JP7380283B2 - thermal transfer sheet - Google Patents

Description

The present disclosure relates to thermal transfer sheets.

2. Description of the Related Art Arcade game machines are known as one of the game machines installed and used in game centers, commercial facilities, and the like. Recently, the usage patterns of arcade game machines have been diversifying, and arcade game machines with built-in infrared scanners and the like have been proposed. Such arcade game machines often use cards on which invisible images are printed as code information for defining characters, as well as visible images showing character images, names, statuses, and the like. One form of this is a card or the like in which an invisible image (sometimes referred to as a stealth ink layer, etc.) and a visible image (sometimes referred to as a thermal transfer image) are formed on a transfer target so that they overlap. It has been known. In recent years, attempts have been made to manufacture such cards using thermal transfer sheets. (For example, see Patent Document 1).

Japanese Patent Application Publication No. 2017-081109

When forming a stealth ink layer on a transfer target such as a card, a stealth ink layer with a light color is required so as not to interfere with a visible image formed overlying the stealth ink layer. However, the light-colored stealth ink layer often had poor light resistance.

The main object of the present disclosure is to provide a thermal transfer sheet that can form a stealth ink layer that is so light in color that it does not interfere with the visible images that are formed overlappingly, and that has excellent light resistance.

The present disclosure for solving the above problems includes a base material and a stealth ink layer provided on one surface of the base material and containing an invisible light absorbing material, wherein the invisible light absorbing material is as follows: This is a thermal transfer sheet characterized by having the structural formula (1).

ただし、上記構造式（１）において、
Ｍは銅または一酸化バナジウムであり、
Ｒ１、Ｒ２、Ｒ３、およびＲ４は、それぞれ独立にＯ－Ａ１、Ｓ－Ａ２、およびＮ－Ａ３Ａ４のいずれかであり、
Ａ１、Ａ２、Ａ３、およびＡ４は、それぞれ独立にアルキル基、アリール基、アラルキル基、アルキルアミノ基、環状アルキルアミノ基、アルコキシ基、ニトロ基、モノホリル基、シアノ基、トリフルオロメチル基、カルボキシル基、エステル基、ハロゲン原子のいずれかである。

However, in the above structural formula (1),
M is copper or vanadium monoxide;
R1, R2, R3, and R4 are each independently O-A1, S-A2, and N-A3A4,
A1, A2, A3, and A4 each independently represent an alkyl group, an aryl group, an aralkyl group, an alkylamino group, a cyclic alkylamino group, an alkoxy group, a nitro group, a monophoryl group, a cyano group, a trifluoromethyl group, a carboxyl group , an ester group, or a halogen atom.

Further, in the thermal transfer sheet of the present disclosure, the maximum absorption wavelength of the invisible light absorbing material may be 850 nm or more and 900 nm or less.

In the thermal transfer sheet of the present disclosure, the stealth ink layer may have a reflectance of 85% or more in the range from 400 nm to 700 nm after being transferred to the transfer target.

Further, in the thermal transfer sheet of the present disclosure, a receptor layer capable of receiving a dye and a dye layer may be further provided in random order on one surface of the base material. .

According to the thermal transfer sheet of the present disclosure, it is possible to form a stealth ink layer that is pale in color to the extent that it does not interfere with the visible image to be superimposed and has excellent light resistance.

FIG. 1 is a schematic cross-sectional view showing an example of a thermal transfer sheet according to an embodiment. FIG. 1 is a schematic cross-sectional view showing an example of a thermal transfer sheet according to an embodiment. FIG. 1 is a schematic cross-sectional view showing an example of a printed matter formed using the thermal transfer sheet of the present embodiment.

Embodiments of the present disclosure will be described below with reference to the drawings and the like. Note that the present disclosure can be implemented in many different ways, and should not be construed as being limited to the contents described in the embodiments exemplified below. In addition, in order to make the explanation more clear, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual aspect, but these are only examples, and the interpretation of this disclosure will be limited. It is not limited. In addition, in the specification of the present application and each figure, the same elements as those described above with respect to the existing figures are denoted by the same reference numerals, and detailed explanations thereof may be omitted as appropriate. Further, for convenience of explanation, the words "up" and "down" will be used in the explanation, but the up and down directions may be reversed. The same applies to the left and right directions.

-Thermal transfer sheet FIG. 1 is a schematic cross-sectional view of a thermal transfer sheet according to an embodiment of the present disclosure.

As shown in FIG. 1, the thermal transfer sheet 10 of this embodiment includes a base material 11 and a stealth ink layer 12 provided on one surface thereof (the upper surface in FIG. 1). Each layer constituting the thermal transfer sheet 10 will be explained below.

(Base material)
The base material 11 has heat resistance to thermal energy (for example, heat from a thermal head) when transferring the stealth ink layer 12 etc. to a transfer target, mechanical strength capable of supporting the stealth ink layer 12 etc., and resistance. As long as it has solvent properties, it can be used without particular restriction. Examples include various plastic films or sheets. Materials for various plastic films or sheets include polyester such as polyethylene terephthalate (PET), polycarbonate, polyimide, polyetherimide, cellulose derivatives, polyethylene, polypropylene, polystyrene, acrylic, polyvinyl chloride, polyvinylidene chloride, nylon, and polyester. Examples include ether ether ketone.

The base material 11 may be composed of a copolymer or a mixture (including an alloy) containing the above resin as a main component. Alternatively, it may be a laminate consisting of multiple layers. Further, the base material 11 may be a stretched film or an unstretched film, but for the purpose of improving strength, it is preferable to use a film stretched in a uniaxial direction or a biaxial direction.

The thickness of the base material 11 is not particularly limited, but is preferably 2.5 μm or more and 50 μm or less, for example. By setting the thickness of the base material within the above numerical range, the transferability of the stealth ink layer 12 and the like can be improved while maintaining mechanical strength.

The base material 11 may be subjected to corona discharge treatment, plasma treatment, ozone treatment, flame treatment, primer (also called anchor coat, adhesion promoter, or adhesive agent) coating treatment, preheating treatment, dust removal treatment, vapor deposition treatment, alkali treatment, or Adhesion-facilitating treatment such as application of a charge-suppressing layer may also be performed. Furthermore, additives such as fillers, plasticizers, colorants, and antistatic agents may be added to the base material 11 as necessary.

(Stealth ink layer)
The stealth ink layer 12 in the thermal transfer sheet 10 of the present embodiment is a layer for forming a stealth ink layer on the transfer target that is invisible in the visible light region but distinguishable in the invisible light region, and has the following structural formula: Contains the invisible light absorbing material (1). Note that in the present disclosure, "visible light" means light with a wavelength greater than 400 nm and less than 750 nm.

ただし、上記構造式（１）において、
Ｍは銅または一酸化バナジウムであり、
Ｒ１、Ｒ２、Ｒ３、およびＲ４は、それぞれ独立にＯ－Ａ１、Ｓ－Ａ２、およびＮ－Ａ３Ａ４のいずれかであり、
Ａ１、Ａ２、Ａ３、およびＡ４は、それぞれ独立にアルキル基、アリール基、アラルキル基、アルキルアミノ基、環状アルキルアミノ基、アルコキシ基、ニトロ基、モノホリル基、シアノ基、トリフルオロメチル基、カルボキシル基、エステル基、ハロゲン原子のいずれかである。

However, in the above structural formula (1),
M is copper or vanadium monoxide;
R1, R2, R3, and R4 are each independently O-A1, S-A2, and N-A3A4,
A1, A2, A3, and A4 each independently represent an alkyl group, an aryl group, an aralkyl group, an alkylamino group, a cyclic alkylamino group, an alkoxy group, a nitro group, a monophoryl group, a cyano group, a trifluoromethyl group, a carboxyl group , an ester group, or a halogen atom.

Note that in the present disclosure, examples of invisible light include infrared rays and ultraviolet rays. "Infrared light" means light with a wavelength of 750 nm or more and 2000 nm or less. "Ultraviolet light" means light with a wavelength of 280 nm or more and 400 nm or less.

By using the phthalocyanine compound of structural formula (1) as the invisible light absorbing material constituting the stealth ink layer 12, the color of the stealth ink layer after transfer can be made thinner to the extent that it does not interfere with the visible image, and It can also have good light resistance.

The maximum absorption wavelength of the invisible light absorbing material is preferably 850 nm or more and 900 nm or less, and the reflectance of the stealth ink layer after being transferred to the object is preferably 85% or more at 400 nm or more and 700 nm or less. By satisfying these conditions, the stealth ink layer after transfer can have good invisibility.

The content of the invisible light absorbing material represented by structural formula (1) is not particularly limited, but is preferably 1% by mass or more and 60% by mass or less, and 5% by mass or more and 40% by mass, based on the entire mass of the stealth ink layer 12. The following are more preferable. By setting the content of the invisible light absorbing material within the above numerical range, it is possible to achieve both transferability when transferring the stealth ink layer 12 and readability of the stealth ink layer after transfer.

The stealth ink layer 12 may contain a binder resin in addition to the invisible light absorbing material represented by structural formula (1).

Examples of the binder resin included in the stealth ink layer 12 include polyester, fluororesin, polystyrene, acrylic resin, cellulose resin, polycarbonate, polyamide, polyvinyl chloride, polyvinyl acetate, polyolefin, polyvinyl alcohol, polyvinylpyrrolidone, polyimide, and phenol. Examples include resins, known resins such as polyurethane, and copolymers thereof.

The content of the binder resin in the stealth ink layer 12 is preferably 40% by mass or more and 99% by mass or less, more preferably 60% by mass or more and 95% by mass or less, based on the entire mass of the stealth ink layer 12. preferable.

Note that if the invisible light absorption material contained in the stealth ink layer has poor dispersibility, the absorption efficiency of invisible light may decrease. Therefore, it is preferable to design the type and content of the binder resin in consideration of the dispersibility of the invisible light absorbing material.

The thickness of the stealth ink layer 12 is preferably 0.1 μm or more and 5 μm or less, more preferably 0.3 μm or more and 2 μm or less.

The stealth ink layer 12 is prepared by preparing a coating liquid by dissolving or dispersing an invisible light absorbing material, a binder resin, and additives added as necessary in a suitable solvent such as water or an organic solvent. Can be formed by coating on materials and drying. As a coating method, gravure printing method, screen printing method, reverse coating method using gravure plate, etc. can be used.

It should be noted that each layer constituting the thermal transfer sheet 10 of this embodiment described below can be formed by the same method as the stealth ink layer 12, unless otherwise specified.

- Other embodiments of thermal transfer sheet FIG. 2 is a schematic cross-sectional view of a thermal transfer sheet according to another embodiment of the present disclosure.

As shown in FIG. 2, the thermal transfer sheet 10 of this embodiment includes a base material 11, a stealth ink layer 12 provided on one surface thereof (the upper surface in FIG. 1), and a receptor layer capable of receiving dyes. 13 and a dye layer 14 containing a dye are arranged in random order on the surface, and furthermore, a back layer 15 is provided on the other surface of the base material 11.

(receptive layer)
The receptor layer 13 in the thermal transfer sheet 10 of this embodiment is a layer for forming a receptor layer capable of receiving a dye on a transfer target. The receptor layer 13 is not particularly limited, and a conventionally known receptor layer is appropriately selected and used.

For example, as a material for forming the receptor layer 13, a conventionally known resin material that easily accepts a heat-transferable coloring material such as a sublimable dye or a heat-melting ink can be used. For example, polyolefins such as polypropylene, halogenated resins such as polyvinyl chloride or polyvinylidene chloride, vinyl resins such as polyvinyl acetate, vinyl chloride-vinyl acetate polymers, ethylene-vinyl acetate copolymers or polyacrylic esters, PET or polyesters such as PBT, cellulose resins such as cellulose diastase, copolymers of olefins and other vinyl polymers, polystyrene, polyamides, ionomers, or polycarbonates, among which vinyl chloride-vinyl acetate copolymers, Or polyvinyl chloride is preferable, and vinyl chloride-vinyl acetate copolymer is particularly preferable.

The thickness of the receiving layer 13 is preferably 0.2 μm or more and 10 μm or less, more preferably 0.5 μm or more and 5 μm or less.

(dye layer)
The dye layer 14 in the thermal transfer sheet 10 of this embodiment is a layer for forming a visible image by transferring the dye to the receiving layer 13 formed on the transfer target. The dye layer 14 is not particularly limited either, and conventionally known dye layers, such as a yellow dye layer, a magenta dye layer, and a cyan dye layer, are appropriately selected and used.

The dye layer 14 preferably contains a sublimable dye, such as diarylmethane dye, triarylmethane dye, thiazole dye, merocyanine dye, pyrazolone dye, methine dye, indoaniline dye, acetophenone azomethine. , pyrazoloazomethine, imidazolazomethine, imidazoazomethine, pyridone azomethine, azomethine dyes, xanthene dyes, oxazine dyes, cyanostyrene dyes such as dicyanostyrene, tricyanostyrene, thiazine dyes, azine dyes, acridine Azo dyes such as benzene azo dyes, pyridone azo, thiophene azo, isothiazo azo, pyrrole azo, pyrazole azo, imidazole azo, thiadiazole azo, triazole azo, disazo, spiropyran dyes, indolino spiropyran dyes, fluoran dyes , rhodamine lactam dyes, naphthoquinone dyes, anthraquinone dyes, quinophthalone dyes, etc. More specifically, MSRedG (manufactured by Mitsui Chemicals, Inc.), Macrolex Red Violet R (manufactured by Bayer), CeresRed 7B Red dyes such as (manufactured by Bayer), Samaron Red F3BS (manufactured by Mitsubishi Chemical Corporation), Holon Brilliant Yellow 6GL (manufactured by Clariant), PTY-52 (manufactured by Mitsubishi Chemical Corporation), Macrolex Yellow 6G (manufactured by Mitsubishi Chemical Corporation), etc. Kayaset Blue 714 (manufactured by Nippon Kayaku Co., Ltd.), Waxorin Blue AP-FW (manufactured by ICI), Holon Brilliant Blue S-R (manufactured by Sandoz), MS Blue 100 (manufactured by Mitsui Chemicals, Inc.), C. I. A blue dye such as Solvent Blue 22 can be used.

The content of the dye in the dye layer 14 is preferably in the range of 50 parts by mass or more and 350 parts by mass, and more preferably in the range of 80 parts by mass or more and 300 parts by mass, based on 100 parts by mass of the total solid content of the binder resin described below. This makes it possible to suppress deterioration in print density and storage stability.

The dye layer 14 preferably contains a binder resin for supporting the dye. Examples of the binder resin include cellulose resin, vinyl resin, acrylic resin, polyurethane, polyamide, polyester, and polyvinyl acetal.

The content of the binder resin in the dye layer 14 is preferably 20% by mass or more and 80% by mass or less.

(back layer)
The back layer 15 in the thermal transfer sheet 10 of the present embodiment is an optional back layer 15 provided to suppress adverse effects such as thermal fusion, sticking, and wrinkles when the back surface of the base material 11 is heated by a thermal head or the like during thermal transfer. This is the layer of

There is no limitation on the material of the back layer 15, and examples include cellulose resins such as ethyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate butyrate, nitrocellulose, cellulose acetate butyrate or cellulose acetate propionate, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral. , vinyl resins such as polyvinyl acetal or polyvinylpyrrolidone, acrylic resins such as polymethyl methacrylate, polyethyl acrylate, polyacrylamide or acrylonitrile-styrene copolymer, polyamide, polyamideimide, coumaron indene resin, polyester, polyurethane, etc. Examples include a single substance or a mixture of resins obtained by modifying silicone resins.

Moreover, it is preferable that the back layer 15 contains a lubricant. Examples of the lubricant include metal soap, wax, silicone oil, fatty acid ester, filler, talc, and surfactant.

(Other layers)
The thermal transfer sheet 10 of this embodiment may include layers that exhibit various functions in addition to the layers described above.

For example, the thermal transfer sheet 10 of this embodiment may be provided with a protective layer in sequence with the stealth ink layer 12. The protective layer is a layer for transferring a layer that protects a visible image formed on a transfer target.

Examples of materials for forming the protective layer include polyester, polycarbonate, vinyl resin, acrylic resin, polystyrene, urethane resin, epoxy resin, polyamide, silicone-modified resins of these resins, and actinic light-curable resins. .

The thickness of the protective layer is preferably 0.2 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less.

Further, the thermal transfer sheet 10 of the present embodiment may include a primer layer between the base material 11 and each of the stealth ink layer 12, receptor layer 13, dye layer 14, and protective layer described above. . The primer layer is also called a base layer, and is a layer that serves as a base when forming various layers on the base material 11.

The resin constituting the primer layer is not particularly limited, and for example, the same resin as the binder resin included in the stealth ink layer 12 described above can be used. The primer layer may also contain inorganic particles, such as silica (collodyl silica), alumina or alumina hydrate (alumina sol, collodyl alumina, cationic aluminum oxide or its hydrate), aluminum silicate, Examples include magnesium silicate, magnesium carbonate, magnesium oxide, and titanium oxide. The average particle diameter of the inorganic particles is preferably 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 3 μm or less. Note that the "average particle diameter" means a volume average particle diameter, and can be measured by a known method using a particle size distribution/particle size distribution measuring device (Nanotrack particle size distribution measuring device, manufactured by Nikkiso Co., Ltd.).

The thickness of the primer layer is preferably 0.02 μm or more and 6 μm or less, more preferably 0.04 μm or more and 4 μm or less.

Furthermore, the thermal transfer sheet 10 of this embodiment may be provided with a release layer or a peeling layer in order to improve the transferability of the stealth ink layer, receptor layer, protective layer, and the like. The release layer is a layer that remains on the substrate side during transfer, while the release layer is a layer that is peeled off from the substrate side during transfer. Note that the details of these release layers and peeling layers are not particularly limited, and can be appropriately selected from various types of release layers and peeling layers conventionally used.

・Transfer object The transfer object used in conjunction with the thermal transfer sheet 10 of the present embodiment described above includes, for example, a thermal transfer image receiving sheet, a paper base material such as plain paper, high-quality paper, and tracing paper, or a plastic Examples include plastic cards mainly composed of film, vinyl chloride, vinyl chloride-vinyl acetate copolymer, and polycarbonate. Furthermore, a material having a predetermined image can be used as the transferred material. Furthermore, the object to be transferred may be colored or transparent.

- Transfer method There are no particular limitations on the method of transferring onto the transfer target, and for example, it is carried out using a thermal transfer printer having a heating device such as a thermal head, or a heating means such as a hot stamp or a heat roll.

- Printed object FIG. 3 is a schematic cross-sectional view showing an example of a printed object formed using the thermal transfer sheet of this embodiment.

In the printed matter 30, a stealth ink layer 12 is provided on a part of one surface of a transfer target 31. A receptive layer 13 is provided thereon over the entire surface. An image 32 is formed on the receptor layer 13 . A protective layer 33 is provided thereon.

Next, the present disclosure will be described in more detail with reference to Examples and Comparative Examples. Hereinafter, unless otherwise specified, parts and percentages are based on mass. Further, the blending amount (parts) is the amount of preparation, and is the value before being converted to solid content.

(Example 1)
A PET film with a thickness of 4.5 μm was used as a base material, and a back layer coating liquid having the following composition was applied onto this so that the dry thickness was 1.0 μm and dried to form a back layer. .

(Coating liquid for back layer)
・Polyvinyl butyral 1.8 parts by mass (S-LEC (registered trademark) BX-1 Sekisui Chemical Co., Ltd.)
・Polyisocyanate 5.5 parts by mass (Burnock (registered trademark) D750 DIC Corporation)
・Phosphate ester surfactant 1.6 parts by mass (Prysurf (registered trademark) A208N Daiichi Kogyo Seiyaku Co., Ltd.)
・Talc 0.35 parts by mass (Micro Ace (registered trademark) P-3 Nippon Talc Industries Co., Ltd.)
・Toluene 18.5 parts by mass ・Methyl ethyl ketone 18.5 parts by mass

A stealth ink layer coating liquid having the following composition is applied to a part of the side opposite to the side on which the back layer of the above substrate is provided so that the thickness when dried is 0.4 μm, and dried, Formed a stealth ink layer.

(Coating liquid for stealth ink layer)
・Acrylic resin 8.5 parts by mass (Dyanal (registered trademark) BR-87 Mitsubishi Chemical Corporation)
・Invisible light absorbing material of the following structural formula (1) (Yamada Chemical Co., Ltd.) 1.5 parts by mass (However, the central metal M and R1 to R4 in the structural formula (1) are listed in Table 1 below. (It is a structure.)

・トルエン ４５質量部
・メチルエチルケトン ４５質量部

・Toluene 45 parts by mass ・Methyl ethyl ketone 45 parts by mass

Apply a coating liquid for a receptive layer having the following composition onto a part of the surface opposite to the side on which the back layer is provided, so that it is surface sequential with the stealth ink layer, to a dry thickness of 0.8 μm. It was coated so as to have the following properties and dried to form a receptive layer.

(Coating liquid for receptor layer)
・Vinyl chloride-vinyl acetate copolymer 15.8 parts by mass (Solvine (registered trademark) CNL Nissin Chemical Industry Co., Ltd.)
- Vinyl chloride-vinyl acetate copolymer 1.0 parts by mass (Solvine (registered trademark) C Nissin Chemical Industry Co., Ltd.)
・Organic modified silicone oil 1.2 parts by mass (X-22-3000T Shin-Etsu Chemical Co., Ltd.)
・Organic modified silicone oil 1.2 parts by mass (X-24-510 Shin-Etsu Chemical Co., Ltd.)
・Organic modified silicone oil 0.8 parts by mass (KF-352A Shin-Etsu Chemical Co., Ltd.)
・Methyl ethyl ketone 40 parts by mass ・Toluene 40 parts by mass

A coating solution for a primer layer having the following composition was applied in plane order with the receiving layer to a dry thickness of 0.1 μm, and dried to form a primer layer.

(Coating liquid for primer layer)
・Alumina sol 2.5 parts by mass (Alumina sol 200 Nissan Chemical Industries, Ltd.)
・Polyvinylpyrrolidone 2.5 parts by mass (PVP K-60 ISP Japan Co., Ltd.)
・Water 47.5 parts by mass ・Isopropyl alcohol 47.5 parts by mass

A yellow dye layer coating liquid (Y), a magenta dye layer coating liquid (M), and a cyan dye layer coating liquid (C) having the following compositions were applied onto this primer layer using a gravure printing machine for each layer. The dye layer was formed by coating and drying so that the dry coating weight was 0.7 μm, and repeating this order one after the other in order to form a dye layer.

(Yellow dye layer coating liquid (Y))
・Solvent Yellow 93 2 parts by mass ・Disperse Yellow 201 5 parts by mass ・Polyvinyl acetal 5 parts by mass (S-LEC (registered trademark) KS-5 Sekisui Chemical Co., Ltd.)
・Toluene 50 parts by mass ・Methyl ethyl ketone 50 parts by mass

(Coating liquid for magenta dye layer (M))
・Disperse Red 60 3 parts by mass ・Disperse Violet 26 4 parts by mass ・Polyvinyl acetal 5 parts by mass (S-LEC (registered trademark) KS-5 Sekisui Chemical Co., Ltd.)
・Toluene 50 parts by mass ・Methyl ethyl ketone 50 parts by mass

(Coating liquid for cyan dye layer (C))
・Solvent Blue 63 4 parts by mass ・Disperse Blue 354 4 parts by mass ・Polyvinyl acetal 5 parts by mass (S-LEC (registered trademark) KS-5 Sekisui Chemical Co., Ltd.)
・Toluene 50 parts by mass ・Methyl ethyl ketone 50 parts by mass

A coating solution for a release layer having the following composition was applied in plane order with the primer layer so that the dry thickness was 0.8 μm, and dried to form a release layer. A primer layer coating liquid having the above composition was applied onto this release layer so that the dry thickness was 0.1 μm and dried to form a primer layer. A coating solution for a protective layer having the following composition was applied onto this primer layer so that the dry thickness was 0.8 μm, and it was dried to form a protective layer to obtain the thermal transfer sheet of Example 1. . Note that the release layer, primer layer, and protective layer are collectively referred to as a transfer layer.

(Coating liquid for release layer)
・Acrylic resin 20 parts by mass (Dyanal (registered trademark) BR-87 Mitsubishi Chemical Corporation Mw: 25000 acid value: 10.5 mgKOH/g)
・Methyl ethyl ketone 40 parts by mass ・Toluene 40 parts by mass

(Coating liquid for protective layer)
・Polyester 24 parts by mass (Vylon (registered trademark) 700 Toyobo Co., Ltd.)
・Ultraviolet absorber 6 parts by mass ・Toluene 35 parts by mass ・Methyl ethyl ketone 35 parts by mass

(Examples 2 to 5)
Same as Example 1 except that M and R1 to R4 of the invisible light absorbing material of structural formula (1) contained in the stealth ink layer coating liquid were changed to the structures listed in Table 1 below. Then, thermal transfer sheets of Examples 2 to 5 were obtained.

(Example 6)
M and R1 to R4 of the invisible light absorbing material of structural formula (1) contained in the stealth ink layer coating solution were changed to the structures shown in Table 1 below, and the acrylic resin was (Registered Trademark) BR-83 manufactured by Mitsubishi Chemical Corporation (Mw: 40000, acid value: 2 mgKOH/g), but in the same manner as in Example 1 to obtain a thermal transfer sheet of Example 6.

(Example 7)
M and R1 to R4 of the invisible light absorbing material of structural formula (1) contained in the stealth ink layer coating solution were changed to the structures shown in Table 1 below, and the acrylic resin was (Registered Trademark) BR-113 manufactured by Mitsubishi Chemical Corporation (Mw: 30000, acid value: 3.5 mgKOH/g), but in the same manner as in Example 1 to obtain a thermal transfer sheet of Example 7.

(Comparative Examples 1-2)
Same as Example 1 except that M and R1 to R4 of the invisible light absorbing material of structural formula (1) contained in the stealth ink layer coating liquid were changed to the structures listed in Table 1 below. Then, thermal transfer sheets of Comparative Examples 1 and 2 were obtained.

(Comparative example 3)
A thermal transfer sheet of Comparative Example 3 was obtained in the same manner as in Example 1 except that the invisible light absorbing material contained in the stealth ink layer coating liquid was changed to a cyanine compound of the following structural formula (2).

(Transferred object)
As a transfer target, a piece of cardboard (OKL card, Oji Paper Co., Ltd.) with a thickness of 380 μm (basis weight 360 g/m ² ) pasted with void PP (Econage SP-U, Mitsui Chemicals Tohcello Co., Ltd.) was prepared. .

(transcription)
The stealth ink layer included in the thermal transfer sheets of the above Examples and Comparative Examples was transferred to the surface of the above transfer object onto which the void PP was bonded using the test printer described below to form a code pattern. The thickness of the stealth ink layer on the transfer target at this time was 0.5 μm.

(test printer)
・Thermal head: KEE-57-12GAN2-STA (Kyocera Corporation)
・Heating element average resistance value: 3303 (Ω)
・Print density in main scanning direction: 300 (dpi)
・Print density in sub-scanning direction: 300 (dpi)
・Printing voltage: 18 (V)
・1 line period: 1.5 (msec.)
・Printing start temperature: 35 (℃)
・Pulse duty ratio: 85%

Using the above test printer, pre-prints were created by transferring the receiving layers of the thermal transfer sheets of Examples and Comparative Examples onto transfer objects and stealth ink layers.

(Measurement of reflection spectrum)
Using an ultraviolet-visible-near-infrared spectrophotometer (UV-3100, Shimadzu Corporation) and an integrating sphere attachment (ISR-3100A, Shimadzu Corporation), bond the void PP of the transfer target described above. The reflectance of the receiving layer surface of the pre-printed product was measured in the range of 400 nm to 1000 nm using the surface as a reference. The wavelength with the lowest reflectance between 400 nm and 1000 nm was defined as the maximum absorption wavelength.

The maximum absorption wavelength can be confirmed by measuring the reflection spectrum. Furthermore, from the lowest reflectance in the range of 400 to 700 nm (visible light region), it can be verified that the stealth ink layer does not absorb visible light. Furthermore, the ease of detecting the code pattern in an actual device can be verified from the reflectance at 850 nm.

(Light resistance evaluation)
Irradiation was performed for 24 hours at 400 kJ (420 nm integrated value) from the receiving layer side of the pre-print using a xenon fade meter (CI4000 Atlas Co., Ltd.). Note that CIRA soda lime was used as a filter. The reflectance of the code pattern before and after light irradiation was measured using a spectrophotometer (i1 X-rite), and the residual rate was calculated using the following formula.
・Calculation formula for residual rate: Absorbance = -log (reflectance at maximum absorption wavelength)
Survival rate = {(absorbance after irradiation)/(absorbance before irradiation)}×100

(Evaluation of color difference with transferred object)
The color of the receiving layer surface of the transfer object and the pre-print was measured using a spectrometer (manufactured by i1 X-rite) under the conditions of a D65 light source and a viewing angle of 2°.
ΔE ^* = ((Difference in L ^* value between the receiving surface of the transferred object and the pre-printed object) ² + (Difference in the a* value of the receiving surface of the transferred object and the pre-printed object) ² + (Difference between the a ^* value of the receiving surface of the transferred object and the pre-printed object) Difference in b ^* value of the receiving surface of the print) ² ) ^1/2
Note that L ^* a ^* b ^* means L ^* a*b ^* defined ⁱⁿ CIE1976, L ^* a ^* b ^* color system (JIS-Z-8729 (1980)).

(Evaluation of dispersibility of invisible light absorption material)
The pre-print was observed from the receiving layer surface using an optical loupe with a magnification of 25 times, and the dispersibility was evaluated according to the following criteria. Note that there is a correlation between the dispersibility of the invisible light absorbing material and the invisible light absorption efficiency.
A: No lumps of invisible light absorbing material are observed B: Slight lumps of invisible light absorbing material are observed C: A large amount of lumps of invisible light absorbing material are observed

An image was formed on the receiving layer of the pre-printed product using the dye layer included in the test printer and the thermal transfer sheets of Examples and Comparative Examples. Note that the created image has the identification number N1 of "high-definition color digital standard image" defined in JIS X 9204:2004.

A transfer layer consisting of a protective layer, a primer layer, and a release layer included in the thermal transfer sheet was transferred onto the receiving layer on which the image was formed, thereby producing a print.

The print was visually inspected to confirm that the code pattern formed by the stealth ink layer did not interfere with the image.

10...Thermal transfer sheet 11...Base material 12...Stealth ink layer 13...Receiving layer 14...Dye layer 15...Back layer 30...Printed object 31...Transferred object 32... Image 33... Protective layer

Claims (4)

base material and
a stealth ink layer provided on one surface of the base material and containing an invisible light absorbing material;
including;
A thermal transfer sheet, wherein the invisible light absorbing material has the following structural formula (1).

However, in the above structural formula (1),
M is copper or vanadium monoxide;
R1, R2, R3, and R4 are each independently O-A1, S-A2, and N-A3A4,
A1, A2, A3, and A4 each independently represent an alkyl group, an aryl group, an aralkyl group, an alkylamino group, a cyclic alkylamino group, an alkoxy group, a nitro group, a monophoryl group, a cyano group, a trifluoromethyl group, a carboxyl group , an ester group, or a halogen atom. The thermal transfer sheet according to claim 1, wherein the invisible light absorbing material has a maximum absorption wavelength of 850 nm or more and 900 nm or less. The thermal transfer sheet according to claim 1 or 2, wherein the stealth ink layer after being transferred to the transfer object has a reflectance of 85% or more in a wavelength range of 400 nm or more and 700 nm or less. On one side of the base material, further:
a receptor layer capable of receiving a dye;
a dye layer;
The thermal transfer sheet according to any one of claims 1 to 3, wherein the thermal transfer sheet is provided in random order but sequentially.

Images