JP4257878B2 - Heat-sensitive non-ablative and waste-free imaging element to provide a lithographic printing plate having a difference in dye concentration between image and non-image areas - Google Patents

Description

該色素は好ましくは該最上層中に好ましくは０．０１〜１ｇ／ｍ²の量で、より好ましくは０．０５〜０．２０ｇ／ｍ²の量で存在する。
【００３１】
最上層又は該最上層の直下の層は好ましくは光を熱に変換することができる化合物を含む。光を熱に変換することができる適した化合物は、好ましくは赤外吸収成分であるが、用いられる化合物の吸収が画像通りの露出に用いられる光源の波長領域内にあれば、吸収の波長は特に重要ではない。特に有用な化合物は、例えば、色素、特に上記のものと同じであり得る赤外色素、カーボンブラック、金属炭化物、ホウ化物、窒化物、炭窒化物、ブロンズ−構造酸化物及びブロンズ群に構造的に関連しているがＡ成分がない酸化物、例えばＷＯ_2.9である。導電性ポリマー分散液、例えばポリピロールもしくはポリアニリンに基づく導電性ポリマー分散液を用いることもできる。光を熱に変換することができる該化合物は好ましくは最上層中に存在するが、下の層中に含まれることもできる。
【００３２】
光を熱に変換することができる該化合物は、画像形成要素中に、好ましくは０．０１〜１ｇ／ｍ²の量で、より好ましくは０．０５〜０．５０ｇ／ｍ²の量で存在する。
【００３３】
１つの態様の場合、最上層は架橋された親水性層中に分散された疎水性粒子を含む。特に適した架橋された親水性層は、ホルムアルデヒド、グリオキサル、ポリイソシアナート又は加水分解されたテトラアルキルオルトシリケートなどの架橋剤を用いて架橋された親水性結合剤から得ることができる。後者が特に好ましく；最も好ましいのはテトラエチルもしくはテトラメチルオルトシリケートである。
【００３４】
親水性結合剤として親水性（コ）ポリマー、例えばアクリルアミド、メチロールアクリルアミド、メチロールメタクリルアミド、アクリル酸、メタクリル酸、ヒドロキシエチルアクリレート、ヒドロキシエチルメタクリレートのホモポリマー及びコポリマーあるいは無水マレイン酸／ビニルメチルエーテルコポリマーを用いることができる。用いられる（コ）ポリマー又は（コ）ポリマー混合物の親水度は好ましくは、少なくとも６０重量パーセント、好ましくは８０重量パーセントの程度まで加水分解されたポリ酢酸ビニルの親水度と同じか又はそれより高い。好ましい親水性結合剤はポリビニルアルコールである。
【００３５】
架橋剤、特にテトラアルキルオルトシリケートの量は、好ましくは親水性結合剤の重量部当たり少なくとも０．２重量部、より好ましくは０．５〜５重量部、最も好ましくは１．０重量部〜３重量部である。
【００３６】
本発明に従って用いられる架橋された親水性層は、好ましくは、層の機械的強度及び多孔度を向上させる物質も含有する。この目的でコロイドシリカを用いることができる。用いられるコロイドシリカは、例えば最高４０ｎｍ、例えば２０ｎｍの平均粒度を有するコロイドシリカのいずれの商業的に入手可能な水−分散液の形態であることもできる。さらに、コロイドシリカより大きな寸法の不活性粒子、例えばＪ．Ｃｏｌｌｏｉｄ ａｎｄ Ｉｎｔｅｒｆａｃｅ Ｓｃｉ．，Ｖｏｌ．２６，１９６８，ｐａｇｅｓ ６２ ｔｏ ６９に記載されている通りＳｔｏｅｂｅｒに従って調製されるシリカあるいはアルミナ粒子あるいは二酸化チタン又は他の重金属酸化物の粒子である少なくとも１００ｎｍの平均直径を有する粒子を加えることができる。これらの粒子の導入により、架橋された親水性層の表面に顕微鏡的丘と谷から成る均一な粗いきめが与えられ、それは背景領域における水のための保存場所として働く。
【００３７】
本実施態様に従う平版印刷ベースの架橋された親水性層の厚さは０．２〜２５μｍの範囲内で変化することができ、好ましくは１〜１０μｍである。
【００３８】
本発明に従って用いるために適した架橋された親水性層の特定の例は、ＥＰ−Ａ−６０１ ２４０、ＧＢ−Ｐ−１ ４１９ ５１２、ＦＲ−Ｐ−２ ３００ ３５４、ＵＳ−Ｐ−３ ９７１ ６６０、ＵＳ−Ｐ−４ ２８４ ７０５及びＥＰ−Ａ ５１４ ４９０に開示されている。
【００３９】
本発明の態様において好ましい疎水性ポリマー粒子は熱可塑性ポリマー粒子である。本発明と関連して用いられる疎水性熱可塑性ポリマー粒子は、好ましくは５０℃より高い、より好ましくは７０℃より高い凝析温度を有する。凝結は、熱の影響下で熱可塑性ポリマー粒子が軟化又は溶融することから生じ得る。熱可塑性疎水性ポリマー粒子の凝結温度に特定の上限はないが、温度はポリマー粒子の分解温度より十分に低くなければならない。好ましくは凝結温度は、ポリマー粒子の分解が起こる温度より少なくとも１０℃低い。該ポリマー粒子が凝結温度より高い温度に供されると、それらは凝結して親水性層中で疎水性凝集塊を形成し、これらの部分において親水性層が疎水性になる。
【００４０】
好ましくは８０℃より高いＴｇを有する本発明と関連して用いるための疎水性ポリマー粒子の特定の例は、好ましくはポリ塩化ビニル、ポリ塩化ビニリデン、ポリアクリロニトリル、ポリビニルカルバゾール、それらのコポリマー又は混合物である。最も好適に用いられるのはポリスチレン、ポリメチルメタクリレート又はそれらのコポリマーである。
【００４１】
ポリマーの重量平均分子量は、ＧＰＣによりポリスチレン標準に対して決定される５，０００〜１，０００，０００ｇ／モルの範囲であることができる。
【００４２】
疎水性粒子は０．０１μｍ〜５０μｍ、より好ましくは０．０５ｍｍ〜１０ｍｍそして最も好ましくは０．０５μｍ〜２μｍの粒度を有することができる。
【００４３】
ポリマー粒子は画像形成層の水性コーティング液中の分散液として存在し、ＵＳ−Ｐ−３ ４７６ ９３７に開示されている方法により調製することができる。熱可塑性ポリマー粒子の水性分散液の調製のために特に適した他の方法は：
−疎水性熱可塑性ポリマーを水に非混和性の有機溶媒に溶解し、
−かくして得られる溶液を水又は水性媒体に分散させ、
−蒸発により有機溶媒を除去する
ことを含む。
【００４４】
画像形成層に含有される疎水性熱可塑性ポリマー粒子の量は、好ましくは少なくとも２０重量％、より好ましくは少なくとも３０重量％そして最も好ましくは少なくとも４０重量％である。
【００４５】
本発明の第２の態様の場合、最上層はスイッチ可能なポリマーを含む。スイッチ可能なポリマーとは、加熱により疎水性から親水性にあるいはその逆に変化するポリマーである。スイッチ可能なポリマーの例はポリ−テトラヒドロピラノールメタクリレートである。
【００４６】
画像形成要素の支持体は柔軟性又は剛性であることができる。
【００４７】
本発明と関連する柔軟性支持体として、例えば紙、ポリエチレンがコーティングされた紙などのすべての種類の柔軟性支持体を用いることができるが、プラスチックフィルム、例えば支持体化ポリエチレンテレフタレートフィルム、酢酸セルロースフィルム、ポリスチレンフィルム、ポリカーボネートフィルム、ポリエチレンフィルム、ポリプロピレンフィルムを用いるのが特に好ましい。プラスチックフィルム支持体は不透明又は透明であることができる。
【００４８】
接着促進層が設けられたポリエステルフィルム支持体を用いるのが特に好ましい。本発明に従って用いるのに特に適した接着促進層は、ＥＰ−Ａ−６１９ ５２４、ＥＰ−Ａ−６２０ ５０２及びＥＰ−Ａ−６１９ ５２５に開示されているような親水性結合剤及びコロイドシリカを含む。好ましくは接着促進層中のシリカの量は２００ｍｇ／ｍ²ないし７５０ｍｇ／ｍ²である。さらに、シリカ対親水性結合剤の比率は好ましくは１より高く、コロイドシリカの表面積は好ましくは少なくとも３００ｍ²／ｇ、より好ましくは少なくとも５００ｍ²／ｇである。
【００４９】
支持体は剛性であることもでき、好ましくはアルミニウム箔である。特に好ましいアルミニウム箔は電気化学的に粗面化され、陽極酸化されたアルミニウム支持体である。陽極酸化されたアルミニウム支持体を処理してその表面の接着性を向上させることができる。例えば、アルミニウム支持体を例えば９５℃などの高められた温度でケイ酸ナトリウム溶液を用いてその表面を処理することによりケイ酸塩化することができる。別の場合、リン酸塩処理を適用することができ、それは酸化アルミニウム表面をリン酸塩溶液で処理することを含み、リン酸塩溶液はさらに無機フッ化物を含有していることができる。さらに、酸化アルミニウム表面をクエン酸又はクエン酸塩溶液で濯ぐことができる。この処理は室温で行うことができるか又は約３０〜５０℃というわずかに高められた温度で行うことができる。さらに興味深い処理は酸化アルミニウム表面を重炭酸塩溶液で濯ぐことを含む。さらに、酸化アルミニウム表面をポリビニルホスホン酸、ポリビニルメチルホスホン酸、ポリビニルアルコールのリン酸エステル、ポリビニルスルホン酸、ポリビニルベンゼンスルホン酸、ポリビニルアルコールの硫酸エステル及びスルホン化脂肪族アルデヒドとの反応により生成するポリビニルアルコールのアセタールを用いて処理することができる。これらの後処理の１つ又はそれ以上を単独でか又は組み合わせて行うことができることはさらに明らかである。これらの処理のもっと詳細な記載はＧＢ−Ａ−１ ０８４ ０７０、ＤＥ−Ａ−４ ４２３ １４０、ＤＥ−Ａ−４ ４１７ ９０７、ＥＰ−Ａ−６５９ ９０９、ＥＰ−Ａ−５３７ ６３３、ＤＥ−Ａ−４ ００１ ４６６、ＥＰ−Ａ−２９２ ８０１、ＥＰ−Ａ−２９１ ７６０及びＵＳ−Ｐ−４ ４５８ ００５に示されている。
【００５０】
支持体と最上層の間に画像形成要素は下塗り層及びハレーション防止層などの他の層を含有することができる。画像形成要素が本発明の色素を含有するか否かにかかわらず、画像形成要素は場合により支持体及び最上層の間に反射層を含有することができる。該反射層はＩＲ−線を反射するいずれの層であることもできるが、好ましくは高い視覚濃度を有するアルミニウム、例えば真空蒸着されたアルミニウムである。
【００５１】
本発明と関連する画像形成はサーマルヘッドを用いて行うことができる。好ましくは赤外又は近赤外、すなわち７００〜１５００ｎｍの波長領域で働くレーザーの使用を含む画像通りの走査露出が用いられる。最も好ましいのは近赤外で発光するレーザーダイオードである。画像形成要素の露出は短い画素滞留時間を有するレーザーならびに長い画素滞留時間を有するレーザーを用いて行うことができる。好ましいのは０．００５μ秒〜２０μ秒の画素滞留時間を有するレーザーである。
【００５２】
露出の後、画像形成要素は平版印刷版として用いられる準備ができている。
【００５３】
以下の実施例は本発明を例示するものであり、本発明はそこに制限されるものではない。すべての部及びパーセンテージは、他に特定されなければ重量による。
【００５４】
【実施例】
実施例１
画像形成層の製造
２１．５％のＴｉＯ₂（平均粒度０．３〜０．５μｍ）及び２．５％のポリビニルアルコールを脱イオン水中に含有する１６．８ｇの分散液を混合することにより分散液を調製した。そこにそれぞれ７．０及び１４ｇの２０％ポリスチレン分散液を加えた。これらの分散液にそれぞれ０．７及び１．４ｍｌの加水分解された２８．４３％テトラメチルオルトシリケート溶液を加えた。０．１ｇのＩＲ−色素化合物Ｉをこれらの分散液に加えた。水を用いて分散液を４０ｍｌの容積に補足した。
【００５５】
これらの分散液を十分に撹拌し、下塗りされたＰＥＴ−支持体上に４０μｍの厚さでコーティングし、熱風を用い６０℃において２時間乾燥した。コーティング量（ｇ／ｍ²）を下記の表に示す。
【００５６】
【表１】

注
ａ）ＰＶＡ＝ポリビニルアルコール
ｂ）ＴＭＯＳ＝テトラメチルオルトシリケート
ｃ）ＰＳＴＣ＝カチオン性安定化ポリスチレン
ｄ）ＰＳＴ＝ノニオン性安定化ポリスチレン
コーティング後、画像形成要素を４９℃の温度及び２０％の相対湿度において５日間保存し、ポリビニルアルコールを硬膜させた。
【００５７】
画像形成要素を
ａ）サーマルヘッドＤｒｙｓｔａｒ ２０００（Ａｇｆａ−Ｇｅｖａｅｒｔ Ｎ．Ｖ．，Ｂｅｌｇｉｕｍの商品名）：画像形成要素をＰＥＴ箔（８μｍ）で覆い、１１８ｍＷの出力レベルで画像形成した；
ｂ）ＩＲ−レーザー：版のレベルにおける３４２ｍＷの出力レベル及び４ｍ／秒のドラムスピードにおいて、直径１１μｍのスポットサイズ（１／ｅ²）を有するダイオードレーザーを用いて版を画像形成した
を用いて画像形成した。
【００５８】
画像形成の後、画像を観察することができた
−サーマルヘッド：明青色の背景に対して暗青色の画像
−レーザー記録：明青色の背景に対して白色の画像。
【００５９】
実施例２
２１．５％のＴｉＯ₂（平均粒度０．３〜０．５μｍ）及び２．５％のポリビニルアルコールを脱イオン水中に含有する１６．８ｇの分散液を混合することにより分散液を調製した。そこに１１．２４ｇの１２．４５％ポリスチレン分散液を加えた。この分散液に０．７ｇの加水分解された２８．４３％テトラメチルオルトシリケート溶液を加えた。０．１ｇの下記に示す構造を有するＩＲ−色素化合物を加えた。水を用いて分散液を３０ｍｌの容積に補足した。
【００６０】
【化２】

この分散液を十分に撹拌し、下塗りされたＰＥＴ−支持体上に３０μｍの厚さでコーティングし、熱風を用い６０℃において２時間乾燥した。
【００６１】
コーティング後、画像形成要素を４９℃の温度及び２０％の相対湿度において５日間保存し、ポリビニルアルコールを硬膜させた。
【００６２】
画像形成要素を
ａ）サーマルヘッドＤｒｙｓｔａｒ ２０００（Ａｇｆａ−Ｇｅｖａｅｒｔ Ｎ．Ｖ．，Ｂｅｌｇｉｕｍの商品名）：画像形成要素をＰＥＴ箔（８μｍ）で覆い、１１８ｍＷの出力レベルで画像形成した；
ｂ）ＩＲ−レーザー：版のレベルにおける３００ｍＷの出力レベル及び４〜１０ｍ／秒のドラムスピードにおいて、直径１１μｍのスポットサイズ（１／ｅ²）を有するダイオードレーザーを用いて版を画像形成した
を用いて画像形成した。
【００６３】
画像形成の後、画像を観察することができた
−サーマルヘッド：暗青色の背景に対して明青色の画像
−レーザー記録：暗青色の背景に対して白色の画像。
本発明の主たる特徴及び態様は以下の通りである。
【００６４】
１．画像通りの露出により画像通りに疎水性及び親水性領域を形成することができる最上層を支持体上に含み、画像形成要素の露出によりその光学濃度を変化させることができるＩＲ−色素を含有することを特徴とする、平板印刷版を与えるための感熱性非−融蝕性で廃棄物のない画像形成要素。
【００６５】
２．該ＩＲ−色素がＩＲ−シアニン色素である上記１項に記載の平版印刷版の作製のための画像形成要素。
【００６６】
３．該ＩＲ−シアニン色素が２つの酸基を含む上記２項に記載の平版印刷版の作製のための画像形成要素。
【００６７】
４．該赤外シアニン色素が２つのインドレニン基を含む上記３項に記載の平版印刷版の作製のための画像形成要素。
【００６８】
５．該赤外シアニン色素が下記の構造
【００６９】
【化３】

を有する化合物Ｉである上記４項に記載の平版印刷版の作製のための画像形成要素。
【００７０】
６．最上層が架橋された親水性層中に分散された疎水性粒子を含み、該架橋された親水性層が架橋剤を用いて架橋された親水性結合剤から得られる上記１〜５項のいずれかに記載の平版印刷版の作製のための画像形成要素。
【００７１】
７．該親水性結合剤がポリビニルアルコールである上記６項に記載の平版印刷版の作製のための画像形成要素。
【００７２】
８．該架橋剤が加水分解されたテトラアルキルオルトシリケートである上記６又は７項に記載の平版印刷版の作製のための画像形成要素。
【００７３】
９．最上層がスイッチ可能なポリマーを含む上記１〜５項のいずれかに記載の平版印刷版の作製のための画像形成要素。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat sensitive non-ablatable wasteless imaging element.
[0002]
More specifically, the present invention relates to a heat-sensitive non-ablative, waste-free imaging element for the production of lithographic printing plates having a difference in dye density between image and non-image areas.
[0003]
BACKGROUND OF THE INVENTION
Lithographic printing is a method of printing from a specially made surface that some areas can accept lithographic printing inks while other areas do not accept ink when wetted with water. The area that receives ink limits the printed image area, and the ink-repellent area limits the background area.
[0004]
In the photographic lithographic technical field, photographic materials are imaged on a hydrophilic background as imagewise on oily or oily inks in exposed areas (negative-working) or non-exposed areas (positive-working). Acceptable.
[0005]
In the case of the production of ordinary lithographic printing plates, also called surface lithographic plates or planographic printing plates, it has an affinity for water or such affinity by chemical treatment. A thin layer of the photosensitive composition is coated on the support to obtain Coatings for that purpose include photosensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and various synthetic photosensitive resins. In particular, diazo-sensitized systems are widely used.
[0006]
When the photosensitive layer is exposed image-wise, the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed using a suitable solution to remove unexposed areas of the diazonium salt or diazo resin.
[0007]
In other cases, printing plates are known that include a photosensitive coating that is rendered image-wise soluble in the exposed areas. In that case, subsequent development removes the exposed areas. A typical example of such a photosensitive coating is a quinone-diazide based coating.
[0008]
Typically, the photographic material from which the printing plate is made is exposed in contact through a photographic film containing the image to be reproduced in a lithographic printing process. Such work methods are cumbersome and labor intensive. However, on the other hand, the printing plates thus obtained are of excellent lithographic printing quality.
[0009]
Thus, except for the need for photographic film in the above method, attempts have been made to obtain a printing plate directly from computer data, particularly showing the image to be reproduced. However, the photosensitive coating described above is not sensitive enough to be directly exposed using a laser. Therefore, it has been proposed to coat a silver halide layer over the photosensitive coating. The silver halide can then be exposed directly using a laser under computer control. Subsequently, the silver halide layer is developed to leave a silver image on the photosensitive coating. The silver image then serves as a mask in the overall exposure of the photosensitive coating. After overall exposure, the silver image is removed and the photosensitive coating is developed. Such a method is disclosed, for example, in JP-A-60-61 752, but has the disadvantage of requiring complex development and associated developer.
[0010]
GB-1 492 070 discloses a method of providing a metal layer or a layer containing carbon black on a photosensitive coating. The metal layer is then ablated using a laser to obtain an image mask on the photosensitive layer. The photosensitive layer is then totally exposed by UV-light through an image mask. After removing the image mask, the photosensitive layer is developed to obtain a printing plate. However, this method still has the disadvantage that the image mask must be removed by a cumbersome process prior to development of the photosensitive layer.
[0011]
Furthermore, methods are known for making printing plates that involve the use of imaging elements that are heat sensitive rather than photosensitive. A special disadvantage of such photosensitive imaging elements for making printing plates is that they must be shielded from light. In addition, they have a sensitivity problem in terms of storage stability, and they exhibit a relatively low dot sharpness. Clearly there is a trend in the market towards heat mode printing plate precursors.
[0012]
US-P-4 708 925 discloses an imaging element comprising a photosensitive composition containing an alkali-soluble novolak resin and an onium salt. The composition can optionally contain an IR-sensitizer. A positive or negative working printing plate is obtained after imagewise exposure of the imaging element to UV-visible- or IR-rays followed by a development step using an aqueous alkaline solution. A processing step is required, and the printing results of lithographic printing plates obtained by irradiation and development of the imaging element are poor.
[0013]
EP-A-625 728 discloses an imaging element that includes a layer that is sensitive to UV- and IR-rays and can be positive or negative working. This layer comprises a resole resin, a novolak resin, a latent Bronsted acid and an IR-absorbing material. A processing step is required, and the printing results of lithographic printing plates obtained by irradiation and development of the imaging element are poor.
[0014]
US-P-5 340 699 is almost the same as EP-A-625 728 but discloses a method for obtaining a negative working IR-laser recording imaging element. The IR-sensitive layer includes a resole resin, a novolac resin, a latent Bronsted acid and an IR-absorbing material. A processing step is required, and the printing results of lithographic printing plates obtained by irradiation and development of the imaging element are poor.
[0015]
Furthermore, EP-A-678 380 discloses a method in which a protective layer is provided on a roughened metal support under a laser-ablative surface layer. When exposed image-wise, the surface layer is completely ablated, as are some parts of the protective layer. The printing plate is then treated with a cleaning solution to remove the rest of the protective layer, thereby exposing the hydrophilic surface layer. Again, a processing stage is necessary.
[0016]
EP-A-97 200 588.8 comprises on a lithographic base having a hydrophilic surface an intermediate layer comprising a polymer soluble in an aqueous alkaline solution and an IR-ray sensitive top layer, wherein the top layer is Disclosed is a heat mode imaging element for the production of a lithographic printing plate in which the volume permeated and / or solubilized by an alkaline aqueous solution is reduced or increased when exposed to IR-rays. This material does not provide selective dissolution of the exposed or unexposed portions of the top and intermediate layers.
[0017]
DD-217 645 has one or more dyes adapted to the wavelength of the laser, contains a non-photosensitive hydrophilic material on the support, and a concentration gradient of the sensitizing dye perpendicular to the surface of the support Discloses a method for providing a lithographic printing plate in which is present by irradiation with a laser.
[0018]
EP-A-652 483 discloses a lithographic printing plate containing a photothermal converter and comprising a support having a thermosensitive coating that becomes more hydrophilic under the action of heat and which does not require a dissolution treatment.
[0019]
DD-217 914 discloses the preparation of a lithographic printing plate by irradiating with a laser a non-photosensitive hydrophilic material coated on an anodized aluminum support that can contain dyes or other additives. The aluminum oxide layer is colored with a dye that absorbs at the wavelength of the laser.
[0020]
DD-213 530 discloses a method for making a printing plate for flexography and lithographic printing by irradiating a layer containing a spectral sensitizer with a laser, the spectrum of which changes upon irradiation. Spectral sensitizers are used.
[0021]
EP-A-694 586 discloses indolenine cyanine disulfonic acid derivatives as IR-absorbing dyes.
[0022]
US-P-4 034 183 discloses an improvement in a method for the production of planographic printing forms, in which the support coated with a hydrophilic layer containing a non-photosensitive compound is exposed image-wise. And improvements include exposing the layer image-wise to laser irradiation of intensity and duration such that the exposed areas are rendered hydrophobic and lipophilic.
[0023]
Research Disclosure no 333, page 2 is an imaging element comprising a hydrophilic layer containing hydrophobic thermoplastic polymer particles on a support, the hydrophilic layer containing polyvinyl alcohol hardened with tetraalkylorthosilicate. The use is disclosed.
[0024]
The systems discussed above require a development step and / or are ablative, and in those two cases produce waste. Research Disclosure no. 33303 discloses a heat mode imaging element comprising a crosslinked hydrophilic layer containing thermoplastic polymer particles and an infrared absorbing pigment such as carbon black on a support. By imagewise exposure to an infrared laser, the thermoplastic polymer particles aggregate imagewise, thereby making the surface of the imaging element ink receptive in these areas without further development. The disadvantage of this method is that it is impossible to visually inspect the printing plate written before printing because there is no visual contrast between the image and non-image areas.
[0025]
OBJECT OF THE INVENTION
It is an object of the present invention to provide a heat-sensitive, non-ablative, waste-free imaging element that can visually distinguish its images and non-image areas after exposure.
[0026]
Further objects of the present invention will become clear from the description below.
[0027]
SUMMARY OF THE INVENTION
According to the present invention, an uppermost layer capable of forming hydrophobic and hydrophilic regions as image-wise by image-wise exposure is included on the support, and its optical density can be changed by exposure of the imaging element. A heat-sensitive, non-ablative, waste-free imaging element for providing a lithographic printing plate characterized in that it contains an IR-dye is provided.
[0028]
Detailed Description of the Invention
In accordance with the present invention, a top layer capable of forming image-wise hydrophobic and hydrophilic regions upon image-wise exposure is included on the support, and the color density can be varied by exposure of the imaging element. Provided is a heat-sensitive, non-ablative, waste-free imaging element for providing a lithographic printing plate, characterized in that it contains a possible IR-dye.
[0029]
The imaging element according to the present invention comprises an IR-dye. Although a mixture of IR-dyes can be used, it is preferred to use only one IR-dye. Preferably the IR-dye is an IR-cyanine dye. Particularly useful IR-cyanine dyes are cyanine dyes having two acid groups, more preferably two sulfone groups. Even more preferred are cyanine dyes having two indolenines and two sulfonic acid groups. Most preferred is Compound I having the structure:
[0030]
[Chemical 1]

The dye is preferably preferably in the top layer in an amount of 0.01 to 1 g / m ^2, more preferably in an amount of 0.05~0.20g / m ^2.
[0031]
The top layer or the layer immediately below the top layer preferably comprises a compound capable of converting light into heat. A suitable compound capable of converting light into heat is preferably an infrared absorbing component, but if the absorption of the compound used is within the wavelength region of the light source used for image-wise exposure, the wavelength of absorption is Not particularly important. Particularly useful compounds are, for example, structural dyes, in particular infrared dyes, carbon blacks, metal carbides, borides, nitrides, carbonitrides, bronze-structure oxides and bronze groups which can be the same as those mentioned above. Oxides related to, but without the A component, such as WO _2.9 . It is also possible to use conductive polymer dispersions, for example conductive polymer dispersions based on polypyrrole or polyaniline. The compound capable of converting light into heat is preferably present in the uppermost layer, but can also be included in the lower layer.
[0032]
The compound capable of converting light into heat is present in the imaging element, preferably present in an amount of 0.01 to 1 g / m ^2, more preferably in an amount of 0.05~0.50g / m ² To do.
[0033]
In one embodiment, the top layer comprises hydrophobic particles dispersed in a cross-linked hydrophilic layer. Particularly suitable crosslinked hydrophilic layers can be obtained from hydrophilic binders crosslinked with a crosslinking agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetraalkylorthosilicate. The latter is particularly preferred; most preferred is tetraethyl or tetramethylorthosilicate.
[0034]
Hydrophilic (co) polymers as hydrophilic binders such as acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate homopolymers and copolymers or maleic anhydride / vinyl methyl ether copolymers Can be used. The hydrophilicity of the (co) polymer or (co) polymer mixture used is preferably equal to or higher than that of polyvinyl acetate hydrolyzed to a degree of at least 60 weight percent, preferably 80 weight percent. A preferred hydrophilic binder is polyvinyl alcohol.
[0035]
The amount of crosslinking agent, especially tetraalkylorthosilicate, is preferably at least 0.2 parts by weight, more preferably 0.5 to 5 parts by weight, most preferably 1.0 to 3 parts by weight per part by weight of the hydrophilic binder. Parts by weight.
[0036]
The cross-linked hydrophilic layer used according to the invention preferably also contains substances that improve the mechanical strength and porosity of the layer. Colloidal silica can be used for this purpose. The colloidal silica used can be in the form of any commercially available water-dispersion of colloidal silica, for example having an average particle size of up to 40 nm, for example 20 nm. In addition, inert particles having a size larger than that of colloidal silica, such as J.I. Colloid and Interface Sci. , Vol. 26, 1968, pages 62 to 69, particles having an average diameter of at least 100 nm can be added which are silica or alumina particles or particles of titanium dioxide or other heavy metal oxides prepared according to Stober. The introduction of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys, which serves as a storage place for water in the background area.
[0037]
The thickness of the lithographic base crosslinked hydrophilic layer according to this embodiment can vary within the range of 0.2 to 25 μm, preferably 1 to 10 μm.
[0038]
Specific examples of cross-linked hydrophilic layers suitable for use in accordance with the present invention include EP-A-601 240, GB-P-1 419 512, FR-P-2 300 354, US-P-3 971 660. U.S. Pat. No. 4,284,705 and EP-A 514 490.
[0039]
In the embodiment of the present invention, the preferred hydrophobic polymer particles are thermoplastic polymer particles. The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50 ° C, more preferably above 70 ° C. Aggregation can result from the softening or melting of the thermoplastic polymer particles under the influence of heat. There is no specific upper limit to the setting temperature of the thermoplastic hydrophobic polymer particles, but the temperature must be well below the decomposition temperature of the polymer particles. Preferably the setting temperature is at least 10 ° C. below the temperature at which decomposition of the polymer particles occurs. When the polymer particles are subjected to a temperature above the setting temperature, they condense to form hydrophobic aggregates in the hydrophilic layer, where the hydrophilic layer becomes hydrophobic.
[0040]
Specific examples of hydrophobic polymer particles for use in connection with the present invention preferably having a Tg higher than 80 ° C. are preferably polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole, copolymers or mixtures thereof. is there. Most preferably used are polystyrene, polymethylmethacrylate or copolymers thereof.
[0041]
The weight average molecular weight of the polymer can range from 5,000 to 1,000,000 g / mol as determined by GPC against polystyrene standards.
[0042]
The hydrophobic particles can have a particle size of 0.01 μm to 50 μm, more preferably 0.05 mm to 10 mm and most preferably 0.05 μm to 2 μm.
[0043]
The polymer particles are present as a dispersion in the aqueous coating liquid of the imaging layer and can be prepared by the method disclosed in US-P-3 476 937. Other methods that are particularly suitable for the preparation of aqueous dispersions of thermoplastic polymer particles are:
-Dissolving the hydrophobic thermoplastic polymer in an organic solvent immiscible in water;
-The solution thus obtained is dispersed in water or an aqueous medium,
-Removing the organic solvent by evaporation.
[0044]
The amount of hydrophobic thermoplastic polymer particles contained in the imaging layer is preferably at least 20% by weight, more preferably at least 30% by weight and most preferably at least 40% by weight.
[0045]
In the second aspect of the invention, the top layer comprises a switchable polymer. A switchable polymer is a polymer that changes from hydrophobic to hydrophilic or vice versa upon heating. An example of a switchable polymer is poly-tetrahydropyranol methacrylate.
[0046]
The support of the imaging element can be flexible or rigid.
[0047]
As the flexible support in connection with the present invention, all kinds of flexible supports such as paper, polyethylene-coated paper, etc. can be used, but plastic films such as supported polyethylene terephthalate film, cellulose acetate, etc. It is particularly preferable to use a film, a polystyrene film, a polycarbonate film, a polyethylene film, or a polypropylene film. The plastic film support can be opaque or transparent.
[0048]
It is particularly preferred to use a polyester film support provided with an adhesion promoting layer. Particularly suitable adhesion promoting layers for use in accordance with the present invention include hydrophilic binders and colloidal silica as disclosed in EP-A-619 524, EP-A-620 502 and EP-A-619 525. . Preferably the amount of silica in the adhesion promoting layer is from 200 mg / m ² to 750 mg / m ² . Furthermore, the ratio of silica to hydrophilic binder is preferably higher than 1, and the surface area of the colloidal silica is preferably at least 300 m ² / g, more preferably at least 500 m ² / g.
[0049]
The support can also be rigid, preferably aluminum foil. A particularly preferred aluminum foil is an electrochemically roughened and anodized aluminum support. The anodized aluminum support can be treated to improve its surface adhesion. For example, an aluminum support can be silicated by treating its surface with a sodium silicate solution at an elevated temperature, such as 95 ° C. In another case, a phosphating treatment can be applied, which involves treating the aluminum oxide surface with a phosphate solution, which can further contain an inorganic fluoride. Furthermore, the aluminum oxide surface can be rinsed with a citric acid or citrate solution. This treatment can be carried out at room temperature or at a slightly elevated temperature of about 30-50 ° C. A further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. Furthermore, the surface of the aluminum oxide is formed by reaction of polyvinyl phosphonic acid, polyvinyl methyl phosphonic acid, polyvinyl alcohol phosphate ester, polyvinyl sulfonic acid, polyvinyl benzene sulfonic acid, polyvinyl alcohol sulfate ester and sulfonated aliphatic aldehyde. It can be processed with acetal. It is further evident that one or more of these post treatments can be performed alone or in combination. A more detailed description of these treatments is GB-A-1 084 070, DE-A-4 423 140, DE-A-4 417 907, EP-A-659 909, EP-A-537 633, DE-A. -4 001 466, EP-A-292 801, EP-A-291 760 and US-P-4 458 005.
[0050]
Between the support and the top layer, the imaging element can contain other layers such as a subbing layer and an antihalation layer. Regardless of whether the imaging element contains the dye of the present invention, the imaging element can optionally contain a reflective layer between the support and the top layer. The reflective layer can be any layer that reflects IR-rays, but is preferably aluminum with a high visual density, such as vacuum deposited aluminum.
[0051]
The image formation associated with the present invention can be performed using a thermal head. Preferably image-wise scanning exposure involving the use of a laser working in the infrared or near-infrared, ie wavelength range of 700-1500 nm is used. Most preferred is a laser diode emitting in the near infrared. The imaging element can be exposed using a laser having a short pixel residence time as well as a laser having a long pixel residence time. Preferred is a laser having a pixel residence time of 0.005 μsec to 20 μsec.
[0052]
After exposure, the imaging element is ready for use as a lithographic printing plate.
[0053]
The following examples illustrate the present invention and the present invention is not limited thereto. All parts and percentages are by weight unless otherwise specified.
[0054]
【Example】
Example 1
Preparation of imaging layer Dispersion by mixing 16.8 g of a dispersion containing 21.5% TiO ₂ (average particle size 0.3-0.5 μm) and 2.5% polyvinyl alcohol in deionized water. A liquid was prepared. 7.0 and 14 g of 20% polystyrene dispersion were added thereto, respectively. To these dispersions were added 0.7 and 1.4 ml of hydrolyzed 28.43% tetramethylorthosilicate solution, respectively. 0.1 g of IR-dye compound I was added to these dispersions. The dispersion was supplemented to a volume of 40 ml with water.
[0055]
These dispersions were thoroughly agitated, coated onto a primed PET-support at a thickness of 40 μm, and dried at 60 ° C. for 2 hours using hot air. The coating amount (g / m ² ) is shown in the table below.
[0056]
[Table 1]

Note a) PVA = polyvinyl alcohol b) TMOS = tetramethylorthosilicate c) PSTC = cationic stabilized polystyrene d) PST = nonionic stabilized polystyrene After coating, the imaging element was subjected to a temperature of 49 ° C. and 20% relative humidity. And stored for 5 days to harden polyvinyl alcohol.
[0057]
A) Thermal head Drystar 2000 (Agfa-Gevaert NV, trade name of Belgium): the imaging element was covered with PET foil (8 μm) and imaged at an output level of 118 mW;
b) IR-laser: imaged using a plate imaged with a diode laser having a spot size of 11 μm in diameter (1 / e ² ) at a power level of 342 mW at the plate level and a drum speed of 4 m / sec. Formed.
[0058]
After image formation, the image could be observed-Thermal head: dark blue image against a light blue background-Laser recording: white image against a light blue background.
[0059]
Example 2
A dispersion was prepared by mixing 16.8 g of a dispersion containing 21.5% TiO ₂ (average particle size 0.3-0.5 μm) and 2.5% polyvinyl alcohol in deionized water. 11.24 g of 12.45% polystyrene dispersion was added thereto. To this dispersion was added 0.7 g of hydrolyzed 28.43% tetramethylorthosilicate solution. 0.1 g of IR-dye compound having the structure shown below was added. The dispersion was supplemented to a volume of 30 ml with water.
[0060]
[Chemical formula 2]

The dispersion was stirred thoroughly, coated onto a subbed PET-support at a thickness of 30 μm, and dried at 60 ° C. for 2 hours using hot air.
[0061]
After coating, the imaging element was stored for 5 days at a temperature of 49 ° C. and a relative humidity of 20% to harden the polyvinyl alcohol.
[0062]
A) Thermal head Drystar 2000 (Agfa-Gevaert NV, trade name of Belgium): the imaging element was covered with PET foil (8 μm) and imaged at an output level of 118 mW;
b) IR-laser: using a plate imaged with a diode laser having a spot size of 11 μm in diameter (1 / e ² ) at a power level of 300 mW at the plate level and a drum speed of 4-10 m / sec. To form an image.
[0063]
Images could be observed after image formation-Thermal head: light blue image against dark blue background-Laser recording: white image against dark blue background.
The main features and aspects of the present invention are as follows.
[0064]
1. Contains a top layer on the support that can form image-wise hydrophobic and hydrophilic regions upon image-wise exposure and contains an IR-dye that can change its optical density upon exposure of the imaging element A heat-sensitive, non-ablative, waste-free imaging element for providing a lithographic printing plate.
[0065]
2. The imaging element for making a lithographic printing plate as described in 1 above, wherein the IR-dye is an IR-cyanine dye.
[0066]
3. The imaging element for making a lithographic printing plate as described in 2 above, wherein the IR-cyanine dye contains two acid groups.
[0067]
4). 4. An imaging element for making a lithographic printing plate as described in 3 above, wherein the infrared cyanine dye contains two indolenine groups.
[0068]
5. The infrared cyanine dye has the following structure:
[Chemical 3]

5. An imaging element for preparing a lithographic printing plate as described in 4 above, which is compound I having
[0070]
6). Any of the above 1-5, wherein the uppermost layer comprises hydrophobic particles dispersed in a crosslinked hydrophilic layer, and the crosslinked hydrophilic layer is obtained from a hydrophilic binder crosslinked using a crosslinking agent An image forming element for the preparation of a lithographic printing plate according to claim 1.
[0071]
7). 7. An image forming element for preparing a lithographic printing plate as described in 6 above, wherein the hydrophilic binder is polyvinyl alcohol.
[0072]
8). 8. An imaging element for preparing a lithographic printing plate as described in 6 or 7 above, wherein the crosslinking agent is a hydrolyzed tetraalkylorthosilicate.
[0073]
9. 6. An imaging element for making a lithographic printing plate according to any of the above 1-5, wherein the top layer comprises a switchable polymer.

Claims (4)

Comprises a top layer capable of forming a hydrophobic and hydrophilic regions of the image-wise by image-wise exposed to a thermal head or an infrared laser on a support, an image forming element thermal head or an infrared laser characterized in that it contains an IR- cyanine dye which can change its optical density by exposure to, for providing a lithographic printing plate, the non - thermosensitive that does not require and development stage ablative Imaging element. The imaging element for making a lithographic printing plate according to claim 1 , wherein the IR-cyanine dye comprises two acid groups. The imaging element for making a lithographic printing plate according to claim 2 , wherein the IR-cyanine dye comprises two indolenine groups. The IR-cyanine dye has the following structure

An imaging element for making a lithographic printing plate according to claim 3 which is Compound I having: