JP2004352902A - Method for producing pigment dispersion liquid and ink for inkjet recording produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion liquid having small pH variation, excellent ejection stability and liquid stability and excellent color definition, a technology relating to a method for the production of a pigment-base ink for inkjet recording by using the pigment dispersion liquid, and provide a pigment dispersion liquid having small pH variation and excellent ejection stability, a pigment-base ink for inkjet recording, an ink set for inkjet recording, an ink cartridge, an inkjet printer, an image-forming method and a material having formed image. <P>SOLUTION: The method for the production of a pigment dispersion liquid for inkjet recording comprises dispersing a mixture at least containing a pigment, a dispersing agent and water. A mixture produced by mixing a pH buffering agent in addition to at least a pigment, a dispersing agent and water is subjected to dispersion treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

」、
（１１）「前記分散剤が、重量基準として顔料１に対し０．０５以上５以下の割合で含まれることを特徴とする前記第（１）項乃至第（１０）項の何れかに記載の顔料系インクジェット用顔料分散液の製造方法」により達成される。
【００１０】
また、上記課題は、本発明の（１２）「前記第（１）項乃至第（１１）項の何れかに記載の製造方法を用いて製造されたことを特徴とするインクジェット用顔料分散液」、
（１３）「前記顔料のうち、ブラック顔料がカーボンブラックであり、前記第（１）項乃至第（５）項の何れかに記載の製造方法を用いて製造されたことを特徴とする顔料系インクジェット用顔料分散液」、
（１４）「前記顔料のうち、イエロー顔料がＰｉｇ．Ｙｅｌｌｏｗ １、２、３、１２、１３、１４、１６、１７、７３、７４、７５、８３、９３、９５、９７、９８、１１４、１２０、１２８、１２９、１３８、１５０、１５１、１５４、１５５、１７４、１８０のうち少なくとも一種であり、前記第（１）項乃至第（５）項の何れかに記載の製造方法を用いて製造されたことを特徴とする顔料系インクジェット用顔料分散液」、
（１５）「前記顔料のうち、マゼンタ顔料がＰｉｇ．Ｒｅｄ ５、７、１２、４８（Ｃａ）、４８（Ｍｎ）、５７（Ｃａ）、５７：１、１１２、１２２、１２３、１４６、１６８、１７６、１８４、１８５、２０２、Ｐｉｇ．Ｖｉｏｌｅｔ １９のうち少なくとも一種であり、前記第（１）項乃至第（５）項の何れかに記載の製造方法を用いて製造されたことを特徴とする顔料系インクジェット用顔料分散液」、
（１６）「前記顔料のうち、シアン顔料がＰｉｇ．Ｂｌｕｅ １、２、３、１５、１５：３、１５：４、１６、２２、６０、６３、６６のうち少なくとも一種であり、前記第（１）項乃至第（５）項の何れかに記載の製造方法を用いて製造されたことを特徴とする顔料系インクジェット用顔料分散液」、
（１７）「前記分散剤が下記一般式（１）で示される化合物の少なくとも一種が使用されたことを特徴とする前記第（１２）項乃至第（１６）項の何れかに記載の顔料系インクジェット用顔料分散液；
【００１１】
【化４】

」、
（１８）「前記分散剤が重量基準として顔料１に対し０．３以上５以下の割合で含まれることを特徴とする前記第（１２）項乃至第（１７）項の何れかに記載の顔料系インクジェット用顔料分散液」により達成される。
【００１２】
また、上記課題は、本発明の（１９）「前記第（１２）項乃至第（１８）項の何れか１に記載の顔料分散液を含有してなる顔料系インクジェット用インク」により達成される。
【００１３】
また、上記課題は、本発明の（２０）「前記第（１９）項に記載の顔料系インクジェット用インクを収容したことを特徴とするインクカートリッジ」により達成される。
【００１４】
また、上記課題は、本発明の（２１）「前記第（１９）項に記載の顔料系インクジェット用インクを画像支持体上に吐出させ記録を行なうことを特徴とするインクジェットプリント装置」により達成される。
【００１５】
また、上記課題は、本発明の（２２）「前記第（１９）項に記載の顔料系インクジェット用インクを用いてインクジェット方式プリント装置で印字することを特徴とする画像形成方法」により達成される。
【００１６】
また、上記課題は、本発明の（２３）「前記第（１９）項に記載の顔料系インクジェット用インクを用いてインクジェットプリント装置で印字された画像形成物」により達成される。
【００１７】
また、上記課題は、本発明の（２４）「前記第（２３）項に記載の画像形成物の画像支持体が紙であることを特徴とする画像形成物」により達成される。
【００１８】
以下、本発明を更に詳しく説明する。
前記のように本発明の特徴は、少なくとも顔料と分散剤、水を含有する混合物を分散するインクジェット用顔料分散液の製造方法であって、該混合物に少なくとも顔料と分散剤、水の他に、更にＰＨ緩衝剤を混合した混合物を分散処理することを特徴とするインクジェット用顔料分散液の製造方法である。
本発明の顔料分散液に含まれているＰＨ緩衝剤は保存でのＰＨ変動を抑制するものであり、ＰＨ緩衝剤の添加時期は混合物作成時期あるいは混合物を分散する過程の何れかでもよいが、分散が終了するまでに入れることが好ましく、分散処理過程で入れる際には初期に入れることが好ましい。また、分散が終了するというのは分散機による分散が終了するという意味であり、その後撹拌機等による撹拌混合時期ではない。また、更に好ましくは混合物作成時期が良い。添加量は混合物作成時あるいは分散機等による粉砕処理・分散処理時に分けて入れてもよく、この比率は特に限定するものではない。好ましくは混合物作成時期のプレミックス等で添加することが良い。
【００１９】
顔料を分散する際に、顔料粗粒子にずり応力、剪断力を有効に作用させて微砕効果を上げるため、また顔料粒子の沈殿・凝集を防止するため、分散剤例えば高分子分散剤の存在下に分散処理を行うことは知られているが、このような場合にはその後のＰＨ変化が著しい。これに対して本発明においては、顔料を分散する際に高分子分散剤ではなくＰＨ緩衝剤の存在下に分散処理することにより、その後の著しいｐＨが回避されることが見い出された。何故、著しいｐＨが回避されるのかの理由は未だ確かではないが、少なくとも、顔料粗粒子から分散された微細粒子に新たに生成した活性な破砕面は、高分子分散剤や界面活性剤によっては必ずしも直ちに不活化されないがＰＨ緩衝剤の存在により比較的速やかに不活化され得ること、及び／又は生成した活性な破砕面の近傍に到達する速度・近傍での存在確率に差異があること等によるものと思われる。
【００２０】
本発明に用いるＰＨ緩衝剤としては、アミノエタンスルホン酸、２−アミノエタンスルホン酸、２−アミノエチル硫酸エステル、Ｎ−アセチル−Ｌ−システイン、カテコール、ピロガロール、ｏ−フェノールスルホン酸、ｐ−フェノールスルホン酸、フロログルシノール、レソルシノール、アスパラギン、アルギニン、Ｌ−アロトレオニン、オルニチン、オルニチン塩酸塩、グルタチオン（還元型）、グルタチオン（酸化型）、グルタミン、シスチン、システイン、３，４−ジヒドロキシフェニルアラニン、シトルニン、Ｌ−セリン、ＤＬ−セリン、チロシン、トリプトファン、Ｌ−トレオニン、ＤＬ−トレオニン、ヒスチジン、フェニルアラニン、ホモシステイン、ＤＬ−メチオニン、Ｌ−メチオニン、リシン、リシン塩酸塩、４−アミノピリジン、ピリドキサール、ピリドキシン塩酸塩、モルホリン、イノシン、ウラシル、グアニン、グアノシン、ヒポキサンチン、プリン、Ｎ，Ｎ−ビス（２−ヒドロキシエチル）−２−アミノエタンスルホン酸、３−モルホリノプロパンスルホン酸、［Ｎトリス（ヒドロキシメチル）メチル−２−アミノ］エタンスルホン酸、Ｎ−２−ヒドキシエチルピペラジン−Ｎ’−２−エタンスルホン酸、ピペラジン−Ｎ−Ｎ’−ビス（２−ヒドキシプロパン）−３−スルホン酸、３−［Ｎ−（トリスヒドロキシメチル）メチルアミノ］−２−ヒドロキシプロパンスルホン酸、３−［Ｎ，Ｎ−ビス（２−ヒドロキシエチル）アミノ］−２−ヒドキシプロパンスルホン酸、Ｎ−２’−ヒドロキシエチルピペラジン−Ｎ−２−ヒドキシプロパン−３−スルホン酸、Ｎ−２−ヒドロキシエチルピペラジン−Ｎ’−２−エタンスルホン酸、トリス（ヒドキシメチル）アミノメタン、Ｎ−［トリス（ヒドキシメチル）メチル］グリシン、グリシルグルシン、Ｎ，Ｎ−ジ（２−ヒドロキシエチル）グリシン、Ｎ−［トリス（ヒドキシメチル）メチル］−３−アミノプロパンスルホン酸、ジエタノールアミン、エタノールアミン、２−アミノ−２−メチル−１，３−プロパンジオール、２−アミノ−２−エチル−１，３−プロパンジオール３−［（１．１ジメチル−２ヒドロキシエチル）アミノ］−２ヒドロキシプロパンスルホン酸、２−シクロヘキシルアミノエタンスルホン酸、Ｎ−シクロヘキシル−２−ヒドロキシ−３−アミノプロパンスルホン酸、３−シクロヘキシルアミノプロパンスルホン酸等が挙げられるが、特に、３−［（１．１ジメチル−２ヒドロキシエチル）アミノ］−２ヒドロキシプロパンスルホン酸、２−シクロヘキシルアミノエタンスルホン酸、Ｎ−シクロヘキシル−２−ヒドロキシ−３−アミノプロパンスルホン酸、３−シクロヘキシルアミノプロパンスルホン酸が特に好ましい。
【００２１】
ＰＨ緩衝剤の添加量としては０．００１％以上１０％以下、好ましくは０．００５％以上５％以下、より好ましくは０．０５％以上２％以下である。ＰＨ緩衝剤の量が０．００１％未満だとＰＨの変化を抑制する効果が小さく、１０％より多いとインクの粘度が大きくなる傾向にある。また、ＰＨ緩衝剤はインク調整時に添加するものより分散液製造過程で入れることでＰＨ変動が小さく、ＰＨ緩衝剤の量も減らすことができる。
【００２２】
本発明の顔料粒子の平均粒径（Ｄ_５０）は１００ｎｍ以下であり、且つ顔料粒子の粒度分布に於ける粒子径標準偏差が平均粒子径（Ｄ_５０）より小さいことにある。
顔料粒子の平均粒子径（Ｄ_５０）は好ましくは７０ｎｍ以下であり、更に好ましくは５０ｎｍ以下である。平均粒子径（Ｄ_５０）が１００ｎｍを超えると彩度が劣る。
なお、本発明に於ける平均粒径（Ｄ_５０）は常法により測定することは可能であるが、たとえば日機装（株）製の粒度分析計ＵＰＡ１５０を使用して測定することができる。また本発明でいう粒子径標準偏差も常法により測定することは可能であるが、これも例えば日機装（株）製の粒度分析計ＵＰＡ１５０を使用して測定して得た測定値ｓｄであることができる。
平均粒子径（Ｄ_５０）及び粒子径標準偏差は、分散機を用いて顔料を分散する際、分散機回転部周速、分散時間、分散液流量、分散液温度によって制御することが可能である。
この場合、顔料粒子の平均粒径（Ｄ_５０）が１００ｎｍ以下であり、且つ顔料粒子の粒度分布に於ける粒子径標準偏差が平均粒子径（Ｄ_５０）より小さするには分散機回転部周速はあまり高過ぎると顔料分散液が凝集しやすく、低すぎると分散効率が悪く生産性が落ちるため、好ましくは６ｍ／ｓ〜１３ｍ／ｓである。
【００２３】
更に、分散時間は上記メディアミル内の分散液滞留時間５分の平均粒径の変化が２％未満で分散を終了することが望ましい。
更に、分散液流量は３００ｍｌ／分以上が好ましく、３００ｍｌ／分以下では分散液温度が上昇し分散安定性に好ましくない。また、循環方式の分散は短時間分散に於いては粒子径標準偏差が大きくなる傾向にあり好ましくない。更に、分散液温度は分散時１０℃未満が好ましく、更に好ましくは４℃〜８℃が分散安定性が良い。
【００２４】
また、下記で説明する分散機としてビーズミルを用いる場合は、分散媒体（ビーズ）の大きさを調節することによって制御可能である。この場合、平均粒子径（Ｄ_５０）を５０ｎｍ以下にするにはビーズを０．１ｍｍ〜１．０ｍｍ程度にすることが好ましく、更に好ましくは０．１ｍｍ〜０．５ｍｍにすれば良い。またこの手法によって本発明における粒子径標準偏差を平均粒子径（Ｄ_５０）より小さくすることができる。
【００２５】
また、本発明の顔料分散液は、分散剤が重量基準として顔料１に対し０．１以上５以下の割合で含まれるのが好ましい。前記割合は顔料１に対し、より好ましくは０．１〜３であり、更に好ましくは０．３〜２である。このような分散剤の使用量を採用することにより、平均粒径（Ｄ_５０）が小さく、かつ粒子径標準偏差も小さくすることができ、これにより彩度、吐出安定性、液安定性に一層優れた顔料分散液を提供することができる。
なお、前記分散剤の使用量が０．０５未満では前記効果が達成されにくいことのほか、顔料分散液及びインクの保存安定性が劣り、その結果、ノズルの目詰まりが発生しやすい傾向があり、５より大きいと顔料分散液およびインクの粘度が高すぎてインクジェット方式での印字が困難になる傾向がある。
【００２６】
本発明の顔料分散液に使用される分散剤は、特に制限されないが、下記一般式（１）で示される化合物の少なくとも一種を使用することにより平均粒径（Ｄ_５０）及び粒子径標準偏差もいずれも小さい顔料分散液を得ることができ好ましい。
【００２７】
【化５】

一般式（１）において、ｎは好ましくは２０以上１００以下、更に好ましくは３０以上５０以下である。ｎが２０未満では分散安定性が低下する傾向があり、ｎが１００より大きいと分散液及びインクの粘度が高くなる傾向がある。
中でもｎが４０である、ＰＯＥ（ｎ＝４０）βナフチルエーテルが更に好ましい。
【００２８】
本発明の顔料分散液に使用されている顔料としては、例えばブラック顔料としてはファーネス法あるいはチャネル法で製造されたカーボンブラック等が挙げられる。
【００２９】
またイエロー顔料としては、ピグメントイエロー１、ピグメントイエロー２、ピグメントイエロー３、ピグメントイエロー１２、ピグメントイエロー１３、ピグメントイエロー１４、ピグメントイエロー１６、ピグメントイエロー１７、ピグメントイエロー７３、ピグメントイエロー７４、ピグメントイエロー７５、ピグメントイエロー８３、ピグメントイエロー９３、ピグメントイエロー９５、ピグメントイエロー９７、ピグメントイエロー９８、ピグメントイエロー１１４、ピグメントイエロー１２０、ピグメントイエロー１２８、ピグメントイエロー１２９、ピグメントイエロー１３８、ピグメントイエロー１５０、ピグメントイエロー１５１、ピグメントイエロー１５４、ピグメントイエロー１５５、ピグメントイエロー１８０等が挙げられる。
【００３０】
またマゼンタ顔料としては、ピグメントレッド５、ピグメントレッド７、ピグメントレッド１２、ピグメントレッド４８（Ｃａ）、ピグメントレッド４８（Ｍｎ）、ピグメントレッド５７（Ｃａ）、ピグメントレッド５７：１、ピグメントレッド１１２、ピグメントレッド１２２、ピグメントレッド１２３、ピグメントレッド１６８， ピグメントレッド１８４， ピグメントレッド２０２，ピグメントバイオレット１９等が挙げられる。
【００３１】
またシアン顔料としては、ピグメントブルー１、ピグメントブルー２、ピグメントブルー３、ピグメントブルー１５、ピグメントブルー１５：３、ピグメントブルー１５：４、ピグメントブルー１６、ピグメントブルー２２、ピグメントブルー６０、バットブルー４、バットブルー６０等が挙げられる。
【００３２】
中でも、イエロー顔料としてピグメントイエロー１３８、マゼンタ顔料としてピグメントレッド１２２、シアン顔料としてピグメントブルー１５：３を用いることにより、色調、耐光性が優れ、バランスの取れたインクジェットインク用インクを得ることができる。
【００３３】
本発明の顔料分散において顔料濃度は５重量％以上３０重量％以下が好ましい。２重量％未満では生産性が劣り、３０重量％より多いと顔料分散液の粘度が高すぎて分散が困難になる傾向がある。
【００３４】
また、本発明の顔料分散液には、水の他に各種添加剤を配合することができる。例えば、水溶性有機媒体としてメタノール、エタノール、１−プロパノール、２−プロパノール等のアルコール、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、プロピレングリコール、グリセリン等の多価アルコール、Ｎ−メチルピロリドン、２−ピロリドン等のピロリドン誘導体、アセトン、メチルエチルケトン等のケトン、モノエタノールアミン、ジエタノールアミン、トリエタノールアミン等のアルカノールアミン等、またノニオン、アニオン、カチオン、両性の各種の界面活性剤、防腐剤等が挙げられる。
【００３５】
本発明の顔料分散液は、前記顔料、分散剤、水、必要に応じて各種添加剤をサンドミル、ボールミル、ロールミル、ビーズミル、ナノマイザー、ホモジナイザー等の公知の分散機で分散することによって得られる。
このとき、分散剤の使用量を前記のように重量基準として顔料１に対し０．０５以上５以下の割合にすると共に、湿式分散処理を採用するのが好適である。なお、本発明でいう湿式分散処理とは顔料、分散剤、水、必要に応じて水溶性有機溶剤の混合物を前記サンドミル、ボールミル、ロールミル、ビーズミル、ナノマイザー、ホモジナイザー等により、いわゆる湿式分散方式で微粉砕・分散する処理のことである。
【００３６】
このようにして得られた本発明の顔料分散液は、特に顔料系インクジェット用インクとして好適に使用することができる。
顔料系インクジェット用インクは公知の方法、例えば本発明の顔料分散液、水、水溶性有機溶剤、界面活性剤等を攪拌混合し、フィルター、遠心分離装置等で粗大粒子をろ過し、脱気することによって得られる。なお、インクの顔料濃度は１重量％以上７重量以下が好ましい。１重量％未満では画像濃度が低いため印字の鮮明さに欠け、７重量％より多いとインクの粘度が高くなる傾向があるばかりでなくノズルの目詰まりが発生しやすくなる。また、インクには前記顔料分散液への添加剤で記した材料と同等の材料を必要に応じて配合することができる。たとえば水溶性有機溶剤の含有量としては、インク全量に対して０重量％以上５０重量％以下、好ましくは５重量％〜４０重量％、更に好ましくは１０重量％〜３５重量である。
【００３７】
このようにして得られた本発明の顔料系インクジェット用インクは、例えばカラー画像を形成するために複数の異なる色相のインクを重ねて画像支持体に画像形成するインクジェット記録用インクセット、これを収容するインクカートリッジに好適に用いることができる。
また、本発明の顔料系インクジェットインクは、これを例えば紙のような画像支持体に吐出させ記録（印字）を行なって画像形成するインクジェットプリント装置により、画像形成することができる印字する方法としては連続噴射型あるいはオンデマンド型が挙げられる。オンデマンド型としてはピエゾ方式、サーマルインクジェット方式、静電方式等が挙げられる。
【００３８】
【実施例】
以下、本発明を実施例および比較例により更に説明するが、本発明はこれらの例に限定されるものではない。なお、例中の部は重量基準である。
（実施例１）

上記の混合物をプレミックス後ディスクタイプのビーズミル（シンマルエンタープライゼス社ＫＤＬ型）で０．３ｍｍジルコニアビーズを用いて周速１０ｍ／ｓ、液温１０℃で１８０分散し、顔料分散液（Ａ）を得た。
【００３９】
（実施例２、３、４）
実施例１のＰＨ調整剤を下記のものにする以外は同様にして実施例２〜４の顔料分散液（Ｂ）、（Ｃ）、（Ｄ）を得た。
実施例２のＰＨ調整剤：２−シクロヘキシルアミノエタンスルホン酸
実施例３のＰＨ調整剤：Ｎ−シクロヘキシル−２−ヒドロキシ−３−アミノプロパンスルホン酸
実施例４のＰＨ調整剤：３−シクロヘキシルアミノプロパンスルホン酸
【００４０】
（実施例５）
実施例１の３−［（１．１ジメチル−２ヒドロキシエチル）アミノ］−２ヒドロキシプロパンスルホン酸の添加量５部を１０部にするのと、ピグメントレッド１２２をピグメントブルー１５：３（東洋インキ製造社製、ＬＩＯＮＯＬ ＢＬＵＥ ＦＧ−７３５１）にする以外は同様にして実施例５の顔料分散液（Ｅ）を得た。
【００４１】
（実施例６、７、８）
実施例２、３、４のピグメントレッド１２２をピグメントブルー１５：３（東洋インキ製造社製、ＬＩＯＮＯＬ ＢＬＵＥ ＦＧ−７３５１）にするのとＰＨ緩衝剤の添加量を１０部にする以外は同様にして実施例６、７、８の顔料分散液（Ｆ）、（Ｇ）、（Ｈ）を得た。
【００４２】
（実施例９）
実施例１の３−［（１．１ジメチル−２ヒドロキシエチル）アミノ］−２ヒドロキシプロパンスルホン酸の添加量５部を２５部にするのと、ピグメントレッド１２２をピグメントイエロー１３８（東洋インキ製造社製、ＬＩＯＮＯＧＥＮ ＹＥＬＬＯＷ １０１０）にする以外は同様にして実施例９の顔料分散液（Ｉ）を得た。
【００４３】
（実施例１０、１１、１２）
実施例２、３、４のピグメントレッド１２２をピグメントイエロー１３８（東洋インキ製造社製、ＬＩＯＮＯＧＥＮ ＹＥＬＬＯＷ １０１０）にするのとＰＨ緩衝剤の添加量を２５部にする以外は同様にして実施例１０、１１、１２の顔料分散液（Ｊ）、（Ｋ）、（Ｌ）を得た。
【００４４】
（比較例１、２、３）
実施例１、５、９において分散時間を６０分にするのとＰＨ緩衝剤を添加しない以外は同様にして比較例１、２、３の顔料分散（Ｍ）、（Ｎ）、（Ｏ）を得た。
【００４５】
（比較例４、５、６）
実施例２、６、１０に於いて分散時間を６０分にするのとＰＨ緩衝剤を分散終了後に添加する以外は同様にして比較例４、５、６の顔料分散液（Ｐ）、（Ｑ）、（Ｒ）を得た。
【００４６】
上記の方法で得られた顔料分散液（Ａ）〜（Ｒ）を用いて下記インク処方１によりインク液を調整し、３０分攪拌後孔径０．８μｍのメンブランフィルターでろ過、真空脱気して（ａ）〜（ｌ）の実施例のインク液を得た。同様に顔料分散液（Ｍ）〜（Ｒ）にインク処方１によりインクを調製し、３０分攪拌後孔径０．８μｍのメンブランフィルターでろ過、真空脱気して（ｍ）〜（ｒ）の比較例のインク液を得た。
【００４７】
（比較例７、８、９）
実施例１、５、９においてＰＨ緩衝剤を分散終了後に添加する以外は同様にして比較例７、８、９の顔料分散液（Ｓ）、（Ｔ）、（Ｕ）を得た。

【００４８】
上記のインク液（ａ）〜（ｕ）に含まれる顔料の平均粒径を測定した。
また、メトラー・トレド（株）製ＰＨメータＭＰ２２０にて初期ＰＨと７０℃３週間保存後のＰＨを測定した。またＥＰＳＯＮ社製インクジェットプリンタＭＪ−９３０Ｃで印字し、吐出安定性及び印字画像をＸｒｉｔｅ濃度計にて測定した。その他インク保存性を下記評価法により評価した。その結果を表１に示す。
【００４９】
【表１】

【００５０】
画像の鮮明性（彩度）
画像サンプルのベタ画像の測色をＸｒｉｔｅ濃度計にて行ない、色度図上にプロットし、色度図上の原点からの距離を言う。より詳しくは色度図上のａ値、ｂ値について
【００５１】
【数１】

をいう。
【００５２】
吐出安定性
吐出安定性については、印刷物を印刷した後、プリンタヘッドにキャップした状態でプリンタを７０℃の環境下で３週間放置した。放置後のプリンタの吐出状態が初期の吐出状態に回復するか否かを下記のクリーニング動作回数によって評価した。
○：１回の動作により回復した。
△：２回〜３回の動作により回復した。
×：３回以上の動作によっても回復がみられなかった。
【００５３】
【発明の効果】
以上、詳細かつ具体的な説明から明らかなように、本発明の顔料分散液及びインクの製造方法は、ＰＨの変動が小さく、吐出安定性も良く更にインク保存性においても優れ、画像の鮮明性（彩度）は従来のものより優れるという極めて優れた効果を奏する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a pigment dispersion and an inkjet ink liquid, and more particularly to a method for dispersing a pigment dispersion using a media mill to produce a recording ink for inkjet, which has a small variation in PH and discharge. The present invention relates to a pigment-based inkjet ink having excellent stability, a method for producing the same, and an image forming method using the ink.
[0002]
[Prior art]
The ink jet recording method has the advantage that the process is simpler than other recording methods, so that full-color printing is easy, and a high-resolution image can be obtained even with a device having a simple configuration. Dye-based inks are used as inkjet inks in which various water-soluble dyes are dissolved in water or a mixture of water and an organic solvent.Dye-based inks have excellent color clarity but lightfastness There was a drawback that the properties were poor. On the other hand, pigment-based inks in which carbon black or various organic pigments are dispersed have been actively studied because of their superior light resistance as compared with dye-based inks. However, pigment-based inks tend to fluctuate in pH over time. In particular, when the pH is lowered, the pigments are likely to aggregate and the ejection stability is deteriorated. There is a risk of giving.
[0003]
As a method for suppressing the decrease in PH, there are disclosed boric acid-potassium chloride-sodium hydride system, glycine-sodium chloride-sodium hydroxide system, potassium dihydrogen phosphate-phosphoric acid described in Patent Documents 1 and 2 and the like. A method of adding a buffer such as disodium hydrogen, sodium carbonate-sodium hydride, potassium citrate dihydride-sodium tetraborate, acetic acid-sodium acetate, sodium dihydrogen phosphate-citric acid, or Patent Document 3 And the like, and a method of adding a buffer such as urea and taurine at the time of preparing the ink described in Patent Document 4 and the like. Is also added at the time of adjusting the ink liquid, there is no track record in the manufacturing process of the dispersion liquid, and the effect of suppressing pH fluctuation or ejection stability is still insufficient. Enoi.
[0004]
Pigment inks are generally prepared by preparing a dispersion in which a coloring material and a dispersant are pre-dispersed in an aqueous solvent such as water or alcohols, and then dispersing the dispersion to a predetermined degree using a media type disperser such as a sand mill. The dispersion is adjusted by performing a dispersion step of dispersing to a predetermined concentration and then diluting to a predetermined concentration.
On the other hand, in recent years, it has been desired to reduce the particle size of the ink in order to improve the definition of an image. However, when the particle diameter is small, the liquid tends to aggregate, and the discharge stability cannot be guaranteed, and there is no solution to this problem.
[0005]
To improve nozzle clogging and color gamut, it is necessary to reduce the average particle size of the pigment. However, styrene-acrylic copolymers and styrene-maleic acid copolymers, which are currently widely used (see Patent Document 5) ), An ink using a polymer dispersant such as sodium formalin condensate of naphthalene sulfonate (see Patent Document 6), polyethylene glycol alkyl phenyl ether (see Patent Document 7), and polyethylene glycol alkyl phenyl ether sulfate (patent). In any of the inks using surfactants such as Reference 8 and polyethylene glycol alkyl phenyl ether phosphate (see Patent Document 9), the average particle size of the pigment is large, and the color tone is clear and the ejection stability is high. And poor liquid stability.
[0006]
[Patent Document 1]
JP-A-64-6067
[Patent Document 2]
JP-A-4-189876
[Patent Document 3]
JP-A-11-189736
[Patent Document 4]
JP-A-03-033366
[Patent Document 5]
JP-A-56-147663
[Patent Document 6]
JP-A-61-083267
[Patent Document 7]
JP-A-5-105837
[Patent Document 8]
JP-A-10-168367
[Patent Document 9]
JP-A-10-88050
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and a pigment dispersion having a small pH variation, excellent ejection stability and liquid stability, and excellent color tone clarity, and a pigment-based inkjet using the same. It is an object of the present invention to provide a technique related to a method for manufacturing a printing ink.
Further, it is possible to provide a pigment dispersion, a pigment-based inkjet ink, an inkjet recording ink set, an ink cartridge, an inkjet printing apparatus, an image forming method, and an image-formed product, which have a small pH fluctuation and excellent ejection stability.
[0008]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by adding and dispersing a buffer at the time of dispersing the pigment and specifying the dispersed state of the pigment, and have reached the present invention.
That is, an object of the present invention is to provide (1) a method for producing a pigment dispersion for inkjet, which comprises dispersing a mixture containing at least a pigment, a dispersant, and water. Further, a method for producing a pigment dispersion liquid for inkjet, which comprises subjecting a mixture obtained by mixing a PH buffer to dispersion treatment,
(2) "The pigment particles in the pigment dispersion have an average particle diameter (D ₅₀ A) a method for producing a pigment dispersion for inkjet according to the above item (1), wherein the dispersion treatment is performed until the dispersion becomes 100 nm or less;
(3) “Average particle diameter (D) of pigment particles dispersed in the pigment dispersion ₅₀ ) Is 100 nm or less, and the particle size standard deviation in the particle size distribution of the pigment particles is the average particle size (D ₅₀ The method for producing a pigment dispersion for inkjet according to the above item (1) or (2), "
(4) "The PH buffer is 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid, 2-cyclohexylaminoethanesulfonic acid, N-cyclohexyl-2-hydroxy-3- (1) The method for producing a pigment dispersion for inkjet according to the above (1) or (2), which is at least one of aminopropanesulfonic acid and 3-cyclohexylaminopropanesulfonic acid;
(5) The inkjet pigment dispersion according to any one of (1) to (4), wherein the amount of the PH buffer added is 0.001% or more and 10% or less. Production method",
(6) “A method for producing a pigment-based inkjet pigment dispersion according to any one of the above items (1) to (5), wherein the black pigment is carbon black among the pigments”. ,
(7) "Of the pigments, the yellow pigment is Pig. Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 120. , 128, 129, 138, 150, 151, 154, 155, 174, 180 at least one of the above-mentioned (1) to (5). Method for producing pigment dispersion for '',
(8) “Among the pigments, the magenta pigment is Pig. Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 168, 176, 184, 185, 202 or Pig.Violet 19, the method for producing a pigment-based inkjet pigment dispersion according to any one of the above items (1) to (5), "
(9) “Among the pigments, the cyan pigment is at least one of Pig. Blue 1, 2, 3, 15, 15: 3, 15: 4, 16, 22, 60, 63, 66. The method for producing a pigment-based inkjet pigment dispersion according to any one of the above items (1) to (5) ",
(10) The pigment system according to any one of the above items (1) to (9), wherein at least one compound represented by the following general formula (1) is used as the dispersant. A method for producing a pigment dispersion for inkjet;
[0009]
Embedded image

"
(11) The method according to any one of the above items (1) to (10), wherein the dispersant is contained at a ratio of 0.05 to 5 based on the weight of the pigment 1 based on weight. Production method of pigment-based inkjet pigment dispersion liquid ".
[0010]
The above object is also achieved by (12) a "pigment dispersion liquid for an ink-jet produced by using the production method according to any one of the above items (1) to (11)". ,
(13) A pigment system wherein the black pigment is carbon black among the pigments, and is produced by using the production method according to any one of the above (1) to (5). Pigment dispersion for inkjet '',
(14) “Of the above pigments, the yellow pigment is Pig. Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 120. , 128, 129, 138, 150, 151, 154, 155, 174, 180, and is manufactured by using the manufacturing method according to any one of the above items (1) to (5). A pigment-based pigment dispersion for inkjet ",
(15) “Of the pigments, the magenta pigment is Pig. Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 168, 176, 184, 185, 202, Pig.Violet 19, and manufactured by using the manufacturing method according to any one of the above items (1) to (5). Pigment-based pigment dispersion for inkjet ",
(16) “Among the pigments, the cyan pigment is at least one of Pig. Blue 1, 2, 3, 15, 15: 3, 15: 4, 16, 22, 60, 63, 66, and the ( Pigment-based inkjet pigment dispersion liquid produced by using the production method according to any one of 1) to (5) ”,
(17) The pigment system according to any one of the above items (12) to (16), wherein the dispersant is at least one compound represented by the following general formula (1). Pigment dispersion for inkjet;
[0011]
Embedded image

"
(18) The pigment according to any one of the above items (12) to (17), wherein the dispersant is contained in a ratio of 0.3 to 5 based on the weight of the pigment 1 based on weight. Pigment dispersion for inkjet printing ".
[0012]
In addition, the above object is achieved by (19) a "pigment-based inkjet ink containing the pigment dispersion liquid described in any one of the above items (12) to (18)" of the present invention. .
[0013]
In addition, the above object is achieved by (20) an “ink cartridge containing the pigment-based inkjet ink described in (19)” of the present invention.
[0014]
Further, the above-mentioned object is achieved by (21) an ink-jet printing apparatus characterized in that recording is carried out by discharging the pigment-based ink-jet ink described in (19) onto an image support. You.
[0015]
In addition, the above object is achieved by (22) an image forming method characterized in that printing is performed by an inkjet printing apparatus using the pigment-based inkjet ink described in (19) above. .
[0016]
In addition, the above object is achieved by (23) the present invention, "an image-formed product printed by an inkjet printing apparatus using the pigment-based inkjet ink described in (19)".
[0017]
Further, the above object is achieved by (24) the present invention, "an image-formed product characterized in that the image support of the image-formed product according to the above mode (23) is paper".
[0018]
Hereinafter, the present invention will be described in more detail.
As described above, the feature of the present invention is a method for producing a pigment dispersion liquid for inkjet which disperses a mixture containing at least a pigment and a dispersant, and water, in addition to at least the pigment and the dispersant, water in the mixture. Further, the present invention provides a method for producing a pigment dispersion for inkjet, which comprises subjecting a mixture obtained by mixing a PH buffer to a dispersion treatment.
The pH buffer contained in the pigment dispersion of the present invention is intended to suppress fluctuations in pH during storage, and the addition time of the PH buffer may be either a mixture preparation time or a process of dispersing the mixture. It is preferable to put it in before the dispersing is completed, and it is preferable to put it in the initial stage when putting in the dispersing process. Further, the terminating of the dispersion means that the dispersion by the dispersing machine is finished, and is not the time of the subsequent mixing and stirring by the stirrer or the like. Further, it is more preferable that the mixture is prepared. The amount of addition may be added separately at the time of preparing the mixture or at the time of pulverization / dispersion by a disperser or the like, and this ratio is not particularly limited. Preferably, it is added in a premix or the like at the time of preparing the mixture.
[0019]
When dispersing the pigment, a dispersing agent such as a polymer dispersing agent is used to effectively apply shear stress and shearing force to the coarse pigment particles to enhance the pulverizing effect and to prevent precipitation and aggregation of the pigment particles. It is known to perform distributed processing below, but in such a case, the subsequent PH change is remarkable. On the other hand, in the present invention, it has been found that the subsequent remarkable pH can be avoided by dispersing the pigment in the presence of a PH buffer instead of a polymer dispersant. It is not yet clear why the significant pH is avoided, but at least the newly generated active crushed surface in the fine particles dispersed from the coarse pigment particles may be different depending on the polymer dispersant or surfactant. It is not necessarily inactivated immediately, but can be inactivated relatively quickly due to the presence of the PH buffer, and / or due to the difference in the speed of reaching the vicinity of the generated active crushed surface and the existence probability in the vicinity. It seems to be.
[0020]
Examples of the PH buffer used in the present invention include aminoethanesulfonic acid, 2-aminoethanesulfonic acid, 2-aminoethyl sulfate, N-acetyl-L-cysteine, catechol, pyrogallol, o-phenolsulfonic acid, and p-phenol. Sulfonic acid, phloroglucinol, resorcinol, asparagine, arginine, L-allothreonine, ornithine, ornithine hydrochloride, glutathione (reduced form), glutathione (oxidized form), glutamine, cystine, cysteine, 3,4-dihydroxyphenylalanine, citrunin , L-serine, DL-serine, tyrosine, tryptophan, L-threonine, DL-threonine, histidine, phenylalanine, homocysteine, DL-methionine, L-methionine, lysine, lysine hydrochloride, 4-amino Lysine, pyridoxal, pyridoxine hydrochloride, morpholine, inosine, uracil, guanine, guanosine, hypoxanthine, purine, N, N-bis (2-hydroxyethyl) -2-aminoethanesulfonic acid, 3-morpholinopropanesulfonic acid, [ N-tris (hydroxymethyl) methyl-2-amino] ethanesulfonic acid, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, piperazine-NN'-bis (2-hydroxypropane)- 3-sulfonic acid, 3- [N- (trishydroxymethyl) methylamino] -2-hydroxypropanesulfonic acid, 3- [N, N-bis (2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid , N-2'-hydroxyethylpiperazine-N-2-hydroxypropane-3-sulfonic acid N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, tris (hydroxymethyl) aminomethane, N- [tris (hydroxymethyl) methyl] glycine, glycylglycine, N, N-di (2-hydroxyethyl) glycine, N- [tris (hydroxymethyl) methyl] -3-aminopropanesulfonic acid, diethanolamine, ethanolamine, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propane Diol 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid, 2-cyclohexylaminoethanesulfonic acid, N-cyclohexyl-2-hydroxy-3-aminopropanesulfonic acid, 3-cyclohexylamino Propane sulfonic acid, etc. Are, in particular, 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid, 2-cyclohexylaminoethanesulfonic acid, N-cyclohexyl-2-hydroxy-3-aminopropanesulfonic acid, 3 -Cyclohexylaminopropanesulfonic acid is particularly preferred.
[0021]
The amount of the PH buffer added is 0.001% or more and 10% or less, preferably 0.005% or more and 5% or less, and more preferably 0.05% or more and 2% or less. If the amount of the PH buffer is less than 0.001%, the effect of suppressing the change in PH is small, and if it is more than 10%, the viscosity of the ink tends to increase. In addition, when the pH buffer is added during the process of manufacturing the dispersion liquid, the fluctuation in PH is reduced and the amount of the PH buffer can be reduced as compared with the one added at the time of adjusting the ink.
[0022]
Average particle size (D) of the pigment particles of the present invention ₅₀ ) Is 100 nm or less, and the standard deviation of the particle size in the particle size distribution of the pigment particles is the average particle size (D ₅₀ ) Is to be smaller.
Average particle size of pigment particles (D ₅₀ ) Is preferably 70 nm or less, more preferably 50 nm or less. Average particle size (D ₅₀ ) Exceeds 100 nm, the chroma is poor.
In the present invention, the average particle size (D ₅₀ Can be measured by an ordinary method, for example, by using a particle size analyzer UPA150 manufactured by Nikkiso Co., Ltd. In addition, the particle size standard deviation referred to in the present invention can be measured by an ordinary method, but this is also a measured value sd obtained by using, for example, a particle size analyzer UPA150 manufactured by Nikkiso Co., Ltd. Can be.
Average particle size (D ₅₀ ) And the standard deviation of the particle diameter can be controlled by the peripheral speed of the rotating part of the disperser, the dispersion time, the flow rate of the dispersion and the temperature of the dispersion when dispersing the pigment using a disperser.
In this case, the average particle size of the pigment particles (D ₅₀ ) Is 100 nm or less, and the particle size standard deviation in the particle size distribution of the pigment particles is the average particle size (D ₅₀ If the peripheral speed of the rotating part of the dispersing machine is too high, the pigment dispersion is likely to agglomerate. If the peripheral speed is too low, the dispersing efficiency is poor and the productivity is low.
[0023]
Further, as for the dispersion time, it is desirable that the dispersion is completed when the change in the average particle size of the dispersion liquid residence time in the media mill for 5 minutes is less than 2%.
Further, the flow rate of the dispersion is preferably 300 ml / min or more, and if it is 300 ml / min or less, the dispersion temperature rises, which is not preferable for dispersion stability. In addition, the dispersion by the circulation method is not preferable because the standard deviation of the particle diameter tends to increase in short-time dispersion. Further, the temperature of the dispersion is preferably less than 10 ° C. at the time of dispersion, and more preferably 4 ° C. to 8 ° C. for good dispersion stability.
[0024]
When a bead mill is used as a dispersing machine described below, it can be controlled by adjusting the size of the dispersing medium (beads). In this case, the average particle diameter (D ₅₀ ) Is set to 50 nm or less, the beads are preferably set to about 0.1 mm to 1.0 mm, and more preferably 0.1 mm to 0.5 mm. Further, by this method, the standard deviation of the particle diameter in the present invention is determined by the average particle diameter (D ₅₀ ) Can be smaller.
[0025]
The pigment dispersion of the present invention preferably contains the dispersant in a ratio of 0.1 to 5 based on the weight of the pigment 1 based on the weight. The ratio is more preferably 0.1 to 3, and even more preferably 0.3 to 2, based on 1 of the pigment. By adopting such an amount of the dispersant, the average particle diameter (D ₅₀ ) And the particle diameter standard deviation can be reduced, whereby a pigment dispersion having more excellent chroma, discharge stability and liquid stability can be provided.
When the amount of the dispersant is less than 0.05, the effect is hard to be achieved, and the storage stability of the pigment dispersion and the ink is poor, and as a result, nozzle clogging tends to occur. If it is larger than 5, the viscosity of the pigment dispersion and the ink tends to be too high, so that printing by the inkjet method tends to be difficult.
[0026]
The dispersant used in the pigment dispersion of the present invention is not particularly limited. However, by using at least one compound represented by the following general formula (1), the average particle diameter (D ₅₀ ) And the particle diameter standard deviation are both preferable, since a pigment dispersion having a small particle diameter can be obtained.
[0027]
Embedded image

In the general formula (1), n is preferably from 20 to 100, more preferably from 30 to 50. If n is less than 20, the dispersion stability tends to decrease, and if n is greater than 100, the viscosity of the dispersion and the ink tends to increase.
Above all, POE (n = 40) β-naphthyl ether in which n is 40 is more preferable.
[0028]
Examples of the pigment used in the pigment dispersion of the present invention include, for example, carbon black produced by a furnace method or a channel method as a black pigment.
[0029]
As the yellow pigment, Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 114, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 129, Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 154, Pigment Yellow 155, Pigment Yellow 180, etc. It is below.
[0030]
Examples of magenta pigments include Pigment Red 5, Pigment Red 7, Pigment Red 12, Pigment Red 48 (Ca), Pigment Red 48 (Mn), Pigment Red 57 (Ca), Pigment Red 57: 1, Pigment Red 112, Pigment Red Red 122, Pigment Red 123, Pigment Red 168, Pigment Red 184, Pigment Red 202, Pigment Violet 19 and the like.
[0031]
Examples of cyan pigments include Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 15, Pigment Blue 15: 3, Pigment Blue 15: 4, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Bat Blue 4, Bat Blue 60 and the like.
[0032]
Above all, by using Pigment Yellow 138 as the yellow pigment, Pigment Red 122 as the magenta pigment, and Pigment Blue 15: 3 as the cyan pigment, a well-balanced ink for ink jet ink having excellent color tone and light resistance can be obtained.
[0033]
In the pigment dispersion of the present invention, the pigment concentration is preferably from 5% by weight to 30% by weight. If it is less than 2% by weight, the productivity is inferior, and if it is more than 30% by weight, the viscosity of the pigment dispersion tends to be too high to make dispersion difficult.
[0034]
The pigment dispersion of the present invention may contain various additives in addition to water. For example, as a water-soluble organic medium, alcohols such as methanol, ethanol, 1-propanol and 2-propanol, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and glycerin, N-methylpyrrolidone, 2-pyrrolidone and the like Pyrrolidone derivatives; ketones such as acetone and methyl ethyl ketone; alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; and nonionic, anionic, cationic, amphoteric surfactants and preservatives.
[0035]
The pigment dispersion of the present invention can be obtained by dispersing the pigment, dispersant, water, and, if necessary, various additives using a known disperser such as a sand mill, a ball mill, a roll mill, a bead mill, a nanomizer, and a homogenizer.
At this time, it is preferable that the dispersant be used in a proportion of 0.05 to 5 with respect to the pigment 1 on a weight basis as described above, and that wet dispersing be employed. Incidentally, the wet dispersion treatment referred to in the present invention is a pigment, dispersant, water, and a mixture of a water-soluble organic solvent, if necessary, is finely divided by a so-called wet dispersion method using a sand mill, a ball mill, a roll mill, a bead mill, a nanomizer, a homogenizer, or the like. This is the process of grinding and dispersing.
[0036]
The pigment dispersion of the present invention thus obtained can be suitably used particularly as a pigment-based inkjet ink.
The pigment-based inkjet ink is a known method, for example, the pigment dispersion liquid of the present invention, water, a water-soluble organic solvent, a surfactant, etc. are stirred and mixed, and a coarse particle is filtered by a filter, a centrifugal separator, etc., and deaerated. Obtained by: The pigment concentration of the ink is preferably from 1% by weight to 7% by weight. If the amount is less than 1% by weight, the image density is low, resulting in poor print clarity. If the amount is more than 7% by weight, not only the viscosity of the ink tends to increase, but also nozzle clogging tends to occur. Further, a material equivalent to the material described as an additive to the pigment dispersion can be blended into the ink as needed. For example, the content of the water-soluble organic solvent is 0% by weight or more and 50% by weight or less, preferably 5% by weight to 40% by weight, more preferably 10% by weight to 35% by weight based on the total amount of the ink.
[0037]
The pigment-based inkjet ink of the present invention thus obtained is, for example, an inkjet recording ink set for forming an image on an image support by superimposing a plurality of inks of different hues to form a color image, and containing the ink set. It can be suitably used for an ink cartridge that performs the following.
Further, the pigment-based inkjet ink of the present invention can be used as a printing method capable of forming an image by an ink-jet printing apparatus that discharges the ink onto an image support such as paper to form an image by performing recording (printing). A continuous injection type or an on-demand type may be used. Examples of the on-demand type include a piezo system, a thermal inkjet system, and an electrostatic system.
[0038]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The parts in the examples are on a weight basis.
(Example 1)

After premixing the above mixture, it was dispersed in a disc type bead mill (Shinmaru Enterprises KDL type) using 0.3 mm zirconia beads by 180 at a peripheral speed of 10 m / s and a liquid temperature of 10 ° C. to obtain a pigment dispersion (A). Got.
[0039]
(Examples 2, 3, and 4)
Pigment dispersions (B), (C) and (D) of Examples 2 to 4 were obtained in the same manner except that the PH adjuster of Example 1 was changed as follows.
PH adjuster of Example 2: 2-cyclohexylaminoethanesulfonic acid
PH adjuster of Example 3: N-cyclohexyl-2-hydroxy-3-aminopropanesulfonic acid
PH adjuster of Example 4: 3-cyclohexylaminopropanesulfonic acid
[0040]
(Example 5)
When 5 parts of 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid of Example 1 was changed to 10 parts, and Pigment Red 122 was changed to Pigment Blue 15: 3 (Toyo Ink) Pigment dispersion liquid (E) of Example 5 was obtained in the same manner except that LIONOL BLUE FG-7351 manufactured by the manufacturer was used.
[0041]
(Examples 6, 7, 8)
Pigment Red 122 of Examples 2, 3, and 4 was changed to Pigment Blue 15: 3 (manufactured by Toyo Ink Mfg. Co., Ltd., LIONOL BLUE FG-7351) except that the amount of the PH buffer added was changed to 10 parts. Pigment dispersions (F), (G), and (H) of Examples 6, 7, and 8 were obtained.
[0042]
(Example 9)
Pigment Red 138 (Toyo Ink Mfg. Co., Ltd.) was used in which the addition amount of 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid in Example 1 was changed to 5 parts and Pigment Red 122 was changed to 25 parts. Pigment dispersion liquid (I) of Example 9 was obtained in the same manner except that LIONOGEN YELLOW 1010) was used.
[0043]
(Examples 10, 11, and 12)
Pigment Red 122 of Examples 2, 3, and 4 was changed to Pigment Yellow 138 (manufactured by Toyo Ink Mfg. Co., Ltd., LIONOGEN YELLOW 1010), and Example 10 was repeated except that the amount of the PH buffer added was 25 parts. Pigment dispersions (J), (K) and (L) of Nos. 11 and 12 were obtained.
[0044]
(Comparative Examples 1, 2, 3)
The pigment dispersions (M), (N), and (O) of Comparative Examples 1, 2, and 3 were prepared in the same manner as in Examples 1, 5, and 9 except that the dispersion time was set to 60 minutes and that no PH buffer was added. Obtained.
[0045]
(Comparative Examples 4, 5, 6)
The pigment dispersions (P) and (Q) of Comparative Examples 4, 5, and 6 were prepared in the same manner as in Examples 2, 6, and 10 except that the dispersion time was set to 60 minutes and that the PH buffer was added after the dispersion was completed. ) And (R) were obtained.
[0046]
Using the pigment dispersions (A) to (R) obtained by the above method, an ink solution was prepared according to the following ink formulation 1, stirred for 30 minutes, filtered through a membrane filter having a pore diameter of 0.8 μm, and degassed in vacuo. The ink liquids of the examples (a) to (l) were obtained. Similarly, inks were prepared from the pigment dispersions (M) to (R) according to the ink formulation 1, stirred for 30 minutes, filtered through a membrane filter having a pore diameter of 0.8 μm, and degassed under vacuum to compare (m) to (r). Example ink liquids were obtained.
[0047]
(Comparative Examples 7, 8, 9)
Pigment dispersions (S), (T), and (U) of Comparative Examples 7, 8, and 9 were obtained in the same manner as in Examples 1, 5, and 9, except that the PH buffer was added after the dispersion was completed.

[0048]
The average particle size of the pigments contained in the ink liquids (a) to (u) was measured.
The initial pH and the pH after storage at 70 ° C. for 3 weeks were measured using a pH meter MP220 manufactured by METTLER TOLEDO. In addition, printing was performed using an inkjet printer MJ-930C manufactured by EPSON, and ejection stability and a printed image were measured using an Xrite densitometer. Other ink storability was evaluated by the following evaluation method. Table 1 shows the results.
[0049]
[Table 1]

[0050]
Image sharpness (saturation)
The color measurement of the solid image of the image sample is performed by an Xrite densitometer, plotted on a chromaticity diagram, and the distance from the origin on the chromaticity diagram. More specifically, about a value and b value on the chromaticity diagram
[0051]
(Equation 1)

Say.
[0052]
Discharge stability
Regarding the ejection stability, after printing the printed matter, the printer was left in a 70 ° C. environment for 3 weeks with the printer head capped. Whether or not the ejection state of the printer after standing was restored to the initial ejection state was evaluated by the following number of cleaning operations.
A: Recovery was achieved by one operation.
Δ: Recovered by two or three operations.
×: No recovery was observed even after three or more operations.
[0053]
【The invention's effect】
As apparent from the detailed and specific description above, the method for producing the pigment dispersion liquid and the ink of the present invention has a small variation in PH, good ejection stability, excellent ink storability, and excellent image clarity. (Saturation) has an extremely excellent effect of being superior to the conventional one.

Claims (24)

What is claimed is: 1. A method for producing an inkjet pigment dispersion in which a mixture containing at least a pigment, a dispersant, and water is dispersed. In addition to at least a pigment, a dispersant, and water, a mixture obtained by further mixing a PH buffer is dispersed. A method for producing a pigment dispersion for inkjet printing, comprising: Method of manufacturing an inkjet pigment dispersion according to claim 1, characterized in that the dispersion treatment until the average particle size of the pigment particles in the pigment dispersion (D ₅₀₎ 100 nm or less. The pigment particles dispersed in the pigment dispersion have an average particle diameter (D ₅₀ ) of 100 nm or less, and the particle diameter standard deviation in the particle size distribution of the pigment particles is smaller than the average particle diameter (D ₅₀ ). The method for producing a pigment dispersion for inkjet according to claim 1 or 2. The PH buffer is 3-[(1.1 dimethyl-2-hydroxyethyl) amino] -2-hydroxypropanesulfonic acid, 2-cyclohexylaminoethanesulfonic acid, N-cyclohexyl-2-hydroxy-3-aminopropanesulfonic acid The method for producing a pigment dispersion for inkjet according to claim 1, wherein the dispersion is at least one of, 3-cyclohexylaminopropanesulfonic acid. The method according to any one of claims 1 to 4, wherein the amount of the PH buffer added is 0.001% or more and 10% or less. The method for producing a pigment-based inkjet pigment dispersion according to any one of claims 1 to 5, wherein a black pigment among the pigments is carbon black. Among the above pigments, the yellow pigment is Pig. Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 120, 128, 129, 138, 150, 151, 154, 155 The method for producing a pigment-based inkjet pigment dispersion according to any one of claims 1 to 5, wherein the method is at least one of 174 and 180. Among the pigments, the magenta pigment is Pig. Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 168, 176, 184, 185, 202, Pig. The method for producing a pigment-based inkjet pigment dispersion according to any one of claims 1 to 5, wherein the method is at least one of Violet19. Among the pigments, the cyan pigment is Pig. The pigment system according to any one of claims 1 to 5, wherein the pigment system is at least one of Blue 1, 2, 3, 15, 15: 3, 15: 4, 16, 22, 60, 63, and 66. A method for producing a pigment dispersion for inkjet. The method according to any one of claims 1 to 9, wherein at least one compound represented by the following general formula (1) is used as the dispersant.

The method for producing a pigment-based inkjet pigment dispersion according to any one of claims 1 to 10, wherein the dispersant is contained in a ratio of 0.05 to 5 based on the weight of the pigment 1 based on the weight of the pigment. A pigment dispersion liquid for inkjet produced by using the production method according to claim 1. A pigment-based inkjet pigment dispersion, wherein the black pigment is carbon black among the pigments, and is produced using the production method according to claim 1. Among the above pigments, the yellow pigment is Pig. Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 120, 128, 129, 138, 150, 151, 154, 155 A pigment-based inkjet pigment dispersion, which is at least one of 174 and 180, and is produced using the production method according to any one of claims 1 to 5. Among the pigments, the magenta pigment is Pig. Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 168, 176, 184, 185, 202, Pig. A pigment-based inkjet pigment dispersion, which is at least one of Violet 19 and is produced using the production method according to any one of claims 1 to 5. Among the pigments, the cyan pigment is Pig. Blue 1, 2, 3, 15, 15: 3, 15: 4, 16, 22, 60, 63, 66, and manufactured using the manufacturing method according to any one of claims 1 to 5. What is claimed is: 1. A pigment-based inkjet pigment dispersion liquid comprising: The pigment-based inkjet pigment dispersion according to any one of claims 12 to 16, wherein the dispersant is at least one compound represented by the following general formula (1).

The pigment-based inkjet pigment dispersion according to any one of claims 12 to 17, wherein the dispersant is contained in a ratio of 0.3 or more and 5 or less based on the weight of the pigment 1 based on the weight of the pigment. A pigment-based inkjet ink comprising the pigment dispersion according to any one of claims 12 to 18. An ink cartridge containing the pigment-based inkjet ink according to claim 19. An ink-jet printing apparatus which performs recording by discharging the pigment-based ink-jet ink according to claim 19 onto an image support. An image forming method, wherein printing is performed by an inkjet printing apparatus using the pigment-based inkjet ink according to claim 19. An image-formed product printed by an inkjet printing apparatus using the pigment-based inkjet ink according to claim 19. An image-formed product, wherein the image support of the image-formed product according to claim 23 is paper.