JPH04303680A - Reversibly fluorescence producing and erasing thermal recording medium - Google Patents

Abstract

PURPOSE:To obtain a reversibly fluorescence producing and erasing thermal recording medium which can conduct both the erasure and production of a fluorescence in an invisible region, which cannot be identified by naked eyes, only by controlling a thermal energy. CONSTITUTION:A recording layer containing an organic fluorescent metal complex which erases a fluorescence in an acid range and is thermally stable and a color developing/reducing agent which is acid under a short-time heating and basic under a long-time heating realizes the reversible production and erasure of a fluorescence.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible fluorescent color-developing thermosensitive recording medium that can carry out both coloring and decolorizing chemical reactions solely by controlling thermal energy.

0002

BACKGROUND ART Conventionally, reversible coloring/discoloring materials have been disclosed, for example, in Japanese Patent Application Laid-open No. 58-191190 and Japanese Patent Application Laid-open No. 6
0-193691, JP 60-193691, U.S. Patent No. 3,666,525, JP 54-
No. 119377, Japanese Patent Application Laid-open No. 63-39377,
JP-A-63-41186, U.S. Patent Specification 402
No. 8118, JP-A-50-81157, JP-A-Sho 5
It is described in the publication No. 0-105555.

[0003] However, among the above documents, US Patent Specification 4
In the methods described in JP-A No. 028118, JP-A-50-81157, and JP-A-50-105555, the image formed changes depending on the temperature, and once the image is formed, it is stored at room temperature. unable to
The image lacks memorability.

[0004] Also, Japanese Patent Application Laid-Open No. 58-191190,
JP-A-60-193691, U.S. Patent Specification 36
The device described in No. 66525 has a recording layer consisting of a color forming agent, a color developer, and a binder, and if necessary, a low vapor pressure solvent or a heat-melting substance is added. Although heat is used, decoloring is performed using water, steam, or some kind of organic solvent, and it is not possible to repeat both coloring and decoloring by controlling thermal energy.

[0005] Furthermore, Japanese Patent Application Laid-Open Nos. 54-119377, 63-39377, and 63-411
The device described in Publication No. 86 has a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material, and the transparency of the heat-sensitive layer can be reversibly changed by thermal energy. It develops and decolors by changing the color. Since this mechanism of action is thought to be based on physical changes, it is only reversible in the visible range.

[0006]

[Problems to be Solved by the Invention] The purpose of the present invention is to provide reversible information expression in the non-visual field that cannot be discerned with the naked eye, that is, to achieve reversible information expression in which both coloring and decolorizing chemical reactions are performed solely by controlling thermal energy. The present invention provides a fluorescent color-depleting thermosensitive recording medium.

[0007]

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned problems. A reversible fluorescent color-developing/coloring thermosensitive recording medium having a recording layer consisting of a color developer/subtractor consisting of an amphoteric compound as a part thereof, and a fluorescent compound which is an organometallic complex that loses its fluorescence in an acidic region, and wherein the organometallic It is also included that the fluorescent compound which is a complex is a complex of 8-hydroxyquinoline or a quinoline derivative and a divalent metal.

[0008]

[Function] The mechanism of fluorescent coloring and fading of the reversible fluorescent coloring and fading thermosensitive recording medium (hereinafter simply referred to as the thermosensitive recording medium) according to the present invention is determined by the combination of 8-hydroxyquinoline or a quinoline derivative and a divalent metal. Considering the example of an organometallic complex, the color development and fading of an organometallic complex of 8-hydroxyquinoline or a quinoline derivative and a divalent metal is expressed by the following equilibrium equation (2).
It is expressed as

[0009]

[Chemical formula 2] MA2 +2H+ ⇔M2+
+2HA (2) (In the formula, M represents a divalent metal, and A represents 8-hydroxyquinoline or a quinoline derivative.)

[0010] The 8-hydroxyquinoline or quinoline derivative on the left side of the equilibrium equation (2) is an organometallic complex, and the lone pair of nitrogen atoms contributes to the complex formation, which is thought to originate from the π-π* lowest excited singlet state. Although fluorescence is observed, the 8-hydroxyquinoline or quinoline derivative on the right side is free and the lowest excited state is brought about by the n-π* transition, so it does not exhibit fluorescence.

Further, from the equilibrium equation (2), it can be seen that when the pH is in the acidic region, the equilibrium tilts to the right, and when the pH is near neutral or basic, the equilibrium tilts to the left.

A color developer and thinner, which is an amphoteric compound, exhibits acidic properties due to the action of phenolic hydroxyl groups or carboxyl groups when heated at high temperature and for a short period of time (several milliseconds to several hundred milliseconds); When heated for a long time (1 second or more) at a temperature near or above the melting point of the compound, it exhibits basic properties due to the action of the amino group.

[0013] Therefore, a recording medium having a recording layer containing an organometallic complex and an amphoteric color developing/decreasing agent loses color (disappears fluorescence) by heating at a high temperature for a short time, and loses its color when heated at a low temperature for a long time. , the color develops again (recovers fluorescence).

[0014] The fluorescent compound in this specification exhibits the generation and disappearance of fluorescence depending on changes in the atmosphere, and compounds whose complex formation is influenced by the atmosphere and is linked to the presence or absence of fluorescence can be used.

Specific examples of these include thermally stable 8-hydroxyquinoline and quinoline derivative metal complexes, such as 8-hydroxyquinoline magnesium complex, 8-hydroxyquinoline calcium complex, and 8-hydroxyquinoline calcium complex. Quinoline strontium complex, 8
-Hydroxyquinoline barium complex, 8-hydroxyquinoline zinc complex, 8-hydroxyquinoline beryllium complex, 8-hydroxyquinaldine magnesium complex, 8-
Hydroxyquinaldine calcium complex, 8-hydroxyquinaldine barium complex, 8-hydroxyquinaldine beryllium complex, 8-(p-tosyl)aminoquinoline zinc complex, 8-(p-tosyl)aminoquinoline calcium complex, 8-(p-tosyl)aminoquinoline calcium complex, -tosyl)aminoquinoline magnesium complex, 8-(p-tosyl)aminoquinoline beryllium complex, 2-quinaldate zinc complex, 2-quinaldate magnesium complex, 2-quinaldate calcium complex, and the like.

[0016] Further, as the color developer and subtractor in this specification, an amphoteric compound having at least one of a phenolic hydroxyl group and a carboxyl group and an amino group as a sensitive group or a part of a salt compound may be used. can. These exhibit acidity under the action of heat or work to cancel out the acidity, and are represented by the following structural formulas (3) and (4), for example.

[0017]

[Formula 3] (wherein, X2 is a hydroxyl group or a carboxyl group, R2
represents a hydrogen atom or a hydroxyl group. )

[0018]

[Formula 4] (In the formula, X3 is an alkyl group having 8 or more carbon atoms, R4 is a hydrogen atom or a methyl group, and m is an integer from 0 to 6.)

[0019] It is preferable that 1 to 10 parts by weight of the color developing and reducing agent be mixed with 1 part by weight of the fluorescent compound.

Further, the recording layer of the thermosensitive recording medium of the present invention may contain a binder. As such a binder, a commonly used polymeric material soluble in water or an organic solvent can be used. Specific examples include polyvinyl alcohol, methylcellulose, ethylcellulose, cellulose acetate, polystyrene,
Polyvinyl chloride, linear saturated polyester, methacrylic resins such as polymethyl methacrylate, polyethyl methacrylate, etc. alone or copolymers, and thermoplastic resins such as polyurethane, polybutyral, and nitrocellulose can be used. The binder may be used in an amount of 5 parts by weight or less per 1 part by weight of the color developer and subtractor.

Next, a method for manufacturing the heat-sensitive recording medium of the present invention will be explained.

First, a coating solution is prepared by dissolving or dispersing a fluorescent compound and a color developer/subtractor in a suitable solvent such as water or an organic solvent. In addition, a liquid property improver such as a thickener and a pigment can be added to the coating liquid. Furthermore, the coating liquid is applied onto the support using a well-known coating method such as bar coating, blade coating, air knife coating, gravure coating, roll coating, or the like. As the support, in addition to paper, plastic materials such as plastic cards can be used. After applying the coating liquid to the support, the coating liquid is dried to form a recording layer. In addition, the coating amount of the coating liquid is preferably 1 to 10 g/m in weight after drying.

Furthermore, a protective layer may be provided on the recording layer for the purpose of improving thermal head matching properties (resistance adhesion to the thermal head, sticking) or imparting durability to the recording layer. For example, the protective layer components may include fillers such as colorless inorganic pigments or waxes, thermoplastic resins used for the recording layer binder, or curable resins such as thermosetting resins and ultraviolet curable resins.

The fluorescence of the recording layer can be changed by short-term heating. The heating required for the change is
The heating time may be extremely short, for example, heating with a thermal head for several milliseconds to several hundred milliseconds. The temperature may be the same as the heating temperature of a normal thermal head, and is usually about 300°C.

[0025] Further, the fluorescence of this recording layer, which had been discolored, is restored by heating for a long time. Long-term heating means heating for a long time compared to the heating time of a thermal head, etc., and the heating time required for this recovery is only 1 to several seconds. The temperature required for recovery is 80-180°C.

[0026]

EXAMPLES The present invention will be explained in detail using examples. Note that the example is a thermosensitive recording medium in which a recording layer is formed on a sheet.

[Example 1] A liquid fluorescent compound

[0028]

[C5] 10.0 parts by weight

Binder methacrylic resin
5.0 parts by weight Solvent Toluene 40.0 parts by weight
B liquid Developing/decreasing agent

[0030]

[C6] 10.0 parts by weight

Binder methacrylic resin
7.5 parts by weight Solvent Toluene 40.0 parts by weight

0
[032] 1 part of each of the above liquids A and B was mixed in a sand mill.
After time pulverization and dispersion or dissolution, 1 part by weight of liquid A,
A coating solution was prepared by thoroughly mixing 10 parts by weight of Solution B. This coating solution was applied onto a 250 μm thick white polyvinyl chloride sheet as a support using a Mayer bar, dry weight 5.
A heat-sensitive recording medium was prepared by coating and drying to a thickness of μm.

A thermal simulator (
Printing conditions: applied voltage 0.2 to 0.47 W/dot, pulse width 2.5 ms ON/OFF, thermal head: Toshiba Corporation thin film head (348 Ω), dot density: 6 d
ot/mm). Changes in fluorescence behavior were observed by irradiation with ultraviolet light at 254 nm, and disappearance of fluorescence (decolorization) was observed.

Next, the sample was pressed for 1 second with a hot plate heated to 80 to 180° C., and the presence or absence of fluorescence caused by 254 nm ultraviolet irradiation was similarly observed. As a result, recovery of fluorescence (color development) was observed. Note that it was difficult to visually distinguish these changes without UV irradiation.

Furthermore, even when the thermosensitive recording medium was subjected to thermal head printing and hot plate pressing again, the fluorescence behavior remained the same, and it was also confirmed that it had reversibility.

[Example 2] A liquid fluorescent compounds

[0037]

[C7] 10.0 parts by weight

Binder polyvinyl alcohol
2.0 parts by weight Solvent Water
32.0 parts by weight
Isopropyl alcohol 8.0 parts by weight Solution B Color developer/reducer

[0039]

[Chemical formula 8] 10.0 parts by weight

Liquidity improver Calcium carbonate
10.0 parts by weight Binder Polyvinyl alcohol 2.0 parts by weight Solvent
water 3
2.0 parts by weight Isopropyl alcohol 8.0 parts by weight

[0041] Above A
After each liquid and B liquid were ground and dispersed in a sand mill for 1 hour, 1 part by weight of liquid A and 7 parts by weight of liquid B were thoroughly mixed to produce a coating liquid. This coating solution was applied onto a support of high-quality paper with a basis weight of 60 g/m 2 using a Mayer bar and dried to a dry weight of 7.5 μm to prepare a heat-sensitive recording medium.

Printing was carried out on the heat-sensitive recording medium under the same conditions as in Example 1, and changes in fluorescence behavior were observed by irradiation with 254 nm ultraviolet rays. Disappearance (discoloration) of fluorescence was observed.

Next, erasing was performed under the same conditions as in Example 1, and the presence or absence of fluorescence due to 254 nm ultraviolet irradiation was similarly observed, and recovery (color development) was observed. Note that it was difficult to visually distinguish these changes without UV irradiation.

It was also confirmed that even if the thermosensitive recording medium was subjected to thermal head printing and hot plate pressing again, the fluorescence behavior remained the same, and that it had reversibility.

[0045]

As described above, according to the reversible fluorescent coloring/decolorizing thermosensitive recording medium according to the present invention, the developer and subtractor in the recording layer exhibits neutral properties before heating, so that the fluorescent compound has fluorescence, but exhibits acidic properties after short-term heating, so the fluorescent compound loses its fluorescence. However, after long-term heating, the color developer exhibits neutral properties, allowing the fluorescent compound to regain its fluorescent properties.

[0046] Therefore, it has become possible to reversibly express information in a region beyond the visual field that cannot be discerned with the naked eye using only heat.

Claims (2)

[Claims] Claim 1: A developer and subtractor comprising an amphoteric compound having at least one of a phenolic hydroxyl group and a carboxyl group and an amino group as a sensitive group or a part of a salt compound; A reversible fluorescent color-developing thermosensitive recording medium having a recording layer comprising a fluorescent compound which is an organometallic complex. 2. The fluorescent compound as an organometallic complex is a complex of 8-hydroxyquinoline or a quinoline derivative represented by the following general formula (1) and a divalent metal. A reversible fluorescent color-depleting thermosensitive recording medium. [Chemical formula 1]