JP5606708B2 - Ink composition, ink set, and inkjet image forming method - Google Patents

Description

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

In recent years, inkjet recording systems have been rapidly spreading due to the advantages of a small main body and low noise. Ink jet printers used for such an ink jet recording system include a type in which glass or silicon is used as a member from the viewpoint of ease of fine processing, processing accuracy, process, and the like.
Ink used in such an ink jet printer generally contains a colorant, a wetting agent and an aqueous medium that are dispersed or dissolved in a solvent. When such an ink is filled in an ink jet printer using a member containing glass or silicon and used or left for a long time, the glass or silicon in contact with the ink may be eluted. For this reason, the design accuracy of the ink jet printer is lowered, and the image quality is sometimes lowered.

  In order to solve such a problem, for example, an aqueous ink composition containing a pigment dispersed with a surfactant, a phosphonium compound, and a silicate ion is disclosed (for example, see Patent Document 1). In addition, an ink composition containing a water-soluble dye and an alkali silicate as a water-soluble antifungal agent is disclosed (for example, see Patent Document 2).

JP 2003-165936 A Japanese Patent Laid-Open No. 9-279074

However, in the water-based ink composition described in Patent Document 1, particularly when a pigment is used as a coloring material, it may be difficult to say that the ink dispersion stability is satisfactory. In addition, the water-based ink composition described in Patent Document 2 is hardly satisfactory in terms of light resistance and water resistance.
An object of the present invention is to provide an ink composition for ink jet which is excellent in ink dispersion stability and in which a decrease in liquid repellency of an ink jet head member is suppressed, an ink set containing the ink composition, and an ink jet image forming method. And

Specific means for solving the above problems are as follows.
<1> Containing water-soluble alkali metal silicate, self-dispersing polymer particles having an I / O value of 0.40 or more and 0.55 or less, and a pigment, and constituting the self-dispersing polymer particles An ink-jet ink composition wherein the copolymerization component of the polymer is methyl methacrylate, isobornyl methacrylate and methacrylic acid .
<2> The ink-jet ink composition according to <1>, wherein the alkali metal silicate is represented by the following general formula (1).
x (M ₂ O) · y (SiO ₂ ) (1)
(In general formula (1), M represents sodium or potassium, x represents 1 or 2, and y represents an integer of 1 to 4)

<3> The ink composition according to <1> or <2>, wherein the self-dispersing polymer particles have a glass transition temperature of 120 ° C. or higher .
<4 > The ink composition according to any one of <1> to < 3 >, wherein the pH at 25 ° C. is 7.5 or more and 10.0 or less.

< 5 > The ink composition according to any one of <1> to < 4 >, wherein the content of the alkali metal silicate salt is 0.0001 to 0.5% by mass.
< 6 > The mass ratio of the alkali metal silicate to the self-dispersing polymer particles (alkali metal silicate / self-dispersing polymer particles) is from 0.0001 to 0.1. The ink composition according to any one of 5 >.

< 7 > An ink set comprising the ink composition according to any one of <1> to < 6 >, and a treatment liquid capable of forming an aggregate upon contact with the ink composition.
< 8 > An ink discharge step of forming an image by discharging the ink composition according to any one of <1> to < 6 > onto a recording medium from an inkjet head including a silicon nozzle plate. Inkjet image forming method.
< 9 > The process further includes a treatment liquid application step of applying a treatment liquid that can form an aggregate upon contact with the ink composition according to any one of <1> to < 6 > on a recording medium. The inkjet image forming method as described in < 8 >.

  According to the present invention, there are provided an ink composition for an ink jet having excellent ink dispersion stability and a reduction in liquid repellency of an ink jet head member, an ink set containing the ink composition, and an ink jet image forming method. Can do.

It is a schematic sectional drawing which shows an example of the internal structure of an inkjet head. It is the schematic which shows an example of the discharge port arrangement | sequence of a nozzle plate.

<Inkjet ink composition>
The ink-jet ink composition of the present invention (hereinafter sometimes simply referred to as “ink composition”) has at least one water-soluble alkali metal silicate salt and an I / O value of 0.40 or more and 0.55. It contains at least one of the following self-dispersing polymer particles and at least one kind of pigment, and contains other components as necessary.
By adopting such an ink composition for inkjet, the ink dispersion stability is excellent, and a decrease in liquid repellency of the inkjet head member is suppressed.

In general, a member constituting an ink jet head is provided with liquid repellency in order to maintain ink ejection performance. This liquid repellency can be imparted, for example, by treating the member surface with a fluorine-based surface treatment agent. Further, it is known that the liquid repellency of the ink jet head member is gradually lowered by using the ink jet head for a long time. Further, in ink containing a pigment as a coloring material, such a decrease in liquid repellency tends to be greater.
On the other hand, there is a case where the nozzle plate is configured to include silicon or the like in order to form particularly fine nozzles (discharge ports) precisely. Even in an inkjet head having such a silicon nozzle plate, a decrease in the liquid repellency of the nozzle plate may affect the ink ejection performance.
The ink-jet ink composition of the present invention can more effectively suppress a decrease in liquid repellency of an ink-jet head member even when used in an ink-jet head having a nozzle plate formed of silicon or the like. it can.

[Alkali metal silicate]
The inkjet ink composition of the present invention contains at least one water-soluble alkali metal silicate salt. The water-soluble alkali metal silicate salt is composed of silicic acid and an alkali metal and is not particularly limited as long as it is a water-soluble compound, such as an alkali metal salt of metasilicic acid, an alkali metal salt of orthosilicate It may also be a mixture thereof.
In the present invention, it is necessary to be an alkali metal salt of silicic acid. In the case of a salt other than an alkali metal, for example, an ammonium salt of silicic acid (for example, tetramethylammonium salt of silicic acid), the ink dispersion is stable. May decrease. Further, in the case of an ammonium salt or the like that can generate a volatile compound, an odor may be generated over time.

Specifically, the alkali metal silicate is preferably at least one compound represented by the following general formula (1).
x (M ₂ O) · y (SiO ₂ ) (1)
In general formula (1), M represents sodium or potassium, x represents 1 or 2, and y represents an integer of 1 to 4. The alkali metal salt of silicic acid represented by the general formula (1) is an alkali metal metasilicate when x = 1 and y = 1, and an alkali metal orthosilicate when x = 2 and y = 1. Each is an alkali metal silicate salt having water solubility.

In general, these alkali metal silicate salts are often a mixture of two or more compounds represented by the general formula (1). However, the alkali metal silicate salt used in the present invention is the above-mentioned general salt. Even if it is 1 type of the compound represented by Formula (1), the mixture which consists of 2 or more types of the compound represented by the said General formula (1) may be sufficient.
In the present invention, a commercially available compound (for example, water glass) may be used as the water-soluble alkali metal silicate, and the silicic acid and the alkali metal carbonate or hydroxide are melted. However, from the viewpoint of ink dispersion stability, it is preferable to use a commercially available compound such as sodium silicate or potassium silicate.

  Although there is no restriction | limiting in particular as content rate of the alkali metal silicate in the inkjet ink composition of this invention, From a viewpoint of liquid-repellent fall suppression, it is 0.0001-0.5 with respect to ink composition total amount. The content is preferably mass%, more preferably 0.001 to 0.4 mass%, and still more preferably 0.01 to 0.3 mass%. By making it within the above range, the liquid repellency reduction can be effectively suppressed.

  Furthermore, the ink composition of the present invention comprises at least one alkali metal silicate represented by the general formula (1) from the viewpoint of suppressing the liquid repellency reduction of the ink jet head member and the ink dispersion stability. The content is preferably 0.0001% by mass to 0.5% by mass with respect to the total amount, and at least one selected from sodium silicate or potassium silicate is 0.001 to 0.4% by mass with respect to the total amount of the ink composition. % Content is more preferable.

[Self-dispersing polymer particles]
The inkjet ink composition of the present invention includes at least one kind of self-dispersing polymer particles having an I / O value of 0.40 or more and 0.55 or less . The self-dispersing polymer particles include a self-dispersing polymer (hereinafter referred to as “first polymer”) including at least one structural unit derived from a hydrophilic monomer and at least one structural unit derived from a hydrophobic monomer. It may be preferable to be configured to include.
By including self-dispersing polymer particles having an I / O value of 0.40 or more and 0.55 or less, an ink composition that is excellent in ink stability and ejection stability and excellent in abrasion resistance of the formed image is formed. be able to.

In the present invention, the self-dispersing polymer means a dispersed state in an aqueous medium due to a functional group (particularly an acidic group or a salt thereof) of the polymer itself when it is dispersed by a phase inversion emulsification method in the absence of a surfactant. Refers to a water-insoluble polymer.
Here, the dispersed state means both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium. It includes the state of.
The self-dispersing polymer in the invention is preferably a self-dispersing polymer 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 the ink composition.

  Examples of a method for preparing an emulsified or dispersed state of the self-dispersing polymer, that is, an aqueous dispersion of the self-dispersing polymer 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 water-soluble 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 in a state in which a salt-forming group (for example, an acidic group) of the polymer is neutralized and removing the solvent.

  Further, the stable emulsified or dispersed state in the self-dispersing polymer of the present invention is 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 100% neutralization of salt-forming groups of the water-insoluble polymer. A neutralizing agent (sodium hydroxide if the salt-forming group is anionic, acetic acid if it is cationic) and 200 g of water are mixed and stirred (apparatus: stirring device with stirring blades, rotation speed 200 rpm, 30 minutes, 25 After the removal of the organic solvent from the mixed solution, the emulsified or dispersed state is stably present at 25 ° C. for at least one week, and the occurrence of precipitation cannot be visually confirmed. .

The stability of the emulsified or dispersed state in the self-dispersing polymer 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 polymer particles obtained by the above method to a solid concentration of 25% by mass, and then centrifuging at 12,000 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 (a value close to 1), the sedimentation of the polymer particles by centrifugation does not occur, that is, the aqueous dispersion of polymer 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.

In the self-dispersing polymer in the present invention, the content of a water-soluble component exhibiting water solubility in a dispersed state is preferably 10% by mass or less, more preferably 8% by mass or less, and 6% by mass. More preferably, it is as follows. When the water-soluble component is 10% by mass or less, swelling of the polymer particles and fusion between the polymer particles can be effectively suppressed, and a more stable dispersion state can be maintained. Further, an increase in the viscosity of the ink composition can be suppressed, and the ejection stability by the ink jet method becomes better.
Here, the water-soluble component is a compound contained in the self-dispersing polymer and is a compound that dissolves in water when the self-dispersing polymer is in a dispersed state. The water-soluble component is a water-soluble compound that is by-produced or mixed when the self-dispersing polymer is produced.

  In the present invention, the glass transition temperature of the first polymer (self-dispersing polymer) is not particularly limited, but the glass transition temperature is preferably 120 ° C. or higher, more preferably 120 ° C. or higher and 250 ° C. or lower, It is more preferably 150 ° C. or higher and 250 ° C. or lower, and further preferably 160 ° C. or higher and 200 ° C. or lower. When the glass transition temperature is 120 ° C. or higher, the blocking resistance (particularly under high temperature and high humidity) of the image formed is improved. Further, when the glass transition temperature is 250 ° C. or less, the abrasion resistance of the image is improved.

  The glass transition temperature of the first polymer can be appropriately controlled by a commonly used method. For example, the glass transition temperature of the first polymer can be appropriately selected by appropriately selecting the type of polymerizable group of the monomer constituting the first polymer, the type of substituent on the monomer, the constituent ratio of the monomer, the molecular weight of the polymer molecule, and the like. Can be controlled within a desired range.

  In the present invention, the measured Tg obtained by actual measurement is applied as the glass transition temperature (Tg) of the first polymer. 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 polymer decomposition or the like, 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 I / O value of the first polymer in the invention, Ru der 0.40 0.55.
When the I / O value of the first polymer is 0.20 or more, the stability of the ink composition is further improved. Moreover, blocking resistance (especially on high temperature, high humidity conditions) improves more because I / O value is 0.55 or less.

The I / O value is a value that treats the polarity of various organic compounds, also called inorganic values / organic values, in an organic concept, and is one of functional group contribution methods for setting parameters for each functional group. It is.
The I / O value is described in detail in an organic conceptual diagram (written by Yoshio Koda, Sankyo Publishing (1984)). The concept of the I / O value is that the properties of a compound are divided into an organic group that represents covalent bonding and an inorganic group that represents ionic bonding, and all organic compounds are orthogonal coordinates named organic axes and inorganic axes. Each of the above points is shown.

In the present invention, the I / O value of the first polymer means that determined by the following method. Based on the organicity (O value) and inorganicity (I value) described in Yoshio Koda, Organic Conceptual Diagram-Fundamentals and Applications (1984), p.13, etc. An I / O value (= I value / O value) is calculated. For each monomer constituting the polymer, the product of (I / O value) and (mol% in the polymer) is calculated, and these are totaled, and the result obtained by rounding off the third decimal place is the first polymer. I / O value.
However, as a method for calculating the inorganic value of each monomer, a double bond is generally added as an inorganic value of 2, but when polymerized, the double bond disappears. The I / O value of the 1st polymer was computed using the numerical value which is not adding the bond part.
In this invention, the polymer which has a desired I / O value can be comprised by adjusting suitably the structure and content rate of the monomer which comprise a 1st polymer.

The first polymer in the present invention has a glass transition temperature of 120 ° C. or higher and 250 ° C. from the viewpoints of the stability of the ink composition, blocking resistance (particularly under high temperature and high humidity conditions), and abrasion resistance of the formed image. The I / O value is preferably 0.40 to 0.55, the glass transition temperature is 150 ° C. to 250 ° C., and the I / O value is 0.40 to 0.54. The glass transition temperature is more preferably 160 ° C. or more and 200 ° C. or less, and the I / O value is further preferably 0.40 or more and 0.50 or less.

  Moreover, the 1st polymer in this invention contains at least 1 sort (s) of the hydrophilic structural unit derived from a hydrophilic monomer, and at least 1 sort (s) of the hydrophobic structural unit derived from a hydrophobic monomer. The main chain skeleton of the first 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 in the present invention is not particularly limited as long as it is derived from a hydrophilic group-containing monomer (hydrophilic monomer), and even if it is derived from one kind of hydrophilic group-containing monomer, two kinds are used. It may be derived from the above hydrophilic group-containing monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, at least one of the hydrophilic groups is preferably a dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state, and is an anionic dissociable group. More preferably. 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 in the present invention 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.

Examples of the hydrophilic structural unit in the present invention include an embodiment containing only a hydrophilic structural unit having an anionic dissociable group, a hydrophilic structural unit having an anionic dissociable group, and a nonionic hydrophilic group. It is preferable that it is either of the aspects containing both the hydrophilic structural unit which has.
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 dissociative group, the acid value (KOHmg / g) is determined from the viewpoint of self-dispersibility, content of water-soluble component, and fixing property when an ink composition is constituted. Therefore, it is preferably 20 or more and 200 or less, more preferably 22 or more and 120 or less, and further preferably 25 or more and 100 or less. Particularly preferred is 30 or more and 80 or less. When the acid value is 20 or more, the particles can be more stably dispersed, and when the acid value is 200 or less, water-soluble components can be reduced.

(Hydrophobic building block)
The hydrophobic structural unit in the present invention 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 kind of hydrophobic group-containing monomer, there are two types. It may be derived from the above 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.
In the present invention, at least one of the hydrophobic monomers is preferably a cyclic aliphatic group-containing monomer from the viewpoint of blocking resistance, abrasion resistance, and dispersion stability, and the cyclic aliphatic group-containing (meth) acrylate ( Hereinafter, it is more preferably “alicyclic (meth) acrylate”.

-Alicyclic (meth) acrylate-
In the present invention, the alicyclic (meth) acrylate includes a structural part derived from (meth) acrylic acid and a structural part derived from alcohol, and the structural part derived from alcohol is unsubstituted or substituted. It has a structure containing at least one cyclic hydrocarbon group (cycloaliphatic 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 in this invention, 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, alkyleneoxy group, mono- or oligo group having 1 to 20 carbon atoms. Preferred examples include an ethyleneoxy group, a mono- or oligopropyleneoxy group, and the like.

Specific examples of the alicyclic (meth) acrylate in the present invention 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% by mass or more and 90% by mass or less, and 40% by mass or more and 90% by mass or less. It is more preferable that Particularly preferred is 50 mass% or more and 80 mass% or less.
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 polymer 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 may be 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; dialkylaminoalkyl 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) Examples include (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides 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 another copolymerizable monomer, the structural unit derived from the aromatic-containing (meth) acrylate is 40% by mass or less from the viewpoint of dispersion stability of the self-dispersing polymer particles. It is preferably 30% by mass or less, and particularly preferably 20% by mass or less.

In addition, when a styrene monomer is used as another copolymerizable monomer, the structural unit derived from the styrene monomer is preferably 20% by mass or less from the viewpoint of stability when the self-dispersing polymer particles are obtained. More preferably, it is 10 mass% or less, More preferably, it is 5 mass% or less, The aspect which does not contain the structural unit derived from a styrene-type monomer is especially preferable.
Here, the styrene monomer refers to styrene, substituted styrene (α-methylstyrene, chlorostyrene, etc.), and a styrene macromer having a polystyrene structural unit.

In the present invention, other copolymerizable monomers may be used singly or in combination of two or more.
When the first polymer contains other structural units, the content is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, and particularly preferably 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.

The first polymer in the present invention is a polymer obtained by polymerizing at least three kinds of alicyclic (meth) acrylate, other copolymerizable monomer, and hydrophilic group-containing monomer from the viewpoint of dispersion stability. Preferably, it is obtained by polymerizing at least three kinds of alicyclic (meth) acrylate, linear or branched alkyl group-containing (meth) acrylate having 1 to 8 carbon atoms, and hydrophilic group-containing monomer. More preferably, it is a polymer.
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 first polymer in the present invention may be a random copolymer in which each constitutional unit is introduced irregularly, or a block copolymer introduced regularly. Each constitutional unit in a certain case may be synthesized in any order of introduction, and the same constitutional component may be used twice or more, but being a random copolymer is versatile and manufacturable. This is preferable.

The molecular weight range of the first polymer in the present invention is a weight average molecular weight of preferably 3000 to 200,000, more preferably 10,000 to 200,000, and still more preferably 30000 to 150,000. 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).

From the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer, the first polymer in the present invention has a structure derived from an alicyclic (meth) acrylate as a copolymerization ratio of 20% by mass to 90% by mass, and a dissociable group-containing monomer. Including a structure derived from and at least one kind of structure derived from a (meth) acrylate containing a chain alkyl group having 1 to 8 carbon atoms, the acid value is 20 to 120, and the total number of hydrophilic structural units A vinyl polymer having a content of 25% by mass or less and a weight average molecular weight of 3000 to 200,000 is preferable.
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 or more and less than 80% by mass, and a structure derived from a carboxyl group-containing monomer having an acid value in the range of 25 to 100, and the total content of hydrophilic structural units A vinyl polymer having a rate 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 Containing the derived structure as a copolymerization ratio of 20% by mass or more and less than 60% by mass, including the structure derived from acrylic acid or methacrylic acid in an acid value range of 30 to 80, and the total content of hydrophilic structural units being 25% by mass %, And a vinyl polymer having a weight average molecular weight of 30,000 to 150,000 is particularly preferable.

  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., I / O value: 0.4 2
Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (40/52/8), glass transition temperature: 160 ° C., I / O value: 0. 48
Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (50/44/6), glass transition temperature: 140 ° C., I / O value: 0.51
Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (85/7/8), glass transition temperature: 120 ° C., I / O value: 0. 58
Methyl methacrylate / benzyl methacrylate / methacrylic acid copolymer (85/7/8), glass transition temperature: 100 ° C., I / O value: 0. 58
Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/72/8), glass transition temperature: 160 ° C., I / O value: 0. 43
Methyl methacrylate / isobornyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/62/10/8), glass transition temperature: 170 ° C., I / O value: 0.4 2

In the calculation of the I / O value, the following numerical values were used as the I / O values of the monomers constituting each polymer.
Methyl methacrylate: 0.60, isobornyl methacrylate: 0.29, dicyclopentanyl methacrylate: 0.32, benzyl methacrylate: 0.34, methacrylic acid: 0.47

There is no restriction | limiting in particular as a manufacturing method of the self-dispersing polymer in this invention, 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 of the present invention, a monomer mixture and, if necessary, a mixture containing an organic solvent and a radical polymerization initiator are subjected to a copolymerization reaction in an inert gas atmosphere, thereby the water-insoluble polymer. A polymer can be produced.

There is no restriction | limiting in particular as a manufacturing method of the aqueous dispersion of the self-dispersing polymer particle in this invention, 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 obtaining a dispersion by stirring a mixture containing a water-insoluble polymer, an organic solvent, a neutralizing agent, and an aqueous medium.
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.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 20 to 100 mol%, still more preferably 30 to 80 mol%, based on 100 mol% of the dissociable group. By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 80 mol% or less.

  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 average particle size of the self-dispersing polymer particles in the present invention is preferably in the range of 1 to 100 nm, more preferably 3 to 80 nm, and further preferably 5 to 60 nm. Most preferably, it is 5-40 nm. Manufacturability is improved when the average particle diameter is 1 nm or more. Moreover, storage stability improves by setting it as an average particle diameter of 100 nm or less.
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 particles are preferably present in a form that does not substantially contain a colorant.
The self-dispersing polymer particles of the present invention are 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 inkjet ink composition of the present invention, the self-dispersing polymer particles may be contained singly or in combination of two or more.
In addition, the content of the self-dispersing polymer particles in the ink composition of the present invention is preferably 1 to 30% by mass with respect to the ink-jet ink composition from the viewpoint of glossiness of the image and the like. It is more preferably 20% by mass, and particularly preferably 2 to 10% by mass.

Furthermore, the mass ratio of the alkali metal silicate to the self-dispersing polymer particles in the ink composition of the present invention (alkali metal silicate / self-dispersing polymer particles) is preferably 0.0001 to 0.1, More preferably, it is 0.001 to 0.05.
When the mass ratio of the water-soluble alkali metal silicate to the self-dispersing polymer particles is 0.0001 or more, a decrease in liquid repellency of the inkjet head member is more effectively suppressed. Moreover, when it is 0.1 or less, the ejection property and the ink dispersion stability are further improved.

  Furthermore, in the ink composition of the present invention, from the viewpoints of ink ejection properties, ink dispersion stability, and suppression of a decrease in liquid repellency of an inkjet head member, self-dispersing polymer particles having an acid value of 20 or more and 200 or less and the above general formula It is preferable that the mass ratio (alkali metal silicate / self-dispersing polymer particles) is 0.0001 to 0.1, including at least one alkali metal silicate represented by (1). It is more preferable that the self-dispersing polymer particles having an acid value of 22 or more and 120 or less and at least one selected from sodium silicate or potassium silicate have a mass ratio of 0.001 to 0.05.

[Pigment]
The inkjet ink composition of the present invention contains at least one pigment as colorant particles.
The pigment is not particularly limited as long as it can be stably present in the ink composition, but is preferably a water-dispersible pigment from the viewpoint of light resistance, dispersion stability, and the like.

Specific examples of the water-dispersible pigment include the following pigments (1) to (4).
(1) Encapsulated pigment, that is, a polymer emulsion in which a pigment is contained in polymer particles. More specifically, the pigment is coated with a water-insoluble polymer dispersant, and is made hydrophilic by a polymer layer on the pigment surface. A pigment is dispersed in water.
(2) Self-dispersed pigments, that is, pigments having at least one hydrophilic group on the surface and exhibiting water dispersibility in the absence of a dispersant, more specifically, surface oxidation treatment is mainly performed on carbon black and the like. It is made hydrophilic so that the pigment alone is dispersed in water.
(3) A resin-dispersed pigment, that is, a pigment dispersed with a water-soluble polymer compound having a weight average molecular weight of 50,000 or less.
(4) A surfactant-dispersed pigment, that is, a pigment dispersed by a surfactant.
Preferred examples in the present invention include (1) encapsulated pigment and (2) self-dispersing pigment, and particularly preferred examples include (1) encapsulated pigment.

(Encapsulated pigment)
The type of the pigment is not particularly limited, and conventionally known organic and inorganic pigments can be used. Specific examples include pigments described in JP-A-2007-100071. In particular, azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, and carbon black pigments are preferably used.

  The water-insoluble polymer dispersant (hereinafter sometimes simply referred to as “dispersant”) is a water-insoluble polymer (hereinafter sometimes referred to as “second polymer”), and can disperse the pigment. There is no particular limitation, and a conventionally known water-insoluble polymer dispersant can be used. The water-insoluble polymer dispersant can be constituted by including, for example, both a hydrophobic structural unit and a hydrophilic structural unit.

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

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

  In the present invention, the water-insoluble polymer dispersant is preferably a vinyl polymer containing a carboxyl group from the viewpoint of dispersion stability of the pigment, and a structural unit derived from at least an aromatic group-containing monomer as a hydrophobic structural unit. And a vinyl polymer having a structural unit containing a carboxyl group as a hydrophilic structural unit.

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

The content of the dispersant in the capsule pigment in the present invention is preferably 5 to 200% by mass of the dispersant with respect to the pigment from the viewpoint of the dispersibility of the pigment, the ink colorability, and the dispersion stability. 100 mass% is more preferable, and 20-80 mass% is especially preferable.
When the content of the dispersant in the capsule pigment is in the above range, the pigment is preferably coated with an appropriate amount of the dispersant, and a capsule pigment having a small particle size and excellent stability over time is easily obtained.

The capsule pigment in the present invention may contain other dispersant in addition to the water-insoluble polymer dispersant. For example, a conventionally known water-soluble low-molecular dispersant, water-soluble polymer, or the like can be used. The content of the dispersant other than the water-insoluble polymer dispersant can be used within the range of the content of the dispersant.
If necessary, other additives such as a basic substance (neutralizing agent) and a surfactant can be added to the capsule pigment.

As the basic substance, a neutralizing agent (organic base, inorganic alkali) can be used. For the purpose of neutralizing the dispersant, the basic substance is preferably added so that the composition containing the dispersant has a pH of 7 to 11, more preferably 8 to 10.
As content of a basic substance, it is preferable that it is 50-150 mol% with respect to 100 mol% of ionic groups of a dispersing agent, it is more preferable that it is 70-120 mol%, and it is 80-100 mol%. It is particularly preferred.
Specific examples of the basic substance are the same as those in the self-dispersing polymer particles described above.

-Manufacturing method of pigment dispersion-
The capsule pigment in the present invention can be obtained as a pigment dispersion by dispersing, for example, a mixture containing a pigment, a dispersant, and optionally a solvent (preferably an organic solvent) with a disperser.

The pigment dispersion in the present invention contains a pigment, a dispersant, an organic solvent for dissolving or dispersing the dispersant, and a basic substance, and after mixing a solution containing water as a main component (mixing / hydration step), It is preferable to manufacture by removing the organic solvent (solvent removal step).
According to this method for producing a pigment dispersion, it is possible to produce a pigment dispersion in which the capsule pigment is finely dispersed and excellent in storage stability.

  The organic solvent in the method for producing a pigment dispersion needs to be able to dissolve or disperse the dispersant in the present invention, but in addition to this, it preferably has a certain degree of affinity for water. Specifically, the solubility in water at 20 ° C. is preferably 10% by mass or more and 50% by mass or less.

  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 dispersant, an organic solvent for dissolving and dispersing the dispersant, a basic substance, and water. Step (2): After the dispersion treatment Removing at least a portion of the organic solvent from the mixture of

In the step (1), first, the dispersant is dissolved or dispersed in an organic solvent to obtain a mixture thereof (mixing step). Next, a pigment, a solution containing a basic substance and 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 pigment. Obtain a dispersion.
There is no limitation in the addition amount (degree of neutralization) of the basic substance. Usually, it is preferable that the finally obtained capsule pigment dispersion has a liquidity close to neutrality, for example, a pH (25 ° C.) of 4.5 to 10. The pH can also be determined by the degree of neutralization according to the dispersant.

  The pigment, the dispersant, and other additives used in the method for producing the pigment dispersion have the same meanings as those described in the above-mentioned capsule pigment, and preferred examples are also the same.

Preferable examples of the organic solvent used in the present invention include alcohol solvents, ketone solvents, and ether solvents. Among these, examples of alcohol solvents include ethanol, isopropanol, n-butanol, tertiary butanol, isobutanol, and diacetone alcohol. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Among these solvents, isopropanol, acetone and methyl ethyl ketone are preferable, and methyl ethyl ketone is particularly preferable.
These organic solvents may be used alone or in combination.

In the production of the pigment dispersion, a two-roll, a three-roll, a ball mill, a tron mill, a disper, a kneader, a kneader, a homogenizer, a blender, a single or twin screw extruder, etc. A kneading and dispersing process can be performed.
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.
If necessary, use a vertical or horizontal sand grinder, pin mill, slit mill, ultrasonic disperser, etc. to finely disperse with beads made of glass with a particle diameter of 0.01 to 1 mm, zirconia, etc. Can be obtained.

  In the method for producing a pigment dispersion in the present invention, the removal of the organic solvent is not particularly limited, and can be removed by a known method such as vacuum distillation.

  The capsule pigment in the pigment dispersion thus obtained maintains a good dispersion state, and the obtained pigment dispersion has excellent stability over time.

(Self-dispersing pigment)
The self-dispersing pigment refers to a large number of hydrophilic functional groups and / or salts thereof (hereinafter referred to as dispersibility-imparting groups) on the pigment surface, either directly or indirectly via an alkyl group, an alkyl ether group, an aryl group or the like. A pigment that is bonded and dispersible in an aqueous medium without a dispersant. Here, “dispersed in an aqueous medium without a dispersant” refers to a state in which the pigment can be dispersed in an aqueous medium without using a dispersant for dispersing the pigment.
Inks containing a self-dispersing pigment as a colorant do not need to contain a dispersant as described above that is contained in order to disperse a normal pigment. It is easy to prepare ink that is excellent in ejection stability.
In the present invention, preferred examples include self-dispersing pigments that are surface-treated by oxidation treatment with hypohalous acid and / or hypohalite or oxidation treatment with ozone. Commercially available products can also be used as the self-dispersing pigment, such as Microjet CW-1 (trade name; manufactured by Orient Chemical Co., Ltd.), CAB-O-JET200, CAB-O-JET300 (above trade names). ; Manufactured by Cabot Corporation).

In the present invention, the average particle size of the pigment is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, and in the case of the ink jet method, the droplet ejection characteristics are good. Moreover, light resistance becomes favorable because an average particle diameter is 10 nm or more.
The particle size distribution of the pigment is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more pigments having a monodispersed particle size distribution may be mixed and used.
The average particle size and particle size distribution of the pigment can be measured using, for example, a dynamic light scattering method.

In the ink composition of the present invention, the above pigments may be used alone or in combination of two or more.
Further, the content of the pigment in the ink composition is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass with respect to the ink composition from the viewpoint of image density. 5 to 15% by mass is more preferable, and 1.5 to 10% by mass is particularly preferable.
Further, the mass ratio of the pigment to the self-dispersing polymer particles (pigment / self-dispersing polymer particles) is preferably 1 / 0.5 to 1/10 from the viewpoint of image scratch resistance and the like. It is more preferable that it is / 1-1 / 4.

[Water-soluble organic solvent]
The inkjet ink composition of the present invention preferably contains an aqueous medium. The aqueous medium contains at least water as a solvent, but preferably contains water and at least one water-soluble organic solvent. The water-soluble organic solvent is used for the purpose of an anti-drying agent, a wetting agent or a penetration accelerator.

The anti-drying agent can effectively prevent nozzle clogging that may occur due to the drying of ink at the ink ejection port. The drying inhibitor is preferably a water-soluble organic solvent having a vapor pressure lower than that of water.
Specific examples of the drying inhibitor include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, Polyvalent alcohols typified by acetylene glycol derivatives, glycerin, trimethylolpropane, etc., polyvalent alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether Lower alkyl ethers of alcohols, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, heterocyclic rings such as N-ethylmorpholine, sulfolane, dimethyls Sulfoxide, sulfur-containing compounds such as sulfolane, diacetone alcohol, polyfunctional compounds such as diethanolamine, and urea derivatives. Of these, polyhydric alcohols such as glycerin and diethylene glycol are preferred as the drying inhibitor. Moreover, said drying inhibitor may be used independently or may be used together 2 or more types. These drying inhibitors are preferably contained in the ink composition in an amount of 10 to 50% by mass.

The penetration accelerator is preferably used for the purpose of allowing the ink composition to penetrate better into the recording medium (printing paper).
Specific examples of penetration enhancers include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, 1,2-hexanediol, sodium lauryl sulfate, sodium oleate, and nonionic surfactants. Etc. can be used suitably. These penetration enhancers exhibit a sufficient effect when contained in the ink composition in an amount of 5 to 30% by mass. Further, it is preferable that the penetration enhancer is used within a range of an addition amount that does not cause bleeding of prints and paper loss (print through).

  In addition to the above, the water-soluble organic solvent can be used for adjusting the viscosity. Specific examples of water-soluble organic solvents that can be used to adjust the viscosity include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, pentanol, hexanol, Cyclohexanol, benzyl alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, Thiodiglycol), glycol derivatives (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether) Tellurium, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, Triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine) Ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine) and other polar solvents (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, sulfolane, 2-pyrrolidone, N -Methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone).

  The water-soluble organic solvent in the inkjet ink composition of the present invention may be used singly or in combination of two or more. The content of the water-soluble organic solvent is preferably 1% by mass to 60% by mass, more preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass from the viewpoints of stability and dischargeability. Particularly preferably used.

  The amount of water used in the present invention is not particularly limited, but is preferably 10% by mass or more and 99% by mass or less, more preferably from the viewpoint of ensuring stability and ejection reliability in the inkjet ink composition. Is 30 mass% or more and 80 mass% or less, More preferably, it is 50 mass% or more and 70 mass% or less.

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

Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like.
In addition, the addition amount of the surface tension adjusting agent is preferably an addition amount that adjusts the surface tension of the ink composition to 20 to 60 mN / m, in order to achieve good droplet ejection by the ink jet method, and is adjusted to 20 to 45 mN / m. The addition amount is more preferable, and the addition amount adjusted to 25 to 40 mN / m is more preferable.
The surface tension of the ink composition can be measured at 25 ° C. using a plate method, for example.

Specific examples of surfactants include fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensation in hydrocarbons Products, anionic surfactants such as polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxy Nonionic surfactants such as ethylene alkylamine, glycerin fatty acid ester and oxyethyleneoxypropylene block copolymer are preferred. Further, SURFYNOLS (Air Products & Chemicals) and Olfine (manufactured by Nissin Chemical Industry Co., Ltd.), which are acetylene-based polyoxyethylene oxide surfactants, are also preferably used. An amine oxide type amphoteric surfactant such as N, N-dimethyl-N-alkylamine oxide is also preferred.
Furthermore, pages (37) to (38) of JP-A-59-157636, Research Disclosure No. The surfactants described in 308119 (1989) can also be used.
Further, fluorine (fluorinated alkyl type) surfactants, silicone type surfactants and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806 are disclosed. By using, the abrasion resistance can be improved.
These surface tension modifiers can also be used as antifoaming agents, and fluorine compounds, silicone compounds, chelating agents represented by EDTA, and the like can also be used.

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

The pH of the ink composition of the present invention is preferably pH 7.5 to 10 and more preferably pH 8 to 9 from the viewpoint of ink stability and aggregation rate. The pH of the ink composition is 25 ° C., and is measured by a commonly used pH measuring device (for example, a multi-water quality meter MM-60R manufactured by Toa DKK Corporation).
The pH of the ink composition can be appropriately adjusted using an acidic compound or a basic compound. As the acidic compound or the basic compound, a commonly used compound can be used without particular limitation.

<Ink set>
The ink set of the present invention includes at least one ink jet ink composition and at least one treatment liquid capable of forming an aggregate upon contact with the ink jet ink composition.
The ink set of the present invention is used in an image forming method using the ink jet ink composition, and is particularly preferable as an ink set used in an image forming method described later.
The ink set of the present invention can be used as an ink cartridge that accommodates them integrally or independently, and is preferable from the viewpoint of easy handling. An ink cartridge including an ink set is known in the art, and can be formed into an ink cartridge by appropriately using a known method.

[Treatment solution]
The treatment liquid in the present invention is an aqueous composition capable of forming an aggregate when contacted with the inkjet ink composition. Specifically, the pigment in the ink composition when mixed with the ink composition. It is possible to constitute at least an aggregating component capable of forming an aggregate by aggregating dispersed particles such as the above and, if necessary, other components. By using the treatment liquid together with the ink composition, it is possible to increase the speed of inkjet recording, and an image with high density and resolution can be obtained even when recording at high speed.

(Aggregating component)
The treatment liquid contains at least one aggregation component capable of forming an aggregate upon contact with the ink composition. By mixing the treatment liquid with the ink composition 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 composition 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 ° C. ± 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 ° C. ± 1 ° C.) of the ink composition is 7.5 or more, and the pH of the treatment liquid (25 (C ± 1 ° C.) is preferably 3 to 5.
The aggregating components can be used alone or in combination of two or more.

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

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

The treatment liquid in the present invention can be configured to further contain an aqueous solvent (for example, water) in addition to the acidic compound.
As content of the acidic compound in a process liquid, it is preferable that it is 5-95 mass% with respect to the total mass of a process liquid from a viewpoint of the aggregation effect, and it is more preferable that it is 10-80 mass%.

  Further, as a preferred example of the treatment liquid for improving the high-speed aggregation property, a treatment liquid to which a polyvalent metal salt or polyallylamine is added can also be mentioned. 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), salts of lanthanides (for example, neodymium), polyallylamine, and polyallylamine derivatives. 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.

  As content in the process liquid of a metal salt, 1-10 mass% is preferable, More preferably, it is 1.5-7 mass%, More preferably, it is the range of 2-6 mass%.

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.).

<Inkjet image forming method>
The ink jet image forming method of the present invention includes an ink discharging step of forming an image by discharging the ink composition for ink jet onto a recording medium from an ink jet head provided with a silicon nozzle plate. It is comprised including a process.
In the present invention, it is preferable to further include a treatment liquid application step of applying a treatment liquid that can form an aggregate upon contact with the inkjet ink composition onto a recording medium.

[Ink ejection process]
In the ink ejection step, the ink-jet ink composition of the present invention described above is applied onto a recording medium by an ink-jet method from an ink-jet head having a silicon nozzle plate. 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 recording using the ink-jet method is performed by supplying energy to obtain a desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and JP-A-8-27693. Publication No. 2-276670, No. 7-276789, No. 9-323475, No. JP-A-62-238783, JP-A-10-153898, No. 10-217473, No. 10- No. 235995, No. 10-337947, No. 10-217597, No. 10-337947, etc. Liquid composition for ink jet paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. This can be done by discharging objects. As a preferable ink jet recording method for 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 ink jet method, 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 head in which recording elements are arranged corresponding to the entire area of one side of the recording medium There is a line system using. 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 ink jet recording method of the present invention can be applied to any of these, but generally, when applied to a line system that does not use a dummy jet, the effect of improving ejection accuracy and image scratch resistance is great.

  Furthermore, in the ink ejection process of the present invention, in the case 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. .

(Inkjet head with silicon nozzle plate)
The ink jet head used in the image forming method of the present invention includes a nozzle plate formed at least partially including silicon. FIG. 1 is a schematic cross-sectional view showing an example of the internal structure of an inkjet head.

  As shown in FIG. 1, the inkjet head 100 includes a nozzle plate 11 having discharge ports (nozzles) and an ink supply unit 20 provided on the opposite side to the discharge direction of the nozzle plate. The nozzle plate 11 is provided with a plurality of ejection ports 12 for ejecting ink.

  As shown in FIG. 2, the nozzle plate 11 is provided with 32 × 60 discharge ports (nozzles) arranged two-dimensionally. This nozzle plate is at least partially formed of silicon, and has a structure in which silicon is exposed on the inner wall of the nozzle opening and the plate surface on the ink ejection direction side. Although not shown, a liquid repellent film is provided on at least a part of the plate surface of the nozzle plate 11 on the ink ejection direction side.

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

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

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

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

[Processing liquid application process]
In the treatment liquid application step, a treatment liquid capable of forming an aggregate by contact with the ink composition is applied to the recording medium, and the treatment liquid is contacted with the ink composition to form an image. In this case, dispersed particles such as polymer particles and pigment in the ink composition are aggregated, and the image is fixed on the recording medium. The details and preferred embodiments of each component in the treatment liquid are as described above.

  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 bread coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, a bar coater or the like can be used. The details of the inkjet method are as described above.

The treatment liquid application step may be provided either before or after the ink ejection step using the ink composition.
In the present invention, an embodiment in which an ink discharge step is provided after the treatment liquid is applied in the treatment liquid application step is preferable. That is, before ejecting the ink composition onto the recording medium, a treatment liquid for aggregating the pigment in the ink composition is applied in advance, and is brought into contact with the treatment liquid applied on the recording medium. An embodiment in which an ink composition is ejected 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, but preferably, the application amount of the aggregation component (for example, a divalent or higher carboxylic acid or a cationic organic compound) is 0.1 g. / M ² or more. Especially, the quantity from which the provision amount of an aggregation component 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 aggregating component is 0.1 g / m ² or more, the agglomeration reaction proceeds favorably, and when it is 1.0 g / m ² or less, the glossiness is not excessively increased.

  In the present invention, an ink discharge 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 onto the recording medium and before the ink composition is discharged. It is preferable to further provide a heat drying step. By heating and drying the treatment liquid in advance before the ink ejection step, ink colorability such as bleeding prevention is improved, and a visible image with good color density and hue can be recorded.

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

[Heat fixing process]
The ink jet recording method of the present invention preferably has a heat fixing step in which, after the ink ejection step, a heat surface is brought into contact with an ink image formed by applying the ink composition to heat and fix. By performing the heat fixing process, the image on the recording medium is fixed, and the resistance against image abrasion can be further improved.

  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.

  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.

-Recording media-
The inkjet recording 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 ink jet recording 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.

  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-8220GPC (manufactured by Tosoh Corporation), and three columns are connected in series using TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, and TSKgeL SuperHZ2000 (all are trade names of Tosoh Corporation). , THF (tetrahydrofuran) was used as an eluent. 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 an IR 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".

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

(Preparation of pigment dispersion C)
Pigment Blue 15: 3 (phthalocyanine blu-A220, manufactured by Dainichi Seika Co., Ltd .; cyan pigment), 4 parts of the polymer dispersant P-1, 42 parts of methyl ethyl ketone, and 1 mol / L NaOH aqueous solution. 4 parts and 87.2 parts of ion-exchanged water were mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
After removing methyl ethyl ketone at 55 ° C. under reduced pressure and removing a part of water in the obtained dispersion, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge, Centrifugation was performed at 8000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. Thereafter, the pigment concentration was determined from the absorbance spectrum, and a pigment dispersion C was obtained as a dispersion of a resin-coated pigment (encapsulated pigment) having a pigment concentration of 10.2% by mass.

(Preparation of self-dispersing polymer particles)
In a 2 liter three-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 540.0 g of methyl ethyl ketone was charged, and the temperature was raised to 75 ° C. in a nitrogen atmosphere. While maintaining the temperature in the reaction vessel at 75 ° C., 216 g of methyl methacrylate (MMA), 280.8 g of isobornyl methacrylate (IBOMA), 43.2 g of methacrylic acid (MAA), 108 g of methyl ethyl ketone, and “V-601” (Wako Pure) A mixed solution consisting of 2.16 g (manufactured by Yakuhin Co., Ltd.) was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, 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 63000, and 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 a dispersion of exemplary compound polymer (B-02) having a solid content concentration of 26.0%.

It was 160 degreeC when the glass transition temperature of the obtained polymer (B-02) was measured with the following method.
The amount of the polymer solution after polymerization, which was 0.5 g as a solid content, was dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid content. Using the obtained polymer solid content, Tg was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. Measurement conditions were such that a sample amount of 5 mg was sealed in an aluminum pan, and the peak top value of DDSC of the measurement data at the second temperature increase in the following temperature profile was defined as Tg in a nitrogen atmosphere.
30 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 230 ° C. (temperature rise at 20 ° C./min)
230 ° C → -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 230 ° C. (temperature rise at 20 ° C./min)

  In the same manner as the dispersion of self-dispersing polymer particles (B-02), dispersions of self-dispersing polymer particles shown in Table 1 below were prepared. In the polymer composition of Table 1, MMA means methyl methacrylate, IBOMA means isobornyl methacrylate, DCPMA means dicyclopentanyl methacrylate, BzMA means benzyl methacrylate, MAA means methacrylic acid, and the numerical values are It means the composition ratio (mass basis) of the monomer.

(Preparation of non-self-dispersing polymer particle dispersion D-1)
Jonkrill 537 (manufactured by BASF Japan, Tg = 49 ° C., acid value 40) 200 g (pH 8.9), sodium oleate (surfactant) 9.0 g and ion-exchanged water 191 g are mixed to prepare a polymer particle dispersion. did. Then, using a high-speed cooling centrifuge 7750 (manufactured by Kubota Seisakusho) and a large-capacity angle rotor AG-2506 (centrifugal radius 14.2 cm), 200 mL of the polymer particle dispersion is placed in a 250 mL centrifuge polybin, and the rotational speed is 13000 rpm. Centrifugation was performed at (centrifugal acceleration = 26830 × g) for 1 hour. After centrifugation, the supernatant of the polymer particle dispersion was filtered with a 32 μm nylon mesh (NBA No-380T manufactured by NBA), and the filtrate was collected to prepare a non-self-dispersing polymer particle dispersion D-1 that was centrifuged.

(Preparation of ink-jet ink composition)
Using the resin-coated pigment dispersion C obtained above, self-dispersing polymer particles B-02, and sodium silicate solution (water glass, solid content concentration 55%, manufactured by Wako Pure Chemical Industries, Ltd.) Each component was mixed so that it might become an ink composition. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to prepare cyan ink (ink jet ink composition) C-1.

~ Ink composition ~
-Cyan pigment (Pigment Blue 15: 3): 4%
The polymer dispersant P-1 (solid content): 1.6%
-Aqueous dispersion of polymer particles (B-02) (solid content): 5%
・ Sodium silicate (solid content): 0.01%
Sodium silicate solution (water glass, solid content 55%, manufactured by Wako Pure Chemical Industries, Ltd.)
・ Glycerin: 20%
(Wako Pure Chemical Industries, water-soluble organic solvent)
・ Diethylene glycol (DEG): 10%
(Wako Pure Chemical Industries, water-soluble organic solvent)
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1%
・ Ion-exchanged water: Amount that is 100% overall

  In the preparation of the cyan ink C-1, the self-dispersing polymer particles or non-self-dispersing polymer particles D-1 shown in Table 2 below were used in place of the self-dispersing polymer particles B-01, respectively, and silicates were used. The cyan ink C was changed in the same manner as above except that the types and contents of the water-soluble organic solvents were changed as shown in Table 2 and the types and contents of the water-soluble organic solvent were changed as shown in Table 2 below. -2 to C-16 were respectively prepared.

<Preparation of treatment liquid>
Each component was mixed so that it might become the following composition, and the process liquid was prepared. The physical properties of the treatment liquid were a viscosity of 2.6 mPa · s, a surface tension of 37.3 mN / m, and a pH of 1.6 (25 ° C.).
~ Composition of treatment liquid ~
Malonic acid: 15.0%
(Divalent carboxylic acid, manufactured by Wako Pure Chemical Industries, Ltd.)
・ Diethylene glycol monomethyl ether: 20.0%
(Wako Pure Chemical Industries, Ltd.)
-N-oleoyl-N-methyl taurine sodium: 1.0%
(Surfactant)
・ Ion exchange water: 64.0%

<Image formation and evaluation>
An ink jet head provided with a silicon nozzle plate as shown in FIG. 1 was prepared, and the ink composition obtained above was refilled in a storage tank connected thereto. The silicon nozzle plate is previously provided with a liquid repellent film using a fluorinated alkylsilane compound. Tokishi Art Double Sided N (Mitsubishi Paper Co., Ltd.) as a recording medium is fixed on a stage that can move in a predetermined linear direction at 500 mm / second, and the stage temperature is kept at 30 ° C. The treated liquid was applied with a bar coater to a thickness of about 1.2 μm, and dried immediately at 50 ° C. for 2 seconds immediately after the application.
Thereafter, the inkjet head is fixedly arranged so that the direction of the line head in which the nozzles are arranged (main scanning direction) is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction of the stage (sub-scanning direction), and recording is performed. While moving the medium at a constant speed in the sub-scanning direction, the ink was ejected by a line method under an ink droplet amount of 2.4 pL, an ejection frequency of 24 kHz, and a resolution of 1200 dpi × 1200 dpi, and a 50% solid image of 2 cm square was printed.
Immediately after printing, the sample was dried at 60 ° C. for 3 seconds, passed between a pair of fixing rollers heated to 60 ° C., and subjected to a fixing process at a nip pressure of 0.25 MPa and a nip width of 4 mm to obtain an evaluation sample.

(Rubbing resistance evaluation)
For the evaluation sample obtained above, immediately after printing, unprinted Tokuhishi art double-sided N (manufactured by Mitsubishi Paper Industries Co., Ltd.) is superimposed on the printing screen and rubbed 10 times with a load of 150 kg / m ^2. The scratches on the image and the degree of ink transfer to the white background of an unprinted recording medium (unused sample) were visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2.
Incidentally, the evaluation C is a level having a problem in practical use.
~Evaluation criteria~
AA: No scratch was observed in the printed image, and no ink was transferred.
A: Slight scratches were observed in the printed image, but the ink transfer was hardly noticeable.
B: Some scratches were observed in the printed image and / or ink transfer was observed.
C: Print image scratches were significant and / or ink transfer was significant.

(Ink dispersion stability)
The temperature of each ink composition prepared above was adjusted to 25 ° C. Using an oscillating viscometer (BROOKFIELD, DV-II + VISCOMETER), the ink composition was measured at 25 ° C. using a cone plate (φ35 mm) at 25 ° C. in an environment of 25 ° C. and a relative humidity of 50%. The average value of data in the range of 20 to 90% torque and 0.5 to 100 rpm was used as the measurement value. The measured value immediately after the preparation was taken as ink viscosity 1.
Next, a part of the ink composition for ink jet was collected in a glass sample bottle, left in a sealed state at 60 ° C. for 2 weeks, and then the ink viscosity 2 after storage was measured in the same manner as described above. . At the same time, the state of the ink composition was visually observed.
The variation rate {100− (ink viscosity 2 / ink viscosity 1) × 100} of the measured ink viscosity before and after the storage was calculated. In addition to the results of visual observation after storage, the ink dispersion stability was evaluated according to the following evaluation criteria. The results are shown in Table 2.

~Evaluation criteria~
AA: The variation rate of the ink viscosity was less than ± 15%, and no change in the ink composition was observed.
A: The variation rate of the ink viscosity was ± 15% or more and less than ± 30%, and no change in the ink composition was observed.
B: The variation rate of the ink viscosity was ± 30% or more and less than ± 50%, and no change in the ink composition was observed.
C: The variation rate of the ink viscosity was ± 50% or more, or separation or gelation of the ink composition was observed.

(Ejection evaluation)
−Evaluation of ejection recovery and image unevenness−
An inkjet head provided with a silicon nozzle plate as shown in FIG. 1 was fixed so that the moving direction of the stage was perpendicular to the nozzle arrangement direction. A liquid repellent film is provided in advance on the surface of the silicon nozzle plate using a fluorinated alkylsilane compound. Next, the ink composition prepared above was refilled in a storage tank connected to this. As a recording medium, Fuji Photo Film Co., Ltd.'s painting photographic finishing Pro was pasted on a stage moving in a direction perpendicular to the nozzle arrangement direction of the head.
Next, the stage is moved at 248 mm / min, and 96 lines are printed in 2000 per nozzle in parallel with the transport direction at an ink droplet amount of 3.4 pL, an ejection frequency of 10 kHz, a nozzle arrangement direction × transport direction of 75 × 1200 dpi. A print sample A was prepared by discharging. The obtained print sample was visually observed to confirm that ink was ejected from all nozzles. In addition, image unevenness of the printed matter was evaluated by visually observing the obtained print sample A.
After ink ejection, the head was left as it was for a predetermined time, a new recording medium was attached, and ink was ejected again under the same conditions to produce a print sample. The obtained print sample was visually observed, and after discharging for a predetermined time, 2,000 discharges were made, and the discharge property was evaluated by the maximum leaving time in which all 96 nozzles could be discharged. The longer the standing time during which no discharge failure occurs, the better the discharge performance, and the discharge recovery performance (dummy jet recoverability) was evaluated according to the following evaluation criteria.
The evaluation D is at a level that causes a problem in practice.
~Evaluation criteria~
A: The leaving time is 45 minutes or more, and no image unevenness is confirmed.
B: The standing time is 30 or more and less than 45 minutes, and image unevenness is not confirmed.
C: The standing time is 20 minutes or more and less than 30 minutes, and image unevenness is not confirmed.
D: The standing time was less than 20 minutes or image unevenness was confirmed.

(Liquid repellency evaluation)
~ Liquid repellent film immersion test ~
A test piece for evaluation in which a liquid repellent film (SAM film) was formed on a 2 cm × 2 cm silicon plate using a fluorinated alkylsilane compound was prepared. Using the prepared test piece, the contact angle of water in the liquid repellent film was measured as follows, and the influence of the ink composition on the liquid repellency of the liquid repellent film was evaluated.
30 ml of the ink composition prepared above was weighed into a 50 ml wide-mouth bottle made of polypropylene (Eyeboy wide-mouth bottle 50 ml (manufactured by ASONE Co., Ltd.)). Next, the test piece was immersed in the ink composition and heated at 60 ° C. for 72 hours. The test piece was taken out and washed with ultrapure water, and the contact angle of water on the surface of the liquid repellent film was measured.
Ultrapure water is used for the measurement of the contact angle of water, and measured using a contact angle measuring apparatus (manufactured by Kyowa Interface Science Co., Ltd., DM-500) in an environment of 25 ° C. and 50 RH%, Evaluation was performed according to the following evaluation criteria.
Incidentally, the contact angle of water before immersion of the ink composition is 106.5 degrees, and the evaluation D is a level having a problem in practical use.
~Evaluation criteria~
AA: 80 degrees or more.
A: 60 degrees or more and less than 80 degrees.
B: 40 degrees or more and less than 60 degrees.
C: 20 degrees or more and less than 40 degrees.
D: Less than 20 degrees.

  From the above, it can be seen that the inkjet ink composition of the present invention is excellent in ink dispersion stability and ejection properties and can suppress a decrease in liquid repellency. It can also be seen that an image having excellent abrasion resistance can be formed by using the inkjet ink composition of the present invention.

11 Nozzle plate 12 Discharge port 100 Inkjet head

Claims (9)

A water-soluble alkali metal silicate salt, self-dispersing polymer particles having an I / O value of 0.40 or more and 0.55 or less, and a pigment ,
An ink-jet ink composition, wherein the copolymer component of the polymer constituting the self-dispersing polymer particles is methyl methacrylate, isobornyl methacrylate, and methacrylic acid . The inkjet ink composition according to claim 1, wherein the alkali metal silicate is represented by the following general formula (1).
x (M ₂ O) · y (SiO ₂ ) (1)
(In general formula (1), M represents sodium or potassium, x represents 1 or 2, and y represents an integer of 1 to 4)   The ink composition according to claim 1, wherein the self-dispersing polymer particles have a glass transition temperature of 120 ° C. or higher.   The ink composition according to any one of claims 1 to 3, wherein the pH at 25 ° C is from 7.5 to 10.0.   The ink composition according to any one of claims 1 to 4, wherein a content of the alkali metal silicate is 0.0001 to 0.5% by mass.   The mass ratio of the alkali metal silicate to the self-dispersing polymer particles (alkali metal silicate / self-dispersing polymer particles) is 0.0001 or more and 0.1 or less. 2. The ink composition according to item 1. An ink set comprising: the ink composition according to any one of claims 1 to 6 ; and a treatment liquid capable of forming an aggregate upon contact with the ink composition. An ink jet image forming method comprising an ink discharging step of forming an image by discharging the ink composition according to any one of claims 1 to 6 onto a recording medium from an ink jet head provided with a silicon nozzle plate. . According to claim 1 in contact with the ink composition aggregate capable of forming processing liquid according to any one of claims 6 to claim 8, further comprising a treatment liquid deposition step of depositing onto a recording medium Inkjet image forming method.