JPH082719B2 - Thermal transfer sheet - Google Patents

Description

Detailed Description of the Invention

 Purpose of the invention

[Industrial applications]

The present invention relates to a thermal transfer sheet which is useful for preventing forgery of important documents such as securities and for preventing copying of confidential documents.

[Prior art]

Hitherto, hidden printing with colorless fluorescent ink has been performed as one means for preventing forgery and copying of documents.
Text and images made with fluorescent ink can be read only when the printed document is irradiated with ultraviolet light. However, the printing method cannot record arbitrary variable information, and the cost is high when the number of sheets is small. Therefore, there has been a demand for a means for easily printing variable information. One of such printing means is thermal transfer, which has been widely used recently as a printing means for word processors and computers.

[Problems to be Solved by the Invention]

It is an object of the present invention to provide a heat-sensitive transfer sheet which can easily print variable information in response to the above-mentioned demand and which is useful for preventing forgery of important documents such as securities and for preventing copying of confidential documents. Structure of the invention

[Means for solving problems]

The heat-sensitive transfer sheet of the present invention is a heat-sensitive transfer sheet having a heat-meltable ink layer on one surface of a base film, wherein at least a part of the heat-meltable ink layer irradiates a colorless heat-meltable ink with ultraviolet rays. It is characterized in that it contains a colorless fluorescent agent which emits fluorescence upon receiving. An embodiment in which a colorless hot-melt ink containing a colorless fluorescent agent that emits ultraviolet light is applied to a part of the base film, and the remaining portion is applied a hot-melt ink containing a colorant , Included in the present invention. In addition to the usual black and blue, red,
It goes without saying that a colorant for color printing such as yellow may be used. The present invention may have many aspects. For example, a heat-meltable ink containing a colorant and a colorless heat-meltable ink containing a colorless fluorescent agent are alternately part-coated in a direction perpendicular to the longitudinal direction of the heat-sensitive transfer sheet, or a colorant is contained. And a colorless hot-melt ink containing a colorless fluorescent agent are part-coated in parallel with each other in the longitudinal direction. As a material for the base film, a commonly used material may be used. Specifically, plastic films such as polyester, polypropylene, cellophane, acetate, and polycarbonate, and papers such as condenser paper and paraffin paper are used. The heat-meltable ink is prepared by mixing a synthetic resin, a wax, and if necessary, a solvent and a colorant. As the synthetic resin, an appropriate one is used alone or as a mixture in consideration of the voltage and melting point of the thermal head. Specific examples include polyethylene, polystyrene, polypropylene, polybutene, petroleum resin, vinyl chloride resin, polyvinyl alcohol, vinylidene chloride resin, methacrylic resin, polyamide, polycarbonate, fluororesin, polyvinyl formal, polyvinyl butyral, acetyl cellulose plastic, nitrocellulose. , Polyacetal and the like. Waxes include beeswax, whale wax, ivowa wax, wool wax, shellac wax, carnauba wax, montan wax, paraffin wax, candelilla wax,
Appropriately selected and used from petrolactam, microcrystalline wax and the like. The solvent is used when the hot-melt ink composition is an ink that can be applied by a usual printing method. Examples are benzene, xylene, toluene, trichlene, white spirit, ethyl acetate, n-butyl acetate, methanol, ethanol, isopropanol, n-butanol, ethylcyclohexane, methyl ethyl ketone, ethyl cellosolve, butyl cellosolve, cyclohexanone. In particular, methyl ethyl ketone, ethyl acetate, methanol, ethanol, xylene and toluene are often used. The colorant is preferably an organic or inorganic dye or pigment suitable for a recording material, that is, a dye having a sufficient coloring density and not discolored by light, heat, humidity or the like. Further, it may be a substance that is colorless when not heated, but that develops color when heated, or a substance that develops color when contacted with the transfer paper. In addition to the colorants forming cyan, magenta, yellow, and black colors, colorants of various other colors can be used. The heat-meltable ink layer is formed by applying the above ink composition by any means such as a hot melt coating method and a gravure coating method. The colorless fluorescent agent is zinc sulfide, zinc silicate, zinc oxide, zinc cadmium sulfide, calcium sulfide, an inorganic substance such as calcium tungstate, or a stilbene system such as diaminostilbenzylsulfonic acid, a diaminodiphenyl system, an imidazole system, a thiazole system, Organic dyes or pigments such as coumarin type, naphthalimide type and thiophene type are used. When a plastic film is used as the base film, it is preferable to provide a layer for preventing sticking to the thermal head on the other side, that is, on the side opposite to the heat-meltable ink layer and in contact with the thermal head. The sticking prevention layer is formed by applying a composition comprising a heat-resistant resin, a substance that acts as a thermal release agent or a lubricant, and a solvent. Heat release agents or lubricants are those that melt when heated, such as amides, esters, and salts of waxes and higher fatty acids, and those that remain solid, such as fluororesins and inorganic powders. Some are useful. Suitable solvents include resins, waxes,
Methyl ethyl ketone, ethyl acetate, methanol, ethanol, xylene, toluene, etc., depending on the thermal release agent or lubricant. The sticking prevention layer is also formed by any means such as a gravure coating method.

[Work]

In the heat-sensitive transfer sheet of the present invention, one using an ink layer containing a colorless fluorescent agent in a colorless heat-fusible ink, when printed with a thermal head, the information in this printed portion is hidden under visible light. Will be printed. As described above, this hidden print emits fluorescence when irradiated with ultraviolet rays, so that information can be read. In addition, hidden information is not copied because it cannot be read by a copying machine. The copy is known to be fake as it no longer fluoresces. In this way counterfeiting is prevented. When a colorless fluorescent agent is added to a heat-meltable ink containing a colorant, the information on this printed part can be read under visible light when printed with a thermal head, but it emits fluorescence when irradiated with ultraviolet light, so it is a true or false It is possible to determine. That is, it can be seen that the one that emits fluorescence is the original, and the one that is not is the copy, which is useful for preventing copying of confidential documents.

Example 1 A hot-melt ink prepared by mixing 10 parts of 145 ° F paraffin wax and 2 parts of a colorless organic fluorescent agent "Ubitech OB" (Ciba Geigy) on a base film of a polyester film having a thickness of 6μ, A thermal transfer ribbon was prepared by coating to a thickness of about 5μ. Using this ribbon in a commercially available thermal transfer printer, and the part where the check face is open,
When characters were printed with a thermal head on both of the printed parts of the face of the ticket, the characters could not be seen under visible light, but the characters could be read by irradiating with ultraviolet light.

[Example 2] On the same base film as in Example 1, 1.5 parts of carbon black was added to 10 parts of 150 ° F paraffin wax, and 1.5 parts of inorganic fluorescent agent ZnO / Zn "GOF" (Nemoto Special Chemical Co., Ltd.) was kneaded. The heat-meltable ink incorporated was coated to a thickness of about 5 μm to prepare a heat-sensitive transfer ribbon. When this ribbon was used in a commercially available thermal transfer printer and the text was printed with a thermal head, the appearance of the text is the same as the appearance of ordinary heat-transferred text, but it turns out to be the original because it emits fluorescence when irradiated with ultraviolet rays. It was a thing. EFFECTS OF THE INVENTION By using the heat-sensitive transfer sheet of the present invention, information can be easily recorded even with only one sheet, so that arbitrary variable information can be recorded and additional printing on a commercialized product is easy. It is useful for preventing forgery of valuable securities, especially important documents such as commuter passes, betting tickets, gift certificates, gift certificates, book coupons, checks, bills and other vouchers, and invoices, and prevention of copying of confidential documents.

Claims (3)

[Claims] 1. A heat-sensitive transfer sheet having a heat-meltable ink layer on one surface of a base film, wherein at least a part of the heat-meltable ink layer is irradiated with ultraviolet rays on a colorless heat-meltable ink. A heat-sensitive transfer sheet comprising a colorless fluorescent agent that emits fluorescence. 2. A part of the heat-meltable ink layer is a colorless heat-meltable ink containing a colorless fluorescent agent that emits fluorescence when irradiated with ultraviolet rays, and the remaining part is a heat-meltable ink. The heat-sensitive transfer sheet according to claim 1, which further comprises a colorant. 3. The heat-sensitive transfer sheet according to claim 1 or 2, wherein the base film is a plastic film, and a layer for preventing sticking to the thermal bed is provided on the other surface.