JPH0433892A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To repeatedly obtain the same degree of concentration for a plurality of times of heated printing by using two sorts or more of microcapsules differing the degree of release of a core material according to an applied heat energy. CONSTITUTION:A core material is dyed in similar colors but it is also possible to contain core materials dyed in totally different colors in a capsule and to obtain totally different colors by the difference in an applied heat energy. As a binder resin, polyvinyl acetal resin is particularly effective because of its heat resistance and compatiblity with dye. Also, the polyvinyl acetal resin has a good coating fitness as a coating liquid with a high ratio of microcapsules and obtains a viscosity fit for coating in an ink with little solid contents. As a substrate sheet, there is used a film or paper of polyester, polyimide, polystyrene, condenser paper, etc. Further, two sorts or more of microcapsules having sublimable or heat-transferable dye as a core material are dispersed in the binder resin so that they are formed into a coating liquid which is then coated or printed for the picture of providing a thermal transfer layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal transfer recording medium used for forming an image using a signal corresponding to image information using thermal energy from a thermal head or the like.

(Prior art) As a thermal transfer recording method that uses thermal energy from a thermal head etc. to make it possible to express gradation in photographic images, a sublimable or heat-transferable dye is dispersed or dissolved in a binder resin. 2. Description of the Related Art Heat-sensitive transfer recording media are known in which an ink layer is formed on one surface of a base sheet such as a polyester film.

The characteristics of such thermal transfer recording media, such as sensitivity and color development, are controlled by the thermal properties of the dye and the thermal properties of the binder resin, but there are also other factors such as the ratio of dye to binder resin and the thickness of the base sheet. The thickness of the anchor layer, the smoothness of the surface of the ink layer, the compatibility of the binder resin with the dye, the adhesion of the binder resin to the base sheet, the matching with the transfer material called receiver paper, etc. This requires consideration from all sides.

Among these considerations, the precipitation of sublimable or heat-transferable dyes on the coated surface is a major problem.
The storage stability of such thermal transfer recording media has become a major consideration.

For example, if the coated surface is formed with a dye with good sublimation properties, when the recording medium is wound up, the dye will stain the other side of the base sheet, resulting in a decrease in density and damage to the heating head.

However, thermal transfer recording media are required to have improved quality even if the thermal energy used during image formation is reduced, or even if the same energy is used, high intensity and color development can be achieved. It is desired that thermal printing can be used repeatedly at the same density.

(Problem to be solved by the invention a) The present invention was developed in view of the storage stability of the coated surface of a thermal transfer recording medium. It is also an attempt to improve the quality of the thermal transfer recording medium so that the same level of density can be obtained repeatedly in multiple thermal printings.

(Means for Solving the Problems) The present invention provides microcapsules comprising a core material made of a sublimable or heat-transferable dye and a shell material surrounding the core material on one surface of a base sheet, and In a thermal recording medium having a thermal transfer layer composed of a resin binder that holds capsules on a base sheet, the microcapsules include two or more types of microcapsules that release different degrees of core material depending on applied heating energy. This is a thermal transfer recording medium characterized in that it is used.

The sublimable or heat-transferable dyes that make up the core material include:
Sublimable dyes conventionally used in thermal transfer recording media and dyes that melt under heat and have migration properties can be used.

Such dyes include disperse dyes, basic dyes, azo dyes, etc. For example, Disperse Red 4
, 5 0 , 6 0 , 1 1 1 , 1 3
5, 22 8, Disperse Violet 26
, Disperse Yellow 3.5.14.42.54.23
1, Disperse Blue 33.56.106.241,
Solvent Yellow 77.125, Solvent Blue 36
．． 63.90.105.112.114 etc. are exemplified.

Such a core material may be in a solid or liquid state. In order to make it into a solid state, methods such as crystallizing the dye as fine crystals, pulverizing it with a pulverizer, or pulverizing it by melting and spraying it, etc. is used. In addition, in order to make it into a liquid state, methods such as dissolving it in a solvent with good solubility or dispersing it in a solvent with insufficient solubility are used.

Differences in the thermal properties of the dyes are used to control this release in various ways using the core material. In other words, the use of dyes with different melting points and sublimation start temperatures, the use of lowering of the melting point by mixing dyes,
Utilizing changes in melting point due to differences in dye crystal forms, additives,
For use in auxiliary dissection, etc., and in liquid form, use the differences due to differences in solvents.

The shell material surrounding the core material can be polyurea, polyurethane,
Various conventionally known materials such as polyamide, melamine metal condensate, gelatin, formalin metal condensate, wax, polyolefin particles, metal powder, metal thin film, etc. can be used. Also,
For encapsulation, various methods such as interfacial polymerization, submerged drying method, spray drying method, fluidized bed coating method, and air impact method can be used as appropriate.

Methods for controlling the release of the core material using the shell material include changing the material of the shell material, changing the thickness of the shell material, and changing the properties by further processing the shell material.

Furthermore, the degree of release may be adjusted by changing both the core material and the shell material, or by changing the particle size and shape.

In addition to using dyes of the same color as the core material, it is also possible to store completely different colors in capsules and obtain completely different colors by applying different thermal energy. It is also possible to adjust the degree of release of the core material gradually in accordance with the thermal history of the shell material, so that the concentration does not decrease even after multiple applications.

In the thermal transfer recording medium having a thermal transfer layer, the binder resin that holds the microcapsules on the base sheet has a molecular weight of 10,000 to 200,000 and a glass transition temperature.
70 to 120°C, and polyvinyl acetal resins in which the acetal group consists of an acetoacetal group or a butyl acetal group are preferred, but in addition to these, epoxy resins,
Acrylic resin, cellulose resin, phenolic resin, polyester resin, etc. can also be used as all or part of the binder resin.

As the binder resin, polyvinyl acetal resin was particularly effective due to its heat resistance and affinity with dyes. This resin also has excellent properties such as adhesion, coated surface smoothness, and abrasion resistance.

The polyvinyl acetal resin easily removes the dye by heating the thermal head during image formation, etc. Therefore, it is easy to obtain images with high sensitivity and high color development, and for this purpose, appropriate thermal instability is required.

From this point of view, polyvinyl acetal resin in which the acetal group is composed of an acetoacetal group has a molecular weight of 10
Those with a glass transition temperature of 70 to 120°C were selected.

In addition, polyvinyl acetal resin has good coating suitability as a coating liquid with a high proportion of microcapsules, and has molecular 11
A resin having a molecular weight of 0,000 to 200,000 can provide a viscosity suitable for coating even in ink with a low solid content.

In addition, polyvinyl acetal resin has acetyl groups and hydroxyl groups remaining in addition to acetal groups due to its manufacturing process, but the acetal group portion is 60 to 90% by weight, the acetyl group portion is 1 to 15% by weight, and the hydroxyl group portion is 60 to 90% by weight. , 1 to 20% by weight showed good results.

In addition, in terms of the stability of the coating liquid and the appropriate affinity with the dye, the acetyl group moiety should be 10 to 15
Desired properties can be obtained by weight percent or even by modifying several percent with carboxyl groups or the like.

Moreover, water-soluble polyvinyl alcohol, polyvinylpyrrolidone, water-soluble acrylic resin, etc. can also be used as the binder resin. These heat-sensitive transfer layers are formed as a water-soluble coating solution.

In addition, the coated surface may be cured with ultraviolet rays or electron beams to form a heat-sensitive transfer layer. Agents can be added.

In the present invention, a film or paper such as polyester, polyimide, polystyrene, or capacitor paper is used as the base sheet.

In consideration of mechanical strength, surface smoothness, etc., polyester films are particularly preferred.

The thickness of the base sheet is preferably from 3 to 10 μm, although a thicker base sheet is better from the viewpoint of mechanical strength and a thinner base sheet is better from the viewpoint of high sensitivity.

Preferably, a heat-resistant coating layer is formed on the other side of the base sheet, and an anchor layer is formed on the heat-sensitive transfer (coating liquid) layer side in order to improve the adhesion of the coating liquid.

The heat-sensitive transfer layer is provided on the anchor layer, which is one surface of the base sheet, to a thickness of preferably 0.3 to 2.0 am. The heat-sensitive transfer layer is formed by dispersing two or more types of microcapsules each containing a sublimable or heat-transferable dye as a core material in a binder resin, forming a coating liquid, and applying or printing the mixture.

The ratio of binder resin to microcapsules is 0.01
/1 to 110.05 is possible, but the coating suitability of the coating liquid, the smoothness of the heat-sensitive recording medium, and the retention of microcapsules to the base sheet are 0.1/1 to 110.1. is appropriate.

To provide the heat-sensitive transfer layer on the base sheet, the binder resin may be mixed with an aromatic solvent such as toluene, xylene, methyl cellosolve, methyl elketone, cyclohexanone, ethanol, isopropyl alcohol, normal butanol, tetrahydrofuran, cellosolve, or ketone. The microcapsules are dissolved in one or more of a welding agent, an alcohol-based solvent, a furan-based solvent, and water, and the microcapsules are dispersed therein to form a coating liquid, which is then provided on a base sheet by coating or printing. When dispersing the coating liquid, a dispersant can be appropriately selected to ensure uniform dispersion of the microcapsules.

In such coating of the heat-sensitive transfer layer, additives such as a fluidity-modifying agent and an anti-skinning agent may be added for the purpose of improving coating suitability.

In addition, other binder resins, plasticizers, activators, oils (petroleum-based), etc. may be added for the purpose of improving coating film properties. However, these components should be contained within 20% by weight of the binder resin. desirable.

An image can be formed using the heat-sensitive transfer recording medium thus produced by, for example, overlapping the heat-sensitive transfer layer of the medium and an image-receiving paper and applying thermal energy with a thermal head or the like. At this time, depending on the degree of thermal energy or thermal history, the dye inside the microcapsules melts, thermally diffuses, and leaches out of the shell.
The dye in the heat-sensitive transfer layer is applied once or twice to the image-receiving paper surface depending on the degree controlled by the difference in thermal properties of the dye, the permeation state and destruction state of the shell material, and the size of the microcapsules. It is possible to migrate multiple times.

(Example) The present invention will be explained below with reference to Examples. In addition, in the example,
All compounding ratios indicate parts by weight.

<Example 1> Polyester stretched film with a thickness of 5.7 μm (manufactured by Toshi Co., Ltd.)
Lumirror 6CF53) 0. An anchor layer with a thickness of 1 to 0.2 μm was formed. (Anchor Layer Polyester) On this anchor layer, an ink for a heat-sensitive transfer layer having the following composition was applied and dried in an oven at 70°C to form a heat-sensitive transfer layer.

The coating amount of this heat-sensitive transfer layer after drying is 1.5 g/rrf
Met.

Furthermore, a heat-resistant silicone resin-based back coat layer was provided on the other side of the polyester film.

[Ink composition]

Capsules with Solvent Blue 63 as core material (film thickness 0.
05μ) ...... 3 parts Capsule with Solvent Blue 63 as core material (film thickness 0.20B)
...3 parts Total 6 parts Polyvinyl acetal resin ...3 parts Toluene ...44 parts Methyl ethyl ketone ...44 parts The polyvinyl acetal resin contains 9.4 parts of polyvinyl alcohol. %, polyvinyl acetate 1.4%, acetoacetal 89.2
%, average degree of polymerization 2400, average molecular weight approximately 150,000, and glass transition point Tg 116°C.

Even when the obtained heat-sensitive recording medium was left in an oven at 60° C. for one week, no dye precipitation was observed, and no change in appearance was observed.

Further, the thermal transfer layer of the obtained thermal transfer recording medium was superimposed on the image receiving paper, and a printing voltage of 13V was applied using a thermal head.
, thermal head resistance 300, pulse width 4.5m5ec
Solid printing was performed under the following conditions.

At this time, the reflection density of the printed portion was 1.60. Furthermore, no background staining occurred in the non-printed areas. Furthermore, a printing test was performed again on the printed area, but no decrease in reflection density was observed.

When solid printing was similarly performed on a thermal transfer recording medium that had been left in an oven at 60° C. for one week, no deterioration in printing characteristics or occurrence of scumming was observed.

<Example 2> A polyester stretched film with a thickness of 4.5 μm was coated with 0.1
An anchor layer of ~0.2 μm was formed.

On this anchor layer, an ink for a heat-sensitive transfer layer having the following composition was applied and dried in an oven at 70°C to form a heat-sensitive transfer layer.

The coating amount of this heat-sensitive transfer layer was 1.2 g/n.

[Ink composition]

Sublimable dye Disperse Red 60 1.6 parts Disperse Violet 26 1.4 parts Disperse Yellow 2
31 3.2 parts Solvent Blue 63
5.3 parts Capsule using a dye mixture having this composition as a core material (thickness: 0.05μ) 7.
5 parts Capsule with dye mixture of this composition as core material (film thickness 0.2μ) 10.0 parts Polyvinyl acetal resin 7.0 parts Toluene
100 parts Methyl isobutyl ketone 100 parts Polyester A heat-resistant back coat layer made of silicone resin was provided on the other side of the stretched film, and solid printing was performed in the same manner as in Example 1.

The reflection density of the printed portion was 1.7, and no scumming occurred in the non-printed portion. Furthermore, a printing test was performed again on the printed area, but no decrease in reflection density was observed. Thereafter, the same storage test as in Example 1 was conducted, but no external changes such as precipitation of dye were observed.

<Example 3> The shell material of the capsule in Example 2 was encapsulated using a material with low airtightness and a material with high airtightness.

(Film thickness 0.1μ) The above capsules are in a ratio of 4:3,
An ink similar to that in Example 2 was prepared and the same tests were conducted.

This heat-sensitive transfer layer was also able to control the release of the core material from the capsules and was suitable for multiple printings.

<Example 4> A core material capsule (thickness 0.05μ) consisting of the dye mixture in Example 2 (melting point around 110°C) and
℃ or higher capsule of black dye alone (film thickness 0.05μ)
The same ink as in Example 2 was prepared by mixing at a ratio of :2 and the same test was conducted.

This heat-sensitive transfer layer also had good control over melting and release of the core material, and had good printing characteristics over multiple times.

<Example 5> A water-soluble acrylic resin was used as the resin and solvent of Example 2. Although there was a low level of decrease in print density, good results were obtained with no problems in print characteristics.

<Example 6> Capsules containing Solgentoflu-63 as the core material (film thickness 0.
05μ) 3 part dispers thread 6
Capsule with 0 as core material (film thickness 0.2μ)
One part of the above capsules was made into ink using the water-soluble acrylic resin of Example 5, and a heat-sensitive transfer layer was formed in the same manner as in Example 1.

When this thermal transfer recording medium was printed with varying thermal energy, it took on a purple hue as the thermal energy increased. In other words, a multicolored print corresponding to changes in thermal energy was observed.

Further, as printing was repeated many times using the same energy, the hue changed to red, and the degree of transfer fatigue of the heat-sensitive transfer layer was indicated by the change in hue.

(Effects) According to the present invention, it is possible to form a heat-sensitive transfer layer with excellent storage stability against dye precipitation, dye migration, etc. due to the action of the microcapsule shell material.

In addition, the presence of two or more different types of capsules in the heat-sensitive transfer layer is equivalent to forming a multilayer heat-sensitive transfer layer with a single layer, and the functionality intended to be obtained by multilayering can be achieved in a single layer. It can also be obtained through coating. This functionality provides remarkable effects such as ensuring print density in multiple printings and printing effects using completely different core materials. Since the stability over time due to encapsulation and the release of dye due to thermal energy are performed in a harmonious manner, a thermal transfer recording medium with excellent printing characteristics can be obtained.

Patent applicant Toppan Printing Co., Ltd. Representative: Kazuo Suzuki

Claims (4)

[Claims] (1) Microcapsules composed of a core material made of a sublimable or heat-transferable dye and a shell material surrounding the core material, and a binder resin for holding the microcapsules on the base sheet, on one surface of the base sheet. A thermal transfer recording medium having a thermal transfer layer composed of two or more types of microcapsules having different degrees of release of core material depending on applied heating energy as the microcapsules. . (2) The thermal transfer recording medium according to claim (1), wherein microcapsules are used in which the degree of release of the core material is adjusted by different shell materials. (3) The thermal transfer recording medium according to claim (1), wherein microcapsules are used in which the degree of release of the core material is adjusted depending on the difference in the core material. (4) The thermal transfer recording medium according to claim (1), wherein microcapsules are used in which the degree of release of the core material is adjusted by the difference between the core material and the shell material.