WO2014045968A1 - Ink composition, ink set, and method for forming image - Google Patents

Abstract

Disclosed is an ink composition containing a pigment, water, a (meth)acrylamide compound represented by general formula (1), a polymerization initiator, and polymer particles having a glass transition temperature of 90°C or higher. In general formula (1), the plurality of R¹ each independently represent a hydrogen atom or a methyl group, and the plurality of R² each independently represent a C₂-C₄ straight-chain or branched alkylene group. In the formula, there is no instance of a structure in which an oxygen atom and a nitrogen atom bonded at both ends of R² are bonded to the same carbon atom in R². The plurality of R³ each independently represent a divalent linking group. The plurality of k each independently represent a 2 or a 3. In the formula, x, y, and z each independently represent an integer of 0-6, and x + y + z is 0-18.

Description

Ink composition, ink set, and image forming method

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

The image forming method based on the ink jet method is an image forming method widely used in the fields of office printers, home printers, and the commercial field because desired image formation is possible on various recording media.

As an image forming method using an inkjet method, a method is known in which an ink containing a polymerizable compound applied on a recording medium is cured by irradiation with an active energy ray such as ultraviolet rays to form an image.
In addition, as an image forming method by the ink jet method, an ink composition and a treatment liquid containing an aggregating component that aggregates the components in the ink composition are used, and the components in the ink composition are aggregated on a recording medium. There is also known a technique for forming an image by the above method.

Further, an image forming method combining these methods has been studied.
For example, as an ink set excellent in image drawability and scratch resistance, an ink composition containing a pigment, polymer particles, and a water-soluble polymerizable compound, and an aggregating component for aggregating the components in the ink composition are included. Ink sets containing a treatment liquid are known (for example, JP 2010-70693 A, JP 2010-69805 A, JP 2011-46872 A, JP 2011-46871 A, (See 2011-174013 and JP2011-195822).

However, in an image formed using an ink composition containing a pigment, water, and a polymerizable compound, image cracking may occur (particularly during drying after application of ink). Further, in this image, gloss unevenness may occur on the image surface.

Although the gloss unevenness tends to be suppressed to some extent when polymer particles are contained in the ink composition, it may be required to further suppress the gloss unevenness. Moreover, it is difficult to suppress the image cracking only by including polymer particles in the ink composition.

The present invention has been made in view of the above, and an object of the present invention is to provide an ink composition, an ink set, and an image forming method capable of forming an image in which uneven gloss is suppressed and image cracking is suppressed.

The present inventor obtained the knowledge that the above problem can be solved by combining a specific polymerizable compound and a polymer particle having a glass transition temperature of a specific value or more, and based on this knowledge, completed the present invention. It was.
That is, specific means for solving the above-described problems are as follows.

<1> An ink composition containing pigment, water, a (meth) acrylamide compound represented by the following general formula (1), a polymerization initiator, and polymer particles having a glass transition temperature of 90 ° C. or higher.

 

In the general formula (1), a plurality of R ^{1 s} each independently represent a hydrogen atom or a methyl group, and a plurality of R ^{2 s} each independently represent a linear or branched alkylene group having 2 to 4 carbon atoms. However, not to take an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom in R ² structure. Several R < ³ > represents a bivalent coupling group each independently. Several k represents 2 or 3 each independently. x, y, and z each independently represent an integer of 0 to 6, and x + y + z satisfies 0 to 18.

<2> The ink composition according to <1>, wherein the content of the polymer particles is 0.5% by mass to 5.0% by mass with respect to the total amount of the ink composition.
<3> The polymer constituting the polymer particle contains at least one selected from the group consisting of a structural unit having an aromatic group and a structural unit having an alicyclic group. <1> or <2> Ink composition.
<4> The polymer constituting the polymer particle contains, as a structural unit having an aromatic group, at least one selected from the group consisting of a structural unit having a benzyl group and a structural unit having a phenoxy group <1>. ~ The ink composition according to any one of <3>.
<5> The polymer constituting the polymer particles contains 3% by mass to 45% by mass of a structural unit having an aromatic group with respect to the total amount of the polymer, according to any one of <1> to <4> Ink composition.
<6> The polymer constituting the polymer particle is 3% by mass in total of at least one selected from the group consisting of a structural unit derived from benzyl (meth) acrylate and a structural unit derived from phenoxyethyl (meth) acrylate. 45 mass%, a total of 5 mass% to 20 mass% of structural units derived from (meth) acrylic acid, and a total of 40 mass% to 90 mass% of structural units derived from alkyl (meth) acrylate. The ink composition according to any one of <1> to <5>.

<7> The ink composition according to any one of <1> to <6>, wherein the polymer particles are polymer particles obtained by a phase inversion emulsification method.
<8> The ink composition according to any one of <1> to <7>, wherein the polymer particles have a glass transition temperature of 100 ° C. or higher.
<9> An ink set comprising the ink composition according to any one of <1> to <8>, and a treatment liquid containing an aggregating component that aggregates the components in the ink composition.

<10> An ink application step of forming an image by applying the ink composition according to any one of <1> to <8> onto a recording medium by an inkjet method, and aggregating the components in the ink composition An image forming method comprising: a treatment liquid application step for applying a treatment liquid containing an aggregating component to be applied onto a recording medium; and a drying step for drying the image after the treatment liquid application step and the ink application step.
<11> The image forming method according to <10>, wherein the recording medium is a coated paper having a base paper and a coating layer containing an inorganic pigment.
<12> The image forming method according to <10> or <11>, wherein the ink application step is provided after the treatment liquid application step.

According to the present invention, it is possible to provide an ink composition, an ink set, and an image forming method capable of forming an image in which gloss unevenness is suppressed and image cracking is suppressed.

It is a schematic block diagram which shows the structural 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.
In the present disclosure, the term “process” is not only included in an independent process, but is included in the term if the intended effect of this process is achieved even when it cannot be clearly distinguished from other processes.
In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the present disclosure, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, the plurality of substances present in the composition unless otherwise specified. Means the total amount.
In the present disclosure, “(meth) acrylamide” means acrylamide or methacrylamide, “(meth) acrylic acid” means acrylic acid or methacrylic acid, and “(meth) acrylate” means acrylate or methacrylate. means.

≪Ink composition≫
The ink composition of the present invention contains pigment, water, a (meth) acrylamide compound represented by the following general formula (1), a polymerization initiator, and polymer particles having a glass transition temperature of 90 ° C. or higher.

 

In the general formula (1), a plurality of R ^{1 s} each independently represent a hydrogen atom or a methyl group, and a plurality of R ^{2 s} each independently represent a linear or branched alkylene group having 2 to 4 carbon atoms. However, not to take an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom in R ² structure. Several R < ³ > represents a bivalent coupling group each independently. Several k represents 2 or 3 each independently. x, y, and z each independently represent an integer of 0 to 6, and x + y + z satisfies 0 to 18.

In an image formed using an ink composition containing a pigment, water, and a polymerizable compound (particularly, an ink composition having a relatively low content of polymer particles), image cracking may occur.
This image cracking tends to occur particularly during drying after ink is applied. Further, when an image is formed by applying two (two colors) or more of ink compositions on a recording medium so as to have an overlapping portion, the ink composition applied as the uppermost layer tends to be remarkably generated. .
A possible cause of image cracking is insufficient image strength when exposed to high temperatures such as when the ink is dried.

In addition, in an image formed using an ink composition containing a pigment, water, and a polymerizable compound (particularly, an ink composition having a relatively low content of polymer particles), uneven gloss may occur on the image surface. is there.
Here, gloss unevenness refers to gloss unevenness that is confirmed when the image surface is visually observed.
As a cause of gloss unevenness, when an ink composition is applied on a recording medium and components such as pigments contained in the ink composition are aggregated to form an image, the degree of aggregation varies depending on the position (unevenness). May occur.

In the ink composition of the present invention, the (meth) acrylamide compound represented by the general formula (1) is used as the polymerizable compound, and the polymer particles having a glass transition temperature of 90 ° C. or higher are used as the polymer particles. The image cracking and the gloss unevenness are suppressed.

One reason that image cracking is suppressed by the present invention is considered to be that the strength of the image is improved by setting the glass transition temperature of the polymer particles in the ink composition to 90 ° C. or higher. Furthermore, in the present invention, when the ink composition contains the (meth) acrylamide compound represented by the general formula (1), the viscosity of the ink composition that is applied to the recording medium and is in the middle of drying increases. Thus, it is considered that image cracking is further suppressed. This increase in viscosity is particularly remarkable when the ink composition is applied to the recording medium together with the treatment liquid. The treatment liquid here is a liquid containing an aggregating component that aggregates the components in the ink composition (details will be described later).

One of the reasons why uneven gloss is suppressed by the present invention is that the aggregation (movement) of pigments and the like is limited to some extent by including polymer particles in the ink composition, thereby suppressing the variation in the degree of aggregation to some extent. It is thought that it is done. Furthermore, in the present invention, the ink composition contains the (meth) acrylamide compound represented by the general formula (1), so that it is applied to the recording medium (preferably together with the treatment liquid) and is in the middle of drying. It is considered that the viscosity of the ink composition increases, thereby further enhancing the effect of the polymer particles (the effect of suppressing variation in the degree of aggregation of the pigment), and thus suppressing uneven gloss.

That is, in the ink composition of the present invention, when the glass transition temperature of the polymer particles is changed to less than 90 ° C., image cracking tends to occur. Further, gloss unevenness tends to occur.
From the viewpoint of further suppressing image cracking, the glass transition temperature is preferably 100 ° C. or higher.
Although there is no restriction | limiting in particular in the upper limit of the said glass transition temperature, For example, it can be set as less than 150 degreeC.
A preferred form of the polymer particles having a glass transition temperature of 90 ° C. or higher will be described later.

In the ink composition of the present invention, a polymerizable compound other than the (meth) acrylamide compound represented by the general formula (1) (for example, a polymerizable compound (for example, When a (meth) acrylamide compound other than the (meth) acrylamide compound represented by the general formula (1) is used, image cracking may occur and gloss unevenness may occur.
The reason for this is considered that the effect of increasing the viscosity of the ink composition in the middle of drying is insufficient.

A preferred form of the (meth) acrylamide compound represented by the general formula (1) will be described later.

Hereinafter, each component in the ink composition of the present invention will be described.

<Polymer particles>
The ink composition of the present invention contains at least one polymer particle having a glass transition temperature of 90 ° C. or higher (hereinafter also referred to as “specific polymer particle”).
Unlike the polymer dispersant described later (a polymer dispersant that covers at least a part of the pigment), the specific polymer particles are particles that exist separately from the pigment. More specifically, the specific polymer particles have a glass transition temperature of 90 ° C. Particles composed of the above-described polymer (hereinafter also referred to as “specific polymer”).
In general, the inclusion of polymer particles in the ink composition improves the adhesion of the image to the recording medium and the scratch resistance of the image.
For example, when an image is formed by applying the ink composition to a recording medium together with a treatment liquid described later, the polymer particles are brought into contact with the treatment liquid or a region where the polymer particles are dried. It has a function of fixing the ink composition by destabilizing and agglomerating in the inside and thickening the ink composition. Thereby, the adhesion of the ink composition to the recording medium and the scratch resistance of the image can be further improved.

Furthermore, as described above, when the glass transition temperature of the polymer particles is 90 ° C. or higher (that is, due to the specific polymer particles), image cracking is suppressed. A preferable range of the glass transition temperature is as described above.

The glass transition temperature (T _g ) of the specific polymer particles can be appropriately controlled by a commonly used method. For example, the glass transition temperature (T _g ) of the specific polymer particle can be selected by appropriately selecting the type of monomer (polymerizable compound) constituting the specific polymer particle, its constituent ratio, the molecular weight of the polymer constituting the specific polymer particle, and the like. It can be controlled within a desired range.

In the present invention, the measured Tg obtained by actual measurement is applied as the glass transition temperature (Tg) of the polymer particles.
Specifically, the measurement Tg means a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. However, when measurement is difficult due to polymer decomposition or the like, calculation Tg calculated by the following calculation formula is applied. The calculation Tg is calculated by the following equation (1).
1 / Tg = Σ (X _i / Tg _i ) (1)
Here, it is assumed that n types of monomer components from i = 1 to n are copolymerized in the polymer to be calculated. X _i is the weight fraction of the i-th monomer (ΣX _i = 1), and Tg _i is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum from i = 1 to n. The homopolymer glass transition temperature value (Tg _i ) of each monomer is the value of Polymer Handbook (3rd Edition) (by J. Brandrup, EH Immergut (Wiley-Interscience, 1989)).

The specific polymer particles are preferably polymer particles obtained by a phase inversion emulsification method, and the following self-dispersing polymer particles (self-dispersing polymer particles) are more preferable.
Here, the self-dispersing polymer is dispersed in an aqueous medium by a functional group (particularly an acidic group or a salt thereof) possessed by the polymer itself when it is dispersed by a 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.
“Water-insoluble” means that the amount dissolved in 100 parts by mass of water (25 ° C.) is 5.0 parts by mass or less.

As the phase inversion emulsification method, for example, a polymer is dissolved or dispersed in a solvent (for example, a water-soluble organic solvent) and then poured into water as it is without adding a surfactant. Examples include a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing in a state in which a group (for example, an acidic group) is neutralized and removing the solvent.

Examples of the self-dispersing polymer particles include self-dispersing polymer particles described in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-068805A. Those having a glass transition temperature of 90 ° C. or higher can be selected and used.

The polymer constituting the specific polymer particles (specific polymer; the same shall apply hereinafter) preferably has at least one of a structural unit having an aromatic group and a structural unit having an alicyclic group. Here, the alicyclic group is synonymous with the cyclic aliphatic group.
Thereby, the strength of the formed image can be further improved (for example, scratch resistance and blocking resistance).
In the present specification, the structural unit contained in the specific polymer may be referred to as “constituent component”.

(Structural unit having an aromatic group)
Examples of the structural unit having an aromatic group include a structural unit having a phenyl group, a structural unit having a benzyl group, a structural unit having a phenoxy group, and a structural unit having a phenethyl group. A structural unit and a structural unit having a phenoxy group (preferably a structural unit having a phenoxyethyl group) are preferred.

The structural unit having an aromatic group is preferably a structural unit derived from a monomer having an aromatic group (hereinafter also referred to as “aromatic group-containing monomer”).
The aromatic group-containing monomer is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomers may be used singly or in combination of two or more.

Examples of the aromatic group-containing monomer include aromatic group-containing (meth) acrylate monomers (for example, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, etc.), styrene monomers, and the like. Can be mentioned. Among these, from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixing property, the aromatic group-containing monomer is preferably an aromatic group-containing (meth) acrylate monomer, such as phenoxyethyl (meth) acrylate, benzyl (meta ) Acrylate and at least one selected from phenyl (meth) acrylate, more preferably phenoxyethyl (meth) acrylate and benzyl (meth) acrylate.

(Structural unit having an alicyclic group)
The structural unit having an alicyclic group is preferably a structural unit derived from a monomer having an alicyclic group (hereinafter also referred to as “alicyclic group-containing monomer”).
The alicyclic group-containing monomer is preferably a monomer having an alicyclic group and an ethylenically unsaturated bond, and a (meth) acrylate having an alicyclic group (hereinafter referred to as “alicyclic (meth) acrylate”. Are also preferred).
The alicyclic (meth) acrylate includes a structural site derived from (meth) acrylic acid and a structural site derived from alcohol, and the structural site derived from alcohol is unsubstituted or substituted. It has a structure containing at least one hydrogen group. The alicyclic hydrocarbon group may be a structural site derived from alcohol itself or may be bonded to a structural site derived from alcohol via a linking group.

The alicyclic hydrocarbon group is not particularly limited as long as it contains a cyclic non-aromatic hydrocarbon group, and is a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, a tricyclic or more polycyclic group. A hydrocarbon group is mentioned. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane.
The alicyclic hydrocarbon group may further have a substituent. Examples of the substituent include an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxy group, a hydroxyl group, a primary amino group, a secondary amino group, a tertiary amino group, an alkyl or arylcarbonyl group, and a cyano group. Is mentioned. Further, the alicyclic hydrocarbon group may further form a condensed ring. The alicyclic hydrocarbon group in the present invention preferably has 5 to 20 carbon atoms in the alicyclic hydrocarbon group portion from the viewpoint of viscosity and solubility.

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

Among these, from the viewpoints of dispersion stability, fixing property, and blocking resistance of self-dispersing polymer particles, as the alicyclic (meth) acrylate, bicyclic (meth) acrylate and tricyclic or more polycyclic It is preferably at least one selected from (meth) acrylates, more preferably at least one selected from isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. .

In the polymer constituting the specific polymer particle in the present invention, the total content of the structural unit having the aromatic group and the structural unit having the alicyclic group is 3% by mass to 95% by mass. preferable. When the total content is within this range, the stability of the self-emulsification or dispersion state can be improved, and further the increase in ink viscosity can be suppressed.

In consideration of the removability (maintenance) of the ink composition from the nozzle and the re-ejection property after removal, it is more preferable that the specific polymer particles have a structural unit having an aromatic group.

In a more preferred embodiment of the specific polymer particle, the polymer constituting the specific polymer particle includes a structural unit having the aromatic group, and the content of the structural unit having the aromatic group is 3 with respect to the total amount of the polymer. It is in the form of mass% to 45 mass% (more preferably 3 to 40 mass%, particularly preferably 5 to 30 mass%).
With this form, it becomes easier to adjust the glass transition temperature of the specific polymer particles to 90 ° C. or higher.

(Hydrophilic structural unit)
The polymer constituting the specific polymer particles preferably includes a hydrophilic structural unit from the viewpoint of dispersibility in the ink composition (self-dispersibility in the case of self-dispersing polymer particles).
The hydrophilic structural unit is preferably a structural unit derived from a monomer having a hydrophilic group (hereinafter also referred to as “hydrophilic group-containing monomer”).
In this case, the hydrophilic structural unit may be derived from one type of hydrophilic group-containing monomer or may be derived from two or more types of hydrophilic group-containing monomers.
The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
The hydrophilic group is preferably a dissociable group, more preferably an anionic dissociable group, from the viewpoint of promoting self-dispersion of the polymer particles and the stability of the formed emulsified or dispersed state. . Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability of an ink composition obtained using the specific polymer.

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

Specific examples of the unsaturated carboxylic acid monomer include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxyethyl succinic acid.
Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, bis- (3-sulfopropyl) -itaconate, and the like. Is mentioned.
Specific examples of the unsaturated phosphoric acid monomer include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2 -Acryloyloxyethyl phosphate and the like.
Among the dissociable group-containing monomers, an unsaturated carboxylic acid monomer is preferable and (meth) acrylic acid is more preferable from the viewpoints of dispersion stability and ejection stability.

The content of the hydrophilic structural unit in the polymer constituting the specific polymer particle is not particularly limited, but from the viewpoint of dispersion stability, the content is 2% by mass with respect to the total amount of the specific polymer particle. Is preferably 30% by mass, more preferably 5% by mass to 20% by mass, and particularly preferably 5% by mass to 15% by mass.

(Structural unit having an alkyl group)
The polymer constituting the specific polymer particles preferably includes a structural unit having an alkyl group from the viewpoint of flexibility of the polymer skeleton and easy control of the glass transition temperature (Tg).
The carbon number of the alkyl group in the structural unit having an alkyl group is preferably 1 to 4.
The structural unit having an alkyl group is preferably a structural unit derived from a monomer having an alkyl group (hereinafter also referred to as “alkyl group-containing monomer”).

Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Ethylenically unsaturated monomers having a hydroxyl group such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate; Dialkylaminoalkyl (meth) acrylates such as ru (meth) acrylate; N-hydroxyalkyl (meth) such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide Acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meta) And (meth) acrylamide such as N-alkoxyalkyl (meth) acrylamide such as N- (n-, iso) butoxyethyl (meth) acrylamide.
Among them, alkyl (meth) acrylate is preferable, alkyl (meth) acrylate having an alkyl group having 1 to 4 carbon atoms is more preferable, methyl (meth) acrylate or ethyl (meth) acrylate is more preferable, methyl (meth) acrylate Is particularly preferred.

The content of the structural unit having an alkyl group in the polymer constituting the specific polymer particle is not particularly limited, but from the viewpoint of dispersion stability, the content is 5 mass with respect to the total amount of the specific polymer particle. % To 90% by weight, more preferably 30% to 90% by weight, still more preferably 40% to 90% by weight, particularly preferably 50% to 90% by weight, most preferably 60% to 85% by weight. preferable.

The polymer constituting the specific polymer particle may contain a structural unit other than the above-described structural unit, if necessary.

From the viewpoints of easily adjusting the glass transition temperature to 90 ° C. or more and maintaining good dispersion stability, preferred forms of the copolymerization ratio of the polymer constituting the specific polymer particles are as follows.
That is, the preferred form from the above viewpoint is that the polymer constituting the specific polymer particle is 3% by mass to 45% by mass in terms of a copolymerization ratio of the structural unit having the aromatic group (preferably benzyl group or phenoxy group). More preferably 3 to 40% by mass, particularly preferably 5 to 30% by mass) and a hydrophilic structural unit as a copolymerization ratio of 2 to 30% by mass (more preferably 5 to 20% by mass, particularly preferably). Is 5% by mass to 15% by mass) and 5% by mass to 90% by mass (more preferably 30% by mass to 90% by mass, and still more preferably 50% by mass to 90% by mass) as a copolymerization ratio of the structural unit having an alkyl group. %, Particularly preferably 60% by mass to 85% by mass).
A more preferable form of the specific polymer particle is 3% by mass to 45% by mass (more preferably) with a copolymerization ratio of at least one of a structural unit derived from benzyl (meth) acrylate or a structural unit derived from phenoxyethyl (meth) acrylate. 3 to 40% by mass, particularly preferably 5 to 30% by mass) and a structural unit derived from (meth) acrylic acid as a copolymerization ratio of 2 to 30% by mass (more preferably 5 to 20% by mass). Particularly preferably 5 to 15% by mass) and a structural unit derived from an alkyl (meth) acrylate as a copolymerization ratio of 40 to 90% by mass (more preferably 50 to 90% by mass, particularly preferably Is 60 mass% to 85 mass%).

The molecular weight range of the polymer constituting the specific polymer particle is preferably 3000 to 200,000, more preferably 5000 to 150,000, and still more preferably 10,000 to 100,000 in terms of weight average molecular weight. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.

The weight average molecular weight of the polymer constituting the specific polymer particle is measured by gel permeation chromatography (GPC). For GPC, HLC-8020GPC (manufactured by Tosoh Corporation) is used, TSKgel, Supermultipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as columns, and THF (tetrahydrofuran) is used as an eluent. ) Is used. As conditions, the sample concentration is 0.45% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and an IR detector is used. The calibration curves are standard samples TSK standard, polystyrene F-40, F-20, F-4, F-1, A-5000, A-2500, A-1000, and n-propylbenzene manufactured by Tosoh Corporation. 8 samples are prepared.

The average particle diameter of the specific polymer particles (particularly self-dispersing polymer particles) in the present invention is preferably in the range of 10 to 400 nm in terms of volume average particle diameter, more preferably in the range of 10 to 200 nm, and still more preferably in the range of 10 to 100 nm. Particularly preferably, it is in the range of 10 to 50 nm. Manufacturability is improved when the volume average particle diameter is 10 nm or more. Moreover, storage stability improves that a volume average particle diameter is 400 nm or less. The particle size distribution of the polymer particles is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Two or more kinds of the polymer particles having different particle size distributions may be mixed and used.
The average particle size and particle size distribution of the specific polymer particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is required.

The ink composition in the present invention may contain one kind of specific polymer particles (preferably self-dispersing polymer particles), or two or more kinds.
The content (total content) of the specific polymer particles (preferably self-dispersing polymer particles) in the ink composition is preferably 0.5 to 5.0% by mass relative to the total amount of the ink composition. 5 to 3.0% by mass is more preferable, and 0.5 to 2.0% by mass is particularly preferable.
In general, an ink composition having a polymer particle content of 5.0% by mass or less tends to cause image cracking and gloss unevenness.
For this reason, when the content of the specific polymer particles (relative to the total amount of the ink composition) in the ink composition of the present invention is 5.0% by mass or less, image cracking caused by the specific polymer particles and the specific (meth) acrylamide compound. The effect of suppression and gloss unevenness suppression is more remarkable.
Further, when the content of the specific polymer particles (relative to the total amount of the ink composition) in the ink composition of the present invention is 5.0% by mass or less, the dischargeability and stability of the ink composition are further improved.

<(Meth) acrylamide compound represented by general formula (1)>
The ink composition of the present invention contains at least one (meth) acrylamide compound represented by the following general formula (1).

 

In the general formula (1), a plurality of R ^{1 s} each independently represent a hydrogen atom or a methyl group, and a plurality of R ^{2 s} each independently represent a linear or branched alkylene group having 2 to 4 carbon atoms. However, not to take an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom in R ² structure. Several R < ³ > represents a bivalent coupling group each independently. Several k represents 2 or 3 each independently. x, y, and z each independently represent an integer of 0 to 6, and x + y + z satisfies 0 to 18.
However, k is the same within one C _k H _2k O unit.

The (meth) acrylamide compound represented by the general formula (1) (hereinafter, also referred to as “specific (meth) acrylamide compound” or “compound represented by the general formula (1)”) has four in one molecule. It is a tetrafunctional (meth) acrylamide compound having a (meth) acrylamide structure. Hereinafter, the (meth) acrylamide structure is also referred to as “(meth) acrylamide group”.
This specific (meth) acrylamide compound is, for example, curability based on polymerization reaction by applying energy such as active energy rays such as α rays, γ rays, X rays, ultraviolet rays, visible rays, infrared rays, electron rays, and heat. Indicates. This enhances the scratch resistance and scratch resistance of the formed image. Furthermore, the said specific (meth) acrylamide compound shows water solubility, and melt | dissolves favorably in water-soluble organic solvents, such as water and alcohol.
Here, the term “water-soluble” means that it can be dissolved in water at a certain concentration or more, and it only needs to have a property that can be dissolved in water-based ink or, in some cases, in a processing liquid. Specifically, the solubility in water is preferably 10% by mass or more, and more preferably 15% by mass or more.

Specific (meth) acrylamide compounds are more soluble in water and more efficient than other tetrafunctional or higher polymerizable compounds (for example, tetrafunctional or higher (meth) acrylamide compounds other than specific (meth) acrylamide compounds). In terms of

When the ink composition of the present invention contains the specific (meth) acrylamide compound, the effect of suppressing variation in the degree of aggregation of the pigment due to the specific polymer particles is further enhanced, and gloss unevenness is suppressed. Furthermore, image cracking is suppressed.
As described above, the reason why image cracking and gloss unevenness are suppressed is that the ink composition contains a specific (meth) acrylamide compound having a structure represented by the general formula (1), so that the recording medium (preferably together with the processing liquid). This is probably because the viscosity of the ink composition that has been applied and is in the middle of drying increases.
Conventionally, a tetrafunctional (meth) acrylamide compound is sometimes contained in an ink composition (for example, JP 2011-174013 A, JP 2011-195822 A, etc.). Then, the effect of a viscosity increase as the (meth) acrylamide compound represented by the general formula (1) cannot be obtained. For this reason, in the ink composition of the present invention, when a conventional tetrafunctional (meth) acrylamide compound is used instead of the (meth) acrylamide compound represented by the general formula (1), the ink composition can be obtained according to the present invention. The effect of suppressing image cracking and the effect of suppressing gloss unevenness cannot be obtained.

In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom. Several R < ¹ > may mutually be same or different.

R ² represents a linear or branched alkylene group having 2 to 4 carbon atoms. A plurality of R ² may be the same as or different from each other. R ² is preferably an alkylene group having 3 to 4 carbon atoms, more preferably an alkylene group having 3 carbon atoms, and particularly preferably a linear alkylene group having 3 carbon atoms. The alkylene group for R ² may further have a substituent, and examples of the substituent include an aryl group and an alkoxy group.

However, R ² does not have a structure in which an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom of R ² . R ² is a linear or branched alkylene group that connects the oxygen atom and the nitrogen atom of the (meth) acrylamide group. Here, when the alkylene group has a branched structure, the —O—C—N— structure (hemaminal structure) in which the oxygen atoms at both ends and the nitrogen atom of the (meth) acrylamide group are bonded to the same carbon atom in the alkylene group. However, the compound represented by the general formula (1) does not include a compound having such a structure. A compound having an —O—C—N— structure in the molecule is likely to decompose at the position of the carbon atom, so that it is easily decomposed during storage and causes a decrease in storage stability when contained in an ink composition. This is not preferable.

R ³ represents a divalent linking group, and a plurality of R ³ may be the same as or different from each other. Examples of the divalent linking group represented by R ³ include an alkylene group, an arylene group, a heterocyclic group, or a group composed of a combination thereof, and an alkylene group is preferable. When the divalent linking group includes an alkylene group, the alkylene group may further include at least one group selected from —O—, —S—, and —NR ^a —. R ^a represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

When R ³ contains an alkylene group, examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, and a nonylene group. The number of carbon atoms of the alkylene group represented by R ³ is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1. The alkylene group for R ³ may further contain at least one selected from —O—, —S—, and —NR ^a —. Examples of the alkylene group containing —O— include —C ₂ H ₄ —O—C ₂ H ₄ —, —C ₃ H ₆ —O—C ₃ H ₆ — and the like. The alkylene group for R ³ may further have a substituent, and examples of the substituent include an aryl group and an alkoxy group.

When R ³ contains an arylene group, examples of the arylene group include a phenylene group and a naphthylene group. The carbon number of the arylene group of R ³ is preferably 6 to 14, and preferably 6 to 10. More preferably, 6 is particularly preferable. The arylene group for R ³ may further have a substituent, and examples of the substituent include an alkyl group and an alkoxy group.

When R ³ contains a heterocyclic group, the heterocyclic group is preferably a 5-membered or 6-membered ring, which may be further condensed. The heterocyclic ring may be an aromatic heterocyclic ring or a non-aromatic heterocyclic ring. Examples of the heterocyclic group include pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, isoquinoline, quinazoline, cinnoline, phthalazine, quinoxaline, pyrrole, indole, furan, benzofuran, thiophene, benzothiophene, pyrazole, imidazole, benzimidazole, And triazole, oxazole, benzoxazole, thiazole, benzothiazole, isothiazole, benzisothiazole, thiadiazole, isoxazole, benzisoxazole, pyrrolidine, piperidine, piperazine, imidazolidine, thiazoline and the like. Among them, an aromatic heterocyclic group is preferable, and pyridine, pyrazine, pyrimidine, pyridazine, triazine, pyrazole, imidazole, benzimidazole, triazole, thiazole, benzothiazole, isothiazole, benzisothiazole, and thiadiazole are preferable. In addition, although the heterocyclic group shown above is illustrated in a form in which the substitution position is omitted, the substitution position is not limited. For example, in the case of pyridine, substitution is made at the 2-position, 3-position, and 4-position. And can include all of these substitutions.
The heterocyclic group may further have a substituent, and examples of the substituent include an alkyl group, an aryl group, and an alkoxy group.

K in the general formula (1) represents 2 or 3. Several k may mutually be same or different. C _k H _2k may be a linear structure or a branched structure.
X, y and z each independently represents an integer of 0 to 6, preferably an integer of 0 to 5, and more preferably an integer of 0 to 3. x + y + z satisfies 0 to 18, preferably satisfies 0 to 15, and more preferably satisfies 0 to 9.

Among the above, R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 2 to 4 carbon atoms, and R ³ represents an alkylene group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms). And k represents 2 or 3, x, y and z each independently represents an integer of 0 to 6, and x + y + z preferably satisfies 0 to 15.

Specific examples of the compound represented by the general formula (1) are shown below. However, the present invention is not limited to these.

 
 

The compound represented by the general formula (1) can be produced, for example, according to the following scheme 1 or scheme 2.

 

In the scheme 1, the first step is a step of obtaining a polycyano compound by reaction of acrylonitrile and trishydroxymethylaminomethane. The reaction in this step is preferably performed at 3 to 60 ° C. for 2 to 8 hours.
The second step is a step of reacting a polycyano compound with hydrogen in the presence of a catalyst to obtain a polyamine compound by a reduction reaction. The reaction in this step is preferably performed at 20 to 60 ° C. for 5 to 16 hours.
The third step is a step of obtaining a polyfunctional acrylamide compound by an acylation reaction between a polyamine compound and acrylic acid chloride or methacrylic acid chloride. The reaction in this step is preferably performed at 3 to 25 ° C. for 1 to 5 hours. The acylating agent may be diacrylic anhydride or dimethacrylic anhydride instead of acid chloride. By using both acrylic acid chloride and methacrylic acid chloride in the acylation step, a compound having an acrylamide structure and a methacrylamide structure in the same molecule can be obtained as the final product.

 
 

In Scheme 2, the first step is a step of obtaining a nitrogen-protected aminoalcohol compound by introducing a protecting group with a benzyl group, benzyloxycarbonyl group or the like into the nitrogen atom of the aminoalcohol. The reaction in this step is preferably performed at 3 to 25 ° C. for 3 to 5 hours.
The second step is a step of obtaining a sulfonyl compound by introducing a leaving group such as a methanesulfonyl group or p-toluenesulfonyl group into the OH group of the nitrogen-protected aminoalcohol compound. The reaction in this step is preferably performed at 3 to 25 ° C. for 2 to 5 hours.
The third step is a step of obtaining an amino alcohol addition compound by SN2 reaction between a sulfonyl compound and trishydroxymethylnitromethane. The reaction in this step is preferably performed at 3 to 70 ° C. for 5 to 10 hours.
The fourth step is a step of reacting an amino alcohol addition compound with hydrogen in the presence of a catalyst to obtain a polyamine compound by hydrogenation reaction. The reaction in this step is preferably performed at 20 to 60 ° C. for 5 to 16 hours.
The fifth step is a step of obtaining a polyfunctional acrylamide compound by an acylation reaction between a polyamine compound and acrylic acid chloride or methacrylic acid chloride. The reaction in this step is preferably performed at 3 to 25 ° C. for 1 to 5 hours. The acylating agent may be diacrylic anhydride or dimethacrylic anhydride instead of acid chloride. By using both acrylic acid chloride and methacrylic acid chloride in the acylation step, a compound having an acrylamide structure and a methacrylamide structure in the same molecule can be obtained as the final product.

The compound obtained through the above steps can be obtained by purifying the reaction product solution by a conventional method. For example, it can be purified by liquid separation extraction using an organic solvent, crystallization using a poor solvent, column chromatography using silica gel, and the like.

The content of the specific (meth) acrylamide compound in the ink composition is preferably 3% by mass or more and 15% by mass or less, more preferably 5% by mass or more and 13% by mass or less, based on the total amount of the ink composition. More preferably, it is at least 13% by mass.
When the content is 3% by mass or more, the uniformity of the viscosity of the ink composition when dried on the recording medium is further improved, so that the effects of image cracking suppression and gloss unevenness suppression are more effectively achieved. Is done.
Similarly, when the content is 15% by mass or less, since the uniformity of the viscosity of the ink composition when dried on the recording medium is further improved, the effects of image cracking suppression and gloss unevenness suppression are more effective. Played.

An embodiment in which the ink composition of the present invention contains at least one (meth) acrylamide compound other than the specific (meth) acrylamide compound together with the specific (meth) acrylamide compound is also suitable.
As the other (meth) acrylamide compound, at least one of (meth) acrylamide compounds represented by the following general formula (2) (excluding the compound represented by the above general formula (1)) is preferable. is there.
Hereinafter, the (meth) acrylamide compound represented by the general formula (2) is also simply referred to as “compound represented by the general formula (2)”.

 

In the general formula (2), Q represents an n-valent group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 1 or more.
However, the range of the compound represented by the general formula (2) when n is 4 does not include the compound represented by the general formula (1).

The compound represented by the general formula (2) is a compound in which an unsaturated vinyl monomer is bonded to the group Q through an amide bond.
The compound in which n in general formula (2) is 1 is a monofunctional (meth) acrylamide compound having one (meth) acrylamide structure in one molecule, and n in general formula (2) is 2 or more. The compound which is an integer is a polyfunctional (meth) acrylamide compound having two or more (meth) acrylamide structures in one molecule.

In the general formula (2), R ¹ represents a hydrogen atom or a methyl group, preferably a hydrogen atom.
The valence n of the group Q is 1 or more, preferably 1 or more, 6 or less, more preferably 1 or more and 4 or less, particularly preferably 1 or more and 3 or less, from the viewpoint of improving permeability, polymerization efficiency, and ejection stability. preferable.

In the general formula (2), the group Q when n is 1 is not particularly limited as long as it is a monovalent group that can be linked to a (meth) acrylamide structure. The group Q when n is 1 is preferably selected from water-soluble groups. Specific examples include monovalent residues obtained by removing one or more hydrogen atoms or hydroxyl groups from a compound selected 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, tri Ji, ditrimethylolpropane, trimethylolethane, di-trimethylolpropane, neopentyl glycol, pentaerythritol, dipentaerythritol, and condensates thereof, polyol compounds such as low molecular polyvinyl alcohol, or sugars; and,
Polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, and polypropylenediamine.

In addition, as the group Q when n is an integer of 2 or more, a substituted or unsubstituted alkylene group having 4 or less carbon atoms such as methylene, ethylene, propylene, butylene group, saturated or unsaturated heterocyclic ring (pyridine ring) A divalent or higher valent linking group having an imidazole ring, a pyrazine ring, a piperidine ring, a piperazine ring, a morpholine ring, or the like, and a divalent or higher residue of a polyol compound containing an oxyalkylene group (preferably an oxyethylene group), A divalent or higher valent residue of a polyol compound containing 3 or more oxyalkylene groups (preferably oxyethylene groups) can be exemplified.

Examples of the compound represented by the general formula (2) include, for example, JP 2010-69805 A, JP 2011-46872 A, JP 2011-178896 A, JP 2011-174013 A, and JP 2011 2011. -195822 can be appropriately selected from water-soluble polymerizable compounds described in JP-A No. 195822.

The ink composition of the present invention is advantageous in terms of penetrability into a coated layer of a coated paper (for example, a coated layer containing an inorganic pigment, the same applies hereinafter) when coated paper is used as a recording medium. From the viewpoint, a monofunctional (meth) acrylamide compound (for example, a compound in which n in the general formula (2) is 1) together with the compound represented by the general formula (1) described above (specific (meth) acrylamide compound) It is preferable to contain. Thereby, not only the image by the ink composition but also the coating layer of the coated paper is cured, so that the adhesion of the image to the recording medium is further improved.
In this case, the content of the monofunctional (meth) acrylamide compound is preferably 10% by mass to 30% by mass, more preferably 10% by mass to 25% by mass with respect to the total amount of the ink composition. % Is particularly preferred.
Examples of monofunctional (meth) acrylamide compounds include hydroxyethyl (meth) acrylamide, hydroxypropyl (meth) acrylamide, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, and isopropyl (meth) acrylamide. Particularly preferred is hydroxyethyl (meth) acrylamide, and most preferred is hydroxyethylacrylamide.

Furthermore, the ink composition of the present invention may contain a cationic polymerizable compound together with the specific (meth) acrylamide.
The cationic polymerizable compound is a compound having a cationic group and a polymerizable group such as an unsaturated double bond, and for example, epoxy monomers and octacene monomers can be suitably used. When the cationic polymerizable compound is contained, the cationic property of the ink composition is increased due to the presence of the cationic group, and color mixing when an anionic ink is used is more effectively prevented.

In the ink composition of the present invention, the total amount of the polymerizable compound (including at least specific (meth) acrylamide) with respect to the total amount of the ink composition is preferably 10% by mass or more and 50% by mass or less, and 15% by mass or more and 35% by mass or less. Is more preferable. When the total amount of the polymerizable compounds is within the above range, the curing reactivity is good and the curing can be made uniform in the entire image.

<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.

The type of the pigment is not particularly limited, and a conventionally known organic pigment or inorganic pigment can be used.

Examples of the organic pigments 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 No. 2007-1000007.

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 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. An 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. That is, the ink composition of the present invention preferably contains at least one dispersant.
The pigment dispersant may be either a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.

As the low molecular surfactant type dispersant, for example, known low molecular surfactant type dispersants described in paragraphs 0047 to 0052 of JP2011-178029A can be used.

Among the polymer dispersants, examples of the water-soluble dispersant include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include plant polymers such as gum arabic, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, quince seed starch, seaweeds such as alginic acid, carrageenan and agar. Examples include molecules, animal polymers such as gelatin, casein, albumin and collagen, and microorganism polymers such as xanthene gum and dextran.

In addition, in hydrophilic polymer compounds modified from natural products, fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starch such as sodium starch glycolate and sodium starch phosphate And seaweed polymers such as sodium alginate, propylene glycol alginate, and the like.
Further, synthetic hydrophilic polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salts thereof, water-soluble styrene acrylic resins, and the like. Acrylic resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic acid resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salts of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium and amino And a polymer compound having a salt of a cationic functional group such as a group in the side chain, and a natural polymer compound such as shellac.

Among these, water-soluble dispersants introduced with carboxyl groups are hydrophilic polymers such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound.

Among the polymer dispersants, as the water-insoluble dispersant, a polymer having both a hydrophobic part and a hydrophilic part can be used. For example, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer, polyethylene glycol ( Examples thereof include a (meth) acrylate- (meth) acrylic acid copolymer, a vinyl acetate-maleic acid copolymer, and a styrene-maleic acid copolymer.

The weight average molecular weight of the polymer dispersant is preferably 3,000 to 100,000, more preferably 5,000 to 50,000, still more preferably 5,000 to 40,000, and particularly preferably 10,000. 000 to 40,000.
In addition, the weight average molecular weight of a polymer dispersing agent is measured similarly to the weight average molecular weight of the polymer which comprises the above-mentioned specific polymer particle.

The polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoints of self-dispersibility and aggregation rate when the treatment liquid comes into contact. The polymer dispersant has a carboxyl group and has an acid value of 100 mgKOH / g or less. A polymer having an acid value of 25 mgKOH / g to 100 mgKOH / g is more preferable. In particular, when the ink composition of the present invention is used together with a treatment liquid that aggregates the components in the ink composition, a polymer dispersant having a carboxyl group and an acid value of 25 mgKOH / g to 100 mgKOH / g is effective. It is. The processing liquid will be described later.

The mixing mass ratio (p: s) between the pigment (p) and the dispersant (s) is preferably in the range of 1: 0.06 to 1: 3, and in the range of 1: 0.125 to 1: 2. Is more preferably 1: 0.125 to 1: 1.5.

In the present invention, a dye may be used in addition to the pigment. In the case of using a dye, a dye held on a water-insoluble carrier can be used. As the dye, known dyes can be used without limitation. For example, the dyes described in JP-A No. 2001-115066, JP-A No. 2001-335714, JP-A No. 2002-249677 and the like are preferably used. . The carrier is not particularly limited as long as it is insoluble or hardly soluble in water, and can be selected from inorganic materials, organic materials, and composite materials thereof. Specifically, carriers described in JP-A Nos. 2001-181549 and 2007-169418 are preferably used.
The carrier holding the dye (water-insoluble colored particles) can be used as an aqueous dispersion using a dispersant. As the dispersant, the above-described dispersants can be suitably used.

In the present invention, from the viewpoint of image light resistance and quality, it is preferable to include a pigment and a dispersant, including an organic pigment and a polymer dispersant, and at least a part of the pigment surface is coated with the polymer dispersant. More preferably, it is contained as a water-dispersible pigment. Furthermore, it is particularly preferable that the ink composition includes an organic pigment and a polymer dispersant containing a carboxyl group, and a water-dispersible pigment in which at least a part of the pigment surface is coated with a polymer dispersant having a carboxyl group. From the viewpoint of cohesiveness, the pigment is preferably coated with a polymer dispersant containing a carboxyl group and is insoluble in water.

The average particle diameter of the pigment in the dispersed state is preferably 10 nm to 200 nm, more preferably 10 nm to 150 nm, and even more preferably 10 nm to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, and the droplet ejection characteristics when droplets are ejected by the ink jet method are good. When the average particle size is 10 nm or more, light resistance is improved. Further, the particle size distribution of the color material is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more color materials having a monodisperse particle size distribution may be mixed and used.
Here, the average particle diameter of the pigment in the dispersed state indicates the average particle diameter in the ink state, but the same applies to the so-called concentrated ink dispersion in the previous stage before the ink is formed.
The average particle size and particle size distribution of the pigment in the dispersed state are determined in the same manner as the average particle size and particle size distribution of the specific polymer particles described above.

<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% by mass to 99% by mass, and more preferably 30% by mass to 90% by mass with respect to the total amount of the ink composition. % By mass, more preferably 30% by mass to 80% by mass, and particularly preferably 50% by mass to 70% 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; and carbon numbers of 1 to 4 such as ethanol, methanol, butanol, propanol, and isopropanol. Alkyl alcohols 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.

<Polymerization initiator>
The ink composition of the present invention contains at least one polymerization initiator.
Thereby, superposition | polymerization of the said specific (meth) acrylamide compound can be started with an active energy ray.
The said polymerization initiator can be used individually by 1 type or in mixture of 2 or more types. The polymerization initiator may be used in combination with a sensitizer.

The polymerization initiator can contain a compound that can initiate a polymerization reaction of the polymerizable compound by active energy rays as appropriate. Examples of the polymerization initiator include polymerization initiators (for example, photopolymerization initiators) that generate active species (radicals, acids, bases, etc.) by radiation or light, or electron beams.

Examples of the photopolymerization initiator include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophene, p-dimethylaminopropiophenone, benzophenone, 2-chlorobenzophenone, p, p′-dichlorobenzophene, p, p'-bisdiethylaminobenzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin isobutyl ether, benzoin n-butyl ether, benzyldimethyl ketal, tetramethylthiuram mono Sulfide, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, azobisisobutyronitrile, benzoin peroxide Di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy- Examples include 2-methyl-1-phenyl-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, and methylbenzoyl formate. Furthermore, for example, aromatic diazonium salts, aromatic halonium salts, aromatic sulfonium salts, metallocene compounds such as triphenylsulfonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate and the like can be mentioned.

The content of the polymerization initiator in the ink composition includes the specific (meth) acrylamide compound described above (or a specific (meth) acrylamide compound when a polymerizable compound other than the specific (meth) acrylamide compound is included). 1 to 40% by mass is preferable, and 5 to 30% by mass is more preferable based on the entire polymerizable compound. When the content of the polymerization initiator is 1% by mass or more, the scratch resistance of the image is further improved, which is advantageous for high-speed recording, and when it is 40% by mass or less, it is advantageous in terms of ejection stability.

Examples of the sensitizer include amines (aliphatic amines, amines containing aromatic groups, piperidine, etc.), ureas (allylic, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, aromatic sulfinic acid). Soluble salts, etc.), nitrile compounds (N, N, di-substituted p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, netium diethyldithiophos feed, etc.), nitrogen compounds (Michler ketone, N-nitriso) Hydroxylamine derivatives, oxazolidine compounds, tetrahydro 1,3-oxazine compounds, formaldehyde, acetaldehyde and diamine condensates, etc.), chlorine compounds (carbon tetrachloride, hexachloroethane, etc.), polymerized amines of reaction products of epoxy resins and amines , Triethanolamine Acrylate, and the like.
A sensitizer can be contained in the range which does not impair the effect of this invention.

<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, for example.
As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactants, cationic surfactants, amphoteric surfactants, nonions Either a surfactant or a betaine surfactant can be used. Further, the above water-soluble polymer (polymer dispersing agent) may be used as a surfactant.

In the present invention, a nonionic surfactant is preferable from the viewpoint of suppression of ink droplet ejection interference, and among them, an acetylene glycol derivative (acetylene glycol surfactant) is more preferable.
Examples of the acetylene glycol surfactants 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 the 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. The amount is preferably within the range that can be adjusted, more preferably from 20 to 45 mN / m, and even more preferably from 25 to 40 mN / m from the viewpoint of surface tension.

When the ink composition of the present invention contains a surfactant, the specific amount of the surfactant is not particularly limited, but is preferably 0.1% by mass or more, more preferably based on the total amount of the ink composition. The content is 0.1 to 10% by mass, more preferably 0.2 to 3% by mass.

<Other ingredients>
The ink composition in the invention may contain other additives in addition to the above components. Other additives include, for example, polymerization inhibitors, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension. Well-known additives, such as a regulator, an antifoamer, a viscosity regulator, a dispersion stabilizer, a rust inhibitor, a chelating agent, are mentioned. These various additives are generally added directly to the ink in the case of an ink composition, and when an oily dye is used as a dispersion, it is generally added to the dispersion after the preparation of the dye dispersion. Sometimes it may be added to the oil or water phase.

<Preferred physical properties of ink composition>
The surface tension (25 ° C.) of the ink composition in the present invention is not particularly limited, but 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.).
Further, the viscosity of the ink composition in the invention is not particularly limited, but the viscosity at 25 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more. It is less than 13 mPa · s, more preferably 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 the condition of 25 ° C. of the ink composition.
The pH of the ink composition in the present invention is not particularly limited, but is preferably 7.5 to 10 and more preferably 8 to 9 from the viewpoint of ink stability and aggregation rate. The pH of the ink composition is 25 ° C., and is measured by a commonly used pH measuring device (for example, multi water quality meter MM-60R manufactured by Toa DKK Co., Ltd.).
The pH of the ink composition can be appropriately adjusted using an acidic compound or a basic compound. As the acidic compound or the basic compound, a commonly used compound can be used without particular limitation.

≪Ink set≫
The ink set of the present invention includes at least one of the ink compositions of the present invention described above and at least one treatment liquid containing an aggregating component that aggregates the components in the ink composition.
By forming an image using the treatment liquid together with the ink composition, it is possible to increase the speed of ink jet recording, and even when recording at a high speed, drawability with high density and resolution (for example, reproducibility of fine lines and fine portions). ) Is excellent.
In general, in the image formation using the processing liquid, gloss unevenness tends to occur because an image is formed by aggregating pigments in the ink composition. For this reason, in the image formation using the processing liquid, the effect of suppressing uneven glossiness according to the present invention is more effectively achieved.
Furthermore, as described above, in image formation using the treatment liquid, the viscosity of the ink composition in the middle of drying is remarkably increased mainly due to the effect of the specific (meth) acrylamide compound contained in the ink composition. Therefore, the effect of suppressing image cracking and the effect of suppressing gloss unevenness according to the present invention are particularly prominent.

<Processing liquid>
The treatment liquid contains at least one aggregation component that aggregates the components in the ink composition.
This aggregating component forms an agglomerate when contacted with the ink composition.
The aggregation component may be a compound capable of changing the pH of the ink composition, a polyvalent metal salt, or a cationic polymer. In the present invention, from the viewpoint of cohesiveness of the ink composition, a compound capable of changing the pH of the ink composition is preferable, and a compound capable of lowering the pH of the ink composition is more preferable.

Examples of the compound that can lower the pH of the ink composition include acids (acidic substances).
Examples of the acid 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, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, derivatives of these compounds, or salts thereof, etc. Are preferable.
An acid may be used individually by 1 type and may use 2 or more types together.

When the treatment liquid contains an acid, the pH (25 ° C.) of the treatment liquid is preferably 6 or less, more preferably 4 or less, still more preferably in the range of 1 to 4, and particularly preferably 1 to 3. At this time, the pH (25 ° C.) of the ink composition is preferably 7.5 or more (more preferably 8.0 or more).
In particular, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ° C.) of the ink composition is 8.0 or more, and the pH (25 ° C.) of the treatment liquid is 0.5 to 4. Some cases are preferred.

Among them, the aggregating component in the present invention is preferably a highly water-soluble acid, preferably an organic acid, more preferably a divalent or higher valent organic acid in terms of enhancing the aggregating property and fixing the whole ink. A trivalent or less acidic substance is particularly preferred. The divalent or higher organic acid is preferably an organic acid having a first pKa of 3.5 or less, more preferably an organic acid of 3.0 or less. Specific examples include phosphoric acid, oxalic acid, malonic acid, citric acid and the like.

As the polyvalent metal salt and the cationic polymer that can be used as the aggregating component, for example, the polyvalent metal salt and the cationic polymer described in paragraphs 0155 to 0156 of JP 2011-042150 A can be used. it can.

The aggregating components can be used alone or in combination of two or more.
The content of the aggregating component in the treatment liquid is preferably 1 to 50% by mass, more preferably 3 to 45% by mass, and still more preferably 5 to 40% by mass.

Further, the treatment liquid can contain at least one polymerization initiator. The preferred range of the polymerization initiator is as described above.

In addition, the processing liquid may further contain other additives as other components within the range not impairing the effects of the present invention. Examples of other additives include anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension adjusters, antifoaming agents Known additives such as an agent, a viscosity modifier, a dispersant, a dispersion stabilizer, a rust inhibitor, and a chelating agent can be used.

≪Image formation method≫
The image forming method of the present invention comprises an ink applying step for forming an image by applying the ink composition of the present invention described above onto a recording medium by an ink jet method, and an aggregating component for aggregating the components in the ink composition. A treatment liquid application step for applying the treatment liquid to the recording medium; and a drying step for drying the image after the treatment liquid application step and the ink application step. The image forming method of the present invention may have other steps as necessary.
According to the image forming method of the present invention, as described above, the ink composition which is applied to the recording medium together with the treatment liquid and is in the middle of drying mainly due to the effect of the specific (meth) acrylamide compound contained in the ink composition. Since the viscosity of the product is remarkably increased, the effect of suppressing image cracking and the effect of suppressing gloss unevenness according to the present invention are particularly remarkable.

<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, when an image is recorded using the ink jet method, energy is applied to the desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and 8-27693. JP-A-2-276670, 7-276789, 9-323475, JP-A-62-238783, JP-A-10-153898, JP-A-10-217473, 10- No. 235995, No. 10-337947, No. 10-217597, No. 10-337947 etc. This can be done by discharging objects. As a preferred ink jet recording method for the present invention, the methods described in paragraph numbers 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 of the methods may be used. As an ink jet method, in particular, the method described in Japanese Patent Laid-Open No. Sho 54-59936 causes a sudden change in volume of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force caused by this state change. Ink jet method can be used effectively.

The inkjet method includes a method of ejecting a large number of 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. A method using ink is included.

In addition, an ink jet head used in the ink jet method may be an on-demand method or a continuous method. Discharge methods include electro-mechanical conversion methods (eg, single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), and electro-thermal conversion methods (eg, 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 onto the recording medium in accordance with an information signal.

(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 quartz vibrator 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), 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 aggregation component that aggregates the components in the ink composition onto a recording medium.
The treatment liquid is as described above, and the preferred range is also as described above.
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 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 application amount of the treatment liquid in the treatment liquid applying step, is not particularly limited as long as it can aggregate the ink composition, preferably, the amount of the applied aggregating component is 0.1 g / m ² or more that Can do. Of these, an amount that gives an aggregation component of 0.2 to 0.7 g / m ² is preferable. When the application amount of the aggregating component is 0.1 g / m ² or more, good high-speed aggregating property can be maintained according to various usage forms of the ink composition. Moreover, it is preferable that the amount of the aggregating component 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.

Heat drying can be performed by a known heating means such as a heater, a blowing means using blowing air 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.

<Drying process>
The drying process in the present invention is a process of drying the image after the treatment liquid application process and the image ink application process after the ink application process.
In general, in an image forming method having such a drying step, image cracks and uneven gloss of images tend to occur. However, in the image forming method of the present invention, since the ink composition of the present invention described above is used, image cracking and gloss unevenness of the image, which are likely to occur in the image forming method having a drying step, are suppressed.
In the drying step, at least a part of water in the image (ink composition) formed on the recording medium is removed by drying. By providing the drying step before the curing step described later and reducing the water content in the ink composition, the curing reaction of the polymerizable compound in the curing step proceeds better. In particular, when image formation is performed at a high speed, such as a method of forming an image by a single pass method in which ink is ejected in the main scanning direction to form one line in one scan, it is possible to ensure the sensitivity with which image formability is established. it can.

For example, when an image is formed at a recording medium conveying speed of 100 to 3000 mm / s, the effect of the present invention is further achieved. Further, when the conveying speed is 150 to 2700 mm / s, more preferably 250 to 2500 mm / s. Moreover, it is excellent in the effect of improving adhesion and scratch resistance due to the provision of the drying step.

In the drying step of the present invention, it is not always necessary to completely dry the water, and the water may remain in the image and the pigment layer. In the drying step, it is preferable to dry to the extent that it does not impair the UV curing reaction.

In the drying step, the drying conditions (hereinafter, sometimes referred to as “dry amount”) in which 60 to 80% by mass of the water contained in the ink composition (image) applied in the maximum applied amount are removed are described below. It is preferable that at least a part of water contained in the ink composition applied on the recording medium in the ink application step is removed. When the amount of water to be removed is 60% by mass or more, cuckling is suppressed, and image adhesion can be maintained satisfactorily. Further, when the amount of water to be removed is 80% by mass or less, the image adhesion is good.

The drying conditions may be set based on the maximum application amount of the ink composition in the ink application process that is appropriately set as necessary. By removing water in the ink composition containing the pigment under such dry conditions, the occurrence of cuckling is suppressed and an image having excellent adhesion can be obtained.

The amount of drying in the drying step can be calculated as follows. That is,
The amount of water W ₀ contained in the image formed with the maximum amount of ink applied without providing the drying step, and the amount of water W ₁ contained in the image formed with the maximum amount of ink applied with the drying step according to the predetermined drying conditions. And are measured respectively. Next, by obtaining the ratio of the difference between W ₀ and W ₁ to W ₀ ((W ₀ −W ₁ ) / W ₀ × 100 [mass%]), drying as the amount of water removed by the drying step is performed. The amount (mass%) is calculated.
The amount of water contained in the image is measured by the Karl Fischer method. As the amount of water in the present invention, the amount of water measured under normal measuring conditions using a Karl Fischer moisture meter MKA-520 (manufactured by Kyoto Electronics Industry Co., Ltd.) is applied.

The amount of water (dry amount) in the ink composition that is removed in the drying step is the total amount of the ink composition that is applied with a maximum application amount of 15 ml / m ² or less from the viewpoint that the curing efficiency after drying is kept good. 60 to 80% by mass is preferable, 65 to 80% by mass is more preferable, and 70 to 80% by mass is still more preferable with respect to the amount of water.

The drying is preferably started within 5 seconds from the point of time when the ink composition droplets have landed on the recording medium in the ink application step. Here, “within 5 seconds from the point of completion of landing” means that the image of the ink droplet is blown or the image of the ink droplet is within 5 seconds from the point of completion of landing of the ink droplet. On the other hand, it means that heat is given. For example, drying is started within 5 seconds from the completion of landing by transporting the recording medium into the drying area within 5 seconds from the completion of landing of ink droplets.
The time from the completion of ink droplet landing to the start of drying is more preferably within 3 seconds.

Drying can be performed by a heating means for heating with a heating element such as a nichrome wire heater, a blowing means using blowing air such as a dryer, or a combination of these.
Examples of the heating method include a method of applying heat from the opposite side of the image forming surface of the recording medium with a heater, a method of applying warm air or hot air to the image forming surface of the recording medium, a heating method using an infrared heater, and the like. Can be mentioned. Heating may be performed by combining a plurality of these.

<Curing process>
The image forming method of the present invention is further applied to the dried image on the recording medium by the ink application process after the drying process (process for applying the treatment liquid application process and the ink application process). The ink composition preferably has a curing step of irradiating the ink composition with active energy rays 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 rays is disposed opposite 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 preferably, for example, 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. Although there is no restriction | limiting in particular in a recording medium, For example, the general printing paper mainly used for celluloses, such as what is called a quality paper, a coated paper, and art paper, used for general offset printing etc. can be used. When general printing paper mainly composed of cellulose is used, image recording by a general ink jet method using water-based ink is relatively slow in absorption and drying of ink, and color material movement is likely to occur after droplet ejection, resulting in poor image quality. 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 color material movement.

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., Oji Paper 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 can be a drive 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 also be adopted. 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 may include, for example, known heating means such as a heater, 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.
In FIG. 1, the recording heads 30K, 30C, 30M, 30Y, 30A, and 30B are arranged in this order. However, the arrangement of the recording heads for the respective colors in the ink ejection unit 14 is not limited to this order, and is appropriately set. Can be changed.

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 recording method capable of relatively high speed recording, for example, a recording method capable of recording by ejecting in the main scanning direction by a single pass forming one line by one scanning. 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.

It is preferable to adjust the application amount of the treatment liquid and the application amount of the ink composition 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 have the same configuration 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 drying the image. 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.

In addition, in the ink jet recording apparatus, heating means for performing a heat treatment on the recording medium can be disposed in the 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.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, “part” and “%” are based on mass.

<Preparation of cyan ink>
(Preparation of Cyan Dispersion C1)
In a reaction vessel, 6 parts of styrene, 11 parts of stearyl methacrylate, 4 parts of styrene macromer AS-6 (manufactured by Toa Gosei Co., Ltd.), 5 parts of Plenmer PP-500 (manufactured by NOF Corporation), 5 parts of methacrylic acid, 2 parts -0.05 part of mercaptoethanol and 24 parts of methyl ethyl ketone were added to prepare a mixed solution.

Meanwhile, in a dropping funnel, 14 parts of styrene, 24 parts of stearyl methacrylate, 9 parts of styrene macromer AS-6 (manufactured by Toagosei Co., Ltd.), 9 parts of Plenmer PP-500 (manufactured by NOF Corporation), 10 parts of methacrylic acid 2-mercaptoethanol (0.13 parts), methyl ethyl ketone (56 parts), and 2,2′-azobis (2,4-dimethylvaleronitrile) (1.2 parts) were added to prepare a mixed solution.

In a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 1 hour. Two hours after the completion of the dropwise addition, a solution prepared by dissolving 1.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) in 12 parts of methyl ethyl ketone was added dropwise over 3 hours. Aged at 80 ° C. for 2 hours to obtain a polymer dispersant solution.

A part of the obtained polymer dispersant solution was isolated by removing the solvent, and the obtained solid content was diluted to 0.1% by mass with tetrahydrofuran to obtain a high-speed GPC (gel permeation chromatography) HLC- Three TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, and TSKgeL SuperHZ2000 (manufactured by Tosoh Corporation) were connected in series at 8220 GPC, and the weight average molecular weight was measured. As a result, the weight average molecular weight was 25,000 in terms of polystyrene. The acid value was 80 mgKOH / g.

Next, 5.0 g of the above polymer dispersant solution in terms of solid content, Pigment Blue 15: 3 (produced by Dainichi Seika Co., Ltd.) as a cyan pigment, 40.0 g of methyl ethyl ketone, 1 mol / L (liter; In the same manner, 8.0 g of sodium hydroxide and 82.0 g of ion-exchanged water were supplied to the vessel together with 300 g of 0.1 mm zirconia beads, and dispersed at 1000 rpm for 6 hours with a ready mill disperser (manufactured by Imex). The obtained dispersion was concentrated under reduced pressure using an evaporator until the methyl ethyl ketone was sufficiently distilled off, and further concentrated until the concentration of the water-dispersible pigment reached 10% by mass to obtain a cyan dispersion C1 in which the water-dispersible pigment was dispersed. Prepared.
The volume average particle diameter (secondary particles) of the obtained cyan dispersion liquid C1 was measured by a dynamic light scattering method using a Microtorac particle size distribution analyzer (Version 10.1.2-211BH (trade name), manufactured by Nikkiso Co., Ltd.). Was 77 nm.

(Synthesis of self-dispersing polymer particles P-1 (polymer particles))
360.0 g of methyl ethyl ketone was charged into a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 75 ° C. Thereafter, while maintaining the temperature in the flask at 75 ° C., 151.2 g of benzyl methacrylate, 172.8 g of methyl methacrylate, 36.0 g of methacrylic acid, 72 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) 1 .44 g of the mixed solution was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution composed of 0.72 g of “V-601” and 36.0 g of methyl ethyl ketone was added thereto, stirred at 75 ° C. for 2 hours, and further a solution composed of 0.72 g of “V-601” and 36.0 g of isopropanol. And stirred at 75 ° C. for 2 hours. Thereafter, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours to obtain a polymer solution of a benzyl methacrylate / methyl methacrylate / methacrylic acid (= 42/48/10 [mass ratio]) copolymer.
The weight average molecular weight (Mw) measured in the same manner as described above of the obtained copolymer was 58000 (calculated in terms of polystyrene by gel permeation chromatography (GPC)), and the acid value was 32.6 mgKOH / g. It was.

Next, 668.3 g of the obtained polymer solution was weighed, 388.3 g of isopropanol and 145.7 ml of 1 mol / L NaOH aqueous solution were added thereto, and the temperature in the reaction vessel was raised to 80 ° C. Next, 720.1 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water, and then the reaction vessel internal temperature was 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. Kept. Thereafter, the pressure in the reaction vessel is reduced, and 913.7 g of isopropanol, methyl ethyl ketone, and distilled water are distilled off in total, and the self-dispersing polymer particles P-1 (polymer particles) having a solid content concentration (polymer particle concentration) of 28.0% by mass ) Was obtained.

Among the constituent components (structural units) of the self-dispersing polymer particles P-1, constituent components derived from benzyl methacrylate (structural units), constituent components derived from methyl methacrylate (structural units), and constituent components derived from methacrylic acid Hereinafter, (structural unit) is also referred to as “component A”, “component B”, and “component C”, respectively.
In addition, the mass ratio of the constituent component A, the constituent component B, and the constituent component C [the mass of the constituent component A / the mass of the constituent component B / the mass of the constituent component C] is hereinafter referred to as the mass ratio of the constituent components [A / B / C].

The glass transition temperature (Tg) of the self-dispersing polymer particles P-1 was measured by the following method and found to be 90 ° C.
-Measurement of glass transition temperature (Tg)-
An aqueous dispersion of self-dispersing polymer particles having a solid content of 0.5 g was dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid content. Using the obtained polymer solid content, Tg was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. The measurement condition was that a sample amount of 5 mg was sealed in an aluminum pan, and the DSC peak top value of the measurement data at the second temperature increase was defined as Tg under the following temperature profile in a nitrogen atmosphere.
30 ℃ → -50 ℃ (cooling at 50 ℃ / min)
-50 ° C → 120 ° C (temperature rise at 20 ° C / min)
120 ° C to -50 ° C (cooled at 50 ° C / min)
-50 ° C → 120 ° C (temperature rise at 20 ° C / min)

(Synthesis of tetrafunctional acrylamide 1)
As a (meth) acrylamide compound (specific (meth) acrylamide compound) represented by the general formula (1), tetrafunctional acrylamide 1 (the aforementioned polymerizable compound a. Hereinafter also referred to as the exemplified compound (a)) is as follows. And synthesized.
-First step-
In a 1 L three-necked flask equipped with a stir bar, 121 g (1 equivalent) of tris (hydroxymethyl) aminomethane (manufactured by Tokyo Chemical Industry Co., Ltd.), 84 ml of 50% by weight potassium hydroxide aqueous solution and 423 ml of toluene were added and stirred. The reaction system was maintained at 20-25 ° C. in a water bath, and 397.5 g (7.5 equivalents) of acrylonitrile was added dropwise over 2 hours. After dropping, the mixture was stirred for 1.5 hours. Thereafter, 540 ml of toluene was added to the reaction system, the reaction mixture was transferred to a separatory funnel, and the aqueous layer was removed. The remaining organic layer was dried over magnesium sulfate, filtered through celite, and the solvent was distilled off under reduced pressure to obtain an acrylonitrile adduct. The results of analysis of the obtained substance by ¹ H-NMR and MS showed a good agreement with the known substance, and it was used for the next reduction reaction without further purification.

-Second step-
In an autoclave having a volume of 1 L, 24 g of the obtained acrylonitrile adduct, 48 g of Ni catalyst (Raney nickel 2400, manufactured by WR Grace & Co.), and 600 ml of 25% by mass aqueous ammonia solution (water: methanol = 1: 1) were placed. The reaction vessel was sealed by suspending. 10 Mpa of hydrogen was introduced into the reaction vessel and reacted at a reaction temperature of 25 ° C. for 16 hours.
The disappearance of the starting material was confirmed by ¹ H-NMR, the reaction mixture was filtered through Celite, and the Celite was washed several times with methanol. The filtrate was evaporated under reduced pressure to obtain a polyamine compound. The obtained material was used in the next reaction without further purification.

-Third process-
To a 2 L three-necked flask equipped with a stirrer, 30 g of the polyamine obtained, 120 g of NaHCO ₃ (14 equivalents), 1 L of dichloromethane and 50 ml of water were added, and 92.8 g (10 equivalents) of acrylic acid chloride was added in an ice bath. The solution was added dropwise over 3 hours. Then, it stirred at room temperature for 3 hours. After confirming disappearance of the starting material by ¹ H-NMR, the reaction mixture was evaporated under reduced pressure. Subsequently, the reaction mixture was dried with magnesium sulfate, filtered through Celite, and the solvent was distilled off under reduced pressure. Finally, by purification by column chromatography (ethyl acetate / methanol = 4: 1), tetrafunctional acrylamide 1 (in the general formula (1), R ¹ = H R ² = C ₃ H ₆ at room temperature) A solid of R ³ = CH ₂ , X = Y = Z = 0) was obtained.
The yield of tetrafunctional acrylamide 1 obtained through the above three steps was 40% by mass.

(Synthesis of tetrafunctional acrylamide 2)
As a (meth) acrylamide compound (specific (meth) acrylamide compound) represented by the general formula (1), tetrafunctional acrylamide 2 (the above-mentioned polymerizable compound b. Hereinafter also referred to as the exemplified compound (b)) is converted to tetrafunctional acrylamide. 1 was synthesized in the same manner as in 1.

(Preparation of cyan ink)
The following composition was mixed, filtered through a glass filter (GS-25) manufactured by ADVANTEC, and then filtered through a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to obtain a cyan ink.
-Composition of cyan ink-
Cyan dispersion C1 (concentration of water-dispersible pigment: 10% by mass) ... 20.0% by mass
・ Hydroxyethylacrylamide (monofunctional acrylamide): 15.0% by mass
Tetrafunctional acrylamide 1 (Exemplary Compound a) 10.0 mass%
・ Sanix GP250 (manufactured by Sanyo Chemical Industries, Ltd .; hydrophilic organic solvent) ... 2.0% by mass
・ Olfin E1010 (manufactured by Nissin Chemical Industry Co., Ltd .; surfactant) ... 1.0% by mass
・ Irgacure 2959 (manufactured by BASF; photopolymerization initiator) ... 3.0% by mass
・ Self-dispersing polymer particles P-1 (solid content): 2.0% by mass
・ Ion-exchanged water: remaining amount of 100.0% by mass in total

<Preparation of magenta ink>
The magenta ink was prepared in the same manner as the cyan ink except that the cyan pigment Pigment Blue 15: 3 was changed to a magenta pigment Pigment Red 122 (manufactured by Dainichi Seika Co., Ltd.) in the preparation of the cyan ink. Was prepared.

≪Preparation of treatment liquid≫
The processing liquid was prepared by mixing components having the following composition.
~ Composition of treatment liquid ~
-Malonic acid (Wako Pure Chemical Industries, Ltd.) ... 25.0% by mass
・ Diethylene glycol monomethyl ether (Wako Pure Chemical Industries, Ltd.) ... 20.0% by mass
・ Emulgen P109 (manufactured by Kao Corporation, nonionic surfactant) ... 1.0% by mass
・ Ion-exchanged water: remaining amount of 100.0% by mass in total

≪Preparation of ink set≫
Prior to image formation, an ink set prepared by combining the cyan ink, magenta ink, and processing liquid prepared above was prepared.

≪Preparation of recording medium≫
In forming an image, a coated paper (OK Top Coat manufactured by Oji Paper Co., Ltd. + (grade: A2 gloss), basis weight 104.7 g / m ² ) was prepared as a recording medium.

≪Image formation (inkjet recording) ≫
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 ejection section 14 for ejecting various ink compositions, an ink drying zone 15 for drying the ejected ink composition, and UV irradiation capable of irradiating ultraviolet rays (UV) An ink jet apparatus provided with a UV irradiation unit 16 provided with a lamp 16S 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 air volume were adjusted and 900% by mass or more of the water in the treatment liquid could be evaporated (dried) by 900 msec after the application of the treatment liquid was 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. Each head has a 1200 dpi / 10 inch width. It was a full line head (drive frequency: 25 kHz), and each color could be discharged and recorded in the main scanning direction by a single pass.
In this embodiment, the arrangement of the magenta ink ejection head 30M and the cyan ink ejection head 30C in FIG. 1 is changed, and the arrangement is changed so that ink can be ejected in the order of magenta and cyan on the recording medium.

The processing liquid, the magenta ink, and the cyan ink are sequentially loaded into storage tanks (not shown) connected to the processing liquid discharge head 12S, the magenta ink discharge head 30M, and the cyan ink discharge head 30C, respectively. The treatment liquid, the magenta ink, and the cyan ink were ejected in this order to form an image.
The amount of treatment liquid applied to the recording medium was 1.5 ml / m ² .
During image formation, magenta ink and cyan ink were ejected from the head at a resolution of 1200 dpi × 1200 dpi and an ink droplet amount of 2.5 pl, respectively. The magenta ink and the cyan ink were ejected under the condition that the total maximum application amount of the magenta ink and the cyan ink was 11 ml / m ² .

Specifically, the image was formed as follows.
First, after the processing liquid is discharged (applied) from the processing liquid discharge head 12S onto the recording medium in a single pass, the processing liquid is dried in the processing liquid drying zone 13, and the processing liquid drying zone is started from the discharge of the processing liquid. Passed by 900 msec. In the treatment liquid drying zone 13, while the deposited treatment liquid is heated from the back side (back side) of the landing surface with an infrared heater so that the film surface temperature is 40 to 45 ° C., the recording surface is 120 ° C. on the recording surface. Drying was performed by applying warm air of 5 m / sec for 5 seconds.
Subsequently, magenta ink is applied to the surface of the recording medium to which the processing liquid is applied (processing liquid application surface) from the ejection head 30M in a single pass with a single dot ratio of 100%, and the applied magenta. An image was obtained by applying cyan ink onto the ink in a solid form with a dot ratio of 100% in a single pass from the ejection head 30C.
On the recording medium on which the image is formed, hot air of 120 ° C. and 5 m / sec is recorded by a blower while heating with an infrared heater from the back side (back side) of the ink landing surface in the ink drying zone 15 as described above. The image was dried by placing it on the surface for 5 seconds.
The UV irradiation unit 16 irradiates the dried image with UV light (a metal halide lamp, maximum irradiation wavelength 365 nm, manufactured by Eye Graphics Co., Ltd.) so that the integrated irradiation amount is ² J / cm ² , and the image is UV cured. did.

≪Evaluation≫
The following evaluation was performed on the image after UV curing. The evaluation results are shown in Table 1 below.

<Image cracking>
The image after UV curing was observed with an optical microscope (magnification 300 times), and image cracking was evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: Image cracking was not observed B: Image cracking was observed in a part of the image, but image cracking did not reach half of the image C: Image cracking was observed in more than half of the image However, the image crack did not reach the entire image D: Image crack was observed in the entire image

<Gloss unevenness>
The UV cured image was visually observed and gloss unevenness was evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: Gloss unevenness was not observed B: Gloss unevenness was slightly observed C: Gloss unevenness was observed in the entire image

[Examples 2 to 36, Comparative Examples 1 to 21]
In Example 1, the tetrafunctional acrylamide 1 (exemplary compound a) and self-dispersing polymer particles contained in the cyan ink (specifically, the type of component A, the mass ratio of each component [component A / component) A cyan ink was prepared in the same manner as in Example 1 except that B / constituent component C]) was changed as shown in Tables 1 and 2 below.
Image formation and evaluation were performed in the same manner as in Example 1 except that the obtained cyan ink was used.
The evaluation results are shown in Tables 1 and 2 below.

 

 

~ Explanation of Table 1 and Table 2 ~
Mw is a weight average molecular weight.
-The tetrafunctional acrylamide 2 is the above-mentioned exemplary compound (b).
Trifunctional acrylamide 1 is a nonionic compound (c) described in paragraph 0158 of JP2011-46872A.
Trifunctional acrylate 1 is nonionic compound 3 described in paragraph 0155 of JP2011-46872A.
The tetrafunctional acrylamide 3 is a tetrafunctional acrylamide other than the specific (meth) acrylamide compound, and specifically, the polymerizable compound 3 described in paragraph 0030 of JP 2011-174013 A.
The tetrafunctional acrylamide 4 is a tetrafunctional acrylamide other than the specific (meth) acrylamide compound, and specifically, the polymerizable compound 21 described in paragraph 0047 of JP2011-195822A.
The tetrafunctional acrylamide 5 is a tetrafunctional acrylamide other than the specific (meth) acrylamide compound, and specifically, the polymerizable compound 35 described in paragraph 0049 of JP2011-195822A.
The mass ratio [A / B / C] of the component indicates the mass ratio [component A / component B (= methyl methacrylate) / component C (= methacrylic acid)].
-Component A is indicated by the monomer name. The abbreviations are as follows.
BzMA: benzyl methacrylate PheOEA: phenoxyethyl acrylate IBOMA: isobornyl methacrylate CyHMA: cyclohexyl methacrylate

As shown in Tables 1 and 2, Examples using cyan ink containing specific (meth) acrylamide compounds (tetrafunctional acrylamide 1 or tetrafunctional acrylamide 2) and polymer particles having a glass transition temperature (Tg) of 90 ° C. or higher In 1 to 36, image cracking and gloss unevenness were suppressed.
In contrast, Comparative Examples 1 to 16 using trifunctional acrylamide, trifunctional acrylate, or tetrafunctional acrylamide other than the specific (meth) acrylamide compound (tetrafunctional acrylamide 3 to 5) instead of the specific (meth) acrylamide compound. And 19 to 21, at least one of image cracking and gloss unevenness was remarkable.
In Comparative Examples 17 and 18 in which polymer particles having a glass transition temperature (Tg) of 90 ° C. or lower were used instead of polymer particles having a glass transition temperature (Tg) of 90 ° C. or higher, image cracking was significant.

In the above examples, evaluation was performed using cyan ink. However, in the case of using inks of colors other than cyan, such as yellow ink and magenta ink, the specific (meth) acrylamide compound and glass are used in the same manner as in the above examples. By using an ink containing polymer particles having a transition temperature (Tg) of 90 ° C. or higher, image cracking and gloss unevenness can be suppressed.

The entire disclosure of Japanese Application No. 2012-214629 is incorporated herein by reference.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims (12)

1. An ink composition comprising a pigment, water, a (meth) acrylamide compound represented by the following general formula (1), a polymerization initiator, and polymer particles having a glass transition temperature of 90 ° C. or higher.
   

   

   
   
   [In the general formula (1), a plurality of R ^{1 s} each independently represent a hydrogen atom or a methyl group, and a plurality of R ^{2 s} each independently represent a linear or branched alkylene group having 2 to 4 carbon atoms. However, not to take an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom in R ² structure. Several R < ³ > represents a bivalent coupling group each independently. Several k represents 2 or 3 each independently. x, y, and z each independently represent an integer of 0 to 6, and x + y + z satisfies 0 to 18. ]
2. The ink composition according to claim 1, wherein the content of the polymer particles is 0.5% by mass to 5.0% by mass with respect to the total amount of the ink composition.
3. The ink composition according to claim 1 or 2, wherein the polymer constituting the polymer particles contains at least one selected from the group consisting of a structural unit having an aromatic group and a structural unit having an alicyclic group. object.
4. The polymer constituting the polymer particle contains, as a structural unit having an aromatic group, at least one selected from the group consisting of a structural unit having a benzyl group and a structural unit having a phenoxy group. 4. The ink composition according to any one of 3 above.
5. The ink composition according to any one of claims 1 to 4, wherein the polymer constituting the polymer particles contains 3 mass% to 45 mass% of a structural unit having an aromatic group with respect to the total amount of the polymer. object.
6. The polymer constituting the polymer particles is a total of 3 mass% to 45 mass% of at least one selected from the group consisting of a structural unit derived from benzyl (meth) acrylate and a structural unit derived from phenoxyethyl (meth) acrylate. %, A total of 5% by mass to 20% by mass of structural units derived from (meth) acrylic acid, and a total of 40% by mass to 90% by mass of structural units derived from alkyl (meth) acrylate. The ink composition according to any one of claims 1 to 5.
7. The ink composition according to any one of claims 1 to 6, wherein the polymer particles are polymer particles obtained by a phase inversion emulsification method.
8. The ink composition according to any one of claims 1 to 7, wherein the polymer particles have a glass transition temperature of 100 ° C or higher.
9. An ink set comprising the ink composition according to any one of claims 1 to 8, and a treatment liquid containing an aggregating component for aggregating the components in the ink composition.
10. An ink applying step of forming an image by applying the ink composition according to any one of claims 1 to 8 onto a recording medium by an inkjet method;
    A treatment liquid application step of applying a treatment liquid containing an aggregation component for aggregating the components in the ink composition onto a recording medium;
    A drying step of drying the image after the treatment liquid applying step and the ink applying step;
    An image forming method comprising:
11. The image forming method according to claim 10, wherein the recording medium is a coated paper having a base paper and a coating layer containing an inorganic pigment.
12. The image forming method according to claim 10 or 11, wherein the ink application step is provided after the treatment liquid application step.

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