JP2004034545A - Inkjet recording method, ink, and inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form high-sharpness images without creasing or curling record media by using an ink of cationic polymerization nature. <P>SOLUTION: The temperature of ink at an output port 15 inside a recording head 21 is adjusted by a head temperature control mechanism 6 to not lower than 30°C and not higher than 100°C. The temperature of ink of the record medium R is adjusted by a media temperature control mechanism 5 to not lower than 20°C and not higher than 40°C after it impacts until it receives irradiation by an ultraviolet light (active energy ray). Moreover, the head temperature control mechanism 6 adjusts the temperature of the ink at the output port 15 to be higher than the temperature after the ink of the record medium R impacts until it receives irradiation with the ultraviolet light. <P>COPYRIGHT: (C)2004,JPO

Description

【０１１６】
式（１）において、Ｒ^１は、水素原子、メチル基、エチル基、プロピル基或いはブチル基等の炭素数１〜６個のアルキル基、炭素数１〜６個のフルオロアルキル基、アリル基、アリール基、フリル基又はチエニル基である。Ｒ^２は、メチル基、エチル基、プロピル基或いは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−ブテニル基或いは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或いは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或いは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或いは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、又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或いは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。
【０１１７】
次に、２個のオキセタン環を有する化合物としては、下記一般式（２）で示される化合物等が挙げられる。
【化２】

式（２）において、Ｒ^１は、前記一般式（１）におけるものと同様の基である。Ｒ^３は、例えば、エチレン基、プロピレン基或いはブチレン基等の線状或いは分枝状アルキレン基、ポリ（エチレンオキシ）基或いはポリ（プロピレンオキシ）基等の線状或いは分枝状ポリ（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或いはブテニレン基等の線状或いは分枝状不飽和炭化水素基、カルボニル基、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、又はカルバモイル基を含むアルキレン基等である。
【０１１８】
又、Ｒ^３は、下記式（３）、（４）及び（５）で示される基から選択される多価基でもある。
【化３】

式（３）において、Ｒ^４は、水素原子、メチル基、エチル基、プロピル基或いは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、プロポキシ基或いはブトキシ基等の炭素数１〜４個のアルコキシ基、塩素原子或いは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、又はカルバモイル基である。
【０１１９】
【化４】

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である。
【０１２０】
【化５】

式（５）において、Ｒ^６は、メチル基、エチル基、プロピル基或いはブチル基等の炭素数１〜４個のアルキル基、又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、プロピル基或いはブチル基等の炭素数１〜４個のアルキル基、又はアリール基である。
【０１２１】
Ｒ^７は、下記式（６）で示される基から選択される基でもある。
【化６】

式（６）において、Ｒ^８は、メチル基、エチル基、プロピル基及びブチル基等の炭素数１〜４個のアルキル基、又はアリール基である。ｍは、０〜１００の整数である。
【０１２２】
２個のオキセタン環を有する化合物の具体例としては、下記式（７）及び（８）で示される化合物等が挙げられる。
【化７】

式（７）で示される化合物は、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。
【０１２３】
【化８】

式（８）で示される化合物は、一般式（２）において、Ｒ^１がエチル基であり、Ｒ３が式（５）においてＲ^６及びＲ^７がメチル基、ｎが１となる置換基である化合物である。
【０１２４】
２個のオキセタン環を有する化合物において、上記した化合物以外の好ましい例としては、下記一般式（９）で示される化合物がある。式（９）において、Ｒ^１は、前記一般式（１）におけるものと同様の基である。
【化９】

【０１２５】
３〜４個のオキセタン環を有する化合物としては、下記一般式（１０）で示される化合物等が挙げられる。
【化１０】

式（１０）において、Ｒ^１は、前記一般式（１）におけるものと同様の基である。Ｒ^９は、例えば下記式（１１）〜（１３）で示される基等の炭素数１〜１２の分枝状アルキレン基、下記式（１４）で示される基等の分枝状ポリ（アルキレンオキシ）基又は下記式（１５）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。
【化１１】

式（１１）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。
【０１２６】
【化１２】

【化１３】

【化１４】

式（１４）において、ｌは１〜１０の整数である。
【０１２７】
【化１５】

３〜４個のオキセタン環を有する化合物の具体例としては、下記式（１６）で示される化合物等が挙げられる。
【化１６】

【０１２８】
さらに、上記した以外の１〜４個のオキセタン環を有する化合物の例としては、下記式（１７）で示される化合物がある。
【化１７】

式（１７）において、Ｒ^８は式（６）におけるものと同様の基である。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。
【０１２９】
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。
【化１８】

【化１９】

【化２０】

【０１３０】
上記オキセタン環を有する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い。上記製造方法は、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。又、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。
【０１３１】
これらの例として、例えば以下の化合物が挙げられる。
【化２１】

ここで、ｐは２０〜２００である。
【０１３２】
【化２２】

ここで、ｑは１５〜１００である。
【０１３３】
【化２３】

ここで、ｓは２０〜２００である。
【０１３４】
本発明においては、インク硬化の際の記録媒体Ｒ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。
【０１３５】
上述のカチオン性光重合開始剤としては、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−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。第１に、ジアゾニウム、アンモニウム、ヨ−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。
【化２４】

【０１３６】
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。
【化２５】

【０１３７】
第３に、ハロゲン化水素を光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。
【化２６】

【０１３８】
第４に、鉄アレン錯体を挙げることができる。
【化２７】

【０１３９】
本発明のインクは、特開平８−２４８５６１、特開平９−０３４１０６をはじめてとし、既に公知となっている活性エネルギ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が好ましい。酸増殖剤を用いることで、さらなる吐出安定性向上を可能とする。
【０１４０】
本発明に係るインクでは、対イオンとしてアリールボレート化合物を有するジアゾニウム、ヨードニウム又はスルホニウムの芳香族オニウム化合物、鉄アレン錯体から選ばれる少なくとも１種の光酸発生剤が含有されることが好ましい。
【０１４１】
上述の色材としては、重合性化合物の主成分に溶解または分散できる色材が使用出来るが、耐候性の点でから顔料が好ましい。
本発明で好ましく用いることのできる顔料を、以下に列挙する。
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、
【０１４２】
また、本発明において、プラスチックフィルムのような透明基材での色の隠蔽性を上げる為に、白インクを用いることが好ましい。特に、軟包装画像形成、ラベル画像形成においては、白インクを用いることが好ましいが、吐出量が多くなるため、前述した吐出安定性、記録媒体Ｒのカール・しわの発生の観点から、自ずと使用量に関しては制限がある。
【０１４３】
上記顔料の分散には、例えば、ボールミル、サンドミル、アトライター、ロールミル、アジテータ、ヘンシェルミキサ、コロイドミル、超音波ホモジナイザー、パールミル、湿式ジェットミル、ペイントシェーカー等を用いることができる。また、顔料の分散を行う際に、分散剤を添加することも可能である。分散剤としては、高分子分散剤を用いることが好ましく、高分子分散剤としてはＡｖｅｃｉａ社のＳｏｌｓｐｅｒｓｅシリーズが挙げられる。
【０１４４】
また、分散助剤として、各種顔料に応じたシナージストを用いることも可能である。これらの分散剤および分散助剤は、顔料１００質量部に対し、１〜５０質量部添加することが好ましい。分散媒体は、溶剤または重合性化合物を用いて行うが、本発明に用いる照射線硬化型インクでは、インク着弾直後に反応・硬化させるため、無溶剤であることが好ましい。溶剤が硬化画像に残ってしまうと、耐溶剤性の劣化、残留する溶剤のＶＯＣの問題が生じる。よって、分散媒体は溶剤では無く重合性化合物、その中でも最も粘度の低いモノマーを選択することが分散適性上好ましい。
【０１４５】
顔料の分散は、顔料粒子の平均粒径を０．０８〜０．５μｍとすることが好ましく、最大粒径は０．３〜１０μｍ、好ましくは０．３〜３μｍとなるよう、顔料、分散剤、分散媒体の選定、分散条件、ろ過条件を適宜設定する。この粒径管理によって、ヘッドノズルの詰まりを抑制し、インクの保存安定性、インク透明性および硬化感度を維持することができる。
本発明に係るインクにおいては、色材濃度としては、インク全体の１質量％乃至１０質量％であることが好ましい。
【０１４６】
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、インク組成物の保存性を高めるため、重合禁止剤を２００〜２００００ｐｐｍ添加することができる。紫外線硬化型のインクは、加熱、低粘度化して射出することが好ましいので、熱重合によるヘッド詰まりを防ぐためにも重合禁止剤を入れることが好ましい。この他にも、必要に応じて、界面活性剤、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。
【０１４７】
記録媒体Ｒ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（揮発性有機化合物）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。
【０１４８】
上述のようなＵＶインクは、インクジェット記録方式により記録媒体Ｒ上に吐出、描画し、次いで紫外線（活性エネルギ線）を照射してインクを硬化させることになる。
ここで、インクが着弾し、紫外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。スクリーン画像形成分野では、総インク膜厚が２０μｍを越えているのが現状であるが、記録媒体Ｒが薄いプラスチック材料であることが多い軟包装画像形成分野では、前述した記録媒体Ｒのカール・しわの問題でだけでなく、画像形成物全体のこし・質感が変わってしまうという問題が有るため使えない。
【０１４９】
インクの吐出条件としては、記録ヘッド及びインクを３０〜１００℃に加熱し、吐出することが吐出安定性の点で好ましい。活性エネルギ線硬化型インクは、温度変動による粘度変動幅が大きく、粘度変動はそのまま液滴サイズ、液滴射出速度に大きく影響を与え、画質劣化を起こすため、インク温度を上げながらその温度を一定に保つことが必要である。インク温度の制御幅としては、設定温度±５℃、好ましくは設定温度±２℃、更に好ましくは設定温度±１℃である。
【０１５０】
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。高精細画像を形成するためには、液滴量がこの範囲であることが必要であるが、この液滴量で吐出する場合、前述した吐出安定性が特に厳しくなり、酸増殖剤が必須となる。
【０１５１】
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秒の間に紫外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ことが特に重要となる。
【０１５２】
光（紫外線）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、ヘッドユニットの両側に光源を設け、シャトル方式で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ヘッドユニット側面に設けた鏡面に当て、記録部へ紫外線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。
【０１５３】
また、紫外線を照射を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紫外線を照射し、かつ、全印字終了後、更に活性エネルギ線を照射する方法も好ましい態様の１つである。紫外線の照射を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媒体Ｒの収縮を抑えることが可能となる。
【０１５４】
本発明では、硬化に有効な波長域における最高照度が０．１〜５０ｍＷ／ｃｍ２の低照度の紫外線を用いることが好ましい。従来、ＵＶインクジェット方式では、インク着弾後のドット広がり、滲みを抑制のために、硬化に有効な波長域における最高照度が５０ｍＷ／ｃｍ^２を超える高照度の光源が用いられるのが通常であった。しかしながら、これらの光源を用いると、特にシュリンクラベルなどでは、記録媒体Ｒの収縮があまりにも大きく、実質上使用できないのが現状であった。本発明では、酸増殖剤を用いることで、硬化に有効な波長域における最高照度が０．１〜５０ｍＷ／ｃｍ^２の低照度の紫外線を用いても、高精細な画像を形成でき、かつ、記録媒体Ｒの収縮もない。
【０１５５】
紫外線照射で用いる光源の例としては、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。
また、本発明では、硬化に有効な波長域における最高照度が５０〜３０００ｍＷ／ｃｍ^２の紫外線を用いることも有効である。従来のＵＶインクジェット記録に用いられる高照度の光源であるが、上述のように記録媒体Ｒの収縮課題が有り、軟包装画像形成・ラベル画像形成分野では実質ＵＶインクジェット記録は使用されていなかった。本発明の構成では、この問題は解消され、従来使われている高照度の光源を用いても、各種プラスチックフィルムへの高精細画像の形成が可能となる。光源の例としては、例えば、高圧水銀ランプ、メタルハライドランプ、無電極ＵＶランプなどが有るが、これらに限定されない。
【０１５６】
本発明で用いることのできる記録媒体Ｒとしては、通常の非コート紙、コート紙などの他、いわゆる軟包装に用いられる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（ポリエチレンテレフタレート）フィルム、ＯＰＳ（延伸ポリスチレン）フィルム、ＯＰＰ（延伸ポリプロピレン）フィルム、ＯＮｙ（延伸ナイロン）フィルム、ＰＶＣ（延伸ポリ塩化ビニル）フィルム、ＰＥ（ポリエチレン）フィルム、ＴＡＣ（トリアセチルセルロース）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（アクリロニトリル・ブタジエン・スチレン）、ポリアセタール、ＰＶＡ（ポロビニルアルコール）、ゴム類などが使用できる。
【０１５７】
また、金属類や、ガラス類にも適用可能である。これらの記録媒体Ｒ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。
【０１５８】
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、記録媒体Ｒ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、表面エネルギーが３５〜６０ｍＮ／ｍの広範囲の記録媒体Ｒに良好な高精細な画像を形成できる。
【０１５９】
本発明において、包装の費用や生産コスト等の記録媒体Ｒのコスト、プリントの作製効率、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）な記録媒体Ｒを使用する方が有利である。
【０１６０】
次ぎに、本発明のインクジェットプリンタＡの動作について説明する。
インクジェットプリンタにおいては、インクカートリッジ、記録媒体Ｒ等をセットし、電源を投入することにより、画像形成可能な状態となる。
インクカートリッジからインクの供給が行われると、制御部３０は、ヘッド温度センサ１９の検知結果に基づいて、インク収納部１８内のインク温度を検知する。そして、制御部３０は、この検知された温度に対応した加熱温度データを選択し、その選択された加熱温度データに基づいて面ヒーター１６およびヘッドヒーター１３の出力状態を制御して、ヘッド内供給路１１のインクが所定温度範囲内（例えば、ヘッド目標設定温度の上下１℃の範囲内）となるように加熱を行う。
【０１６１】
次に、記録媒体Ｒが給紙されてから排紙されるまでの動作を説明する。
まず、ここでは、オペレータの手動操作により、操作盤、キーボード等の入力手段５３に設定情報が打ち込まれる。この場合、設定情報は、形態：ロール状のフィルム、材質：ＰＥＴ，厚み：０．０５ｍｍ等の記録媒体Ｒが有する性質に関する情報となっている。これにより、入力手段５３はインターフェイス３１を介して設定情報を制御部３０に入力する。この設定情報は制御部３０のメモリ３３に記憶される。
【０１６２】
インクジェットプリンタＡ内では、スピンドル（図示しない）にセットされた記録媒体Ｒの先端が給紙ガイド（図示しない）に沿って搬送ローラ１ａまで誘導され、記録媒体Ｒ先端の位置合わせが行われる。
【０１６３】
位置合わせされた記録媒体Ｒは、搬送ローラ１ａにより画像形成部２へ搬送される。この間、メディア温度検出手段５２としての温度センサ５２ａは、記録ヘッド２１により画像形成が行われるべき記録媒体Ｒの温度を検出する。温度センサ５２ａは、検出温度情報を、インターフェイス３１を介して制御部３０に入力する。この検出温度情報は制御部３０のメモリ３３に記憶される。
【０１６４】
そして、制御部３０のＣＰＵ３２は、メモリ３３に記憶された検出温度情報と、設定情報に対応する設定温度とを読み出し、比較演算する。そして、ＣＰＵ３２は、その演算結果に伴い記録媒体Ｒの温度の上昇又は下降が必要であると判断した場合には、作動信号をメディア温度調節手段５１にインターフェイス３１を介して入力する。すると、メディア温度調節手段５１は作動する。この場合、ヒータ５１ａが作動してヒータ５１ａから輻射熱が発生し、記録媒体Ｒを画像形成面側から加熱する。
【０１６５】
また、当該演算結果に伴い記録媒体Ｒの温度の上昇又は下降が不必要であると判断した場合には、ＣＰＵ３２は、作動信号をメディア温度調節手段５１に入力しない。従って、メディア温度調節手段５１としてのヒータ５１ａは作動せず、記録媒体Ｒの加熱は行われない。
【０１６６】
このようにして、メディア温度調節機構５は、メディア温度検出手段５２による検出温度情報に基づいて、記録媒体Ｒのインクが着弾する時から紫外線の照射を受ける時までの温度を、インクが紫外線の照射によって速やかに硬化するよう制御する。
【０１６７】
引き続き、メディア温度調節機構５により温度が制御された状態で、記録媒体Ｒは、ガイド部材４により非画像形成面側が支持されるとともに搬送方向Ｆにガイドされ、搬送経路上を搬送される。なお、この記録媒体Ｒは、ガイド部材４により非画像形成面側が支持されるが、上述したようにプラテン４ａによって吸引保持された状態となっている。
【０１６８】
そして、非画像形成面が支持されている記録媒体Ｒの画像形成面に、記録ヘッド２１により画像形成が行われる。詳しくは、記録媒体Ｒの非画像形成面がプラテン４ａにより吸引保持された状態で、キャリッジ２２の動作に付随して記録ヘッド２１が走査方向に移動しながら記録媒体の画像形成面にＵＶインクを吐出し、画像形成が行われるのである。画像形成が行われた後の記録媒体Ｒは、記録ヘッド２１より搬送方向Ｆの下流側、すなわちＵＶランプ３の直下へと搬送される。
【０１６９】
引き続き、ＵＶランプ３の直下に搬送された記録媒体Ｒ、言い換えればＵＶインクが付着した記録媒体Ｒに、ＵＶランプ３からＵＶが照射され、記録媒体Ｒに付着したＵＶインクが硬化することになる。そして、以上の工程を経た記録媒体Ｒは、排紙ガイド（図示しない）を通過して排紙されるのである。
【０１７０】
なお、インクジェットプリンタＡによる画像形成中は、吐出口１５におけるインクの温度はヘッド温度調節機構６により制御されている。この制御により、吐出口１５におけるインクの温度は、ＵＶインクが最適の粘度を具備し、且つ記録媒体ＲのＵＶインクが着弾してから紫外線照射を受けるまでの間の温度よりも高い温度に調整されている。
【０１７１】
また、インクジェットプリンタＡによる画像形成中は、乾燥剤により湿度が減じられた空気が湿度調節機構７によってＵＶランプ３と記録媒体Ｒとの間の空間に供給されている。このことで、記録媒体Ｒが紫外線照射を受ける位置及び該位置近傍の湿度はＵＶインクが紫外線照射によって速やかに硬化できる湿度に調整される。
【０１７２】
なお、この実施の形態においては、ヘッド温度調節機構６のヘッド温度調節手段６１、メディア温度調節機構５のメディア温度調節手段５１、湿度調節機構７の湿度調節手段７２、７３いずれもが共通の制御装置で構成されている。これにより、インクジェットプリンタの構成要素が少なくて済むと共に、双方の制御を連動させて効率的にヘッド内のＵＶインクの温度制御と、ＵＶ照射前の記録媒体の温度制御と、ＵＶインクに紫外線が照射される場所での湿度制御とを行うことができる。
【０１７３】
次に、上述の実施形態に係るインクジェットプリンタ１の実施例について説明する。
【０１７４】
［第一の実施例］
第一の実施例では、高照度（５５０〜７００ｍＷ／ｃｍ^２）による紫外線照射を行なって記録媒体Ｒ上のＵＶインクを硬化させた。
【０１７５】
第一の実施例では、まず濃ブラック（Ｋ）、濃シアン（Ｃ）、濃マジェンタ（Ｍ）、濃イエロー（Ｙ）、淡ブラック（Ｌｋ）、淡シアン（Ｌｃ）、濃マジェンタ（Ｌｍ）、淡イエロー（Ｌｙ）の各インクを、表１〜表３に示す組成で調合し、インク組成物１〜インク組成物３を得た。
【０１７６】
【表１】

【表２】

【表３】

【０１７７】
ここで、表１ににおいて、開始剤１は化学式（２４）に示すスルホニウムイオンのボレート塩である。表２において、熱塩基１は化学式（２５）に示すアンモニウムイオンのボレート塩であり、開始剤２は化学式（２６）に示すスルホニウムイオンのボレート塩である。また、表３において、熱塩基２は化学式（２７）に示すアンモニウムイオンのボレート塩である。
【０１７８】
【化２８】

【０１７９】
インク組成物１〜インク組成物３をインクとして用い、インクジェットプリンタＡによる記録媒体Ｒに対する画像形成を行なった。インクジェットプリンタＡにおいて、記録ヘッド２１にＵＶインクを供給するインク供給系は、インクタンク、供給パイプ、前室インクタンク及びフィルター付き配管で形成した。さらに、上記インク供給系はほぼ全経路にわたって断熱材とヒータとを備え、供給パイプ内部でＵＶインクの温度が６０℃に維持される構成とした。
【０１８０】
記録ヘッド２１は吐出口１５から一回あたり２ｐｌ又は１５ｐｌの２通りの吐出量でインクを吐出可能であり、且つ７２０×７２０ｄｐｉ（ｄｏｔｓ　ｐｅｒ　ｉｎｃｈ）という解像度で記録媒体Ｒにインクドットを形成することができる構成とした。さらに、記録ヘッド２１内部の吐出口１５におけるＵＶインクの温度は、面ヒーター１６及びヘッドヒーター１３によって６０℃に調節した。
【０１８１】
記録媒体Ｒとしては、表４に示すようにＯＰＰ、ＯＮｙ、ＰＥＴ、ＰＶＣ、ＯＰＳといった非インク吸収性の材質や、キャストコート紙、和紙といったインク吸収性の材質からなる幅６００ｍｍ、長さ１０００ｍｍの長尺記録材料を用いた。ＵＶランプ３は、表４に示すものを各試料ごとに適用した。記録媒体Ｒにおける紫外線の照度は、ＵＶランプ３と記録媒体Ｒとの距離を調節することで制御した。
【０１８２】
各試料（試料Ｎｏ．１〜３０）における画像形成のため、画像形成条件ＵＶランプ３は、記録ヘッド２１の走査方向に隣接した位置に設置した。照射タイミングは、ＵＶインクが記録媒体Ｒに着弾後、０．２秒後に紫外線照射を受けるように設定した。また、ＵＶインク、記録媒体、記録媒体温度、ＵＶランプ、記録媒体における照度及びピーク波長及び照射エネルギーは、表４にそれぞれ示すように設定した。
【０１８３】
【表４】

【０１８４】
画像形成後、各試料ごとに画像を評価した結果を表５にまとめる。表５において、各評価項目ごとの凡例は下記の通りである。また、各試料についてトータルインク膜厚を測定したところ、トータルインク膜厚の範囲は２．３〜１３μｍであった。
【０１８５】
【表５】

【０１８６】
表５において、「文字品質」は、記録媒体ＲにＹ、Ｍ、Ｃ、Ｋ各色で６ポイントＭＳ明朝体を印字後、ルーペで拡大することで印字された文字のガサツキを評価した。評価のうち、◎は「ガサツキなし」を示す。○は「僅かにガサツキあり」を示す。△は「ガサツキはあるが文字として判読は可能。実用ぎりぎりのレベル」を示す。×は「ガサツキがひどく、文字がかすれていて判読不能」を示す。
【０１８７】
「色混じり（にじみ）」は隣り合う各色インクドットをルーペで拡大し、目視して評価した。評価のうち、◎は「隣り合うドットが真円を保ち、滲みがない」を示す。○は「隣り合うドットが真円を保ち、ほとんど滲みがない」を示す。△は「隣り合うドットが少し滲んでいてドット形状が崩れているが、実用ぎりぎりのレベル」を示す。×は「隣り合うドットが滲んで交じり合っており、実用にならないレベル」を示す。
【０１８８】
「印刷物しわ、カール」は、画像形成直後に印刷物を手にとって目視で評価した。○は「良好」を示す。△は「やや良好、実用ぎりぎりのレベル」を示す。×は「悪い」を示す。
【０１８９】
表５によれば、記録媒体温度（記録媒体Ｒのインクが着弾した時から紫外線照射を受ける時までの温度）を１０℃に設定した試料Ｎｏ．１〜６では、「印刷物しわ、カール」の項目では全て○の評価だったが、「文字品質」及び「色混じり（にじみ）」の項目では△以下の評価が多く、特に「色混じり（にじみ）」では半数が×の評価であった。
【０１９０】
また、記録媒体温度を５０℃に設定した試料Ｎｏ．７〜１２では、「文字品質」及び「色混じり（にじみ）」の項目では○の評価のものもあるが、半数以上は△以下の評価であった。また、「印刷物しわ、カール」の項目ではプラスチック系の材質を記録媒体Ｒに適用した場合でいずれも×の評価であった。
【０１９１】
一方、記録媒体温度を、３５℃に設定した試料Ｎｏ．１３〜３０では、「文字品質」及び「色混じり（にじみ）」ではいずれも◎又は○の評価であり、「印刷物しわ、カール」では全て○の評価であった。
【０１９２】
実施例１の結果より、本発明に係るインクジェット記録法、インクジェットプリンタでは、記録媒体Ｒのインクが着弾した時から紫外線照射を受ける時までの温度を、ＵＶインクが吐出される時の温度（６０℃）よりも低く、且つ２０℃以上４０℃以下である３５℃に設定して画像形成を行なったことで、記録媒体Ｒに画像を高画質で形成できることが分かった。さらに、記録媒体の温度を上述の様に設定することで、熱収縮性の材質からなる記録媒体Ｒに対しても、印刷物にしわ、カールを発生させることなく高画質で画像を形成できることが分かった。
【０１９３】
［第二の実施例］
第二の実施例では、低照度（２．５〜１５ｍＷ／ｃｍ^２）による紫外線照射を行なって記録媒体Ｒ上のＵＶインクを硬化させた。
【０１９４】
第二の実施例では、まず濃ブラック（Ｋ）、濃シアン（Ｃ）、濃マジェンタ（Ｍ）、濃イエロー（Ｙ）、白（Ｗ）、淡ブラック（Ｌｋ）、淡シアン（Ｌｃ）、濃マジェンタ（Ｌｍ）、淡イエロー（Ｌｙ）の各インクを、表６〜表８に示す組成で調合し、インク組成物４〜インク組成物６を得た。
【０１９５】
【表６】

【表７】

【表８】

【０１９６】
ここで、表７ににおいて、化合物１は化学式（２８）に示すスルホン化物であり、開始剤３は化学式（２９）に示すヨードニウムイオンのホスフェート塩である。表８において、化号物２は化学式（３０）に示すスルホン化物であり、開始剤４は化学式（３１）に示すヨードニウムイオンのボレート塩である。
【０１９７】
【化２９】

【０１９８】
インク組成物４〜インク組成物６をインクとして用い、インクジェットプリンタＡによる記録媒体Ｒに対する画像形成を行なった。インクジェットプリンタＡにおいて、記録ヘッド２１にＵＶインクを供給するインク供給系は、インクタンク、供給パイプ、前室インクタンク及びフィルター付き配管で形成した。さらに、上記インク供給系はほぼ全経路にわたって断熱材とヒータとを備え、供給パイプ内部でＵＶインクの温度が５０℃に維持される構成とした。
【０１９９】
記録ヘッド２１は吐出口１５から一回あたり２ｐｌ又は１５ｐｌの２通りの吐出量でインクを吐出可能であり、且つ７２０×７２０ｄｐｉ（ｄｏｔｓ　ｐｅｒ　ｉｎｃｈ）という解像度で記録媒体Ｒにインクドットを形成することができる構成とした。さらに、記録ヘッド２１内部の吐出口１５におけるＵＶインクの温度は、面ヒーター１６及びヘッドヒーター１３によって５０℃に調節した。
【０２００】
記録媒体Ｒとしては、表９に示すようにＯＰＰ、ＯＮｙ、ＰＥＴ、シュリンクＰＶＣ、シュリンクＯＰＳ、ユポ粘着紙といった非インク吸収性の材質からなる幅６００ｍｍ、長さ１０００ｍｍの長尺記録材料を用いた。ＵＶランプ３は、表９に示すものを各試料ごとに適用した。記録媒体Ｒにおける紫外線の照度は、ＵＶランプ３と記録媒体Ｒとの距離を調節することで制御した。
【０２０１】
各試料（試料Ｎｏ．１〜３０）における画像形成のため、画像形成条件ＵＶランプ３は、記録ヘッド２１の走査方向に隣接した位置に設置した。照射タイミングは、ＵＶインクが記録媒体Ｒに着弾後、０．１５秒後に紫外線照射を受けるように設定した。また、ＵＶインク、記録媒体、記録媒体温度、ＵＶランプ、記録媒体における照度及びピーク波長及び照射エネルギーは、表９にそれぞれ示すように設定した。
【０２０２】
【表９】

【０２０３】
画像形成後、各試料ごとに画像を評価した結果を表１０にまとめる。表１０において、各評価項目ごとの凡例は表５の場合と共通である。また、各試料についてトータルインク膜厚を測定したところ、トータルインク膜厚の範囲は２．３〜１３μｍであった。
【０２０４】
【表１０】

【０２０５】
表１０によれば、記録媒体温度（記録媒体Ｒのインクが着弾した時から紫外線照射を受ける時までの温度）を１０℃に設定した試料Ｎｏ．１〜６では、「印刷物しわ、カール」の項目では全て○の評価だったが、「文字品質」及び「色混じり（にじみ）」の項目では△以下の評価が多く、「文字品質」では６例中４例、「色混じり（にじみ）」では６例中３例がそれぞれ×の評価であった。
【０２０６】
また、記録媒体温度を５０℃に設定した試料Ｎｏ．７〜１２では、「文字品質」及び「色混じり（にじみ）」の項目では半数以上が○の評価で、残りが△の評価であった。また、「印刷物しわ、カール」の項目では、全ての例が△以下の評価であり、２例は×の評価であった。
【０２０７】
一方、記録媒体温度を、３５℃に設定した試料Ｎｏ．１３〜３０では、「文字品質」及び「色混じり（にじみ）」ではいずれも◎又は○の評価であり、「印刷物しわ、カール」では全て○の評価であった。
【０２０８】
実施例２の結果より、本発明に係るインクジェット記録法、インクジェットプリンタでは、記録媒体Ｒのインクが着弾した時から紫外線照射を受ける時までの温度を、ＵＶインクが吐出される時の温度（６０℃）よりも低く、且つ２０℃以上４０℃以下である３５℃に設定して画像形成を行なったことで、照射エネルギーが２０〜４５ｍＪ／ｃｍ^２と低い場合でも、記録媒体Ｒに画像を高画質で形成できることが分かった。さらに、記録媒体の温度を上述の様に設定することで、熱収縮性の材質からなる記録媒体Ｒに対しても、印刷物にしわ、カールを発生させることなく高画質で画像を形成できることが分かった。
【０２０９】
この様に、カチオン重合性のＵＶインクで画像形成を行なう形態のインクジェットプリンタＡにおいて、ヘッド温度調節機構６で記録ヘッド２１から吐出される時のＵＶインクの温度を３０℃以上１００℃以下に調節し、メディア温度調節機構で記録媒体ＲのＵＶインクが着弾する時から紫外線が照射される時までの温度を２０℃以上４０℃以下に調節するとともに、記録ヘッド２１から吐出される時のＵＶインクの温度を記録媒体ＲのＵＶインクが着弾する時から紫外線が照射される時までの温度よりも高い温度に調節することで、空気中の湿気によって阻害されることなく、記録媒体Ｒ上でのＵＶインクを硬化させることができる。よって、記録媒体Ｒに画像を高画質で形成することができる。
【０２１０】
特に、記録ヘッド２１から吐出される時のＵＶインクの温度を記録媒体ＲのＵＶインクが着弾する時から紫外線が照射される時までの温度よりも高い温度に調節することで、記録媒体Ｒ上でのＵＶインクの温度を容易に調節することができる。このことで、記録媒体Ｒ上で紫外線照射により速やかにＵＶインクを硬化させることができるので、記録媒体Ｒに画像をきわめて高画質で形成することができる。
【０２１１】
また、記録媒体ＲのＵＶインクが着弾する時から紫外線が照射される時までの温度を４０℃以下とすることで、熱伸縮性の材質からなる記録媒体Ｒに画像を形成するような場合でも、記録媒体Ｒにしわやカールを発生させることなく、記録媒体Ｒに画像を高画質で形成することができる。
【０２１２】
さらに、湿度調節機構７により、記録媒体Ｒが紫外線の照射を受ける位置及び該位置近傍の湿度を５％以上４０％以下に調節することで、ＵＶインクに紫外線を照射する際に湿気によるＵＶインク硬化阻害を防止することができる。よって、４０℃以下という比較的低温な条件でも効率的に記録媒体Ｒ上のＵＶインクを硬化させることができる。このことにより、記録媒体Ｒにしわやカールを発生させることなく、記録媒体Ｒに画像をきわめて高画質で形成することができる。
【０２１３】
なお、今回開示された実施の形態は、すべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。
【０２１４】
本発明に係るインクジェット記録方法、インクジェットプリンタは、紫外線により硬化するインクを適用するものとは限らない。カチオン重合性のものであれば、活性エネルギ線として、紫外線以外に電子線、赤外線、可視光線等の電磁波により硬化するインクを適用することとしてもよい。
【０２１５】
また、本発明に係るインクジェットプリンタに適用されるメディア温度調節機構は上述の例に限らない。
ここで、メディア温度調節機構５の変形例を図５、図６を参照して説明する。なお、詳細には、図５、図６に示す変形例において、図２に示すメディア温度調節手段５１又はメディア温度検出手段５２の少なくとも一方が異なり、それ以外の構成要素は上記例と同様である。従って、これら構成要素には上記例と同様の符号を付し、詳細な説明は割愛する。
【０２１６】
図５に示すように、メディア温度調節手段５１としてペルチェ素子を用いた加熱・冷却システムを適用する。この加熱・冷却システムは、ペルチェ素子を内蔵したペルチェ素子内蔵ローラ５１ｆ、５１ｇを備えている。これらペルチェ素子内蔵ローラ５１ｆ、５１ｇは、記録媒体Ｒを間に介在させるように互いに隣接して配置され、互いに逆回転駆動し記録媒体Ｒを挟持した状態で搬送方向Ｆへ搬送する。これらペルチェ素子内蔵ローラ５１ｆ、５１ｇにおいて、内蔵されたペルチェ素子が作動すると、挟持した記録媒体Ｒを画像形成面及び非画像形成面の両面側から加熱もしくは冷却できるようになっている。なお、ペルチェ素子は吸熱と放熱を同時に行うので、例えば、冷却を行う場合には、ペルチェ素子内蔵ローラ５１ｆ、５１ｇを空洞にし、この空洞となった部分にファン等によって送風し、放熱する必要がある。
【０２１７】
また、図５の実施例ではメディア温度検出手段５２として熱電対センサ５２ｂを適用する。熱電対センサ５２ｂは、二つの異なる種類の金属を環状に連結し二接点の温度差により発生する熱電量から記録媒体Ｒの温度を検出する。従って、この場合、メディア温度検出手段５２としての熱電対センサ５２ｂによる検出温度情報に基づいて、このペルチェ素子を用いた冷却システムを作動させ、記録ヘッド２１により画像形成が行われる記録媒体Ｒを冷却し、この記録媒体Ｒの温度を目標設定温度に制御している。
【０２１８】
さらに、図６に示すように、メディア温度調節手段５１としてヒータ５１ｈ及び輻射ランプ５１ｉを用いた加熱システムを適用する。ヒータ５１ｈは、ガイド部材４の背面側に配置されている。ヒータ５１ｈが作動すると、ガイド部材４（又はプラテン４ａ）を媒介して、ガイド部材４（又はプラテン４ａ）により非画像形成面側が支持された記録媒体Ｒを、非画像形成面側から加熱できるようになっている。なお、ガイド部材４（又はプラテン４ａ）は、熱伝導率の大きい材料で形成されていることが好ましく、記録媒体Ｒを加熱することを迅速かつ効率的に媒介することのできる材料で形成されていることが好ましい。輻射ランプ５１ｉは、画像形成部２のキャリッジレール２３に固定されているとともに、赤外線を輻射するものである。輻射ランプ５１ｉが作動すると、赤外線を記録媒体Ｒの画像形成面側に輻射し、画像形成面側から記録媒体Ｒを加熱できるようになっている。また、メディア温度検出手段５２として図４に示すものと同様の熱電対センサ５２ｂを適用する。
【０２１９】
従って、この場合、メディア温度検出手段５２としての熱電対センサ５２ｂによる検出温度情報に基づいて、これらヒータ５１ｈ及び輻射ランプ５１ｉを用いた加熱システムを作動させ、記録ヘッド２１により画像形成が行われる記録媒体Ｒを加熱し、この記録媒体Ｒの温度を目標設定温度に制御している。なお、この場合、ヒータ５１ｈ及び輻射ランプ５１ｉの一方だけの加熱システムを設けるようにして、記録媒体Ｒの温度を制御してもよい。
【０２２０】
以上、図５、図６に示す変形例においても、図１に示す上記例と同様の効果を奏する。また、図１及び図５、図６に示した例では、メディア温度調節機構５により記録媒体Ｒの温度を４０℃以下に制御しているので、ＵＶ照射による記録媒体Ｒの温度が高温化するのを抑えることができ、記録媒体Ｒが変質するのを防止することができる。
【０２２１】
なお、図１及び図５、図６に示した例では、記録ヘッド２１より搬送方向Ｆの上流側の位置又は記録ヘッド２１に対向する位置にメディア温度調節手段５１を設けて、画像形成が行われる前又は画像形成中（画像形成の前後を僅かに含む）の記録媒体Ｒの加熱もしくは加熱及び冷却を行っているが、それに加えて、メディア温度調節手段５１を記録ヘッド２１より搬送方向Ｆの下流側の位置（但しＵＶ照射手段よりは上流側）に設けて画像形成が行われた後の記録媒体Ｒの加熱又は冷却を行ってもよい。
【０２２２】
また、ここで、図６に示すヒータ５１ｈのように、メディア温度調節手段５１を記録媒体Ｒの非画像形成面側に備え、かつ、記録媒体Ｒの非画像形成面側から記録媒体Ｒの加熱もしくは加熱と冷却とを行うことが好ましい。何故なら、記録媒体Ｒの画像形成面側が温度調節手段５１による加熱もしくは加熱と冷却との影響を直接受けることはないので、画像形成面の表面が変質し画像形成品質に影響するということはなく、これにより、画像形成品質の劣化を防止でき、高品質の画像形成を保持することができるからである。また、図６に示すヒータ５１ｈのように、ガイド部材４（又はプラテン４ａ）の背面側にメディア温度調節手段５１を設ける場合には、ガイド部材４（又はプラテン４ａ）が熱伝導率の大きい材料で形成されていることが好ましく、記録媒体Ｒを加熱又は冷却することを迅速かつ効率的に媒介することのできる材料で形成されていることが好ましい。
【０２２３】
【発明の効果】
本発明によれば、湿気によって反応阻害を受けやすいカチオン重合性のインクを適用した場合でも、湿気に影響されることなく記録媒体上に画像を高画質で形成することができる。それに加えて、熱収縮性の材質を記録媒体に適用した場合でも、記録媒体にしわやカールを発生させることなく画像を高画質で形成することができる。
【図面の簡単な説明】
【図１】本発明に係るインクジェットプリンタＡの概略を示す要部側面図である。
【図２】インクジェットプリンタＡの概略を示す要部ブロック図である。
【図３】インクジェットプリンタＡに適用される記録ヘッド２１の斜視図である。
【図４】インクジェットプリンタＡに適用される記録ヘッド２１の正断面図（ａ）及び側断面図（ｂ）である。
【図５】インクジェットプリンタＡの別の実施例を示す要部側面図である。
【図６】インクジェットプリンタＡの別の実施例を示す要部側面図である。
【符号の説明】
５　　　　　メディア温度調節機構
６　　　　　ヘッド温度調節機構
７　　　　　湿度調節機構
１５　　　吐出口
２１　　　記録ヘッド
３０　　　制御部
３１　　　インターフェイス
３２　　　ＣＰＵ
３３　　　メモリ
５１　　　温度調節手段
５２　　　温度検出手段
６１　　　ヘッド温度調節手段
７１　　　送風管
７２　　　送風ファン
７３　　　乾燥カラム
７３ａ　活性化ヒータ
７４　　　湿度センサ
Ａ　　　　　インクジェットプリンタ
Ｒ　　　　記録媒体[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inkjet recording method, an ink, and an inkjet printer.
[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, an inkjet recording system (inkjet printer) that ejects and controls fine dots, ink that has improved color reproduction range, durability, and ejection suitability, ink absorbency, color material coloring, and surface gloss It is possible to obtain image quality comparable to silver halide photography by using a combination of special paper with dramatically improved features.
[0003]
The image quality of today's ink jet recording system has been improved only when an ink jet printer and all of the ink and special paper used in the ink jet printer are available.
[0004]
However, in an ink jet printer that requires special paper, since the recording medium is limited, the cost of the recording medium is increased, and the application range of the ink jet printer is narrowed.
[0005]
Therefore, many attempts have been made to perform recording on a recording 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.
[0006]
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.
[0007]
However, even if these inks are used, the dot diameter after landing greatly changes depending on the type of recording medium and the working environment, and it is not possible to form a high-definition image on all recording media. It is possible. Further, the ink used in the conventional UV inkjet method has a problem that the recording medium is easily shrunk. In particular, thin-film plastic films used in flexible packaging such as food packaging and adhesive labels are particularly susceptible to shrinkage. As a result, the UV inkjet method has not yet been put to practical use in flexible packaging printing and label printing. is the current situation.
[0008]
[Problems to be solved by the invention]
By the way, as the UV ink (photo-curable ink), for example, a radical-curable ink and a cation-curable ink are known. It has been found that by using a cation-curable ink, it is possible to prevent shrinkage during image formation even in the above-mentioned thin-film plastic films and pressure-sensitive adhesive labels.
[0009]
However, the cationic curable ink is easily affected by water (humidity). For example, when an image is formed by landing a UV ink on a recording medium, the ink is sufficiently exposed to ultraviolet light due to the influence of ambient humidity. There is a problem that the UV ink does not cure.
[0010]
In a UV inkjet printer, when the UV ink discharged from a recording head lands on a recording medium, it spreads along the surface of the recording medium from droplets to form dots. Here, in order to form a high-definition image on a recording medium, it is preferable that the diameter of each of a large number of dots formed on the recording medium does not greatly differ between the dots or between the formed images. As described above, if the UV ink is not cured in a short time after being irradiated with ultraviolet rays due to the influence of humidity or the like, the dot diameter changes and the dot diameter becomes unstable.
[0011]
When an image is formed by a UV inkjet printer, inks of different colors are landed on a recording medium in a state of being overlapped or adjacent to each other. If the UV ink is not cured in a short time, inks of different colors are mixed with each other, and the image quality is adversely affected.
[0012]
Japanese Patent Application Laid-Open No. 2002-137375 discloses a proposal for solving the problem caused by the influence of water of the cation-curable ink, by heating an ultraviolet-curable ink (UV ink) that has landed on a print medium (recording medium). An ink-jet printer provided with a heating means for heating is described.
According to the above publication, it is described that the UV ink that has landed on the storage medium is heated, and the UV ink is cured even in a humid state by irradiating the UV ink with ultraviolet rays.
[0013]
However, heating the UV ink after it lands on the recording medium has a time lag until the temperature of the UV ink rises, and the time for the time lag depends on the ink temperature when ejected from the recording head. Become. Therefore, even if the UV ink can be sufficiently cured, the time from when the UV ink is heated to when the UV ink is cured is not always constant. Therefore, it was difficult to form a high-definition image. Further, when the above-mentioned time lag becomes long, there is a possibility that UV inks of different colors are mixed.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide an ink-jet printer capable of recording a high-definition image with excellent character quality, no occurrence of color mixture, and various types of recording media.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 discharges an ink curable by irradiation of an active energy ray toward a recording medium, and irradiates the recording medium on which the ink has landed with the active energy ray. An ink-jet recording method for forming an image, wherein the recording medium is transported from a position where the ink lands to a position where the active energy ray is irradiated, wherein the ink contains a cationically polymerizable component, The temperature at which the ink is ejected is adjusted to 30 ° C. or more and 100 ° C. or less, and the temperature from when the ink on the recording medium lands to when it is irradiated with the active energy ray is 20 ° C. to 40 ° C. C. or less, and the temperature at which the ink is ejected is such that the recording medium is irradiated with the active energy ray from the time the ink lands. Characterized in that it is adjusted to a temperature higher than the temperature up.
[0016]
According to the first aspect of the present invention, the ink is composed including a cationically polymerizable component. The temperature of the ink when ejected from the head is adjusted to 30 ° C. or more and 100 ° C. or less, and the temperature from when the ink on the recording medium lands to when the active energy ray is irradiated is 20 ° C. or more and 40 ° C. or less. Is adjusted to Further, the temperature of the ink when ejected from the head is adjusted to a temperature higher than the temperature from when the ink on the recording medium lands to when the active energy ray is irradiated.
[0017]
An ink containing a cationic polymerizable component has a property that polymerization is easily inhibited by moisture in the air when irradiated with an active energy ray, but the ink of the recording medium is activated from the time the ink of the recording medium lands. By irradiating the ink on the recording medium with the active energy ray while controlling the temperature until the energy ray is irradiated to 20 ° C. or more, the ink can be efficiently polymerized without being hindered by moisture. it can. Accordingly, it is possible to effectively prevent the ink from bleeding on the recording medium and to form a high-quality image. In addition, by adjusting the temperature from the time when the recording medium ink lands on the recording medium to the time when the active energy ray is irradiated to 40 ° C. or less, the recording medium can be thermally shrunk such as a plastic film. Even in the case of a material that is easy to wrinkle, it is possible to prevent wrinkles and curls from occurring on the recording medium.
[0018]
Further, the temperature at which the ink is ejected is adjusted to 30 ° C. or more and 100 ° C. or less, and the temperature at which the ink is ejected is set to the temperature of the portion where the ink lands on the recording medium and the portion where the active energy ray is irradiated. By adjusting the temperature to a higher temperature, the ink can easily be maintained at a temperature at which it can be efficiently cured after the ink has landed on the recording medium to form an ink dot and is irradiated with an active energy ray. As a result, the ink is quickly cured upon being irradiated with the active energy ray, so that the shape of the ink dots can be easily controlled, and it is possible to prevent the ink dots adjacent to each other and having different colors from being mixed. it can. Therefore, an image can be formed on a recording medium with high image quality.
[0019]
The invention according to claim 2 is the ink jet recording method according to claim 1, wherein the ink has a viscosity at 25 ° C. of 25 mPa · s or more and 500 mPa · s or less, and a viscosity when ejected. It is not less than 8 mPa · s and not more than 20 mPa · s.
[0020]
According to the invention described in claim 2, by setting the viscosity of the ink at 25 ° C. to be not less than 25 mPa · s and not more than 500 mPa · s, after the ink lands on the recording medium until it is irradiated with an active energy ray, It can be in close contact with the recording medium and can be appropriately leveled on the recording medium. This makes it possible to easily control the shape of the ink dots made of the ink that has landed on the recording medium to form a high-quality image, and to impart high strength to the image formed on the recording medium.
[0021]
Further, by setting the viscosity at the time of ejection to be 8 mPa · s or more and 20 mPa · s or less, it is possible to prevent the ink from being clogged at the ejection port for ejecting the ink and to smoothly eject the ink. Therefore, a high-quality image can be formed with high efficiency.
[0022]
According to a third aspect of the present invention, in the inkjet recording method according to the first or second aspect, the position at which the recording medium is irradiated with the active energy ray and the humidity near the position are adjusted. It is characterized by.
[0023]
According to the third aspect of the invention, by adjusting the position where the recording medium receives the active energy ray and the humidity near the position, when the ink that has landed on the recording medium is irradiated with the active energy ray, Can be efficiently cured without being hindered by moisture. Accordingly, the ink forming the ink dots on the recording medium can be quickly cured without setting the temperature of the recording medium at the time of receiving the irradiation of the active energy rays to be higher than 40 ° C. Therefore, it is possible to prevent wrinkles and curls from occurring on the recording medium, and to form a high-quality image on the recording medium.
[0024]
According to a fourth aspect of the present invention, in the inkjet recording method according to the third aspect, a position where the recording medium is irradiated with the active energy ray and a humidity near the position are 5% or more and 40% or less. It is characterized by being adjusted to.
[0025]
According to the fourth aspect of the present invention, by adjusting the position where the recording medium is irradiated with the active energy ray and the humidity near the position to 5% or more and 40% or less, the ink on the recording medium can be more efficiently used. Can be cured. Therefore, generation of wrinkles and curls on the recording medium can be effectively prevented, and a high-quality image can be formed on the recording medium.
[0026]
The invention according to claim 5 is an ink used in the inkjet recording method according to any one of claims 1 to 4,
The viscosity at 25 ° C. is from 25 mPa · s to 500 mPa · s, and the viscosity at the time of ejection is from 8 mPa · s to 20 mPa · s.
[0027]
According to the fifth aspect of the invention, the same effects as those of the second aspect of the invention can be obtained.
[0028]
According to a sixth aspect of the present invention, the curable ink is ejected toward the recording medium by irradiating the active energy ray onto the recording medium, and the ink lands on the recording medium on which the ink dots are formed. An inkjet printer that performs image formation by irradiating, a recording head having an ejection port that ejects the ink, an irradiation unit that irradiates the recording medium on which the ink has landed with the active energy ray, and the recording medium, A transport unit configured to transport the ink from a position where the ink lands to a position where the active energy ray is irradiated, and an in-head ink heating unit provided in the vicinity of the discharge port, wherein the temperature of the ink at the discharge port is adjusted. A head temperature adjusting mechanism that is provided near the transport path of the transport unit, and is configured to activate the active energy when the ink of the recording medium lands. A medium temperature adjustment mechanism for adjusting the temperature until the irradiation of the line is performed, wherein the ink contains a cationically polymerizable component, and the medium temperature adjustment mechanism is used when the ink of the recording medium lands. To a temperature of 20 ° C. or more and 40 ° C. or less until the irradiation with the active energy ray is performed, and the head temperature adjusting mechanism adjusts the temperature of the ink at the discharge port to 30 ° C. or more and 100 ° C. or less. Wherein the head temperature adjustment mechanism adjusts the temperature of the ink at the ejection port to a temperature higher than a temperature in a region from a portion where the ink lands on the recording medium to a portion where the active energy ray is irradiated on the recording medium. It is characterized by.
[0029]
According to the sixth aspect of the present invention, the temperature from when the ink on the recording medium lands to when the recording medium is irradiated with the active energy ray is adjusted to 20 ° C. or more and 40 ° C. or less by the medium temperature adjusting mechanism provided near the conveying means. The temperature at which the ink is ejected from the ejection port by the head temperature adjustment mechanism is adjusted to 30 ° C. or more and 100 ° C. or less. Further, the head temperature adjustment mechanism adjusts the temperature at which the ink is ejected from the ejection port to a temperature higher than the temperature from when the ink on the recording medium lands to when it is irradiated with active energy rays. Thus, the same effect as the first aspect can be obtained.
[0030]
The invention according to claim 7 is the ink jet printer according to claim 6, wherein the ink has a viscosity at 25 ° C. of 25 mPa · s or more and 500 mPa · s or less, and a viscosity at the time of ejection of 8 mPa · s. It is not less than s and not more than 20 mPa · s.
[0031]
According to the seventh aspect, the same effects as those of the second aspect can be obtained.
[0032]
The invention according to claim 8 is the ink jet printer according to claim 6 or 7, wherein a position on the conveyance path of the recording medium where the recording medium is irradiated with the active energy ray and a vicinity of the position. A humidity adjusting mechanism for adjusting the humidity of the air.
[0033]
According to the eighth aspect of the present invention, the position at which the recording medium is irradiated with the active energy ray and the humidity near the position are adjusted by the humidity adjusting mechanism. Thereby, the same effect as the invention described in claim 3 can be obtained.
[0034]
According to a ninth aspect of the present invention, in the inkjet printer according to the eighth aspect, the humidity adjustment mechanism includes a position on the conveyance path of the recording medium where the recording medium is irradiated with the active energy ray. The ink jet printer according to claim 8, wherein the humidity near the position is adjusted to 5% or more and 40% or less.
[0035]
According to the ninth aspect of the present invention, the position at which the recording medium is irradiated with the active energy ray and the humidity near the position are adjusted to 5% or more and 40% or less by the humidity adjusting mechanism. Thereby, the same effect as the invention described in claim 4 can be obtained.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the inkjet printer of the present invention will be described with reference to the drawings.
[0037]
FIG. 1 is a cross-sectional view of a main part of an ink jet printer for explaining an image forming process on a sheet-shaped recording medium in an easy-to-understand manner.
[0038]
As shown in FIG. 1, the inkjet printer A includes transport rollers (transporting means) 1a and 1b which have a role of transporting a recording medium R such as a sheet of paper or a resin film, and the transport rollers 1a and 1b. An image forming unit 2 for forming an image on the recording medium R conveyed by the printer, a UV lamp (irradiating means) 3 for irradiating the recording medium R with ink attached thereto by the image forming unit 2 with UV, and conveying the recording medium R A guide member 4 for guiding in the direction F. A transport path along which the recording medium R transported by the transport roller 1a is further transported by the transport roller 1b via the image forming unit 2 is established along the transport direction F.
[0039]
In this embodiment, an example in which a resin film (thin plastic film) wound in a roll is used as a paper supply source is shown, and this roll-shaped resin film is referred to as a “recording medium R”. Further, the recording medium R is not limited to the above-mentioned roll-shaped resin film but may be, for example, a cut sheet shape. Further, the storage medium may be various kinds of paper, various cloths or nonwoven fabrics. May be. Further, the recording medium R may be made of another material, for example, a metal. Further, the recording medium R is not limited to a sheet shape, but may be a plate shape.
[0040]
As shown in FIG. 1, the transport rollers 1 a and 1 b are spaced apart from each other at positions before and after an image is formed on the recording medium R in the image forming unit 2. The transport rollers 1a and 1b are rotationally driven in the same direction as each other, and feed the recording medium R in the transport direction F, thereby transporting the recording medium R from a position where the UV ink lands to a position where irradiation of ultraviolet rays is received.
[0041]
The image forming section 2 includes an ink-jet type recording head 21, a carriage 22 having the recording head 21, and a carriage rail 23 for guiding the movement of the carriage 22.
[0042]
To the recording head 21, inks such as cyan (C), magenta (M), yellow (Y), and black (B) are supplied by a tube or an ink cartridge (not shown). This ink has a high viscosity at room temperature, has a low viscosity when heated, and has a property of being cured when irradiated with UV. Hereinafter, this ink is referred to as “UV ink”. In this embodiment, a cationic curing type UV ink is used, and details of the UV ink will be described later.
[0043]
The carriage 22 has a recording head 21 and is connected to a carriage rail 23 via a connecting portion 22a. The carriage rail 23 is a rail that extends substantially perpendicular to the transport direction F of the recording medium R, and extends in a direction substantially perpendicular to the transport direction F (a direction from the front side to the back side or a direction from the back side to the front side in the plane of FIG. 1). The carriage 22 is guided. The direction in which the carriage rail 23 extends is referred to as a “scanning direction” and will be described below.
[0044]
When an image is formed on the recording medium R, UV ink is ejected from the recording head 21 onto the recording medium R while the carriage 22 is guided by the carriage rail 23 and moves in the scanning direction. .
[0045]
The UV lamp (active energy ray irradiating means) 3 irradiates UV to the image forming surface of the recording medium R to which the UV ink has adhered after the process in the image forming unit 2. By irradiating UV, the UV ink attached to the recording medium R is cured. Here, in FIG. 1, the UV lamp 3 is fixed to the above-described carriage rail 23 via the connecting portion 3a, and is installed at only one position downstream of the recording heads 21, 21,... In the F direction. , The drawing is taken as an example. In addition, the number of the recording heads 21, 21,... It is good also as installing according to.
[0046]
The guide member 4 is a plate-shaped member having a width equal to or larger than the width of the recording medium R. The guide member 4 is arranged to face the recording head 21, supports a recording medium R on which an image is formed by the recording head 21 from the non-image forming surface side, and guides the recording medium R in the transport direction F. Is what you do. The “non-image forming surface” is a surface on the opposite side of the image forming surface of the recording medium R, that is, a surface on which no image is formed.
[0047]
Note that, in detail, a portion of the guide member 4 that is disposed to face the recording head 21 is a platen 4a. A suction chamber (not shown) is provided on the back side of the platen 4a, and a suction port (not shown) including a plurality of small holes communicating with the suction chamber is provided. The platen 4a suction-holds the non-image forming surface of the recording medium R.
[0048]
By combining the above-described components, the carriage 22 moves in the scanning direction while the recording medium R conveyed by the conveying rollers 1a and 1b is supported by the guide member 4 from the non-image forming surface side. Then, the UV ink is ejected from the recording head 21 onto the image forming surface of the recording medium R, and the image is formed.
[0049]
Here, the configuration of the characteristic portion of the present invention will be described.
The ink jet printer A is provided with a medium temperature adjusting mechanism 5, a head temperature adjusting mechanism 6, and a humidity adjusting mechanism 7 shown in FIG.
[0050]
The medium temperature adjusting mechanism 5 controls the temperature of the recording medium R on which an image is formed by the recording head 21 in an area from immediately below the recording head 21 to immediately below the UV lamp 3. Accordingly, the temperature of the recording medium R is adjusted to a set temperature from the time when the ink lands to the time when the ink is irradiated, and the UV ink that lands on the recording medium R is irradiated with the ultraviolet light. It is adjusted to the set temperature. In this way, by controlling the temperature of the UV ink that has landed on the recording medium R, the cation-curable UV ink can be quickly cured in a manner complementary to the humidity adjustment by the humidity adjustment mechanism 7.
[0051]
Here, the set temperature set for controlling the temperature of the recording medium R from the time when the UV ink lands to the time when the UV ink is irradiated is determined by factors such as the material and thickness of the recording medium R and the type of UV ink. The range is preferably from 20 ° C. to 40 ° C.
[0052]
When the temperature of the recording medium R from when the UV ink lands to when it is irradiated with ultraviolet rays is lower than 20 ° C., the cation-curable UV ink is hindered from reacting by moisture in the air. Cannot be quickly cured when exposed to ultraviolet radiation. As a result, the shape of the ink dots formed on the recording medium R cannot be controlled, or adjacent ink dots of different colors intermingle with each other, thereby deteriorating the image quality of the image formed on the recording medium R. It becomes.
[0053]
On the other hand, when the temperature of the recording medium R from when the UV ink lands to when it is irradiated with ultraviolet rays is higher than 40 ° C., for example, the recording medium R made of a heat-shrinkable material contracts on the transport path. It becomes wrinkled and curled. In this case, the quality of the printed matter obtained by forming an image on the recording medium R is degraded.
[0054]
As shown in FIG. 2, the medium temperature adjustment mechanism 5 schematically includes a medium temperature adjustment unit 51, a medium temperature detection unit 52, an input unit 53, and a medium temperature control unit (here, the control unit 30 corresponds to the medium temperature adjustment unit 51. ). The medium temperature adjusting means 51, the medium temperature detecting means 52, the input means 53, and the medium temperature controlling means (control section 30) are connected to each other via an interface 31.
[0055]
The medium temperature adjusting unit 51 is provided near at least a part of a conveying path of the recording medium R conveyed by the conveying rollers 1a and 1b as a conveying unit, and heats the recording medium R. Specifically, as shown in FIG. 1, the medium temperature adjusting means 51 is disposed on the image forming surface side of the recording medium R before the image is formed by the recording head 21, and includes a heater 51a and a reflector 51b. And
[0056]
During the temperature control, if the temperature of the recording medium R is too high due to heating or if the temperature around the recording medium R is too high, not only the heating function but also the cooling function is provided to the medium temperature adjusting means. It may be provided to control the temperature of the recording medium.
[0057]
The heater 51a has a function as a heat source extending in the width direction of the recording medium R (a direction from the front side to the back side or a direction from the back side to the front side in the plane of FIG. 1).
The reflector 51b is arranged so as to cover the heater 51a in a state where the image forming surface side of the recording medium R is open, and reflects the radiant heat from the heater 51a generated by operating the heater 51a.
Therefore, the heater 51a and the reflector 51b have a function as a medium temperature adjusting unit 51 for heating the recording medium R from the image forming surface side.
[0058]
The medium temperature detecting means 52 is arranged near at least a part of the conveying path of the recording medium R conveyed by the conveying rollers 1a and 1b in FIG. 1 and detects the temperature of the recording medium R. Specifically, the medium temperature detecting means 52 is arranged on the image forming surface side of the recording medium R before the image is formed by the recording head 21, and corresponds to the temperature sensor 52a shown in FIG. .
[0059]
As shown in FIG. 1, the temperature sensor 52a is a non-contact type sensor that is fixed to the above-described reflector 51b and does not directly contact the surface of the recording medium R. The temperature of the recording medium R is detected by the temperature sensor 52a. Then, the temperature sensor 52a as the temperature detecting means 52 inputs the temperature information of the recording medium R as a detection result (hereinafter, referred to as "detected temperature information") to the control unit 30, as shown in FIG.
[0060]
The input unit 53 is an operation panel, a keyboard, or the like, and inputs information (hereinafter, referred to as “setting information”) relating to the type (form, material, thickness, etc.) of the recording medium R to the control unit 30. The input unit 53 inputs the input setting information to the control unit 30 when the setting information is input to an operation panel, a keyboard, or the like by a manual operation of an operator. Specifically, the setting information is information on the properties of the recording medium R, such as the form: film, material: resin, and thickness: 0.05 mm.
[0061]
In the present embodiment, the control unit 30 is formed as a component that also serves as a medium temperature control unit and a head temperature control unit and a humidity control unit described below, and includes a memory 33, a CPU 32, and an interface 31. .
[0062]
The interface 31 is connected to each component of the inkjet printer A. The interface 31 mediates the transfer of various information and signals between the control unit 30 and the medium temperature adjusting unit 51, the medium temperature detecting unit 52 or the input unit 53 described above.
[0063]
The memory 33 includes a storage area for storing various data such as image data formed on the storage medium R, and a work area for temporarily storing programs and data when the CPU 32 performs calculations.
[0064]
The memory 33 stores, in a storage area, detected temperature information output from the media temperature detecting means 52, setting information output from the input means, and the like. Further, the memory 33 stores set temperature information (hereinafter, referred to as “set temperature information”) corresponding to the set information as a data table. Therefore, in the memory 33, the target temperature information can be switched according to the setting information by the input means 53. Specifically, when setting information such as form: roll film, material: resin, and thickness: 0.05 mm is changed to setting information such as form: roll paper, material: paper, thickness: 0.01 mm, The set temperature information can be switched such that the set temperature also switches from 30 ° C. to 35 ° C.
[0065]
The set temperature may be changed based on a manual change of the set information by the input unit, or the set temperature may be automatically changed by acquiring the set information and other conditions by a sensor or the like.
[0066]
The CPU 32 develops a designated program from various programs stored in the memory 33 in a work area of the memory 33, and executes various processes according to the programs in accordance with input signals from each sensor.
[0067]
The CPU 32 reads out the detected temperature information and the set temperature information stored in the memory 33, performs various calculations such as comparing these information, and controls the medium temperature adjusting means 51 based on the calculation results to control the recording medium. The temperature is controlled from when the R UV ink lands to when it is irradiated with ultraviolet light.
[0068]
Next, the head temperature adjusting mechanism 6 will be described.
The head temperature adjusting mechanism 6 adjusts the temperature of the UV ink at an ejection port 15 described later in the recording head 21 so that the UV ink can be ejected in a stable and low-viscosity state. In addition, by controlling the temperature of the UV ink at the ejection port 15, the temperature of the UV ink from when it lands on the recording medium R to when it is irradiated with ultraviolet light is reliably controlled.
[0069]
That is, the head temperature adjustment mechanism 6 controls the temperature of the ink that lands on the recording medium R, the temperature of which is controlled by the medium temperature adjustment mechanism 5, at a temperature at which the ink is efficiently cured by ultraviolet irradiation in the recording head 21, and a stable ejection. The temperature is controlled so that the viscosity of the UV ink is reduced to a viscosity that is possible, and the temperature is kept substantially constant without changing the temperature due to environmental conditions and the like.
[0070]
Here, the temperature of the UV ink discharge port 15 is set so that the viscosity of the UV ink is optimized and is adjusted by the head temperature adjusting mechanism 6, and the temperature is in the range of 30 ° C. or more and 100 ° C. or less. In addition, it is more preferable that the temperature is higher than the temperature from when the UV ink of the recording medium R lands to when it is irradiated with ultraviolet rays.
[0071]
When the temperature of the UV ink at the ejection port 15 is lower than 30 ° C., the UV ink is highly viscous, so that the UV ink is not ejected from the ejection port 15 as controlled, or the UV ink is clogged at the ejection port 15 or the ink nozzle 12 described later. Problems occur.
[0072]
On the other hand, when the temperature at the UV ink discharge port 15 exceeds 100 ° C., there is a problem that the life of the recording head 21 is shortened. Discharge means, which will be described later, for generating a driving force for discharging the UV ink from the discharge port 15 has low heat resistance. If the temperature is maintained at a high temperature exceeding 100 ° C., the UV ink cannot be discharged in a controlled manner. Therefore, if the temperature exceeds 100 ° C., the life of the recording head 21 is shortened, and it becomes difficult to maintain and manage the inkjet printer A.
[0073]
Further, by maintaining the temperature of the UV ink ejection port 15 at a temperature higher than the temperature between the time when the UV ink of the recording medium R lands and the time when the recording medium R is irradiated with UV light, the UV ink on the recording medium R It becomes easy to control the temperature at the time of irradiation to a temperature at which curing can be performed efficiently. This makes it easy to control the shape of the ink dots on the recording medium R, and also prevents adjacent ink dots of different colors from intermingling. Therefore, an image can be formed on the recording medium R with high image quality.
[0074]
As shown in FIG. 2, the head temperature adjustment mechanism 6 includes a head temperature adjustment unit (a surface heater 16 and a head heater 13), a head temperature detection unit (a head temperature sensor) 19, and a head temperature control unit ( Here, the control unit 30 corresponds). The head temperature adjustment unit, the head temperature detection unit, and the head temperature control unit (control unit 30) are connected to each other via an interface 31.
[0075]
As shown in FIG. 3 or FIG. 4, the recording head 21 has an ink inlet 17 into which ink is injected, a plurality of ejection ports 15 for ejecting ink, and guides ink from the ink inlet 17 to the ejection port 15. A supply path 11 in the head, a head temperature sensor (head temperature detecting means) 19 for detecting an ink temperature in the supply path 11 in the head, and a surface heater (head) for heating ink from at least a part of the outside of the supply path 11 in the head. A temperature adjusting means (ink heating means in the head) 16 and a head heater (head temperature adjusting means (ink heating means in the head)) 13 for heating ink in at least a part of the supply path 11 in the head are provided. ing.
[0076]
As shown in FIGS. 4A and 4B, the ink inlet portion 17 is formed in a funnel shape that tapers from the side of the recording head 21 toward the inside. The ink inlet 17 is connected to an ink supply path (not shown), and ink is supplied from an ink tank (not shown) via the ink supply path.
[0077]
The ejection ports 15 are provided on the lower surface (nozzle surface 15a) of the recording head 21, and are arranged at regular intervals along a center line on the lower surface.
[0078]
In the process of guiding the ink from the ink inlet 17 to the discharge port 15, the supply path 11 in the head includes an ink storage section 18 for temporarily storing the ink, an ink nozzle 12 for guiding the ink from the ink storage section 18 to the discharge port 15, An ejection unit (not shown) composed of, for example, a piezo element for generating a driving force for ejecting ink is provided.
[0079]
The ink storage section 18 is formed in a trapezoidal shape in a side view that becomes thinner toward the front (left side in FIG. 4A). The front end of the ink inlet 17 is connected to the rear surface of the ink container 18, and both the ink container 18 and the ink inlet communicate with each other.
[0080]
In the ink storage section 18, a plurality of ink nozzles 12 for guiding ink to the discharge ports 15 are provided on the lower surface facing the nozzle surface 15a so as to correspond to each discharge port. That is, the ink nozzles 12 are arranged at equal intervals along the flow direction of the ink flowing from the ink inlet 17.
[0081]
As described above, when the ink nozzles 12 are arranged along the ink flow direction, the pressure of the ink flowing into the ink nozzles 12 located at a position distant from the ink inlet 17 is weakened, and stable ejection may not be performed. There is. For this reason, in the present embodiment, the pressure of the ink flowing into each ink nozzle is prevented from fluctuating by forming the shape of the ink storage portion 18 into a trapezoidal shape in a side view that becomes thinner toward the front.
[0082]
A head temperature sensor (head temperature detecting means) 19 extends inward from the vicinity of the ink inlet 17, that is, from the rear surface of the ink storage 18, in order to detect the temperature of the ink flowing from the ink inlet 17. The state is provided.
[0083]
The surface heater 16 is formed in a U-shape so as to cover the in-head supply path 11 inside the recording head 21, and the surface heater 16 heats the ink in the in-head supply path 11 to reduce the viscosity.
[0084]
The head heater 13 is formed in a cylindrical shape, and is stretched from the front end to the rear end of the ink storage unit 18 so as to be in a state along the ink nozzles 12 below the ink storage unit 18. Then, the ink is heated by the head heater 13 so that each temperature of the ink ejected from each ejection port falls within a predetermined temperature range.
[0085]
As described above, since the head heater 13 is in a state in which the ink nozzles 12 are arranged below the ink storage unit 18, it is possible to heat the ink before flowing into each of the ink nozzles 12 without variation.
[0086]
As shown in FIG. 2, the head temperature control means (corresponding to the control unit 30) is composed of an interface 31, a CPU 32, a memory 33, and the like, and interfaces with a control program and control data written in the memory 33. Various devices connected to the control unit 31 are controlled.
[0087]
The interface 31 is electrically connected to a surface heater (head temperature adjusting means) 16, a head heater (head temperature adjusting means) 13, a head temperature sensor (head temperature detecting means) 19 and the like.
[0088]
In the memory 33, various data in ink supply, various control programs and control data related to the operation of each unit of the inkjet printer, and the like are written.
The CPU 32 performs calculations based on various data written in the memory 33 and the temperature detected by the head temperature sensor 19, so that the temperature of the UV ink at the ejection port 15 falls within the above range and the viscosity of the UV ink is optimized. The surface heater 16 and the head heater 13 are controlled to control the temperature of the UV ink at the discharge port 15 so that
[0089]
Next, the humidity control mechanism 7 will be described.
The humidity adjusting mechanism 7 controls the humidity near the region immediately below the UV lamp 3 in the transport path along which the recording medium R is transported by the transport rollers 1a and 1b, so that the recording medium R is irradiated with ultraviolet light. The humidity near the position is adjusted.
[0090]
Here, the position where the recording medium R is irradiated with ultraviolet rays and the humidity near the position are preferably controlled to 5% or more and 40% or less.
If the recording medium R is irradiated with ultraviolet rays and the humidity near the position is lower than 5%, the components of the ink jet printer A are housed in a highly airtight chassis to control the humidity. Therefore, there arises a problem that the inkjet printer A becomes expensive.
[0091]
On the other hand, when the position where the recording medium R is irradiated with the ultraviolet light and the humidity near the position exceed 40%, there is a problem that the ink that has landed on the recording medium R is not efficiently cured by the irradiation of the ultraviolet light. In order to prevent wrinkles and curls from occurring in the recording medium R, the medium temperature adjusting mechanism 5 adjusts the temperature when the recording medium R is irradiated with ultraviolet rays to 40 ° C. or less.
[0092]
When the UV ink is irradiated with ultraviolet rays at this temperature, the cationically curable UV ink is susceptible to reaction inhibition due to moisture in the air, so that the UV ink cannot be quickly cured in an environment where the humidity exceeds 40%. At this time, a problem arises in that the shape of the ink dots on the recording medium R cannot be controlled, or ink dots of different colors adjacent to each other intersect, so that an image cannot be printed on the recording medium R with high image quality.
[0093]
As shown in FIGS. 1 and 2, the humidity control mechanism 7 includes a blower tube 71, a blower fan (humidity control means) 72, a drying column (humidity control means) 73, and a humidity sensor (humidity detection). Means) 74 and humidity control means (here, the control unit 30 corresponds).
[0094]
The blower tube 71 guides the air introduced from the inkjet printer A and adjusted in humidity by the drying column 73 to a position where the recording medium R is irradiated with ultraviolet rays. One end of the blower tube 71 is exposed and installed outside the inkjet printer A. The other end of the blower tube 71 is formed in a shape corresponding to the width of the recording medium R, and is installed in the vicinity of the UV lamp 3 so that air can be sent out toward the space between the UV lamp 3 and the recording medium R. .
[0095]
Inside the blower tube 71, a blower fan 72, a drying column 73, a humidity sensor 74 and the like are installed.
The blower fan 72 blows air from the outside of the inkjet printer A to the UV lamp 3 side and blows air from the UV lamp side 3 to the outside of the inkjet printer A under the control of the control unit 30. Here, the wind speed at the time of blowing air from the outside of the ink jet printer A to the UV lamp 3 side can keep the humidity of the space between the UV lamp 3 and the recording medium R in the above-described range, and the recording head 21 to the recording medium. The determination is made on the condition that it does not affect the flight path of the UV ink when the UV ink is ejected toward R.
[0096]
The drying column 73 is formed by filling the inside of the blower tube 71 with a reversibly hygroscopic desiccant such as silica gel or zeolite in a gas-permeable form. Further, the drying column 73 is provided with an activation heater 73a for heating and reactivating the desiccant when the moisture absorbing ability of the desiccant is reduced.
The humidity sensor 74 is installed at a position closer to the UV lamp 3 than the drying column 73 inside the blower tube 71. The humidity sensor 74 detects the humidity and transmits the detected humidity data to the control unit 30.
[0097]
The control unit 30 controls the blower fan 72 and the activation heater 73a based on the humidity detected by the humidity sensor 74 to adjust the location where the recording medium R is irradiated with ultraviolet rays and the humidity near the location.
When an image is formed on the recording medium R by discharging the UV ink from the recording head 21 and subsequently irradiating the UV light by the UV lamp 3, the control unit 30 sends the UV lamp 3 from outside the inkjet printer A to the blower fan 72. By blowing air toward the side, air from which moisture has been removed by the drying column 73 is sent into the space between the UV lamp 3 and the recording medium R. At this time, the humidity sensor 74 detects the humidity of the air sent toward the UV lamp and sends it to the control unit 30.
[0098]
When the humidity increases and the humidity of the position where the recording medium R is irradiated with the ultraviolet light and the humidity at the position reach the upper limit value at which the ink can be rapidly cured by the irradiation of the ultraviolet light, the control unit 30 controls the ink jet printer to perform image formation. A series of operations related to image formation of each component A is stopped.
[0099]
After each component is stopped, the control unit 30 controls the activation heater 73a and the blower fan 72 to reactivate the desiccant filled in the drying column 73. The reactivation of the desiccant is performed by heating the desiccant with the activation heater 73a while blowing the desiccant from the UV lamp 3 side to the inkjet printer A with the blower fan 72, so that the water absorbed by the desiccant is discharged outside the inkjet printer A. This is done by diffusing it into After the reactivation operation is performed for a predetermined time to reactivate the desiccant, the control unit 30 subsequently resumes the operation for image formation by each component.
[0100]
In addition, as a method for the control unit 30 to determine the end of the desiccant reactivation, in addition to performing the above-described predetermined time, a humidity sensor 74 is installed outside the inkjet printer A from the drying column 73, There is a method of detecting the humidity of the air exhausted by the humidity sensor 74, and the like.
[0101]
Here, the ink used in the inkjet printer will be described. The UV ink is of a cationically curable type as described above, and at least a cationically polymerizable compound which is polymerized and cured by UV irradiation and a cationically polymerizable compound for initiating the polymerization reaction of the cationically polymerizable compound by UV irradiation. It contains a photopolymerization initiator (photoacid generator) and a coloring material for producing a color as an ink. Further, at least a part of well-known various additives used for the cationically curable photocurable resin may be added to the UV ink.
[0102]
Further, in this example, the UV ink is used. However, it is not necessarily limited to the one that is started to be cured by ultraviolet rays, and the one that uses a cationic polymerization initiator that starts polymerization with active energy rays such as active energy rays and electromagnetic waves. Is also good. That is, the active energy ray is basically an electromagnetic wave including light such as ultraviolet light, infrared light, and visible light (the initiator which absorbs visible light has a color, which is less preferable). In recent years, electron beam-curable inks have been developed, and an electron beam may be used as an active energy beam. As described above, in this example, a case where ultraviolet rays are used as energy rays is described as an example.
[0103]
Further, the ink applied to the ink jet recording method and the ink jet printer according to the present invention has a viscosity at 25 ° C. of 25 mPa · s or more and 500 mPa · s or less, and a viscosity at the time of ejection of 8 mPa · s or more and 20 mPa · s. It is preferable that the composition is as follows.
[0104]
When the viscosity of the ink at 25 ° C. is less than 25 mPa · s, the ink ejected from the recording head 21 and landed on the recording medium R spreads out on the recording medium R immediately after landing, so that the ink dot shape can be controlled. The image quality of the image is deteriorated. On the other hand, if the viscosity of the ink at 25 ° C. exceeds 500 mPa · s, the ink that has landed on the recording medium R cannot be appropriately leveled after landing, and the shape of the ink dots cannot be controlled, and the image quality of the image cannot be improved. At the same time, the ink dots cannot be adhered to the recording medium R with a sufficient adhesive force, resulting in a problem that the strength of the image decreases.
[0105]
If the viscosity at the time when the ink is ejected is less than 8 mPa · s, the ink drips from the ejection port 15 irrespective of the operation of the ejection means, so that useless ink dots are formed on the recording medium R and the image is printed. Reduce image quality. On the other hand, if the viscosity at which the ink is ejected exceeds 20 mPa · s, it becomes difficult to control the amount of ink ejected from the ejection port 15 at one time, and the image quality is degraded. Further, ink clogging is likely to occur in the discharge port 15 and the supply path 11 in the head, and it becomes difficult to maintain the ink jet printer A.
[0106]
Various known cationically polymerizable monomers can be used as the photocationically polymerizable compound. For example, epoxy compounds exemplified 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. , Vinyl ether compounds, oxetane compounds and the like.
[0107]
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.
[0108]
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.
[0109]
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.
[0110]
Among these epoxides, in consideration of the rapid curing property, an aromatic epoxide and an alicyclic epoxide are preferable, and an alicyclic epoxide is particularly preferable. In the present invention, one of the above epoxides may be used alone, or two or more may be used in appropriate combination.
[0111]
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.
[0112]
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.
[0113]
The oxetane compound used 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.
[0114]
When a compound having five or more oxetane rings is used, the viscosity of the composition becomes high, which makes it difficult to handle, and the glass transition temperature of the composition becomes high, so that the obtained cured product has sufficient tackiness. Will be gone. The compound having an oxetane ring used in the present invention is preferably a compound having 1 to 4 oxetane rings.
Examples of the compound having one oxetane ring include a compound represented by the following general formula (1).
[0115]
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[0116]
In the 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. It is. R²Is 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 1-propenyl group, a 2-propenyl group, a 2-methyl-1-propenyl group, a 2-methyl-2- Aromatic ring such as alkenyl group having 2 to 6 carbon atoms such as propenyl group, 1-butenyl group, 2-butenyl group or 3-butenyl group, phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group or phenoxyethyl group Or an alkoxycarbonyl 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 or a butylcarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group or a butoxycarbonyl group. Group, ethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group or Carbons 2-6, such as Chi carbamoyl group 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.
[0117]
Next, examples of the compound having two oxetane rings include a compound represented by the following general formula (2).
Embedded image

In the formula (2), R¹Is the same group as 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 or butenylene group, carbonyl group, alkylene group containing carbonyl group, alkylene group containing carboxyl group, alkylene group containing carbamoyl group, etc. It is.
[0118]
Also, R³Is also a polyvalent group selected from the groups represented by the following formulas (3), (4) and (5).
Embedded image

In equation (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 or a butyl group, or an alkoxy group having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group or a butoxy group. , A halogen atom such as a chlorine atom or a bromine atom, a nitro group, a cyano group, a mercapto group, a lower alkylcarboxyl group, a carboxyl group, or a carbamoyl group.
[0119]
Embedded image

In the formula (4), R⁵Represents an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO₂, C (CF₃)₂Or C (CH₃)₂It is.
[0120]
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In the formula (5), R⁶Is 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 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 or a butyl group, or an aryl group.
[0121]
R⁷Is also a group selected from the group represented by the following formula (6).
Embedded image

In equation (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.
[0122]
Specific examples of the compound having two oxetane rings include compounds represented by the following formulas (7) and (8).
Embedded image

The compound represented by the formula (7) is a compound represented by the formula (2)¹Is an ethyl group, R³Is a carboxyl group.
[0123]
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The compound represented by the formula (8) is a compound represented by the formula (2)¹Is an ethyl group, and R3 is a group represented by the formula (5)⁶And R⁷Is a methyl group, and n is a substituent which is 1.
[0124]
Among the compounds having two oxetane rings, preferred examples other than the above-mentioned compounds include compounds represented by the following general formula (9). In equation (9), R¹Is the same group as in the general formula (1).
Embedded image

[0125]
Examples of the compound having 3 to 4 oxetane rings include a compound represented by the following general formula (10).
Embedded image

In the formula (10), R¹Is the same group as in the general formula (1). R⁹Is, for example, a branched alkylene group having 1 to 12 carbon atoms such as groups represented by the following formulas (11) to (13), or a branched poly (alkyleneoxy) group such as a group represented by the following formula (14) Or a branched polysiloxy group such as a group represented by the following formula (15). j is 3 or 4.
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In the formula (11), R¹⁰Is a lower alkyl group such as a methyl group, an ethyl group or a propyl group.
[0126]
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In the formula (14), 1 is an integer of 1 to 10.
[0127]
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Specific examples of the compound having 3 to 4 oxetane rings include a compound represented by the following formula (16).
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[0128]
Further, examples of the compound having 1 to 4 oxetane rings other than those described above include a compound represented by the following formula (17).
Embedded image

In equation (17), R⁸Is the same group as in formula (6). 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.
[0129]
Preferred specific examples of the oxetane compound used in the present invention include the following compounds.
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Embedded image

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[0130]
The method for producing the compound having an oxetane ring is not particularly limited, and may be a conventionally known method. The above production method includes, for example, a method of synthesizing an oxetane ring from a diol, which is disclosed by Pattyson (DB Pattison, J. Am. Chem. Soc., 3455, 79 (1957)). Other than these, compounds having a high molecular weight of about 1,000 to 5,000 and having 1 to 4 oxetane rings are also exemplified.
[0131]
Examples of these include the following compounds.
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Here, p is 20 to 200.
[0132]
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Here, q is 15 to 100.
[0133]
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Here, s is 20 to 200.
[0134]
In the present invention, at least one oxetane compound as a photopolymerizable compound and at least one compound selected from an epoxy compound and a vinyl ether compound are contained for the purpose of suppressing shrinkage of the recording medium R upon curing of the ink. Is preferred.
[0135]
As the above-mentioned cationic photopolymerization initiator, for example, a chemical amplification type photoresist or a compound used for photocationic polymerization is used (Organic Materials Research Society, "Organic Materials for Imaging", Bunshin Publishing Co., Ltd.). (1993), pp. 187-192). Examples of compounds suitable for the present invention are given below. 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.
Embedded image

[0136]
Secondly, a sulfonate that generates sulfonic acid can be mentioned. Specific compounds are exemplified below.
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[0137]
Third, halides that photogenerate hydrogen halides can also be used. Specific compounds are shown below.
Embedded image

[0138]
Fourth, an iron allene complex can be mentioned.
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[0139]
The ink of the present invention contains, for the first time, an acid proliferating agent that newly generates an acid by an acid generated by irradiation with active energy rays, which is disclosed in JP-A-8-248561 and JP-A-9-034106. Is preferred. The use of the acid breeding agent makes it possible to further improve ejection stability.
[0140]
The ink according to the present invention preferably contains at least one photoacid generator selected from aromatic onium compounds of diazonium, iodonium or sulfonium having an aryl borate compound as a counter ion, and iron arene complexes.
[0141]
As the above-mentioned coloring material, 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 in terms of weather resistance.
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. 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,
[0142]
Further, in the present invention, it is preferable to use a white ink in order to improve the color concealing property on a transparent substrate such as a plastic film. In particular, it is preferable to use white ink in the formation of a soft package image or a label image. However, since the ejection amount is large, the white ink is naturally used from the viewpoint of the ejection stability and the occurrence of curling and wrinkling of the recording medium R described above. There are restrictions on the amount.
[0143]
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. In dispersing the pigment, a dispersant may be added. As the dispersant, a polymer dispersant is preferably used, and as the polymer dispersant, Solsperse series of Avecia is mentioned.
[0144]
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 dispersing medium is performed using a solvent or a polymerizable compound. However, in the case of the radiation-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.
[0145]
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 curing sensitivity can be maintained.
In the ink according to the present invention, the colorant concentration is preferably 1% by mass to 10% by mass of the whole ink.
[0146]
Various additives other than those described above can be used in the ink according to the present invention. For example, in order to improve the storage stability of the ink composition, a polymerization inhibitor can be added in an amount of 200 to 20,000 ppm. Since it is preferable that the ultraviolet curable ink is heated and reduced in viscosity before ejection, it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization. In addition, if necessary, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, waxes, etc. Can be added.
[0147]
In order to improve the adhesion to the recording medium R, it is also effective to add a trace amount of an organic solvent. In this case, the addition is effective within a range that does not cause a problem of solvent resistance and VOC (volatile organic compound), and the amount of use is 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.
[0148]
The above-described UV ink is ejected and drawn on the recording medium R by an ink jet recording method, and then the ink is cured by irradiating ultraviolet rays (active energy rays).
Here, the total ink film thickness after the ink lands and is cured by irradiating ultraviolet rays is preferably 2 to 20 μm. In the field of screen image formation, the total ink film thickness is over 20 μm at present, but in the field of flexible packaging image formation where the recording medium R is often a thin plastic material, the curl It cannot be used not only because of the problem of wrinkles but also because of the problem that the stiffness and texture of the entire image-formed product change.
[0149]
As for the ink ejection conditions, it is preferable that the recording head and the ink are heated to 30 to 100 ° C. and ejected from the viewpoint of ejection stability. Active energy ray-curable inks have large fluctuations in viscosity due to temperature fluctuations, and fluctuations in viscosity directly affect the droplet size and droplet ejection speed, causing image quality degradation. It is necessary to keep it. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., and more preferably set temperature ± 1 ° C.
[0150]
In the present invention, it is preferable that the amount of liquid droplets ejected from each nozzle is 2 to 15 pl. In order to form a high-definition image, it is necessary that the droplet amount is within this range. However, in the case of discharging with this droplet amount, the above-described discharge stability becomes particularly severe, and an acid multiplying agent is essential. Become.
[0151]
In the image recording method of the present invention, as the irradiation condition of the generated light beam, it is preferable that ultraviolet light is irradiated during 0.001 to 2.0 seconds after the ink has landed, more preferably 0.001 to 1.0 seconds. It is. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.
[0152]
A basic method of irradiating light (ultraviolet light) is disclosed in JP-A-60-132767. According to this, light sources are provided on both sides of the head unit, and the 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. Pat. 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 a side surface of a head unit to irradiate a recording unit with ultraviolet rays. . In the image forming method of the present invention, any of these irradiation methods can be used.
[0153]
Further, a method of irradiating ultraviolet rays into two stages, first irradiating ultraviolet rays by 0.001 to 2.0 seconds after landing of the ink by the above-described method, and further irradiating active energy rays after completion of all printing. Is also one of the preferred embodiments. By dividing the irradiation of the ultraviolet light into two stages, it is possible to further suppress the contraction of the recording medium R that occurs when the ink is cured.
[0154]
In the present invention, it is preferable to use ultraviolet rays having a low illuminance of 0.1 to 50 mW / cm2 in the wavelength range effective for curing. Conventionally, in a UV inkjet system, the maximum illuminance in a wavelength region effective for curing is 50 mW / cm in order to suppress dot spread and bleeding after ink landing.²In general, a light source with a high illuminance of more than is used. However, when these light sources are used, particularly in the case of a shrink label or the like, the contraction of the recording medium R is so large that it cannot be practically used. In the present invention, by using an acid multiplying agent, the maximum illuminance in a wavelength range effective for curing is 0.1 to 50 mW / cm.²Even when ultraviolet light having a low illuminance is used, a high-definition image can be formed and the recording medium R does not shrink.
[0155]
Examples of the light source used for ultraviolet irradiation include, but are not limited to, a low-pressure mercury lamp, a UV laser, a xenon flash lamp, an insect lamp, a black light, a germicidal lamp, a cold cathode tube, and an LED.
In the present invention, the maximum illuminance in the wavelength range effective for curing is 50 to 3000 mW / cm.²It is also effective to use ultraviolet rays. Although it is a high illuminance light source used for conventional UV inkjet recording, there is a problem of shrinkage of the recording medium R as described above, and practically UV inkjet recording has not been used in the field of soft packaging image formation / label image formation. According to the configuration of the present invention, this problem is solved, and a high-definition image can be formed on various plastic films using a conventionally used high-illuminance light source. Examples of the light source include, but are not limited to, a high-pressure mercury lamp, a metal halide lamp, and an electrodeless UV lamp.
[0156]
As the recording medium R that can be used in the present invention, in addition to ordinary uncoated paper, coated paper, etc., various non-absorbable plastics and films thereof used for so-called soft packaging can be used. Are, for example, PET (polyethylene terephthalate) film, OPS (stretched polystyrene) film, OPP (stretched polypropylene) film, ONy (stretched nylon) film, PVC (stretched polyvinyl chloride) film, PE (polyethylene) film, TAC (tril. Acetylcellulose) film. As other plastics, polycarbonate, acrylic resin, ABS (acrylonitrile-butadiene-styrene), polyacetal, PVA (polyvinyl alcohol), rubbers and the like can be used.
[0157]
Further, the present invention can be applied to metals and glasses. Among these recording media R, the configuration 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 that 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.
[0158]
The surface energies of these various plastic films are greatly different, and there has conventionally been a problem that the dot diameter after ink landing varies depending on the recording medium R. In the configuration of the present invention, a good high-definition image is formed on a wide range of recording media R having a surface energy of 35 to 60 mN / m, including an OPP film having a low surface energy, an OPS film, and a PET having a relatively large surface energy. it can.
[0159]
In the present invention, it is better to use a long (web) recording medium R in terms of the cost of the recording medium R such as packaging cost and production cost, the production efficiency of prints, and the ability to cope with prints of various sizes. It is advantageous.
[0160]
Next, the operation of the inkjet printer A of the present invention will be described.
In an ink jet printer, an image can be formed by setting an ink cartridge, a recording medium R, and the like, and turning on the power.
When the ink is supplied from the ink cartridge, the control unit 30 detects the temperature of the ink in the ink storage unit 18 based on the detection result of the head temperature sensor 19. Then, the control unit 30 selects heating temperature data corresponding to the detected temperature, controls the output states of the surface heater 16 and the head heater 13 based on the selected heating temperature data, and controls the in-head supply. Heating is performed so that the ink in the passage 11 is within a predetermined temperature range (for example, within 1 ° C. above and below the head target set temperature).
[0161]
Next, the operation from when the recording medium R is fed to when it is discharged will be described.
First, here, setting information is entered into input means 53 such as an operation panel and a keyboard by a manual operation of the operator. In this case, the setting information is information on the properties of the recording medium R such as a form: a roll-shaped film, a material: PET, and a thickness: 0.05 mm. Thus, the input unit 53 inputs the setting information to the control unit 30 via the interface 31. This setting information is stored in the memory 33 of the control unit 30.
[0162]
In the inkjet printer A, the leading end of the recording medium R set on a spindle (not shown) is guided to the transport roller 1a along a paper feed guide (not shown), and the leading end of the recording medium R is aligned.
[0163]
The aligned recording medium R is transported to the image forming unit 2 by the transport roller 1a. During this time, the temperature sensor 52a as the medium temperature detecting means 52 detects the temperature of the recording medium R on which an image is to be formed by the recording head 21. The temperature sensor 52a inputs the detected temperature information to the control unit 30 via the interface 31. This detected temperature information is stored in the memory 33 of the control unit 30.
[0164]
Then, the CPU 32 of the control unit 30 reads the detected temperature information stored in the memory 33 and the set temperature corresponding to the set information, and performs a comparison operation. When the CPU 32 determines that the temperature of the recording medium R needs to be increased or decreased according to the calculation result, the CPU 32 inputs an operation signal to the medium temperature adjusting unit 51 via the interface 31. Then, the medium temperature adjusting means 51 operates. In this case, the heater 51a operates to generate radiant heat from the heater 51a, thereby heating the recording medium R from the image forming surface side.
[0165]
When it is determined that the temperature of the recording medium R does not need to be increased or decreased according to the calculation result, the CPU 32 does not input the operation signal to the medium temperature adjusting unit 51. Therefore, the heater 51a as the medium temperature adjusting means 51 does not operate, and the recording medium R is not heated.
[0166]
In this manner, the medium temperature adjustment mechanism 5 determines the temperature from the time the ink on the recording medium R lands to the time the ink is irradiated with ultraviolet light based on the temperature information detected by the medium temperature detection means 52. It is controlled to cure quickly by irradiation.
[0167]
Subsequently, in a state where the temperature is controlled by the medium temperature adjusting mechanism 5, the recording medium R is supported on the non-image forming surface side by the guide member 4, is guided in the transport direction F, and is transported on the transport path. Although the non-image forming surface side of the recording medium R is supported by the guide member 4, the recording medium R is in a state of being sucked and held by the platen 4a as described above.
[0168]
Then, an image is formed by the recording head 21 on the image forming surface of the recording medium R on which the non-image forming surface is supported. More specifically, in a state where the non-image forming surface of the recording medium R is suction-held by the platen 4a, the recording head 21 moves in the scanning direction along with the operation of the carriage 22 to apply UV ink to the image forming surface of the recording medium. Discharge and image formation are performed. The recording medium R on which the image formation has been performed is conveyed downstream of the recording head 21 in the conveying direction F, that is, immediately below the UV lamp 3.
[0169]
Subsequently, the recording medium R conveyed immediately below the UV lamp 3, that is, the recording medium R to which the UV ink has adhered is irradiated with UV from the UV lamp 3, and the UV ink adhered to the recording medium R is cured. . Then, the recording medium R that has gone through the above steps is discharged through a discharge guide (not shown).
[0170]
During the image formation by the inkjet printer A, the temperature of the ink at the ejection port 15 is controlled by the head temperature adjustment mechanism 6. By this control, the temperature of the ink at the ejection port 15 is adjusted to a temperature higher than the temperature between the time when the UV ink of the recording medium R lands and the time when the UV ink is irradiated with ultraviolet light, when the UV ink has the optimum viscosity. Have been.
[0171]
During image formation by the inkjet printer A, air whose humidity has been reduced by the desiccant is supplied to the space between the UV lamp 3 and the recording medium R by the humidity adjustment mechanism 7. Thereby, the humidity at which the recording medium R is irradiated with the ultraviolet light and the humidity in the vicinity of the position are adjusted to the humidity at which the UV ink can be rapidly cured by the ultraviolet light irradiation.
[0172]
In this embodiment, the head temperature adjusting means 61 of the head temperature adjusting mechanism 6, the medium temperature adjusting means 51 of the medium temperature adjusting mechanism 5, and the humidity adjusting means 72, 73 of the humidity adjusting mechanism 7, all have common control. It is composed of devices. As a result, the number of components of the ink jet printer can be reduced, and the temperature control of the UV ink in the head, the temperature control of the recording medium before UV irradiation, and the UV ink Humidity control can be performed at the irradiation place.
[0173]
Next, an example of the inkjet printer 1 according to the above-described embodiment will be described.
[0174]
[First embodiment]
In the first embodiment, high illuminance (550 to 700 mW / cm²) Was performed to cure the UV ink on the recording medium R.
[0175]
In the first embodiment, first, dark black (K), dark cyan (C), dark magenta (M), dark yellow (Y), light black (Lk), light cyan (Lc), dark magenta (Lm), Each light yellow (Ly) ink was prepared with the compositions shown in Tables 1 to 3 to obtain Ink Compositions 1 to 3.
[0176]
[Table 1]

[Table 2]

[Table 3]

[0177]
Here, in Table 1, the initiator 1 is a borate salt of a sulfonium ion represented by the chemical formula (24). In Table 2, the thermal base 1 is a borate salt of an ammonium ion represented by the chemical formula (25), and the initiator 2 is a borate salt of a sulfonium ion represented by the chemical formula (26). In Table 3, the thermal base 2 is a borate salt of an ammonium ion represented by the chemical formula (27).
[0178]
Embedded image

[0179]
Using ink compositions 1 to 3 as inks, an image was formed on a recording medium R by an inkjet printer A. In the ink jet printer A, an ink supply system for supplying UV ink to the recording head 21 was formed of an ink tank, a supply pipe, a front chamber ink tank, and a pipe with a filter. Further, the ink supply system is provided with a heat insulating material and a heater over almost all paths, and the temperature of the UV ink is maintained at 60 ° C. inside the supply pipe.
[0180]
The recording head 21 is capable of ejecting ink from the ejection port 15 at two ejection amounts of 2 pl or 15 pl at a time, and forms ink dots on the recording medium R with a resolution of 720 × 720 dpi (dots per inch). It was configured to be able to. Further, the temperature of the UV ink at the ejection port 15 inside the recording head 21 was adjusted to 60 ° C. by the surface heater 16 and the head heater 13.
[0181]
As shown in Table 4, the recording medium R has a width of 600 mm and a length of 1000 mm made of a non-ink-absorbing material such as OPP, ONy, PET, PVC, and OPS, and an ink-absorbing material such as cast-coated paper and Japanese paper. A long recording material was used. The UV lamp 3 shown in Table 4 was applied to each sample. The illuminance of ultraviolet light on the recording medium R was controlled by adjusting the distance between the UV lamp 3 and the recording medium R.
[0182]
In order to form an image on each sample (Sample Nos. 1 to 30), the image forming condition UV lamp 3 was installed at a position adjacent to the recording head 21 in the scanning direction. The irradiation timing was set so that the UV ink was irradiated 0.2 seconds after landing on the recording medium R. Further, the UV ink, the recording medium, the recording medium temperature, the UV lamp, the illuminance, the peak wavelength, and the irradiation energy of the recording medium were set as shown in Table 4.
[0183]
[Table 4]

[0184]
Table 5 summarizes the results of image evaluation for each sample after image formation. In Table 5, legends for each evaluation item are as follows. When the total ink film thickness of each sample was measured, the range of the total ink film thickness was 2.3 to 13 μm.
[0185]
[Table 5]

[0186]
In Table 5, "character quality" was evaluated by printing a 6-point MS Mincho in Y, M, C, and K colors on the recording medium R and then enlarging the loupe with a loupe to evaluate the roughness of the printed character. Among the evaluations, は indicates “no roughness”. ○ indicates “slightly rough”. The symbol Δ indicates “there is a rough but readable character. The level is almost at the limit of practical use”. X indicates "Grassiness is severe, characters are faint and unreadable".
[0187]
The “color mixture (bleeding)” was evaluated by visually observing adjacent color ink dots with a magnifying glass and visually observing. Of the evaluations, ◎ indicates “adjacent dots keep a perfect circle and no bleeding”. ○ indicates that “adjacent dots keep a perfect circle and have almost no bleeding”. The symbol Δ indicates “adjacent dots are slightly blurred and the dot shape is distorted, but the level is just barely practical”. X indicates “a level that is not practical because adjacent dots are blurred and intermingled”.
[0188]
“Wrinkles and curls of printed matter” were evaluated by visually observing the printed matter by hand immediately after image formation. ○ indicates “good”. Δ indicates “Somewhat good, just before practical use”. × indicates “bad”.
[0189]
According to Table 5, the sample No. in which the recording medium temperature (the temperature from when the ink of the recording medium R lands to when it receives ultraviolet irradiation) is set to 10 ° C. In items 1 to 6, the items of “printed material wrinkles and curls” were all evaluated as “○”, but in the items of “character quality” and “color mixture (bleeding)”, there were many evaluations of “△” or less, especially “color mixture (bleeding)”. ) ", Half of them were evaluated as x.
[0190]
Sample No. 1 in which the recording medium temperature was set to 50 ° C. In 7 to 12, some of the items of “character quality” and “color mixture (bleeding)” were evaluated as “○”, but more than half of them were evaluated as “△” or less. In addition, in the item of “printed material wrinkles and curls”, all cases where the plastic material was applied to the recording medium R were evaluated as x.
[0191]
On the other hand, when the recording medium temperature was set to 35 ° C., Sample No. 13 to 30, all of the “character quality” and “color mixture (bleeding)” were evaluated as ◎ or 、, and “printed wrinkles and curls” were all evaluated as ○.
[0192]
According to the result of the first embodiment, in the ink jet recording method and the ink jet printer according to the present invention, the temperature from when the ink of the recording medium R lands to the time when the recording medium R is irradiated with the ultraviolet light is set to the temperature when the UV ink is ejected (60). (° C.) and 35 ° C. which is 20 ° C. or more and 40 ° C. or less, and it was found that an image could be formed on the recording medium R with high image quality. Further, it is found that by setting the temperature of the recording medium as described above, it is possible to form an image with high image quality even on the recording medium R made of a heat-shrinkable material without causing wrinkles or curls in printed matter. Was.
[0193]
[Second embodiment]
In the second embodiment, low illuminance (2.5 to 15 mW / cm²) Was performed to cure the UV ink on the recording medium R.
[0194]
In the second embodiment, first, dark black (K), dark cyan (C), dark magenta (M), dark yellow (Y), white (W), light black (Lk), light cyan (Lc), dark Magenta (Lm) and pale yellow (Ly) inks were prepared with the compositions shown in Tables 6 to 8 to obtain Ink Compositions 4 to 6.
[0195]
[Table 6]

[Table 7]

[Table 8]

[0196]
Here, in Table 7, the compound 1 is a sulfonated product represented by the chemical formula (28), and the initiator 3 is a phosphate salt of iodonium ion represented by the chemical formula (29). In Table 8, compound 2 is a sulfonated compound represented by the chemical formula (30), and initiator 4 is a borate salt of iodonium ion represented by the chemical formula (31).
[0197]
Embedded image

[0198]
Using ink compositions 4 to 6 as inks, an image was formed on recording medium R by inkjet printer A. In the ink jet printer A, an ink supply system for supplying UV ink to the recording head 21 was formed of an ink tank, a supply pipe, a front chamber ink tank, and a pipe with a filter. Further, the ink supply system is provided with a heat insulating material and a heater over almost all the paths, and the temperature of the UV ink is maintained at 50 ° C. inside the supply pipe.
[0199]
The recording head 21 is capable of ejecting ink from the ejection port 15 at two ejection amounts of 2 pl or 15 pl at a time, and forms ink dots on the recording medium R with a resolution of 720 × 720 dpi (dots per inch). It was configured to be able to. Further, the temperature of the UV ink at the ejection port 15 inside the recording head 21 was adjusted to 50 ° C. by the surface heater 16 and the head heater 13.
[0200]
As shown in Table 9, a long recording material made of a non-ink-absorbing material such as OPP, ONy, PET, shrink PVC, shrink OPS, and YUPO adhesive paper was used as the recording medium R, as shown in Table 9. . The UV lamp 3 shown in Table 9 was applied to each sample. The illuminance of ultraviolet light on the recording medium R was controlled by adjusting the distance between the UV lamp 3 and the recording medium R.
[0201]
In order to form an image on each sample (Sample Nos. 1 to 30), the image forming condition UV lamp 3 was installed at a position adjacent to the recording head 21 in the scanning direction. The irradiation timing was set so as to receive the ultraviolet irradiation 0.15 seconds after the UV ink landed on the recording medium R. Further, the UV ink, the recording medium, the recording medium temperature, the UV lamp, the illuminance, the peak wavelength, and the irradiation energy of the recording medium were set as shown in Table 9, respectively.
[0202]
[Table 9]

[0203]
Table 10 summarizes the results of image evaluation for each sample after image formation. In Table 10, legends for each evaluation item are common to those in Table 5. When the total ink film thickness of each sample was measured, the range of the total ink film thickness was 2.3 to 13 μm.
[0204]
[Table 10]

[0205]
According to Table 10, the recording medium temperature (the temperature from the time when the ink of the recording medium R lands to the time when it is irradiated with ultraviolet rays) is set to 10 ° C., and the sample No. In items 1 to 6, “wrinkled prints and curls” were all evaluated as “○”, but “character quality” and “color mixture (bleeding)” were evaluated as “△” and “character quality” in 6 items. In four of the examples, and in "color mixture (bleeding)", three of the six cases were evaluated as x.
[0206]
Sample No. 1 in which the recording medium temperature was set to 50 ° C. In 7 to 12, more than half of the items of “character quality” and “color mixture (bleeding)” were evaluated as ○, and the rest were evaluated as Δ. In addition, in the item of “printed material wrinkles and curls”, all the examples were evaluated as Δ or less, and two examples were evaluated as x.
[0207]
On the other hand, when the recording medium temperature was set to 35 ° C., Sample No. 13 to 30, all of the “character quality” and “color mixture (bleeding)” were evaluated as ◎ or 、, and “printed wrinkles and curls” were all evaluated as ○.
[0208]
According to the result of the second embodiment, in the ink jet recording method and the ink jet printer according to the present invention, the temperature from the time when the ink on the recording medium R lands to the time when the ultraviolet ray is irradiated is set to the temperature when the UV ink is ejected (60). C), and the image formation was performed at a temperature of 35 ° C., which is 20 ° C. to 40 ° C., so that the irradiation energy was 20 to 45 mJ / cm.²It was found that an image could be formed on the recording medium R with high image quality even when the image quality was low. Further, it is found that by setting the temperature of the recording medium as described above, it is possible to form an image with high image quality even on the recording medium R made of a heat-shrinkable material without causing wrinkles or curls in printed matter. Was.
[0209]
As described above, in the inkjet printer A in which the image is formed with the cationic polymerizable UV ink, the temperature of the UV ink when ejected from the recording head 21 by the head temperature adjusting mechanism 6 is adjusted to 30 ° C. or more and 100 ° C. or less. The medium temperature adjusting mechanism adjusts the temperature from the time when the UV ink of the recording medium R lands to the time when the ultraviolet light is irradiated to 20 ° C. or more and 40 ° C. or less, and the UV ink when ejected from the recording head 21. Is adjusted to a temperature higher than the temperature from the time when the UV ink lands on the recording medium R to the time when the ultraviolet rays are irradiated thereon, so that the temperature on the recording medium R is not hindered by moisture in the air. UV ink can be cured. Therefore, an image can be formed on the recording medium R with high image quality.
[0210]
In particular, by adjusting the temperature of the UV ink when ejected from the recording head 21 to a temperature higher than the temperature from when the UV ink lands on the recording medium R to when it is irradiated with ultraviolet light, the temperature on the recording medium R Temperature of the UV ink can be easily adjusted. This makes it possible to quickly cure the UV ink on the recording medium R by irradiating ultraviolet rays, so that an image with extremely high image quality can be formed on the recording medium R.
[0211]
Also, by setting the temperature from the time when the UV ink lands on the recording medium R to the time when the ultraviolet ray is irradiated on the recording medium R to 40 ° C. or less, even when an image is formed on the recording medium R made of a heat-stretchable material, In addition, it is possible to form an image on the recording medium R with high image quality without causing wrinkles and curls on the recording medium R.
[0212]
Further, the humidity adjustment mechanism 7 adjusts the humidity at which the recording medium R is irradiated with the ultraviolet light and the vicinity of the position to 5% or more and 40% or less, so that when the UV ink is irradiated with the ultraviolet light, Inhibition of curing can be prevented. Therefore, the UV ink on the recording medium R can be efficiently cured even under a relatively low temperature condition of 40 ° C. or less. This makes it possible to form an image on the recording medium R with extremely high image quality without generating wrinkles or curls on the recording medium R.
[0213]
It should be noted that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0214]
The ink-jet recording method and the ink-jet printer according to the present invention are not limited to those using an ink that is cured by ultraviolet rays. As long as it is a cationic polymerizable ink, an ink that is cured by an electromagnetic wave such as an electron beam, an infrared ray, or a visible light beam in addition to ultraviolet rays may be used as the active energy ray.
[0215]
Further, the media temperature adjustment mechanism applied to the inkjet printer according to the present invention is not limited to the above-described example.
Here, a modified example of the medium temperature adjusting mechanism 5 will be described with reference to FIGS. In detail, in the modified examples shown in FIGS. 5 and 6, at least one of the medium temperature adjusting means 51 and the medium temperature detecting means 52 shown in FIG. 2 is different, and the other components are the same as those in the above example. . Therefore, these components are denoted by the same reference numerals as in the above example, and detailed description is omitted.
[0216]
As shown in FIG. 5, a heating / cooling system using a Peltier element as the medium temperature adjusting means 51 is applied. This heating / cooling system includes Peltier device built-in rollers 51f and 51g each having a Peltier device built therein. These Peltier element built-in rollers 51f and 51g are arranged adjacent to each other with the recording medium R interposed therebetween, and are driven to rotate in opposite directions to convey the recording medium R in the conveying direction F while sandwiching the recording medium R. When the built-in Peltier device operates in the Peltier device built-in rollers 51f and 51g, the sandwiched recording medium R can be heated or cooled from both sides of the image forming surface and the non-image forming surface. Since the Peltier device simultaneously absorbs and dissipates heat, for example, in the case of cooling, it is necessary to make the Peltier device built-in rollers 51f and 51g hollow, and to blow the hollow portion with a fan or the like to dissipate heat. is there.
[0219]
In the embodiment of FIG. 5, a thermocouple sensor 52b is applied as the medium temperature detecting means 52. The thermocouple sensor 52b connects two different types of metals in a ring shape and detects the temperature of the recording medium R from the thermoelectric quantity generated by the temperature difference between the two contacts. Therefore, in this case, the cooling system using the Peltier element is operated based on the temperature information detected by the thermocouple sensor 52b as the medium temperature detecting means 52, and the recording medium R on which the image is formed by the recording head 21 is cooled. Then, the temperature of the recording medium R is controlled to the target set temperature.
[0218]
Further, as shown in FIG. 6, a heating system using a heater 51h and a radiation lamp 51i as the medium temperature adjusting means 51 is applied. The heater 51h is arranged on the back side of the guide member 4. When the heater 51h is activated, the recording medium R whose non-image forming surface is supported by the guide member 4 (or platen 4a) can be heated from the non-image forming surface through the guide member 4 (or platen 4a). It has become. Note that the guide member 4 (or the platen 4a) is preferably formed of a material having high thermal conductivity, and is formed of a material that can mediate heating of the recording medium R quickly and efficiently. Is preferred. The radiation lamp 51i is fixed to the carriage rail 23 of the image forming unit 2 and radiates infrared rays. When the radiation lamp 51i operates, infrared rays are radiated to the image forming surface side of the recording medium R, and the recording medium R can be heated from the image forming surface side. Further, a thermocouple sensor 52b similar to the one shown in FIG.
[0219]
Therefore, in this case, based on the temperature information detected by the thermocouple sensor 52b as the medium temperature detecting means 52, the heating system using the heater 51h and the radiation lamp 51i is operated, and the recording is performed by the recording head 21. The medium R is heated, and the temperature of the recording medium R is controlled to a target set temperature. In this case, the temperature of the recording medium R may be controlled by providing a heating system for only one of the heater 51h and the radiation lamp 51i.
[0220]
As described above, the modifications shown in FIGS. 5 and 6 have the same effects as those of the above-described example shown in FIG. In the examples shown in FIGS. 1, 5 and 6, since the temperature of the recording medium R is controlled to 40 ° C. or lower by the medium temperature adjusting mechanism 5, the temperature of the recording medium R is increased by UV irradiation. Can be suppressed, and the recording medium R can be prevented from being deteriorated.
[0221]
In the examples shown in FIGS. 1, 5 and 6, the medium temperature adjusting means 51 is provided at a position on the upstream side of the recording head 21 in the transport direction F or at a position facing the recording head 21 to perform image formation. Heating or heating and cooling of the recording medium R is performed before or during image formation (including slightly before and after image formation). In addition, the medium temperature adjusting means 51 is moved from the recording head 21 in the transport direction F by the recording head 21. Heating or cooling of the recording medium R after image formation may be provided at a downstream position (however, upstream of the UV irradiation means).
[0222]
Also, here, as in a heater 51h shown in FIG. 6, the medium temperature adjusting means 51 is provided on the non-image forming surface side of the recording medium R, and heats the recording medium R from the non-image forming surface side of the recording medium R. Alternatively, it is preferable to perform heating and cooling. Because the image forming surface side of the recording medium R is not directly affected by the heating or the heating and cooling by the temperature adjusting means 51, the surface of the image forming surface is not deteriorated and does not affect the image forming quality. Thereby, deterioration of image formation quality can be prevented, and high quality image formation can be maintained. When the media temperature adjusting means 51 is provided on the back side of the guide member 4 (or the platen 4a) as in the heater 51h shown in FIG. 6, the guide member 4 (or the platen 4a) is made of a material having a large thermal conductivity. It is preferable that the recording medium R be formed of a material that can mediate heating or cooling of the recording medium R quickly and efficiently.
[0223]
【The invention's effect】
According to the present invention, an image can be formed on a recording medium with high image quality without being affected by moisture, even when a cationically polymerizable ink that is easily affected by moisture is used. In addition, even when a heat-shrinkable material is applied to a recording medium, an image can be formed with high image quality without causing wrinkling or curling of the recording medium.
[Brief description of the drawings]
FIG. 1 is a main part side view schematically showing an inkjet printer A according to the present invention.
FIG. 2 is a main block diagram schematically illustrating an inkjet printer A.
FIG. 3 is a perspective view of a recording head 21 applied to the inkjet printer A.
FIGS. 4A and 4B are a front sectional view and a side sectional view of a recording head 21 applied to the ink jet printer A. FIGS.
FIG. 5 is a main part side view showing another embodiment of the ink jet printer A.
FIG. 6 is a main part side view showing another embodiment of the ink jet printer A.
[Explanation of symbols]
5 Media temperature control mechanism
6 Head temperature adjustment mechanism
7 Humidity control mechanism
15 outlet
21 recording head
30 control unit
31 interface
32 CPU
33 memory
51 ° temperature control means
52 ° temperature detecting means
61 Head temperature adjustment means
71 air duct
72 fan
73 drying column
73a activation heater
74 humidity sensor
A inkjet printer
R recording medium

Claims (9)

An ink jet recording method for ejecting an ink curable by irradiation of an active energy ray toward a recording medium, and irradiating the active energy ray on the recording medium on which the ink has landed to form an image, comprising:
The recording medium is transported from a position where the ink lands to a position where the active energy ray is irradiated,
The ink contains a cationically polymerizable component,
The temperature at which the ink is ejected is adjusted to 30 ° C. or more and 100 ° C. or less, and the temperature from the time when the ink lands on the recording medium to the time when the active energy ray is irradiated is 20 ° C. to 40 ° C. ℃ or less,
An ink jet recording method, wherein a temperature at which the ink is ejected is adjusted to a temperature higher than a temperature from a time when the ink lands to a time when the ink is irradiated with the active energy ray. . The ink-jet recording method according to claim 1, wherein the ink has a viscosity at 25 ° C. of 25 mPa · s or more and 500 mPa · s or less, and a viscosity when ejected is 8 mPa · s or more and 20 mPa · s or less. Recording method. 3. The ink jet recording method according to claim 1, wherein a position where the recording medium is irradiated with the active energy ray and a humidity near the position are adjusted. 4. The ink jet recording method according to claim 3, wherein a position where the recording medium is irradiated with the active energy ray and a humidity near the position are adjusted to 5% or more and 40% or less. An ink used in the inkjet recording method according to any one of claims 1 to 4,
An ink having a viscosity at 25 ° C. of 25 mPa · s or more and 500 mPa · s or less, and a viscosity at the time of ejection of 8 mPa · s or more and 20 mPa · s or less. Ink jet printer that ejects curable ink toward a recording medium by irradiating with an active energy ray, and irradiates the active energy ray onto a recording medium on which ink dots are formed as the ink lands, thereby forming an image. And
A recording head having an ejection port for ejecting the ink,
Irradiating means for irradiating the recording medium on which the ink has landed with the active energy ray, and conveying means for conveying the recording medium from a position at which the ink lands to a position at which the active energy ray is irradiated,
A head temperature adjustment mechanism that has an in-head ink heating unit provided near the ejection port, and adjusts the temperature of the ink at the ejection port;
A medium temperature adjustment mechanism that is provided near the conveyance path of the recording medium and adjusts a temperature from when the ink of the recording medium lands to when it is irradiated with the active energy ray;
The ink contains a cationically polymerizable component,
The medium temperature adjustment mechanism adjusts the temperature from the time when the ink of the recording medium lands to the time when the active energy ray is irradiated to 20 ° C. or more and 40 ° C. or less, and the head temperature adjustment mechanism includes: While adjusting the temperature of the ink at the discharge port to 30 ° C or higher and 100 ° C or lower,
The head temperature adjusting mechanism adjusts the temperature of the ink at the ejection port to a temperature higher than a temperature in a region from a portion where the ink lands on the recording medium to a portion where the active energy ray is irradiated. Characteristic inkjet printer. The inkjet ink according to claim 6, wherein the ink has a viscosity at 25 ° C of 25 mPa · s or more and 500 mPa · s or less, and a viscosity at the time of ejection of 8 mPa · s or more and 20 mPa · s or less. Printer. 8. The recording medium conveyance path according to claim 6, further comprising a humidity adjustment mechanism for adjusting a position on the conveyance path of the recording medium to which the recording medium is irradiated with the active energy ray and a humidity near the position. Inkjet printer. The humidity adjustment mechanism adjusts a humidity of a position on the conveyance path of the recording medium where the recording medium is irradiated with the active energy ray and a humidity near the position to 5% or more and 40% or less. 9. The inkjet printer according to 8.

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