JPH0517038B2 - - 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 hebenic 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 No. 63-39377.) However, although these devices provide a certain degree of contrast because the heat-sensitive recording layer is provided directly on the colored layer, the contrast is still low. It was inadequate and unsatisfactory.

In addition, in a heat-sensitive recording medium, especially a magnetic card, which has a magnetic recording layer together with a heat-sensitive recording layer, it may be necessary to partially color or print the heat-sensitive recording layer. In order to prevent the color properties of the colored layer or printed layer formed by the heat-sensitive recording layer from being impaired, it is required to separately provide a white layer to hide the color of the colored image used as the background of the heat-sensitive recording layer. Ru. however,
Until now, it has been difficult to sufficiently hide the background color of the heat-sensitive recording layer.

(Problems to be Solved by the Invention) As mentioned above, all of the reversible thermosensitive storage media that have been proposed so far have the problem that the contrast is still insufficient when viewed with reflected light. However, when applying partial coloring or printing on the heat-sensitive recording layer, there was a problem in that the background color of the heat-sensitive recording layer could not be sufficiently hidden.

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

Another object of the present invention is to provide a reversible thermosensitive recording medium that does not impair the color properties of the colored layer or printed layer when the thermosensitive recording layer is partially colored or printed.

(Means and effects for solving the problem) As a result of study, the present inventors have found that by using a light-transmitting substrate having a metal thin film on the surface and having a specific refractive index, transmittance, and thickness, The inventors have discovered that the above objects can be achieved, 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 reflective layer made of a thin metal film is provided on the other surface of the substrate.

Another thermosensitive recording medium of the present invention has a light refractive index
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 reflective layer made of a thin metal film is provided on the other surface of the substrate, and a magnetic recording layer is provided on the reflective layer.

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 Figure 1,
Reference numeral 1 denotes a light-transmissive substrate provided with a reflective layer 2 made of a metal thin film on one surface, and a heat-sensitive recording layer 3 provided on the opposite surface to the surface provided with the reflective layer. A protective layer 4 is further provided on the heat-sensitive layer. In FIG. 2, a magnetic recording layer 5 is provided on a reflective layer 2 provided on one surface of a light-transmitting substrate 1. As shown in FIG. A protective layer 6 is further provided on the magnetic recording layer. Further, on the surface of the heat-sensitive recording layer 3 provided on the other surface of the light-transmitting substrate 1, a printing layer 8 is partially provided with a white concealing layer 7 interposed therebetween, and furthermore, a portion where the heat-sensitive recording layer is exposed is provided. A protective layer 4 is provided on the printed layer.

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 KO115 and JIS K6714-58.

As the reflective layer, one that has a specular reflectance of 35% or more in the wavelength range of 500 to 600 nm can be used.
Preferably 50% or more, and further wavelength range 400 to 700 nm
It is more preferable to have a reflectance of 70% or more.
Here, specular reflectance is determined by the integrating sphere reflectance measurement method using a spectrophotometer, and is a value obtained from the relationship (total reflectance) - (diffuse reflectance) = (specular reflectance). be. Also, 500~600n
The wavelength range of m is the region where visibility with respect to brightness is highest.

Metals such as aluminum, tin, silver, zinc, magnesium, copper, gold, and platinum are used as materials for forming the reflective layer, and these are thin films formed by vapor deposition, sputtering, electroless plating, etc. Can be applied in the form of layers. In terms of reflection characteristics and mechanical strength, the thickness of this thin film layer is approximately 0.001 to 5 μm, preferably 0.03 μm in the case of a metal thin film layer.
~1μm range, and in the case of metal foil, 1~50μm
degree, preferably in the range of 5 to 30 μm.

The heat-sensitive recording layer has a structure in which an organic low-molecular substance is dispersed in an organic high-molecular substance, and has a property that its transparency changes reversibly with temperature changes.

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, halogenoalkanes, halogenoalkenes, halogenoalkynes, cycloalkanes, cycloalkenes, cycloalkynes, saturated or unsaturated mono- or dicarboxylic acids and their esters, amides, or ammonium salts, saturated or unsaturated halogenofatty acids and their Esters, amides, or ammonium salts, 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. 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
In terms of weight ratio, the organic low molecular weight substance is preferably in the range of 5 parts to 200 parts, particularly preferably in the range of 10 parts to 100 parts, to 100 parts of the organic high molecular weight substance. If the amount of the organic low molecular weight substance is less than 5 parts, 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 10 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.

In the thermosensitive recording medium of the present invention, when a magnetic recording layer is provided on the reflective layer, a magnetic material normally used in magnetic recording media is dispersed in an organic polymer material. As the organic polymer material, thermoplastic or thermosetting 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.

In the thermosensitive recording medium of the present invention, 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 containing a resin such as polymethacrylate resin, silicone resin, acrylic resin, alkyd resin, photo-curable or electron beam-curable urethane-acrylate resin, or epoxy-acrylate resin as a main component may be provided.

In addition, a layer may be added between the heat-sensitive recording layer and the protective layer to prevent the organic low-molecular substance in the heat-sensitive recording layer from migrating to other layers, or to increase the adhesion between the heat-sensitive recording layer and the protective layer. Layers may be provided.

Further, a printing layer may be partially formed on the heat-sensitive recording layer, and in this case, in order to make the color of the printing layer vivid, a white layer may be provided in advance on the part where the printing layer is to be formed. good.

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

(Example) In the following examples, all "parts" mean parts by weight.

Example 1 Barium ferrite BaO・6 (Fe ₂ O ₃ ) (coercive force
2750 Oersted Specific surface area 8m 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-2304, manufactured by Nippon Polyurethane Co., Ltd.) 20 parts Toluene 60 parts Methyl ethylene ketone After dispersing a mixture consisting of 60 parts of methyl isobutyl ketone for 8 hours in a ball mill, 5 parts of polyisocyanate resin was added and the mixture was further dispersed for 1 hour to obtain a paint for forming a magnetic recording layer.

On the other hand, the optical refractive index is 1.66, the optical transmittance is 87.5% and the thickness is
On one side of a 188 μm transparent polyester film,
Aluminum is vapor-deposited to form an aluminum vapor-deposited film, and on top of the vapor-deposited film, the above paint for forming a magnetic recording layer is applied to a thickness of 15 μm, and while the paint is still wet, it is applied to a magnetic field orientation device. Then, an orientation treatment was performed and the film was dried at 100°C for 5 minutes.

Next, behenic acid 5 parts vinyl chloride-vinyl acetate copolymer (VYHH,
A paint for forming a heat-sensitive recording layer consisting of 20 parts of tetrahydrofuran, 40 parts of methyl ethyl ketone, and 20 parts of toluene was applied to the surface of the transparent polyester film opposite to the surface on which the aluminum vapor-deposited film was formed. It was dried for a minute 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 thus obtained using a UV offset printing method, and a protective layer with a thickness of 1 μm was formed on the heat-sensitive recording layer and the magnetic recording layer. was formed to obtain a reversible thermosensitive recording medium.

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.

Example 2 Tin vapor deposition was performed on one side to form a tin vapor deposition film.
A coating material for forming a magnetic recording layer having the same composition as in Example 1 was applied to a thickness of 15 μm on a tin vapor-deposited film of 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.
The coating was applied to a thickness of 100°C and completed at 100°C for 5 minutes.

Next, behenic acid 5 parts vinyl chloride-vinyl acetate copolymer (VYHH,
A paint for forming a heat-sensitive recording layer consisting of 20 parts (manufactured by UCC), 40 parts of tetrahydrofuran, 20 parts of methyl ethyl ketone, and 20 parts of toluene was applied to the opposite side of the transparent polyester film to the side on which the tin vapor deposition film was formed, and the coating was heated at 100°C for 5 minutes. Dry to a thickness of approx.
A 20 μm heat-sensitive recording layer was formed.

White pigment (titanium oxide) 70 parts polyester resin (V-200, manufactured by Toyobo Co., Ltd.)
A white ink consisting of 25 parts isocyanate curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.), 5 parts isophorone, and 50 parts xylene was applied by screen printing, dried at 100°C for 5 minutes, and then dried at 60°C for 40 minutes.
Heat treatment is performed for a period of time to complete the curing reaction, and the thickness
A partially obscuring layer of 5 μm was formed.

Full-color printing was performed on the formed hiding layer by UV offset printing.

Furthermore, on both sides of the obtained thermosensitive/magnetic sheet,
A photocurable urethane-acrylic resin was printed using UV offset printing to form a protective layer with a thickness of 1 μm on the heat-sensitive recording layer and the magnetic recording layer, thereby obtaining a reversible heat-sensitive recording medium.

The obtained reversible thermosensitive recording medium was treated in the same manner as in Example 1 to obtain a transparent thermosensitive/magnetic card. When heating printing was carried out at the same time as in Example 1, a white thermally recorded image with very good contrast could be obtained. Moreover, this recorded image could be similarly erased.

Comparative example: On a milky white polyester film with a thickness of 188μm,
A coating material for forming a magnetic recording layer having the same composition as in Example 1 was applied to form a magnetic recording layer having a thickness of about 15 μm.

Next, a paint for forming a heat-sensitive recording layer having the same composition as in Example 1 was applied to the surface opposite to the magnetic recording layer.
It was dried at .degree. C. for 5 minutes to form a heat-sensitive recording layer with a thickness of about 20 .mu.m.

A photocurable urethane-acrylic resin was printed on both sides of the heat-sensitive/magnetic sheet thus obtained using a UV offset printing method, and a protective layer with a thickness of 1 μm was formed on the heat-sensitive recording layer and the magnetic recording layer. was formed to obtain a reversible thermosensitive recording medium.

The obtained reversible thermosensitive recording medium was treated in the same manner as in Example 1 to obtain a transparent thermosensitive/magnetic card. When heating printing was performed at the same time as in Example 1, the contrast of the white image formed was poor.

(Effects of the Invention) As described above, in the heat-sensitive recording medium of the present invention, since the transparent support exists between the reflective layer made of a metal thin film and the heat-sensitive recording layer, light does not leak to the back surface of the heat-sensitive recording layer. The contrast between the cloudy areas that develop color due to heating recording and the uncolored areas 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 is obtained. In addition, the reflective layer made of a thin metal film has poor adhesion to the heat-sensitive recording layer, but in the heat-sensitive recording medium of the present invention, a transparent support is interposed between the heat-sensitive recording layer and the reflective layer made of a thin metal film. This also results in the effect that the adhesion of the reflective layer made of a metal thin film is also improved.

[Brief explanation of the drawing]

1 and 2 are schematic cross-sectional views of an example of the reversible thermosensitive recording medium of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Light-transparent substrate, 2... Reflective layer, 3... Heat-sensitive recording layer, 4... Protective layer, 5... Magnetic recording layer, 6
...Protective layer, 7...White hiding layer, 8...Printing 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. 1. A heat-sensitive recording medium comprising: a heat-sensitive recording layer whose transparency changes reversibly depending on temperature; and a reflective layer made of a thin metal film provided on the other surface of the base. 2 An organic low-molecular substance is dispersed in an organic high-molecular substance on one side 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, and is reversible depending on temperature. 1. A heat-sensitive recording medium comprising: a heat-sensitive recording layer whose transparency changes; a reflective layer made of a thin metal film is provided on the other surface of the substrate; and a magnetic recording layer is provided on the reflective layer. 3. The heat-sensitive recording medium according to claim 1 or 2, wherein a protective layer is provided on the surface of the heat-sensitive recording layer. 4. The thermosensitive recording medium according to claim 2, wherein a protective layer is provided on the surface of the magnetic recording layer.