed. On the other hand, when the ink of Comparative Example 1 was used, the phenomenon of “cracking” could be confirmed.
[0093]
When the same ink was used for printing on a transparency film (trade name: CF101) manufactured by Canon Co., Ltd. with a coating layer, and evaluated for “cracking”, the ink of Comparative Example 1 was used. In this case, the phenomenon of “cracking” was recognized more markedly than when printing on CF102. However, no “cracking” was observed when the ink of Example 3 was used.
(Other examples)
FIG. 4 is a schematic perspective view showing the configuration of a serial type printing apparatus 5 showing another apparatus that can use the ink according to each of the embodiments of the present invention. In FIG. 4, the same elements as those shown in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0094]
A recording sheet 103 that is a print medium is inserted from a sheet feeding 105 and discharged through a printing unit 126. In the print unit 126, the carriage 107 is mounted with print heads 101Bk, 101C, 101M and 101Y, and is configured to be reciprocally movable along the guide rail 109 by a driving force of a motor (not shown). The print head 101Bk discharges the black ink according to this embodiment. The print heads 101C, 101M, and 101Y discharge cyan ink, magenta ink, and yellow ink, respectively, and are driven to discharge ink onto the recording paper 103 in this order.
[0095]
Each head is supplied with ink from an ink tank 108Bk, 108C, 108M, 108Y containing the corresponding ink to be ejected, and at the time of ink ejection, an electrothermal transducer (heater) provided for each ejection port of each head. ), A thermal signal is applied to the ink to generate bubbles, and ink is ejected using the pressure at the time of foaming. Each head is provided with 64 ejection openings at a density of 360 dpi, which are arranged in substantially the same direction as the conveyance direction Y of the recording paper 103, that is, in a direction substantially perpendicular to the scanning direction by each head. . And the discharge amount for each discharge port is 23 pl.
[0096]
In the above configuration, the distance between the heads for each color ink is 1/2 inch, the distance Di between the heads 101Bk and 101C is 1 inch, the print density in the scanning direction is 720 dpi, and the ejection frequency of each head. Is 7.2 kHz.
[0097]
FIG. 5 is a diagram for explaining a printing process by the serial type printing apparatus shown in FIG. 4, and schematically shows a state where the printing unit 126 is viewed from above. In FIG. 5, the carriage 107 reciprocates above the recording paper 103 being conveyed in the X direction substantially perpendicular to the conveying direction Y. The discharge ports (indicated by dots in the drawing) of the black discharge portions 101Bk and the color discharge portions (101C, 101M, 101Y) mounted on the carriage 107 are opened in the direction in which ink is discharged to the recording paper 103.
[0098]
In each ejection unit, ejection ports are arranged so that printing with a width d can be performed along the conveyance direction Y of the recording paper 103 by one scanning. Further, in order to provide a time difference between the ink ejection by the black ejection unit 101Bk and the color ink ejection, the black ejection unit 101Bk and the color ink ejection unit are arranged at positions shifted along the transport direction by the distance of the print width d. ing. This discharge time difference is the time when the black ink substantially completes penetration into a predetermined range in the thickness direction of the recording paper. With this configuration, the ink ejection of the black ejection unit 101Bk and the color ink ejection with respect to a predetermined position of the recording paper 103 are shifted by one scanning of the carriage 107 (the scanning cycle is 1.5 seconds), The above-described predetermined time difference is performed, and thus the problem of blurring at the boundary between the Bk image and the color image can be solved.
[0099]
FIG. 6 is a perspective view showing another example of an ink jet printer according to another embodiment. Elements similar to those shown in FIGS. 3 and 4 are denoted by the same reference numerals, and description thereof is omitted. . As shown in FIG. 6, the ink according to the embodiment of the present invention can be used as a black ink in a monocolor printer.
[0100]
【The invention's effect】
As is apparent from the above description, according to the present invention, a pigment (second pigment) that can be dispersed in an aqueous medium for the first time by the action of a self-dispersing pigment (first pigment) and a dispersant, and the dispersion In the ink containing the agent, the first pigment itself functions as a dispersant for the second pigment, or the second pigment is stably dispersed in the ink even if the content of the dispersant is small. Ink with excellent storage stability. On the other hand, when this ink is used for printing, for example, the aggregation of the pigment caused by the interaction between the second pigment and the dispersant generated on the recording medium is alleviated by the first pigment. Excellent particle size, uniform dispersion in ink dots, dot diameter with appropriate spread, uniform image density distribution within the dots, almost no feathering, etc. Ink dots can be obtained.
[0101]
Furthermore, in the ink containing the first pigment, the second pigment, the dispersant, and the dye according to another aspect of the present invention, the aggregation force of the pigment is further relaxed by the dye, or the aggregation of the pigment on the recording medium. Things become fine particles. On the other hand, the dye takes in the surroundings of the particulate pigment, and the print image as a whole is suppressed from unevenness due to aggregation. The effect is most significant in that the occurrence of “cracking” on the ink dots can be extremely effectively suppressed or prevented even when this ink is ink-jet recorded on a print medium having poor ink absorption. Can be observed.
[0102]
In the present specification, “part” or “%” is based on weight unless otherwise specified.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating a “cracking” phenomenon of a pigment ink, which is a problem to be solved by the present invention.
FIG. 2 is a diagram illustrating a result of printing using ink according to an embodiment of the present invention.
FIG. 3 is a side view showing a schematic configuration of an inkjet printing apparatus according to an embodiment of the present invention.
FIG. 4 is a perspective view showing an ink jet printer according to another embodiment of the present invention.
5 is a diagram for explaining a printing operation in the printer shown in FIG. 4; FIG.
FIG. 6 is a perspective view showing an ink jet printer according to still another embodiment of the present invention.
FIG. 7 is a schematic explanatory diagram of an image forming method according to an embodiment of the present invention.
FIG. 8 is a schematic explanatory diagram of an image forming method according to another embodiment of the present invention.
FIG. 9 is a schematic explanatory diagram of an image forming method according to an embodiment of the present invention.
FIG. 10 is a schematic explanatory diagram of an image forming method according to another embodiment of the present invention.
[Explanation of symbols]
101g head group
101Bk, 101C, 101M, 101Y Print head
103 Recording paper
111 Conveyor belt
112 Laura
113 Laura
114 Registration Roller
115 Guide plate
116 Stocker
701, 801 Inkjet head for first ink ejection
702, 802 Second ink jet ink jet head
703, 803 Print media

Claims (14)

An ink comprising a first pigment and a second pigment dispersed in an aqueous medium as a coloring material, wherein the first pigment has at least one anionic group directly or via another atomic group Self-dispersing pigment bonded to the surface of the first pigment or self-dispersing pigment in which at least one cationic group is bonded to the surface of the first pigment directly or through other atomic groups The second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink further has a high polarity of the same polarity as the group bonded to the surface of the first pigment. ink comprising the molecular dispersion agent.   The ink according to claim 1, wherein the polymer dispersant is at least one of a sulfonic acid polymer dispersant and a carboxylic acid polymer dispersant.   The ink according to claim 1, comprising more of the first pigment than the second pigment. An ink for use in an image recording method in which an ink jet recording method is used to eject an orifice and apply it onto a print medium to form an element of an image, wherein the first pigment and the second pigment are used as a coloring material in an aqueous medium A self-dispersing pigment comprising at least one anionic group containing at least one anionic group bonded to the surface of the first pigment directly or through another atomic group A self-dispersing pigment in which two cationic groups are bonded to the surface of the first pigment directly or through other atomic groups, and the second pigment is dispersed in an aqueous medium by a polymer dispersant a pigment which can be an ink, which comprises the ink further the polarity of the polymeric dispersing agent and a base coupled to the surface of the pigment of the first.   The ink according to claim 4, wherein the polymer dispersant is at least one of a sulfonic acid polymer dispersant and a carboxylic acid polymer dispersant.   The ink according to claim 4 or 5, wherein a ratio of the first pigment is larger than that of the second pigment. An ink jet printing method comprising: ejecting ink toward a print medium using an ink jet recording method to record an image on the print medium, wherein the ink contains a first pigment and a second pigment in an aqueous medium. In a dispersed state, wherein the first pigment has at least one anionic group bonded to the surface of the first pigment directly or through other atomic groups, or at least one A self-dispersing pigment in which a cationic group is bonded to the surface of the first pigment directly or through another atomic group, and the second pigment is dispersed in the aqueous medium by a polymer dispersant a pigment that can be inkjet, characterized in that said ink is an ink further comprising a group of the same polarity as the polymer dispersing agent that is bonded to the surface of the pigment of the first Lint way.   The ink jet printing method according to claim 7, wherein the polymer dispersant is at least one of a sulfonic acid polymer dispersant and a carboxylic acid polymer dispersant.   The inkjet printing method according to claim 7 or 8, wherein the proportion of the first pigment is larger than that of the second pigment. A self-dispersing pigment in which at least one anionic group is bonded to the surface of the first pigment directly or via other atomic groups or at least one cationic group directly or through other atomic groups A first ink containing a self-dispersing pigment bonded to the surface of the first pigment through the same group as the group bonded to the surface of the self-dispersing pigment in the first ink. A first ink containing a polar polymer dispersant and a pigment that can be dispersed in an aqueous medium by the polymer dispersant is liquid on the surface of the print medium. An image forming method comprising a step of forming an image by applying the image to a print medium so as to be in contact with each other. A self-dispersing pigment in which at least one anionic group is bonded to the surface of the first pigment directly or via other atomic groups or at least one cationic group directly or through other atomic groups A first ink containing a self-dispersing pigment bonded to the surface of the first pigment via a pigment, a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the first ink a second ink containing a group of the same polarity as the polymer dispersing agent that is coupled to the self-dispersion of surface of the pigment, a group of the same polarity of the dye are bonded to the surface of the pigments in the self-dispersible And a step of applying the third ink to the print medium so that the first ink, the second ink, and the third ink are in liquid contact with each other on the surface of the print medium. Image forming method. An ink container containing ink, wherein the ink includes a first pigment and a second pigment dispersed in an aqueous medium as a coloring material, and the first pigment has at least one anionic group directly Or a self-dispersed pigment or at least one cationic group bonded to the surface of the first pigment through another atomic group, or the surface of the first pigment directly or through another atomic group And the second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink further binds to the surface of the first pigment. ink container, which comprises a group of the same polarity as the polymer dispersant being. A first pigment and a second pigment are dispersed in an aqueous medium as a coloring material, and the first pigment contains at least one anionic group directly or through another atomic group. A self-dispersing carbon black bonded to the surface of the first pigment or a self-dispersing carbon black in which at least one cationic group is bonded to the surface of the first pigment directly or through another atomic group The second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink further has a polymer dispersion having the same polarity as the group bonded to the surface of the first pigment. An ink set comprising a combination of black ink containing an agent , yellow ink, magenta ink, and cyan ink. A first pigment and a second pigment are dispersed in an aqueous medium as a coloring material, and the first pigment contains at least one anionic group directly or through another atomic group. A self-dispersing carbon black bonded to the surface of the first pigment or a self-dispersing carbon black in which at least one cationic group is bonded to the surface of the first pigment directly or through another atomic group The second pigment is a pigment that can be dispersed in the aqueous medium by a polymer dispersant, and the ink further has a polymer dispersion having the same polarity as the group bonded to the surface of the first pigment. each and black ink, yellow ink, magenta ink, and with each receiving ink containing portion and a cyan ink, said black ink, said yellow ink, the magenta ink and the cyan ink containing agent An ink jet recording apparatus characterized by comprising a means for separately ejecting the ink-jet printing method.

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