JP7688322B2 - Image recording method, and ink set of processing liquid and metallic ink - Google Patents

Description

The present invention relates to an image recording method and an ink set of a treatment liquid and a metallic ink.

2. Description of the Related Art In recent years, print media have become increasingly diversified, and are used in a wide range of fields, from office printing to large-scale printing such as commercial printing.
A printed matter printed on the printing medium can express a full-color image by mixing various colors.

Printed materials that have images containing a silver colorant with metallic luster, especially high specular clarity, have great industrial value because full-color images with high clarity can be obtained by mixing the silver colorant with other colors.

For example, Patent Document 1 discloses a technology in which a reactive liquid (a liquid that promotes pigment aggregation when mixed with ink) containing anionic colloidal silica is applied to a non-permeable medium or a low-absorbency medium, and then a white ink or a metallic ink is applied to the reactive liquid, as a recording method that can prevent bleeding between inks and suppress uneven aggregation of the ink. However, although the text states that the surface tension of both the reactive liquid and the metallic ink is preferably 40 mN/m or less, there is no clear description of the relationship between the reactive liquid and the metallic ink.
Furthermore, Patent Document 2 discloses that by forming a relatively thick ink receiving layer using an undercoat liquid containing fine particles capable of forming a porous structure and then applying a silver ink containing silver, the silver ink can obtain high brilliance.
Patent Document 3 discloses an ink set for obtaining high-quality printed matter, which is composed of a recording liquid containing an anionic component and a treatment liquid containing a component reactive with a component in the recording liquid, the recording liquid containing a coloring material, the treatment liquid containing cationic inorganic particles, and a surface tension γ of 10≦γ≦35 [mN/m], and the surface tension of the treatment liquid is smaller than that of the recording liquid. In the example, the surface tension of the recording liquid is 33.0 mN/m.

The present invention aims to provide an image recording method that can obtain a high 20° gloss in an image recording method in which a treatment liquid is first applied to a recording medium and then a metallic ink is applied.

The present invention is an image recording method as described below.
An image recording method including a step of applying a treatment liquid containing a porous layer-forming material onto a recording medium to form a porous layer, and a metallic ink applying step of applying a metallic ink containing a metal pigment onto the porous layer,
a surface tension of the treatment liquid at 23° C. and a surface tension of the metallic ink at 23° C. satisfy the following relational expression (1),
Surface tension of metallic ink ≧ Surface tension of treatment liquid (1)
The image recording method, wherein the metallic ink has a surface tension at 23° C. of 19 mN/m or more and 28 mN/m or less.

The image recording method of the present invention makes it possible to obtain recorded material with a high 20° gloss.

1 is a perspective view showing an example of an image recording apparatus according to the present invention; 1 is a cross-sectional view showing an example of the overall configuration of an image recording apparatus according to the present invention. FIG. 11 is a perspective view showing another example of an image recording apparatus according to the present invention. FIG. 2 is a perspective view of an example of a main tank. FIG. 2 is a cross-sectional view showing an example of an apparatus for applying a treatment liquid. 5B is a cross-sectional view showing the inside of the pressure roller 9 shown in FIG. 5A. 11A and 11B are explanatory diagrams showing states from ink landing to fixation when the treatment liquid has a high surface tension and when the treatment liquid has a low surface tension; 1 is a micrograph showing droplet marks observed when silver ink is applied onto a recording medium using an inkjet head. 1 shows images printed in the bleeding rank evaluation in the examples.

The present invention is described in (1) below, but the embodiments also include (2) to (11) below, so these will also be described.
(1) An image recording method including a step of applying a treatment liquid containing a porous layer-forming material onto a recording medium to form a porous layer, and a metallic ink applying step of applying a metallic ink containing a metallic pigment onto the porous layer,
a surface tension of the treatment liquid at 23° C. and a surface tension of the metallic ink at 23° C. satisfy the following relational expression (1),
Surface tension of metallic ink ≧ Surface tension of treatment liquid (1)
The image recording method according to claim 1, wherein the metallic ink has a surface tension of 19 mN/m or more and 28 mN/m or less at 23°C.
(2) The image recording method according to (1) above, wherein the metallic ink has a surface tension of 21 mN/m or more and 25 mN/m or less, and the treatment liquid has a surface tension of 18 mN /m or more and 23 mN/m or less.
(3) The image recording method according to (1) or (2) above, wherein the material for forming a porous medium is inorganic particles.
(4) The image recording method according to (3) above, wherein the inorganic particles are made of silica or alumina.
(5) The image recording method according to (3) or (4) above, wherein the inorganic particles are beaded fine particles including secondary particles formed by agglomeration of two or more primary particles.
(6) The image recording method according to any one of (1) to (5) above, wherein the content of the material for forming a porous medium in the treatment liquid is 0.5% by mass or more and 20% by mass or less.
(7) The image recording method according to any one of (1) to (6) above, wherein the material for forming a porous medium in the treatment liquid and the solid content in the metallic ink are both anionic or both cationic.
(8) The image recording method according to any one of (1) to (7) above, wherein the treatment liquid and the metallic ink are reactive with each other.
(9) The image recording method according to any one of (1) to (8) above, wherein the treatment liquid and the metallic ink are applied by a pre-applying method in which both are ejected onto the recording medium from an inkjet head.
(10) The image recording method according to any one of (1) to (8) above, wherein the treatment liquid is applied onto the recording medium by a pre-coating method.
(11) An ink set of a treatment liquid and a metallic ink for use in the image recording method according to any one of (1) to (10) above.

In the present invention, the treatment liquid contains a porous forming material, and a porous layer (hereinafter also referred to as an ink receiving layer) is formed on the recording medium by applying the treatment liquid onto the recording medium.
The porous layer may have pores that absorb the solution and resin contained in the ink without absorbing the metallic pigment in the ink.
In the present invention, the pores refer to voids observed when the porous layer formed on the recording medium is observed from the porous surface side. The observation method includes a method of observing an image of the porous layer on the recording medium using a SEM.
By using a porous material (such as colloidal silica or colloidal alumina), an ink receiving layer that is both highly smooth and highly absorbent can be formed. When a metallic ink is applied onto the ink receiving layer that is both highly smooth and highly absorbent, the pigment in the metallic ink forms an ink layer along the highly smooth ink receiving layer, and since the ink dries quickly due to its high water absorption, unevenness and beading are unlikely to occur, so that an extremely smooth ink layer can be formed.

It is important that the surface tension of the treatment liquid at 23° C. and the surface tension of the metallic ink at 23° C. satisfy the following relational expression (1).
Surface tension of metallic ink≧Surface tension of treatment liquid (1)
This is because it is desirable for the treatment liquid to wet the recording medium more easily.
However, the surface tension value in the present invention is a value measured using an automatic surface tensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. as a measuring instrument.

When forming an image by ejecting treatment liquid using the pre-deposition method, if the metallic ink deposited on top of the dots formed by the treatment liquid exceeds the area wetted by the treatment liquid and becomes wet, the excess area will have a different glossiness than the area that does not, causing the edges to be bordered, resulting in an image that gives the impression of an overall reduced glossiness. It is desirable for the dots formed by the treatment liquid to be the same diameter or larger than the dots formed by the metallic ink.

It is desirable for the treatment liquid to have a relatively high viscosity. When the treatment liquid has a high viscosity and low surface tension, the effect of improving image quality is further enhanced. It is preferable for the treatment liquid to have a viscosity of about 3 to 30 mPa·s. The treatment liquid has low surface tension and a relatively high viscosity, making it slow to penetrate. A treatment liquid with slow penetration is preferable because it spreads in droplets thinly and widely over the surface of the recording medium with a relatively small amount of application, making it possible to suppress bleeding of metallic inks that are applied in layers, and it also dries relatively quickly.
When observing the cross section of a printed matter, it is found that the thickness of the layer differs when the treatment liquid and metallic ink are printed in the same volume and proportion, and that the print printed with the low surface tension treatment liquid has a thinner color material layer and a lower strike-through density. Based on the above-mentioned reasoning, this phenomenon can be explained with reference to the following Figure 6. However, the present invention does not depend on this reasoning.
The above viscosity values were measured at 25° C. using a C-type viscometer.

Step 1 Immediately after ink landing When a high surface tension treatment liquid is used, the treatment liquid does not embed itself into the recording medium well, whereas in the case of a high viscosity, low surface tension treatment liquid, the high viscosity prevents the liquid from penetrating immediately, and the low surface tension causes the liquid droplets to break up and spread widely, embedding the liquid on the surface of the recording medium and providing good embedment.

Step 2 to Step 3: Coagulation reaction to fixation When a high surface tension treatment liquid is used, the penetration depth of the treatment liquid becomes deeper, so the ions are required to travel a greater distance, and the reaction takes longer. During this time, unreacted coloring material spreads and causes feathering, and the coloring material penetrates deep into the recording medium from areas where it is not filled well, causing strike-through. In addition, the surface roughness of the ink layer surface of the metallic ink is significantly different between areas with and without treatment liquid, resulting in unevenness.
In contrast, with a high-viscosity, low-surface tension treatment liquid, the treatment liquid spreads widely, so the penetration depth of the treatment liquid is shallow, and since the required distance for ions to travel is short, it is thought that coagulation occurs in a relatively short time. This reduces feathering and color bleeding. It is also thought that the surface tension of the ink is lowered, but because the treatment liquid fills the recording medium well, it cannot penetrate to the back and spreads sideways, resulting in better filling of the coloring material. This improves the 20° gloss of the ink layer of the metallic ink and reduces unevenness.

Even when an image is formed by applying treatment liquid to the entire surface of a recording medium using a pre-coating method, a treatment liquid with low surface tension can form a flatter ink-receiving layer, and the ink layer formed on top of that is affected by the surface roughness of the ink-receiving layer, so it is preferable for the surface tension of the treatment liquid to be low. In contrast, the surface tension of metallic ink needs to be low enough to allow solids to fulfill 100% duty, taking into account the trade-off with defects such as image bleeding, feathering, and color boundary bleeding, and it is important that the surface tension of the treatment liquid is equal to or lower than that of the metallic ink.

Specifically, the surface tension of the metallic ink must be 19 mN/m or more and 28 mN/m or less, and is preferably 21 mN/m or more and 25 mN/m or less. If the surface tension is greater than 28 mN/m, the metallic ink will not wet and spread sufficiently, and high glossiness will not be obtained. The ink receiving layer formed by the treatment liquid of the present invention has high water absorption, so the solvent of the metallic ink easily penetrates and does not wet and spread easily. If the surface tension is less than 19 mN/m, the metallic ink will wet too easily, which is undesirable as it will cause bleeding or bleeding at the color boundary with the color ink.
In order to set the surface tension of the metallic ink to 19 mN/m or more and 28 mN/m or less, the metallic ink preferably contains a surfactant.
In order to lower the surface tension of the metallic ink, the metallic ink may also contain a surfactant.

The surface tension of the treatment liquid is preferably from 17 to 25 mN/m, and more preferably from 18 to 23 mN/m.
It is preferable that the difference between the surface tension of the metallic ink and the surface tension of the treatment liquid is 0 or that the surface tension of the metallic ink is greater than the surface tension of the treatment liquid.

<Material for forming porous>
The porous material is not particularly limited as long as it can be applied to a recording medium to form a porous layer that absorbs the solution and resin contained in the ink without absorbing the metallic pigment in the ink, and examples of the porous material include inorganic particles, hollow resin fine particles, and inorganic hollow particles. As the porous material, it is preferable to use inorganic particles, particularly silica or alumina, which have excellent film-forming properties, film uniformity, adhesion, and safety on paper, polyethylene terephthalate (PET), resin-based substrates such as vinyl chloride, and non-absorbent recording media. A commercially available recording medium with a coating layer containing silica or alumina may be used, but the porous layer according to the present invention can be formed by applying the porous material onto the coating layer.
The physical properties of the treatment liquid, such as viscosity and surface tension, can be controlled by the particle size of the porous forming material, such as alumina or silica, the type of solvent, a surfactant, etc. By controlling the physical properties of the treatment liquid, it is possible to prepare a treatment liquid that has ejection suitability for ejecting from an inkjet head, for example.
The material forming the porous layer, such as alumina or silica, can be detected by fluorescent X-ray analysis.
The porous layer preferably has an average pore size of more than 200 nm and not more than 400 nm, and an average thickness of 5 μm or more and 30 μm or less.

The water absorption performance of the porous material is preferably 0.004 (ml/m2·ms) or more and 0.16 (ml/m2·ms) or less, and more preferably 0.014 (ml/ ^m2 ·ms) or more and 0.11 (ml/m2·ms) or less, in terms of the penetration rate of pure water (contact time: average penetration rate at five points (33 ms, ⁷² ms, ¹²⁷ ms, 197 ms, 283 ms) between 33 ms and ²⁸³ ms from the start).
The content of the porous material in the ink is preferably from 0.5% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass.

The treatment liquid preferably contains at least one of silica and alumina as a porous forming material, and may further contain, as necessary, a solvent, a resin, a surfactant, a defoamer, an antiseptic/fungal agent, an antirust agent, a pH adjuster, etc. In order to lower the surface tension of the treatment liquid, it is preferable that the treatment liquid contains a surfactant.
The solvent includes an organic solvent and water.
In addition, commercially available sol or gel coating materials of silica or alumina can also be used.

<<Silica or Alumina>>
The shape of silica or alumina as a porous material may be spherical, or the particles may be specially treated to be connected in a beaded shape or branched (e.g., chain-like, pearl necklace-like, etc.) Beaded fine particles containing secondary particles formed by agglomeration of two or more primary particles are preferred.
Furthermore, those whose surfaces are modified with ions or compounds such as ammonia, calcium, alumina, etc. may also be used.
As the silica, commercially available products can be used, for example, Snowtex S, Snowtex N, Snowtex UP, Snowtex PS-M, Snowtex PS-S, ST-XS, ST-O-40, ST-O, ST-OS, ST-OXS, ST-C, ST-20, ST-30, Snowtex OUP, Snowtex PS-MO, Snowtex PS-SO, (all manufactured by Nissan Chemical Industries, Ltd.), Cataloid SI-350, Cataloid SI-30, SN, SA, S-20L, S-20H, S-30L, S-30H (all manufactured by JGC Catalysts and Chemicals Industries, Ltd.), Aerosil 200, 200V, 200CF, 300 (all manufactured by Nippon Aerosil Co., Ltd.), and the like.
As the alumina, commercially available products can be used, and examples thereof include AS-200 (manufactured by Nissan Chemical Industries, Ltd.), AS-3J (manufactured by JGC Catalysts and Chemicals Industries, Ltd.), Alumina Clearsol 5S, F1000, F3000, A2, 10A, 10D, and CSA-110AD (all manufactured by Kawaken Fine Chemicals Co., Ltd.).
Snowtec AK (both manufactured by Nissan Chemical Industries, Ltd.) is an example of silica whose surface has been modified with alumina.
The preferred primary particle size of inorganic particles such as silica and alumina is 10 nm or more and 200 nm or less.
The smaller the primary particle size, the flatter the porous layer becomes, and the more lustrous the layer tends to be.
Furthermore, if the primary particle diameter is the same, particles consisting of a plurality of beads linked together tend to be more porous and have higher brilliance.

The silica and alumina content is preferably 20% by mass or less, more preferably 15% by mass or less. When both silica and alumina are included, the total content is preferably 20% by mass or less, more preferably 15% by mass or less.

<<Charge of inorganic particles>>
In metallic inks, the charge of the pigment is adjusted to be anionic or cationic to ensure the dispersibility of the pigment.
Similarly, it is desirable to adjust the charge of inorganic particles in the treatment liquid to anionic or cationic to ensure dispersibility.
Here, when the material for forming a porous medium in the treatment liquid and the solid content in the metallic ink are both anionic or cationic, the metallic ink and the treatment liquid are not reactive with each other.

If the metallic ink and the treatment liquid are not reactive, a head that ejects the metallic ink and treatment liquid can be easily mounted on the same carriage, and the treatment liquid can be first applied to the recording medium using the inkjet method, after which the metallic ink can be applied to the recording medium using the inkjet method to form an image.

When the porous forming material in the treatment liquid and the solid content in the metallic ink are anionic or cationic, respectively, and the metallic ink and the treatment liquid are reactive, it is not easy to mount a head that ejects the metallic ink and the treatment liquid on the same carriage due to concerns about clogging of the inkjet head. In such a case, for example, a common maintenance unit cannot be used. It is necessary to prepare a structure and system that prevents the metallic ink and the treatment liquid from mixing with each other on the respective nozzles. In order to incorporate these systems, the housing of the image recording device becomes large and expensive.
When the treatment liquid contains a cationic component and the metallic ink contains an anionic component, or when the treatment liquid contains an anionic component and the metallic ink contains a cationic component, the inorganic particles and the metal pigment undergo an aggregation reaction.

In the solid content of the metallic ink, the metal pigment is anionic or cationic, and is preferably anionic when the treatment liquid contains a cationic component, and is preferably cationic when the treatment liquid contains an anionic component. The bleeding and abrasion resistance of the metallic ink are improved by aggregation of the metal pigment and the components in the treatment liquid.
In order to ensure the storage stability of the metallic ink, the solid components in the metallic ink other than the metallic pigment (surfactants, resins, etc.) must be of the same nature as the metallic pigment or nonionic and must not coagulate with the metallic pigment.

The content of the metal pigment in the ink is preferably from 1.0% by mass to 30% by mass, and more preferably from 2.5% by mass to 20% by mass from the viewpoint of ejection stability.
When the treatment liquid contains a cationic component, the content of the anionic component is preferably equal to or greater than the amount of the cationic component, but not more than 1.5 times the amount of the cationic component.
When the treatment liquid contains an anionic component, it is preferable that the content of the cationic component is equal to or greater than the amount of the anionic component, but not exceed 1.5 times the amount.
If the amount of the pigment contained in the ink is 0.4% by mass or less, even if the pigment contains cationic pigments relative to anionic pigments, or cationic pigments relative to anionic pigments, the effects of bleed resistance and abrasion resistance are within an acceptable range.

When the metallic ink and the treatment liquid are reactive, it is possible to form images using the pre-deposition method by preparing a structure and system in which the heads are mounted on different carriages, or the inkjet heads that eject the metallic ink and treatment liquid are positioned sufficiently apart.

A pre-coating method can also be used as an image recording method using metallic ink and a processing liquid.
The pre-coating method is an image recording method in which a treatment liquid is first applied to a recording medium using a roller or wire bar, and then a metallic ink is applied using an inkjet head.
If a pre-coating method is used, even if the metallic ink and the treatment liquid are reactive, the inkjet head that ejects the metallic ink is less likely to become clogged.

On the other hand, however, there are also advantages to the treatment liquid being reactive with the metallic ink.
Even if the drying of the treatment liquid is not yet sufficient to form an ink receiving layer, the metallic ink applied on top of the treatment liquid will react and separate into two layers: a layer made of the porous forming material in the treatment liquid and an ink layer made of the metallic pigment, and will aggregate. Because of this, the treatment liquid and the metallic ink are less likely to mix, making it possible to overlay the metallic ink while the treatment liquid is still semi-dried, and it is possible to form images faster than when the treatment liquid is not reactive with the metallic ink.
Furthermore, by coagulating, the metallic ink becomes less likely to wet and spread, thereby suppressing bleeding, and since it becomes less likely to be redispersed, bleeding at color boundaries is also suppressed.

Regardless of whether the treatment liquid and metallic ink are reactive or not, applying the metallic ink onto the ink receiving layer after the treatment liquid has sufficiently dried to form the ink receiving layer will result in a flatter surface roughness of the ink receiving layer when the ink receiving layer is formed, allowing an ink layer to be formed with a higher metallic ink, resulting in a recorded product with high brilliance.

Sufficient time and heat are required to thoroughly dry the treatment liquid, and when performing serial inkjet printing and pre-printing, control is required to ensure that the treatment liquid and metallic ink are printed on the recording medium without overlapping in the same pass.

As a guideline for the drying state, if the treatment liquid is allowed to reach a solvent evaporation rate of 50% or more and the metallic ink is applied after the solid-gas interface of the ink receiving layer has been formed, the surface roughness of the ink layer produced by the metallic ink will not be too rough, and a highly lustrous recorded product can be obtained.
If the solvent evaporation rate of the treatment liquid is less than 50%, and the treatment liquid and the metallic ink are not reactive, the treatment liquid and the metallic ink will mix after landing, making it difficult to obtain high brilliance.
If the treatment liquid and the metallic ink are reactive, the metallic ink and the treatment liquid can be separated into two layers to form an ink-receiving layer and a metallic ink layer. However, this still makes it difficult to obtain high brilliance because the individual interfaces between the ink-receiving layer and the metallic ink layer are not flat.

When forming the ink receiving layer, the layer may be naturally dried at room temperature, or may be heated to accelerate drying. The preferred drying temperature range is 30°C to 80°C, and 40°C to 70°C is more preferred from the standpoint of both the drying ability of the treatment liquid and preventing thickening of the liquid components near the nozzles of the head.

The inkjet method is preferably used to form the porous ink receiving layer, but other methods, such as blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating, can also be used to apply the treatment liquid onto the recording medium to form a porous layer.

<Organic Solvent>
The organic solvent used in the treatment liquid and metallic ink of the present invention is not particularly limited, and any water-soluble organic solvent can be used, such as ethers such as polyhydric alcohols, polyhydric alcohol alkyl ethers, and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, and the like. polyhydric alcohols such as pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and petriol; ethylene glycol monoethyl ether; and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate, and ethylene carbonate.
It is preferable to use an organic solvent having a boiling point of 250° C. or less, since this not only functions as a wetting agent but also provides good drying properties.

Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also suitably used. Specific examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.
Specific examples of the glycol ether compound include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

Polyol compounds with 8 or more carbon atoms and glycol ether compounds can improve the permeability of the treatment liquid when paper is used as the recording medium.

The content of the organic solvent in the treatment liquid is not particularly limited and can be selected appropriately depending on the purpose, but from the viewpoint of the drying property and ejection reliability of the treatment liquid, it is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

<Water>
Water is the main medium of the treatment liquid, and preferred water is pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, or ultrapure water, with the aim of minimizing ionic impurities. In addition, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide, since this can prevent the growth of mold and bacteria when the treatment liquid is stored for a long period of time.
The water content in the treatment liquid is not particularly limited and can be appropriately selected depending on the purpose. However, from the viewpoints of reducing the environmental load and allowing the inclusion of other components, the water content is preferably 10% by mass or more and 75% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

<Resin>
The type of the resin is not particularly limited and can be appropriately selected depending on the purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, acrylic silicone resin, etc. can be mentioned. Resin particles made of these resins may be used. It is possible to obtain a porous forming material by mixing the resin particles in a resin emulsion state in which the resin particles are dispersed using water as a dispersion medium with materials such as a coloring material and an organic solvent. As the resin particles, those appropriately synthesized may be used, or commercially available products may be used. In addition, these may be used alone or in combination of two or more types of resin particles.

As the resin, a water-soluble resin is also preferably used. The water-soluble resin is not particularly limited, and examples thereof include proteins such as gelatin and casein, natural gums such as gum arabic, glucoxides such as savonin, cellulose derivatives such as methylcellulose, carboxymethylcellulose, and hydroxymethylcellulose, natural polymers such as lignin sulfonates and shellac, polyacrylates, polyacrylamides, styrene-acrylic acid copolymer salts, vinylnaphthalene-acrylic acid copolymer salts, styrene-maleic acid copolymer salts, vinylnaphthalene-maleic acid copolymer salts, sodium salts of β-naphthalenesulfonic acid formalin condensates, ionic polymers such as polyphosphoric acid, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polypropylene glycol, polyethylene oxide, polyvinyl methyl ether, and polyethyleneimine.

The content of the resin is preferably 0.05% by mass or more and 10.0% by mass or less, and more preferably 0.3% by mass or more and 4.0% by mass or less, based on the total amount of the treatment liquid. Within this range, the resin's functions are optimally exerted, and good abrasion resistance is obtained. It is also preferable because a suitable metallic luster is obtained.

<Surfactant>
As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
There are no particular limitations on the silicone surfactant, and it can be appropriately selected depending on the purpose.
Among them, those that do not decompose even at high pH are preferred, and examples thereof include side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they show good properties as an aqueous surfactant. In addition, as the silicone surfactant, a polyether modified silicone surfactant can also be used, and examples thereof include a compound in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane, etc.
As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compound, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate compound, perfluoroalkyl ethylene oxide adduct, and polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain are particularly preferred because they have low foaming properties. As the perfluoroalkyl sulfonic acid compound, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. are included. As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. are included. As the polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain, for example, sulfate ester salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, etc. are included. Examples of counter ions of the salts in these fluorosurfactants include _Li , Na, K, _NH4 , _NH3CH2CH2OH , _NH2 ( _{CH2CH2OH ) 2} , and _NH ( _CH2CH2OH ) _{3 .}
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

（但し、一般式（Ｓ－１）式中、ｍ、ｎ、ａ、及びｂは、それぞれ独立に、整数を表わし、Ｒは、アルキレン基を表し、Ｒ’は、アルキル基を表す。）
上記のポリエーテル変性シリコーン系界面活性剤としては、市販品を用いることができ、例えば、ＫＦ－６１８、ＫＦ－６４２、ＫＦ－６４３（信越化学工業株式会社）、ＥＭＡＬＥＸ－ＳＳ－５６０２、ＳＳ－１９０６ＥＸ（日本エマルジョン株式会社）、ＦＺ－２１０５、ＦＺ－２１１８、ＦＺ－２１５４、ＦＺ－２１６１、ＦＺ－２１６２、ＦＺ－２１６３、ＦＺ－２１６４（東レ・ダウコーニング・シリコーン株式会社）、ＢＹＫ－３３、ＢＹＫ－３８７（ビックケミー株式会社）、ＴＳＦ４４４０、ＴＳＦ４４５２、ＴＳＦ４４５３（東芝シリコン株式会社）などが挙げられる。 The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the silicone surfactant include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end side-chain modified polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant.
Such surfactants may be synthesized appropriately or may be commercially available products, such as those available from BYK-Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.
The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be a surfactant represented by the general formula (S-1) in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.

(In the general formula (S-1), m, n, a, and b each independently represent an integer, R represents an alkylene group, and R′ represents an alkyl group.)
As the polyether-modified silicone surfactant, commercially available products can be used, for example, KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), and the like.

上記一般式（Ｆ－１）で表される化合物において、水溶性を付与するためにｍは０～１０の整数が好ましく、ｎは０～４０の整数が好ましい。
一般式（Ｆ－２）
Ｃ_nＦ_2n+1－ＣＨ₂ＣＨ(ＯＨ)ＣＨ₂－Ｏ－(ＣＨ₂ＣＨ₂Ｏ)_a－Ｙ
上記一般式（Ｆ－２）で表される化合物において、ＹはＨ、又はＣ_mＦ_2m+1でｍは１～６の整数、又はＣＨ₂ＣＨ(ＯＨ)ＣＨ₂－Ｃ_mＦ_2m+1でｍは４～６の整数、又はＣ_pＨ_2p+1でｐは１～１９の整数である。ｎは１～６の整数である。ａは４～１４の整数である。
上記のフッ素系界面活性剤としては市販品を使用してもよい。
この市販品としては、例えば、サーフロンＳ－１１１、Ｓ－１１２、Ｓ－１１３、Ｓ－１２１、Ｓ－１３１、Ｓ－１３２、Ｓ－１４１、Ｓ－１４５（いずれも、旭硝子株式会社製）；フルラードＦＣ－９３、ＦＣ－９５、ＦＣ－９８、ＦＣ－１２９、ＦＣ－１３５、ＦＣ－１７０Ｃ、ＦＣ－４３０、ＦＣ－４３１（いずれも、住友スリーエム株式会社製）；メガファックＦ－４７０、Ｆ－１４０５、Ｆ－４７４（いずれも、大日本インキ化学工業株式会社製）；ゾニール（Ｚｏｎｙｌ）ＴＢＳ、ＦＳＰ、ＦＳＡ、ＦＳＮ－１００、ＦＳＮ、ＦＳＯ－１００、ＦＳＯ、ＦＳ－３００、ＵＲ、キャプストーンＦＳ－３０、ＦＳ－３１、ＦＳ－３１００、ＦＳ－３４、ＦＳ－３５（いずれも、Ｃｈｅｍｏｕｒｓ社製）；ＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ（いずれも、株式会社ネオス社製）、ポリフォックスＰＦ－１３６Ａ，ＰＦ－１５６Ａ、ＰＦ－１５１Ｎ、ＰＦ－１５４、ＰＦ－１５９（オムノバ社製）、ユニダインＤＳＮ－４０３Ｎ（ダイキン工業株式会社製）などが挙げられ、これらの中でも、良好な印字品質、特に発色性、紙に対する浸透性、濡れ性、均染性が著しく向上する点から、Ｃｈｅｍｏｕｒｓ社製のＦＳ－３１００、ＦＳ－３４、ＦＳ－３００、株式会社ネオス製のＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ、オムノバ社製のポリフォックスＰＦ－１５１Ｎ及びダイキン工業株式会社製のユニダインＤＳＮ－４０３Ｎが特に好ましい。 The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
Examples of the fluorine-based surfactant include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains.
Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferred because they have little foaming property, and in particular, the fluorine-based surfactants represented by the general formulas (F-1) and (F-2) are preferred.

In the compound represented by the above general formula (F-1), m is preferably an integer of 0 to 10, and n is preferably an integer of 0 to 40 in order to impart water solubility.
General formula (F-2)
C _n F _2n+1 -CH ₂ CH(OH)CH ₂ -O-(CH ₂ CH ₂ O) _a -Y
In the compound represented by the above general formula (F-2), Y is H, or C _m F _2m+1 where m is an integer from 1 to 6, or CH ₂ CH(OH)CH ₂ -C _m F _2m+1 where m is an integer from 4 to 6, or C _p H _2p+1 where p is an integer from 1 to 19. n is an integer from 1 to 6. a is an integer from 4 to 14.
As the above fluorosurfactant, a commercially available product may be used.
Examples of commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megafa F-470, F-1405, F-474 (all manufactured by Dainippon Ink & Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR, Capstone FS-30, FS-31, FS-3100, FS-34, FS-35 (all manufactured by Chemours); FT-110, FT- 250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omnova), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.), and the like. Among these, preferred are those which have good print quality, particularly color development and paper adhesion. From the viewpoint of significantly improving the permeability, wettability and uniform dyeing property, FS-3100, FS-34 and FS-300 manufactured by Chemours Corporation, FT-110, FT-250, FT-251, FT-400S, FT-150 and FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omnova Co., Ltd. and Unidyne DSN-403N manufactured by Daikin Industries, Ltd. are particularly preferred.

The content of the surfactant in the treatment liquid is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of excellent wettability and ejection stability and improved image quality, it is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less.

<Antifoaming agent>
The defoaming agent is not particularly limited, and examples thereof include silicone-based defoaming agents, polyether-based defoaming agents, and fatty acid ester-based defoaming agents. These may be used alone or in combination of two or more. Among these, silicone-based defoaming agents are preferred because of their excellent foam breaking effect.

<Preservative and fungicide>
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

<Rust inhibitor>
The rust inhibitor is not particularly limited, and examples thereof include acid sulfite and sodium thiosulfate.

<pH Adjuster>
The pH adjuster must be adjusted to a value that aids in the dispersion of the porous material contained therein. It must be formulated according to this condition. For example, in the case of an anionic treatment liquid having a pH of 7 or more, amines such as diethanolamine and triethanolamine can be used.

The viscosity of the treatment liquid at 25°C is preferably 5 mPa·s or more and 30 mPa·s or less, more preferably 5 mPa·s or more and 25 mPa·s or less, in order to improve the print density and character quality and obtain good ejection properties. Here, the viscosity can be measured using, for example, a rotational viscometer (Toki Sangyo Co., Ltd., RE-80L). The measurement conditions are 25°C, a standard cone rotor (1°34' x R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.

<Metal Pigments>
The metallic ink according to the present embodiment contains a metal pigment. As the metal pigment contained in the metallic ink, any one can be used within the range in which droplets of the metallic ink can be ejected by the inkjet recording method. The glitter pigment has a function of imparting glitter when the metallic ink is attached onto a layer of a resin ink, and can also impart glitter to the attached matter. Examples of such glitter pigments include pearl pigments and metal particles. Representative examples of pearl pigments include pigments having pearlescent or interference luster, such as titanium dioxide-coated mica, fish scale foil, and bismuth oxychloride. On the other hand, examples of metal particles include particles of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, copper, etc., and at least one selected from these simple substances, their alloys, and mixtures thereof can be used. The metal pigment used in the present embodiment can be any pearl pigment or metal particle, and the effect of the implementation can be obtained, but it is preferable to use silver particles from the viewpoint of high gloss (glitter). Below, a silver ink will be used as a specific example of a metallic ink containing a metal pigment.

<Metallic ink application step and metallic ink application unit>
The metallic ink applying step is a step of applying a metallic ink onto a porous layer formed by applying a treatment liquid onto a recording medium, and is performed by a metallic ink applying device.
As an example of the metallic ink applying step, the metallic ink can be applied onto the porous layer using, for example, a bar coater or an inkjet head.
Examples of the metallic ink applying means include a bar coater and an inkjet head.
The metallic ink application step is preferably performed continuously with the step of forming the porous layer. When the metallic ink application step and the step of forming the porous layer are performed continuously, the metallic ink application step and the step of forming the porous layer may be performed in separate devices, but are preferably performed in the same device. By performing the steps in the same device, productivity can be improved and the landing of the metallic ink on the porous layer can be appropriately controlled, thereby obtaining a recorded product with better metallic luster and image clarity.

<<Ink containing silver>>
The ink containing silver (hereinafter, sometimes referred to as silver ink) contains silver, and may further contain additives such as polymer dispersants, organic solvents, water, resins, surfactants, defoamers, antiseptics and antifungals, rust inhibitors, and pH adjusters, if necessary. The silver ink may also be prepared as a silver ink by mixing the silver colloid containing the silver with water and a solvent having a moisturizing function, and the additives may be added if necessary. Silver is a metal with a high whiteness among various metals, and is preferable because it can realize various metallic colors by combining it with inks of other colors. In addition, silver is stable even in water because it has a low reactivity with water. As a result, it is preferable because it can be developed into a water-based glittering ink that can reduce the environmental load.
The organic solvent, the water, the resin, the surfactant, the defoaming agent, the antiseptic and antifungal agent, and the pH adjuster can be the same as those in the treatment liquid according to the present invention.
Furthermore, the effects of the additives, the content of the additives, and the physical properties of the silver ink can also be obtained in the silver ink, similarly to the treatment liquid according to the present invention.

<<Silver>>
The silver can improve the image clarity and metallic gloss of the recorded matter. The silver is preferably silver particles. The number average particle diameter of the silver particles is preferably 15 nm or more and 100 nm or less, more preferably 30 nm or more and 60 nm or less. When the number average particle diameter is 15 nm or more, silver penetrates into the porous medium, and a large number of nanoparticles are present on the bottom surface of the recorded matter, which can suitably suppress the color tone from becoming unnatural due to the reflection of the color tone (yellow) of the silver nanoparticles, and can satisfactorily improve the metallic gloss. In addition, when the number average particle diameter is 100 nm or less, silver in the ink does not settle over time, and ejection stability can be improved.
The number-average particle size can be measured by a laser diffraction particle size distribution measuring device. As the laser diffraction particle size distribution measuring device, for example, a particle size distribution meter using a dynamic light scattering method as a measurement principle (for example, "Microtrac UPA", manufactured by Nikkiso Co., Ltd.) can be used.

The content of silver in the silver ink is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 2.5% by mass or more and 10% by mass or less, based on the total amount of ink. When the content is 1.0% by mass or more, high image clarity and metallic luster can be achieved. Furthermore, when the content is 15.0% by mass or less, good silver dispersion stability, storage stability of the silver ink, and ejection stability can be obtained.

<<Silver colloid liquid>>
It is preferable that silver is dispersed in an aqueous dispersion medium as a silver colloid with a protective colloid attached to its surface. This makes the dispersibility of silver in an aqueous dispersion medium particularly excellent, and the storage stability of the silver ink is significantly improved. The silver colloid may be prepared by any method, and can be obtained, for example, by preparing a solution containing silver ions and reducing the silver ions with a reducing agent in the presence of a protective colloid (see, for example, JP-A-2006-299329). When producing silver colloid by these methods, adding a surfactant or the like to the aqueous solution at any time before or after the reduction reaction further improves the dispersion stability of the silver particles. The protective colloid is not particularly limited as long as it is an organic substance that plays a role in protecting the silver surface, but an organic compound having a carboxyl group and a polymer dispersant are preferable, and one of them may be used alone or two or more of them may be used in combination, but it is more preferable to use them in combination because a synergistic effect can be obtained.

<<Organic compounds having a carboxyl group>>
The number of carboxyl groups in the organic compound having a carboxyl group is not particularly limited as long as it is 1 or more per molecule, and is, for example, preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. In the organic compound having a carboxyl group, a part or all of the carboxyl groups may form a salt (e.g., a salt with an amine, a metal salt, etc.). In particular, in the present invention, an organic compound in which a carboxyl group (particularly, all of the carboxyl groups) does not form a salt (particularly, a salt with a basic compound [a salt with an amine or an amine salt, etc.]) (i.e., an organic compound having a free carboxyl group) can be preferably used.

The organic compound having a carboxyl group is not particularly limited as long as it has a carboxyl group, and can be appropriately selected depending on the purpose. It may also have a functional group other than a carboxyl group (or a coordinating group for a metal compound or metal nanoparticles, etc.).

Examples of such functional groups (or coordinating groups) other than carboxyl groups include groups (or functional groups) having at least one heteroatom selected from halogen atoms, nitrogen atoms, oxygen atoms, and sulfur atoms, or groups that form salts of these (ammonium bases, etc.). These functional groups may be present alone or in combination of two or more types in an organic compound having a carboxyl group.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
Examples of the group having a nitrogen atom include an amino group, a substituted amino group (e.g., a dialkylamino group), an imino group (-NH-), a nitrogen ring group (e.g., a 5- to 8-membered nitrogen ring group such as a pyridyl group, a carbazole group, a morpholinyl group, etc.), an amide group (-CON<), a cyano group, and a nitro group.
Examples of the group having an oxygen atom include a hydroxyl group, an alkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms, such as a methoxy group, an ethoxy group, a propoxy group, or a butoxy group), a formyl group, a carbonyl group (-CO-), an ester group (-COO-), and an oxygen ring group (a 5- to 8-membered oxygen ring group, such as a tetrahydropyranyl group).
Examples of the group having a sulfur atom include a thio group, a thiol group, a thiocarbonyl group (-SO-), an alkylthio group (such as an alkylthio group having 1 to 4 carbon atoms, such as a methylthio group or an ethylthio group), a sulfo group, a sulfamoyl group, and a sulfinyl group (-SO ₂ -).

Of these functional groups, the organic compound having a carboxyl group is preferably a compound that does not have a basic group (especially an amino group, a substituted amino group, an imino group, an ammonium base, etc.) that can form a salt with the carboxyl group.

Representative organic compounds having a carboxyl group include carboxylic acids. Examples of such carboxylic acids include monocarboxylic acids, polycarboxylic acids, and hydroxycarboxylic acids (or oxycarboxylic acids).

Examples of the monocarboxylic acid include saturated aliphatic monocarboxylic acids, unsaturated aliphatic monocarboxylic acids, and aromatic monocarboxylic acids.
Examples of the saturated aliphatic monocarboxylic acid include aliphatic monocarboxylic acids having 1 to 34 carbon atoms (preferably aliphatic monocarboxylic acids having 1 to 30 carbon atoms), such as acetic acid, propionic acid, butyric acid, caprylic acid, caproic acid, hexanoic acid, capric acid, lauric acid, myristic acid, cyclohexanecarboxylic acid, dehydrocholic acid, and cholanic acid.
Examples of the unsaturated aliphatic monocarboxylic acid include unsaturated aliphatic monocarboxylic acids having 4 to 34 carbon atoms (preferably unsaturated aliphatic monocarboxylic acids having 10 to 30 carbon atoms), such as oleic acid, erucic acid, linoleic acid, and abietic acid.
Examples of the aromatic monocarboxylic acid include aromatic monocarboxylic acids having 7 to 12 carbon atoms, such as benzoic acid and naphthoic acid.

Examples of the polycarboxylic acid include saturated aliphatic polycarboxylic acids, unsaturated aliphatic polycarboxylic acids, and aromatic polycarboxylic acids.
Examples of the aliphatic saturated polycarboxylic acid include aliphatic saturated polycarboxylic acids having 2 to 14 carbon atoms (preferably aliphatic saturated polycarboxylic acids having 2 to 10 carbon atoms), such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and cyclohexanedicarboxylic acid.
Examples of the aliphatic unsaturated polycarboxylic acid include aliphatic unsaturated polycarboxylic acids having 4 to 14 carbon atoms (preferably aliphatic unsaturated polycarboxylic acids having 4 to 10 carbon atoms), such as maleic acid, fumaric acid, itaconic acid, sorbic acid, and tetrahydrophthalic acid.
Examples of the aromatic polycarboxylic acid include aromatic polycarboxylic acids having 8 to 12 carbon atoms, such as phthalic acid and trimellitic acid.

Examples of the hydroxycarboxylic acid include hydroxymonocarboxylic acid and hydroxypolycarboxylic acid.
Examples of the hydroxymonocarboxylic acid include aliphatic hydroxymonocarboxylic acids and aromatic hydroxymonocarboxylic acids.
Examples of the aliphatic hydroxymonocarboxylic acid include aliphatic hydroxymonocarboxylic acids having 2 to 50 carbon atoms (preferably aliphatic hydroxymonocarboxylic acids having 2 to 34 carbon atoms, more preferably aliphatic hydroxymonocarboxylic acids having 2 to 30 carbon atoms), such as glycolic acid, lactic acid, oxybutyric acid, glyceric acid, 6-hydroxyhexanoic acid, cholic acid, deoxycholic acid, chenodeoxycholic acid, 12-oxokenodeoxycholic acid, glycocholic acid, lithocholic acid, hyodeoxycholic acid, ursodeoxycholic acid, apocholic acid, and taurocholic acid.
Examples of the aromatic hydroxymonocarboxylic acid include aromatic hydroxymonocarboxylic acids having 7 to 12 carbon atoms, such as salicylic acid, hydroxybenzoic acid, and gallic acid.
Examples of the hydroxypolycarboxylic acid include aliphatic hydroxypolycarboxylic acids.
Examples of the aliphatic hydroxypolycarboxylic acid include aliphatic hydroxypolycarboxylic acids having 2 to 10 carbon atoms, such as tartronic acid, tartaric acid, citric acid, and malic acid.

The carboxylic acid may form a salt, an anhydride, a hydrate, or the like. Here, as with the above, the carboxylic acid often does not form a salt (particularly a salt with a basic compound such as a salt with an amine).

The organic compounds having a carboxyl group may be used alone or in combination of two or more kinds.
The organic compound having a carboxyl group is preferably a hydroxycarboxylic acid such as an aliphatic hydroxycarboxylic acid (an aliphatic hydroxymonocarboxylic acid and an aliphatic hydroxypolycarboxylic acid).
The aliphatic hydroxycarboxylic acid is preferably an alicyclic hydroxycarboxylic acid (or a hydroxycarboxylic acid having an alicyclic skeleton).
The alicyclic hydroxycarboxylic acid (or hydroxycarboxylic acid having an alicyclic skeleton) is preferably an alicyclic hydroxycarboxylic acid having 6 to 34 carbon atoms such as cholic acid, more preferably an alicyclic hydroxycarboxylic acid having 10 to 34 carbon atoms, and particularly preferably an alicyclic hydroxycarboxylic acid having 16 to 30 carbon atoms.

Furthermore, the polycyclic aliphatic hydroxycarboxylic acids such as cholic acid, and the polycyclic aliphatic carboxylic acids such as dehydrocholic acid and cholanic acid have a bulky structure and are highly effective in suppressing the aggregation of silver particles, and are therefore preferred.
Examples of the polycyclic aliphatic hydroxycarboxylic acid include condensed polycyclic aliphatic hydroxycarboxylic acids, preferably condensed polycyclic aliphatic hydroxycarboxylic acids having from 10 to 34 carbon atoms, more preferably condensed polycyclic aliphatic hydroxycarboxylic acids having from 14 to 34 carbon atoms, and particularly preferably condensed polycyclic aliphatic hydroxycarboxylic acids having from 18 to 30 carbon atoms.
Examples of the polycyclic aliphatic carboxylic acid include condensed polycyclic aliphatic carboxylic acids, preferably condensed polycyclic aliphatic carboxylic acids having from 10 to 34 carbon atoms, more preferably condensed polycyclic aliphatic hydroxycarboxylic acids having from 14 to 34 carbon atoms, and particularly preferably condensed polycyclic aliphatic carboxylic acids having from 18 to 30 carbon atoms.

The number average molecular weight of the organic compound having a carboxyl group is, for example, preferably 1,000 or less, more preferably 800 or less, and even more preferably 600 or less. The pKa value of the organic compound having a carboxyl group is, for example, preferably 1 or more, more preferably 2 or more, and even more preferably 2 or more and 8 or less. The number average molecular weight can be measured, for example, by gel permeation chromatography (GPC).

<<Polymer Dispersant>>
In the present invention, it is preferable to form the protective colloid by combining the organic compound having a carboxyl group and a polymer dispersant. By forming the protective colloid with such a combination, a silver colloid containing silver with significantly fewer coarse particles can be obtained. In particular, in the present invention, the combination of the specific protective colloids allows the proportion of silver to be increased despite the small amount of coarse particles, and the storage stability of the silver colloid (or its dispersion) is also excellent.

Examples of polymer dispersants include styrene resins, acrylic resins, water-soluble urethane resins, water-soluble acrylic urethane resins, water-soluble epoxy resins, water-soluble polyester resins, cellulose derivatives, polyvinyl alcohols, polyalkylene glycols, natural polymers, polyethylene sulfonates, formalin condensates of naphthalene sulfonic acid, etc. These may be used alone or in combination of two or more.
Examples of the styrene-based resin include a styrene-(meth)acrylic acid copolymer and a styrene-maleic anhydride copolymer.
Examples of the acrylic resin include methyl (meth)acrylate-(meth)acrylic acid copolymers.
Examples of the cellulose derivatives include cellulose ethers such as alkyl celluloses such as nitrocellulose and ethyl cellulose, alkyl-hydroxyalkyl celluloses such as ethylhydroxyethyl cellulose, hydroxyalkyl celluloses such as hydroxyethyl cellulose and hydroxypropyl cellulose, and carboxyalkyl celluloses such as carboxymethyl cellulose.
Examples of the polyalkylene glycol include gelatin and dextrin.
Examples of the natural polymer include liquid polyethylene glycol and liquid polypropylene glycol.

Typical polymer dispersants (amphiphilic polymer dispersants) include resins (or water-soluble resins, water-dispersible resins) that contain hydrophilic units (or hydrophilic blocks) composed of hydrophilic monomers.

Examples of the hydrophilic monomer include addition polymerization monomers such as carboxyl group or acid anhydride group-containing monomers and hydroxyl group-containing monomers, and condensation monomers such as alkylene oxides (eg, ethylene oxide).
Examples of the acid anhydride group-containing monomer include (meth)acrylic monomers such as acrylic acid and methacrylic acid, unsaturated polycarboxylic acids such as maleic acid, and maleic anhydride.
Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, and vinylphenol.
The condensation monomer may form a hydrophilic unit by reacting with an active group such as a hydroxyl group (for example, the hydroxyl group-containing monomer).
The hydrophilic monomer may be one type alone or two or more types in combination to form a hydrophilic unit.

The polymer dispersant may contain at least a hydrophilic unit (or a hydrophilic block), and may be a homopolymer or copolymer of a hydrophilic monomer (e.g., polyacrylic acid or a salt thereof, etc.), or may be a copolymer of a hydrophilic monomer and a hydrophobic monomer, such as the styrene-based resin and acrylic-based resin exemplified above.

Examples of the hydrophobic monomer (nonionic monomer) include (meth)acrylic monomers such as (meth)acrylic acid esters, styrene-based monomers such as styrene, α-methylstyrene, vinyl toluene, and the like, α-olefin-based monomers having from 2 to 20 carbon atoms, vinyl acetate, vinyl butyrate, and the like. The hydrophobic monomers may be used alone or in combination of two or more to constitute the hydrophobic unit.
Examples of the (meth)acrylic acid ester include alkyl (meth)acrylates having 1 to 20 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; cycloalkyl (meth)acrylates, such as cyclohexyl (meth)acrylate; aryl (meth)acrylates, such as phenyl (meth)acrylate; and aralkyl (meth)acrylates, such as benzyl (meth)acrylate and 2-phenylethyl (meth)acrylate.
Examples of the α-olefin monomer having 2 to 20 carbon atoms include ethylene, propylene, 1-butene, isobutylene, 1-hexene, 1-octene, and 1-dodecene.

When the polymeric dispersant is a copolymer (e.g., a copolymer of a hydrophilic monomer and a hydrophobic monomer), the copolymer may be a random copolymer, an alternating copolymer, a block copolymer (e.g., a copolymer composed of a hydrophilic block composed of a hydrophilic monomer and a hydrophobic block composed of a hydrophobic monomer), a comb copolymer (or a comb graft copolymer), etc.
The structure of the block copolymer is not particularly limited, and may be a diblock structure, a triblock structure (ABA type, BAB type), etc. In the comb copolymer, the main chain may be composed of the hydrophilic block, may be composed of the hydrophobic block, or may be composed of a hydrophilic block and a hydrophobic block.

As mentioned above, the hydrophilic unit can also be composed of a condensation block such as a hydrophilic block (polyalkylene oxide such as polyethylene oxide or polyethylene oxide-polypropylene oxide) composed of alkylene oxide (e.g., ethylene oxide).

The hydrophilic block (eg, polyalkylene oxide) and the hydrophobic block (eg, polyolefin block) may be bonded via a linking group such as an ester bond, an amide bond, an ether bond, or a urethane bond.
The bonds may be formed, for example, by modifying a hydrophobic block (such as a polyolefin) with a modifying agent and then introducing a hydrophilic block.
Examples of the modifying agent include unsaturated carboxylic acids or anhydrides thereof (maleic anhydride, etc.), lactams or aminocarboxylic acids, hydroxylamines, diamines, and the like.

In addition, a comb copolymer (a comb copolymer whose main chain is composed of hydrophobic blocks) may be formed by reacting (or bonding) a polymer obtained from a monomer having a hydrophilic group such as a hydroxyl group or a carboxyl group (such as the above-mentioned hydroxyalkyl (meth)acrylate) with the above-mentioned condensation-type hydrophilic monomer (such as ethylene oxide).

Furthermore, the balance between hydrophilicity and hydrophobicity may be adjusted by using a hydrophilic nonionic monomer as a copolymerization component.
Examples of such components include monomers or oligomers having an alkyleneoxy (particularly ethyleneoxy) unit, such as 2-(2-methoxyethoxy)ethyl (meth)acrylate and polyethylene glycol monomethacrylate (eg, number average molecular weight of about 200 to 1000).
The balance between hydrophilicity and hydrophobicity may also be adjusted by modifying (eg, esterifying) a hydrophilic group (such as a carboxyl group).

The polymer dispersant may have a functional group. Examples of such functional groups include an acid group (or an acidic group, such as a carboxyl group (or an acid anhydride group), a sulfo group (sulfonic acid group), etc.), and a hydroxyl group. The polymer dispersant may have one type of these functional groups alone or two or more types in combination.

Of these functional groups, it is preferable that the polymer dispersant has an acid group, in particular a carboxyl group.
When the polymer dispersant has an acid group (such as a carboxyl group), at least a part or all of the acid groups (such as the carboxyl group) may form a salt (such as a salt with an amine, a metal salt, etc.). In particular, in the present invention, a polymer dispersant in which an acid group such as a carboxyl group (particularly all of the carboxyl groups) does not form a salt [particularly a salt with a basic compound (such as a salt with an amine or an amine salt)] [i.e., a polymer dispersant having a free acid group (particularly a carboxyl group)] can be preferably used.

The acid value of a polymer dispersant having an acid group (particularly a carboxyl group) is, for example, preferably from 1 mgKOH/g to 100 mgKOH/g, more preferably from 3 mgKOH/g to 90 mgKOH/g, even more preferably from 5 mgKOH/g to 80 mgKOH/g, and particularly preferably from 7 mgKOH/g to 70 mgKOH/g. In addition, in a dispersant polymer having an acid group, the amine value may be 0 mgKOH/g (or approximately 0 mgKOH/g).

In the polymer dispersant, the position of the functional group is not particularly limited, and may be located on the main chain, on a side chain, or on both the main chain and the side chain.
Such functional groups may be, for example, functional groups derived from hydrophilic monomers or units (e.g., hydroxyl groups, etc.), or may be introduced into the polymer by copolymerization of copolymerizable monomers having functional groups (e.g., maleic anhydride, etc.).
The polymer dispersants may be used alone or in combination of two or more kinds.
As the polymer dispersant, a polymer dispersant (polymer pigment dispersant) described in JP-A-2004-207558 may be used.
The polymer dispersant may be a synthetic one or a commercially available one.

Specific examples of commercially available polymeric dispersants (or dispersants composed of at least an amphipathic dispersant) include the Solsperse series (manufactured by Avecia Corporation) such as Solsperse 13240, Solsperse 13940, Solsperse 32550, Solsperse 31845, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, and Solsperse 41090; Disperbyk 160, Disperbyk 161, Disperbyk 2100, and Disperbyk 2200; Disperbyk series such as Disperbyk 162, Disperbyk 163, Disperbyk 164, Disperbyk 166, Disperbyk 170, Disperbyk 180, Disperbyk 182, Disperbyk 184, Disperbyk 190, Disperbyk 191, Disperbyk 192, Disperbyk 193, Disperbyk 194, Disperbyk 2001, and Disperbyk 2050 [manufactured by BYK-Chemie Co., Ltd.]; EFKA-46, EFKA -47, EFKA-48, EFKA-49, EFKA-1501, EFKA-1502, EFKA-4540, EFKA-4550, Polymer 100, Polymer 120, Polymer 150, Polymer 400, Polymer 401, Polymer 402, Polymer 403, Polymer 450, Polymer 451, Polymer 452, Polymer 453 [manufactured by EFKA Chemical Co., Ltd.]; Ajisper PB711, Ajisper PAl11, Ajisper PB811, Ajisper PB821, Ajisper PW and the Ajisper series such as 911 [manufactured by Ajinomoto Co., Inc.]; the Florene series such as Florene DOPA-158, Florene DOPA-22, Florene DOPA-17, Florene TG-700, Florene TG-720W, Florene-730W, Florene-740W, and Florene-745W [manufactured by Kyoeisha Chemical Co., Ltd.]; and the Joncryl series such as Joncryl 678, Joncryl 679, and Joncryl 62 [manufactured by Johnson Polymer Corporation].
Among these, examples of polymer dispersants having an acid group include Disperbyk 190 and Disperbyk 194.
The number average molecular weight of the polymer dispersant is, for example, preferably 1,500 to 100,000, more preferably 2,000 to 80,000, further preferably 3,000 to 50,000, and particularly preferably 7,000 to 20,000.
In recent years, silver colloidal solutions have been commercially available from a number of manufacturers, and inks can be prepared using these commercially available products by the preparation method described above.

<Color ink application step and color ink application means>
The image recording method of the present invention may include a color ink applying step.
The color ink applying step is a step of applying color ink containing a coloring material to a recording medium, and is carried out by a color ink applying unit.
As an example of the color ink applying step, the color ink can be applied to the recording medium using, for example, a bar coater or an inkjet head.
Examples of the color ink applying means include a bar coater and an inkjet head.

<<Color ink>>
The color ink contains a coloring material other than the metal pigment, and may further contain, as necessary, a solvent, a resin, a surfactant, a defoaming agent, an antiseptic/fungal agent, an antirust agent, a pH adjuster, and the like.
The color ink is an ink containing a coloring material other than a metal pigment, and is clearly different from a metallic ink containing a metal pigment. The color ink refers to, for example, achromatic ink such as black ink and white ink, and chromatic ink such as yellow ink, magenta ink, and cyan ink.
By applying the color inks, it is possible to reproduce various metallic colors other than silver.
The solvent includes an organic solvent and water.
The organic solvent, the water, the resin, the surfactant, the defoaming agent, the antiseptic and antifungal agent, and the pH adjuster can be the same as those in the treatment liquid according to the present invention.
Furthermore, the effects of the additives, the content of the additives, and the physical properties of the color ink can also be obtained in the color ink, similarly to the treatment liquid according to the present invention.

<<Coloring materials>>
The coloring material is not particularly limited, and a pigment or a dye can be used.
As the pigment, inorganic pigments or organic pigments can be used. These can be used alone or in combination of two or more. Mixed crystals can also be used.
Examples of the pigment that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, and orange pigments.
As inorganic pigments, titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, as well as carbon black produced by known methods such as the contact method, furnace method, and thermal method can be used.
As organic pigments, azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Among these pigments, those having good affinity with the solvent are preferably used. In addition, resin hollow particles and inorganic hollow particles can also be used.
Specific examples of pigments for black colors include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black; metals such as copper, iron (C.I. Pigment Black 11), and titanium oxide; and organic pigments such as aniline black (C.I. Pigment Black 1).
Further, for color, C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C.I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (Red ochre), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38, C.I. Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63, C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.
The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. One type of dye may be used alone, or two or more types may be used in combination.
Examples of the dyes include C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35.

The content of colorant in the ink is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, from the viewpoints of improving image density, good fixing property and ejection stability.

Methods for dispersing a pigment to obtain an ink include a method of introducing a hydrophilic functional group into the pigment to make it a self-dispersing pigment, a method of dispersing the pigment by coating the surface of the pigment with a resin, and a method of dispersing the pigment using a dispersant.
As a method for making a pigment self-dispersible by introducing a hydrophilic functional group into the pigment, for example, a method for making the pigment dispersible in water by adding a functional group such as a sulfone group or a carboxyl group to the pigment (e.g., carbon) can be mentioned.
As a method for dispersing a pigment by coating its surface with a resin, there is a method in which the pigment is encapsulated in a microcapsule to make it dispersible in water. This can be called a resin-coated pigment. In this case, it is not necessary for all of the pigments blended in the ink to be coated with a resin, and uncoated or partially coated pigments may be dispersed in the ink as long as the effect of the present invention is not impaired.
Examples of the method for dispersing using a dispersant include a method for dispersing using a known low molecular weight dispersant or a known polymeric dispersant, such as a surfactant.
As the dispersant, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. can be used depending on the pigment.
RT-100 (nonionic surfactant) manufactured by Takemoto Oil Co., Ltd. and sodium naphthalenesulfonate formalin condensate can also be suitably used as dispersants.
The dispersants may be used alone or in combination of two or more.

<Pigment Dispersion>
It is possible to obtain ink by mixing a pigment with materials such as water or an organic solvent, or it is also possible to manufacture ink by mixing a pigment with other materials such as water or a dispersant to prepare a pigment dispersion, and then mixing the resulting mixture with materials such as water or an organic solvent.
The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and other components as required, and adjusting the particle size. Dispersion is preferably performed using a dispersing machine.
The particle size of the pigment in the pigment dispersion is not particularly limited, but in terms of improving the dispersion stability of the pigment and improving the image quality such as ejection stability and image density, the maximum frequency calculated as the maximum number is preferably 20 nm or more and 500 nm or less, and more preferably 20 nm or more and 150 nm or less. The particle size of the pigment can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).
The content of the pigment in the pigment dispersion is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoints of obtaining good ejection stability and increasing image density, the content of the pigment is preferably from 0.1% by mass to 50% by mass, and more preferably from 0.1% by mass to 30% by mass.
It is preferable that the pigment dispersion is degassed, if necessary, by filtering coarse particles using a filter, a centrifugal separator, or the like.

<<Printed layer containing silver>>
By applying the silver ink to a recording medium to which the treatment liquid has been applied, a print layer containing silver is formed.
The silver-containing print layer is mainly composed of silver, and may contain residual water, solvents, amines, and dispersants contained in the silver ink. Furthermore, it is preferable that the silver-containing print layer contains a resin, which improves the scratch resistance and metallic gloss of the recorded matter.
The content of the resin is preferably 0.2% by mass or more and 50.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total amount of the silver-containing printing layer. When the content is 0.2% by mass or more and 50.0% by mass or less, the function of the resin is preferably exerted, good scratch resistance is obtained, and a suitable metallic luster can also be obtained.
The silver-containing printed layer is preferably formed on a porous layer.

-Thickness of the silver-containing printing layer-
The thickness of the silver-containing printing layer is the thickness after drying, and is the average thickness of the silver-containing printing layer. The thickness of the silver-containing printing layer is preferably in the range of 50 nm to 300 nm, and a recording material excellent in metallic gloss and image clarity can be obtained. In the present invention, the surface of the printing layer is called the "printed surface". When the thickness of the silver-containing printing layer is 50 nm to 300 nm, the brown color tone derived from the plasmon absorption of the metal particles is low, and the metallic gloss and image clarity are improved. In addition, the vehicle of the silver-containing ink can be immediately absorbed by the porous material, and the metallic gloss and image clarity are improved. Note that a layer thickness of at least one silver particle is necessary, and the interaction between the particles increases in the horizontal direction in which the particles are arranged, resulting in the original metallic image clarity. In addition, within the range of the particle diameter of eight silver particles in the vertical direction, the vehicle of the silver-containing ink is immediately absorbed and adsorbed by the porous material, and a printing surface excellent in metallic gloss and image clarity can be obtained.

-About b* value-
In the present invention, in order to ensure high image clarity and a silvery printed surface, the b* value is preferably -7 to +4. The more negative the b* value, the stronger the blueness, and conversely, the more positive the b* value, the stronger the yellowness. When the yellowness becomes stronger, the silver-containing ink of the present invention approaches gold, and when the b* value exceeds +4, the gold color is strongly expressed and the color tone becomes difficult to call silver, and conversely, when the b* value falls below -7, the blueness becomes stronger and the color tone becomes dark and different from silver. The b* value can be easily measured using a spectrophotometer.

<<Printed layer containing color materials other than silver ink>>
The average thickness of the printing layer containing color materials other than the silver ink (printing layer of color ink) is preferably 1 nm or more and 300 nm or less, more preferably 2 nm or more and 250 nm or less. In particular, when toning with silver, it is preferable not to conceal the silver color, and in that case, the average thickness is particularly preferably 3 nm or more and 100 nm or less. If the color is toned within this range, a colored metallic image can be obtained, and a printed surface with good texture in terms of both image clarity and color tone can be obtained. As for the order of toning, it is preferable to print with silver ink, and then print color ink on the silver ink printed part to tone the color.

<<Method for measuring the thickness of a printed layer>>
The printed material can be cut and the cross section observed using a microscope such as an optical microscope, a laser microscope, an SEM, or a transmission electron microscope (also known as a TEM), thereby measuring the thickness of the printed layer containing silver and the printed layer containing a colorant other than silver ink.

<<Recording Media>>
The recording medium is not particularly limited as long as it is possible to form a porous layer on the surface with the treatment liquid of the present invention, and although plain paper, glossy paper, special paper, cloth, etc. can be used, good image formation is also possible using a non-permeable substrate. A receiving layer (such as a porous layer) may or may not be formed in advance on the surface of the recording medium.
In particular, the present invention has the effect of providing excellent media compatibility in that images with excellent image clarity and metallic luster can be formed on the non-permeable substrate, which is usually a porous substrate and does not have an ink-receiving layer formed thereon.

The non-permeable substrate is a substrate having a surface with low water permeability and absorbency, and includes materials that have many cavities inside but are not open to the outside. More quantitatively, the non-permeable substrate is a substrate having a water absorption amount of 10 mL/ ^m2 or less from the start of contact to 30 msec1 ^/2 in the Bristow method.
As the non-permeable substrate, for example, a plastic film such as a polyvinyl chloride resin film, a polyethylene terephthalate (PET) film, a polypropylene film, a polyethylene film, a polycarbonate film, etc. can be suitably used. This is because a plastic film usually does not have a porous surface, making it difficult to obtain gloss and image clarity of silver ink, and therefore the effects of the present invention can be significantly obtained.

The recording medium is not limited to those generally used as recording media, but may be wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc., as appropriate. In addition, by adjusting the configuration of the path for transporting the recording medium, ceramics, glass, metal, etc. may also be used.

Commercially available products can be used as recording media having a pre-existing porous layer. Examples of such commercially available products include IJ film RM-1GP01 (manufactured by Ricoh Co., Ltd., average pore size of porous film: 230 nm), NB-WF-3GF100 (average pore size of porous film: 210 nm), NB-RC-3GR120 (average pore size of porous film: 250 nm) (manufactured by Mitsubishi Paper Mills Co., Ltd.), PT-201A420 (average pore size of porous film: 270 nm), SD-101A450 (average pore size of porous film: 250 nm), GL-101A450 (average pore size of porous film: 240 nm), GP 501A450 (Porous average pore size: 250 nm), SP-101A450 (Porous average pore size: 210 nm), PT-101A420 (Porous average pore size: 240 nm), PR101 (Porous average pore size: 270 nm) ), EJK-QTNA450 (porous average pore diameter: 200 nm), EJK-EPNA450 (porous average pore diameter: 210 nm), EJK-CPNA450 (porous average pore diameter: 220 nm), EJK-RCA450 (porous average pore diameter: 220 nm), Average pore size of porous particles: 240 nm), EJK-CGNA450 (average pore size of porous particles: 190 nm), EJK-GANA450 (average pore size of porous particles: 180 nm), EJK-NANA450 (average pore size of porous particles: 170 nm), EJK-EGNA450 (average pore size of porous particles: 200 nm) (manufactured by ELECOM Co., Ltd.), WPA455VA (average pore size of porous particles: 200 nm), WPA450PRM (average pore size of porous particles: 210 nm), G3A450A (average pore size of porous particles: 2 20 nm), G3A450A (average pore size of porous: 210 nm), WPA420HIC (average pore size of porous: 280 nm) (manufactured by Fujifilm Corporation), KA420SCKR (average pore size of porous: 240 nm), KA450PSKR (average pore size of porous: 230 nm), KA450SLU (average pore size of porous: 210 nm) (manufactured by Seiko Epson Corporation), BP71GAA4 (average pore size of porous: 220 nm) (manufactured by Brother Industries, Ltd.), etc.

- Abrasion resistance of silver-containing ink -
After applying a treatment liquid and a silver-containing ink to a recording medium to form an image, a transparent resin layer (hereinafter sometimes referred to as a laminate layer) can be provided on the silver-containing printed layer to improve abrasion resistance.
Furthermore, after applying an ink containing silver to a recording medium, a transparent resin layer may be provided on the printed layer to which a color ink containing a color material other than silver has been applied.

<Laminate layer forming step and laminate layer forming means>
The laminate layer forming step is a step of further forming a laminate layer on the region to which the silver ink has been applied after the silver ink applying step, and is performed by a laminate layer forming means.
The resin of the laminate layer on the printed layer is preferably highly transparent, and typical examples of such resins include polyethylene terephthalate (PET) and polypropylene (PP). Nylon may also be used, and a method of covering the surface of the printed layer or the entire printed matter by a so-called lamination process is preferred. Alternatively, the printed layer may be covered with an overcoat formed by dissolving a transparent resin in water or a solvent and applying the solution.
In the laminate layer forming step, for example, the layer can be formed by a blade coating method, a gravure coating method, a bar coating method, a roll coating method, a dip coating method, a curtain coating method, a slide coating method, a die coating method, a spray coating method, or the like.
Examples of the laminate layer forming means include a bar coater and a pressure roller.
The average thickness of the resin layer formed on the print layer is preferably 5 μm to 300 μm. When the average thickness of the resin layer is 5 μm or more, the effect of coating is obtained, such as excellent abrasion resistance and durability of the coating film, and the coating film is not easily scratched or broken. When the average thickness of the resin layer is 300 μm or less, in addition to high image clarity, the b* value is 4 or less, and the color tone is excellent.

The method of laminating is preferably to cover the printed portion of the printed matter or the entire printed matter with a resin film and apply heat or pressure without applying heat to cover the printed surface or the entire printed matter by lamination.
As an alternative to lamination, a method of covering with an overcoat made by dissolving a transparent resin in water or a solvent and applying it may be used.

(Recordings)
The recorded matter of the present invention has a porous layer on a recording medium, and a metallic ink layer on the porous layer. It is also preferable that the recorded matter has a plurality of porous droplet marks when observed from the image forming surface side with a scanning electron microscope, and it is also preferable that the recording medium is a non-permeable substrate. Furthermore, a pigment other than the metallic ink pigment may be present on the porous layer.
An image can be recorded by an inkjet image recording apparatus and an inkjet image recording method to produce a recorded matter.

<Droplet trace>
When the porous layer is formed by an inkjet method, multiple droplet marks caused by ink droplets are observed, and therefore the porous layer can be clearly distinguished from the coating layer on the recording medium.
The droplet marks are marks caused by droplets discharged from an inkjet head, and may be circular or may be formed by overlapping circular droplets. When droplets overlap, the droplet marks may be mixed, but as shown in Fig. 7, they have rounded edges and are clearly distinguishable from the uniform marks made by using a bar coater or the like.
Incidentally, droplet marks are observed not only when a treatment liquid is applied to a recording medium using an inkjet method, but also when a silver ink and a color ink, which contain silver, are applied to a recording medium.
Also, FIG. 7 shows droplet marks 501 observed when silver ink is applied onto a recording medium using an inkjet head, but droplet marks like those in FIG. 7 are also observed when color inks and treatment liquid are applied onto a recording medium using an inkjet head.
The droplet marks can be observed, for example, by using a scanning electron microscope (SEM).

<Image recording method 1: Pre-deposition type image recording method>
In the image recording method of the present invention, which is a pre-deposition type image recording method, a treatment liquid is first selectively applied to the recording medium by an inkjet recording method, targeting the areas where the metallic ink is to be applied, and then, metallic ink is applied to the recording medium to which the treatment liquid has been applied, also by using an inkjet recording method.
For the treatment liquid and metallic ink, a serial type image recording device may be used, with both a head that ejects the treatment liquid and a head that ejects the metallic ink mounted on the same carriage. However, if the treatment liquid is reactive with the metallic ink and/or other color inks, it is necessary to construct a system that can maintain ejection stability so as not to cause nozzle clogging.

<Image recording method 2: Pre-coating type image recording method>
The image recording method of the present invention, which is a first-coating type image recording method, is an image recording method in which a treatment liquid is first applied to a part or the entirety of a recording medium by a roller, a bar coater, a spray coating, or the like, and then a metallic ink is applied to the recording medium on which the treatment liquid has been applied by using an inkjet recording method.
The coating area of the treatment liquid is larger than the coating area of the metallic ink.

<Recording device and recording method>
The following describes the case where black (K), cyan (C), magenta (M), and yellow (Y) are used, but metallic inks containing metal pigments may be used instead of or in addition to these. In addition to these, a treatment liquid is also used.
The ink of the present invention can be suitably used in various recording devices using the ink jet recording method, such as printers, facsimile machines, copying machines, printer/fax/copier combination machines, and three-dimensional modeling devices.
In the present invention, the recording apparatus and recording method refer to an apparatus capable of ejecting ink and various treatment liquids onto a recording medium, and a method of recording using the apparatus. The recording medium refers to an object onto which ink and various treatment liquids can be attached even temporarily.
This recording device can include not only a head portion that ejects ink, but also means related to feeding, transporting, and discharging the recording medium, as well as other devices called pre-processing devices and post-processing devices.
The recording apparatus and the recording method may have a heating means used in the heating step and a drying means used in the drying step. The heating means and the drying means include, for example, a means for heating and drying the printed surface and the back surface of the recording medium. The heating means and the drying means are not particularly limited, but for example, a hot air heater or an infrared heater can be used. Heating and drying can be performed before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, those that form patterns such as geometric designs and those that form three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move.
Furthermore, this recording device includes not only desktop types, but also wide-width recording devices that can print on A0-sized recording media, such as continuous-feed printers that can use continuous paper wound into a roll as the recording medium.

<Inkjet recording method>
The inkjet recording method of the present invention preferably comprises at least a step of ejecting the metallic ink (hereinafter also referred to as ink) of the present invention onto a recording medium (also referred to as substrate).
The ink ejection process is a process in which a stimulus is applied to the ink to make it fly and print. There is no particular limitation on the means for ejecting the ink, and it can be appropriately selected according to the purpose, and examples thereof include various recording heads (ink ejection heads). In particular, it is preferable to have a head having a plurality of nozzle rows and a sub-tank that stores ink supplied from an ink cartridge and supplies the ink to the head. It is preferable that the sub-tank has a negative pressure generating means for generating a negative pressure in the sub-tank, an atmosphere opening means for opening the inside of the sub-tank to the atmosphere, and a detection means for detecting the presence or absence of ink based on a difference in electrical resistance.

The stimulus can be generated, for example, by a stimulus generating means. The stimulus is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include heat (temperature), pressure, vibration, light, etc. These may be used alone or in combination of two or more. Among these, heat and pressure are preferred.
Examples of the stimulus generating means include a heating device, a pressure device, a piezoelectric element, a vibration generating device, an ultrasonic oscillator, a light, etc. Specific examples include a piezoelectric actuator such as a piezoelectric element, a thermal actuator that utilizes a phase change caused by film boiling of a liquid using an electrothermal conversion element such as a heating resistor, a shape memory alloy actuator that uses a metal phase change caused by a temperature change, and an electrostatic actuator that uses an electrostatic force.

The manner in which the ink is ejected is not particularly limited and varies depending on the type of the stimulus. For example, when the stimulus is "heat", thermal energy corresponding to a recording signal is applied to the ink in the recording head using, for example, a thermal head, and the thermal energy generates bubbles in the ink, and the pressure of the bubbles causes the ink to be ejected as droplets from the nozzle holes of the recording head. When the stimulus is "pressure", a voltage is applied to a piezoelectric element attached to a position called a pressure chamber in the ink flow path of the recording head, causing the piezoelectric element to bend and the volume of the pressure chamber to shrink, causing the ink to be ejected as droplets from the nozzle holes of the recording head.

Among these, the method of ejecting ink by applying a voltage to a piezoelectric element is preferred. The piezoelectric method is advantageous for ejecting ink containing resin because it does not generate heat, and is an effective method with less nozzle clogging, particularly when using ink with a low content of wetting agent. In addition, in order to prevent nozzle dropout, it is preferable to perform an empty scan by applying a voltage to the piezoelectric element that is strong enough not to eject ink. Furthermore, it is preferable to eject ink into the ink reservoir before reaching the empty scan for printing one page. It is also preferable to have a scraping means for scraping off ink that has adhered to the empty ejection receiver. As the scraping means, either a wiper or a cutter is preferable.

In the present invention, in order to increase the spreading of the ejected ink on the substrate, it is also possible to provide a heating device for heating the substrate before or simultaneously with the deposition of the ink.
As the heating means, one or more heating devices can be appropriately selected from many known heating devices. Examples of the heating device include devices for forced air heating, radiant heating, conductive heating, high frequency drying, and microwave drying. Such a heating device may be built into an existing inkjet printer or may be attached externally to an existing inkjet printer.

1 is a schematic diagram showing an example of an inkjet recording apparatus according to the present invention. Note that the following description corresponds to a serial (shuttle) type inkjet recording apparatus in which a carriage scans, but the apparatus of the present invention can also be applied to a line type inkjet recording apparatus equipped with a line type head.
1 has an apparatus main body 101, a paper feed tray 102 for loading substrates mounted on the apparatus main body 101, a paper discharge tray 103 for stocking substrates mounted on the apparatus main body 101 and printed thereon, and an ink cartridge loading section 104. An operation section 105 including operation keys and a display is disposed on the top surface of the ink cartridge loading section 104. The ink cartridge loading section 104 has an openable front cover 115 for attaching and detaching the ink cartridge 200. Reference numeral 111 denotes the top cover, and 112 denotes the front surface of the front cover.

As shown in FIG. 2, within the apparatus body 101, there are a guide rod 131 and a stay 132 which are guide members that are hung between left and right side plates, and which hold a carriage 133 slidably in the main scanning direction and are moved and scanned by a main scanning motor.
The carriage 133 is mounted with a recording head 134, which consists of four inkjet recording heads that eject ink droplets of each color, yellow (Y), cyan (C), magenta (M), black (Bk), and silver (Si), and has multiple ink ejection ports arranged in a direction intersecting the main scanning direction, with the ink droplet ejection direction facing downward.
The silver ink contains silver nanopigments.

The inkjet recording head constituting the recording head 134 may be provided with a piezoelectric actuator such as a piezoelectric element, a thermal actuator using an electrothermal conversion element such as a heating resistor to utilize a phase change caused by film boiling of a liquid, a shape memory alloy actuator using a metal phase change caused by a temperature change, an electrostatic actuator using electrostatic force, etc. as a stimulus generating means for ejecting ink. The recording head may also have a heater mechanism for heating the ink inside.
Further, sub-tanks 135 of each color are mounted on the carriage 133 to supply ink of each color to the recording head 134. The sub-tanks 135 are replenished with ink supplied from the ink cartridges 200 loaded in the ink cartridge loading section 104 via ink supply tubes.

On the other hand, as a paper feeding section for feeding the substrates 142 loaded on the substrate loading section (pressure plate) 141 of the paper feed tray 102, there is provided a half-moon roller (paper feed roller 143) that separates and feeds the substrates 142 one by one from the substrate loading section 141, and a separation pad 144 that faces the paper feed roller 143 and is made of a material with a large friction coefficient, and this separation pad 144 is biased towards the paper feed roller 143.
As a transport section for transporting the substrate 142 fed from this paper feed section below the recording head 134, there are provided a transport belt 151 for electrostatically adsorbing and transporting the substrate 142, a counter roller 152 for sandwiching and transporting the substrate 142 fed from the paper feed section via a guide 145 between the transport belt 151, a transport guide 153 for changing the direction of the substrate 142 fed approximately vertically upward by approximately 90° to conform to the surface of the transport belt 151, and a tip pressure roller 155 urged toward the transport belt 151 by a pressing member 154, and a charging roller 156 which is a charging means for charging the surface of the transport belt 151.

Although FIG. 2 shows a double-sided paper feed unit 181, in the embodiment of the present invention, this double-sided paper feed unit 181 is replaced with a pre-coating device shown in FIG. 5A.

The pre-coating device of this embodiment is connected to a paper feeder that has the function of storing and sequentially feeding paper, which is the recording medium used for printing, and to a printing device that forms images using an inkjet method. When paper is transported from the paper feeder, the device is set up to apply a specified treatment liquid to the transported paper and transport the coated paper to the printing device.

The pre-coating device of this embodiment is also configured with various components shown in FIG. 5A, such as an application roller 5 that applies treatment liquid 1 to paper 16, a pressure roller 9 that is pressed against and comes into contact with the application roller 5, a transport roller 18 that transports paper 16, a guide roller 17 that guides the transported paper 16, and a control unit 24 that controls the entire device. This allows the treatment liquid 1 in the supply pan 2 to be applied from the application roller 5 to the paper 16 via the squeeze roller 3.

As shown in FIG. 5B, a heater lamp 23 is provided inside the pressure roller 9, and the pressure roller 9 can be heated under the control of the control unit 24. This allows the paper 16 to be heated by the pressure roller 9, which is in NIP contact with the application roller 5, when the treatment liquid 1 is applied to the paper 16 by the application roller 5.

The configuration and operation of the pre-coating device of this embodiment will be described in detail below.
First, the treatment liquid 1 stored in the cartridge 12 is sucked up by the pump 14, which is an electrically driven ink delivery means such as a tubing pump or a diaphragm pump, and is supplied to the supply pan 2 via the supply path 13 and an electromagnetic valve 15. This electromagnetic valve 15 is an opening/closing means for the supply path 13 that is configured to be electrically openable and closable, such as a solenoid valve or a ball valve.

The amount of processing liquid 1 supplied to the supply pan 2 is detected by the liquid level detection sensor 27. When the liquid level detection sensor 27 detects that the amount of processing liquid 1 has fallen below a predetermined threshold, the solenoid valve 15 opens and the pump 14 sucks up the liquid from the cartridge 12 and supplies it up to a preset amount. When the set amount of liquid is reached, the solenoid valve 15 closes and the pump 14 stops, thereby keeping the amount of liquid in the supply pan 2 constant.

In this way, the solenoid valve 15 opens only when the processing liquid 1 is being supplied, and because its operating time is short, the valve is closed except when power is applied. By using a normally closed type, the power consumption of the solenoid valve 15 can be reduced.

Then, the treatment liquid 1 stored in the supply pan 2 is pumped up by the rotation of the squeeze roller 3 driven by the motor 20. If the squeeze roller 3 is an anilox roller or wire bar with grooves on the roller surface, the pumping is less affected by the viscosity of the treatment liquid 1 and the printing speed, making it easier to control the amount of liquid.

The treatment liquid 1 pumped up by the squeeze roller 3 has the excess scraped off by the metering blade 4 and is transported to the NIP point with the application roller 5. The NIP point is the point where adjacent rollers are pressed against each other and come into contact, and is usually arranged in a straight line in the axial direction of the rollers.

The metering blade 4 may be made of metal such as SUS, plastic, or rubber, but a plastic material is preferable from the standpoint of wear on the squeeze roller 3, the ability to scrape off excess liquid, and the lifespan.

The treatment liquid 1 that is transported to the NIP point between the application roller 5 and the squeeze roller 3 is applied to the application roller 5 while being uniformly stretched in the axial direction between the application roller 5 and the squeeze roller 3. The application roller 5 has a circumferential surface covered with an elastic material such as rubber, and is driven by the motor 6 via the one-way clutch 7.

The treatment liquid 1 applied to the application roller 5 is transferred to the paper 16 by NIP between the pressure roller 9 and the application roller 5. The pressure roller 9 is rotatably supported via a bearing in the center of a swingable arm 21, and is driven by the paper 16 by NIP.

5B, the inside of the pressure roller 9 is hollow and contains a heater lamp 23. Since this device has a mechanism for simultaneously performing application and NIP of the paper, by containing the heater lamp 23 in the pressure roller 9, it is possible to apply heat only to the area where the liquid is to be applied.
This allows only the minimum necessary area to be heated, preventing excessive heating of the paper and paper deformation. Furthermore, by incorporating the heater lamp 23 in the pressure roller 9, the device can be prevented from becoming large.

A temperature sensor 22 for detecting temperature is disposed near the pressure roller 9, and a temperature sensor 25 is disposed near the paper immediately after application. A control unit 24 controls a heater lamp 23 based on the temperatures measured by the temperature sensors 22 and 25. After the pressure roller 9 is heated to a predetermined set temperature, the paper 16 and application roller 5 are nipped to heat the paper 16.
In this way, the heater lamp 23 functions as a heating device that heats the paper 16 at the position of contact with the application roller 5 .

The conveyor belt 151 is an endless belt, stretched between a conveyor roller 157 and a tension roller 158, and can rotate in the belt conveying direction. The conveyor belt 151 has a surface layer that is a substrate adsorption surface formed of a resin material (e.g., a copolymer of tetrafluoroethylene and ethylene (ETFE)) with a thickness of about 40 μm that is not subjected to resistance control, and a back layer (medium resistance layer, earth layer) made of the same material as the surface layer and subjected to resistance control with carbon. On the back side of the conveyor belt 151, a guide member 161 is arranged corresponding to the printing area by the recording head 134. The evaluation machine of the present invention is a modified machine equipped with a film heater on the guide member. It is possible to heat the guide member to any temperature and heat the recording medium to print.
In addition, as a paper discharge section for discharging the substrate 142 recorded by the recording head 134, a separation claw 171 for separating the substrate 142 from the conveyor belt 151, a paper discharge roller 172 and a paper discharge roller 173 are provided, and the substrate 142 is dried with hot air by an additional fan heater 174, and then output to the paper discharge tray 103 below the paper discharge roller 172.

<Serial type inkjet recording device>
An example of a recording apparatus will be described with reference to Figs. 3 and 4. Fig. 3 is a perspective view of the apparatus. Fig. 4 is a perspective view of a main tank. An image forming apparatus 400 as an example of a recording apparatus is a serial type image recording apparatus. A mechanism section 420 is provided in an exterior 401 of the image recording apparatus 400. Each ink storage section 411 of the main tanks 410 (410k, 410c, 410m, 410y, 410si) for each color of black (K), cyan (C), magenta (M), yellow (Y), and silver (Si) is formed of a packaging material such as an aluminum laminate film. The ink storage section 411 is stored in a storage container case 414 made of plastic, for example. As a result, the main tanks 410 are used as ink cartridges of each color.
On the other hand, a cartridge holder 404 is provided at the rear of the opening when the cover 401c of the apparatus body is opened. A main tank 410 is detachably attached to the cartridge holder 404. This allows each ink outlet 413 of the main tank 410 to communicate with an ejection head 434 for each color via a supply tube 436 for each color, making it possible to eject ink from the ejection head 434 onto a recording medium.

This recording apparatus includes not only a portion that ejects ink, but also a pre-treatment device that applies a treatment liquid, and may include a device called a post-treatment device.
As one aspect of the pre-treatment device and post-treatment device, a liquid storage section having a treatment liquid and a post-treatment liquid and a liquid ejection head are added, as in the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y), and the like, and the treatment liquid and the post-treatment liquid are ejected by an inkjet recording method.
As another embodiment of the pre-treatment device and the post-treatment device, there is an embodiment in which a pre-treatment device and a post-treatment device using a method other than the inkjet recording method, for example, a blade coating method, a roll coating method, or a spray coating method, are provided.

The ink can be used in a wide variety of ways, not just inkjet recording. In addition to inkjet recording, other methods include blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating.

The use of the ink of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and can be applied to, for example, printed matter, paint, coating material, undercoat, etc. Furthermore, the ink can be used not only as an ink for forming two-dimensional characters and images, but also as a material for three-dimensional modeling for forming three-dimensional images (three-dimensional objects).
A known three-dimensional modeling device for forming a three-dimensional object can be used, and is not particularly limited. For example, a device equipped with an ink storage means, supply means, discharge means, drying means, etc. can be used. The three-dimensional object includes a three-dimensional object obtained by applying ink over and over. Also included is a molded product obtained by processing a structure to which ink is applied on a substrate such as a recording medium. The molded product is, for example, a recording material or structure formed in a sheet or film shape, which is molded by heat stretching, punching, etc., and is preferably used for applications in which the surface is molded after decoration, such as meters and operation panel of automobiles, office automation equipment, electric and electronic equipment, cameras, etc.

In addition, in the terminology of this invention, image formation, recording, printing, printing, etc. are all synonymous.

Recording medium, media, and printed material are all synonymous.

The following describes examples of the present invention, but the present invention is not limited to these examples.

<Preparation of Processing Solution>
<Preparation of White Pigment Dispersion Liquid/Inorganic Hollow Particle Dispersion 1>
In a beaker, 10.0 g of DISPERBYK-2008 (acrylic copolymer manufactured by BYK, active ingredient 60%) was dissolved in 294.0 g of highly purified water, and the mixture was stirred for 30 minutes at 5,000 rpm using an Excel Auto Homogenizer manufactured by Nippon Seiki Seisakusho. While stirring for 30 minutes, 50.0 g of inorganic hollow particles (Silinax: hollow silica manufactured by Nittetsu Mining Co., Ltd. (primary particle diameter 80 to 130 nm, silica film thickness 5 to 15 nm)) was added in 10 portions and mixed until the mixture was dispersed without any lumps. The rotation speed was gradually increased, and the mixture was stirred for 30 minutes at 10,000 rpm.
The obtained pigment dispersion was treated with an ultrasonic homogenizer US-300T (tip φ26) manufactured by Nippon Seiki Seisakusho at 200 μA for 1 hour while being cooled with water, and then filtered with a 5 μm membrane filter (cellulose acetate membrane) to obtain an inorganic hollow particle dispersion 1 containing 14.1 mass % of inorganic hollow particles.
Treatment solutions 1 to 12 were prepared according to the formulations shown in Table 1 below.

<Preparation of Metallic Ink>
(Preparation of Silver Particle Dispersion 1)
66.8 g of silver nitrate, 5.2 g of a dispersant polymer having a carboxyl group (manufactured by Big Chemie Japan Co., Ltd., product name: "Disperbyk 190 (BYK-190)" solvent: water, non-volatile components 40 mass%, acid value: 10 mg KOH / g, amine value: 0 mg KOH / g), and 1.8 g of cholic acid (manufactured by Wako Pure Chemical Industries, Ltd.) were added to 35 g of ion-exchanged water and vigorously stirred to obtain a suspension. To this suspension, 9.1 g of an amine aqueous solution (dimethylaminoethanol 23.3% aqueous solution) obtained by mixing 1.1 g of dimethylaminoethanol (manufactured by Wako Pure Chemical Industries, Ltd.) with 7.0 g of water was gradually added so that the water temperature did not exceed 50 ° C., and then heated and stirred in a water bath at a water temperature of 60 ° C. for 2.5 hours. The obtained reaction solution was filtered through a glass filter (GC-90, manufactured by ADVANTEC Corporation, average pore size: 0.8 μm) to obtain Silver Particle Dispersion 1 containing 40 mass % silver, a BYK-190 nonvolatile content of 3%, and 1% dimethylaminoethanol. The particle size distribution of the silver particles in the obtained Silver Particle Dispersion 1 was measured using a particle size analyzer (Nanotrac Wave-EX150, manufactured by Nikkiso Co., Ltd.), and the number average particle diameter (D50) of the primary particles was 20 nm.
Metallic inks 1 to 5 were prepared according to the formulations shown in Table 2 below.

<Examples 1 to 11 and Comparative Examples 1 to 6>
A print was produced by printing using an ink set consisting of the treatment liquid and metallic ink shown in Table 3, according to the image recording method 1 described below. Each print was ranked according to <20° gloss>, <bleeding>, and <unevenness>. The results of each ranking are shown in Table 3.

<Image recording method 1: Pre-deposition type image recording method>
The prints of Examples 1 to 11 and Comparative Examples 1 to 6 were created using a modified RICOH Pro VC60000, a line-type inkjet recording device. The prints were created by ejecting treatment liquid from the head on the upstream side of the paper feed and metallic ink from the head on the downstream side. Both heads were sufficiently separated so that printing was possible without causing nozzle clogging. In the modified machine, a drying mechanism for drying the treatment liquid on the recording medium is provided between the head group ejecting treatment liquid on the upstream side and the head group ejecting metallic ink on the downstream side.
The recording medium used was OK Topcoat+ (127.9 g/m ² ) (manufactured by Oji Paper Co., Ltd.), and printing was performed at a resolution of 600 dpi×600 dpi and a paper feed speed of 5 m/min.
In addition, by observing an image of the porous layer on the recording medium taken with an SEM, it was confirmed that the porous layer had pores.

<20° Gloss> Rank Evaluation The 20° gloss of the recorded material after drying was measured using a gloss meter (Micro Trigloss, manufactured by BYK Gardener).
When printing on coated paper is assumed, the 20° gloss value is preferably at least 40. More preferably, it is at least 100. In the present invention, the acceptable range is set to 40 or more (rank B or more).
[Evaluation Criteria]
S: 20 degree gloss 225 or more AAA: 20 degree gloss 200 or more and less than 225 AA: 20 degree gloss 160 or more and less than 200 A: 20 degree gloss 100 or more and less than 160 B: 20 degree gloss 40 or more and less than 100 C: 20 degree gloss less than 40

<Bleeding> Rank Evaluation A printout (Figure 8) was created in which the character "Todoroki" was printed in 6-point white in a solid area formed with metallic ink, and the bleeding within the character "Todoroki" was observed and ranked.
Using the pre-coating method, the processing liquid is printed inside the character "Todoroki."
With the pre-printing method, the processing liquid is not printed inside the character "Todoroki."
The acceptable range is rank B or higher.
[Evaluation Criteria]
A: No feathering occurs. Characters are not blurred. B: Slight feathering occurs and bleeding is observed. Characters are readable. C: Obvious feathering occurs. Characters are not clear.

<Unevenness> Rank Evaluation A 15 cm x 15 cm solid print was printed at 600 dpi x 600 dpi with 100% duty for each of the treatment liquid and metallic ink. The solid print was observed and evaluated based on the following evaluation criteria.
[Evaluation Criteria]
A: No unevenness occurs. The solid color is uniform.
B: Slight unevenness. When viewed from a distance of 5m or more, no unevenness in the solid can be recognized.
C: There is obvious unevenness. The solid is not uniform.
The acceptable range is rank B or higher.

<Comparative Example 7, Examples 12 to 14>
In Comparative Example 7 and Examples 12, 13 and 14, printed matter was prepared by printing using the same ink set as in Comparative Example 4 and Examples 2, 10 and 11 according to Image Recording Method 2 described below.
Each print was ranked for <20° gloss>, <bleeding>, and <unevenness> in the same manner as in Comparative Example 4, and Examples 2, 10, and 11. The results of each ranking are shown in Table 4.
The recording medium used was OK top coat+ (127.9 g/m ² ).

<Image recording method 2: Pre-coating type image recording method>
A pre-coating type image recording method is an image recording method in which a treatment liquid is first applied to a part or the entirety of a recording medium using a roller, a bar coater, a spray coating, or the like, and then a metallic ink is applied to the recording medium on which the treatment liquid has been applied, using an inkjet recording method.
The printed matter of Comparative Example 7 and Examples 12 to 14 was produced using a modified serial-type inkjet recording device (IPSiO GXe5500 manufactured by Ricoh Company, Ltd.). The duplex feed unit 181 was replaced with the pre-coating unit shown in Fig. 5A, and the printout was produced by applying treatment liquid to the recording medium with the application roller 5 and ejecting metallic ink from the head on the lower side. In the modified machine, a drying mechanism for drying the treatment liquid on the recording medium is provided below the transport path of the recording medium to which the treatment liquid has been applied on the upper side.
The recording medium used was OK Topcoat+ (127.9 g/m ² ) (manufactured by Oji Paper Co., Ltd.), and printing was performed with metallic ink at a resolution of 600 dpi×600 dpi in standard mode on high-grade plain paper.
In addition, by observing an image of the porous layer on the recording medium taken with an SEM, it was confirmed that the porous layer had pores.

LIST OF SYMBOLS 1 Treatment liquid 2 Supply pan 3 Squeeze roller 4 Metering blade 5 Application roller 6, 20 Motor 7 One-way clutch 9 Pressure roller 12 Cartridge 13 Supply path 14 Pump 15 Solenoid valve 16 Paper 17 Guide roller 18 Transport roller 21 Arm 22, 25 Temperature sensor 23 Heater lamp 24 Control unit 27 Liquid level sensor 101 Apparatus body 102 Paper feed tray 103 Paper discharge tray 104 Ink cartridge loading unit 105 Operation unit 111 Top cover 112 Front surface of front cover 115 Front cover 131 Guide rod 132 Stay 133 Carriage 134 Recording head 135 Sub-tank 141 Substrate placement unit 142 Substrate 143 Paper feed roller 144 Separation pad 145 Guide 151 Conveyor belt 152 Counter roller 153 Conveyor guide 154 Pressing member 155 Pressure roller 156 Charge roller 157 Conveyor roller 158 Tension roller 161 Modified guide member (with film heater)
171 Separation claw 172 Paper discharge roller 173 Paper discharge roller 174 Fan heater 181 Double-sided paper feed unit 182 Manual paper feed unit 200 Ink cartridge 400 Image forming device 401 Exterior 401c Cover of device body 404 Cartridge holder 410 Main tank 410k, 410c, 410m, 410y, 410si Main tanks for each color of black (K), cyan (C), magenta (M), yellow (Y), and silver (Si) 411 Ink storage unit 413 Ink outlet 414 Storage container case 420 Mechanical unit 434 Discharge head 436 Supply tube

JP 2015-147405 A JP 2019-025905 A Patent No. 4963783

Claims (11)

An image recording method including a step of applying a treatment liquid containing a porous layer-forming material onto a recording medium to form a porous layer, and a metallic ink applying step of applying a metallic ink containing a metal pigment onto the porous layer,
a surface tension of the treatment liquid at 23° C. and a surface tension of the metallic ink at 23° C. satisfy the following relational expression (1),
Surface tension of metallic ink ≧ Surface tension of treatment liquid (1)
The image recording method according to claim 1, wherein the metallic ink has a surface tension of 19 mN/m or more and 28 mN/m or less at 23°C. 2. The image recording method according to claim 1, wherein the metallic ink has a surface tension of 21 mN/m or more and 25 mN/m or less, and the treatment liquid has a surface tension of 18 mN /m or more and 23 mN/m or less. The image recording method according to claim 1 or 2, wherein the porous forming material is inorganic particles. The image recording method according to claim 3, wherein the inorganic particles are made of silica or alumina. The image recording method according to claim 3 or 4, wherein the inorganic particles are beaded fine particles containing secondary particles formed by agglomeration of two or more primary particles. The image recording method according to any one of claims 1 to 5, wherein the content of the porous material in the treatment liquid is 0.5% by mass or more and 20% by mass or less. The image recording method according to any one of claims 1 to 6, wherein the material for forming a porous material in the treatment liquid and the solid content in the metallic ink are both anionic or both cationic. The image recording method according to any one of claims 1 to 7, wherein the treatment liquid and the metallic ink are reactive. The image recording method according to any one of claims 1 to 8, wherein the treatment liquid and the metallic ink are applied by a pre-applying method in which both are ejected from an inkjet head onto the recording medium. The image recording method according to any one of claims 1 to 8, wherein the treatment liquid is applied onto the recording medium by a pre-coating method. An ink set of a treatment liquid and a metallic ink used in the image recording method according to any one of claims 1 to 10.

Images