WO2019058920A1

WO2019058920A1 - Aqueous ink composition for inkjet recording, image forming method, and resin fine particles

Info

Publication number: WO2019058920A1
Application number: PCT/JP2018/032170
Authority: WO
Inventors: 史子玉國
Original assignee: 富士フイルム株式会社
Priority date: 2017-09-20
Filing date: 2018-08-30
Publication date: 2019-03-28
Also published as: JPWO2019058920A1; JP6795704B2

Abstract

Provided are: an aqueous ink composition for inkjet recording containing an aqueous medium and resin fine particles, wherein the resin fine particles each have a core-shell structure including a core polymer and a shell polymer covering the core polymer, the shell polymer has specific structural units (I) and (II), the glass transition temperature of the core polymer is higher than the glass transition temperature of the shell polymer, and the glass transition temperature of the shell polymer is 20-130ºC; an image forming method; and the resin fine particles.

Description

Aqueous ink composition for ink jet recording, image forming method and resin fine particle

The present invention relates to an aqueous ink composition for ink jet recording, an image forming method, and resin fine particles.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are recording methods such as an electrophotographic method, a sublimation type and a fusion type thermal transfer method, and an inkjet method.
The inkjet recording method does not require a printing plate, and discharges the ink only to the image forming unit to form an image directly on the recording medium. Therefore, the ink can be used efficiently and the running cost is reduced. Furthermore, the ink jet recording method is relatively low in cost, can be miniaturized, and has less noise as compared with the conventional printing machine. Thus, the inkjet recording method has various advantages as compared with other image recording methods.

The ink used in the ink jet recording method is required to have discharge stability capable of stably discharging a desired amount of ink from the nozzle in order to form a target image accurately and stably. In addition, the ink is also required to be capable of forming an image showing mechanical strength (abrasion resistance) which is not scratched or peeled off when a force is applied from the outside.

Improvements are being made to the ink to meet the above requirements. For example, various inks containing resin fine particles having a core-shell structure have been proposed (see Patent Documents 1 to 4).
Specifically, Patent Document 1 describes an ink composition for inkjet recording containing polymer fine particles having a core-shell structure in which the glass transition temperature of the core polymer and the shell polymer is specified. In addition, Patent Document 2 describes a clear ink for ink jet containing a polymer particle having a core-shell structure obtained by polymerizing a core polymer in the presence of a shell polymer having a unit derived from a specific monomer. Further, Patent Document 3 describes an aqueous ink containing a specific resin particle having a core and a shell, and a polyvalent metal ion. Patent Document 4 describes an inkjet ink containing a colorant and resin particles having a specific shell part and a specific core part.

JP, 2014-208738, A JP, 2011-11449, A JP 2017-101178 A JP, 2013-136744, A

The ink jet recording method has been mainly used in the field of office printers, home printers and the like. Furthermore, in recent years, its use has expanded to the commercial printing field, and the speeding up of ink jet recording has been advanced. Along with this, the demand for the ejection stability of the ink is in a state of becoming more and more advanced year by year. The ink jet recording method has a unique and urgent problem that the nozzle is clogged if the nozzle is left after image formation, for example, once the image formation is paused (interrupted). For this reason, the ink used in the ink jet recording method is strongly required to have characteristics (also referred to as latency and restorability) which can be normally ejected even after pausing. Moreover, in the ink used for the inkjet recording method, the performance (blocking resistance) to prevent the color transfer between the front and back of the stacked recording media or the adhesion between the recording media when the recording media on which the image is formed is stacked, etc. It is required to be able to form an image having the same.

The present invention provides an aqueous ink composition for inkjet recording, which is excellent in latency when applied to an inkjet recording method, and can form an image excellent in abrasion resistance and blocking resistance, and the aqueous ink composition for inkjet recording. An object is to provide an image forming method used.
Further, the present invention can impart high latency to the aqueous ink composition for ink jet recording by blending into the aqueous ink composition for ink jet recording, and further, the abrasion resistance and blocking resistance of the formed image. It is an object of the present invention to provide resin fine particles which can also enhance

As a result of intensive investigations in view of the above problems, the present inventor has identified a specific structural unit (repeating unit) in which a specific acidic group such as a carboxy group or the like or a salt thereof is bound via a specific group. The core-shell resin fine particles are contained in an aqueous medium using at least a polymer having a structural unit having an alkyleneoxy group as a shell polymer as a shell polymer and controlling the relationship of the glass transition temperature between the core and the shell polymer It has been found that the aqueous ink composition is excellent in latency when used as an ink for ink jet recording, and further, the abrasion resistance and blocking resistance of an image formed using this aqueous ink composition are excellent. The present invention has been further studied based on these findings and has been completed.

The above problems of the present invention are solved by the following means.
<1> An aqueous ink composition for inkjet recording comprising an aqueous medium and resin fine particles,
The resin fine particles have a core-shell structure containing a core polymer and a shell polymer covering the core polymer,
The shell polymer has a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2A) or the formula (2B),
An aqueous ink composition for ink jet recording, wherein the glass transition temperature of the core polymer is higher than the glass transition temperature of the shell polymer, and the glass transition temperature of the shell polymer is 20 to 130 ° C.

In the formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ² represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, or an aromatic ring group. A ¹ represents an alkylene group having 2 to 20 carbon atoms. m ¹ is an integer of 1 to 100.
In formulas (2A) and (2B), R ³ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. L ^1A represents a single bond or a linking group having a minimum number of 6 or less linking the carbonyl carbon atom in the formula and Y ^1A . Y ^1A represents —OM when L ^1A is a single bond, and —C (= O) OM, —S (= O) ₂ OM or —OS (= O) when L ^1A is a linking group ₂ indicates OM. Y ^1B represents —C (= O) OM, —S (= O) ₂ OM or —OS (= O) ₂ OM. M represents a hydrogen atom, an alkali metal ion or an ammonium ion.

The aqueous | water-based ink composition for inkjet recording as described in <1> whose structural unit represented by <2> Formula (1) is a structural unit represented by following formula (3).

In the formula, R ¹ and R ² are as described above. m ² is an integer of 2 to 100.

The aqueous ink composition for inkjet recording as described in <1> or <2> whose absolute value of the difference of the glass transition temperature of <3> core polymer and the glass transition temperature of shell polymer is 20 degreeC or more.
The aqueous ink composition for inkjet recording according to any one of <1> to <3>, wherein the content of the structural unit represented by Formula (1) in the <4> shell polymer is 30% by mass or less. object.
<5> The inkjet recording according to any one of <1> to <4>, wherein at least one of the core polymer and the shell polymer has a structural unit derived from an ethylenically unsaturated compound having an aromatic ring or an aliphatic ring. Water-based ink composition.

The aqueous | water-based for inkjet recording as described in <5> by which the structural unit derived from the ethylenically unsaturated compound which has a <6> aromatic ring or an aliphatic ring is represented with either of the following general formula (A)-(E). Ink composition.

In formulas (A) to (E), R ¹¹ and R ^{12 each} represent a methyl or hydrogen atom. R ¹³ represents a linear or branched alkyl group having 1 to 10 carbon atoms. N in the general formula (A) and the general formula (B) is an integer of 0 to 5, and n in the general formula (C) is an integer of 0 to 11. L ¹¹ represents a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C (= O)-or a divalent linking group formed by linking two or more of these.

The content of the structural unit represented by any one of formulas (A) to (E) in the <7> core polymer is 10 to 90% by mass,
The aqueous ink composition for inkjet recording according to <6>, wherein the content of the structural unit represented by any of the general formulas (A) to (E) in the shell polymer is 70% by mass or less.
The aqueous ink for inkjet recording according to any one of <1> to <7>, wherein the content of the fine resin particles is 1 to 15% by mass with respect to the total mass of the aqueous ink composition for inkjet recording Composition.
<9> The aqueous ink composition for inkjet recording according to any one of <1> to <8>, which contains a pigment.
<10> An image forming method comprising an ink applying step of applying an aqueous ink composition for inkjet recording according to <9> onto a recording medium by an inkjet method to form an image.
<11> The image forming method according to <10>, wherein the aqueous ink composition for inkjet recording is directly applied onto a low water absorption recording medium or a non-water absorption recording medium.

A fine resin particle having a core-shell structure containing a <12> core polymer and a shell polymer for covering the core polymer,
The shell polymer has a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2A) or the formula (2B),
Resin fine particles, wherein the glass transition temperature of the core polymer is higher than the glass transition temperature of the shell polymer, and the glass transition temperature of the shell polymer is 20 to 130 ° C.

The resin particle as described in <12> whose structural unit represented by <13> Formula (1) is a structural unit represented by following formula (3).

In the present specification, unless otherwise specified, when there are a plurality of substituents, linking groups, ligands, structural units and the like (hereinafter referred to as substituents and the like), which are represented by specific symbols, When the groups are simultaneously or alternatively defined, each substituent may be the same as or different from each other. The same applies to the definition of the number of substituents and the like.
In the present specification, the “group” of each group described as an example of each substituent is used to include both the unsubstituted form and the form having a substituent. For example, "alkyl group" means an alkyl group which may have a substituent.
In the present specification, “(meth) acrylate” is used to mean including both acrylate and methacrylate. The same applies to "(meth) acrylic acid", "(meth) acrylamide" and "(meth) acryloyl group".
In the present specification, a numerical range represented using “to” means a range including numerical values described before and after “to” as the lower limit value and the upper limit value.

The aqueous ink composition for inkjet recording of the present invention can form an image excellent in latency when applied to an inkjet recording method, and excellent in abrasion resistance and blocking resistance. The image forming method of the present invention can stably (unclogged) form an image excellent in abrasion resistance and blocking resistance. The resin fine particle of the present invention can impart latency suitable for the ink jet recording method to the aqueous ink composition by blending the same into the aqueous ink composition, and further, an image excellent in abrasion resistance and blocking resistance. Can be formed.
The above and other features and advantages of the present invention will become more apparent from the following description.

The preferred embodiments of the aqueous ink composition for inkjet recording of the present invention (hereinafter sometimes simply referred to as the aqueous ink composition of the present invention), the image forming method and the resin fine particles are described below.

[Water-based ink composition for inkjet recording]
The aqueous ink composition of the present invention contains an aqueous medium and specific resin fine particles. In addition, the aqueous ink composition of the present invention usually contains a pigment. When the aqueous ink composition of the present invention does not contain a pigment, it can be used as a clear ink, and when it contains a pigment, it can be used for color imaging applications.

<Aqueous medium>
The aqueous medium used in the present invention contains at least water, and optionally contains at least one water-soluble organic solvent.
- water -
As water used in the present invention, it is preferable to use water which does not contain ionic impurities such as ion exchange water and distilled water. The content of water in the aqueous ink composition is appropriately selected according to the purpose, but generally 10 to 95% by mass, preferably 30 to 80% by mass, and more preferably 50 to 50% by mass. More preferably, it is 70% by mass.

-Water soluble organic solvent-
The aqueous medium in the present invention preferably contains at least one water-soluble organic solvent. By containing the water-soluble organic solvent, it is possible to obtain the effect of the anti-drying, the wetting or the permeation acceleration. Here, the prevention of drying means that the ink adheres to the ink discharge port of the jet nozzle and is dried to prevent aggregation and clogging. For the purpose of preventing drying or wetting, a water-soluble organic solvent having a vapor pressure lower than that of water is preferred. Further, the water-soluble organic solvent can be used as a penetration accelerator for enhancing the ink permeability to paper.

Examples of the water-soluble organic solvent include, for example, alkyl alcohols having 1 to 4 carbon atoms, alkanediols (polyhydric alcohols), sugar alcohols, glycol ethers and the like.
The alkyl alcohol having 1 to 4 carbon atoms is not particularly limited, and examples thereof include ethanol, methanol, butanol, propanol and isopropanol.
The alkane diol is not particularly limited, but glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, dipropylene glycol, 1,2-butanediol, 1,2-hexanediol, 1 And 2-heptanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, and those described later.

The glycol ethers are not particularly limited, and the following compounds may be mentioned.
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monopentyl ether, ethylene glycol monohexyl ether, ethylene glycol monoheptyl ether, ethylene glycol monooctyl ether, ethylene glycol monononyl Ether, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol monomethyl ether acetate,
Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, diethylene glycol monooctyl ether, diethylene glycol monononyl ether, diethylene glycol mono-2-ethylhexyl ether ,
Triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monopentyl ether, triethylene glycol monohexyl ether, triethylene glycol monoheptyl ether, triethylene glycol monooctyl ether, triethylene glycol monononyl ether, triethylene Glycol mono-2-ethylhexyl ether,
Propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monopentyl ether, propylene glycol monohexyl ether, propylene glycol monoheptyl ether, propylene glycol monooctyl ether, propylene glycol mono- 2-ethylhexyl ether,
Dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopentyl ether, dipropylene glycol monohexyl ether, dipropylene glycol monoheptyl ether, dipropylene glycol Monooctyl ether, dipropylene glycol mono-2-ethylhexyl ether,
Tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monopentyl ether, tripropylene glycol monohexyl ether, tripropylene glycol monoheptyl ether, tripropylene glycol monooctyl ether, tripropylene glycol mono-2-ethylhexyl ether,
1-Methyl-1-methoxybutanol

The water-soluble organic solvents can be used singly or in combination of two or more.
Polyhydric alcohols are useful for the purpose of preventing drying or moistening, for example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 2 And 3-butanediol. These may be used alone or in combination of two or more.

For the purpose of permeation promotion, polyol compounds are preferred, and aliphatic diols are preferred. Examples of aliphatic diols include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol, and the like. And -ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol and the like. Among these, 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol can be mentioned as preferable examples.

The water-soluble organic solvent in the invention may also contain at least one of the compounds represented by the following structural formula (S) from the viewpoint of suppressing the occurrence of curling in the recording medium.

In structural formula (S), t, u and v each independently represent an integer of 1 or more, satisfy t + u + v = 3-15, t + u + v is preferably in the range of 3-12, more preferably in the range of 3-10 . When the value of t + u + v is 3 or more, a good curl suppressing power is exhibited, and when it is 15 or less, good dischargeability is obtained. In Structural Formula (S), AO represents at least one of an ethyleneoxy group (EO) and a propyleneoxy group (PO), and among them, a propyleneoxy group is preferable. Each AO in the above (AO) _t , (AO) _u , and (AO) _v may be the same or different. In the above structural formula (S), EO and PO are bonded with the ethylene group or propylene group located on the hydroxyl group side.

In the present invention, the water-soluble organic solvent may be used singly or in combination of two or more.
The content of the water-soluble organic solvent in the aqueous ink composition is preferably 1% by mass to 60% by mass, more preferably 5% by mass to 40% by mass, and still more preferably 7% by mass to 30%. It is less than mass%.

<Resin fine particles>
The aqueous ink composition of the present invention contains resin fine particles having a core-shell structure containing a core polymer and a shell polymer for coating the core polymer. In the fine resin particles, at least a shell polymer has a structural unit (I) represented by the following formula (1) and a structural unit (II) represented by the following formula (2A) or the formula (2B) There is. The fine resin particles have a glass transition temperature of the core polymer higher than that of the shell polymer and a glass transition temperature of the shell polymer of 20 to 130 ° C. This resin fine particle is also simply referred to as "resin fine particle used in the present invention".

When the aqueous ink composition of the present invention contains the above-mentioned resin fine particles, it is possible to form an image excellent in latency when applied to an ink jet recording method and excellent in abrasion resistance and blocking resistance. Although the detailed reason is not clear, it is considered as follows.
That is, the shell polymer forming the resin fine particles contains the structural unit (II) having a specific group Y ^1A or Y ^1B , and this specific group functions as a so-called charge repellent group in the resin fine particles. Thus, the shell polymer can cause the resin particles to electrostatically repel each other, and can exert a dispersion stabilizing action of the resin particles. Moreover, the shell polymer is a structural unit (a group represented by-(A ¹ -O) m ^{1-in the} formula (1)) in combination with the structural unit (II) (a group represented by-(A ¹ -O) m ^1- ) I). By the cooperation of such structural units (I) and (II), the stability of the resin fine particles in the aqueous ink composition is improved, gelation of the aqueous ink composition, and further resin fine particles to aqueous The aggregation of the ink composition is suppressed, and the above-mentioned dispersion stabilizing action is effectively developed. As a result, clogging of the nozzles is less likely to occur, which is considered to indicate high latency.
On the other hand, in the resin fine particles containing the shell polymer having the structural unit (I) and the structural unit (II) in the specific combination described above, the glass transition temperature of the shell polymer is set to 20 to 130 ° C. By setting the glass transition temperature higher than that of the shell polymer, each of the polymers forming the core-shell structure of the resin fine particles in the image formation with the aqueous ink composition of the present invention does not impair the expression of the above-mentioned action. It can assume different functions. As a result, both abrasion resistance and blocking resistance can be enhanced. That is, it is considered that the fine resin particles can exhibit and maintain the thermal adhesion by the shell polymer having a low glass transition temperature and the thermal stability by a core polymer having a high glass transition temperature in a well-balanced manner. Therefore, the resin fine particles of the present invention can enhance the abrasion resistance and the blocking resistance of the image while exhibiting an excellent latency.

As described above, this resin fine particle has a core-shell structure containing a core polymer and a shell polymer that coats the core polymer. In this core-shell structure, the core polymer (core layer formed by the core polymer) may be at least partially covered with the shell polymer, and the amount of the core polymer coated is not particularly limited. Moreover, the layer thickness of the shell layer which consists of shell polymers is not specifically limited, either. In the present invention, the coating amount and the layer thickness of the shell layer can be specified by, for example, the mass ratio of the core polymer to the shell polymer, and it is indicated by the mass ratio [core polymer: shell polymer], for example, 80 to The ratio is preferably 20:20 to 80, and more preferably 70:30 to 30:70.
The core polymer and the shell polymer (both may be collectively referred to as core / shell polymer) which form the resin fine particles may be one kind or two or more kinds respectively. The resin fine particles may have a polymer different from the core polymer and the shell polymer as long as the effects of the present invention are not impaired.

The shell polymer has, as structural units, at least one of structural units (I) described later and at least one of structural units (II). The shell polymer preferably has, in addition to the structural unit (I) and the structural unit (II), other structural units (III) described later.
The core polymer may have any structural unit as long as the conditions of the glass transition temperature are satisfied. For example, the core polymer does not necessarily have to have the structural unit (I) and the structural unit (II), and has one or both of the structural unit (I) and the structural unit (II) You do not have to. The core polymer preferably has the other structural unit (III) described later, and may be one or two or more polymers of the structural unit (III), and the structural unit (III) and And a copolymer with either or both of the structural unit (I) and the structural unit (II).
The type of structural unit forming each of the core polymer and the shell polymer is selected so that the glass transition temperature of the shell polymer and the difference (absolute value) between the glass transition temperatures of both polymers satisfy the ranges described later.

The aqueous ink composition of the present invention preferably contains 1 to 15% by mass, more preferably 1 to 10% by mass, and still more preferably 4 to 10% by mass of resin fine particles used in the present invention. . The aqueous ink composition of the present invention is improved in the ejection stability and latency of the aqueous ink composition by containing 1 to 15% by mass of the resin fine particles used in the present invention.

Below, the structural unit which forms a core polymer and a shell polymer is demonstrated concretely.
-Structural unit (I)-
Structural unit (I) is represented by following formula (1).

In the formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ¹ is preferably a hydrogen atom or methyl, more preferably methyl.

R ² represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, or an aromatic ring group. R ² is preferably a hydrogen atom or a linear or branched alkyl group, more preferably a hydrogen atom or a linear alkyl group.
The alkyl group is preferably an alkyl group having 1 to 15 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, still more preferably an alkyl group having 1 to 10 carbon atoms, and particularly preferably It is an alkyl group of 1 to 8 and most preferably methyl.

The aromatic ring group is not particularly limited as long as it is a group consisting of an aromatic ring, and may be a single ring or a condensed ring, and may be an aromatic hydrocarbon ring group or an aromatic heterocyclic group. The aromatic hydrocarbon ring forming the aromatic hydrocarbon ring group is not particularly limited, but one having 6 to 12 carbon atoms is preferable. The aromatic heterocycle forming an aromatic heterocycle group contains, as a ring member atom, at least one or more hetero atoms and carbon atoms. The hetero atom includes, for example, a nitrogen atom, an oxygen atom and a sulfur atom, and the number thereof is not particularly limited, and is, for example, 1 to 2. The number of ring carbon atoms is not particularly limited, but preferably 3 to 20, more preferably 3 to 12. Further, the number of ring members of the aromatic ring (in the case of a condensed ring, a ring forming the condensed ring) is also not particularly limited, but a 5- or 6-membered ring is preferable.
As an aromatic hydrocarbon ring, a benzene ring, a naphthalene ring, an anthracene ring, a binaphthyl group etc. are mentioned, for example.
Examples of the aromatic heterocycle include a thiophene ring, a furan ring, a pyrrole ring, an imidazole ring, an oxazole ring, a thiazole ring, a 5-membered ring such as thienothiophene or a fused ring containing a 5-membered ring, a pyridine ring, a pyrimidyl ring, And 6-membered rings such as pyrazine ring, quinoline ring and isoquinoline ring, or fused rings containing 6-membered rings.
The aromatic ring group is preferably an aromatic hydrocarbon ring group, more preferably a benzene ring group.

R ² may have a substituent. Such a substituent is not particularly limited, and examples thereof include (cyclo) alkyl group, (cyclo) alkenyl group, (cyclo) alkynyl group, aromatic hydrocarbon ring group, aromatic heterocyclic group and the like. Among them, an alkyl group, an aromatic hydrocarbon ring group and an aromatic heterocyclic group are preferable, and an alkyl group is more preferable.
When R ² has a substituent, the substituent may be directly linked to R ² or may be linked via a linking group. The linking group is not particularly limited. For example, -NH-, -S-, -O-, -C (= O)-, or a divalent linking group formed by linking two or more of these Can be mentioned. In this linking group, the number to which -NH-, -S-, -O- and -C (= O)-are linked is not particularly limited, but is preferably 2 to 5. As a linking group formed by linking two or more of the above groups, for example, —C (= O) —NH—, —C (= O) —S—, —NH—C (= O) —NH— And -NH-C (= O) -S-, -C (= O) -O-, -C (= O) -O-C (= O)-and the like.

A ¹ represents an alkylene group having 2 to 20 carbon atoms, preferably an alkylene group having 2 to 15 carbon atoms, more preferably an alkylene group having 2 to 10 carbon atoms, still more preferably 2 or 3 carbon atoms And an alkylene group, particularly preferably an ethylene group.
The alkylene group may be linear, branched or cyclic, preferably linear or branched, and more preferably linear.
In the structural unit (I), A ¹ may be one kind or two or more kinds. When A ¹ is two or more, the binding mode of two (-A ¹ -O-) units may be block or random. If A ¹ is 2 or more, a combination of ethylene and propylene are preferred.
A ¹ may have a substituent. Such a substituent is not particularly limited, and examples thereof include substituents which R ² may have.

m ¹ is an integer of 1 to 100, and is preferably an integer of 2 to 100, and more preferably, from the viewpoint that even a resin fine particle having a structural unit (II) can effectively suppress gelation or aggregation thereof. Is an integer of 2 to 80, more preferably an integer of 2 to 50.

The structural unit represented by Formula (1) has a preferable structural unit represented by following formula (3).

In the formula (3), ^{R 1} and ^{R 2} have the same meanings as ^{R 1} and ^{R 2} of formula (1), it is preferable also the same.
m ² is an integer of 2 to 100. m ² is preferably an integer of 2 to 80, more preferably an integer of 2 to 50, in that the resin fine particles having the structural unit (II) can effectively suppress gelation or aggregation thereof. is there.

Preferred specific examples of the structural unit (I) are shown below, but the present invention is not limited thereto. In the following structural units, any alkyl group that can be taken as R ² is linear. * Indicates a linking site.

Each polymer of the core / shell polymer may have one or more structural units (I).

-Structural unit (II)-
Structural unit (II) is represented by following formula (2A) or Formula (2B), and what is represented by Formula (2A) is preferable.

In formula (2A), R ³ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which has the same meaning as R ^{1 in} formula (1), and preferred examples are also the same.

L ^1A represents a single bond or a linking group having a minimum number of 6 or less linking the carbonyl carbon atom in the formula (2A) and Y ^1A . The divalent linking group that can be taken as L ^1A is not particularly limited as long as the minimum number of atoms is 6 or less, and, for example, a linear, branched or cyclic alkylene group, an arylene group, -O-, -NH-,- S- or -C (= O)-or a divalent linking group formed by linking two or more of them. The number of linking groups is not particularly limited as long as it is 2 or more, and for example, 2 to 5 are preferable, and 2 to 3 are more preferable. The linking group is an alkylene group, -NH-alkylene group, -O-alkylene group, -S-alkylene group, -O-arylene group, -NH-arylene group, -O-alkylene group -OC (= O) -Alkylene group or -NH-arylene group is more preferable, and -O-alkylene group or -NH-alkylene group is more preferable.

The alkylene group may be linear or branched, but is preferably linear from the viewpoint of discharge stability, latency, and stability of the resin fine particles.
The number of carbon atoms of the alkylene group is not particularly limited as long as it satisfies that the minimum number of atoms described later is 6 or less. For example, when L ^1A is an alkylene group, the carbon number of the alkylene group is 6 or less, preferably 5 or less, and more preferably 2 or 3. When L ^1A contains an alkylene group (when it is a linking group formed by linking two or more as described above), the number of carbon atoms of the alkylene group is preferably 1 to 3, and 1 or 2 is more preferable. preferable.
L ^1A has at least 6 or less atoms connecting the carbonyl carbon atom in the formula (2A) and Y ^1A . In other words, the number of bonds of atoms constituting the shortest chain among the atomic chains connecting the carbonyl carbon atom and Y ^1A is 6 or less. When the structural unit (I) to which Y ^1A is bonded via such a relatively short chain linking group L ^1A is included, the stability of the resin fine particles in the aqueous ink composition is improved. In addition, since the linking group L ^1A is a relatively short chain, the affinity with other monomers or organic solvents is increased, and there is an advantage that handling at the time of synthesis becomes easy. On the other hand, when the linking group L ^1A is a short chain, the function originally exhibited by Y ^1A is not effectively exhibited, and the resin fine particles gel or aggregate, resulting in a high aqueous ink composition for inkjet recording. It becomes impossible to provide latency and excellent image forming characteristics (abrasion resistance and blocking resistance). However, in the present invention, such a structural unit (II) is combined with the structural unit (I) to be incorporated into a shell polymer forming resin fine particles. Thereby, as described above, the resin fine particle of the present invention can enhance the abrasion resistance and the blocking resistance of the image while exhibiting an excellent latency.

L ^1A may have a substituent. Such a substituent is not particularly limited, and examples thereof include substituents which R ² may have.

Y ^1A represents -OM when L ^1A is a single bond, and -C (= O) OM, -S (= O) ₂ OM or -OS (= O when L ^1A is the above linking group ₂ ) Show the OM. In the case where L ^1A is the above-mentioned linking group, this Y ^1A is compatible with the latency, and the abrasion resistance and the blocking resistance of the image at a high level, -C (= O) OM or -S (= O) ₂ OM is preferable, and -C (= O) OM is more preferable.
M represents a hydrogen atom, an alkali metal ion or an ammonium ion. M is preferably an alkali metal ion, more preferably a sodium ion or a potassium ion, and still more preferably a potassium ion, from the viewpoint of discharge stability, latency, and stability of the resin fine particles.
In the aqueous ink composition of the present invention, M may be separated (free).

In formula (2B), R ³ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which has the same meaning as R ^{1 in} formula (1), and preferred ones are also the same.

Y ^1B represents —C (= O) OM, —S (= O) ₂ OM or —OS (= O) ₂ OM. Y ^{1 B} is preferably —C (= O) OM or —S (= O) ₂ OM, from the viewpoint that it is compatible with latency, image scratch resistance and blocking resistance at a high level, and —C (= O) OM is more preferred.
M represents a hydrogen atom, an alkali metal ion or an ammonium ion, and has the same meaning as M which Y ^1A may have, and preferred examples are also the same.
In the benzene ring in the formula (2), the position to which Y ^1B is bonded is not particularly limited, but is preferably in the para-position to the ring-constituting carbon atom bonded to the carbon atom having R ³ .
The benzene ring in Formula (2) may have a substituent. Such a substituent is not particularly limited, and examples thereof include the substituents which R ² may have, and further, Y ^{1 B} described above and the like.

Preferred specific examples of the structural unit (II) are shown below, but the present invention is not limited thereto. In the following structural units, * indicates a linking site. In addition, although the preferable specific example of structural-unit (II) shown below shows the structure whose M in a said Formula (2A) and M in a formula (2B) is a hydrogen atom, it replaces with this hydrogen atom, and is an alkali The form which employ | adopted metal ion or ammonium ion is also preferable as said structural unit (II).

Each polymer of the core / shell polymer may have one or more structural units (II). When one structural unit (II) is contained, it may be a structural unit represented by the formula (2A) or a structural unit represented by the formula (2B). Moreover, when it has 2 or more types of structural unit (II), it may have 2 or more types of structural units represented by Formula (2A) or Formula (2B), and is a structural unit represented by Formula (2A) And at least one structural unit represented by the formula (2B).

Although the combination of structural unit (I) and structural unit (II) is not specifically limited, The preferable thing of structural unit (I) and the preferable thing of structural unit (II) can be combined suitably. For example, the structural unit represented by the said Formula (3) as structural unit (I), and the structural unit represented by said Formula (2A) as structural unit (II) can be combined.

-Other structural units (III)-
The structural unit (referred to as “other structural unit (III)”) other than the structural unit (I) and the structural unit (II) constituting at least one of the core / shell polymer is not particularly limited, and is preferable As examples, there can be mentioned structural units described in JP-A-2001-181549 and JP-A-2002-88294.

At least one of the core / shell polymers preferably contains, as another structural unit (III), a structural unit (i) of an ethylenically unsaturated compound having an aromatic ring or an aliphatic ring.
The aromatic ring or aliphatic ring contained in the structural unit (i) includes a benzene ring, a naphthalene ring, an anthracene ring, and an aliphatic hydrocarbon ring having 5 to 20 carbon atoms, and the benzene ring and carbon Aliphatic hydrocarbon rings of several 6 to 10 are preferred.
These aromatic rings or aliphatic rings may have a substituent. When the aromatic ring or the aliphatic ring has a substituent, the substituent is not particularly limited, and examples of the substituent include substituents other than those described above which can be taken as Y ^1A and Y ^1B .

As the ethylenically unsaturated compound having an aromatic ring or aliphatic ring leading to the structural unit (i), an ethylenically unsaturated compound having an ethylenically unsaturated group at the compound end is preferable, and styrene or (meth) acrylate is preferable The compound or the (meth) acrylamide compound is more preferable, and the styrene which may have a substituent or the (meth) acrylate compound is more preferable.
Examples of the above-mentioned ethylenically unsaturated compound include, but are not particularly limited to, compounds which lead to structural units represented by the following general formulas (A) to (E), and more specifically styrene, benzyl ( Examples include meta) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate and the like.

The structural unit (i) preferably contains a structural unit represented by any one of the following general formula (A) to general formula (E) from the viewpoint of the production aptitude (filterability) of the obtained image From the viewpoint of the stability of particles in the ink, it is more preferable to include a structural unit represented by the following general formula (A).

In formulas (A) to (E), R ¹¹ and R ¹² each independently represent a methyl group or a hydrogen atom. Each R ¹³ independently represents a linear or branched alkyl group having 1 to 10 carbon atoms. N in the general formula (A) and the general formula (B) represents an integer of 0 to 5. N in the general formula (C) is an integer of 0 to 11. L ¹¹ represents a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C ( OO) — or a divalent linking group formed by linking two or more of these.

In formula (A), R ¹¹ is preferably a hydrogen atom.
In the general formulas (B) to (E), R ¹² is preferably a methyl group.
In formulas (A) to (C), each of R ^{13 s} independently preferably represents a linear or branched alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group. When the structural unit represented by each formula has a plurality of R ¹³ 's, they may be combined with each other to form a ring. However, in the structural unit represented by the general formula (C), when a plurality of R ¹³ combine with each other to form a ring, the structural unit represented by the general formulas (D) and (E) can not be obtained. .
In any formula, n is preferably an integer of 0 to 2, more preferably 0 or 1, and still more preferably 0.

In the general formula (B), L ¹¹ is preferably a divalent linking group containing -O- or -NH- at the bonding site to the carbonyl carbon atom described in the general formula (B), and the carbonyl carbon atom More preferably a divalent linking group containing -O- or -NH- at the bonding site with and containing a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, and -OCH _2- Or -NHCH _2- is more preferred, and -OCH ₂ -is particularly preferred.
In the general formulas (C) to (E), L ¹¹ contains -O- or -NH- at the bonding site to the carbonyl carbon atom described in the general formulas (C) to (E) A divalent linking group is preferred, -O- or -NH- is more preferred, and -O- is more preferred.

The structural unit represented by the general formula (A) is preferably a structural unit derived from styrene.
The structural unit represented by the general formula (B) is preferably a structural unit derived from benzyl (meth) acrylate.
The structural unit represented by the general formula (C) is preferably a structural unit derived from cyclohexyl (meth) acrylate.
The structural unit represented by the general formula (D) is preferably a structural unit derived from isobornyl (meth) acrylate.
The structural unit represented by the general formula (E) is preferably a structural unit derived from dicyclopentanyl (meth) acrylate.

At least one of the core / shell polymers may have a structural unit (ii) other than the structural unit (i) as the other structural unit (III).
The structural unit (ii) is not particularly limited as long as it is derived from a compound that can be polymerized with the above structural unit, and is preferably a structural unit derived from a (meth) acrylamide compound or a (meth) acrylate compound, It is more preferable that it is a structural unit derived from an acrylate compound.

The structural unit (ii) is preferably an alkyl (meth) acrylate compound or an alkyl (meth) acrylamide compound in which the alkyl group has 1 to 18 carbon atoms, and an alkyl (meth) acrylate compound is more preferable. The alkyl (meth) acrylate compound is more preferably an alkyl (meth) acrylate compound in which the alkyl group has 1 to 10 carbon atoms.
The above-mentioned alkyl group possessed by the structural unit (ii) may be linear or branched, and has a cyclic structure (except those included in the above general formula (C) to general formula (E)). It may be done.
The structural unit (ii) may have a substituent. Although it does not specifically limit as a substituent which structural unit (ii) may have, For example, substituents other than said ^Y1A and ^Y1B , for example, a hydroxyl group, an amino group, are mentioned.

Each polymer of the core / shell polymer may have one or more structural units (ii).
At least one of the core / shell polymers may have a structural unit other than the above structural units as the other structural unit (III). Such a structural unit is not particularly limited, and examples thereof include structural units derived from (meth) acrylic acid compounds or salts thereof (including the above-mentioned alkali metal salts or ammonium salts).

The content of the structural unit forming each of the core polymer and the shell polymer is the difference between the glass transition temperature of the shell polymer and the glass transition temperature of both polymers, taking into account the type and content of other structural units, etc. (absolute The value is selected to satisfy the range described later.

The content of the structural unit (I) in the shell polymer is, for example, from the viewpoint of being compatible with the latency (discharge stability) and the abrasion resistance and the blocking resistance of the image at a high level, From the viewpoint of stability, the content is preferably more than 0% by mass and 30% by mass or less, more preferably 0.5 to 30% by mass, still more preferably 1 to 25% by mass, and 2 to 20% by mass Is particularly preferred. When the shell polymer contains a plurality of structural units (I), the content of the structural unit (I) is the sum of the contents of the structural units.
When the core polymer has the structural unit (I), the content of the structural unit (I) in the core polymer is the same as the content of the shell polymer.

The content of the structural unit (II) in the shell polymer is, for example, from the viewpoint of being compatible with the latency, the abrasion resistance and the blocking resistance of the image at a high level, further from the viewpoint of the stability of the resin fine particles. The content is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, and still more preferably 2 to 15% by mass. When the shell polymer contains a plurality of structural units (II), the content of the structural unit (II) is the sum of the content of each structural unit.
When the core polymer has the structural unit (II), the content of the structural unit (II) in the core polymer is the same as the content of the shell polymer.

The content of the structural unit (i) of the other structural units (III) in each of the core / shell polymer is set in the following range, taking into consideration the production suitability (filterability) of the resin fine particles Is preferred. The content of the structural unit (i) in the shell polymer is preferably 0 to 80% by mass, more preferably 0 to 75% by mass, and still more preferably 0 to 70% by mass. The content of the structural unit (i) in the core polymer is preferably 1 to 100% by mass, more preferably 5 to 95% by mass, and still more preferably 10 to 90% by mass. When each polymer contains multiple types of structural unit (i), the said content is made into the sum total of content of each structural unit.
The structural unit derived from styrene, which is particularly preferable among the structural units (i), is contained in the shell polymer, considering the viewpoint of discharge stability, scratch resistance, and optionally the production suitability (filterability) of the resin fine particles The amount is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, and still more preferably 0 to 35% by mass. The content of structural units derived from styrene in the core polymer is preferably 1 to 100% by mass, more preferably 10 to 90% by mass, and still more preferably 15 to 80% by mass.

The content of the structural unit (ii) of the other structural units (III) in each of the core / shell polymer is preferably 0 to 90% by mass from the viewpoint of dischargeability and abrasion resistance, respectively. And 0 to 70% by mass is more preferable. The above content is the total of the content of each structural unit, when each polymer contains plural kinds of structural units (ii).

In the present invention, the core polymer and the shell polymer each contain the above structural units (I), (II) and (III), and the total content of these structural units is preferably 100% by mass. .
When the core polymer or shell polymer has a structural unit other than the above structural units, the content of structural units other than the above structural units is preferably 0 to 20% by mass, and 0 to 15% by mass in the core polymer or shell polymer More preferably, 0 to 10% by mass is more preferable.

The glass transition temperature (hereinafter sometimes referred to as the glass transition temperature of the resin fine particles) of the resin fine particles (the entire resin including the core polymer and the shell polymer) used in the present invention is the scratch resistance and blocking resistance of the obtained image. Accordingly, the temperature is preferably 20 to 150 ° C., more preferably 40 to 130 ° C., and still more preferably 50 to 120 ° C.
The glass transition temperature of the shell polymer forming the resin fine particles used in the present invention is 20 to 130.degree. By this, it is possible to secure the fusion bondability by the shell polymer and to further improve the abrasion resistance of the image, and further to maintain the high thermal stability of the core polymer and to further enhance the blocking resistance. The glass transition temperature of the shell polymer is preferably 20 to 130 ° C., and more preferably 30 to 100 ° C.

The core polymer forming the resin fine particles used in the present invention has a glass transition temperature higher than that of the shell polymer. By this, it is possible to secure the fusion bondability by the shell polymer and to further improve the abrasion resistance of the image, and further to maintain the high thermal stability of the core polymer and to further enhance the blocking resistance. The absolute value of the difference (Tg difference) between the glass transition temperature of the core polymer and the glass transition temperature of the shell-shell polymer is not particularly limited as long as it exceeds 0 ° C. From the viewpoint of achieving compatibility at a high level, it is preferably 20 ° C. or more, more preferably 25 ° C. or more, and still more preferably 30 ° C. or more. When the difference in Tg is too small, the difference in thermal stability between the core polymer and the shell polymer may be small, and one of scratch resistance and blocking resistance may be poor. The upper limit of the difference with the glass transition temperature is not particularly limited, but is practically 80 ° C. or less.
The glass transition temperature of the core-shell polymer may be higher than the glass transition temperature of the shell polymer, and for example, 70 to 150 ° C. is preferable from the viewpoint of achieving both latency and high levels of abrasion resistance and blocking resistance of the image. 80 to 130 ° C. is more preferable.

The glass transition temperature of the resin fine particles, the core polymer and the shell polymer can be appropriately controlled by a conventionally known method. For example, the glass transition temperature of the resin fine particles can be adjusted by appropriately adjusting the kind or the composition ratio of the monomer used for the synthesis of each polymer of the core / shell polymer constituting the resin fine particles, and the molecular weight of the polymer constituting the resin fine particles. It can be controlled to a desired range.

In the present invention, the glass transition temperature applies the measured Tg obtained by measurement. The measurement Tg is a temperature at which the baseline starts to change along with the glass transition when measured at a temperature rising rate of 5 ° C./min using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nano Technology Inc., It is measured as the average with the temperature returning to baseline again.
However, when measurement is difficult due to decomposition of the resin, sensitivity, etc., the calculated Tg calculated by the following formula is applied. The calculated Tg is calculated by the following equation.

1 / Tg = Σ (X _i / T g _i )

Here, in the resin to be calculated, n kinds of monomers from i = 1 to n are copolymerized. X _i is the i-th mass fraction of the monomer components, Tg _i is the i-th glass transition temperature of the homopolymer of monomer (absolute temperature). However, Σ takes the sum of i = 1 to n. In addition, the value (Tg _i ) of the glass transition temperature of the homopolymer of each monomer adopts the value of Polymer Handbook (3rd Edition) (J. Brandrup, E. H. Immergut (Wiley-Interscience, 1989)). .

The weight average molecular weight (Mw) of the resin constituting the resin fine particles used in the present invention is preferably 70,000 or more, more preferably 80,000 to 1,000,000, and further preferably 100,000 to 800,000. preferable. By setting the weight average molecular weight to 70,000 or more, mechanical properties of the obtained film can be further improved. The weight average molecular weight can be measured by gel permeation chromatography (GPC) by a known method.

The resin constituting the resin fine particles used in the present invention and each polymer of the core / shell polymer may be either a block copolymer or a random copolymer.

In the aqueous ink composition of the present invention, the particle size of the resin fine particles used in the present invention is preferably 1 to 400 nm, more preferably 5 to 300 nm, and more preferably 20 to 200 nm from the viewpoint of ink dischargeability. It is more preferable that there be some, 20 to 100 nm is particularly preferable, and 20 to 80 nm is most preferable.
The above particle size of the resin fine particles means a volume average particle size. This volume average particle diameter can be measured by the method described in the examples described later.

The resin fine particles are produced by a method capable of producing particles of a resin having a core-shell structure, using the structural unit (I), the structural unit (II), the structural unit (III) and the like as required. be able to. As a method for producing resin particles, known methods can be applied without particular limitation. For example, there is a polymerization method having a core polymerization step of synthesizing a core polymer and a shell polymerization step of synthesizing a shell polymer. If necessary, Y ^1A and / or Y ^1B cation M exchange reaction can also be performed during core polymerization, during shell polymerization, and further after shell polymerization.
The resin fine particles can be prepared by an emulsion polymerization method. The emulsion polymerization method is a method of preparing resin fine particles by polymerizing an emulsion prepared by adding a monomer, a polymerization initiator, an emulsifying agent, and, if necessary, a chain transfer agent in an aqueous medium (for example, water). It is. A known emulsifier may be added separately as long as the ejection stability is not reduced. Examples of the emulsifier include surfactants (anionic surfactant, nonionic surfactant and cationic surfactant) described later that may be contained in the aqueous ink composition of the present invention.

The polymerization initiator is not particularly limited, and inorganic persulfates (eg, potassium persulfate, sodium persulfate, ammonium persulfate etc.), azo initiators (eg, 2,2′-azobis (2-amidinopropane) ) Dihydrochloride, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 4,4′-azobis (4-cyanovaleric acid)), organic peroxides (eg, Peroxypivalic acid-t-butyl, t-butyl hydroperoxide, disuccinic acid peroxide) or the like, or salts thereof can be used. These can be used alone or in combination of two or more. Among them, it is preferable to use an azo initiator or an inorganic peroxide.
The amount of the polymerization initiator used in the present invention is usually 0.01 to 5 parts by mass, preferably 0.2 to 2 parts by mass, with respect to 100 parts by mass of all the monomers.

As the chain transfer agent, known compounds such as carbon tetrahalides, dimers of styrenes, dimers of (meth) acrylic esters, mercaptans and sulfides can be used. Among them, dimers of styrenes or mercaptans described in JP-A-5-17510 can be suitably used.

The resin fine particles used in the present invention are preferably dispersed in the aqueous medium as described above. The resin fine particles used in the present invention are more preferably self-dispersible resin fine particles.
In the present invention, a self-dispersible resin fine particle is a water-insoluble resin which can be dispersed in an aqueous medium by a functional group of the resin itself (in particular, an acidic group or a salt thereof, specifically Y ^1A or Y ^1B ). Refers to fine particles consisting of The dispersed state means an emulsified state in which a water-insoluble resin is dispersed in a liquid state in an aqueous medium (emulsion) and a dispersed state in which a water-insoluble resin is dispersed in a solid state in an aqueous medium (suspension) Is included. "Water insoluble" indicates that the amount of dissolution in 100 parts by mass of water (25 ° C) is 5.0 parts by mass or less.
The resin fine particles used in the present invention do not function as a pigment dispersant, and therefore do not contain the pigment inside the particles.

<Pigment>
The aqueous ink composition of the present invention preferably has a form in which one or more pigments are dispersed.
There is no restriction | limiting in particular in the kind of pigment used for the water-based ink composition of this invention, A normal organic or inorganic pigment can be used.
Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, an azo pigment or a polycyclic pigment is preferable. As an azo pigment, an azo lake, an insoluble azo pigment, a condensation azo pigment, a chelate azo pigment is mentioned, for example. Examples of polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of dye chelates include basic dye chelates and acid dye chelates.

Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chromium yellow and carbon black.

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

The volume average particle size of the pigment in the aqueous ink composition of the present invention is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the volume average particle diameter is 200 nm or less, the color reproducibility becomes good, and in the case of the ink jet system, the droplet deposition characteristics become good. Moreover, light resistance becomes favorable because a volume average particle diameter is 10 nm or more. The volume average particle size of the pigment in the aqueous ink composition can be measured by a known measurement method. Specifically, it can be measured by a centrifugal sedimentation light transmission method, an X-ray transmission method, a laser diffraction / scattering method, or a dynamic light scattering method.
The particle size distribution of the pigment in the aqueous ink composition of the present invention is not particularly limited, and may be any of a wide particle size distribution or a monodispersed particle size distribution. Further, two or more colorants having a monodisperse particle size distribution may be mixed and used.
The volume average particle size of the pigment can be measured by the same method as the measurement of the volume average particle size of the above-mentioned resin fine particles.

When the aqueous ink composition of the present invention contains a pigment, the content of the pigment in the aqueous ink composition is preferably 1 to 20% by mass, and more preferably 1 to 10% by mass, from the viewpoint of colorability and storage stability. preferable.

-Dispersant-
When the aqueous ink composition of the present invention contains a pigment, as the pigment, colored particles (hereinafter simply referred to as "colored particles") in which the pigment is dispersed in an aqueous medium by a dispersing agent are prepared, and these are used It is preferable to use as a raw material of goods.
The dispersant may be a polymer dispersant or a low molecular weight surfactant type dispersant. The polymer dispersant may be either a water-soluble polymer dispersant or a water-insoluble polymer dispersant.

As the low molecular weight surfactant type dispersant, for example, a known low molecular weight surfactant type dispersant described in paragraphs 0047 to 0052 of JP-A-2011-178029 can be used.

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

Also, among hydrophilic polymer compounds modified with natural products as raw materials, cellulose polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose, starches such as sodium starch glycolate and sodium starch phosphate ester And seaweed polymers such as sodium alginate and propylene glycol alginate.
Furthermore, as synthetic hydrophilic polymer compounds, vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salts thereof, water-soluble styrene acrylic resin, etc. Acrylic resin, water soluble styrene maleic resin, water soluble vinyl naphthalene acrylic resin, water soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salt of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium, amino Examples thereof include polymer compounds having a salt of a cationic functional group such as a group in a side chain, and natural polymer compounds such as shellac.

Among these, hydrophilic polymer compounds into which a carboxy group is introduced are preferable, such as homopolymers of acrylic acid or methacrylic acid, and copolymers of acrylic acid or methacrylic acid and other monomers.

The water-insoluble polymer dispersant is a water-insoluble polymer and is not particularly limited as long as the pigment can be dispersed, and a conventionally known water-insoluble polymer dispersant can be used. The water-insoluble polymer dispersant can, for example, be configured to include both hydrophobic structural units and hydrophilic structural units.

Here, as a monomer component which comprises a hydrophobic structural unit, a styrene-type monomer component, an alkyl (meth) acrylate component, an aromatic group containing (meth) acrylate component etc. can be mentioned.
Moreover, as a monomer component which comprises a hydrophilic structural unit, if it is a monomer component containing a hydrophilic group, there will be no restriction | limiting in particular. Examples of the hydrophilic group include nonionic groups, carboxy groups, sulfonic acid groups, and phosphoric acid groups. The nonionic group may, for example, be a hydroxyl group, an amide group (with nitrogen atom not substituted), a group derived from an alkylene oxide polymer (for example, polyethylene oxide or polypropylene oxide), or a group derived from sugar alcohol.
From the viewpoint of dispersion stability, the hydrophilic structural unit preferably contains at least a carboxy group, and is preferably in a form containing both a nonionic group and a carboxy group.

Specific examples of the water-insoluble polymer dispersant include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, and (meth) acrylic acid ester- (meth) acrylic acid And acrylic acid copolymer, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, styrene-maleic acid copolymer and the like.

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

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

The content of the dispersant in the colored particles is preferably 10 to 90 parts by mass with respect to 100 parts by mass of the pigment, from the viewpoint of pigment dispersibility, ink colorability, and dispersion stability, and preferably 20 to 70 The parts by mass are more preferable, and 30 to 50 parts by mass are particularly preferable.
When the content of the dispersing agent in the colored particles is in the above range, the pigment is coated with an appropriate amount of the dispersing agent, which tends to easily obtain colored particles having a small particle size and excellent in temporal stability.

The colored particles can be obtained, for example, by dispersing a mixture containing a pigment, a dispersant, and if necessary, a solvent (preferably an organic solvent) and the like with a disperser.
More specifically, for example, after a step of adding an aqueous solution containing a basic substance to a mixture of a pigment, a dispersant, and an organic solvent for dissolving or dispersing the dispersant (mixing / hydration step), an organic solvent Can be manufactured as a dispersion by providing a process (solvent removal process) excluding. Thereby, the pigment is finely dispersed, and a dispersion of colored particles excellent in storage stability can be produced.

The organic solvent needs to be able to dissolve or disperse the dispersant, but in addition to that, it is preferable to have a certain degree of affinity for water. Specifically, it is preferable that the solubility in water at 20 ° C. is 10 to 50% by mass or less.
Preferred examples of the organic solvent include water-soluble organic solvents. Among them, isopropyl alcohol, acetone and methyl ethyl ketone are preferable, and methyl ethyl ketone is particularly preferable. The organic solvents may be used alone or in combination of two or more.

The above basic substance is used for the neutralization of an anionic group (preferably a carboxy group) which may be possessed by the polymer. There is no particular limitation on the degree of neutralization of the anionic group. In general, it is preferable that the liquid property of the finally obtained colorant particle dispersion is, for example, pH 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the polymer.

The method of removing the organic solvent in the production process of the colored particle dispersion is not particularly limited, and can be removed by a known method such as vacuum distillation.

In the aqueous ink composition of the present invention, the colored particles may be used singly or in combination of two or more.

<Surfactant>
The aqueous ink composition of the present invention may contain a surfactant as a surface tension regulator.
As the surfactant, any of anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and betaine surfactants can be used.

Specific examples of anionic surfactants include sodium dodecyl benzene sulfonate, sodium lauryl sulfate, sodium alkyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, sodium dialkyl sulfosuccinate, sodium stearate, sodium stearate, potassium oleate, sodium dioctyl Sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, sodium dialkyl sulfosuccinate, sodium oleate, sodium t-octylphenoxyethoxypolyethoxyethyl sulfate, etc. Can be selected, and one or more of these can be selected.

Specific examples of the nonionic surfactant include, for example, acetylene diol derivatives such as ethylene oxide adduct of acetylene diol, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl Examples thereof include phenyl ether, oxyethylene • oxypropylene block copolymer, t-octyl phenoxyethyl polyethoxyethanol, nonyl phenoxyethyl polyethoxyethanol and the like, and one or more of these can be selected.

Examples of the cationic surfactant include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridinium salts, imidazolium salts, etc. Specifically, for example, dihydroxyethyl stearylamine, 2-heptadecenyl -Hydroxyethyl imidazoline, lauryl dimethyl benzyl ammonium chloride, cetyl pyridinium chloride, stearamido methyl pyridinium chloride and the like.
Among these surfactants, in terms of stability, nonionic surfactants are preferable, and acetylene diol derivatives are more preferable.

The content of the surfactant in the aqueous ink composition is preferably such an amount that the aqueous ink composition can be brought into the range of the surface tension described below. More specifically, the content of the surfactant in the aqueous ink composition is preferably 0.1% by mass or more, more preferably 0.1 to 10% by mass, and still more preferably 0.2. It is up to 3% by mass.

<Other ingredients>
The aqueous ink composition of the present invention may further contain, if necessary, a drying inhibitor (swelling agent), a coloring inhibitor, a penetration accelerator, a UV absorber, a preservative, a rust inhibitor, a defoaming agent, a clay regulator, You may mix additives, such as a pH adjuster and a chelating agent. The mixing method is not particularly limited, and a commonly used mixing method can be appropriately selected to obtain the aqueous ink composition of the present invention.

Physical Properties of Aqueous Ink Composition
The viscosity at 30 ° C. of the aqueous ink composition of the present invention is preferably 1.2 mPa · s to 15.0 mPa · s, more preferably 2 mPa · s to less than 13 mPa · s, and still more preferably 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity of the aqueous ink composition is measured at a temperature of 30 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

The aqueous ink composition of the present invention preferably has a pH of 6 to 11 at 25 ° C. from the viewpoint of dispersion stability.

When the aqueous ink composition of the present invention is used in an ink jet recording system, it is preferable to adjust the amount of surfactant so that the surface tension of the aqueous ink composition is 20 to 60 mN / m from the viewpoint of ink dischargeability. The amount is more preferably 20 to 45 mN / m, and still more preferably 25 to 40 mN / m.
The surface tension of the aqueous ink composition is measured at a temperature of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[Image formation method]
The image forming method of the present invention includes an ink applying step of applying the aqueous ink composition of the present invention onto a recording medium by an inkjet method to form an image.
In the image forming method of the present invention, the step of drying and removing the aqueous medium in the aqueous ink composition applied to the recording medium (hereinafter also referred to as "ink drying step"), if necessary, the aqueous ink composition. It may further include other processes such as a process of melting and fixing resin fine particles contained in a substance (hereinafter, also referred to as a “heat fixing process”).
The ink application step is preferably a step of directly applying the aqueous ink composition of the present invention onto a low water absorption recording medium or a non water absorption recording medium to form an image.
Direct application of the ink on the low water absorption recording medium or non-water absorption recording medium means that the provided ink and the low water absorption recording medium or non-water absorption recording medium are in direct contact with each other. For example, in the case where a treatment liquid known in the field of an image forming method using an aqueous ink composition is applied in advance for the purpose of aggregation of components such as resin fine particles contained in the aqueous ink composition, the aqueous ink composition And the low water absorption recording medium or the non water absorption recording medium are not in direct contact with each other. Examples of the above-mentioned known processing solution include the processing solutions described in JP-A-2012-40778.
Further, in the image forming method of the present invention, it is preferable that the above-mentioned known processing liquid is not applied after the ink application step. That is, the image forming method of the present invention preferably does not include the step of applying the above-mentioned known processing liquid.

In the inkjet method using a conventional aqueous ink composition, particularly when using a low water absorption recording medium or a non water absorption recording medium as a recording medium, for example, a precoat liquid or a top coat liquid is used on the recording medium. There is known a method of aggregating the components in the aqueous ink composition to be discharged to suppress the spread of the aqueous ink composition to improve the image quality.
However, since the aqueous ink composition of the present invention exhibits the above-described excellent properties and can impart high performance to an image, it is possible to use a low water absorption recording medium or non-water absorption without using a precoat solution or a topcoat solution. An image with excellent image quality can be formed on the recording medium.

<Recording medium>
The recording medium used in the image forming method of the present invention is not particularly limited, but is preferably a paper medium. That is, general printing paper mainly composed of cellulose such as so-called high quality paper, coated paper, art paper, etc., which are used for general offset printing and the like can be used.

As the recording medium, those commercially available on the market can be used. For example, “OK Prince Fine” manufactured by Oji Paper Co., Ltd., “Shiraoi” manufactured by Nippon Paper Industries, and “New NPI” manufactured by Nippon Paper Co., Ltd. High quality paper such as “high quality” (A), high quality coated paper such as “Silver Diamond” manufactured by Nippon Paper Industries Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., and fine paint such as “Aurora S” manufactured by Nippon Paper Industries Co., Ltd. Paper, lightweight coated paper (A3) such as OK Coat L manufactured by Oji Paper Co., Ltd. and Aurora L manufactured by Nippon Paper Co., Ltd. OK Top Coat + manufactured by Oji Paper Co., Ltd. manufactured by Nippon Paper Co., Ltd. "Aurora coat", coated paper such as "Yulight" (A2, B2), "OK Kinto +" manufactured by Oji Paper Co., Ltd., and art paper (A1) such as "Tokubishi Art" manufactured by Mitsubishi Paper Co., Ltd. . It is also possible to use various types of photo paper for inkjet recording.

Among the recording media, so-called coated paper (coated paper) used for general offset printing and the like is preferable. The coated paper is obtained by applying a coating material to the surface of a generally non-surface-treated high-quality paper mainly made of cellulose, neutral paper or the like to provide a coat layer. Coated paper is likely to cause quality problems such as gloss and abrasion resistance of the image in image formation by a common aqueous ink jet, but when using the aqueous ink composition of the present invention, uneven gloss is suppressed It is possible to obtain an image with good gloss and scratch resistance. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. Art paper, coated paper, lightweight coated paper or finely coated paper is more preferred.

Among the above, from the viewpoint of obtaining a high-quality image having a large effect of suppressing pigment movement and having better color density and hue than in the prior art, use a low water absorption recording medium or a non water absorption recording medium as a recording medium. Is preferred. In the present invention, the low water absorption recording medium is one having an absorption coefficient Ka of water of 0.05 to 0.5 mL / m ² · ms ^1/2 , and 0.1 to 0.4 mL / m ^2. It is preferably ms ^1/2 , more preferably 0.2 to 0.3 mL / m ² · ms ^1/2 . Further, the non-water-absorbent recording medium refers to one having an absorption coefficient Ka of water of less than 0.05 mL / m ² · ms ^1/2 .
The water absorption coefficient Ka is the same as that described in JAPAN TAPPI Paper and Pulp Test Method No. 51: 2000 (issued by the Japan Institute of Paper and Pulp Technology), and specifically, the absorption coefficient Ka is an automatic scanning liquid absorption meter It is calculated from the difference between the transfer amount of water at a contact time of 100 ms and a contact time of 900 ms using KM500Win (manufactured by Kumagaya Riki Co., Ltd.).

<Ink application process>
In the ink application step, the aqueous ink composition of the present invention containing a pigment is applied onto a recording medium. The method of applying the aqueous ink composition is not particularly limited as long as it is an inkjet method capable of applying the aqueous ink composition onto the image, and a known ink applying method can be used. The inkjet method has advantages such as compactness of the recording apparatus and high-speed recording performance.
In the image formation by the inkjet method (method), by supplying energy, the aqueous ink composition is discharged onto the recording medium to form a colored image. The method described in paragraph Nos. 0093 to 0105 of JP-A-2003-306623 can be applied as an inkjet recording method preferable for the present invention.

The inkjet method is not particularly limited, and known methods, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element, Either an acoustic inkjet method that converts an electrical signal into an acoustic beam and ejects the ink using radiation pressure by irradiating the ink, or a thermal inkjet method that forms a bubble by heating the ink and uses the generated pressure. May be
Further, the inkjet head used in the inkjet method may be an on-demand method or a continuous method. Furthermore, the ink nozzle and the like used when performing recording by the above-mentioned ink jet method are not particularly limited, and can be appropriately selected according to the purpose.
The ink jet method includes a method of emitting a large number of low density inks called photo ink in a small volume, a method of improving the image quality using a plurality of inks having substantially the same hue and different densities, and a colorless and transparent ink The method used is included.

In addition, as the inkjet method, a shuttle type which performs recording while scanning the head in the width direction of the recording medium using a short serial head, and a line head in which recording elements are arranged corresponding to the whole area of one side of the recording medium There is a line method using In the line method, image recording can be performed on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the arrangement direction of the recording elements, and a conveyance system such as a carriage for scanning a short head becomes unnecessary. In addition, since the complex movement control of the carriage and the recording medium becomes unnecessary and only the recording medium is moved, the recording speed can be increased compared to the shuttle method.

When the ink application process is carried out by an ink jet system, the amount of droplets of the aqueous ink composition discharged by the ink jet system is preferably 1.5 to 10 pL from the viewpoint of forming a high definition print, 1.5 to 10 pL. It is more preferable than it is 6 pL. The amount of droplets of the aqueous ink composition to be discharged can be adjusted by appropriately adjusting the discharge conditions.

<Ink drying process>
The image forming method of the present invention comprises an ink drying step of drying and removing an aqueous medium (for example, water, the above-mentioned water-soluble organic solvent, etc.) in an aqueous ink composition applied on a recording medium, if necessary. It may be The ink drying step is not particularly limited as long as at least a part of the aqueous medium in the aqueous ink composition can be removed, and a commonly used method can be applied.

<Heat fixing process>
The image forming method of the present invention preferably comprises a heat fixing step after the ink drying step, if necessary. By performing the heat fixing process, the image on the recording medium is fixed, and the scratch resistance of the image can be further improved. As the heat fixing step, for example, the heat fixing step described in paragraph Nos. 0112 to 0120 of JP 2010-221415 A can be adopted.

<Ink removal process>
The image forming method of the present invention may, if necessary, include an ink removing step of removing the aqueous ink composition (for example, the solid ink solidified by drying) attached to the head for inkjet recording with a maintenance liquid. Good. The maintenance liquid and the ink removal process described in WO 2013/180074 can be preferably applied to the details of the maintenance liquid and the ink removal process.

[Resin fine particles]
The resin fine particles of the present invention are the resin fine particles used in the present invention described above. As described above, this resin fine particle has a core-shell structure containing a core polymer and a shell polymer, and the shell polymer has a structural unit (I) and a structural unit (II), and the glass transition temperature of the core polymer Is a resin fine particle whose temperature is higher than the glass transition temperature of the shell polymer and whose glass transition temperature of the shell polymer is 20 to 130.degree.
The resin fine particles of the present invention can be typically obtained as a form of a reaction liquid when the resin fine particles are prepared by the above-mentioned emulsion polymerization method, but the form is not particularly limited. The resin fine particles of the present invention can be suitably used in the aqueous ink composition of the present invention.

In the resin particle of the present invention, the Mw, Tg, Tg difference (absolute value) and particle diameter of the resin particle are the Mw, Tg, Tg difference (absolute value) of the resin particle contained in the aqueous ink composition of the present invention and It is the same as the particle size.
The resin fine particles of the present invention are preferably present in the form of being dispersed in water or a mixture of water and a water-soluble organic solvent, that is, an aqueous medium. The preferred form of this aqueous medium is the same as the above-mentioned aqueous medium used for the aqueous ink composition of the present invention.
When the resin particles of the present invention are present in the form of being dispersed in an aqueous medium (when present as a resin particle dispersion), the content of the resin particles in this dispersion is preferably 1 to 50% by mass, 20 to 40% by mass is more preferable.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, "part" and "%" showing a composition are mass references | standards.

[Synthesis of resin fine particles]
Hereinafter, core polymers and shell polymers constituting resin fine particles P-1 to P-15 and CP-1 to CP-8 used in Examples and Comparative Examples are shown. The fine resin particle CP-5 is a fine particle of a resin which does not have a core-shell structure and is formed only of the following core polymer.
In each of the following core polymer and shell polymer, the number of each structural unit represents a mass ratio. Also, "*" shown in each structural unit indicates a linking site for incorporation into a polymer.

<Synthesis of Resin Fine Particle P-1 and Preparation of Aqueous Dispersion of Resin Fine Particle P-1>
Water (314 g), Neoperex G-15 (16 mass% sodium dodecylbenzene sulfonate aqueous solution, manufactured by Kao Corporation) (a 1-liter three-necked flask equipped with a stirrer, thermometer, reflux condenser and nitrogen gas inlet) 7.50 g) was charged, and the temperature was raised to 80 ° C. under a nitrogen stream. A mixed solution consisting of potassium persulfate (radical polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd.) (0.61 g), potassium hydrogen carbonate (0.47 g) and water (30 g) was added thereto and stirred for 10 minutes. Next, a monomer solution consisting of methyl methacrylate (36.00 g) and styrene (24.00 g) is dropped at the same speed so that the dropping is completed in 2 hours, and after the dropping of the monomer solution is completed, The mixture was further stirred for 2 hours (core polymerization step).
Subsequently, a mixed solution consisting of potassium persulfate (0.30 g), potassium hydrogen carbonate (0.24 g) and water (30 g) is added to the obtained dispersion, and then methyl methacrylate (18.00 g), A monomer solution consisting of benzyl methacrylate (33.00 g), methoxypolyethylene glycol monomethacrylate (6.00 g) and methacrylic acid (3.00 g) is dropped at an equal speed so that the dropping is completed in 2 hours. After completion of the dropwise addition, stirring was further performed for 3 hours (shell polymerization step). The resulting reaction mixture was adjusted to pH 8.0 with 1N KOH aqueous solution and filtered through a mesh of 50 μm mesh to obtain an aqueous dispersion of resin fine particles P-1.
The resulting aqueous dispersion of resin fine particles P-1 had a solid content concentration of 24%. The resin fine particles in the aqueous dispersion had a volume average particle size of 38 nm (measured with Microtrac UPA EX-150 (manufactured by Nikkiso Co., Ltd.)). The fine resin particles P-1 had a core-shell structure, and the weight ratio of the core polymer to the shell polymer [core polymer: shell polymer] was 50:50. The differences (absolute values) between the glass transition temperatures Tg of the core polymer and the shell polymer and the glass transition temperatures of the core polymer and the shell polymer are shown in Table 1 below.

The Tg of each polymer was measured as follows. That is, it was measured at a temperature rising rate of 5 ° C./min using a sample obtained by drying an aqueous dispersion of a resin and using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nano Technology.
The volume average particle diameter of the resin fine particles prepared in the following and the Tg of each polymer were also measured by the above-mentioned measuring apparatus and measuring method.

<Synthesis of Resin Fine Particles P-2 to P-15 and CP-1 to CP4 and CP-6 to CP-8>
In the synthesis of the resin fine particles P-1, the type of monomer used in each polymerization step is changed to the type of monomer leading to the structural unit, and the amount of monomer used in each polymerization step is the mass ratio of the structural unit Resin fine particle P in the same manner as the resin fine particle P-1 except that the weight ratio of the core polymer to the shell polymer is changed to the “mass ratio **” shown in Table 1 and Aqueous dispersions of -2 to P-15 and CP-1 to CP4 and CP-6 to CP-8 were obtained, respectively. When Y ^1A or Y ^1B is a sodium cation or ammonium cation, Y ^1A or Y ^1B was converted to a sodium salt or ammonium salt by a conventional method using a sodium salt or ammonia.
Physical properties of the obtained P-2 to P-15 and CP-1 to CP4 and CP-6 to CP-8 are shown in Table 1.

<Synthesis of Resin Fine Particle CP-5>
In the synthesis of the resin fine particles P-1, the shell polymerization process is carried out by changing the kind and amount of the monomer used in the core polymerization step to an amount satisfying the mass ratio of the monomer leading to the structural unit and the structural unit. An aqueous dispersion of resin fine particles CP-6 was obtained in the same manner as in the synthesis of the resin fine particles P-1 except for the absence. Physical properties of the obtained CP-5 are shown in Table 1. The Tg of the resin fine particle CP-5 is shown in the glass transition temperature column of the core polymer.

In Table 1, “minimum number of atoms *” indicates the number of bonds of atoms constituting the shortest chain of L ^1A in formula (2A).
The “-” in the column of the minimum number of atoms indicates that the shell polymer forming the corresponding resin fine particle has no structural unit represented by the formula (2A).
"Mass ratio **" represents the mass of core polymer: mass of shell polymer.
Further, since the resin fine particle CP-5 does not have a shell polymer, “-” is described in the shell polymer column of glass transition temperature and the absolute value column of difference.

Example 1
Preparation of Aqueous Ink Composition
(Preparation of Black Ink Composition K-1)
-Synthesis of water-soluble polymer dispersant Q-1-
A monomer feed composition was prepared by mixing methacrylic acid (172 parts), benzyl methacrylate (828 parts) and isopropanol (375 parts). An initiator feed composition was also prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, isopropanol (187.5 parts) was heated to 80 ° C. under a nitrogen atmosphere, and a mixture of the monomer feed composition and the initiator feed composition was added dropwise thereto over 2 hours. After completion of the dropwise addition, the obtained solution was kept at 80 ° C. for further 4 hours, and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a water-soluble polymer dispersant Q-1 having a weight average molecular weight of about 30,000 and an acid value of 112 mg KOH / g.

-Preparation of black pigment dispersion-
After neutralizing 0.8 equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant Q-1 (150 parts) obtained above with a potassium hydroxide aqueous solution, the concentration of the water-soluble polymer dispersant is 25 mass The mixture was further adjusted by adding ion exchange water to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (124 parts), carbon black MA-100 (black pigment) (48 parts), water (75 parts) and dipropylene glycol (30 parts) are mixed to obtain a bead mill (beads). Dispersion was carried out until the desired volume average particle diameter was obtained with a diameter of 0.1 mmφ, zirconia beads), to obtain a dispersion (uncrosslinked dispersion) of polymer-coated black pigment particles having a pigment concentration of 15%.
In this uncrosslinked dispersion (136 parts), a crosslinking agent: Denacol EX-321 (manufactured by Nagase ChemteX Corp.) (1.3 parts) and an aqueous boric acid solution (boric acid concentration: 4% by mass) (14.3 parts) The reaction mixture was allowed to react at 50.degree. C. for 6 and a half hours, and then cooled to 25.degree. C. to obtain a crosslinked dispersion. Next, ion-exchanged water is added to the obtained cross-linked dispersion, and ultrafiltration is performed using a stirring ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (manufactured by ADVANTEC, molecular weight cut off 50,000, Q0500076 E ultra filter). It filtered. After refine | purifying so that the dipropylene glycol density | concentration in a crosslinked dispersion may be 0.1 mass% or less, the black pigment dispersion was obtained by concentrating until a pigment concentration becomes 15 mass%. The pigment contained in the black pigment dispersion is a polymer-coated pigment (encapsulated pigment) whose surface is coated with a crosslinked polymer in which the water-soluble polymer dispersant Q-1 is crosslinked by a crosslinking agent.

-Preparation of Black Ink Composition K-1-
Each component was mixed so that it might become the following composition, and each polymer containing ink composition was adjusted. After the preparation, coarse particles were removed using a 1 μm filter to prepare a black ink composition K-1. The content of the resin fine particles P-1 in the black ink composition K-1 was 5% by mass.
〔composition〕
Black pigment dispersion: An amount that the concentration of black pigment is 4 parts by mass Water-soluble organic solvent 1: Diethylene glycol monohexyl ether (manufactured by Wako Pure Chemical Industries, Ltd.): 3 parts by mass Water-soluble organic solvent 2: Diethylene glycol (sum Kojun Pharmaceutical Co., Ltd. product: 15 parts by mass Aqueous dispersion of the above resin fine particles P-1 (solid content concentration: 24 mass%): 21 parts by mass Surfactant Capstone FS-3100 (manufactured by DuPont): 0.1 Parts by weight Water: balance Total: 100 parts by weight

(Preparation of Black Ink Compositions K-2 to K-15 and CK-1 to CK-8)
In preparation of the black ink composition K-1, each aqueous dispersion of resin fine particles P-2 to P-15 and CP-1 to CP-8 was used in place of the aqueous dispersion of resin fine particles P-1 The content of resin fine particles in each black ink composition was set to 5% by mass.) Black ink composition K-2 to K as an aqueous ink composition in the same manner as black ink composition K-1 -15 and CK-1 to CK-8 were prepared respectively.
The viscosities of the black ink compositions prepared above were all within the range of 3 to 15 mPa · s at 30 ° C. This viscosity was measured by VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
The surface tension was measured by platinum plate method using CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. The surface tensions of the black ink compositions prepared above were all in the range of 20 to 60 mN / m.

[Test example]
The following tests were conducted on each of the black ink compositions prepared as described above (hereinafter sometimes simply referred to as "ink"). The results are shown in Table 2 below.

Latency test
An image was drawn directly on a recording medium ("painting photo finishing Pro" manufactured by Fujifilm Corporation) under the following ink application conditions, and dried. Thereafter, one nozzle check pattern image was drawn (the image here is taken as an "initial image sample"). Thereafter, the environment of the recording head nozzle portion was maintained at 25 ° C. and 50% RH, and left for 30 minutes and for 15 hours. After leaving for a predetermined time, one sheet of the same nozzle check pattern image as described above was drawn again on the same recording medium as used above (here, the image after leaving for 30 minutes and leaving for 15 hours Let them be “post-image samples”, and put both together into “post-standing image samples”.
For each of the image samples after standing, nozzle missing (image missing) was observed with a nozzle check pattern image with an optical microscope to determine the ejection rate, and the presence or absence of non-ejection was evaluated according to the following evaluation criteria. In this test, "B" or more is a pass level also after leaving for 30 minutes and after leaving for 15 hours.
The ejection rate (%) was determined from “(number of ejection nozzles in image sample after standing / number of ejection nozzles in initial image sample) × 100”.

~ Ink application condition ~
Head: A 1,200 dpi (dot per inch) / 20 inch wide piezo full line head was used.
The amount of discharged droplets: 2.4 pL.
Drive frequency: 24 kHz (recording medium conveyance speed 500 mm / sec).

Evaluation criteria
AA: The discharge rate is 95% or more.
A: The ejection rate is 90% or more and less than 95%.
B: The ejection rate is 85% or more and less than 90%.
C: Discharge rate is 80% or more and less than 85%.
D: Discharge rate is less than 80%.

<Abrasion resistance test>
The abrasion resistance test was performed on each ink of which the result of the latency after leaving for 30 minutes is the evaluation rank "B" or more in the above-mentioned <latency (restorability to recover from standing) test>. That is, in Comparative Examples 1, 2 and 4 in which the result of latency after leaving for 30 minutes is the evaluation rank “C” or “D”, the ink resistance is not performed because the ink performance is already poor (Table 2) In “.”)).
Under the following ink application conditions, a solid black image with a recording duty of 100% was formed directly on coated paper (trade name "OK Top Coat +", manufactured by Oji Paper Co., Ltd.) as a recording medium using predetermined black inks. . The recording duty of 100% is based on the condition that one drop of approximately 2.4 pL of ink is applied to a unit area (one pixel) of 1/1200 inch × 1/1200 inch (1 inch = 2.54 cm) at a resolution of 1200 dpi × 1200 dpi. Refers to a recorded image.
~ Ink application condition ~
-Head: 1,200 dpi (dot per inch) / 20 inch wide piezo full line head-Discharge amount: 2.4 pL
Drive frequency: 30 kHz (recording medium conveyance speed 635 mm / sec)
Single Pass Method The solid image thus formed was left under an environment of 25 ° C. and 50% relative humidity for 24 hours. The surface of the solid image was rubbed 50 times with a Silon paper loaded at 2 × 10 ⁴ N / m ² . The condition of the abraded surface of the solid image was visually confirmed, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below. In this test, "B" or more is a pass level.

Evaluation criteria
AA: No abrasion marks were observed on the abraded surface, and no transfer of the image (ink) was observed on the rubbed paper (silphone paper).
A: Although no abrasion marks were observed on the abraded surface, image transfer was observed on the rubbed paper at an area rate of less than 5% of the contact area.
B: A slight abrasion mark was observed on the abraded surface.
C: An abrasion mark was confirmed on the abraded surface, and a white background (surface) of the recording medium was seen.

<Blocking resistance test>
The blocking resistance test was performed on each ink of which the result of the latency after leaving for 30 minutes is the evaluation rank "B" or more in the above-mentioned <latency (restorability to recover from standing) test>. That is, for Comparative Examples 1, 2 and 4 in which the result of latency after leaving for 30 minutes is the evaluation rank "C" or "D", the ink resistance is already poor, so the blocking resistance test was not conducted (Table 2) In “.”)).
On the coated paper (trade name "OK Top Coat +", manufactured by Oji Paper Co., Ltd.) as a recording medium under the same ink application conditions as the ink application conditions in the above <abrasion resistance test>, the black color is given by each predetermined black ink The solid image with a recording duty of 100% was directly printed. Immediately after printing, it was dried with warm air of 60 ° C. for 2 seconds to obtain a print sample.
The print sample was cut into two pieces of 3 cm square size. Next, the four corners were aligned and overlapped so that the two printed surfaces face each other. This was placed on an 80 ° C. hot plate. A 2.0 cm × 2.0 cm × 0.3 cm flat rubber plate is placed with the 2.0 cm × 2.0 cm face on the paper side, and a 2.0 cm × 2.0 cm face on it. The plastic plate of 2.0 cm × 2.0 cm × 0.3 cm was placed on the rubber plate. A 500 g weight was placed on a plastic plate and allowed to stand for 1 hour, and then the two superposed sheets of paper were peeled off and the blocking resistance was evaluated according to the following evaluation criteria. In this test, "B" or more is a pass level.

Evaluation criteria
A: Peeled off naturally. Or, although there was resistance at the time of peeling, there was no color transfer of the print sample.
B: Color transfer of the print sample was observed in the range of less than 10% of the area of the print surface, but it was at a level causing no problem in practical use.
C: Color transfer of the print sample was observed in a wide range of 10% or more of the area of the print surface, which was a level at which problems in practical use occur.

As shown in Table 2, each of the aqueous ink compositions (CK-1 to CK-8) for inkjet recording of the comparative example not containing the resin fine particles specified in the present invention has latency, abrasion resistance and blocking resistance. It was not something that had sex.
On the other hand, all of the aqueous ink compositions (K-1 to K-15) for inkjet recording of the examples containing the resin fine particles defined in the present invention have high latency, abrasion resistance and blocking resistance. It combines in the level. That is, although the water-based ink composition for ink jet recording of the example exhibits excellent latency, when it is discharged (landed) onto the recording medium, the recording medium is the above-mentioned low water absorption recording medium or non-water absorbing recording medium It can be seen that even a medium can be formed directly on the recording medium with an image showing high abrasion and blocking resistance.

In addition, the cyan ink composition and the magenta ink composition prepared using the cyan pigment and the magenta pigment were tested in the same manner as the above black ink composition, and the same results were shown.

While the present invention has been described in conjunction with its embodiments, we do not intend to limit our invention in any detail of the description unless otherwise specified, which is contrary to the spirit and scope of the invention as set forth in the appended claims. I think that it should be interpreted broadly without.

The present application claims priority based on Japanese Patent Application No. 2017-180192 filed in Japan on September 20, 2017, the contents of which are incorporated herein by reference. Capture as part.

Claims

An aqueous ink composition for ink jet recording comprising an aqueous medium and resin fine particles,
The resin fine particles have a core-shell structure containing a core polymer and a shell polymer covering the core polymer,
The shell polymer has a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2A) or the formula (2B),
An aqueous ink composition for ink jet recording, wherein the glass transition temperature of the core polymer is higher than the glass transition temperature of the shell polymer, and the glass transition temperature of the shell polymer is 20 to 130 ° C.

In the formula (1), R 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R 2 represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, or an aromatic ring group. A 1 represents an alkylene group having 2 to 20 carbon atoms. m 1 is an integer of 1 to 100.
In formulas (2A) and (2B), R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. L 1A represents a single bond or a linking group having a minimum number of 6 or less linking the carbonyl carbon atom in the formula and Y 1A . Y 1A represents —OM when L 1A is a single bond, and —C (= O) OM, —S (= O) 2 OM or —OS (= O) when L 1A is a linking group 2 indicates OM. Y 1B represents —C (= O) OM, —S (= O) 2 OM or —OS (= O) 2 OM. M represents a hydrogen atom, an alkali metal ion or an ammonium ion.
The aqueous ink composition for inkjet recording according to claim 1, wherein the structural unit represented by the formula (1) is a structural unit represented by the following formula (3).

In the formula, R 1 and R 2 are as described above. m 2 is an integer of 2 to 100.
The aqueous ink composition for ink jet recording according to claim 1 or 2, wherein the absolute value of the difference between the glass transition temperature of the core polymer and the glass transition temperature of the shell polymer is 20 ° C or more.
The aqueous ink composition for inkjet recording according to any one of claims 1 to 3, wherein the content of the structural unit represented by the formula (1) in the shell polymer is 30% by mass or less.
The aqueous ink for ink jet recording according to any one of claims 1 to 4, wherein at least one of the core polymer and the shell polymer has a structural unit derived from an ethylenically unsaturated compound having an aromatic ring or an aliphatic ring. Composition.
The aqueous ink for inkjet recording according to claim 5, wherein the structural unit derived from the ethylenically unsaturated compound having an aromatic ring or an aliphatic ring is represented by any one of the following general formulas (A) to (E). Composition.

In formulas (A) to (E), R 11 and R 12 each represent a methyl or hydrogen atom. R 13 represents a linear or branched alkyl group having 1 to 10 carbon atoms. N in the general formula (A) and the general formula (B) is an integer of 0 to 5, and n in the general formula (C) is an integer of 0 to 11. L 11 represents a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C (= O)-or a divalent linking group formed by linking two or more of these.
The content of the structural unit represented by any one of the general formulas (A) to (E) in the core polymer is 10 to 90% by mass.
The aqueous ink composition for inkjet recording according to claim 6, wherein the content of the structural unit represented by any one of the general formulas (A) to (E) in the shell polymer is 70% by mass or less.
The aqueous ink composition for ink jet recording according to any one of claims 1 to 7, wherein the content of the resin fine particles is 1 to 15% by mass with respect to the total mass of the aqueous ink composition for ink jet recording.
The aqueous ink composition for ink jet recording according to any one of claims 1 to 8, which contains a pigment.
An image forming method, comprising: applying the aqueous ink composition for inkjet recording according to claim 9 onto a recording medium by an inkjet method to form an image.
The image forming method according to claim 10, wherein the aqueous ink composition for inkjet recording is directly applied onto a low water absorption recording medium or a non-water absorption recording medium.
A fine resin particle having a core-shell structure containing a core polymer and a shell polymer coating the core polymer,
The shell polymer has a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2A) or the formula (2B),
Resin fine particles, wherein the glass transition temperature of the core polymer is higher than the glass transition temperature of the shell polymer, and the glass transition temperature of the shell polymer is 20 to 130 ° C.

In the formula (1), R 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R 2 represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, or an aromatic ring group. A 1 represents an alkylene group having 2 to 20 carbon atoms. m 1 is an integer of 1 to 100.
In formulas (2A) and (2B), R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. L 1A represents a single bond or a linking group having a minimum number of 6 or less linking the carbonyl carbon atom in the formula and Y 1A . Y 1A represents —OM when L 1A is a single bond, and —C (= O) OM, —S (= O) 2 OM or —OS (= O) when L 1A is a linking group 2 indicates OM. Y 1B represents —C (= O) OM, —S (= O) 2 OM or —OS (= O) 2 OM. M represents a hydrogen atom, an alkali metal ion or an ammonium ion.
The resin fine particle of Claim 12 whose structural unit represented by said Formula (1) is a structural unit represented by following formula (3).

In the formula, R 1 and R 2 are as described above. m 2 is an integer of 2 to 100.