JP3506781B2 - Reversible thermosensitive recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium, and more particularly, to a recording medium having good coloring properties and high recording and erasing temperatures to improve recording stability. The present invention relates to a reversible thermosensitive recording medium. 2. Description of the Related Art Various cards, such as ID cards and prepaid cards, require visible recording in addition to magnetic recording. Such visible recording is widely used because thermal recording is inexpensive and has good coloring. As the heat-sensitive recording material, a material in which a leuco dye and a color developer are dispersed in a binder is used. However, once a color is formed, it cannot be returned to its original state, so that reversible recording cannot be performed. Therefore, in order to perform reversible thermosensitive recording in response to a request for rewriting the recording, Japanese Patent Laid-Open No. 2-18 / 1990
As described in JP-A No. 8293 and JP-A-2-188294, there is a developer using a complex of a molecule having a phenolic hydroxyl group and a molecule having a basic amino group as a color developer. According to this, color development and decoloration occur by the developer acting as an acid or an alkali depending on the heating temperature, and reversible thermosensitive recording can be performed. However, the color developer acts as an acid or an alkali depending on the heating temperature, and the color density is low. Not only is the recording not clear, but also the color reaction and color erasing are repeated, and the durability is not sufficient. As another example of performing reversible thermosensitive recording, as described in JP-A-6-72035, a long-chain alkyl group in a molecule as a color developer and a carboxyl group or a phosphate group as an acid component. Some use compounds having the formula: This is because, since there is a long-chain alkyl group in the developer molecule, the arrangement of the developer changes depending on the heating temperature and acts on the leuco dye, so that color development and decoloration occur.
According to this material, since the reaction relating to the decoloring is physical, the repeated durability of the coloring and decoloring is improved, but the temperature at which the coloring and decoloring occur is not sufficiently high. Therefore, for example, when applied to a card, there is a problem that even when energy for coloring or erasing is not supplied from the outside, coloring or erasing occurs due to the influence of the ambient temperature or the like, and recording stability is lacking. Was. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, performs satisfactory recording with sufficient coloring properties, and reduces the temperature of coloring and decoloring by a conventional material. An object of the present invention is to provide a reversible thermosensitive recording medium which has a higher temperature than that of the above and has improved recording stability. According to the present invention, a reversible thermosensitive recording medium has a reversible thermosensitive recording layer containing a color former, a developer and a binder, and the developer is generally In equation (1)
Use the indicated material. [0007] A leuco dye is used as a color former contained in the reversible thermosensitive recording layer. As the leuco dye, a leuco dye having a fluoran skeleton and a triphenylmethane leuco dye are preferable. For example, 2-anilino-3-
Methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6-dibutylaminofluoran, 2-anilino-3-methyl-6- [N-ethyl-N-isobutyl] aminofluoran, 2-anilino- 3-methyl-6
-(N-propyl-N-methylamino) fluoran, 2
-Anilino-3-methyl-6- (N-isopropyl-N
-Methylamino) fluoran, 2-anilino-3-methyl-6- (N-isopropyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran, 2- (m-
Trichloromethylanilino) -3-methyl-6-diethylaminofluoran, 3- [4- (4-phenylaminophenyl) aminophenyl] amino-6-methyl-7-
Chlorofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylaminobenzo [a] fluoran, 3-diethylamino-7-dibenzoylaminofluoran, 3 -Cyclohexylamino-6-chlorofluoran, 3,3-bis (p-dimethylaminophenyl)
-6-dimethylaminophthalide (crystal violet lactone) or the like can be used. The color developer is a feature of the present invention,
It has a long-chain alkyl group having 8 or more carbon atoms, an aromatic skeleton and a carboxyl group, and is represented by the following general formula (1). [0010] (Here, R is a long-chain alkyl group having 8 or more carbon atoms.) Specific examples of the compound represented by the general formula (1) include the following compounds. Monooctyl terephthalate, monodecyl terephthalate, monododecyl terephthalate, monotetradecyl terephthalate, monohexadecyl terephthalate, monooctadecyl terephthalate. As the binder, a polymer material soluble in water or an organic solvent can be used. For example,
Polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylates, polymethacrylates, acrylic Acid copolymers, maleic acid copolymers, polyvinyl alcohols and the like. The layer structure may be only a reversible thermosensitive recording layer, but if necessary, a protective layer may be provided, or an intermediate layer may be provided between the layer and the support. Each may be composed of a plurality of layers. Furthermore, a recordable material such as light, electricity, or magnetism may be applied to the back surface. A solution containing the above color former, developer and binder is coated on a support to obtain a reversible thermosensitive recording medium of the present invention. The reversible thermosensitive recording medium of the present invention is generally 100
The color develops above 70 ° C and disappears at 70-75 ° C. In addition, the color recurs upon heating at 100 ° C. or higher after decoloring, and has reversibility. Although the mechanism of coloring and decoloring of the reversible thermosensitive recording medium of the present invention is not always clear, what is presumed will be described below. When the reversible thermosensitive recording medium is heated, the color former and the developer melt and mix to form a color, and when rapidly cooled from this state, a structure in which the color developer and the developer interact with each other forms a regularly aggregated structure, which is stable. Into a colored state. next,
When heating is performed from this state, the regular aggregated structure collapses and the color disappears. When the developer is gradually cooled from this state, the developer molecules are aggregated and crystallized independently, so that the decolored state is maintained. In the reversible thermosensitive recording medium of the present invention, the developer and the color former are melted and mixed by heating, and the carboxyl group in the developer molecule interacts with the color former to form a color. In the molten color-developed state, the long-chain alkyl group in the developer molecule takes a regular aggregation structure by rapid cooling to maintain the color-developed state. Next, when the colored state breaks down the regular aggregation structure by heating and becomes unstable, the developer stops interacting with the color former. Thereafter, when the cooling agent is gradually cooled, the cohesive force between the developer molecules acts strongly due to the long-chain alkyl group in the developer molecules, so that the developer coagulates alone. At this time, the interaction with the color former is broken, and the decolored state can be stably maintained. Therefore, color development and decoloration can be performed reversibly by heating. According to the present invention, since the color developer has a skeleton similar to that of a substance conventionally used as a plasticizer, it has good dispersibility, so that no sensitizer is required, and the color development is excellent. In addition, the thermosensitive recording layer can be easily formed because of good compatibility with the binder resin, and the production of the thermosensitive recording medium is easy. Furthermore, since the coloring temperature and the decoloring temperature are relatively high, coloring or decoloring occurs only when heating for coloring or decoloring is performed, and depending on the influence of the temperature of the external environment, for example, an increase in the external temperature, Does not develop or lose color easily. Therefore, the recording stability is good, for example, there is no possibility that the recorded content changes when applied to a card or the like,
Tampering, forgery, etc. can be prevented. Next, the coloring and decoloring of the reversible thermosensitive recording medium of the present invention will be described with reference to FIG. FIG. 1 shows the relationship between the color density and the temperature of the reversible thermosensitive recording medium of the present invention. Initially, the reversible thermosensitive recording medium is in a decolored state at room temperature (state A in the figure).
From 2, the color former and the developer melt and mix, and the color begins to develop,
It becomes a colored state (state B in the figure). At this time, when the reversible thermosensitive recording medium is rapidly cooled to room temperature, the color development state is maintained (state C in the figure). Next, when the temperature of the reversible thermosensitive recording medium is increased, the color density starts to decrease from the temperature T1 and becomes a decolored state (state D in the figure). The decolored state is maintained (state A in the figure). Here, T1 is the decolorization temperature, and T1
The temperature from 1 to T2 is the color erasing temperature range. Next, examples of the reversible thermosensitive recording medium according to the present invention will be described in detail. Example 1 Leuco dye (2-anilino-3-methyl-6- [N-ethyl-N-isobutyl] aminofluorane Nippon Soda Co., Ltd., trade name PSD184) 10 parts Monododecyl terephthalate 20 parts Vinyl chloride -Vinyl acetate copolymer (VYHH, Union Carbide Co.) 40 parts Toluene 150 parts Methyl ethyl ketone 150 parts After the above composition is dispersed in a ball mill, it is coated on a white polyethylene terephthalate film with a wire bar, dried and dried. A reversible thermosensitive recording medium having a recording layer having a thickness of about 5 μm was obtained. When the coloring temperature of this heat-sensitive recording medium was examined using a thermal gradient tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), it was colored at 97 ° C. and returned to room temperature to maintain the colored state. Next, when the color-developed medium was stored in a constant temperature bath at 70 ° C. for 30 seconds, the color was erased, and even when the temperature was returned to room temperature, the erased state was maintained. Such a coloring and decoloring operation was repeated 10 times to confirm reversibility. In the composition of Example 1 described above,
Although monododecyl terephthalate is used as monoalkyl terephthalate, the following table shows the color development, color erasing temperature, color development, and color erasing density including the case where another alkyl group CnH _{2n + 1} is used instead of the dodecyl group. 1 is shown. The coloring and decoloring densities are reflection densities measured with a Macbeth reflection densitometer. [Table 1] From the above results, the length n of the alkyl group is 8
In the case of the above long-chain alkyl groups, all exhibited sufficient coloring and decoloring densities, and reversibility was confirmed. Further, it can be seen that the longer the length n of the alkyl group (the larger n), the higher the color development and decolorization temperatures. Example 2 Leuco dye (2-anilino-3-methyl-6-dibutylaminofluoran, trade name PSD290, Nippon Soda Co., Ltd.) 10 parts Monododecyl terephthalate 20 parts Vinyl chloride-vinyl acetate copolymer (Union 40 parts of toluene 150 parts of methyl ethyl ketone 150 parts After dispersing the above composition in a ball mill in the same manner as in Example 1, coating on a white polyethylene terephthalate film with a wire bar and drying, About 5
A reversible thermosensitive recording medium having a μm recording layer was obtained. When the color temperature of this heat-sensitive recording medium was examined using a thermal gradient tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), the color was formed at 100 ° C., and the color maintained even when the temperature was returned to room temperature. Next, the colored medium is heated to 70 ° C.
When stored in a constant temperature bath for 30 seconds, the color was erased, and when the temperature was returned to room temperature, the color was erased. Such a coloring and decoloring operation was repeated 10 times to confirm reversibility. Example 3 Leuco dye (2-anilino-3-methyl-6-diethylaminofluoran, trade name PSD-V, Nippon Soda Co., Ltd.) 10 parts Monododecyl terephthalate 20 parts Vinyl chloride-vinyl acetate copolymer ( Union Carbide VYHH) 40 parts Toluene 150 parts Methyl ethyl ketone 150 parts After dispersing the above composition in a ball mill in the same manner as in Example 1, coating on a white polyethylene terephthalate film with a wire bar and drying, About 5 thick
A reversible thermosensitive recording medium having a μm recording layer was obtained. When the coloring temperature of this heat-sensitive recording medium was examined using a thermal gradient tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), the recording medium was colored at 110 ° C. Next, the color-developed medium was erased when stored in a 70 ° C. constant temperature bath for 30 seconds. Such a coloring and decoloring operation was repeated 10 times to confirm reversibility. According to the present invention, since the color developer has a skeleton similar to that of a substance conventionally used as a plasticizer, it has good dispersibility, so that a sensitizer is not required, and Is excellent. In addition, the thermosensitive recording layer can be easily formed because of good compatibility with the binder resin, and the production of the thermosensitive recording medium is easy. Further, since the coloring temperature and the decoloring temperature are high, the coloring or decoloring is caused only when heating for coloring or decoloring is performed, and easily depending on the temperature of the external environment, for example, the rise of the external temperature. Does not develop or lose color. Therefore, the stability of the recording is good. For example, when applied to a card or the like, there is no possibility that the recorded content changes,
Forgery and the like can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the color density and the temperature of a reversible thermosensitive recording medium according to the present invention. [Explanation of Signs] T1 T2 Temperature

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Haruhiko Osawa 4-14-12 Koishikawa, Bunkyo-ku, Tokyo Kyodo Printing Co., Ltd. (56) References JP-A-4-29883 (JP, A) JP-A 5-85048 (JP, A) JP-A-7-40661 (JP, A) JP-A-6-320860 (JP, A) JP-A-62-280089 (JP, A) JP-A-6-328858 (JP, A) A) JP-A-59-120492 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (1)

(57) [Claims] [Claim 1] Including a color former, a developer and a binder
Having a reversible thermosensitive recording layer, the developer has the following general formula
Reversible feeling characterized by being a substance represented by (1)
Thermal recording medium. Embedded image (Here, R is a long-chain alkyl group having 8 or more carbon atoms.)