JP2024077000A - Inkjet recording method, inkjet recording device and set of aqueous ink and aqueous reaction liquid - Google Patents

Abstract

To provide an inkjet recording method or the like which can suppress image irregularities and record an image having excellent color development even when a pigment having a specific skeleton is used in a non-absorbing recording medium.SOLUTION: There is provided an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reaction agent reacting with the ink. The aqueous ink contains a pigment having a specific skeleton dispersed by the action of an anionic group. The aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group of a tertiary amine and a quaternary ammonium salt. The water absorption amount of the recording medium from the start of contact to 30 msec1/2 in the Bristow method is 10 mL/m2 or less.SELECTED DRAWING: None

Description

The present invention relates to an inkjet recording method, an inkjet recording device, and a set of an aqueous ink and an aqueous reaction liquid.

In recent years, inkjet recording methods have been increasingly used in the field of sign and display, such as printing posters and large-format advertisements. In this field, inkjet recording devices are characterized by a larger recording area compared to home inkjet recording devices. In addition, because images need to be eye-catching, inks that can record images with high color development are required.

In the sign and display field, non-absorbent recording media are often used, whose surfaces are made of polyvinyl chloride (PVC) or polyethylene terephthalate (PET), which have almost no ink absorption. For this reason, it is necessary to suppress bleeding of images on non-absorbent recording media. Hereinafter, recording media whose surfaces have almost no ink absorption will also be referred to as "non-absorbent recording media." In the inkjet recording method for recording on non-absorbent recording media, it is important to suppress bleeding by preventing ink dots from being repelled by the recording medium. To do this, it is necessary to rapidly thicken and fix the ink after it is applied to the recording medium.

Methods for recording on non-absorbent recording media include those using solvent-based inks that contain organic solvents as the main component, and those using curable inks that contain polymerizable monomers. However, in recent years, from the standpoint of environmental impact and safety, there has been an increasing need for a recording method that can record on non-absorbent recording media using water-based inks.

Methods for recording on non-absorbent recording media using aqueous ink include evaporating the water content of the ink on the surface of the non-absorbent recording media, and using a reaction liquid that causes the ink components to coagulate. The former is advantageous in terms of running costs because there is no need to provide a means for applying the reaction liquid, but it requires a slower recording speed, making it less productive. For this reason, methods that use a reaction liquid are being considered.

In addition, in the field of signs and displays, a wide color gamut is required to produce images with high color development. For this reason, in addition to the basic ink colors of black, cyan, magenta, and yellow, a method is used that uses so-called special color inks such as red, orange, green, and blue. It is also required that these special color inks be able to print images with high color development.

So far, liquid compositions have been developed that use pigments such as violet, green, and orange, and adjust the zeta potential to a specific range in order to obtain image performance such as beading resistance (see Patent Document 1).

JP 2020-084102 A

The inventors of the present invention used ink prepared using the liquid composition described in Patent Document 1 to record on a non-absorbent medium and examined various image performances. As a result, they found that image unevenness occurs when a pigment having a specific skeleton is used.

Therefore, an object of the present invention is to provide an inkjet recording method that can suppress image unevenness and record images with excellent color development even when a pigment having a specific skeleton is used on a non-absorbent recording medium. Another object of the present invention is to provide an inkjet recording device for use in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

That is, according to the present invention, there is provided an inkjet recording method for recording an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, the inkjet recording method comprising: a reaction liquid application step of applying the aqueous reaction liquid to the recording medium; and an ink application step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied, the aqueous ink containing a pigment that is dispersed by the action of an anionic group, the pigment having at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton, the aqueous reaction liquid containing a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt, and the amount of water absorbed by the recording medium from the start of contact until 30 msec ^1/2 in the Bristow method is 10 mL/m ² or less.

According to the present invention, it is possible to provide an inkjet recording method that can suppress image unevenness and record images with excellent color development even when a pigment having a specific skeleton is used on a non-absorbent recording medium. In addition, according to the present invention, it is possible to provide an inkjet recording device used in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. 1 is a side view diagrammatically illustrating an embodiment of an inkjet recording apparatus of the present invention.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, the aqueous ink and reaction liquid for inkjet printing may be simply referred to as "ink" and "reaction liquid." Physical property values are values at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

The present inventors first investigated the reason why image unevenness occurs in ink prepared using a liquid composition containing the orange pigment described in Patent Document 1. As a result, it was found that the orange pigment has a lower tendency to aggregate when it comes into contact with a reaction liquid on the surface of a recording medium compared to other pigments. Since the pigment in the ink is generally dispersed by the action of anionic groups, the dispersion state is destabilized and the pigment aggregates when it comes into contact with a reactant in the reaction liquid. However, some of the orange pigment is difficult to aggregate. As a result, it is considered that the image unevenness occurs when the non-aggregated orange pigment moves on the surface of the recording medium. The present inventors also investigated pigments other than the orange pigment described in Patent Document 1. As a result, it was found that a similar phenomenon occurs with pigments having at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton.

The reason for the occurrence of image unevenness in images recorded with ink containing a pigment having the above skeleton is thought to be related to the affinity of the pigment particle surface to aqueous media. The above skeleton also has multiple ring structures and heterocycles. While ring structures are generally hydrophobic, some of the heterocycles in the above skeleton are easily polarized and are hydrophilic. Therefore, even if the dispersion of a pigment having the above skeleton becomes unstable due to the action of anionic groups caused by a reactant, it is thought that aggregation is suppressed to some extent by the hydrophilic parts of the skeleton. As a result, the pigment's tendency to aggregate is reduced.

The inventors therefore considered that image unevenness could be suppressed by making it harder for a pigment with low coagulation to move on a recording medium, and conducted further investigations. As a result, they discovered that by using a specific cationic resin as a reactant, image unevenness can be suppressed and images with excellent color development can be recorded, even when a pigment with a specific skeleton is used.

That is, the inkjet recording method of the present invention has the following characteristics. First, the aqueous ink contains a pigment that is dispersed by the action of an anionic group. The pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton. The aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt. The recording medium has an amount of water absorption of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. The aqueous reaction liquid and the aqueous ink are applied to the recording medium so that they are at least partially overlapped. The present inventors speculate that the mechanism by which the above configuration suppresses image unevenness and allows images with excellent color development to be recorded is as follows.

The ink is a pigment that is dispersed by the action of anionic groups. The pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton. Therefore, upon contact with a reaction liquid containing a cationic resin as a reactant, the dispersion state is destabilized and the pigment aggregates. However, when a pigment having the above skeleton comes into contact with a reaction liquid, some of the pigment does not aggregate, resulting in image unevenness.

The cationic resin used as the reactant is a water-soluble resin having at least one structure selected from the group consisting of tertiary amines and quaternary ammonium salts. The above cationic resin has multiple cationic sites in its molecule that react with the pigment. Therefore, it reacts with many of the anionic groups that disperse the pigment, and can make the aggregates that are formed larger. The formation of large aggregates in the recording medium physically suppresses the movement of non-aggregated pigment. As a result, it is believed that image unevenness can be suppressed.

If the cationic resin is a resin particle, not a water-soluble resin, then even if it has multiple cationic sites, only the cationic sites present on the surface of the resin particle can react with the anionic groups dispersing the pigment. As a result, the aggregates formed do not grow large, resulting in image unevenness. If the cationic resin is only a resin having at least one structure selected from the group consisting of primary amines and secondary amines, it has lower reactivity with the anionic groups dispersing the pigment than tertiary amines and quaternary ammonium salts. Therefore, the aggregates formed do not grow large, resulting in image unevenness. If only an organic acid or a polyvalent metal salt is used as a reactant, the speed at which the pigment is aggregated is higher than that of the cationic resin, but the aggregates formed are smaller than those of the above cationic resin. As a result, the movement of non-aggregated pigments cannot be suppressed, resulting in image unevenness.

<Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reaction liquid>
The inkjet recording method of the present invention is a method of ejecting an aqueous ink and an aqueous reaction liquid from an inkjet recording head and applying them to a recording medium to record an image. The inkjet recording method of the present invention includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium, and an ink applying step of applying the aqueous ink so as to overlap at least a part of the area of the recording medium to which the aqueous reaction liquid is applied. The aqueous ink contains a pigment that is dispersed by the action of an anionic group. The pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton. The aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt. The recording medium is a recording medium in which the amount of water absorbed from the start of contact to 30 msec ^1/2 in the Bristow method is 10 mL/m ² or less.

The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid are ejected from an inkjet recording head and applied to a recording medium to record an image. The inkjet recording apparatus is an apparatus suitable for use in the above-mentioned recording method. In the inkjet recording method and inkjet recording apparatus of the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

The set of aqueous ink and aqueous reaction liquid of the present invention is a set used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink are ejected from a recording head to record an image on a recording medium. The set is suitable for use in the above recording method. The form of the set includes a set of multiple ink cartridges each containing multiple inks (reaction liquids) independently, and an ink cartridge formed integrally by combining multiple ink storage sections each containing multiple inks (reaction liquids). The set of the present invention is not limited to the above form and may be in any form as long as it is configured so that the inks and reaction liquids can be used in combination.

The inkjet recording method and inkjet recording device of the present invention (hereinafter, simply referred to as the "recording method and recording device") will be described in detail below.

FIG. 1 is a perspective view showing an embodiment of the inkjet recording apparatus of the present invention. FIG. 2 is a side view showing an embodiment of the inkjet recording apparatus of the present invention. As shown in FIGS. 1 and 2, the recording apparatus of this embodiment includes an inkjet recording head 22 that ejects ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. A recording head that ejects ink by the action of thermal energy applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element, thereby ejecting the ink from the ejection port. Here, a recording head that ejects ink by the action of thermal energy is given as an example, but a recording head that ejects ink by the action of mechanical energy may also be used. The recording head may include a mechanism (temperature control mechanism) that heats the water-based ink ejected from the recording head. When the recording head includes a temperature control mechanism, the temperature of the ink ejected from the recording head is preferably 35° C. or higher and 70° C. or lower.

[Heating process]
The recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink (and reaction liquid) has been applied. Heating the recording medium to which the ink has been applied can promote drying and increase the strength of the image.

Examples of the means for heating the recording medium include known heating means such as a heater, air blowing means using air blowing such as a dryer, and combinations of these. Examples of the heating means include the above heating means, air blowing means, and combinations of these. Examples of the heat treatment method include a method of applying heat from the opposite side (back side) to the recording surface (ink application surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used.

The heating temperature of the recording medium to which the ink has been applied is preferably 50°C or higher and 90°C or lower, in order to increase the abrasion resistance of the image. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined according to the type of ink and recording medium.

In the recording device shown in Figures 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 1 to which ink has been applied is heated by the heater 25. Examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 to the recording medium 1. Furthermore, the heater cover 26 is also a member for protecting the heater 25. The recording medium 1 to which ink has been applied ejected from the recording head 22 is wound by a winding spool 27 to form a roll-shaped wound medium 24.

(recoding media)
In the recording method and recording device of the present invention, a low-absorbency or non-absorbency recording medium (low to non-absorbency recording medium) is used. A low to non-absorbency recording medium is a recording medium having a water absorption amount of 0 mL/ ^m2 or more and 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51 "Liquid Absorbency Test Method for Paper and Paperboard". In the present invention, a recording medium that satisfies the above water absorption amount condition is defined as a "low to non-absorbency recording medium". A recording medium for inkjet recording (glossy paper, matte paper, etc.) having a coating layer (ink receiving layer) formed of inorganic particles, and plain paper without a coating layer are "absorbency recording media" having the above water absorption amount of more than 10 mL/ ^m2 .

Examples of low to non-absorbent recording media that can be used include plastic films; recording media in which a plastic film is adhered to the recording surface of a substrate; and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred. Note that the recording medium in this specification does not refer to a transfer medium, but rather refers to a recording medium on which an image is recorded as a recorded matter.

(Reaction solution)
The recording method of the present invention has a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to a recording medium. In particular, it is preferable to have a reaction liquid applying step before an ink applying step of applying the aqueous ink to the recording medium, or to perform the ink applying step and the reaction liquid applying step in parallel. Each component used in the reaction liquid will be described in detail below.

[Reactants]
The reaction liquid reacts with the ink upon contact with it, causing the components in the ink (components having anionic groups, such as resins, surfactants, and self-dispersing pigments) to aggregate, and contains a specific water-soluble cationic resin as a reactant.

The water-soluble cationic resin contained in the reaction solution is a resin having at least one structure selected from the group consisting of tertiary amines and quaternary ammonium salts. Hereinafter, the water-soluble cationic resin is also simply referred to as cationic resin. The content (mass%) of the cationic resin in the reaction solution is preferably 0.10 mass% or more and 10.0 mass% or less, and preferably 0.10 mass% or more and 5.0 mass% or less, based on the total mass of the reaction solution. Specific examples of the cationic resin include resins having structures such as polydiallyl dimethyl allyl chloride, polydimethylamine epichlorohydrin copolymer, polydiallyl methyl ethyl ammonium ethyl sulfate, polymethyl diallylamine, diallyl dimethyl ammonium chloride, and alkylamine-epichlorohydrin condensate. A cationic resin having a structure of primary to tertiary amines may be subjected to a quaternary treatment to form a quaternary ammonium salt. The cationic resin is preferably a resin having a structure of a quaternary ammonium salt. Among them, the cationic resin is preferably a dimethylamine-epichlorohydrin resin or a diallyldimethylammonium chloride resin. The dimethylamine-epichlorohydrin resin is a resin having a structure (dimethylamine-epichlorohydrin) represented by the following formula (1). The diallyldimethylammonium chloride resin is a resin having a structure (diallyldimethylammonium chloride) represented by the following formula (2). The cationic resin having the above structure exhibits a stronger interaction with the pigment and the anionic groups of the resin particles, and therefore can more effectively suppress image unevenness.

(In formula (1) and formula (2), n represents a natural number.)

The weight average molecular weight of the cationic resin is preferably 9,000 or less. The weight average molecular weight of the cationic resin can be measured, for example, as a polystyrene-equivalent value measured by gel permeation chromatography. If the weight average molecular weight exceeds 9,000, the aggregates may become too large, and sufficient color development of the image may not be obtained. The weight average molecular weight of the cationic resin is preferably 1,000 or more, and more preferably 3,000 or more.

The reaction liquid preferably further contains at least one reactant selected from the group consisting of organic acids and polyvalent metal salts. The above reactants have a higher rate of agglomerating pigments than cationic resins, so by using them in combination with cationic resins, image unevenness can be more effectively suppressed and the color development of the image can be further improved.

The reaction liquid containing an organic acid has a buffering ability in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into the acid form and causes them to aggregate. Examples of organic acids include monocarboxylic acids and their salts, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furan carboxylic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts and hydrogen salts, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and their salts and hydrogen salts, such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts and hydrogen salts, such as pyromellitic acid. The content (mass %) of the organic acid in the reaction solution is preferably 1.0 mass % or more and 5.0 mass % or less based on the total mass of the reaction solution.

The polyvalent metal salt is a compound formed of a divalent or higher metal ion (polyvalent metal ion) and an anion. The polyvalent metal salt dissociates in the reaction liquid to become a polyvalent metal ion, and aggregates the pigment dispersed by the anionic group in the ink. The polyvalent metal salt may be a hydrate. Examples of the polyvalent metal ion constituting the polyvalent metal salt include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , and Zn ²⁺ , and trivalent metal ions such as Fe ³⁺ , Cr ³⁺ , Y ³⁺ , and Al ³⁺ . Examples of the anion include inorganic anions such as Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; HCOO ⁻ , (COO ⁻ ) ₂ , COOH(COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₅ COO ⁻ , CH ₃ CH(OH)COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , and CH ₃ SO ₃ The content (mass %) of the polyvalent metal salt in the reaction solution is preferably 1.0 mass % or more and 20.0 mass % or less based on ^the total mass of the reaction solution.

When the aqueous reaction liquid further contains at least one reactant selected from the group consisting of organic acids and polyvalent metal salts, the content (mass%) of the cationic resin in the aqueous reaction liquid is preferably 0.10 mass% or more and 0.50 mass% or less based on the total mass of the reaction liquid. If the content is less than 0.10 mass%, the amount of cationic resin is too small, making it difficult to form large aggregates, and image unevenness may not be sufficiently suppressed. If the content is more than 0.50 mass%, the aggregates may become too large, and sufficient color development of the image may not be obtained.

The total content (mass%) of the organic acid and the polyvalent metal salt in the aqueous reaction liquid is preferably 1.0 times or more in mass ratio to the content (mass%) of the cationic resin. As described above, the organic acid and the polyvalent metal salt have a higher rate of agglomerating the pigment than the cationic resin. Therefore, by making the mass ratio 1.0 times or more, the pigment can be quickly aggregated, and the synergistic effect of the formation of large aggregates by the cationic resin can more effectively suppress image unevenness. The mass ratio is preferably 20.0 times or less.

[Aqueous medium]
The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. The aqueous medium used in the reaction liquid can contain a water-soluble organic solvent, which can be contained in the ink, as described below. Among them, it is preferable to contain a surfactant. By containing a surfactant, the wettability to the surface of the recording medium can be improved, and various performances of the image can be improved. The content (mass %) of the surfactant in the reaction liquid is preferably 0.1 mass % or more and 5.0 mass % or less based on the total mass of the reaction liquid. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. Among them, it is preferable that the reaction liquid contains a nonionic surfactant, since it is less likely to affect the reaction between the ink and the reaction liquid and can easily wet and spread on the surface of the recording medium with a small amount.

[Other ingredients]
The reaction liquid may contain various other components as necessary. Examples of the other components include the same components as those that can be contained in the ink, which will be described later.

[Properties of reaction solution]
The reaction liquid that can be suitably used in the recording method of the present invention is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property value. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction liquid at 25°C is preferably 5.0 or more and 9.5 or less, more preferably 6.0 or more and 9.0 or less.

<Ink>
The ink used in the recording method of the present invention is a water-based ink for ink-jet recording, which contains a pigment having a specific skeleton that is dispersed by the action of an anionic group. Each component constituting the ink will be described in detail below.

[Colorant]
The ink contains a pigment that is dispersed by the action of an anionic group. The content (mass %) of the pigment in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

The pigment is required to have at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton. In the present invention, a pigment having a perinone skeleton means that it has a structure represented by the following formula (A). Examples of pigments having a perinone skeleton include C.I. Pigment Orange 43 and C.I. Pigment Red 194.

The benzimidazolone skeleton is represented by the following formula (B). Examples of pigments having a benzimidazolone skeleton include C.I. Pigment Orange 36 and C.I. Pigment Orange 64.

The diketopyrrolopyrrole skeleton is represented by the following formula (C). Examples of pigments having a diketopyrrolopyrrole skeleton include C.I. Pigment Orange 71, C.I. Pigment Red 254, C.I. Pigment Red 255, C.I. Pigment Red 264, C.I. Pigment Red 270, and C.I. Pigment Red 272.

The pyrazolone skeleton is represented by the following formula (D). An example of a pigment having a pyrazolone skeleton is C.I. Pigment Orange 34.

Among these, from the viewpoint of image color development, C.I. Pigment Orange 43, C.I. Pigment Orange 71, C.I. Pigment Orange 34, and C.I. Pigment Red 254 are preferred. Furthermore, pigments having a perinone skeleton are preferred, and C.I. Pigment Orange 43 is even more preferred.

The ink may contain pigments other than the pigment having a specific skeleton (other pigments). Examples of other pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, and dioxazine. The pigments and other pigments may be used alone or in combination of two or more.

As a method for dispersing pigments, resin-dispersed pigments using resin as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the pigment particle surface, and microencapsulated pigments in which the pigment particle surface is coated with resin can be used. It is also possible to use a combination of pigments with different dispersion methods. In particular, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microencapsulated pigments. In other words, it is preferable that the pigment is dispersed by a resin (resin dispersant) having an anionic group.

As a resin dispersant for dispersing the pigment in an aqueous medium, one that can disperse the pigment in an aqueous medium by the action of anionic groups is used. As the resin dispersant, a resin such as that described below, especially a water-soluble resin, can be used. The content (mass%) of the resin having an anionic group in the ink is preferably 0.05 to 0.20 times the mass ratio of the content (mass%) of the pigment. If the mass ratio is less than 0.05, the proportion of the resin having an anionic group is too small, making it difficult to form pigment aggregates, and image unevenness may occur. On the other hand, if the mass ratio is more than 0.20, the proportion of the resin having an anionic group is too high, making the formed pigment aggregates too large, and the color development of the image may not be sufficient.

As the self-dispersing pigment, an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group can be bonded to the particle surface of the pigment directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. A group that is a combination of these groups may also be used.

The volume-based cumulative 50% particle diameter ( _D50 ) of the pigment is preferably 10 nm or more and 300 nm or less, and more preferably 20 nm or more and 200 nm or less. The volume-based cumulative 50% particle diameter of the pigment is the diameter of a particle that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in a particle diameter integration curve. The volume-based cumulative 50% particle diameter of the pigment can be measured based on a particle size analyzer and measurement conditions described in the section on resins below.

[resin]
The ink may contain a resin. The content (mass %) of the resin in the ink is preferably from 0.1% by mass to 20.0% by mass, and more preferably from 0.5% by mass to 15.0% by mass, based on the total mass of the ink.

The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) to improve various properties of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations of these. Also, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin may be used alone or in combination of two or more types.

[Resin Composition]
Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among them, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferable. These resins are easily interacted with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and the like.

Urethane-based resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting a chain extender. Examples of olefin-based resins include polyethylene and polypropylene.

[Resin properties]
In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which no particles whose particle size can be measured by a dynamic light scattering method are formed. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, as a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 100 mgKOH/g or more and 250 mgKOH/g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

The ink preferably contains resin particles having an anionic group. By adding the resin particles having an anionic group, the ink reacts with the cationic resin when it comes into contact with the reaction liquid on the surface of the recording medium. As a result, the resin particles having an anionic group also form large aggregates in addition to the pigment, and image unevenness can be more effectively suppressed. The acid value of the resin constituting the resin particles is preferably 5 mgKOH/g or more and 100 mgKOH/g or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, and more preferably 100,000 or more and 3,000,000 or less. The cumulative 50% particle diameter (D ₅₀ ) based on volume of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less, and more preferably 100 nm or more and 300 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particles that is 50% of the total volume of the measured particles in the particle diameter accumulation curve, calculated from the small particle diameter side. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the dynamic light scattering particle size analyzer and measurement conditions described above. In addition, whether a certain resin is a resin particle can be determined by whether the volume-based cumulative 50% particle diameter is measured using the above method. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, and more preferably 50°C or more and 100°C or less. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain a coloring material.

[Surfactant]
The ink preferably contains a surfactant. The content (mass%) of the surfactant in the ink is preferably 0.1 mass% or more and 5.0 mass% or less, and preferably 0.1 mass% or more and 2.0 mass% or less. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. Among them, the ink preferably contains a nonionic surfactant because it is less likely to affect the reaction between the ink and the reaction liquid and can easily wet and spread on the surface of the recording medium with a small amount. In addition, by making it easier to wet and spread, the pigment can be fixed more uniformly on the recording medium, and image unevenness can be more effectively suppressed. Examples of the nonionic surfactant include various surfactants such as hydrocarbon-based, fluorine-based, and silicone-based. Among them, from the viewpoint of suppressing image unevenness, the nonionic surfactant contained in the ink is preferably a silicone-based surfactant.

A silicone-based nonionic surfactant (hereinafter also referred to as a silicone-based surfactant) is a surfactant in which a hydrophilic group is introduced into a polyorganosiloxane having a main skeleton of a siloxane structure (SiO) in which silicon (Si) and oxygen atoms (O) are alternately linked. Examples of silicone-based nonionic surfactants include polyether-modified siloxane compounds. Among them, it is preferable that the silicone-based surfactant is a compound having a structure in which at least one silicon atom other than the terminal of a polyorganosiloxane chain having a repeating siloxane structure as the main skeleton is substituted with at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxyl group. Hereinafter, such a structure is also referred to as a side chain type. In addition to the side chain type, a straight chain type (a hydrophilic group is substituted for the silicon atom at one or both terminals of the polyorganosiloxane chain) is known depending on the position of introduction of the hydrophilic group. Examples of hydrophilic groups include an alkylene oxide group and a hydroxyl group. Examples of the alkylene oxide group include an ethylene oxide group, a propylene oxide group, and a butylene oxide group. Of these, an ethylene oxide group and a propylene oxide group are preferred. An example of a side chain type structure is shown in the following formula (3), and an example of a straight chain type structure is shown in the following formula (4).

(In formula (3) and formula (4), m, n, X, and Y represent natural numbers. R ₁ , R ₂ , and R ₃ each independently represent an alkylene group, and EO represents an ethylene oxide group.)

Side-chain silicone surfactants are inhibited from adsorbing to the pigment particle surface by the substituted hydrophilic groups. However, straight-chain silicone surfactants are more likely to adsorb to the pigment particle surface than side-chain types, and may inhibit aggregation due to reaction with the cationic resin. As a result, image unevenness is more likely to occur.

[Wax particles]
The ink may contain particles formed of wax (wax particles). By using an ink containing wax particles, an image with further improved abrasion resistance can be recorded. In this specification, the wax may be a composition containing components other than wax, or the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. The wax may be used alone or in combination of two or more kinds. The content (mass %) of the wax particles in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the ink.

In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends of these (blended waxes), and modified products of these (modified waxes).

Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among these, a blend of multiple types of wax is more preferable, and a blend of petroleum-based wax and synthetic wax is especially preferable.

The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if the chain is straight, and the lower the melting point if the chain is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, it is possible to obtain a wax having a desired melting point. The melting point of the wax in the ink can be measured in accordance with the above test method, for example, after the ink is subjected to ultracentrifugation, the wax separated is washed and dried.

[Aqueous medium]
The ink used in the recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, the content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. The water-soluble organic solvent may be used alone or in combination of two or more.

[Other ingredients]
The ink may contain various other components as necessary. Examples of other components include various additives such as defoamers, other surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain a reactant to be contained in the reaction liquid.

[Ink properties]
The ink is a water-based ink applied to an inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25° C. is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25° C. is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, the terms "parts" and "%" used to describe the amounts of components are based on mass.

<Preparation of cationic resin>
Table 1 shows the composition of the cationic resin used in the preparation of the reaction liquid. When preparing the reaction liquid, an appropriate amount of ion-exchanged water was added to prepare a liquid containing each cationic resin such that the resin content was 10.0%. As the cationic resin 11, cationic polyurethane resin particles (product name "Superflex 620", resin content: 30.0%, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were used, and an appropriate amount of ion-exchanged water was added to prepare a liquid containing the cationic resin 11 with a resin content of 10.0%. In Table 1, "class number" indicates the class number of the amine, and in the case of a quaternary ammonium salt, "quaternary" was written. In addition, in the case of primary to tertiary amines, "primary", "secondary", and "tertiary", respectively, were written.

<Preparation of reaction solution>
The components (unit: %) shown in Tables 2 and 3 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each reaction solution. "Proxel GXL(S)" is the trade name of a preservative manufactured by Arch Chemicals.

<Preparation of resin dispersant>
(Resin Dispersant 1)
Resin 1, which is a styrene/acrylic acid copolymer (water-soluble resin, composition (molar) ratio = 84.6/15.4, acid value 120 mgKOH/g), was used as the resin dispersant 1. Sodium hydroxide was added in an amount equimolar to the acid value of resin 1, and resin 1 was dissolved in ion-exchanged water to prepare an aqueous solution of resin dispersant 1 with a resin content of 20.0%.

(Resin Dispersant 2)
An aqueous solution of resin dispersant 2 having a resin content of 20.0% was prepared in the same manner as resin dispersant 1 described above, except that the resin dispersant was changed to a butyl acrylate/benzyl methacrylate/methoxypolyethylene glycol monomethacrylate copolymer (resin dispersant 2, water-soluble resin, composition (molar) ratio = 30.0/60.0/10.0, acid value 0 mgKOH/g).

<Preparation of Pigment Dispersion>
The components shown in Table 4 and ion-exchanged water were mixed to obtain a mixture. Ion-exchanged water was added so that the total amount of the components was 100.0 parts. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, the mixture was filtered under pressure with a cellulose acetate filter with a pore size of 3.0 μm (manufactured by Advantec) to prepare pigment dispersions 1 to 13.

<Production of Resin Particles>
(Resin Particles 1)
In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 74.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 24.0 parts of ethyl methacrylate, 1.5 parts of methacrylic acid, and 0.3 parts of a reactive surfactant were mixed to prepare an emulsion. As the reactive surfactant, the product name "ADEKA REASOAP ER20" (manufactured by ADEKA, nonionic surfactant, number of moles of ethylene oxide group added: 20) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and polymerization reaction was carried out for 2 hours while stirring at 80 ° C. After cooling to 25 ° C., ion-exchanged water and an aqueous solution containing potassium hydroxide equimolar to the acid value of the resin particles were added to prepare an aqueous dispersion of resin particles 1 having a resin particle (solid content) content of 25.0%.

(Resin Particles 2)
In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 81.8 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 16.1 parts of ethyl methacrylate, 1.6 parts of methoxypolyethylene glycol methacrylate, and 0.3 parts of the above-mentioned reactive surfactant were mixed to prepare an emulsion. As the methoxypolyethylene glycol methacrylate, the product name "Blenmer PME1000" (manufactured by NOF Corp., number of moles of ethylene oxide group added: about 23) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and polymerization reaction was carried out for 2 hours while stirring at 80 ° C. After cooling to 25 ° C., ion-exchanged water was added to prepare an aqueous dispersion of resin particles 2 with a resin particle (solid content) content of 25.0%.

<Preparation of Silicone Surfactant>
(Silicone-based surfactant 1)
Silicone surfactant 1 was synthesized as follows using a glass vessel equipped with a thermometer and stirring means. In the vessel, an addition reaction was carried out in the presence of a platinum catalyst using a polysiloxane compound represented by the following formula (a) and a polyoxyethylene compound represented by the following formula (b) as main components to synthesize silicone surfactant 1. The addition reaction was continued until a surfactant having a weight average molecular weight as described below was obtained. The obtained silicone surfactant 1 was a compound corresponding to the side chain type represented by the following formula (5). The weight average molecular weight of this surfactant was about 1,000.
Si( _CH3 ) ₃ -O-(Si( _CH3 ) ₂ -O) ₂ -Si( _CH3 )H-O-Si( _CH3 ) ₃ ...(a)
CH ₂ ═CHCH ₂ —O—(C ₂ H ₄ O) ₁₃ —H (b)

(In formula (5), EO represents an ethylene oxide group.)

(Silicone-based surfactant 2)
Silicone surfactant 2 was prepared in the same manner as silicone surfactant 1, except that the polysiloxane compound and polyoxyethylene compound were changed to those of the following formula (c) and formula (d), respectively. The resulting surfactant was a compound corresponding to the side chain type represented by the following formula (6). The weight average molecular weight of this surfactant was about 900.
Si( _CH3 ) ₃ -O-(Si( _CH3 ) ₂ -O) ₂ -Si( _CH3 )H-O-Si( _CH3 ) ₃ ...(c)
CH ₂ ═CHCH ₂ —O—(C ₂ H ₄ O) ₅ —(C ₂ H ₃ CH ₃ O) ₄ —H...(d)

(In formula (6), EO represents an ethylene oxide group, and PO represents a propylene oxide group.)

(Silicone-based surfactant 3)
Silicone surfactant 3 was prepared in the same manner as silicone surfactant 1, except that the polysiloxane compound and polyoxyethylene compound were changed to those of the following formula (e) and formula (f), respectively. The resulting surfactant was a straight-chain compound represented by the following formula (7). The weight-average molecular weight of this surfactant was about 1,100.
H-(Si( _CH3 ) ₂ -O) ₅ -Si( _CH3 ) ₂ -H... (e)
CH ₂ ═CHCH ₂ —O—(CH ₂ H ₄ O) ₆ —H (f)

(In formula (7), EO represents an ethylene oxide group.)

<Ink Preparation>
The components (unit: %) shown in Tables 5 and 6 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. "Acetylenol E100" is the trade name of a hydrocarbon-based nonionic surfactant manufactured by Kawaken Fine Chemicals.

<Preparing the recording medium>
The following recording media 1 to 3 were prepared.
Recording medium 1: Product name "Scotchcal Graphic Film IJ1220-10" (manufactured by 3M, material: polyvinyl chloride, in the Bristow method, the amount of water absorbed from the start of contact to 30 msec ^1/2 is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 )
Recording medium 2: Product name "GIY-0305" (manufactured by Lintec, material: PET, the amount of water absorbed from the start of contact to 30 msec ^1/2 in the Bristow method is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 )
Recording medium 3: Product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201" (Canon, in the Bristow method, the amount of water absorbed from the start of contact to 30 msec ^1/2 is more than 10 mL/m ² )

<Evaluation>
The prepared reaction liquid and ink were filled in a cartridge, and the cartridge was set in an inkjet recording device (product name "imagePROGRAF PRO-2000", manufactured by Canon) equipped with a recording head that ejects ink by thermal energy. A heating device for drying the recording medium to which the reaction liquid and ink were applied was incorporated in this recording device at a position downstream of the recording head in the conveying direction of the recording medium. The surface temperature of the recording medium was set to 80°C by heating with the heating device. The recording environment was set to a temperature of 25°C and a relative humidity of 50%. Using the above inkjet recording device, 20 types of solid images of 2 cm x 2 cm were recorded by applying the reaction liquid and ink shown in Table 7, in which the recording duty of the reaction liquid was 30% and the recording duty of the ink was changed in 10% increments between 10% and 200%. At this time, the reaction liquid application process and the ink application process were performed in parallel to record the solid images. In addition, the types of recording media shown in Table 7 were used.

In Reference Examples 3 to 6, color development was not evaluated, and the color development evaluation column is marked with "-". In this embodiment, an image recorded under conditions in which one drop of 4.0 ng of ink is applied to a unit area of 1/1200 inch x 1/1200 inch is defined as having a recording duty of 100%. In the present invention, the evaluation criteria for each item below are set as "AA", "A" and "B" as acceptable levels, and "C" as an unacceptable level. The evaluation results are shown on the right side of Table 7.

(Suppression of image unevenness)
For a solid image with an ink recording duty of 100%, image unevenness was visually observed at distances of 30 cm, 40 cm, and 50 cm from the solid image, and suppression of image unevenness was evaluated according to the following evaluation criteria.
AA: No image unevenness was observed even when observed from a position of 30 cm. A: Image unevenness was observed when observed from a position of 30 cm, but not when observed from a position of 40 cm. B: Image unevenness was observed when observed from positions of 30 cm and 40 cm, but not when observed from a position of 50 cm. C: Image unevenness was observed even when observed from a position of 50 cm.

(Color development)
The chroma (C ^* ) of 20 types of solid images was measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta). The measurement conditions were light source: D50, viewing angle: 2 degrees, incident angle: 45 degrees, reflection angle: 0 degrees, and filter: ANSI A. ^C* is the chroma according to the color difference display method specified by CIE. The color development of the image was evaluated according to the evaluation criteria shown below. The higher the chroma, the more vivid the image and the better the color development. The chroma was measured after placing white high-quality paper (product name "PB PAPER", A5 size, manufactured by Canon) under the recorded image.
AA: The maximum chroma C ^* was 105 or more. A: The maximum chroma C ^* was 100 or more and less than 105. B: The maximum chroma C ^* was 95 or more and less than 100. C: The maximum chroma C ^* was less than 95.

The evaluation result for suppression of image unevenness for Example 29 was "A", the same as for Example 28, but Example 29 was superior.

Claims (14)

An inkjet recording method for recording an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
The aqueous ink contains a pigment that is dispersed by the action of an anionic group,
the pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton,
the aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt,
The ink-jet recording method according to claim 1, wherein the recording medium absorbs water in an amount of 10 mL/ ^m2 or less from the start of contact until 30 msec ^1/2 in a Bristow method. The inkjet recording method according to claim 1, wherein the cationic resin is a dimethylamine-epichlorohydrin resin or a diallyldimethylammonium chloride resin. The inkjet recording method according to claim 1, wherein the weight average molecular weight of the cationic resin is 9,000 or less. The inkjet recording method according to claim 1, wherein the aqueous reaction liquid further contains at least one reactant selected from the group consisting of an organic acid and a polyvalent metal salt. The inkjet recording method according to claim 4, wherein the content (mass%) of the cationic resin in the aqueous reaction liquid is 0.10 mass% or more and 0.50 mass% or less based on the total mass of the reaction liquid. The inkjet recording method according to claim 4, wherein the total content (mass%) of the organic acid and the polyvalent metal salt in the aqueous reaction liquid is 1.0 times or more the mass ratio of the content (mass%) of the cationic resin. the pigment is dispersed by a resin having an anionic group,
2. The inkjet recording method according to claim 1, wherein the content (mass %) of the resin having an anionic group in the aqueous ink is 0.05 to 0.20 times the content (mass %) of the pigment. The inkjet recording method according to claim 1, wherein the aqueous ink contains resin particles having anionic groups. The inkjet recording method according to claim 1, wherein the aqueous ink contains a nonionic surfactant. The inkjet recording method according to claim 9, wherein the nonionic surfactant is a silicone-based surfactant. The inkjet recording method according to claim 10, wherein the silicone surfactant is a compound having a structure in which at least one silicon atom other than the terminal of a polyorganosiloxane chain having a repeating siloxane structure as the main skeleton is substituted with at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxyl group. The inkjet recording method according to claim 1, wherein the pigment is C.I. Pigment Orange 43. An inkjet recording apparatus used to record an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium;
an ink applying means for applying the water-based ink so as to overlap at least a portion of an area of the recording medium to which the water-based reaction liquid is applied,
The aqueous ink contains a pigment that is dispersed by the action of an anionic group,
the pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton,
the aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt,
An ink jet recording apparatus, characterized in that the recording medium has an absorption amount of water of 10 mL/ ^m2 or less from the start of contact until 30 msec ^1/2 in the Bristow method. A set of an aqueous ink and an aqueous reaction liquid used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
the inkjet recording method includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
The aqueous ink contains a pigment that is dispersed by the action of an anionic group,
the pigment has at least one skeleton selected from the group consisting of a perinone skeleton, a benzimidazolone skeleton, a diketopyrrolopyrrole skeleton, and a pyrazolone skeleton,
the aqueous reaction liquid contains a water-soluble cationic resin having at least one structure selected from the group consisting of a tertiary amine and a quaternary ammonium salt,
A set of an aqueous ink and an aqueous reaction liquid, characterized in that the recording medium absorbs water in an amount of 10 mL/ ^m2 or less from the start of contact until 30 msec ^1/2 in the Bristow method.

Images