JPH0239996A - Thermal transfer sheet and production thereof - Google Patents

Abstract

PURPOSE:To ensure that ground contamination due to friction with an image- receiving material scarcely occurs at the time of transfer, adhesion of an ink layer to a base film is enhanced, exfoliation of the ink layer does not occur, adhesion of the ink layer to be image-receiving material is enhanced, and generation of characters with voids in the image areas thereof or the like is prevented by causing the ink layer to comprise thermoplastic resin particles dispersed in a uniform phase comprising a wax and a thermoplastic resin. CONSTITUTION:A thermal transfer sheet comprises, on a base film 1, a heat- fusible ink layer 2 comprising thermoplastic resin particles 4 dispersed in a uniform phase 3 comprising a wax and a thermoplastic resin. Pigment particles are covered by the wax and the thermoplastic resin, so that ground contamination due to friction with an image-receiving material scarcely occurs at the time of transfer. Since the thermoplastic resin with favorable adhesiveness is used as a component of a vehicle in the ink layer, adhesion of the ink layer to be base film is enhanced, and exfoliation problem does not occur. For the same reason, adhesion of the ink layer to the image-receiving material is enhanced, and generation of characters with voids in the image areas thereof does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal transfer sheet and a method for manufacturing the same, and more particularly to a thermal transfer sheet that provides a high-quality transferred image and a method for manufacturing the same.

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

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 20 μm, or 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.

Thermal transfer sheets as described above are formed by hot-melt coating a molten liquid containing wax and pigments on a base film, but this method requires relatively high temperatures during coating, which causes various problems. There was. As a method for solving these problems, a method has been proposed in which an emulsion ink is prepared by mixing an aqueous emulsion of wax and an aqueous dispersion of a pigment, and the ink is applied and dried using a conventional method.

In this emulsion ink method, when the drying temperature after coating is set to a relatively low temperature, the ink layer is formed as an aggregate of emulsion particles, which results in better ink removal during thermal transfer and improved resolution. Problems with peeling of the ink layer, problems with white spots in transfer printing due to uneven drying, problems such as background stains on the transfer material due to the pigment being exposed on the surface and rubbing against the transfer material during transfer, Furthermore, problems such as poor adhesion to the transfer material occur.

The above adhesion problem can be solved to some extent by using a thermoplastic resin with good adhesion in the wax and increasing the drying temperature of the ink layer to form a uniform layer. The presence of such particles causes a problem in that the film cutting properties of the ink layer during transfer (sharpness of printed characters, etc.) are reduced.

Therefore, an object of the present invention is to provide a thermal transfer sheet that solves the above-mentioned problems.

(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 in which a hot-melt ink layer is provided on a base film, in which the ink layer is formed by dispersing thermoplastic resin particles in a uniform phase consisting of wax and thermoplastic resin. A dispersion in which particles of wax, pigment, and thermoplastic resin are integrated and particles of thermoplastic resin are dispersed in a liquid medium is coated on the characteristic thermal transfer sheet and base film, and then the melting point of the integrated particles is This is a method for producing a thermal transfer sheet characterized by drying at a temperature above and below the melting point of the thermoplastic resin particles.

(Function) By forming a thermal transfer sheet using a dispersion liquid in which wax, pigment and thermoplastic resin are integrated and dispersed in a liquid medium, pigment particles are coated with wax and thermoplastic resin. Therefore, background stains are less likely to occur due to friction with the transfer material during transfer.

Furthermore, since the vehicle contains a thermoplastic resin with good adhesiveness as one component, the adhesiveness to the base film is improved and the problem of foil falling does not occur.

Furthermore, for the same reason, the adhesion to the transfer material is improved, and no characters or the like are generated in the white areas.

Furthermore, by setting the drying temperature of the ink layer during manufacturing to a temperature higher than the melting point of the homogeneous phase of wax and thermoplastic resin and lower than the melting point of the thermoplastic resin particles, the ink layer becomes a uniform layer consisting of wax and thermoplastic resin. Thermoplastic resin particles become dispersed in the ink layer, reducing the film strength of the ink layer and improving film tearability during thermal transfer, enabling sharp, high-resolution printing.

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

The thermal transfer sheet of the present invention, as schematically shown in FIG.
A thermal transfer sheet comprising a heat-fusible ink layer 2 provided on a base film 1, characterized in that the ink layer 2 is made up of thermoplastic resin particles 4 dispersed in a uniform phase 3 made of wax and thermoplastic resin. It is said that

A thermal transfer sheet having such a structure is obtained by coating a specific dispersion liquid (emulsion ink) on a base film and drying it.

The emulsion ink used in the present invention is composed of wax, pigment, thermoplastic resin, and liquid medium as main components, and the wax, pigment, and thermoplastic resin are dispersed in the liquid medium in the form of integrated particles, and further It is characterized by having thermoplastic resin particles dispersed therein.

The wax used in the present invention is a main component of the vehicle of the ink layer of the thermal transfer sheet, and representative examples of the wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. Furthermore,
Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax.

Various waxes include petrolactam, polyester wax, optional wax, fatty acid ester, and fatty acid amide.

Furthermore, most of the pigments used in the present invention are black pigments, of which carbon black is a typical example, but in the case of thermal transfer sheets for color image formation, known pigments of yellow, cyan, and magenta are used. Further, for special purposes, metallic luster pigments, fluorescent pigments, extender pigments, etc. can also be used, and the type of pigment is not particularly limited. Also, dyes can be used similarly.

The thermoplastic resin used in the present invention is a resin with a relatively low melting point, such as ethylene-vinyl acetate copolymer (
EVA), ethylene-acrylic acid ester copolymer (E
E^), polyethylene, polystyrene, polypropylene, polypden, petroleum resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, polyvinyl alcohol, vinylidene chloride resin, methacrylic resin, polyamide, polycarbonate, fluororesin, polyvinyl formal, polyvinyl Examples include butyral, acetylcellulose, nitrocellulose, polyvinyl acetate, polyisobutylene, ethylcellulose, polyacetal, etc., and in particular those with relatively low softening points conventionally used as heat-sensitive adhesives, such as 5
Those having a softening point of 0 to 80°C are preferred.

The liquid medium of the emulsion ink used in the present invention is either an aqueous medium or a non-aqueous medium, and when the liquid medium is an aqueous medium, it becomes an aqueous emulsion ink,
On the other hand, when the liquid medium is non-aqueous, the ink becomes a non-aqueous emulsion ink.

The aqueous medium of the aqueous emulsion ink contains water as a main component, and may contain a water-soluble organic solvent, a surfactant, an antistatic agent, a dispersant, a protective colloid, a leveling agent, an antifoaming agent, and the like.

In the case of water-based emulsion ink, first, the components to be made into integrated particles are heated to a temperature of around 100°C, the whole is made into a molten liquid, mixed uniformly, and then dispersed in an aqueous medium. The components to be made into particles are dissolved and dispersed in a solvent such as methanol, ethanol, propatool, acetone, methyl ethyl ketone, toluene, xylene, ethyl acetate, butyl acetate, etc., and heated if necessary to mix uniformly. An aqueous dispersion of integrated particles is obtained by a method such as dispersing in an aqueous medium, and this is simply mixed with an aqueous dispersion of a thermoplastic resin.

Many aqueous dispersions of thermoplastic resin particles are commercially available.
Any of these commercially available emulsions, latexes, dispersions, etc. can be used, but it is preferable to select a resin whose melting point is about 2 to 20"C higher than that of the above-mentioned integrated particles. As long as the melting point is high. , these resin particles may be a mixture with the wax.

On the other hand, the dispersion medium for non-aqueous emulsion ink is an organic solvent that does not dissolve the wax and thermoplastic resin at room temperature, such as toluene, xylene, cyclohexane, methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, Examples include methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, and the like. Some of these organic solvents can dissolve wax and thermoplastic resin at room temperature when used alone, but by forming a mixture with other poor solvents, the solubility can be adjusted appropriately. These non-aqueous solvents can further contain less than 50% water, small amounts of surfactants, antistatic agents, dispersants, protective colloids, leveling agents, and the like.

The dispersion liquid of the integrated particles contains 1 component of the components to be made into integrated particles.
A method of heating the whole to a temperature of around 00°C to make it into a molten liquid, mixing it uniformly, and dispersing it in a non-aqueous medium. - The components to be formed into image particles are placed in an organic solvent that has low solubility at room temperature. In addition, it can be obtained by a method of heating and dissolving and cooling the stiffness to precipitate particles, or a method of dissolving the components to be integrated in a good solvent and mixing it with a poor solvent to precipitate integrated particles.

In addition, many non-aqueous dispersions of thermoplastic resin particles are commercially available, and any of these commercially available emulsions, latexes, dispersions, etc. can be used.
It is preferable to select a resin whose melting point is about 2 to 20 parts higher than that of the above-mentioned imaged particles. These resin particles may be mixed with the wax as long as the melting point is high.

A non-aqueous emulsion ink can be obtained by simply mixing the above-mentioned dispersion of imaged particles and the above-mentioned dispersion of resin particles.

An ink composition consisting of the above-mentioned components has the following properties: - The weight ratio of wax, pigment and thermoplastic resin in the imaging particles is 5 to 50 parts of pigment and 5 to 1,000 parts of thermoplastic resin per 100 parts of wax. The total solids content in the dispersion preferably ranges from about 10 to 60% by weight.

The weight ratio of the -imaged particles to the thermoplastic resin particles is preferably in the range of 10 to 300 parts per 100 parts of the integrated particles.

The aqueous or non-aqueous emulsion ink obtained by the method described above has wax, pigment, and thermoplastic resin particles integrated into each particle, whereas conventional similar inks have wax and pigment particles dispersed separately. It is characterized by the fact that it is in a solid state, and that thermoplastic resin particles are also mixed therein.

The method for manufacturing the thermal transfer sheet of the present invention using the emulsion ink as described above is to apply the above ink onto a base film and dry it.

As the base film, the same base film used in 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 preferably, for example, 2 to 25 μm.
It is.

Examples of methods for applying the emulsion ink onto the base film include gravure coating, gravure reverse coating, roll coating, air knife coating, and many other methods, and the drying temperature after application may be arbitrary. For example,
If the drying temperature is below the melting point of the integrated particles, an ink layer that maintains the particle shape will be formed, whereas if the drying temperature is above the melting point of the imaging particles and below the melting point of the thermoplastic resin particles, the wax+ An ink layer is formed in which resin particles are dispersed in a uniform layer of resin. The thickness of the ink layer formed is
It 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.

A surface layer may be formed on the ink layer, and the surface layer to be formed is preferably formed from wax as described above, and may be formed by any method, but preferred methods include:
This method uses an aqueous or non-aqueous dispersion containing wax.

When a heat-sensitive material is used for the base film, it is preferable to provide a layer on the surface in contact with the thermal head to prevent sticking of the thermal head. The anti-sticking layer basically includes a heat-resistant resin and a substance that functions as a heat release agent or a lubricant. Heat-resistant resins include synthetic resins with a glass transition point of 60°C or higher, or thermoplastic resins having OH or COOH groups, and a compound having two or more amino groups, or diisocyanate or triisocyanate added to slightly crosslink and cure. Preferably, those that cause Thermal molding agents or lubricants include those that melt when heated, such as waxes and amides, esters, and salts of higher fatty acids, and those that remain solid, such as fluororesin and inorganic substance powders. There is.

By providing such an anti-sticking layer, it is possible to perform thermal printing without causing sticking even on thermal transfer sheets based on heat-sensitive plastic films, and it is possible to print them thermally without causing sticking, thereby reducing the resistance to cutting and ease of processing that plastic films have. You can take advantage of the advantages of

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),
A thermal transfer sheet is formed by coating a base film with an inorganic pigment such as silica, calcium carbonate, etc. dispersed in an appropriate solvent to provide a matte layer, and then coating a heat-melting ink layer. good. Alternatively, the base film itself may be matted and used (this is also the technique of Japanese Patent Application No. 1983-208307 proposed by the applicant).

Since it goes without saying that the present invention can be applied to thermal transfer sheets for color printing, multicolor thermal transfer sheets are also included within the scope of the present invention. Further, as a thermal transfer printer, it can be applied to either a line or serial type.

(Effects) According to the present invention as described above, by creating a thermal transfer sheet using a dispersion liquid in which wax, pigment, and thermoplastic resin are integrated and dispersed in a liquid medium, pigment particles can be mixed with wax and thermoplastic resin. Since it is coated with thermoplastic resin, there is less occurrence of scumming due to friction with the transferred material during transfer.

Furthermore, since the vehicle contains a thermoplastic resin with good adhesiveness as one component, the adhesiveness to the base film is improved and the problem of foil falling does not occur.

Furthermore, for the same reason, the adhesion to the transfer material is improved, and no characters or the like are generated in the white areas.

Furthermore, by setting the drying temperature of the ink layer during manufacturing to a temperature higher than the melting point of the homogeneous phase of wax and thermoplastic resin and lower than the melting point of the thermoplastic resin particles, the ink layer becomes a homogeneous layer consisting of wax and thermoplastic resin. Thermoplastic resin particles become dispersed in the ink layer, reducing the film strength of the ink layer and improving film tearability during thermal transfer, enabling sharp, high-resolution printing.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EVA Flex 310, manufactured by Mitsui Polychemicals) 10 parts paraffin wax (paraffin 15
0F, manufactured by Nippon Seiro) 50 parts carnauba wax 25 parts The above components were melt-kneaded using an attritor at about 100 to 120°C, and the melt-kneaded solution was added to 200 parts of water containing 0.5% nonionic surfactant. The mixture was injected with vigorous stirring using Daysilver, and stirred for an additional 30 minutes to obtain a black aqueous emulsion with a solids content of about 33%. Furthermore, ethylene/
20 parts of an aqueous dispersion (solid content 30%) of vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) was added and mixed to obtain an aqueous ink composition.

The above ink composition was applied to the surface of a polyethylene terephthalate film with a thickness of 3.5 μm at a solid content of 3 g/rn” using a gravure roll method, and then
The thermal transfer sheet of the present invention was obtained by drying at a temperature of 75°C to 75°C.

The above thermal transfer sheet does not peel off the ink layer even when folded, and does not stain the filter paper even if the surface is lightly rubbed with filter paper.Also, high-quality paper with high smoothness is used as the transfer paper, and a commercially available thermal transfer sheet is used. When thermal transfer printing was performed using the head, printing with excellent abrasion resistance was obtained, and no background staining occurred on the transfer paper.

Example 2 Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 10 parts paraffin wax (paraffin 15
0F, manufactured by Nippon Seiro) 50 parts carnauba wax 25 parts The above ingredients were melted and kneaded using an attritor at about 100 to 120°C,
This melted and kneaded solution was poured into 200 parts of isopropyl alcohol containing 0.5% nonionic surfactant while vigorously stirring with a Daysilver, and stirred for an additional 30 minutes until the solid liquid was about 33% black. A non-aqueous emulsion was obtained. Furthermore, 20 parts of an isopropyl alcohol dispersion (solid content 30%) of an ethylene/vinyl acetate copolymer (EV^Flex 31O1 manufactured by Mitsui Polychemicals) was added and mixed to obtain a non-aqueous ink composition.

The above ink composition is applied to the surface of a polyethylene terephthalate film with a thickness of 3.5 μm at a solid content of 3 g/d using a gravure roll method, and then dried at a temperature of about 70 to 75° C. to achieve thermal transfer of the present invention. Got a sheet.

The above thermal transfer sheet does not peel off the ink layer even when folded, and does not stain the filter paper even if the surface is lightly rubbed with filter paper.Also, high-quality paper with high smoothness is used as the transfer paper, and a commercially available thermal transfer sheet is used. When thermal transfer printing was performed using the head, printing with excellent abrasion resistance was obtained, and no background staining occurred on the transfer paper.

Example 3 EVA Flex 310 and Diablack G were melt-kneaded at a weight ratio of 1:1 to form an aqueous emulsion with a solid content of 30% in the same manner as in Example 1.

20 parts of the emulsion was added to 100 parts of the 33% black aqueous emulsion of Example 1, and the same procedure as in Example 1 was carried out to obtain a thermal transfer sheet of the present invention having excellent stain resistance and abrasion resistance. Ta.

Example 4 The emulsion in Example 3 was an isopropyl alcohol emulsion, and the drying temperature was 100 to 120°C.
A thermal transfer sheet of the present invention having excellent stain resistance and abrasion resistance was obtained in the same manner as in Example 3 except for the following.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a thermal transfer sheet of the present invention. 1: Base film 2: Ink layer Figure 1 3: Uniform phase 4: Particles

Claims (5)

[Claims] (1) A thermal transfer sheet comprising a heat-melting ink layer provided on a base film, characterized in that the ink layer is made up of thermoplastic resin particles dispersed in a homogeneous phase consisting of wax and thermoplastic resin. Heat transfer sheet. (2) On the base film, a dispersion liquid in which particles in which wax, pigment, and thermoplastic resin are integrated and particles of thermoplastic resin are dispersed in a liquid medium is coated, and then A method for producing a thermal transfer sheet, comprising drying at a temperature below the melting point of thermoplastic resin particles. (3) The weight ratio of wax, pigment and thermoplastic resin in the integrated particles is 5 to 50 parts pigment per 100 parts wax;
The thermal transfer sheet and manufacturing method according to claims 1 and 2, wherein the thermoplastic resin is in a range of 5 to 1,000 parts. (4) The thermal transfer sheet and manufacturing method according to Claims 1 and 2, wherein the thermoplastic resin particles contain 10 to 500 parts of pigment per 100 parts of the resin. (5) The thermal transfer sheet and manufacturing method according to Claims 1 and 2, wherein the weight ratio of the integrated particles to the thermoplastic resin particles is in the range of 10 to 300 parts per 100 parts of the integrated particles.