JPH04265800A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain the above thermal recording material having a smooth surface and capable of carrying out sharp and uniform printing by introducing a smooth layer between the substrate and undercoat layer of the thermal recording material and setting the thickness of the undercoat layer to 2mum or less. CONSTITUTION:In the thermal recording material wherein an undercoat layer containing a resin is provided on a substrate and a low m.p. metal membrane is provided on the undercoat layer and a part thereof is heated to melt and perforate the membrane to perform printing, the thickness of the undercoat layer is set to 2mum or less. More pref., a color layer, a smooth layer, an undercoat layer, a metal layer, a protective layer (a) and a protective layer (b) are laminated to the substrate.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a heat-sensitive recording material in which printing is performed by heating a part of a heat-sensitive recording layer made of a thin film of a low-melting point metal provided on an underlayer to melt holes in the thin film. , relates to technical improvements for providing highly uniform and clear printing.

0002

[Prior Art] Thermal recording method, which prints by heating a part of a heat-sensitive recording layer made of a thin film of a low-melting point metal provided on a base layer to create holes in the thin film, cannot be rewritten. Because of its excellent stability over time, it has been used for various purposes such as printing and displaying amounts, counts, dates, etc.

[0003] As shown in Japanese Patent Laid-Open Publication No. 59-199284, this type of heat-sensitive recording material has a magnetic recording layer provided on a base, and a thin film of a non-magnetic metal or alloy is coated on the magnetic recording layer. It has been proposed to provide a heat-sensitive recording layer, a colored layer between the heat-sensitive recording layer and the magnetic recording layer, a colored layer and a protective layer on the heat-sensitive recording layer, or an adhesive layer between each layer. There is.

That is, in general, nylon, cellulose diacetate, cellulose triacetate, polystyrene,
A magnetic layer is formed on the surface of a plastic substrate such as polyethylene, polypropylene, polyester, polyimide, polycarbonate, etc., and a magnetic layer is formed on the surface of a substrate made of plastic such as polyethylene, polypropylene, polyester, polyimide, or polycarbonate.
A thin film of a low-melting point metal such as indium, aluminum, lead, or zinc is formed by vacuum evaporation, plating, or other methods, and it can provide visible information as well as magnetic information. A method of obtaining visible information is to melt this low-melting point metal using a heating means such as a thermal head, laser beam, or hot stamp, and create a hole in the thin film to create a bar code. , OCR characters, etc. are recorded. This recording method provides outstanding thermal and chemical stability of the print compared to other reaction-based types such as chemical color formers.

Previously, the present inventors conducted studies to obtain clearer prints in this type of heat-sensitive recording material, and proposed materials and manufacturing methods for the underlayer and metal layer (Patent Application No.
-140270).

[0006] Furthermore, in this printing method, we have conducted intensive studies with the aim of printing with low energy and extending the life of the thermal head, and have devised several measures (pending application).

However, there is still room for improvement in the current system from the viewpoint of stability of print quality. In other words, print density and font sharpness are determined by the smoothness of the substrate surface.
It is affected by the uniformity of the film thickness of the base layer and metal layer, and the variation in resistance of each element of the thermal head, so it is difficult to avoid the influence of these variations between each printed character, and as a result, the print quality was causing a decline in In particular, in the case of a structure in which a magnetic layer is provided at the bottom and serves as both a black colored layer and a magnetic recording layer, the unevenness of the surface of the magnetic layer is generally large, and this has a large effect.

[0008]

Problems to be Solved by the Invention If there is variation in density or sharpness of font between printed characters, non-uniformity in appearance occurs, resulting in a problem of deterioration of print quality.

Accordingly, the present invention provides a heat-sensitive recording material that can provide clear and uniform printing by particularly improving the structure of the underlayer and smoothing the surface.

0010

[Means for solving the problem] As mentioned above, the causes of variation in print density and sharpness of fonts include unevenness on the surface of the substrate or the colored layer on the substrate (hereinafter referred to as the substrate, etc.), and the unevenness of the base layer and metal layer. Examples include unevenness in film thickness and variation in resistance between each element of the thermal head. In other words, if there are irregularities on the surface of the substrate or the colored layer on the substrate, the underlying layer and metal layer formed on it will also have irregularities, which will cause unevenness in the distance from the thermal head during heating, resulting in uneven heating and print density. This results in non-uniformity of the font and causes disturbances at the edges of the font. Furthermore, unevenness in the thickness of the base layer and the metal layer results in unevenness in the degree of melting of these layers in the heated portion, resulting in uneven printing density.

Furthermore, variations in resistance between elements of the thermal head inevitably cause variations in printing energy, resulting in non-uniform density. Among these, the unevenness on the surface of the substrate etc. has the greatest influence, and by improving this, the above-mentioned variations can be significantly improved. This is particularly noticeable in the case of a structure in which a magnetic layer is provided at the bottom and serves as both a black colored layer and a magnetic recording layer. However, at this time, it goes without saying that improving the surface irregularities must not cause a decrease in other characteristics, such as a decrease in average print density.

[0012] Smoothening of the surface of the substrate etc. can be achieved simply by increasing the thickness of the underlying layer. However, in this case, a large amount of energy is required to melt and flow the underlayer when heated by the thermal head, resulting in a decrease in print density. This is because the printing principle of this method is that the base layer is melted together with the metal layer, causing the thin metal film to coagulate and deform into particles.In other words, it is basically more expensive to make the base layer as thin as possible. Print density can be obtained.

Therefore, the present inventors devised a structure in which a smoothing resin layer (hereinafter referred to as the smooth layer) is provided between the base layer and the substrate, and the base layer itself is made as thin as possible. The inserted resin layer should be thick enough to sufficiently smooth the surface of the substrate, etc., and the glass transition temperature or melting point of this resin should be higher than that of the base layer as previously filed. was used so that this layer itself did not act as a base layer.

Furthermore, as proposed in (Japanese Patent Application No. 2-140270), the thermal property of the underlayer resin is such that the temperature at which it reaches the flow region after being heated is 20°C or more lower than the melting point of the metal, in order to achieve high printing density. It is advantageous to obtain. This is because the lower the flow temperature, the greater the degree of softening of the base layer resin when heated by the thermal head, which reduces the mechanical resistance for the molten metal to coagulate and deform, allowing smooth aggregation. It's for a reason.

Acrylic, vinyl chloride-vinyl acetate copolymer, acrylic silicone, polyvinyl butyral, various other thermoplastic resins and thermoplastic elastomers, and mixtures thereof can be used as the underlayer material having such properties. Further, as the smooth layer material, urethane, phenol, epoxy, acrylic silicone, and other various thermosetting resins and mixtures thereof can be used.

The necessary thickness of the smooth layer varies depending on the condition of the substrate or the surface of the substrate, but generally the unevenness of the base film and coating surface is in the range of ±0.1 to 5 microns, and the necessary thickness is adjusted accordingly. The thickness is determined. For example, when a magnetic recording layer containing a magnetic coating material such as barium ferrite is used as a colored layer, the smooth layer is usually coated to a similar thickness because the unevenness of the surface is relatively thick and about 2 to 3 microns.

The thickness of the underlayer varies depending on the type of material and the forming method, but it is usually 2 microns or less, and if it becomes thicker than this, the overall printing density will decrease. However, in general, when the thickness is less than 0.2 microns, it is difficult to function as an underlayer.

As the substrate, conventionally used nylon, cellulose diacetate, cellulose triacetate, polystyrene, polyethylene, polypropylene, polyester, polyimide, polycarbonate, polyethylene terephthalate, polyethylene can be used. Plastics such as naphthalate can be used.

In order to obtain high-contrast printing, it is desirable to include a colored pigment in the base layer or to form a transparent layer by providing the base layer on a coating film containing a colored pigment. For coating films containing colored pigments, the binder may be vinyl chloride-vinyl acetate copolymer, cellulose resin, polyvinyl butyral resin, polyurethane resin, polyester resin, acrylic resin, or phenol resin. Resins, isocyanate compounds, etc. can be used. Among them, it is desirable to use a urethane resin, a vinyl chloride-vinyl acetate copolymer, or a vinyl chloride resin having an acrylic hydroxyl group as a coating film containing a colored pigment.

[0020] The colored pigment must have a color that can be visually recognized between the pigment and the metal thin film, but black is preferable from the viewpoint of contrast, and coloring for display and recording are attempted at the same time. In some cases, magnetic powder is desirable.

The thin film of the low melting point metal can be formed on the base layer by vacuum deposition, plating, sputtering, or the like.

[0022] The heat-sensitive recording material produced in this manner can be prepared by melting the low melting point metal and forming holes in the thin film using a heating means such as a thermal head, a laser beam, or a hot stamp. As a result, clear and uniform print quality can be achieved even when printing is performed using energy as low as chemical coloring.

It is also possible to provide a protective layer on the heat-sensitive recording layer thus formed to protect the print itself from heat, light, chemicals, moisture, and the like. Naturally, it is necessary that the protective layer has the property of satisfactorily transmitting light.

[0024]

[Example] Colored layer (2) and smooth layer (3) on base (1)
A thermosensitive recording material having a structure formed by sequentially laminating an underlayer (4), a low melting point metal thin film (5), and a double protective layer (6a, 6b) was prepared. A. Formation of colored layer (2) 80 parts by weight of barium ferrite magnetic powder (average particle size 0
．． 8 microns), 10 parts by weight of acrylic hydroxyl group-containing vinyl chloride-vinyl acetate copolymer (VAGF manufactured by U.C.C.
), 7 parts by weight of polyurethane resin (Pandex T5201 manufactured by Dainippon Ink and Chemicals), 1 part by weight of trifunctional polyisocyanate compound (Coronate manufactured by Nippon Polyurethane Industries), 4 parts by weight of carbon. Black, 260 parts by weight of toluene and 260 parts by weight of cyclohexanone were mixed and mixed and dispersed in a ball mill for 100 hours to prepare a magnetic paint. Thickness of polyethylene terephthalate 18
This magnetic paint was coated on a sheet substrate (1) with a thickness of 8 microns by a gravure method and dried to form a black colored layer with a thickness of 15 microns. The unevenness on the surface of this colored layer was measured by a stylus method and found to be ±2.5 microns at most.

B. Formation of smooth layer (3) On top of the above colored layer, urethane resin with a glass transition point of 130°C was dissolved in a mixed solvent of cyclohexanone and toluene at the following two film thicknesses (a) and (b). A smooth layer (3) was formed by applying and drying using a gravure method. stomach. Thickness: 3 microns, b. 1 micron thick.

C. Formation of base layer (4) On the smooth layer, coat a copolymerized acrylic resin with a silane compound using a gravure method to form a base layer (4) in the following two thicknesses A and B. E-A, E-B
Four types of smooth layer and base layer combinations were obtained: , Rho-A, and Rho-B. This resin has a glass transition point of 65°C and a temperature at which it reaches the flow range at 160°C. A. Thickness 0.5 micron, B
．． Thickness: 2.5 microns.

For comparison, an undercoat layer was formed directly on the colored layer to a thickness of 3.5 microns without using a smooth layer. Let this be C.

D. Formation of low melting point metal thin film (5) Using a metal sample containing 1.0% by weight of lead to 1 part of tin as an evaporation source, vacuum deposition was performed using a resistive heating evaporation apparatus manufactured by ULBAC, EBX-6. At a temperature of 1/100,000 torr and a deposition rate of 50 angstroms/sec, vacuum evaporation was performed on the five types of base layers without heating the base layer.
A metal thin film (5) with a thickness of 900 angstroms was formed, and five types of samples were obtained.

When the composition of the metal thin film was analyzed, the ratio of lead to tin was 2%, and it was observed that lead was concentrated in the thin film. This is thought to be because lead has a higher vapor pressure than tin, so tin was dissipated during heating.

[0030] The melting point of each metal thin film at that time was measured and found to be 202°C. The melting point was expressed as the temperature at which melting started by differential thermal analysis.

Incidentally, when the melting point of pure tin was measured using this method, it was 232°C.

E. Formation of protective layer (6) A paint having the same composition as the base layer paint is applied to the surface of the metal thin film of the five types of samples obtained in step D to form a 2 micron thick acrylic silicone resin film, Furthermore, UV-curable epoxy acrylate (V5510 manufactured by Dainippon Ink Co., Ltd.) was applied to a thickness of 1 micron after drying to form a double protective layer (6a
, 6b) to form I-A, E-B, Ro-A, Ro-B.
Five types of heat-sensitive recording bodies of C and C were obtained.

F. Printing test For the five types of heat-sensitive recording materials mentioned above, the dot density was 8 lines/
Using a thin film thermal head with dot dimensions of 120 x 120 microns (mm), the printing energy is 45 mm.
, 40, 35, and 30 mJ/mm2, and printing was performed using a KUA-501 type thermal printing type magnetic card reader/writer manufactured by Kyushu Matsushita Electric. 45 mJ/mm2 is the standard energy of this method's thermal recording medium, and 30 m
J/mm2 is the standard energy for heat-sensitive recording materials using chemical reactions.

G. Evaluation of Printing Print density was evaluated by measuring so-called reflection density. Reflection density was measured using a Macbeth RD915 densitometer. The measurement was performed on a 3 mm square (24 x 24 dots) square printed area, and the average density including the unmelted area between each dot was determined.

Further, the variation in print density was determined by measuring the distribution of reflectance within the character A. The reflectance was measured at 10 locations in a field of 0.2 mmφ.

[0036]

[Effect of the invention] Table 1 shows the experimental results.

[Table 1]

However, regarding the print density, the reflection density is 1.
◎ for 0 or more, ○ for 0.7 to 1.0, 0.5
A value of ~0.7 was expressed as △, and a value of 0.5 or less was expressed as ×. Regarding the variation in reflectance, ◎ indicates that the variation range is within 5%, ○ indicates that the variation range is 5 to 15%, and ○ indicates that the variation range is within 5%.
Those with 30% were expressed as △, and those with 30% or more were expressed as ×.

As can be seen from the above table, samples E-A and E-B using a smooth layer with a thickness of 3 microns had little variation in reflectance, and fonts with uniform density were obtained. Among the two, the E-A sample with a thin base layer of 0.5 microns has a higher average print density and print energy of 30 mJ/
A dark print with a reflection density of 1.0 or more was obtained even in square mm. On the other hand, the RO-A and RO-B samples using a smooth layer with a thickness of 1 micron had large variations in print density.
The effect of smoothing was confirmed. However, in Low-A, the average print density was high because the underlying layer was thin. In addition, Sample C, which had a thicker base layer without providing a smoothing layer, had relatively little variation in print density, but the average density was low and sufficient density could not be obtained even at a printing energy of 45 mJ/mm2. .

Based on these results, a resin having a high glass transition temperature or melting point is applied to smooth the substrate, etc.
Furthermore, it has been found that uniform and high print density can be obtained by combining this with a thin coating of a resin that flows easily when heated as an underlayer.

As described above, it has been found that the heat-sensitive recording medium according to the present invention can produce uniform, high-density, and clear printing even at low printing energy similar to heat-sensitive recording using chemical coloring, etc., and the printing quality is improved. improvement was obtained.

Claims (6)

[Claims] [Claim 1] Part of a heat-sensitive recording layer consisting of a base layer containing a resin provided on a substrate and a thin film of a low melting point metal provided on the base layer is heated to melt and form holes in the thin film. 1. A heat-sensitive recording material for printing, characterized in that the thickness of the base layer is thinner than 2 microns. 2. In the heat-sensitive recording material of claim 1, a resin layer serving as a buffer layer is formed between the underlayer and the substrate, and the glass transition temperature or melting point of this resin is lower than the glass transition temperature or melting point of the underlayer resin. 1. A heat-sensitive recording material characterized in that the resin layer has a high heat resistance and a sufficient thickness to smooth the surface of the substrate. 3. The heat-sensitive recording material according to claim 1, wherein the thermal property of the underlayer resin is such that the temperature at which it reaches the flow region upon heating is 20° C. or more lower than the melting point of the metal. 4. The heat-sensitive recording material according to claim 1, wherein the underlayer contains a colored pigment. 5. The heat-sensitive recording material according to claim 1, wherein the base layer is a transparent layer provided on a coating film containing a colored pigment. 6. The heat-sensitive recording material according to claim 4, wherein the colored pigment is a magnetic powder.