JP5680360B2 - Black ink-jet recording ink composition and ink-jet image forming method - Google Patents

Description

  The present invention relates to a black ink jet recording ink composition and an ink jet image forming method.

Various techniques for obtaining high-quality recorded matter such as color density, fixability, and resolution have been studied for recording media for ink jet recording and inks used therefor.
Pigments are widely used as colorants used in ink for ink jet recording from the viewpoint of light resistance and water resistance. Carbon black is generally used as a pigment for black ink in recording liquids for ink jet printers.

In general, black ink using carbon black tends to have a reddish black color tone in a region where the print density is low.
On the other hand, various black ink compositions that can output neutral black by using complementary color pigments have been developed. For example, an ink jet recording liquid containing carbon black and a water-insoluble phthalocyanine-based dye is disclosed, and is excellent in blackness, gloss, and scratch resistance (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 4461222 JP 2009-144007 A

However, in the ink jet recording liquids described in Patent Documents 1 and 2, it is sometimes difficult to say that the formed image has sufficient abrasion resistance.
An object of the present invention is to provide a black inkjet recording ink composition that can form an image having excellent abrasion resistance and excellent dischargeability, and an inkjet image forming method using the same.

Specific means for solving the above problems are as follows.
<1> A carbon black pigment, at least one color pigment selected from a phthalocyanine pigment and a quinacridone pigment whose primary particle size is controlled by a salt milling treatment, and an aqueous medium, and an average primary particle size is 50 nm or less. A black ink jet recording ink composition, wherein the ratio of the average secondary particle diameter to the average primary particle diameter (average secondary particle diameter / average primary particle diameter) is 2.0 to 3.0.

<2> The black ink jet recording ink composition according to <1>, further including resin particles.

<3> The black ink jet recording ink composition according to <1> or <2>, wherein the average primary particle diameter is 35 nm or less.

<4> The content ratio of the color pigment to the carbon black pigment (color pigment / carbon black pigment) is 50% by mass or more and 200% by mass or less, according to any one of <1> to <3>. Black ink-jet recording ink composition.

<5> The black color according to any one of <1> to <4>, wherein a content ratio of the quinacridone pigment to the phthalocyanine pigment (quinacridone pigment / phthalocyanine pigment) is 100% by mass or more and 180% by mass or less. -Based inkjet recording ink composition.

<6> The black resin according to any one of <2> to <5>, wherein the resin particles include a structural unit derived from an alicyclic (meth) acrylate and an anionic hydrophilic structural unit. Ink composition for inkjet recording.

<7> The black inkjet recording ink composition according to any one of <2> to <6>, wherein the resin particles have a glass transition temperature of 100 ° C. or higher and 200 ° C. or lower.

<8> The carbon black pigment and the colored pigment are water-insoluble resins having phenoxyethyl (meth) acrylate as a hydrophobic unit, and are pigments on which at least a part of the surface is coated. Any one of <1> to <7> The black ink-jet recording ink composition as described in one.
<9> An inkjet image forming method including an ink application step of applying the black inkjet recording ink composition according to any one of <1> to < 8 > onto a recording medium by an inkjet method.

< 10 > The inkjet image forming method according to < 9 >, wherein the recording medium is a coated paper having a base paper and a coating layer containing an inorganic pigment.

<1 1 > A treatment liquid application step of applying a treatment liquid capable of aggregating the components of the black ink jet recording ink composition onto a recording medium by contacting with the black ink jet recording ink composition. The inkjet image forming method according to < 9 > or < 10 >.

<1 2 > The method according to any one of < 9 > to <1 1 >, further including a heat fixing step of heat-pressing the recording medium to which the black ink-jet recording ink composition is applied. Inkjet image forming method.

  According to the present invention, it is possible to provide a black ink jet recording ink composition that can form an image having excellent abrasion resistance and excellent dischargeability, and an ink jet image forming method using the same.

The black ink-jet recording ink composition of the present invention (hereinafter also simply referred to as “ink composition”) is a color pigment selected from a carbon black pigment and a phthalocyanine pigment and a quinacridone pigment whose primary particle diameter is controlled by a salt milling treatment. The average primary particle diameter is 50 nm or less, and the ratio of the average secondary particle diameter to the average primary particle diameter (average secondary particle diameter / average primary particle diameter) is 2.0. It is -3.0.
With such an embodiment, an image having excellent color tone and abrasion resistance can be formed in image formation by an inkjet method.

  This can be considered as follows, for example. Even when the average primary particle diameter of the carbon black pigment is small, the primary particles are bonded to each other to form a structure and form secondary particles having a large particle diameter. When an ink composition containing a carbon black pigment having such a structure is applied to a recording medium to form an image, the carbon black pigment in the image tends to be thick without being compactly packed. is there. An image formed with such a bulky carbon black pigment may have low abrasion resistance. In the present invention, the average primary particle diameter is a predetermined numerical value or less, and the ratio of the average secondary particle diameter to the average primary particle diameter is a small value, so that the carbon black pigment in the image is compactly collected, and the image It can be considered that the rubbing resistance is improved.

In the ink composition of the present invention, the average primary particle diameter is 50 nm or less, but from the viewpoint of abrasion resistance and dispersion stability, the average primary particle diameter is preferably 10 nm or more and 35 nm or less, and 20 nm or more and 30 nm or less. It is more preferable that
In the ink composition of the present invention, the ratio of the average secondary particle diameter to the average primary particle diameter (average secondary particle diameter / average primary particle diameter) is 2.0 to 3.0. From the viewpoint of dischargeability, the ratio of the average secondary particle diameter to the average primary particle diameter is preferably 2.2 to 3.0, and more preferably 2.5 to 3.0.

In the present invention, the average primary particle size of the ink composition is determined by using a transmission electron microscope (TEM 2010, acceleration voltage 200 kV, manufactured by JEOL Ltd.) after the ink composition is dropped on a carbon support film and dried. It is calculated as an arithmetic average of the particle diameters (equivalent circle diameters) of 1000 particles observed and arbitrarily selected. In addition, when the particle | grains observed comprise the secondary particle | grains which the primary particle couple | bonded, the particle diameter of each primary particle | grains which comprise a secondary particle is measured.
The average secondary particle diameter of the ink composition is a volume average particle diameter measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.).

As a method of averaging the primary particle diameter 50nm or less, for example, a method of selecting appropriate carbon black pigment and coloring pigment used from commercial, there may be mentioned a method in which salt milling process pigments, colored pigments Salt The primary particle size is controlled by milling.
Moreover, as a method of controlling the ratio of the average secondary particle diameter to the average primary particle diameter to 2.0 to 3.0, for example, a method using a pigment dispersion manufactured by a method for manufacturing a pigment dispersion described later, etc. Can be mentioned.

In the present invention, salt milling that is preferably used as a method for controlling the average primary particle size will be described.
In salt milling, for example, a pigment particle is efficiently refined and refined by kneading a mixture containing a pigment, a water-soluble inorganic salt, and a water-soluble organic solvent and grinding the pigment. A pigment grind having a narrow particle size distribution is obtained.

In the salt milling method, grinding is performed by kneading a mixture of a pigment before grinding (hereinafter sometimes referred to as “crude pigment”), a water-soluble inorganic salt, and a water-soluble organic solvent. It includes a process, and can include other processes as necessary.
The method for kneading the mixture is not particularly limited as long as it can mechanically knead the mixture, and a commonly used method can be used. For example, batch-type kneaders such as kneaders, batch-type kneaders such as Supermixer (manufactured by Kawata Co., Ltd.) and Trimix (manufactured by Inoue Seisakusho Co., Ltd.), continuous single-screw kneader KCK mill (Asada Tekko Co., Ltd.) The method using a continuous kneader such as (made)) can be mentioned. In the present invention, it is preferable to use a continuous kneader from the viewpoints of refinement efficiency and particle size distribution.

  The continuous kneader includes, for example, a fixed blade and a rotating blade that can give the crude pigment three actions of compression, shearing, and mixing (substitution) whose grinding part is an element necessary for kneading and dispersing. It is preferable to have. In addition, the crests and crests of the fixed blade and the rotating blade form a gap (gap), and a shearing action occurs in the gap, and the material between the valleys of the rotating blade and the fixed blade mutually forms a cavity slice. It is preferable to have received.

  The shapes of the fixed blade and the rotating blade are not particularly limited, but are preferably selected from three types, a chrysanthemum shape, a fan shape, and a mortar shape. It is preferable that the stationary blades and the rotating blades are alternately stacked in multiple stages, whereby cavities can be radially formed on both surfaces of each blade. Further, it is preferable that the rotating blade and the intermediate screw are alternately incorporated on the rotating shaft, and the fixed blade is preferably fixed to the feed cylinder by the tie rod alternately with the shear chamber cylinder. Thus, the kneaded product can be extruded.

Furthermore, it is preferable that the continuous kneader has at least six temperature control sections in the mixture charging section, grinding section and extrusion section. Thereby, the temperature range in the grinding process of a crude pigment can be set widely.
There is no restriction | limiting in particular as processing temperature in the said grinding process, For example, although it can be set as 5-200 degreeC, it is preferable that it is 5-50 degreeC from a viewpoint of discoloration of a pigment particle and a particle size distribution, 10-10. More preferably, it is 35 degreeC.

  Moreover, it is preferable that the continuous kneader can change the discharge amount according to the mixing ratio of the crude pigment, the water-soluble inorganic salt and the water-soluble organic solvent, or the shaft rotation speed. By changing the discharge amount, the ground particle diameter of the pigment can be easily controlled to a desired particle diameter.

The method for producing a pigment ground product by salt milling may include other steps as needed in addition to the grinding step. As other steps, for example, the mixture after the grinding step is put into water or the like and stirred, and then the pigment ground product is separated by filtration or the like to remove the water-soluble inorganic salt and the water-soluble organic solvent. Examples thereof include a washing step, a drying step for drying the pigment ground product obtained in the washing step, and the like.
In these washing steps and drying steps, a method usually used in a so-called solvent salt milling method can be applied without particular limitation in the present invention.

(Water-soluble inorganic salt)
As the water-soluble inorganic salt, a commonly used water-soluble inorganic salt can be used without particular limitation. Specific examples include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate and the like. The particle diameter of the water-soluble inorganic salt is not particularly limited, but from the viewpoint of controlling the particle diameter of the secondary aggregate of pigment, the water-soluble inorganic salt has a volume-based median diameter of 0.5 to 50 μm. It is preferable that it is 1-20 micrometers, It is more preferable that it is 1-10 micrometers.

  The content of the water-soluble inorganic salt in the mixture can be appropriately selected according to the type of the crude pigment. For example, it can be set to 1 to 30 parts by mass with respect to 1 part by mass of the crude pigment, and is preferably 3 to 20 parts by mass and more preferably 5 to 15 parts by mass from the viewpoint of productivity. .

(Water-soluble organic solvent)
The water-soluble organic solvent is not particularly limited as long as it is an organic solvent that dissolves in water and does not substantially dissolve the water-soluble inorganic salt. The water-soluble organic solvent can be used to adjust a mixture containing a crude pigment and a water-soluble inorganic salt to a hardness applicable to kneading. Examples of the water-soluble organic solvent include monohydric alcohols, polyhydric alcohols, and polyhydric alcohol derivatives. More specifically, monohydric alcohol solvents such as propyl alcohol, 2-butyl alcohol and tert-butyl alcohol; alkylenes such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and polypropylene glycol Glycol solvents; and their derivatives ethylene glycol monoalkyl ether, diethylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, dipropylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, and other glycol monoether systems Solvent; glycerin, diglycerin, polyglycerin, etc. , And the like and a water-soluble organic solvents such as glycerol ether derivatives thereof; glycerin-based solvent.
The water-soluble organic solvent used in the present invention is not limited to the above.

  The content of the water-soluble organic solvent in the mixture can be appropriately selected according to the type of the crude pigment and the content of the water-soluble inorganic salt. It can be 5 mass parts, Preferably it is 2-3 mass parts.

(Carbon black pigment)
The black ink-jet recording ink composition of the present invention contains at least one carbon black pigment. Although there is no restriction | limiting in particular as a carbon black pigment, From the point of the abrasion resistance of an image, image density, and storage stability, it is preferable that it is a carbon black pigment whose pH is an acidic to neutral area | region. Furthermore, the average primary particle diameter of the carbon black pigment is preferably 10 to 50 nm, and more preferably 10 to 30 nm.
The average primary particle size is a particle size (equivalent to a circle) of 1000 primary particles arbitrarily selected from an image taken using a transmission electron microscope TEM2010 (pressurized voltage 200 kV) manufactured by JEOL Ltd. Diameter) is measured and calculated as the arithmetic average.

The pH of the carbon black pigment is preferably in the acidic to neutral range, since easy dispersibility can be obtained, more preferably pH 2.0 to pH 8.5, and pH 2.5 to pH 8.0. It is particularly preferred.
The pH of the carbon black pigment is measured as the pH (25 ° C.) of the aqueous dispersion of the carbon black pigment.

The DBP absorption amount of the carbon black pigment is not particularly limited, but is preferably 30 ml / 100 g or more and 130 ml / 100 g or less, and more preferably 50 ml / 100 g or more and 100 ml / 100 g or less from the viewpoint of color tone and print density. .
The DBP absorption is measured by the JIS K6221 A method.

Also, the carbon black BET specific surface area of the pigment is not particularly limited, from the viewpoint of printing density and storage stability, is preferably not more than ^{30 m} 2 / g or more ^{450m 2 / g, 200m 2 /} g or more 400 meters ² / g The following is more preferable.

Examples of the carbon black pigment include those produced by known methods such as a contact method, a furnace method, and a thermal method.
Specific examples include Raven7000, Raven5750, Raven5250, Raven5000ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1200, Raven1190 ULTRAII, Raven1170, Raven1170, Raven1170 Regal 330R, Regal 660R, Mogul L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (above, manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S150, Color Black S160, Color Black S160, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black S150 , Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, NIPEX 180-IQ, NIPEX 170-IQ (manufactured by Degussa), No. 25, no. 33, no. 40, no. 45, no. 47, no. 52, no. 900, no. 2200B, no. 2300, no. 990, no. 980, no. 970, no. 960, no. 950, no. 850, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical Corporation). However, it is not limited to these.

The above carbon black pigments may be used singly or in combination of two or more.
The content ratio of the carbon black pigment in the ink composition of the present invention is not particularly limited. It is more preferable that

(Color pigment)
The ink composition of the present invention contains at least one color pigment selected from phthalocyanine pigments and quinacridone pigments in addition to the carbon black pigment. The phthalocyanine pigment and quinacridone pigment can be appropriately selected from known organic pigments according to the purpose. Specific examples of the organic pigment used in the present invention are shown below.

  As the phthalocyanine pigment, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. C.I. preferably at least one selected from CI Pigment Blue 16. I. Pigment blue 15: 3, C.I. I. More preferably, it is at least one selected from CI Pigment Blue 15: 4.

  As the quinacridone pigment, C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 209, C.I. I. It is preferably at least one selected from pigment violet 19.

  The colored pigment in the present invention more preferably contains at least one phthalocyanine pigment and at least one quinacridone pigment from the viewpoints of color tone and abrasion resistance.

  In the present invention, the content ratio of the color pigment to the carbon black pigment (color pigment / carbon black pigment) is not particularly limited, but may be 50% by mass or more and 200% by mass or less from the viewpoint of color tone and abrasion resistance. Preferably, it is 60 mass% or more and 100 mass% or less.

  Further, the content ratio of the quinacridone pigment to the phthalocyanine pigment in the colored pigment (quinacridone pigment / phthalocyanine pigment) is not particularly limited, but is preferably 100% by mass or more and 180% by mass or less from the viewpoint of color tone and abrasion resistance. More preferably, it is at least 150% by mass.

(Water-insoluble resin)
The carbon black pigment and the colored pigment in the present invention (hereinafter collectively referred to simply as “pigment”) are water-dispersible pigment particles in which at least a part of the surface thereof is coated with at least one kind of water-insoluble resin. The ink composition of the present invention is preferably constituted.
That is, the water-insoluble resin preferably functions as a polymer dispersant.

  The water-insoluble resin in the present invention is not particularly limited as long as it is a resin that dissolves in an organic solvent and covers at least a part of the pigment so that it can be dispersed in water. Examples thereof include nonionic polymer compounds, anionic polymer compounds, cationic polymer compounds, and amphoteric polymer compounds that are copolymers of monomers having an ethylenically unsaturated group.

In the water-insoluble resin in the present invention, the pigment can be stably present in an aqueous medium, the adhesion or deposition of aggregates is alleviated, and from the viewpoint of facilitating the removal of the adhered aggregates, hydrophilic structural units. And a resin comprising a hydrophobic structural unit.
Furthermore, the water-insoluble resin preferably includes at least one structural unit represented by the following general formula (I) as the hydrophobic structural unit.

In the general formula (I), R ¹ represents a hydrogen atom or a methyl group, preferably a methyl group.

Ar represents an unsubstituted or substituted aromatic ring group. Examples of the substituent when the aromatic ring group is substituted include a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, and a cyano group.
The aromatic ring group may form a condensed ring. Examples of the case where a condensed ring is formed include a group derived from a condensed aromatic ring having 8 or more carbon atoms and a group derived from an aromatic ring condensed with a heterocycle. Furthermore, Ar may be a group derived from a compound in which two or more aromatic rings are linked.

The “condensed aromatic ring having 8 or more carbon atoms” includes an aromatic ring in which at least two benzene rings are condensed, at least one aromatic ring and a condensed alicyclic hydrocarbon ring. Is an aromatic compound having 8 or more carbon atoms. Specific examples include naphthalene, anthracene, fluorene, phenanthrene, acenaphthene and the like.
The “aromatic ring condensed with a heterocycle” is a compound in which an aromatic compound containing no hetero atom (preferably a benzene ring) and a cyclic compound having a hetero atom are condensed. Here, the cyclic compound having a hetero atom is preferably a 5-membered ring or a 6-membered ring. As a hetero atom, a nitrogen atom, an oxygen atom, or a sulfur atom is preferable. The cyclic compound having a hetero atom may have a plurality of hetero atoms. In this case, the heteroatoms may be the same or different from each other. Specific examples of the aromatic ring condensed with a heterocycle include phthalimide, acridone, carbazole, benzoxazole, and benzothiazole.

  Examples of the group derived from a compound in which two or more aromatic rings are linked include a biphenyl group and a triphenylmethyl group.

The aromatic ring represented by Ar is bonded to the main chain of the water-insoluble resin through an ester group and an ethyleneoxy group, and the aromatic ring is not directly bonded to the main chain. A suitable distance is maintained between the hydrophilic structural unit and the hydrophilic structural unit. Therefore, the water-insoluble resin is likely to interact with the pigment, and is strongly adsorbed on the pigment to enhance dispersibility.
Among these, as Ar, an unsubstituted benzene ring and an unsubstituted naphthalene ring are preferable, and an unsubstituted benzene ring is particularly preferable.

  n represents the number of repetitions obtained by averaging ethyleneoxy groups in the water-insoluble resin. The range of n is 1-6, preferably 1-2.

  Specific examples of the monomer forming the structural unit represented by the general formula (I) include the following monomers including phenoxyethyl (meth) acrylate. In addition, this invention is not limited to these.

Among the structural units represented by the general formula (I), when R ¹ is a methyl group, Ar is an unsubstituted benzene ring, and n is 1 to 2 in terms of dispersion stability Is particularly preferred.

  The content ratio of the structural unit represented by the general formula (I) in the water-insoluble resin is preferably in the range of 30 to 70% by mass, more preferably 40 to 50% by mass with respect to the total mass of the water-insoluble resin. Range. When the content is 30% by mass or more, the dispersibility is excellent. When the content is 70% by mass or less, the adhesion / deposition of the aggregates is suppressed, and the attached aggregates are easily removed (maintenance). The occurrence of image failure can be suppressed.

The water-insoluble resin may further contain at least one hydrophobic structural unit other than the hydrophobic structural unit represented by the general formula (I).
As other hydrophobic structural units, for example, they do not belong to hydrophilic structural units (for example, have no hydrophilic functional group), for example, (meth) acrylates, (meth) acrylamides, styrenes, vinyl esters, etc. And a structural unit derived from vinyl monomers and the like, as well as a hydrophobic structural unit having an aromatic ring via a linking group at the atom forming the main chain. These structural units can be used individually by 1 type or in mixture of 2 or more types.

Examples of the (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, and the like. ) Acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate are preferable, and methyl (meth) acrylate and ethyl (meth) acrylate are particularly preferable.
Examples of the (meth) acrylamides include N-cyclohexyl (meth) acrylamide, N- (2-methoxyethyl) (meth) acrylamide, N, N-diallyl (meth) acrylamide, N-allyl (meth) acrylamide, and the like. (Meth) acrylamides.
Examples of the styrenes include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, n-butyl styrene, tert-butyl styrene, methoxy styrene, butoxy styrene, acetoxy styrene, chlorostyrene, dichlorostyrene, Examples thereof include bromostyrene, chloromethylstyrene, hydroxystyrene protected with a group that can be deprotected by an acidic substance (for example, t-Boc), methyl vinylbenzoate, α-methylstyrene, vinylnaphthalene, and the like. Styrene and α-methylstyrene are preferred.
Examples of the vinyl esters include vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl methoxyacetate, and vinyl benzoate. Of these, vinyl acetate is preferable.

  In the “hydrophobic structural unit having an aromatic ring via a linking group on an atom constituting the main chain”, the aromatic ring is bonded to the atom constituting the main chain of the water-insoluble resin via the linking group, and the main chain of the water-insoluble resin is obtained. Since a suitable distance is maintained between the hydrophobic aromatic ring and the hydrophilic structural unit, the water-insoluble resin and the pigment are likely to interact with each other. Adsorbs firmly and dispersibility is further improved.

  The “hydrophobic structural unit having an aromatic ring via a linking group on the atom constituting the main chain” is a structural unit represented by the following general formula (II) (the structural unit represented by the general formula (I) Except).

In the general formula (II), R ¹ represents a hydrogen atom, a methyl group, or a halogen atom.
L ¹ represents ^* —COO—, ^* —OCO—, ^* —CONR ² —, ^* —O—, or a substituted or unsubstituted phenylene group, and R ² represents a hydrogen atom having 1 to 10 carbon atoms. Represents an alkyl group. Incidentally, symbol * in the group represented by L ¹ represents a connecting point with the main chain. Although it does not specifically limit as a substituent in case the phenylene group is substituted, For example, a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, a cyano group etc. are mentioned.

L ² represents a single bond, an imino group (—NH—), a sulfamoyl group, or a divalent linking group having 1 to 30 carbon atoms, and when it is a divalent linking group, preferably 1 to 25 carbon atoms. More preferably, it is a C1-C20 coupling group, More preferably, it is a C1-C15 coupling group.
Among them, particularly preferably, an alkyleneoxy group having 1 to 25 carbon atoms (more preferably 1 to 10), an imino group (—NH—), a sulfamoyl group, and 1 to 20 carbon atoms (more preferably 1 to 15). A divalent linking group containing an alkylene group, such as an alkylene group or an ethylene oxide group [— (CH ₂ CH ₂ O) _n —, n = 1 to 6], etc., and a group in which two or more of these are combined is there.

In the general formula (II), Ar ¹ represents a monovalent group derived from an aromatic ring compound.
The aromatic ring compound in Ar ¹ is not particularly limited, and examples thereof include benzene, a condensed aromatic compound having 8 or more carbon atoms, an aromatic ring compound in which a heterocycle is condensed, and a compound in which two or more aromatic rings are connected. It is done. The details of the condensed aromatic ring compound having 8 or more carbon atoms, the aromatic ring compound in which the heterocycle is condensed, and the compound in which two or more aromatic rings are connected are as described above.

  Hereinafter, specific examples of monomers capable of forming a hydrophobic structural unit having an aromatic ring via a linking group at the atom forming the main chain will be given. However, the present invention is not limited to the following specific examples.

  The hydrophilic structural unit in the water-insoluble resin is not particularly limited as long as it is a structural unit derived from a monomer containing a hydrophilic group. The hydrophilic group may be any of anionic, cationic and nonionic. In the present invention, from the viewpoint of dispersibility, the hydrophilic structural unit preferably includes at least one structural unit including an anionic hydrophilic group, and includes a structural unit derived from at least one of acrylic acid and methacrylic acid. It is preferable.

The water-insoluble resin in the present invention preferably contains a structural unit derived from at least one of acrylic acid and methacrylic acid, but may contain other hydrophilic structural unit. Examples of other hydrophilic structural units include structural units derived from monomers having a nonionic hydrophilic group or a cationic hydrophilic group.
Examples of the nonionic or cationic “hydrophilic functional group” include a hydroxyl group, an amino group, an amide group (the nitrogen atom is unsubstituted), and alkylene oxides such as polyethylene oxide and polypropylene oxide described later.

  Examples of the monomer having a nonionic or cationic hydrophilic group include (meth) acrylates, (meth) acrylamides, and vinyl esters having a nonionic or cationic hydrophilic functional group. Mention may be made of structural units derived from vinyl monomers.

  Monomers that form a hydrophilic structural unit having a nonionic or cationic hydrophilic group include a functional group capable of forming a polymer such as an ethylenically unsaturated bond and a nonionic or cationic hydrophilic function. If it has a group, there will be no restriction | limiting in particular, It can select from a well-known monomer. Specific examples include hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, (meth) acrylamide, aminoethyl acrylate, aminopropyl acrylate, and (meth) acrylate containing an alkylene oxide polymer. Can do.

  The hydrophilic structural unit having a nonionic or cationic hydrophilic group can be formed by polymerization of a corresponding monomer, but a hydrophilic functional group may be introduced into the polymer chain after polymerization.

  The hydrophilic structural unit having a nonionic hydrophilic group is more preferably a hydrophilic structural unit having an alkylene oxide structure. The alkylene moiety of the alkylene oxide structure is preferably an alkylene moiety having 1 to 6 carbon atoms, more preferably an alkylene moiety having 2 to 6 carbon atoms, and particularly preferably an alkylene moiety having 2 to 4 carbon atoms from the viewpoint of hydrophilicity. Moreover, as a polymerization degree of an alkylene oxide structure, 1-120 are preferable, 1-60 are more preferable, and 1-30 are especially preferable.

  Moreover, it is also a preferable aspect that the hydrophilic structural unit having a nonionic hydrophilic group is a hydrophilic structural unit containing a hydroxyl group. The number of hydroxyl groups in the structural unit is not particularly limited, and is preferably 1 to 4, more preferably 1 to 3, from the viewpoint of hydrophilicity of the water-insoluble resin and compatibility with the solvent and other monomers during polymerization. 1-2 is particularly preferred.

The content ratio of the hydrophilic structural unit in the water-insoluble resin in the present invention differs depending on the ratio of the hydrophobic structural unit. For example, when the water-insoluble resin is composed only of acrylic acid and / or methacrylic acid [hydrophilic structural unit] and a hydrophobic structural unit, the content ratio of acrylic acid and / or methacrylic acid is “100- (hydrophobic (Mass% of structural unit) ”.
A hydrophilic structural unit can be used individually by 1 type or in mixture of 2 or more types.

As the water-insoluble resin in the present invention, the composition of the hydrophilic structural unit and the hydrophobic structural unit (including the structural unit represented by the general formula (I)) also affects the degree of hydrophilicity and hydrophobicity of each. However, the ratio of the hydrophilic structural unit is preferably 15% by mass or less. At this time, the proportion of the hydrophobic structural unit is preferably more than 80% by mass and more preferably 85% by mass or more with respect to the total mass of the water-insoluble resin.
When the content of the hydrophilic structural unit is 15% by mass or less, the amount of components that are dissolved in water alone is suppressed, and various properties such as pigment dispersion are improved, and good ink ejection properties are obtained during inkjet recording. It is done.

  A preferable content ratio of the hydrophilic structural unit is in the range of more than 0% by mass and 15% by mass or less, more preferably in the range of 2 to 15% by mass, and still more preferably, with respect to the total mass of the water-insoluble resin. It is in the range of 5 to 15% by mass, particularly preferably in the range of 8 to 12% by mass.

  The content of the aromatic ring contained in the water-insoluble resin is preferably 27% by mass or less, more preferably 25% by mass or less, and more preferably 20% by mass or less with respect to the total mass of the water-insoluble resin. More preferably it is. Especially, it is preferable that it is 15-20 mass%, and the range of 17-20 mass% is more preferable. When the content ratio of the aromatic ring is within the above range, the scratch resistance is improved.

The acid value of the water-insoluble resin in the present invention is preferably from 30 mgKOH / g to 100 mgKOH / g and more preferably from 30 mgKOH / g to 85 mgKOH / g from the viewpoint of pigment dispersibility and storage stability. It is preferably 50 mgKOH / g or more and 85 mgKOH / g or less.
The acid value is defined by the mass (mg) of KOH required to completely neutralize 1 g of the water-insoluble resin, and is measured by the method described in JIS standards (JIS K0070, 1992).

The molecular weight of the water-insoluble resin in the present invention is preferably 30,000 or more in terms of weight average molecular weight (Mw), more preferably 30,000 to 150,000, still more preferably 30,000 to 100,000, particularly preferably 30,000 to 50,000. When the molecular weight is 30,000 or more, the steric repulsion effect as a dispersant tends to be good, and the steric effect makes it easy to adsorb to the pigment.
Further, the number average molecular weight (Mn) is preferably in the range of 1,000 to 100,000, particularly preferably in the range of 3,000 to 50,000. When the number average molecular weight is within the above range, a function as a coating film in the pigment or a function as a coating film of the ink composition can be exhibited. The water-insoluble resin in the present invention is preferably used in the form of an alkali metal or organic amine salt.

  The molecular weight distribution (weight average molecular weight / number average molecular weight) of the water-insoluble resin in the present invention is preferably in the range of 1 to 6, and more preferably in the range of 1 to 4. When the molecular weight distribution is within the above range, the dispersion stability and ejection stability of the ink can be improved.

  The number average molecular weight and the weight average molecular weight are measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corporation), TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) as columns, and THF (tetrahydrofuran) as an eluent. The molecular weight is obtained by conversion with polystyrene as a standard substance. The conditions are a sample concentration of 0.35 mass%, a flow rate of 0.35 ml / min, a sample injection amount of 10 μl, a measurement temperature of 40 ° C., and an RI detector. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

The water-insoluble resin in the present invention can be synthesized by various polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, precipitation polymerization, bulk polymerization, and emulsion polymerization. The polymerization reaction can be performed by a known operation such as a batch system, a semi-continuous system, or a continuous system. The polymerization initiation method includes a method using a radical initiator, a method of irradiating light or radiation, and the like. These polymerization methods and polymerization initiation methods are described in, for example, the revised version of Tsuruta Junji “Polymer Synthesis Method” (published by Nikkan Kogyo Shimbun, 1971), Takatsu Otsu and Masato Kinoshita, “Experimental Methods for Polymer Synthesis” , Published in 1972, pages 124-154.
Among the polymerization methods, a solution polymerization method using a radical initiator is particularly preferable. Solvents used in the solution polymerization method are, for example, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, benzene, toluene, acetonitrile And various organic solvents such as methylene chloride, chloroform, dichloroethane, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and the like. A solvent may be used individually by 1 type or in combination of 2 or more types. Moreover, you may use as a mixed solvent with water. The polymerization temperature needs to be set in relation to the molecular weight of the polymer to be produced, the type of initiator, etc., and is usually about 0 ° C. to 100 ° C., but the polymerization is preferably performed in the range of 50 to 100 ° C. . Although reaction pressure can be selected suitably, it is 1-100 kg / cm < ² > normally, and about 1-30 kg / cm < ² > is especially preferable. The reaction time is about 5 to 30 hours. The obtained resin may be subjected to purification such as reprecipitation.

  Hereinafter, preferred specific examples of the water-insoluble resin in the present invention will be shown. However, the present invention is not limited to the following. In addition, the numerical value of the lower right parenthesis of B-11-B-13 represents the mass%.

  The ratio (p: r) between the pigment (p) and the water-insoluble resin (r) in the present invention is preferably 100: 25 to 100: 140, more preferably 100: 25 to 100: 50, by mass ratio. If the ratio of the water-insoluble resin is 100: 25 or more, the dispersion stability and the abrasion resistance tend to be improved, and if it is 100: 140 or less, the dispersion stability tends to be improved.

In the present invention, a method for obtaining an aqueous pigment dispersion from the pigment and the water-insoluble resin is not particularly limited, but is preferably performed as follows.
The method for producing a pigment dispersion in the present invention is basically preferably a method called a phase inversion emulsification method. The phase inversion emulsification method is 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 further contain a curing agent or a polymer compound. Here, the mixed molten material refers to a mixed state that is not dissolved, a state that is dissolved and mixed, or a state that includes both of these states. For a specific method by the “phase inversion emulsification method”, for example, the method described in JP-A-10-140065 can be referred to.
In general, in the phase inversion emulsification method, since the water-insoluble resin acts as a dispersant, it is not necessary to use a dispersant other than the water-insoluble resin, but other resin dispersants may be used as long as the effects of the present invention are not impaired. .

-Manufacturing method of pigment dispersion-
The pigment dispersion in the present invention contains a pigment (at least one of a carbon black pigment and a colored pigment), a water-insoluble resin (dispersant), an organic solvent that dissolves or disperses the water-insoluble resin, and a basic substance. It is preferable to manufacture by mixing at least a part of the organic solvent (solvent removal step) after mixing a solution containing selenium as a main component (mixing / hydration step).
According to this method for producing a pigment dispersion, the pigment coated with the water-insoluble resin is finely dispersed, and a pigment dispersion excellent in storage stability can be produced. Moreover, the ratio of the average secondary particle diameter to the average primary particle diameter can be easily controlled within a desired range.

  Although the pigment dispersion in this invention can be manufactured with the manufacturing method containing the process (1) and process (2) shown in detail below, it is not limited to this.

Step (1): A step of dispersing a mixture containing a pigment, a water-insoluble resin, an organic solvent for dissolving and dispersing the water-insoluble resin, a basic substance, and water. Step (2): Dispersion Removing at least a portion of the organic solvent from the mixture after treatment;

In the step (1), first, the water-insoluble resin is dissolved or dispersed in an organic solvent to obtain a mixture thereof (mixing step). Next, a pigment, a basic substance-containing solution containing water as a main component, water, and, if necessary, a surfactant or the like are added to the mixture and mixed and dispersed to obtain an oil-in-water color. A material particle dispersion is obtained.
Preferred embodiments of the water-insoluble resin used as the dispersant are as described above.

  Preferable examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents. Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable, and methyl ethyl ketone is more preferable.

  As the pigment, at least two of the carbon black pigment and the color pigment described above are used. In the method for producing the pigment dispersion, the carbon black pigment and the color pigment can be separately dispersed to obtain each pigment dispersion. However, the carbon black pigment and the color pigment are mixed, and this mixture is mixed. It is preferable to obtain a pigment dispersion by dispersion treatment. Thereby, the ratio of the average secondary particle diameter to the average primary particle diameter can be controlled to a desired range more efficiently.

Examples of basic substances include alcohol amines (eg, diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol), alkali metal hydroxides (eg, lithium hydroxide, water, etc.). Sodium hydroxide, potassium hydroxide, etc.), ammonium hydroxide (eg, ammonium hydroxide, quaternary ammonium hydroxide), phosphonium hydroxide, alkali metal carbonate, etc., sodium hydroxide, potassium hydroxide Are preferably used.
There is no limitation in the addition amount (degree of neutralization) of the basic substance. Usually, it is preferable that the liquid property of the pigment dispersion finally obtained is liquid property close to neutrality, for example, pH (25 degreeC) is 4.5-10. The pH can also be determined by the degree of neutralization according to the water-insoluble resin.

In the method for producing the pigment dispersion, a strong shearing force is applied using a two-roll, a three-roll, a ball mill, a tron mill, a disper, a kneader, a kneader, a homogenizer, a blender, a single screw or a twin screw extruder, and the like. The kneading and dispersing process can be carried out.
For details on kneading and dispersing, see T.W. C. “Paint Flow and Pigment Dispersion” by Patton (published by John Wiley and Sons, 1964) and the like.
In addition, if necessary, using a sand grinder, a pin mill, a slit mill, an ultrasonic disperser, etc., and using beads made of glass having a particle diameter of 0.01 to 1 mm, zirconia, etc. It can be obtained by performing distributed processing.

Moreover, in the manufacturing method of the pigment dispersion in this invention, the removal of the said organic solvent is not specifically limited, It can remove by well-known methods, such as vacuum distillation.
A resin-coated pigment particle dispersion in which the pigment particle surface is coated with a water-insoluble resin can be obtained by removing the organic solvent and performing phase inversion to an aqueous system. It is preferable that the organic solvent in the obtained dispersion is substantially removed. The amount of the organic solvent after removal here is preferably 0.2% by mass or less, and more preferably 0.1% by mass or less.

Furthermore, in the method for producing a pigment dispersion in the present invention, it is also preferable to add the water-insoluble resin in two portions and disperse it.
That is, a first dispersion step in which a first water-insoluble resin, an organic solvent, a pigment, and water are mixed and dispersed, and a second dispersion step in which a second water-insoluble resin is further added and dispersed, A removal step of removing at least a part of the organic solvent from the aqueous dispersion obtained in the second dispersion step, and preferably including other steps as necessary.
By adding the first water-insoluble resin in the first dispersion step without mixing the water-insoluble resin all at once, and then adding the second water-insoluble resin in the second dispersion step. A pigment dispersion in which pigments and the like are finely dispersed as fine particles can be produced, and when the ink composition is constituted, the ratio of the average secondary particle diameter to the average primary particle diameter is controlled within a desired range. Becomes easier.

The first water-insoluble resin used in the first dispersion step and the second water-insoluble resin used in the second dispersion step may be the same or different. It is preferable to use an insoluble resin.
By using the same water-insoluble resin as the first and second water-insoluble resins, the pigment in the pigment dispersion is finely dispersed and can be made into a pigment dispersion excellent in dispersion stability. Further, the ink for ink jet recording containing the pigment dispersion has excellent storage stability and ejection stability.

More specifically, the method for producing a pigment dispersion suitably used in the present invention includes, for example,
(1) A first water-insoluble resin, an organic solvent, water, and preferably a basic compound (neutralizing agent) are further mixed.
(2) After the pigment is mixed with the obtained mixed liquid to form a suspension, a step of dispersing the pigment with a disperser or the like to obtain an aqueous dispersion (first dispersion step);
(3) Step of obtaining an aqueous dispersion by mixing a second water-insoluble resin with the obtained dispersion to obtain a suspension and then dispersing the pigment with a disperser or the like (second dispersion step) When,
(4) It is preferable that the method includes a step (removal step) of removing the organic solvent by, for example, distillation, coating the pigment with a water-insoluble resin, and dispersing the pigment in water to obtain an aqueous dispersion.

You may use the 1st and 2nd water-insoluble resin as described in said (1) or (2) as a solution melt | dissolved in the organic solvent.
The organic solvent used in the first dispersion step (1) may be the same as or different from the organic solvent used in the second dispersion step (3). It is preferable that they are the same in obtaining a fine emulsion by phase emulsification.

  In the second dispersion step, the second water-insoluble resin is added to the aqueous dispersion of the first dispersion step, but the addition may be performed all at once or continuously in small portions. Also good. When the water-insoluble resin is added as a solid, or when the water-insoluble resin is dissolved and added as a solution, it can be added in the same manner.

In the second dispersion step (3), the second water-insoluble resin is added to the dispersion obtained in the first dispersion step, and the timing of the addition is determined in the first dispersion step. It is a preferred embodiment that the pigment dispersion particles to be added are added when the rate of decrease (change rate) in the particle diameter has decreased.
The standard of the particle diameter of the pigment dispersed particles is not particularly limited, but is preferably 70 to 120 nm.

In the removing step (4), phase inversion emulsification is completed by removing at least part of the organic solvent from the aqueous dispersion. By performing this step, the dispersion stability of the pigment dispersion is improved.
The dispersion treatment and the removal of the organic solvent are as described above.

(Aqueous medium)
The ink composition of the present invention contains at least water as a medium, but the amount of water is not particularly limited. Especially, the preferable content of water is 10 to 99% by mass, more preferably 30 to 80% by mass, and still more preferably 50 to 70% by mass.

-Water-soluble organic solvent-
The ink composition of the present invention preferably contains at least one water-soluble organic solvent. By containing the water-soluble organic solvent, the effect of preventing drying, wetting or promoting penetration can be obtained. Here, the drying prevention effect and the wetting effect mean an effect of preventing clogging due to the water-based ink adhering and drying at the ink ejection port of the nozzle. As the drying inhibitor and wetting agent, a water-soluble organic solvent having a vapor pressure lower than that of water is preferable.
Further, the penetration promoting effect means an effect of allowing water-based ink to penetrate into paper better.

The water-soluble organic solvent contained in the water-based ink for ink-jet recording in the present invention can be appropriately selected from known water-soluble organic solvents in consideration of the function as a drying inhibitor, a wetting agent or a penetration accelerator. .
Examples of water-soluble organic solvents include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol, 2- Butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol Alkane polyols (polyhydric alcohols) such as 4-methyl-1,2-pentanediol; C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether , Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl Ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t -Butyl ether, propylene glycol Cole mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, etc. 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like 1 type, or 2 or more types of these can be used.

  In addition to water-soluble organic solvents, sugars such as glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose; sugar alcohols; hyaluron Acids; it is also preferred to use so-called solid wetting agents such as ureas in combination.

  For the purpose of drying inhibitors and wetting agents, polyhydric alcohols are useful, such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol. 2,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, tetraethylene glycol, 1,6-hexanediol, 2-methyl-2, Examples include 4-pentanediol, polyethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, and the like. These may be used individually by 1 type and may use 2 or more types together.

  For the purpose of the penetrant, a polyol compound is preferable, and examples of the aliphatic diol include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2- Diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol, Examples include 5-hexene-1,2-diol and 2-ethyl-1,3-hexanediol. Among these, preferred examples include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

The said organic solvent can be used individually by 1 type or in mixture of 2 or more types.
As content in the aqueous ink of an organic solvent, 1-60 mass% is preferable, More preferably, it is 5-40 mass%.

(Resin particles)
The ink composition of the present invention preferably further contains at least one kind of resin particles. As a result, the abrasion resistance of the formed image is more effectively improved.
The resin particles are not particularly limited, but are preferably self-dispersing resin particles (hereinafter also referred to as “self-dispersing polymer particles”).

The glass transition temperature Tg of the resin particles is not particularly limited, but the glass transition temperature Tg is preferably 100 ° C or higher, more preferably 100 ° C to 200 ° C, and 120 ° C to 180 ° C. More preferably.
By being 100 ° C. or higher, the abrasion resistance of the image is improved, and an image having press blocking resistance can be formed. Furthermore, it is excellent in ejection recovery even under scratch resistance and particularly under high temperature and high humidity conditions, and an image having good blocking resistance can be formed.

  As the glass transition temperature (Tg) of the resin particles, a measured Tg obtained by actual measurement is applied. Specifically, the measurement Tg means a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology.

However, when measurement is difficult due to decomposition of the polymer constituting the resin particles, the calculation Tg calculated by the following calculation formula is applied.
Calculation Tg is calculated by the following formula (1).
1 / Tg = Σ (X _i / Tg _i ) (1)
Here, it is assumed that n types of monomer components from i = 1 to n are copolymerized in the polymer to be calculated. X _i is the weight fraction of the i-th monomer (ΣX _i = 1), and Tg _i is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum from i = 1 to n. The homopolymer glass transition temperature value (Tg _i ) of each monomer is the value of Polymer Handbook (3rd Edition) (by J. Brandrup, EH Immergut (Wiley-Interscience, 1989)).

The self-dispersing polymer particles are dispersed in an aqueous medium due to the functional group of the polymer itself (especially acidic group or salt thereof) when dispersed by the phase inversion emulsification method in the absence of a surfactant. This refers to particles of water-insoluble polymer.
Here, the dispersed state means both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in a liquid state in an aqueous medium, and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in a solid state in an aqueous medium. It includes the state of.
The self-dispersing polymer particles in the present invention are self-dispersing polymer particles that can be in a dispersed state in which a water-insoluble polymer is dispersed in a solid state from the viewpoint of ink fixing properties when contained in an ink composition. preferable.

  Examples of a method for preparing an emulsified or dispersed state of self-dispersing polymer particles, that is, a method for preparing an aqueous dispersion of self-dispersing polymer particles include a phase inversion emulsification method. As the phase inversion emulsification method, for example, a self-dispersing polymer is dissolved or dispersed in a solvent (for example, a hydrophilic organic solvent) and then poured into water as it is without adding a surfactant. Examples include a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing with the salt-forming groups (for example, acidic groups) of the polymer particles neutralized and removing the solvent.

  Further, the stable emulsified or dispersed state in the self-dispersing polymer particles of the present invention means a solution in which 30 g of a water-insoluble polymer is dissolved in 70 g of an organic solvent (for example, methyl ethyl ketone), and the salt-forming group of the water-insoluble polymer is 100%. A neutralizing agent (sodium hydroxide if the salt-forming group is anionic, acetic acid if it is cationic) and water 200 g are mixed and stirred (apparatus: stirring device with stirring blades, rotation speed 200 rpm, 30 minutes, 25 ° C.), the emulsified or dispersed state is stable at 25 ° C. for at least one week even after removing the organic solvent from the mixed solution, and the occurrence of precipitation cannot be visually confirmed. Say.

The stability of the emulsified or dispersed state in the self-dispersing polymer particles can also be confirmed by an accelerated sedimentation test by centrifugation. The stability of the sedimentation acceleration test by centrifugation is, for example, adjusted by adjusting the aqueous dispersion of resin particles obtained by the above method to a solid content concentration of 25% by mass and then centrifuging at 12000 rpm for 1 hour. It can be evaluated by measuring the solid content concentration of the supernatant after separation.
If the ratio of the solid content concentration after centrifugation to the solid content concentration before centrifugation is large (if it is a value close to 1), the resin particles will not settle by centrifugation, that is, the aqueous dispersion of resin particles Means more stable. In the present invention, the ratio of the solid content concentration before and after centrifugation is preferably 0.8 or more, more preferably 0.9 or more, and particularly preferably 0.95 or more.

  The water-insoluble polymer means a polymer having a dissolution amount of 10 g or less when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferable. Is 5 g or less, more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

The self-dispersing polymer particles preferably have a water-soluble component content that exhibits water solubility in a dispersed state of 10% by mass or less, more preferably 8% by mass or less, and 6% by mass or less. More preferably it is. When the water-soluble component is 10% by mass or less, swelling of the resin particles and fusion between the resin particles can be effectively suppressed, and a more stable dispersion state can be maintained. In addition, an increase in the viscosity of the ink composition can be suppressed. For example, when the ink composition is applied to an ink jet method, the ejection stability becomes better.
Here, the water-soluble component is a compound contained in the polymer constituting the self-dispersing polymer particles, and is a compound that dissolves in water when the self-dispersing polymer particles are in a dispersed state. The water-soluble component is a water-soluble compound that is by-produced or mixed in the production of self-dispersing polymer particles.

  The self-dispersing polymer particles preferably include at least one hydrophilic constituent unit derived from a hydrophilic monomer and at least one hydrophobic constituent unit derived from a hydrophobic monomer. The main chain skeleton of the self-dispersing polymer is not particularly limited, but from the viewpoint of dispersion stability of polymer particles, a vinyl polymer is preferable, and a (meth) acrylic polymer is preferable. Here, the (meth) acrylic polymer means a polymer containing at least one of a structural unit derived from a methacrylic acid derivative and a structural unit derived from an acrylic acid derivative.

~ Hydrophilic structural unit ~
The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer (hydrophilic monomer). Even if it is derived from one kind of hydrophilic group-containing monomer, two or more types of hydrophilic structural units are used. It may be derived from a hydrophilic group-containing monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
From the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state, at least one of the hydrophilic groups is preferably a dissociable group, and preferably an anionic dissociable group. More preferred. Examples of the anionic dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among these, a carboxyl group is particularly preferable from the viewpoint of fixability when an ink composition is formed.

The hydrophilic group-containing monomer is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility, and is preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond.
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. It is done. Specific examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the dissociable group-containing monomers, from the viewpoints of dispersion stability and ejection stability, unsaturated carboxylic acid monomers are preferable, and at least one of acrylic acid and methacrylic acid is more preferable.

Examples of the monomer having a nonionic hydrophilic group include 2-methoxyethyl acrylate, 2- (2-methoxyethoxy) ethyl acrylate, 2- (2-methoxyethoxy) ethyl methacrylate, ethoxytriethylene glycol methacrylate, and methoxypolyethylene. Ethylenically unsaturated monomers containing (poly) ethyleneoxy groups or polypropyleneoxy groups such as glycol (molecular weight 200 to 1000) monomethacrylate, polyethylene glycol (molecular weight 200 to 1000) monomethacrylate, hydroxymethyl (meth) acrylate, 2 -Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate Rate, ethylenically unsaturated monomer having a hydroxyl group such as hydroxymethyl (meth) acrylate.
In addition, as a monomer having a nonionic hydrophilic group, an ethylenically unsaturated monomer having a terminal alkyl ether is more stable in terms of particle stability and content of water-soluble components than an ethylenically unsaturated monomer having a terminal hydroxyl group. It is preferable from the viewpoint.

As the hydrophilic structural unit, an embodiment containing only a hydrophilic structural unit having an anionic dissociable group, a hydrophilic structural unit having an anionic dissociative group, and a hydrophilic having a nonionic hydrophilic group It is preferable that it is either of the aspects containing both sex structural units.
In addition, an embodiment containing two or more hydrophilic structural units having an anionic dissociative group, a hydrophilic structural unit having an anionic dissociative group, and two hydrophilic structural units having a nonionic hydrophilic group are provided. It is also preferable that more than one species be used in combination.

The content of the hydrophilic structural unit in the self-dispersing polymer is preferably 25% by mass or less, more preferably 1 to 25% by mass, and more preferably 2 to 23% by mass from the viewpoints of viscosity and stability over time. % Is more preferable, and 4 to 20% by mass is particularly preferable.
Moreover, when it has 2 or more types of hydrophilic structural units, it is preferable that the total content rate of a hydrophilic structural unit exists in the said range.

The content of the hydrophilic structural unit having an anionic dissociative group in the self-dispersing polymer is preferably in a range where the acid value is in a suitable range described later.
In addition, the content of the structural unit having a nonionic hydrophilic group is preferably 0 to 25% by mass, more preferably 0 to 20% by mass, from the viewpoint of ejection stability and temporal stability. Particularly preferred is 0 to 15% by mass.

When the self-dispersing polymer has an anionic dissociable group, the acid value (mgKOH / g) is determined from the viewpoint of self-dispersibility, the content of water-soluble components, and the fixing property when an ink composition is constituted. From 50 mgKOH / g to 75 mgKOH / g, preferably from 52 mgKOH / g to 75 mgKOH / g, more preferably from 55 mgKOH / g to 72 mgKOH / g. Particularly preferred is 60 mg KOH / g or more and 70 mg KOH / g or less.
When the acid value is 50 mgKOH / g or more, the ejection responsiveness and ejection recovery property of the ink composition using the polymer are improved, and when the acid value is 75 mgKOH / g or less, the viscosity is increased and the anti-blocking property is improved. It tends to improve.

~ Hydrophobic structural unit ~
The hydrophobic structural unit is not particularly limited as long as it is derived from a hydrophobic group-containing monomer (hydrophobic monomer), and even if it is derived from one type of hydrophobic group-containing monomer, two or more types It may be derived from a hydrophobic group-containing monomer. The hydrophobic group is not particularly limited and may be any of a chain aliphatic group, a cyclic aliphatic group, and an aromatic group.
From the viewpoint of blocking resistance, abrasion resistance, and dispersion stability, at least one of the hydrophobic monomers is preferably a cyclic aliphatic group-containing monomer, and a cyclic aliphatic group-containing (meth) acrylate (hereinafter, “ More preferably, it may be referred to as “alicyclic (meth) acrylate”.

-Alicyclic (meth) acrylate-
The alicyclic (meth) acrylate includes a structural site derived from (meth) acrylic acid and a structural site derived from alcohol, and the structural site derived from alcohol is unsubstituted or substituted. It has a structure containing at least one hydrogen group. The alicyclic hydrocarbon group may be a structural part derived from alcohol itself or may be bonded to a structural part derived from alcohol via a linking group.
The “alicyclic (meth) acrylate” means methacrylate or acrylate having an alicyclic hydrocarbon group.

The alicyclic hydrocarbon group is not particularly limited as long as it contains a cyclic non-aromatic hydrocarbon group, and is a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, a tricyclic or more polycyclic group. A hydrocarbon group is mentioned.
Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane.

The alicyclic hydrocarbon group may further have a substituent. Examples of the substituent include alkyl groups, alkenyl groups, aryl groups, aralkyl groups, alkoxy groups, hydroxyl groups, primary amino groups, secondary amino groups, tertiary amino groups, alkyl or arylcarbonyl groups, and cyano groups. Is mentioned.
The alicyclic hydrocarbon group may further form a condensed ring.
As an alicyclic hydrocarbon group, it is preferable that carbon number of an alicyclic hydrocarbon group part is 5-20 from a viscosity or a soluble viewpoint.

  Examples of the linking group that connects the alicyclic hydrocarbon group and the structural portion derived from the alcohol include an alkylene group, alkenylene group, alkynylene group, arylalkylene group, oxyalkylene group, mono- or oligo group having 1 to 20 carbon atoms. Suitable examples include oxyethylene groups, mono- or oligooxypropylene groups.

Specific examples of the alicyclic (meth) acrylate are shown below, but the present invention is not limited thereto.
Monocyclic (meth) acrylates include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, and cyclononyl. Examples thereof include cycloalkyl (meth) acrylates having 3 to 10 carbon atoms in the cycloalkyl group such as (meth) acrylate and cyclodecyl (meth) acrylate.
Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate.
Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate.
These can be used alone or in admixture of two or more.

  Among these, at least one kind of bicyclic (meth) acrylate or tricyclic or higher polycyclic (meth) acrylate is used from the viewpoints of dispersion stability, fixing property and blocking resistance of the self-dispersing polymer particles. Preferably, it is at least one selected from isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate.

In the present invention, the content of the structural unit derived from the alicyclic (meth) acrylate contained in the self-dispersing polymer particles is based on the stability of the self-dispersing state and the hydrophobic interaction between the alicyclic hydrocarbon groups. From the viewpoint of stabilizing the particle shape in an aqueous medium and reducing the amount of water-soluble components due to appropriate hydrophobicity of the particles, it is preferably 20 to 90% by mass, more preferably 40 to 90% by mass. . Particularly preferred is 50 to 80% by mass.
Fixing property and blocking can be improved by making the structural unit derived from the alicyclic (meth) acrylate 20% by mass or more. On the other hand, the stability of the resin particles is improved when the structural unit derived from the alicyclic (meth) acrylate is 90% by mass or less.

  In the present invention, the self-dispersing polymer particles are preferably configured to further include other structural units as necessary in addition to the structural units derived from the alicyclic (meth) acrylate as hydrophobic structural units. The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the alicyclic (meth) acrylate and the above-described hydrophilic group-containing monomer, and a known monomer may be used. it can.

  Specific examples of the monomer that forms the other structural unit (hereinafter sometimes referred to as “other copolymerizable monomer”) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, and isopropyl (meth) acrylate. Alkyl (meth) acrylates such as n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; Aromatic ring-containing (meth) acrylates such as benzyl (meth) acrylate and phenoxyethyl (meth) acrylate; styrenes such as styrene, α-methylstyrene and chlorostyrene; dialkylaminoalkyls such as dimethylaminoethyl (meth) acrylate (Meth) acrylate; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxyalkyl (meth) acrylamide such as N-hydroxybutyl (meth) acrylamide; N-methoxymethyl (meth) acrylamide N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N- (n-, iso ) (Meth) acrylamide such as N-alkoxyalkyl (meth) acrylamide such as butoxyethyl (meth) acrylamide.

  Among these, from the viewpoint of the flexibility of the polymer skeleton and the ease of controlling the glass transition temperature (Tg) and the viewpoint of the dispersion stability of the self-dispersing polymer, it contains a chain alkyl group having 1 to 8 carbon atoms (meth). It is preferably at least one acrylate, more preferably a (meth) acrylate having a chain alkyl group having 1 to 4 carbon atoms, and particularly preferably methyl (meth) acrylate or ethyl (meth) acrylate. . Here, the chain alkyl group refers to an alkyl group having a straight chain or a branched chain.

In the present invention, (meth) acrylates containing an aromatic group can also be preferably used.
In the case of containing an aromatic-containing (meth) acrylate as a copolymerizable monomer, from the viewpoint of dispersion stability of the self-dispersing polymer particles, the aromatic-containing (meth) acrylate is added to the total mass of the self-dispersing polymer. The derived structural unit is preferably 40% by weight or less, more preferably 30% by weight or less, and particularly preferably 20% by weight or less.

In addition, when a styrene monomer is used as another copolymerizable monomer, the structural unit derived from the styrene monomer is based on the total mass of the self-dispersing polymer from the viewpoint of stability when the self-dispersing polymer particles are used. It is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and an embodiment that does not include a structural unit derived from a styrenic monomer is particularly preferable.
Here, the styrene monomer refers to styrene, substituted styrene (α-methylstyrene, chlorostyrene, etc.), and a styrene macromer having a polystyrene structural unit.

Other copolymerizable monomers may be used singly or in combination of two or more.
When other structural units are contained, the content thereof is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, and particularly preferably based on the total mass of the self-dispersing polymer. Is 20 to 70% by mass. When using the monomer which forms another structural unit in combination of 2 or more types, it is preferable that the total content is the said range.

From the viewpoint of dispersion stability, the self-dispersing polymer is preferably a polymer obtained by polymerizing at least three types of alicyclic (meth) acrylate, other copolymerizable monomer, and hydrophilic group-containing monomer. , An alicyclic (meth) acrylate, a linear or branched alkyl group-containing (meth) acrylate having 1 to 8 carbon atoms, and a polymer obtained by polymerizing at least three kinds of hydrophilic group-containing monomers. It is more preferable.
In the present invention, from the viewpoint of dispersion stability, substitution with a large hydrophobicity derived from a (meth) acrylate having a linear or branched alkyl group having 9 or more carbon atoms, an aromatic group-containing macromonomer, or the like The content of the structural unit having a group is preferably substantially not contained, and more preferably not contained at all.

  The polymer constituting the self-dispersing polymer particles may be a random copolymer in which each constitutional unit is introduced irregularly or a block copolymer introduced regularly. Each structural unit in the case of a coalescence may be synthesized in any order of introduction, and the same structural component may be used twice or more, but a random copolymer is versatile and manufactured. From the viewpoint of sex.

The molecular weight range of the polymer constituting the self-dispersing polymer particles is preferably 3000 to 200,000, more preferably 10,000 to 200,000, and still more preferably 30000 to 150,000 in terms of weight average molecular weight. . By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.
The weight average molecular weight can be measured by gel permeation chromatography (GPC).

The polymer constituting the self-dispersing polymer particles preferably has an acid value of 50 to 75 mgKOH / g from the viewpoint of viscosity adjustment of the ink composition, ejection response, and ejection recovery, and is 52 to 75 mgKOH / g. More preferably, it is more preferably 55 to 72 mgKOH / g, and particularly preferably 60 to 70 mgKOH / g.
When the acid value is 50 mgKOH / g or more, the ejection response and ejection recovery properties of the ink composition using the polymer are improved, and when the acid value is 75 mgKOH / g or less, the viscosity tends to increase.
In the present invention, the acid value is determined by the method described in JIS standard (JIS K 0070: 1992).

The polymer constituting the self-dispersing polymer particles preferably has a degree of neutralization of 40 to 60%, more preferably 45 to 55%, from the viewpoints of viscosity adjustment, discharge response, and discharge recovery. It is especially preferable that it is 47 to 53%.
When the degree of neutralization is 40% or more, the effect of increasing the viscosity and the effect of improving the discharge response are obtained, and when it is 60% or less, the discharge recovery property is improved.
Further, when the degree of neutralization is 40% or less, or 60% or more, there are also problems such as that the self-dispersing polymer particles cannot be stably produced.
The degree of neutralization refers to the mol% of alkali added when the dissociable group contained in the polymer constituting the self-dispersing polymer particles is 100 mol% during the production of the self-dispersing polymer particles.

  The self-dispersing polymer particles preferably have an acid value of 52 to 75 mgKOH / g and a neutralization degree of 45 to 55% as a combination of the acid value and the neutralization degree, and the acid value is 55 to 72 mgKOH / g. More preferable when the sum is 45 to 55%, more preferable when the acid value is 55 to 65 mgKOH / g and the degree of neutralization is 47 to 53%.

The self-dispersing polymer particles are derived from a dissociable group-containing monomer having a structure derived from an alicyclic (meth) acrylate as a copolymerization ratio of 20% by mass to 90% by mass from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. Including the structure and at least one structure derived from a (meth) acrylate containing a linear alkyl group having 1 to 8 carbon atoms, the acid value is 20 to 120, and the total content of hydrophilic structural units Is a vinyl polymer having a weight average molecular weight of 3000 to 200,000.
Moreover, it contains a chain alkyl group having 1 to 4 carbon atoms and a structure derived from a bicyclic or tricyclic or higher polycyclic (meth) acrylate as a copolymerization ratio of 20% by mass or more and less than 90% by mass. A structure derived from (meth) acrylate as a copolymerization ratio of 10% by mass to less than 80% by mass, and a structure derived from a carboxyl group-containing monomer in an acid value of 50 to 75 mgKOH / g, A vinyl polymer having a total content of 25% by mass or less and a weight average molecular weight of 10,000 to 200,000 is more preferable.
Furthermore, a structure derived from a bicyclic or tricyclic or higher polycyclic (meth) acrylate having a copolymerization ratio of 40% by mass or more and less than 80% by mass, at least methyl (meth) acrylate or ethyl (meth) acrylate A structure derived from a copolymerization ratio of 20% by mass to less than 60% by mass, a structure derived from acrylic acid or methacrylic acid in an acid value of 50 to 75 mgKOH / g, and a total content of hydrophilic structural units. The vinyl polymer is particularly preferably 25% by mass or less and having a weight average molecular weight of 30,000 to 150,000.

  Hereinafter, as specific examples of the self-dispersing polymer, exemplary compounds are listed, but the present invention is not limited thereto. In addition, the parenthesis represents the mass ratio of the copolymerization component.

Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8), glass transition temperature: 180 ° C., acid value: 52.1 mg KOH / g
Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (40/52/8), glass transition temperature: 160 ° C., acid value: 52.1 mgKOH / g
・ Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (38/52/10), glass transition temperature: 160 ° C., acid value: 65.1 mgKOH / g
・ Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (42/52/6), glass transition temperature: 161 ° C., acid value: 39.1 mgKOH / g
・ Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (36.5 / 52 / 11.5), glass transition temperature: 160 ° C., acid value: 74.8 mgKOH / g
Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (36/52/12), glass transition temperature: 160 ° C., acid value: 78.1 mgKOH / g
Methyl methacrylate / isobornyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/62/10/8), glass transition temperature: 170 ° C., acid value: 52.1 mgKOH / g
Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/72/8), glass transition temperature: 160 ° C., acid value: 52.1 mgKOH / g
・ Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (18/72/10), glass transition temperature: 161 ° C., acid value: 65.1 mgKOH / g

There is no restriction | limiting in particular as a manufacturing method of a self-dispersing polymer, It can manufacture by copolymerizing a monomer mixture by a well-known polymerization method. Among these polymerization methods, from the viewpoint of droplet ejection stability when used as an ink composition, polymerization in an organic medium is more preferable, and solution polymerization is particularly preferable.
In the method for producing a self-dispersing polymer, the water-insoluble polymer is produced by copolymerizing a monomer mixture and, if necessary, a mixture containing an organic solvent and a radical polymerization initiator in an inert gas atmosphere. can do.

There is no restriction | limiting in particular as a manufacturing method of the aqueous dispersion of a self-dispersing polymer particle, It can be set as the aqueous dispersion of a self-dispersing polymer particle by a well-known method. The step of obtaining the self-dispersing polymer as an aqueous dispersion is preferably a phase inversion emulsification method including the following step (1) and step (2).
Step (1): A step of stirring a mixture containing a water-insoluble polymer, an organic solvent, a neutralizing agent, and an aqueous medium to obtain a dispersion.
Step (2): A step of removing at least a part of the organic solvent from the dispersion.

The step (1) is preferably a treatment in which the water-insoluble polymer is first dissolved in an organic solvent, and then a neutralizer and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. Thus, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents.
Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether and dioxane. Among these organic solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable.
It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination. By using this solvent in combination, it is possible to obtain self-dispersing polymer particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles. This can be considered, for example, because the polarity change during the phase inversion from the oil system to the water system becomes mild.

  The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer has an anionic dissociative group as a dissociable group, examples of the neutralizing agent used include basic compounds such as organic amine compounds, ammonia, and alkali metal hydroxides. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanol Examples include amines and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  In the step (2), the aqueous dispersion of the self-dispersing polymer particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and inversion into an aqueous system. You can get things. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The volume average particle diameter of the self-dispersing polymer particles (hereinafter, also simply referred to as “average particle diameter”) is not particularly limited, but is 0.1 in terms of thickening and dischargeability (discharge response, discharge recovery). It is preferable that it is -10 nm, It is more preferable that it is 0.5-8 nm, 1-7 nm is more preferable, 1-5 nm is further more preferable. Especially preferably, it is 1-4 nm.
An average particle size of 0.1 nm or more is preferable in terms of further improving the production suitability and ejection recovery property, and an average particle size of 10 nm or less improves storage stability and the ink thickening effect. Further, by giving the self-dispersibility a thickening effect, it is possible to improve the discharge response by reducing the amount of the thickener added as a result.
Further, the particle size distribution of the self-dispersing polymer particles is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Further, two or more kinds of water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the self-dispersing polymer particles can be measured using, for example, a light scattering method.

In the ink composition of the present invention, the self-dispersing polymer is preferably present in a form containing substantially no pigment.
The self-dispersing polymer of the present invention is excellent in self-dispersibility, and the stability when dispersed alone is very high. However, for example, since the function as a so-called dispersant for stably dispersing the pigment is not high, if the self-dispersing polymer in the present invention is present in the ink composition in a form containing the pigment, as a result, the entire ink composition The stability of the may be greatly reduced.

In the ink composition of the present invention, resin particles (preferably self-dispersing polymer particles) may be contained singly or in combination of two or more.
The content of the resin particles (preferably self-dispersing polymer particles) in the ink composition of the present invention is 5% by mass with respect to the total mass of the ink composition from the viewpoints of abrasion resistance and press blocking resistance. It is preferable to contain above, it is preferable that it is 5-30 mass%, it is more preferable that it is 5-20 mass%, and it is especially preferable that it is 5-10 mass%.
In addition, the content ratio (pigment particles / resin particles) of the pigment particles and the resin particles in the ink composition of the present invention is 1 / 0.5 to 1/10 from the viewpoint of image abrasion resistance. Preferably, it is 1/1 to 1/4.

(Surfactant)
The ink composition of the present invention preferably contains at least one surfactant. The surfactant is used as a surface tension adjusting agent, and examples thereof include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants.
The surfactant preferably contains an amount capable of adjusting the surface tension of the water-based ink to 20 to 60 mN / m in order to eject droplets well by the ink jet method. Especially, content of surfactant is the quantity which can adjust surface tension to 20-45 mN / m, More preferably, it is quantity which can be adjusted to 25-40 mN / m.

  As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Any of the surfactants can be used.

  Specific examples of anionic surfactants include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, sodium dioctyl. Sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, sodium stearate, sodium oleate, t-octylphenoxyethoxypolyethoxyethyl Examples include sodium sulfate, etc., and select one or more of these Rukoto can.

Examples of the cationic surfactant include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like. Specific examples thereof include dihydroxyethyl stearylamine and 2-heptadecenyl. -Hydroxyethyl imidazoline, lauryl dimethyl benzyl ammonium chloride, cetyl pyridinium chloride, stearamide methyl pyridium chloride and the like.
Amphoteric surfactants include lauryl dimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, coconut oil fatty acid amidopropyldimethylaminoacetic acid betaine, polyoctylpolyaminoethylglycine and other imidazoline derivatives. There is.

  Specific examples of the nonionic surfactant include acetylene glycol surfactants, acetylene alcohol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, and the like. In the present invention, from the viewpoint of suppressing the foaming of the water-based ink, it is preferable to use a nonionic surfactant, and an acetylene glycol surfactant is more preferable.

  Examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3, Examples include 5-dimethyl-1-hexyn-3-ol, or a substance obtained by adding an average of 1 to 30 ethyleneoxy groups or propyleneoxy groups to each of a plurality of hydroxyl groups in each of these substances. Moreover, as an acetylene glycol type surfactant, a commercial item can also be used, for example, "Orphine E1010" and "Orphine STG" (above, Nissin Chemical Industry Co., Ltd. product) etc. are mentioned.

  Examples of polyoxyethylene alkyl ether and polyoxyethylene phenyl ether include polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, and oxyethylene / oxypropylene block. Examples thereof include copolymers, t-octylphenoxyethyl polyethoxyethanol, and nonylphenoxyethyl polyethoxyethanol.

In this invention, surfactant can be used individually by 1 type or in combination of 2 or more types.
Further, the content of the surfactant in the water-based ink for inkjet recording is not particularly limited and is preferably 0.1% by mass or more, more preferably 0.1 to 2.0% by mass, and still more preferably 0.00. It is 5-1.5 mass%.
Especially, it is preferable that 0.1-2.0 mass% of acetylene glycol type-surfactants are included in water-based ink as surfactant, More preferably, it is 0.5-1.5 mass%.

<Other ingredients>
In addition to the above components, the water-based ink for inkjet recording according to the present invention includes, for example, an ultraviolet absorber, an antifading agent, an antifungal agent, an antirust agent, an antioxidant, an emulsion stabilizer, an antiseptic, You may contain other components, such as an antifoamer, a viscosity modifier, a dispersion stabilizer, and a chelating agent.

~ Physical properties of ink composition ~
The surface tension (25 ° C.) of the ink composition is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less.
The surface tension is measured using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) and a water-based ink at 25 ° C.

The viscosity of the ink composition at 20 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and further preferably 2 It is not less than 5 mPa · s and less than 10 mPa · s.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under a condition of 20 ° C. with a water-based ink.

<Inkjet image forming method>
The inkjet image forming method of the present invention includes an ink application step of applying the black ink-jet recording ink composition onto a recording medium by an inkjet method, and includes other steps as necessary. .
The ink jet image forming method of the present invention may be a recording form (first recording form) in which an image is recorded on a desired recording medium by ejecting the ink jet method according to image information to be recorded. In addition to the first recording form, both the ink composition and a treatment liquid containing a component capable of aggregating particles such as pigments in the ink composition when in contact with the ink composition are used. A recording form (second recording form) may be used in which an image is recorded by contacting the treatment liquid.

  The ink jet image forming method of the present invention includes an ink application step of applying the black ink jet recording ink composition onto a recording medium by an ink jet method, and contacting the black ink jet recording ink composition with the black ink jet recording composition. It is preferable to have a treatment liquid application step of applying a treatment liquid capable of aggregating the components of the ink jet recording ink composition onto the recording medium.

-Ink application process-
In the ink application step, the above-described ink composition of the present invention is applied to a recording medium by an ink jet method (single pass method). The single path method will be described later.
In this step, the ink composition can be selectively applied onto the recording medium, and a desired visible image can be formed. Details of each component in the ink composition of the present invention and details such as preferred embodiments are as described above.

  Specifically, the image formation using the ink jet method is performed by supplying energy to a desired recording medium, that is, plain paper, resin-coated paper, such as JP-A-8-169172 and JP-A-8-27693. JP-A-2-276670, JP-A-7-276789, JP-A-9-323475, JP-A-62-238783, JP-A-10-153789, JP-A-10-217473, JP-A-10-235995. No. 10-337947, No. 10-217597, No. 10-337947, etc. Inkjet exclusive paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. This can be done by discharging. As a preferred image forming method of the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, an electric method An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink with ink and ejects the ink using radiation pressure, and a thermal ink jet (bubble jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

In addition, an ink jet head used in the ink jet method may be an on-demand method or a continuous method. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (registered trademark) type, an electrostatic suction type (for example, an electric field control type, a slit jet type, etc.) and a discharge type (for example, a spark jet type). However, any discharge method may be used.
There are no particular restrictions on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.

As an inkjet head, a short serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line in which recording elements are arranged corresponding to the entire area of one side of the recording medium ( There is a line (single pass) system using a single pass) head.
In the image forming method of the present invention, an ink composition is applied onto a recording medium by a single pass method using this single pass head.
In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system.
The image forming method of the present invention can suppress the occurrence of press blocking by using the ink composition of the present invention, and the discharge accuracy is improved by discharging the ink composition by a single pass method. In addition, the effect of suppressing erosion due to contact between the nozzle plate and the ink is great.

  Furthermore, in the image forming process of the present invention, because of the line method, not only one type of ink composition is used, but also two or more types of ink compositions are used, and an ink composition (nth color ( n ≧ 1), for example, the second color), and the ink composition (n + 1th color, for example, the third color) to be ejected subsequently is preferably set to 1 second or less for the ejection (droplet ejection) interval to perform recording. be able to. In the present invention, an ejection interval of 1 second or less in the line method prevents bleeding and color mixing between ink droplets, and has excellent scratch resistance under high-speed recording higher than that of the prior art, and occurrence of blocking. A suppressed image can be obtained. In addition, an image having excellent hue and drawability (reproducibility of fine lines and fine portions in the image) can be obtained.

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

-Treatment liquid application process-
The treatment liquid application step is a step of applying a treatment liquid containing an aggregating agent for aggregating the components in the ink composition onto the recording medium.
That is, a processing liquid capable of forming an aggregate is applied to a recording medium, and the processing liquid is brought into contact with the ink composition to form an image. In this case, dispersed particles such as polymer particles and color materials (for example, pigments) in the ink composition aggregate to fix the image on the recording medium. In addition, the detail and preferable aspect of each component in a process liquid are explained in full detail.

<Processing liquid>
The treatment liquid in the present invention is configured to be able to form an aggregate by contact with the ink composition described above. Specifically, the treatment liquid preferably includes at least an aggregating agent capable of aggregating dispersed particles such as colorant particles (pigments and the like) in the ink composition to form an aggregate, and if necessary, It can be constructed using other components. By using the treatment liquid together with the ink composition, it is possible to increase the speed of ink jet recording, and an image with excellent density and resolution can be obtained even when recording at high speed (for example, reproducibility of fine lines and fine portions).

(Flocculant)
The treatment liquid can contain at least one flocculant capable of forming an aggregate upon contact with the ink composition. By mixing the treatment liquid with the ink composition ejected by the ink jet method, aggregation of pigments and the like stably dispersed in the ink composition is promoted.

Examples of the treatment liquid include a liquid capable of generating an aggregate by changing the pH of the ink composition. At this time, the pH (25 ° C. ± 1 ° C.) of the treatment liquid is preferably 1 to 6, more preferably 1.2 to 5, more preferably 1.5 from the viewpoint of the aggregation rate of the ink composition. More preferably, it is ~ 4. In this case, the pH (25 ± 1 ° C.) of the ink composition used in the ejection step is preferably 7.5 to 9.5 (more preferably 8.0 to 9.0).
Among these, in the present invention, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ± 1 ° C.) of the ink composition is 7.5 or more, and the pH of the treatment liquid (25 ± 1 ° C) is preferably 1.5 to 3.
The flocculants can be used alone or in combination of two or more.

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

  Examples of the compound having a carboxyl group include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, and tartaric acid. , Lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, or organic acids such as nicotinic acid, or derivatives of organic acids Or a salt of an organic acid (for example, a polyvalent metal salt) or the like, preferably an organic acid. These compounds may be used alone or in combination of two or more.

  Examples of the treatment liquid include a treatment liquid to which a polyvalent metal salt is added as a flocculant, and can improve high-speed aggregation. Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and cations from Group 13 of the periodic table. (For example, aluminum) and the salt of lanthanides (for example, neodymium) can be mentioned. As the metal salt, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.

  The content of the metal salt in the treatment liquid is preferably 1 to 10% by mass, more preferably 1.5 to 7% by mass, and still more preferably 2 to 6% by mass from the viewpoint of the aggregation effect. It is.

  Further, the treatment liquid can use at least one cationic organic compound as a flocculant. Examples of the cationic organic compound include poly (vinyl pyridine) salt, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide, polyguanide, and polyallylamine and derivatives thereof. Mention may be made of cationic polymers.

  As content in the processing liquid of a cationic organic compound, 1-50 mass% is preferable from a viewpoint of the aggregation effect, More preferably, it is 2-30 mass%.

  Of the above, the aggregating agent is preferably a divalent or higher valent organic acid or a divalent or higher cation organic compound from the viewpoint of aggregability and image scratch resistance.

  The viscosity of the treatment liquid is preferably in the range of 1 to 30 mPa · s, more preferably in the range of 1 to 20 mPa · s, still more preferably in the range of 2 to 15 mPa · s, from the viewpoint of the aggregation rate of the ink composition. The range of 10 mPa · s is particularly preferable. The viscosity is measured under a condition of 20 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

  The surface tension of the treatment liquid is preferably 20 to 60 mN / m, more preferably 20 to 45 mN / m, and more preferably 25 to 40 mN / m from the viewpoint of the aggregation rate of the ink composition. More preferably. The surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

(Water-soluble organic solvent)
The treatment liquid contains the flocculant (preferably an organic acid), but preferably further contains a water-soluble organic solvent together with water. The details of the water-soluble organic solvent are the same as those in the ink composition described above (other components).
The treatment liquid in the present invention can be configured using various other additives within a range not impairing the effects of the present invention.
Other additives include, for example, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension adjusters, Known additives such as foaming agents, viscosity modifiers, dispersants, dispersion stabilizers, rust inhibitors, chelating agents and the like are listed, and specific examples of other additives included in the ink composition described above are listed. Can be applied.

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

  The treatment liquid applying step may be provided either before or after the image forming step using the ink composition.

  In the present invention, an embodiment in which the image forming step is provided after the treatment liquid is applied in the treatment liquid application step is preferable. That is, before applying the ink composition to the recording medium, a treatment liquid for aggregating the coloring material (preferably pigment) in the ink composition is applied in advance, and the treatment applied on the recording medium. An embodiment in which an ink composition is applied so as to come into contact with the liquid to form an image is preferable. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

The application amount of the treatment liquid is not particularly limited as long as the ink composition can be aggregated. / M ² or more. Especially, the quantity from which the provision amount of a flocculant will be 0.1-1.0 g / m < ² > is preferable, More preferably, it is 0.2-0.8 g / m < ² >. When the amount of the flocculant applied is 0.1 g / m ² or more, the agglomeration reaction proceeds favorably, and when it is 1.0 g / m ² or less, the glossiness is not excessively increased.

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

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

-Heat fixing process-
The image forming method of the present invention preferably further includes a heating and fixing step of heating and fixing an ink image formed by applying the ink composition by bringing a heating surface into contact with the ink image after the image forming step. By performing the heat fixing process, the image on the recording medium is fixed, and the resistance against image abrasion can be further improved.

Heating is preferably performed at a temperature equal to or higher than the minimum film-forming temperature (MFT) of the polymer particles in the image. By heating to MFT or higher, the polymer particles become a film and the image is enhanced. The heating temperature is preferably in the temperature range of MFT or higher. Specifically, the heating temperature is preferably in the range of 40 to 80 ° C, more preferably in the range of 50 ° C to 75 ° C, and still more preferably in the range of 55 ° C to 70 ° C.
The minimum film forming temperature (MFT) of the polymer particles is controlled by the Tg of the polymer and the type and amount of the ink solvent. Generally, the lower the Tg, the lower the I / O value of the ink solvent, the more the amount of the ink solvent The greater the number, the lower the MFT.

  The pressure at the time of pressurizing with heating is preferably in the range of 0.1 to 3.0 MPa, more preferably in the range of 0.1 to 1.0 MPa, and still more preferably 0.1 in terms of surface smoothing. It is the range of -0.5MPa.

  The method of heating is not particularly limited, but a non-contact drying method such as a method of heating with a heating element such as a nichrome wire heater, a method of supplying warm air or hot air, a method of heating with a halogen lamp, an infrared lamp, etc. Preferably, it can be mentioned. The heating and pressing method is not particularly limited. For example, a method of pressing a hot plate against the image forming surface of a recording medium, a pair of heating and pressing rollers, a pair of heating and pressing belts, or a recording medium Using a heating and pressing device equipped with a heating and pressing belt arranged on the image recording surface side and a holding roller arranged on the opposite side, heat fixing by bringing them into contact, such as a method of passing a pair of rollers, etc. The method of performing is mentioned suitably.

  In the case of heating and pressing, a preferable nip time is 1 to 10 seconds, more preferably 2 to 1 second, and further preferably 4 to 100 milliseconds. Moreover, a preferable nip width is 0.1 mm to 100 mm, more preferably 0.5 mm to 50 mm, and still more preferably 1 to 10 mm.

  The heat and pressure roller may be a metal metal roller, or a metal core bar provided with a coating layer made of an elastic body and, if necessary, a surface layer (also referred to as a release layer). Good. The latter metal core can be formed of, for example, a cylindrical body made of iron, aluminum, SUS, or the like, and the surface of the metal core is preferably at least partially covered with a coating layer. The coating layer is particularly preferably formed of a silicone resin or fluororesin having releasability. Further, it is preferable that a heating element is built in one core metal of the heat and pressure roller, and heat treatment and pressure treatment are performed simultaneously or necessary by passing a recording medium between the rollers. Accordingly, the recording medium may be sandwiched and heated using two heating rollers. As the heating element, for example, a halogen lamp heater, a ceramic heater, a nichrome wire or the like is preferable.

  As a belt base material constituting the heat and pressure belt used in the heat and pressure apparatus, seamless nickel brass is preferable, and the thickness of the base material is preferably 10 to 100 μm. Further, as the material of the belt base material, aluminum, iron, polyethylene or the like can be used in addition to nickel. When silicone resin or fluororesin is provided, the thickness of the layer formed using these resins is preferably 1 to 50 μm, more preferably 10 to 30 μm.

  Further, in order to realize the pressure (nip pressure), for example, an elastic member such as a spring having tension so that a desired nip pressure can be obtained in consideration of the nip gap at both ends of a roller such as a heat and pressure roller. Select and install.

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

It is also a preferable aspect that the image forming method of the present invention has a removing step of removing ink adhering to an inkjet head that performs ejection by a single pass method.
By performing the removing step, that is, by removing the ink composition adhering to the ink jet head, the fixed matter derived from the ink composition, or other adhering matter, the ink ejection properties immediately after ejection and after aging are further improved. This is preferable.

-Recording media-
The image forming method of the present invention records an image on a recording medium.
The recording medium is not particularly limited, and general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing and the like can be used. General printing paper mainly composed of cellulose is relatively slow in ink absorption and drying in image recording by a general ink jet method using water-based ink, and color material movement is likely to occur after droplet ejection, and image quality is likely to deteriorate. However, according to the image forming method of the present invention, it is possible to record a high quality image excellent in color density and hue by suppressing the movement of the color material.

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

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

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

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

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.
The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corporation), TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) as columns, and THF (tetrahydrofuran) as an eluent. ) Was used. The conditions were as follows: the sample concentration was 0.35% by mass, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and the RI detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

(Synthesis Example 1)
-Synthesis of resin dispersant P-1 (water-insoluble resin)-
To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. To this, 50 g of methyl ethyl ketone was added with 0.85 g of dimethyl-2,2′-azobisisobutyrate and phenoxy. A solution in which 60 g of ethyl methacrylate, 10 g of methacrylic acid, and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution prepared by dissolving 0.42 g of dimethyl-2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in an excess amount of hexane, the precipitated resin was dried, and phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid (copolymerization ratio [mass ratio] = 60/30/10) 96.5 g of a polymer (resin dispersant P-1) was obtained.
The composition of the obtained resin dispersant P-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 43500. Furthermore, when the acid value of this polymer was determined by the method described in JIS standard (JIS K 0070: 1992), it was 65.2 mgKOH / g.

(Synthesis Example 2)
~ Synthesis of resin particles ~
In a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 540.0 g of methyl ethyl ketone was charged and heated to 75 ° C. While maintaining the temperature in the reaction vessel at 75 ° C., 108 g of methyl methacrylate, 388.8 g of isobornyl methacrylate, 43.2 g of methacrylic acid, 108 g of methyl ethyl ketone, and 2.16 g of “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) The mixed solution consisting of was dropped at a constant speed so that the dropping was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 1.08 g of “V-601” and 15.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.54 g of “V-601” and 15.0 g of methyl ethyl ketone was added. After stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours.
The weight average molecular weight (Mw) of the obtained copolymer was 61000 (calculated in terms of polystyrene by gel permeation chromatography (GPC), the columns used were TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by Tosoh Corporation)), The acid value was 52.1 (mgKOH / g).

Next, 588.2 g of the polymerization solution was weighed, 165 g of isopropanol and 120.8 ml of 1 mol / L NaOH aqueous solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 718 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water. Then, the solvent was distilled off by keeping the temperature in the reaction vessel at 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. Furthermore, the pressure in the reaction vessel was reduced, and isopropanol, methyl ethyl ketone, and distilled water were distilled off to obtain an aqueous dispersion of a self-dispersing polymer (B-01) having a solid content concentration of 26.0%.
In addition, the number of each structural unit of the following compound example (B-01) represents mass ratio. Hereinafter, the same applies to each structural formula.
B-01: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8)
Moreover, it was 16 nm when the volume average particle diameter of the obtained resin particle was measured by the dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (made by Nikkiso Co., Ltd.).
Furthermore, it was 180 degreeC when the glass transition temperature of the obtained resin particle was measured on the normal measurement conditions using the differential scanning calorimeter (DSC) EXSTAR 6220 by SII nanotechnology.

<Example 1>
~ Preparation of pigment dispersion ~
Each component was mixed so as to have the following composition, and dispersed using a bead mill for 2 hours using 0.1 mmφ zirconia beads. Subsequently, by removing methyl ethyl ketone from the obtained dispersion at 55 ° C. under reduced pressure, and further removing a part of water, the resin-coated carbon black particles and the resin so that the carbon black concentration becomes 10.0% by mass. A dispersion of coated colored pigments was prepared

-Composition of pigment dispersion-
-Carbon black pigment: 8.4 parts (primary particle size: 20 nm)
-Phthalocyanine pigment: 2.8 parts (CI Pigment Blue 15: 3, primary particle size 40 nm)
-Quinacridone pigment-3.8 parts (CI Pigment Red 122, primary particle size 35 nm)
Resin dispersant P-1 6.8 parts Methyl ethyl ketone 18.0 parts 1 mol / L NaOH aqueous solution 5.6 parts Ion exchange water 54.6 parts

The carbon black pigment used above had a DBP absorption of 75 ml / g, a BET surface area of 370 m ² / g, and a pH of 7.5.

The quinacridone pigment PR122 and the phthalocyanine pigment PB15: 3 were subjected to the following salt milling treatment to control the average primary particle size.
(Salt milling of pigment)
In a tank of a kneader (trade name: KHD-2, Inoue Seisakusho), C.I. I. 100 parts by mass of Pigment Red 122, 1000 parts by mass of sodium chloride having a particle size of 20 μm, and 240 parts by mass of diethylene glycol were added, and kneaded at 50 ° C. for 6 hours to perform salt milling. Next, 1300 parts by mass of the obtained kneaded material was put into 3 liters of warm water and stirred for 1 hour while heating to 70 ° C. to form a slurry. Filtration and washing were repeated to remove sodium chloride and diethylene glycol, followed by drying at 40 ° C. to obtain salt milled pigment red 122.
C. I. A similar salt milling treatment was performed for CI Pigment Blue 15: 3.

~ Preparation of ink composition ~
Using the pigment dispersion obtained above, each component was mixed so as to have the following composition to prepare an ink composition.

-Composition of ink composition-
Pigment dispersion: 20.0 parts Resin particles (solid content): 7.0 parts Glycerin: 2.0 parts Sannics GP-250: 8.0 parts (New Pole GP-250 Sanyo Chemical Industries, Ltd.)
Triethylene glycol monomethyl ether: 3.0 parts Dipropylene glycol: 5.0 parts Proxel XL-2 (manufactured by Arch Chemicals Japan Co., Ltd.): 0.05 parts Benzotriazole・ ・ ・ 0.05 part ・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ・ ・ ・ 1.0 part ・ Ion-exchanged water ・ ・ ・ 33.9 parts

(Preparation of treatment solution)
The components were mixed and dissolved so as to have the following composition to prepare a treatment liquid.
-Composition of treatment liquid-
Malonic acid 11.25% by mass
DL-malic acid 14.5% by mass
Diethylene glycol monobutyl ether 4.0% by mass
Tripropylene glycol monomethyl ether (MFTG) 4.0% by mass
Ion-exchanged water 66.25% by mass
When the pH was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 1.10. Further, the surface tension was measured by FASE Automatic Surface Tensionmeter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. and found to be 41.3 mN / m.

<Examples 2-6, Comparative Examples 1-4>
Pigment dispersions having different average primary particle diameters were prepared by changing the pigment selection and salt milling treatment time.
Moreover, the average secondary particle diameter was also controlled by changing the dispersion time and strength, and ink compositions of Examples 2 to 6 and Comparative Examples 1 to 4 as shown in Table 1 were prepared.

<Evaluation>
The ink composition obtained above was evaluated as follows. The evaluation results are shown in Table 1.

(Measurement of average primary particle size)
About the ink composition obtained above, the average primary particle diameter was measured as follows.
The ink composition was dropped on a carbon support film and dried, and then observed with a transmission electron microscope (TEM 2010, acceleration voltage 200 kV, manufactured by JEOL Ltd.), and the particle size of 1000 particles arbitrarily selected. The average primary particle diameter was calculated as an arithmetic average of (equivalent circle diameter). In addition, when the observed particle | grains comprised the secondary particle which primary particles couple | bonded, the particle diameter of each primary particle which comprises a secondary particle was measured.

(Measurement of average secondary particle size)
About the ink composition obtained above, the average secondary particle diameter was measured as follows.
The average secondary particle diameter of the ink composition is a volume average particle diameter measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.).
The ratio of the average secondary particle diameter to the average primary particle diameter (particle diameter ratio) was calculated using the average primary particle diameter and the average secondary particle diameter obtained above.

(Image formation)
An A4 size OK topcoat (basis weight 104.7 g / m ² , Oji Paper Co., Ltd.) was used as a recording medium, and the above-mentioned treatment liquid and ink composition were used in combination under the following image recording conditions. The drawing was recorded.

-Treatment liquid application process-
Immediately before drawing by applying the ink composition to the recording medium, the treatment liquid was applied to the surface of the medium so as to be 1.7 g / m 2 using a coating bar.

Next, the recording medium provided with the treatment liquid was dried under the following conditions.
-Drying conditions for treatment liquid (fan drying)-
Wind speed: 15m / s
Temperature: The recording medium was heated from the back side of the recording surface with a contact type flat heater so that the surface temperature of the recording medium was 60 ° C.
Air blowing area: 450 mm (drying time 0.7 seconds)

-Ink application forming process-
A solid image was formed by applying the ink composition on the recording medium to which the treatment liquid was applied under the following conditions.
Head: 1,200 dpi / 20 inch wide piezo full line heads were arranged for four colors.
The amount of ejected droplets was 2.4 pL.
Drive frequency: 30 kHz (recording medium conveyance speed 635 mm / sec)

Next, the recording medium provided with ink was dried under the following conditions.
--Drying conditions for ink (air drying)-
Wind speed: 15m / s
Temperature: The recording medium was heated from the back side of the recording surface with a contact type flat heater so that the surface temperature of the recording medium was 60 ° C.
Air blowing area: 640 mm (drying time 1 second)

Next, heat fixing treatment was performed under the following conditions.
--Fixing--
Silicone rubber roller (hardness 50 °, nip width 5mm)
Roller temperature: 90 ° C
Pressure: 0.8 MPa

(Abrasion resistance)
A non-printed OK top coat (basis weight 104.7 g / m ² , manufactured by Oji Paper Co., Ltd.) was layered on the image area, and a load of 150 kg / m ² was applied and rubbed 10 times with a stroke of 20 mm. The method of scratching the image area was visually evaluated in four stages.
~Evaluation criteria~
○: Scratch marks were hardly seen on the image surface.
Δ: A trace of the image surface was slightly removed. Practical use limit.
X: The image was shaved, and some of the color of the ink was removed, and there was a deep scratch that could see the paper notebook.

(Dischargeability)
Using the printer for evaluation, 2000 images were continuously printed in an environment of 23 ° C. and 20% RH, and the images output on the 10th and 2000th images were compared by visual observation. The ejection stability was evaluated according to the criteria described above. The evaluation results are shown in Table 1 below.
~Evaluation criteria~
○: Neither print bending nor streaking (print loss due to non-ejection) was observed in any of the 10th and 2000th images.
Δ: Occurrence of print bending was observed in less than 10 places on the 2000th image.
×: Print bending and streaking were observed in 10 or more places on the 2000th image.

(Color tone)
The color tone of the formed image was evaluated as follows.
Black solid images of density 1.5 and density 2.0 were printed and compared by visual evaluation. As a result, no significant difference was observed in the visual evaluation for Examples 1 to 6 and Comparative Examples 1 to 4.

<Comparative Example 5>
In Example 1, an ink composition was prepared in the same manner as in Example 1 except that the pigment was 15 parts of carbon black alone, and the color tone was evaluated in the same manner as described above.
That is, when the color tone of the formed image was printed with a black solid image having a density of 1.5 and a density of 2.0 in the same manner as described above and compared by visual evaluation, a remarkable difference was recognized.

  From Table 1, it can be seen that the ink composition of the present invention is excellent in ejection properties. It can also be seen that an image having excellent abrasion resistance can be formed by using the ink composition of the present invention.

<Example 7>
~ Preparation of pigment dispersion ~
Each component was mixed so as to have the following composition, and dispersed using a bead mill for 2 hours using 0.1 mmφ zirconia beads. Subsequently, the methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed, so that the carbon black concentration was 10.0% by mass, and the resin-coated carbon black particles and A dispersion of resin-coated colored pigment was prepared.

-Composition of pigment dispersion-
-Carbon black pigment: 5.4 parts (primary particle size: 20 nm)
-Phthalocyanine pigment: 3.6 parts (CI Pigment Blue 15: 3, primary particle diameter: 40 nm)
-Quinacridone pigment: 6.0 parts (CI Pigment Red 122, primary particle size: 35 nm)
Resin dispersant P-1 6.8 parts Methyl ethyl ketone 18.0 parts 1 mol / L NaOH aqueous solution 5.6 parts Ion exchange water 54.6 parts

  An ink composition was prepared in the same manner as in Example 1 except that the pigment dispersion was prepared as described above.

<Examples 8 to 10, Comparative Examples 6 and 7>
Pigment dispersions having different average primary particle sizes were prepared by changing the selection of the pigment and the time of salt milling.
Moreover, the average secondary particle diameter was also controlled by changing the dispersion time and strength, and ink compositions of Examples 8 to 10 and Comparative Examples 6 and 7 as shown in Table 2 were produced.

<Evaluation>
Evaluation was performed in the same manner as described above except that the ink composition obtained above was used. The evaluation results are shown in Table 2.

  From Table 2, it can be seen that the ink composition of the present invention having a particle size ratio of 2.0 to 3.0 is excellent in ejection property even when the ratio of the carbon black pigment and the color pigment is changed. It can also be seen that an image having excellent abrasion resistance can be formed by using the ink composition of the present invention.

Claims (12)

Carbon black pigment, at least one color pigment selected from phthalocyanine pigment and quinacridone pigment whose primary particle diameter is controlled by a salt milling treatment, and an aqueous medium,
The average primary particle size is 50 nm or less,
A black ink-jet recording ink composition having a ratio of an average secondary particle diameter to an average primary particle diameter (average secondary particle diameter / average primary particle diameter) of 2.0 to 3.0.   The black ink-jet recording ink composition according to claim 1, further comprising resin particles.   The black ink-jet recording ink composition according to claim 1 or 2, wherein the average primary particle diameter is 35 nm or less.   The black inkjet according to any one of claims 1 to 3, wherein a content ratio of the color pigment to the carbon black pigment (color pigment / carbon black pigment) is 50% by mass or more and 200% by mass or less. A recording ink composition.   5. The black ink jet recording according to claim 1, wherein a content ratio of the quinacridone pigment to the phthalocyanine pigment (quinacridone pigment / phthalocyanine pigment) is 100% by mass or more and 180% by mass or less. Ink composition.   The black ink-jet recording ink according to any one of claims 2 to 5, wherein the resin particles include a structural unit derived from an alicyclic (meth) acrylate and an anionic hydrophilic structural unit. Composition.   The black ink-jet recording ink composition according to claim 2, wherein the resin particles have a glass transition temperature of 100 ° C. or higher and 200 ° C. or lower. The carbon black pigment and the color pigment are each a pigment in which at least one part of the surface is coated with a water-insoluble resin having phenoxyethyl (meth) acrylate as a hydrophobic unit. Item 4. A black ink-jet recording ink composition described in the item. An inkjet image forming method comprising an ink application step of applying the black ink-jet recording ink composition according to any one of claims 1 to 8 onto a recording medium by an inkjet method. The inkjet image forming method according to claim 9 , wherein the recording medium is a coated paper having a base paper and a coated layer containing an inorganic pigment. By contact with the black-based ink jet recording ink composition, further comprising a treatment liquid deposition step of depositing a component of the black-based ink jet recording ink composition capable of aggregation treatment liquid onto the recording medium, according to claim 9 Alternatively, the inkjet image forming method according to claim 10 . The inkjet image forming method according to any one of claims 9 to 11, further comprising a heat-fixing step of heat-pressing the recording medium to which the black ink-jet recording ink composition is applied.