JPH06127126A - Heat reversible thermal record medium - Google Patents

Abstract

PURPOSE:To prevent degradation of image density and improve preservation property by providing a protective layer through an intermediate layer on a top face of a heat reversible thermal recording layer which contains an electron donative coloring compound and an electron acceptive compound, and generates coloring recording state and record erasing state. CONSTITUTION:A heat reversible thermal record medium is equipped with a heat reversible thermal recording layer 2 arranged on a top face of a support body 1. While the recording layer 2 generates a coloring recording state by means of thermal fusion of the electron donative coloring compound and the electron acceptive compound, it generates a record erasing state by heating with a temperature lower than a coloring recording temperature. In this case, a protective layer 6 is provided on the top face of the recording layer 2 through an intermediate layer 7. In the intermediate layer 7, a reaction product of a styrene-maleic acid anhydride copolymer and a lower alcohol is added. Further, the thickness of the intermediate layer 7 is set to 5mum or less. Thus, a coupler of the recording layer 2 is dispersed in the protective layer 6, so that degradation of image density is prevented and preservation property will be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoreversible thermosensitive recording medium utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound.

[0002] Conventionally, in a thermosensitive recording medium utilizing a color-forming reaction between an electron-donating color-developing compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent), color development and decolorization are performed. There are some proposals for reversibly performing. For example, Japanese Patent Application Laid-Open No. 60-193691 discloses a color developer using a combination of gallic acid and phloroglucinol. 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 record storability, and furthermore, there is a problem that the erasing device for erasing the color developing material becomes large. Japanese Unexamined Patent Publication No. 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 gradually cooling it to form a coloring material, while heating the coloring material once to a temperature higher than the coloring 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-62-140881, JP-A-62-138568 and JP-A-62-138556 disclose a homogenous solution of a color former, a developer and a carboxylic acid ester. This product shows a completely colored state at a low temperature and a completely decolored state at a high temperature, and can keep the colored or decolored state at an intermediate temperature between them, and by printing with a thermal head on this medium, the colored background White characters (decolored body) can be recorded on (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, as a color developer, a salt of gallic acid and a higher aliphatic amine and bis (hydroxyphenyl) which reversibly perform color developing and color reducing actions, respectively. ) A salt of acetic acid or butyric acid and a higher aliphatic amine is used. This product can be thermally colored in a specific temperature range and decolorized by heating at a higher temperature than that, but since its color developing action and color reducing action occur competitively, these actions are thermally suppressed. It is difficult to control, and it is difficult to obtain good image quality contrast. As described above, the conventional thermoreversible thermosensitive recording medium utilizing the reaction between the color former and the developer has various problems and is still unsatisfactory.

[0003]

The object of the present invention is to solve the above-mentioned problems found in the prior art in a reversible thermochromic composition utilizing the reaction between a color former and a developer. , 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. The object is to obtain a heat-sensitive recording medium that can be repeatedly formed and erased by changing the temperature, and to provide the heat-sensitive recording medium with further storability.

[0004]

According to the present invention, an electron-donating color-forming compound and an electron-accepting compound are heated and melted to form a color recording state, and recording is erased by heating at a temperature lower than the color recording temperature. There is provided a reversible thermosensitive recording medium comprising a reversible thermosensitive recording medium forming a state and a protective layer provided on the recording layer via an intermediate layer.

The heat-sensitive recording medium of the present invention instantly develops color upon heating, and the color-developed state thereof is stable even at room temperature. On the other hand, the recording layer in the color-developed state is instantly heated by heating at a temperature below the color-developing temperature. Is erased, and the erased state is stable even at room temperature.

The principle of coloring and erasing of the thermosensitive recording medium of the present invention, that is, image formation and image erasing will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density and the horizontal axis represents the temperature. The solid line 1 shows the image forming process by heating and the broken line 3 shows 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 heating a temperature of T ₁ or higher, C is the density at the temperature of T _{0 in} the completely colored state, and D is T ₁ ~ It shows the concentration when heat erasing is performed at a temperature between T ₀ .

The thermal recording medium 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. Even if the recorded image is returned to the temperature of T ₀ or less according to the solid line 2, 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, to obtain 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. 1 is a support, and 2 is a thermoreversible thermosensitive recording layer comprising the composition of the present invention. Image forming process (A)
(B) is achieved by recording and printing with a heat source for image formation, for example, the thermal head 4 at a temperature of T ₁ or higher in FIG. 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.

FIG. 3 shows a thermoreversible thermosensitive recording medium of the present invention in which a protective layer is provided on a recording layer 2 on a support 1 via an intermediate layer 7.

The thermoreversible thermosensitive recording medium of the present invention contains a color former and a developer as essential components. Then, the coloring state is formed by heating and melting the color-developing agent and the color-developing agent, while the coloring state is erased by heating at a temperature lower than the coloring temperature, and the coloring state and the erasing state exist stably at room temperature. Is.

In the recording layer of the present invention, a color former, a developer and a binder are used as main components. The color former exhibits an electron donating property, and is itself a colorless or light-colored dye precursor, and is not particularly limited. For example, a triphenylmethanephthalide compound, a fluoran compound, a phenothiazine compound known in the art can be used. A compound, a leuco auramine-based compound, an indolinophtalide-based compound or the like is used, and a fluoran-based compound is particularly preferably used. Developers are, for example, long-chain alkylphosphonic acids, long-chain α-
Hydroxy fatty acid, long chain alkyl thiomalic acid, long chain alkyl malonic acid and the like are preferably used.

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 and polyacrylic acid. Soda, polyvinylpyrrolidone, polyacrylamide, maleic acid copolymer, acrylic acid copolymer, polystyrene, polyvinyl chloride, polyvinyl acetate, polyacrylic acid esters, polymethacrylic acid esters, vinyl chloride / vinyl acetate copolymer Coalesce, styrene copolymer, polyester,
There is polyurethane etc.

In the present invention, in order to obtain a thermosensitive 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. In order to prevent the recording material from diffusing into the protective layer, a protective layer is not directly provided on the recording layer,
A protective layer is provided on the recording layer via an intermediate layer. For the intermediate layer of the present invention, a reaction product of a styrene-maleic anhydride copolymer and a lower alcohol is particularly preferable. By interposing such an intermediate layer, it is possible to prevent the recording agent from diffusing into the protective layer and effectively suppress the decrease in image density. Particularly, when the solvent used for forming the protective layer dissolves the recording layer forming material even partially, or when the recording layer forming binder and the protective layer material are compatible with each other, a remarkable effect is exhibited.

The above-mentioned product used for the intermediate layer of the present invention can be easily obtained, for example, by reacting a styrene-maleic anhydride copolymer in excess alcohol at 50 to 70 ° C. for 1 to 3 hours. . It is considered that this compound is obtained by ring-opening maleic anhydride to form an ester, and can be used as it is or after being appropriately diluted with another solvent. If the thickness of this intermediate layer is too thick, the heat conduction from the thermal head will deteriorate and the color density will decrease, resulting in a thickness of 5 μm.
The following is desirable.

Next, the protective layer of the present invention will be described. For the protective layer of the present invention, a water-soluble polymer, a polymer aqueous emulsion, an ultraviolet curable resin or the like is used, and the kind thereof is not limited, and various conventionally known ones can be used. Specific examples of the water-soluble polymer include, for example, polyvinyl alcohol, modified polyvinyl alcohol, starch and its derivatives, cellulose derivatives (methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, etc.), casein, gelatin, polyvinyl pyrrolidone, styrene-maleic anhydride copolymer. Polymer, diisobutylene-maleic anhydride copolymer, polyacrylamide, modified polyacrylamide, methyl vinyl ether-maleic anhydride copolymer,
Carboxy-modified polyethylene, polyvinyl alcohol /
Acrylic miniblock copolymers, melamine-formaldehyde resins, urea-formaldehyde resins and the like can be mentioned. Examples of the aqueous emulsion include polyvinyl acetate, polyurethane, styrene / butadiene copolymers, styrene / butadiene / acrylic copolymers. Examples thereof include polymers, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene / vinyl acetate copolymers, and the like. These may be used alone or as a mixture, and if necessary, a curing agent may be added to cure the resin.

As the ultraviolet curable resin, any monomer or oligomer (or prepolymer) which undergoes a polymerization reaction upon irradiation with ultraviolet rays and is cured to become a resin can be used. Examples of such monomers or oligomers include (poly) ester acrylate, (poly) urethane acrylate, epoxy acrylate, polybutadiene acrylate, silicone acrylate, and melamine acrylate. The (poly) ester acrylate is obtained by reacting a polyhydric alcohol such as 1,6-hexadiol, propylene glycol (as propylene oxide) or diethylene glycol with a polybasic acid such as adipic acid, phthalic anhydride or trimellitic acid and acrylic acid. It is a thing.

Although there is no particular limitation on the coating method and coating amount of the protective layer, the coating amount of the coating layer on the recording medium is 0.1 to 1 in view of the performance and economical efficiency of the protective layer. 20
The range of μm, more preferably within the range of 0.5 to 10 μm, is a thickness range in which the performance as the protective layer is sufficiently exhibited and the performance of the recording medium is not deteriorated. Further, the improvement of the light resistance of the heat-sensitive recording medium of the present invention is achieved by including a light stabilizer in the protective layer. As the light stabilizer used in the present invention, an ultraviolet absorber, an antioxidant, an antiaging agent, a quencher of singlet oxygen, and a quencher of superoxide anion are used.

The support of the thermal recording medium of the present invention may be paper, synthetic paper, plastic film or a composite thereof depending on the purpose of use and is not particularly limited. Depending on the purpose of use, the recording image may be formed with a hot pen, thermal head,
There is no particular limitation such as laser heating. 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. It is also possible to perform so-called overwriting, 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. All parts and% in the following are based on weight.

Example 1 [Recording Layer] The following composition was pulverized and classified to a particle size of 1 to 4 μm with a ball mill to prepare a recording layer coating solution. 3-Diethylamino-7- (o-chlorophenyl) -aminofluorane 3 parts Octadecylphosphonic acid 10 parts Vinyl chloride / vinyl acetate copolymer (VYHH, Union Carbide Co.) 10 parts Toluene 45 parts Methyl ethyl ketone 45 parts Applying the coating solution prepared as above to a polyester film with a thickness of 100 μm using a wire bar
It was applied and dried so as to have a thickness of μm. [Intermediate Layer] Next, an intermediate layer coating solution was prepared as follows. 9
5 g of ethyl alcohol is stirred at 50 ° C., and 5 g of powder of styrene / maleic anhydride copolymer (Aldrich, molecular weight 350,000) is added thereto. First insoluble styrene /
The maleic anhydride copolymer reacts with alcohol and gradually dissolves, eventually becoming a viscous colorless transparent state.
Stirring was continued at the same temperature for a time to prepare an intermediate layer coating solution. This intermediate layer coating solution was applied onto the recording layer of the recording sheet using a wire bar so that the coating thickness was about 1.5 μm, and dried to form an intermediate layer. [Protective Layer] Next, as a protective layer coating liquid, 100 g of a urethane acrylate-based UV curable resin (Unidick C7-157, manufactured by Dainippon Ink and Chemicals, Inc.) was diluted with 50 g of ethyl acetate to prepare a protective layer coating liquid. This coating solution for protective layer was applied onto the intermediate layer of the recording sheet using a wire bar, dried and then cured with an 80 W / cm ultraviolet lamp to give about 4
A μm protective layer was provided.

Example 2 A thermoreversible thermosensitive recording sheet was prepared and evaluated in the same manner as in Example 1 except that the following composition was used as the recording layer coating liquid. 3- {N-ethyl-N- (P-methylphenyl) amino} 3 parts 6-methyl-7-phenylaminofluorane eicosylthiomalic acid 10 parts Vinyl chloride / vinyl acetate copolymer (Union Carbide Co.) , VYHH) 10 parts Toluene 45 parts Methyl ethyl ketone 45 parts

Example 3 A thermoreversible thermosensitive recording sheet was prepared in the same manner as in Example 1 except that the coating liquids for the recording layer, the intermediate layer and the protective layer were changed to the compositions described below, and the same evaluation was carried out. [Recording layer] 3-dibutylamino-7- (o-chlorophenyl) -aminofluorane 3 parts Octadecyl malonic acid 10 parts Ethyl cellulose (manufactured by Kanto Chemical Co., Inc.) 5 parts Toluene 45 parts Methyl ethyl ketone 45 parts [Intermediate layer] 95 g of isopropyl alcohol And 5 g of styrene / maleic anhydride copolymer (manufactured by Aldrich,
A coating solution for the intermediate layer was prepared in the same manner as in Example 1 using a molecular weight of 350,000). [Protective layer] Urethane acrylate UV curable resin 100 parts (Dainippon Ink and Chemicals, Unidick 17-824-19) Ethyl acetate 50 parts

Example 4 Example-except that the following composition was used as the coating liquid for the recording layer.
A thermoreversible thermosensitive recording sheet was prepared in the same manner as 3 and evaluated in the same manner. 3-dibutylamino-7- (o-chlorophenyl) -aminofluorane 3 parts α-hydroxyoctadecanoic acid 10 parts Acrylic resin (BR-102 manufactured by Mitsubishi Rayon Co., Ltd.) 10 parts Toluene 45 parts Methyl ethyl ketone 45 parts

Comparative Example-1 A thermoreversible heat-sensitive recording sheet obtained by directly providing a protective layer on a recording layer without providing an intermediate layer was prepared as Comparative Example-1.

Comparative Example-2 A thermoreversible thermosensitive recording sheet was prepared in the same manner as in Example-1 except that a 5% ethanol / toluene solution of ethyl cellulose (manufactured by Kanto Chemical Co., Inc.) was used as the intermediate layer. Was prepared as Comparative Example-2.

Comparative Example-3 A thermoreversible thermosensitive recording sheet was prepared in the same manner as in Example-3 except that polyacrylic emulsion (John Cryl 390, manufactured by Johnson Co.) was used as the intermediate layer in Example-1. It was produced and designated as Comparative Example-3.

The thermoreversible thermosensitive recording sheet thus prepared was brought into contact with a plate heated to 120 ° C. for 10 seconds to obtain a black image, and the following evaluation test was conducted. The results are shown in Table-1. [Coloring Density] The density immediately after coloring was measured with a Macbeth densitometer (Macbeth RD-914). [Decoloring Density] The recording sheet was put in a constant temperature bath at 75 ° C. for 3 minutes to decolor the image, and the density was measured with a Macbeth densitometer. [Storability] The recording sheet was stored at 40 ° C. and 50% RH for 72 hours, and then the image density was measured with a Macbeth densitometer to determine the density reduction rate (%) before the storage.

[0029]

[Table 1]

[0030]

According to the present invention, since the protective layer is provided on the recording layer via the intermediate layer, the image density is prevented from lowering due to the diffusion of the color former and the developer contained in the recording layer into the protective layer. A thermoreversible thermosensitive recording medium excellent in storability can be obtained without inviting.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between color density and temperature of a thermoreversible thermosensitive recording medium of the present invention, and is an explanatory diagram of the principle of color development and decolorization. A solid line (A → B → C) shows an image forming process, and a 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.

FIG. 3 shows a schematic sectional view of a thermoreversible thermosensitive recording medium of the present invention.

[Explanation of symbols]

 1 Support 2 Thermoreversible Recording Layer 3 Colored Image 4 Thermal Head 5 Heating Roller 6 Protective Layer 7 Intermediate Layer

Claims (3)

[Claims] 1. A thermoreversible thermosensitive recording layer in which an electron-donating color-forming compound and an electron-accepting compound are heated and melted to form a color-recorded state, and a recording erased state is formed by heating at a temperature lower than the color-recording temperature. A thermoreversible thermosensitive recording medium having a protective layer provided thereon via an intermediate layer. 2. The thermoreversible thermosensitive recording medium according to claim 1, wherein the intermediate layer contains a reaction product of a styrene-maleic anhydride copolymer and a lower alcohol. 3. The thermoreversible thermosensitive recording medium according to claim 1, wherein the intermediate layer has a thickness of 5 μm or less.