JP2014055202A - Inkjet ink set, recording method and recorded material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set which is excellent in visibility and can record an image having desired sensitivity to an active energy ray of a specific wavelength region, and to provide a recording method using the same and a recorded material obtained by the method.SOLUTION: There is provided an inkjet ink set which comprises a plurality of inks and is provided with a first ink containing a photochromic compound as a colorant and a second ink, wherein the photochromic compound develops a color by being irradiated with an active energy ray of a specific wavelength region and after the first ink and the second ink are irradiated with the active energy ray of a specific wavelength region, a hue angle of the first ink is different from that of the second ink by 70° or more.

Description

  The present invention relates to an ink jet ink set, a recording method, and a recorded matter.

  2. Description of the Related Art Conventionally, photochromic compounds that can reversibly change colors such as coloring and decoloring are widely known. The discoloration of the photochromic compound is caused by the chemical structure of the photochromic compound being changed by irradiation with an active energy ray in a specific wavelength range. As such a photochromic compound, for example, a compound having an arylethene structure (see Patent Document 1 and Patent Document 2), a compound having a diacetylene structure (see Patent Document 3), and the like are known.

  The photochromic compound can be used, for example, as an indicator for detecting an active energy ray having a specific wavelength or knowing an integrated dose (irradiation amount) by utilizing the color developing action.

JP 2005-255538 A Japanese Patent No. 395664 JP 2006-519383 A

  However, when the above photochromic compound is used as an indicator, there has been a problem that it is difficult to visually recognize a change in color due to irradiation with active energy rays.

  Also, an indicator using a photochromic compound usually has a color change sensitivity set in advance by the indicator producer. Therefore, the user was able to know the irradiation amount of the active energy ray irradiated only with the set sensitivity range.

  Some embodiments according to the present invention are for inkjet which can record an image having excellent visibility and a desired sensitivity to active energy rays in a specific wavelength region by solving at least a part of the above-described problems. An ink set, a recording method using the ink set, and a recorded matter obtained thereby.

  The present invention can be realized as the following aspects or application examples.

[Application Example 1]
One aspect of the ink set for inkjet according to the present invention is as follows:
An inkjet ink set comprising a plurality of inks,
A first ink containing a photochromic compound as a colorant;
A second ink;
With
The photochromic compound develops color when irradiated with active energy rays in a specific wavelength range,
After the first ink and the second ink are irradiated with active energy rays in the specific wavelength range, the first ink and the second ink have a hue angle of 70 ° or more different.

  According to the aspect described in the application example 1, it is possible to record an image having excellent visibility and a desired sensitivity with respect to an active energy ray in a specific wavelength range.

[Application Example 2]
In application example 1,
The second ink contains a colorant,
The colorant contained in the second ink may be a photochromic compound or a colorant that is not the photochromic compound.

[Application Example 3]
In application example 1 or application example 2,
Furthermore, at least one of a third ink containing a sensitizer and a fourth ink containing a desensitizer can be provided.

[Application Example 4]
In application example 3,
The desensitizer is metal particles or metal oxide particles,
The average particle size of the desensitizer may be 100 nm or less.

[Application Example 5]
In application example 3 or application example 4,
The third ink and the fourth ink may be substantially free of a colorant.

[Application Example 6]
In any one of Application Examples 1 to 5,
Three or more inks of cyan ink, magenta ink, and yellow ink can be provided.

[Application Example 7]
One aspect of the recording method according to the present invention is:
A mixed color image is formed using the inkjet ink set described in any one of Application Examples 1 to 6.

[Application Example 8]
In Application Example 7,
The color mixture image can be changed in color by being irradiated with an active energy ray in a specific wavelength region.

[Application Example 9]
One aspect of the recorded matter according to the present invention is:
The recording method described in Application Example 7 or Application Example 8 is used.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

1. Inkjet ink set An inkjet ink set according to an embodiment of the present invention is an inkjet ink set including a plurality of inks, and includes a first ink containing a photochromic compound as a colorant, and a second ink. The photochromic compound is colored by irradiating active energy rays in a specific wavelength region, and after irradiating the first ink and the second ink with active energy rays in the specific wavelength region, The hue angle of the ink is different from the hue of the second ink by a hue angle of 70 ° or more.

  The color mixture image obtained by using the first ink and the second ink changes its color when at least the photochromic compound contained in the first ink is colored by being irradiated with an active energy ray in a specific wavelength range. Since the first ink and the second ink constituting the inkjet ink set according to the present embodiment have a hue angle different by 70 ° or more, discoloration of the recorded image is easily visually recognized.

  Further, according to the ink set for ink jet according to the present embodiment, since each ink constituting the ink set is ejected from the nozzles of the ink jet recording apparatus to form an image, the ejection amount of the first ink is changed. Thus, the sensitivity of the recorded image to the active energy ray can be easily adjusted. Therefore, it is possible to easily obtain an image having a desired sensitivity with respect to an active energy ray in a specific wavelength range.

  Hereinafter, each ink constituting the inkjet ink set according to the present embodiment (hereinafter also simply referred to as “ink set”) will be described in detail.

1.1. First ink 1.1.1. Photochromic compound The first ink contains a photochromic compound as a colorant. When the photochromic compound is irradiated with an active energy ray in a specific wavelength range, the chemical structure is changed, and color change such as color development or decoloration occurs. For example, as a mode of discoloration of a photochromic compound, color development is caused by irradiation with light having a first wavelength, and color is erased by irradiation with light having a second wavelength different from the first wavelength. Can be mentioned.

  Here, the active energy rays refer to α rays, β rays, γ rays, X rays, ultraviolet rays, visible rays, infrared rays, electron rays, and the like.

  Examples of the photochromic compound include diarylethene derivatives and fulgide derivatives. A photochromic compound may be used individually by 1 type, and may be used together 2 or more types.

  Specific examples of the diarylethene derivative and fulgide derivative include compounds represented by the following general formulas (1) to (4).

In general formulas (1) to (4), X ¹ and X ² are the same or different and each independently represent a substituent represented by the following general formula (5) to (8). In the general formula (4), R ¹ represents an aromatic group, a heterocyclic group, an aliphatic group, or a combination thereof.

In general formulas (5) to (8), X ³ , X ⁴ and X ⁵ each independently represent a hydrogen atom, an aromatic group, a heterocyclic group, an aliphatic group or a combination thereof. X ³ , X ⁴ and X ⁵ may be bonded to form a ring. In the general formula (8), R ² represents an aromatic group, a heterocyclic group, an aliphatic group, or a combination thereof.

X ³ , X ⁴ and X ⁵ can be each independently hydrogen and a substituent represented by the following general formula (9).

(Y ^A ) _y1 −Z− (Y ^D ) _y2 (9)
In the general formula (9), Y ^A represents an electron acceptor group, Y ^D represents an electron donor group, and Z represents a bonding group. Moreover, y1 and y2 represent an integer greater than or equal to 0.

In the general formula (9), as Z, for example,
(A) one or two or more aromatic hydrocarbon groups having 6 to 60 carbon atoms (eg, —C ₆ H ₄ —, —C ₆ H ₄ —C ₆ H ₄ —, etc.),
(B) one or more aromatic hydrocarbon groups conjugated via one or more ethenyl or ethynyl bonds having 8 to 60 carbon atoms (for example, —C ₆ H ₄ —CH═CH—C ₆ H ₄ —, — _{C 6 H 4 -C≡C-C 6} H 4 - , etc.),
(C) a polycyclic aromatic hydrocarbon group having 10 to 60 carbon atoms (for example, 1,4-C ₁₀ H ₆ , 1,5-C ₁₀ H _{6 and the} like), and (d) the number of atoms (carbon atoms and One or more aromatic heterocyclic groups having a total number of heteroatoms of 5 or more and 30 or less (for example, furan, benzofuran, dibenzofuran, etc. in which the heteroatom is oxygen, and 1,4 in which the heteroatom is sulfur) -Dithiine, benzo-1,4-dithiin, dibenzo-1,4-dithiin, tetrathiafulvalene, thiophene, benzothiophene, dibenzothiophene, etc., pyrrole, indole, carbazole, pyrazole, imidazole, etc. where the hetero atom is nitrogen, hetero Selenophen, benzoselenophene, dibenzoselenophene, etc., where the atom is selenium, tellurophene, benzotellof, where the heteroatom is tellurium , Dibenzoterlophene, etc.),
Etc.

Z may also be an aliphatic hydrocarbon, for example
(A) a linear alkyl group having 4 to 30 carbon atoms (for example, pentyl, decyl, dodecyl, etc.),
(B) an alkyl group having a branched structure and having 5 to 40 carbon atoms (isopentyl, 2-propyl-pentyl),
(C) an alicyclic group having 3 to 8 (preferably 4 to 7) carbon atoms in the ring (for example, cyclopentyl, cyclohexyl, etc.), or a polycyclic group (alicyclic group) in which two or more of these are bonded. Wherein one or more hydrogen atoms are an alkyl group having 1 to 20 carbon atoms, an arylalkyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms (preferably 4 to 7 carbon atoms), or carbon Optionally substituted with an alkylcycloalkyl group having a number of 4 to 30),
(D) an arylalkyl group or alkylaryl group having 7 to 30 carbon atoms (for example, p-methyl-benzyl, 3- (p-ethyl-phenyl) -propyl, 5- (1-naphthyl) -pentyl, etc.) ,
Etc.

The Y ^D,
(A) an atom selected from the group consisting of N, O, S, P, Cl, Br and I, wherein the valence of the atom is satisfied;
(B) ferrocenyl,
(C) azulenyl,
(D) C1-C20 alkyl groups (methyl, ethyl, etc.) with a linear or branched structure, etc. are mentioned.

Other parts (one or more) that satisfy the valence requirements for Y ^D atoms include, for example:
(A) a hydrogen atom,
(B) a linear alkyl group having 1 to 20 carbon atoms (for example, pentyl, decyl, and dodecyl),
(C) an alkyl group having a branched structure having 3 to about 40 carbon atoms (for example, isopropyl, isopentyl, and 2-propyl-pentyl),
(D) a cycloalkyl group having 4 to 7 carbon atoms in the ring (for example, cyclopentyl and cyclohexyl),
And (e) an aryl group having 7 to 30 carbon atoms, an arylalkyl group or an alkylaryl group (for example, p-methyl-benzyl, 3- (p-ethyl-phenyl) -propyl, and 5- (1-naphthyl) -Pentyl etc.),
Is mentioned.

The Y ^A,
(A) aldehyde (-CO-H),
(B) R is a linear alkyl group having 1 to 20 carbon atoms (for example, methyl, ethyl, pentyl, decyl, dodecyl, etc.); an alkyl group having 3 to about 40 carbon atoms with a branched structure ( For example, isopropyl, isopentyl, and 2-propyl-pentyl); a cycloalkyl group having 4 to 7 carbon atoms in the ring (such as cyclopentyl and cyclohexyl); an arylalkyl group or alkylaryl group having 7 to 30 carbon atoms ( Ketones (-CO-R), which may be, for example, p-methyl-benzyl, 3- (p-ethyl-phenyl) -propyl, and 5- (1-naphthyl) -pentyl),
(C) R is a linear alkyl group having 1 to 20 carbon atoms (for example, pentyl, decyl, dodecyl, etc.); a C 3-40 alkyl group having a branched structure (for example, isopropyl, isopentyl, and 2-propyl-pentyl, etc.); a cycloalkyl group having 4 to 7 carbon atoms in the ring (for example, cyclopentyl and cyclohexyl); an arylalkyl group or alkylaryl group having 7 to 30 carbon atoms (for example, p-methyl- Benzyl, 3- (p-ethyl-phenyl) -propyl, and 5- (1-naphthyl) -pentyl, and the like), esters (-COOR),
(D) carboxylic acid (-COOH),
(E) cyano (CN),
(F) Nitro (NO ₂ ),
(G) Nitroso (N = O),
(H) a sulfur-based group (eg, —SO ₂ —CH ₃ , —SO ₂ —CF ₃ , —SO ₃ Na),
(I) a fluorine atom,
(J) Each R is independently a linear alkyl group having 1 to 20 carbon atoms (eg, pentyl, decyl, dodecyl, etc.); a branched alkyl group having 3 to 40 carbon atoms (eg, isopropyl, isopentyl, and 2-propyl-pentyl, etc.); a cycloalkyl group having 4 to 7 carbon atoms in the ring (for example, cyclopentyl and cyclohexyl); an arylalkyl group or alkylaryl group having 7 to 30 carbon atoms (for example, p-methyl- Alkene (—CH═CR ₂ or —CH═CHR), which may be benzyl, 3- (p-ethyl-phenyl) -propyl, and 5- (1-naphthyl) -pentyl),
(K) a boron atom,
Is mentioned.

  Among these, diarylethene derivatives are preferable, and compounds represented by the following general formulas (10) to (12) are more preferably used.

In the above formula (10), R ^Y each independently represents an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, propyl group, butyl group). Further, when (I) is irradiated with ultraviolet rays, its chemical structure changes to (I) ′, which is a closed ring of (I), and exhibits a yellow color. On the other hand, when (I) ′ is irradiated with visible light, its chemical structure changes to (I) and changes its color to colorless (disappears). In particular, when R ^Y is a methyl group, yellow color developability can be improved.

In the formula (11), R ^M are each independently represents an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, propyl group, butyl group). Further, when (II) is irradiated with ultraviolet rays, its chemical structure changes to (II) ′, which is a closed ring of (II), and exhibits a magenta color. On the other hand, when (II) ′ is irradiated with visible light, its chemical structure changes to (II) and changes its color to colorless (disappears). In particular, when R ^M is a propyl group, it can be improved chromogenic magenta.

In said formula (12), R < ^C > represents a C1-C4 alkyl group (a methyl group, an ethyl group, a propyl group, a butyl group) each independently. Further, when (III) is irradiated with ultraviolet rays, its chemical structure changes to (III) ′, which is a closed ring of (III), and exhibits a cyan color. On the other hand, when (III) ′ is irradiated with visible light, its chemical structure changes to (III) and changes its color to colorless (discolors). In particular, when R ^C is an ethyl group, cyan color developability can be improved.

  The content of the photochromic compound can be appropriately set according to the application and is not particularly limited, but is preferably 0.1% by mass or more and 5% by mass or less with respect to the total mass of the first ink, More preferably, it is 0.5 mass% or more and 3 mass% or less. When the content of the photochromic compound is within the above range, particularly not less than 0.1% by mass, the visibility of the recorded image tends to be good. Further, when the content of the photochromic compound is within the above range, particularly not exceeding 5% by mass, the solubility (or dispersibility) of the photochromic compound in the first ink is improved, and the ejection stability of the first ink is improved. Tend to improve.

1.1.2. Other ingredients (water)
The first ink according to the present embodiment may be a water-based ink in which the main solvent (for example, a solvent contained in an amount of 50% by mass or more with respect to the total mass of the ink) is water, or an organic solvent. A certain non-aqueous (solvent) ink may be used.

  When the first ink according to the present embodiment is a water-based ink, the reactivity to a piezoelectric element that may be used in a recording head or an organic binder included in a recording medium is weak. In some cases, corrosion can be reduced. In addition, the water-based ink may be able to form an image having excellent drying properties as compared with a non-water-based ink containing a large amount of a solvent having a high boiling point and a low viscosity. Further, the water-based ink has an advantage that it is good for the environment because 50% or more of the composition is water.

(Wetting agent)
The first ink according to this embodiment may contain a wetting agent. Thereby, clogging in the vicinity of the nozzle portion of the ink discharge head can be effectively reduced.

As the wetting agent, for example, glycerin, 1,2,6-hexanetriol, trimethylolpropane, pentamethylene glycol, trimethylene glycol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, number Polyethylene glycol having an average molecular weight of 2000 or less, dipropylene glycol, tripropylene glycol, isobutylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol Polyhydric alcohols such as mesoerythritol and pentaerythritol, as well as glucose, mannose, fructose, ribose, xylose, arabinose, galactose, Sugars such as ludonic acid, glucitol (sorbit), maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose, so-called solid wetting agents such as sugar alcohols, hyaluronic acids, and ureas, and ethanol, methanol, butanol, C1-C4 alkyl alcohols such as propanol and isopropanol, and 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, Examples include sorbitan, acetin, diacetin, triacetin, and sulfolane, and one or more of these can be used in combination.

(Penetration enhancer)
The first ink according to this embodiment may contain a penetration enhancer. The penetration enhancer has a function of further improving the wettability of the ink with respect to the recording medium and applying it uniformly. As a result, it is possible to further reduce the density unevenness and bleeding of the ink of the recorded image, and to further improve the color density of the image.

  Examples of such penetration enhancers include alkyl alcohol alkyl ethers (also referred to as glycol ethers), 1,2-alkyl diols, and the like.

  Examples of the alkyl ether of polyhydric alcohol include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono Isopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, Lopylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether , Dipropylene glycol monoisopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and the like. Examples of the 1,2-alkyldiol include 1,2-pentanediol and 1,2-hexanediol. In addition to these, straight-line such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol. Examples thereof include diols of chain hydrocarbons, and one or more of these can be used in combination.

(Surfactant)
The first ink according to this embodiment may contain a surfactant. The surfactant is not particularly limited, and any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant can be used.

  Among these, it is preferable to use a surfactant having high wettability of ink, and specific examples include acetylene glycol surfactants and silicon surfactants.

  The acetylene glycol surfactant is a nonionic surfactant having an acetylene group in the center and a symmetrical structure, and is applied to aqueous materials in various directions as a wetting agent that hardly foams. The acetylene glycol surfactant is excellent in functions such as wetting, defoaming, and dispersion. The glycol has a very stable molecular structure, has a small molecular weight, and has the effect of lowering the surface tension of water. Therefore, the permeability and bleeding of the ink to the recording medium can be controlled appropriately, and the fixing property of the ink to the recording medium can be controlled. Can be increased.

  Specific examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, , 5-dimethyl-1-hexyn-3-ol and the like. Commercially available acetylene glycol surfactants include, for example, Surfinol 104 (series), 420, 440, 465, 485 (trade name, manufactured by Air Products), Olphine STG, PD-001, SPC, E1004, E1010. PD-002W (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), acetylenol E00, E40, E100, LH (trade name, manufactured by Kawaken Fine Chemical Co., Ltd.) and the like.

  The silicon-based surfactant can appropriately control the wettability to the surface of the recording medium, the permeability to the recording medium and the bleeding, and can improve the fixing property of the ink to the recording medium.

  As the silicon-based surfactant, a polysiloxane compound or the like is preferably used, and examples thereof include polyether-modified organosiloxane. More specifically, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (above trade names, manufactured by Big Chemie Japan Co., Ltd.), KF-351A, KF- 352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF- 6012, KF-6015, KF-6017 (above trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) and the like.

(resin)
The first ink according to the present embodiment may contain a resin. One of the functions of the resin is to improve image fixability and abrasion resistance on the recording medium.

  Examples of the resin include acrylic resin, urethane resin, polyolefin resin, ester resin, rosin modified resin, terpene resin, polyamide resin, epoxy resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer Known resins such as coalescence, ethylene vinyl acetate resin, fluorene resin, polyolefin wax and the like can be mentioned.

(Preservatives and fungicides)
The first ink according to this embodiment may contain a preservative and a fungicide. Examples of antiseptics and fungicides include sodium benzoate, sodium pentachlorophenol, 2-pyridinethiol-1-oxide sodium, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazoline-3-one Etc. Examples of commercially available products include Proxel XL2, Proxel GXL (above trade name, manufactured by Avicia), Denside CSA, NS-500W (above trade name, manufactured by Nagase ChemteX Corporation), and the like.

  Examples of the rust inhibitor include benzotriazole.

  Examples of the chelating agent include ethylenediaminetetraacetic acid and salts thereof (such as ethylenediaminetetraacetic acid dihydrogen disodium salt).

(PH adjuster)
The first ink according to this embodiment may contain a pH adjuster. Examples of the pH adjuster include potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, triisopropanolamine, potassium carbonate, sodium carbonate, Examples thereof include sodium hydrogen carbonate.

1.2. Second ink When an active energy ray in a specific wavelength region is irradiated, the hue angle of the second ink is different from that of the first ink by 70 ° or more. Therefore, by forming a mixed color image using the first ink and the second ink, it is possible to record an image having a wide color expression area that cannot be expressed when only the first ink is used.

  In particular, when two or more colors of ink are used, an achromatic color such as composite black may be formed on the recording medium. Composite black is a black color formed by mixing two or more inks. In the case of forming composite black using two colors of ink, it can be obtained, for example, by using a green ink and a magenta ink and mixing each ink in an appropriate ratio on a recording medium. In addition, when forming composite black using three colors of ink, for example, cyan ink, magenta ink, and yellow ink are used to mix each ink at an appropriate ratio on a recording medium.

  In the present invention, the term “mixed color” refers to a mixture of different ink droplets (dots) mixed with each other, as well as a mixture of both dots that are adjacent to or in contact with different ink droplets. Including those capable of expressing the same color as.

In the present invention, an achromatic color means a color having a saturation C ^* defined by the CIELAB color space of 15 or less. The black color means a color having a lightness L * defined in the CIELAB color space of 50 or less and a saturation C * of 15 or less.

The CIELAB color space is an approximate uniform color space recommended by the International Commission on Illumination (CIIE) in 1976, and this committee has designated CIE 1976 (L ^* a ^* b ^* ).

The hue angle in the present invention means a hue angle (h °) defined in the CIELAB color space, and is a value calculated from the values of a ^* and b ^* using the following formula. Specifically, the hue angle h ° is h ° = tan ⁻¹ (b ^* / a ^* ), a ^* ≦ 0, and a ^* ≧ 0 and b ^* ≧ 0 (first quadrant). In the case of b ^* ≧ 0 (second quadrant), h ° = 180 + tan ⁻¹ (b ^* / a ^* ), and in the case of a ^* ≦ 0 and b ^* ≦ 0 (third quadrant), h ° = 180 + tan ⁻¹ (b ^* / a ^* ), a ^* ≧ 0, and b ^* ≦ 0 (fourth quadrant), calculation is performed using the equation h ° = 360 + tan ⁻¹ (b ^* / a ^* ). .

In the present invention, the hue angle (h °) of the ink was measured using a colorimeter Gretag Spectrolino (trade name, manufactured by Gretag) when an ink image was recorded on neutral paper of pH 7. It refers to the hue angle (h °) of the image. In addition, as the neutral paper of pH 7, paper showing a range of 70 ≦ L ^* ≦ 100, −4.5 ≦ a ^* ≦ 2, −6 ≦ b ^* ≦ 2.5 is used. Here, when a photochromic compound is used as the colorant, the color of the image when the color is developed by irradiation with an active energy ray in a specific wavelength range is measured.

1.2.1. Colorant The second ink according to the present embodiment preferably contains a colorant. Examples of the colorant contained in the second ink include a photochromic compound or a colorant that is not the photochromic compound (described later).

  Among these, as the colorant contained in the second ink, it is preferable to use a colorant that is not a photochromic compound. When the second ink contains a colorant that is not a photochromic compound, the mixed color image obtained using the first ink and the second ink is excellent in visibility both before and after irradiation with active energy rays. This is because the change in color becomes remarkable. That is, before the irradiation with the active energy ray, the mixed color image composed of the first ink and the second ink becomes a color derived from the second ink, and thus has excellent visibility. Further, after the irradiation with the active energy ray, the color change of the mixed color image of the first ink and the second ink becomes clear as the first ink is colored.

  When the second ink contains the colorant, the content thereof can be appropriately set depending on the application and is not particularly limited. For example, the content is 0.1% by mass or more and 10% by mass with respect to the total mass of the second ink. % Or less, more preferably 0.5% by mass or more and 5% by mass or less.

(Coloring agents that are not photochromic compounds)
When the second ink contains a colorant that is not a photochromic compound (described above), the second ink does not contain a photochromic compound as a colorant.

  Examples of the colorant that is not a photochromic compound include pigments (for example, organic pigments and inorganic pigments) and dyes.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone. Polycyclic pigments such as pigments, dye chelates (for example, basic dye type chelates, acidic dye type chelates), dyeing lakes (basic dye type lakes, acid dye type lakes), nitro pigments, nitroso pigments, aniline black, A daylight fluorescent pigment is mentioned. The said pigment may be used individually by 1 type, and may use 2 or more types together.

More specifically, examples of the inorganic pigment used for black include, for example, the following carbon black, for example, No. manufactured by Mitsubishi Chemical. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, or No2200B, etc .; Columbia-made Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc .; 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc .; or Color Black FW2, Wck, Col Black FW2, Cck, FW2C, Decksa Color Black FW2, Cck Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Speck 4 or Speck.

  Although it does not specifically limit as a yellow organic pigment, For example, C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180, 185, 213 and the like.

  Although it does not specifically limit as a magenta organic pigment, For example, C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, 254, 264 or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50 and the like.

  Although it does not specifically limit as a cyan organic pigment, For example, C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 15:34, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60 and the like.

  The organic pigments other than magenta, cyan and yellow are not particularly limited. I. Pigment green 7, 10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, and the like.

  As the dye, for example, various dyes that are usually used for inkjet recording such as direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, and reactive disperse dyes are used. can do.

  Although it does not specifically limit as a yellow dye, For example, C.I. I. Acid Yellow 1, 3, 11, 17, 19, 23, 25, 29, 36, 38, 40, 42, 44, 49, 59, 61, 70, 72, 75, 76, 78, 79, 98, 99, 110, 111, 127, 131, 135, 142, 162, 164, 165, C.I. I. Direct Yellow 1, 8, 11, 12, 24, 26, 27, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 110, 132, 142, 144, C.I. I. Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37, 42, C.I. I. Food Yellow 3, 4, C.I. I. Solvent yellow 15, 19, 21, 30, 109 etc. are mentioned.

The magenta dye is not particularly limited. I. Acid Red 1, 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 37, 42, 51, 52, 5
7, 75, 77, 80, 82, 85, 87, 88, 89, 92, 94, 97, 106, 111, 114, 115, 117, 118, 119, 129, 130, 131, 133, 134, 138, 143, 145, 154, 155, 158, 168, 180, 183, 184, 186, 194, 198, 209, 211, 215, 219, 249, 252, 254, 262, 265, 274, 282, 289, 303, 317, 320, 321, 322, C.I. I. Direct Red 1, 2, 4, 9, 11, 13, 17, 20, 23, 24, 28, 31, 33, 37, 39, 44, 46, 62, 63, 75, 79, 80, 81, 83, 84, 89, 95, 99, 113, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229, 230, 231, C.I. I. Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 49, 50, 58, 59, 63, 64, C.I. I. Sorbize red 1, C.I. I. Food red 7, 9, 14 etc. are mentioned.

  Although it does not specifically limit as a cyan dye, For example, C.I. I. Acid Blue 1, 7, 9, 15, 22, 23, 25, 27, 29, 40, 41, 43, 45, 54, 59, 60, 62, 72, 74, 78, 80, 82, 83, 90, 92, 93, 100, 102, 103, 104, 112, 113, 117, 120, 126, 127, 129, 130, 131, 138, 140, 142, 143, 151, 154, 158, 161, 166, 167, 168, 170, 171, 182, 183, 184, 187, 192, 199, 203, 204, 205, 229, 234, 236, 249, C.I. I. Direct Blue 1, 2, 6, 15, 22, 25, 41, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 120, 123, 158, 160, 163, 165, 168, 192, 193, 194, 195, 196, 199, 200, 201, 202, 203, 207, 225, 226, 236, 237, 246, 248, 249, C.I. I. Reactive Blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33 , 34, 37, 38, 39, 40, 41, 43, 44, 46, C.I. I. Solvize Bat Blue 1, 5, 41, C.I. I. Bat Blue 4, 29, 60, C.I. I. Food Blue 1, 2, C.I. I. Basic blue 9, 25, 28, 29, 44 etc. are mentioned.

  The dyes other than magenta, cyan and yellow are not particularly limited. I. Acid Green 7, 12, 25, 27, 35, 36, 40, 43, 44, 65, 79, C.I. I. Direct Green 1, 6, 8, 26, 28, 30, 31, 37, 59, 63, 64, C.I. I. Reactive Green 6, 7, C.I. I. Acid Violet 15, 43, 66, 78, 106, C.I. I. Direct violet 2, 48, 63, 90, C.I. I. Reactive violet 1, 5, 9, 10, C.I. I. Direct black 154 etc. are mentioned.

(Photochromic compound)
When the second ink according to this embodiment contains a photochromic compound, it does not contain a colorant other than the photochromic compound.

  Specific examples and functions of the photochromic compound that can be used in the second ink are the same as those described in the first ink, and thus the description thereof is omitted.

  When a photochromic compound is used as the colorant contained in the second ink, the photochromic compound contained in the second ink is irradiated with active energy rays in the wavelength region where the photochromic compound contained in the first ink develops color. Further, it is preferable to develop a color.

1.2.2. Other Components The second ink according to the present embodiment is made of water, a wetting agent, a penetration accelerator, a surfactant, a resin, an antiseptic / antifungal agent, a pH adjuster, etc. for the purpose of further improving the performance of the ink. You may contain a component. Specific examples and functions of these components are the same as the contents described in the first ink, and thus description thereof is omitted.

1.3. Other Inks The ink set according to the present embodiment may further include one or more inks in addition to the first ink and the second ink.

1.3.1. Third Ink The ink set according to the present embodiment may include a third ink containing a sensitizer. When the ink set according to the present embodiment includes the third ink, the mixed color image formed using the first ink, the second ink, and the third ink has a sensitivity to the active energy ray due to the action of the sensitizer. Rise. Thereby, even if the irradiation amount of the active energy ray with respect to the said color mixture image is small, a color mixture image can be developed.

For example, when forming a mixed color image composed of the first ink, the second ink, and the third ink, the sensitivity to the active energy ray of the obtained mixed color image can be easily controlled by changing the ejection amount of the third ink. Can do.
(Sensitizer)
The sensitizer is not particularly limited as long as it can exhibit the above functions, and examples thereof include a radical generator.

  Radical generators include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), hexaarylbiimidazole compounds, ketoxime ester compounds , Borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Specific examples of such radical generators include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, Carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4-isopropylphenyl) 2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Thioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, etc. Is mentioned.

The content of the sensitizer is preferably 0.01% by mass to 3.0% by mass and more preferably 0.5% by mass to 1.5% by mass with respect to the total mass of the third ink. It is more preferable. When the content of the sensitizer is within the above range, the above-described action may be further promoted.
(Other)
The third ink according to the present embodiment contains components such as water, a wetting agent, a penetration accelerator, a surfactant, a resin, a preservative / antifungal agent, and a pH adjuster for the purpose of further improving the performance of the ink. May be. Specific examples and functions of these components are the same as the contents described in the first ink, and thus description thereof is omitted.

  In addition, it is preferable that the third ink according to the present embodiment does not substantially contain a colorant from the viewpoint of not affecting the color of the mixed color image.

  In the present invention, “substantially free of A” means that A is not intentionally added when the ink is produced, and the ink is inevitably mixed or generated during production or storage. It may contain a trace amount of A. Specific examples of “substantially free” include, for example, 1.0% by mass or more, preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and still more preferably 0% by mass. 0.05% by mass or less, particularly preferably 0.01% by mass or less.

1.3.2. Fourth Ink The ink set according to the present embodiment may include a fourth ink containing a desensitizer.

  When the active energy ray was irradiated beyond the dose (irradiation amount) of all the photochromic compounds contained in the image, the detailed dose might not be known. In such a case, if the fourth ink is used for forming the mixed color image, the sensitivity of the mixed color image (photochromic compound) to the active energy rays can be reduced by the action of the desensitizer, so the detailed value of the dose can be set. I can know.

For example, when forming a mixed color image composed of the first ink, the second ink, and the fourth ink, the sensitivity to the active energy ray of the obtained mixed color image can be easily controlled by changing the ejection amount of the fourth ink. Can do.
(Desensitizer)
The desensitizer is not particularly limited as long as it has the above action, and examples thereof include metal particles or metal oxide particles. These may be used alone or in combination of two or more.

Examples of the material constituting the metal particles include molybdenum (Mo), tungsten (W), lead (Pb), and the like. Examples of the material constituting the metal oxide particles include barium oxide (BaO), cerium oxide (CeO), gadolinium oxide (Gd ₂ O ₃ ), dysprosium oxide (Dy ₂ O ₃ ), and titanium oxide (TiO ₂ ). ) And the like.

  The volume-based average particle diameter of the desensitizer (hereinafter referred to as “average particle diameter”) is preferably 100 nm or less, and more preferably 10 nm or more and 100 nm or less. When the average particle diameter of the desensitizer is 100 nm or less, the color of the desensitizer itself is lightened, so that it is possible to reduce the color mixture image from being colored by the color of the desensitizer itself.

  The average particle size of the desensitizer can be measured by a particle size distribution measuring apparatus based on the laser diffraction scattering method. Examples of the particle size distribution measuring apparatus include a particle size distribution meter (for example, “Microtrack UPA” manufactured by Nikkiso Co., Ltd.) having a dynamic light scattering method as a measurement principle.

The content of the desensitizer is preferably 0.5% by mass or more and 5.0% by mass or less, and 1.0% by mass or more and 3.0% by mass or less with respect to the total mass of the fourth ink. It is more preferable.
When the content of the desensitizer is within the above range, the above-described action may be further promoted. (Other)
The fourth ink according to the present embodiment contains components such as water, a wetting agent, a penetration accelerator, a surfactant, a resin, a preservative / antifungal agent, and a pH adjuster for the purpose of further improving the performance of the ink. May be. Specific examples and functions of these components are the same as the contents described in the first ink, and thus description thereof is omitted.

  The fourth ink according to this embodiment preferably does not substantially contain a colorant from the viewpoint of not affecting the color of the mixed-color image.

  The ink set according to the present embodiment preferably includes both the third ink and the fourth ink in addition to the first ink and the second ink. By doing so, for example, the first mixed color image composed of the first ink and the second ink, the second mixed color image composed of the first ink, the second ink, and the third ink, the first ink, the first ink, A third mixed color image composed of two inks and a fourth ink can be formed. Since each color mixture image obtained in this way has different sensitivities to active energy rays, it can be suitably used as an indicator applicable to various environments (environments with different irradiation amounts of active energy rays).

1.3.3. Others The ink set according to the present embodiment may include one or more inks other than the inks described above (hereinafter also referred to as “fifth ink”).

  When the active energy ray in the specific wavelength range is irradiated, the hue angle of the fifth ink is preferably different from the hue angle of the first ink and the hue angle of the second ink by 70 ° or more. Thereby, various colors can be expressed, and the visibility of the mixed-color image may be improved.

  The fifth ink can contain the above-described photochromic compound or the above-described colorant (pigment, dye, etc.) other than the photochromic compound as a colorant. The fifth ink may contain components such as water, a wetting agent, a penetration enhancer, a surfactant, a resin, a preservative / fungicide, and a pH adjuster. Specific examples of these components and their functions are the same as those described for the first ink and the second ink, and thus the description thereof is omitted.

  When a photochromic compound is used as the colorant contained in the fifth ink, the photochromic compound contained in the fifth ink is irradiated with active energy rays in the wavelength region where the photochromic compound contained in the first ink develops color. Further, it is preferable to develop a color.

  The ink set according to the present embodiment preferably includes three or more types of inks, cyan ink, magenta ink, and yellow ink. As described above, by using an ink set including three or more kinds of inks of cyan ink, magenta ink, and yellow ink, composite black can be easily formed or a color expression area may be widened. Thereby, it is possible to form a mixed color image having excellent visibility.

  When used as an ink set including three or more inks of cyan ink, magenta ink, and yellow ink, at least one of the three colors of cyan ink, magenta ink, and yellow ink is the first ink, and at least one of them One type may be the second ink, and the fifth ink may be used as appropriate. For example, it can be obtained by preparing the first ink, the second ink, and the fifth ink described above for each color.

In the present invention, the cyan ink refers to an ink that exhibits a cyan color when an image made of the ink is recorded on neutral paper of pH 7. The cyan color means a color defined in the CIELAB color space having a lightness L ^* of 50 to 85, a saturation C ^* of 40 to 80, and a hue angle h of 230 ° to 260 °.

In the present invention, magenta ink refers to ink that exhibits a magenta color when an image made of the ink is recorded on neutral paper of pH 7. The magenta color is a color defined in the CIELAB color space having a lightness L ^* of 40 to 70, a saturation C ^* of 60 to 100, and a hue angle h of 330 ° to 360 °.

In the present invention, the yellow ink refers to an ink that exhibits a yellow color when an image made of the ink is recorded on neutral paper of pH 7. The yellow color means a color defined in the CIELAB color space having a lightness L ^* of 70 to 100, a saturation C ^* of 55 to 90, and a hue angle h of 80 ° to 110 °.

  Here, the color of an ink using a photochromic compound as a colorant indicates a color when color is developed by irradiation with active energy rays in a specific wavelength range.

The brightness L ^* , saturation C ^* , and hue angle h of an image made of each ink can be measured using a colorimeter Gretag Spectrolino (trade name, manufactured by Gretag).

1.4. Ink Preparation Method Each of the above-described inks can be obtained by mixing the above-described components in an arbitrary order and removing impurities by filtering or the like as necessary. As a method for mixing the components, a method in which materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirred and mixed is suitably used. As a filtration method, centrifugal filtration, filter filtration, or the like can be performed as necessary.

1.5. Ink physical properties Each of the inks described above preferably has a surface tension at 20 ° C. of 20 mN / m or more and 50 mN / m, preferably 25 mN / m or more and 40 mN, from the viewpoint of the balance between the recording quality and the reliability as an inkjet ink. / M or less is more preferable. The surface tension is measured by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) by confirming the surface tension when the platinum plate is wetted with ink in an environment of 20 ° C. be able to.

  From the same viewpoint, the viscosity of each ink at 20 ° C. is preferably 2 mPa · s or more and 15 mPa · s or less, and more preferably 2 mPa · s or more and 10 mPa · s or less. The viscosity is measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), increasing the Shear Rate to 10 to 1000 in an environment of 20 ° C., and reading the viscosity at Shear Rate 200. Can be measured.

2. Recording Method A recording method according to an embodiment of the present invention forms a mixed-color image using the inkjet ink set.

The recording method according to the present embodiment can be performed using an ink jet recording apparatus. Examples of the ink jet recording apparatus include a known ink jet printer (hereinafter also simply referred to as “printer”). Hereinafter, the recording method according to the present embodiment will be described by taking a case where a printer is used as an example. In addition, this invention is not limited to the following aspects.

  First, the first ink droplets are ejected from the nozzles of the recording head of the printer to adhere the first ink droplets onto the recording medium. Next, the second ink droplet is ejected from the nozzle of the recording head of the printer, and the second ink droplet is brought into contact with or adjacent to the first ink droplet on the recording medium. Thereby, it is possible to obtain a recorded matter in which a mixed color image composed of the droplets of the first ink and the second ink is recorded on the recording medium.

  Here, the recording method in which the second ink is ejected after the first ink is ejected first is shown, but the present invention is not limited to this, and the first ink and the second ink may be ejected simultaneously. The first ink may be ejected after the second ink is ejected first.

  The first ink droplet (dot) and the second ink droplet (dot) may be mixed on the recording medium, or may be in contact with each other or adjacent to each other.

  The recording method according to the present embodiment can express a color change due to the color change of the first ink, and can also record a mixed color image of at least two types of inks. Therefore, compared with the case where each ink is used alone. Can expand the color expression area.

  In addition to the first ink and the second ink, when the third ink, the fourth ink, and the fifth ink described above are used, the same method as the method of forming a mixed color image using the first ink and the second ink, A mixed color image can be formed.

  As a recording medium used in the recording method according to the present embodiment, any recording medium may be used as desired. For example, in addition to paper such as plain paper, special paper having an ink receiving layer, etc., for example, ink The region including the surface to which is applied is various plastics, ceramics, glass, metal, fiber, leather, or a substrate composed of these composite materials.

3. Examples Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the present embodiments are not limited to these examples.

3.1. Preparation of Ink Each component shown in Table 1 was mixed and stirred to produce photochromic ink Y (hereinafter also referred to as “PC-Y”), photochromic ink M (hereinafter also referred to as “PC-M”), and photochromic. Ink C (hereinafter also referred to as “PC-C”), color ink Y (hereinafter also referred to as “N-Y”), color ink M (hereinafter also referred to as “NM”), color ink C (Hereinafter, also referred to as “NC”) was prepared.

Among the components listed in Table 1, components described by abbreviations or trade names are as follows.
Photochromic compound Y (compound having the structure of formula (10) described above, wherein R ^Y is a methyl group)
Photochromic compound M (compound having the structure of the formula (11) described above and R ^M is a propyl group)
Photochromic compound C (compound having the structure of the above formula (12) and R ^C is an ethyl group)
・ Yellow pigment (CI Pigment Yellow 74)
-Magenta pigment (CI Pigment Violet 19)
・ Cyan pigment (CI Pigment Blue 15: 3)
・ TEGmBE (triethylene glycol monobutyl ether)
・ Orphine E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol surfactant)
・ Surfinol 104PG50 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol surfactant)

3.2. Ink set Each ink prepared as described above was filled into a dedicated cartridge of an ink jet printer PX-B510 (trade name, manufactured by Seiko Epson Corporation), and combined inks described in Examples 1 to 5 in Table 2 Set.

  In addition, after printing an image on the recording medium P paper (trade name, manufactured by Fuji Xerox Co., Ltd., pH 7 neutral paper) under the same conditions for each ink constituting the ink set, ultraviolet rays (wavelength 200 nm to 380 nm) are applied. When irradiated, the hue angles of the images differed by 70 ° or more.

3.3. Evaluation Test Each ink constituting the ink set was ejected from the nozzle of the printer to form a mixed color image on a recording medium (trade name “Photomat Paper”, manufactured by Seiko Epson Corporation). At this time, the ink was ejected so that the dots of each ink were in contact with each other.

  The mixed color image thus obtained was irradiated with ultraviolet rays (wavelength: 200 nm to 380 nm), and the color change of the mixed color image was visually confirmed.

3.4. Evaluation results The results of the evaluation tests are also shown in Table 2 above.

  As shown in Examples 1 to 5, when ink containing a photochromic compound and ink having a hue angle different from the hue of the ink by 70 ° or more can be used, images of various colors can be formed. Indicated.

  In particular, it was shown that when the ink sets used in Examples 2 to 5 were used, images with excellent visibility were obtained both before and after irradiation with active energy rays.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (9)

An inkjet ink set comprising a plurality of inks,
A first ink containing a photochromic compound as a colorant;
A second ink;
With
The photochromic compound develops color when irradiated with active energy rays in a specific wavelength range,
An ink-jet ink set, wherein after the first ink and the second ink are irradiated with active energy rays in the specific wavelength region, the hue angle of the first ink differs from the second ink by 70 ° or more. In claim 1,
The second ink contains a colorant,
The inkjet ink set, wherein the colorant contained in the second ink is a photochromic compound or a colorant that is not the photochromic compound. In claim 1 or claim 2,
Furthermore, an inkjet ink set comprising at least one of a third ink containing a sensitizer and a fourth ink containing a desensitizer. In claim 3,
The desensitizer is metal particles or metal oxide particles,
The ink set for inkjet which has an average particle diameter of the desensitizer of 100 nm or less. In claim 3 or claim 4,
The third ink and the fourth ink are ink-jet ink sets that contain substantially no colorant. In any one of Claims 1 thru | or 5,
An ink jet ink set comprising three or more inks of cyan ink, magenta ink, and yellow ink.   A recording method for forming a mixed-color image using the inkjet ink set according to claim 1. In claim 7,
The recording method according to claim 1, wherein the color mixture image changes color when irradiated with an active energy ray in a specific wavelength region.   A recorded matter obtained by using the recording method according to claim 7 or 8.