JP2719160B2 - Reversible thermosensitive recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reversible thermosensitive recording material for performing image formation (recording) and erasing by utilizing a reversible change in transparency of a thermosensitive material depending on temperature.

Prior art JP-A-54-119377, JP-A-55-154198, JP-A-63-3
No. 9378 proposes a reversible recording material having a heat-sensitive layer in which a low-molecular organic substance such as a higher fatty acid is dispersed in a resin base material such as a vinyl chloride-based resin. Is a non-colored state using a change in transparency due to the temperature of the heat-sensitive layer, which is performed by a transparent portion (colorless portion) and an opaque portion (white turbid portion). Met.

An object of the present invention is to improve the contrast during image formation (recording) by forming a color state without impairing the reversibility of a conventional reversible thermosensitive recording material, and to enhance the visibility more strongly while simultaneously realizing two colors. It is an object of the present invention to provide a reversible thermosensitive recording material capable of forming (recording) images as described above.

Configuration The reversible thermosensitive recording material of the present invention is a thermosensitive material having a base material and an organic low-molecular substance dispersed in the base material as main components, and having a transparency that reversibly changes depending on temperature. The base material is a polymer liquid crystal material.

The present invention is characterized in that one or more liquid crystal substances are used as a base material, and the liquid crystal substance is preferably a thermotropic polymer cholesteric liquid crystal derivative.
By using a liquid crystal substance as the mother phase, a color change can be reversibly obtained depending on the temperature.

This is because the helical pitch of the polymer cholesteric liquid crystal changes depending on the temperature, has the property of selectively reflecting or transmitting light of a specific wavelength corresponding to the pitch length, and rapidly cools after heating to the corresponding temperature. As a result, the helical pitch is also fixed, and the color state due to reflection or transmission of a specific wavelength can be stabilized.

The type of coloration and the coloration temperature can be arbitrarily changed depending on the selected thermotropic polymer cholesteric liquid crystal.

 The present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram showing an example of the configuration of the reversible thermosensitive recording material of the present invention. The basic structure is a structure in which a heat-sensitive layer T made of a polymer liquid crystal material in which an organic low-molecular substance is dispersed is provided on a support B, and a protective layer P is appropriately provided as necessary.

The support B is a transparent or colored material, and a known material such as a plastic film, for example, a polyester film (Mylar), a glass plate, or a metal plate can be used.
The thickness of the support B is preferably about 10 to 300 μm.

The protective layer P is preferably a transparent material, for example, silicone rubber, silicone resin (JP-A-63-221087), polysiloxane graft polymer (Japanese Patent Application No. 62-152550).
Transparent film such as UV-curable resin (Japanese Patent Application No. 62-310969), and the thickness is preferably 10 μm or less.

The thickness of the heat-sensitive T is 1 to 100 μm, preferably 10 to 50 μm.
m is good. When the thickness is 1 μm or less, the turbidity decreases, and the contrast decreases. When the thickness is 100 μm or more, the thermal sensitivity decreases. The material constituting the heat-sensitive layer will be described in detail below.

The recording principle of the recording material of the present invention utilizes a change in transparency of an organic low-molecular substance and a change in coloration of a liquid crystal substance depending on the temperature of a heat-sensitive material. This will be described with reference to FIG. Thermosensitive layer in FIG. 2, for example, in the T ₀ lower at room temperature in cloudy opaque state. When this is heated to a temperature between T _{1 and} T ₂ , it becomes a transparent state. In this state, even when the temperature is returned to room temperature equal to or lower than T _{0, a} transparent and almost colorless state is maintained. The whole was transparent material, after further partially heated by a thermal head or the like T ₃ temperature above, when rapidly cooled to T ₀ or less at room temperature, only the heated portion without taking transparent state, the first It becomes an opaque part according to the opaque state. On the other hand, the liquid crystal material in partial heating portion heated to T ₃ or more temperature is stabilized colored. Therefore, in this state, image formation (recording) with a markedly improved contrast composed of colored opaque portions with the transparent portions as the background is achieved. The recording material of the present invention,
Color was colored in two or more colors to reflect light of a specific wavelength corresponding to the changed helical pitch of thermotropic polymer liquid crystal depending on the temperature by heating to T ₃ or more different two or more temperature It is also possible to form different images.

Alternatively, the whole when rapidly cooled to T ₀ or less at room temperature and heating the recording material to the overall first T ₃ or more temperature opaque state is maintained in a color development state. After the whole it was heated partially by a thermal head or the like at a temperature between the color former and further T ₁ opacifying material and through T _2, when quenched to T ₀ or less at room temperature, partial heating portion is made transparent stable Therefore, image formation (recording) with good contrast composed of the transparentized portion with the colored opaque portion as the background is achieved.

Note that the transparent part looks transparent because the organic low-molecular substance dispersed in the base material of this part is composed of large crystal particles, so that light incident from one side is not scattered, and the other It is considered that the light is transmitted to the side. The opaque part looks white because the organic low-molecular substance dispersed in the base material of this part is composed of polycrystalline particles in which fine crystals are aggregated, and the crystal axes of the individual crystals are oriented in various directions. It is considered that the light incident from one side is refracted and scattered many times at the interface of each crystal.

Recording and erasing of the above-described laminar thermal member can be repeated at least 10 about ⁴ times.

As described above, according to the present invention, there is provided a reversible thermosensitive recording material capable of forming an image (recording) by utilizing a reversible change in transparency to opacity with a color state corresponding to a heating temperature. .

The polymer liquid crystal material used in the present invention is preferably a thermotropic polymer cholesteric liquid crystal derivative. In any case, it is necessary that the main chain or the bent chain contains an optically active unit, and the mesogen group is bonded to a vinyl monomer (acrylate ester, methacrylate ester, etc.) with or without a spacer. A polymer obtained by adding a vinyl-substituted mesogen monomer to the Si-H bond of poly [oxy (methylsilylene)], which binds a reactive mesogen monomer to the backbone of a liquid crystal monomer or a polymer, Or cholesteryl-ω- (4-methacryloyloxyphenylalkanoate), cholesterol Siloxa with derivative and nematic liquid crystal molecule Derivatives or copolymers, copolymers of benzyl and dodecyl esters of polyglutamic acid and the like are known as typical thermotropic polymer cholesteric liquid crystals.

Hereinafter, specific examples of the polymer liquid crystal substance used in the present invention are shown below.

i) Main-chain type liquid crystal polymer Homopolymer or copolymer of polyester, polyesteramide, polycarbonate, polyether or the like having the following structure: ii) Side chain type liquid crystal polymer Homopolymer or copolymer such as vinyl polymer or siloxane polymer having the following structure: iii) Rigid main chain type liquid crystal polymer In addition to a polypeptide having the following structure, a homopolymer or copolymer of a polyisocyanate and a cellulose derivative: (R and R ′ each represent an alkyl, alkoxyalkyl, aralkyl, aryl group, or the like.) Alternatively, a liquid crystal polymer of the following mixed type of a rigid main chain type and a side chain type: (R represents an alkyl group or the like.) Next, specific structural examples of preferred cholesteric liquid crystal polymers used in the present invention are shown.

In the heat-sensitive layer, the organic low-molecular substance exists in a dispersed state as fine particles in a polymer liquid crystal substance as a base material.

On the other hand, the organic low-molecular substance may be appropriately selected in accordance with the selection of the temperatures T _{0 to} T ₃ in FIG.
Material corresponding to a temperature of T ₂ through T ₃ is selected according to the purpose,
For example, those having a melting point of 30 to 200 ° C, particularly about 50 to 150 ° C are preferable. Such low-molecular organic material, preferably include higher fatty acid or a derivative thereof is more than C ₈ carbon atoms, is used at least 1 or more. Examples of such organic low molecular weight substances include: alkanol; alkanediol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyne; halogen alkane; Saturated or 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;
Halogen allylic carboxylic acids or their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or 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
10-38, especially 10-30 is preferred. The alcohol group in the ester may be saturated or unsaturated, 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 2, -S} -, - S-S -, - O-, it is preferably a compound containing a halogen and the like.

More specifically, these compounds include lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid,
Stearic acid, behenic acid, nonadecanoic acid, arachiic acid,
Higher fatty acids such as oleic acid; esters of higher fatty acids such as methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, docosyl behenate; And ether or thioether.

The ratio between the organic low-molecular substance and the base material in the heat-sensitive layer is preferably about 1: 0.5 to 1:16 by weight, more preferably 1: 1 to 1: 3. If the ratio of the base material is less than this, it becomes difficult to form a film holding the organic low-molecular substance in the base material,
On the other hand, if it is more than this, the amount of the organic low-molecular substance is small, so that it is difficult to make the material opaque.

The method of forming the heat-sensitive layer T includes: (i) a method of dissolving both an organic low-molecular substance and a high-molecular liquid crystal substance in a solvent, and evaporating the solvent to precipitate the organic low-molecular substance as fine particles; A method of dissolving a polymer liquid crystal substance using a solvent that dissolves only the polymer liquid crystal substance, and pulverizing and dispersing the organic low molecular substance therein by various methods, or (iii) using an organic solvent without using a solvent. There is a method of heating, melting and mixing both the molecular substance and the high-molecular liquid crystal substance, and then cooling to form a heat-sensitive layer sheet.

As the solvent for forming the heat-sensitive layer, various solvents can be used depending on the type of the organic low-molecular substance and the high-molecular liquid crystal substance. Examples include organic solvents such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene and benzene.

As a coating method, a conventionally known coating method such as a casting method can be arbitrarily used.

Hereinafter, the present invention will be described with reference to examples. "Department"
And "%" are by weight.

Example 1 Poly [oxy (methylsilylene)] to which cholesterol derivative and nematic liquid crystal molecule are added 10 parts Stearic acid 4.8 parts Tetrahydrofuran / chloroform 60 parts (1/1 volume ratio mixed solvent) are mixed and dissolved. Is coated on a transparent polyester film (Mylar) with a thickness of 50 μm with a wire bar, dried at 150 ° C, and then directly oriented by applying shear stress with a hot roller at 70 to 80 ° C, cooled to room temperature and almost colorless. A heat-sensitive recording sheet provided with a transparent heat-sensitive layer having a thickness of 30 μm was obtained.

Next, when the recording sheet thus obtained was printed from the surface thereof at 135 ° C. by using a thermal head, the printed portion was colored and a greenish opaque printed image was obtained.

When the recording sheet was entirely heated in an oven at 70 ° C. and allowed to cool to room temperature, a recording sheet having a transparent printed portion was obtained.

Example 2 L-glutamic acid-γ-benzyl / L-glutamic acid-γ
-Dodecyl copolymer (dodecyl group content 37.5%) 8 parts Behenic acid 5 parts Stearyl stearic acid ester 1 part Tetrahydrofuran / chloroform 77 parts (2/1 volume ratio mixed solvent) Was coated on a transparent polyester film (Mylar) with a wire bar, dried at 150 ° C., and allowed to cool to room temperature to obtain a cloudy and opaque heat-sensitive recording sheet. Further, several recording sheets were prepared under the same conditions. The heat-sensitive layer thickness of each sheet was in the range of 12 to 18 μm.

Next, when the recording sheet thus obtained was printed from the surface using a thermal head at 130 ° C., a yellowish opaque printed image with a greenish tint was obtained at the printed portion.

In addition, when printing was performed at 140 ° C. using a thermal head on each of the other portions of the same recording sheet, a pink-red opaque printed image was obtained at the printed portion, and printing was performed at 150 ° C. on the other portion. The printed portion was a greenish blue opaque printed image. In this way, a multicolor recorded image with good contrast, which was colored in different colors with the cloudy opaque portion as the background, was obtained.

When the recording sheet was entirely heated in an oven at 70 ° C. and allowed to cool to room temperature, the whole was made transparent, and the colored image was left as it was at the portion printed at each temperature. Overhead projector (OHP)
When projected in, the remaining colors of each color, that is, green and yellow printed at 130 ° C is blue, pink red printed at 140 ° C is blue green,
Green-blue printed at 150 ° C. was projected and displayed as a pink-red recording image.

Any of the images formed in Examples 1 and 2 can be erased by heating, and another image can be formed again.

Effect As described above, by using a thermotropic polymer cholesteric liquid crystal material as a base material of the heat-sensitive layer and dispersing an organic low-molecular material, the cholesteric spiral pitch changes simultaneously with the change in transparency depending on the heating temperature,
Various color changes can be made by selective reflection or transmission of a specific wavelength corresponding thereto, so that contrast is improved and
Since image formation (recording) and erasing of colors or more can be repeatedly performed reversibly, it is useful as various reversible thermosensitive recording materials, display materials, and storage materials.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of the configuration of the reversible thermosensitive recording material of the present invention. FIG. 2 is an explanatory view of the principle of recording and erasing of the reversible thermosensitive recording material of the present invention. B: Support, T: Thermosensitive layer P: Protective layer

Continuation of the front page (72) Inventor Yasuyuki Takiguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-2-117892 (JP, A) JP-A-63-145080 (JP, A) JP-A-62-209186 (JP, A) JP-A-59-10930 (JP, A) JP-A-60-179294 (JP, A) JP-A-62-154340 (JP, A)

Claims (1)

(57) [Claims] 1. A thermosensitive material comprising a base material and an organic low-molecular substance dispersed in the base material as main components, wherein the transparency is reversibly changed depending on temperature, wherein the base material is a polymer. A reversible thermosensitive recording material characterized by being a liquid crystal substance.