JPH061078A - Thermal recording medium - Google Patents

Abstract

(57) [Summary] [Structure] A thermal recording medium comprising a base material, a magnetic layer, a metal thin film layer, and a heat-melt coating film layer provided adjacent to at least one surface of the metal thin film layer. The hot-melt coating layer contains colloidal inorganic metal oxide particles. [Effect] Even when contacted with water, acid, or alkali, the metal thin film layer is not corroded, and clear printing can be performed.

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, and more particularly to a heat-sensitive recording medium capable of irreversibly writing visible information such as utilization status information by a heat-sensitive recording means. INDUSTRIAL APPLICABILITY The thermal recording medium of the present invention can be effectively used, for example, for printing numbers or the like corresponding to the magnetic recording contents of various prepaid type magnetic cards to make the magnetic recording contents visible.

[0002]

2. Description of the Related Art With the widespread use of prepaid type magnetic cards, there is an increasing demand for printing characters, numbers, etc. corresponding to magnetic recording contents to make the magnetic recording contents visible. For example, in a prepaid card or the like, when the card is used a plurality of times, it is convenient if the user can visually check the usage contents and amount of money each time, and the balance of the card. In order to cope with such a demand, a heat-sensitive recording medium capable of irreversibly recording information by a heat-sensitive recording means has been developed.

This conventional heat-sensitive recording medium having a heat-sensitive recording layer comprises a magnetic layer, a heat-melting type coating undercoat layer, a metal thin film layer, a heat-melting type coating topcoating layer, and a protective layer on a substrate. It has a structure in which the layers are sequentially laminated. Thermal recording on the metal thin film layer is performed by bringing the thermal head of the thermal recording device into contact with the surface of the protective layer to partially melt the metal thin film layer and form a hole in this portion. By exhibiting black or brown of the lower magnetic layer,
Visually record letters and symbols. The undercoating layer and / or the overcoating layer formed of the heat-melting type coating layer functions to absorb and disperse the molten metal particles to give a visually distinct print.

[0004]

In the conventional thermal recording medium as described above, the metal thin film layer has a thickness of 300 to 1000 Å of a metal such as tin or aluminum which is easily corroded and which reflects visible light well. Since it is used, it is relatively easily corroded (oxidized), and the corroded portion becomes tin oxide or aluminum oxide depending on the use conditions, and the hiding property becomes poor, so that the color of the lower magnetic layer can be seen through. This corroded portion not only deteriorates the appearance of the thermal recording medium because it is distributed irregularly, but also becomes the same state as the printed portion, so that the visible information formed on the irreversible thermosensitive recording layer is visible. It also reduces sex.

An object of the present invention is to provide a thermal recording medium capable of effectively preventing the corrosion of the metal thin film layer, preventing the deterioration of the appearance of the thermal recording medium, and ensuring the visibility of visible information. I am trying.

[0006]

A thermal recording medium according to the present invention comprises a magnetic layer, a metal thin film layer, and a heat-melting type coating film adjacent to at least one surface of the metal thin film layer on one surface of a substrate. In the thermosensitive recording medium provided with a layer, the heat-melting type coating layer is characterized in that the matrix mainly composed of the heat-melting type resin contains colloidal metal oxide particles.

As a result of research on the corrosion of the metal thin film layer, the present inventor has found that by incorporating colloidal metal oxide particles in the heat-melting type coating film layer adjacent to the metal thin film layer, the metal thin film layer is corroded. It was found that this can be effectively prevented.

Although it is not clear yet why the tin adjacent to the hot-melt coating film layer can be prevented from being corroded by containing the colloidal metal oxide particles in the matrix constituting the hot-melt coating film layer. Is densely packed with colloidal metal oxide particles, which results in a denser structure of the heat-melting type coating layer and prevents corrosive substances (water, oxygen, various ions, etc.) from contacting the metal thin film layer. It is thought to be due to acting as a barrier that effectively blocks.

As the colloidal metal oxide particles dispersed in the hot-melt coating layer, colloidal silica, colloidal alumina, colloidal titania, colloidal silicate, etc. can be used alone or as a mixture of two or more kinds. However, the case where colloidal silica is used will be described below.

The colloidal silica added to the hot-melt coating layer is 5 to 40% by weight, preferably 10 to 40% by weight, based on the solid content of the resin. It was found that the corrosion resistance was improved.

When the proportion of the colloidal silica added to the hot-melt coating layer is 5% by weight or less, the colloidal silica is not densely packed in the hot-melt coating layer, so that the effect of improving the corrosion resistance is improved. Is low, and when it is 40% by weight or more, the coating strength of the hot-melt coating layer itself decreases, and cracks are generated.

Another drawback in the case where the proportion of colloidal silica added to the hot-melt coating film layer is 40% by weight or more is that when a metal thin film layer is formed on the hot-melt coating film layer, a metal thin film is formed. In some cases, the vapor deposition surface is oxidized during vapor deposition of the layer, so that vapor deposition burning is likely to occur. When the metal thin film layer is burnt by vapor deposition, the metallic luster of the metal thin film layer is lost, the metal thin film layer turns brown and the appearance is deteriorated, and the contrast between the metal thin film layer and the magnetic layer is deteriorated.

The colloidal silica used in the present invention is
Generally commercially available products may be used. Usually, colloidal silica is classified into several types according to its particle size range, for example, 4 to 6 nm, 7 to 9 nm, 10 to 20.
nm, 40 to 50 nm, etc. Although any of these types can be used in the present invention,
It was found that the smaller the particle size, the more improved the corrosion resistance of the metal thin film layer.

The hot-melt coating film layer may be provided adjacent to either the upper or lower side of the metal thin film layer, or it may be provided adjacent to both upper and lower surfaces of the metal thin film layer so as to sandwich the metal thin film layer. .

In the present invention, not only when the heat-melting type coating layer is not provided on the metal thin film layer, but also when it is provided, the surface is protected and the printing generally performed is facilitated. Therefore, it is desirable to provide a protective layer on the uppermost layer.

As the protective layer, materials usually used for this purpose, such as polyester resin, cellulose resin, urethane resin, vinyl resin, epoxy resin, acrylic resin, etc. A material having good heat resistance can be used. Further, to these resins, phthalic acid ester, fatty acid ester, phosphoric acid ester or the like can be added as a plasticizer, and low molecular weight polyethylene, oleyl amide, stearyl amide, silicone or the like can be added as a substance imparting lubricity. It can be added.

In the heat-sensitive recording medium of the present invention thus constructed, even if the heat-sensitive recording medium comes into contact with water, or acid or alkali, the metal thin film layer is unlikely to corrode, and is uniform and highly reflective for a long period of time. The rate can be maintained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a partial vertical sectional view of a card type thermal recording medium according to an embodiment of the present invention.

In FIG. 1, a magnetic layer 2, a first heat melting type coating layer 3, a metal thin film layer 4, and a second layer are formed on one surface of a substrate 1.
The heat-melting type coating layer 5 and the protective layer 6 are formed in this order.

The structure of each layer is as follows: Substrate 1 : Width 410 mm, thickness 188 μm (nominal) white P
ET film (“E-24” manufactured by Toray) Magnetic layer 2 : Thickness of about 10 μm Magnetic pigment: Ba ferrite Coercive force: 2750 Oe Squareness ratio: 0.85 Residual magnetic flux: about 1.4 Mx / cm Magnetic pigment (Ba ferrite) Was dispersed in a binder and applied by a reverse roll coater to form a film. First hot-melt coating layer 3 : Thickness of about 3 μm Vinyl chloride / vinyl acetate copolymer 20 parts by weight (Union Carbide's “VMCH”) Isocyanate curing agent 1.2 parts by weight (Nippon Polyurethane Industry “ Coronate L ") Methyl ethyl ketone 40 parts by weight Toluene 40 parts by weight Colloidal silica 4 parts by weight (Catalyst Kasei's" OSCAL No. 1132 ") Metal thin film layer 4 : Tin having a thickness of about 1000Å by a vacuum deposition method.
It was vapor-deposited so that. Second heat-melting type coating layer 5 : For the purpose of protecting the metal thin film layer, a hot-melting type coating layer having a thickness of about 2 μm was formed using a reverse roll coater with the following coating composition.

Polyvinyl butyral lure resin 5 parts by weight (“S-REC B BM-S” manufactured by Sekisui Chemical Co., Ltd.) Vinyl chloride / vinyl acetate copolymer 5 parts by weight (“VAGH” manufactured by Union Carbide Inc.) Isocyanate curing agent 0.25 Parts by weight (“Coronate L” manufactured by Nippon Polyurethane Industry) toluene / cellosolve acetate (1: 1) 90 parts by weight colloidal silica 2 parts by weight (“OSCAL No. 1132” manufactured by Catalyst Kasei) The sheet was cut into a sheet having a length of about 580 mm for printing.

This sheet can be printed by printing as it is, but in order to improve the durability, the UV offset ink (T & K) for the OP layer is formed by offset printing.
A protective layer 6 having a thickness of about 1 μm was formed using a UV peeling OP varnish “UP-2” manufactured by TOKA).

(Comparative Example) A recording medium having the same structure as that of the above example was prepared except that colloidal silica was not contained as the heat melting type coating layer (undercoating layer and overcoating layer).

Regarding the recording media of Examples and Comparative Examples,
A comparative test was performed on corrosion resistance and thermal printing characteristics. The results are shown below.

(Corrosion resistance test) The recording medium of the embodiment is 5
When the corrosion state of the metal thin film layer was examined by immersing it in a CH ₃ COOH aqueous solution for 24 hours, no corrosion was observed at all.

When the recording medium of the comparative example was tested under the same conditions, it was found that a black portion was generated in the edge portion and in-plane of the card due to corrosion of the metal thin film layer.

(Thermal print test) Test print condition Dot pitch: 6 dots / m
m Printing power: 0.5 W / dot Printing energy: 3.0 mJ / dot Under the above printing conditions, the recording media of Examples and Comparative Examples were 5
When a square mm pattern was printed and the density was measured with a Macbeth RD918 density tester, both samples had a background density of 0.
25, the color density was 0.95, and no difference was observed.

[0028]

As described above, the thermal recording medium of the present invention is
By adding colloidal metal oxide particles to the heat-melting type coating layer adjacent to the metal thin film layer, the metal thin film layer is effectively protected, and even if it is contacted with not only water but also acid and alkali, The thin film layer is not corroded, very clear printing can be performed, and the appearance is not deteriorated.

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of a thermal recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base material 2 Magnetic layer 3 First heat-melting type coating layer 4 Metal thin film layer 5 Second heat-melting type coating layer 6 Protective layer

Claims (5)

[Claims] 1. A heat-sensitive recording medium comprising a magnetic layer, a metal thin film layer, and a heat-melt type coating layer adjacent to at least one surface of the metal thin film layer on one surface of a substrate,
The heat-melt type coating layer contains a colloidal metal oxide particle in a matrix mainly composed of a heat-melt type resin. 2. The heat-sensitive recording medium according to claim 1, wherein the colloidal metal oxide particles are any one of colloidal silica, colloidal alumina, colloidal titania, and colloidal silicate, or a mixture of two or more thereof. 3. The thermosensitive recording medium according to claim 1, wherein the colloidal metal oxide particles have a particle diameter of 4 to 50 nm. 4. The thermal recording medium according to claim 1, wherein the colloidal metal oxide particles are contained in an amount of 10 to 30% by weight based on the matrix. 5. The thermal recording medium according to claim 1, wherein a protective layer is provided on the uppermost layer.