JP6352213B2 - Ink composition, method for producing the same, and image forming method - Google Patents

Description

  The present invention relates to an ink composition, a method for producing the same, and an image forming method.

As an image recording method for recording a color image, a method using an ink jet technique is known. Conventionally, inkjet technology has been applied to fields such as office printers and home printers, but in recent years, it has been applied to commercial printing.
In the field of ink jet technology, ink containing pigment (that is, pigment ink) is widely used as ink (also referred to as “ink composition”).

In recent years, water-based inks that use water as an ink solvent have attracted attention in consideration of the environment.
However, the water-based ink has a problem that drying is slower than an ink using a solvent having a low boiling point such as an organic solvent. In order to solve this problem, various inks that can absorb infrared rays and accelerate drying by infrared irradiation have been proposed.

  For example, for the purpose of realizing quick drying of the ink, the ink has an absorption maximum wavelength of 700 nm to 1500 nm, and an absorption coefficient in a wavelength region of 400 nm to less than 700 nm is 10 of the absorption coefficient at the absorption maximum wavelength. It has been proposed to contain a near-infrared absorbing material that is not more than% (for example, see Patent Document 1).

  In the invisible ink field, various inks containing near-infrared absorbing materials have been proposed (see, for example, Patent Document 2).

Further, an ink composition containing a polymer dispersant that disperses a near-infrared absorbing dye together with a near-infrared absorbing dye has been proposed as an ink composition that suppresses paper cockle and hardly impairs the color of an image ( For example, see Patent Document 3).
Moreover, as an ink composition having the same effect as the invention described in Patent Document 3, the ink composition contains a specific near-infrared-absorbing dye that generates a large amount of heat due to decomposition during infrared absorption and that dries the ink composition quickly. Has been proposed (see, for example, Patent Document 4).

  Near-infrared irradiation can quickly fix the color material on the recording medium. As an ink excellent in scratching, drying and ejection properties, a water-insoluble near-infrared absorber is converted into water-dispersible resin particles. A water-based ink that is adsorbed or encapsulated and dispersed has been proposed (see, for example, Patent Document 5).

JP 2001-226618 A JP 2008-255323 A Japanese Patent Application Laid-Open No. 2014-0473302 JP, 2014-0473303, A JP 2013-189596 A

The near-infrared absorbing dye absorbs infrared rays when irradiated with infrared rays, and has a function of converting the absorbed infrared rays into heat, so that an ink composition containing a near-infrared absorbing dye is used on a recording medium. The image formed on the substrate can be efficiently heated and dried.
However, in general, near-infrared absorbing dyes also have absorption in the visible light wavelength range, so when an image is formed using an ink composition containing near-infrared absorbing dyes, the color caused by the near-infrared absorbing dyes. Tends to cause so-called color turbidity that overlaps with the inherent color of the ink and causes a change in color.

Regarding the above-mentioned points, the cyanine-based near-infrared absorbing dye used in the ink compositions described in Patent Documents 3 and 4 has a large color turbidity, particularly when it is used for yellow ink, and becomes greenish. There is a problem that a vivid image cannot be obtained.
In addition, since the water-based ink described in Patent Document 5 needs to contain a large amount of near-infrared absorbing agent (that is, a near-infrared absorbing dye), the coloring of the original ink is caused by coloring caused by the near-infrared absorbing dye. It becomes a different color from the above, and a vivid image cannot be obtained. In the water-based ink described in Patent Document 5, the reason for using a large amount of the near-infrared absorbing dye is not clear, but many of the near-infrared absorbing dyes are relatively unstable. In the process of adsorbing or encapsulating resin fine particles, near infrared absorbing dyes are decomposed by receiving strong energy, or near infrared rays are absorbed by the near infrared absorbing dyes due to the effect of light scattering generated on the surface of resin fine particles. It may be because it is difficult.
And the near-infrared absorption material (namely, near-infrared absorption pigment | dye) described in patent document 1 is difficult to synthesize | combine, has no practicality, and cannot be said to be stable enough. Moreover, the near-infrared absorbing material (that is, the near-infrared absorbing dye) described in Patent Document 2 is a cyanine-based near-infrared absorbing dye as in Patent Document 3, and has a large color turbidity. Note that the ink described in Patent Document 2 is an ink that is used for invisible use and contains almost no organic pigment, so that the color of the image is not considered in the first place.

This invention is made | formed in view of the above situations, and makes it a subject to achieve the following objectives.
That is, an object of the present invention is to provide an ink composition that is less likely to impair the color of an image, can suppress the clogging of a recording medium such as paper, and has excellent storage stability, and a method for producing the same. .
It is another object of the present invention to provide an image forming method that hardly impairs the color of an image and that can suppress clogging of a recording medium such as paper.

  Specific means for solving the problems include the following aspects.

<1> As a near-infrared absorbing dye, containing a diimonium salt compound represented by the following general formula (1), a polymer dispersant covering at least a part of the diimonium salt compound, a colorant, and water,
The content of the diimonium salt compound is 0.001% by mass to 0.9% by mass with respect to the total mass of the ink composition,
The acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy XY ≧ 10, and
The ratio of the content of the polymer dispersant to the content of the dimonium salt compound (content of the polymer dispersant / content of the dimonium salt compound) is 0.05 to 1.2 on a mass basis. Ink composition.

In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each represents an organic group which may be the same or different, and X ⁻ Represents an anion.

<2> The ink composition according to <1>, wherein the polymer dispersant has an acid value X of 30 mgKOH / g or more.

<3> The ink composition according to <1> or <2>, wherein the polymer dispersant is a star polymer.

<4> In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ are each independently an alkyl group having 4 to 8 carbon atoms < The ink composition according to any one of 1> to <3>.

<5> The ink composition according to any one of <1> to <4>, wherein X ⁻ in the general formula (1) is an anion having at least one fluorine atom.

<6> X in the general formula (1) ^- is, PF ₆ ^-, anions represented by the following general formula (2), or an anion represented by the following general formula (3) <1> to <5 > The ink composition according to any one of

In general formula (2), R ⁹ and R ¹⁰ may be the same or different and each represents a fluorinated alkyl group having at least one fluorine atom.

In General Formula (3), R ¹¹ and R ¹² may be the same or different and each represents a fluorinated alkyl group having at least one fluorine atom.

<7> The ink composition according to any one of <1> to <6>, which is a yellow ink or a magenta ink.

<8> The ink composition according to any one of <1> to <7>, which is used as an inkjet recording ink.

<9> At least a diimonium salt compound represented by the following general formula (1) as a near-infrared absorbing dye, a polymer dispersant that covers at least a part of the diimonium salt compound, and a medium containing water are mixed. Mixing step to obtain an aqueous mixture,
Dispersing the aqueous mixture obtained in the mixing step to obtain an aqueous dispersion in which the near-infrared absorbing dye is dispersed with the polymer dispersant, and at least the aqueous obtained in the dispersing step A method for producing an ink composition comprising a preparation step of preparing an ink composition by mixing a dispersion and a colorant.

In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each represents an organic group which may be the same or different, and X ⁻ Represents an anion.

<10> An image forming step of forming an image by applying the ink composition according to any one of <1> to <8> to a recording medium;
An infrared irradiation step of irradiating an infrared ray having a maximum emission wavelength in a wavelength region of 700 nm to 1,600 nm with respect to the image formed in the image forming step;
An image forming method comprising:

<11> The image forming method according to <10>, wherein the recording medium includes paper.

ADVANTAGE OF THE INVENTION According to this invention, the ink composition which is hard to impair the color of an image, can suppress the cuckling of recording media, such as paper, and is excellent in storage stability, and its manufacturing method are provided.
In addition, according to the present invention, there is provided an image forming method that hardly impairs the color of an image and that can suppress the clogging of a recording medium such as paper.

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 of the recording paper used in the examples. It is a schematic diagram which shows the pattern which irradiates infrared rays to the image formed using the ink composition of an Example and a comparative example. 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.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. can do.

In the present specification, a numerical range indicated using “to” means a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In this specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. Means.

  In this specification, the term “process” is not limited to an independent process, and is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. It is.

  In the present specification, in the notation of substituents (atomic groups), the notation that does not indicate substitution and non-substitution is used in the meaning including those having further substituents together with the unsubstituted ones, unless otherwise specified. The For example, when describing as “alkyl group”, the alkyl group is used in a meaning including an unsubstituted alkyl group and an alkyl group further having a substituent. The same applies to other substituents (atomic groups).

  In the present specification, “(meth) acrylic acid” is a concept including both acrylic acid and methacrylic acid, “(meth) acrylate” is a concept including both acrylate and methacrylate, and “( “Meth) acryloyl” is a concept that encompasses both acryloyl and methacryloyl.

  In the present specification, “cuckle” is also called “cockling” or “wave ring”, and refers to a phenomenon in which the surface of a recording medium becomes finely wrinkled when printing on a recording medium such as paper.

[Ink composition]
The ink composition of the present invention (hereinafter also simply referred to as “ink”) is a diimonium salt compound represented by the following general formula (1) as a near infrared absorbing dye (hereinafter also referred to as “specific diimonium salt compound”). And a polymer dispersing agent (hereinafter also simply referred to as “polymer dispersing agent”), a colorant, and water covering at least a part of the specific diimonium salt compound, and the content of the specific diimonium salt compound is 0.001% by mass to 0.9% by mass with respect to the total mass of the composition, and the acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy XY ≧ 10, The ratio of the content of the polymer dispersant to the content of the specific dimonium salt compound (content of the polymer dispersant / content of the specific dimonium salt compound) is 0.05 to 1.2 on a mass basis. Composition A.

In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each represents an organic group which may be the same or different, and X ⁻ Represents an anion.

The ink composition of the present invention is less likely to impair the color of an image, can suppress clogging of a recording medium such as paper, and is excellent in storage stability.
The reason why the ink composition of the present invention can exhibit such an effect is not clear, but the present inventors presume as follows.

In general, near-infrared absorbing dyes also have absorption in the visible light wavelength range, so that the color caused by the near-infrared absorbing dye overlaps with the inherent color of the ink, causing a change in color. Easy to cause color turbidity.
The diimonium salt compound, which is a near-infrared absorbing dye, has little visible light absorption and is advantageous in terms of color turbidity, but is hardly soluble in water, so when used in water-based inks, methods such as dispersion and emulsification It is necessary to introduce into an aqueous medium.
However, since the diimonium salt compound is difficult to disperse and easily aggregates and settles, the amount of infrared absorption decreases with the passage of time. In addition, the distribution of the diimonium salt compound in the aqueous medium becomes non-uniform and cannot be dried uniformly. As a result, there is a problem in that the amount of heat generated by the diimonium salt compound is reduced and the drying property of the ink is deteriorated. When the drying property of the ink is deteriorated, it is not preferable because the recording medium such as paper tends to be clogged.

In contrast, the present inventors easily disperse diimonium salt compounds that are difficult to disperse by using a polymer dispersant having a specific acid value and base number as a dispersant for the specific diimonium salt compound, It has been found that it can be stably introduced into water-based inks.
That is, in the ink composition of the present invention, a specific diimonium salt compound as a near-infrared absorbing pigment, and a polymer dispersant in which an acid value X mgKOH / g and a base value Y mgKOH / g satisfy XY ≧ 10. By containing, the specific diimonium salt compound is well dispersed by the polymer dispersing agent, and thus the storage stability is excellent.
Further, since the specific dimonium salt compound is favorably dispersed by the polymer dispersant, the specific dimonium salt compound efficiently absorbs infrared rays and generates heat. As a result, the amount of solvent (for example, the amount of residual water) after image formation can be quickly reduced, and when paper is used as the recording medium, it is possible to suppress cockle.

Further, as described above, in the ink composition of the present invention, since the dispersibility of the specific diimonium salt compound is good, the drying property is high even if the specific diimonium salt compound is small.
In the ink composition of the present invention, when the content of the specific diimonium salt compound is 0.001% by mass to 0.9% by mass with respect to the total mass of the ink composition, the color resulting from the specific diimonium salt compound. Since turbidity is suppressed, it is difficult to impair the color of the image.

Further, as described above, since the diimonium salt compound is liable to cause aggregation or the like, when an ink containing the diimonium salt compound is used as an ink for ink jet recording, there is a problem that the discharge property is deteriorated.
In the ink composition of the present invention, the ratio of the content of the polymer dispersant in which the acid value X mgKOH / g and the base value Y mgKOH / g satisfy XY ≧ 10 with respect to the content of the specific diimonium salt compound is By being 0.05 to 1.2 on the basis of mass, the inkjet discharge property is also excellent.

[Diimonium salt compound represented by general formula (1)]
The ink composition of the present invention contains at least one diimonium salt compound (that is, a specific diimonium salt compound) represented by the general formula (1) as a near-infrared absorbing dye.
The specific diimonium salt compound is dispersed in the ink composition.
The specific dimonium salt compound can efficiently absorb near infrared rays and generate heat. Since the ink composition of the present invention contains the specific diimonium salt compound, the amount of the solvent in the image area formed on the recording medium is rapidly reduced and the drying property is increased. Suppression is possible.

In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ represent an organic group and may be the same or different.
The organic group is not particularly limited. Preferred organic groups include linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, cyclohexyl alkyl groups having 1 to 10 carbon atoms in the alkyl moiety, and phenyls having 1 to 10 carbon atoms in the alkyl moiety. An alkyl group etc. are mentioned. The organic group may be a halogenated alkyl group in which hydrogen is replaced with a halogen atom among carbon-hydrogen bonds of these alkyl groups.

Examples of the alkyl group having 1 to 10 carbon atoms include methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, and n-amyl. Group, iso-amyl group, 1-methylbutyl group, 2-methylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 2-dimethylpropyl group, 1,1-dimethylpropyl group, n-pentyl, neopentyl group, n- A hexyl group, a cyclohexyl group, etc. are mentioned.
Among these, as an alkyl group having 1 to 10 carbon atoms, an n-propyl group, an n-butyl group, an n-pentyl, an n-hexyl, or an iso-butyl group is particularly preferable because of easy synthesis. .

Examples of the halogenated alkyl group having 1 to 10 carbon atoms include 2-halogeno group, 2,2-dihalogenoethyl group, 2,2,2-trihalogenoethyl group, 3-halogenopropyl group, and 3,3-dihalogeno group. Propyl group, 3,3,3-trihalogenopropyl group, 4-halogenobutyl group, 4,4-dihalogenobutyl group, 4,4,4-trihalogenobutyl group, 5-halogenopentyl group, 5,5- A dihalogenopentyl group, a 5,5,5-trifluoropentyl group, etc. are mentioned.
Specific examples include monofluoroalkyl groups such as 2-fluoroethyl group, 3-fluoropropyl group, 4-fluorobutyl group and 5-fluoropentyl group, preferably 3-fluoropropyl group, 4-fluorobutyl. Group or a 5-fluoropentyl group, particularly preferably a 3-fluoropropyl group.

  The cyclohexylalkyl group can be represented by the following general formula (4).

In General formula (4), A represents a C1-C10 alkylene group, and it is preferable that it is a C1-C4 alkylene group from a viewpoint of the availability of a raw material.
In the general formula (4), R ²² represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and is preferably a hydrogen atom or a methyl group from the viewpoint of availability of raw materials.

  Examples of the cyclohexylalkyl group represented by the general formula (4) include a cyclohexylmethyl group, a cyclohexylethyl group, a cyclohexylpropyl group, a cyclohexylbutyl group, a methyl 2-ethylcyclohexylmethyl group, a 3-methylcyclohexylmethyl group, and a 4-methylcyclohexyl group. A methyl group, a 4-methylcyclohexylethyl group, a 4-methylcyclohexylpropyl group, a 4-methylcyclohexylbutyl group, a 4-fluorocyclohexylmethyl group and the like can be mentioned. From the viewpoint of availability of raw materials, a cyclohexylmethyl group is preferable.

  The phenylalkyl group can be represented by the following general formula (5).

In General formula (5), B represents a C1-C10 alkylene group, and it is preferable that it is a C1-C4 alkylene group from a viewpoint of the availability of a raw material.
In General Formula (5), R ²³ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and is preferably a hydrogen atom or a methyl group from the viewpoint of availability of raw materials.

  Specific examples of the phenylalkyl group represented by the general formula (5) include a benzyl group, a methylbenzyl group, an ethylbenzyl group, a propylbenzyl group, and a butylbenzyl group.

Among the above, the organic groups represented by R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ are each independently a straight chain from the viewpoint of storage stability. Or a branched alkyl group having 1 to 10 carbon atoms is preferable, and an alkyl group having 4 to 8 carbon atoms is more preferable.
The organic groups represented by R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ may be the same or different and are easy to synthesize. R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , and R ⁷ and R ⁸ are each preferably the same group combination, and R ¹ , R ² , R ³ , R ⁴ , It is particularly preferred that all the organic groups represented by R ⁵ , R ⁶ , R ⁷ and R ⁸ are the same.

In the general formula (1), X ⁻ represents an anion.
2X ⁻ may represent a divalent anion.
The anion represented by X ⁻ is a counter anion necessary for neutralizing the charge of the cation of the specific diimonium salt compound.
X ^- include anions represented by the inorganic anion, organic acid anion, and the like.

Specific examples of the anion represented by X ⁻ include F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , HO ⁻ , CN ⁻ , SO ₄ ²⁻ , HSO ₄ ⁻ , SO ₃ ²⁻ , and 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.
Moreover, as an anion represented by X ⁻ , anions specifically shown in paragraphs [0039] to [0048] of Japanese Patent No. 3627903 are also preferable examples.
Among these, as the anion represented by X ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , CN ⁻ , SO ₄ ²⁻ , PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ^{− are used} from the viewpoint of availability of raw materials. , Sulfonate anion, carboxylate anion, phosphonate anion, or phosphate anion.

The anion represented by X ⁻ is more preferably an anion having at least one fluorine atom, and is represented by PF ₆ ⁻ , an anion represented by the following general formula (2), or the following general formula (3). More preferred is an anion.
X ^- When anion represented by is an anion having at least one fluorine atom, because the degradation of specific diimmonium salt compound by reaction with water is suppressed, the storage stability of the ink is further improved.

In the general formula (2), R ⁹ and R ¹⁰ represent a fluorinated alkyl group having at least one fluorine atom, and may be the same or different.
The fluorinated alkyl group represented by R ⁹ and R ¹⁰ is preferably a fluorinated alkyl group having 1 to 12 carbon atoms in the alkyl moiety.
The number of fluorine atoms contained in the fluorinated alkyl group is preferably 1 to 25, more preferably 3 to 9, and still more preferably 3.
Specific examples of the fluorinated alkyl group represented by R ⁹ and R ¹⁰ include a perfluoroalkyl group having 1 to 12 carbon atoms in the alkyl moiety, a monofluoromethyl group, a difluoromethyl group, 2,2,2 -Trifluoroethyl group, 3,3,4,4,4-pentafluorobutyl group, 2,2,3,3,4,4,4-heptafluorobutyl group and the like.
The fluorinated alkyl groups represented by R ⁹ and R ¹⁰ are preferably the same since synthesis is easy.

In the general formula (3), R ¹¹ and R ¹² represent a fluorinated alkyl group having at least one fluorine atom, and may be the same or different.
The fluorinated alkyl group represented by R ¹¹ and R ¹² is preferably a fluorinated alkyl group having 1 to 12 carbon atoms in the alkyl moiety.
The number of fluorine atoms contained in the fluorinated alkyl group is preferably 1 to 25, more preferably 3 to 9, and still more preferably 3.
Specific examples of the fluorinated alkyl group represented by R ¹¹ and R ¹² include a perfluoroalkyl group having 1 to 12 carbon atoms in the alkyl moiety, a monofluoromethyl group, a difluoromethyl group, 2,2,2 -Trifluoroethyl group, 3,3,4,4,4-pentafluorobutyl group, 2,2,3,3,4,4,4-heptafluorobutyl group and the like.
The fluorinated alkyl groups represented by R ¹¹ and R ¹² are preferably the same since synthesis is easy.

  Specific examples (DI-1 to DI-4) of the diimonium salt compound represented by the general formula (1) (that is, the specific diimonium salt compound) are shown below, but the specific diimonium salt compound is limited to these. It is not a thing.

  The specific dimonium salt compound can be synthesized by a conventionally known method, for example, the method described in JP-B No. 43-25335.

The content of the specific diimonium salt compound in the ink composition of the present invention is 0.001% by mass to 0.9% by mass with respect to the total mass of the ink composition.
When the content of the specific dimonium salt compound is 0.001% by mass or more based on the total mass of the ink composition, the ink composition can be quickly dried.
Moreover, coloring of the ink composition resulting from a specific diimonium salt compound can be suppressed because content of a specific diimonium salt compound is 0.9 mass% or less with respect to the total mass of an ink composition.
The content of the specific diimonium salt compound in the ink composition of the present invention is preferably 0.005% by mass to 0.5% by mass with respect to the total mass of the ink composition, and 0.01% by mass to 0%. More preferably, it is 1% by mass.

(Polymer dispersant)
The ink composition of the present invention contains at least one polymer dispersant that covers at least a part of the specific diimonium salt compound described above.
In the present specification, “covering at least a part of the diimonium salt compound” means coating a part of the diimonium salt compound present as a dispersion in the ink.
In the polymer dispersant contained in the ink composition of the present invention, the acid value X mgKOH / g and the base value Y mgKOH / g satisfy XY ≧ 10.
The ink composition of the present invention contains the polymer dispersant as described above, so that the specific diimonium salt compound is sufficiently and stably dispersed in the water-based ink composition. Drying can be realized, and as a result, recording medium such as paper can be suppressed.
In the present specification, the “polymer” in the polymer dispersant means that the weight average molecular weight (Mw) is 3,000 or more.

As the polymer dispersant, a water-insoluble polymer dispersant is preferable from the viewpoint of storage stability and dischargeability when used as an ink for inkjet recording.
In this specification, “water-insoluble” of a water-insoluble polymer means that when the polymer is dried under reduced pressure at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the amount dissolved is 5. It means less than 0 g.

The water-insoluble polymer dispersant is not particularly limited as long as it can disperse at least the specific diimonium salt compound and the colorant and satisfies XY ≧ 10. Can be used.
The water-insoluble polymer dispersant preferably includes a structural unit having an acidic group in order to coat at least a part of the specific diimonium salt compound and stably disperse the specific diimonium salt compound.
The acidic group is preferably a group having an acid dissociation constant (pKa) in water of 10 or less. For example, the acidic group is at least one selected from a carboxy group, a sulfonic acid group, a phosphoric acid group, an acetoacetyl group, and a phenol group. It is preferable that Among these, from the viewpoint of dispersion stability, the acidic group is more preferably a carboxy group.
The structural unit having an acidic group contained in the water-insoluble polymer dispersant may be only one kind or two or more kinds.

  Specific examples of the structural unit having an acidic group are shown below, but the present invention is not limited thereto. Among the following specific examples, as the structural unit having an acidic group, (M-4), (M-10), (M-13), and (M-17) are preferable from the viewpoint of dispersion stability. (M-4) and (M-13) are more preferable.

In addition to the structural unit having an acidic group, the water-insoluble polymer dispersant contains at least one structural unit selected from a structural unit having a basic group, a hydrophobic structural unit, and a hydrophilic structural unit. It is preferable that it is comprised.
Examples of the structural unit having a basic group include, for example, a general formula —NR ⁱ R ⁱⁱ (wherein R ⁱ and R ⁱⁱ each independently represent a hydrocarbon group which may contain a hydrogen atom or a hetero atom, and are the same Or R ⁱ and / or R ⁱⁱ may be bonded to form a cyclic structure.), And a structural unit having a structure represented by:
The structural unit having a basic group contained in the water-insoluble polymer dispersant may be only one kind or two or more kinds.
As a monomer that forms a structural unit having a structure represented by the general formula -NR ⁱ R ⁱⁱ , (meth) acryloyloxypropyldimethylamine, (meth) acryloyloxyethyldimethylamine, (meth) acryloyloxypropyldiethylamine, ( And (meth) acryloyloxyethyl diethylamine.

Examples of the monomer that forms the hydrophobic structural unit include styrene monomers, alkyl (meth) acrylates, aromatic group-containing (meth) acrylates, and the like.
The monomer forming the hydrophilic structural unit is not particularly limited as long as it is a monomer containing a hydrophilic group. Examples of the hydrophilic group include a nonionic group such as a hydroxyl group, a group having a structure derived from an alkylene oxide polymer (for example, polyethylene oxide and polypropylene oxide), and a salt of the above acidic group (for example, a lithium salt, a sodium salt, or a potassium salt). Salts, calcium salts, magnesium salts, ammonium salts, and primary to tertiary amine salts).
The hydrophilic structural unit contained in the water-insoluble polymer dispersant may be only one type or two or more types.
From the viewpoint of dispersion stability, the hydrophilic structural unit is preferably in a form containing at least an alkali metal salt of a carboxy group, and is a form containing both a nonionic group and an alkali metal salt of a carboxy group. Is also preferable.

  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- (meta ) Acrylic acid copolymer, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, styrene-maleic acid copolymer and the like.

  The polymer dispersant is preferably a vinyl polymer containing a carboxy group from the viewpoint of dispersion stability, has a structural unit derived from at least an aromatic group-containing monomer as a hydrophobic structural unit, and is hydrophilic. More preferred is a vinyl polymer having a structural unit containing a carboxy group as the structural unit of the nature.

The structure of the polymer dispersant is not particularly limited. Examples of the structure of the polymer dispersant include a random structure, a block structure, a comb structure, and a star structure.
The polymer dispersant is particularly preferably a star polymer having a star structure from the viewpoint of dispersion stability of the specific diimonium salt compound.
In the present specification, the “star polymer” means a polymer in which three or more polymer chains (that is, arm polymers) are radially branched from the center. Star polymers include so-called normal star polymers with the same type of arm polymer, as well as asymmetric star polymers with different types and molecular weights of each arm polymer, and arm polymers with a graft structure or hyperbranch structure are also asymmetric. Included in type polymers.

In the polymer dispersant, the acid value X mgKOH / g and the base value Y mgKOH / g satisfy XY ≧ 10, preferably 200 ≧ XY ≧ 15, more preferably 120 ≧ XY ≧ 30 and more preferably 70 ≧ X−Y ≧ 50.
When the acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy XY ≧ 10, the dispersion stability of the specific diimonium salt compound is improved, so that the storage stability of the ink is improved. It will be excellent.
In the present specification, the “acid value” represents an acid value per 1 g of the solid content of the polymer dispersant, and can be determined by potentiometric titration according to JIS K 0070 (1992).
In the present specification, the “base number” represents a base number per gram of the solid content of the polymer dispersant, obtained by a potentiometric titration method using a 0.1 mon / L hydrochloric acid aqueous solution, and then hydroxylated. It can be determined by converting to an equivalent of potassium. The “base number” is also generally referred to as “amine number”.
When using a plurality of polymer dispersants, it can be expressed as the weight average.
As described later, commercially available products can be used as the polymer dispersant. When the polymer dispersant is a commercial product, the catalog data of the commercial product is preferentially adopted.

The acid value X of the polymer dispersant is preferably 15 mgKOH / g or more, more preferably 30 mgKOH / g or more, and further preferably 50 mgKOH / g or more.
When the acid value X of the polymer dispersant is 15 mgKOH / g or more, the specific diimonium salt compound can be coated more favorably.
Further, the acid value X of the polymer dispersant is preferably 200 mgKOH / g or less, more preferably 120 mgKOH / g or less, and further preferably 70 mgKOH / g or less.
When the acid value X of the polymer dispersant is 200 mgKOH / g or less, the dispersion stability of the specific diimonium salt compound becomes better, so that the storage stability and ejection property of the ink are further improved.
Further, the base number Y of the polymer dispersant is not particularly limited, and may be, for example, 0 mgKOH / g.

  A commercially available product can be used as the polymer dispersant. Examples of commercially available polymer dispersants include DISPERBYK (registered trademark) series 190 (X: 10, Y: 0, XY = 10, block copolymer), 191 (X: 30, Y: 20). , XY = 10), 194 (X: 70, Y: 0, XY = 70), 2015 (X: 10, Y: 0, XY = 10, acrylic copolymer), 2090 ( X: 61, Y: 0, XY = 61, star polymer), 2091 (X15, Y: 0, XY = 15, star polymer), 2095 (X: 36, Y: 0, XY = 36, salt of polyamine / amide and polyester), etc. [above, manufactured by Big Chemie Japan Co., Ltd.], TEGO Disperse (registered trademark) series 651 (X: 30, Y: 0, XY = 30, both ether type) Polymer), 655 (X: 190, Y: 0, X Y = 190, ester copolymer), 715W (X: 120, Y: 0, XY = 120, sodium salt of acrylic copolymer), 750W (X: 10, Y: 0, XY) = 10), 755W (X: 10, Y: 0, XY = 10), etc. [above, manufactured by Evonik Japan Ltd.].

The weight average molecular weight (Mw) of the polymer dispersant is preferably 3,000 to 1,000,000, more preferably 5,000 to 500,000, from the viewpoint of dispersion stability of the specific diimonium salt compound. More preferably, it is 8,000-100,000.
The weight average molecular weight (Mw) of the polymer dispersant is a value measured by gel permeation chromatography (GPC) under the following conditions.

~conditions~
Measuring device: High-speed GPC HLC-8020 GPC (Tosoh Corporation)
Detector: differential refractometer (RI) RI-8020 (Tosoh Corporation)
Column: TSKgeL Super Multipore HZ-H (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation) is used. Column temperature: 40 ° C.
Eluent: Tetrahydrofuran (THF)
Sample concentration: 0.45 mass%
Injection volume: 10 μL
Flow rate: 0.35 mL / min

  The calibration curve is “Standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”. , “A-2500”, “A-1000”, and “n-propylbenzene”.

Ratio of content of polymer dispersant to content of specific diimonium salt compound in ink composition of the present invention (content of polymer dispersant / content of specific diimonium salt compound) 0.05 to 1 on a mass basis .2, preferably 0.1 to 1.0, and more preferably 0.3 to 0.8.
When the ratio of the content of the polymer dispersant to the content of the specific diimonium salt compound in the ink composition of the present invention is within the above range, the specific diimonium salt compound is sufficiently and stably dispersed in the ink composition. Therefore, the ink composition can be quickly and uniformly dried, and as a result, the recording medium such as paper can be prevented from being clogged. In addition, when the ink composition of the present invention is used as an ink for ink jet recording, excellent ejection stability can be obtained.

  Further, the content of the polymer dispersant in the ink composition of the present invention is preferably 5% by mass with respect to the total mass of the colorant described later, from the viewpoint of dischargeability when used as an ink for inkjet recording. It is -200 mass%, More preferably, it is 10 mass%-100 mass%, More preferably, it is 20 mass%-80 mass%.

<Colorant>
The ink composition of the present invention contains a colorant.
The ink composition of the present invention may contain a colorant alone or in combination of two or more.
The colorant is not particularly limited, and can be arbitrarily selected from known colorants such as pigments and water-soluble dyes. Among these, it is more preferable to include a pigment from the viewpoint of excellent weather resistance and rich color reproducibility.

There is no restriction | limiting in particular as a pigment, According to the objective, it can select suitably, For example, a well-known organic pigment and an inorganic pigment are mentioned.
Examples of organic pigments and inorganic pigments include yellow pigments (yellow pigments), red pigments, magenta pigments, blue pigments, cyan pigments, green pigments, orange pigments, purple pigments, brown pigments, black pigments, and white pigments. .

  Regarding colorants such as pigments, paragraphs [0180] to [0188] of JP-A No. 2014-040529 can be appropriately referred to.

  Examples of the pigment include commercially available pigment dispersions and surface-treated pigments. For example, a resin-coated pigment in which all or part of the surface of the pigment is coated with a water-insoluble resin is used from the viewpoints of dispersion stability and ejection reliability of the ink composition, and abrasion resistance and light resistance of the formed image. Therefore, it is preferable.

  The resin-coated pigment can be produced by a conventional physical or chemical method using a water-insoluble resin, a pigment or the like. 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 of the method for producing a resin-coated pigment include phase inversion emulsification methods and acid precipitation methods described in JP-A-9-151342 and JP-A-10-140065. Among these, From the viewpoint of dispersion stability, the phase inversion emulsification method is preferred.

The phase inversion emulsification method is basically a self-dispersion (phase inversion emulsification) method in which a mixed melt of a water-insoluble resin having self-dispersibility or solubility and a pigment is dispersed in water. The mixed melt may contain a curing agent or a polymer compound. Here, the “mixed melt” 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 of the “phase inversion emulsification method” are disclosed in JP-A-10-140065, JP-A-2009-212251 (particularly, paragraphs [0074] to [0082]), JP-A-2011-195684 (particularly, , Paragraphs [0042] to [0052]) can be appropriately referred to.

In the resin-coated pigment, the water-insoluble resin for coating the pigment preferably contains at least one structural unit having an acidic group, and if necessary, is preferably formed to contain other structural units.
The water-insoluble resin can be stably present in the ink composition, reduces adhesion or accumulation of aggregates, and facilitates removal of the adhered aggregates, so that at least one hydrophilic structural unit is present. It is preferable to include a seed and at least one hydrophobic structural unit, and it is more preferable that an acidic group is included in at least one hydrophilic structural unit.
Here, 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 kind of hydrophilic functional group, and may contain an ionic hydrophilic group or a nonionic hydrophilic group. It may contain a group.
The hydrophilic structural unit is preferably a hydrophilic structural unit having an acidic group, and the hydrophilic structural unit having an acidic group may be a structural unit derived from an acidic group-containing monomer or an acidic group. An acidic group may be introduced into a structural unit that does not have (polymer chain after polymerization) by a polymer reaction.

  The acidic group is not particularly limited, and examples thereof include a carboxy group, a phosphoric acid group, and a sulfonic acid group from the viewpoint of stability in an emulsified or dispersed state. Among these, from the viewpoint of dispersion stability, the acidic group is preferably a carboxy group.

  It is preferable that the water-insoluble resin includes a structural unit having an acidic group and further includes at least one hydrophobic structural unit. The hydrophobic structural unit is not particularly limited as long as it is a structural unit containing a hydrophobic functional group. For example, it is preferable that at least one structural unit having an aromatic ring is contained.

  The ink composition of the present invention is a yellow ink containing a yellow colorant such as a yellow pigment, in that the absorption of near-infrared light is relatively small and does not interfere with efficient heat generation of the specific diimonium salt compound by near-infrared irradiation, or A magenta ink containing a magenta colorant such as a magenta pigment is preferable.

The content of the colorant in the ink composition of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on the total mass of the ink composition. More preferably, it is 5 mass% or more.
When the content of the colorant is 0.5% by mass or more, the optical density of the image is further improved.
The upper limit of the content of the colorant is not particularly limited. For example, the content of the colorant in the ink composition of the present invention is preferably 9% by mass or less, more preferably 7% by mass or less, and more preferably 5% by mass with respect to the total mass of the ink composition. % Or less is more preferable.

  The mass ratio of the colorant content to the content of the specific dimonium salt compound in the ink composition of the present invention (colorant / specific dimonium salt compound) is preferably 1/2 to 1 / 6,000, 1/3 to 1/600 is more preferable, and 1/6 to 1/300 is still 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 water content in the ink composition of the present invention is not particularly limited, and can be appropriately set according to the purpose. For example, from the viewpoints of dispersion stability and ejection properties, the water content is preferably 10% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 80% by mass with respect to the total amount of the ink composition. % Or less, and more preferably 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.
Here, the “polymer particle” means a particulate polymer dispersed in the ink composition.
When the ink composition contains polymer particles, when the polymer particles come into contact with the treatment liquid described later or a region where the treatment liquid is dried, the ink composition is dispersed and destabilized and aggregates, so that the ink composition The image is fixed on the recording medium by thickening. Thereby, the fixing property, rubbing resistance and cohesion of the image are further improved.

Self-dispersing polymer particles are suitable as the polymer particles.
Here, the “self-dispersing polymer particle” means a functional group (particularly an acidic group or its group) that the polymer itself has when dispersed (particularly, dispersed by phase inversion emulsification) in the absence of a surfactant. Salt) means water-insoluble polymer particles that can be dispersed in an aqueous medium and that do 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 JP2011-068805A are used. Can be used.
Self-dispersing polymer particles can be suitably prepared by a phase inversion emulsification method.

The molecular weight of the polymer forming the polymer particles (for example, self-dispersing polymer particles) is preferably 3,000 to 200,000, more preferably 5,000 to 150,000 in terms of weight average molecular weight. More preferably, it is 000-100,000.
By setting the weight average molecular weight of the polymer forming the polymer particles to 3,000 or more, the amount of the water-soluble component in the ink composition can be effectively suppressed.
Moreover, self-dispersion stability can be improved by making the weight average molecular weight of the polymer which forms a polymer particle into 200,000 or less.

When the ink composition of the present invention contains polymer particles (for example, self-dispersing polymer particles), the content of the polymer particles is 0.1% by mass to 20% by mass with respect to the total mass of the ink composition. It is preferable that the content is 0.1% by mass to 10% by mass.
The particle size distribution of the polymer particles is not particularly limited, and may have a wide particle size distribution or a monodispersed particle size distribution. Two or more polymer particles having a monodispersed particle size distribution may be mixed and used.

A preferred embodiment of the polymer particles (for example, self-dispersing polymer particles) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer is an alicyclic (meth) acrylate (preferably bicyclic or tricyclic or higher polycyclic (meth). A structural unit derived from acrylate) 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 carboxy group or a phosphate group). And at least one group selected from sulfonic acid groups, particularly preferably a carboxy group) containing a structural unit derived from a monomer containing 25% by mass or less and a chain alkyl group having 1 to 8 carbon atoms (meth) And an acid value of 20 mg KOH / g to 120 mg KOH / g (more preferably 25 mg KOH / g to 10). A mg KOH / g), weight average molecular weight of 3,000～20 one million (preferably embodiment is a vinyl polymer which is 10,000～20 50,000).
In this embodiment, the structural unit derived from a bicyclic or tricyclic or higher polycyclic (meth) acrylate is derived from 40% by mass to 80% by mass and at least methyl (meth) acrylate or ethyl (meth) acrylate. Including 20 to 60 mass% of structural units and 25 mass% or less of structural units derived from acrylic acid or methacrylic acid, having an acid value of 30 mgKOH / g to 80 mgKOH / g, and having a weight average molecular weight It is more preferable that it is a vinyl polymer which is 30000-150,000.

Another preferred embodiment of polymer particles (for example, self-dispersing polymer particles) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer is a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably phenoxyethyl ( It is an embodiment containing 15% by mass to 80% by mass of the total mass of the polymer particles, with a copolymerization ratio of (a structural unit derived from (meth) acrylate and / or a structural unit derived from benzyl (meth) acrylate).
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 carboxy 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 carboxy 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 And a structural unit derived from an alkyl ester of The value is 25 mg KOH / g to 100 mg KOH / g, the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 mg KOH / g to 95 mg KOH / g, and the weight average molecular weight is 5000 to 150,000. It is more preferable.

<Colloidal silica>
The ink composition of the present invention preferably contains colloidal silica.
When the ink composition of the present invention contains colloidal silica, when used as an ink for inkjet recording, it may be provided on the nozzle ejection surface (for example, on the nozzle ejection side) when the ink is repeatedly ejected. Deterioration of the surface of the liquid repellent film can be more effectively suppressed. Such an 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).

“Colloidal silica” as used herein is a colloid composed of fine particles of inorganic oxide containing silicon having a volume average particle diameter of 100 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.
The 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.
The dispersion medium for colloidal silica is not particularly limited, and may be any of water, an organic solvent, and a mixture thereof. The organic solvent may be a water-soluble organic solvent or a water-insoluble organic solvent, but is preferably a water-soluble organic solvent. Specific examples include water-soluble organic solvents such as methanol, ethanol, isopropyl alcohol, and n-propanol.
As the colloidal silica, for example, known colloidal silica described in paragraphs [0014] to [0022] of JP2011-195684A can be used.

When the ink composition of the present invention contains colloidal silica, the colloidal silica may be contained alone or in combination of two or more.
When the ink composition of the present invention contains colloidal silica, the content of colloidal silica is not particularly limited. For example, it is 0.0001% by mass to 10% by mass with respect to the total mass of the ink composition. It is preferably 0.01% by mass to 3.0% by mass, more preferably 0.02% by mass to 0.5% by mass, and 0.03% by mass to 0.2% by mass. It is particularly preferred.
When the content of colloidal silica in the ink composition is 10% by mass or less, the dischargeability of the ink composition is further improved, and the influence of the silica particles on the ink jet head is more effectively affected. Can be suppressed.
When the content of colloidal silica in the ink composition is 0.0001% by mass or more, a decrease in liquid repellency on the nozzle discharge surface (for example, deterioration of the liquid repellent film) can be more effectively suppressed.

<Urea>
The ink composition of the present invention may contain urea.
Urea can be used as a solid wetting agent because of its high moisturizing function.
The ink composition of the present invention contains urea, whereby drying and coagulation are more effectively suppressed.
In addition, the ink composition of the present invention contains the above colloidal silica together with urea, so that when used as an ink for ink jet recording, the maintenance performance (cleaning removal property or wiping property) of the ink jet head or the like is more effective. Improve.

  When the ink composition of the present invention contains urea, the urea content is 1% by mass to 20% by mass with respect to the total mass of the ink composition from the viewpoint of improving maintenance properties (wiping properties). It is preferably 1% by mass to 15% by mass, more preferably 3% by mass to 10% by mass.

  When the ink composition of the present invention contains urea and colloidal silica, the ratio of the urea content to the colloidal silica content (urea content / colloidal silica content) is not particularly limited. The standard is preferably 5 to 1000, and more preferably 10 to 700.

The ink composition of the present invention may contain a solid wetting agent other than urea.
For the solid wetting agent other than urea and the particularly preferable form in the case where the ink composition contains urea and colloidal silica, refer to paragraphs [0026] to [0030] of JP 2011-195684 A, for example. it can.

<Surfactant>
The ink composition of the present invention may contain at least one surfactant as required. According to the surfactant, the surface tension of the ink can be adjusted more effectively.
The surfactant is not particularly limited, and can be appropriately selected from known surfactants. As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively, and an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a 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 the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 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 these compounds. Examples of commercially available products of these compounds include Olfin (registered trademark) E series such as Olphine (registered trademark) E1010 and E1020.
As the surfactant other than the acetylene glycol surfactant, a fluorine surfactant is preferable.
Examples of the fluorine-based surfactant include anionic surfactants, nonionic surfactants, and betaine-based surfactants, and among these, anionic surfactants are more preferable.
Examples of the anionic surfactant include Capstone (registered trademark) FS-63, FS-61 (above, manufactured by Dupont), and Footgent (registered trademark) 100, 110, 150 (over, manufactured by Neos Co., Ltd.). ), CHEMGUARD S-760P (manufactured by Chemguard Inc.), and the like.

  When the ink composition of the present invention contains a surfactant, the content of the surfactant is not particularly limited, and may be, for example, 0.1% by mass or more based on the total mass of the ink composition. Preferably, it is 0.1 mass%-10 mass%, More preferably, it is 0.2 mass%-3 mass%.

<Water-soluble organic solvent>
The ink composition of the present invention preferably contains at least one water-soluble organic solvent.
In this specification, “water-soluble organic solvent” means an organic solvent that dissolves 5 g or more in 100 g of water at 25 ° C., and preferably 10 g or more.
Since the ink composition of the present invention contains a water-soluble organic solvent, nozzle clogging that may occur due to drying of the ink at the ink ejection port when the ink composition is ejected by the inkjet method to record an image. Can be effectively prevented.
In order to prevent drying, a water-soluble organic solvent having a vapor pressure lower than that of water is preferable.
Specific examples of water-soluble organic solvents suitable for preventing drying include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, methylpropylene triglycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propane. Polyols represented by diol, 1,2,6-hexanetriol, acetylene glycol derivatives, glycerin, trimethylolpropane and the like, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2- Examples thereof include heterocycles such as imidazolidinone and N-ethylmorpholine, sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 3-sulfolene, polyfunctional compounds such as diacetone alcohol and diethanolamine, and urea derivatives. Among these, polyhydric alcohols such as glycerin, propylene glycol, and methylpropylene triglycol are preferable.

<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, wax agents, penetration enhancers, ultraviolet absorbers, antiseptics, antifungal agents, pH adjusters, surface tension adjusters, antifoaming agents, and viscosity adjusters. Well-known additives such as an agent, a dispersion stabilizer, a rust inhibitor, and a chelating agent can be used.
These various additives may be added directly after the ink composition is prepared, or may be added when the ink composition is prepared.
For other additives, the description in paragraphs [0153] to [0162] of JP-A-2007-100071 can be referred to as appropriate.

<Physical properties of ink composition>
(viscosity)
When the ink composition is applied to the recording medium by an ink jet method, the viscosity of the ink composition is preferably 1 mPa · s to 30 mPa · s from the viewpoint of droplet ejection stability and aggregation speed. It is more preferably 20 mPa · s, further preferably 2 mPa · s to 15 mPa · s, and particularly preferably 2 mPa · s to 10 mPa · s.
The viscosity of the ink composition of the present invention refers to the viscosity of the ink composition at a liquid temperature of 30 ° C. measured using a viscometer (model name: VISCOMETER TV-22, manufactured by TOKI SANGYO CO. LTD).

(surface tension)
When the ink composition is applied to the recording medium by an ink jet method, from the viewpoint of ejection stability, the surface tension of the ink composition is preferably 20 mN / m to 60 mN / m, and preferably 20 mN / m to 45 mN / m. It is more preferable that it is 25mN / m-40mN / m.
The surface tension of the ink composition of the present invention was measured using a surface tension meter (model name: Automatic Surface Tensiometer CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.), and the ink composition at a liquid temperature of 25 ° C. Refers to surface tension.

(PH)
The ink composition of the present invention 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 12, and more preferably pH 8 to pH 10, from the viewpoint of ink stability and aggregation rate.
The pH of the ink composition of the present invention is the pH of the ink composition at a liquid temperature of 30 ° C. measured using an electric conductivity / pH meter (model name: WM-50EG, manufactured by Toa DDK Co., Ltd.). Point to.
The pH of the ink composition can be appropriately adjusted using an acidic compound or a basic compound. As an acidic compound or a basic compound, the compound used normally can be especially used without a restriction | limiting.

<Use of ink composition>
The ink composition of the present invention can suppress clogging of a recording medium such as paper, and is excellent not only in storage stability but also in dischargeability when used in inkjet recording. As the ink for use, it can be suitably used. In particular, from the viewpoint of suppressing cockle, it is suitable as an ink for ink jet recording using paper as a recording medium.

[Method for producing ink composition]
The method for producing the ink composition of the present invention is not particularly limited as long as the above ink composition can be produced.
As a method for producing the ink composition of the present invention, the method for producing the ink composition of the present embodiment described below is preferable from the viewpoint of easily obtaining the ink composition of the present invention.

The ink composition production method of the present embodiment (hereinafter also referred to as “production method of the present embodiment”) includes at least a diimonium salt compound (specific diimonium salt) represented by the general formula (1) as a near-infrared absorbing dye. Salt compound), a polymer dispersant that coats at least a part of the diimonium salt compound, and a medium containing water, and a mixing step for obtaining an aqueous mixed solution, and an aqueous mixed solution obtained by the mixing step The dispersion process is performed to obtain an aqueous dispersion in which the near-infrared absorbing dye is dispersed with the polymer dispersant, and at least the aqueous dispersion obtained in the dispersion process and the colorant are mixed. And a preparation step of preparing the ink composition.
The manufacturing method of this embodiment may have another process as needed.
According to the manufacturing method of this embodiment, the ink composition of the present invention described above can be easily manufactured.

Hereinafter, each process in the manufacturing method of this embodiment is demonstrated in detail.
Note that specific examples and preferred embodiments of the components used in each step are as described in the above-described section of the ink composition, and thus description thereof is omitted here.

<Mixing process>
The mixing step is a step of obtaining an aqueous mixed liquid by mixing at least a specific diimonium salt compound as a near-infrared absorbing dye, a polymer dispersant covering at least a part of the specific diimonium salt compound, and a medium containing water. It is.

  The medium may contain other components as needed in addition to water. Other components include water-soluble organic solvents that can be mixed with water. Since the water-soluble organic solvent is the same as that described in the above-mentioned ink composition, the description thereof is omitted here.

The content of the specific diimonium salt compound and the polymer dispersant in the aqueous mixture is, for example, such that the content in the finally prepared ink composition is the amount described in the above-mentioned ink composition section. Each may be adjusted.
The amount of the medium containing water in the aqueous mixed solution is not particularly limited, and is appropriately selected depending on the type and amount of components contained in the aqueous mixed solution.

Each component to be mixed may be simply mixed, and all the components may be mixed at once, or each component may be divided into several parts and mixed.
The mixing method is not particularly limited, and examples thereof include mixing by stirring.

<Dispersing process>
The dispersion step is a step of subjecting the aqueous mixture obtained in the mixing step to a dispersion treatment to obtain an aqueous dispersion in which the near-infrared absorbing dye is dispersed with the polymer dispersant.
The method for the dispersion processing is not particularly limited, and examples thereof include dispersion using a dispersion device.
Examples of the dispersing device include dispersing devices such as a ball mill, a bead mill, a sand mill, a salt mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker.
Among these, a bead mill dispersion device is preferable in that an aqueous dispersion excellent in dispersibility can be obtained.
For dispersion using a bead mill dispersion device, beads having an average particle diameter of preferably 0.01 mm to 3.0 mm, more preferably 0.05 mm to 1.5 mm, and still more preferably 0.1 mm to 1.0 mm are used. Thus, an aqueous dispersion superior in dispersibility can be obtained.

The dispersion step may include a step of filtering the aqueous dispersion.
Since the dispersion step includes a step of filtering the aqueous dispersion, for example, when dispersed using a bead mill dispersion device, beads can be effectively removed, and coarse particles can be removed. The discharge property can be improved.

<Preparation process>
The preparation step is a step of preparing an ink composition by mixing at least the aqueous dispersion obtained in the dispersion step and a colorant.
In the preparation process, by mixing the aqueous dispersion obtained in the dispersion process and the colorant, the dispersibility of the colorant is superior to the case where the colorant is mixed in the mixing process. It becomes.
What is necessary is just to adjust the quantity of the coloring agent mixed with an aqueous dispersion so that content in the prepared ink composition may turn into the quantity as described in the term of the above-mentioned ink composition.

In the preparation step, other components may be mixed together with the aqueous dispersion and the colorant. Examples of the other components include polymer particles (for example, self-dispersing polymer particles), colloidal silica, urea, a surfactant, and a water-soluble organic solvent described in the above-described ink composition.
When these other components are used, the amount of other components used is not particularly limited, and is appropriately set depending on the purpose within a range not impairing the effects of the present invention.

  The mixing method is not particularly limited, and examples thereof include mixing by stirring.

The manufacturing method of this embodiment may have other processes other than a mixing process, a dispersion | distribution process, and a preparation process as needed in the range which does not impair the effect of this invention.
Examples of the other steps include a step of ultrasonically treating the ink composition in order to improve dischargeability when used as an inkjet recording ink.

(Image forming method)
The image forming method of the present invention includes an image forming step of forming an image by applying the above-described ink composition of the present invention to a recording medium, and 700 nm to 1,600 nm with respect to the image formed in the image forming step. And an infrared irradiation step of irradiating infrared rays having a maximum emission wavelength in the wavelength region.
Since the image forming method of the present invention includes the image forming step and the infrared irradiation step, it is possible to make it difficult to impair the color of an image obtained when an image is formed. In addition, when a recording medium such as paper is used, it is also possible to suppress cockle.

<Image forming process>
The image forming step is a step of forming an image by applying the ink composition of the present invention to a recording medium.

The recording medium is not particularly limited.
The recording medium may be, for example, a recording medium including paper such as printing paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, and the like.
According to the ink composition of the present invention described above, when an image is formed on a recording medium containing paper, the recording medium such as paper can be prevented from being clogged. Therefore, the recording medium includes paper. Is preferred.

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, general offset printing, and the like 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 Ink jet paper described in JP-A-10-153898, JP-A-10-217473, JP-A-10-235995, JP-A-10-217597, JP-A-10-337947, etc. Also good.
General printing paper mainly composed of cellulose is relatively slow in absorption, drying, etc. of ink in image recording by a general ink jet method using water-based ink. It's easy to do. However, according to the image forming method of the present invention, since the movement of the coloring material after the droplet ejection is suppressed, it is possible to form a high-quality image excellent in color density and hue.

  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., Nippon Paper Industries Co., Ltd. Fine coated paper such as “New NPI Premium” manufactured by Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., Lightweight coated paper (A3) such as “OK Coat L” manufactured by Oji Paper Co., Ltd., “Aurora L” manufactured by Nippon Paper Industries Co., Ltd., “OK Top Coat +” manufactured by Oji Paper Co., Ltd., Nippon Paper Industries Co., Ltd. Coated paper (A2, B2) such as “Aurora Coat” manufactured by Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Oji Paper Co., Ltd., “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. Etc. In addition, as a recording medium including paper, it is also possible to use various types of photographic paper for ink jet recording.

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

  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 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 an automatic scanning liquid absorption meter KM500Win (manufactured by Kumagai Riki Co., Ltd.).

  As the recording medium, so-called coated paper used for general offset printing or the like is preferable. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper or the like mainly composed of cellulose and generally not subjected to surface treatment. The coated paper is liable to cause quality problems such as glossiness and scratch resistance of the image in ordinary aqueous ink jet image formation. However, in the image forming method of the present invention, gloss unevenness is suppressed and glossiness and resistance to wear are reduced. A good image such as rubbing property can be obtained. As the recording medium, it is particularly preferable to use a coated paper having a base paper and a coating layer containing kaolin and / or calcium bicarbonate. More specifically, the recording medium is more preferably art paper, coated paper, lightweight coated paper, or finely coated paper.

The method for applying the ink composition of the present invention to a recording medium is not particularly limited.
Examples of the application method include application methods such as spray coating, coating with a coating roller, ejection by an inkjet method, and immersion, and ejection by an inkjet method is preferable. As a method for ejecting the ink composition of the present invention by an ink jet method and applying it to a recording medium, the methods described in paragraphs [0093] to [0105] of JP-A No. 2003-306623 can be applied.

  Regarding the inkjet method, paragraphs [0172] to [0187] of JP-A No. 2014-0473302 can be appropriately referred to.

  Hereinafter, an inkjet head equipped with a nozzle plate, which is preferably used in the image forming method of the present invention, will be described with reference to the drawings. In addition, each figure shown below (FIG.1 and FIG.2) is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.

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 ejection holes (nozzles) arranged in a two-dimensional array. The number of ejection holes is not limited and can be appropriately selected in consideration of speeding up of image formation, and can be, for example, 32 × 60.
As the nozzle plate 11, a nozzle plate containing silicon (silicon nozzle plate) can be used. 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 flow path 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.
Thus, 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 is an electric that supplies a drive signal from the outside. Wiring 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 infrared irradiation step is a step of irradiating the image formed in the image forming step with infrared rays having a maximum emission wavelength in a wavelength region of 700 nm to 1,600 nm.
The specific diimonium salt compound contained in the ink composition of the present invention is considered to generate heat by absorbing infrared light having a maximum light emission wavelength in a wavelength region of 700 nm to 1,600 nm and rapidly decompose. Therefore, it is difficult for the color tone of the image to change due to the remaining near-infrared absorbing dye.

The method for irradiating the image with infrared rays is not particularly limited.
Examples of the infrared source include a xenon flash lamp, a xenon lamp, a xenon short arc lamp, a near infrared halogen heater, an infrared LED, an infrared laser (solid laser, semiconductor laser, etc.) in addition to a normal infrared lamp. Can do.
Among these, as the infrared source, a xenon flash lamp, a xenon lamp, a near-infrared halogen heater, an infrared LED, a solid-state laser that emits infrared light having a wavelength of 700 nm to 1,600 nm, or a semiconductor laser is preferable.

<Other processes>
The image forming method of the present invention further includes other steps such as an image fixing step, a treatment liquid applying step, a maintenance step, and a curing step, as necessary, in addition to the above-described image forming step and infrared irradiation step. Also good.

(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 (especially, suppression of cuckling of a recording medium such as paper) are not impaired.
Examples of the image fixing step include a step of heating an image by a non-contact heating method other than infrared irradiation, a step of heating an image by a contact heating method of pressing a heating plate or a heating and pressing roller against the image, and the like. It is done.
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 image non-contact heating method is not particularly limited, and examples thereof include a method of heating with a heating element such as a nichrome wire heater, a method of supplying warm air or hot air, and the like.
Further, the contact heating method is not particularly limited, and 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 surface of a recording medium There is a method of performing heat fixing by contact, such as a method of passing a pair of rollers, etc., using a heating and pressing device provided with a heating and pressing belt arranged on the side and a holding roller arranged on the opposite side. Preferably mentioned.

  The conveyance speed of the recording medium when using a heat pressure roller or a heat pressure belt is preferably 200 mm / second to 700 mm / second, more preferably 300 mm / second to 650 mm / second, and still more preferably 400 mm / second. 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 it comes into contact with the ink composition to a recording medium.
The treatment liquid applying step may be before the image forming step, after the image forming step, and before the infrared irradiation step.
When the treatment liquid applied to the recording medium comes into contact with the ink composition, components (colorant, specific dimonium salt compound, 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 the treatment liquid application step, the 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.

Application of the treatment liquid to the recording medium can be performed by applying a known method such as a coating method, an ink jet method, or an immersion method.
Examples of the coating method include known coating methods 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, and the like.

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

  In the image forming method of the present invention, when the treatment liquid application step is included before the image formation step, after the treatment liquid is applied on the recording medium and before the ink composition is applied, It is preferable to further have a heat drying step of heat drying the treatment liquid. By heating and drying the treatment liquid in advance before the image forming step, bleeding can be prevented and ink colorability is improved, and a visible image with good color density and hue can be recorded.

Heating and drying of the treatment liquid applied on the recording medium can be performed by a known heating means such as a heater, a blowing means using blowing air such as a dryer, or a combination of these.
Specifically, the heating method includes 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, and an infrared heater. The method of using and heating is mentioned, You may heat combining these methods in combination.

-Treatment liquid-
The treatment liquid contains at least one aggregation component that forms an aggregate when it comes into contact with the ink composition.
The contact between the treatment liquid containing an aggregating component and the ink composition promotes aggregation of a colorant, a specific diimonium salt compound, and the like stably dispersed in the ink composition.
The treatment liquid may contain one aggregation component alone or in combination of two or more.

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 0.1 to 5.0 and more preferably 0.3 to 4.0 from the viewpoint of the aggregation rate of the ink composition. Preferably, it is 0.5-3.0.

Examples of the aggregating component include at least one acidic compound.
Examples of the acidic compound include a compound having at least one group selected from a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, and a carboxy group, or a salt thereof (for example, , Polyvalent metal salts).
Among these, as the acidic compound, from the viewpoint of the aggregation rate of the ink composition, a compound having at least one group selected from a phosphate group and a carboxy group is more preferable, and a compound having a carboxy group is more preferable.

Examples of compounds having a carboxy 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, pyrrolidone carboxylic acid, and pyrone. Compounds such as 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) are preferable. .
The treatment liquid may contain one of these compounds 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, the treatment liquid may contain a polyvalent metal salt, a cationic polymer, or the like described in paragraphs [0155] and [0156] of JP2011-042150A as an aggregation component.

The viscosity of the treatment liquid is preferably 1 mPa · s to 30 mPa · s, more preferably 1 mPa · s to 20 mPa · s, from the viewpoint of the aggregation rate of the ink composition, and 2 mPa · s to 15 mPa · s. s is more preferable, and 2 mPa · s to 10 mPa · s is particularly preferable. The viscosity of the treatment liquid is measured under a condition of 25 ° C. using a viscometer (model name: 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 -40mN / m. The surface tension is measured under a condition of 25 ° C. using a surface tension meter (model name: Automatic Surface Tensiometer CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.).

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

Examples of the method for removing the ink composition or the like from the nozzle ejection surface in the maintenance process include a method such as scraping with a wiper blade, wiping with a cloth, paper, or the like.
The maintenance process may include applying a maintenance liquid to the vicinity of the inkjet head (for example, an ink flow path or the like (hereinafter also referred to as “head or the like”)). By applying the maintenance liquid to the head or the like, the ink fixed matter derived from the ink composition on the nozzle surface is further easily removed by dissolution, swelling or the like.
The maintenance liquid may be applied before or after scraping with a wiper blade, wiping with a cloth, paper, or the like.
Preferably, after the maintenance liquid is applied, the nozzle surface is rubbed with a wiper blade (wiping), the ink adhering matter is scraped off, the ink composition is removed by wind pressure, maintenance liquid pressure, cloth, paper, etc. For example, a method of wiping off the ink composition or the like with the above. Among these, as a method for removing the ink composition or the like, a method of scraping with a wiper blade and a method of wiping with a cloth, paper, or the like 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 fluororesin or the like may be used.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples as long as the gist thereof is not exceeded.

  The weight average molecular weight (Mw) of the water-soluble polymer and the self-dispersing polymer particles synthesized in this example was measured by gel permeation chromatography (GPC) under the following conditions.

~conditions~
Measuring device: High-speed GPC HLC-8020 GPC (Tosoh Corporation)
Detector: differential refractometer (RI) RI-8020 (Tosoh Corporation)
Column: TSKgeL Super Multipore HZ-H (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation) is used. Column temperature: 40 ° C.
Eluent: Tetrahydrofuran (THF)
Sample concentration: 0.45 mass%
Injection volume: 10 μL
Flow rate: 0.35 mL / min

  The calibration curve is “Standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, “ It was prepared from 8 samples of “A-2500”, “A-1000”, and “n-propylbenzene”.

  The acid value of the water-soluble polymer and the self-dispersing polymer particles synthesized in this example was measured by the method described in JIS standard (JISK0070, 1992).

[Preparation of near-infrared absorbing dye dispersion A1]
Each component of the following composition A1 was mixed, and the obtained mixture was dispersed with a bead mill for 3 hours using 0.1 mmφ zirconia beads. About the obtained dispersion, the volume average particle diameter was measured by a dynamic light scattering method using a Nanotrac particle size distribution analyzer (model number: UPA-EX150, manufactured by Nikkiso Co., Ltd.), and it was 70 nm.
Then, the density | concentration of the coloring agent was calculated | required from the absorbance spectrum, ion-exchange water was added, and the near-infrared absorption pigment | dye dispersion liquid A1 was obtained as a dispersion with a pigment | dye concentration of 8.0 mass%.

-Composition A1-
Diimonium salt compound DI-1 [the following structure, near-infrared absorbing dye] 10.0% by mass
DISPERBYK (registered trademark) 2090 [trade name, polymer dispersant, manufactured by Big Chemie Japan Co., Ltd.] 0.7% by mass
・ Ion-exchanged water 89.3 mass%

[Preparation of near-infrared absorbing dye dispersions A2 to A21]
Near-infrared absorbing dye dispersions A2 to A21 having the compositions shown in Tables 1 and 2 were prepared in the same manner as in the near-infrared absorbing dye dispersion A1.
The structures of the near infrared absorbing dyes (diimonium salt compounds DI-2 to DI-4) used for the preparation of the near infrared absorbing dye dispersions A8 to A10 are shown below.

[Preparation of comparative near infrared absorbing dye dispersions CA1 to CA10]
Comparative near-infrared absorbing dye dispersions CA1 to CA10 having the compositions shown in Table 3 were prepared in the same manner as in the near-infrared absorbing dye dispersion A1.
The structure of the near-infrared absorbing dye (cyanine compound CYN-1) used for the preparation of the comparative near-infrared absorbing dye dispersion CA1 is shown below.

“-” In Tables 1 to 3 means that the corresponding component is not used.
“Polymer dispersant / near infrared absorbing dye” in Tables 1 to 3 means the ratio (mass basis) of the content of the polymer dispersant to the content of the near infrared absorbing dye.

Table 4 shows details of the polymer dispersant used for the preparation of the near infrared absorbing dye dispersions A1 to A21 and the comparative near infrared absorbing dye dispersions CA1 to CA8.
In Table 4, “TEGO Disperse” is a registered trademark of Evonik Japan Co., Ltd., and “TEGO Disperse” series polymer dispersants are pigment dispersants manufactured by Evonik Japan Co., Ltd. is there.
In Table 4, “DISPERBYK” is a registered trademark of Big Chemie Japan Co., Ltd., and the polymer dispersants in the “DISPERBYK” series are all pigment dispersants manufactured by Big Chemie Japan Co., Ltd.
“Acid value” and “base number” in Table 4 are catalog values.

[Synthesis of water-soluble polymer dispersant Q-1]
A monomer supply composition was prepared by mixing methacrylic acid (172.0 parts by mass), benzyl methacrylate (828.0 parts by mass), and isopropanol (375.0 parts by mass).
In addition, an initiator supply composition was prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.1 parts by mass) and isopropanol (187.5 parts by mass).
Next, while isopropanol (187.5 parts by mass) was heated to 80 ° C. in a nitrogen atmosphere, the mixture of the monomer supply composition and the initiator supply composition was added dropwise over 2 hours. After the completion of dropping, the mixture was further maintained at 80 ° C. for 4 hours, and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a water-soluble polymer dispersant Q-1 (water-soluble polymer) having a weight average molecular weight of about 30,000 and an acid value of 112 mgKOH / g.

[Preparation of Yellow Pigment Dispersion Liquid DY1]
After neutralizing 0.8 equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant Q-1 (150.0 parts by mass) obtained above with an aqueous potassium hydroxide solution, ion-exchanged water was further added. Thus, the water-soluble polymer dispersant concentration was adjusted to 25.0% by mass to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (216.0 parts by mass), Pigment Yellow 74 (yellow pigment) (120.0 parts by mass) and pure water (464.0 parts by mass) were mixed, and a bead mill (bead diameter) : 0.1 mmφ, zirconia beads) until a desired volume average particle diameter was obtained, and a dispersion of polymer-coated yellow pigment particles (uncrosslinked dispersion DY1) having a pigment concentration of 15.0% by mass was obtained.
Dencol EX-521 (manufactured by Nagase ChemteX Corp., crosslinking agent) (0.3 parts by mass) and an aqueous boric acid solution (boric acid concentration: 4.0) were added to this uncrosslinked dispersion PC1 (136.0 parts by mass). (Mass%) (13.7 parts by mass) was added and reacted at 70 ° C. for 6 and a half hours, and then cooled to 25 ° C. to obtain a crosslinked dispersion. Next, the obtained crosslinked dispersion was applied to a polyethersulfone (PESU) membrane (micropore size: 0.1 μm) attached to an ultrafiltration device (cross flow type UF, manufactured by Sartorius) at 25 ° C. Ultrafiltration was carried out at a flow rate of 600 ml for 1 minute at ambient temperature. This ultrafiltration was performed 10 times, with 1 time the volume magnification of the charged solution as one time. Thereafter, a yellow pigment dispersion DY1 was obtained by adding pure water to the crosslinked dispersion after ultrafiltration so that the pigment concentration was 12.0% by mass.
The pigment contained in the yellow pigment dispersion DY1 is a polymer-coated pigment (encapsulated pigment) whose surface is coated with a crosslinked polymer obtained by crosslinking the water-soluble polymer dispersant Q-1 with a crosslinking agent.

[Preparation of Magenta Pigment Dispersion DM1]
In the production of the yellow pigment dispersion DY1, except that Pigment Red 122 (magenta pigment) was used instead of Pigment Yellow 74 (yellow pigment) used as the pigment, A magenta pigment dispersion DM1 was obtained.

[Preparation of Cyan Pigment Dispersion Liquid DC1]
In the preparation of the yellow pigment dispersion DY1, the same procedure as in the preparation of the yellow pigment dispersion DY1 was performed except that Pigment Blue 15: 3 (cyan pigment) was used instead of Pigment Yellow 74 (yellow pigment) used as the pigment. Thus, a cyan pigment dispersion DC1 was obtained.

[Preparation of black pigment dispersion DK1]
In the preparation of the yellow pigment dispersion DY1, black carbon black (black pigment) was used in place of Pigment Yellow 74 (yellow pigment) used as the pigment in the same manner as in the preparation of the yellow pigment dispersion DY1. A pigment dispersion DK1 was obtained.

[Preparation of self-dispersing polymer particle (resin particle) dispersion P1]
360.0 g of methyl ethyl ketone was charged into a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 75 ° C. under a nitrogen atmosphere. Thereafter, while maintaining the temperature in the flask at 75 ° C. (hereinafter refluxed until the end of the reaction), 151.2 g of isobornyl methacrylate, 172.8 g of methyl methacrylate, 36.0 g of methacrylic acid, 72.0 g of methyl ethyl ketone, and “V— A mixed solution consisting of 1.4 g of “601” (manufactured by Wako Pure Chemical Industries, Ltd.) was dropped at a constant speed so that the dropping was completed in 2 hours.

A solution consisting of 0.8 g of “V-601” and 36.0 g of methyl ethyl ketone was added to the solution after completion of the dropwise addition, and the mixture was stirred at 75 ° C. for 2 hours, and further from 0.7 g of “V-601” and 36.0 g of isopropanol. The resulting solution was added and stirred at 75 ° C. for 2 hours. Thereafter, the temperature in the reaction vessel was raised to 85 ° C., and the stirring was further continued for 2 hours to obtain a polymer of isobornyl methacrylate / methyl methacrylate / methacrylic acid (= 42/48/10 [mass ratio]) copolymer. A solution was obtained.
The weight average molecular weight (Mw) of the obtained copolymer was 58,000, and the acid value was 32.6 mgKOH / g.

  Next, 668.3 g of the obtained polymer solution was weighed, 388.3 g of isopropanol and 145.7 ml of 1 mol / L NaOH aqueous solution were added to this polymer solution, and the temperature in the reaction vessel was raised to 80 ° C. Next, 720.1 g of pure water was added dropwise at a rate of 20 ml / min to disperse in water, and then the reaction vessel internal temperature was 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. I kept time. Subsequently, the pressure in the reaction vessel was reduced, and 913.7 g of isopropanol, methyl ethyl ketone, and pure water were distilled off in total. Finally, pure water was added so that the solid content concentration (polymer particle concentration) was 23.0% by mass to obtain a self-dispersing polymer particle (resin particle) dispersion P1.

  It was 150 degreeC when the glass transition temperature (Tg) of the polymer particle (resin particle) in the obtained self-dispersing polymer particle (resin particle) dispersion P1 was measured with the following method.

-Measurement of glass transition temperature (Tg)-
An aqueous dispersion of self-dispersing polymer particles having a solid content of 0.5 g was dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid content. The glass transition temperature (Tg) was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology, Inc. using the obtained polymer solid content. The measurement condition was that a sample amount of 5 mg was sealed in an aluminum pan, and the DSC peak top value of the measurement data at the second temperature increase was defined as Tg under the following temperature profile in a nitrogen atmosphere.
30 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 220 ° C. (temperature rising at 20 ° C./min)
220 ° C to -50 ° C (cooling at 50 ° C / min)
−50 ° C. → 220 ° C. (temperature rising at 20 ° C./min)

[Preparation of Yellow Ink Composition Y1]
Components of the following composition were mixed, and coarse particles were removed through a membrane filter (pore size 0.5 μm) to obtain a yellow ink composition Y1 (ink composition of Example 1).
The produced yellow ink composition Y1 has the following physical properties: viscosity 5.5 mPa · s (30 ° C.), surface tension 27.0 mN / m (25 ° C.), pH 8.3 (30 ° C.), and electric conductivity 155 mS / m ( 30 ° C.).
Here, the viscosity and the surface tension are respectively a viscometer (model name: VISCOMETER TV-22, manufactured by TOKI SANGYO CO. LTD), a surface tension meter (model name: Automatic Surface Tensiometer CBVP-Z, Kyowa Interface Science Co., Ltd.) ).
Moreover, pH and electrical conductivity were measured using the electrical conductivity and pH meter (model name: WM-50EG, Toago DDK Co., Ltd. product).

-Composition of yellow ink composition Y1-
-Yellow pigment dispersion DY1 30.00% by mass
-Self-dispersing polymer particle (resin particle) dispersion P1 30.00% by mass
Near-infrared absorbing dye dispersion A4 (diimonium salt compound DI-1)
0.01% by mass
・ Methylpropylene triglycol (MFTG) (water-soluble organic solvent, manufactured by Nippon Emulsifier Co., Ltd.)
2.00% by mass
・ Propylene glycol (PG) (water-soluble organic solvent, manufactured by ADEKA)
14.00 mass%
・ Glycerin (water-soluble organic solvent) 2.50% by mass
・ PVP K-15 (trade name, water-soluble polymer, manufactured by ISB Japan Co., Ltd.)
0.10% by mass
・ Urea 5.00% by mass
・ Orphine (registered trademark) E1010 (trade name, surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)
0.25% by mass
・ Orphine (registered trademark) E1020 (trade name, surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)
1.00% by mass
・ Potassium nitrate 0.05% by mass
・ Cerosol (registered trademark) 524 (trade name, wax agent, manufactured by Chukyo Yushi Co., Ltd.)
6.50% by mass
-Snowtex (registered trademark) XS (trade name, colloidal silica, solid content concentration: 20% by mass, volume average particle size: 5 nm, manufactured by Nissan Chemical Co., Ltd.)
0.28% by mass
Capstone (registered trademark) FS-63 (trade name, fluorosurfactant, manufactured by Dupont)
0.01% by mass
・ BYK-024 (trade name, antifoaming agent, manufactured by Big Chemie Japan Co., Ltd.)
0.01% by mass
・ Remaining amount when pure water is 100% by mass

[Preparation of Yellow Ink Compositions Y2 to Y29 and CY1 to CY12]
In preparing the yellow ink composition Y1, instead of blending the near-infrared absorbing dye dispersion A4 in an amount of 0.01% by mass with respect to the total mass of the ink composition, the near-infrared absorption shown in Tables 5 to 8 The yellow ink compositions Y2 to Y29 (the inks of Examples 2 to 29) were prepared in the same manner as in the preparation of the yellow ink composition Y1, except that the pigment dispersion was blended in the amounts shown in Tables 5 to 8. Composition) and CY1 to CY12 (ink compositions of Comparative Examples 1 to 12) were prepared.

[Preparation of Cyan Ink Composition C1]
A cyan ink composition C1 (ink composition of Example 30) was obtained in the same manner as in the preparation of the yellow ink composition Y1, except that the following composition was used in the preparation of the yellow ink composition Y1.
The produced cyan ink composition C1 has physical properties of a viscosity of 5.4 mPa · s (30 ° C.), a surface tension of 28.4 mN / m (25 ° C.), a pH of 8.2 (30 ° C.), and an electric conductivity of 153 mS / m ( 30 ° C.). The measuring method of these physical properties is the same as the measuring method in the yellow ink composition Y1.

-Composition of cyan ink composition C1-
-Cyan pigment dispersion DC1 19.00% by mass
-Self-dispersing polymer particle (resin particle) dispersion P1 38.00% by mass
Near-infrared absorbing dye dispersion A4 (diimonium salt compound DI-1)
2.00% by mass
・ Methylpropylene triglycol (MFTG) (water-soluble organic solvent, manufactured by Nippon Emulsifier Co., Ltd.)
2.00% by mass
・ Propylene glycol (PG) (water-soluble organic solvent, manufactured by ADEKA)
13.50 mass%
・ Glycerin (water-soluble organic solvent) 2.50% by mass
・ PVP K-15 (trade name, water-soluble polymer, manufactured by ISB Japan Co., Ltd.)
0.10% by mass
・ Urea 5.00% by mass
Olfin (registered trademark) E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
0.25% by mass
・ Orphine (registered trademark) E1020 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
1.00% by mass
・ Potassium nitrate 0.05% by mass
・ Cerosol (registered trademark) 524 (trade name, wax agent, manufactured by Chukyo Yushi Co., Ltd.)
6.50% by mass
-Snowtex (registered trademark) XS (trade name, colloidal silica, solid content concentration: 20% by mass, volume average particle size: 5 nm, manufactured by Nissan Chemical Co., Ltd.)
0.28% by mass
Capstone (registered trademark) FS-63 (trade name, fluorosurfactant, manufactured by Dupont)
0.01% by mass
・ BYK-024 (trade name, antifoaming agent, manufactured by Big Chemie Japan Co., Ltd.)
0.01% by mass
・ Remaining amount when pure water is 100% by mass

[Preparation of Magenta Ink Composition M1]
A magenta ink composition M1 (ink composition of Example 31) was obtained in the same manner as in the preparation of the yellow ink composition Y1, except that the following composition was used in the preparation of the yellow ink composition Y1.
The physical properties of the produced magenta ink composition M1 are as follows: viscosity 5.5 mPa · s (30 ° C.), surface tension 27.3 mN / m (25 ° C.), pH 8.4 (30 ° C.), and electric conductivity 92 mS / m ( 30 ° C.). The measuring method of these physical properties is the same as the measuring method in the yellow ink composition Y1.

-Composition of magenta ink composition M1-
-Magenta pigment dispersion DM1 42.00% by mass
Self-dispersing polymer particle (resin particle) dispersion P1 19.00% by mass
Near-infrared absorbing dye dispersion A4 (diimonium salt compound DI-1)
2.00% by mass
・ Methylpropylene triglycol (MFTG) (water-soluble organic solvent, manufactured by Nippon Emulsifier Co., Ltd.)
2.00% by mass
・ Propylene glycol (PG) (water-soluble organic solvent, manufactured by ADEKA)
12.00% by mass
・ Glycerin (water-soluble organic solvent) 2.50% by mass
・ PVP K-15 (trade name, water-soluble polymer, manufactured by ISB Japan Co., Ltd.)
0.10% by mass
・ Urea 5.00% by mass
Olfin (registered trademark) E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
0.25% by mass
・ Orphine (registered trademark) E1020 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
1.00% by mass
・ Cerosol (registered trademark) 524 (trade name, wax agent, manufactured by Chukyo Yushi Co., Ltd.)
6.00 mass%
-Snowtex (registered trademark) XS (trade name, colloidal silica, solid content concentration: 20% by mass, volume average particle size: 5 nm, manufactured by Nissan Chemical Co., Ltd.)
0.28% by mass
Capstone (registered trademark) FS-63 (trade name, fluorosurfactant, manufactured by Dupont)
0.01% by mass
・ BYK-024 (trade name, antifoaming agent, manufactured by Big Chemie Japan Co., Ltd.)
0.01% by mass
・ Remaining amount when pure water is 100% by mass

[Preparation of Black Ink Composition K1]
In the production of the yellow ink composition Y1, a black ink composition K1 (ink composition of Example 32) was obtained in the same manner as in the production of the yellow ink composition Y1, except that the following composition was used.
The physical properties of the produced black ink composition K1 are as follows: viscosity 5.5 mPa · s (30 ° C.), surface tension 28.5 mN / m (25 ° C.), pH 8.2 (30 ° C.), and electric conductivity 154 mS / m ( 30 ° C.). The measuring method of these physical properties is the same as the measuring method in the yellow ink composition Y1.

-Composition of black ink composition K1-
Black pigment dispersion DK1 16.50% by mass
-Cyan pigment dispersion DC1 3.00% by mass
-Magenta pigment dispersion DM1 4.50% by mass
-Self-dispersing polymer particle (resin particle) dispersion P1 34.00% by mass
Near-infrared absorbing dye dispersion A4 (diimonium salt compound DI-1)
1.00% by mass
・ Methylpropylene triglycol (MFTG) (water-soluble organic solvent, manufactured by Nippon Emulsifier Co., Ltd.)
2.00% by mass
・ Propylene glycol (PG) (water-soluble organic solvent, manufactured by ADEKA)
12.00% by mass
・ Glycerin (water-soluble organic solvent) 2.50% by mass
Newpol (registered trademark) PE-108 (trade name, nonionic surfactant, manufactured by Sanyo Chemical Industries, Ltd.)
0.05% by mass
・ PVP K-15 (trade name, water-soluble polymer, manufactured by ISB Japan Co., Ltd.)
0.10% by mass
・ Urea 5.00% by mass
・ Orphine (registered trademark) E1010 (trade name, surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)
0.25% by mass
・ Orphine (registered trademark) E1020 (trade name, surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)
1.00% by mass
・ Potassium nitrate 0.05% by mass
・ Cerosol (registered trademark) 524 (trade name, wax agent, manufactured by Chukyo Yushi Co., Ltd.)
6.50% by mass
-Snowtex (registered trademark) XS (trade name, colloidal silica, solid content concentration: 20% by mass, volume average particle size: 5 nm, manufactured by Nissan Chemical Co., Ltd.)
0.28% by mass
Capstone (registered trademark) FS-63 (trade name, fluorosurfactant, manufactured by Dupont)
0.01% by mass
・ BYK-024 (trade name, antifoaming agent, manufactured by Big Chemie Japan Co., Ltd.)
0.01% by mass
・ Remaining amount when pure water is 100% by mass

[Preparation of treatment liquid UC1]
The component of the following composition was mixed and the process liquid UC1 was obtained.
The physical properties of the prepared treatment liquid UC1 were a viscosity of 4.5 mPa · s (25 ° C.), a pH of 0.7 (25 ° C.), and an electric conductivity of 19.3 mS / m (25 ° C.). The measuring method of these physical properties is the same as the measuring method in the yellow ink composition Y1.

-Composition of treatment liquid UC1-
・ Tripropylene glycol monomethyl ether (TPGmME) (water-soluble organic solvent, manufactured by Tokyo Chemical Industry Co., Ltd.)
4.8% by mass
・ Diethylene glycol monobutyl ether (DEGmBE) (water-soluble organic solvent, manufactured by Tokyo Chemical Industry Co., Ltd.)
4.8% by mass
-Malonic acid (organic acidic compound) 9.1% by mass
DL-malic acid (organic acidic compound) 7.7% by mass
・ 1,2,3-propanetricarboxylic acid (organic acidic compound) 2.4% by mass
-Phosphoric acid 85 mass% aqueous solution (inorganic acidic compound) 6.7 mass%
・ Sodium dodecylbenzenesulfonate (surfactant) 0.5% by mass
・ TSA-739 (trade name, antifoaming agent, solid content: 15% by mass, manufactured by Momentive Performance Materials Japan GK)
0.1% by mass
・ Benzotriazole 1.2% by mass
・ Ion-exchanged water Total remaining amount of 100% by mass

<Image formation>
An ink jet head provided with a silicon nozzle plate was prepared, and a storage tank connected thereto was sequentially refilled with each 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.
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 process>
A description will be given according to the schematic diagram of the recording paper shown in FIG.
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 treated liquid UC1 prepared above is applied to the retained recording paper with a bar coater to a thickness of about 1.2 μm (1.5 g / m ² ), and dried immediately at 50 ° C. for 2 seconds immediately after the application. It was. Thereafter, the inkjet head is fixedly arranged so that the direction of the line head in which the nozzles are arranged (main scanning direction) is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction of the stage (sub-scanning direction), and recording paper Is moved at a constant speed in the sub-scanning direction, and in a line system with an ink droplet amount of 5.0 pL, an ejection frequency of 25.5 kHz, and a resolution of 1200 dpi × 1200 dpi, a paper grain direction (y direction in FIG. 3) and A stripe image having a width (y direction) of 50 mm and a length (x direction) of 140 mm was formed in an orthogonal direction (x direction in FIG. 3). In addition, dpi means “dot per inch”.

<Infrared irradiation process>
In FIG. 4, the schematic diagram showing the pattern which irradiates infrared rays to the image formed using the ink composition of an Example and a comparative example is shown. FIG. 4 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 the left to the right in FIG. 4 indicates that the recording paper on which an image is formed with head 1 is conveyed in the direction of the arrow. That is, FIG. 4 shows that the recording paper is subjected to infrared irradiation and hot air blowing while the recording paper is conveyed.

  An infrared heater and a hot air blower were installed on the recording paper conveyance path as shown in FIG. 4 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.

<Evaluation>
(1) Evaluation of storage stability Each ink composition obtained above was put in a glass vial, and the rate of change in viscosity after storage at 50 ° C. for 2 weeks was calculated by the following formula. From the calculated rate of change, storage stability was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 5 to 9.
The smaller the rate of change, the better the storage stability. If it is less than 20%, there is no practical problem.
Rate of change (%) = | (viscosity after storage−viscosity before storage) | / viscosity before storage × 100

-Evaluation criteria-
A: The rate of change is less than 5%.
B: The rate of change is 5% or more and less than 10%.
C: Change rate is 10% or more and less than 15%.
D: The rate of change is 15% or more and less than 20%.
E: Change rate is 20% or more.

(2) Evaluation of inkjet ejection properties After adjusting the non-ejection nozzle to be 0, 20 test images were continuously printed using each of the ink compositions obtained above. Thereafter, the nozzle check image was printed after standing for 24 hours without printing, and the number of nozzles that failed to discharge was measured. From the measured number of nozzles, the inkjet dischargeability was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 5 to 9.
The smaller the number of non-ejection nozzles, the better the inkjet ejection properties. When the number of non-ejection nozzles is 10 or more, streaks due to ejection defects become conspicuous and the value of the printed matter is impaired.

-Evaluation criteria-
A: The number of non-ejection nozzles is zero.
B: The number of non-ejection nozzles is 1 or more and 3 or less.
C: The number of non-ejection nozzles is 4 or more and 6 or less.
D: The number of non-ejection nozzles is 7 or more and 10 or less.
E: The number of non-ejection nozzles is 10 or more.

(3) Measurement of residual water amount The moisture content of the dried recording paper is determined by punching out the printed part of the paper with a size of 30 mm × 20 mm, and measuring a trace moisture (model name: CA-200, Mitsubishi Chemical Analytech Co., Ltd.). ).
Images were formed using each of the ink compositions obtained above, and measurements were made 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. A value obtained by subtracting the amount of water retained by the paper before printing from the calculated amount of water was defined as the amount of remaining water [g / m ² ].
The moisture content of the recording paper itself was separately measured using a blank paper before image formation.
The same operation was repeated three times to produce three identical images, the residual water amount was measured for each, and the average value of the three residual water amounts [g / m ² ] was calculated. From the average value of the calculated residual water amount, the drying property was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 5 to 9.
The smaller the amount of residual water, the better the drying property. If it is less than about 3 g / m ^2, there will be no practical problem. The evaluation criteria are shown below.

-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: The amount of residual water is 2 g / m ² or more and less than 3 g / m ² .
E: The amount of residual water is 3 g / m ² or more.

(4) Measurement of the amount of paper curl FIG. 3 shows a state in which an image portion 52 of a rectangular image of vertical (x direction) 140 mm × horizontal (y direction) 50 mm is formed on a 150 mm square recording paper 54. ing.
In the recording paper shown in FIG. 3, 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. 3 was formed by the same method as described above for the image formation except that the shape of the image was changed.

  In FIG. 3, the cockle in a straight line 56 portion in a 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. 3 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 cockle forms the image shown in FIG. 3 using each of the ink compositions obtained above, and within 2 minutes after drying, the height of the wrinkles of the recording paper 54 on the straight line 56 Z (displacement profile in the z direction of the recording paper 54) 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, the amount of cockle was measured for each, and the average value of the three amounts of cockle was calculated.

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√ (Δxi2 + Δzi2)”.
Note that Δxi and Δzi in the equation are parameters shown in FIG.
From the average value of the calculated amount of cockle, the cockle was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 5 to 9.
The range that does not cause a practical problem is A, B, C, or D, preferably C, more preferably B, 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 0.08%.
C: The amount of cockle is 0.08% or more and less than 0.15%.
D: The amount of cockle is 0.15% or more and less than 0.25%.
E: The amount of cockle is 0.25% or more.

(5) Evaluation of color difference The presence or absence of the color change of the image by a near-infrared absorption pigment | dye was evaluated from the color difference of each stripe image formed using each ink composition obtained above.
Specifically, first, L * a * b * of each stripe image formed using each of the ink compositions obtained above was subjected to a spectrophotometer (model name: SpectroEye, manufactured by SpectroEye GRETAG MACBETH). And measured.
Next, L * of an image formed using an ink composition of the same color (yellow (Y), magenta (M), cyan (C), and black (K)) and not containing a diimonium salt compound. A difference between a * b * (referred to as “E0”) and L * a * b * (referred to as “E1”) of an image formed using an ink composition containing a diimonium salt compound. = | E1-E0 |) was calculated, and the color difference was evaluated based on the following evaluation criteria. The evaluation results are shown in Tables 5 to 9.
The range that does not cause a practical problem is A, B, C, or D, preferably C, more preferably B, and most preferably A.

-Evaluation criteria-
A: ΔE is less than 1.
B: ΔE is 1 or more and less than 2.
C: ΔE is 2 or more and less than 3.5.
D: ΔE is 3.5 or more and less than 5.
E: ΔE is 5 or more.

In Tables 5 to 9, “mixing amount (mass%)” in the column of the near-infrared absorbing pigment dispersion means the blending amount (mass%) of the near-infrared absorbing pigment dispersion in the ink composition.
“Content (mass%)” in the column of near-infrared absorbing dye means the content (mass%) of the near-infrared absorbing dye with respect to the total mass of the ink composition.
“Polymer dispersant / near-infrared absorbing dye” in the column of polymer dispersant means the ratio (mass basis) of the content of the polymer dispersant to the content of the near-infrared absorbing dye.
“XY” in the column of the polymer dispersant means that X represents the acid value (unit: mgKOH / g) of the polymer dispersant, and Y represents the base value (unit: mgKOH / g) of the polymer dispersant. Means.
The “star polymer” described in the remarks column of the polymer dispersant means that the polymer dispersant is a star polymer having a star structure.

As shown in Tables 5 to 9, the composition contains a specific diimonium salt compound, a polymer dispersant, a colorant, and water as a near-infrared absorbing dye, and the content of the specific diimonium salt compound is based on the total mass of the ink composition. The acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy XY ≧ 10, and the specific diimonium salt compound is 0.001% by mass to 0.9% by mass The ink compositions of Examples 1 to 32 in which the ratio of the content of the polymer dispersant to the content of 0.05 to 1.2 on a mass basis is all about storage stability, paper cockle, and color difference. In the evaluation, excellent results were shown.
On the other hand, the ink compositions of Comparative Examples 1 to 12 showed inferior results in at least one evaluation of storage stability, paper curl, and color difference.
Moreover, the residual water amount after drying of the image formed using the ink composition of Examples 1-32 was small, and showed favorable drying property.
Furthermore, the ink compositions of Examples 1 to 32 showed good results also in the evaluation of the ink jetting properties.

The ink composition of Comparative Example 1 containing no near-infrared-absorbing dye could not suppress paper cuckling.
The ink composition of Comparative Example 2 in which the content of the specific dimonium salt compound was 1.5% by mass with respect to the total mass of the ink composition showed inferior results in the evaluation of storage stability and color difference. Moreover, the evaluation of inkjet discharge property was also inferior.
The ink composition of Comparative Example 3 containing a cyanine compound instead of the specific diimonium salt compound as a near-infrared absorbing dye resulted in poor storage stability and color difference evaluation.
The ratio of the content of the polymer dispersant to the content of the specific dimonium salt compound is 0.04 on a mass basis, and the ink composition of Comparative Example 5 is 1.30. In the evaluation of storage stability, the results were inferior. Further, the ink composition of Comparative Example 5 was inferior in the evaluation of the ink jetting property.
The ink compositions of Comparative Examples 6 to 12 in which the acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant do not satisfy XY ≧ 10 resulted in poor storage stability evaluation. It was.

11 Nozzle plate 12 Discharge hole 13 Liquid repellent film 100 Inkjet head

Claims (11)

A diimonium salt compound represented by the following general formula (1) as a near-infrared absorbing dye, a polymer dispersant covering at least a part of the diimonium salt compound, a colorant, and water,
The content of the diimonium salt compound is 0.001% by mass to 0.9% by mass with respect to the total mass of the ink composition,
The acid value X of the polymer dispersant is 15 mgKOH / g or more and 120 mgKOH / g or less,
The base number Y of the polymer dispersant is 0 mgKOH / g or more and 20 mgKOH / g or less,
The acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy 120 ≧ X−Y ≧ 10, and
The ink composition wherein the ratio of the content of the polymer dispersant to the content of the diimonium salt compound is 0.05 to 1.2 on a mass basis.


In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each represents an organic group which may be the same or different, and X ⁻ Represents an anion.   The ink composition according to claim 1, wherein the polymer dispersant has an acid value X of 30 mg KOH / g or more.   The ink composition according to claim 1, wherein the polymer dispersant is a star polymer. R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ in the general formula (1) are each independently an alkyl group having 4 to 8 carbon atoms. The ink composition according to claim 3. The ink composition according to claim 1, wherein X ⁻ in the general formula (1) is an anion having at least one fluorine atom. The X ⁻ in the general formula (1) is PF ₆ ⁻ , an anion represented by the following general formula (2), or an anion represented by the following general formula (3). 2. The ink composition according to item 1.


In general formula (2), R ⁹ and R ¹⁰ may be the same or different and each represents a fluorinated alkyl group having at least one fluorine atom.


In General Formula (3), R ¹¹ and R ¹² may be the same or different and each represents a fluorinated alkyl group having at least one fluorine atom.   The ink composition according to claim 1, which is a yellow ink or a magenta ink.   The ink composition according to any one of claims 1 to 7, which is used as an ink for inkjet recording. At least a diimonium salt compound represented by the following general formula (1) as a near-infrared absorbing dye, a polymer dispersant that covers at least a part of the diimonium salt compound, and a medium containing water are mixed to form an aqueous solution. A mixing step for obtaining a liquid mixture
Dispersing the aqueous mixture obtained in the mixing step to obtain an aqueous dispersion in which the near-infrared absorbing dye is dispersed by the polymer dispersant, and at least the aqueous obtained in the dispersing step the dispersion, a colorant, a mixed, seen including a preparation step of preparing an ink composition,
The content of the diimonium salt compound is 0.001% by mass to 0.9% by mass with respect to the total mass of the ink composition,
The acid value X of the polymer dispersant is 15 mgKOH / g or more and 120 mgKOH / g or less,
The base number Y of the polymer dispersant is 0 mgKOH / g or more and 20 mgKOH / g or less,
The acid value X mgKOH / g and the base value Y mgKOH / g of the polymer dispersant satisfy 120 ≧ X−Y ≧ 10, and
A method for producing an ink composition, wherein a ratio of the content of the polymer dispersant to the content of the diimonium salt compound is 0.05 to 1.2 on a mass basis .


In the general formula (1), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each represents an organic group which may be the same or different, and X ⁻ Represents an anion. An image forming step of forming an image by applying the ink composition according to any one of claims 1 to 8 to a recording medium;
An infrared irradiation step of irradiating the image formed in the image forming step with an infrared ray having a maximum emission wavelength in a wavelength region of 700 nm to 1,600 nm;
An image forming method comprising:   The image forming method according to claim 10, wherein the recording medium includes paper.