JP2880283B2 - 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 novel thermal transfer sheet having a back layer excellent in thermal head fusion prevention, thermal head residue prevention, cushioning, and the like. It relates to a thermal transfer sheet.

(Conventional technology and its problems) Conventionally, when printing output prints of a computer, word processor, facsimile, etc. by a thermal transfer method, a thermal transfer sheet provided with a heat-meltable ink layer on one surface of a base film is used. Have been.

This conventional thermal transfer sheet has a thickness as a base film.
Using a 10-20 μm thick paper such as condenser paper or paraffin paper or a 3-20 μm thick plastic film such as polyester or cellophane, a wax is mixed with a coloring agent such as a pigment or dye to form a hot-melt ink layer. It is manufactured by coating.

Also, when a heat-sensitive material such as a plastic film is used as the base film, the thermal head sticks (sticks) at the time of printing, and the peeling and slipping property of the thermal head is impaired, or the base film is broken. Or other problems occur. For this reason, a method of forming a heat-resistant layer made of a thermosetting resin or the like having high heat resistance has been proposed.

However, in the case of a back layer made of a thermosetting resin, excellent heat resistance is obtained, but the back layer is very hard,
If the thermal head is worn, and the material to be transferred is coarse, such as paper, the thermal transfer sheet is too hard to have sufficient cushioning properties, resulting in white spots and chipping on printing. In addition, a relatively high temperature curing process is required in the process, and the base film may be damaged. At a relatively low temperature, a processing time of several tens of hours is required. When a resin is used, there is a problem that stable coating is difficult and a back layer having a uniform thickness is not formed.

As a method for solving the above problem, it has been proposed to form the back layer using a thermoplastic resin having a relatively high softening temperature. However, in this case, it is difficult to use a general inexpensive solvent, and furthermore, a cushioning property is required. That was not enough.

Accordingly, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a novel thermal transfer sheet having a back layer excellent in anti-fusing property, cushioning property and the like of a thermal head.

(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 comprising a transfer ink layer which is melted by heating on one surface of a base film, and a back layer provided on the other surface of the base film in contact with the thermal head. Has a glass transition temperature (Tg) of 80
A thermal transfer sheet comprising an acrylic resin having a molecular weight of 250,000 to 320,000 or more.

(Function) By using an acrylic resin having a specific Tg and a specific molecular weight as a resin forming the back layer, a novel thermal transfer sheet having a back layer excellent in anti-fusing property, cushioning property, etc. of a thermal head is provided. You. Further, since a general-purpose solvent can be used as the solvent for the resin, the process is advantageous.

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

As the substrate film used in the present invention, the same substrate film as used in the conventional thermal transfer sheet can be used as it is, and other materials can be used without any particular limitation.

Specific examples of preferred base film include, for example, polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chloride rubber, ionomer, etc. Paper, such as plastic film, condenser paper, paraffin paper, and non-woven fabric.
A base film in which these are combined may be used.

The thickness of the base film can be appropriately changed depending on the material so that the strength and the thermal conductivity become appropriate, and the thickness is 0.5 to 50 μm, preferably 3 to 10 μm.

The back layer which mainly characterizes the present invention is provided on one surface of the above-mentioned base film, and as the base film, for example, one having relatively excellent heat resistance such as polyethylene terephthalate film is used. preferable.

In the present invention, the back layer is formed from a binder resin and necessary additives.

The binder resin used in the present invention is an acrylic resin having a Tg of 80 ° C. or higher and a molecular weight of 250,000 to 320,000. Such an acrylic resin is obtained by copolymerizing other comonomer as needed with methyl methacrylate as a main component, and obtained, for example, under the trade names such as DIANAL BR-85 and BR-95. It can be used in the present invention. Even if the same acrylic resin has a Tg of less than 80 ° C., the heat-sealing prevention property is insufficient even if the molecular weight is in the range of 250,000 to 320,000, and the preferred Tg is in the range of 100 ° C. to 105 ° C. . On the other hand, when the molecular weight is less than 250,000, the cushioning property of the back layer formed is insufficient even when the Tg is 80 ° C. or higher.On the other hand, when the molecular weight exceeds 320,000, the type of solvent used is limited, and In addition, the solution viscosity becomes too high, and the coatability deteriorates.

Further, another adhesive resin, preferably a polyester resin, can be used in combination to improve the adhesiveness of the back layer to the base film. When the back layer requires more excellent heat resistance, 10 to 50 parts by weight (as a solid content) of a crosslinking agent such as polyisocyanate can be added to 100 parts by weight of the binder resin.

Further, when the adhesiveness between the back layer and the base film is insufficient, a method of using a small amount of another adhesive resin or a method of previously forming a primer layer on the base film with these adhesive resins is known. Can be used.

A preferred adhesive resin is an amorphous linear saturated polyester resin having a glass transition point of 50 ° C. or higher, and examples thereof include products such as Byron (manufactured by Toyobo), Heritaire (manufactured by Unitika), Polyester (manufactured by Nippon Synthetic Chemical), and the like. Various grades by name are available from the market, all of which can be used in the present invention. As a particularly preferred example, Byron RV290
(Toyobo Co., Ltd., epoxy group-introduced product, molecular weight of 20,000-
25,000, Tg of 77 ° C, softening point of 180 ° C, and hydroxyl value of 5 to 8).

In the present invention, a wax, a higher fatty acid amide, an ester, a surfactant, a fatty acid metal soap, a metal salt of an alkyl phosphate, or the like is used in forming the back layer from the above-mentioned materials as long as the object of the present invention is not hindered. Thermal release agents and lubricants can be included.

Further, in order to improve the heat resistance of the back layer, it is preferable to include plastic pigments such as urea resin crosslinked powder, styrene / acrylic resin crosslinked powder, amino resin crosslinked powder, and silicone powder.

Also, a conductive agent such as carbon black can be added for the purpose of imparting antistatic properties to the back layer.

To form the back layer, the material as described above is acetone,
A coating solution is prepared by dissolving or dispersing in a suitable solvent such as methyl ethyl ketone, toluene, xylene and the like, and the coating solution is applied by a conventional coating means such as a gravure coater, a roll coater, a wire bar and dried. Formed by

The coating amount, that is, the thickness of the back layer is also important.In the present invention, the solid content is 0.5 g / m ² or less, preferably 0.1 to 0.5 g.
A back layer having sufficient performance can be formed with a thickness of / m ² . If the back layer is too thick, the sensitivity at the time of transfer decreases, which is not preferable.

It is also effective to form a primer layer made of a polyester resin, a polyurethane resin, or the like on the base film before forming the back layer.

In the present invention, a heat-meltable ink layer is formed on the other surface of the base film from an ink containing necessary materials.

The ink for forming a hot-melt ink layer used in the present invention comprises a colorant and a vehicle, and may further contain various additives as necessary.

As the coloring agent, among organic or inorganic pigments or dyes, those having good characteristics as a recording material, for example, those having a sufficient coloring density and not discoloring by light, heat, temperature or the like are preferable.

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 polyethylenes, wood wax, beeswax, spermaceti, Ibota wax, wool wax, shellac wax, candelilla wax, petrolatum, partially modified wax, fatty acid ester, fatty acid amide and the like are used. Can be

Further, a heat conductive substance can be added to the heat fusible ink in order to give the heat fusible ink layer good heat conductivity and melt transferability. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

As a method for forming a hot-melt ink layer directly or indirectly on a base film, a hot-melt coat, a hot lacquer coat, a gravure coat, a gravure reverse coat, a roll coat, and the like are applied by various methods. And the like. The thickness of the ink layer to be formed should be determined so as to balance the required density with the thermal sensitivity, and is in the range of 0.1 to 30 μm, preferably 1 to 20 μm.

In the present invention, a surface layer can be further formed on the ink layer. The surface layer forms part of a transfer film,
It forms a surface in contact with the paper to be transferred, has a function of stopping the printed portion of the paper at the time of transfer, preventing background stains, and improving the adhesiveness of the ink layer to the paper to be transferred.

The wax used for forming the surface layer is the same substance as the wax used for the above-mentioned hot-melt ink layer.

The surface layer made of the wax is formed by applying and cooling a wax melt, applying and drying an organic solvent solution containing the wax, and further applying and drying an aqueous dispersion containing the wax particles.

Coating of the surface layer can also be performed by various techniques as in the formation of the ink layer. In the present invention, the thickness of this layer is preferably 0.1 μm so that the sensitivity may not be insufficient even when the printing energy is low as in a high-speed type printer.
m or more and less than 5 μm.

It is recommended that an appropriate amount of extender be added to the surface layer. Thereby, bleeding and tailing of the print can be prevented more favorably.

A thermal transfer image generally has a glossy print and is beautiful, but on the other hand, matte printing may be desirable because the document may be difficult to read. In such a case, for example, as proposed by the applicant (Japanese Patent Application No. 58-208306), an inorganic pigment such as silica, calcium carbonate or the like dispersed in an appropriate solvent is dispersed on a base film. It is preferable to form a thermal transfer sheet by coating and providing a mat layer, and then coating a hot-melt ink layer. Alternatively, the base film itself may be used after mat processing (the technique of Japanese Patent Application No. 58-208307 also proposed by the applicant).

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.

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

Examples 1-2 Ink composition for back layer (1) Acrylic resin (Dianal BR-85, Tg = 105 ° C, molecular weight 280,000, manufactured by Mitsubishi Rayon Co., Ltd.) 6.0 parts Linear saturated polyester resin (Eritaire UE3200, 0.3 parts zinc stearyl phosphate (LBT 1830, manufactured by Sakai Chemical Co., Ltd.) 3.0 parts urea resin crosslinked powder (organic filler, manufactured by Nippon Kasei Co., Ltd.) 3.0 parts melamine crosslinked resin powder (Eposter S, Japan Kasei Co., Ltd.
1.5 parts Solvent (MEK / toluene = 1/1) 86.2 parts Ink composition for back layer (2) Acrylic resin (Dianal BR-95, Tg = 80 ° C, molecular weight)
320,000, Mitsubishi Rayon Co., Ltd. 6.0 parts Styrene / acrylonitrile copolymer (Sebian LD, manufactured by Daicel Chemical Co., Ltd.) 6.0 parts Linear saturated polyester resin (Vylon 200, Toyobo Co., Ltd.) 0.3 parts Stearic acid Aluminum (SA 1000, Sakai Chemical Co., Ltd.)
4.5 parts Polyethylene wax (Mark FC113, manufactured by Adeka Argus Co., Ltd.) 1.0 parts Fluorocarbon (Mold Vitz F57, manufactured by Axel Plastics Co., Ltd.) 1.0 parts Solvent (MEK / toluene = 1/1) 87.2 parts After stirring and mixing, the mixture was dispersed for 3 hours using a paint shaker, and an appropriate amount of a diluting solvent (MEK / toluene = 1/1) was added to obtain ink for each back layer.

Each of the above inks was applied to a polyester film (thickness 6
μm, Lumirror F-53, manufactured by Toray Industries, Inc.) on a surface of a wire bar coater at a solid content of 0.2 g / m ² and 0.5 g / m ² , followed by hot-air drying to form a back layer. .

Separately, a transfer ink composition having the following composition was kneaded for 6 hours while heating to 100 ° C. using a blade kneader.

Ink composition for forming transfer ink layer Paraffin wax 10 parts Carnauba wax 10 parts Ethylene / vinyl acetate copolymer (Smitate HC-10, manufactured by Sumitomo Chemical Co., Ltd.) 1 part Carbon black (Seast 3, manufactured by Tokai Electrode Co., Ltd.) 2 parts) The above ink composition was heated at a temperature of 100 ° C., and the coating amount was adjusted to about 5.0 g / m ² on the other surface of each of the base films on which the back layer was formed by a roll coating method using hot melt. To form a thermal transfer ink layer to obtain a thermal transfer sheet of the present invention.

Comparative Example 1 Instead of Dianal BR-85 in Example 1, Dianal BR-100 (Tg = 105 ° C., molecular weight 120,000) was used.
Other than that was carried out similarly to Example 1, and obtained the thermal transfer sheet of the comparative example.

Comparative Example 2 A thermal transfer sheet of Comparative Example was obtained in the same manner as in Example 1 except that in Example 1, Dianal BR-90 (Tg = 20 ° C., molecular weight 360,000) was used instead of Dianal BR-85. Was.

Using the thermal transfer sheets of the present invention and the comparative examples obtained above, using a thermal printer, output 1 W / dot, pulse width
Printing was performed on plain paper under the conditions of 0.3 to 4.5 msec. And a dot density of 3 dots / mm, and the heat-fusing prevention property and printing quality were examined. The results shown in Table 1 below were obtained.

(Effects) According to the present invention as described above, by using an acrylic resin having a specific Tg and a specific molecular weight as a resin forming the back layer, the back layer having excellent anti-fusing properties and cushioning properties of a thermal head can be obtained. Is provided.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-17192 (JP, A) JP-A-4-189190 (JP, A) JP-A-4-70385 (JP, A) JP-A-2- 192996 (JP, A) JP-A-61-144393 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41M 5/38-5/40

Claims (4)

(57) [Claims] 1. A thermal transfer sheet having a transfer ink layer which is melted by heating on one surface of a base film and a back layer provided on the other surface of the base film in contact with a thermal head, wherein the back layer is A thermal transfer sheet comprising an acrylic resin having a glass transition temperature of 80 ° C. or higher and a molecular weight of 250,000 to 320,000. 2. The back layer comprises a polyester resin.
4. The thermal transfer sheet according to 1. 3. The thermal transfer sheet according to claim 1, wherein the back layer contains a polyisocyanate. 4. The back layer comprises a polyester resin.
4. The thermal transfer sheet according to 1.