JP2919477B2 - Thermal recording material and recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a thermosensitive recording material and a recording method, and more particularly, to a thermosensitive recording material such as a thermal printer, which can record and record information by leaving it. Provide a heat-sensitive recording material that disappears naturally.

(Prior Art and Problems Thereof) Conventionally, as a simple recording method, a method using a wax type thermal transfer sheet or thermal recording paper as a recording agent and a printer having a thermal head as recording means has been widely used. .

Although the recorded matter by the above method is excellent in preservability, etc., it is unsuitable for applications in which materials are not required to be left after use, for example, for use as a memo for transmitting secret information or secret materials for meetings, For this purpose, a shredder or the like that cuts the recorded material is used, but it is difficult to maintain confidentiality strictly even if the material is lost, discarded, or discarded.

As a method of solving such a problem, there is a method of using water-soluble paper as the recording paper, but this method is ineffective for losing the material, and it is necessary to always prepare water or to dissolve it. Operation is required.

As another method, a recording material using a dye that changes color by light, that is, a photochromic material has been proposed. However, these recording materials require expensive and complicated devices for operations such as printing. In addition, light irradiation is necessary for erasing the record. For example, when the record is overlaid or sandwiched between books, there is a problem that natural erasure cannot be performed by natural light, and practical use has become a problem. Not.

In addition, a method of forming a recording layer which easily sublimates by heat on a substrate such as paper and printing by a thermal printer is also conceivable, but in this case, the recording layer is easily deteriorated by heat,
Heating is also required each time the recording is erased, and similarly, there is a problem of lack of practicality.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a recording material and a recording method which can be easily printed by a simple recording device such as a thermal printer, and in which recorded information can be naturally erased by leaving.

(Means for Solving the Problems) The above object is achieved by the present invention described below.

That is, the present invention provides a thermosensitive recording material comprising a thermosensitive recording layer containing a dye in an oxidized state and a reducing saccharide as a reducing agent, on a substrate, and using the recording material. This is a recording method characterized by performing thermal recording.

(Operation) For example, a dye that is colorless in a reduced state and colored in an oxidized state is used as a dye of a recording layer, and a reducing saccharide (hereinafter, simply referred to as a reducing agent) is used as a dye in the oxidized state (colored).
At the same time, if they are included in the recording layer, the reaction between them is slow at normal temperature, and the colored state is maintained.

When printing is performed on the recording layer in this state with a thermal head, the dyed portion reacts with the dye by heating to be in a reduced state, the dye is erased, and information is recorded in a white state.

If this is left as it is, the white print is oxidized by oxygen in the air and develops color, and becomes the same as the ground color, so that the information is naturally erased.

Therefore, no operation is required for erasing the recorded matter, and no secret information is leaked.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

The heat-sensitive recording material of the present invention is characterized in that, as shown in FIG. 1, a heat-sensitive recording layer 2 containing a dye that changes color by oxidation and a reducing agent is provided on a substrate 1.

As the substrate 1 used in the present invention, various papers,
Any material conventionally used for recording, such as synthetic paper, plastic film, metal foil, or a composite thereof, can be used and is not particularly limited. Particularly when paper is used as the base material, the dye and the reducing agent may be impregnated into the paper to form a recording layer. However, preferably, the recording layer is sealed in order to eliminate irregularities on the surface of the paper and bleeding of the ink. Processing, and a recording layer 2
To form

The heat-sensitive recording layer formed on the base material contains a dye that changes color by oxidation and a reducing agent.

The dye used in the present invention may be any known dye as long as it changes color (coloration, decoloration) in an oxidized state-reduced state. Preferred dyes are colored in an oxidized state and colorless in a reduced state. The dye is a light-colored dye. Preferred dyes include the following dyes.

(1) As basic structure A thiazine dye having the following formula: for example, methylene blue, etc. (2) As a basic structure Indigo dyes having the following formula: for example, potassium indigo sulfonate, etc. (3) As a basic structure (4) as a basic structure (R represents -H, an alkyl group or an allyl group); for example, CI sulfur blue 7 and the like, and a particularly preferred dye is a thiazine dye methylene blue. The dyes described above are used in an oxidized state, that is, in a colored state.

The reducing agent used in combination with the dye is a reducing saccharide. Examples of such a reducing saccharide include monosaccharides such as D-maltose, D-glucose, D-fructose, D-exalose, and D-arabinose; maltose, Reducing oligosaccharides composed of glycoside bonds of a certain number of monosaccharide molecules such as lactose are used, and the amount of the dye used is 1 part of the above dye (weight basis; hereinafter, parts and% in the specification are by weight). Is preferably 1 to 100 parts.

Since the reaction between the dye and the reducing agent is promoted by the presence of an alkaline substance at the time of heating, it is preferable that an appropriate alkaline substance is present in the recording layer,
Such an alkaline substance may be any substance as long as it comes to pH 8 or more upon contact with water, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide, calcium carbonate, hydrogen carbonate. Sodium, potassium bicarbonate, calcium bicarbonate,
Magnesium hydroxide, sodium acetate, potassium acetate,
Hydroxides such as potassium sodium tartrate and potassium 2-ethylhexanoate, carboxylate salts, various salts and the like can be mentioned. The amount used is 1 to 100 with respect to 1 part of the dye.
Parts are preferred.

It is preferable to use a binder for forming the recording layer composed of the above-mentioned components. A suitable binder is a thermoplastic resin which can suppress the reaction between the dye and the reducing agent even at a normal temperature even if it is solid, and can melt or soften during heating to promote the reaction between the two. Specific examples include one or more of cellulose derivatives such as ethylcellulose, ethylhydroxyethylcellulose, and cellulose acetylpropionate, butyral resins, polyester resins, acrylic resins, polyether resins, polyamide resins, and petroleum resins.

These binders are preferably an aroma type such as toluene and xylene; an ester type such as ethyl acetate and butyl acetate; a ketone type such as methyl ethyl ketone and methyl isobutyl ketone; an alcohol type such as methanol, ethanol and isopropyl alcohol; It is used by being dissolved or dispersed in an organic solvent such as glycol monoethers or glycols such as ethylene glycol or water. The binder is preferably used by dissolving or dispersing 5 to 20 parts with respect to 100 parts of the solvent.

The ink composition for forming the recording layer is the resin solution described above.
It is obtained by dissolving or dispersing the above-mentioned component system at a ratio of 5 to 40 parts with respect to 100 parts. As a method of dissolving or dispersing, all the components may be mixed and kneaded by a general means such as a sand mill, a ball mill, a roll mill, an attritor, etc. Is desirable.

Incidentally, it is necessary to add a polyhydric alcohol such as glycerin or ethylene glycol to the above ink composition in an amount of about 5% based on the total amount of the coloring matter during recording (discoloration).
It is effective in hastening. In addition, various additives such as nonionic surfactants and auxiliaries can be added to the ink composition.

The ink was prepared in a two-pack type, that is, a dye (and an alkaline substance) was added to a binder liquid to prepare a liquid A, while a reducing agent was added to the binder liquid to prepare a liquid B. By mixing and using the two liquids immediately before forming the recording layer, the storage stability of the ink can be improved. Further, the storage stability of the recording layer can be further improved by separately applying and drying the solution A and the solution B on the substrate, and superimposing the dye layer and the reducing agent layer to form a recording layer. I can do it. If a thin thermoplastic resin layer is formed between the dye layer and the reducing agent layer, the storage stability of the recording layer can be further improved.

Furthermore, by separately adding another dye which is not reduced in the composition of the ink composition and is different in color from the dye for the recording layer, the recording print is not colorless or pale, Printing in a different color from the recording area can be performed.
As such a dye, a general pigment or dye which has been widely used as a coloring agent for a conventional printing ink or paint can be used as it is. These other dyes can be added in an amount of about 0.5 to 5% based on the whole ink composition.

The ink composition configured as described above is applied to at least one surface of the substrate by a printing method such as gravure printing, offset printing, letterpress printing, screen printing, or a coating method, and then dried. Thereby, a heat-sensitive recording layer is formed. The recording layer is preferably about 1 to 10 g / m ² (when dried).

Further, in the present invention, it is preferable to form a top coat layer made of the above-mentioned thermoplastic resin on the recording layer. With this top coat layer, the oxidation of the reducing agent in the recording layer can be prevented by absorbing oxygen from the surface, and the preservability of the recording material can be improved. Of course, at the time of recording, such a top coat layer is melted by heat, so that there is no problem in recording, and after recording, the melting at the time of recording makes the film permeable to oxygen, so that the natural erasure of the record is not hindered. Further, in order to prevent the thermal head from adhering to the recording layer during recording, it is also preferable to form the top coat layer from a resin or a release agent having good release properties. In order to prevent sticking during recording, a recording layer may be formed on a heat-resistant film such as a polyester film, and thermal recording may be performed from the polyester surface. Further, paper may be laminated on the surface of the recording layer.

The recording method of the present invention is characterized by thermally recording a heat-sensitive recording layer of a recording material as described above.

As a recording means, a thermal pen plotter or the like which can heat the recording layer in an image form may be used, but a printer of a thermal head type conventionally used in a thermal recording method can be preferably used as it is.

As shown in FIG. 2, the thermal head 3
, The heated area is discolored and character 4 is printed. The thermal recording may be performed from the surface of the substrate as long as the thermal conductivity of the substrate is good. As shown in FIG. 3, the printed character 4 absorbs oxygen in the air and returns to the original color as it is left, and becomes the same color as the ground color 5, so that the recorded information naturally disappears.

(Effects) According to the present invention as described above, there is provided a recording material and a recording method which can be easily printed by a simple recording device such as a thermal printer and can erase recorded information naturally by leaving.

(Examples) Next, the present invention will be described more specifically with reference to examples.

Example 1 0.5 part of methylene blue 20 parts of glucose 20 parts of magnesium hydroxide 5 parts of glycerin 5 parts of polyvinyl butyral resin 15 parts of solvent 40 parts An ink having the above composition was prepared, and this was made of high quality paper (50 g / m ² ).
Was solid-printed at a rate of 10 g / m ² on a solid basis by a gravure method to form a recording layer, and a heat-sensitive recording material of the present invention was obtained.

Example 2 Methylene blue 0.5 part Fructose 20 parts Magnesium hydroxide 20 parts Ethylene glycol 7.5 parts Cellulose acetate propionate 15 parts Solvent 37.5 parts An ink having the above composition was prepared, and this was made of high quality paper (50 g / m ² ).
Was solid-printed at a rate of 10 g / m ² on a solid basis by a gravure method to form a recording layer, and a heat-sensitive recording material of the present invention was obtained.

Example 3 The same heat-resistant recording material of the present invention was obtained in the same manner as in Example 1, except that the high-quality paper of Example 1 was replaced with the same high-quality paper capped with a cyclized rubber resin solution. .

Example 4 The heat-sensitive recording material of the present invention was obtained in the same manner as in Example 2 except that the same high-quality paper treated with a cyclized rubber resin solution was used instead of the high-quality paper of Example 2. .

Example 5 On the surface of the recording layer of the recording material of Example 3, a 10% solution of a chlorinated rubber-based resin was subjected to solid printing by a gravure method at a ratio of ² g / m ^{2 on} a solid basis to form a top coat layer. A heat-sensitive recording material of the present invention was obtained.

Example 6 On the surface of the recording layer of the recording material of Example 1, a 10% solution of a chlorinated rubber-based resin was subjected to solid printing by a gravure method at a ratio of ² g / m ^{2 on} a solid basis to form a top coat layer. A heat-sensitive recording material of the present invention was obtained.

Examples 7 to 12 The heat-sensitive recording materials of the present invention were obtained in the same manner as in Example 1 except that the dyes and reducing agents shown in Table 1 below were used in place of the dyes and reducing agents of Example 1.

Example 13 Using the recording material of the present invention, 1 W /
When characters were printed with dots, white characters were immediately and clearly recorded. When this printed matter was allowed to stand at room temperature, the print disappearance time (elapsed time when the print became unreadable) was as shown in Table 2 below.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a cross section of the thermosensitive recording material of the present invention, and FIGS. 2 and 3 are diagrams schematically illustrating a method of the present invention. 1: Base material 2: Recording layer 3: Thermal head 4: Print image 5: Background color

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-83884 (JP, A) JP-A-58-191190 (JP, A) JP-A-56-166093 (JP, A) JP-A-63-1988 227375 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B41M 5/28-5/36

Claims (5)

(57) [Claims] 1. A heat-sensitive recording material comprising a substrate and a thermosensitive recording layer containing a dye in an oxidized state and a reducing saccharide as a reducing agent. 2. The heat-sensitive recording material according to claim 1, wherein the recording layer also contains a binder. 3. The heat-sensitive recording material according to claim 1, wherein the dye is a thiazine dye in an oxidized state. 4. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording layer contains an alkaline substance. 5. A recording method comprising: performing thermal recording on a thermosensitive recording material provided with a thermosensitive recording layer containing a dye in an oxidized state and a reducing saccharide as a reducing agent on a base material.