JP3596709B2 - Reversible thermosensitive recording medium - Google Patents

Description

一般式（３）で表されるカルボン酸化合物の具体例を下記表１にｐ，ｑ，ｒ，ｓ，Ａ、Ｂ、Ｘ、Ｙの数または構造で示す。
【００２６】
【表１−１】

【００２７】
【表１−２】

【００２８】
【表１−３】

【００２９】
【表１−４】

【００３０】
【表１−５】

【００３１】
【表１−６】

【００３２】
【表１−７】

【００３３】
【表１−８】

【００３４】
【表１−９】

【００３５】
【表１−１０】

【００３６】
【表１−１１】

【００３７】
【表１−１２】

【００３８】
また、顕色剤に用いるカルボン酸化合物としては、下記一般式（４）で表される化合物が例示できる。
【００３９】
【化４】

一般式（４）で表されるカルボン酸化合物の具体例を下記表２にｎ、ｐ、ｑ、ｒ、Ｒ、Ｘ、Ｙの数または構造で示す。
【００４０】
【表２−１】

【００４１】
【表２−２】

【００４２】
【表２−３】

【００４３】
【表２−４】

【００４４】
【表２−５】

【００４５】
【表２−６】

【００４６】
顕色剤には、分子間凝集力を制御する構造をもつフェノール化合物も好ましく用いられる。これには、たとえば下記の一般式（５）で表されるフェノール化合物が例示できる。
【００４７】
【化５】

一般式（５）で表されるフェノール化合物の具体例を下記表３にｐ，ｑ，ｒ，ｓ，Ｘ，Ａ，Ｙ，Ｚの数または構造で示す。ただし、これらのそれぞれの具体例においてフェノール部のｎは１から３であり、たとえば４−ヒドロキシフェニル、３−ヒドロキシフェニル、２−ヒドロキシフェニル、２，４−ジヒドロキシフェニル、３，４−ジヒドロキシフェニルまたは３，４，５−トリヒドロキシフェニルなどの水酸基を少なくとも一つ以上有するフェニル基である。このフェニル基には、水酸基以外の置換基を有していてもよい。また、フェノール性水酸基を有するものであれば、他の芳香環であってもよい。
【００４８】
【表３−１】

【００４９】
【表３−２】

【００５０】
【表３−３】

【００５１】
【表３−４】

【００５２】
【表３−５】

【００５３】
【表３−６】

【００５４】
【表３−７】

【００５５】
【表３−８】

本発明においては顕色剤として上記に記載した化合物に限られるものではなく、その他の電子受容性の種々の化合物を使用することができる。
【００５６】
本発明の可逆性感熱発色組成物は、基本的に前記の顕色剤と発色剤を組み合わせることによって構成されるものである。本発明で用いる発色剤は電子供与性を示すものであり、それ自体無色あるいは淡色の染料前駆体（ロイコ染料）であり、特に限定されず、従来公知のもの、例えばトリフェニルメタンフタリド系化合物、フルオラン系化合物、フェノチアジン系化合物、ロイコオーラミン系化合物、インドリノフタリド系化合物などから選択できる。その発色剤を以下に示す。
本発明に用いる好ましい発色剤として次の一般式の化合物がある。
【００５７】
【化６】

【００５８】
【化７】

（ただし、Ｒ_１は水素または炭素数１〜４のアルキル基、Ｒ_２は炭素数１〜６のアルキル基、シクロアルキル基又は置換されていてもよいフェニル基を示す。フェニル基に対する置換基としては、メチル基、エチル基などのアルキル基、メトキシ基、エトキシ基などのアルコキシ基又はハロゲン等が示される。Ｒ_３は水素、炭素数１〜２のアルキル基、アルコキシ基又はハロゲンを表わす。Ｒ_４は水素、メチル基、ハロゲン又は置換されていてもよいアミノ基を表わす。アミノ基に対する置換基としては、例えば、アルキル基、置換されていてもよいアリール基、置換されていてもよいアラルキル基を示す。ここでの置換基はアルキル基、ハロゲン、アルコキシ基などである。）このような発色剤の具体例としては、例えば次の化合物が挙げられる。
【００５９】
２−アニリノ−３−メチル−６−ジエチルアミノフルオラン、
２−アニリノ−３−メチル−６−ジ（ｎ−ブチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−ｎ−プロピル−Ｎ−メチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−イソプロピル−Ｎ−メチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−イソブチル−Ｎ−メチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−ｎ−アミル−Ｎ−メチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−ｓｅｃ−ブチル−Ｎ−エチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−ｎ−アミル−Ｎ−エチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−イソアミル−Ｎ−エチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−ｎ−プロピル−Ｎ−イソプロピルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−シクロヘキシル−Ｎ−メチルアミノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−アニリノ−３−メチル−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−（ｍ−トリクロロメチルアニリノ）−３−メチル−６−ジエチルアミノフルオラン、
２−（ｍ−トリフルオロメチルアニリノ）−３−メチル−６−ジエチルアミノフルオラン、
２−（ｍ−トリクロロメチルアニリノ）−３−メチル−６−（Ｎ−シクロヘキシル−Ｎ−メチルアミノ）フルオラン、
２−（２，４−ジメチルアニリノ）−３−メチル−６−ジエチルアミノフルオラン、
２−（Ｎ−エチル−ｐ−トルイジノ）−３−メチル−６−（Ｎ−エチルアニリノ）フルオラン、
２−（Ｎ−エチル−ｐ−トルイジノ）−３−メチル−６−（Ｎ−プロピル−ｐ−トルイジノ）フルオラン、
【００６０】
２−アニリノ−６−（Ｎ−ｎ−ヘキシル−Ｎ−エチルアミノ）フルオラン、
２−（ｏ−クロロアニリノ）−６−ジエチルアミノフルオラン、
２−（ｏ−クロロアニリノ）−６−ジブチルアミノフルオラン、
２−（ｍ−トリフルオロメチルアニリノ）−６−ジエチルアミノフルオラン、
２−（ｐ−アセチルアニリノ）−６−（Ｎ−ｎ−アミル−Ｎ−ｎ−ブチルアミノ）フルオラン、
２−ベンジルアミノ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−ベンジルアミノ−６−（Ｎ−メチル−２，４−ジメチルアニリノ）フルオラン、
２−ベンジルアミノ−６−（Ｎ−エチル−２，４−ジメチルアニリノ）フルオラン、
２−ジベンジルアミノ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−ジベンジルアミノ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−（ジ−ｐ−メチルベンジルアミノ）−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−（α−フェニルエチルアミノ）−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−メチルアミノ−６−（Ｎ−メチルアニリノ）フルオラン、
２−メチルアミノ−６−（Ｎ−エチルアニリノ）フルオラン、
２−メチルアミノ−６−（Ｎ−プロピルアニリノ）フルオラン、
２−エチルアミノ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−メチルアミノ−６−（Ｎ−メチル−２，４−ジメチルアニリノ）フルオラン、
２−エチルアミノ−６−（Ｎ−エチル−２，４−ジメチルアニリノ）フルオラン、
２−ジメチルアミノ−６−（Ｎ−メチルアニリノ）フルオラン、
２−ジメチルアミノ−６−（Ｎ−エチルアニリノ）フルオラン、
２−ジエチルアミノ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−ジエチルアミノ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−ジプロピルアミノ−６−（Ｎ−メチルアニリノ）フルオラン、
２−ジプロピルアミノ−６−（Ｎ−エチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−メチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−エチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−プロピルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−アミノ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−アミノ−６−（Ｎ−プロピル−ｐ−トルイジノ）フルオラン、
２−アミノ−６−（Ｎ−メチル−ｐ−エチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−エチル−ｐ−エチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−プロピル−ｐ−エチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−メチル−２，４−ジメチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−エチル−２，４−ジメチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−プロピル−２，４−ジメチルアニリノ）フルオラン、
２−アミノ−６−（Ｎ−メチル−ｐ−クロロアニリノ）フルオラン、
２−アミノ−６−（Ｎ−エチル−ｐ−クロロアニリノ）フルオラン、
２−アミノ−６−（Ｎ−プロピル−ｐ−クロロアニリノ）フルオラン、
【００６１】
２，３−ジメチル−６−ジメチルアミノフルオラン、
３−メチル−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−クロロ−６−ジエチルアミノフルオラン、
２−ブロモ−６−ジエチルアミノフルオラン、
２−クロロ−６−ジプロピルアミノフルオラン、
３−クロロ−６−シクロヘキシルアミノフルオラン、
３−ブロモ−６−シクロヘキシルアミノフルオラン、
２−クロロ−６−（Ｎ−エチル−Ｎ−イソアミルアミノ）フルオラン、
２−クロロ−３−メチル−６−ジエチルアミノフルオラン、
２−アニリノ−３−クロロ−６−ジエチルアミノフルオラン、
２−（ｏ−クロロアニリノ）−３−クロロ−６−シクロヘキシルアミノフルオラン、
２−（ｍ−トリフルオロメチルアニリノ）−３−クロロ−６−ジエチルアミノフルオラン、
２−（２，３−ジクロロアニリノ）−３−クロロ−６−ジエチルアミノフルオラン、
１，２−ベンゾ−６−ジエチルアミノフルオラン、
１，２−ベンゾ−６−（Ｎ−エチル−Ｎ−イソアミルアミノ）フルオラン、
１，２−ベンゾ−６−ジブチルアミノフルオラン、
１，２−ベンゾ−６−（Ｎ−メチル−Ｎ−シクロヘキシルアミノ）フルオラン、１，２−ベンゾ−６−（Ｎ−エチル−Ｎ−トルイジノ）フルオラン、その他。
【００６２】
本発明において好ましく用いられる他の発色剤の具体例を示すと以下のとおりである。
２−アニリノ−３−メチル−６−（Ｎ−２−エトキシプロピル−Ｎ−エチルアミノ）フルオラン、
２−（ｐ−クロロアニリノ）−６−（Ｎ−ｎ−オクチルアミノ）フルオラン、
２−（ｐ−クロロアニリノ）−６−（Ｎ−ｎ−パルミチルアミノ）フルオラン、
２−（ｐ−クロルアニリノ）−６−（ジ−ｎ−オクチルアミノ）フルオラン、
２−ベンゾイルアミノ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−（ｏ−メトキシベンゾイルアミノ）−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−ジベンジルアミノ−４−メチル−６−ジエチルアミノフルオラン、
２−ジベンジルアミノ−４−メトキシ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−ベンジルアミノ−４−メチル−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−（α−フェニルエチルアミノ）−４−メチル−６−ジエチルアミノフルオラン、
２−（ｐ−トルイジノ）−３−（ｔ−ブチル）−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
２−（ｏ−メトキシカルボニルアニリノ）−６−ジエチルアミノフルオラン、
２−アセチルアミノ−６−（Ｎ−メチル−ｐ−トルイジノ）フルオラン、
３−ジエチルアミノ−６−（ｍ−トリフルオロメチルアニリノ）フルオラン、
４−メトキシ−６−（Ｎ−エチル−ｐ−トルイジノ）フルオラン、
２−エトキシエチルアミノ−３−クロロ−６−ジブチルアミノフルオラン、
２−ジベンジルアミノ−４−クロロ−６−（Ｎ−エチル−ｐートルイジノ）フルオラン、
２−（α−フェニルエチルアミノ）−４−クロロ−６−ジエチルアミノフルオラン、
２−（Ｎ−ベンジル−ｐ−トリフルオロメチルアニリノ）−４−クロロ−６−ジエチルアミノフルオラン、
２−アニリノ−３−メチル−６−ピロリジノフルオラン、
２−アニリノ−３−クロロ−６−ピロリジノフルオラン、
２−アニリノ−３−メチル−６−（Ｎ−エチル−Ｎ−テトラヒドロフルフリルアミノ）フルオラン、
２−メシジノ−４’，５’−ベンゾ−６−ジエチルアミノフルオラン、
２−（ｍ−トリフルオロメチルアニリノ）−３−メチル−６−ピロリジノフルオラン、
２−（α−ナフチルアミノ）−３，４−ベンゾ−４’−ブロモ−６−（Ｎ−ベンジル−Ｎ−シクロヘキシルアミノ）フルオラン、
２−ピペリジノ−６−ジエチルアミノフルオラン、
２−（Ｎ−ｎ−プロピル−ｐ−トリフロロメチルアニリノ）−６−モルフォリノフルオラン、
２−（ジ−Ｎ−ｐ−クロロフェニル−メチルアミノ）−６−ピロリジノフルオラン、
２−（Ｎ−ｎ−プロピル−ｍ−トリフルオロメチルアニリノ）−６−モルフォリノフルオラン、
１，２−ベンゾ−６−（Ｎ−エチル−Ｎ−ｎ−オクチルアミノ）フルオラン、
１，２−ベンゾ−６−ジアリルアミノフルオラン、
１，２−ベンゾ−６−（Ｎ−エトキシエチル−Ｎ−エチルアミノ）フルオラン、
【００６３】
ベンゾロイコメチレンブルー、
２−［３，６−ビス（ジエチルアミノ）］−６−（ｏ−クロロアニリノ）キサンチル安息香酸ラクタム、
２−［３，６−ビス（ジエチルアミノ）］−９−（ｏ−クロロアニリノ）キサンチル安息香酸ラクタム、
３，３−ビス（ｐ−ジメチルアミノフェニル）−フタリド、
３，３−ビス（ｐ−ジメチルアミノフェニル）−６−ジメチルアミノフタリド（別名クリスタルバイオレットラクトン）、
３，３−ビス（ｐ−ジメチルアミノフェニル）−６−ジエチルアミノフタリド、３，３−ビス（ｐ−ジメチルアミノフェニル）−６−クロロフタリド、
３，３−ビス（ｐ−ジブチルアミノフェニル）フタリド、
３−（２−メトキシ−４−ジメチルアミノフェニル）−３−（２−ヒドロキシ−４，５−ジクロロフェニル）フタリド、
３−（２−ヒドロキシ−４−ジメチルアミノフェニル）−３−（２−メトキシ−５−クロロフェニル）フタリド、
３−（２−ヒドロキシ−４−ジメトキシアミノフェニル）−３−（２−メトキシ−５−クロロフェニル）フタリド、
３−（２−ヒドロキシ−４−ジメチルアミノフェニル）−３−（２−メトキシ−５−ニトロフェニル）フタリド、
３−（２−ヒドロキシ−４−ジエチルアミノフェニル）−３−（２−メトキシ−５−メチルフェニル）フタリド、
３−（２−メトキシ−４−ジメチルアミノフェニル）−３−（２−ヒドロキシ−４−クロロ−５−メトキシフェニル）フタリド、
３，６−ビス（ジメチルアミノ）フルオレンスピロ（９，３’）−６’−ジメチルアミノフタリド、
３−（１−エチル−２−メチルインドール−３−イル）−３−（２−エトキシ−４−ジエチルアミノフェニル）−４−アザフタリド、
３−（１−オクチル−２−メチルインドール−３−イル）−３−（２−エトキシ−４−ジエチルアミノフェニル）−４−アザフタリド、
３−（１−エチル−２−メチルインドール−３−イル）−３−（２−エトキシ−４−ジエチルアミノフェニル）−７−アザフタリド、
３，３−ビス（２−エトキシ−４−ジエチルアミノフェニル）−４−アザフタリド、
３，３−ビス（２−エトキシ−４−ジエチルアミノフェニル）−７−アザフタリド、
６’−クロロ−８’−メトキシ−ベンゾインドリノ−スピロピラン、
６’−ブロモ−２’−メトキシ−ベンゾインドリノ−スピロピラン、その他。
【００６４】
上記の本発明で使用される顕色剤及び発色剤の具体例は、特開平５−１２４３６０、特開平６−８６２４及び特開平６−２４１３２号公報に詳記されている。
【００６５】
本発明において、耐光性向上のため熱発色性組成物に添加されるグアニジン誘導体は下記一般式（６）又は（７）で表わされるものである。
【００６６】
【化８】

（Ｒ_１は電子供与性基を表わし、ｎは１〜３０の整数）
【００６７】
【化９】

（Ｒ_２は電子供与性基を表わし、Ｒ_３はハロゲンを表わし、ｍ，ｌは１又は２の整数）
【００６８】
本発明で使用されるグアニジン誘導体を具体的に例示すると下のとおりであるが、本発明はこれらに限定されるものではない。
１，３−ジシクロヘキシル−２−（３’−メトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（２’，４’−ジメトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（２’，５’−ジメトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（４’−エトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（２’，４’−ジブトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’，４’，５’−トリメトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（４’−ジエチルアミノフェニル）グアニジン
【００６９】
１，３−ジシクロヘキシル−２−（２’−クロル−３’−メチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−４’−メチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−ブロム−６’−エチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（２’−ブロム−４’−メチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−フロロ−６’−メチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−６’−メトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−６’−ブトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−ブロム−６’−エトキシフェニル）グアニジン、
【００７０】
１，３−ジシクロヘキシル−２−（２’，５’−ジクロル−４’−メチルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’，５’−ジクロル−４’−メトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’，５’−ジクロル−４’−ブトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−４’，６’−ジメトキシフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−４’，６’−ジノルマルプロピルフェニル）グアニジン、
１，３−ジシクロヘキシル−２−（３’−クロル−２’，６’−ジエチルフェニル）グアニジン
１，３−ジシクロヘキシル−２−（２’−クロル−４’−ジメチルアミノフェニル）グアニジン等。
【００７１】
またビタミンＫとしては、
ビタミンＫ_１（２−メチル−３−フィチル−１，４−ナフトキノン）、
ビタミンＫ_２（２−ファルネシル−３−メチル−１，４−ナフトキノン）、
ビタミンＫ_３（２−メチル−１，４−ナフトキノン）等。
【００７２】
耐光性向上のためには、前記のグアニジン誘導体又はビタミンＫを１種又は２種以上混合して添加すればよく、その添加量は発色剤に対して１〜３０重量％未満、好ましくは５〜２０重量％未満であり、添加量過少では耐光性向上効果が小さく、過大の場合は発色濃度及び画像保存性が低下するうえ、３０重量％以上添加しても耐光性が更に向上することはない。
【００７３】
本発明の組成物において顕色剤の添加量は発色剤の１〜２０モル倍、好ましくは２〜１０モル倍であり、この範囲であれば顕色剤及び発色剤に単一品を使用しても２種以上の混合物を使用してもよい。しかし、この範囲より顕色剤が少なくとも、また多くても発色状態の濃度が低くなり実用上の問題となる。
【００７４】
また、上記の好ましい範囲にあっても、発色剤と顕色剤の割合によって消色特性は変化し、比較的顕色剤が多い場合には消色開始温度が低くなり、比較的少ない場合には消色が温度に対してシャープになる。したがって、この割合は用途や目的に応じて適当に選択しなければならない。
【００７５】
本発明の可逆的感熱記録媒体は、支持体上に前記組成物を含む記録層を積層したものであり、通常は記録層上に保護層を積層して耐久性を向上させるが、保護層はなくてもよい。支持体は、紙、合成紙、プラスチックフィルム、或いはこれらの複合体、ガラス等であり、記録層を保持できるものであればよい。
【００７６】
記録層は、前記の組成物が存在すればどのような態様のものでもよく、顕色剤と発色剤とを混合・溶融して膜とし、これを冷却して記録層としてもよい。しかし、通常はバインダー樹脂内に顕色剤と発色剤とを十分よく分散して記録層とするのがよく、この方法で寿命の長い可逆的感熱記録媒体を得ることができる。また、この場合の記録層形成は従来公知の方法に従って行うことができる。即ち、発色剤及び顕色剤をバインダー樹脂と共に、水又は有機溶剤により均一に分散若しくは溶解し、これを支持体上に塗布・乾燥すればよい。
【００７７】
本発明の可逆的感熱記録媒体では必要に応じて、塗布特性或いは記録特性の向上を目的に、通常の感熱記録紙に用いられている種々の添加剤、例えば分散剤、界面活性剤、高分子カチオン系導電剤、填料、発色画像安定剤、酸化防止剤、光安定化剤、滑剤等を記録層に加えることもできる。
【００７８】
記録層やアンダーコート層、記録層と保護層間の中間層等に用いられるバインダー樹脂は特に限定されず、公知のバインダー樹脂はいずれも使用可能である。バインダー樹脂を具体的に例示すれば、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース、メトキシセルロース、カルボキシメチルセルロース、メチルセルロース、酢酸セルロース、ゼラチン、カゼイン、澱粉、ポリアクリル酸ソーダ、ポリビニルピロリドン、ポリアクリルアミド、ポリ塩化ビニル、ポリ酢酸ビニル、塩化ビニル−酢酸ビニル共重合体、ポリスチレン、スチレン系共重合体、フェノキシ樹脂、ポリエステル、芳香族ポリエステル、ポリウレタン、ポリカーボネート、ポリアクリル酸エステル類、ポリメタクリル酸エステル類、アクリル酸共重合体、マレイン酸共重合体、ポリビニルアルコール、塩素化塩化ビニル樹脂、これらの樹脂の混合物などが挙げられる。
【００７９】
記録層のバインダー樹脂の役割は、発色・消色の繰り返しによって可逆的熱発色性組成物が凝集するのを防止し、該組成物が均一に分散した状態を保持することにある。特に、発色時の熱の印加で組成物が凝集して不均一化することが多いため、バインダー樹脂は耐熱性の高いものが好ましい。なお、バインダー樹脂の各種特性は熱発色性組成物の挙動に大きな影響を与えているものと思われる。
【００８０】
保護層は、熱印加時の熱と圧力で表面が変形したり変色したりすることを防止するほか、耐薬品性、耐水性、耐摩擦性、ヘッドマッチング性等を向上させる役割を持たせることもできる。そのため、保護層形成材料は耐熱性に優れると共に強度の大きいものがよく、シリコーン系ゴム、シリコーン樹脂（特開昭６３−２２１０８７号公報）、ポリシロキサングラフトポリマー（特開昭６３−３１７３８５号公報）、熱硬化性樹脂、紫外線硬化性樹脂、電子線硬化性樹脂等が使用されるが、水溶性高分子や疎水性高分子化合物の水性エマルジョンで形成されたものでもよい。このような保護層の形成で、前記のように耐熱性が向上すると共に、有機溶剤、可塑剤、油、汗、水等の接触に対する抵抗力も増加し、悪い環境でも画像の形成及び消去を問題なく繰り返すことのできる記録媒体を得ることができる。また、保護層中に光安定化剤を含有させることで画像及び地肌の耐光性が著しく改良された記録媒体が得られ、高分子カチオン系導電剤の添加で帯電防止を可能とし、さらに保護層に有機又は無機フィラー及び滑剤を加えることでサーマルヘッド等との接触で生じるスティッキングも防止され、信頼性及びヘッドマッチング性の高い感熱記録媒体を得ることができる。保護層の形成方法は、保護層成分を水又は有機溶剤によって均一に分散若しくは溶解し、これを記録層上に均一に塗布・乾燥させればよく、保護層の厚さは０．５〜１０μｍ程度がよい。
【００８１】
本発明の可逆的感熱記録媒体では、必要に応じて支持体と記録層との間にアンダーコート層を設置してもよい。アンダーコート層は、断熱性向上、支持体と記録層間の接着性向上、記録層作成時の溶剤に対する支持体の耐性向上等の目的で設置するものであり、支持体の種類を勘案して設置の有無を定めればよい。アンダーコート層の重要な役割の一つは断熱性向上であるが、これは印加熱エネルギーを無駄なく熱記録形成や熱消去に役立たせるためのものであり、断熱層の設置によって発色及び消色をシャープに行うことができる。断熱を目的とするアンダーコート層を形成するには、支持体上に有機又は無機材質より成る微小中空体粒子を塗工すればよく、具体的にはガラス又はセラミックス、或いはプラスチック等で形成された粒径１０〜５０μｍ程度の微小中空体を、バインダー樹脂と共に溶剤によく分散させて支持体上に均一に塗布・乾燥させればよい。なお、断熱層を設ける代わりに断熱性支持体を使用しても印加熱エネルギーの節約が可能であり、断熱性支持体としてはプラスチックフィルムや合成紙等が用いられる。
【００８２】
さらに本発明の可逆性感熱記録媒体では記録層と保護層の間に中間層を設置してもよい。
中間層は記録層と保護層の接着性向上、保護層作成時の溶剤に対する記録層の耐性向上の目的で設置するものである。
【００８３】
記録画像の形成は、使用目的によって熱ペン、サーマルヘッド、レーザー加熱等特に限定されない。同様に記録画像の消去も加熱ローラ、面状発熱体、恒温槽、温風、サーマルヘッド等消去の温度条件が与えられるものであれば特に限定はされない。また、記録画像を消去温度に設定したサーマルヘッドにより消去しながら、同時に記録温度に設定した別のサーマルヘッドにより記録画像の形成を行うことも可能である。
【００８４】
【実施例】
以下、本発明を実施例によって更に詳細に説明するが、本発明はこの実施例によって限定されるものではない。なお、以下における部及び％はいずれも重量基準である。
【００８５】
参考実施例１〜２０、実施例１〜６
下記組成物をボールミルで粒径約１〜３μｍとなるように粉砕・分散し、可逆的感熱記録層形成用塗布液を調製した。
２−（ｏークロルアニリノ）−６−ジブチルアミノフルオラン ３部
オクタデシルホスホン酸 １０部
塩化ビニル／酢酸ビニル共重合体、
（ユニオンカーバイト社製、ＶＹＨＨ） １０部
添加剤
（表４、表５に記載の参考実施例１〜２０、実施例１〜６の添加剤と添加量）
トルエン ４５部
メチルエチルケトン ４５部
この塗布液を、白色ＰＥＴフィルム（ルミラーＥ２０、東レ社製）にワイヤーバーで塗布・乾燥し、膜厚約６μｍの可逆的感熱記録層を設けた。
【００８６】
次に、前記可逆的感熱記録層の上につぎの組成の保護層形成用塗布液をワイヤーバーで塗布・乾燥し、乾燥後に８０Ｗ／ｃｍの強さの紫外線を照射して塗布・乾燥物を硬化させ、膜厚約３μｍの保護層を積層した。
ウレタンアクリレート系紫外線硬化性樹脂 １００部
（大日本インキ化学社製；ユニディックＣ７−１５７）
酢酸エチル ５０部
【００８７】
以上のようにして作製した可逆的感熱記録媒体を、１２０℃のホットプレートに約２０秒間接触させて発色画像を得、マクベス社製反射濃度計ＲＤ−９１４で発色濃度を測定した。次に、発色させた記録媒体を７０℃の恒温槽に１０分間入れて画像を消去し、前記ＲＤ−９１４で消色濃度を測定した。また、発色画像を５キロルックス（Ｋ ｌｕｘ）の蛍光灯に４８時間暴露した後の画像濃度、及び該画像を前記したのと同一方法で消色した時の消色濃度についても測定した。
さらに発色画像を５０℃の恒温槽に入れ、２４時間後の濃度を測定し耐熱性を調べた。これらをまとめて表１及び表２に示す。
【００８８】
参考比較例
参考実施例において添加剤を添加しなかったもの及び従来のグアニジン誘導体を添加したものについて、参考実施例と同様にして可逆性感熱媒体を作製し同様の評価をした（表４）。
【００８９】
【表４−１】

【００９０】
【表４−２】

【００９１】
【化１０】

＊２；電子供与性呈色性化合物に対する割合（ｗｔ％）
＊３、＊５；

＊４；（差）＝試験後消色濃度−初期消色濃度
【００９２】
【表５】

【００９３】
【発明の効果】
以上詳細かつ具体的に説明したように、本発明の可逆的熱発色性組成物及び可逆的感熱記録媒体は、組成物中にビタミンＫを含有させたことにより、光が当たった後でも消し残りの少ない消色状態が得られ、耐光性が改良される。また、発色状態の熱安定性に優れ、発色良好な画像保存性が達成できる。
【図面の簡単な説明】
【図１】本発明の可逆的感熱記録媒体の、発色及び消色原理を温度−発色濃度の関係グラフにより説明する図である。
【図２】画像形成工程と画像消去工程を説明する図である。
【符号の説明】
１ 加熱による画像形成過程
２ 冷却による画像定着過程
３ 加熱による画像消去過程
４ 支持体
５ 可逆的感熱記録層
６ 発色画像
７ サーマルヘッド
８ 加熱ローラ
Ａ 画像の完全消去状態
Ｂ 飽和発色状態
Ｃ 完全発色状態
Ｄ 加熱消去状態[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reversible thermosensitive recording medium utilizing a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound, and more specifically, the formation and erasing of a color image by controlling thermal energy. It relates to a possible reversible thermosensitive recording medium.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, heat-sensitive recording media utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter, also referred to as a color former) and an electron-accepting compound (hereinafter, also referred to as a color developer) are widely known. , Facsimile, automatic ticket vending machines, scientific measuring machine printers, CRT medical measuring printers, etc. However, all of the conventional products have an irreversible color development and cannot alternately repeat the color development and the decoloration.
[0003]
On the other hand, according to patent publications and the like, some heat-sensitive recording media utilizing a color-forming reaction between a color-forming agent and a color-developing agent for reversibly forming and erasing colors have been proposed. For example, Japanese Patent Application Laid-Open No. 60-193691 discloses a developer using a combination of gallic acid and phloroglucinol as a color developer. A colored body obtained by thermally coloring this is decolorized with water or steam. However, in the case of this heat-sensitive recording medium, there is a problem in that it is difficult to make the recording medium water-resistant, and there is a problem in the recording preservability.
[0004]
JP-A-61-237684 discloses a rewritable optical recording medium using a compound such as phenolphthalene, thymolphthalein, bisphenol or the like as a color developer. This can form a colored body by heating it and then gradually cooling it, and on the other hand, once the colored body is heated to a temperature higher than the coloring temperature and then rapidly cooled, it can be decolorized. However, in the case of this recording medium, the steps of coloring and decoloring are complicated, and the decolored body obtained by decoloring the colored body still shows some coloring, so that a color image with good contrast is obtained. I can't.
[0005]
JP-A-62-140881, JP-A-62-138568 and JP-A-62-138556 disclose a homogeneous solution of a color former, a color developer and a carboxylic acid ester. It shows a completely colored state at low temperatures and a completely decolored state at high temperatures, and can maintain the colored or decolored state at an intermediate temperature between them. White characters (decolorable) can be recorded on the background (colored). Therefore, in the case of this recording medium, since the image to be recorded is a negative image, its use is limited, and it is necessary to maintain the image within a specific temperature range in order to retain the recorded image.
[0006]
JP-A-2-188294 and JP-A-2-188293 disclose a salt of gallic acid and a higher aliphatic amine which reversibly perform a color developing action and a color reducing action as a color developing agent, and bis (hydroxyphenyl). ) The use of a salt of acetic acid or butyric acid with a higher aliphatic amine is disclosed. This product develops heat in a specific temperature range and can be decolorized by heating at a higher temperature.However, since the color developing effect and the color reducing effect occur competitively, these effects are thermally controlled. And it is difficult to obtain good image contrast.
As described above, the conventional reversible thermosensitive recording medium utilizing the reaction between the color former and the developer contains various problems and is still unsatisfactory.
[0007]
We first used organic phosphoric acid, a carboxyl compound, or a phenol compound having a long-chain aliphatic group as a color developer, and combined this with a leuco compound as a color former to heat the color development and decolorization. It can be easily carried out only by itself, and its color developing state and color erasing state can be maintained at room temperature, and the color erasing temperature is lower than the color developing temperature. A reversible thermochromic composition which can be repeated over and over again and a reversible thermosensitive recording medium containing the same in a recording layer have been proposed (JP-A-5-124360). The reversible thermosensitive recording medium proposed by us is a reversible thermosensitive recording medium that has many advantages that are incomparable to conventional reversible thermosensitive recording media, but when light is applied to the recording medium in a colored state. There have been problems such as a change in the color hue, and in the case where the color is erased by heating to a temperature lower than the color development temperature, the color erasure does not proceed smoothly.
The use of an antioxidant or an ultraviolet absorber alone or in combination to solve this problem can be solved to some extent, but such a recording medium has a disadvantage that the heat-resistant storage stability of a recorded image is deteriorated, and the quality is poor. It turns out that the problem still remains.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a reversible thermochromic composition utilizing a reaction between a color former and a developer, in which a hue change of a color-developed state or poor color erasure occurs even when irradiated with light. An object of the present invention is to provide a reversible thermosensitive recording medium which is excellent in light resistance and excellent in heat-resistant storage stability in a colored state.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present invention has been completed.
That is, according to the present invention, a reversible material containing a color former and a developer as main components, forms a color-developed state by heating and melting, and forms a decolored state by heating to a temperature lower than the color-developing temperature. There is provided a reversible thermosensitive recording medium characterized in that vitamin K ₁ , vitamin K ₂ or vitamin K ₃ is added to a recording layer and / or a layer adjacent to the recording layer.
[0010]
The reversible thermochromic composition of the present invention (hereinafter, also simply referred to as composition) develops color instantaneously by heating, and its color development state is stably present even at room temperature. On the other hand, the composition in the color-developed state can be decolored by heating at a temperature lower than the color-developing temperature, and the decolored state is stably maintained at room temperature.
[0011]
With respect to a reversible thermosensitive recording medium containing the composition of the present invention in a recording layer, the principle of color development and decoloration, that is, the principle of image formation and image erasure will be described with reference to the graph of FIG.
The vertical axis of the graph represents the color density and the horizontal axis represents the temperature. The solid line 1 shows the image forming process by heating, and the broken line 3 shows the image erasing process by heating. (A) is the density in the completely erased state, (B) is the density in the saturated color development state when heated to a temperature equal to or higher than (T ₁ ), and (C) is the density below (T ₀ ) in the full color development state. (D) shows the density when the heating and erasing are performed at a temperature between (T ₀ ) and (T ₁ ).
[0012]
The reversible thermosensitive recording medium of the present invention is in a colorless state (A) at a temperature of (T ₀ ) or lower. In order to perform recording, it is sufficient that the recording head is heated to a temperature of (T ₁ ) or higher by a thermal head or the like. Even if the temperature of the recorded image is returned to a temperature equal to or lower than (T ₀ ) according to the solid line 2, the state (C) is maintained as it is, and the memory property of the recording is not lost.
Note that the color density at the time of forming a recorded image increases with temperature rise at a temperature equal to or higher than (T ₁ ) and reaches a saturation density at point B.
[0013]
Next, in order to erase the recorded image, the formed recorded image may be heated to a temperature between (T ₀ ) and (T ₁ ) lower than the coloring temperature, and the image becomes a colorless state (D). This state is maintained as it is even when the temperature is returned to (T ₀ ) or lower (A). In other words, the process of forming a recorded image reaches (C) along the paths indicated by solid lines (A), (B), and (C), and the recording is held. The process of erasing the recorded image reaches (A) through the paths indicated by broken lines (C), (D) and (A), and the erased state is maintained. The behavior characteristics of the formation and erasure of the recorded image are reversible and can be repeated many times.
[0014]
FIG. 2 is an explanatory view showing an example of image formation and image erasure using the reversible thermosensitive recording medium of the present invention, wherein (4) is a support and (5) is a recording layer. The image forming steps (A) → (B) are achieved by performing recording and printing at a temperature equal to or higher than (T ₁ ) in FIG. 1 by a heat source for image formation, for example, a thermal head (7). Next, the image erasing step (B) → (A) is achieved by heating to a temperature between (T ₀ ) and (T ₁ ) by an image erasing heat source, for example, a heating roller (8). In FIG. 2, (3) shows a color image.
[0015]
The composition of the present invention contains a color former, a developer and vitamin K ₁ , vitamin K ₂ or vitamin K ₃ as essential components. The color development of the composition is obtained by cooling the color forming composition formed by heating, melting and mixing the color developer and the color developing agent to room temperature. Since this color forming composition has a decoloring temperature region on a lower temperature side than the melting temperature, rapid cooling is preferable for cooling to normal temperature while maintaining color development from the molten color forming state. Slow cooling often results in some decoloring when passing through the decoloring temperature range, resulting in a decrease in density.
[0016]
It is considered that the color former composition is one in which the molecules of the color former and the developer interact, and the lactone ring of the color former is opened to form a color. The composition that has been quenched from the molten state contains color former molecules and color developer molecules that are not directly involved in the formation of the color former, in addition to the color former molecules. In the reversible thermosensitive recording medium of the present invention, the color forming composition at room temperature is in a solidified state due to the cohesion between these molecules. In addition, the aggregate structure of the color forming composition shows some regularity, but there are cases where the regularity is very high and cases where the regularity is not so high. This depends on the combination and amount ratio of the developer and the color former, or the cooling conditions. The formation of such an aggregated structure acts between the long chain structure portion of the developer molecule forming the color former and the excess long chain structure portion of the developer molecule not forming the color former. It is presumed that cohesion is mainly acting.
[0017]
The color forming composition can be decolorized by heating the color forming state to a specific temperature range. In this decoloring process, the aggregate structure of the color-developing state changes, and finally the developer molecules are separated and crystallized from the color-forming body composition to form crystals of the color developing agent alone, resulting in a stable decoloring state. Confirmed by X-ray analysis.
Thus, in the reversible thermosensitive recording medium of the present invention, it is clear that the long-chain portion of the developer plays a large role in the formation of the color-forming state and the decoloring process, and this is the reversible thermosensitive recording medium of the present invention. This is a characteristic of the color forming composition formed on the heat-sensitive recording medium.
[0018]
The composition of the present invention is a composition obtained by combining the developer, the color former, and vitamin K ₁ , vitamin K ₂ or vitamin K ₃ or vitamin K ₁ , vitamin K ₂ or vitamin K ₃ with a granidine derivative , Preferred color formers exist for each developer. The combination of the developer and the color former used in this composition is a color-developed state composition obtained by heating both above the melting temperature, and the easiness of decoloring that occurs when the composition is heated to a temperature lower than the melting temperature, that is, It is appropriately selected according to the characteristics such as the decoloring property and the color tone of the color development state. Among these, the color erasing property can be determined by the presence or absence of an exothermic peak appearing in the heating process in the differential thermal analysis (DTA) or the differential scanning calorimetry (DSC) of the color-forming composition obtained by the combination. This exothermic peak corresponds to the decoloring phenomenon that characterizes the present invention, and serves as a criterion for selecting a good combination of decoloring properties. In the composition of the present invention, vitamin K ₁ , vitamin K ₂ or vitamin K ₃ exclusively participates in light fastness and does not directly participate in the formation of a color-developed state or a decolored state. Further, even if a third substance such as vitamin K ₁ , vitamin K ₂ or vitamin K ₃ is present in the composition, the reversible decoloring behavior can be maintained. Similarly, a third substance may be present in the heat-sensitive recording layer of the reversible heat-sensitive recording medium of the present invention. For example, even if a polymer compound is present, its reversible decoloring behavior can be maintained.
[0019]
Next, the developer used in combination with the color former in the reversible thermosensitive recording medium of the present invention will be described. As disclosed in Japanese Patent Application Laid-Open No. 5-124360, a color developing agent can be formed in the molecule as disclosed in Japanese Patent Application Laid-Open No. 5-124360 together with typical examples of a phosphoric acid compound and a fatty acid compound having a long-chain hydrocarbon group. A compound having both a structure having color developing ability and a structure controlling cohesion between molecules is used. As a structure having a color developing ability, similar to a general thermosensitive recording medium, for example, an acidic group such as a phenolic hydroxyl group, a carboxyl group, or a phosphoric acid group is used. It is good to have. These include, for example, thiourea groups, carboxylic acid metal salts and the like. A typical structure for controlling cohesion between molecules is a hydrocarbon group such as a long-chain alkyl group. In general, the number of carbon atoms of the hydrocarbon group is preferably 8 or more in order to obtain good color-developing and decoloring characteristics. The hydrocarbon group may contain an unsaturated bond, and also includes a branched hydrocarbon group. Also in this case, the main chain portion preferably has 8 or more carbon atoms. Further, this hydrocarbon group may be substituted with a group such as a halogen atom, a hydroxyl machine, or an alkoxy group.
[0020]
As described above, the color developer has a structure in which a structure having a color developing ability and a structure controlling cohesion represented by a hydrocarbon group are connected. A divalent group containing a hetero atom as described below or a group obtained by combining a plurality of these groups may be bonded to the linking portion.
In addition, an aromatic ring or a heterocyclic ring such as phenylene and naphthylene may be bonded, or both may be bonded.
The hydrocarbon group may have a divalent group similar to the above in its chain structure, that is, a divalent group containing an aromatic ring or a hetero atom.
[0021]
Hereinafter, the color developer used in the present invention will be specifically exemplified.
Examples of the organic phosphoric acid developer include the following compounds.
Dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid, ditetradecyl phosphate, dihexadecyl phosphate, phosphoric acid Dioctadecyl ester, dieicosyl phosphate, dibehenyl phosphate, and the like.
[0022]
The following compounds can be exemplified as the aliphatic carboxylic compound.
2-hydroxytetradecanoic acid, 2-hydroxyhexadecanoic acid, 2-hydroxyoctadecanoic acid, 2-hydroxyeicosanoic acid, 2-hydroxydocosanoic acid, 2-bromohexadecanoic acid, 2-bromooctadecanoic acid, 2-bromoeicosanoic acid 2-bromodocosanoic acid, 3-bromooctadecanoic acid, 3-bromodocosanoic acid, 2,3-dibromooctadecanoic acid, 2-fluorodecanoic acid, 2-fluorotetradecanoic acid, 2-fluorohexadecanoic acid, 2-fluorooctadecanoic acid, 2 -Fluoroeicosanoic acid, 2-fluorodocosanoic acid, 2-iodohexadecanoic acid, 2-iodooctadecanoic acid, 3-iodohexadecanoic acid, 3-iodooctadecanoic acid, perfluoctadecanoic acid and the like.
[0023]
The following compounds can be exemplified as the aliphatic dicarboxylic acid and tricarboxylic acid compounds.
2-dodecyloxysuccinic acid, 2-tetradecyloxysuccinic acid, 2-hexadecyloxysuccinic acid, 2-octadecyloxysuccinic acid, 2-eicosyloxysuccinic acid, 2-dodecyloxysuccinic acid, 2-dodecylthiosuccinic acid 2-hexadecylthiosuccinic acid, 2-octadecylthiosuccinic acid, 2-eicosylthiosuccinic acid, 2-docosylthiosuccinic acid, 2-tetracosylthiosuccinic acid, 2-hexadecylthiosuccinic acid, 2-tetradecylthiosuccinic acid, Octadecyldithiosuccinic acid, 2-eicosyldithiosuccinic acid, dodecylsuccinic acid, tetradecylsuccinic acid, pentadecylsuccinic acid, hexadecylsuccinic acid, octadecylsuccinic acid, eicosylsuccinic acid, docosylsuccinic acid, 2,3-dihexadecylsuccinic acid, 2,3 −Dioctadesi Succinic acid, 2-methyl-3-hexadecylsuccinic acid, 2-methyl-3-octadecylsuccinic acid, 2-octadecyl-3-hexadecylsuccinic acid, hexadecylmalonic acid, octadecylmalonic acid, eicosylmalonic acid, docosylmalonic acid, Dihexadecylmalonic acid, dioctadecylmalonic acid, didocosylmalonic acid, methyloctadecylmalonic acid, 2-hexadecylglutaric acid, 2-octadecylglutaric acid, 2-eicosylglutaric acid, docosylglutaric acid, 2-pentadecyladipate 2-octadecyladipic acid, 2-eicosyladipic acid, 2-docosyladipic acid, 2-hexadecanoyloxypropane-1,2,3-tricarboxylic acid, 2-octadecanoyloxypropane-1,2,2 3-tricarboxylic acid and the like.
[0024]
As the carboxylic acid compound, a compound represented by the following general formula (3) can also be used.
[0025]
Embedded image

Specific examples of the carboxylic acid compound represented by the general formula (3) are shown in Table 1 below by the numbers or structures of p, q, r, s, A, B, X, and Y.
[0026]
[Table 1-1]

[0027]
[Table 1-2]

[0028]
[Table 1-3]

[0029]
[Table 1-4]

[0030]
[Table 1-5]

[0031]
[Table 1-6]

[0032]
[Table 1-7]

[0033]
[Table 1-8]

[0034]
[Table 1-9]

[0035]
[Table 1-10]

[0036]
[Table 1-11]

[0037]
[Table 1-12]

[0038]
Examples of the carboxylic acid compound used for the color developer include a compound represented by the following general formula (4).
[0039]
Embedded image

Specific examples of the carboxylic acid compound represented by the general formula (4) are shown in Table 2 below by the number or structure of n, p, q, r, R, X, and Y.
[0040]
[Table 2-1]

[0041]
[Table 2-2]

[0042]
[Table 2-3]

[0043]
[Table 2-4]

[0044]
[Table 2-5]

[0045]
[Table 2-6]

[0046]
A phenol compound having a structure for controlling intermolecular cohesion is also preferably used as the developer. For example, a phenol compound represented by the following general formula (5) can be exemplified.
[0047]
Embedded image

Specific examples of the phenol compound represented by the general formula (5) are shown in Table 3 below by the numbers or structures of p, q, r, s, X, A, Y, and Z. However, in each of these specific examples, n of the phenol moiety is from 1 to 3, for example, 4-hydroxyphenyl, 3-hydroxyphenyl, 2-hydroxyphenyl, 2,4-dihydroxyphenyl, 3,4-dihydroxyphenyl or It is a phenyl group having at least one hydroxyl group such as 3,4,5-trihydroxyphenyl. This phenyl group may have a substituent other than a hydroxyl group. Other aromatic rings may be used as long as they have a phenolic hydroxyl group.
[0048]
[Table 3-1]

[0049]
[Table 3-2]

[0050]
[Table 3-3]

[0051]
[Table 3-4]

[0052]
[Table 3-5]

[0053]
[Table 3-6]

[0054]
[Table 3-7]

[0055]
[Table 3-8]

In the present invention, the color developer is not limited to the compounds described above, and various other electron-accepting compounds can be used.
[0056]
The reversible thermosensitive color-forming composition of the present invention is basically constituted by combining the above-mentioned developer and color former. The color former used in the present invention has an electron donating property and is itself a colorless or light-colored dye precursor (leuco dye), and is not particularly limited, and is a conventionally known one such as a triphenylmethanephthalide-based compound. Fluoran compounds, phenothiazine compounds, leuco auramine compounds, indolinophthalide compounds and the like. The coloring agent is shown below.
Preferred color formers for use in the invention include compounds of the following general formula:
[0057]
Embedded image

[0058]
Embedded image

(However, R ₁ represents hydrogen or an alkyl group having 1 to 4 carbon atoms, R ₂ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group or an optionally substituted phenyl group. As a substituent for the phenyl group, Represents an alkyl group such as a methyl group or an ethyl group, an alkoxy group such as a methoxy group or an ethoxy group, a halogen, etc. R ₃ represents hydrogen, an alkyl group having 1 to 2 carbon atoms, an alkoxy group or a halogen. _{And 4} represents hydrogen, a methyl group, a halogen, or an amino group which may be substituted, such as an alkyl group, an aryl group which may be substituted or an aralkyl group which may be substituted; The substituent here is an alkyl group, a halogen, an alkoxy group, etc.) Specific examples of such a color former include, for example, the following compounds. I can do it.
[0059]
2-anilino-3-methyl-6-diethylaminofluoran,
2-anilino-3-methyl-6-di (n-butylamino) fluoran,
2-anilino-3-methyl-6- (Nn-propyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (N-sec-butyl-N-ethylamino) fluoran,
2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluoran,
2-anilino-3-methyl-6- (N-isoamyl-N-ethylamino) fluoran,
2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluoran,
2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran,
2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluoran,
2-anilino-3-methyl-6- (N-methyl-p-toluidino) fluoran,
2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluoran,
2- (m-trifluoromethylanilino) -3-methyl-6-diethylaminofluoran,
2- (m-trichloromethylanilino) -3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran,
2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluoran,
2- (N-ethyl-p-toluidino) -3-methyl-6- (N-ethylanilino) fluoran,
2- (N-ethyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluoran,
[0060]
2-anilino-6- (Nn-hexyl-N-ethylamino) fluoran,
2- (o-chloroanilino) -6-diethylaminofluoran,
2- (o-chloroanilino) -6-dibutylaminofluoran,
2- (m-trifluoromethylanilino) -6-diethylaminofluoran,
2- (p-acetylanilino) -6- (Nn-amyl-Nn-butylamino) fluoran,
2-benzylamino-6- (N-ethyl-p-toluidino) fluoran,
2-benzylamino-6- (N-methyl-2,4-dimethylanilino) fluoran,
2-benzylamino-6- (N-ethyl-2,4-dimethylanilino) fluoran,
2-dibenzylamino-6- (N-methyl-p-toluidino) fluoran,
2-dibenzylamino-6- (N-ethyl-p-toluidino) fluoran,
2- (di-p-methylbenzylamino) -6- (N-ethyl-p-toluidino) fluoran,
2- (α-phenylethylamino) -6- (N-ethyl-p-toluidino) fluoran,
2-methylamino-6- (N-methylanilino) fluoran,
2-methylamino-6- (N-ethylanilino) fluoran,
2-methylamino-6- (N-propylanilino) fluoran,
2-ethylamino-6- (N-methyl-p-toluidino) fluoran,
2-methylamino-6- (N-methyl-2,4-dimethylanilino) fluoran,
2-ethylamino-6- (N-ethyl-2,4-dimethylanilino) fluoran,
2-dimethylamino-6- (N-methylanilino) fluoran,
2-dimethylamino-6- (N-ethylanilino) fluoran,
2-diethylamino-6- (N-methyl-p-toluidino) fluoran,
2-diethylamino-6- (N-ethyl-p-toluidino) fluoran,
2-dipropylamino-6- (N-methylanilino) fluoran,
2-dipropylamino-6- (N-ethylanilino) fluoran,
2-amino-6- (N-methylanilino) fluoran,
2-amino-6- (N-ethylanilino) fluoran,
2-amino-6- (N-propylanilino) fluoran,
2-amino-6- (N-methyl-p-toluidino) fluoran,
2-amino-6- (N-ethyl-p-toluidino) fluoran,
2-amino-6- (N-propyl-p-toluidino) fluoran,
2-amino-6- (N-methyl-p-ethylanilino) fluoran,
2-amino-6- (N-ethyl-p-ethylanilino) fluoran,
2-amino-6- (N-propyl-p-ethylanilino) fluoran,
2-amino-6- (N-methyl-2,4-dimethylanilino) fluoran,
2-amino-6- (N-ethyl-2,4-dimethylanilino) fluoran,
2-amino-6- (N-propyl-2,4-dimethylanilino) fluoran,
2-amino-6- (N-methyl-p-chloroanilino) fluoran,
2-amino-6- (N-ethyl-p-chloroanilino) fluoran,
2-amino-6- (N-propyl-p-chloroanilino) fluoran,
[0061]
2,3-dimethyl-6-dimethylaminofluoran,
3-methyl-6- (N-ethyl-p-toluidino) fluoran,
2-chloro-6-diethylaminofluoran,
2-bromo-6-diethylaminofluoran,
2-chloro-6-dipropylaminofluoran,
3-chloro-6-cyclohexylaminofluoran,
3-bromo-6-cyclohexylaminofluoran,
2-chloro-6- (N-ethyl-N-isoamylamino) fluoran,
2-chloro-3-methyl-6-diethylaminofluoran,
2-anilino-3-chloro-6-diethylaminofluoran,
2- (o-chloroanilino) -3-chloro-6-cyclohexylaminofluoran,
2- (m-trifluoromethylanilino) -3-chloro-6-diethylaminofluoran,
2- (2,3-dichloroanilino) -3-chloro-6-diethylaminofluoran,
1,2-benzo-6-diethylaminofluoran,
1,2-benzo-6- (N-ethyl-N-isoamylamino) fluoran,
1,2-benzo-6-dibutylaminofluoran,
1,2-benzo-6- (N-methyl-N-cyclohexylamino) fluoran, 1,2-benzo-6- (N-ethyl-N-toluidino) fluoran, and others.
[0062]
Specific examples of other color formers preferably used in the present invention are as follows.
2-anilino-3-methyl-6- (N-2-ethoxypropyl-N-ethylamino) fluoran,
2- (p-chloroanilino) -6- (Nn-octylamino) fluoran,
2- (p-chloroanilino) -6- (Nn-palmitylamino) fluoran,
2- (p-chloroanilino) -6- (di-n-octylamino) fluoran,
2-benzoylamino-6- (N-ethyl-p-toluidino) fluoran,
2- (o-methoxybenzoylamino) -6- (N-methyl-p-toluidino) fluoran,
2-dibenzylamino-4-methyl-6-diethylaminofluoran,
2-dibenzylamino-4-methoxy-6- (N-methyl-p-toluidino) fluoran,
2-benzylamino-4-methyl-6- (N-ethyl-p-toluidino) fluoran,
2- (α-phenylethylamino) -4-methyl-6-diethylaminofluoran,
2- (p-toluidino) -3- (t-butyl) -6- (N-methyl-p-toluidino) fluoran,
2- (o-methoxycarbonylanilino) -6-diethylaminofluoran,
2-acetylamino-6- (N-methyl-p-toluidino) fluoran,
3-diethylamino-6- (m-trifluoromethylanilino) fluoran,
4-methoxy-6- (N-ethyl-p-toluidino) fluoran,
2-ethoxyethylamino-3-chloro-6-dibutylaminofluoran,
2-dibenzylamino-4-chloro-6- (N-ethyl-p-toluidino) fluoran,
2- (α-phenylethylamino) -4-chloro-6-diethylaminofluoran,
2- (N-benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluoran,
2-anilino-3-methyl-6-pyrrolidinofluoran,
2-anilino-3-chloro-6-pyrrolidinofluoran,
2-anilino-3-methyl-6- (N-ethyl-N-tetrahydrofurfurylamino) fluoran,
2-mesidino-4 ′, 5′-benzo-6-diethylaminofluoran,
2- (m-trifluoromethylanilino) -3-methyl-6-pyrrolidinofluoran,
2- (α-naphthylamino) -3,4-benzo-4′-bromo-6- (N-benzyl-N-cyclohexylamino) fluoran,
2-piperidino-6-diethylaminofluoran,
2- (Nn-propyl-p-trifluoromethylanilino) -6-morpholinofluoran,
2- (di-N-p-chlorophenyl-methylamino) -6-pyrrolidinofluoran,
2- (Nn-propyl-m-trifluoromethylanilino) -6-morpholinofluoran,
1,2-benzo-6- (N-ethyl-Nn-octylamino) fluoran,
1,2-benzo-6-diallylaminofluoran,
1,2-benzo-6- (N-ethoxyethyl-N-ethylamino) fluoran,
[0063]
Benzolecomethylene blue,
Lactam 2- [3,6-bis (diethylamino)]-6- (o-chloroanilino) xanthylbenzoate,
Lactam 2- [3,6-bis (diethylamino)]-9- (o-chloroanilino) xanthylbenzoate,
3,3-bis (p-dimethylaminophenyl) -phthalide,
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone),
3,3-bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide,
3,3-bis (p-dibutylaminophenyl) phthalide,
3- (2-methoxy-4-dimethylaminophenyl) -3- (2-hydroxy-4,5-dichlorophenyl) phthalide,
3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide,
3- (2-hydroxy-4-dimethoxyaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide,
3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5-nitrophenyl) phthalide,
3- (2-hydroxy-4-diethylaminophenyl) -3- (2-methoxy-5-methylphenyl) phthalide,
3- (2-methoxy-4-dimethylaminophenyl) -3- (2-hydroxy-4-chloro-5-methoxyphenyl) phthalide,
3,6-bis (dimethylamino) fluorenespiro (9,3 ′)-6′-dimethylaminophthalide,
3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide,
3- (1-octyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide,
3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide,
3,3-bis (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide,
3,3-bis (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide,
6'-chloro-8'-methoxy-benzoindolino-spiropyran,
6'-bromo-2'-methoxy-benzoindolino-spiropyran and others.
[0064]
Specific examples of the color developer and color former used in the present invention are described in detail in JP-A-5-124360, JP-A-6-8624 and JP-A-6-24132.
[0065]
In the present invention, the guanidine derivative added to the thermochromic composition for improving light resistance is represented by the following general formula (6) or (7).
[0066]
Embedded image

(R ₁ represents an electron donating group, n is an integer of 1 to 30)
[0067]
Embedded image

(R ₂ represents an electron donating group, R ₃ represents halogen, and m and l are integers of 1 or 2)
[0068]
Specific examples of the guanidine derivative used in the present invention are as follows, but the present invention is not limited thereto.
1,3-dicyclohexyl-2- (3′-methoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (2 ′, 4′-dimethoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (2 ′, 5′-dimethoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (4′-ethoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (2 ′, 4′-dibutoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3 ′, 4 ′, 5′-trimethoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (4′-diethylaminophenyl) guanidine
1,3-dicyclohexyl-2- (2′-chloro-3′-methylphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-chloro-4′-methylphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-bromo-6′-ethylphenyl) guanidine,
1,3-dicyclohexyl-2- (2′-bromo-4′-methylphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-fluoro-6′-methylphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-chloro-6′-methoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-chloro-6′-butoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-bromo-6′-ethoxyphenyl) guanidine,
[0070]
1,3-dicyclohexyl-2- (2 ′, 5′-dichloro-4′-methylphenyl) guanidine,
1,3-dicyclohexyl-2- (3 ′, 5′-dichloro-4′-methoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3 ′, 5′-dichloro-4′-butoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-chloro-4 ′, 6′-dimethoxyphenyl) guanidine,
1,3-dicyclohexyl-2- (3′-chloro-4 ′, 6′-dinorpropylphenyl) guanidine,
1,3-dicyclohexyl-2- (3'-chloro-2 ', 6'-diethylphenyl) guanidine 1,3-dicyclohexyl-2- (2'-chloro-4'-dimethylaminophenyl) guanidine and the like.
[0071]
Also, as vitamin K,
Vitamin K ₁ (2-methyl-3-phytyl-1,4-naphthoquinone),
Vitamin K ₂ (2-farnesyl-3-methyl-1,4-naphthoquinone),
Vitamin _K 3 (2-methyl-1,4-naphthoquinone) and the like.
[0072]
In order to improve the light fastness, the above-mentioned guanidine derivative or vitamin K may be added alone or in combination of two or more, and the amount added is 1 to less than 30% by weight, preferably 5 to 30% by weight based on the color former. When the amount is less than 20% by weight, the effect of improving light resistance is small when the amount is too small, and when the amount is too large, the color density and image storability are reduced, and even when added in an amount of 30% by weight or more, the light resistance is not further improved. .
[0073]
In the composition of the present invention, the added amount of the color developer is 1 to 20 times, preferably 2 to 10 times the molar amount of the color former, and within this range, the developer and the color former may be used alone. May be used as a mixture of two or more. However, at least, and even if the amount of the developer is larger than this range, the density of the color-developed state becomes low, which is a practical problem.
[0074]
Further, even in the preferred range described above, the decoloring characteristics change depending on the ratio of the color former and the developer, and the decoloration start temperature becomes lower when the developer is relatively large, and when the developer is relatively small. The decolorization becomes sharp with temperature. Therefore, this ratio must be appropriately selected according to the application and purpose.
[0075]
The reversible thermosensitive recording medium of the present invention is obtained by laminating a recording layer containing the composition on a support, and usually improves the durability by laminating a protective layer on the recording layer. It is not necessary. The support is paper, synthetic paper, plastic film, or a composite thereof, glass, or the like, as long as it can hold the recording layer.
[0076]
The recording layer may be in any form as long as the above-mentioned composition is present. The recording layer may be formed by mixing and melting a developer and a color former, and then cooling this to form a recording layer. However, usually, the developer and the color former are preferably sufficiently dispersed in the binder resin to form a recording layer, and a reversible thermosensitive recording medium having a long life can be obtained by this method. In this case, the recording layer can be formed according to a conventionally known method. That is, the color former and the developer may be uniformly dispersed or dissolved in water or an organic solvent together with the binder resin, and the resultant may be coated on a support and dried.
[0077]
In the reversible thermosensitive recording medium of the present invention, various additives used in ordinary thermosensitive recording paper, such as dispersants, surfactants, and polymers, for the purpose of improving coating characteristics or recording characteristics, if necessary, A cationic conductive agent, a filler, a color image stabilizer, an antioxidant, a light stabilizer, a lubricant and the like can be added to the recording layer.
[0078]
The binder resin used for the recording layer, the undercoat layer, the intermediate layer between the recording layer and the protective layer, etc. is not particularly limited, and any known binder resin can be used. Specific examples of the binder resin include hydroxyethylcellulose, hydroxypropylcellulose, methoxycellulose, carboxymethylcellulose, methylcellulose, cellulose acetate, gelatin, casein, starch, sodium polyacrylate, polyvinylpyrrolidone, polyacrylamide, polyvinyl chloride, and polyvinyl chloride. Vinyl acetate, vinyl chloride-vinyl acetate copolymer, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylate, polymethacrylate, acrylic acid copolymer , Maleic acid copolymer, polyvinyl alcohol, chlorinated vinyl chloride resin, and a mixture of these resins.
[0079]
The role of the binder resin in the recording layer is to prevent the reversible thermochromic composition from aggregating due to repetition of coloring and decoloring, and to maintain a state in which the composition is uniformly dispersed. In particular, since the composition often aggregates and becomes non-uniform due to application of heat at the time of color development, a binder resin having high heat resistance is preferable. It is considered that various properties of the binder resin greatly affect the behavior of the thermochromic composition.
[0080]
The protective layer prevents the surface from being deformed or discolored by heat and pressure when applying heat, and also has a role to improve chemical resistance, water resistance, friction resistance, head matching, etc. You can also. Therefore, the material for forming the protective layer preferably has excellent heat resistance and high strength. Silicone rubber, silicone resin (JP-A-63-221087), polysiloxane graft polymer (JP-A-63-317385). A thermosetting resin, an ultraviolet curable resin, an electron beam curable resin, or the like is used, but a resin formed from an aqueous emulsion of a water-soluble polymer or a hydrophobic polymer compound may be used. With the formation of such a protective layer, the heat resistance is improved as described above, and the resistance to contact with an organic solvent, a plasticizer, oil, sweat, water, etc. is also increased. It is possible to obtain a recording medium that can be repeated without any problem. In addition, by including a light stabilizer in the protective layer, a recording medium having significantly improved light fastness of an image and a background can be obtained. By adding a polymeric cationic conductive agent, antistatic can be performed. By adding an organic or inorganic filler and a lubricant to the ink, sticking caused by contact with a thermal head or the like can be prevented, and a thermosensitive recording medium having high reliability and high head matching can be obtained. The protective layer may be formed by uniformly dispersing or dissolving the protective layer components in water or an organic solvent, and uniformly applying and drying the protective layer on the recording layer. The protective layer has a thickness of 0.5 to 10 μm. Good degree.
[0081]
In the reversible thermosensitive recording medium of the present invention, an undercoat layer may be provided between the support and the recording layer, if necessary. The undercoat layer is provided for the purpose of improving heat insulation, improving the adhesion between the support and the recording layer, improving the resistance of the support to a solvent when the recording layer is formed, and taking into account the type of the support. May be determined. One of the important roles of the undercoat layer is to improve the heat insulation properties. This is to make the applied heat energy useful for thermal recording formation and heat erasure. Can be performed sharply. In order to form an undercoat layer for the purpose of heat insulation, fine hollow particles made of an organic or inorganic material may be coated on a support, and specifically, formed of glass, ceramics, plastic, or the like. A fine hollow body having a particle size of about 10 to 50 μm may be well dispersed in a solvent together with a binder resin, and may be uniformly applied and dried on a support. In addition, even if a heat insulating support is used instead of providing a heat insulating layer, the applied heat energy can be saved, and a plastic film, synthetic paper, or the like is used as the heat insulating support.
[0082]
Further, in the reversible thermosensitive recording medium of the present invention, an intermediate layer may be provided between the recording layer and the protective layer.
The intermediate layer is provided for the purpose of improving the adhesion between the recording layer and the protective layer, and improving the resistance of the recording layer to a solvent when the protective layer is formed.
[0083]
The formation of the recorded image is not particularly limited, such as a hot pen, a thermal head, or laser heating, depending on the purpose of use. Similarly, the erasing of the recorded image is not particularly limited as long as the erasing temperature conditions are given, such as a heating roller, a sheet heating element, a thermostat, a hot air, and a thermal head. It is also possible to simultaneously form a recorded image with another thermal head set at the recording temperature while erasing the recorded image with the thermal head set at the erasing temperature.
[0084]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following, all parts and percentages are based on weight.
[0085]
Reference Examples 1 to 20 and Examples 1 to 6
The following composition was pulverized and dispersed in a ball mill so as to have a particle size of about 1 to 3 μm to prepare a coating solution for forming a reversible thermosensitive recording layer.
2- (o-chloroanilino) -6-dibutylaminofluoran 3 parts Octadecylphosphonic acid 10 parts Vinyl chloride / vinyl acetate copolymer,
(VYHH, manufactured by Union Carbide Co., Ltd.) 10 parts of additives (additives and amounts of Reference Examples 1 to 20 and Examples 1 to 6 shown in Tables 4 and 5 )
Toluene 45 parts Methyl ethyl ketone 45 parts This coating solution was applied to a white PET film (Lumirror E20, manufactured by Toray Industries, Inc.) using a wire bar and dried to provide a reversible thermosensitive recording layer having a thickness of about 6 μm.
[0086]
Next, a coating solution for forming a protective layer having the following composition is applied on the reversible thermosensitive recording layer with a wire bar and dried, and after drying, the coated / dried product is irradiated with ultraviolet light having a strength of 80 W / cm. After curing, a protective layer having a thickness of about 3 μm was laminated.
Urethane acrylate UV curable resin 100 parts (Dainippon Ink & Chemicals, Inc .; Unidick C7-157)
Ethyl acetate 50 parts
The reversible thermosensitive recording medium produced as described above was brought into contact with a hot plate at 120 ° C. for about 20 seconds to obtain a color image, and the color density was measured with a reflection densitometer RD-914 manufactured by Macbeth. Next, the color-developed recording medium was placed in a constant temperature bath at 70 ° C. for 10 minutes to erase the image, and the erasing density was measured by the RD-914. In addition, the image density after exposing the color image to a fluorescent lamp of 5 klux (Klux) for 48 hours, and the decoloring density when the image was decolored by the same method as described above were measured.
Further, the color image was placed in a thermostat at 50 ° C., and the density after 24 hours was measured to examine the heat resistance. These are summarized in Tables 1 and 2.
[0088]
Reference comparative example
The reversible heat-sensitive medium was prepared and evaluated in the same manner as in the Reference Example for those in which no additive was added and those in which the conventional guanidine derivative was added in the Reference Example (Table 4).
[0089]
[Table 4-1]

[0090]
[Table 4-2]

[0091]
Embedded image

* 2: Ratio to electron-donating color-forming compound (wt%)
* 3, * 5;

* 4; (Difference) = Decoloring density after test-Initial decoloring density
[Table 5]

[0093]
【The invention's effect】
As described above in detail and specifically, the reversible thermochromic composition and the reversible thermosensitive recording medium of the present invention contain vitamin K in the composition, so that the composition remains unerased even after exposure to light. And the light fastness is improved. Further, it is excellent in thermal stability in a color-developing state, and can achieve good color-preserving image storability.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of color development and color erasure of a reversible thermosensitive recording medium of the present invention with reference to a relationship graph between temperature and color density.
FIG. 2 is a diagram illustrating an image forming step and an image erasing step.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming process by heating 2 Image fixing process by cooling 3 Image erasing process by heating 4 Support 5 Reversible thermosensitive recording layer 6 Colored image 7 Thermal head 8 Heating roller A Completely erased state of image B Saturated colored state C Completely colored state D Heat-erasing state

Claims (2)

A recording layer containing an electron-donating color-forming compound and an electron-accepting compound as main components and capable of forming a relatively colored state and a decolored state due to a difference in a heating temperature and / or a cooling rate after heating. A reversible thermosensitive recording medium provided on a support, wherein the recording layer or a layer adjacent to the recording layer contains vitamin K ₁ , vitamin K ₂ or vitamin K ₃ . The amount of vitamin K ₁ , vitamin K ₂ or vitamin K ₃ added to the recording layer and / or the layer adjacent to the recording layer is not less than 1.0% by weight and less than 30% by weight based on the electron-donating color-forming compound. 2. The reversible thermosensitive recording medium according to claim 1, wherein:

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