JP2004189928A - Preparation method for pigment dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a pigment dispersion which contains fine colorant particles comprising a pigment whose surface is uniformly covered with a polymer shell with a desired thickness and which is used for preparing an inkjet ink giving an image excellent in transparency, glossiness, and scratch resistance. <P>SOLUTION: This method prepares the pigment dispersion which is used for the inkjet ink and in which the fine colorant particles prepared by covering the pigment with the polymer are dispersed. The fine colorant particles are prepared by causing the surface of the pigment to adsorb a compound having a hydrophilic part and a hydrophobic part to form a reaction field and then conducting polymerization to form the polymer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５６】
一般式（１）において、Ｒ¹は炭素原子数７〜２０の直鎖アルキル基、分岐アルキル基、または置換もしくは無置換の芳香族基を表し、例えば、上記Ａ項に記載のヘプチル基、オクチル基、ノニル基、デシル基、ドデシル基などの直鎖アルキル基、２−エチルヘキシル基などの分岐アルキル基、フェニル基、ノニルフェニル基、ナフチル基などの芳香族置換基などが挙げられる。
【００５７】
Ｒ²はラジカル重合可能な重合性基を有する置換基を表し、例えば、上記Ｃ項に記載のエチレン性不飽和基であるアクリレート基、メタクリレート基、マレイミド基等が挙げられる。Ｙ¹はスルホン酸、カルボン酸、またはそれらの塩を表す。
【００５８】
本発明に係る一般式（１）で表される化合物は、当業者が公知の方法で合成して得ることができる。また、市販品より容易に入手することができ、例えば、花王社製の「ラテムル Ｓ−１２０」、「ラテムル Ｓ−１２０Ａ」、「ラテムルＳ−１８０」、「ラテムル Ｓ−１８０Ａ」や、三洋化成工業社製の「エレミノール ＪＳ−２」等を挙げることができる。
【００５９】
【化２】

【００６０】
一般式（２）において、Ｒ³、Ｒ⁴は、上記一般式（１）のＲ¹、Ｒ²のそれぞれと同義である。Ｙ²は水素原子、スルホン酸もしくはそれらの塩、またはカルボン酸もしくはそれらの塩を表す。ＡＯはアルキレンオキサイドを表す。
【００６１】
本発明に係る一般式（２）で表される化合物は、当業者が公知の方法で合成して得ることができる。また、市販品より容易に入手することができ、例えば、旭電化工業社製の「アデカリアソープ ＮＥ−１０」、「アデカリアソープ ＮＥ−２０」、「アデカリアソープ ＮＥ−３０」等のＮＥシリーズ、「アデカリアソープ ＳＥ−１０Ｎ」、「アデカリアソープ ＳＥ−２０Ｎ」、「アデカリアソープ ＳＥ−３０Ｎ」等のＳＥシリーズ、第一工業製薬社製の「アクアロン ＲＮ−１０」、「アクアロン ＲＮ−２０」、「アクアロン ＲＮ−３０」、「アクアロン ＲＮ−５０」等のＲＮシリーズ、「アクアロン ＨＳ−０５」、「アクアロン ＨＳ−１０」、「アクアロン ＨＳ−２０」、「アクアロン ＨＳ−３０」等のＨＳシリーズ、あるいはアクアロン ＢＣシリーズ等を挙げることができる。
【００６２】
【化３】

【００６３】
一般式（３）において、Ｒ⁵、Ｒ⁶、Ｙ³及びＡＯは、一般式（１）のＲ¹、Ｒ²、Ｙ¹及び一般式（２）のＡＯのそれぞれと同義である。
【００６４】
本発明に係る一般式（３）で表される化合物は、当業者が公知の方法で合成して得ることができる。また、市販品より容易に入手することができ、例えば、第一工業製薬社製の「アクアロン ＫＨ−０５」、「アクアロン ＫＨ−１０」、「アクアロン ＫＨ−２０」等を挙げることができる。
【００６５】
上記一般式（２）及び（３）において、アルキレンオキサイド鎖（ＡＯ）の平均重合度ｎが、１〜１０であることが好ましく、例えば、上記の第一工業製薬社製の「アクアロン ＫＨ−０５」、「アクアロン ＫＨ−１０」、「アクアロンＨＳ−０５」、「アクアロン ＨＳ−１０」等を挙げることができる。
【００６６】
また、本発明においては、反応性乳化剤が、アニオン性であることが好ましく、例えば、上述の「アデカリアソープ ＳＥシリーズ」（旭電化工業社製）、「アクアロン ＨＳシリーズ」（第一工業製薬社製）、「ラテムル Ｓシリーズ」（花王社製）、「エレミノール ＪＳシリーズ」（三洋化成工業社製）等を挙げることができる。
【００６７】
これらのモノマーは、予め均一な混合液として、反応場に加えても良いし、組成を変更しながら、加えても良い。好ましくは、初めは疎水部のみのモノマーを主成分にしたモノマー液で顔料表面を重合し、後半に親水部を有するモノマーを疎水部のみに有するモノマーに混ぜて加え、顔料粒子の表面を親水化することが好ましい。
【００６８】
上記モノマーの重合に用いる重合開始剤としては、特に制限はなく、例えば、過酸化ベンゾイル、ジ−ｔ−ブチルペルオキシド、クメンヒドロペルオキシド、ｔ−ブチルペルオキシドもしくは２−エチルヘキサノエートの如き、各種の過酸化物；またはアゾビスイソブチロニトリルもしくはアゾビスイソバレロニトリルの如き、各種のアゾ化合物などを挙げることができる。
【００６９】
本発明においては、顔料粒子表面にポリマーがシェルとして被覆されているかを評価することが重要である。本発明においては、後述のごとく、個々の着色微粒子の粒子径が２００ｎｍ以下と非常に微小であるため、用いることのできる分析手法は、分解能の観点から限られる。このような目的に沿う分析手法としては、ＴＥＭやＴＯＦ−ＳＩＭＳなどが適用できる。ＴＥＭによりコア／シェル化した微粒子を観察する場合、カーボン支持膜上に分散液を塗布、乾燥させ観察することができる。ＴＥＭの観察像は、有機物であるポリマーの種類のみではコントラスト差が小さい場合があるため、コア／シェル化されているかどうかを評価するために、微粒子を、４酸化オスミウム、４酸化ルテニウム、クロロスルホン酸／酢酸ウラニル、硫化銀等を用いて染色することが好ましい。コアだけの微粒子を染色しそのＴＥＭ観察を行い、シェルを設けたものと比較する。さらに、シェルを設けた微粒子と設けていない微粒子を混合後、染色し、染色度合いの異なる微粒子の割合がシェルの有無に一致しているかの確認を行う。
【００７０】
ＴＯＦ−ＳＩＭＳような質量分析装置では、粒子表面にシェルを設けることで表面近傍の色材量がコアだけの時よりも減少していることを確認する。色材にシェルのポリマーに含有されていない元素がある場合、その元素をプローブとして色材含有量の少ないシェルが設けられたかを確認することができる。
【００７１】
そのような元素がない場合、適当な染色剤を用いてシェル中の色材含有量をシェルを設けていないものと比較することができる。例えば、コア／シェル粒子をエポキシ樹脂内に埋胞し、ミクロトームで超薄い切片を作製、染色を行うことでコア／シェル化をより明瞭に観察できる。上記のように、ポリマーや、色材にプローブとなりうる元素がある場合、ＴＯＦ−ＳＩＭＳやＴＥＭによってコア／シェルの組成、色材のコアとシェルへの分布量を見積もることもできる。
【００７２】
本発明においては、着色微粒子の体積平均粒径が、１０ｎｍ以上、２００ｎｍ以下であることが好ましい。
【００７３】
本発明に係るコア／シェル型の着色微粒子は、体積平均粒子径が５ｎｍ以下になると単位体積あたりの表面積が非常に大きくなるため、顔料をシェルポリマー中に封入する効果が小さくなる。一方、２００ｎｍを越えるほど大きな粒子では、ヘッドに詰まりやすく、またインク中での沈降が起き易く、停滞安定性が劣化する。従って着色微粒子の平均粒子径は５〜２００ｎｍであることが好ましく、１０〜１５０ｎｍがより好ましく、平均粒子径が１５０ｎｍを越えると、インクジェット用水性インクとした場合、光沢メディアに記録した画像では光沢感の劣化が起こり、トランスペアレンシーメディアに記録した画像では著しい透明感の劣化が起こる。また、着色微粒子の平均粒径が１０ｎｍ未満になると着色微粒子の安定性が悪くなり易く、インクの保存安定性が劣化し易くなる。１０〜１００ｎｍが最も好ましい。
【００７４】
体積平均粒子径は、動的光散乱法を利用して測定することができ、例えば、大塚電子製レーザー粒径解析システムや、マルバーン社製ゼータサイザーを用いて求める事が出来る。
【００７５】
次いで、本発明で用いることのできる顔料について説明する。
本発明で用いることのできる顔料としては、特に制限はなく、公知の顔料を用いることができるが、好ましくは有機顔料またはカーボンブラックであり、例えば、アゾレーキ、不溶性アゾ顔料、縮合アゾ顔料、キレートアゾ顔料等のアゾ顔料や、フタロシアニン顔料、ペリレン及びペリレン顔料、アントラキノン顔料、キナクリドン顔料、ジオキサンジン顔料、チオインジゴ顔料、イソインドリノン顔料、キノフタロニ顔料等の多環式顔料や、塩基性染料型レーキ、酸性染料型レーキ等の染料レーキや、ニトロ顔料、ニトロソ顔料、アニリンブラック、昼光蛍光顔料等の有機顔料、カーボンブラック等の無機顔料が挙げられるが、顔料（有機顔料）としては、アゾ顔料、キナクリドン顔料及びフタロシアニン顔料から選ばれる少なくとも１種であることが好ましい。
【００７６】
本発明で用いることのできる顔料としては以下に限定されるものではないが、特に好ましい具体例として、カーボンブラック顔料としては三菱化成社製Ｎｏ．２３００、Ｎｏ．９００、ＭＣＦ−８８、Ｎｏ．３３、Ｎｏ．４０、Ｎｏ．４５、Ｎｏ．５２、ＭＡ７、ＭＡ８、ＭＡ１００、Ｎｏ．２２００Ｂ、コロンビア社製Ｒａｖｅｎ ７００、Ｒａｖｅｎ ５７５０、Ｒａｖｅｎ ５２５０、Ｒａｖｅｎ ５０００、Ｒａｖｅｎ ３５００、Ｒａｖｅｎ １２５５、キャボット社製Ｒｅｇａｌ ４００Ｒ、Ｒｅｇａｌ ３３０Ｒ、Ｒｅｇａｌ ６６０Ｒ、Ｍｏｇｕｌ Ｌ、Ｍｏｎａｒｃｈ ７００、Ｍｏｎａｒｃｈ ８００、Ｍｏｎａｒｃｈ ８８０、Ｍｏｎａｒｃｈ ９００、Ｍｏｎａｒｃｈ １０００、Ｍｏｎａｒｃｈ １１００、Ｍｏｎａｒｃｈ １３００、Ｍｏｎａｒｃｈ １４００、デグサ社製Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ１、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ２、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ２Ｖ、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ１８、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、関西熱化学（株）社製マックスソーブ Ｇ−４０、マックスソーブ Ｇ−１５、マックスソーブ Ｇ−０８等を使用することが出来る。
【００７７】
イエロー顔料としては、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ２、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １２、Ｃ．Ｉ．ＰｉｇｍｅｎｔＹｅｌｌｏｗ １３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １４、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １６、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １７、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ７３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ７４、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ７５、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ８３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ９３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ９５、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ９７、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ ９８、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １１４、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １２８、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １２９、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １５１、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｙｅｌｌｏｗ １５４、
マゼンタ顔料としては、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ５、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ７、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ １２、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ４８（Ｃａ）、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ４８（Ｍｎ）、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ５７（Ｃａ）、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ ５７：１、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ １１２、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ １２３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ １６８、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ １８４、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｒｅｄ２０２、
シアン顔料としては、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ １、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ ２、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ ３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ １５：３、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ １５：３４、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ １６、Ｃ．Ｉ．ＰｉｇｍｅｎｔＢｌｕｅ ２２、Ｃ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ ６０、Ｃ．Ｉ．ＶａｔＢｌｕｅ ４、Ｃ．Ｉ．Ｖａｔ Ｂｌｕｅ ６０等が挙げられる。
【００７８】
本発明で用いる顔料粒子は、ポリマーで表面を被覆する前に、分散状態で微粒子化しておくことが好ましく、従来の界面活性剤または高分子分散剤によって分散された顔料、顔料表面にスルホン酸等の親水性基を置換して分散能を持たせた自己分散顔料を用いることができる。
【００７９】
本発明でいう表面に親水性基を有する顔料粒子とは、顔料粒子表面に直接親水性基で修飾させた顔料、あるいは有機顔料母核を有する有機物で直接に又はジョイントを介して極性基が結合しているものを挙げることができる。
【００８０】
親水性基としては、例えば、スルホン酸基、カルボン酸基、燐酸基、硼酸基、水酸基が挙げられるが、好ましくはスルホン酸基、カルボン酸基であり、更に好ましくは、スルホン酸基である。
【００８１】
本発明において、表面に親水性基を有する顔料粒子を得る方法としては、例えば、ＷＯ９７／４８７６９号公報、特開平１１−５７４５８号公報、同１１−１８９７３９号公報、特開２０００−２６５０９４公報等に記載の顔料粒子表面をスルホン化剤、酸化剤等を用いて修飾する方法、特開平１１−４９９７４号公報、特開２０００−２７３３８３公報、同２０００−３０３０１４公報等に記載の顔料誘導体をミリングなどの処理で顔料粒子表面に吸着させる方法、特願２０００−３７７０６８、同２００１−１４９５、同２００１−２３４９６６に記載の顔料を顔料誘導体と共に溶媒で溶解した後、貧溶媒中で晶析させる方法等を挙げることができ、いずれの方法でも容易に、表面に親水性基を有する顔料粒子を得ることができる。
【００８２】
顔料の分散方法としては、ボールミル、サンドミル、アトライター、ロールミル、アジテータ、ヘンシェルミキサ、コロイドミル、超音波ホモジナイザー、パールミル、湿式ジェットミル、ペイントシェーカー等各種を用いることができる。
【００８３】
上記分散において使用できる顔料分散剤としては、例えば、高級脂肪酸塩、アルキル硫酸塩、アルキルエステル硫酸塩、アルキルスルホン酸塩、スルホコハク酸塩、ナフタレンスルホン酸塩、アルキルリン酸塩、ポリオキシアルキレンアルキルエーテルリン酸塩、ポリオキシアルキレンアルキルフェニルエーテル、ポリオキシエチレンポリオキシプロピレングリコール、グリセリンエステル、ソルビタンエステル、ポリオキシエチレン脂肪酸アミド、アミンオキシド等の活性剤、あるいはスチレン、スチレン誘導体、ビニルナフタレン誘導体、アクリル酸、アクリル酸誘導体、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、フマル酸誘導体から選ばれた２種以上の単量体からなるブロック共重合体、ランダム共重合体およびこれらの塩をあげることができる。
【００８４】
本発明において、顔料分散体の平均粒径は、１０ｎｍ以上、１８０ｎｍ以下であることが好ましく、１０ｎｍ以上、１４０ｎｍ以下がさらに好ましい。顔料分散体の粒径測定は、光散乱法、電気泳動法、レーザードップラー法等を用いた市販の粒径測定機器により求めることができる。
【００８５】
次いで、本発明の製造方法に従って調製されたが顔料分散液を用いたインクジェットインクについて説明する。
【００８６】
本発明に係るインクジェットインク（以下、単にインクともいう）は水を媒体とし、上記顔料をポリマーで被覆した着色微粒子するサスペンジョンであり、該サスペンションには従来公知の各種添加剤、例えば、多価アルコール類のような湿潤剤、無機塩、界面活性剤、防腐剤、防黴剤、ｐＨ調整剤、シリコーン系等の消泡剤、粘度調整剤又はＥＤＴＡ等のキレート剤、又、亜硫酸塩等の酸素吸収剤等を必要に応じて添加してもよい。
【００８７】
本発明に係るインクジェットインクでは、粘度が１．２ｍＰａ・ｓ以上、１５ｍＰａ・ｓ以下であることが好ましい態様であり、粘度調整剤を用いたり、あるいはインク中の着色微粒子を含めた添加剤濃度を適宜調整することにより、所望の粘度に調整することができる。
【００８８】
また、本発明に係るインクジェットインクでは、インクの表面張力が、２０ｍＮ／ｍ以上、５０ｍＮ／ｍ以下であることが好ましい態様であり、より好ましくは３０〜４０ｍＮ／ｍである。本発明に係るインクジェットインクの表面張力の調整手段としては、各種界面活性剤を用いて、その種類及び添加量を適宜調整することが好ましい。
【００８９】
また、本発明に係るインクジェットインクでは、インクのｐＨが、６．０以上１１．０以下であることが好ましく、更に好ましくは８．０以上１０．０以下である。本発明に係るインクジェットインクで用いられるｐＨ調整剤としては、例えば、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各種有機アミン、水酸化ナトリウム、水酸化リチウム、水酸化カリウム等のアルカリ金属の水酸物等の無機アルカリ剤、有機酸や、鉱酸が挙げられる。
【００９０】
また、本発明に係るインクジェットインクでは、インク溶剤含有量が、１質量％以上６０質量％以下であることが好ましく、より好ましくは１０〜５０質量％であり、より好ましくは２０〜５０質量％である。
【００９１】
本発明でいうインク溶剤は、特に制限はないが、水溶性の有機溶媒が好ましく、具体的にはアルコール類（例えば、メタノール、エタノール、プロパノール、イソプロパノール、ブタノール、イソブタノール、セカンダリーブタノール、ターシャリーブタノール、ペンタノール、ヘキサノール、シクロヘキサノール、ベンジルアルコール等）、多価アルコール類（例えば、エチレングリコール、ジエチレングリコール、トリエチレングリコール、ポリエチレングリコール、プロピレングリコール、ジプロピレングリコール、ポリプロピレングリコール、ブチレングリコール、ヘキサンジオール、ペンタンジオール、グリセリン、ヘキサントリオール、チオジグリコール等）、多価アルコールエーテル類（例えば、エチレングリコールモノメチルエーテル、エチレングリコールモノエチルエーテル、エチレングリコールモノブチルエーテル、エチレングリコールモノフェニルエーテル、ジエチレングリコールモノメチルエーテル、ジエチレングリコールモノエチルエーテル、ジエチレングリコールモノブチルエーテル、ジエチレングリコールジメチルエーテル、プロピレングリコールモノメチルエーテル、プロピレングリコールモノブチルエーテル、エチレングリコールモノメチルエーテルアセテート、トリエチレングリコールモノメチルエーテル、トリエチレングリコールモノエチルエーテル、トリエチレングリコールモノブチルエーテル、トリエチレングリコールジメチルエーテル、ジプロピレングリコールモノプロピルエーテル、トリプロピレングリコールジメチルエーテル等）、アミン類（例えば、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、Ｎ−メチルジエタノールアミン、Ｎ−エチルジエタノールアミン、モルホリン、Ｎ−エチルモルホリン、エチレンジアミン、ジエチレンジアミン、トリエチレンテトラミン、テトラエチレンペンタミン、ポリエチレンイミン、ペンタメチルジエチレントリアミン、テトラメチルプロピレンジアミン等）、アミド類（例えば、ホルムアミド、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジメチルアセトアミド等）、複素環類（例えば、２−ピロリドン、Ｎ−メチル−２−ピロリドン、Ｎ−シクロヘキシル−２−ピロリドン、２−オキサゾリドン、１，３−ジメチル−２−イミダゾリジノン等）、スルホキシド類（例えば、ジメチルスルホキシド等）、スルホン類（例えば、スルホラン等）、スルホン酸塩類（例えば１−ブタンスルホン酸ナトリウム塩等）、尿素、アセトニトリル、アセトン等が挙げられる。
【００９２】
本発明に係るインクジェットインクにおいては、アニオン界面活性剤、ノニオン界面活性剤、カチオン界面活性剤を用いることができる。本発明で用いることのできる各界面活性剤として、特に制限はないが、前述の着色微粒子の調製で用いたのと同様の界面活性剤を挙げることができ、例えば、ジアルキルスルホコハク酸塩類、アルキルナフタレンスルホン酸塩類、脂肪酸塩類等のアニオン性界面活性剤、ポリオキシエチレンアルキルエーテル類、ポリオキシエチレンアルキルアリルエーテル類、アセチレングリコール類、ポリオキシエチレン・ポリオキシプロピレンブロックコポリマー類等のノニオン性界面活性剤、アルキルアミン塩類、第四級アンモニウム塩類等のカチオン性界面活性剤が挙げられる。特にアニオン性界面活性剤およびノニオン性界面活性剤を好ましく用いることができる。
【００９３】
また、本発明においては、高分子界面活性剤も用いることができる。
本発明に係るインクジェットインクには、更に、水溶性高分子または水不溶性高分子分散液を含有してのよい。
【００９４】
水溶性高分子としての好ましい例としては天然高分子が挙げられ、その具体例としては、にかわ、ゼラチン、ガゼイン、若しくはアルブミンなどのたんぱく質類、アラビアゴム、若しくはトラガントゴムなどの天然ゴム類、サボニンなどのグルコシド類、アルギン酸及びアルギン酸プロピレングリコールエステル、アルギン酸トリエタノールアミン、若しくはアルギン酸アンモニウムなどのアルギン酸誘導体、メチルセルロース、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、若しくはエチルヒドロキシルセルロースなどのセルロース誘導体が挙げられる。
【００９５】
更に、水溶性高分子の好ましい例として合成高分子が挙げられ、ポリビニルアルコール類、ポリビニルピロリドン類、ポリアクリル酸、アクリル酸−アクリルニトリル共重合体、アクリル酸カリウム−アクリルニトリル共重合体、酢酸ビニル−アクリル酸エステル共重合体、若しくはアクリル酸−アクリル酸エステル共重合体などのアクリル系樹脂、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、スチレン−メタクリル酸−アクリル酸エステル共重合体、スチレン−α−メチルスチレン−アクリル酸共重合体、若しくはスチレン−α−メチルスチレン−アクリル酸−アクリル酸エステル共重合体などのスチレンアクリル酸樹脂、スチレン−マレイン酸共重合体、スチレン−無水マレイン酸共重合体、ビニルナフタレン−アクリル酸共重合体、ビニルナフタレン−マレイン酸共重合体、及び酢酸ビニル−エチレン共重合体、酢酸ビニル−脂肪酸ビニルエチレン共重合体、酢酸ビニル−マレイン酸エステル共重合体、酢酸ビニル−クロトン酸共重合体、酢酸ビニル−アクリル酸共重合体などの酢酸ビニル系共重合体及びそれらの塩が挙げられる。これらの中で、特に好ましい例としては、ポリビニルピロリドン類が挙げられる。
【００９６】
また、本発明で用いることのできる水不溶性高分子分散液（以下、ラテックスともいう）として、特に制限はないが、例えば、スチレン−ブタジエン共重合体、ポリスチレン、アクリロニトリル−ブタジエン共重合体、アクリル酸エステル共重合体、ポリウレタン、シリコン−アクリル共重合体およびアクリル変性フッ素樹脂等のラテックスが挙げられる。ラテックスは、乳化剤を用いてポリマー粒子を分散させたものであっても、また乳化剤を用いないで分散させたものであってもよい。乳化剤としては界面活性剤が多く用いられるが、スルホン酸基、カルボン酸基等の水に可溶な基を有するポリマー（例えば、可溶化基がグラフト結合しているポリマー、可溶化基を持つ単量体と不溶性の部分を持つ単量体とから得られるポリマー）を用いることも好ましい。
【００９７】
また本発明に係るインクジェットインクでは、ソープフリーラテックスを用いることもできる。ソープフリーラテックスとは、乳化剤を使用していないラテックス、およびスルホン酸基、カルボン酸基等の水に可溶な基を有するポリマー（例えば、可溶化基がグラフト結合しているポリマー、可溶化基を持つ単量体と不溶性の部分を持つ単量体とから得られるポリマー）を乳化剤として用いたラテックスのことを指す。
【００９８】
近年ラテックスのポリマー粒子として、粒子全体が均一であるポリマー粒子を分散したラテックス以外に、粒子の中心部と外縁部で組成を異にしたコア・シェルタイプのポリマー粒子を分散したラテックスも存在するが、このタイプのラテックスも好ましく用いることができる。
【００９９】
本発明に係るインクジェットインクにおいて、ラテックス中のポリマー粒子の平均粒径は１０ｎｍ以上、３００ｎｍ以下であり、１０ｎｍ以上、１００ｎｍ以下であることがより好ましい。ラテックスの平均粒径が３００ｎｍを越えると、画像の光沢感の劣化が起こり、１０ｎｍ未満であると耐水性、耐擦過性が不十分となる。ラテックス中のポリマー粒子の平均粒子径は、光散乱法、電気泳動法、レーザードップラー法を用いた市販の粒径測定機器により求めることができる。
【０１００】
本発明のインクでは、上記説明した以外に、必要に応じて、出射安定性、プリントヘッドやインクカートリッジ適合性、保存安定性、画像保存性、その他の諸性能向上の目的に応じて、公知の各種添加剤、例えば、粘度調整剤、比抵抗調整剤、皮膜形成剤、紫外線吸収剤、酸化防止剤、退色防止剤、防ばい剤、防錆剤等を適宜選択して用いることができ、例えば、流動パラフィン、ジオクチルフタレート、トリクレジルホスフェート、シリコンオイル等の油滴微粒子、特開昭５７−７４１９３号、同５７−８７９８８号及び同６２−２６１４７６号に記載の紫外線吸収剤、特開昭５７−７４１９２号、同５７−８７９８９号、同６０−７２７８５号、同６１−１４６５９１号、特開平１−９５０９１号及び同３−１３３７６号等に記載されている退色防止剤、特開昭５９−４２９９３号、同５９−５２６８９号、同６２−２８００６９号、同６１−２４２８７１号および特開平４−２１９２６６号等に記載されている蛍光増白剤等を挙げることができる。
【０１０１】
本発明で用いられる記録媒体としては、普通紙、コート紙、インク液を吸収して膨潤するインク受容層を設けた膨潤型インクジェット用記録紙、多孔質のインク受容層を持った空隙型インクジェット用記録紙、また基紙の代わりにポリエチレンテレフタレートフィルムなどの樹脂支持体を用いたものも用いることができるが、記録媒体としては、空隙型の多孔質インクジェット記録媒体を用いることが好ましく、この組み合わせにより本発明の効果を最も発揮することができる。
【０１０２】
多孔質インクジェット記録媒体としては、具体的には、空隙型インクジェット用記録紙又は空隙型インクジェット用フィルムを挙げることができ、これらはインク吸収能を有する空隙層が設けられている記録媒体であり、空隙層は、主に親水性バインダーと無機微粒子の軟凝集により形成されるものである。
【０１０３】
空隙層の設け方は、皮膜中に空隙を形成する方法として種々知られており、例えば、二種以上のポリマーを含有する均一な塗布液を支持体上に塗布し、乾燥過程でこれらのポリマーを互いに相分離させて空隙を形成する方法、固体微粒子及び親水性又は疎水性バインダーを含有する塗布液を支持体上に塗布し、乾燥後に、インクジェット記録用紙を水或いは適当な有機溶媒を含有する液に浸漬して固体微粒子を溶解させて空隙を作製する方法、皮膜形成時に発泡する性質を有する化合物を含有する塗布液を塗布後、乾燥過程でこの化合物を発泡させて皮膜中に空隙を形成する方法、多孔質固体微粒子と親水性バインダーを含有する塗布液を支持体上に塗布し、多孔質微粒子中や微粒子間に空隙を形成する方法、親水性バインダーに対して概ね等量以上の容積を有する固体微粒子及び／又は微粒子油滴と親水性バインダーを含有する塗布液を支持体上に塗布して固体微粒子の間に空隙を作製する方法などが挙げられるが、本発明に係るインクを用いる上では、いずれの方法で設けられても、良い結果を与える。
【０１０４】
本発明に係るインクを用いたインクジェット画像形成方法で用いることのできるインクジェットヘッドとしては、オンデマンド方式でもコンティニュアス方式でも構わない。また、吐出方式としては、電気−機械変換方式（例えば、シングルキャビティー型、ダブルキャビティー型、ベンダー型、ピストン型、シェアーモード型、シェアードウォール型等）、電気−熱変換方式（例えば、サーマルインクジェット型、バブルジェット（Ｒ）型等）、静電吸引方式（例えば、電界制御型、スリットジェット型等）及び放電方式（例えば、スパークジェット型等）などを具体的な例として挙げることができるが、いずれの吐出方式を用いても構わない。
【０１０５】
【実施例】
以下、実施例を挙げて本発明を更に詳細に説明するが、本発明は、これら実施例に限定されるものではない。
【０１０６】
実施例１
《顔料分散液の調製》
（顔料分散液１の調製：本発明）
スルホコハク酸ナトリウムビス２−エチルヘキシルで分散したＣ．Ｉ．ピグメントレッド１２２の水分散液（顔料濃度１０質量％）を１４ｇ採取して、これをイオン交換水２００ｍｌに添加し、この混合液を温度センサーと、窒素導入管と、攪拌装置とを装着した内容積が２００ｍｌの円筒形セパラブルフラスコに添加した。
【０１０７】
次いで、この混合液に、窒素気流下で、ドデシル硫酸ナトリウム（ＳＤＳ）の２．０ｇと、スチレンモノマー０．４ｇとを加え、室温で１時間攪拌した後、内温を７０℃までゆっくりと昇温し、内温を７０℃に保持しながら過硫酸カリウムの０．１ｇを溶解した水溶液１０ｍｌを添加し、次いでスチレンモノマー１．４ｇを６時間かけてゆっくりと滴下した。滴下終了後、更にスチレン／メタクリル酸（質量比１／１）の混合モノマーの０．４ｇを２時間かけてゆっくりと滴下し、更に２時間攪拌を継続して、ポリマーによるシェリングを終了した。
【０１０８】
次いで、この反応液を冷却し、０．２％の水酸化ナトリウム水溶液を添加して反応液のｐＨを８．２に調整した後、限外濾過装置で顔料濃度が１０質量％になるまで濃縮、精製して、顔料表面をポリマーで被覆した着色微粒子を含む顔料分散液１を調製した。
【０１０９】
（顔料分散液２〜１７の調製：本発明）
上記顔料分散液１の調製において、モノマーの種類及びその添加量、界面活性剤の種類とその添加量及び吸着時間、顔料の種類を、表１に記載のように変更した以外は同様にして、顔料分散液２〜１７を調製した。
【０１１０】
（顔料分散液１８の調製：比較例）
上記顔料分散液１の調製において、ドデシル硫酸ナトリウム（ＳＤＳ）を除いた以外は同様にして、顔料分散液１８を調製した。
【０１１１】
（顔料分散液１９の調製：比較例）
上記顔料分散液１の調製において、窒素気流下で、ドデシル硫酸ナトリウム（ＳＤＳ）の０．２ｇと、スチレンモノマー０．１５ｇとを加えた後、直ちに７０℃に昇温して過硫酸カリウムを加えて重合を開始した以外は同様にして、顔料分散液１９を調製した。
【０１１２】
（顔料分散液２０、２１の調製：比較例）
上記顔料分散液１８、１９の調製において、顔料をＣ．Ｉ．ピグメントレッド１２２に代えて、カーボンブラック（ＣＢ）を用いた以外は同様にして、顔料分散液２０、２１を調製した。
【０１１３】
（顔料分散液２２の調製：比較例）
メタクリル酸メチル（ＭＭＡ）／アクリル酸ブチル（ＢＡ）／メタクリル酸２−ヒドロキシエチル（ＨＥＭＡ）／メタクリル酸（ＭＡＡ）（質量比＝７０／４．３／１５／１０．７）からなる高分子溶液（固形分量＝４８質量％）の２３．４ｇと、Ｃ．Ｉ．ピグメントレッド１２２の１４．２５ｇと、ジメチルアミノメチルキナクリドンの０．７５ｇと、メチルエチルケトンの７６．９ｇと、スーパー・ベッカミンＬ−１０９−６０（メラミン樹脂 大日本インキ化学工業社製）の４．７ｇとを混合した後、０．５ｍｍセラミックビーズで分散し、ペースト状にした。次いで、このペースト５０ｇとジエタノールアミン０．４ｇとを混合攪拌した後、イオン交換水５０ｇを超音波を照射しながら、徐々に加えて転相乳化させた後、減圧留去によりメチルエチルケトンを除いて顔料分散液２２を調製した。
【０１１４】
（顔料分散液２３の調製：比較例）
上記顔料分散液１の調製において、界面活性剤及びモノマーの種類と添加量を表１に記載のように変更した以外は同様にして、顔料分散液２３を調製した。
【０１１５】
なお、下記表１に記載の各化合物の略称の詳細は、以下の通りである。
ＰＲ１２２；Ｃ．Ｉ．ピグメントレッド１２２
ＣＢ；カーボンブラック
ＰＢ１５：３；Ｃ．Ｉ．ピグメントブルー１５：３
ＰＹ１３８；Ｃ．Ｉ．ピグメントイエロー１３８
ＩＪＸ２６６；Ｃａｂｏｊｅｔ ＩＪＸ２６６
ＳＤＳ；ドデシル硫酸ナトリウム
ＳＡ１；デモールＭＳ（特殊芳香族スルホン酸ホルマリン縮合物） 花王社製
ＳＡ２；レベノールＷＸ（ポリオキシエチレンアルキルエーテル硫酸エステル） 花王社製
ＳＡ３；ジョンクリル７０（スチレンアクリル系高分子分散剤） ジョンソンポリマー社製
ＳＡ４；エマルゲン１０９（ポリエキシエチレンラウリルエーテル） 花王社製
Ｓｔ；スチレン
ＭＭＡ；メタクリル酸メチル
ＥＨＡ；２−エチルヘキシルメタクリレート
ＳＭＡ；メタクリル酸ステアリル
ＭＡＡ；メタクリル酸
ＨＥＭＡ；メタクリル酸２−ヒドロキシエチル
ＨＳ−１０；アクアロンＨＳ−１０ アクリル系反応性界面活性剤 第一工業製薬社製
ＢＡ；アクリル酸ブチル
ＢＭＡ；ブチルメタクリレート
Ｂ_ZＭＡ；ベンジルメタクリレート
モノマー１；Ｓｔ／ＭＭＡ＝７／３（質量比）
モノマー２；Ｓｔ／ＭＭＡ＝３／１（質量比）
モノマー３；Ｓｔ／ＭＭＡ／ＥＨＡ＝７／２／１（質量比）
モノマー４；Ｓｔ／ＭＭＡ／ＳＭＡ＝２／１／１（質量比）
モノマー５；Ｓｔ／ＨＥＭＡ／ＭＡＡ＝２／１／１（質量比）
モノマー６；Ｓｔ／イタコン酸＝１／１（質量比）
モノマー７；ＢＭＡ／Ｂ_ZＭＡ＝１／１（質量比）
《顔料分散液の特性評価》
（ポリマー被覆率の測定）
上記調製した各顔料分散液中に含有される着色微粒子について、顔料質量及びそれを被覆しているポリマー質量を、熱質量分析法により測定し、被覆しているポリマーの質量Ａと、顔料の質量Ｂより、ポリマー被覆率（比率Ａ／Ｂ）を求めた。なお、熱質量分析法で分解を起こす顔料については、顔料を硫酸中に溶解して比色定量法により顔料質量Ｂを求め、別途ポリマー質量Ａと顔料質量Ｂとの合計質量を遠心分離法により求めた値（Ａ＋Ｂ）より、被覆しているポリマーの質量Ａを求め、計算によりポリマー被覆率（比率Ａ／Ｂ）を求めた。
【０１１６】
（着色微粒子の体積平均粒径の測定）
上記調製した各顔料分散液を超純水で希釈した後、マルバーン製ゼータサイザー１０００ＨＳを用いて、体積平均粒径（ｎｍ）を求めた。
【０１１７】
以上により得られた結果を、表１に示す。
【０１１８】
【表１】

【０１１９】
《顔料インクの調製》
次いで、上記で調製した顔料分散液１〜２３を用いて、下記の構成からなる顔料インク１〜２３を調製した。
【０１２０】
顔料分散液 顔料濃度として３．０質量％
エチレングリコール １０．０質量％
グリセリン １０．０質量％
トリエチレングリコールモノブチルエーテル １０．０質量％
オルフィンＥ１０１０（日信化学社製） ０．３質量％
純水を添加して、１００質量％に仕上げた。
【０１２１】
また、界面活性剤としてドデシル硫酸ナトリウムを適宜添加して、表面張力値が３２ｍＮ／ｍとなるように調整した。上記調製した各顔料インクの粘度は、３．０〜３．３ｍＰａ・ｓの範囲にあり、またｐＨは８．２であった。
【０１２２】
《インクジェット画像の印字》
〔画像の出力〕
上記調製した各顔料インクをインクジェットカートリッジに収納した後、ノズル孔径２０μｍ、駆動周波数１２ｋＨｚ、１色当たりのノズル数１２８、同色間のノズル密度１８０ｄｐｉであるピエゾ型ヘッドを搭載し、最大記録密度７２０×７２０ｄｐｉのオンデマンド型のインクジェットプリンタを使用して、記録媒体として、空隙型の多孔質インク吸収層を有するコニカ（株）製インクジェットペーパー フォトライクＱＰを用いて画像１〜２３を出力した。なお、本発明で言うｄｐｉとは、２．５４ｃｍ当たりのドット数をいう。出力画像としては、出力濃度を０％から１００％の間を１６段階に分割したウェッジ画像（各濃度について３ｃｍ×３ｃｍのパッチ状に出力）を用いた。また、同じ画像データを、デジタルミニラボＱＤ−２１ ＰＬＵＳ（コニカ製）を用い、コニカカラーＱＡペーパータイプＡ７上に出力し、現像処理して比較用のカラー銀塩写真画像を作成して、以下の評価に用いた。
【０１２３】
〔出力画像の評価〕
以上のようにして作成した画像１〜２３について、下記の評価を行った。
【０１２４】
（透明感の評価）
透明感の評価は、印字した画像が、カラー銀塩写真画像と同等の透明感が得られたか否かを判定するため、上記で作成したウェッジ画像を、同時に作成した比較用のカラー銀塩写真画像と比較評価した。評価は２０人の一般評価者による目視評価を行い、以下の基準に則り判定した。
【０１２５】
◎：銀塩写真と同等と評価した人が１８人以上
○：銀塩写真と同等と評価した人が１５人〜１７人
△：銀塩写真と同等と評価した人が１１人〜１４人
×：銀塩写真と同等と評価した人が１０人以下
（光沢感の評価）
光沢感についても、銀塩写真同等の光沢が得られたか否かを判定するため、上記で作成したウェッジ画像を、同時に作成した比較用のカラー銀塩写真画像と比較評価した。評価は２０人の一般評価者による目視評価を行い、以下の基準に則り判定した。
【０１２６】
◎：銀塩写真と同等と評価した人が１８人以上
○：銀塩写真と同等と評価した人が１５人〜１７人
△：銀塩写真と同等と評価した人が１１人〜１４人
×：銀塩写真と同等と評価した人が１０人以下
（耐擦過性の評価）
耐擦過性については、上記で作成した各ウェッジ画像の最も画像濃度が高いパッチ画像（出力濃度１００％）に対し、事務用消しゴム（ＭＯＮＯ トンボ鉛筆社製）でその表面を５回の往復擦過を行い、２０人の一般評価者による残存濃度の目視評価を行い、以下の基準に則り判定した。
【０１２７】
◎：ほぼ原画像の濃度が残存していると評価した人が１６人以上
○：ほぼ原画像の濃度が残存していると評価した人が１２〜１５人
△：ほぼ原画像の濃度が残存していると評価した人が８〜１１人
×：ほぼ原画像の濃度が残存していると評価した人が７人以下
以上により得られた結果を、表２に示す。
【０１２８】
【表２】

【０１２９】
表２より明らかなように、本発明の製造方法で調製した顔料分散液を含む顔料インクにより形成した画像は、比較例に対し、画像の透明感及び光沢感が、カラー銀塩写真画像に匹敵する良好な画像特性を有すると共に、形成した画像表面の耐擦過性に優れていることが分かる。
【０１３０】
実施例２
（インクセットの作成）
実施例１で調製した顔料インク２０（イエローインク）、顔料インク９（マゼンタインク）、顔料インク１９（シアンインク）及び顔料インク１８（ブラックインク）からなるインクセットを作成した。
【０１３１】
（画像の印字と評価）
上記インクセットを、脱気状態が保たれるように工夫したパックに詰め、カラーインクジェットプリンターＣＬ−７００（エプソン製）を用いてフルカラー画像を作成した。比較として、カラーインクジェットプリンターＣＬ−７００用の純正顔料インクを用いた。記録媒体としては、コニカ（株）製インクジェットペーパー フォトライクＱＰを用い、財団法人・日本規格協会発行の高精細カラーデジタル標準画像データ「Ｎ５・自転車」（１９９５年１２月発行）を出力画像として使用し、同じ画像データを、デジタルミニラボＱＤ−２１ ＰＬＵＳ（コニカ製）を用い、コニカカラーＱＡペーパータイプＡ７上に出力し、現像処理して比較用のカラー銀塩写真画像を作成した。
【０１３２】
以上のようにして出力した画像について、実施例１に記載の方法に従って、透明感、光沢感及び耐擦過性の評価を行った結果、本発明の製造方法で調製した顔料分散液を含む顔料インクセットにより形成した画像は、比較の純正インクセットに対し、画像の透明感及び光沢感が、カラー銀塩写真画像に匹敵する良好な画像特性を有すると共に、形成した画像表面の耐擦過性に優れていることを確認することができた。
【０１３３】
【発明の効果】
本発明により、画像の透明感、光沢感及び耐擦過性に優れたインクジェットインクに用いる顔料表面に所望の厚さを有するポリマーシェルを均一に被覆した着色微粒子を含む顔料分散液の製造方法を提供することができた。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a pigment dispersion used for an inkjet ink, and more particularly, to a method for producing a pigment dispersion used for an inkjet ink in which a formed image has improved transparency, glossiness and abrasion resistance.
[0002]
[Prior art]
Ink jet recording is a technique in which fine droplets of ink are made to fly by various operating principles and adhere to a recording medium to record images, characters, etc., but relatively high speed, low noise, and easy multicolor printing are possible. There is an advantage that there is.
[0003]
In addition, with recent technological advances, inkjet printing using dye ink has been accelerated in popularity along with high image quality approaching silver halide photography and inexpensive devices.
[0004]
The dye is soluble in the solvent, and the dye molecules are colored in a molecular state or a cluster state. Accordingly, since the environment of each molecule is similar, its absorption spectrum is sharp, and it exhibits high purity and clear coloration. Furthermore, since there is no granular pattern due to particles and no scattered light or reflected light is generated, an ink-jet image having a high transparency and a clear hue can be obtained.
[0005]
However, on the other hand, when a molecule is destroyed by a photochemical reaction or the like, the decrease in the number of molecules is directly reflected on the coloring density, and thus has a disadvantage that light resistance is poor. Ink jet recorded images using dye inks have high image quality, but image quality is greatly reduced by storage over time, and at present, no technology has emerged that surpasses silver halide photography in terms of image storability.
[0006]
Pigment inks that use a pigment having good light resistance as a colorant are used as inks for applications that require an image that is resistant to fading due to light, in contrast to dye inks. However, since pigments are present as pigment particles as compared with dyes, they tend to be scattered by light, resulting in reduced image clarity and reduced abrasion resistance due to aggregation of the pigment particles on the printing surface, or low Since it gives an image without gloss and gloss, there is a drawback that the properties of printed images and color reproducibility are inferior to dyes.
[0007]
In general, pigment-based ink-jet inks require a high degree of dispersion stability in the pigment ink in order to prevent clogging of the nozzles of the ink-jet head, but there is a trade-off with the image performance required depending on the application. In many cases.
[0008]
One example is high image quality, scratch resistance, and water resistance. Pigment images have the drawback that, because the image is formed on the recording medium surface, the image can be rubbed off by rubbing or the like, so-called poor rub resistance, and poor water resistance due to water dispersibility, which overcomes this For this purpose, various methods have been proposed. For example, a method of adding a water-soluble polymer or latex particles to pigment ink has been proposed (for example, see Patent Documents 1 to 4). According to the method proposed above, the rub resistance and water resistance of the image are remarkably improved, but the dispersion stability of the pigment ink is reduced due to the effect of the added water-soluble polymer and latex particles. However, the trade-off relationship was not improved.
[0009]
On the other hand, polymer-coated pigments have been proposed with the aim of achieving both scratch resistance, water resistance and ejection stability of images.
[0010]
As this polymer-coated pigment,
1) After the monomer is adsorbed on the pigment surface, a polymerization initiator is added to polymerize the monomer (for example, refer to Patent Documents 5 and 6 and Non-Patent Document 1).
2) A method in which a pigment is dispersed together with a polymerizable surfactant, and then a monomer is added to polymerize the pigment (for example, see Patent Document 7).
3) A method in which a polymerization initiator is bonded to a pigment surface, and then a monomer is added to perform polymerization (for example, see Non-Patent Document 2).
4) A method of graft polymerization on the pigment surface (for example, see Patent Documents 8 and 9).
5) A method in which an amphoteric polymer and a pigment are dispersed in an organic solvent and then phase-inverted and emulsified into an aqueous phase (for example, see Patent Document 10 and Non-Patent Document 3).
Various proposals have been made. In these methods, for the purpose of the image in terms of scratch resistance, water resistance, and ejection stability, some improvement is recognized. However, in the methods described in 1) and 2), the polymerizable polymer is directly polymerized. Because the adsorption and desorption are in an equilibrium relationship in order to adsorb the monomer of the above, if the amount of the monomer is increased to increase the polymer coating amount, new particles are generated by polymerization of the non-adsorbed monomers, There is a disadvantage that the generated polymer particles further hinder ejection stability. Further, in the method described in 3), since the polymerization initiator is present only on the pigment surface, it is polymerized only in the vicinity of the pigment surface, and it is difficult to increase the polymer coating amount. Further, in the method described in 4), since the reactive groups on the surface of the pigment particles are partially limited, it is difficult to completely cover the particle surface. Furthermore, in the method described in 5), if the amount of the polymer added is increased in order to essentially increase the polymer coating amount, the polymers are aggregated during phase inversion emulsification, and agglomeration of the pigment occurs. There are drawbacks, and the conventional method cannot achieve a polymer-coated pigment with a satisfactory high polymer coverage, and is trying to obtain high-quality images equivalent to advanced silver halide photographs, which are increasingly required in the future. In such a case, further technical development is currently desired.
[0011]
[Patent Document 1]
JP-A-4-18462 (Claims)
[0012]
[Patent Document 2]
JP-A-6-145570 (Claims)
[0013]
[Patent Document 3]
JP-A-2000-351931 (Claims)
[0014]
[Patent Document 4]
JP-A-2002-30235 (Claims)
[0015]
[Patent Document 5]
JP-A-63-191864 (Claims)
[0016]
[Patent Document 6]
JP-A-4-234467 (Claims)
[0017]
[Patent Document 7]
JP-A-2002-161223 (Claims)
[0018]
[Patent Document 8]
Japanese Patent Publication No. 1-49369 (Claims)
[0019]
[Patent Document 9]
JP-A-10-95943 (Claims)
[0020]
[Patent Document 10]
JP-A-10-140065 (Claims)
[0021]
[Non-patent document 1]
"Journal of the Society of Colorants", 70, p503 (1997)
[0022]
[Non-patent document 2]
"Journal of the Society of Colorants", 69, p743 (1996)
[0023]
[Non-Patent Document 3]
"Journal of Coloring Material Association", 72, p. 748 (1998)
[0024]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a polymer shell having a desired thickness on a pigment surface, which is used for an inkjet ink having excellent transparency, glossiness and abrasion resistance of an image. It is an object of the present invention to provide a method for producing a pigment dispersion containing colored fine particles coated on a substrate.
[0025]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following configurations.
[0026]
1. In a method for producing a pigment dispersion used for an inkjet ink in which colored fine particles coated with a polymer are dispersed, the colored fine particles form a reaction field by adsorbing a compound having a hydrophilic part and a hydrophobic part at a pigment interface. And then polymerizing the mixture to produce a pigment dispersion.
[0027]
2. 2. The method for producing a pigment dispersion according to claim 1, wherein after the monomer is adsorbed in the reaction field, polymer polymerization is performed to coat the pigment surface.
[0028]
3. The method for producing a pigment dispersion according to claim 1 or 2, wherein the pigment is an organic pigment or carbon black.
[0029]
4. 4. The method for producing a pigment dispersion according to any one of Items 1 to 3, wherein a volume average particle diameter of the colored fine particles is 10 nm or more and 200 nm or less.
[0030]
5. The method for producing a pigment dispersion according to any one of Items 1 to 4, wherein the compound having a hydrophilic part and a hydrophobic part is a surfactant or a water-soluble polymer.
[0031]
6. The ratio A / B of the mass A of the polymer coating the pigment to the mass B of the pigment is 0.6 or more and 10.0 or less, any one of the above items 1 to 5, The method for producing a pigment dispersion according to claim 1.
[0032]
7. 7. The method for producing a pigment dispersion according to any one of items 1 to 6, wherein at least one kind of the pigment is at least one kind selected from an azo pigment, a quinacridone pigment, and a phthalocyanine pigment.
[0033]
The present inventors have conducted intensive studies in view of the above problems, and as a result, in a method for producing a pigment dispersion used in an inkjet ink in which colored fine particles coated with a polymer are dispersed, the colored fine particles have a pigment interface. After forming a reaction field by adsorbing a compound having a hydrophilic part and a hydrophobic part on the surface, polymer polymerization is performed, and then, after the monomer is adsorbed on the reaction field, polymer polymerization is performed, and the pigment surface is formed. By the method for producing a pigment dispersion that coats the pigment, it is possible to obtain colored fine particles in which a polymer shell having a desired thickness is uniformly coated on the surface of the pigment, and the pigment dispersion containing the colored fine particles is applied to an inkjet ink. It has been found out that an image excellent in transparency, gloss and scratch resistance can be obtained.
[0034]
In other words, the present inventors presumed that in order to obtain a high-quality image equivalent to a silver salt photograph, it is necessary to adjust the coating high molecular weight of the polymer-coated pigment to an appropriate thickness, and the pigment surface After the hydrophobic adsorption field is formed, the monomer is sequentially supplied to the hydrophobic adsorption field and polymerized, so that the polymer coating amount on the pigment can be freely controlled, and as a result, the desired thickness can be obtained. Thus, they have found that pigment particles can be coated. Furthermore, by appropriately changing the composition ratio of the monomers to be successively supplied, the composition ratio of the coating polymer can be continuously changed from the side close to the pigment surface to the hydrophilic medium side. Accordingly, it has been found that a transparent polymer which contributes to gloss can be coated thickly and a polymer necessary for dispersion can be thinly wound outside, and the invention has been reached.
[0035]
The above effect of the present invention is further achieved by using an organic pigment or carbon black as a pigment, further using at least one selected from azo pigments, quinacridone pigments and phthalocyanine pigments as at least one kind of pigment, The volume average particle size is 10 nm or more and 200 nm or less, the compound having a hydrophilic part and a hydrophobic part is a surfactant or a water-soluble polymer, the mass A of the polymer coating the pigment, and the It has been found that by setting the ratio A / B to the mass B to be 0.6 or more and 10.0 or less, the object effect of the present invention can be further exhibited.
[0036]
Hereinafter, details of the present invention will be described.
The method for producing a pigment dispersion of the present invention is a method for producing a pigment dispersion used in an inkjet ink in which colored fine particles each having a pigment coated with a polymer are dispersed, wherein the colored fine particles have a hydrophilic part and a hydrophobic part at a pigment interface. After forming a reaction field by adsorbing a compound having the above, the polymer is polymerized to produce, and further, after adsorbing the monomer in the reaction field, polymer polymerization is performed to coat the pigment surface. By doing so, it is preferable to produce core-shell type colored fine particles in which the core portion is a pigment and the shell portion is a polymer.
[0037]
In the present invention, a method in which a monomer is gradually dropped into an aqueous suspension of a pigment serving as a core, and the monomer is adsorbed on the surface of the pigment, followed by polymerization is particularly preferable.
[0038]
In the method for producing a pigment dispersion liquid containing the above-described colored fine particles, in the present invention, a compound having a hydrophilic part and a hydrophobic part is adsorbed on a pigment interface to form a reaction field, and then a monomer is adsorbed on the reaction field. After that, the polymer is polymerized to coat the pigment surface.
[0039]
In the method for producing a pigment dispersion of the present invention, the ratio A / B of the mass A of the polymer coating the pigment to the mass B of the pigment is 0.6 or more and 10.0 or less. Is preferred.
[0040]
In the present invention, the method for measuring the mass of the pigment particles and the mass of the polymer covering the pigment particles is not particularly limited, but known analytical instruments, for example, thermal mass spectrometry, NMR (nuclear magnetic resonance), IR Can be easily obtained by quantifying the mass of the pigment or the polymer by a colorimetric method using Vis., Vis.
[0041]
Hereinafter, after forming a reaction field by adsorbing a compound having a hydrophilic part and a hydrophobic part according to the present invention, a monomer is adsorbed to the reaction field, and the colored fine particles having a pigment surface coated with a polymer obtained by polymerizing the monomer are described. The details will be described.
[0042]
The colored fine particles according to the present invention are prepared by previously adsorbing a compound having a hydrophilic part and a hydrophobic part on a reaction surface capable of adsorbing a monomer at an interface between a pigment particle surface and a dispersion medium finely divided by a known method. Then, after adding a monomer and adsorbing and immobilizing in the reaction field, a polymerization initiator and the like are added to polymerize, and a pigment particle surface is coated with a polymer to produce colored fine particles. is there.
[0043]
A feature of the method for producing a pigment dispersion containing colored fine particles of the present invention is that a polymer shell having a desired thickness can be uniformly coated on the entire particle without generating new polymer particles in a polymerization process. Can be formed, and by sequentially changing the type of the monomer to be added, there is an advantage that the polymer composition can be arbitrarily adjusted and produced between the pigment surface and the shell surface.
[0044]
In the present invention, the compound having a hydrophilic part and a hydrophobic part that form a reaction field at the pigment interface is not particularly limited, but one of preferred compounds is a surfactant, or an emulsifier, a dispersant. Can be.
[0045]
Examples of the surfactant that can be used in the present invention include cationic surfactants such as aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. And the like.
[0046]
Examples of the anionic surfactant include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, N-acylglutamate, alkyl ether carboxylate, acylated peptide, Alkyl sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfo acetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate , Secondary higher alcohol sulfate, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkyl phenyl ether sulfate, monoglyculfate, fatty acid alkylolamide sulfate, alkyl ether phosphate Salts, alkyl phosphate salts and the like.
[0047]
Examples of the amphoteric surfactant include a carboxybetaine type, a sulfobetaine type, an aminocarboxylate, and imidazolinium betaine.
[0048]
Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene alkyl phenyl ether (eg, Emulgen 911), polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, polyoxyethylene Polyoxypropylene alkyl ether (for example, Newpol PE-62), polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester , Fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester , Sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, alkyl amine oxides, acetylene glycol, acetylene alcohol, and the like. In addition, examples of the surfactant include, for example, a dispersant Demol SNB, MS, N, SSL, ST, and P (trade name) manufactured by Kao Corporation.
[0049]
In addition, a water-soluble resin can also be used as the polymer surfactant. Examples of the water-soluble resin that can be preferably used include a styrene-methacrylic acid-alkyl methacrylate copolymer and a styrene-methacrylic acid copolymer. Styrene-maleic acid-alkyl methacrylate copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer Examples thereof include a polymer, a vinyl naphthalene-methacrylic acid copolymer, and a vinyl naphthalene-maleic acid copolymer. Other examples of the polymer surfactant include acryl-styrene-based resin such as john krill (Johnson). Two or more of these polymeric surfactants can be used in combination.
[0050]
In the present invention, the amount of the surfactant or emulsifier used is preferably from 1 to 10,000 parts, more preferably from 10 to 1,000 parts, per 100 parts by mass of the pigment.
[0051]
In addition, water-soluble polymers can be used as other preferable compounds that form a reaction field in the present invention, for example, polyvinyl alcohols such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and modified polyvinyl alcohol; Cellulose derivatives such as hydroxyethylcellulose, hydroxypropylcellulose and carboxymethylcellulose salts; natural polysaccharides such as guar gum; and the like, and these can be used alone or in combination of two or more.
[0052]
In the present invention, the amount of the water-soluble polymer used is preferably from 1 to 10,000 parts, more preferably from 10 to 1,000 parts, per 100 parts by mass of the pigment.
[0053]
Next, the polymer that coats the pigment will be described.
Monomers having a polymerizable unsaturated double bond that is adsorbed in a reaction field formed by adsorbing the aforementioned compound having a hydrophilic part and a hydrophobic part to form a polymer coated as a shell include ethylene, propylene, butadiene, and chloride. It is a compound selected from vinyl, vinylidene chloride, vinyl acetate, styrene, (meth) acrylates, (meth) acrylamide and the like. In particular, the styrene and ester portions are CH _Three To C ₁₈ H ₃₇ A monomer selected from monomers having only a hydrophobic portion such as (meth) acrylic acid ester and a monomer having a hydroxyl group such as hydroxyethyl (meth) acrylate, and a carboxylic acid such as (meth) acrylic acid, itaconic acid and maleic acid. Preferred is a combination with a monomer having a hydrophilic portion such as a monomer having a sulfonic acid such as styrenesulfonic acid and sulfobutyl (meth) acrylate, and a monomer having an amide group such as (meth) acrylamide.
[0054]
The monomer having a hydrophilic portion also includes a reactive emulsifier. Representative examples of the reactive emulsifier include the following general formulas (1) to (3).
[0055]
Embedded image

[0056]
In the general formula (1), R ¹ Represents a linear alkyl group having 7 to 20 carbon atoms, a branched alkyl group, or a substituted or unsubstituted aromatic group, for example, a heptyl group, an octyl group, a nonyl group, a decyl group, a dodecyl described in the above section A. And a branched alkyl group such as a 2-ethylhexyl group, an aromatic substituent such as a phenyl group, a nonylphenyl group, and a naphthyl group.
[0057]
R ^Two Represents a substituent having a polymerizable group capable of radical polymerization, and examples thereof include an acrylate group, a methacrylate group, and a maleimide group, which are the ethylenically unsaturated groups described in the above section C. Y ¹ Represents a sulfonic acid, a carboxylic acid, or a salt thereof.
[0058]
The compound represented by the general formula (1) according to the present invention can be obtained by a person skilled in the art by a known method. In addition, it can be easily obtained from commercial products. For example, “Latemul S-120”, “Latemul S-120A”, “Latemul S-180”, “Latemul S-180A”, and Sanyo Chemical "Eleminol JS-2" manufactured by Kogyo Co., Ltd. can be mentioned.
[0059]
Embedded image

[0060]
In the general formula (2), R ^Three , R ^Four Is R in the above general formula (1) ¹ , R ^Two Is synonymous with each of Y ^Two Represents a hydrogen atom, a sulfonic acid or a salt thereof, or a carboxylic acid or a salt thereof. AO represents an alkylene oxide.
[0061]
The compound represented by the general formula (2) according to the present invention can be obtained by a person skilled in the art by synthesizing by a known method. In addition, it can be easily obtained from commercial products. For example, NE such as "Adekaria Soap NE-10", "Adekaria Soap NE-20", and "Adekaria Soap NE-30" manufactured by Asahi Denka Kogyo Co., Ltd. Series, SE series such as "Adekalia Soap SE-10N", "Adekaria Soap SE-20N", "Adekaria Soap SE-30N", "AQUALON RN-10", "AQUALON RN" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. RN series such as "-20", "AQUALON RN-30", "AQUALON RN-50", "AQUALON HS-05", "AQUALON HS-10", "AQUALON HS-20", "AQUALON HS-30", etc. HS series or Aqualon BC series.
[0062]
Embedded image

[0063]
In the general formula (3), R ^Five , R ⁶ , Y ^Three And AO are R in the general formula (1) ¹ , R ^Two , Y ¹ And the same as each of AO in the general formula (2).
[0064]
The compound represented by the general formula (3) according to the present invention can be obtained by a person skilled in the art by synthesizing it by a known method. In addition, it can be easily obtained from commercial products, and examples thereof include "AQUALON KH-05", "AQUALON KH-10", and "AQUALON KH-20" manufactured by Daiichi Kogyo Seiyaku.
[0065]
In the general formulas (2) and (3), the average degree of polymerization n of the alkylene oxide chain (AO) is preferably 1 to 10, and for example, “AQUALON KH-05” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. , "AQUALON KH-10", "AQUALON HS-05", "AQUALON HS-10", and the like.
[0066]
Further, in the present invention, the reactive emulsifier is preferably anionic. For example, the above-mentioned "Adecaria Soap SE Series" (manufactured by Asahi Denka Kogyo), "Aqualon HS Series" (Daiichi Kogyo Seiyaku) ), "Latemul S Series" (manufactured by Kao Corporation), "Eleminol JS Series" (manufactured by Sanyo Chemical Industries) and the like.
[0067]
These monomers may be added to the reaction field in advance as a uniform mixture, or may be added while changing the composition. Preferably, the pigment surface is first polymerized with a monomer liquid mainly composed of a monomer having only a hydrophobic portion, and then a monomer having a hydrophilic portion is mixed with a monomer having only a hydrophobic portion in the second half, and the surface of the pigment particles is hydrophilized. Is preferred.
[0068]
The polymerization initiator used for the polymerization of the monomer is not particularly limited, and various polymerization initiators such as benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, t-butyl peroxide or 2-ethylhexanoate can be used. Peroxide; or various azo compounds such as azobisisobutyronitrile or azobisisovaleronitrile.
[0069]
In the present invention, it is important to evaluate whether the polymer is coated as a shell on the pigment particle surface. In the present invention, as will be described later, the particle diameter of each colored fine particle is very small, 200 nm or less, so that the analysis method that can be used is limited from the viewpoint of resolution. TEM, TOF-SIMS, and the like can be applied as an analysis method that meets such a purpose. When observing the core / shell fine particles by TEM, the dispersion can be applied to a carbon support film, dried, and observed. In the TEM observation image, the contrast difference may be small only with the kind of polymer which is an organic substance. Therefore, in order to evaluate whether or not a core / shell is formed, fine particles are osmium tetroxide, ruthenium tetroxide, chlorosulfone It is preferable to dye using acid / uranyl acetate, silver sulfide or the like. The fine particles of only the core are stained and observed by TEM, and compared with those provided with a shell. Further, after mixing the fine particles provided with the shell and the fine particles not provided with the shell, dyeing is performed, and it is confirmed whether or not the ratio of the fine particles having different dyeing degrees matches the presence or absence of the shell.
[0070]
In a mass spectrometer such as TOF-SIMS, it is confirmed that by providing a shell on the particle surface, the amount of coloring material near the surface is smaller than when only the core is used. When the coloring material includes an element that is not contained in the polymer of the shell, it is possible to confirm whether a shell having a small coloring material content is provided by using the element as a probe.
[0071]
In the absence of such an element, the colorant content in the shell can be compared to that without the shell using a suitable dye. For example, by embedding core / shell particles in an epoxy resin, preparing an ultrathin section with a microtome, and performing staining, the core / shell formation can be more clearly observed. As described above, in the case where a polymer or a coloring material includes an element that can serve as a probe, the composition of the core / shell and the distribution amount of the coloring material to the core and the shell can be estimated by TOF-SIMS or TEM.
[0072]
In the present invention, the volume average particle diameter of the colored fine particles is preferably 10 nm or more and 200 nm or less.
[0073]
The core / shell type colored fine particles according to the present invention have a very large surface area per unit volume when the volume average particle diameter is 5 nm or less, so that the effect of enclosing the pigment in the shell polymer is reduced. On the other hand, particles larger than 200 nm tend to clog the head, easily settle in the ink, and degrade stagnation stability. Therefore, the average particle diameter of the colored fine particles is preferably from 5 to 200 nm, more preferably from 10 to 150 nm. When the average particle diameter exceeds 150 nm, when the aqueous ink for inkjet is used, the glossiness of an image recorded on a glossy medium is reduced. And the transparency recorded in the image recorded on the transparency medium is remarkably deteriorated. On the other hand, if the average particle diameter of the colored fine particles is less than 10 nm, the stability of the colored fine particles tends to deteriorate, and the storage stability of the ink tends to deteriorate. 10-100 nm is most preferred.
[0074]
The volume average particle diameter can be measured using a dynamic light scattering method, and can be determined using, for example, a laser particle size analysis system manufactured by Otsuka Electronics Co., Ltd., or a Zetasizer manufactured by Malvern Corporation.
[0075]
Next, the pigment that can be used in the present invention will be described.
The pigment that can be used in the present invention is not particularly limited, and known pigments can be used.Preferable organic pigments or carbon black, for example, azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments Azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, polycyclic pigments such as thioindigo pigments, isoindolinone pigments, quinophthaloni pigments, basic dye lakes, acid dyes Dye lakes such as mold lakes; organic pigments such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments; and inorganic pigments such as carbon black. Pigments (organic pigments) include azo pigments and quinacridone pigments. And at least one selected from phthalocyanine pigments There it is preferable.
[0076]
The pigment that can be used in the present invention is not limited to the following, but as a particularly preferred specific example, the carbon black pigment No. manufactured by Mitsubishi Kasei Co., Ltd. 2300, no. 900, MCF-88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, No. 2200B, Columbia Raven 700, Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Cabot Regal 400R, Regal 330R, Regal 660R, Mochl, Mon, 800, Mon, 800, Mon, 800, Mon Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW18, Color Black FW18, Color Black FW1, Degussa Co., Ltd. Lack S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4A, Special Black Seki Max G4 G-15, Maxsorb G-08 and the like can be used.
[0077]
As the yellow pigment, 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,
Examples of the magenta pigment 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 (Ca), C.I. I. Pigment Red 48 (Mn), C.I. I. Pigment Red 57 (Ca), C.I. I. Pigment Red 57: 1, C.I. I. Pigment Red 112, C.I. I. Pigment Red 123, C.I. I. Pigment Red 168, C.I. I. Pigment Red 184, C.I. I. Pigment Red 202,
Examples of the cyan pigment include C.I. I. Pigment Blue 1, C.I. I. Pigment Blue 2, C.I. I. Pigment Blue 3, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 15:34, C.I. I. Pigment Blue 16, C.I. I. PigmentBlue 22, C.I. I. Pigment Blue 60, C.I. I. VatBlue 4, C.I. I. Vat Blue 60 and the like.
[0078]
It is preferable that the pigment particles used in the present invention are finely divided in a dispersed state before coating the surface with a polymer, and the pigment dispersed by a conventional surfactant or polymer dispersant, sulfonic acid, etc. Self-dispersing pigments having a dispersing ability by substituting a hydrophilic group of the above can be used.
[0079]
The pigment particles having a hydrophilic group on the surface referred to in the present invention are pigments directly modified with a hydrophilic group on the surface of the pigment particles, or a polar group bonded directly or through an joint with an organic substance having an organic pigment mother nucleus. What you do.
[0080]
Examples of the hydrophilic group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a boric acid group, and a hydroxyl group, preferably a sulfonic acid group and a carboxylic acid group, and more preferably a sulfonic acid group.
[0081]
In the present invention, as a method for obtaining pigment particles having a hydrophilic group on the surface, for example, WO97 / 48769, JP-A-11-57458, JP-A-11-189739, JP-A-2000-265094, etc. A method of modifying the surface of pigment particles using a sulfonating agent, an oxidizing agent, etc., and milling a pigment derivative described in JP-A-11-49974, JP-A-2000-273383, JP-A-2000-303014, etc. A method in which the pigment described in Japanese Patent Application Nos. 2000-377068, 2001-1495, and 2001-234966 is dissolved in a solvent together with a pigment derivative by a treatment, and then crystallized in a poor solvent. In any case, pigment particles having a hydrophilic group on the surface can be easily obtained.
[0082]
As a method for dispersing the pigment, various types such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used.
[0083]
Examples of pigment dispersants that can be used in the above dispersion include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, and polyoxyalkylene alkyl ethers. Activator such as phosphate, polyoxyalkylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivative, vinyl naphthalene derivative, acrylic acid A block copolymer comprising two or more monomers selected from acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, and fumaric acid derivatives; Coalescence, and it is possible to increase the salts thereof.
[0084]
In the present invention, the average particle size of the pigment dispersion is preferably from 10 nm to 180 nm, more preferably from 10 nm to 140 nm. The particle size of the pigment dispersion can be measured by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, a laser Doppler method, or the like.
[0085]
Next, an inkjet ink prepared according to the production method of the present invention and using a pigment dispersion will be described.
[0086]
The ink-jet ink according to the present invention (hereinafter also simply referred to as ink) is a suspension of colored fine particles in which water is used as a medium and the above pigment is coated with a polymer, and various known additives such as polyhydric alcohol are added to the suspension. , Such as wetting agents, inorganic salts, surfactants, preservatives, fungicides, pH adjusters, defoamers such as silicones, viscosity adjusters or chelating agents such as EDTA, and oxygen such as sulfites. An absorbent or the like may be added as necessary.
[0087]
In the ink-jet ink according to the present invention, the viscosity is preferably 1.2 mPa · s or more and 15 mPa · s or less, and the viscosity of the ink may be adjusted by using a viscosity modifier or by adding the additive concentration including the colored fine particles in the ink. The viscosity can be adjusted to a desired value by appropriately adjusting the viscosity.
[0088]
In the inkjet ink according to the present invention, the surface tension of the ink is preferably 20 mN / m or more and 50 mN / m or less, more preferably 30 to 40 mN / m. As a means for adjusting the surface tension of the inkjet ink according to the present invention, it is preferable to appropriately adjust the type and the amount of addition using various surfactants.
[0089]
In the inkjet ink according to the invention, the pH of the ink is preferably 6.0 or more and 11.0 or less, more preferably 8.0 or more and 10.0 or less. Examples of the pH adjuster used in the inkjet ink according to the present invention include various organic amines such as monoethanolamine, diethanolamine and triethanolamine, and alkali metal hydroxides such as sodium hydroxide, lithium hydroxide and potassium hydroxide. Inorganic acids, organic acids, and mineral acids.
[0090]
In the inkjet ink according to the present invention, the content of the ink solvent is preferably 1% by mass to 60% by mass, more preferably 10% by mass to 50% by mass, and more preferably 20% by mass to 50% by mass. is there.
[0091]
The ink solvent in the present invention is not particularly limited, but is preferably a water-soluble organic solvent. Specifically, alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol) Pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentane) Diols, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl Ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate , Triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol dimethyl ether, etc. , Amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentane Methyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocycles (eg, 2-pyrrolidone, N-methyl-2-pyrrolidone) , N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides (eg, dimethyl sulfoxide), sulfo (Eg, sulfolane), sulfonates (eg, 1-butanesulfonic acid sodium salt), urea, acetonitrile, acetone, and the like.
[0092]
In the inkjet ink according to the present invention, an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. Each surfactant that can be used in the present invention is not particularly limited, and examples thereof include the same surfactants used in the preparation of the above-described colored fine particles. Examples thereof include dialkyl sulfosuccinates and alkylnaphthalene. Anionic surfactants such as sulfonic acid salts and fatty acid salts, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers And cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.
[0093]
In the present invention, a polymeric surfactant can also be used.
The inkjet ink according to the present invention may further contain a water-soluble polymer or a water-insoluble polymer dispersion.
[0094]
Preferred examples of the water-soluble polymer include natural polymers, specific examples of which include proteins such as glue, gelatin, casein, or albumin, natural gums such as gum arabic, or tragacanth, and savonin. Examples include glucosides, alginic acid and alginic acid derivatives such as alginic acid propylene glycol ester, alginic acid triethanolamine or ammonium alginate, and cellulose derivatives such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and ethylhydroxylcellulose.
[0095]
Further, preferred examples of the water-soluble polymer include synthetic polymers, such as polyvinyl alcohols, polyvinylpyrrolidones, polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, and vinyl acetate. Acrylic resin such as acrylic ester copolymer or acrylic acid-acrylic ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer Styrene-acrylic acid resin such as styrene-α-methylstyrene-acrylic acid copolymer or styrene-α-methylstyrene-acrylic acid-acrylate copolymer, styrene-maleic acid copolymer, styrene-anhydride Maleic acid copolymer, vinyl naphthalene-a Crylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer Examples include polymers, vinyl acetate-based copolymers such as vinyl acetate-acrylic acid copolymers, and salts thereof. Among them, particularly preferred examples include polyvinylpyrrolidones.
[0096]
The water-insoluble polymer dispersion (hereinafter also referred to as latex) that can be used in the present invention is not particularly limited, and examples thereof include styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, and acrylic acid. Latexes such as ester copolymers, polyurethanes, silicone-acrylic copolymers and acrylic-modified fluororesins are mentioned. The latex may be one in which polymer particles are dispersed using an emulsifier, or one in which polymer particles are dispersed without using an emulsifier. Surfactants are often used as emulsifiers, and polymers having water-soluble groups such as sulfonic acid groups and carboxylic acid groups (for example, polymers having a solubilizing group grafted thereto, and those having a solubilizing group It is also preferable to use a polymer obtained from a monomer and a monomer having an insoluble portion.
[0097]
In the inkjet ink according to the present invention, soap-free latex can also be used. Soap-free latex refers to a latex that does not use an emulsifier and a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer having a solubilizing group grafted thereto, a solubilizing group And a polymer obtained from a monomer having an insoluble portion and a monomer having an insoluble portion as an emulsifier.
[0098]
In recent years, latex polymer particles other than latex in which polymer particles in which the whole particles are uniform are dispersed, as well as latex in which core-shell type polymer particles having different compositions at the center and outer edges of the particles are also present. A latex of this type can also be preferably used.
[0099]
In the inkjet ink according to the present invention, the average particle size of the polymer particles in the latex is 10 nm or more and 300 nm or less, and more preferably 10 nm or more and 100 nm or less. If the average particle size of the latex exceeds 300 nm, the glossiness of the image deteriorates, and if the average particle size is less than 10 nm, the water resistance and scratch resistance become insufficient. The average particle size of the polymer particles in the latex can be determined by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, or a laser Doppler method.
[0100]
In the ink of the present invention, in addition to the above description, if necessary, according to the purpose of improving ejection stability, compatibility of a print head or an ink cartridge, storage stability, image storability, and other various performances, a known method can be used. Various additives, for example, a viscosity adjusting agent, a specific resistance adjusting agent, a film forming agent, an ultraviolet absorber, an antioxidant, an anti-fading agent, a sunscreen, a rust inhibitor, etc. can be appropriately selected and used. Oil droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil; ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988 and JP-A-62-261476; JP-A-74192, JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376. And a fluorescent whitening agent described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-242871, and JP-A-4-219266. be able to.
[0101]
Examples of the recording medium used in the present invention include plain paper, coated paper, swellable ink jet recording paper provided with an ink receiving layer that absorbs ink liquid and swells, and porous ink jet recording paper having a porous ink receiving layer. A recording paper, or a paper using a resin support such as a polyethylene terephthalate film instead of a base paper can also be used.However, as a recording medium, it is preferable to use a porous porous inkjet recording medium. The effects of the present invention can be exhibited most.
[0102]
As the porous inkjet recording medium, specifically, there can be mentioned a gap type inkjet recording paper or a gap type inkjet film, and these are recording media provided with a gap layer having an ink absorbing ability, The void layer is formed mainly by soft aggregation of the hydrophilic binder and the inorganic fine particles.
[0103]
Various methods of forming a void layer are known as a method of forming voids in a film. For example, a uniform coating solution containing two or more polymers is coated on a support, and these polymers are dried in a drying process. To form voids by phase separation from each other, a coating solution containing solid fine particles and a hydrophilic or hydrophobic binder is coated on a support, and after drying, the ink jet recording paper contains water or a suitable organic solvent. A method of forming voids by dissolving solid fine particles by immersing in a liquid, after applying a coating solution containing a compound having the property of foaming at the time of film formation, foaming this compound in the drying process to form voids in the film Method, a method of applying a coating solution containing porous solid fine particles and a hydrophilic binder on a support, and forming voids in the porous fine particles or between the fine particles, generally with respect to the hydrophilic binder A method in which a coating solution containing a solid fine particle and / or a fine particle oil droplet having a volume of not less than the amount and a hydrophilic binder and a hydrophilic binder is applied on a support to form a void between the solid fine particles, and the like, In using such an ink, a good result is obtained regardless of which method is used.
[0104]
The inkjet head that can be used in the inkjet image forming method using the ink according to the present invention may be an on-demand type or a continuous type. Further, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shared mode type, a shared wall type, etc.), and an electro-thermal conversion method (for example, thermal Specific examples include an ink jet type, a bubble jet (R) type, etc., an electrostatic suction type (eg, an electric field control type, a slit jet type, etc.) and a discharge type (eg, a spark jet type, etc.). However, any discharge method may be used.
[0105]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0106]
Example 1
<< Preparation of pigment dispersion >>
(Preparation of Pigment Dispersion 1: The Present Invention)
C. dispersed in sodium bis-2-ethylhexyl sulfosuccinate. I. Pigment Red 122 in an aqueous dispersion (pigment concentration: 10% by mass) was collected in an amount of 14 g, added to 200 ml of ion-exchanged water, and mixed with a temperature sensor, a nitrogen inlet tube, and a stirrer. The volume was added to a 200 ml cylindrical separable flask.
[0107]
Next, 2.0 g of sodium dodecyl sulfate (SDS) and 0.4 g of styrene monomer were added to this mixture under a nitrogen stream, and the mixture was stirred at room temperature for 1 hour, and then the internal temperature was slowly raised to 70 ° C. While maintaining the internal temperature at 70 ° C., 10 ml of an aqueous solution in which 0.1 g of potassium persulfate was dissolved was added, and then 1.4 g of a styrene monomer was slowly added dropwise over 6 hours. After completion of the dropwise addition, 0.4 g of a mixed monomer of styrene / methacrylic acid (mass ratio 1/1) was slowly added dropwise over 2 hours, and stirring was continued for another 2 hours to complete the shelling with the polymer.
[0108]
Next, the reaction solution was cooled, and the pH of the reaction solution was adjusted to 8.2 by adding a 0.2% aqueous sodium hydroxide solution, and then concentrated using an ultrafiltration apparatus until the pigment concentration became 10% by mass. Purification was performed to prepare a pigment dispersion liquid 1 containing colored fine particles having the pigment surface coated with a polymer.
[0109]
(Preparation of pigment dispersions 2 to 17: the present invention)
In the preparation of the pigment dispersion 1, in the same manner except that the type of monomer and its addition amount, the type of surfactant and its addition amount and adsorption time, the type of pigment were changed as shown in Table 1, Pigment dispersions 2 to 17 were prepared.
[0110]
(Preparation of Pigment Dispersion Liquid 18: Comparative Example)
Pigment Dispersion Liquid 18 was prepared in the same manner as in Preparation of Pigment Dispersion Liquid 1, except that sodium dodecyl sulfate (SDS) was omitted.
[0111]
(Preparation of Pigment Dispersion Liquid 19: Comparative Example)
In the preparation of Pigment Dispersion 1, 0.2 g of sodium dodecyl sulfate (SDS) and 0.15 g of styrene monomer were added under a nitrogen stream, and then immediately heated to 70 ° C., and potassium persulfate was added. Pigment dispersion liquid 19 was prepared in the same manner except that polymerization was started.
[0112]
(Preparation of Pigment Dispersions 20, 21: Comparative Example)
In the preparation of the pigment dispersions 18 and 19, the pigment was C.I. I. Pigment Dispersions 20 and 21 were prepared in the same manner except that carbon black (CB) was used instead of Pigment Red 122.
[0113]
(Preparation of Pigment Dispersion Liquid 22: Comparative Example)
Polymer solution consisting of methyl methacrylate (MMA) / butyl acrylate (BA) / 2-hydroxyethyl methacrylate (HEMA) / methacrylic acid (MAA) (mass ratio = 70 / 4.3 / 15 / 10.7) (Solid content = 48% by mass) and 23.4 g of C.I. I. Pigment Red 122, 0.75 g of dimethylaminomethylquinacridone, 76.9 g of methyl ethyl ketone, and 4.7 g of Super Beckamine L-109-60 (melamine resin manufactured by Dainippon Ink and Chemicals, Inc.). Was mixed and dispersed with 0.5 mm ceramic beads to form a paste. Next, 50 g of this paste and 0.4 g of diethanolamine were mixed and stirred, and then 50 g of ion-exchanged water was gradually added while irradiating ultrasonic waves to effect phase inversion emulsification. Liquid 22 was prepared.
[0114]
(Preparation of Pigment Dispersion Liquid 23: Comparative Example)
Pigment Dispersion Liquid 23 was prepared in the same manner as in Preparation of Pigment Dispersion Liquid 1, except that the types and amounts of the surfactant and the monomer were changed as shown in Table 1.
[0115]
The details of the abbreviations of the compounds described in Table 1 below are as follows.
PR122; I. Pigment Red 122
CB; carbon black
PB15: 3; I. Pigment Blue 15: 3
PY138; I. Pigment Yellow 138
IJX266; Cabojet IJX266
SDS; sodium dodecyl sulfate
SA1: Demol MS (special aromatic sulfonic acid formalin condensate) manufactured by Kao Corporation
SA2: Levenol WX (polyoxyethylene alkyl ether sulfate) manufactured by Kao Corporation
SA3: John Krill 70 (styrene acrylic polymer dispersant) manufactured by Johnson Polymer
SA4: Emulgen 109 (polyethylene lauryl ether) manufactured by Kao Corporation
St; styrene
MMA; methyl methacrylate
EHA; 2-ethylhexyl methacrylate
SMA; Stearyl methacrylate
MAA; methacrylic acid
HEMA; 2-hydroxyethyl methacrylate
HS-10; AQUALON HS-10 Acrylic reactive surfactant Daiichi Kogyo Seiyaku Co., Ltd.
BA; butyl acrylate
BMA; butyl methacrylate
B _Z MA; benzyl methacrylate
Monomer 1: St / MMA = 7/3 (mass ratio)
Monomer 2: St / MMA = 3/1 (mass ratio)
Monomer 3: St / MMA / EHA = 7/2/1 (mass ratio)
Monomer 4: St / MMA / SMA = 2/1/1 (mass ratio)
Monomer 5: St / HEMA / MAA = 2/1/1 (mass ratio)
Monomer 6; St / itaconic acid = 1/1 (mass ratio)
Monomer 7; BMA / B _Z MA = 1/1 (mass ratio)
<< Evaluation of characteristics of pigment dispersion >>
(Measurement of polymer coverage)
For the colored fine particles contained in each of the pigment dispersions prepared above, the pigment mass and the polymer mass covering the pigment mass were measured by a thermomass spectrometry method, and the mass A of the coating polymer and the mass of the pigment were measured. From B, the polymer coverage (ratio A / B) was determined. For pigments that are decomposed by thermal mass spectrometry, the pigment is dissolved in sulfuric acid to determine pigment mass B by colorimetry, and the total mass of polymer mass A and pigment mass B is separately determined by centrifugation. From the obtained value (A + B), the mass A of the coated polymer was obtained, and the polymer coverage (ratio A / B) was obtained by calculation.
[0116]
(Measurement of volume average particle size of colored fine particles)
After diluting each of the pigment dispersions prepared above with ultrapure water, the volume average particle diameter (nm) was determined using Maltaburn Zetasizer 1000HS.
[0117]
Table 1 shows the results obtained as described above.
[0118]
[Table 1]

[0119]
<< Preparation of pigment ink >>
Next, using the pigment dispersions 1 to 23 prepared above, pigment inks 1 to 23 each having the following structure were prepared.
[0120]
Pigment dispersion 3.0 mass% as pigment concentration
Ethylene glycol 10.0 mass%
Glycerin 10.0% by mass
Triethylene glycol monobutyl ether 10.0 mass%
Olfin E1010 (Nissin Chemical Co., Ltd.) 0.3% by mass
Pure water was added to finish to 100% by mass.
[0121]
Also, sodium dodecyl sulfate was appropriately added as a surfactant to adjust the surface tension value to 32 mN / m. The viscosity of each of the pigment inks prepared above was in the range of 3.0 to 3.3 mPa · s, and the pH was 8.2.
[0122]
<< Inkjet image printing >>
[Image output]
After storing each of the pigment inks prepared above in an inkjet cartridge, a piezo-type head having a nozzle hole diameter of 20 μm, a driving frequency of 12 kHz, a number of nozzles of 128 per color, and a nozzle density of 180 dpi between the same colors was mounted, and a maximum recording density of 720 × Using a 720 dpi on-demand ink jet printer, images 1 to 23 were output using an ink jet paper Photo-like QP manufactured by Konica Corporation having a void type porous ink absorbing layer as a recording medium. In the present invention, dpi means the number of dots per 2.54 cm. As the output image, a wedge image in which the output density was divided into 16 steps from 0% to 100% (each density was output as a patch of 3 cm × 3 cm) was used. The same image data was output on a Konica Color QA paper type A7 using a digital minilab QD-21 PLUS (manufactured by Konica), developed and processed to create a color silver halide photographic image for comparison. Used for evaluation.
[0123]
[Evaluation of output image]
The following evaluations were performed on the images 1 to 23 created as described above.
[0124]
(Evaluation of transparency)
Transparency evaluation, the printed image, to determine whether the same transparency as the color silver halide photographic image was obtained, the wedge image created above, the color silver halide photograph for comparison created simultaneously The image was compared and evaluated. The evaluation was carried out by visual evaluation by 20 general evaluators, and judged according to the following criteria.
[0125]
◎: 18 or more people evaluated as equivalent to silver halide photography
：: 15 to 17 people evaluated as equivalent to silver halide photography
Δ: 11 to 14 people evaluated as equivalent to silver halide photography
×: 10 or less people evaluated as equivalent to silver halide photography
(Evaluation of glossiness)
Regarding the glossiness, in order to determine whether gloss equivalent to that of a silver halide photograph was obtained, the wedge image created above was compared and evaluated with a comparative color silver halide photograph image created at the same time. The evaluation was carried out by visual evaluation by 20 general evaluators, and judged according to the following criteria.
[0126]
◎: 18 or more people evaluated as equivalent to silver halide photography
：: 15 to 17 people evaluated as equivalent to silver halide photography
Δ: 11 to 14 people evaluated as equivalent to silver halide photography
×: 10 or less people evaluated as equivalent to silver halide photography
(Evaluation of scratch resistance)
Regarding the abrasion resistance, the patch image (output density 100%) having the highest image density of each of the wedge images created above was reciprocally rubbed five times with an office eraser (manufactured by MONO Tombo Pencil). The residual concentration was visually evaluated by 20 general evaluators, and determined according to the following criteria.
[0127]
：: 16 or more people evaluated that the density of the original image remained almost
：: 12 to 15 people evaluated that the density of the original image remained almost
Δ: 8 to 11 people evaluated that the density of the original image remained almost
×: Seven or less people evaluated that the density of the original image remained almost
Table 2 shows the results obtained as described above.
[0128]
[Table 2]

[0129]
As is evident from Table 2, the image formed by the pigment ink containing the pigment dispersion prepared by the production method of the present invention has a transparency and glossiness comparable to those of the color silver halide photographic image compared to the comparative example. It can be seen that the resulting image has good image characteristics and the formed image surface has excellent scratch resistance.
[0130]
Example 2
(Create ink set)
An ink set including the pigment ink 20 (yellow ink), the pigment ink 9 (magenta ink), the pigment ink 19 (cyan ink), and the pigment ink 18 (black ink) prepared in Example 1 was prepared.
[0131]
(Image printing and evaluation)
The above-mentioned ink set was packed in a pack devised so as to maintain a degassed state, and a full-color image was created using a color inkjet printer CL-700 (manufactured by Epson). For comparison, a genuine pigment ink for a color inkjet printer CL-700 was used. As a recording medium, Konica Corporation's Inkjet Paper Photo-like QP is used, and high-definition color digital standard image data "N5 Bicycle" (issued in December 1995) issued by the Japan Standards Association is used as an output image. Then, the same image data was output on a Konica Color QA paper type A7 using a digital minilab QD-21 PLUS (manufactured by Konica) and processed to produce a color silver halide photographic image for comparison.
[0132]
The image output as described above was evaluated for transparency, glossiness and abrasion resistance according to the method described in Example 1. As a result, a pigment ink containing the pigment dispersion prepared by the production method of the present invention was obtained. The image formed by the set has, compared to the genuine ink set of the comparative example, transparency and glossiness of the image having good image characteristics comparable to color silver halide photographic images, and excellent scratch resistance of the formed image surface. I was able to confirm that.
[0133]
【The invention's effect】
According to the present invention, there is provided a method for producing a pigment dispersion containing colored fine particles in which a polymer shell having a desired thickness is uniformly coated on the surface of a pigment used for an inkjet ink having excellent transparency, glossiness and abrasion resistance of an image. We were able to.

Claims (7)

In a method for producing a pigment dispersion liquid used in an inkjet ink in which colored fine particles in which a pigment is coated with a polymer are dispersed, the colored fine particles form a reaction field by adsorbing a compound having a hydrophilic part and a hydrophobic part at a pigment interface. And then polymerizing it to produce a pigment dispersion. The method for producing a pigment dispersion according to claim 1, wherein after adsorbing the monomer in the reaction field, polymer polymerization is performed to coat the pigment surface. 3. The method according to claim 1, wherein the pigment is an organic pigment or carbon black. The method for producing a pigment dispersion according to any one of claims 1 to 3, wherein the volume average particle diameter of the colored fine particles is 10 nm or more and 200 nm or less. The method for producing a pigment dispersion according to any one of claims 1 to 4, wherein the compound having a hydrophilic part and a hydrophobic part is a surfactant or a water-soluble polymer. The ratio A / B between the mass A of the polymer coating the pigment and the mass B of the pigment is 0.6 or more and 10.0 or less. The method for producing a pigment dispersion according to claim 1. The method for producing a pigment dispersion according to any one of claims 1 to 6, wherein at least one kind of the pigment is at least one kind selected from an azo pigment, a quinacridone pigment, and a phthalocyanine pigment.