JPH09123611A - Reversible thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent contrast and storage properties by a method wherein a barbituric acid derivative having at least one specific alkyl group is used for a developer contained in a reversible thermal recording layer in a reversible thermal recording medium. SOLUTION: This reversible thermal recording medium being used for an ID card, a prepaid card and the like has a reversible thermal recording layer containing a coloring agent, a developer and a binder, and a barbituric acid derivative having at least one 6 or higher C alkyl group is used for the developer. As for the coloring agent, a leuco dye, a leuco dye having a fluoran skeleton, preferably, or a leuco dye of a triphenylmethane series is used. The barbituric acid derivative having at least one 6 or higher C alkyl group, which is expressed by the formula (R1 to R3 are the 6 or higher C alkyl groups or hydrogen H and at least one of R1 to R3 is the 6 or higher C alkyl group), is used herein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium, and more particularly to a reversible thermosensitive recording medium having good contrast and storage characteristics.

[0002]

2. Description of the Related Art Various cards such as ID cards and prepaid cards require visible recording in addition to magnetic recording, for example. As such a visible recording, heat-sensitive recording is widely used because it is inexpensive and has good color developability. As a heat-sensitive recording material, a leuco dye and a color developer dispersed in a binder are used, but normally, once the color is developed, it cannot be restored, and therefore reversible recording cannot be performed.

Therefore, various reversible thermosensitive recording materials are known in order to perform reversible thermosensitive recording in response to a request for rewriting the recording. For example, JP-A-54-11
As described in JP-A No. 9377 and JP-A No. 55-154198, reversible changes to white turbidity and transparency due to physical change by utilizing changes in refractive index and light scattering property due to phase separation or phase change due to heat. There is.

On the other hand, there is a reversible method for color development and decolorization by a chemical change using a leuco dye. As this chemical change type, for example, Japanese Patent Laid-Open Nos. 50-81157 and 5-5.
No. 0-105555 describes a temperature-indicating material using a leuco dye, but it can maintain a colored or decolored state only at a specific temperature.

Further, as described in JP-A-59-120492, there are some which reversibly change by utilizing the hysteresis of leuco dye, but a heating source and a cooling source are necessary, and coloring and decoloring are required. The temperature range that can be maintained is narrow.

Further, as described in JP-A-2-188293 and JP-A-2-188294, a complex of a molecule having a phenolic hydroxyl group and a molecule having a basic amino group is used as a developer. There is something. According to this, the color developer acts as an acid or an alkali depending on the heating temperature to cause color development and color erasing, and reversible thermosensitive recording can be performed. However, the color developer acts as an acid or an alkali depending on the heating temperature, and there are some that act as an acid and an alkali, so both color development and decolorization reactions occur at the same time, so the color density is low and contrast cannot be obtained. Is not clear, and the density of the color-developed portion decreases over time, resulting in poor recording stability. Also,
Since it is a chemical reaction, the repeated durability of coloring and decoloring cannot be said to be sufficient.

As another example of reversible thermosensitive recording, as described in JP-A-6-72035, a long-chain alkyl group in the molecule as a developer and a carboxyl group or a phosphate group as an acid component, etc. Some use compounds with. 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 decolorization occur.
According to this material, since the reaction involved in decoloring is physical, the repeated durability of coloring / decoloring is improved, but the temperature at which coloring / decoloring occurs is not sufficiently high. Therefore, when applied to a card, for example, even if the energy for coloring or erasing is not supplied from the outside, coloring or erasing occurs due to the influence of the ambient temperature, etc., and there is a problem that the stability of recording is lacking. It was

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and performs good recording with a sufficient contrast of color development, and also has good storage characteristics to improve recording stability. An object is to provide an improved reversible thermosensitive recording medium.

[0009]

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 has 6 or more carbon atoms. A barbituric acid derivative having at least one alkyl group of is used.

A leuco dye is used as a color former contained in the reversible thermosensitive recording layer. The leuco dye is preferably a leuco dye having a fluorane skeleton or a triphenylmethane leuco dye. For example, 2-anilino-3-
Methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- [N-ethyl-N-isobutyl] aminofluorane, 2-anilino- 3-methyl-6
-(N-propyl-N-methyl) aminofluorane, 2
-Anilino-3-methyl-6- (N-isopropyl-N
-Methyl) aminofluorane, 2-anilino-3-methyl-6- (N-isopropyl-N-ethyl) aminofluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methyl) amino Fluoran, 2- (m-
Trichloromethylanilino) -3-methyl-6-diethylaminofluorane, 3- [4- (4-phenylaminophenyl) aminophenyl] amino-6-methyl-7-
Chlorofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylaminobenzo [a] fluorane, 3-diethylamino-7-dibenzoylaminofluorane, 3 -Cyclohexylamino-6-chlorofluorane, 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 is a barbituric acid derivative having at least one alkyl group having 6 or more carbon atoms and is represented by the following general formula (2).

[0012]

Embedded image

(Wherein R ₁ , R ₂ and R ₃ are an alkyl group having 6 or more carbon atoms or hydrogen (H), and R ₁ , R ₂ and
At least one of R ₃ is an alkyl group having 6 or more carbon atoms. )

At least one of R ₁ , R ₂ and R ₃ is an alkyl group having 6 or more carbon atoms, and the rest is hydrogen (including the case where all of R ₁ , R ₂ and R ₃ are alkyl groups).
When R ₂ and R ₃ are both hydrogen, R ₁
Is preferably an alkyl group having 12 or more carbon atoms.
Examples of the alkyl group having 6 or more carbon atoms in R ₁ , R ₂ and R ₃ include hexyl group, heptyl group, octyl group, 2-ethylhexyl group, nonyl group, decyl group, undecyl group, dodecyl group, tetradecyl group, Examples thereof include a hexadecyl group, an octadecyl group, an eicosyl group, a docosyl group, a tetracosyl group, and a hexacosyl group, but preferably have 12 or more carbon atoms, and more preferably have 12 to 3 carbon atoms.
0, and more preferably an alkyl group having 12 to 22 carbon atoms. These alkyl groups may be branched, but linear ones are preferable.

Specific examples of the compound represented by the general formula (1) include the following compounds. 5-octadodecyl barbituric acid, 5-hepta dodecyl barbituric acid, 5-
Hexadecyl barbituric acid, 5-tetradecyl barbituric acid, 5-dodecyl barbituric acid, 5-eicosyl barbituric acid, 5-docosyl barbituric acid, 5-tetracosyl barbituric acid, 5-hexaco Sylbarbituric acid, 5-
Decyl barbituric acid, 5- (2-ethylhexyl) barbituric acid, 5-octyl barbituric acid, 5-heptyl barbituric acid, 5,5-dioctadecyl barbituric acid,
5,5-dihexadecyl barbituric acid, 5,5-ditetradecyl barbituric acid, 5,5-didodecyl barbituric acid, 5-dodecyl-5-octadecyl barbituric acid, 1
-Docosyl barbituric acid, 1-octadecyl barbituric acid, 1-dodecyl barbituric acid, 1-hexadecyl barbituric acid (except 5- (2-ethylhexyl) barbituric acid, the alkyl group is linear) is there.)

The barbituric acid derivative used in the present invention is
It can be obtained by a general method for producing barbituric acids, for example, by reacting a corresponding ester of alkylmalonic acid with a corresponding urea in an organic solvent such as alcohol in the presence of an alkali agent such as alkali metal alcoholate. The ester of alkylmalonic acid is prepared by a general production method, for example, by heating the corresponding alkyl halide with an ester of malonic acid in an organic solvent such as alcohol in the presence of an alkali agent such as an alkali metal or its alcoholate. Obtainable.

One example of a concrete synthesis example: For example, 5-n-octadecyl barbituric acid, 20.4 parts by weight of sodium ethoxide is dissolved in 150 parts by weight of dry ethanol, and 18 parts by weight of urea is added thereto. Was dissolved, 123.6 parts by weight of diethyl-n-octadecyl malonate was added dropwise, the temperature was raised to 80 ° C., and the mixture was heated under reflux for 8 hours. As the reaction proceeds, a white precipitate is gradually formed. The white precipitate thus obtained was added dropwise to 2500 parts by weight of ice water together with the reaction solution, neutralized with about 200 parts by weight of dilute hydrochloric acid, filtered and washed with water to give 5-n-octadecyl barbituric acid 10
0 parts by weight can be obtained.

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, polyacrylic acid esters, polymethacrylic acid Examples thereof include esters, acrylic acid copolymers, maleic acid copolymers and polyvinyl alcohol.

The mixing ratio of the color former and the developer is 0.5 to 20 parts by weight, preferably 3 to 8 parts by weight, relative to 1 part by weight of the color developer. The mixing ratio with the binder is 0.1 parts by weight of the binder with respect to 1 part by weight of the total of the color former and the developer.
It is from 20 to 20 parts by weight, and when the amount of the binder is large, the color density and the color sensitivity are lowered, and when the amount of the binder is low, the durability of the reversible thermosensitive recording layer is lowered, so that it is more preferably 0.3 to 3 parts by weight. . The reversible thermosensitive recording layer is preferably formed to have a thickness of 3 to 15 μm.

The layer structure may be only the reversible thermosensitive recording layer, but if necessary, a protective layer may be provided or an intermediate layer may be provided between the support and the support. Each may be composed of multiple layers. Further, a recordable material such as light, electricity or magnetism may be applied.

As the intermediate layer and the protective layer, the materials conventionally used as the intermediate layer and the protective layer in a thermal recording medium or the like can be used. For example, a cellulose resin, a urethane resin, a polyester resin, An alkyd resin, a vinyl resin, an epoxy resin, an acrylic resin, or an acrylic or epoxy ultraviolet curable resin or an electron beam curable resin can be used. Further, oleyl amide, stearyl amide, silicone or the like can be added to the protective layer for imparting lubricity. The thickness of each of the intermediate layer and the protective layer is, for example, 5 μm or less, preferably about 1 to 2 μm.

A composition consisting of the above-mentioned color former, developer, binder, and a suitable solvent for dissolving the binder is dispersed by a ball mill or the like, and thereafter, a means such as a bar coater, a gravure coater, or a knife coater is placed on the support. And then dried for 1 minute at a temperature at which the substrate is not deformed, for example, 80 ° C., to obtain the reversible thermosensitive recording medium of the present invention.

Examples of the support include synthetic resin sheets such as polyethylene terephthalate, polyacetate, polystyrene, polyvinyl chloride and polycarbonate,
Alternatively, synthetic paper or the like can be used.

[0024]

When the reversible thermosensitive recording medium of the present invention is heated by the thermal head, the reversible thermosensitive recording medium has a small area of several meters at a relatively high temperature.
s The temperature of the reversible thermosensitive recording medium does not become uniform in the thickness direction because it is momentarily heated. Therefore, when the reversible thermosensitive recording medium is left to stand at room temperature, the reversible thermosensitive recording layer is affected by a low temperature part (for example, a support). Is cooled relatively quickly, and a color is developed in a rapid cooling step described later. When heated by a heating plate, a large area is heated for a relatively long time (several seconds) as compared with a thermal head, so that the temperature of the reversible thermosensitive recording medium is likely to be relatively uniform including the support and the like. If it is left to stand, it will be cooled gradually and uniformly, and the color will be erased in the slow cooling step described later.

The reversible thermosensitive recording medium of the present invention specifically develops color at about 0.25 mJ / dot to 0.40 mJ / dot by heating with a thermal head of 8 dot / mm, and erases by hot plate pressure bonding at 120 ° C. To do. In addition, after the color is erased, the color is regenerated by heating with a thermal head, and it has reversibility.

Although the mechanism of coloring and decoloring of the reversible thermosensitive recording medium of the present invention is not always clear, the presumed part will be described below. When the reversible thermosensitive recording medium is heated, the color former and the color developer are melted and mixed to form a color, and when rapidly cooled from this state, the color former and the color developer interact to form an amorphous aggregated structure. Then, the color is developed. Next, when heat-slow cooling is performed from this state, the color-developing agent molecules aggregate and crystallize independently, and thus the decolored state is maintained.

According to the present invention, since the coloring temperature and the erasing temperature are relatively high, the coloring or erasing occurs only when heating for coloring or erasing, and the influence of the temperature of the external environment, For example, it does not easily develop or disappear due to an increase in external temperature. Therefore, the storage stability of the record is good, and there is no fear that the recorded content will change when applied to a card or the like, and tampering or forgery 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 color density and 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), and when the temperature is raised from this state, the temperature T
From 2 the color developer and the developer are melted and mixed, and the color begins to develop,
The color is developed (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 raised, 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). Where T1 is the decolorization temperature,
The temperature from 1 to T2 is the erasing temperature range.

[0029]

EXAMPLES Examples of the reversible thermosensitive recording medium according to the present invention will be described in detail below.

Example 1 A reversible thermosensitive recording medium of the present invention having a protective layer was obtained by the following materials and procedures.

Base Material A white polyethylene terephthalate film (PET) having a thickness of 188 μm was used as a base material.

Reversible thermosensitive recording layer Leuco dye (3-diethylamino-6-methyl-7-anilinofluoran (Yamamoto Kasei Co., Ltd., trade name ODB)) 1 part by weight Developer of the following formula (3) Barbituric acid derivative 3 parts by weight

[0033]

Embedded image

However, R ₁ = n-C ₁₈ H ₃₇ , R ₂ = H, R
₃ = H

Binder Acrylic resin (trade name BR-80) manufactured by Mitsubishi Rayon Co., Ltd. 9 parts by weight Solvent Toluene 45 parts by weight

As a reversible thermosensitive recording layer, the above composition was dispersed in a ball mill for 24 hours, and then coated on the above white polyethylene terephthalate film with a wire bar,
It was dried at 80 ° C. for 1 minute to obtain a reversible thermosensitive recording layer having a film thickness of about 6 μm.

Protective Layer Paint UV-curable resin (trade name C3-374, manufactured by Dainippon Ink and Chemicals, Inc.) As a protective layer, the above composition was applied onto the reversible thermosensitive recording layer with a wire bar, and at 80 ° C. for 1 minute. Dry and irradiate with UV light 160W / cm, 30m / min, once, film thickness about 2
A protective layer of μm was obtained.

Example 2 In the composition of the reversible thermosensitive recording layer, 8 parts by weight of the color developer was used. A reversible thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except for the above.

Example 3 In the composition of the reversible thermosensitive recording layer, a developer was added as shown in (4) below.
The barbituric acid derivative of the formula was 8 parts by weight. A reversible thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except for the above.

[0040]

Embedded image

However, R ₁ = n-C ₁₂ H ₂₅ , R ₂ = H, R
₃ = H

Comparative Example In the composition of the reversible thermosensitive recording layer, the developer was bis (p-
It was 4.5 parts by weight of a complex salt of hydroxyphenyl) acetic acid and 3-dodecyloxypropylamine. Others are Example 1.
A reversible thermosensitive recording medium for comparison was obtained in the same manner as.

The reversible thermosensitive recording media of Examples 1, 2, 3 and Comparative Example above were subjected to color development under a printing condition of 0.35 mJ / dot using a thermal head of 8 dots / mm, and 120 ° C., 200 g / dot. The color was erased under the erasing condition of cm ² for 1 second on a hot plate and the background density, the print density and the erasing density were measured by a Macbeth reflection densitometer RD918.

The print density after storage, the background density after storage, and the print residual rate (print density after storage-background density after storage) / under storage conditions of storage at 40 ° C. and 90% RH for 24 hours
(Print density-background density) was measured. Further, the background fog (background density after storage-background density) was measured.

The measurement results are shown in Table 1 below. In addition, color development,
Decolorization density is the reflection density measured with a Macbeth reflection densitometer.

[0046]

[Table 1]

As can be seen from Table 1 above, Examples 1 to 1
In all three cases, sufficient print density can be obtained with respect to the background density,
At the time of erasing, an erasing density close to the background density was obtained. Further, in Comparative Example, the print density after printing and storage was not sufficient, but in all of Examples 1 to 3, good density was obtained. Further, the background density after storage of the part that does not develop color (background part) due to printing was sufficiently close to the background density. The difference between the print density and the background density after storage with respect to the difference between the print density and the background density, that is, the residual rate of printing is extremely low and insufficient in Comparative Examples, whereas all of Examples 1 to 3 are good values. was gotten. Further, there was almost no background fog, which was the difference between the background density after storage and the background density.

[0048]

According to the present invention, since the barbituric acid derivative of the above chemical formula is used as the color developer, good contrast can be obtained, there is no background fog, and the colored portion does not fade over time. A reversible thermosensitive recording medium having good storage characteristics can be obtained. Therefore, since the storage stability of the record is good, there is no fear that the recorded content will change when applied to a card or the like, and tampering or forgery can be prevented. Further, since the color can be erased in a short time, the usage characteristics are good.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between color density and temperature of a reversible thermosensitive recording medium according to the present invention.

[Explanation of symbols]

 T1 T2 temperature

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruhiko Osawa 4-14-12 Koishikawa, Bunkyo-ku, Tokyo Joint Printing Co., Ltd. (72) Shinichi Koizumi 4-14-12 Koishikawa, Bunkyo-ku, Tokyo Joint printing Incorporated (72) Inventor Masayuki Seiyanagi 1-11-2 Fujimi, Chiyoda-ku, Tokyo Nihon Kayaku Co., Ltd.

Claims (3)

[Claims] 1. A reversible thermosensitive recording layer containing a color former, a developer and a binder, wherein the developer is a barbituric acid derivative having at least one alkyl group having 6 or more carbon atoms. Characteristic reversible thermosensitive recording medium. 2. The reversible thermosensitive recording medium according to claim 1, wherein the barbituric acid derivative is represented by the following general formula (1). Embedded image (Here, R ₁ , R ₂ , and R ₃ are alkyl groups having 6 or more carbon atoms or hydrogen (H), and at least one of R ₁ , R ₂ , and R ₃ is an alkyl group having 6 or more carbon atoms. ) 3. The reversible thermosensitive recording medium according to claim 2, wherein R ₁ is an alkyl group having 12 or more carbon atoms, and R ₂ and R ₃ are hydrogen.