JP2009190379A - Ink composition, ink set, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set excelling in liquid stability and discharge property and suppressing a curl and image deformation of a recorded medium after ink has adhered thereto. <P>SOLUTION: The ink set has an ink composition containing (a) a pigment, (b) a water-soluble solvent, (c) water and (d) resin particles, wherein (a) the pigment is a polymer-coated pigment obtained through a process of crosslinking with a crosslinking agent after dispersing the pigment using a water-soluble dispersant; and a colorless ink composition containing a coagulation accelerator for accelerating coagulation of the ink composition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

In recent years, due to advances in ink jet recording technology, ink jet recording methods have come to be used for high-definition images that have been intended for use in photography and offset printing, and high-quality recording is required.
An ink containing a sugar alkyleneoxy derivative or an aggregate thereof has been disclosed as an ink that can be printed with little bleeding on a recycled paper and hardly clogs (for example, Patent Document 1).
Further, a water-soluble solvent having an SP value of 16.5 or more and less than 24.6 is contained at 30% by mass or more of the total ink, water is contained at 10% by mass or more and less than 50% by mass, and the pigment is an alkali-soluble polymer dispersant. Inkjet ink dispersed by the above is disclosed (for example, Patent Document 2).
Also disclosed is an ink containing a pigment dispersion obtained by dispersing a pigment with a carboxylic acid-containing dispersant and then performing a crosslinking reaction using a bifunctional or higher polyvalent epoxy group as a crosslinking agent. (For example, patent document 3).
Japanese Patent Laid-Open No. 2002-30092 JP 2007-145887 International Publication No. 06/064193 Pamphlet

However, although the effect of ejectability is recognized to some extent in Patent Document 1, there is a problem that curling cannot be suppressed only by containing a sugar alcohol derivative. Further, although Patent Document 2 describes that the curl characteristics are excellent, the stability of the ink is lowered, and there is a problem that droplet ejection interference is likely to occur when used in combination with a medium having a low penetration rate. was there. Further, although Patent Document 3 describes the effect of dispersion stability, there are problems in terms of droplet ejection interference and fixing property during high-speed printing.
In view of the above problems, an object of the present invention is to provide an ink set that has good liquid stability and ejection properties, and can suppress curling and image deformation of a recording medium after ink application.
Another object of the present invention is to provide an image forming method using an ink set that has good liquid stability and ejection properties, and can suppress curling and image deformation of a recording medium after ink application. To do.

<1> (a) a pigment, (b) a water-soluble solvent, (c) water, and (d) resin fine particles, wherein the (a) pigment is dispersed with a water-soluble dispersant and then crosslinked with a crosslinking agent. An ink composition which is a pigment coated with a polymer obtained through the step of:
An ink set comprising: a colorless ink composition containing an aggregation accelerator that promotes aggregation of the ink composition.
<2> The ink set according to <1>, wherein the water-soluble solvent (b) contains 90% by mass or more of a water-soluble solvent having an SP value of 27.5 or less.
<3> The ink set according to <1> or <2>, wherein the content of the water-soluble solvent (b) is 10 to 30% by mass of the total ink composition.
<4> The ink set according to any one of <1> to <3>, wherein the water-soluble solvent (b) includes a compound represented by the following structural formula (1).

(In the formula, l, m, and n are each independently an integer of 1 or more and l + m + n = 3 to 15. AO represents ethyleneoxy and / or propyleneoxy.)

<5> The ink set according to <4>, wherein in the compound of the structural formula (1), AO is propyleneoxy.
<6> The ink set according to any one of <1> to <5>, wherein the amount of the compound of the structural formula (1) accounts for 50% by mass or more of the entire water-soluble solvent.
<7> Any one of the above <1> to <6>, wherein the water-soluble dispersant contains a carboxyl group or a salt thereof in the molecule, and the crosslinking agent is a bifunctional or higher functional epoxy compound. The ink set according to item.
<8> The ink set according to any one of <1> to <7>, wherein the water-soluble dispersant has an acid value of 135 to 250 mgKOH / g.
<9> The ink set according to any one of <1> to <8>, wherein the aggregation accelerator is an acid.
<10> An image forming method using the ink set according to any one of <1> to <9>.
<11> A first step of applying the colorless ink composition in the ink set according to any one of <1> to <9> to a recording medium, and the colorless ink composition is applied. The image forming method according to <10>, further comprising a second step of applying the ink composition to a recording medium.
<12> The image forming method according to <11>, wherein the method of applying the colorless ink composition to the recording medium is a method of ejecting droplets by ink jetting.
<13> The image forming method according to <11>, wherein the method of applying the colorless ink composition to the recording medium is a method of applying using a coating apparatus.
<14> In an image forming method for printing by applying an ink composition onto an ink receiver recording medium,
The ink composition comprises (a) a pigment, (b) a water-soluble solvent, (c) water, and (d) resin fine particles,
The (a) pigment is a pigment coated with a polymer obtained by dispersing the pigment with a water-soluble dispersant and then crosslinking with a crosslinking agent, and the recording medium causes the ink composition to aggregate. An image forming method, characterized by being provided with a coagulation promoter to be promoted.

According to the present invention, it is possible to provide an ink set that has good liquid stability and ejection properties, and can suppress curling and image deformation of a recording medium after ink application.
In addition, according to the present invention, it is possible to provide an image forming method using an ink set that has good liquid stability and ejectability and can suppress curling and image deformation of a recording medium after ink application. it can.

The ink set of the present invention includes (a) a pigment, (b) a water-soluble solvent, (c) water, and (d) resin fine particles. (A) The pigment is crosslinked after the pigment is dispersed using a water-soluble dispersant. An ink composition which is a pigment coated with a polymer obtained through a step of crosslinking with an agent;
A colorless ink composition containing an aggregation accelerator that promotes aggregation of the ink composition.
By adopting the above-described configuration, an ink set in which the liquid stability and dischargeability of the ink composition in the present invention is good, and curling and image deformation of the recording medium after the ink composition is applied can be suppressed. Obtainable. In particular, by using a polymer-coated pigment obtained by crosslinking with a crosslinking agent in combination with (a) an ink composition containing a pigment and a colorless ink composition containing an aggregation accelerator that promotes aggregation of the pigment, The effect of the present invention is remarkable.
Hereinafter, the components of the present invention will be described.

<Ink composition>
(A) Pigment The ink composition of the present invention contains a pigment as a colorant, and the pigment is coated with a polymer obtained through a step of cross-linking with a cross-linking agent after the pigment is dispersed with a water-soluble dispersant. (Hereinafter also referred to as “water-dispersible pigment”).

Examples of the water-soluble dispersant include polyvinyls, polyurethanes, and polyesters, among which polyvinyls are preferable.
The water-soluble dispersant needs to have a group that is cross-linked by a cross-linking agent in the molecule. The cross-linking group is not particularly limited, and examples thereof include a carboxyl group or a salt thereof, an isocyanate group, and an epoxy group, but it is preferable to have a carboxyl group or a salt thereof from the viewpoint of improving dispersibility.
As a method for synthesizing the water-soluble dispersant, a copolymer obtained using a carboxyl group-containing monomer as a copolymerization component is preferable. Examples of the carboxyl group-containing monomer include methacrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, crotonic acid and the like. Among these, from the viewpoint of crosslinkability and dispersion stability, methacrylic acid and β-carboxyl are used. Ethyl acrylate is preferred.

  In the present invention, the acid value of the water-soluble dispersant (mg number of KOH necessary for neutralizing 1 g of the water-soluble dispersant) is 135 to 250 mg KOH / g from the viewpoint of pigment dispersibility and dispersion stability. Preferably, it is 135-200 mgKOH / g, more preferably 135-180 mgKOH / g.

  In addition, hydrophilic monomers and hydrophobic monomers can be used as copolymerization components. The hydrophilic monomer may be ionic or nonionic. The hydrophobic monomer is not particularly limited, but an alkyl methacrylate having 1 to 20 carbon atoms or an alkyl acrylate having 1 to 20 carbon atoms is preferable. The polymer as the water-soluble dispersant may be a random polymer or a block or graft polymer.

  The method for synthesizing the polymer as the water-soluble dispersant is not particularly limited, but random polymerization of vinyl monomers is preferable from the viewpoint of dispersion stability.

The cross-linking agent is not particularly limited as long as it is a compound having two or more sites that react with the water-soluble dispersant, but preferably two or more from the viewpoint of excellent reactivity with a carboxyl group. It is a compound (2 or more functional epoxy compound) which has an epoxy part.
Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol glycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether. Polyethylene glycol diglycidyl ether and diethylene glycol diglycidyl ether are preferable.

  The molar ratio between the crosslinking site of the crosslinking agent and the cross-linked site of the dispersant is preferably 1: 1.1 to 1:10, from the viewpoint of the speed of the crosslinking reaction and the stability of the dispersion after crosslinking, and preferably 1: 1. 1-1: 5 is more preferable, and 1: 1.1-1: 3 is most preferable.

As the usage-amount of the said water-soluble dispersing agent in this invention, 10 mass%-200 mass% are preferable with respect to a pigment, 20 mass%-150 mass% are more preferable, 30 mass%-100 mass% are especially preferable. .
The method for preparing the water-dispersible pigment in the present invention is particularly limited as long as the pigment is a pigment coated with a polymer obtained through a step of crosslinking with a crosslinking agent after dispersing the pigment with a water-soluble dispersant. Not. Although an example of the adjustment method of a water dispersible pigment is shown below, it is not limited to this.

(1) A step of obtaining a pigment dispersion in which a pigment and a water-soluble dispersant are dispersed in water or an aqueous solution of a polar solvent (pigment dispersion step).
(2) Subsequently, a step of obtaining a pigment (water-dispersible pigment) coated with a polymer by adding a crosslinking agent to the dispersion obtained in (1) and heating to cause a crosslinking reaction (crosslinking reaction step).
(3) A step of purifying the crosslinked water-dispersible pigment obtained above (pigment purification step).
The water-soluble pigment can be prepared through the steps (1) to (3).
Other known steps may be appropriately added to the above steps as necessary. A well-known thing can be used suitably for the polar solvent used at the said process etc.

  There is no restriction | limiting in particular as a pigment used in the said water-dispersible pigment 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 quinofullerone 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 those of Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170 (Manufactured by Carbon), 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 (above made by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S150, Color Black Sr, 160 , 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 are 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.

  The content of the pigment (a) in the present invention is 0.1% by mass or more and 15% by mass in the total ink composition from the viewpoints of color developability, granularity, ink stability, and ejection reliability. It is preferably at most mass%, more preferably at least 0.5 mass% and at most 12 mass%, particularly preferably at least 1 mass% and at most 10 mass%.

<(B) Water-soluble solvent>
The ink composition uses a water-soluble solvent for the purpose of an anti-drying agent, a wetting agent or a penetration accelerator.
In particular, when a water-soluble solvent is used as a water-based ink composition of an ink jet recording system, a water-soluble organic solvent can be preferably used for the purpose of a drying inhibitor, a wetting agent, or a penetration accelerator.
Anti-drying agents and wetting agents are used for the purpose of preventing clogging due to drying of the ink-jet ink at the nozzles, and the anti-drying agents and wetting agents are water-soluble organic compounds having a vapor pressure lower than water. Solvents are preferred.
In addition, a water-soluble organic solvent is preferably used as a penetration accelerator for the purpose of allowing the ink composition (particularly, the ink-jet ink composition) to penetrate into paper better.

In the present invention, for the purpose of suppressing curling, the water-soluble solvent (a) preferably contains 90% by mass or more of a water-soluble solvent having an SP value of 27.5 or less.
Here, the “water-soluble solvent having an SP value of 27.5 or less” and the “compound represented by the structural formula (1)” may be the same or different.
The solubility parameter (SP value) of the water-soluble solvent referred to in the present invention is a value represented by the square root of the molecular cohesive energy. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1967), and this numerical value is adopted in the present invention.
In the present invention, the fact that (b) the water-soluble solvent contains a compound represented by the following structural formula (1) can also improve the liquid stability and dischargeability of the ink composition, and record after ink is applied. This is preferable in terms of improving curling prevention of the medium.

In the structural formula (1), l, m, and n are each independently an integer of 1 or more and represent 1 + m + n = 3-15.
Among the above, from the viewpoint of curling suppression, l + m + n is preferably 3 to 12, and more preferably 3 to 10.
In the structural formula (1), AO represents ethyleneoxy and / or propyleneoxy, and among them, propyleneoxy is preferable.
Each AO of (AO) ₁ , (AO) _m , and (AO) _n may be the same or different.

  Examples of the water-soluble solvent having an SP value of 27.5 or less and the compound represented by the structural formula (1) are shown below together with the SP value (in parentheses). However, the present invention is not limited to this.

Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Triethylene glycol monobutyl ether (21.1)
Dipropylene glycol monomethyl ether (21.3)
Dipropylene glycol (27.2)

_{· NC 4 H 9 O (AO} ) 4 -H ( in AO = EO or PO, the ratio of EO: PO = 1: 1) (20.1)
_{· NC 4 H 9 O (AO} ) 10 -H ( in AO = EO or PO, the ratio of EO: PO = 1: 1) (18.8)
HO (A′O) ₄₀ −H (A′O = EO or PO, the ratio is EO: PO = 1: 3) (18.7)
HO (A ″ O) ₅₅ −H (A ″ O = EO or PO, the ratio is EO: PO = 5: 6) (18.8)
HO (PO) ₃ -H (24.7)
・ HO (PO) _7- H (21.2)
・ 1,2-Hexanediol (27.4)
In the present invention, EO and PO represent ethyleneoxy and propyleneoxy, respectively.

The proportion (content) of the compound of the structural formula (1) in the (a) water-soluble solvent is preferably 10% or more, more preferably 30% or more, and further preferably 50% or more. Even if the value is high, no problem arises.
By setting it in the above range, curling can be suppressed without deteriorating the stability and dischargeability of the ink, which is preferable.

In the present invention, other solvents may be used in combination as long as the ratio of the solvent having an SP value of 27.5 or less does not become less than 90%.
Examples of water-soluble organic solvents that can be used in combination include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol, 2 -Butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentane Alkanediols (polyhydric alcohols) such as diol and 4-methyl-1,2-pentanediol; glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol, maltose, cellobiose Saccharides such as lactose, lactose, sucrose, trehalose, maltotriose; sugar alcohols; hyaluronic acids; so-called solid wetting agents such as ureas; alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol ;

Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono -Iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene Glycol mono t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono- Glycol ethers such as iso-propyl ether; 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin , Sulfolane and the like, and one or more of these can be used.

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

  For the purpose of the penetrant, a polyol compound is preferable. 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-hexane Examples include diol, 5-hexene-1,2-diol, and 2-ethyl-1,3-hexanediol. Among these, preferred examples include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

The water-soluble solvent (a) used in the present invention may be used alone or in combination of two or more.
(A) The content of the water-soluble solvent is preferably 1% by mass or more and 60% by mass or less, and more preferably 5% by mass or more and 40% by mass or less from the viewpoint of ensuring stability and ejection reliability in the entire ink composition. Preferably, 10 mass% or more and 30 mass% or less are used especially preferably.

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

(D) Resin Fine Particles In the present invention, resin fine particles are included from the viewpoint of scratch resistance, imparting cohesiveness for avoiding droplet ejection interference, and stability of the ink composition. The resin fine particles are preferably resin fine particles of polymer latex.
Examples of the polymer latex that can be used in the present invention include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, styrene resins, crosslinked acrylic resins, Mentioned are latexes such as cross-linked styrene resins, benzoguanamine resins, phenol resins, silicone resins, epoxy resins, urethane resins, paraffin resins, and fluorine resins. Among these, acrylic resins, acrylic-styrene resins, styrene resins, crosslinked acrylic resins, and latexes of crosslinked styrene resins can be cited as preferred examples.
The weight average molecular weight of the resin in the polymer latex is preferably 10,000 or more and 200,000 or less, more preferably 100,000 or more and 200,000 or less, from the viewpoint of the stability of the ink composition.
The average particle size of the resin fine 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 20 to 100 nm, and particularly preferably in the range of 20 to 50 nm.
The addition amount of the polymer latex is preferably 0.5 to 20% by mass and 3 to 20% by mass in terms of solid content with respect to the ink composition from the viewpoint of fixability, scratch resistance, and viscosity of the ink composition. More preferably, 5-15 mass% is further more preferable.
The glass transition temperature Tg of the resin fine particles is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher, from the viewpoint of the storage stability of the ink composition.
Moreover, there is no restriction | limiting in particular regarding the particle size distribution of polymer latex, What has a wide particle size distribution or a thing with a monodispersed particle size distribution may be sufficient. Two or more kinds of polymer latexes having a monodispersed particle size distribution may be mixed and used.

<Surfactant>
Examples of the surface tension adjusting agent include nonionic, cationic, anionic and betaine surfactants. The addition amount of the surface tension adjusting agent is preferably an amount capable of adjusting the surface tension of the ink composition and the colorless ink composition in the present invention to a numerical value range described later in order to eject ink droplets well by inkjet.
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 dispersing agent) 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 nonionic surfactants include, for example, acetylene diol derivatives such as ethylene oxide adducts of acetylene diol, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl. Examples thereof include phenyl ether, oxyethylene / oxypropylene block copolymer, t-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.
From the viewpoint of avoiding ink droplet ejection interference, a nonionic surfactant is preferable, and among them, an acetylenic diol derivative is most preferable.
The amount of the surfactant to be added to the inkjet liquid composition in the present invention is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5 to 10% by mass, More preferably, it is 1-3 mass%.

<Other ingredients>
Other additives may be contained. 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 and chelating agents are included.

  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 recording ink 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.

<Colorless ink composition>
The ink set of the present invention contains a colorless ink composition in order to improve good printability without image deformation, and the colorless ink composition contains an aggregation accelerator that promotes aggregation of the ink composition.

(Aggregation accelerator)
The colorless ink composition in the invention contains an aggregation accelerator, and examples of the aggregation accelerator include acids.
The acid may be any of inorganic acid and organic acid, but 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, sulfonic acid, orthophosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, or derivatives of these compounds, or these It is preferable to be selected from the salts of These compounds may be used alone or in combination of two or more.
The content of the aggregation accelerator is preferably from 0.1 to 30 mass%, more preferably from 0.5 to 20 mass%, based on the total mass of the colorless ink composition, from the viewpoints of aggregation rate control and image deformation suppression. 1 to 15% by mass is more preferable.
By setting the content of the aggregation accelerator in the above-mentioned range, it is preferable that ink droplet interference can be avoided and image deformation can be suppressed.

  In the present invention, a preferred example of the colorless ink composition that can be used for improving the printability is a colorless ink composition that generates an aggregate by changing the pH of the ink composition. At this time, the pH of the colorless ink composition is preferably 1 to 6, more preferably 2 to 5, and still more preferably 3 to 5. The pH can be adjusted using the above acid or other known pH adjusting agents.

In the present invention, it is preferable to add a polyvalent metal salt or polyallylamine to the colorless ink composition in order to prevent image deformation that can be used and improve printability.
Alkaline earth metals of group 2A of the periodic table (eg, magnesium and calcium) as polyvalent metal salts; transition metals of group 3B of the periodic table (eg, lanthanum); cations from group 3A of the periodic table (eg, aluminum) Lanthanides (for example, neodymium); and polyallylamine and polyallylamine derivatives. Preferred examples include calcium and magnesium.
Anions that are preferably employed as a counter salt of calcium or magnesium include carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate.
The amount of salt added to the colorless ink composition is about 1 to about 10% by weight, preferably about 1.5 to about 7% by weight, more preferably about 2 to about 6% by weight. Can be present inside.

<Physical properties of ink composition and colorless ink composition>
The surface tension of the ink composition and the colorless ink composition is preferably 20 mN / m or more and 60 mN / m or less independently from the viewpoint of ejection stability when used in an ink jet recording method. 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 viscosity of the ink composition and the colorless ink composition at 20 ° C. is preferably independently from 1.2 mPa · s to 15.0 mPa · s, more preferably from 2 mPa · s to less than 13 mPa · s. More preferably, it is 2.5 mPa · s or more and less than 10 mPa · s.

  The ink set of the present invention can be used for general writing instruments, recorders, pen plotters, and the like, but is particularly preferably used for an ink jet recording method.

<Image forming method>
The image forming method of the present invention includes a step of forming an image using the ink set of the present invention (image forming step) (first aspect).
The step of forming the image preferably includes the following first step and second step.
(1) First step: a step of applying the colorless ink composition to a recording medium (colorless ink composition applying step)
(2) Second step: a step of applying the ink composition to a recording medium to which the colorless ink composition is applied (ink composition applying step).
In the process of forming the image, other processes (dry removal process, heat fixing process, etc.) can be appropriately selected and added according to the purpose.

There is no restriction | limiting in particular as said drying removal process except removing a solvent by drying, According to the objective, it can select suitably.
The heat fixing step is not particularly limited except that the latex particles contained in the ink composition are melt-fixed, and can be appropriately selected according to the purpose.

(First step)
As a method for applying the colorless ink composition to a recording medium (a known image receiving material), a method of ejecting droplets by inkjet and a method of applying using a coating apparatus are preferable.

The method of ejecting droplets by inkjet is performed by supplying energy to the colorless ink composition and applying the colorless ink composition to the following known recording material (image receiving material).
Examples of the known image receiving material include plain paper, resin-coated paper, such as JP-A-8-169172, JP-A-8-27693, JP-A-2-276670, JP-A-7-276789, and JP-A-9-323475. No. 1, JP-A-62-238783, JP-A-10-153898, JP-A-10-217473, JP-A-10-235995, JP-A-10-337947, JP-A-10-217597, Inkjet exclusive paper, film, electrophotographic co-paper, cloth, glass, metal, ceramics, etc. described in JP-A-337947.
In addition, the description of paragraph number 0093-0105 of Unexamined-Japanese-Patent No. 2003-306623 is applicable as a method of ejecting with an inkjet preferable for this invention.

The method of applying using the coating apparatus is not particularly limited, and is performed by applying a colorless ink composition to the known recording medium (image receiving material) using the following known coating apparatus.
Examples of known coating apparatuses include slit coaters, spinners, wheelers, roller coaters, curtain coaters, knife coaters, wire bar coaters, and extruders.

(Second step)
The ink composition application step is a step of applying the ink composition to the recording medium to which the colorless ink composition is applied.
As a method for applying the ink composition, a coating method using a coating device and a method for ejecting ink using an ink jet can be used as in the first step, and a method for ejecting ink using an ink jet is preferable.
The method of ejecting droplets by inkjet is performed by applying an ink composition supplied with energy to a recording medium to which a colorless ink composition has been applied to form an image.
In addition, the description of Paragraph Nos. 0093 to 0105 in JP-A No. 2003-306623 can be applied as an inkjet method preferable for the present invention.

  In forming an image, a polymer latex compound may be used in combination for the purpose of imparting glossiness or water resistance or improving weather resistance. The timing of applying the latex compound to the image receiving material may be before, after, or simultaneously with the application of the colorant, and therefore the addition location may be in the image receiving paper. It may be in ink or may be used as a liquid material of polymer latex alone. Specifically, the methods described in JP2002-166638, JP2002-121440, JP2002-154201, JP2002-144696, and JP2002-080759 are preferably used. be able to.

  In the image forming method of the present invention, by applying the colorless ink composition to a recording medium, the pigment fixing property of the subsequently applied ink composition becomes good, and the effect of suppressing image deformation becomes remarkable. Is preferable.

The image forming method of the present invention is an image forming method in which an ink composition is applied onto a recording medium for printing, and the ink composition comprises (a) a pigment, (b) a water-soluble solvent, and (c) water. (D) An ink composition containing resin fine particles, wherein the pigment (a) is obtained by subjecting the pigment to pigment dispersion using a water-soluble dispersant and then crosslinking with a crosslinking agent. The recording medium is provided with an aggregation promoter that promotes aggregation of the ink composition (second aspect).
Here, the ink composition, the aggregation accelerator, and the like are the same as those described in the above-described sections of the ink composition and the colorless ink composition, and preferable examples thereof are also the same.

  Since the recording medium used in the present invention is provided with an aggregation accelerator that promotes aggregation of the ink composition, by applying the ink composition to the recording medium, the pigment fixing property is good. An image with little deformation can be formed.

The image forming method (second aspect) of the present invention does not include the first step in the first aspect and includes the aggregation promoter in advance instead of the recording medium in the second step. Except for using the recording medium, the process is the same as the process of the first aspect, and the process that can be added is the same.
The recording medium containing the aggregation accelerator in advance is preferably a recording medium obtained by applying the colorless ink composition according to the first aspect.
The coating amount of the aggregation accelerator is aggregation rate control, in terms of image deformation suppression, 0.3 g / ^{m 2} or more, more preferably 0.3~2g / ^{m 2,} 0.5~1g / ^{m 2} is more preferable. By setting the coating amount of the aggregation accelerator within the above range, it is preferable because it can avoid ink droplet ejection interference and suppress image deformation.

  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.

[Synthesis Example] (Synthesis of water-soluble resin dispersant P-1)
Synthesized according to the following.

  While isopropanol (187.5 parts) was heated to 80 ° C. under a nitrogen atmosphere, methyl methacrylate (478 parts) / methacrylic acid (172 parts) / 2-ethylhexyl methacrylate (350 parts) / 2,2′- A mixture of azobis (2-methylbutyronitrile) (22.05 parts) was added dropwise over 2 hours. After completion of dropping, the mixture was kept at 80 ° C. for further 4 hours, and then cooled to 25 ° C. By removing the solvent under reduced pressure, water-soluble resin dispersant P-1 (water-soluble dispersant) having an average weight molecular weight of about 30,000 and an acid value of 154 mgKOH / g was obtained.

  Other water-soluble resin dispersants in the present invention can be synthesized in the same manner.

[Preparation of latex]
<Synthesis Example 1>
120 g of water, latemul ASK (manufactured by Kao Corporation, carboxylate emulsifier) 19.8 g, 5 mol / L aqueous sodium hydroxide solution 6 g, 2,2′-azobis (2-amidinopropane) dihydrochloride 0.3 g Was added and dissolved uniformly. The mixture was heated to 70 ° C., and a monomer mixture of 25.9 g of styrene, 26.3 g of butyl acrylate, and 5.1 g of acrylic acid was added over 2 hours under a nitrogen stream. Then, it heated at 70 degreeC for 2 hours and 80 degreeC for 3 hours. After cooling to room temperature, a 1 mol / L aqueous sodium hydroxide solution was added with stirring so that the pH was around 9, and latex PL-01 was obtained. The volume average particle diameter of the obtained latex was 115 nm. The solid content of the latex dispersion was 33% by mass.

[Preparation of Dispersion N1 of Uncrosslinked Pigment-Containing Resin Particles and Dispersion 1 of Crosslinked Pigment-Containing Resin Particles]
Water-soluble resin dispersant P-1 (150 parts) is dissolved in water and neutralized with an aqueous potassium hydroxide solution so that the pH after neutralization is 10.1 and the water-soluble resin dispersant concentration is 30.6%. A dispersant aqueous solution was prepared. To 147 parts of this water-soluble resin dispersant aqueous solution, 90 parts of Pigment Blue 15: 3 (Phthalocyaniburu-A220 manufactured by Dainichi Seika Co., Ltd.) and 362 parts of water are mixed, and a bead mill (0.1 mmΦ zirconia beads) is used. Dispersion was performed for 3 hours to obtain a dispersion N1 of uncrosslinked pigment-containing resin particles having a pigment concentration of 15%.
By adding 0.35 part of polyethylene glycol diglycidyl ether to 170 parts of dispersion N of uncrosslinked pigment-containing resin particles, reacting at 50 ° C. for 6 hours and a half, and then cooling to 25 ° C., the pigment concentration is 14. A dispersion 1 of 9% crosslinked pigment-containing resin particles was obtained.

[Example 1]
[Preparation of ink set 1]
Ink set 1 of the following ink composition A1 and colorless ink composition B1 was produced.

(Preparation of ink composition A1 (crosslinked pigment))
Using the dispersion 1 of the crosslinked pigment-containing resin particles obtained above, the following compositions were mixed, and then filtered through a 5 μm membrane filter to prepare an ink composition A1.
(1) Dispersion 1 of the above-mentioned crosslinked pigment-containing resin particles 1 26.8 parts (2) Latex PL-01 24.2 parts (3) Compound 1 (l + m + n = 9) (21.7) 15 parts (4) Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 part (5) Ion-exchanged water Remaining amount of 100

(Preparation of colorless ink composition B1)
A colorless ink composition (aggregation accelerator liquid) was prepared by mixing the following materials.
(composition)
(1) Citric acid 15g
(2) Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ... 1g
(3) Ion exchange water ... 84g

(Image formation)
The following evaluation was performed using a DYMATICS Material Printer DMP-2831 (manufactured by FUJIFILM Daimatics Co., Ltd.) (the cartridge was modified so that 10 pl discharge (DMC-11610) can be supplied from the outside). The colorless ink composition B1 was ejected onto the following inkjet recording medium 1 at 5 g / m ^2, and after 1 minute, the ink composition A1 was ejected to form an image.

[Preparation of inkjet recording medium 1 (no application of colorless ink composition (acid treatment))]
<Preparation of coating liquid for topcoat layer>
100 parts of kaolin (trade name: Kaoblite 90, manufactured by Shiraishi Calcium Co., Ltd.) and 1.2 parts of 40% sodium polyacrylate (trade name: Aron T-50, manufactured by Toagosei Co., Ltd.) are mixed in water. And 100 parts of 7% PVA245 (Kuraray Co., Ltd.) aqueous solution and 3.7 parts of 10% Emulgen 109P (Kao Co., Ltd.) aqueous solution are added, and the final solid content concentration is 27%. A layer coating solution was prepared.

<Soft calendar processing>
For high-quality paper (product name: Shirai, 76.5 g / m ² products, manufactured by Nippon Paper Industries Co., Ltd.), using a soft calender with a roll pair in which a metal roll and a resin roll make a pair, Soft calendering was performed under conditions of a surface temperature of 50 ° C. and a nip pressure of 50 kg / cm.

<Application>
On both surfaces of the above-mentioned calendered fine paper, the prepared coating solution for the overcoat layer is applied on each side using an extrusion die coater so that the dry weight per side is 20 g / m ² . The film was dried at a temperature of 70 ° C. and a wind speed of 10 m / sec for 1 minute to form an overcoat layer to obtain a recording medium.

[Evaluation of ink composition]
<Dispersion stability>
About the ink composition obtained above, the particle diameter and the viscosity after storage for 14 days in a thermostat at 60 ° C. were measured, and the following pass / fail was judged. The results are shown in Table 1.
(1) Particle size change is within 10 nm (2) Viscosity change is within 10% -Evaluation criteria-
○ ・ ・ ・ If both items are acceptable △ ・ ・ ・ If only one item is acceptable × ・ ・ ・ If both items are unacceptable

(Measurement of particle diameter)
The volume average particle size of the pigment dispersion obtained by the dynamic light scattering method was measured using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). Measurement conditions: 10 ml of ion exchanged water was added to 10 μl of water-based ink to prepare a measurement solution, and measurement was performed at 25 ° C.

(Measurement of viscosity)
The water-based ink was measured under the condition of 25 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

<Curl>
The inkjet recording medium after solid printing with an ink coating amount of 5 g / m ² is cut to 5 × 50 mm in the curl direction and left for 24 hours under conditions of a temperature of 25 ° C. and a humidity of 50%. The curl behavior (curl value) was confirmed. The evaluation results are shown in Table 1.

~Evaluation criteria~
○: Curvature C does not exceed 20 ×: Curvature C exceeds 20

~ Measurement method of curvature ~
The sample cut to 5 × 50 mm in the curl direction is applied to the curl measurement plate, and the curl value (C) is read. The curl is regarded as an arc of a circle with a radius R and is expressed as follows. C = 1 / R (m)

<Discharge stability>
The following pass / fail was determined during printing using the inkjet recording apparatus. The image unevenness was visually observed.
(1) The discharge rate after a continuous discharge test for 60 minutes is 90% or more.
(2) The discharge rate after discharging for 1 minute and resting for 30 minutes is 90% or more.
(3) No image unevenness is observed.

-Evaluation criteria-
○ ・ ・ ・ When all three items are acceptable △ ・ ・ ・ When two items are acceptable × ・ ・ ・ Two or more items are unacceptable

<Image transformation>
When a sample printed with a size of 5 cm × 5 cm was dried and fixed and heated at 100 ° C. for 10 seconds, the following pass / fail was determined.
(1) Change in image area is within ± 5% (2) No cracks or unevenness in image observed No determination was made based on the following criteria.

-Evaluation criteria-
○ ・ ・ ・ If both items are acceptable △ ・ ・ ・ If only one item is acceptable × ・ ・ ・ If both items are unacceptable

[Example 2]
In Example 1, it carried out similarly except having changed the water-soluble solvent of (3) Compound 1 of ink composition A1 into the water-soluble solvent of Table 1.

[Example 3]
In Example 1, the water-soluble solvent of the ink composition A1 (3) Compound 1 was changed to the water-soluble solvent shown in Table 1, and the ink jet recording medium 1 was changed to the following ink jet recording medium A1 to form an image. The same procedure was performed except that the droplet ejection of the colorless ink composition B1 was omitted.

[Preparation of Inkjet Recording Medium A1 (With Colorless Ink Composition (Acid Treatment))]
<Preparation of coating liquid for topcoat layer>
100 parts of kaolin (trade name: Kaoblite 90, manufactured by Shiraishi Calcium Co., Ltd.) and 1.2 parts of 40% sodium polyacrylate (trade name: Aron T-50, manufactured by Toagosei Co., Ltd.) are mixed in water. And 100 parts of 7% PVA245 (Kuraray Co., Ltd.) aqueous solution and 3.7 parts of 10% Emulgen 109P (Kao Co., Ltd.) aqueous solution are added, and the final solid content concentration is 27%. A layer coating solution was prepared.

<Soft calendar processing>
For high-quality paper (product name: Shirai, 76.5 g / m ² products, manufactured by Nippon Paper Industries Co., Ltd.), using a soft calender with a roll pair in which a metal roll and a resin roll make a pair, Soft calendering was performed under conditions of a surface temperature of 50 ° C. and a nip pressure of 50 kg / cm.

<Application>
On both sides of the above-mentioned calendered quality paper, the prepared coating solution for the topcoat layer was applied one side at a time using an extrusion die coater so that the dry weight per side was 20 g / m ² . The film was dried at a temperature of 70 ° C. and a wind speed of 10 m / sec for 1 minute to form an overcoat layer to obtain a recording medium.

<Preparation of colorless ink composition B1 (aggregation accelerator liquid)>
The aggregation accelerator liquid (colorless ink composition) was prepared by mixing the following materials.
(composition)
・ Citric acid 15g
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ... 1g
・ Ion exchange water: 84g

<Applying colorless ink composition B1 (acid treatment)>
The colorless ink composition B1 (aggregation accelerator liquid) was applied (applied) to the recording medium so as to be 5 g / m ² and dried at 60 ° C. and 15 m / s for 1 minute to obtain an inkjet recording medium A1. It was.

[Comparative Example 1]
In Example 1, the following ink composition N1 was used instead of the ink composition A1, and the same procedure was performed except that the ink droplet formation of the colorless ink composition B1 during image formation was omitted.

(Preparation of ink composition N1)
Using the dispersion N1 of pigment-containing resin particles, an ink composition N1 was prepared with the following composition.
(1) Pigment-containing resin particle dispersion N1 26.8 parts (2) Latex PL-01 24.2 parts (3) Compound having 3 moles of ethyleneoxy group added to sorbitol (SP value 35.1) 5 Parts (4) DPGmBE (SP value 20.5) 4 parts (5) DEGmBE (SP value 23.7) 8 parts (6) glycerin (SP value 41.0) 15 parts (7) thiodiglycol (SP value 31) .2) 2 parts (8) 1,5-pentanediol (SP value 29.0) 1 part (9) Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 part (10) Ion-exchanged water Remaining amount

[Comparative Example 2]
In the ink composition N1 of Comparative Example 1, (2) The latex was not used, and the water-soluble solvents (3) to (8) were used in the same manner except that the water-soluble solvents listed in Table 1 were used. Ink composition N2 was obtained. The same ink jet recording medium as in Comparative Example 1 was used.

[Comparative Example 3]
In Comparative Example 2, the pigment-containing resin particle dispersion N1 was changed to the crosslinked pigment-containing resin particle dispersion 1, and the water-soluble solvents (3) to (8) were listed in Table 1. The procedure was the same except that the solvent was changed.

Details of materials used in Examples and Comparative Examples are shown below.
Compound 1: Compound represented by structural formula (1) in which AO and l + m + n are defined in Table 1. DPGmBE: Dipropylene glycol monobutyl ether DEGmBE: Diethylene glycol monobutyl ether DPGmME: Dipropylene glycol monomethyl ether EGmBE: Ethylene glycol mono Butyl ether

  As is clear from Table 1, the comparative example was not good in all of the evaluations of curl, dispersion stability, and ejection stability, but the example was found to be excellent in all the evaluation items.

Claims (14)

(A) a pigment, (b) a water-soluble solvent, (c) water, and (d) resin fine particles, wherein the (a) pigment is dispersed with a water-soluble dispersant and then crosslinked with a crosslinking agent. An ink composition which is a pigment coated with a polymer,
An ink set comprising: a colorless ink composition containing an aggregation accelerator that promotes aggregation of the ink composition. 2. The ink set according to claim 1, wherein the water-soluble solvent (b) contains 90% by mass or more of a water-soluble solvent having an SP value of 27.5 or less. The ink set according to claim 1 or 2, wherein the content of the water-soluble solvent (b) is 10 to 30% by mass of the total ink composition. The ink set according to any one of claims 1 to 3, wherein the water-soluble solvent (b) includes a compound represented by the following structural formula (1).

(In the formula, l, m, and n are each independently an integer of 1 or more and l + m + n = 3 to 15. AO represents ethyleneoxy and / or propyleneoxy.) The ink set according to claim 4, wherein AO in the compound represented by the structural formula (1) is propyleneoxy. 6. The ink set according to claim 1, wherein the amount of the compound of the structural formula (1) occupies 50% by mass or more of the entire water-soluble solvent. The said water-soluble dispersant contains a carboxyl group or its salt in a molecule | numerator, and the said crosslinking agent is an epoxy compound more than bifunctional, The one of Claims 1-6 characterized by the above-mentioned. Ink set. The ink set according to claim 1, wherein the water-soluble dispersant has an acid value of 135 to 250 mg KOH / g. The ink set according to claim 1, wherein the aggregation accelerator is an acid. An image forming method using the ink set according to claim 1. A first step of applying the colorless ink composition in the ink set according to any one of claims 1 to 9 to a recording medium; and a recording medium to which the colorless ink composition is applied. The image forming method according to claim 10, further comprising a second step of applying the ink composition. 12. The image forming method according to claim 11, wherein the colorless ink composition is applied to the recording medium by ink jetting. The image forming method according to claim 11, wherein the colorless ink composition is applied to the recording medium by a coating method using a coating apparatus. In an image forming method for printing by applying an ink composition on an ink receiver recording medium,
The ink composition comprises (a) a pigment, (b) a water-soluble solvent, (c) water, and (d) resin fine particles,
The (a) pigment is a pigment coated with a polymer obtained by dispersing the pigment with a water-soluble dispersant and then crosslinking with a crosslinking agent, and the recording medium causes the ink composition to aggregate. An image forming method, characterized by being provided with a coagulation promoter to be promoted.