JPH083067B2 - Thermosensitive coloring ink and thermosensitive coloring plastic card coated with the ink - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a heat-sensitive color-developing ink, and more specifically, by using a vehicle consisting of a combination of a specific solvent and a resin, good printing can be achieved especially on a plastic sheet. The present invention relates to a thermosensitive coloring ink to be given and a thermosensitive plastic card.

In recent years, the thermosensitive color recording method is used for printing information by a thermal printer used as a terminal of an electronic computer, a thermal pen recorder for various medical devices such as an electrocardiogram, a printer for an industrial measuring instrument, or a recording for a thermosensitive facsimile. Widely applied in the field.

Further, as one of the heat-sensitive color-forming ink compositions used for such purpose, a heat-sensitive agent composed of a phenolic compound and a leuco dye which reacts with the phenolic compound under heating to form a color, and a support for them. It is known to consist of a vehicle for sticking to.

In such a heat-sensitive color-developing system, a phenolic compound and a leuco dye are dispersed in a vehicle in the form of fine particles, and a dispersion printing ink layer is formed by coating and forming on a support. Below, at least one of them melts or sublimes to come into intimate contact with each other to react and develop color.

Therefore, the solvent and the resin constituting the vehicle in which the phenolic compound (developing agent) and the leuco dye (color former) (hereinafter sometimes collectively referred to as "heat-sensitive agent") are dispersed are as follows: Nature is required.

i. At room temperature, the vehicle must be inert and insoluble in the heat-sensitive agent in order to keep the colorless ink before use and the dispersed printing ink layer after use stable.

ii. In order to separate the heat-sensitive agents (color former and developer) from each other,
The vehicle must have a high viscosity above a certain level.

iii. Since the thermosensitive coloring layer formed after printing is subjected to sliding friction by a high temperature thermal head, the vehicle must form a tough film even at high temperatures.

Conventionally, in order to satisfy the above requirements, most of vehicles are those obtained by dissolving a water-soluble polymer compound such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, starch and polyacrylamide in water. It is used.

However, the use of such a water-soluble vehicle has some drawbacks.

That is, first of all, since the water-soluble polymer is used, the formed heat-sensitive layer is poor in water resistance and cannot withstand long-term storage when spilling water or high humidity.

In addition, the heat-sensitive layer that has absorbed moisture is apt to be softened by heat, exhibits adhesiveness when heated, and has a drawback that stable printing and image recording cannot be performed because the thermal head of the terminal device adheres and hinders running properties.

As a method for improving this, a method of adding an isobutylene-maleic anhydride copolymer, dialdehyde starch and the like to a vehicle has been carried out (Japanese Patent Laid-Open No. 54-1040).

However, in this method, the film performance of the heat-sensitive layer to be formed is certainly improved, but since water is used as a solvent, in the coating step for forming the heat-sensitive layer, the drying is slow and the work efficiency is extremely low. There is.

Further, it is difficult to obtain a uniform dispersion system of a leuco paint with an aqueous vehicle, and when the resin concentration is increased, a thickening or gelation phenomenon is exhibited, and when water is increased to decrease the viscosity, sedimentation separation occurs. It becomes impossible to apply evenly. As a result, the heat-sensitive layer formed on the support causes spot rings (mottling), swimming, satin, etc., resulting in an undesired finish, and uneven density in the color image due to heat-sensing, which is clear. The recording pattern cannot be obtained.

It is also known that when paper is used as a support, a non-aqueous vehicle in which a terpene resin, petroleum resin, cyclic rubber or the like is dissolved in a petroleum solvent is applied to prevent the paper from stretching or wrinkling during application. (Japanese Patent Publication No. 50-14533).

However, the use of such a water-insoluble vehicle also does not provide an essential solution to the drawbacks associated with the use of aqueous vehicles as described above, rather than using aqueous paper as the support, as described above. Gives worse results than using the vehicle.

Ordinary aliphatic petroleum solvents have low solubility in binder resins, and depending on the petroleum resin or the like that is easily soluble in the petroleum solvent, the printing film does not have good film properties. Further, the aromatic petroleum solvent having a dissolving power dissolves the leuco dye to develop a color, which causes a fog phenomenon. For this reason, the printing effect is poor and clear heat-sensitive recording cannot be obtained, and when the thermal head slides on the heat-sensitive layer, a large amount of adhered dust is left unusable.

Generally, what is called petroleum has a wide range, petroleum ether (BP20-60 ° C pentane, hexane) ligroin, light naphtha (BP60-120 ° C hexane, heptane), gasoline (BP40-205 ° C), kerosene (BP175- 325 ℃, gas oil (BP2
(75 ° C or higher) is a general term, and such chain hydrocarbons have low solubility and are insufficient for vehicles. Also,
Generally, some industrial gasolines contain naphthene-based fractions depending on the properties of crude oil, but they also have boiling points (40
Widely, what is called naphthenic petroleum contains aromatic hydrocarbons such as benzene, toluene and xylene, and it is said that those with a large content reach 40% by weight.

Therefore, it is necessary to select the combination of the solvent and the resin used for the vehicle of the heat-sensitive color-forming ink in consideration of the solubility and the strength of the formed film.

The vehicle used in the heat-sensitive color-forming ink composition as described above, whether aqueous or non-aqueous, did not have good dispersion characteristics and film characteristics.

Therefore, the conventional thermosensitive color-forming ink composition has been used by a method of providing a uniform thermosensitive color-developing layer on the entire surface by coating on a support using a roll coater or an air knife. However, considering the actual demand, the thermosensitive coloring layer does not need to be solidly coated, pattern printing is often necessary, and it is not preferable to coat even an unnecessary portion economically.

In order to solve such a problem, as a thermosensitive coloring ink composition capable of pattern printing by gravure printing or the like, a phenolic compound and a leuco dye that reacts with the phenolic compound under heating to develop a color are dispersed in a vehicle. In the heat-sensitive color-forming ink composition, the heat-sensitive color-forming ink is proposed in which the vehicle is a combination of a vinyltoluene copolymer resin or a rosin ester resin dissolved in a naphthene hydrocarbon solvent having a boiling point of 50 to 150 ° C. ( Japanese Patent Publication No. 62-16986).

However, this ink exhibits good printability for printing on paper, but has a drawback that printability on a plastic sheet or film is poor.

Currently, prepaid cards (prepaid cards) such as telephone cards, ticket cards, video rental cards, etc.
Shows the balance display such as the remaining balance or the number of valid balances with a hole punch at a predetermined position of the card. In such a punch hole method, the exact numerical value is unknown, and punched punch scraps are apt to cause a machine failure, so recently, a thermosensitive coloring card for displaying the balance by the thermosensitive method has begun to be used.

As a material for such a prepaid card, synthetic paper or a plastic sheet is usually used because of its high durability.

The heat-sensitive color-forming ink using the vinyltoluene resin-based vehicle has poor adhesion to a plastic sheet, and thus has a drawback that it cannot be used for such a plastic card.

The vehicle of the heat-sensitive coloring ink used for plastic cards such as prepaid cards, in addition to the above-mentioned adhesive property and non-reactivity with the heat-sensitive agent, requires a more excellent dispersion property of the heat-sensitive agent. Since it is used, it can be provided with a tough film that can withstand the sliding friction of a high temperature thermal head even if it is thick or thin.
Further, it is necessary to satisfy the properties such as good fluidity, excellent printability, and rapid evaporation and drying after printing.

As a result of intensive studies, the present inventors have found that good printability and tough film properties for the above-mentioned plastic sheet can be obtained by using a specific acrylic resin having polarity as a vehicle resin. The present invention has been completed by combining it with a specific solvent that is soluble in the resin.

That is, the present invention is a thermosensitive color-forming ink composition comprising a phenolic compound and a leuco dye that reacts with the phenolic compound under heating to form a color in a vehicle, wherein the vehicle is a dialkylaminoalkyl (meth).
A copolymer resin composed of an acrylate unit and a styrene unit or a tertiary butyl methacrylate unit,
The present invention provides a thermosensitive coloring ink characterized by being dissolved in a solvent mainly composed of an aliphatic hydrocarbon and / or a naphthenic hydrocarbon, and a thermosensitive coloring plastic card coated with this ink.

As the combination of the phenolic compound and the leuco dye used in the present invention, all known compounds can be preferably used.

That is, the phenolic compound used in the present invention,
A compound having a phenolic hydroxyl group, for example, phenol, o-cresol, p-cresol, p
-Ethylphenol, tertiary butylphenol,
2,6-ditertiary butyl-4-methylphenol,
Nonylphenol, dodecylphenol, styrenated phenol, 2,2'-methylene-bis (4-methyl-6-
Tertiary butylphenol), α-naphthol, β
-Saftol, hydroquinone monomethyl ether, guaiacol, eugenol, p-chlorophenol, p
-Bromophenol, o-bromophenol, o-chlorophenol, 2,4,6-trichlorophenol, o-phenylphenol, p-phenylphenol, p- (p-
(Chlorophenyl) phenol, o- (o-chlorophenyl) phenol, salicylic acid, methyl p-oxybenzoate, ethyl p-oxybenzoate, propyl p-oxybenzoate, butyl p-oxybenzoate, octyl p-oxybenzoate, Dodecyl p-oxybenzoate, catechol, hydroquinone, resorcin, 3-methylcatechol, 3-isopropylcatechol, p-tert-butylcatechol, 2,5-ditert-butylhydroquinone, 4,4'-methylenediphenol, bisphenol A , 1,2-dioxynaphthalene, 2,3-dioxynaphthalene, chlorcatechol, bromocatechol, 2,4-dihydroxybenzophenone, phenolphthalein, o-
Cresolphthalein, methyl protocatechuate, ethyl protocatechuate, propyl protocatechuate, octyl protocatechuate, dodecyl protocatechuate, pyrogallol, oxyhydroquinone, phloroglucin, 2,4,6-trioxymethyl Benzene, 2,3,4-
Trioxyethylbenzene gallic acid, methyl gallate,
Ethyl gallate, propyl gallate, butyl gallate,
Hexyl gallate, octyl gallate, dodecyl gallate, cetyl gallate, stearyl gallate, 2,3,5-trioxynaphthalene, phenolic tannate resin, phenylbis (4-hydroxyphenyl) methane, 4,4 ' −
(Phenylethylidene) bisphenol, 4,4 '-[1,4
-Phenylene bis (1-methylethylidene)] bisphenol, 4,4'-dihydroxydiphenyl ether, 4,
4'-ethylidene bisphenol, 1,4-bis (hydroxycumyl) benzene, 4,4 '-[1,3-phenylene bis (1-methylethylidene)] bisphenol, 2,6-dihydroxynaphthalene, α, α' a ″ -tris (4-hydroxyphenyl) -1,3,5-triisopropylbenzene, 2,6-bis [(2-hydroxy-5-methylphenyl) methyl] -4-methylphenol, 4,4′- (1-
Methylpropylidene) bisphenol, 4,4'-cyclohexylidenebisphenol, 4,4 '-(1-methylpentylidene) bisphenol, 4,4'-(phenylmethylene) bisphenol, 2,2'-methylenebis (4- Tertiary butylphenol), methylene-dicresol, 2,2'-methylenebis (4-methylphenol),
4,4'-methylene-bisresorcinol, isopropylidene-di-resorcinol, diphenylbis (4-hydroxyphenyl) methane and the like can be used.

Examples of leuco dyes include triphenylmethane-based compounds such as crystal violet lactone and malachite green lactone; fluoran-based compounds such as 1,2-benz-6-diethylaminofluorane; auramine-based compounds such as N-benzoylauramine; and other phenothiazine-based dyes: Phenoxidine type:
Leuco dyes such as triphenylmethane phthalide type: indolyl phthalide type: rhodamine lactam type: diphenylmethane type: chromenoindole type: spiropyran type are used.

The vehicle resin component used in the present invention is a copolymer resin of a dialkylaminoalkyl (meth) acrylate unit and a styrene unit or a tertiary butyl (meth) acrylate unit.

The copolymer resin of the present invention can be obtained by copolymerizing dialkylaminoalkyl (meth) acrylate with styrene or dialkylaminoalkyl (meth) acrylate with tertiary butyl methacrylate.

The dialkylaminoalkyl (meth) acrylate monomer used for this copolymerization can be represented by the following formula.

In this formula, R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms, R ₂ is-(CH ₂ E-CHR ₅ ) n-, n is an integer of 1 to 4, R ₅ Is hydrogen or an alkyl group having 1 to 3 carbon atoms, and R ₃ and R ₄ are alkyl groups having 1 to ₄ carbon atoms.

As a specific compound having such a structure, for example, dimethylaminoethyl methacrylate, dimethylaminobutyl methacrylate, dimethylaminoethyl acrylate, dimethylaminobutyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate and the like can be preferably used.

The vehicle copolymer resin used in the present invention is prepared by dissolving the dialkylaminoalkyl (meth) acrylate and styrene or tertiary butyl methacrylate in a solvent and adding an organic peroxide as a polymerization initiator.
A resin can be obtained by heating and copolymerizing.

The copolymer resin used in the vehicle of the present invention has a dialkylaminoalkyl (meth) acrylate unit of 0.5 to 2
Those having 0% by weight and 99.5 to 80% by weight of styrene unit or tertiary butyl (meth) acrylate unit can be preferably used.

The vehicle-forming solvent used in the present invention is mainly composed of an aliphatic hydrocarbon and / or a naphthenic hydrocarbon, and the aromatic hydrocarbon content is preferably 20% by weight or less. it can.

The hydrocarbon solvent used here has an initial boiling point of 35 ° C and an end point of 170
Those having a distillation property of ° C are suitable, and those having an initial boiling point of 50 ° C and an end point of 120 ° C can be preferably used.

When the initial boiling point of the solvent used is 35 ° C. or lower, the viscosity of the vehicle increases due to evaporation, causing on-machine troubles such as plate clogging, and uniform printing cannot be performed.

Further, when the end point of the solvent exceeds 150 ° C., the drying is slow and the printing speed does not increase, resulting in uneven printing such as spot rings (mottling) and satin. Further, due to insufficient drying, the solvent remains in the heat-sensitive layer to cause blocking, which is a very undesirable phenomenon.

Industrial volatile oils such as rubber volatile oils, extracted volatile oils, benzine K, and gravizole can be preferably used as such aliphatic hydrocarbons.

On the other hand, a naphthenic hydrocarbon can be used as a solvent for the vehicle of the present invention.

As a specific example of such a naphthene-based hydrocarbon,
Cyclopentane, methylcyclopentane, 1,1- or 1,3-dimethylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,2,4-
Trimethylcyclohexane and the like can be mentioned. Of these, cyclohexane and ethylcyclohexane are the most desirable solvents. In the present invention, each of the above hydrocarbons may be used in combination of two or more.

As the vehicle solvent used in the present invention, it is preferable to use the above aliphatic hydrocarbons and / or naphthene hydrocarbons. However, it is also possible to use together up to 20% by weight based on the total amount of aromatic hydrocarbons or up to 5% by weight based on the total amount of chlorine-containing hydrocarbons such as trichloroethylene, perchlorethylene and diethylene chloride.

If the content of aromatic hydrocarbon solvent exceeds 20% by weight,
It is not desirable because it dissolves the leuco dye to cause so-called dissolution coloring.

Further, if the chlorine content exceeds 5% by weight, it cannot be used in a large amount because it is unfavorable in terms of smell and hygiene.

The vehicle of the present invention comprises 50 to 99% by weight of the above-mentioned solvent and 1 to 50% by weight of the above copolymer resin, and an auxiliary component is added within the range of 1 to 5% by weight based on the total amount. Then, it is possible to adjust the film characteristics of the heat-sensitive recording layer.

The thermosensitive color-forming ink of the present invention is prepared by placing the phenolic compound and the leuco dye in separate containers, adding the vehicle obtained above, and kneading with a dispersing machine such as a sand mill, a ball mill, an attritor or a shot mill. Then, the respective dispersions are obtained, and then both are combined and further mixed by an ordinary mixing device such as a propeller mixer, to thereby manufacture. In the production of this heat-sensitive color-forming ink, the phenolic compound and the leuco dye in the composition can each be adjusted in a concentration range of 2 to 50% by weight to suit the required color-forming concentration.

In the ink composition of the present invention, according to a conventional method, if necessary, a coloring agent such as a pigment or a dye, calcium carbonate,
Precipitable barium sulfate, alumina, acid clay, silica gel, clay, magnesium carbonate, silicon oxide and other inorganic fillers, paraffin wax solid at room temperature as auxiliary agent, polyethylene wax, carnauba wax, microcrystalline wax, amide wax, etc. Kinds; plasticizers such as phthalic acid ester, citric acid ester, and adipic acid ester, and anionic, nonionic, or cationic surfactants can also be added.

The heat-sensitive color-forming ink composition of the present invention can be applied to a support such as a plastic film, a fiber sheet, and a paper by a conventional coating method using a roll coater, a reverse coater, a doctor coater, etc. as in the conventional case. The characteristic feature is that the thermal recording layer can be formed by printing by the gravure printing method.

In particular, when used for a prepaid card or the like, a synthetic paper or a plastic film, for example, a resin sheet of polyester, polyamide, polypropylene, polycarbonate, polyvinyl chloride or the like can be used.

In addition, printing by letterpress, flexo and silk screen methods is also possible. For use in such printing applications, the viscosity of the heat-sensitive color forming ink composition of the present invention is preferably in the range of 1 to 500 poise. The thermal recording layer is
It is usually formed as a film of 0.5 to 10 g / m ^{2 on} a dry weight basis.

The heat-sensitive recording layer printed or applied in this manner has 50 to 50
It develops a sharp color at a temperature of 250 ° C. A clear print or image can be displayed with a thermal head, a hot pen, etc. of the terminal.

[Example] An example of the present invention will be described in more detail.

[Production of Vehicle I] 50 g of Solvesso and 300 g of styrene were charged into a four-necked flask equipped with a thermometer, a reflux condenser, a stirrer and a dropping funnel, and heated in an oil bath until the internal temperature reached 110 ° C.

Then, a mixed solution of 200 g of styrene, 10 g of dimethylaminoethyl methacrylate and 2.5 g of azobisisobutyronitrile was added dropwise to the flask through the dropping funnel over 90 minutes.

After maintaining the same temperature for 30 minutes after dropping and continuing stirring,
Azobisisovaleronitrile 2.5 to 210 g Solvesso 150
The solution with g added was added over 210 minutes.

After the dropping was completed, heating and stirring of the flask were continued for another 30 minutes.

Then, while cooling, 240 g of Solvesso 150 was added and diluted, and after the temperature reached room temperature, the resin solution inside was taken out to obtain Vehicle I.

Vehicle I has a viscosity of 60.5 poise (25 ° C), 105 ° C
The heating residue after heating for 3 hours was 50.9% by weight.

[Production of Vehicle II] Using the same equipment as in the production of Vehicle I, 200 g of ligroin was initially charged, heated to an internal temperature of 90 ° C., and then 500 g of tertiary butyl methacrylate, 10 g of dimethylaminoethyl methacrylate and azobisisometh Butyronitrile
A solution consisting of 1.5 g was added dropwise with a dropping funnel over 120 minutes.

After the dropping, the temperature was maintained at the same temperature for 60 minutes to continue the polymerization, and then a solution obtained by adding 2.5 g of azobisisobutyronitrile to 110 g of ligroin was added dropwise from the dropping funnel over 120 minutes.

After completion of the dropping, further, after polymerizing for 60 minutes at the same temperature, diluted with 190 g of ligroin, cooled and taken out,
Vehicle II was obtained as a resin solution.

Vehicle II has a viscosity of 65.0 poise (25 ° C), 105
The heating residue after heating at 0 ° C. for 3 hours was 50.7% by weight.

Example 1 Ink No. 1 Fluoran-based leuco dye 20 parts (NC-BK-3, Hodogaya Chemical Co., Ltd.) Vehicle I 30 parts Rubber volatile oil 40 parts Cyclohexane 10 parts 100 parts Ink No. 2 Bisphenol A 20 parts Vehicle I 30 parts Rubber volatilized oil 40 parts Cyclohexane 10 parts 100 parts Ink No. 1 and Ink No. 2 were prepared in the above mixing ratio and dispersed for 1 hour in a disperser using glass beads. Ink No. 1 and ink No. 2 are in a weight ratio of 1:
The mixture was mixed at a ratio of 2 and stirred with a propeller mixer to obtain a thermosensitive coloring ink.

This heat-sensitive coloring ink is applied to opalescent polyester film (25
(0 μ) was coated with a gravure printing method so that the dry weight was about 5 g / m ² to obtain a thermosensitive color recording film.

Gravure printing uses rubber volatile oil as a diluent solvent,
Ink viscosity is 15 to 20 with Zahn cup # 3 (manufactured by Riaisha)
Adjusted to be seconds.

This heat-sensitive white film developed a black color when heated and exhibited the following color development characteristics. (Macbeth reflection densitometer was used for optical density measurement.) In addition, a thermal line printer (manufactured by Takasago Seisakusho, applied voltage 15 V, applied time 2.0 msec, head resistance 387 Ω) was used for printing to obtain a clear black colored image. In the continuous printing test, no print residue was attached to the thermal head, and especially in high temperature and high humidity, it is superior in terms of low adhesiveness to the head and blocking compared to the case of using a water-soluble resin. The practical superiority in was remarkable.

Example 2 Ink No. 1 Fluoran leuco dye 20 parts (NC-R, Hodogaya Chemical Co., Ltd.) Vehicle II 30 parts Gravisol 30 parts Ethylcyclohexane 20 parts 100 parts Ink No. 2 Bisphenol A 20 parts Vehicle II 30 parts Grabizole 30 parts Ethylcyclohexane 20 parts 100 parts Ink No. 1 and Ink No. 2 prepared with the above formulation were dispersed for 1 hour by a disperser using glass beads.
These ink No. 1 and ink No. 2 were mixed in a weight ratio of 1: 2, and stirred with a propeller mixer to obtain a heat-sensitive coloring ink.

This heat-sensitive coloring ink is applied to opalescent polyester film (25
0 μ) was partially coated by a gravure printing method so as to have a dry amount of about 5 g / m ² to obtain a thermosensitive color recording film.

Gravure printing uses gravizole as a diluting solvent, and the ink viscosity is 15 with a Zahn cup # 3 (manufactured by Riaisha).
Adjusted to ~ 20 seconds.

 This heat-sensitive white film was heated to develop a red color.

Example 3 An ink was prepared by using a triphenylmethane-based leuco dye (Hodogaya Chemical Co., Ltd., NC-B) in place of the fluorane-based leuco dye of Ink No. 1 in Example 2.
This ink and Ink No. 2 of Example 2 were mixed at a ratio of 1: 2 and stirred with a propeller mixer to obtain each thermosensitive coloring ink. A partial print (striped print) was obtained by gravure printing using these thermal inks.

Comparative Example 1 A vinyltoluene copolymer vehicle (heating residue 51.2% by weight) was used in place of the vehicle II in Example 2,
The same operation as in Example 2 was carried out according to the formulation shown.

Comparative Example 2 The same operation as in Example 2 was performed by using the aromatic petroleum resin vehicle (heating residue 50.1% by weight) in place of the vehicle II in Example 2 and by mixing the indicated components.

The formulations of the above Examples and Comparative Examples and the Macbeth reflection density test results are shown in Table 1, and the ink suitability of the heat-sensitive color-forming ink,
The test results of printability and recordability are shown in Table 2.

The test methods for suitability and the like shown in Table 2 were carried out as follows.

Storage stability The state of the ink was observed after being left at room temperature for 3 months.

The overall evaluation was indicated by ○, △, × by observing 1. sedimentation degree, 2. gel generation, and 3. discoloration generation.

PET adhesion Adhesion after PET film printing It was judged by a cellophane tape peeling test.

A 1 mm square base-shaped cut was made, a cellophane tape was attached, this was peeled off, and the amount adhered to the cellophane tape was judged.

On-machine stability It was judged by observing the ink state during gravure printing.

It was judged by comprehensive evaluation by observing 1. separation, 2. gelation, and 3. discoloration.

Dryability It was judged by the residual solvent amount of the ink during printing.

Blocking resistance The state of PET original fabric during printing was observed and judged by the presence or absence of blocking.

Film strength A scratch test was performed on the state of the coated material after printing to make a judgment.

Printer proper Printing was performed with a printer, and the conditions of the following items were observed for comprehensive evaluation.

1. Head dirt, 2. Printing, color development Storage stability of printing After the printing test, the following items were observed and comprehensively evaluated.

1. Light resistance, 2. Oil resistance, 3. Heat resistance, 4. Water resistance [Advantages of the Invention] The thermosensitive coloring ink of the present invention has good printability on a plastic sheet and storage stability in an ink state and The printed film after printing is excellent in stability at room temperature, and the strength of the film against sliding friction of a high temperature thermal head is large, so that it can be suitably used for thermosensitive coloring plastic cards such as flip-paid cards.

The plastic card coated with the ink of the present invention has an advantage that the balance display is clearly visible and the durability is great against repeated use.

Front Page Continuation (72) Inventor Toru Tachiwada 4-3-25 Ryoke, Kawaguchi City, Saitama Prefecture Inside Kawaguchi Manufacturing Works, Dainichi Seika Co., Ltd. (72) Katsumi Iiho 4-3-25 Ryoke, Kawaguchi City, Saitama Prefecture Nissei Chemical Industry Co., Ltd. Kawaguchi Manufacturing Office (72) Inventor Masahiro Kondo 4-3-25 Ryoke, Kawaguchi City, Saitama Prefecture Dainichi Seiko Co., Ltd. Kawaguchi Manufacturing Office (72) Masanobu Dainaga 4 Ryoke, Kawaguchi City, Saitama Prefecture ―3―25 Kawaguchi Manufacturing Office of Dainichi Seika & Co., Ltd.

Claims (2)

[Claims] 1. A thermosensitive color-forming ink composition comprising a phenolic compound and a leuco dye, which reacts with the phenolic compound under heating to develop a color, dispersed in a vehicle, wherein the vehicle is a dialkylaminoalkyl (meth) acrylate unit. A heat-sensitive color-forming ink, characterized in that a copolymer resin composed of a styrene unit or a tertiary butyl (meth) acrylate unit is dissolved in a solvent composed mainly of an aliphatic hydrocarbon and / or a naphthene-based hydrocarbon. . 2. A thermosensitive coloring plastic card coated with the ink according to claim 1.