WO2025164730A1 - Ink and sheet for thermal transfer recording - Google Patents

Abstract

This ink contains a medium, and carrier particles dyed with a compound represented by general formula (1) and a compound represented by general formula (2).

Description

Ink and thermal transfer recording sheet

The present invention relates to ink and thermal transfer recording sheets.

In the apparel industry, the large amount of industrial wastewater generated during the dyeing process for various fabrics is seen as a problem in terms of the environmental impact. For this reason, digital textile printing methods using inkjet or electrophotography have been actively developed in recent years as a way to provide printed products with low energy and cost. For example, there are methods that use ink containing pigments, ink containing resin particles dyed with dye, and ink containing sublimation dyes.

Water-based inks containing pigments (water-based pigment inks) have excellent lightfastness, but have the problem of tending to have poor color development. Furthermore, inks containing dye-dyed resin particles have difficulty achieving both lightfastness and color development. For example, Patent Document 1 reports an inkjet ink that uses resin particles colored with a coumarin dye as a colorant, but the inventors' investigations have shown that further improvement in lightfastness is required.

Furthermore, in the field of writing instruments (especially ballpoint pens), there is growing demand for user requirements such as writing feel, initial writing performance, and consistent, continuous writing, depending on the ink and function. Ballpoint pens come in a variety of types, including oil-based ballpoint pens, water-based ballpoint pens, and gel ink ballpoint pens, and in a variety of colors, including black, red, blue, yellow, pink, green, and orange. Dyes, pigments, and mixtures of these are used as colorants in ink. For example, oil-based inks using pigments have excellent writing durability, but suffer from storage stability issues due to the pigments' tendency to aggregate and settle in the ink. Using oil-based inks with aggregated or settled pigments can result in poor writing results. In contrast, oil-based inks using dyes have the characteristic that the dyes are easily soluble in solvents, making them less prone to aggregation and settling than pigments and providing better storage stability, but they tend to have inferior lightfastness. For example, Patent Document 2 reports a ballpoint pen paste (ink for writing instruments) that uses a methine dye or a coumarin dye as a colorant, but the inventors' investigations have revealed that further improvement is required in terms of lightfastness.

Furthermore, in image recording methods using sublimation transfer inks containing sublimation dyes, not only are images with high optical density required, but suppression of color bleeding due to heat press temperatures is also required to ensure color tone stability when repeatedly recording images. For example, Patent Document 3 reports an example of using ink that combines fluorescent and non-fluorescent sublimation dyes, but the inventors' investigations have found that the stability of image density (color development stability) due to differences in yellow image density and heat press temperature is insufficient.

Furthermore, sublimation dyes can also be used in image recording methods using thermal transfer recording, which allows printing using a dry process. In thermal transfer recording, each colorant layer is typically formed by mixing two or three types of compounds. This poses the problem of discoloration due to color mixing between compounds of the same color during image recording. Therefore, studies have been conducted to prevent this discoloration in thermal transfer recording sheets; for example, Patent Document 4 proposes a solution by incorporating an anti-fading agent into the colorant layer. However, the inventor's studies have shown that further improvement is needed to prevent discoloration due to mixing of the same colors (hereinafter also referred to as same-color mixing fading).

Japanese Patent Application Laid-Open No. 2022-187337 Japanese Patent Application Publication No. 8-20669 JP 2016-190932 A Japanese Patent Application Laid-Open No. 2001-158879

An object of the present invention is to provide an ink that has good storage stability and high light resistance. Another object of the present invention is to provide an ink that has high optical density and excellent color development stability during heat pressing. Still another object of the present invention is to provide a thermal transfer recording sheet in which fading due to mixing of the same colors is suppressed when two different types of yellow colorants are used in the yellow colorant layer of the thermal transfer recording sheet.

According to one aspect of the present invention, there is provided an ink containing a medium and carrier particles dyed with a compound represented by the following general formula (1) and a compound represented by the following general formula (2):

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group;
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group.

According to another aspect of the present invention, there is provided an ink comprising an aqueous medium, a dispersant, a compound represented by the following general formula (1), and a compound represented by the following general formula (2):

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group;
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group.

According to another aspect of the present invention, there is provided a thermal transfer recording sheet having a substrate and a yellow colorant layer formed on the substrate,
A thermal transfer recording sheet, wherein the yellow colorant layer contains a compound represented by the following general formula (1) and a compound represented by the following general formula (2):

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group.
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group.

According to one aspect of the present invention, it is possible to provide an ink that has good storage stability and high light resistance. According to another aspect of the present invention, it is possible to provide an ink that has a high optical density and excellent color development stability during heat pressing. According to yet another aspect of the present invention, it is possible to provide a thermal transfer recording sheet in which fading due to mixing of the same colors is suppressed when two different types of yellow colorants are used in the yellow colorant layer of the thermal transfer recording sheet.

The present invention is described in detail below.

[First embodiment]
As a result of intensive research conducted by the present inventors to solve the above problems, they have found that by using a medium and carrier particles dyed with compounds represented by general formulas (1) and (2), it is possible to provide an ink having good storage stability and high light resistance.

In the past, inks using carrier particles dyed solely with a compound represented by general formula (1) were prone to aggregation and had storage stability issues. On the other hand, inks using carrier particles dyed solely with a compound represented by general formula (2) did not aggregate, but had the issue of poor light resistance.

The inventors' research has revealed that inks using carrier particles dyed with compounds represented by general formulas (1) and (2) have good storage stability and high lightfastness. The mechanism by which the aforementioned effects are achieved by mixing these compounds represented by general formulas (1) and (2) is not clearly understood, but the inventors speculate as follows.

This is because the compounds represented by general formulas (1) and (2) are structurally similar in size, and the two compounds overlap due to the π-π stacking interaction of the benzene rings imparted by the dialkylamino groups of each compound. It is believed that this overlap stabilizes the two compounds, thereby achieving the aforementioned effects. In particular, in general formula (2), when _X1 is N-H, the hydrogen atom of N-H and the oxygen atom of C=O in the coumarin skeleton form a stable six-membered ring structure through hydrogen bonding, thereby achieving the greatest aforementioned effects.

The composition of the ink used in this embodiment is described in detail below.

The ink according to this embodiment contains a medium and carrier particles dyed with compounds represented by general formulas (1) and (2). The ink according to this embodiment is suitable as an ink because it has good storage stability and high light resistance due to the use of carrier particles dyed with two specific types of compounds.

[Colorant]
First, a compound represented by the following general formula (1), which is one of the colorants, will be described.

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group;
_R4 represents an alkyl group or an aryl group.

In general formula (1), the alkyl groups for R ₁ to R ₄ are not particularly limited, but specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Among these, a linear or branched alkyl group having 1 to 4 carbon atoms is preferred. In particular, a methyl group or an ethyl group is more preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

In general formula (1), the aryl group in _R3 and _R4 is not particularly limited, and both unsubstituted aryl groups and substituted aryl groups can be used. Examples of the substituent include alkyl groups, alkoxy groups, carboxamide groups, and sulfonate salt groups such as sodium sulfonate. Specific examples of the aryl group include phenyl groups, naphthyl groups, methylphenyl groups, methoxyphenyl groups, and benzenecarboxamide groups (aminocarbonylphenyl groups). In particular, a phenyl group is more preferred because the use of dyed resin particles makes it easier to obtain an ink with good storage stability and high lightfastness.

In general formula (1), the alkoxy group for _R3 is not particularly limited, but examples thereof include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Among these, an alkoxy group having 1 to 4 carbon atoms is preferred. In particular, a methoxy group or an ethoxy group is more preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

As shown in the reaction scheme below, the compound represented by general formula (1) has a cis-trans structural isomer represented by general formula (3), which is within the scope of the present invention. R ₁ to R ₄ in the reaction scheme have the same meanings as defined above. Note that the description of chemical formulas from this paragraph onwards will only depict structures similar to general formula (1), but will include both cis-trans structural isomers. Furthermore, the compound represented by general formula (1) may be a mixture of these structural isomers.

Preferred examples of compounds represented by general formula (1) include compounds (1-1) to (1-5) shown below, but are not limited to these compounds.

The compound represented by the general formula (1) above may be used alone, or two or more may be used in combination to adjust the color tone, etc., depending on the application. Furthermore, the compound may be used in combination with known pigments or dyes, as long as the effects of the present invention are not impaired. The known pigments or dyes to be combined may be one type alone, or two or more types.

Among these, compounds in which, in general formula (1), _R1 and _R2 are each independently an alkyl group having 1 to 4 carbon atoms, and _R3 is an alkoxy group having 1 to 4 carbon atoms are preferred. Compounds (1-2), (1-4), and (1-5) are particularly preferred. When resin particles dyed with any of these compounds are used, an ink having good storage stability and high lightfastness is likely to be obtained.

The compound represented by general formula (1) can be synthesized by known methods, but it is also available as a commercially available product.

Next, we will explain another colorant, the compound represented by the following general formula (2).

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , and _R9 represents a hydrogen atom or an alkyl group.

In general formula (2), the alkyl group for _R5 and _R6 is not particularly limited, but specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Among these, a linear or branched alkyl group having 1 to 4 carbon atoms is preferred. In particular, a methyl group or an ethyl group is more preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

In general formula (2), the alkyl group for _R7 and _R8 is not particularly limited, but specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Among these, a linear or branched alkyl group having 1 to 4 carbon atoms is preferred. In particular, a methyl group or an ethyl group is more preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

In general formula (2), the aryl group for _R7 and _R8 is not particularly limited, but examples include an unsubstituted phenyl group, a methylphenyl group, a methoxyphenyl group, etc. Among these, an unsubstituted phenyl group is particularly preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

In general formula (2), the alkoxy group for _R7 and _R8 is not particularly limited, but examples thereof include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, etc. Among these, a methoxy group or an ethoxy group is preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

In general formula (2), the halogen atom in _R7 and _R8 is not particularly limited, but examples include a chlorine atom, a bromine atom, a fluorine atom, etc. Among these, a chlorine atom is preferred because the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high light resistance.

In general formula (2), the alkyl group for _R9 is not particularly limited, but examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a 2-ethylpropyl group, and a 2-ethylhexyl group. Among these, a linear or branched alkyl group having 1 to 8 carbon atoms is preferred. In particular, a methyl group or an ethyl group is preferred, since the use of dyed resin particles makes it easier to obtain an ink that has good storage stability and high lightfastness.

Preferred examples of compounds having the structure represented by general formula (2) include compounds (2-1) to (2-21) shown below, but are not limited to these compounds.

The compound represented by the general formula (2) above may be used alone, or two or more may be used in combination to adjust the color tone, etc., depending on the application. Furthermore, the compound may be used in combination with known pigments or dyes, as long as the effects of the present invention are not impaired. The known pigments or dyes to be combined may be one type alone, or two or more types.

Among these, compounds represented by general formula (2) in which _R5 and _R6 are each independently an alkyl group having 1 to 4 carbon atoms, and _X1 is O, N-H, or N- _CH3 are preferred. Compounds (2-1), (2-4), and (2-11) are particularly preferred. When carrier particles dyed with any of these compounds are used, an ink having good storage stability and high lightfastness is likely to be obtained.

The compound represented by general formula (2) can be synthesized by known methods, but is also available as a commercially available product.

In the ink, the total amount of the compound represented by general formula (1) and the compound represented by general formula (2) is not particularly limited. Preferably, it is 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 7.0% by mass or less, based on the total mass of the ink. Furthermore, the blending ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is not particularly limited. Preferably, the mass ratio is in the range of 5 parts by mass or more and 90 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). More preferably, it is in the range of 10 parts by mass or more and 70 parts by mass or less, and even more preferably, it is in the range of 30 parts by mass or more and 50 parts by mass or less. Using carrier particles dyed with a colorant within this range makes it easier to obtain an ink with good storage stability and high lightfastness.

[Carrier particles]
In this specification, "carrier particles" refers to carriers that can be dispersed in a medium and exist in the medium in a state of particle size. Carrier particles exist in a dispersed state in the ink. When the medium is an aqueous medium, the carrier particles exist in a dispersed state in the aqueous medium, i.e., in a carrier emulsion state. Carrier particles dyed with a colorant exist in a state in which the colorant is dispersed or colored in the carrier particles.

The cumulative 50% particle diameter (D50) of the volume-based particle size distribution of the carrier particles is preferably 140 nm or more and 300 nm or less. If D50 is 140 nm or more, a decrease in the lightfastness of the image can be suppressed. On the other hand, if D50 is 300 nm or less, a larger value can suppress a decrease in the ink ejection stability.

When the compounds represented by general formulas (1) and (2) are dyed onto carrier particles, the compounding ratio between the compounds represented by general formulas (1) and (2) and the carrier particles is not particularly limited. Preferably, the total amount of the compounds represented by general formulas (1) and (2) is 0.5 parts by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less, per 100 parts by mass of carrier particles.

Furthermore, the content of dyed carrier particles is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 6% by mass or less, based on the total amount of ink.

Carrier particles include resins and cellulose nanofibers. Examples of resin types include styrene-based polymers, acrylic acid-based polymers, methacrylic acid-based polymers, polyester resins, polyvinyl ether resins, polyvinyl methyl ether resins, polyvinyl alcohol resins, polyvinyl butyral resins, polyurethane resins, and polypeptide resins. These resins may be used alone, or in combination with two or more types as needed. When carrier particles are made of resin, they may also be referred to as "resin particles."

Cellulose nanofibers are selected depending on the application, but for example, they can be obtained by chemically and/or mechanically defibrating plant fibers, and are ultrafine fibers with an average width of approximately several nm to 20 nm and an average length of approximately 0.5 μm to several μm. The size (fiber diameter) of these cellulose nanofibers varies depending on the type of cellulose nanofiber. Furthermore, fiber diameters are selected within an appropriate range based on factors such as thickening effect, stability over time, and color development, as long as they do not impair the properties required for various applications.

Materials that contain cellulose fibers include plants such as wood, bamboo, kenaf, hemp, jute, wood pulp, waste paper, crystalline cellulose, agricultural waste, and recycled pulp, as well as animals such as sea squirts, algae, and microorganisms.

Cellulose nanofibers are commercially available and can also be used. Examples of commercially available products include "Leocrysta I-2AX," "CNF 03," and "CNF 04" (all manufactured by Daiichi Chemical Industry Co., Ltd.), "ELLEX-S" (manufactured by Daio Paper Co., Ltd.), and "na noforest-S" (manufactured by Chuetsu Pulp Industry Co., Ltd.).

[Colorant]
As described above, the ink contains a combination of at least one compound represented by general formula (1) and one compound represented by general formula (2) as the colorant, but may also contain a known colorant, etc., within the range that does not impair the solubility or dispersibility in the medium. Examples of such a colorant include, but are not limited to, a condensed azo compound, an azo metal complex, and a methine compound.

The amount of colorant contained in the ink is set appropriately depending on the application and is not particularly limited. Preferably, the total amount, including any known colorant, is 1.0 to 30.0 parts by mass per 1,000 parts by mass of the medium, more preferably 2.0 to 20.0 parts by mass, and even more preferably 3.0 to 15.0 parts by mass. Within the above ranges, sufficient coloring power is obtained, and the colorant dispersibility is also good.

[Method for producing dyed carrier particles]
When resin particles are used as carrier particles, the resin particles can be produced by a conventionally known method, such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, phase inversion emulsification, etc. Examples of methods for dyeing resin particles include a method of forming resin particles by polymerizing a monomer mixture in which compounds represented by general formulas (1) and (2) are dissolved, and a method of adding compounds represented by general formulas (1) and (2) to resin particles and heating them.

When cellulose nanofibers are used as carrier particles, the cellulose nanofibers can be dyed, for example, by contacting the cellulose nanofibers with compounds represented by general formulas (1) and (2) in an aqueous medium. Then, if necessary, heating or oxidation treatment is carried out, and the medium is then distilled off to obtain dyed cellulose nanofibers.

[Media]
In this embodiment, the term "medium" refers to, but is not limited to, water or an organic solvent, and is selected depending on the application and purpose of the ink. When an organic solvent is used as the medium, the type of organic solvent is selected depending on the application and purpose of the ink, and is not limited to the type of organic solvent.

Examples of organic solvents include alcohols such as methanol, ethanol, isopropanol, butanol, 2-methyl-2-butanol, 3-pentanol, benzyl alcohol, and cyclohexanol; glycols such as methyl cellosolve, diethylene glycol, and diethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, butyl acetate, and cellosolve acetate; aliphatic hydrocarbons such as octane, petroleum ether, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ethers such as diethyl ether, dimethyl glycol, trioxane, and tetrahydrofuran; acetals such as diethyl acetal; organic acids such as formic acid, acetic acid, and propionic acid; and sulfur- or nitrogen-containing organic compounds such as monoethanolamine, pyridine, dimethyl sulfoxide, and dimethylformamide.

Furthermore, polymerizable monomers can also be used as the organic solvent. Examples of polymerizable monomers include addition polymerizable monomers and condensation polymerizable monomers, with addition polymerizable monomers being preferred. Specific examples of polymerizable monomers include styrene-based monomers such as styrene, methylstyrene, and ethylstyrene; acrylate-based monomers such as methyl acrylate, ethyl acrylate, behenyl acrylate, 2-ethylhexyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, acrylonitrile, and acrylic acid amide; methacrylate-based monomers such as methyl methacrylate, ethyl methacrylate, diethylaminoethyl methacrylate, methacrylonitrile, and methacrylic acid amide; ethylene, propanediol, and the like. Examples include olefin-based monomers such as propylene, butylene, butadiene, isoprene, isobutylene, and cyclohexene; halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl iodide; vinyl ester-based monomers such as vinyl acetate, vinyl propionate, and vinyl benzoate; vinyl ether-based monomers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; and vinyl ketone-based monomers such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone. These may be used alone or in combination of two or more types as necessary.

The amount of medium contained in the ink is selected according to the purpose and use of the ink, and is not particularly limited.

In the ink, components other than the aforementioned dyed resin particles are selected appropriately depending on the application of the ink, including the medium. Furthermore, the following additives may be added as appropriate, provided they do not impair the properties for various applications: Polyhydric alcohols such as trimethylolpropane and trimethylolethane; urea derivatives such as urea and ethyleneurea; water-soluble resins, undyed resin particles, surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, anti-reducing agents, evaporation accelerators, chelating agents, and cellulose nanofibers.

Examples of ultraviolet absorbers include benzophenone-based, benzotriazole-based, cyanoacrylate-based, and triazine-based.

Commercially available UV absorbers include, for example, Tinuvin P, Tinuvin 326, Tinuvin 571, and Tinuvin 360 (all manufactured by BASF), and Adeka STAB LA-24, LA-29, LA-31RG, LA-32, LA-36, LA-46, LA-F70, and 1413 (all manufactured by ADEKA Corporation). Adeka STAB LA-29, LA-32, LA-36, and LA-46 are preferred, with Adeka STAB LA-29, LA-32, and LA-36 being particularly preferred.

The antioxidant may include a phenolic compound.
Commercially available antioxidants include, for example, Adekastab AO-20, AO-30, AO-40, AO-50, AO-50F, AO-60, AO-60G, AO-80, and AO-330 (all manufactured by ADEKA Corporation).

[Ink preparation method]
The ink according to this embodiment can be prepared as follows.

Carrier particles dyed with compounds represented by general formulas (1) and (2) are prepared according to the method described above. The prepared carrier particles dyed with compounds represented by general formulas (1) and (2), along with other colorants, emulsifiers, resins, etc., as needed, are gradually added to a medium selected according to the application while stirring, and thoroughly blended into the medium. Furthermore, mechanical shear force is applied using a disperser to stably dissolve or finely disperse the particles, thereby obtaining the ink of the present invention.

[Dispersing machine]
The disperser for dispersing each component in the medium is not particularly limited, but media-type dispersers such as a rotary shear homogenizer, a ball mill, a sand mill, and an attritor, and a high-pressure counter-collision type disperser can be used.

The ink according to this embodiment is also suitable as an ink for oil-based writing instruments, an ink for water-based writing instruments, an ink for inkjet printing, an ink for textile printing, and an ink for paints. Of these, it is preferable to use it as an ink for oil-based writing instruments, an ink for water-based writing instruments, or an inkjet ink. Specific examples of applications of the ink according to this embodiment will be explained below. Note that for items not specifically explained, the same explanations given for the ink according to this embodiment apply as is.

[Oil-based writing ink]
The ink for oil-based writing instruments contains resin particles dyed with the compounds represented by the general formulas (1) and (2) described above, and a medium preferably containing an alcohol or glycol ether. In addition, it preferably contains a resin present in a dissolved state in the medium. The content of the carrier particles dyed with the compounds represented by the general formulas (1) and (2) is appropriately selected depending on the application and is not particularly limited.

[Medium containing alcohol or glycol ether]
Examples of alcohols include unsubstituted alkyl monoalcohols such as ethanol, isopropanol, n-butanol, isobutanol, tert-butanol, sec-butanol, 2-methyl-2-butanol, 3-pentanol, octanol, and cyclohexanol; substituted alkyl monoalcohols such as 2-phenoxyethanol and 3-methyl-3-methoxy-1-butanol; alkyl polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 3-methyl-1,3-butanediol, and 1,3-butanediol; and aromatic alcohols such as benzyl alcohol. Examples of the substituent in the substituted alkyl monoalcohol include an alkoxy group and an aryloxy group.

Glycol ethers also include monoalcohol monoethers, but these are listed as alcohols. Examples of diethers include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and diethylene glycol dipropyl ether.

In addition to alcohol and glycol ether, the medium may also contain water; ester solvents such as 3-methyl-3-methoxybutyl acetate, butyl acetate, and methyl propionate.

The amount of medium used is not particularly limited and can be selected appropriately depending on the type of writing instrument, such as a ballpoint pen, felt-tip pen, or marking pen.

[Resin present in a dissolved state in a medium]
In order to adjust the viscosity of the ink and improve the scratch resistance, it is preferable that the ink contains a resin that exists in a dissolved state in the medium.

The resin is determined depending on the purpose and application of the ink, and is not particularly limited. Examples include butyral resin, ketone resin, polyvinylpyrrolidone resin, styrene resin, styrene-acrylic resin, styrene-maleic acid resin, terpene resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, terpene phenolic resin, rosin-modified maleic resin, rosin phenolic resin, maleic acid resin, phenolic resin, xylene resin, urea resin, polyamide resin, phenoxy resin, and cellulose-based resin. Of these, butyral resin and ketone resin are preferably used to achieve a writing feel that does not cause smearing.

Commercially available butyral resins and ketone resins may be used. Examples of commercially available ketone resins include low-polymerization types under the trade names "S-LEC BL-1," "BL-2," and "BL-10," and high-polymerization types under the trade names "BH-3," "BH-6," "BX-1," "BX-5," and "BH-S" (all manufactured by Sekisui Chemical Co., Ltd.).

Commercially available ketone resins include, for example, "Ketone Resin K-90" (manufactured by Arakawa Chemical Industries, Ltd.), and "Hilac 901," "Hilac 110H," and "Hilac 111" (all manufactured by Hitachi Chemical Co., Ltd.). By incorporating these resins into the ink, viscosity adjustment is easy, wear on the nib can be prevented, and a stable, satisfactory writing feel can be achieved. Furthermore, because film-forming properties can be moderately suppressed, ink solidification can be prevented even if the nib is left exposed for an extended period of time, and the "blurring phenomenon" when starting to write can be suppressed.

The amount of these resins contained can be selected appropriately and is not particularly limited.

[Additives]
Furthermore, if necessary, additives may be added within a range that does not adversely affect the ink, such as rust inhibitors, surfactants, lubricants, wetting agents, UV absorbers, antifoaming agents, antioxidants, pH adjusters, leveling agents, preservatives, and cellulose nanofibers.

[Water-based writing ink]
The aqueous writing ink preferably contains a resin or cellulose nanofibers dyed with the compounds represented by the general formulas (1) and (2), an aqueous medium, a dispersant (hereinafter also referred to as a "first dispersant"), and a water-soluble resin. The content of the carrier particles dyed with the compounds represented by the general formulas (1) and (2) is not particularly limited and can be selected appropriately depending on the application.

[Aqueous medium]
The aqueous medium contains at least water and may further contain a water-soluble organic solvent.

The water content in the ink is preferably 50% by mass or more and 95% by mass or less, based on the total mass of the ink. Furthermore, the water-soluble organic solvent can be any solvent commonly used in inks. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The content of the water-soluble organic solvent in the ink can be selected appropriately and is not particularly limited.

[First dispersant]
When water is used as the medium, a first dispersant may be added as needed to obtain good dispersion stability of the colorant. The first dispersant is not particularly limited, but examples thereof include cationic surfactants, anionic surfactants, and nonionic surfactants.

Examples of cationic surfactants include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide.

Anionic surfactants include, for example, fatty acid soaps such as sodium stearate and sodium dodecanoate, sodium dodecyl sulfate, sodium dodecylbenzene sulfate, and sodium lauryl sulfate.

Examples of nonionic surfactants include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, nonylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan monooleate polyoxyethylene ether, and monodecanoyl sucrose. The content of the first dispersant in the ink is selected appropriately and is not particularly limited.

[Water-soluble resin]
A water-soluble resin may be added to the water-based writing ink, if necessary.

[Additives]
The water-based writing ink can be suitably used in water-based ballpoint pens, gel ink water-based ballpoint pen inks, felt-tip pens, marking pens, etc. Additives such as dispersants, lubricants, pH adjusters, rust inhibitors, preservatives, and antibacterial agents may be added to the water-based writing ink as appropriate, within limits that do not impair the properties for various applications.

[Inkjet ink]
The inkjet ink preferably contains a resin or cellulose nanofibers dyed with the compounds represented by the general formulas (1) and (2), an aqueous medium, and a dispersant (hereinafter also referred to as a "second dispersant"). The content of the carrier particles dyed with the compounds represented by the general formulas (1) and (2) is not particularly limited and can be appropriately selected depending on the application.

Furthermore, the aqueous medium used in inks for water-based writing instruments can be used as is.

[Second dispersant]
The second dispersant may be an ionic surfactant, a nonionic surfactant, or a polymer surfactant.

Ionic surfactants include, for example, aliphatic monocarboxylates, polyoxyethylene alkyl ether carboxylates; N-acyl sarcosinates, N-acyl glutamates, dialkyl sulfosuccinates; alkanesulfonates, alpha olefin sulfonates, linear or branched alkylbenzene sulfonates, naphthalene sulfonate formaldehyde condensates, alkyl naphthalene sulfonates; N-methyl-N-acyltaurates; alkyl sulfates, polyoxyethylene alkyl ether sulfates, fat and oil sulfate esters; alkyl phosphates, polyoxyethylene alkyl ethers Examples include anionic surfactants such as tertiary phosphates and polyoxyethylene alkyl phenyl ether phosphates; cationic surfactants such as alkylamine salts, alkyltrimethylammonium chloride, bromide or iodide, dialkyldimethylammonium chloride, bromide or iodide, alkylbenzalkonium chloride, and alkylpyridinium chloride; and amphoteric surfactants such as alkylbetaine, fatty acid amidopropyl betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, alkyl or dialkyldiethylenetriaminoacetic acid, and alkylamine oxide.

Nonionic surfactants include glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters; polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polyoxypropylene glycols; fatty acid polyethylene glycols, fatty acid polyoxyethylene sorbitan, fatty acid alkanolamides, etc.

Examples of polymer surfactants include anionic polymers such as polyacrylates, styrene-acrylic acid copolymer salts, vinylnaphthalene-acrylic acid copolymer salts, styrene-maleic acid copolymer salts, vinylnaphthalene-maleic acid copolymer salts, and polyphosphoric acid; and nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyalkylene glycol.

Commercially available products include, for example, X-200, X-1, X-205, and X-220 (all manufactured by Seiko PMC Corporation), Nopcosperse 6100 (manufactured by San Nopco Ltd.), BYK-190, BYK-187, BYK-191, BYK-194N, BYK-199, and BYKJET-9171 (all manufactured by BYK Corporation), Aron A-6114 (all manufactured by Toagosei Co., Ltd.), BYK-184, BYK-182, BYK-183, and BYK-185 (all manufactured by BYK Corporation), and TEGO Disperse 710 (manufactured by Evonic Tego Chemi).

Preferred are BYK-190, BYK-187, BYK-191, BYK-194N, BYK-199, BYKJET-9171, etc., with BYK-190 and BYKJET-9171 being particularly preferred.

The content of the second dispersant in the inkjet ink can be selected appropriately and is not particularly limited. The content (mass %) of the dispersant in the ink is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 15% by mass or less, based on the total mass of the ink.

When making an inkjet ink, in addition to the components listed above, various additives may be added as needed, such as pH adjusters, rust inhibitors, preservatives, anti-mold agents, antioxidants, anti-reducing agents, evaporation accelerators, chelating agents, and water-soluble polymers.

[Textile printing ink]
When the ink according to this embodiment is used as a textile printing ink, the type of fabric that can be used for textile printing is not particularly limited as long as it can be dyed, and examples thereof include fabrics made of fibers containing polyester, acetate, or triacetate. The fabric may be in the form of a woven fabric, knitted fabric, nonwoven fabric, or the like. Fabrics made of cotton, silk, linen, polyurethane, acrylic, nylon, wool, or rayon fibers, or fabrics made of a combination of two or more of these fibers, can also be used.

The thickness of the yarn that makes up the fabric is preferably in the range of 10 to 100 denier. There are no particular restrictions on the thickness of the fibers that make up the yarn, but it is preferably 1 denier or less.

[Second embodiment]
As a result of extensive research to solve the above problems, the present inventors have found that the following ink can provide an ink that has high optical density and excellent color development stability during heat pressing.

The ink according to this embodiment is characterized by containing an aqueous medium, a dispersant, a compound represented by general formula (1), and a compound represented by general formula (2).

When compounds represented by the above general formulas (1) and (2) are used, inks with high optical density and excellent color stability during heat pressing can be obtained. The mechanism contributing to this color stability is not clearly understood, but the inventors speculate as follows.

This is thought to be due to the fact that the compounds represented by general formulas (1) and (2) are structurally similar in size, and that the overlapping occurs due to the π-π stacking interaction of the benzene rings imparted by each dialkylamino group, resulting in stabilization. In particular, when _X1 in general formula (2) is N-H, the hydrogen of N-H and the oxygen atom of C=O in the coumarin skeleton form a stable six-membered ring structure through hydrogen bonding, resulting in the greatest effect.

In addition, the ink according to this embodiment can be used in textile applications that have been expanding in recent years, such as dyeing polyester fibers, sports apparel made by interweaving polyester with polyurethane, and high-end dresses with processed fiber shapes.

The components of the ink according to this embodiment will be described in detail. Note that the compounds represented by general formulas (1) and (2) and the disperser used to disperse each component in the medium can be the same as those described in the first embodiment, so further description will be omitted.

(Dispersant)
The dispersant is not particularly limited, but examples thereof include anionic dispersants, nonionic dispersants, and polymer dispersants.

Anionic dispersants are not particularly limited, but examples include formalin condensates of aromatic sulfonic acids, formalin condensates of β-naphthalenesulfonic acids, formalin condensates of alkylnaphthalenesulfonic acids, and formalin condensates of creosote oil sulfonic acids.

The aromatic sulfonic acids mentioned above are not particularly limited, but examples include creosote oil sulfonic acid, cresol sulfonic acid, phenol sulfonic acid, alkylnaphthalene sulfonic acids such as β-naphthol sulfonic acid, methylnaphthalene sulfonic acid, and butylnaphthalene sulfonic acid, mixtures of β-naphthalene sulfonic acid and β-naphthol sulfonic acid, mixtures of cresol sulfonic acid and 2-naphthol-6-sulfonic acid, and lignin sulfonic acid.

Nonionic dispersants include, but are not limited to, alkylene oxide adducts of phytosterols, alkylene oxide adducts of cholestanols, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylamines, glycerin fatty acid esters, EO-PO block polymers primarily composed of copolymers of ethylene oxide (EO) and propylene oxide (PO), and substituted derivatives of these.

Polymer dispersants are not particularly limited, but examples include partial alkyl esters of polyacrylic acid, polyalkylene polyamines, polyacrylates, styrene-acrylic acid copolymers, and vinylnaphthalene-maleic acid copolymers.

Among the above dispersants, EO-PO block polymers, which are primarily copolymers of ethylene oxide (EO) and propylene oxide (PO), are particularly preferred because they are highly concentrated and tend to produce inks with excellent color stability during heat pressing. Commercially available EO-PO block polymers may be used, such as those sold under the trade names "DisperBYK 183," "DisperBYK 185," and "DisperBYK 190" (all manufactured by BYK-Chemie).

The content (mass %) of dispersant in the ink is preferably 0.1% to 20% by mass, and more preferably 0.5% to 15% by mass, based on the total mass of the ink.

(aqueous medium)
The ink is preferably an aqueous ink containing at least water as an aqueous medium, and may further contain a water-soluble organic solvent as an aqueous medium.

The water content (mass %) in the ink is preferably 50% to 95% by mass, and particularly 55% to 90% by mass, based on the total mass of the ink. Furthermore, the water-soluble organic solvent can be any of those commonly used in inks. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The water-soluble organic solvent content (mass %) in the ink is preferably 3% to 50% by mass, and particularly 5% to 40% by mass, based on the total mass of the ink.

(Other additives)
In addition to the components described above, the ink may contain the following additives as needed: polyhydric alcohols such as trimethylolpropane and trimethylolethane; urea and urea derivatives such as ethyleneurea; water-soluble resins, undyed resin particles, surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, etc.

(Physical properties of ink)
It is preferable to use ink whose surface tension and viscosity are appropriately controlled in accordance with the characteristics of the inkjet recording head to be used. Specifically, the surface tension of the ink at 25° C. is preferably 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 60 mN/m or less, and particularly preferably 30 mN/m or more and 50 mN/m or less.

Furthermore, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10 mPa·s or less, and more preferably 1.0 mPa·s or more and 5 mPa·s or less.

(Recording method)
The ink according to this embodiment can be applied to printers of the sublimation transfer method or direct printing method.

Below, we will explain the sublimation transfer method as an example of a recording method using the ink according to this embodiment, but it is not limited to this method.

The dye sublimation transfer recording method consists of two steps: (1) printing onto transfer paper, and (2) transferring onto fabric.

(Printing process onto transfer paper)
In the printing process onto the transfer paper, the ink according to the present embodiment is applied to the transfer paper by an inkjet method. The transfer paper is not particularly limited, but it is preferable to use sublimation transfer printing paper.

Heads that can be used with the inkjet method include those that use a piezoelectric method or a method that ejects ink by heating the ink to create bubbles.

(Transfer process to fabric)
The transfer paper to which ink has been applied in the printing process is placed on a fabric, and then the fabric is heated and pressurized using a heat press or other heat press. This transfers the image to the fabric, allowing the image to be recorded on the fabric. The heat pressurization time is preferably 30 seconds or more and 180 seconds or less. The lower limit of the heating temperature in this process is not particularly limited, but is preferably 180°C or more and 220°C or less, more preferably 185°C or more and 205°C or less, and particularly preferably 190°C or more and 200°C or less.

The heat press pressure in this process is not particularly limited, but is preferably between 30 PSI and 120 PSI, and particularly preferably between 40 PSI and 90 PSI.

Instead of the heat press, a sublimation transfer machine (for example, trade name: PSH-4230, manufactured by Europort Co., Ltd.) that transfers at low temperatures under vacuum can also be used.
On the other hand, when the recording method using the ink according to this embodiment is a direct printing method, unlike the sublimation transfer method, an image is recorded on a fabric by applying the ink directly to the fabric using an inkjet method without going through a printing process on transfer paper. The image is then fixed to the fabric by heating and pressurizing the ink-applied fabric using a heating and pressurizing device such as a heat press. The heating and pressurizing time is preferably 30 seconds or more and 180 seconds or less. The heating temperature in this process is not particularly limited, but is preferably 180°C or more and 220°C or less, more preferably 185°C or more and 205°C or less, and particularly preferably 190°C or more and 200°C or less.

(Recording medium)
The recording medium is not particularly limited as long as it can be dyed with the ink according to this embodiment, and examples thereof include fabrics made of fibers containing polyester, acetate, or triacetate. The fabric may be in any form, such as woven fabric, knitted fabric, or nonwoven fabric. Fabrics made of cotton, silk, linen, polyurethane, acrylic, nylon, wool, or rayon fibers, or fabrics made of a combination of two or more of these fibers, can also be used.

In particular, with conventional sublimation dyes, the color development tends to vary depending on the heat press temperature when dyeing polyester and polyurethane blend materials, which are often used in sportswear and other products these days. However, the ink according to this embodiment makes it possible to obtain dyed products with excellent color development stability during heat press.

The thickness of the yarn that makes up the fabric is preferably in the range of 10 denier to 100 denier. There are no particular restrictions on the thickness of the fibers that make up the yarn, but it is preferably 1 denier or less.

Other objects that can be used include polyester-coated mugs and other three-dimensional objects such as sheets, spheres, and rectangular parallelepipeds.

[Third embodiment]
The thermal transfer recording sheet according to this embodiment is characterized in that, in the thermal transfer recording sheet having a substrate and a yellow colorant layer formed on the substrate, the yellow colorant layer contains a compound represented by general formula (1) and a compound represented by general formula (2).

Conventionally, inks that use a single compound represented by general formula (1) as the yellow colorant have been prone to aggregation and have had storage stability issues. On the other hand, inks that use a single compound represented by general formula (2) as the yellow colorant have had the issue of poor lightfastness, although they do not aggregate.

After extensive research, the inventors discovered that although the compounds represented by general formula (1) and general formula (2) each have their own problems when used alone as yellow colorants, the use of a combination of these compounds suppresses same-color mixed color fading.

The mechanism by which this yellow colorant exhibits the effect of suppressing color fading caused by mixing compounds of the same color but with different structures is not clearly understood, but the inventor speculates as follows.

When compounds having structures represented by general formulas (1) and (2) are used as in this embodiment, the ink exhibits good storage stability, and image recording (printed) samples are thermal transfer recording sheets in which same-color mixing and fading are suppressed. This is because the compounds represented by general formulas (1) and (2) are structurally similar in size, and the π-π stacking interaction of the benzene rings imparted by the dialkylamino groups in each compound causes the compounds to overlap with each other. It is believed that this overlapping provides stabilization, resulting in the aforementioned effects. In particular, in compounds represented by general formula (2), when _X1 is N-H, the most stable structure is formed when the hydrogen atom of N-H and the oxygen atom of C═O in the coumarin skeleton form a six-membered ring through hydrogen bonding, thereby maximizing the aforementioned effects.

The configuration of the thermal transfer recording sheet is described in detail below. Note that the compounds represented by general formulas (1) and (2) used in the thermal transfer recording sheet are the same as those described in the first embodiment, so further description is omitted.

The thermal transfer recording sheet according to this embodiment is a thermal transfer recording sheet having a substrate and a yellow colorant layer formed on the substrate, wherein the yellow colorant layer contains the compound represented by the aforementioned general formula (1) and the compound represented by the general formula (2).

The thermal transfer recording sheet preferably further has a magenta colorant layer and a cyan colorant layer, and it is preferable that the yellow colorant layer, the magenta colorant layer, and the cyan colorant layer are formed in face-sequential order on the substrate.

(I-1) Substrate The substrate of the thermal transfer recording sheet is preferably one that supports at least the three colorant layers described above. The substrate is not particularly limited, and any substrate that has been conventionally known in the field of thermal transfer recording sheets and has appropriate heat resistance and strength can be used.

Substrate Materials Examples of substrates include polyethylene terephthalate films, polyethylene naphthalate films, polycarbonate films, polyimide films, polyamide films, aramid films, polystyrene films, 1,4-polycyclohexylene dimethylene terephthalate films, polysulfone films, polypropylene films, polyphenylene sulfide films, polyvinyl alcohol films, cellophane films, cellulose derivative films, polyethylene films, polyvinyl chloride films, nylon films, condenser paper, and paraffin paper. Among these, polyethylene terephthalate films are preferred as substrates from the viewpoints of mechanical strength, solvent resistance, and economy.

Thickness of the Substrate The thickness of the substrate can be set to 0.5 μm or more and 50 μm or less, and from the viewpoint of transferability, it is preferably set to 3 μm or more and 10 μm or less.

Adhesion Treatment When a dye-containing composition (ink) is applied to a substrate to form each colorant layer, the coating liquid (dye composition) may lack wettability, adhesiveness, etc. Therefore, it is preferable to subject the substrate to an adhesion treatment on the coated surface as needed.

The adhesive treatment is not particularly limited, and methods known in the field of thermal transfer recording sheets can be used. Examples of adhesive treatments include ozone treatment, corona discharge treatment, ultraviolet treatment, plasma treatment, low-temperature plasma treatment, primer treatment, and chemical treatment. Two or more of these treatments may also be combined.

Furthermore, the substrate may be subjected to adhesion treatment by applying an adhesive layer onto the substrate. There are no particular restrictions on the adhesive layer, and any adhesive layer known in the field of thermal transfer recording sheets can be used. Materials used for the adhesive layer include, for example, organic materials such as polyester resin, polystyrene resin, polyacrylate resin, polyamide resin, polyether resin, polyvinyl acetate resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinyl alcohol resin, and polyvinyl butyral resin, and inorganic fine particles such as silica, alumina, magnesium carbonate, magnesium oxide, and titanium oxide.

(I-2) Heat-Resistant Slipping Layer For the purpose of improving heat resistance and running performance of a thermal head, the thermal transfer recording sheet preferably has a heat-resistant slipping layer on the surface of the substrate opposite to the surface on which the coloring material layer is provided.

The heat-resistant slip layer is composed of a layer containing a heat-resistant resin. There are no particular limitations on the heat-resistant resin, and the following resins can be used, for example: polyvinyl butyral resin, polyvinyl acetal resin, polyester resin, polyether resin, polybutadiene resin, vinyl chloride-vinyl acetate copolymer resin, styrene-butadiene copolymer resin, polyurethane acrylate, polyester acrylate, polyimide resin, polycarbonate resin, etc.

The heat-resistant slip layer may also contain additives such as crosslinking agents, release agents, lubricants, and slip-imparting agents. Examples of the lubricants include amino-modified silicone compounds and carboxy-modified silicone compounds. Examples of the slip-imparting agents include heat-resistant fine particles such as silica.

The heat-resistant slipping layer can be formed by applying a heat-resistant slipping layer coating liquid, which is prepared by adding the above-mentioned heat-resistant resin and additives to a solvent and dissolving or dispersing the liquid, to a substrate and drying the liquid. There are no particular restrictions on the method for applying the heat-resistant slipping layer coating liquid, and methods using, for example, a bar coater, gravure coater, reverse roll coater, rod coater, or air doctor coater can be used. Among these, a coating method using a gravure coater is preferred, as it is easy to adjust the film thickness.

From the standpoint of transferability, it is preferable to apply the heat-resistant slip layer coating solution to the substrate in such an amount that the thickness of the heat-resistant slip layer after drying is in the range of 0.1 μm to 5 μm.

(I-3) Protective Layer The thermal transfer recording sheet may have one or two transferable protective layers on the substrate for protecting the image surface after image formation, in face order with the colorant layer described below. This protective layer may also be formed on a sheet (substrate) different from the colorant layer. In this case, the thermal transfer recording sheet according to this embodiment includes a sheet having a substrate and a colorant layer (colorant layer sheet) and a sheet having a substrate and a protective layer (protective layer sheet).

The protective layer can be formed by applying the composition for each layer to the substrate and drying it. There are no particular limitations on the method for applying the composition for each layer to the substrate, and examples include methods using a bar coater, gravure coater, reverse roll coater, rod coater, air doctor coater, etc. Among these, the application method using a gravure coater is preferred, as it allows for easy adjustment of the film thickness.

Furthermore, the drying conditions after applying the composition for each layer are not particularly limited as long as sufficient drying is achieved. For example, drying can be carried out at a temperature range of 50°C to 120°C for 1 second to 5 minutes.

The binder resin used in the protective layer is not particularly limited, but suitable examples include acrylic resins such as polystyrene, polymethyl methacrylate, and polyethyl acrylate; styrene resins such as poly-α-methylstyrene; vinyl resins such as polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, and polyvinyl acetal; and synthetic resins such as polyamide resin, epoxy resin, polyurethane resin, petroleum resin, ionomer, ethylene-acrylic acid copolymer, and ethylene-acrylic acid ester copolymer.

The thickness of the protective layer is preferably in the range of 0.1 μm to 5 μm.

Furthermore, it is more preferable that a release layer containing an acrylic resin such as polymethyl methacrylate or polyethyl acrylate and having a thickness of 0.1 μm to 1.5 μm be provided under the yellow colorant layer containing the aforementioned compound to facilitate release from the sheet.

The release layer is formed on the aforementioned substrate.

(I-4) Colorant Layer In the thermal transfer recording sheet, the yellow colorant layer contains the compounds represented by the above-mentioned general formulas (1) and (2) as yellow colorants.

The two types of compounds mentioned above can also be used in combination with other yellow colorants, as long as the effects of the present invention are not impaired. The other yellow colorants are those used in the field of thermal transfer recording sheets, and can be any that transfer when heated, without any particular restrictions.

Furthermore, from the viewpoint of transferability and storage stability, the melting points of the compounds represented by general formulas (1) and (2) are preferably 40°C or higher and 200°C or lower. More preferably, they are 50°C or higher and 180°C or lower, and particularly preferably, they are 60°C or higher and 150°C or lower.

The compounding ratio between the compound represented by general formula (1) and the compound represented by general formula (2) is not particularly limited. Preferably, the mass ratio is 10 parts by mass of the compound represented by general formula (1) to 5 parts by mass or more and 90 parts by mass or less of the compound represented by general formula (2). A range of 10 parts by mass or more and 70 parts by mass or less is more preferable, and a range of 30 parts by mass or more and 50 parts by mass or less is even more preferable. Within such a range, it is easy to obtain a thermal transfer recording sheet in which same-color mixing and fading is suppressed for the two different types of yellow colorants used in the yellow colorant layer.

(I-4-1) Components Contained in the Colorant Layer Hereinafter, each component contained in the colorant layer other than the above-mentioned two types of compounds will be described.

(i) Other Coloring Compounds The magenta coloring material used in the magenta coloring material layer and the cyan coloring material used in the cyan coloring material layer are not particularly limited as long as they are used in the field of thermal transfer recording sheets and are thermally transferable. In addition, the coloring compounds of each color can be used alone or in combination of two or more.

(ii) Binder Resin The binder resin that can be used in each colorant layer of the thermal transfer recording sheet is not particularly limited, and various resins can be used. Among them, the following water-soluble resins and organic solvent-soluble resins are preferably used.
Water-soluble resins: cellulose resins, polyacrylic resins, starch resins, epoxy resins, and the like.
Organic solvent-soluble resins: polyacrylate resins, polymethacrylate resins, polystyrene resins, polycarbonate resins, polyethersulfone resins, polyvinyl butyral resins, ethyl cellulose resins, acetyl cellulose resins, polyester resins, AS resins, phenoxy resins, and the like.

These binder resins may be used alone or in combination of two or more types as needed.

(iii) Surfactant A surfactant may be added to each colorant layer of the thermal transfer recording sheet to provide sufficient lubricity during heating with a thermal head (during image recording). Examples of surfactants that can be added to each colorant layer include cationic surfactants, anionic surfactants, and nonionic surfactants.

Examples of the cationic surfactant include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide.

Examples of the anionic surfactants include fatty acid soaps such as sodium stearate and sodium dodecanoate, sodium dodecyl sulfate, sodium dodecylbenzene sulfate, and sodium lauryl sulfate.

Examples of the nonionic surfactants include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, nonylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan monooleate polyoxyethylene ether, and monodecanoyl sucrose.

(iv) Wax Wax may be added to each color material layer of the thermal transfer recording sheet to provide sufficient lubricity when the thermal head is not heated. Examples of wax that can be added to each color material layer include, but are not limited to, polyethylene wax, paraffin wax, and fatty acid ester wax.

(v) Other Additives In addition to the additives described above, ultraviolet absorbers, preservatives, antioxidants, antistatic agents, viscosity adjusters, etc. may be added to each colorant layer of the thermal transfer recording sheet, if necessary.

Examples of ultraviolet absorbers include benzophenone-based, benzotriazole-based, cyanoacrylate-based, and triazine-based ones.
Commercially available ultraviolet absorbers include, for example, Tinuvin P, Tinuvin 326, Tinuvin 571, and Tinuvin 360 (all manufactured by BASF), and Adekastab LA-24, LA-29, LA-31RG, LA-32, LA-36, LA-46, LA-F70, and 1413 (all manufactured by ADEKA Corporation).

Preferred are ADK STAB LA-29, LA-32, LA-36, and LA-46, with ADK STAB LA-29, LA-32, and LA-36 being particularly preferred.

The antioxidant may include a phenolic compound.
Commercially available antioxidants include, for example, Adekastab AO-20, AO-30, AO-40, AO-50, AO-50F, AO-60, AO-60G, AO-80, and AO-330 (all manufactured by ADEKA Corporation).

(vi) Medium The medium that can be used to prepare each colorant composition for the thermal transfer recording sheet is not particularly limited, but examples include water and organic solvents. Examples of preferred organic solvents include: alcohols such as methanol, ethanol, isopropanol, and isobutanol; cellosolves such as methyl cellosolve and ethyl cellosolve; aromatic hydrocarbons such as toluene, xylene, and chlorobenzene; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; halogenated hydrocarbons such as methylene chloride, chloroform, and trichloroethylene; ethers such as tetrahydrofuran and dioxane; N,N-dimethylformamide, N-methylpyrrolidone, and the like. These organic solvents may be used alone or in combination of two or more types as needed. Furthermore, water and organic solvents may be used in combination.

(I-4-2) Composition of colorant composition for forming colorant layer Content of colorant (amount used)
From the viewpoint of sheet storage stability, the amount of each colorant (yellow colorant, magenta colorant, or cyan colorant) used in each colorant composition is preferably 1 part by mass or more and 200 parts by mass or less relative to 100 parts by mass of binder resin. From the viewpoint of colorant dispersion, it is more preferably 50 parts by mass or more and 180 parts by mass or less relative to 100 parts by mass of binder resin. Note that, when two or more types of colorants are used in combination, the amount of the colorant used refers to the total amount in parts by mass of each colorant. For example, even when the compounds of the general formulas (1) and (2) above are used in combination with an existing colorant as a yellow colorant, the amount of the colorant used refers to the total number of parts by mass of these colorants.

・Content of other ingredients (amount used)
The amounts of other components (additives) used can be set appropriately and are not particularly limited.

(I-5) Other Layers (i) Black Colorant Layer The thermal transfer recording sheet preferably has three colorant layers including a yellow colorant layer, a magenta colorant layer, and a cyan colorant layer, but may further have a conventionally known black colorant layer as a colorant layer. The black colorant layer can be formed using a composition containing a black colorant or an existing yellow colorant, magenta colorant, and cyan colorant, and this black colorant layer can also contain the compounds of the general formulas (1) and (2) described above.

(I-6) Method for Producing Thermal Transfer Recording Sheet The method for producing a thermal transfer recording sheet is not particularly limited, but it can be produced, for example, as follows: As an example, a yellow colorant layer will be described.

First, the compounds (colorants) represented by general formulas (1) and (2), as well as binder resins, surfactants, and waxes, if necessary, are gradually added to a medium (e.g., an organic solvent) while stirring, and the mixture is thoroughly mixed into the medium.

In this process, mechanical shear force is applied using a disperser to stably dissolve or disperse these components into fine particles in the medium, preparing the colorant composition (ink). This colorant composition can be applied to a base film, which serves as the substrate, and then dried to create the desired colorant layer.

The dispersing machine used in preparing the colorant composition is not particularly limited, but examples that can be used include media-type dispersing machines such as rotary shear homogenizers, ball mills, sand mills, and attritors, as well as high-pressure counter-impingement dispersing machines.

In a thermal transfer recording sheet, each color material layer is formed in surface order on a substrate. For example, a yellow color material layer, a magenta color material layer, a cyan color material layer, and a protective layer can be repeatedly formed on a substrate (substrate sheet) along the direction of substrate movement. When a thermal transfer sheet having color material layers in this order is used, a yellow image is formed first, followed by a magenta image and then a cyan image, resulting in a series of image formations to form a full-color image. Finally, a protective layer is formed, and this series of image formations is repeated. Note that color material layers other than these can also be added as appropriate; for example, a black color material layer (heat-fusible black layer) can be added to the substrate.

The colorant layers can be formed by applying the colorant composition for each layer to the substrate and drying it. There are no particular limitations on the method for applying the composition for each layer to the substrate, and examples include methods using a bar coater, gravure coater, reverse roll coater, rod coater, air doctor coater, etc. Among these, application methods using a gravure coater are preferred, as they allow for easy adjustment of film thickness.

Furthermore, the drying conditions after applying the colorant composition for each layer are not particularly limited as long as sufficient drying is achieved. For example, drying can be carried out at a temperature range of 50°C to 120°C for 1 second to 5 minutes.

By thoroughly drying each dye composition, it becomes easier to prevent background scumming and the dye ink from bleeding through to the back when the film is wound up. It also makes it easier to prevent the bled dye ink from re-transferring to a colorant layer of a different hue when the film is rewound.

From the standpoint of transferability, it is preferable to apply the colorant composition in such an amount that the thickness of the colorant layer after drying is in the range of 0.1 μm to 5 μm.

(I-7) Method of Using Thermal Transfer Recording Sheet A thermal transfer recording sheet is superimposed on a transferee, for example, an image receiving sheet having a colorant-receiving layer on its surface, and the thermal transfer recording sheet is heated using a heating method such as a thermal head, thereby transferring the colorant in the sheet to the image receiving sheet, thereby forming an image. If the thermal transfer recording sheet has the transferable protective layer described above, the sheet containing this protective layer is superimposed on the image formed on the image receiving sheet. Then, by heating using a heating method such as a thermal head, the protective layer can be transferred (formed) on the image.

The heating method used to heat the thermal transfer recording sheet for image recording is not particularly limited, but can be the usual method using a thermal head, or infrared or laser light. It can also be used as an electrically conductive dye transfer sheet by using an electrically conductive heat-generating film that generates heat by passing electricity through the base film itself.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" in the text are by mass unless otherwise specified.

<Example of the first embodiment>
[Compounds represented by general formulas (1) and (2)]
The compounds represented by the general formulas (1) and (2) were synthesized by known methods. The compounds represented by the general formulas (1) and (2) used in this example are listed in Table 1-1.

The resulting compound was identified using a ¹ H nuclear magnetic resonance spectroscopy ( ¹ H-NMR) analyzer (trade name: "AVANCE-600 NMR spectrometer", manufactured by BRUKER) and a MALDI-TOF/MS (trade name: "MALDI-TOF/MS ultraFleXtreme", manufactured by BRUKER).

[Comparative Compounds]
The following comparative compounds (1) to (5) were used as comparative compounds.

[Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-12]
[Preparation of aqueous dispersion of resin particles (A)]
A reaction vessel was charged with 1,178 parts of water at 70°C and mixed with 466 parts of monomer (50% styrene, 47% acrylonitrile, 3% methacrylic acid), and a polymerization initiator (an aqueous solution of 1.9 parts of potassium persulfate in 659 parts of water) was added dropwise over 60 minutes. The mixture was further stirred at 70°C for 30 minutes to obtain an aqueous solution of core resin particles.

Next, the aqueous solution of core resin particles was heated to 80°C, and 80 parts of a mixed monomer solution (85% styrene, 15% methacrylic acid) and a polymerization initiator (an aqueous solution prepared by adding 0.1 parts of potassium persulfate to 133 parts of water) were added dropwise over 10 minutes. Stirring was continued for a further 120 minutes to synthesize resin particles (A) that would form a shell film (core-shell structure) on the core resin.

Next, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. Furthermore, a total of 29 parts (5% of the resin particles) of powder of the compounds shown in Table 1-1 (the compounding ratio of each compound is as shown in Table 1-1) and 29 parts of ethanol/butanol (8/2) were added, and the temperature was raised to 80°C. The mixture was then stirred for 2 hours. After the solvent was distilled off under reduced pressure, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. Water was added so that the resin particle content was 20%, yielding an aqueous dispersion of resin particles (A).

[Preparation of aqueous dispersion of resin particles (B)]
Under a nitrogen atmosphere, 100 parts of monomer (30% styrene, 30% n-butyl acrylate, 40% methacrylic acid) was added to 100 parts of methyl ethyl ketone at 78°C in a reaction vessel and mixed, and a polymerization initiator (a mixed liquid of 1 part azobisisobutyronitrile and 20 parts methyl ethyl ketone) was added dropwise over 2 hours. After further reacting for 2 hours, the mixture was cooled to 30°C, and 100 parts of dimethylethanolamine and 100 parts of water were added. Thereafter, the solvent was distilled off by concentration under reduced pressure, to obtain a resin particle solution (B).

Meanwhile, under a nitrogen atmosphere, an aqueous solution prepared by adding 1 part sodium bicarbonate and 1 part sodium lauryl sulfate to 178 parts water was heated to 80°C, and 1 part potassium persulfate was added. To this was added dropwise over 2 hours a solution prepared by adding 200 parts methyl methacrylate, 140 parts butyl acrylate, 5 parts glycidyl methacrylate, and a total of 5 parts of the compounds shown in Table 1-1 (the compounding ratios of each compound are shown in Table 1-1), and 6 parts sodium lauryl sulfate to 178 parts water. Subsequently, 119 parts of the resin particle solution (B) obtained above were added dropwise over 30 minutes, followed by the dropwise addition of 35 parts of a 1% aqueous ammonium persulfate solution over 30 minutes. The mixture was allowed to react at 80°C for 2 hours, yielding an aqueous dispersion of resin particles (B) with a solids concentration of 40%.

[Ink Preparation]
50 parts of the aqueous dispersion of resin particles (A) or (B), 10 parts of glycerin, 10 parts of triethylene glycol, 1 part of Acetylenol E100 (Kawaken Fine Chemicals), and 35 parts of water were mixed and stirred, and then pressure filtered through a microfilter (Fujifilm) with a pore size of 3.0 μm to prepare each of the inks listed in Table 1-1. The pH of each of the prepared inks was in the range of 8.5 to 9.0.

[Evaluation of storage stability of aqueous dispersion of resin particles]
The aqueous dispersion of resin particles (A) or (B) was sealed and stored at 10° C. for one month, and the presence or absence of aggregates and precipitates after storage was visually confirmed. The results are shown in Table 1-1.

The evaluation criteria were as follows: In the evaluation, the storage stability was judged to be good if "almost no aggregates and precipitates of the compound were observed" or "a small amount of aggregates and precipitates of the compound were observed."
A: Almost no compound aggregates or precipitates were observed. B: A small amount of compound aggregates and precipitates were observed. C: A large amount of compound aggregates and precipitates were observed.

[Evaluation of light resistance of printed matter (image recording matter)]
[Creating image samples]
Each of the prepared inks was filled into an ink cartridge, and an image was recorded using an inkjet recording apparatus (trade name "PIXUS Pro-10", manufactured by Canon) to obtain a monochrome image sample.

[Lightfastness evaluation method]
Each of the obtained monochrome image samples was placed in a xenon test device (trade name: AtlasCi4000, manufactured by Suga Test Instruments Co., Ltd.) and exposed for 24 hours under conditions of illuminance: 0.28 W/m ² at 340 nm, temperature: 40° C., and relative humidity: 50%.

The reflection density of the monochrome image sample was measured before and after exposure using a reflection densitometer FD-7 (product name, manufactured by Konica Minolta).

When the initial chromaticities before exposure were a ₀ ^* , b ₀ ^* , and L ₀ ^* , and the chromaticities after exposure were a ^* , b ^* , and L ^* , respectively, the color difference ΔE was defined and calculated as follows:

The evaluation criteria are as follows: If ΔE after 20 hours is less than 7, it is considered to have good lightfastness.

[Evaluation criteria]
A: ΔE<5
B: 5≦ΔE<7
C: 7≦ΔE

As is clear from Table 1-1 above, inks using resin particles dyed with a combination of compounds of general formulas (1) and (2) described in the examples had good storage stability and improved lightfastness of the printed images. In contrast, comparative inks using resin particles dyed with a compound of general formula (1) or (2) alone or with a comparative compound whose structure is different from general formulas (1) and (2) had poor storage stability or lightfastness.

[Examples 1-12]
[Preparation of aqueous dispersion of resin particles (C)]
In the preparation of the aqueous dispersion (B) of resin particles in Example 1-1, 10 parts of ADK STAB LA-36 (manufactured by ADEKA CORPORATION) was added to a total of 5 parts of the compounds shown in Table 1-1 (the compounding ratio of each compound is as shown in Table 1-1), and an aqueous dispersion (C) of resin particles having a solid content concentration of 40% was obtained in the same manner as in Example 1-1.

The storage stability of this aqueous dispersion of resin particles was rated A, and when an image sample was prepared and the lightfastness of the print evaluated, the ΔE after 24 hours was 2.21, demonstrating improved lightfastness.

<Preparation of Ink for Oil-Based Writing Instruments>
[Example 1-13]
To a mixed solution of 78 parts of 1-phenoxy-2-propanol and 22 parts of benzyl alcohol, 9 parts of Elec BL-1 (manufactured by Sekisui Chemical Co., Ltd.) as a resin and 1 part of polyvinylpyrrolidone resin K-90 (manufactured by Nippon Shokubai Co., Ltd.) were added and dissolved by heating to 70°C. The mixture was then cooled to room temperature, and 3 parts of Compound 1-2, which is a compound represented by general formula (1), 12 parts of Compound 2-1, which is a compound represented by general formula (2), and 3 parts of Plysurf A208N were added as colorants. The mixed solution was dispersed for 3 hours using an Attritor (manufactured by Mitsui Mining Co., Ltd.) to prepare ink (1) for an oil-based writing instrument.

[Comparative Example 1-13-1]
Comparative oil-based ink for writing instruments (1) was prepared in the same manner as in Example 1-13, except that in Example 1-13, the colorant was changed to only 15 parts of Compound 1-2, which is a compound represented by general formula (1).

[Comparative Example 1-13-2]
Comparative oil-based ink for a writing instrument (2) was prepared in the same manner as in Example 1-13, except that in Example 1-13, the colorant was changed to only 15 parts of compound 2-1, which is a compound represented by general formula (2).

<Evaluation of storage stability of ink for oil-based writing instruments>
20 mL of each of the oil-based writing inks obtained above was added to a 50 mL sample bottle, sealed, and left at 60°C for one month. After leaving the bottle, the surface condition was observed at 20x magnification using a phase-contrast microscope (trade name: BX53, manufactured by Olympus Corporation). The observation revealed that when the compounds of general formulas (1) and (2) were used alone, particle aggregation was observed, but when both compounds of general formulas (1) and (2) were used, no aggregation was observed. This confirmed the improvement in storage stability due to the use of both compounds of general formulas (1) and (2).

<Production of oil-based writing implements and evaluation of lightfastness>
Each of the oil-based inks for writing instruments obtained above was filled into a polypropylene ink reservoir tube with an inner diameter of 1.2 mm and a length of 140 mm. A ballpoint pen for evaluation test (ball diameter 0.7 mm) equipped with this ink reservoir tube and a phosphor bronze tip was prepared, and a 2 cm square image sample was created using a constant writing pressure.

The obtained image sample was placed in a xenon test device (Atlas Weather-Ometer Ci4000, manufactured by Toyo Seiki Seisakusho, Ltd.). After placement, it was exposed for 10 hours under conditions of illuminance: 0.28 W/ ^m2 at 340 nm, black panel temperature: 40°C, and relative humidity: 50%. Compared to when the compounds represented by general formulas (1) and (2) were used alone, when both compounds represented by general formulas (1) and (2) were used, the residual optical density (O.D.) rate (%) was 10% higher, confirming improved lightfastness.

The O.D. retention rate (%) was measured using an image sample reflection densitometer (product name "FD-7", manufactured by Konica Minolta), and is the rate of change in the O.D. of yellow between the initial and 10 hours later.

<Preparation of Water-Based Writing Ink>
[Example 1-14]
As colorants, 3 parts of Compound 1-2, which is a compound represented by general formula (1), and 12 parts of Compound 2-1, which is a compound represented by general formula (2), 0.6 parts of Plysurf A208N (Dai-ichi Kogyo Seiyaku Co., Ltd.), 1 part of methanol, and 0.5 parts of cellulose nanofiber Rheocrysta I-2AX (Dai-ichi Kogyo Seiyaku Co., Ltd.) were added, followed by the addition of 99 parts of ion-exchanged water. The mixture was heated to an internal temperature of 80°C and stirred for 2 hours while removing the methanol. After allowing to cool to room temperature, the mixture was dispersed in a homogenizer for 5 minutes to prepare aqueous ink for a writing instrument (1).

[Comparative Example 1-14-1]
Comparative oil-based ink for writing instruments (1) was prepared in the same manner as in Example 9, except that in Example 1-14, the colorant was changed to only 15 parts of Compound 1-2, which is a compound represented by general formula (1).

[Comparative Example 1-14-2]
Comparative oil-based ink for writing instruments (2) was prepared in the same manner as in Example 1-14, except that in Example 9, the colorant was changed to only 15 parts of Compound 2-1, which is a compound represented by general formula (2).

<Evaluation of storage stability of ink for water-based writing instruments>
20 mL of each of the obtained aqueous writing inks was added to a 50 mL sample bottle, sealed, and left at 60°C for one month. After leaving the bottle, the surface condition was observed at 20x magnification using a phase contrast microscope (trade name: BX53, manufactured by Olympus Corporation). The observation revealed that when the compounds of general formulas (1) and (2) were used alone, particle aggregation was observed, but when both compounds of general formulas (1) and (2) were used, no aggregation was observed. This confirmed the improvement in storage stability due to the use of both compounds of general formulas (1) and (2).

<Production of water-based writing implements and evaluation of lightfastness>
The resulting water-based writing ink was filled into a polypropylene ink reservoir tube with an inner diameter of 1.2 mm and a length of 140 mm. A ballpoint pen for evaluation test was prepared using this ink reservoir tube and a phosphor bronze tip (ball diameter: 0.7 mm), and a 2 cm square image sample was created using a constant writing pressure.

The obtained image sample was placed in a xenon test device (product name: Atlas Weather-Ometer Ci4000, manufactured by Toyo Seiki Seisaku-sho, Ltd.). After placement, it was exposed for 10 hours under conditions of illuminance: 0.28 W/ ^m2 at 340 nm, black panel temperature: 40°C, and relative humidity: 50%. After exposure, when compared with the case where the compounds of general formulas (1) and (2) were used alone, the case where both compounds represented by general formulas (1) and (2) were used had an O.D. residual rate (%) that was 8.5% higher, confirming improved lightfastness.

The O.D. residual rate (%) was determined in the same manner as in Example 1-13.

<Example of the second embodiment>
[Compounds represented by general formulas (1) and (2)]
The compounds represented by the general formulas (1) and (2) were synthesized by known methods. The compounds represented by the general formulas (1) and (2) used in this example are listed in Table 2-1.

The resulting compound was identified using a ¹ H nuclear magnetic resonance spectroscopy ( ¹ H-NMR) analyzer (trade name: "AVANCE-600 NMR spectrometer", manufactured by BRUKER) and a MALDI-TOF/MS (trade name: "MALDI-TOF/MS ultraFleXtreme", manufactured by BRUKER).

[Comparative Compounds]
The following comparative compounds were used:

(Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-6)
[Ink production]
A total of 2 parts of the compounds shown in Table 2-1 (the compounding ratio of each compound is as shown in Table 2-1), 16 parts of water, 0.8 parts of a dispersant (trade name: DisperBYK190, manufactured by BYK-Chemie), and 80 parts of 0.2 mmφ zirconia beads were placed in a zirconia container and dispersed for 4 hours at 300 rpm in a planetary ball mill. The dispersion was diluted with a 15% aqueous glycerin solution to a solids concentration of 5%, and then filtered through a 0.5 μm filter to obtain an ink.

[Printing process onto transfer paper]
The ink was filled into a modified Canon printer equipped with a piezo-type recording head, and a solid image with 100% duty was printed on a sublimation transfer paper (trade name LUCY, manufactured by Dairiki Co., Ltd.).

[Transfer process to fabric]
The obtained solid image was dried and then transferred to a polyester fabric (Polyester Amunzen, manufactured by Tajimaya Co., Ltd.) using a heat press machine (trade name: AIR FUSION, manufactured by STAHLS) at a heat press pressure of 60 SPI and a heat press temperature shown in Table 2-1.

<Evaluation>
(Yellow Optical Density Evaluation)
For the polyester fabrics produced in the examples and comparative examples at a heat press temperature of 200°C, the yellow optical density (O.D.) of the images obtained at each press temperature was measured using a reflection densitometer (product name: FD-7, manufactured by Konica Minolta, Inc.). The measurement results were evaluated for density according to the following evaluation criteria. The evaluation results are shown in the "Y density" column in Table 2-1. In the evaluation, if the yellow O.D. was 1.50 or higher, it was determined that the optical density was high.

[Evaluation criteria]
A: Yellow O.D. is 1.70 or more. B: Yellow O.D. is 1.50 or more and less than 1.70. C: Yellow O.D. is less than 1.50.

(Evaluation of color development stability by heat press)
The color development stability during heat pressing was calculated using the following formula: The method for measuring the yellow optical density (O.D.) of the image at each heat pressing temperature was the same as the method for evaluating the yellow optical density described above, except that the heat pressing temperatures were different.
Color stability (%) during heat pressing at 180°C to 210°C =
|O.D. of yellow when heat-pressed at 210°C -O.D. of yellow when heat-pressed at 180°C | (absolute value)
Color stability (%) during heat pressing at 190°C to 200°C =
|O.D. of yellow when heat-pressed at 200°C -O.D. of yellow when heat-pressed at 190°C | (absolute value)

The results were evaluated according to the following criteria. A yellow O.D. difference (absolute value) of less than 0.50 was considered to indicate good color stability.

[Evaluation criteria]
A: The O.D. difference (absolute value) of yellow is less than 0.30. B: The O.D. difference (absolute value) of yellow is 0.30 or more and less than 0.50. C: The O.D. difference (absolute value) of yellow is 0.50 or more.

As is clear from Table 2-1 above, by using ink containing compounds represented by general formulas (1) and (2), it was possible to obtain image recordings with high optical density and high thermal stability.

[Example 2-12]
Two parts of the compound of Example 2-8, one part of Adekastab LA-36 (manufactured by ADEKA Corporation), 15 parts of water, 0.8 parts of a dispersant (trade name: DisperBYK190, manufactured by BYK-Chemie), and 80 parts of 0.2 mmφ zirconia beads were added and dispersed in a planetary ball mill at 300 rpm for four hours. The dispersion was diluted with a 15% aqueous glycerin solution to a solids concentration of 5%, and then filtered through a 0.5 μm filter to obtain an ink.

This ink was evaluated for yellow optical density and heat press color stability in the same manner as in Example 2-8. The evaluation results are shown in Table 2-2 below. As shown in Table 2-2, Example 2-12 showed even greater improvement in color stability during heat press compared to Example 2-8.

<Example of the third embodiment>
[Compounds represented by general formulas (1) and (2)]
The compounds represented by the general formulas (1) and (2) were synthesized by known methods. The compounds represented by the general formulas (1) and (2) used in this example are listed in Table 3-1.

The resulting compound was identified using a ¹ H nuclear magnetic resonance spectroscopy ( ¹ H-NMR) analyzer (trade name: "AVANCE-600 NMR spectrometer", manufactured by BRUKER) and a MALDI-TOF/MS (trade name: "MALDI-TOF/MS ultraFleXtreme", manufactured by BRUKER).

[Comparative Compounds]
The following comparative compounds (1) to (5) were used as comparative compounds.

Examples 3-1 to 3-15 and Comparative Examples 3-1 to 3-13
(I) Thermal Transfer Recording Sheet [Preparation of Each Colorant Composition]
<Preparation of Colorant Composition>
Five parts of polyvinyl butyral resin (product name "KS-3", manufactured by Sekisui Chemical Co., Ltd.) was added little by little to a mixed solution of 45 parts of methyl ethyl ketone and 45 parts of toluene and dissolved therein. Five parts of a compound of the type shown in Table 3-1 below was added to this solution and dissolved therein, thereby obtaining a colorant composition.

[Preparation of Thermal Transfer Recording Sheet]
A polyethylene terephthalate film (trade name "Lumirror", manufactured by Toray Industries, Inc.) having a thickness of 4.5 μm was used as the substrate, and the colorant composition was applied onto this substrate and then dried to prepare a thermal transfer recording sheet having a yellow colorant layer having a thickness of 1 μm after drying.

[Creating image samples]
Using the thermal transfer recording sheet having the prepared yellow colorant layer, a monochrome image was transferred onto a recording paper using a modified machine (trade name "Selphy", manufactured by Canon) (the amount of heat supplied for thermal transfer was reduced to about 80%), to prepare image samples (1) to (15) in the case of using colorant compositions (1) to (15), and comparative image samples (1) to (13) in the case of using comparative colorant compositions (1) to (13).

The color of the image samples was measured using a reflection densitometer (product name "FD-7", manufactured by Konica Minolta).

[evaluation]
[Evaluation of storage stability of ink (colorant composition)]
The colorant compositions used in Examples 3-1 to 3-15 and Comparative Examples 3-1 to 3-13 were placed in 100 mL mayonnaise bottles, sealed, and stored at 10° C. for one month, and the presence or absence of aggregates after storage was visually confirmed. The results are shown in Table 3-1.

The evaluation criteria are as follows: In the evaluation, storage stability was determined to be good if "almost no compound aggregates were observed" or "a small amount of compound aggregates were observed."

[Evaluation criteria]
A: Almost no compound aggregates were observed. B: A small amount of compound aggregates were observed. C: A large amount of compound aggregates were observed.

[Evaluation of light resistance of printed matter (image recording matter)]
Each monochrome image sample obtained in Examples 3-1 to 3-15 and Comparative Examples 3-1 to 3-13 was placed in a xenon test device (trade name "AtlasCi4000", manufactured by Suga Test Instruments Co., Ltd.) and exposed for 20 hours under conditions of illuminance: 0.28 W/m ² at 340 nm, temperature: 40°C, and relative humidity: 50%.

The reflection density of the print was then measured before and after the test.

When the initial chromaticities were a ₀ ^* , b ₀ ^* , and L ₀ ^* , and the chromaticities after exposure were a ^* , b ^* , and L ^* , respectively, the color difference ΔE was defined and calculated as follows:

The evaluation criteria are as follows: If ΔE after 20 hours is less than 7, it is considered to have good lightfastness.

[Evaluation criteria]
A: ΔE<5
B: 5≦ΔE<7
C: 7≦ΔE

As is clear from Table 3-1 above, the image samples formed using the thermal transfer recording sheets described in the examples showed suppressed same-color fading of the yellow dye in the yellow colorant layer, and a thermal transfer recording sheet was obtained.

The present invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to clarify the scope of the present invention.

This application claims priority based on Japanese Patent Applications Nos. 2024-013021, 2024-013022, and 2024-013023 filed on January 31, 2024, and No. 2025-011690 filed on January 27, 2025, the entire contents of which are incorporated herein by reference.

Claims (19)

The medium and
An ink containing a compound represented by the following general formula (1) and carrier particles dyed with a compound represented by the following general formula (2):

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group;
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group. The ink according to claim 1, which contains a dispersant. The ink described in claim 1 or 2, further containing a resin present in a dissolved state in the medium. The ink according to any one of claims 1 to 3 is for use in oil-based writing instruments, water-based writing instruments, or inkjet printers. an aqueous medium;
a dispersant; and
A compound represented by the following general formula (1),
A compound represented by the following general formula (2),
An ink characterized in that it comprises:

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group;
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group. The ink according to claim 5, which is water-based. The ink described in claim 5 or 6 is for inkjet printing. The ink according to any one of claims 1 to 7, wherein in the general formula (1), _R1 and _R2 each independently represent an alkyl group having 1 to 4 carbon atoms, and _R3 represents an alkoxy group having 1 to 4 carbon atoms. The ink according to any one of claims 1 to 8, wherein in the general formula (2), _R5 and _R6 each independently represent an alkyl group having 1 to 4 carbon atoms, and _X1 represents O, N-H, or N- _CH3 . The ink according to any one of claims 1 to 9, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 5 parts by mass or more and 90 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). The ink according to any one of claims 1 to 10, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 10 parts by mass or more and 70 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). The ink according to any one of claims 1 to 11, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 30 parts by mass or more and 50 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). A thermal transfer recording sheet having a substrate and a yellow colorant layer formed on the substrate,
A thermal transfer recording sheet, wherein the yellow colorant layer contains a compound represented by the following general formula (1) and a compound represented by the following general formula (2):

[In general formula (1),
_R1 and _R2 each independently represent an alkyl group;
_R3 represents an alkyl group, an aryl group, or an alkoxy group.
_R4 represents an alkyl group or an aryl group.

[In general formula (2),
_R5 and _R6 each independently represent an alkyl group;
_R7 and _R8 each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or a halogen atom;
_X1 represents O, S, or N- _R9 , where _R9 represents a hydrogen atom or an alkyl group. The thermal transfer recording sheet according to claim 13, further comprising a magenta colorant layer and a cyan colorant layer, the yellow colorant layer, the magenta colorant layer, and the cyan colorant layer being formed in face-sequential order on the substrate. 15. The thermal transfer recording sheet according to claim 13, wherein in the general formula (1), R ₁ and R ₂ are each independently an alkyl group having 1 to 4 carbon atoms, and R ₃ is an alkoxy group having 1 to 4 carbon atoms. The thermal transfer recording sheet according to any one of claims 13 to ₁₅ , wherein in the general formula (2), _R5 and _R6 each independently represent an alkyl group having 1 to 4 carbon atoms, and _X1 represents O, N-H, or N-CH3. The thermal transfer recording sheet according to any one of claims 13 to 16, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 5 parts by mass or more and 90 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). The thermal transfer recording sheet according to any one of claims 13 to 17, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 10 parts by mass or more and 70 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1). The thermal transfer recording sheet according to any one of claims 13 to 18, wherein the mass ratio of the compound represented by general formula (1) to the compound represented by general formula (2) is 30 parts by mass or more and 50 parts by mass or less of the compound represented by general formula (2) per 10 parts by mass of the compound represented by general formula (1).