JP5591753B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming method for forming an image using an inkjet method.

  Various image recording methods for recording color images have been proposed in recent years, but in any case, there are high demands on the quality and quality of images and recorded matter.

  Recently, a technique for forming a high-quality image at a higher speed has attracted attention. When it is intended to realize this by an ink jet method, a plurality of discharge nozzles are used instead of the shuttle scan method which has been widely applied conventionally. Various technologies, such as a single-pass method that forms images by ejecting multiple ink droplets from a two-dimensionally arranged nozzle plate to a wide area at once, or a method that enhances printability to form images on both sides Is being considered.

  In conventional ink jet methods such as the shuttle scan method, since the recording speed is slow, the ink solvent easily dries or penetrates into the recording medium during recording, and the ink dots that have landed on the medium maintain a certain level of strength. It was. Further, since the ink speed is low, images are not formed on a large amount of recording media in a short time, and the recording media are not stacked within a short time after recording.

  However, when high-speed recording is performed using, for example, the single-pass method, the drying time is shortened and the recording media on which image formation has been completed are continuously stacked, so that the solvent evaporates in the overlapping portions of the media. A large amount remains without being constrained, and as a result, the image portions are stacked in a soft state, that is, before the image strength is secured.

  If the images are stacked before being sufficiently dried and cured, scratches may occur on the surface of the image in the process of moving the recorded recording medium from the stacking unit, sorting, and the like, which may hinder the image quality. Such a phenomenon becomes more conspicuous as the number of stacked recording media increases, the size of the recording media increases, and the recording media in which ink or its solvent penetrates more slowly.

  On the other hand, in offset printing, from the viewpoint of preventing blocking, it is generally performed to spray solid particles immediately after printing. The offset ink is usually configured to be oily or ultraviolet curable, and a film is formed by oxidative polymerization or polymerization using ultraviolet rays, so that scratches on the image are relatively unlikely to occur. On the other hand, in the case of water-based inks, the image is cured by removing moisture from the ink film to some extent, so if the layers are stacked with insufficient drying, the solvent is further increased in the stacked state. It is hard to come off. Therefore, as described above, the image is likely to be scratched due to the movement or sorting of the recording medium.

  In relation to such a situation, an ink jet recording printing method has been disclosed in which an image is formed by ejecting a water-based ink composition onto a non-absorbing or low-absorbing recording medium for ink (for example, , See Patent Document 1). In this printing method, it is said that the resin particles contain resin fixing agent particles and wax particles, so that the printed material has excellent abrasion resistance.

  Moreover, there is a disclosure relating to a printing method for printing using an anti-blocking powder (see, for example, Patent Document 2).

JP 2010-90266 A JP 2006-231565 A

  In the conventional printing method, from the viewpoint of abrasion resistance, wax particles are used and excellent in abrasion resistance. However, when viewed from the ejection head, the recording medium conveyance speed is 200 mm / sec or more. At the time of recording, the actual situation is that drying does not catch up and the abrasion resistance of the image cannot be secured sufficiently.

  In the printing field, a technique using powder as a countermeasure against blocking is known. However, since the properties of ink used for printing and the curing mechanism are different from those of water-based inks, the strength of the image itself is not maintained before printing. It is considered that there is little problem with scratches on the image surface.

  The present invention has been made in view of the above, and shows excellent scratch resistance when processing a large number of sheets at a high speed when the conveyance speed of the recording medium is 200 mm / sec or more as viewed from the ejection head, and scratches in the image. An object of the present invention is to provide an image forming method in which the occurrence of image defects such as the above is prevented, and to achieve the object.

Specific means for achieving the above object are as follows.
<1> A resin-coated pigment in which at least a part of pigment particles is coated with a water-insoluble resin, resin particles, wax particles, 1,2-alkylenediol, a polyhydric alcohol, a pyrrolidone derivative, and an acetylene glycol surfactant. An ink application step of applying an ink composition from a discharge head to a recording medium, applying an ink at a moving speed in the sub-scanning direction between the discharge head and the recording medium of 200 mm / sec or more, and the recording applied with the ink A drying step for drying the medium, a stacking step for stacking the recording medium after drying by providing a step of attaching 1 to 1000 mg / m ² of a powdery substance having an average particle diameter of 1 to 100 μm to the recording medium; Have

<2> The image forming method according to <1>, wherein the wax particles are carnauba wax particles .
<3> The image forming method according to <1> or <2>, wherein the pyrrolidone derivative includes polyvinylpyrrolidone.
<4> The method according to any one of <1> to <3>, further including a treatment liquid application step of applying a treatment liquid containing an aggregation component that aggregates the components in the ink composition to a recording medium. This is an image forming method.

<5> The image forming method according to any one of <1> to <4>, wherein the powder is powder particles that have been subjected to hydrophobic treatment.
<6> The image forming method according to any one of <1> to <5>, wherein the recording medium includes a coating layer and has an area of 1250 cm ² or more.

  According to the present invention, when a large number of sheets are processed at a high speed at which the conveyance speed of the recording medium is 200 mm / sec or more as viewed from the ejection head, excellent scratch resistance is exhibited, and image defects such as scratches in the image are generated. An image forming method that is prevented can be provided.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus that performs an image forming method of the present invention.

Hereinafter, the image forming method of the present invention will be described in detail.
The image forming method of the present invention comprises a resin-coated pigment in which at least a part of pigment particles is coated with a water-insoluble resin, resin particles, wax particles, 1,2-alkylenediol, polyhydric alcohol, pyrrolidone derivative, and acetylene glycol interface. An ink application step of applying an ink composition containing an activator from a discharge head to a recording medium, and applying the ink at a moving speed in the sub-scanning direction between the discharge head and the recording medium of 200 mm / sec or more; A drying step of drying the applied recording medium, and an accumulation step of stacking the recording medium after drying by providing a step of attaching 1 to 1000 mg / m ² of a powdery substance having a particle diameter of 1 to 100 μm to the recording medium; Is provided. The image forming method of the present invention further includes a treatment liquid application step for applying a treatment liquid containing an aggregating component for aggregating the components in the ink composition, if necessary, and a cooling step for cooling the recording medium. This process can be provided and configured.

  In the present invention, when ink-jet recording is performed at a high speed at which the conveyance speed of the recording medium is 200 mm / sec or more as viewed from the ejection head, the ink composition is easy to form a fine image, and image defects such as scratches are formed after the ink composition is formed. By making the composition hard to occur and applying powdery substances not only after recording but also during the accumulation process, even if the film is not fully cured and the film is not completely cured, the recording medium can be moved and sorted. Therefore, image defects such as scratches and peeling on the formed image after accumulation due to the like are prevented. Thus, a high-quality image with few image defects can be stably formed during high-speed image formation.

Hereafter, each process which comprises the image forming method of this invention is explained in full detail.
-Ink application process-
In the ink application process according to the present invention, a resin-coated pigment in which at least a part of pigment particles is coated with a water-insoluble resin, resin particles, wax particles, 1,2-alkylenediol, polyhydric alcohol, pyrrolidone derivative, and acetylene glycol interface An ink composition containing an activator is applied from the ejection head to the recording medium, with the moving speed in the sub-scanning direction between the ejection head and the recording medium being 200 mm / sec or more.

  In the present invention, ink is applied by setting the moving speed in the sub-scanning direction between the ejection head and the recording medium, that is, the conveyance speed of the recording medium viewed from the ejection head to a high speed of 200 mm / sec or more. From the viewpoint of speeding up image formation, the movement is preferably faster, and the conveyance speed is more preferably 250 mm / s or more, and still more preferably 400 mm / s or more.

Formation of an image using an ink jet method can be performed by ejecting an ink composition onto a desired recording medium by supplying energy. As a preferred image forming method of the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.
The ink jet method is not particularly limited, and a known method, for example, a charge control method in which ink is ejected using electrostatic attraction, and a piezoelectric element that generates mechanical distortion by application of voltage is used to supply ink. Piezo ink-jet method to eject, acoustic ink-jet method to change the electrical signal into an acoustic beam, irradiate the ink and eject the ink using the radiation pressure, and thermal to use the pressure generated by heating the ink to form bubbles Any of an ink jet (bubble jet (registered trademark)) system and the like may be used.
The inkjet method uses a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method used is included.

  As the ink jet method in the present invention, a piezo ink jet method is suitable. By combining the ink composition of the present invention or an ink set containing the ink composition and the piezo ink jet method, the continuous ejection property and ejection stability of the ink are further improved. In the piezo ink jet system, the distortion form of the piezoelectric element may be any of a bending mode, a longitudinal mode, and a shear mode. A known technique can be adopted for the configuration of the piezoelectric element and the structure of the piezo head without particular limitation.

There are no particular restrictions on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.
As an inkjet method applicable to the present invention, as long as the conveyance speed can be maintained at 200 mm / sec or more as described above, a shuttle system that performs recording while using a short serial head to scan the head in the width direction of the recording medium. However, a mode in which a line method using a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium is applied is preferable. In the case of the line method, image recording can be performed on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements (that is, the sub-scanning direction).

  The droplet amount of the ink composition to be ejected is preferably 0.5 to 6 pl (picoliter), more preferably 1 to 5 pl, and further preferably 2 to 4 pl from the viewpoint of obtaining a high-definition image.

Next, details of the ink composition in the present invention will be described.
(Resin-coated pigment)
The ink composition in the present invention contains at least one resin-coated pigment in which at least a part of pigment particles is coated with a water-insoluble resin. In this case, the pigment does not necessarily need to be entirely coated on the particle surface, and may be in a state where at least a part of the particle surface is coated.

Examples of the water-insoluble resin include [1] a polymer containing a repeating unit (a) represented by the following general formula (1) and a repeating unit (b) having an ionic group, or [2] salt Preferred examples include a polymer containing a structural unit derived from the product group-containing monomer (c) and a structural unit derived from a styrenic macromer (d) and / or a hydrophobic monomer (e). Among them, the polymer [1] is preferable. Details of the polymer [2] can be referred to the details described in paragraphs 0012 to 0031 of JP-A-2009-84501.
The term “water-insoluble” means that when a polymer is mixed in an aqueous medium at 25 ° C., the amount of the polymer dissolved in the aqueous medium is 10% by mass or less as a mass ratio with respect to all the mixed polymers.

  Hereinafter, [1] a polymer including the repeating unit (a) represented by the general formula (1) and the repeating unit (b) having an ionic group will be specifically described.

  This polymer includes at least one repeating unit represented by the following general formula (1) and at least one repeating unit having an ionic group, and, if necessary, further represented by the general formula (1). Other structural units such as a hydrophobic repeating unit other than the repeating unit and a hydrophilic repeating unit having a nonionic functional group can be included.

<(A) Repeating unit represented by general formula (1)>

In the general formula (1), R ₁ represents a hydrogen atom, a methyl group, or a halogen atom (for example, a chlorine atom, a bromine atom, an iodine atom, etc.), and L ₁ represents ^* —COO—, ^* —OCO—, ^* —CONR ₂ —, ^* —O—, or a substituted or unsubstituted phenylene group, R ₂ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Incidentally, symbol * in the group represented by L ₁ represents a connecting point with the main chain. L ₂ represents a single bond or a divalent linking group. Ar represents a monovalent group derived from an aromatic ring.

In the general formula (1), R ₁ represents a hydrogen atom, a methyl group, or a halogen atom, preferably a methyl group.

L ₁ represents ^* —COO—, ^* —OCO—, ^* —CONR ₂ —, ^* —O—, or a substituted or unsubstituted phenylene group. When L ₁ represents a phenylene group, unsubstituted is preferred. R ₂ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

L ₂ represents a single bond or a divalent linking group. The divalent linking group is preferably a linking group having 1 to 30 carbon atoms, more preferably a linking group having 1 to 25 carbon atoms, still more preferably a linking group having 1 to 20 carbon atoms, Particularly preferred is a linking group having 1 to 15 carbon atoms.
Among them, most preferably, an alkyleneoxy group having 1 to 25 carbon atoms (more preferably 1 to 10), an imino group (—NH—), a sulfamoyl group, and 1 to 20 carbon atoms (more preferably 1 to 15). A divalent linking group containing an alkylene group such as an alkylene group or an ethylene oxide group [— (CH ₂ CH ₂ O) _n —, n = 1 to 6], etc., and a group in which two or more of these are combined is there.

Ar represents a monovalent group derived from an aromatic ring.
The aromatic ring of the monovalent group represented by Ar is not particularly limited, but includes a benzene ring, a condensed aromatic ring having 8 or more carbon atoms, an aromatic ring condensed with a hetero ring, or two or more benzene rings. A condensed aromatic ring can be mentioned.

  The “condensed aromatic ring having 8 or more carbon atoms” includes an aromatic ring in which at least two benzene rings are condensed, at least one aromatic ring and a condensed alicyclic hydrocarbon ring. Is an aromatic compound having 8 or more carbon atoms. Specific examples include naphthalene, anthracene, fluorene, phenanthrene, acenaphthene and the like.

The “aromatic ring condensed with a heterocycle” is a compound in which an aromatic compound containing no hetero atom (preferably a benzene ring) and a cyclic compound having a hetero atom are condensed. Here, the cyclic compound having a hetero atom is preferably a 5-membered ring or a 6-membered ring. As a hetero atom, a nitrogen atom, an oxygen atom, or a sulfur atom is preferable. The cyclic compound having a hetero atom may have a plurality of hetero atoms. In this case, the heteroatoms may be the same or different from each other.
Specific examples of the heterocyclic ring condensed with an aromatic ring include phthalimide, acridone, carbazole, benzoxazole, and benzothiazole.

  Specific examples of the monomer forming the repeating unit represented by the general formula (1) include vinyl monomers such as (meth) acrylates, (meth) acrylamides, styrenes, and vinyl esters. it can.

  In the present invention, as in the repeating unit represented by the general formula (1), in a hydrophobic structural unit having an aromatic ring via a linking group to an atom forming the main chain, the aromatic ring is connected via a linking group. It has a structure that is bonded to the main chain atom of the water-insoluble resin and not directly bonded to the main chain atom of the water-insoluble resin, so that an appropriate distance is maintained between the hydrophobic aromatic ring and the hydrophilic structural unit. Therefore, an interaction is likely to occur between the water-insoluble resin and the pigment, and it is strongly adsorbed to further improve dispersibility.

  Furthermore, the following monomers etc. can be mentioned as a specific example of the monomer which forms the repeating unit represented by the said General formula (1). However, the present invention is not limited to these.

  As (a) Ar in the repeating unit represented by the general formula (1), from the viewpoint of dispersion stability of the coated pigment, benzyl (meth) acrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, acridone, or A monovalent group derived from phthalimide is preferred.

The said repeating unit can be used individually by 1 type or in mixture of 2 or more types.
The content ratio of the repeating unit represented by the general formula (1) in the polymer is preferably in the range of 5 to 25% by mass, more preferably in the range of 10 to 18% by mass with respect to the total mass of the polymer. . When the content is 5% by mass or more, the occurrence of image failure such as white spots tends to be remarkably suppressed, and when the content is 25% by mass or less, the polymerization in a polymerization reaction solution (for example, methyl ethyl ketone). This is preferable because there is a tendency that problems in production suitability due to a decrease in solubility do not occur.

<Other hydrophobic repeating units>
The polymer [1] may further have a hydrophobic repeating unit other than the repeating unit represented by the general formula (1) as a hydrophobic structural unit. Examples of other hydrophobic repeating units do not belong to hydrophilic structural units (for example, have no hydrophilic functional group), such as (meth) acrylates, (meth) acrylamides, styrenes, and vinyl esters. And a structural unit derived from a vinyl monomer, a hydrophobic structural unit having an aromatic ring via a linking group at the atom constituting the main chain, and the like. These structural units can be used individually by 1 type or in mixture of 2 or more types.

Examples of the (meth) acrylates include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and hexyl (meth) acrylate. Of these, alkyl esters of 1 to 4 carbon atoms of (meth) acrylic acid are preferred. Among these, methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate are preferable, and methyl (meth) acrylate and ethyl (meth) acrylate are particularly preferable.
Examples of the (meth) acrylamides include N-cyclohexyl (meth) acrylamide, N- (2-methoxyethyl) (meth) acrylamide, N, N-diallyl (meth) acrylamide, N-allyl (meth) acrylamide, and the like. (Meth) acrylamides.
Examples of the styrenes include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, n-butyl styrene, tert-butyl styrene, methoxy styrene, butoxy styrene, acetoxy styrene, chlorostyrene, dichlorostyrene, Examples thereof include bromostyrene, chloromethylstyrene, hydroxystyrene protected with a group that can be deprotected by an acidic substance (for example, t-Boc), methyl vinylbenzoate, α-methylstyrene, vinylnaphthalene, and the like. Styrene and α-methylstyrene are preferred.
Examples of the vinyl esters include vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl methoxyacetate, and vinyl benzoate. Of these, vinyl acetate is preferable.

<(B) Repeating unit having an ionic group>
Examples of the repeating unit having an ionic group include a repeating unit derived from a monomer having an ionic group such as a carboxyl group, a sulfo group, or a phosphonate group. Examples thereof include vinyl monomers having an ionic functional group such as (meth) acrylic acid, (meth) acrylates, (meth) acrylamides, and vinyl esters. The repeating unit having an ionic group can be introduced by polymerization of the corresponding monomer, but may be one in which an ionic group is introduced into the polymer chain after polymerization.

  Among these, the repeating unit derived from acrylic acid and methacrylic acid is preferable, and it is preferable to include one or both of a structural unit derived from acrylic acid and a structural unit derived from methacrylic acid.

In this polymer [1], (b) the proportion of the repeating unit having an ionic group is 15% by mass or less of the total mass of the polymer, and at least a structural unit derived from (meth) acrylic acid as the repeating unit having an ionic group The aspect containing is preferable.
(B) When the content of the repeating unit having an ionic group is 15% by mass or less of the total mass of the polymer, the dispersion stability is excellent. Among these, the proportion of the repeating unit (b) having an ionic group is preferably 5% by mass or more and 15% by mass or less, and more preferably 7% by mass or more and 13% by mass or less from the viewpoint of dispersion stability.

  This polymer [1] can exist stably in the aqueous ink composition, and for example, the adhesion and deposition of aggregates with an ink jet head or the like are alleviated, and the removability of the adhered aggregates is excellent. From this point of view, (a) a hydrophobic structural unit other than the repeating unit represented by the general formula (1), and a hydrophilic structural unit other than the “(b) repeating unit having an ionic group” May further be included.

<Hydrophilic repeating unit>
Examples of the other hydrophilic structural unit include a repeating unit derived from a monomer having a nonionic hydrophilic group. For example, (meth) acrylates having a hydrophilic functional group, (meth) acrylamides, And vinyl monomers having a hydrophilic functional group, such as vinyl esters.

  Examples of the “hydrophilic functional group” include a hydroxyl group, an amino group, an amide group (unsubstituted with a nitrogen atom), and alkylene oxides such as polyethylene oxide and polypropylene oxide described later.

  The monomer that forms a hydrophilic repeating unit having a nonionic hydrophilic group has a functional group capable of forming a polymer such as an ethylenically unsaturated bond and a nonionic hydrophilic functional group. If it is, there will be no restriction | limiting in particular, It can select from a well-known monomer. Specific examples include hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, (meth) acrylamide, aminoethyl acrylate, aminopropyl acrylate, and (meth) acrylate containing an alkylene oxide polymer. Can do.

  The hydrophilic repeating unit having a nonionic hydrophilic group can be formed by polymerization of the corresponding monomer, but a hydrophilic functional group may be introduced into the polymer chain after polymerization.

  The hydrophilic repeating unit having a nonionic hydrophilic group is more preferably a hydrophilic structural unit having an alkylene oxide structure. The alkylene moiety of the alkylene oxide structure is preferably an alkylene group having 1 to 6 carbon atoms, more preferably an alkylene having 2 to 6 carbon atoms, and particularly preferably an alkylene having 2 to 4 carbon atoms from the viewpoint of hydrophilicity. Moreover, as a polymerization degree of an alkylene oxide structure, 1-120 are preferable, 1-60 are more preferable, and 1-30 are especially preferable.

  Moreover, it is also a preferable aspect that the hydrophilic repeating unit having a nonionic hydrophilic group is a hydrophilic repeating unit containing a hydroxyl group. The number of hydroxyl groups in the repeating unit is not particularly limited, and is preferably 1 to 4, more preferably 1 to 3, from the viewpoint of the hydrophilicity of the water-insoluble resin and the compatibility with the solvent and other monomers during polymerization. 1-2 is particularly preferred.

As the polymer [1], the composition of the hydrophilic repeating unit and the hydrophobic repeating unit (including the structural repeat represented by the general formula (1)) affects the degree of hydrophilicity and hydrophobicity of each. The ratio of hydrophilic repeating units is preferably 15% by mass or less. At this time, it is preferable that a hydrophobic repeating unit is a ratio exceeding 80 mass% with respect to the whole mass of a water-insoluble resin, and it is more preferable that it is 85 mass% or more.
When the content of the hydrophilic repeating unit is 15% by mass or less, the amount of the component dissolved alone in the aqueous medium is suppressed, and various properties such as pigment dispersion are improved. Is obtained.

  A preferred content ratio of the hydrophilic repeating unit is in the range of more than 0% by mass and 15% by mass or less, more preferably in the range of 2 to 15% by mass, still more preferably, based on the total mass of the water-insoluble resin. It is in the range of 5 to 15% by mass, particularly preferably in the range of 8 to 12% by mass.

  The content of the aromatic ring contained in the water-insoluble resin is preferably 27% by mass or less, more preferably 25% by mass or less, and more preferably 20% by mass or less with respect to the total mass of the water-insoluble resin. More preferably it is. Especially, it is preferable that it is 15-20 mass%, and the range of 17-20 mass% is more preferable. When the content ratio of the aromatic ring is within the above range, the scratch resistance is improved.

Hereinafter, specific examples (molar ratio (mass%), weight average molecular weight Mw, acid value) of polymer [1] are listed. However, the present invention is not limited to the following.
・ Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
・ Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
・ Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
・ Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
・ Benzyl methacrylate / methyl methacrylate / methacrylic acid copolymer (60/30/10)
・ Phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid copolymer (50/39/11)
-(M-25 / M-27) mixture / ethyl methacrylate / methacrylic acid copolymer (molar ratio: 15/75/10, MW 49400, acid value 65.2 mgKOH / g)
-(M-25 / ethyl methacrylate / methacrylic acid copolymer (molar ratio: 18/69/13, MW 41600, acid value 84.7 mgKOH / g)
-(M-28 / M-29) mixture / ethyl methacrylate / methacrylic acid copolymer (molar ratio: 15/85/10, MW 38600, acid value 65.2 mgKOH / g)
(M-28) / ethyl methacrylate / methacrylic acid copolymer (molar ratio: 20/73/7, MW 45300, acid value 45.6 mgKOH / g)

The acid value of the water-insoluble resin in the present invention is preferably from 30 mgKOH / g to 100 mgKOH / g and more preferably from 30 mgKOH / g to 85 mgKOH / g from the viewpoint of pigment dispersibility and storage stability. It is preferably 50 mgKOH / g or more and 85 mgKOH / g or less.
The acid value is defined by the mass (mg) of KOH required to completely neutralize 1 g of the water-insoluble resin, and is measured by the method described in JIS standards (JIS K 0070, 1992). .

The molecular weight of the water-insoluble resin in the present invention is preferably 30,000 or more in terms of weight average molecular weight (Mw), more preferably 30,000 to 150,000, still more preferably 30,000 to 100,000, particularly preferably 30,000 to 80,000. When the molecular weight is 30,000 or more, the steric repulsion effect as a dispersant tends to be good, and the steric effect makes it easy to adsorb to the pigment.
Further, the number average molecular weight (Mn) is preferably in the range of 1,000 to 100,000, particularly preferably in the range of 3,000 to 50,000. When the number average molecular weight is within the above range, a function as a coating film in the pigment or a function as a coating film of the ink composition can be exhibited. The polymer [1] is preferably used in the form of an alkali metal or organic amine salt.

  Moreover, as molecular weight distribution (weight average molecular weight / number average molecular weight) of water-insoluble resin, the range of 1-6 is preferable, and the range of 1-4 is more preferable. When the molecular weight distribution is within the above range, the dispersion stability and ejection stability of the ink can be improved.

  The number average molecular weight and the weight average molecular weight are measured by gel permeation chromatography (GPC). For GPC, HLC-8020GPC (manufactured by Tosoh Corporation) was used, TSKgel and Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) were used as columns, and THF (tetrahydrofuran) as an eluent. It is the molecular weight calculated | required by detecting with solvent THF using and converting using polystyrene as a standard substance.

The water-insoluble resin can be synthesized by various polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, precipitation polymerization, bulk polymerization, and emulsion polymerization. The polymerization reaction can be performed by a known operation such as a batch system, a semi-continuous system, or a continuous system. The polymerization initiation method includes a method using a radical initiator, a method of irradiating light or radiation, and the like. These polymerization methods and polymerization initiation methods are described in, for example, the revised version of Tsuruta Junji “Polymer Synthesis Method” (published by Nikkan Kogyo Shimbun, 1971), Takatsu Otsu, Masaaki Kinoshita, “Experimental Methods for Polymer Synthesis” , Published in 1972, pages 124-154.
Among the polymerization methods, a solution polymerization method using a radical initiator is particularly preferable. Examples of the solvent used in the solution polymerization method include various organic solvents such as ethyl acetate, butyl acetate, acetone, and methyl ethyl ketone. Moreover, you may use as a mixed solvent with water.
Regarding the polymerization conditions, the polymerization temperature is usually about 0 ° C to 100 ° C, but a range of 50 to 100 ° C is preferable. Moreover, although reaction pressure can be selected suitably, it is 1-100 kg / cm < ² > normally, and about 1-30 kg / cm < ² > is especially preferable. The reaction time is about 5 to 30 hours. The obtained resin may be subjected to purification such as reprecipitation.

The resin-coated particles obtained by coating the pigment particles with a water-insoluble resin are preferably in a form in which the pigment is coated with the water-insoluble resin by a phase inversion emulsification method from the viewpoint of dispersion stability.
The phase inversion emulsification method is basically a self-dispersion (phase inversion emulsification) method in which a mixed melt of a resin having a self-dispersing ability or a dissolving ability and a pigment is dispersed in water. The mixed melt may contain a curing agent or a polymer compound. Here, the mixed molten material refers to a mixed state that is not dissolved, a state that is dissolved and mixed, or a state that includes both of these states. A more specific production method of the “phase inversion emulsification method” includes the method described in JP-A-10-140065.
More specific production methods of the phase inversion emulsification method and the acid precipitation method include methods described in JP-A-9-151342 and JP-A-10-140065.

The resin-coated pigment is preferably obtained by providing a preparation step of preparing a dispersion of the resin-coated pigment using a water-insoluble resin by a method including the following step (1) and step (2). In addition, the ink composition can be prepared by a method of using a dispersion of the resin-coated pigment obtained in the preparation step together with water and an organic solvent to obtain an aqueous ink.
Step (1): A step of dispersing a mixture containing a water-insoluble resin, an organic solvent, a neutralizing agent, a pigment, and water by stirring or the like to obtain a dispersion. Step (2): The organic solvent from the dispersion. Removing process

  The stirring method is not particularly limited, and a commonly used mixing and stirring device, and a dispersing device such as an ultrasonic dispersing device, a high-pressure homogenizer, and a bead mill can be used as necessary.

  In addition, as an organic solvent, an alcohol solvent, a ketone solvent, and an ether solvent are mentioned preferably, The details are described in the item of the following resin particle. The neutralizing agent is used in order to form an emulsified or dispersed state in which the dissociable group is partially or completely neutralized and the specific copolymer is stable in water. Details of the neutralizing agent will be described later.

In the step (2), the organic solvent is distilled off from the dispersion obtained in the step (1) by a conventional method such as vacuum distillation, and the phase is changed to an aqueous system. A dispersion of resin-coated pigment particles coated with coalescence can be obtained. The organic solvent in the obtained dispersion is substantially removed, and the amount of the organic solvent here is preferably 0.2% by mass or less, and more preferably 0.1% by mass or less. More specifically, for example, (1) a step of neutralizing a copolymer having an anionic group or a solution obtained by dissolving the copolymer in an organic solvent and a basic compound (neutralizing agent); ) After the pigment is mixed with the obtained mixed liquid to form a suspension, a step of dispersing the pigment with a disperser or the like to obtain a pigment dispersion, and (3) removing the organic solvent by distillation, for example, Coating the pigment with a specific copolymer having an anionic group, and dispersing the pigment in an aqueous medium to form an aqueous dispersion.
More specifically, the descriptions in JP-A-11-209672 and JP-A-11-172180 can be referred to.

  In the present invention, the dispersion treatment can be performed by, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring type disperser, an ultrasonic homogenizer, or the like.

  The content of the resin-coated pigment in which at least part of the pigment particles is coated with a water-insoluble resin in the ink composition is preferably in the range of 0.1 to 15% by mass with respect to the total mass of the ink composition. The range of 1-10 mass% is more preferable, and the range of 1-7 mass% is especially preferable.

(Resin particles)
The ink composition in the present invention contains at least one kind of resin particles. By containing the resin particles in addition to the resin covering the pigment, the fixability of the ink composition to the recording medium and the scratch resistance of the image can be further improved. In addition, when an image is formed using a processing liquid described later, the ink composition has a function of fixing by aggregating and thickening the ink composition when contacting the processing liquid or a region where the processing liquid is dried. Have.

  The resin particles are preferably water-insoluble resin particles. Water-insoluble means that when the resin is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the dissolved amount is 10 g or less. From the viewpoint of improving the continuous ejection property and ejection stability of the ink, the dissolved amount is preferably 5 g or less, more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

  Examples of the resin particles include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine resins, chlorides, and the like. Amino resins such as polyvinyl resins such as vinyl, vinyl acetate, polyvinyl alcohol, or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd co-condensation resins, urea resins, urea resins, etc. Examples thereof include particles of a resin such as a system material or a copolymer or a mixture thereof. Among these, anionic acrylic resins include, for example, an acrylic monomer having an anionic group (anionic group-containing acrylic monomer) and, if necessary, other monomers copolymerizable with the anionic group-containing acrylic monomer. Obtained by polymerization in a solvent. Examples of the anionic group-containing acrylic monomer include an acrylic monomer having one or more selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. Among them, an acrylic monomer having a carboxyl group (for example, acrylic acid) Methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like), and acrylic acid or methacrylic acid is particularly preferred.

As the resin particles, self-dispersing resin particles are preferable from the viewpoint of ejection stability and liquid stability (particularly dispersion stability) of a system containing a pigment. Self-dispersing resin is water that can be dispersed in an aqueous medium due to functional groups (particularly acidic groups or salts thereof) of the polymer itself when dispersed by the phase inversion emulsification method in the absence of a surfactant. An insoluble polymer.
Here, the dispersed state refers to an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium. It includes both states.
The self-dispersing resin is preferably a self-dispersing resin that can be in a dispersed state in which a water-insoluble polymer is dispersed in a solid state from the viewpoint of ink fixing properties when contained in the ink composition.

  As a method for preparing an emulsified or dispersed state of the self-dispersing resin, that is, an aqueous dispersion of the self-dispersing resin, a phase inversion emulsification method may be mentioned. As the phase inversion emulsification method, for example, a self-dispersing resin is dissolved or dispersed in a solvent (for example, a water-soluble organic solvent) and then poured into water as it is without adding a surfactant. Examples include a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing in a state in which a salt-forming group (for example, acidic group) possessed by the resin is neutralized and removing the solvent.

  In addition, a stable emulsified or dispersed state in the self-dispersing resin is a solution in which 30 g of a water-insoluble polymer is dissolved in 70 g of an organic solvent (for example, methyl ethyl ketone), and the salt-forming group of the water-insoluble polymer can be neutralized 100%. Mixing agent (sodium hydroxide if the salt-forming group is anionic, acetic acid if it is cationic) and water 200g, stirring (device: stirring device with stirring blades, rotation speed 200rpm, 30 minutes, 25 ° C) Then, even after removing the organic solvent from the mixed solution, it means that the emulsified or dispersed state is stably present at 25 ° C. for at least one week, and the occurrence of precipitation cannot be visually confirmed.

The stability of the emulsified or dispersed state in the self-dispersing resin can also be confirmed by an accelerated sedimentation test by centrifugation. The stability of the sedimentation acceleration test by centrifugation is, for example, adjusted by adjusting the aqueous dispersion of polymer particles obtained by the above method to a solid concentration of 25% by mass, and then centrifuging at 12,000 rpm for 1 hour. It can be evaluated by measuring the solid content concentration of the supernatant after separation.
If the ratio of the solid content concentration after centrifugation to the solid content concentration before centrifugation is large (a value close to 1), the sedimentation of the polymer particles by centrifugation does not occur, that is, the aqueous dispersion of polymer particles Means more stable. In the present invention, the ratio of the solid content concentration before and after centrifugation is preferably 0.8 or more, more preferably 0.9 or more, and particularly preferably 0.95 or more.

The self-dispersing resin preferably has a water-soluble component content that is water-soluble when in a dispersed state of 10% by mass or less, more preferably 8% by mass or less, and 6% by mass or less. More preferably. When the water-soluble component is 10% by mass or less, swelling of the polymer particles and fusion between the polymer particles can be effectively suppressed, and a more stable dispersion state can be maintained. In addition, an increase in the viscosity of the aqueous ink composition can be suppressed. For example, when the aqueous ink composition is applied to an ink jet method, the ejection stability becomes better.
The water-soluble component is a compound that is contained in a self-dispersing resin and that dissolves in water when the self-dispersing resin is in a dispersed state. The water-soluble component is a water-soluble compound that is by-produced or mixed in the production of the self-dispersing resin.

  The main chain skeleton of the water-insoluble resin is not particularly limited, and examples thereof include vinyl polymers and condensation polymers (epoxy resins, polyesters, polyurethanes, polyamides, celluloses, polyethers, polyureas, polyimides, polycarbonates, etc.). Of these, vinyl polymers are particularly preferable.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  From the viewpoint of self-dispersibility, the self-dispersing resin particles preferably contain a water-insoluble polymer containing a hydrophilic constituent unit and a constituent unit derived from an aromatic group-containing monomer or a cyclic aliphatic group-containing monomer.

The “hydrophilic structural unit” is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and two or more hydrophilic groups may be derived from one hydrophilic group-containing monomer. It may be derived from a functional group-containing monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
The hydrophilic group is preferably a dissociable group and more preferably an anionic dissociative group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

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

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

  The self-dispersing resin particles preferably contain a polymer having a carboxyl group, from the viewpoint of self-dispersibility and the aggregation rate at the time of contact with the processing liquid when forming an image using the processing liquid, and having a carboxyl group, It is more preferable to include a polymer having an acid value of 25 to 100 mgKOH / g. Furthermore, the acid value is more preferably 30 to 90 mgKOH / g, and particularly preferably 35 to 65 mgKOH / g, from the viewpoints of self-dispersibility and aggregation rate when the treatment liquid comes into contact. In particular, when the acid value is 25 mgKOH / g or more, the stability of self-dispersibility is good, and when it is 100 mgKOH / g or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
Further, the polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer in the present invention is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixability, and include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth). At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

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

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

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

  Among these, from the viewpoints of dispersion stability, fixing property, and blocking resistance of the self-dispersing resin particles, at least one bicyclic (meth) acrylate or a tricyclic or higher polycyclic (meth) acrylate is used. Preferably, it is at least one selected from isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate.

The self-dispersing resin is preferably an acrylic resin containing a structural unit derived from a (meth) acrylate monomer, and an acrylic resin containing a structural unit derived from an aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate. A resin is preferable, and further, it includes a structural unit derived from an aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate, and the content is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate is 10% by mass to 95% by mass, self-emulsification or dispersion stability is improved, and ink viscosity is further increased Can be suppressed.
From the viewpoints of stability in a self-dispersing state, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings, and reduction in the amount of water-soluble components due to appropriate hydrophobicity of particles, 15% by mass to 90% by mass. %, More preferably 15% by mass to 80% by mass, and particularly preferably 25% by mass to 70% by mass.

  The self-dispersing resin includes, for example, a structural unit derived from an aromatic group-containing monomer or a cycloaliphatic group-containing monomer (preferably an alicyclic (meth) acrylate) and a structural unit derived from a dissociable group-containing monomer. Can be configured. Furthermore, other structural units may be further included as necessary.

The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylic ester monomers such as ethylenically unsaturated monomers having a hydroxyl group such as t-butyl (meth) acrylate and dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate; N-hydroxymethyl N-hydroxyalkyl (meth) acrylamides such as (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide, and N-methoxymethyl (meth) acrylami N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N- (n-, iso And (meth) acrylamide monomers such as (meth) acrylamide such as N-alkoxyalkyl (meth) acrylamide such as butoxyethyl (meth) acrylamide.

The molecular weight of the water-insoluble polymer constituting the self-dispersing resin particles is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. Further preferred. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.
The weight average molecular weight is measured by gel permeation chromatography (GPC). The details of GPC are as described above.

The water-insoluble polymer constituting the self-dispersing resin particles is derived from a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably phenoxyethyl (meth) acrylate) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. A structural unit and / or a structural unit derived from benzyl (meth) acrylate) or a cyclic aliphatic group-containing monomer (preferably alicyclic (meth) acrylate) as a copolymerization ratio of 15 to 15 to the total mass of the self-dispersing resin particles. It is preferable that 80 mass% is included.
In addition, the water-insoluble polymer has a copolymerization ratio of 15 to 80% by mass of a structural unit derived from an aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate, from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. It preferably contains a structural unit derived from a carboxyl group-containing monomer and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and phenoxyethyl (meth) Structural unit derived from acrylate and / or structural unit derived from benzyl (meth) acrylate, structural unit derived from isobornyl (meth) acrylate and / or structural unit derived from adamantyl (meth) acrylate and / or dicyclopenta Structural units derived from nyl (meth) acrylate 15-80 mass% as a polymerization ratio, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid) A structural unit), an acid value of 25 to 100 and a weight average molecular weight of 3000 to 200,000, and an acid value of 30 to 90 and a weight average. More preferably, the molecular weight is 5000-150,000.

  Hereinafter, specific examples of the water-insoluble resin forming the water-insoluble resin particles A will be given. However, the present invention is not limited to these. The values in parentheses represent the mass ratio of the copolymer component.

B-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
B-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
B-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
B-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
B-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
B-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
B-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
B-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
B-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
B-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
B-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
B-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
B-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
B-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)
B-21: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8), glass transition temperature: 180 ° C., I / O value: 0.44
B-22: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (40/52/8), glass transition temperature: 160 ° C., I / O value: 0.50
B-23: Methyl methacrylate / isobornyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/62/10/8), glass transition temperature: 170 ° C., I / O value: 0.44
B-24: Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/72/8), glass transition temperature: 160 ° C., I / O value: 0.47
B-25: Methyl methacrylate / methoxyethyl acrylate / benzyl methacrylate / methacrylic acid copolymer (46/11/35/8)

This water-insoluble resin contains a polymer synthesized in an organic solvent from the viewpoint of aggregation rate, the polymer has a carboxyl group, and the polymer (preferably has an acid value of 25 to 100, more preferably an acid value). Part or all of the carboxyl groups having a valence of 30 to 90, more preferably an acid value of 35 to 65) was neutralized and prepared as a polymer dispersion (dispersion) having water as a continuous phase. It is preferable. That is, the production of water-insoluble resin particles is preferably carried out by providing a step of synthesizing a polymer in an organic solvent and a dispersion step of preparing an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. .
The dispersion step preferably includes the following step (1) and step (2).
-Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium-Step (2): Step of removing the organic solvent from the mixture

  The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. Thus, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing resin having a particle size with higher storage stability without requiring a strong shearing force. Particles can be obtained. There is no restriction | limiting in particular in the stirring method of a mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

  Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents. Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable. It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination for the purpose of moderating the polarity change during the phase inversion from oil to water. By using the solvent in combination, it is possible to obtain self-dispersing resin particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles.

  The neutralizing agent is used so that a part or all of the dissociable groups are neutralized and the polymer forms a stable emulsified or dispersed state in water. When the water-insoluble resin particles have an anionic dissociative group (for example, a carboxyl group) as a dissociable group, examples of the neutralizing agent used include basic compounds such as organic amine compounds, ammonia, and alkali metal hydroxides. . Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolanine, monoisopropanolamine, di Examples include isopropanolamine and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing resin particles of the present invention in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 100 mol% or less.

  In the step (2), the aqueous dispersion of the self-dispersing resin particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and phase-inversion into an aqueous system. A dispersion can be obtained. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The average particle size of the self-dispersing resin particles is preferably 10 nm to 400 nm, more preferably 10 to 200 nm, and still more preferably 10 to 100 nm in terms of volume average particle size. When the volume average particle size is 10 nm or more, the production suitability is improved, and when it is 1 μm or less, the storage stability is improved.
Further, the particle size distribution of the self-dispersing resin particles is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Further, two or more water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the self-dispersing resin particles are measured by the dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). Is required.

  The glass transition temperature (Tg) of the resin particles is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and still more preferably 50 ° C. or higher, from the viewpoint of the storage stability of the ink composition.

  The content of the resin particles in the ink composition is preferably 0.5 to 10% by mass, more preferably 1 to 9% by mass, and further preferably 3 to 9% by mass with respect to the total mass of the ink composition. . When the content of the water-insoluble resin particles is 0.5% by mass or more, the scratch resistance of the image is improved, and when the content is 10% by mass or less, it is advantageous in terms of long-term ejection stability.

(Wax particles)
The ink composition in the present invention contains at least one wax particle. By containing the wax, the scratch resistance can be further improved.

  As wax particles, for example, plant waxes such as carnauba wax, candeli wax, beeswax, rice wax, lanolin, petroleum waxes such as animal wax, paraffin wax, microcrystalline wax, polyethylene wax, oxidized polyethylene wax, petrolatum, Particles of natural wax or synthetic wax such as montan wax, mineral wax such as ozokerite, synthetic wax such as carbon wax, Hoechst wax, polyolefin wax, stearamide, α-olefin / maleic anhydride copolymer, etc. A mixed particle etc. are mentioned.

The wax is preferably added in the form of a dispersion. For example, the wax can be contained in the ink composition as a dispersion such as an emulsion. As a solvent in the case of a dispersion, water is preferable, but it is not limited thereto. For example, a commonly used organic solvent can be appropriately selected and used during dispersion. Regarding the organic solvent, reference can be made to the description of paragraph number [0027] of JP-A-2006-91780.
Wax particles can be used singly or as a mixture of plural kinds.

  As the wax particles, commercially available products may be used. Examples of commercially available products include Nopcoat PEM17 (manufactured by Sannopco), Chemipearl W4005 (manufactured by Mitsui Chemicals), AQUACER 515, AQUACER 593 (all manufactured by Big Chemie Japan Co., Ltd.), Cerosol 524 (Chukyo Yushi Co., Ltd.) Manufactured) and the like.

  Of the above, preferred waxes are carnauba wax and polyolefin wax, and carnauba wax is particularly preferred from the viewpoint of ink stability over time.

  The content ratio of the resin particles to the wax particles is preferably in the range of resin particles: wax particles = 1: 1 to 5: 1 (solid content ratio). When the content ratio is within this range, the image has excellent abrasion resistance.

(1,2-alkylenediol)
The ink composition in the invention contains at least one 1,2-alkylenediol. 1,2-Alkyldiol is contained together with an acetylene glycol-based surfactant described later, and has the effect of synergistically improving the wettability of the ink composition with respect to the recording medium. Enhanced.

  Examples of the 1,2-alkyldiol include 1,2-alkyldiols having 4 to 8 carbon atoms such as butanediol, pentanediol, hexanediol, heptanediol, and octanediol. Among these, 1,2-alkyldiols having 6 to 8 carbon atoms such as 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol are preferable. When the number of carbon atoms is 4 or more, the wettability with respect to the recording medium is improved, and the occurrence of uneven density and blurring in the image is further suppressed. Further, when the number of carbon atoms is 8 or less, water solubility is maintained, and a necessary amount can be added without impairing the storage stability of the ink.

  The content of the 1,2-alkyldiol in the ink composition is preferably 1 to 8% by mass and more preferably 1.5 to 5.0% by mass with respect to the total mass of the ink composition. When the content of 1,2-alkyldiol is 1% by mass or more, the wettability of the ink composition with respect to the recording medium is good, and an image with little occurrence of density unevenness and bleeding is obtained. Further, when the content of 1,2-alkyldiols is 8% by mass or less, it is difficult for the residue to remain after drying, which is advantageous for ensuring the drying property. Moreover, it is advantageous also in terms of suppressing odor.

(Polyhydric alcohol)
The ink composition in the present invention contains at least one polyhydric alcohol. The polyhydric alcohol suppresses drying and solidification of ink at the nozzle portion of the ejection head, and prevents clogging of the ink, bending in the ejection direction, ejection failure, and the like.

In the present invention, a polyhydric alcohol having a high vapor pressure is preferable in that it can be easily removed by evaporation together with moisture during drying.
Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, trimethylolpropane, glycerin and the like. Among these, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, trimethylolpropane, and glycerin are preferable because they have a high vapor pressure and do not impair the drying property after droplet ejection.

  The content of the polyhydric alcohol in the ink composition is preferably 2 to 20% by mass and more preferably 10 to 19% by mass with respect to the total mass of the ink composition. When the content of the polyhydric alcohol is 2% by mass or more, drying and solidification of the ink can be suppressed, ink clogging, ejection direction bending, ejection failure, and the like can be prevented, and the content is 20% by mass or less. The polyhydric alcohol hardly remains after drying, which is advantageous for ensuring the drying property. Moreover, it is advantageous also in terms of suppressing odor.

(Pyrrolidone derivative)
The ink composition in the invention contains at least one pyrrolidone derivative. The pyrrolidone derivative has a function of accelerating the formation of a film with resin particles when the ink is dried, and promoting the solidification and fixing of the ink on the recording medium. For example, in a usage pattern in which ink ejection and ejection pause are repeated, ink ejection bends and non-ejections are suppressed, and ink ejection properties, and thus the desired high-definition image formability, are stabilized.

  Examples of pyrrolidone derivatives include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-pyrrolidone, N-butyl-2-pyrrolidone, and 5-methyl. -2-pyrrolidone, polyvinylpyrrolidone, and the like. Among these, 2-pyrrolidone and polyvinyl pyrrolidone are preferable from the viewpoints of ensuring the storage stability of the ink composition, promoting film formation by the resin particles, and reducing odor.

  The content of the pyrrolidone derivative in the ink composition is preferably 1 to 8% by mass and more preferably 2 to 4% by mass with respect to the total mass of the ink composition. When the content of the pyrrolidone derivative is 1% by mass or more, the film formation by the resin particles in the ink composition is excellent, and the solidification and fixing of the ink are improved. Further, when the content of the pyrrolidone derivative is 8% by mass or less, the pyrrolidone derivative does not easily remain after drying, which is advantageous for ensuring the drying property. Moreover, it is advantageous also in terms of suppressing odor.

  The total amount of the pyrrolidone derivative and the 1,2-alkyldiol is preferably 10% by mass or less with respect to the total mass of the ink composition. When the total amount is 10% by mass or less, the pyrrolidone derivative and the 1,2-alkyldiol hardly remain after drying, which is advantageous for ensuring the drying property. Moreover, it is advantageous also in terms of suppressing odor.

(Acetylene glycol surfactant)
The ink composition in the present invention contains at least one acetylene glycol surfactant. The acetylene glycol-based surfactant is easy to keep the surface tension and the interfacial tension between the printer member (head nozzle and the like) in contact with the ink and foam less easily than other surfactants. Therefore, the ejection stability when ejecting the ink composition is improved. In addition, the inclusion of an acetylene glycol surfactant improves the wettability and penetrability of the recording medium, suppresses unevenness of ink density and ink bleeding, and is advantageous for fine image formation.

  Examples of the acetylene glycol surfactant include Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 104S, 420, 440, 465, 485, SE, SE-F, 504, 61, DF37, CT111, CT121, CT131, CT136, TG, GA (all of which are Air Products and Chemicals. Inc. Orphine B, Y, P, A, STG, SPC, E1004, E1010, PD-001, PD-002W, PD-003, PD-004, EXP. 4001, the same EXP. 4036, EXP. 4051, AF-103, AF-104, AK-02, SK-14, AE-3 (all of which are manufactured by Nissin Chemical Industry Co., Ltd.), acetylenol E00, E00P, E40, E100 (all of which are manufactured by Kawaken Fine Chemical Co., Ltd.) and the like.

  The content of the acetylene surfactant in the ink composition is preferably from 0.1 to 1.5% by mass, more preferably from 0.5 to 1.0% by mass, based on the total mass of the ink composition. When the content of the acetylene glycol surfactant is 0.1% by mass or more, the ink tends to spread uniformly on the recording medium, and a uniform image can be obtained while suppressing unevenness in density and bleeding of the ink. Further, when the content of the acetylene glycol surfactant is 1.5% by mass or less, the ink composition is excellent in storage stability and ejection stability.

(water)
The ink composition in the present invention contains water, but the amount of water is not particularly limited. Among them, the amount of water is preferably 10% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 80% by mass with respect to the total mass of the ink composition from the viewpoint of ensuring stability and ejection reliability. % Or less, and more preferably 50% by mass or more and 70% by mass or less.

  The water is preferably water from which ionic impurities such as pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water or ultrapure water are removed as much as possible. Further, when water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, it is preferable in terms of preventing generation of mold and bacteria when the pigment dispersion and the ink composition using the same are stored for a long period of time. .

(Other ingredients)
In addition to the above-described components, the ink composition in the present invention includes additives such as a penetrating solvent, a humectant, an antiseptic / antifungal agent, a pH adjuster, and a chelating agent as necessary. Can be contained. For details of these additives, reference can be made to the descriptions of [0067] to [0076] of JP 2010-90266 A.

(recoding media)
The recording medium used in the image forming method of the present invention is not particularly limited, but the effect of the present invention is more effective when a non-absorbing or low-absorbing recording medium is used for the ink composition. Played.

A preferable recording medium in the present invention is a recording medium having a coating layer and an area of 1250 cm ² or more. The recording medium having a coating layer is so-called coated paper used for general offset printing and the like. 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.
Note that the area is 1250 cm ² or more, which shows a case applied amount of ink applied during the image formation is relatively large, it tends to become insufficient drying in the case of 1250 cm ² or more, the abrasion resistance And the effect of preventing the occurrence of image defects is great.

The recording medium preferably has a coating layer of 12 g / m ² or more on both sides, more preferably 18 g / m ² or more. The coated layer having a coating layer of 12 g / m ² or more on both sides is a coated paper used for general offset printing. When the coating layer is within the above range, the ink absorption amount is large, and the effect exhibited in the present invention is large.
The basis weight of the recording medium is preferably 70 to 350 g / m ² , more preferably 70 to 200 g / m ² . The coated paper used for general offset printing has a basis weight within this range. When the basis weight is within the above range, the ink absorption amount is large, and the effect exhibited in the present invention is large.

  In the case of conventional paper-based image formation by water-based inkjet, the coated paper has a slow ink absorption, and in the case of forming an image on both sides at a high speed, the absorption and drying of the ink cannot catch up. In an image forming system in which sheets are stacked and stacked, image defects such as scratches and peeling easily occur due to rubbing or scratching between recording media. In the image forming method of the present invention, excellent abrasion resistance is obtained. And a high quality image with few image defects can be formed.

  Among the above, coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate is particularly preferable. More specifically, the coated paper is more preferably art paper, coated paper, lightweight coated paper, or fine coated paper.

  The coated paper can be obtained and used on the market. For example, coated paper for general printing can be used. Specifically, fine coated paper such as “OK Everlight Coat” manufactured by Oji Paper Co., Ltd. and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd. Lightweight coated paper (A3) such as “OK Coat L” manufactured by Oji Paper Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. “OK Top Coat +” manufactured by Oji Paper Co., Ltd., Nippon Paper Industries Co., Ltd. Coated paper (A2, B2) such as “Aurora Coat” and “Ulite” manufactured by Co., Ltd., Art paper (A1) such as “Tokuhishi Art” manufactured by Mitsubishi Paper Industries, and Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. can be mentioned.

Among them, from the viewpoint of obtaining a high-quality image having a large color material movement suppression effect and better color density and hue than conventional, the water absorption coefficient Ka is 0.05 to 0.5 and mL / m ^2. A recording medium of ms ^1/2 is preferable, a recording medium of 0.1 to 0.4 mL / m ² · ms ^1/2 is more preferable, and a recording medium of 0.2 to 0.3 mL / m ² · ms ¹ is more preferable. ^{/ 2} recording medium.

  The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI paper pulp test method No. 51: 2000 (issued by Japan Paper Pulp Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning absorption meter. It is calculated from the difference in the amount of water transferred between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co., Ltd.).

-Drying process-
In the drying process of the present invention, the recording medium to which ink has been applied in the ink application process is dried. The liquid medium contained in the ink composition attached on the recording medium, specifically, water, pyrrolidone derivative, 1,2-alkyldiol, and polyhydric alcohol are evaporated and scattered to form a colored resin film. It is formed. As a result, a high-quality image with few image defects such as scratches and peeling can be formed at high speed on the recording medium and on the recording medium that is non-absorbing or low-absorbing with respect to the ink composition.

  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. As a heating method, you may heat combining these two or more.

  There is no restriction | limiting in particular as temperature at the time of heat drying, What is necessary is just to select the temperature range which can be dried. For example, the recording medium may be heated so that the temperature of the recording medium is 45 to 70 ° C. by air blowing, or may be dried so that the temperature of the recording medium is 45 to 70 ° C. by contacting with a drying drum of 45 to 70 ° C. . These may be used in combination and dried.

~ Cooling process ~
In the image forming method of the present invention, a cooling step may be provided in which the recording medium is preliminarily cooled after being once heated and dried in the drying step. In the cooling step, it is preferable to cool the temperature of the recording medium after drying to 35 ° C. or lower.

  The temperature of the recording medium is a value [° C.] measured as the temperature at the time when the recording medium is collected after being cooled and dried (immediately after the accumulation). By cooling to a temperature range of preferably 35 ° C. or less in the accumulation stage, it is possible to improve the abrasion resistance when the accumulation state is achieved. The temperature of the recording medium is measured at the time of accumulation (immediately after the accumulation) by an inter-sheet temperature / humidity meter (HYGROPALM, manufactured by Rotronic) arranged between the desired recording media.

  The temperature after cooling is preferably 35 ° C. or lower, and preferably 30 ° C. or lower from the viewpoint of preventing scratches and peeling. There is no particular limitation on the lower limit of the temperature after cooling.

  As a cooling method, any method may be used as long as it is a cooling step capable of actively lowering the temperature of the recording medium. Examples of the cooling method include a method of passing a recording medium through a cooling zone, a method of applying cold air to the recording medium, and a method of bringing the recording medium into contact with a cooled object.

-Treatment liquid application process-
In addition to the above steps, the image forming method of the present invention preferably further comprises a treatment liquid application step for applying a treatment liquid containing an aggregation component for aggregating the components in the ink composition described above to the recording medium. Is done.

  The treatment liquid is a liquid that aggregates components in the ink composition when in contact with the ink composition to form an aggregate. In the present invention, the ink composition may be discharged after the treatment liquid is applied in advance, or the treatment liquid may be applied after the ink composition is first applied. When the treatment liquid is applied onto the recording medium so as to come into contact with the ink composition, and when the treatment liquid comes into contact with the ink composition, dispersed particles such as resin particles and pigment in the ink composition are aggregated on the recording medium. The image is fixed. As a result, the speed of ink-jet recording is further increased, and an image excellent in drawability (for example, reproducibility of fine lines and fine portions) with high density and resolution can be obtained even at high speed recording.

The treatment liquid can be applied by applying a known method such as a coating method, an ink jet method, or an immersion method. Examples of the coating method include known coating methods using a bar coater, an extrusion die coater, an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, and the like. The details of the ink jet method are as described above.
In the present invention, from the viewpoint of keeping the amount of treatment liquid applied low, it is preferable to use an ejection method by an inkjet method.

The treatment liquid contains at least one aggregation component that forms an aggregate by aggregating components in the ink composition when in contact with the ink composition. By mixing the treatment liquid with the ink composition, aggregation of pigments and the like stably dispersed in the ink composition is promoted. Examples of such a treatment liquid include a liquid capable of generating an aggregate by changing the pH of the ink composition. At this time, the pH (25 ° C. ± 1 ° C.) of the treatment liquid is preferably 6 or less, more preferably 1 to 6, further preferably 1.2 to 5, particularly preferably from the viewpoint of the aggregation rate of the ink composition. 1.5-4. In this case, the pH (25 ± 1 ° C.) of the ink composition is preferably 7.5 to 9.5 (more preferably 8.0 to 9.0).
Among them, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ± 1 ° C.) of the ink composition is 7.5 or more, and the pH (25 ± 1 ° C.) of the treatment liquid is 1. The case of 5-3 is preferable.
The aggregating components can be used alone or in combination of two or more.

  The treatment liquid can be suitably configured using at least one acidic compound as an aggregation component. As the acidic compound, a compound having a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxyl group, or a salt thereof (for example, a polyvalent metal salt) may be used. it can. Among these, from the viewpoint of the aggregation rate of the ink composition, a compound having a phosphate group or a carboxyl group is more preferable, and a compound having a carboxyl group is more preferable.

  Examples of the compound having a carboxyl group include 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, and 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 (for example, polyvalent metals) Salt) and the like.

  Moreover, as a process liquid, you may use the liquid containing a polyvalent metal salt and / or polyallylamine as an aggregation component, and can improve a high-speed aggregation property. Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and cations from Group 13 of the periodic table. (For example, aluminum), salts of lanthanides (for example, neodymium), polyallylamine, and polyallylamine derivatives. As the metal salt, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.

  The content of the polyvalent metal salt and / or polyallylamine in the treatment liquid is preferably 1 to 10% by mass, more preferably 1.5 to 7% by mass, and still more preferably 2 from the viewpoint of the aggregation effect. It is in the range of ˜6% by mass.

The treatment liquid may be a liquid containing a cationic organic compound as an aggregating component. Examples of the cationic organic compound include poly (vinyl pyridine) salt, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide, polyguanide, and polyallylamine and derivatives thereof. Mention may be made of cationic polymers.
The weight average molecular weight of the cationic polymer is preferably smaller in terms of the viscosity of the treatment liquid. When the treatment liquid is applied to the recording medium by an ink jet method, a range of 1,000 to 500,000 is preferable, a range of 1,500 to 200,000 is more preferable, and a range of 2,000 to 100,000 is more preferable. Range. When the weight average molecular weight is 1000 or more, it is advantageous from the viewpoint of the aggregation rate, and when it is 500,000 or less, it is advantageous from the viewpoint of ejection reliability. However, this is not the case when the treatment liquid is applied to the recording medium by a method other than inkjet.

As the cationic organic compound, for example, a primary, secondary, or tertiary amine salt type compound is preferable. Examples of the amine salt type compounds include compounds such as hydrochloride or acetate (for example, laurylamine, cocoamine, stearylamine, rosinamine), quaternary ammonium salt type compounds (for example, lauryltrimethylammonium chloride, cetyltrimethyl). Ammonium chloride, lauryldimethylbenzylammonium chloride, benzyltributylammonium chloride, benzalkonium chloride, etc.), pyridinium salt type compounds (eg cetylpyridinium chloride, cetylpyridinium bromide etc.), imidazoline type cationic compounds (eg 2-heptadecenyl- Hydroxyethyl imidazoline etc.), ethylene oxide adducts of higher alkylamines (eg dihydroxyethyl stearylamine etc.), etc. And cationic compounds, for example, amino acid type amphoteric _{surfactants, R-NH-CH 2 CH} 2 -COOH type compounds (R represents an alkyl group.), Carboxylic acid salt type amphoteric surfactants (e.g. , Stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, and the like), amphoteric surfactants such as sulfate ester type, sulfonic acid type, and phosphate ester type amphoteric surfactants exhibiting a cationic property in a desired pH range. . Of these, divalent or higher cationic organic compounds are preferred.

  When the cationic organic compound is used, the content of the cationic organic compound in the treatment liquid is preferably 1 to 50% by mass, more preferably 2 to 30% by mass from the viewpoint of the aggregation effect.

  Among the above, the aggregating component is preferably a divalent or higher carboxylic acid or a divalent or higher cationic organic compound, and more preferably a divalent or higher carboxylic acid in terms of aggregability and image scratch resistance.

The viscosity of the treatment liquid is preferably in the range of 1 to 30 mPa · s, more preferably in the range of 1 to 20 mPa · s, still more preferably in the range of 2 to 15 mPa · s, from the viewpoint of the aggregation rate of the ink composition. The range of 10 mPa · s is particularly preferable. The viscosity is measured under the condition of 20 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO.LTD).
The surface tension of the treatment liquid is preferably in the range of 20 to 60 mN / m, more preferably in the range of 20 to 45 mN / m, and further in the range of 25 to 40 mN / m from the viewpoint of the aggregation rate of the ink composition. preferable. The surface tension is measured at 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

The amount of the treatment liquid applied to the recording medium is not particularly limited as long as the components in the ink composition can be aggregated, but preferably the aggregation component (for example, a compound having a carboxyl group or a cationic organic compound) is imparted. The amount can be set to an amount of 0.1 g / m ² or more. Especially, the quantity from which the provision amount of an aggregation component will be 0.1-1.0 g / m < ² > is preferable, More preferably, it is 0.2-0.8 g / m < ² >. When the amount of the aggregating component applied is 0.1 g / m ² or more, the aggregating reaction proceeds well. Moreover, the glossiness of the grade which is not too high is acquired by making application amount into 1.0 g / m < ² > or less.

  When the treatment liquid is applied on the recording medium in advance before the ink application step, the treatment liquid on the recording medium is heated and dried after the treatment liquid is applied and before the ink composition is applied in the ink application step. It is preferable that a heat drying step is further provided. If the treatment liquid is heated and dried in advance before the ink application step, the fineness of the image such as prevention of bleeding is increased, and a visible image having a good color density and hue can be obtained.

  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.

-Heat fixing process-
In the present invention, it is preferable to further provide a heat fixing step for heat fixing the ink on the recording medium after the ink application step, if necessary. In the heat fixing step, the image recorded by applying the ink composition or the treatment liquid and the ink composition is heated and fixed on the recording medium. By performing the heat fixing process, the image on the recording medium is fixed, and the scratch resistance of the image can be further improved. Therefore, it is preferable to provide a heat fixing step in the image forming method of the present invention.

  Heating is preferably performed at a temperature equal to or higher than the minimum film-forming temperature (MFT) of the resin particles in the image. By heating to MFT or higher, the particles become a film and the image is enhanced. You may pressurize with heating. When heating is performed under pressure, the pressure during pressurization is preferably in the range of 0.1 to 3.0 MPa, more preferably in the range of 0.1 to 1.0 MPa, in terms of surface smoothing. Preferably it is the range of 0.1-0.5 MPa.

  The heating method is not particularly limited, but a non-contact drying method such as a method of heating with a heating element such as a nichrome wire heater, a method of supplying warm air or hot air, a method of heating with a halogen lamp, an infrared lamp or the like. Preferably, it can be mentioned. The heating and pressing method is not particularly limited. For example, a method of pressing a hot plate against the image forming surface of a recording medium, a pair of heating and pressing rollers, a pair of heating and pressing belts, or a recording medium Using a heating and pressing device equipped with a heating and pressing belt arranged on the image recording surface side and a holding roller arranged on the opposite side, heat fixing by bringing them into contact, such as a method of passing a pair of rollers, etc. The method of performing is mentioned suitably.

  In the case of heating and pressing, a preferable nip time is 1 to 10 seconds, more preferably 2 to 1 second, and further preferably 4 to 100 milliseconds. Moreover, a preferable nip width is 0.1 mm to 100 mm, more preferably 0.5 mm to 50 mm, and still more preferably 1 mm to 10 mm.

  As the heating and pressing roller, a metal metal roller, or a coating layer made of an elastic body and a surface layer (also referred to as a release layer) as necessary around a metal cored bar is provided. But you can. The latter metal core can be formed of, for example, a cylindrical body made of iron, aluminum, SUS, or the like, and the surface of the metal core is preferably at least partially covered with a coating layer. The coating layer is particularly preferably formed of a silicone resin or fluororesin having releasability. Further, it is preferable that a heating element is built in one core metal of the heat and pressure roller, and heat treatment and pressure treatment are performed simultaneously or necessary by passing a recording medium between the rollers. Accordingly, the recording medium may be sandwiched and heated using two heating rollers. As the heating element, for example, a halogen lamp heater, a ceramic heater, a nichrome wire or the like is preferable.

  As a belt base material constituting the heat and pressure belt used in the heat and pressure apparatus, seamless nickel brass is preferable, and the thickness of the base material is preferably 10 to 100 μm. Further, as the material of the belt base material, aluminum, iron, polyethylene or the like can be used in addition to nickel. When silicone resin or fluororesin is provided, the thickness of the layer formed using these resins is preferably 1 to 50 μm, more preferably 10 to 30 μm.

  Further, in order to realize the pressure (nip pressure), for example, an elastic member such as a spring having tension so that a desired nip pressure can be obtained in consideration of the nip gap at both ends of a roller such as a heat and pressure roller. Select and install.

  The conveyance speed of the recording medium when using a heat and pressure roller or a heat and pressure belt is preferably 200 to 700 mm / second, more preferably 300 to 650 mm / second, and still more preferably 400 to 600 mm / second. .

-Accumulation process-
In the collecting step in the present invention, the recording medium after drying in the drying step is provided with a step of attaching 1 to 1000 mg / m ² of a powdery substance having a particle diameter of 1 to 100 μm to the recording medium, and the powdery substance is attached. The recorded recording media are stacked and accumulated.

  The recording medium is collected by stacking sheet-like recording media in an arbitrary stacking portion and collecting them in a bundle. The recording media are collected by freely falling within an area corresponding to the planar size of the recording medium. In the present invention, it is possible to prevent the occurrence of image defects such as scratches and peeling on the image, which are likely to occur when the number of recording media stacked in this way becomes, for example, 50 or more.

  As the stacking means, those similar to the stacking means such as a discharge tool, a discharge port, and a paper stack provided in a conventionally used inkjet image forming apparatus can be used. For example, when a powdery material is attached to the recording medium, the recording medium to which the powdery material is attached is discharged from the discharge port of the apparatus and stacked on a paper stack.

The particle size of the powder is preferably 1 to 100 μm. When the particle diameter is within the above range, the abrasion resistance of the image on the recording medium is improved, and the occurrence of image defects such as scratches and peeling in the image is suppressed. If the particle size of the powdery material is too large, the roughness of the image and the stains due to the powdery material in the machine cannot be ignored, and if the particle size is too small, the effect of improving the rub resistance decreases. For this reason, from the viewpoint of enhancing the abrasion resistance of the image and more effectively preventing the occurrence of image defects, the particle diameter is preferably 5 to 50 μm, more preferably 10 to 40 μm, and more preferably 15 to 35 μm.
In the present invention, “particle diameter” refers to a volume average particle diameter.

In addition, the amount of powder attached to the recording medium is 1-1000 mg / m ² . When the adhesion amount is within the above range, the abrasion resistance of the image on the recording medium is improved, and the occurrence of image defects such as scratches and peeling in the image is suppressed. From the viewpoint of preventing the occurrence of a more enhanced the image defect abrasion resistance of the image more effectively, the accumulation amount is preferably from 1-500 mg / ^{m 2,} more preferably 10-100 mg / ^{m 2,} 20 to 100 mg / M ² is more preferable.

  As the means for applying the powdery material, a member similar to a powder spray nozzle or the like conventionally used as a powder applying means for preventing blocking in the printing field can be used. Further, either a blower type or an electronic spray type may be used.

  The powder particles may be either inorganic particles or organic particles. Moreover, the antiblocking powder conventionally used in the printing field can also be used.

  Examples of powders include particles of a material selected from the group consisting of starch coated with silicone resin, silica (silicon dioxide), acrylic resin, styrene resin, silicone resin, and metal oxide (hereinafter referred to as powder) Also referred to as particles).

Examples of the acrylic resin include polymethyl acrylate and polymethyl methacrylate (PMMA).
Examples of the styrenic resin include polystyrene.
Examples of the metal oxide include titanium oxide, magnesium oxide, and aluminum oxide.

  Ink compositions used for ink jet recording have a higher water content than printing inks used in the normal printing field, so that powder particles are hydrophobic in order to improve abrasion resistance and prevent image defects from occurring in images. Is preferable. For example, a powder subjected to hydrophobic treatment such as starch coated with a silicone resin is more preferable.

  The image forming method of the present invention can be suitably performed using, for example, an ink jet recording apparatus (image forming apparatus) configured as shown in FIG. FIG. 1 is a schematic configuration diagram showing an example of an ink jet recording apparatus for carrying out the image forming method of the present invention.

  As shown in FIG. 1, the ink jet recording apparatus 100 records processing liquid in order from the upstream side in the conveyance direction (arrow direction) of the recording medium 1 along the conveyance path in which the recording medium 1 is conveyed by the conveyance belt 2. A processing liquid discharge head (processing liquid applying means) 31 for discharging onto the medium, an ink discharging head (ink applying means) 32 for discharging ink, and a heating and drying means 4 for heating and drying the ink image formed by discharge; As a fixing unit for fixing the image by heating and pressing the dried ink image, a pair of fixing rolls including a heating roll 5 and a pressure roll 6, a cooling unit 7 for cooling the fixed image, and an image were formed. A powder sprayer (powder applying means) 8 for attaching powder (powder) to a recording medium, and an accumulation tray (stacking means) for accumulating and accumulating the recording medium to which the powder is adhered And a 9.

  When the recording medium 1 is fed into the conveyance path of the image forming apparatus 100 by the conveyance belt 2, the treatment liquid is applied in advance to the recording medium 1 from the treatment liquid discharge head 31, which is a treatment liquid application unit, before the ink is applied. As the treatment liquid applying means, an ink jet nozzle, a roller or the like can be used. Thereafter, an ink composition is ejected toward the treatment liquid application surface of the recording medium 1 from an ink ejection head 32 which is an example of an ink application unit such as an inkjet nozzle, and an image is formed with the ink ejected on the recording medium. . A recording medium (printed material) 1 on which an image is formed is heat-dried by a heat dryer 4 provided with a hot air jet nozzle such as a dryer and a heater such as an IR heater, and a pair of fixing rolls arranged as fixing means. It is conveyed to. The fixing means is provided with a thermocompression roller in which the heating roller 5 and the pressure roller 6 are pressed against each other, and the conveyed printed material passes between the heating roller 5 and the pressure roller 6. The image formed on the recording medium 1 is fixed by being thermocompression bonded when passing. Next, the recording medium 1 is cooled by a blower (cooling means) 7 and cooled to a temperature lower by, for example, 5 ° C. or less than immediately after the heat drying step in the heat dryer 4. In the subsequent collecting step, after powder is applied from the powder sprayer (powder applying means) 8 to the image forming surface of the recording medium, the recording medium 1 to which the powder adheres is discharged from the discharge port, and the collecting means 9 such as a collecting tray. Are stacked and accumulated.

  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” is based on mass.

The weight average molecular weight is a molecular weight measured by gel permeation chromatography (GPC) and expressed in terms of polystyrene. GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and as a column, TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, TSKgeL SuperHZ2000 (both trade names made by Tosoh Corporation) are connected in series. THF (tetrahydrofuran) was used as an eluent.
Moreover, the acid value was calculated | required by the method prescribed | regulated to a JIS specification (JISK0070: 1992).

Example 1
<Preparation of polymer particles>
-Preparation of aqueous dispersion of self-dispersing polymer particles B-01-
In a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 560.0 g of methyl ethyl ketone was charged and heated to 87 ° C. While maintaining the reflux state in the reaction vessel (hereinafter referred to as reflux until completion of the reaction), 266.8 g of methyl methacrylate, 63.8 g of methoxyethyl acrylate, 203 g of benzyl methacrylate, 46.4 g of methacrylic acid, and “V— A mixed solution composed of 2.32 g of “601” (manufactured by Wako Pure Chemical Industries, Ltd.) was dropped at a constant speed so that the dropping was completed in 2 hours. After completion of dropping, the mixture was stirred for 1 hour. Thereafter, a solution consisting of 1.16 g of V-601 and 6.4 g of methyl ethyl ketone was added and stirred for 2 hours (step (1)). Subsequently, this step (1) was repeated four times, and a solution consisting of 1.16 g of V-601 and 6.4 g of methyl ethyl ketone was added, and stirring was continued for 3 hours. After completion of the polymerization reaction, the temperature of the solution was lowered to 65 ° C., 163.0 g of isopropanol was added and the mixture was allowed to cool, and a copolymer (methyl methacrylate / methoxyethyl acrylate / benzyl methacrylate / methacrylic acid = 46/11/35). / 8) resin solution was obtained. The weight average molecular weight (Mw) of the obtained copolymer was 63000, and the acid value was 65.1 mgKOH / g.

  Next, 317.3 g (solid content concentration: 41.0% by mass) of the obtained resin solution was weighed, and 46.4 g of isopropanol, 1.65 g of a 20% by mass maleic anhydride aqueous solution (water-soluble acidic compound; copolymer) On the other hand, maleic acid (corresponding to 0.3% by mass) and 2 mol / L NaOH aqueous solution 40.77 g were added, and the temperature in the reaction vessel was raised to 70 ° C. Next, 380 g of distilled water was added dropwise at a rate of 10 ml / min to disperse in water. Thereafter, the pressure in the reaction vessel was kept at 70 ° C. under reduced pressure for 1.5 hours, and 287.0 g of isopropanol, methyl ethyl ketone, and distilled water were distilled off in total, and Proxel GXL (S) (manufactured by Arch Chemicals Japan Co., Ltd.) ) 0.278 g (440 ppm as benzoisothiazolin-3-one with respect to resin solids) was added. Thereafter, filtration was performed with a 1 μm filter, and the filtrate was collected to obtain an aqueous dispersion of self-dispersing polymer particles B-01 having a solid content concentration of 26.5%.

<Preparation of pigment dispersion>
~ Synthesis of resin dispersant P-1 ~
To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. To this, 50 g of methyl ethyl ketone was added with 0.85 g of dimethyl-2,2′-azobisisobutyrate and phenoxy. A solution in which 50 g of ethyl methacrylate, 11 g of methacrylic acid, and 39 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution obtained by dissolving 0.42 g of dimethyl-2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone (MEK) was added, heated to 78 ° C. and heated for 4 hours. . MEK was added to the resulting reaction solution, and phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid (copolymerization ratio [mass ratio] = 50/39/11) copolymer (resin dispersant P-1) 40% by mass of MEK. A solution was obtained.
The composition of the obtained resin dispersant P-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 49400. Furthermore, when the acid value of this copolymer was determined by the method described in JIS standard (JIS K 0070: 1992), it was 71.7 mgKOH / g.

-Preparation of black pigment dispersion K-
Carbon black (# 2600, manufactured by Mitsubishi Chemical Corporation) as a pigment, 57 g of phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid copolymer (resin dispersant P-1) as solids, and 155.8 g of methyl ethyl ketone As a pH adjuster, 80.8 g of 1 mol / L sodium hydroxide (degree of neutralization with respect to methacrylic acid 110 mol%) and 491 g of ion-exchanged water were predispersed with a disper, and 0.1 mmφ zirconia beads were further dispersed with a bead mill disperser. Used to disperse. After dispersion, the mixture was filtered through a filter having a pore size of 1 μm, and the filtrate was recovered. Thereafter, the pigment concentration was determined from the absorbance spectrum, and a dispersion (black pigment dispersion K) of resin-coated pigment particles having a pigment concentration of 15% was obtained.

-Preparation of Cyan Pigment Dispersion C-
A cyan pigment dispersion C was obtained in the same manner as the black pigment dispersion K, except that in the preparation of the black pigment dispersion K, the pigment was changed from carbon black to pigment blue 15: 3 (PB15: 3). .

-Preparation of magenta pigment dispersion M-
A magenta pigment dispersion M was obtained in the same manner as the black pigment dispersion K except that the pigment was changed from carbon black to pigment red 122 (PR122) in the preparation of the black pigment dispersion K.

-Preparation of yellow pigment dispersion Y-
A yellow pigment dispersion Y was obtained in the same manner as the black pigment dispersion K, except that the pigment was changed from carbon black to pigment yellow 74 (PY74) in the preparation of the black pigment dispersion K.

<Ink composition>
Each component was mixed so as to have the ink composition shown in Table 1 below. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to prepare each color ink (ink composition).

<Preparation of treatment liquid>
Various components having the following composition were mixed to prepare a treatment liquid. The pH of the treatment liquid was 1.0.
<Composition of treatment liquid>
-Malonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) ... 11% by mass
・ DL-malic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) ... 15% by mass
・ Diethylene glycol monobutyl ether (Wako Pure Chemical Industries, Ltd.) 4% by mass
・ Tripropylene glycol monomethyl ether: 4% by mass
(Wako Pure Chemical Industries, Ltd.)
・ Ion exchange water: 66% by mass

<Image formation and evaluation>
~ Image formation ~
An ink jet recording apparatus shown in FIG. 1 is prepared, and on the transport belt 2, as a recording medium 1, Tokuhishi art double-sided N (area 2982 cm ² (Chrysanthemum size), basis weight 104.7 g / m ² , manufactured by Mitsubishi Paper Industries Co., Ltd.) Supplied. Here, in the ink jet recording apparatus 100, the ink storage tank (not shown) communicated with the cyan, magenta, yellow, and black ejection heads 32 is sequentially filled with the ink, and the ink is not communicated with the processing liquid ejection head 31. The illustrated treatment liquid storage tank was filled with treatment liquid.

First, the treatment liquid is applied from the treatment liquid discharge head 31 to the recording medium (special art double-sided N) 1 conveyed by the conveyance belt 2 at a conveyance speed of 250 mm / sec, and then the recording medium 1 to which the treatment liquid is applied. Was dried by a hot air jet nozzle (not shown) (blowed at 70 ° C. hot air 9 m ³ / min) and an IR heater (180 ° C.) 4 to dry a part of the solvent in the treatment liquid.

Thereafter, ink of each color was ejected from the ink ejection head 32 onto the treatment liquid application surface of the recording medium 1 at 600 dpi × 1200 dpi × 2 pL to form a solid gray image on the recording medium 1. A recording medium (printed material) 1 on which an image has been formed is heated and dried at 60 ° C. after being heated and dried with a dryer, and then passed between fixing rollers composed of a heating roller 5 and a pressure roller 6 that are in pressure contact with each other. This fixed the image. Further, the recording medium 1 was blown with a blower (cooling means) 7 to be cooled to a temperature 20 ° C. lower than the fixing temperature and accumulated. At the time of accumulation, starch (manufactured by Toho Seiki Co., Ltd., trade name: crown, particle size 23 μm) as powder was sprayed and adhered from the powder sprayer 8 to the image forming surface of the recording medium 1. Thereafter, the recording medium 1 to which the powder adhered was discharged from the discharge port, and 1000 sheets were stacked. At this time, the kind of powder or the applied amount on the image forming surface of the recording medium was changed as shown in Table 1 below.
Next, it was stored for 2 hours under an environmental condition of 25 ° C. and 60% RH in a state where 1000 sheets were stacked, and an image was formed on the back surface by the same method as described above.

~ Evaluation ~
As described above, the abrasion resistance and the degree of image defects when the kind or amount of powder was changed were evaluated by the following methods. The evaluation results are shown in Table 2 below.

-1. Abrasion resistance
An unprinted special diamond art double side N cut to 10 mm x 50 mm is wrapped around a paperweight (weight 470 g, size 15 mm x 30 mm x 120 mm) (unprinted special diamond art double side N and the evaluation sample are in contact with each other) The area was 150 mm ² ), and the sample 5 minutes after the image formation on the back surface was rubbed 3 times (corresponding to a load of 260 kg / m ² ). The printed surface after rubbing and the surface of the special diamond art wound around the paperweight were visually observed and evaluated according to the following evaluation criteria.
<Evaluation criteria>
AA: The peeling of the image on the printed surface was not visually recognized at all, and the color transfer to the special diamond art paper wrapped around the paperweight was not visually recognized.
A: While peeling of the image on the printed surface was not visible at all, the color transfer to the Tokuhishi art paper wrapped around the paperweight was slightly visible.
B: Peeling of the image on the printed surface was slightly visually recognized, and color transfer to the special diamond art paper wrapped around the paperweight was slightly visually recognized, but at a level that was not a problem for practical use.
C: The peeling of the image on the printed surface was visible, and there was a color transfer to the Tokuhishi art paper wrapped around the paperweight, which was a practically problematic level.
D: The peeling of the image on the printed surface was remarkable, and the color transfer to the special diamond art paper wrapped around the paperweight was remarkable, and there was a problem in practical use.

-2. Image defects
After 1000 sheets of recording media stacked and stacked on the discharge tray are stored for 24 hours under an environmental condition of 25 ° C. and 60% RH, the formed image is visually observed to form an image-formed recording medium The occurrence of an image defect between the 500th sheet and the 501st sheet (white color omission occurs where printing should be originally performed) was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: Image defects were not visually recognized.
B: Image defects were observed in a very small part of the image forming surface (about 1 place in 10 cm ² ).
C: Image defects were observed on the entire image forming surface.

  As shown in Table 2, in the present invention, good abrasion resistance was obtained, and the image was free from image defects such as scratches and peeling, and a high quality image was obtained.

DESCRIPTION OF SYMBOLS 1 ... Recording medium 2 ... Conveyor belt 4 ... IR heater (heating means)
5 ... Heating roller 6 ... Pressure roller 7 ... Cooling means 8 ... Powder sprayer (powder applying means)
9 ... discharge tray (stacking means)
31 ... Processing liquid discharge head 32 ... Ink discharge head

Claims (6)

An ink composition comprising a resin-coated pigment in which at least a part of pigment particles is coated with a water-insoluble resin, resin particles, wax particles, 1,2-alkylenediol, a polyhydric alcohol, a pyrrolidone derivative, and an acetylene glycol surfactant. An ink application step for applying ink from a discharge head to a recording medium, with a moving speed in the sub-scanning direction between the discharge head and the recording medium of 200 mm / sec or more;
A drying step of drying the recording medium provided with ink;
A stacking step of stacking the recording medium after drying by providing a step of attaching 1 to 1000 mg / m ² of a powdery material having an average particle diameter of 1 to 100 μm to the recording medium;
An image forming method comprising: The wax particles, the image forming method according to claim 1 which is particles of carnauba wax.   The image forming method according to claim 1, wherein the pyrrolidone derivative contains polyvinylpyrrolidone.   The image forming method according to any one of claims 1 to 3, further comprising a treatment liquid application step of applying a treatment liquid containing an aggregating component for aggregating the components in the ink composition to a recording medium.   The image forming method according to claim 1, wherein the powder is powder particles that have been subjected to hydrophobic treatment. The image forming method according to claim 1, wherein the recording medium has a coating layer and has an area of 1250 cm ² or more.