JPH07110939B2 - Reversible thermosensitive coloring / erasing composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reversible thermosensitive coloring / erasing composition.

More specifically, it relates to a reversible thermosensitive coloring / erasing composition that develops color by heating for a short time and decolorizes by heating for a long time.

(Prior Art) Conventionally, reversible color-developing materials include, for example, JP-A-58-191190, JP-A-60-193691, US Pat. No. 3,666,525, and JP-A-54-119377. JP-A-63-39377, JP-A-63-41186, U.S. Pat.No. 4,028,118, JP-A-50-81157, JP-A-50.
-105555, etc.

However, among the above-mentioned documents, U.S. Pat. No. 4,028,118
In the methods described in JP-A Nos. 50-81157 and 50-105555, the image formed changes with temperature, and the image once formed is stored at room temperature. Cannot be done, and the image lacks in memory.

Further, those described in JP-A-58-191190, JP-A-60-193691, and U.S. Pat.No. 3,666,525,
It comprises a recording layer comprising a color former, a developer and a binder, and optionally a low vapor pressure solvent or a heat-melting substance is added, and the color is developed by using heat.
Decoloring is performed with water, water vapor or some kind of organic solvent, and it is not possible to repeat both coloring and decoloring by controlling heat energy.

Further, those disclosed in JP-A-54-119377, JP-A-63-39377, and JP-A-63-41186 include a resin base material and an organic substance dispersed in the resin base material. It has a heat-sensitive layer containing a low-molecular substance as a main component, and reversibly changes the transparency of the heat-sensitive layer by heat energy to perform coloring and decoloring. That is, it does not chemically develop or erase color.

On the other hand, Japanese Patent Application No. 2-505365 (named "reversible thermosensitive recording medium composition") filed by the applicant on April 6, 1990, is a chemical reaction of both coloring and erasing. It describes a composition which can be carried out only by controlling the thermal energy.

As a result, the composition is applied to a base material such as a plastic card and is heated by a thermal head or the like for a short time (several milliseconds to several tens of milliseconds) to develop a color, which is then heated for a long time (several seconds). As a result, the result of erasing is obtained.
Coloring and erasing can be repeated, for example, 100 to several thousand times can be repeated.

(Problems to be Solved by the Invention) However, the composition described in Japanese Patent Application No. 2-505365 (named "reversible thermosensitive recording medium composition") dated April 6, 1990 is Because of its erasing, 120
It is necessary to heat at a temperature of 1 to 130 ° C for about 1 second. However, even under normal conditions, even under the harsh conditions, for example, in a high temperature state such as in a car in the summer, the composition is below the above-described decolorization temperature, but this composition starts decoloring incompletely and its concentration decreases. .

Therefore, the present invention provides a reversible thermosensitive coloring / erasing composition that is less likely to be decolored at a temperature lower than the decoloring temperature, and further rapidly erases when the decoloring temperature is reached, thereby preventing the disappearance of visible information. To aim.

(Means for Solving the Problems) To achieve this object, the present invention provides a reversible sensation comprising an acidic substance having at least one of a phenolic hydroxyl group and a carboxyl group, a basic substance having an amino group, and a leuco compound. A reversible thermosensitive coloring and decoloring composition, characterized in that the basic substance is an amine represented by the general formula [1].

R ₁ XC _m H _2m NH ₂ [1] (wherein R ₁ is an alkyl group of C ₆ or more and C ₁₈ or less, X is an oxygen atom or a sulfur atom, and m is an integer of 2 to 4) (Detailed description of the invention) The composition according to the present invention is composed of an acidic substance, a basic substance, and a leuco compound.

The acidic substance and the basic substance cause a color developing reaction and a color erasing reaction of the leuco compound by heat. That is, the phenolic hydroxyl group or the carboxyl group opens the lactone ring of the colorless leuco compound by the energy of heat, and develops a colorless to colored color. However, the compound in which the lactone ring is opened returns to the original colorless compound having the lactone ring when contacted with a basic substance.

Since the acidic substance has an acidic group consisting of a phenolic hydroxyl group or a carboxyl group, and the basic substance has a basic group consisting of an amino group, the coloring reaction and the decoloring reaction probably occur at the same time by heating. . Under heating conditions, the reaction rate of the color development reaction is faster than the reaction rate of the decolorization reaction. Therefore, it can be inferred that the color development state is maintained by heating and cooling for a short time. Further, it is presumed that the equilibrium state is the decolored state under the heating condition. Therefore, the color is erased by heating for a long time, and this decolored state is maintained even after cooling to room temperature. This reaction rate formula is g (t) = A {exp (−t / τ
_a ) −exp (−t / τ _b )}. In the formula,
g (t) is the color density, t is the heating time, τ _a and τ _b are constants determined by the types of acidic substance and basic substance, and A is a constant. A similar formula can be derived even if it is considered that the color-development reaction is followed by the decolorization reaction.

The acidic substance mainly develops a color of the leuco compound under heating conditions and is a compound having at least one of a phenolic hydroxyl group and a carboxyl group. A compound having both of them is preferable.

Examples of such acidic substances include compounds represented by the following general formula [A] or [B] or esters thereof.

(In the formula, n represents an integer of 1 to 3, preferably 2 or 3.) (In the formula, R ₂ represents a hydrogen atom or a methyl group, and n ₁ is 0 to 6
Represents the integer. ) Specific examples of the compound represented by the above general formula [A] include 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid (n = 1); 3,4-dihydroxybenzoic acid. , 3,5-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-
Dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid,
3,6-dihydroxybenzoic acid, 4,5-dihydroxybenzoic acid, 4,6-dihydroxybenzoic acid, 4-hydroxysalicylic acid, 5-hydroxysalicylic acid and the like (n = 2); gallic acid and the like (n = 3) To be

As the ester of the compound represented by the general formula [A], hexyl gallate, heptyl gallate, octyl gallate, nonyl gallate, decyl gallate, undecyl gallate, lauryl gallate, tridecyl gallate, Examples include tetradecyl gallate, pentadecyl gallate, cetyl gallate, heptadecyl gallate, stearyl gallate, and the like.

Further, as the compound represented by the above general formula [B], 2,
2-bis (4-hydroxyphenyl) ethanoic acid, 2,2-bis (4-hydroxyphenyl) propionic acid, 3,3-bis (4-hydroxyphenyl) propionic acid, 4,4-bis (4-hydroxyphenyl) ) Butanoic acid, 4,4-bis (4-hydroxyphenyl) heptanoic acid, 5,5-bishydroxyphenyl) pentanoic acid, 5,5-bis (4-hydroxyphenyl) hexanoic acid, 6,6-bis (4 -Hydroxyphenyl) heptanoic acid, 7,7-bis (4-hydroxyphenyl) heptanoic acid, 8,8-bis (4-hydroxyphenyl) octanoic acid, 7,7-bis (4-hydroxyphenyl) octanoic acid, 8 Examples include 8,8-bis (4-hydroxyphenyl) nonanoic acid and the like.

In addition, the basic substance is a substance that decolorizes the leuco compound under heating conditions, does not decolor below a specific decoloring temperature, and maintains its concentration at a sufficient level. It is necessary to have a specific structure in order to rapidly erase the color. That is, this basic substance must be an amine represented by the following general formula [1].

R ₁ XC _m H _2m NH ₂ [1] (However, R ₁ is an alkyl group of C ₆ or more and C ₁₈ or less, X is an oxygen atom or a sulfur atom, and m is an integer of 2 to 4.) X is an oxygen atom. In this case, the basic compound is an alkoxyalkylamine represented by the following general formula [2].

R ₁ OC _m H _2m NH ₂ [2] (provided that R ₁ is an alkyl group of C ₆ or more and C ₁₈ or less, m is an integer of 2 to 4), and when X is a sulfur atom, this base The compound is a thioalkoxyalkylamine represented by the following general formula [3].

R ₁ SC _m H _2m NH ₂ [3] (provided that R ₁ is an alkyl group of C ₆ or more and C ₁₈ or less, m is an integer of 2 to 4) As the alkoxyalkylamine represented by the general formula [2], , For example, 2- (hexyloxy) -ethylamine, 2- (heptyloxy) -ethylamine, 2- (octyloxy) -ethylamine, 2- (nonyloxy)
-Ethylamine, 2- (decyloxy) -ethylamine, 2- (dodecyloxy) -ethylamine, 2- (undecyloxy) -ethylamine, 2- (tridecyloxy) -ethylamine, 2- (tetradecyloxy)-
Ethylamine, 2- (pentadecyloxy) -ethylamine, 2- (hexadecyloxy) -ethylamine, 2
-(Heptadecyloxy) -ethylamine, 2- (octadecyloxy) -ethylamine, 3- (hexyloxy) -propylamine, 3- (heptyloxy) -propylamine, 3- (octyloxy) -propylamine, 3- (Nonyloxy) -propylamine, 3- (decyloxy) -propylamine, 3- (dodecyloxy) -propylamine, 3- (undecyloxy) -propylamine, 3- (tridecyloxy) -propylamine, 3- (Tetradecyloxy) -propylamine,
3- (pentadecyloxy) -propylamine, 3-
(Hexadecyloxy) -propylamine, 3- (heptadecyloxy) -prohiruamine, 3- (octadecyloxy) -prohiruamine, 4- (hexyloxy)
-Butylamine, 4- (heptyloxy) -butylamine, 4- (octyloxy) -butylamine, 4- (nonyloxy) -butylamine, 4- (decyloxy)-
Butylamine, 4- (dodecyloxy) -butylamine, 4- (undecyloxy) -butylamine, 4-
(Tridecyloxy) -butylamine, 4- (tetradecyloxy) -butylamine, 4- (pentadecyloxy) -butylamine, 4- (hexadecyloxy) -butylamine, 4- (heptadecyloxy) -butylamine, 4- Examples thereof include (octadecyloxy) -butylamine.

Examples of the thioalkoxyalkylamine represented by the general formula [3] include 2- (hexyltioxy) -ethylamine, 2- (heptyltioxy) -ethylamine, 2-
(Octyltioxy) -ethylamine, 2- (nonyloxy) -ethylamine, 2- (decyltioxy) -ethylamine, 2- (dodecyltioxy) -ethylamine, 2
-(Undecyltioxy) -ethylamine, 2- (tridecyltioxy) -ethylamine, 2- (tetradecyloxy) -ethylamine, 2- (pentadecyltioxy) -ethylamine, 2- (hexadecyltioxy) −
Ethylamine, 2- (heptadecyltioxy) -ethylamine, 2- (octadecyltioxy) -ethylamine, 3- (hexyltioxy) -propylamine, 3-
(Heptylthioxy) -propylamine, 3- (octyloxy) -propylamine, 3- (nonylthiooxy)
-Propylamine, 3- (decyltioxy) -propylamine, 3- (dodecyltioxy) -propylamine,
3- (undecyltioxy) -propylamine, 3-
(Tridecylthioxy) -propylamine, 3- (tetradecylthioxy) -propylamine, 3- (pentadecylthioxy) -propylamine, 3- (hexadecylthioxy) -propylamine, 3- (hepta Decyltioxy) -prohiruamine, 3- (octadecyltioxy) -prohiruamine, 4- (hexyltioxy) -butylamine, 4- (heptyltioxy) -butylamine, 4- (octyltioxy) -butylamine, 4-
(Nonylthioxy) -butylamine, 4- (decylthioxy) -butylamine, 4- (dodecylthioxy) -butylamine, 4- (undecylthioxy) -butylamine, 4- (tridecylthioxy) -butylamine, 4-
(Tetradecyltioxy) -butylamine, 4- (pentadecyltioxy) -butylamine, 4- (hexadecyltioxy) -butylamine, 4- (heptadecyltioxy) -butylamine, 4- (octadecyltioxy)
-Butylamine and the like can be exemplified.

Leuco compounds are those that develop and decolor when heated.
For example, crystal violet lactone, 3-indolino-3-p-dimethylaminophenyl-6-dimethylaminophthalide, 3-ciethylamino-7-chlorofluorane, 2- (2-fluorophenylamino) -6-diethylaminofluorane. , 2- (2-fluorophenyl) -6-di-n-butylaminofluorane, 3-diethylamino-7-cyclohexylaminofluorane, 3
-Diethylamino-5-methyl-7-t-butylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-futylanilinofluorane, 3-cyclohexyl Amino-
6-chlorofluorane, 2-anilino-3-methyl-6
-(N-ethyl-p-toluidino) -fluorane, 3-
Pyrrolidino-6-methyl-7-anilinofluorane, 3
-Pyrrolidino-7-cyclohexylaminofluorane,
3-N-methylsirohexylamino-6-methyl-7-
Anilinofluorane, 3-N-ethylpentylamino-
6-methyl-7-anilinofluorane and the like can be mentioned.

The composition of the present invention may further contain a binder. As such a binder, a commonly used polymer material that is soluble in water or an organic solvent can be used. Specific examples of such a polymer material include polyvinyl alcohol, methyl cellulose, ethyl cellulose, cellulose acetate, polystyrene, polyvinyl chloride, linear saturated polyester, methacrylic resin such as polymethyl methacrylate and polyethyl methacrylate alone. Alternatively, a thermoplastic resin such as a copolymer, polyurethane, polyvinyl butyral, or nitrocellulose may be used.

The composition of the present invention can be obtained by mixing an acidic substance, a basic substance, a leuco compound and a necessary binder.

The acidic substance and the basic substance may be added and mixed separately, but it is desirable to react them in advance and add and mix them as a salt or complex salt of both. This is because the impurities contained in each of them are easily removed, and the characteristics of the composition are easily designed to be constant.

It is desirable that the acidic substance and the basic substance are mixed in equivalent amounts.

The leuco compound is preferably mixed in an amount of 0.1 to 1.0 part by weight with respect to 1 part by weight of the total amount of the acidic substance and the basic substance. Further, the binder may be 5 parts by weight or less based on 1 part by weight of the total amount of the acidic substance and the basic substance.

The composition of the present invention can be used as a recording layer by dissolving or dispersing it in water or an appropriate solvent such as an organic solvent to form a coating, and coating the coating on a suitable support. In coating, a liquidity improver such as a thickener or a pigment can be added to the paint. As the support, in addition to paper, a plastic material such as a plastic card can be used. The coating can be carried out by a well-known coating method such as bar coating, blade coating, air knife coating, gravure coating or roll coating. The coating amount is preferably 4 to 10 g / m ^{2 by} weight after drying.

A protective layer may be provided on the recording layer to protect the recording layer. For example, wax, the above-mentioned thermoplastic resin, or a curable resin such as a thermosetting resin or an ultraviolet curable resin.

This recording layer develops color by heating for a short time. The heating required for color development is for a very short time, and for example, heating with a thermal head for several milliseconds to several hundreds of milliseconds may be sufficient. The temperature may be the same as the heating temperature of a normal thermal head,
It is usually around 300 ° C.

Further, this recording layer is erased by heating for a long time. The long-time heating means heating for a longer time than the time required for color development, and the "long-time heating" required for this decoloring is only 1 to several seconds. The temperature required for erasing is
The temperature is 80 to 110 ° C., and almost no color is erased at a temperature lower than this decolorization, and the color development information can be sufficiently maintained.

(Example 1) The solutions A and B were pulverized and dispersed in a sand mill for 1 hour, respectively, and then 1 part by weight of the solution A and 4 parts by weight of the solution B were sufficiently mixed to produce a coating solution. This coating liquid has a thickness of 250 μm
Was coated and dried on a white polyvinyl chloride sheet (1) using a Meyer bar so as to have a dry film thickness of 5.5 μm, thereby producing a reversible sheet having no background fog.

(Example 2) The solutions A and B were pulverized and dispersed by a sand mill for 1 hour respectively, and then 1 part by weight of the solution A and 7 parts by weight of the solution B were sufficiently mixed to prepare a coating solution. Using a Mayer bar, a dry film thickness of 7.5 μm was obtained by applying this coating liquid onto a wood free paper having a basis weight of 60 g / m ^2.
Was coated and dried to produce a reversible sheet with no background fog.

(Example 3) The solutions A and B were pulverized and dispersed by a sand mill for 1 hour, respectively, and then 1.0 part by weight of the solution A and 5.0 parts by weight of the solution B were sufficiently mixed to prepare a coating solution. Apply this coating solution to a thickness of 188μ
m white polyester sheet was coated and dried using a Meyer bar so that the dry film thickness was 7.0 μm, to produce a reversible sheet having no background fog.

(Example 4) Solution C Methacrylic resin 10.0 parts by weight Calcium carbonate 10.0 parts by weight Toluene 40.0 parts by weight The solutions A and B are pulverized and dispersed for 1 hour in a sand mill, respectively, and then solution A 1.0 parts by weight and solution B 2.5 parts by weight are thoroughly mixed. To produce a coating liquid. Apply this coating solution to a thickness of 188μ
m white bar on a white polyester sheet, and the coating was dried using a Meyer bar so that the dry film thickness was 6.0 μm. Then, using the Mayer bar, the liquid C is dried to a film thickness of 1.5 μm.
Was coated and dried to give a reversible sheet free of background fog.

(Comparative Example 1) A reversible sheet was produced in the same manner as in Example 1 except that the solution B having the following composition was used.

(Comparative Example 2) A reversible sheet was produced in the same manner as in Example 2 except that the liquid B having the following composition was used.

(Evaluation) The sheets of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated by the following methods.

In other words, each sheet is a thermal simulator (printing conditions: applied voltage 0.47W / dot, pulse width 2.5msec ON / O
FF, thermal head: Thin film head manufactured by Toshiba Corporation (348
Ω), dot density: 6 dots / mm), and a solid image with a width of 10 mm was printed, and the color density was measured by a reflection densitometer (RD-918 manufactured by MACBETH).

Next, a hot stamp plate heated to 80 ° C. and 120 ° C. was pressed for 1 second to erase the color, and the reflection density at this time was measured by the same method.

The results are shown in Table 1. In the table, "hue" is the hue at the time of coloring, "base" and "coloring" are before coloring,
It means the reflection density at the time of color development, and “80 ° C.” and “120 ° C.” mean the reflection densities after erasing with the hot stamp plates at 80 ° C. and 120 ° C., respectively.

Each sheet was repeatedly colored and decolored several hundred times, but it is difficult to decolor below the decoloring temperature and exhibits the property of resisting the disappearance of display information, while it rapidly decolors above the decoloring temperature. Had a property.

(Effect) As described above, according to the present invention, color is developed only by heat.
It is a reversible color-erasing composition that can be repeatedly erased, and at the temperature below the optimum color-erasing temperature, the image information formed by color formation does not easily disappear. A composition having the properties described above can be obtained.

Therefore, it can be coated on the surface of a plastic card or the like to reversibly print or print, and the operating environment conditions can be greatly expanded.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C09B 11/28 H 67/44 C

Claims (1)

[Claims] 1. A reversible thermosensitive decolorizing composition comprising an acidic substance having at least one of a phenolic hydroxyl group and a carboxyl group, a basic substance having an amino group, and a leuco compound, wherein the basic substance is A reversible thermosensitive coloring / erasing composition, which is an amine represented by the general formula [1]. R ₁ XC _m H _2m NH ₂ [1] (provided that R ₁ is an alkyl group of C ₆ or more and C ₁₈ or less, X is an oxygen atom or a sulfur atom, and m is an integer of 2 to 4)