JP2011063725A - Ink composition, ink set, and inkjet image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition which can suppress occurrence of curling, ensures good discharge reliability of the ink, and can suppress reduction in water repellency of an ink head. <P>SOLUTION: The ink composition includes water, a colorant, a water-soluble organic solvent, a surfactant and a water-soluble silicate, the water-soluble silicate being comprised in an amount of 0.0001-0.5 mass% with respect to a total mass of the ink composition, and the water-soluble organic solvent including a water-soluble organic solvent having a value of solubility parameter (SP) of ≤27.5 in an amount of ≥40 mass% with respect to a total mass of the water-soluble organic solvent. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

Various recording media such as plain paper, coated paper, glossy paper, OHP sheet, and back print film are commercially available for recording by the ink jet recording method. However, they are inexpensive for business use in general offices. Often plain paper is used. As the required characteristics at this time, it is possible to reduce or suppress a curl (paper warp or curl) phenomenon that occurs when a large amount of ink is applied to the paper while satisfying the normally required characteristics. Here, not only curling during recording but also relaxation and suppression of post-recording curl caused by drying and evaporation of moisture after recording become important.
It is also important that the occurrence of image unevenness resulting from image deformation is suppressed in the formed image.

In relation to the above, an ink containing a diglycerin derivative is known as an ink that has no image omission or unevenness and good fixability (see, for example, Patent Document 1).
Further, as a method of reducing or suppressing the occurrence of curling, for example, a method of suppressing curling by using a water-based ink containing 30% or more of a low polarity solvent with respect to the total mass of the ink is known ( For example, see Patent Document 2).
In addition, as a method for suppressing the occurrence of nozzle clogging, preventing discoloration of the recording liquid, and preventing the occurrence of antifungal, a water-based inkjet ink containing a water-soluble dye, an alkali silicate, a water-soluble antifungal agent, and water. A recording liquid is disclosed (for example, see Patent Document 3).
Also disclosed is an aqueous ink composition in which pH and zeta potential are specified for an ink used in an ink jet printer formed of a film provided with silicon, glass or the like as having excellent ink ejection, dissolution and dispersion stability. (For example, Patent Document 4).

Japanese Patent Laid-Open No. 10-168373 JP 2007-152873 A JP 2003-165936 A Japanese Patent Laid-Open No. 9-279074

However, the ink described in Patent Document 1 cannot suppress curling. Further, the ink described in Patent Document 2 tends to deteriorate the storage stability and image deformability of the ink.
Further, the aqueous recording liquid described in Patent Document 3 cannot sufficiently suppress the occurrence of curling. In addition, the ink described in Patent Document 4 is not sufficient in terms of suppressing curling and improving light resistance.
The present invention can suppress the occurrence of curling, has good ink ejection reliability, and can suppress a decrease in water repellency of an ink head, an ink set including the ink composition, and an inkjet It is an object to provide an image forming method.

<1>
Containing water, a coloring material, a water-soluble organic solvent, a surfactant, and 0.0001% by mass or more and 0.5% by mass or less of a water-soluble silicate based on the total mass, the water-soluble An ink composition comprising 40% by mass or more of a water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less among organic solvents.
<2>
The ink composition according to <1>, wherein the water-soluble silicate is a compound represented by the following general formula (1).
x (A ₂ O) · y (SiO ₂ ) General formula (1)
(In general formula (1), A represents sodium, potassium, tetraalkylammonium (NR ₄ ), x represents 1 or 2, y represents an integer of 1 to 4, and R represents an alkyl group having 1 to 4 carbon atoms. Represents.)
<3>
The ink composition according to <2>, wherein the water-soluble silicate is at least one selected from sodium silicate, potassium silicate, and tetramethylammonium silicate.
<4>
The ink composition according to any one of <1> to <3>, wherein the water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less has the following structural formula.

(In the structural formula, l, m, and n are each independently an integer of 1 or more and l + m + n = 3 to 15. AO represents an oxyethylene group (EO) or an oxypropylene group (PO)). Represents at least one.)
<5>
The ink composition according to any one of <1> to <4>, wherein the content of the water-soluble organic solvent is 30% by mass or less based on the total mass.
<6>
The water solubility organic solvent whose said solubility parameter (SP value) is 27.5 or less contains 50 mass% or more with respect to the said water soluble organic solvent total mass, Any one of said <1>-<5>. Ink composition.
<7>
The ink composition according to any one of <1> to <6>, wherein the color material is a resin-coated pigment.
<8>
An ink set comprising the ink composition according to any one of the above <1> to <7>, and a treatment liquid capable of forming an aggregate upon contact with the ink composition.
<9>
Inkjet image formation including an ink ejection step of ejecting the ink composition according to any one of <1> to <7> above onto a recording medium from an inkjet head including a silicon nozzle plate. Method.
<10>
<9> further including 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 <7> above on a recording medium. 2. An ink jet image forming method according to 1.
<11>
The ink jet image forming method according to <9> or <10>, wherein the recording medium is plain paper or coated paper.

  According to the present invention, an ink composition that can suppress the occurrence of curling, has good ink ejection reliability, and can suppress a decrease in liquid repellency of an ink jet head, and an ink including the ink composition A set as well as an inkjet image forming method can be provided.

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.

<Ink composition>
The ink composition of the present invention comprises water, a coloring material, a water-soluble organic solvent, a surfactant, and a water-soluble silicate of 0.0001% by mass to 0.5% by mass based on the total mass. Among the water-soluble organic solvents, a water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less is 40% by mass or more.
By including a specific solvent in a specific ratio as described above and a specific ratio of the water-soluble silicate, curling can be suppressed and the liquid repellency of the inkjet head can be suppressed. Deterioration (decrease in ink contact angle) can be suppressed. In particular, curling can be suppressed even when images are formed on plain paper other than ink jet dedicated paper, general-purpose coated paper, or the like by the ink jet method. Further, the ink ejection reliability is improved, and the occurrence of image deformation during image formation can be suppressed.

The ink composition of the present invention can comprise a surfactant, resin particles, and other components as necessary in addition to the above essential components.
The ink composition of the present invention can be used for full-color image formation. In order to form a full color image, a magenta color ink, a cyan color ink, and a yellow color ink can be used, and a black color ink may be further used to adjust the color tone. Further, red, green, blue and white inks other than yellow, magenta and cyan color inks, and so-called special color inks in the printing field can be used.

[Water-soluble silicate]
The ink composition of the present invention contains at least one water-soluble silicate. In the present invention, examples of the water-soluble silicate include alkali metal salts of silicic acid and ammonium salts of silicic acid.
Here, water-soluble means to dissolve 1% by mass or more in 20 ° C. water.
The alkali metal salt of silicic acid is composed of silicon dioxide and a metal oxide and is not particularly limited as long as it is a water-soluble compound, and examples thereof include an alkali metal salt of metasilicic acid and an alkali metal salt of orthosilicic acid.
Examples of the ammonium salt of silicic acid include ammonium salt of metasilicic acid and ammonium salt of orthosilicic acid.
In the present invention, the water-soluble silicate may be used alone or as a mixture thereof.
In the present invention, by using at least one of an alkali metal salt of silicic acid and an ammonium salt of silicic acid, a decrease in liquid repellency (decrease in contact angle) of the inkjet head can be suppressed.

Specifically, the water-soluble alkali metal silicate or the ammonium salt of silicic acid is preferably at least one compound represented by the following general formula (1).
x (A ₂ O) · y (SiO ₂ ) General formula (1)
In general formula (1), A represents sodium, potassium, and tetraalkylammonium (NR ₄ ), x represents 1 or 2, and y represents an integer of 1 to 4. R represents an alkyl group having 1 to 4 carbon atoms (methyl, ethyl, propyl, or butyl).
In the case of the alkyl metal salt of silicic acid represented by the general formula (1) (A = alkali metal), when x = 1 and y = 1, the alkali metal salt of metasilicate and when x = 2 and y = 1 These are each called an alkali metal orthosilicate and each is a water-soluble alkali metal silicate.
In the ammonium salt of silicic acid represented by the general formula (1), (A = tetraalkylammonium) is a tetraalkylammonium salt of metasilicic acid when x = 1 and y = 1, and x = 2. , Y = 1 is a tetraalkylammonium salt of orthosilicic acid, both of which are water-soluble ammonium silicate salts.

In the present invention, a commercially available compound (for example, water glass) may be used as the water-soluble alkali metal silicate, and silicic acid and an alkali metal carbonate or hydroxide are melted. You may use what is obtained. In addition, the water-soluble ammonium silicate salt may be a commercially available compound or may be obtained by preparation.
Among the above-mentioned compounds, at least one selected from sodium silicate, potassium silicate, and tetramethylammonium silicate is preferable from the viewpoint of suppressing a decrease in liquid repellency of the inkjet head.

The content of the water-soluble silicate contained in the ink composition of the present invention is 0.0001% by mass or more and 0.001% by mass or more based on the total mass of the ink composition from the viewpoint of suppressing the decrease in liquid repellency. When the content is less than 0.0001% by mass, the decrease in liquid repellency (decrease in the contact angle of the ink composition with respect to the liquid repellent film) cannot be suppressed. Moreover, when it exceeds 0.5 mass%, discharge reliability will deteriorate.
Among these, 0.001 to 0.4 mass% is more preferable, and 0.01 to 0.3 mass% is even more preferable.

[Water-soluble organic solvent]
The ink composition of the present invention contains at least one water-soluble organic solvent, and among the water-soluble organic solvents, the content of at least one water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less. It is 40 mass% or more with respect to the total mass of all the water-soluble organic solvents.
In addition to the water-soluble organic solvent having an SP value of 27.5 or less, a water-soluble organic solvent having an SP value exceeding 27.5 can be added to the ink composition of the present invention as necessary.
In the present invention, the water-soluble organic solvent means an organic solvent that dissolves 5 g or more in 100 g of water.

The SP value in the present invention means a solubility parameter (SP value) of an organic solvent, and is a value represented by the square root of the molecular cohesive energy. The SP value is described in Polymer Handbook (Second Edition), Chapter IV, Solubility Parameter Values, and this value is used as the SP value in the present invention. Moreover, a unit is (MPa) ^1/2 and points out the value in 25 degreeC.
In addition, R.D. F. The value calculated by the method described in Fedors, Polymer Engineering Science, 14, p147-154 (1974) is used as the SP value in the present invention.

In the present invention, the content of the water-soluble organic solvent having an SP value of 27.5 or less is 40% by mass or more with respect to the total water-soluble organic solvent. On the other hand, it is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and particularly preferably 80% by mass or more.
When the said content rate is less than 40 mass%, the curl suppression effect will fall.

The water-soluble organic solvent having an SP value of 27.5 or less in the present invention (hereinafter sometimes referred to as “first water-soluble organic solvent”) is not particularly limited as long as the SP value is 27.5 or less. From the viewpoint of curling suppression, the SP value is preferably 16 to 27.5, and more preferably 18 to 26.5.
Here, a water-soluble organic solvent having an SP value greater than 27.5 may be referred to as a “second water-soluble organic solvent”.

Although the specific example of the water-soluble organic solvent whose SP value is 27.5 or less is shown below with SP value, this invention is not limited to these.
Diethylene glycol monoethyl ether (DEGmEE) (SP value 22.4)
・ Diethylene glycol monobutyl ether (DEGmBE) (SP value 21.5)
Triethylene glycol monobutyl ether (TEGmBE) (SP value 21.1)
Propylene glycol monoethyl ether (PGmEE) (SP value 22.3)
Dipropylene glycol (DPG) (SP value 27.1)
Dipropylene glycol monomethyl ether (DPGmME) (SP value 21.3)
Triethylene glycol monoethyl ether (TEGmEE) (SP value 21.7)
Tripropylene glycol monomethyl ether (TPGmME) (SP value 20.4)
Triethylene glycol monomethyl ether (TEGmME) (SP value 22.1)
Tripropylene glycol (TPG) (SP value 24.7, for example, PP-200 (manufactured by Sanyo Chemical Industries))
-Heptapropylene glycol (SP value 21.2, for example, PP-400 (manufactured by Sanyo Chemical Industries)),
1,2-hexanediol (SP value 24.1)
POP (3) glyceryl ether (SP value 26.4, for example, GP-250 (manufactured by Sanyo Chemical Industries))
POP (4) glyceryl ether (SP value 24.9)
POP (5) glyceryl ether (SP value 23.9)
POP (6) glyceryl ether (SP value 23.2, for example GP-400 (manufactured by Sanyo Chemical Industries))
POP (7) glyceryl ether (SP value 22.6)
POP (8) glyceryl ether (SP value 22.1)
POP (9) glyceryl ether (SP value 21.7, for example, GP-600 (manufactured by Sanyo Chemical Industries))
POP (10) glyceryl ether (SP value 21.4)
POP (16) glyceryl ether (SP value 20.2, for example GP-1000 (manufactured by Sanyo Chemical Industries, Ltd.))
POP (4) diglyceryl ether (SP value 26.1, for example, SC-P400 (manufactured by Sakamoto Pharmaceutical Co., Ltd.)),
POP (9) diglyceryl ether (SP value 22.7, for example, SC-P750 (manufactured by Sakamoto Pharmaceutical Co., Ltd.)),
POE (20) diglyceryl ether (SP value 22.4, for example, SC-E1000 (manufactured by Sakamoto Pharmaceutical Co., Ltd.)),
POE (40) diglyceryl ether (SP value 21.0, for example, SC-E2000 (manufactured by Sakamoto Pharmaceutical Co., Ltd.)).
Dioxyethylene dioxypropylene butyl ether (SP value 20.1, for example, 50HB-55 (manufactured by Sanyo Chemical Industries, Ltd.))
Pentaoxyethylene pentaoxypropylene butyl ether (SP value 18.8, for example, 50HB-100 (manufactured by Sanyo Chemical Industries)),
Decaoxyethylene heptaoxypropylene butyl ether (SP value 18.8, for example, 50HB-260 (manufactured by Sanyo Chemical Industries)),
Dodecaoxyethylene dodecaoxypropylene butyl ether (SP value 18.8, for example, 50HB-400 (manufactured by Sanyo Chemical Industries, Ltd.)),
Decaoxyethylene triacontoxypropylene butyl ether (SP value 18.7, for example, PE-62 (manufactured by Sanyo Chemical Industries)),
Pentacosaoxyethylene tricontoxypropylene butyl ether (SP value 18.8, for example, PE-64 (manufactured by Sanyo Chemical Industries, Ltd.)).

  POP (3) glyceryl ether means an ether derivative of glycerin in which three propylene oxides are added to glycerin, and the same applies to others.

  The water-soluble organic solvent having an SP value of 27.5 or less in the present invention is also preferably a compound represented by the following structural formula.

In the structural formula, l, m, and n each independently represent an integer of 1 or more and represent 1 + m + n = 3-15. When l + m + n is 3 or more, a sufficient curl suppressing effect can be obtained. Further, when it is 15 or less, the discharge property is improved. Among them, l + m + n is preferably 3 to 12, and more preferably 3 to 10.
In the above structural formula, AO represents at least one of an oxyethylene group (EO) and an oxypropylene group (PO), and among these, an oxypropylene group is preferable. In addition, each AO of (AO) l, (AO) m, and (AO) n may be the same or different.

In the present invention, the water-soluble organic solvent having an SP value of 27.5 or less may be used alone or in combination of two or more.
When the ink composition of the present invention contains two or more water-soluble organic solvents having an SP value of 27.5 or less, the type of each water-soluble organic solvent is not particularly limited. For example, a water-soluble organic solvent represented by the above structural formula and another organic solvent (preferably, polyalkylene glycol, polyalkylene glycol alkyl ether, or the like) can be used in combination.

  As the first water-soluble organic solvent in the present invention, from the viewpoint of curling suppression, propylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, And at least one selected from tripropylene glycol monomethyl ether (hereinafter sometimes referred to as “water-soluble organic solvent A”), polyoxypropylene glyceryl ether having a propyleneoxy group content of 3 to 9, and ethylene At least one selected from polyoxyethylene polyoxypropylene butyl ether having a sum of oxy group content and propyleneoxy group content of 3 to 20 (hereinafter referred to as “ And a propyleneoxy group containing at least one selected from diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol, and tripropylene glycol monomethyl ether; At least one selected from polyoxypropylene glyceryl ether having a number of 3 to 6 and polyoxyethylene polyoxypropylene butyl ether having a sum of ethyleneoxy group content and propyleneoxy group content of 3 to 12; It is more preferable to contain.

  Further, the content ratio of the water-soluble organic solvent A and the water-soluble organic solvent B is not particularly limited, but from the viewpoint of curling suppression, the content ratio of the water-soluble organic solvent A: water-soluble organic solvent B is based on mass. It is preferably 1: 3 to 3: 1, more preferably 1: 2 to 2: 1, and even more preferably 2: 3 to 3: 2.

  In the ink composition of the present invention, in addition to the water-soluble organic solvent having an SP value of 27.5 or less, the water-soluble organic solvent having an SP value of more than 27.5 is less than 60% by mass with respect to the total water-soluble organic solvent. It may contain with the content rate of. By including a water-soluble organic solvent (second water-soluble organic solvent) having an SP value exceeding 27.5, it is possible to more effectively obtain a drying prevention effect, a wetting effect or a penetration promoting effect.

Here, the drying prevention effect and the wetting effect mean an effect that can prevent clogging due to drying of the inkjet ink at the ink ejection port of the nozzle. As the drying inhibitor and wetting agent, a water-soluble organic solvent having a vapor pressure lower than that of water is preferable.
Further, the penetration promoting effect means an effect of allowing the ink to penetrate into paper better, and a water-soluble organic solvent is preferably used.

  Examples of the second water-soluble organic solvent in the present invention include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-pentanediol, 4-methyl- Alkanediols (polyhydric alcohols) such as 1,2-pentanediol; alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl Glycols such as ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol Ethers; 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like, These 1 type (s) or 2 or more types can be used.

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

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

The second water-soluble organic solvent used in the present invention may be used alone or in combination of two or more.
The content of the total water-soluble organic solvent in the ink composition of the present invention is 30% by mass or less with respect to the total mass of the ink composition from the viewpoints of ink storage stability and ejection properties, but 5-30. It is more preferable that it is mass%, and it is still more preferable that it is 5-25 mass%.

[Pigment]
The ink composition of the present invention contains at least one color material. A water-dispersible pigment is preferable as the color material used in the present invention, but any pigment having a function of forming an image by coloring can be used, and dyes and colored fine particles can also be used.

Specific examples of the water-dispersible pigment include the following pigments (1) to (4).
(1) A resin-coated pigment (hereinafter also referred to as “encapsulated pigment”), that is, a polymer emulsion in which a pigment is contained in polymer fine particles. More specifically, the pigment is coated with a hydrophilic water-insoluble resin. The pigment is dispersed in water by making it hydrophilic in the resin layer on the pigment surface.
(2) Self-dispersing pigments, that is, pigments having at least one hydrophilic group on the surface and exhibiting at least one of water dispersibility and water solubility in the absence of a dispersant, more specifically, mainly carbon black Etc. are hydrophilized by surface oxidation treatment 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.
Among them, preferable examples include (1) encapsulated pigment and (2) self-dispersing pigment, and particularly preferable examples include (1) encapsulated pigment.

(Resin-coated pigment)
The encapsulated pigment will be described in detail. The encapsulated pigment resin is not limited, but is a polymer compound having self-dispersibility or solubility in a mixed solvent of water and water-soluble organic and having an anionic group (acidic group). Preferably there is. This resin usually has a number average molecular weight of preferably about 1,000 to 100,000, and particularly preferably about 3,000 to 50,000. Further, it is preferable that this resin is dissolved in an organic solvent to form a solution. When the number average molecular weight of the resin is within this range, the function as a coating film in the pigment or as a coating film in the ink composition can be sufficiently exhibited. The resin is preferably used in the form of an alkali metal or organic amine salt.

Specific examples of encapsulated pigment resins include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, and fluorine-based resins. Molecular compounds, polyvinyl compounds such as polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol and polyvinyl butyral, polyesters such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd cocondensation resins, urea resins, urea resins And other materials having an anionic group such as an amino material or a copolymer or a mixture thereof.
Among the above resins, anionic acrylic resins include, for example, acrylic monomers having an anionic group (hereinafter referred to as anionic group-containing acrylic monomers), and other monomers that can be copolymerized with these monomers as necessary. Is obtained by polymerization in a solvent. Examples of the anionic group-containing acrylic monomer include acrylic monomers having one or more anionic groups selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic acid group. Among these, an acrylic monomer having a carboxyl group is included. Monomers are particularly preferred.

Specific examples of the acrylic monomer having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like. Among these, acrylic acid or methacrylic acid is preferable.
The encapsulated pigment can be produced by conventional physical and chemical methods using the above-described components. According to a preferred embodiment of the present invention, JP-A-9-151342, JP-A-10-140065, JP-A-11-209672, JP-A-11-172180, JP-A-10-25440, or JP-A-11-43636 And preferably by a phase inversion emulsification method.

In the present invention, self-dispersing pigments can also be mentioned as preferred examples. 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.
An ink containing a self-dispersing pigment as a pigment does not need to contain a dispersing agent as described above to be contained in order to disperse a normal pigment, so there is almost no foaming due to a decrease in defoaming property caused by the dispersing agent. Inks with excellent ejection stability are easy to prepare.
Examples of dispersibility-imparting groups to be bonded to the surface of the self-dispersion _{pigment, -COOH, -CO -, - OH} , -SO 3 H, -PO 3 H 2 and quaternary ammonium and can be exemplified salts thereof, These are produced by subjecting a pigment as a raw material to physical treatment or chemical treatment to bond (graft) an active species having a dispersibility-imparting group or a dispersibility-imparting group to the surface of the pigment. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, and a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. It can be illustrated.
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).

(Pigment)
There is no restriction | limiting in particular as a pigment used in this invention, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient.
Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of the dye chelates include basic dye chelates and acidic dye chelates.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as said carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, and a thermal method, is mentioned, for example.

  Specific examples of carbon black include Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1200, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170 Chemical)), Regal 400R, Regal 330R, Regal 660R, Mogu L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarc 1300, Monarch 1400 (manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW200, Color Black S150, Color Black S150, Color Black S150, Color Black S150, Color Black SFW, 170 , Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No. 25, no. 33, no. 40, no. 45, no. 47, no. 52, no. 900, no. 2200B, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned, but the invention is not limited thereto.

  Examples of the organic pigment that can be used in the present invention include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 14C, 16, 17, 24, 34, 35, 37, 42, 53, 55, 65, 73, 74, 75, 81, 83, 93, 95, 97, 98, 100, 101, 104, 108, 109, 110, 114, 117, 120, 128, 129, 138, 150, 151, 153, 154, 155, 180 etc. are mentioned.

  Examples of magenta ink pigments include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 48 (Ca), 48 (Mn), 48: 2, 48: 3, 48: 4, 49, 49: 1, 50, 51, 52, 52: 2, 53: 1, 53, 55, 57 (Ca), 57: 1, 60, 60: 1, 63: 1, 63: 2, 64, 64: 1, 81, 83, 87, 88, 89, 90, 101 (Bengara) ), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 163, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 209, 2 9,269, etc., and C. I. Pigment violet 19, especially C.I. I. Pigment Red 122 is preferable.

Further, as pigments for cyan ink, C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 16, 17: 1, 22, 25, 56, 60, C.I. I. Bat blue 4, 60, 63 and the like. I. Pigment Blue 15: 3 is preferable.
The above pigments may be used alone or in combination of a plurality selected from the above-mentioned groups or between the groups.

(Dispersant)
In the present invention, a nonionic compound, an anionic compound, a cationic compound, an amphoteric compound, and the like can be used as the dispersant used in the encapsulated pigment or the resin dispersion pigment.
Examples thereof include a copolymer of monomers having an α, β-ethylenically unsaturated group. Examples of monomers having an α, β-ethylenically unsaturated group include ethylene, propylene, butene, pentene, hexene, vinyl acetate, allyl acetate, acrylic acid, methacrylic acid, crotonic acid, crotonic acid ester, itaconic acid, itacone Acid monoester, maleic acid, maleic acid monoester, maleic acid diester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bismethacryloxy Styrene derivatives such as ethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, styrene, α-methylstyrene, vinyltoluene , Vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylates that may be substituted with aromatic groups, phenyl esters of acrylate, alkyl methacrylates that may be substituted with aromatic groups, phenyl esters of methacrylic acid, methacryl Acid cycloalkyl ester, crotonic acid alkyl ester, itaconic acid dialkyl ester, maleic acid dialkyl ester, vinyl alcohol, and derivatives of the above compounds.

A copolymer obtained by copolymerizing a single monomer or a plurality of monomers having the α, β-ethylenically unsaturated group is used as a polymer dispersant. Specifically, acrylic acid alkyl ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid copolymer, styrene-alkyl acrylic acid ester-acrylic acid copolymer, styrene-methacrylic acid phenyl ester-methacrylic acid, Styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, styrene-styrenesulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinylnaphthalene-maleic Examples include acid copolymers, vinyl naphthalene-methacrylic acid copolymers, vinyl naphthalene-acrylic acid copolymers, polystyrene, polyester, and polyvinyl alcohol.
The dispersant in the present invention is preferably 2,000-60,000 in terms of weight average molecular weight. In the dispersant of the present invention, the ratio of the amount added to the pigment is preferably in the range of 10% to 100%, more preferably 20% to 70%, and still more preferably 40% to 50%, based on mass. .

  The content of the color material in the ink composition of the present invention is preferably 0.1 to 15% by mass and more preferably 1 to 10% by mass from the viewpoints of image density and image storage stability.

[Surfactant]
The ink composition of the present invention contains at least one surfactant. The surface tension of the ink composition can be adjusted by adding a surfactant. As the surfactant, any of nonionic, cationic, anionic, and betaine surfactants may be used. The addition amount of the surfactant is preferably an amount for adjusting the surface tension (25 ° C.) of the ink of the present invention to 20 to 60 mN / m, and more preferably 20 to 45 mN / m, in order to deposit ink well by inkjet. More preferably, the amount can be adjusted to 25 to 40 mN / m.
As the surfactant in the present invention, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactants, cationic surfactants, amphoteric surfactants can be used. Any of the nonionic surfactants can be used. Furthermore, the above-mentioned polymer substance (polymer dispersant) can also be used as a surfactant.

Specific examples of anionic surfactants include, for example, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, sodium dioctyl Sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, sodium stearate, sodium oleate, t-octylphenoxyethoxypolyethoxyethyl Examples include sodium sulfate, etc., and select one or more of these Rukoto can.
Specific examples of the nonionic surfactant include, for example, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, oxyethylene / oxypropylene block copolymer, t- Examples include octylphenoxyethyl polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, and the like, and one or more of these can be selected.
Examples of the cationic surfactant include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like. Specific examples thereof include dihydroxyethyl stearylamine and 2-heptadecenyl. -Hydroxyethyl imidazoline, lauryl dimethyl benzyl ammonium chloride, cetyl pyridinium chloride, stearamide methyl pyridium chloride and the like.
The amount of the surfactant added to the ink composition in the invention is not particularly limited, but is preferably 1% by mass or more, more preferably 1 to 10% by mass, and still more preferably 1 to 3%. % By mass.

[Resin particles]
The ink composition in the present invention may contain at least one resin particle. By including the resin particles, the fixability of the ink composition to the recording medium and the scratch resistance of the recorded image can be further improved. Resin particles are aggregated or destabilized when brought into contact with a liquid composition that improves printability, which will be described later (hereinafter sometimes referred to as “treatment liquid”), thereby increasing the viscosity of the ink composition. It is preferable to have a function of fixing the composition, that is, the image.

Examples of the resin particles include (meth) acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, styrene resins, crosslinked acrylic resins, and crosslinked styrene. Particles such as resin, benzoguanamine resin, phenol resin, silicone resin, epoxy resin, urethane resin, paraffin resin and fluorine resin can be used. It is preferable to use particles of (meth) acrylic resin, acrylic-styrene resin, styrene resin, cross-linked acrylic resin, and cross-linked styrene resin, and (meth) acrylic resin particles are particularly preferable.
The (meth) acrylic resin can be copolymerized with, for example, a (meth) acrylic monomer having an anionic group (anionic group-containing (meth) acrylic monomer) and, if necessary, the anionic group-containing (meth) acrylic monomer. It is obtained by polymerizing other monomers in a solvent. Examples of the anionic group-containing (meth) acrylic monomer include a (meth) acrylic monomer having one or more selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic acid group, and particularly has a carboxyl group. (Meth) acrylic monomers (for example, acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, etc.) are preferable, and acrylic acid or methacrylic acid is particularly preferable.

  Specifically, latex (aqueous dispersion of resin particles) can be suitably used as the resin particles, such as (meth) acrylic latex, vinyl acetate latex, styrene latex, polyester latex, and the like. The latex can be suitably used. In particular, (meth) acrylic latex is preferred.

  The resin particles are preferably self-dispersing polymer particles, more preferably self-dispersing polymer particles having a carboxyl group, from the viewpoint of ejection stability and liquid stability (particularly dispersion stability) when a pigment is used. . Self-dispersing polymer particles (hereinafter, also referred to as “self-dispersing polymer particles”) are water-based in the absence of other surfactants due to functional groups (particularly acidic groups or salts thereof) possessed by the polymer itself. It means water-insoluble polymer particles which can be dispersed in a medium and do not contain a free emulsifier.

Here, the dispersed state means both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in a liquid state in an aqueous medium, and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in a solid state in an aqueous medium. It includes the state of.
The water-insoluble polymer is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state from the viewpoint of aggregation speed and fixing property when the ink composition is used.

  The dispersion state of the self-dispersing polymer particles refers to 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), a neutralizing agent that can neutralize the salt-forming group of the water-insoluble polymer 100% If the group is anionic, sodium hydroxide, acetic acid if it is cationic) and 200 g of water are mixed and stirred (apparatus: stirring apparatus with stirring blades, rotation speed 200 rpm, 30 minutes, 25 ° C.), and then mixed. It means a state in which even after removing the organic solvent from the liquid, it can be visually confirmed that the dispersed state exists stably at 25 ° C. for at least one week.

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

  The aqueous medium includes water, and may include a hydrophilic organic solvent as necessary. In the present invention, it is preferably composed of water and 0.2% by mass or less of a hydrophilic organic solvent, more preferably composed of water.

  The main chain skeleton of the water-insoluble polymer is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. it can. Among them, a vinyl polymer is particularly preferable from the viewpoint of dispersion stability of the polymer particles.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation system polymer and a condensation system polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  The self-dispersing polymer particles preferably include a water-insoluble polymer having a hydrophilic constituent unit and a hydrophobic constituent unit from the viewpoint of self-dispersibility, and the hydrophobic constituent unit is an aromatic group-containing monomer. More preferably, it is a structural unit derived from.

The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

The hydrophilic group-containing monomer is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility and aggregability, 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, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability.

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 a water-soluble component than an ethylenically unsaturated monomer having a terminal hydroxyl group. It is preferable from the viewpoint.

As the hydrophilic structural unit in the present invention, an embodiment containing only a hydrophilic unit having an anionic dissociable group, a hydrophilic structural unit having an anionic dissociative group, and a nonionic hydrophilic group It is preferable that it is either of the aspects containing both the hydrophilic structural unit which has.
Also, an embodiment containing two or more hydrophilic units having an anionic dissociable group, a hydrophilic structural unit having an anionic dissociative group, and a hydrophilic structural unit having a nonionic hydrophilic group It is also preferable that two or more are used in combination.

The content of the hydrophilic constituent 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 viewpoint 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 structural unit having an anionic dissociable 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.

The self-dispersing polymer particles preferably contain a polymer having a carboxyl group from the viewpoint of self-dispersibility and the aggregation rate when contacting with the treatment liquid, and have a carboxyl group and an acid value (mgKOH / g) of 25. More preferably, it contains a polymer of ~ 100. Furthermore, the acid value is more preferably from 25 to 80, and particularly preferably from 30 to 65, from the viewpoints of self-dispersibility and the aggregation rate when contacted with the treatment liquid.
In particular, when the acid value is 25 or more, the stability of self-dispersibility is good, and when it is 100 or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
The polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixing property, and phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth) are preferred. At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

The self-dispersing polymer particles include a structural unit derived from an aromatic group-containing (meth) acrylate monomer, and the content is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate monomer is 10% by mass to 95% by mass, the stability of the self-emulsification or dispersion state can be improved, and further the increase in ink viscosity can be suppressed.
In the present invention, from the viewpoints of stability in a self-dispersing state, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings, and reduction in the amount of water-soluble components due to appropriate hydrophobicization of particles. More preferably, the content is from mass% to 90 mass%, more preferably from 15 mass% to 80 mass%, and particularly preferably from 25 mass% to 70 mass%.

Further, when using a styrene monomer as the aromatic group-containing monomer, from the viewpoint of stability when making the self-dispersing polymer particles, the structural unit derived from the styrene monomer is preferably 20% by mass or less, The content is more preferably 10% by mass or less, still more preferably 5% by mass or less, and an embodiment that does not include a structural unit derived from a styrene monomer is particularly preferable.
Here, the styrene monomer refers to styrene, substituted styrene (α-methylstyrene, chlorostyrene, etc.), and a styrene macromer having a polystyrene structural unit.

  In addition to the structural unit derived from the aromatic group-containing monomer as a hydrophobic structural unit, the self-dispersing polymer may further include other structural units as necessary. The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the hydrophilic group-containing monomer and the aromatic group-containing monomer, and a known monomer can be used.

  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; Dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide and the like Droxyalkyl (meth) acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, Examples include (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides such as N-ethoxyethyl (meth) acrylamide and N- (n-, iso) 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, other copolymerizable monomers may be used singly or in combination of two or more.
When the self-dispersing polymer particles contain other constituent 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 water-insoluble polymer constituting the self-dispersing polymer particles is a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably a structure derived from phenoxyethyl (meth) acrylate) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. Unit) and / or a structural unit derived from benzyl (meth) acrylate), the copolymerization ratio preferably includes 15 to 80% by mass of the total mass of the self-dispersing polymer particles.
In addition, the water-insoluble polymer has a constitution derived from a carboxyl group-containing monomer having a copolymerization ratio of 15 to 80% by mass of a constitutional unit derived from an aromatic group-containing (meth) acrylate monomer from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. And a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and a structural unit derived from phenoxyethyl (meth) acrylate and / or Alternatively, a structural unit derived from benzyl (meth) acrylate as a copolymerization ratio of 15 to 80% by mass, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably (meth) A structural unit derived from an alkyl ester having 1 to 4 carbon atoms of acrylic acid) More preferably, the acid value is 25 to 100 and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 to 95, and the weight average molecular weight is 5000 to 150,000. It is more preferable that

  The self-dispersing polymer may be a random copolymer in which each constituent unit is irregularly introduced, or a block copolymer that is regularly introduced. Each constitutional unit may be synthesized in any order of introduction, and the same constitutional component may be used twice or more, but is preferably a random copolymer in terms of versatility and manufacturability. .

  The molecular weight range of the water-insoluble polymer constituting the self-dispersing polymer particles is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. Further preferred. 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 is measured by gel permeation chromatography (GPC). For GPC, HLC-8020GPC (manufactured by Tosoh Corporation) is used, and TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (4.6 mm ID × 15 cm) manufactured by Tosoh Corporation are used as eluents as columns. Use THF (tetrahydrofuran). As conditions, the sample concentration is 0.3% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and an IR detector is 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 is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

  Further, the glass transition point (Tg) of the self-dispersing polymer is preferably 50 ° C. or higher, more preferably 80 ° C. or higher, still more preferably 130 ° C. or higher, and particularly preferably 160 ° C. or higher. . When the glass transition point is 50 ° C. or higher, the scratch resistance and blocking property of an image formed using the ink composition are further improved.

  Specific examples of the water-insoluble polymer constituting the self-dispersing polymer particles are listed below as exemplary compounds B-01 to B-19, but the present invention is not limited thereto. The values in parentheses represent the mass ratio of the copolymer component.

B-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
B-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
B-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
B-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
B-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
B-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
B-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
B-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
B-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
B-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
B-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
B-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
B-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
B-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)

  There is no particular limitation on the method for producing the water-insoluble polymer constituting the self-dispersing polymer particles. For example, emulsion polymerization is carried out in the presence of a polymerizable surfactant to covalently bond the surfactant and the water-insoluble polymer. Examples thereof include a method of copolymerizing a monomer mixture containing the hydrophilic group-containing monomer and the aromatic group-containing monomer by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Among the polymerization methods, a solution polymerization method is preferable and a solution polymerization method using an organic solvent is more preferable from the viewpoint of aggregation rate and droplet ejection stability when an ink composition is used.

  The self-dispersing polymer particles include a polymer synthesized in an organic solvent from the viewpoint of the aggregation rate, and the polymer has a carboxyl group (preferably having an acid value of 20 to 100). Part or all of the groups are preferably neutralized and prepared as a polymer dispersion having water as a continuous phase. That is, the production of self-dispersing polymer particles can be performed by providing a step of synthesizing a polymer in an organic solvent and a step of dispersing the polymer to form an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. preferable.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium Step (2): Step of removing the organic solvent from the mixture

The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. In this way, 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, Dispersers, 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 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 for the purpose of moderating the polarity change during the phase inversion from oil to water. 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.

  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 (for example, a carboxyl group) as a dissociable group, examples of the neutralizing agent used include basic compounds such as organic amine compounds, ammonia, and alkali metal hydroxides. It is done. 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 in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 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 100 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 phase-inversion into an aqueous system. A dispersion can be obtained. 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 weight average molecular weight of the resin particles is preferably 10,000 or more and 200,000 or less, more preferably 100,000 or more and 200,000 or less.

The average particle diameter of the resin particles (latex particles) is preferably in the range of 10 nm to 1 μm, more preferably in the range of 10 to 200 nm, still more preferably in the range of 10 to 100 nm, and particularly preferably in the range of 10 to 50 nm. preferable. When the volume average particle diameter is 10 nm or more, the production suitability is improved, and when it is 1 μm or less, the storage stability is improved.
Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a resin particle, Any of what has a wide particle size distribution or a monodispersed particle size distribution may be sufficient. Further, two or more types of water-insoluble particles may be mixed and used, or two or more types of resin particles having a monodispersed particle size distribution may be mixed.
The average particle size and the particle size distribution of the resin particles are obtained by measuring the particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is.

The resin particles (particularly self-dispersing polymer particles) can be used alone or in combination of two or more.
The content of the resin particles in the ink composition is preferably 0.5 to 20% by mass, more preferably 2 to 20% by mass, and further preferably 3 to 15% by mass with respect to the total mass of the ink composition.

[Other ingredients]
The ink composition of the present invention may contain other additives other than those described above. Other additives include, for example, ultraviolet absorbers, anti-fading agents, anti-mold agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents, viscosity modifiers, and dispersion stabilizers. Known additives such as agents, chelating agents, solid wetting agents and the like can be mentioned.

  Examples of the UV absorber include benzophenone UV absorbers, benzotriazole UV absorbers, salicylate UV absorbers, cyanoacrylate UV absorbers, nickel complex salt UV absorbers, and the like.

  As the antifading agent, various organic and metal complex antifading agents can be used. Organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, etc. Complex, zinc complex and the like.

  Antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one, sodium sorbate, sodium pentachlorophenol, etc. Can be mentioned. These are preferably used in the ink in an amount of 0.02 to 1.00% by mass.

  The pH adjuster is not particularly limited as long as it can adjust the pH to a desired value without adversely affecting the ink composition to be prepared, and can be appropriately selected according to the purpose. Amines (eg, diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol), alkali metal hydroxides (eg, lithium hydroxide, sodium hydroxide, potassium hydroxide), ammonium Examples thereof include hydroxides (for example, ammonium hydroxide and quaternary ammonium hydroxides), phosphonium hydroxides, alkali metal carbonates, and the like.

  Examples of the rust inhibitor include acidic sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

  Examples of the antioxidant include phenol antioxidants (including hindered phenol antioxidants), amine antioxidants, sulfur antioxidants, phosphorus antioxidants, and the like.

  Examples of the chelating agent include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uramil diacetate and the like.

  Examples of the solid wetting agent include sugars such as glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose; sugar alcohols; hyaluronic acids Ureas etc. are mentioned.

(Physical properties of ink composition)
The surface tension of the ink composition of the present invention is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less. The surface tension can be adjusted to a desired range by containing a surfactant, for example.
The viscosity of the ink composition of the present invention at 20 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and still more preferably 2. 5 mPa · s or more and less than 10 mPa · s. The viscosity can be adjusted to a desired range, for example, by changing the molecular weight or content of the water-soluble organic solvent.

<Ink set>
The ink set of the present invention includes at least one of the ink compositions and at least one treatment liquid capable of forming an aggregate upon contact with the ink composition.
The ink set of the present invention is used in an image forming method using the 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 it comes into contact with the ink composition. Specifically, when mixed with the ink composition, a colored particle ( It includes at least an aggregating component capable of aggregating dispersed particles such as a pigment and the like to form an aggregate, and may include other components as necessary. 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, pyrrolidonecarboxylic acid, and pyrone. It is selected from carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, derivatives of these compounds, or salts thereof (for example, polyvalent metal salts). Is preferred. These compounds may be used alone or in combination of two or more.

The treatment liquid 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. In addition, surface tension is measured on 25 degreeC conditions using Automatic Surface Tensiometer CBVP-Z (made by Kyowa Interface Science Co., Ltd.).

<Inkjet image forming method>
The ink jet image forming method of the present invention includes an ink discharge step of forming an image by discharging the ink composition from an ink jet head having a silicon nozzle plate onto a recording medium, and other steps as necessary. Consists of including.
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 ink composition onto a recording medium.

[Ink ejection process]
In the ink ejection step, the ink composition of the present invention described above is applied onto a recording medium by an ink jet method from an ink jet head provided with 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 the vibration pressure of a piezo element, and an electric method. An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink by using ink and ejects the ink by using radiation pressure, and a thermal ink jet (Bubble Jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

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

  As an inkjet head, a short serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line 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 (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 coloring material (for example, 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 discharging the ink composition onto the recording medium, a treatment liquid for aggregating the coloring material (preferably pigment) in the ink composition is applied in advance, and the treatment applied on the recording medium. An embodiment in which an image is formed by discharging the ink composition so as to come into contact with the liquid 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. 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 to 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. Is mentioned. It is also possible to use various photographic papers for ink jet recording.

Among the above, from the viewpoint of obtaining a high-quality image having a large color material movement suppressing 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 generally surface-treated. The coated paper tends to cause quality problems such as image gloss and scratch resistance in image formation by ordinary aqueous inkjet, but in the inkjet recording method of the present invention, gloss unevenness is suppressed and gloss and resistance are reduced. An image having good rubbing properties can be obtained. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. More specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

  The present invention will be described more specifically with reference to the following examples. The scope of the present invention is not limited to the specific examples shown below. Unless otherwise specified, “part” and “%” are based on mass.

<Example 1>
~ Preparation of ink composition ~
[Preparation of pigment (coloring material) dispersion]
(Preparation of polymer dispersant P-1)
To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. A solution in which 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution in which 0.42 g of dimethyl 2,2′-azobisisobutyrate was dissolved 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 a large excess of hexane, and the precipitated resin was dried to obtain 96 g of a polymer dispersant P-1.
The composition of the obtained resin was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44600. Furthermore, when the acid value of this polymer was calculated | required by the method of JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

(Preparation of cyan dispersion)
10 parts of Pigment Blue 15: 3 (Phthalocyanine A220 manufactured by Dainichi Seika Kogyo Co., Ltd.), 5 parts of the polymer dispersant P-1 obtained above, 42 parts of methyl ethyl ketone, 1 mol / L NaOH 5.5 parts of the aqueous solution 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.
Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed to obtain a cyan dispersion having a pigment concentration of 10.2% by mass.
As described above, a cyan dispersion liquid as a coloring material was prepared.

  Using the color material (cyan dispersion) obtained above, each component was mixed so as to have the following ink composition. This was passed through a 5 μm membrane filter to prepare ink 1 (ink composition).

(Composition of ink 1)
Cyan pigment (Pigment Blue 15: 3): 4%
Polymer dispersant (P-1): 2%
Sodium silicate: 0.01%
Sannicks GP-250 (New Paul GP-250): 10%
(First water-soluble organic solvent, manufactured by Sanyo Chemical Industries, Ltd.)
Tripropylene glycol monomethyl ether (TPGmME): 10%
(First water-soluble organic solvent, manufactured by Wako Pure Chemical Industries, Ltd.)
Diethylene glycol (DEG): 5%
Olfin E1010 (Nissin Chemical Industry Co., Ltd., surfactant): 1%
Ion exchange water: 67.9%

<Examples 2 to 11 and Comparative Examples 1 to 6>
Ink 2 to Ink 17 were produced in the same manner as in Example 1, except that the type and content of the solvent and silicate were changed as shown in Table 1 below.

<Evaluation>
~ Measurement method of curvature ~
The sample curvature C applied with the ink jet recording liquid was measured in an environment of 25 ° C. and a relative humidity of 50%. Note that the curl value is expressed as in the following formula 1, assuming that the curl is an arc of a circle having a radius R.
C = 1 / R (m) (Formula 1)

[Curl property]
As a recording medium, 1 g / m of the following colorless ink composition (liquid composition for improving printability) was applied to Tokuhishi Art Double Sided N (Mitsubishi Paper Co., Ltd., 104.7 g / m ² product). ² was applied with an application bar and dried with 100 ° C. warm air for 4 seconds.
The colorless ink composition was prepared by mixing the following materials.
(Colorless ink composition)
・ Citric acid: 15g
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ・ ・ ・ 1g
・ Ion-exchanged water ... 84g

A recording medium after solid-printing the ink jet recording liquids (ink 1 to ink 17) produced as described above with an evaluation apparatus used in the evaluation of ejection properties to be described later at an ink coating amount of 5 g / m ^2. Was dried with 100 ° C. warm air for 3 seconds and allowed to stand for 1 hour, and then cut into 5 × 50 mm so that the curl direction was 50 mm to prepare a sample. Thereafter, the sample was left for 24 hours under conditions of a temperature of 25 ° C. and a relative humidity of 50%, and the curvature C of the sample was measured.

~Evaluation criteria~
A: The curvature C of the sample did not exceed 5.
B: The curvature C of the sample did not exceed 10.
C: The curvature C of the sample did not exceed 20.
D: The curvature C of the sample exceeded 20.

[Discharge reliability]
The ink composition (ink 1 to ink 17) prepared above was evaluated for ink ejection reliability as follows. The evaluation environment was 25 ° C. and relative humidity 50%.
As an evaluation apparatus, a dimatics material printer DMP-2831 (manufactured by FUJIFILM DYMATICS) equipped with a dimatics material cartridge DMC-11610 (10 pl) (manufactured by FUJIFILM DYMATIS) was used. Evaluation items (i) to (iii) were evaluated, and the results were evaluated according to the following evaluation criteria. The results are shown in Table 1.
The ink cartridge was modified so that the filling liquid capacity was 100 ml. Further, as a recording medium, a sample (Tokuhishi Art N (manufactured by Mitsubishi Paper Industries, Ltd., 84.9 g / m ² )) cut to 5 × 50 mm in the same manner as described above was used.

~Evaluation item~
(I) Those in which no image unevenness was observed were considered good.
(Ii) After a continuous discharge for 1 minute, after leaving uncap for 30 minutes, the discharge rate when re-discharged was 90% or more (the non-discharge rate was less than 10%).
(Iii) A discharge rate after continuous discharge for 60 minutes is 90% or more (non-discharge rate is less than 10%).

~Evaluation criteria~
AA: All of (i) to (iii) were satisfied.
A: The two items (i) and (ii) were satisfied.
B: Only (i) was satisfied.
C: All of (i) to (iii) were not satisfied.

[Liquid repellency evaluation]
~ Liquid repellent film immersion test ~
A test piece in which a liquid repellent film (SAM film) was formed using a fluorinated alkylsilane compound on a 2 cm × 2 cm silicon plate was produced. 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.

  As is apparent from Table 1, it can be seen that the ink composition of the present invention exhibits a good curl suppressing effect and is excellent in ejection reliability. Moreover, it turns out that the liquid repellency fall of an inkjet head member can be suppressed.

DESCRIPTION OF SYMBOLS 11 ... Nozzle plate 12 ... Discharge port (nozzle) 20 ... Ink supply unit 21 ... Pressure chamber 22 ... Nozzle communication channel 23 ... Ink supply channel 24 ... Supply adjustment channel 25 ... Common liquid chamber 30 ... Piezoelectric element (piezoelectric actuator; pressure generating means)
DESCRIPTION OF SYMBOLS 31 ... Diaphragm 32 ... Adhesion layer 33 ... Lower electrode 34 ... Piezoelectric layer 35 ... Upper electrode 41 ... Circulation stop 42 ... Circulation path 200 ... Inkjet head

Claims (11)

  Containing water, a coloring material, a water-soluble organic solvent, a surfactant, and 0.0001% by mass or more and 0.5% by mass or less of a water-soluble silicate based on the total mass, the water-soluble An ink composition comprising 40% by mass or more of a water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less among organic solvents. The ink composition according to claim 1, wherein the water-soluble silicate is a compound represented by the following general formula (1).
x (A ₂ O) · y (SiO ₂ ) General formula (1)
(In general formula (1), A represents sodium, potassium, and tetraalkylammonium (NR ₄ ). X represents 1 or 2, y represents an integer of 1 to 4, and R represents an alkyl group having 1 to 4 carbon atoms. Represents.)   The ink composition according to claim 2, wherein the water-soluble silicate is at least one selected from sodium silicate, potassium silicate, and tetramethylammonium silicate. The ink composition according to any one of claims 1 to 3, wherein the water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less has the following structural formula.

(In the structural formula, l, m, and n are each independently an integer of 1 or more and l + m + n = 3 to 15. AO represents an oxyethylene group (EO) or an oxypropylene group (PO)). Represents at least one.)   5. The ink composition according to claim 1, wherein the content of the water-soluble organic solvent is 30% by mass or less based on the total mass.   The ink according to any one of claims 1 to 5, wherein the water-soluble organic solvent having a solubility parameter (SP value) of 27.5 or less is 50% by mass or more based on the total mass of the water-soluble organic solvent. Composition.   The ink composition according to claim 1, wherein the color material is a resin-coated pigment.   An ink set comprising: the ink composition according to any one of claims 1 to 7; 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 7 onto a recording medium from an ink jet head having a silicon nozzle plate. .   The process liquid application | coating process which further provides on the recording medium the process liquid which can be contacted with the ink composition of any one of Claims 1-7, and can form an aggregate. Inkjet image forming method.   The ink jet image forming method according to claim 9 or 10, wherein the recording medium is plain paper or coated paper.

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