JPH0765036B2 - Reversible thermochromic material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reversible thermochromic material which is sensitive to, for example, the photothermal conversion action of a semiconductor laser and reversibly changes its colored state by heat. The present invention relates to a reversible thermochromic material capable of providing a novel display device.

[Outline of Invention]

The present invention provides an electron-donating color-forming organic compound having a lactone ring, an electron-accepting compound having a phenolic hydroxyl group, a melting point in a film-forming state mixed with these compounds, and a freezing point at a temperature lower than the melting point. Providing a novel reversible thermochromic material capable of coloring and erasing at a practical rate by forming a film of a mixture of crystalline polymers that it has, for example, providing a new display device using a semiconductor laser as a scanning source. It is intended to try.

[Conventional technology]

Conventionally, temperature display of indoor thermometers, foods, foods and drinks due to color change, temperature detection by color in various industries, and use of color change to add fashionability to toys, teaching materials, stationery, etc. For the purpose, development of a thermochromic material whose color reversibly changes with heat is under way.

For example, in JP-A-55-157677 and JP-A-57-90085, a thermochromic material mainly composed of an electron-donating color-developing organic compound and a compound having a phenolic hydroxyl group as a developer is disclosed. It is disclosed.

These thermochromic materials change their colors to various colors or change from colored to colorless in a temperature range of approximately -50 ° C to 150 ° C, and are expected to have various uses as temperature-indicating functional materials.

[Problems to be solved by the invention]

However, the conventional thermochromic materials are not satisfactory in response speed to heat and it is difficult to control discoloration locally.

Therefore, the present invention has an object to provide a reversible coloring and decoloring material which is excellent in response speed to heat and is capable of repeating coloring and decoloring in response to heat generated by the photothermal conversion action of a semiconductor laser, for example. An object of the present invention is to provide a reversible thermochromic material that is useful as a display panel of a display device.

[Means for solving problems]

The present inventor discovered the following phenomenon in the course of research on thermochromic materials.

That is, when a certain type of leuco dye (pigment precursor) is dissolved in a high molecular weight polymer having a long alkyl group in the side chain together with a suitable phenolic compound (developing agent), it is colored (colored) at room temperature. On the other hand, when it is heated to a temperature exceeding the melting point of the high molecular weight substance, it changes to a colorless and transparent state, and conversely, when it is cooled to a temperature below the freezing point of this high molecular weight substance, it returns to the colored state. Moreover, this phenomenon was reversible and showed the same behavior over and over.

As a result of further investigation, this behavior depends largely on the phase change of the high molecular weight polymer in which the former two compounds (dye precursor and developer) are dissolved, and As a result, it has been found that the color change can be controlled by heat.

The present invention has been completed based on such findings, and an electron-donating color-forming organic compound having a lactone ring, and an electron-accepting compound having a phenolic hydroxyl group,
It is characterized in that it is made of a crystalline polymer having a melting point and a freezing point at a temperature lower than the melting point in a film-forming state mixed with these compounds, and these films are film-formed.

The thermochromic decolorizing material of the present invention becomes colorless and transparent to visible light by appropriately selecting the density condition and the like at the time of decoloring, and thus does not need a black base unlike thermochromic materials utilizing cholesteric liquid crystals. If a uniform film is formed on a transparent support such as a film or glass by utilizing the film forming property of the high molecular weight substance, it functions as a light shutter and is suitable for use as a display panel material or the like. Can be said to be a thing.

In the present invention, the crystalline polymer used as a high molecular weight substance, dissolving an electron-donating compound having an electron-donating color-forming organic compound or a phenolic hydroxyl group, having a melting point similar to crystals, It is required that the freezing point be lower than the melting point.

Here, in particular, regarding the melting point, the sample and the thermally inactive reference substance are placed in the same container, respectively, and both are placed under equivalent conditions while the ambient temperature is raised or lowered at a constant chromaticity. It can be confirmed by a differential thermal analysis in which the temperature difference (differential temperature) between the two is continuously measured.
That is, when a substance having a melting point is subjected to a differential thermal analysis, the heat of fusion (the amount of heat required for a substance in the solid phase to change to a liquid phase at the same temperature) is required at the time of melting, Temperature difference (differential temperature) becomes large. Therefore, if there is an endothermic peak due to this differential temperature, it is determined to have a melting point.

In addition, the fact that the freezing point is lower than the melting point means that, for example, the behavior as shown in FIG. 1 is exhibited when the high molecular weight substance is heated and cooled.

That is, in the example shown in FIG. 1, when the sample is heated, the sample suddenly begins to change into a liquid phase from around 47 ° C. as shown by a curve A in the figure, and most of the sample is in the liquid phase at 48 to 49 ° C. Be in phase. On the other hand, when the sample in the liquid phase is cooled, the liquid phase state is maintained up to around 45 ° C as shown by the curve B in the figure, and when the temperature is lower than that, the solid phase is rapidly changed. Go. Therefore, if this sample is kept at a temperature below the melting point and above the freezing point (hereinafter referred to as the bias temperature), the thermally stimulated portion will keep the liquefied state when thermally stimulated by some means. It will be.

As described above, the crystalline polymer used as the high molecular weight substance needs to exhibit so-called hysteresis behavior. Note that this hysteresis-like behavior may be due to the characteristics of the crystalline polymer itself, or may be due to the freezing point depression due to the incorporation of the electron-donating color-forming organic compound or the electron-accepting compound having a phenolic hydroxyl group. Good.

Examples of the crystalline polymer include polyethylene, polyacrylate, polymethacrylate, polyacrylamide, etc., and homopolymers or copolymers thereof can be used. For example, by a method such as radical polymerization or radical copolymerization, higher fatty acid ester of acrylic acid or methacrylic acid is polymerized alone or linearly polymerized in the presence of another monomer to obtain a high molecular weight, and thus synthesized. be able to. However, even in the case of a copolymer, it is necessary to maintain crystallinity. The physical properties of the obtained high molecular weight substance are variously changed depending on the property of the monomer (polymerizable monomer) used, and this property is dependent on the change temperature of the color fading and fading of the reversible thermochromic material of the present invention. It greatly affects the degree of color change.

On the other hand, the electron-donating color organic compound is a colorless or light-colored compound itself, and is an organic compound that changes to a colored state by donating an electron to the electron-accepting compound described later, and examples thereof include leuco dyes. To be However, in the present invention, any compound may be used as long as it is a leuco dye, and it is necessary to use a leuco dye having a lactone ring in order to exhibit the above-mentioned color fading behavior.

The leuco dyes having a lactone ring are roughly classified into triphenylmethanephthalides, fluoranes, thiofluoranes, indolylphthalides, rhodamine lactams, and azaphthalides, and the following compounds are exemplified.

First, examples of triphenylmethanephthalides include crystal violet lactone and malachite green lactone, and examples of fluoranes include 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-6
-Benzyloxyfluorane, 1,2-benz-6-diethylaminofluorane, 3,6-di-p-toluidino-4,5-
Dimethylfluorane-phenylhydrazide-γ-lactam, 3-amino-5-methylfluorane, 2-methyl-3-
Amino-6-methyl-7-methylfluorane, 2,3-butylene-6-di-n-butylaminofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7- (paratoluidino)- Fluorane, 7-acetamino-3-diethylaminofluorane, 2-bromo-6-cyclohexylaminofluorane, 2,7-dichloro-3-methyl-6-n-butylaminofluorane and the like can be mentioned.

Further, as thiofluoranes, 3-diethylamino-
6-methyl-7-dimethylamino-thiofluorane, 3-
Diethylamino-7-dibenzylamino-thiofluorane and the like can be mentioned, and as indolylphthalides, 8-
(4-Diethylaminophenyl) -8- (1-ethyl-
2-Methylindol-8-yl) phthalide, 3,3-bis (1-ethyl-2-methyl-8-yl) phthalide, 3,3-
Bis (2-phenylindol-3-yl) phthalide, 3
-(4-Di-n-butylaminophenyl) -3- (2-
Phenylindol-3-yl) phthalide, 8- [4-
(Dimethylamino) phenyl] -3- [N, N-bis-
(4-octylphenyl) amino] phthalide and the like can be mentioned.

Further, the rhodamine lactams include rhodamine lactone, and the azaphthalides include 3,3-bis (1-ethyl-2-methylidol-3-yl) -7-azaphthalide.

Further, the electron-accepting compound plays a role as a developer, and in the present invention, a compound having a phenolic hydroxyl group can be used.

For example, tertiary butylphenol, nonylphenol, dodecylphenol, styrenated phenols, 2,2-methylenebis- (4-methyl-6-tertiarybutylphenol), α-naphthol, β-
Naphthol, hydroquinone monomethyl ether, guaiacol, eugenol, p-chlorophenol, p-bromophenol, o-chlorophenol, o-bromophenol, o-phenylphenol, p-phenylphenol, p-
(P-chlorophenyl) -phenol, o- (o-chlorophenyl) -phenol, methyl p-oxybenzoate, p-
Ethyl oxybenzoate, p-Propyl oxybenzoate, p-
Butyl oxybenzoate, p- Octyl oxybenzoate, p-
Dodecyl oxybenzoate, 3-isopropylcatechol, p
-Tert-butyl catechol, 4,4-methylenediphenol, 4,4-thio-bis- (6-tert-butyl-
3-methylphenol), 1,1-bis- (4-hydroxyphenyl) -cyclohexane, 4,4-butylidene-bis-
(6-tert-butyl-3-methylphenol),
Bisphenol A, bisphenol S, 1,2-dioxynaphthalene, 2,3-dioxynaphthalene, chlorcatechol,
Bromocatechol, 2,4-dihydroxybenzophenone,
Phenolphthalein, o-cresolphthalein, methyl protocatechuate, ethyl protocatechuate, propyl protocatechuate, octyl protocatechuate, dodecyl protocatechuate, 2,4,6-trioxymethylbenzene , 2,3,4-Trioxyethylbenzene, methyl gallate, ethyl gallate, propyl gallate, butyl gallate, hexyl gallate, octyl gallate, dodecyl gallate, cetyl gallate, stearyl gallate, 2,3 Examples include 5,5-trioxynaphthalene and tannic acid.

The heat-decoloring material of the present invention is obtained by mixing the above-mentioned components and forming a film by utilizing the film-forming property of the high molecular weight substance.

The above film plays a role as a recording holding layer,
When it is heated above the melting point of the crystalline polymer, it becomes decolorized,
This decolored state is maintained at a temperature equal to or higher than the freezing point, and the color is developed below the freezing point.

The crystalline polymer contained in the film has different melting points and freezing points, and this property is reflected even in the case of a film exhibiting coloration / decoloration behavior, and the color change exhibits hysteresis with respect to temperature. Therefore, if the entire film is kept at the bias temperature, when a thermal stimulus is applied by some means, the stimulated part is liquefied and becomes colorless, but the non-stimulated part is initially colored. keep. In addition, maintaining the bias temperature also has the meaning of suppressing the amount of thermal stimulation energy required for causing the phase transition as much as possible.

Here, in order to maintain the film at the bias temperature, heating is performed by sandwiching the film on a glass substrate and supporting this glass substrate with a metal frame, or by providing a nesa film on the surface of the glass substrate, resistance heating by the nesa film is performed. And the like.

For the reversible thermochromic decolorizing material configured as described above, for example, if a semiconductor laser beam with an output of about 10 mW is image-wise scanned as a thermal stimulus source, an image in which the scanning part is colorless and transparent is formed, and the bias is applied. The image is retained (recorded) as long as the temperature is maintained. Further, in order to erase the image, the temperature may be set to a temperature below the freezing point of the crystalline polymer by cooling. Before this cooling operation, an operation of heating the entire coating film to a melting point or higher may be added.

With these series of techniques, it is possible to provide a high quality still image display device that can be rewritten by opening a new use as a display device. Such a display device is capable of displaying a still image by a series of thermal cycles, being capable of directly looking at a good contrast from any direction, having high resolution,
It has the characteristics that it is possible to form high-quality images in terms of halftone expression, there is no image flicker, it is possible to suppress eye fatigue of the viewer, and it is easy to increase the screen size. .

In terms of apparatus, a panel coated with the thermochromic material of the present invention, a heater (not necessarily required) for keeping the panel at a bias temperature, a scanning optical system, and a semiconductor laser as an image scanning source. Therefore, it is thinner and lighter than, for example, a cathode ray tube, and is easy to manufacture and inexpensive.

There is a heat-writable liquid crystal as a similar device which can be written by such a semiconductor laser, and it is a device for blackening a light scattering structure (white turbid state) thermally formed in the liquid crystal by projection. The display device using the thermochromic material of the present invention has an advantage that the on-off image of visible light can be directly viewed without projecting.

Of course, the heat source for selectively erasing the heat-decolorable material of the present invention is not limited to the above-mentioned semiconductor laser, but may be, for example, a thermal head (line type, serial type, etc.), a thermal pen, a xenon lamp, or another thermal source. A radiator can be used, and it does not matter whether it is in contact or not.

In particular, when a light source such as a xenon lamp or a semiconductor laser is used as a heat source and the heat generated by the photothermal conversion action is used, a dye that absorbs heating light is added to the heat-decoloring material film or the glass substrate that supports it. The efficiency may be increased.

[Action]

The reversible thermochromic material of the present invention uses a crystalline polymer having a melting point and a critical phase change, and has an electron-donating color-forming organic compound having a lactone ring and a phenolic hydroxyl group. It is characterized by dissolving an electron-accepting compound in a molecular form, and the electronic state of a color former (electron-donating color-forming organic compound) in such a crystalline polymer changes with a phase change. Are estimated to be reflected in the thermochromic behavior.

In fact, when the reversible thermochromic material of the present invention is heated above the melting point of the crystalline polymer, it becomes in a decolored state, and this decolored state is maintained at a temperature of solidification or higher, and at the solidification point or lower, it becomes a colored state.

〔Example〕

 Hereinafter, the present invention will be described based on experimental examples.

The method of synthesizing the crystalline polymer and the method of expressing the coloration and decoloration behavior, which are indispensable for realizing the present invention, are described in Experimental Examples 1 to 3, and a writing experiment using a semiconductor laser as a scanning heat source is performed. 4 shows.

Experimental Example 1 45 g of n-stearyl acrylate (0.14
Mol) and the polymerization initiator azobisisobutyronitrile
0.5 g (0.003 mol) was added, and 100 g of ethyl alcohol as a reaction solvent was further added and dissolved.

Next, while maintaining the inside of the round bottom flask at 80 ° C., heating and stirring were continued for 1 hour under a nitrogen stream. After the solution became cloudy, the mixture was cooled to room temperature and a large amount of white precipitate formed.

Then, the white precipitate was collected by filtration, repeated reprecipitation from a toluene-methanol mixed solvent, and dried at 40 ° C. under reduced pressure to obtain about 40 g of white powder.

The obtained powder was slightly soluble in polar solvents such as alcohol and acetone, and easily soluble in nonpolar solvents such as toluene, and was clearly different from the starting monomer.
Moreover, its melting point was about 48 ℃, and it showed a reversible solid-liquid change like wax.

The white powder was analyzed by DSC (Differential Thermal Scanning Calorimeter) and found to have a sharp melting point at 48 ° C and 41
It was found to have a freezing point at ~ 43 ° C.

Next, this white powder (hereinafter, referred to as high molecular weight substance I).
And a leuco dye (electron-donating color organic compound) as a dye precursor and a developer (electron-accepting compound) were mixed in the following composition, and the whole was kept at 180 ° C. for 15 minutes to be compatible with each other.

Composition [leuco dye] 2- (2'-chlorophenylamino) -6-n-dibutylaminofluorane 0.06 g [Developer] benzyl p-hydroxybenzoate 0.24 g [crystalline polymer] Polymer I 2.0 g As shown in Fig. 2, the width of this compatible solution (1) remains liquid.
When injected into a glass cell (2) having a void of 50 μm (t = 50 μm in the figure) and cooled to room temperature to solidify,
The non-colored state changed to a blackened state. When heated again, when the glass temperature of the glass cell (2) reached about 45 ° C., a remarkable color change (black → transparent) was shown, and similar color change was reversibly repeated by heating and cooling. However, the change from the transparent state to the black state occurred at about 40 ° C, and the reversible change showed hysteresis.

The above-described color fading behavior is shown by a change in the absorption spectrum of the glass cell (2) in the direction shown in the figure [that is, the absorption spectrum when the incident light I ₀ is the transparent light I]. FIG. 3 shows a comparison between absorption spectra when colored and when colorless. In the figure, curve a shows the absorption spectrum when colored, and curve b shows the absorption spectrum when colorless.

Experimental Example 2 45 g (0.14 mol) of n-stearyl acrylate, 8.2 g (0.07 mol) of ethyl methacrylate and 0.5 g (0.003 mol) of azobisisobutylnitrile as a polymerization initiator were dissolved in 100 g of ethyl alcohol, and the same as in Experimental Example 1. When the solution was heated and stirred by various methods, the solution became cloudy and a large amount of white precipitate was obtained by cooling to room temperature.

The white precipitate was collected by filtration, washed with ethanol, dissolved in toluene to remove insoluble components by filtration, and reprecipitated with methanol. When this reprecipitation operation was repeated, in comparison with Experimental Example 1, about 45 g of a slightly transparent powder was obtained.

The obtained powder is easily soluble in acetone, toluene, etc.,
It was found that when dissolved in these materials and applied and dried, a film having more flexibility than the high molecular weight substance I was formed.

As a result of DSC measurement, this powder showed a broad melting point around 33 to 40 ° C and did not show a clear freezing point. However, the reversible change of liquid (40 ℃ or more) and solid (room temperature) could be repeated.

Next, the obtained powder (hereinafter referred to as high molecular weight substance II).
And leuco dye and developer with the following composition in toluene (solvent)
Was applied to a synthetic paper so that the applied thickness when wet was 200 μm, dried at 60 ° C. for 15 minutes, and then cooled to room temperature to obtain a colored (blackened) film.

Composition [Leuco dye] 2- (2'-chlorophenylamino) -6-n-dibutylaminofluorane 0.2g [Developer] Bisphenol A 0.6g [Crystalline polymer] Polymer II II 7.0g [Coating solvent] Toluene 10.0 g Further, a polyethylene terephthalate film having a lubricating layer on the blackened film was subjected to thermocompression bonding (so-called lamination) to obtain a thermal paper-like film. The structure of the prepared film is shown in FIG. In other words, this heat-sensitive paper-like film is formed by applying a leuco dye, a synthetic paper (11) as a support,
A structure in which a heat-sensitive layer (12) containing a color developer and a high molecular weight material [the above-mentioned blackened film], a polyethylene terephthalate film (13) which is a transparent support, and a lubricating layer (14) exhibiting heat resistance are sequentially laminated. I have.

The obtained film was mounted on a video graphic printer (Sony, UP701) and printing was performed in a negative mode.
Note that the printing was done in the negative mode because in order for the output image to be equivalent to that of normal thermal paper, the printing section (that is, the heating section) should be whitened due to the operating principle of this film. It depends on what you have to do.

As a result, it was possible to obtain an image in which the contrast, gradation, and resolution were almost the same as those of commercially available thermal paper, and the sensitivity was more excellent. This image was kept at room temperature for about 5 minutes and then slowly disappeared.

In addition, after the image is formed on the film, the entire surface is heated (whitened) to erase the image, and then cooled again to blacken the film.
When printing was performed again, the same image formation as the first time was performed, showing that repeated printing was possible.

Experimental Example 3 A high molecular weight substance III was synthesized in the same manner as in Experimental Example 1 using n-stearyl methacrylate as a starting monomer. As a result of DSC measurement, this high molecular weight substance III was found to have a slightly broad melting point (melting point width 3 to 4 ° C.) near 40 ° C. and a freezing point near 28 ° C.

Next, the high molecular weight substance III, the leuco dye and the color developer having the following composition were dissolved in a toluene-acetone mixed solvent, and a synthetic paper was formed into a film by the same method as in Experimental Example 2 and the same as shown in FIG. A heat-sensitive paper-like film having the constitution was obtained. The obtained film was colored blue.

Composition [leuco dye] Crystal violet lactone 0.1 g [Developer] Octyl gallate 0.3 g [Crystalline polymer] High molecular weight polymer III 4.0 g [Coating solvent] Toluene-acetone mixed solvent 5.0 g At this room temperature ( At this time, the film is in a colored state.) A xenon lamp light with an output of 500 W was condensed by a lens, irradiated, and exposed. In addition, the irradiated xenon lamp light is a total light ray excluding ultraviolet rays with a filter, and the light intensity is 1.6 mW /
It was exposed for 0.5 seconds at cm ² .

As a result, the exposed portion became colorless. However, in this case, since the base synthetic paper was white, it was actually observed as whitened.

In addition, when the exposure was stopped and cooled to room temperature, the colorless portion returned to the initial colored state (blue state), and repeated exposure-cooling operations caused color changes between coloring (blue) and decoloring (white). Was repeated.

It was confirmed that the film obtained in Experimental Example 2 also showed similar changes (color change between black and white).

Experimental Example 4 In Experimental Example 3, a method of making a colored body colorless by visible light was shown. However, when an infrared light emitting semiconductor laser having an output of about 10 mW is used as a heat source to obtain a similar change, a leuco dye is generally used. It is difficult to obtain a practical writing speed because the color developing material does not have absorption in a desired wavelength range (emission wavelength range of a semiconductor laser) and has low photothermal conversion efficiency.

Therefore, a dye having a large absorption in the wavelength range of the semiconductor laser is allowed to coexist in the film exhibiting the above-mentioned color fading behavior, or a layer containing the above dye is provided in a portion in close contact with this film, and laser light is applied. Efficient conversion to heat solves this problem. Further, when it is required to be colorless at the time of decoloring, it is preferable that the infrared light absorbing dye is colorless and transparent to visible light.

From this point of view, in the present experimental example, a squalium-based dye (having a sensitivity in the vicinity of a wavelength of 780 nm in this example) was selected as a dye satisfying the above requirements, and an attempt was made to sensitize it to infrared rays (laser light) by using it. It was

First, a color fading material having the following composition was obtained, and a glass cell having a color fading layer having a thickness of 10 μm was obtained in the same manner as in Experimental Example 1. The squalium dye was insoluble in the high molecular weight substance I alone, but could be dissolved by coexisting with the color developer.

Composition [leuco dye] 2- (2'-chlorophenylamino) -6-n-dibutylaminofluorane 0.1 g [Developer] Octyl gallate 0.2 g [Crystalline polymer] Polymer I 2.0 g [red] External sensitizing dye] Squalium dye 0.007g Next, as shown in FIG. 5, the glass cell (22) having the color fading and decoloring layer (21) was attached to a holder having a heater for heating, and the tungsten color lamp (23) was used as a light source for the color fading and decoloring. The image formed on the layer (21) was placed so as to be projected onto the screen (25) via the projection length (24). The light from the tungsten lamp (23) was filtered through the infrared light blocking filter (26) to remove the infrared light, and the glass cell (22) was irradiated by the condensing lamp (27).

On the other hand, laser light from the laser diode (30) connected to the power supply unit (28) and the pattern generator (29) is applied to the galvano-scanner mirror (31) on the coloration / decoloration layer (21) of the glass cell (22). ), A condenser lens (32), and a half mirror (33) to selectively decolor the coloring / decoloring layer (21) to form an image.

That is, while keeping the temperature of the entire glass cell (22) at 42 ° C., a laser beam having a wavelength of 780 nm is focused on the coloration / decoloration layer (21) with a diameter of about 10 μm, and an image is formed at 400 μsec per dot. Scanned. As a result, the portion of the coloring / discoloring layer (21) irradiated with the laser light was erased, and a blank image was projected on a black background on the screen (25). This image also shows the glass cell temperature (here 42
(° C) was kept as it was.

The writing speed of the image and the contrast of the obtained image are determined by the concentration ratio of the components contained in the color fading layer (21), the holding temperature of the glass cell (22), the thickness of the color fading layer (21), the laser light intensity. However, when writing is performed under the above conditions with a laser light intensity (in the oscillation part) of 20 mW using the coloring / discoloring layer having the composition shown in this experimental example, the coloring / discoloring layer becomes colorless. To do this, 400 μsec was required for each dot.

Further, it was confirmed that when the laser light irradiation time per dot is changed, light and shade are generated in the image, and even if the laser light irradiation time is about 40 μsec / dot, a decoloring reaction occurs to some extent under the above conditions. Therefore, it was proved that the above-mentioned coloring / decoloring layer (21) has a gradation expression capability.

Under the conditions described above (scanning with laser light at 400 μsec / dot), the contrast of the obtained image was 6: 1 on the screen (25).

In the above-mentioned experimental examples, the coloration / decoloration behavior at room temperature or higher was described with emphasis on practicality, but it is also possible to cause the color-decoloration reaction at a relatively low temperature. For example, when a crystalline polymer obtained by polymerizing lauryl / tridecyl mixed acrylate is used, it shows a transition point at 0 ° C. or lower, and it is possible to develop and decolor in a low temperature region.

〔The invention's effect〕

As is clear from the above description, the reversible thermochromic material of the present invention comprises an electron-donating color-forming organic compound having a lactone ring, an electron-accepting compound having a phenolic hydroxyl group, and a mixture of these compounds. A crystalline polymer having a freezing point at a melting point and a temperature lower than the melting point in a formed film state, and these are formed into a film,
Since it exhibits reversible coloration / decoloration behavior due to heat and excellent thermal response, it is possible to display and rewrite images and the like at a practical speed.

Therefore, for example, it can be applied to a display device using a semiconductor laser as a scanning source, and it is possible to provide a high-quality display device capable of image observation by transmission, reflection, direct view or projection.

INDUSTRIAL APPLICABILITY The reversible thermochromic material of the present invention is capable of displaying a still image by a series of thermal cycles, being capable of directly looking at a good contrast in all directions, capable of forming a high-quality image, and having no image flicker. Since it has features such as easy enlargement of the screen, and can easily form a film at low cost, it is extremely useful as a display functional material.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a hysteresis characteristic in a phase change of a crystalline polymer. FIG. 2 is a schematic perspective view showing a method for measuring an absorption spectrum of a reversible thermochromic material, and FIG. 3 shows an example of an absorption spectrum of the reversible thermochromic material when it is colored and when it is decolorized. It is a characteristic diagram. FIG. 4 is an enlarged cross-sectional view of an essential part showing a structural example when the reversible thermochromic material of the present invention is used as a film. FIG. 5 is a schematic diagram showing a structural example of a display device which displays an image by the photothermal conversion action of a semiconductor laser using the reversible thermochromic material of the present invention.

Claims (1)

[Claims] 1. An electron-donating color-forming organic compound having a lactone ring, an electron-accepting compound having a phenolic hydroxyl group, and a melting point and a freezing point at a temperature lower than the melting point in a film-forming state in which these compounds are mixed. A reversible thermochromic material which is formed of a crystalline polymer having the following features.