JPH01113286A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To ensure that ground contamination does not occur even upon high- speed thermal transfer and clear printing can be performed even on a transfer recording paper having a low surface smoothness, by composing a surface layer of a wax and a thermoplastic resin, in a thermal transfer sheet comprising a transferrable film. CONSTITUTION:A thermal transfer sheet comprises a heat-fusible ink layer 2 on one side of a base film 1, and a surface layer 3 comprising a wax and a thermoplastic resin which layer is provided on the ink layer 2. A heat-fusible ink tto be used comprises a coloring agent and a vehicle. The amount of the thermoplastic resin used is preferably 5-75 pts.wt. per 100 pts.wt. of the wax. With the thermoplastic resin thus used, in addition to the wax, for forming the surface layer, adhesiveness of an ink layer to a transfer recording material is further enhanced, and high-speed printing can be performed without causing ground contamination or bleeding, even on a transfer recording paper having a rough surface.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to the improvement of heat-sensitive transfer sheets, and more specifically, the present invention relates to the improvement of heat-sensitive transfer sheets, and more particularly to the prevention of scumming of transfer paper due to a heat-melting ink layer, and the improvement of coatings with low surface smoothness. The present invention relates to a heat-sensitive transfer sheet that can provide high-quality printing even on transfer paper.

(Prior Art) Conventionally, when printing output from a computer or a word processor using a thermal transfer method, a thermal transfer sheet having a base film and a heat-melting ink layer provided on one side has been used. This conventional thermal transfer sheet uses paper such as capacitor paper or paraffin paper with a thickness of 10 to 20 μm, or a paper with a thickness of 3 to 2 μm as a base film.
It is manufactured by coating a 0 μm plastic film such as polyester or cellophane with a layer of heat-melting ink made by mixing wax with a coloring agent such as a pigment or dye.

When output printing is performed on transfer paper using a conventional thermal transfer sheet, the ink layer comes into direct contact with the transfer paper surface, and smudges often occur in non-printing areas due to the 1 m layer of both.

Further, although the thermal transfer method can print on plain paper, it cannot print clearly on all kinds of plain paper. When the smoothness of the transfer paper is expressed by Bekk smoothness,
Calendar-treated high-quality paper or coated paper that exhibits a value of 100 seconds or more provides the best printing, and even high-quality paper that takes about 50 seconds can provide sufficient print quality. However, if a transfer paper with low smoothness that does not reach 50 seconds is used, the sharpness of the print will decrease.1 This is because paper with a highly uneven surface
This is because the pressing pressure of the thermal head does not allow the ink layer and paper to come into complete contact, and areas where they do not make contact result in poor transfer.

Furthermore, the printing speed of the thermal transfer method is slower than that of the impact method, and an improvement is desired. In order to increase the speed of printing, it is necessary to increase the level of thermal energy that can be applied to the thermal head, which may cause the printing to smear, making the above-mentioned background smudge even worse.

As a method for eliminating background smudges and blurring of prints during printing as described above, a method of forming a wax layer on the surface of a heat-melting ink layer is known.

As a method for forming this wax layer, a method is used in which a solution of wax in an organic solvent or a dispersion of wax in an organic solvent is applied to the surface of the hot-melt ink layer and dried.

(Problems to be Solved by the Invention) According to the above-mentioned conventional method, the scumming of the transfer paper and the blurring of printed characters can be solved to some extent, but the organic solvent used to form the wax layer may cause the ink layer to 1. This causes uneven thickness of the ink layer and agglomeration of pigments. A problem arises in that the quality of the ink layer deteriorates. In addition, if the surface smoothness of the paper to be transferred is even lower, the wax layer formed in this way will have insufficient adhesion of the surface layer to the paper to be transferred, so it is necessary to reduce the pressure of the thermal head. If high-speed printing is carried out using this method, there is a problem in that sufficiently clear printing cannot be obtained.

The present invention was made against the background of the above-mentioned circumstances,
The purpose is to provide a heat-sensitive transfer sheet that does not cause background smearing even when high-speed heat-sensitive transfer is performed and can provide clear prints even on transfer paper with low surface smoothness.

(Means for Solving the Problems) As a result of prototyping and testing thermal transfer sheets having various configurations, the present inventor found that the object of the present invention can be achieved by providing a specific surface layer on the surface that contacts the transfer paper. was found to be effective.

That is, the present invention provides a heat-sensitive transfer sheet in which a transfer film consisting of two layers, a heat-melting ink layer and a surface layer that seals the printed area of the transfer paper during transfer, is formed on one side of a base film. The present invention is a heat-sensitive transfer sheet characterized in that the surface layer is formed from wax and a thermoplastic resin.

(Function) By using a thermoplastic resin in addition to wax when forming the surface layer, the adhesion of the ink layer to the transfer material is further improved, and even if the transfer paper has a rough surface, there will be no scumming or scumming. High-speed printing is possible without causing printing to bleed.

Further, in a preferred embodiment, by forming the surface layer with an aqueous dispersion of wax containing thermoplastic resin particles, a surface layer having a finely textured surface can be formed without damaging the heat-melting ink layer. During printing, at least the pressure of the thermal head is concentrated on the convex portions of the uneven surface, which improves the adhesion between the surface layer and the transfer paper, making it possible to print at high speed without causing background smudges. .

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

The heat-sensitive transfer sheet of the present invention has a heat-melting ink layer 2 on one surface of a base film 1, as shown schematically in a part of its cross section in FIG. A surface layer 3 made of resin is formed.

As the base film used in the present invention, the same base film used in conventional thermal transfer sheets can be used as is, and other base 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, ionomer, etc. Examples include plastics, papers such as condenser paper and paraffin paper, and nonwoven fabrics, and base films made of composites of these materials may also be used.

The J thickness of this base film can be changed as appropriate depending on the material so that its strength and thermal conductivity are appropriate, but its thickness is preferably, for example, 2 to 25 mm.
It is μm.

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

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.

Further, 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, partially modified wax, fatty acid ester, fatty acid amide, etc. are used. It will be done.

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

Methods for directly or indirectly forming a hot-melt ink layer on the base film include applying the above-mentioned ink by hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating, and many other methods. Examples include methods. 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, the surface layer formed on the ink layer forms a part of the transfer film, forms the surface in contact with the transfer paper, seals the printed part of the transfer paper during transfer, and serves as a base layer. It has the function of preventing staining and improving the adhesion of the ink layer to the transfer paper.

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

Examples of such thermoplastic resin include ethylene-
Vinyl acetate copolymer (EVA), ethylene-acrylic acid ester copolymer (EEA), polyethylene, polystyrene, polypropylene, polybdenum, petroleum resin, vinyl chloride resin, polyvinyl alcohol, vinylidene chloride resin, methacrylic resin, polyamide, polycarbonate, Fluororesins, polyvinyl formal, polyvinyl butyral, acetyl cellulose, nitrocellulose, polyvinyl acetate, polyisobutylene, ethyl cellulose, polyacetal, etc. are used, and in particular, those having a comparatively low softening point, such as 50 to 50, are used. 80℃
Those having a softening point of .

The ratio of wax to thermoplastic resin is 10% wax
A weight ratio range of 5 to 300% thermoplastic resin to 0% is preferred.

The surface layer consisting of the wax and thermoplastic resin can be formed by coating and cooling a melt containing a mixture thereof, coating and drying an organic solvent solution containing the mixture, and further coating and drying an aqueous dispersion containing particles of the mixture. Formed by drying etc.

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 0.5 mm to prevent insufficient sensitivity even when printing energy is low as in high-speed printers.
It is 1 μm or more and less than 5 μm. If the thickness is less than 0.1, there is a risk that the transfer paper and the ink layer will rub against each other, causing scumming.

In a preferred embodiment of the invention, the surface layer is formed from an aqueous dispersion of wax and thermoplastic resin. These dispersions are preferably prepared by mixing a wax dispersion and a thermoplastic resin aqueous dispersion in appropriate proportions.

Aqueous dispersions of wax are known per se, and various ones are commercially available and can be used in the present invention. Alternatively, the wax can be obtained by dissolving the wax in a water-soluble organic solvent and adding this to water, or by adding water to precipitate the wax to obtain an aqueous solution. It can also be made into a dispersion. As the organic solvent, water-miscible organic solvents such as ketones such as acetone, alcohols, and glycols can be used, but if there is too much organic solvent in the aqueous dispersion of wax, there is a risk of damaging the underlying ink layer. Therefore, the content in the medium should be 70% or less, preferably 50% or less. The particle size of the wax in these aqueous dispersions is not particularly limited, but the preferred range is o, o5y'
y to about 5 μm.

Furthermore, particles of thermoplastic resin can be used in the present invention manually in the form of emulsions in various forms from the market, and can also be easily produced in the same manner as in the case of wax. The particle size thereof is preferably about 0.05 to 5 μm.

An aqueous dispersion containing the above wax and thermoplastic resin,
A desired surface layer is formed by coating and drying on the ink layer using the same method as for forming the ink layer. If the drying temperature after coating is such that the wax particles and thermoplastic resin particles melt, a smooth surface layer will be formed.

On the other hand, in a preferred embodiment, the temperature is such that at least one of the particles can maintain its particle shape without melting. For example, a temperature below the softening point of the wax or thermoplastic;
For example, by drying at a temperature of about 40 to 60° C., a surface layer having micro-irregularities is formed on the surface by the existing particles.

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.

Excessively large particle sizes of extender pigments are inappropriate.

Suitable as extender pigments are inorganic fillers such as silica, talc, calcium carbonate, precipitated barium sulphate, alumina, titanium white, clay, magnesium carbonate, carbon black or tin oxide.

A small amount of extender pigment will not be effective, while a large amount will reduce the dispersibility and make it difficult to prepare the ink.
Since the coated material may easily fall off from the base film, it is preferably added in a range of 0.1 to 60% by weight.

As described above, the surface layer may or may not contain a colorant, if necessary. If a coloring agent is used, it will overlap with the coloring agent in the hot-melt ink layer and provide a record of sufficient density.
If only a colorless vehicle is used, it is possible to prevent background smudges due to rubbing between the transfer paper and the heat-fusible ink layer.

When a heat-resistant 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 basic components of the anti-sticking layer 5 are 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 release agent or lubricant is
There are those that melt when heated, such as waxes and amides, esters, and salts of higher fatty acids, and those that are useful as solids, such as fluororesins and powdered inorganic substances.

By providing such an anti-sticking layer 4, it is possible to perform thermal printing without causing sticking even on a thermal transfer sheet based on a plastic film that is sensitive to heat. Benefits such as ease of use can be taken advantage 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), the base film may be coated with an inorganic pigment, such as silica, calcium carbonate, etc., dispersed in an appropriate solvent. It is preferable to form a heat-sensitive transfer sheet by coating the matte layer with a heat-melting ink layer. Alternatively, the base film itself may be matted and used.
307 technology).

It goes without saying that the present invention can be applied to heat-sensitive transfer sheets for color printing, and therefore multi-colored heat-sensitive transfer sheets are also included within the scope of the present invention.

(Effects) According to the present invention as described above, by using a thermoplastic resin in addition to wax when forming the surface layer, the adhesion of the ink layer to the transfer material is further improved, and it is possible to improve the adhesion of the ink layer to the material to be transferred. Even with transfer paper, high-speed printing is possible without causing background smudges or printing blur.

Further, in a preferred embodiment, by forming the surface layer with an aqueous dispersion of wax containing thermoplastic resin particles, a surface layer having a finely textured surface can be formed without damaging the heat-melting ink layer. During printing, at least the pressure of the thermal head is concentrated on the uneven convex portions, which improves the adhesion between the surface layer and the transfer paper, enabling high-speed printing without causing background smudges.

(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 A polyethylene terephthalate film with a thickness of 3.5 μm was used as a base film, and on one side of the base film, a heat-melting ink and a surface layer material having the following compositions were prepared, applied and dried by the methods described respectively. A thermal transfer sheet of the present invention was obtained.

Shinshu Kashidate E2 Mayu Carbon Black (Dia Black G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EVA Flex 310, manufactured by Mikata Polychemical) 8 parts paraffin wax (paraffin 150)
F, made by Nippon Seiro Co., Ltd.) 50 parts carnauba wax 25 parts Attritor was kneaded at 120°C for 6 hours, and a 3°5
g/m'' (dry state) and dried.

Human blood Δ 155F paraffin wax emulsion (WE-70
, Bond Wax Co., Ltd., solid content 40% aqueous emulsion) 20 parts ionomer resin (Chemivar S-100, Mikata Petrochemical Co., Ltd., solid content 274k)
10 parts 60% isopropanol aqueous solution
It was applied at a rate of 0.8 g/rn'' (dry state) by a 15-part gravure coating method and dried at 60°C to form a matte surface layer.

The thickness of the ink layer and the surface layer is 3.5 μm and 0.8 μm, respectively.
Thermal transfer printing was carried out using the above-mentioned heat-sensitive transfer sheet of M, and several kinds of paper to be transferred were selected from high-quality paper to medium-quality paper with low smoothness, using a commercially available thermal head. High-speed printing of 40 characters/second with a thermal head energy of 0.7 W/dot was possible on all transfer papers with high quality and no scumming.

Example 2 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention. Carbon black (dia black G, manufactured by Mitsubishi Kasei)
15 parts ethylene/vinyl acetate copolymer (EV^Flex 310, manufactured by Mikata Polychemical) 8 parts paraffin wax (paraffin 15
0F, manufactured by Nippon Seiro) 50 parts carnauba wax 25 parts Attritor was kneaded at 120°C for 6 hours, and the ink temperature was 3.5% by hot melt roll coating at 120°C.
g/rn'' (dry state) and dried.

Surface layer 155F paraffin wax emulsion (WE-70
, manufactured by Bond Wax Co., Ltd., solid content 40% aqueous emulsion) 70 parts EVA resin emulsion (
Bond Wax 62-357, manufactured by Bond Wax Co., Ltd., solid content 40%) 10 parts 50% isopropanol aqueous solution 50 parts Apply by gravure coating at a rate of 0.5 g/m'' (dry state),
It was dried at 73°C to form a surface layer with a smooth surface.

The thickness of the ink layer and surface layer is 3.5 μm and 0.5 μm, respectively.
This heat-sensitive transfer sheet of Example 1 also exhibited good transfer performance as in Example 1.

Example 3 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention.

Carbon black (dia black G, made by Sanyi Kasei)
15 parts ethylene/vinyl acetate copolymer (EVA Flex 310, manufactured by Mikata Polychemical) 8 parts paraffin wax (paraffin 15
0F, manufactured by Nippon Seiro) 50 parts carnauba wax 25 parts Attritor was kneaded at 120°C for 6 hours, and the ink temperature was 3.5% by hot melt roll coating at 120°C.
g/m'' (dry state) and dried.

Human blood tank carnauba wax 10 parts ethylene/
After melting 2 parts of vinyl acetate copolymer resin (Evaflex 310, manufactured by Mikata Polychemical Co., Ltd.), the resulting emulsion (solid content: 20%) was coated with 0% by roll coating method.
．． It was applied at a rate of 3 g/rn'' (dry state) and dried at 60°C to form a matte surface layer.

The thickness of the ink layer and the surface layer is 3.5 μm and 0.3 μm, respectively.
The transfer sheet of this example also exhibited good transfer performance with no scumming.

Example 4 Using a polyethylene terephthalate film with a thickness of 6 μm as a base film, yellow (Y) with the following composition,
An ink layer and a surface layer were formed using heat-melting inks of magenta (M), cyan (C), and black (B) colors and a surface layer ink to obtain a thermal transfer sheet of the present invention.

Ema-dori pigment (yellow, magenta, cyan or black pigment), 4-part ethylene/vinyl acetate copolymer (G-10 in Sumitate, manufactured by Sumitomo Chemical)
7.5 parts oxidized paraffin ester complex compound (
Amidopolymer T-820, made by Denka Polymer) 12.5
1 part paraffin wax (paraffin 5P-0145, manufactured by Nihon Ko! 111) 15 parts microcrystalline wax (HIMIC 2065, manufactured by Hiki Seiro) 10 parts isopropanol
5 parts xylene
46 parts An ink layer was formed by sequentially printing yellow, magenta, cyan, and black in this order by a gravure printing method using the above four-color ink composition. The coating weight at that time was 4 g/ba (dry).

Surface layer carnauba emulsion (WE-95, manufactured by Bond Wax Co., Ltd., solid content 40%) 30 parts ethylene/vinyl acetate copolymer emulsion (Policy 71/EVA
AD-5, Showa Kobunshi M, solid content 56%)
10 parts 75% isopropanol aqueous solution
60 parts The above ink composition is dried by gravure printing onto the heat-melting ink layer previously printed in yellow, magenta, cyan, and black. a
A surface layer was formed by coating at o-7 g/male. The drying conditions at that time were 65°C for 3 seconds.

When printing was performed with a color thermal printer using the thermal transfer sheet of the present invention created through the above steps,
There was no background staining caused by rubbing the paper and film. Also, although the paper had a Beck smoothness of 20 seconds, the printing was clear.

In addition, since it contains ethylene-vinyl acetate copolymer, which is a hot-melt resin, it has good adhesion to the transfer paper, and the printing effect is improved. Furthermore, since color overlapping printing was performed, the transfer of the magenta layer onto the first printed yellow layer was improved compared to the case where no thermoplastic resin was added.

Example 5 A surface layer was formed by replacing the surface layer ink composition of Example 4 with the following and applying the same to a dry weight of 1.5 g/rn'. The drying conditions at that time were 85° C. for 5 seconds.

Surface layer paraffin emulsion (61-137, manufactured by Bond Wax, solid content 40%) 40 parts ethylene-vinyl acetate copolymer emulsion (Polysol EVAAD
-5, manufactured by Showa Kobunshi, solid content 56%)
10 parts 60% ethanol aqueous solution 50
When printing was performed in the same manner as in Example 4 using the thermal transfer sheet of the present invention prepared as described above, there was no scumming and beautiful color printing was possible even on pound paper with a smoothness of 5 seconds.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a part of the cross section of the heat-sensitive transfer sheet of the present invention. Base film 2: Hot-melt ink layer 3: Surface layer 4: Anti-sticking layer Fig. 1

Claims (4)

[Claims] (1) On one side of the base film, there are two layers: a heat-melting ink layer and a surface layer that seals the printed area of the transfer paper during transfer.
1. A heat-sensitive transfer sheet on which a transfer film consisting of layers is formed, wherein the surface layer is formed from wax and a thermoplastic resin. (2) The heat-sensitive transfer sheet according to claim (1), wherein the weight ratio of wax:thermoplastic resin is 100:5 to 300. (3) The heat-sensitive transfer sheet according to claim (1), wherein the surface layer is formed from an aqueous dispersion containing wax and a thermoplastic resin. (4) The heat-sensitive transfer sheet according to claim (1), wherein the surface layer is formed of wax particles and thermoplastic resin particles.