JP2022161525A - Thermal transfer sheet - Google Patents

Abstract

To provide a thermal transfer sheet that shows excellent cuttability during thermal transfer, and can achieve high reflection density even when a thermal transfer pigment layer is made thin.SOLUTION: A thermal transfer sheet 1 has a substrate 10, and a thermal transfer pigment layer 20 that is provided on one side of the substrate and contains a binder resin, a coloring pigment, and a dispersant. The mass ratio of the coloring pigment to the binder resin is 70% or more and 150% or less. The mass ratio of the dispersant to the coloring pigment is 10% or more and 40% or less. The thermal transfer pigment layer has a thickness of 0.6 μm or more and 3 μm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a thermal transfer sheet used in a thermal transfer recording system.

A sublimation thermal transfer method and a fusion transfer method are known as thermal transfer recording methods for forming an image on a transfer material using a printer having a thermal head. In the sublimation transfer method, a thermal transfer sheet having a dye layer made of sublimation dye and binder resin is placed on a transfer material, and heat is applied to transfer the sublimation dye to the transfer material, forming an image. be.
The sublimation-type thermal transfer method is capable of expressing high-definition gradation by controlling the amount of heat, but its application to fields requiring durability, particularly heat resistance and light resistance, is limited.

On the other hand, the fusion transfer method is a method in which a thermal transfer sheet having a thermal transfer pigment layer composed of a coloring pigment and a binder resin on a base material is used, and the thermal transfer pigment layer is thermally fused onto a transfer material to form an image. be. An image formed by the fusion type transfer method has high density and excellent durability, and is suitable for recording binary images such as characters and line drawings.

In recent years, from the viewpoint of improving the resolution of a transfer product obtained by thermal transfer and improving the transfer sensitivity, it is required to make the thermal transfer pigment layer thinner. Regarding the improvement of the resolution, if the thermal transfer pigment layer has poor sharpness, the thermal transfer pigment layer in the non-heat-applied portion is taken to the transfer-receiving body side during thermal transfer, and the resolution deteriorates significantly. Therefore, the sharpness must be improved. As for thinning, it is necessary to increase the pigment concentration in the thermal transfer pigment layer in order to obtain a thin film while maintaining the reflection density at the time of thermal transfer.
In addition to the printing of photographs, the fusion-type transfer method can also be used to form fine patterns such as dot patterns and fine line patterns, solid patterns with large areas, etc. using a thermal transfer pigment layer. It can also be used for the purpose of decorating and shielding plastic moldings, electronic parts, optical parts, etc., such as display boards, picture frames and housings of tablets and smartphone terminals.

As an example of improving the cuttability of a thermal transfer pigment layer during thermal transfer, in Patent Document 1, a thermal transfer pigment layer containing a coloring pigment, an epoxy resin, and silica fine particles is provided on a base material, and the thickness of the thermal transfer pigment layer is 0. A thermal transfer sheet having a thickness of 0.5 μm to 1.0 μm, a softening point of an epoxy resin of 70 to 150° C., and a coloring pigment of 20% to 30% with respect to a binder resin has been proposed.

Further, as an example of providing a transfer product having a high reflection density with a thin thermal transfer pigment layer by increasing the pigment concentration in the thermal transfer pigment layer, Patent Document 2 discloses a heat-melting coloring agent containing a coloring pigment on a base material. It is a thermal transfer sheet coated with ink, and a thermal transfer sheet using a metal phthalocyanine compound as a dispersant in heat-meltable colored ink has been proposed.

Japanese Unexamined Patent Application Publication No. 2001-213053 JP-A-4-250094

In the thermal transfer sheet of Patent Document 1, since the amount of the coloring pigment is not so large with respect to the resin, it is difficult to increase the reflection density of the transferred material, and it is difficult to cope with the thinning described above.

The thermal transfer sheet of Patent Document 2 can contain a high concentration of color pigment in the thermal transfer pigment layer, but no consideration is given to cuttability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal transfer sheet which has good cuttability during thermal transfer and which can achieve a high reflection density even if the thermal transfer pigment layer is made thin.

The present invention is a thermal transfer sheet comprising a substrate and a thermal transfer pigment layer provided on one side of the substrate and containing a binder resin, a color pigment, and a dispersant.
The mass ratio of the color pigment to the binder resin is 70% or more and 150% or less, and the mass ratio of the dispersant to the color pigment is 10% or more and 40% or less. The thickness of the thermal transfer pigment layer is 0.6 μm or more and 3 μm or less.

According to the present invention, it is possible to provide a thermal transfer sheet which has good cuttability during thermal transfer and can achieve high reflection density even when the thermal transfer pigment layer is thinned.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section which shows the thermal transfer sheet which concerns on one Embodiment of this invention. (a) is a schematic plan view showing another aspect of the same thermal transfer sheet, and (b) is a schematic cross-sectional view. (a) is a schematic plan view showing another aspect of the same thermal transfer sheet, and (b) is a schematic cross-sectional view.

One embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of a thermal transfer sheet 1 according to this embodiment. The thermal transfer sheet 1 includes a long substrate 10 and a thermal transfer pigment layer 20 formed on the substrate 10 .

(Base material)
Various plastic films can be used as the substrate 10 . For example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins such as polypropylene, polyvinyl chloride, cellophane, acetate, polycarbonate, polysulfone, polyimide, polyvinyl alcohol, aromatic polyamide, aramid, polystyrene, Synthetic resin films such as polyamide, and papers such as condenser paper and paraffin paper can be used alone or in combination. The thickness of the substrate 10 can be appropriately selected according to the material so that its strength, heat resistance, etc. are appropriate. Considering handleability such as workability, the thickness is preferably about 2 μm or more and 9 μm or less.

(Thermal transfer pigment layer)
The thermal transfer pigment layer 20 contains at least a binder resin, a color pigment, and a dispersant.
Various thermoplastic resins can be used as the binder resin, including styrene resins such as polystyrene and polyα-methylstyrene, acrylic resins such as polymethyl methacrylate and polyethyl acrylate, phenol derivative resins, ethylene copolymers, Vinyl resins such as polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polyvinyl acetal, polyester resin, polyamide resin, epoxy resin, polyurethane resin, petroleum resin, ionomer, ethylene acrylic acid copolymer Synthetic resins such as coalescence, ethylene-acrylic acid ester copolymer, cellulose derivatives such as nitrocellulose, ethyl cellulose, cellulose acetate propionate, rosin, rosin-modified maleic acid, ester gum, polyisobutylene rubber, butyl rubber, styrene butadiene rubber, Thermoplastic resins such as derivatives of natural resins such as butadiene acrylonitrile rubber, polyamide resins, polychlorinated olefins, and synthetic rubbers can be used as main components.

Various known pigments can be used as the color pigment.
One type of thermal transfer pigment layer 20 may be provided on the substrate 10, or a plurality of types may be provided. For example, a thermal transfer sheet for monochrome printing in which only a thermal transfer pigment layer containing carbon black as a coloring pigment is formed on the substrate 10 is one aspect of the thermal transfer sheet according to the present embodiment.

2 and 3 show configuration examples having a plurality of thermal transfer pigment layers. In the thermal transfer sheet 1A shown in FIG. 2, a thermal transfer pigment layer Y containing a pigment forming yellow, a thermal transfer pigment layer M containing a pigment forming magenta, and a thermal transfer pigment layer containing a pigment forming cyan are formed on a substrate 10. C has three thermal transfer pigment layers with different colors. The thermal transfer sheet 1B shown in FIG. 3 has four thermal transfer pigment layers including a thermal transfer pigment layer Bk containing carbon black/ink as a pigment.
In the thermal transfer sheets 1A and 1B, a plurality of thermal transfer pigment layers form one unit together with the detection mark 25, and this unit is repeatedly formed in the longitudinal direction of the substrate 10. As shown in FIG.
In addition to the above, the number and types of thermal transfer pigment layers can be appropriately set according to the use of the thermal transfer sheet.
The particle size of the color pigment is preferably 0.05 μm or more and 0.5 μm or less. As used herein, the term "particle size" refers to the volume average particle size, which can be measured by, for example, the BET method or electron microscope observation results by image analysis type particle size distribution measurement software analysis.

A dispersant is added to the thermal transfer pigment layer for the purpose of improving the smoothness of the layer and the dispersibility of the pigment.
The dispersant is not particularly limited as long as it is compatible with the composition in the transfer pigment layer, and a surfactant can be used. For example, fatty acid salts, higher alcohol sulfates, sulfates of fatty amines or aliphatic amides, fatty alcohol phosphates, sulfonates of dibasic fatty acid esters, fatty amide sulfonates, alkylallylsulfonic acids Salts, anionic surfactants such as naphthalene sulfonates of formalin condensation, cationic surfactants such as aliphatic amine salts, quaternary ammonium salts, alkylpyridinium salts, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenols Ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, nonionic surfactants such as polyoxyethylene sorbitan alkyl esters, carboxylic acid derivatives, amphoteric surfactants such as imidazoline derivatives, etc., perfluoroalkyl carboxylic acids , copolymers of fluoroaliphatic group-containing acrylates or fluoroaliphatic group-containing methacrylates and polyoxyalkylene acrylates or polyoxyalkylene methacrylates, and perfluoroalkylsulfonamides.

In the thermal transfer sheets 1A and 1B, a heat resistant lubricating layer 11 is provided on the side of the substrate 10 on which the thermal transfer pigment layer is not provided.
The heat-resistant lubricating layer 11 has an arbitrary structure, and by providing it on the base material 10, it is possible to improve the heat resistance and the running property in contact with a heating unit such as a thermal head during printing.
Materials constituting such a heat-resistant lubricating layer include resins such as cellulose-based resins, polyester-based resins, acrylic-based resins, vinyl-based resins, polyurethane-based resins, polyether-based resins, polycarbonate-based resins, and acetal-based resins. Fluorocarbon resins, silicone resins, silicone oils, polyethylene waxes, those containing lubricants such as phosphoric acid esters, silicone-modified resins, and the like can be used. In addition, fillers such as silica, calcium carbonate, talc, and resin beads may be contained, and a cross-linking agent may be used in combination for the purpose of improving heat resistance.
The heat-resistant lubricating layer 11 is formed by adding a single material or a plurality of materials selected from the above materials and, if necessary, various additives, etc., and dissolving or dispersing them in an appropriate solvent such as water or an organic solvent. A lubricating layer coating solution is prepared, applied by a solvent coating method such as bar coating, blade coating, air knife coating, gravure coating, roll coating, etc., and dried. The coating thickness of the heat-resistant lubricating layer 11 is preferably 0.1 to 4 μm.

The inventors have made various studies on a structure that has good cuttability and can secure a sufficient reflection density in a transferred printed matter even when the thermal transfer pigment layer is thinned to 3 μm or less. As a result, the mass ratio of the color pigment to the binder resin is 70% or more and 150% or less, and the mass ratio of the dispersant to the color pigment is 10% or more and 40% or less. It has been found that both sharpness and reflection density can be improved when the thickness is 0.6 μm or more and 3 μm or less.

The thermal transfer sheet 1 according to the present embodiment has been completed based on the above findings, and achieves both sharpness and reflection density while reducing the thickness of the thermal transfer pigment layer 20 to 0.6 μm or more and 3 μm or less.

The thermal transfer sheet 1 can be produced by applying a coating liquid obtained by diluting a binder resin, a coloring pigment, and a dispersant satisfying the above ratios with a solvent onto the base material 10 and drying the coating liquid. Various known coating methods can be appropriately selected and used, and the drying conditions can be, for example, 100° C. and 1 minute.

The thermal transfer sheet of the present embodiment will be further described using examples and comparative examples. The technical scope of the present invention is in no way limited only by the specific contents of Examples and Comparative Examples.
In the following description, "parts" means parts by mass unless otherwise specified.

(Example 1)
A resin film was prepared as a base material.
A thermal transfer pigment layer coating liquid having the following composition was applied onto the substrate by a gravure coating method so that the film thickness after drying would be 1.5 μm. Then, by drying at 100° C. for 1 minute, a thermal transfer pigment layer was formed, and a thermal transfer sheet according to Example 1 was produced. This thermal transfer sheet has a black thermal transfer pigment layer.
<Coating liquid for thermal transfer pigment layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 20 parts Color pigment: Carbon black (average particle size 0.14 μm) 20 parts Dispersant: Fluorine surfactant 4 parts Solvent: Ethyl acetate 28 parts Methyl ethyl ketone 28 copies

(Example 2)
A thermal transfer sheet according to Example 2 was produced in the same manner as in Example 1, except that the amount of the dispersant in the thermal transfer pigment layer coating liquid was changed to 6 parts.
(Example 3)
A thermal transfer sheet according to Example 3 was produced in the same manner as in Example 1, except that the amount of the color pigment in the thermal transfer pigment layer coating liquid was changed to 16 parts.
(Example 4)
A thermal transfer sheet according to Example 4 was produced in the same manner as in Example 1, except that the amount of the color pigment in the thermal transfer pigment layer coating liquid was changed to 26 parts.
(Example 5)
A thermal transfer sheet according to Example 5 was produced in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid was applied so that the film thickness after drying was 0.7 μm.

(Comparative example 1)
A thermal transfer sheet according to Comparative Example 1 was produced in the same manner as in Example 1, except that the amount of the dispersant in the thermal transfer pigment layer coating liquid was changed to 9 parts.
(Comparative example 2)
A thermal transfer sheet according to Comparative Example 2 was produced in the same manner as in Example 1, except that the amount of the dispersant in the thermal transfer pigment layer coating liquid was changed to 1 part.
(Comparative Example 3)
A thermal transfer sheet according to Comparative Example 3 was produced in the same manner as in Example 1, except that the amount of the color pigment in the thermal transfer pigment layer coating liquid was changed to 10 parts.
(Comparative Example 4)
A thermal transfer sheet according to Comparative Example 4 was prepared in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid was applied so that the film thickness after drying was 0.3 μm.
(Comparative Example 5)
A thermal transfer sheet according to Comparative Example 5 was produced in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid was applied so that the film thickness after drying was 3.5 μm.

The following evaluations were performed using the thermal transfer sheet of each example.
(Transfer to transferred material)
A surface-untreated polyethylene terephthalate sheet was used as an object to be transferred.
The thermal transfer pigment layers of the thermal transfer sheets of each example were superimposed on each other with the thermal transfer pigment layer facing the transfer material, and the thermal transfer pigment layer was transferred to the transfer material using a thermal simulator for evaluation. Transfer conditions are as follows.
(transcription conditions)
Printing environment: 23°C 50% RH (relative humidity)
Applied voltage: 17V
Transfer speed: 0.33 inch/msec
Print density: main scanning 300dpi, sub-scanning 300dpi

The transcripts according to each example were evaluated for the following items.
<Cutability>
In the thermally transferred pigment layer transferred to the transfer material, the irregularities at the edges (protrusion from the set shape) were measured using a Keyence Digital Microscope VHX-1000. The evaluation criteria were the following three grades, and ⊚ and ◯ were regarded as passed.
◎ (very good): maximum unevenness is less than 50 μm ○ (good): maximum unevenness is less than 100 μm × (bad): maximum unevenness is 100 μm or more

<Reflection Density>
The reflection density (OD) of the surface of the thermal transfer pigment layer transferred to the transfer material was measured using X-rite 528 manufactured by X-rite. The evaluation criteria were the following three grades, and ⊚ and ◯ were regarded as passed.
◎ (very good): OD is 2.5 or more ○ (good): OD is 1.5 or more and less than 2.5 × (bad): OD is less than 1.5

Furthermore, the following items were evaluated for the coating liquid according to each example.
<Coating liquid stability>
The thermal transfer pigment layer coating solution of each example was left for 1 hour after preparation, and the presence or absence of aggregates was visually evaluated. Evaluation was made into the following two grades, and (circle) was made into the pass.
○ (good): Aggregates are not observed × (bad): Aggregates are observed

Table 1 shows the parameters and evaluation results for each example. In Table 1, the "color pigment ratio" is the mass ratio of the color pigment to the binder resin, and the "dispersant ratio" is the mass ratio of the dispersant to the color pigment.

In Example 2, the amount of dispersant was larger than in other examples, so the cutability was slightly reduced, and in Example 3, the amount of coloring pigment was smaller than in other examples, so the reflection density was slightly reduced. Example 1 also gave good results.

In Comparative Example 1, the reflection density was good, but the amount of the dispersing agent exceeded the above range, so that the cuttability deteriorated to an unacceptable level. In Comparative Example 2, although the sharpness was good, the amount of the dispersing agent was less than the above range, so the dispersion was not sufficient and the stability of the coating solution was deteriorated.
In Comparative Example 3, since the amount of the coloring pigment was less than the above range, the reflection density was remarkably lowered. In Comparative Examples 4 and 5, the thickness of the thermal transfer pigment layer was changed, and the reflection density and sharpness were remarkably deteriorated.

Although one embodiment of the present invention has been described above, the technical scope of the present invention is not limited to the above content, and various modifications are made to each component within the scope of the present invention. It is possible to Some modifications are exemplified below, but not all of them, and other modifications are possible. Two or more of these changes may be appropriately combined.

- In the substrate, the surface on which the thermal transfer pigment layer is provided may be subjected to an adhesion treatment to enhance the adhesion of the thermal transfer pigment layer. As the adhesion treatment, known techniques such as corona treatment, flame treatment, ozone treatment, ultraviolet treatment, radiation treatment, roughening treatment, plasma treatment, and primer treatment can be applied, and two or more of these treatments can be used in combination. You may

- In the substrate, the surface on which the thermal transfer pigment layer is not provided may be provided with a layer or treated to improve lubricity and heat resistance.

1, 1A, 1B Thermal transfer sheet 10 Base material 20, Bk, C, M, Y Thermal transfer pigment layer

Claims (3)

a substrate;
a thermal transfer pigment layer provided on one surface of the substrate and containing a binder resin, a coloring pigment, and a dispersant;
with
The mass ratio of the coloring pigment to the binder resin is 70% or more and 150% or less,
The mass ratio of the dispersant to the color pigment is 10% or more and 40% or less,
The thermal transfer pigment layer has a thickness of 0.6 μm or more and 3 μm or less.
Thermal transfer sheet. The particle size of the color pigment is 0.05 μm or more and 0.5 μm or less,
The thermal transfer sheet according to claim 1. A plurality of the thermal transfer pigment layers are repeatedly provided on the substrate,
The thermal transfer sheet according to claim 1 or 2.

Images