JP3599162B2 - Reversible thermosensitive recording medium - Google Patents

Description

【００３１】
【化２】

【００３２】
【化３】

ＣＯＯＨ基変性エポキシアクリレート以外にも水溶解型としてオニウム塩変性エポキシアクリレートが開発されており、本発明においてはこれを用いることもできる。
【００３３】
【化４】

【００３４】
酸性の官能基をもつ高分子材料としては放射線により硬化反応するものが好ましく、更に、多官能のアクリレートモノマー、メタクリレートモノマー若しくはオリゴマーが好ましい。ＮＨ₃を捕獲する効果は上記酸性基の量により決定される。上記高分子材料のカルボキシル基数が少ないと捕獲効果が不十分となる。したがって、上記高分子材料の酸価は６０ｍｇ／ＫＯＨ／ｇ以上であり、更に好ましくは８０ｍｇ／ＫＯＨ／ｇ以上である。
また、上記高分子材料のカルボキシル基数が多いと、高分子材料の密度が低下し、アンモニアガスが透過しやすくなると考えられる。したがって、上記高分子材料の酸価は１２０ｍｇ／ＫＯＨ／ｇ以下であり、更に好ましくは１００ｍｇ／ＫＯＨ／ｇ以下である。
【００３５】
また、感熱層中の低分子のカルボキシル基等の酸性の官能基とアンモニア等の塩基性物質の反応を防ぐためには感熱層上の層は気体透過性を低くすることが好ましい。気体透過性は層の厚みによって変化する。感熱層上の層の総膜厚は５μｍ以上が好ましい。また、感熱層上の上の総膜厚が厚くなると印字感度が高くなり、印字時に過剰なエネルギーが必要となり可逆性感熱記録媒体の繰り返し印字消去後の媒体表面の打痕、傷等が目立つようになる不具合が生じる。よって、感熱層上の層の総膜厚は２０μｍ以下が好ましく、更に好ましくは１５μｍ以下であり、特に好ましくは１０μｍ以下である。
【００３６】
高分子材料の気体透過性は高分子の主鎖の充填度に影響を受ける。高分子の立体配置により充填度がよくなると、気体透過性は減少する。また、分子構造が単純になるに従い充填度が良好となる。更に結晶は気体透過性が低く透過速度を減少させる。よって、感熱層上の少なくとも１層の高分子材料の主鎖の成分が結晶性のある構造であることが好ましい。好ましくは結晶構造の主鎖が材料構造中の７０％以上であり、更に好ましくは９０％以上である。
可逆性感熱記録媒体を繰り返し印字消去すると、その熱的影響によりクラックが生じ、塩基性物質が透過しやすい状態になる。したがって、保護層は耐熱性の高い樹脂が好ましく、そのＴｇは１３０℃以上が好ましく、更に好ましくは１４０℃以上であり、１６０℃以上であればなお好ましい。
【００３７】
本発明の可逆性感熱記録媒体の保護層について説明する。
保護層の形成に用いられる紫外線硬化樹脂としては、紫外線照射により重合反応を起こし、硬化して樹脂となるモノマー又はオリゴマー（又はプレポリマー）であれば全て使用できるが、前記酸性の官能基を含有しているモノマー又はオリゴマー（又はプレポリマー）、または前記酸性の官能基を含有しているモノマー又はオリゴマー（又はプレポリマー）とその他のものとの混合系が好ましい。
また、保護層の架橋密度は高い方が好ましく、そのために使用するモノマー又はオリゴマー（又はプレポリマー）は多官能のものが好ましく、充填度を上げるために分子量３００以下のモノマーを混合することが好ましい。
紫外線硬化樹脂としては紫外線照射により重合反応を起こし、硬化して樹脂となるモノマー又はオリゴマー（又はプレポリマー）としては、モノマー又はオリゴマーとしては（ポリ）エステルアクリレート、（ポリ）ウレタンアクリレート、エポキシアクリレート、ポリブタジエンアクリレート、シリコーンアクリレート等やメラミンアクリレートがある。（ポリ）エステルアクリレートは１，６−ヘキサンジオール、プロピレングリコール（プロピレンオキサイドとして）、ジエチレングリコール等の多価アルコールとアジピン酸、無水フタル酸、トリメリット酸等の多塩基酸とアクリル酸とを反応させたものである。その構造例を（ａ）〜（ｃ）に示す。
【００３８】
（ａ）アジピン酸／１，６−ヘキサンジオール／アクリル酸
【００３９】
【化５】

（ｂ）無水フタル酸／プロピレンオキサイド／アクリル酸
【００４０】
【化６】

（ｃ）トリメリット酸／ジエチレングリコール／アクリル酸
【００４１】
【化７】

【００４２】
（ポリ）ウレタンアクリレートは、トリレンジイソシアネート（ＴＤＩ）のようなイソシアネート基を有する化合物に、ヒドロキシル基を有するアクリレートを反応させたものである。その構造例を（ｄ）に示す。なお、ＨＥＡは２−ヒドロキシエチルアクリレート、ＨＤＯは１，６−ヘキサンジオール、ＡＤＡはアジピン酸の略である。
（ｄ）ＨＥＡ／ＴＤＩ／ＨＤＯ／ＡＤＡ／ＨＤＯ／ＴＤＩ／ＨＥＡ
【００４３】
【化８】

【００４４】
エポキシアクリレートは、構造から大別してビスフェノールＡ型、ノボラック型及び脂環型とがあり、これらエポキシ樹脂のエポキシ基をアクリル酸でエステル化し官能基をアクリロイル基としたものである。その構造例を（ｅ）〜（ｇ）に示す。
（ｅ）ビスフェノールＡ−エピクロルヒドリン型／アクリル酸
【００４５】
【化９】

（ｆ）フェノールノボラック−エピクロルヒドリン型／アクリル酸
【００４６】
【化１０】

（ｇ）脂環型／アクリル酸
【００４７】
【化１１】

【００４８】
ポリブタジエンアクリレートは、末端ＯＨ基含有１，２ポリブタジエンにイソシアネートや１，２−メルカプトエタノール等を反応させてから、更にアクリル酸等を反応させたものである。その構造例を（ｈ）に示す。
（ｈ）
【００４９】
【化１２】

シリコーンアクリレートは、例えば、有機官能性トリメトキシシランとシラノール基含有ポリシロキサンとの縮合反応（脱メタノール反応）によりメタクリル変性したものであり、その構造例を（ｉ）に示す。
（ｉ）
【００５０】
【化１３】

【００５１】
これらの硬化性樹脂を硬化する際の雰囲気中の酸素が硬化を阻害するため、表面の硬化度合が低くなることが知られている。これが、保護層のキズ、印字痕の原因となる。
上記酸素阻害を防止する方法としては、酸素濃度が８％以下の雰囲気で硬化性樹脂を硬化することが挙げられる。好ましくは、酸素濃度５％以下であり、更に好ましくは２％以下である。酸素阻害を防止することで、硬化性樹脂は表面まで完全に硬化キズ、印字痕を防ぐことができるのである。
【００５２】
一方、電子線硬化性樹脂の材料としては紫外線硬化性樹脂をそのまま用いることができる。
ところで電子線は紫外線に比べてエネルギーが大きく、また透過力も大きい。また、Ｏ_３の発生を防止するためＮ_２雰囲気中にて硬化を行う。このため、表面の酸素阻害は発生せず、特に保護層中に顔料等を入れた時は、電子線の方が内部まで到達することができる。こうして電子線硬化の方が紫外線硬化より、いっそう綿密で均一な網目構造を形成できるので、更に優れた耐久性を示すことが期待できる。また、電子線は紫外線に比べて、硬化に要するエネルギーは約３分の１ですみ、設備投資は大きくても、需要が多いことによりコストを下げることも期待できる。
【００５３】
次にバリアー層について説明する。本発明のバリアー層とは感熱層中の有機低分子物質と塩基性物質との接触（反応）を防ぐための層である。
バリアー層に用いられる高分子材料は透明性がよく、機械的に安定であり、気体透過性が低い高分子が好ましく、ポリ塩化ビニル又は塩化ビニル系共重合体、ポリ塩化ビニリデン又は塩化ビニリデン系共重合体等の結晶性の樹脂又は結晶性の樹脂系共重合体が挙げられる。共重合体の場合の結晶性の樹脂の共重合比は８０％以上が好ましく、更に好ましくは９０％以上である。
また、前記酸性の官能基を含有しているモノマー又はオリゴマー（又はプレポリマー）を含んだ架橋材等にて架橋することが好ましい。これにより保護層を透過してきた塩基性物質を吸着させる働きをもたせるとともに機械的安定性を上げることができる。上記架橋材は多官能性のものが好ましい。
【００５４】
次に本発明に用いられる感熱層の樹脂母材について説明する。
樹脂の軟化点については、低温側にすることにより、より透明化温度巾拡大の効果がある。そのため軟化点は好ましくは７０℃以下であり更に好ましくは６５℃以下であり、特に好ましくは６０℃以下である。この場合に下限値は白濁時の有機低分子物質結晶化温度よりも高いことが好ましい。
【００５５】
またこれらの軟化点の測定方法としては、支持体上に記録層を任意の膜厚で形成し、その後に支持体より膜を剥離して、熱機械的分析装置（ＴＭＡ）や動的粘弾性測定装置を用いて測定することができる。また更に前記したように、形成された記録層を剥離せずに剛体振り子法動的粘弾性測定装置により測定することができる。
【００５６】
軟化点の低い樹脂としては、例えば、長い側鎖を持つ樹脂や、低軟化点の樹脂を共重合したものが挙げられる。長い側鎖を持つ樹脂の側鎖は、アルキル基に換算して炭素数３以上が好ましい。また、側鎖中にエーテル結合エステル結合等があってもよい。更に、側鎖の末端にカルボキシル基やヒドロキシル基があってもよい。主鎖の例としては、ポリ塩化ビニル、ポリカーボネート、フェノキシ樹脂、ポリスチレン、塩素化塩ビ樹脂やこれらの共重合体が挙げられる。
【００５７】
本発明で用いられる塩化ビニル−ビニルエステル共重合体は、ビニルエステルを構成する脂肪酸の炭素数が３以上、即ちプロピオン酸以上のものである。
このような塩化ビニル−ビニルエステル共重合体としては次のものが挙げられる。
【００５８】
塩化ビニル−プロピオン酸ビニル共重合体、
塩化ビニル−ブチル酸ビニル共重合体、
塩化ビニル−バレリアン酸ビニル共重合体、
塩化ビニル−カプロン酸ビニル共重合体、
塩化ビニル−エナント酸ビニル共重合体、
塩化ビニル−カプリル酸ビニル共重合体、
塩化ビニル−ペラルゴン酸ビニル共重合体、
塩化ビニル−カプリン酸ビニル共重合体、
塩化ビニル−ウンデカン酸ビニル共重合体、
塩化ビニル−ラウリン酸ビニル共重合体、
塩化ビニル−トリデシル酸ビニル共重合体、
塩化ビニル−ミリスチン酸ビニル共重合体、
塩化ビニル−ペンタデシル酸ビニル共重合体、
塩化ビニル−パルミチン酸ビニル共重合体、
塩化ビニル−マルガリン酸ビニル共重合体、
塩化ビニル−ステアリン酸ビニル共重合体、
塩化ビニル−ノナデシル酸ビニル共重合体、
塩化ビニル−アラキジン酸ビニル共重合体、
塩化ビニル−ベヘン酸ビニル共重合体、
塩化ビニル−リグノセリン酸ビニル共重合体、
塩化ビニル−セロチン酸ビニル共重合体、
塩化ビニル−モンタン酸ビニル共重合体、
塩化ビニル−メリシン酸ビニル共重合体。
【００５９】
また、上記ビニルエステルの構造は直鎖状のノルマル体が分岐状となってもよく、具体的には下記のものが挙げられる。
塩化ビニル−イソプロピオン酸ビニル共重合体
塩化ビニル−イソブチル酸ビニル共重合体
塩化ビニル−イソバレリアン酸ビニル共重合体
塩化ビニル−イソカプロン酸ビニル共重合体
等が挙げられるがこれらに限定されるものではない。
これらの非重合体の共重合比は塩化ビニル単位／ビニルエステル単位重量比が９９／１〜２０／８０が好ましい。
また更に平均重合度（Ｐ）としてはＰ＝１００以上が好ましく、更に好ましくはＰ＝２００以上であり、特に好ましくはＰ＝３００以上である。
【００６０】
次に本発明で用いる塩化ビニル−エチレン共重合体としては、低エチレングレードから高エチレングレードまでの中でエチレン含有量１％以上が好ましく、更に好ましくは２％以上であり、特に好ましくは４％以上である。エチレン含有量が多くなるにつれて、軟化温度が低温へシフトするため、エチレン含有量が多い方が好ましい。
また更にこれらの平均重合度（Ｐ）としてはＰ＝２００以上が好ましく、更に好ましくはＰ＝３００以上であり、特に好ましくはＰ＝４００以上である。
【００６１】
また前記樹脂の他に低軟化点の樹脂としては、下記一般式で表わされる塩化ビニル−ビニルエーテル共重合体も挙げることができる。
ビニルアルキルエーテルのアルキル基の炭素数は３以上が好ましい。
【００６２】
【化１４】

【００６３】
前記した樹脂は少なくとも１種で或いは２種以上混合して用いてもよく、また更にこれら樹脂と下記の樹脂を混合して用いてもよい。
ポリ塩化ビニル：塩化ビニル−酢酸ビニル共重合体、塩化ビニル−酢酸ビニル−ビニルアルコール共重合体、塩化ビニル−酢酸ビニル−マレイン酸共重合体、塩化ビニル−アクリレート共重合体等の塩化ビニル系共重合体；ポリ塩化ビニリデン、塩化ビニリデン−塩化ビニル共重合体、塩化ビニリデン−アクリロニトリル共重合体等の塩化ビニリデン系共重合体；ポリエステル；ポリアミド；ポリアクリレート又はポリメタクリレート或いはアクリレート、メタクリレート共重合体；シリコーン樹脂、ポリエチレン、ポリプロピレン、ポリスチレン、ポリアクリルアミド、ポリビニルピロリドン、天然ゴム、ポリビニルアルコール、ポリアクロレイン、ポリカーボネート等が挙げられる。
【００６４】
一方、有機低分子物質としては記録層中で粒子状になるものであればよく、塩基性物質と反応する官能基をもたないことが好ましいが、これに限定されるわけではない。一般に融点３０〜２００℃、好ましくは５０〜１５０℃程度のものが使用される。このような有機低分子物質としてはアルカノール；アルカンジオール；ハロゲンアルカノール又はハロゲンアルカンジオール；アルキルアミン；アルカン；アルケン；アルキン；ハロゲンアルカン；ハロゲンアルケン；ハロゲンアルキン；シクロアルカン；シクロアルケン；シクロアルキン；飽和又は不飽和モノ又はジカルボン酸又はこれらのエステル、アミド又はアンモニウム塩；飽和又は不飽和ハロゲン脂肪酸又はこれらのエステル、アミド又はアンモニウム塩；アリルカルボン酸又はそれらのエステル、アミド又はアンモニウム塩；ハロゲンアリルカルボン酸又はそれらのエステル、アミド又はアンモニウム塩；チオアルコール；チオカルボン酸又はそれらのエステル、アミド又はアンモニウム塩；チオアルコールのカルボン酸エステル等が挙げられる。これらは単独で又は２種以上混合して使用される。これらの化合物の炭素数は１０〜６０、好ましくは１０〜３８、特に１０〜３０が好ましい。エステル中のアルコール基部分は飽和していてもよく、飽和していなくてもよく、またハロゲン置換されていてもよい。いずれにしても有機低分子物質は分子中に酸素、窒素、硫黄及びハロゲンの少なくとも１種、例えば−ＯＨ，−ＣＯＯＨ，−ＣＯＮＨ，−ＣＯＯＲ，−ＮＨ−，−ＮＨ₂，−Ｓ−，−Ｓ−Ｓ−，−Ｏ−，ハロゲン等を含む化合物であることが好ましい。
本発明においては、有機低分子物質として、少なくとも１種が酸性の官能基を有するものを用いる。
【００６５】
本発明において前記有機低分子物質としては、低融点の有機低分子物質と、高融点の有機低分子物質とを組み合わせて用いることにより、透明化温度巾を更に拡大させることができるものが好ましい。前記低融点有機低分子物質と高融点有機低分子物質の融点の差は２０℃以上が好ましく、更に好ましくは３０℃以上であり、特に好ましくは４０℃以上である。
【００６６】
低融点有機低分子物質材料としては、融点４０℃〜１００℃のものが好ましく、５０℃〜８０℃のものが更に好ましい。高融点有機低分子物質としては、融点１００℃〜２００℃のものが好ましく、１１０℃〜１８０℃のものが更に好ましい。
【００６７】
これらの有機低分子物質のうち、低融点有機低分子物質としては次の脂肪酸エステル、二塩基酸エステル、多価アルコールジ脂肪酸エステルが好ましい。これらは少なくとも１種あるいは２種以上混合して用いられる。
【００６８】
本発明で用いられる脂肪酸エステルは、同じ炭素数の脂肪酸（２分子会合状態）より融点が低く、逆に同じ融点の脂肪酸よりも炭素数が多いという特徴を持つ。
【００６９】
サーマルヘッドでの画像の印字−消去の繰り返しによる劣化は、樹脂母材と有機低分子物質の加熱時の相溶による有機低分子物質粒子の分散状態の変化が原因と考えられ、樹脂母材と有機低分子物質の相溶性は有機低分子物質の炭素数が多いほど低下し、画像の印字−消去の劣化が少ないものと考えられる。更に白濁度も炭素数に比例して増加する傾向にある。
【００７０】
そのため、同じ透明化温度（融点付近にある）の可逆性感熱記録媒体において、樹脂母材中に分散させる有機低分子物質として脂肪酸エステルを用いることにより、脂肪酸を用いた場合に比較し、白濁度が高く、つまりコントラストが高く、しかも繰り返し耐久性が向上するものと思われる。
【００７１】
そして、このような脂肪酸エステルと高融点の有機低分子物質を混合して用いることにより、透明化温度巾を広くすることができ、サーマルヘッドでの消去の性能も高く、そのため、保存により多少消去特性が変動しても、消去可能であり、材料自身の特性から繰り返し耐久性も向上させることができる。
【００７２】
本発明で用いられる脂肪酸エステルは、例えば次の一般式（Ｉ）で表わされるものである。
Ｒ_３−ＣＯＯ−Ｒ_４ ・・・（Ｉ）
（式中、Ｒ_３，Ｒ_４は炭素数１０以上のアルキル基を表わす）
脂肪酸エステルの炭素数は２０以上が好ましく、２５以上が更に好ましく、３０以上が特に好ましい。炭素数が多くなると白濁度が高く、繰り返し耐久性が向上するという特長を有する。脂肪酸エステルの融点は４０℃以上が好ましい。
これらは１種又は２種以上を選択して用いられる。
【００７３】
二塩基酸エステルとしては、モノエステル、ジエステルのいずれでもよく、下記一般式（ＩＩ）で表わされるものがある。
Ｒ_５ＯＯＣ−（ＣＨ_２）ｎ−ＣＯＯＲ_６ ・・・（ＩＩ）
（式中、Ｒ_５、Ｒ_６は水素原子、又は炭素数１〜３０のアルキル基を表わし、Ｒ_５，Ｒ_６は同一であっても異なっていてもよいが、同時に水素原子である場合を除く。ｎは０〜４０の整数を表わす）
上記一般式（ＩＩ）で表わされる二塩基酸エステルにおいて、Ｒ_５，Ｒ_６のアルキル基の炭素数は１〜２２が好ましく、ｎは、１〜３０が好ましく、２〜２０が更に好ましい。また融点は４０℃以上が好ましい。
【００７４】
本発明で用いる有機低分子物質の多価アルコールジ脂肪酸エステルとしては、下記の一般式（ＩＩＩ）で表わされるものが挙げられる。
ＣＨ_３（ＣＨ_２）ｍＣＯ−Ｏ（ＣＨ_２）ｎＯ−ＯＣ（ＣＨ_２）ｍＣＨ_３ ・・・（ＩＩＩ）
（式中、ｎは２〜４０、好ましくは３〜３０、更に好ましくは４〜２２の整数である。ｍは２〜４０、好ましくは３〜３０、更に好ましくは４〜２２の整数である。）
【００７５】
多価アルコールジ脂肪酸エステルは同じ炭素数で比較すると脂肪酸より融点が低く、逆に同じ融点で比較すると脂肪酸より炭素数が多いという特徴を持つ。サーマルヘッドでの印字の繰り返し耐久性は樹脂と有機低分子物質の加熱時での相溶性が原因と考えられ、樹脂と有機低分子物質の相溶性は有機低分子物質の炭素数が多いほど低下すると考えられる。
【００７６】
さらに白濁度も炭素数に比例し、増加する傾向にあり、そのため多価アルコールジ脂肪酸エステルを用いることにより、同じ透明化温度（融点付近にある）の可逆性感熱記録媒体において脂肪酸と比較し、繰り返し耐久性が向上すると思われる。
【００７７】
また、多価アルコールジ脂肪酸エステルは低融点で、それより高融点の脂肪酸と白濁度、繰り返し耐久性の面で同程度の特徴を持つため、これらより高融点の有機低分子物質と混合し、透明化温度範囲を広げた際に、脂肪酸を用いた場合と同程度の白濁度、繰り返し耐久性等の性能を持ちながら透明化温度範囲を広げることができ、ひいてはサーマルヘッド等による、短時間での加熱による画像消去（透明化）を向上させることができ、更に、画像消去のマージンが増えることにより経時により画像消去エネルギーが変動しても、実用上問題なく、サーマルヘッドでの消去も可能となる。
【００７８】
また次に、本発明で用いられる高融点有機低分子物質としては、脂肪族飽和ジカルボン酸、高級アルキル基を有するケトン、該ケトンから誘導されるセミカルバゾン、α−ホスホノ脂肪酸などが挙げられ、次のものが好ましいが、これらに限定されるものではない。
これらは、１種又は２種以上選択して用いられる。
【００７９】
これら融点１００℃以上の有機低分子物質の具体例を以下に示す。
脂肪族ジカルボン酸の、例えば融点１００〜１３５℃程度の具体例としては、例えば、コハク酸、グルタル酸、アジピン酸、ピメリン酸、スベリン酸、アゼライン酸、セバシン酸、ウンデカン二酸、ドデカン二酸、テトラデカン二酸、ペンタデカン二酸、ヘキサデカン二酸、ヘプタデカン二酸、オクタデカン二酸、ノナデカン二酸、エイコサン二酸、ヘンエイコサン二酸、ドコサン二酸等が挙げられる。
【００８０】
本発明において用いるケトンは、ケトン基と高級アルキル基を必須の構成基として含み、その他無置換又は置換基を有する芳香環あるいは被素環を含むこともできる。前記ケトンの全炭素数は１６個以上が好ましく、更に好ましくは２１個以上である。また、本発明に用いるセミカルバゾンは、上記ケトンから誘導されたものである。
【００８１】
本発明で用いるαーホスホノ脂肪酸は例えばＥ．Ｖ．Ｋａｕｒｅｒ等、Ｊ．Ａｋ．Ｏｉｌ Ｃｈｅｋｉｓｔ’ｓ Ｓｏｃ，４１，２０５（１９６４）の方法に従って脂肪酸をＨｅｌｌ−Ｖｏｌｈａｒｄ−Ｚｅｌｉｎｓｋｉｎ反応によって臭素化してα−臭素化酸臭化物とし、次いでエタノールを加えα−ブロモ脂肪酸エステルを得、さらにトリエチルホスファイトと加熱反応してα−ホスホノ脂肪酸エステルとし、濃塩酸による加水分解を行なって生成物をトルエンから再結晶することにより得ることができる。
【００８２】
これらの低融点有機低分子物質と高融点有機低分子物質の混合重量比は９５：５〜５：９５が好ましく、９０：１０〜１０：９０が更に好ましく、８０：２０〜２０：８０が特に好ましい。また、これらの低融点有機低分子物質、高融点有機低分子物質以外に前記した他の有機低分子物質を混合して用いてもよい。これらは次のものが挙げられる。
【００８３】
これら化合物としてはラウリン酸、ドデカン酸、ミリスチン酸、ペンタデカン酸、パルミチン酸、ステアリン酸、ベヘン酸、ノナデカン酸、アラギン酸、オレイン酸等の高級脂肪酸等のエーテル又はチオエーテル等がある。中でも本発明では高級脂肪酸、特にパルミチン酸、ペンタデカン酸、ノナデカン酸、アラキン酸、ステアリン酸、ベヘン酸、リグノセリン酸等の炭素数１６以上の高級脂肪酸が好ましく、炭素数１６〜２４の高級脂肪酸が更に好ましい。
【００８４】
前記したように本発明において、透明化できる温度の巾を広げるには、この明細書において記載した有機低分子物質を適宜組み合わせるか、又は、そうした有機低分子物質と融点の異なる他の材料とを組み合わせればよい。これらは例えば特開昭６３−３９３７８号公報、特開昭６３−１３０３８０号公報などや、特願昭６３−１４７５４号、特願平３−２０８９号（特開平４−２３５０９５号公報）などの明細書に開示されているが、これらに限定されるものではない。
【００８５】
なお、感熱層中の有機低分子物質と樹脂（架橋構造を有する樹脂）との割合は、重量比で２：１〜１：１６程度が好ましく、１：２〜１：８が更に好ましい。樹脂の比率がこれ以下になると、有機低分子物質を樹脂中に保持した膜に形成することが困難となり、またこれ以上になると、有機低分子物質の量が少ないため、不透明化が困難になる。
【００８６】
感熱層には以上の成分の他に、透明画像の形成を容易にするために、界面活性剤、可塑剤等の添加物を添加することができる。これらの添加物の具体例は次のとおりである。
【００８７】
可塑剤としては、リン酸エステル、脂肪酸エステル、フタル酸エステル、二塩基酸エステル、グリコール、ポリエステル系可塑剤、エポキシ系可塑剤が挙げられ、具体例としては下記のものが挙げられる。
リン酸トリブチル、リン酸トリ−２−エチルヘキシル、リン酸トリフェニル、リン酸トリクレジル、オレイン酸ブチル、フタル酸ジメチル、フタル酸ジエチル、フタル酸ジブチル、フタル酸ジヘプチル、フタル酸ジ−ｎ−オクチル、フタル酸ジ−２−エチルヘキシル、フタル酸ジイソノニル、フタル酸ジオクチルデシル、フタル酸ジイソデシル、フタル酸ブチルベンジル、アジピン酸ジブチル、アジピン酸ジ−ｎ−ヘキシル、アジピン酸ジ−２−エチルヘキシル、アゼライン酸ジ−２−エチルヘキシル、セバシン酸ジブチル、セバシン酸ジ−２−エチルヘキシル、ジエチレングリコールジベンゾエート、トリエチレングリコールジ−２−エチルブチラート、アセチルリシノール酸メチル、アセチルリシノール酸ブチル、ブチルフタリルブチルグリコレート、アセチルクエン酸トリブチルなど。
【００８８】
界面活性剤、その他の添加物の例としてはつぎのものが挙げられる；すなわち、多価アルコール高級脂肪酸エステル；多価アルコール高級アルキルエーテル；多価アルコール高級脂肪酸エステル、高級アルコール、高級アルキルフェノール、高級脂肪酸高級アルキルアミン、高級脂肪酸アミド、油脂又はポリプロピレングリコールの低級オレフィンオキサイド付加物；アセチレングリコール；高級アルキルベンゼンスルホン酸のＮａ、Ｃａ、Ｂａ又はＭｇ塩；芳香族カルボン酸、高級脂肪酸スルホン酸、芳香族スルホン酸、硫酸モノエステル又はリン酸モノ−又はジ−エステルのＣａ、Ｂａ又はＭｇ塩；低度硫酸化油；ポリ長鎖アルキルアクリレート；アクリル系オリゴマー；ポリ長鎖アルキルメタクリレート；長鎖アルキルメタクリレート−アミン含有モノマー共重合体；スチレン−無水マレイン酸共重合体；オレフィン−無水マレイン酸共重合体など。
【００８９】
本発明における感熱層中の樹脂を架橋させる手段としては、加熱することにより又は紫外線照射、電子線照射により行なうことができるが、これらの中で電子線照射するのが最適である。これら架橋させる方法は具体的には以下のとおりである。（ｉ）樹脂に架橋性のあるものを用いる方法、（ｉｉ）架橋剤の添加による方法、（ｉｉｉ）紫外線、又は電子線の照射によって架橋させる方法、（ｉｖ）架橋剤の存在下で紫外線、又は電子線の照射によって架橋させる方法、等がある。
【００９０】
架橋剤としてはウレタンアクリレート系、エポキシアクリレート系、ポリエステルアクリレート系、ポリエーテルアクリレート系、ビニル系、不飽和ポリエステル等のオリゴマーや、各種単官能、多官能のアクリレート、メタクリレート、ビニルエステル、スチレン誘導体、アリル化合物等のモノマーが挙げられる。また、非官能性モノマー、官能性モノマーとしては、具体的には前記したバリアー層で用いるモノマーと同様なものが挙げられる。
【００９１】
これらの架橋剤は単独で又は２種以上が混合して使用される。これらの架橋剤の添加量としては、樹脂１重量部に対して０．００１〜１．０重量部が好ましく、更に好ましくは０．０１〜０．５重量部である。添加量が０．００１重量部以下であると架橋効率が悪くなり、逆に１．０重量部以上になると白濁度が低下し、コントラストが低くなる。
【００９２】
前記したように、架橋剤の添加量を少量にして架橋効率を向上させるためには、前記した架橋剤の中では、非官能性モノマーより官能性モノマーが好ましく、更に単官能モノマーよりも多官能モノマーが好ましい。
【００９３】
また次に本発明における感熱層の樹脂を架橋させる手段としては、紫外線照射を用いる場合には次のような架橋剤、光重合開始剤、光重合促進剤を用いてもよい。具体的には次のものなどが挙げられる。
【００９４】
架橋剤としては光重合性プレポリマーと光重合性モノマーに大別することができ、光重合性モノマーとしては前記した電子線照射で用いる架橋剤として挙げた単官能性モノマー及び多官能性モノマーと同じものを挙げることができる。
【００９５】
また次に光重合性プレポリマーとしてはポリエステルアクリレート、ポリウレタンアクリレート、エポキシアクリレート、ポリエーテルアクリレート、オリゴアクリレート、アルキドアクリレート、ポリオールアクリレートなどが挙げられる。
【００９６】
これらの架橋剤は単独で又は２種以上が混合して使用される。これらの架橋剤の添加量としては、樹脂１重量部に対して０．００１〜１．０重量部が好ましく、更に好ましくは０．０１〜０．５重量部である。添加量が０．００１重量部以下であると架橋効率が悪くなり、逆に１．０重量部以上になると白濁度が低下し、コントラストが低くなる。
【００９７】
次に光重合開始剤としてはラジカル反応型とイオン反応型に大別でき、更にラジカル反応型は光開裂型と水素引抜き型とに分けられる。具体的にはつぎのものが挙げられ、これらは前記したバリアー層においても同様に用いることができる。
（ｉ）ベンゾインエーテル類例えばイソブチルベンゾインエーテル、イソプロピルベンゾインエーテル、ベンゾインエチルエーテル、ベンゾインメチルエーテル、
（ｉｉ）α−アシロキシムエステル類例えば１−フェニル−１，２−プロパンジオン−２−（ｏ−エトキシカルボニル）オキシム、
（ｉｉｉ）ベンジルケタール類例えば２，２−ジメトキシ−２−フェニルアセトフェノン、ベンジル、ヒドロキシシクロヘキシルフェニルケトン、
（ｉｖ）アセトフェノン誘導体類例えばジエトキシアセトフェノン、２−ヒドロキシ−２−メチル−１−フェニルプロパン−１−オン、
（ｖ）ケトン−（ケトン−アミン系）類例えばベンゾフェノン、クロロチオキサントン、２−クロロチオキサントン、イソプロピルチオキサントン、２−メチルチオキサントン、塩素置換ベンゾフェノン、
これらの光重合開始剤は、単独で又は２種以上混合して使用される。
添加量としては架橋剤１重量部に対して０．００５〜１．０重量部が好ましく、更に好ましくは０．０１〜０．５重量部である。
【００９８】
次に光重合促進剤としては、ベンゾフェノン系やチオキサントン系などの水素引抜きタイプの光重合開始剤に対し、硬化速度を向上させる効果があり、芳香族系の第３級アミンや脂肪族アミン系がある。具体的には次のものが挙げられる。
Ｐ−ジメチルアミノ安息香酸イソアミルエステル
Ｐ−ジメチルアミノ安息香酸エチルエステル
これら光重合促進剤は単独で又は２種以上混合して使用される。
【００９９】
添加量としては光重合開始剤１重量部に対して０．１〜５重量部が好ましく、更に好ましくは０．３〜３重量部である。
【０１００】
また、本発明に用いる紫外線照射装置は、光源、灯具、電源、冷却装置、搬送装置から構成されている。光源には水銀ランプ、メタルハライドランプ、カリウムランプ、水銀キセノンランプ、フラッシュランプがあるが、前記した光重合開始剤及び光重合促進剤の紫外線吸収波長に対応した発光スペクトルを有する光源を使用すればよい。また紫外線照射条件については、樹脂を架橋するために必要な照射エネルギーに応じてランプ出力、搬送速度を決めればよい。
【０１０１】
本発明において、可逆性感熱記録媒体の感熱層の樹脂を架橋するのに特に効果的な電子線（ＥＢ）照射法は以下のとおりである。
【０１０２】
まず、ＥＢ照射装置としては、走査形（スキャンビーム）あるいは非走査形（エリアビーム）の２種に大別できるが、照射面積、照射線量等の目的に応じて決めればよい。次に、ＥＢ照射条件については、樹脂を架橋するために必要な線量に応じて、電子流、照射幅、搬送スピードを考慮し次式から決められる。
【０１０３】
Ｄ＝（△Ｅ／△Ｒ）・η・Ｉ／（Ｗ・Ｖ）
Ｄ：必要線量（Ｍｒａｄ）
△Ｅ／△Ｒ：平均エネルギー損失
η：効率
Ｉ：電子流（ｍＡ）
Ｗ：照射幅（ｃｍ）
Ｖ：搬送速度（ｃｍ／ｓ）
工業的には、これを簡略化し、
Ｄ・Ｖ＝Ｋ・Ｉ／Ｗ
とし、装置定格をＭｒａｄ・ｍ／ｍｉｎで示す。
電子流定格は、実験器では２０〜３０ｍＡ、パイロット機では５０〜１００ｍＡ、生産機では１００〜５００ｍＡ程度が選ばれる。
【０１０４】
ここで、樹脂を架橋するために必要な線量については、樹脂の種類および重合度、架橋剤の種類および添加量、可塑剤の種類および添加量等により架橋効率が変わり、線量に対してのゲル分率が一定でないため、これらの可逆性感熱記録媒体の感熱層の構成因子水準を決めて記録層を作成し、ゲル分率目標値を決め、それに応じての線量を決めればよい。
【０１０５】
また、照射線量は、樹脂を架橋させるために高エネルギーを必要とする場合には、支持体または樹脂等が照射により発生する熱によって変形、熱分解をするのを防ぐため、照射を複数回に分けて、１回当たりの照射で高熱になるのを防ぐことが好ましい。
【０１０６】
そして、ＥＢ照射を行なう前に、記録層に含有される有機低分子物質の少なくとも一部を溶融する温度以上で加熱した後、架橋することが好ましく、また更に、有機低分子物質が全て溶融する温度以上に加熱した後、架橋することが好ましい。
【０１０７】
感熱層構成因子それぞれがゲル分率との関係は前記したとおりである。
まず、樹脂の種類としては前記した樹脂が選択できるが、これらの重合度は平均重合度（Ｐ）が高くなるにつれてゲル分率が向上する傾向にあり、好ましくはＰ＝３００以上であり、更に好ましくはＰ＝６００以上である。
【０１０８】
架橋剤の種類及び添加量については前記したとおりであり、また可塑剤の種類としては、前記した可塑剤の中で脂肪酸エステル、ポリエステル系可塑剤、エポキシ系可塑剤等が好ましく、特にエポキシ系可塑剤が照射変色、架橋効率からみて最適である。可塑剤の添加量については、その添加量の増加につれてゲル分率が向上する傾向にあり、樹脂１重量部に対して０．０１〜１．０重量部が好ましく、更に好ましくは０．０５〜０．５重量部である。
【０１０９】
上記手段の他に、繰り返し耐久性を向上させるためには、以下の方法がある。第１に、感熱層の軟化温度を高温側へ上げることによって耐久性は向上する。軟化温度がより高い方が更に耐久性は向上する。軟化温度の測定方法としては、ゲル分率測定で用いたものと同様な膜を用いて、熱機械分析装置（ＴＭＡ）や動的粘弾性測定装置を用いて測定することができる。
また、更に前記したように形成された記録層を剥離せずに剛体振り子法・動的粘弾性測定装置により測定することができる。
また、その軟化点については経時による変動が少ない方が前記した経時の消去特性の変動が少なくなる。
【０１１０】
第２の方法としては、後に述べるように、支持体上に形成された感熱層上に前記した保護層を積層し、その積層間の層間強度を強くすることによっても耐久性は向上する。層間強度がより強い方がより耐久性は向上する。層間強度測定方法はＴａｐｐｉ ＵＭ−４０３に準じて行うことができる。
【０１１１】
第３の方法としては、感熱層のＴＭＡ針入測定による針入度が少ない方が耐久性は向上する。針入度がより少ない方が更に耐久性は向上する。針入度測定方法としては、支持体上に形成された記録層を用いて、軟化温度測定に用いたＴＭＡを用い、先端断面積の小さなプローブ（針入プローブ）を記録層上に乗せ荷重を加え、必要により加熱してその変位量により測定することができる。
【０１１２】
第４の方法としては、ＥＢ架橋後に感熱層中に残存する架橋剤量が少ない方が耐久性は向上する。残存量がより少ない方が耐久性は更に向上する。残存量測定方法としては下記方法が挙げられる。
【０１１３】
測定装置としてフーリエ変換赤外分光光度計に取り付けられるＡＴＲ測定付属装置を用い、測定サンプルとしては上記ゲル分率測定に用いた感熱層塗膜を使用し、ＥＢ照射後の試料の８１０ｃｍ^−１付近に現われるアクリロイル基のＣＨ面外変角振動による吸収帯強度を測定する。この吸収帯強度は架橋剤残存量と比例関係にあり、残存量が減れば、強度も減少する。これにより残存量を知ることができる。
残存量値としては感熱層中樹脂１重量部に対して０．２重量部以下がよく、好ましくは０．１重量部以下であり、更に好ましくは０．０５重量部以下であり、特に好ましくは０．０１重量部以下である。
【０１１４】
この測定方法においては、上記測定の他にＵＶ硬化で用いられる光重合開始剤、光増感剤及び熱硬化で用いられる触媒等の残存量も知ることができ、また、それぞれの残存成分の定性分析により、感熱総中の樹脂の架橋が、ＥＢ硬化かＵＶ硬化或いは熱硬化のうち、どの方法を用いたのかを判定することができる。いずれの方法においても残存成分が少ない方が耐久性がよくなる。
また、この測定方法では、塗膜表面の数μｍオーダの薄い総のみの知見が得られるため、支持体上に形成した感熱層をそのまま測定することも可能である。
また、これらの他に、感熱層中の樹脂と有機低分子物質粒子との界面及び／又は粒子中に樹脂及び粒子の屈折率と異なる空隙があると、白濁状態での画像濃度が向上し、コントラストが向上する効果がある。空隙の大きさが不透明状態を検知するために用いる光の波長の１／１０以上であるとより効果が顕著である。
【０１１５】
本発明の可逆性感熱記録媒体に形成される画像を反射画像として用いる場合には、記録層の背面に光を反射する層を設けるのが望ましい。また、反射層があると記録層の厚みを薄くとてもコントラストを上げることができる。具体的には特開昭６４−１４０７９号公報に記載されるようにＡｌ、Ｎｉ、Ｓｎ等を蒸着することが挙げられる。
【０１１６】
感熱層の厚さは１〜３０μｍが好ましく、２〜２０μｍがさらに好ましい。記録層が厚すぎると層内での熱の分布が発生し均一に透明化することが困難となる。また、感熱層が薄すぎると白濁度が低下しコントラストが低くなる。なお、記録層中の脂肪酸の量を増加させると白濁度を増すことができる。
【０１１７】
本発明の可逆性感熱記録媒体を作るには、まず例えば次の方法により支持体上に感熱層を形成する。場合によっては、支持体上を用いることなくシート状の可逆性感熱記録媒体として成形することもできる。
１）樹脂母材及び有機低分子物質を溶媒中に溶解し、これを支持体上に塗布し、溶媒を蒸発させ皮膜あるいはシート状にする方法。
２）樹脂母材のみを溶解させる溶媒に樹脂母材を溶解させ、その中に有機低分子物質を種々の方法で粉砕又は分散し、これを支持体上に塗布し、溶媒を蒸発させ皮膜あるいはシート状にする方法。
３）溶媒を用いず、樹脂母材と有機低分子物質を加熱溶融混合し、これを皮膜あるいはシート状に成形して冷却する方法。
【０１１８】
また、感熱層は樹脂を架橋することにより、繰り返し耐久性が大幅に向上するため、上記感熱層形成の途中又は後に架橋することが好ましい。
【０１１９】
感熱層又は感熱記録材料作成用溶剤としては、樹脂母材及び有機低分子物質の種類によって種々選択できるが、例えばテトラヒドロフラン（ＴＨＦ）、メチルエチルケトン、メチルイソブチルケトン、クロロホルム、四塩化炭素、エタノール、トルエン、ベンゼン等が挙げられる。なお、分散液を使用した場合はもちろんであるが、溶液を使用した場合も、得られる感熱層中では有機低分子物質は微粒子として析出し、分散状態で存在する。
【０１２０】
支持体の材料としては従来と同様、各種プラスチック、ガラス、金属等が使用される、支持体の厚さは用途により任意に選択できる。
中間層用の樹脂としてはポリアミド、例えば記録層中の樹脂母材として挙げたものの他に、次のような各種の熱可塑性樹脂、熱硬化性樹脂が使用可能である。具体的にはポリエチレン、ポリプロピレン、ポリスチレン、ポリビニルアルコール、ポリビニルブチラール、ポリウレタン、飽和ポリエステル樹脂、不飽和ポリエステル樹脂、エポキシ樹脂、フェノール樹脂、ポリカーボネート、ポリアミド等が挙げられる。
【０１２１】
本発明では支持体と記録層の間に視認性をよくするために着色層を設けることもできる。着色層は着色材及び樹脂バインダーを主成分とする溶液又は分散液を対象面に塗布、乾燥するか、或いは単に着色シートを貼り合わせることにより形成される。ここで着色剤としては上層の記録層の透明及び白濁の変化を反射画像として認識できればよく、赤、黄、青、紺、紫、黒、茶、灰、橙、緑などの色を有する染料、顔料等が使用される。また、樹脂バインダーとしては各種熱可塑性、熱硬化性又は紫外線硬化性樹脂が使用される。
【０１２２】
また、支持体と記録層との間に、空気を有する非密着部である空気層を設けることができる。空気層を設けると、記録層の主成分として用いられた有機高分子材料の屈折率が１．４〜１．６程度で、空気の屈折率１．０との差が大きいため、感熱記録層側フィルムと非密着部との界面で光が反射し、記録層が白濁状態のとき白濁度が増幅され、視認性が向上するので、この非密着部位を表示部として用いることが望ましい。
【０１２３】
非密着部位は非密着部の内部に空気を有するため、その非密着部が断熱層となり、感熱度が向上する。更に、非密着部位はクッションの役目もなし、サーマルヘッドで圧力をかけて押さえつけても実際に感熱部材に加わる圧力は低くなり、熱を加えても記録層の変形は少なく、有機低分子物質粒子の拡大もなく、繰り返し耐久性が向上する。
【０１２４】
さらに、支持体裏面に接着剤層又は粘着剤層を設けて、可逆性感熱記録ラベルとして用いることも可能である。このラベルシートは被貼着体と貼り合わされる。被貼着体としては、例えば、クレジットカード等の塩ビカード、ＩＣカード、ＩＤカード、紙、フィルム、合成紙、ボーディングパス、定期券等が挙げられるが、これらに限定されるものではない。また、支持体がＡｌ蒸着層のような樹脂との接着力に乏しい材質の場合には、支持体と記録層との間に前記したような接着層等を設けてもよい（特開平３−７３７７号公報参照）。
【０１２５】
また、本発明の可逆性感熱記録媒体を用いた画像表示を行うための感熱記録画像表示装置としては、多種多様なものが挙げられるが、その代表的なものは可逆性感熱記録媒体に画像形成・消去を行うための画像形成手段と画像消去手段が同一の発熱体、例えばサーマルヘッドで、サーマルヘッドに印字加するエネルギーを変化させることにより画像処理を行うことができる感熱記録画像表示装置、又は、画像形成手段がサーマルヘッドであり、画像消去手段がサーマルヘッド、ホットスタンプ、ヒートローラ、ヒートブロック等の発熱体を接着させる接触押圧型手段か、或いは温風、赤外線、レーザー光などを用いた非接触型手段のうち一つから選択される感熱記録画像表示装置がある。なお、本発明は先に説明したロイコ系感熱記録材料等の他の可逆性感熱記録材料でも、ＮＨ_３ガスで劣化を起こすものならば有効である。
【０１２６】
前記のように、本発明の可逆性記録媒体は、記録部分として上記のような可逆的感熱層の他に、磁気記憶層、ＩＣチップ及び／又は書換可能なバーコードを設けたものをその範囲に包含し、さらに、支持体上に光反射層を設けたもの及び／又は記録層上に保護層を設けたものを包含する。また、可逆性感熱層の他に着色層を設けその上に可逆的感熱層を有するものが、可逆的可視像を目視し易くするために好ましい。この場合、着色層を可視光に対する反射率の異なる２種以上の部位からなるものとすることができる。
【０１２７】
特に、本発明の可逆性記録媒体が、書換可能なバーコードを設けたものである場合には反射率の異なる２種以上の部位からなるものとすることが好ましい。というのは、人間が目視する場合には、例えば白濁状態の画像部と着色状態の非画像部とは光量差に加えて色調差があり、かつ、目視する角度によっては非画像部からの過度の反射光によるグレアがなくなるので可逆的可視像を目視し易くするが、一方、これを反射濃度計やバーコード読取り装置のような装置で読み取る場合には、通常、光を斜めから入射させ面に対し垂直方向にセンサーを置き読み取ることになり、これは、とりもなおさず、着色層により可視光の少なくとも一部が吸収されコントラストが低くなった結果を計測するに過ぎないためである。而して、本発明の可逆性感熱記録媒体における着色層は、可視光に対する反射率の異なる２種以上の部位からなり、かつ、その少なくとも一方の部位が可視光を吸収する層であり、他の少なくとも一部が可視光を反射する層からなるものとして、目視でも画像を認識しやすく、かつ、装置による測定でも高コントラストが得られるものすることができる。
【０１２８】
可逆性（可逆的）感熱層においてバーコードを読み取るのに必要な高いコントラストを得るには、有機低分子物質の平均粒子径が０．１〜２．０μｍの範囲にあることが好ましく、より適切な白濁度になる。これは、この可逆性感熱記録カードの記録、消去が有機低分子物質の単結晶状態と多結晶状態という結晶状態の差異により光散乱、光透過を利用するプロセスであるので、光散乱、透過を起こさせるための結晶成長やその効果は自ずと樹脂母材中に分散された有機低分子物質の粒子径に依存するためと推定されている。即ち、有機低分子物質の結晶性の変化（単結晶⇔多結晶）は有機低分子物質と樹脂母材との相互作用が考えられ、粒子の大きさにより樹脂母材との相互作用の大きさに差が生じ、透明状態と白濁状態の変化の度合いに差が発生するものと考えられている。そして、分散された有機低分子物質の平均粒子径が大きくなればなるほど多結晶状態になり難くなり、光を散乱させる効果が小さくなって、白濁度が低下してコントラストが低くなり、逆に、分散された有機低分子物質の平均粒子径が小さくなればなるほど結晶の成長において分散されたマトリックス中で多結晶状態を形成しにくくなり、この場合も白濁度が低下してコントラストが低くなるためと考えられる。さらに、バーコードを読み取る関係から、有機低分子物質の粒子の平均粒子径がバーコードを読み取る際の光源の波長の１／８から２倍までの範囲にあるとき、バーコードの読み取り時のコントラストがさらに向上する。こうした現象が何故生じるかはいまだに明らかにされていないが、大よそ次のように推察されている。即ち、白濁度つまり光の散乱度は有機低分子物質粒子中の結晶の大きさで決まると考えられ、さらにこの結晶の大きさは有機低分子物質粒子の大きさで決まってくると考えられる。これは、有低分子物質粒子の大きさにより、樹脂母材とその樹脂母材中に分散されている有機低分子物質との界面の面積が決まり、この界面の面積から樹脂母材と有機低分子物質との相互作用の強さが決まり、その相互作用の強さが粒子中の結晶の大きさに影響を与えるためと推測されている。また、ある波長の光を一番散乱しやすい結晶の大きさがあり、これは個々の材料によって異なるが、光の波長より小さい結晶がその波長の光を散乱しやすい。つまり、有機低分子物質の平均粒子径がバーコードを読み取る光の波長の１／８から２倍までの範囲にあるとき白濁状態の有機低分子物質粒子中の多結晶の個々の結晶の大きさがその波長の光を最も散乱しやすい大きさになっているものと考えられている。前記の平均粒子径が読み取り光源の波長の１／８未満となると、散乱効果が減少し、白濁度が下がり、コントラストが減少し、逆に、２倍を越えると樹脂母材と有機低分子物質の界面の表面積が減少し、樹脂母材と有機低分子物質との相互作用が減少し、有機低分子物質粒子中の結晶の制御がしにくくなると考えられており、白濁度が下がり、コントラストが減少する。なお、有機低分子物質の粒径を制御する方法としては貧溶媒の混入、記録層形成液塗工時の加熱乾燥の制御、分散性を制御するための界面活性剤の添加等が考えられるがこれらに限定されるものではない。
【０１２９】
ところで、従来バーコードを読み取るための光源の波長は６００ｎｍ以上と規定され（ＪＩＳ Ｂ９５５０）、通常６００ｎｍから１０００ｎｍの範囲の波長の光源が用いられている。具体的にはＬＥＤ（６６０ｎｍ及び９４０ｎｍの波長のものが良く用いられる）、レーザー（Ｈｅ−Ｎｅレーザーで６００ｎｍ、半導体レーザーで６８０ｎｍ、７８０ｎｍ、及び９６０ｎｍが良く用いられる）が挙げられる。
【０１３０】
本発明の可逆性記録媒体におけるバーコード表示体によれば、上記したような６６０ｎｍ以上の波長の光源を用いてバーコードを読み取ることは勿論可能であるが、より短い波長の光源を用いることもでき、むしろ短い波長の光源を用いた方がより高いコントラストが得られる。例えば、４００〜６００ｎｍの光を用いれば、６００ｎｍ〜１００００ｎｍの光に比べ、コントラストは最大で２倍近くになる。これは波長の短い光の方が有機低分子物質に対する屈折率が大きくなり、光の散乱が増え、そのため白濁度が向上するためであると考えられる。
【０１３１】
なお、ここでいう「バーコード」とは、光の強弱や波長の変化等の光学的変化を可視光の波長域であってもなくても情報として認識しうるものであればよく、従って、二次元バーコード、ＯＣＲ、カルラコードに代表される他の光学的認識パターン表示体をも包含する。
【０１３２】
本発明の可逆性感熱記録媒体では、着色層と可逆的感熱層との間に低屈折率層を設けることにより、白濁状態の感熱層を透過した光はその感熱層と低屈折率との界面で反射する割合が増えるため、コントラストを向上させることができるようになる。低屈折率の材料としては、可逆性感熱層に用いられる樹脂より低屈折率のものならなんでもよいが、ＡＳＴＭ、Ｄ５４２測定法で屈折率１．５以下のものが好ましく、更には１．４以下のものが好ましい。例えばポリプロピレン（屈折率１．４９）、ポリ−メチルベンゼン−１（屈折率１．４６５）、メタクリル樹脂（屈折率１．４９）、四フッ化エチレン樹脂（屈折率１．３５）、フッ化ビニリデン樹脂（屈折率１．４２）、ポリアセタール（屈折率１．４８）、セルロースアセテート（屈折率１．３３）、空気（屈折率１．０）等が挙げられる。
【０１３３】
本発明の可逆性記録媒体では、磁気記録層を設けることにより、磁気記録した情報の一部を感熱層上に表示することができる等、この可逆性記録媒体の利便性が向上する。磁気記録層は可逆的感熱層の反対面の支持体が着色層と支持体層との間に設けることができる。磁気記録層が着色層をかねることも可能である。磁気記録層としては通常用いられる酸化鉄、バリウムフェライト等と樹脂が用いられる。
【０１３４】
磁気記録の他に、ＩＣ、光メモリ、光磁気メモリ等の情報記憶部を設け、記憶された情報の一部を必要に応じ可逆性感熱層に表示することも可能である。磁気記録層を有する具体例、ＩＣチップを組み込んだ具体例は、後に詳細に説明される。しかしながら、本発明で使用する可逆性記録媒体には、バーコード情報、磁気記録情報、ＩＣ、光メモリ、光磁気メモリ等による情報記憶は必ずしも設けなくてもよい。
【０１３５】
したがって、例えば図３に示されるように、本発明の可逆性感熱記録媒体は支持体（１１）上に、アルミ反射層（１２）、可逆性感熱記録層（１３）、保護層（１４）を設けてなるフィルムをカード状に加工した形であることができ、また例えば図４に示されるように、これに代えて、透明ＰＥＴフィルムベース上に、可逆性感熱記録層（１３）、保護層（１４）設けてなるフィルムと支持体（１１）とを低屈折率層としての空気層（１６）を介在させた接着層（１７）で張り合わせたものをカード状に加工した形であることができる。
【０１３６】
さらに、例えば図５ａに示されるように、支持体（１１）上に、アルミ反射層（１２）、可逆性感熱記録層（１３）、保護層（１４）を設けてなるフィルムをカード状に加工し、ＩＣチップを納める窪み部（２３）を形成するとともにカード状に加工した形であることができる。この例においては、カード状の可逆性感熱記録媒体に書き換え記録部（２４）がラベル加工されるとともに、可逆性感熱記録媒体の裏面側には所定箇所にＩＣチップ埋め込み用窪み部（２３）が形成されており、この窪み部（２３）に、図５ｂに示されるようなウェハ（２３１）が組込まれて固定される。ウェハ（２３１）は、ウェハ基板（２３２）上に集積回路（２３３）が設けられると共に、この集積回路（２３３）に電気的に接続されている複数の接触端子（２３４）がウェハ基板（２３２）に設けられる。この接触端子（２３４）はウェハ基板（２３２）の裏面側に露出しており、専用のプリンタ（リーダライタ）がこの接触端子（２３４）に電気的に接触して所定の情報を読み出したり書き換えたりできるように構成されている。この可逆的感熱記録カードの機能例を、図６を参照しつつ説明する。
【０１３７】
図６（ａ）は、集積回路（２３３）を示す概略の構成ブロック図であり、（ｂ）はＲＡＭの記憶データの１例を示す構成ブロック図である。集積回路（２３３）は、例えばＬＳＩで構成されており、その中には制御動作を所定の手順で実行することのできるＣＰＵ（２３５）と、ＣＰＵ（２３５）の動作プログラムデータを格納するＲＯＭ（２３６）と、必要なデータの書き込み及び読み出しができるＲＡＭ（２３７）を含む。さらに集積回路（２３３）は、入力信号を受けてＣＰＵ（２３５）に入力データを与えるとともにＣＰＵ（２３５）からの出力信号を受けて外部に出力する入出力インターフェース（２３８）と、図示していないが、パワーオンリセット回路、クロック発生回路、パルス分周回路（割込パルス発生回路）、アドレスデコーダ回路とを含む。ＣＰＵ（２３５）は、パルス分周回路から定期的に与えられる割込パルスに応じて、割込制御ルーチンの動作を実行することが可能となる。また、アドレスデコード回路はＣＰＵ（２３５）からのアドレスデータをデコードし、ＲＯＭ（２３６）、ＲＡＭ（２３７）、入出力インターフェース（２３８）にそれぞれ信号を与える。入出力インターフェース（２３８）には、複数（図中では８個）の接触端子（２３４）が接続されており、前記の専用プリンタ（リーダライタ）からの所定データがこの接触端子（２３４）から入出力インターフェース（２３８）を介してＣＰＵ（２３５）に入力される。ＣＰＵ（２３５）は、入力信号に応答して、かつＲＯＭ（２３６）内に格納されたプログラムデータに従って、各動作を行い、かつ、所定のデータ、信号を入出力インターフェース（２３８）を介してカードリーダライタに出力する。
【０１３８】
図６（ｂ）に示されるように、ＲＡＭ（２３７）は複数の記憶領域（２３９ａ）〜（２３９ｆ）を含む。例えば領域（２３９ａ）にはカード番号が記憶され、（２３９ｂ）には例えばカード所有者の氏名、住所、電話番号等のＩＤデータが記憶され、領域（２３９ｃ）には例えば所有者の使用しうる残存有価価値又は有価物に相当する情報が記憶され、領域（２３９ｄ）（２３９ｅ）（２３９ｆ）及び（２３９ｇ）には使用済の有価価値又は有価物に相当する情報が記憶される。
【０１３９】
【実施例】
以下、本発明を実施例をあげてより具体的に説明する。なお、ここでの部及び％はいずれも重量基準である。
【０１４０】
実施例１
１８８μｍ厚の透明ＰＥＴ（ポリエチレンテレフタレート：帝人社製、ＨＳＬ−１８８）フイルム上に約５００Å厚のＡｌ層を光反射層として真空蒸着により形成した。その上に、塩化ビニル−酢酸ビニル−リン酸エステル共重合体（電気化学工業社製、♯１０００Ｐ）の接着層を設けた支持体上に、
塩化ビニル−酢酸ビニル共重合体 ３．７部
（電気化学工業社製、デンカビニル ＭＴ２）
ベヘン酸（ミヨシ油脂社製、ベヘン酸９５） ０．５部
エイコサン２酸（岡村製油社製、ＳＬ−２０−９９） ０．５部
ＴＨＦ（関東化学社製） ２３．９部
ｎ−ペンチルアルコール（東京化成社製） ２．７部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥をして膜厚１０μｍの感熱層を成膜した。更にこの上に、
ウレタンアクリレート系ＵＶ硬化性樹脂の １３．４部
７５％酢酸ブチル溶液
（大日本インキ社製、ユニディックＣ７−１５７）
カルボキシル基変性メタクリレート（日本化薬社製、ＳＡ） ５．０部
イソプロピルアルコール １０．０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４１】
実施例２
実施例１と同様の支持体に
塩化ビニル−酢酸ビニル共重合体 ３．３部
（電気化学工業社製、デンカビニル ＭＴ２）
ベヘン酸（ミヨシ油脂社製、ベヘン酸９５） ０．５部
エイコサン２酸（岡村製油社製、ＳＬ−２０−９９） ０．５部
Ｃ４−７８２（大日本インキ社製、ユニディックＣ４−７８２） ０．２部
架橋剤 ０．２部
（日本化薬社製、ＫＡＹＡＲＡＤ ＤＰＣＡ−１２０）
ＴＨＦ（関東化学社製） ２３．９部
ｎ−ペンチルアルコール（東京化成社製） ２．７部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約１０．０μｍの感熱層を成膜した。更にその上に実施例１の保護層を成膜し、可逆性感熱記録媒体を作成した。
【０１４２】
実施例３（参考例）
実施例１の感熱層上に
塩化ビニリデン−アクリルニトリル共重合体 ６．０部
（旭化成工業社製、サランレジンＲ２０２）
ＴＨＦ（関東化学社製） ３０．０部
トルエン（丸善石油社製） ６．０部
からなる溶液を塗布し、加熱乾燥をして膜厚６μｍのバリアー層を成膜した。更にその上に、
ウレタンアクリレート系ＵＶ硬化性樹脂の １０．０部
７５％酢酸ブチル溶液 （大日本インキ社製、ユニディックＣ７−１５７）
イソプロピルアルコール １０．０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４３】
実施例４
実施例１の感熱層上に
塩化ビニリデン−アクリルニトリル共重合体 ５．０部
（旭化成工業社製、サランレジンＲ２０２）
カルボキシル基変性エポキシアクリレート（新中村化学社製） １．０部
ＴＨＦ（関東化学社製） ３０．０部
トルエン（丸善石油社製） ６．０部
からなる溶液を塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍのバリアー層を形成した。更にその上に、
ウレタンアクリレート系ＵＶ硬化性樹脂の １３．４部
７５％酢酸ブチル溶液
（大日本インキ社製、ユニディックＣ７−１５７）
カルボキシル基変性エポキシアクリレート（新中村化学社製） ５．０部
イソプロピルアルコール １０．０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４４】
実施例５
実施例１の可逆性感熱記録媒体上に約２．０μｍのＯＰ層を積層した可逆性感熱記録媒体を作成した。
実施例６
実施例２の支持体を透明５０μｍＰＥＴとした可逆性感熱記録媒体を作成した。
【０１４５】
実施例７
実施例１の感熱層上に、
ジペンタエリスリトールヘキサアクリレート ６部
（日本化薬社製、ＤＰＨＡ）
カルボキシル基変性アクリレート（新中村化学社製、ＣＢ−１） ６部
イルガキュア１８４（日本チバガイギー社製） ０．０６部
イソプロピルアルコール ２０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４６】
実施例８
実施例１の感熱層上に、
ジペンタエリスリトールヘキサアクリレート ４部
（日本化薬社製、ＤＰＨＡ）
カルボキシル基変性エポキシアクリレート ４部
（共栄社化学社製、３０００ＳＡ）
カルボキシル基変性エステルアクリレート ４部
（新中村化学社製、ＣＢＸ−１）
イルガキュア１８４（日本チバガイギー社製） ０．０６部
イソプロピルアルコール ２０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４７】
実施例９
実施例１の感熱層上に、
ジペンタエリスリトールヘキサアクリレート ４部
（日本化薬社製、ＤＰＨＡ）
ウレタンアクリレート（新中村化学社製、Ｕ−３２４ＨＡ） １部
カルボキシル基変性エポキシアクリレート ２部
（共栄社化学社製、３０００ＳＡ）
カルボキシル基変性エステルアクリレート ２部
（新中村化学社製、ＣＢＸ−１）
カルボキシル基変性アクリレート（新中村化学社製、ＣＢ−１） １部
イルガキュア１８４（日本チバガイギー社製） ０．０６部
イソプロピルアルコール ２０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４８】
比較例１
１８８μｍ厚の透明ＰＥＴ（帝人社製、ＨＳＬ−１８８）フイルム上に約５００Å厚のＡｌ層を光反射層として真空蒸着により形成した。その上に、塩化ビニル−酢酸ビニル−リン酸エステル共重合体（電気化学工業社製、♯１０００Ｐ）の接着層を設けた支持体上に、
塩化ビニル−酢酸ビニル共重合体 ３．７部
（電気化学工業社製、デンカビニル ＭＴ２）
ベヘン酸（ミヨシ油脂社製、ベヘン酸９５） ０．５部
エイコサン２酸（岡村製油社製、ＳＬ−２０−９９） ０．５部
ＴＨＦ（関東化学社製） ２３．９部
ｎ−ペンチルアルコール（東京化成社製） ２．７部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥をして膜厚１０μｍの感熱層を成膜した。更にこの上に、
ウレタンアクリレート系ＵＶ硬化性樹脂の １０．０部
７５％酢酸ブチル溶液
（大日本インキ社製、ユニディックＣ７−１５７）
イソプロピルアルコール １０．０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１４９】
比較例２
比較例１の感熱層上に、
エチレン−酢酸ビニル共重合体 １５．０部
ＴＨＦ（関東化学社製） ３０．０部
トルエン（丸善石油社製） ６．０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥をして膜厚２．０μｍのバリアー層を形成した。更にその上に比較例１と同様の保護層を作成し、可逆性感熱記録媒体を作成した。
【０１５０】
比較例３
比較例１の保護層膜厚を７μｍとした可逆性感熱記録媒体を作成した。
比較例４
実施例１の感熱層上に、
カルボキシル基変性エポキシアクリレート ６部
（共栄社化学社製、３０００ＳＡ）
カルボキシル基変性エステルアクリレート ６部
（新中村化学社製、ＣＢＸ−１）
イルガキュア１８４（日本チバガイギー社製） ０．０６部
イソプロピルアルコール ２０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１５１】
比較例５
実施例１の感熱層上に、
ジペンタエリスリトールヘキサアクリレート ４部
（日本化薬社製、ＤＰＨＡ）
カルボキシル基変性アクリレート（新中村化学社製、ＣＢ−１） ８部
イルガキュア１８４（日本チバガイギー社製） ０．０６部
イソプロピルアルコール ２０部
からなる溶液をワイヤーバーにて塗布し、加熱乾燥後１２０Ｗ／ｃｍの紫外線ランプで硬化させ、約３．０μｍの保護層が形成された可逆性感熱記録媒体を作成した。
【０１５２】
以上のように作成した可逆性感熱記録媒体についてＮＨ_３暴露法後の印字濃度変化率を測定した結果を表１に示した。なお、実施例６のサンプルの印字濃度は前記透明なフィルムの支持体の場合の印字濃度測定方法にて測定した。
【０１５３】
【表１】

注）実施例３は参考例である。
【０１５４】
【発明の効果】
以上、詳細且つ具体的な説明から明らかなように、本発明の可逆性感熱記録媒体は、長期保管しても印字濃度の劣化がなく、視認性の優れたものである。
【図面の簡単な説明】
【図１】本発明に係る感熱層の熱による透明度の変化を表わした図である。
【図２】本発明に係る記録層の熱による色濃度の変化を表わした図である。
【図３】本発明に係る可逆性感熱記録媒体の１構成例を説明する図である。
【図４】本発明に係る可逆性感熱記録媒体の他の１構成例を説明する図である。
【図５】本発明に係る可逆性感熱記録媒体の更に他の１構成例を説明する図である。
【図６】本発明に係る可逆性感熱記録媒体の更に他の１構成例を説明する図である。
【符号の説明】
１１ 支持体
１２ アルミニウム反射層
１３ 可逆性感熱記録層
１４ 保護層
１５ 透明ＰＥＴフイルム
１６ 空気層
１７ 接着層
２０ 磁気塗工層
２１ カード
２２ 書き換え記録部
２３ ＩＣチップ用窪み部
２４ 書き換え記録部のラベル加工
２３１ ウエハ
２３２ ウエハ基板
２３３ 集積回路
２３４ 接触端子
２３５ ＣＰＵ
２３６ ＲＯＭ
２３７ ＲＡＭ
２３８ 入出力用インターフェース
２３９ ＲＡＭ記憶領域の情報[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a reversible thermosensitive recordingMediumMore specifically, reversible thermosensitive recording in which writing and erasing of information can be repeatedly performed using reversible transparency or color tone change depending on the temperature of the thermosensitive layer.MediumAbout.
The present invention also relates to an image forming / erasing method using the reversible thermosensitive recording medium.
[0002]
[Prior art]
In recent years, reversible thermosensitive recording materials that can temporarily form an image (write information) and can erase the image (erasure of information) when it is no longer needed have attracted attention. A typical example is a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature (Tg) of 50 to 60 ° C. to less than 80 ° C., such as a higher fatty acid. A reversible thermosensitive recording material in which an organic low-molecular substance is dispersed is known (JP-A-54-119377, JP-A-55-154198, etc.). There is a drawback that the width is as narrow as 2 to 4 ° C., and it is difficult to control the temperature when forming an image by utilizing light transmission / transparency and light shielding / white turbidity.
[0003]
In consideration of this point, we have disclosed in Japanese Patent Application Laid-Open Nos. 63-39378, 2-1363, 3-2089, 5-294066, etc. We have proposed reversible thermosensitive recording materials that have expanded the temperature range in which they become transparent by changing the types of low-molecular substances or using several types in combination. The erasing (clearing) of the cloudy image was sufficiently possible by heating for a relatively long time, but the erasing (clearing) of the image by short-time heating with a thermal head or the like was insufficient.
[0004]
For this reason, by using a material in which the rate of change of the temperature at which the reversible thermosensitive recording material starts to be transparent or the rate of change of the transparency or the thickness of the heat-sensitive layer is specified in EPO Patent Publication No. A reversible thermosensitive recording material with improved erasing characteristics is proposed. The use of this reversible thermosensitive recording material considerably alleviates the aforementioned disadvantages.
[0005]
By the way, this kind of reversible thermosensitive recording material is used or left under various environments because of its high durability and repetitive use, especially when this recording material is used for rewritable cards such as point cards. In such a case, the method of storing the card differs considerably depending on the user. Therefore, it is necessary for this type of recording medium to maintain the initial quality even in various storage environments.
However, recently, in this type of reversible thermosensitive recording material, after being left for a long period of time (several months) in an image forming state (white turbid state) or an image erasing state (transparent state), an image is formed by a thermal head or the like. It has been found that when this is performed, there is a problem that the image density is remarkably deteriorated as compared with the image density before standing (cloudy reflection density), the contrast is lowered, and the visibility is deteriorated.
This problem is a new problem, and no solution has been proposed so far.
[0006]
An object of the present invention is to solve the above-described problems, and the image density after image formation by a thermal head or the like does not deteriorate even when the image formation state or the image erasure state is left for a long time. Another object of the present invention is to provide a reversible thermosensitive recording medium which does not lower contrast and has excellent visibility.
Another object of the present invention is to provide an image forming / erasing method using the reversible thermosensitive recording medium.
[0007]
Such an object of the present invention is as follows. (1) “The main component is a resin base material and an organic low-molecular substance dispersed in the resin base material on a support, and the transparency reversibly changes depending on temperature. Heat-sensitive layer andAt least on the thermosensitive layerIn a reversible thermosensitive recording medium provided with a protective layer,The heat-sensitive layer contains at least one kind of organic low-molecular substance having an acidic functional group, and at least one layer on the heat-sensitive layer has an acidic functional group having an acid value of 60 to 120 mgKOH / g. Contains at least one molecular materialReversible thermosensitive recording medium, "(2)When the acid value of the polymer material is 80-100 mgKOH / g(3) The reversible thermosensitive recording medium according to the above (1),The polymeric material is derived from an acrylate monomer, methacrylate monomer or oligomer(4) The reversible thermosensitive recording medium according to the above (1) or (2),The layer containing the polymer material is the protective layer(5) The reversible thermosensitive recording medium according to any one of the above (1) to (3),NH of reversible thermosensitive recording medium ₃ The print density change rate of the exposure test is 100% or less.(6) The reversible thermosensitive recording medium according to any one of the above (1) to (4),The resin contained in the thermosensitive layer has been cross-linked by irradiation.(7) The reversible thermosensitive recording medium according to any one of the above (1) to (5),At least one of a printing layer and a transparent layer was provided on the protective layer.(8) The reversible thermosensitive recording medium according to any one of the above (1) to (6),Intermediate layer provided between heat-sensitive layer and protective layer(9) The reversible thermosensitive recording medium according to any one of the above (1) to (7),The glass transition temperature of the protective layer is 140 ° CThe reversible thermosensitive recording medium according to any one of the above (1) to (8), "(10)" on the thermosensitive layerTotal thickness of layer is 5μm or moreThe reversible thermosensitive recording medium according to any one of the above items (1) to (9), wherein ”, (11)At least one polymer main chain on the heat-sensitive layer is a crystalline polymer.The reversible thermosensitive recording medium according to any one of the above (1) to (10), ”(12)Information storage(1) to (1), whereinItem 11)The reversible thermosensitive recording medium according to any one of (1) to (3),A magnetic storage unit, in which the magnetic recording layer is formed on the entire surface or a part between the support and the heat-sensitive layer, the entire surface or a part of the back surface of the support, or the magnetic stripe is formed on a part of the display surface.The above (Item 12)Reversible thermosensitive recording medium ", (14)"The information storage unit is based on IC or optical memory or barcode information, and is provided in a part of the medium.The above (Item 12) or (13)Reversible thermosensitive recording medium ", (15)"A reversible thermosensitive recording medium according to any one of the above (1) to (14), wherein a support made by laminating two or more types of sheets is used.Solved by
[0008]
Further, (16) an image forming / erasing method, wherein an image is formed and / or erased by heating the reversible thermosensitive recording medium according to any one of the above (1) to (15). (17) "The image forming / erasing method according to the above (16), wherein the heating is performed using at least one of a thermal head and a laser", (18) (16) The image forming / erasing method according to the above (16), wherein the method is performed using at least one of a head, a ceramic heater, a hot stamp, a heat block, and a laser.
[0009]
The thermosensitive layer of the reversible thermosensitive recording material is a material that causes a visible change reversibly due to a temperature change. The visible change can be divided into a change in color state and a change in shape, and the present invention mainly uses a material that causes a change in color state. Changes in color state include changes in optical transmittance, reflectance, absorption wavelength, scattering degree, and the like. In an actual reversible thermosensitive recording material, information is displayed by a combination of these changes. More specifically, any type may be used as long as the degree of transparency and color tone is reversibly changed by heat. For example, the first color state is obtained at a first specific temperature higher than room temperature, and the first specific state is obtained. One that is heated at a second specific temperature higher than the temperature and then cooled to be in a second color state, and the like.
[0010]
In particular, those whose color states change at the first specific temperature and the second specific temperature are preferably used. Examples of these are a transparent state at a first specific temperature and a cloudy state at a second specific temperature (Japanese Patent Application Laid-Open No. 55-154198). Those that decolor at a specific temperature (JP-A-4-224996, JP-A-4-247895, JP-A-4-267190, etc.) become cloudy at a first specific temperature and become opaque at a second specific temperature. A transparent state (JP-A-3-169590), a color developing black, red, blue or the like at a first specific temperature and a decoloring at a second specific temperature (JP-A-2-188293, JP-A-2-188294).
Among these, the following two materials are particularly typical examples.
(1) A material that changes reversibly between a transparent state and a cloudy state
(2) Materials that change color reversibly, such as dyes
[0011]
A typical example of (1) is a thermosensitive layer in which an organic low molecular weight substance such as a higher alcohol or a higher fatty acid is dispersed in a resin base material such as a polyester as repeatedly shown in the prior art. . As a typical example of (2), a leuco-based thermosensitive recording material having enhanced reversibility is given. Among them, in the present invention, (1) a heat-sensitive layer of a material in which a transparent state and a cloudy state are reversibly changed is most preferable.
[0012]
The heat-sensitive layer of the present invention, which is the heat-sensitive layer of the type (1) that causes a change in the transparency, is mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material. As described later, the reversible thermosensitive recording material has a transparent temperature range.
The reversible thermosensitive recording material of the present invention utilizes the change in transparency (transparent state, cloudy opaque state) of (1) as described above, and its mechanism is presumed as follows.
[0013]
That is, in the case of (I) transparent, the particles of the organic low-molecular substance dispersed in the resin base material are in close contact with the organic low-molecular substance and the resin base material without any gap, and there are no voids in the particle portion. Light incident from one side is transmitted to the other side without being scattered, so that it appears transparent. (II) In the case of cloudiness, the particles of the organic low-molecular substance are composed of fine crystals of the organic low-molecular substance. There is a gap at the interface of the crystal or the interface between the particle and the resin base material, and the light incident from one side is refracted and scattered at the interface between the gap and the crystal, and between the gap and the resin. .
[0014]
FIG. 1 is a graph for easily explaining a temperature-transparency change in one example of the reversible thermosensitive recording medium of the present invention, and FIG. 2 is a temperature-transparency change in another example of the reversible thermosensitive recording medium of the present invention. It is to explain. In FIG. 1, a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material is made of, for example, T₀It is cloudy and opaque at the following room temperature.
[0015]
As this is heated, the temperature T₁From the beginning, the temperature T₂~ T₃, It becomes transparent when heated to T₀Even if it returns to the following normal temperature, it will remain transparent. This is the temperature T₁The resin begins to soften from the vicinity, and as the softening progresses, the resin shrinks and reduces the interface between the resin and the organic low-molecular substance particles or the voids in the particles.₂~ T₃In this case, the organic low-molecular-weight substance is in a semi-molten state, becomes transparent by filling the remaining voids with the molten organic low-molecular-weight substance, and crystallizes at a relatively high temperature when cooled while the seed crystal remains. It is considered that, because of the softened state, the resin follows the volume change of the particles due to crystallization, and no void is formed, so that the transparent state is maintained.
[0016]
Further T₄Heating to the above temperature results in a translucent state intermediate between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the state returns to the original cloudy and opaque state without taking the transparent state again. This is the temperature T₄After the organic low-molecular-weight substance is completely melted, the supercooled state is reached and T₀This is probably because the crystallization occurs at a slightly higher temperature, and at that time, the resin cannot follow the change in volume accompanying the crystallization, and voids are generated.
However, the temperature-transparency change curve shown in FIG. 1 is only a typical example, and the turbidity or color density of each state may change depending on the material by changing the material. For example, a reversible thermosensitive recording medium having a recording layer having a temperature-color density curve shown in FIG. 2 as another example can be used.
[0017]
As described above, the melting point of the organic low-molecular substance and the softening point of the resin are important for the change in transparency due to the heat of the heat-sensitive layer, and the reflection density in image creation or image erasure after leaving for a long period of time is deteriorated. No, it does not lower the contrast, visibility, that is, in order to improve the stability over time, it is necessary to prevent fluctuations in the melting point of the organic low molecular weight substance and the softening point of the resin over time. It is believed that there is.
[0018]
We left the reversible thermosensitive recording material in the image forming state (white turbid state) or the image erasing state (transparent state) for a long time (several months), The reason why the image density was significantly deteriorated compared to the previous image density (cloudy reflection density), the contrast was lowered, and the visibility deteriorated was examined.
[0019]
As a result, first, it was found that the decrease in image density was observed both when the image formation was performed by applying heat on the order of several msec such as a thermal head or when the heat was applied on the order of several seconds such as a hot stamp. Furthermore, when the relationship between the printing energy (printing temperature) and the reflection density was confirmed with both the thermal head and the hot stamp, the printing energy value (hereinafter referred to as "white turbidity saturation energy") for obtaining the white turbid saturated state before being left for a long time (hereinafter referred to as "initial"). Alternatively, after standing for a long time (hereinafter referred to as aging) as compared with the printing temperature (hereinafter referred to as the turbid saturation temperature), the turbid saturation energy or the turbid saturation temperature is largely shifted to a higher energy and higher temperature side, that is, the It was confirmed that the heat sensitivity was greatly reduced, and sometimes it was impossible to make the film completely opaque.
[0020]
We studied to elucidate the mechanism of the phenomenon. As a result, it was found that the above phenomenon often occurs when the recording medium is stored for a long time in a place where the concentration of a basic substance (particularly ammonia) in the atmosphere is high. After examining the thermophysical properties of the film and the chemical structure of the material constituting the recording layer, the thermophysical properties were first measured by DSC, and after storage, the melting point of the organic low-molecular substance (particularly, the binary system of the organic low-molecular substance (low melting point and high melting point) In the case of (combination), the high melting point organic low molecular weight substance) is greatly shifted to the high temperature side, and then the IR measurement of the chemical structure revealed that the carboxyl group peak in the structure of the organic low molecular weight substance disappeared after storage. As a result, it was found that a new O, N ion binding absorption band peak was observed.
[0021]
That is, the shift of the melting point of the organic low-molecular-weight substance to the high-temperature side described above is such that the carboxyl group in the structure of the organic low-molecular-weight substance reacts with and binds to ammonia of the basic substance to form an ammonium carboxylate, and thus the melting point increases. Conceivable.
From these facts, the mechanism that the above-mentioned cloudiness saturation energy and temperature shift to high energy and high temperature side, that is, the mechanism of lowering the thermal sensitivity for image formation, causes the melting point of the organic low-molecular substance to fluctuate to high temperature over time. More specifically, due to the increase in the melting point, the temperature for completely melting the organic low-molecular substance at the time of transition from the transparent state to the white turbid state becomes high, that is, it is possible to completely melt at the initial stage. At such a temperature, it is considered that the image forming density cannot be completely melted after the lapse of time, so that the image forming density over time deteriorates from the initial image forming density.
[0022]
As a result of repeated studies to improve the above-described problem, the present inventors have found that, as described above, `` a resin base material on a support and an organic low-molecular substance dispersed in the resin base material as a main component, In a reversible thermosensitive recording medium provided with a thermosensitive layer whose transparency changes reversibly depending on the temperature and a protective layer, the NH of the reversible thermosensitive recording material₃It has been found that the object of the present invention is surely achieved by the "reversible thermosensitive recording medium characterized in that the change rate of the print density in the exposure test is 100% or less". Preferred embodiments in this case are as follows.
[0023]
The print density change rate of the reversible thermosensitive recording medium in the present invention refers to the change rate of the saturated print density before and after storage in an initial state and a special environment, and the smaller the value, the better the printability after storage. Is shown. The print density change rate after the ammonia exposure method for achieving such an object is preferably 100% or less, preferably 60% or less, and more preferably 30% or less.
[0024]
The print density change rate of the present invention is obtained by the following method. When a reversible thermosensitive recording medium is printed stepwise from the low energy side with an energy width of 0.01 mJ / dot using a thermal head, the printing energy that is two steps higher than the printing energy value that shows the maximum cloudiness density for the first time. This is called the saturation printing sensitivity, and the cloudiness density at that time is defined as the initial printing density. Next, after storing the medium in a special environment, the print density when printing at the initial saturation print sensitivity of the medium is defined as the print density over time, and the obtained numerical value is substituted into the following equation (a). The print density change rate is determined.
[0025]
(Equation 1)
Print density change rate (%) = (ODa−ODf) / ODf × 100 (a)
ODf: Initial print density
ODa: print density over time
[0026]
The print density is the reflection density measured by a Macbeth densitometer (RD-914).
The printing density mentioned here is the reflection density when the reflective layer is provided on the support by metal deposition such as Al deposition. When the support is transparent, the reflection OD of the reversible thermosensitive recording medium is 2. Place on two or more Al vapor-deposited films (eg, Panac Co., Lumirror Metal Me TS, 50 μm), and place the medium and the vapor-deposited film in close contact with distilled water so that no air layer is interposed between the medium and the vapor-deposited film, and measure. .
[0027]
NH of the present invention₃In the exposure method, 0.1 g of 25% aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd.) is dropped into a sealable container having a capacity of 900 ml, and a medium is placed therein and sealed. The medium is exposed to an atmosphere of ammonia for one hour in a 40 ° C. environment. By this method, a state in which the medium is left in a place where the concentration of the basic substance is high is reproduced instead.
It is also possible to evaluate a basic substance by immersing it in an alkaline artificial sweat solution.₃The above method is considered to be equivalent to about 100 hours, compared to the storage time of 1 hour in the exposure method. However, the result of immersion in a liquid may vary depending on the surface energy of the medium surface and the like.
[0028]
As a means for achieving the object of the present invention, in order to prevent a reaction between an acidic functional group such as a low-molecular carboxyl group in a heat-sensitive layer and a basic substance such as ammonia, a basic compound reaching a low molecule in the heat-sensitive layer is used. We found that we just needed to get rid of the substance.
In the present invention, the above is achieved by causing at least one layer on the heat-sensitive layer to contain a material having an acidic functional group for adsorbing a basic substance permeating to the heat-sensitive layer.
[0029]
Examples of the acidic functional group used in the present invention include a carboxyl group, a sulfone group, a hydroxyl group, a phosphono group, and a phenolic hydroxyl group.₃A carboxyl group or a sulfone group, which is a strongly acidic functional group that easily causes a reaction with, is preferred.
The layer containing the resin material having the above functional group needs at least one layer on the heat-sensitive layer, but is more preferably contained in a plurality of layers. Further, it may be contained in the heat-sensitive layer material. Representative examples of the resin material having an acidic functional group include a carboxyl group, a sulfone group, and an epoxy acrylate modified with an onium base. Representative examples are shown below.
[0030]
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[0031]
Embedded image

[0032]
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In addition to the COOH group-modified epoxy acrylate, an onium salt-modified epoxy acrylate has been developed as a water-soluble type, and this can be used in the present invention.
[0033]
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[0034]
As the polymer material having an acidic functional group, a material that undergoes a curing reaction by radiation is preferable, and a polyfunctional acrylate monomer, methacrylate monomer or oligomer is more preferable. NH_ThreeIs determined by the amount of the acidic group. If the number of carboxyl groups in the polymer material is small, the capturing effect becomes insufficient. Therefore, the acid value of the polymer material is 60 mg / KOH / g or more.IsAnd more preferably 80 mg / KOH / g or more.
Further, it is considered that when the number of carboxyl groups in the above-mentioned polymer material is large, the density of the polymer material is reduced, and ammonia gas is easily transmitted. Accordingly, the acid value of the polymer material is 120 mg / KOH / g or less.Is, More preferably 100 mg / KOH / g or less.
[0035]
Further, in order to prevent a reaction between an acidic functional group such as a low-molecular carboxyl group or the like in the heat-sensitive layer and a basic substance such as ammonia, the layer on the heat-sensitive layer preferably has low gas permeability. Gas permeability varies with layer thickness. The total thickness of the layers on the heat-sensitive layer is preferably 5 μm or more. Also, when the total film thickness on the heat-sensitive layer becomes thicker, the printing sensitivity becomes higher, excessive energy is required at the time of printing, and dents, scratches, etc. on the medium surface after repeated printing and erasing of the reversible thermosensitive recording medium become noticeable. Occurs. Therefore, the total thickness of the layer on the heat-sensitive layer is preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less.
[0036]
The gas permeability of a polymer material is affected by the degree of filling of the polymer main chain. As the degree of packing increases due to the configuration of the polymer, the gas permeability decreases. Further, as the molecular structure becomes simpler, the filling degree becomes better. In addition, crystals have low gas permeability and reduce the permeation rate. Therefore, it is preferable that the main chain component of at least one polymer material on the heat-sensitive layer has a crystalline structure. Preferably, the main chain of the crystal structure accounts for at least 70% of the material structure, more preferably at least 90%.
When a reversible thermosensitive recording medium is repeatedly printed and erased, cracks are generated due to the thermal effects, and the basic substance is easily transmitted. Therefore, the protective layer is preferably made of a resin having high heat resistance, and its Tg is preferably 130 ° C. or higher, more preferably 140 ° C. or higher, and still more preferably 160 ° C. or higher.
[0037]
The protective layer of the reversible thermosensitive recording medium of the present invention will be described.
As the ultraviolet-curable resin used for forming the protective layer, any monomer or oligomer (or prepolymer) that undergoes a polymerization reaction upon irradiation with ultraviolet light and cures to become a resin can be used, but contains the acidic functional group. Preferred is a mixed monomer or oligomer (or prepolymer) or a mixture of the monomer or oligomer (or prepolymer) containing the acidic functional group and the other.
The crosslink density of the protective layer is preferably higher, and the monomer or oligomer (or prepolymer) used for this purpose is preferably polyfunctional, and it is preferable to mix a monomer having a molecular weight of 300 or less to increase the degree of filling. .
As a UV-curable resin, a monomer or an oligomer (or a prepolymer) which undergoes a polymerization reaction upon irradiation with ultraviolet rays and cures to become a resin, includes (poly) ester acrylate, (poly) urethane acrylate, epoxy acrylate as a monomer or oligomer. Examples include polybutadiene acrylate, silicone acrylate, and melamine acrylate. (Poly) ester acrylate is obtained by reacting polyhydric alcohols such as 1,6-hexanediol, propylene glycol (as propylene oxide) and diethylene glycol with polybasic acids such as adipic acid, phthalic anhydride and trimellitic acid and acrylic acid. It is a thing. Examples of the structure are shown in (a) to (c).
[0038]
(A) adipic acid / 1,6-hexanediol / acrylic acid
[0039]
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(B) phthalic anhydride / propylene oxide / acrylic acid
[0040]
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(C) trimellitic acid / diethylene glycol / acrylic acid
[0041]
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[0042]
(Poly) urethane acrylate is obtained by reacting a compound having an isocyanate group such as tolylene diisocyanate (TDI) with an acrylate having a hydroxyl group. An example of the structure is shown in FIG. In addition, HEA is 2-hydroxyethyl acrylate, HDO is 1,6-hexanediol, and ADA is abbreviation of adipic acid.
(D) HEA / TDI / HDO / ADA / HDO / TDI / HEA
[0043]
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[0044]
Epoxy acrylates are broadly classified into bisphenol A type, novolak type, and alicyclic type according to their structures. The epoxy groups of these epoxy resins are esterified with acrylic acid to make the functional groups acryloyl groups. Examples of the structure are shown in (e) to (g).
(E) Bisphenol A-epichlorohydrin type / acrylic acid
[0045]
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(F) Phenol novolak-epichlorohydrin type / acrylic acid
[0046]
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(G) Alicyclic type / acrylic acid
[0047]
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[0048]
The polybutadiene acrylate is obtained by reacting 1,2-polybutadiene having a terminal OH group with isocyanate, 1,2-mercaptoethanol and the like, and further reacting with acrylic acid and the like. An example of the structure is shown in FIG.
(H)
[0049]
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Silicone acrylate is, for example, methacryl-modified by a condensation reaction (de-methanol reaction) between an organofunctional trimethoxysilane and a silanol group-containing polysiloxane, and a structural example thereof is shown in (i).
(I)
[0050]
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[0051]
It is known that oxygen in the atmosphere at the time of curing these curable resins hinders curing, so that the degree of surface curing is reduced. This causes scratches on the protective layer and print marks.
As a method of preventing the oxygen inhibition, curing the curable resin in an atmosphere having an oxygen concentration of 8% or less can be mentioned. Preferably, the oxygen concentration is 5% or less, more preferably 2% or less. By preventing oxygen inhibition, the curable resin can completely prevent curing scratches and print marks up to the surface.
[0052]
On the other hand, as a material of the electron beam curable resin, an ultraviolet curable resin can be used as it is.
By the way, an electron beam has higher energy and higher transmission power than ultraviolet light. Also, O₃N to prevent the occurrence of₂Curing is performed in an atmosphere. Therefore, oxygen inhibition on the surface does not occur, and especially when a pigment or the like is put in the protective layer, the electron beam can reach the inside. In this way, the electron beam curing can form a more detailed and uniform network structure than the ultraviolet curing, so that it can be expected to exhibit more excellent durability. Also, the energy required for curing of an electron beam is about one-third that of ultraviolet rays, and even though capital investment is large, cost reduction can be expected due to high demand.
[0053]
Next, the barrier layer will be described. The barrier layer of the present invention is a layer for preventing contact (reaction) between the organic low-molecular substance and the basic substance in the heat-sensitive layer.
The polymer material used for the barrier layer is preferably a polymer having good transparency, mechanical stability, and low gas permeability, and is preferably a polyvinyl chloride or a vinyl chloride copolymer, a polyvinylidene chloride or a vinylidene chloride copolymer. A crystalline resin such as a polymer or a crystalline resin-based copolymer may be used. In the case of a copolymer, the copolymerization ratio of the crystalline resin is preferably 80% or more, more preferably 90% or more.
Further, it is preferable to crosslink with a crosslinker or the like containing a monomer or oligomer (or prepolymer) containing the acidic functional group. As a result, it is possible to have a function of adsorbing the basic substance that has passed through the protective layer, and to increase the mechanical stability. The cross-linking material is preferably a polyfunctional one.
[0054]
Next, the resin base material of the heat-sensitive layer used in the present invention will be described.
By setting the softening point of the resin to a lower temperature side, there is an effect of further increasing the transparency temperature range. Therefore, the softening point is preferably 70 ° C. or lower, more preferably 65 ° C. or lower, and particularly preferably 60 ° C. or lower. In this case, it is preferable that the lower limit is higher than the crystallization temperature of the organic low-molecular substance at the time of cloudiness.
[0055]
As a method for measuring these softening points, a recording layer is formed at an arbitrary thickness on a support, and then the film is peeled off from the support, and a thermomechanical analyzer (TMA) or dynamic viscoelasticity is used. It can be measured using a measuring device. Further, as described above, the measurement can be performed by a rigid pendulum method dynamic viscoelasticity measuring apparatus without peeling the formed recording layer.
[0056]
Examples of the resin having a low softening point include a resin having a long side chain and a resin obtained by copolymerizing a resin having a low softening point. The side chain of the resin having a long side chain preferably has 3 or more carbon atoms in terms of an alkyl group. Further, there may be an ether bond ester bond or the like in the side chain. Further, there may be a carboxyl group or a hydroxyl group at the terminal of the side chain. Examples of the main chain include polyvinyl chloride, polycarbonate, phenoxy resin, polystyrene, chlorinated PVC resin, and copolymers thereof.
[0057]
The vinyl chloride-vinyl ester copolymer used in the present invention is one in which the fatty acid constituting the vinyl ester has 3 or more carbon atoms, that is, propionic acid or more.
Examples of such a vinyl chloride-vinyl ester copolymer include the following.
[0058]
Vinyl chloride-vinyl propionate copolymer,
Vinyl chloride-vinyl butyrate copolymer,
Vinyl chloride-vinyl valerate copolymer,
Vinyl chloride-vinyl caproate copolymer,
Vinyl chloride-vinyl enanthate copolymer,
Vinyl chloride-vinyl caprylate copolymer,
Vinyl chloride-vinyl pelargonic acid copolymer,
Vinyl chloride-vinyl caprate copolymer,
Vinyl chloride-vinyl undecanoate copolymer,
Vinyl chloride-vinyl laurate copolymer,
Vinyl chloride-vinyl tridecylate copolymer,
Vinyl chloride-vinyl myristate copolymer,
Vinyl chloride-vinyl pentadecylate copolymer,
Vinyl chloride-vinyl palmitate copolymer,
Vinyl chloride-vinyl margallate copolymer,
Vinyl chloride-vinyl stearate copolymer,
Vinyl chloride-vinyl nonadecylate copolymer,
Vinyl chloride-vinyl arachidate copolymer,
Vinyl chloride-vinyl behenate copolymer,
Vinyl chloride-vinyl lignoserate copolymer,
Vinyl chloride-vinyl citrate copolymer,
Vinyl chloride-vinyl montanate copolymer,
Vinyl chloride-vinyl mericinate copolymer.
[0059]
Further, the structure of the vinyl ester may be such that a linear normal body may be branched, and specific examples thereof include the following.
Vinyl chloride-vinyl isopropionate copolymer
Vinyl chloride-vinyl isobutylate copolymer
Vinyl chloride-vinyl isovalerate copolymer
Vinyl chloride-vinyl isocaproate copolymer
And the like, but are not limited thereto.
The copolymerization ratio of these non-polymers is preferably a vinyl chloride unit / vinyl ester unit weight ratio of 99/1 to 20/80.
Further, the average degree of polymerization (P) is preferably P = 100 or more, more preferably P = 200 or more, and particularly preferably P = 300 or more.
[0060]
Next, the vinyl chloride-ethylene copolymer used in the present invention has an ethylene content of preferably 1% or more, more preferably 2% or more, and particularly preferably 4%, from low ethylene grade to high ethylene grade. That is all. As the ethylene content increases, the softening temperature shifts to a lower temperature. Therefore, a higher ethylene content is preferable.
Further, the average degree of polymerization (P) is preferably P = 200 or more, more preferably P = 300 or more, and particularly preferably P = 400 or more.
[0061]
In addition to the above resins, examples of the resin having a low softening point include a vinyl chloride-vinyl ether copolymer represented by the following general formula.
The alkyl group of the vinyl alkyl ether preferably has 3 or more carbon atoms.
[0062]
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[0063]
The above-mentioned resins may be used alone or as a mixture of two or more kinds, and furthermore, these resins may be used in combination with the following resins.
Polyvinyl chloride: vinyl chloride copolymers such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer Polymer; polyvinylidene chloride, vinylidene chloride copolymer such as vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate or acrylate, methacrylate copolymer; silicone Resins, polyethylene, polypropylene, polystyrene, polyacrylamide, polyvinylpyrrolidone, natural rubber, polyvinyl alcohol, polyacrolein, polycarbonate and the like.
[0064]
On the other hand, the organic low-molecular substance may be any substance that becomes particulate in the recording layer, and preferably does not have a functional group that reacts with a basic substance, but is not limited thereto. Generally, those having a melting point of 30 to 200 ° C, preferably about 50 to 150 ° C are used. Such organic low molecular weight substances include alkanol; alkane diol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyne; halogen alkane; halogen alkene; halogen alkyne; cycloalkane; Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; Esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or their esters,DoOr ammonium salts; carboxylic acid esters of thioalcohols and the like. These may be used alone or in combination of two or more. These compounds have 10 to 60 carbon atoms, preferably 10 to 38 carbon atoms, and more preferably 10 to 30 carbon atoms. The alcohol group in the ester may be saturated, may not be saturated, and may be halogen-substituted. In any case, the organic low molecular weight substance contains at least one of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -COOR, -NH-, -NH_Two, -S-, -SS-, -O-, halogen and the like.
In the present invention, at least one kind of organic low-molecular substance having an acidic functional group is used.
[0065]
In the present invention, as the organic low-molecular substance, a substance that can further increase the transparency temperature range by using a combination of a low-melting organic low-molecular substance and a high-melting organic low-molecular substance is preferable. The difference between the melting points of the low-melting point organic low-molecular substance and the high-melting point organic low-molecular substance is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and particularly preferably 40 ° C. or higher.
[0066]
The low-melting point organic low-molecular substance material preferably has a melting point of 40 ° C to 100 ° C, more preferably 50 ° C to 80 ° C. The high-melting organic low-molecular substance preferably has a melting point of 100 ° C to 200 ° C, more preferably 110 ° C to 180 ° C.
[0067]
Among these organic low molecular weight substances, the following fatty acid esters, dibasic acid esters and polyhydric alcohol difatty acid esters are preferable as the low melting point organic low molecular weight substances. These are used alone or in combination of two or more.
[0068]
The fatty acid ester used in the present invention is characterized in that it has a lower melting point than fatty acids having the same carbon number (in a state of two molecules associated), and conversely has more carbon atoms than fatty acids having the same melting point.
[0069]
Deterioration due to repeated printing and erasing of images with the thermal head is considered to be caused by a change in the dispersion state of the organic low-molecular substance particles due to compatibility between the resin base material and the organic low-molecular substance during heating. It is considered that the compatibility of the organic low-molecular substance decreases as the number of carbon atoms of the organic low-molecular substance increases, and that the deterioration of image printing-erasing is small. Further, the turbidity also tends to increase in proportion to the carbon number.
[0070]
Therefore, in a reversible thermosensitive recording medium having the same clearing temperature (near the melting point), by using a fatty acid ester as an organic low-molecular substance to be dispersed in a resin base material, the opacity is higher than when a fatty acid is used. Is high, that is, the contrast is high, and the repetition durability is considered to be improved.
[0071]
By using a mixture of such a fatty acid ester and a high-melting organic low-molecular substance, the transparency temperature range can be widened, and the erasing performance with a thermal head is high. Even if the characteristics fluctuate, it can be erased, and the durability of the material can be improved due to the characteristics of the material itself.
[0072]
The fatty acid ester used in the present invention is, for example, one represented by the following general formula (I).
R₃-COO-R₄ ... (I)
(Where R₃, R₄Represents an alkyl group having 10 or more carbon atoms)
The fatty acid ester preferably has 20 or more carbon atoms, more preferably 25 or more carbon atoms, and particularly preferably 30 or more carbon atoms. When the number of carbon atoms increases, the degree of white turbidity is high, and there is a feature that the repetition durability is improved. The melting point of the fatty acid ester is preferably 40 ° C. or higher.
These are used alone or in combination of two or more.
[0073]
The dibasic acid ester may be either a monoester or a diester, and includes those represented by the following general formula (II).
R₅OOC- (CH₂) N-COOR₆ ... (II)
(Where R₅, R₆Represents a hydrogen atom or an alkyl group having 1 to 30 carbon atoms;₅, R₆May be the same or different, except that they are simultaneously hydrogen atoms. n represents an integer of 0 to 40)
In the dibasic acid ester represented by the general formula (II),₅, R₆The alkyl group preferably has 1 to 22 carbon atoms, n is preferably 1 to 30, and more preferably 2 to 20. The melting point is preferably 40 ° C. or higher.
[0074]
Examples of the polyhydric alcohol difatty acid ester of the organic low molecular weight substance used in the present invention include those represented by the following general formula (III).
CH₃(CH₂) MCO-O (CH₂) NO-OC (CH₂) MCH₃ ... (III)
(In the formula, n is an integer of 2 to 40, preferably 3 to 30, and more preferably 4 to 22. m is an integer of 2 to 40, preferably 3 to 30, and more preferably 4 to 22. )
[0075]
Polyhydric alcohol difatty acid esters have the characteristic that they have a lower melting point than fatty acids when compared at the same carbon number, and conversely have more carbon atoms than fatty acids when compared at the same melting point. The repetition durability of printing with the thermal head is considered to be due to the compatibility of the resin and the organic low-molecular substance during heating, and the compatibility between the resin and the organic low-molecular substance decreases as the number of carbon atoms in the organic low-molecular substance increases. It is thought that.
[0076]
Furthermore, the turbidity also tends to increase in proportion to the number of carbon atoms. Therefore, by using a polyhydric alcohol difatty acid ester, compared with a fatty acid in a reversible thermosensitive recording medium having the same clearing temperature (near the melting point), It is thought that the repeated durability is improved.
[0077]
In addition, polyhydric alcohol difatty acid esters have a low melting point, and have characteristics similar to those of higher melting fatty acids in terms of cloudiness and repetition durability. When the transparency temperature range is extended, the transparency temperature range can be extended while having the same degree of white turbidity and repetitive durability as in the case of using a fatty acid. The image erasing (transparency) can be improved by heating, and even if the image erasing energy fluctuates over time by increasing the image erasing margin, erasing with a thermal head is possible without any practical problem. Become.
[0078]
Next, examples of the high melting point organic low molecular weight substance used in the present invention include aliphatic saturated dicarboxylic acids, ketones having higher alkyl groups, semicarbazones derived from the ketones, α-phosphono fatty acids, and the like. Are preferred, but are not limited thereto.
These are used alone or in combination of two or more.
[0079]
Specific examples of these low-molecular organic substances having a melting point of 100 ° C. or higher are shown below.
Specific examples of the aliphatic dicarboxylic acid having, for example, a melting point of about 100 to 135 ° C. include, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecanedioic acid, Examples include tetradecandioic acid, pentadecandioic acid, hexadecandioic acid, heptadecandioic acid, octadecandioic acid, nonadecandioic acid, eicosantioic acid, heneicosandioic acid, docosantioic acid, and the like.
[0080]
The ketone used in the present invention contains a ketone group and a higher alkyl group as essential constituent groups, and may further contain an unsubstituted or substituted aromatic ring or a substituted ring. The total carbon number of the ketone is preferably 16 or more, more preferably 21 or more. The semicarbazone used in the present invention is derived from the above ketone.
[0081]
The α-phosphono fatty acid used in the present invention is, for example, E. coli. V. Kaurer et al. Ak. According to the method of Oil Chemist's Soc, 41, 205 (1964), the fatty acid is brominated by the Hell-Volhard-Zelinskin reaction to obtain α-brominated acid bromide, and then ethanol is added to obtain α-bromo fatty acid ester. It can be obtained by heating and reacting with phyto to form an α-phosphono fatty acid ester, hydrolyzing with concentrated hydrochloric acid, and recrystallizing the product from toluene.
[0082]
The mixing weight ratio of these low-melting organic low-molecular substances to high-melting organic low-molecular substances is preferably from 95: 5 to 5:95, more preferably from 90:10 to 10:90, particularly preferably from 80:20 to 20:80. preferable. Further, in addition to these low melting point organic low molecular weight substances and high melting point organic low molecular weight substances, other organic low molecular weight substances described above may be mixed and used. These include the following:
[0083]
Examples of these compounds include ethers and thioethers of higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, alginic acid and oleic acid. Among them, in the present invention, higher fatty acids, especially higher fatty acids having 16 or more carbon atoms such as palmitic acid, pentadecanoic acid, nonadecanoic acid, arachinic acid, stearic acid, behenic acid, and lignoceric acid are preferable, and higher fatty acids having 16 to 24 carbon atoms are further preferable. preferable.
[0084]
As described above, in the present invention, in order to widen the range of temperatures that can be made transparent, the organic low-molecular substances described in this specification are appropriately combined, or such an organic low-molecular substance and another material having a different melting point are used. You can combine them. These are described in, for example, JP-A-63-39378 and JP-A-63-130380, and JP-A-63-14754 and JP-A-3-2089 (JP-A-4-235095). But is not limited thereto.
[0085]
The ratio between the organic low-molecular substance and the resin (the resin having a crosslinked structure) in the heat-sensitive layer is preferably about 2: 1 to 1:16, more preferably 1: 2 to 1: 8 by weight. When the ratio of the resin is less than this, it is difficult to form the organic low-molecular substance in the film held in the resin, and when the ratio is more than this, it is difficult to make the film opaque because the amount of the organic low-molecular substance is small. .
[0086]
In addition to the above components, additives such as a surfactant and a plasticizer can be added to the heat-sensitive layer in order to facilitate formation of a transparent image. Specific examples of these additives are as follows.
[0087]
Examples of the plasticizer include a phosphoric acid ester, a fatty acid ester, a phthalic acid ester, a dibasic acid ester, a glycol, a polyester-based plasticizer, and an epoxy-based plasticizer. Specific examples include the following.
Tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, phthalate Di-2-ethylhexyl acid, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2 azelate -Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl Rikoreto, such as acetyl tributyl citrate.
[0088]
Examples of surfactants and other additives include the following: polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkyl phenol, higher fatty acid higher Lower amine olefin oxide adducts of alkylamines, higher fatty acid amides, oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids; Ca, Ba or Mg salts of sulfuric acid monoester or phosphoric acid mono- or di-ester; low sulfated oil; poly long chain alkyl acrylate; acrylic oligomer; poly long chain alkyl methacrylate; long chain alkyl methacrylate Amine-containing monomer copolymer; a styrene - maleic anhydride copolymer; olefin - maleic anhydride copolymer and the like.
[0089]
The means for crosslinking the resin in the heat-sensitive layer in the present invention can be carried out by heating, or by irradiating ultraviolet rays or electron beams. Of these, electron beam irradiation is optimal. The method for crosslinking is specifically as follows. (I) a method using a crosslinkable resin, (ii) a method by adding a crosslinking agent, (iii) a method of crosslinking by irradiation with ultraviolet rays or electron beams, (iv) an ultraviolet ray in the presence of a crosslinking agent, Alternatively, there is a method of crosslinking by irradiation with an electron beam.
[0090]
Examples of the crosslinking agent include oligomers such as urethane acrylates, epoxy acrylates, polyester acrylates, polyether acrylates, vinyls, and unsaturated polyesters, and various monofunctional and polyfunctional acrylates, methacrylates, vinyl esters, styrene derivatives, and allyls. And monomers such as compounds. Examples of the non-functional monomer and the functional monomer include the same monomers as those used in the barrier layer.
[0091]
These crosslinking agents are used alone or in combination of two or more. The amount of the crosslinking agent to be added is preferably 0.001 to 1.0 part by weight, more preferably 0.01 to 0.5 part by weight, per 1 part by weight of the resin. When the amount is 0.001 part by weight or less, the crosslinking efficiency is deteriorated. On the other hand, when the amount is 1.0 part by weight or more, the cloudiness is reduced and the contrast is lowered.
[0092]
As described above, in order to improve the cross-linking efficiency by reducing the amount of the cross-linking agent to be added, among the cross-linking agents described above, a functional monomer is preferable to a non-functional monomer, and a polyfunctional monomer is more preferable than a monofunctional monomer. Monomers are preferred.
[0093]
Next, as means for crosslinking the resin of the heat-sensitive layer in the present invention, when ultraviolet irradiation is used, the following crosslinking agents, photopolymerization initiators, and photopolymerization accelerators may be used. Specific examples include the following.
[0094]
The crosslinking agent can be roughly classified into a photopolymerizable prepolymer and a photopolymerizable monomer, and the photopolymerizable monomer includes the monofunctional monomer and the polyfunctional monomer listed as the crosslinking agent used in the electron beam irradiation described above. The same can be mentioned.
[0095]
Next, examples of the photopolymerizable prepolymer include polyester acrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate, oligoacrylate, alkyd acrylate, and polyol acrylate.
[0096]
These crosslinking agents are used alone or in combination of two or more. The amount of the crosslinking agent to be added is preferably 0.001 to 1.0 part by weight, more preferably 0.01 to 0.5 part by weight, per 1 part by weight of the resin. When the amount is 0.001 part by weight or less, the crosslinking efficiency is deteriorated. On the other hand, when the amount is 1.0 part by weight or more, the cloudiness is reduced and the contrast is lowered.
[0097]
Next, the photopolymerization initiator can be roughly classified into a radical reaction type and an ion reaction type, and the radical reaction type is further classified into a photocleavage type and a hydrogen abstraction type. Specific examples include the following, which can be similarly used in the above-described barrier layer.
(I) benzoin ethers such as isobutyl benzoin ether, isopropyl benzoin ether, benzoin ethyl ether, benzoin methyl ether,
(Ii) α-acyloxime esters such as 1-phenyl-1,2-propanedione-2- (o-ethoxycarbonyl) oxime,
(Iii) benzyl ketals such as 2,2-dimethoxy-2-phenylacetophenone, benzyl, hydroxycyclohexyl phenyl ketone,
(Iv) acetophenone derivatives such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one,
(V) ketone- (ketone-amine) s such as benzophenone, chlorothioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, 2-methylthioxanthone, chlorine-substituted benzophenone,
These photopolymerization initiators are used alone or in combination of two or more.
The addition amount is preferably 0.005 to 1.0 part by weight, more preferably 0.01 to 0.5 part by weight, based on 1 part by weight of the crosslinking agent.
[0098]
Next, as a photopolymerization accelerator, an aromatic tertiary amine or an aliphatic amine has an effect of improving the curing rate with respect to a hydrogen abstraction type photopolymerization initiator such as a benzophenone type or a thioxanthone type. is there. Specifically, the following are mentioned.
P-dimethylaminobenzoic acid isoamyl ester
P-dimethylaminobenzoic acid ethyl ester
These photopolymerization accelerators are used alone or in combination of two or more.
[0099]
The addition amount is preferably from 0.1 to 5 parts by weight, more preferably from 0.3 to 3 parts by weight, based on 1 part by weight of the photopolymerization initiator.
[0100]
The ultraviolet irradiation device used in the present invention includes a light source, a lamp, a power supply, a cooling device, and a transport device. Light sources include a mercury lamp, a metal halide lamp, a potassium lamp, a mercury xenon lamp, and a flash lamp, and a light source having an emission spectrum corresponding to the ultraviolet absorption wavelength of the above-described photopolymerization initiator and photopolymerization accelerator may be used. . Regarding the ultraviolet irradiation conditions, the lamp output and the conveying speed may be determined according to the irradiation energy required for crosslinking the resin.
[0101]
In the present invention, an electron beam (EB) irradiation method particularly effective for crosslinking the resin of the heat-sensitive layer of the reversible thermosensitive recording medium is as follows.
[0102]
First, EB irradiators can be broadly classified into two types, a scanning type (scan beam) and a non-scan type (area beam). Next, the EB irradiation condition is determined from the following equation in consideration of the electron flow, the irradiation width, and the transport speed according to the dose required for crosslinking the resin.
[0103]
D = (△ E / △ R) · η · I / (W · V)
D: Required dose (Mrad)
ΔE / ΔR: average energy loss
η: efficiency
I: Electron current (mA)
W: irradiation width (cm)
V: Transfer speed (cm / s)
Industrially, this is simplified,
DV = KI / W
And the device rating is indicated by Mrad · m / min.
The electron flow rating is selected to be about 20 to 30 mA for an experimental device, about 50 to 100 mA for a pilot machine, and about 100 to 500 mA for a production machine.
[0104]
Here, regarding the dose required to crosslink the resin, the crosslinking efficiency varies depending on the type and degree of polymerization of the resin, the type and amount of the crosslinking agent, the type and amount of the plasticizer, and the like. Since the fraction is not constant, the recording layer is prepared by determining the component level of the thermosensitive layer of these reversible thermosensitive recording media, the gel fraction target value is determined, and the dose in accordance therewith is determined.
[0105]
When high energy is required to crosslink the resin, the irradiation is performed several times in order to prevent the support or the resin from being deformed or thermally decomposed by the heat generated by the irradiation. It is preferable to prevent the heat from becoming high due to one irradiation.
[0106]
Before the EB irradiation, it is preferable that at least a part of the organic low-molecular substance contained in the recording layer is heated to a temperature at which the organic low-molecular substance is melted or more, and then the organic low-molecular substance is crosslinked. It is preferable to crosslink after heating to a temperature or higher.
[0107]
The relationship between each component of the thermosensitive layer and the gel fraction is as described above.
First, as the kind of resin, the above-mentioned resins can be selected. However, the degree of polymerization of these resins tends to increase as the average degree of polymerization (P) increases, and is preferably P = 300 or more. Preferably, P = 600 or more.
[0108]
The type and amount of the cross-linking agent are as described above. As the type of the plasticizer, fatty acid esters, polyester-based plasticizers, epoxy-based plasticizers and the like are preferable among the aforementioned plasticizers, and particularly, epoxy-based plasticizers. The agent is optimal in view of irradiation discoloration and crosslinking efficiency. As for the addition amount of the plasticizer, the gel fraction tends to increase as the addition amount increases, and is preferably 0.01 to 1.0 part by weight, more preferably 0.05 to 1.0 part by weight, per 1 part by weight of the resin. 0.5 parts by weight.
[0109]
In addition to the above-mentioned means, there are the following methods for improving the repetition durability. First, durability is improved by raising the softening temperature of the heat-sensitive layer to a higher temperature side. The higher the softening temperature, the more the durability is improved. As a method of measuring the softening temperature, a film similar to the one used in the measurement of the gel fraction can be used, and can be measured using a thermomechanical analyzer (TMA) or a dynamic viscoelasticity analyzer.
Further, it can be measured by a rigid pendulum method / dynamic viscoelasticity measuring apparatus without peeling the recording layer formed as described above.
In addition, as for the softening point, the smaller the variation with the passage of time, the smaller the variation of the erasing characteristic with the passage of time.
[0110]
As a second method, as described later, the durability is also improved by laminating the above-described protective layer on a heat-sensitive layer formed on a support and increasing the interlayer strength between the laminated layers. The higher the interlayer strength, the higher the durability. The interlayer strength measurement method can be performed according to Tappi UM-403.
[0111]
As a third method, the lower the penetration by the TMA penetration measurement of the heat-sensitive layer, the higher the durability. The lower the penetration, the higher the durability. The penetration is measured by using a recording layer formed on a support, using the TMA used for measuring the softening temperature, placing a probe with a small tip cross-sectional area (a penetration probe) on the recording layer, and applying a load. In addition, it can be measured by the amount of displacement by heating as necessary.
[0112]
As a fourth method, the smaller the amount of the crosslinking agent remaining in the heat-sensitive layer after the EB crosslinking, the higher the durability. The durability is further improved as the residual amount is smaller. The method for measuring the residual amount includes the following method.
[0113]
As a measuring device, an ATR measuring attachment attached to a Fourier transform infrared spectrophotometer was used. As a measurement sample, the thermosensitive layer coating film used for the gel fraction measurement was used.^-1The absorption band intensity of the acryloyl group appearing in the vicinity due to the CH out-of-plane bending vibration is measured. The strength of the absorption band is proportional to the residual amount of the cross-linking agent, and the lower the residual amount, the lower the strength. Thereby, the remaining amount can be known.
The residual amount is preferably 0.2 parts by weight or less, preferably 0.1 part by weight or less, more preferably 0.05 part by weight or less, particularly preferably 1 part by weight with respect to 1 part by weight of the resin in the thermosensitive layer. It is 0.01 part by weight or less.
[0114]
In this measurement method, in addition to the above measurement, the residual amount of the photopolymerization initiator, the photosensitizer, and the catalyst used in the thermal curing used in the UV curing can be known. By the analysis, it is possible to determine which method among the EB curing, the UV curing, and the heat curing is used for the crosslinking of the resin in the total heat-sensitive. In any of the methods, the less the residual components, the better the durability.
Further, according to this measurement method, since only a thin total of several μm on the surface of the coating film can be obtained, it is possible to measure the heat-sensitive layer formed on the support as it is.
Further, in addition to these, if there is a gap between the resin in the heat-sensitive layer and the organic low-molecular substance particles and / or in the particles having a refractive index different from that of the resin and the particles, the image density in a cloudy state is improved, This has the effect of improving the contrast. The effect is more remarkable when the size of the gap is 1/10 or more of the wavelength of the light used for detecting the opaque state.
[0115]
When an image formed on the reversible thermosensitive recording medium of the present invention is used as a reflection image, it is desirable to provide a light reflecting layer on the back surface of the recording layer. In addition, the presence of the reflective layer makes it possible to make the recording layer thinner and to increase the contrast very much. Specifically, as described in JP-A-64-14079, there is a method of depositing Al, Ni, Sn or the like.
[0116]
The thickness of the heat-sensitive layer is preferably from 1 to 30 μm, more preferably from 2 to 20 μm. If the recording layer is too thick, heat distribution will occur in the layer, making it difficult to make it transparent uniformly. On the other hand, if the heat-sensitive layer is too thin, the turbidity decreases and the contrast decreases. The turbidity can be increased by increasing the amount of the fatty acid in the recording layer.
[0117]
In order to produce the reversible thermosensitive recording medium of the present invention, first, a thermosensitive layer is formed on a support by, for example, the following method. In some cases, a sheet-like reversible thermosensitive recording medium can be formed without using a support.
1) A method of dissolving a resin base material and an organic low-molecular substance in a solvent, applying this on a support, and evaporating the solvent to form a film or sheet.
2) Dissolve the resin base material in a solvent that dissolves only the resin base material, pulverize or disperse the organic low-molecular substance therein by various methods, apply this on a support, evaporate the solvent, and form a film or How to make a sheet.
3) A method in which a resin base material and an organic low-molecular substance are melted and mixed by heating without using a solvent, and the resulting mixture is formed into a film or a sheet and cooled.
[0118]
In addition, since the heat-sensitive layer significantly improves the repetitive durability by cross-linking the resin, it is preferable to cross-link the heat-sensitive layer during or after the formation of the heat-sensitive layer.
[0119]
The solvent for forming the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the types of the resin base material and the organic low-molecular substance. For example, tetrahydrofuran (THF), methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, Benzene and the like can be mentioned. It should be noted that, not only when a dispersion is used, but also when a solution is used, the organic low-molecular substance is precipitated as fine particles in the resulting heat-sensitive layer and exists in a dispersed state.
[0120]
As the material of the support, various plastics, glass, metals and the like are used as in the prior art. The thickness of the support can be arbitrarily selected depending on the application.
As the resin for the intermediate layer, in addition to polyamide, for example, those listed as the resin base material in the recording layer, the following various thermoplastic resins and thermosetting resins can be used. Specific examples include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester resin, unsaturated polyester resin, epoxy resin, phenol resin, polycarbonate, polyamide and the like.
[0121]
In the invention, a colored layer may be provided between the support and the recording layer to improve visibility. The coloring layer is formed by applying and drying a solution or a dispersion containing a coloring material and a resin binder as main components on the target surface, or simply attaching a coloring sheet. Here, as the coloring agent, it is sufficient that the change in transparency and white turbidity of the upper recording layer can be recognized as a reflection image, and a dye having a color such as red, yellow, blue, navy blue, purple, black, brown, ash, orange, or green, Pigments and the like are used. Various thermoplastic, thermosetting or ultraviolet curable resins are used as the resin binder.
[0122]
In addition, an air layer, which is a non-contact portion having air, can be provided between the support and the recording layer. When the air layer is provided, the organic polymer material used as the main component of the recording layer has a refractive index of about 1.4 to 1.6 and a large difference from the refractive index of air of 1.0. Light is reflected at the interface between the side film and the non-contact portion, and when the recording layer is in a cloudy state, the degree of white turbidity is amplified and visibility is improved. Therefore, it is desirable to use the non-contact portion as a display portion.
[0123]
Since the non-contact portion has air inside the non-contact portion, the non-contact portion serves as a heat insulating layer, and the heat sensitivity is improved. Furthermore, the non-adhered portion also does not serve as a cushion, so that even if pressure is applied by the thermal head and pressed, the pressure actually applied to the heat-sensitive member is reduced, and even if heat is applied, the recording layer is less deformed, and organic low-molecular substance particles The durability is improved repeatedly without expansion.
[0124]
Furthermore, it is also possible to provide an adhesive layer or a pressure-sensitive adhesive layer on the back surface of the support and use it as a reversible thermosensitive recording label. This label sheet is attached to the adherend. Examples of the adherend include, but are not limited to, a PVC card such as a credit card, an IC card, an ID card, paper, a film, a synthetic paper, a boarding pass, and a commuter pass. When the support is made of a material such as an Al vapor-deposited layer that has poor adhesion to a resin, the above-described adhesive layer or the like may be provided between the support and the recording layer. No. 7377).
[0125]
The thermal recording image display device for displaying an image using the reversible thermosensitive recording medium of the present invention includes a wide variety of types. A thermosensitive recording image display device in which the image forming means for erasing and the image erasing means are the same heating element, for example, a thermal head, and which can perform image processing by changing the energy applied to the thermal head by printing; or The image forming means is a thermal head, and the image erasing means is a contact pressing type means for adhering a heating element such as a thermal head, a hot stamp, a heat roller, a heat block, or using hot air, infrared rays, laser light or the like. There is a thermal recording image display device selected from one of the non-contact type means. The present invention is applicable to other reversible thermosensitive recording materials such as the leuco-based thermosensitive recording material described above,₃Any material that causes deterioration by gas is effective.
[0126]
As described above, the reversible recording medium of the present invention includes a recording medium provided with a magnetic storage layer, an IC chip, and / or a rewritable barcode in addition to the reversible thermosensitive layer as described above. And those in which a light reflecting layer is provided on a support and / or those in which a protective layer is provided on a recording layer. Further, a layer provided with a coloring layer in addition to the reversible thermosensitive layer and having a reversible thermosensitive layer thereon is preferable in order to make a reversible visible image easily visible. In this case, the coloring layer may be composed of two or more types of portions having different reflectances with respect to visible light.
[0127]
In particular, when the reversible recording medium of the present invention is provided with a rewritable barcode, it is preferable that the medium comprises two or more types of portions having different reflectances. This is because when viewed by a human, for example, there is a color tone difference in addition to a light amount difference between an image portion in a cloudy state and a non-image portion in a colored state, and depending on the viewing angle, excessive The glare caused by reflected light is eliminated, making it easier to see a reversible visible image.On the other hand, when reading this image with a device such as a reflection densitometer or a barcode reader, light is usually incident obliquely. The sensor is placed and read in the direction perpendicular to the surface, because the color layer only measures the result of absorbing at least a part of the visible light and lowering the contrast. Thus, the colored layer in the reversible thermosensitive recording medium of the present invention is composed of two or more types of portions having different reflectances with respect to visible light, and at least one of the portions is a layer that absorbs visible light. Is formed of a layer that reflects visible light, at least a part of which can easily recognize an image visually and can obtain high contrast even when measured by an apparatus.
[0128]
In order to obtain a high contrast required for reading a barcode in the reversible (reversible) heat-sensitive layer, the average particle diameter of the organic low-molecular substance is preferably in the range of 0.1 to 2.0 μm, and more preferably White turbidity. This is a process in which recording and erasing of this reversible thermosensitive recording card utilize light scattering and light transmission due to the difference between the single crystalline state and polycrystalline state of the organic low molecular weight substance. It is presumed that the crystal growth and its effect for raising naturally depend on the particle size of the organic low-molecular substance dispersed in the resin base material. In other words, the change in the crystallinity of the organic low-molecular substance (single crystal / polycrystal) is considered to be due to the interaction between the organic low-molecular substance and the resin base material, and the magnitude of the interaction with the resin base material depends on the size of the particles. It is considered that a difference occurs in the degree of change between the transparent state and the cloudy state. And, as the average particle diameter of the dispersed organic low-molecular substance increases, it becomes difficult to be in a polycrystalline state, the effect of scattering light decreases, the opacity decreases, the contrast decreases, and conversely, The smaller the average particle size of the dispersed organic low molecular weight material, the more difficult it is to form a polycrystalline state in the dispersed matrix during crystal growth, and also in this case, the turbidity decreases and the contrast decreases. Conceivable. Further, when reading the bar code, when the average particle diameter of the particles of the organic low-molecular substance is in the range of 1/8 to 2 times the wavelength of the light source for reading the bar code, the contrast at the time of reading the bar code is low. Is further improved. It is not yet clear why these phenomena occur, but it is generally speculated that: That is, the degree of turbidity, that is, the degree of light scattering, is considered to be determined by the size of the crystal in the organic low-molecular substance particles, and the size of the crystal is considered to be determined by the size of the organic low-molecular substance particles. This is because the area of the interface between the resin base material and the organic low-molecular substance dispersed in the resin base material is determined by the size of the low-molecular substance particles, and from the area of this interface, the resin base material and the organic low-molecular substance are dispersed. It is speculated that the strength of the interaction with the molecular substance is determined, and the strength of the interaction affects the size of the crystals in the particles. In addition, there is a size of a crystal that is most likely to scatter light of a certain wavelength, which differs depending on each material. However, a crystal smaller than the wavelength of light easily scatters light of that wavelength. In other words, when the average particle size of the organic low-molecular substance is in the range of 1/8 to 2 times the wavelength of the light for reading the bar code, the size of the individual crystals of the polycrystal in the organic low-molecular substance particles in the cloudy state Is considered to have a size that most easily scatters light of that wavelength. When the average particle diameter is less than 1/8 of the wavelength of the reading light source, the scattering effect is reduced, the turbidity is reduced, and the contrast is reduced. It is thought that the surface area of the interface decreases, the interaction between the resin base material and the organic low-molecular substance decreases, and it becomes difficult to control the crystals in the organic low-molecular substance particles. Decrease. As a method for controlling the particle size of the organic low-molecular substance, mixing of a poor solvent, control of heating and drying during application of the recording layer forming liquid, addition of a surfactant for controlling dispersibility, and the like are considered. It is not limited to these.
[0129]
By the way, the wavelength of a light source for reading a barcode is conventionally defined to be 600 nm or more (JIS B9550), and a light source having a wavelength in the range of 600 nm to 1000 nm is usually used. Specific examples include an LED (a wavelength of 660 nm and 940 nm is often used) and a laser (600 nm of a He-Ne laser and 680 nm, 780 nm, and 960 nm of a semiconductor laser are often used).
[0130]
According to the barcode display in the reversible recording medium of the present invention, it is of course possible to read a barcode using a light source having a wavelength of 660 nm or more as described above, but it is also possible to use a light source having a shorter wavelength. In fact, higher contrast can be obtained by using a shorter wavelength light source. For example, when light of 400 to 600 nm is used, the contrast is at most twice as high as that of light of 600 to 10,000 nm. It is considered that this is because light having a shorter wavelength has a higher refractive index with respect to the organic low-molecular substance, increases light scattering, and therefore improves turbidity.
[0131]
Note that the `` bar code '' here is not particularly limited as long as optical changes such as light intensity and wavelength change can be recognized as information regardless of whether it is in the visible light wavelength range. It also includes other optical recognition pattern displays represented by two-dimensional barcodes, OCR, and Carla codes.
[0132]
In the reversible thermosensitive recording medium of the present invention, by providing a low refractive index layer between the coloring layer and the reversible thermosensitive layer, light transmitted through the thermosensitive layer in a cloudy state causes an interface between the thermosensitive layer and the low refractive index. , The ratio of reflection increases, so that the contrast can be improved. Any material having a lower refractive index than the resin used for the reversible thermosensitive layer may be used as the material having a low refractive index, but a material having a refractive index of 1.5 or less according to ASTM or D542 measurement method is preferable, and further preferably 1.4 or less. Are preferred. For example, polypropylene (refractive index 1.49), poly-methylbenzene-1 (refractive index 1.465), methacrylic resin (refractive index 1.49), ethylene tetrafluoride resin (refractive index 1.35), vinylidene fluoride Examples include resin (refractive index: 1.42), polyacetal (refractive index: 1.48), cellulose acetate (refractive index: 1.33), and air (refractive index: 1.0).
[0133]
In the reversible recording medium of the present invention, by providing the magnetic recording layer, the convenience of the reversible recording medium is improved, for example, a part of the magnetically recorded information can be displayed on the thermosensitive layer. In the magnetic recording layer, the support opposite to the reversible heat-sensitive layer can be provided between the colored layer and the support layer. It is possible that the magnetic recording layer also serves as the colored layer. For the magnetic recording layer, commonly used iron oxide, barium ferrite and the like and a resin are used.
[0134]
In addition to magnetic recording, an information storage unit such as an IC, an optical memory, or a magneto-optical memory may be provided, and a part of the stored information may be displayed on the reversible thermosensitive layer as needed. Specific examples having a magnetic recording layer and specific examples incorporating an IC chip will be described later in detail. However, the reversible recording medium used in the present invention does not necessarily need to be provided with information storage such as barcode information, magnetic recording information, IC, optical memory, magneto-optical memory, and the like.
[0135]
Therefore, as shown in FIG. 3, for example, the reversible thermosensitive recording medium of the present invention comprises an aluminum reflective layer (12), a reversible thermosensitive recording layer (13), and a protective layer (14) on a support (11). The formed film may be processed into a card shape. Alternatively, for example, as shown in FIG. 4, a reversible thermosensitive recording layer (13) and a protective layer may be formed on a transparent PET film base. (14) The card may be formed by laminating a film provided and a support (11) with an adhesive layer (17) having an air layer (16) as a low refractive index layer interposed therebetween. it can.
[0136]
Further, as shown in, for example, FIG. 5A, a film in which an aluminum reflective layer (12), a reversible thermosensitive recording layer (13), and a protective layer (14) are provided on a support (11) is processed into a card shape. Then, a recessed portion (23) for accommodating the IC chip is formed, and the shape can be processed into a card shape. In this example, a rewritable recording portion (24) is label-processed on a card-like reversible thermosensitive recording medium, and a recess (23) for embedding an IC chip is provided at a predetermined location on the back side of the reversible thermosensitive recording medium. A wafer (231) as shown in FIG. 5b is assembled and fixed in the recess (23). In the wafer (231), an integrated circuit (233) is provided on a wafer substrate (232), and a plurality of contact terminals (234) electrically connected to the integrated circuit (233) are formed on the wafer substrate (232). Is provided. The contact terminals (234) are exposed on the back side of the wafer substrate (232), and a dedicated printer (reader / writer) electrically contacts the contact terminals (234) to read or rewrite predetermined information. It is configured to be able to. An example of the function of the reversible thermosensitive recording card will be described with reference to FIG.
[0137]
FIG. 6A is a schematic block diagram showing an integrated circuit (233), and FIG. 6B is a block diagram showing an example of data stored in a RAM. The integrated circuit (233) is composed of, for example, an LSI. The integrated circuit (233) includes a CPU (235) capable of executing a control operation in a predetermined procedure, and a ROM (ROM) for storing operation program data of the CPU (235). 236) and a RAM (237) capable of writing and reading necessary data. Further, the integrated circuit (233) receives an input signal, provides input data to the CPU (235), and receives an output signal from the CPU (235) and outputs the same to the outside, and an input / output interface (238) not shown. Includes a power-on reset circuit, a clock generation circuit, a pulse divider circuit (interrupt pulse generation circuit), and an address decoder circuit. The CPU (235) can execute the operation of the interrupt control routine according to the interrupt pulse periodically given from the pulse divider circuit. The address decode circuit decodes address data from the CPU (235) and supplies signals to the ROM (236), the RAM (237), and the input / output interface (238). A plurality of (eight in the figure) contact terminals (234) are connected to the input / output interface (238), and predetermined data from the dedicated printer (reader / writer) is input from the contact terminals (234). The data is input to the CPU (235) via the output interface (238). The CPU (235) performs each operation in response to the input signal and according to the program data stored in the ROM (236), and transmits predetermined data and signals to the card via the input / output interface (238). Output to reader / writer.
[0138]
As shown in FIG. 6B, the RAM (237) includes a plurality of storage areas (239a) to (239f). For example, the area (239a) stores a card number, the (239b) stores ID data such as the name, address, and telephone number of the card owner, and the area (239c) can be used by the owner, for example. Information corresponding to the remaining valuables or valuables is stored, and information corresponding to the used valuables or valuables is stored in the areas (239d), (239e), (239f), and (239g).
[0139]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. In addition, all parts and% here are on a weight basis.
[0140]
Example 1
On a transparent PET (polyethylene terephthalate: HSL-188, manufactured by Teijin Limited) film having a thickness of 188 μm, an Al layer having a thickness of about 500 mm was formed as a light reflecting layer by vacuum evaporation. On a support provided with an adhesive layer of a vinyl chloride-vinyl acetate-phosphate ester copolymer (manufactured by Denki Kagaku Kogyo Co., Ltd., # 1000P),
3.7 parts of vinyl chloride-vinyl acetate copolymer
(Denka vinyl MT2 manufactured by Denki Kagaku Kogyo Co., Ltd.)
0.5 parts of behenic acid (manufactured by Miyoshi Oil & Fat Co., Ltd., behenic acid 95)
0.5 parts of eicosane diacid (SL-20-99, manufactured by Okamura Oil Co., Ltd.)
23.9 parts of THF (manufactured by Kanto Chemical Co., Ltd.)
2.7 parts of n-pentyl alcohol (Tokyo Kasei)
Was applied with a wire bar and dried by heating to form a heat-sensitive layer having a thickness of 10 μm. Further on this,
13.4 parts of urethane acrylate UV curable resin
75% butyl acetate solution
(Unidick C7-157 manufactured by Dainippon Ink and Chemicals, Inc.)
Carboxyl group-modified methacrylate (manufactured by Nippon Kayaku Co., Ltd., SA) 5.0 parts
Isopropyl alcohol 10.0 parts
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0141]
Example 2
On the same support as in Example 1
3.3 parts of vinyl chloride-vinyl acetate copolymer
(Denka vinyl MT2 manufactured by Denki Kagaku Kogyo Co., Ltd.)
0.5 parts of behenic acid (manufactured by Miyoshi Oil & Fat Co., Ltd., behenic acid 95)
0.5 parts of eicosane diacid (SL-20-99, manufactured by Okamura Oil Co., Ltd.)
0.2 parts of C4-782 (Dainippon Ink Co., Ltd., Unidick C4-782)
0.2 parts of crosslinking agent
(Kayarad DPCA-120, manufactured by Nippon Kayaku Co., Ltd.)
23.9 parts of THF (manufactured by Kanto Chemical Co., Ltd.)
2.7 parts of n-pentyl alcohol (Tokyo Kasei)
Was applied with a wire bar, dried by heating, and then cured with a 120 W / cm ultraviolet lamp to form a heat-sensitive layer having a thickness of about 10.0 μm. Further, the protective layer of Example 1 was formed thereon to form a reversible thermosensitive recording medium.
[0142]
Example 3(Reference example)
On the heat-sensitive layer of Example 1
6.0 parts of vinylidene chloride-acrylonitrile copolymer
(Saran resin R202, manufactured by Asahi Kasei Corporation)
THF (Kanto Chemical) 30.0 parts
Toluene (Maruzen Oil Co., Ltd.) 6.0 parts
Was applied and dried by heating to form a barrier layer having a thickness of 6 μm. In addition,
10.0 parts of urethane acrylate UV curable resin
75% butyl acetate solution (Dainippon Ink Co., Ltd., Unidick C7-157)
Isopropyl alcohol 10.0 parts
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0143]
Example 4
On the heat-sensitive layer of Example 1
5.0 parts of vinylidene chloride-acrylonitrile copolymer
(Saran resin R202, manufactured by Asahi Kasei Corporation)
Carboxyl group-modified epoxy acrylate (Shin Nakamura Chemical Co., Ltd.) 1.0 part
THF (Kanto Chemical) 30.0 parts
Toluene (Maruzen Oil Co., Ltd.) 6.0 parts
Was applied, dried by heating, and then cured with a 120 W / cm ultraviolet lamp to form a barrier layer of about 3.0 μm. In addition,
13.4 parts of urethane acrylate UV curable resin
75% butyl acetate solution
(Unidick C7-157 manufactured by Dainippon Ink and Chemicals, Inc.)
Carboxyl group-modified epoxy acrylate (Shin Nakamura Chemical Co., Ltd.) 5.0 parts
Isopropyl alcohol 10.0 parts
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0144]
Example 5
A reversible thermosensitive recording medium was prepared by laminating an OP layer of about 2.0 μm on the reversible thermosensitive recording medium of Example 1.
Example 6
A reversible thermosensitive recording medium in which the support of Example 2 was made of transparent 50 μm PET was prepared.
[0145]
Example 7
On the heat-sensitive layer of Example 1,
Dipentaerythritol hexaacrylate 6 parts
(DPHA, manufactured by Nippon Kayaku)
Carboxyl group-modified acrylate (CB-1 manufactured by Shin-Nakamura Chemical Co., Ltd.) 6 parts
Irgacure 184 (Nippon Ciba Geigy) 0.06 parts
20 parts of isopropyl alcohol
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0146]
Example 8
On the heat-sensitive layer of Example 1,
Dipentaerythritol hexaacrylate 4 parts
(DPHA, manufactured by Nippon Kayaku)
Carboxyl group modified epoxy acrylate 4 parts
(3000SA manufactured by Kyoeisha Chemical Co., Ltd.)
Carboxyl group modified ester acrylate 4 parts
(CBX-1 manufactured by Shin-Nakamura Chemical Co., Ltd.)
Irgacure 184 (Nippon Ciba Geigy) 0.06 parts
20 parts of isopropyl alcohol
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0147]
Example 9
On the heat-sensitive layer of Example 1,
Dipentaerythritol hexaacrylate 4 parts
(DPHA, manufactured by Nippon Kayaku)
Urethane acrylate (Shin-Nakamura Chemical Co., Ltd., U-324HA) 1 copy
Carboxyl group-modified epoxy acrylate 2 parts
(3000SA manufactured by Kyoeisha Chemical Co., Ltd.)
Carboxyl group modified ester acrylate 2 parts
(CBX-1 manufactured by Shin-Nakamura Chemical Co., Ltd.)
1 part of carboxyl group-modified acrylate (CB-1 manufactured by Shin-Nakamura Chemical Co., Ltd.)
Irgacure 184 (Nippon Ciba Geigy) 0.06 parts
20 parts of isopropyl alcohol
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0148]
Comparative Example 1
On a transparent PET (HSL-188, Teijin Limited) film having a thickness of 188 μm, an Al layer having a thickness of about 500 ° was formed as a light reflecting layer by vacuum evaporation. On a support provided with an adhesive layer of a vinyl chloride-vinyl acetate-phosphate ester copolymer (manufactured by Denki Kagaku Kogyo Co., Ltd., # 1000P),
3.7 parts of vinyl chloride-vinyl acetate copolymer
(Denka vinyl MT2 manufactured by Denki Kagaku Kogyo Co., Ltd.)
0.5 parts of behenic acid (manufactured by Miyoshi Oil & Fat Co., Ltd., behenic acid 95)
0.5 parts of eicosane diacid (SL-20-99, manufactured by Okamura Oil Co., Ltd.)
23.9 parts of THF (manufactured by Kanto Chemical Co., Ltd.)
2.7 parts of n-pentyl alcohol (Tokyo Kasei)
Was applied with a wire bar and dried by heating to form a heat-sensitive layer having a thickness of 10 μm. Further on this,
10.0 parts of urethane acrylate UV curable resin
75% butyl acetate solution
(Unidick C7-157 manufactured by Dainippon Ink and Chemicals, Inc.)
Isopropyl alcohol 10.0 parts
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0149]
Comparative Example 2
On the heat-sensitive layer of Comparative Example 1,
15.0 parts of ethylene-vinyl acetate copolymer
THF (Kanto Chemical) 30.0 parts
Toluene (Maruzen Oil Co., Ltd.) 6.0 parts
Was applied by a wire bar and dried by heating to form a barrier layer having a thickness of 2.0 μm. Further, a protective layer similar to that of Comparative Example 1 was formed thereon, and a reversible thermosensitive recording medium was formed.
[0150]
Comparative Example 3
A reversible thermosensitive recording medium of Comparative Example 1 having a protective layer thickness of 7 μm was prepared.
Comparative Example 4
On the heat-sensitive layer of Example 1,
Carboxyl group modified epoxy acrylate 6 parts
(3000SA manufactured by Kyoeisha Chemical Co., Ltd.)
Carboxyl group modified ester acrylate 6 parts
(CBX-1 manufactured by Shin-Nakamura Chemical Co., Ltd.)
Irgacure 184 (Nippon Ciba Geigy) 0.06 parts
20 parts of isopropyl alcohol
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0151]
Comparative Example 5
On the heat-sensitive layer of Example 1,
Dipentaerythritol hexaacrylate 4 parts
(DPHA, manufactured by Nippon Kayaku)
Carboxyl group-modified acrylate (Shin-Nakamura Chemical Co., Ltd., CB-1) 8 parts
Irgacure 184 (Nippon Ciba Geigy) 0.06 parts
20 parts of isopropyl alcohol
Was applied with a wire bar, dried by heating, and then cured with an ultraviolet lamp of 120 W / cm to prepare a reversible thermosensitive recording medium having a protective layer of about 3.0 μm formed thereon.
[0152]
For the reversible thermosensitive recording medium prepared as described above, NH₃Table 1 shows the results of measuring the print density change rate after the exposure method. The print density of the sample of Example 6 was measured by the print density measurement method for the transparent film support.
[0153]
[Table 1]

Note) Example 3 is a reference example.
[0154]
【The invention's effect】
As is clear from the detailed and specific description above, the reversible thermosensitive recording medium of the present invention has no deterioration in print density even after long-term storage, and has excellent visibility.
[Brief description of the drawings]
FIG. 1 is a diagram showing a change in transparency due to heat of a heat-sensitive layer according to the present invention.
FIG. 2 is a diagram showing a change in color density due to heat of a recording layer according to the present invention.
FIG. 3 is a diagram illustrating one configuration example of a reversible thermosensitive recording medium according to the present invention.
FIG. 4 is a diagram illustrating another configuration example of the reversible thermosensitive recording medium according to the present invention.
FIG. 5 is a diagram illustrating still another configuration example of the reversible thermosensitive recording medium according to the present invention.
FIG. 6 is a diagram illustrating still another configuration example of the reversible thermosensitive recording medium according to the present invention.
[Explanation of symbols]
11 Support
12 Aluminum reflective layer
13 Reversible thermosensitive recording layer
14 Protective layer
15 Transparent PET film
16 air layer
17 Adhesive layer
20 Magnetic coating layer
21 Card
22 Rewriting recording section
23 Depression for IC chip
24 Label processing of rewrite recording section
231 wafer
232 wafer substrate
233 Integrated Circuit
234 contact terminal
235 CPU
236 ROM
237 RAM
238 I / O interface
239 Information on RAM storage area

Claims (18)

A heat-sensitive layer whose main component is a resin base material on a support and an organic low-molecular substance dispersed in the resin base material, and at least a protective layer on the heat- sensitive layer whose transparency reversibly changes depending on temperature, and In the provided reversible thermosensitive recording medium, the thermosensitive layer contains at least one kind of organic low-molecular substance having an acidic functional group, and at least one layer on the thermosensitive layer has an acid value of 60 to 120 mgKOH / g. reversible thermosensitive recording medium characterized that you containing at least one polymeric material having an acidic functional group is. The reversible thermosensitive recording medium according to claim 1, wherein the polymer material has an acid value of 80 to 100 mgKOH / g . 3. The reversible thermosensitive recording medium according to claim 1 , wherein the polymer material is obtained from an acrylate monomer, a methacrylate monomer or an oligomer . The reversible thermosensitive recording medium according to any one of claims 1 to 3, wherein the layer containing the polymer material is a protective layer . Reversible thermosensitive recording medium according to any one of claims 1 to 4 NH ₃ exposure test printing density change rate of the reversible thermosensitive recording medium is characterized in der Rukoto 100% or less. Reversible thermosensitive recording medium according to any one of claims 1 to 5, characterized in der Rukoto those resin contained in the thermosensitive layer is cross-linked by irradiation. The reversible thermosensitive recording medium according to any one of claims 1 to 6, wherein at least one of a printing layer and a transparent layer is provided on the protective layer . The reversible thermosensitive recording medium according to any one of claims 1 to 7, wherein an intermediate layer is provided between the thermosensitive layer and the protective layer . 9. The reversible thermosensitive recording medium according to claim 1, wherein the protective layer has a glass transition temperature of 140 [deg.] C. or higher. The reversible thermosensitive recording medium according to any one of claims 1 to 9, wherein a total thickness of the layers on the thermosensitive layer is 5 µm or more . The reversible thermosensitive recording medium according to any one of claims 1 to 10, wherein at least one main layer of the polymer material on the thermosensitive layer is a crystalline polymer material . The reversible thermosensitive recording medium according to any one of claims 1 to 11 , further comprising an information storage unit . The information storage unit is a magnetic storage unit, and the magnetic recording layer is provided on the entire surface or a part between the support and the thermosensitive layer, the entire back surface or a part of the support, or a magnetic stripe is provided on a part of the display surface. The reversible thermosensitive recording medium according to claim 12 , wherein: 14. The reversible thermosensitive recording medium according to claim 12, wherein the information storage unit is based on an IC, an optical memory, or barcode information and is provided in a part of the medium. The reversible thermosensitive recording medium according to any one of claims 1 to 14, wherein a support in which two or more sheets are laminated is used. An image forming and erasing method, comprising: forming an image and / or erasing the reversible thermosensitive recording medium according to any one of claims 1 to 15 by heating . The heated thermal head, the image forming and erasing method according to claim 16, wherein the performing using one or even no less Les Za. 17. The image forming / erasing method according to claim 16, wherein the image erasing is performed using at least one of a thermal head, a ceramic heater, a hot stamp, a heat block, and a laser.

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