JP2004091610A - Ink for liquid jetting recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent nozzle clogging; to make a colorant taken well on a recording medium; to obtain a good pixel shape; and to achieve a high quality image recording. <P>SOLUTION: The recording liquid is for use in a liquid jetting recording head which makes recording by jetting the recording liquid through a minute orifice whose size Φ is ≤ 25 μm, putting the drops of the recording liquid on the paper on which the change in the contact angle of the recording liquid to the paper almost ceases to occur within 100 ms after the adhesion of the recording liquid to the recording medium. The recording liquid comprises the dispersion of fine particles with a dispersant in a solvent or the dispersion of the fine particles in the solvent, after they are surface-treated. When the size of the fine particle is Dp and the size of the minute orifice is Do, the relationship between Dp and Do meets the formula: 0.0005 ≤ Dp/Do ≤ 0.02. The fine particle is smaller than the thickness of the fibers of the paper and not larger than the gap formed by the interlaced fibers. <P>COPYRIGHT: (C)2004,JPO

Description

【００７４】
【表２】

【００７５】
【表３】

【００７６】
【表４】

【００７７】
表１、表２の結果より、顔料粒子径は、紙の繊維の太さより小さい場合が、良好な画素が得られることがわかる。また、紙の繊維が重なりあって形成される間隙以下の大きさにすることによって、良好な画素が得られることがわかる。
表３、表４の結果より、顔料粒子径は、紙あるいは樹脂部材表面の塗工物質の平均粒子径以下にすることにより、良好な画素が得られることがわかる。また、塗工表面の平滑度より小さくすることによって、良好な画素が得られることがわかる。
【００７８】
次に、本発明に適用されるインクを別の側面から検討した結果について説明する。一般に、着色剤として顔料を分散させたインクジェット用途に限らないインクはその用途、コストならびに作製技術に応じて、顔料粒子径が０．５〜１００μｍとされる。本発明では、前述のように、紙の繊維が織り成す凹凸面においても良好な画素を形成できるようにするため、また、インクジェット用途ということより、より微小な顔料粒子径とする必要がある。しかしながら、より微小な顔料粒子は凝集しやすく、単純には溶媒中に分散しない。そこで、本発明では、詳細な説明は後述するが、顔料粒子をインクの溶媒中に分散剤とともに分散させる、もしくは顔料粒子の表面を処理してインクの溶媒中に分散させるようにしている。そうすることによって顔料粒子の溶媒中への分散の粒子径下限値を０．００５μｍにまで拡大することができた。
【００７９】
本発明で使用するカラーインクに使用される分散剤は、アルカリ可溶性の水溶性脂樹であり、重量平均分子量は１，０００〜３０，０００であり、好ましくは、３，０００〜１５，０００の範囲である。具体的には、スチレン，スチレン誘導体，ビニルナフタレン，ビニルナフタレン誘導体，アクリル酸のアルキルエステル，メタクリル酸のアルキルエステル等の疎水性モノマーと，α，β−エチレン性不飽和カルボン酸及びその脂肪族アルコールエステル，アクリル酸，メタクリル酸，マレイン酸，イタコン酸，フマール酸及びそれらの誘導体等の親水性モノマーからなる共重合体及びそれらの塩等である。共重合体はランダム，ブロック，グラフト等の何れの構造を有していてもよく、酸価は１００〜４３０、好ましくは、１３０〜３６０の範囲である。
【００８０】
本発明に使用される分散剤としては、更に、ポリビニルアルコール，カルボキシメチルセルロース等の水溶性ポリマー，ナフタレンスルホン酸ホルムアルデヒド縮合物，ポリスチレンスルホン酸等の水溶性樹脂も使用することが可能である。しかし、アルカリ可溶性の水溶性脂樹の方が分散液の低粘度化が可能で、分散も容易であるという利点がある。これらの分散剤の使用量は、選択した顔料と分散剤とを用いて実験的に決定されるが、顔料に吸着せず溶解している樹脂の量は、インク中で４重量％以下であることが好ましい。
【００８１】
上記分散剤を水系にて用いるには塩基が必要である。そのために好適な塩基としては、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−メチルエタノールアミン，Ｎ−エチルジエタノールアミン，２−アミノ−２−メチルプロパノール，２−エチル−２−アミノ−１，３−プロパンジオール，２−（２−アミノエチル）エタノールアミン，トリス（ヒドロキシメチル）アミノメタン，アンモニア，ピペリジン，モルフォリン，β−ジヒドロキシエチル尿素等の有機塩基，水酸化ナトリウム，水酸化カリウム，水酸化リチウム等の無機塩基が挙げられる。最適な塩基種は選択した顔料及び分散剤の種類によって異なるが不揮発性で安定、かつ保水性の高いものが好ましい。用いる塩基の量は基本的には分散剤の酸価から計算される量から、それを中和するに必要な塩基量として夫々用いられる。場合によっては、酸の当量を上回る量の塩基を用いる場合がある。それは、分散性向上、インクのｐＨ調整、記録性能の調整、保湿性の向上等の目的で行う。
【００８２】
本発明においてインクに用いられる溶剤としては、水と混和性がある有機溶剤類である。有機溶剤としては、下記の如く３群に分けることができる。即ち、保湿性が高く、蒸発しにくく、親水性に優れる第１群の溶剤、有機性があり疎水性の表面への濡れ性がよく、蒸発乾燥性もある第２群の溶剤、適度の濡れ性を有し低粘度の第３群の溶剤（一価アルコール類）である。
【００８３】
第１群に属する溶媒としては、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，トリプロピレングリコール，グリセリン，１，２，４−ブタントリオール，１，２，６−ヘキサントリオール，１，２，５−ペンタントリオール，１，２−ブタンジオール，１，３−ブタンジオール，１，４−ブタンジオール，ジメチルスルホキシド，ダイアセトンアルコール，グリセリンモノアリルエーテル，プロピレングリコール，ブチレングリコール，ポリエチレングリコール３００，チオジグリコール，Ｎ−メチル−２−ピロリドン，２−ピロリドン，γ−ブチロラクトン，１，３−ジメチル−２−イミダゾリジノン，スルフォラン，トリメチロールプロパン，トリメチロールエタン，ネオペンチルグリコール，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イソプロピルエーテル，エチレングリコールモノアリルエーテル，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，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，プロピレングリコールモノメチルエーテル，ジプロピレングリコールモノメチルエーテル，β−ジヒドロキシエチルウレア，ウレア，アセトニルアセトン，ヘンタエリスリトール，１，４−シクロヘキサンジオール等が挙げられる。
【００８４】
第２群に属する溶媒としては、ヘキシレングリコール，エチレングリコールモノプロピルエーテル，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イソブチルエーテル，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ジエチルエーテル，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モノイソブチルエーテル，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，トリエチレングリコールジエチルエーテル，テトラエチレングリコールジメチルエーテル，テトラエチレングリコールジエチルエーテル，プロピレングリコールモノブチルエーテル，ジプロピレングリコールモノメチルエーテル，ジプロピレングリコールモノエチルエーテル，ジプロピレングリコールモノプロピルエーテル，ジプロピレングリコールモノブチルエーテル，トリプロピレングリコールモノメチルエーテル，グリセリンモノアセテート，グリセリンジアセテート，グリセリントリアセテート，エチレングリコールモノメチルエーテルアセテート，ジエチレングリコールモノメチルエーテルアセテート，シクロヘキサノール，１，２−シクロヘキサンジオール，１−ブタノール，３−メチル−１，５−ペンタンジオール，３−ヘキセン−２，５−ジオール，２，３−ブタンジオール，１，５−ペンタンジオール，２，４−ペンタンジオール，２，５−ヘキサンジオール等が挙げられる。
【００８５】
第３群に属する溶媒としては，エタノール，ｎ−プロパノール，２−プロパノール，１−メトキシ−２−プロパノール，フルフリルアルコール，テトラヒドロフルフリルアルコール等が挙げられる。以上のような水溶性溶媒の総量は、おおむねインク全体に対して５〜４０重量％の範囲で使用することが好ましい。
【００８６】
本発明のインクを構成する各水性顔料インクには、界面活性剤，ｐＨ調整剤，防腐剤等を添加することが可能である。界面活性剤は浸透性の高いカラーインクの調製、インクジェット方式としてバブルインクジェット方式を使用した場合における発熱ヒーター、吐出ノズル表面への濡れ性の調節等に有益である。材料としては既存の市販品から適宜選択することができる。以上のような材料から構成される各インクの物性をまとめると、黒色インクは、高い表面張力（概略３０〜６０ｄｙｎ／ｃｍ）を有し、一方、カラーインクは低い表面張力（概略１０〜４０ｄｙｎ／ｃｍ）を有することが好ましい。
【００８７】
このように分散剤を用いて顔料が安定分散するような本発明のインクの具体的製法の１例を以下に示す。この例は、スチレン／アクリル酸／エチルアクリレートからなる、酸価２９０、重量平均分子量５，０００、ガラス転移温度７７℃の共重合体Ｐをモノエタノールアミンを用いて溶解した水溶液を用い、アントラキノン系顔料ピグメントレッド−１７７分散体を作製し、インクとする例である。
【００８８】
・共重合体Ｐ水溶液（固形分１５重量％）・・・・・・・・・・４０部
・ピグメントレッド−１７７（クロモフタールレッドＡ２Ｂ、チバガイギー製）・・・・・・・・・・・・・・・・・・・・・・・・２４部
・ジエチレングリコール・・・・・・・・・・・・・・・・・・２０部
・イソプロピルアルコール・・・・・・・・・・・・・・・・・１０部
・水・・・・・・・・・・・・・・・・・・・・・・・・・・１３０部
【００８９】
これらの材料をバッチ式縦型サンドミル（アイメックス製）に仕込み、１ｍｍ径のガラスビーズをメディアとして充填し、水冷しつつ３時間分散処理を行った。分散後の液の粘度は３０ｃＰ、ｐＨ＝９．８の粗分散体を得た。この分散液を遠心分離機にかけ粗大粒子を除去し、また、遠心分離の条件を種々変えることによって顔料の平均粒径を０．００５〜４μｍまで変えた分散体を得た。この分散体を水、ジエチレングリコール、エチレングリコールモノブチルエーテル（６０：２５：１５重量比）にて希釈し、粘度３ｃＰ、表面張力４０ｄｙｎ／ｃｍ、ｐＨ＝９．５の赤色塩基性インクジェット用インクを得た。最終調製物の固形分は約７．５重量％であった。なお、このインク中の最終的な顔料含有率は５重量％である。
【００９０】
以上は、インク製法の１例であるが、このような製法によって製作される本発明における黒色水性顔料インクとカラーインクにおいて顔料粒子径を最適化し、また、使用する紙とインクの濡れを最適化してカラー記録を行うと、黒の文字等が鮮明であり、画像やグラフと黒の文字が隣り合っていても相互滲みがなく夫々明瞭である。
【００９１】
次に、顔料の安定分散を得る他の例について説明する。上記例は、分散剤を利用して顔料の分散性を向上させるものであるが、ここでは顔料の表面処理により分散性を向上させる例として、カーボンブラックの表面をグラフト重合処理によって親水化して分散性を高める方法について説明する。たとえば、グラフト重合するには、金属アクリレートやアンモニウムアクリレートといった過酸化物とともにカーボンブラックを撹拌し、グラフト反応位置を生成した後、ラジカル重合開始剤及びアミンラジカル重合促進剤の存在下でモノマーを重合させればよい。
そして、このグラフトカーボンブラックを使用したインクジェット記録用インクはグラフトカーボンブラックを含む重合反応懸濁液を希釈し、湿潤剤のような慣用のインクジェット添加物を添加することによって得られる。
【００９２】
他の例としては、カーボンブラックを、（１）常圧下で紫外線処理またはオゾン処理する工程と、（２）ビニル基を有するモノマーを熱重合によってグラフト重合させる工程とからなる製造方法において表面処理したカーボンブラックを、水または／及び水溶性有機溶剤に分散させる方法がある。
後者の場合、インク中に塩やラジカル重合剤といったような不純物を含まずにグラフト重合させることができ、印写のにじみ防止には好都合である。後者の例についてより詳細に説明する。
【００９３】
本発明におけるカーボンブラックとしては、コンタクト法，ファーネス法，サーマル法等の通常公知の方法によって製造されたカーボンブラックが使用できるが、その表面にはカルボキシル基，水酸基，カルボニル基等の官能基が存在する。これらの官能基と本発明に使用するビニル基を有するモノマーを重合させると水や水溶性有機溶剤への分散性が優れたカーボンブラックが得られる。
【００９４】
本発明に使用するビニル基を有するモノマーとしては具体的に、アクリルアミド，Ｎ，Ｎ−ジメチルアクリルアミド，アクリル酸，アクリロニトリル，メタクリル酸，メタクリル酸メチル，ビニル酢酸（ビニル酢酸より誘導されるポリビニルアルコール）等が挙げられ、アクリルアミドが最も好ましい。
紫外線処理またはオゾン処理はカーボンブラック表面の活性度を高める。具体的にはカーボンブラック表面に過酸化物を生成し、ビニル基を有するモノマーがカーボンブラックの表面に直接グラフト重合するためのものである。処理時間としては５分から２時間である。より長い処理時間は逆に生成した過酸化物を分解してしまうため好ましくない。
【００９５】
重合は、重合禁止剤となる酸素を取り除くために窒素を吹き込んでから熱をかけることによって行う。このとき、カーボンブラック表面の過酸化物から水酸基の結合が切れ、モノマーの重合とグラフト化が同時に起こる。
反応時間は３０分から６時間である。より長い反応時間は害はないが不経済である。また、反応させる温度は３０℃から８０℃である。冷却後に、副生成物として生成したホモポリマーは凍結乾燥や遠心分離といった慣用の方法で除去することが可能である。また未反応モノマーは水への溶解性が高いので熱水を用いて洗浄する。
【００９６】
本発明において処理されたカーボンブラックを得るのに際し、カーボンブラックの表面処理を均一に行い、カーボンブラックとビニル基を有するモノマーとを強固に結合させ、得られた処理カーボンブラックの水系インクジェット記録用インク中での分散性を高めるために、カーボンブラック／ビニル基を有するモノマーの比率は重量比で１０／１〜１０／１００とするのが好ましい。
【００９７】
このようにして得られた表面処理されたカーボンブラックは水や水溶性有機溶剤に容易に分散する。水溶性有機溶剤として具体的には、グリセリン，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＃２００，＃３００，＃４００等の多価アルコール類，トリエチレングリコールモノメチルエーテルメタノール等の多価アルコール類のアルキルエーテル誘導体類，グリセリルモノアセテート等の多価アルコールのエステル誘導体類，Ｎ−メチル−２−ピロリドン等の含窒素環状化合物，エタノール，ｎ−プロパノール，ｉｓｏ−プロパノール等の炭素数１〜６の低級アルコール等が挙げられる。
【００９８】
上記水溶性有機溶剤の使用量は、インクの全重量に対して４０重量％以下で、好ましくは３〜３０重量％である。
表面処理されたカーボンブラックの水及び水溶性有機溶剤への分散は容易なので、ボールミルやサンドミル、ロールミルといったような分散機での高剪断力を必要とせず、超音波ホモジナイザーのような超音波分散機を使用すれば十分に分散させることができる。
インクに使用する表面処理カーボンブラックの使用量は表面処理による重合度を考慮する必要があるが、インクの色濃度及び、インク吐出ノズルの目詰まり防止を考慮して、２〜１０重量％とされる。これについては後述する。
【００９９】
そのほかにも、インク物性を調節するための粘度調整剤や表面張力調整剤、ｐＨ調整剤等の添加剤や、防カビ剤、防腐剤、また、バインダーとしての樹脂を適宜添加することができる。
以下、この方法によって製作したインクの例を具体的に説明する。
【０１００】
例１
成分Ａ
カーボンブラック　　＃２５　（三菱化学製）・・・・・・・・・・・・２０部
アクリルアミド・・・・・・・・・・・・・・・・・・・・・・・・・・１０部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・９０部
成分Ｂ
表面処理カーボンブラック・・・・・・・・・・・・・・・・・・・・・・５部
グリセリン・・・・・・・・・・・・・・・・・・・・・・・・・・・・・２部
エタノール・・・・・・・・・・・・・・・・・・・・・・・・・・・・・６部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・８７部
【０１０１】
カーボンブラックを高圧水銀ランプ（８００Ｗ）下で２０分間紫外線処理し、その処理済みのカーボンブラック等の成分Ａを混合し、窒素ガスを溶液中に吹き込みながら、７０℃で撹拌し、５０分重合させた。重合物を遠心分離機で１２０００回転×７０分でホモポリマーを十分に除去し、熱水で１５０分攪拌しながら洗浄した後乾燥させ、次に、成分Ｂを混合し、超音波ホモジナイザーで粒径を整え、０．２μｍのメンブランフィルターで粗大粒子及びごみを除去してインクジェット記録用インクを得たが、このインクは顔料分散状態が良好であり、保存安定性に優れたものであった。
【０１０２】
例２
成分Ａ
カーボンブラック　　ＭＡ−７（三菱化学製）・・・・・・・・・・・・１０部
アクリル酸・・・・・・・・・・・・・・・・・・・・・・・・・・・・９０部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・２１０部
成分Ｂ
表面処理カーボンブラック・・・・・・・・・・・・・・・・・・・・・・３部
グリセリン・・・・・・・・・・・・・・・・・・・・・・・・・・・・１０部
１−プロパノール・・・・・・・・・・・・・・・・・・・・・・・・・・４部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・８３部
【０１０３】
カーボンブラックを高圧水銀ランプ（８００Ｗ）下で１５分間紫外線処理し、その処理済みのカーボンブラック等の成分Ａを混合し、窒素ガスを溶液中に吹き込みながら、６５℃で撹拌し、１００分重合させた。重合物を遠心分離機で１３０００回転×９０分でホモポリマーを十分に除去し、熱水で１８０分攪拌しながら洗浄した後乾燥させ、次に、成分Ｂを混合し、超音波ホモジナイザーで粒径を整え、０．２μｍのメンブランフィルターで粗大粒子及びごみを除去してインクジェット記録用インクを得たが、このインクは顔料分散状態が良好であり、保存安定性に優れたものであった。
【０１０４】
例３
成分Ａ
カーボンブラック　　ＭＡ−６００　　　（三菱化学製）・・・・・・・１０部
Ｎ、Ｎ−ジメチルアクリルアミド・・・・・・・・・・・・・・・・・・５０部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・２００部
成分Ｂ
表面処理カーボンブラック・・・・・・・・・・・・・・・・・・・・・・３部
エチレングリコール・・・・・・・・・・・・・・・・・・・・・・・・・４部
エタノール・・・・・・・・・・・・・・・・・・・・・・・・・・・・・５部
水・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・８８部
【０１０５】
カーボンブラックを電圧６０Ｖ、周波数５０Ｈｚ、酸素流量４０ｍｌ／ｍｉｎのオゾン発生装置でオゾン処理し、その処理済みのカーボンブラック等の成分Ａを混合し、窒素ガスを溶液中に吹き込みながら、５０℃で撹拌し、１５０分重合させた。重合物を遠心分離機で１２０００回転×８０分でホモポリマーを十分に除去し、熱水で１８０分攪拌しながら洗浄した後乾燥させ、次に、成分Ｂを混合し、超音波ホモジナイザーで粒径を整え、０．２μｍのメンブランフィルターで粗大粒子及びごみを除去してインクジェット記録用インクを得たが、このインクは顔料分散状態が良好であり、保存安定性に優れたものであった。
【０１０６】
以上、分散剤を利用して顔料の分散性を向上させる場合と顔料の表面処理により分散性を向上させる場合について説明してきたが、本発明ではこのような工夫により、従来にはない非常に微細な粒子径（最小０．００５μｍ）をもつ顔料であっても安定した分散が得られるとともに、保存安定性に優れた良好なインクが得られるようになった。
【０１０７】
次に、本発明の顔料インクと被記録体との濡れの関係について検討した結果について説明する。被記録体の代表例である紙の場合、濡れは紙へのインクの浸透に先立って起こる現象である。
前述のように“紙とは植物繊維を水中に懸濁させた後、水を漉して、薄く平らに絡み合わせたもの”であるが、近年、製紙／塗工技術の進歩、高画質記録への要求等により、紙を単に“繊維の集合体”という扱いではなく、インクと接触した場合に、インクの挙動がどうなるかを、数１０ミリ秒のオーダーでとらえる必要が出てきている。本発明ではこの点に鑑み、被記録体に本発明のインクが付着した場合の濡れと画質の関係を調べたものである。
【０１０８】
一般に、このような紙とインクの濡れ性の関係は、Ｗｉｌｈｅｌｍｙ法を用いた動的濡れ性試験機（たとえは、製品名称ＷＥＴ−３０００レスカ株式会社製）等によって測定されるが、ここでは静的濡れ性測定機として知られるゴニオメーターを用い、紙の上にインクを滴下し、その接触角を測定した。ただし、接触角の時間的挙動を追跡するため、高速度カメラを併用し、数〜数１０ミリ秒のオーダーで接触角変化を記録した。また、そのインクと紙を使用した場合の画素形状の良否を、１００倍の顕微鏡画像を見ながら官能評価で判断した。
画素形成に使用したヘッド、インクなどの諸条件は、前述の紙の表面性状と画素形状の評価を行った場合と同じである。また使用した顔料インクの顔料粒子径は、０．０５μｍのものである。
【０１０９】
図７は、上記のような方法で、接触角の時間的変化を測定した結果である。使用した紙は、Ａ〜Ｆまでの６種類である（Ｄは樹脂部材〜ポリエチレンフィルムに粒子径１μｍの炭酸カルシウムを塗工したもの）が、各紙の繊維太さは５〜１０μｍ、繊維が重なりあってできる間隙は１〜２μｍ、紙もしくは樹脂部材の表面平滑度は１〜２ｓである。
【０１１０】
なお、Ａ〜Ｆまでの紙（Ｄ除く）の紙の密度は、それぞれ、
Ａ　０．９６ｇ／ｃｍ^３
Ｂ　０．４１ｇ／ｃｍ^３
Ｃ　０．７８ｇ／ｃｍ^３
Ｅ　０．５８ｇ／ｃｍ^３
Ｆ　０．６２ｇ／ｃｍ^３
である。ただし、ここでいっている密度とは、製紙業界で一般に適用している密度のことであり、秤量（１ｍ２あたりの重さ（グラム数））を厚さで除して算出したものである（いわゆる物理学でいうところの密度とは厳密には同じではない）。
【０１１１】
画素形状評価結果は、それぞれの画素径はΦ６０μｍ〜Φ７０μｍまで変動したが、紙Ａ，Ｂのドット形状がいびつでもっとも悪く、紙Ｃは良好、樹脂部材Ｄ、紙Ｅ、Ｆは大変良好な丸い形状であった。なお評価は、１００倍の顕微鏡画像による官能評価で、各々２０個ずつピックアップして評価したものである。
すなわち、紙（もしくは樹脂部材）Ｃ，Ｄ，Ｅ，Ｆのように、紙もしくは樹脂表面にインクが付着してから、１００ｍｓ以内に接触角の変動がなくなり、ほぼ一定の値になるような紙（もしくは樹脂部材）とインクの組み合わせにすれば、良好な丸い画素が得られることがわかった。また、紙Ａ，Ｂのように、接触角の変動がいつまでも続くものは、画素形状が悪く、非実用的であることがわかった。また、それらは、接触角が比較的高い（１００度以上）ものであった。
【０１１２】
なお、この結果は、インク滴が付着してから３００ｍｓまでの挙動を調べたものであるが、紙Ａ，Ｂであっても、３０〜４０秒後には紙の中にインクが浸透、あるいは溶媒成分が乾燥し、接触角という概念はなくなる。紙（もしくは樹脂部材）Ｃ，Ｄ，Ｅ，Ｆも同様である。また、画素形状の評価は、完全に紙の中にインクが浸透、あるいは溶媒成分が乾燥した後に行っている。
【０１１３】
以上の説明より明らかなように、上記のように被記録体とインクの組み合わせを最適化すれば、一般の普通紙（例えば、上質紙、中質紙あるいはボンド紙等）、コート紙、ＯＨＰ用のプラスチックフィルム等の何れでも使用することができる。前述のように、本発明は全てのインクジェット記録方式に適用できるが、中でも、熱エネルギーによるインクの発泡現象によってインクを吐出させるタイプのインクジェット記録方法に使用する場合に特に好適であり、インクの吐出が極めて安定し、サテライトドットの発生等が生じないという特徴がある。但し、この場合に熱的な物性、例えば、比重、熱膨張係数及び熱伝導率等を調整する必要が生ずることもある。
【０１１４】
次に、本発明のより特徴的な点について説明する。前述のように、本発明は、微細な開口からインクを吐出させるといういわゆるインクジェット記録方式に関するものであり、インクジェット記録方式にとって、吐出口部における目詰まりは致命的なものである。これは染料インクを使用するものより、本発明のように、溶媒中に微粒子を分散させた顔料インクを使用するものでは、顔料が染料のように溶解しているわけではなく分散しているだけなので、より目詰まりが起こりやすい。さらに、本発明では、従来にはない微細な吐出口径、例えば、吐出口径がΦ２５μｍ以下（面積でいうならば５００μｍ^２未満）であるようなインクジェット記録ヘッドを想定しているので、この目詰まりは大変深刻な問題である。
【０１１５】
ところで、目詰まりとは、微細な開口からインクが噴射するというインクジェット記録方式の原理そのものに由来するものである。つまり、開口が微細であるがゆえに生じるものである。よって、その開口の大きさと、いわばインク中の異物とでもいうべき顔料の大きさには密接な関係がある。
【０１１６】
本発明は、この点に鑑み、吐出口の大きさと顔料粒子の大きさに着目し、目詰まりの生じにくさとそれらの関係を見い出したものである。具体的には、顔料粒子径を変えたインクを調合し、吐出口の大きさがわかっているインクジェット記録ヘッドを使用し、一定時間インク噴射を行った後、一定時間放置し、インク噴射を再開し、吐出口の目詰まりの有無を調べた。その場合、吐出口の完全閉塞だけではなく、部分的な目詰まりおよびそれに至る事前の兆候（わずかな目詰まり）も目詰まりとみなしてテストした。
【０１１７】
使用したヘッドは、図１に示したような構成の熱エネルギーを使用するインクジェット記録方式のヘッドである。但し、図１に示したヘッドは、流路の先端がそのまま吐出口になっているものを示したが、実験に使用したものは、図３に示すように、この先端に流路の配列密度４と同じ配列密度で形成したノズル２１を有するノズル板２０を設けたものである（図３（Ａ）はノズル板２０を取り付ける前の斜視図、図３（Ｂ）は取り付けた後の斜視図である）。また、その吐出口（ノズル）の数も、図１、図３に示したものは説明を簡単にするため吐出口が４個しかないもの、あるいは部分的に示したものであるが、実際に使用したのは吐出口の数が２５６個で、その配列密度が６００ｄｐｉのものである。また、発熱体の大きさは２０μｍ×８５μｍで、その抵抗値は１０５Ωであり、インク噴射の駆動電圧は２２Ｖ、駆動パルス巾は６μｓ、駆動周波数は１２ｋＨｚとした。
なお、記録ヘッドはＨ１〜Ｈ４まで用意した（それぞれの吐出口径をＨ１＝Φ２５μｍ、Ｈ２＝Φ２０μｍ、Ｈ３＝Φ１５μｍ、Ｈ４＝Φ１０μｍとした）。また、そのノズル板の厚さは、全て４０μｍとした。
【０１１８】
使用したインクは、以下のような組成および製法によるものであるが、顔料粒径が０．００３〜２μｍまで変えたものを準備し、吐出口径の異なるＨ１〜Ｈ４と組み合わせてテストした。また、一定時間インク噴射を行った後の放置の条件は、温度４０℃、湿度３０％の雰囲気中で１０時間放置である。
【０１１９】
インクの製法を以下に示す。スチレン／メタクリル酸／ブチルアクリレートからなる、酸価３２５、重量平均分子量１１，０００、ガラス転移温度８４℃の共重合体Ｐをカリウムを用いて溶解した水溶液を用い、以下のカーボンブラック分散体を作製した。
【０１２０】
・共重合体Ｐ水溶液（固形分２０重量％）・・・・・・・・・・４０部
・カーボンブラック　　ＭＡ−８００（三菱化学製）・・・・・２５部
・ジエチレングリコール・・・・・・・・・・・・・・・・・・２０部
・イソプロピルアルコール・・・・・・・・・・・・・・・・・１０部
・水・・・・・・・・・・・・・・・・・・・・・・・・・・１３０部
【０１２１】
これらの材料をバッチ式縦型サンドミル（アイメックス製）に仕込み、１ｍｍ径のガラスビーズをメディアとして充填し、水冷しつつ３時間分散処理を行った。分散後の液の粘度は１６ｃＰ、ｐＨ＝９．７の粗分散体を得た。この分散液を遠心分離機にかけ粗大粒子を除去し、また、遠心分離の条件を種々変えることによって顔料の平均粒径を０．００５〜１μｍまで変えた分散体Ｄ１〜Ｄ２２を得た。これらの分散体を水にて希釈し、粘度２．４ｃＰ、表面張力４６ｄｙｎ／ｃｍ、ｐＨ＝９．５の黒色塩基性インクジェット用インクＢ１〜Ｂ２２を得た。最終調製物の固形分は約７重量％であった。なお、これらのインク中の最終的な顔料含有率は５重量％である。なお、平均粒径は、動的光散乱法による粒度分布測定装置ＥＬＳ−８００（大塚電子製）にて測定を行い、平均量は自己相関関数の初期勾配から得られる値で示した。
【０１２２】
これらのインクＢ１〜Ｂ２２と上記の吐出口径を変えたヘッドＨ１〜Ｈ４を組み合わせて、目詰まりの発生状況を調べた結果を表５〜表８に記す。
但し、表５はヘッドＨ１（吐出口径Ｄｏ＝Φ２５μｍ）の場合、表６はヘッドＨ２（吐出口径Ｄｏ＝Φ２０μｍ）の場合、表７はヘッドＨ３（吐出口径Ｄｏ＝Φ１５μｍ）の場合、表８はヘッドＨ４（吐出口径Ｄｏ＝Φ１０μｍ）の場合を示す。判定の○は実用的に良好に使用できる場合、△は使うことは可能であるがあまり好ましくない場合、×は全く実用的ではない場合を示している。
【０１２３】
【表５】

【０１２４】
【表６】

【０１２５】
【表７】

【０１２６】
【表８】

【０１２７】
以上の結果より、吐出口径がΦ１０μｍ〜Φ２５μｍの噴射ヘッドを用いた場合、顔料粒径Ｄｐと吐出口径Ｄｏとは、０．０００５≦Ｄｐ／Ｄｏ≦０．０２の関係を満足するようにすれば目詰まりのない安定したインク噴射が得られることがわかる。なお、実験では、吐出口が丸いもので行っているが、他の形状（多角形等）の場合は、その面積比で換算した範囲内にすればよい。
【０１２８】
次に本発明の他の特徴について説明する。前述のように本発明は、顔料インクを前提に考えている。すなわち、記録液体中の着色剤は、水などの溶媒に溶解している染料ではなく、顔料である微粒子が分散しているものである。よって、その顔料含有量や固形分を含む顔料の分散剤のインク中の含有量は、目詰まりに対して大きな影響をおよぼす。そこで、ここでは、それらの含有量と吐出口の目詰まりの関係について調べた。
【０１２９】
使用したヘッドは、前記ヘッドＨ２（吐出口径Ｄｏ＝Φ２０μｍ）と同じものであり、顔料粒径Ｄｐ＝０．０３μｍのインク（Ｂ５）において、その顔料含有量と顔料分散剤としてのスチレン／メタクリル酸／ブチルアクリレートからなる共重合体Ｐの量を変えて、最終的なインク中の固形分の量と目詰まりのしやすさを調べた。目詰まりテストの方法などは、前述の方法と同じである。結果を表９，表１０に示す。判定の○は実用的に良好に使用できる場合、×は全く実用的ではない場合を示している。
【０１３０】
【表９】

【０１３１】
【表１０】

【０１３２】
以上の結果より、インク中の顔料含有量は１〜１０重量％にすればよく、それより多くすると目詰まりが生ずることがわかる。また、顔料含有量だけでなく、顔料も含む最終的な固形分の量も１５重量％以下にしなければならないこともわかる。なお、顔料含有量が１重量％の場合は目詰まりの心配はないが、このインクだけで使用する場合は濃度が低くて実用的ではない。ただし、複数の種類のいわゆる濃淡インクを用いる記録装置の淡いインクとして好適に使用できる。また、このインクだけで使用する場合であっても、染料を添加して濃度不足分を補うことは可能である。
【０１３３】
次に、本発明のさらに他の特徴について説明する。本発明が適用されるインクジェット記録ヘッドは、一般的にはカラー記録に好適に適用されるので、ここでは、本発明が好適に適用されるカラーインクジェット記録ヘッドの構成を説明する。
【０１３４】
図８は、本発明のインクジェットヘッドの一例を示す図で、本発明では、図示のように、１枚の共通の発熱体基板部３０の上に、複数色のインク吐出エレメント３１Ｙ，３１Ｍ，３１Ｃを形成してなる。この例では、複数色のインクとして、イエロー（Ｙ），マゼンタ（Ｍ），シアン（Ｃ）の３色の例を示している。なお、この例、およびこれ以降の例で、各色のインク吐出エレメント、吐出口は、図を簡単にするため、各色４個あるいは５個で説明するが、実際には、各色６４〜１０２４個が好適に使用される。
【０１３５】
図９は、図８の記録ヘッド部に、それぞれＹ，Ｍ，Ｃのインクが供給されるようなインクタンク部４０を設けた図を示す。なお、この図は、記録ヘッド部とインクタンク部とで構成される本発明のインクジェット記録ヘッドの概念を示す図であり、実際のもの（後述する）とは異なる。
【０１３６】
図１０は、本発明によるインクジェットヘッドをキャリッジ上に搭載して記録を行う、いわゆるシリアルプリンタの構成を示す図で、図中、５０は本発明によるインクジェットヘッド、５１は記録紙、５２はキャリッジ、５３はキャリッジのガイドロッド、５４はキャリッジを移動させるためのネジ棒、５５は記録紙搬送ローラ、５６は記録紙おさえコロで、周知のように、縦方向（記録紙５１の移動方向）にＹ、Ｍ、Ｃと１列に配列された記録ヘッド５０（図示例の場合、図９に示したヘッドが搭載されている）を、記録紙５１の前をＸ方向に往復運動しながら記録を行う。本発明では、キャリッジを１回走査するごとに記録紙を図の矢印Ｙ方向に移動していく。従って、１回の走査で記録される領域は、ヘッドの吐出エレメント、つまり、吐出口の列の長さ分だけである。また、Ｙ，Ｍ，Ｃは縦方向に１列に並んでいるので、２回以上の走査によって、Ｙ，Ｍ，Ｃのインクによる印写領域がオーバーラップすることにより、はじめてフルカラー記録を行うことができる。
【０１３７】
なお、以上の説明は、Ｙ，Ｍ，Ｃの３色の例を示したが、本発明では、これにブラック（Ｂ）を加えた４色の吐出口列を持つインクジェットにも適用される。
図１１にその例を示すが、この場合、図示のように、図８に示した例に、更にブラック用のインク吐出エレメント３１Ｂを付加したものとなる。
【０１３８】
図１２は、４色の吐出口列を持つ他の例である。図１１には、各色のインク流路を独立に製作した例を示しているが、この図は、４色分の流路を一体的にプラスチック６０の成形で製作した例である。こうすることにより、そのアセンブリコストは著しく下げることができる。
【０１３９】
通常、カラーインクジェット記録装置は、図１に示したような１つの記録ヘッドに１色のインクを充填し、これを複数色分、図１３のように、キャリッジ７０上に並べて構成する。７１Ｂ，７１Ｃ，７１Ｍ，７１Ｙはそれぞれブラック，シアン，マゼンタ，イエローの各カラーインクを吐出するための記録ヘッドである。これは、一つには目詰まり対策等の信頼性確保のためである。例えば、図１３のように４色のインクを充填したヘッド７１Ｂ，７１Ｃ，７１Ｍ，７１Ｙを独立にキャリッジ７０上に並べて構成した場合、仮にどれか１色のヘッドが目詰まりを起こした場合、その１色のヘッドを交換することにより、もとの状態に回復させることができる。
【０１４０】
一方、本発明では、図８〜図１２に示した、複数色にインクを吐出させるための記録ヘッドを一体的に形成している。前述のように、目詰まりを起こした場合の回復措置を考えると、図１３に示したように、複数色のインクを充填したヘッドを独立にキャリッジ上に並べて構成するほうが有利ではあるが、本発明では前述のように、その顔料粒径、含有率あるいはインク中の固形分の量を鋭意検討して最適化したため、目詰まりの不安は解消している。よって、図１３に示したような複数色のインクを充填したヘッドを独立にキャリッジ上に並べて構成する必要はなく、アセンブリコストの低減、コンパクト性の実現、複数色のドット位置精度の高精度化のために、図８〜図１２に示したように、複数色のインクを吐出させるための記録ヘッドを一体的に形成している。
【０１４１】
なお、ここでいう一体的形成とは、図８〜図１２に示したバブルインクジェットヘッドの例のように発熱体基板を共通の１枚の基板にした例のみならず、図１４に示すように複数色のインクを充填したヘッド、例えば、７１Ｂ，７１Ｃ，７１Ｍ，７１Ｙを積層して一体化したものも含む。この例では、流路の先端７２Ｂ，７２Ｃ，７２Ｍ，７２Ｙに共通の１枚のノズル板７３を設けた例を示しており（図１４（Ａ）はノズル板７３を取り付ける前、図１４（Ｂ）は取り付けた後の斜視図）、この場合は、高精度に穿孔、アセンブリ化、一体化された共通の１枚のノズル板７３を設けているため、製造コストの低減のみならず、複数色のドット位置精度も高精度が得られる。
【０１４２】
図１５は、複数色（この例では、Ｙ，Ｍ，Ｃの３色）のインクを噴射できるヘッドユニットをインク容器部と一体的に形成した例であり、図１５（Ａ）は全体斜視図、図１５（Ｂ）は分解斜視図で、図中、１００はヘッドユニット、１０１はヘッドチップ、１０２はプリントサーキット、１０３は上蓋、１０４はインク容器部、１０５（１０５Ｙ，１０５Ｍ，１０５Ｃ）はステレスメッシュフィルタ、１０６（１０６Ｙ，１０６Ｍ，１０６Ｃ）はインクを含んだフォーム材、１０７は底蓋、この例では、ヘッド部およびそれに連絡するインク容器部を内部で３つに分けて、Ｙ，Ｍ，Ｃののインクを別々に充填したものである。このように、複数色を一体型にしたヘッドユニットは、非常にコンパクトに形成できるので、キャリッジに搭載する際、軽量小型であるため、小さなキャリッジですみ、また、キャリッジを駆動するモータも小型、省エネルギーが実現できる。
【０１４３】
図１６は、図１５に示した複数色のインク容器一体型ヘッドユニットにおいて、インク容器部のみを分離可能な構成とした場合の例を説明するための図で、図１６（Ａ）はヘッドユニット１１０の全体斜視図、図１６（Ｂ）は該ヘッドユニット１１０を記録ヘッド部１１１とインク容器部１１２を分離した状態の斜視図を示す。これにより、カラーイメージ印写で大量にインクを消費してもインク容器部１１２のみを交換すればよいので、コスト低減が実現する。しかも、図１５で説明したカラーの一体型ヘッドの利点はそのまま維持される。
【０１４４】
図１７は、上記のような一体型ヘッドユニットで、インクの色ごとにインク容器部を分離できるようにした例を説明するための図で、図１７（Ａ）は全体斜視図、図１７（Ｂ）はヘッドユニット１１０の記録ヘッド部１１１と各色のインク容器部１１２（１１２Ｙ，１１２Ｍ，１１２Ｃ）を分離した状態の斜視図を示す。このようにすることのメリットは、カラーイメージ印写では、必ずしもＹ、Ｍ、Ｃのインクが同じスピードで消費されるわけではないので、もし、図１５、図１６の例において、どれかのインクがなくなった時に他のインクが残っていても、ヘッドユニットあるいは一体型インク容器全体を交換しなければならず、ランニングコストの面で不利であるのに対して、本発明のように各色のインク容器を別々にしておくことにより、なくなったインクの容器のみ交換することで、より一層のランニングコストの低減が実現する。
【０１４５】
なお、以上の説明は全てバブルインクジェットの例で説明したが、本発明はこれに限定されることなく、微細な吐出口を有し、顔料インクを使用する全てのインクジェットに適用されるものである。また、記録ヘッド例も単色のインクの例をあげて説明しているが、カラーインクジェットにも適用できるのはいうまでもない。
【０１４６】
【発明の効果】
本発明によれば、着色材として微粒子である顔料を分散させた記録液体（インク）において、微粒子径を吐出口径ならびに紙の繊維の太さあるいはその間隙の関係において最適化、あるいは使用する紙の濡れとの関係において最適化したので、Ф２５μｍ以下であるような従来にはない非常に微細な吐出口（ノズル）を用いる噴射ヘッドに使用しても、ノズル目詰まりが生じず、高い信頼性が得られるとともに、紙上で色材が良好に付着し、かつ良好な画素形状が得られ、高画質記録が実現するとともに、高耐水性、高耐光性も実現できた。
【０１４７】
また、着色材として微粒子である顔料を分散させた記録液体（インク）において、微粒子径を吐出口径ならびに紙の表面の塗工物質の粒子の大きさ等の関係において最適化、あるいは、使用する紙の濡れとの関係において最適化したので、Ф２５μｍ以下であるような従来にはない非常に微細な吐出口（ノズル）を用いる噴射ヘッドに使用しても、ノズル目詰まりが生じず、高い信頼性が得られるようになった。また紙上で色材が良好に付着し、かつ良好な画素形状が得られ、高画質記録が実現するとともに、高耐水性、高耐光性も実現できた。
【０１４８】
また、着色材として微粒子である顔料を分散させた記録液体（インク）において、微粒子径を吐出口径ならびに記録される樹脂部材の表面の塗工物質の粒子の大きさ等の関係において最適化、あるいは使用する樹脂部材の表面の濡れとの関係において最適化したので、Ф２５μｍ以下であるような従来にはない非常に微細な吐出口（ノズル）を用いる噴射ヘッドに使用しても、ノズル目詰まりが生じず、高い信頼性が得られるようになった。また樹脂部材の表面で色材が良好に付着し、かつ良好な画素形状が得られ、高画質記録が実現するとともに、高耐水性、高耐光性も実現できた。
【０１４９】
また、着色材として微粒子である顔料を分散させた記録液体（インク）において、記録液体（インク）中の微粒子の含有率ならびに固形分の量を最適化し、記録液体（インク）の溶媒は被記録体の内部深さ方向に浸透させ、固形分を被記録体の表面に付着、保持してなるようにしたので、実用上十分な濃度が得られ、かつ顔料が安定分散し、高耐水性、高耐光性を実現するとともに、従来にはない非常に微細な吐出口（ノズル）を用いる噴射ヘッドに使用しても、吐出口の目詰まりがなくなり信頼性が向上し、かつ良好な画素形状が得られ、高画質記録が得られるようになった。
【０１５０】
また、上述のような記録液体（インク）を、記録液体吐出部であるヘッド部と記録液体貯留部（インク容器部）とが分離可能であるヘッドユニットに使用するようにしたので、請求項１乃至４の効果に加え、この記録液体（インク）を使用するインクジェット記録装置のランニングコストを低減することができた。
【０１５１】
更には、上記のような記録液体（インク）を、記録液体の種類に応じて分離可能である記録液体貯留部に充填されているようにしたので、どれかの記録液体（インク）がなくなったときは、記録液体（インク）の種類に応じて記録液体貯留部（インク容器部）のみを交換すればよいので、前記の効果に加え、カラー記録を行うにあたってさらに一層のランニングコスト低減が実現できた。
【０１５２】
更には、上記のような記録液体（インク）を、記録液体（インク）中に熱によって気泡を発生させ、その作用力で記録液体（インク）を噴射するサーマルインクジェット方式に適用した場合、使用条件が過酷になるが、本発明の条件を選ぶことによって、本発明のようにФ２５μｍ以下であるような従来にはない非常に微細な吐出口（ノズル）を用いる噴射ヘッドに使用しても、ノズル目詰まりのない安定噴射が行え、信頼性が高く、高画質印写が実現した。
【０１５３】
さらに、サーマルインクジェット方式の場合、噴射ヘッド部が半導体製造プロセスを利用して製作できるので、本発明のようにФ２５μｍ以下であるような従来にはない非常に微細な吐出口（ノズル）を用い、高精度印写を行うのに必要な噴射ヘッドであって、その発熱体部や吐出口部が非常に微細かつ高密度に配列される場合にも簡単かつコンパクトに、しかも高歩留まり、すなわち低コストで製作できる。よって、本発明の記録液体（インク）を使用するこのような液体噴射記録装置のよりコンパクト化、製造コストの低減が実現した。
【０１５４】
【図面の簡単な説明】
【図１】バブルインクジェット型記録ヘッドの一例を説明するための図である。
【図２】バブルインクジェット方式のインクジェットのインク滴吐出の原理を説明するための図である。
【図３】ノズル板を有するインクジェットヘッドの例を示す図である。
【図４】紙表面の拡大イメージ図である。
【図５】大粒径顔料が紙表面に付着した場合のイメージ図である。
【図６】繊維より小さい顔料粒子が紙表面に付着した場合のイメージ図である。
【図７】紙表面にインク滴が付着した場合の接触角の時間変化を示す図である。
【図８】本発明のインクジェットヘッドの一例を示す図である。
【図９】図８の記録ヘッド部にインクタンクを設けた例を示す図である。
【図１０】インクジェットヘッドを搭載したシリアルプリンタの構成例を示す図である。
【図１１】４色の吐出口列を持つ例を示す図である。
【図１２】４色のヘッドを一体化した例を示す図である。
【図１３】４色のヘッドをキャリッジ上に独立して並べた例を示す図である。
【図１４】複数色のヘッドを積層して一体化した例を示す図である。
【図１５】ヘッドユニットとインク容器部とを一体的に形成した例を示す図である。
【図１６】インク容器部のみを分離可能な構成にした場合の例を示す図である。
【図１７】インクの色ごとにインク容器を分離できるようにした例を示す図である。
【符号の説明】
１…蓋基板、２…発熱体基板、３…記録液体流入口、４…吐出口、５…流路、６…共通液室、７…個別制御電極、８…共通電極、９…発熱体、１０…インク、１０′…インク柱、１１…気泡、１２…液滴、２０…ノズル板、２１…ノズル、３０…発熱体基板、３１Ｙ、３１Ｍ、３１Ｃ、３１Ｂ…インク吐出エレメント、４０…インクタンク、５０…記録ヘッド、５１…記録紙、５２…キャリッジ、５３…ガイドロッド、５４…ネジ棒、５５…記録紙送りローラ、５６…記録紙おさえコロ、７０…キャリッジ、７１Ｂ、７１Ｃ、７１Ｍ、７１Ｙ…ヘッド、７２Ｂ、７２Ｃ、７２Ｍ、７２Ｙ…吐出口、７３…ノズル板、１００…ヘッドユニット、１０１…ヘッドチップ、１０２…ＦＰＣ、１０３…上蓋、１０４…インク容器部、１０５…フィルタ、１０６…インク含浸用フォーム材、１０７…底蓋、１１０…ヘッドユニット、１１１…記録ヘッド部、１１２…インク容器部。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a recording liquid in which fine particles are dispersed for use in a liquid jet recording apparatus.
[0002]
[Prior art]
The non-impact recording method has recently attracted attention in that the generation of noise during recording is extremely small to a negligible level. Among them, the so-called inkjet recording method, which can perform high-speed recording and can perform recording on so-called plain paper without requiring a special fixing process, is an extremely powerful recording method, and various methods have been used. Some have been proposed and commercialized with improvements, while others are still being put to practical use.
[0003]
In such an ink jet recording method, recording is performed by flying droplets of a recording liquid called so-called ink and attaching the droplets to a recording member. Depending on the method for controlling the flying direction of the generated recording liquid droplet, there are various methods as follows.
[0004]
For example, it is of a Teletype type disclosed in U.S. Pat. No. 3,060,429, in which droplets of a recording liquid are generated electrostatically, and the generated droplets of the recording liquid are generated according to a recording signal. There is an electrostatic suction type in which an electric field is controlled and recording is performed by selectively adhering a recording liquid droplet onto a recording member.
[0005]
In addition, it is of the Sweet type disclosed in U.S. Pat. No. 3,596,275, U.S. Pat. No. 3,298,030, etc., and generates small droplets of a recording liquid whose charge amount is controlled by a continuous vibration generation method. There are a continuous flow type and a charge control type in which a droplet having a controlled charge amount is caused to fly between deflection electrodes to which a uniform electric field is applied, thereby performing recording on a recording member.
[0006]
As another method, for example, a Hertz method disclosed in US Pat. No. 3,416,153, in which an electric field is applied between a discharge port and a ring-shaped charging electrode, and a recording liquid is applied by a continuous vibration generating method. There is a method of recording by generating and atomizing small droplets. That is, in this method, the atomization state of the small droplet is controlled by modulating the electric field intensity applied between the ejection port and the charging electrode in accordance with the recording signal, and the image is recorded with the gradation of the recorded image.
[0007]
Further, as another method, for example, there is a Stemme method disclosed in US Pat. No. 3,747,120. This system is fundamentally different in principle from the above three systems. That is, in each of the three methods, the droplets of the recording liquid ejected from the ejection port are electrically controlled while flying, and the droplets carrying the recording signal are selectively attached to the recording member. On the other hand, in the Stemme method, recording is performed by ejecting a small droplet of recording liquid from an ejection port in accordance with a recording signal. That is, in the Stemme method, an electric recording signal is applied to a piezoelectric vibrating element attached to a recording head having a discharge port for discharging a recording liquid, and the electric recording signal is converted into mechanical vibration of the piezoelectric vibrating element. The recording is performed by ejecting a small droplet of the recording liquid from the ejection port in accordance with the mechanical vibration and attaching the droplet to a recording member, which is a so-called drop-on-demand type.
[0008]
Further, as another method, there is a method proposed by the present applicant in Japanese Patent Publication No. 56-9429. This method is also a so-called drop-on-demand type in which small droplets of a recording liquid are ejected and ejected from an ejection port in accordance with a recording signal to perform recording.However, the ink in the liquid chamber is heated to generate bubbles in the ink. This is a so-called bubble ink jet type in which ink droplets are ejected from ejection openings by the action of bubbles.
[0009]
As described above, there are various types of ink jet recording methods depending on the principle, but it is common to say that droplets of a recording liquid called so-called ink are made to fly and adhere to a recording member. The point is to record. As a recording liquid called this ink, a recording liquid in which a water-soluble dye is dissolved is generally used. However, in recent years, importance has been placed on water resistance and light resistance, and it is expected that a pigment having high robustness will be used as a colorant for a recording liquid for inkjet recording.
[0010]
For example, aqueous pigment inks for inkjet satisfying basic problems such as print quality, ejection characteristics, storage stability, and fixing properties are described in JP-A-2-255875, JP-A-4-334870 and JP-A-4-334870. JP-A-57859 and JP-A-4-57860 disclose inks.
However, since this pigment is not dissolved in a liquid medium like a dye but is dispersed, the stability in the liquid medium is poor, and the aggregation, sedimentation, separation of the pigment in the ink and the occurrence of a nozzle The problem of clogging of parts has not been solved yet.
[0011]
On the other hand, in recent years, the image quality and accuracy of ink jet recording have been improved, and the ejection port (nozzle) of the head used has conventionally been Φ33 μm to Φ34 μm (900 μm in terms of area).²Φ50 μm to Φ51 μm (in terms of area, 2000 μm²) Was common, but finer discharge ports have been required. At that time, if a recording liquid in which a water-soluble dye was dissolved was used as the ink as in the past, the problem of clogging could be dealt with because the dye was dissolved in the liquid medium. However, for pigment-based inks, clogging is a serious problem when a finer ejection opening (for example, Φ25 μm or less) is obtained.
[0012]
In addition, if a recording liquid in which a water-soluble dye is dissolved is used as the ink as in the related art, since the dye is dissolved in the liquid medium, the droplet lands and adheres to the paper as the recording medium. In this case, it can penetrate between the fibers of the paper, and perform good pixel formation / image formation. However, the recording liquid in which the above-mentioned pigment is dispersed is not dispersed in a liquid medium like a dye, but is merely dispersed, so that when a droplet lands on a paper and adheres, The liquid medium penetrates between the paper fibers, but the pigment particles and solids in the liquid medium do not penetrate into the paper fibers, but remain on the surface to form colored pixels. Is done.
[0013]
Therefore, there is a problem that a good pixel shape cannot be obtained unless the size of the pigment particles is optimized. For example, when pigment particles equivalent to pixels formed on a paper surface are used for forming pixels, it is difficult to obtain good round pixels, and high-quality printing cannot be expected.
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and a first object of the present invention is to disperse fine particles in a liquid to form a recording liquid, discharge the recording liquid from a fine opening, and attach the recording liquid to a recording medium. In the recording liquid used for the liquid jet recording head that performs recording by performing the recording, the nozzle clogging is prevented from occurring, the coloring material adheres well on the recording medium, and a good pixel shape is obtained, and high image quality is obtained. The goal is to make records available.
[0015]
The second object is the same as the first object, but is to propose another configuration for realizing it.
Further, the third object is the same as the first object, but is to propose still another configuration for realizing it.
A fourth object is to propose more detailed conditions for preventing clogging of nozzles in such a recording liquid.
[0016]
A fifth object is to reduce the running cost of a liquid jet recording apparatus using such a recording liquid.
Further, a sixth object is to reduce running costs when a liquid jet recording apparatus using such a recording liquid is applied to color recording.
A seventh object is to make the liquid jet recording apparatus using such a recording liquid more compact and reduce the manufacturing cost.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention firstly discharges a recording liquid from a fine opening having a size of Ф25 μm or less, and waits for 100 ms after the recording liquid adheres to a recording medium. Within a recording liquid used in a liquid jet recording head for performing recording by adhering droplets of the recording liquid to paper on which the contact angle change of the recording liquid substantially disappears, the recording liquid is obtained by dispersing fine particles in a solvent. And the surface of fine particles is treated and dispersed in a solvent of the recording liquid, and when the size of the fine particles is Dp and the size of the fine openings is Do, 0005 ≦ Dp / Do ≦ 0.02, and the fine particles are made smaller than the thickness of the fiber of the paper, and the size is made smaller than the gap formed by overlapping the fibers.
[0018]
Secondly, the recording liquid is ejected from a fine opening having a size of Ф25 μm or less, and the contact angle change of the recording liquid within 100 ms after the recording liquid adheres to the recording medium. In a recording liquid used in a liquid jet recording head that performs recording by adhering droplets of the recording liquid to paper that almost disappears, the recording liquid is obtained by dispersing fine particles together with a dispersant in a solvent, or cleaning the surface of the fine particles. A recording liquid that has been processed and dispersed in a solvent of the recording liquid, wherein when the size of the fine particles is Dp and the size of the fine opening is Do, 0.0005 ≦ Dp / Do ≦ 0.02. At the same time, the fine particles were made smaller than the average particle diameter of the particulate matter coated on the paper surface and smaller than the smoothness of the paper surface.
[0019]
Third, the recording liquid is ejected from a fine opening having a size of Ф25 μm or less, and the contact angle of the recording liquid changes within 100 ms after the recording liquid adheres to the recording medium. In a recording liquid used in a liquid jet recording head for performing recording by adhering droplets of the recording liquid to a resin member substantially disappearing, the recording liquid is obtained by dispersing fine particles together with a dispersant in a solvent, or a surface of the fine particles. Is a recording liquid dispersed in a solvent of the recording liquid, and when the size of the fine particles is Dp and the size of the fine opening is Do, 0.0005 ≦ Dp / Do ≦ 0.02 In addition, the fine particles are made to have an average particle diameter equal to or smaller than the average particle diameter of the particulate matter applied to the surface of the resin member, and smaller than the smoothness of the surface of the resin member.
[0020]
Fourthly, in the recording liquid according to any one of the first to third aspects, the content of the fine particles in the recording liquid is 2 to 10% by weight, and the fine particles in the recording liquid are included. The solid content is set to 15% by weight or less so that the solvent of the recording liquid permeates in the depth direction of the recording medium, and the solid content adheres to and is retained on the surface of the recording medium. .
[0021]
Fifth, in the recording liquid according to any one of the first to fourth aspects, the recording liquid is used in a head unit in which a recording liquid ejection unit and a recording liquid storage unit are separable. I did it.
[0022]
Sixth, in the recording liquid according to the fifth aspect, the recording liquid is filled in a recording liquid storage section that can be separated according to the type of the recording liquid.
Seventh, in the recording liquid according to any one of the first to sixth aspects, the recording liquid is used for thermal inkjet.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the configuration and principle of the inkjet to which the present invention is applied will be described. As described above, there are various inkjet recording methods. Here, an example of a bubble ink jet type will be described as a representative example, but it is needless to say that the present invention is not limited to this method, but is applicable to all ink jet recording methods. However, among various ink jet recording methods, the so-called bubble ink jet recording method in which ink is heated to generate air bubbles, the ink is exposed to severe conditions (heat cycle), thereby causing deterioration and accelerating chemical reactions. In addition, there is a technical problem that is more unfavorable for ink-jet such as clogging than other ink-jet recording methods in terms of dispersion instability of the pigment and the like.
The present invention is particularly suitably applied to a bubble ink jet recording method exposed to such severe conditions.
[0024]
1A and 1B are views for explaining an example of a bubble ink jet recording head. FIG. 1A is a perspective view of the head, FIG. 1B is a perspective view of a lid substrate constituting the head, and FIG. FIG. 1D is a perspective view of the heating element substrate, wherein 1 is a lid substrate, 2 is a heating element substrate, 3 is a recording liquid inlet, and 4 is a perspective view of the heating element substrate. The discharge port 5, 5 is a flow path, 6 is a region for forming a liquid chamber, 7 is an individual (independent) control electrode, 8 is a common electrode, and 9 is a heating element.
[0025]
Here, the lid substrate 1 can be manufactured by forming a flow path 5 and a liquid chamber 6 on a glass substrate or a metal substrate by a method such as etching, but the most preferable manufacturing method is a method of forming by molding plastic. . Although this involves a relatively high cost for the first mold production, it can be mass-produced thereafter, so that the production cost per piece can be very low.
[0026]
FIG. 2 is a diagram for explaining the principle of ink droplet ejection of a bubble inkjet type inkjet. FIG. 2A shows a steady state in which the ink 10, the surface tension, and the external pressure are in an equilibrium state on the ejection port surface. FIG. 2B shows a state in which the heating element 9 is heated until the surface temperature of the heating element 9 rises rapidly and a boiling phenomenon occurs in the adjacent ink layer, and minute bubbles 11 are scattered.
[0027]
FIG. 2C shows a state in which the adjacent ink layer, which has been rapidly heated over the entire surface of the heating element 9, is instantaneously vaporized to form a boiling film, and the bubbles 11 grow. At this time, the pressure in the ejection port rises by the amount of the bubble that has grown, the balance with the external pressure on the ejection port surface is lost, and the ink column 10 'starts to grow from the ejection port.
[0028]
FIG. 2D shows a state in which the bubble 11 has grown to the maximum, and ink corresponding to the volume of the bubble is pushed out from the ejection port surface. At this time, no current is flowing through the heating element 9 and the surface temperature of the heating element 9 is decreasing. The maximum value of the volume of the bubble 11 is slightly delayed from the timing of applying the electric pulse.
[0029]
FIG. 2E shows a state in which the bubble 11 is cooled by ink or the like and starts to contract. At the front end of the ink column 10 ′, the ink column 10 ′ moves forward while maintaining the extruded velocity, and at the rear end, the ink flows backward from the discharge port surface into the discharge port due to a decrease in the pressure inside the discharge port due to the contraction of the bubbles, and the ink column 10 ′. There is a constriction 10 ″.
[0030]
FIG. 2F shows a state in which the bubbles 11 further contract, the ink 10 comes into contact with the surface of the heating element 9, and the heating element surface is cooled more rapidly. On the discharge port surface, the external pressure becomes higher than the discharge port internal pressure, so that the meniscus greatly enters the discharge port.
The tip of the ink column becomes a droplet 12 and is flying at a speed of 8 to 15 m / s in the direction of the recording paper.
FIG. 2G shows that bubbles are completely eliminated during the process in which ink is again supplied (refilled) to the ejection ports by capillary action and returns to the state of FIG. 2A.
[0031]
FIG. 3 is different from the head shown in FIG. 1 in that a nozzle plate 20 is separately provided at the tip of the flow path. FIG. 3A shows a state before the nozzle plate 20 is attached, and FIG. ) Shows the state after the attachment. Also in this case, the nozzle plate is formed in a resin (plastic) film by, for example, perforating the nozzle 21 with an excimer laser, or by etching, electroforming, or punching a metal.
[0032]
The above is the general configuration and principle of the bubble ink jet recording head using heat, but it is not necessarily limited to this principle. For example, the present invention can be applied to all ink jet recording methods including a piezo method as well as a bubble ink jet method based on a principle that droplets fly without contracting generated bubbles.
[0033]
According to the present invention, a pigment having excellent water resistance and light resistance is used as a colorant for a recording liquid (ink) used in the above-described inkjet recording method. However, when this pigment is used as a colorant for a recording liquid, the pigment is not dissolved in the liquid medium as in the dye, but is dispersed, so that the stability in the liquid medium is poor, and the pigment in the ink is poor. There is a problem that aggregation, sedimentation and separation of the pigment occur and clogging of the nozzle portion occurs. In particular, clogging of the nozzle portion is a fatal problem for ink jet since ink is not ejected.
[0034]
In order to solve this problem, the present invention has made intensive studies on the material constituting the ink, the structure of the nozzle portion, the particle size of the pigment used, the pigment content in the ink, and the like. In the present invention, a pigment ink is assumed. That is, the colorant in the recording liquid is not a dye dissolved in a solvent such as water, but a fine particle serving as a pigment dispersed therein.
[0035]
In the present invention, as described above, a pigment having excellent water resistance and light resistance is used as a colorant of a recording liquid (ink) used in an ink jet recording method. When used as a liquid colorant, unlike when using a recording liquid in which a water-soluble dye is dissolved, when liquid droplets land on and adhere to paper, the liquid medium penetrates between the paper fibers. However, the pigment particles and solids in the liquid medium do not penetrate into the paper fibers. Therefore, since the colored particles are formed while the pigment particles remain on the surface of the paper, a good pixel shape cannot be obtained unless the size of the pigment particles is optimized. In the present invention, in order to solve this problem, the relationship between the surface properties of the paper and the particle size of the pigment has been intensively studied.
[0036]
Examples of the black pigment ink suitably applied to the present invention include a black pigment having a neutral or basic pH, a tertiary amine salt or an acrylate monomer or acrylamide monomer having a quaternary ammonium group. And a dispersion treatment using a water-soluble polymer having at least a constituent component.For inks of other hues, for example, inks of yellow, magenta, and cyan, pigments of these hues are also converted into carboxyl groups. Alternatively, it is obtained by performing a dispersion treatment using an anionic polymer dispersant having a sulfone group as a water-soluble group.
[0037]
In addition, the pH of the black pigment referred to herein generally refers to the pH value of a solution in which the pigment is dispersed in pure water, similarly to the method used for measuring physical properties of carbon black. Further, when the recording material used for recording is plain paper, the interfacial tension of the black pigment ink in the interfacial tension of the ink with respect to the plain paper is higher than the interfacial tension of the color ink. It is preferable that the penetration speed of the black pigment ink is lower than that of the color ink.
[0038]
When color recording is performed by optimizing the pigment particle diameter in the ink as described above, and optimizing the wetting of the paper and the ink to be used, it is possible to obtain an image with good fixability, high density, and little boundary bleeding. . Even when recording is performed on a recording material having transparency, a clear projected image can be obtained. Needless to say, since the ink is a pigment ink, the resistance to light and water is extremely excellent as compared with the case where a conventional dye ink is used.
[0039]
The polymer dispersant used in the present invention is obtained mainly by polymerization of a vinyl monomer, and the cationic monomer constituting at least a part of the obtained polymer includes the following tertiary amine monomers And their quaternized compounds.
[0040]
That is, N, N-dimethylaminoethyl methacrylate [CH2 = C (CH3) -COO-C2H4N (CH3) 2], N, N-dimethylaminoethyl acrylate [CH2 = CH-COO-C2H4N (CH3) 2], N , N-dimethylaminopropyl methacrylate [CH2 = C (CH3) -COO-C3H6N (CH3) 2], N, N-dimethylaminopropyl acrylate [CH2 = CH-COO-C3H6N (CH3) 2], N, N- Dimethylacrylamide [CH2 = CH-CON (CH3) 2], N, N-dimethylmethacrylamide [CH2 = C (CH3) -CON (CH3) 2], N, N-dimethylaminoethylacrylamide [CH2 = CH-CONHC2H4N (CH3) 2], N, N-dimethylaminoethyl methacrylate Amide [CH2 = C (CH3) -CONHC2H4N (CH3) 2], N, N-dimethylaminopropylacrylamide [CH2 = CH-CONH-C3H6N (CH3) 2], N, N-dimethylaminopropylmethacrylamide [CH2 = C (CH3) -CONH-C3H6N (CH3) 2].
[0041]
In the case of a tertiary amine, compounds forming a salt include hydrochloric acid, sulfuric acid, acetic acid and the like, and compounds used for quaternization include methyl chloride, dimethyl sulfate, benzyl chloride, epichlorohydrin and the like. Is mentioned. Among them, methyl chloride, dimethyl sulfate and the like are preferable in preparing the dispersant. The tertiary amine salt or the quaternary ammonium compound as described above behaves as a cation in water, and under neutralized conditions, acidity is a stable dissolution region. The content of these monomers in the copolymer is preferably in the range of 20 to 60% by weight.
[0042]
Other monomers used in the composition of the polymer dispersant include, for example, 2-hydroxyethyl methacrylate, acrylates having a hydroxy group such as acrylates having a long ethylene oxide chain in a side chain, and styrene-based monomers. And the like, and water-soluble monomers soluble in water having a pH of about 7, include acrylamides, vinyl ethers, vinylpyrrolidones, vinylpyridines, and vinyloxazolines. As the hydrophobic monomer, a hydrophobic monomer such as styrene, a styrene derivative, vinyl naphthalene, a vinyl naphthalene derivative, an alkyl ester of (meth) acrylic acid, and acrylonitrile is used. In the polymer dispersant obtained by the copolymerization, the water-soluble monomer is used in an amount of 15 to 35% by weight in order to make the copolymer stably exist in an aqueous solution, and the hydrophobic monomer is used in the copolymer. In order to enhance the dispersing effect on the pigment, it is preferable to use it in the range of 20 to 40% by weight.
[0043]
Examples of the carbon black pigment (CI Pigment Black 7) used in the black ink of the present invention include # 2600, # 2300, # 990, # 980, # 960, # 950, # 900, # 850, and # 750. , # 650, MCF-88, MA-600, # 95, # 55, # 52, # 47, # 45, # 45L, # 44, # 40, # 33, # 32, # 30, # 25, # 20 , # 10, # 5 (manufactured by Mitsubishi Chemical), Printex95, Printex90, Printex85, Printex80, Printex75, Printex45, Printex40, PrintexP, Printex60, Printex300, Printex30, Printex35, Printex25, Printex25. PrintexG, PrintexL6, PrintexL (manufactured by Degussa), Raven850, Raven780ULTRA, Raven760ULTRA, Raven790ULTRA, Raven520, Raven500, Raven410, Raven420, Raven430, Raven450, Raven460, Raven890, Raven1020 (manufactured by Columbia), Regal415R, Regal330R, Regal250R, Regal 995R, Monarch 800, Monarch 880, Monarch 900, Monarch 460, Monarch 280, Monarch 120 (all manufactured by Cabot) and the like.
[0044]
Examples of the pigment used for the yellow ink include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 2, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 16, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 73, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 75, C.I. I. Pigment Yellow 83, C.I. I. Pigment Yellow 93, C. I. Pigment Yellow 95, C.I. I. Pigment Yellow 97, C.I. I. Pigment Yellow 98, C.I. I. Pigment yellow 114, C.I. I. Pigment Yellow 128, C.I. I. Pigment yellow 129, C.I. I. Pigment Yellow 151, C.I. I. Pigment Yellow 154 and the like.
[0045]
Pigments used for magenta ink 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 and the like.
[0046]
Pigments used for cyan ink 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. Pigment Blue 22, C.I. I. Pigment Blue 60, C.I. I. Bat Blue 4, C.I. I. Bat Blue 60 and the like.
[0047]
In addition to the above, when an intermediate color other than the three primary colors of red, green, blue and the like is required, it is preferable to use the following pigments alone or in combination. For example, C.I. I. Pigment Red 209, C.I. I. Pigment Red 122, C.I. I. Pigment Red 224, C.I. I. Pigment Red 177, C.I. I. Pigment Red 194, C.I. I. Pigment Orange 43, C.I. I. Bat violet 3, C.I. I. Pigment Violet 19, C.I. I. Pigment Green 36, C.I. I. Pigment Green 7, C.I. I. Pigment Violet 23, C.I. I. Pigment Violet 37, C.I. I. Pigment Blue 15: 6, C.I. I. Pigment Blue 209 and the like.
[0048]
Dyes such as those listed below may coexist in the color ink. Examples of the dye used for the yellow ink include C.I. I. Acid Yellow 11, C.I. I. Acid Yellow 17, C.I. I. Acid Yellow 23, C.I. I. Acid Yellow 25, C.I. I. Acid Yellow 29, C.I. I. Acid Yellow 42, C.I. I. Acid Yellow 49, C.I. I. Acid Yellow 61, C.I. I. Acid Yellow 71, C.I. I. Direct Yellow 12, C.I. I. Direct Yellow 24, C.I. I. Direct Yellow 26, C.I. I. Direct Yellow 44, C.I. I. Direct Yellow 86, C.I. I. Direct Yellow 87, C.I. I. Direct Yellow 98, C.I. I. Direct Yellow 100, C.I. I. Direct Yellow 130, C.I. I. Direct Yellow 142 and the like.
[0049]
Dyes used for magenta ink include C.I. I. Acid Red 1, C.I. I. Acid Red 6, C.I. I. Acid Red 8, C.I. I. Acid Red 32, C.I. I. Acid Red 35, C.I. I. Acid Red 37, C.I. I. Acid Red 51, C.I. I. Acid Red 52, C.I. I. Acid Red 80, C.I. I. Acid Red 85, C.I. I. Acid Red 87, C.I. I. Acid Red 92, C.I. I. Acid Red 94, C.I. I. Acid Red 115, C.I. I. Acid Red 180, C.I. I. Acid Red 254, C.I. I. Acid Red 256, C.I. I. Acid Red 289, C.I. I. Acid Red 315, C.I. I. Acid Red 317, C.I. I. Direct Red 1, C.I. I. Direct Red 4, C.I. I. Direct Red 13, C.I. I. Direct Red 17, C.I. I. Direct Red 23, C.I. I. Direct Red 28, C.I. I. Direct Red 31, C.I. I. Direct Red 62, C.I. I. Direct Red 79, C.I. I. Direct Red 81, C.I. I. Direct Red 83, C.I. I. Direct Red 89, C.I. I. Direct Red 227, C.I. I. Direct Red 240, C.I. I. Direct Red 242, C.I. I. Direct Red 243 and the like.
[0050]
Dyes used for cyan ink include C.I. I. Acid Blue 9, C.I. I. Acid Blue 22, C.I. I. Acid Blue 40, C.I. I. Acid Blue 59, C.I. I. Acid Blue 93, C.I. I. Acid Blue 102, C.I. I. Acid blue 104, C.I. I. Acid Blue 113, C.I. I. Acid Blue 117, C.I. I. Acid Blue 120, C.I. I. Acid Blue 167, C.I. I. Acid Blue 229, C.I. I. Acid Blue 234, C.I. I. Acid Blue 254, C.I. I. Direct Blue 6, C.I. I. Direct Blue 22, C.I. I. Direct Blue 25, C.I. I. Direct Blue 71, C.I. I. Direct Blue 78, C.I. I. Direct Blue 86, C.I. I. Direct Blue 90, C.I. I. Direct Blue 106, C.I. I. Direct Blue 199 and the like. However, even when these dyes coexist, the pigment particle size and the pigment content in the ink must be within the ranges described below.
[0051]
In the present invention, when dispersing a pigment using the cationic water-soluble polymer described above as a dispersant, as a preferable pigment in terms of physical properties, a pigment whose isoelectric point is adjusted to 6 or more, or a pigment A pigment having a neutral or basic pH, for example, a pigment having a pH of 7 to 10 is preferable in terms of dispersibility. This is understood because the ionic interaction between the pigment and the cationic water-soluble polymer is strong.
In order to obtain an aqueous dispersion of fine particles of a pigment using the above materials, it is preferable to employ the following method.
[0052]
(1) In the case of carbon black: carbon black is premixed in a cationic dispersant solution, then milled by a high shear rate dispersing device, diluted, and then centrifuged to remove coarse particles. . Thereafter, a material for a desired ink formulation is added, and an aging treatment is performed in some cases. Thereafter, centrifugation is performed to finally obtain a pigment dispersion having a desired average particle size. The pH of the ink thus produced is preferably in the range of 3 to 9.
[0053]
(2) In the case of pigments of other hues: basically the same as carbon black except that an anionic dispersant is used. However, in the case of an organic pigment that is difficult to reduce the particle size, a surfactant treatment was performed simultaneously with or during the synthesis of the pigment to suppress crystal growth of the pigment particles and increase wettability. It is desirable to use a processed pigment.
[0054]
The pH of the ink thus produced is preferably in the range of 5 to 10. In both the carbon black ink and the color ink, the average particle diameter is required to be in the range of 0.005 to 2 μm for the stability of the dispersion. This is an essential condition from the viewpoint of stability of the dispersion, but from the viewpoint that it is essential for a so-called ink jet that ejects ink from a fine opening, considering this average particle size, the fine opening, that is, at the ejection opening Clogging must be taken into account, which will be described later. Further, in order to form better pixels on the paper surface, it is necessary to consider the relationship with the properties of the paper surface described later. The surface tension of a good ink is in the range of 10 to 60 dyn / cm.
[0055]
Next, points to be noted when printing on a recording medium using these inks will be described from the viewpoint of paper, which is a typical example of the recording medium.
The definition of orthodox paper is "paper is a suspension of plant fibers in water, then strained with water and entangled thinly and flatly", but the point is grass, wood, bamboo, etc. It is an aggregate of fibers obtained by decomposing plants. Regardless of Western paper or Japanese paper, the raw material of paper is a material having a characteristic property of cellulose fiber, and the paper is obtained by processing and thinning it by a unique method called papermaking technology.
[0056]
The cellulose fiber used here is a wood fiber having a length of 1 to 3 mm, a width of 20 to 40 μm, and a thickness of 3 to 6 μm in the case of Western paper. . By adopting such a configuration, the characteristics of a highly porous and smooth material having high affinity of cellulose fibers can be obtained. Japanese paper is a paper using the same cellulose fiber. However, unlike wood fiber, it is a relatively thin fiber (width 5 to 20 μm, length 3 to 7 mm), which is called bast fiber. It has different characteristics and is distinguished from handmade or machine-made Japanese paper.
[0057]
FIG. 4 shows an image diagram of the surface of the paper. In FIG. 4, the lines indicate cellulose fibers, and paper has such overlapping cellulose fibers, and there is a gap formed by overlapping each fiber.
[0058]
Although the definition of paper is as described above, paper consisting of simply overlapping cellulose fibers is so-called base paper, and what is actually used is to increase opacity, whiteness, smoothness, air permeability, etc. In addition, filler particles having a particle diameter of about 0.2 to 10 μm, such as talc, clay, calcium carbonate, and titanium dioxide, are filled between the fibers.
[0059]
Depending on the purpose of the paper, kaolin (Al₂O₃・ 2SiO₂・ 2H₂O), calcium carbonate (CaCO₃), Sachin White (3CaO.Al₂O₃・ 3CaSO₄・ 31-32H₂There is a coated paper coated with a coating liquid in which particles having a particle diameter of about 0.5 to 1 μm such as O) are dispersed together with a binder such as latex or starch.
[0060]
Further, the above-mentioned kaolin (Al) is applied to a resin sheet such as a polyethylene film such as an OHP sheet.₂O₃・ 2SiO₂・ 2H₂O), calcium carbonate (CaCO₂₃), Sachin White (3CaO.Al₂O₃・ 3CaSO₄・ 31-32H₂O) or the like and a coating liquid in which particles having a particle size of about 0.5 to 1 μm are dispersed together with a binder such as latex or starch are applied as needed.
[0061]
In addition, paper varieties include newspaper rolled paper, uncoated printing paper (high-grade, intermediate-grade, lower-grade, thin-leaf printing paper), fine-coated printing paper (fine-coated fine paper, fine-coated printing paper), and coated paper. Industrial printing paper (art paper, coated paper, etc.), information paper (copying paper, photosensitive paper, foam paper, PPC paper, thermal paper, etc.), packaging paper (kraft paper, imitation paper, etc.), sanitary paper (tissue paper, dust paper) , Toilet paper, towel paper, etc.), hybrid paper (base paper for building materials, laminate base paper, condenser paper, rice paper, glassine paper, etc.), cardboard base paper (liner, shinshin base paper, etc.), etc.
[0062]
In any case, the surface of the paper in which such cellulose fibers are overlapped, the thickness of the cellulose fibers, the gap formed by overlapping them, and in the case of the coated paper as described above, the coating material Depending on the size of the particles and the like, it is microscopically uneven. Such microscopic unevenness is one of the factors hindering high-quality recording by inkjet recording.
[0063]
As described above, in the present invention, recording is performed using a recording liquid (pigment ink) in which a pigment is dispersed. In the case where recording is performed using a recording liquid (dye ink) in which a dye is dissolved as in the related art, since the dye is dissolved in a solvent, ink droplets due to the recording liquid adhere to the paper, and pixels are formed. When forming the ink, when the ink penetrates into the fibers of the paper, the dissolved dye penetrates together with the solvent, so that high-quality recording was realized by optimizing the relationship between the ink and the paper. However, in the case of the pigment ink to which the present invention is applied, since the solvent of the ink penetrates the paper, the conventional relationship between the dye ink and the paper may be followed. What should be done in relation to this is not yet studied.
[0064]
In view of this point, the present invention has examined the surface properties of paper and the size of pigment particles. As described above, the cellulose fiber generally has a width (thickness) of about 5 to 40 μm, although it depends on the type of paper. Paper is not usually made of fibers of such a size as it is. In general, in the paper manufacturing process, a process called softening is performed by applying a mechanical force to fibers to make them soft. Since it is manufactured through the process, the fiber size of the actually completed paper is smaller than this. Usually, the thickness or thickness of the fiber of the paper manufactured through beating is about 3 to 6 μm.
[0065]
In the present invention, the pigment particles adhere to the surface of the paper in which such fibers are superimposed, and play a role as a coloring material. An important factor in forming a round pixel is the size of the pigment particles. For example, suppose that a pigment or an aggregate of the pigment larger than the size of the fiber (here, the thickness or thickness of the fiber after beating) or the gap between the fibers is attached (FIG. 5). However, good round pixels cannot be formed by ink. In addition, since such a large pigment or an aggregate of the pigment does not enter a gap formed by overlapping fibers, there is a problem that adhesion stability is poor.
[0066]
In view of this point, in the present invention, the size of the pigment particles dispersed in the ink solvent is set to a value smaller than the thickness of the fiber of the paper (here, after beating). In addition, the size of the pigment particles is set to be equal to or smaller than the gap formed by overlapping the paper fibers. FIG. 6 shows the image diagram. 5 and 6 are enlarged views of FIG.
Further, in addition to the irregularities formed by the fibers of the paper, the surface properties of the paper vary depending on the particle size of the coating substance of the coated paper as described above, which affects the favorable pixel formation. Exert.
[0067]
An example of the result of examining these points will be described. Here, papers having different surface properties (fiber size, presence or absence of a coating material) are prepared, pixels are formed with inks having different pigment particle diameters, and the quality of the pixel shape is determined.
The head used was an ink jet recording type head using thermal energy having a configuration as shown in FIG. However, in the head shown in FIG. 1, the tip of the flow path is the discharge port as it is. However, the head used in the experiment is, as shown in FIG. A nozzle plate 20 having nozzles 21 formed at the same array density as the nozzle plate 20 is provided (FIG. 3A is a perspective view before the nozzle plate 20 is attached, and FIG. 3B is a perspective view after the nozzle plate 20 is attached). Is). The number of discharge ports (nozzles) shown in FIGS. 1 and 3 is only four or partially shown for simplicity of explanation. The number of discharge ports used was 256 and the arrangement density was 600 dpi. The discharge port diameter is Φ20 μm (314 μm in terms of area)²).
[0068]
The size of the heating element was 20 μm × 85 μm, the resistance value was 106 Ω, the driving voltage for ink ejection was 23 V, the driving pulse width was 6 μs, and the driving frequency was 12 kHz. The thickness of the nozzle plate was 40 μm.
The inks used had the following composition and manufacturing method, and ten kinds of inks were prepared in which the pigment particle diameter was changed from 0.005 to 20 μm.
The method for producing the ink is shown below. The following carbon black dispersion was prepared using an aqueous solution in which a copolymer P composed of styrene / methacrylic acid / butyl acrylate and having an acid value of 325, a weight average molecular weight of 11,000 and a glass transition temperature of 84 ° C. was dissolved using potassium. did.
[0069]
・ Copolymer P aqueous solution (solid content 20% by weight) 40 parts
・ Carbon black @ MA-800 (Mitsubishi Chemical) 25 parts
・ Diethylene glycol 20 parts
・ Isopropyl alcohol ... 10 parts
・ Water ・ ・ ・ ・ ・ ・ ・ ・ 130 copies
[0070]
These materials were charged into a batch-type vertical sand mill (manufactured by Imex), filled with glass beads having a diameter of 1 mm as a medium, and subjected to a dispersion treatment for 3 hours while cooling with water. After the dispersion, a crude dispersion having a viscosity of 16 cP and a pH of 9.7 was obtained. This dispersion was centrifuged to remove coarse particles, and various conditions of centrifugation were changed to obtain 10 types of dispersions in which the average particle size of the pigment was changed from 0.005 to 20 μm. These dispersions were diluted with water to obtain 10 kinds of black basic inkjet inks having a viscosity of 2.4 cP, a surface tension of 46 dyn / cm, and a pH of 9.5. The solids content of the final preparation was about 8% by weight. The final pigment content in these inks is 5% by weight. The average particle size was measured by a particle size distribution analyzer ELS-800 (manufactured by Otsuka Electronics Co., Ltd.) using a dynamic light scattering method, and the average amount was indicated by a value obtained from an initial gradient of an autocorrelation function.
[0071]
The above heads are filled with inks having different particle diameters of these 10 kinds of pigments, and three types of papers (uncoated paper 2, coated paper 2) having different surface properties (fiber size, presence or absence of a coating material). An ink droplet was attached to paper 1) and a resin member (polyethylene film) to form a dot having a pixel diameter of about Φ60 μm to Φ65 μm, and the quality of the pixel shape was determined by sensory evaluation. In the case of an ink having a large pigment particle diameter, clogging occurs immediately and cannot be evaluated as an image.However, pixels ejected before complete clogging occurs and droplet ejection cannot be performed are picked up. Was evaluated.
[0072]
The three types of paper are filled with 10% clay particles of 10 μm as filler particles between paper fibers. The gap formed by the fiber thickness and the fiber overlap is an average value obtained by SEM observation of the paper surface, randomly extracting 20 places each, and measuring. The coated surface smoothness of the coated paper and the polyethylene film was measured with a palpable surface roughness meter.
The results are shown in Tables 1 to 4. Here, the pass / fail of the determination (○, ×) is determined by sensory evaluation while looking at a microscope image of 100 times (each 20 pieces are picked up and evaluated).
[0073]
[Table 1]

[0074]
[Table 2]

[0075]
[Table 3]

[0076]
[Table 4]

[0077]
From the results in Tables 1 and 2, it can be seen that good pixels are obtained when the pigment particle diameter is smaller than the thickness of the paper fiber. Also, it can be seen that good pixels can be obtained by setting the size to be equal to or smaller than the gap formed by overlapping the paper fibers.
From the results in Tables 3 and 4, it can be seen that good pixels can be obtained by setting the pigment particle diameter to be equal to or less than the average particle diameter of the coating substance on the paper or resin member surface. It can also be seen that good pixels can be obtained by making the surface smoother than the coated surface.
[0078]
Next, the result of studying the ink applied to the present invention from another aspect will be described. In general, an ink in which a pigment is dispersed as a colorant is not limited to inkjet applications, and the pigment particle size is 0.5 to 100 μm depending on the application, cost, and production technique. In the present invention, as described above, in order to form a good pixel even on the uneven surface woven by paper fibers, it is necessary to have a finer pigment particle diameter than for ink jet use. However, smaller pigment particles tend to agglomerate and do not simply disperse in the solvent. Therefore, in the present invention, the pigment particles are dispersed in the solvent of the ink together with the dispersant, or the surface of the pigment particles is treated to be dispersed in the solvent of the ink, which will be described in detail later. By doing so, the lower limit value of the dispersion of the pigment particles in the solvent could be increased to 0.005 μm.
[0079]
The dispersant used in the color ink used in the present invention is an alkali-soluble water-soluble aliphatic tree, and has a weight average molecular weight of 1,000 to 30,000, preferably 3,000 to 15,000. Range. Specifically, hydrophobic monomers such as styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, alkyl esters of acrylic acid and alkyl esters of methacrylic acid, α, β-ethylenically unsaturated carboxylic acids and their aliphatic alcohols Copolymers comprising hydrophilic monomers such as esters, acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid and derivatives thereof, and salts thereof. The copolymer may have any structure such as random, block and graft, and the acid value is in the range of 100 to 430, preferably 130 to 360.
[0080]
As the dispersant used in the present invention, a water-soluble polymer such as polyvinyl alcohol and carboxymethyl cellulose, a water-soluble resin such as a naphthalenesulfonic acid formaldehyde condensate, and polystyrenesulfonic acid can also be used. However, an alkali-soluble water-soluble oily tree has the advantage that the viscosity of the dispersion can be reduced and the dispersion is easy. The amount of these dispersants used is determined experimentally using the selected pigment and dispersant, but the amount of resin dissolved without adsorbing on the pigment is 4% by weight or less in the ink. Is preferred.
[0081]
To use the above dispersant in an aqueous system, a base is required. Suitable bases therefor include ethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N-ethyldiethanolamine, 2-amino-2-methylpropanol, 2-ethyl-2-amino-1,3-propane. Organic bases such as diol, 2- (2-aminoethyl) ethanolamine, tris (hydroxymethyl) aminomethane, ammonia, piperidine, morpholine, β-dihydroxyethylurea, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. Inorganic base. The optimum base type varies depending on the type of the selected pigment and dispersant, but is preferably a non-volatile, stable and highly water-retaining one. The amount of the base to be used is basically used from the amount calculated from the acid value of the dispersant as the amount of the base necessary for neutralizing the same. In some cases, more than the equivalent of acid is used. This is performed for the purpose of improving dispersibility, adjusting the pH of the ink, adjusting the recording performance, improving the moisture retention, and the like.
[0082]
The solvent used in the ink of the present invention is an organic solvent miscible with water. Organic solvents can be divided into three groups as described below. That is, a first group of solvents having a high moisturizing property, hardly evaporating, and excellent in hydrophilicity, a second group of solvents having good wettability to an organic and hydrophobic surface and also having an evaporative drying property, and a moderate degree of wetting. A third group of solvents (monohydric alcohols) having properties and low viscosity.
[0083]
Solvents belonging to the first group include ethylene glycol, diethylene glycol, triethylene glycol, tripropylene glycol, glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,5-pentanetriol. , 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dimethyl sulfoxide, diacetone alcohol, glycerin monoallyl ether, propylene glycol, butylene glycol, polyethylene glycol 300, thiodiglycol, N- Methyl-2-pyrrolidone, 2-pyrrolidone, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, sulfolane, trimethylolpropane, trimethylolethane, neopentylglycol, ethyleneglycol Monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoallyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, Examples include propylene glycol monomethyl ether, β-dihydroxyethylurea, urea, acetonylacetone, gentaerythritol, 1,4-cyclohexanediol and the like.
[0084]
Solvents belonging to the second group include hexylene glycol, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monophenyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, and triethylene glycol monoisobutyl ether. Ethylene glycol monobutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dip Pyrene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, glycerin monoacetate, glycerin diacetate, glycerin triacetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, cyclohexanol, 1,2-cyclohexanediol, 1-butanol, 3-methyl-1,5-pentanediol, 3-hexene-2,5-diol, 2,3-butanediol, 1,5-pentanediol, 2,4-pentanediol, 2,5- Hexanediol and the like can be mentioned.
[0085]
Examples of the solvents belonging to the third group include ethanol, n-propanol, 2-propanol, 1-methoxy-2-propanol, furfuryl alcohol, and tetrahydrofurfuryl alcohol. It is preferable that the total amount of the water-soluble solvents as described above is generally in the range of 5 to 40% by weight based on the whole ink.
[0086]
A surfactant, a pH adjuster, a preservative and the like can be added to each aqueous pigment ink constituting the ink of the present invention. The surfactant is useful for preparing a color ink having a high permeability, for adjusting the wettability to the surface of a heating nozzle and a discharge nozzle when a bubble ink jet system is used as the ink jet system, and the like. The material can be appropriately selected from existing commercial products. To summarize the physical properties of each ink composed of the above materials, the black ink has a high surface tension (about 30 to 60 dyn / cm), while the color ink has a low surface tension (about 10 to 40 dyn / cm). cm).
[0087]
An example of a specific method for producing the ink of the present invention in which the pigment is stably dispersed using the dispersant as described above is shown below. This example uses an aqueous solution obtained by dissolving a copolymer P having an acid value of 290, a weight average molecular weight of 5,000 and a glass transition temperature of 77 ° C. using monoethanolamine, which is composed of styrene / acrylic acid / ethyl acrylate. This is an example in which a pigment pigment red-177 dispersion is prepared and used as an ink.
[0088]
.Copolymer P aqueous solution (solid content 15% by weight) 40 parts
・ Pigment Red-177 (Chromophtal Red A2B, Ciba-Geigy) ・ ・ ・ ・ ・ 24 parts
・ Diethylene glycol 20 parts
・ Isopropyl alcohol ... 10 parts
・ Water ・ ・ ・ ・ ・ ・ ・ ・ 130 copies
[0089]
These materials were charged into a batch-type vertical sand mill (manufactured by Imex), filled with glass beads having a diameter of 1 mm as a medium, and subjected to a dispersion treatment for 3 hours while cooling with water. After the dispersion, a crude dispersion having a viscosity of 30 cP and a pH of 9.8 was obtained. This dispersion was centrifuged to remove coarse particles, and the dispersion in which the average particle size of the pigment was changed from 0.005 to 4 μm was obtained by variously changing the conditions of centrifugation. This dispersion was diluted with water, diethylene glycol, ethylene glycol monobutyl ether (60:25:15 weight ratio) to obtain a red basic inkjet ink having a viscosity of 3 cP, a surface tension of 40 dyn / cm, and a pH of 9.5. . The solids content of the final preparation was about 7.5% by weight. The final pigment content in the ink is 5% by weight.
[0090]
The above is one example of the ink manufacturing method. The pigment particle diameter is optimized in the black aqueous pigment ink and the color ink according to the present invention manufactured by such a manufacturing method, and the wettability of the paper and the ink used is optimized. When color recording is performed, black characters and the like are clear, and even if an image or graph and black characters are adjacent to each other, they are clear without mutual bleeding.
[0091]
Next, another example of obtaining a stable dispersion of the pigment will be described. The above example is to improve the dispersibility of the pigment by using a dispersant. Here, as an example of improving the dispersibility by surface treatment of the pigment, the surface of carbon black is hydrophilized by graft polymerization treatment and dispersed. A method for improving the performance will be described. For example, for graft polymerization, carbon black is stirred with a peroxide such as metal acrylate or ammonium acrylate to generate a graft reaction site, and then the monomer is polymerized in the presence of a radical polymerization initiator and an amine radical polymerization accelerator. Just do it.
The ink for inkjet recording using the grafted carbon black is obtained by diluting a polymerization reaction suspension containing the grafted carbon black and adding a conventional inkjet additive such as a wetting agent.
[0092]
As another example, carbon black was subjected to surface treatment in a production method comprising (1) a step of performing ultraviolet treatment or ozone treatment under normal pressure, and (2) a step of graft-polymerizing a monomer having a vinyl group by thermal polymerization. There is a method of dispersing carbon black in water and / or a water-soluble organic solvent.
In the latter case, the graft polymerization can be carried out without including impurities such as salts and radical polymerization agents in the ink, which is advantageous for preventing bleeding of a printed image. The latter example will be described in more detail.
[0093]
As the carbon black in the present invention, carbon black produced by a generally known method such as a contact method, a furnace method, and a thermal method can be used, and a functional group such as a carboxyl group, a hydroxyl group, or a carbonyl group is present on the surface. I do. When these functional groups and the monomer having a vinyl group used in the present invention are polymerized, carbon black excellent in dispersibility in water or a water-soluble organic solvent can be obtained.
[0094]
Specific examples of the monomer having a vinyl group used in the present invention include acrylamide, N, N-dimethylacrylamide, acrylic acid, acrylonitrile, methacrylic acid, methyl methacrylate, vinyl acetic acid (polyvinyl alcohol derived from vinyl acetic acid) and the like. And acrylamide is most preferred.
UV treatment or ozone treatment increases the activity of the carbon black surface. Specifically, a peroxide is generated on the surface of carbon black, and a monomer having a vinyl group is directly graft-polymerized on the surface of carbon black. The processing time is 5 minutes to 2 hours. A longer treatment time is not preferable because the generated peroxide is decomposed.
[0095]
The polymerization is carried out by blowing nitrogen and then applying heat to remove oxygen, which is a polymerization inhibitor. At this time, the bond of the hydroxyl group is broken from the peroxide on the surface of the carbon black, and the polymerization and the grafting of the monomer occur simultaneously.
The reaction time is between 30 minutes and 6 hours. Longer reaction times are harmless but uneconomical. The reaction temperature is from 30 ° C to 80 ° C. After cooling, the homopolymer formed as a by-product can be removed by a conventional method such as lyophilization or centrifugation. Since the unreacted monomer has high solubility in water, it is washed with hot water.
[0096]
In obtaining the carbon black treated in the present invention, the surface treatment of the carbon black is performed uniformly, and the carbon black and the monomer having a vinyl group are firmly bound to each other, and the obtained ink for aqueous ink jet recording of the treated carbon black is obtained. In order to enhance the dispersibility in the composition, the ratio of the carbon black / vinyl group-containing monomer is preferably 10/1 to 100/100 by weight.
[0097]
The surface-treated carbon black thus obtained is easily dispersed in water or a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol # 200, # 300, and # 400; and polyhydric alcohols such as triethylene glycol monomethyl ether methanol. Alkyl ether derivatives, ester derivatives of polyhydric alcohols such as glyceryl monoacetate, nitrogen-containing cyclic compounds such as N-methyl-2-pyrrolidone, and those having 1 to 6 carbon atoms such as ethanol, n-propanol and iso-propanol. And lower alcohols.
[0098]
The amount of the water-soluble organic solvent used is 40% by weight or less, preferably 3 to 30% by weight, based on the total weight of the ink.
Since the surface-treated carbon black can be easily dispersed in water and water-soluble organic solvents, it does not require high shearing force with a disperser such as a ball mill, sand mill, or roll mill, and an ultrasonic disperser such as an ultrasonic homogenizer. Can be sufficiently dispersed.
The amount of the surface-treated carbon black to be used in the ink needs to be considered in consideration of the degree of polymerization due to the surface treatment. However, in consideration of the color density of the ink and prevention of clogging of the ink discharge nozzle, the amount is 2 to 10% by weight. You. This will be described later.
[0099]
In addition, additives such as a viscosity adjuster, a surface tension adjuster, and a pH adjuster for adjusting the physical properties of the ink, a fungicide, a preservative, and a resin as a binder can be appropriately added.
Hereinafter, an example of the ink manufactured by this method will be specifically described.
[0100]
Example 1
Component A
Carbon black {# 25} (Mitsubishi Chemical) 20 parts
Acrylamide ... 10 parts
Water: 90 parts
Component B
Surface treated carbon black: 5 parts
Glycerin: 2 copies
Ethanol 6 parts
Water: 87 copies
[0101]
The carbon black is subjected to ultraviolet treatment under a high-pressure mercury lamp (800 W) for 20 minutes, mixed with the treated component A such as carbon black, and stirred at 70 ° C. while blowing nitrogen gas into the solution to polymerize for 50 minutes. Was. The homopolymer was sufficiently removed from the polymer by a centrifuge at 12,000 rpm for 70 minutes, washed with hot water for 150 minutes while stirring, dried, then mixed with the component B, and the particle size was measured with an ultrasonic homogenizer. Was prepared and coarse particles and dust were removed with a 0.2 μm membrane filter to obtain an ink for inkjet recording. This ink had a good pigment dispersion state and excellent storage stability.
[0102]
Example 2
Component A
Carbon black @ MA-7 (Mitsubishi Chemical) 10 parts
Acrylic acid 90 parts
Water: 210 parts
Component B
Surface treated carbon black: 3 parts
Glycerin 10 parts
1-propanol 4 parts
Water: 83 parts
[0103]
The carbon black is subjected to ultraviolet treatment under a high-pressure mercury lamp (800 W) for 15 minutes, mixed with the treated component A such as carbon black, stirred at 65 ° C. while blowing nitrogen gas into the solution, and polymerized for 100 minutes. Was. The homopolymer was sufficiently removed from the polymer by a centrifuge at 13000 rpm for 90 minutes, washed with hot water for 180 minutes while stirring, and dried. Then, the component B was mixed, and the particle size was measured with an ultrasonic homogenizer. Was prepared and coarse particles and dust were removed with a 0.2 μm membrane filter to obtain an ink for inkjet recording. This ink had a good pigment dispersion state and excellent storage stability.
[0104]
Example 3
Component A
Carbon black {MA-600} (Mitsubishi Chemical) 10 parts
N, N-dimethylacrylamide 50 parts
Water: 200 parts
Component B
Surface treated carbon black: 3 parts
Ethylene glycol 4 parts
Ethanol 5 parts
Water: 88 parts
[0105]
The carbon black is ozone-treated with an ozone generator having a voltage of 60 V, a frequency of 50 Hz, and an oxygen flow rate of 40 ml / min. The component A such as the treated carbon black is mixed, and the mixture is stirred at 50 ° C. while blowing nitrogen gas into the solution. And polymerized for 150 minutes. The homopolymer was sufficiently removed from the polymer by a centrifugal separator at 12,000 rotations × 80 minutes, washed with hot water for 180 minutes while stirring, dried, and then mixed with the component B, and the particle size was measured with an ultrasonic homogenizer. Was prepared and coarse particles and dust were removed with a 0.2 μm membrane filter to obtain an ink for inkjet recording. This ink had a good pigment dispersion state and excellent storage stability.
[0106]
As described above, the case where the dispersibility of a pigment is improved by using a dispersant and the case where the dispersibility is improved by a surface treatment of a pigment have been described. Even with a pigment having an appropriate particle size (minimum of 0.005 μm), stable dispersion can be obtained, and a good ink excellent in storage stability can be obtained.
[0107]
Next, the result of studying the relationship between the pigment ink of the present invention and the recording medium will be described. In the case of paper, which is a typical example of a recording medium, wetting is a phenomenon that occurs prior to the penetration of ink into the paper.
As mentioned above, “paper is a product in which vegetable fibers are suspended in water, then water is strained, and the fibers are entangled thinly and flatly.” It has become necessary to understand the behavior of ink when it comes into contact with ink, in the order of several tens of milliseconds, instead of treating paper as simply "aggregate of fibers". In the present invention, in view of this point, the relationship between the wetting and the image quality when the ink of the present invention adheres to a recording medium is examined.
[0108]
Generally, such a relationship between paper and ink wettability is measured by a dynamic wettability tester (for example, product name WET-3000 Resca Co., Ltd.) using the Wilhelmy method. Using a goniometer known as a target wettability measuring device, ink was dropped on paper and the contact angle was measured. However, in order to track the temporal behavior of the contact angle, a change in the contact angle was recorded on the order of several to several tens of milliseconds using a high-speed camera. Further, the quality of the pixel shape when the ink and the paper were used was judged by sensory evaluation while observing a microscope image of 100 times.
Various conditions such as the head and ink used for forming the pixels are the same as those in the case where the surface properties and the pixel shape of the paper were evaluated. The pigment particle diameter of the used pigment ink is 0.05 μm.
[0109]
FIG. 7 shows the result of measuring the change over time of the contact angle by the method described above. The paper used was of six types from A to F (D is a resin member to a polyethylene film coated with calcium carbonate having a particle diameter of 1 μm), but the fiber thickness of each paper was 5 to 10 μm, and the fibers overlapped. The resulting gap is 1-2 μm, and the surface smoothness of the paper or resin member is 1-2 s.
[0110]
In addition, the density of the paper of A to F (excluding D) is respectively
A 0.96g / cm³
B 0.41g / cm³
C 0.78g / cm³
E 0.58g / cm³
F 0.62g / cm³
It is. However, the density referred to here is a density generally applied in the papermaking industry, and is calculated by dividing a weighing (weight per 1 m 2 (gram number)) by a thickness (so-called “density”). It is not exactly the same as the density in physics).
[0111]
The pixel shape evaluation results show that the pixel diameter of each pixel fluctuated from Φ60 μm to Φ70 μm, but the dot shape of the papers A and B was the worst, the paper C was good, and the resin members D, E and F were very good round. It was a shape. The evaluation was a sensory evaluation using a 100-times microscope image, in which 20 pieces were picked up and evaluated.
That is, a paper such as paper (or resin member) C, D, E, or F, in which the contact angle does not fluctuate within 100 ms after the ink adheres to the paper or resin surface, and becomes a substantially constant value It was found that a good round pixel could be obtained by using a combination of (or a resin member) and ink. In addition, it was found that, as in the case of the papers A and B, those in which the contact angle fluctuates forever have a bad pixel shape and are impractical. Further, they had a relatively high contact angle (100 degrees or more).
[0112]
The results were obtained by examining the behavior from the time the ink droplets adhered to 300 ms. Even if the paper A or B was used, the ink penetrated into the paper 30 to 40 seconds later, The components dry and the concept of contact angle disappears. The same applies to papers (or resin members) C, D, E, and F. The evaluation of the pixel shape is performed after the ink has completely penetrated the paper or the solvent component has dried.
[0113]
As is clear from the above description, if the combination of the recording medium and the ink is optimized as described above, general plain paper (for example, high quality paper, medium quality paper or bond paper, etc.), coated paper, OHP Any of the above plastic films can be used. As described above, the present invention can be applied to all ink jet recording methods, and is particularly suitable for use in an ink jet recording method of a type in which ink is ejected by a bubbling phenomenon of ink due to thermal energy. Is extremely stable and does not generate satellite dots. However, in this case, it may be necessary to adjust thermal physical properties such as specific gravity, thermal expansion coefficient, and thermal conductivity.
[0114]
Next, more characteristic points of the present invention will be described. As described above, the present invention relates to a so-called ink jet recording method in which ink is ejected from a fine opening, and clogging at an ejection port is fatal to the ink jet recording method. This is more than the one using a dye ink, as in the present invention, the one using a pigment ink in which fine particles are dispersed in a solvent, the pigment is not dissolved like a dye but only dispersed. Therefore, clogging is more likely to occur. Furthermore, according to the present invention, a discharge opening having a finer diameter than ever before, for example, a discharge opening having a diameter of 25 μm or less (500 μm in terms of area).²This clogging is a very serious problem since an ink jet recording head is assumed.
[0115]
By the way, clogging is derived from the principle of an ink jet recording system in which ink is ejected from a fine opening. In other words, this occurs because the openings are fine. Therefore, there is a close relationship between the size of the opening and the size of the pigment, which may be called foreign matter in the ink.
[0116]
In view of this point, the present invention pays attention to the size of the discharge port and the size of the pigment particles, and finds out the relationship between the difficulty of clogging and their relationship. Specifically, the ink with the pigment particle diameter changed is prepared, using an ink jet recording head with a known ejection port size, after performing the ink ejection for a certain time, leaving it for a certain time, and restarting the ink ejection, The discharge port was examined for clogging. In this case, not only the complete obstruction of the discharge port, but also partial clogging and the prior signs (slight clogging) leading to it were considered as clogging and tested.
[0117]
The head used was an ink jet recording type head using thermal energy having a configuration as shown in FIG. However, in the head shown in FIG. 1, the tip of the flow path is the discharge port as it is, but the head used in the experiment is, as shown in FIG. 4 is provided with a nozzle plate 20 having nozzles 21 formed at the same array density (FIG. 3A is a perspective view before the nozzle plate 20 is attached, and FIG. 3B is a perspective view after the nozzle plate 20 is attached). Is). The number of discharge ports (nozzles) shown in FIGS. 1 and 3 is only four or partially shown for simplicity of explanation. The number of discharge ports used was 256 and the arrangement density was 600 dpi. The size of the heating element was 20 μm × 85 μm, the resistance value was 105 Ω, the driving voltage for ink ejection was 22 V, the driving pulse width was 6 μs, and the driving frequency was 12 kHz.
Note that the recording heads were prepared from H1 to H4 (the discharge port diameters were H1 = φ25 μm, H2 = φ20 μm, H3 = φ15 μm, and H4 = φ10 μm). The thickness of each of the nozzle plates was 40 μm.
[0118]
The ink used had the following composition and manufacturing method. Pigments having a pigment particle diameter varied from 0.003 to 2 [mu] m were prepared and tested in combination with H1 to H4 having different ejection opening diameters. In addition, the condition for leaving after the ink is ejected for a certain period of time is that the ink is left for 10 hours in an atmosphere at a temperature of 40 ° C. and a humidity of 30%.
[0119]
The method for producing the ink is shown below. The following carbon black dispersion was prepared using an aqueous solution in which a copolymer P composed of styrene / methacrylic acid / butyl acrylate and having an acid value of 325, a weight average molecular weight of 11,000 and a glass transition temperature of 84 ° C. was dissolved using potassium. did.
[0120]
・ Copolymer P aqueous solution (solid content 20% by weight) 40 parts
・ Carbon black @ MA-800 (Mitsubishi Chemical) 25 parts
・ Diethylene glycol 20 parts
・ Isopropyl alcohol ... 10 parts
・ Water ・ ・ ・ ・ ・ ・ ・ ・ 130 copies
[0121]
These materials were charged into a batch-type vertical sand mill (manufactured by Imex), filled with glass beads having a diameter of 1 mm as a medium, and subjected to a dispersion treatment for 3 hours while cooling with water. After the dispersion, a crude dispersion having a viscosity of 16 cP and a pH of 9.7 was obtained. The dispersion was centrifuged to remove coarse particles, and dispersions D1 to D22 were obtained in which the average particle size of the pigment was changed from 0.005 to 1 μm by changing the conditions of centrifugation in various ways. These dispersions were diluted with water to obtain black basic inkjet inks B1 to B22 having a viscosity of 2.4 cP, a surface tension of 46 dyn / cm, and a pH of 9.5. The solids content of the final preparation was about 7% by weight. The final pigment content in these inks is 5% by weight. The average particle size was measured by a particle size distribution analyzer ELS-800 (manufactured by Otsuka Electronics Co., Ltd.) using a dynamic light scattering method, and the average amount was indicated by a value obtained from an initial gradient of an autocorrelation function.
[0122]
Tables 5 to 8 show the results of examining the state of occurrence of clogging by combining these inks B1 to B22 and the heads H1 to H4 having the above-described different ejection apertures.
However, Table 5 is for the head H1 (discharge port diameter Do = Φ25 μm), Table 6 is for the head H2 (discharge port diameter Do = Φ20 μm), Table 7 is for the head H3 (discharge port diameter Do = Φ15 μm), and Table 8 is The case of the head H4 (discharge port diameter Do = Φ10 μm) is shown. In the judgment, a circle indicates a case where it can be used practically satisfactorily, a triangle indicates a case where it can be used but is not so preferable, and a cross indicates a case where it is not practical at all.
[0123]
[Table 5]

[0124]
[Table 6]

[0125]
[Table 7]

[0126]
[Table 8]

[0127]
From the above results, when using an ejection head having a discharge port diameter of Φ10 μm to Φ25 μm, the pigment particle diameter Dp and the discharge port diameter Do should satisfy the relationship of 0.0005 ≦ Dp / Do ≦ 0.02. It can be seen that stable ink ejection without clogging can be obtained. In the experiment, the discharge port is round, but in the case of another shape (polygon or the like), it may be within a range converted by the area ratio.
[0128]
Next, other features of the present invention will be described. As described above, the present invention is based on the premise of a pigment ink. That is, the colorant in the recording liquid is not a dye dissolved in a solvent such as water, but a fine particle serving as a pigment dispersed therein. Therefore, the pigment content and the content of the pigment dispersant including the solid content in the ink have a great influence on clogging. Therefore, here, the relationship between their contents and clogging of the discharge port was examined.
[0129]
The head used was the same as the head H2 (discharge aperture Do = Φ20 μm). In the ink (B5) having a pigment particle diameter Dp = 0.03 μm, the pigment content and styrene / methacrylic acid as a pigment dispersant were used. The amount of the solids in the final ink and the easiness of clogging were examined by changing the amount of the copolymer P composed of / butyl acrylate. The clogging test method and the like are the same as those described above. The results are shown in Tables 9 and 10. In the judgment, the symbol “○” indicates that the sample can be used satisfactorily in practical use, and the symbol “X” indicates that the sample is not practical.
[0130]
[Table 9]

[0131]
[Table 10]

[0132]
From the above results, it can be seen that the content of the pigment in the ink may be set to 1 to 10% by weight, and if the content is more than that, clogging occurs. It is also understood that not only the pigment content but also the final solid content including the pigment must be 15% by weight or less. When the pigment content is 1% by weight, there is no fear of clogging, but when this ink is used alone, the density is low and it is not practical. However, it can be suitably used as a light ink for a recording apparatus using a plurality of types of so-called dark and light inks. Further, even when the ink is used alone, it is possible to add a dye to compensate for the insufficient density.
[0133]
Next, still another feature of the present invention will be described. The inkjet printhead to which the present invention is applied is generally suitably applied to color printing, and therefore, the configuration of the color inkjet printhead to which the present invention is suitably applied will be described.
[0134]
FIG. 8 is a view showing an example of the ink jet head of the present invention. In the present invention, as shown in the drawing, a plurality of ink ejection elements 31Y, 31M, 31C of a plurality of colors are placed on one common heating element substrate 30. Is formed. In this example, three color inks of yellow (Y), magenta (M), and cyan (C) are shown. In addition, in this example and the following examples, the ink ejection elements and ejection ports of each color are described with four or five colors for simplification of the drawing. It is preferably used.
[0135]
FIG. 9 shows a diagram in which an ink tank unit 40 for supplying Y, M, and C inks is provided in the recording head unit of FIG. This drawing is a diagram showing the concept of an ink jet recording head of the present invention comprising a recording head section and an ink tank section, and is different from an actual one (to be described later).
[0136]
FIG. 10 is a diagram showing a configuration of a so-called serial printer in which the inkjet head according to the present invention is mounted on a carriage to perform recording. In the drawing, reference numeral 50 denotes an inkjet head according to the present invention, 51 denotes recording paper, 52 denotes a carriage, 53 is a guide rod of the carriage, 54 is a screw rod for moving the carriage, 55 is a recording paper transport roller, and 56 is a recording paper holding roller. As is well known, Y is a vertical direction (moving direction of the recording paper 51). , M, and C, the recording head 50 (in the illustrated example, the head shown in FIG. 9 is mounted) is printed while reciprocating in the X direction in front of the recording paper 51. . In the present invention, each time the carriage is scanned once, the recording paper is moved in the direction of arrow Y in the drawing. Therefore, the area recorded in one scan is only the length of the ejection element of the head, that is, the length of the row of ejection ports. In addition, since Y, M, and C are arranged in one line in the vertical direction, full-color printing is performed for the first time by overlapping the printing areas of the Y, M, and C inks by two or more scans. Can be.
[0137]
In the above description, an example of three colors of Y, M, and C has been described. However, the present invention is also applied to an ink jet having a discharge port array of four colors in which black (B) is added thereto.
FIG. 11 shows an example of this. In this case, as shown in the figure, the ink ejection element 31B for black is further added to the example shown in FIG.
[0138]
FIG. 12 shows another example having a discharge port array of four colors. FIG. 11 shows an example in which the ink flow paths for each color are independently manufactured, but this figure is an example in which the flow paths for four colors are integrally manufactured by molding a plastic 60. By doing so, the assembly cost can be significantly reduced.
[0139]
Normally, a color ink jet recording apparatus is configured such that one recording head as shown in FIG. 1 is filled with one color ink, and a plurality of inks are arranged on a carriage 70 as shown in FIG. 71B, 71C, 71M, and 71Y are recording heads for ejecting black, cyan, magenta, and yellow color inks, respectively. This is partly for ensuring reliability such as measures against clogging. For example, as shown in FIG. 13, when the heads 71B, 71C, 71M, and 71Y filled with four colors of ink are independently arranged on the carriage 70, if any one of the color heads becomes clogged, The original state can be restored by replacing the head of one color.
[0140]
On the other hand, in the present invention, the recording heads shown in FIGS. 8 to 12 for ejecting ink in a plurality of colors are integrally formed. As described above, in consideration of recovery measures in the event of clogging, it is advantageous to arrange the heads filled with inks of a plurality of colors independently on a carriage as shown in FIG. In the present invention, as described above, the pigment particle size, the content or the amount of the solid content in the ink has been carefully studied and optimized, so that the fear of clogging has been resolved. Therefore, it is not necessary to independently arrange the heads filled with the inks of a plurality of colors as shown in FIG. 13 on the carriage, thereby reducing the assembly cost, realizing compactness, and improving the dot position accuracy of the plurality of colors. For this purpose, as shown in FIGS. 8 to 12, a recording head for ejecting a plurality of colors of ink is integrally formed.
[0141]
Note that the integral formation here means not only an example in which the heating element substrate is a single common substrate as in the example of the bubble ink jet head shown in FIGS. 8 to 12, but also as shown in FIG. Also includes a head filled with a plurality of color inks, for example, a head in which 71B, 71C, 71M, and 71Y are stacked and integrated. This example shows an example in which one common nozzle plate 73 is provided at the front ends 72B, 72C, 72M, and 72Y of the flow paths (FIG. 14A shows the state before the nozzle plate 73 is attached, and FIG. ) Is a perspective view after mounting). In this case, since a common single nozzle plate 73 that is perforated, assembled, and integrated with high precision is provided, not only can the manufacturing cost be reduced, but also a plurality of colors can be obtained. High dot position accuracy can be obtained.
[0142]
FIG. 15 is an example in which a head unit capable of ejecting inks of a plurality of colors (three colors of Y, M, and C in this example) is formed integrally with an ink container portion, and FIG. FIG. 15B is an exploded perspective view in which 100 is a head unit, 101 is a head chip, 102 is a print circuit, 103 is an upper cover, 104 is an ink container, and 105 (105Y, 105M, 105C) is stainless steel. A mesh filter, 106 (106Y, 106M, 106C) is a foam material containing ink, 107 is a bottom cover, and in this example, a head part and an ink container part connected to the head part are internally divided into three parts, and Y, M, and C are separately filled. As described above, since the head unit in which a plurality of colors are integrated can be formed very compact, when mounted on a carriage, the head unit is lightweight and small, so that only a small carriage is required, and the motor for driving the carriage is also small. Energy saving can be realized.
[0143]
FIG. 16 is a diagram for explaining an example in which only the ink container portion is configured to be separable in the ink container integrated type head unit of a plurality of colors shown in FIG. 15, and FIG. FIG. 16B is a perspective view of the head unit 110 in a state where the recording head unit 111 and the ink container unit 112 are separated from each other. As a result, even if a large amount of ink is consumed for printing a color image, only the ink container unit 112 needs to be replaced, so that cost reduction is realized. In addition, the advantage of the integrated color head described with reference to FIG. 15 is maintained.
[0144]
FIG. 17 is a view for explaining an example in which the ink container section can be separated for each color of ink with the integrated head unit as described above. FIG. 17A is an overall perspective view, and FIG. 3B is a perspective view showing a state in which the recording head unit 111 of the head unit 110 and the ink container units 112 (112Y, 112M, 112C) of each color are separated. The advantage of this is that, in color image printing, the Y, M, and C inks are not necessarily consumed at the same speed, so if any of the inks shown in FIGS. Even if other ink remains when the ink runs out, the head unit or the entire integrated ink container must be replaced, which is disadvantageous in terms of running cost. By keeping the containers separate, it is possible to further reduce the running cost by replacing only the used ink container.
[0145]
Although all of the above description has been made with reference to the example of bubble ink jet, the present invention is not limited to this, but has a fine discharge port and is applicable to all ink jets using pigment ink. . Also, the recording head is described using an example of a single-color ink, but it goes without saying that the recording head can also be applied to a color inkjet.
[0146]
【The invention's effect】
According to the present invention, in a recording liquid (ink) in which a pigment, which is fine particles, is dispersed as a colorant, the fine particle diameter is optimized in relation to the ejection opening diameter and the thickness of the paper fiber or the gap between them, or the paper used is Optimized in relation to wetting, nozzle clogging does not occur and high reliability can be achieved even when used in an ejection head that uses a very fine ejection port (nozzle) that is not conventionally available, such as Ф25 μm or less. As a result, the coloring material adhered well on the paper, and a good pixel shape was obtained. As a result, high-quality recording was realized, and high water resistance and high light resistance were also realized.
[0147]
Further, in a recording liquid (ink) in which a pigment as fine particles is dispersed as a coloring material, the diameter of the fine particles is optimized in relation to the discharge port diameter and the size of the particles of the coating substance on the surface of the paper, or the paper to be used. Optimized in relation to the wetting of the nozzle, nozzle clogging does not occur even when used in an ejection head that uses a very fine ejection port (nozzle) that is not conventional, such as Ф25 μm or less, and high reliability Can be obtained. In addition, the color material adhered well on the paper, and a good pixel shape was obtained. As a result, high-quality recording was realized, and high water resistance and high light resistance were also realized.
[0148]
Further, in a recording liquid (ink) in which a pigment, which is a fine particle, is dispersed as a colorant, the diameter of the fine particle is optimized in relation to the discharge port diameter and the size of the particles of the coating material on the surface of the resin member to be recorded, or Optimized in relation to the wetting of the surface of the resin member to be used, nozzle clogging will not occur even when used for an ejection head that uses an extremely fine ejection port (nozzle) that is not conventionally available, such as Ф25 μm or less. It did not occur and high reliability was obtained. In addition, the coloring material adhered well on the surface of the resin member, a good pixel shape was obtained, and high-quality recording was realized, and high water resistance and high light resistance were also realized.
[0149]
Further, in a recording liquid (ink) in which a pigment, which is fine particles, is dispersed as a coloring material, the content ratio and solid content of the fine particles in the recording liquid (ink) are optimized, and the solvent of the recording liquid (ink) is used for recording. Penetrated in the depth direction of the body, the solid content adhered to the surface of the recording medium, so that it was held, so that a practically sufficient concentration is obtained, and the pigment is stably dispersed, high water resistance, In addition to realizing high light resistance, even when used in an ejection head that uses an extremely fine ejection port (nozzle), the ejection port is not clogged, reliability is improved, and a good pixel shape is achieved. As a result, high-quality recording can be obtained.
[0150]
Further, the recording liquid (ink) as described above is used for a head unit in which a recording liquid ejecting section and a recording liquid storing section (ink container section) are separable. In addition to the effects of 1 to 4, the running cost of an ink jet recording apparatus using this recording liquid (ink) could be reduced.
[0151]
Further, since the recording liquid (ink) as described above is filled in the recording liquid storage section which can be separated according to the type of the recording liquid, any of the recording liquid (ink) is used up. At this time, since only the recording liquid storage portion (ink container portion) needs to be replaced in accordance with the type of the recording liquid (ink), in addition to the above effects, further reduction in running cost can be realized when performing color recording. Was.
[0152]
Further, when the above-described recording liquid (ink) is applied to a thermal ink jet system in which bubbles are generated by heat in the recording liquid (ink) and the recording liquid (ink) is ejected by the acting force, the usage conditions However, by selecting the conditions of the present invention, even if it is used for an ejection head using an extremely fine discharge port (nozzle) which is not heretofore and is not more than $ 25 μm as in the present invention, Stable injection without clogging was performed, high reliability and high quality printing were realized.
[0153]
Further, in the case of the thermal ink jet system, since the ejection head portion can be manufactured using a semiconductor manufacturing process, an extremely fine discharge port (nozzle) which is not conventionally used and is not larger than Ф25 μm as in the present invention is used. An injection head necessary for high-precision printing, which is simple and compact even when the heating elements and discharge ports are arranged very finely and densely, and has a high yield, that is, low cost. Can be manufactured with Therefore, such a liquid jet recording apparatus using the recording liquid (ink) of the present invention can be made more compact and reduced in manufacturing cost.
[0154]
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a bubble ink jet recording head.
FIG. 2 is a diagram for explaining the principle of ink droplet ejection of a bubble inkjet type inkjet.
FIG. 3 is a diagram illustrating an example of an inkjet head having a nozzle plate.
FIG. 4 is an enlarged image diagram of a paper surface.
FIG. 5 is an image diagram when a large particle size pigment adheres to the paper surface.
FIG. 6 is an image diagram when pigment particles smaller than fibers adhere to the paper surface.
FIG. 7 is a diagram illustrating a change over time of a contact angle when an ink droplet adheres to a paper surface.
FIG. 8 is a diagram illustrating an example of the ink jet head of the present invention.
9 is a diagram illustrating an example in which an ink tank is provided in the recording head unit in FIG.
FIG. 10 is a diagram illustrating a configuration example of a serial printer equipped with an inkjet head.
FIG. 11 is a diagram showing an example having ejection port arrays of four colors.
FIG. 12 is a diagram showing an example in which heads of four colors are integrated.
FIG. 13 is a diagram illustrating an example in which heads of four colors are independently arranged on a carriage.
FIG. 14 is a diagram illustrating an example in which heads of a plurality of colors are stacked and integrated.
FIG. 15 is a diagram illustrating an example in which a head unit and an ink container are integrally formed.
FIG. 16 is a diagram illustrating an example in which only the ink container portion is configured to be separable.
FIG. 17 is a diagram showing an example in which ink containers can be separated for each color of ink.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Lid board | substrate, 2 ... Heating element board, 3 ... Recording liquid inflow port, 4 ... Discharge port, 5 ... Flow path, 6 ... Common liquid chamber, 7 ... Individual control electrode, 8 ... Common electrode, 9 ... Heating element, DESCRIPTION OF SYMBOLS 10 ... Ink 10 '... Ink pillar, 11 ... Bubble, 12 ... Droplet, 20 ... Nozzle plate, 21 ... Nozzle, 30 ... Heating substrate, 31Y, 31M, 31C, 31B ... Ink ejection element, 40 ... Ink tank , 50: recording head, 51: recording paper, 52: carriage, 53: guide rod, 54: screw rod, 55: recording paper feed roller, 56: recording paper holding roller, 70: carriage, 71B, 71C, 71M, 71Y ... Heads, 72B, 72C, 72M, 72Y ... Discharge ports, 73 ... Nozzle plate, 100 ... Head unit, 101 ... Head chip, 102 ... FPC, 103 ... Top cover, 104 ... Ink container part, 105 ... Filter 106 ... ink impregnated foam, 107 ... bottom lid, 110 ... head unit 111 ... recording head unit, 112 ... ink container portion.

Claims (7)

The recording liquid is ejected from a fine opening having an opening size of Ф25 μm or less, and the recording liquid is almost completely changed within 100 ms after the recording liquid adheres to the recording medium. In a recording liquid used for a liquid jet recording head that performs recording by adhering liquid droplets, the recording liquid is obtained by dispersing fine particles together with a dispersant in a solvent or treating the surface of the fine particles with the recording liquid. Wherein the size of the fine particles is Dp and the size of the fine openings is Do, 0.0005 ≦ Dp / Do ≦ 0.02, and the fine particles are dispersed in a solvent. A recording liquid having a size smaller than a thickness of a fiber of the paper and a size equal to or smaller than a gap formed by overlapping the fibers. The recording liquid is ejected from a fine opening having an opening size of Ф25 μm or less, and the recording liquid is almost completely changed within 100 ms after the recording liquid adheres to the recording medium. In a recording liquid used for a liquid jet recording head that performs recording by adhering liquid droplets, the recording liquid is obtained by dispersing fine particles together with a dispersant in a solvent or treating the surface of the fine particles with the recording liquid. Wherein the size of the fine particles is Dp and the size of the fine openings is Do, 0.0005 ≦ Dp / Do ≦ 0.02, and the fine particles are dispersed in a solvent. A recording liquid having a size smaller than the average particle diameter of the particulate matter applied to the surface of the paper and smaller than the smoothness of the surface of the paper. The recording liquid is ejected from a fine opening having an opening size of Ф25 μm or less, and a change in the contact angle of the recording liquid almost disappears within 100 ms after the recording liquid adheres to the recording medium. In a recording liquid used in a liquid jet recording head for performing recording by attaching droplets of the recording liquid, the recording liquid is obtained by dispersing fine particles together with a dispersant in a solvent or treating the surface of the fine particles to perform the recording. A recording liquid dispersed in a liquid solvent, wherein when the size of the fine particles is Dp and the size of the fine opening is Do, 0.0005 ≦ Dp / Do ≦ 0.02, A recording liquid having a particle size smaller than the average particle diameter of the particulate matter applied to the surface of the resin member and smaller than the smoothness of the surface of the resin member. The content of the fine particles in the recording liquid is 2 to 10% by weight, the solid content including the fine particles in the recording liquid is 15% by weight or less, and the solvent of the recording liquid is The recording liquid according to claim 1, wherein the recording liquid permeates in an internal depth direction, and the solid content adheres to and is held on a surface of the recording medium. The recording liquid according to any one of claims 1 to 4, wherein the recording liquid is used for a head unit in which a recording liquid ejection unit and a recording liquid storage unit are separable. The recording liquid according to claim 5, wherein the recording liquid is filled in a recording liquid storage part that can be separated according to a type of the recording liquid. The recording liquid according to any one of claims 1 to 6, wherein the recording liquid is used for thermal inkjet.

Images