JP2004034441A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method, by which a bleeding resistance is enhanced and an even and high grade image can be stably formed with a recording material having a poor ink absorbency. <P>SOLUTION: In the image forming method, in which an ink having the viscosity at 25°C of at least 15 mPa s and being capable of curing under the exposure with light is jetted to a substrate by an inkjet recording system so as to form the image under the exposure with active light to the jetted ink, a means for controlling the viscosity of the ink down to not more than 12 mPa s by heating the ink up to at least 40°C before jetting is provided and the ink is irradiated by light under the condition that the viscosity of the ink is kept not more than 15 mPa s after the jetting of the ink to the substrate. <P>COPYRIGHT: (C)2004,JPO

Description

【００５２】
一般式（１）において、Ｒ^１は水素原子やメチル基、エチル基、プロピル基、ブチル基等の炭素数１〜６のアルキル基、炭素数１〜６のフルオロアルキル基、アリル基、アリール基、フリル基またはチエニル基である。Ｒ^２は、メチル基、エチル基、プロピル基、ブチル基等の炭素数１〜６個のアルキル基、１−プロペニル基、２−プロペニル基、２−メチル−１−プロペニル基、２−メチル−２−プロペニル基、１−ブテニル基、２−ブテニル基、３−ブテニル基等の炭素数２〜６個のアルケニル基、フェニル基、ベンジル基、フルオロベンジル基、メトキシベンジル基、フェノキシエチル基等の芳香環を有する基、エチルカルボニル基、プロピルカルボニル基、ブチルカルボニル基等の炭素数２〜６個のアルキルカルボニル基、エトキシカルボニル基、プロポキシカルボニル基、ブトキシカルボニル基等の炭素数２〜６個のアルコキシカルボニル基、またはエチルカルバモイル基、プロピルカルバモイル基、ブチルカルバモイル基、ペンチルカルバモイル基等の炭素数２〜６個のＮ−アルキルカルバモイル基等である。本発明で使用するオキセタン化合物としては、１個のオキセタン環を有する化合物を使用することが、得られる組成物が粘着性に優れ、低粘度で作業性に優れるため、特に好ましい。
【００５３】
２個のオキセタン環を有する化合物の一例としては、下記一般式（２）で示される化合物等が挙げられる。
【００５４】
【化２】

【００５５】
一般式（２）において、Ｒ^１は、上記一般式（１）におけるそれと同様の基である。Ｒ^３は、例えば、エチレン基、プロピレン基、ブチレン基等の線状または分枝状アルキレン基、ポリ（エチレンオキシ）基、ポリ（プロピレンオキシ）基等の線状または分枝状ポリ（アルキレンオキシ）基、プロペニレン基、メチルプロペニレン基、ブテニレン基等の線状または分枝状不飽和炭化水素基、またはカルボニル基またはカルボニル基を含むアルキレン基、カルボキシル基を含むアルキレン基、カルバモイル基を含むアルキレン基等である。
【００５６】
また、Ｒ^３としては、下記一般式（３）、（４）及び（５）で示される基から選択される多価基も挙げることができる。
【００５７】
【化３】

【００５８】
一般式（３）において、Ｒ^４は、水素原子やメチル基、エチル基、プロピル基、ブチル基等の炭素数１〜４個のアルキル基、メトキシ基、エトキシ基、プロポキシ基、ブトキシ基等の炭素数１〜４個のアルコキシ基、塩素原子、臭素原子等のハロゲン原子、ニトロ基、シアノ基、メルカプト基、低級アルキルカルボキシル基、カルボキシル基、またはカルバモイル基である。
【００５９】
【化４】

【００６０】
一般式（４）において、Ｒ^５は、酸素原子、硫黄原子、メチレン基、ＮＨ、ＳＯ、ＳＯ_２、Ｃ（ＣＦ_３）_２、又はＣ（ＣＨ_３）_２を表す。
【００６１】
【化５】

【００６２】
一般式（５）において、Ｒ^６は、メチル基、エチル基、プロピル基、ブチル基等の炭素数１〜４個のアルキル基、またはアリール基である。ｎは０〜２０００の整数である。Ｒ^７はメチル基、エチル基、プロピル基、ブチル基の炭素数１〜４個のアルキル基、またはアリール基である。Ｒ^７としては、更に、下記一般式（６）で示される基から選択される基も挙げることができる。
【００６３】
【化６】

【００６４】
一般式（６）において、Ｒ^８は、メチル基、エチル基、プロピル基、ブチル基等の炭素数１〜４個のアルキル基、またはアリール基である。ｍは０〜１００の整数である。
【００６５】
２個のオキセタン環を有する化合物の具体例としては、下記化合物が挙げられる。
【００６６】
【化７】

【００６７】
例示化合物１は、前記一般式（２）において、Ｒ^１がエチル基、Ｒ^３がカルボキシル基である化合物である。また、例示化合物２は、前記一般式（２）において、Ｒ^１がエチル基、Ｒ^３が前記一般式（５）でＲ^６及びＲ^７がメチル基、ｎが１である化合物である。
【００６８】
２個のオキセタン環を有する化合物において、上記の化合物以外の好ましい例としては、下記一般式（７）で示される化合物がある。一般式（７）において、Ｒ^１は、前記一般式（１）のＲ^１と同義である。
【００６９】
【化８】

【００７０】
また、３〜４個のオキセタン環を有する化合物の一例としては、下記一般式（８）で示される化合物が挙げられる。
【００７１】
【化９】

【００７２】
一般式（８）において、Ｒ^１は、前記一般式（１）におけるＲ^１と同義である。Ｒ^９としては、例えば、下記Ａ〜Ｃで示される基等の炭素数１〜１２の分枝状アルキレン基、下記Ｄで示される基等の分枝状ポリ（アルキレンオキシ）基又は下記Ｅで示される基等の分枝状ポリシロキシ基等が挙げられる。ｊは、３又は４である。
【００７３】
【化１０】

【００７４】
上記Ａにおいて、Ｒ^１０はメチル基、エチル基又はプロピル基等の低級アルキル基である。また、上記Ｄにおいて、ｐは１〜１０の整数である。
【００７５】
３〜４個のオキセタン環を有する化合物の一例としては、例示化合物３が挙げられる。
【００７６】
【化１１】

【００７７】
さらに、上記説明した以外の１〜４個のオキセタン環を有する化合物の例としては、下記一般式（９）で示される化合物が挙げられる。
【００７８】
【化１２】

【００７９】
一般式（９）において、Ｒ^８は前記一般式（６）のＲ^８と同義である。Ｒ^１１はメチル基、エチル基、プロピル基又はブチル基等の炭素数１〜４のアルキル基又はトリアルキルシリル基であり、ｒは１〜４である。
【００８０】
本発明で使用するオキセタン化合物の好ましい具体例としては、以下に示す化合物がある。
【００８１】
【化１３】

【００８２】
上述したオキセタン環を有する各化合物の製造方法は、特に限定されず、従来知られた方法に従えばよく、例えば、パティソン（Ｄ．Ｂ．Ｐａｔｔｉｓｏｎ，Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．，３４５５，７９（１９５７））が開示している、ジオールからのオキセタン環合成法等がある。また、これら以外にも、分子量１０００〜５０００程度の高分子量を有する１〜４個のオキセタン環を有する化合物も挙げられる。これらの具体的化合物例としては、以下の化合物が挙げられる。
【００８３】
【化１４】

【００８４】
本発明においては、インク硬化の際の記録材料の収縮を抑える目的で、光重合性化合物として少なくとも１種のオキセタン化合物と、エポキシ化合物及びビニルエーテル化合物から選ばれる少なくとも１種の化合物とを含有することが好ましい。
【００８５】
カチオン重合型インクで用いる開始剤としては、例えば、化学増幅型フォトレジストや光カチオン重合に利用される化合物が用いられる（有機エレクトロニクス材料研究会編、「イメージング用有機材料」、ぶんしん出版（１９９３年）、１８７〜１９２ページ参照）。本発明に好適な化合物の例を以下に挙げる。
【００８６】
第１に、ジアゾニウム、アンモニウム、ヨードニウム、スルホニウム、ホスホニウムなどの芳香族オニウム化合物のＢ（Ｃ_６Ｆ_５）_４ ⁻，ＰＦ_６ ⁻，ＡｓＦ_６ ⁻，ＳｂＦ_６ ⁻，ＣＦ_３ＳＯ_３ ⁻塩を挙げることができる。対アニオンとしてボレート化合物をもつものが酸発生能力が高く好ましい。オニウム化合物の具体的な例を以下に示す。
【００８７】
【化１５】

【００８８】
第２に、スルホン酸を発生するスルホン化物を挙げることができる。具体的な化合物を以下に例示する。
【００８９】
【化１６】

【００９０】
第３に、ハロゲン化水素を発生するハロゲン化物も用いることができる。以下に具体的な化合物を例示する。
【００９１】
【化１７】

【００９２】
第４に、鉄アレン錯体を挙げることができる。
【００９３】
【化１８】

【００９４】
本発明に係るインクには、上記説明した構成要素の他に、各種の添加剤を用いることができる。
【００９５】
本発明においては、吐出安定性、保存性を向上させる目的で、熱塩基発生剤も用いることができる。
【００９６】
熱塩基発生剤としては、例えば、加熱により脱炭酸して分解する有機酸と塩基の塩、分子内求核置換反応、ロッセン転位、ベックマン転位等の反応により分解してアミン類を放出する化合物や、加熱により何らかの反応を起こして塩基を放出するものが好ましく用いられる。具体的には、英国特許第９９８，９４９号記載のトリクロロ酢酸の塩、米国特許第４，０６０，４２０号に記載のアルファースルホニル酢酸の塩、特開昭５９−１５７６３７号に記載のプロピール酸類の塩、２−カルボキシカルボキサミド誘導体、特開昭５９−１６８４４０号に記載の塩基成分に有機塩基の他にアルカリ金属、アルカリ土類金属を用いた熱分解性酸との塩、特開昭５９−１８０５３７号に記載のロッセン転位を利用したヒドロキサムカルバメート類、加熱によりニトリルを生成する特開昭５９−１９５２３７号に記載のアルドキシムカルバメート類等が挙げられる。その他、英国特許第９９８，９４５号、米国特許第３，２２０，８４６号、英国特許第２７９，４８０号、特開昭５０−２２６２５号、同６１−３２８４４号、同６１−５１１３９号、同６１−５２６３８号、同６１−５１１４０号、同６１−５３６３４号〜同６１−５３６４０号、同６１−５５６４４号、同６１−５５６４５号等に記載の熱塩基発生剤が有用である。更に具体的に例を挙げると、トリクロロ酢酸グアニジン、トリクロロ酢酸メチルグアニジン、トリクロロ酢酸カリウム、フェニルスルホニル酢酸グアニジン、ｐ−クロロフェニルスルホニル酢酸グアニジン、ｐ−メタンスルホニルフェニルスルホニル酢酸グアニジン、フェニルプロピオール酸カリウム、フェニルプロピオール酸グアニジン、フェニルプロピオール酸セシウム、ｐ−クロロフェニルプロピオール酸グアニジン、ｐ−フェニレン−ビス−フェニルプロピオール酸グアニジン、フェニルスルホニル酢酸テトラメチルアンモニウム、フェニルプロピオール酸テトラメチルアンモニウムがある。上記の熱塩基発生剤は広い範囲で用いることができる。
【００９７】
本発明のインクは、特開平８−２４８５６１号、同９−３４１０６号をはじめとし、既に公知となっている活性光線の照射で発生した酸により新たに酸を発生する酸増殖剤を含有することも可能である。
【００９８】
請求項６に係る発明においては、インクの２５℃における表面張力が、２５〜４０ｍＮ／ｍの範囲にあることが好ましい。２５℃におけるインクの表面張力が２５ｍＮ／ｍ未満では、安定した出射が得られにくく、また４０ｍＮ／ｍを越えると所望のドット径を得ることができない。２５〜４０ｍＮ／ｍの範囲外では、本発明のように、インクの粘度や含水率を制御しながら出射、光照射しても、様々な支持体に対して均一なドット径を得ることが困難となる。
【００９９】
表面張力を調整するために、必要に応じて、界面活性剤を含有させてもよい。本発明に係るインクに好ましく使用される界面活性剤としては、例えば、ジアルキルスルホコハク酸塩類、アルキルナフタレンスルホン酸塩類、脂肪酸塩類等のアニオン性界面活性剤、ポリオキシエチレンアルキルエーテル類、ポリオキシエチレンアルキルアリルエーテル類、アセチレングリコール類、ポリオキシエチレン・ポリオキシプロピレンブロックコポリマー類等のノニオン性界面活性剤、アルキルアミン塩類、第４級アンモニウム塩類等のカチオン性界面活性剤、重合性基を有する界面活性化合物などが挙げられる。これらの中で特に、シリコーン変性アクリレート、フッ素変性アクリレート、シリコーン変性エポキシ、フッ素変性エポキシ、シリコーン変性オキセタン、フッ素変性オキセタンなど、不飽和結合やオキシラン、オキセタン環など重合性基を有する界面活性化合物が好ましい。
【０１００】
本発明に係るインクには、上記説明した以外に様々な添加剤を用いることができる。例えば、レベリング添加剤、マット剤、膜物性を調整するためのポリエステル系樹脂、ポリウレタン系樹脂、ビニル系樹脂、アクリル系樹脂、ゴム系樹脂、ワックス類を添加することが出来る。記録媒体との密着性を改善するため、極微量の有機溶剤を添加することも有効である。この場合、耐溶剤性やＶＯＣの問題が起こらない範囲での添加が有効であり、その使用量は０．１〜５％の範囲であり、好ましくは０．１〜３％である。また、ラジカル重合性モノマーと開始剤を組み合わせ、ラジカル・カチオンのハイブリッド型硬化インクとすることも可能である。
【０１０１】
本発明の画像形成方法においては、インク組成物をインクジェット記録方式により記録材料上に吐出、描画し、次いで紫外線などの活性光線を照射してインクを硬化させる。
【０１０２】
本発明において、インクが着弾し、活性光線を照射して硬化した後の総インク膜厚が２〜２０μｍであることが好ましい。スクリーン印刷分野の活性光線硬化型インクジェット記録では、総インク膜厚が２０μｍを越えているのが現状であるが、記録材料が薄いプラスチック材料であることが多い軟包装印刷分野では、前述した記録材料のカール・しわの問題でだけでなく、印刷物全体のこし・質感が変わってしまうという問題が有るため使えない。また、本発明では、各ノズルより吐出する液滴量が２〜１５ｐｌであることが好ましい。
【０１０３】
本発明の画像記録方法においては、発生光線の照射条件として、インク着弾後０．００１〜２．０秒の間に活性光線が照射されることが好ましく、より好ましくは０．００１〜１．０秒である。高精細な画像を形成するためには、照射タイミングができるだけ早い方が好ましいが、本発明においては、インクの粘度または含水率が好ましい状態となるタイミングで光照射を開始することが好ましい。
【０１０４】
活性光線の照射方法として、その基本的な方法が特開昭６０−１３２７６７号に開示されている。これによると、記録ヘッドユニットの両側に光源を設け、シャトル方式で記録ヘッドと光源を走査する。照射は、インク着弾後、一定時間を置いて行われることになる。更に、駆動を伴わない別光源によって硬化を完了させる。米国特許第６，１４５，９７９号では、照射方法として、光ファイバーを用いた方法や、コリメートされた光源を記録ヘッドユニット側面に設けた鏡面に当て、記録部へＵＶ光を照射する方法が開示されている。本発明の画像形成方法においては、これらのいずれの照射方法も用いることができる。
【０１０５】
また、活性光線を照射を２段階に分け、まずインク着弾後０．００１〜２．０秒の間に前述の方法で活性光線を照射し、かつ、全印字終了後、更に活性光線を照射する方法も好ましい態様の１つである。活性光線の照射を２段階に分けることで、よりインク硬化の際に起こる記録材料の収縮を抑えることが可能となる。
【０１０６】
活性光線照射で用いる光源の例としては、高圧水銀ランプ、メタルハライドランプ、無電極ＵＶランプ、低圧水銀ランプ、ＵＶレーザー、キセノンフラッシュランプ、捕虫灯、ブラックライト、殺菌灯、冷陰極管、ＬＥＤをなどがあるが、これらに限定されない。
【０１０７】
また、本発明では、硬化に有効な波長域におけるピーク照度が０．１ｍＷ／ｃｍ^２以上、３０００ｍＷ／ｃｍ^２以下の活性光線を用いる。
【０１０８】
本発明で用いることのできる基材としては、通常の非コート紙、コート紙などの他に、非吸収性支持体を用いることができるが、その中でも、請求項４に係る発明においては、基材として非吸収性支持体を用いることが好ましい。
【０１０９】
本発明においては、非吸収性支持体としては、各種非吸収性のプラスチックおよびそのフィルムを用いることができ、各種プラスチックフィルムとしては、例えば、ＰＥＴフィルム、ＯＰＳフィルム、ＯＰＰフィルム、ＯＮｙフィルム、ＰＶＣフィルム、ＰＥフィルム、ＴＡＣフィルムを挙げることができる。その他のプラスチックとしては、ポリカーボネート、アクリル樹脂、ＡＢＳ、ポリアセタール、ＰＶＡ、ゴム類などが使用できる。また、金属類や、ガラス類にも適用可能である。これらの記録材料の中でも、特に熱でシュリンク可能な、ＰＥＴフィルム、ＯＰＳフィルム、ＯＰＰフィルム、ＯＮｙフィルム、ＰＶＣフィルムへ画像を形成する場合に本発明の構成は、有効となる。これらの基材は、インクの硬化収縮、硬化反応時の発熱などにより、フィルムのカール、変形が生じやすいばかりでなく、インク膜が基材の収縮に追従し難い。
【０１１０】
これら、各種プラスチックフィルムの表面エネルギーは大きく異なり、記録材料によってインク着弾後のドット径が変わってしまうことが、従来から問題となっていた。本発明の構成では、表面エネルギーの低いＯＰＰフィルム、ＯＰＳフィルムや表面エネルギーの比較的大きいＰＥＴまでを含むが、請求項５に係る発明においては、基材として、濡れ指数が４０〜６０ｍＮ／ｍであることが好ましい。
【０１１１】
本発明でいう濡れ指数とは、表面張力が順を追って異なるような一連の混合液体を基材表面に塗設して、ちょうど基材表面を濡らすと判定された混合液体の表面張力（ｍＮ／ｍ）の値を、濡れ指数と定義し、具体的には「ポリエチレンおよびポリプロピレンフィルムのぬれ試験方法」（ＪＩＳ　Ｋ　６７６８）に準じて測定して、求めることができる。
【０１１２】
本発明において、包装の費用や生産コスト等の記録材料のコスト、プリントの作成効率、各種のサイズのプリントに対応できる等の点で、長尺（ウェブ）な記録材料を使用する方が有利である。
【０１１３】
【実施例】
実施例により本発明をさらに具体的に説明するが、本発明はこれら実施例における形態に限定されるものではない。
【０１１４】
実施例１
《インクの調製》
（シアン顔料分散物の調製）
下記に記載の方法に従って、シアン顔料分散物を調製した。なお、分散条件は、シアン顔料粒子の平均粒径が０．２〜０．３μｍの範囲となるように、公知の分散装置を用いて、分散条件を適宜調整して行い、次いで加熱下でフィルター濾過を行って調製した。
【０１１５】
Ｃ．Ｉ．ピグメントブルー１５：３　　　　　　　　　　　　　１５質量部
高分子分散剤（Ｚｅｎｅｃａ社製　Ｓｏｌｓｐｅｒｓｅシリーズ）２質量部
アロンオキセタンＯＸＴ−２２１（東亜合成社製）　　　　　　８３質量部
（シアンインクの調製）
上記調製したシアン顔料分散物を用いて、下記に記載の方法に従いシアンインクを調製した。
【０１１６】
シアン顔料分散物　　　　　　　　　　　　　　　　　　　　　１７質量部
アロンオキセタンＯＸＴ−２２１（東亜合成社製）　　　　　　４８質量部
セロキサイド２０２１Ｐ（ダイセルＵＣＢ社製）　　　　　　　３０質量部
ＳＰ−１５２（旭電化社製　光酸発生剤）　　　　　　　　　　　５質量部
以上の様にして調製したシアンインクを絶対ろ過精度０．８μｍのメンブランフィルターにてろ過した後、シアンインクを５０℃に加熱ながら減圧処理を行って脱水して、シアンインクを調製した。
【０１１７】
上記調製したシアンインクの２５℃における粘度は２５．４ｍＰａ・ｓ、表面張力は３４．８ｍＮ／ｍ、含水率は１．０質量％（カールフィッシャー法にて測定）であった。また、２３℃、８０％ＲＨの雰囲気下で２４時間調湿させた後の含水率は２．１質量％であり、本発明ではこれを平衡含水率と定義した。
【０１１８】
《インクジェット画像記録》
上記調製したシアンインクを用いて、下記に記載の画像形成方法１、画像形成方法２に従って画像記録を行った。
【０１１９】
（画像形成方法１）
室内環境として、１５℃、３０％ＲＨの雰囲気下と３０℃、７０％ＲＨの雰囲気下で、ピエゾ型インクジェットノズル（ノズルピッチ３６０ｄｐｉ）を有するインクジェット記録装置を用いて、基材への記録を行った。インク供給系は、元タンク、供給配管、インクジェットヘッド直前のインク供給タンク、フィルター、ピエゾ型のインクジェットヘッドから成り、インク供給タンクからインクジェットヘッド部分までと基材搬送部について、それぞれ断熱および加熱を行った。温度センサーは、インク供給タンクおよびインクジェットヘッドのノズル付近および基材搬送部にそれぞれ設けて温度制御を行った。ピエゾ型のインクジェットヘッドにより、インク液滴サイズ７ｐｌとし、シングルサイズドットおよび７２０×７２０ｄｐｉの解像度でベタ画像を射出した。なお、インク射出の際には、ノズル毎にインクを５０℃まで加熱して、インク粘度を８．２ｍＰａ・ｓとした。基材としては、コロナ放電処理を施したＯＰＰ（ｏｒｉｅｎｔｅｄ　ｐｏｌｙｐｒｏｐｙｌｅｎｅ）フィルム、コロナ放電処理を施したＰＥＴ（ｐｏｌｙｅｔｈｌｅｎｅ　ｔｅｒｅｐｈｔｈａｌａｔｅ）フィルムを使用した。なお、ＯＰＰフィルムの濡れ指数は４２ｍＮ／ｍ、ＰＥＴフィルムの濡れ指数は５５ｍＮ／ｍであった。なお、本発明でいうｄｐｉとは、２．５４ｃｍ当たりのドット数を表す。
【０１２０】
各インクを基材上へ着弾した後、インク粘度が１５ｍＰａ・ｓを越えない様に、基材搬送部のヒートプレート条件を適宜制御して、基材温度を３０℃にコントロールした。３０℃におけるこのインクの粘度は、１３．９ｍＰａ・ｓである。
【０１２１】
次いで、着弾したインクに光照射を行った。光照射光源は、高圧水銀ランプ（ウシオ社製、ＳＰ５）から光ファイバーにより、インク着弾画像部に照射されるように配置し、ピーク波長は３６５ｎｍ、露光照度は１００ｍＷ／ｃｍ^２である。光照射は、インク液滴が着弾してから１００ｍｓ後に開始し、２００ｍｓの時間照射して、インクを硬化させた。これは、照射エネルギーとして２０ｍＪ／ｃｍ^２に相当する。
【０１２２】
インク着弾後、１００ｍｓの時間を経過した場合には、基材に接しているインクの温度がほぼ基材の温度と等しくなることから、光照射時のインクの粘度は、基材とほぼ同じ温度におけるインク粘度となる。
【０１２３】
画像形成方法１における各特性値をまとめて以下に示す。
２５℃におけるインク粘度：２５．４ｍＰａ・ｓ
射出前のインク粘度：８．２ｍＰａ・ｓ
基材の濡れ指数：ＯＰＰ＝４２ｍＮ／ｍ、ＰＥＴ＝５５ｍＮ／ｍ
光照射時のインク粘度：１３．９ｍＰａ・ｓ（室内環境１５℃、３０％ＲＨ、３０℃、７０％ＲＨ共）
（画像形成方法２）
上記画像形成方法１において、インク着弾の際に基材温度を３０℃に制御しないで行った以外は同様にして、画像形成を行った。
【０１２４】
画像形成方法２における各特性値をまとめて以下に示す。
２５℃におけるインク粘度：２５．４ｍＰａ・ｓ
射出前のインク粘度：８．２ｍＰａ・ｓ
基材の濡れ指数：ＯＰＰ＝４２ｍＮ／ｍ、ＰＥＴ＝５５ｍＮ／ｍ
基材着弾後のインク粘度：２６．８ｍＰａ・ｓ（室内環境１５℃、３０％ＲＨ）、１６．４ｍＰａ・ｓ（室内環境３０℃、７０％ＲＨ）
《形成画像の評価》
以上のようにして作成した各画像について、下記の方法に従って各評価を行った。
【０１２５】
（着弾インクのドット径の測定）
上記作成したシングルサイズドットについて、ドット径を画像解析装置（ニレコ製、ルーゼックス、測定条件：画素数１６０００、１画素）により求め、５０回測定した平均値を求め、これをドット径とした。
【０１２６】
（表面凹凸感の評価）
上記作成したベタ画像表面を、目視および触感による観察を行い、下記の基準に則り表面凹凸感の評価を行った。
【０１２７】
○：目視および触感の観察で、表面の凹凸が殆ど気にならない
△：目視観察では表面の凹凸は気にならないが、触感では表面の凹凸がやや気になるが、実用上許容される品質である
×：目視および触感の観察で、表面の凹凸によるザラツキ感が明らかに認めら、実用上好ましくない品質である
（滲み耐性の評価）
上記作成したシングルサイズドットおよびベタ画像を目視観察し、下記の基準に則り滲み耐性の評価を行った。
【０１２８】
○：シングルサイズドットが真円を保ち、またベタ画像境界線の乱れもなく、滲みは認められない
△：シングルサイズドットの真円度のくずれ及びベタ画像境界線の乱れがやや認められるが、実用上許容される品質である
×：シングルサイズドットの真円度のくずれ及びベタ画像境界線の乱れが明らかに認められ、実用上好ましくない品質である
以上により得られた結果を、表１に示す。
【０１２９】
【表１】

【０１３０】
表１より明らかなように、光照射時のインク粘度を１５ｍＰａ・ｓ以下として光照射を開始した本発明の画像形成方法で得られた画像は、異なる基材や異なる印字環境下でも、ドット径や凹凸などの質感が良好で、かつ滲みの少ない画質が得られることが分かる。なお、上記画像形成方法１では、照射時のインク粘度の制御を基材からの熱伝導と着弾から露光開始までの時間を制御することにより行ったが、インクのみを別の手段で加熱制御したり、インクを加熱制御することなく、出射時におけるインクの温度を調整することにより着弾・冷却後の粘度を調整する方法や露光開始までの時間を制御することで、着弾インクの冷却・増粘の度合いを制御する方法をとっても同様の効果を得ることができる。
【０１３１】
実施例２
実施例１に記載のインクジェット画像記録において、画像形成方法１、２に代えて、下記画像形成方法３、４を用いた以外は同様にして、画像形成を行った。
【０１３２】
《インクの調製》
実施例１と同様に、インクの含水率が１．０質量％（カールフィッシャー法にて測定）であるシアンインクを用いた。
【０１３３】
《インクジェット画像記録》
（画像形成方法３）
実施例１に記載の画像形成方法２において、基材上にインクの含水率を２．１質量％に調整したインク液滴を着弾させた後、その画像形成部に相対湿度２０％の空気を吹き付けながら、着弾したインクに光照射を行った以外は同様にして画像形成を行った。
【０１３４】
なお、湿度２０％におけるこのインクの含水率は、０．４質量％であり、含水率１．０％に調整されたインクは着弾後、脱水による湿度変動が起こるが、含水率が１．７％以下の範囲から外れることはない。
【０１３５】
画像形成方法３における各特性は、以下の通りであった。
インクの相対湿度８０％における平衡含水率：２．１質量％
出射前のインクの含水率：１．０質量％
光照射時のインクの含水率：０．４〜１．０質量％（室内環境１５℃、３０％ＲＨ、３０℃、７０％ＲＨともに）
（画像形成方法４）
上記の画像形成方法３において、基材上にインク液滴を着弾させた後、その画像形成部に相対湿度２０％の空気を吹き付けないで、着弾したインクに光照射を行った以外は同様にして画像形成を行った。
【０１３６】
画像形成方法４における各特性は、以下の通りであった。
インクの相対湿度８０％における平衡含水率：２．１質量％
出射前のインクの含水率：１．０質量％
光照射時のインクの含水率：１．０質量％未満（室内環境１５℃、３０％ＲＨ）、１．９質量％（室内環境３０℃、７０％ＲＨ）
なお、上記に記載の室内環境３０℃、７０％ＲＨにおける光照射時の含水率の算出は、まず、光照射後のドット径変化が起こらなくなる感度を算出しておく。次いで、インクをワイヤーバーにて基材に塗布し、環境湿度を変化させ、光照射を行い、算出した露光感度と等しくなる湿度環境を求める。露光感度と等しくなる環境にてインクの平衡含水率を求め、着弾、露光時の含水率を推定した。我々の検討では、インク射出後、僅か５０〜２５０ｍｓの短時間で環境の含水率に等しくなることが確認された。
【０１３７】
《形成画像の評価》
以上のようにして作成した各画像について、実施例１に記載の方法と同様にして着弾インクのドット径の測定、表面凹凸感の評価及び滲み耐性の評価を行い、得られた結果を、表２に示す。
【０１３８】
【表２】

【０１３９】
表２より明らかなように、インク含水率が０．２〜２％である条件で、光照射を開始する本発明の画像形成方法で形成した画像は、異なる基材・異なる環境下でも、ドット径、凹凸などの質感が良好で、かつ滲み耐性に優れた画質を得ることができた。なお、画像形成方法３では、照射時のインク含水率の制御を調湿された空気を画像形成部に送ることと着弾から露光開始までの時間を制御することにより行ったが、着弾インクが外部環境に応じて吸水或いは脱水した後の含水率の差が少なくなるように、出射時におけるインクの含水率を調整する手法、露光開始までの時間を制御することで、着弾インクの吸水或いは脱水の度合いを制御する方法をとっても同様の効果を得ることができる。
【０１４０】
【発明の効果】
本発明により、インク吸収性の乏しい記録材料に対し、滲み耐性に優れ、凹凸感のない高画像を安定して形成することができる画像形成方法を提供することができた。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming method in which visible light, ultraviolet light, infrared light, γ-rays, and irradiating an electron beam are used to form an image by an ink jet recording method using a photocurable ink that can be reacted and cured, and that the light is fixed. In particular, the present invention relates to an image forming method capable of obtaining a high-quality image without bleeding or unevenness on a substrate having poor ink absorption.
[0002]
[Prior art]
In recent years, the ink jet recording method has been applied to various printing fields such as photographs, various printings, special printings such as markings and color filters, since images can be easily and inexpensively formed. In particular, a recording device that emits and controls fine dots, and ink with improved color gamut, durability, ejection suitability, etc., ink absorptivity, coloring of coloring materials, surface gloss, etc. have been dramatically improved. Using special paper, it is also possible to obtain image quality comparable to silver halide photography. Improvement in image quality of today's ink jet recording system has been achieved only when all of the recording device, ink, and special paper are provided.
[0003]
However, an ink jet system that requires special paper has a problem that the recording medium is limited and the cost of the recording medium is increased. Therefore, many attempts have been made to perform recording on a transfer-receiving medium different from dedicated paper by an inkjet method. Specifically, a phase-change inkjet method using a wax ink that is solid at room temperature, a solvent-based inkjet method using a fast-drying organic solvent-based ink, and a UV inkjet method that performs crosslinking by ultraviolet (UV) light after recording. It is.
[0004]
Above all, the UV inkjet system has been attracting attention in recent years in that it has a relatively low odor compared to the solvent-based inkjet system, and is capable of recording on a recording medium that is quick drying and has no ink absorption. JP-A-54667, JP-A-6-200204, and JP-T-2000-504778 disclose an ultraviolet-curable inkjet ink.
[0005]
However, even when these inks are used, the dot diameter after landing greatly changes depending on the type of recording material and the working environment, and it is difficult to form high-definition images on various recording materials. It is.
[0006]
As a UV ink, a radical polymerization type and a cationic polymerization type are mainly known. In the ultraviolet curing ink jet recording method, the image quality, that is, the landing dot diameter, the light irradiation timing after landing, light irradiation illuminance, energy, ink droplet size, ink sensitivity, surface energy, viscosity, substrate wettability, It is controlled by factors such as the landing arrangement and the error diffusion pattern. In particular, factors that greatly affect the image quality include ink sensitivity, viscosity, surface area, substrate wettability, and exposure conditions. Among them, the ink sensitivity is greatly affected by the ink film thickness and the exposure illuminance because of the influence of polymerization inhibition by oxygen in the case of the radical polymerization system, and greatly depends on the temperature and humidity in the cationic polymerization system.
[0007]
In the case of radical polymerization type ultraviolet curable ink, in order to improve polymerization inhibition by oxygen, a method of purifying monomers, initiators and initiation aids which are not subject to oxygen inhibition, or purging with an inert gas such as nitrogen is used. Are known.
[0008]
As for the cationic polymerization type ultraviolet curable ink, a method of heating the landed ink is known as disclosed in JP-A-2002-137375 in order to improve the influence of humidity dependency.
[0009]
In the ultraviolet curing type ink jet recording method, since the volume does not decrease even when the ink is cured, unevenness is generated on a substrate having poor ink absorption, and there is a defect that the texture is impaired. It is necessary to cure the ink in a state where it is leveled, and from the viewpoint of being able to record on various substrates, which is a feature of the ultraviolet curable ink jet recording method, the same image quality (dot) Diameter) is desired.
[0010]
As a means for obtaining the same image quality even for different base materials as described above, there is a method of setting the timing of light irradiation, intensity, etc. for each base material, but these methods alone are not necessarily sufficient. . In other words, when individually setting conditions, for the light source to be used, there are restrictions on the device such as cost, arrangement space, etc., and the wettability, heat conductivity, etc. differ for each base material. It is very difficult to uniformly obtain high-quality images on various supports, and in fact, it was necessary to prepare inks having different physical properties depending on the base material.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image capable of stably forming a high image having excellent bleeding resistance and no unevenness on a recording material having poor ink absorption. It is to provide a forming method.
[0012]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following configurations.
[0013]
In an image forming method, an ink which has a viscosity at 1.25 ° C. of 15 mPa · s or more and is curable by light irradiation is jetted to a base material using an ink jet recording method, and then irradiated with actinic rays to form an image. Having means for controlling the viscosity of the ink to 12 mPa · s or less by heating the ink to 40 ° C. or higher before jetting, and the viscosity of the ink after the ink is jetted to the base material. An image forming method comprising irradiating light when the pressure is 15 mPa · s or less.
[0014]
2. Injecting an ink curable by light irradiation with an equilibrium water content of 1.5% or more as measured by the Karl Fischer method at a relative humidity of 80% onto a substrate using an ink jet recording method, and then irradiating with an actinic ray In the image forming method for forming an image by the method, the ink is jetted in a state where the water content of the ink is 1.5% or less, and after the ink is jetted to the base material, the water content of the ink is 1.7% or less. An image forming method comprising irradiating light at a certain time.
[0015]
3. The ink has a viscosity at 25 ° C. of 15 mPa · s or more, and has a means for controlling the viscosity of the ink to 12 mPa · s or less by heating the ink to 40 ° C. or more before jetting. 3. The image forming method according to claim 2, wherein, after the ink is ejected onto a substrate, the ink is irradiated when the viscosity of the ink is 15 mPa · s or less.
[0016]
4. 4. The image forming method according to any one of items 1 to 3, wherein the substrate is a non-absorbable support that does not absorb ink.
[0017]
5. The image forming method according to any one of Items 1 to 4, wherein the substrate has a wetting index of 40 to 60 mN / m.
[0018]
6. The image forming method according to any one of Items 1 to 5, wherein a surface tension of the ink at 25 ° C. is 25 to 40 mN / m.
[0019]
7. 7. The image forming method according to any one of items 1 to 6, wherein the ink contains a cationically polymerizable compound.
[0020]
8. 8. The image forming method according to any one of items 1 to 7, wherein the ink contains a cationically polymerizable monomer having an oxetane group.
[0021]
Hereinafter, details of the present invention will be described.
In the invention according to the first aspect, an image having a viscosity at 25 ° C. of 15 mPa · s or more, which is curable by light irradiation, is jetted to a base material using an ink jet recording method, and then irradiated with actinic rays to form an image. In the image forming method, the ink is heated to 40 ° C. or higher before jetting, thereby having means for controlling the viscosity of the ink to 12 mPa · s or lower, and the ink is jetted to the base material. Thereafter, light irradiation is performed when the viscosity of the ink is 15 mPa · s or less.
[0022]
The actinic radiation-curable ink has a higher viscosity than ordinary aqueous inkjet inks in order to obtain favorable sensitivity and physical properties. The actinic ray-curable ink does not allow stable ejection of the ink as it is, so that by heating, the viscosity can be reduced and favorable ejection suitability can be obtained. In the present invention, an ink having a viscosity of 15 mPa · s or more at 25 ° C., preferably 15 to 100 mPa · s, is heated to 40 ° C. or more, so that the viscosity of the ink is 12 mPa · s or less, preferably It is controlled to 3 to 12 mPa · s. The means for controlling the viscosity of the ink to 12 mPa · s or less is not particularly limited, but measures the relationship between the viscosity and the temperature of the ink to be used in advance, measures the ink temperature based on the relational expression, Alternatively, the temperature of the ink may be controlled by a cooling body so as to have a predetermined viscosity.
[0023]
After the ink heated by the above method lands on the substrate, it is cooled by the ambient temperature or the substrate, but in the present invention, the ink viscosity is controlled to a range of 12 mPa · s or less before ejection, and After the ink is ejected, the ink is exposed to the external environment, the temperature of the ink is lowered or raised, and the viscosity fluctuates.In order to prevent the wettability to the base material from fluctuating, the ink viscosity is preferably 15 mPas or less, preferably In the state of 6 to 15 mPa · s, it has been found that by starting light irradiation for ink curing, the dot diameter can be stabilized without depending on the environmental temperature. It is.
[0024]
When exposure is started under an ink viscosity condition exceeding 15 mPa · s, when an image is formed on a different support, the difference in dot diameter is large, and unevenness occurs in terms of unevenness, density, and the like. In such an image forming method, it is necessary to prepare inks having different physical properties for each type of the support.
[0025]
In the invention according to claim 2, an ink which has an equilibrium water content of 1.5% or more as measured by the Karl Fischer method at a relative humidity of 80% and is curable by light irradiation is jetted onto a base material using an ink jet recording system. Then, in an image forming method of forming an image by irradiating an actinic ray, the ink is jetted in a state where the water content of the ink is 1.5% or less, and after the ink is jetted to a base material, It is characterized in that light irradiation is performed when the water content is 1.7% or less.
[0026]
In the actinic radiation curable ink, it is important to control the water content of the ink in order to obtain storage stability in a heated state and long-term emission stability as described above. In particular, in a cationic polymerization type ink in which the sensitivity level greatly fluctuates depending on the humidity, the obtained sensitivity is greatly affected by the humidity at the time of exposure, so that the humidity atmosphere at the time of printing affects the dot diameter and is obtained. This causes a problem that the image quality fluctuates.
[0027]
The present inventor has conducted intensive studies in view of the above problems, and as a result, has been found that the light irradiation is performed at an equilibrium water content of 1.5% or more, preferably 1.5 to 4.0%, as measured by the Karl Fischer method at a relative humidity of 80%. A curable ink is jetted onto a substrate using an ink jet recording method, and the water content of the ink is controlled to 1.5% or less, preferably 0.2 to 1.5% or less before ejection, and In order to prevent the ink from being exposed to the external environment after the ink is ejected and changing the sensitivity due to water absorption or dehydration, the water content is preferably in the range of 1.7 to 1.7%, preferably 0.2 to 1.7. It has been found that by starting light irradiation when the water content is%, the dot diameter can be stabilized without depending on the environmental humidity, and the present invention has been reached.
[0028]
Further, in the invention according to claim 3, as an actinic ray-curable ink, an actinic ray-curable ink satisfying both the viscosity condition defined in claim 1 and the water content condition defined in claim 2 is used. Exposure is preferably started using the above conditions, and the above conditions allow more accurate control of the ink dot diameter.
[0029]
Next, the details of the actinic ray curable ink used in the present invention will be described.
As the ink according to the present invention, any of radical polymerization type ink, cationic polymerization type ink, and hybrid type thereof can be used, and all inks also contain a coloring material, an initiator, and a polymerizable compound as main components. I do.
[0030]
As the coloring material according to the present invention, a coloring material that can be dissolved or dispersed in the main component of the polymerizable compound can be used, but a pigment is preferable from the viewpoint of weather resistance.
[0031]
Pigments that can be preferably used in the present invention are listed below.
C. I. Pigment @ Yellow-1, 3, 12, 13, 14, 17, 81, 83, 87, 95, 109, 42,
C. I. Pigment @ Orange-16, 36, 38,
C. I. Pigment Red-5, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 144, 146, 185, 101,
C. I. Pigment @ Violet-19, 23,
C. I. Pigment Blue-15: 1, 15: 3, 15: 4, 18, 60, 27, 29,
C. I. Pigment @ Green-7, 36,
C. I. Pigment @ White-6, 18, 21,
C. I. Pigment @ Black-7,
For dispersion of the pigment, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, and the like can be used. It is also possible to add a dispersant when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used, and as the polymer dispersant, Solsperse series of Avecia is mentioned. In addition, as a dispersing aid, a synergist corresponding to various pigments can be used. These dispersants and dispersing aids are preferably added in an amount of 1 to 50 parts by mass based on 100 parts by mass of the pigment. The dispersion medium is performed using a solvent or a polymerizable compound. However, in the case of the actinic ray curable ink used in the present invention, it is preferable to use no solvent in order to react and cure immediately after the ink lands. If the solvent remains in the cured image, problems such as deterioration of the solvent resistance and VOC of the remaining solvent occur. Therefore, it is preferable from the viewpoint of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.
[0032]
The pigment is dispersed preferably such that the average particle size of the pigment particles is 0.08 to 0.5 μm, and the maximum particle size is 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of the dispersion medium, the dispersion conditions, and the filtration conditions are appropriately set. By controlling the particle size, clogging of the head nozzle can be suppressed, and the storage stability of the ink, the transparency of the ink, and the sensitivity of curing can be maintained.
[0033]
In the ink according to the present invention, the colorant concentration is preferably 1% by mass to 10% by mass of the whole ink.
[0034]
Next, the radical polymerization type ink will be described.
Examples of the radical polymerizable compound used in the radical polymerization type ink include, for example, JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, and JP-A-7-231444. And the like. Further, a photocurable material using a photopolymerizable composition described in Japanese Patent Application No. 7-231444, and a cationically polymerizable photocurable resin can be used. Known and recently, a photo-cationic polymerizable photocurable resin sensitized to a long wavelength region of visible light or longer, for example, compounds described in JP-A-6-43633 and JP-A-8-324137. Can be mentioned.
[0035]
The radically polymerizable compound is a compound having a radically polymerizable ethylenically unsaturated bond, and may be any compound as long as it has at least one radically polymerizable ethylenically unsaturated bond in the molecule. , Oligomers, polymers and the like having a chemical form. Only one radically polymerizable compound may be used, or two or more radically polymerizable compounds may be used in an optional ratio in order to improve desired properties.
[0036]
Examples of the compound having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, and salts, esters, urethanes and amides thereof. And anhydrides, acrylonitrile, styrene, and various other radically polymerizable compounds such as unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Specifically, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaery Litol tetraacrylate, trimethylolpropane triacrylate, tetramethylol methanetetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, acrylic acid derivatives such as epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Lauryl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylol Methacryl derivatives such as tantrimethacrylate, trimethylolpropane trimethacrylate, and 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, and triallyl trimellitate More specifically, Shinzo Yamashita, "Handbook of Crosslinking Agents," (1981 Taiseisha); Kiyomi Kato, "UV / EB Curing Handbook (Raw Materials)," (1985, Polymer Publications) Association); Radtec Research Association, "Applications and Markets of UV / EB Curing Technology", 79 pages, (1989, CMC); Eiichiro Takiyama, "Polyester Resin Handbook", (1988, Nikkan Kogyo Shimbun) Commercially available products described in or the like radical polymerizable or cross-linkable monomer known in the industry, Oligomers and polymers can be used.
[0037]
Examples of the radical polymerization initiator used in the radical polymerization type ink include triazine derivatives described in JP-B-59-1281, JP-B-61-9621, and JP-A-60-60104, and JP-A-59-1504. And organic peroxides described in JP-A-61-243807, JP-B-43-23684, JP-B-44-6413, JP-B-44-6413 and JP-B-47-1604. The diazonium compounds described in each gazette and U.S. Pat. No. 3,567,453, and U.S. Pat. Nos. 2,848,328, 2,852,379 and 2,940,853 are described in each specification. The organic azide compounds described in JP-B-36-22062, JP-B-37-13109, JP-B-38-18015, JP-B-45-9610, etc. Quinonediazides, various onium compounds described in JP-B-55-39162, JP-A-59-14023, etc. and in "Macromolecules", Vol. 10, p. 1307 (1977). Azo compounds described in JP-A-59-142205, JP-A-1-54440, European Patent No. 109,851, European Patent No. 126,712, etc .; Science (J. Imag. Sci.) ", Vol. 30, p. 174 (1986), which are described in Japanese Patent Application Nos. 4-56831 and 4-89535. (Oxo) sulfonium organoboron complex described above, titanocenes described in JP-A-61-151197, "Cordine Transition chemistry containing a transition metal such as ruthenium described in Coordination Chemistry Review, Vol. 84, pp. 85-277 (1988) and JP-A-2-182701. Examples include 2,4,5-triarylimidazole dimer, carbon tetrabromide and organic halogen compounds described in JP-A-59-107344 described in JP-A-3-209777. These polymerization initiators are preferably contained in the range of 0.01 to 10 parts by mass based on 100 parts by mass of the radically polymerizable compound having an ethylenically unsaturated bond.
[0038]
Next, the cationic polymerization type ink will be described.
In the invention according to claim 7, the ink preferably contains a cationically polymerizable compound.
[0039]
Various known cationically polymerizable monomers can be used as the photocationically polymerizable monomer. For example, epoxy disclosed in JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937, and JP-A-2001-220526 are exemplified. Compounds, vinyl ether compounds, oxetane compounds and the like.
[0040]
Preferred as aromatic epoxides are di- or polyglycidyl ethers produced by the reaction of a polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof with epichlorohydrin, such as bisphenol A or its alkylene oxide. Examples thereof include di- or polyglycidyl ether of an adduct, di- or polyglycidyl ether of a hydrogenated bisphenol A or an alkylene oxide adduct thereof, and a novolak-type epoxy resin. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.
[0041]
The alicyclic epoxide is obtained by epoxidizing a compound having a cycloalkane ring such as at least one cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid. Compounds containing cyclohexene oxide or cyclopentene oxide are preferred.
[0042]
Preferred examples of the aliphatic epoxide include di- or polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol and Diglycidyl ethers of alkylene glycols such as diglycidyl ether of 1,6-hexanediol, polyglycidyl ethers of polyhydric alcohols such as di- or triglycidyl ether of glycerin or alkylene oxide adduct thereof, polyethylene glycol or alkylene oxide adduct thereof Of polyalkylene glycols such as diglycidyl ethers of polypropylene glycol or diglycidyl ether of an alkylene oxide adduct thereof Glycidyl ether, and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.
[0043]
Among these epoxides, in view of rapid curability, aromatic epoxides and alicyclic epoxides are preferred, and alicyclic epoxides are particularly preferred. In the present invention, one of the above epoxides may be used alone, or two or more may be used in appropriate combination.
[0044]
As the vinyl ether compound, for example, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexane dimethanol divinyl ether, trimethylol Di or trivinyl ether compounds such as propane trivinyl ether, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexane dimethanol monovinyl ether, n-pro Vinyl ether, isopropyl vinyl ether, isopropenyl ether -O- propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.
[0045]
Among these vinyl ether compounds, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable in consideration of curability, adhesion, and surface hardness. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in an appropriate combination.
[0046]
In the invention according to claim 8, it is preferable that the ink contains a cationically polymerizable monomer having an oxetane group.
[0047]
The oxetane compound referred to in the present invention is a compound having an oxetane ring, and any known oxetane compound as disclosed in JP-A-2001-220526 and JP-A-2001-310937 can be used.
[0048]
In the oxetane compound according to the present invention, when a compound having five or more oxetane rings is used, the viscosity of the ink composition becomes high, so that handling becomes difficult, or the glass transition temperature of the ink composition becomes high, The resulting cured product has insufficient tackiness. The compound having an oxetane ring used in the present invention is preferably a compound having 1 to 4 oxetane rings.
[0049]
Hereinafter, specific examples of the compound having an oxetane ring according to the present invention will be described, but the present invention is not limited thereto.
[0050]
As an example of the compound having one oxetane ring, a compound represented by the following general formula (1) can be given.
[0051]
Embedded image

[0052]
In the general formula (1), R¹Is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, a furyl group or a thienyl group. R²Is an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a 1-propenyl group, a 2-propenyl group, a 2-methyl-1-propenyl group, a 2-methyl-2- Aromatic rings such as alkenyl groups having 2 to 6 carbon atoms such as propenyl group, 1-butenyl group, 2-butenyl group and 3-butenyl group, phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group and phenoxyethyl group A group having 2 to 6 carbon atoms such as an alkylcarbonyl group having 2 to 6 carbon atoms such as an ethylcarbonyl group, a propylcarbonyl group and a butylcarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group and a butoxycarbonyl group; Group, ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group, pentylcarbamoyl group, etc. Of 2-6 carbon atoms which is N- alkylcarbamoyl group. As the oxetane compound used in the present invention, it is particularly preferable to use a compound having one oxetane ring, since the resulting composition has excellent tackiness, low viscosity and excellent workability.
[0053]
Examples of the compound having two oxetane rings include a compound represented by the following general formula (2).
[0054]
Embedded image

[0055]
In the general formula (2), R¹Is a group similar to that in the general formula (1). R³Is, for example, a linear or branched alkylene group such as an ethylene group, a propylene group or a butylene group, or a linear or branched poly (alkyleneoxy) group such as a poly (ethyleneoxy) group or a poly (propyleneoxy) group. Linear or branched unsaturated hydrocarbon groups such as propenylene group, methylpropenylene group, butenylene group, or alkylene group containing carbonyl group or carbonyl group, alkylene group containing carboxyl group, alkylene group containing carbamoyl group, etc. It is.
[0056]
Also, R³Examples thereof include polyvalent groups selected from the groups represented by the following general formulas (3), (4) and (5).
[0057]
Embedded image

[0058]
In the general formula (3), R⁴Is an alkyl group having 1 to 4 carbon atoms such as a hydrogen atom, a methyl group, an ethyl group, a propyl group, and a butyl group; an alkoxy group having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. A nitro group, a cyano group, a mercapto group, a lower alkylcarboxyl group, a carboxyl group, or a carbamoyl group.
[0059]
Embedded image

[0060]
In the general formula (4), R⁵Represents an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO₂, C (CF₃)₂Or C (CH₃)₂Represents
[0061]
Embedded image

[0062]
In the general formula (5), R⁶Is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group, or an aryl group. n is an integer of 0 to 2000. R⁷Is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group, or an aryl group. R⁷Examples further include groups selected from groups represented by the following general formula (6).
[0063]
Embedded image

[0064]
In the general formula (6), R⁸Is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group, or an aryl group. m is an integer of 0 to 100.
[0065]
Specific examples of the compound having two oxetane rings include the following compounds.
[0066]
Embedded image

[0067]
Exemplified compound 1 is a compound represented by the general formula (2)¹Is an ethyl group, R³Is a carboxyl group. In addition, Exemplified Compound 2 is a compound represented by the general formula (2)¹Is an ethyl group, R³Is R in the general formula (5).⁶And R⁷Is a methyl group and n is 1.
[0068]
Among the compounds having two oxetane rings, preferred examples other than the above compounds include compounds represented by the following general formula (7). In the general formula (7), R¹Is the R of the above general formula (1)¹Is synonymous with
[0069]
Embedded image

[0070]
In addition, as an example of the compound having 3 to 4 oxetane rings, a compound represented by the following general formula (8) can be given.
[0071]
Embedded image

[0072]
In the general formula (8), R¹Is R in the general formula (1).¹Is synonymous with R⁹Examples thereof include a branched alkylene group having 1 to 12 carbon atoms such as a group represented by the following A to C, a branched poly (alkyleneoxy) group such as a group represented by the following D, or the following E: And a branched polysiloxy group such as a group. j is 3 or 4.
[0073]
Embedded image

[0074]
In the above A, R¹⁰Is a lower alkyl group such as a methyl group, an ethyl group or a propyl group. In the above D, p is an integer of 1 to 10.
[0075]
As an example of the compound having 3 to 4 oxetane rings, Exemplified Compound 3 is given.
[0076]
Embedded image

[0077]
Further, examples of the compound having 1 to 4 oxetane rings other than those described above include a compound represented by the following general formula (9).
[0078]
Embedded image

[0079]
In the general formula (9), R⁸Is R in the above general formula (6)⁸Is synonymous with R¹¹Is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group or a trialkylsilyl group, and r is 1 to 4.
[0080]
Preferred specific examples of the oxetane compound used in the present invention include the following compounds.
[0081]
Embedded image

[0082]
The method for producing each compound having an oxetane ring described above is not particularly limited, and may be in accordance with a conventionally known method. For example, Pattisson (DB Pattison, J. Am. Chem. Soc., 3455, 79) (1957)) discloses an oxetane ring synthesis method from a diol. In addition to these, compounds having 1 to 4 oxetane rings having a high molecular weight of about 1,000 to 5,000 are also exemplified. Specific examples of these compounds include the following compounds.
[0083]
Embedded image

[0084]
In the present invention, for the purpose of suppressing shrinkage of the recording material upon curing of the ink, the photopolymerizable compound contains at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound. Is preferred.
[0085]
As the initiator used in the cationic polymerization type ink, for example, a chemical amplification type photoresist or a compound used for photocationic polymerization is used (Organic Materials Research Association, "Organic Materials for Imaging", Bunshin Publishing (1993) Year), pages 187-192). Examples of compounds suitable for the present invention are given below.
[0086]
First, B (C) of an aromatic onium compound such as diazonium, ammonium, iodonium, sulfonium, and phosphonium is used.₆F₅)₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, CF₃SO₃ ⁻Salts may be mentioned. Those having a borate compound as a counter anion are preferable because of high acid generating ability. Specific examples of the onium compound are shown below.
[0087]
Embedded image

[0088]
Secondly, a sulfonate that generates sulfonic acid can be mentioned. Specific compounds are exemplified below.
[0089]
Embedded image

[0090]
Third, halides that generate hydrogen halide can also be used. Specific compounds are shown below.
[0091]
Embedded image

[0092]
Fourth, an iron allene complex can be mentioned.
[0093]
Embedded image

[0094]
In the ink according to the present invention, various additives can be used in addition to the components described above.
[0095]
In the present invention, a thermal base generator can also be used for the purpose of improving ejection stability and storage stability.
[0096]
As the thermal base generator, for example, a salt of an organic acid and a base that decomposes and decomposes by heating, a compound that decomposes by a reaction such as an intramolecular nucleophilic substitution reaction, a Rossen rearrangement, a Beckmann rearrangement, and releases amines, Those which cause some reaction by heating to release a base are preferably used. Specifically, salts of trichloroacetic acid described in British Patent No. 998,949, salts of alpha-sulfonylacetic acid described in U.S. Pat. No. 4,060,420, and propylic acids described in JP-A-59-157637 are disclosed. Salts, 2-carboxycarboxamide derivatives, salts with a thermally decomposable acid using an alkali metal or an alkaline earth metal in addition to an organic base as a base component described in JP-A-59-168440; And the aldoxime carbamates described in JP-A-59-195237, which produce nitriles by heating, and the like. In addition, UK Patent No. 998,945, US Patent No. 3,220,846, UK Patent No. 279,480, JP-A-50-22625, JP-A-61-32844, JP-A-61-51139, and JP-A-61-61139 The thermal base generators described in JP-A-52638, JP-A-61-51140, JP-A-61-53634 to JP-A-61-53640, JP-A-61-55644, and JP-A-61-55645 are useful. More specifically, examples include guanidine trichloroacetate, methylguanidine trichloroacetate, potassium trichloroacetate, guanidine phenylsulfonylacetate, guanidine p-chlorophenylsulfonylacetate, guanidine p-methanesulfonylphenylsulfonylacetate, potassium phenylpropiolate, and phenylpropiol. There are guanidine acid, cesium phenylpropiolate, guanidine p-chlorophenylpropiolate, guanidine p-phenylene-bis-phenylpropiolate, tetramethylammonium phenylsulfonylacetate, and tetramethylammonium phenylpropiolate. The above-mentioned thermal base generator can be used in a wide range.
[0097]
The ink of the present invention contains, as disclosed in JP-A-8-248561 and JP-A-9-34106, an acid multiplying agent which newly generates an acid by an acid generated by irradiation with an actinic ray, which is already known. Is also possible.
[0098]
In the invention according to claim 6, the surface tension of the ink at 25 ° C. is preferably in the range of 25 to 40 mN / m. If the surface tension of the ink at 25 ° C. is less than 25 mN / m, it is difficult to obtain stable ejection, and if it exceeds 40 mN / m, a desired dot diameter cannot be obtained. If the viscosity is outside the range of 25 to 40 mN / m, it is difficult to obtain a uniform dot diameter for various supports even when the ink is emitted and irradiated with light while controlling the viscosity and water content of the ink as in the present invention. It becomes.
[0099]
In order to adjust the surface tension, a surfactant may be contained as necessary. The surfactant preferably used in the ink according to the present invention includes, for example, anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl. Nonionic surfactants such as allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and surfactants having a polymerizable group And the like. Among these, particularly, a silicone-modified acrylate, a fluorine-modified acrylate, a silicone-modified epoxy, a fluorine-modified epoxy, a silicone-modified oxetane, a fluorine-modified oxetane, and the like, a surface-active compound having a polymerizable group such as an unsaturated bond, an oxirane, and an oxetane ring are preferable. .
[0100]
Various additives other than those described above can be used in the ink according to the present invention. For example, a leveling additive, a matting agent, a polyester-based resin, a polyurethane-based resin, a vinyl-based resin, an acrylic-based resin, a rubber-based resin, and waxes for adjusting film properties can be added. It is also effective to add a trace amount of an organic solvent in order to improve the adhesion to the recording medium. In this case, the addition is effective within a range in which the problem of solvent resistance and VOC does not occur, and the amount used is in the range of 0.1 to 5%, preferably 0.1 to 3%. It is also possible to combine a radical polymerizable monomer and an initiator to obtain a radical-cation hybrid cured ink.
[0101]
In the image forming method of the present invention, the ink composition is ejected onto a recording material by an ink jet recording method, drawing is performed, and the ink is cured by irradiation with actinic rays such as ultraviolet rays.
[0102]
In the present invention, it is preferable that the total ink film thickness after the ink lands and is cured by irradiation with actinic rays is 2 to 20 μm. In the actinic ray-curable ink jet recording in the screen printing field, the total ink film thickness currently exceeds 20 μm. However, in the flexible packaging printing field where the recording material is often a thin plastic material, the recording material described above is used. Not only because of the problem of curls and wrinkles, but also because of the problem of changing the stiffness and texture of the whole printed matter. In the present invention, it is preferable that the amount of liquid droplets ejected from each nozzle is 2 to 15 pl.
[0103]
In the image recording method of the present invention, as the irradiation condition of the generated light beam, it is preferable that the active light beam is irradiated during 0.001 to 2.0 seconds after ink landing, more preferably 0.001 to 1.0. Seconds. In order to form a high-definition image, it is preferable that the irradiation timing is as early as possible, but in the present invention, it is preferable to start the light irradiation at a timing when the viscosity or the water content of the ink is in a preferable state.
[0104]
A basic method of irradiating actinic rays is disclosed in JP-A-60-132767. According to this, light sources are provided on both sides of the recording head unit, and the recording head and the light source are scanned in a shuttle system. Irradiation is performed at a fixed time after the ink has landed. Further, the curing is completed by another light source without driving. U.S. Patent No. 6,145,979 discloses a method using an optical fiber or a method in which a collimated light source is applied to a mirror provided on the side of a recording head unit to irradiate a recording unit with UV light. ing. In the image forming method of the present invention, any of these irradiation methods can be used.
[0105]
The irradiation of the actinic ray is divided into two stages. First, the actinic ray is irradiated by the above-described method for 0.001 to 2.0 seconds after the ink has landed, and the actinic ray is further irradiated after the completion of all printing. The method is also one of the preferred embodiments. By dividing the irradiation of the actinic ray into two stages, it is possible to further suppress the contraction of the recording material that occurs when the ink is cured.
[0106]
Examples of light sources used for actinic ray irradiation include high-pressure mercury lamps, metal halide lamps, electrodeless UV lamps, low-pressure mercury lamps, UV lasers, xenon flash lamps, insect traps, black lights, germicidal lamps, cold cathode tubes, and LEDs. But not limited to these.
[0107]
In the present invention, the peak illuminance in a wavelength range effective for curing is 0.1 mW / cm.²3000 mW / cm²The following actinic rays are used.
[0108]
As the substrate that can be used in the present invention, a non-absorbable support can be used in addition to ordinary uncoated paper, coated paper, and the like. It is preferable to use a non-absorbable support as the material.
[0109]
In the present invention, various non-absorbable plastics and films thereof can be used as the non-absorbable support. Examples of the various plastic films include PET films, OPS films, OPP films, ONy films, and PVC films. , PE film and TAC film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Further, the present invention can be applied to metals and glasses. Among these recording materials, the structure of the present invention is particularly effective when an image is formed on a PET film, an OPS film, an OPP film, an ONy film, or a PVC film which can be shrunk by heat. These base materials not only tend to curl and deform the film due to the curing shrinkage of the ink and the heat generated during the curing reaction, but also make it difficult for the ink film to follow the shrinkage of the base material.
[0110]
These various plastic films have greatly different surface energies, and there has conventionally been a problem that the dot diameter after ink landing varies depending on the recording material. In the configuration of the present invention, an OPP film having a low surface energy, an OPS film, and even a PET having a relatively high surface energy are included. In the invention according to claim 5, the substrate has a wetting index of 40 to 60 mN / m. Preferably, there is.
[0111]
The wetting index referred to in the present invention refers to the surface tension (mN / mN / mN / m) of a mixed liquid determined to wet a base material surface by applying a series of mixed liquids having different surface tensions in order. The value of m) is defined as a wetting index, and specifically, can be determined by measuring according to the “wetting test method for polyethylene and polypropylene films” (JIS K 6768).
[0112]
In the present invention, it is more advantageous to use a long (web) recording material in terms of the cost of the recording material such as packaging cost and production cost, the print production efficiency, and the ability to cope with prints of various sizes. is there.
[0113]
【Example】
The present invention will be described more specifically with reference to examples, but the present invention is not limited to the embodiments in these examples.
[0114]
Example 1
《Preparation of ink》
(Preparation of cyan pigment dispersion)
A cyan pigment dispersion was prepared according to the method described below. The dispersion conditions are appropriately adjusted using a known dispersing apparatus so that the average particle size of the cyan pigment particles is in the range of 0.2 to 0.3 μm. Prepared by filtration.
[0115]
C. I. Pigment Blue 15: 3-15 parts by mass
2 parts by mass of polymer dispersant (Zeneca's Solsperse series)
Aron Oxetane OXT-221 (Toa Gosei Co., Ltd.) 83 parts by mass
(Preparation of cyan ink)
Using the above-prepared cyan pigment dispersion, a cyan ink was prepared according to the method described below.
[0116]
17 parts by mass of cyan pigment dispersion
Aron Oxetane OXT-221 (manufactured by Toa Gosei) 48 parts by mass
Celloxide 2021P (manufactured by Daicel UCB) @ 30 parts by mass
SP-152 (Asahi Denka Co., Ltd. photoacid generator) 5 parts by mass
After the cyan ink prepared as described above was filtered through a membrane filter having an absolute filtration accuracy of 0.8 μm, the cyan ink was dehydrated by heating under reduced pressure while heating to 50 ° C. to prepare a cyan ink.
[0117]
The viscosity of the prepared cyan ink at 25 ° C. was 25.4 mPa · s, the surface tension was 34.8 mN / m, and the water content was 1.0% by mass (measured by the Karl Fischer method). The moisture content after conditioning for 24 hours in an atmosphere of 23 ° C. and 80% RH was 2.1% by mass, which was defined as an equilibrium moisture content in the present invention.
[0118]
《Inkjet image recording》
Using the cyan ink prepared above, image recording was performed according to the following image forming method 1 and image forming method 2.
[0119]
(Image forming method 1)
Recording on a substrate is performed using an inkjet recording apparatus having a piezo-type inkjet nozzle (nozzle pitch of 360 dpi) under an atmosphere of 15 ° C. and 30% RH and an atmosphere of 30 ° C. and 70% RH as indoor environments. Was. The ink supply system consists of an original tank, a supply pipe, an ink supply tank immediately before the inkjet head, a filter, and a piezo-type inkjet head, and insulates and heats from the ink supply tank to the inkjet head portion and the substrate transport section, respectively. Was. Temperature sensors were provided near the nozzles of the ink supply tank and the inkjet head and at the base material transporting section to control the temperature. With a piezo-type inkjet head, the ink droplet size was 7 pl, and a solid image was ejected at a single size dot and a resolution of 720 × 720 dpi. At the time of ink ejection, the ink was heated to 50 ° C. for each nozzle, and the ink viscosity was set to 8.2 mPa · s. As the base material, an OPP (oriented polypropylene) film subjected to a corona discharge treatment and a PET (polyethylene terephthalate) film subjected to a corona discharge treatment were used. The OPP film had a wetting index of 42 mN / m, and the PET film had a wetting index of 55 mN / m. The term “dpi” in the present invention indicates the number of dots per 2.54 cm.
[0120]
After each ink landed on the substrate, the temperature of the substrate was controlled at 30 ° C. by appropriately controlling the heat plate conditions of the substrate transport section so that the ink viscosity did not exceed 15 mPa · s. The viscosity of this ink at 30 ° C. is 13.9 mPa · s.
[0121]
Next, the landed ink was irradiated with light. The light irradiation light source is arranged so that the ink landing image area is irradiated with an optical fiber from a high pressure mercury lamp (manufactured by Ushio, SP5), the peak wavelength is 365 nm, and the exposure illuminance is 100 mW / cm.²It is. The light irradiation started 100 ms after the ink droplets landed, and was irradiated for 200 ms to cure the ink. This is 20 mJ / cm as irradiation energy.²Is equivalent to
[0122]
When 100 ms elapses after the ink has landed, the temperature of the ink in contact with the base material becomes substantially equal to the temperature of the base material. At which the ink viscosity becomes.
[0123]
The respective characteristic values in the image forming method 1 are summarized below.
Ink viscosity at 25 ° C: 25.4 mPa · s
Ink viscosity before injection: 8.2 mPa · s
Substrate wetting index: OPP = 42 mN / m, PET = 55 mN / m
Ink viscosity during light irradiation: 13.9 mPa · s (indoor environment 15 ° C, 30% RH, 30 ° C, 70% RH)
(Image forming method 2)
In the above-described image forming method 1, an image was formed in the same manner as above except that the temperature of the base material was not controlled at 30 ° C. during the ink landing.
[0124]
The respective characteristic values in the image forming method 2 are collectively shown below.
Ink viscosity at 25 ° C: 25.4 mPa · s
Ink viscosity before injection: 8.2 mPa · s
Substrate wetting index: OPP = 42 mN / m, PET = 55 mN / m
Ink viscosity after substrate landing: 26.8 mPa · s (indoor environment 15 ° C., 30% RH), 16.4 mPa · s (indoor environment 30 ° C., 70% RH)
<< Evaluation of formed image >>
Each image prepared as described above was evaluated according to the following method.
[0125]
(Measurement of dot diameter of landing ink)
With respect to the single-size dots created above, the dot diameter was determined by an image analyzer (Lirex, manufactured by Nireco, measurement conditions: 16,000 pixels, 1 pixel), and the average value measured 50 times was determined, and this was defined as the dot diameter.
[0126]
(Evaluation of surface unevenness)
The surface of the solid image created above was observed visually and by tactile sensation, and the surface unevenness was evaluated according to the following criteria.
[0127]
：: Almost no noticeable surface irregularities observed by visual observation and tactile sensation
Δ: The surface irregularities are not bothersome by visual observation, but are slightly bothersome by tactile sensation, but are of a practically acceptable quality.
×: Grassiness due to unevenness of the surface is clearly recognized by visual observation and tactile sensation, and the quality is not preferable for practical use.
(Evaluation of bleeding resistance)
The single-size dots and the solid images prepared above were visually observed, and the bleeding resistance was evaluated according to the following criteria.
[0128]
：: Single-size dots maintain a perfect circle, no solid image boundary is disturbed, and no bleeding is observed
Δ: Deterioration of roundness of single-size dots and disturbance of solid image boundary lines are slightly recognized, but the quality is practically acceptable.
×: Disturbance in roundness of single-size dots and disturbance of solid image boundary lines are clearly recognized, and the quality is not preferable for practical use.
Table 1 shows the results obtained as described above.
[0129]
[Table 1]

[0130]
As is clear from Table 1, the image obtained by the image forming method of the present invention in which the light irradiation was started with the ink viscosity at the time of light irradiation of 15 mPa · s or less, the dot diameter was different even under different substrates and different printing environments. It can be seen that the image quality with good texture such as unevenness and unevenness and less blurring can be obtained. In the image forming method 1, the viscosity of the ink at the time of irradiation is controlled by controlling the heat transfer from the base material and the time from the landing to the start of exposure. However, only the ink is heated and controlled by another means. Or control the viscosity after landing and cooling by adjusting the temperature of the ink at the time of ejection without controlling the heating of the ink, and by controlling the time until the start of exposure to cool and thicken the landing ink. The same effect can be obtained by adopting a method of controlling the degree of the difference.
[0131]
Example 2
In the inkjet image recording described in Example 1, an image was formed in the same manner except that the following image forming methods 3 and 4 were used instead of the image forming methods 1 and 2.
[0132]
《Preparation of ink》
As in Example 1, a cyan ink having a water content of 1.0% by mass (measured by the Karl Fischer method) was used.
[0133]
《Inkjet image recording》
(Image forming method 3)
In the image forming method 2 described in Example 1, ink droplets having the water content of the ink adjusted to 2.1% by mass are landed on a base material, and then air having a relative humidity of 20% is applied to the image forming portion. An image was formed in the same manner except that the landed ink was irradiated with light while spraying.
[0134]
The water content of this ink at a humidity of 20% is 0.4% by mass, and the ink adjusted to a water content of 1.0% undergoes dehydration after landing, but the water content is 1.7. %.
[0135]
Each characteristic in the image forming method 3 was as follows.
Equilibrium water content at a relative humidity of 80% of the ink: 2.1% by mass
Water content of ink before ejection: 1.0% by mass
Water content of ink at the time of light irradiation: 0.4 to 1.0 mass% (indoor environment 15 ° C, 30% RH, 30 ° C, 70% RH)
(Image forming method 4)
In the image forming method 3 described above, the same procedure was performed except that the ink droplets were landed on the base material, and the landed ink was irradiated with light without blowing air having a relative humidity of 20% to the image forming portion. To form an image.
[0136]
Each characteristic in the image forming method 4 was as follows.
Equilibrium water content at a relative humidity of 80% of the ink: 2.1% by mass
Water content of ink before ejection: 1.0% by mass
Water content of ink at the time of light irradiation: less than 1.0% by mass (indoor environment 15 ° C, 30% RH), 1.9% by mass (indoor environment 30 ° C, 70% RH)
In the calculation of the water content at the time of light irradiation in the indoor environment at 30 ° C. and 70% RH described above, first, the sensitivity at which the dot diameter does not change after light irradiation is calculated. Next, the ink is applied to the substrate with a wire bar, the environmental humidity is changed, light irradiation is performed, and a humidity environment that is equal to the calculated exposure sensitivity is determined. The equilibrium water content of the ink was determined in an environment that was equal to the exposure sensitivity, and the water content at the time of impact and exposure was estimated. In our study, it was confirmed that the water content of the environment was equal to the water content of the environment in a short time of only 50 to 250 ms after the ink ejection.
[0137]
<< Evaluation of formed image >>
For each image created as described above, measurement of the dot diameter of the landing ink, evaluation of the surface unevenness and evaluation of the bleeding resistance were performed in the same manner as in the method described in Example 1, and the obtained results were tabulated. It is shown in FIG.
[0138]
[Table 2]

[0139]
As is clear from Table 2, the image formed by the image forming method of the present invention in which light irradiation is started under the condition that the water content of the ink is 0.2 to 2% is a dot even under different base materials and different environments. It was possible to obtain an image with good texture such as diameter and unevenness and excellent bleeding resistance. In the image forming method 3, the control of the water content of the ink at the time of irradiation is performed by sending the conditioned air to the image forming unit and controlling the time from landing to the start of exposure. The method of adjusting the water content of the ink at the time of ejection and the time until the start of exposure are controlled so that the difference in the water content after water absorption or dehydration is reduced according to the environment, thereby controlling the water absorption or dehydration of the landing ink. The same effect can be obtained by controlling the degree.
[0140]
【The invention's effect】
According to the present invention, it is possible to provide an image forming method which is excellent in bleeding resistance and can stably form a high image without unevenness on a recording material having poor ink absorption.

Claims (8)

In an image forming method in which an ink having a viscosity at 25 ° C. of 15 mPa · s or more and curable by light irradiation is jetted to a substrate using an ink jet recording method, and then an image is formed by irradiating with an actinic ray, Before heating the ink to 40 ° C. or more, the ink has a means for controlling the viscosity of the ink to 12 mPa · s or less, and after the ink is ejected onto the base material, the viscosity of the ink is 15 mPa · s. An image forming method, wherein light irradiation is performed when the value is equal to or less than s. Injecting an ink curable by light irradiation with an equilibrium water content of 1.5% or more as measured by the Karl Fischer method at a relative humidity of 80% onto a substrate using an ink jet recording method, and then irradiating with an actinic ray In the image forming method for forming an image by the method, the ink is jetted in a state where the water content of the ink is 1.5% or less, and after the ink is jetted to the base material, the water content of the ink is 1.7% or less. An image forming method comprising irradiating light at a certain time. The ink has a viscosity at 25 ° C. of 15 mPa · s or more, and has a means for controlling the viscosity of the ink to 12 mPa · s or less by heating the ink to 40 ° C. or more before jetting. 3. The image forming method according to claim 2, wherein after the ink is ejected onto the base material, the ink is irradiated when the viscosity of the ink is 15 mPa · s or less. The image forming method according to claim 1, wherein the substrate is a non-absorbable support that does not absorb ink. The image forming method according to claim 1, wherein the substrate has a wetting index of 40 to 60 mN / m. The image forming method according to claim 1, wherein a surface tension of the ink at 25 ° C. is 25 mN / m to 40 mN / m. The image forming method according to claim 1, wherein the ink contains a cationically polymerizable compound. The image forming method according to any one of claims 1 to 7, wherein the ink contains a cationically polymerizable monomer having an oxetane group.