JPH0664314A - Thermal recording medium - Google Patents

Abstract

PURPOSE:To obtain a thermal recording medium on which both a reversible recording and a nonreversible recording (recording cannot be made thereon two or more times) can be made. CONSTITUTION:On at least one surface of a substrate 1, a nonreversible thermal recording layer 2 having a remarkably high light-absorption in an infrared range when coloring, an infrared light transmitting hiding layer 3, and a reversible thermal recording layer 4 provided by dispersing an organic low-molecular substance in a resin are successively laminated. On the reversible thermal recording layer 4 of the medium, a reversible recording can be made under heat up to a transparent temperature and erased under heat up to an opacifying temperature. On the nonreversible thermal recording layer 2, a nonreversible recording can be made by heating it up to a color forming temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used for forms such as prepaid cards, pass tickets, entrance tickets, tickets, computer output sheets, and OA materials, and by heating with a thermal head, a laser beam, etc. The present invention relates to a thermosensitive recording medium capable of recording image information.

[0002]

2. Description of the Related Art In recent years, cards such as magnetic recording media on which machine-readable information is recorded are remarkably prominent and are used in many fields. This kind of card
A magnetic recording layer is provided on a card substrate and information is recorded on the magnetic recording layer. Although magnetically recorded information is invisible to the naked eye, higher security is required for these cards.For example, magnetic identification is used as an identification function to determine the authenticity of cards other than the magnetic recording section. Or one that arranges a visible recording medium other than magnetic,
Alternatively, a concealing layer for concealing the magnetic recording layer of the magnetic recording portion is formed so that the magnetic recording contents cannot be easily read from the outside.

By the way, in recent years, in addition to recording fixed information or identification information and variable information on the magnetic recording layer, information that is visible at the time of use is recorded on the surface of the card for the convenience of the card owner. In particular, prepaid cards can visually recognize the same value information as magnetic recording without being read by a reader.

Conventionally, a heat-sensitive recording method for recording image information such as characters and figures by causing a chemical change or a physical change by thermal energy from a thermal head or a laser beam has been known. A method of recording an image by transferring a wax-based ink layer to a medium having a recording layer and an image receiving layer by using an auxiliary material, and a medium in which a low melting point metal thin film layer such as Sn is hidden on a colored layer. There are two methods: a method in which the concealing property is lost by melting and destroying it by heat to perform a visible recording, and a machine side does not require auxiliary materials. The former is widely used in the output of electronic computers and color printers, taking advantage of its high storage stability and easy colorization. The latter has the advantages of excellent environmental resistance, low cost because no auxiliary materials are used, and no need for maintenance on the machine side.

However, any of these image information recording is irreversible, and once recorded, the recording cannot be erased or rewritten, and is used only as a permanent storage of image information or a disposable recording medium. It is a thing.

Therefore, a new heat-sensitive recording material has been studied for the purpose of reversible recording, and an image recording method utilizing a change in transmittance due to a difference in heating / cooling temperature has been proposed, and both a transmission method and a reflection method are proposed. A recognition method is possible. For these recording materials, a mixture of organic low molecular weight substances such as stearic acid dispersed in a resin such as vinyl chloride resin or polyester resin is used as the recording layer, and the transparency of this recording layer is changed by changing the applied temperature. To do. This recording layer can be repeatedly recorded reversible, the degree of transparency when returned to room temperature becomes transparent state goes from raising from opaque state to a temperature T _A, the temperature of a transparent state _{T B (T A <T B} )
This is to utilize the hysteresis phenomenon that the transparency decreases and the state returns to a cloudy state again after raising the temperature to room temperature.

On the other hand, in the field of irreversible recording, there has been an ink jet printing apparatus which has a thermosensitive recording layer containing a leuco dye such as a fluoran dye as a coloring agent on the medium side and directly causes a chemical change by a thermal head to print. In recent years, it has come to be used not only for visual recognition of images but also for machine readable applications using leuco dyes having a remarkable light absorption in the infrared region.

[0008]

As described above, the thermal recording medium has been conventionally used in various fields, and in recent years, the functions required for them have been enhanced. One of them is one in which a reversible recording and an irreversible recording (which can be recorded only once) are desired in a thermal recording medium. However, at present, there is no thermosensitive recording medium that simultaneously satisfies such requirements.

[0009]

The invention according to claim 1 is
An irreversible thermosensitive recording layer having a remarkable light absorption in the infrared region when a color is formed on at least one side of the support, an infrared transmissive hiding layer, and a reversible thermosensitive recording layer in which an organic low molecular weight substance is dispersed in a resin. And a heat-resistant protective layer, which are successively laminated, to provide a heat-sensitive recording medium.

A second aspect of the present invention is based on the first aspect of the invention and is characterized in that a magnetic recording layer and a magnetic concealing layer are provided between the support and the irreversible thermosensitive recording layer. Is.

[0011]

The thermal recording medium manufactured according to this embodiment is
As shown in FIG. 2, it has both the functions of reversible recording and irreversible recording.

In FIG. 2, T _O is room temperature and T _A is 60-100.
Erasing (clearing) temperature of the reversible thermosensitive recording layer at about ℃, T _B
Indicates reversible recording at temperatures above the transparency temperature to about 130 ° C (whitening)
The temperature and T _C indicate the irreversible recording (coloring of leuco dye etc.) temperature of about 130 to 300 ° C. That is, T _O →
Is reversible recording when heated () cooling until after T _O () to T _B, also reversible recording portion T _O → T _A heated () cooling until after T _O () Then erased. The T _O → irreversibly recorded on the thermosensitive recording layer of the leuco like when heated to T _C (color) is performed. The cloudy reversible thermosensitive recording layer does not transmit light in the infrared and visible regions, and the transparent reversible thermosensitive recording layer transmits light in the infrared and visible regions.

The structure of the thermal recording medium according to the present invention is shown in FIG.

In FIG. 1, an irreversible thermosensitive recording layer 2, which has remarkable light absorption in the infrared region when color is developed on the upper layer of the support 1, an infrared transmissive masking layer 3, and a reversible thermosensitive substance in which an organic low molecular substance is dispersed. The basic structure in which the recording layer 4 is provided is shown below. The heat-resistant protective layer 5 is formed on the reversible thermosensitive recording layer 4, and the magnetic recording layer and the magnetic concealing layer are provided between the support 1 and the irreversible thermosensitive recording layer. It does not depart from the invention.

The support 1 is made of polyethylene terephthalate film, which is mechanically tough and has flexibility and flexibility, a plastic film made of polycarbonate, polyvinyl chloride, or other polymer material, information recording paper, art paper, or the like. Paper such as coated paper, metal plate, glass plate and the like are used as necessary. Generally, a thickness of 50 to 1000 μ
A film having a thickness of m and having heat resistance capable of withstanding a momentary high temperature of 250 ° C. or higher is suitable as a support for a thermal recording medium.

The irreversible thermosensitive recording layer 2 is mainly composed of a thermosensitive coloring material and a polymer binder, and the thermosensitive coloring material is dispersed in water or an appropriate solvent to prepare a polymer binder. The dissolved dispersion is applied and dried by a solvent coating method such as bar coating, blade coating, air knife coating, gravure coating or roll coating, or a known coating method such as screen printing to form a dispersion.

Since the image (information) recorded by heating and coloring the irreversible thermosensitive recording layer 2 is read by detecting the difference in absorption (rate) in the infrared region, the irreversible thermosensitive recording layer is read. It is essential that the heat-sensitive coloring material used has a remarkable light absorption in the infrared region when it is colored. Numerically speaking, absorption of 75% or more is required.

The heat-sensitive color developing material is not particularly limited as long as it satisfies the above-mentioned conditions, but it is not limited to leuco dyes having light absorption in the near infrared region and acidic substances (electron acceptors) such as phenol. Combinations are preferably used.

The main examples include leuco dyes such as fluorane compounds, fluorene compounds and phthalide derivatives, and fluorane compounds include 3-dimethylamino-6-methoxyfluorane and 7-acetamino-3-dimethyl. Aminofluorane, 3-dimethylamino-5,7
-Dimethylfluorane, 3-dimethylamino-5,7-
There are dimethylfluorane and 3,6-bis-β-methoxyethoxyfluorane.
There is (p-aminophenyl) fluorene, and in the phthalide derivative, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3,3-bis (p
-Dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-nitrophthalide, 3,3-bis ( There is p-dibutylaminophenyl) -phthalide.

Examples of the color developer include bisphenol A and bisphenol S. By mixing these coloring materials and the developer together with the binder in an appropriate ratio, it is possible to print arbitrary characters, figures, etc. with a thermal head or the like.

Further, as the polymer binder, homo- or copolymerization of hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, starch, styrene-maleic acid copolymer, methacrylic resin such as polymethylmethacrylate, polyethylmethacrylate, etc. And polystyrene, acrylic-styrene copolymer, polyester resin, coumarone resin, ABS resin, nitrocellulose and the like.

The color development temperature of the irreversible thermosensitive recording layer 2 must be higher than the clouding and transparency temperatures of the reversible thermosensitive recording layer described below.

The infrared-transmissive hiding layer 3 is for preventing the change in the irreversible thermosensitive recording layer 2 from being visually observed due to color development, and
The reversible thermosensitive recording layer 4, which will be described later, is provided to make it easier to see (increase the contrast), and is formed by coating and drying a material that transmits infrared rays but does not transmit visible light.

As a material for forming the infrared-transparent concealing layer 3, for example, a gray ink obtained by mixing process inks (yellow, magenta, cyan) in an appropriate ratio is preferably used by offset or screen printing method. It is formed to a thickness of 10 μm. The process ink is a subtractive color mixture of three primary colors (yellow, magenta, and cyan) that absorbs only certain visible wavelengths.
Is produced, and it becomes black or gray when mixed, but there is almost no absorption in the infrared region.

The reversible thermosensitive recording layer 4 is a resin in which an organic low molecular weight substance is dispersed. As a usable resin, it has high transparency, is stable to heat and light, and has little discoloration such as yellowing. Moreover, it is desirable that it has excellent adhesion to metal.
Specifically, polyvinyl chloride resin, polyvinyl acetate resin,
Examples thereof include vinyl chloride-vinyl acetate copolymer, polyvinyl acetal resin, phenol resin, polyester resin, acrylic resin, and epoxy resin.

Organic low molecular weight substances include stearic acid, palmitic acid, behenic acid, oleic acid, lauric acid, linoleic acid, linolenic acid and other higher fatty acids or their esters, derivatives of amides, myristyl alcohol, cetyl alcohol and stearyl alcohol. , Higher alcohols such as polyethylene glycol, and their derivatives, and petroleum waxes such as straight-chain hydrocarbons, branched-chain hydrocarbons, naphthene-based hydrocarbons and aromatic hydrocarbons having about 10 to 50 carbon atoms, Other various natural waxes are used.

The mixing ratio of the transparent resin and the organic low molecular weight substance is preferably 10 to 100 parts with respect to 100 parts by weight of the resin, and the thickness of the reversible thermosensitive recording layer is 5 to 30 μm.
It is desirable to use it in the range of 10 .mu.m.

Further, a heat resistant protective layer 5 may be provided on the reversible thermosensitive recording layer 4 in order to improve the resistance (scratch resistance, weather resistance, etc.) of the thermosensitive recording medium. The heat-resistant protective layer 5 is made of a heat-resistant resin, a lubricant, and various fillers.

As the resin that can be used, a hard resin having heat resistance such as a thermoplastic acrylic resin, a thermosetting acrylic resin, a heat-resistant acrylic emulsion resin, various ultraviolet-curing resins, and an OP printing varnish for offset printing is used. Silicone-based materials, metal soaps such as zinc stearate, and fluorine-based materials can be used as the lubricant, but wax-based lubricants should be used in consideration of abrasion resistance, coating protection during heating, and sliding performance. It is preferable to use paraffin wax, microcrystalline wax, carnauba wax, rice wax, montan wax, low molecular weight polyethylene wax, oxidized polyethylene wax, low molecular weight polypropylene wax, various fatty acids, and monoamide type wax having a melting point of 30 to 150 ° C. , Various natural and synthetic waxes such as bisamide, beef tallow, etc. are added alone or in a mixture.

As additives, calcium carbonate,
Fillers such as talc, silica and alumina, various surfactants, stabilizers and curing agents are used as necessary. The coating material and ink made of these are provided in a film thickness of about 1 to 10 μm by various coating methods such as gravure coating, reverse roll coating, knife coating, blade coating and the like, and printing methods such as gravure printing and screen printing.

[0031]

EXAMPLES Hereinafter, examples will be described in detail.

A thermosensitive recording medium having the following layer structure was formed on a support 1 made of a milky white polyethylene terephthalate film having a thickness of 188 μm.

As the irreversible thermosensitive recording layer 2, a thermosensitive color coating composition having the following composition was applied by a gravure method at a coating thickness of 4 μm and dried at a drying temperature of 80 ° C. for about 3 minutes. In addition,
The color development temperature of the irreversible thermosensitive recording layer is 110 ° C.

Leuco dye 3- (p-aminophenyl) fluorene 30 parts Developer bisphenol A 70 parts Polyvinyl alcohol (nonvolatile content 30%) THB-1: Hodogaya Chemical Co., Ltd. 150 parts Dispersant demol EP: Kao 0. 2 parts diluted solvent water 200 parts

The infrared-transparent concealing layer 3 was prepared by mixing the following inks (gray color) and then printing to about 2 μm by the offset printing method.

Yellow UV STP standard color Yellow: Toka dye 30 parts Magenta UV STP standard color Crimson: Toka dye 50 parts Cyan UV STP standard color Indigo: Toka dye 40 parts

As the reversible thermosensitive recording layer 4, a coating material having the following composition was applied by a gravure method at a drying temperature of 90 ° C. and a coating thickness of 5 μm. The reversible thermosensitive recording layer has a clearing temperature of 70 ° C and a clouding temperature of 100 ° C.

Polyester resin (30% lacquer) Byron 20SS: Toyobo 100 parts Stearic acid 20 parts Diluting solvent Toluene / MEK 50 parts

As the heat-resistant protective layer 5, a UV-curable offset OP varnish (Dicure ROP varnish: manufactured by Dainippon Ink) was printed with an offset printing machine to a thickness of about 1.5 μm to obtain a thermosensitive recording medium. It was

The reversible thermosensitive recording layer of the thermosensitive recording medium produced by the above method is heated to 100 ° C. by a heating roll,
The whole was made cloudy and it was in the initial state.

Next, when a part of the thermal recording medium was heated to 70 ° C. by a thermal head, the part became transparent and the color (gray) of the lower infrared ray transmissive hiding layer was exposed to give a visible image. Although it appeared, when this image was observed using an IR scope, no image could be observed in the portion where the color of the infrared transmissive masking layer was exposed.

After that, the entire reversible thermosensitive recording layer of the thermosensitive recording medium was heated again with a heating roll to make the whole cloudy.

Further, the information was recorded on the irreversible thermosensitive recording layer by heating to 110 ° C. with a thermal head. In addition,
The reversible thermosensitive recording layer remained in a cloudy state.

Next, after heating to 70 ° C. with a thermal head to expose the color (gray) of the lower infrared-transparent concealing layer, when this part was observed using an IR scope, an image (coloring) was obtained. Had been formed. The infrared absorption rate of the image was 90%.

[0045]

The thermosensitive recording medium produced by the present invention has both a reversible recording function and an irreversible recording function, and can be used for various purposes.

For example, as a prepaid card, the amount of money used, the balance, date, etc. are usually printed on the reversible thermosensitive recording layer,
Even if the reversible thermosensitive recording layer is illegally rewritten by applying energy enough to print the irreversible thermosensitive recording layer when the remaining amount becomes zero, causing the leuco dye etc. to develop color and printing the letters and symbols indicating the used state. Even if it were, the irreversible thermosensitive recording layer could be identified by reading it with an optical reading device using near infrared rays, and the reversible thermosensitive recording layer could be tampered with or altered without the convenience of confirming the data visually. It can have a high prevention effect.

[0047]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a thermosensitive recording medium according to the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the heating temperature and the reflection density of the thermosensitive recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support 2 Irreversible thermosensitive recording layer 3 Infrared transparent concealing layer 4 Reversible thermosensitive recording layer 5 Heat-resistant protective layer

Claims (2)

[Claims] 1. An irreversible thermosensitive recording layer having a remarkable light absorption in the infrared region when a color is developed, an infrared permeable concealing layer, and an organic low molecular weight substance dispersed in a resin on at least one side of a support. A heat-sensitive recording medium comprising a reversible heat-sensitive recording layer at least sequentially laminated. 2. A magnetic recording layer and a magnetic concealment layer are provided between the support and the irreversible thermosensitive recording layer.
The heat-sensitive recording medium described.