JPH0523958B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermosensitive recording medium on which images can be recorded and erased reversibly by heating.

(Prior Art) In recent years, new recording materials have been proposed that are capable of reversibly recording and erasing images by changing heating temperatures and that have image fixability at room temperature. (Refer to Japanese Patent Application Laid-Open No. 55-154198.) This recording material has a heat-sensitive layer in which an organic low-molecular substance such as behenic acid is dispersed in a resin such as polyester resin or vinyl chloride resin, and the heating temperature can be selected. By doing so, the transparency of the heat-sensitive layer changes. Furthermore, after heating this recording material,
Even when cooled to room temperature, a transparent state or a cloudy state can be stably maintained, and these states can be reversibly maintained. That is, this recording material can be used as a heat-sensitive recording medium that can be reversibly printed and erased.

However, with this recording material itself, a white image is formed on a colorless transparent background or a transparent image is formed on a white background, so the visibility of the image is poor when viewed with reflected light. Therefore, for the purpose of improving the contrast, a reversible recording material has been proposed in which a heat-sensitive layer containing this reversible heat-sensitive recording material is combined with a colored support or a colored layer. (Refer to JP-A-62-257883 and JP-A-63-39377) However, although these devices provide a certain degree of contrast because a linear thermosensitive recording layer is provided on the colored layer, the contrast is still low. It was inadequate and unsatisfactory.

(Problems to be Solved by the Invention) As described above, all of the reversible heat-sensitive recording materials proposed so far have had the problem that the contrast is still insufficient when viewed with reflected light.

Therefore, it is an object of the present invention to solve these problems in the conventional technology and to provide a heat-sensitive recording medium that can provide images with excellent contrast that are easy to see with reflected light.

(Means and effects for solving the problem) As a result of study, the present inventors achieved the above object by using a light-transmitting substrate having a specific refractive index, transmittance, and thickness. They have discovered that this can be done, and have achieved the present invention.

That is, the thermosensitive recording medium of the present invention has a light refractive index of
1.4-1.7, light transmittance of 70% or more, organic low-molecular substance is dispersed in an organic polymer substance on one side of a light-transmissive substrate with a thickness of 3-500 μm, and the transparency changes reversibly depending on the temperature. A heat-sensitive recording layer is provided on the other surface of the substrate, and a light-transmitting colored layer or a light-impermeable colored layer and a magnetic recording layer are provided on the other surface of the substrate.

Next, the thermosensitive recording medium of the present invention will be explained with reference to the drawings.

FIG. 1 and FIG. 2 are each a schematic cross-sectional view of an example of the thermosensitive recording medium of the present invention. In the figure, 1
is a light-transmitting substrate, on one side of which is provided a heat-sensitive recording layer 2, and on top of which is provided a protective layer 3. In FIG. 1, only the light-impermeable colored layer 4 is provided on the other surface of the light-transmitting substrate 1, and in FIG. are provided in a stacked state with

Next, each layer constituting the thermosensitive recording medium of the present invention will be explained.

The light-transmitting substrate has a light refractive index of 1.4 to 1.7 and a light transmittance.
An organic polymer film consisting of 70% or more and a thickness of 3 to 500 μm is used. Specifically, films such as vinyl chloride-vinyl acetate copolymer, polyester, polycarbonate, acetate, and polyimide are used. These films have a light refractive index of
1.4 to 1.7, a light transmittance of 70% or more, and a thickness of 3 to 500 μm. In particular, a light refractive index of 1.5 to 1.7 is required.
1.6, preferably has a light transmittance of 85% or more and a thickness of 50 to 300 μm.

In addition, in the present invention, the optical refractive index is ASTM
means the refractive index of visible light based on D542−70,
The light transmittance means the transmittance of visible light based on JIS K0115 and JIS K6714-58.

The heat-sensitive recording layer is made of an organic low-molecular substance dispersed in an organic high-molecular substance, and has a property that its transparency changes reversibly depending on the temperature.

As the organic polymer substance, one having good transparency, excellent mechanical strength, and good film-forming properties is preferable. Specific examples include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. , polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, polyester resin, polyamide resin, acrylic resin, silicone resin, and the like. Among these, particularly preferred are vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and polyester resin.

Examples of organic low-molecular substances include alkanols, alkanediols, halogenoalkanols, halogenoalkanediols, alkylamines, alkanes,
Alkenes, alkynes, halogenoalkane, halogenoalkenes, halogenoalkylnes, cycloalkanes, cycloalkenes, cycloalkynes, saturated or unsaturated mono- or dicarboxylic acids and their esters, amides, or ammonium salts, saturated or unsaturated halogeno fatty acids and the like esters, amides, or ammonium salts of halogenoallyl carboxylic acids and their esters, amides or ammonium salts, thioalcohols, thiocarboxylic acid polymers and their esters, amides or ammonium salts, carboxylic acid esters of thioalcohols, etc. Carbon number is 10-40, molecular weight is 100
~700 things can be mentioned. Particularly preferred are higher fatty acids such as lauric acid, palmitic acid, stearic acid, arachidic acid, and behenic acid, and their esters, amides, and ammonium salts, which have melting points in the range of 50 to 150°C.

The mixing ratio of organic polymer material and organic low molecular material is
The weight ratio of the organic low molecular weight substance to 100 parts of the organic high molecular weight substance is preferably 5 to 200 times, particularly preferably 10 to 100 parts. If the amount of the organic low molecular weight substance is less than 5 times, the heat-sensitive recording layer will not become cloudy enough, making it difficult to obtain contrast. Also, if there are more than 200 copies,
The film formability of the heat-sensitive recording layer deteriorates.

The thickness of the heat-sensitive recording layer is preferably in the range of 5 to 50 μm, more preferably in the range of 10 to 30 μm. If the thickness is less than 5 μm, the heat-sensitive recording layer will not become cloudy enough, making it difficult to obtain contrast. Moreover, if it is thicker than 50 μm, the heat conductivity during printing will be poor, and the sensitivity of the heat-sensitive recording layer will be reduced.

As the light-impermeable colored layer provided on the other light-transmissive surface, a colorant such as an organic or inorganic pigment or dye is dispersed or dissolved in an organic polymer material. As the colorant, any known colorant can be used, and as the organic polymer material, thermoplastics such as vinyl chloride-vinyl acetate resin, polyester resin, urethane resin, acrylic resin, and epoxy resin can be used. Alternatively, thermosetting resin can be used. The thickness of the light-opaque colored layer can be set within an appropriate range.

As the magnetic recording layer, a material in which a magnetic material normally used in magnetic recording media is dispersed in an organic polymer material is used. As the organic polymer material, thermoplastic or heat-effect resins such as vinyl chloride-vinyl acetate resins, polyester resins, urethane resins, acrylic resins, and epoxy resins can be used. Additives such as conductive fillers and abrasives may be added to the magnetic recording layer. The thickness of the magnetic recording layer can be set as appropriate.

The thermosensitive recording medium of the present invention is composed of the above-mentioned layers, but the following layers can be provided as necessary.

For example, when recording with a heat-sensitive head, in order to improve the heat resistance of the heat-sensitive recording layer and maintain matching properties with the heat-sensitive head, a thermoplastic or thermosetting resin such as A heat-resistant protective layer may be provided whose main component is a resin such as a polymethacrylate resin, a silicone resin, an acrylic resin, an alkyd resin, a photo-curable or electron beam-curable urethane-acrylate resin, or an epoxy-acrylate resin.

In addition, when a light-impermeable colored layer and a magnetic recording layer are provided in the heat-sensitive recording medium of the present invention, in order to make the color of the light-impermeable colored layer vivid, the magnetic recording layer and the light-impermeable colored layer are combined. A white concealing layer may be provided between the two layers, or a metal thin film layer formed by a vapor deposition method, a sputtering method, an electroless plating method, or the like may be provided.

Furthermore, when the thermosensitive recording medium of the present invention is provided with a magnetic recording layer, in order to prevent wear of the magnetic recording layer, a thermoplastic or thermosetting resin, such as a polymethacrylate resin, is applied to the surface of the magnetic recording layer. ,
Photo-curable or electron beam-curable urethanes such as silicone resins, acrylic resins, and alkyd resins.
A protective layer mainly composed of a resin such as an acrylate resin or an epoxy-acrylate resin may be provided.

(Example) In the Examples, "part" means part by weight.

Example 1 Blue pigment dispersion (Multilace 700 Blue, manufactured by Toyo Ink Co., Ltd.) 70 parts polyester resin (V-200, manufactured by Toyobo Co., Ltd.)
A blue paint consisting of 25 parts isocyanate curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.), 5 parts toluene, 50 parts methyl ethyl ketone, and a light refractive index of 1.66 and a light transmittance.
A transparent polyester film having a thickness of 188 μm was coated at 87.5% to form a light-impermeable colored layer.

Next, behenic acid 5 parts vinyl chloride-vinyl acetate copolymer (VYHH,
A heat-sensitive recording layer forming paint consisting of 20 parts tetrahydrofuran, 40 parts methyl ethyl ketone, 20 parts toluene, and 20 parts toluene, was applied to the surface of the transparent polyester film opposite to the surface on which the light-impermeable colored layer was formed. It was dried at .degree. C. for 5 minutes to form a heat-sensitive recording layer with a thickness of about 20 .mu.m.

On both sides of the heat-sensitive sheet obtained in this way,
A protective layer with a thickness of 1 μm was formed on the heat-sensitive recording layer and the light-impermeable colored layer by printing a photocurable urethane-acrylic resin using a UV offset printing method.
A reversible thermosensitive recording medium was obtained.

The obtained reversible thermosensitive recording medium was punched out into a card shape to obtain a thermosensitive card. This heat sensitive card is
Although it had developed a white color due to thermal history, it became transparent by holding it at 70°C for 10 seconds and returning it to room temperature.

When thermal printing was performed on this transparent thermal card with a printing energy of 70 mJ, the printed area turned white and a recorded image with very good contrast could be obtained. Furthermore, when this was held at 70°C for 10 seconds, the printed area became transparent and the recorded image could be erased.

Example 2 A blue pigment dispersion (Multilace 700 Blue, manufactured by Toyo Ink Co., Ltd.) and 70 parts of polyester resin (V-200, manufactured by Toyobo Co., Ltd.) were placed on a transparent polyester film with a light refractive index of 1.66 and a light transmittance of 87.5% and a thickness of 250 μm.
A blue paint consisting of 25 parts isocyanate curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.), 5 parts toluene, 50 parts methyl ethyl ketone, and 50 parts was applied, dried at 100°C for 5 minutes, and then heat treated at 60°C for 4 hours. The curing reaction was completed to form a light-opaque colored layer with a thickness of 5 μm.

Furthermore, white pigment (titanium oxide) 70 parts polyester resin (V-200, manufactured by Toyobo Co., Ltd.)
A blue paint consisting of 25 parts isocyanate curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.), 5 parts toluene, 50 parts methyl ethyl ketone, and 50 parts was applied, dried at 100°C for 5 minutes, and then heat treated at 60°C for 4 hours. The curing reaction was completed to form a hiding layer with a thickness of 5 μm.

On top of this layer, a coating material for forming a magnetic recording layer having the following composition was applied and dried at 100°C for 5 minutes.
A magnetic recording layer with a thickness of 15 μm was formed.

Barium ferrite BaO・6 (Fe ₂ O ₃ ) (coercive force
2750 Oersted specific surface area 8 m ² /g) 100 parts carbon black 3 parts lecithin 1 part vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH, manufactured by UCC) 20 parts polyurethane resin Nitsuporan N-2340, manufactured by Nippon Polyurethane Co., Ltd.) A mixture consisting of 20 parts toluene, 60 parts methyl ethyl ketone, 60 parts methyl isobutyl ketone, and 60 parts was dispersed in a ball mill for 8 hours, and then 5 parts of polyisocyanate resin was added to the surface of the transparent polyester film on which the light-impermeable colored layer was formed. On the other side, behenic acid 5 parts vinyl chloride-vinyl acetate copolymer (VYHH,
UCC) 20 parts tetrahydrofuran 40 parts methyl ethyl ketone 20 parts toluene A paint for forming a heat-sensitive recording layer was applied and heated to 100°C.
The film was dried for 5 minutes to form a heat-sensitive recording layer with a thickness of about 20 μm.

A photocurable urethane-acrylic resin was printed on both sides of the heat-sensitive/magnetic sheet obtained in this way using a UV offset printing method, and a protective film with a thickness of 1 μm was applied on the heat-sensitive recording layer and the magnetic recording layer. form a layer,
A reversible thermosensitive recording medium was obtained.

The obtained reversible thermosensitive recording medium was punched out into a card shape to obtain a thermosensitive/magnetic card. This heat-sensitive card had a white color due to its thermal history, but
It became transparent by keeping it at ℃ for 10 seconds and returning it to room temperature.

When thermal printing was performed on this transparent thermosensitive/magnetic card with a printing energy of 70 mJ, the printed area turned white and a recorded image with very good contrast could be obtained. Also, heat this at 70℃ for 10
When held for a second, the printed portion became transparent and the recorded image could be erased.

Comparative Example A magnetic recording layer-forming paint having the same composition as in Example 2 was applied onto a milky white polyester film with a light transmittance of 1.0% and a thickness of 188 μm to form a film with a thickness of approximately 15 μm.
A magnetic recording layer of m was formed.

Subsequently, the same blue paint as in Example 2 was applied to the surface opposite to the magnetic recording layer, and cured in the same manner as in Example 2.

Furthermore, a paint for forming a heat-sensitive recording layer having the same composition as in Example 1 was applied thereon and dried at 100°C for 5 minutes to form a heat-sensitive recording layer with a thickness of about 20 μm.

A photocurable urethane-acrylic resin was printed on both sides of the heat-sensitive/magnetic sheet obtained in this way using a UV offset printing method, and a protective film of 1 μm thick was applied on the heat-sensitive recording layer and the magnetic recording layer. form a layer,
A reversible thermosensitive recording medium was obtained.

The obtained reversible thermosensitive recording medium was treated in the same manner as in Example 2 to obtain a transparent thermosensitive/magnetic card. When heating printing was carried out in the same manner as in Example 2, the printed portion was colored white, but the contrast was inferior to that in Examples 1 and 2.

(Effects of the Invention) In the heat-sensitive recording medium of the present invention, since the transparent support is present between the light-impermeable colored layer and the heat-sensitive recording layer as described above, light does not leak to the back surface of the heat-sensitive recording layer. The contrast between the colored portion and the transparent portion produced by heating recording is significantly higher than that of conventional reversible thermosensitive recording media, and an image with excellent contrast that is easy to see with reflected light can be obtained.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are both schematic cross-sectional views of an example of the reversible thermosensitive recording medium of the present invention. 1... Light-transmitting substrate, 2... Heat-sensitive recording layer, 3...
...Protective layer, 4... Light-opaque colored layer, 5... Magnetic recording layer, 6... Hiding layer.

Claims (1)

[Scope of Claims] 1. An organic low-molecular substance is dispersed in an organic high-molecular substance on one surface of a light-transmitting substrate having a light refractive index of 1.4 to 1.7, a light transmittance of 70% or more, and a thickness of 3 to 500 μm. A thermosensitive recording comprising: a thermosensitive recording layer whose transparency changes reversibly depending on temperature; and a light-transmitting colored layer or a light-transmitting colored layer and a magnetic recording layer on the other surface of the substrate. Medium. 2. The heat-sensitive recording medium according to claim 1, wherein a protective layer is provided on the surface of the heat-sensitive recording layer.