JP3544431B2 - Reversible thermosensitive recording material - Google Patents

Description

【００１２】
式（１）中、Ｒ¹〜Ｒ⁴は同じでも異なっていてもよく、それぞれアルキル基、アルケニル基、シクロアルキル基、アラルキル基、アリール基、複素環残基を示し、また、Ｒ¹〜Ｒ⁴から選ばれる任意の２個の基は互いに連結して環状構造を形成していてもよい。Ｘ^-はアニオンを示す。
【００１３】
【化５】

【００１４】
式（２）中、Ｒ⁵〜Ｒ⁷は同じでも異なっていてもよく、それぞれアルキル基、アルケニル基、シクロアルキル基、アラルキル基、アリール基、複素環残基を示し、また、Ｒ⁵〜Ｒ⁷から選ばれる任意の２個の基は互いに連結して環状構造を形成していてもよい。Ｙ^-はアニオンを示す。
【００１５】
【発明の実施の態様】
本発明に用いる消色促進剤は上記一般式（１）または（２）で表されるオニウム塩で、Ｒ¹〜Ｒ⁴およびＲ⁵〜Ｒ⁷のいずれか一つに炭素数１０以上２４以下の長鎖アルキル基を持つものが特に好ましい。また、Ｘ^-およびＹ^-はそれぞれアニオンであるが、ハロゲン、スルホン酸アニオン、置換ボレート、置換ホスフェート、置換アルゼナート、置換アンチモネートが好ましい。
【００１６】
一般式（１）または（２）の化合物の好ましい添加量は染料前駆体に対し０．０５重量％以上１００重量％以下である。これ未満では効果が十分でなくこれを超えると画像の耐熱保存性又は消色性のいずれかに悪影響が出る可能性が有る。
【００１７】
一般式（１）または（２）で表される化合物の具体例を以下に示すが本発明はこれに限定されない。また、これらの化合物は１種または２種以上併用して用いられる。これらの化合物は例えばChem. Ber. 122, 113(1989)、Synthesis 155(1989)、または特開平２−２６８１６３号公報に記載の方法や以下の実施例に示すアルキル化法により容易に合成できる。
【００１８】
【化６】

【００１９】
【化７】

【００２０】
【化８】

【００２１】
これらの化合物の具体的製造方法についてその一部を以下に例示する。
【００２２】
例示化合物（１）−１の合成法
トリフェニルホスフィン８．５９ｇと臭化n−ヘキサデシル１０ｇを窒素気流中、浴温１８０℃で１０時間加熱した。放冷後、析出した固体を砕きアセトンにて洗浄した。収量８．４８ｇ（mp. １２５〜１２８℃）。
【００２３】
例示化合物（１）−２の合成法
テトラメチルアンモニウムハイドロキサイド（１０％メタノール溶液）９１．２ｇに氷水で冷却下濃塩酸１２ｇを 加え、メタノールを減圧溜去し、残渣をエタノール２００ｍｌに溶かし、不溶物を瀘取した後エタノールを減圧溜去し、テトラメチルアンモニウムクロリド１１．５ｇを無色固体として得た。
ナトリウムテトラフェニルボレート７．２３ｇをアセトニトリル２８０ｍｌに溶かし、上記の粗製クロライド１１．５ｇをアセトニトリル７０ｍｌに溶かして混合した。析晶を瀘取し水洗乾燥し、テトラメチルアンモニウムテトラフェニルボレート７．９５ｇを無色固体として得た。mp. ２９０℃以上。
トリフェニルヘキサデシルホスホニウムブロマイド２．０ｇをエタノール４０ｍｌにとかし、テトラメチルアンモニウムテトラフェニルボレート１．５９ｇを加えた。１５分水浴上で加熱後、水８０ｍｌを加え、瀘取。水洗後乾燥する。収量１．６ｇ（mp. ３００℃以上）。
【００２４】
例示化合物（２）−１の合成法。
攪拌機を付けたフラスコ内に、n-オクタデカンチオール５．７ｇ、ナトリウムメトキサイド１．２ｇ、メタノール３０ｍｌを仕込み、６０℃の油浴上で１０分間攪拌した。そこにヨウ化メチル３．０ｇを滴加した。そのまま３０分間攪拌した後、反応混合物を水に投入し、析出した結晶を減圧下濾別し、無色の固体としてメチルオクタデシルスルフィド６ｇを得た。
粗製メチルオクタデシルスルフィド３．０ｇ、ヨウ化メチル２．１ｇ、アセトン５０ｍｌを攪拌機を付けたフラスコに仕込み、室温で一昼夜攪拌した。析出した結晶を減圧下濾別し、アセトンから再結晶した。収量３．４ｇ（mp. ８２．５℃）。
【００２５】
一方、本発明に用いられる可逆性顕色剤はフェノール系の電子受容性化合物が好ましく、電子供与性染料前駆体の共存下の加熱により可逆的な色調変化を生じるものであれば特に限定されないが、発色濃度や消色性の点で下記一般式（３）で表されるものが特に好ましい結果を与えた。また、下記一般式（３）の化合物と同様の特性化合物であれば本発明の方法に用いる事が出来る。尚、一般式（３）の化合物は特開平６−２１０９５４号、特願平５−１６０５４７号、特願平５−２５６８２５号、特願平５−３１７５５５号、特願平５−３２８１０１号及び特願平６−１０３１０号に記載している。
【００２６】
【化９】

【００２７】
式（３）中、ｎは１から３の整数、ｊ、ｋ及びｌは各々０または１を表す。但し、ｊが１の場合、ｋは１を示す。Ｒ⁸及びＲ⁹は炭素数１から１８の二価の炭化水素基、Ｒ¹⁰は炭素数１から２４の炭化水素基を表す。Ｌ¹は−ＣＯＮＨ−結合を少なくとも１つ以上持つ二価の基を表し、Ｌ²は−ＣＯＮＨ−結合を少なくとも１つ以上持つ二価の基、酸素原子或いは硫黄原子を表す。
【００２８】
また、上記一般式（３）で表される化合物中、Ｒ⁸及びＲ⁹は炭素数１から１８の二価の炭化水素基であるが、基中に芳香環を含んでもよく、また芳香環のみであってもよい。Ｌ¹及びＬ²で示される−ＣＯＮＨ−結合を少なくとも一つ以上持つ二価の基とは、具体例にはアミド（−ＣＯＮＨ−、−ＮＨＣＯ−）、尿素（−ＮＨＣＯＮＨ−）、ウレタン（−ＮＨＣＯＯ−、−ＯＣＯＮＨ−）、ジアシルアミン（−ＣＯＮＨＣＯ−）、ジアシルヒドラジド（−ＣＯＮＨＮＨＣＯ−）、しゅう酸ジアミド（−ＮＨＣＯＣＯＮＨ−）、アシル尿素（−ＣＯＮＨＣＯＮＨ−、−ＮＨＣＯＮＨＣＯ−）、３−アシルカルバジド酸エステル（−ＣＯＮＨＮＨＣＯＯ−）、セミカルバジド（−ＮＨＣＯＮＨＮＨ−、−ＮＨＮＨＣＯＮＨ−）、アシルセミカルバジド（−ＣＯＮＨＮＨＣＯＮＨ−、−ＮＨＣＯＮＨＮＨＣＯ−）、ジアシルアミノメタン（−ＣＯＮＨＣＨ₂ＮＨＣＯ−）、１−アシルアミノ−１−ウレイドメタン（−ＣＯＮＨＣＨ₂ＮＨＣＯＮＨ−、−ＮＨＣＯＮＨＣＨ₂ＮＨＣＯ−）、マロンアミド（−ＮＨＣＯＣＨ₂ＣＯＮＨ−）等の基である。
【００２９】
一般式（３）で表される電子受容性化合物は、ロイコ染料を発色させる能力を持ち、さらに温度によっては特異的に消色効果、すなわち可逆効果も持ち合わせている。なお、通常の感熱記録材料に用いている電子受容性化合物、即ち、２，２−ビス（４−ヒドロキシフェニル）プロパン、ビス（４−ヒドロキシフェニル）スルホン、４−ヒドロキシ安息香酸ベンジル等ではこのような可逆効果は全く見られない。以下に、一般式（３）で示される電子受容性化合物の具体例を挙げるが、本発明はこれに限定されるものではない。
【００３０】
例えば、式（３）中、ｊ＝０／ｋ＝０／ｌ＝０である化合物としては、４′−ヒドロキシヘキサデカンアニリド、Ｎ−オクタデシル−４−ヒドロキシベンズアミド、Ｎ−（４−ヒドロキシフェニル）−Ｎ´−オクタデシル尿素、Ｎ−（４−ヒドロキシベンゾ）−Ｎ´−オクタデカノヒドラジド、Ｎ−（３，４−ジヒドロキシフェニル−Ｎ´−オクタデシルオキサミド等、
【００３１】
式（３）中、ｊ＝０／ｋ＝１／ｌ＝０である化合物としては、Ｎ−〔２−（４−ヒドロキシフェニル）エチル〕−Ｎ´−オクタデシル尿素、Ｎ−〔３−（４−ヒドロキシフェニル）プロピオノ〕−Ｎ´−オクタデカノヒドラジド、Ｎ−〔３−（４−ヒドロキシフェニル）プロピオノ〕−Ｎ´−ドコサノヒドラジド、１−〔３−（４−ヒドロキシフェニル）プロピオニル〕アミノ−１−オクタデカノイルアミノメタン、１−（４−ヒドロキシフェニルアセチル）−４−オクタデシルセミカルバジド等、
【００３２】
式（３）中、ｊ＝１／ｋ＝１／ｌ＝０である化合物としては、Ｎ−ヘキサデシル−（４−ヒドロキシフェニルチオ）アセトアミド、Ｎ−〔２−（４−ヒドロキシフェニルチオ）エチル〕−Ｎ´−オクタデシル尿素、Ｎ−（４−ヒドロキシフェニルチオ）アセト−Ｎ´−ドコサノヒドラジド、Ｎ−〔１１−（４−ヒドロキシフェニルチオ）ウンデカノ〕−Ｎ´−デカノヒドラジド、Ｎ−〔２−（４−ヒドロキシフェニルチオ）エチル〕−Ｎ´−オクタデシルオキサミド、Ｎ−〔４−（４−ヒドロキシフェニルチオ）フェニル〕−Ｎ´−オクタデシルオキサミド、Ｎ−〔４−（４−ヒドロキシフェニルチオメチル）ベンゾ〕−Ｎ´−ドコサノヒドラジド等、
【００３３】
式（３）中、ｊ＝０／ｋ＝０／ｌ＝１である化合物としては、Ｎ−（４−ヒドロキシフェニル）−３−ドデシルチオプロパンアミド、Ｎ−（４−ヒドロキシフェニル）−Ｎ´−３−オクタデシルチオプロピル尿素、４−ヒドロキシ−４´−オクタデシルオキシベンズアニリド、４−ヒドロキシ−４´−ドデシルチオベンズアニリド、２−（４−オクタデカノイルアミノフェニル）−４´−ヒドロキシアセトアニリド、２−〔４−（Ｎ´−オクタデシルウレイド）フェニル〕−４´−ヒドロキシアセトアニリド等、
【００３４】
式（３）中、ｊ＝０／ｋ＝１／ｌ＝１である化合物としては、Ｎ−〔３−（４−ヒドロキシフェニル）プロピオノ〕−Ｎ´−（３−ドデシルチオプロピオノ）ヒドラジド、Ｎ−〔３−（３，４−ジヒドロキシフェニル）プロピオノ〕−Ｎ´−（１１−デシルチオウンデカノ）ヒドラジド等、
【００３５】
式（３）中、ｊ＝１／ｋ＝１／ｌ＝１である化合物としては、Ｎ−〔３−（４−ヒドロキシフェニルチオ）プロピオノ〕−Ｎ´−（３−オクタデシルチオプロピオノ）ヒドラジド、Ｎ−〔１１−（３，４，５−トリヒドロキシフェニルチオ）ウンデカノ〕−Ｎ´−（１１−オクタデシルチオウンデカノ）ヒドラジド等が挙げられる。
【００３６】
これらの可逆性顕色剤は単独でもよいが、２種以上を併用することもでき、染料前駆体に対する可逆性顕色剤の使用量は、５〜５０００重量％、好ましくは１０〜３０００重量％である。
【００３７】
本発明に用いられる電子供与性染料前駆体は一般に感圧記録紙や感熱記録紙等に用いられる公知な化合物で代表されるが、特に制限されるものではない。具体的な例としては、例えば下記に挙げるものなどがあるが、本発明はこれに限定されるものではない。
【００３８】
（１）トリアリールメタン系化合物
３，３−ビス（ｐ−ジメチルアミノフェニル）−６−ジメチルアミノフタリド（クリスタルバイオレットラクトン）、３，３−ビス（ｐ−ジメチルアミノフェニル）フタリド、３−（ｐ−ジメチルアミノフェニル）−３−（１，２−ジメチルインドール−３−イル）フタリド、３−（ｐ−ジメチルアミノフェニル）−３−（２−メチルインドール−３−イル）フタリド、３−（ｐ−ジメチルアミノフェニル）−３−（２−フェニルインドール−３−イル）フタリド、３，３−ビス（１，２−ジメチルインドール−３−イル）−５−ジメチルアミノフタリド、３，３−ビス（１，２−ジメチルインドール−３−イル）−６−ジメチルアミノフタリド、３，３−ビス（９−エチルカルバゾール−３−イル）−５−ジメチルアミノフタリド、３，３−ビス（２−フェニルインドール−３−イル）−５−ジメチルアミノフタリド、３−ｐ−ジメチルアミノフェニル−３−（１−メチルピロール−２−イル）−６−ジメチルアミノフタリド等。
【００３９】
（２）ジフェニルメタン系化合物
４，４′−ビス（ジメチルアミノフェニル）ベンズヒドリルベンジルエーテル、Ｎ−クロロフェニルロイコオーラミン、Ｎ−２，４，５−トリクロロフェニルロイコオーラミン等。
【００４０】
（３）キサンテン系化合物
ローダミンＢアニリノラクタム、ローダミンＢ−ｐ−クロロアニリノラクタム、３−ジエチルアミノ−７−ジベンジルアミノフルオラン、３−ジエチルアミノ−７−オクチルアミノフルオラン、３−ジエチルアミノ−７−フェニルフルオラン、３−ジエチルアミノ−７−クロロフルオラン、３−ジエチルアミノ−６−クロロ−７−メチルフルオラン、３−ジエチルアミノ−７−（３，４−ジクロロアニリノ）フルオラン、３−ジエチルアミノ−７−（２−クロロアニリノ）フルオラン、
【００４１】
３−ジエチルアミノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−エチル−Ｎ−トリル）アミノ−６−メチル−７−アニリノフルオラン、３−ピペリジノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−エチル−Ｎ−トリル）アミノ−６−メチル−７−フェネチルフルオラン、３−ジエチルアミノ−７−（４−ニトロアニリノ）フルオラン、３−ジブチルアミノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−メチル−Ｎ−プロピル）アミノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−エチル−Ｎ−イソアミル）アミノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−メチル−Ｎ−シクロヘキシル）アミノ−６−メチル−７−アニリノフルオラン、３−（Ｎ−エチル−Ｎ−テトラヒドロフリル）アミノ−６−メチル−７−アニリノフルオラン等。
【００４２】
（４）チアジン系化合物
ベンゾイルロイコメチレンブルー、ｐ−ニトロベンゾイルロイコメチレンブルー等。
【００４３】
（５）スピロ系化合物
３−メチルスピロジナフトピラン、３−エチルスピロジナフトピラン、３，３′−ジクロロスピロジナフトピラン、３−ベンジルスピロジナフトピラン、３−メチルナフト−（３−メトキシベンゾ）スピロピラン、３−プロピルスピロベンゾピラン等。
【００４４】
上記染料前駆体は単独でも、２種以上を併用してもよい。
【００４５】
本発明の可逆性感熱記録材料の製造方法の具体例としては、染料前駆体と可逆性顕色剤を主成分とし、更に、本発明の消色促進剤を添加し、これを支持体上に塗布して可逆性感熱記録層を形成する方法が挙げられる。
【００４６】
染料前駆体と可逆性顕色剤及び本発明の化合物を可逆性感熱記録層に含有させるための塗液は、各々の化合物を単独で溶媒に溶解もしくは分散媒に分散してから混合する方法、各々の化合物を混ぜ合わせてから溶媒に溶解もしくは分散媒に分散する方法、各々の化合物を加熱溶解し均一化した後冷却し、溶媒に溶解もしくは分散媒に分散する方法等があるが、特に指定はない。また、分散の際に必要なら分散助剤を使用してもよい。分散媒として水を使うときの分散助剤としてはポリビニルアルコール等の水溶性高分子や各種の界面活性剤が挙げられる。また、エタノール等の水溶性有機溶媒を混合してもよい。また、炭化水素類に代表される有機溶媒を分散媒として使う場合は、レシチンや燐酸エステル類等を分散剤に用いてもよい。
【００４７】
また、可逆性感熱記録層の強度を向上する等の目的でバインダーを可逆性感熱記録層中に添加する事も可能である。バインダーの具体例としては、デンプン類、ヒドロキシエチルセルロース、メチルセルロース、カルボキシメチルセルロース、ゼラチン、カゼイン、ポリビニルアルコール、変性ポリビニルアルコール、ポリアクリル酸ソーダ、アクリル酸アミド／アクリル酸エステル共重合体、アクリル酸アミド／アクリル酸エステル／メタクリル酸３元共重合体、スチレン／無水マレイン酸共重合体のアルカリ塩、エチレン／無水マレイン酸共重合体のアルカリ塩等の水溶性高分子、ポリ酢酸ビニル、ポリウレタン、ポリアクリル酸エステル、スチレン／ブタジエン共重合体、アクリロニトリル／ブタジエン共重合体、アクリル酸メチル／ブタジエン共重合体、エチレン／酢酸ビニル共重合体、エチレン／塩化ビニル共重合体、ポリ塩化ビニル、エチレン／塩化ビニリデン共重合体、ポリ塩化ビニリデン等のラテックスなどがあげられるが特にこれらに限定されるものではない。
【００４８】
また、可逆感熱記録層の発色感度を調節するための添加剤として、熱溶媒を可逆性感熱記録層中に含有させることもできる。これらの化合物は６０℃〜２００℃の融点を有するものが好ましく、特に８０℃〜１８０℃の融点の化合物が良い結果を与えた。この他に一般の感熱記録紙に用いられている増感剤を使用することもできる。これらの化合物としては、Ｎ−ヒドロキシメチルステアリン酸アミド、ベヘン酸アミド、ステアリン酸アミド、パルミチン酸アミドなどのワックス類、２−ベンジルオキシナフタレン等のナフトール誘導体、ｐ−ベンジルビフェニル、４−アリルオキシビフェニル等のビフェニル誘導体、１，２−ビス（３−メチルフェノキシ）エタン、２，２′−ビス（４−メトキシフェノキシ）ジエチルエーテル、ビス（４−メトキシフェニル）エーテル等のポリエーテル化合物、炭酸ジフェニル、シュウ酸ジベンジル、シュウ酸ビス（ｐ−メチルベンジル）エステル等の炭酸またはシュウ酸ジエステル誘導体等があげられ、２種以上併用して添加することもできる。
【００４９】
本発明の可逆感熱記録材料の支持体としては、紙、各種不織布、織布、ポリエチレンテレフタレートやポリプロピレン等の合成樹脂フィルム、ポリエチレン、ポリプロピレン等の合成樹脂をラミネートした紙、合成紙、金属箔、ガラス等、あるいはこれらを組み合わせた複合シートを目的に応じて任意に用いることができるが、これらに限定されず、不透明、半透明或いは透明の指示体なら利用できる。地肌を白色その他の特定の色に見せるために、白色顔料や有色染顔料や気泡を支持体中又は表面に含有させても良い。特にフィルム類等に水性の液を塗布する場合において支持体の親水性が小さく可逆性感熱記録層の塗布困難な場合は、コロナ放電等による表面の親水化処理やバインダーに用いるのと同様の水溶性高分子類を、支持体表面に塗布するなどの処理も効果がある。
【００５０】
本発明の可逆感熱記録材料の層構成は、可逆性感熱記録層のみであっても良い。必要に応じて、可逆性感熱記録層上に保護層や、可逆感熱記録層と支持体の間に水溶性高分子や白色ないし有色染顔料や中空粒子のいずれか一つ以上を含む中間層を設けることもできる。この場合、保護層および／または中間層は２層ないしは３層以上の複数の層で構成されていてもよい。可逆性感熱記録層も各成分を一層ずつに含有させたり層別に配合比率を変化させたりして２層以上の多層にしてもよい。更に、可逆性感熱記録層中および／または他の層および／または可逆性感熱記録層が設けられている面と反対側の面に、電気的、光学的、磁気的に情報が記録可能な材料を含んでも良い。また、可逆性感熱記録層が設けられている面と反対側の面にブロッキング防止、カール防止、帯電防止を目的としてバックコート層を設けることもできる。
【００５１】
なお、本発明における各層を支持体上に積層し、本発明の可逆性感熱記録材料を形成する方法は特に制限されるものではなく、従来の方法により形成することができる。例えば、エアーナイフコーター、ブレードコーター、バーコーター、カーテンコーター等の塗抹装置、平版、凸版、凹版、フレキソ、グラビア、スクリーン、ホットメルト等の方式による各種印刷機等を用いる事も出来る。さらに通常の乾燥工程の他、ＵＶ照射・ＥＢ照射により各層を保持させる事が出来る。
【００５２】
可逆感熱記録層は、各成分を微粉砕して得られる各々の分散液を混合し、支持体上に塗布乾燥する方法、各成分を溶媒に溶解して得られる各々の溶液を混合し、支持体上に塗布乾燥する方法などにより得ることができる。乾燥条件は水等の分散媒ないし溶媒によっても異なる。この他に各成分を混合し加熱して可融分を溶融し熱時塗布する方法もある。
【００５３】
また、可逆性感熱記録層及び／または保護層及び／または中間層には、ケイソウ土、タルク、カオリン、焼成カオリン、炭酸カルシウム、炭酸マグネシウム、酸化チタン、酸化亜鉛、酸化ケイ素、水酸化アルミニウム、尿素−ホルマリン樹脂等の顔料、その他に、ヘッド摩耗防止、スティッキング防止等の目的でステアリン酸亜鉛、ステアリン酸カルシウム等の高級脂肪酸金属塩、パラフィン、酸化パラフィン、ポリエチレン、酸化ポリエチレン、ステアリン酸アミド、カスターワックス等のワックス類を、また、ジオクチルスルホコハク酸ナトリウム等の分散剤、さらに界面活性剤、蛍光染料などを含有させることもできる。
【００５４】
次に、本発明の可逆性感熱記録材料の発色及び消色方法について述べる。発色を行うには、加熱に引き続き急速な冷却が起これば良く、例えばサーマルヘッド、レーザー光等による加熱が適している。又、加熱後ゆっくり冷却すれば消色がおこる、例えばサーマルヘッド、熱ロール、熱スタンプ、高周波加熱、熱風、電熱ヒーター及びタングステンランプ、ハロゲンランプ等の光源などからの輻射熱等を用いることにより消去可能である。
【００５５】
【作用】
本発明の感熱記録材料の画像形成及び消去の機構は明確ではないが、以下の様に考えられる。通常無色ないし淡色の染料前駆体は、フェノール性化合物のような電子受容性化合物と共に加熱すると染料前駆体から電子受容性化合物への電子移動が起こり発色する。この時、電子受容性化合物分子は発色した染料分子の極めて近傍に存在していると考えられる。また、発色した染料分子から電子受容性化合物分子を引き離すと、発色した染料分子は再び電子を受け取り、発色前の染料前駆体の状態となる。本発明は加熱により、電子受容性化合物分子と染料分子との距離を変化させ発色及び消色を行うものと考えられる。
【００５６】
さらに詳しく述べるならば、これまでに可逆性顕色剤と呼ばれる電子受容性化合物の多くは、その構造の中に脂肪鎖を持つため、染料前駆体分子および発色した染料分子との相溶性が低く、凝固した状態では互いに殆ど溶け合わないと考えられる。また、加熱溶融状態の様に染料前駆体分子と可逆性顕色剤分子が自由に運動できる状態では、染料前駆体分子と可逆性顕色剤分子は互いにある割合で溶け合い、発色状態となる。それ故、発色している溶融状態の混合物をゆっくり冷却すると、降温するに従い可逆顕色剤分子と染料分子は互いに溶け合わなくり相分離し、消色する。特に、本発明の式化６で表される電子受容性化合物は分子内に、アミド結合等の水素結合能力を持つ結合を含有しているため、分子間水素結合により速やかに結晶化してしまうと考えられる。一方、急速に冷却を行うと、相分離する前、即ち発色状態のままで固化するため、発色状態が固定され固化後も発色状態が安定に保持される。
【００５７】
本発明に於いて用いられる式化４または化５で表される消色促進化合物は、その構造上の特徴によって電子供与性染料前駆体と電子受容性可逆性顕色剤の相分離時に、消色現象をより加速しているものと考えられるが詳細は未だ明らかではない。

【００５８】
【実施例】
次に実施例を用いて本発明の方法を更に詳しく説明する。実施例中の部数や百分率は重量基準である。
【００５９】
実施例１
（Ａ）可逆性感熱塗液の作成
３−ジエチルアミノ−６−メチル−７−アニリノフルオラン４０部を２.５％ポリビニルアルコール水溶液９０部と共にペイントコンディショナーで粉砕し、染料前駆体分散液（Ａ液）を得た。次いで３−（４−ヒドロキシフェニル）プロパノイル−ドコサノイックヒドラジド２００部を１.２５％ポリビニルアルコール水溶液４００部と共にペイントコンディショナーで粉砕し可逆性顕色剤分散液（Ｂ液）を得た。更に、炭酸マグネシウム２０部と０.２％ポリビニルアルコール水溶液４７部を同様に粉砕した（Ｃ液）。又、n−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）１０部を１.２５％ポリビニルアルコール水溶液４０部と共にペイントコンディショナーで粉砕し消色促進剤分散液（Ｄ液）を得た。これらＡ、Ｂ、Ｃ及びＤ液の４種の分散液を混合した後、１０％ポリビニルアルコール水溶液１７０部、水３５０部を添加、よく混合し、可逆性感熱塗液を作成した。
【００６０】
（Ｂ）可逆性感熱記録材料の作成
（Ａ）で調製した可逆性感熱塗液をポリエチレンテレフタレート（ＰＥＴ）シートに、固形分塗抹量２．６ｇ／ｍ²となる様に塗抹乾燥後、その上に５％ポリビニルアルコール水溶液を固形分塗抹量２ｇ／ｍ²となる様に塗抹乾燥し、スーパーカレンダーで処理して可逆性感熱記録材料を得た。
【００６１】
実施例２
実施例１で用いたn−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）のかわりにn−ヘキサデシルトリフェニルホスホニウムテトラフェニルボレート（例示化合物（１）−２）を使用した他は、実施例１と同様にして可逆性感熱記録材料を得た。
【００６２】
実施例３
実施例１で用いたn−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）のかわりにテトラメチルホスホニウムテトラフェニルボレート（例示化合物（１）−３）を使用した他は、実施例１と同様にして可逆性感熱記録材料を得た。
【００６３】
実施例４
実施例１で用いたn−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）のかわりにヨウ化ジメチルオクタデシルスルホニウム（例示化合物（２）−１）を使用した他は、実施例１と同様にして可逆性感熱記録材料を得た。
【００６４】
比較例１
実施例１で用いたn−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）を除いた他は、実施例１と同様にして可逆性感熱記録材料を得た。
【００６５】
比較例２
実施例１で用いたn−ヘキサデシルトリフェニルホスホニウムブロミド（例示化合物（１）−１）のかわりに、ステアリン酸アミドを使用した他は、実施例１と同様にして可逆性感熱記録材料を得た。
【００６６】
試験１（発色濃度＝熱応答性）
実施例１〜４および比較例１、２で得た感熱記録材料を、京セラ製印字ヘッドＫＪＴ−２５６−８ＭＧＦ１付き大倉電気製感熱ファクシミリ印字試験機ＴＨ−ＰＭＤを用いて印加パルス１．１ミリ秒で印加電圧２６ボルトの条件で印字し、得られた発色画像の濃度を濃度計マクベスＲＤ９１８を用いて測定した。結果を表１に示した。
【００６７】
試験２（画像の消去性）
実施例１〜４および比較例１、２で得た感熱記録材料を、京セラ製印字ヘッドＫＪＴ−２５６−８ＭＧＦ１付き大倉電気製感５熱ファクシミリ印字試験機ＴＨ−ＰＭＤを用いて印加パルス１．１ミリ秒で印加電圧２６ボルトの条件で印字し、これを熱スタンプを用いて１００℃で１秒間加熱した後、試験１と同様にして濃度を測定した。結果を表１に示した。
【００６８】
試験３（消色開始温度）
実施例１〜４および比較例１、２で得た感熱記録材料を、京セラ製印字ヘッドＫＪＴ−２５６−８ＭＧＦ１付き大倉電気製感熱ファクシミリ印字試験機ＴＨ−ＰＭＤを用いて印加パルス１．１ミリ秒で印加電圧２６ボルトの条件で印字し、これを熱スタンプを用いて６０℃から１５０℃まで１０℃間隔で計１０箇所、各々１秒間加熱した後、試験１と同様にしてそれぞれの濃度を測定した。印字画像の光学濃度が０.１５を下回った加熱温度を消色開始温度とした。結果を表１に示した。
【００６９】
試験４（発色濃度の経時変化＝画像安定性）
実施例１〜４および比較例１、２で得た感熱記録材料を、京セラ製印字ヘッドＫＪＴ−２５６−８ＭＧＦ１付き大倉電気製感熱ファクシミリ印字試験機ＴＨ−ＰＭＤを用いて、印加パルス１．１ミリ秒で印加電圧２６ボルトの条件で印字し、温度５０℃、相対湿度１０％の雰囲気下に２４時間保存した後、試験１と同様にして、発色部の濃度を測定し、下記数１により画像残存率を計算した。結果を表１に示した。
【００７０】
【数１】
Ａ＝（Ｃ／Ｂ）×１００
Ａ：画像残存率（％）
Ｂ：試験前の画像濃度
Ｃ：試験後の画像濃度
【００７１】
【表１】

【００７２】
【発明の効果】
表１に示したように、通常無色ないし淡色の染料前駆体と、加熱により該染料前駆体に可逆的な色調変化を生じせしめる可逆性顕色剤とを含有する可逆性感熱記録材料において、一般式（１）または（２）の一般式で表される化合物を含有させる事により明瞭なコントラストで画像の形成・消去が可能で、日常生活の環境下で経時的に、より安定な画像を保持可能な可逆性感熱記録材料を得ることができた。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reversible thermosensitive recording material capable of forming and erasing images by controlling thermal energy.
[0002]
[Prior art]
As disclosed in JP-B-43-4160 and JP-B-45-14039, a heat-sensitive recording material comprises an electron-donating, usually colorless or pale-colored dye precursor and an electron-accepting developer on a support. Is a recording material having a thermosensitive recording layer containing as a main component, a leuco dye and a developer react instantaneously by heating with a thermal head, a hot pen, a laser beam or the like to form an image.
[0003]
One of the disadvantages of the above-mentioned type of heat-sensitive recording material is that once an image is formed, that part cannot be erased, and therefore cannot be corrected. Further, recording of additional information is limited to a portion where no image is formed, and if the area of the recording portion is determined in advance, the amount of recordable information is limited.
[0004]
In recent years, reversible thermosensitive recording materials capable of repeatedly forming and erasing images have been devised for the purpose of improving these drawbacks and expanding the uses of thermosensitive recording materials. For example, JP-A-54-119377, JP-A-63-39377, and JP-A-63-41186 describe heat-sensitive recording materials composed of low-molecular organic molecules dispersed in a resin base material. I have. In this method, an image is formed by reversibly changing the transparency of a heat-sensitive recording material due to heat energy. This type of recording material has excellent stability, but on the other hand, the contrast between the image-formed portion and the non-image-formed portion is insufficient, the image is difficult to discriminate, and the residual ratio after erasure is high, and the like. there were.
[0005]
Also, the methods described in JP-A-50-81157 and JP-A-50-105555 have a problem in image stability, and the image forming temperature and the erasing temperature fluctuate. It was difficult to maintain a stable temperature range.
[0006]
Further, JP-A-59-120492 discloses a reversible recording material utilizing the hysteresis characteristic of a color component. In this method, a heating source and a cooling source are required for image formation and erasing, and a temperature region in which image formation and erasing can be maintained is limited to a hysteresis temperature region, which is disadvantageous in a daily temperature environment.
[0007]
On the other hand, JP-A-2-188293, JP-A-2-188294, and International Publication No. WO90 / 11898 disclose a reversible sensation comprising a combination of a leuco dye and a color-degrading agent that causes the leuco dye to develop and decolor the color by heating. A thermal recording medium is described. The color-developing agent is an amphoteric compound having an acidic group for coloring the leuco dye and a basic group for decolorizing the colored leuco dye, and has a color-forming action by an acidic group or a decolorizing action by a basic group by controlling thermal energy. One is preferentially generated to perform color development and decoloration. However, in this method, it is impossible to completely switch between the coloring reaction and the decoloring reaction only by controlling the heat energy, and since both reactions occur at a certain ratio at the same time, a sufficient coloring density cannot be obtained. Can't do it perfectly. Therefore, a sufficient image contrast cannot be obtained. Further, the decolorizing action of the basic group also acts on the color-developed portion at room temperature, and the phenomenon that the density of the color-developed portion decreases with time cannot be avoided. Further, Japanese Patent Application Laid-Open No. 5-124360 describes a reversible thermosensitive recording medium for coloring and decoloring a leuco dye by heating, and as an electron accepting compound, an organic phosphoric acid compound, an α-hydroxy aliphatic carboxylic acid, Specific phenol compounds such as fatty acid dicarboxylic acids and alkylthiophenols having an aliphatic group having 12 or more carbon atoms, alkyloxyphenols, alkylcarbamoylphenols, and alkyl gallic esters are exemplified. However, this recording material also has the disadvantage that the color density is low or the erasing is incomplete for the above reasons. These two problems could not be solved at the same time by examining various conditions. Further, the temporal stability of the image is not satisfactory in practical use. Further, Japanese Patent Application Laid-Open No. Hei 5-294,063 discloses various esters of fatty acids, waxes, higher alcohols, phosphoric acid / benzoic acid / phthalic acid or oxyacids as color erasing accelerators for improving the erasability of the reversible thermosensitive recording medium. , A silicone oil, a liquid crystal compound, a surfactant, and a saturated fatty acid hydrocarbon having 10 or more carbon atoms, but the effect is small, and the image density at the time of erasing is high, which is not practical.
[0008]
As described above, according to the conventional techniques, it is difficult to produce a practical reversible thermosensitive recording material having a clear image contrast, capable of forming a high-density image and completely erasing, and having good stability over time. On the other hand, JP-A-6-210954 describes that a recording material having excellent temporal stability can be produced by combining a reversible developer with an electron-donating dye precursor. As a result of the additional test, it was necessary to greatly improve the image density at the time of erasing, the erasing start temperature, the erasing temperature range, and the like in order to make a practical recording material.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a reversible thermosensitive recording material which forms an image with good contrast, is erasable at a low temperature, has good erasability, and has good stability over time.
[0010]
[Means for Solving the Problems]
The present inventors have proposed a reversible sensitizer containing a colorless or pale-colored dye precursor on a support and a reversible color developer that causes a reversible color change in the dye precursor due to a difference in cooling rate after heating. As a result of intensive studies on a thermal recording material to obtain a recording material having improved erasability without impairing the aging stability of an image, at least one of specific compounds represented by the following general formula (1) or (2) is obtained. By coexisting one type, it has been found that the image can be completely and uniformly erased in a wide temperature range of low temperature without deteriorating the stability over time, and the object of the present invention has been completed.
[0011]
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[0012]
In the formula (1), R ^{1 to} R ⁴ may be the same or different and each represent an alkyl group, an alkenyl group, a cycloalkyl group, an aralkyl group, an aryl group, a heterocyclic residue, and R ^{1 to} R 4 Any two groups selected from ⁴ may be linked to each other to form a cyclic structure. X ^- represents an anion.
[0013]
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[0014]
Wherein (2), R ⁵ ~R ⁷ may be the same or different, each represents an alkyl group, an alkenyl group, a cycloalkyl group, an aralkyl group, an aryl group, a heterocyclic residue, also, R ⁵ to R Any two groups selected from ⁷ may be linked to each other to form a cyclic structure. Y ^- represents an anion.
[0015]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The decoloring accelerator used in the present invention is an onium salt represented by the above general formula (1) or (2), and has ^one of R ^{1 to} R ⁴ and R ^{5 to} R ⁷ having 10 to 24 carbon atoms. Those having a long-chain alkyl group are particularly preferred. X ^- and Y ^- are each anions, and are preferably halogen, sulfonic acid anion, substituted borate, substituted phosphate, substituted arsenate and substituted antimonate.
[0016]
The preferable addition amount of the compound of the general formula (1) or (2) is 0.05% by weight or more and 100% by weight or less based on the dye precursor. If it is less than this, the effect is not sufficient, and if it exceeds this, there is a possibility that any of the heat-resistant storage stability and the decoloring property of the image is adversely affected.
[0017]
Specific examples of the compound represented by Formula (1) or (2) are shown below, but the present invention is not limited thereto. These compounds are used alone or in combination of two or more. These compounds can be easily synthesized, for example, by the method described in Chem. Ber. 122 , 113 (1989), Synthesis 155 (1989), or JP-A-2-268163 or the alkylation method shown in the following Examples.
[0018]
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[0019]
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[0020]
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[0021]
Some of the specific production methods of these compounds are exemplified below.
[0022]
Synthesis method of Exemplified compound (1) -1 8.59 g of triphenylphosphine and 10 g of n-hexadecyl bromide were heated in a nitrogen stream at a bath temperature of 180 ° C for 10 hours. After cooling, the precipitated solid was crushed and washed with acetone. Yield 8.48 g (mp. 125-128 ° C).
[0023]
Synthetic Method of Exemplified Compound (1) -2 To 91.2 g of tetramethylammonium hydroxide (10% methanol solution) was added 12 g of concentrated hydrochloric acid under cooling with ice water, methanol was distilled off under reduced pressure, and the residue was dissolved in 200 ml of ethanol. After filtering off the insoluble matter, the ethanol was distilled off under reduced pressure to obtain 11.5 g of tetramethylammonium chloride as a colorless solid.
7.23 g of sodium tetraphenylborate was dissolved in 280 ml of acetonitrile, and 11.5 g of the above crude chloride was dissolved in 70 ml of acetonitrile and mixed. The precipitated crystals were collected by filtration, washed with water and dried to obtain 7.95 g of tetramethylammonium tetraphenylborate as a colorless solid. mp. 290 ° C or higher.
2.0 g of triphenylhexadecylphosphonium bromide was dissolved in 40 ml of ethanol, and 1.59 g of tetramethylammonium tetraphenylborate was added. After heating on a water bath for 15 minutes, 80 ml of water was added and filtered. After washing with water, dry. Yield 1.6 g (mp. 300 ° C. or higher).
[0024]
Synthesis method of exemplary compound (2) -1.
In a flask equipped with a stirrer, 5.7 g of n-octadecanethiol, 1.2 g of sodium methoxide, and 30 ml of methanol were charged, and the mixture was stirred on a 60 ° C. oil bath for 10 minutes. Thereto, 3.0 g of methyl iodide was added dropwise. After stirring for 30 minutes as it was, the reaction mixture was poured into water, and the precipitated crystals were separated by filtration under reduced pressure to obtain 6 g of methyl octadecyl sulfide as a colorless solid.
3.0 g of crude methyl octadecyl sulfide, 2.1 g of methyl iodide and 50 ml of acetone were charged into a flask equipped with a stirrer, and stirred at room temperature for 24 hours. The precipitated crystals were separated by filtration under reduced pressure and recrystallized from acetone. Yield 3.4 g (mp. 82.5 ° C).
[0025]
On the other hand, the reversible developer used in the present invention is preferably a phenolic electron-accepting compound, and is not particularly limited as long as it causes a reversible color change by heating in the presence of an electron-donating dye precursor. Those represented by the following general formula (3) gave particularly preferable results in terms of coloring density and decoloring property. In addition, any compound having the same characteristics as the compound of the following general formula (3) can be used in the method of the present invention. The compounds of the general formula (3) are described in JP-A-6-210954, Japanese Patent Application No. 5-160547, Japanese Patent Application No. 5-256825, Japanese Patent Application No. 5-317555, Japanese Patent Application No. 5-328101, and No. 6-10310.
[0026]
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[0027]
In the formula (3), n represents an integer of 1 to 3, and j, k and l each represent 0 or 1. However, when j is 1, k indicates 1. R ⁸ and R ⁹ represent a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ¹⁰ represents a hydrocarbon group having 1 to 24 carbon atoms. L ¹ represents a divalent group having at least one —CONH— bond, and L ² represents a divalent group having at least one —CONH— bond, an oxygen atom or a sulfur atom.
[0028]
In the compound represented by the above general formula (3), R ⁸ and R ⁹ are divalent hydrocarbon groups having 1 to 18 carbon atoms, and may contain an aromatic ring in the group. It may be only. L ¹ and the divalent group having -CONH- bond the at least one represented by L ^2, the specific example the amide (-CONH -, - NHCO-), urea (-NHCONH-), urethane (- NHCOO-, -OCONH-), diacylamine (-CONHCO-), diacylhydrazide (-CONHNHCO-), oxalic acid diamide (-NHCOCONH-), acylurea (-CONHCONH-, -NHCONHCO-), 3-acylcarbazide acid ester (-CONHNHCOO-), semicarbazide (-NHCONHNH -, - NHNHCONH-), acyl semicarbazide (-CONHNHCONH -, - NHCONHNHCO-), diacyl aminomethane (-CONHCH ₂ NHCO -), 1- acylamino-1- Ureidometan (- CON _{HCH 2 NHCONH -, - NHCONHCH 2} NHCO-), a group such as malonamide (-NHCOCH ₂ CONH-).
[0029]
The electron-accepting compound represented by the general formula (3) has the ability to form a leuco dye, and has a specific decoloring effect, that is, a reversible effect depending on the temperature. In the case of electron-accepting compounds used in ordinary thermosensitive recording materials, that is, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, benzyl 4-hydroxybenzoate, etc. No reversible effect is seen at all. Hereinafter, specific examples of the electron-accepting compound represented by the general formula (3) will be described, but the present invention is not limited thereto.
[0030]
For example, in the formula (3), as the compound wherein j = 0 / k = 0 / l = 0, 4'-hydroxyhexadecaneanilide, N-octadecyl-4-hydroxybenzamide, N- (4-hydroxyphenyl)- N'-octadecyl urea, N- (4-hydroxybenzo) -N'-octadecanohydrazide, N- (3,4-dihydroxyphenyl-N'-octadecyl oxamide, etc.
[0031]
In the formula (3), as a compound in which j = 0 / k = 1 / l = 0, N- [2- (4-hydroxyphenyl) ethyl] -N′-octadecylurea and N- [3- (4 -Hydroxyphenyl) propiono] -N'-octadecanohydrazide, N- [3- (4-hydroxyphenyl) propiono] -N'-docosanohydrazide, 1- [3- (4-hydroxyphenyl) propionyl] amino -1-octadecanoylaminomethane, 1- (4-hydroxyphenylacetyl) -4-octadecyl semicarbazide and the like,
[0032]
In the formula (3), as the compound wherein j = 1 / k = 1 / l = 0, N-hexadecyl- (4-hydroxyphenylthio) acetamide, N- [2- (4-hydroxyphenylthio) ethyl] -N'-octadecyl urea, N- (4-hydroxyphenylthio) aceto-N'-docosanohydrazide, N- [11- (4-hydroxyphenylthio) undecano] -N'-decanohydrazide, N- [ 2- (4-hydroxyphenylthio) ethyl] -N'-octadecyl oxamide, N- [4- (4-hydroxyphenylthio) phenyl] -N'-octadecyl oxamide, N- [4- (4-hydroxy Phenylthiomethyl) benzo] -N'-docosanohydrazide;
[0033]
In the formula (3), examples of the compound where j = 0 / k = 0 / l = 1 include N- (4-hydroxyphenyl) -3-dodecylthiopropanamide and N- (4-hydroxyphenyl) -N ′ -3-octadecylthiopropylurea, 4-hydroxy-4'-octadecyloxybenzanilide, 4-hydroxy-4'-dodecylthiobenzanilide, 2- (4-octadecanoylaminophenyl) -4'-hydroxyacetanilide, 2- [4- (N'-octadecylureido) phenyl] -4'-hydroxyacetanilide and the like;
[0034]
In the formula (3), as the compound wherein j = 0 / k = 1 / l = 1, N- [3- (4-hydroxyphenyl) propiono] -N ′-(3-dodecylthiopropiono) hydrazide; N- [3- (3,4-dihydroxyphenyl) propiono] -N '-(11-decylthioundecano) hydrazide and the like;
[0035]
In the formula (3), as the compound wherein j = 1 / k = 1 / l = 1, N- [3- (4-hydroxyphenylthio) propiono] -N ′-(3-octadecylthiopropiono) hydrazide And N- [11- (3,4,5-trihydroxyphenylthio) undecano] -N '-(11-octadecylthioundecano) hydrazide.
[0036]
These reversible developers may be used alone, or two or more thereof may be used in combination. The amount of the reversible developer based on the dye precursor is 5 to 5000% by weight, preferably 10 to 3000% by weight. It is.
[0037]
The electron-donating dye precursor used in the present invention is typically represented by a known compound used for pressure-sensitive recording paper, heat-sensitive recording paper, and the like, but is not particularly limited. Specific examples include, for example, the following, but the present invention is not limited thereto.
[0038]
(1) Triarylmethane compound 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- ( p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- ( p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3- Bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5 Dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6 -Dimethylaminophthalide and the like.
[0039]
(2) Diphenylmethane compounds 4,4'-bis (dimethylaminophenyl) benzhydryl benzyl ether, N-chlorophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like.
[0040]
(3) Xanthene compounds rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7 -Phenylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3-diethylamino- 7- (2-chloroanilino) fluoran,
[0041]
3-diethylamino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-ani Linofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-phenethylfluoran, 3-diethylamino-7- (4-nitroanilino) fluoran, 3-dibutylamino-6-methyl-7 -Anilinofluoran, 3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-ani Linofluoran, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl 7-anilinofluoran like.
[0042]
(4) Thiazine compounds benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like.
[0043]
(5) Spiro compounds 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxybenzo) ) Spiropyran, 3-propylspirobenzopyran and the like.
[0044]
The above dye precursors may be used alone or in combination of two or more.
[0045]
As a specific example of the method for producing a reversible thermosensitive recording material of the present invention, a dye precursor and a reversible developer are used as main components, and further, a decolorization accelerator of the present invention is added, and this is placed on a support. A method of forming a reversible thermosensitive recording layer by coating.
[0046]
A coating solution for containing the dye precursor, the reversible developer and the compound of the present invention in the reversible thermosensitive recording layer, a method in which each compound is dissolved alone in a solvent or dispersed in a dispersion medium and then mixed, There is a method of mixing each compound and dissolving it in a solvent or dispersing it in a dispersion medium, a method of heating and dissolving each compound to homogenize it, then cooling it, and dissolving it in a solvent or dispersing it in a dispersion medium. There is no. In addition, a dispersing aid may be used if necessary at the time of dispersion. When water is used as the dispersion medium, examples of the dispersion aid include water-soluble polymers such as polyvinyl alcohol and various surfactants. Further, a water-soluble organic solvent such as ethanol may be mixed. When an organic solvent typified by hydrocarbons is used as a dispersion medium, lecithin or phosphates may be used as a dispersant.
[0047]
In addition, a binder can be added to the reversible thermosensitive recording layer for the purpose of improving the strength of the reversible thermosensitive recording layer. Specific examples of the binder include starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylate copolymer, acrylamide / acryl. Water-soluble polymers such as acid ester / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, polyvinyl acetate, polyurethane, polyacrylic acid Ester, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl chloride copolymer, polyvinyl chloride, ethylene Vinylidene chloride copolymers, such as latex of polyvinylidene chloride and the like but not particularly limited thereto.
[0048]
Further, a thermal solvent may be contained in the reversible thermosensitive recording layer as an additive for adjusting the color development sensitivity of the reversible thermosensitive recording layer. These compounds preferably have a melting point of 60 ° C to 200 ° C, and particularly compounds having a melting point of 80 ° C to 180 ° C gave good results. In addition, sensitizers used in general thermosensitive recording paper can also be used. These compounds include waxes such as N-hydroxymethyl stearamide, behenamide, stearamide, palmitamide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzylbiphenyl, 4-allyloxybiphenyl Biphenyl derivatives such as 1,2-bis (3-methylphenoxy) ethane, 2,2'-bis (4-methoxyphenoxy) diethyl ether, bis (4-methoxyphenyl) ether and other polyether compounds, diphenyl carbonate, Examples thereof include carbonic acid or oxalic acid diester derivatives such as dibenzyl oxalate and bis (p-methylbenzyl) oxalate, and two or more thereof may be added in combination.
[0049]
As the support of the reversible thermosensitive recording material of the present invention, paper, various nonwoven fabrics, woven fabrics, synthetic resin films such as polyethylene terephthalate and polypropylene, paper laminated with synthetic resins such as polyethylene and polypropylene, synthetic paper, metal foil, glass Etc., or a composite sheet combining these can be used arbitrarily according to the purpose, but is not limited thereto, and any opaque, translucent or transparent indicator can be used. In order to make the background look white or another specific color, a white pigment, a colored dye or a bubble may be contained in or on the support. In particular, when applying an aqueous liquid to a film or the like, when the hydrophilicity of the support is small and it is difficult to apply the reversible thermosensitive recording layer, if the surface is made hydrophilic by corona discharge or the like, the same aqueous solution as used for the binder is used. A treatment such as applying a hydrophilic polymer to the surface of the support is also effective.
[0050]
The layer structure of the reversible thermosensitive recording material of the present invention may be only the reversible thermosensitive recording layer. If necessary, a protective layer on the reversible thermosensitive recording layer, and an intermediate layer containing at least one of a water-soluble polymer, a white or colored dye or hollow particles between the reversible thermosensitive recording layer and the support. It can also be provided. In this case, the protective layer and / or the intermediate layer may be composed of two or three or more layers. The reversible thermosensitive recording layer may also be a multilayer of two or more layers by containing each component one by one or by changing the mixing ratio for each layer. Further, a material capable of recording information electrically, optically, and magnetically in the reversible thermosensitive recording layer and / or on the surface opposite to the surface on which the reversible thermosensitive recording layer is provided. May be included. Further, a back coat layer may be provided on the surface opposite to the surface on which the reversible thermosensitive recording layer is provided for the purpose of preventing blocking, curling and charging.
[0051]
The method for forming the reversible thermosensitive recording material of the present invention by laminating each layer in the present invention on a support is not particularly limited, and it can be formed by a conventional method. For example, a smearing device such as an air knife coater, a blade coater, a bar coater, a curtain coater, and the like, various printing machines using a method such as lithographic, letterpress, intaglio, flexo, gravure, screen, and hot melt can be used. Further, each layer can be held by UV irradiation or EB irradiation in addition to the usual drying step.
[0052]
The reversible thermosensitive recording layer is obtained by mixing each dispersion obtained by pulverizing each component, coating and drying on a support, mixing each solution obtained by dissolving each component in a solvent, and supporting the mixture. It can be obtained by a method of coating and drying on the body. Drying conditions vary depending on a dispersion medium or solvent such as water. In addition, there is a method in which the components are mixed and heated to melt the fusible component, and the composition is heated and applied.
[0053]
The reversible thermosensitive recording layer and / or protective layer and / or intermediate layer include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, and urea. -Pigments such as formalin resin, and other metal salts of higher fatty acids such as zinc stearate and calcium stearate, paraffin, paraffin oxide, polyethylene, polyethylene oxide, polyethylene oxide, stearamide, caster wax, etc. for the purpose of preventing head abrasion and sticking. The waxes may also contain a dispersant such as sodium dioctyl sulfosuccinate, a surfactant, a fluorescent dye and the like.
[0054]
Next, a method for coloring and decoloring the reversible thermosensitive recording material of the present invention will be described. In order to perform color development, rapid cooling may be performed subsequent to heating. For example, heating using a thermal head, laser light, or the like is suitable. In addition, the color can be erased if it is cooled slowly after heating. For example, it can be erased by using radiant heat from a light source such as a thermal head, a hot roll, a hot stamp, high-frequency heating, hot air, an electric heater, a tungsten lamp, a halogen lamp, and the like. It is.
[0055]
[Action]
Although the mechanism of image formation and erasure of the heat-sensitive recording material of the present invention is not clear, it can be considered as follows. Usually, when a colorless or pale-colored dye precursor is heated together with an electron-accepting compound such as a phenolic compound, electron transfer from the dye precursor to the electron-accepting compound occurs, and color is formed. At this time, it is considered that the electron accepting compound molecule exists very close to the colored dye molecule. When the electron-accepting compound molecule is separated from the dye molecule that has developed color, the dye molecule that has developed color receives electrons again, and is in a state of a dye precursor before color development. It is considered that the present invention changes the distance between the electron-accepting compound molecule and the dye molecule by heating to perform coloring and decoloring.
[0056]
More specifically, many electron-accepting compounds so far called reversible developers have a fatty chain in their structure, and therefore have low compatibility with the dye precursor molecules and the dye molecules that have developed color. It is considered that they hardly dissolve in the solidified state. In a state where the dye precursor molecule and the reversible color developer molecule can freely move, such as in a heat-melted state, the dye precursor molecule and the reversible color developer molecule are dissolved at a certain ratio to each other to form a color. Therefore, when the colored mixture in the molten state is slowly cooled, the reversible developer molecules and the dye molecules are not dissolved with each other but phase-separated and the color is erased as the temperature is lowered. In particular, since the electron-accepting compound represented by Formula 6 of the present invention contains a bond having a hydrogen bonding ability, such as an amide bond, in the molecule, if it is rapidly crystallized by an intermolecular hydrogen bond, Conceivable. On the other hand, when cooling is performed rapidly, the color is solidified before the phase separation, that is, in the color-developed state.
[0057]
Color erasure accelerator compound represented by formalized 4 or Formula 5 used in the present invention, the structural features of their upon phase separation of the electron-donating dye precursor and an electron-accepting reversible color developer, It is thought that the decoloring phenomenon has been accelerated, but details are not yet clear.

[0058]
【Example】
Next, the method of the present invention will be described in more detail with reference to examples. Parts and percentages in the examples are on a weight basis.
[0059]
Example 1
(A) Preparation of reversible thermosensitive coating solution 40 parts of 3-diethylamino-6-methyl-7-anilinofluoran were pulverized together with 90 parts of a 2.5% aqueous solution of polyvinyl alcohol by a paint conditioner to obtain a dye precursor dispersion (A). Liquid). Next, 200 parts of 3- (4-hydroxyphenyl) propanoyl-docosanoic hydrazide were pulverized with a paint conditioner together with 400 parts of a 1.25% aqueous solution of polyvinyl alcohol to obtain a reversible developer dispersion (liquid B). Further, 20 parts of magnesium carbonate and 47 parts of a 0.2% aqueous solution of polyvinyl alcohol were ground in the same manner (liquid C). Further, 10 parts of n-hexadecyltriphenylphosphonium bromide (exemplified compound (1) -1) were pulverized with a paint conditioner together with 40 parts of a 1.25% aqueous solution of polyvinyl alcohol to obtain a discoloration accelerator dispersion (D liquid). . After mixing these four types of dispersion liquids A, B, C and D, 170 parts of a 10% aqueous polyvinyl alcohol solution and 350 parts of water were added and mixed well to prepare a reversible thermosensitive coating liquid.
[0060]
(B) Preparation of reversible thermosensitive recording material The reversible thermosensitive coating liquid prepared in (A) was smear-dried on a polyethylene terephthalate (PET) sheet so that the solid content was 2.6 g / m ^2, and then dried. Then, a 5% aqueous solution of polyvinyl alcohol was smear-dried to give a solid smear amount of 2 g / m ^2, and treated with a super calender to obtain a reversible thermosensitive recording material.
[0061]
Example 2
Except that n-hexadecyltriphenylphosphonium tetraphenylborate (exemplified compound (1) -2) was used instead of n-hexadecyltriphenylphosphonium bromide (exemplified compound (1) -1) used in Example 1. A reversible thermosensitive recording material was obtained in the same manner as in Example 1.
[0062]
Example 3
Example 1 was repeated except that tetramethylphosphonium tetraphenylborate (exemplified compound (1) -3) was used instead of n-hexadecyltriphenylphosphonium bromide (exemplified compound (1) -1) used in Example 1. A reversible thermosensitive recording material was obtained in the same manner as described above.
[0063]
Example 4
Example 1 was repeated except that dimethyloctadecylsulfonium iodide (Exemplified Compound (2) -1) was used instead of n-hexadecyltriphenylphosphonium bromide (Exemplified Compound (1) -1) used in Example 1. In the same manner, a reversible thermosensitive recording material was obtained.
[0064]
Comparative Example 1
A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that n-hexadecyltriphenylphosphonium bromide (exemplified compound (1) -1) used in Example 1 was omitted.
[0065]
Comparative Example 2
A reversible thermosensitive recording material was obtained in the same manner as in Example 1, except that stearamide was used in place of n-hexadecyltriphenylphosphonium bromide (exemplified compound (1) -1) used in Example 1. Was.
[0066]
Test 1 (color density = thermal response)
The heat-sensitive recording materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were applied for 1.1 milliseconds by using a thermal facsimile printing tester TH-PMD manufactured by Okura Electric with Kyocera's print head KJT-256-8MGF1. And the density of the obtained color image was measured using a densitometer Macbeth RD918. The results are shown in Table 1.
[0067]
Test 2 (Erasability of image)
The thermal recording materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were applied to an Okura Electric 5 thermal facsimile printing tester TH-PMD equipped with a Kyocera print head KJT-256-8MGF1 with an applied pulse 1.1. Printing was performed under the conditions of an applied voltage of 26 volts in milliseconds, and this was heated at 100 ° C. for 1 second using a heat stamp, and the density was measured in the same manner as in Test 1. The results are shown in Table 1.
[0068]
Test 3 (Decoloring start temperature)
The thermal recording materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were applied for 1.1 milliseconds by using an Okura Denki thermal facsimile printing tester TH-PMD with a Kyocera print head KJT-256-8MGF1. Printed under the condition of applied voltage of 26 volts and heated it for 10 seconds at 60 ° C to 150 ° C at 10 ° C intervals using a heat stamp for 1 second each, and then measured each concentration in the same manner as in Test 1. did. The heating temperature at which the optical density of the printed image was lower than 0.15 was defined as the decolorization start temperature. The results are shown in Table 1.
[0069]
Test 4 (Change over time in color density = image stability)
The heat-sensitive recording materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were applied to a heat-sensitive facsimile printing tester TH-PMD manufactured by Okura Electric with a print head KJT-256-8MGF1 manufactured by Kyocera to apply an applied pulse of 1.1 mm. After printing for 24 hours under the conditions of an applied voltage of 26 volts and storing for 24 hours in an atmosphere at a temperature of 50 ° C. and a relative humidity of 10%, the density of the color-developed portion was measured in the same manner as in Test 1, and the image was obtained by the following equation 1. The survival rate was calculated. The results are shown in Table 1.
[0070]
(Equation 1)
A = (C / B) × 100
A: Image remaining rate (%)
B: Image density before test C: Image density after test
[Table 1]

[0072]
【The invention's effect】
As shown in Table 1, in a reversible thermosensitive recording material containing a generally colorless or pale color dye precursor and a reversible developer that causes the dye precursor to reversibly change color tone, By containing a compound represented by the general formula (1) or (2), an image can be formed / erased with a clear contrast, and a more stable image can be maintained over time in an environment of daily life. A possible reversible thermosensitive recording material was obtained.

Claims (3)

In a reversible thermosensitive recording material containing a colorless or pale-colored dye precursor on a support and a reversible developer that causes a reversible color change in the dye precursor due to a difference in cooling rate after heating, A reversible thermosensitive recording material comprising at least one onium salt compound represented by the following general formula (1) or (2) as a color accelerator.

(In the formula ^(1), R 1 ~R ⁴ may be the same or different, each represents an alkyl group, an alkenyl group, a cycloalkyl group, an aralkyl group, an aryl group, a heterocyclic residue, also, R ¹ ~ Any two groups selected from R ⁴ may be linked to each other to form a cyclic structure. X ⁻ represents an anion.)

(In the formula (2), R ⁵ ~R ⁷ may be the same or different, each represents an alkyl group, an alkenyl group, a cycloalkyl group, an aralkyl group, an aryl group, a heterocyclic residue, also, R ⁵ ~ Any two groups selected from R ⁷ may be linked to each other to form a cyclic structure. Y ⁻ represents an anion.) At least one of R ^{1 to} R ⁴ and R ^{5 to} R ⁷ in the general formula (1) or (2) is a long-chain alkyl group having 10 to 24 carbon atoms. 2. The reversible thermosensitive recording material according to 1. The reversible thermosensitive recording material according to claim 1, wherein the reversible developer is a compound represented by the following general formula (3).

(In the formula (3), n is an integer of 1 to 3, and j, k, and l each represent 0 or 1. However, when j is 1, k represents 1. R ⁸ and R ⁹ represent the number of carbon atoms. A divalent hydrocarbon group of 1 to 18, R ¹⁰ represents a hydrocarbon group of 1 to 24 carbon atoms, L ¹ represents a divalent linking group having at least one —CONH— bond, and L ² represents Represents a divalent group having at least one -CONH- bond, or an oxygen atom or a sulfur atom.)