JPH0648027A - Reversible thermal coloring composition and reversible thermal recording medium using the same composition - Google Patents

Abstract

PURPOSE:To obtain a reversible thermal coloring composition which colors and discharges due to heating by blending higher fatty acid having hydroxyl as a discharge promoter with an electron-donative color developer and an electron-receptive compound as principal ingredients. CONSTITUTION:0.5 to 50wt.% of higher fatty acid having hydroxyl such as 2-hydroxy butyric acid or 2-hydroxy-2-methylpropanic acid for an electron- donative color developing compound such as a triphenyl methanepthalide compound, an electro-receptive compound such as an organic phosphate compound, are evenly dispersed or dissolved in water or an organic solvent, with said electron-receptive compound, and if desired, with a binder. Thus, a reversible thermal coloring composition is prepared. This reversible thermal coloring composition is applied on the surface of a substrate as plastic film or synthetic paper, and then is dried to form a laminated thermal recording layer. This reversible thermal recording medium obtained has an image with a sharp contrast and an extended discharge temperature range, contributing toward the improvement of image erasing properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermochromic composition utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound, and a reversible thermosensitive recording medium using the same. It is a thing.

[0002]

2. Description of the Related Art Conventionally, electron-donating color-forming compounds (hereinafter referred to as
A heat-sensitive recording medium utilizing a color-developing reaction between a color former and an electron-accepting compound (hereinafter also referred to as a developer) is widely known, and the output of a computer, a facsimile,
Widely applied to automatic ticket vending machines, printers for scientific measuring machines, CRT medical measuring printers, etc. However, all conventional products have irreversible color development,
Coloring and erasing cannot be repeated alternately.

On the other hand, according to the patent publication, there have been proposed some thermosensitive recording media which utilize a color-forming reaction between a color-developing agent and a color-developing agent to reversibly perform color-developing and decoloring. For example, according to JP-A-60-193691,
The use of a combination of gallic acid and phloroglucinol as a color developer is shown. The color-developing material obtained by thermally coloring this material is decolorized with water or steam. However, in the case of this heat-sensitive recording medium, there is a problem in that it is difficult to make it water resistant, and there is a problem in the storage stability of the recording medium, and further, the erasing device for erasing the color developing body becomes large. JP-A-61-237684 discloses a rewritable optical recording medium using a compound such as phenolphthalene, thymolphthalene or bisphenol as a developer. This product can be decolored by heating it and removing it to form a color-forming material, while heating the color-forming material once to a temperature higher than the color density and then rapidly cooling it. However, in the case of this recording medium, the coloring and erasing steps are complicated, and some color is still seen in the erasable body obtained by erasing the chromophore, and a colored image with good contrast is obtained. I can't. JP-A-62-14088
1, JP-A-62-138568 and JP-A-62-1.
No. 38,556 discloses a homogeneous compatible solution of a color former, a developer and a carboxylic acid ester. This one shows a completely colored state at a low temperature and a completely decolored state at a high temperature, and it is possible to maintain the colored or decolored state at an intermediate temperature between them, by printing on this medium with a thermal head,
White characters (decolored body) can be recorded on the colored background (colored body). Therefore, in the case of this recording medium, since the image to be recorded is a negative image, its use is limited, and it is necessary to keep the image within a specific temperature range for storing the recorded image. JP-A-2-188294 and JP-A-2-188293 disclose a salt of gallic acid and a higher aliphatic amine and bis (hydroxyphenyl) that reversibly perform a color developing action and a color reducing action, respectively, as a color developing agent. The use of a salt of acetic acid or butyric acid and a higher aliphatic amine is shown. This product can be colored by heat in a specific temperature range and decolorized by heating at a higher temperature.
Since the color developing action and the color reducing action occur competitively, it is difficult to thermally control these actions, and it is difficult to obtain a good image contrast.

As described above, the conventional reversible thermosensitive recording medium utilizing the reaction between the color former and the developer has various problems and is still unsatisfactory. The present applicant previously used a compound such as an organic phosphoric acid having a long-chain aliphatic group as a color developer, a carboxyl compound, a phenol compound, or a hydroxyphosphonic acid, and combined this with a fluoran compound as a color developing agent. By doing so, the coloring and decoloring can be easily performed only by heating, and the coloring and decoloring states can be maintained at room temperature, and the decoloring temperature is lower than the coloring temperature. Above, a reversible thermochromic composition capable of repeating image formation and erasing many times by temperature change, and a reversible thermosensitive recording medium containing the same in a recording layer have been proposed. However, such a reversible thermochromic composition cannot be said to be sufficient as a reversible thermosensitive recording medium because the temperature range of decoloring is narrow.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a thermochromic composition utilizing the reaction between a color former and a developer.
The above problems found in the prior art can be solved, the coloring and decoloring can be easily performed only by heating, and the coloring and decoloring states can be maintained at room temperature, and the decoloring can be performed. To provide a reversible thermochromic composition having a temperature lower than a coloring temperature and capable of repeating image formation and erasing many times by a temperature change without problems, and a reversible thermosensitive recording medium using the same. Is the task.

[0006]

The present inventor has completed the present invention as a result of intensive studies to solve the above-mentioned problems. That is, according to the present invention, a color-forming body containing an electron-donating color-forming compound and an electron-accepting compound and formed by heating at a melting temperature or higher is decolored by heating at a temperature lower than the melting temperature. There is provided a reversible thermochromic composition, wherein a higher fatty acid having a hydroxyl group is contained as a decolorization accelerator in the reversible thermochromic composition. The present invention also provides a reversible thermosensitive recording medium containing the thermochromic composition as a thermosensitive recording layer.

The thermochromic composition of the present invention (hereinafter, also simply referred to as a composition) instantaneously develops a color by heating to form a colorant, and the color development state thereof is stable even at room temperature.
On the other hand, this color-developing body instantaneously decolorizes it by heating at a color-forming temperature or lower, and the erased state is stable even at room temperature.

The principle of coloring and erasing of the composition of the present invention, that is, image formation and image erasing on a thermosensitive recording medium will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density, the horizontal axis represents the temperature, the solid line 1 represents the image forming process by heating, and the broken line 3 represents the image erasing process by heating. A is the density in the completely erased state, B is the density in the completely colored state when heated to a temperature of T ₁ or higher, C is the density at the temperature of T ₀ or lower in the completely colored state, and D is T _0. It shows the concentration when erased by heating at a temperature between T _{1 and} T ₁ . The thermosensitive recording medium using the composition of the present invention is in a colorless state (A) at a temperature of T ₀ or lower. In order to record, a color image (B) is formed by heating to a temperature of T ₁ or higher with a thermal head or the like to form a recorded image. This recorded image is T ₀ according to the solid line 2.
Even if the temperature is returned to the following temperature, the state (C) is maintained as it is and the recording memory property is not lost.

Next, in order to erase the recorded image, the formed recorded image is heated to a temperature between T _{0 and} T _{1 which} is lower than the coloring temperature. This leads to a colorless state (D). In this state, the colorless state (A) is maintained as it is even when the temperature is returned to T ₀ or lower. That is, the process of forming the recorded image reaches C by the path of the solid line ABC and the recording is held. Next, in the process of erasing the recorded image, the erased state is maintained by reaching A through the path of the broken line CDA. The behavior characteristics of formation and erasure of the recorded image are reversible and can be repeated many times. FIG. 2 is an explanatory view showing an example of image formation and image erasure, in which 1 is a support and 2 is a reversible thermosensitive recording layer comprising the composition of the present invention. In the image forming process (A) → (B), a heat source for image formation, for example, the thermal head 5 is used.
It is achieved by recording and printing at a temperature of T ₁ or higher. Next, the image erasing step (B) → (A) is achieved by heating the image erasing heat source, for example, the heating roller 5 to a temperature between T _{0 and} T ₁ . In FIG. 2, 3 indicates a color image. The composition of the present invention contains a color former and a color developer as essential components. Then, the color-developing agent and the color-developing agent are heated and melted to form a color-developed state (color-forming body), while the color-developed state is erased by heating at a temperature lower than the color-developing temperature, and the color-developed state and the decolorized state are stable at room temperature. Is present in.

The above-mentioned peculiar color-developing behavior observed in the composition of the present invention is the compatibility of the color-developing agent and the color-developing agent by heating and melting, the strength of both actions in the color-developing state, and the color-developing agent. The solubility of the color former, the crystallinity of the developer, etc. are related, but in principle, the color developer formed by heating and melting causes the developer to be separated from the color developer by heating at a temperature lower than the color development temperature. It is separated and erased by this. Therefore, any color former / developer system exhibiting such behavior can be used as the composition component of the present invention. Further, those having such characteristics show endothermic change due to melting and exothermic change due to crystallization in thermal analysis, so that the color former / developer system applicable to the present invention can be easily analyzed by thermal analysis. You can check. It was also confirmed that the composition of the present invention may retain the third substance, for example, retain the reversible decoloring behavior even when the polymer substance is present.

The color former used in the present invention is a compound exhibiting an electron donating property, and is itself a colorless or light-colored dye precursor, and is not particularly limited, and conventionally known ones such as triphenylmethanephthalide. Compounds, fluoran compounds, phenothiazine compounds, leuco auramine compounds, rhodamine lactam compounds, spiropyran compounds, indolinophtalide compounds and the like. Particularly preferable color formers used in the present invention include the followings. 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3-cyclohexylamino-6-chlorofluorane, 3-cyclohexylamino-6-bromofluorane, 3-diethylamino-7
-Chlorofluorane, 3-diethylamino-7-bromofluorane, 3-dipropylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-phenylamino-fluorane, 3-pyrrolidino-6-chloro- 7
-Phenylamino-fluorane, 3-diethylamino-
6-chloro-7- (m-trifluoromethylphenyl) amino-fluorane, 3-cyclohexylamino-6-chloro-7- (o-chlorophenyl) amino-fluorane, 3-diethylamino-6-chloro-7- ( 2 ',
3'dichlorophenyl) amino-fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
Dibutylamino-6-chloro-7-ethoxyethylamino-fluorane, 3-diethylamino-7- (o-chlorophenyl) amino-fluorane, 3-diethylamino-7- (o-bromophenyl) amino-fluorane, 3
-(N-propyl-N-phenylamino) -7-amino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -7-amino-fluorane, 3- {N
-Ethyl-N- (p-methylphenyl) amino} -7-
Amino-fluorane, 3- {N-propyl-N- (p-
Methylphenyl) amino} -7-amino-fluorane,
3- {N-methyl-N- (p-ethylphenyl) amino} -7-amino-fluorane, 3- {N-ethyl-N
-(P-Ethylphenyl) amino} -7-amino-fluorane, 3-diethylamino-7,8 benzofluorane, 3- (N-ethyl-N-isoamylamino) -7,
8-benzofluorane, 3- (N-ethyl-Nn-octylamino) -7,8-benzofluorane, 3-N,
N-dibutylamino-7,8-benzofluorane, 3-
(N-methyl-N-cyclohexylamino) -7,8-
Benzofluorane and the like.

Next, the color developers preferably used in the present invention are exemplified as follows. As described above, the color developers applicable to the present invention can be easily found by thermal analysis. It will be clear that it is not limited to (1) Organic phosphoric acid compound R ₁ —PO (OH) ₂ (1) represented by the following general formula (1) (wherein R ₁ is a linear or branched alkyl group or alkenyl having 8 to 30 carbon atoms) Group) (2) Organic acid having a hydroxyl group at the α-position carbon represented by the following general formula (2) R ₂ —CH (OH) COOH (2) (wherein R ₂ is a straight chain having 6 to 28 carbon atoms). Represents a chain or branched alkyl group or alkenyl group) (3) Dibasic acid represented by the following general formula (3) (However, R ₃ is a linear or branched alkyl group or alkenyl group having 8 to 30 carbon atoms, Z is an oxygen atom or a sulfur atom, and f is an integer of 0, 1 or 2.) (4) The following general Dibasic acid represented by formula (4) (Wherein, R ₄ represents a linear or branched alkyl or alkenyl group, R ₅ is a hydrogen atom or an alkyl group having 1 to 30 carbon atoms from 8 to 30 carbon atoms) (5) the following formula (4 phenol compound represented _{by) HO-Ph-SR 6 (} 5) ( wherein, R ₆ represents a linear or branched alkyl or alkenyl group having 8 to 30 carbon atoms)

In the present invention, the color developers are used alone or as a mixture of two or more kinds. Similarly, the color-developing agent can be applied alone or in a mixture of two or more kinds. In the composition of the present invention, a higher fatty acid having a hydroxyl group is added as a decolorization accelerator together with a color former and a color developer. Examples of the higher fatty acid having a hydroxyl group used as the decolorization accelerator include the followings. 2-hydroxybutyric acid, 3-hydroxybutyric acid, 2-hydroxy-2-methylpropanoic acid, 2-hydroxy-4
-Methylpentanoic acid, 3-hydroxy-3-pentanecarboxylic acid, 16-hydroxy-hexadecanoic acid, 10-
Hydroxystearic acid, 12-hydroxystearic acid, 2-hydroxy-n-octanoic acid, 2-hydroxy-palmitic acid, 16-hydroxy-palmitic acid, 1
5-hydroxy-pentadecanoic acid, 3-hydroxy-lauric acid, 10-hydroxy-decanoic acid and the like.

Among the above, those having a small number of carbon atoms may cause fogging of the recording medium, so that it is particularly preferable to use a material having a carbon number of 8 or more. The addition amount of the higher fatty acid having a hydroxyl group is 0.5 to 50% by weight with respect to the color developer.
It is preferably about 0.5% by weight, and when it is less than 0.5% by weight, the effect of promoting decolorization is poor, and when it exceeds 50% by weight, the image density is greatly reduced during storage. The higher fatty acid having a hydroxyl group used as the decolorization accelerator may be used alone or in combination of two or more kinds.

The heat-sensitive recording medium of the present invention is uniformly dispersed or dissolved in water or an organic solvent together with a color former, a color developer, a decoloring accelerator and, if necessary, a binder and other additives, and coated on a support. It suffices to form a heat-sensitive recording layer that uniformly contains the decolorization accelerator.
As the binder, various conventional binders can be appropriately used, and examples thereof include polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, methoxy cellulose, carboxymethyl cellulose, methyl cellulose, cellulose acetate, gelatin, casein, starch, sodium polyacrylate. , Polyvinylpyrrolidone, polyacrylamide, maleic acid copolymer,
Acrylic acid copolymer, polystyrene, polyvinyl chloride, polyvinyl acetate, polyacrylic acid esters, polymethacrylic acid esters, vinyl chloride / vinyl acetate copolymer, styrene copolymer, polyester, polyurethane and the like.

The composition of the present invention contains various additives, such as a dispersant and a surfactant, which are used in ordinary thermal recording paper for the purpose of improving coating properties or recording properties as required. Fillers, color image stabilizers, antioxidants, light stabilizers, lubricants and the like can also be added.

In the heat-sensitive recording medium of the present invention, a reversible heat-sensitive layer composed of the above-mentioned color former and developer is provided on a support, which is provided with a heat-insulating layer containing hollow fine particles and a heat insulating material of chemical composition as a main component. The heat-sensitive recording layer may be manufactured by a method of providing a recording layer, and by providing the heat-insulating layer, the ability to retain heat is increased, so that the coloring and decoloring properties of the thermosensitive recording layer are improved. As the chemical compound heat insulating material for forming the heat insulating layer, a polymer foam such as polyurethane foam, polystyrene foam, vinyl chloride foam, or a corrugated plate member of plastic corrugated is used. Further, instead of providing the heat insulating layer, a heat insulating support may be used, and a plastic film, synthetic paper or the like is used as the heat insulating support.

In the present invention, in order to obtain a heat-sensitive recording medium having excellent chemical resistance, water resistance, abrasion resistance, light resistance and head matching property, a protective layer is provided as an overcoat layer on the upper surface of the recording layer. You can also The protective layer includes a film formed mainly of an aqueous emulsion of a water-soluble polymer or a hydrophobic polymer compound, a film formed mainly of an ultraviolet curable resin or an electron beam curable resin, and the like. By forming such a protective layer, an organic solvent,
It is possible to obtain a recording medium capable of repeating image formation and erasing due to temperature change without any problem even by contact with a plasticizer, oil, sweat, water or the like. Further, by containing a light stabilizer in the protective layer, it is possible to obtain a recording medium in which the light resistance of the image and the background are remarkably improved, and by further adding an organic or inorganic filler and a lubricant to the protective layer, It is possible to obtain a thermosensitive recording medium excellent in reliability and head matching property without a problem such as sticking caused by contact with a thermal head or the like. Incidentally, it is possible to give an antistatic effect by adding a conductive compound-for example, a quaternary ammonium compound-in the protective layer, and by this effect, discomfort due to static electricity when using a thermal recording medium is prevented. It is easy to handle.

The formation of a recorded image is not particularly limited by a hot pen, a thermal head, laser heating, etc. depending on the purpose of use. Similarly, the erasing of the recorded image is not particularly limited as long as the erasing temperature conditions such as the heating roller, the sheet heating element, the constant temperature bath, the warm air, and the thermal head are given. Further, so-called overwriting is possible in which the recorded image is erased by the thermal head set to the erasing temperature and at the same time the recorded image is formed by another thermal head set to the recording temperature.

[0020]

EXAMPLES The present invention will now be described in more detail by way of examples. In the following, all parts and% are based on weight. Examples 1 to 3 The following compositions were pulverized and dispersed by a ball mill to a particle size of 1 to 4 μm to prepare recording layer coating solutions. 3-Dibutylamino-7- (o-chlorophenyl) aminofluorane 10 parts Hexadecylphosphonic acid 30 parts Hydroxyl-containing higher fatty acid (Higher-hydroxyl-containing fatty acid of Examples 1 to 3 in Table 1 and addition amount) Vinyl chloride-acetic acid Vinyl copolymer (VYHH manufactured by Union Carbide Co., Ltd.) 30 parts Methyl ethyl ketone 135 parts Toluene 135 parts The coating solution prepared as described above is coated on a polyester film having a thickness of 100 μm using a wire bar to a thickness of about 5
A reversible thermosensitive recording sheet was obtained by coating and drying so as to have a thickness of μm. The recording sheet thus produced was put in a constant temperature bath at 130 ° C. for 30 seconds, and a black image was obtained.
The color density of this image was measured with a Macbeth densitometer RD-914. Next, this color development image sample was subjected to a pressure of 2 kg / cm ² and a time of 1 with a thermal tilt tester (manufactured by Toyo Seiki Seisakusho)
After heating to 90 ° C in steps of 50 ° C to 1 ° C for 2 seconds,
The sample was allowed to cool to room temperature and placed on wood free paper to measure the reflection density. The density of less than 0.40 was erased, and the temperature range was defined as the erased temperature width. The respective results are shown in Table 1.
Further, the color image sample is 4 at 40 ° C and 50% relative temperature.
After storing for 8 hours, the image density was measured to determine the density reduction rate. The results are also shown in Table 1.

Examples 4 to 6 Reversible thermosensitive recording sheets were prepared in the same manner as in Example 1 using the following compositions. 3-{(N-ethyl-N- (p-methylphenyl) amino} -6-methyl-7-phenylaminofluorane 10 parts Eicosylsuccinic acid 30 parts Higher fatty acid having a hydroxyl group (Examples 4 to 1 in Table 1) Higher fatty acid having hydroxyl group of 6 and addition amount) Vinyl chloride-vinyl acetate copolymer (VYHH manufactured by Union Carbide Co., Ltd.) 30 parts Methyl ethyl ketone 135 parts Toluene 135 parts This reversible thermosensitive recording sheet was tested in the same manner as in Example 1. The results are shown in Table 1.

Examples 7 to 9 Reversible thermosensitive recording sheets were prepared in the same manner as in Example 1 using the following compositions. 3-Diethylamino-7-chlorofluorane 10 parts α-hydroxyoctadecanoic acid 30 parts Hydroxyl-containing higher fatty acid (higher-hydroxyl-containing fatty acid of Examples 7 to 9 in Table 1 and addition amount) Vinyl chloride-vinyl acetate Copolymer (VYHH, manufactured by Union Carbide) 30 parts Tetrahydrofuran 170 parts Toluene 100 parts This reversible thermosensitive recording sheet was tested in the same manner as in Example 1. The results are shown in Table 1.

[0026]

[Table 1]

[0023]

The reversible thermochromic composition and reversible thermosensitive recording medium of the present invention can be colored by heating and melting the color former and the developer contained therein.
The color developing material can be decolored by heating at a temperature lower than the melting temperature. Further, such coloring and erasing can be repeated, and the coloring and erasing states can be maintained at room temperature. Also,
In the present invention, the obtained image has high contrast, is excellent in image erasability, and the hue of the color image is not limited at all, and the hue can be freely selected by changing the color former. Furthermore, since the reversible thermochromic composition and reversible thermosensitive recording medium of the present invention contain a decolorization accelerator composed of a higher fatty acid having a hydroxyl group, the decolorization temperature range is expanded and the decolorization density is also reduced. Therefore, it can be advantageously applied.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between color density and temperature of a reversible thermosensitive recording medium of the present invention, and is an explanatory view of the principle of color development and color erasing. The solid line (A → B → C) indicates the image forming process, and the broken line (C
→ D → A) shows an image erasing process.

FIG. 2 is a diagram illustrating an image forming process and an image erasing process using the reversible thermosensitive recording medium of the present invention.

[Explanation of symbols]

 1 Support 2 Reversible Recording Layer 3 Colored Image 4 Thermal Head 5 Heating Roller

Claims (4)

[Claims] 1. A reversible heat that contains an electron-donating color-forming compound and an electron-accepting compound, and a color-forming body formed by heating above a melting temperature is decolored by heating to a temperature lower than the melting temperature. A reversible thermochromic composition, characterized in that the composition contains a higher fatty acid having a hydroxyl group as a decolorization accelerator. 2. The reversible thermochromic composition according to claim 1, wherein the higher fatty acid having a hydroxyl group used as a decolorization accelerator has 8 or more carbon atoms. 3. The composition according to claim 1, wherein the content of the higher fatty acid having a hydroxyl group used as a decolorization accelerator is 0.5 to 50% by weight based on the color developing agent. 4. A reversible thermosensitive recording medium containing the composition according to claim 1 as a thermosensitive recording layer.