JPH079760A - Thermal recording medium - Google Patents

Abstract

PURPOSE:To prevent the contamination of a head without lowering printing characteristics by providing a magnetic recording layer, a metal membrane layer and a protective layer on the single surface of a base material and adding porous silica with a specific particle size to the protective layer in a specific ratio and applying calendering press processing to the protective layer. CONSTITUTION:A thermal recording medium 1 having a printable and recordable surface such as a vapor deposition destruction type prepaid card is constituted by successively laminating a magnetic recording layer 12, a metal membrane layer 13 and a protective layer 14 on the single surface of a base material such as a synthetic resin sheet-like article or synthetic paper. In this case, 10-50wt.%, pref., 20-40wt.% of porous silica with an average particle size of 1-2mum is added to the protective layer 14 and calendering press processing is applied to the protective layer 14. The wt. ratio of the sum solid of the binder and curing agent in the paint used in the protective layer and porous silica is set to 10:2-10:8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor deposition destruction type heat-sensitive recording medium capable of printing and recording on the surface of a medium, and more particularly to a heat-sensitive recording medium which is excellent in printability and metallic luster and is capable of sufficiently removing head stains. .

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium having a magnetic recording layer on a part of the surface of a base material has been widely known and used in various fields.

A typical example of such a magnetic recording medium is a prepaid card used for public telephone service. This prepaid card generally has a structure in which a magnetic recording layer, a masking layer, and a protective layer are laminated in this order on one surface of a substrate, and a printing layer and a protective layer are laminated in this order on the other surface of the substrate. Therefore, recording and erasing of information on the magnetic recording layer and reading of information can be performed by magnetic means.

In recent years, this prepaid card has been
As it is widely used in various fields such as tickets for buses and tickets, express tickets, entrance tickets for amusement parks, purchases of goods, etc., it will be visible on the surface of the prepaid card in a form visible to the user. There has been a demand for printing and recording usage records and balance displays.

In order to meet this demand, in addition to the conventional magnetic recording layer, a thermal recording medium having a thermal recording layer capable of printing and recording visible information using a thermal printing means such as a thermal head is provided. It has come to be used.

In one of the thermal recording media of this type, a metal thin film layer is provided on a part of a base material, and the metal thin film layer is partially melted and broken by heating with a thermal head and provided under the metal thin film layer. There is known a vapor deposition destruction type heat-sensitive recording medium in which print recording is performed by revealing the color of a formed layer, for example, a magnetic recording layer.

This vapor deposition destruction type heat-sensitive recording medium is usually
It has a structure in which a magnetic recording layer, a metal thin film layer, and a protective layer are laminated in this order on one surface of the base material, and visible information is printed and recorded by melting and breaking the metal thin film layer with a thermal head. You can do it. An anchor layer may be provided on the upper layer and / or the lower layer of the metal thin film layer for the purpose of improving print recording characteristics and improving adhesion between the layers.

Generally, the magnetic recording layer has a black or dark brown color, while the metal thin film layer provided on the magnetic recording layer generally has a silver white color or a bluish white color, depending on the metal material used. ing. Therefore, the vapor deposition destruction type heat-sensitive recording medium has a high-grade metallic luster.

When this metal thin film layer is heated from above the protective layer with a thermal head, the metal thin film layer at the heated location is melted and destroyed, and the magnetic recording layer provided below the metal thin film layer appears as a transparent image. The image is recognized as visible information and becomes a printed record. When the color tone of the print recording is not black or dark brown of the magnetic recording layer, it is possible to provide a colored layer between the magnetic recording layer and the metal thin film layer.

In this thermal recording medium, a protective layer is provided on the uppermost layer for the purpose of protecting the surface of the medium and the thermal recording layer. Usually, printing recording, engraving and writing such as a signature with a thermal head are performed on this protective layer.

This protective layer is generally prepared by adding a wax and an extender pigment to a binder to prepare a protective layer-forming coating,
This is coated with a reverse roll coater and then dried to form the uppermost layer of the thermal recording medium. The strength of the protective layer formed is provided by the cured binder.

Of the components added to the coating material for forming the protective layer, the extender pigment is added for the purpose of reducing stains on the thermal head when the protective layer contacts the thermal head.

[0013]

However, in the conventional vapor deposition destruction-type heat-sensitive recording medium, recording is performed by melting and destroying the metal thin film layer, and therefore, compared with the conventional leuco-type heat-sensitive coloring type heat-sensitive recording medium. Requires high printing energy.
Further, the thermal recording medium has a resin component or wax in the protective layer of the thermal recording medium which is transferred to and adheres to the thermal head due to the heat of the thermal head during printing. The number of the vapor deposition destruction type thermal recording medium is larger than that of the color developing type thermal recording medium.

In order to make up for such drawbacks, the extender pigment of the vapor deposition destruction type thermosensitive recording medium is added with more extender pigment than in the case of the leuco thermosensitive coloring type thermosensitive recording medium. However, when the amount of the extender pigment added increases, the amount of the extender pigment present on the metal thin film increases, and the surface of the protective layer becomes rough. Therefore, the metallic luster on the surface of the medium is lost, the high-grade feeling is lost, and the commercial value is significantly reduced.

Further, since the surface of the protective layer becomes rough,
There has been a problem that printing suitability such as printing sensitivity is lowered.

Therefore, according to the present invention, even if a sufficient amount of an extender pigment for removing dirt on the thermal head is added to the coating material for forming the protective layer, the metallic luster is not lost and the printability is excellent. An object is to provide a thermal recording medium.

[0017]

In order to achieve such an object, the present invention provides a heat-sensitive recording medium in which a magnetic recording layer, a metal thin film layer and a protective layer are provided in this order on at least one surface of a substrate. , The protective layer has an average particle diameter of 1 to 2 μm.
The porous silica is contained in an amount of 10 to 50% by weight of the entire protective layer, and the protective layer is calendered.

In the coating material used for forming the protective layer, the weight ratio of the total solid content of the binder and the curing agent to the porous silica is preferably in the range of 10: 2 to 10: 8.

In the heat-sensitive recording medium of the present invention, in order to carry out an effective calendar press working, the temperature is 70 to 100 ° C. and the pressing pressure (linear pressure) is 250.
It is desirable to be ~ 350 Kg / cm.

[0020]

The porous layer having an average particle diameter of 1 to 2 μm is contained in the protective layer in an amount of 10 to 50% by weight based on the entire protective layer, and calender press processing is performed on the protective layer so that the surface of the protective layer has an appropriate roughness and smoothness. A delicate balance is obtained, and as a result,
There is very little dirt on the thermal head during printing, and
It has become possible to form a protective layer that does not lose the metallic luster and that also satisfies printability.

That is, by setting the proportion of the porous silica in the protective layer within the above range, the proportion of the highly heat resistant porous silica on the surface of the formed protective layer is increased, and the binder component in which the porous silica is softened is increased. And, by absorbing the wax component, it becomes possible to improve the heat resistance and thus the sticking resistance. Further, porous silica is Si used in the surface protective layer of the thermal head.
Since it has a hardness slightly smaller than that of O ₂ , it is possible to remove the binder component and the wax component attached to the thermal head without damaging the thermal head.

The above effects can be obtained only when porous silica having an average particle diameter of 1 to 2 μm is used as an extender pigment and the content thereof is 10 to 50% by weight of the whole protective layer. .

Such a protective layer is used as a paint for forming the protective layer such that the weight ratio of the total solid content of the binder and the curing agent to the porous silica is in the range of 10: 2 to 10: 8. Use paint. By setting the content of the porous silica in the coating material within the above range, it is possible to obtain a protective layer containing 10 to 50% by weight of the entire protective layer after the formation of the protective layer.

In the present invention, when the average particle diameter of the porous silica used is less than 1 μm, the thermal head is markedly soiled during printing, and when it exceeds 2 μm,
The resulting protective layer has a low metallic luster.

When the ratio of the porous silica to the total weight of the protective layer is less than 10%, the heat resistance of the protective layer is weakened, and the dirt attached to the thermal head cannot be removed sufficiently. On the other hand, if it exceeds 50%, the smoothness of the protective layer is remarkably deteriorated and the printability is deteriorated.

That is, by calender pressing the protective layer formed by using the coating composition having the above-mentioned specific composition, appropriate heat and pressure are applied to the protective layer to smooth the surface. Therefore, it is possible to form a protective layer having a surface smoothness that recovers the metallic luster that has been lost in the state where the paint is applied, and that also satisfies the printability such as the print sensitivity required for the thermal recording medium. It will be possible.

The calender pressing process is performed at a temperature of 70 to 10
It is preferable to carry out under conditions of 0 ° C. and a pressing pressure (linear pressure) of 250 to 350 Kg / cm.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the thermal recording medium of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view of a thermal recording medium of the present invention. In FIG. 1, a thermal recording medium 1 has a structure in which a magnetic recording layer 12, a metal thin film layer 13 and a protective layer 14 are laminated in this order on one surface of a substrate 11.

As the base material 11, a sheet material made of synthetic resin such as polyethylene terephthalate, polyvinyl acetate, polystyrene, polyvinyl chloride, polycarbonate, polypropylene, or a composite base material or synthetic paper made of these synthetic resins is used. be able to. Substrate 1
The thickness of 1 can be appropriately determined depending on the application of the thermal recording medium.

As the magnetic recording layer 12, those generally used as magnetic recording layers in conventional magnetic recording media can be used. For example, Ba-ferrite, Sr
Coating a magnetic coating material containing a known magnetic material such as ferrite, γ-iron oxide, and γ-iron oxide coated with Co in a binder on the substrate 11 by a known general coating method such as a gravure coating method. Can be formed. As the binder used in the magnetic paint, polyester resin, alkyd resin, vinyl resin, polyurethane resin, or a mixed resin thereof can be used. The mixing ratio of the binder resin and the magnetic material is appropriately set in consideration of the adhesiveness to the base material, the coating film strength, the detection voltage of the magnetic head, etc., and the weight ratio can be in the range of 1: 1 to 1:10. Yes, and a suitable range is preferably 1: 2 to 1: 8. The thickness of such a magnetic recording layer 12 is about 8 to 12 μm.

The metal thin film layer 13 is used as a recording film for visible information, and is melted and destroyed by the heating of the thermal head, and the ground color of the magnetic recording layer 12 therebelow appears to form visible information. is there. This metal thin film layer 1
3 is magnetic recording by a known thin film forming method such as a vacuum deposition method or a sputtering method using a simple substance or an alloy of a low melting point metal such as tin, bismuth, selenium, tellurium, zinc, lead, indium and cadmium. It can be formed on the layer 12. The preferable thickness of the metal thin film layer 13 is about 0.03 to 0.3 μm.

The protective layer 14 is used for physically and chemically protecting the metal thin film layer, and is a cellulose derivative such as ethyl cellulose, hydroxyethyl cellulose, cellulose acetate propionate or cellulose acetate, a polyurethane resin or a polyester. It is formed by using a resin such as a vinyl resin, a vinyl chloride resin, a vinyl acetate resin, an epoxy resin, or an acrylic resin as a binder and a coating material containing porous silica having an average particle diameter of 1 to 2 μm as an extender pigment. .

The protective layer-forming coating material has a porous silica content such that the weight ratio of the total solid content of the binder and the curing agent in the coating material to the porous silica is preferably 10: 2 to 10: 8. Is added, and a curing agent and a wax are further added. This protective layer forming paint,
It is formed by coating on the metal thin film layer 13 by a coating method such as a reverse roll coater and then drying. The preferable thickness of such a protective layer is about 1 to 2 μm. By setting the addition amount of the porous silica within the above range, a protective layer containing 10 to 50% by weight of the porous silica is formed. In the present invention, the porous silica as an extender pigment is contained in the protective layer-forming coating material for the purpose of improving the heat resistance of the protective layer and removing stains adhering to the thermal head.

If the heat resistance of the protective layer is not sufficient, the binder component in the protective layer is softened by the heat of the thermal head during printing and recording, and a sticking phenomenon occurs in which the protective layer and the thermal head are in close contact with each other. When this sticking phenomenon occurs, the softened binder component and wax component move to the thermal head side, and are intervened between the thermal head and the protective layer to form stains. Therefore, the heat of the thermal head is sufficiently magnetically recorded. It will not reach the surface of the medium and will interfere with printing and recording.

In order to improve the heat resistance of this protective layer and to remove the binder component and wax component that have become dirty due to migration to the thermal head side, the present invention uses porous silica, which is a highly heat resistant material. And 10 to 50% by weight, preferably 20 to 50% by weight of the entire protective layer.
The range is 40% by weight.

When the proportion of the porous silica in the protective layer is within the above range, the heat resistance of the protective layer, and thus the sticking resistance can be improved by absorbing the binder component and the wax component in which the silica is softened. . Further, it becomes possible to remove the binder component and the wax component attached to the thermal head.

The wax is contained in the coating material for forming the protective layer, if necessary, for the purpose of improving lubricity, and in view of heat resistance, a synthetic wax having a melting point of 100 ° C. or higher is preferable. As such a synthetic wax, Fischer
Tropsch wax, polyethylene wax, 12-hydroxystearic acid, stearic acid amide, polytetrafluoroethylene, and mixed wax of polytetrafluoroethylene and other wax are suitable, and as a proportion of the coating for forming the protective layer. Is preferably about 100: 5 to 100: 20 by weight ratio of the solid content of the coating material and the wax.

As described above, the protective layer 14 provided on the metal thin film layer 13 has excellent heat resistance and stain removal of the thermal head in the state of being coated and dried, but has a rough surface. Sa (Ra) is 0.5 to 0.
It is in the range of 6 μm and shows a low value in smoothness. Therefore, the printing sensitivity is low and the metallic luster is also lost. In order to improve the lowered printing sensitivity and restore the metallic luster, calender press processing is performed. The preferable conditions of this calendar press working are a temperature of 70 to 100 ° C. and a press pressure (linear pressure) of 25.
It is in the range of 0 to 350 Kg / cm. As a result, external force of heating and pressurization is applied to the protective layer 14, smoothness is improved, and the surface roughness (Ra) is equivalent to that when formed with a protective layer-forming coating material to which porous silica is not added. Is a value,
It is possible to achieve 0.1 to 0.2 μm.

The calender pressing applied to the protective layer 14 is less than 70 ° C. and the pressing pressure (linear pressure) is 250 Kg / cm.
If it is less than 100, the smoothness tends to be inferior, and 100
If the temperature exceeds ℃, the binder component in the protective layer and the metal thin film layer may melt. Also, the press pressure (linear pressure) is 3
If the pressure exceeds 50 kg / cm, the protective layer may collapse, so the pressing pressure in the above range is desirable.

Although not shown in FIG. 1, the substrate 11
A printed layer having an arbitrary pattern can be provided on the other surface of the protective layer 14 or on the other surface. This print layer can be formed by printing a predetermined pattern by a known offset printing method and then curing it by irradiating with ultraviolet rays. The thickness of such a printed layer is 2-3 μm.

Similarly, although not shown in FIG. 1, print recording characteristics and adhesion between the respective layers are provided between the magnetic recording layer 12 and the metal thin film layer 13 and / or between the metal thin film layer 13 and the protective layer 14. An anchor layer can be provided for the purpose of improving the property. This anchor layer is softened by heating of the thermal head, and similarly finely granulates the metal thin film layer material melted by heating and receives it. Such an anchor layer is, for example, a self-oxidizing resin such as nitrocellulose or a solvent-soluble polyurethane-based, polyester-based,
Various thermoplastic resins such as vinyl chloride-based, polystyrene-based, acrylic-based and water-soluble polyvinyl alcohol are used as binders, and wax, curing agent, plasticizer, etc. are added to these as needed, and those dissolved in organic solvent are used. It can be formed by coating the magnetic recording layer 12 and / or the metal thin film layer 13 with a known coating method such as a gravure coating method as an anchor layer forming coating material. The thickness of such an anchor layer is about 0.5 to 8 μm.

Next, a preferred configuration example of the present invention is shown below.

The base material 11 has a width of 410 mm and a length of 80.
White polyethylene terephthalate film having a thickness of 0 m and a thickness of 188 μm [trade name: Lumirror E-24 (manufactured by Toray Industries, Inc.)]
And a reverse roll coater on one side of the base material 11 with a magnetic paint prepared by dispersing Ba-ferrite magnetic powder in a binder solution composed of a vinyl chloride-vinyl acetate copolymer resin, a polyurethane resin and an isocyanate curing agent. Coating and drying to a coercive force of 27 μm with a thickness of 10 μm.
A magnetic recording layer 12 having 50 oersteds, a squareness ratio of 0.85 and a residual magnetic flux density of about 1.4 Mx / cm was formed.

On the magnetic recording layer 12, tin was vacuum deposited by the vacuum deposition method to form a metal thin film layer 13 having a thickness of 0.1 μm.

Next, a protective layer-forming coating material having the following composition was coated on the metal vapor-deposited layer 13 by a reverse roll coater and dried to form a protective layer 14 having a thickness of 2 μm. The content of porous silica in the protective layer 14 is about 32.
%. At this time, the surface roughness Ra of the protective layer 14 is 0.5.
was μm. Composition of coating material for forming protective layer Polyvinyl butyral resin [Product name / S-REC B BM-S (manufactured by Sekisui Chemical Co., Ltd.)] 5 parts by weight Vinyl chloride / vinyl acetate copolymer [Product name / VAGH (manufactured by Union Carbide Co.)] 5 parts by weight Isocyanate curing agent [Product name: Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.)] 0.25 parts by weight Fine powder (porous) silica [Mizukasil P-527 (manufactured by Mizusawa Chemical Co., Ltd.)] 5 parts by weight Toluene / Cellosolve acetate 1: 1 84.25 parts by weight Polyethylene wax (melting point 140 ° C.) [Product name: Ceridust 3910 (manufactured by Hoechst Japan Co.)] 0.5 parts by weight Next, calender pressing (pressing pressure) between heated metal rolls (70 ° C.) (Linear pressure) 300 Kg / cm) and the thermal recording medium 1 having the protective layer 14 with improved surface smoothness.
Was produced. At this time, the surface roughness Ra of the protective layer 14 is 0.
It was 1 μm.

As a comparative example, a heat-sensitive recording medium which was not subjected to calendar press working in the above example was prepared.

The thermal recording media of Examples and Comparative Examples of the present invention produced as described above were evaluated as follows. 1. Reflection Density To compare metallic luster, Macbeth reflection densitometer "RD
918 (manufactured by Macbeth) ”was used to measure the reflection density.

In the example, the value was 0.5, and a sufficient metallic luster was obtained, but in the comparative example, the metallic luster was 0.2 and the metallic luster was lost. 2. Thermal Printing Suitability Printing was carried out on the examples and comparative examples under the following printing conditions, and the effect of dirt on the thermal head was examined.

Test Printing Conditions Dot Pitch 6 dot / mm Printing Power 0.5 W / dot Printing Energy 3.0 mJ / dot In the examples, there was almost no stain on the thermal head, and there was no effect on printing. Similar results were obtained in the comparative example.

In order to examine the printing sensitivity, the printing energy was lowered to 1.0 mJ / dot and the printing states were compared.

In the example, clear printing was possible, but in the comparative example, printing defects such as print defects occurred. 3. Abrasion resistance When a magnetic head with a load of 500 g was brought into contact with the protective layer 1000 times back and forth, no change was observed in the examples and the comparative examples.

The results of the above tests are summarized in Table 1 below.
Shown in. In Table 1, ◯ means good and x means bad.

[0054]

[Table 1] As is clear from the above results, the thermal recording medium of the present invention is capable of sufficiently removing the dirt on the head without lowering the printability and the metallic luster, as compared with the conventional magnetic recording medium shown in the comparative example. I was able to.

[0055]

As described above, according to the present invention, the protective layer of the thermal recording medium contains 10 to 50% by weight of the entire protective layer of porous silica having an average particle diameter of 1 to 2 μm, and Since the protective layer is subjected to calendar press processing, the effect of effectively removing the dirt on the head can be obtained without lowering the printability and metallic luster.

[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]

 1 Thermal recording medium 11 Base material 12 Magnetic recording layer 13 Metal thin film layer 14 Protective layer

Claims (4)

[Claims] 1. A heat-sensitive recording medium in which at least a magnetic recording layer, a metal thin film layer, and a protective layer are provided in this order on one surface of a substrate, wherein the protective layer is porous with an average particle size of 1 to 2 μm. A heat-sensitive recording medium, characterized in that silica is contained in an amount of 10 to 50% by weight of the entire protective layer, and that the protective layer is subjected to calender pressing. 2. The thermal recording medium according to claim 1, wherein the porous silica is contained in an amount of 20 to 40% by weight based on the weight of the entire protective layer. 3. The coating material used for forming the protective layer contains at least a binder, a curing agent, and an average particle size of 1 to 2 μm.
And porous silica, wherein the weight ratio of the total solid content of the binder and the curing agent in the coating material to the porous silica is in the range of 10: 2 to 10: 8. The thermal recording medium according to claim 1. 4. The calender pressing process is performed at a temperature of 70.degree.
100 ° C, press pressure (linear pressure) 250 to 350 Kg / cm
It is performed under the conditions of the range of 1.
Or the heat-sensitive recording medium according to 2.