JP3915369B2 - Ink jet recording method and ink jet recording ink - Google Patents

Description

【００６１】
上記式中、ＨＬＢｘは各親水部または各疎水部のみのＨＬＢを、Ｗｘは各親水部または各疎水部それぞれの重量を示す。なお、親水基の基数は正、疎水基の基数は負で示される値である。
【００６２】
これら水溶性高分子のうち、特に好ましいものは、ノニオン性の水溶性高分子および−ＣＯＯ^-Ｍ⁺基を有するアニオン性の水溶性高分子である。
ノニオン性の水溶性高分子としては、ノニオン高分子界面活性剤、ポリエチレングリコール、ポリプロピレングリコール等が挙げられる。−ＣＯＯ^-Ｍ⁺基を有するアニオン性の水溶性高分子としては、アクリル酸系共重合体、メタクリル酸系共重合体等が挙げられる。
【００６３】
また、水溶性高分子としては、界面活性作用を有し、インク中に単独で添加した時に、インク表面張力を３５〜５０ｍＮ／ｍの範囲内にし得るものが好ましい。かかる機能を有する水溶性高分子としては、ノニオン性およびアニオン性の水溶性高分子が挙げられ、ノニオン性の水溶性高分子としては、ポリオキシエチレン／ポリオキシプロピレンブロック共重合体、ポリプロピレングリコール等が挙げられる。アニオン性の水溶性高分子としては、スチレン／アクリル酸共重合体、スチレン／メタクリル酸共重合体、ｎ−ブチルメタクリレート／アクリル酸共重合体、ｎ−ブチルメタクリレート／メタクリル酸共重合体、２−エチルへキシルメタクリレート／アクリル酸共重合体、２−エチルへキシルメタクリレート／メタクリル酸共重合体等が挙げられる。
【００６４】
（界面活性剤）
本発明のインク中には、印字時のドライング時間短縮のために、公知の各種界面活性剤を含有する。界面活性剤としては、公知の各種界面活性剤を挙げることができ、ノニオン、アニオン、カチオンあるいは両性界面活性剤の何れでもよいが、自己分散顔料の親水官能基や水溶性高分子のイオン性との相互作用を抑えるため、同種のイオン性またはノニオン性が好ましく、特にノニオン性界面活性剤が好ましい。界面活性剤は前記水溶性高分子と併用して使用される。
【００６５】
ノニオン界面活性剤としては、例えば、ポリオキシエチレンノニルフェニルエーテル、ポリオキシエチレンオクチルフェニルエーテル、ポリオキシエチレンドデシルフェニルエーテル、ポリオキシエチレンアルキルエーテル、ポリオキシエチレン脂肪酸エステル、ソルビタン脂肪酸エステル、ポリオキシエチレン／ポリオキシプロピレンブロック共重合体、ポリオキシエチレンソルビタン脂肪酸エステル、脂肪酸アルキロールアミド、アセチレングリコール誘導体（サーフィノール）等が挙げられる。
【００６６】
アニオン界面活性剤としては、アルキルベンゼンスルホン酸塩、アルキルナフタレンスルホン酸塩、アルキルナフタリンスルホン酸塩のホルマリン縮合物、高級脂肪酸塩、高級脂肪酸エステルの硫酸エステル塩、高級脂肪酸エステルのスルホン酸塩、高級アルコールエーテルの硫酸エステル塩およびスルホン酸塩、高級アルキルスルホンアミドのアルキルカルボン酸塩、スルホコハク酸塩およびそのエステル塩、アルキル亜リン酸塩、アルキルリン酸塩、アルキルフォスフォン酸塩およびそのエステル、高級アルコールリン酸エステル塩等が挙げられる。
【００６７】
カチオン界面活性剤としては、第一、第二、第三級のアミン塩、第四級アンモニウム塩等が挙げられる。
また、両性界面活性剤としては、ベタイン、スルホベタイン、サルフェートベタイン等が挙げられる。
【００６８】
その他、ポリシロキサンポリオキシエチレン付加物等のシリコーン系界面活性剤、パーフルオロアルキルカルボン酸、パーフルオロアルキルスルフォン酸、オキシエチレンパーフルオロアルキルエーテル等のフッ素系界面活性剤、天然もしくはバイオサーファクタント類のレシチン、スピクリスポール酸、ラムノリピド、サポニン、コール酸塩等が挙げられる。
【００６９】
これらの界面活性剤は、単独でもあるいは２種以上混合して用いてもよい。これら界面活性剤の分子量は、１５０〜１０００の範囲であることが必要である。分子量１５０未満の界面活性剤は、実質的に存在しない。一方、分子量が１０００〜２０，０００の場合は、水溶性高分子として使用することができる。
本発明における界面活性剤の含有量は、インク全量に対し０．０１〜１．５重量％の範囲とすることが好ましく、より好ましくは０．０１〜１重量％の範囲である。０．０１重量％未満では、界面活性剤の添加効果が得られない。また、１．５重量％を超えると、記録媒体上での浸透作用が高くなりすぎ画質劣化を招いてしまう場合がある。
【００７０】
本発明において、界面活性剤のＨＬＢとしては５〜１４の範囲であることが好ましく、より好ましくは５〜１２の範囲である。ＨＬＢが５より低いと、水に十分に溶解出来なくなる場合がある。一方、ＨＬＢが１４を超えると、親水性が高くなりすぎ、光学濃度を高く保てない場合がある。また、界面活性剤のＨＬＢは水溶性高分子のＨＬＢと近いことが望ましい。両者のＨＬＢの差としては、好ましくは±５以内、より好ましくは２．５以内である。
【００７１】
（低分子アルコールおよび尿素）
本発明のインク中には、分散安定性や目詰まり防止等の信頼性向上のため低分子アルコールおよび／または尿素をインク中に含有することが好ましい。低分子アルコールおよび尿素は、それぞれ単独で使用してもよいし、併用してもよい。目的に合わせて使用することができる。
【００７２】
低分子アルコールとしては、メタノール、エタノール、１−プロパノール、２−プロパノール、２−メチル−２−プロパノール、１−ブタノール、２−ブタノール、イソブタノール、１−ペンタノール、２−ペンタノール、３−ペンタノール、アリルアルコール、プロパルギルアルコール、ベンジルアルコール、シクロヘキサノール等の炭素数１０以下のアルコール類が挙げられる。
【００７３】
低分子アルコールの含有量としては、インク全量に対し０．１〜１０重量％の範囲、好ましくは０．５〜５重量％の範囲とすることが望ましい。０．１重量％以下では、低分子アルコール添加によるインクの信頼性向上効果が得られない。一方、１０重量％を超えると、用紙上の滲み劣化が進行し印字品質を低下させてしまう場合がある。
【００７４】
尿素の含有量としては、インク全量に対し１〜１０重量％の範囲塗することが好ましく、より好ましくは２〜７重量％の範囲である。１重量％未満では、尿素添加によるインクの信頼性向上効果が得られない。一方、１０重量％を超えると、用紙上で析出してしまい、画像に凹凸が現れ、印字品質を低下させてしまう場合がある。
【００７５】
（各種添加剤）
本発明のインクには、必要に応じて、その他添加剤を添加することができる。該その他添加剤としては、ｐＨ調整剤、ハイドロトロピー剤、キレート化剤、包接化合物、酸化剤、酸化防止剤、還元剤、酵素、殺菌剤、消泡剤、研磨剤等を挙げることができる。
【００７６】
必要に応じてｐＨ調整を行うためのｐＨ調整剤としては、水酸化ナトリウム、水酸化カリウム、水酸化リチウム、硫酸ナトリウム、酢酸塩、乳酸塩、安息香酸塩、トリエタノールアミン、アンモニア、２−アミノ−２−メチル−１−プロパノール（ＡＭＰ）、リン酸アンモニウム、リン酸ナトリウム、リン酸リチウム等のアルカリや、酢酸、塩酸、硝酸、硫酸、リン酸、プロピオン酸、Ｐ−トルエンスルフォン酸等の有機酸または無機酸が挙げられる。また、その他一般のｐＨバッファ類、グッドバッファ類等も挙げられる。しかし、ｐＨ調整剤としては、これらに限定されるものではない。なお、本発明のインクのｐＨについては、後述する。
【００７７】
ハイドロトロピー剤としては、酪酸ナトリウム、サリチル酸ナトリウム等のカルボン酸塩、トルエンスルホン酸ナトリウム等の芳香族スルホン酸塩、エチルアルコール等の低級アルコール、尿素、アセトアミド等が挙げられる。
キレート化剤としては、エチレンジアミンテトラ酢酸（ＥＤＴＡ）、イミノ二酢酸（ＩＤＡ）、エチレンジアミン−ジ（ｏ−ヒドロキシフェニル酢酸）（ＥＤＤＨＡ）、ニトリロ三酢酸（ＮＴＡ）、ジヒドロキシエチルグリシン（ＤＨＥＧ）、ｔｒａｎｓ−１，２−シクロヘキサンジアミン四酢酸（ＣｙＤＴＡ）、ジエチレントリアミン−Ｎ，Ｎ，Ｎ’，Ｎ”，Ｎ”−五酢酸（ＤＴＰＡ）、グリコールエーテルジアミン−Ｎ，Ｎ，Ｎ’，Ｎ’−四酢酸（ＧＥＤＴＡ）等が挙げられる。
【００７８】
包接化合物としては、チオ尿素、デスオキシコール酸、ビス−（Ｎ，Ｎ’−テトラメチレンベンジジン）、シクロファン等が挙げられる。
その他、酸化剤、酸化防止剤、還元剤、酵素、殺菌剤、消泡剤、研磨剤等についても、従来公知のものを問題無く使用することができる。
【００７９】
〔インクの物性〕
本発明のインクは、物性として、下記（ｂ）〜（ｅ）の条件を満たすものである。
（ｂ）表面張力が、３０〜５０ｍＮ／ｍの範囲
（ｃ）粘度が、１．５〜５．０ｍＰａ・ｓの範囲
（ｄ）導電率が、０．００１〜０．４Ｓ／ｍの範囲
（ｅ）ｐＨが、６〜１１の範囲
以下、各物性毎に説明する。
【００８０】
（ｂ）表面張力
本発明のインクの表面張力としては、３０〜５０ｍＮ／ｍの範囲に調整される。表面張力がこの範囲より低いと、記録媒体としてのいわゆる普通紙に印字した場合、にじみが発生し易くなり、高解像の画像が得られない。一方、表面張力がこの範囲より高いと、記録媒体への浸透が遅くなり、画像の乾燥時間が長くなるので問題となる。本発明のインクの表面張力としては、３０〜４５ｍＮ／ｍの範囲とすることが望ましく、自己分散可能な顔料としてカーボンブラックを用いた場合には、当該望ましい範囲に調整することが、にじみの発生がなく、高解像度の画像が得られる点で特に望ましい。
【００８１】
インクの表面張力は、既述の水溶性高分子または／および界面活性剤の種類、添加量等を適宜コントロールすることで、調整することができる。
なお、本発明において表面張力は、２３℃、５５％ＲＨの環境において、ウイルヘルミー型表面張力計を用いて測定した値を用いた。
【００８２】
（ｃ）粘度
本発明のインクの粘度としては、１．５〜５．０ｍＰａ・ｓの範囲に調整されることが必須であり、好ましくは１．５〜３．５ｍＰａ・ｓの範囲、より好ましくは１．７〜３．５ｍＰａ・ｓの範囲に調整される。粘度が１．５ｍＰａ・ｓよりも小さい場合には、インクの保存安定性が低下する。一方、粘度が５．０ｍＰａ・ｓより大きい場合には、インクの吐出力が低下し、吐出ノズルが目詰まりした場合に回復し難い等の問題が生じる。特に、自己分散可能な顔料として、親水化処理したカーボンブラックを用いた場合には、インクの吐出性の点で、前記より好ましい範囲とすることが望ましい。
【００８３】
インクの粘度は、水溶性有機溶媒の種類および添加量、水溶性高分子の種類、分子量、添加量等で調整することができる。
なお、本発明において粘度は、レオマット１１５（Ｃｏｎｔｒａｖｅｓ製）を測定装置として用いて測定した値を用いた。測定は、被測定インクを測定容器に入れ、前記測定装置における所定の方法で、前記測定装置に装着して行った。測定温度は２３℃、せん断速度は１４００ｓ^-1とした。
【００８４】
（ｄ）導電率
本発明のインクの導電率としては、０．００１〜０．４Ｓ／ｍの範囲に調整されることが必須であり、好ましくは０．００５〜０．３Ｓ／ｍの範囲に調整される。導電率が０．００１Ｓ／ｍ未満では、印字を停止して長期間放置した場合に吐出が回復しにくくなり、また０．４Ｓ／ｍを超えると、インクの保存安定性が劣化し易い。特に、自己分散可能な顔料として、親水化処理したカーボンブラックを用いた場合には、長期放置後の吐出回復性の点で、０．００５〜０．３Ｓ／ｍの範囲とすることが望ましい。
【００８５】
インクの導電率は、水の量、水溶性有機溶媒の種類および添加量や、電解質物質の種類や量、その他組成により調整することができる。
なお本発明において導電率は、２３℃の環境において、導電率計ＡＯＬ−４０−３３０２（ＤＫＫ社製）を測定装置として用いて測定した値を用いた。
【００８６】
（ｅ）ｐＨ
本発明のインクのｐＨとしては、６．０〜１１．０の範囲に調整されることが必須であり、好ましくは７．５〜９．０の範囲に調整される。ｐＨが６．０未満では、インクが目詰まりしやすく、１１．０を超えるとヘッド構成部材を腐食あるいは溶解し易くなる。特に、自己分散可能な顔料として親水化処理したカーボンブラックを用いた場合には、ノズルの目詰まり性の点で、６．０〜９．５の範囲とすることが望ましい。
【００８７】
インクのｐＨは、各種酸、各種塩、ｐＨ調整剤、あるいは、バッファ類等の添加により調整することができる。
なお本発明においてｐＨは、２３℃の環境において、ガラスｐＨ電極を用いて測定した値を用いた。
【００８８】
〔インクの調製〕
本発明のインクは、既述の各構成成分を混合し、溶解および／または分散させることにより調製することができる。特に、自己分散可能な顔料を本発明における所定の分散粒子の数平均粒子径に調整する為に、前記顔料を水性媒体（水を主体とした液体組成物であり、水溶性有機溶媒、水溶性高分子、界面活性剤等を含んでいてもよい。）に分散する工程を少なくとも１工程以上設けることが好ましい。
【００８９】
前記顔料を水性媒体に分散する工程では、各種の攪拌、分散装置が使用できるが、ガラス、セラミック、金属等のボール或いはビーズ等、所謂分散メディアを使用する分散機を使用すると、顔料の粉砕、分散工程で分散メディアおよび分散容器の摩耗により、無機不純物が顔料分散液やインク中に大量に混入する場合が多い。したがって、分散メディアを用いない分散装置の使用が望ましい。特に超音波ホモジナイザー、高圧ホモジナイザーからなる群から選択された少なくとも１種以上の装置によって分散するのが好ましい。超音波ホモジナイザーで分散する際、真空引き、加温、市販の脱泡／脱気装置等により脱泡、脱気を行ってから分散するのが望ましい。分散メディアを使用する分散装置を使った場合は、必要に応じ、混入した無機不純物の除去を行う。
【００９０】
＜インクジェット記録方法＞
本発明のインクジェット記録方法は、以上説明した本発明のインクを、ドロップ量が５〜２５ｐｌとなるように記録媒体に印字することを特徴とするものである。なお、勿論本発明において「印字」とは、文字を記録することのみならず、記録媒体に文字、絵、記号、模様、写真等あらゆる画像を記録すること全てを含む概念である。
【００９１】
インクジェット記録方法としては、静電誘引力を利用してインクを吐出させるいわゆる電荷制御方式、ピエゾ素子の振動圧力を利用してインクを吐出させるいわゆる圧力パルス方式およびインクを加熱して気泡を形成、成長させることにより生じる圧力を利用してインク液滴を形成する所謂サーマルインクジェット方式等を挙げることができる。これらの中でも特にフルカラー画像を小型で安価に提供できる点で、サーマルインクジェット方式が好ましい。
【００９２】
本発明において、印字の際に排出されるインクのドロップ量は、５〜２５ｐｌであることが必須であり、より好ましくは５〜２０ｐｌである。インクのドロップ量が５ｐｌより低いと、顔料の分散粒子が流路で詰まりやすくなるため、使用することが困難である。一方、インクのドロップ量が２５ｐｌを超えると、急激に画質が悪化してしまう。本発明においては、前記本発明のインクを用い、かつインクのドロップ量を５〜２５ｐｌとすることで初めて高画質、ドライング時間の短縮および信頼性の確保が出来るものである。
【００９３】
上記本発明のインクジェット記録方法により、本発明のインクを単独で記録することもできるが、被画像部および／またはその隣接部に、１種または複数種の液体組成物を付着させることが好ましい。当該液体組成物の付着は、インクによる印字に先立ち、あるいは印字と同時に、行われる。前記液体組成物を記録媒体に付着させることで、乾燥時間の短縮、光学濃度の上昇、多色インクとの接触による混色の防止、画像定着強度の向上などの効果を発揮する。
【００９４】
前記液体組成物は、水、水溶性有機溶媒を主体として、必要に応じて着色剤、界面活性剤、定着促進剤、その他添加剤を含んでもよい。
前記液体組成物における水、水溶性有機溶媒、界面活性剤としては、公知の物質を使用する事ができ、本発明のインク用として述べたものが問題無く使用できる。着色剤を含有する場合、当該着色剤としては、染料、顔料およびこれら混合物何れでもよいが、染料が好ましい。染料および顔料としては公知のものが使用できる。
【００９５】
前記液体組成物における定着促進剤としては、各種の水溶性高分子およびポリマーエマルションが使用できる。水溶性高分子あるいはポリマーエマルションとしては、例えば、アクリル系高分子、ポリエステル、ポリビニルアルコール、ポリビニルピロリドン、ポリウレタン等が好ましい。本発明のインク中の顔料がアニオン性の親水性官能基を有し、かつ、定着促進剤がカチオン性基を有する水溶性高分子である組み合わせが特に好ましい。
【００９６】
カチオン性基を有する水溶性高分子としては、カチオン性の官能基を有するモノマー、例えばＮ，Ｎ−ジメチルアミノエチルメタクリレート、Ｎ，Ｎ−ジメチルアミノエチルアクリレート、Ｎ，Ｎ−ジメチルアミノメタアクリルアミド、Ｎ，Ｎ−ジメチルアミノアクリルアミド、ビニルピリジン、ビニルピロリドン等を少なくとも含有する共重合体または単独重合体やポリエチレンイミン、ポリアミン類、ポリアミド類等が好ましい。
【００９７】
また本発明のインク中の顔料が有する親水性官能基が少なくともアニオン性基からなる場合、定着剤促進剤として無機の多価カチオンを含有すことも好ましい。無機の多価カチオンとしては、例えば、Ｃａ²⁺、Ｍｇ²⁺、Ａｌ³⁺、Ｆｅ²⁺、Ｆｅ³⁺、Ｚｎ²⁺、Ｎｉ²⁺、Ｃｏ²⁺、Ｃｕ²⁺等が挙げられる。
【００９８】
前記液体組成物には、界面活性剤を含有させることが、画像乾燥性の点で好ましい。前記液体組成物の表面張力としては、２０〜４０ｍＮ／ｍの範囲であることが好ましい。
【００９９】
上記本発明のインクジェット記録方法においては、インクによる印字に先立ち、あるいは印字の前後に、被記録用紙を５０℃〜２００℃で加熱し、印字定着を促進する機能を持たせた装置を使用することもできる。また、普通紙、光沢紙、特殊紙、布、フィルム、ＯＨＰ等の記録媒体に直接印字する方法の他に、ドラム状あるいはベルト状等の中間体に印字し、該中間体表面でインク画像を整えてから記録媒体に転写して印字してもよい。
【０１００】
【実施例】
［顔料分散液の作製］
（分散体１）
ＣＡＢ−Ｏ−ＪＥＴ３００（ＣＡＢＯＴ社製／固形分１５．２％、自己分散性指標１００％）を８０００ｒｐｍで３０分間遠心処理した後、純水で希釈し固形分１０％の顔料分散体にし、分散体１とした。
【０１０１】
（分散体２）
スチレン／メタクリル酸共重合体Ｎａ塩（モノマー比５０／５０、重量平均分子量＝７０００、計算ＨＬＢ＝１４．１）の水溶性高分子を顔料分散の分散剤として使用した。
【０１０２】
上記水溶性高分子４５重量部（固形分１０％水溶液）とイオン交換水２１０重量部とを混合し、攪拌しながら、カーボンブラックＢＰＬ（ＣＡＢＯＴ社製、自己分散性指標０％）４５重量部を加え３０分間攪拌した。その後、マイクロフルイダイザーで１００００ｐｓｉ／３０ｐａｔｈ分散した。分散後、１Ｎ−ＮａＯＨ水溶液を用いて、ｐＨを９に調整した。さらに、遠心分離装置で遠心分離を８０００ｒｐｍで１５分間実施した後、２μｍメンブランフィルターを通過させた。得られた分散液を純水で希釈して固形分１０％の顔料分散体にし、分散体２とした。
【０１０３】
［インクジェット記録インクの調製］
純水３０重量部に、下記表１および表２に従い、顔料分散体を除くインクの各構成成分を添加し、３０分間攪拌した。得られた液体に顔料分散体を添加し、さらに全量が１００重量部になるように純水を加えた。その後、超音波ホモジナイザー（３００Ｗ、４００μＡ）で１５分間処理をして粒度を調整した。さらに、２μｍメンブランフィルターを通過させ、インクジェット記録インクを調製した。
【０１０４】
【表１】

【０１０５】
【表２】

【０１０６】
［インク物性の測定］
得られた実施例および比較例の各インクについて、以下の物性を測定した。結果を下記表３に示す。
１）粘度
インクの粘度は、レオマット１１５（Ｃｏｎｔｒａｖｅｓ製）を用い測定した。具体的には、被測定インクを測定容器に入れ、前記装置における所定の方法で装置に装着して行った。測定温度は２３℃、せん断速度は１４００ｓ^-1で測定した。
【０１０７】
２）表面張力
インクの表面張力は、ウイルヘルミー型表面張力計を用いて測定した。測定環境は、温度２３℃、湿度５５％ＲＨで測定した。
【０１０８】
３）導電率
インクの導電率は、導電率計ＡＯＬ−４０−３３０２（ＤＫＫ社製）を用いて測定した。測定温度は２３℃で測定した。
【０１０９】
４）ｐＨ
インクのｐＨは、ガラスｐＨ電極を用いて測定した。測定温度は２３℃で測定した。
【０１１０】
５）顔料の分散粒子径
顔料の分散粒子の平均径（分散粒子径）は、マイクロトラックＵＰＡ粒度分析計９３４０（Ｌｅｅｄｓ ＆ Ｎｏｒｔｈｒｕｐ社製）を用い、希釈なしで測定した。入力パラメータとしては、粘度はインク粘度、分散粒子の密度は１．８ｇ／ｃｍ²とした。
【０１１１】
［印字テスト］
前記得られた実施例および比較例の各インクを用い、２３℃、５５％ＲＨの環境において、試作したインクジェットプリンターで印字テストを行った。使用ヘッドとしては、ドロップ量が異なる２種、具体的には、８００ｄｐｉ（ドロップ量約１５ｐｌ）および４００ｄｐｉ（ドロップ量約５０ｐｌ）のものを使用した。使用した用紙は、代表的な普通紙としてＦＸ−Ｌ紙（富士ゼロックス社製）を使用した。印字した画像は、ソリッドパッチ（３ｃｍ四方）および１ドットラインの２種類である。得られた画像について、以下の評価を行った。
【０１１２】
１）光学濃度測定
印字一日後のソリッドパッチ部を、エックスライト４０４（エックスライト社製）を用いて測定した。
【０１１３】
２）印字品質評価試験
１ドットライン部を、以下の基準で官能評価した。
１：滲みなし
２：わずかに滲みが認められるが許容範囲
３：滲みあり
４：多くの部分でヒゲ状の滲みあり
【０１１４】
３）乾燥時間
インクの乾燥時間は、ソリッドパッチ部において、印字直後からインク液体分が消えるまで（目視判定）の時間を計測した。
【０１１５】
［インクの信頼性］
前記得られた実施例および比較例の各インクについて、その信頼性に関する以下の試験を行った。結果を下記表３に示す。
１）安定性試験
各インク５０ｇを蓋のついたガラス管に密閉し、７０℃雰囲気で４時間放置、−２０℃雰囲気で４時間放置、を１サイクルとして、計４サイクルの加速テストを行った。テスト前と後のサンプルを５ｇ採り、１μｍメッシュのフィルターおよび有効濾過径が２．５ｃｍ²のガラスホルダーを用いて減圧濾過を行い、サンプル全量を濾過するのに要した時間を測定し、以下の基準で評価した。
【０１１６】
◎：加速テスト後のフィルター通過時間の増加が２０％未満
○：加速テスト後のフィルター通過時間の増加が２０％以上５０％未満
△：加速テスト後のフィルター通過時間の増加が５０％以上１００％未満
×：加速テスト後のフィルター通過時間の増加が１００％以上
【０１１７】
２）回復性試験
既述の８００ｄｐｉヘッド装着の印字装置を用いて、正常に印字できることを確認後、２３℃、５５％ＲＨ環境で一ヶ月間キャップしない状態で放置した。バキュームによる回復操作を正常に印字できるまで繰り返して、その回数を記録し、以下の基準で評価した。
◎：当初から正常に印字、または、１回で回復
○：２〜３回で回復
△：４〜５回で回復
×：５回で回復しない
【０１１８】
【表３】

【０１１９】
【発明の効果】
以上のように、本発明のインクジェット記録方法およびインクジェット記録インクによれば、普通紙上に画像を鮮明に再現し、優れた印字品質を得ることができる。また、高速印字適性を有する乾燥時間の短縮を普通紙上で実現することができる。さらに、保存時および使用時の高い信頼性を実現することができる。
【０１２０】
従って、本発明によれば、レポート用紙、コピー用紙、ボンド紙、上質紙等の普通紙、さらに、鮮明な画像を形成することが困難であった再生紙に於いても、短い乾燥時間と鮮明な画像を形成することができる。本発明は、熱インクジェット方式、ピエゾ方式、超音波、電界等を利用したインクジェット記録について、好適に適用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inkjet recording method for recording an image by ejecting ink, and an inkjet recording ink used in the inkjet recording method.
[0002]
[Prior art]
A so-called ink jet recording printer that discharges liquid or molten solid ink from nozzles, slits, porous films, etc. and records on paper, cloth, film, etc. has various advantages such as small size, low cost, quietness, In particular, three colors or four colors can be printed at a time, and a full color image can be easily printed.
[0003]
However, in general, an ink containing a liquid as a main component has a lower resolution / edge sharpness on a recording medium such as plain paper, and print quality deteriorates. In order to improve the printing quality, generally low penetrability ink is used to suppress bleeding on the paper, but the drying time of the ink is very slow and the high-speed printing suitability is not exhibited.
[0004]
On the other hand, in order to shorten the drying time, the ink is generally highly permeable. For example, Japanese Patent Laid-Open No. 5-125309 discloses a method for reducing the ink surface tension. Japanese Patent Application Laid-Open No. 5-194899 discloses a method of adding alcohol into ink. Japanese Patent Application Laid-Open No. 6-256696 discloses a method of adding a surfactant to ink. These methods improve the permeability and are effective in shortening the drying time, but the printing quality is not satisfactory.
As described above, the compatibility between the short drying time having high-speed printing suitability and the high printing quality equivalent to that of a laser printer has not reached a satisfactory level.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide an ink jet recording method and an ink jet recording ink that can satisfy the following three points in ink jet printing.
(1) To reproduce images clearly on plain paper and obtain excellent print quality.
(2) Realize shortening of drying time on plain paper with high-speed printing suitability.
(3) Realize high reliability during storage and use.
[0006]
[Means for Solving the Problems]
  As a result of intensive studies, the present inventors have found that the above object can be achieved by the following present invention. That is, the inkjet recording method of the present invention contains at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant, and the following (a) to (fThe ink jet recording ink satisfying the above condition is printed on a recording medium so that the drop amount is 5 to 25 pl.
(A) The number average particle diameter of the dispersed particles of the pigment is in the range of 10 to 60 nm.
(B) The surface tension is in the range of 30 to 50 mN / m.
(C) Viscosity in the range of 1.5 to 5.0 mPa · s
(D) Conductivity is in the range of 0.001 to 0.4 S / m
(E) pH is in the range of 6-11
(F) The water-soluble polymer has a surface active action, and the weight average molecular weight is in the range of 1000 to 200000.
(G) The molecular weight of the surfactant ranges from 150 to 1000
(H) The content ratio of the water-soluble polymer to the surfactant in the ink is in the range of 20: 1 to 2: 1.
[0007]
  The inkjet recording ink of the present invention is an inkjet recording ink used in the inkjet recording method of the present invention, and contains at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer, and a surfactant. And the above (a) to (f) Is satisfied.
[0008]
With the ink jet recording method and ink jet recording ink of the present invention, all of excellent print quality, short drying time, and high reliability could be satisfied.
The print quality deteriorates when the horizontal penetration of the recording medium (for example, paper) increases, and conversely improves when it decreases. Further, the drying time on the surface of the recording medium is not actually the time for the liquid in the ink to dry, but the effect of the time for penetrating the recording medium. Therefore, in order to shorten the so-called drying time, it is necessary to increase the permeability.
[0009]
From the viewpoint of print quality, it is necessary to suppress horizontal permeability on the surface of the recording medium. On the other hand, from the viewpoint of drying time, it is necessary to increase the permeability in the direction perpendicular to the recording medium.
Conventional penetrants such as surfactants used in inks have high penetrability in both the horizontal and vertical directions, so it has not been possible to shorten the drying time while obtaining high print quality.
According to the present invention, it is possible to suppress penetration in the horizontal direction of the recording medium, and it is possible to achieve both high print quality and a short drying time.
[0010]
The specific configuration of the present invention is as follows.
As the colorant, a pigment which is a particle having a good edge sharpness is employed in order to obtain high image quality. In order to shorten the drying time, a penetrant is added. Generally, the penetrant has a surface active action and a hydrophobic action. In the case of a pigment dispersed with an ordinary dispersant, it is difficult to ensure dispersion stability because the penetrant is adsorbed / displaced with the dispersant on the pigment surface. For this reason, in the present invention, a self-dispersing pigment in which a hydrophilic functional group is chemically bonded directly to the pigment surface is employed.
[0011]
On the other hand, the addition of general carbitol or other low-molecular surfactants as penetrants added to shorten the drying time penetrates in both the horizontal and vertical directions of the recording medium and suppresses horizontal penetration. May not be possible, leading to degradation of print quality. Therefore, in the present invention, the above contradictory functions are made compatible by adding a water-soluble polymer together with the surfactant. Although it is not clear about the mechanism which can make the said contradictory function compatible by such structure, it is interpreted by the following effects.
[0012]
It is estimated that low surface tension ink containing a pigment with high image sharpness and the water-soluble polymer can achieve both high print quality and short drying time due to the effect of suppressing penetration in the horizontal direction of the recording medium. Is done. That is, at the same time that the ink lands on the surface of the recording medium, the water-soluble polymer contained in the ink is richly present at the gas-liquid interface of the landed ink due to its surface active action. Further, it is considered that the water-soluble polymer is rapidly thickened at the gas-liquid interface due to moisture permeation. It is estimated that this thickening shortens the drying time while maintaining the high image quality by suppressing ink movement in the horizontal direction (gas-liquid interface).
[0013]
It has been found from experiments that these effects only work when the ink drop amount is in the range of 5 to 25 pl. That is, when the ink is a small drop of 5 to 25 pl, the image quality is dramatically improved by the thickening action of the water-soluble polymer when the ink lands on the recording medium. However, when the ink drop amount exceeds 25 pl, the image quality deteriorates. This can be interpreted to be because if the amount of ink drop becomes too large, the weight of the ink drop will break the barrier due to the increase in viscosity of the water-soluble polymer.
[0014]
In general, when the amount of the water-soluble polymer is increased, the dispersion stability of the ink, clogging resistance (pigment solubility when water evaporates at the nozzle tip), or recovery from storage (long-term storage stability) deteriorates. To do. This is considered to be because the water-soluble polymer is surrounded by the pigment and the water-soluble polymers are mutually bonded. It has been clarified that the addition of a low molecular weight surfactant (preferably a small amount) to this state dramatically improves the reliability without causing image quality degradation. In other words, by adding a low molecular surfactant, it is considered that the low molecular surfactant enters between the water-soluble polymers surrounding the pigment, and the hydrophilic group of the pigment itself functions sufficiently to maintain the reliability.
As described above, according to the present invention, high print quality, shortening of drying time, and high reliability can be achieved.
[0015]
  In the present invention, the ink-jet recording ink (including the ink-jet recording ink of the present invention, hereinafter may be abbreviated as “ink of the present invention” or simply “ink”) in the ink-jet recording method of the present invention. The weight average molecular weight of the molecule is in the range of 1000-20000Need to beThe HLB is preferably in the range of 5-16. The water-soluble polymer desirably has a surface-active action that can bring the ink surface tension within a range of 35 to 50 mN / m by adding it alone to the ink. In addition, the water-soluble polymer may be nonionic, or —COO^-M⁺It is desirable that it is anionic including a group (M is an alkali metal, ammonium, or organic onium compound).
[0016]
  In the present invention, the molecular weight of the surfactant is in the range of 150 to 1000.Need to be, HLB is preferably in the range of 5 to 14, and is preferably a nonionic surfactant.
  The content ratio of the water-soluble polymer and the surfactant in the ink is in the range of 20: 1 to 2: 1.Is necessaryThe content is preferably in the range of 0.01 to 4% by weight with respect to the total amount of ink.
[0017]
The self-dispersible pigment in the ink is preferably carbon black.
It is desirable that the ink further contains a low molecular alcohol or urea.
[0018]
In the ink jet recording method of the present invention, it is desirable that one or more liquid compositions be adhered to a recording medium prior to printing with the ink jet recording ink or simultaneously with printing. At this time, the liquid composition preferably contains a surfactant, and the surface tension of the liquid composition is preferably 20 to 40 mN / m. The liquid composition preferably contains a colorant, and the colorant is preferably a dye.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
<Inkjet recording ink>
The ink of the present invention will be described separately for its constituent components, physical properties, and preparation thereof.
[0020]
[Components of ink]
The ink of the present invention preferably contains at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant, and further contains at least one kind of low molecular alcohol or urea. In addition, other additives such as pH adjusters, hydrotropic agents, chelating agents, inclusion compounds, oxidizing agents, antioxidants, reducing agents, enzymes, bactericides, antifoaming agents, abrasives, etc. are added as necessary. can do.
[0021]
(Self-dispersible pigment)
In the ink of the present invention, the pigment used is a pigment that does not contain a so-called polymer dispersant and can be dispersed in a solvent by itself. In general, a self-dispersible pigment has a hydrophilic functional group on its surface.
In the present invention, whether or not a pigment is “self-dispersible” is confirmed by the following self-dispersibility test.
[0022]
・ Self-dispersibility test
Add the pigment to be measured in water, disperse it without a dispersant using an ultrasonic homogenizer, nanomizer, microfluidizer, ball mill, etc., and dilute with water so that the initial pigment concentration is about 5%. A dispersion is prepared. The initial pigment concentration and 100 g of the dispersion are placed in a 40 mm diameter glass bottle and allowed to stand for 1 day, and then the pigment concentration in the upper layer portion is measured. When the ratio of the pigment concentration after standing for 1 day to the initial pigment concentration (hereinafter referred to as “self-dispersibility index”) is 98% or more, it was evaluated as “self-dispersibility”.
[0023]
At this time, the method for measuring the pigment concentration is not particularly limited, and any method such as a method of measuring the solid content by drying a sample or a method of obtaining the transmittance by diluting to an appropriate concentration may be used. If there is a method of obtaining accurately, it is of course possible to use that method.
[0024]
The hydrophilic functional group possessed by the self-dispersing pigment may be any nonionic, anionic or cationic hydrophilic functional group, particularly a carboxyl group, a hydroxyl group, a sulfonic acid group, or a phosphoric acid group. Alternatively, a combination of two or more is preferable, and among them, a carboxyl group alone or a combination of two or more containing a carboxyl group is more preferable. When it has a carboxyl group, a sulfonic acid group, or a phosphoric acid group, it can be used as it is in the free acid state, but a case where a part or all of them form a salt is advantageous and preferable in terms of dispersibility. As the substance forming the salt, various basic substances can be used, but an alkali metal, ammonia, or an organic onium compound alone or a combination of two or more thereof is preferable.
[0025]
The number of hydrophilic functional groups on the pigment surface differs depending on the type of hydrophilic functional group and the type of substance that forms the salt if a salt is formed. When is -COONa, 0.8-4 mmol / g is preferable.
[0026]
As a pigment into which a hydrophilic functional group is introduced, both inorganic and organic pigments can be used. As the black pigment, carbon black pigments such as furnace black, lamp black, acetylene black, channel black and the like are preferable. , Raven 1080ULTRA, Raven 1060 ULTRA, Raven 790 ULTRA, Raven 780 ULTRA, Raven 760 ULTRA (made by Columbia), Regal 400R, Regal 330R, Regal 660R, Mogu L Black Pearls L, Black Pearls 1300, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (manufactured by Cabot Corporation), Color B1, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex35, PrintexU, PrintexV, Printex140U, Printex140V, Special No. 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No. 6 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be used, but are not limited thereto. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the black pigment.
[0027]
Examples of cyan pigments include C.I. I. Pigment Blue-1, C.I. I. Pigment Blue-2, C.I. I. Pigmet Blue-3, C.I. I. Pigmet Blue-15, C.I. I. Pigment Blue-15: 1, C.I. I. Pigment Blue-15: 3, C.I. I. Pigment Blue-15: 34, C.I. I. Pigment Blue-16, C.I. I. Pigment Blue-22, C.I. I. Pigment Blue-60 and the like, but are not limited thereto.
[0028]
Examples of magenta pigments include C.I. I. Pigment Red 5, C.I. I. Pigment Red 7, C.I. I. Pigment Red 12, C.I. I. Pigment Red 48, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 57, C.I. I. Pigment Red 112, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 146, C.I. I. Pigment Red 168, C.I. I. Pigment Red 184, C.I. I. Pigment Red 202 and the like, but are not limited thereto.
[0029]
Examples of yellow pigments include C.I. I. Pigment Yellow-1, C.I. I. Pigment Yellow-2, C.I. I. Pigment Yellow-3, C.I. I. Pigment Yellow-12, C.I. I. Pigment Yellow-13, C.I. I. Pigment Yellow-14, C.I. I. Pigment Yellow-16, C.I. I. Pigment Yellow-17, C.I. I. Pigment Yellow-73, C.I. I. Pigment Yellow-74, C.I. I. Pigment Yellow-75, C.I. I. Pigment Yellow-83, C.I. I. Pigment Yellow-93, C.I. I. Pigment Yellow-95, C.I. I. Pigment Yellow-97, C.I. I. Pigment Yellow-98, C.I. I. Pigment Yellow-114, C.I. I. Pigment Yellow-128, C.I. I. Pigment Yellow-129, C.I. I. Pigment Yellow-151, C.I. I. Pigment Yellow-154 and the like, but are not limited thereto.
[0030]
In addition, for the present invention, a newly synthesized pigment may be used, or two or more pigments may be mixed and used.
In addition to the three primary color pigments of black and cyan, magenta, and yellow, specific color pigments such as red, green, blue, brown, and white, metallic luster pigments such as gold and silver, colorless extender pigments, and plastic pigments are used. May be. A particularly preferable pigment is carbon black.
[0031]
For these pigments, a known method or any of the newly invented methods can be used as a method for introducing a hydrophilic functional group onto the surface of the pigment. For example, oxidation treatment with oxidizing agents (eg nitric acid, permanganate, dichromate, hypochlorite, ammonium persulfate, hydrogen peroxide, ozone, etc.), treatment with coupling agents such as silane compounds, polymer grafting In addition to known methods such as chemical treatment and plasma treatment, newly developed methods can also be used, and these methods may be combined.
[0032]
It is desirable to purify the obtained pigment with the hydrophilic functional group introduced by removing impurities such as the remaining oxidant, other inorganic impurities, and organic impurities. In particular, it is desirable that calcium, iron, and silicon in the ink be 10 ppm or less, preferably 5 ppm or less, respectively. In the present invention, the content of these inorganic impurities was measured by a high frequency inductively coupled plasma emission spectrometry. These impurities can be removed, for example, by washing with water, a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange method or the like, or an adsorption method using activated carbon, zeolite or the like alone or in combination.
[0033]
As the self-dispersible pigment into which these hydrophilic functional groups have been introduced, commercially available self-dispersible hydrophilic treated pigments can be used in addition to those newly prepared for the present invention. Examples of commercially available self-dispersible hydrophilic treatment pigments include MICROJET BLACK CW-1 (manufactured by Orient Chemical Co., Ltd.), CAB-O-JET200 (manufactured by Cabot Corporation), CAB-O-JET300 (manufactured by Cabot Corporation). Etc. All of these commercially available self-dispersible hydrophilic pigments have a self-dispersibility index of 100%.
It is preferable to reduce the number of coarse particles in advance in the pigment dispersion by a method such as dispersion treatment, centrifugation, or filtration.
[0034]
The self-dispersible pigment is generally used in the range of 0.5 to 20 wt%, preferably 2 to 10 wt%, based on the total weight of the ink. An increase in the pigment content is not preferable because clogging is likely to occur at the nozzle tip and the scratch resistance of the image is also deteriorated. On the other hand, if it is 0.5 wt% or less, it is difficult to obtain an effective optical density.
[0035]
The number average particle diameter of the dispersed particles of the pigment in the ink must be in the range of 10 to 60 nm, preferably 15 to 50 nm, and more preferably 20 to 50 nm. If the number average particle diameter is less than 10 nm, the viscosity of the ink tends to increase and clogging tends to occur. On the other hand, if it exceeds 60 nm, the reliability of the ink tends to decrease.
[0036]
In addition, the particle size distribution mv / mn represented by the ratio of the volume average particle size mv and the number average particle size mn of the dispersed particles of the pigment in the ink is preferably 3 or less, more preferably 2.2 or less. It is. When the particle size distribution becomes wide, the permeation rate becomes slow and the scratch resistance tends to decrease. In particular, when a hydrophilic carbon black is used as a self-dispersible pigment, it is desirable that the pigment is 2.2 or less in view of scratch resistance of an image. The particle size distribution mv / mn is 1 in monodispersion and ideally approaches this, but in reality it is difficult to achieve a monodispersed state with particle size distribution mv / mn = 1. , 1.1 or more.
[0037]
In the present invention, the particle diameter of the dispersed particles of the pigment in the ink is determined by using a Microtrac UPA particle size analyzer 9340 (manufactured by Leeds & Northrup) and an ink in which the pigment to be measured is dispersed (hereinafter, “measured” Ink ") was measured without dilution. As parameters input at the time of measurement, the viscosity of the ink to be measured was input as the viscosity, and the density of the pigment was input as the density of the dispersed particles. The density of the latter is, for example, 1.8 g / cm in the case of a pigment obtained by hydrophilizing carbon black.²It was.
[0038]
Preferably, among the dispersed particles of the pigment contained per liter of ink, the number of particles having a particle diameter of 0.5 μm or more is 7.5 × 10^TenOr less. For the number of dispersed particles of 0.5 μm or more, it is preferable to use Accumizer ™ 770 Optical Particle Sizer (manufactured by Particle Sizing Systems) as a measuring device. This apparatus detects particles passing through a measuring unit by an optical method. For the measurement, 2 μl of the ink to be measured is put in a measurement cell, and the value converted into the value in 1 liter is used according to the predetermined measuring method of the measuring apparatus.
[0039]
(water)
The water used in the ink of the present invention is not particularly limited, but it is preferable to use ion exchange water, ultrapure water, distilled water, or ultrafiltered water in order to prevent impurities from being mixed.
[0040]
(Water-soluble organic solvent)
As the water-soluble organic solvent used in the ink of the present invention, polyhydric alcohols and derivatives thereof such as alkyl ethers can be used as those capable of preventing solidification of the ink and adjusting the viscosity. For example, glycerin, diethylene glycol, (2 (2 butoxyethoxy) ethanol), diethylene glycol phenyl ether, propylene glycol, propylene glycol monomethyl ether, butylene glycol, triethylene glycol, thiodiglycol, hexylene glycol, ethylene glycol methyl ether, diethylene glycol methyl Ether, pentanediol, hexanetriol, trimethylolpropane and the like. You may use these individually or in mixture of 2 or more types.
[0041]
Other components include alcohols such as hexyl alcohol and benzyl alcohol, amides such as dimethylformamide and dimethylacetamide, ketones such as acetone and diacetone alcohol, ketoalcohols, triethanolamine, diethanolamine, pyrrolidone, and N-methyl. High-boiling nitrogen-containing solvents such as 2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone, sulfur-containing solvents such as dimethyl sulfoxide, diethyl sulfoxide, sulfolane and thiodiethanol, glucose, maltose, amylose ( Dextrin), cellulose, saccharides such as sodium alginate and derivatives thereof, gum arabic and the like can be used, but are not limited thereto.
[0042]
Among these water-soluble organic solvents, a solvent selected from ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, thiodiethanol, propylene glycol, and dipropylene glycol is most preferable because of its high compatibility with water-soluble polymers.
[0043]
These water-soluble organic solvents can be used alone or in combination of two or more. The content of the water-soluble organic solvent is preferably 1 to 50% by weight with respect to the total ink weight. If it is less than 1% by weight, the moisturizing action may not be obtained. On the other hand, if it exceeds 50% by weight, ejection failure may be induced due to an increase in ink viscosity.
[0044]
(Water-soluble polymer)
The water-soluble polymer used in the ink of the present invention may be any of natural, semi-synthetic and synthetic water-soluble polymers. Further, it may be in the form of an aqueous polymer colloid (polymer emulsion).
Examples of the natural water-soluble polymers include starch such as candied starch, potato starch, tapioca starch, wheat starch, corn starch, mannan such as konjac, seaweed such as fungi, galactan, sodium alginate, trorooy, tragacanth gum And mucous substances such as gum arabic, dextran and levan, and proteins such as glue, gelatin, casein and collagen.
[0045]
Examples of the semi-synthetic water-soluble polymer include celluloses such as viscose, methyl cellulose, ethyl cellulose, hydroxy cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, soluble starch, carboxymethyl starch, dialdehyde starch, and hydroxymethyl. Examples thereof include starches such as starch, starch acetate, dextrin, and cyclodextrin.
[0046]
As the copolymer in the synthetic water-soluble polymer,
(1) Hydrophobic part and SO_ThreeA homopolymer of a hydrophilic monomer component comprising a hydrophilic part having an H group, or a salt thereof
(2) Hydrophobic monomer component and SO_ThreeCopolymer or salt thereof with hydrophilic monomer component having H group
(3) A polymer obtained by hydrophilizing a homopolymer of a hydrophobic monomer component or a copolymer of two or more hydrophobic monomer components by sulfonation or a salt thereof
(4) Hydrophobic part and H_ThreePO_FourHomopolymer of a hydrophilic monomer component comprising a hydrophilic part having a group, or a salt thereof
(5) Hydrophobic monomer component and H_ThreePO_FourCopolymer or salt thereof with hydrophilic monomer component having a group
(6) A homopolymer of a hydrophilic monomer component comprising a hydrophobic part and a hydrophilic part having a COOH group, or a salt thereof
(7) A copolymer of a hydrophobic monomer component and a hydrophilic monomer component having a COOH group or a salt thereof
Etc. In addition, other components can be copolymerized as necessary. Furthermore, these can also be used together.
[0047]
The copolymer may have any structure such as random, graft or block. These salts are preferably an alkali metal, ammonia, or an organic onium compound alone or in combination of two or more, but are not limited thereto.
[0048]
SO_ThreeExamples of the hydrophilic monomer component having an H group include styrene sulfonic acid, styrene sulfonic acid derivative, benzene sulfonic acid, benzene sulfonic acid derivative, naphthalene sulfonic acid, naphthalene sulfonic acid derivative, toluene sulfonic acid, toluene sulfonic acid derivative, vinyl sulfonic acid. And vinyl sulfonic acid derivatives.
[0049]
H_ThreePO_FourExamples of the hydrophilic monomer component having a group include higher alkyl phosphate salts and phosphate esters of higher alcohol ethylene oxide adducts.
Examples of the hydrophilic monomer component having a COOH group include α, β-ethylenically unsaturated carboxylic acid and its aliphatic alcohol ester, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itacon Examples thereof include acids, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, and the like.
Hydrophobic monomer components include styrene, styrene derivatives, vinyl toluene, vinyl toluene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, butadiene, butadiene derivatives, isoprene, isoprene derivatives, ethylene, ethylene derivatives, propylene, propylene derivatives, alkyl alkyls Examples thereof include esters and alkyl esters of methacrylic acid.
[0050]
Examples of other components that can be copolymerized include acrylamide, acrylamide derivatives, dimethylaminoethyl methacrylate, ethoxyethyl methacrylate, butoxyethyl methacrylate, ethoxytriethylene methacrylate, vinyl pyrrolidone, vinyl pyridine, alkyl ether, methoxypolyethylene glycol methacrylate, and polyethylene glycol methacrylate. Examples thereof include components containing polyoxyethylene such as hydroxymethyl methacrylate, hydroxyethyl methacrylate, and components containing hydroxyl groups such as vinyl alcohol.
In addition to the above, a condensation polymer (polyester condensation polymer) of an unsaturated carboxylic acid and an alcohol or glycol can be used as a hydrophobic component, and a hydrophilic monomer component can be added to form a water-soluble polymer by addition polymerization. .
[0051]
The monomer ratio between the hydrophobic unit and the hydrophilic unit of these water-soluble polymers is preferably 30:70 to 60:40. If the hydrophobic unit decreases from 30:70, the hydrophilicity becomes strong and the optical density may not be kept high. On the other hand, if the hydrophobic unit is higher than 60:40, it may be difficult to dissolve in water.
[0052]
Furthermore, the synthetic water-soluble polymer may be a synthetic product obtained by adding ethylene oxide to glycerin, diglycerin or the like. Examples of the single composition synthetic polymer include polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, and polypropylene glycol.
[0053]
A so-called polymeric surfactant may be used as the synthetic water-soluble polymer. Examples of the polymer surfactant include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Examples thereof include silicone surfactants such as ethylene / polyoxypropylene block copolymers, polyoxyethylene sorbitan fatty acid esters and polysiloxane polyoxyethylene adducts, and fluorine surfactants such as oxyethylene perfluoroalkyl ether. However, it is not limited to these.
[0054]
Examples of the polymer colloid include acrylic resin emulsion, vinyl acetate resin emulsion, urethane resin emulsion, acrylic-styrene resin emulsion, butadiene resin emulsion, styrene resin emulsion, polyester resin emulsion, and silicone resin emulsion. , Fluorine resin emulsion, acrylic silicone resin emulsion, and the like.
These water-soluble polymers may be used alone or in combination of two or more.
[0055]
  The molecular weight of the water-soluble polymer in the present invention is in the range of 1000 to 20000 on a weight average.Need to bePreferably, it is the range of 2000-15000. If the weight average molecular weight is less than 1000, high print quality can be obtained.Absent.On the other hand, if the weight average molecular weight exceeds 20,000, clogging due to thickening on the nozzle surface and injection failure may occur.Mae.As a measuring method of the weight average molecular weight, a light scattering method, an X-ray small angle scattering method, a sedimentation equilibrium method, a diffusion method, an ultracentrifugation method, various chromatographies, or a value in terms of polyethylene glycol measured by, for example, the GPC method is used. Can do.
[0056]
In the present invention, the content of the water-soluble polymer is preferably in the range of 0.01 to 4% by weight, more preferably in the range of 0.03 to 3% by weight, based on the total amount of the ink. If it is less than 0.01% by weight, the effect of adding a water-soluble polymer cannot be obtained. On the other hand, when it exceeds 4% by weight, reliability such as dispersion stability and clogging is deteriorated.
[0057]
  In the present invention, the content ratio of the water-soluble polymer and the surfactant is within the range of 20: 1 to 2: 1.Need to be, 20: 1 to 5: 1And preferThat's right. If the ratio of water-soluble polymer exceeds 20: 1, the reliability of the ink deteriorates.End up.On the other hand, when the ratio of the surfactant is higher than 2: 1, image quality deterioration is caused.Rub.Furthermore, in the present invention, the ratio of the self-dispersible pigment and the water-soluble polymer is preferably in the range of 1: 1 to 10: 0.1, and preferably 2: 1 to 10: 0.3. It is more preferable to be within the range. When the ratio of the water-soluble polymer is increased, the reliability of the ink may be deteriorated.
[0058]
The HLB of the water-soluble polymer is preferably in the range of 5-16, more preferably in the range of 5-14. If the HLB is lower than 5, it may not be soluble in water. On the other hand, if the HLB exceeds 16, the hydrophilicity becomes too high and the optical density may not be kept high.
[0059]
Various methods have been proposed for the measurement and calculation of HLB, and there are slight differences in the values obtained by the methods. Therefore, in the present invention, values calculated based on the method proposed by Davies in 1957 were used (new surfactant introduction, Takehiko Fujimoto, Sanyo Chemical Industries, Ltd., page 133, page 2). Chapter 6). In particular, the HLB calculation method in the case of a polymer polymer is divided into a hydrophilic part and a hydrophobic part, and the HLB of each part is calculated by the following (formula 1). Next, the value obtained by weighted averaging the respective HLB values using the following (Formula 2) was defined as the polymer polymer HLB.
[0060]
[Expression 1]

[0061]
In the above formula, HLBx represents the HLB of each hydrophilic part or each hydrophobic part, and Wx represents the weight of each hydrophilic part or each hydrophobic part. The number of hydrophilic groups is positive, and the number of hydrophobic groups is negative.
[0062]
Among these water-soluble polymers, particularly preferred are nonionic water-soluble polymers and —COO.^-M⁺An anionic water-soluble polymer having a group.
Examples of nonionic water-soluble polymers include nonionic polymer surfactants, polyethylene glycol, and polypropylene glycol. -COO^-M⁺Examples of the anionic water-soluble polymer having a group include acrylic acid copolymers and methacrylic acid copolymers.
[0063]
The water-soluble polymer is preferably one having a surface active action and capable of bringing the ink surface tension within a range of 35 to 50 mN / m when added alone to the ink. Examples of the water-soluble polymer having such a function include nonionic and anionic water-soluble polymers, and examples of the nonionic water-soluble polymer include polyoxyethylene / polyoxypropylene block copolymers, polypropylene glycol, and the like. Is mentioned. Examples of the anionic water-soluble polymer include styrene / acrylic acid copolymer, styrene / methacrylic acid copolymer, n-butyl methacrylate / acrylic acid copolymer, n-butyl methacrylate / methacrylic acid copolymer, 2- Examples thereof include ethylhexyl methacrylate / acrylic acid copolymer and 2-ethylhexyl methacrylate / methacrylic acid copolymer.
[0064]
(Surfactant)
The ink of the present invention contains various known surfactants in order to shorten the drying time during printing. Examples of the surfactant include various known surfactants, and any of nonionic, anionic, cationic or amphoteric surfactants may be used. The hydrophilic functional group of the self-dispersing pigment and the ionicity of the water-soluble polymer may be used. In order to suppress this interaction, the same kind of ionicity or nonionicity is preferable, and a nonionic surfactant is particularly preferable. The surfactant is used in combination with the water-soluble polymer.
[0065]
Nonionic surfactants include, for example, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene / Examples include polyoxypropylene block copolymers, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylolamides, acetylene glycol derivatives (Surfinol), and the like.
[0066]
Examples of anionic surfactants include alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl naphthalene sulfonate formalin condensate, higher fatty acid salt, higher fatty acid ester sulfate ester salt, higher fatty acid ester sulfonate salt, higher alcohol Sulfate esters and sulfonates of ethers, alkyl carboxylates of higher alkyl sulfonamides, sulfosuccinates and their ester salts, alkyl phosphites, alkyl phosphates, alkyl phosphonates and their esters, higher alcohols Examples include phosphate ester salts.
[0067]
Examples of the cationic surfactant include primary, secondary and tertiary amine salts and quaternary ammonium salts.
Examples of amphoteric surfactants include betaine, sulfobetaine, sulfate betaine and the like.
[0068]
In addition, silicone surfactants such as polysiloxane polyoxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylic acid, perfluoroalkyl sulfonic acid, and oxyethylene perfluoroalkyl ether, natural or biosurfactant lecithin , Spikrispolic acid, rhamnolipid, saponin, cholate and the like.
[0069]
  These surfactants may be used alone or in combination of two or more. The molecular weight of these surfactants should be in the range of 150-1000.is necessary. There is substantially no surfactant with a molecular weight of less than 150. On the other hand, when the molecular weight is 1000 to 20,000, it can be used as a water-soluble polymer.
  The surfactant content in the present invention is preferably in the range of 0.01 to 1.5% by weight, more preferably in the range of 0.01 to 1% by weight, based on the total amount of the ink. If it is less than 0.01% by weight, the effect of adding the surfactant cannot be obtained. On the other hand, if it exceeds 1.5% by weight, the penetrating action on the recording medium may become too high and the image quality may be deteriorated.
[0070]
In this invention, it is preferable that it is the range of 5-14 as HLB of surfactant, More preferably, it is the range of 5-12. If the HLB is lower than 5, it may not be sufficiently soluble in water. On the other hand, if the HLB exceeds 14, the hydrophilicity becomes too high and the optical density may not be kept high. It is desirable that the surfactant HLB is close to the water-soluble polymer HLB. The difference between the two HLBs is preferably within ± 5, more preferably within 2.5.
[0071]
(Low molecular alcohol and urea)
The ink of the present invention preferably contains a low molecular alcohol and / or urea in the ink in order to improve reliability such as dispersion stability and prevention of clogging. The low molecular alcohol and urea may be used alone or in combination. Can be used according to the purpose.
[0072]
As low molecular weight alcohol, methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-pen Examples thereof include alcohols having 10 or less carbon atoms such as butanol, allyl alcohol, propargyl alcohol, benzyl alcohol, and cyclohexanol.
[0073]
The content of the low molecular alcohol is in the range of 0.1 to 10% by weight, preferably in the range of 0.5 to 5% by weight, based on the total amount of the ink. If the amount is 0.1% by weight or less, the ink reliability improvement effect due to the addition of the low molecular alcohol cannot be obtained. On the other hand, if it exceeds 10% by weight, the deterioration of bleeding on the paper may progress and the print quality may be lowered.
[0074]
The urea content is preferably 1 to 10% by weight, more preferably 2 to 7% by weight, based on the total amount of ink. If it is less than 1% by weight, the effect of improving the reliability of the ink by adding urea cannot be obtained. On the other hand, if it exceeds 10% by weight, it may be deposited on the paper, resulting in irregularities in the image, which may reduce the print quality.
[0075]
(Various additives)
If necessary, other additives can be added to the ink of the present invention. Examples of the other additives include pH adjusters, hydrotropic agents, chelating agents, inclusion compounds, oxidizing agents, antioxidants, reducing agents, enzymes, bactericides, antifoaming agents, abrasives, and the like. .
[0076]
As a pH adjuster for adjusting pH as required, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium sulfate, acetate, lactate, benzoate, triethanolamine, ammonia, 2-amino 2-methyl-1-propanol (AMP), alkalis such as ammonium phosphate, sodium phosphate, lithium phosphate, and organic substances such as acetic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, propionic acid, and P-toluenesulfonic acid An acid or an inorganic acid is mentioned. Other examples include general pH buffers and good buffers. However, the pH adjuster is not limited to these. The pH of the ink of the present invention will be described later.
[0077]
Examples of the hydrotropic agent include carboxylates such as sodium butyrate and sodium salicylate, aromatic sulfonates such as sodium toluenesulfonate, lower alcohols such as ethyl alcohol, urea, and acetamide.
Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), ethylenediamine-di (o-hydroxyphenylacetic acid) (EDDDHA), nitrilotriacetic acid (NTA), dihydroxyethylglycine (DHEG), trans- 1,2-cyclohexanediaminetetraacetic acid (CyDTA), diethylenetriamine-N, N, N ′, N ″, N ″ -pentaacetic acid (DTPA), glycol ether diamine-N, N, N ′, N′-tetraacetic acid ( GEDTA) and the like.
[0078]
Examples of the inclusion compound include thiourea, desoxycholic acid, bis- (N, N′-tetramethylenebenzidine), cyclophane, and the like.
In addition, conventionally known oxidizing agents, antioxidants, reducing agents, enzymes, bactericides, antifoaming agents, abrasives, and the like can be used without problems.
[0079]
[Ink physical properties]
The ink of the present invention satisfies the following conditions (b) to (e) as physical properties.
(B) The surface tension is in the range of 30 to 50 mN / m.
(C) Viscosity in the range of 1.5 to 5.0 mPa · s
(D) Conductivity is in the range of 0.001 to 0.4 S / m
(E) pH is in the range of 6-11
Hereinafter, each physical property will be described.
[0080]
(B) Surface tension
The surface tension of the ink of the present invention is adjusted to a range of 30 to 50 mN / m. If the surface tension is lower than this range, when printing on so-called plain paper as a recording medium, bleeding tends to occur and a high resolution image cannot be obtained. On the other hand, when the surface tension is higher than this range, the penetration into the recording medium is delayed, and the drying time of the image becomes longer, which is a problem. The surface tension of the ink of the present invention is preferably in the range of 30 to 45 mN / m. When carbon black is used as a self-dispersible pigment, adjustment to the desired range may cause bleeding. This is particularly desirable in that a high-resolution image can be obtained.
[0081]
The surface tension of the ink can be adjusted by appropriately controlling the kind of water-soluble polymer and / or surfactant described above, the amount of addition, and the like.
In the present invention, the surface tension is a value measured using a Wilhelmy surface tension meter in an environment of 23 ° C. and 55% RH.
[0082]
(C) Viscosity
The viscosity of the ink of the present invention must be adjusted to a range of 1.5 to 5.0 mPa · s, preferably 1.5 to 3.5 mPa · s, more preferably 1.7. It is adjusted to a range of ˜3.5 mPa · s. When the viscosity is less than 1.5 mPa · s, the storage stability of the ink is lowered. On the other hand, when the viscosity is greater than 5.0 mPa · s, the ink ejection force is reduced, and problems such as difficulty in recovery when the ejection nozzle is clogged occur. In particular, when carbon black subjected to a hydrophilic treatment is used as a self-dispersible pigment, it is desirable that the above range is more preferable from the viewpoint of ink ejection.
[0083]
The viscosity of the ink can be adjusted by the type and addition amount of the water-soluble organic solvent, the type of water-soluble polymer, the molecular weight, the addition amount, and the like.
In the present invention, the viscosity is a value measured using Rheomat 115 (manufactured by Contraves) as a measuring device. The measurement was performed by placing the ink to be measured in a measurement container and mounting the ink to the measurement device by a predetermined method in the measurement device. Measurement temperature is 23 ° C, shear rate is 1400s^-1It was.
[0084]
(D) Conductivity
The conductivity of the ink of the present invention must be adjusted in the range of 0.001 to 0.4 S / m, and preferably in the range of 0.005 to 0.3 S / m. When the electrical conductivity is less than 0.001 S / m, it becomes difficult to recover the ejection when printing is stopped and left for a long time, and when it exceeds 0.4 S / m, the storage stability of the ink tends to deteriorate. In particular, when hydrophilic carbon black is used as a self-dispersible pigment, it is desirable that the range be 0.005 to 0.3 S / m from the viewpoint of ejection recovery after standing for a long time.
[0085]
The conductivity of the ink can be adjusted by the amount of water, the type and amount of the water-soluble organic solvent, the type and amount of the electrolyte substance, and other compositions.
In the present invention, the conductivity is a value measured using a conductivity meter AOL-40-3302 (manufactured by DKK) as a measuring device in an environment of 23 ° C.
[0086]
(E) pH
The pH of the ink of the present invention must be adjusted to the range of 6.0 to 11.0, and is preferably adjusted to the range of 7.5 to 9.0. If the pH is less than 6.0, the ink is likely to be clogged, and if it exceeds 11.0, the head constituting member is easily corroded or dissolved. In particular, when carbon black subjected to a hydrophilic treatment is used as a self-dispersible pigment, it is desirable that the range is 6.0 to 9.5 in terms of nozzle clogging.
[0087]
The pH of the ink can be adjusted by adding various acids, various salts, pH adjusting agents, buffers or the like.
In the present invention, the pH is a value measured using a glass pH electrode in an environment of 23 ° C.
[0088]
[Preparation of ink]
The ink of the present invention can be prepared by mixing, dissolving and / or dispersing the above-described constituent components. In particular, in order to adjust the self-dispersible pigment to the number average particle size of the predetermined dispersed particles in the present invention, the pigment is an aqueous medium (a liquid composition mainly composed of water, water-soluble organic solvent, water-soluble It is preferable to provide at least one step of dispersing in a polymer (which may contain a polymer, a surfactant, etc.).
[0089]
In the step of dispersing the pigment in the aqueous medium, various agitation and dispersion devices can be used, but if a disperser using a so-called dispersion medium such as a ball or bead of glass, ceramic, metal, or the like is used, the pigment is pulverized, In many cases, inorganic impurities are mixed in a large amount in the pigment dispersion or ink due to abrasion of the dispersion medium and the dispersion container in the dispersion process. Therefore, it is desirable to use a distributed device that does not use distributed media. In particular, the dispersion is preferably carried out by at least one device selected from the group consisting of an ultrasonic homogenizer and a high-pressure homogenizer. When dispersing with an ultrasonic homogenizer, it is desirable to carry out defoaming and degassing by evacuation, heating, a commercially available defoaming / degassing apparatus, etc. before dispersing. When a dispersion apparatus using a dispersion medium is used, the mixed inorganic impurities are removed as necessary.
[0090]
<Inkjet recording method>
The inkjet recording method of the present invention is characterized in that the ink of the present invention described above is printed on a recording medium so that the drop amount is 5 to 25 pl. Of course, in the present invention, “printing” is a concept that includes not only recording characters but also recording all images such as characters, pictures, symbols, patterns, and photographs on a recording medium.
[0091]
As an ink jet recording method, a so-called charge control method for discharging ink using electrostatic attraction, a so-called pressure pulse method for discharging ink using vibration pressure of a piezoelectric element, and forming bubbles by heating the ink, A so-called thermal ink jet method for forming ink droplets by using the pressure generated by the growth can be exemplified. Among these, the thermal ink jet method is particularly preferable in that a full color image can be provided in a small size and at a low cost.
[0092]
In the present invention, it is essential that the amount of ink discharged during printing is 5 to 25 pl, and more preferably 5 to 20 pl. If the ink drop amount is lower than 5 pl, the dispersed particles of the pigment are likely to be clogged in the flow path, so that it is difficult to use. On the other hand, when the ink drop amount exceeds 25 pl, the image quality deteriorates rapidly. In the present invention, only when the ink of the present invention is used and the ink drop amount is 5 to 25 pl, high image quality, shortening of the drying time and ensuring of reliability can be ensured.
[0093]
Although the ink of the present invention can be recorded alone by the ink jet recording method of the present invention, it is preferable to attach one or more kinds of liquid compositions to the image-receiving portion and / or its adjacent portion. The liquid composition is attached prior to or simultaneously with printing with ink. By adhering the liquid composition to the recording medium, effects such as shortening the drying time, increasing the optical density, preventing color mixing due to contact with multicolor ink, and improving the image fixing strength are exhibited.
[0094]
The liquid composition is mainly composed of water and a water-soluble organic solvent, and may contain a colorant, a surfactant, a fixing accelerator, and other additives as necessary.
As water, water-soluble organic solvent, and surfactant in the liquid composition, known substances can be used, and those described for the ink of the present invention can be used without any problem. When a colorant is contained, the colorant may be a dye, a pigment, or a mixture thereof, but a dye is preferred. Known dyes and pigments can be used.
[0095]
As the fixing accelerator in the liquid composition, various water-soluble polymers and polymer emulsions can be used. As the water-soluble polymer or polymer emulsion, for example, acrylic polymer, polyester, polyvinyl alcohol, polyvinyl pyrrolidone, polyurethane and the like are preferable. A combination in which the pigment in the ink of the present invention has an anionic hydrophilic functional group and the fixing accelerator is a water-soluble polymer having a cationic group is particularly preferable.
[0096]
Examples of the water-soluble polymer having a cationic group include monomers having a cationic functional group, such as N, N-dimethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminomethacrylamide, N , N-dimethylaminoacrylamide, vinyl pyridine, vinyl pyrrolidone, or a copolymer or homopolymer containing at least, polyethyleneimine, polyamines, polyamides and the like are preferable.
[0097]
Moreover, when the hydrophilic functional group which the pigment in the ink of this invention has consists of an anionic group at least, it is also preferable to contain an inorganic polyvalent cation as a fixing agent accelerator. As an inorganic polyvalent cation, for example, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, Fe³⁺, Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺Etc.
[0098]
The liquid composition preferably contains a surfactant from the viewpoint of image drying property. The surface tension of the liquid composition is preferably in the range of 20 to 40 mN / m.
[0099]
In the ink jet recording method of the present invention, an apparatus having a function of accelerating print fixing by heating a recording paper at 50 ° C. to 200 ° C. before or after printing with ink is used. You can also. In addition to direct printing on recording media such as plain paper, glossy paper, special paper, cloth, film, and OHP, printing is performed on an intermediate such as a drum or belt, and an ink image is printed on the surface of the intermediate. It may be transferred to a recording medium and printed after preparation.
[0100]
【Example】
[Preparation of pigment dispersion]
(Dispersion 1)
CAB-O-JET300 (manufactured by CABOT / 15.2% solid content, 100% self-dispersibility index) was centrifuged at 8000 rpm for 30 minutes and then diluted with pure water to obtain a pigment dispersion having a solid content of 10%. Body 1 was designated.
[0101]
(Dispersion 2)
A water-soluble polymer of styrene / methacrylic acid copolymer Na salt (monomer ratio 50/50, weight average molecular weight = 7000, calculated HLB = 14.1) was used as a dispersant for pigment dispersion.
[0102]
45 parts by weight of the above water-soluble polymer (10% solid content aqueous solution) and 210 parts by weight of ion-exchanged water are mixed, and 45 parts by weight of carbon black BPL (manufactured by CABOT, self-dispersibility index 0%) is mixed. The mixture was stirred for 30 minutes. Thereafter, dispersion was performed at 10,000 psi / 30 path with a microfluidizer. After dispersion, the pH was adjusted to 9 using 1N NaOH aqueous solution. Further, centrifugation was performed at 8000 rpm for 15 minutes with a centrifugal separator, and then passed through a 2 μm membrane filter. The obtained dispersion was diluted with pure water to obtain a pigment dispersion having a solid content of 10%, and Dispersion 2 was obtained.
[0103]
[Preparation of inkjet recording ink]
In accordance with Tables 1 and 2 below, each component of the ink excluding the pigment dispersion was added to 30 parts by weight of pure water and stirred for 30 minutes. The pigment dispersion was added to the obtained liquid, and pure water was further added so that the total amount was 100 parts by weight. Then, the particle size was adjusted by treating for 15 minutes with an ultrasonic homogenizer (300 W, 400 μA). Further, the ink was passed through a 2 μm membrane filter to prepare an ink jet recording ink.
[0104]
[Table 1]

[0105]
[Table 2]

[0106]
[Measurement of ink properties]
The following physical properties were measured for each of the inks of the obtained Examples and Comparative Examples. The results are shown in Table 3 below.
1) Viscosity
The viscosity of the ink was measured using Rheomatt 115 (manufactured by Contraves). Specifically, the measurement ink was placed in a measurement container and attached to the apparatus by a predetermined method in the apparatus. Measurement temperature is 23 ° C, shear rate is 1400s^-1Measured with
[0107]
2) Surface tension
The surface tension of the ink was measured using a Wilhelmy type surface tension meter. The measurement environment was measured at a temperature of 23 ° C. and a humidity of 55% RH.
[0108]
3) Conductivity
The conductivity of the ink was measured using a conductivity meter AOL-40-3302 (manufactured by DKK). The measurement temperature was measured at 23 ° C.
[0109]
4) pH
The pH of the ink was measured using a glass pH electrode. The measurement temperature was measured at 23 ° C.
[0110]
5) Dispersion particle size of pigment
The average particle size (dispersion particle size) of the pigment dispersed particles was measured without dilution using a Microtrac UPA particle size analyzer 9340 (Leeds & Northrup). As input parameters, the viscosity is ink viscosity, and the density of dispersed particles is 1.8 g / cm.²It was.
[0111]
[Print test]
Using each of the inks of the obtained Examples and Comparative Examples, a printing test was performed with a prototype ink jet printer in an environment of 23 ° C. and 55% RH. Two types of heads with different drop amounts, specifically, 800 dpi (drop amount of about 15 pl) and 400 dpi (drop amount of about 50 pl) were used. The paper used was FX-L paper (manufactured by Fuji Xerox Co., Ltd.) as typical plain paper. There are two types of printed images: solid patches (3 cm square) and 1 dot line. The following evaluation was performed about the obtained image.
[0112]
1) Optical density measurement
The solid patch portion one day after printing was measured using X-Rite 404 (manufactured by X-Rite).
[0113]
2) Print quality evaluation test
The 1-dot line portion was subjected to sensory evaluation based on the following criteria.
1: No bleeding
2: Slight bleeding is observed but acceptable
3: There is bleeding
4: There are beard-like blurs in many parts
[0114]
3) Drying time
The ink drying time was measured from the time immediately after printing until the ink liquid disappeared (visual determination) in the solid patch portion.
[0115]
[Ink reliability]
The following tests relating to the reliability of each of the inks obtained in Examples and Comparative Examples were performed. The results are shown in Table 3 below.
1) Stability test
50 g of each ink was sealed in a glass tube with a lid, and the acceleration test was performed for a total of 4 cycles, where 1 cycle was left in a 70 ° C. atmosphere for 4 hours and left in a −20 ° C. atmosphere for 4 hours. Take 5g sample before and after the test, 1μm mesh filter and effective filtration diameter 2.5cm²Using a glass holder under reduced pressure, the time required to filter the entire sample was measured and evaluated according to the following criteria.
[0116]
A: Increase in filter passage time after acceleration test is less than 20%
○: Increase in filter passage time after acceleration test is 20% or more and less than 50%
Δ: Increase in filter passage time after acceleration test is 50% or more and less than 100%
×: Increase in filter passage time after acceleration test is 100% or more
[0117]
2) Recovery test
Using the above-described printing apparatus with an 800 dpi head, after confirming that printing can be performed normally, the printing apparatus was left uncapped at 23 ° C. and 55% RH for one month. The vacuum recovery operation was repeated until normal printing was possible, and the number of times was recorded and evaluated according to the following criteria.
A: Normal printing from the beginning, or recovery in one time
○: Recovered 2 to 3 times
Δ: Recovered 4 to 5 times
×: Does not recover after 5 times
[0118]
[Table 3]

[0119]
【The invention's effect】
As described above, according to the ink jet recording method and ink jet recording ink of the present invention, an image can be clearly reproduced on plain paper and excellent print quality can be obtained. Further, it is possible to reduce the drying time having high-speed printability on plain paper. Furthermore, high reliability during storage and use can be achieved.
[0120]
Therefore, according to the present invention, even with plain paper such as report paper, copy paper, bond paper, and high-quality paper, and even recycled paper for which it is difficult to form a clear image, a short drying time and a clear image are obtained. An image can be formed. The present invention can be suitably applied to ink jet recording using a thermal ink jet method, a piezoelectric method, an ultrasonic wave, an electric field, and the like.

Claims (8)

An ink jet recording ink containing at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant and satisfying the following conditions (a) to ( h ): An ink jet recording method comprising printing on a recording medium so as to be 25 pl.
(A) The number average particle size of the dispersed particles of the pigment is in the range of 10 to 60 nm. (B) The surface tension is in the range of 30 to 50 mN / m. (C) The viscosity is 1.5 to 5.0 mPa · s. Range (d) Conductivity is in the range of 0.001 to 0.4 S / m (e) pH is in the range of 6 to 11
(F) The water-soluble polymer has a surface active action, and the weight average molecular weight is in the range of 1000 to 200000.
(G) The molecular weight of the surfactant ranges from 150 to 1000
(H) The content ratio of the water-soluble polymer to the surfactant in the ink is in the range of 20: 1 to 2: 1. The inkjet according to claim 1, wherein the water-soluble polymer is a nonionic water-soluble polymer selected from the group consisting of a polyoxyethylene / polyoxypropylene block copolymer and polypropylene glycol. Recording method. Water-soluble polymer is styrene / acrylic acid copolymer, styrene / methacrylic acid copolymer, n-butyl methacrylate / acrylic acid copolymer, n-butyl methacrylate / methacrylic acid copolymer, 2-ethylhexyl methacrylate. It is an anionic water-soluble polymer selected from the group consisting of: / acrylic acid copolymer and 2-ethylhexyl methacrylate / methacrylic acid copolymer. Inkjet recording method. The number average particle diameter of the dispersed particles of the pigment is in the range of 37.5 to 40.5 nm, the surface tension is in the range of 36.4 to 41 mN / m, and the viscosity is in the range of 1.99 to 2.12 mPa · s. The inkjet recording method according to any one of claims 1 to 3, wherein the pH is in the range of 7.6 to 7.8. An ink jet recording ink for use in the ink jet recording method according to any one of claims 1 to 4 , comprising at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer, and a surfactant. And the inkjet recording ink characterized by satisfying the following conditions (a) to ( f ).
(A) The number average particle size of the dispersed particles of the pigment is in the range of 10 to 60 nm. (B) The surface tension is in the range of 30 to 50 mN / m. (C) The viscosity is 1.5 to 5.0 mPa · s. Range (d) Conductivity is in the range of 0.001 to 0.4 S / m (e) pH is in the range of 6 to 11
(F) The water-soluble polymer has a surface active action, and the weight average molecular weight is in the range of 1000 to 200000.
(G) The molecular weight of the surfactant ranges from 150 to 1000
(H) The content ratio of the water-soluble polymer to the surfactant in the ink is in the range of 20: 1 to 2: 1. 6. The ink according to claim 5, wherein the water-soluble polymer is a nonionic water-soluble polymer selected from the group consisting of a polyoxyethylene / polyoxypropylene block copolymer and polypropylene glycol. . Water-soluble polymer is styrene / acrylic acid copolymer, styrene / methacrylic acid copolymer, n-butyl methacrylate / acrylic acid copolymer, n-butyl methacrylate / methacrylic acid copolymer, 2-ethylhexyl methacrylate. 7. An anionic water-soluble polymer selected from the group consisting of: an acrylic acid / acrylic acid copolymer and a 2-ethylhexyl methacrylate / methacrylic acid copolymer. ink. The number average particle diameter of the dispersed particles of the pigment is in the range of 37.5 to 40.5 nm, the surface tension is in the range of 36.4 to 41 mN / m, and the viscosity is in the range of 1.99 to 2.12 mPa · s. The ink according to claim 5, wherein the pH is in the range of 7.6 to 7.8.