JP2004269738A - Electrostatic inkjet ink composition and charge control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an oil-based ink composition for an electrostatic type inkjet printer which, in an electrostatic inkjet head of colorant concentration discharge type, is excellent in dispersion stability, control of electrical charge polarity, and the temporal stability of electrical charge, and can print dots having a high density and few blots stably at a high speed, and to provide a charge control method for its colorant particles. <P>SOLUTION: The ink composition, as one for an electrostatic inkjet recording device, contains a nonaqueous solvent having a dielectric constant of 1.5-20 and a surface tension of 15-60 mN/m (at 25°C), a colorant insoluble in the nonaqueous solvent, a resin insoluble in the nonaqueous solvent, and a charge regulator soluble in the nonaqueous solvent. The resin insoluble in the nonaqueous solvent is a resin having an acid group, and the charge regulator contains at least one compound represented by formula (1). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２０】
式（１）中、Ｒ^ｌおよびＲ^２はそれぞれ水素原子、アルキル基、アリール基、アラルキル基、アシル基、アルキルスルホニル基又はアリールスルホニル基を表し、それぞれ置換されていてもよい。Ｒ^ｌ、Ｒ^２はそれぞれ同じであっても異なっていてもよく、Ｒ^ｌおよびＲ^２で環を形成していてもよい。Ａはアルキレン基を表す。Ｘは１価から４価までの金属又は４級アンモニウム陽イオンを示す。ｎは１から４までの正の整数を示す。
Ｘが金属を表す場合、金属にその原子価を満足するだけ該カルボン酸が結合していない場合、残存する原子価は他の配位子によって飽和されていてもよい。
【００２１】
２）インク組成物の２５℃における体積抵抗率が１０^８Ω・ｃｍ以上であり、かつインク組成物中の色材粒子の粒子電導度が１００ｐＳ／ｃｍ以上である事を特徴とする上記１）記載の静電インクジェットインク組成物。
【００２２】
３）インクを複数の記録電極が配置された記録ヘッドに導入し、前記記録電極に電圧を印加して、前記インクに静電力を作用させて色材粒子が濃縮された形でインク滴を飛翔させて、対向する様に配置された記録媒体上に印字ドットを形成し記録を行う色材濃縮吐出型の静電インクジェット記録装置用であることを特徴とする上記１）又は２）記載の静電インクジェットインク組成物。
【００２３】
４）インク組成物を複数の記録電極が配置された記録ヘッドに導入し、前記記録電極に電圧を印加して、前記インクに静電力を作用させて色材粒子が濃縮された形でインク滴を飛翔させて、対向する様に配置された記録媒体上に印字ドットを形成し記録を行う色材濃縮吐出型の静電インクジェット画像形成方法において、前記インク組成物が、比誘電率１．５〜２０及び表面張力１５〜６０ｍＮ／ｍ（２５℃において）を有する非水溶媒、前記非水溶媒に不溶な色材、前記非水溶媒に不溶な酸性基を有する樹脂、及び前記非水溶媒に可溶な上記一般式（１）で表される荷電調節剤を含む事を特徴とする静電インクジェット画像形成方法。
【００２４】
５）インク組成物の２５℃における体積抵抗率が１０^８Ω・ｃｍ以上であり、かつインク組成物中の色材粒子の粒子電導度が１００ｐＳ／ｃｍ以上である事を特徴とする上記４）記載の静電インクジェット画像形成方法。
【００２５】
本発明の非水溶媒に不溶な酸性基を有する樹脂と、上記の一般式（１）で表されるアミノ酸化合物を含有することからなる荷電調節剤の組み合わせによる荷電調節機構は以下のように考えられる。
即ち、一般式（１）において置換基Ｒ^ｌ、Ｒ^２はこれらの化合物の脂溶性を向上させ、キャリャー液中への溶解を助けるためのものであり、窒素原子は好ましいイオン解離を促進するためのものである。一般にキャリャー液可溶型の荷電調節剤が効力を発揮するためには、まず非極性の溶媒中でイオン解離し、ついで解離したイオン種のうち一方がトナーの粒子表面に選択的に吸着しなければならない。あるいはトナー粒子表面よりイオンを奪って自身がイオン化することが必要である。
一般式（１）で表される非水溶媒に可溶なアミノ酸化合物からなる荷電調節剤は、酸性基を有する樹脂により色材が被覆された色材粒子（以下、「色材樹脂粒子」とも称する）表面の該酸性基から陽イオンを奪うと推定されるが、その際、下記の一般式（１′）で表されるように、陽イオン種に対し配位能力のある窒素原子が分子内の都合のよい位置にあるためこのイオン化が促進され、生成した陽イオン種がＲ^ｌ、Ｒ^２の効果でキャリャー液中に安定に可溶化するものと考えられる。一方、色材樹脂粒子は陰イオン化して負帯電になる。色材樹脂粒子表面の酸性基と下記の荷電調節剤の荷電安定化機構により、色材粒子に高い粒子電導度を付与でき、また、荷電量の経時変化がなく安定していると考えている。
【００２６】
【化３】

【００２７】
本発明によれば、色材粒子が高い粒子電導度を有し、高濃度で滲みが少ないドットを高速で安定に印字することができる、色材濃縮吐出型の静電インクジェットヘッド用のインクを実現することができる。色材粒子の荷電量を示す粒子電導度は、インク組成物の全体の比電導度から、インク組成物を遠心分離器にかけた上澄みの比電導度を差し引いて求めた値である。
【００２８】
【発明の実施の形態】
以下に本発明について更に詳細に述べる。
本発明で使用される比誘電率１．５〜２０及び表面張力１５〜６０ｍＮ／ｍ（２５℃において）を有する非極性の絶縁性溶剤に必要な特性としては、毒性の少ないこと、引火性が少ないこと、臭気が少ないことであり、直鎖状又は分岐状の脂肪族炭化水素、脂環式炭化水素、芳香族炭化水素、石油ナフサ及びこれらのハロゲン置換体等から選ばれた溶媒が挙げられる。例えばヘキサン、オクタン、イソオクタン、デカン、イソデカン、デカリン、ノナン、ドデカン、イソドデカン、エクソン社のアイソパーＥ、アイソパーＧ、アイソパーＨ、アイソパーＬ、フィリップ石油社のソルトール、出光石油化学社のＩＰソルベント、石油ナフサではシェル石油化学社のＳ．Ｂ．Ｒ．、シェルゾール７０、シエルゾール７１、モービル石油社のベガゾール等から選ばれた溶媒を単独又は混合して用いることができる。
【００２９】
好ましい炭化水素溶剤としては、沸点が１５０〜３５０℃の範囲にある高純度のイソパラフィン系炭化水素が挙げられ、市販品としては前述のエクソン化学製のアイソパーＧ，Ｈ，Ｌ，Ｍ，Ｖ（商品名）、ノーパー１２，１３，１５（商品名）、出光石油化学製のＩＰソルベント１６２０，２０２８（商品名）、日本石油化学製のアイソゾール３００，４００（商品名）、アムスコＯＭＳ、アムスコ４６０溶剤（アムスコ；スピリッツ社の商品名）等が挙げられる。これらの製品は、極めて純度の高い脂肪族飽和炭化水素であり、２５℃における粘度は３ｃＳｔ以下、２５℃における表面張力は２２．５〜２８．０ｍＮ／ｍ、２５℃における比抵抗は１０^１０Ω・ｃｍ以上である。また、反応性が低く安定であり、低毒性で安全性が高く、臭気も少ないという特徴がある。
【００３０】
ハロゲン置換の炭化水素系溶媒としてフルオロカーボン系溶媒があり、例えばＣ_７Ｆ_１６、Ｃ_８Ｆ_１８などのＣ_ｎＦ_２ｎ＋２で表されるパーフルオロアルカン類（住友３Ｍ社製「フロリナートＰＦ５０８０」、「フローリナートＰＦ５０７０」（商品名）等）、フッ素系不活性液体（住友３Ｍ社製「フロリナートＦＣシリーズ」（商品名）等）、フルオロカーボン類（デュポンジャパンリミテッド社製「クライトックスＧＰＬシリーズ」（商品名）等）、フロン類（ダイキン工業株式会社製「ＨＣＦＣ−１４１ｂ 」（商品名）等）、［Ｆ（ＣＦ_２）_４ＣＨ_２ＣＨ_２Ｉ］、［Ｆ（ＣＦ_２）_６Ｉ］等のヨウ素化フルオロカーボン類（ダイキンファインケミカル研究所製「Ｉ−１４２０」、「Ｉ−１６００」（商品名）等）等が挙げられる。
【００３１】
本発明で使用される非水系の溶媒として、更に高級脂肪酸エステルや、シリコーンオイルも使用できる。シリコーンオイルの具体例としては、低粘度の合成ジメチルポリシロキサンが挙げられ、市販品としては、信越シリコーン製のＫＦ９６Ｌ（商品名）、東レ・ダウコーニング・シリコーン製のＳＨ２００（商品名）等がある。
シリコーンオイルとしてはこれらの具体例に限定されるものではない。これらのジメチルポリシロキサンは、その分子量により非常に広い粘度範囲のものが入手可能であるが、１〜２０ｃＳｔの範囲のものを用いるのが好ましい。これらのジメチルポリシロキサンは、イソパラフィン系炭化水素同様、１０^１０Ω・ｃｍ以上の体積抵抗率を有し、高安定性、高安全性、無臭性といった特徴を有している。またこれらのジメチルポリシロキサンは、表面張力が低いことに特徴があり、１８〜２１ｍＮ／ｍの表面張力を有している。
【００３２】
これらの有機溶媒とともに、混合して使用できる溶媒としては、アルコール類（例えばメチルアルコール、エチルアルコール、プロピルアルコール、ブチルアルコール、フッ化アルコール等）、ケトン類（例えばアセトン、メチルエチルケトン、シクロヘキサノン等）、カルボン酸エステル類（例えば酢酸メチル、酢酸エチル、酢酸プロピル、酢酸ブチル、プロピオン酸メチル、プロピオン酸エチル等）、エーテル類（例えばジエチルエーテル、ジプロピルエーテル、テトラヒドロフラン、ジオキサン等）及びハロゲン化炭化水素類（例えばメチレンジクロリド、クロロホルム、四塩化炭素、ジクロロエタン、メチルクロロホルム等）、等の溶媒が挙げられる。
【００３３】
次に本発明で使用される色材について詳細に述べる。
色材としては、特に限定されるものではなく、一般に市販されているすべての有機顔料及び無機顔料、もくしは顔料を分散媒に不溶性の樹脂等に分散させたもの、又は顔料表面に樹脂をグラフト化したもの等を用いる事ができる。また樹脂粒子を染料で染色したもの等も用いる事ができる。有機顔料及び無機顔料の具体例としては、例えば、イエロー色を呈するものとして、Ｃ．Ｉ．ピグメントイエロー１（ファストイエローＧ等）， Ｃ．Ｉ．ピグメントイエロー７４の如きモノアゾ顔料、 Ｃ．Ｉ．ピグメントイエロー１２（ジスアジイエローＡＡＡ等）， Ｃ．Ｉ．ピグメントイエロー１７の如きジスアゾ顔料、 Ｃ．Ｉ．ピグメントイエロー１８０の如き非ベンジジン系のアゾ顔料、 Ｃ．Ｉ．ピグメントイエロー１００（タートラジンイエローレーキ等）の如きアゾレーキ顔料、 Ｃ．Ｉ．ピグメントイエロー９５（縮合アゾイエローＧＲ等）の如き縮合アゾ顔料、 Ｃ．Ｉ．ピグメントイエロー１１５（キノリンイエローレーキ等）の如き酸性染料レーキ顔料、 Ｃ．Ｉ．ピグメントイエロー１８（チオフラビンレーキ等）の如き塩基性染料レーキ顔料、フラバントロンイエロー（Ｙ−２４）の如きアントラキノン系顔料、イソインドリノンイエロー３ＲＬＴ（Ｙ−１１０）の如きイソインドリノン顔料、キノフタロンイエロー（Ｙ−１３８）の如きキノフタロン顔料、イソインドリンイエロー（Ｙ−１３９）の如きイソインドリン顔料、 Ｃ．Ｉ．ピグメントイエロー１５３（ニッケルニトロソイエロー等）の如きニトロソ顔料、 Ｃ．Ｉ．ピグメントイエロー１１７（銅アゾメチンイエロー等）の如き金属錯塩アゾメチン顔料等が考えられる。
【００３４】
マゼンタ色を呈するものとして、Ｃ．Ｉ．ピグメントレッド３（トルイジンレッド等）の如きモノアゾ系顔料、 Ｃ．Ｉ．ピグメントレッド３８（ピラゾロンレッドＢ等）の如きジスアゾ顔料、 Ｃ．Ｉ．ピグメントレッド５３：１（レーキレッドＣ等）やＣ．Ｉ．ピグメントレッド５７：１（ブリリアントカーミン６Ｂ）の如きアゾレーキ顔料、 Ｃ．Ｉ．ピグメントレッド１４４（縮合アゾレッドＢＲ等）の如き縮合アゾ顔料、 Ｃ．Ｉ．ピグメントレッド１７４（フロキシンＢレーキ等）の如き酸性染料レーキ顔料、 Ｃ．Ｉ．ピグメントレッド８１（ローダミン６Ｇ’レーキ等）の如き塩基性染料レーキ顔料、 Ｃ．Ｉ．ピグメントレッド１７７（ジアントラキノニルレッド等）の如きアントラキノン系顔料、Ｃ．Ｉ．ピグメントレッド８８（チオインジゴボルドー等）の如きチオインジゴ顔料、 Ｃ．Ｉ．ピグメントレッド１９４（ペリノンレッド等）の如きペリノン顔料、 Ｃ．Ｉ．ピグメントレッド１４９（ペリレンスカーレット等）の如きペリレン顔料、 Ｃ．Ｉ．ピグメントレッド１２２（キナクリドンマゼンタ等）の如きキナクリドン顔料、 Ｃ．Ｉ．ピグメントレッド１８０（イソインドリノンレッド２ＢＬＴ等）の如きイソインドリノン顔料、 Ｃ．Ｉ．ピグメントレッド８３（マダーレーキ等）の如きアリザリンレーキ顔料等が考えられる。
【００３５】
シアン色を呈する顔料として、Ｃ．Ｉピグメントブルー２５（ジアニシジンブルー等）の如きジスアゾ系顔料、 Ｃ．Ｉ．ピグメントブルー１５（フタロシアニンブルー等）の如きフタロシアニン顔料、 Ｃ．Ｉ．ピグメントブルー２４（ピーコックブルーレーキ等）の如き酸性染料レーキ顔料、 Ｃ．Ｉ．ピグメントブルー１（ビクロチアピュアブルーＢＯレーキ等）の如き塩基性染料レーキ顔料、 Ｃ．Ｉ．ピグメントブルー６０（インダントロンブルー等）の如きアントラキノン系顔料、 Ｃ．Ｉ．ピグメントブルー１８（アルカリブルーＶ−５：１）の如きアルカリブルー顔料等が考えられる。
【００３６】
ブラック色を呈する顔料として、ＢＫ−１（アニリンブラック）の如きアニリンブラック系顔料等の有機顔料や酸化鉄顔料、及びファーネスブラック、ランプブラック、アセチレンブラック、チャンネルブラック等のカーボンブラック顔料類が考えられる。カーボンブラック顔料の具体例としては、三菱化学（株）のＭＡ−８，ＭＡ−１０，ＭＡ−１１，ＭＡ−１００，ＭＡ−２２０，＃２５，＃４０，＃２６０，＃２６００，＃２７００Ｂ，＃３２３０Ｂ，ＣＦ−９，ＭＡ−１００Ｒ、ＭＡ−２００ＲＢや、デグサ社のプリンテックス７５，９０、キャボット社のモナーク８００，１１００などが挙げられる。 また、金、銀、銅などの色再現のために金属粉の応用も考えられる。 また、金、銀、銅などの色再現のために金属粉の応用も考えられる。
【００３７】
その他、ロジンエステル樹脂や塩化ビニル−酢酸ビニル樹脂等に顔料微粒子を分散させた加工顔料が市販されており、これを用いても良い。市販加工顔料の具体例としては、チバスペシャリティケミカルズ社のマイクロリス顔料等が挙げられ、好ましい加工顔料の例としては、ロジンエステル樹脂で顔料を被覆したマイクロリス−Ｔ顔料が挙げられる。
【００３８】
本発明のインク組成物における色材の濃度は、インク組成物の総量に対して０．５〜２０質量％、特に好ましくは２〜１５質量％の範囲であることが好ましい。色材の濃度が０．５質量％以上において、十分な印字濃度が得られ、また、２０質量％以下において、良好なインクの粘度が保たれ、安定なインク吐出が行うことができ、好ましい。
【００３９】
次に本発明のインク組成の特徴である荷電調節剤について詳しく説明する。本発明の荷電調節剤は、上記一般式（１）で示される化合物を少なくとも一種含有する。
【００４０】
上記式（１）において、Ｒ^ｌおよびＲ^２はそれぞれ、好ましくは、水素原子、炭素数１〜２２までのアルキル基、置換アルキル基（置換基としては炭素数１〜１０の、ジアルキルアミノ基、アルキルオキシ基、アルキルチオ基等が挙げられる）、アリール基、置換アリール基（置換基としては炭素数１〜１０までの、アルキル基、ジアルキルアミノ基、クロル基、ブロム基等が挙げられる）、アラルキル基、炭素数１〜２２までの、アシル基、アルキルスルホニル基、又はアリールスルホニル基を表す。Ｒ^ｌ、Ｒ^２はそれぞれ同じであっても異なっていてもよく、Ｒ^ｌおよびＲ^２で環を形成していてもよい。
【００４１】
Ａは、好ましくは、炭素数１〜１０のアルキレン基又は置換アルキレン基を表す。Ｘは１価から４価までの金属、又は４級アンモニウム陽イオンを示す。ｎは１から４までの正の整数を示す。
【００４２】
一般式（１）にて、Ｘが金属を表す場合において、金属にその原子価を満足するだけ該カルボン酸が結合していない場合、残存する原子価は他の配位子によって飽和されていてもよい。配位子としては例えば、ハロゲン、水酸基、酸素原子、水、アンモニア、アミン類、ホスフィン類、サルファイド類などが挙げられる。
【００４３】
本発明に用いられる一般式（１）の化合物において、Ｒ^ｌとＲ^２の炭素数の合計が８〜１０の範囲内であることが好ましく、またＲ^ｌとＲ^２のどちらかがアシル基であることが好ましい。またＸは、カルシウム、バリウム、マンガン、銅、リチウム、チタン、亜鉛、鉛、ジルコニウム、コバルト、ニツケル、アルミニウム、セリウム、ランタン、クロム、ストロンチウム、バナジウム、スズ、マグネシウム、鉄、カドミウムから選ばれる金属であることが好ましい。
【００４４】
本発明のアミノ酸化合物を含有することからなる荷電調節剤は、特公平５−２９９０４号（特許文献６）に開示されているように電子写真用液体現像剤の荷電調節剤として既に知られている。しかしながら、特公平５−２９９０４号では、顔料と非水溶媒に不溶な樹脂の記述があるものの、本発明の如く、非水溶媒に不溶な酸性基を有する樹脂とアミノ酸化合物を含有することからなる荷電調節剤の組み合わせの記載がなく、又、両者の組み合わせにより特異的に色材粒子の粒子電導度が高くなる効果についても記載がない。更に、静電型インクジェツトプリンターに用いるインクは色材粒子に１００ｐｓ／ｃｍ以上の高い粒子電導度を付与することが必要なため、特公平５−２９９０４号公報の実施例に開示されている電子写真用液体現像剤中の色材粒子では、その粒子電導度が小さいために良好な描画画像が得られず静電型インクジェツト用インクとして使用することができないものであった。
【００４５】
以下に、本発明の特徴である一般式（１）のアミノ酸化合物の金属塩の合成方法を示す。
アシル化アミノ酸の合成に関しては、Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．，７８，１７２（１９５６）に記載されているように、アミノ酸のアシル化反応を用いる事ができる。
その他のアミノ酸化合物の合成に関しては一般的な手法が応用できる。金属塩の合成には、該カルボン酸又はスルホン酸のアルカリ金属塩と該金属の無機塩とを反応させるか、あるいは該カルボン酸又はスルホン酸と有機金属化合物（例えば特開昭５０−１５１１５４号、特公昭５６−２９５２号、特公昭５８−９４１６号記載のもの）、金属水酸化物又は金属酸化物とを直接反応させてもよい。
【００４６】
以下に本発明のアミノ酸化合物の具体例を挙げるが、これらに限定されるものではない。
【００４７】
【化４】

【００４８】
【化５】

【００４９】
本発明における荷電調節剤の濃度は、インクの総量に対して０．０００１〜２．０質量％の範囲であることが好ましい。荷電調節剤の濃度がこの範囲内において、色材粒子に高い比伝導度を付与する効果が有効に得られ、またインクの体積抵抗率低下による印字濃度低下も生じることもなく、好ましい。
【００５０】
本発明では、上記のアミノ酸化合物を含有することからなる荷電調節剤と組み合わせて、非水溶媒に不溶な酸性基を有する樹脂が用いられる。上記の樹脂は、荷電調節剤との組み合わせで、色材粒子に高い負極性の粒子荷電量を付与すると共に、色材と混合して分散を向上させる機能、あるいは色材の定着性を向上させる機能をも有する。
【００５１】
非水溶媒に不溶な酸性基を有する樹脂としては、種々公知の天然又は合成樹脂を用いることが出来る。例えば、アクリル樹脂、エポキシ樹脂、ポリエステル樹脂、エチレン−酢酸ビニル樹脂、塩化ビニル−酢酸ビニル樹脂、スチレン−ブタジエン樹脂、スチレン−アクリル樹脂等に、上記樹脂の原料モノマーと共重合可能な酸性基を有する酸性単量体（以下、酸性単量体（Ａ）と称することもある）を用いることにより、本発明の非水溶媒に不溶な酸性基を有する樹脂とすることができる。酸性単量体（Ａ）はカルボン酸基、スルホン酸基、スルフィン酸基、燐酸基及び亜燐酸基から選ばれる少なくとも１つの酸性基を含有する単量体であり、分子中に複数個の上記酸性基を含有してもよい。
【００５２】
好ましい樹脂としては、顔料を分散媒に不溶性の樹脂等に分散させたものに吸着し、且つ非水系溶媒中に良く分散する機能を有するために、溶媒に溶媒和する部分と溶媒に溶媒和しにくい部分及び酸性基を有する部分を持っている樹脂が好ましい。例えば、重合後に溶媒に溶媒和する部分に相当するモノマーとしては、ラウリルメタクリレート、ステアリルメタクリレート、２−エチルヘキシルメタクリレート、ブチルメタクリレート、セチルメタクリレート等が挙げられる。重合後に溶媒に溶媒和しにくい部分に相当するモノマーとしては、メチルメタクリレート、エチルメタクリレート、スチレン、ビニルトルエン等が挙げられる。酸性基を含む酸性単量体（Ａ）としては、アクリル酸、メタクリル酸、イタコン酸、フマル酸、マレイン酸、スチレンスルホン酸またはそのアルカリ塩などの酸性基モノマーが挙げられる。
【００５３】
酸性単量体（Ａ）は、重合性単量体の総量に対して、好ましくは１〜４５質量％、より好ましくは３〜３０質量％で用いる。
【００５４】
以下に、酸性単量体（Ａ）の具体例を示す。本発明はこれらに限定されるものではない（下記具体例中、Ｙは−ＣＯ_２Ｈ基、−ＳＯ_３Ｈ基、−ＳＯ_２Ｈ基、−ＰＯ_３Ｈ_２基又は−ＯＰＯ_３Ｈ_２基を表す）。
【００５５】
【化６】

【００５６】
【化７】

【００５７】
酸性基を有する樹脂により色材が被覆された色材粒子（色材樹脂粒子）は、色材をバインダー樹脂で被覆して着色混和物を形成した後、該着色混和物を非水溶媒中で微粒子状に分散することにより形成することができる。まず、色材をバインダー樹脂で被覆して着色混和物を作る工程について説明する。着色混和物は例えば以下の方法で調製する。
【００５８】
（ｉ）着色材とバインダー樹脂とを、バインダー樹脂の軟化点以上の温度でロールミル、バンバリミキサー、ニーダー等の混練機を用いて溶融混練し、冷却後に粉砕して着色混和物を得る方法。
（ｉｉ）バインダー樹脂を溶剤に溶解し、着色材を加え、ボールミル、アトライター、サンドグラインダー等で湿式分散し、溶剤を蒸発させて着色混和物を得るか、又は、分散物を該バインダー樹脂の非溶剤中に注ぎ、沈殿させて混和物を得、その後乾燥させて着色混和物を得る方法。
（ｉｉｉ）フラッシング法で、顔料の含水ペースト（ウェットケーキ）を樹脂または樹脂溶剤と共に混練し、水を樹脂又は樹脂溶液で置換した後、水及び溶剤を減圧乾燥して着色混和物を得る方法。
【００５９】
次に上記で説明した着色混和物を非水溶媒中で微粒子状に分散する分散工程について述べる。
分散工程では、微粒子状に分散し且つ非水溶媒中で分散安定化させるために顔料分散剤を使用することが好ましい。着色混和物と顔料分散剤の使用としては、例えば次のような方法があり、これらのいずれによっても目的とする効果が得られる。
【００６０】
（１）着色混和物と顔料分散剤を予め混合した顔料組成物を非水系溶媒中に添加して分散する。
（２）非水系溶媒に着色混和物と顔料分散剤を別々に添加して分散する。
（３）非水系溶媒に着色混和物と顔料分散剤を予め別々に分散し得られた分散体を混合する。この場合、顔料分散剤を溶剤のみで分散しても良い。
（４）非水系溶媒に着色混和物を分散した後、得られた顔料分散体に顔料分散剤を添加する。
【００６１】
上記の着色混和物を非水系溶媒中で混合あるいは分散する機械としては、ディゾルバー、ハイスピードミキサー、ホモミキサー、ニーダー、ボールミル、ロールミル、サンドミル、アトライター等が使用できる。この着色混和物を分散し形成された色材粒子の平均粒径の範囲は０．１〜４μｍが好ましく、より好ましくは０．３〜２μｍの範囲である。
【００６２】
本発明における基本的な構成材料は以上のような物であるが、このほかに色材と混合して分散を向上させるために顔料分散剤や界面活性剤、各種添加剤を適宜加えても良い。
【００６３】
色材を非水溶媒中で分散する顔料分散剤としては、該非水溶媒中で適用される一般の顔料分散剤が使用できる。顔料分散剤としては前記非極性の絶縁性溶媒に相溶し、安定的に顔料を微粒子分散できるものであれば良い。顔料分散剤の具体例としては、ソルビタン脂肪酸エステル（ソルビタンモノオレエート、ソルビタンモノラウレート、ソルビタンセスキオレエート、ソルビタントリオレエート等）、ポリオキシエチレンソルビタン脂肪酸エステル（ポリオキシエチレンソルビタンモノステアレート、ポリオキシエチレンソルビタンモノオレエート等）、ポリエチレングリコール脂肪酸エステル（ポリオキシエチレンモノステアレート、ポリエチレングリコールジイソステアレート等）、ポリオキシエチレンアルキルフェニルエーテル（ポリオキシエチレンノニルフェニルエーテル、ポリオキシエチレンオクチルフェニルエーテル等）、脂肪族ジエタノールアミド系などのノニオン系界面活性剤、及び高分子系分散剤としては、分子量１０００以上の高分子化合物が良く、例えば、スチレン−マレイン酸樹脂、スチレン−アクリル樹脂、ロジン、ＢＹＫ−１６０、１６２、１６４、１８２（ビックケミー社製のウレタン系高分子化合物）、ＥＦＫＡ−４７、ＬＰ−４０５０（ＥＦＫＡ社製のウレタン系分散剤）、ソルスパーズ２４０００（ゼネカ社製のポリエステル系高分子化合物）、ソルスパース１７０００（ゼネカ社の脂肪族ジエタノールアミド系）等が挙げられる。
【００６４】
高分子系顔料分散剤としては上記の他に更に、溶媒に溶媒和するラウリルメタクリレート、ステアリルメタクリレート、２−エチルヘキシルメタクリレート、セチルメタクリレート等のモノマーと、溶媒に溶媒和しにくいメチルメタクリレート、エチルメタクリレート、スチレン、ビニルトルエン等のモノマーを含有することからなるランダム共重合体、又は特開平３−１８８４６９号に記載されているグラフト共重合体が挙げられる。また、この他にはスチレン−ブタジエン共重合体、特開昭６０−１０２６３号に記載されているスチレンと長鎖アルキルメタクリレートのブロック共重合体等が挙げられる。好ましい顔料用分散剤としては、特開平３−１８８４６９号に開示されているグラフト共重合体等が挙げられる。顔料分散剤の使用量は、顔料１００質量部に対して、０．１〜３００質量部が好ましい。顔料分散剤の添加量が０．１質量部より少ないと顔料分散効果が小さく好ましくない。また、３００質量部より多く用いても用いた分の効果が得られない。
【００６５】
本発明のインク組成物には、所望により各種添加剤を加えてもよい。インクジェット方式又はインクジェット吐出ヘッド、インク供給部、インク循環部の材質・構造等によって、任意に選択されインク組成物として含有される。例えば、甘利武司監修「インクジェットプリンタ−技術と材料」第１７章、（株）シーエムシー刊（１９９８年）等に記載されている添加剤が使用される。
【００６６】
具体的には、脂肪酸類（例えば、炭素数６〜３２のモノカルボン酸、多塩基酸；例えば、２−エチルヘキシン酸、ドデセニルコハク酸、ブチルコハク酸、２−エチルカプロン酸、ラウリル酸、パルミチン酸、エライジン酸、リノレイン酸、リシノール酸、オレイン酸、ステアリン酸、エナント酸、ナフテン酸、エチレンジアミン四酢酸、アビエチン酸、デヒドロアビエチン酸、水添ロジン等）、樹脂酸、アルキルフタル酸、アルキルサリチル酸等の金属塩（金属イオンの金属としては、Ｎａ、Ｋ、Ｌｉ、Ｂ、Ａｌ、Ｔｉ、Ｃａ、Ｐｂ、Ｍｎ、Ｃｏ、Ｚｎ、Ｍｇ、Ｃｅ、Ａｇ、Ｚｒ、Ｃｕ、Ｆｅ、Ｂａ等）、界面活性化合物類（例えば、有機リン酸又はその塩類として、炭素数３〜１８のアルキル基から成るモノ、ジ又はトリアルキルリン酸等、有機スルホン酸又はその塩類として、長鎖脂肪族スルホン酸、長鎖アルキルベンゼンスルホン酸、ジアルキルスルホコハク酸等又はその金属塩、両性界面活性化合物として、レシチン、ケファリン等のリン脂質等が挙げられる）、フッ素原子及び／又はジアルキルシロキサン結合基を含有するアルキル基含有の界面活性剤類、脂肪族アルコール類（例えば、炭素数９〜２０の分岐状アルキル基から成る高級アルコール類、ベンジルアルコール、フェネチルアルコール、シクロヘキシルアルコール等）、多価アルコール類｛例えば、炭素数２〜１８のアルキレングリコール（エチレングリコール、１，２−プロピレングリコール、１，３−プロピレングリコール、１，４−ブタンジオール、ネオペンチルグリコール、１，６−ヘキサンジオール、ドデカンジオールなど）｝；炭素数４〜１０００のアルキレンエーテルグリコール（ジエチレングリコール、トリエチレングリコール、ジプロピレングリコール、ポリエチレングリコール、ポリプロピレングリコール、ポリテトラメチレンエーテルグリコールなど）；炭素数５〜１８の脂環式ジオール（１，４−シクロヘキサンジメタノール、水素添加ビスフェノールＡなど）；炭素数１２〜２３のビスフェノール類（ビスフェノールＡ、ビスフェノールＦ、ビスフェノールＳなど）の炭素数２〜１８のアルキレンオキサイド（エチレンオキサイド、プロピレンオキサイド、ブチレンオキサイド、α−オレフィンオキサイドなど）付加物、グリセリン、トリメチロールエタン、トリメチロールプロパン、ペンタエリスリトール、ソルビトール等のポリオール類；３価〜８価またはそれ以上のフェノール類（トリスフェノールＰＡ、フェノールノボラック、クレゾールノボラックなど）；上記３価以上のポリフェノール類の炭素数２〜１８のアルキレンオキサイド付加物（付加モル数は２〜２０）、上記多価アルコールのエーテル誘導体（ポリグリコールアルキルエーテル類、アルキルアリールポリグリコールエーテル等）、多価アルコールの脂肪酸エステル誘導体、多価アルコールのエーテルオレート誘導体（例えば、エチレングリコールモノエチルアセテート、ジエチレングリコールモノブチルアセテート、プロピレングリコールモノブチルプロピオレート、ソルビタンモノメチルジオキサルト等）、アルキルナフタレンスルホネート、アルキルアリールスルホネート等の化合物が挙げられるが、これらに限定されるものではない。各種添加剤の使用量は、インク組成物の表面張力が１５〜６０ｍＮ／ｍ（２５℃において）及び粘度が１．０〜４０ｃＰの範囲となるように調整して用いることが好ましい。
【００６７】
次に、インクの作製方法について説明する。インクの作製には、各種顔料インクの作製方法として公知である一般的な手法を用いることが出来る。例えば、所定の配合比になるように秤量した色材、樹脂、本発明の特徴である荷電調節剤、その他の補助添加剤を適当な粘度範囲になるように分散媒と混合した物を、ビーズミル、アトライター、ボールミル等の分散機を用いて、数時間から数十時間程度混合粉砕する事により、数十ｎｍ〜数μｍ程度の色材が分散されたインクの濃縮液を作製した後、使用する際の所定濃度まで分散倍で希釈し、インク組成物の表面張力が１５〜６０ｍＮ／ｍ及び粘度が１．０〜４０ｃＰのインクを作製する方法がある。また、色材、樹脂、補助添加剤を混合して、樹脂の軟化点以上の温度でロールミル、バンバリミキサー、ニーダー等の混練機を用いて溶融混練し、冷却後に粉砕した後に、上記と同様に分散し、希釈した後に、本発明の特徴である荷電調節剤を加える方法もある。いずれの方法を用いても同様の効果が得られる。
インク組成物中の、樹脂で被覆された色材粒子の平均粒径は、吐出性能と色材粒子の沈降防止との兼ね合いから、０．１〜４μｍ程度が好ましく、更に好ましくは０．３〜２μｍの範囲である。
【００６８】
以下、本発明の荷電調節剤を用いたインク組成物が静電型インクジェット記録装置用のインクとして有用な事を示す。静電型インクジェットプリンタとしては、色材粒子を用いたインクを使用するものであれば、特に方式に限定されずに適用できる。好ましい例としては、色材濃縮吐出型の静電インクジェットプリンタが挙げられる。
【００６９】
色材濃縮吐出型の静電インクジェットプリンタについて更に説明する。図１及び図２は吐出ヘッドの例を説明する概略図で、図１はライン走査型マルチチャンネルインクジェットヘッドの構成を示す図で、記録ドットに対応した吐出電極の断面を示している。同図においてインク１００はポンプを含む循環機構１１１から、ヘッドブロック１０１に接続されたインク供給流路１１２を通して、ヘッド基板１０２と吐出電極基板１０３間に供給され、同じくヘッドブロック１０１に形成されたインク回収流路１１３を通してインク循環機構１１１に回収される。この吐出電極基板１０３は、貫通孔１０７を有する絶縁性基板１０４と、この貫通孔１０７の周囲で記録媒体側に形成されている吐出電極１０９とから構成されている。一方ヘッド基板１０２上には凸状インクガイド１０８が前記貫通孔１０７の略中心位置に配置されている。この凸状インクガイド１０８はプラスチック樹脂、セラミックスなど絶縁性部材からなり、前記貫通孔１０７と中心が等しくなるように同じ列間隔、ピッチで配置され、所定の方法でヘッド基板１０２上に保持されている。各凸状インクガイド１０８は厚みが一定の平板の先端を三角形あるいは台形状に切り出した形状で、その先端部がインク滴飛翔位置１１０となる。各凸状インクガイド１０８はその先端部からスリット状の溝を形成しても良く、そのスリットの毛細管現象により、インク飛翔位置１１０へのインク供給がスムースに行われ、記録周波数を向上することが出来る。またインクガイドの任意の表面は必要に応じて導電性を有していても良く、その場合には導電部分は電気的に浮遊状態とする事によって、吐出電極への少ない電圧印加で有効にインク飛翔位置に電界を形成できる。各凸状インクガイド１０８は、それぞれの貫通孔からほぼ垂直に所定の距離だけインク滴飛翔方向に突きだしている。凸状インクガイド１０８の先端に対向して記録紙である記録媒体１２１が配置され、この記録媒体１２１のヘッド基板１０２と反対側の背面に、記録媒体１２１を案内するプラテンの役割を兼ねる対向電極１２２が配置されている。また、ヘッド基板１０２と吐出電極基板１０３間によって形成される空間の底部には泳動電極１４０が形成されており、これに所定の電圧を印加する事により、インクガイドの吐出位置方向にインク中の荷電粒子を電気泳動させ、吐出の応答性を上げることが出来る。
【００７０】
吐出電極基板１０３の具体的構成例について図２を用いて説明する。図２は、吐出電極基板１０３を記録媒体１２１側から見た図で、複数個の吐出電極が主走査方向に二列でアレイ状に配列されて、各吐出電極の中心に貫通孔１０７が形成され、この貫通孔１０７の周辺にはそれぞれ個別の吐出電極１０９が形成されている。本実施例では吐出電極１０９の内径は貫通孔１０７の径より一回り大きく設けられているが、貫通孔１０７の径と同径でも良い。ここでは、絶縁性基板１０４は２５から２００μｍ程度の厚さのポリイミドからなり、吐出電極１０９は１０から１００μｍ程度の厚さの銅箔からなり、貫通孔１０７の内径は１５０から２５０μｍΦ程度である。
【００７１】
次に、静電方式のインクジェット記録装置の記録動作を説明する。ここでは負荷電した色材を含むインクを用いた場合を例にとって説明するが、本発明は本例に限定される物ではない。記録時には、インク循環機構１１１からインク供給流路１１２を経て供給されたインク１００は貫通孔１０７から凸状インクガイド１０８の先端のインク飛翔位置１１０に供給されると共に、一部はインク回収流路１１３を経てインク循環機構１１１に回収される。ここで、吐出電極１０９にはバイアス電圧源１２３から常時バイアスとして例えば−１．５ｋＶの電圧が与えられ、これに信号電圧源１２４からの画像信号に応じた信号電圧として例えばＯＮ時に−５００Ｖのパルス電圧が吐出電圧１０９に重畳される。またこの際、泳動電極１４０は−１．８ｋＶの電圧が印加されている。一方、記録媒体１２１の背面に設けられた対向電極１２２は、図のように接地電圧０Ｖに設定されている。場合によっては記録媒体１２１側を例えば−１．５ｋＶに帯電させてバイアス電圧としても良い。この場合には、対向電極１２２表面に絶縁層を設け、記録媒体にコロナチャージャー、スコロトロンチャージャー、固体イオン発生器等により帯電を行い、かつ吐出電極１０９は例えば接地され、これに信号電圧源１２４からの画像信号に応じた信号電圧として例えばＯＮ時に−５００Ｖのパルス電圧が吐出電圧１０９に重畳される。またこの際、泳動電極１４０は−２００Ｖの電圧が印加される。今、吐出電圧１０９がＯＮ状態（−５００Ｖが印加された状態）となり、バイアスＤＣ−１．５ｋＶに−５００Ｖのパルス電圧が重畳された合計−２ｋＶの電圧が加わると、凸状電極１０８先端のインク滴飛翔位置１１０から、インク滴１１５が飛び出し、対向電極１２２方向に引っ張られて、該記録媒体１２１に向けて飛翔して画像を形成する。なお、飛翔後のインク液滴の飛翔を精密制御し記録媒体上での着弾精度を向上するため、吐出電極と記録媒体間に中間電極を設ける、あるいは吐出電極間に電界干渉抑制用のガード電極を設ける、等の手段がしばしば講じられるが、本実施例においても必要により好適に使用されることはもちろんである。また、ヘッド基２８板１０２と吐出電極基板１０３間に多孔質体を設けても良く、この場合にはインクジェットヘッドの移動等によるインク内圧の変化の影響を防止できると共にインク滴吐出後の貫通孔１０７部へのインク液供給が迅速に達成される。したがって、インク滴１１５の飛翔が安定化され、記録媒体１２１上に濃度の安定した良好な画像を高速に記録することができる。
【００７２】
【実施例】
以下に本発明の実施例を例示するが、本発明はこれらに限定されるものではない。
【００７３】
合成例１（例示化合物（１）の合成）
ｎ−オクチルアミン（５１６ｇ，４．０モル）、ハイドロキノン（２００ｍｇ）およびメタノール（４００ｍｌ）の混合物へ氷冷下攪拌しながらアクリル酸（１４４ｇ，２．０モル）を滴下した。滴下終了後４時間加熱還流し室温へもどした後、ＮａＯＨ（８０ｇ，２．０モル）を加え中和した。
反応混合物をアセトン６Ｌへ分散させ口過、乾燥を行うことによりＮ−ｎ−オクチルーβ−アラニンＮａ塩を融点２４２℃の白色結晶として得た（３４９ｇ，収率７８％）。
次にこのＮａ塩（２２３ｇ，１．０モル）を水２Ｌへ溶解させ、氷冷下攪拌しながら塩化ミリストイル（２４６．５ｇ，１．０モル）とＮａＯＨ水溶液（ＮａＯＨ５０ｇ，水５００ｍｌ）を同時滴下した。滴下終了後１時間攪拌を続けた後濃塩酸（１２０ｍｌ）を加え晶出する結晶を口取乾燥させた。Ｎ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニンを溶融４７℃の白色結晶として得た（３４８ｇ，収率８５％）。この結晶はアセトンより再結晶することにより融点５８〜５９℃の純品とすることができた。元素分析値Ｃ：７２．７９％，Ｈ：１２．０２％，Ｎ：３．３４％（Ｃ_２５Ｈ_４９Ｎ_１Ｏ_３としての計算値Ｃ：７２．９４％，Ｈ：１２．００％，Ｎ：３．４％）。
【００７４】
Ｎ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニン（２０６ｇ，０．５モル）をＮａＯＨ（２１．１ｇ，０．５モル）の水溶液２リットル中へ溶解させた。ＮｉＣｌ_２・６Ｈ_２Ｏ （５９．４，０．２５モル）を水（２００ｍｌ）に溶解させたものを攪拌しながら添加し、１時間攪拌を続けた後クロロホルム（１リットル）にて抽出した。有機層をＮａ_２ＳＯ_４で乾燥した後溶媒を留去し、例示化合物（１）を緑色の粘調なオイルとして得た。このオイルは放置により固体化した（１９６ｇ，収率８９％，融点６８〜７０℃）。
【００７５】
合成例２（例示化合物（２）の合成）
合成例１においてＮｉＣｌ_２・６Ｈ_２Ｏの代わりにＣｏＣｌ_２・６Ｈ_２Ｏを用いてＮ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニンのＣｏ塩を赤紫色の粘調なオイルとして得た（収率９１％）。
【００７６】
合成例３（例示化合物（３）の合成）
Ｎ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニン（４．１１，０．０１モル）をクロロホルム１００ｍｌに溶解し、四塩化チタンのクロロホルム溶液（１．９０ｇ，０．０１モル，クロロホルム５０ｍｌ）を加えた。室温で攪拌しながらトリエチルアミン（４．０４ｇ，０．０４モル）を滴下し、終了後加熱還流下に１時間攪拌を続けた。冷却後ｎ−ヘキサン６００ｍｌを加え、析出するトリエチルアミン塩酸塩を口過で除いたのち口液を濃縮し、粘調なオイルを得た。これをｎ−ヘキサン１００ｍｌに溶解したのち、水洗をくり返し、分液した有機層をＮａ_２ＳＯ_４で乾燥したのち溶媒を留去し例示化合物（３）を含む混合物を淡黄色の粘調なオイルとして得た（３．５ｇ）。
【００７７】
合成例４（例示化合物（４）の合成）
合成例３において四塩化チタンのかわりに四塩化ジルコニウムを用い、例示化合物（４）を含む混合物を淡黄色の粘調なオイルとして得た。
【００７８】
合成例５（例示化合物（５）の合成）
Ｎ−ステアロイル−Ｎ−ｎ−ドデシル−β−アラニン（５．２３ｇ，０．０１モル）を水１リットルへ分散させた後ＮａＯＨ（０．４２ｇ，０．０１モル）を加え、加熱攪拌して溶解させた。ＮｉＣｌ_２・６Ｈ_２Ｏ （１．１９ｇ，０．００５モル）を水１００ｍｌに溶解させたものを攪拌しながら添加し、生成する結晶を口取し、水洗した後乾燥した。例示化合物（５）を融点６℃の緑白色結晶として得た（４．８２ｇ、収率８８％）。
【００７９】
合成例６（例示化合物（６）の合成）
合成例５においてＮ−ステアロイル−Ｎ−ｎードデシル−β−アラニンのかわりにＮ−ステアロイル−Ｎ−ｎ−ブチル−β−アラニンを、ＮｉＣｌ_２・６Ｈ_２ＯのかわりにＣｏＣｌ_２・６Ｈ_２Ｏを用いて例示化合物（６）を融点５３−５４℃の赤紫色の結晶として得た。
【００８０】
合成例７（例示化合物（８）の合成）
Ｎ−ステアロイル−Ｎ−フエニル−β−アラニンを用い、上記合成例６と同様の操作を行うことにより例示化合物（８）を融点６７℃の赤紫色の結晶として得た。
【００８１】
合成例８（例示化合物（１２）の合成）
ジ−ｎ−オクチルアミン（２４１ｇ，１．０モル）、トリエチルアミン（１０１ｇ，１．０モル）、メタノール（２００ｍｌ）およびハイドロキノン（１００ｍｇ）の混合液に水冷下攪拌しながらアクリル酸（７２ｇ，１．０モル）を滴下した。終了後加熱還流しながら４時間攪拌を続けた。一夜室温に放置したのちＮａＯＨの水溶液（４３ｇ，５０ｍｌ）を加え、アセトン３Ｌ中へ内容物を注ぎ生成する白色沈澱を口取、乾燥した（１８９．３ｇ，収率５７％）。つぎにこの粗生成物３３．５ｇ（１モル）を水１Ｌに溶解させ、ＮｉＣｌ_２・６Ｈ_２Ｏ （１１．９ｇ，０．０５モル）の水溶液（５０ｍｌ）を添加した。生成する油状物質の分散物をクロロホルム（３００ｍｌ）で抽出し、Ｎａ_２ＳＯ_４で乾燥した後溶媒を留去して例示化合物（１２）を緑色の粘調なオイルとして得た（８．３ｇ，収率２４％）。
【００８２】
合成例９ （例示化合物（１５）の合成）
Ｎ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニン（４．１１ｇ，０．０１モル）をＫＯＨ（０．６６ｇ，含量８５％）のメタノール（１００ｍｌ）溶液へ溶解させ、臭化セチルトリメチルアンモニウム（３．６４ｇ、０．０１モル）を添加した。室温で３０分間攪拌したのち、水（１００ｍｌ）とｎ−ヘキサン（１００ｍｌ）を加え抽出した。有機層をＮａ_２ＳＯ_４で乾燥した後溶媒を留去し例示化合物（１５）をワックス状の固体として得た（５．３２ｇ，収率７７％）。
【００８３】
合成例１０（例示化合物（１６）の合成）
Ｎ−ラウロイルザルコシンＮａ塩（１５．５ｇ，０．０５モル）を水（２００ｍｌ）に溶解させた。ＣｏＣｌ_２・６Ｈ_２Ｏ（５．９５ｇ，０．０２５モル）を水（１００ｍｌ）に溶解させたものを攪拌しながら添加し、１時間攪拌を続けた後生成する結晶を口取、水洗後乾燥した。融点１０５〜１１０℃の結晶が１４．６５ｇ得られた（収率９８％）。
【００８４】
合成例１１（例示化合物（１７）の合成）
Ｎ−フェニルグリシン（１５．１ｇ，０．１モル）をＮａＯＨ水溶液（ＮａＯＨ５．９５ｇ，水１００ｍｌ）へ溶解させ、氷冷下攬拌しながら塩化ステアロイル（１５．１ｇ，０．１モル）とＮａＯＨ水溶液（ＮａＯＨ５．０ｇ，水５０ｍｌ）を同時滴下した。１時間攪拌を続けた後塩酸で中和し、析出する結晶を口取乾燥させた（１０．４ｇ，収率２５％）。つぎにこの結晶を用い合成例６と同様の操作を行うことにより例示化合物（１７）を融点６４〜６５℃の赤紫色結晶として得た。
【００８５】
合成例１２
Ｎ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニン（４．１１ｇ，０．０１モル）をイソプロピルアルコール５０ｍｌに分散させ、室温で攪拌しながらチタンテトライソプロポキシド（２．８４ｇ，０．０１モル）を滴下した。滴下終了後１時間加熱還流し、室温にもどした後ｎ−ヘキサン５０ｍｌを加え、全体を水１００ｍｌ中へ加えた。分離した有機層を水５０ｍｌと飽和食塩水５０ｍｌで洗浄した後、有機層をＮａ_２ＳＯ_４で乾燥し、溶媒を留去して淡黄色の粘調オイルを得た（収量３．７９ｇ）。このオイルは放置によりワックス状に固体化し、次に示す物性値を示した。元素分析値Ｃ：６０．８２％，Ｈ：１０．３７％，Ｎ：２．５０％，残存灰分：１５．６％，赤外吸収スペクトル（ＫＢｒ）：カルボニル基の伸縮振動数ν_Ｃ＝０＝１７３０、１６４０（ショルダー）、１６０２、１５６０ｃｍ^−１ 。
この固体を反応混合物（１）とする。元素分析値より推定する反応混合物（１）には下記の様な構造が考えられるが、赤外吸収スペクトルよりこれはＮ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニンとそのＴｉ塩とのほぼ１：１の混合物であることがわかった。
【００８６】
【化８】

【００８７】
反応混合物（１）はアセトン中に分散させ、洗浄をくり返すことにより遊離の酸を含まない粉末（反応混合物−２）とすることができる（この場合洗液よりＮ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニンが回収される）。反応混合物（２）は次に示す物性値を示した。
【００８８】
融点２１７〜２１９℃、元素分析値Ｃ：５１．８３％，Ｈ：８．５８％，Ｎ：１．９１％，残存灰分：２７．０％，赤外吸収スペクトル（ＫＢｒ）：カルボニル基の伸縮振動数ν_Ｃ＝０＝１６４０、１５６０ｃｍ^−１ 。これらの値より反応混合物（２）は約２当量のＴｉを含むＮ−ミリストイル−Ｎ−ｎ−オクチル−β−アラニンのＴｉ塩であると推定できる。
【００８９】
実施例１：インク組成物（ＩＪ−１）
青色顔料としてリノールブルーＦＧ−７３５０（Ｐｉｇｍｅｎｔ Ｂｌｕｅ１５：３東洋インキ社製）１００質量部、樹脂としてスチレン／ビニルトルエン／ラウリルメタクリレート／（２−メタクリルアミド−２，２−ジメチル）エタンスルホン酸リチウム塩共重合体（４８／４８／１／３モル比）２００質量部をトリオブレンダーで予備粉砕しよく混合した後に、１００℃に加熱した卓上型ニーダーＰＢＶ（入江商会社製）で溶融混練（１２０分）した。上記の顔料混練物をピンミルで粉砕した。次に顔料混練物２０質量部、アイソパーＧ１３０質量部、下記構造の顔料分散剤（Ｄ−１）をアイソパーＧに加熱溶解して調液した２０ｗｔ％溶液を５０質量部及び３Ｇ−Ｘガラスビーズ４００質量部とともにペイントシェイカー（東洋精機ＫＫ）で１２０分間混合した。分散液中の顔料樹脂粒子の体積平均粒径を、超遠心式自動粒度分布測定装置ＣＡＰＡ７００（堀場製作所）にて測定した所、０．４１μｍであった。
【００９０】
【化９】

【００９１】
ガラスビーズをろ過により除去した上記顔料樹脂粒子分散液を、アイソパーＧで顔料樹脂粒子成分が３．０％になる様に希釈した。次いで荷電調節剤として、上記例示化合物（１）を０．０１ｗｔ％になる様に添加してインク組成物（ＩＪ−１）を調液した。得られたインク組成物の粘度は１．４ｃＰ（Ｅ型粘度計、温度２５℃で測定）、表面張力は２３ｍＮ／ｍ（協和界面科学社製の自動表面張力計、温度２５℃で測定）であった。また、インク組成物の荷電量は、ＬＣＲメーター（安藤電気（株）社製ＡＧ−４３１１）及び液体用電極（川口電機製作所（株）社製ＬＰ−０５型）を使用し、印加電圧５Ｖ、周波数ｌｋＨｚの条件で測定した比電導度より求めた。顔料樹脂粒子の粒子電導度は、インク組成物の全体の比電導度から、インク組成物を遠心分離器にかけた上澄みの比電導度を差し引いて求めた。また遠心分離は、小型高速冷却遠心機（トミー精工（株）社製ＳＲＸ−２０１）を使用し、回転速度１４５００ｒｐｍ、温度２３°Ｃの条件で３０分間行った。インク組成物（ＩＪ−１）は全体の比電導度が５５１ｐＳ／ｃｍを示し、また明瞭な負荷電性を示した青色樹脂粒子は、その粒子電導度が４９６ｐＳ／ｃｍを示しインク組成物の荷電量の九割以上が顔料樹脂粒子についていた。また、４５℃、一週間強制経時後のインク組成物の全体比電導度及び顔料樹脂粒子の粒子電導度はそれぞれ５２８ｐＳ／ｃｍ、４８３ｐＳ／ｃｍを示し、荷電量変化が殆ど無く極めて安定している事が判った。
【００９２】
インクジェット装置として、図１に示すヘッド構造の１００ｄｐｉ ６４チャンネルの静電式インクジェツトヘッドを使用し、インク組成物（ＩＪ−１）をインクタンクに充填した。エアーポンプ吸引により記録媒体であるコート記録紙表面の埃除去を行った後、吐出ヘッドを描画位置までコート記録紙に近づけ、描画解像度６００ｄｐｉでインクを吐出し描画した。この際、パルス電圧を調節してドット径１５μｍから６０μｍの範囲で１６段階でドット面積を変化させながら描画した。描画画像は滲みのない均一なドットで安定に印字されていて、満足し得る濃度の良質の明瞭な画像を与えた。インクヘッドからの吐出安定性も良好で、詰まりを生じる事が無く、長期間の連続画像描画でも安定したドット形状の印字ができた。
更に、４５℃、一週間の強制経時後のインク組成物を用いて同様に描画したところ、描画画像は滲みのない均一なドットで満足し得る濃度の良質の明瞭な画像を与え、また吐出安定性も良好で、長期間の連続画像描画でも安定したドット形状の印字ができた。
【００９３】
比較例１〜３：比較用インク組成物（ＩＪＲ−１）〜（ＩＪＲ−３）
実施例１において、酸性基を有する樹脂の代わりに、酸性基を有しない樹脂としてスチレン／ビニルトルエン／ラウリルメタクリレート共重合体（４９．５／４９．５／１モル比）を用いた他は、荷電調節剤として例示化合物（１）を用いる等、実施例１と全く同様にして比較用インク組成物（ＩＪＲ−１）を調液した（比較例１）。
【００９４】
また、実施例１において、顔料樹脂粒子分散液をアイソパーＧで顔料樹脂粒子成分が３．０％になる様に希釈し、荷電調節剤として例示化合物（１）の代わりに、金属石鹸のナフテン酸ジルコニウム（日本化学産業（株）製）を金属含量が０．０１ｗｔ％になる様に添加した他は、実施例１と全く同様にして比較用インク組成物（ＩＪＲ−２）を調液した（比較例２）。更に、同様に、例示化合物（１）の代わりに大豆レシチンを０．０１ｗｔ％になる様に添加した他は、実施例１と全く同様にして比較用インク組成物（ＩＪＲ−３）を調液した（比較例３）。
【００９５】
比較用インク組成物（ＩＪＲ−１）〜（ＩＪＲ−３）の粘度はいずれも１．４ｃＰ、表面張力も２３ｍＮ／ｍであった。比較用インク組成物（ＩＪＲ−１）の全体の比電導度は１４３ｐＳ／ｃｍを示し、青色樹脂粒子の粒子電導度は１１３ｐＳ／ｃｍと低く、且つ、くし型電極による荷電極性は正と負が混在したものであった。このため次の静電式インクジェツト描画テストに使用することができなかった。
【００９６】
比較用インク組成物（ＩＪＲ−２）の全体の比電導度は２４３ｐＳ／ｃｍを示したが、青色樹脂粒子の粒子電導度は２０４ｐＳ／ｃｍと低く、くし型電極による荷電極性が正と負が混在したものであったため、比較用インク組成物（ＩＪＲ−２）も次の静電式インクジェツト描画テストに使用することができなかった。
【００９７】
比較用インク組成物（ＩＪＲ−３）の全体の比電導度は２４７ｐＳ／ｃｍ、青色樹脂粒子の粒子電導度は２２２ｐＳ／ｃｍを示し、くし型電極による荷電極性は負極性であった。４５℃、一週間強制経時後の比較用インク組成物（ＩＪＲ−３）の全体比電導度はそれぞれ１１９ｐＳ／ｃｍ、を示し、青色樹脂粒子の粒子電導度は１０１ｐＳ／ｃｍと初期の荷電量に比べ五割以下に低下し荷電量変化が大きい事が判った。 次に、比較用インク組成物（ＩＪＲ−３）を用いて実施例１と同様に静電式インクジェット描画した所、初期の描画画像は滲みがある低濃度の画像を与えた。４５℃、一週間の強制経時後の比較用インク組成物（ＩＪＲ−３）を用いて同様に描画したところ、吐出不良が発生したために、画像欠落が見られ満足する画像が得られなかった。
【００９８】
実施例１および比較例１〜３の結果より、本発明の如く、非水溶媒に不溶な酸性基を有する樹脂と、且つ、アミノ酸化合物を含有することからなる本発明の荷電調節剤の組み合わせからなるインクにより、色材粒子に高い粒子電導度を付与でき、また、荷電量の経時変化がなく安定しているために静電式インクジェツト描画に良好に使用できることが判る。
【００９９】
実施例２〜１１：インク組成物（ＩＪ−２）〜（ＩＪ−１１）
実施例１において、顔料樹脂粒子分散液をアイソパーＧで顔料樹脂粒子成分が３．０％になる様に希釈し、かつ、荷電調節剤として例示化合物（１）の代わりに、表１記載の各化合物を用いた他は、実施例１と全く同様にしてインク組成物（ＩＪ−２）〜（ＩＪ−１１）を調液した。
インク組成物（ＩＪ−２）〜（ＩＪ−１１）の青色樹脂粒子の粒子電導度及びその印字評価を表１に示す。また、４５℃、一週間強制経時後のインク組成物（ＩＪ−２）〜（ＩＪ−１１）の青色樹脂粒子それぞれの粒子電導度と印字評価を表１に示す。
【０１００】
【表１】

【０１０１】
〔印字評価〕
○ 描画画像が滲みのない満足し得る濃度、連続して安定に印字。
× 描画画像に滲みがあるか、低濃度か、連続して安定に印字できない場合。
【０１０２】
実施例１２：インク組成物（ＩＪ−１２）
黒色顔料としてカーボンブラック＃４０（三菱化学社製）１００質量部および酸性基を有する樹脂としてメチルメタクリレート／ブチルメタクリレート／（２−メタクリルアミド−２，２−ジメチル）エタンスルホン酸リチウム塩共重合体（７０／２０／１０モル比）２００質量部をトリオブレンダーで予備粉砕しよく混合した後に、１４０℃に加熱した三本ロールミルで溶融混練（２０分）した。上記の顔料混練物を実施例１と同様にしてペイントシェイカー（東洋精機ＫＫ）で１２０分間分散した所、分散液中の顔料樹脂粒子の体積平均粒径は０．４４μｍであった。この混練物をアイソパーＧで顔料樹脂粒子成分が４．０％になる様に希釈し、荷電調節剤の例示化合物（１２）の反応物を０．００１ｗｔ％添加した他は、実施例１と全く同様にしてインク組成物（ＩＪ−１２）を調液した。
得られたインク組成物（ＩＪ−１２）の粘度は１．４ｃＰ、表面張力は２３ｍＮ／ｃｍ、全体の粒子伝導度は８２３ｐＳ／ｃｍで、黒色樹脂粒子の粒子電導度が７８１ｐＳ／ｃｍであった。インク組成物の荷電量の九割以上が顔料樹脂粒子についていて且つ明瞭な負荷電性を示した。
４５℃、一週間強制経時後のインク組成物の比電導度及び顔料樹脂粒子の粒子電導度はそれぞれ７９９ｐＳ／ｃｍ、７５７ｐＳ／ｃｍであり、荷電量の変化が殆ど無く極めて安定している事が判った。
インク組成物（ＩＪＲ−１２）を用いて実施例１と同様に静電式インクジェツト描画した所、描画画像は滲みのない均一なドットで満足し得る濃度の良質の明瞭な画像を与え、また吐出安定性も良好で、長期間の連続画像描画でも安定したドット形状の印字ができた。また、４５℃、一週間強制経時後の描画画像もサーモ強制経時前と同様に、滲みのない満足し得る濃度の良質の明瞭な画像を与えた。
【０１０３】
比較例４：比較用インク組成物（ＩＪＲ−４）
実施例１２において、酸性基を有する樹脂の代わりに、酸性基を有しない樹脂として、メチルメタクリレート／ブチルメタクリレート共重合体（７０／３０モル比）を用い、荷電調節剤の例示化合物（１２）の反応物を０．０５ｇ／リットル添加した他は、実施例１２と全く同様にして比較用インク組成物（ＩＪＲ−４）を調液した。比較用インク組成物（ＩＪＲ−４）の粘度は１．４ｃＰ、表面張力は２３ｄｙｎｅ／ｃｍであった。比較用インク組成物（ＩＪＲ−４）の全体の比電導度は２３５ｐＳ／ｃｍ、黒色樹脂粒子の粒子電導度は１６６ｐＳ／ｃｍを示し、くし型電極による荷電極性は負極性であった。４５℃、一週間強制経時後の比較用インク組成物（ＩＪＲ−４）の全体比電導度はそれぞれ２１６ｐＳ／ｃｍを示し、青色樹脂粒子の粒子電導度は１５３ｐＳ／ｃｍと荷電量変化は小さかった。
【０１０４】
次に、比較用インク組成物（ＩＪＲ−４）を用いて実施例１と同様に静電式インクジェット描画した所、初期及び強制経時後の描画画像は滲みがあり画像濃度も低い事が判った。また長期間の連続画像描画では吐出不良が発生したために、画像欠落が見られ満足する画像が得られなかった。
実施例１２と特公平５−２９９０４号記載の実施例８に基づいた比較例４の結果より、本発明の非水溶媒に不溶な酸性基を有する樹脂と、且つ、アミノ酸化合物を含有することからなる本発明の荷電調節剤の組み合わせからなるインクによってのみ、色材粒子に高い粒子電導度を付与でき、荷電量の経時変化がなく安定しているために長期間の静電式インクジェット描画に良好に使用できることが判る。これらの特異的効果は特公平５−２９９０４号の記載からは予測できるものではない。
【０１０５】
【発明の効果】
非水溶媒中で、非水溶媒に不溶な色材と、非水溶媒に不溶な酸性基を有する樹脂と、非水溶媒に可溶な特定構造のアミノ酸化合物の金属塩を含有することからなる荷電調節剤を主成分とする本発明の静電型インクジェットインク組成物により、色材濃縮吐出型の静電インクジェットヘッドにおいて、分散安定性、荷電極性の制御や荷電の経時安定性に優れる静電方式インクジェットプリンタ用油性インク組成物を提供できる。また、高濃度で滲みの少ないドットを高速で安定に印字することができる静電方式インクジェットプリンタ用油性インク組成物を提供できる。
【図面の簡単な説明】
【図１】ライン走査型マルチチャンネルインクジェツトヘッドの構成例を示し、記録ドットに対応した 吐出電極の断面を示す図である。
【図２】吐出電極を記録媒体側から見た図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oil-based ink for use in an electrostatic ink jet recording apparatus that ejects ink and forms characters and images on a transfer medium such as recording paper. Particularly, the oil-based ink has long-term charge aging stability. It is about.
[0002]
[Prior art]
The ink jet recording method that performs printing by flying ink onto a recording medium to form recording dots is attracting interest as a non-impact recording method that can be easily colored and recorded directly on plain paper. Printers using this method Have been put to practical use. Inkjet recording methods include, for example, Takeshi Aoiin “Real Color Hard Copy” Sangyo Tosho Co., Ltd. (1993), Shin Ohno “Non-impact Printing—Technology and Materials”, CMC (1986), Takeshi Amari. It is described in a book such as “inkjet printer technology and material” CMC Co., Ltd. (1998), and there are on-demand (optional injection) and continuous (continuous injection) systems. Further, there are known recording methods such as an electrostatic method (Sweet type, Hertz type) for the continuous type and a piezoelectric method, a shear mode piezoelectric method, and a thermal ink jet method for the on-demand type. As one of the on-demand ink jet recording methods, Susumu Ichinose, Yuji Ohba, IEICE Transactions Vol. J66-C (No. 1), p. 47 (1983), Tadayoshi Ohno, Mamoru Mizuguchi, Journal of the Institute of Image Electronics Engineers of Japan, Vol. 10, (No. 3), p. 157 (1981) or the like, a method called electrostatic acceleration type inkjet or slit jet is known.
[0003]
In this method, a voltage is applied to a plurality of recording electrodes arranged opposite to the recording medium and a counter electrode arranged on the back surface of the recording medium, and is supplied onto the recording electrodes due to a potential difference generated between both electrodes. A specific mode is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 56-170) and the like. In this method, instead of the nozzles in the conventional inkjet head, an elongated slit-like ink discharge port having a large number of recording electrodes on the inner wall is used, and ink is supplied to the slit-like ink chamber, and these electrodes are selected. In particular, by applying a high voltage, recording is performed by ejecting ink in the vicinity of the electrode onto a recording sheet that is in close proximity to the slit.
For this reason, there is less concern about ink clogging, and a simple construction of the head can be expected to reduce the manufacturing cost, and a so-called long line head having a length that can cover a wide range in the width direction of the recording medium. This is also an effective way to achieve this.
[0004]
An example of a drop-on-demand type full-color recording head configured by the electrostatic acceleration type ink jet method is disclosed in, for example, Patent Document 2 (Japanese Patent Laid-Open No. 58-215253), Non-Patent Document 1 (Papers of the Institute of Electrical Communication) Vol. J68-C, 2 (1985), pages 93 to 100).
In this electrostatic acceleration type inkjet head, an oil-based ink in which a dye is dissolved in an organic solvent is preferably used, and the constituent material of the ink is not described in detail, but in the example shown in the above Non-Patent Document 1, Volume resistivity (electrical resistivity) is 10 ⁷ -10 ⁸ An ink having physical properties of Ω · cm, surface tension of 22 mN / m, and viscosity of 3.1 to 6.9 cP is used.
However, such oil-based ink has a surface tension lower than that of water-based ink generally used in other in-jet methods, and therefore has a very high permeability to recording paper. In particular, printing is performed on plain paper. In some cases, there has been a problem that print density is reduced, blurred, or show-through easily occurs.
[0005]
On the other hand, a color material concentration discharge type electrostatic system that does not use a slit-shaped recording head is disclosed in Japanese Patent Laid-Open Nos. 9-193389 (Patent Document 3) and 10-138493 (Patent Document 4). This is a control comprising a plurality of individual electrodes for applying an electrostatic force to a colorant component in ink, and an insulating substrate having a through hole and a control electrode formed corresponding to the through hole. It consists of an electrode substrate and a convex ink guide arranged almost at the center of this through hole. The surface of this convex ink guide is transported to the ink droplet flying position by surface tension, and a predetermined voltage is applied to the control electrode. Is applied to cause ink droplets to fly on the recording medium for recording.
[0006]
In this color material concentration discharge type electrostatic ink jet system, color material particles are concentrated on the discharge port portion by electrophoresis, and ink droplets are ejected in a form in which the color material is concentrated at a high concentration. For this reason, unlike the above-described method, the ink components are not discharged while containing a large amount of liquid components in a uniform state, but instead of being discharged in a state where the color material is aggregated and the liquid components are small. The above-mentioned problems are solved. Further, by using a pigment as a coloring material, advantageous results can be obtained in terms of water resistance and light resistance of a printed image as compared with an ink jet head using a conventional dye.
[0007]
In such a color material concentration discharge type electrostatic inkjet ink, first, in order to obtain good print characteristics with high print density and no blurring or show-through, the volume resistivity of the ink is sufficiently high. Things are necessary. As a result, an electric field formed by the recording electrode and the counter electrode and applied to the ink can reach the colorant particles. Also, if the volume resistivity of the ink is low, the ink is charged and charged by the voltage applied by the recording electrode, and the ink is discharged while containing a large amount of liquid component due to electrostatic repulsion. The tendency becomes stronger. Next, since it is necessary to concentrate the color material particles at the discharge port portion by electrophoresis at a sufficient speed, it is necessary that the color material particles have a sufficient charge amount, that is, the color material particles have a positive polarity or a negative polarity. It is necessary to have a high particle conductivity. Furthermore, the average particle diameter of the color material particles is preferably about 0.1 to 4 μm in consideration of the discharge performance and the prevention of sedimentation of the color material particles.
[0008]
Specifically, for example, Patent Document 3 discloses an electrical resistivity of 10 ¹⁰ In a dielectric liquid of Ω · cm or more, developer particles having a zeta potential of 60 mV or more with respect to the dielectric liquid and an average particle diameter in the range of 0.01 to 5 μm (a solid having at least a colorant component) 10) by dispersing resin particles). ⁸ The use of inks adjusted to have an electrical resistivity of Ω · cm or higher is disclosed. Such ink is, for example, 10 as an insulating liquid. ¹⁰ Hydrocarbon solvents having a volume resistivity of Ω · cm or more, and coloring materials using carbon black, organic pigments, and those containing pigments in or on binders made of resin or wax, other dispersants, metals It can be prepared by preparing a colorant dispersion in a system to which a charge control agent such as soap is added. However, details of the composition, the preparation method, and the ink property value adjustment method are not described, and there is a problem that it is difficult to stably maintain the charge of the color material particles for a long period of time.
[0009]
JP-A-2001-139856 (Patent Document 5) and the like disclose an aliphatic hydrocarbon solvent-based highly electrically insulating dispersion medium, a colorant insoluble in the dispersion medium, and a dispersion as a charge control agent. An electrostatic ink jet head ink containing an acrylic ester polymer soluble in a medium and a metal soap and a method for controlling charging of the color material are disclosed. As a charge control agent, a high zeta potential can be imparted to the colorant particles by including a combination of an acrylic acid ester polymer soluble in a dispersion medium and a metal soap, such as carbon black and organic pigments. There has been a problem that it is difficult to stably maintain the charge of the color material particles for a long period of time. The mechanism of charge generation for carbon black and organic pigments dispersed in aliphatic hydrocarbon solvents is largely unknown, but in the case of metal soaps, it is thought that pigment polarity control is determined by a selective adsorption model. . That is, the oil-soluble metal soap is dissociated, and the dissociated metal ions are adsorbed on the pigment particles to give a positive charge. On the other hand, the counter ion forms a micelle structure with the metal soap and is stabilized in the dispersion as a negative charge. However, due to the charge generation mechanism based on the adsorption equilibrium, there is a problem that it is easily affected by the environment such as moisture, and the charge of the pigment particles cannot be held stably for a long time.
[0010]
On the other hand, in Japanese Patent Publication No. 5-29904 (Patent Document 6), a specific amino acid compound is known as a charge control agent for an electrophotographic liquid developer. However, a particular problem relating to electrostatic inkjet is described. Not.
[0011]
[Patent Document 1]
JP-A-56-170
[Non-Patent Document 1]
IEICE Transactions, Vol. J68-C, 2 (1985), pages 93 to 100
[Patent Document 2]
JP 58-215253 A
[Patent Document 3]
Japanese Patent Laid-Open No. 9-193389
[Patent Document 4]
JP 10-138493 A
[Patent Document 5]
JP 2001-139856 A
[Patent Document 6]
Japanese Patent Publication No. 5-29904
[0012]
[Problems to be solved by the invention]
As the demand for higher speed and higher image quality of printers increases, even in the above-mentioned ink jet heads with concentrated color material discharge, small ink droplets with high color material concentration can be stably and rapidly extended over a long period of time. There is a need for a technique for printing a higher-definition image at a high speed by discharging.
[0013]
It has been confirmed that such printing performance largely depends on the physical properties of the ink. In order to obtain sufficient printing performance, it is preferable to prepare ink as described in the section of the prior art. 10 ⁸ While maintaining a high volume resistivity of Ω · cm or higher, it is necessary to impart a high particle conductivity of 100 pS / cm or higher to the colorant particles. If the particle conductivity of the color material particles is less than 100 pS / cm, the color material particles cannot be moved at high speed to the discharge port, that is, the discharge electrode tip by electrophoresis, and the supply of the color material particles becomes insufficient. The cohesiveness of the color material particles is deteriorated and the discharge response frequency is lowered.
[0014]
Furthermore, since the electrical repulsive force between the surface of the discharge electrode and the color material particles is weak, stable discharge may not be possible if the color material particles adhere to and accumulate on the discharge electrode. For these reasons, there arise problems that a sufficient print density cannot be obtained and stable and high-speed printing cannot be performed.
[0015]
For this reason, it is necessary to sufficiently charge the coloring material in the ink by adding a metal soap soluble in the dispersion medium, an ionic compound or a surfactant as a charge control agent. There are few effective methods for providing sufficiently high particle conductivity to color material particles while satisfying the requirements for ink physical properties such as volume resistivity, and in particular, the charge amount of color material particles is stably maintained over a long period of time. The fact is that no effective method has been disclosed so far.
[0016]
In order to solve the above-mentioned problems, the present inventors have studied a method for controlling charging of colorant particles in ink, and as a result, have reached the present invention. The present invention solves the above-mentioned conventional problems, and the color material particles in the ink have a high negative polarity specific conductivity, so that a high density and low-bleed dot can be printed at high speed. Providing ink for electrostatic ink jet head of material concentration discharge type, and coloring material concentration discharge type that can stably print for a long time because the charge amount of color material particles can be stably maintained for a long time An object is to provide an ink for an electrostatic inkjet head.
[0017]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the following configuration can solve the problem.
[0018]
1) a nonaqueous solvent having a relative dielectric constant of 1.5 to 20 and a surface tension of 15 to 60 mN / m (at 25 ° C.), a colorant insoluble in the nonaqueous solvent, a resin insoluble in the nonaqueous solvent, And an ink composition for an electrostatic ink jet recording apparatus having a charge control agent soluble in the non-aqueous solvent as a main component, wherein the resin insoluble in the non-aqueous solvent is a resin having an acidic group, and The electrostatic ink jet ink composition, wherein the charge control agent contains at least one compound represented by the following general formula (1).
[0019]
[Chemical 2]

[0020]
In formula (1), R ^l And R ² Represents a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, an acyl group, an alkylsulfonyl group or an arylsulfonyl group, which may be substituted. R ^l , R ² Each may be the same or different and R ^l And R ² And may form a ring. A represents an alkylene group. X represents a monovalent to tetravalent metal or a quaternary ammonium cation. n represents a positive integer from 1 to 4.
When X represents a metal, when the carboxylic acid is not bonded to the metal so as to satisfy the valence, the remaining valence may be saturated with another ligand.
[0021]
2) The volume resistivity of the ink composition at 25 ° C. is 10 ⁸ The electrostatic ink-jet ink composition as described in 1) above, wherein the particle conductivity of the colorant particles in the ink composition is 100 pS / cm or more.
[0022]
3) Ink is introduced into a recording head having a plurality of recording electrodes, a voltage is applied to the recording electrodes, electrostatic force is applied to the ink, and ink droplets are ejected in a form in which color material particles are concentrated. The electrostatic recording apparatus according to 1) or 2), wherein the electrostatic recording apparatus is a color material concentration discharge type electrostatic ink jet recording apparatus that performs recording by forming print dots on a recording medium arranged to face each other. Electric inkjet ink composition.
[0023]
4) The ink composition is introduced into a recording head in which a plurality of recording electrodes are arranged, a voltage is applied to the recording electrodes, an electrostatic force is applied to the ink, and the ink droplets are concentrated in the form of coloring material particles. In the color material concentration discharge type electrostatic ink jet image forming method in which printing is performed by forming a printing dot on a recording medium disposed so as to face the recording medium, the ink composition has a relative dielectric constant of 1.5. To 20 and a non-aqueous solvent having a surface tension of 15 to 60 mN / m (at 25 ° C.), a coloring material insoluble in the non-aqueous solvent, a resin having an acidic group insoluble in the non-aqueous solvent, and the non-aqueous solvent. An electrostatic inkjet image forming method comprising a soluble charge control agent represented by the general formula (1).
[0024]
5) The volume resistivity of the ink composition at 25 ° C. is 10 ⁸ 4. The electrostatic ink jet image forming method as described in 4) above, wherein the particle conductivity of the colorant particles in the ink composition is 100 pS / cm or more.
[0025]
The charge control mechanism by the combination of the resin having an acidic group insoluble in the non-aqueous solvent of the present invention and the charge control agent comprising the amino acid compound represented by the general formula (1) is considered as follows. It is done.
That is, in the general formula (1), the substituent R ^l , R ² Is for improving the fat solubility of these compounds and assisting in dissolution in the carrier liquid, and the nitrogen atom is for promoting preferable ion dissociation. In general, in order for a carrier liquid-soluble charge control agent to be effective, it must first be ionically dissociated in a nonpolar solvent, and then one of the dissociated ionic species must be selectively adsorbed on the toner particle surface. I must. Alternatively, it is necessary that ions are taken from the toner particle surface to be ionized.
The charge control agent comprising an amino acid compound soluble in the non-aqueous solvent represented by the general formula (1) is a color material particle (hereinafter referred to as “color material resin particle”) coated with a color material by a resin having an acidic group. It is estimated that a cation is deprived from the acidic group on the surface. At this time, as represented by the following general formula (1 ′), a nitrogen atom having a coordination ability to the cation species is a molecule. This convenient ionization facilitates this ionization, and the produced cationic species is R ^l , R ² It is thought that it is solubilized stably in the carrier liquid due to the effect of. On the other hand, the color material resin particles are anionized and become negatively charged. It is believed that the acid group on the surface of the colorant resin particle and the charge stabilization mechanism of the following charge control agent can impart high particle conductivity to the colorant particle, and it is stable with no change in charge over time. .
[0026]
[Chemical 3]

[0027]
According to the present invention, there is provided an ink for a color material concentration discharge type electrostatic ink jet head, in which color material particles have high particle conductivity, and can stably print high density and low blur dots at high speed. Can be realized. The particle conductivity indicating the charge amount of the color material particles is a value obtained by subtracting the specific conductivity of the supernatant obtained by applying the ink composition to the centrifuge from the specific conductivity of the entire ink composition.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in further detail below.
Properties required for a nonpolar insulating solvent having a relative dielectric constant of 1.5 to 20 and a surface tension of 15 to 60 mN / m (at 25 ° C.) used in the present invention include low toxicity and flammability. A solvent selected from linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, petroleum naphtha, and halogen-substituted products thereof. . For example, hexane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, Isopar E from Exxon, Isopar G, Isopar H, Isopar L, Saltol from Philippe Petroleum, IP Solvent from Idemitsu Petrochemical, Petroleum Naphtha Then, S. of Shell Petrochemical Co., Ltd. B. R. , Shellzol 70, Cielzol 71, Mobil Petroleum's begazole, and the like can be used alone or in combination.
[0029]
Preferable hydrocarbon solvents include high-purity isoparaffinic hydrocarbons having a boiling point in the range of 150 to 350 ° C., and commercially available products such as Isopar G, H, L, M, and V (manufactured by Exxon Chemical Co., Ltd.) Name), Noper 12, 13, 15 (trade name), IP Solvent 1620, 2028 (trade name) manufactured by Idemitsu Petrochemical, Isosol 300,400 (trade name) manufactured by Nippon Petrochemical, Amsco OMS, Amsco 460 solvent ( Amsco; a brand name of Spirits). These products are highly saturated aliphatic saturated hydrocarbons, the viscosity at 25 ° C. is 3 cSt or less, the surface tension at 25 ° C. is 22.5 to 28.0 mN / m, and the specific resistance at 25 ° C. is 10 ¹⁰ Ω · cm or more. In addition, it is characterized by low reactivity and stability, low toxicity, high safety, and low odor.
[0030]
Examples of halogen-substituted hydrocarbon solvents include fluorocarbon solvents such as C ₇ F ₁₆ , C ₈ F ₁₈ C such as _n F _{2n + 2} Perfluoroalkanes represented by (Sumitomo 3M "Fluorinert PF5080", "Florinato PF5070" (trade name), etc.), fluorine-based inert liquid (Sumitomo 3M "Fluorinert FC series" (trade name), etc. ), Fluorocarbons ("Crytox GPL series" (trade name) manufactured by DuPont Japan Limited), chlorofluorocarbons ("HCFC-141b" (trade name) manufactured by Daikin Industries, Ltd.), [F (CF ₂ ) ₄ CH ₂ CH ₂ I], [F (CF ₂ ) ₆ I] and the like (“I-1420”, “I-1600” (trade name), etc., manufactured by Daikin Fine Chemical Laboratory) and the like.
[0031]
As the non-aqueous solvent used in the present invention, higher fatty acid esters and silicone oils can also be used. Specific examples of silicone oil include low-viscosity synthetic dimethylpolysiloxane, and commercially available products include KF96L (trade name) manufactured by Shin-Etsu Silicone, SH200 (trade name) manufactured by Toray Dow Corning Silicone, and the like. .
The silicone oil is not limited to these specific examples. These dimethylpolysiloxanes are available in a very wide viscosity range depending on the molecular weight, but it is preferable to use those in the range of 1 to 20 cSt. These dimethylpolysiloxanes, like isoparaffinic hydrocarbons, are 10 ¹⁰ It has a volume resistivity of Ω · cm or more, and has characteristics such as high stability, high safety, and odorlessness. These dimethylpolysiloxanes are characterized by low surface tension and have a surface tension of 18 to 21 mN / m.
[0032]
Solvents that can be used in combination with these organic solvents include alcohols (eg, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, fluorinated alcohol), ketones (eg, acetone, methyl ethyl ketone, cyclohexanone, etc.), carvone Acid esters (eg, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, etc.), ethers (eg, diethyl ether, dipropyl ether, tetrahydrofuran, dioxane, etc.) and halogenated hydrocarbons ( Examples thereof include methylene dichloride, chloroform, carbon tetrachloride, dichloroethane, methyl chloroform, and the like.
[0033]
Next, the color material used in the present invention will be described in detail.
The color material is not particularly limited, and all commercially available organic pigments and inorganic pigments, or those obtained by dispersing a pigment in a resin that is insoluble in a dispersion medium, or a resin on the pigment surface. Grafted ones can be used. Moreover, what dye | stained the resin particle with dye can be used. Specific examples of organic pigments and inorganic pigments include, for example, C.I. I. Pigment Yellow 1 (Fast Yellow G etc.), C.I. I. Monoazo pigments such as CI Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Disazo pigments such as CI Pigment Yellow 17; I. Non-benzidine azo pigments such as CI Pigment Yellow 180; I. An azo lake pigment such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as CI Pigment Yellow 153 (nickel nitroso yellow, etc.); I. Metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.) are conceivable.
[0034]
As a magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as CI Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as CI Pigment Red 144 (condensed azo red BR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Red 174 (Phloxine B Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Red 81 (Rhodamine 6G ′ lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Red 177 (eg, dianthraquinonyl red); I. Thioindigo pigments such as C.I. Pigment Red 88 (Thioindigo Bordeaux, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Quinacridone pigments such as C.I. Pigment Red 122 (quinacridone magenta, etc.); I. Isoindolinone pigments such as C.I. Pigment Red 180 (isoindolinone red 2BLT, etc.); I. Alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.) are conceivable.
[0035]
As a pigment exhibiting a cyan color, C.I. Disazo pigments such as CI Pigment Blue 25 (dianisidine blue, etc.); I. Phthalocyanine pigments such as C.I. Pigment Blue 15 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Blue 1 (such as Viclotia Pure Blue BO Lake); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. An alkali blue pigment such as CI Pigment Blue 18 (Alkali Blue V-5: 1) can be considered.
[0036]
As pigments exhibiting a black color, organic pigments such as aniline black pigments such as BK-1 (aniline black), iron oxide pigments, and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black are considered. . Specific examples of the carbon black pigment include MA-8, MA-10, MA-11, MA-100, MA-220, # 25, # 40, # 260, # 2600, # 2700B, manufactured by Mitsubishi Chemical Corporation. # 3230B, CF-9, MA-100R, MA-200RB, Degussa Printex 75, 90, Cabot Monarch 800, 1100, and the like. In addition, application of metal powder is also conceivable for color reproduction of gold, silver, copper and the like. In addition, application of metal powder is also conceivable for color reproduction of gold, silver, copper and the like.
[0037]
In addition, processed pigments in which pigment fine particles are dispersed in rosin ester resin, vinyl chloride-vinyl acetate resin, or the like are commercially available, and these may be used. Specific examples of commercially available processed pigments include microlith pigments manufactured by Ciba Specialty Chemicals, and preferred examples of processed pigments include Microlith-T pigments in which the pigment is coated with a rosin ester resin.
[0038]
The concentration of the color material in the ink composition of the present invention is preferably 0.5 to 20% by mass, particularly preferably 2 to 15% by mass, based on the total amount of the ink composition. When the color material concentration is 0.5% by mass or more, a sufficient printing density is obtained, and when the color material concentration is 20% by mass or less, favorable ink viscosity is maintained, and stable ink discharge can be performed.
[0039]
Next, the charge control agent that is a feature of the ink composition of the present invention will be described in detail. The charge control agent of the present invention contains at least one compound represented by the general formula (1).
[0040]
In the above formula (1), R ^l And R ² Are preferably a hydrogen atom, an alkyl group having 1 to 22 carbon atoms, and a substituted alkyl group (substituents include a dialkylamino group, alkyloxy group, alkylthio group and the like having 1 to 10 carbon atoms), Aryl group, substituted aryl group (substituents include C1-C10 alkyl groups, dialkylamino groups, chloro groups, bromine groups, etc.), aralkyl groups, C1-C22 acyl groups Represents an alkylsulfonyl group or an arylsulfonyl group. R ^l , R ² Each may be the same or different and R ^l And R ² And may form a ring.
[0041]
A preferably represents a C 1-10 alkylene group or substituted alkylene group. X represents a monovalent to tetravalent metal or a quaternary ammonium cation. n represents a positive integer from 1 to 4.
[0042]
In the general formula (1), when X represents a metal, and the carboxylic acid is not bonded to the metal so as to satisfy the valence, the remaining valence is saturated by another ligand. Also good. Examples of the ligand include halogen, hydroxyl group, oxygen atom, water, ammonia, amines, phosphines, sulfides and the like.
[0043]
In the compound of the general formula (1) used in the present invention, R ^l And R ² The total number of carbon atoms of is preferably in the range of 8 to 10, and R ^l And R ² Is preferably an acyl group. X is a metal selected from calcium, barium, manganese, copper, lithium, titanium, zinc, lead, zirconium, cobalt, nickel, aluminum, cerium, lanthanum, chromium, strontium, vanadium, tin, magnesium, iron and cadmium. Preferably there is.
[0044]
The charge control agent comprising the amino acid compound of the present invention is already known as a charge control agent for an electrophotographic liquid developer as disclosed in Japanese Patent Publication No. 5-29904 (Patent Document 6). . However, although Japanese Patent Publication No. 5-29904 describes a resin insoluble in a pigment and a non-aqueous solvent, it comprises a resin having an acidic group insoluble in a non-aqueous solvent and an amino acid compound as in the present invention. There is no description of the combination of charge control agents, and there is no description of the effect of specifically increasing the particle conductivity of the colorant particles by the combination of both. Furthermore, since the ink used for the electrostatic ink jet printer needs to impart a high particle conductivity of 100 ps / cm or more to the color material particles, the electron disclosed in the example of Japanese Patent Publication No. 5-29904. The colorant particles in the photographic liquid developer cannot be used as an electrostatic ink jet ink because the particle conductivity is small and a good drawn image cannot be obtained.
[0045]
Below, the synthesis | combining method of the metal salt of the amino acid compound of General formula (1) which is the characteristics of this invention is shown.
For the synthesis of acylated amino acids, see J. Am. Am. Chem. Soc. , 78 , 172 (1956), an amino acid acylation reaction can be used.
General methods can be applied to the synthesis of other amino acid compounds. For the synthesis of the metal salt, the alkali metal salt of the carboxylic acid or sulfonic acid is reacted with the inorganic salt of the metal, or the carboxylic acid or sulfonic acid and an organic metal compound (for example, JP-A-50-151154, JP-B 56-2952 and JP-B 58-9416), metal hydroxide or metal oxide may be directly reacted.
[0046]
Although the specific example of the amino acid compound of this invention is given to the following, it is not limited to these.
[0047]
[Formula 4]

[0048]
[Chemical formula 5]

[0049]
The concentration of the charge control agent in the present invention is preferably in the range of 0.0001 to 2.0 mass% with respect to the total amount of ink. When the concentration of the charge control agent is within this range, the effect of imparting high specific conductivity to the colorant particles can be effectively obtained, and the print density is not lowered due to the decrease in the volume resistivity of the ink, which is preferable.
[0050]
In the present invention, a resin having an acidic group insoluble in a non-aqueous solvent is used in combination with a charge control agent comprising the amino acid compound. The above resin, in combination with a charge control agent, imparts a high negative polarity particle charge to the color material particles, and also improves the function of mixing with the color material to improve dispersion, or improving the fixability of the color material. It also has a function.
[0051]
As the resin having an acidic group insoluble in a non-aqueous solvent, various known natural or synthetic resins can be used. For example, an acrylic resin, an epoxy resin, a polyester resin, an ethylene-vinyl acetate resin, a vinyl chloride-vinyl acetate resin, a styrene-butadiene resin, a styrene-acrylic resin, or the like has an acidic group that can be copolymerized with the raw material monomer of the resin. By using an acidic monomer (hereinafter sometimes referred to as acidic monomer (A)), a resin having an acidic group insoluble in the non-aqueous solvent of the present invention can be obtained. The acidic monomer (A) is a monomer containing at least one acidic group selected from a carboxylic acid group, a sulfonic acid group, a sulfinic acid group, a phosphoric acid group, and a phosphorous acid group. It may contain an acidic group.
[0052]
As a preferred resin, it has a function of adsorbing to a pigment dispersed in a resin that is insoluble in a dispersion medium, and well dispersing in a non-aqueous solvent. A resin having a difficult part and a part having an acidic group is preferred. For example, examples of the monomer corresponding to the portion solvated with the solvent after polymerization include lauryl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, butyl methacrylate, and cetyl methacrylate. Examples of the monomer corresponding to the portion that is difficult to solvate with the solvent after polymerization include methyl methacrylate, ethyl methacrylate, styrene, and vinyl toluene. Examples of the acidic monomer (A) containing an acidic group include acidic group monomers such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, styrene sulfonic acid, and alkali salts thereof.
[0053]
The acidic monomer (A) is preferably used in an amount of 1 to 45% by mass, more preferably 3 to 30% by mass, based on the total amount of the polymerizable monomer.
[0054]
Specific examples of the acidic monomer (A) are shown below. The present invention is not limited to these (in the following specific examples, Y represents —CO ₂ H group, -SO ₃ H group, -SO ₂ H group, -PO ₃ H ₂ Group or -OPO ₃ H ₂ Represents a group).
[0055]
[Chemical 6]

[0056]
[Chemical 7]

[0057]
Color material particles (color material resin particles) coated with a color material with a resin having an acidic group are formed by coating the color material with a binder resin to form a color mixture, and then, the color mixture in a non-aqueous solvent. It can be formed by dispersing fine particles. First, a process of making a color mixture by coating a color material with a binder resin will be described. The colored mixture is prepared by the following method, for example.
[0058]
(I) A method in which a coloring material and a binder resin are melt-kneaded using a kneader such as a roll mill, a Banbury mixer, or a kneader at a temperature equal to or higher than the softening point of the binder resin, and pulverized after cooling to obtain a colored mixture.
(Ii) Dissolve the binder resin in a solvent, add a coloring material, and wet-disperse with a ball mill, attritor, sand grinder, etc., and evaporate the solvent to obtain a colored mixture, or disperse the dispersion of the binder resin. A method of pouring into a non-solvent and precipitating to obtain an admixture, followed by drying to obtain a colored admixture.
(Iii) A method of kneading a water-containing pigment paste (wet cake) with a resin or a resin solvent by a flushing method, substituting water with the resin or resin solution, and drying the water and the solvent under reduced pressure to obtain a colored mixture.
[0059]
Next, a dispersion process for dispersing the colored admixture described above in the form of fine particles in a non-aqueous solvent will be described.
In the dispersion step, it is preferable to use a pigment dispersant in order to disperse in fine particles and stabilize the dispersion in a non-aqueous solvent. Examples of the use of the color admixture and the pigment dispersant include the following methods, and the desired effect can be obtained by any of these methods.
[0060]
(1) A pigment composition in which a colored admixture and a pigment dispersant are mixed in advance is added and dispersed in a non-aqueous solvent.
(2) A colored admixture and a pigment dispersant are separately added and dispersed in a non-aqueous solvent.
(3) A dispersion obtained by separately dispersing a colored admixture and a pigment dispersant in advance in a non-aqueous solvent is mixed. In this case, the pigment dispersant may be dispersed only with a solvent.
(4) After dispersing the colored admixture in a non-aqueous solvent, a pigment dispersant is added to the obtained pigment dispersion.
[0061]
As a machine for mixing or dispersing the above colored admixture in a non-aqueous solvent, a dissolver, a high speed mixer, a homomixer, a kneader, a ball mill, a roll mill, a sand mill, an attritor or the like can be used. The range of the average particle diameter of the colorant particles formed by dispersing the colored admixture is preferably from 0.1 to 4 μm, more preferably from 0.3 to 2 μm.
[0062]
The basic constituent materials in the present invention are as described above. In addition, a pigment dispersant, a surfactant, and various additives may be added as appropriate in order to improve the dispersion by mixing with a colorant. .
[0063]
As the pigment dispersant for dispersing the coloring material in a non-aqueous solvent, a general pigment dispersant applied in the non-aqueous solvent can be used. Any pigment dispersant may be used as long as it is compatible with the nonpolar insulating solvent and can stably disperse the pigment in fine particles. Specific examples of the pigment dispersant include sorbitan fatty acid esters (sorbitan monooleate, sorbitan monolaurate, sorbitan sesquioleate, sorbitan trioleate, etc.), polyoxyethylene sorbitan fatty acid esters (polyoxyethylene sorbitan monostearate, polyoxyethylene Oxyethylene sorbitan monooleate), polyethylene glycol fatty acid ester (polyoxyethylene monostearate, polyethylene glycol diisostearate, etc.), polyoxyethylene alkyl phenyl ether (polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether) Etc.), nonionic surfactants such as aliphatic diethanolamides, and polymer dispersants having a molecular weight of 1000 or more Good, for example, styrene-maleic acid resin, styrene-acrylic resin, rosin, BYK-160, 162, 164, 182 (urethane polymer compound manufactured by Big Chemie), EFKA-47, LP-4050 (EFKA) For example, urethane dispersants manufactured by the manufacturer, Solspers 24000 (polyester polymer compound manufactured by Zeneca), Solsperse 17000 (aliphatic diethanolamide manufactured by Zeneca), and the like.
[0064]
In addition to the above, the polymeric pigment dispersants include monomers such as lauryl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, and cetyl methacrylate that are solvated in a solvent, and methyl methacrylate, ethyl methacrylate, and styrene that are difficult to solvate in a solvent. And a random copolymer comprising a monomer such as vinyltoluene, or a graft copolymer described in JP-A-3-188469. Other examples include styrene-butadiene copolymers and block copolymers of styrene and long-chain alkyl methacrylates described in JP-A-60-10263. Preferred examples of the dispersant for pigment include a graft copolymer disclosed in JP-A-3-188469. The amount of the pigment dispersant used is preferably 0.1 to 300 parts by mass with respect to 100 parts by mass of the pigment. When the addition amount of the pigment dispersant is less than 0.1 parts by mass, the pigment dispersion effect is small, which is not preferable. Moreover, even if it uses more than 300 mass parts, the effect of the used part will not be acquired.
[0065]
Various additives may be added to the ink composition of the present invention as desired. The ink composition is arbitrarily selected depending on the material and structure of the ink jet system or the ink jet discharge head, the ink supply unit, and the ink circulation unit, and is contained as an ink composition. For example, additives described in Takeshi Amari “Inkjet Printer Technology and Materials”, Chapter 17, published by CMC Co., Ltd. (1998) are used.
[0066]
Specifically, fatty acids (for example, monocarboxylic acid having 6 to 32 carbon atoms, polybasic acid; for example, 2-ethylhexynoic acid, dodecenyl succinic acid, butyl succinic acid, 2-ethylcaproic acid, lauric acid, palmitic acid, elaidin Acid, linolenic acid, ricinoleic acid, oleic acid, stearic acid, enanthic acid, naphthenic acid, ethylenediaminetetraacetic acid, abietic acid, dehydroabietic acid, hydrogenated rosin etc.), resin acid, alkylphthalic acid, alkylsalicylic acid, etc. (As metals of metal ions, Na, K, Li, B, Al, Ti, Ca, Pb, Mn, Co, Zn, Mg, Ce, Ag, Zr, Cu, Fe, Ba, etc.), surface active compounds (For example, as organic phosphoric acid or salts thereof, mono-, di- or trialkyl phosphoric acid composed of an alkyl group having 3 to 18 carbon atoms, etc. Organic sulfonic acids or salts thereof include long-chain aliphatic sulfonic acids, long-chain alkylbenzene sulfonic acids, dialkylsulfosuccinic acids and the like or metal salts thereof, and amphoteric surfactant compounds include phospholipids such as lecithin and kephalin), fluorine Alkyl group-containing surfactants containing atomic and / or dialkylsiloxane bonding groups, aliphatic alcohols (for example, higher alcohols comprising branched alkyl groups having 9 to 20 carbon atoms, benzyl alcohol, phenethyl alcohol, cyclohexyl) Alcohols), polyhydric alcohols {for example, alkylene glycols having 2 to 18 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1, 6-hexanedio , Dodecanediol, etc.); C4-C1000 alkylene ether glycol (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc.); C5-C18 alicyclic Diol (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); C12-C23 bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) C2-C18 alkylene oxide (ethylene oxide, propylene) Oxide, butylene oxide, α-olefin oxide, etc.) adduct, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol Polyols such as trihydric to octahydric or higher (trisphenol PA, phenol novolak, cresol novolak, etc.); C 2-18 alkylene oxide adducts (addition moles) of the above trivalent or higher polyphenols The number is 2 to 20), polyhydric alcohol ether derivatives (polyglycol alkyl ethers, alkylaryl polyglycol ether, etc.), polyhydric alcohol fatty acid ester derivatives, polyhydric alcohol ether oleate derivatives (for example, ethylene glycol mono Ethyl acetate, diethylene glycol monobutyl acetate, propylene glycol monobutyl propiolate, sorbitan monomethyl dioxalto), alkyl naphthalene sulfonate, alkyl aryl sulfonate, etc. Including without being limited thereto. The amount of each additive used is preferably adjusted so that the surface tension of the ink composition is in the range of 15 to 60 mN / m (at 25 ° C.) and the viscosity is in the range of 1.0 to 40 cP.
[0067]
Next, a method for producing ink will be described. For the production of the ink, a general method known as a production method of various pigment inks can be used. For example, a bead mill is prepared by mixing a colorant, a resin, a charge control agent, which is a feature of the present invention, and other auxiliary additives with a dispersion medium so as to have an appropriate viscosity range. Using a dispersing machine such as an attritor or a ball mill, the mixture is pulverized for several hours to several tens of hours to prepare an ink concentrate in which a color material of several tens of nm to several μm is dispersed, and then used. There is a method of preparing an ink having a surface tension of 15 to 60 mN / m and a viscosity of 1.0 to 40 cP. Also, after mixing the colorant, resin, and auxiliary additives, melt kneading using a kneader such as a roll mill, Banbury mixer, kneader, etc. at a temperature higher than the softening point of the resin, pulverizing after cooling, and the same as above There is also a method of adding a charge control agent which is a feature of the present invention after being dispersed and diluted. The same effect can be obtained by using either method.
In the ink composition, the average particle diameter of the color material particles coated with the resin is preferably about 0.1 to 4 μm, more preferably 0.3 to 3 in view of the balance between ejection performance and prevention of sedimentation of the color material particles. The range is 2 μm.
[0068]
Hereinafter, it is shown that the ink composition using the charge control agent of the present invention is useful as an ink for an electrostatic ink jet recording apparatus. Any electrostatic ink jet printer can be used as long as it uses ink using color material particles, without being limited to a particular method. A preferable example is a color material concentration discharge type electrostatic ink jet printer.
[0069]
A color material concentration discharge type electrostatic ink jet printer will be further described. 1 and 2 are schematic diagrams for explaining an example of an ejection head. FIG. 1 is a diagram showing a configuration of a line scanning type multi-channel inkjet head, and shows a section of ejection electrodes corresponding to recording dots. In the drawing, ink 100 is supplied between a head substrate 102 and a discharge electrode substrate 103 from a circulation mechanism 111 including a pump through an ink supply channel 112 connected to the head block 101, and the ink formed in the head block 101 is also the same. The ink is recovered by the ink circulation mechanism 111 through the recovery channel 113. The discharge electrode substrate 103 includes an insulating substrate 104 having a through hole 107 and a discharge electrode 109 formed on the recording medium side around the through hole 107. On the other hand, a convex ink guide 108 is disposed on the head substrate 102 at a substantially central position of the through hole 107. The convex ink guide 108 is made of an insulating member such as plastic resin or ceramics, and is arranged at the same row interval and pitch so that the center is equal to the through hole 107, and is held on the head substrate 102 by a predetermined method. Yes. Each convex ink guide 108 has a shape in which the tip of a flat plate having a constant thickness is cut into a triangle or a trapezoid, and the tip becomes the ink droplet flying position 110. Each convex ink guide 108 may form a slit-like groove from the tip thereof, and the ink supply to the ink flying position 110 is smoothly performed by the capillary action of the slit, thereby improving the recording frequency. I can do it. In addition, any surface of the ink guide may have conductivity as required. In that case, the conductive portion is electrically floated so that the ink can be effectively applied with a small voltage applied to the ejection electrode. An electric field can be formed at the flight position. Each convex ink guide 108 protrudes in the ink droplet flying direction by a predetermined distance substantially perpendicularly from each through hole. A recording medium 121, which is a recording sheet, is disposed opposite to the tip of the convex ink guide 108, and a counter electrode that also serves as a platen for guiding the recording medium 121 on the back surface of the recording medium 121 opposite to the head substrate 102. 122 is arranged. In addition, a migration electrode 140 is formed at the bottom of the space formed between the head substrate 102 and the ejection electrode substrate 103. By applying a predetermined voltage to the migration electrode 140, the migration of the ink in the ink guide in the ejection position direction is performed. Charged particles can be electrophoresed to increase ejection responsiveness.
[0070]
A specific configuration example of the discharge electrode substrate 103 will be described with reference to FIG. FIG. 2 is a view of the discharge electrode substrate 103 as viewed from the recording medium 121 side. A plurality of discharge electrodes are arranged in an array in two rows in the main scanning direction, and a through hole 107 is formed at the center of each discharge electrode. In addition, individual discharge electrodes 109 are formed around the through-holes 107, respectively. In this embodiment, the inner diameter of the discharge electrode 109 is set to be slightly larger than the diameter of the through hole 107, but it may be the same as the diameter of the through hole 107. Here, the insulating substrate 104 is made of polyimide having a thickness of about 25 to 200 μm, the discharge electrode 109 is made of copper foil having a thickness of about 10 to 100 μm, and the inner diameter of the through hole 107 is about 150 to 250 μmΦ.
[0071]
Next, the recording operation of the electrostatic ink jet recording apparatus will be described. Here, a case where ink containing a negatively charged color material is used will be described as an example, but the present invention is not limited to this example. At the time of recording, the ink 100 supplied from the ink circulation mechanism 111 via the ink supply channel 112 is supplied from the through hole 107 to the ink flying position 110 at the tip of the convex ink guide 108, and a part of the ink recovery channel. The ink is recovered by the ink circulation mechanism 111 through 113. Here, a voltage of −1.5 kV, for example, is always applied as a bias from the bias voltage source 123 to the ejection electrode 109, and a pulse of −500 V is applied to this as a signal voltage corresponding to the image signal from the signal voltage source 124. The voltage is superimposed on the ejection voltage 109. At this time, a voltage of −1.8 kV is applied to the migration electrode 140. On the other hand, the counter electrode 122 provided on the back surface of the recording medium 121 is set to a ground voltage of 0 V as shown in the figure. In some cases, the recording medium 121 side may be charged to, for example, −1.5 kV to obtain a bias voltage. In this case, an insulating layer is provided on the surface of the counter electrode 122, the recording medium is charged by a corona charger, a scorotron charger, a solid ion generator or the like, and the discharge electrode 109 is grounded, for example, and a signal voltage source 124 is connected thereto. As a signal voltage corresponding to the image signal from, for example, a pulse voltage of −500 V is superimposed on the ejection voltage 109 at the time of ON. At this time, a voltage of −200 V is applied to the migration electrode 140. Now, when the discharge voltage 109 is in an ON state (a state in which −500 V is applied) and a voltage of a total of −2 kV in which a pulse voltage of −500 V is superimposed on a bias DC of −1.5 kV is applied, the tip of the convex electrode 108 is applied. An ink droplet 115 is ejected from the ink droplet flying position 110 and pulled toward the counter electrode 122 to fly toward the recording medium 121 to form an image. In order to improve the accuracy of landing on the recording medium by precisely controlling the flying of the ink droplets after the flight, an intermediate electrode is provided between the ejection electrode and the recording medium, or a guard electrode for suppressing electric field interference between the ejection electrodes. Of course, a means such as providing the above is used, but it should be understood that the present embodiment can be suitably used in this embodiment as needed. Further, a porous body may be provided between the head base plate 102 and the discharge electrode substrate 103. In this case, it is possible to prevent the influence of the change in the ink internal pressure due to the movement of the ink jet head and the like, and the through hole after the ink droplet discharge Ink liquid supply to 107 parts is quickly achieved. Therefore, the flying of the ink droplet 115 is stabilized, and a good image with a stable density can be recorded on the recording medium 121 at high speed.
[0072]
【Example】
Examples of the present invention are illustrated below, but the present invention is not limited thereto.
[0073]
Synthesis Example 1 (Synthesis of Exemplified Compound (1))
Acrylic acid (144 g, 2.0 mol) was added dropwise to a mixture of n-octylamine (516 g, 4.0 mol), hydroquinone (200 mg) and methanol (400 ml) with stirring under ice cooling. After completion of the dropwise addition, the mixture was heated to reflux for 4 hours and returned to room temperature, and then neutralized with NaOH (80 g, 2.0 mol).
The reaction mixture was dispersed in 6 L of acetone, filtered and dried to obtain Nn-octyl-β-alanine Na salt as white crystals having a melting point of 242 ° C. (349 g, yield 78%).
Next, this Na salt (223 g, 1.0 mol) was dissolved in 2 L of water, and myristoyl chloride (246.5 g, 1.0 mol) and an aqueous NaOH solution (NaOH 50 g, water 500 ml) were simultaneously added dropwise with stirring under ice cooling. did. After completion of the dropwise addition, stirring was continued for 1 hour, and then concentrated hydrochloric acid (120 ml) was added to dry the crystals that crystallized out by mouth. N-myristoyl-Nn-octyl-β-alanine was obtained as white crystals having a melting point of 47 ° C. (348 g, yield 85%). This crystal was recrystallized from acetone, so that it could be a pure product having a melting point of 58 to 59 ° C. Elemental analysis value C: 72.79%, H: 12.02%, N: 3.34% (C ₂₅ H ₄₉ N ₁ O ₃ As calculated C: 72.94%, H: 12.00%, N: 3.4%).
[0074]
N-myristoyl-Nn-octyl-β-alanine (206 g, 0.5 mol) was dissolved in 2 liters of an aqueous solution of NaOH (21.1 g, 0.5 mol). NiCl ₂ ・ 6H ₂ A solution of O (59.4, 0.25 mol) dissolved in water (200 ml) was added with stirring, and stirring was continued for 1 hour, followed by extraction with chloroform (1 liter). The organic layer is Na ₂ SO ₄ After drying, the solvent was distilled off to obtain Exemplified Compound (1) as a green viscous oil. The oil solidified upon standing (196 g, yield 89%, melting point 68-70 ° C.).
[0075]
Synthesis Example 2 (Synthesis of Exemplified Compound (2))
In Synthesis Example 1, NiCl ₂ ・ 6H ₂ CoCl instead of O ₂ ・ 6H ₂ Using O, a Co salt of N-myristoyl-Nn-octyl-β-alanine was obtained as a reddish purple viscous oil (yield 91%).
[0076]
Synthesis Example 3 (Synthesis of Exemplified Compound (3))
N-myristoyl-Nn-octyl-β-alanine (4.11, 0.01 mol) was dissolved in 100 ml of chloroform, and a chloroform solution of titanium tetrachloride (1.90 g, 0.01 mol, 50 ml of chloroform) was dissolved. added. Triethylamine (4.04 g, 0.04 mol) was added dropwise with stirring at room temperature, and after completion, stirring was continued for 1 hour under heating and reflux. After cooling, 600 ml of n-hexane was added, the precipitated triethylamine hydrochloride was removed by mouth, the mouth liquor was concentrated, and a viscous oil was obtained. This was dissolved in 100 ml of n-hexane, washed repeatedly with water, and the separated organic layer was washed with Na. ₂ SO ₄ After drying, the solvent was distilled off to obtain a mixture containing Exemplified Compound (3) as a pale yellow viscous oil (3.5 g).
[0077]
Synthesis Example 4 (Synthesis of Exemplified Compound (4))
In Synthesis Example 3, zirconium tetrachloride was used instead of titanium tetrachloride, and a mixture containing the exemplified compound (4) was obtained as a pale yellow viscous oil.
[0078]
Synthesis Example 5 (Synthesis of Exemplified Compound (5))
N-stearoyl-Nn-dodecyl-β-alanine (5.23 g, 0.01 mol) was dispersed in 1 liter of water, NaOH (0.42 g, 0.01 mol) was added, and the mixture was heated and stirred. Dissolved. NiCl ₂ ・ 6H ₂ A solution prepared by dissolving O (1.19 g, 0.005 mol) in 100 ml of water was added with stirring, and the resulting crystals were taken out, washed with water and dried. The exemplified compound (5) was obtained as greenish white crystals having a melting point of 6 ° C. (4.82 g, yield 88%).
[0079]
Synthesis Example 6 (Synthesis of Exemplary Compound (6))
Instead of N-stearoyl-Nndodecyl-β-alanine in Synthesis Example 5, N-stearoyl-Nn-butyl-β-alanine was replaced with NiCl. ₂ ・ 6H ₂ CoCl instead of O ₂ ・ 6H ₂ Exemplified compound (6) was obtained as magenta crystals having a melting point of 53-54 ° C. using O.
[0080]
Synthesis Example 7 (Synthesis of Exemplified Compound (8))
The same operation as in Synthesis Example 6 was performed using N-stearoyl-N-phenyl-β-alanine to obtain Exemplified Compound (8) as red purple crystals having a melting point of 67 ° C.
[0081]
Synthesis Example 8 (Synthesis of Exemplified Compound (12))
Acrylic acid (72 g, 1. mol) was stirred in a mixture of di-n-octylamine (241 g, 1.0 mol), triethylamine (101 g, 1.0 mol), methanol (200 ml) and hydroquinone (100 mg) under water cooling. 0 mol) was added dropwise. After completion, stirring was continued for 4 hours while heating under reflux. After standing overnight at room temperature, an aqueous solution of NaOH (43 g, 50 ml) was added, and the content was poured into 3 L of acetone, and the resulting white precipitate was mouthed and dried (189.3 g, yield 57%). Next, 33.5 g (1 mol) of this crude product was dissolved in 1 L of water, and NiCl ₂ ・ 6H ₂ An aqueous solution (50 ml) of O 2 (11.9 g, 0.05 mol) was added. The resulting oil dispersion was extracted with chloroform (300 ml) and Na ₂ SO ₄ After drying, the solvent was distilled off to obtain Exemplified Compound (12) as a green viscous oil (8.3 g, yield 24%).
[0082]
Synthesis Example 9 (Synthesis of Exemplified Compound (15))
N-myristoyl-Nn-octyl-β-alanine (4.11 g, 0.01 mol) was dissolved in a solution of KOH (0.66 g, 85% content) in methanol (100 ml) and cetyltrimethylammonium bromide ( 3.64 g, 0.01 mol) was added. After stirring at room temperature for 30 minutes, water (100 ml) and n-hexane (100 ml) were added for extraction. The organic layer is Na ₂ SO ₄ After drying, the solvent was distilled off to obtain Exemplified Compound (15) as a waxy solid (5.32 g, yield 77%).
[0083]
Synthesis Example 10 (Synthesis of Exemplified Compound (16))
N-lauroyl sarcosine Na salt (15.5 g, 0.05 mol) was dissolved in water (200 ml). CoCl ₂ ・ 6H ₂ A solution prepared by dissolving O (5.95 g, 0.025 mol) in water (100 ml) was added with stirring. After stirring for 1 hour, the resulting crystals were taken out, washed with water and dried. 14.65 g of crystals having a melting point of 105 to 110 ° C. were obtained (yield 98%).
[0084]
Synthesis Example 11 (Synthesis of Exemplified Compound (17))
N-phenylglycine (15.1 g, 0.1 mol) was dissolved in an aqueous NaOH solution (5.95 g of NaOH, 100 ml of water), and stearoyl chloride (15.1 g, 0.1 mol) and NaOH were stirred with ice cooling. An aqueous solution (5.0 g NaOH, 50 ml water) was added dropwise at the same time. After stirring for 1 hour, the mixture was neutralized with hydrochloric acid, and the precipitated crystals were dried by mouth (10.4 g, yield 25%). Next, the same operation as in Synthesis Example 6 was carried out using this crystal to obtain Exemplified Compound (17) as a reddish purple crystal having a melting point of 64-65 ° C.
[0085]
Synthesis Example 12
N-myristoyl-Nn-octyl-β-alanine (4.11 g, 0.01 mol) was dispersed in 50 ml of isopropyl alcohol, and titanium tetraisopropoxide (2.84 g, 0.01 mol) was stirred at room temperature. ) Was added dropwise. After completion of the dropwise addition, the mixture was heated to reflux for 1 hour, returned to room temperature, 50 ml of n-hexane was added, and the whole was added to 100 ml of water. The separated organic layer was washed with 50 ml of water and 50 ml of saturated brine, and then the organic layer was washed with Na. ₂ SO ₄ And the solvent was distilled off to obtain a pale yellow viscous oil (yield 3.79 g). This oil solidified in the form of a wax upon standing and exhibited the following physical property values. Elemental analysis value C: 60.82%, H: 10.37%, N: 2.50%, residual ash: 15.6%, infrared absorption spectrum (KBr): stretching frequency ν of carbonyl group _{C = 0} = 1730, 1640 (shoulder), 1602, 1560 cm ^-1 .
This solid is designated as reaction mixture (1). The following structure can be considered in the reaction mixture (1) estimated from the elemental analysis values. From the infrared absorption spectrum, this is almost the same between N-myristoyl-Nn-octyl-β-alanine and its Ti salt. It was found to be a 1: 1 mixture.
[0086]
[Chemical 8]

[0087]
The reaction mixture (1) can be dispersed in acetone and repeated washing to obtain a free acid-free powder (reaction mixture-2) (in this case, N-myristoyl-Nn- from the washing solution). Octyl-β-alanine is recovered). The reaction mixture (2) exhibited the following physical property values.
[0088]
Melting point: 217-219 ° C. Elemental analysis C: 51.83%, H: 8.58%, N: 1.91%, residual ash: 27.0%, infrared absorption spectrum (KBr): stretching of carbonyl group Frequency ν _{C = 0} = 1640, 1560cm ^-1 . From these values, it can be estimated that the reaction mixture (2) is a Ti salt of N-myristoyl-Nn-octyl-β-alanine containing about 2 equivalents of Ti.
[0089]
Example 1: Ink composition (IJ-1)
100 parts by mass of linole blue FG-7350 (Pigment Blue 15: 3 manufactured by Toyo Ink Co., Ltd.) as a blue pigment, styrene / vinyltoluene / lauryl methacrylate / (2-methacrylamide-2,2-dimethyl) ethanesulfonic acid lithium salt as a resin 200 parts by mass of a polymer (48/48/1/3 molar ratio) was pre-ground with a trioblender and mixed well, and then melt kneaded with a desktop kneader PBV (manufactured by Irie Trading Company) heated to 100 ° C. (120 minutes) did. The pigment kneaded product was pulverized with a pin mill. Next, 20 parts by mass of a pigment kneaded product, 130 parts by mass of Isopar G, 50 parts by mass of a 20 wt% solution prepared by dissolving and dissolving a pigment dispersant (D-1) having the following structure in Isopar G, and 3G-X glass beads 400 The mixture was mixed with a mass part for 120 minutes with a paint shaker (Toyo Seiki KK). The volume average particle size of the pigment resin particles in the dispersion was 0.41 μm when measured with an ultracentrifugal automatic particle size distribution analyzer CAPA700 (Horiba Seisakusho).
[0090]
[Chemical 9]

[0091]
The pigment resin particle dispersion from which the glass beads were removed by filtration was diluted with Isopar G so that the pigment resin particle component was 3.0%. Subsequently, the ink composition (IJ-1) was prepared by adding the exemplified compound (1) as a charge control agent so as to be 0.01 wt%. The viscosity of the obtained ink composition is 1.4 cP (E-type viscometer, measured at a temperature of 25 ° C.), and the surface tension is 23 mN / m (automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd., measured at a temperature of 25 ° C.). there were. The charge amount of the ink composition was determined by using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.). It calculated | required from the specific conductivity measured on the conditions of frequency 1kHz. The particle conductivity of the pigment resin particles was determined by subtracting the specific conductivity of the supernatant obtained by subjecting the ink composition to a centrifuge from the specific conductivity of the entire ink composition. Centrifugation was performed using a small high-speed cooling centrifuge (SRX-201 manufactured by Tommy Seiko Co., Ltd.) for 30 minutes under the conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C. The ink composition (IJ-1) showed an overall specific conductivity of 551 pS / cm, and the blue resin particles showing a clear negative charge showed a particle conductivity of 496 pS / cm and the charge of the ink composition. More than 90% of the amount was related to the pigment resin particles. Further, the overall specific conductivity of the ink composition after forced aging at 45 ° C. for one week and the particle conductivity of the pigment resin particles were 528 pS / cm and 483 pS / cm, respectively, and there was almost no change in the charge amount, which was extremely stable. I understand.
[0092]
A 100 dpi 64-channel electrostatic ink jet head having a head structure shown in FIG. 1 was used as an ink jet apparatus, and an ink composition (IJ-1) was filled in an ink tank. After removing dust on the surface of the coated recording paper as a recording medium by air pump suction, the ejection head was brought close to the coated recording paper to the drawing position, and ink was ejected and drawn at a drawing resolution of 600 dpi. At this time, the drawing was performed while adjusting the pulse voltage and changing the dot area in 16 steps within a dot diameter range of 15 μm to 60 μm. The drawn image was stably printed with uniform dots without blurring, and gave a clear image of good quality with a satisfactory density. The ejection stability from the ink head was also good, there was no clogging, and stable dot-shaped printing was possible even during long-term continuous image drawing.
Furthermore, when drawing was similarly performed using the ink composition after forced aging at 45 ° C. for one week, the drawn image gave a clear image of good quality with satisfactory density with uniform dots without bleeding, and stable ejection. The dot shape was also stable, and even with long-term continuous image drawing, stable dot-shaped printing was possible.
[0093]
Comparative Examples 1 to 3: Ink compositions for comparison (IJR-1) to (IJR-3)
In Example 1, instead of the resin having an acidic group, a styrene / vinyltoluene / lauryl methacrylate copolymer (49.5 / 49.5 / 1 molar ratio) was used as a resin having no acidic group, A comparative ink composition (IJR-1) was prepared in exactly the same manner as in Example 1 using the exemplified compound (1) as a charge control agent (Comparative Example 1).
[0094]
In Example 1, the pigment resin particle dispersion was diluted with Isopar G so that the pigment resin particle component was 3.0%, and naphthenic acid of metal soap was used instead of the exemplified compound (1) as a charge control agent. A comparative ink composition (IJR-2) was prepared in exactly the same manner as in Example 1 except that zirconium (manufactured by Nippon Chemical Industry Co., Ltd.) was added so that the metal content was 0.01 wt% ( Comparative Example 2). Further, similarly, the comparative ink composition (IJR-3) was prepared in the same manner as in Example 1 except that soy lecithin was added in an amount of 0.01 wt% instead of the exemplified compound (1). (Comparative Example 3).
[0095]
The comparative ink compositions (IJR-1) to (IJR-3) each had a viscosity of 1.4 cP and a surface tension of 23 mN / m. The overall specific conductivity of the comparative ink composition (IJR-1) is 143 pS / cm, the particle conductivity of the blue resin particles is as low as 113 pS / cm, and the charge polarity by the comb electrode is positive or negative. It was a mixture. For this reason, it could not be used for the next electrostatic ink jet drawing test.
[0096]
The overall specific conductivity of the comparative ink composition (IJR-2) was 243 pS / cm, but the particle conductivity of the blue resin particles was as low as 204 pS / cm, and the charge polarity by the comb electrode was positive or negative. Since these were mixed, the comparative ink composition (IJR-2) could not be used in the next electrostatic ink jet drawing test.
[0097]
The overall specific conductivity of the comparative ink composition (IJR-3) was 247 pS / cm, the particle conductivity of the blue resin particles was 222 pS / cm, and the charge polarity by the comb electrode was negative. The total specific conductivity of the comparative ink composition (IJR-3) after forced aging at 45 ° C. for one week was 119 pS / cm, and the particle conductivity of the blue resin particles was 101 pS / cm, which was the initial charge amount. Compared to 50% or less, it was found that the charge amount change was large. Next, electrostatic ink jet drawing was performed in the same manner as in Example 1 using the comparative ink composition (IJR-3), and the initial drawn image gave a low density image with blur. When drawing was performed in the same manner using the comparative ink composition (IJR-3) after forced aging at 45 ° C. for one week, a discharge failure occurred, and a satisfactory image could not be obtained due to missing images.
[0098]
From the results of Example 1 and Comparative Examples 1 to 3, as in the present invention, from the combination of a resin having an acidic group insoluble in a non-aqueous solvent and the charge control agent of the present invention comprising an amino acid compound. It can be seen that the resulting ink can impart high particle conductivity to the colorant particles and is stable without any change in the amount of charge over time, so that it can be used favorably for electrostatic ink jet drawing.
[0099]
Examples 2 to 11: Ink compositions (IJ-2) to (IJ-11)
In Example 1, the pigment resin particle dispersion was diluted with Isopar G so that the pigment resin particle component was 3.0%, and each of the compounds described in Table 1 was used instead of the exemplified compound (1) as a charge control agent. Ink compositions (IJ-2) to (IJ-11) were prepared in exactly the same manner as in Example 1, except that the compounds were used.
Table 1 shows the particle conductivity of the blue resin particles of the ink compositions (IJ-2) to (IJ-11) and the printing evaluation thereof. Table 1 shows the particle conductivity and print evaluation of each of the blue resin particles of the ink compositions (IJ-2) to (IJ-11) after forced aging at 45 ° C. for one week.
[0100]
[Table 1]

[0101]
(Print evaluation)
○ The printed image is satisfactorily printed with satisfactory density without blurring.
× When the drawn image is blurred, has low density, or cannot be printed continuously and stably.
[0102]
Example 12: Ink composition (IJ-12)
100 parts by mass of carbon black # 40 (manufactured by Mitsubishi Chemical Corporation) as a black pigment and methyl methacrylate / butyl methacrylate / (2-methacrylamide-2,2-dimethyl) ethanesulfonic acid lithium salt copolymer as a resin having an acidic group ( (70/20/10 molar ratio) 200 parts by mass were pre-ground with a trioblender and mixed well, and then melt-kneaded (20 minutes) with a three-roll mill heated to 140 ° C. When the above pigment kneaded material was dispersed with a paint shaker (Toyo Seiki KK) for 120 minutes in the same manner as in Example 1, the volume average particle size of the pigment resin particles in the dispersion was 0.44 μm. Except that this kneaded product was diluted with Isopar G so that the pigment resin particle component was 4.0%, and 0.001 wt% of the reaction product of the exemplary compound (12) of the charge control agent was added. In the same manner, an ink composition (IJ-12) was prepared.
The obtained ink composition (IJ-12) had a viscosity of 1.4 cP, a surface tension of 23 mN / cm, an overall particle conductivity of 823 pS / cm, and the particle conductivity of the black resin particles was 781 pS / cm. . 90% or more of the charge amount of the ink composition was attached to the pigment resin particles, and showed a clear negative chargeability.
The specific conductivity of the ink composition after forced aging at 45 ° C. for one week and the particle conductivity of the pigment resin particles are 799 pS / cm and 757 pS / cm, respectively, and there is almost no change in the amount of charge, which is extremely stable. understood.
When the electrostatic ink jet drawing was carried out using the ink composition (IJR-12) in the same manner as in Example 1, the drawn image gave a clear image with a satisfactory density with a uniform dot without bleeding, and The ejection stability was also good, and stable dot-shaped printing was possible even for long-term continuous image drawing. In addition, the drawn image after forced aging at 45 ° C. for one week also gave a clear image of good quality with satisfactory density without bleeding, as before the forced aging of thermo.
[0103]
Comparative Example 4: Comparative ink composition (IJR-4)
In Example 12, a methyl methacrylate / butyl methacrylate copolymer (70/30 molar ratio) was used as a resin not having an acidic group instead of a resin having an acidic group, and the example compound (12) of the charge control agent was used. A comparative ink composition (IJR-4) was prepared in exactly the same manner as in Example 12 except that 0.05 g / liter of the reaction product was added. The viscosity of the comparative ink composition (IJR-4) was 1.4 cP, and the surface tension was 23 dyne / cm. The overall specific conductivity of the comparative ink composition (IJR-4) was 235 pS / cm, the particle conductivity of the black resin particles was 166 pS / cm, and the charge polarity by the comb electrode was negative. The total specific conductivity of the comparative ink composition (IJR-4) after forced aging at 45 ° C. for one week was 216 pS / cm, and the particle conductivity of the blue resin particles was 153 pS / cm, and the change in charge amount was small. .
[0104]
Next, when the electrostatic ink jet drawing was performed in the same manner as in Example 1 using the comparative ink composition (IJR-4), it was found that the drawn images after the initial and forced aging were blurred and the image density was low. . Further, since a discharge failure occurred in continuous image drawing for a long period of time, an image was missing and a satisfactory image could not be obtained.
From the result of Comparative Example 4 based on Example 12 and Example 8 described in JP-B-5-29904, it contains a resin having an acidic group insoluble in the non-aqueous solvent of the present invention and an amino acid compound. Only by the ink comprising the combination of charge control agents of the present invention, high color conductivity can be imparted to the colorant particles, and since there is no change in the charge amount over time, it is good for long-term electrostatic inkjet drawing It can be seen that it can be used. These specific effects cannot be predicted from the description of Japanese Patent Publication No. 5-29904.
[0105]
【The invention's effect】
In a non-aqueous solvent, comprising a coloring material insoluble in the non-aqueous solvent, a resin having an acidic group insoluble in the non-aqueous solvent, and a metal salt of an amino acid compound having a specific structure soluble in the non-aqueous solvent The electrostatic ink-jet ink composition of the present invention, the main component of which is a charge control agent, is an electrostatic ink jet head that is excellent in dispersion stability, charge polarity control and charge aging stability in a color material concentration discharge type electrostatic ink-jet head. An oil-based ink composition for an inkjet printer can be provided. In addition, it is possible to provide an oil-based ink composition for an electrostatic ink jet printer that can stably print dots with high density and little bleeding at high speed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of a line scanning type multi-channel inkjet head, and is a diagram illustrating a cross section of an ejection electrode corresponding to a recording dot.
FIG. 2 is a diagram of ejection electrodes as viewed from the recording medium side.

Claims (5)

A non-aqueous solvent having a relative dielectric constant of 1.5 to 20 and a surface tension of 15 to 60 mN / m (at 25 ° C.); a colorant insoluble in the non-aqueous solvent; a resin insoluble in the non-aqueous solvent; An ink composition for an electrostatic ink jet recording apparatus containing a charge control agent soluble in an aqueous solvent, wherein the resin insoluble in the non-aqueous solvent is a resin having an acidic group, and the charge control agent Contains at least one compound represented by the following general formula (1).

In the formula (1), R ¹ and R ² each represent a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, an acyl group, an alkylsulfonyl group or an arylsulfonyl group, and each may be substituted. R ¹ and R ² may be the same or different from each other, and R ¹ and R ² may form a ring. A represents an alkylene group. X represents a monovalent to tetravalent metal or a quaternary ammonium cation. n represents a positive integer from 1 to 4.
When X represents a metal, when the carboxylic acid is not bonded to the metal so as to satisfy the valence, the remaining valence may be saturated with another ligand. The volume resistivity at 25 ° C. of the ink composition is 10 ⁸ Ω · cm or more, and the particle conductivity of the colorant particles in the ink composition is 100 pS / cm or more. An electrostatic inkjet ink composition. Ink is introduced into a recording head in which a plurality of recording electrodes are arranged, voltage is applied to the recording electrodes, electrostatic force is applied to the ink, and ink droplets are ejected in a form in which color material particles are concentrated. 3. The electrostatic ink jet ink according to claim 1, wherein the ink jet ink is used for a color material concentration discharge type electrostatic ink jet recording apparatus for recording by forming print dots on a recording medium arranged to face each other. Composition. An ink composition is introduced into a recording head in which a plurality of recording electrodes are arranged, a voltage is applied to the recording electrodes, an electrostatic force is applied to the ink, and ink droplets fly in a form in which color material particles are concentrated. In the color material concentration discharge type electrostatic ink jet image forming method in which printing dots are formed on a recording medium arranged to face each other and recording is performed, the ink composition has a relative dielectric constant of 1.5 to 20. And a non-aqueous solvent having a surface tension of 15 to 60 mN / m (at 25 ° C.), a coloring material insoluble in the non-aqueous solvent, a resin having an acidic group insoluble in the non-aqueous solvent, and a solubility in the non-aqueous solvent An electrostatic inkjet image forming method comprising a charge control agent represented by the general formula (1) according to claim 1. 5. The volume resistivity at 25 ° C. of the ink composition is 10 ⁸ Ω · cm or more, and the particle conductivity of the colorant particles in the ink composition is 100 pS / cm or more. Electrostatic inkjet image forming method.

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