JP3009057B2 - Thermal transfer sheet - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thermal transfer sheet, and more particularly, to a thermal transfer sheet capable of forming an image with excellent print quality even when the transfer target paper is a relatively coarse plain paper. Regarding the sheet.

(Conventional technology and its problems) Conventionally, when printing an output print of a computer, a word processor, a facsimile, or the like by a thermal transfer method, a thermal transfer sheet provided with a transfer ink layer on one surface of a base film is used. I have.

The above-mentioned conventional thermal transfer sheet is manufactured by using a polyethylene terephthalate film having a thickness of 3 to 20 μm as a base film, and providing a transfer ink layer obtained by mixing a coloring agent such as a pigment or a dye with wax by coating.

One drawback of the above thermal transfer sheet is that when printing on a relatively coarse-grained transfer paper such as plain paper or recycled paper, the ink transfer is insufficient, resulting in printing with so-called white spots and chipping, resulting in high quality images. There is a problem that cannot be formed.

Various proposals have been made to solve such problems, but all of these methods have the problem that the configuration of the thermal transfer sheet is complicated and the cost is high.

Another problem is that the use of high-strength polyester film as the base film results in poor shredding properties even when trying to shred to prevent secret leakage from the used thermal transfer sheet. Problem.

As a method for solving the above problems, the present applicant has proposed to use a polypropylene film having specific properties as a base film. According to this proposal, many problems of the prior art are solved, but the polypropylene film has low adhesion of the ink layer and / or the back layer, and causes problems such as foil drop or powder drop of the ink layer and the back layer. .

Accordingly, an object of the present invention is to solve the above-mentioned drawbacks and to provide a thermal transfer sheet capable of forming an image with excellent print quality even with relatively coarse paper.

(Means for Solving the Problems) The above object is achieved by the present invention described below. That is,
The present invention provides a thermal transfer sheet having a transfer ink layer formed on one surface of a base film, wherein the base film has a surface tension of 35 to 40 dyne / cm by corona-treating at least the transfer ink layer surface. A heat transfer sheet, characterized in that the heat transfer sheet is a polypropylene film.

(Function) By using a polypropylene film having a surface tension of 35 to 40 dyne / cm by corona-treating at least the surface of the transfer ink layer as a base film, the adhesiveness of the ink layer is excellent and the thermal head is further marked. Pressure is sufficiently transmitted to a material to be transferred, and a thermal transfer sheet capable of forming an image with excellent print quality even with relatively coarse paper is provided.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

The thermal transfer sheet of the present invention may be the same as a conventional thermal transfer sheet, except that the base film used is a polypropylene film that has been corona-treated to have a specific range of surface tension, and is not particularly limited.

The corona treatment of the polypropylene film may employ a conventionally known method, and the surface of the untreated polypropylene film usually has a surface tension of 30 dyne / cm, but in the present invention, the base film for forming the ink layer is used. By setting the surface tension of the surface in the range of 35 to 40 dyne / cm, the adhesiveness with the ink layer is improved, and powder and foil falling are effectively prevented.

In addition, when both surfaces are corona-treated in the above, the blocking of the polypropylene film itself becomes remarkable. Therefore, it is preferable that at least one surface is provided with irregularities of about 0.1 to 0.5 μm to form a mat. This matting may be performed before or after corona treatment.

The polypropylene film used as the base film in the present invention may be any conventionally known polypropylene film, but a preferred material has a breaking strength of 15 to 35 kg in the MD direction, 15 to 35 kg in the TD direction, and an elongation percentage of MD. Direction 40
~ 200, TD direction 40 ~ 200 and Young's modulus is MD direction 200
~600kg / cm ^2, a TD direction 200 to 600 kg / cm ² of polypropylene film. If the breaking strength is less than the above range, the strength of the base film is insufficient and the printer may be damaged during use.On the other hand, if it exceeds the above range, the film becomes hard and the printing pressure of the thermal head is reduced. Insufficient transmission to the skin and shredder after use. Similarly, when the elongation is less than the above range, the printing pressure of the thermal head is hardly transmitted to the paper, and when the elongation exceeds the above range, the resolution of printing deteriorates. The thickness of the base film is preferably 3 to 7 μm.

In the present invention, the transfer ink layer is formed on the surface of the base film from an ink containing necessary materials. The transfer ink layer in the thermal transfer sheet of the present invention comprises a colorant and a vehicle, and may further contain various additives as necessary. The colorant is preferably an organic or inorganic pigment or dye having good properties as a recording material, for example, a colorant having a sufficient coloring density and not discoloring by light, heat, temperature, or the like. In addition, a substance which is colorless when not heated but develops a color when heated, or a substance which develops a color when it comes into contact with a substance applied to a transfer target body may be used. In addition to the colorants that form cyan, magenta, yellow, and black, colorants of various other colors can also be used.

As the vehicle, a mixture of wax as a main component, and other components such as a wax and a derivative of a drying oil, a resin, a mineral oil, cellulose, and rubber is used.

Representative examples of the wax include microcrystalline wax, carnauba wax, and paraffin wax. Furthermore, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylene, wood wax, beeswax, spermaceti, Ibota wax, wool wax, shellac wax, candelilla wax, petrolactam, partially modified wax, fatty acid ester, fatty acid amide, etc. Used.

Further, in order to impart good thermal conductivity and melt transfer property to the transfer ink layer, a heat conductive substance can be added to the hot melt ink. Examples of such a substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

The thickness of the ink layer to be formed should be determined so that the required density and thermal sensitivity can be harmonized. For example, in the case of one-time printing, the thickness of the ink layer is about 2 to 7 μm. The thickness is preferably in the range of about 5 to 20 [mu] m for printing many times. The melt viscosity of such an ink layer is preferably in the range of 50 to 3,000 cps at 100 ° C.

In the present invention, a layer made of a heat-sensitive adhesive, that is, a thermoplastic resin having a relatively low melting point can be formed on the surface of the ink layer. Examples of such a heat-sensitive adhesive include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylate copolymer (EEA), polybutene, petroleum resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate and the like. Is formed from a resin having a higher melt viscosity than the vehicle used for forming the ink layer. The heat-sensitive adhesive layer may be colored in the same manner as the ink layer. The thickness of the formed heat-sensitive adhesive layer may be, for example, about 0.5 to 2 μm. The melt viscosity of such a heat-sensitive adhesive layer is preferably in the range of 15 to 1,200 in terms of melt index.

As a method of forming the ink layer and the heat-sensitive adhesive layer, a hot lacquer coat,
A gravure coat, a gravure reverse coat, a roll coat and many other means can be used.

In the present invention, a sealing layer can be further formed on the surface of the heat-sensitive adhesive layer. Such a sealing layer is formed by selecting a wax having a lower melt viscosity than the vehicle used for forming the ink layer, and the rough surface of the material to be transferred at the time of printing is stopped by the sealing layer.

The sealing layer may be formed by the same method as the formation of the ink layer and the heat-sensitive adhesive layer, or may be formed by a method using an aqueous emulsion containing wax. For example,
By applying a water emulsion of the wax on the heat-sensitive adhesive layer and drying at a temperature lower than the melting point of the wax, the sealing layer is formed while maintaining the particle shape of the wax.

In the present invention, the thickness of the sealing layer formed as described above is preferably 0.1 μm or more and less than 5 μm so that the sensitivity does not become insufficient even when the printing energy is reduced as in a high-speed type printer. is there. The melt viscosity of such a sealing layer is preferably in the range of 5 to 40 cps at 100 ° C.

Since the polypropylene film used as the base film is relatively weak to heat, it is preferable to provide a back layer having a heat-resistant lubricating property to improve the sliding property of the thermal head and prevent sticking on the surface in contact with the thermal head. preferable. The back layer has a heat-resistant resin and a substance acting as a heat releasing agent or a lubricant as basic constituent components. By providing such a back layer, thermal printing can be performed without sticking even on a thermal transfer sheet based on a plastic film that is vulnerable to heat, making the plastic film difficult to cut and easy to process. You can take advantage of such advantages.

Needless to say, the present invention can be applied to a thermal transfer sheet for color printing, and a multicolor thermal transfer sheet is also included in the scope of the present invention. Further, the thermal transfer printer can be applied to either a line or serial type.

Examples Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following description, parts and% are based on weight unless otherwise specified.

Example 1 A transfer ink composition having the following composition was kneaded for 6 hours while heating to 90 ° C. using a blade kneader.

Ink composition for transfer ink layer formation Paraffin wax 8 parts Carnauba wax 2 parts Ethylene / vinyl acetate copolymer 1 part Carbon black 2 parts Heat the above ink composition at a temperature of 100 ° C, and roll-back with hot melt A heat-resistant lubricating layer is formed on the surface, and the ink-coated surface is corona treated to reduce the surface tension to 36 dyne / c.
3.8 m thick polypropylene film (trade name "Trefane 4D" manufactured by Toray Industries, Inc.)
The composition was applied so as to be 4 g / m ² to form a thermal transfer ink layer.

The melt viscosity of this ink layer at 100 ° C was 100 cps.
Met.

Next, the following composition was applied on the surface of the ink layer in the same manner as the ink layer at a coating amount of 1 g / m ² to form a heat-sensitive adhesive layer.

The heat-sensitive adhesive layer had a melt index of 400.

Coating composition for heat-sensitive adhesive layer Ethylene / vinyl acetate copolymer (Evaflex 41
0) 8 parts carbon black 2 parts
The thermal transfer sheet of the present invention was obtained by coating at a rate of 5 g / m ² to form a sealing layer.

The melt viscosity at 100 ° C. of the sealing layer was 28 cps.

Example 2 As a polypropylene film in Example 1, a 4.3 μm-thick polypropylene film (trade name “Trefane 4X”, manufactured by Toray Industries, Inc.) having a surface tension of 36 dyne / cm by corona-treating the ink-coated surface was used. A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the thermal transfer sheet was used.

Example 3 The polypropylene film in Example 1 was subjected to corona treatment on the ink-coated surface and the back surface to reduce both surface tensions to 36.
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that a dyne / cm-thick 5.8 μm-thick polypropylene film (trade name “Trefane 6D”, manufactured by Toray Industries, Inc.) was used.

The physical properties of the polypropylene film before the corona treatment used in the above examples are as shown in Table 1 below.

Example 4 The procedure of Example 3 was repeated, except that the surface coated with the ink layer of the double-sided corona treatment “Trefane 4D” in Example 3 was matted, and a back slip layer made of a polyurethane resin and a lubricant was formed on the back. Thus, the thermal transfer sheet of the present invention was obtained.

Comparative Example 1 The base film in Example 1 was 4.5 μm thick.
Polyester film (trade name "F53", Toray Industries, Inc.)
The heat transfer sheet of the comparative example was obtained in the same manner as in Example 1 except that the heat transfer sheet was used.

Comparative Example 2 A thermal transfer sheet of Comparative Example was obtained in the same manner as in Example 6, except that untreated "Trefane 4D" was used as the base film in Example 4.

Evaluation Example 1 Using the thermal transfer sheets of Examples 1 to 4 and Comparative Example 1, printing was performed under the following printing conditions, and printing quality was evaluated. The results shown in Table 2 below were obtained.

Printing conditions Apparatus: Toshiba simulator equipped with a thin-film thermal head Printing energy: 0.8 mJ / dot (constant) Transfer object: Plain paper (4 types of Beck smoothness of 20, 25, 30, and 50 seconds) Evaluation Example 2 When the adhesiveness of the ink layer and the back layer of the thermal transfer sheets of Examples 1 to 4 and Comparative Example 2 were examined, the results shown in Table 3 below were obtained.

(Effects) According to the present invention as described above, by using a polypropylene film having a surface tension of 35 to 40 dyne / cm by corona-treating at least the surface of the transfer ink layer as a substrate film, the adhesion of the ink layer can be improved. A thermal transfer sheet is provided which is excellent in printing properties, furthermore the printing pressure of the thermal head is sufficiently transmitted to the material to be transferred, and is capable of forming an image with excellent print quality even on relatively coarse paper.

Further, in a preferred embodiment, by using a polypropylene film having specific physical properties, the printing pressure of the thermal head is sufficiently transmitted to the material to be transferred, and an image having excellent print quality can be obtained even with relatively coarse paper. A heat transfer sheet that can be formed is provided.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/38-5/40

Claims (3)

(57) [Claims] 1. A thermal transfer sheet having a transfer ink layer formed on one surface of a base film, wherein the base film has a surface tension of 35 to 40 dyne / cm by corona-treating at least the transfer ink layer surface. A thermal transfer sheet characterized in that it is a polypropylene film. 2. The thermal transfer sheet according to claim 1, wherein both surfaces of the polypropylene film are corona-treated. 3. The breaking strength MD direction of a polypropylene film.
15-35kg, TD direction 15-35kg, elongation MD direction 40-200, TD
The thermal transfer sheet according to claim 1 which is the direction 40 to 200 and a Young's modulus MD direction 200~600kg / mm ^2, TD directions 200 to 600 kg / mm ^2.