JP2013185135A - Ink set, and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set capable of suppressing gloss unevenness in a black-color image formed by agglomerating components of a black-color ink composition containing only a small amount of polymer particles.SOLUTION: An ink set contains: a black-color ink composition containing a polymer-coated carbon black pigment, at least a part of the surface of a carbon black pigment of which is coated with a crosslinked water-soluble polymer, a sugar alcohol, and water, wherein the content of the polymer particle is <2 mass% with respect to the total amount of the ink composition; and a treating liquid containing an agglomerating component to agglomerate the components in the black-color ink composition.

Description

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

The image forming method based on the ink jet method is an image forming method that is widely expected in the fields of office printers, home printers, and the like and the commercial field because desired images can be formed on various recording media.
As a kind of image forming method by the inkjet method, an ink set including a combination of an ink containing a pigment and a treatment liquid containing an aggregating component for aggregating the components in the ink is used. There is a method of forming an image on a recording medium by aggregation.
As such an ink set, for example, a polymer containing a pigment, a water-soluble solvent, water, and resin fine particles, obtained through a step of crosslinking the pigment with a water-soluble dispersant and then crosslinking with a crosslinking agent. An ink set is known that includes an ink composition that is a pigment coated with an ink composition and a colorless ink composition (treatment liquid) containing an aggregation accelerator that promotes aggregation of the ink composition (for example, Patent Documents). 1).

JP 2009-190379 A

As described in Patent Document 1, an ink composition containing resin fine particles (polymer particles) is used in a conventional ink set. Here, in order to further improve the discharge properties of the ink composition, it is conceivable to reduce the content of polymer particles from the ink composition.
However, in an ink set having a black ink composition containing polymer particles and a treatment liquid containing an aggregating component for aggregating the components in the black ink composition, the content of polymer particles from the black ink composition It has been found that if the reduction is reduced, gloss unevenness may occur in the formed black image.

  The present invention has been made in view of the above, and an ink set and an image forming method capable of suppressing gloss unevenness in a black image formed by aggregating components in a black ink composition having a small content of polymer particles It is an object to provide this and to achieve the object.

The present inventor has disclosed a polymer-coated carbon black pigment in which at least a part of the surface of a carbon black pigment is coated with a crosslinked water-soluble polymer, a sugar alcohol, and a black ink composition having a low content of polymer particles. Thus, the inventors have obtained the knowledge that the gloss unevenness of the black image described above can be suppressed, and the present invention has been completed based on this finding.
That is, specific means for achieving the above-described problem are as follows.

<1> A polymer-coated carbon black pigment in which at least a part of the surface of the carbon black pigment is coated with a crosslinked water-soluble polymer, a sugar alcohol, and water, and the content of the polymer particles is the total amount of the ink composition. An ink set comprising a black ink composition of less than 2% by mass and a treatment liquid containing an aggregating component for aggregating the components in the black ink composition.
<2> The ink set according to <1>, wherein the sugar alcohol has five or more hydroxyl groups in one molecule.
<3> The ink set according to <1> or <2>, wherein the sugar alcohol is at least one selected from the group consisting of pentitol and hexitol.
<4> The ink set according to any one of <1> to <3>, wherein the black ink composition further contains at least one color pigment selected from a magenta pigment and a cyan pigment.
<5> The ink set according to any one of <1> to <4>, wherein the black ink composition further contains a polymerizable compound.
<6> The black ink composition further contains a polymerizable compound, and at least one of the polymerizable compounds is a polymerizable compound having a (meth) acrylamide structure in the molecule <1> to <5. The ink set according to any one of the above.
<7> The ink set according to any one of <1> to <6>, wherein the amount of the crosslinked water-soluble polymer is 50% by mass to 150% by mass with respect to the amount of the carbon black pigment. is there.
<8> The ink set according to any one of <5> to <7>, wherein at least one of the treatment liquid and the black ink composition further contains a polymerization initiator.
<9> The ink set according to any one of <1> to <8>, wherein the aggregation component is at least one selected from an acid, a polyvalent metal salt, and a cationic polymer.
<10> In the polymer-coated carbon black pigment, at least a part of the surface of the carbon black pigment is coated with a water-soluble polymer having a carboxyl group, and at least a part of the carboxyl group has a glycidyl group in one molecule. The ink set according to any one of <1> to <9>, which is crosslinked by a reaction with two or more glycidyl ether compounds.

<11> The ink set according to any one of <1> to <10> is used, and a treatment liquid application step of applying the treatment liquid onto a recording medium, and the black ink composition by an inkjet method. An image forming method comprising: an ink applying step for forming an image by applying on a recording medium; and a drying step for drying the image after the treatment liquid applying step and the ink applying step.
<12> The ink application step is provided after the treatment liquid application step, and the recording medium has a single or multilayer pigment layer on at least one surface on a support mainly composed of cellulose pulp. , the transfer amount of pure water measured by a dynamic scanning liquid absorption meter, the contact time be at 1 ml / ^{m 2} or more 15 ml / ^{m 2} or less in 100 ms, and the contact time 2 ml / ^{m 2} or more 20 ml / ^{m 2} or less at 400ms The image forming method according to <11>.
<13> The image forming method according to <12>, wherein the recording medium is coated paper, lightweight coated paper, or finely coated paper.
<14> The image forming method according to any one of <11> to <13>, further including a curing step of irradiating the image after the drying step with an active energy ray to cure the image.
<15> The image according to any one of <11> to <14>, wherein the drying step starts drying within 5 seconds from the time when the droplet of the black ink composition has landed on the recording medium. It is a forming method.
<16> The image forming method according to any one of <11> to <15>, wherein a maximum application amount of the black ink composition in the ink application step is 15 ml / m ² or less.
<17> The drying step is performed under a drying condition in which 60 to 80% by mass of the water content in the black ink composition applied on the recording medium is removed with a maximum application amount of 15 ml / m ² or less. The image forming method according to any one of <11> to <16>, wherein at least a part of water in the black ink composition for forming an image on the recording medium is removed.

  ADVANTAGE OF THE INVENTION According to this invention, the ink set and image formation method which can suppress the gloss nonuniformity in the black-type image formed by aggregating the component in a black-type ink composition with little content of polymer particles can be provided.

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

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

≪Ink set≫
The ink set of the present invention contains a polymer-coated carbon black pigment in which at least a part of the surface of the carbon black pigment is coated with a crosslinked water-soluble polymer, a sugar alcohol, and water, and the content of polymer particles is an ink. A black ink composition (hereinafter also referred to as “black ink”) that is less than 2% by mass based on the total amount of the composition, and a treatment liquid containing an aggregating component that aggregates the components in the black ink composition; ,including.

According to the study of the present inventors, an image is obtained using an ink set including a black ink composition having a low content of polymer particles and a treatment liquid containing an aggregating component that aggregates the components in the black ink composition. When it was formed, it was found that gloss unevenness (gloss unevenness on the surface of the black image visually observed, the same applies hereinafter) may occur in the formed black image.
According to the ink set of the present invention having the above-described configuration, it is possible to form a black image in which gloss unevenness is suppressed even though the black ink composition having a small content of polymer particles is used.

The reason why the above effect can be obtained by the ink set of the present invention is presumed as follows.
That is, in general, in an ink set including an ink composition (hereinafter also referred to as “ink”) and a treatment liquid containing an aggregating component for aggregating the components in the ink composition, an essential component in the ink composition. As the polymer particles, the agglomeration property when the components in the ink composition are aggregated by the treatment liquid (hereinafter referred to as “ink aggregation property”, “ink aggregation property”, or “aggregation”). Also called “sex”). Therefore, in the conventional ink set having the ink containing the polymer particles, if the polymer particles are reduced from the ink for the purpose of further improving the discharge property, the cohesiveness of the ink tends to be lowered.
The above-described gloss unevenness of the black image is formed by drying in a state where the aggregation is insufficient when the black ink is formed by aggregating the components in the black ink having a small content of polymer particles. It is considered that the surface of the black image formed is rough.
In this regard, in the ink set of the present invention, the content of the polymer particles is small (specifically, the polymer particles are less than 2% by mass with respect to the total amount of the ink). By containing a polymer-coated carbon black pigment on which at least a part of the surface of the black pigment is coated and a sugar alcohol, the cohesiveness of a black ink having a small content of polymer particles is improved and a black image is obtained. It is considered that surface roughness of the surface is suppressed, and as a result, gloss unevenness can be suppressed.
The reason why the black ink with few polymer particles improves the cohesion by the ink set of the present invention is not clear, but is presumed as follows.
That is, when the treatment liquid and the black ink composition come into contact with each other and components (polymer-coated carbon black pigment, etc.) in the black ink composition agglomerate (having a relatively large number of hydroxyl groups in one molecule). This is presumed to be because the hydroxyl group of the sugar alcohol and the crosslinked structure of the polymer-coated carbon black pigment interact with each other by hydrogen bonding, and as a result, the cohesiveness between the polymer-coated carbon black pigments is enhanced.

In addition, sugar alcohol may be used as a wetting agent (humectant) for ink, but in the present invention, when urea used as a wetting agent in the same manner as sugar alcohol is used instead of sugar alcohol, The effect of suppressing gloss unevenness according to the present invention cannot be obtained.
Further, in the present invention, carbon black is replaced with a non-crosslinked (uncrosslinked) water-soluble polymer instead of a polymer-coated carbon black pigment in which at least a part of the surface of the carbon black pigment is coated with a crosslinked water-soluble polymer. Even when a polymer-coated carbon black pigment in which at least a part of the surface of the pigment is coated is used, the effect of suppressing gloss unevenness according to the present invention cannot be obtained.

As described above, according to the ink set of the present invention, the cohesiveness of the black ink composition having a small content of polymer particles is improved, so that the strength of the image formed using the black ink composition is improved. As a result, image scratch resistance and adhesion (adhesion to the recording medium) are improved.
Furthermore, according to the ink set of the present invention, curling of a recording medium on which a black image is formed is reduced. The reason why curling is reduced is not clear, but by improving the cohesiveness of the black ink composition, the aggregated black ink composition has a higher effect of retaining water (delaying water penetration), This effect is presumed to be due to a decrease in the amount of water penetrating into the recording medium.
Furthermore, since the black image formed using the ink set of the present invention has improved cohesiveness of the image (black ink composition), other colors of ink are used on the black image. When drawing thin lines, deformation and movement of ink droplets of other colors after landing on the black image are suppressed, and fine line reproducibility is excellent (that is, the line width of the fine lines is uniform). Excellent).

  The effect of suppressing uneven glossiness (improving ink cohesiveness) by the ink set of the present invention is such that the cohesiveness of black ink tends to be a problem (for example, when forming an image on a recording medium with relatively slow liquid penetration, This is particularly noticeable when the time from image formation (after application of ink) to the start of drying is relatively short). Details of these will be described later.

  Hereinafter, the black ink composition and the treatment liquid, which are components of the ink set of the present invention, will be described.

<Black ink composition>
The ink set of the present invention includes a polymer-coated carbon black pigment (hereinafter also referred to as “specific polymer-coated carbon black pigment”), a sugar alcohol, in which at least a part of the surface of the carbon black pigment is coated with a crosslinked water-soluble polymer. And a black ink composition (hereinafter referred to as “black ink (composition) in the present invention” or “black system”) containing water and polymer particles in an amount of less than 2% by mass based on the total amount of the ink composition. Ink (composition) ”).
Hereinafter, each component of the black ink composition in the present invention will be described.

(Specific polymer-coated carbon black pigment)
The black ink composition includes at least one specific polymer-coated carbon black pigment.
The specific polymer-coated carbon black pigment has a structure in which at least a part of the surface of the carbon black pigment is coated with a water-soluble polymer and at least a part of the water-soluble polymer is crosslinked. Here, the carbon black pigment may be entirely coated with a water-soluble polymer, or may be partially (partially) coated.
The specific polymer-coated carbon black pigment can be suitably prepared by dispersing the carbon black pigment using a water-soluble polymer (dispersing agent) and then crosslinking with a crosslinking agent. A detailed method will be described later.

~ Carbon black pigment ~
There is no restriction | limiting in particular as said carbon black pigment, A well-known carbon black pigment can be used.
The average primary particle size of the carbon black pigment is not particularly limited, but the average primary particle size is, for example, 10 nm to 70 nm, and preferably 10 nm to 50 nm.
The average primary particle size is a particle size (corresponding to an area circle) of 1000 primary particles arbitrarily selected from an image taken using a transmission electron microscope TEM2010 (pressurized voltage 200 kV) manufactured by JEOL Ltd. Diameter) is measured and calculated as the arithmetic average. That is, the average primary particle diameter represents the arithmetic average particle diameter of the equivalent area circle diameter.

The DBP absorption amount of the carbon black pigment is not particularly limited, but is preferably 30 ml / 100 g or more and 200 ml / 100 g or less, and more preferably 50 ml / 100 g or more and 150 ml / 100 g or less from the viewpoint of color tone and printing density. .
The DBP absorption is measured by the JIS K6221 A method.

The BET specific surface area of the carbon black pigment is not particularly limited, but is preferably 30 m ² / g or more and 450 m ² / g or less, and 200 m ² / g or more and 400 m ² / g from the viewpoint of printing density and storage stability. The following is more preferable.

Examples of the carbon black pigment include those produced by known methods such as a contact method, a furnace method, and a thermal method.
Specific examples For example, Raven1250, Raven1200, Raven1190 ULTRA, Raven1170, Raven1255, Raven1080ULTRA, Raven1060ULTRA, Raven1040, Raven1035, Raven1020, Raven1000, Raven900, Raven890, Raven850, Raven780ULTRA, Raven860Ultra, Raven520, Raven500, Raven450, Raven460, Raven415, Raven14 , Conductex 7055 Ultra (from Colombian Carbon), Regal 400R, Regal 330R, Regal 660R, Mogu L, Black Pearls L, egal99, Regal350, MONARCH280, MONARCH120 (above, manufactured by Cabot), Color Black S160, Color Black S170, Printex35, Printex U, Printex V, Printex 140U, Printex 140V, Printex 140V, Print Black 4A, Special Black 4, Special Black 550, Special Black 350, Special Black 250, Special Black 100, NEROX 3500, NEROX 1000, NEROX 2500 (and above, Evonik) Degussa Co., Ltd.), No. 10, no. 20, no. 25, no. 33, no. 40, no. 45, no. 47, no. 52, no. 85, no. 95, no. 260, MA7, MA8, MA11, MA77, MA100, MA220, MA230, MA600 (above, manufactured by Mitsubishi Chemical Corporation). However, it is not limited to these.

In the black ink composition, the carbon black pigment may be used alone or in combination of two or more.
The content ratio of the carbon black pigment in the black ink composition (the total content ratio in the case of two or more types) is not particularly limited. It is preferably 0.0% by mass, and more preferably 0.8 to 3.5% by mass.

~ Water-soluble polymer ~
As the water-soluble polymer for coating the carbon black pigment, it is preferable to use a water-soluble polymer dispersant that disperses the carbon black pigment in an aqueous medium.
The term “water-soluble” as used herein means that the polymer is dissolved in distilled water at 25 ° C. at 2% by mass or more, preferably 5% by mass or more, and preferably 10% by mass or more. More preferred. Further, when the polymer has a salt-forming group, it is preferable that the solubility is in the above range when neutralized with an equimolar amount of base or acid.
Examples of the water-soluble polymer include hydrophilic polymer compounds.

Examples of the water-soluble polymer in the present invention include polyvinyls, polyurethanes, and polyesters, among which polyvinyls are preferable.
The water-soluble polymer in the present invention is preferably a water-soluble polymer having a functional group that can be cross-linked by a cross-linking agent.
The crosslinkable functional group is not particularly limited, and examples thereof include a carboxyl group or a salt thereof, an isocyanate group, and an epoxy group. From the viewpoint of improving dispersibility, a carboxyl group or a salt thereof is preferable, and a carboxyl group is particularly preferable. preferable.

The water-soluble polymer having a carboxyl group is preferably a copolymer obtained using a carboxyl group-containing monomer as a copolymerization component.
Examples of the carboxyl group-containing monomer include (meth) acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, crotonic acid and the like. Among these, from the viewpoint of crosslinkability and dispersion stability, (meth) Acrylic acid and β-carboxyethyl acrylate are preferred. (Meth) acrylic acid means at least one of acrylic acid and methacrylic acid.
The copolymer component preferably contains at least one hydrophobic monomer. Examples of hydrophobic monomers include alkyl (meth) acrylates having 1 to 20 carbon atoms, (meth) acrylates having aromatic ring groups such as benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, and styrene and derivatives thereof. Among them, alkyl (meth) acrylates having 1 to 20 carbon atoms and (meth) acrylates having an aromatic ring group are preferable.
The method for synthesizing the copolymer is not particularly limited, but random polymerization of vinyl monomers is preferable from the viewpoint of dispersion stability.

  As the water-soluble polymer in the present invention, a copolymer obtained by using a carboxyl group-containing monomer and at least one of an alkyl (meth) acrylate having 1 to 20 carbon atoms and a (meth) acrylate having an aromatic ring group is used. Preferably, a copolymer obtained by copolymerizing (meth) acrylic acid and benzyl (meth) acrylate (that is, a structural unit derived from benzyl (meth) acrylate and a structural unit derived from (meth) acrylic acid) It is particularly preferable that the copolymer contains at least

  A structural unit derived from a carboxyl group-containing monomer (for example, (meth) acrylic acid or β-carboxyethyl acrylate), which is a preferred form of the water-soluble polymer in the present invention, and a hydrophobic monomer (for example, having 1 to 20 carbon atoms) And a structural unit derived from at least one of alkyl (meth) acrylate and (meth) acrylate having an aromatic ring group), the content ratio of the structural unit derived from the carboxyl group-containing monomer is 10 mass%-80 mass% are preferable with respect to the total mass of coalescence, 10 mass%-50 mass% are more preferable, and 10 mass%-30 mass% are especially preferable. In this copolymer, the content ratio of the structural unit derived from the hydrophobic monomer is preferably 20% by mass to 90% by mass, and more preferably 50% by mass to 90% by mass with respect to the total mass of the copolymer. 70 mass% to 90 mass% is particularly preferable.

The acid value of the water-soluble polymer before crosslinking is preferably from 67 to 200 mgKOH / g, more preferably from 67 to 150 mgKOH / g, from the viewpoint of dispersibility of the pigment.
The acid value of the crosslinked water-soluble polymer (crosslinked water-soluble polymer) is preferably 55 to 100 mgKOH / g from the viewpoints of stability and ink aggregation.

  The weight average molecular weight of the water-soluble polymer before crosslinking is not particularly limited, but is preferably 3,000 to 100,000, more preferably 5,000 to 80,000 from the viewpoint of pigment dispersibility. More preferably, it is 10,000-60,000.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and three columns of TSKgeL Super HZM-H, TSKgeL Super HZ4000, TSKgeL Super HZ2000 (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm), THF (tetrahydrofuran) is used as the eluent. As conditions, the sample concentration is 0.35% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and an IR detector is used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

  The specific polymer-coated carbon black pigment is, for example, a carbon black pigment coated with a water-soluble polymer by dispersing the carbon black pigment using a water-soluble polymer, and then coated with the water-soluble polymer. The water-soluble polymer of the pigment can be produced by crosslinking with a crosslinking agent. When the carbon black pigment is dispersed using the water-soluble polymer, the carbon black pigment is added in an amount of 10 to 150% by mass (preferably 30 to 120% by mass) with respect to the amount of the carbon black pigment. It is preferable to disperse using a water-soluble polymer in an amount of preferably 50 to 100% by mass.

Specifically, for example, a step of dispersing the mixture by adding an aqueous solution containing a basic substance to a mixture of a carbon black pigment, a water-soluble polymer dispersant, and an organic solvent capable of dissolving or dispersing the water-soluble polymer dispersant. (Mixing / hydration step), a step of adding a crosslinking agent to the dispersion obtained by the dispersion treatment and heating to cause a crosslinking reaction (crosslinking step) to obtain a specific polymer-coated carbon black pigment, and water after crosslinking A pigment dispersion of the specific polymer-coated carbon black pigment can be produced by a production method including a step of purifying the dispersible specific polymer-coated carbon black pigment to remove impurities (purification step). Thereby, the carbon black pigment is finely dispersed, and a carbon black pigment dispersion excellent in storage stability can be produced.
More specifically, for example, the pigment dispersion can be produced by a method for producing a pigment dispersion described in JP2009-190379A.

The water-soluble polymer described above may be used in combination with a water-insoluble polymer (for example, a water-insoluble dispersant).
As the water-insoluble polymer, a water-insoluble polymer having a hydrophobic structural unit and a hydrophilic structural unit can be used. The hydrophilic structural unit is preferably a structural unit having an acidic group, and more preferably a structural unit having a carboxyl group.
Examples of the water-insoluble polymer include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid. Examples include copolymers, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymers, vinyl acetate-maleic acid copolymers, and styrene-maleic acid copolymers.
More specifically, for example, water-insoluble polymers described in JP-A-2005-41994, JP-A-2006-238991, JP-A-2009-084494, JP-A-2009-191134, and the like are preferably used in the present invention. Can be used.

~ Crosslinking agent ~
The specific polymer-coated carbon black pigment in the present invention is obtained by crosslinking a polymer-coated carbon black pigment (specifically, a water-soluble polymer that coats the carbon black pigment in the polymer-coated carbon black pigment) with a crosslinking agent. be able to.
The cross-linking agent is not particularly limited as long as it is a compound having two or more sites that react with a water-soluble polymer, but preferably has a high reactivity with a carboxyl group. A compound having two or more epoxy groups (a bifunctional or more functional epoxy compound), more preferably a glycidyl ether compound having two or more glycidyl groups in one molecule.
That is, in a preferred form of the specific polymer-coated carbon black pigment, at least a part of the surface of the carbon black pigment is coated with a water-soluble polymer having a carboxyl group, and at least a part of the carboxyl group is in one molecule. This is a form formed by crosslinking with a glycidyl ether compound having two or more glycidyl groups.
Furthermore, the more preferable form of the specific polymer-coated carbon black pigment has a structural unit derived from (meth) acrylic acid, a structural unit derived from an alkyl (meth) acrylate having 1 to 20 carbon atoms, and an aromatic ring group ( At least a part of the surface of the carbon black pigment is covered with a water-soluble polymer having at least one of structural units derived from (meth) acrylate, and at least a part of the carboxyl groups of the water-soluble polymer has a glycidyl group. This is a form formed by crosslinking with a reaction with two or more glycidyl ether compounds.
Specific examples of the crosslinking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, Examples thereof include polypropylene glycol diglycidyl ether and trimethylolpropane triglycidyl ether, and polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether and trimethylolpropane triglycidyl ether are preferable.

  A commercial item can also be used as said crosslinking agent. As a commercial item, Dencol EX-321, EX-821, EX-830, EX-850, EX-851 (made by Nagase ChemteX Corporation) etc. can be used, for example.

  The molar ratio of the crosslinking site (for example, epoxy group) of the crosslinking agent to the crosslinked site (for example, carboxyl group) of the water-soluble polymer is from 1: 1.1 to 1 in terms of the crosslinking reaction rate and the dispersion stability after crosslinking. : 10 is preferable, 1: 1.1 to 1: 5 is more preferable, and 1: 1.1 to 1: 3 is most preferable.

The average particle size of the specific polymer-coated carbon black pigment is preferably 10 to 200 nm, more preferably 10 to 150 nm, further preferably 40 to 150 nm, further preferably 50 to 150 nm, and particularly preferably 50 to 130 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good. The particle size distribution of the specific polymer-coated carbon black pigment is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Further, two or more kinds of specific polymer-coated carbon black pigments having a monodisperse particle size distribution may be mixed and used.
Here, the average particle diameter of the specific polymer-coated carbon black pigment indicates the average particle diameter in an ink state, but the same applies to a so-called concentrated ink dispersion in a stage before ink conversion.

  The average particle size and the particle size distribution of the specific polymer-coated carbon black pigment are determined by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is calculated | required by measuring.

In the black ink composition of the present invention, the mass ratio (%) of the amount of the crosslinked water-soluble polymer (D) to the amount of the carbon black pigment (P) (hereinafter referred to as “D / P ratio” ( %)) Can be, for example, 10 to 150% by mass, more preferably 30 to 120% by mass, and still more preferably 50 to 100% by mass.
Here, the preferable range of the D / P ratio is a preferable range of the mass ratio of the crosslinked water-soluble polymer to the carbon black pigment in the specific polymer-coated carbon black pigment. The above range is also preferable for the mass ratio (preparation ratio) of the amount of the water-soluble polymer to the amount of the carbon black pigment at the time of preparation.

~ Coloring pigment ~
The black ink composition in the present invention comprises at least one color pigment selected from a magenta pigment and a cyan pigment in addition to the specific polymer-coated carbon black pigment from the viewpoint of further suppressing gloss unevenness in a black image. It is preferable to include.

Examples of magenta pigments include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.
Among these, from the viewpoints of adhesion and abrasion resistance, C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 209, C.I. I. C.I. preferably at least one selected from CI pigment violet 19. I. Pigment red 122, C.I. I. Pigment violet 19 is particularly preferred.

Examples of cyan pigments include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment Green 7, and siloxane-crosslinked aluminum phthalocyanine described in US Pat. No. 4,311,775.
Among these, from the viewpoints of adhesion and abrasion resistance, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. C.I. preferably at least one selected from CI Pigment Blue 16. I. Pigment blue 15: 3, C.I. I. More preferably, it is at least one selected from CI Pigment Blue 15: 4.

When the black ink composition in the present invention contains at least one color pigment selected from a magenta pigment and a cyan pigment, the content ratio of the color pigment to the total amount of the carbon black pigment and the color pigment (color pigment / ( The carbon black pigment + colored pigment)) is not particularly limited, but is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 50% by mass, and more preferably 20% by mass to 40% by mass. It is particularly preferred that
When the content ratio is 5% by mass or more, gloss unevenness in the black image is further suppressed. Although the cause is unknown, the black image is more resistant to rubbing and is less likely to be scratched when the black image is scratched.
When the content ratio is 60% by mass or less, the color tone of the black image becomes better and the color density is further improved.

  When the colored pigment includes a cyan pigment and a magenta pigment, the content ratio of the magenta pigment to the cyan pigment (magenta pigment / cyan pigment) is not particularly limited, but is 100% by mass from the viewpoint of adhesion, abrasion resistance, and color tone. It is preferably 180% by mass or less, more preferably 120% by mass or more and 160% by mass or less, and particularly preferably 130% by mass or more and 160% by mass or less.

When the black ink composition of the present invention contains the color pigment, at least one of the color pigments is coated with the above-mentioned water-soluble polymer from the viewpoint of dispersion stability (that is, polymer-coated color pigment). In the form of a black ink composition. Furthermore, from the viewpoint of ink aggregation and storage stability, in the form of the polymer-coated colored pigment, the water-soluble polymer that coats the colored pigment is crosslinked by the crosslinking agent (that is, the polymer-coated colored pigment is More preferably, it is in the form of a crosslinked polymer-coated colored pigment.
The polymer-coated colored pigment can be produced by a method similar to the method for producing the specific polymer-coated carbon black pigment described above.
When the black ink composition in the present invention contains the polymer-coated color pigment, the black ink composition includes, for example, a dispersion of a specific polymer-coated carbon black pigment and a dispersion of the polymer-coated color pigment (for example, At least one of a dispersion of a polymer-coated cyan pigment in which at least a part of the cyan pigment is coated with a water-soluble polymer, and a dispersion of a polymer-coated magenta pigment in which at least a part of the magenta pigment is coated with a water-soluble polymer ), Sugar alcohol, water, and (and other components as necessary) can be suitably prepared.
In the polymer-coated cyan pigment, the mass ratio (%) of the amount of the water-soluble polymer (D) to the amount of the cyan pigment (P) (“D / P ratio”) is, for example, 10 to 150 mass%. 30-120 mass% is more preferable, and 50-100 mass% is still more preferable. The above range is also preferable for the mass ratio (preparation ratio) of the amount of the water-soluble polymer to the amount of the cyan pigment in producing the polymer-coated cyan pigment.
In the polymer-coated magenta pigment, the mass ratio (%) of the amount of the water-soluble polymer (D) to the amount of the magenta pigment (P) (“D / P ratio”) is, for example, 10 to 150 mass%. 10 to 120% by mass is more preferable, and 20 to 100% by mass is even more preferable. The above range is also preferable for the mass ratio (preparation ratio) of the amount of the water-soluble polymer to the amount of the magenta pigment when preparing the polymer-coated magenta pigment.

(Sugar alcohol)
The black ink composition contains at least one sugar alcohol.
As described above, the combined action of the sugar alcohol and the crosslinked structure of the specific polymer-coated carbon black pigment improves the cohesiveness of the black ink composition, thereby suppressing the uneven glossiness of the black image. Is done.
In the present invention, “sugar alcohol” refers to a polyhydric alcohol corresponding to those obtained by reducing the aldehyde group and the ketone group of the sugar to give primary and secondary alcohol groups, respectively.

  The sugar alcohol may be a sugar alcohol derived from a monosaccharide, or a sugar alcohol derived from a polysaccharide containing an oligosaccharide. Among these, the sugar alcohol is preferably a sugar alcohol derived from monosaccharide or oligosaccharide, more preferably a sugar alcohol derived from monosaccharide or disaccharide, from the viewpoint of further suppressing uneven gloss. Preferably, sugar alcohols derived from monosaccharides are particularly preferred.

The sugar alcohol preferably has 5 or more hydroxyl groups in one molecule from the viewpoint of further suppressing uneven glossiness of black images.
More specific examples of the sugar alcohol include tritol, tetritol, pentitol, hexitol, heptitol, octitol and the like. Of these, from the viewpoint of ink aggregation, at least one selected from the group consisting of pentitol, hexitol, heptitol, and octitol is preferable. Furthermore, at least one selected from the group consisting of pentitol and hexitol is preferred from the viewpoints of ink cohesion and ease of availability and synthesis.

Hereinafter, although the specific example of sugar alcohol is shown, this invention is not limited to the following specific examples.
Examples of the tritol include glycerin.
Examples of the tetritol include erythritol (erythritol), D-threitol, L-threitol and the like.
Examples of the pentitol include xylitol, D-arabinitol, L-arabinitol, ribitol and the like.
Examples of the hexitol include sorbitol, D-iditol, galactitol, mannitol and the like.
Examples of heptitol include boremitol and perseitol.
Examples of the octitol include D-erythro-D-galacto-octitol.

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

The SP value of the sugar alcohol is not particularly limited, but is preferably 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less, 18. 00 (cal / cm ³ ) ^1/2 or more and 18.80 (cal / cm ³ ) ^1/2 or less is more preferable. Examples of sugar alcohols having an SP value of 17.80 (cal / cm ³ ) ^1/2 or more and 19.00 (cal / cm ³ ) ^1/2 or less include pentitol and hexitol.
The “SP value” (solubility parameter, unit: (cal / cm ³ ) ^1/2 ) is a value calculated by the following formula according to the Fedors method.
SP value (δ) = [ΣE _coh / ΣV] ^1/2
Here, ΣE _coh represents cohesive energy, and ΣV represents molar molecular volume.
Details of the “Fedors method” are described in R.A. F. Fedors, Polymer Engineering Science, 14, p. 147 to 154 (1967), and the SP value is calculated by the method described in this document.

  The content of the sugar alcohol in the black ink composition in the invention is not particularly limited, but is preferably 0.1 to 20% by mass, and preferably 0.1 to 10% by mass with respect to the total amount of the black ink composition. % Is more preferable, and 1 to 10% by mass is particularly preferable.

(Polymer particles)
In the black ink composition of the present invention, the content of polymer particles is less than 2% by mass with respect to the total amount of the black ink composition.
The polymer particles are components different from the water-soluble polymer (dispersant) that coats the carbon black pigment (and the color pigment if necessary), and the particulate polymer is dispersed in the ink composition. It is.
The polymer particles are generally used to destabilize and aggregate when contacted with a treatment liquid or a region where the treatment liquid is dried, thereby thickening and fixing the ink.
Examples of the polymer particles include self-dispersing polymer particles. Here, when the self-dispersing polymer particles are in a dispersed state (particularly, a dispersed state by a phase inversion emulsification method) in the absence of a surfactant, the functional group of the polymer itself (particularly an acidic group or a salt thereof) Water-insoluble polymer particles that can be dispersed in an aqueous medium and do not contain a free emulsifier. The self-dispersing polymer particles are described, for example, in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-068805A.

In the present invention, the content of polymer particles “less than 2% by mass” means that the black ink composition does not actively contain polymer particles, and in general, this is the case. In this case, the cohesiveness of the ink is likely to be reduced, and uneven glossiness of the black image is likely to occur. Therefore, when the content of the polymer particles is less than 2% by mass, the effect of suppressing gloss unevenness according to the present invention is remarkably exhibited.
Further, when the content of the polymer particles is less than 2% by mass with respect to the total amount of the ink composition, the black ink composition can be discharged (for example, discharged from a nozzle) or washed away (for example, a nozzle). This is advantageous in terms of the washing and removal property of the ink composition adhering to the ink.

  In the black ink composition of the present invention, the content of the polymer particles is preferably as small as possible from the viewpoint of obtaining the effects of the present invention more specifically, and specifically, it is preferably less than 1% by mass. It is more preferably less than 5% by mass, particularly preferably less than 0.1% by mass, and most preferably 0% by mass (the black ink composition in the present invention does not contain polymer particles). .

(Polymerizable compound)
The black ink composition in the invention preferably contains at least one polymerizable compound from the viewpoints of image strength, adhesion to a recording medium, suppression of gloss unevenness, and the like.
The polymerizable compound is preferably a water-soluble polymerizable compound.
Here, “water-soluble” means that it can be dissolved in water at a certain concentration or more. Specifically, the solubility in water at 25 ° C. is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more. The water-soluble polymerizable compound is preferably one that can be dissolved (desirably uniformly) in the aqueous black ink composition. Further, the solubility may be increased by adding a water-soluble organic solvent to be described later, and it may be dissolved (desirably uniformly) in the ink composition.

When the black ink composition in the invention contains a polymerizable compound, the polymerizable compound may be contained alone or in combination of two or more.
When the black ink composition in the invention contains a polymerizable compound, the total content of the polymerizable compound is preferably 5% by mass to 40% by mass with respect to the total amount of the ink composition. It is preferable that it is 40 mass%, and it is more preferable that it is 15 mass%-40 mass%.
When the content is 5% by mass or more, the strength of the image and the adhesion to the recording medium are further improved, and uneven gloss is further suppressed. When the content is 40% by mass or less, the level difference (pile height) of the image is suppressed, and the scratch resistance and glossiness of the image are further improved.
Among them, the total content of the polymerizable compound is preferably 20% by mass to 35% by mass.
A polymeric compound can be contained individually by 1 type or in combination of 2 or more types.

There is no restriction | limiting in particular as said polymeric compound, For example, the compound which has an ethylenic double bond in a molecule | numerator can be used.
More specifically, examples of the polymerizable compound include a compound having a (meth) acrylamide structure in the molecule, a compound having a (meth) acrylic ester structure in the molecule, an epoxy monomer compound, and an octacene monomer compound.
Here, the (meth) acrylic ester structure means at least one of a methacrylic ester structure and an acrylic ester structure, and the (meth) acrylamide structure means at least one of a methacrylamide structure and an acrylamide structure.

  Examples of the compound having a (meth) acrylic ester structure in the molecule include (meth) acrylic ester of polyhydric alcohol, (meth) acrylic ester of glycidyl ether of polyhydric alcohol, and (meth) acrylic of polyethylene glycol. Examples include ultraviolet curable monomers and oligomers such as acid esters, (meth) acrylic acid esters of polyhydric alcohol ethylene oxide addition compounds, and reaction products of polybasic acid anhydrides and hydroxyl group-containing (meth) acrylic acid esters. The polyhydric alcohol may be chain-extended with an ethylene oxide chain by addition of ethylene oxide.

The polymerizable compound is preferably a compound having a (meth) acrylamide structure in the molecule from the viewpoint of further improving the cohesiveness of the ink and further suppressing uneven glossiness.
Examples of the compound having a (meth) acrylamide structure in the molecule include a compound represented by the following general formula (1).

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

The compound represented by the general formula (1) is a compound in which an unsaturated vinyl monomer is bonded to the group Q by an amide bond. R ¹ represents a hydrogen atom or a methyl group, preferably a hydrogen atom. The valence n of the group Q is 1 or more from the viewpoint of improving penetrability, polymerization efficiency, and ejection stability, with 1 to 6 being preferred and 1 to 4 being more preferred. In the present invention, when coated paper is used as a recording medium, it contains monofunctional acrylamide where n = 1 from the viewpoint of being advantageous in terms of penetrability into the coating layer of the coated paper. More preferably, the monofunctional acrylamide is more preferably contained in an amount of 10% by mass or more based on the total mass of the ink composition. Moreover, it is preferable to use together the monofunctional (meth) acrylamide which is n = 1 excellent in permeability, and the polyfunctional (meth) acrylamide whose polymerization efficiency is 2 or more.

The compound represented by the general formula (1) is a compound in which an unsaturated vinyl monomer is bonded to the group Q by an amide bond.
R ¹ represents a hydrogen atom or a methyl group, preferably a hydrogen atom.
The valence n of the group Q is 1 or more, preferably 1 or more and 6 or less, and more preferably 1 or more and 4 or less from the viewpoint of improving permeability, polymerization efficiency, and ejection stability.

  A monofunctional (meth) acrylamide in which n = 1 is preferable in terms of high permeability to a pigment layer (coat layer) when coated paper is used as a recording medium. When the monofunctional (meth) acrylamide is contained, the content of the monofunctional acrylamide in the black ink composition is preferably 5% by mass to 30% by mass with respect to the total amount of the black ink composition. It is more preferable that it is 20 mass%-20 mass%.

A polyfunctional (meth) acrylamide having n ≧ 2 is preferable in terms of enhancing the polymerization property and polymerization efficiency when curing an image by irradiation with ultraviolet rays, and further improving the scratch resistance and scratch resistance of the image. When polyfunctional (meth) acrylamide is contained, the content of the polyfunctional (meth) acrylamide in the black ink composition is 3% by mass to 20% by mass with respect to the total amount of the black ink composition. Preferably, 5% by mass to 15% by mass is more preferable.
As n in the said polyfunctional (meth) acrylamide, 2-6 are preferable and 2-4 are more preferable from a viewpoint of coexistence of solubility and curability.

  In the general formula (1), the group Q in the case of n = 1 is not particularly limited as long as it is a monovalent group that can be linked to a (meth) acrylamide structure. The group Q in the case of n = 1 is preferably selected from groups having water solubility. Specific examples include monovalent residues obtained by removing one or more hydrogen atoms or hydroxyl groups from a compound selected from the following compound group X.

(Compound group X)
Ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4 -Butanediol, 2,3-butanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4 -Pentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,5 -Pentanetriol, thioglycol, tri Tyrolol propane, ditrimethylol propane, trimethylol ethane, ditrimethylol ethane, neopentyl glycol, pentaerythritol, dipentaerythritol, and their condensates, low molecular weight polyvinyl alcohol, or polyol compounds such as sugars, and ethylenediamine, diethylenetriamine, Polyamine compounds such as triethylenetetramine, polyethyleneimine, and polypropylenediamine.

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

  Specific examples of (meth) acrylamide having a (meth) acrylamide structure in the molecule are shown below. However, the present invention is not limited to these.

  Moreover, as said polyfunctional (meth) acrylamide, the compound represented by following General formula (2) is preferable at the point provided with high polymerization ability and hardening ability. This compound has four acrylamide groups or methacrylamide groups as polymerizable groups in the molecule. In addition, this compound exhibits curability based on a polymerization reaction due to application of energy such as active energy rays such as α rays, γ rays, X rays, ultraviolet rays, visible rays, infrared rays, and electron beams, and heat. The compound represented by the following general formula (2) exhibits water solubility and dissolves well in water-soluble organic solvents such as water and alcohol. Further, when a compound represented by the following general formula (2) is used as the polymerizable compound, the cohesiveness of the black ink composition is further improved, and uneven glossiness in the black image is further suppressed.

In the general formula (2), R ¹ represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom. Several R < ¹ > may mutually be same or different.

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

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

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

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

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

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

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

  Specific examples of the compound represented by the general formula (2) are shown below. However, the present invention is not limited to these.

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

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

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

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

(Polymerization initiator)
At least one of the black ink composition and the treatment liquid described later in the present invention may contain at least one polymerization initiator. Thereby, superposition | polymerization of the said polymeric compound can be started with an active energy ray.
The said polymerization initiator can be used individually by 1 type or in mixture of 2 or more types. The polymerization initiator may be used in combination with a sensitizer.
In the present invention, the polymerization initiator may be contained in either or both of the black ink composition and the treatment liquid. However, the polymerization reactivity and curability are improved, and as a result, the image adhesion and scratch resistance are improved. From this viewpoint, an embodiment in which the polymerization initiator is contained in at least the black ink composition is preferable.

  A polymerization initiator can select and contain the compound which can start the polymerization reaction of a polymeric compound with an active energy ray suitably. Examples of the polymerization initiator include polymerization initiators (for example, photopolymerization initiators) that generate active species (radicals, acids, bases, etc.) by radiation or light, or electron beams.

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

  In the case where the black ink composition contains a polymerization initiator, the content of the polymerization initiator in the black ink composition is preferably 1 to 40% by mass with respect to the polymerizable compound, and 5 to 30. The mass% is more preferable. When the content of the polymerization initiator is 1% by mass or more, the scratch resistance of the image is further improved, which is advantageous for high-speed recording, and when it is 40% by mass or less, it is advantageous in terms of ejection stability.

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

(water)
The black ink composition in the present invention contains water.
That is, the black ink composition in the present invention is an aqueous ink composition.
As water in the present invention, it is preferable to use water in which the content of ionic impurities such as ion-exchanged water and distilled water is reduced.
Although there is no restriction | limiting in particular in content of the water in the said black-type ink composition, Preferably it is 10-99 mass% with respect to the whole quantity of an ink composition, More preferably, it is 30-90 mass%, More preferably. Is 50-90 mass%.

(Water-soluble organic solvent)
The black ink composition in the invention may contain at least one water-soluble organic solvent.
Examples of the water-soluble organic solvent include paragraphs 0124 to 0135 of JP2011-074150, paragraphs 0115 to 0128 of JP2011-042150, paragraphs 0104 to 0119 of JP2011-079901, and the like. A known water-soluble organic solvent described in 1) can also be used.

  When the black ink composition in the invention contains a water-soluble organic solvent, the content thereof is preferably 40% by mass or less, preferably 20% by mass or less, and preferably 10% by mass or less with respect to the total amount of the ink composition. Preferably, it is less than 3% by mass. Here, the content of the water-soluble organic solvent being less than 3% by mass means that the ink composition does not actively contain the water-soluble organic solvent, and most preferably the water-soluble organic solvent is added. It is not included (content: 0% by mass).

(Surfactant)
The black ink composition in the present invention can contain at least one surfactant as required. The surfactant can be used as a surface tension adjusting agent, for example.
As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactants, cationic surfactants, amphoteric surfactants, nonions Either a surfactant or a betaine surfactant can be used. Further, the above water-soluble polymer (polymer dispersing agent) may be used as a surfactant.

In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing ink droplet ejection interference, and an acetylene glycol derivative (acetylene glycol surfactant) is more preferable.
Examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4, An alkylene oxide adduct of 7-diol can be used, and at least one selected from these is preferable. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

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

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

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

(Preferred physical properties of black ink composition)
The surface tension (25 ° C.) of the black ink composition in the invention is not particularly limited, but is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN / m or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less. The surface tension is measured using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) and a black ink composition at 25 ° C.
The viscosity of the black ink composition in the present invention is not particularly limited, but the viscosity at 25 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s. s or more and less than 13 mPa · s, more preferably 2.5 mPa · s or more and less than 10 mPa · s. The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under conditions of 25 ° C.

(Production method)
The black ink composition can be produced by a conventional method. For example, a pigment dispersion containing the specific polymer-coated carbon black pigment, a sugar alcohol, water, and other components as necessary (polymerizable compound, polymerization initiator, surfactant, colored pigment dispersion (for example, The polymer-coated colored pigment dispersion), etc.) can be mixed. The mixing method is not particularly limited, and a commonly used mixing method can be appropriately selected and applied.

The black ink composition according to the present invention has been described above. However, the ink set of the present invention may include the above black ink composition according to the present invention alone or in combination of two or more. Also good.
The ink set of the present invention is at least one of other ink compositions other than the black ink composition of the present invention (which may be a black ink composition or an ink having a hue other than black). It may be a composition). The other ink composition is not particularly limited, but an ink composition that can be agglomerated by a treatment liquid is preferable, and contains a polymer-coated pigment in which at least a part of the surface of the pigment is coated with a polymer and water. Ink compositions are more preferred.
From the viewpoints of ink aggregation and ink ejection properties, the other ink composition includes a polymer-coated pigment in which at least a part of the surface of the pigment is coated with a crosslinked water-soluble polymer, a sugar alcohol, And an ink composition containing less than 2% by mass of the polymer particles with respect to the total amount of the ink composition (except for the type of pigment, the same composition as the black ink composition in the present invention is preferable) The range is also the same).
Examples of the ink composition having a hue other than black include a cyan ink composition (hereinafter also referred to as “cyan ink (composition)”) and a magenta ink composition (hereinafter referred to as “magenta ink (composition)”. And a yellow color ink composition (hereinafter also referred to as “yellow ink (composition)”).

<Processing liquid>
The ink set of the present invention includes at least one treatment liquid containing an aggregating component that aggregates the components in the black ink composition when it comes into contact with the black ink composition of the present invention described above.
The treatment liquid contains at least an aggregation component that aggregates the components in the black ink composition described above. The treatment liquid can be configured using other components as required.
By forming a black image using the treatment liquid together with the black ink composition, it is possible to increase the speed of ink jet recording, and even with high speed recording, drawing properties with high density and resolution (for example, fine lines and A black image excellent in reproducibility of fine portions) can be obtained.

  The aggregation component may be a compound capable of changing the pH of the black ink composition, a polyvalent metal salt, or a cationic polymer. In the present invention, from the viewpoint of aggregation of the black ink composition, a compound capable of changing the pH of the black ink composition is preferable, and a compound capable of lowering the pH of the black ink composition is more preferable.

Examples of the compound that can lower the pH of the black ink composition include acids (acidic substances).
Examples of the acid include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, Lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, derivatives of these compounds, or salts thereof, etc. Are preferable.
An acid may be used individually by 1 type and may use 2 or more types together.

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

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

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

The aggregating components can be used alone or in combination of two or more.
As content in the process liquid of the said aggregation component, 1-50 mass% is preferable, More preferably, it is 3-45 mass%, More preferably, it is the range of 5-40 mass%.

  The treatment liquid contains at least one polymerization initiator that initiates polymerization of the polymerizable compound in the black ink composition by active energy rays with or without being contained in the black ink composition. be able to. A polymerization initiator can be used individually by 1 type or in mixture of 2 or more types or with a sensitizer.

  Further, as described above, at least one of the treatment liquid and the black ink composition in the present invention described above can contain at least one polymerization initiator. The preferred range of the polymerization initiator is as described above.

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

≪Image formation method≫
The image forming method of the present invention uses the ink set of the present invention described above, a treatment liquid application step of applying the treatment liquid onto a recording medium, and the black ink composition on the recording medium by an inkjet method. And an ink application step of forming an image by applying. The image forming method of the present invention may further include other steps as necessary.
In the image forming method of the present invention, when the black ink composition and the treatment liquid are in contact with each other, components in the black ink composition are aggregated to form a black image. As described above, uneven glossiness of the black image is suppressed by the combined action of the sugar alcohol and the crosslinked structure of the specific polymer-coated carbon black pigment.

In the image forming method of the present invention, since the black ink composition and the treatment liquid may be in contact with each other, the ink application process may be provided either before or after the treatment liquid application process.
In a preferred aspect of the present invention, the ink application step is provided after the treatment liquid application step. In the ink application process in this aspect, the black ink composition is applied to the treatment liquid applied to the recording medium in the treatment liquid application process (that is, the treatment liquid application surface of the recording medium to which the treatment liquid is applied). According to this aspect, inkjet recording can be performed at high speed, and an image with high density and resolution can be obtained even at high speed recording.

<Recording medium>
The recording medium used in the image forming method of the present invention is not particularly limited, and a recording medium usually used in the ink jet method can be used.
In the present invention, as the recording medium, a recording medium in which liquid permeation is relatively gentle is preferable.
When a black image is formed on the recording medium with relatively slow liquid penetration, gloss unevenness tends to become more prominent. Therefore, when such a recording medium is used, the effect of reducing gloss unevenness in the present invention is achieved. Is more prominently obtained.
As the recording medium having a relatively slow liquid permeation, specifically, at least one surface on a support mainly composed of cellulose pulp has a single or multiple pigment layer, and a dynamic scanning liquid absorption The recording medium (hereinafter referred to as “transition amount of pure water” measured by a meter is 1 ml / m ² or more and 15 ml / m ² or less at a contact time of 100 ms and 2 ml / m ² or more and 20 ml / m ² or less at a contact time of 400 ms) , Also referred to as “specific recording medium”).
Hereinafter, components of the specific recording medium will be described.

(Support)
As the support mainly composed of cellulose pulp, chemical pulp, mechanical pulp, waste paper recovered pulp and the like are mixed and used at an arbitrary ratio. If necessary, an internal sizing agent, a yield improver, and a paper strength enhancer. The raw material added with the agent or the like is made by paper making using a long web former or a gap type twin wire former, and a hybrid former or the like in which the latter half of the long web is composed of twin wires.
Here, the “main component” refers to a component contained in an amount of 50% by mass or more based on the mass of the support.

  Regarding the details of the pulp used for the support, reference can be made to the description in paragraph 0024 of JP2011-42150A. Moreover, a filler, an internally added sizing agent, or the like can be used for the support. For details of the filler, the internally added sizing agent, and the like, reference can be made to the descriptions in paragraphs 0025 to 0027 of JP2011-42150A.

(Pigment layer)
The specific recording medium has one or more pigment layers on at least one surface of the support.

  The pigment used in the pigment layer is not particularly limited, and conventionally known organic pigments and inorganic pigments can be used. Regarding specific examples of the pigment, the description in paragraph 0029 of JP2011-42150A can be referred to, and a white inorganic pigment is preferable from the viewpoint of maintaining the transparency of the recording medium and increasing the image density.

The pigment layer further includes additives such as an aqueous binder, an antioxidant, a surfactant, an antifoaming agent, an antifoaming agent, a pH adjusting agent, a curing agent, a coloring agent, a fluorescent brightening agent, a preservative, and a water-proofing agent. Can be contained.
Examples of the aqueous binder include styrene / maleate copolymer, styrene / acrylate copolymer, polyvinyl alcohol, silanol-modified polyvinyl alcohol, starch, cationized starch, casein, gelatin, carboxymethylcellulose, hydroxyethylcellulose, Examples thereof include water-soluble polymers such as polyvinyl pyrrolidone, water-dispersible polymers such as styrene butadiene latex and acrylic emulsion.

  The method for forming the pigment layer on the support can be appropriately selected according to the purpose without particular limitation. For example, a pigment layer can be formed by applying a dispersion liquid in which a pigment is dispersed in water to a base paper and drying.

The amount of pigment in the pigment layer is preferably ^{0.1g / m 2 ~20g / m 2} , the range of 0.5g / ^{m 2} ~10g / m 2 is more preferable. When the amount of the pigment is 0.1 g / m ² or more, the blocking resistance is good, and when the amount of the pigment is 20 g / m ² or less, it is advantageous in terms of brittleness. The pigment contained in the pigment layer is preferably contained in an amount of 10% by mass or more, more preferably 14% by mass or more, and further preferably 18% by mass or more based on the total solid content of the layer.

-Physical properties of specific recording media-
The specific recording medium has a transfer amount of pure water measured by a dynamic scanning absorption meter to the recording medium of 1 ml / m ^{2 to} 15 ml / m ^{2 at} a contact time of 100 ms and ² ml / m ^{2 at} a contact time of 400 ms. m ² or more and 20 ml / m ² or less.
In the image forming method of the present invention, even when a specific recording medium having a relatively small ink absorption amount within the range of the transfer amount is used, uneven glossiness of a black image can be suppressed. Furthermore, even when the specific recording medium is used, a recorded image with high resolution and excellent water resistance and abrasion resistance can be obtained. In other words, according to the image forming method of the present invention, it is possible to use a recording medium that exhibits a transfer amount exceeding the range of the transfer amount and that can absorb a large amount of ink (for example, an exclusive inkjet paper). The inkjet method can suppress uneven glossiness of a black image, and can further provide a recorded image with high resolution and excellent water resistance and abrasion resistance.

Note that relates the transfer amount, the contact time 100 ms 1 ml / ^{m 2} or more, and 2 ml / ^{m 2} or more at and contact time 400 ms, indicating that it has a pigment layer recording medium capable of absorbing ink. The contact time 100 ms 15 ml / ^{m 2} or less in, and the 20 ml / ^{m 2} or less at a contact time 400 ms, indicating that a relatively small amount of absorption of the ink.
That is, “the amount of transfer of pure water to the recording medium measured with a dynamic scanning absorption meter” within the above range means that the recording medium has a pigment layer and the amount of ink permeation is small. To do.

  Here, the dynamic scanning absorptiometer (DSA, Papa-Pagi Gikyo, Vol. 48, May 1994, pp. 88-92, Kuju Shigenori) It is a device that can measure accurately. The dynamic scanning absorptiometer reads the liquid absorption speed directly from the movement of the meniscus in the capillary, makes the sample a disk, and then scans the liquid absorption head in a spiral, and changes the scanning speed according to a preset pattern. The measurement is automated by a method of automatically changing and measuring the number of points required for one sample. A liquid supply head for a paper sample is connected to a capillary via a Teflon (registered trademark) tube, and the position of the meniscus in the capillary is automatically read by an optical sensor. Specifically, the transfer amount of pure water or ink is measured using a dynamic scanning absorption meter (K350 series D type, manufactured by Kyowa Seiko Co., Ltd.). The transfer amount at the contact time of 100 ms and the contact time of 400 ms can be obtained by interpolation from the measured value of the transfer amount at the contact time adjacent to each contact time. The measurement is performed at 23 ° C. and 50% RH.

In the specific recording medium, the transfer amount of pure water to the recording medium at a contact time of 100 ms measured by a dynamic scanning absorption meter is 1 ml / m ^{2 to} 15 ml / m ² , and 1 ml / m ^{2 to} 10 ml. / M ² is more preferable, and 1 ml / m ^{2 to} 8 ml / m ² is more preferable. If the amount of pure water transferred at a contact time of 100 ms is too small, beading may easily occur. Further, if the transfer amount exceeds 15 ml / m ² and becomes too large, the ink dot diameter after recording may be too smaller than the desired diameter.
Note that beading is the surface of a recording medium that is not completely absorbed by the recording medium during the period from when an ink droplet is struck onto the recording medium until the next ink droplet is struck during ink jet recording. In other words, it is a phenomenon in which the colorant in the ink partially becomes a mass by mixing with ink droplets that remain in a liquid state and are ejected later, resulting in density unevenness.

In the specific recording medium, the transfer amount of pure water to the recording medium at a contact time of 400 ms measured by a dynamic scanning absorption meter is 2 ml / m ^{2 to} 20 ml / m ² , and 2 ml / m ^{2 to} 15 ml. / M ² is more preferable, and 2 ml / m ^{2 to} 10 ml / m ² is more preferable. If the transfer amount at a contact time of 400 ms is too small, the drying property is insufficient, and thus spur marks may be easily generated. Further, when the transfer amount exceeds 20 ml / m ² and becomes too large, bleeding is likely to occur, and the gloss of the image area after drying tends to be low.

  The pigment layer of the specific recording medium has a configuration mainly composed of a pigment and a resin binder. The transfer amount can be adjusted in the direction in which the transfer amount decreases by making the resin compounding amount rich, and the transfer amount can be adjusted in the direction in which the transfer amount increases by making the pigment compounding amount rich. It is also possible to increase the transfer amount by increasing the specific surface area of the pigment particles constituting the pigment layer, for example, by reducing the particle diameter or using a kind of pigment having a large specific surface area.

  As the specific recording medium, for example, so-called coated paper used for general offset printing or the like can be used. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not surface-treated. In general, image formation by normal aqueous ink jet using coated paper as a recording medium tends to cause quality problems such as uneven glossiness of black images, blurring of images, and abrasion resistance. In the method, uneven glossiness of a black image is suppressed, blurring of the image is suppressed, generation of uniform and uneven density is prevented, and an image with high image resolution and good abrasion resistance can be recorded.

As the specific recording medium, coated paper, light-weight coated paper, or finely coated paper can be suitably used, and high-quality images can be effectively formed on these recording media.
The coated paper can be obtained and used on the market. For example, coated paper for general printing can be used. Specifically, for A2 gloss paper, “OK Top Coat +” (manufactured by Oji Paper), “Aurora Coat” (manufactured by Nippon Paper Industries), “Pearl Coat” ( “Mitsubishi Paper”, “S Utrillo Coat” (Daiou Paper), “Mucoat Neos” (Hokuetsu Paper), “Thunderbird Coat” (manufactured by Chuetsu Pulp), “New Age” (Oji Paper) for A2 matte paper, “ “OK Top Coat Mat” (Oji Paper), “Ulite” (Nippon Paper Industries), “New V Mat” (Mitsubishi Paper), “Thunderbird Mat Coat N” (manufactured by Chuetsu Pulp), A1 gloss art paper “ OK Kinto + (Oji Paper), Tokuhishi Art (Mitsubishi Paper), Thunderbird Toku Art (Chuetsu Pulp), A1 Dal Art Paper, Satin Kinto + (Oji Paper), Super Matte Art " (Mitsubishi Paper), “Thunderbird Dull Art” (manufactured by Chuetsu Pulp), A0 Art Paper “SA Kinfuji +” (manufactured by Oji Paper), “High Grade Art” (manufactured by Mitsubishi Paper Industries), “Thunderbird Super Art N” (manufactured by Chuetsu Pulp ), “Ultra Satin Kanfuji +” (manufactured by Oji Paper), “Diamond Premier Dal Art” (manufactured by Mitsubishi Paper Industries), and the like.

<Ink application process>
The ink application step is a step of forming an image by applying the black ink composition of the present invention described above onto a recording medium by an ink jet method.
In this step, a black ink composition can be selectively applied on the recording medium, and a desired visible image can be formed.
In the image formation by the ink jet method, by applying energy, the black ink composition is ejected onto the recording medium to form a black image. As a preferable inkjet method for the present invention, the method described in paragraphs 0093 to 0105 of JP-A No. 2003-306623 can be applied.

There are no particular restrictions on the ink jet method, and there are known methods such as a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, Either an acoustic ink jet method that changes the signal into an acoustic beam and irradiates the ink using the radiation pressure to eject the ink, or a thermal ink jet method that heats the ink to form bubbles and uses the generated pressure. May be. As an ink-jet method, in particular, the method described in Japanese Patent Application Laid-Open No. 54-59936 causes a sudden volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force caused by this state change. Ink jet method can be used effectively.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

  In the ink application process, for example, an image can be formed by changing the conveyance speed of the recording medium. The conveying speed is not particularly limited as long as the image quality is not impaired, and is preferably 100 to 3000 mm / s, more preferably 150 to 2700 mm / s, and further preferably 250 to 2500 mm / s. .

In the ink application step, the maximum application amount of the ink composition to the recording medium is preferably 15 ml / m ² or less. When the maximum application amount is 15 ml / m ² or less, the adhesion of the image is more excellent. Further, the maximum application amount is more preferably 8 to 15 ml / m ² , further preferably 8 to 12 ml / m ² , and particularly preferably 8 to 11 ml / m ² from the viewpoint of image adhesion and density. The maximum application amount can be controlled by adjusting the discharge method from the discharge nozzle.

<Processing liquid application process>
The treatment liquid application step in the present invention is a step of applying the treatment liquid in the ink set of the present invention onto a recording medium.
In this step, the processing liquid applied to the recording medium comes into contact with the black ink composition to form a black image. Specifically, components in the black ink composition (for example, the specific polymer-coated carbon black pigment) are aggregated, and a black image is fixed on the recording medium.

  The treatment liquid can be applied by applying a known method such as a coating method, an ink jet method, or an immersion method. As a coating method, a direct gravure coater, an offset gravure coater, an extrusion die coater, an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, a bar coater and the like are performed. be able to. The details of the inkjet method are as described above.

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

  In the present invention, an ink application step is provided after the treatment liquid application step, and the treatment liquid on the recording medium is applied after the treatment liquid is applied on the recording medium and before the black ink composition is applied. It is preferable to further provide a heat drying step for heat drying. By heating and drying the treatment liquid in advance before the ink application step, ink colorability such as bleeding prevention is improved, and a visible image with good color density and hue can be recorded.

  Heating and drying can be performed by known heating means such as a heater, air blowing means using air blowing such as a dryer, or a combination of these. As the heating method, for example, a method of applying heat with a heater or the like from the side opposite to the treatment liquid application surface of the recording medium, a method of applying warm air or hot air to the treatment liquid application surface of the recording medium, or an infrared heater was used. The heating method etc. are mentioned, You may heat combining these two or more.

<Drying process>
The image forming method of the present invention further includes a drying step of drying the image after the ink application step and the treatment liquid application step.
By the drying step, the black image can be dried in a state where the components in the black ink composition are suitably aggregated. For this reason, a black image in which gloss unevenness is suppressed is formed. Further, the formed black image is excellent in adhesion to the recording medium and scratch resistance.
In the drying step, at least a part of water in the black image (black ink composition) formed on the recording medium is removed by drying. By providing the drying step before the curing step described later and reducing the water content in the black ink composition, the curing reaction of the polymerizable compound in the curing step proceeds better. In particular, when image formation is performed at a high speed, such as a method of forming an image by a single pass method in which ink is ejected in the main scanning direction to form one line in one scan, it is possible to ensure the sensitivity with which image formability is established. it can.

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

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

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

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

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

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

In addition, the drying is preferably started within 5 seconds from the time when the black ink composition droplets land on the recording medium. Here, “within 5 seconds from the time of landing” means that the image is blown or heat is applied within 5 seconds from the landing of the ink droplet. For example, drying is started within 5 seconds after landing by transporting the recording medium into the drying area within 5 seconds after landing of the ink droplet.
The time from the ink droplet landing to the start of drying is more preferably within 3 seconds.

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

<Curing process>
The image forming method of the present invention preferably further includes a curing step of curing the image by irradiating the formed image with active energy rays after the drying step.
In this step, by irradiating active energy rays, the polymerizable compound in the black ink composition is polymerized to form a cured film containing the pigment. As a result, the scratch resistance of the black image to be formed and the adhesion to the recording medium are further improved, and gloss unevenness is further suppressed.

  The active energy ray is not particularly limited as long as it can polymerize the polymerizable compound. For example, ultraviolet rays, electron beams and the like can be mentioned. Among them, ultraviolet rays are preferable from the viewpoint of versatility. Examples of the source of active energy rays include an ultraviolet irradiation lamp (such as a halogen lamp and a high-pressure mercury lamp), a laser, an LED, and an electron beam irradiation device.

  As the means for irradiating ultraviolet rays, a commonly used means may be used, and an ultraviolet irradiation lamp is particularly suitable. As the ultraviolet irradiation lamp, a so-called low-pressure mercury lamp, high-pressure mercury lamp, mercury lamp coated with a phosphor, UV-LED light source, or the like whose mercury vapor pressure is 1 to 10 Pa during lighting is suitable. The emission spectrum in the ultraviolet region of mercury lamps and UV-LEDs is 450 nm or less, particularly in the range of 184 nm to 450 nm, and is suitable for efficiently reacting a polymerizable compound in a black or colored ink composition. Yes. Further, it is suitable for mounting a power source in a printer in that a small power source can be used. As the mercury lamp, for example, a metal halide lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a xenon flash lamp, a deep UV lamp, a lamp that uses a microwave to excite a mercury lamp from the outside without using an electrode, a UV laser, and the like are in practical use. Since the above-mentioned range is included as the emission wavelength region, it is basically applicable if the power source size, input intensity, lamp shape, etc. are allowed. The light source is selected in accordance with the sensitivity of the polymerization initiator used.

The ultraviolet intensity is preferably 500 to 5000 mW / cm ² in a wavelength region effective for curing. When the irradiation intensity is weak, formation of an image having high quality and fastness cannot be achieved. On the other hand, if the irradiation intensity is too high, the recording medium may be damaged or the color material may be faded.

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

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

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

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

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

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

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

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

The ink ejection heads 30K, 30C, 30M, and 30Y each eject ink corresponding to an image from ejection nozzles arranged to face the recording surface of the recording medium. Thus, each color ink is applied on the recording surface of the recording medium, and a color image is recorded.
When the image forming method of the present invention is carried out using this ink jet recording apparatus, the black ink composition of the present invention is ejected from the ejection nozzles of the ink ejection head 30K to form a black image.

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

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

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

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

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

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

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

<< Synthesis of water-soluble polymer dispersant P-1 >>
Synthesized according to the following.
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 prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, while isopropanol (187.5 parts) was heated to 80 ° C. in a nitrogen atmosphere, the mixture of the monomer supply composition and the initiator supply composition was added dropwise over 2 hours. After completion of dropping, the mixture was kept at 80 ° C. for further 4 hours, and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a water-soluble polymer dispersant P-1 (water-soluble polymer) having a weight average molecular weight of about 30,000 and an acid value of 112 mgKOH / g.

<< Preparation of Black Ink K1 (Black Ink Composition) >>
<Preparation of Black Pigment Dispersion K>
The water-soluble polymer dispersant P-1 (150 parts) obtained above is neutralized with 0.8 potassium equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant using an aqueous potassium hydroxide solution, and further ion-exchanged water. Was added to adjust the water-soluble polymer dispersant concentration to 25% to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (147 parts), carbon black pigment (# 95, manufactured by Mitsubishi Chemical Corporation) (52.5 parts), water (75.5 parts), dipropylene glycol (75 parts) And a bead mill (bead diameter 0.1 mmφ, zirconia beads) until a desired volume average particle diameter is obtained, and a dispersion of polymer-coated carbon black pigment particles having a pigment concentration of 15% (uncrosslinked dispersion) K) was obtained.
Dencol EX-321 (cross-linking agent manufactured by Nagase ChemteX Corporation) (1.4 parts) and boric acid aqueous solution (boric acid concentration 4 mass% aqueous solution) (15) with respect to the uncrosslinked dispersion K (136 parts) .4 parts) was added, reacted at 50 ° C. for 6 and a half hours, and then cooled to 25 ° C. to obtain a crosslinked dispersion K. Next, the obtained crosslinked dispersion K was subjected to ion-exchanged water using a stirring type ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractionated molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC Co., Ltd.). And purified so that the dipropylene glycol concentration in the dispersion is 0.1% by mass or less, and then concentrated to a pigment concentration of 15% by mass to obtain a black pigment dispersion K. It was.

<Preparation of Cyan Pigment Dispersion C>
The water-soluble polymer dispersant P-1 (150 parts) obtained above is neutralized with 0.8 potassium equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant using an aqueous potassium hydroxide solution, and further ion-exchanged water. Was added to adjust the water-soluble polymer dispersant concentration to 25% to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (124 parts), Pigment Blue 15: 3 (cyan pigment) (48 parts), water (75 parts) and dipropylene glycol (75 parts) are mixed, and a bead mill ( A dispersion of polymer-coated cyan pigment particles having a pigment concentration of 15% (uncrosslinked dispersion C) was obtained by dispersing with a bead diameter of 0.1 mmφ and zirconia beads) until a desired volume average particle size was obtained.
Dencol EX-321 (1.3 parts) and an aqueous boric acid solution (4 mass% boric acid aqueous solution) (14.3 parts) were added to the uncrosslinked dispersion C (136 parts) at 50 ° C. After the reaction for 6 and a half hours, the mixture was cooled to 25 ° C. to obtain a crosslinked dispersion C. Next, the obtained crosslinked dispersion C was subjected to ion-exchanged water using a stirring ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractionated molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC). And purified so that the dipropylene glycol concentration in the dispersion is 0.1% by mass or less, and then concentrated to a pigment concentration of 15% by mass to obtain Cyan Pigment Dispersion C. It was.

<Preparation of Magenta Pigment Dispersion M>
The water-soluble polymer dispersant P-1 (150 parts) obtained above is neutralized with 0.8 potassium equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant using an aqueous potassium hydroxide solution, and further ion-exchanged water. Was added to adjust the water-soluble polymer dispersant concentration to 25% to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (56 parts), Pigment Red 122 (magenta pigment) (47 parts), water (144 parts), and dipropylene glycol (75 parts) were mixed, and a bead mill (bead diameter 0.1 mmφ, zirconia beads) was dispersed until a desired volume average particle diameter was obtained, and a dispersion (uncrosslinked dispersion M) of polymer-coated magenta pigment particles having a pigment concentration of 15% was obtained.
Dencol EX-321 (0.4 part) and boric acid aqueous solution (4% by weight boric acid aqueous solution) (4.7 parts) were added to the uncrosslinked dispersion M (136 parts) at 50 ° C. After the reaction for 6 and a half hours, the mixture was cooled to 25 ° C. to obtain a crosslinked dispersion M. Next, ion-exchanged water is added to the obtained crosslinked dispersion M, and a stirring type ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractional molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC Co., Ltd.) are used. By carrying out ultrafiltration, the dipropylene glycol concentration in the dispersion is refined to 0.1% by mass or less, and then concentrated to a pigment concentration of 15% by mass to obtain a magenta pigment dispersion M. It was.

<Preparation of black ink K1>
The following composition was mixed and filtered through a glass filter (GS-25) manufactured by ADVANTEC, and then filtered through a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to prepare a black ink K1.

-Composition of black ink K1-
-Black pigment dispersion K ... 16.5 parts-Cyan pigment dispersion C-3.3 parts-Magenta pigment dispersion M-4.8 parts-Hydroxyethyl acrylamide-15 parts-Polymerizable compound a- 10 parts sorbitol ... 6 parts Olfine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) ... 1 part Irgacure 2959 (manufactured by BASF Japan KK; photopolymerization initiator) ... 3 parts ion exchange water … Remaining amount of 100 copies

<< Production of black inks K2 to K11 >>
Black inks K2 to K11 were prepared in the same manner as the black ink K1 except that the composition of the ink was changed as shown in Table 1 below in the preparation of the black ink K1.

~ Description of Table 1 ~
The amount of each component indicates the amount (parts by mass) when the total ink is 100 parts by mass.
As the pigment dispersion, only the amount of pigment and the D / P ratio (%) are shown.
Ink K8 was prepared using (uncrosslinked) black pigment dispersion obtained by ultrafiltration of uncrosslinked dispersion K.

<< Production of Cyan Ink C1 >>
The following composition was mixed and filtered with a glass filter (GS-25) manufactured by ADVANTEC, and then filtered with a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to prepare cyan ink C1.
-Composition of cyan ink C1-
-Cyan pigment dispersion C ... 16.7 parts-Hydroxyethyl acrylamide-15 parts-Polymerizable compound 1-10 parts-Sorbitol-5.6 parts-Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surface activity) Agent) ... 1 part · Irgacure 2959 (manufactured by BASF Japan KK; photopolymerization initiator) · · · 3 parts · ion-exchanged water ... the remaining amount of 100 parts in total

≪Magenta ink M1 production≫
The following composition was mixed and filtered through a glass filter (GS-25) manufactured by ADVANTEC, and then filtered through a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to produce magenta ink M1.
-Magenta ink M1 composition-
・ Magenta pigment dispersion M 36.7 parts ・ Hydroxyethyl acrylamide 15 parts ・ Polymerizable compound 1 10 parts ・ Sorbitol 2.5 parts ・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surface activity) Agent) ... 1 part · Irgacure 2959 (manufactured by BASF Japan KK; photopolymerization initiator) · · · 3 parts · ion-exchanged water ... the remaining amount of 100 parts as a whole

≪Preparation of yellow ink Y1≫
<Preparation of yellow pigment dispersion Y>
The water-soluble polymer dispersant P-1 (150 parts) obtained above is neutralized with 0.8 potassium equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant using an aqueous potassium hydroxide solution, and further ion-exchanged water. Was added to adjust the water-soluble polymer dispersant concentration to 25% to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (124 parts), Pigment Yellow 74 (yellow pigment) (48 parts), water (116 parts), and dipropylene glycol (30 parts) were mixed, and a bead mill (bead diameter 0.1 mmφ, zirconia beads) was dispersed until the desired volume average particle diameter was obtained, and a dispersion (uncrosslinked dispersion Y) of polymer-coated yellow pigment particles having a pigment concentration of 15% was obtained.
Dencol EX-321 (cross-linking agent manufactured by Nagase ChemteX Corp.) (0.9 parts) and boric acid aqueous solution (boric acid concentration 4 mass% aqueous solution) (uncrosslinked dispersion Y (136 parts)) ( 9.6 parts) was added, reacted at 50 ° C. for 6 and a half hours, and then cooled to 25 ° C. to obtain a crosslinked dispersion Y. Next, the obtained crosslinked dispersion Y was subjected to ion-exchanged water using a stirring type ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractionated molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC). And purified so that the dipropylene glycol concentration in the dispersion is 0.1% by mass or less, and then concentrated to a pigment concentration of 15% by mass to obtain a yellow pigment dispersion Y. It was.

<Preparation of yellow ink Y1>
The following composition was mixed and filtered through a glass filter (GS-25) manufactured by ADVANTEC, and then filtered through a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to produce yellow ink Y1.

-Composition of yellow ink Y1-
Yellow pigment dispersion Y 26.7 parts Hydroxyethyl acrylamide 15 parts The above polymerizable compound 1 10 parts sorbitol 2 parts Olfin E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) 1 part ・ Irgacure 2959 (manufactured by BASF Japan Ltd .; photopolymerization initiator) 3 parts ・ Ion-exchanged water ・ Remaining amount of 100 parts

≪Preparation of treatment liquid≫
<Processing liquid 1>
The component of the following composition was mixed and the processing liquid 1 was prepared.
~ Composition of treatment liquid 1 ~
・ Malonic acid (manufactured by Wako Pure Chemical Industries, Ltd.)… 25 parts ・ Diethylene glycol monomethyl ether (manufactured by Wako Pure Chemical Industries, Ltd.)… 20 parts ・ Emulgen P109 (manufactured by Kao Corporation, nonionic surfactant) 1 part ・ Ion-exchanged water… The remaining amount is 100 parts

<Processing liquid 2>
The component of the following composition was mixed and the processing liquid 2 was prepared.
-Composition of treatment liquid 2-
Magnesium nitrate hexahydrate (polyvalent metal salt) 25 parts Isobutyl benzoin ether 10 parts Triethylene glycol monobutyl ether 10 parts Glycerin 10 parts Ion-exchanged water Remaining 100 parts in total amount

<Processing liquid 3>
(Preparation of aqueous cationic polymer solution)
Guanidine acetate (65 g) and 1,6-hexamethylenediamine (66.7 g) were charged into a 250 ml round bottom flask and mixed, and then the mixture was heated to 120 ° C. with stirring in a nitrogen gas atmosphere. Continued for hours. The temperature was then raised to 150 ° C. and the reaction mixture was stirred at this temperature for an additional 20 hours. The reaction mixture was allowed to cool to room temperature, then mixed with the same volume of distilled water, heated to 80 ° C. and held at this temperature until a homogeneous solution was obtained. The solution was cooled, the pH was adjusted to 7 using acetic acid, and ion-exchanged water was mixed to dilute the solid content to 25% by mass to obtain a cationic polymer aqueous solution.
The obtained cationic polymer aqueous solution had an average molecular weight (Mw) of 1120 as measured by gel permeation chromatography.

Using the above cationic polymer aqueous solution, components in the following composition were mixed to prepare a treatment liquid 3.
~ Composition of treatment liquid 3 ~
・ Cationic polymer aqueous solution (solid content: 25% by mass) 20 parts 2-pyrrolidone 9 parts Thiodiethylene glycol 9 parts cyclohexanol 2 parts ion-exchanged water The whole is 100 parts amount

≪Preparation of recording medium≫
For image formation, each recording medium shown in Table 2 below was prepared.

[Examples 1 to 21, Comparative Examples 1 and 2]
≪Preparation of ink set≫
An ink set was prepared by combining the black ink (hereinafter also referred to as “K ink”) and the treatment liquid as shown in Table 3 below. Further, the cyan ink C1, the magenta ink M1, and the yellow ink Y1 were prepared for thin line drawing on a black solid image.

≪Image formation≫
First, as shown in FIG. 1, the treatment liquid application unit 12 including a treatment liquid ejection head 12 </ b> S that ejects the treatment liquid sequentially in the direction of conveyance of the recording medium (the arrow direction in the drawing) is applied. A treatment liquid drying zone 13 for drying the treatment liquid, an ink discharge unit 14 for discharging various inks, an ink drying zone 15 for drying the discharged ink, and a UV irradiation lamp 16S capable of irradiating ultraviolet rays (UV) are provided. An ink jet apparatus provided with the UV irradiation unit 16 was prepared.
Although not shown, the processing liquid drying zone 13 is provided with a blower for drying by sending dry air to the recording surface side of the recording medium, and an infrared heater on the non-recording surface side of the recording medium. The temperature and the air volume are adjusted to evaporate (dry) 70% by mass or more of the water in the treatment liquid until 900 msec after the application of the treatment liquid is started in the application unit. The ink discharge unit 14 includes a black ink discharge head 30K, a cyan ink discharge head 30C, a magenta ink discharge head 30M, and a yellow ink discharge head 30Y, which are sequentially arranged in the transport direction (arrow direction). Each head is a 1200 dpi / 10 inch wide full-line head (driving frequency: 25 kHz, transport speed of recording medium: 500 mm / s), and can record by discharging each color in the main scanning direction by a single pass.

The processing liquid and black ink in the ink set are sequentially loaded into storage tanks (not shown) connected to the processing liquid discharge head 12S and the black ink discharge head 30K of the ink jet apparatus configured as shown in FIG. did. Further, the cyan ink C1, the magenta ink M1, and the yellow ink Y1 are stored in storage tanks (not shown) connected to the cyan ink discharge head 30C, the magenta ink discharge head 30M, and the yellow ink discharge head Y, respectively. Each was loaded sequentially.
Using these treatment liquids and inks, a black solid image (hereinafter also referred to as “black solid image”) and a cyan, magenta, or yellow 1200 dpi line image were formed on a recording medium.
The amount of treatment liquid applied to the recording medium was 1.5 ml / m ² . As the recording medium, seven types described in Table 3 were used.
Upon image formation, the black ink is prepared from the head resolution 1200 dpi × 1200 dpi, an ink droplet amount 2.5～3.6Pl, was discharged by the maximum application amount 11 ml / ^{m 2} or 16 ml / ^{m 2} of the ink.
The black solid image was formed by ejecting black ink at a dot ratio of 100% on the entire surface of a sample obtained by cutting the recording medium into A5 size.

Specifically, the black solid image was formed under the conditions shown in Table 3 below.
First, after the processing liquid is discharged (applied) from the processing liquid discharge head 12S onto the recording medium in a single pass, the processing liquid is dried in the processing liquid drying zone 13, and the processing liquid drying zone is started from the discharge of the processing liquid. Passed by 900 msec. In the treatment liquid drying zone 13, while the deposited treatment liquid is heated from the back side (back side) of the landing surface with an infrared heater so that the film surface temperature is 40 to 45 ° C., 120 ° C. on the recording surface by a blower. Drying was performed by applying warm air of 5 m / sec for 5 seconds. Subsequently, after black ink is ejected from the ejection head 30K in a single pass to form a black solid image, the ink drying zone 15 is heated with an infrared heater from the back side (back surface) of the ink landing surface in the same manner as described above. A warm air of 120 ° C. was dried by a blower so as to obtain a predetermined drying amount shown in Table 3 below by changing the air volume. At this time, the conveyance speed is set so that the time from when the black ink droplets land on the recording medium to the ink drying zone 15 until the drying starts is the desired time (the time shown in Table 3 below). It was adjusted. A method for measuring the dry amount will be described later. After the image was dried, the UV irradiation unit 16 irradiated UV light (a metal halide lamp, maximum irradiation wavelength 365 nm, manufactured by Eye Graphics Co., Ltd.) so that the integrated irradiation amount was ² J / cm ² to cure the image.
The cyan, magenta, or yellow line image is formed by adding cyan, magenta, or yellow ink in a linear form after the black ink is discharged and before drying in the ink drying zone 15 in the formation of the black solid image. (I.e., a cyan, magenta, or yellow line image was formed on a black solid image).

≪Measurement of dry amount≫
In the formation of the above-described black solid image, after applying the treatment liquid (application amount 1.5 ml / m ² ) on the recording medium, the maximum application amount of black ink 11 ml / m ² or 16 ml as shown in Table 3 below. A black solid image was output at / m ² . The solid image was output without heating / blowing in the ink drying zone 15 and UV irradiation in the UV irradiation unit 16. The resulting image by the Karl Fischer moisture meter MKA-520 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.) for, by the Karl Fischer method, was measured moisture content W ₀ contained in the image.
Further, in the same manner as described above except that heating and blowing in the ink drying zone 15 are performed under predetermined drying conditions, an image obtained without UV irradiation is similarly applied to the image by the Karl Fischer method. the water content W ₁ contained were measured and calculated dry weight (%) by the following equation 1.
(W ₀ −W ₁ ) / W ₀ × 100 (Equation 1)

≪Evaluation≫
The following evaluation was performed on the image obtained by the image formation. The evaluation results are shown in Table 4 below.

<Adhesion>
A5 size sample with a black solid image formed on the entire surface is left for 10 minutes in an environment of 25 ° C. and 50% RH, and then the cellophane tape (manufactured by Nichiban Co., Ltd.) is attached to the black solid image and then peeled off. Were evaluated according to the following evaluation criteria.
~Evaluation criteria~
A: The image was not transferred to the tape.
B: A part of the image surface was transferred to the tape, but most of the image remained without being transferred.
C: A part of the image was transferred to the tape, and the surface of the recording medium without the image was partially exposed.
D: The image was transferred over the entire surface, and the surface of the recording medium was exposed.

<Scratch resistance>
An A5 size sample with a black solid image formed on the entire surface is left in an environment of 25 ° C. and 50% RH for 1 hour. Made by using a 0.1 mm stainless steel scratching needle while changing the load from 0 to 200 gf. The load at which scratches occurred on the surface of the black solid image was evaluated according to the following criteria.
~Evaluation criteria~
A: No scratch is observed even at 200 gf.
B: Scratches occurred at 100 gf or more and less than 200 gf.
C: Scratches occurred at 30 gf or more and less than 100 gf.
D: Scratches occurred at less than 30 gf.

<Curl properties>
An A5 size sample having a black solid image formed on the entire surface was cut into a size of 5 × 50 mm so that the curl direction was a 50 mm long direction, and a sample piece was produced. The sample piece was left under conditions of a temperature of 35 ° C. and a relative humidity of 80%, the curvature C of the sample was measured by the following method, and the curl property was evaluated according to the following evaluation criteria.
~ Measurement method of curvature ~
The curvature C of the sample piece left under the above conditions was measured in an environment at a temperature of 25 ° C. and a relative humidity of 50%. The curvature C is expressed by the following formula 2 considering the generated curl as an arc having a radius R, and the curvature C was used as an index for evaluating the curl property.
C = 1 / R (m) (Formula 2)
~Evaluation criteria~
A: Curvature C was less than 10.
B: Curvature C was 10 or more and less than 15.
C: Curvature C was 15 or more and less than 20.
D: Curvature C was 20 or more.

<Thin wire reproducibility>
As described above, cyan, magenta, or yellow monochromatic line images each having a width of 1 mm were formed on the black solid image. The line width of the formed monochrome line image of each color was observed visually and with a microscope (magnification: 30 times), and evaluated according to the following evaluation criteria.
~Evaluation criteria~
A: No variation in line width is observed in visual observation and microscopic observation.
B: Although the fluctuation of the line width is recognized by microscopic observation, the fluctuation of the line width is not recognized by visual observation, and is within a practical allowable range.
C: In visual observation and microscopic observation, variation in line width was recognized and exceeded the practically acceptable range.

<Gloss unevenness>
The surface of the black solid image formed as described above was visually observed, and gloss unevenness on the surface of the black solid image was evaluated according to the following evaluation criteria.
A: There was no abnormal feeling on the surface of the black solid image, good gloss was exhibited, and gloss unevenness was not recognized.
B: Although a slight decrease in glossiness was observed on the surface of the black solid image, no gloss unevenness was observed, and it was within a practically acceptable range.
C: A slight decrease in gloss and slight gloss unevenness were observed on the surface of the black solid image, but they were within a practically acceptable range.
D: A partial reduction in glossiness was observed on the surface of the black solid image, which was visually recognized as uneven glossiness, and exceeded the practically acceptable range.

As shown in Table 4, in Examples 1 to 21 using a black ink containing a sugar alcohol and a crosslinked water-soluble polymer, gloss unevenness in a black solid image was suppressed. Furthermore, in Examples 1 to 21, the black solid image was excellent in adhesion and scratch resistance, curling of the recording medium on which the black solid image was formed was suppressed, and a line image was formed on the black solid image. The fine line reproducibility was also excellent.
On the other hand, in Comparative Example 1 using an uncrosslinked water-soluble polymer and Comparative Example 2 using urea instead of sugar alcohol, gloss unevenness occurred on the surface of the black solid image.

DESCRIPTION OF SYMBOLS 12 ... Treatment liquid provision part 12S ... Treatment liquid discharge head 13 ... Treatment liquid drying zone 14 ... Ink discharge part 15 ... Ink drying zone 16 ... Ultraviolet irradiation part 16S ... Ultraviolet irradiation lamps 30K, 30C, 30M, 30Y ... Ink ejection head

Claims (17)

A polymer-coated carbon black pigment in which at least a part of the surface of the carbon black pigment is coated with a crosslinked water-soluble polymer, a sugar alcohol, and water are contained, and the content of polymer particles is 2 with respect to the total amount of the ink composition. A black ink composition that is less than mass%;
A treatment liquid containing an aggregating component for aggregating the components in the black ink composition;
Ink set containing.   The ink set according to claim 1, wherein the sugar alcohol has five or more hydroxyl groups in one molecule.   The ink set according to claim 1, wherein the sugar alcohol is at least one selected from the group consisting of pentitol and hexitol.   The ink set according to any one of claims 1 to 3, wherein the black ink composition further contains at least one color pigment selected from a magenta pigment and a cyan pigment.   The ink set according to any one of claims 1 to 4, wherein the black ink composition further contains a polymerizable compound. The black ink composition further contains a polymerizable compound,
The ink set according to claim 1, wherein at least one of the polymerizable compounds is a polymerizable compound having a (meth) acrylamide structure in a molecule.   The ink set according to any one of claims 1 to 6, wherein an amount of the crosslinked water-soluble polymer is 50% by mass to 150% by mass with respect to an amount of the carbon black pigment.   The ink set according to any one of claims 5 to 7, wherein at least one of the treatment liquid and the black ink composition further contains a polymerization initiator.   The ink set according to any one of claims 1 to 8, wherein the aggregation component is at least one selected from an acid, a polyvalent metal salt, and a cationic polymer.   In the polymer-coated carbon black pigment, at least a part of the surface of the carbon black pigment is coated with a water-soluble polymer having a carboxyl group, and at least a part of the carboxyl group has two or more glycidyl groups in one molecule. The ink set according to any one of claims 1 to 9, wherein the ink set is crosslinked by a reaction with a glycidyl ether compound. The ink set according to any one of claims 1 to 10, is used,
A treatment liquid application step of applying the treatment liquid onto a recording medium;
An ink application step of applying the black ink composition onto a recording medium by an inkjet method to form an image;
A drying step of drying the image after the treatment liquid applying step and the ink applying step;
An image forming method comprising: The ink application step is provided after the treatment liquid application step;
The recording medium has a single or multi-layered pigment layer on at least one surface on a support mainly composed of cellulose pulp, and the transfer amount of pure water measured by a dynamic scanning absorptivity is determined based on the contact time. 12. The image forming method according to claim 11, wherein the image forming method is 1 ml / m ² or more and 15 ml / m ² or less at 100 ms and 2 ml / m ² or more and 20 ml / m ² or less at a contact time of 400 ms.   The image forming method according to claim 12, wherein the recording medium is coated paper, lightweight coated paper, or finely coated paper.   The image forming method according to claim 11, further comprising a curing step of irradiating the image after the drying step with active energy rays to cure the image.   The image forming method according to claim 11, wherein the drying step starts drying within 5 seconds from the time when the droplet of the black ink composition has landed on the recording medium. The image forming method according to claim 11, wherein a maximum application amount of the black ink composition in the ink application process is 15 ml / m ² or less. The drying step is performed under a drying condition in which 60 to 80% by mass of the water content in the black ink composition applied on the recording medium is removed at a maximum application amount of 15 ml / m ² or less. The image forming method according to any one of claims 11 to 16, wherein at least a part of water in the black ink composition forming the above image is removed.