JPH0324918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-time 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, this type of thermal transfer sheet has only been coated with a heat-melting ink composition consisting of a colorant and its binder on a base material, and once printing has been performed. When used for printing, the ink composition in that area is transferred onto the recording paper surface, making it impossible to use the same thermal transfer sheet more than once for printing. 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. (Tokukai Akira
57-160691). However, in such thermal transfer sheets, powder such as carbon black does not contribute at all to the formation of printed images;
A printed image is formed using a soluble dye.

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

(2) In addition, a thermal transfer sheet has been proposed in which a heat-resistant resin layer with many continuous micropores is formed on a base material, and melt-resistant ink is impregnated into the micropores of the heat-resistant resin layer. (Unexamined Japanese Patent Publication No. 1983-
(See Publication No. 105579). 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, the density of the printed image becomes uneven, 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 (see Japanese Unexamined Patent Publication No. 1982-68253).

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

[Object of the invention] This invention was made in order to solve the above-mentioned problems, and it does not stain the printing paper.
With low printing energy equivalent to that of conventional one-time thermal transfer sheets, the print density is high, uneven printing can be eliminated, and printing can be performed multiple times. Further, the present invention provides a thermal transfer sheet that has excellent storage stability and can be printed many times.

[Means and effects for solving the problems] This invention provides a coloring agent to the saturated fatty acid represented by the general formula CH ₃ (CH ₂ ) nCOOH (where n = 14 to 20), which is an essential component. When producing a heat-melting ink by mixing a low melting point agent and a low melting point agent, when the amount of the saturated fatty acid is X and the amount of the low melting point agent mixed with this saturated fatty acid is Y, N=100X/(X+Y) In the formula, the blending amount of saturated fatty acid and the blending amount of low melting point agent are adjusted so that N is 40 to 95%, and the heat-melting ink is mixed in a water-soluble resin solution containing polyvinyl alcohol as the main component. By uniformly finely dispersing the ink composition into a film base material and drying it, a fine continuous porous layer consisting of a water-soluble resin is formed. This method enables thermal ink to be uniformly dispersed, and thermal transfer can be performed multiple times with sufficient print density even at the same position with low printing energy.

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

FIG. 1 is a diagram showing a schematic cross-sectional view of a multiple thermal transfer sheet, in which a thermal transfer sheet 10 is a film base material 1.
1, a heat-fusible ink-containing layer 12 is applied. The film base material 11 used in this example is made of polyester, polyimide, polycarbonate, polysulfonate, polyester, polyimide, polycarbonate, polysulfone, etc., which have a heat resistance temperature of 150°C or higher.
Examples include films made of polyether sulfone, polyphenylene sulfide, polyether-ether ketone, etc., and papers such as capacitor paper and glassine paper, and the thickness thereof is preferably in the range of about 3 to 20 microns. Further, as shown in FIG. 1, in order to prevent staking, a staking prevention layer 13 made of silicone, heat-resistant 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 is composed of a water-soluble resin (water-soluble polymer) 14 whose main component is polyvinyl alcohol, and a heat-melting ink 15.

As a component of the water-soluble resin 14 whose main component is polyvinyl alcohol, polyvinyl alcohol alone can provide sufficient performance, but when polyethylene glycol is added to it, the transferability is further improved. In addition, water-soluble resins such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, sodium polyacrylate, polyacrylamide, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, etc. By using polyvinyl alcohol alone, it is possible to achieve an effect equal to or greater than that of 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. As a solid fatty acid, the general formula is CH ₃ (CH ₂ )nCOOH [however, n=14
~20], and are solid at room temperature, such as palmitic acid, margaric acid, stearic acid, nondecylic acid, arachidic acid, and behenic acid. Based on the experimental results described later, it is desirable that the amount added is appropriately adjusted within the range of 40 to 95% in the low melting point agent.

As the low melting point agent mixed with the solid fatty acid,
Paraffin wax, microcrystalline wax, oxidized paraffin wax, candelilla wax, carnauba wax, montan wax, ceresin wax, polyethylene wax, oxidized polyethylene wax that is insoluble in water and has a melting point of 40 to 100°C. Tux, castor wax, hardened tallow oil, lanolin, wood wax, sorbitan stearate, sorbitan palmitate, stearyl alcohol, polyamide wax, oleylamide, stearinamide, hydroxystearic acid, synthetic ester wax, synthetic metal-containing wax, etc. In addition to waxy substances,
petroleum resin, rosin, ester gum, ketone resin,
Examples include low-melting thermoplastic resins such as epoxy resins, ethylene-vinyl acetate copolymer resins, and ethylene-α-olefin copolymer resins.

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

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 15 is added to the thus prepared water-soluble resin solution containing polyvinyl alcohol as a main component while being heated and stirred to emulsify it. At this time, as emulsifiers to be used, a span-based surfactant, preferably sorbitan stearate, distearate, tristearate, etc., which are solid at room temperature, are added to the heat-melting ink 15, and one water-soluble resin solution is added to the water-soluble resin solution. , Tween-based surfactant or polyoxyethylene alkyl ether. 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 an optimum particle size (several microns or less) and for making the particle size uniform throughout the system.

By this emulsification, a hot-melt ink composition for coating on the film base material 11 can be easily obtained, and the hot-melt ink composition has a uniform particle system and is more uniform than conventional mechanical grinding using a ball mill or the like. It is a distributed state.

The hot-melt ink composition obtained as described above is suitably diluted with a diluent such as ethyl alcohol, and then subjected to a reverse coater, a gravicoater,
The film base material 11 is coated with a coating device such as a wire bar coater, comma coater, roll coater, doctor blade, or the like. If the coating thickness at this time is too thick or too thin, it will cause problems in multiple thermal transfers. In addition, it has affinity with the heat-melting ink composition,
An undercoat bonding layer made of acrylic resin, vinyl chloride resin, etc. may also be provided.

The hot-melt ink composition applied to the film base material 11 is placed in a dryer, and the water contained therein is evaporated off. The drying temperature at this time is 80 to 120
Set to ℃. This is achieved by applying a temperature higher than the melting point of the low-melting point agent contained in the applied heat-melting ink particles 15.
This is done in order to moderately condense the particles and form a continuous phase of heat-fusible ink particles 15 in the heat-fusible ink-containing layer 12, as shown in FIG.

As a result, in the multiple thermal transfer sheet 10 according to this embodiment, the heat-melting ink particles 15 are uniformly and continuously formed on the film base material 11 with approximately the same particle diameter (several microns or less). The thermofusible ink-containing layer 12 is held dispersed in a fine continuous porous layer 14 made of resin.

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 kneader 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 colorant more uniformly dispersed. Hereinafter, this kneaded product will be referred to as the first composition for convenience.

Next, the solid fatty acid and dye are heated and stirred.
The heating temperature at this time is around 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 produce a water-soluble resin solution containing polyvinyl alcohol as the main component. generate.

(3) Production process of hot-melt ink composition (emulsification process) The water-soluble resin solution produced as described above was
While stirring at high speed with a stirrer in a tank whose temperature is adjusted to around 0.degree. C., the hot-melt ink at the kneading temperature is added dropwise little by little until a predetermined ratio is reached. After further stirring for a predetermined period of time, the mixture is switched to gentle stirring and immediately cooled to room temperature using a refrigerant from the outside.

(4) Coating liquid preparation step A diluent is added little by little while stirring the heat-melting ink composition to dilute it to a predetermined degree, and the whole is sufficiently 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 coating process 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 is 30
The thickness was set to ~100μ.

(6) Drying process Finally, the coating liquid is applied onto the film base material 11 obtained in the above process, and then the coating liquid is applied as described above.
Place in a dryer set at a temperature of 80 to 120°C to evaporate the remaining water as a solvent. In this drying process, in addition to removing water, the heat-melting ink particles are placed in the fine continuous porous tank 14 made of the water-soluble resin remaining on the film base material 11 as described above.
This is done to form a continuous phase of 5. The heat-melting ink-containing layer 12 at this time
The thickness is 5 to 30μ.

The manufacturing process of the multi-time thermal transfer sheet is completed above, and the multi-time thermal transfer sheet 10 as shown in FIG.
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 Part Amount of stearic acid (solid fatty acid) above (X%)
and amount of candelilla wax (low melting point agent) (Y
%) as appropriate and produce a thermal transfer sheet multiple times according to the manufacturing process described above. When printing is performed on printing paper with a smoothness of 60 seconds (Beck smoothness) at a thermal head printing energy of 30 mJ/ ^mm2 , the amount of solid fatty acids (X
%) to the amount (Y%) of the low-melting point agent 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 is no low melting point agent at all (when X = 100)
In this case, the heat-melting ink-containing layer 12 was partially peeled off from the film base material 11 during printing.

In Figure 4, the density P is measured using a commonly used optical reflection density measuring device, and when the reflectance of light to the printed area is R, it is expressed as P=log(100/R). . Further, the proportion N of solid fatty acids is expressed as N=100X/(X+Y). Furthermore, --.-- indicates the initial (first) printing result, and --x-- indicates the fifth printing result.

Also, the experimental results regarding the type of solid fatty acids used are shown below.

A. Solid fatty acids with a carbon number of 15 or less (n≦13) such as lauric acid and myristic acid. Solid fatty acids with carbon numbers of 15 or less (n≦13) lower the melting point of heat-melt ink, making the ink sticky and easily staining printing paper. There is a problem with the storage stability of thermal transfer sheets.

B. Solid fatty acids with a carbon number of 16 to 22 (14≦n≦20) such as palmitic acid, margaric acid, stearic acid, nondecylic acid, arachidic acid, and behenic acid.
℃), and it was possible to print many times without staining the printing paper (see Figures 5 and 6). Also,
There are no problems with the storage stability of the thermal transfer sheet.

C 23 or more carbon atoms such as lignoceric acid (n≧21)
Since the above solid fatty acids have a high melting point for hot-melt ink, a lot of printing energy is required, and the ink quality is hard, so a large amount of ink is transferred at one time, so it is difficult to print multiple times. I didn't want to go.

Among solid fatty acids having 10 or more carbon atoms, those with an odd number of carbon atoms are rarely produced naturally and are expensive because they are produced synthetically.

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, EVA, The above resins can hardly obtain transferability. Nakatsuta.

b Vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride
The transferability of the acetic acid-vinyl alcohol copolymer, these resins plus the above group a resins, and the above group b resins is 0.5 or less based on the initial concentration. 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 unsuitable for practical use.

B Water-soluble resin c Polyvinylpyrrolidone, water-based urethane, water-based acrylic, methyl cellulose, ethyl cellulose, styrene-maleic anhydride copolymer The above resins could hardly provide transferability.

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

e Hydroxyethyl cellulose, hydroxypropyl cellulose The above resins can provide transferability of around 0.5 at initial concentration, but are considerably inferior to polyvinyl alcohol.

Therefore, it has been 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 A Hot-melt ink components: 4 parts by weight Stearic acid 60% Candelilla wax 15% Sorbitan distearate 5% Carbon black [MA-7 manufactured by Mitsubishi Kasei Corporation]
6% Oil black [Oil black HBB manufactured by Orient Kasei Co., Ltd.] 9% Nigrosine base [Nigrosine base LTD manufactured by BASF] 4% Methyl violet [Methyl violet base manufactured by Hodogaya Chemical Co., Ltd.] 1% Total 100% B Resin component 10 parts by weight polyvinyl alcohol [B manufactured by Denki Kagaku Kogyo Co., Ltd.
-24] 10% Polyothycintylene oleyl ether 2% Water 88% Total 100% C Diluent 14 parts by weight Ethyl alcohol 100% Heat and mix the above A components thoroughly to form a uniform melt. Next, while the solution of component B is heated to 75 to 80° C., the melt of component A is added while vigorously stirring at 1000 rpm or more. After continuing stirring for about 3 to 5 minutes, the stirring is switched to gentle stirring and the temperature is immediately lowered to room temperature using a refrigerant from outside. After the emulsion reaches room temperature, 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. The coating film thickness is adjusted as necessary within the range of 5 to 20 μm after drying. Incidentally, the amounts of water and ethyl alcohol added to the above B and C components should be determined depending on suitability for application and do not need to be as described above.

When printing was performed as described below using the thermal transfer sheet 10 manufactured in this way, the fifth
As shown in the figure and FIG. 6, it has been found that printing can be performed at least 15 times at the same location on the thermal transfer sheet 10, and the printed image density is the same as the first printed image density up to the fourth printing. Although there was almost no change in the density and the density gradually decreased after the 5th printing, the printed image density was still sufficient to withstand use even in the 15th printing.

Here, based on FIG. 3, the printing operation when printing is performed using the multiple thermal transfer sheet 10 according to this embodiment will be explained.

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-fusible ink-containing layer 12 is not coated is brought into contact with the heating element 17 of the thermal head 16 of the printing device, and the surface on which the heat-fusible ink-containing layer 12 is coated is brought into contact with the heating element 17 of the thermal head 16 of the printing device. is a printing paper 18 attached to a platen (not shown)
is faced. 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 heating element 1
The thermal energy emitted from 7 is transferred to the film base material 1.
1 to the heat-fusible ink-containing layer 12. The heat generating element 17 is heated by the transferred thermal energy.
Heat-melting ink particles 1 only in the part where is in contact with
5 is melted, and the melted ink adheres to the opposing printing paper 18, thereby causing the printing paper 18 to
Predetermined dots 19 are formed thereon. By aggregating a large number of these dots 19, predetermined characters, symbols, etc. are printed.

The printing conditions in Figure 5 are: -Printing energy 30mJ/ ^mm2 -Smoothness of printing paper 60 seconds (Beck smoothness) -Thermal transfer sheet Base material 6.5μ polyester Ink coating thickness 13-14μ The printing conditions in the figure are the same as those shown in FIG. 5 for the printing energy and thermal transfer sheet, but only the smoothness of the printing paper was set to 350 seconds (Beck smoothness).

As a result, as shown in Fig. 5 and Fig. 6, regardless of the smoothness of the printing paper, the paper (A) printed with the multiple thermal transfer sheet of this example is better than the paper printed with conventional components or methods. The print density was much higher than that printed with the manufactured thermal transfer sheet (B, C), and there was no density unevenness, and the difference in performance was obvious.

Example 2 A Hot-melt ink components...9 parts by weight Palmitic acid 50% Candelilla wax 35% Carbon black 10% Nigrosine base 4% Methyl violet 1% total 100% B Resin components...25 parts by weight Polyvinyl alcohol 10% Polyethylene glycol [Daiichi Kogyo Seiyaku #6000] 2% Polyoxyethylene oleyl ether 2% Water 86% total 100% C Diluent...35 parts by weight Ethyl alcohol 100% Example 3 A Heat-melt ink components... 3 parts by weight Behenic acid 26% Palmitic acid 23% Candelilla wax 20% Carbon black 20% Oleic acid 5% Nigrosine base 5% Methyl violet 1% total 100% B Resin component 5 parts by weight Polyvinyl alcohol 12% Water 86% Total: 100% C Diluent: 8 parts by weight Ethyl alcohol 100% Then, as described above, the heat-melting ink particles 15 of the heat transfer sheet 10 are uniformly dispersed in the fine continuous porous layer 14 made of a water-soluble resin, In addition, it is maintained in a state where a continuous phase is formed, and in such a state, the fine continuous porous layer 14 made of a water-soluble resin allows the melted heat-fusible ink particles 15 to seep out toward the printing paper 18 side. Acts as a barrier. Therefore, the melted heat-fusible ink particles 15 do not ooze out at once during one printing, and the barrier effect of the fine continuous porous layer 14 allows thermal transfer to be performed multiple times.

Moreover, since the heat-melting ink particles 15 exist as a continuous phase in the fine continuous porous layer 14, even the heat-melting ink particles 15 on the film base material 11 side are used for printing without wasting. Therefore, it is possible to print many times with the same thermal transfer sheet 10, which is much more economical than conventional sheets that can only be used once, and the maintenance costs of the printing device can be reduced as follows. It can be done cheaply.

Comparison of lining costs for thermal transfer ribbons (cost when printing 1200 characters on A4 size 45kg high-quality paper) Multi-use thermal transfer sheet of this invention 7 yen (including 4 yen for ribbon cost) Conventional one-time thermal transfer ribbon 20 yen (including 4 yen for ribbon cost) Ribbon cost: 17 yen) Reference (Thermal paper: 12 yen) Furthermore, in this thermal transfer sheet 10, the heat-melting ink-containing layer 12 is generated by emulsification, so it has fine continuous pores 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 in the adhesive layer 14 uniform throughout, and it is possible to obtain a printed image having constant printing quality without uneven printing density.

[Effects of the Invention] As detailed above, this invention is an essential component and a main component. When producing a heat-melting ink by mixing a colorant and a low melting point agent with a saturated fatty acid represented by the general formula CH ₃ (CH ₂ ) nCOOH (where n = 14 to 20), the amount of the saturated fatty acid When X is the amount of the low melting point agent mixed with this saturated fatty acid and Y is the amount of the low melting point agent mixed with this saturated fatty acid, in the formula N = 100 The heat-melting ink was uniformly and finely dispersed in a water-soluble resin solution containing polyvinyl alcohol as the main component, and the ink composition was applied to the film base material and dried. A thermal transfer sheet that can be printed multiple times without staining the paper and can provide sufficient printing performance, quality, and repeatable printing with the same low printing energy as a one-time thermal transfer sheet, and has excellent storage stability. The effect it provides is extremely large.

[Brief explanation of the drawing]

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. 4 is a solid state. Figures 5 and 6, which show the relationship between the proportion of fatty acids and the concentration, are diagrams showing changes in density 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.

Claims (1)

[Claims] 1. A saturated fatty acid represented by the general formula CH ₃ (CH ₂ ) nCOOH (where n = 14 to 20), which is an essential component, is mixed with a desorption agent and a low melting point agent and heated. When producing meltable ink, when the amount of the saturated fatty acid is X and the amount of the low melting point agent mixed with the saturated fatty acid is Y, in the formula N=100X/(X+Y), N is 40 to 95 % of the saturated fatty acids and _the low melting point agent. 1. A thermal transfer sheet capable of multiple printing, characterized in that the ink composition is uniformly and finely dispersed in a resin solution, and the resulting ink composition is applied to a film base material and dried.