JP4169443B2 - Reversible recording medium and recording method using the reversible recording medium - Google Patents

Description

【化４】

（式中Ｚ、Ｙは各々独立してコレステリル基、ジハイドロコレステリル基、水素原子
又はアルキル基を、Ｒは水素原子又はアルキル基を表し、式中ｍ、ｎは各々独立し
て１以上の整数であるものとし、ＺおよびＹの少なくともいずれか一方はコレステ
リル基またはジハイドロコレステリル基を表す）。
【０００５】
本発明の可逆記録媒体および該可逆記録媒体を用いた記録方法においては、可逆記録媒体の前記等方相または高温でのコレステリック液晶相を示す温度からの冷却速度が早くなるにつれ、コレステリック液晶化合物が温度に追随した配向ができなくなり、高温側でとる配向が崩れる前に、例えばガラス転移温度以下、あるいは常温となり構造が固定されてしまうため、コレステリック液晶化合物相の高温側で観測される選択反射波長が固定され、所望の色の記録を行うことができる。
【０００６】
すなわち、本発明で使用するコレステリック液晶化合物は、加熱して等方相あるいは高温でのコレステリック液晶相とした後、ガラス転移温度以下、あるいは常温まで急冷すると、前記加熱状態のコレステリック化合物はその分子配列を保持したままガラス状固体になり、選択反射色が観測される。
前記の所望のコレステリック反射色の固定は、ガラス転移温度以下まで冷却して行うのが好ましい。
【０００７】
本発明で使用するコレステリック液晶化合物は、ガラス転移温度以上でコレステリック液晶相を示し、さらにそれ以上の温度で等方相を示し、また前記のようなコレステリック反射色の固定が可能なものであれば特にその種類は限定されないが、室温で安定に記録を保存するために、ガラス転移点が３０℃以上のものが好ましい。
【０００８】
前記のような特性を有するコレステリック液晶化合物としては、例えば下記式（Ｉ）および（II）に示すものが挙げられる。
【０００９】
【化５】

【００１０】
【化６】

（式中Ｚ、Ｙは各々独立してコレステリル基、ジハイドロコレステリル基、水素原子
又はアルキル基を、Ｒは水素原子又はアルキル基を表し、式中ｍ、ｎは各々独立し
て１以上の整数であるものとし、ＺおよびＹの少なくともいずれか一方はコレステ
リル基またはジハイドロコレステリル基を表す）。
【００１１】
前式（Ｉ）および（II）で示される液晶記録材料として用いるコレステリック液晶化合物は、その分子量が２０００以下で、ガラス転移温度が３０℃以上で、ガラス転移温度以上でコレステリック液晶相を示し、さらにそれ以上の温度で等方相を示すものである。
コレステリック液晶化合物としては、特に、下式（III）のコレステリック液晶（以下Ｃ８ＤＹ８Ｃ）がガラス状態の室温での安定が良いので好ましい。さらに、Ｃ８ＤＹ８Ｃのコレステロール部位をジハイドロコレステロールに変えた、下式(IV)（以下Ｉ−８−ＤｉＨＣと言う）が、高温での熱安定性が良いのでより好ましい。
本発明で使用するコレステリック液晶化合物は、その複数種類を混合して用いても良い。
【００１２】
【化７】

（III）
【００１３】
【化８】

（IV）
【００１４】
本発明の可逆記録媒体基板としては、ガラス、あるいは、ＰＥＳ、ＰＥＴなどのプラスチックフィルムを使用することが出来るが、特にその種類は限定されない。
また、記録層と接する側の表面に配向膜を形成した基板も使用可能であり、例えば、以下の方法で作成できる。可溶性ポリイミド溶液（ＪＳＲオプトマーＡＬ３０４６）を使用して、１重量％濃度で溶解させ塗布液を、洗浄処理したガラス基板上にスピンコートし、乾燥処理を経て樹脂薄膜を形成する。
次に、平面部材に一般的なＬＣＤ配向膜用のラビング布を貼りつけ、ポリイミド面と接離可能に配置させた。ガラス基板あるいは平面部材を往復運動させ、どちらか一方向に移動する時のみラビング布とポリイミド面を均一加重で接触させて一方向に摺擦する。ラビング処理したポリイミド膜面が内側になるようにして、可逆記録媒体基板として使用する。
【００１５】
前記等方相を得るための加熱手段は、特にその種類は制限されるものではないが、必要とする加熱速度に応じて、適宜、適当な加熱手段および加熱条件を選択できるが、加熱手段としては、例えばホットプレート、レーザー光、サーマルへッドなどを使用することが出来る。ただし、加熱手段はこれらに限定されるものではない。
【００１６】
前記コレステリック反射色を固定する急冷手段も、特にその種類は制限されるものではないが、例えば所望するコレステリック反射色に応じて必要とする冷却速度に応じて、適宜、適当な冷却手段および冷却条件を選択できる。冷却手段としては、例えば水冷、空冷、金属板、ガラス板等などを使用することが出来る。ただし、冷却手段はこれらに限定されるものではない。
【００１７】
さらに、前記コレステリック反射色を固定する急冷方法としては、例えば以下のような方法も採用することができる。
（１）記録層の膜厚方向に急冷速度に変化を持たせることにより、膜厚方向に異なる反射色の固定を行うか、
（２）基板表面上にパターンを温度の相違として形成し、前記パターンにより記録層の冷却速度に変化を持たせ、異なる反射色の固定を行うか、あるいは
（３）冷却手段として、基板上に該基板とは熱容量および／または熱伝導率が異なる物質でパターンを形成した冷却板を用いて冷却し、該パターンにより記録層の冷却速度に変化を持たせ、異なる反射色の固定を行なう。
前記パターンが形成された部分と前記パターンが形成されていない部分では、冷却速度に差異をもたせることができるので、容易に異なる反射色の固定をすることができる。
【００１８】
以下、本発明の可逆記録方法の実施態様を示す。
【００１９】
実施態様１
Ｃ８ＤＹ８Ｃまたは該化合物を含む混合物を含有する感熱記録材料で構成される記録層を、等方相を示す温度までその一部、あるいは全部の領域を到達させた後、１５〜３５℃／秒の冷却速度でガラス転移温度以下まで冷却することにより、該冷却した領域に赤色の反射色を固定することができた。
【００２０】
実施態様２
Ｃ８ＤＹ８Ｃまたは該化合物を含む混合物を含有する感熱記録材料で構成される記録層を、等方相を示す温度までその一部、あるいは全部の領域を到達させた後、７０〜１００℃／秒の冷却速度でガラス転移温度以下まで冷却することにより、該冷却した領域に緑色の反射色を固定することができた。
【００２１】
実施態様３
Ｃ８ＤＹ８Ｃまたは該化合物を含む混合物を含有する感熱記録材料で構成される記録層を、等方相を示す温度までその一部、あるいは全部の領域を到達させた後、１５５〜３３０℃／秒の冷却速度でガラス転移温度以下まで冷却することにより、該冷却した領域に青色の反射色を固定することができた。
【００２２】
前記実施態様１〜３の結果を下表１に示す。
【表１】

なお、前記実施態様および実施例においては、冷却速度の測定は、コレステリック液晶化合物の冷却過程を赤外線カメラを用いてビデオ撮影し、その撮影記録を低速で再生し、決定した。
【００２３】
【実施例】
以下、本発明を実施例に基づいて具体的に説明する．
【００２４】
実施例１
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、−１５℃に冷却した銅板上に載せることにより３３０℃／秒で冷却したところ、青色を固定できた。しかし、拡大すると、わずかに白色部が観測されその後、３３０℃／秒が上限と判断した。
【００２５】
実施例２
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、−１０℃に冷却した銅板上に載せることにより２４０℃／秒で冷却したところ、青色を固定できた。
【００２６】
実施例３
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、−５℃に冷却した銅板上に載せることにより１５５℃／秒で冷却したところ、青色を固定できた。しかし、拡大すると、一部緑色が観測され、１５５℃／秒が下限と判断した。
【００２７】
実施例４
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、０℃に冷却した銅板上に載せることにより１００℃／秒で冷却したところ、緑色を固定できた。しかし、拡大すると、一部、青色が観測され、１００℃／秒が上限と判断した。
【００２８】
実施例５
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、２５℃の銅板上に載せることにより７０℃／秒で冷却したところ、緑色を固定できた。しかし、拡大すると、一部、赤緑色部が観測され、７０℃／秒が下限と判断した。
【００２９】
実施例６
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、１０℃のガラス基板上に載せることにより３５℃／秒で冷却したところ、赤色を固定できた。しかし、拡大すると、一部、赤緑色部が観測され、３５℃／秒が上限と判断した。
【００３０】
実施例７
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、２５℃のガラス基板上に載せることにより１５℃／秒で冷却したところ、赤色を固定できた。しかし、拡大すると、一部、白色が観測され、１５℃／秒が下限と判断した。
【００３１】
実施例８
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、ガラス基板より小さな−１０℃に冷却した三角形の銅板上に載せることにより、その部分のみを２４０℃／秒で冷却したところ、三角形の部分のみ青色が固定され、その他の部分は白色となり、青色のパターンが記録された。
【００３２】
実施例９
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、０℃の銅板と−１０℃に冷却した銅板を近接させ、これら二つの銅板に跨るように前記各基板を載せることにより、それぞれの温度の異なる領域において１００℃／秒および２４０℃／秒で冷却され、０℃の銅板上では緑色、−１０℃に冷却した銅板上では青色が固定され、色の異なるパターンが記録された。
【００３３】
実施例１０
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、２５℃の銅板と２５℃のガラス板を近接させ、これら二つの板に跨るよう前記各基板を載せることにより、前記それぞれの材質の異なる領域において、７０℃／秒および２０℃／秒で冷却され、銅板上では緑色、ガラス板上では赤色が固定され、色の異なるパターンが記録された。
【００３４】
実施例１１
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＣ８ＤＹ８Ｃを等方相となる温度（１３０℃）に加熱後、０℃に冷却した銅板と３０℃のガラス板の間に挟んだところ、黄色の反射色を得た。それぞれの側の色を観測するために、銅板とガラス板に挟まれたＣ８ＤＹ８Ｃを剥がし、銅板で冷却した側とガラス板で冷却した側に分けて色を観測したところ、銅板側は緑色、ガラス板側は赤色に固定されていることが分かった。
前記実施例１〜１１において固定された色は、室温で６月以上安定に保存できた。
【００３５】
実施例１２
ホットプレート上で、二枚のガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたコレステリック液晶〔前式（Ｉ）において、Ｚ、Ｙはどちらもコレステリル基、Ｒは水素、ｍ＝ｎ＝６である、８，１２−エイコサジエンジオン酸ジコレステリルエステル〕を等方相となる温度（１５０℃）に加熱後、室温の水中に漬け急冷したところ、青色を固定できた。この青色は２週間保持できた。
【００３６】
実施例１３
ホットプレート上で、二枚のラビングされた配向膜を形成したガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＩ−８−ＤｉＨＣを等方相となる温度（１３５℃）に加熱後、−１５度に冷却した銅板上に載せることにより、毎秒３３０度で冷却したところ、黄緑色を固定出来た。
【００３７】
実施例１４
ホットプレート上で、二枚のラビングされた配向膜を形成したガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＩ−８−ＤｉＨＣを等方相となる温度（１３５℃）に加熱後、１０度のガラス基板上に載せることにより、毎秒３５度で冷却したところ、黄緑色を固定出来たが一部結晶化した。そこで、毎秒３５度が下限と判断した。
【００３８】
実施例１５
ホットプレート上で、二枚のラビングされた配向膜を形成したガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＩ−８−ＤｉＨＣを等方相となる温度（１３５℃）に加熱後、ガラス基板より小さな、−１０度に冷却した三角形の銅板上に載せることにより、その部分のみを毎秒２４０度で冷却したところ、三角形の部分のみが固定され、その他の部分は白色となり、黄緑色のパターンが記録された。
【００３９】
実施例１６
ホットプレート上で、二枚のラビングされた配向膜を形成したガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＩ−８−ＤｉＨＣを等方相となる温度（１３５℃）に加熱後、２５度のガラス板と１０度に冷却したガラス板を近接させ、それら二つの銅板に跨るように該基板を載せることにより、それぞれの温度の異なる領域において毎秒１５度および３５度で冷却され、２５度のガラス板上では白色、１０度に冷却したガラス板上では黄緑色が固定され、色の異なるパターンが記録された。
【００４０】
実施例１７
ホットプレート上で、二枚のラビングされた配向膜を形成したガラス基板（厚さ１３０マイクロメートル）に厚みを１０マイクロメートルとして挟まれたＩ−８−ＤｉＨＣを等方相となる温度（１３５℃）に加熱後、０度の銅板と２５度のガラス板を近接させ、それら二つの板に跨るように該基板を載せることにより、それぞれの材質の異なる領域において毎秒１００度および１５度で冷却され、銅板上では黄緑色、ガラス板上では白色が固定され、色の異なるパターンが記録された。
【００４１】
実施例１８
上記実施例で固定したＣ８ＤＹ８ＣおよびＩ−８−ＤｉＨＣのコレステリックガラスをホットプレート上で１０秒間の耐熱試験を行ったところ、Ｃ８ＤＹ８Ｃは９５度で白色化してしまったが、Ｉ−８−ＤｉＨＣは白色化せず、Ｉ−８−ＤｉＨＣのコレステリックガラスの方が高温に対し安定であることが分かった。
【００４２】
【効果】
１．
等方相あるいは高温でのコレステリック液晶相からの冷却速度をコントロールすることのみで、簡単に目的の反射光を固定でき、かつ固定された反射色の室温での安定性に優れた可逆記録媒体が提供される。
２．
一括書き込みが簡単な可逆記録媒体が提供される。
３．
等方相あるいは高温でのコレステリック液晶相からの冷却速度をコントロールすることのみで、簡単に目的の反射光を固定できる可逆記録方法が提供される。
４．
記録濃度を落とすことなく、三原色による多値記録が可能な可逆記録方法が提供される。
５．
冷却速度に変化を持たせる手段として、熱容量および／または熱伝導率が異なる物質を用いたので、一括書き込みが簡単で、冷却手段の繰り返し使用が可能である。
６．
材質を変えることなく、一括書き込みが簡単で、かつパターンの変更が容易であり、冷却の繰り返し使用が可能な可逆記録方法が提供される。
７．
Ｃ８ＤＹ８Ｃにおいて、等方相からの冷却速度をコントロールすることのみで、赤を固定できる。
８．
Ｃ８ＤＹ８Ｃにおいて、等方相からの冷却速度をコントロールすることのみで、緑を固定できる。
９．
Ｃ８ＤＹ８Ｃにおいて、等方相からの冷却速度をコントロールすることのみで、青を固定できる。
１０．
Ｉ−８−ＤｉＨＣにおいて、等方相からの冷却速度をコントロールすることのみで、黄緑色を固定できる。
【図面の簡単な説明】
【図１】コレステリック液晶化合物の相変化を説明した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reversible recording medium capable of thermal reversible rewriting and a reversible rewriting method using the reversible recording medium.
[0002]
[Prior art]
A recording material made of a cholesteric liquid crystal compound having a molecular weight of 2000 or less and a glass transition temperature of 35 ° C. or higher or a material containing the compound has a longer cholesteric liquid crystal phase reflection color at room temperature by quenching from the cholesteric liquid crystal phase state. Recording media that can be stored for a long time and can be repeatedly written by reheating to return to the liquid crystal phase state are known (N. Tamaki, AV Parfenov, A. Masaki, H. Matsuda, Adv. Mater). 1997, 9, 1102-1104).
The recording material can be applied to rewritable full color recording and multi-value recording media.
[0003]
[Problems to be solved by the invention]
The recording material has promising characteristics as a recording material for rewritable full-color recording and multi-value recording media as described above. However, a part or all of the heat-sensitive recording material is heated by heating means. After reaching the temperature showing the isotropic phase, the temperature is lowered to a temperature at which the recording layer reflects the target reflected light, and then the quenching operation is performed from there. There is a problem that the recording operation becomes complicated.
An object of the present invention is to provide a reversible recording medium capable of simply fixing a target reflected light by simply controlling the cooling rate, and a reversible recording method using the reversible recording medium.
[0004]
[Means for Solving the Problems]
The present invention comprises a recording layer composed of a heat-sensitive recording material made of a cholesteric liquid crystal compound or a mixture containing the compound, sandwiched between two transparent substrates, and the recording layer However, after heating a part or all of the region to a temperature showing an isotropic phase or a cholesteric liquid crystal phase at a high temperature, the recording material is cooled at an appropriate cooling rate in accordance with the selected wavelength desired to be fixed. A reversible recording medium that can be recorded with a desired cholesteric reflection color fixed in the cooled region by cooling to a temperature below the glass transition temperature of the cholesteric liquid crystal compound or at room temperature. The reversible recording medium, wherein the cholesteric liquid crystal compound constituting the compound is represented by the following formula (I) and / or ( II ), and the reversible recording medium By providing a recording method using a body, the above problem could be solved.
[Chemical 3]

[Formula 4]

Wherein Z and Y are each independently a cholesteryl group, dihydrocholesteryl group, hydrogen atom or alkyl group, R is a hydrogen atom or alkyl group, and m and n are each independently an integer of 1 or more. And at least one of Z and Y represents a cholesteryl group or a dihydrocholesteryl group).
[0005]
In the reversible recording medium of the present invention and the recording method using the reversible recording medium, the cholesteric liquid crystal compound increases as the cooling rate of the reversible recording medium from the temperature showing the isotropic phase or the cholesteric liquid crystal phase at a high temperature increases. The selective reflection wavelength observed on the high temperature side of the cholesteric liquid crystal compound phase becomes impossible, for example, at a temperature below the glass transition temperature or at room temperature before the alignment following the temperature is lost and the alignment taken on the high temperature side is broken. Is fixed and recording of a desired color can be performed.
[0006]
That is, the cholesteric liquid crystal compound used in the present invention is heated to form an isotropic phase or a cholesteric liquid crystal phase at a high temperature, and then rapidly cooled to the glass transition temperature or below or to room temperature. It becomes a glassy solid while maintaining the color, and a selective reflection color is observed.
The fixation of the desired cholesteric reflection color is preferably performed by cooling to a glass transition temperature or lower.
[0007]
The cholesteric liquid crystal compound used in the present invention has a cholesteric liquid crystal phase at a glass transition temperature or higher, an isotropic phase at a temperature higher than that, and is capable of fixing the cholesteric reflection color as described above. The type of the glass transition point is not particularly limited, but those having a glass transition point of 30 ° C. or higher are preferred in order to stably store the recording at room temperature.
[0008]
Examples of the cholesteric liquid crystal compound having the above-described characteristics include those represented by the following formulas (I) and (II).
[0009]
[Chemical formula 5]

[0010]
[Chemical 6]

Wherein Z and Y are each independently a cholesteryl group, dihydrocholesteryl group, hydrogen atom or alkyl group, R is a hydrogen atom or alkyl group, and m and n are each independently an integer of 1 or more. And at least one of Z and Y represents a cholesteryl group or a dihydrocholesteryl group).
[0011]
The cholesteric liquid crystal compound used as the liquid crystal recording material represented by the above formulas (I) and (II) has a molecular weight of 2000 or less, a glass transition temperature of 30 ° C. or more, and exhibits a cholesteric liquid crystal phase at or above the glass transition temperature. It shows an isotropic phase at higher temperatures.
As the cholesteric liquid crystal compound, a cholesteric liquid crystal represented by the following formula (III) (hereinafter referred to as C8DY8C) is particularly preferable because it is stable at room temperature in a glass state. Furthermore, the following formula (IV) (hereinafter referred to as I-8-DiHC) in which the cholesterol portion of C8DY8C is changed to dihydrocholesterol is more preferable because of high thermal stability at high temperatures.
A plurality of cholesteric liquid crystal compounds used in the present invention may be mixed.
[0012]
[Chemical 7]

(III)
[0013]
[Chemical 8]

(IV)
[0014]
As the reversible recording medium substrate of the present invention, glass or a plastic film such as PES or PET can be used, but the type is not particularly limited.
Further, a substrate in which an alignment film is formed on the surface in contact with the recording layer can be used. For example, the substrate can be formed by the following method. A soluble polyimide solution (JSR Optmer AL3046) is used to spin-coat a coating solution dissolved at a concentration of 1% by weight on a cleaned glass substrate, and a resin thin film is formed through a drying process.
Next, a rubbing cloth for a general LCD alignment film was attached to the flat member, and the flat member was disposed so as to be in contact with and away from the polyimide surface. Only when the glass substrate or the planar member is reciprocated and moved in one direction, the rubbing cloth and the polyimide surface are brought into contact with uniform load and rubbed in one direction. It is used as a reversible recording medium substrate so that the rubbed polyimide film surface is inside.
[0015]
The type of heating means for obtaining the isotropic phase is not particularly limited, but appropriate heating means and heating conditions can be appropriately selected according to the required heating rate. For example, a hot plate, a laser beam, a thermal head, or the like can be used. However, the heating means is not limited to these.
[0016]
The type of quenching means for fixing the cholesteric reflection color is not particularly limited, but for example, appropriate cooling means and cooling conditions are appropriately selected according to the cooling rate required according to the desired cholesteric reflection color. Can be selected. As a cooling means, water cooling, air cooling, a metal plate, a glass plate etc. can be used, for example. However, the cooling means is not limited to these.
[0017]
Further, as a rapid cooling method for fixing the cholesteric reflection color, for example, the following method can also be employed.
(1) fixing different reflection colors in the film thickness direction by changing the quenching speed in the film thickness direction of the recording layer;
(2) A pattern is formed on the surface of the substrate as a difference in temperature, and the cooling rate of the recording layer is changed by the pattern, and different reflection colors are fixed, or (3) as a cooling means on the substrate The substrate is cooled by using a cooling plate having a pattern formed of a material having a different heat capacity and / or thermal conductivity, and the cooling rate of the recording layer is changed by the pattern to fix different reflection colors.
Since the cooling rate can be made different between the portion where the pattern is formed and the portion where the pattern is not formed, different reflection colors can be easily fixed.
[0018]
Hereinafter, embodiments of the reversible recording method of the present invention will be described.
[0019]
Embodiment 1
The recording layer composed of the heat-sensitive recording material containing C8DY8C or a mixture containing the compound is allowed to reach a part or all of the region to a temperature showing an isotropic phase, and then cooled at 15 to 35 ° C./second. By cooling to the glass transition temperature or less at a speed, a red reflected color could be fixed in the cooled region.
[0020]
Embodiment 2
A recording layer composed of a heat-sensitive recording material containing C8DY8C or a mixture containing the compound is allowed to reach a part or all of the region to a temperature showing an isotropic phase, and then cooled at 70 to 100 ° C./second. By cooling at a rate below the glass transition temperature, the green reflected color could be fixed in the cooled area.
[0021]
Embodiment 3
A recording layer composed of a heat-sensitive recording material containing C8DY8C or a mixture containing the compound is allowed to reach a part or all of the region to a temperature showing an isotropic phase, and then cooled at 155 to 330 ° C./second. By cooling at a rate below the glass transition temperature, the blue reflected color could be fixed in the cooled area.
[0022]
The results of Embodiments 1 to 3 are shown in Table 1 below.
[Table 1]

In the above embodiments and examples, the cooling rate was determined by taking a video of the cooling process of the cholesteric liquid crystal compound using an infrared camera and reproducing the recorded image at a low speed.
[0023]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
[0024]
Example 1
On a hot plate, a C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm was heated to an isotropic phase (130 ° C.) and then cooled to −15 ° C. When it was cooled at 330 ° C./s by placing it on top, the blue color could be fixed. However, when enlarged, a slightly white portion was observed, and then 330 ° C./second was judged as the upper limit.
[0025]
Example 2
On a hot plate, a C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm was heated to an isotropic phase (130 ° C.) and then cooled to −10 ° C. When it was cooled at 240 ° C./s by placing it on top, the blue color could be fixed.
[0026]
Example 3
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 micrometers) with a thickness of 10 micrometers was heated to an isotropic phase temperature (130 ° C.) and then cooled to −5 ° C. When it was cooled at 155 ° C./second by placing it on top, the blue color could be fixed. However, when enlarged, a part of the green color was observed, and 155 ° C./second was judged as the lower limit.
[0027]
Example 4
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic phase (130 ° C.) and then cooled to 0 ° C. When it was cooled at 100 ° C./second by placing it on the surface, the green color could be fixed. However, when enlarged, a part of the blue color was observed, and the upper limit was determined to be 100 ° C./second.
[0028]
Example 5
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic temperature (130 ° C.) and then placed on a 25 ° C. copper plate. When it was cooled at 70 ° C./second, the green color could be fixed. However, when enlarged, a red-green part was partially observed, and 70 ° C./second was judged as the lower limit.
[0029]
Example 6
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic phase temperature (130 ° C.) and then placed on a 10 ° C. glass substrate. When it was cooled at 35 ° C./second by placing it, the red color could be fixed. However, when enlarged, a part of reddish green was observed, and the upper limit was determined to be 35 ° C./second.
[0030]
Example 7
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic phase temperature (130 ° C.) and then placed on a 25 ° C. glass substrate. When it was cooled at 15 ° C./second by placing it, the red color could be fixed. However, when enlarged, a part of white was observed, and 15 ° C./second was judged as the lower limit.
[0031]
Example 8
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic phase temperature (130 ° C.), then −10 ° C. smaller than the glass substrate When only the portion was cooled at 240 ° C./second by placing it on a triangular copper plate cooled in the same manner, blue was fixed only in the triangular portion, and the other portion became white, and a blue pattern was recorded.
[0032]
Example 9
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 micrometers) with a thickness of 10 micrometers was heated to an isotropic phase temperature (130 ° C.), and then a 0 ° C. copper plate and −10 A copper plate cooled to 0 ° C. is brought close to each other, and each of the substrates is placed so as to straddle the two copper plates, whereby cooling is performed at 100 ° C./sec and 240 ° C./sec in different regions of the respective temperatures. In green, blue was fixed on a copper plate cooled to −10 ° C., and patterns with different colors were recorded.
[0033]
Example 10
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 micrometers) with a thickness of 10 micrometers is heated to an isotropic temperature (130 ° C), then a copper plate at 25 ° C and 25 ° C The glass plates are placed close to each other, and the substrates are placed so as to straddle the two plates, so that they are cooled at 70 ° C./second and 20 ° C./second in different regions of the respective materials. The red color was fixed on the plate, and patterns with different colors were recorded.
[0034]
Example 11
On a hot plate, C8DY8C sandwiched between two glass substrates (thickness 130 μm) with a thickness of 10 μm is heated to an isotropic phase (130 ° C.) and then cooled to 0 ° C. When sandwiched between 30 ° C. glass plates, a yellow reflected color was obtained. In order to observe the color of each side, the C8DY8C sandwiched between the copper plate and the glass plate was peeled off, and the color was observed separately on the side cooled with the copper plate and the side cooled with the glass plate. It was found that the board side was fixed in red.
The fixed colors in Examples 1 to 11 could be stably stored at room temperature for 6 months or more.
[0035]
Example 12
A cholesteric liquid crystal sandwiched between two glass substrates (thickness 130 μm) on a hot plate with a thickness of 10 μm [In the formula (I), Z and Y are both cholesteryl groups, R is hydrogen, m = n = 6, 8,12-eicosadienedioic acid dicholesteryl ester] was heated to an isotropic phase temperature (150 ° C.), then immersed in room temperature water and rapidly cooled to fix the blue color. . This blue color could be maintained for 2 weeks.
[0036]
Example 13
On the hot plate, I-8-DiHC sandwiched between two glass substrates (thickness 130 μm) on which a rubbed alignment film is formed with a thickness of 10 μm is an isotropic phase (135 ° C. ), After heating to 330 degrees per second by placing on a copper plate cooled to -15 degrees, yellowish green could be fixed.
[0037]
Example 14
On the hot plate, I-8-DiHC sandwiched between two glass substrates (thickness 130 μm) on which a rubbed alignment film is formed with a thickness of 10 μm is an isotropic phase (135 ° C. ), After heating, it was placed on a glass substrate at 10 degrees and cooled at 35 degrees per second. Therefore, 35 degrees per second was determined as the lower limit.
[0038]
Example 15
On the hot plate, I-8-DiHC sandwiched between two glass substrates (thickness 130 μm) on which a rubbed alignment film is formed with a thickness of 10 μm is an isotropic phase (135 ° C. ), After being heated on a triangular copper plate cooled to -10 degrees smaller than the glass substrate, only that part was cooled at 240 degrees per second, only the triangular part was fixed, and the other parts were white A yellow-green pattern was recorded.
[0039]
Example 16
On the hot plate, I-8-DiHC sandwiched between two glass substrates (thickness 130 μm) on which a rubbed alignment film is formed with a thickness of 10 μm is an isotropic phase (135 ° C. ), The glass plate cooled at 25 degrees and the glass sheet cooled to 10 degrees are brought close to each other, and the substrate is placed so as to straddle the two copper plates. When the glass plate was cooled at 25 ° C. and white on the glass plate cooled to 10 ° C., the yellow-green color was fixed, and patterns with different colors were recorded.
[0040]
Example 17
On the hot plate, I-8-DiHC sandwiched between two glass substrates (thickness 130 μm) on which a rubbed alignment film is formed with a thickness of 10 μm is an isotropic phase (135 ° C. ), A 0 degree copper plate and a 25 degree glass plate are brought close to each other, and the substrate is placed so as to straddle the two plates, thereby cooling at 100 degrees and 15 degrees per second in different regions of the respective materials. A yellow-green color was fixed on the copper plate and a white color was fixed on the glass plate, and patterns with different colors were recorded.
[0041]
Example 18
When the cholesteric glass of C8DY8C and I-8-DiHC fixed in the above example was subjected to a heat resistance test for 10 seconds on a hot plate, C8DY8C was whitened at 95 degrees, but I-8-DiHC was white. It was found that I-8-DiHC cholesteric glass was more stable to high temperatures.
[0042]
【effect】
1.
By controlling the cooling rate from the cholesteric liquid crystal phase at the isotropic phase or at high temperature, it is possible to easily fix the target reflected light , and a reversible recording medium excellent in stability at room temperature of the fixed reflected color. Provided.
2.
A reversible recording medium that is easy to batch write is provided.
3.
There is provided a reversible recording method in which the target reflected light can be easily fixed only by controlling the cooling rate from the cholesteric liquid crystal phase at the isotropic phase or at a high temperature.
4).
Provided is a reversible recording method capable of multi-value recording with three primary colors without reducing the recording density.
5.
As means for changing the cooling rate, substances having different heat capacities and / or thermal conductivities are used, so that batch writing is easy and the cooling means can be used repeatedly.
6).
There is provided a reversible recording method that is easy to batch write without changing the material, can easily change the pattern, and can be used repeatedly for cooling.
7).
In C8DY8C, red can be fixed only by controlling the cooling rate from the isotropic phase.
8).
In C8DY8C, green can be fixed only by controlling the cooling rate from the isotropic phase.
9.
In C8DY8C, blue can be fixed only by controlling the cooling rate from the isotropic phase.
10.
In I-8-DiHC, the yellowish green color can be fixed only by controlling the cooling rate from the isotropic phase.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a phase change of a cholesteric liquid crystal compound.

Claims (11)

The recording layer is composed of a heat-sensitive recording material made of a cholesteric liquid crystal compound or a mixture containing the compound and sandwiched between two transparent substrates, and the recording layer is one of the recording layers. After heating a part or all of the region to an isotropic phase or a temperature showing a cholesteric liquid crystal phase at a high temperature, the recording material is cholesteric by selecting an appropriate cooling rate according to a selected wavelength desired to be fixed. A reversible recording medium capable of performing recording by fixing a desired cholesteric reflection color in the cooled region by cooling to a temperature equal to or lower than the glass transition temperature of the liquid crystal compound, and a cholesteric liquid crystal constituting a recording layer A reversible recording medium , wherein the compound is represented by the following formula (I) and / or ( II ) .

Wherein Z and Y are each independently a cholesteryl group, dihydrocholesteryl group, hydrogen atom or alkyl group, R is a hydrogen atom or alkyl group, and m and n are each independently an integer of 1 or more. And at least one of Z and Y represents a cholesteryl group or a dihydrocholesteryl group).   The reversible recording medium according to claim 1, wherein the cholesteric liquid crystal compound constituting the recording layer is a cholesteric liquid crystal compound having a molecular weight of 2000 or less. A transparent substrate has a pattern formed on the substrate with materials having different heat capacities and / or thermal conductivities, and the cooling rate is different between a portion where the pattern is formed and a portion where the pattern is not formed. The reversible recording medium according to claim 1 , wherein the reversible recording medium is a product. The reversible recording medium according to any one of claims 1 to 3 , after heating a part or all of the recording layer of the recording medium to a temperature showing an isotropic phase or a high temperature cholesteric liquid crystal phase, The recording material is cooled to a temperature equal to or lower than the glass transition temperature of the cholesteric liquid crystal compound by selecting an appropriate cooling rate in accordance with a selected wavelength desired to be fixed, so that a desired cholesteric reflection color is applied to the cooled region. A recording method for a reversible recording medium, wherein the recording is performed with the recording medium fixed. 5. A reversible recording medium recording method according to claim 4, wherein the recording is performed by changing the cooling rate with respect to the film thickness direction of the recording material and fixing different reflection colors in the film thickness direction in the same recording pit. As a cooling means, cooling is performed using a cooling plate in which a pattern is formed of a material having a different heat capacity and / or thermal conductivity from the substrate on the cooling substrate, and the cooling rate is changed by the pattern, so that different reflection colors are used. The reversible recording medium recording method according to claim 4, wherein recording is performed with fixing. 5. A reversible recording medium recording method according to claim 4 , wherein a pattern is formed on the surface of the cooling substrate as a difference in temperature, the cooling rate is changed by the pattern, and the recording is performed while fixing different reflection colors. 8. The recording method for a reversible recording medium according to claim 4 , wherein Dicholesteryl 10,12-Docosadiynedioate is used as the cholesteric liquid crystal compound, and the red reflection color is fixed by cooling at 15 to 35 [deg.] C./sec. The recording method for a reversible recording medium according to any one of claims 4 to 7 , wherein Dicholesteryl 10,12-Docosadiynedioate is used as the cholesteric liquid crystal compound, and the green reflective color is fixed by cooling at 70 to 100 ° C / second. The recording method for a reversible recording medium according to any one of claims 4 to 7 , wherein Dicholesteryl 10,12-Docosadiynedioate is used as the cholesteric liquid crystal compound, and the blue reflective color is fixed by cooling at 155 to 330 ° C / second. As the cholesteric liquid crystal, a cholesteric liquid crystal in which Z and Y are both dihydrocholesteryl groups and m = n = 8 in the above formula (II) is used, and the cooling rate from the isotropic phase is 35 ° C / sec. The recording method of the reversible recording medium according to claim 4 , wherein the yellow-green reflection color is fixed as described above.

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