JPH07257051A - Heat-sensitive recording medium - Google Patents

Abstract

PURPOSE:To improve recognition, resolution and resistance to scratching of recording by forming a masking layer to be formed on a base by means of a material to turn to be transparent by heating. CONSTITUTION:A masking layer 2 is formed on a transparent base 1 composed of a polyester film or the like to form a heat-sensitive recording medium. A base 1 or a colored layer formed on the base 1 is masked by the masking layer 2, and a material, in which a resin component is melted, re-solidified and turned to be transparent by the heat of a thermal head or the like at the time of printing so that a base 1 or a colored layer is recognized, is used. As the resin component, a material with its glass transition point in the range of approximately 30 deg.C or over to approximately 150 deg.C or under such as an acrylic resin, polyester resin or the like is used. When the melting point is 150 deg.C or over, the base 1 is heat distorted, which is not preferable. When the melting point is 30 deg.C or under, preservation properties are lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording medium,
More specifically, it relates to a thermal recording medium having good printability and excellent scratch resistance, and can be used for OHP applications when a transparent substrate is used.

[0002]

2. Description of the Related Art Thermal transfer recording media are widely used for output printing of facsimiles, computers, word processors and the like. Generally, a heat-sensitive transfer recording medium is one in which a heat-sensitive recording layer is formed on a substrate, and the heat-sensitive recording layer is colored by being heated by a thermal head in accordance with character information and image information. In such a heat-sensitive recording layer, for example, a developer and a color-developing agent that reacts under heat to develop a color are present in the binder, and those having a high thermal sensitivity and a good color-forming property are used.

[0003]

However, while the conventional thermal transfer recording medium has a high coloring property by the thermal head, it easily develops a color when pressure is applied or due to the presence of an organic solvent such as alcohol. Sisters,
There is a problem that the scratch resistance and the solvent resistance are low.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermal transfer recording medium which has high recognizability and resolution of recording and is excellent in scratch resistance.

[0005]

In order to achieve such an object, the present invention provides a thermal recording medium having a masking layer on a substrate, wherein the masking layer is transparent by heating.

[0006]

Since the concealing layer is a porous film that is whitened during drying of the resin varnish consisting of the resin component, the hydrophilic solvent for the resin component, and the poor solvent, the colored layer under the concealing layer is more reliably protected by the concealing layer. In addition to being concealed, the concealing layer becomes transparent when the resin component is melted and solidified again by the heat of a thermal head or the like during printing. Therefore, only the heated region of the concealing layer is made transparent, and the concealing layer is recognized in the unheated region, so that clear printing can be performed by the contrast between the transparent region and the concealed region. Furthermore, when a transparent substrate is used, a good OHP recording medium can be obtained due to the contrast between the transparent region and the region that is still hidden.

The heat-sensitive recording medium of the present invention has a concealing layer 2 provided on a substrate 1 as shown in FIG. FIG. 2 shows another example of the present invention, in which the colored layer 3 is provided on the base material 1 and the concealing layer 2 is provided thereon. Further, as shown in FIG. 3, a protective layer 4 may be further provided on the protective layer 4 if necessary.

As the base material, any of the general base materials used in conventional thermal recording media can be used. As the transparent base material, a polyester film, a polyolefin film such as a polyethylene film or a polypropylene film, or a polycarbonate film can be used. A transparent plastic film such as a film, a triacetate film, a polyether sulfone (PES) film, a polyether ether ketone (PEEK) film, a vinyl chloride film, various acrylic films such as methyl methacrylate or cellophane film is used. . Examples of the opaque substrate include synthetic paper, high-quality paper, art paper, coated paper, cast coated paper, synthetic resin-impregnated paper, metal and glass. It is also possible to use a laminate of any combination of the above base materials.

The thickness of such a substrate can be arbitrarily set according to the purpose of use of the thermosensitive recording medium, and is, for example, 5 to 5.
100 μm, and 1000 when used for cards
It can be about μm. When used for OHP applications, a transparent substrate is used among the above-mentioned substrates, and a concealing layer is formed thereon to make only the heated region of the concealing layer transparent during printing, and the concealing layer in the unheated region. Is recognized,
A good OHP recording medium is formed by the contrast between the transparent area and the area which is hidden. The thermosensitive recording medium can also be used as a seal by providing an adhesive layer and a release paper in this order on the surface of the base material opposite to the surface on which the hiding layer is provided.

The colored layer, which is formed on the above-mentioned substrate as required, comprises a binder and a colorant, and the binder is not particularly limited, such as a thermoplastic resin, a thermosetting resin and an ionizing radiation curable resin. However, for example, cellulose derivatives such as ethyl cellulose, hydroxy cellulose, cellulose acetate, cellulose acetate propionate, polystyrene, styrene resins such as poly-α-methylstyrene or styrene copolymers, polymethylmethacrylate, polyethylmethacrylate, polyacryl Acrylic resins or methacrylic resins such as ethyl acetate and polybutyl acrylate, or copolymers thereof, rosin, rosin-modified phenolic resins, rosin ester resins such as polymerized rosin, polyvinyl acetate resins, vinyltoluene resins, vinyl chloride resins, polyesters Le resins, polyurethane resins, butyral resins, ethylene-vinyl acetate copolymer, synthetic rubber, natural rubber, and the like.

As the colorant, various inorganic and organic pigments and dyes having chromatic colors such as red, blue and yellow can be used. Further, naturally, it is also possible to use carbon black or the like to obtain an achromatic color.

The colored layer contains, in addition to the above binder and colorant, a plasticizer, a stabilizer, a wax, a curing agent, if necessary.
A dispersant or the like can be added. Then, using such a coloring layer composition, a gravure coat, a roll coat,
A colored layer having a thickness of 0.1 to 5 μm is formed by coating the substrate with a known coating method such as die coating or knife coating.

The hiding layer formed on the base material or on the coloring layer provided as necessary hides the above coloring layer, and at the time of printing, the resin component is melted and resolidified by the heat of the thermal head or the like. By doing so, it is made transparent so that the underlying substrate or colored layer can be recognized. Such a hiding layer, a resin component, a solvent having a high solubility in the resin, and a poor solvent having a low solubility in the resin are used in combination, in the step of forming the hiding layer, the solvent having a low boiling point is first evaporated, The balance of the solvent that dissolves the resin is lost, and some of the resin becomes insoluble, cloudy, precipitated, and partially gelled, and is obtained by evaporating the poor solvent as the drying process progresses. Porous layers are preferred.
This porous layer becomes an opaque layer to form a hiding layer having a sufficient hiding property. The pore size of the porous hiding layer thus formed is preferably 0.1 μm to 3 μm. In order to form the pore diameter within this range, the drying temperature, the amount of drying air, the drying time, and the mixing ratio of the poor solvent and the hydrophilic solvent are optimized. If the pore size is as small as 0.1 μm, a good whitening state cannot be obtained, and sufficient hiding properties cannot be obtained. When it is larger than 2 μm, the film strength is lowered, or the transparency when melted and re-solidified becomes insufficient.

The formed concealing layer becomes transparent when the resin component is melted and solidified again by the heat of the thermal head or the like during printing. Therefore, the colored layer is recognized in the heated region of the concealing layer and only the concealing layer is recognized in the unheated region, so that clear printing can be performed by the contrast between the colored layer and the concealing layer. The concealing layer formed on the base material or the coloring layer provided as necessary has a thickness of 0.5 to 20 μm.
Then, the transmittance in the wavelength region of 400 to 1000 nm is 0% or more and 50% or less, or the reflectance is 20% or more and 9% or more.
It has a good hiding property of 0% or less.

The resin component used in the concealing layer is preferably an acrylic resin, a polyester resin, or a vinyl chloride / vinyl acetate copolymer. The glass transition point thereof is preferably 30 ° C. or higher and 150 ° C. or lower, particularly preferably 50 to 130 ° C. When the melting point is higher than 150 ° C., when the porous layer is melted, the base material also suffers from thermal deformation, which is not preferable. It is not preferable to use a resin having a temperature of 30 ° C. or lower because of the problem of storage stability. For the above resin components,
Examples of the poor solvent include aliphatic hydrocarbons, aromatic hydrocarbons, hydrocarbon solvents such as terpene hydrocarbons, halogenated hydrocarbons and alcohols. Further, with respect to the resin component,
As a lyophilic solvent, for solvent-soluble resins, acetone, methyl ethyl ketone, ketones such as cyclohexanone, ethyl acetate, butyl acetate, esters such as ethylene glycol monomethyl ether acetate, or, depending on the resin, aromatic hydrocarbon, Alcohols are applicable.
When a water-soluble resin is used, the poor solvent for the solvent-soluble resin becomes a hydrophilic solvent, and the hydrophilic solvent is appropriately used depending on the compatibility with the resin so that the hydrophilic solvent becomes a poor solvent. When the hydrophilic solvent and the poor solvent are used in combination, those which are mutually soluble and have a boiling point higher than that of the hydrophilic solvent and slow in evaporation are used so that the dispersed state of the varnish is kept stable.
In order to form a porous layer having a good hiding property, a resin varnish is formed using 10 to 70 parts by weight of a poor solvent with respect to 100 parts by weight of a resin component.

As a heating source for the concealing layer, a known heating means such as a thermal head, a laser beam or heat sealing can be used according to the purpose.

In the present invention, the protective layer provided as necessary is formed on the above-mentioned concealing layer to protect the concealing layer, and is made of an acrylic resin, an epoxy resin, a polyimide resin, a melamine resin or the like. It can be formed using a transparent resin or a transparent inorganic compound such as silicon dioxide. Further, the protective layer may contain a lubricant, an antioxidant and the like. The thickness of such a protective layer is 0.1 to 5 μm.
A degree is preferable.

[0018]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the text, parts and% are based on weight unless otherwise specified. Example 1 First, the surface of a transparent polyester film having a thickness of 75 μm (Lumirror manufactured by Toray Industries, Inc.) as a base material was coated with a hiding layer ink 1 having the following composition at 3 g / g by a gravure coating method.
A thermosensitive recording medium 1 of the present invention was obtained by applying a coating amount of m ² and drying to form a porous hiding layer. Ink for hiding layer 1 Vinyl chloride resin (manufactured by Denka Rack Denki Kagaku KK) 30 parts Acrylic resin (manufactured by DIANAL Mitsubishi Rayon Co., Ltd.) 1 part Poor solvent n-butanol 25 parts Affinity solvent acetone 35 parts

Example 2 First, an ink for a colored layer having the following composition was applied to a surface of a transparent polyester film having a thickness of 75 μm (Lumirror manufactured by Toray Industries, Inc.) as a base material at 2 g / m ² by a gravure coating method.
A colored layer was formed by coating and drying at a coating amount of. Ink for coloring layer Carbon black 20 parts Ethylene-vinyl acetate copolymer 10 parts Acrylic emulsion 40 parts Isopropyl alcohol 30 parts Next, on the coloring layer, the same hiding layer ink 1 as in Example 1 was used.
Was coated by a gravure coating method at a coating amount of 3 g / m ² and dried to form a porous hiding layer, to obtain a thermosensitive recording medium 2 of the present invention.

Example 3 A thermal recording medium 3 of the present invention was obtained in the same manner as in Example 2 except that the hiding layer ink 1 was replaced with the hiding layer ink 2 having the following composition. Ink for hiding layer 2 Acrylic resin (RB-85 manufactured by Mitsubishi Rayon Co., Ltd.) 20 parts Poor solvent propanol 20 parts Friendly solvent Toluene: Methyl ethyl ketone (1: 1) 56 parts

Example 4 A thermal recording medium 4 of the present invention was obtained in the same manner as in Example 2 except that the hiding layer ink 1 was replaced with the hiding layer ink 3 having the following composition. Ink for hiding layer 3 Polyester resin (Byron 290 Toyobo Co., Ltd.) 20 parts Poor solvent propanol 20 parts Solvent friendly Toluene: Methyl ethyl ketone (1: 1) 56 parts

Example 5 Example 2 was repeated except that a protective layer coating solution having the following composition was used to form a protective layer by coating on the hiding layer by a gravure coating method at a coating amount of 3 g / m ² and drying. A thermal recording medium 5 of the present invention was obtained in the same manner as in. Coating liquid for protective layer Acrylic resin 20 parts Methyl ethyl ketone 75 parts

Comparative Example 1 For comparison, a thermosensitive coloring ink having the following composition was applied to the surface of a transparent polyester film having a thickness of 75 μm (Lumirror manufactured by Toray Industries, Inc.) by a gravure coating method at 10 g / m ²
A thermosensitive recording medium of Comparative Example 1 was obtained by forming a colored layer by coating and drying at a coating amount of. Thermosensitive coloring ink leuco dye 1 part of bisphenol A 5 parts 1 part of stearic acid amide 5 parts of polyvinyl alcohol Water 85 parts

Next, the thermal recording medium prepared as described above was printed under the following conditions, and the densities at the printed portion and the non-printed portion were measured by a Macbeth reflection densitometer RD914. In addition, in Example 1, since the heated region was transparent, the densities at the printed portion and the non-printed portion were measured by a Macbeth transmission densitometer TD904. Printing conditions Printing printer; word processor Applied energy; 0.2 mJ / dot (constant) pulse width; 2 msec

Next, heat resistance and chemical resistance were evaluated under the following conditions. Evaluation of heat resistance The state after standing for 1 hour in an environment of 50 ° C. was evaluated. Chemical resistance evaluation A Kimwipe dipped in ethanol and methyl ethyl ketone was placed on a thermosensitive recording medium, and the temperature was set to 1 at room temperature (20 ° C).
It was left for 0 minutes, and the stability was visually evaluated.

[0026]

[Table 1]

[0027]

As described above, in the heat-sensitive recording medium of the present invention, since the concealing layer is a porous film which is whitened during drying of the resin varnish consisting of the resin component, the hydrophilic solvent for the resin component and the poor solvent, At this time, the resin component is melted and re-solidified by the heat of the thermal head or the like to be transparent. Therefore, only the heated region of the concealing layer is made transparent, and the concealing layer is recognized in the unheated region, so that clear printing can be performed by the contrast between the transparent region and the concealed region. Furthermore, when a transparent substrate is used, a good OHP recording medium can be obtained due to the contrast between the transparent region and the region that is still hidden.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a thermal recording medium of the present invention.

FIG. 2 is a sectional view showing an example of a thermal recording medium of the present invention.

FIG. 3 is a sectional view showing an example of a thermal recording medium of the present invention.

[Explanation of symbols]

 1. Base material 2. Hiding layer 3. Colored layer 4. Protective layer

Claims (5)

[Claims] 1. A thermal recording medium having a concealing layer on a substrate, wherein the concealing layer becomes transparent by heating. 2. The heat-sensitive recording medium according to claim 1, wherein the concealing layer is a porous film that is whitened during drying of a resin varnish composed of a resin component, a hydrophilic solvent for the resin component, and a poor solvent. 3. The thermosensitive recording medium according to claim 1, wherein the base material is transparent. 4. The thermal recording medium according to claim 1, wherein the base material is opaque. 5. The thermosensitive recording medium according to claim 1, wherein a colored layer is provided on the base material, and a concealing layer is provided on the colored layer.