JP2013053173A - Ink composition, ink set, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition that can strike a balance between maintenance characteristics and heat stability with time.SOLUTION: The ink composition comprises: a pigment; water; a polymerizable compound having an acrylamide structure; a polymerization initiator; and a sugar alcohol having an SP value of 17.80 to 19.00 (cal/cm).

Description

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

Inkjet technology is known as an image recording method for recording a color image. Ink jet technology has been applied to fields such as office printers and home printers, but in recent years, it has been applied to commercial printing fields.
A pigment is widely used as one of the components of ink (ink composition) used in the ink jet technology. Various studies have been made so far regarding ink containing pigment (pigment ink) and an image forming method using the pigment ink.

For example, as an ink jet recording method excellent in density, gloss, image reliability, etc., an ink jet recording method is known in which an image containing a pigment and a wetting agent (such as sugar) is formed on a specific medium (recording medium). (For example, refer to Patent Document 1).
An ink composition comprising a pigment and a resin dispersant having an aromatic partial structure and a radically polymerizable group as an ink composition that can form an image having excellent glossiness and has excellent ejection stability and recoverability. Is known (see, for example, Patent Document 2).
Also, an ink composition for ink jet that includes a pigment, water, a permeable solvent, a wetting agent, and an ultraviolet curable resin emulsion as an ink composition that can suppress curling and cockling of the recording medium and has good drying properties. A thing is known (for example, refer patent document 3).

In addition, when the water in the ink evaporates and solidifies, the pigment ink remains solidified and hardly dissolves again. For this reason, when the pigment ink adheres to a member such as an ink-jet head and solidifies, clogging or non-ejection of the ink may occur at the nozzle tip.
Accordingly, liquids for cleaning (removing) or wiping off ink adhering to a member such as an ink jet head have been studied. Such a liquid is called a maintenance liquid, a cleaning liquid, or a cleaning liquid.
As a maintenance liquid used in the inkjet recording method, an inkjet maintenance liquid containing water and 0.3% by mass to 15% by mass of an alkylene glycol monoalkyl ether has been disclosed (for example, see Patent Document 4).

JP 2008-137369 A JP 2011-57830 A JP 2009-227762 A Japanese Patent Laid-Open No. 2005-7703

However, an aqueous curable ink containing a pigment, water, a polymerizable compound, and a polymerization initiator tends to be particularly difficult to remove (that is, poor in maintainability) when adhering to a member such as an inkjet head. Furthermore, if the removal property (maintenance property) is improved by adding a wetting agent to the aqueous curable ink, the thermal aging stability of the ink may be lowered.
This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives.
That is, an object of the present invention is to provide an ink composition having both maintainability and thermal aging stability, and an ink set including the ink composition.
Another object of the present invention is to provide an image forming method in which the ink set is used and an image can be stably formed over a long period of time.

As a result of intensive studies, the present inventor has incorporated a sugar alcohol having an SP value in a specific range into an aqueous curable ink containing a pigment, water, a polymerizable compound, and a polymerization initiator, and a polymerizable compound. By using a polymerizable compound having an acrylamide structure as the above, the inventors have obtained knowledge that both maintenance and thermal aging stability can be achieved, and the present invention has been completed based on this knowledge.
That is, specific means for achieving the above-described problem are as follows.

<1> A pigment, water, a polymerizable compound having an acrylamide structure, a polymerization initiator, and an SP value of 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less An ink composition comprising a sugar alcohol.

<2> The ink composition according to <1>, wherein the polymerizable compound having an acrylamide structure includes a compound represented by the following general formula (1).

[In General Formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 2 or more. ]

<3> The ink composition according to <1> or <2>, wherein the sugar alcohol is at least one selected from the group consisting of pentitol and hexitol.
<4> The sugar alcohol is at least one selected from the group consisting of sorbitol, xylitol, D-arabinitol, L-arabinitol, ribitol, D-iditol, galactitol, and mannitol <1> to <3> The ink composition according to any one of the above.
<5> The ink composition according to any one of <1> to <4>, wherein at least a part of a surface of the pigment is coated with a resin.
<6> The ink composition according to any one of <1> to <5>, wherein the polymerization initiator is a compound represented by the following general formula (A).

[In General Formula (A), m and n each independently represent an integer of 0 or more, and m + n represents an integer of 0 to 3]

<7> An ink set comprising the ink composition according to any one of <1> to <6>, and a treatment liquid containing a flocculant that aggregates the components in the ink composition.
<8> The ink set according to <7>, wherein the flocculant is at least one selected from an acidic compound, a polyvalent metal salt, and a cationic polymer.

<9> A treatment liquid application step in which the ink set according to <7> or <8> is used, the application of the treatment liquid onto a recording medium, and an ink application step of applying the ink composition onto the recording medium; And an image forming method.
<10> The image forming method according to <9>, further comprising a curing step of irradiating the ink composition applied on the recording medium with an active energy ray to cure the ink composition.
<11> The ink application step is a step of providing the ink composition on the treatment liquid provided on the recording medium, provided after the treatment liquid application step. <9> or <10> The image forming method described in 1.
<12> The image forming method according to any one of <9> to <11>, wherein the recording medium is a coated paper having a base paper and a coat layer containing an inorganic pigment.

According to the present invention, it is possible to provide an ink composition having both maintainability and thermal aging stability, and an ink set including the ink composition.
Further, according to the present invention, it is possible to provide an image forming method in which the ink set is used and an image can be stably formed over a long period of time.

It is a schematic block diagram which shows an example of the inkjet recording device used for implementation of the image forming method of this invention.

  Hereinafter, the ink composition, the ink set, and the image forming method of the present invention will be described in detail.

≪Ink composition≫
The ink composition of the present invention (hereinafter also referred to as “ink”) has a pigment, water, a polymerizable compound having an acrylamide structure, a polymerization initiator, and an SP value of 17.80 (cal / cm ³ ) ^1/2. The sugar alcohol which is above 19.00 (cal / cm ³ ) ^1/2 or less is included.
By making the ink composition of the present invention as described above, the maintenance property is improved and the thermal aging stability is improved.
The reason why this effect is obtained is that maintenance performance is improved by the sugar alcohol in the above SP value range, and the thermal aging stability of the ink is improved by the polymerizable compound having the sugar alcohol and acrylamide structure. Is done.
With respect to the effect of improving the thermal aging stability, it is presumed that the sugar alcohol is less likely to be reduced. It is estimated that the SP value of the sugar alcohol contributes to the effect of improving maintainability.
However, the present invention is not limited by the above reason.

In the “maintenance” in the present invention, the inkjet head for ejecting the ink composition and its ejection performance are maintained at or close to the initial state and maintained (maintenance), and the inkjet head is washed (cleaned). To maintain and maintain in better condition.
“Maintenance” in the present invention refers to detergency (removability) with respect to an ink composition (for example, an ink fixed substance).
Hereinafter, each component of the ink composition of the present invention will be described.

<Sugar alcohol having an SP value of 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less>
The ink composition of the present invention has an SP value of 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less, hereinafter referred to as “specific sugar alcohol”. At least one).
When the SP value is less than 17.80 (cal / cm ³ ) ^1/2 and when the SP value exceeds 19.00 (cal / cm ³ ) ^1/2 , both of them are ink compositions. The maintainability is reduced.
From the viewpoint of further improving maintainability, the SP value of the sugar alcohol is preferably 18.00 (cal / cm ³ ) ^1/2 or more and 18.80 (cal / cm ³ ) ^1/2 or less.

The “SP value” (solubility parameter, unit: (cal / cm ³ ) ^1/2 ) in the present invention is a value calculated by the following formula according to the Fedors method.
SP value (δ) = [ΣE _coh / ΣV] ^1/2
Here, ΣE _coh represents cohesive energy, and ΣV represents molar molecular volume.
Details of the “Fedors method” are described in R.A. F. Fedors, Polymer Engineering Science, 14, p. 147 to 154 (1967), and the SP value in the present invention is calculated by the method described in this document.

  Further, in the present invention, “sugar alcohol” refers to a polyhydric alcohol corresponding to those obtained by reducing the aldehyde group and the ketone group of the sugar to form primary and secondary alcohol groups, respectively.

The specific sugar alcohol is not particularly limited as long as the SP value is a sugar alcohol having the above range, and may be a sugar alcohol derived from a monosaccharide or a sugar alcohol derived from a polysaccharide including an oligosaccharide. May be.
From the viewpoint of more effectively achieving the effects of the present invention, it is preferably a sugar alcohol derived from a monosaccharide or oligosaccharide, more preferably a sugar alcohol derived from a monosaccharide or disaccharide. Derived sugar alcohols are particularly preferred.
Among these, the specific sugar alcohol is preferably at least one selected from the group consisting of pentitol and hexitol.
Hereinafter, although the specific example of the said specific sugar alcohol is shown, this invention is not limited to the following specific examples. In the following specific examples, numerical values in parentheses indicate SP values (unit: (cal / cm ³ ) ^1/2 ).
Examples of the pentitol include xylitol (18.11), D-arabinitol (18.11), L-arabinitol (18.11), ribitol (18.11) and the like.
Examples of the hexitol include sorbitol (18.65), D-iditol (18.65), galactitol (18.65), mannitol (18.65) and the like.

  The specific sugar alcohol is preferably at least one selected from the group consisting of sorbitol, xylitol, D-arabinitol, L-arabinitol, ribitol, D-iditol, galactitol, and mannitol, particularly preferably sorbitol, It is at least one selected from the group consisting of xylitol and mannitol, most preferably sorbitol or mannitol.

  Although there is no limitation in particular in content of the said specific sugar alcohol in the ink composition of this invention, 0.1-20 mass% is preferable with respect to the whole quantity of an ink composition, and 0.1-10 mass% is more. 1 to 10% by mass is preferable.

<Polymerizable compound having acrylamide structure>
The ink composition of the present invention contains at least one polymerizable compound having an acrylamide structure.
When the ink composition of the present invention contains a polymerizable compound having an acrylamide structure, the ink composition does not contain the polymerizable compound (for example, when a polymerizable compound having no acrylamide structure is used). The thermal aging stability of the product is improved.
Furthermore, the ink composition of the present invention contains a polymerizable compound having an acrylamide structure, so that it does not contain the polymerizable compound (for example, when a polymerizable compound having no acrylamide structure is used) The effect of improving the curing sensitivity can also be obtained.

  The polymerizable compound having an acrylamide structure is preferably a compound that polymerizes when irradiated with active energy rays (for example, radiation or light, or an electron beam).

  The polymerizable compound having an acrylamide structure is not particularly limited, but is preferably a water-soluble compound. Here, the term “water-soluble” means that it can be dissolved in water at a certain concentration or higher, and any substance that can be dissolved in water-based ink (preferably uniformly) may be used. Further, the solubility may be increased by adding a water-soluble organic solvent to be described later, and it may be dissolved (desirably uniformly) in the ink. Specifically, the solubility in water at 25 ° C. is preferably 5% by mass or more, and more preferably 10% by mass or more.

The polymerizable compound having an acrylamide structure may be a monofunctional polymerizable compound having an acrylamide structure or a polyfunctional polymerizable compound having an acrylamide structure.
Examples of the monofunctional polymerizable compound having an acrylamide structure include hydroxyethyl (meth) acrylamide, hydroxypropyl (meth) acrylamide, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, and the like. Hydroxyethyl (meth) acrylamide, most preferably hydroxyethyl acrylamide.
Here, “(meth) acrylamide” means acrylamide or methacrylamide.
Examples of the polyfunctional polymerizable compound having an acrylamide structure include a compound represented by the following general formula (1).

  The polymerizable compound having an acrylamide structure of the present invention preferably includes a polyfunctional polymerizable compound having an acrylamide structure from the viewpoint of improving curing sensitivity, and includes a compound represented by the following general formula (1). Is more preferable.

In general formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 2 or more.

The compound represented by the general formula (1) is a compound in which an unsaturated monomer is bonded to the linking group Q by an amide bond.
R ¹ represents a hydrogen atom or a methyl group, preferably a hydrogen atom.
Although there is no restriction | limiting in the valence n of the coupling group Q, from a viewpoint of improving superposition | polymerization efficiency and discharge stability, n = 2-6 is more preferable, and n = 2-4 is still more preferable.

  The linking group Q is not particularly limited as long as it is a group that can be linked to an acrylamide structure, but it is preferable that the linking group Q is selected from linking groups that satisfy the above-mentioned water solubility. Specific examples include residues from which one or more hydrogen atoms or hydroxyl groups have been removed from the following compound group X.

-Compound group X-
Ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4 -Butanediol, 2,3-butanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4 -Pentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,5 -Pentanetriol, thioglycol, Methylolpropane, ditrimethylolpropane, trimethylolethane, ditrimethylolethane, neopentyl glycol, pentaerythritol, dipentaerythritol, and their condensates, low molecular weight polyvinyl alcohol, or polyols such as sugars, ethylenediamine, diethylenetriamine, triethylene Polyamines such as tetramine, polyethyleneimine, and polypropylenediamine.

  Furthermore, a saturated or unsaturated group such as a methylene, ethylene, propylene, butylene group or a substituted or unsubstituted alkylene chain having 4 or less carbon atoms, and a pyridine ring, imidazole ring, pyrazine ring, piperidine ring, piperazine ring, morpholine ring, The functional group etc. which have the heterocyclic ring of can be illustrated.

  Of these, the linking group Q is preferably a residue of a polyol containing an oxyalkylene group (preferably an oxyethylene group), and a polyol containing three or more oxyalkylene groups (preferably an oxyethylene group). It is particularly preferred that it is a class of residues.

  Specific examples of the polymerizable compound having an acrylamide structure include the following polymerizable compounds.

The polymerizable compound having an acrylamide structure can be contained singly or in combination of two or more.
The content of the polymerizable compound having an acrylamide structure in the ink composition is preferably 5 to 50% by mass, more preferably 10 to 30% by mass with respect to the total mass of the ink composition, and 15 to 25% by mass. Is most preferred.

<Pigment>
The ink composition of the present invention contains at least one pigment.
There is no restriction | limiting in particular as said pigment, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient.
The pigment is preferably a pigment that is almost insoluble or hardly soluble in water from the viewpoint of ink colorability.

  There is no restriction | limiting in particular in the kind as said pigment, A conventionally well-known organic pigment or an inorganic pigment can be used.

  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 the pigment that can be used in the present invention include pigments described in paragraph numbers [0142] to [0145] of JP-A-2007-100071.

The above pigments may be used alone or in combination of a plurality of types selected from within each group or between groups.
The content of the pigment in the ink composition is preferably an amount of 1 to 25% by mass with respect to the total mass of the ink composition from the viewpoint of color density, granularity, ink stability, and ejection reliability. The amount of 2 to 20% by mass is more preferable.

(Dispersant)
In the ink composition of the present invention, the pigment is preferably dispersed by a dispersant.
The dispersant may be a polymer dispersant or a low molecular surfactant type dispersant, but a polymer dispersant is preferred. The polymer dispersant may be either a water-soluble polymer dispersant or a water-insoluble polymer dispersant.
Furthermore, in the ink composition of the present invention, it is preferable that at least a part of the surface is coated with a resin by dispersing the pigment with a polymer dispersant (resin). Hereinafter, a pigment having at least a part of its surface coated with a resin is also referred to as a “resin-coated pigment”.

The polymer dispersant may be either a water-soluble polymer dispersant or a water-insoluble polymer dispersant.
The polymer dispersant is preferably a water-insoluble polymer dispersant from the viewpoint of dispersion stability and dischargeability when applied to an ink jet system.

-Water-insoluble polymer dispersant-
The water-insoluble polymer dispersant (hereinafter, sometimes simply referred to as “dispersant”) is a water-insoluble polymer and is not particularly limited as long as the pigment can be dispersed. Can be used. The water-insoluble polymer dispersant can be constituted by including, for example, both a hydrophobic structural unit and a hydrophilic structural unit.
Here, “water-insoluble” means that the amount dissolved in 100 parts by mass (25 ° C.) of water is 5.0 parts by mass or less.

  Examples of the monomer constituting the hydrophobic structural unit include styrene monomers, alkyl (meth) acrylates, aromatic group-containing (meth) acrylates, and the like.

  Moreover, as a monomer which comprises the said hydrophilic structural unit, if it is a monomer containing a hydrophilic group, there will be no restriction | limiting in particular. Examples of the hydrophilic group include a nonionic group, a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Examples of the nonionic group include a hydroxyl group, an amide group (nitrogen atom is unsubstituted), a group derived from an alkylene oxide polymer (for example, polyethylene oxide, polypropylene oxide, etc.), a group derived from a sugar alcohol, and the like. .

  From the viewpoint of dispersion stability, the hydrophilic structural unit preferably includes at least a carboxyl group, and preferably includes a nonionic group and a carboxyl group.

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

  The water-insoluble polymer dispersant is preferably a vinyl polymer containing a carboxyl group from the viewpoint of pigment dispersion stability, and has at least a structural unit derived from an aromatic group-containing monomer as a hydrophobic structural unit. A vinyl polymer having a structural unit containing a carboxyl group as a hydrophilic structural unit is more preferable.

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

The content of the resin (water-insoluble polymer) in the resin-coated pigment is preferably 10 to 100% by mass with respect to the pigment from the viewpoint of pigment dispersibility, ink colorability, and dispersion stability. % By mass is more preferable, and 30 to 60% by mass is particularly preferable.
When the content of the dispersant in the resin-coated pigment is within the above range, the pigment is preferably coated with an appropriate amount of the dispersant, and it tends to be easy to obtain colored particles having a small particle size and excellent stability over time.

  The resin-coated pigment may contain other dispersant in addition to the water-insoluble polymer dispersant. For example, a conventionally known water-soluble low-molecular dispersant, water-soluble polymer, or the like can be used. The content of the dispersant other than the water-insoluble polymer dispersant can be used within the range of the content of the dispersant.

The resin-coated pigment is preferably configured to contain the pigment and the water-insoluble polymer dispersant from the viewpoints of dispersion stability and dischargeability.
The resin-coated pigment can be obtained as a dispersion of a resin-coated pigment, for example, by dispersing a mixture containing a pigment, a dispersant, and optionally a solvent (preferably an organic solvent) with a disperser.

The dispersion of the resin-coated pigment is, for example, a step of adding an aqueous solution containing a basic substance to a mixture of the pigment, the water-insoluble polymer dispersant, and an organic solvent that dissolves or disperses the dispersant (mixing / hydration). After the step), a step of removing the organic solvent (solvent removal step) can be provided to produce a dispersion. As a result, a dispersion of resin-coated pigment that is finely dispersed and excellent in storage stability can be produced.
Here, it is preferable that the organic solvent can dissolve or disperse the dispersant, but in addition, it is preferable that the organic solvent has a certain degree of affinity for water. Specifically, the solubility in water at 20 ° C. is preferably 10% by mass or more and 50% by mass or less.

  More specifically, the dispersion of the resin-coated pigment can be produced by a production method including the following step (1) and step (2), but is not limited thereto.

Step (1): A step of dispersing a mixture containing a basic substance and a solution containing water as a main component together with a pigment, a dispersant, and an organic solvent in which the dispersant is dissolved or dispersed Step (2): Removing at least a portion of the organic solvent from the mixture after the dispersion treatment;

  In the step (1), first, the dispersant is dissolved or dispersed in an organic solvent to obtain a mixture (mixing step). Next, a solution containing a colorant and a basic substance and containing water as a main component, water, and, if necessary, a surfactant and the like are added to the mixture and mixed and dispersed to obtain an oil-in-water dispersion. Get.

  The basic substance is used for neutralization of an anionic group (preferably a carboxyl group) that the polymer may have. There is no particular limitation on the degree of neutralization of the anionic group. Usually, the liquid property of the finally obtained dispersion of colorant particles is preferably, for example, a pH of 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the polymer.

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

In the production of the dispersion of the resin-coated pigment, a strong shearing force is used using a two-roll, three-roll, ball mill, tron mill, disper, kneader, kneader, homogenizer, blender, single-screw or twin-screw extruder, etc. Kneading and dispersing treatment can be performed while giving Details of kneading and dispersion are described in “Paint Flow and Pigment Dispersion” by TC Patton (published by John Wiley and Sons, 1964).
If necessary, use a vertical or horizontal sand grinder, pin mill, slit mill, ultrasonic disperser, etc., and fine dispersion using beads made of glass having a particle diameter of 0.01 to 1 mm, zirconia, etc. It can be obtained by performing processing.

  The method of removing the organic solvent in the production of the resin-coated pigment dispersion is not particularly limited, and can be removed by a known method such as vacuum distillation.

  The resin-coated pigment in the resin-coated pigment dispersion thus obtained maintains a good dispersion state, and the resulting colored particle dispersion has excellent temporal stability.

  In the present invention, the volume average particle diameter of the resin-coated pigment is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the volume average particle size is 200 nm or less, the color reproducibility is good, and in the case of the ink jet method, the droplet ejection characteristics are good. Moreover, light resistance becomes favorable because a volume average particle diameter is 10 nm or more.

The particle size distribution of the resin-coated pigment is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Further, two or more types of resin-coated faces having a monodisperse particle size distribution may be mixed and used.
The volume average particle size and particle size distribution of the resin-coated pigment can be measured using, for example, a light scattering method.

  In the present invention, the above resin-coated pigments may be used alone or in combination of two or more.

<Polymerization initiator>
The ink composition of the present invention contains at least one polymerization initiator.
A known polymerization initiator can be used as the polymerization initiator. Among these, a radical polymerization initiator is preferable.
Examples of the radical polymerization initiator include (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic oxides, (e) thio compounds, (f) hexa An arylbiimidazole compound, (g) a ketoxime ester compound, (h) a borate compound, (i) an azinium compound, (j) a metallocene compound, (k) an active ester compound, (l) a compound having a carbon halogen bond, and ( m) alkylamine compounds and the like.
Specific examples of the polymerization initiator include, for example, polymerization initiators described on pages 65 to 148 of “Ultraviolet curing system” written by Kiyosuke Kato (published by General Technology Center Co., Ltd .: 1989). Can do.

  As the polymerization initiator in the present invention, a water-soluble polymerization initiator or the like can be used. The term “water-soluble” as used herein means that 0.5% by mass or more dissolves in distilled water at 25 ° C. The water-soluble polymerization initiator is preferably dissolved at 1% by mass or more in distilled water at 25 ° C., more preferably at least 3% by mass.

Examples of the water-soluble polymerization initiator include compounds represented by the following general formula (A), compounds described in JP-A-2005-307198, and the like.
Especially, it is preferable that it is a water-soluble polymerization initiator represented with the following general formula (A) from a viewpoint which shows the effect of this invention more effectively.

In general formula (A), m and n each independently represent an integer of 0 or more, and m + n represents an integer of 0 to 3.
In the general formula (A), m is preferably 0 to 3 and n is preferably 0 or 1, more preferably m is 0 or 1 and n is 0.
Specific examples of the compound represented by the general formula (A) are shown below, but the present invention is not limited thereto.

  The compound represented by the general formula (A) may be a compound synthesized according to the description in JP-A-2005-307198 or a commercially available compound. Examples of commercially available compounds represented by the general formula (A) include Irgacure 2959 (m = 0, n = 0).

In the ink composition of the present invention, the polymerization initiator may be used alone or in combination of two or more.
The content of the polymerization initiator in the ink composition of the present invention is preferably in the range of 0.1 to 30% by mass in terms of solid content, more preferably in the range of 0.5 to 20% by mass, More preferably, it is in the range of 1.0 to 15% by mass.
Moreover, 0.1-20 mass% is preferable with respect to the whole quantity of an ink composition, as for content of the said polymerization initiator, 0.1-10 mass% is more preferable, and 1-10 mass% is especially preferable.

<Water>
The ink composition of the present invention contains water.
That is, the ink composition of the present invention is an aqueous ink composition.
As water in this invention, it is preferable to use water which does not contain ionic impurities, such as ion-exchange water and distilled water.
The water content in the ink composition is appropriately selected according to the purpose, but is preferably 10 to 95% by mass, and more preferably 30 to 90% by mass.

<Water-soluble organic solvent>
The ink composition in the invention may contain at least one water-soluble organic solvent.
Examples of the water-soluble organic solvent include, for example, alkanediols (polyhydric alcohols) such as glycerin, ethylene glycol, and propylene glycol; sugar alcohols; C 1 to C 4 such as ethanol, methanol, butanol, propanol, and isopropanol. Alkyl glycols of 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, triethylene glycol monoethyl 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, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether , Dipropylene glycol mono-iso-propyl ether, tripropylene glycol monomethyl Glycol ethers such as ether, and the like. These can be used individually by 1 type or in combination of 2 or more types.

  As the water-soluble organic solvent, for example, known water-soluble organic solvents described in paragraphs 0124 to 0135 of JP2011-074150, paragraphs 0104 to 0119 of JP2011-079901A, and the like may be used. it can.

  When the ink composition in the present invention contains a water-soluble organic solvent, the content thereof is preferably 60% by mass or less, and more preferably 40% by mass or less based on the total amount of the ink composition.

<Resin particles>
The ink composition in the present invention can contain resin particles as necessary.
The resin particles have a function of fixing the ink composition, that is, the image by increasing the viscosity of the ink by aggregating or destabilizing the ink when contacting the processing liquid described above or the paper region where the processing liquid is dried. It is preferable to have. Such resin particles are preferably dispersed in at least one of water and an organic solvent.

Resin particles include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, styrene resins, crosslinked acrylic resins, crosslinked styrene resins, and benzoguanamine resins. A phenol resin, a silicone resin, an epoxy resin, a urethane resin, a paraffin resin, a fluorine resin, or a latex thereof can be used. Preferred examples include acrylic resins, acrylic-styrene resins, styrene resins, cross-linked acrylic resins, and cross-linked styrene resins.
The resin particles can also be used in the form of latex.

The weight average molecular weight of the resin particles is preferably 10,000 or more and 200,000 or less, more preferably 20,000 or more and 200,000 or less.
The volume average particle size of the resin particles is preferably in the range of 1 nm to 1 μm, more preferably in the range of 1 to 200 nm, still more preferably in the range of 1 to 100 nm, and particularly preferably in the range of 1 to 50 nm. The volume average particle diameter of the resin particles can be measured by a nanotrack particle size distribution measuring apparatus UPA-EX150 (manufactured by Nikkiso Co., Ltd.).

  The glass transition temperature Tg of the resin particles is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher.

It is preferable to use self-dispersing resin particles (self-dispersing resin particles) as the resin particles.
Here, the self-dispersing resin is dispersed in an aqueous medium by a functional group (particularly an acidic group or a salt thereof) of the polymer itself when dispersed by the phase inversion emulsification method in the absence of a surfactant. A water-insoluble polymer that can be in a state.
Here, the dispersed state refers to an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium. It includes both states.
As the self-dispersing resin particles, the self-dispersing resin particles described in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-068805A can be used. .

The content of the resin particles is preferably 0.1 to 20% by mass, more preferably 0.1 to 15% by mass, and further preferably 0.1 to 10% by mass with respect to the total amount of the ink composition.
Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a resin microparticle, What has a wide particle size distribution or a thing with a monodispersed particle size distribution may be sufficient. Two or more kinds of resin particles having a monodispersed particle size distribution may be mixed and used.

<Surfactant>
The ink composition in the present invention can contain at least one surfactant as required. The surfactant can be used as a surface tension adjusting agent.

As a surface tension modifier, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Either a surfactant or a betaine surfactant can be used. Further, the above dispersant (polymer dispersant) may be used as a surfactant.
In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing ink droplet ejection interference, and an acetylene glycol derivative (acetylene glycol surfactant) is more preferable.

  Examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4, An alkylene oxide adduct of 7-diol can be used, and at least one selected from these is preferable. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

  When a surfactant (surface tension adjusting agent) is contained in the ink composition, the surfactant has a surface tension of 20 to 60 mN / m from the viewpoint of satisfactorily discharging the ink composition by an ink jet method. It is preferable to contain the quantity of the range which can be adjusted, More preferably, it is 20-45 mN / m from the point of surface tension, More preferably, it is 25-40 mN / m.

  The specific amount of the surfactant in the ink composition of the surfactant is not particularly limited except that the range of the surface tension is preferable, and is preferably 0.1% by mass or more, more preferably 0.8%. It is 1-10 mass%, More preferably, it is 0.2-3 mass%.

<Other ingredients>
The ink composition of the present invention can contain various additives as other components, if necessary.
Examples of the various additives include, for example, ultraviolet absorbers, antifading agents, antifungal agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents, viscosity modifiers, and dispersions. Known additives such as stabilizers or chelating agents can be used.

  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 anti-fading agent, various organic and metal complex anti-fading agents can be used. Examples of organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, and metal complexes. There are nickel complex, zinc complex and the like.

Examples of the antifungal agent include, for example, sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, ethyl p-hydroxybenzoate, 1,2-benzisothiazolin-3-one, sodium sorbate, pentachlorophenol Sodium etc. are mentioned.
The antifungal agent preferably has a content in the ink composition 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. For example, alcohol amines (for example, diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol, etc.), alkali metal hydroxides (for example, lithium hydroxide, sodium hydroxide, potassium hydroxide) Etc.), ammonium hydroxide (for example, ammonium hydroxide, quaternary ammonium hydroxide, etc.), phosphonium hydroxide, alkali metal carbonate 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.

<Physical properties of ink composition>
The surface tension (25 ° C.) 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 / m or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less.
The surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

The viscosity at 25 ° C. of the ink composition of the present invention 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. Is 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under conditions of 25 ° C.

≪Ink set≫
The ink set of the present invention has at least one of the ink compositions of the present invention described above and at least one treatment liquid containing a flocculant that aggregates the components in the ink composition.
By using the treatment liquid together with the ink composition of the present invention described above, it is possible to increase the speed of ink jet recording, and even with high speed recording, images with high density and high resolution (for example, reproducibility of fine lines and fine parts). Is obtained.
In addition, when the treatment liquid contains a flocculant, an image having excellent image quality and excellent blocking resistance can be formed.

(Flocculant)
The treatment liquid contains an aggregating agent that aggregates the components in the ink composition.
The aggregating agent is capable of aggregating (fixing) the ink composition by contacting the ink composition on the recording medium, and functions as a fixing agent. For example, when the treatment liquid is applied to a recording medium (preferably coated paper), the ink composition further drops and comes into contact with the aggregating agent in the state where the aggregating agent is present on the recording medium. In addition, the components in the ink composition can be aggregated to fix the ink composition on the recording medium.

  Examples of the component for fixing the component in the ink composition include an acidic compound, a cationic polymer, and a polyvalent metal salt. These can be used alone or in combination of two or more.

-Acidic compounds-
Examples of the acidic compound include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, 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, metaphosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, and derivatives of these compounds, In addition, preferable examples thereof include salts thereof.

Among these, acidic compounds with high water solubility are preferable. Further, from the viewpoint of fixing the whole ink by reacting with the ink composition, an acidic compound having a valence of 3 or less is preferable, and an acidic compound having a valence of 2 to 3 is particularly preferable.
An acidic compound may be used individually by 1 type, and may use 2 or more types together.

  When the treatment liquid contains an acidic compound, the pH (25 ° C.) of the treatment liquid is preferably 0.1 to 6.8, more preferably 0.5 to 6.0, 0.8 More preferably, it is -5.0.

The content of the acidic compound is preferably 40% by mass or less, and more preferably 15 to 40% by mass with respect to the total mass of the treatment liquid. By setting the content of the acidic compound to 15 to 40% by mass, the components in the ink composition can be more efficiently fixed.
Furthermore, it is preferable that content of an acidic compound is 15 mass%-35 mass% with respect to the total mass of the said processing liquid.

-Multivalent metal salt-
The polyvalent metal salt is a compound containing a divalent or higher metal such as an alkaline earth metal or a zinc group metal, and examples thereof include acetates and oxides of metal ions such as Ca ²⁺ , Cu ²⁺ and Al ^3+. Can do.

  When the ink composition is ejected onto a recording medium to which the treatment liquid containing the polyvalent metal salt is applied, the aggregation reaction of the ink composition is stable dispersion of particles such as pigments dispersed in the ink composition. This can be achieved by reducing the properties and increasing the viscosity of the entire ink composition. For example, when particles such as pigments in the ink composition have weakly acidic functional groups such as carboxyl groups, the particles are dispersed and stabilized by the action of the weakly acidic functional groups. It can be reduced by interacting with the polyvalent metal salt, and the dispersion stability can be lowered. Therefore, the polyvalent metal salt as the immobilizing agent contained in the treatment liquid needs to have a valence of 2 or more, that is, multivalent from the viewpoint of the aggregation reaction, and from the viewpoint of the aggregation reactivity, 3 A polyvalent metal salt composed of a polyvalent metal ion having a valence higher than that is preferable.

  From the above viewpoint, the polyvalent metal salt that can be used in the treatment liquid in the present invention is any one or more of the following salts of polyvalent metal ions and anions, polyaluminum hydroxide, and polyaluminum chloride. Preferably there is.

Examples of the polyvalent metal ions include Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Sr ²⁺ , Zn ²⁺ , Ba ²⁺ , Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ , Fe ²⁺ , La ³⁺ , Nd ³⁺ , Y ³⁺ , Zr ^{4+ and the} like. In order to contain these polyvalent metal ions in the treatment liquid, the polyvalent metal salt may be used.
The salt is a metal salt composed of the above polyvalent metal ions and an anion that binds to these ions, but is preferably soluble in a solvent. Here, the said solvent is a medium which comprises a process liquid with a polyvalent metal salt, for example, water and the organic solvent mentioned later are mentioned.

Preferred anions for forming a salt with the polyvalent metal ion include, for example, Cl ⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ⁻ , CH ₃ COO ⁻ , SO ₄ ^{2− and the} like. .
A polyvalent metal ion and an anion can form a salt of a polyvalent metal ion and an anion, respectively, using a single species or a plurality of species.

  Examples of other polyvalent metal salts include polyaluminum hydroxide and polyaluminum chloride.

Examples of the polyvalent metal salt, reactivity and coloring properties, more in view of ease of handling, it is preferable to use a salt of a polyvalent metal ion and an anion, the polyvalent metal ion, Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Al ³⁺ and Y ³⁺ are preferred, and Ca ²⁺ is more preferred.
Further, as the anion, NO ₃ ⁻ is particularly preferable from the viewpoint of solubility and the like.
The said polyvalent metal salt can be used individually by 1 type or in mixture of 2 or more types.

It is preferable that content of the said polyvalent metal salt is 15 mass% or more with respect to the total mass of the said process liquid. Thereby, the component in an ink composition can be more effectively fixed.
The content of the polyvalent metal salt is preferably 15% by mass to 35% by mass with respect to the total mass of the treatment liquid.

The amount of the polyvalent metal salt applied to the recording medium is not particularly limited as long as it is an amount sufficient to aggregate the ink composition, but 0.5 g / m ² from the viewpoint that the ink composition can be easily fixed. it is preferably to 4.0 g / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

-Cationic polymer-
The cationic polymer includes at least one cationic polymer selected from poly (vinyl pyridine) salt, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide, and polyguanide. It is.
A cationic polymer may be used individually by 1 type, and may use 2 or more types together.

  Among the cationic polymers, polyguanides (preferably poly (hexamethyleneguanidine) acetate, polymonoguanide, polymeric biguanide), polyethyleneimine, and poly (vinylpyridine), which are advantageous from the viewpoint of aggregation rate, are preferable.

  The weight average molecular weight of the cationic polymer is preferably smaller in terms of the viscosity of the treatment liquid. When the treatment liquid is applied to the recording medium by an inkjet method, a range of 500 to 500,000 is preferable, a range of 700 to 200,000 is more preferable, and a range of 1,000 to 100,000 is more preferable. . When the weight average molecular weight is 500 or more, it is advantageous from the viewpoint of aggregation speed, and when it is 500,000 or less, it is advantageous from the viewpoint of ejection reliability. However, this is not the case when the treatment liquid is applied to the recording medium by a method other than inkjet.

  When the treatment liquid contains a cationic polymer, the pH (25 ° C.) of the treatment liquid is preferably 1.0 to 10.0, more preferably 2.0 to 9.0, and 3. More preferably, it is 0-7.0.

The content of the cationic polymer is preferably 1% by mass to 35% by mass and more preferably 5% by mass to 25% by mass with respect to the total mass of the treatment liquid.
The amount of the cationic polymer applied to the coated paper is not particularly limited as long as it is an amount sufficient to stabilize the ink composition, but 0.5 g / m from the viewpoint that the ink composition is easily fixed. it is preferably ^{2 ~4.0g} / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

≪Image formation method≫
In the image forming method of the present invention, the ink set of the present invention described above is used, and an ink applying step of applying the ink composition of the present invention described above onto the recording medium, and applying the treatment liquid onto the recording medium. And a treatment liquid applying step. The image forming method of the present invention may further include other steps as necessary.

<Ink application process>
The ink application step is a step of applying the ink composition of the present invention described above onto a recording medium by, for example, an inkjet method.
In this step, the ink composition can be selectively applied onto the recording medium, and a desired visible image can be formed. The details of the ink composition, such as details and preferred embodiments of the ink composition, are as described above in the description of the ink composition.

  Specifically, the image recording using the ink-jet method is performed by supplying energy to obtain a desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and JP-A-8-27693. Publication No. 2-276670, No. 7-276789, No. 9-323475, No. JP-A-62-238783, JP-A-10-153898, No. 10-217473, No. 10- No. 235995, No. 10-337947, No. 10-217597, No. 10-337947, etc. Liquid composition for ink jet paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. This can be done by discharging objects. As a preferable ink jet recording method for the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

  The inkjet method is not particularly limited, and is a known method, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, an electric method An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink with ink and ejects the ink using radiation pressure, and a thermal ink jet (bubble jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used. As an ink jet method, in particular, the method described in Japanese Patent Application Laid-Open No. Sho 54-59936 causes an abrupt volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force due to this state change. Ink jet method can be used effectively.

  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, thermal 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.

Specific examples of the ink jet recording method are shown below.
As an ink jet recording method, there is (1) a method called an electrostatic attraction method. In the electrostatic suction method, a strong electric field is applied between the nozzle and the acceleration electrode arranged in front of the nozzle, and droplet-like ink is continuously ejected from the nozzle, and the ink droplet passes between the deflection electrodes. In the meantime, by supplying a printing information signal to the deflection electrode, the ink droplets are blown onto the recording medium to fix the ink on the recording medium, and the image is recorded or printing is performed without deflecting the ink droplets. In this method, an image is fixed on a recording medium by ejecting ink droplets from a nozzle toward the recording medium in accordance with an information signal.

  Further, (2) there is a method of forcibly ejecting ink droplets from the nozzles by applying pressure to the ink liquid with a small pump and mechanically vibrating the ink-jet nozzle with a crystal resonator or the like. The ink droplet ejected from the nozzle is charged at the same time as it is ejected, and while the ink droplet passes between the deflection electrodes, a print information signal is given to the deflection electrode to fly the ink droplet toward the recording medium, This is a method for recording an image on a recording medium.

  Next, (3) a method of simultaneously applying pressure and a print information signal to the ink liquid by a piezoelectric element, ejecting ink droplets from the nozzles toward the recording medium, and recording an image on the recording medium (piezo), (4) A method for recording an image on a recording medium by injecting the ink liquid from a nozzle toward a recording medium by expanding the bubbles by heating the ink liquid using microelectrodes in accordance with print signal information (bubble Jet (registered trademark).

  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 image forming 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.

  The amount of ink droplets ejected from the inkjet head is preferably 1 to 10 pl (picoliter) and more preferably 1.5 to 6 pl from the viewpoint of obtaining a high-definition image. In addition, from the viewpoint of improving the unevenness of the image and the continuous gradation, it is also effective to discharge different amounts of liquids in combination, and even in such a case, the present invention can be suitably used.

<Processing liquid application process>
The treatment liquid application step is a step of applying a treatment liquid containing an aggregating agent for aggregating components in the ink composition onto a recording medium.
The treatment liquid applied on the recording medium in this step and the ink composition applied on the recording medium in the ink application step contact to form an image. In this case, dispersed particles such as pigments in the ink composition aggregate and the image is fixed on the recording medium. The treatment liquid contains at least a flocculant, and details and preferred embodiments of each component 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 blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater or the like can be used. The details of the inkjet method are as described above.

The treatment liquid application step may be provided either before or after the ink application step using the ink composition.
In the present invention, an embodiment in which an ink application process is provided after the treatment liquid application process is preferable. In other words, the above-described ink application step is a step of providing the above-described ink composition on the treatment liquid provided on the recording medium in the main-treatment liquid application step provided after the main-treatment liquid application step. It is preferable. Specifically, before applying the ink composition onto the recording medium, the treatment liquid is applied in advance, and the ink composition is applied so as to come into contact with the processing liquid applied onto the recording medium. A mode of imaging is preferred. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

The amount of the treatment liquid applied in the treatment liquid application step is not particularly limited as long as the ink composition can be aggregated, but preferably the amount of the aggregation agent applied is 0.1 g / m ² or more. Can do. Especially, the quantity from which the provision amount of a flocculant will be 0.2-0.7 g / m < ² > is preferable. When the applied amount of the flocculant is 0.1 g / m ² or more, good high-speed flocculence can be maintained according to various usage forms of the ink composition. Further, it is preferable that the amount of the flocculant applied is 0.7 g / m ² or less because the surface properties of the applied recording medium are not adversely affected (such as a change in gloss).

  In the present invention, an ink application step is provided after the treatment liquid application step, and the treatment liquid on the recording medium is heated and dried after the treatment liquid is applied on the recording medium and before the ink composition is applied. It is preferable to further provide a heat drying step. By heating and drying the treatment liquid in advance before the ink application 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.

<Curing process>
The image forming method of the present invention preferably further includes a curing step of irradiating the ink composition applied onto the recording medium in the ink applying step with an active energy ray to cure the ink composition.
Examples of the active energy rays used here include α rays, γ rays, electron rays, X rays, ultraviolet rays, visible light, and infrared rays. Of these, ultraviolet rays are preferable.
By the curing step, the monomer component (polymerizable compound) in the image can be surely polymerized and cured. At this time, if the light source for irradiating the active energy ray is disposed opposite to the recording surface of the recording medium and the entire recording surface is irradiated, the entire image can be cured. Note that an ultraviolet irradiation lamp, a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation apparatus, or the like can be adopted as a light source for irradiating active energy rays.
The curing step is provided at least after the ink application step, but is preferably provided after the ink application step and the treatment liquid application step.

The irradiation condition of the active energy ray is not particularly limited as long as the polymerizable compound can be polymerized and cured. For example, the wavelength of the active energy ray is, for example, preferably 200 to 600 nm, more preferably 300 to 450 nm, and further preferably 350 to 420 nm.
The output of the actinic energy ray is preferably at 5000 mJ / cm ² or less, more preferably 10~4000mJ / cm ^2, further preferably 20~3000mJ / cm ^2.

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

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

  Among the recording media, coated paper used for general offset printing is preferable. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not surface-treated. The coated paper is liable to cause quality problems such as glossiness and scratch resistance of the image in normal aqueous inkjet image formation. However, in the image forming method of the present invention, gloss unevenness is suppressed and glossiness and resistance to abrasion are reduced. An image having good rubbing properties can be obtained. In particular, a coated paper having a base paper and a coat layer containing an inorganic pigment is preferably used, and a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate is more preferably used. Specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

<Inkjet recording apparatus>
Next, an example of an ink jet recording apparatus suitable for carrying out the image forming method of the present invention will be specifically described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating a configuration example of the entire inkjet recording apparatus.

  As shown in FIG. 1, the ink jet recording apparatus includes a processing liquid application unit 12 including a processing liquid discharge head 12S that sequentially discharges a processing liquid in the recording medium conveyance direction (the arrow direction in the figure); A treatment liquid drying zone 13 provided with a heating means (not shown) for drying the applied treatment liquid, an ink ejection part 14 for ejecting various ink compositions, and an ink drying zone 15 for drying the ejected ink composition. Are arranged. Further, an ultraviolet irradiation unit 16 including an ultraviolet irradiation lamp 16S is disposed on the downstream side of the ink drying zone 15 in the conveyance direction of the recording medium.

  The recording medium supplied to the ink jet recording apparatus includes a processing liquid application unit 12, a processing liquid drying zone 13, and an ink discharging unit by a conveying roller from a paper feeding unit that feeds the recording medium from a case loaded with the recording medium. 14, the ink drying zone 15, and the ultraviolet irradiation unit 16 are sequentially sent and accumulated in the accumulation unit. In addition to the method using a conveyance roller, the conveyance may be performed by a drum conveyance method using a drum-shaped member, a belt conveyance method, a stage conveyance method using a stage, or the like.

  Among the plurality of transport rollers, at least one roller may be a driving roller to which the power of a motor (not shown) is transmitted. By rotating a driving roller rotated by a motor at a constant speed, the recording medium is conveyed in a predetermined direction by a predetermined conveyance amount.

  The treatment liquid application unit 12 is provided with a treatment liquid discharge head 12S connected to a storage tank that stores the treatment liquid. The treatment liquid ejection head 12S can eject the treatment liquid from ejection nozzles arranged to face the recording surface of the recording medium, and can apply the treatment liquid on the recording medium. The treatment liquid application unit 12 is not limited to a method of discharging from a nozzle-shaped head, and an application method using an application roller can be employed. In this coating method, the treatment liquid can be easily applied to almost the entire surface including the image area where the ink droplets land on the recording medium by the ink discharge unit 14 disposed on the downstream side. In order to make the thickness of the processing liquid on the recording medium constant, for example, an air knife or a member having a sharp corner is provided with a gap corresponding to the specified amount of the processing liquid provided between the recording medium and the recording medium. You may provide the method of doing.

  A treatment liquid drying zone 13 is disposed downstream of the treatment liquid application unit 12 in the recording medium conveyance direction. The treatment liquid drying zone 13 can be configured by using a known heating means such as a heater, an air blowing means using air blowing such as a dryer, or a combination of these. The heating means may be a method of installing a heating element such as a heater on the side opposite to the barrier layer forming surface of the recording medium (for example, below the conveyance mechanism that carries the recording medium when the recording medium is automatically conveyed) Examples include a method of applying warm air or hot air to the surface of the medium on which the barrier layer is formed, a heating method using an infrared heater, and the like.

In addition, since the surface temperature of the recording medium changes depending on the type (material, thickness, etc.) of the recording medium, the environmental temperature, etc., the measuring unit for measuring the surface temperature of the recording medium and the surface of the recording medium measured by the measuring unit It is preferable to provide a control mechanism that feeds back the temperature value to the heating control unit to form the blocking layer while controlling the temperature. As a measurement part which measures the surface temperature of a recording medium, a contact or non-contact thermometer is preferable.
Further, the solvent may be removed using a solvent removal roller or the like. As another embodiment, a method of removing excess solvent from the recording medium with an air knife is also used.

  The ink discharge unit 14 is disposed downstream of the treatment liquid drying zone 13 in the recording medium conveyance direction. The ink discharge section 14 includes a recording head (ink discharge head) 30K connected to each of the ink storage sections that store black (K), cyan (C), magenta (M), and yellow (Y) color inks. 30C, 30M, and 30Y are arranged. Each ink storage unit (not shown) stores an ink composition corresponding to each hue, and is supplied to each of the ink ejection heads 30K, 30C, 30M, and 30Y as necessary when recording an image. It has become. Further, as shown in FIG. 1, a recording head 30A for spot color ink discharge is provided on the downstream side in the transport direction of the ink discharge heads 30K, 30C, 30M, and 30Y so that spot color ink can be discharged as needed. 30B can be further provided.

  The ink ejection heads 30K, 30C, 30M, and 30Y each eject ink corresponding to an image from ejection nozzles arranged to face the recording surface of the recording medium. Thus, each color ink is applied on the recording surface of the recording medium, and a color image is recorded.

  In each of the treatment liquid discharge head 12S and the ink discharge heads 30K, 30C, 30M, 30Y, 30A, and 30B, a large number of discharge ports (nozzles) are arranged over the maximum recording width of the image recorded on the recording medium. Has become a full line head. Compared to the serial type in which recording is performed while reciprocating a short shuttle head in the width direction of the recording medium (direction perpendicular to the conveying direction on the recording medium conveying surface), it is possible to record an image on the recording medium at a higher speed. it can. In the present invention, either a serial type recording or a method capable of relatively high-speed recording, for example, a method capable of recording by ejecting in the main scanning direction by a single pass forming one line in one scan. However, according to the image recording method of the present invention, a high-quality image with high reproducibility can be obtained even by a single-pass method.

  Here, the treatment liquid discharge head 12S and the ink discharge heads 30K, 30C, 30M, 30Y, 30A, and 30B all have the same structure.

  The application amount of the treatment liquid and the application amount of the ink composition are preferably adjusted as necessary. For example, the application amount of the treatment liquid may be changed according to the recording medium in order to adjust the physical properties such as the viscoelasticity of the aggregate formed by mixing the treatment liquid and the ink composition.

  The ink drying zone 15 is disposed downstream of the ink discharge unit 14 in the recording medium conveyance direction. The ink drying zone 15 can be configured in the same manner as the treatment liquid drying zone 13.

The ultraviolet irradiation unit 16 is arranged further downstream in the recording medium conveyance direction of the ink drying zone 15, and is irradiated with ultraviolet rays by an ultraviolet irradiation lamp 16S provided in the ultraviolet irradiation unit 16, and in the image after image drying. The monomer component is polymerized and cured. The ultraviolet irradiation lamp 16S irradiates the entire recording surface with a lamp disposed opposite to the recording surface of the recording medium, so that the entire image can be cured. The ultraviolet irradiation unit 16 is not limited to the ultraviolet irradiation lamp 16S, and a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation device, or the like can also be employed.
The ultraviolet irradiation unit 16 may be installed either before or after the ink drying zone 15, or may be installed both before and after the ink drying zone 15.

  Further, in the ink jet recording apparatus, a heating unit that performs a heat treatment on the recording medium can be arranged in a conveyance path from the paper feeding unit to the stacking unit. For example, the temperature of the recording medium is raised to a desired temperature by disposing a heating unit at a desired position such as the upstream side of the treatment liquid drying zone 13 or between the ink discharge unit 14 and the ink drying zone 15. Thus, drying and fixing can be effectively performed.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

[Examples 1 to 17 and Comparative Examples 1 to 7]
<< Preparation of ink composition >>
Cyan inks (C1) to (C24), magenta ink (M1), yellow ink (Y1), and black ink (K1) were prepared as ink compositions as follows.

<Preparation of cyan ink (C1)>
(Synthesis of polymer dispersant P-1)
To a 1000 ml three-necked flask equipped with a stirrer and a condenser tube, 88 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Here, 50 g of methyl ethyl ketone was mixed with 0.85 g of dimethyl 2,2′-azobisisobutyrate and 60 g of benzyl methacrylate. Then, 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 of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess of hexane, and the precipitated resin was dried to obtain 96 g of a polymer dispersant P-1 having the following structure.

The composition of the obtained resin was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

(Preparation of resin-coated cyan pigment dispersion (C))
10 parts of Pigment Blue 15: 3 (phthalocyanine blue A220, manufactured by Dainichi Seika Co., Ltd.), 5 parts of the above polymer dispersant P-1, 42 parts of methyl ethyl ketone, and 5 mol of 1 mol / L NaOH aqueous solution. 0.5 part 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 under reduced pressure at 55 ° C., and a part of water was further removed to obtain a dispersion of resin-coated cyan pigment having a pigment concentration of 10.2% by mass (resin-coated cyan pigment). Dispersion (C)) was obtained.

(Preparation of cyan ink (C1))
Components of the following composition were mixed, and then filtered through a 5 μm membrane filter to prepare cyan ink C-1.

-Composition of cyan ink (C1)-
Resin-coated cyan pigment dispersion (C): 6% (solid content concentration)
・ Irgacure 2959 (polymerization initiator; manufactured by BASF Japan Ltd.) 3%
・ Polymerizable compound 2 (polymerizable compound having an acrylamide structure) 20%
・ Orphine E1010 (manufactured by Nissin Chemical Co., Ltd .; surfactant) 1%
Sorbitol (SP value 18.65 (cal / cm ³ ) ^1/2 ) 3%
・ Ion-exchanged water: Remaining amount (added so that the total amount of ink is 100%)

The polymerizable compound 2 was synthesized as follows.
First, 40.0 g (182 mmol) of 4,7,10-trioxa-1,13-tridecanediamine, 37.8 g (450 mmol) of sodium bicarbonate, 100 g of water and 300 mL of tetrahydrofuran were added to a 1 L three-necked flask equipped with a stirrer. In an ice bath, 35.2 g (389 mmol) of acrylic acid chloride was added dropwise over 20 minutes. After dropping, the mixture was stirred at room temperature for 5 hours, and then tetrahydrofuran was distilled off from the obtained reaction mixture under reduced pressure. Next, the aqueous layer was extracted four times with 200 ml of ethyl acetate, and the obtained organic layer was dried over magnesium sulfate, filtered, and evaporated under reduced pressure to obtain 35.0 g of a white solid of polymerizable compound 2 ( 107 mmol, 59% yield).

<Preparation of cyan inks (C2) to (C24)>
In the preparation of cyan ink (C1), the same procedure as in the preparation of cyan ink (C1) was conducted, except that polymerizable compound 2 and sorbitol were changed as shown in the polymerizable compound column and the wetting agent column in Table 1 below, respectively. Thus, cyan inks (C2) to (C24) were prepared.
In the wetting agent column in Table 1 below, the types of wetting agents and their SP values (unit: (cal / cm ³ ) ^1/2 ) are shown.

The structures of the polymerizable compounds 1, 8, and 10 in the following Table 1 are as described above.
The polymerizable compound 1 was synthesized as follows.
First, acrylamide 40.0 g (563 mmol), butanediol diglycidyl ether 57.0 g (282 mmol), potassium carbonate 15.6 g (113 mmol), benzyltriethylammonium chloride 25.7 g (113 mmol) were added to a 1 L three-necked flask equipped with a stir bar. ), 500 mL of dioxane was added, and the mixture was heated and stirred at 90 ° C. for 10 hours. The obtained reaction mixture was filtered, dioxane was distilled off under reduced pressure, 200 mL of saturated brine was added, and the mixture was extracted 3 times with 300 mL of butanol. The obtained organic layer was dried over magnesium sulfate, filtered, and evaporated under reduced pressure to obtain 58.2 g (169 mmol, yield 60%) of polymerizable compound 1.

  The polymerizable compounds 8 and 10 can be synthesized according to the synthesis method of the polymerizable compounds 1 and 2.

  Further, as the urethane acrylate resin emulsion in Table 1 (Cyan ink C24), the urethane acrylate resin emulsion EM-92 manufactured by Arakawa Chemical Co., Ltd. described in paragraph 0031 of JP-A-2009-227762 was used.

<Preparation of magenta ink (M1)>
In the preparation of the cyan ink (C1) (specifically, the preparation of the resin-coated cyan pigment dispersion (C)), the cyan pigment phthalocyanine blue A220 was replaced with the magenta pigment Chromophal Jet Magenta DMQ (Pigment Red 122, BASF Japan). A magenta ink (M1) was prepared in the same manner as in the preparation of the cyan ink (C1) except that the product was changed to “manufactured”.

<Preparation of yellow ink (Y1)>
In the preparation of the cyan ink (C1) (specifically, the preparation of the resin-coated cyan pigment dispersion (C)), the cyan pigment phthalocyanine blue A220 is replaced with the yellow pigment Irgalite Yellow GS (Pigment Yellow 74, BASF Japan Ltd.). A yellow ink (Y1) was prepared in the same manner as in the preparation of the cyan ink (C1) except that the product was changed to “manufactured”.

<Preparation of black ink (K1)>
In the preparation of the cyan ink (C1) (specifically, the preparation of the resin-coated cyan pigment dispersion (C)), the cyan pigment phthalocyanine blue A220 was replaced with the black pigment CAB-O-JETTM 200 (carbon black, CABOT Corporation). A black ink (K1) was prepared in the same manner as in the preparation of the cyan ink (C1) except that the production method was changed to “manufactured”.

≪Preparation of treatment liquid≫
<Preparation of treatment liquid 1>
Each component of the following composition was mixed and the processing liquid 1 was produced. It was 1.0 when the pH (25 degreeC) of the processing liquid 1 was measured with the pH meter WM-50EG by Toa DKK Co., Ltd.
-Composition of treatment liquid 1-
-Malonic acid (manufactured by Tateyama Kasei Co., Ltd .; acidic compound) 25.0%
・ Tripropylene glycol monomethyl ether (water-soluble organic solvent) 5%
・ Ion-exchanged water: Remaining amount (added so that the total amount of treatment liquid is 100%)

<Preparation of treatment liquid 2>
Each component of the following composition was mixed and the processing liquid 2 was produced. It was 4.0 when pH (25 degreeC) of the processing liquid 2 after pH adjustment was measured with the pH meter WM-50EG by Toa DKK Co., Ltd ..
-Composition of treatment liquid 2-
・ Polyethyleneimine (Nippon Shokubai Co., Ltd .; cationic polymer) 13.0%
・ Ion-exchanged water: Remaining amount (added so that the total amount of treatment liquid is 100%)

<Preparation of treatment liquid 3>
Each component of the following composition was mixed and the processing liquid 3 was produced. The pH (25 ° C.) of the treatment solution 3 was measured with a pH meter WM-50EG manufactured by Toa DKK Co., Ltd., and was 4.0.
-Composition of treatment liquid 3-
・ Magnesium nitrate 15%
・ Diethylene glycol monoethyl ether (Wako Pure Chemical Industries, Ltd.) 4%
Surfactant A (10%, _{Structure: C 7 H 15 -CH = CH} -C 7 H 14 -C (= O) -N (CH 3) -CH 2 CH 2 -SO 3 Na) ... 1%
・ Ion-exchanged water: Remaining amount (added so that the total amount of treatment liquid is 100%)

≪Ink set≫
An ink set prepared by combining the ink and the treatment liquid prepared above as shown in Table 1 below was prepared.

≪Image formation (inkjet recording) ≫
Using the above ink set, image formation (inkjet recording) was performed as follows.

In the case of inkjet recording, an OK top coat + (basis weight 104.7 g / m ² ) was prepared as a recording medium (coated paper).
Next, a line image and a solid image were formed by four-color single-pass printing using the ink set of the combination of the ink and the treatment liquid shown in Table 1 by the method shown below.

  First, as shown in FIG. 1, the treatment liquid application unit 12 including a treatment liquid ejection head 12 </ b> S that ejects the treatment liquid sequentially in the direction of conveyance of the recording medium (the arrow direction in the drawing) is applied. A treatment liquid drying zone 13 for drying the treatment liquid, an ink discharge unit 14 for discharging various inks, an ink drying zone 15 for drying the discharged ink, and a UV irradiation lamp 16S capable of irradiating ultraviolet rays (UV) are provided. An ink jet apparatus provided with the UV irradiation unit 16 was prepared.

  Although not shown, the processing liquid drying zone 13 is provided with a blower for drying by sending dry air to the recording surface side of the recording medium, and an infrared heater on the non-recording surface side of the recording medium. The temperature and the air volume are adjusted to evaporate (dry) 70% by mass or more of water in the aqueous treatment liquid until 900 msec after the application of the treatment liquid is started in the application unit. The ink discharge unit 14 includes a black ink discharge head 30K, a cyan ink discharge head 30C, a magenta ink discharge head 30M, and a yellow ink discharge head 30Y, which are sequentially arranged in the transport direction (arrow direction). Each head is a 1200 dpi / 20 inch wide full-line head, and can record by discharging each color in the main scanning direction by a single pass.

  One of the processing liquid 1, black ink K1, and cyan inks C1 to C24 is stored in a storage tank (not shown) connected to the processing liquid discharge head and the ink discharge head of the ink jet apparatus configured as shown in FIG. In addition, magenta ink M1 and yellow ink Y1 were loaded, and a solid image and a 1200 dpi line image were recorded on the recording medium.

A line image is recorded by ejecting a 1200-dpi line with a width of 1 dot, a line with a width of 2 dots, and a line with a width of 4 dots in a single pass in the main scanning direction, and a solid image is a sample in which the recording medium is cut to A5 size. Ink was ejected over the entire surface to obtain a solid image.
The conditions for recording are as follows.

(1) Treatment liquid application process The treatment liquid was ejected from the treatment liquid ejection head 12S onto the recording medium in a single pass. The treatment liquid was discharged so that the application amount was 1.4 g / m ² .

(2) Processing Step The processing liquid was dried in the processing liquid drying zone 13 and passed through the processing liquid drying zone by 900 msec from the start of discharge of the aqueous processing liquid. The recording medium on which the treatment liquid was discharged under the following conditions was subjected to a drying treatment and a permeation treatment.
・ Wind speed: 10m / s
-Temperature: Heated by a contact type flat heater from the opposite side (back side) of the recording surface of the recording medium so that the surface temperature of the recording surface of the recording medium was 60 ° C.

(3) Ink application process Thereafter, black ink, cyan ink, magenta ink, and yellow ink were ejected in a single pass by an ink ejection head to record an image. The ink composition was ejected by the inkjet method on the ejection surface of the recording medium on which the treatment liquid was ejected under the following conditions to form a line image and a solid image, respectively.
・ Head: 1,200 dpi / 20 inch wide piezo full line head for 4 colors ・ Discharged droplet volume: 2.0 pL
・ Drive frequency: 30kHz

(4) Ink drying step In the ink drying zone 15, the recording medium provided with the ink composition was dried under the following conditions.
・ Drying method: blow drying ・ wind speed: 15m / s
-Temperature: Heated by a contact type flat heater from the opposite side (back side) of the recording surface of the recording medium so that the surface temperature of the recording surface of the recording medium was 60 ° C.

(5) UV exposure process After the image is dried, the UV irradiation unit 16 irradiates the UV light (a metal halide lamp manufactured by Eye Graphics Co., Ltd. with a maximum irradiation wavelength of 365 nm) so that the integrated irradiation amount is 3 J / cm ^2. Cured.

(6) Fixing process Next, the heat fixing process was implemented by letting a roller pair pass on condition of the following.
・ Silicon rubber roller (hardness 50 °, nip width 5mm)
・ Roller temperature: 70 ℃
・ Pressure: 0.2 MPa

≪Evaluation≫
The following evaluations were performed on the cyan inks C1 to C24 prepared in “Preparation of ink composition” and images formed using them.
The evaluation results are shown in Table 1 below.

<Ink thermal stability over time>
(Measurement of ink viscosity before thermal aging (immediately after preparation))
Using an oscillating viscometer (BROOKFIELD, DV-II + VISCOMETER) in an environment of 25 ° C. and a relative humidity of 50% immediately after preparation (within 1 hour from the completion of preparation; the same shall apply hereinafter) (stock solution, liquid temperature 25 ° C) was measured.
The viscosity was measured using a cone plate (φ35 mm), and the average value of the measured values in the range of 20 to 90% of the torque and 0.5 to 100 rpm was determined as the ink viscosity 1.

(Measurement of ink viscosity after thermal aging)
Next, a part of the ink immediately after preparation (within 1 hour from the completion of preparation) was collected in a glass sample bottle and stored for 2 weeks in an environment of 60 ° C. in a sealed state (thermal aging).
With respect to the ink after the heat aging, the ink viscosity (liquid temperature 25 ° C.) was measured by the same method as the measurement of the ink viscosity immediately after preparation (that is, before the heat aging) to obtain an ink viscosity of 2.
Furthermore, the state of the ink after the thermal aging was visually observed.

The variation rate of the ink viscosity before and after the above thermal aging was calculated by the following formula.
Ink viscosity variation rate (%) = ((ink viscosity 2−ink viscosity 1) / ink viscosity 1) × 100

From the absolute value of the ink viscosity variation rate and the result of visual observation of the ink after heat aging, the thermal aging stability of the ink was evaluated according to the following evaluation criteria.
-Evaluation criteria for thermal aging stability of ink-
A: The absolute value of the variation rate of the ink viscosity was less than 15%, and neither the separation of the components in the ink nor the gelation of the ink was observed.
B: The absolute value of the variation rate of the ink viscosity was 15% or more and less than 30%, and neither separation of components in the ink nor gelation of the ink was observed.
C: The absolute value of the variation rate of the ink viscosity was 30% or more and less than 50%, and neither separation of components in the ink nor gelation of the ink was observed.
D: This corresponds to at least one of the absolute value of the variation rate of the ink viscosity being 50% or more, separation of components in the ink, and gelation of the ink.
* C and D are practically problematic levels.

<Maintenance (Removability of ink)>
The ink contained in the ink set was sprayed onto the surface of the test piece to produce an ink deposit having a droplet diameter of 50 μm and dried for 1 hour in an environment of 23 ° C. and 50% RH. The material of the surface of this test piece is the same material as the liquid repellent film having a fluoroalkyl group provided on the surface of the head substrate of the ink jet recording apparatus.
The test piece after drying the ink deposit is immersed in the following maintenance liquid 1 for 1 second, then taken out from the maintenance liquid 1 and observed with an optical microscope to determine the area of the ink deposit after immersion. Asked.

(Preparation of maintenance liquid 1)
Each component having the following composition was mixed to prepare maintenance liquid 1.
In the composition below, the amount of hydrochloric acid corresponds to about 0.4 equivalents of trishydroxymethylaminomethane in acid equivalents.
-Composition of maintenance liquid 1-
・ DEGmBE: 25%
・ Trishydroxymethylaminomethane… 0.9%
・ 1N hydrochloric acid 3%
・ Ion exchange water: 71.1%

~Evaluation criteria~
A: Adhesion of ink was not observed on the surface of the test piece after immersion.
B: The area of the ink deposit after immersion was less than 5% with respect to the area of the ink deposit before immersion.
C: The area of the ink deposit after immersion was 5% or more with respect to the area of the ink deposit before immersion.
* C is a practically problematic level.

<Image blocking resistance>
A solid image (cyan solid image) with each of the cyan inks C1 to C24 was formed by the inkjet recording method. Each formed cyan solid image was evaluated for blocking resistance as follows.
Immediately after printing (within 30 minutes from printing), an unrecorded recording medium (same recording medium used for recording; hereinafter, this evaluation) on a solid A5 size recording medium on which a cyan solid image was recorded In this case, the sample was left unused for 24 hours under an environmental condition of 60 ° C. and 30% RH with a load of 350 kg / m ² . After standing, the degree of ink transfer to the white background of the unused sample was visually observed and evaluated according to the following evaluation criteria.

~Evaluation criteria~
A: There was no transfer of ink.
B: Ink transfer was hardly noticeable.
C: Some transfer of ink was observed, which was a practically acceptable limit level.
D: Ink transfer was remarkable.
* D is a practically problematic level.

The unit of SP value in Table 1 is (cal / cm ³ ) ^1/2 .

As shown in Table 1, in Examples 1 to 17, the ink cleaning property (maintenance property) and the thermal aging stability of the ink were compatible. Furthermore, in Examples 1 to 17, images excellent in blocking resistance could be formed.
On the other hand, Comparative Examples 1 and 2 using a sugar alcohol having an SP value of less than 17.80 (cal / cm ³ ) ^{1/2 and} a sugar having an SP value of more than 19.00 (cal / cm ³ ) ^1/2 In Comparative Examples 4 to 6 using alcohol, the detergency (maintenance) of the ink was lowered.
In Comparative Example 3 using urea as the wetting agent and Comparative Example 7 using urethane acrylate resin emulsion as the polymerizable compound, the thermal stability with time of the ink decreased.

  Next, when the anti-blocking property was evaluated in the same manner as in Examples 1 to 17 except that the treatment liquid 1 was changed to the treatment liquid 2 or the treatment liquid 3, the treatment liquid 2 and the treatment liquid 3 were used. In any of the cases where No. 1 was used, an image excellent in blocking resistance could be formed as in Examples 1 to 17 using the treatment liquid 1.

Claims (12)

Pigment, water, polymerizable compound having acrylamide structure, polymerization initiator, and sugar alcohol having SP value of 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less An ink composition comprising: The ink composition according to claim 1, wherein the polymerizable compound having an acrylamide structure includes a compound represented by the following general formula (1).

[In General Formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 2 or more. ]   The ink composition according to claim 1, wherein the sugar alcohol is at least one selected from the group consisting of pentitol and hexitol.   The sugar alcohol is at least one selected from the group consisting of sorbitol, xylitol, D-arabinitol, L-arabinitol, ribitol, D-iditol, galactitol, and mannitol. 2. The ink composition according to item 1.   5. The ink composition according to claim 1, wherein at least a part of the surface of the pigment is coated with a resin. The ink composition according to any one of claims 1 to 5, wherein the polymerization initiator is a compound represented by the following general formula (A).

[In General Formula (A), m and n each independently represent an integer of 0 or more, and m + n represents an integer of 0 to 3]   An ink set comprising: the ink composition according to any one of claims 1 to 6; and a treatment liquid containing an aggregating agent that aggregates the components in the ink composition.   The ink set according to claim 7, wherein the flocculant is at least one selected from an acidic compound, a polyvalent metal salt, and a cationic polymer. The ink set according to claim 7 or claim 8 is used,
A treatment liquid application step of applying the treatment liquid onto a recording medium;
An ink application step of applying the ink composition onto a recording medium;
An image forming method comprising:   The image forming method according to claim 9, further comprising a curing step of irradiating the ink composition applied on the recording medium with an active energy ray to cure the ink composition.   11. The ink application step according to claim 9, wherein the ink application step is a step of applying the ink composition onto the treatment liquid provided after the treatment liquid application step and applied onto the recording medium. Image forming method.   The image forming method according to claim 9, wherein the recording medium is a coated paper having a base paper and a coat layer containing an inorganic pigment.