JPH02117888A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To enhance contrast and enable reversible formation and erasure of images in two or more colors to be repeated by using a high molecular weight liquid crystal substance as a base material of a thermal recording layer, and dispersing an organic low molecular weight substance in the base material. CONSTITUTION:A reversible thermal recording material comprises a thermal recording layer T comprising an organic low molecular substance dispersed in a high molecular weight liquid crystal substance, on a support B, with a protective layer P being provided, as required. The thermal recording layer is in a cloudy opaque state at room temperature of not higher than T0, for example. When the layer is heated to a temperature of T1 to T2, the layer becomes transparent, and the transparent and substantially colorless state is maintained even when the layer made to be transparent is returned to the room temperature of not higher than T0. When the material made to be transparent entirely is partially heated further to a temperature of not lower than T3 by a thermal head or the like and then rapidly cooled to room temperature of not higher than T0, only the part heated to or above T3 becomes an opaque part corresponding to the initial opaque state. The liquid crystal substance in the partially heated part, heated to or above T3, is stabilized with coloration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reversible thermosensitive recording material that performs image formation (recording) and erasing by utilizing reversible changes in transparency of a thermosensitive member depending on temperature.

Japanese Patent Application Publication No. 54-119377, Japanese Patent Application Publication No. 15419-1982
No. 8, JP-A No. 63-39378, etc., have proposed a reversible recording material having a heat-sensitive layer in which an organic low-molecular substance such as a higher fatty acid is dispersed in a resin base material such as a vinyl chloride resin. The image formation (recording) and erasing utilizes the change in transparency of the heat-sensitive layer depending on the temperature. The contrast obtained by this method was poor.

Purpose The present invention aims to improve the contrast during image formation (recording) by forming a colored state without impairing the reversibility of conventional reversible thermosensitive recording materials, thereby further improving visibility and at the same time The object of the present invention is to provide a reversible thermosensitive recording material that enables image formation with more than one color (Reference #I).

Structure The reversible thermosensitive recording material of the present invention is a thermosensitive material whose main components are a base material and an organic low-molecular substance dispersed in the base material, and whose transparency changes reversibly depending on the temperature. hand,
The base material is a polymeric liquid crystal material.

The invention is characterized by the use of one or more liquid crystal substances as a host, the liquid crystal substances preferably being thermotropic polymeric cholesteric liquid crystal derivatives. By using a liquid crystal material as a base material, a temperature-dependent color change can be obtained reversibly.

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

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

The present invention will be explained in more detail with reference to the accompanying drawings.

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

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

Protection [P is preferably a transparent material, e.g.

Silicone rubber, silicone resin (Japanese Patent Application Laid-open No. 63-22
1087), polysiloxane graft polymer (Japanese Patent Application No. 152550/1983), ultraviolet curing resin (Japanese Patent Application No.
A transparent film such as No. 2-310969) can be used, and its thickness is preferably 10 μm or less.

The thickness of the heat-sensitive layer T is 1 to 100 μm, preferably 10 to 100 μm.
Approximately 50 μm is preferable; when the thickness is 1 μm or less, the white turbidity decreases and the contrast becomes low; when the thickness is 100 μm or more, the thermal sensitivity decreases.

The materials constituting the heat-sensitive layer will be detailed below.

The recording principle of the recording material of the present invention utilizes changes in the transparency of an organic low-molecular substance and changes in color of a liquid crystal substance depending on the temperature of a heat-receptor, and this will be explained with reference to FIG. In FIG. 2, the heat-sensitive layer is in a cloudy, opaque state at a room temperature of T0 or higher, for example.

When this is heated to a temperature between 11 and 12, it becomes transparent, and even if it is returned to room temperature above T0 in this state, it remains transparent and almost colorless. When this completely transparent material is heated partially with a thermal head or the like to a temperature higher than T1, and then rapidly cooled to room temperature higher than T0, only the heated parts remain in the initial opaque state without becoming transparent. On the other hand, the liquid crystal material in the partially heated part heated to a temperature of 13 or higher becomes colored and stabilized. Therefore, in this state, the recording material of the present invention achieves the formation (recording) of an image with significantly improved contrast, which is composed of colored opaque areas against a transparent area as a background. By heating it to a certain temperature, it reflects light of a specific wavelength that corresponds to the helical pitch that changes depending on the temperature of the thermotropic polymer liquid crystal, so it is possible to form images with different colors of two or more colors. .

Alternatively, if the entire recording material is first heated to a temperature of T1 or higher and rapidly cooled to a room temperature of T0 or higher, the entire recording material remains colored and opaque. If this material, which has become entirely colored and opaque, is further partially heated to a temperature between 11 and 12 using a thermal head, etc., and then rapidly cooled to room temperature above T0, the partially heated parts become transparent and stabilized. , image formation (recording) with good contrast consisting of a transparent portion with a colored opaque portion as a background is achieved.

The transparent part appears transparent because the organic low-molecular substance dispersed in the base material of this part is composed of large crystal particles, so light incident from one side is not scattered and is transmitted to the other side. This is thought to be because it is transmitted to the side. Also, the reason why the opaque area appears white is because the organic low-molecular substance dispersed in the base material of this area is composed of polycrystalline particles that are aggregation of microcrystals, and the crystal axes of the individual crystals are oriented in various directions. This is thought to be because light incident from one side is refracted and scattered many times at the interface of each crystal.

Recording and erasing on the layered heat-sensitive member as described above can be repeated at least about 10 times.

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

The polymeric liquid crystal material used in the present invention is preferably a thermotropic polymeric cholesteric liquid crystal derivative.

In either case, it is necessary that the main chain or bent chain contains an optically active unit, and the mesogenic group is bonded to the vinyl monomer (acrylic acid ester, methacrylic acid ester, etc.) with or without a spacer. an addition polymer of a liquid crystal monomer, or a polymer in which a vinyl-substituted mesogen monomer is added to the side chain of the 5L-H bond of poly[oxy(methylsilylene) co, in which a reactive mesogen monomer is bonded to the backbone chain of the polymer; Alternatively, there is an esterification reaction with low-molecular mesogens or cholesterol derivatives added to functional groups, or polypeptides that form cholesteric liquid crystals, such as cholesteryl-ω-(
4-methacryloyloxyphenylalkanoate)
, siloxane derivatives or copolymers with added cholesterol derivatives and nematic liquid crystal molecules, and copolymers of benzyl ester and dodecyl ester of polyglutamic acid are known as typical thermotropic polymeric cholesteric liquid crystals.

Specific examples of polymeric liquid crystal materials used in the present invention are shown below.

i) Main chain type liquid crystal polymer Polyester, polyesteramide having the following structure,
Homopolymer or copolymer such as polycarbonate or polyether knee+M-X engineering+-+p, -x, + -◎-◎-coo-◎-2-◎-N=CH-■-1-◎
−C=CH−◎−, etc.; A: −+CH2+nt −
(-CHzCHzO+n+ +CH-C)120+n.

■ CH:1-a1. -W+-+co, +n, - and l++cH, +n
.

H3CH3 (* indicates an optically active carbon atom) X□, X2: -Coo-, -CONH-, -0
CO-, -0-, etc.

ii) Side-chain type liquid crystal polymer A homopolymer or copolymer such as a vinyl polymer or a siloxane polymer having the following structure. 0+n,
+CH-CH, 0+n etc.; CH.

M: −◎−◎−R, −0−◎−◎−R2−◎−coo
-◎-R, -0-◎-coo-◎-R.

-◎-0CO-@-R, -0-◎-oco-◎-R1-
◎-◎-Coo-@-R.

−〇−■−◎−oco−◎−R2−◎−oco−◎, −
◎-R1CH3CH,CH.

Cholesterol derivatives, etc.; 1ii) Rigid main chain type liquid crystal polymer In addition to polypeptides having the following structure, homopolymers or copolymers of polyisocyanates and cellulose derivatives: C0ORC0ORC0OR' (R and R' are alkyl, alkoxyalkyl , aralkyl, aryl group, etc.) Or, the following mixed liquid crystal polymers of rigid main chain type and side chain type: R +Co-CH-NH→- and -+CH-G square]
1 (CI, ), C0 COOR0R (R represents an alkyl group, etc.) Next, a specific structural example of a preferable cholesteric liquid crystal polymer used in the present invention will be shown.

+0-◎-coo-◎-oco+cHz)z-5u-c
o, -c+.

CH.

, , , , , (-0-@-C-C)I-◎-co+
coz)4-co-), -x lυ CH.

! +CH, -C+ COO-◎+CH2)n-COOCztH4s.

CH3CN3 1+CH,-C+x ,,,,,,,,,,,,,
-C-CH, -C+, Xcoo-◎-coo-@-◎-
CN coocH, -6+-co, co3゜茅CH3 +CH2-fJ-x, , , , , , , , , .

Coo+CH,)G-◎-COO-◎-◎-QC)! .

CH3 night ,,1. ,,,+CH,-C),-x sound Hff CH3CN.

1+5i-0+x ,,,,,,,,,,,,,,,
,,,(Si-0)-,-x(CH2)nr-0-◎-
COO-◎-OCH, (C)1. )3-COOC,ff
H,S.

-+NH-CH-CO+ ■ CH, CH2-C00CH, -@-0R (R: -C
Hze-CsHLi, -Cz2Hzg, -CxJaay
-CxzH*s).

-←NH-CH-Co)x , , , , , , , ,
-+NH-CH-Co→-1-su CH2CH2-Coo
(CH, ), CIl, coOc2) In the 1° heat-sensitive layer, the organic low-molecular substance exists in a dispersed state as fine particles in the polymeric liquid crystal substance as the base material.

On the other hand, the organic low-molecular substance may be appropriately selected depending on the temperature T0 to T3 in FIG. 2, and a material whose melting point or freezing point corresponds to the temperature T2 to T3 is selected depending on the purpose, such as , melting point 30-200°C, especially 50-150°C
Examples of such organic low-molecular substances, which preferably have a temperature of about 0.degree. Examples of such organic low molecular weight substances include alkanols; alkanediols; halogenalkanols or halogenalkanediols; alkylamines; halogenalkanes; halogenalkenes, halogenalkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or unsaturated Mono- or dicarboxylic acids or their esters, amides, or ammonium salts; Saturated or unsaturated halogenated fatty acids or their esters, amides, or ammonium salts; Allylcarboxylic acids or their esters, amides, or ammonium salts;
Examples include halogenallyl 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 preferably have 10 to 60 carbon atoms, preferably 10 to 38 carbon atoms, and particularly preferably 10 to 30 carbon atoms. The alcohol moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low-molecular substance contains at least one of oxygen, nitrogen, sulfur, and halogen in the molecule, such as monoOH, -COO.
H, -CONH, -GOOR, -NH-.

Compounds containing -NH, -S-, -S-S-, -〇-, halogen, etc. are preferred.

More specifically, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, balmitic acid, stearic acid, behenic acid, nonadecanoic acid, arachidic acid, and oleic acid; methyl stearate, and tetradecyl stearate. , octadecyl stearate, octadecyl laurate, tetradecyl balmitate.

Esters of higher fatty acids such as tocosyl behenate; C□H.
, -o-cl, oj, t(:xaHzs-S-Cxa
H3jc1g”21-s-cLIo3ff-Ct
z”zs-S-CtzHzsCtsH3g-S-Clg
Has, Ct□H, -S-S-C Eng2H2.

C)+2' CHx ”OCOClz Hz s
CHt ”CHz 'COOC1a f(a tC
H.

to CH2・CH,・ococm)Izt ■ CH.

There are ethers and thioethers such as

The ratio of the organic low-molecular substance to the base material in the heat-sensitive layer is preferably about 1:0.5 to 1:16 in terms of weight ratio, and 1:1 to 1:
3 is more preferable. When the ratio of the base material is less than this,
It becomes difficult to form a film that retains the organic low-molecular substance in the base material, and on the other hand, if the amount exceeds this range, it becomes difficult to make it opaque because the amount of the organic low-molecular substance is small.

Methods for forming the heat-sensitive layer T include (i) a method in which both an organic low-molecular substance and a high-molecular liquid crystal substance are dissolved in a solvent, and when the solvent is evaporated, the organic low-molecular substance is precipitated as fine particles; (ii) A method of dissolving a polymeric liquid crystal material using a solvent that dissolves only the polymeric liquid crystal material, and pulverizing and dispersing the organic low molecular material therein using various methods, or (iii) dissolving the organic low molecular material without using a solvent. There is a method in which both a molecular substance and a polymeric liquid crystal substance are heated, melted, and mixed, and then cooled 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 organic low-molecular substance and high-molecular liquid crystal substance. For example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene. , benzene, and other organic solvents.

Any conventionally known coating method such as a casting method can be used as the coating method.

(The following is a blank space.) The present invention will be described below with reference to Examples. In addition, “department”
and “%J are all based on weight.

Example 1 Stearic acid 4.
The components consisting of 8 parts were mixed and dissolved, and this was applied onto a 50 μm thick transparent polyester film (Mylar) with a wire bar, dried at 150°C, and then heated in a hot oven at 70 to 80°C.
Direct shear stress was applied with a roller to orient the sheet, and the sheet was cooled to room temperature to obtain a transparent, almost colorless thermal recording sheet provided with a 30 μm thick thermal layer.

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

Further, when this recording sheet was heated as a whole in an oven at 70° C. and then allowed to cool to room temperature, a recording sheet with transparent printed portions was obtained.

Example 2 Behenic acid 5
Partial stearic acid stearyl ester
A heat-sensitive record that is made cloudy and opaque by mixing and dissolving two parts of the ingredients, coating it on a 50 μm thick transparent polyester film (Mylar) with a wire bar, drying it at 150°C, and cooling it to room temperature. Got a sheet. Furthermore, several recording sheets were created under similar conditions. The heat-sensitive layer thickness of each sheet was within the range of 12 to 18 μm.

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

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

In addition, when this recording sheet was heated as a whole in an oven at 70°C and then allowed to cool to room temperature, the whole became transparent, and the colored images remained as they were in the areas printed at each temperature. Overhead projector (○HP
), the remaining colors of each color, i.e., the green-yellow printed at 130°C becomes blue, the pink-red printed at 140°C becomes bluish-green, and the green-blue printed at 150°C becomes pink-red. Projection display is now available.

Any of the images formed in Examples 1 to 3 can be erased by heating, and it is possible to form another image again.

Effects As mentioned above, by using a thermotropic polymeric cholesteric liquid crystal substance as the base material of the heat-sensitive layer and dispersing an organic low-molecular substance, the cholesteric helix pitch changes simultaneously with the transparency change depending on the heating temperature. , various color changes can be made by selective reflection or transmission of corresponding specific wavelengths, which improves contrast and enables reversible and repeated image formation (recording) and erasing of two or more colors. It is useful as a reversible thermosensitive recording material, display material, and memory material.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the structure of the reversible thermosensitive recording material of the present invention. FIG. 2 is an explanatory diagram of the recording and erasing principle of the reversible thermosensitive recording material of the present invention. B11. Support Tol, heat sensitive layer P, 6. Protective layer Figure 1 Figure 2 Temperature

Claims (1)

[Claims] 1. In a thermosensitive material whose main components are a base material and an organic low-molecular substance dispersed in the base material, and whose transparency changes reversibly depending on temperature, the base material is a polymeric liquid crystal substance. A reversible thermosensitive recording material characterized by the following.