JPH04197793A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To enhance the properties such as fusion prevention and cushioning of a thermal head by providing a transferable ink layer which melts due to heating on one surface of base film, and a rear layer consisting of specific acrylic resin on the other surface adjoining the thermal head. CONSTITUTION:A rear layer is formed by applying binder resin and a required additive to one surface of a base film, and the binder resin used is acrylic resin with a glass transition temperature (Tg) of 80 deg.C or higher and a molecular weight of 250,000 to 320,000. In addition, a thermally melting ink layer is formed using ink consisting of blended necessary materials, on a base film. Further, to enhance the adhesiveness of the rear layer to the base film, any other adhesive resin, preferably polyester resin is jointly used. If it is desired that the rear layer be highly heat-resistant, it is recommended that 10 to 15 pts.wt. (solid portion) of cross-linking agent of polyisocyanate by added to 100 pts.wt. of binder resin.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more specifically, a novel thermal transfer sheet having a back layer that has excellent thermal head adhesion prevention properties, thermal head sludge prevention properties, cushioning properties, etc. Regarding thermal transfer sheets.

(Prior art and its problems) Conventionally, when printing output prints from computers, word processors, facsimile machines, etc. using a thermal transfer method, a thermal transfer sheet with a heat-melting ink layer provided on one side of a base film is used. has been done.

This conventional thermal transfer sheet has a thickness of 1 mm as a base film.
Using paper such as capacitor paper or paraffin paper with a thickness of 0 to 204 zm, or a plastic film such as polyester or cellophane with a thickness of 3 to 20 μm, a layer of heat-melting ink made by mixing coloring agents such as pigments and dyes with wax is applied. It is manufactured by coating.

In addition, when using a heat-resistant material such as a plastic film as the base film, the thermal head may become sticky during printing, impairing the peeling and slipping properties of the thermal head, or causing the base film to become sticky. Problems such as tearing may occur. For this reason, a method of forming a heat-resistant layer made of a highly heat-resistant thermosetting resin or the like has been proposed.

However, in the case of a back layer made of 5 thermosetting resin, excellent heat resistance can be obtained, but the back layer is very hard and wears out the thermal head, and the material to be transferred is rough like paper. In this case, the thermal transfer sheet is hard and lacks cushioning properties, resulting in white spots and chips in the print.Furthermore, the process requires curing treatment at a relatively high temperature, and the base film There is a risk that the
Processing time of several tens of hours is required at relatively low temperatures, and when using a two-component thermosetting resin, stable coating is difficult and a back layer with a uniform thickness cannot be formed. be.

As a method to solve the above problem, it has been proposed to form the back layer using a thermoplastic resin with a relatively high softening temperature, but in this case, it is difficult to use common inexpensive solvents, and it also has poor cushioning properties. It wasn't enough in that respect either.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a new thermal transfer sheet having a back layer that has excellent properties for preventing thermal head adhesion, cushioning properties, etc.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides a thermal transfer sheet having a transfer ink layer that melts when heated on one side of a base film, and a back layer provided on the other side of the base film that is in contact with a thermal head. is glass transition temperature (Tg) 8
This is a thermal transfer sheet characterized by being made of an acrylic resin having a temperature of 0° C. or higher and a molecular weight of 250,000 to 320,000.

(Function) By using an acrylic resin having a specific Tg and molecular weight as the resin forming the back layer, a new thermal transfer sheet having a back layer with excellent thermal head adhesion prevention properties, cushioning properties, etc. is provided. be done. Furthermore, since a general-purpose solvent can be used as the solvent for the resin, it is advantageous in terms of the process.

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

As the base film used for xylophone light, the same base film used for conventional thermal transfer sheets can be used as is, and other films can also be used, and there are no particular limitations.

Specific examples of preferred base films include polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride,
Polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber,
Examples include plastic films such as ionomers, papers such as condenser paper and paraffin paper, nonwoven fabrics, and base films made of composites of these materials.

The thickness of this base film can be changed as appropriate depending on the material so that its strength and thermal conductivity are appropriate, but the thickness is 0.5 to 50 μm, preferably 3 to 10 μm.
It is m.

The back layer, which mainly characterizes the present invention, is provided on one side of the above-mentioned base film, and it is preferable to use a material with relatively excellent heat resistance, such as a polyethylene terephthalate film, as the base film. preferable.

In the present invention, the above-mentioned 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 acrylic resins are obtained by copolymerizing methyl methacrylate as a main component and other comonomers as necessary.
It can be obtained under a trade name such as 95 and used in the present invention. Even with similar acrylic resins, if the Tg is less than 80"C, the thermal adhesion prevention property will be insufficient even if the molecular weight is in the range of 250,000 to 320,000, and the preferable Tg is 100 to 105 °C.
is within the range of On the other hand, if the molecular weight is less than 250,000, Tg
Even if the molecular weight is 80°C or higher, the cushioning properties of the back layer formed will be insufficient, and if the molecular weight exceeds 320,000, the type of solvent to be used will be limited, and the solution viscosity will become too high, resulting in poor coating properties. becomes worse.

Further, in order to improve the adhesiveness of the back layer to the base film, other adhesive resins, preferably polyester resins, can be used in combination. If superior heat resistance is required for the back layer, 10 to 50 parts by weight (as solid content) of a crosslinking agent such as polyisocyanate can be added to 100 parts by weight of the binder resin.

In addition, if the adhesiveness between the back layer and the base film is insufficient, it is possible to use a small amount of other adhesive resin or to form a brimer layer on the base film in advance using these adhesive resins. Can be used.

Preferred adhesive resins are amorphous linear saturated polyester resins with a glass transition point of 50°C or higher, such as products such as Vylon (manufactured by Toyobo), Elitere (manufactured by Unitika), and Polyester (manufactured by Nippon Gosei Kajikun). Various grades are available on the market, and any of them can be used in the present invention.

As a particularly preferable example, Byron RV290 (manufactured by Toyobo ■, epoxy group-introduced product, molecular weight 20,000 to 25,000,
Tg: 77°C, softening point: 180°C, hydroxyl value: 5 to 8).

In the present invention, when forming the back layer from the above-mentioned materials, waxes, higher fatty acid amides, esters, surfactants, fatty acid metal soaps, alkyl phosphate metal salts, etc. Thermal release agents and lubricants can be included.

In addition, in order to improve the heat resistance of the back layer, urea resin cross-linked powder,
It is preferred to include plusdec pigments such as styrene/acrylic resin crosslinked powder, amino resin crosslinked powder, and silicone powder.

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

To form the back layer, prepare a coating solution by dissolving or dispersing the above materials in a suitable solvent such as acetone, methyl ethyl ketone, toluene, xylene, etc., and apply this coating solution to a gravure coater, roll coater, etc. It is formed by coating with a conventional coating means such as , wire bar, etc. and drying.

The coating amount, that is, the thickness of the back layer is also important, and in the present invention, the solid content is 0.5 g/rrr or less, preferably 0.
．． A back layer having sufficient performance can be formed with a thickness of 1 to 0.5 g/rrr. If the back layer is too thick, the sensitivity during transfer will decrease, which is not preferable.

It is also effective to form a brimer layer made of polyester resin, polyurethane resin, etc. on the base film before forming the above-mentioned back layer.

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

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

The coloring agent is preferably an organic or inorganic pigment or dye that has good properties as a recording material, for example, one that has sufficient color density and does not discolor or fade due to light, heat, temperature, etc.

Alternatively, it may be a substance that is colorless when not heated but develops color when heated, or a substance that develops color when it comes into contact with something coated on the transfer target. In addition to the colorants forming cyan, magenta, yellow, and black, colorants of various other colors can also be used.

The vehicle used includes wax as a main component, and mixtures of wax with drying oil, resin, mineral oil, cellulose, rubber derivatives, and the like.

Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. Furthermore, various waxes such as Fischer-Tropsch wax, various low-molecular-weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolatum, assorted waxes, fatty acid esters, and fatty acid amides are used. It will be done.

Further, in order to provide the hot-melt ink layer with good thermal conductivity and melt transferability, a thermally conductive substance can be blended into the hot-melt ink. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

In addition to hot melt coating, methods for forming a hot melt ink layer directly or indirectly on a base film include:
Examples include hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods of applying the ink. The thickness of the ink layer formed should be determined to balance the required concentration and thermal sensitivity, and is in the range of 0.1 to 30 μm, preferably in the range of 1 to 20 μm.

In the present invention, a surface layer can be further formed on the ink layer. The surface layer forms a part of the transfer film, forms the surface in contact with the transfer paper, seals the printed area of the transfer paper during transfer, prevents scumming, and prevents the ink layer from being covered. It has the function of improving adhesion to transfer paper.

The wax used to form the surface layer is the same substance as the wax used in the hot-melt ink layer described above.

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

The coating of the surface layer, as well as the formation of the ink layer, can also be done by various techniques. In the present invention, the thickness of this layer is preferably 0.1 part m or more and less than 5 μm in order to avoid insufficient sensitivity even when printing energy is low (such as in a high-speed printer).

It is recommended that an appropriate amount of extender pigment be added to the surface layer. This is because bleeding and trailing of printed characters can be better prevented.

Thermal transfer images generally have glossy and beautiful prints, but the documents may become difficult to read, so matte prints are sometimes desirable. 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, etc. is dispersed in a suitable solvent on a base film. It is preferable to form a thermal transfer sheet by coating a matte layer and then coating a heat-melting ink layer. Alternatively, the base film itself may be matted and used (the technique of Japanese Patent Application No. 58-208307, also proposed by the applicant).
.

It goes without saying that the present invention can be applied to thermal transfer sheets for color printing, so multicolor thermal transfer sheets are also included within the scope of the present invention.

(Example) Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Examples 1-2 Ink, 1 Acrylic resin (Dianal BR-85, Tg=105
°C, molecular weight 280,000, made by Mitsubishi Rayon ■) 6.0 parts linear saturated polyester resin (Elytail UE3200,
Unitika ■) 0.3 part zinc stearyl phosphate (LB71830, Sakai Chemical ■)
3.0 parts urea resin crosslinked powder (organic filler, manufactured by Nippon Kasei ■)
3.0 parts melamine crosslinked resin powder (Eposter S, manufactured by Nippon Kasei ■) 1.5 parts dark blue (MEK/) luene = 1/1)
86. Part 2 1 Ink 2 Acrylic resin (Dianal BR-95, Tg=80℃
, molecular weight 320,000, made by Mitsubishi Rayon ■) 6.0 parts styrene/acrylonitrile copolymer (Sepian LD,
Daicel Chemical ■) 6.0 parts linear saturated polyester resin (Byron 200, Toyobo ■)
0.3 parts aluminum stearate (
SA 1000, manufactured by Sakai Chemical ■) 4.5 parts Polyethylene wax (Mark FC113, manufactured by Adeka Argus ■) 1.0 part Fluorocarbon (Mold Vitz F 57, manufactured by Axel Plastic ■) 1.0 part Dark blue 1j (MEK/) Luen = 1/11 87.
After stirring and mixing 2 parts of the above composition, dispersion treatment was performed in a paint shaker for 3 hours, and a diluting solvent (MEK/) luene 1/l) was added.
An appropriate amount of was added to prepare ink for each back layer.

Each of the above inks was applied to a polyester film (thickness 6 μm).
Solid content 0.2g/d and 0.5g1r on one side of Lumirror F-53 (manufactured by Toshi ■) using a wire bar coater.
After coating at a ratio of d, it was dried with hot air to form a back layer.

Separately, a transfer ink composition having the composition shown below was kneaded using a blade kneader for 6 hours while being heated to 100°C.

Bar Ink Ink, paraffin wax 10 parts Carnauba wax 10 parts Ethylene/vinyl acetate copolymer (Sumitate HC-10, manufactured by Sumitomo Chemical ■)
1 part carbon black (GEST 3, manufactured by Tokai Electrode ■) 2 parts The other surface of each base film on which the above-mentioned ink composition was heated at a temperature of 100°C and the above-mentioned back layer was formed by hot-melt roll coating. Then, a thermal transfer ink layer was formed by applying the ink at a coating amount of about 5.0 g/rrr to obtain a thermal transfer sheet of the present invention.

Comparative Example 1 In Example 1, Dianal BR-100 (Tg=105°C, molecular weight 12
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that 10,000) was used.

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

Using the thermal transfer sheets of the present invention and comparative examples obtained above, the output IW/dot, pulse width 0.3 to 4.5 m5ec, and dot density 3 dots/m were produced using a thermal printer.
The results shown in Table 1 below were obtained by printing on plain paper under the conditions of m and examining the thermal adhesion prevention property and print quality.

○: Good ×: Poor (Effect) According to the present invention as described above, by using an acrylic resin having a specific Tg and molecular weight as the resin forming the back layer, the anti-fusing properties of the thermal head and the cushioning properties are improved. A novel thermal transfer sheet having a back layer with excellent properties and the like is provided.

Patent applicant: Dai Nippon Printing Co., Ltd.

Claims (4)

[Claims] (1) In a thermal transfer sheet that has a transfer ink layer that melts when heated on one side of a base film and a back layer on the other side of the base film that contacts the thermal head, the back layer has a glass transition. A thermal transfer sheet comprising an acrylic resin having a temperature of 80° C. or higher and a molecular weight of 250,000 to 320,000. (2) The thermal transfer sheet according to claim 1, wherein the back layer contains a polyester resin. (3) The thermal transfer sheet according to claim 1, wherein the back layer contains polyisocyanate. (4) The thermal transfer sheet according to claim 3, wherein the back layer contains a polyester resin.