JPS6168290A - Repeatedly usable thermal transfer medium - Google Patents

Abstract

PURPOSE:To obtain a thermal transfer medium capable of being repeately used for printing with high printed density and with low printing energy, by a method wherein a composition prepared by finely dispersing a heat-fusible ink in a solution of a water-soluble resin is applied to a film base, and is dried. CONSTITUTION:A heat-fusible ink is finely dispersed in a solution comprising polyvinyl alcohol as a main constituent and comprising other water-soluble resin such as methyl cellulose. The ink comprises a solid fatty acid, e.g., lauric acid or myristic acid, a coloring agent, e.g., carbon black or Lake Red, a low melting point agent, e.g., a wax, and other additives. An emulsifier is suitably used when dispersing the ink in the solution. The composition thus obtained is applied to a film base 11, followed by drying to provide an ink-containing layer 12 in which heat-fusible ink particles 15 are dispersed uniformly and continuously in open-microporous layer 14 consisting of the water-soluble resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a multiple thermal transfer medium used in a printing device such as a thermal printer that performs printing by thermal transfer.

[Prior art and problems to be solved by the invention] Conventionally,
The thermal transfer sheet of this mallet is simply a base material coated with a heat-melting ink composition consisting of a colorant and its binder, and once used for printing, the ink composition in that area is transferred onto the recording paper surface. It was impossible to use the same thermal transfer sheet for printing more than once. Therefore, such a one-time type thermal transfer sheet is extremely uneconomical.

In order to eliminate such uneconomical problems, the following thermal transfer sheets have recently been proposed that are capable of printing multiple times with the same thermal transfer sheet.

(1) First, a multiple thermal transfer sheet has been proposed in which a cohesive powder such as carbon black is mixed into an ink composition consisting of a soluble dye and a low melting point agent, and this is applied to a base material. (Refer to Japanese Patent Application Laid-Open No. 57-160691). However, in such a thermal transfer sheet, powder such as carbon black does not contribute to the formation of a printed image at all, and the printed image is formed using a soluble dye.

Therefore, considering that printed images formed with dyes are highly susceptible to fading, there is a problem in the fastness of the printed images, and they lack storage stability.

(2) In addition, a thermal transfer sheet has been proposed in which a heat-resistant resin layer having many continuous micropores is formed on a base material, and the micropores of the heat-resistant resin layer are impregnated with heat-melting ink. (Refer to Japanese Unexamined Patent Publication No. 105579/1983). However, such thermal transfer sheets require complicated operations to form a porous resin layer on the substrate, and furthermore, it is difficult to efficiently and uniformly impregnate the hot melt ink into the porous resin layer. is difficult.

Therefore, with such a thermal transfer sheet, unevenness occurs in the density of the printed image, and the printing quality is not satisfactory.

(3) Furthermore, after coating the base material with a dispersed solution of heat-melting ink in a resin solution, the solvent is evaporated and removed to continuously contain heat-melting ink in the microporous layer of the resin. A thermal transfer sheet has been proposed for
(See Publication No. 68253).

However, with almost all the combinations shown in this publication, when used as a thermal transfer sheet for multiple times, it is necessary to apply printing energy that is far greater than that required when printing with a conventional one-time thermal transfer sheet. Transferability could not be obtained.

[Purpose of the Invention] The present invention has been made to solve the above-mentioned problems, and provides a high-density print with the same low printing energy as the conventional one-time thermal transfer sheet, and also eliminates printing unevenness. and can be printed multiple times.

Further, the present invention provides an inexpensive multi-use thermal transfer medium that can be manufactured through extremely simple steps.

[Means and effects for solving the problems] This invention has the following features:
A heat-melting ink made by mixing a colorant and a low melting point agent or an additive with a solid fatty acid as a product is finely dispersed in a water-soluble resin solution whose main component is polyvinyl alcohol, and the ink composition is applied to a film base material. By applying it to the surface and drying it, it is extremely easy to form a fine continuous porous layer made of water-soluble resin, and the hot-melt ink is uniformly dispersed in the porous layer, resulting in low printing energy. This enables thermal transfer to be performed multiple times with sufficient print density even at the same position.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

Figure m1 is a diagram showing a schematic cross-sectional view of a multi-time thermal transfer medium, and the thermal transfer sheet 10 has a film base material 11 coated with a heat-fusible ink-containing layer 12.

The film base material 11 used in this example is a film or capacitor paper made of polyester, polyimide, polycarbonate, polysal 7one, polyether sulfone, polyphenylene sulfide, polyether-ether ketone, etc. with a heat resistance temperature of 150° C. or higher. , glassine paper, etc., and the thickness thereof is preferably in the range of about 3 to 20 μm. Also, as shown in Figure 1,
In order to prevent sticking, an anti-sticking layer 13 made of silicone, heat-resistant 4J4 resin, or the like is provided on the surface opposite to the coated surface of the heat-fusible ink-containing layer 12.

The heat-melting ink-containing layer 12 includes a water-soluble resin (water-soluble polymer) 14 containing polyvinyl alcohol as a main component;
It is composed of a heat-melting ink 15.

Water-soluble resin 1 containing polyvinyl alcohol as a main component
As component 4, polyvinyl alcohol alone can provide sufficient performance, but adding polyethylene glycol to it further improves transferability. In addition, methylcellulose, ethylcellulose, and droxyethylcellulose,
Hydroxypropylcellulose, carboxymethylcellulose.

Polyvinylpyrrolidone, polyacrylate.

By using a water-soluble resin such as polyacrylamide, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, etc., the same or higher effect can be achieved than when using polyvinyl alcohol alone.

The heat-melting ink 15 is composed of a solid fatty acid as a main component, a coloring agent, and other low-melting point agents and additives. Solid fatty acids include lauric acid and myristic acid, which are solid at room temperature.

There are palmitic acid, stearic acid, arachidic acid, behenic acid, etc., and the amount added thereof is desirably adjusted appropriately within the range of 40 to 95% in the low melting point agent based on the experimental results described below.

Examples of the low melting point agent to be mixed with the solid fatty acid include paraffin wax and microcrystalline wax which are water-insoluble and have a melting point of 40 to 1 oO''C.

Oxidized paraffin wax, candelilla wax.

Carnauba wax, montan wax, ceresin wax, polyethylene wax, oxidized polyethylene wax, castor wax, hardened tallow oil.

Lanolin, wood wax, sorbitan stearate. Sorbitan palmitate, stearyl alcohol.

Polyamide wax, oleylamide, stearylamide, hydroxystearic acid 1 synthetic ester wax,
In addition to ant-like substances such as synthetic metal-containing waxes, petroleum resins, rosins, ester gums, and ketone resins.

Epoxy resin, ethylene-vinyl acetate copolymer resin, ethylene-
Examples include low melting point thermoplastic resins such as α-olefin copolymer resins.

Carbon black is used as a coloring agent.

Inorganic and organic pigments such as lake red, alkali blue, and navy blue are used, as well as oil-soluble or basic dyes that are highly soluble in fatty acids such as nigrosine, oil black, and methyl violet.

Note that dyes are added as auxiliary agents to produce colors that cannot be produced by pigments alone, or to adjust the tone.

Furthermore, when preparing such a heat-melting ink, a dispersant such as lecithin may be added to promote dispersion of the colorant into the low-melting point agent.

Next, the heat-melting ink 1 is added to the thus prepared water-soluble resin solution containing polyvinyl alcohol as a main component.
Add 5 while heating and stirring to emulsify. At this time, as an emulsifier to be used, in the heat-melting ink 15, a span-based surfactant, preferably sorbitan stearate, distearate, tristearate, etc., which are solid at room temperature, are added.
A Tween-based surfactant, polyoxyethylene alkyl ether, or the like is added to one of the water-soluble resin solutions. However, since the water-soluble resin solution has a considerable viscosity, it is not necessary to use these emulsifiers since it can be sufficiently emulsified with this viscosity alone.

The heating temperature during this emulsification is set to be higher than the melting point of the hot-melt ink 15. This is to perform emulsification in a liquid-liquid system and to ensure that emulsification is performed uniformly throughout the system. Furthermore, the stirring operation is important for making the particle size of the heat-melting ink after emulsification to an optimum particle size (several microns or less) and for making the particle size uniform throughout the system.

Through this emulsification, a hot-melt ink composition to be applied to the film base material 11 can be easily obtained, and the hot-melt ink composition can be produced more uniformly in particle size than by conventional mechanical grinding such as a ball mill. It is a distributed state.

The hot-melt ink composition prepared as described above is diluted with a diluent such as ethyl alcohol, and then coated with a reverse coater or a graphic coater.

Wire bar coater, comma coater, roll coater
, the film base material 11 is coated with a coating device such as a doctor blade.
is applied to. If the coating thickness at this time is too thick or too thin, it will cause problems in multiple thermal transfers. Note that an undercoat bonding layer may be provided that has affinity with the heat-melting ink composition and is made of acrylic resin, vinyl chloride resin, or the like.

The heat-melting ink composition applied to the film base material 11 is placed in a dryer, and the moisture contained therein is removed. The drying temperature at this time is set at 80 to 120°C.

As shown in FIG. This step is performed to form a continuous phase of heat-fusible ink particles 15 in the fusible ink-containing layer 12.

As a result, the multiple thermal transfer sheet 10 according to this embodiment
In this example, heat-melting ink particles 15 are uniformly and continuously dispersed in a fine continuous porous layer 14 made of a water-soluble resin on a film base material 11 with almost the same particle size (several microns or less). This retains the meltable ink-containing layer 12.

Next, a method for manufacturing a multiple thermal transfer sheet according to this embodiment will be explained based on FIG.

(1) Step of producing heat-melting ink First, the pigment and the low-melting point agent are kneaded at a temperature at least higher than the melting point of the low-melting point agent, for example, about 70'C or higher. For kneading, a commonly used kneading machine such as a three-roll mill, sentry mill, sand mill, ball mill, resolver, etc. is used. The reason for heating the kneading temperature at this time to a temperature higher than the melting point of the low melting point agent is to make the low melting point agent liquid and to make the dispersion of the colorant more uniform. In addition, this kneaded material will be referred to as "No. 1" below for convenience.
It is called a composition.

Next, the solid fatty acid and dye are heated and stirred. The heating temperature at this time is approximately 100°C. Then, this mixture (hereinafter referred to as the second composition for convenience) is added to the first composition while stirring while heating, and the span surfactant is also added.

(2) Production process of water-soluble resin solution Polyvinyl alcohol and a small amount of other water-soluble resins are dissolved in warm water, and an appropriate amount of Tween-based surfactant is added to form a water-soluble resin solution containing polyvinyl alcohol as the main component. generate.

(3) Step of producing a hot-melt ink composition (emulsifying step) The water-soluble resin solution produced as described above is stirred at high speed with a stirrer in a tank whose temperature is adjusted to around 80°C, and the above-mentioned Hot-melt ink at crosstalk temperature is added dropwise little by little until a predetermined ratio is achieved. After further stirring for a predetermined period of time, the mixture is switched to gentle stirring and immediately cooled to temperature V using a refrigerant from the outside.

(4) Preparation step of coating liquid A diluent is added little by little to the hot-melt ink composition while stirring to dilute it to a predetermined degree, and the whole is thoroughly stirred and mixed to obtain a coating liquid. This coating liquid has hot-melt ink particles uniformly dispersed in a water-soluble resin solution consisting of a resin component and a diluent.

(5) Coating liquid application step The coating liquid is applied to the film base material 11 using the appropriate coating device. The coating thickness at this time needs to be set slightly thicker, taking into consideration that water as a solvent will be evaporated and removed in the next drying step. In this example, the coating thickness was set to 30 to 100 microns.

(6) Drying process Finally, the film base material 11 obtained in the above process is coated with the coating liquid and placed in a dryer set at a temperature of 80 to 120°C as described above, and the remaining solvent is removed. is removed by evaporation. This drying is performed not only to remove water but also to form a continuous phase of heat-fusible ink particles 15 in the fine continuous porous layer 14 made of the water-soluble resin remaining on the film base 11 as described above. It is what is known. The thickness of the heat-fusible ink-containing layer 12 at this time is 5 to 30 microns.

The manufacturing process of the multiple thermal transfer sheet is thus completed, and the multiple thermal transfer sheet 10 as shown in FIG. 1 is obtained.

In the manufacturing process, the hot-melt ink was dispersed by emulsification, but after the hot-melt ink consisting of the first composition and the second composition was roughly pulverized in a pulverizer, the ink and the water-soluble resin were dispersed. It goes without saying that the solution may be dispersed and mixed using a ball mill or the like.

Next, an experiment for determining the usage ratio of fixed fatty acids will be explained.

Experimental example A, hot-melt ink components: 18 parts by weight Stearic acid X% Candelilla wax Y% Black dye
13% carbon black 6
% total 100% B, polyvinyl alcohol aqueous solution...50 parts by weight C, ethyl alcohol...70 parts Amount (x%) of the above stearic acid (solid fatty acid) and ff1 (of the candelilla wax (low melting point agent)) Change Y %) as appropriate,
A multiple thermal transfer sheet is produced according to the manufacturing process described above. Then, on printing paper with a smoothness of 60 seconds (Beck smoothness),
When printing with a thermal head printing energy of 30 mJ/mrI, as shown in Figure 4, the solid fatty acid l(X
As the ratio N of the low melting point agent (%) to ff1 (Y%) increases, the print density becomes darker and print unevenness disappears. In particular, it has been found that if the ratio N is in the range of 40 to 95%, it is sufficiently practical. In addition, when there was no low melting point agent at all (X-100>), the hot-melt ink-containing layer 12 was partially peeled off from the film base material 11 during printing.

In FIG. 4, the density P is measured with a commonly used optical reflection density meter, and if the reflectance of light to the printed area is R, then P = Jloy < 100
/R). In addition, the proportion N of solid fatty acids is N-10
It is expressed as 0X/(X+Y). Further, -Φ- indicates the initial (first) printing result, and -→←- indicates the fifth printing result.

Furthermore, experimental results regarding the resin layer material containing the heat-melting ink in a microporous manner are shown below.

A, water-insoluble resin a, nitrocellulose, polyester, copolymerized nylon, polystyrene, acrylonitrile-styrene copolymer, ABS, acrylic resin, polyvinyl butyral, E
△: The above resins could hardly improve transferability.

b. Vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-acetate vinyl alcohol copolymer, these resins + 128 group resin, the transferability of the resins in the above groups is 0.5 at an initial temperature of 111 degrees.
It is as follows. Furthermore, in both cases, the solid fatty acid migrates to the surface of the ink layer, resulting in a white powder buildup (bloom), which makes them unusable for practical use.

B, water-soluble resin C, polyvinylpyrrolidone, water-based urethane, water-based acrylic, methylcellulose, ethylcellulose, styrene-
Maleic anhydride copolymer and the above resins could hardly obtain transferability.

d, carboxymethyl cellulose The solution viscosity was high and a good coating liquid could not be obtained.

Resins higher than e, hydroxyethyl cellulose and hydroxypropyl cellulose can provide transferability of around 0.5 at initial concentration, but are considerably inferior to polyvinyl alcohol.

Therefore, it was found that a water-soluble resin containing polyvinyl alcohol as a main component is most suitable as the material for the resin layer.

Examples of the multiple thermal transfer medium of the present invention are as follows.

Example 1 △9 Hot-melt ink ingredients...4 parts Stearic acid 60% Candelilla wax 15% Sorbitan distearate
5% carbon black 6
% [Mitsubishi Kasei Corporation Jino MA-71 Oil Black 9% [Oil Black HBB manufactured by Orient Chemical Co., Ltd.] Nigrosine base 4% [BASF
Nigroshibase LTDI Methyl Violet 1% [Methyl Violet Base manufactured by Odugaya Chemical Co., Ltd.] Total 100% B, Resin component 10 parts by weight Polyvinyl alcohol 10% [Manufactured by Denka Co., Ltd.] 8-
241 Polyothycintylene oleyl ether 2% water
88% total
100% C1 diluent: 14 parts by weight Ethyl alcohol 100% Heat and mix with the above synthetic components A to form a uniform melt. Next, the solution of the above B component was heated to 75 to 80°C and heated to 1000 ml) 1
Add the melted solution of component A while stirring vigorously at a speed of 11 or more. After continuing stirring for about 3 to 5 minutes, switch to gentle stirring and immediately lower the temperature to air temperature using a refrigerant from outside. After reaching room temperature, the diluent C is added little by little while stirring the emulsion, and finally the whole is sufficiently stirred and mixed to obtain a coating liquid. This coating liquid is applied onto a polyester film using a reverse coater.

Paint 1! The J thickness is adjusted as necessary within the range of 5 to 20 μm after drying. The amounts of water and ethyl alcohol to be added to the above B and C components should be determined depending on suitability for application and do not have to be as described above.

When the thermal transfer sheet 10 manufactured in this way was used to perform printing as described later, as shown in FIGS. 5 and 6, printing was performed at least 15 times at the same location on the thermal transfer sheet 10. It was found that the printed image density was almost the same as the first printed image density until the 4th printing, and although the temperature gradually decreased after the 5th printing, it was sufficiently usable even in the 15th printing. It had a print @ density that could withstand.

Now, referring to FIG. 3, a description will be given of the printing operation when printing is performed using the multiple thermal transfer sheet according to this embodiment.

FIG. 3 is a schematic sectional view showing a printing state, and the thermal transfer sheet 10 produced by the above method is applied to a thermal transfer type printing device such as a thermal printer. In the figure, the surface of the thermal transfer sheet 10 on which the heat-melting ink-containing layer 12 is not coated is the heating element 1 of the thermal head 16 of the printing device.
A printing paper 18 mounted on a platen (not shown) is opposed to the surface that is in contact with the printing paper 7 and coated with the heat-fusible ink-containing layer 12 . When the thermal head 16 is selectively driven according to the printing information, the thermal head 16 moves so as to come into contact with the printing paper 18, and the thermal energy emitted from the heating element 17 is transferred to the heat-melting ink-containing layer through the film base material 11. 12.

The transferred thermal energy melts the heat-melting ink particles 15 only in the portion where the heating element 17 is in contact, and the melted ink adheres to the opposing printing paper 18.
As a result, predetermined dots 19 are formed on the printing paper 18. A predetermined character, symbol, etc. is printed by gathering a large number of these dots.

The printing conditions in Fig. 5 are as follows: -Printing energy: 30111J/+1110'
The smoothness of the printing paper is 60 seconds (Beck smoothness), the thermal transfer sheet base l material is 6.5μ, the polyester ink coating thickness is 13 to 14μ, and the printing conditions in Figure 6 are the same as those in Figure 5, and the printing energy and thermal transfer sheet are the same. The conditions were that only the smoothness of the printing paper was set to 350 seconds (Beck smoothness 1!It).

As a result, as shown in Fig. 5 and Fig. 6, regardless of the smoothness of the printing paper, both cases were printed using the multiple thermal transfer sheet of this example (A> was printed using conventional components or methods. Printed using the manufactured thermal transfer sheet (B, C
), the print density is much darker, and there is no temperature unevenness, and the difference in performance is obvious.

Example 2 A. Heat-melting ink components: 9-layered palmitic acid 50% candelilla wax 35% carbon black
10% nigrosine base 4
%Methyl violet 1% total
100% B, resin component 25 parts by weight Polyvinyl alcohol 10% Polyethylene glycol 2% [Onoe Kogyo Seiyaku #6000] Polyoxyethylene oleyl ether 2% Water
86% total
100% C8 diluent: 35 parts by weight Ethyl alcohol 100% Example 3 A, Hot-melt ink component: 16 parts by weight Stearic acid 75% Candelilla wax 8% castor wax
5% carbon black 6
% Nigrosine base 5% total
100% S, S fat component: 29 parts by weight Polyvinyl alcohol 14% Total 100% C1 diluent: 45 parts by weight Ethyl alcohol 100% As described above, the heat-melting ink particles 15 of the thermal transfer sheet 10 are uniformly dispersed in the fine continuous porous layer 14 made of water-soluble resin and are held in a continuous phase state. In this case, the fine continuous porous layer 14 made of a water-soluble resin acts as a barrier when the melted heat-melting ink particles 15 seep out toward the printing paper 18 side. Therefore, the melted thermofusible ink particles 15 do not ooze out all at once during one printing, and the barrier effect of the fine continuous porous layer 14 enables multiple thermal transfers.

Further, the heat-melting ink particles 15 are formed in the fine continuous porous layer 14.
Since it exists as a continuous phase in the film base material 11
Even the heat-melting ink particles 15 on the sides are used for printing without waste. Therefore, it is possible to print many times with the same thermal transfer sheet 10, which is much more economical than conventional thermal transfer sheets that can only be used once (wait-time type thermal transfer sheet), and the maintenance cost of the printing device is reduced. can be made cheaper as follows.

Comparison of lining costs for thermal transfer ribbons (A4 size 45
Price for printing 1200 characters on 1 high-quality paper) ・Multi-time thermal transfer sheet of this invention 7 yen (including 4 yen ribbon cost) ・Conventional one-time thermal transfer ribbon 20 yen (including 17 yen ribbon cost) For reference (thermal Furthermore, since the heat-melting ink-containing layer 12 is generated by emulsification in this thermal transfer sheet 10, the fine J-continuous porous layer 14 is made of a water-soluble resin whose main component is polyvinyl alcohol. It is extremely easy to make the particle diameters of the heat-fusible ink particles 15 uniform over the entire area, and it is possible to obtain a printed image having constant printing quality without uneven printing density.

[Effect of the invention 1 As detailed above, the present invention provides a solution in which a coloring agent and a low-melting point agent or an additive are mixed into a solid fatty acid, which is the main component, in a water-soluble resin solution whose main component is polyvinyl alcohol. By finely dispersing the heat-melting ink, applying the ink composition to the film base material, and drying it, we achieved sufficient printing performance with low printing energy comparable to that of one-time thermal transfer sheets, which was completely unprecedented. , high quality and repeatability can be obtained, and since it can be manufactured by an extremely simple process, it is possible to provide an inexpensive multi-use thermal transfer medium, and its effects are extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a thermal transfer sheet showing an embodiment of the present invention, FIG. 2 is a flowchart showing the manufacturing process, FIG. 3 is a schematic sectional view showing the state of printing by the thermal transfer sheet, and FIG.
The figure shows the relationship between the proportion of solid fatty acids and the concentration, and FIGS. 5 and 6 show the change in concentration when printing is performed multiple times using a thermal transfer sheet. In the figure, 10 is a multiple thermal transfer sheet, 11 is a film base material, 12 is a heat-melting ink-containing layer, 14 is a fine continuous porous layer made of a water-soluble resin, and 15 is a heat-melting ink. Fig. 1 Fig. 3 Fig. 4 Fig. 4 a to ``Maintenance of Japanese horse mackerel'' bN (@MU) Kureshi Yue〈Work 1, Indication of the incident 1982 Patent Application No. 191312 2, Title of the invention Detailed description of the invention in the multiple thermal transfer medium specification

Claims (1)

[Claims] 1. In a water-soluble resin solution whose main component is polyvinyl alcohol, a heat-melting ink made by mixing a solid fatty acid, which is the main component, with a coloring agent and a low-melting point agent or an additive, is finely dispersed.
A multi-time thermal transfer medium characterized in that the ink composition is applied to a film base material and then dried. 2. The multiple thermal transfer medium according to claim 1, wherein the heat-melting ink is added to the water-soluble resin solution while stirring while heating, and the ink composition is produced by emulsification. .