JP7639466B2 - Ink, image forming apparatus, and image forming method - Google Patents

Description

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

In recent years, the uses of printed recording media (hereinafter sometimes referred to as "printed matter") have become increasingly diverse in a wide range of fields, including office and commercial use. As a result, in addition to printed matter expressed with conventional color materials (cyan, magenta, yellow, black, etc.), there is a demand for printed matter expressed with color materials that have unprecedented visual effects, such as metallic luster.

Silver colorants are widely used as colorants with metallic luster because they can exhibit high gloss and image clarity. Furthermore, by mixing a silver colorant with a conventional colorant, it is possible to obtain a printed matter having a full-color image with high gloss and image clarity, which can be used for a variety of purposes.

In recent years, a printing method has been proposed that uses an ink composition containing a metal colloid and other colorants in a dispersion medium to obtain a toned metallic color (see Patent Document 1). Furthermore, an ink containing silver particles with an average particle size of 100 nm or less and a specific compound has been proposed for the purpose of forming an image that has a metallic color with no unevenness in chromaticity and reduced yellowness (see Patent Documents 2 and 3). Also, a water-based ink composition containing a discoloration inhibitor and silver colloid has been proposed for the purpose of preventing discoloration of silver (see Patent Document 4).

The present invention aims to provide an ink that maintains high gloss, improves storage stability, and can form images with uniform chromaticity and a metallic color with reduced yellowness.

The ink of the present invention as a means for solving the above problems is
An ink comprising silver particles and a dye,
The average particle size of the silver particles is 100 nm or less,
The dye has a maximum absorption wavelength of 600 nm or more and 680 nm or less,
The ink has a dye content of 0.01% by mass or more and less than 0.1% by mass with respect to the total mass of the ink.

The present invention provides an ink that maintains high gloss, improves storage stability, and is capable of forming images with uniform chromaticity and a metallic color with reduced yellowness.

FIG. 1 is a perspective view illustrating an example of a recording apparatus. FIG. 2 is a perspective view illustrating an example of a main tank.

(ink)
The ink of the present invention is an ink containing silver particles and a dye, wherein the average particle size of the silver particles is 100 nm or less, the maximum absorption wavelength of the dye is 600 nm or more and 680 nm or less, the content of the dye is 0.01 mass % or more and less than 0.1 mass % with respect to the total mass of the ink, and further contains other components as necessary.
In the present invention, the "ink" may be referred to as silver ink.

The conventional technology described in the above-mentioned Patent Document 1 (Patent No. 4165860) had problems with uneven chromaticity and reduced gloss when metal colloid (silver colloid) was mixed with other colorants.

In addition, there is a problem that the surface of an image formed using an ink composition that generally contains silver (silver colloid) as a colorant discolors in a relatively short period of time. This is because the silver particles react with sulfide gas (sulfur gas) in the air, producing a silver sulfide coating on the surface of the image.

After extensive research, the inventors have discovered that by using an ink containing silver particles with an average particle size of 100 nm or less, to which is added a dye having a maximum absorption wavelength of 600 nm or more and 680 nm or less in an amount of 0.01% by mass or more and less than 0.1% by mass, based on the total mass of the ink, it is possible to form an image that retains high gloss, improves storage stability, is uniform in chromaticity, and has a metallic color with reduced yellowness.

Therefore, in the present invention, an ink containing silver particles and a dye, in which the average particle diameter of the silver particles is 100 nm or less, the maximum absorption wavelength of the dye is 600 nm or more and 680 nm or less, and the content of the dye is 0.01 mass % or more and less than 0.1 mass % with respect to the total mass of the ink, can be provided that retains high gloss, improves storage stability, and is capable of forming images with uniform chromaticity and a metallic color with reduced yellowness.

[Silver particles]
The ink of the present invention contains silver particles.
In general, silver is a metal with a high whiteness among various metals, and various metallic colors can be realized by combining it with coloring materials of other colors or inks containing coloring materials of other colors. In addition, silver is stable in water because it has low reactivity with water. As a result, it is possible to develop it into a water-based glittering ink that can reduce the environmental load, which is preferable.

The average particle size of the silver particles in the present invention is 100 nm or less.
When the average particle size of the silver particles is 100 nm or less, high dispersion stability in the ink can be obtained, and an ink capable of forming an image exhibiting excellent gloss and image clarity can be obtained.
Furthermore, from the viewpoint of obtaining a high gloss level, the average particle size of the silver particles is preferably 50 nm or less, and more preferably 5 nm or more and 50 nm or less.
In the present invention, the "average particle size of silver particles" refers to a value determined by the following measurement method.
First, several μl of silver particle dispersion or ink is taken and a frozen body is prepared by high-pressure freezing. The frozen body is then cut and a carbon replica film of the cross section is prepared. The carbon replica film is placed on a transmission electron microscope (TEM) grid and observed with the TEM. The maximum diameter of 20 silver particles in a TEM image of an area of 5 μm x 5 μm is measured, and the average of the measured values is taken as the average particle diameter.

The content of silver particles in the present invention is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 2.0% by mass or more and 13% by mass or less, based on the total mass of the ink. When the content of the silver particles is 1.0% by mass or more, based on the total mass of the ink, the image clarity of the print layer formed on the recording medium using the ink is improved, which is preferable. Furthermore, when the content of the silver particles is 15.0% by mass or less, based on the total mass of the ink, the dispersion stability and storage stability of the silver particles in the ink are improved, and the ejection stability when the ink is ejected by the inkjet method is excellent, which is preferable.

<Dispersion morphology of silver particles>
The silver particles are preferably dispersed in the aqueous dispersion medium as silver colloids having a protective colloid attached to the surface thereof, which provides excellent dispersibility of the silver particles in the aqueous dispersion medium and improves the storage stability of the ink.
The method for preparing the silver colloid is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a method in which a solution containing silver ions is prepared and the silver ions are reduced using a reducing agent in the presence of a protective colloid (see, for example, JP-A-2006-299329), etc. When producing the 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 (silver colloid).

The protective colloid is not particularly limited as long as it is an organic material that protects the surface of the silver particles, and can be selected according to the purpose, but from the viewpoint of stability, organic compounds having a carboxyl group and polymer dispersants are preferred. These may be used alone or in combination, but from the viewpoint of obtaining a synergistic effect, it is preferable to use multiple materials in combination.

- Organic compounds having a carboxyl group -
The organic compound having a carboxyl group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include carboxylic acids.
The carboxylic acid is not particularly limited as long as it can coat the silver particles, and can be appropriately selected depending on the purpose, and examples thereof include monocarboxylic acids such as aliphatic monocarboxylic acids and aromatic monocarboxylic acids; polycarboxylic acids such as aliphatic polycarboxylic acids and aromatic polycarboxylic acids; and hydroxycarboxylic acids (or oxycarboxylic acids) such as hydroxymonocarboxylic acids and hydroxypolycarboxylic acids. Among these, hydroxycarboxylic acids are preferred. These may be used alone or in combination of two or more.

The hydroxycarboxylic acid is not particularly limited and can be appropriately selected depending on the purpose, but aliphatic hydroxycarboxylic acids such as aliphatic hydroxymonocarboxylic acids and aliphatic hydroxypolycarboxylic acids are preferred.
The aliphatic hydroxycarboxylic acid is not particularly limited and can be appropriately selected depending on the purpose, but is preferably a hydroxycarboxylic acid having an alicyclic skeleton.
The hydroxycarboxylic acid having an alicyclic skeleton is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include alicyclic hydroxycarboxylic acids having 6 to 34 carbon atoms, such as cholic acid. Among these, alicyclic hydroxycarboxylic acids having 10 to 34 carbon atoms are preferred, and alicyclic hydroxycarboxylic acids having 16 to 30 carbon atoms are more preferred.
In particular, polycyclic aliphatic hydroxycarboxylic acids such as cholic acid are preferred because they have a bulky structure and are highly effective in suppressing the aggregation of silver particles.

The carboxylic acid may be in the form of a salt, an anhydride, a hydrate, or the like.
The carboxylic acid is preferably an organic compound that does not form a salt (particularly, a salt with a basic compound such as an amine).

The molecular weight of the organic compound having a carboxyl group is not particularly limited, but from the viewpoint of ease of handling, it is 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 not particularly limited, but is preferably 1 or more, and more preferably 2 or more.

- Polymer dispersant -
The polymer dispersant is not particularly limited as long as it can cover the silver particles, and can be selected depending on the purpose. Examples of the polymer dispersant include general polymer dispersants used for dispersing colorants in the fields of paints and inks.
Specific examples of the polymer dispersant include styrene-based resins such as styrene-(meth)acrylic acid copolymer and styrene-maleic anhydride copolymer; acrylic resins such as methyl (meth)acrylate-(meth)acrylic acid copolymer; water-soluble urethane resin, water-soluble acrylic urethane resin, water-soluble epoxy resin, water-soluble polyester-based resin, alkyl cellulose such as ethyl cellulose; alkyl-hydroxyalkyl cellulose such as ethylhydroxyethyl cellulose; hydroxyalkyl cellulose such as hydroxyethyl cellulose and hydroxypropyl cellulose; cellulose derivatives such as carboxyalkyl cellulose such as carboxymethyl cellulose; polyvinyl alcohol, liquid polyethylene glycol, polypropylene glycol, and other polyalkylene glycols; natural polymers such as gelatin and dextrin; polyethylene sulfonate and formalin condensates of naphthalene sulfonic acid.
As the polymer dispersant, an amphiphilic polymer dispersant (or an oligomer-type dispersant) can be suitably used, and examples thereof include a resin (water-soluble resin or water-dispersible resin) containing a hydrophilic unit constituted by a hydrophilic monomer.

The polymer dispersant may have a functional group.
The functional group is not particularly limited and can be appropriately selected depending on the purpose. Examples of the functional group include an acid group and an acidic group.
Specific examples of the functional group include a carboxyl group (or an acid anhydride group), a sulfo group (sulfonic acid group), a hydroxyl group, etc. Among these, the polymer dispersant preferably has an acid group, and more preferably has a carboxyl group.
The polymer dispersant may have one type of these functional groups alone, or may have two or more types of these functional groups.

When the polymer dispersant has an acid group (such as a carboxyl group), at least a part of the acid groups, or all of the acid groups of the polymer dispersant, may form a salt (such as a salt with an amine or a metal salt).
However, in the present invention, it is preferable that the polymer dispersant is one in which the acid group such as a carboxyl group does not form a salt (particularly a salt with a basic compound).

The number average molecular weight of the polymer dispersant is not particularly limited and can be appropriately selected depending on the purpose, but is preferably from 1,500 to 100,000, more preferably from 2,000 to 80,000, even more preferably from 3,000 to 50,000, and particularly preferably from 7,000 to 20,000.

The polymer dispersant may be a suitably synthesized one or a commercially available product.
Commercially available polymer dispersants include, for example, the Solsperse series, such as Solsperse 13240, Solsperse 13940, Solsperse 32550, Solsperse 31845, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, and Solsperse 41090 (all manufactured by Avecia Co., Ltd.); Disperbyk 160, Disperbyk 161, Disperbyk 162, Disperbyk 163, Disperbyk 164, Disperbyk 165, Disperbyk 166, Disperbyk 167, Disperbyk 168, Disperbyk 169, Disperbyk 200, Disperbyk 201, Disperbyk 202, Disperbyk 203, Disperbyk 204, Disperbyk 205, Disperbyk 206, Disperbyk 207, Disperbyk 208, Disperbyk 210, Disperbyk 211, Disperbyk 212, Disperbyk 213, Disperbyk 214, Disperbyk 215, Disperbyk 216, Disperbyk 217, Disperbyk 218, Disperbyk 220, Disperbyk 221, Disperbyk 222, Disperbyk 223, Disperbyk 224, Disperbyk 225, Disperbyk 226, Disperbyk 227, Disperbyk 228, Disperbyk 229, Disperbyk 230, Disperbyk 231, Disperbyk 232, Disperbyk 23 Disperbyk series such as Disperbyk 164, Disperbyk 166, Disperbyk 170, Disperbyk 180, Disperbyk 182, Disperbyk 184, Disperbyk 190, Disperbyk 191, Disperbyk 192, Disperbyk 193, Disperbyk 194, Disperbyk 2001, Disperbyk 2050 (all manufactured by BYK-Chemie Co., Ltd.): EFKA-46, EFKA-47, EFKA-48, EFKA-49, EFKA-50, EFKA-51, EFKA-52, EFKA-53, EFKA-54, EFKA-55, EFKA-56, EFKA-57, EFKA-58, EFKA-59, EFKA-60, EFKA-61, EFKA-62, EFKA-63, EFKA-64, EFKA-65, EFKA-66, EFKA-67, EFKA-68, EFKA-69, EFKA-70, EFKA-71, EFKA-72, EFKA-73, EFKA-74, EFKA-75, EFKA-76, EFKA-77, EFKA-78, EFKA-79, EFKA-80, EFKA-81, EFKA-82, EFKA-83, EFKA-84, EFKA-85, EFKA-86, EFKA-87, EFKA-88, EFKA-89, EFKA-90, EFKA-91, EFKA-92, EFKA-93, EFKA-94, EFKA-95, EFKA-96, EFKA-97, EFKA-9 -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 (all manufactured by EFKA Chemical Co., Ltd.): Ajisper PB711, Ajisper PAl11, Ajisper PB811, Ajisper PB821, Ajisper PW911, and other Ajisper Examples of the dispersing agent include the FLOWRENE series, such as FLOWRENE DOPA-158, FLOWRENE DOPA-22, FLOWRENE DOPA-17, FLOWRENE TG-700, FLOWRENE TG-720W, FLOWRENE-730W, FLOWRENE-740W, and FLOWRENE-745W (all manufactured by Kyoeisha Chemical Co., Ltd.); and the JONCRYL series, such as JONCRYL 678, JONCRYL 679, and JONCRYL 62 (all manufactured by Johnson Polymer Co., Ltd.). Among these, preferred are Disperbyk 190 and Disperbyk 194, which are polymer dispersants having an acid group.

[dye]
The ink of the present invention contains a dye having a maximum absorption wavelength of 600 nm or more and 680 nm or less. In the present invention, the "dye having a maximum absorption wavelength of 600 nm or more and 680 nm or less" is sometimes referred to as the "dye".
By using an ink containing the dye, it is possible to form an image that maintains high gloss, is free of chromaticity unevenness, has improved storage stability, and exhibits a metallic color with reduced yellowness.

<Maximum absorption wavelength>
In the present invention, the term "maximum absorption wavelength" refers to the wavelength of the absorption peak in an absorption spectrum that shows the relationship between wavelength and absorbance. The absorption spectrum is a two-dimensional graph in which the horizontal axis represents wavelength and the vertical axis represents absorbance.
The absorption peak refers to a peak in the absorption spectrum where the absorbance changes from increasing to decreasing. When two or more absorption peaks appear in the absorption spectrum, the wavelength of the absorption peak having the maximum absorbance among these absorption peaks is defined as the maximum absorption wavelength.
The maximum absorption wavelength means an absorption peak in the visible light wavelength region (400 to 800 nm).

It is preferable that the dye has a maximum absorption wavelength of 600 nm or more and 680 nm or less, since this allows for an ink that exhibits an appropriate silver color to be obtained.
The method for measuring the maximum absorption wavelength of the dye is not particularly limited, and examples thereof include a method in which the ink is dissolved or diluted so that the absorbance (Abs.) is approximately 1.0, and then the absorption spectrum is measured using a spectrophotometer (U3900; manufactured by Hitachi High-Tech Science Corporation).

The ink of the present invention contains a dye having a maximum absorption wavelength of 600 nm or more and 680 nm or less in an amount of 0.01% by mass or more and less than 0.1% by mass, based on the total mass of the ink.
When the content of the dye is 0.01% by mass or more based on the total mass of the ink, an ink exhibiting high gloss is obtained, which is preferable, and when the content of the dye is less than 0.1% by mass based on the total mass of the ink, an ink exhibiting a sufficient silver color is obtained, which is preferable.

The dye is not particularly limited and can be appropriately selected depending on the purpose. Examples of the dye include reactive dyes, acid dyes, and other dyes.
Specific examples of the reactive dye include Reactive Blue 2, Reactive Blue 4, Reactive Blue 5, Reactive Blue 13, Reactive Blue 14, Reactive Blue 15, Reactive Blue 19, Reactive Blue 21, Reactive Blue 25, Reactive Blue 27, Reactive Blue 28, Reactive Blue 38, Reactive Blue 39, Reactive Blue 41, Reactive Blue 49, Reactive Blue 52, Reactive Blue 63, Reactive Blue 72, Reactive Blue 77, Reactive Blue 79, Reactive Blue 104, Reactive Blue 119, Reactive Blue 122, Reactive Blue 147, Reactive Blue 160, Reactive Blue 162, Reactive Blue 163, Reactive Blue 164, Reactive Blue 165, Reactive Blue 166, Reactive Blue 167, Reactive Blue 169, Reactive Blue 170, Reactive Blue 171, Reactive Blue 172, Reactive Blue 173, Reactive Blue 174, Reactive Blue 175, Reactive Blue 176, Reactive Blue 177, Reactive Blue 178, Reactive Blue 179, Reactive Blue 180, Reactive Blue 181, Reactive Blue 182, Reactive Blue 183, Reactive Blue 184, Reactive Blue 185, Reactive Blue 186, Reactive Blue 187, Reactive Blue 188, Reactive Blue 189, Reactive Blue 190, Reactive Blue 191, Reactive Blue 192, Reactive Blue 193, Reactive Blue 194, Reactive Blue 195, Reactive Blue 196, Reactive Blue 197, Reactive Blue 198, Reactive Blue 200, Reactive Blue 201, Reactive Blue 202, Reactive Blue 203, Reactive Blue 20 Reactive Blue 166, Reactive Blue 176, Reactive Blue 182, Reactive Blue 184, Reactive Blue 187, Reactive Blue 190, Reactive Blue 191, Reactive Blue 194, Reactive Blue 195, Reactive Blue 198, Reactive Blue 203, Reactive Blue 204, Reactive Blue 207, Reactive Blue 209, Reactive Blue 211, Reactive Blue 214, Reactive Blue 216, Reactive Blue 217, Reactive Blue 220, Reactive Blue 221, Reactive Blue 222, Reactive Blue 227, Reactive Blue 228, Reactive Blue 230, Reactive Blue 231, Reactive Blue 235, and the like.
Specific examples of the acid dye include Acid Blue 1, Acid Blue 3, Acid Blue 7, Acid Blue 9, Acid Blue 20, Acid Blue 25, Acid Blue 29, Acid Blue 193, Acid Blue 199, and Acid Blue 260.
Examples of the other dyes include Direct Blue 199.
Among these, Reactive Blue 2, Reactive Blue 4, Reactive Blue 13, Reactive Blue 15, Reactive Blue 21, Reactive Blue 49, Reactive Blue 72, Acid Blue 20, Acid Blue 25, Acid Blue 193, and Direct Blue 199 are preferable.

The dye preferably has a vinylsulfone group or a chlorotriazine group.
An example of the dye having a vinyl sulfone group is Reactive Blue 2.
Examples of the dye having a chlorotriazine group include Reactive Blue 21.

[Other ingredients]
The other components include organic solvents, water, resins, additives, and the like.

<Organic Solvent>
The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. For example, a water-soluble organic solvent can be used.
Examples of the water-soluble organic solvent include ethers such as polyhydric alcohols, polyhydric alcohol alkyl ethers, and polyhydric alcohol aryl ethers; nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and other organic solvents.

- Ethers -
--Polyhydric alcohols--
Specific examples of the polyhydric alcohols 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, and 1,4-pentanediol. , 2,4-pentanediol, 1,5-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.

--Polyhydric alcohol alkyl ethers--
Specific examples of the polyhydric alcohol alkyl ethers 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.

--Polyhydric alcohol aryl ethers--
Specific examples of the polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

-Nitrogen-containing heterocyclic compound-
Specific examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone.

- Amides -
Specific examples of the amides include formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide.

-Amines-
Specific examples of the amines include monoethanolamine, diethanolamine, and triethylamine.

- Sulfur-containing compounds -
Specific examples of the sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol.

-Other organic solvents-
Examples of the other organic solvents include propylene carbonate and ethylene carbonate.

In addition to the above organic solvents, polyol compounds having 8 or more carbon atoms, glycol ether compounds, and oxetane compounds can also be suitably used.
Specific examples of the polyol compound 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.
Specific examples of the oxetane compound include 3-ethyl-3-hydroxymethyloxetane.

The boiling point of the organic solvent is preferably 250°C or less. This is preferable because the organic solvent not only functions as a wetting agent but also has good drying properties.

<Water>
The water is not particularly limited and can be appropriately selected depending on the purpose.
The content of water is preferably from 10% by mass to 90% by mass, and more preferably from 20% by mass to 60% by mass, based on the total mass of the ink, from the viewpoints of drying property and ejection reliability of the ink.

<Resin>
The ink of the present invention preferably contains a resin.
When a print layer is formed on a recording medium using an ink containing the resin, the silver particles can be stably maintained in a spread-out structure without agglomeration, and even if the silver particles aggregate, the area of aggregation can be reduced. Therefore, when the recorded matter is stored at high temperature for a long period of time, the b ^* value, which is the chromaticity (color value) of the image, does not change significantly.

The resin is not particularly limited and can be selected appropriately depending on the purpose, but a water-soluble resin that is soluble in water and a water-dispersible resin that can be dispersed in water are preferred.

- Water-soluble resin -
The water-soluble resin is not particularly limited and can be appropriately selected depending on the purpose. Examples of the water-soluble resin include proteins such as gelatin and casein; natural rubbers such as gum arabic; glucoxides such as savonin; cellulose derivatives such as methylcellulose, carboxymethylcellulose and hydroxymethylcellulose; natural polymers such as lignin sulfonate and shellac; ionic polymers such as polyacrylates, polyacrylamides, styrene-acrylic acid copolymer salts, vinylnaphthalene-acrylic acid copolymer salts, styrene-maleic acid copolymer salts, vinylnaphthalene-maleic acid copolymer salts, sodium salt of β-naphthalenesulfonic acid formalin condensate, and polyphosphoric acid; polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polypropylene glycol, polyethylene oxide, polyvinyl methyl ether, and polyethyleneimine.
These may be used alone or in combination of two or more.
As the water-soluble resin, a suitably synthesized resin or a commercially available product may be used.

- Water-dispersible resin -
The water-dispersible resin is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include 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. Resin particles made of these resins may also be used.
These may be used alone or in combination of two or more.
The resin particles are dispersed in water as a dispersion medium in the form of a resin emulsion, and the resin particles are mixed with materials such as silver particles and an organic solvent to obtain an ink.
As the water-dispersible resin, a suitably synthesized resin or a commercially available product may be used.

The average particle size of the resin particles is not particularly limited and may be appropriately selected depending on the purpose, but is preferably 10 nm or more and 30 nm or less in terms of obtaining good image clarity and glossiness.
A printed layer formed on a recording medium using an ink containing resin particles with an average particle size of 10 nm to 30 nm can stably maintain a structure in which silver particles are spread out without agglomeration, and even if silver particles aggregate, the area of aggregation can be reduced. Therefore, when the recorded matter is stored at high temperature for a long period of time, the b ^* value, which is the chromaticity (color value) of the image, does not change significantly.

The average particle size of the resin particles present in the ink of the present invention can be measured, for example, as follows.
First, several μl of ink or dispersion is collected and a frozen body is prepared by high-pressure freezing. The frozen body is then cut and a carbon replica film of the cross section is prepared. The carbon replica film is placed on a grid for a TEM (transmission electron microscope) and observed with the TEM. The maximum diameter of 20 resin particles in a TEM image within an area of 5 μm x 5 μm is measured, and the average of the measured values is taken as the average particle diameter.

The content of the resin is not particularly limited and can be appropriately selected depending on the purpose, but in order to obtain good abrasion resistance, image clarity, and metallic luster, it is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 10.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 2.0% by mass or less, based on the total mass of the ink.

The mass ratio of the resin content to the silver particle content (resin content/silver particle content) is preferably 0.001 or more and 0.2 or less, and more preferably 0.01 or more and 0.1 or less.

<Surfactant>
The ink of the present invention preferably contains a surfactant.
The surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the surfactant include silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants.

- Silicone surfactant -
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 terminal modified polydimethylsiloxane, one terminal modified polydimethylsiloxane, and both terminal modified polydimethylsiloxane.
These may be used alone or in combination of two or more.

The side-chain modified polydimethylsiloxane refers to, for example, a polydimethylsiloxane having a modifying group introduced into the Si side chain of the polydimethylsiloxane represented by the following general formula (S-1).
The both-end-modified polydimethylsiloxane refers to a polydimethylsiloxane represented by the following general formula (S-1), in which modifying groups are introduced at both ends.
The one-end-modified polydimethylsiloxane refers to a polydimethylsiloxane represented by the following general formula (S-1), in which a modifying group is introduced into either one of the ends.
The side chain both terminal modified polydimethylsiloxane indicates, for example, that modifying groups are introduced into the Si side chain and both terminals of a polydimethylsiloxane represented by the following general formula (S-1).

General formula (S-1)
(In the general formula (S-1), m and n each independently represent an integer, and X represents a side chain.)

For example, the side chain modified polydimethylsiloxane can be made into a polyether modified silicone surfactant by introducing a polyalkylene oxide structure represented by the following general formula (S-2) into the Si part side chain X of the dimethylpolysiloxane represented by the general formula (S-1).

General formula (S-2)
(In the general formula (S-2), a and b each independently represent an integer, R represents an alkylene group, and R′ represents an alkyl group.)

The modifying group is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyoxyethylene groups, polyoxyethylene polyoxypropylene groups, and polyalkylene oxide structures. Among these, polyoxyethylene groups and polyoxyethylene polyoxypropylene groups are preferred because they exhibit good properties as aqueous surfactants.

As the silicone-based surfactant, a suitably synthesized product or a commercially available product may be used.
Commercially available silicone surfactants are available from, for example, BYK Chemical Co., Ltd., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd., and the like.
As the polyether-modified silicone surfactant, commercially available products can be used. For example, KF-618, KF-642, KF-643 (all manufactured by Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, EMALEX-SS-1906EX (all manufactured by Nippon Emulsion Co., Ltd.), DOWSIL FZ-2105, DOWSIL FZ-2118, DOWSIL FZ-2154, DOWSIL FZ-2161, DOWSIL FZ-2162, FZ-2163, DOWSIL FZ-2164 (both from Dow Corning Toray Silicone Co., Ltd.); BYK-33, BYK-387 (both from BYK-Chemie Co., Ltd.); TSF4440, TSF4452, TSF4453 (both from Momentive Performance Materials Japan LLC).
These may be used alone or in combination of two or more.

-Fluorosurfactants-
The fluorine-based surfactant is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of low foaming, however, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferred.
Examples of the perfluoroalkylsulfonic acid compound include perfluoroalkylsulfonic acid and perfluoroalkylsulfonate salts.
Examples of the perfluoroalkyl carboxylic acid compound include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylic acids.
Examples of polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain include sulfate ester salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group on the side chain, and salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group on the side chain.
These may be used alone or in combination of two or more.
Examples of the counter ion of the salt in the fluorosurfactant include _Li , Na, _K , _NH4 , _NH3CH2CH2OH , _NH2 ( _CH2CH2OH ) ₂ , and _NH ( _CH2CH2OH ) _{3 .}

--Amphoteric surfactant--
The amphoteric surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the amphoteric surfactant include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
These may be used alone or in combination of two or more.

-Nonionic surfactants-
The nonionic surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the nonionic surfactant 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.
These may be used alone or in combination of two or more.

-Anionic surfactants-
The anionic surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

The content of the surfactant in the ink of the present invention is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoint of excellent wettability and ejection stability and improved image quality, the content is preferably from 0.001% by mass to 5% by mass, and more preferably from 0.05% by mass to 5% by mass, relative to the total mass of the ink.
The content of the silicone surfactant in the ink of the present invention is not particularly limited and may be appropriately selected depending on the purpose. However, the content is preferably from 0.001% by mass to 5% by mass, more preferably from 0.05% by mass to 5% by mass, and even more preferably from 0.5% by mass to 1.0% by mass, relative to the total mass of the ink.

<Additives>
Examples of the additives include antifoaming agents, antiseptic and antifungal agents, rust inhibitors, and pH adjusters.

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

- Antiseptic 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.
These may be used alone or in combination of two or more.

- pH adjuster -
The pH adjuster is not particularly limited as long as it can adjust the pH to 7 or more, and examples of the pH adjuster include amines such as diethanolamine and triethanolamine.
These may be used alone or in combination of two or more.

[Ink properties]
The physical properties of the ink are not particularly limited and can be appropriately selected depending on the purpose. For example, the viscosity, surface tension, pH, etc. are preferably within the following ranges.
The viscosity of the ink at 25° C. is preferably from 5 mPa·s to 30 mPa·s, more preferably from 5 mPa·s to 25 mPa·s, in order to improve print density and character quality and to obtain good ejection properties.
The viscosity can be measured using, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) The measurement conditions are 25° C., a standard cone rotor (1°34′×R24), a sample liquid amount of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.
The surface tension of the ink is preferably 35 mN/m or less, and more preferably 32 mN/m or less at 25° C., in order to ensure that the ink is appropriately leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably 7 or more and 12 or less, and more preferably 8 or more and 11 or less, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

[Recording medium]
In this specification, the term "recording medium" refers to an object on which recording is performed using the ink of the present invention.
The recording medium refers to any material to which the ink of the present invention or various treatment liquids described below can be attached, even if only temporarily.
The recording medium is not particularly limited and can be appropriately selected depending on the purpose. For example, a non-permeable base material or glossy paper having a receiving layer on the surface may be used.
The glossy paper having a receiving layer may or may not have a receiving layer (porous or the like) formed in advance on the surface of the recording medium.
The recording medium is not limited to those generally used as recording media, and may be appropriately used wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc. Also, by adjusting the configuration of the path for conveying the recording medium, ceramics, glass, metal, etc. may be used.

The non-permeable substrate is a substrate having a surface with low water permeability and absorbency, and includes a material having many cavities inside but not open to the outside. More quantitatively, it refers to a substrate having a water absorption amount of 10 mL/m2 or ^less from the start of contact to 30 msec ^1/2 in the Bristow method.
Examples of the non-permeable substrate include plastic films such as polyvinyl chloride resin films, polyethylene terephthalate (PET) films, polypropylene, polyethylene, and polycarbonate films.

As the glossy paper (recording medium) having the receiving layer, a commercially available product can be used.
Commercially available glossy paper (recording medium) having the receiving layer includes, for example, IJ film RM-1GP01 (average pore size: 230 nm) (manufactured by Ricoh Co., Ltd.), NB-WF-3GF100 (average pore size: 210 nm), NB-RC-3GR120 (average pore size: 250 nm) (manufactured by Mitsubishi Paper Mills Co., Ltd.), PT-201A420 (average pore size: 270 nm), SD-101A450 (average pore size: 250 nm), GL-101A450 (average pore size: 250 nm), Average pore size: 240 nm), GP501A450 (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) (manufactured by Canon Inc.): 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 (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) (all 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: diameter: 220 nm), G3A450A (average pore size of porous: 210 nm), WPA420HIC (average pore size of porous: 280 nm) (all 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) (all manufactured by Seiko Epson Corporation); BP71GAA4 (average pore size of porous: 220 nm) (manufactured by Brother Industries, Ltd.).

[Recording device and recording method]
In this specification, the term "recording apparatus" refers to an apparatus that has a storage section that stores the ink of the present invention, and a discharge section that discharges the ink onto the recording medium, and may also have other means as necessary.
The recording apparatus can be made into an image forming apparatus by forming an image using the ink of the present invention.
The "recording method" in this specification can be carried out using the above-mentioned recording device.
The recording method can be an image forming method by forming an image using the image forming apparatus.
The image forming method includes a step of forming an image using the ink of the present invention, and may include other steps as necessary.

<Storage section>
The container is a means for containing the ink.
The container is not particularly limited, and examples thereof include known ink cartridges for inkjet printers.
The container is easy to store, transport, and handle, and can therefore be detachably attached to an ink cartridge, an image forming apparatus, or the like, and used to replenish ink.
The container is not particularly limited and can be appropriately selected from known containers. For example, the container may have a container body and a cap.

The shape of the container is not particularly limited and may be appropriately selected depending on the purpose, but is preferably cylindrical. Furthermore, it is preferable that the inner peripheral surface is formed with a spiral irregularity so that the ink content can be transferred to the outlet side by rotating the container, and that a part or all of the spiral irregularity has a bellows function.
The material of the storage section is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of good dimensional accuracy, however, resins such as polyester resin, polyethylene resin, polypropylene resin, polystyrene resin, polyvinyl chloride resin, polyacrylic acid, polycarbonate resin component ABS resin, polyacetal resin, etc. are preferred.
The structure and size of the storage section are not particularly limited and can be appropriately selected depending on the purpose.

<Discharge section>
The ejection section is a means for ejecting the ink.
The ink ejection section is not particularly limited, and any known ink ejection means can be used, such as an inkjet system.

<Other Means and Other Steps>
The other means are not particularly limited and can be appropriately selected depending on the purpose. Examples of the other means include pre-treatment means, post-treatment means, heat drying means, and means related to feeding, conveying, and discharging of the recording medium.
The other steps are not particularly limited and can be appropriately selected depending on the purpose. Examples of the other steps include a pre-treatment step, a post-treatment step, a heat drying step, and steps related to feeding, transporting, and discharging of a recording medium.

-Pretreatment means and pretreatment process-
The pretreatment unit is a unit that applies a pretreatment liquid to the recording medium before applying the ink.
The pretreatment step is a step of applying a pretreatment liquid to the recording medium before applying the ink.
The pretreatment step can be suitably carried out by the pretreatment means.
The pretreatment means is not particularly limited and can be appropriately selected depending on the purpose. Examples of the pretreatment means include a means in which the pretreatment liquid is stored in an ink storage means like a normal ink and applied to a recording medium by an inkjet method, a blade coating method, a roll coating method, a spray coating method, and the like.

--Pretreatment solution--
The pretreatment liquid contains a flocculant, an organic solvent, and water, and may contain, as necessary, a surfactant, an antifoaming agent, a pH adjuster, an antiseptic/fungal agent, an antirust agent, and the like.
The organic solvent, the surfactant, the defoaming agent, the pH adjuster, the antiseptic and antifungal agent, and the rust inhibitor can be similar to the materials used in the ink, and other materials used in known treatment liquids can be used.
The type of the flocculant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, and polyvalent metal salts.

-Post-processing means and post-processing process-
The post-treatment unit is a unit that applies a post-treatment liquid to the recording medium after applying the ink.
The pretreatment step is a step of applying a posttreatment liquid to the recording medium after applying the ink.
The post-treatment step can be suitably carried out by the post-treatment means.
The post-treatment means is not particularly limited and can be appropriately selected depending on the purpose. Examples of the post-treatment means include a means in which the post-treatment liquid is stored in an ink storage means like a normal ink and applied to a recording medium by an inkjet method, a blade coating method, a roll coating method, a spray coating method, and the like.

--Post-processing solution--
The post-treatment liquid is not particularly limited as long as it can form a transparent layer. The post-treatment liquid is obtained by selecting and mixing organic solvents, water, resins, surfactants, defoamers, pH adjusters, antiseptics, antifungals, rust inhibitors, etc. as necessary. The post-treatment liquid may be applied to the entire recording area formed on the recording medium, or may be applied only to the area where an image is formed.

The heating means includes, for example, a means for heating the print surface or the back surface of the recording medium.
The drying means includes, for example, a means for drying the printed surface and the back surface of the recording medium.
The heating means and drying means are not particularly limited, and for example, a hot air heater, an infrared heater, etc. Heating and drying can be carried out before, during, or after printing.

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.
The recording apparatus and the recording method are not limited to those that visualize meaningful images such as characters and figures with ink, but also include those that form patterns such as geometric patterns and those that form three-dimensional images.
Unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the discharge head is moved and a line type apparatus in which the discharge head is not moved.
The recording device includes not only desktop types, but also wide recording devices capable of printing on A0 size recording media, and continuous feed printers that can use continuous paper wound into a roll as a recording medium.

An example of a recording apparatus will be described below with reference to Figures 1 and 2. Note that the present invention is not limited to the embodiment described below.
FIG. 1 is a perspective view showing an example of a recording apparatus. FIG. 2 is a perspective view showing an example of a main tank. An image forming apparatus 400, which is an example of a recording apparatus, is a serial type image forming apparatus. A mechanism section 420 is provided inside an exterior 401 of the image forming apparatus 400. Each ink storage container 411 of the main tanks 410 (410s, 410c, 410m, 410y) for each color of silver (S), cyan (C), magenta (M), and yellow (Y) is formed of a packaging material such as an aluminum laminate film. The ink storage container 411, which is a storage section, is stored in a storage container case 414 made of, for example, plastic. 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, which is an ejection section 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.
The above-mentioned silver (S) ink is the ink of the present invention. The color inks of cyan (C), magenta (M), and yellow (Y) are not particularly limited, and known inks can be appropriately selected according to the purpose. In addition to the three colors other than the above-mentioned silver (S), inks such as black (K) and white (W) may be additionally used. When using additional inks, a liquid storage section having the additional ink and a liquid ejection head are added to the recording device. By applying inks containing coloring materials other than these silver to the position on the recording medium to which the silver ink of the present invention has been applied, it is possible to reproduce various colors having metallic luster other than silver.

The recording device can include not only a portion that ejects ink, but also devices called pre-processing devices and post-processing devices.
As an aspect of the pre-treatment device and the post-treatment device, a liquid storage section having a pre-treatment liquid and a liquid ejection head, similar to the case of inks such as silver (S), cyan (C), magenta (M), and yellow (Y), and the like, are added, and the pre-treatment liquid and the post-treatment liquid are ejected by an inkjet recording method.
In another embodiment of the pre-treatment device and the post-treatment device, a device other than the inkjet recording method, for example, a pre-treatment device and a post-treatment device using a blade coating method, a roll coating method, or a spray coating method, are provided.

The method of using the ink of the present invention is not limited to the inkjet recording method, and can be appropriately selected depending on the purpose.
In addition to the inkjet recording method, examples of the method include blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating.

[Printed matter]
In this specification, the term "printed matter" refers to a printed layer formed on the recording medium using the ink of the present invention. The printed layer may include the image.
The printed layer preferably contains the resin, which can further improve the image clarity and scratch resistance of the printed layer.
The content of the resin in the printed layer is preferably from 0.01% by mass to 50% by mass, and more preferably from 0.01% by mass to 20% by mass, based on the total mass of the printed layer.
When the content of the resin in the printed layer is from 0.01% by mass to 50% by mass, both inclusive, with respect to the total mass of the printed layer, the image clarity, metallic gloss, and abrasion resistance of the printed layer are improved.
The resin contained in the print layer is preferably resin particles having an average particle size of 10 nm or more and 30 nm or less.

<Thickness of Printing Layer>
The average thickness of the printed layer must be equal to or greater than the particle diameter of at least one silver particle. By arranging the silver particles in the planar direction on the recording medium for one layer or more, the interaction between the silver particles increases, and a printed layer with excellent metallic image clarity can be formed.
The average thickness of the printed layer is preferably 50 nm or more and 300 nm or less, more preferably 50 nm or more and 250 nm or less, even more preferably 50 nm or more and 200 nm or less, and particularly preferably 50 nm or more and 180 nm or less.
When the average thickness of the printed layer is 50 nm or more and 300 nm or less, the structural color tone resulting from the plasmon absorption of the silver particles is reduced, and a printed layer having excellent metallic luster and image clarity can be formed.
If the amount of ink applied is such that the average thickness of the printed layer is 50 nm or more and 300 nm or less, when the recording medium has a porous structure, the ink vehicle can be immediately absorbed, and a printed layer with excellent metallic luster and image clarity can be formed.
The average thickness of the printed layer is an average value of values measured at 10 arbitrary points on the printed layer, and is measured after the ink applied to the recording medium has sufficiently dried.

<Method for measuring the average thickness of the printed layer>
The method for measuring the average thickness of the printed layer is not particularly limited and can be appropriately selected depending on the purpose. For example, a method can be used in which the printed material is cut and the cut surface is observed with a microscope such as an optical microscope, a laser microscope, a SEM (scanning electron microscope), or a TEM.
The average particle size of the silver particles or resin particles on the printed matter can be measured by observing and analyzing with a SEM.
The average particle size of the silver particles and resin particles in the print layer is determined by measuring the maximum diameters of 20 silver particles and resin particles in a TEM image of an area of 10 μm×10 μm, and averaging the measured values.

<Chromaticity of Printed Layer>
The chromaticity (b ^* value) of the print layer is based on the color difference display method according to the L ^* a ^* b ^* color system standardized by CIE (Commission International del'Eclairage).
In order for the printed layer to have high image clarity and a silver color, the b ^* value is preferably −7 or more and 0 or less.
The more the b ^* value is negative, the stronger the blue tone becomes, and conversely, the more the value is positive, the stronger the yellow tone becomes. As the yellow tone becomes stronger, the printed layer approaches gold, and when the b ^* value exceeds 0, the gold color becomes more pronounced and the color tone becomes difficult to describe as silver. Conversely, when the b ^* value is below -7, the blue tone becomes stronger and the color tone becomes darker and different from silver.
The b ^* value can be easily measured using a spectrophotometer.

<Color ink printing layer>
The printed matter may further include a color ink printed layer formed on the printed layer formed on the recording medium.
The color ink printed layer is formed by applying ink containing a color material other than silver particles, and is a layer containing a color material other than silver particles.
The average thickness of the color ink printed layer is preferably 1 nm to 300 nm, more preferably 2 nm to 250 nm. When the silver color of the printed layer is toned, it is necessary not to conceal the silver color, and in this case, the average thickness of the color ink printed layer is preferably 3 nm to 100 nm.
When the average thickness of the color ink printed layer is from 1 nm to 300 nm, a colored metallic image can be obtained, and a recorded matter having good image clarity, color tone, and texture can be obtained.

When forming the color ink printed layer, the order of color matching is preferably such that a printed layer is formed with the ink of the present invention, and then a color ink printed layer is formed on the printed layer.
The method for measuring the average thickness of the color ink printed layer is not particularly limited and can be appropriately selected depending on the purpose. For example, a method can be used in which the printed material is cut and the cut surface is observed with a microscope such as an optical microscope, a laser microscope, a SEM, or a TEM.

[Application]
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, by using it as an ink, it can be used not only to form two-dimensional characters and images, but also as a material for three-dimensional modeling for forming a three-dimensional solid image (three-dimensional model).
The three-dimensional modeling device for forming the three-dimensional object may be a known one, and is not particularly limited, but may be, for example, one equipped with ink storage means, supply means, ejection means, drying means, etc.
The three-dimensional object includes a three-dimensional object obtained by applying ink over and over, etc. Also included is a molded product obtained by processing a structure having ink applied onto a substrate such as a recording medium.
The molded product is, for example, a recording material or structure formed into a sheet or film shape, which is subjected to molding such as heat stretching or punching, and is suitably 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.

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

(Preparation of Resin Dispersion Containing Resin Particles)
<Preparation of polyester urethane resin dispersion 1>
The following materials were reacted in a nitrogen-purged vessel equipped with a thermometer, a nitrogen gas inlet tube, and a stirrer. Dibutyltin dilaurate (DMTDL) was used as a catalyst.
-material-
Polyester polyol (product name: PTMG1000, manufactured by Mitsubishi Chemical Corporation, average molecular weight: 1,000) 200.4 g
2,2-Dimethylolpropionic acid 15.7g
Isophorone diisocyanate 48.0g
Methyl ethyl ketone 77.1g
Dibutyltin dilaurate (DMTDL, manufactured by Tokyo Chemical Industry Co., Ltd.) 0.06 g
After the reaction was continued for 4 hours, 30.7 g of methyl ethyl ketone was added as a dilution solvent to continue the reaction. After the reaction was continued for a total of 6 hours, 1.4 g of methanol was added to terminate the reaction, thereby obtaining a solution of a urethane resin in an organic solvent.
The carboxyl group of the urethane resin was neutralized by adding 13.4 g of a 48% by mass potassium hydroxide aqueous solution to the organic solvent solution of the urethane resin, and then 715.3 g of water was added and thoroughly stirred, followed by aging and desolvation to obtain a polyester urethane resin dispersion 1 containing resin particles with a solid content concentration of 30% by mass.

<Preparation of polyester urethane resin dispersion 2>
In the preparation of the polyester urethane resin dispersion 1, except that the content of DMTDL was changed from 0.06 g to 0.12 g and the total reaction time was changed to 15 hours, a polyester urethane resin dispersion 2 containing resin particles with a solid content concentration of 30 mass% was obtained in the same manner as in the preparation of the polyester urethane resin dispersion 1.

<Preparation of polyester urethane resin dispersion 3>
In the preparation of the polyester urethane resin dispersion 1, except that the content of DMTDL was changed from 0.06 g to 0.2 g and the total reaction time was changed to 8 hours, a polyester urethane resin dispersion 3 containing resin particles with a solid content concentration of 30 mass% was obtained in the same manner as in the preparation of the polyester urethane resin dispersion 1.

<Preparation of polyester urethane resin dispersion 4>
In the preparation of the polyester urethane resin dispersion 1, except that the content of DMTDL was changed from 0.06 g to 0.2 g and the reaction time was changed to 5 hours, a polyester urethane resin dispersion 4 containing resin particles with a solid content concentration of 30 mass% was obtained in the same manner as in the preparation of the polyester urethane resin dispersion 1.

<Preparation of polyester urethane resin dispersion 5>
In the preparation of the polyester urethane resin dispersion 1, except that the content of DMTDL was changed from 0.06 g to 0.12 g and the reaction time was changed to 10 hours, a polyester urethane resin dispersion 5 containing resin particles with a solid content concentration of 30 mass% was obtained in the same manner as in the preparation of the polyester urethane resin dispersion 1.

<Preparation of polycarbonate urethane resin dispersion>
The following materials were placed in a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer under a nitrogen stream, and the mixture was heated to 60° C. to dissolve the DMPA.
-material-
Polycarbonate diol (reaction product of 1,6-hexanediol and dimethyl carbonate (number average molecular weight (Mn): 1,200)) 1,500 g
2,2-Dimethylolpropionic acid (DMPA) 220g
N-methylpyrrolidone (NMP) 1,347g
Next, 1,445 g (5.5 mol) of 4,4'-dicyclohexylmethane diisocyanate and 1.8 g of dibutyltin dilaurate (catalyst) were added and heated to 90°C to carry out a urethane reaction over 3 hours to obtain an isocyanate-terminated urethane prepolymer.
Next, these reaction mixtures were cooled to 80°C, and 149 g of triethylamine was added and mixed, from which 4,340 g was extracted and added to a mixed solution of 5,400 g of water and 15 g of triethylamine under strong stirring. Next, 1,500 g of ice was added, and then 626 g of a 35% by mass aqueous solution of 2-methyl-1,5-pentanediamine was added to carry out a chain extension reaction, and the solvent was distilled off so that the solid content concentration became 30% by mass, thereby obtaining a polycarbonate urethane resin dispersion having a structure derived from an alicyclic diisocyanate.

A few μl of each of the polyester urethane resin dispersions 1 to 5 and the polycarbonate urethane resin dispersion was taken and frozen bodies were prepared by high-pressure freezing. The frozen bodies were then fractured and a carbon replica film of the cross section was prepared. The carbon replica film was placed on a TEM grid and observed with a TEM. The maximum diameter of 20 resin particles in a TEM image of an area of 5 μm x 5 μm was measured, and the average particle diameter of the resin particles was calculated from the measured values. The results are shown in Table 1.

(Preparation of Silver Particle Dispersion)
<Preparation of Silver Particle Dispersion 1>
The following materials were mixed vigorously to obtain a suspension:
-material-
・Silver nitrate 66.8g
Carboxyl group-containing dispersant polymer (product name: Disperbyk 190, manufactured by BYK Japan K.K., solvent: water, non-volatile components: 40% by mass, acid value: 10 mg KOH/g, amine value: 0 mg KOH/g) 7.2 g
Cholic acid (Wako Pure Chemical Industries, Ltd.) 2.2 g
・Ion-exchanged water 100g
To the resulting suspension, 100 g of dimethylaminoethanol (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added so that the water temperature did not exceed 50° C., and then the mixture was heated and stirred for 3 hours in a water bath at a water temperature of 50° C. to obtain a reaction liquid. The resulting reaction liquid was filtered through a glass filter (product name: GC-90, manufactured by ADVANTEC Corporation, average pore size: 0.8 μm) to obtain silver particle dispersion 1 containing 20% by mass of silver particles.
A few μl was taken from the obtained silver particle dispersion 1, and a frozen body was produced by high-pressure freezing. The frozen body was then fractured, and a carbon replica film of the cross section was produced. The carbon replica film was placed on a TEM grid and observed with a TEM. The maximum diameter of 20 silver particles in a TEM image of an area of 5 μm x 5 μm was measured, and the average particle diameter of the silver particles was calculated from the measured values. The results are shown in Table 2. Furthermore, when the shape of the silver particles was confirmed with a TEM, they were spherical.

<Preparation of Silver Particle Dispersions 2 to 6>
Silver particle dispersions 2 to 6 containing 15 mass % of silver particles were obtained in the same manner as in the preparation of silver particle dispersion 1, except that in the preparation of silver particle dispersion 1, the rate at which dimethylaminoethanol was added and the water temperature were adjusted to change the average particle diameter of the silver particles as shown in Table 2 below. The average particle diameter of the silver particles in the obtained silver particle dispersions 2 to 6 was determined in the same manner as for silver particle dispersion 1. The results are shown in Table 2.

<Preparation of Silver Particle Dispersion 7>
Silver Particle Dispersion Liquid 7 was obtained in the same manner as in the preparation of Silver Particle Dispersion Liquid 1, except that cholic acid was replaced with propionic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.). For the obtained Silver Particle Dispersion Liquid 7, the average particle size of the silver particles was determined in the same manner as for Silver Particle Dispersion Liquid 1. The results are shown in Table 2.

<Preparation of Silver Particle Dispersion 8>
50 g of silver nitrate was dissolved in 1 L of distilled water to obtain a first solution. Next, 22.2 g of oxalic acid was dissolved in 1 L of distilled water to obtain a second solution. The first solution and the second solution were mixed to obtain a mixed solution 1 containing silver oxalate. From the obtained mixed solution 1, impurities were removed by filtration to obtain a mixed solution 2. 3 g of polyethylene glycol (dispersant) was added to 1 L of mixed solution 2, and mixed solution 3 in which silver oxalate was dispersed was obtained by stirring for 50 minutes while adding ultrasonic waves. The obtained mixed solution 3 was put into an autoclave (jacketed AC type; manufactured by Nitto Koatsu Co., Ltd.) and pressurized at a pressure of 0.5 MPa to obtain a mixed solution 4. The obtained mixed solution 4 was heated to 140 ° C. while stirring at a speed of 1300 rpm, and stirring was performed for 30 minutes while maintaining the temperature, to obtain a liquid containing fine particles mainly composed of silver. The average value of the arithmetic mean roughness Ra of the microparticles was 2.0 nm.
The obtained liquid containing silver-based microparticles was centrifuged to separate it into precipitate 1 and supernatant, and excess polyethylene glycol (supernatant) was removed. Furthermore, the precipitate 1 was put into ethylene glycol monoethyl ether acetate (ECA), stirred, and centrifuged to separate it into precipitate 2 and supernatant, and excess ethylene glycol monoethyl ether acetate (supernatant) was removed. The precipitate 2 obtained by centrifugation was subjected to heat drying for a predetermined period of time to obtain silver particle dispersion liquid 8, which is a fine silver particle-containing composition. The obtained silver particle dispersion liquid 8 contains 90% by mass of silver particles and 10% by mass of other substances (mainly ethylene glycol monoethyl ether acetate).
For the obtained Silver Particle Dispersion Liquid 8, the average particle size of the silver particles was determined in the same manner as for Silver Particle Dispersion Liquid 1. The results are shown in Table 2. Furthermore, when the shape of the silver particles was confirmed by TEM, they were found to be flaky.

<Preparation of Silver Particle Dispersion 9>
Silver particle dispersion liquid 9 was obtained in the same manner as in the preparation of silver particle dispersion liquid 8, except that the mixed liquid 4 charged in the autoclave was stirred at 1000 rpm. The results are shown in Table 2. In addition, when the shape of the silver particles was confirmed by TEM, they were found to be flaky.

Preparation of Silver-Based Inks
<Preparation of Silver-Based Ink 1>
The following materials were added, and the remaining amount of ion-exchanged water was added so that the total was 100% by mass. The mixture was then mixed and stirred, and filtered through a polypropylene filter with an average pore size of 0.2 μm (product name: Syringe Filter, manufactured by Sartorius) to obtain silver-based ink 1.
-material-
・Silver particle dispersion liquid 1 20.0% by mass
Dimethylaminoethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 0.01% by mass
1,2-propanediol (Tokyo Chemical Industry Co., Ltd.) 36.0% by mass
3-Ethyl-3-hydroxymethyloxetane (Tokyo Chemical Industry Co., Ltd.) 7.0% by mass
LS-106 (polyoxyalkylene alkyl ether; manufactured by Kao Corporation) 1.0% by mass
Proxel LV (Avecia) 0.1% by mass
LS-106 was used as a surfactant, and Proxel LV was used as an antiseptic and antifungal agent.

<Preparation of Silver-Based Ink 2>
The following materials were added, and the remaining amount of ion-exchanged water was added so that the total was 100% by mass. The mixture was then mixed and stirred, and filtered through a polypropylene filter with an average pore size of 0.2 μm (product name: Syringe Filter, manufactured by Sartorius) to obtain silver-based ink 2.
-material-
・Silver particle dispersion liquid 2 14.0% by mass
Dimethylaminoethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 0.01% by mass
1,2-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 25.0% by mass
3-Ethyl-3-hydroxymethyloxetane (Tokyo Chemical Industry Co., Ltd.) 7.0% by mass
BYK-33 (manufactured by BYK-Chemie) 1.0% by mass
Proxel LV (Avecia) 0.1% by mass
BYK-33 was used as a surfactant, and Proxel LV was used as an antiseptic and antifungal agent.

Preparation of Silver-Based Inks 3 to 9
Silver-based inks 3 to 9 were obtained in the same manner as in the preparation of silver-based ink 2, except that silver particle dispersion 2 was changed to silver particle dispersions 3 to 9.

The average particle diameter of the silver particles in the obtained silver-based inks 1 to 9 was examined using a transmission electron microscope (manufactured by JEOL Ltd.) in the same manner as for silver particle dispersion 1, and it was confirmed to be the same as the average particle diameter of the silver particles in the silver particle dispersion used.

The compositions of silver-based inks 1 to 9 are shown in Tables 3 and 4.

(Examples 1 to 33 and Comparative Examples 1 to 13)
<Preparation of ink>
Reactive Blue 2, Reactive Blue 4, Reactive Blue 13, Reactive Blue 15, Reactive Blue 21, Reactive Blue 49, Reactive Blue 72, Acid Blue 20, Acid Blue 25, Acid Blue 193, Direct Blue 199, Pigment Blue 15:3, Pigment Blue 15:4, Naphthol Green B, and Acid Red 52 were added to Silver-based Inks 1 to 9 as shown in Tables 5 and 6 to prepare inks of Examples 1 to 33 and Comparative Examples 1 to 13.
The inks of Examples 1 to 32 and Comparative Examples 1 to 13 were prepared so that the polyester urethane resin dispersions 1 to 5 or the polycarbonate urethane resin dispersions contained 1.7% by mass (resin solids content: 0.5% by mass) relative to the numerical values (mass %) of the silver particle dispersions shown in Tables 3 and 4.

Using an inkjet printer (IPSiO GXe5500 manufactured by Ricoh Co., Ltd.) filled with each of the obtained inks, each ink was ejected onto a recording medium (EJK-EGNA450; manufactured by ELECOM Co., Ltd.) in an environment of 25° C. to form a solid image.
The obtained solid image was evaluated for glossiness, chromaticity (b ^* value), chromaticity unevenness, abrasion resistance, and storage stability according to the following evaluation criteria.

<Evaluation of Glossiness>
The 20° gloss of the obtained solid image was measured using a gloss meter (Micro Trigloss, manufactured by BYK Gardener) and evaluated according to the following criteria. The results are shown in Tables 7 and 8. The desired level is rank S or higher.
-Evaluation criteria-
SS: 20° glossiness is 500 or more. S: 20° glossiness is 400 or more and less than 500. A: 20° glossiness is 300 or more and less than 400. B: 20° glossiness is 100 or more and less than 300. C: 20° glossiness is less than 100.

<Evaluation of chromaticity (b ^* value)>
The "chromaticity (color value (b ^* value))" of the CIE L ^* a ^* b ^* color coordinates was measured using an X-Rite 938 spectrophotometric densitometer (manufactured by X-Rite Corporation) and evaluated according to the following criteria. The results are shown in Tables 7 and 8. The desired level is Rank A.
-Evaluation criteria-
Rank A: b ^* value is -3 or less Rank B: b ^* value is greater than -3 and less than 0 Rank C: b ^* value is greater than 0

<Evaluation of chromaticity unevenness>
The chromaticity unevenness refers to the variation in the b ^* value. A solid image measuring 15 cm x 4 cm was divided into 10 equal parts in the horizontal direction, and the b ^* value was measured at 10 points using an X-Rite 938 spectrophotometric densitometer (manufactured by X-Rite Corporation), and the unevenness was evaluated based on the difference between the maximum and minimum values obtained. The results are shown in Tables 7 and 8. The desired level is rank B or higher.
-Evaluation criteria-
Rank A: The difference between the maximum and minimum measured values is 0.5 or less. Rank B: The difference between the maximum and minimum measured values is more than 0.5 and 1 or less. Rank C: The difference between the maximum and minimum measured values is more than 1.

<Evaluation of Scratch Resistance>
The dried print was set in a Gakushin-type abrasion fastness tester AB-301 (manufactured by Tester Sangyo Co., Ltd.) and rubbed 10 times with a friction element (load: 300 g) with a white cotton cloth (compliant with JIS L 0803) attached to the contact area, and the degree of deterioration was visually observed and evaluated according to the following criteria. The results are shown in Tables 7 and 8. The desired level is rank A or higher.
-Evaluation criteria-
S: The number of scratches is less than 5, and the base is not visible.
A: The number of scratches is between 5 and 10, and the base is not visible.
B: There are 10 or more scratches and the base is exposed.

<Evaluation of storage stability>
The inks of Examples 1 to 33 and Comparative Examples 1 to 13 were stored at 60°C for 2 weeks, and the viscosity change rate was calculated from the viscosity values before and after storage, and the viscosity change rate was evaluated according to the following criteria. The results are shown in Tables 7 and 8. The viscosity value can be measured using an E-type viscometer "ELD type viscometer" (manufactured by Toki Sangyo Co., Ltd.). The desired level is rank A or higher.
-Evaluation criteria-
S: Viscosity change rate is within ±3% A: Viscosity change rate is within ±5% B: Viscosity change rate is within ±10% C: Viscosity change rate exceeds ±10%

For example, aspects of the present invention are as follows.
<1> An ink containing silver particles and a dye,
The average particle size of the silver particles is 100 nm or less,
The dye has a maximum absorption wavelength of 600 nm or more and 680 nm or less,
The ink is characterized in that the content of the dye is 0.01% by mass or more and less than 0.1% by mass with respect to the total mass of the ink.
<2> The ink according to <1>, wherein the dye has a vinyl sulfone group or a chlorotriazine group.
<3> The ink according to <1>, wherein the dye includes at least one selected from the group consisting of Reactive Blue 2, Reactive Blue 4, Reactive Blue 13, Reactive Blue 15, Reactive Blue 21, Reactive Blue 49, Reactive Blue 72, Acid Blue 20, Acid Blue 25, Acid Blue 193, and Direct Blue 199.
<4> The ink according to any one of <1> to <3>, further comprising resin particles having an average particle diameter of 10 nm or more and 30 nm or less.
<5> The ink according to any one of <1> to <4>,
a storage section for storing the ink;
The image forming apparatus further comprises an ejection section that ejects the ink.
<6> An image forming method, comprising the step of forming an image by using the ink according to any one of <1> to <4>.

The ink described in any one of <1> to <4>, the image forming apparatus described in <5>, and the image forming method described in <6> can solve the problems of the prior art and achieve the object of the present invention.

400 Image forming apparatus 401 Exterior of image forming apparatus 401c Cover of apparatus body 404 Cartridge holder 410 Main tank 410s Main tank for silver (S) 410c Main tank for cyan (C) 410m Main tank for magenta (M) 410y Main tank for yellow (Y) 411 Ink storage container 413 Ink discharge port 414 Storage container case 420 Mechanical section 434 Discharge head 436 Supply tube

Patent No. 4165860 JP 2020-125396 A JP 2020-075981 A Patent No. 4078283

Claims (6)

An ink comprising silver particles and a dye,
The average particle size of the silver particles is 100 nm or less,
The dye has a maximum absorption wavelength of 600 nm or more and 680 nm or less,
The ink has a dye content of 0.01% by mass or more and less than 0.1% by mass with respect to the total mass of the ink. The ink according to claim 1, wherein the dye has a vinyl sulfone group or a chlorotriazine group. The ink according to claim 1, wherein the dye comprises at least one selected from Reactive Blue 2, Reactive Blue 4, Reactive Blue 13, Reactive Blue 15, Reactive Blue 21, Reactive Blue 49, Reactive Blue 72, Acid Blue 20, Acid Blue 25, Acid Blue 193, and Direct Blue 199. The ink according to any one of claims 1 to 3, containing resin particles having an average particle size of 10 nm or more and 30 nm or less. An ink according to any one of claims 1 to 4,
a storage section for storing the ink;
An image forming apparatus comprising an ejection section that ejects the ink. An image forming method comprising a step of forming an image using the ink according to claim 1 .

Images