JP2014047302A - Ink composition, and image-forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an ink composition in which cockle is suppressed, and color reproducibility is excellent; and an image-forming method.SOLUTION: An ink composition includes: water; an organic pigment; a polymer dispersant that disperses a near infrared absorption coloring agent; a water insoluble near infrared absorption coloring agent that has an absorption maximal wave length in a range of at least 700 nm and at most 1,500 nm.

Description

  The present invention relates to an ink composition and an image forming method.

Inkjet technology is known as an image recording method for recording a color image. Ink jet technology has been applied to fields such as office printers and home printers, but in recent years, it has been applied to commercial printing fields.
As ink (ink composition) used in the ink jet technology, ink containing pigment (pigment ink) is widely used.

In recent years, water-based inks using water as an ink solvent have been widely used in consideration of the environment. However, water-based inks dry more slowly than inks using solvents having a low boiling point such as organic solvents. Therefore, an ink that can absorb infrared rays and accelerates drying by infrared irradiation is disclosed.
For example, for the purpose of realizing quick drying of the ink, the ink has an absorption maximum wavelength in the range of 700 nm to 1500 nm, and the absorption coefficient in the wavelength region of 400 nm to less than 700 nm is 10% of the absorption coefficient in the absorption maximum wavelength. It is disclosed that the composition includes the following infrared absorbing material (see, for example, Patent Document 1).

  In the invisible ink field, various inks containing an infrared absorbing material are disclosed (for example, see Patent Documents 2 to 4).

JP 2001-226618 A JP 2002-187955 A JP 2001-234000 A JP 2008-255323 A

In a water-based ink composition using water as a solvent, when an image is formed on a recording medium containing paper in image formation, the paper swells by absorbing water, hydrogen bonds are broken, and the fibers of the paper are disordered. It becomes a state. After drying, recombination occurs in a state where the arrangement of fibers remains disordered, so that the paper is easily curled or uncooked.
Note that “cuckling” is also referred to as “cockling” or “wave wave” and refers to a phenomenon in which the surface of the recording medium becomes finely wrinkled during printing on the recording medium.

  By including a near-infrared absorbing pigment in the ink composition, it is possible to selectively overheat the image portion, so that it is easy to suppress cockle. However, since the near-infrared absorbing dye is colored, it is desirable that it is stably dispersed in the ink composition and rapidly decomposed by infrared irradiation when the image is dried. If the dispersion in the ink composition is insufficient, the near-infrared absorbing dye is not sufficiently decomposed even by infrared irradiation, and tends to remain in the ink composition. For this reason, since the color of the colorant in the ink composition and the color of the near-infrared absorbing pigment may overlap and change color, color reproducibility cannot be satisfied.

According to Patent Document 1, although the near-infrared absorbing dye attempts to disperse with a low molecular weight surfactant, the dispersibility of the near-infrared absorbing dye is not sufficient.
Moreover, the near infrared absorption pigment | dye is used for the ink composition shown by patent documents 2-4 for an invisible use, without including an organic pigment.

In order to form a visible image with the ink composition, it is desired that the organic pigment is stably dispersed in the ink composition in the presence of the organic pigment, and the dispersion stability of the near-infrared absorbing dye is compatible. The present invention has been made in view of the above, and it is an object of the present invention to provide an ink composition and an image forming method that suppress cuckling and are excellent in color reproducibility.

  Specific means for solving the problems are as follows.

<1> An ink composition comprising water, an organic pigment, a polymer dispersant for dispersing a near-infrared absorbing dye, and a water-insoluble near-infrared absorbing dye having an absorption maximum wavelength of 700 nm to 1500 nm.

<2> The ink composition according to <1>, wherein the content of the near-infrared absorbing dye is 0.05% by mass to 0.3% by mass with respect to the total mass of the ink composition.

<3> The ink composition according to <1> or <2>, which is a colored ink composition.
The ink composition is preferably a visible colored ink composition.

<4> The ratio of the organic pigment to the near-infrared absorbing dye (organic pigment: near-infrared absorbing dye) is any one of <1> to <3>, which is 10: 1 to 100: 1 on a mass basis. It is an ink composition as described.

<5> The ink composition according to any one of <1> to <4>, wherein the near-infrared absorbing dye is represented by the following general formula (I) or the following general formula (II).

In General Formula (I), A ¹ and A ² each independently represent a functional group represented by any one of the following General Formulas (1) to (5), and n ¹ and n ² are 0 or more. Represents an integer. Ar ¹ and Ar ² each independently represents an aryl group, and B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ are each independently a hydrogen atom, a halogen atom, an alkyl group, Represents an aryl group, an alkenyl group or an alkynyl group, and any two may form a ring. D ¹ and D ² each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, X ⁻ represents a counter anion, and Y ¹ , Y ² , Z ¹ and Z ² are each independently non- Represents a divalent linking group comprising a metal atom.

In the general formulas (1) to (5), L represents a polyvalent linking group composed of a nonmetallic atom, R ¹ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group or a cyclic imide group, R ² , R ³ represents an alkyl group, an aryl group, an alkenyl group, or an alkynyl group, R ⁴ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group, or —SO ₂ —R ¹¹ , and R ⁵ , R ^6, and R ⁷ are Each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, one of R ⁸ and R ⁹ represents a hydrogen atom, the other represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group or an alkynyl group; ¹⁰ represents an alkyl group, an alkenyl group or an alkynyl ^{group, R 11} is an alkyl group, an aryl group, an alkenyl group or an alkynyl ^group, of R 5, ^{R 6} and ^{R 7} Any may be formed of two or three in the ring, it may form a ring with ^{R 8} and ^{R 10} or ^{R 9} and ^{R 10.} X represents O or S.

In the general formula _{(II), R 1, R} 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10, R 11, R 12, R 13, R 14, R ₁₅ and R ₁₆ each independently represent a hydrogen atom or a substituent, and at least one of R _{1 to} R ₁₆ represents an R ₁₇ -X- group, or is adjacent in R _{1 to} R _16. It contains at least one structure in which two are condensed. X is, -S -, - NH -, - NR 18 -, or -O- and _{represents, R 17} and _{R 18} each independently represent an aliphatic group or an aryl group. M represents a divalent substituted metal atom including two atoms selected from the group consisting of a hydrogen atom and a monovalent metal atom, a divalent metal atom, or a trivalent or tetravalent metal atom.

<6> The ink composition according to any one of <1> to <5>, which is an inkjet ink.

<7> The ink composition according to <6>, which is a yellow ink.

<8> An image forming step of forming an image by applying the ink composition according to any one of <1> to <7> to a recording medium; an infrared irradiation step of irradiating the formed image with infrared rays; Is an image forming method.

<9> The image forming method according to <8>, wherein the recording medium includes paper.

<10> The image forming method according to <8> or <9>, further comprising a treatment liquid application step of applying a treatment liquid containing an aggregation component that forms an aggregate when contacted with the ink composition to the recording medium. is there.

  According to the present invention, it is possible to provide an ink composition and an image forming method which can suppress cuckling and have excellent color reproducibility.

It is a schematic sectional drawing which shows an example of the internal structure of an inkjet head. It is the schematic which shows an example of the discharge hole arrangement | sequence of a nozzle plate. It is a schematic diagram which shows the pattern which irradiates infrared rays to the image formed in the Example and the comparative example. It is a schematic diagram of the printing paper used for paper curl evaluation. FIG. 6 is a diagram schematically showing the state of recording sheet cuckling when the vertical axis represents the position z in the height direction of the recording paper ridge and the horizontal axis represents the horizontal position x of the recording paper.

<Ink composition>
The ink composition of the present invention contains water, an organic pigment, a polymer dispersant that disperses the near-infrared absorbing dye, and a water-insoluble near-infrared absorbing dye having an absorption maximum wavelength of 700 nm to 1500 nm.
When the ink composition has the above-described configuration, it is possible to form an image with excellent color reproducibility while suppressing cuckling when an image is formed.
The reason for this is not clear, but is presumed to be due to the following reason.

When the entire recording medium is heated to dry the image formed on the recording medium, the recording medium swells when the recording medium absorbs the water in the ink composition in the image portion to which the ink composition has been applied. However, the hydrogen bonds are broken and the arrangement of the paper fibers is disturbed. Further, by drying the image portion, the hydrogen bonds are recombined in a state where the arrangement of the fibers remains disordered.
On the other hand, when the entire recording medium is heated, the non-image area to which the ink composition is not applied contracts.

Therefore, the shrinkage difference between the fibers in the image portion and the non-image portion is increased, and the problem that the recording medium curls or generates cuffing easily occurs.
In order to suppress such a problem, it is conceivable to selectively heat only the image portion without heating the non-image portion. That is, by adding a near-infrared absorbing dye that generates heat by infrared irradiation to the ink composition, only the image area can be selectively heated when the recording medium on which the image is formed is irradiated with infrared rays.
As a result, there is almost no shrinkage of the non-image part, so the difference in shrinkage between the fibers of the image part and the non-image part is reduced, and the occurrence of cockle can be suppressed.

  However, if the near-infrared absorbing dye is not sufficiently dispersed in the ink composition, when the ink composition is irradiated with infrared rays, the ink composition cannot be heated quickly, and the ink composition tends to dry. Was found to occur. In a system in which the near-infrared absorbing dye is not sufficiently dispersed, the dispersion of the organic pigment tends to be insufficient, so that it is difficult to maintain the hue of the ink composition. For this reason, the hue of the image portion may change each time image formation is repeated.

  Further, even when an ink composition is formed after dissolving a water-insoluble near-infrared absorbing dye in an organic solvent, the dispersion stability of the near-infrared absorbing dye is insufficient. Furthermore, when the near-infrared absorbing dye is dissolved in the ink composition, the near-infrared absorbing dye is likely to penetrate into the recording medium, so that the near-infrared absorbing dye hardly remains on the image. Therefore, the heat drying of the image area is not sufficiently promoted and it is difficult to suppress cockle.

  On the other hand, the water-insoluble near-infrared absorbing dye has sufficient dispersibility in the ink composition due to the polymer dispersant, and the organic pigment is made of the ink composition having the above-described configuration. Excellent dispersibility. Therefore, when an image is formed with the ink composition of the present invention, the near-infrared absorbing pigment dispersed in the ink composition without heat is generated by the irradiation of infrared rays, and the ink composition is uniformly and rapidly dried. Conceivable. Further, since the dispersibility of the organic pigment is good, an image obtained by image formation is considered to have excellent hue reproducibility.

Hereinafter, the ink composition and the image forming method of the present invention will be described in detail.
The “ink composition” may be simply referred to as “ink”. In addition, aggregation of components in the ink (composition) may be referred to as “ink (composition) aggregation”.

[Water-insoluble near-infrared absorbing dye having an absorption maximum wavelength of 700 nm to 1500 nm]
The ink composition of the present invention contains at least one water-insoluble near-infrared absorbing dye (hereinafter also referred to as “specific IR dye”) having an absorption maximum wavelength of 700 nm to 1500 nm. Further, the absorption maximum wavelength may be referred to as λmax.
The near-infrared absorbing dye has a function of converting absorbed infrared rays into heat. Therefore, when the specific IR dye is included in the ink composition, an image portion is formed on a recording medium such as paper using the ink composition, and only the image portion containing the specific IR dye is heated when irradiated with infrared rays. can do. Therefore, the image portion can be efficiently dried and the image portion is selectively heated, so that the cockle can be suppressed.

The specific IR dye is not particularly limited as long as it has a λmax of 700 nm to 1500 nm and is insoluble in water, and various near infrared absorbing dyes can be used.
Here, λmax of the specific IR dye is a value when a dye solution obtained by dissolving or dispersing the specific IR dye with dimethyl sulfoxide is measured at 25 ° C. using V-570 manufactured by JASCO Corporation. . In addition, about the pigment | dye which has two or more (lambda) max, if at least 1 (lambda) max exists in 700 nm-1500 nm and it is water-insoluble, it will be contained in specific IR pigment | dye.
In addition, the fact that the pigment is insoluble in water specifically means that the amount dissolved in 100 g of water at 25 ° C. is 5 g or less.
The specific IR dye preferably has a λmax of 700 nm to 1200 nm from the viewpoint of the spectrum of the infrared heater used for drying.

  Specific IR dyes exhibiting the above physical properties include azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium And dyes such as salts and metal thiolate complexes.

  Preferred dyes include, for example, cyanine dyes described in JP-A-58-125246, JP-A-59-84356, JP-A-59-202829, JP-A-60-78787, and the like. Methine dyes described in JP-A-58-173696, JP-A-58-181690, JP-A-58-194595, JP-A-58-112793, JP-A-58-224793, JP-A-59- 48187, JP-A-59-73996, JP-A-60-52940, JP-A-60-63744, etc., naphthoquinone dyes, JP-A-58-112792, etc. And cyanine dyes described in British Patent 434,875.

Of these, cyanine dyes, squarylium dyes, pyrylium salts, nickel thiolate complexes, and phthalocyanine dyes are preferable. Furthermore, cyanine dyes and phthalocyanine dyes are preferred.
As the cyanine dye, a compound represented by the following general formula (I) is preferable, and as the phthalocyanine dye, a compound represented by the following general formula (II) is preferable.
The compound represented by the general formula (I) may be referred to as “specific IR dye (I)”, and the compound represented by the general formula (II) may be referred to as “specific IR dye (II)”.

[Compound represented by formula (I)]
The compound [specific IR (I)] represented by the general formula (I), which is one of preferred embodiments of the specific IR dye, is represented by the following structural formula.

In General Formula (I), A ¹ and A ² each independently represent a functional group represented by any one of the following General Formulas (1) to (5), and n ¹ and n ² are 0 or more. Represents an integer. Ar ¹ and Ar ² each independently represents an aryl group, and B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ are each independently a hydrogen atom, a halogen atom, an alkyl group, Represents an aryl group, an alkenyl group or an alkynyl group, and any two may form a ring. D ¹ and D ² each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, X ⁻ represents a counter anion, and Y ¹ , Y ² , Z ¹ and Z ² are each independently non- Represents a divalent linking group comprising a metal atom.

In the general formulas (1) to (5), L represents a polyvalent linking group composed of a nonmetallic atom, R ¹ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group or a cyclic imide group, R ² , R ³ represents an alkyl group, an aryl group, an alkenyl group, or an alkynyl group, R ⁴ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group, or —SO ₂ —R ¹¹ , and R ⁵ , R ^6, and R ⁷ are Each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, one of R ⁸ and R ⁹ represents a hydrogen atom, the other represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group or an alkynyl group; ¹⁰ represents an alkyl group, an alkenyl group or an alkynyl ^{group, R 11} is an alkyl group, an aryl group, an alkenyl group or an alkynyl ^group, of R 5, ^{R 6} and ^{R 7} Any may be formed of two or three in the ring, it may form a ring with ^{R 8} and ^{R 10} or ^{R 9} and ^{R 10.} X represents O or S.

When R ^{1 to} R ¹¹ represent an alkyl group, examples of the alkyl group include linear, branched and cyclic alkyl groups having 1 to 20 carbon atoms. Specific examples thereof include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, hexadecyl group, octadecyl group. , Eicosyl group, isopropyl group, isobutyl group, s-butyl group, t-butyl group, isopentyl group, neopentyl group, 1-methylbutyl group, isohexyl group, 2-ethylhexyl group, 2-methylhexyl group, cyclohexyl group, cyclopentyl group , 2-norbornyl group and the like. The alkyl group may further have a substituent.
Among these, linear alkyl groups having 1 to 12 carbon atoms, branched alkyl groups having 3 to 12 carbon atoms, and cyclic alkyl groups having 5 to 10 carbon atoms are more preferable.

When R ^{1 to} R ¹¹ represent an aryl group, examples of the aryl group include those in which 1 to 3 benzene rings form a condensed ring, and those in which a benzene ring and a 5-membered unsaturated ring form a condensed ring. Specific examples include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, an indenyl group, an acenaphthenyl group, a fluorenyl group, and the like. The aryl group may further have a substituent.
In these, a phenyl group and a naphthyl group are more preferable. The aryl group includes a heterocyclic (hetero) aryl group in addition to the carbocyclic aryl group. Examples of the heterocyclic aryl group include those having 3 to 20 carbon atoms and 1 to 5 hetero atoms such as a pyridyl group, a furyl group, and other quinolyl groups condensed with a benzene ring, a benzofuryl group, a thioxanthone group, and a carbazole group. Used.

When R ^{1 to} R ¹¹ represent an alkenyl group, examples of the alkenyl group include an alkenyl group having 2 to 30 carbon atoms, specifically, a vinyl group, an allyl group, a prenyl group, a geranyl group, an oleyl group, and the like. Can be mentioned. The alkenyl group may further have a substituent. The alkenyl group preferably has 2 to 8 carbon atoms.

When R ^{1 to} R ¹¹ represent an alkynyl group, examples of the alkynyl group include alkynyl groups having 2 to 20 carbon atoms. The alkynyl group may further have a substituent. Among these, a C2-C10 alkynyl group is preferable and a C2-C8 alkynyl group is more preferable. Specific examples thereof include an ethynyl group, a phenylethynyl group, and a trimethylsilylethynyl group.

  Examples of the substituent include substituents shown in paragraphs [0025] to [0029] of Patent 3627903, and among them, a halogen atom (—F, —Br, —Cl, —I), an alkoxy group, an aryloxy group, Alkylthio group, arylthio group, N-alkylamino group, N, N-dialkylamino group, acyloxy group, N-alkylcarbamoyloxy group, N-arylcarbamoyloxy group, acylamino group, formyl group, acyl group, carboxyl group, alkoxy Carbonyl group, aryloxycarbonyl group, carbamoyl group, N-alkylcarbamoyl group, N, N-dialkylcarbamoyl group, N-arylcarbamoyl group, N-alkyl-N-arylcarbamoyl group, sulfo group, sulfonate group, sulfamoyl group, N-alkylsulfamoyl N, N-dialkylsulfamoyl group, N-arylsulfamoyl group, N-alkyl-N-arylsulfamoyl group, phosphono group, phosphonate group, dialkylphosphono group, diarylphosphono group, monoalkylphosphono group A phono group, an alkyl phosphonate group, a monoaryl phosphono group, an aryl phosphonate group, a phosphonooxy group, a phosphonate oxy group, an aryl group and an alkenyl group are preferred.

  In the general formulas (1) to (5), the polyvalent linking group consisting of a nonmetallic atom represented by L includes 1 to 60 carbon atoms, 0 to 10 nitrogen atoms, and 0 Linking groups consisting of from 1 to 50 oxygen atoms, 1 to 100 hydrogen atoms, and 0 to 20 sulfur atoms.

  More specifically, the functional groups represented by the general formulas (1) to (5) include the following functional groups. However, these do not limit the contents of the present invention.

Among the functional groups, R ²¹ , R ²² , and R ²³ represent a hydrogen atom, an alkyl group, an aryl group, an alkenyl group, or an alkynyl group, and any two groups may form a ring. E ⁻ represents a counter anion.

The alkyl group, aryl group, alkenyl group, and alkynyl group represented by R ²¹ , R ²² , and R ²³ have the same meaning as the alkyl group, aryl group, alkenyl group, and alkynyl group represented by R ^{1 to} R ^11. It is.
More specifically, examples of the substituent include alkyl groups, aryl groups, alkenyl groups, and alkynyl groups shown in paragraph numbers [0024] to [0037] of Japanese Patent No. 3627903. Among them, preferred as R ²¹ and R ²³ are an alkyl group, a substituted alkyl group, an aryl group, and a substituted aryl group, and preferred as R ²² are a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, A substituted aryl group;

The counter anion represented by E ⁻ is an anion having a negative charge and forms an ion pair with the positive charge in the ammonium group (—N ⁺ R ⁴¹ R ⁴² R ⁴³ ) which is a hydrophilic functional group. Therefore, the counter anion represented by E ⁻ is present in the number of moles equal to the positive charge present in the ammonium group.
Specific counter anions _{^{F-, Cl-, Br-, I-,}} HO-, CN -, SO 4 2-, HSO 4 -, SO 3 2-, HSO 3 -, NO 3 -, CO 3 2 _{^{-, HCO 3 -, PF 6}} -, BF 4 -, ClO 4 -, ClO 3 -, ClO 2 -, ClO -, BrO 4 -, BrO 3 -, BrO 2 -, BrO -, IO 4 -, IO 3 _{^{-, IO 2 -, IO -}} , a sulfonate anion, carboxylate anion, phosphonate anion, and phosphate anions.
Further, anions specifically shown in paragraphs [0039] to [0048] of Patent 3627903 are also preferable.
Among these, Cl ⁻ , Br ⁻ , I ⁻ , CN ⁻ , SO ₄ ²⁻ , PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , sulfonate anion, carboxylate anion, phosphonate anion, phosphate anion, and The sulfonate group represented by the general formula (III) is preferable.

In the general formula (III), L ¹ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group, or a cyclic imide group.

When L ¹ represents an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkenyl group, a substituted alkenyl group, an alkynyl group, or a substituted alkynyl group, specific examples of these functional groups include the functional groups as described above. It is done.
When L ¹ represents a cyclic imide group, as the cyclic imide, those having 4 to 20 carbon atoms such as succinic imide, phthalic imide, cyclohexane dicarboxylic imide, norbornene dicarboxylic imide can be used.
Of these, preferred as L ¹ are an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, and a cyclic imide group.
Specific examples of the thermally decomposable sulfonic acid ester group are shown below, but the present invention is not limited thereto.

In the general formula (I), ^{n 1} and ^{n 2} each independently represents an integer of 0 or more. n ¹ and n ² may be the same or different. Both n ¹ and n ² are preferably 0.
Subsequently, Ar ¹ , Ar ² , B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , C ³ , D ¹ , D ² , X ⁻ , Y ¹ , Y ² , in the general formula (I) Z ¹ and Z ² will be described.

Examples of the aryl group represented by Ar ¹ and Ar ² in the general formula (I) include the aryl groups mentioned in the description of R ^{1 to} R ¹¹ . The aryl group may further have a substituent. Among these, a phenyl group, a substituted phenyl group, a naphthyl group, a substituted naphthyl group, an anthracenyl group, and a substituted anthracenyl group are particularly preferable.

In the general formula (I), when B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ represent a halogen atom, F, Cl, Br, and I may be used as the halogen atom. it can.
In the general formula (I), the alkyl group, aryl group, alkynyl group, and alkenyl group represented by B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ include R ^{1 to} R ^The alkyl group, aryl group, alkynyl group, and alkenyl group mentioned in the description of ¹¹ can be used. The alkyl group, aryl group, alkynyl group, and alkenyl group represented by B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ may further have a substituent.

Among the above, preferable as B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ are a hydrogen atom, a halogen atom, an alkyl group, a substituted alkyl group, an aryl group, and a substituted aryl group. In particular, it is particularly preferred that any two groups form a ring.
Examples of the alkyl group, aryl group, alkenyl group, and alkynyl group represented by D ¹ and D ² in the general formula (I) include the alkyl group, aryl group, alkenyl group, and alkynyl mentioned in the description of R ^{1 to} R ^11. Groups can be used. The alkyl group, aryl group, alkenyl group, and alkynyl group represented by D ¹ and D ² may further have a substituent. Of these, an alkyl group and a substituted alkyl group are particularly preferable.

The counter anion represented by X ⁻ in the general formula (I) is an anion having a negative charge, and forms an ion pair with the positive charge in the compound. Therefore, the counter anion represented by X ⁻ is present in the number of moles equal to the positive charge present in the compound.
More specific counter anions include the anions described as counter anions represented by E ⁻ . Among these anions, the anions preferably used in the present invention are Cl ⁻ , Br ⁻ , I ⁻ , CN ⁻ , SO ₄ ²⁻ , PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , sulfonate anion, A carboxylate anion, a phosphonate anion, and a phosphate anion.

In the general formula (I), the divalent linking group consisting of non-metal atoms represented by Y ¹ and Y ² is 1 to 60 carbon atoms, 0 to 10 nitrogen atoms, 0 to It consists of up to 50 oxygen atoms, 1 to 100 hydrogen atoms, and 0 to 20 sulfur atoms. More specific examples of the linking group include those formed by combining the following structural units.

When the divalent linking group has a substituent, examples of the substituent include an alkyl group having 1 to 20 carbon atoms such as a methyl group and an ethyl group, an aryl group having 6 to 16 carbon atoms such as a phenyl group and a naphthyl group, A hydroxyl group, a carboxyl group, a sulfonamide group, an N-sulfonylamide group, an acyloxy group having 1 to 6 carbon atoms such as an acetoxy group, an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group, chlorine, Use a halogen atom such as bromine, an alkoxycarbonyl group having 2 to 7 carbon atoms such as a methoxycarbonyl group, an ethoxycarbonyl group or a cyclohexyloxycarbonyl group, a cyano group, or a carbonate group such as t-butyl carbonate. Can do.
The divalent linking group consisting of a non-metal atom represented by Z ¹ or Z ² is 0 to 60 carbon atoms, 0 to 10 nitrogen atoms, 0 to 50 oxygen atoms. , Consisting of 0 to 100 hydrogen atoms and 0 to 20 sulfur atoms. More specific examples of the linking group include those formed by combining the following structural units.

When the divalent linking group has a substituent, examples of the substituent include an alkyl group having 1 to 20 carbon atoms such as a methyl group and an ethyl group, an aryl group having 6 to 16 carbon atoms such as a phenyl group and a naphthyl group, A hydroxyl group, a carboxyl group, a sulfonamide group, an N-sulfonylamide group, an acyloxy group having 1 to 6 carbon atoms such as an acetoxy group, an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group, chlorine, Use a halogen atom such as bromine, an alkoxycarbonyl group having 2 to 7 carbon atoms such as a methoxycarbonyl group, an ethoxycarbonyl group or a cyclohexyloxycarbonyl group, a cyano group, or a carbonate group such as t-butyl carbonate. Can do.
Specific examples [IR (I) -1 to IR (I) -12] of the specific IR dye (I) represented by the general formula (I) are shown below, but the present invention is limited to these. is not.

Among the above specific examples, as the specific IR (I), from the viewpoint that heat is generated by infrared irradiation of the ink composition and that it quickly decomposes and does not affect the color of the image.
IR (I) -1, IR (I) -2, IR (I) -4, IR (I) -5, and IR (I) -7 are preferred, IR (I) -1, IR (I)- 5 and IR (I) -7 are more preferred.

[Compound represented by formula (II)]
The compound [specific IR (II)] represented by the general formula (II), which is one of the preferred embodiments of the specific IR dye, is represented by the following structural formula.

In the general formula _{(II), R 1, R} 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10, R 11, R 12, R 13, R 14, R ₁₅ and R ₁₆ each independently represent a hydrogen atom or a substituent, and at least one of R _{1 to} R ₁₆ represents an R ₁₇ -X- group, or is adjacent in R _{1 to} R _16. It contains at least one structure in which two are condensed. X is, -S -, - NH -, - NR 18 -, or -O- and _{represents, R 17} and _{R 18} each independently represent an aliphatic group or an aryl group. M represents a divalent substituted metal atom including two atoms selected from the group consisting of a hydrogen atom and a monovalent metal atom, a divalent metal atom, or a trivalent or tetravalent metal atom.

Examples of the substituent represented by R _{1 to} R ₁₆ in the general formula (II) include the substituents described in the general formulas (1) to (5). Moreover, the substituent shown by paragraph number [0025] of Unexamined-Japanese-Patent No. 2011-241349 is also preferable.
Among them, the substituent represented by R _{1 to} R ₁₆ in the general formula (II) includes an aliphatic group, an aryl group, an aliphatic oxy group, an aryloxy group, an aliphatic thio group, an arylthio group, and an aliphatic amino group. , An arylamino group and a halogen atom are preferable.
Here, the term “aliphatic” means that the aliphatic moiety is linear, branched, or cyclic and may be either saturated or unsaturated. For example, an alkyl group, an alkenyl group, a cycloalkyl group, a cyclo Contains an alkenyl group. The aliphatic group may be unsubstituted or substituted with a substituent. As an aliphatic group, a C1-C15 aliphatic group is preferable. “Aryl” may be either a single ring or a condensed ring, and may be unsubstituted or substituted with a substituent.

In the general formula (II), the aliphatic group represented by R _{1 to} R ₁₆ may be unsubstituted or substituted, may be saturated or unsaturated, and may be cyclic. An aliphatic group having 1 to 15 carbon atoms is preferable, and an aliphatic group having 1 to 10 carbon atoms is more preferable. Examples of the aliphatic group include alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a nonyl group, a dodecyl group, an octadecyl group, and a 2-ethylhexyl group, a vinyl group, an allyl group, an ethynyl group, and an isopropenyl group. And alkenyl groups and the like.

In the general formula (II), the aryl group represented by R _{1 to} R ₁₆ may be unsubstituted or may have a substituent, and is preferably an aryl group having 6 to 16 carbon atoms in total, and 6 to 12 carbon atoms in total. The aryl group is more preferable. For example, phenyl group, 4-nitrophenyl group, 2-nitrophenyl group, 2-chlorophenyl group, 2,4-dichlorophenyl group, 2,4-dimethylphenyl group, 2-methylphenyl group, 4-methoxyphenyl group, 2 -Methoxyphenyl group, 2-methoxycarbonyl-4-nitrophenyl group and the like.

The aliphatic oxy group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, may be saturated or unsaturated, and is cyclic. May be. As the aliphatic oxy group, an aliphatic oxy group having 1 to 12 carbon atoms is preferable, and an aliphatic oxy group having 1 to 10 carbon atoms is more preferable. For example, a methoxy group, an ethoxy group, a propoxy group, an ethoxyethoxy group, a phenoxyethoxy group, a thiophenoxyethoxy group, and the like can be given.

The aryloxy group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, and an aryloxy group having 6 to ₁₆ total carbon atoms in the aryl moiety is preferable. An aryloxy group having 6 to 12 total carbon atoms in the aryl moiety is preferred. The aryl moiety is, for example, phenyl, 4-nitrophenyl, 2-nitrophenyl, 2-chlorophenyl, 2,4-dichlorophenyl, 2,4-dimethylphenyl, 2-methylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, Examples include 2-methoxycarbonyl-4-nitrophenyl.

The aliphatic thio group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, may be saturated or unsaturated, and is cyclic. May be. As the aliphatic thio group, an aliphatic thio group having 1 to 16 carbon atoms is preferable, and an aliphatic thio group having 1 to 10 carbon atoms is more preferable. Examples thereof include a methylthio group, an ethylthio group, and an ethoxyethylthio group.

The arylthio group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, and is preferably an arylthio group having 6 to 22 carbon atoms, and 6 to 14 carbon atoms in total. Of the arylthio group is preferred. For example, a phenylthio group etc. are mentioned.

The aliphatic amino group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, may be saturated or unsaturated, and is cyclic. May be. As the aliphatic amino group, an aliphatic amino group having 1 to 16 carbon atoms is preferable, and an aliphatic amino group having 1 to 10 carbon atoms is more preferable. For example, a methylamino group, an ethylamino group, etc. are mentioned.

The arylamino group represented by R _{1 to} R ₁₆ in the general formula (II) may be unsubstituted or substituted, and is preferably an arylamino group having 6 to 22 carbon atoms, and 6 carbon atoms in total. An arylamino group of ˜14 is more preferred. For example, an anilino group etc. are mentioned.

Examples of the halogen atom represented by R _{1 to} R ₁₆ in the general formula (II) include a chlorine atom, a bromine atom, and an iodine atom, and a chlorine atom is preferable.

In addition, at least one of R _{1 to} R _{16 in} the general formula (II) represents an R ₁₇ —X— group, or two adjacent ones in R _{1 to} R ₁₆ (eg, R ₂ and R ₃ , R ₆ and R _7, etc.). At this time, X is, -S -, - NH -, - NR 18 -, or an -O-. R ₁₇ and R ₁₈ each independently represents an aliphatic group or an aryl group.

The aliphatic group represented by R ₁₇ and R ₁₈ has the same meaning as the aliphatic group represented by R _{1 to} R ₁₆ , and the preferred embodiments are also the same. _Further, the aryl group represented by _{R 17,} and _{R 18} in the general formula (II) has the same meaning as the aryl group represented by _R 1 _{to R 16,} preferable embodiments thereof are also the same.

Of the R ₁₇ —X— groups, the R ₁₇ —S— group and the R ₁₇ —O— group are preferred, and the R ₁₇ —S— group is more preferred, because they exhibit better light resistance. Among them, the R ₁₇ —X— group when R ₁₇ is an aryl group is particularly preferable.

Moreover, among the substituents represented by R _{1 to} R ₁₆ , when two adjacent substituents form a condensed ring structure, among R _{1 to} R ₁₆ , R ₂ and R ₃ , R ₆ And R ₇ , R ₁₀ and R ₁₁ , R ₁₄ and R ₁₅ are bonded to each other to form a ring. As the ring structure, a naphthalene ring aromatic 6-membered ring to a benzene ring are condensed to R ₁ etc. is attached (naphthalocyanine structure), aliphatic 6-membered ring to a benzene ring to which R ₁ and the like are attached are condensed A ring structure represented by the following structural formula (A) is preferred.

In the structural formula (A), X and Y each have the same meaning as X in R _{1 to} R ₁₆ , and are preferably —S— or —O—. R _a and R _b represent a hydrogen atom or a substituent. The substituent here is synonymous with the substituent represented by R _{1 to} R ₁₆ in the general formula (II), and the preferred embodiment is also the same. R _a and R _b are bonded to each other to further form a ring structure. (Example: benzene ring) may be formed.

  M in the general formula (II) is a divalent atom containing two atoms, a divalent metal atom, or a trivalent or tetravalent metal atom selected from the group consisting of a hydrogen atom and a monovalent metal atom. Represents a substituted metal atom. Preferable M includes two hydrogen atoms, a divalent metal atom, a divalent metal oxide, a divalent metal hydroxide, or a divalent metal chloride.

Specific examples of M include VO, TiO, Zn, Mg, Si, Sn, Rh, Pt, Pd, Mo, Mn, Pb, Cu, Ni, Mg, Sn, Pd, Co, Fe, AlCl, InCl, and FeCl. , TiCl ₂ , SnCl ₂ , SiCl ₂ , GeCl ₂ , Si (OH) ₂ , H _{2 and the} like.
Among these, M is preferably VO, Zn, Cu, Mn, Ni, Mg, Sn, Pd, Co, or H ₂ , more preferably Cu, VO, or Zn, and particularly preferably Cu.

The phthalocyanine skeleton has a structure in which four benzene rings are condensed outside the tetraazaporphyrin skeleton, and each benzene ring has a portion (carbon atom) into which four substituents can enter. From the viewpoint of showing light resistance, in the near-infrared absorbing dye represented by the general formula (II) [specific IR dye (II)], hydrogen atoms are located at two β positions far from the tetraazaporphyrin skeleton of each benzene ring. Bound compounds are preferred. Furthermore, R ₁₇ -X-groups (R ₁₇ = aryl group) were bonded to two α positions near the tetraazaporphyrin skeleton of each benzene ring, and hydrogen atoms were bonded to two β positions far from the skeleton. Compounds are preferred. At this time, for the same reason, M is preferably Cu.

  Among the specific IR dyes (II), a compound represented by the following general formula (II-2) is preferable in that it exhibits better light resistance.

  In General Formula (II-2), M includes 2 atoms selected from the group consisting of a hydrogen atom and a monovalent metal atom, a divalent metal atom, or a trivalent or tetravalent metal atom. Represents a valent substituted metal atom.

In the general formula (II-2), M includes two hydrogen atoms, a divalent metal atom, a divalent metal oxide, a divalent metal hydroxide, or a divalent metal chloride. Specific examples similar to M in formula (II) can be given. Among them, M is, VO, Zn, Cu, Mn , Ni, Mg, Sn, Pd, Co, H 2 is preferable, Cu, VO, Zn is more preferably used, more preferably Cu.

In General Formula (II-2), Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ , Ar ₅ , Ar ₆ , Ar ₇ , and Ar ₈ each independently represent a substituted or unsubstituted aryl group. Ar _{1 to} Ar ₈ may be the same or different from each other.

In the general formula (II-2), the aryl group represented by Ar _{1 to} Ar ₈ may be unsubstituted or may have a substituent, and is preferably an aryl group having 6 to 16 carbon atoms in total. 6-12 aryl groups are more preferred. Among these, an alkylphenyl group and / or an alkoxyphenyl group (preferably, the number of carbon atoms in the alkyl moiety is 1 to 10 is preferred). Examples of the aryl group include a phenyl group, 2,4-dimethylphenyl group, 2-methylphenyl group, 2-ethylphenyl group, 4-methoxyphenyl group, 2-methoxyphenyl group, 4-octyloxyphenyl group, 4 -T-butylphenyl group, etc. are mentioned.

  Specific examples [IR (II) -1 to IR (II) -75] of the compound [specific IR (II)] represented by the general formula (II) are shown below. However, the present invention is not limited to these compounds.

  Among the above specific examples, the specific IR (II) includes IR (II) -1, IR (II) -24, IR (II) -6, IR (II) -22, and IR from the viewpoint of dispersibility. (II) -23 is preferred, and IR (II) -1, IR (II) -24, and IR (II) -23 are more preferred.

  Any of the specific IR dyes described above can be synthesized with reference to conventionally known synthesis methods.

The content of the specific IR dye in the ink composition of the present invention is not particularly limited, but is preferably 0.05% by mass to 0.3% by mass with respect to the total mass of the ink composition. When the content of the specific IR dye is 0.05% by mass or more, the ink composition can be quickly dried, and when the content is 0.3% by mass, the ink composition is attributed to the specific IR dye. The coloring of can be suppressed.
The content of the specific IR dye in the ink composition is more preferably 0.06% by mass to 0.28% by mass with respect to the total mass of the ink composition, and 0.07% by mass to 0.25%. More preferably, it is mass%.

(Polymer dispersant)
The ink composition of the present invention contains at least one polymer dispersant that disperses near-infrared absorbing pigments.
When the ink composition contains a polymer dispersant, the specific IR dye and the organic pigment described above are sufficiently dispersed in the ink composition, and the ink composition can be quickly and uniformly dried. .
Here, in the polymer dispersant, the polymer specifically means that the weight average molecular weight (Mw) is 3,000 or more.

  As the polymer dispersant, a water-insoluble polymer dispersant (hereinafter sometimes simply referred to as “dispersant”) is preferable. The water-insoluble polymer is not particularly limited as long as the specific IR dye and the organic pigment can be dispersed, and a conventionally known water-insoluble polymer dispersant can be used. The water-insoluble polymer dispersant can be constituted by including, for example, both a hydrophobic structural unit and a hydrophilic structural unit.

Examples of the monomer constituting the hydrophobic structural unit include styrene monomers, alkyl (meth) acrylates, aromatic group-containing (meth) acrylates, and the like.
Moreover, as a monomer which comprises a hydrophilic structural unit, if it is a monomer containing a hydrophilic group, there will be no restriction | limiting in particular. Examples of hydrophilic groups include nonionic groups, carboxyl groups, sulfonic acid groups, and phosphoric acid groups.
From the viewpoint of dispersion stability, the hydrophilic structural unit preferably contains at least a carboxyl group, and preferably includes a nonionic group and a carboxyl group.

  Specific examples of the polymer dispersant include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth). Examples include acrylic acid copolymers, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymers, and styrene-maleic acid copolymers. Here, “(meth) acrylic acid” means acrylic acid or methacrylic acid.

  The polymer dispersant is preferably a vinyl polymer containing a carboxyl group from the viewpoint of dispersion stability of the specific IR dye, and has at least a structural unit derived from an aromatic group-containing monomer as a hydrophobic structural unit. A vinyl polymer having a structural unit containing a carboxyl group as a hydrophilic structural unit is more preferable.

  The weight average molecular weight of the polymer dispersant is preferably 3,000 to 200,000, more preferably 5,000 to 100,000, and still more preferably 5,000, from the viewpoint of the dispersion stability of the specific IR dye. -80,000, particularly preferably 10,000-60,000.

The content of the polymer dispersant in the ink composition of the present invention is based on the dispersibility of the specific IR dye and the organic pigment, and from the viewpoint of quick and uniform drying of the ink composition, with respect to the total mass of the specific IR dye, The polymer dispersant is preferably 10% by mass to 100% by mass, more preferably 15% by mass to 80% by mass, and particularly preferably 20% by mass to 60% by mass.
Moreover, it is preferable that a polymer dispersing agent is 5 mass%-200 mass% with respect to the total mass of an organic pigment, It is more preferable that it is 10 mass%-100 mass%, It is 20 mass%-80 mass%. It is particularly preferred.

[Organic pigments]
The ink composition of the present invention contains an organic pigment.
There is no restriction | limiting in particular as an organic pigment, According to the objective, it can select suitably.

Examples thereof include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, aniline black, and the like. Among these, azo pigments and polycyclic pigments are more preferable.
Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments.
Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone. And pigments.
Examples of dye chelates include basic dye chelates and acid dye chelates.

  Examples of the quinacridone compound constituting the quinacridone pigment include unsubstituted quinacridone, 2,9-dimethylquinacridone, 2,9-dichloroquinacridone, 2,9-dimethoxyquinacridone, 3,10-dimethylquinacridone, 3,10- Examples include dichloroquinacridone, 3,10-dimethoxyquinacridone, 4,11-dimethylquinacridone, 4,11-dichloroquinacridone, 4,11-dimethoxyquinacridone, and quinacridonequinone.

  Examples of quinacridone pigments include C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, and C.I. I. And CI Pigment Violet 19.

  The ink composition may contain only one type of organic pigment or may contain two or more types.

(Inorganic pigment)
The ink composition of the present invention may further contain an inorganic pigment.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, a thermal method, is mentioned, for example.

  Further, for example, pigments described in paragraphs 0142 to 0145 of JP2007-100071A may be used.

-Pigment coated with water-insoluble resin (resin-coated pigment)-
The organic pigment (in the case where the ink composition contains an inorganic pigment, the organic pigment and the inorganic pigment) is preferably a resin-coated pigment in which the entire surface or a part thereof is coated with a water-insoluble resin. Thereby, the dispersion stability and ejection reliability of the ink composition are excellent, and the abrasion resistance and light resistance of the formed image are improved.

[Water-insoluble resin]
The water-insoluble resin preferably includes at least one structural unit having an acidic group, and preferably includes other structural units as necessary. The water-insoluble resin can be stably present in the ink composition, eases the adhesion or deposition of aggregates, and facilitates the removal of the adhered aggregates. It is preferable that at least one kind and at least one kind of hydrophobic structural unit (B) are included, and it is more preferable that an acidic group is contained in at least one kind of hydrophilic structural unit (A).
The water-insoluble resin means a resin having a dissolution amount of 5 g or less with respect to 100 g of water at 25 ° C. The “dissolution amount” is the dissolution amount when the acidic group of the water-insoluble resin is neutralized 100% with sodium hydroxide.

  The hydrophilic structural unit in the water-insoluble resin is not particularly limited as long as it contains at least one hydrophilic functional group, and includes an ionic hydrophilic group and a nonionic hydrophilic group. May be. In the present invention, a hydrophilic structural unit having an acidic group is preferable. In addition, even if the hydrophilic structural unit having an acidic group is a structural unit derived from an acidic group-containing monomer, the acidic group is introduced into the structural unit having no acidic group (polymer chain after polymerization) by a polymer reaction. It may be what you did.

  The acidic group is not particularly limited, and examples thereof include a carboxyl group, a phosphoric acid group, and a sulfonic acid group from the viewpoint of stability in an emulsified or dispersed state. Among them, from the viewpoint of dispersion stability when an ink composition is configured. A carboxyl group is preferred.

  The water-insoluble resin includes a structural unit having an acidic group, but preferably further includes at least one hydrophobic structural unit (B). The hydrophobic structural unit is not particularly limited as long as it is a structural unit containing a hydrophobic functional group, but preferably contains at least one kind of structural unit having an aromatic ring.

  In the ink composition of the present invention, the specific IR dye is sufficiently dispersed using a polymer dispersing agent that disperses the near-infrared absorbing dye, and the ink composition is efficiently and quickly dried. It is considered that the image remains on the recording medium before being absorbed into the image and the image is easily fixed to the recording medium. Accordingly, when the image portion is irradiated with an infrared heater, the image portion can be efficiently heated and dried.

Near-infrared-absorbing dyes often have some absorption in the visible region, so if the near-infrared-absorbing dye remains in the ink composition even after infrared irradiation, the color and organic color derived from the near-infrared absorbing dye It may overlap with the color of the pigment and affect the color reproducibility of the image. In particular, when the ink composition is yellow ink or the like, it is easy to affect.
However, in the ink composition of the present invention, the near-infrared absorbing dye is unlikely to clump in the ink composition and is sufficiently dispersed by the polymer dispersant. Therefore, the near-infrared absorbing pigment is sufficiently decomposed by infrared irradiation of the ink composition, and the influence on the yellow ink can be sufficiently suppressed.

The content of the organic pigment in the ink composition of the present invention (the total content when two or more organic pigments are used) is preferably 1.0% by mass or more based on the total mass of the ink composition. Furthermore, the content of the organic pigment in the ink composition is more preferably 2.0% by mass or more, and particularly preferably 4.0% by mass or more with respect to the total mass of the ink composition.
When the content of the organic pigment is 1.0% by mass or more, the optical density of the image is further improved. The upper limit of the content of the organic pigment is not particularly limited, but is preferably 20.0% by mass, more preferably 15.0% by mass, further preferably 10.0% by mass, further preferably 9.0% by mass, 8.0 mass% is particularly preferable.

  When the pigment is a resin-coated pigment, the ratio (p: r) of the pigment (p) to the water-insoluble resin (r) is preferably 100: 25 to 100: 140, more preferably 100: 25. ~ 100: 50. The ratio (p: r) tends to improve the dispersion stability and abrasion resistance when the specific polymer is 100: 25 or more, and the dispersion stability when the specific polymer is 100: 140 or less. Tend to improve.

  The resin-coated pigment can be produced by a conventional physical or chemical method using a water-insoluble resin and a pigment. For example, as described in JP-A-9-151342, JP-A-10-140065, JP-A-11-209672, JP-A-11-172180, JP-A-10-25440, or JP-A-11-43636. It can be manufactured by a method. Specific examples include the phase inversion emulsification method and the acid precipitation method described in JP-A-9-151342 and JP-A-10-140065. Among them, the phase inversion emulsification method is preferable in terms of dispersion stability. preferable.

The phase inversion emulsification method is basically a self dispersion (phase inversion emulsification) method in which a mixed melt of a polymer having a self-dispersing ability or a dissolving ability and a pigment is dispersed in water. The mixed melt may contain a curing agent or a polymer compound. Here, the mixed molten material refers to a mixed state that is not dissolved, a state that is dissolved and mixed, or a state that includes both of these states.
Specific methods by the “phase inversion emulsification method” are disclosed in JP-A-10-140065, JP-A-2009-221251 (particularly paragraphs 0074 to 0082) and JP-A-2011-195684 (particularly paragraphs 0042-0052). Can be referred to.

  The content of the polymer-coated pigment in the ink composition (the total content in the case of two or more types) is 1.0% with respect to the total amount of the ink composition from the viewpoint of dispersion stability and concentration of the ink composition. -15.0 mass% is preferable and 2.0-10.0 mass% is more preferable.

  The ratio of the organic pigment to the near-infrared absorbing dye [specific IR dye] (organic pigment: near-infrared absorbing dye) is preferably 10: 1 to 100: 1 on a mass basis, and 15: 1 to 90: 1 is more preferable, and 20: 1 to 85: 1 is more preferable.

〔water〕
The ink composition of the present invention contains water.
As water, it is preferable to use water that does not contain ionic impurities such as ion-exchanged water and distilled water.
The content of water in the ink composition is appropriately selected according to the purpose, but from the viewpoint of ensuring stability and ejection reliability, it is preferably 10% by mass to 99% by mass with respect to the total amount of the ink composition. More preferably, they are 30 mass% or more and 80 mass% or less, More preferably, they are 50 mass% or more and 70 mass% or less.

(Polymer particles)
The ink composition of the present invention preferably contains at least one polymer particle from the viewpoints of fixability, abrasion resistance, and aggregation.
The polymer particles here are particulate polymers dispersed in the ink composition.
When the ink composition contains polymer particles, when the polymer particles come into contact with a treatment liquid described later or a region where the treatment liquid has been dried, the ink composition is dispersed and destabilized and aggregates to increase the viscosity of the ink composition. Thus, the image is fixed on the recording medium. Thereby, the fixing property, abrasion resistance and cohesion of the image are further improved.

Self-dispersing polymer particles are preferred as the polymer particles.
When the self-dispersing polymer particles are in a dispersed state (particularly, a dispersed state by a phase inversion emulsification method) in the absence of a surfactant, the polymer itself has functional groups (particularly acidic groups or salts thereof) in an aqueous medium. Means a water-insoluble polymer particle which can be dispersed in a water-insoluble polymer which does not contain a free emulsifier.
As the self-dispersing polymer particles, the self-dispersing polymer particles described in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-066805A can be used.
Self-dispersing polymer particles can be suitably prepared by a phase inversion emulsification method.

  The molecular weight of the polymer constituting the polymer particles (for example, self-dispersing polymer particles) is preferably 3000 to 200,000, more preferably 5000 to 150,000 in terms of weight average molecular weight, and 10,000 to 100,000. More preferably. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.

  The content of the polymer particles (for example, self-dispersing polymer particles) is preferably 0.1% by mass to 20% by mass and more preferably 0.1% by mass to 10% by mass with respect to the total mass of the ink composition. Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a polymer particle, What has a wide particle size distribution or a thing with a monodispersed particle size distribution may be sufficient. Two or more polymer particles having a monodispersed particle size distribution may be mixed and used.

From the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer, preferred embodiments of the polymer particles (for example, self-dispersing polymer particles) are alicyclic (meth) acrylate (preferably bicyclic or tricyclic) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. A structural unit derived from a polycyclic (meth) acrylate of the formula or more is 20% by mass to 90% by mass (preferably 40% by mass to 80% by mass) and a dissociable group (preferably an anionic dissociable group), More preferably, a structural unit derived from a monomer containing a carboxyl group, a phosphoric acid group, a sulfonic acid group, particularly preferably a carboxyl group) contains 25% by mass or less and a linear alkyl group having 1 to 8 carbon atoms (meth). An acid value of 20 mg KOH / g to 120 mg KOH / g (more preferably 25 mg KOH / g). A ~100mgKOH / g), weight average molecular weight of 3,000 to 200,000 (preferably embodiment a vinyl polymer is 10,000 to 200,000).
In this embodiment, the structural unit derived from a bicyclic or tricyclic or higher polycyclic (meth) acrylate is 40% by mass to 80% by mass, and at least methyl (meth) acrylate or ethyl (meth) acrylate. The structural unit derived from 20% by mass to 60% by mass and the structural unit derived from acrylic acid or methacrylic acid by 25% by mass or less, having an acid value of 30 mgKOH / g to 80 mgKOH / g, and having a weight average A vinyl polymer having a molecular weight of 30,000 to 150,000 is preferable.

  Another preferred embodiment of the polymer particles (for example, self-dispersing polymer particles) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer is a structure derived from an aromatic group-containing (meth) acrylate monomer from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. A unit (preferably a structural unit derived from phenoxyethyl (meth) acrylate and / or a structural unit derived from benzyl (meth) acrylate) as a copolymerization ratio is 15% by mass to 80% by mass of the total mass of the self-dispersing polymer particles. %. In this embodiment, the structural unit derived from the aromatic group-containing (meth) acrylate monomer is 15% by mass to 80% by mass as the copolymerization ratio, the structural unit derived from the carboxyl group-containing monomer, and the alkyl group-containing monomer. A structural unit derived from phenoxyethyl (meth) acrylate and / or a structure derived from benzyl (meth) acrylate, preferably a structural unit (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid). 15% by mass to 80% by mass as a copolymerization ratio, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably having 1 to 4 carbon atoms of (meth) acrylic acid A structural unit derived from an alkyl ester of The acid value is preferably 25 mgKOH / g to 100 mgKOH / g and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 mgKOH / g to 95 mgKOH / g and the weight average molecular weight is 5000 to 150,000. More preferably.

(Colloidal silica, alkali silicate)
The ink composition preferably contains at least one of colloidal silica and alkali silicate.
Thereby, deterioration of the nozzle ejection surface (for example, the surface of the liquid repellent film that may be provided on the ejection side of the nozzle) when the ink composition is repeatedly ejected can be more effectively suppressed. This effect is more remarkable when a nozzle (for example, a silicon nozzle plate) containing silicon is used as the nozzle (for example, a nozzle plate).
As an alkali metal silicate salt, the well-known alkali metal silicate salt described in Paragraph 0015-0019 of Unexamined-Japanese-Patent No. 2011-57754 can be used, for example.

-Colloidal silica-
Colloidal silica is a colloid composed of fine particles of inorganic oxide containing silicon having an average particle size of several hundred nm or less. Silicon dioxide (including hydrates thereof) may be included as a main component, and aluminate may be included as a minor component. Examples of the aluminate that may be contained as a minor component include sodium aluminate and potassium aluminate.
In addition, colloidal silica may contain inorganic salts such as sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonium hydroxide, and organic salts such as tetramethylammonium hydroxide. These inorganic salts and organic salts act, for example, as colloid stabilizers.
There is no restriction | limiting in particular as a dispersion medium of colloidal silica, Any of water, an organic solvent, and these mixtures may be sufficient. The organic solvent may be a water-soluble organic solvent or a water-insoluble organic solvent, but is preferably a water-soluble organic solvent. Specifically, methanol, ethanol, isopropyl alcohol, n-propanol etc. can be mentioned.
As the colloidal silica, for example, known colloidal silica described in paragraphs 0014 to 0022 of JP 2011-195684 A can be used.

Colloidal silica may be used alone or in combination of two or more.
When the ink composition contains colloidal silica, the content of colloidal silica (total content in the case of two or more types) is not particularly limited. For example, the content is 0.0001% by mass to the total amount of the ink composition. 10% by mass, preferably 0.01% by mass to 3.0% by mass, more preferably 0.02% by mass to 0.5% by mass, and particularly preferably 0.03% by mass. % To 0.2% by mass. When the content in the ink composition is equal to or lower than the upper limit value, the dischargeability of the ink composition is further improved, and the influence on the inkjet head due to the abrasive effect of the silica particles can be more effectively suppressed. Moreover, by being more than a lower limit, the liquid-repellent fall (for example, deterioration of a liquid-repellent film) of a nozzle discharge surface can be suppressed more effectively.

(urea)
The ink composition may contain urea.
Since urea has a high moisturizing function, it can more effectively suppress ink drying and coagulation as a solid wetting agent.
Furthermore, the ink composition of the present invention includes the above-described colloidal silica and urea, so that the maintainability (cleaning removal property or wiping property) of the ink jet head or the like is more effectively improved.

  The content of urea in the ink composition is preferably 1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less, from the viewpoint of improving maintainability (wiping properties). More preferred is 10% by mass or less.

  When the ink composition contains urea and colloidal silica, the ratio of the urea content to the colloidal silica content is not particularly limited, but the urea content ratio (urea / colloidal silica) is 5 with respect to the colloidal silica. It is preferable that it is -1000, and it is more preferable that it is 10-700.

The ink composition may contain a solid wetting agent other than urea.
As for a particularly preferable form when the solid wetting agent other than urea or the ink composition contains urea and colloidal silica, paragraphs 0026 to 0030 of JP2011-195684A can be referred to, for example.

(Surfactant)
The ink composition of the present invention contains at least a polymer dispersant that disperses the near-infrared absorbing dye, disperses the specific IR dye and the organic pigment, and may contain at least one surfactant as required. Good. The surfactant can be used as a surface tension adjusting agent, for example.
As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Either a surfactant or a betaine surfactant can be used.

The surfactant is preferably a nonionic surfactant from the viewpoint of suppressing ink droplet ejection interference, and more preferably an acetylene glycol derivative (acetylene glycol-based surfactant).
Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7. -Alkylene oxide adduct of diol etc. can be mentioned, It is preferable that it is at least 1 sort (s) chosen from this. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

  When the ink composition contains a surfactant, the specific amount of the surfactant is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.1% by weight based on the total amount of the ink composition. It is 10 mass% to 10 mass%, More preferably, it is 0.2 mass% to 3 mass%.

(Other additives)
The ink composition of the present invention may contain other additives as necessary in addition to the above components.
Other additives include, for example, antifading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, antiseptics, antifungal agents, pH adjusters, surface tension adjusters, antifoaming agents, viscosity adjusters, and dispersions. Well-known additives, such as a stabilizer, a rust preventive agent, a chelating agent, are mentioned. These various additives may be added directly after the ink-jet ink composition is prepared, or may be added when the ink-jet ink composition is prepared. Specific examples include other additives described in paragraphs 0153 to 0162 of JP-A-2007-100071.

Further, the ink composition may be configured as an active energy ray (for example, ultraviolet ray) curable ink composition by containing at least one polymerizable compound. In this case, it is preferable that the ink composition (at least one of the ink composition and the processing liquid when a processing liquid described later in image formation is used) contains a polymerization initiator.
Examples of the polymerizable compound include known water-soluble polymerizable compounds described in paragraphs 0128 to 0144 of 2011-184628 and paragraphs 0019 to 0034 of JP2011-178896A. A known (meth) acrylamide compound (preferably a bifunctional or higher functional (meth) acrylamide compound) may be mentioned.
Examples of the polymerization initiator include known polymerization initiators described in paragraphs 0186 to 0190 of JP2011-184628A and paragraphs 0126 to 0130 of JP2011-178896A.

  The viscosity of the ink composition is preferably in the range of 1 mPa · s to 30 mPa · s, preferably in the range of 1 mPa · s to 20 mPa · s from the viewpoint of droplet ejection stability and agglomeration speed when ink is applied by an inkjet method. Is more preferable, the range of 2 mPa · s to 15 mPa · s is further preferable, and the range of 2 mPa · s to 10 mPa · s is particularly preferable. The viscosity of the ink composition can be measured at 20 ° C. using a Brookfield viscometer, for example.

The ink composition is preferably alkaline.
Although details of the image forming method of the present invention will be described later, a particularly preferable form in image formation using a processing liquid is a form in which the ink composition is alkaline and the processing liquid is acidic from the viewpoint of the cohesiveness of the ink. is there.
The pH of the ink composition is preferably pH 7.5 to pH 10 and more preferably pH 8 to pH 9 from the viewpoints of ink stability and aggregation rate. The pH of the ink composition is 25 ° C., and is measured by a commonly used pH measuring device (for example, a multi-water quality meter MM-60R manufactured by Toa DKK Corporation).
The pH of the ink composition can be appropriately adjusted using an acidic compound or a basic compound. As the acidic compound or the basic compound, a commonly used compound can be used without particular limitation.

<Image forming method>
The image forming method of the present invention includes an image forming step of forming an image by applying the ink composition of the present invention to a recording medium, and an infrared irradiation step of irradiating the formed image with infrared rays.
The image forming method of the present invention preferably further includes a treatment liquid application step of applying a treatment liquid containing an aggregation component that forms an aggregate when contacted with the ink composition to a recording medium.
When the image forming method is configured as described above, when an image is formed using a recording medium including paper, the color is reproducible while suppressing cuckling and the image obtained by the image formation.

[Image formation process]
In the image forming step, the ink composition of the present invention is applied to a recording medium to form an image.

(recoding media)
The recording medium used in the image forming method of the present invention is not particularly limited.
For example, in addition to a recording medium including paper such as printing paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, and the like may be used.
Among these, the ink composition of the present invention can suppress clogging when an image is formed on a recording medium containing paper. Therefore, the recording medium preferably contains paper.

As the recording medium including paper, for example, general printing paper mainly used for cellulose, such as so-called high-quality paper, coated paper, and art paper, which is used for plain paper and general offset printing, can be used. JP-A-8-169172, JP-A-8-27693, JP-A-2-276670, JP-A-7-276789, JP-A-9-323475, JP-A-62-238783, and JP-A-10 Ink jet papers described in JP-A Nos. 153939 / 10-217473, 10-235995, 10-217597, and 10-337947 may be used.
General printing paper mainly composed of cellulose is relatively slow in ink absorption and drying in image recording by a general ink jet method using water-based ink, and color material movement is likely to occur after droplet ejection, and image quality is likely to deteriorate. However, according to the inkjet image forming method of the present invention, it is possible to record a high quality image excellent in color density and hue by suppressing the movement of the coloring material.

  As the recording medium containing paper, commercially available media can be used. For example, “OK Prince Quality” manufactured by Oji Paper Co., Ltd., “Shiraoi” manufactured by Nippon Paper Industries Co., Ltd., and Japan Fine coated paper such as "New NPI fine quality" manufactured by Paper Industries Co., Ltd. (A), "OK Everlight Coat" manufactured by Oji Paper Co., Ltd., and "Aurora S" manufactured by Nippon Paper Industries Co., Ltd. Lightweight coated paper (A3) such as “OK Coat L” manufactured by Oji Paper Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. “OK Top Coat +” manufactured by Oji Paper Co., Ltd. and Nippon Paper Industries Co., Ltd. Coated paper (A2, B2) such as “Aurora Coat” manufactured by Co., Ltd., “OK Kanito +” manufactured by Oji Paper Co., Ltd., and art paper (A1) such as “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. ) And the like. It is also possible to use various photographic papers for ink jet recording.

Among the above, the water absorption coefficient Ka is preferably 0.05 mL / m ² · ms from the viewpoint of obtaining a high-quality image having a large effect of suppressing color material movement and better color density and hue than before. ^1/2 is a recording medium ~0.5mL ^/ m 2 ^{· ms 1/2,} more preferably ^{0.1mL / m 2 · ms 1/2 ~0.4mL} / m 2 · ms 1/2 of the recording medium , and still more preferably it is a recording medium of ^{0.2mL / m 2 · ms 1/2 ~0.3mL} / m 2 · ms 1/2.

  The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI paper pulp test method No. 51: 2000 (issued by Japan Paper Pulp Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning absorption meter. It is calculated from the difference in the amount of water transferred between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co., Ltd.).

  Among the recording media, so-called coated paper used for general offset printing is preferable. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not surface-treated. The coated paper is likely to cause quality problems such as glossiness and scratch resistance of the image in image formation by ordinary aqueous inkjet, but in the inkjet image formation method of the present invention, gloss unevenness is suppressed and glossiness is reduced. An image with good abrasion resistance can be obtained. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. More specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

(Ink application method)
The method for applying the ink composition of the present invention to the recording medium is not particularly limited, and examples thereof include spray coating, coating using a coating roller, etc., coating by an ink jet method, and immersion, and the ink jet method is preferable. The ink composition can be ejected by an ink jet method, for example, by ejecting the ink composition onto a desired recording medium by supplying energy. As a preferred ink ejection method for the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

There are no particular restrictions on the ink jet method, and there are known methods such as a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink with ink and ejects the ink using radiation pressure, and a thermal ink jet (bubble jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used.
The inkjet method uses a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method used is included.

In addition, an ink jet head used in the ink jet method may be an on-demand method or a continuous method.
In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (registered trademark) type, an electrostatic suction type (for example, an electric field control type, a slit jet type, etc.) and a discharge type (for example, a spark jet type). However, any discharge method may be used.
In addition, there is no restriction | limiting in particular about the nozzle etc. which are used for the inkjet method, According to the objective, it can select suitably.

The ink composition is ejected by an ink jet method using a short serial head, which performs recording while scanning the head in the width direction of the recording medium, and the entire area of one side (one side in the width direction) of the recording medium. Correspondingly, there is a line system using a line head in which recording elements are arranged. A nozzle plate is provided on the discharge surface side of the line head, and discharge holes are provided in the nozzle plate at positions corresponding to the recording elements.
In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system.
The image forming method of the present invention can be applied to any of these, but in general, when applied to a line system that does not perform a dummy jet, the ejection accuracy (ink from a nozzle ejection surface (for example, a liquid repellent film described later)) The effect of improving the cutting ability is great.
Particularly in the line method, the single pass method, in which an image is formed by a single scan of the recording medium, is effective in improving the discharge accuracy (the ink cutting property from a nozzle discharge surface (for example, a liquid repellent film described later)). Becomes particularly prominent.

  Further, in the image forming process, in the case of the line method, two or more kinds of ink compositions are used, and the ink composition to be ejected first (the nth color (n ≧ 1), for example, the second color) and subsequently Recording can be suitably performed by setting the ejection (droplet ejection) interval between the ink composition to be ejected (the (n + 1) th color, for example, the third color) to 1 second or less. In the present invention, an ejection interval of 1 second or less in the line method prevents bleeding and color mixing between ink droplets, and has excellent scratch resistance under high-speed recording higher than that of the prior art, and occurrence of blocking. A suppressed image can be obtained. In addition, an image having excellent hue and drawability (reproducibility of fine lines and fine portions in the image) can be obtained.

  The amount of ink droplets ejected from the inkjet head is preferably 0.5 pl (picoliter) to 6 pl, more preferably 1 pl to 5 pl, and even more preferably 2 pl to 4 pl from the viewpoint of obtaining a high-definition image. .

In this step, the ink composition of the present invention is applied by discharging from a nozzle plate in which a plurality of discharge holes are two-dimensionally arranged and a liquid repellent film containing a fluorine compound is provided on the discharge hole forming surface (discharge surface). It is preferable.
Hereinafter, an ink jet head provided with a nozzle plate, a liquid repellent film containing a fluorine compound, and a nozzle plate suitably used in the image forming method of the present invention will be described.

(Nozzle plate)
The nozzle plate has a configuration in which a plurality of ejection holes are two-dimensionally arranged.
The number of the plurality of ejection holes is not particularly limited, and can be appropriately selected in consideration of speeding up of image formation.

As the nozzle plate, a nozzle plate containing silicon (hereinafter, also referred to as “silicon nozzle plate”) is suitable.
As the silicon, single crystal silicon or polysilicon can be used.
Examples of the silicon nozzle plate include a metal oxide (silicon oxide, titanium oxide, chromium oxide, tantalum oxide (preferably Ta ₂ O ₅ )), metal nitride (titanium nitride, silicon nitride) on a silicon substrate. Etc.), and a film provided with a metal (zirconium, chromium, titanium, etc.) can also be used.
Here, the silicon oxide may be a SiO ₂ film formed by oxidizing all or part of the surface of the silicon substrate.
The silicon nozzle plate may be configured by replacing a part of silicon with glass (eg, borosilicate glass, photosensitive glass, quartz glass, soda lime glass).
Among these, in particular, a film made of tantalum oxide such as tantalum pentoxide has very excellent ink resistance to ink, and particularly good corrosion resistance to alkaline ink. It is done.

One mode of a method for forming a film (SiO ₂ film) made of silicon oxide will be described.
For example, a SiO ₂ film can be formed on a silicon substrate by accommodating a silicon substrate in a chemical vapor deposition (CVD) reactor and introducing SiCl ₄ and water vapor.
At this time, the partial pressure of SiCl ₄ is 0.05 to 40 torr (6.67 to 5.3 × 10 ³ Pa) (for example, 0.1 to 5 torr (13.3 to 666.5 Pa)). The partial pressure of H ₂ O can be between 0.05 and 20 torr (for example, 0.2 to 10 torr). The deposition temperature is generally between room temperature and 100 degrees Celsius.
As another aspect, the SiO ₂ film can be formed by sputtering on a silicon substrate.
In any embodiment, it is preferable that the surface of the silicon substrate on which the SiO ₂ film is to be formed be cleaned (for example, by applying oxygen plasma) before forming the SiO ₂ film.

(Liquid repellent film containing fluorine compound)
A liquid repellent film containing a fluorine compound is provided on the discharge hole forming surface (discharge surface) of the nozzle plate.
The SP value of the liquid repellent film containing a fluorine compound is not particularly limited, but from the viewpoint of further improving the ink cutting performance, the SP value of the liquid repellent film calculated by the Okitsu method is 16.00 MPa ^1/2 or less. Is preferable, 15.00 MPa ^1/2 or less is more preferable, and 13.00 MPa ^1/2 or less is particularly preferable.

As the fluorine compound contained in the liquid repellent film, for example, a compound having a fluorinated alkyl group can be suitably used.
The liquid repellent film in the present invention is preferably a liquid repellent film prepared using, for example, a fluorinated alkylsilane compound.
As the fluorinated alkylsilane compound, a fluorinated alkylsilane compound represented by the following general formula (F) can be suitably used. The fluorinated alkylsilane compound represented by the following general formula (F) is a silane coupling compound.
_{C n F 2n + 1 -C m} H 2m -Si-X 3 ... Formula (F)
In general formula (F), n represents an integer of 1 or more, and m represents 0 or an integer of 1 or more. X represents an alkoxy group, an amino group, or a halogen atom. A part of X may be substituted with an alkyl group.

Examples of the fluorinated alkylsilane compound include C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ (also referred to as “1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane” and “FDTS”), CF ₃ ( CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ and other fluoroalkyltrichlorosilanes, CF ₃ (CF ₂ ) ₈ C ₂ H ₄ Si (OCH ₃ ) ₃ , 3,3,3-trifluoropropyltrimethoxysilane, tri Examples thereof include fluoroalkylalkoxysilanes such as decafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane and heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane.

In the general formula (F), n is an integer of 1 to 14, m is an integer of 0 or 1 to 5, and X is alkoxy in terms of liquid repellency and durability of the liquid repellent film. The group is preferably a group or a halogen atom, more preferably n is an integer of 1 to 12, m is an integer of 0 to 3, and X is an alkoxy group or a halogen atom.
Among these, C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ is most preferable.

  Although there is no restriction | limiting in particular as thickness of the liquid repellent film containing a fluorine compound, The range of 0.2-30 nm is preferable, and the range of 0.4-20 nm is more preferable. Even if the thickness of the liquid repellent film exceeds 30 nm, there is no particular problem, but if it is 30 nm or less, it is advantageous in terms of film uniformity, and if it is 0.2 nm or more, the water repellency to ink is good. .

  As the liquid repellent film containing a fluorine compound, for example, a monomolecular film (SAM film) of a fluorinated alkylsilane compound or a laminated film of a fluorinated alkylsilane compound can be used. Here, the laminated film of the fluorinated alkylsilane compound includes not only a film in which the fluorinated alkylsilane compound is stacked without being polymerized but also a polymerized film of the fluorinated alkylsilane compound.

  The liquid repellent film containing a fluorine compound can be formed by, for example, the method described in paragraphs 0114 to 0124 of JP2011-111527A.

(Inkjet head with nozzle plate)
FIG. 1 is a schematic cross-sectional view showing an example of an inkjet head provided with a nozzle plate, which is preferably used in the image forming method of the present invention.
As shown in FIG. 1, the inkjet head 100 includes a nozzle plate 11 having ejection holes (nozzles), and an ink supply unit 20 provided on the side opposite to the ejection direction of the nozzle plate. The nozzle plate 11 is provided with a plurality of ejection holes 12 for ejecting ink. A liquid repellent film 13 containing a fluorine compound is provided on the discharge surface side of the nozzle plate 11.

FIG. 2 is a perspective view conceptually showing the ejection surface (the surface on which the liquid repellent film 13 is formed) of the nozzle plate 11.
As shown in FIG. 2, the nozzle plate 11 is provided with a plurality of discharge holes (nozzles) arranged in a two-dimensional array. The number of ejection holes is not limited, and can be selected as appropriate in consideration of high-speed image formation. For example, the number can be 32 × 60.
The nozzle plate 11 may be a nozzle plate (silicon nozzle plate) containing silicon as described above. For example, a silicon nozzle plate having a structure in which silicon is exposed at least on the inner wall of the nozzle opening and the plate surface on the ink ejection direction side is preferable. .
Although not shown, the nozzle plate 11 may be a silicon nozzle plate including a silicon substrate and a silicon oxide film provided on the silicon substrate. In this case, the silicon oxide film is disposed between the silicon substrate and the liquid repellent film 13 containing a fluorine compound.

  The ink supply unit 20 includes a plurality of pressure chambers 21 that communicate with each of the plurality of ejection holes 12 of the nozzle plate 11 via the nozzle communication path 22, and a plurality of ink supplies that supply ink to each of the plurality of pressure chambers 21. A flow path 23, a common liquid chamber 25 that supplies ink to the plurality of ink supply flow paths 23, and a pressure generation unit 30 that deforms each of the plurality of pressure chambers 21 are provided.

The ink supply channel 23 is formed between the nozzle plate 11 and the pressure generating means 30 so that the ink supplied to the common liquid chamber 25 is fed. One end of a supply adjustment path 24 connected to the pressure chamber 21 is connected to the ink supply flow path 23, and the amount of ink supplied from the ink supply flow path 23 is reduced to a required amount to the pressure chamber 21. The liquid can be sent. A plurality of supply adjustment paths 24 are provided in the ink supply flow path 23, and ink is supplied to the pressure chamber 21 provided adjacent to the pressure generating means 30 via the ink supply flow path 23.
In this way, a large amount of ink can be supplied to the plurality of ejection holes.

  The pressure generating means 30 is configured by sequentially stacking a diaphragm 31, an adhesive layer 32, a lower electrode 33, a piezoelectric layer 34, and an upper electrode 35 from the pressure chamber 21 side, and electric wiring for supplying a driving signal from the outside is provided. It is connected. The piezoelectric element is deformed according to the image signal, so that ink is ejected from the nozzle 12 via the nozzle communication path 22.

  Further, a circulation restrictor 41 is provided in the vicinity of the discharge hole 12 so that ink is always collected into the circulation path 42. Thereby, it is possible to prevent thickening of the ink in the vicinity of the ejection holes during non-ejection.

[Infrared irradiation process]
The image forming method of the present invention includes an infrared irradiation step of irradiating the formed image with infrared rays after the image forming step.
By irradiating the image with infrared rays, the specific IR dye contained in the image generates heat, and only the image portion on the recording medium is heated. In addition, the ink composition of the present invention contains a polymer dispersant that sufficiently disperses the specific IR dye, and the specific IR dye is not biased in the ink composition and is considered to maintain a dispersed state. Therefore, the image formed with the ink composition is excellent in quick-drying property and can suppress cuckling. In addition, since the polymer pigment contained in the ink composition is excellent in dispersibility of the organic pigment, the ink composition is dried and fixed on the recording medium as an image while maintaining the dispersed state of the organic pigment. Conceivable. Therefore, even when image formation is repeated, the color hardly changes and the color reproducibility is excellent.

  The method of irradiating the image with infrared rays is not particularly limited. Examples of infrared sources include, for example, a normal infrared lamp, a xenon flash lamp, a xenon lamp, a xenon short arc lamp, a near infrared halogen heater, an infrared LED, An infrared laser etc. can be mentioned. Preferably, a xenon flash lamp, a xenon lamp, a near-infrared halogen heater, an infrared LED, a solid-state laser or a semiconductor laser that emits infrared light having a wavelength of 700 nm to 1500 nm can be used.

(Image fixing process)
The image forming method of the present invention may further include an image fixing step as long as the effects of the present invention (particularly, suppression of cockle) are not impaired.
Examples of the image fixing step include a step of heating the image by a non-contact heating method other than infrared irradiation, and a step of heating the image by a contact heating method in which a hot plate or a heating and pressing roller is pressed against the image for heating. .
The image fixing step is a step of further improving the fixation of the image formed on the recording medium to the recording medium, and can further improve the resistance against image abrasion.

  The method for non-contact heating of the image is not particularly limited, and examples thereof include a method of heating with a heating element such as a nichrome wire heater, and a method of supplying warm air or hot air. The contact heating method is not particularly limited. For example, a method of pressing a hot plate against an image forming surface of a recording medium, a pair of heating and pressing rollers, a pair of heating and pressing belts, or an image recording on a recording medium. A method of performing heat-fixing by contact, such as a method of passing a pair of rollers using a heat-pressure device provided with a heat-pressure belt arranged on the surface side and a holding roller arranged on the opposite side Are preferable.

  The conveyance speed of the recording medium when using a heat and pressure roller or a heat and pressure belt is preferably in the range of 200 mm / second to 700 mm / second, more preferably 300 mm / second to 650 mm / second, and still more preferably 400 mm. / Second to 600 mm / second.

[Processing liquid application process]
The image forming method of the present invention preferably further includes a treatment liquid application step of applying a treatment liquid containing an aggregation component that forms an aggregate when contacted with the ink composition to a recording medium.
The treatment liquid applying step may be before the image forming step or after the image forming step.
The treatment liquid applied to the recording medium contacts with the ink composition to form an image. Thereby, components (organic pigment, specific IR dye, etc.) in the ink composition are aggregated, and the image is fixed on the recording medium.
Since the image forming method of the present invention includes this step, inkjet image formation can be speeded up, and an image with high density and resolution can be obtained even when the speed is increased.
In addition, the detail and preferable aspect of each component in a process liquid are mentioned later.

  The treatment liquid can be applied to the recording medium by applying a known method such as a coating method, an ink jet method, or an immersion method. As a coating method, a known coating method using a bar coater, an extrusion die coater, an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater or the like can be used. The details of the inkjet method are as described above.

The amount of the treatment liquid applied to the recording medium is not particularly limited as long as the ink composition can be aggregated. Preferably, the amount of the aggregation component applied is 0.1 g / m ² or more. it can. The amount of the applied aggregating component is 0.1g ^{/ m 2} ~1.0g ^/ m 2 and is more preferably ^{0.2g / m 2 ~0.8g / m 2} . When the amount of the aggregating component is 0.1 g / m ² or more, the agglomeration reaction proceeds favorably, and when it is 1.0 g / m ² or less, the glossiness is not excessively increased.

  In the present invention, it is preferable to further provide a heating and drying step of heating and drying the treatment liquid on the recording medium after the treatment liquid is applied on the recording medium and before the ink composition is applied. By heating and drying the treatment liquid in advance before the image forming step, ink colorability such as bleeding prevention is improved, and a visible image having a good color density and hue can be recorded.

  Heating and drying can be performed by known heating means such as a heater, air blowing means using air blowing such as a dryer, or a combination of these. As the heating method, for example, a method of applying heat with a heater or the like from the side opposite to the treatment liquid application surface of the recording medium, a method of applying warm air or hot air to the treatment liquid application surface of the recording medium, or an infrared heater was used. The heating method etc. are mentioned, You may heat combining these two or more.

(Processing liquid)
The treatment liquid in the present invention contains at least one aggregation component that forms an aggregate when it comes into contact with the ink composition. That is, the aggregation component contained in the treatment liquid causes the components (organic pigment, specific IR dye, etc.) in the ink composition to aggregate when the ink composition and the treatment liquid come into contact with each other.
By using the treatment liquid together with the ink composition, image formation (particularly, ink jet recording) can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

Examples of the treatment liquid include a liquid composition capable of generating an aggregate by changing the pH of the ink composition.
The treatment liquid is preferably acidic.
Specifically, the pH (25 ° C.) of the treatment liquid is preferably 1 to 6, more preferably 1.2 to 5, and more preferably 1.5 to 5, from the viewpoint of the aggregation rate of the ink composition. More preferably, it is 4. In this case, the pH (25 ° C.) of the ink composition used in the image forming step is preferably 7.5 to 9.5 (more preferably 8.0 to 9.0).
Among these, in the present invention, from the viewpoint of image density, resolution, and speed-up of inkjet image formation, the pH (25 ° C.) of the ink composition is 7.5 or more, and the pH (25 ° C.) of the treatment liquid is The case of 3-5 is preferable.
The aggregating components can be used alone or in combination of two or more.

-Aggregation component-
The treatment liquid contains at least one aggregation component capable of forming an aggregate upon contact with the ink composition. By mixing the treatment liquid with the ink composition used for image formation (for example, the ink composition ejected by the inkjet method), for example, an organic pigment or a specific IR dye that is stably dispersed in the ink composition Aggregation such as is promoted.

Examples of the aggregating component include at least one acidic compound.
As the acidic compound, a compound having a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxyl group, or a salt thereof (for example, a polyvalent metal salt) may be used. it can. Among these, from the viewpoint of the aggregation rate of the ink composition, a compound having a phosphate group or a carboxyl group is more preferable, and a compound having a carboxyl group is more preferable.

  Examples of the compound having a carboxyl group include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, pyrrolidonecarboxylic acid, and pyrone. It is selected from carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, derivatives of these compounds, or salts thereof (for example, polyvalent metal salts). Is preferred. These compounds may be used alone or in combination of two or more.

The treatment liquid can further comprise an aqueous solvent (for example, water) in addition to the acidic compound.
When the treatment liquid contains an acidic compound, the content of the acidic compound in the treatment liquid is preferably 5% by mass to 95% by mass with respect to the total mass of the treatment liquid from the viewpoint of the aggregation effect. It is more preferable that it is% -80 mass%.

  Further, as the aggregating component, polyvalent metal salts and cationic polymers described in paragraphs 0155 to 0156 of JP2011-042150A may be used.

The viscosity of the treatment liquid is preferably in the range of 1 mPa · s to 30 mPa · s, more preferably in the range of 1 mPa · s to 20 mPa · s, from the viewpoint of the aggregation rate of the ink composition. The range is more preferable, and the range of 2 mPa · s to 10 mPa · s is particularly preferable. The viscosity is measured under a condition of 20 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
The surface tension of the treatment liquid is preferably 20 mN / m to 60 mN / m, more preferably 20 mN / m to 45 mN / m, and more preferably 25 mN / m from the viewpoint of the aggregation rate of the ink composition. More preferably, it is ˜40 mN / m. The surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[Other processes]
The image forming method of the present invention may have other processes such as a maintenance process and a curing process as necessary.

(Maintenance process)
In the image forming method of the present invention, when an image is formed by an inkjet method, an ink composition or an ink fixed substance derived from the ink composition (hereinafter also referred to as “ink composition etc.”) is applied to a nozzle ejection surface ( For example, you may have the maintenance process removed from the liquid repellent film provided in the nozzle.

In the maintenance process, the ink composition or the fixed matter derived from the ink composition is removed by scraping with a wiper blade, wiping with a cloth or paper.
The maintenance process may include applying a maintenance liquid to the vicinity of the inkjet head (eg, ink flow path or the like; hereinafter, also referred to as a head or the like). By applying the maintenance liquid to the head or the like, the ink adhering matter derived from the ink on the nozzle surface is dissolved or swelled and becomes easier to remove.
The maintenance liquid may be applied before or after scraping with a wiper blade, wiping with a cloth or paper. Preferably, after applying the maintenance liquid, the nozzle surface is rubbed with a wiper blade (wiping), the ink adhering matter is scraped off, the air pressure or the maintenance liquid is removed, etc., and wiped with cloth or paper. A method is mentioned. Among these, scraping with a wiper blade and wiping with a cloth or paper are preferable.
The material of the wiper blade is preferably rubber having elasticity, and specific materials include butyl rubber, chloroprene rubber, ethylene propylene rubber, silicone rubber, urethane rubber, nitrile rubber and the like. In order to impart ink repellency to the wiper blade, a wiper blade coated with a fluorine resin or the like may be used.

(Curing process)
In the image forming method of the present invention, when the ink composition further contains a polymerizable compound, the image forming method further includes a curing step of irradiating the image formed by the image forming step with an active energy ray to cure the image. You may have.
Thereby, the abrasion resistance of the formed image and the adhesion to the recording medium are further improved.
The active energy ray is not particularly limited as long as it can polymerize a polymerizable compound. For example, ultraviolet rays, electron beams and the like can be mentioned. Among them, ultraviolet rays are preferable from the viewpoint of versatility. Examples of the source of active energy rays include an ultraviolet irradiation lamp (such as a halogen lamp and a high-pressure mercury lamp), a laser, an LED, and an electron beam irradiation device.

UV intensity, at wavelength region effective to cure ^is preferably ^{500mW / cm 2 ~5000mW / cm 2} .
As the means for irradiating ultraviolet rays, a commonly used means may be used, and an ultraviolet irradiation lamp is particularly suitable. As the ultraviolet irradiation lamp, a so-called low-pressure mercury lamp, high-pressure mercury lamp, mercury lamp coated with a phosphor, UV-LED light source, or the like whose mercury vapor pressure is 1 to 10 Pa during lighting is suitable. The emission spectrum in the ultraviolet region of mercury lamps and UV-LEDs is 450 nm or less, particularly in the range of 184 nm to 450 nm, and is suitable for efficiently reacting a polymerizable compound in a black or colored ink composition. Yes. Further, it is suitable for mounting a power source in a printer in that a small power source can be used. As the mercury lamp, for example, a metal halide lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a xenon flash lamp, a deep UV lamp, a lamp that uses a microwave to excite a mercury lamp from the outside, and a UV laser are practically used. Since the above-mentioned range is included as the emission wavelength region, it is basically applicable if the power source size, input intensity, lamp shape, etc. are allowed. The light source is selected in accordance with the sensitivity of the polymerization initiator used.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

<Ink preparation of Examples 1 to 15>
(Preparation of near-infrared absorbing pigment dispersion A1)
Each component of the following composition A1 was mixed and dispersed by a bead mill using 0.1 mmφ zirconia beads for 4 hours. Using a 50 mL centrifuge, centrifugation was performed at 5000 rpm for 5 minutes, and the supernatant other than the precipitate was collected. When the volume average particle size was measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 61 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion exchange water was added to obtain a near-infrared absorbing dye dispersion A1 as a dispersion having a dye concentration of 7.4%.

-Composition A1-
・ Near-infrared absorbing dye (IR-1) [the following structure, specific IR dye] ... 10%
・ SOLSPERSE 44000 ... 8.4%
[Water-soluble polymer dispersant manufactured by Lubrizol Co.]
・ Ion-exchanged water: 100% of the total amount

(Synthesis of water-insoluble resin P-1)
To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. To this, 50 g of methyl ethyl ketone was added with 0.85 g of dimethyl-2,2′-azobisisobutyrate and phenoxy. A solution in which 50 g of ethyl methacrylate, 13 g of methacrylic acid, and 37 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution prepared by dissolving 0.42 g of dimethyl-2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in an excess amount of hexane, the precipitated resin was dried, and phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid (copolymerization ratio [mass ratio] = 50/37/13) 96.5 g of a polymer (water-insoluble resin P-1) was obtained.
The composition of the obtained water-insoluble resin P-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 49400. Furthermore, when the acid value of this water-insoluble resin P-1 was determined by the method prescribed in JIS standard (JIS K 0070: 1992), it was 84.8 mgKOH / g.

(Preparation of yellow pigment aqueous dispersion B1)
C. I. 10 parts of Pigment Yellow 74, 4.5 parts of water-insoluble resin P-1, 18 parts of methyl ethyl ketone, and 8.0 parts of 1 mol / L NaOH aqueous solution are added, and 2 to 8 hours as required by a roll mill. After kneading, the kneaded material was dispersed in 60 parts of ion exchange water. Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed.
After cooling to room temperature, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho Co., Ltd.), using a 50 mL centrifuge, centrifugation was performed at 10,000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 [manufactured by Nikkiso Co., Ltd.], it was 93 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a yellow pigment aqueous dispersion B1 as a dispersion of resin-coated pigment particles having a pigment concentration of 14% by mass.

(Preparation of self-dispersing polymer particles C-1)
In a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 560.0 g of methyl ethyl ketone was charged, and the temperature was raised to 87 ° C. in a nitrogen atmosphere. While maintaining the reflux state in the reaction vessel (hereinafter referred to as reflux until completion of the reaction), 232.0 g of methyl methacrylate, 301.6 g of isobornyl methacrylate, 46.4 g of methacrylic acid, 108 g of methyl ethyl ketone, and “V-601” (Wako Pure) A mixed solution consisting of 2.32 g (manufactured by Yakuhin Co., Ltd.) was added dropwise at a constant speed so that the addition was completed in 2 hours.

  After completion of the dropwise addition, the mixture was stirred for 1 hour, (1) a solution consisting of 1.16 g of “V-601” and 6.4 g of methyl ethyl ketone was added, and the mixture was stirred for 2 hours. Subsequently, the step (1) was repeated four times, and a solution consisting of 1.16 g of “V-601” and 6.4 g of methyl ethyl ketone was added and stirring was continued for 3 hours. After completion of the polymerization reaction, the temperature of the solution was lowered to 65 ° C., and 163.0 g of isopropanol was added and allowed to cool. The weight average molecular weight (Mw) of the obtained copolymer was 63000, and the acid value was 65.1 (mgKOH / g).

  Next, 317.3 g of the obtained polymerization solution (solid content concentration 41.0%) was weighed, 46.4 g of isopropanol, 1.65 g of a 20% maleic anhydride aqueous solution (based on the water-soluble acidic compound and copolymer). 40.77 g of 2 mol / L NaOH aqueous solution was added, and the temperature in the reaction vessel was raised to 70 ° C. Next, 380 g of distilled water was added dropwise at a rate of 10 ml / min to disperse in water.

  Thereafter, under reduced pressure, the temperature in the reaction vessel was kept at 70 ° C. for 1.5 hours, and 287.0 g of isopropanol, methyl ethyl ketone and distilled water were distilled off in total (solvent removal step), and Proxel GXL (S) (Arch Chemicals, Inc.) 0.278 g (manufactured by Japan Co., Ltd.) (440 ppm as benzoisothiazolin-3-one with respect to the solid content of the polymer) was added. Thereafter, filtration was performed with a 1 μm filter, and the filtrate was recovered to obtain an aqueous dispersion of self-dispersing polymer particles C-1 having a solid content concentration of 26.5%. The obtained self-dispersing polymer particles C-1 were diluted with ion-exchanged water and measured for properties of a 25.0% liquid. As a result, pH 7.8, electric conductivity 461 mS / m, viscosity 14.8 mPa · s, volume The average particle size was 2.8 nm.

(Preparation of ink Y1)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y1 were used, and the respective components were mixed so as to be the composition Y1. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain an ink Y1 which is a yellow ink composition.

~ Composition Y1 of ink Y1
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near-infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 2.2%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ... 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of magenta pigment aqueous dispersion B2)
C. I. 10 parts of CI Pigment Red 122, 4.2 parts of water-insoluble resin P-1, 20 parts of methyl ethyl ketone, and 7.8 parts of 1 mol / L NaOH aqueous solution are added for 2 to 8 hours as required by a roll mill. After kneading, the kneaded material was dispersed in 60 parts of ion exchange water. Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed to obtain a solid component.
Next, the solid component is cooled to room temperature, and a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho Co., Ltd.) is used to centrifuge at 10000 rpm for 30 minutes using a 50 mL centrifuge, and the supernatant liquid other than the precipitate is collected. did. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 83 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a magenta pigment aqueous dispersion B2 as a dispersion of resin-coated pigment particles having a pigment concentration of 14% by mass.

(Preparation of ink M1)
Using the aqueous magenta pigment dispersion B2, the aqueous dispersion of self-dispersing polymer particles C-1, and other components shown in the composition M1, the components were mixed so as to be the composition M1. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M1 which is a magenta ink composition.

~ Composition M1 of ink M1
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near-infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 2.2%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of cyan pigment aqueous dispersion B3)
C. I. 10 parts of Pigment Blue 15: 3, 4.6 parts of water-insoluble resin P-1, 20 parts of methyl ethyl ketone, and 8.3 parts of 1 mol / L NaOH aqueous solution, and 2 to 2 in a roll mill as necessary. After kneading for 8 hours, the kneaded product was dispersed in 60 parts of ion-exchanged water. Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed to obtain a solid component.
Next, the solid component is cooled to room temperature, and a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho Co., Ltd.) is used to centrifuge at 10000 rpm for 30 minutes using a 50 mL centrifuge, and the supernatant liquid other than the precipitate is collected. did. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 78 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a cyan pigment aqueous dispersion B3 as a dispersion of resin-coated pigment particles having a pigment concentration of 14% by mass.

(Preparation of ink C1)
Using the cyan pigment aqueous dispersion B3, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition C1, each component was mixed so as to be the composition C1. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink C1 which is a cyan ink composition.

~ Composition C1 of ink C1
・ Cyan pigment (CI pigment blue 15: 3) ・ ・ ・ ・ 3%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.3%
・ Near-infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 2.2%
-Self-dispersing polymer particle C-1 ... 8.2%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] ・ Olfin E1010 (Nissin Chemical Industry Co., Ltd., surfactant)... 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink Y2)
Using the yellow pigment aqueous dispersion B1 and other components shown in the composition Y2, each component was mixed so as to be the composition Y2. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain an ink Y2 which is a yellow ink composition.

~ Composition Y2 of ink Y2
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near-infrared absorbing pigment dispersion A1 ・ ・ ・ 2.7%
2-pyrrolidone [Wako Pure Chemical Industries, water-soluble organic solvent] 6.0%
・ Diethylene glycol (DEG) (manufactured by Wako Pure Chemical Industries, Ltd., water-soluble organic solvent) ・ ・ 14.0%
・ Sanix GP250 [manufactured by Sanyo Kasei Kogyo Co., Ltd., water-soluble organic solvent] 18.0%
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) ・ ・ ・ ・ 1.2%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink M2)
Using the magenta pigment aqueous dispersion B2 and the other components shown in the composition M2, the components were mixed so as to obtain the composition M2. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M2 which is a magenta ink composition.

~ Composition M2 of ink M2
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near-infrared absorbing pigment dispersion A1... 0.82%
2-pyrrolidone [Wako Pure Chemical Industries, water-soluble organic solvent] 6.0%
・ Diethylene glycol (DEG) (manufactured by Wako Pure Chemical Industries, Ltd., water-soluble organic solvent) ・ ・ 14.0%
・ Sanix GP250 [manufactured by Sanyo Chemical Industries, water-soluble organic solvent] ... 18.0%
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) ・ ・ ・ ・ 1.2%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of near-infrared absorbing pigment dispersion A2)
Each component of the following composition A2 was mixed and dispersed for 6 hours using 0.3 mmφ zirconia beads by a bead mill. Using a 50 mL centrifuge, centrifugation was performed at 5000 rpm for 5 minutes, and the supernatant other than the precipitate was collected. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 148 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a near-infrared absorbing dye dispersion A2 as a dispersion having a dye concentration of 6.9%.

-Composition A2-
・ Near-infrared absorbing dye (IR-2) [the following structure, specific IR dye] ... 10%
・ SOLSPERSE 44000 ... 8.4%
[Water-soluble polymer dispersant manufactured by Lubrizol Co.]
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink M3)
Using the magenta pigment aqueous dispersion B2, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition M3, the respective components were mixed so as to be the composition M3. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M3, which is a magenta ink composition.

~ Composition M3 of ink M3
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near infrared absorbing pigment dispersion A2 ・ ・ ・ ・ 2.5%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of near-infrared absorbing pigment dispersion A3)
Each component of the following composition A3 was mixed and dispersed for 6 hours using 0.3 mmφ zirconia beads by a bead mill. Using a 50 mL centrifuge, centrifugation was performed at 5000 rpm for 5 minutes, and the supernatant other than the precipitate was collected. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 124 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a near-infrared absorbing dye dispersion A3 as a dispersion having a dye concentration of 7.1%.

-Composition A3-
-Near-infrared absorbing dye (IR-3) [the following structure, specific IR dye] ... 10%
・ SOLSPERSE 44000 ... 8.4%
[Water-soluble polymer dispersant manufactured by Lubrizol Co.]
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink M4)
Using the magenta pigment aqueous dispersion B2, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition M4, the respective components were mixed so as to be the composition M4. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M4 which is a magenta ink composition.

~ Composition M4 of ink M4 ~
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near-infrared absorbing pigment dispersion A3 ・ ・ ・ ・ 2.3%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea: 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink C2)
Using the cyan pigment aqueous dispersion B3 and the other components shown in the composition C2, each component was mixed so as to be the composition C2. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink C2 which is a cyan ink composition.

~ Composition C2 of ink C2
・ Cyan pigment (CI pigment blue 15: 3) ・ ・ ・ ・ 3%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.3%
・ Near infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 1%
2-pyrrolidone [Wako Pure Chemical Industries, water-soluble organic solvent] 6.0%
・ Diethylene glycol (DEG) (manufactured by Wako Pure Chemical Industries, Ltd., water-soluble organic solvent) ・ ・ 14.0%
・ Sanix GP250 [manufactured by Sanyo Chemical Industries, water-soluble organic solvent] ... 18.0%
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) ・ ・ ・ ・ 1.2%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink Y3)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y3 were used, and the respective components were mixed so as to obtain the composition Y3. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink Y3 which is a yellow ink composition.

~ Composition Y3 of ink Y3
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 0.7%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink Y4)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y4 were used, and the respective components were mixed so as to obtain the composition Y4. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink Y4 which is a yellow ink composition.

~ Composition Y4 of ink Y4 ~
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 4%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.] ... 2.0%
・ Dipropylene glycol (DPG)
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink C3)
Using the cyan pigment aqueous dispersion B3 and the other components shown in the composition C3, the respective components were mixed so that the composition C3 was obtained. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink C3 which is a cyan ink composition.

~ Composition of ink C3 ~
・ Cyan pigment (CI pigment blue 15: 3) ・ ・ ・ ・ 3%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.3%
・ Near infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 4%
-Self-dispersing polymer particle C-1 ... 8.2%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink C4)
Using the cyan pigment aqueous dispersion B3 and other components shown in the composition C4, the respective components were mixed so that the composition C4 was obtained. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink C4 which is a cyan ink composition.

~ Composition C4 of ink C4 ~
・ Cyan pigment (CI pigment blue 15: 3) ・ ・ ・ ・ 3%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.3%
・ Near-infrared absorbing pigment dispersion A1... 2.6%
-Self-dispersing polymer particle C-1 ... 8.2%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 [manufactured by Sanyo Chemical Industries, water-soluble organic solvent] ... 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink M5)
Using the magenta pigment aqueous dispersion B2, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition M5, the respective components were mixed so as to be the composition M5. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M5, which is a magenta ink composition.

~ Composition M5 of ink M5
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near infrared absorbing pigment dispersion A1 ・ ・ ・ ・ 0.9%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 [manufactured by Sanyo Chemical Industries, water-soluble organic solvent] ... 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of ink M6)
Using the magenta pigment aqueous dispersion B2, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition M6, the respective components were mixed so as to be the composition M6. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M6, which is a magenta ink composition.

~ Composition M6 of ink M6 ~
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Near-infrared absorbing pigment dispersion A1... 0.95%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 [manufactured by Sanyo Chemical Industries, water-soluble organic solvent] ... 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle size 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

<Ink preparation of Comparative Examples 1 to 5>
(Preparation of near-infrared absorbing pigment dispersion A4)
Each component of the following composition A4 was mixed and dispersed for 4 hours using 0.1 mmφ zirconia beads by a bead mill. Using a 50 mL centrifuge, centrifugation was performed at 5000 rpm for 5 minutes, and the supernatant other than the precipitate was collected. When the volume average particle size was measured by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.), it was 180 nm. Thereafter, the pigment concentration was determined from the absorbance spectrum, and ion-exchanged water was added to obtain a near-infrared absorbing dye dispersion A4 as a dispersion having a dye concentration of 6.3% by mass.

-Composition A4-
・ Near infrared absorbing dye (IR-1) [specific IR dye] ... 10%
・ Sodium oleate (10% aqueous solution) [Surfactant] ... 30%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink Y5)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y5 were used, and the respective components were mixed so as to obtain the composition Y5. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink Y5 which is a yellow ink composition.

~ Composition Y5 of ink Y5
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near infrared absorbing pigment dispersion A4 ・ ・ ・ ・ 2.5%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea ・ ・ ・ ・ 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ... 1.5%
・ Ion-exchanged water: 100% of the total amount

(Preparation of near-infrared absorbing dye solution D1)
4 g of near-infrared absorbing dye (IR-1) was dissolved in 96 g of 2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain a solution D1.

(Preparation of ink Y6)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y6 were used, and the respective components were mixed so as to obtain the composition Y6. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink Y6, which is a yellow ink composition.

~ Composition Y6 of ink Y6 ~
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
・ Near infrared absorbing dye solution D1 ・ ・ ・ ・ 3%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea: 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink Y7)
The yellow pigment aqueous dispersion B1, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition Y7 were used, and the respective components were mixed so as to obtain the composition Y7. This was packed in a plastic disposable syringe and filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink Y7 which is a yellow ink composition.

~ Composition Y7 of ink Y7 ~
・ Yellow pigment (CI Pigment Yellow 74) ・ ・ ・ ・ 4%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.8%
-Self-dispersing polymer particle C-1 ... 6.5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea: 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink M7)
Using the magenta pigment aqueous dispersion B2, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition M7, the respective components were mixed so as to be the composition M7. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink M7 which is a magenta ink composition.

~ Composition M7 of ink M7 ~
・ Magenta pigment (CI Pigment Red 122) ・ ・ ・ ・ 6%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 2%
・ Self-dispersing polymer particles C-1 ... 5%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea: 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

(Preparation of ink C5)
Using the cyan pigment aqueous dispersion B3, the aqueous dispersion of the self-dispersing polymer particles C-1 and other components shown in the composition C5, the respective components were mixed so as to be the composition C5. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain ink C5, which is a cyan ink composition.

~ Composition C5 of ink C5
・ Cyan pigment (CI pigment blue 15: 3) ・ ・ ・ ・ 3%
・ Water-insoluble resin P-1 ・ ・ ・ ・ 1.3%
-Self-dispersing polymer particle C-1 ... 8.2%
・ Tripropylene glycol monomethyl ether (TPGmME) ... 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Dipropylene glycol (DPG) ・ ・ ・ ・ ・ 2.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, water-soluble organic solvent) ・ ・ 10.0%
・ Urea: 5.0%
・ Colloidal silica (solid content) ・ ・ ・ ・ 0.01%
[Snowtex XS, solid content concentration 20%, volume average particle diameter 5 nm, manufactured by Nissan Chemical Industries, Ltd.] Olfin E1010 [manufactured by Nissin Chemical Industry Co., Ltd., surfactant] ・ ・ ・ 1.5%
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

<Preparation of treatment solution>
The component shown to composition S1 was mixed and the processing liquid 1 was prepared.

-Composition S1 of treatment liquid 1
・ Malonic acid ・ ・ ・ ・ 11.25%
DL-malic acid 14.5%
・ Diethylene glycol monobutyl ether (DEGmBE) ・ ・ ・ ・ 4.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
Tripropylene glycol monomethyl ether (TPGmME) 4.0%
[Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.]
・ Ion-exchange water ・ ・ ・ ・ Total amount of 100%

  About the obtained processing liquid 1, when pH was measured with Toa DDK Co., Ltd. product pH meter WM-50EG, pH value was 1.10. Further, the surface tension was measured by FASE Automatic Surface Tensionmeter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. and found to be 41.3 mN / m.

<Image formation 1> -With processing solution-
An ink jet head provided with a silicon nozzle plate was prepared, and the storage tank connected thereto was sequentially refilled with the ink composition of the example or the comparative example. A liquid repellent film formed using a fluorinated alkylsilane compound is provided in advance on the surface of the silicon nozzle plate.
Further, as the recording medium, a piece of paper obtained by cutting “OK Top Coat +” (basis weight 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd. into A5 size was used.

(Image forming step 1)
A piece of paper (recording paper) cut to 150 mm square was fixed on a stage movable in a predetermined linear direction at 500 mm / second, and the stage temperature was kept at 30 ° C. The treatment liquid 1 was applied to this with a bar coater so as to have a thickness of about 1.2 μm (1.5 g / m ² ), and dried immediately at 50 ° C. for 2 seconds. Thereafter, the ink jet head is fixedly disposed so that the direction of the line head (main scanning direction) in which the nozzles are aligned is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction of the stage (sub scanning direction), and the recording medium Is orthogonal to the paper grain direction (y direction in FIG. 4) in a line system with an ink droplet amount of 5.0 pL, a discharge frequency of 25.5 kHz, and a resolution of 1200 dpi × 1200 dpi while moving the ink at a constant speed in the sub-scanning direction. A stripe image having a width (y direction) of 50 mm and a length (x direction) of 140 mm was created in the direction (x direction in FIG. 4). In addition, dpi means “dot per inch”.

(Infrared irradiation process 1)
FIG. 3 is a schematic diagram showing a pattern of irradiating infrared rays on images formed in Examples and Comparative Examples. FIG. 3 shows an inkjet head (head 1) that discharges ink, infrared heaters 1 to 3 (IR1 to IR3), and hot air blowers 1 to 3 (HA1 to HA3) that eject hot air. . An arrow extending from left to right in FIG. 3 indicates that a recording medium on which an image is formed with head 1 is conveyed in the direction of the arrow. That is, FIG. 3 shows that the recording medium is subjected to infrared irradiation and hot air blowing while the recording medium is being conveyed.

  An infrared heater and a hot air blower were installed on the recording medium conveyance path as shown in FIG. 3 to dry the paper on which ink was deposited. As the infrared heater, a short wavelength infrared heater ZKG2400 / 340G manufactured by Heraeus Co. was used, and three halogen lamps having a maximum energy wavelength of 1.3 μm, an output of 2400 W, and a light emission length of 340 mm were used. As the hot air blower, three blowers for blowing air at an air temperature of 60 ° C. and an air speed of 5 m / s were used.

<Image formation 2> -Without processing solution-
An ink jet head provided with a silicon nozzle plate was prepared, and the storage tank connected thereto was sequentially refilled with the ink composition obtained above. A liquid repellent film formed using a fluorinated alkylsilane compound is provided in advance on the surface of the silicon nozzle plate.
Further, as the recording medium, a piece of paper obtained by cutting “OK Top Coat +” (basis weight 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd. into A5 size was used.

(Image forming step 2)
A piece of paper (recording paper) cut to 150 mm square was fixed on a stage movable in a predetermined linear direction at 500 mm / second, and the stage temperature was kept at 30 ° C. Thereafter, the ink jet head is fixedly disposed so that the direction of the line head (main scanning direction) in which the nozzles are aligned is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction of the stage (sub scanning direction), and the recording medium Is orthogonal to the paper grain direction (y direction in FIG. 4) in a line system with an ink droplet amount of 5.0 pL, a discharge frequency of 25.5 kHz, and a resolution of 1200 dpi × 1200 dpi while moving the ink at a constant speed in the sub-scanning direction A stripe image having a width (y direction) of 50 mm and a length (x direction) of 140 mm was created in the direction (x direction in FIG. 4).

(Infrared irradiation process 2)
Similar to the infrared irradiation step 1, the image formed on the recording medium was irradiated with infrared rays through the conveyance path shown in FIG.

<Evaluation>
~ Residual water measurement method ~
The amount of water contained in the dried printing paper was measured using a trace moisture measurement system CA-200 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) after punching out the printed portion of the paper with a size of 30 mm × 20 mm. Images were formed and measurements were taken within 2 minutes after drying. The measured moisture content [g] was divided by the punched area to calculate the moisture content [g / m ² ] per unit area.
Further, a residual water amount [g / m ² ] was defined as a value obtained by subtracting the amount of water held by the paper before printing from the above. The moisture content of the printing paper itself was separately measured using a white paper before image formation.
The same operation was repeated three times to produce three identical images, each of which was measured to calculate the average value of the three remaining water amounts [g / m ² ].
Based on the following evaluation criteria, the remaining water amount was evaluated from the calculated remaining water amount. The results are shown in Table 5.

<Evaluation criteria>
A: The amount of residual water is less than 0.5 g / m ² .
B: The amount of residual water is 0.5 g / m ² or more and less than 1 g / m ² .
C: The amount of residual water is 1 g / m ² or more and less than 2 g / m ² .
D: Residual water amount is 2 g / m ² or more

~ Paper curl evaluation method ~
FIG. 4 is a schematic diagram of a printing paper used for paper curl evaluation.
FIG. 4 shows a state in which an image portion 52 of a rectangular image having a vertical (x direction) 140 mm × horizontal (y direction) 50 mm is formed on a 150 mm square recording paper 54.
In the recording paper shown in FIG. 4, the grain direction (paper making direction) of the recording paper is the width direction (y direction) of the rectangular image. Further, the rectangular image shown in FIG. 4 was formed by the same method as the image forming 1 or the image forming 2 described above, except that the shape of the image was changed.

  In FIG. 4, the cockle in a straight line 56 portion in the direction (x direction) orthogonal to the grain direction (y direction) of the recording paper 54 was measured. When the cockle in the straight line 56 portion is schematically represented, it is shown as a curve shown in FIG. FIG. 5 is a graph showing the cross-sectional shape of the recording paper 54 when the recording paper 54 is cut along a straight line 56 as the displacement in the x and z directions. 4 and 5, the x direction is the same direction and is a direction orthogonal to the grain direction (y direction) of the recording paper 54. The z direction is the height direction of the wrinkles in the image portion 52 of the recording paper 54.

More specifically, the evaluation of the cockle is performed by forming the image shown in FIG. 4 and, within 2 minutes after drying, the ridge height Z of the recording paper 54 along the straight line 56 (displacement profile of the recording paper 54 in the z direction). Was measured with a laser displacement meter (Laser displacement meter LK-080 manufactured by Keyence). As an index representing the degree of cockle, the amount of cockle = (L′−L) / L was used.
The same operation was repeated three times to produce three identical images, each of which was measured to calculate the average value of the three amounts of cockle.

Here, L represents the measurement length (150 mm), L ′ is the path integral length of the displacement profile, and is calculated from the equation “L ′ = Σ√ (Δx _i ² + Δz _i ² )”.
Note that Δx _i and Δz _i in the equation are parameters shown in FIG.
Based on the amount of cockle calculated from (L′−L) / L, the evaluation of the cockle was performed according to the following evaluation criteria, and the evaluation results are shown in Table 5.
The range is C or more, preferably B or more, and most preferably A.

<Evaluation criteria>
A: The amount of cockle is less than 0.03%.
B: The amount of cockle is 0.03% or more and less than 0.07%.
C: The amount of cockle is 0.07% or more and less than 0.13%.
D: The amount of cockle is 0.13% or more.

~ Infrared absorbing dye dispersion stability in ink ~
The color reproducibility was evaluated from the evaluation of the infrared absorbing dye dispersion stability in the ink.
The ink compositions of Examples and Comparative Examples were stored at room temperature for 14 days in a storage tank connected to an inkjet head equipped with a silicon nozzle plate. Thereafter, ink near the bottom in the tank (hereinafter referred to as “ _under ink”) was sucked out with a dropper, and an image was formed using the ink _underneath . Similarly, suction ink (referred to _on the ink) in the vicinity of the ink liquid level in the tank was allowed to stand 14 days in a dropper, to form an image using the _above ink. The image forming method was the same as the image forming 1 or 2 described above. They were then compared with _under color of the image formed by using a _lower ink, and _the color of the image formed by using the _above ink.
The color of the image is measured by measuring L * a * b * with a spectrophotometer (SpectroEye manufactured by GRETAG MACBETH), and ΔE (= | color) based on the color of the image formed _on the ink. _Bottom -color _top |) was calculated and evaluated. The results are shown in Table 5.
It is considered that the color reproducibility of an image greatly depends on the infrared absorbing dye dispersion stability in the ink. The smaller the ΔE and the better the dispersion stability, the better the quick-drying of the image, and the effect of quick-drying that does not change even when the ink is stored for a long time can continue to be obtained. Further, it is considered that the hue change of the image is small, that is, the color reproducibility is excellent.

<Evaluation criteria>
A: ΔE is 3 or less.
B: ΔE is greater than 3.

  Table 5 shows the organic pigment when the content of the specific IR dye (shown as “IR dye” in the table) in the ink composition and the total mass of the near infrared absorbing dye is 1 (part). The ratio (parts) and the state of the specific IR dye during ink preparation are also shown.

Table 1 shows the composition outline of the near-infrared absorbing dye dispersions A1 to A4 and the near-infrared absorbing dye solution D1.
Further, Tables 2 to 4 show the composition outlines of the ink Y, the ink M, and the ink C used in Examples and Comparative Examples, respectively. In Tables 2 to 4, the numerical value shown in the “Pigment” column is the concentration in terms of pigment, not the amount that the “aqueous pigment dispersion” occupies in the ink.
Ink amounts of pigment aqueous dispersions B1 to B3 are 28.6% for yellow pigment aqueous dispersion B1 in Table 2, 42.9% for magenta pigment aqueous dispersion B2 in Table 3, and cyan pigment aqueous dispersion in Table 4. B3 is 21.4%.

As can be seen from Table 5, in Comparative Example 1 where the ink was prepared without using the polymer dispersant, it is presumed that the dispersibility of the specific IR dye is insufficient and color reproducibility cannot be obtained. Similarly, in Comparative Example 2 in which an ink was prepared using an organic solvent without using a polymer dispersant, the stability was not excellent. Furthermore, in the inks of Comparative Examples 3 to 5 that did not use the specific IR dye, cuckling occurred.
The inks of Examples 1 to 15 were excellent in both cockle and stability.

Claims (10)

  An ink composition comprising water, an organic pigment, a polymer dispersant that disperses a near-infrared absorbing dye, and a water-insoluble near-infrared absorbing dye having an absorption maximum wavelength of 700 nm to 1500 nm.   The ink composition according to claim 1, wherein a content of the near-infrared absorbing dye is 0.05% by mass to 0.3% by mass with respect to the total mass of the ink composition.   The ink composition according to claim 1, which is a colored ink composition.   The ratio between the organic pigment and the near-infrared absorbing dye (organic pigment: near-infrared absorbing dye) is 10: 1 to 100: 1 on a mass basis. Ink composition. The ink composition according to claim 1, wherein the near-infrared absorbing dye is represented by the following general formula (I) or the following general formula (II).

[In General Formula (I), A ¹ and A ² each independently represent a functional group represented by any one of the following General Formulas (1) to (5), and n ¹ and n ² are 0 or more. Represents an integer. Ar ¹ and Ar ² each independently represents an aryl group, and B ¹ , B ² , B ³ , B ⁴ , C ¹ , C ² , and C ³ are each independently a hydrogen atom, a halogen atom, an alkyl group, Represents an aryl group, an alkenyl group or an alkynyl group, and any two may form a ring. D ¹ and D ² each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, X ⁻ represents a counter anion, and Y ¹ , Y ² , Z ¹ and Z ² are each independently non- Represents a divalent linking group comprising a metal atom. ]

[In the general formula (1) ~ (5), L represents a polyvalent linking group comprising non-metal atom, R ¹ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group or a cyclic imido group, R ² , R ³ represents an alkyl group, an aryl group, an alkenyl group, or an alkynyl group, R ⁴ represents an alkyl group, an aryl group, an alkenyl group, an alkynyl group, or —SO ₂ —R ¹¹ , and R ⁵ , R ^6, and R ⁷ Each independently represents an alkyl group, an aryl group, an alkenyl group or an alkynyl group, one of R ⁸ and R ⁹ represents a hydrogen atom, the other represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group or an alkynyl group, R ¹⁰ represents an alkyl group, an alkenyl group or an alkynyl ^{group, R 11} is an alkyl group, an aryl group, an alkenyl group or an alkynyl ^group, R 5, ^{R 6} and ^{R 7} Any may be formed of two or three in ring, it may form a ring with ^{R 8} and ^{R 10} or ^{R 9} and ^{R 10.} X represents O or S. ]

[In general formula (II), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ each independently represent a hydrogen atom or a substituent, and at least one of the R _{1 to} R ₁₆ represents an R ₁₇ -X- group, or in the R _{1 to} R ₁₆ At least one structure in which two adjacent ones are condensed. X is, -S -, - NH -, - NR 18 -, or -O- and _{represents, R 17} and _{R 18} each independently represent an aliphatic group or an aryl group. M represents a divalent substituted metal atom including two atoms selected from the group consisting of a hydrogen atom and a monovalent metal atom, a divalent metal atom, or a trivalent or tetravalent metal atom. ]   The ink composition according to any one of claims 1 to 5, which is an inkjet ink.   The ink composition according to claim 6, which is a yellow ink.   An image having an image forming step of forming an image by applying the ink composition according to any one of claims 1 to 7 to a recording medium, and an infrared irradiation step of irradiating the formed image with infrared rays Forming method.   The image forming method according to claim 8, wherein the recording medium includes paper.   10. The image forming method according to claim 8, further comprising a treatment liquid application step of applying a treatment liquid containing an aggregation component that forms an aggregate when contacted with the ink composition to a recording medium.