JPH06171279A - Heat-sensitive recording medium - Google Patents

Abstract

PURPOSE:To prevent the softening of the resin of a protecting layer due to the heat resulting from a high energy exerted by a thermal head on a heat- sensitive recording medium using a thin metal film at the time of printing and consequent contamination of the thermal head with the aforesaid resin. CONSTITUTION:In a heat-sensitive recording medium comprising at least one colored layer, a thin metal film layer and a protecting layer built up on a base material and a heating means for destroying the thin metal film layer to record visible information therein, the molecular weight of the protecting layer between the crosslinking points is within the range of 1000-100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording medium using a metal thin film, and more particularly to improvement of its protective layer. The protective layer of the present invention is particularly effective as a protective layer for a thermal recording medium using a metal thin film having high printing energy.

[0002]

2. Description of the Related Art Thermal recording media using metal thin films are widely used for prepaid cards such as telephone cards and boarding cards, and other information recording media. Generally, a heat-sensitive recording medium is formed by laminating at least one colored layer, a heat-destructible metal thin film layer, and a protective layer in this order on a substrate, and the metal thin film layer is a printing (information recording that applies high printing energy heat). )
At the time of printing, the printed part melts and is destroyed by the action of surface tension,
The lower colored layer is exposed through the printed portion and can be seen through from the protective layer. Once printed, it is permanently fixed.

[0003]

The thermal recording medium using a metal thin film has a higher energy applied from the thermal head during printing than that using a leuco dye or a transfer ribbon, and the heat applied to the protective layer is high. Therefore, the resin of the protective layer is softened, and as a result, the resin of the protective layer adheres to the thermal head. When printing with a card issuing machine and various terminals, a large number of sheets are processed, so even if a small amount of protective layer resin adheres to the thermal head, that resin accumulates and the accumulated resin carbonizes, causing the thermal head to run out of bits. There is a possibility that head spacing with the recording medium may occur during printing or printing, which may deteriorate printing quality or shorten the life of the thermal head.

[0004]

In order to solve such problems, the present inventor has determined the composition of the protective layer of the thermosensitive recording medium, in particular, the degree of crosslinking of the thermosetting resin and the molecular weight between crosslinking points (M
As a result of a study focusing on c), it was found that the molecular weight between cross-linking points greatly affects the head adhesion and print quality. That is, according to the present invention, the value of the molecular weight (Mc) between cross-linking points is 1000 to 10 as a protective layer for a thermal recording medium.
When using a thermosetting resin in the range of 0, preferably in the range of 600 to 100, the problem of head adhesion described above does not occur and the print quality is good.

The heat-sensitive recording medium basically comprises a substrate, at least one colored layer, a heat-sensitive destructible metal thin film layer, and a protective layer. It may also be used in combination with a magnetic recording medium, in which case a gravure, die, knife,
A magnetic recording layer is formed using a coating technique such as rolls, and a colored layer and a heat-sensitive destructible metal thin film layer are formed on the magnetic recording layer.
And a protective layer. The colored layer can also serve as the magnetic recording layer itself. An anchor layer may be applied and formed on the substrate or on the magnetic recording layer for the purpose of improving the adhesion to the metal thin film layer, the chemical resistance and the like. Also,
The anchor layer may be colored in order to improve printing quality, and a black pigment such as carbon black or a part of black dye may be used as the colorant.

The metal thin film layer has a relatively low melting point of Sn, Te, Al, Bi, Pb, which is well known for heat-sensitive breakdown recording media.
A metal such as Zn or an alloy thereof can be formed by vapor deposition or the like. In the method of recording a visible information pattern on a thermal recording medium using a metal thin film, the thermal recording layer (metal thin film layer) is heated to a predetermined pattern by a thermal head through a protective layer. At the heated portion, the constituent metal of the thermosensitive recording layer is melted and atomized (usually referred to as a ball-up phenomenon). This causes the protective layer to contact the anchor layer or create cavities at the heated site. Since the protective layer and the uncolored anchor layer are almost transparent, the underlying magnetic layer or the colored anchor layer can be seen through. Since the metal thin film layer has high lightness, if the ball-up phenomenon is complete, the heated portion exhibits a sufficient black color and is recognized as a recording pattern.

For the protective layer formed on the metal thin film layer, various resins such as polyester, vinyl chloride, epoxy, acryl and polystyrene are used alone or in combination, and as the crosslinking agent, crosslinking agents such as isocyanate, epoxy and aziridine are used. Is adjusted so as to have various molecular weights between crosslinking points. The protective layer has a molecular weight (Mc) between crosslinking points of 1000 to 10
It should be 0, preferably in the range of 600-100. If it exceeds 1000, the resin of the thermal head will adhere. If it is less than 100, the coating film becomes hard and brittle, which is not preferable in practical use.

[0008]

【Example】

Example 1 A coercive force of 2750 on a polyester substrate having a thickness of 188 μm.
A barium ferrite-based magnetic paint of Oe was applied by a gravure method so that the applied thickness was about 15 μm to form a magnetic recording layer. The magnetic paint was prepared with the composition shown in Table 1.

[0009]

[Table 1]

An anchor layer having a thickness of about 2.0 μm was applied and formed on the upper layer of the magnetic recording layer for the purpose of improving the adhesion to the metal thin film layer, the chemical resistance and the like. Table 2 shows the coating composition used for the anchor layer.

[0011]

[Table 2]

Sn is used for the metal thin film layer, and a vacuum evaporation method is used for forming the thin film.
The film was formed so as to be 0 ± 0.5Ω / □. A protective layer having a thickness of 2.0 μm was formed on the Sn vapor deposition layer. Table 3 for the protective layer
The resin shown in 1 was used, and isocyanate was used as a cross-linking agent so as to have various molecular weights between cross-linking points. The molecular weight between cross-linking points of the protective layer was determined by Mc = 3ρRT / E _h . Here, Mc = molecular weight between crosslinking points, ρ = density of coating film, T
= Temperature at which high temperature elastic modulus is reached, R = gas constant (8.3144J
/ K · mol), E _h = high temperature elastic modulus. Table 3 shows the molecular weight between cross-linking points of various protective layer compositions. These test pieces were subjected to solid printing with a thin film thermal head manufactured by TDK and the density of the printed portion was measured with a Macbeth RD918 type reflection densitometer to evaluate the printing quality. The applied energy from the thermal head was 1 mJ / dot, and the printing was performed at 6 dot / mm. The resin adhesion to the thermal head after printing was confirmed by observing the head with an optical microscope.

[0013]

[Table 3]

Results Table 4 shows the results of the print quality evaluation and the resin adhesion evaluation on the Sn vapor deposition type thermal recording medium in which the protective layer having the respective values of the crosslink density and the molecular weight between crosslink points formed in Example 1 was formed. .

[0015]

[Table 4]

No. 1 having a large Mc value of 6852.7. In the sample of No. 8, although there are many resin head deposits and the printing density is low, the Mc value is as small as 408.1, that is, the crosslinking density is high. Sample No. 10 has no head deposit and has a high print density. Table 5 shows the results of the head adhesion and print density on the first and 5000th sheets when the same pattern was continuously printed 5000 times. According to this, in the sample having a high Mc value, the head adhesion and the print density are good in the initial printing, but the thermal head after passing 5000 sheets has a large resin adhesion and the print density is lowered. This is because the resin deposits deposited on the thermal head become spacing and it becomes difficult for the applied energy to be transmitted, and smooth ball-up of the Sn layer cannot be performed. On the other hand, in the sample having a small Mc value and a high crosslink density, there was almost no difference in the print density between the initial and 5000th sheets, and almost no resin adhesion to the head was confirmed.

[0017]

[Table 5]

From the above results, when the thermosensitive recording medium protective layer using a metal thin film uses a thermosetting resin, the value of the molecular weight between crosslinking points of the protective layer is the resin adhesion to the thermal head and the printing quality (printing quality). It is found that the protective layer above the metal thin film layer has a molecular weight Mc between crosslinking points of 1
It is in the range of 000 to 100, and by setting it to 600 or less, it is possible to form a high-quality image without causing head adhesion, and further to maintain the initial quality even after repeated continuous printing. It was

[0019]

As described above, when the structure of the present invention is adopted, the adhesion of the protective layer resin to the thermal head is reduced, and the print quality due to the head spacing between the thermal head and the recording medium is reduced during printing. Deterioration can be prevented and the life of the thermal head can be extended.

Claims (1)

[Claims] 1. A thermosensitive recording medium in which at least one colored layer, a metal thin film layer and a protective layer are provided on a substrate, and the metal thin film layer is destroyed by heating means to record visible information. A thermosensitive recording medium having a molecular weight between points of 1000 to 100.