JP7779100B2 - Thermal transfer sheets and transfers - Google Patents

Description

The present invention relates to a thermal transfer sheet. It also refers to a transfer product formed using this thermal transfer sheet.

Thermal transfer, one of the image formation methods, allows for a great degree of freedom as it allows for the combination of multiple colors in any shape. Furthermore, compared to methods such as silk printing, it allows for thin, thin designs to be applied, giving it an advantage in terms of making touch panels lighter and more compact.

2. Description of the Related Art As thermal transfer recording methods for forming an image on a transfer medium using a printer having a thermal head, a dye sublimation thermal transfer method and a melt transfer method are known.
The dye-sublimation transfer method involves placing a thermal transfer sheet with a dye layer made of sublimable dye and binder resin on a target object and applying heat. In the dye-sublimation transfer method, the dye transfers to the target object to form an image. The dye-sublimation transfer method allows for high-resolution gradation expression by controlling the amount of heat, but its application to fields requiring durability, especially heat resistance and light resistance, is limited.

On the other hand, the melt transfer method uses a thermal transfer sheet with a thermal transfer pigment layer made of colored pigment and binder resin on a substrate, and forms an image by heat fusing the thermal transfer pigment layer onto a receiving material. Images formed using the melt transfer method are highly dense and durable, and are suitable for recording binary images such as characters and line drawings.

In recent years, with the spread of smartphones and tablets and the adoption of touch panels in home appliances, automobiles, and more, capacitive switches are now being installed in a wide variety of electrical appliances. In addition to the design flexibility that allows them to be processed into any shape, touch panels with capacitive switches require features such as light-blocking properties to prevent backlight leakage and insulation (high resistance) to prevent false detection by the touch panel.

Carbon black is widely known as a light-shielding material, but since carbon black is generally a conductive substance, it is difficult to use when high resistance is required.
In relation to this problem, Patent Document 1 describes that by reducing the weight ratio of carbon black in the coating film to 30% or less and further adding red, blue, and yellow pigments, it is possible to realize a sheet with high light-blocking properties while suppressing electrical conductivity.

Patent No. 4533446

The method described in Patent Document 1 requires the use of four or more pigments, making production cumbersome. Furthermore, because three pigments (red, blue, and yellow) are required to reproduce black, the pigment ratio in the coating film is higher than in a coating made using only carbon black when attempting to achieve the same transmission density, limiting the achievable light-blocking properties.

In light of the above circumstances, the present invention aims to provide a thermal transfer sheet that can form a layer that has both high light-blocking properties and high insulation properties.

A first aspect of the present invention is a thermal transfer sheet comprising a substrate and a thermal transfer pigment layer formed on the substrate.
The thermal transfer pigment layer contains a binder resin, carbon black insulated with an epoxy resin , and a dispersant.
The amount of the insulating coated carbon black is 60% or more and 130% or less of the mass of the binder resin, and the amount of the dispersant is 10% or more and 40% or less of the mass of the insulating coated carbon black.

A second aspect of the present invention is a transfer having a black layer formed by thermal transfer.
The black layer contains a binder resin, carbon black insulated and coated with an epoxy resin , and a dispersant.
The amount of the insulating coated carbon black is 60% or more and 130% or less of the mass of the binder resin, and the amount of the dispersant is 10% or more and 40% or less of the mass of the insulating coated carbon black.

The thermal transfer sheet of the present invention can form a layer on the receiving material that combines high light-blocking properties and high insulation properties.

1 is a schematic cross-sectional view of a thermal transfer sheet according to one embodiment of the present invention.

An embodiment of the present invention will be described with reference to FIG.
Fig. 1 is a schematic cross-sectional view showing a thermal transfer sheet 1 of this embodiment. As shown in Fig. 1, the thermal transfer sheet 1 includes a substrate 10 and a thermal transfer pigment layer 20. The thermal transfer pigment layer 20 is provided on a first surface 10a of the substrate 10.

The substrate 10 must be heat-resistant and strong enough not to soften or deform under the heat and pressure of thermal transfer, and may be made of, for example, synthetic resin films such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cellophane, acetate, polycarbonate, polysulfone, polyimide, polyvinyl alcohol, aromatic polyamide, aramid, polystyrene, or other papers, either alone or in combination. Of these, polyethylene terephthalate is preferred in terms of physical properties, processability, cost, and the like.
From the viewpoint of operability and processability, the thickness of the substrate 10 can be in the range of 2 μm to 50 μm, but taking into consideration handling such as transferability and processability, a thickness of approximately 2 μm to 9 μm is more preferable.

In the substrate 10, a second surface 10b opposite to the first surface 10a may be subjected to a treatment to impart lubricity or heat resistance.
The substrate 10 may be subjected to an adhesion treatment on the first surface 10a on which the thermal transfer pigment layer 20 is formed. 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 may be applied, and two or more of these treatments may be used in combination.

The thermal transfer pigment layer 20 is a layer containing a binder resin, carbon black having an insulating coating (hereinafter referred to as "insulating carbon"), and a dispersant.
The amount of insulating carbon in the thermal transfer pigment layer 20 is 60% to 130% by mass relative to the binder resin. The amount of dispersant in the thermal transfer pigment layer 20 is 10% to 40% by mass relative to the insulating carbon.

Examples of thermoplastic resins that are the main component of the binder resin include epoxy resins, polyester resins, acrylic resins, urethane resins, styrene-based resins, phenol-derived resins, ethylene copolymer resins, and vinyl acetate resins.
There are no particular restrictions on the material of the insulating coating of the insulating carbon, but examples include various resins such as epoxy resin.

There are no specific requirements for the dispersant material, and any known dispersant can be selected and used, including polymeric, non-ionic, anionic, and cationic types. Specific examples include acrylics, esters such as carboxylic acid esters, carboxylates, sulfonates, and silicones. Examples of products include DISPERBYK-161 (manufactured by BYK Japan) and DISPERLON DA-7301 (manufactured by Kusumoto Chemicals). Having a dispersant ratio of 10% or more to the insulating carbon improves the stability of the dispersion, while having a ratio of 40% or less improves the adhesion of the thermal transfer pigment layer 20.

The thermal transfer pigment layer 20 can be formed by preparing a coating liquid for the thermal transfer pigment layer containing at least a binder resin, insulating carbon, and a dispersant, applying the coating liquid to the first surface 10a, and drying it.
The thickness of the thermal transfer pigment layer 20 can be set as appropriate, but is preferably, for example, 0.5 μm or more and 3.0 μm or less.

The thermal transfer pigment layer 20 according to this embodiment uses only black insulating carbon as the pigment, and therefore can form a black transfer layer with high electrical resistance on the transfer target while exhibiting high light blocking properties even at a thickness of approximately 0.5 μm to 3.0 μm. Therefore, a transfer product having a black layer formed using the thermal transfer sheet 1 according to this embodiment is suitable for manufacturing touch panels that use electrostatic capacitance and are installed in various electrical appliances.
Furthermore, since the thermal transfer pigment layer 20 contains only one type of pigment, the coating liquid for forming the thermal transfer pigment layer can be easily prepared, and the thermal transfer sheet can be produced efficiently.

The thermal transfer sheet of the present invention will be further explained using examples and comparative examples, but the present invention is not limited by the contents of the examples and comparative examples.
In the text, "parts" means parts by mass unless otherwise specified.

<Preparation of Coating Solution for Thermal Transfer Pigment Layer>
Example 1
The composition of the coating liquid for the thermal transfer pigment layer in Example 1 is shown below.
<Coating Solution 1 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 17 parts Dispersant 3.5 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

Coating Solution 1 for Thermal Transfer Pigment Layer was applied by gravure coating to a first surface of a polyethylene terephthalate substrate (thickness: 4.5 μm) so that the film thickness after drying would be 1.5 μm. This was then dried at 100° C. for 1 minute to form a thermal transfer pigment layer on the first surface of the substrate.
In this manner, the thermal transfer sheet according to Example 1 was produced.

Example 2
A thermal transfer sheet according to Example 2 was prepared in the same manner as in Example 1, except that Coating Liquid 2 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating liquid 2 for thermal transfer pigment layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 10.2 parts Dispersant 2.04 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

Example 3
A thermal transfer sheet according to Example 3 was prepared in the same manner as in Example 1, except that Coating Liquid 3 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating liquid 3 for thermal transfer pigment layer>
Binder resin: Epoxy resin (jER (registered trademark) 1007 manufactured by Mitsubishi Chemical Corporation) 17 parts Insulating carbon 22.1 parts Dispersant 4.42 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

Example 4
A thermal transfer sheet according to Example 4 was prepared in the same manner as in Example 1, except that Coating Liquid 1 for Thermal Transfer Pigment Layer was replaced with Coating Liquid 4 for Thermal Transfer Pigment Layer having the following composition.
<Coating Solution 4 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 17 parts Dispersant 5.1 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

Example 5
A thermal transfer sheet according to Example 5 was prepared in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid 1 was applied so that the film thickness after drying would be 0.8 μm.
Example 6
A thermal transfer sheet according to Example 6 was prepared in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid 1 was applied so that the film thickness after drying would be 3.5 μm.
Example 7
A thermal transfer sheet according to Example 7 was prepared in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid 1 was applied so that the film thickness after drying would be 0.5 μm.
(Example 8)
A thermal transfer sheet according to Example 8 was prepared in the same manner as in Example 1, except that the thermal transfer pigment layer coating liquid 1 was applied so that the film thickness after drying would be 3.0 μm.

(Comparative Example 1)
The composition of the coating liquid for the thermal transfer pigment layer according to Comparative Example 1 is shown below.
<Coating Solution 5 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (jER (registered trademark) 1007, manufactured by Mitsubishi Chemical Corporation) 17 parts Carbon black (without insulating coating) 8.5 parts Dispersant: 0.68 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts Coating Solution 5 for thermal transfer pigment layer was applied by gravure coating to a first surface of the same substrate as in Example 1 so that the film thickness after drying would be 0.8 μm. This was then dried at 100° C. for 1 minute to form a thermal transfer pigment layer on the first surface of the substrate.
In this manner, a thermal transfer sheet according to Comparative Example 1 was prepared.

(Comparative Example 2)
A thermal transfer sheet according to Comparative Example 2 was prepared in the same manner as in Example 1, except that Coating Liquid 6 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating Solution 6 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (jER (registered trademark) 1007 manufactured by Mitsubishi Chemical Corporation) 17 parts Insulating carbon 3.4 parts Dispersant 0.68 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

(Comparative Example 3)
A thermal transfer sheet according to Comparative Example 3 was prepared in the same manner as in Example 1, except that Coating Liquid 7 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating Solution 7 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 23.8 parts Dispersant 4.76 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 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 Coating Liquid 8 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating Solution 8 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 17 parts Dispersant 7.65 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

(Comparative Example 5)
A thermal transfer sheet according to Comparative Example 5 was prepared in the same manner as in Example 1, except that Coating Liquid 9 for Thermal Transfer Pigment Layer having the following composition was used instead of Coating Liquid 1 for Thermal Transfer Pigment Layer.
<Coating Solution 9 for Thermal Transfer Pigment Layer>
Binder resin: Epoxy resin (Mitsubishi Chemical Corporation jER (registered trademark) 1007) 17 parts Insulating carbon 17 parts Dispersant 0.765 parts Solvent: Butyl acetate 40 parts Methyl ethyl ketone 26.5 parts

The thermal transfer pigment layer side of the thermal transfer sheet according to each example was placed facing an untreated polyethylene terephthalate sheet, and transfer was performed using a thermal simulator. As a result, a transfer product according to each example was obtained, in which a black layer was transferred onto the polyethylene terephthalate sheet. The transfer conditions were as follows:
Printing environment: 23°C, 50% RH (relative humidity)
Applied voltage: 17V
Transfer speed: 0.33 inch/ms
Print density: Main scanning 300 dpi, sub scanning 300 dpi

The transcripts according to each example were used to carry out the following evaluations.
<Cutting ability>
The maximum unevenness at the edge of the black layer was measured using a digital microscope VHX-1000 manufactured by Keyence Corp. The evaluation criteria were rated on the following four levels: △ or above is a level that presents no practical problems.
◎ (Excellent): The maximum unevenness is less than 50 μm. ◯ (Good): The maximum unevenness is 50 μm or more and less than 90 μm. △ (Fair): The maximum unevenness is 90 μm or more and less than 110 μm. × (Bad): The maximum unevenness is 110 μm or more. <Reflection density>
The reflection density (OD) of the black layer was measured using an X-rite 528 manufactured by X-rite Co., Ltd. Evaluation criteria were based on the following three levels: Good or better is a level that presents no practical problems.
◎ (Good): OD 2.5 or more ◯ (Fair): OD 1.5 or more but less than 2.5 × (Bad): OD less than 1.5 <Resistance value>
The electrical resistance of the black layer was measured using a Hiresta MCP-HT450 manufactured by Mitsubishi Chemical Corp. Evaluation criteria were based on the following two levels, with ○ representing pass.
○ (Good): Resistance value 10 ¹³ Ω·m or more × (Bad): Resistance value less than 10 ¹³ Ω·m

In addition, the following items were evaluated:
<Coating solution stability>
The coating liquid for the thermal transfer pigment layer of each example was left to stand for 1 hour after preparation, and the presence or absence of aggregates was confirmed. Evaluation was based on the following two-level scale, with ◯ being considered a pass.
◯ (Good): No aggregation occurs × (Bad): Aggregates occur <blocking>
Using a thermal head printer different from the thermal simulator, printing was carried out on ordinary image receiving paper. The evaluation criteria were based on the following two levels, with 0 being considered pass.
◯ (Good): Printing possible without problems × (Bad): Jamming occurred and printing was not possible The results are shown in Table 1.

The transfer products of each Example had practically acceptable levels in all evaluation items. From the reflection density results of Example 2, it was considered preferable that the amount of insulating carbon be 70% or more relative to the binder resin. From the results of cuttability of Example 5, it was considered that cuttability was good when the thickness of the thermal transfer pigment layer was 1 μm or less, and in that case, it was considered that sufficient reflection density could be achieved by setting the amount of insulating carbon to 110% or more relative to the binder resin.
The results of the cutting performance in Examples 6 and 8 suggest that the thickness of the thermal transfer pigment layer should preferably be 3.0 μm or less. The results of the reflection density in Examples 7 and 8 suggest that the thickness of the thermal transfer pigment layer should preferably be 0.5 μm or more.

In Comparative Example 1, in which carbon black without an insulating coating was used, sufficient insulating properties could not be imparted to the black layer.
The results of Comparative Examples 1 and 2 show that when the amount of carbon is less than 50% relative to the binder resin, problems arise in terms of light-shielding properties.
The results of Comparative Example 3 show that when the amount of insulating carbon exceeds 130% relative to the binder resin, problems arise in terms of cutting property and blocking.
The results of Comparative Example 4 show that when the amount of dispersant exceeds 40% relative to the insulating carbon, problems arise in terms of cutting ability.
The results of Comparative Example 5 show that when the amount of dispersant is less than 10% relative to the insulating carbon, problems arise in terms of coating solution stability.

The above describes one embodiment of the present invention, but the specific configuration is not limited to this embodiment, and configuration changes and combinations that do not deviate from the gist of the present invention are also included.

1 Thermal transfer sheet 10 Substrate 20 Thermal transfer pigment layer

Claims (3)

A substrate;
a thermal transfer pigment layer formed on the substrate, the thermal transfer pigment layer including a binder resin, carbon black insulated with an epoxy resin , and a dispersant;
Equipped with
the amount of the carbon black is 60% or more and 130% or less based on the mass of the binder resin,
the amount of the dispersant is 10% or more and 40% or less based on the mass of the carbon black;
Thermal transfer sheet. the thickness of the thermal transfer pigment layer is 0.5 μm or more and 3.0 μm or less;
The thermal transfer sheet according to claim 1 . A transfer having a black layer formed by thermal transfer,
the black layer contains a binder resin, carbon black insulated with an epoxy resin , and a dispersant;
the amount of the carbon black is 60% or more and 130% or less based on the mass of the binder resin,
the amount of the dispersant is 10% or more and 40% or less based on the mass of the carbon black;
Transcripts.