JP6866642B2 - Ink sets, ink cartridges, printing methods and printing equipment - Google Patents

Description

The present invention relates to inks, ink sets, ink cartridges, printing methods and printing devices.

In recent years, image recordings in which the image changes in response to external stimuli include ballpoint pens that disappear due to frictional heat using ink that has hysteresis characteristics in the color density-temperature curve, and mercury (II) iodide metal that reversibly changes color with temperature. Temperature-indicating records using complex salts have been developed.
Inks for moisture indicators that develop or decolorize with moisture have also been developed. In the old days, discoloration of hydrated complexes of cobalt salts was used, and in recent years, inks using pH-sensitive dyes have been developed. These are mechanisms that detect moisture by combining colored dyes with acidic components eluted under the influence of moisture and making them colorless.

On the other hand, inks that change the light transmission to a transparent state by being stimulated from the white state instead of the presence or absence of such coloring are also required from the variety of image expressions.
Generally, as a pigment for white ink, titanium dioxide, which is a white pigment having excellent hiding power, coloring power and the like, is widely used. Similarly, inks using hollow particles have been reported. The hiding property of the hollow particles is obtained by utilizing the difference in the refractive index between the hollow shell after the coating film is dried and the pores from which the liquid component of the ink has escaped.

In Patent Document 1 below, a white hollow having a porosity of 40% or more and 80% or less, a number average particle size of 50 nm or more and 200 nm or less, and a particle size of 1 μm or more of 1000 ppm or less. Inkjet inks containing particles have been proposed. The white hollow particles described in Patent Document 1 are resins having styrene or the like as a skeleton.
Further, Patent Document 2 describes a sticking member including a base material and an image recording layer recorded on the base material, and the image recording layer has a white ink composition containing hollow resin particles as a white color material. It is composed of a white color material layer recorded by an object and a color color material layer recorded by a process color ink composition, and the white color material layer is heated or can be used with a solvent. A sticking member that is made transparent by permeating is disclosed.

Since hollow resin particles are used in the prior art, there is a problem that the solvent resistance and the heat resistance are low, and the hollow shape cannot be maintained and the initial concealing property cannot be maintained when the transparency is repeatedly performed.

Therefore, an object of the present invention is to provide an ink having excellent concealing property and solvent resistance in an ink used for printing in which the brightness of an image changes due to the application of a liquid.

The above problem is solved by the configuration of 1) below.
1) An ink set comprising a first white ink containing hollow inorganic particles and a second white ink containing solid inorganic particles.

According to the present invention, it is possible to provide an ink having excellent concealing property and solvent resistance in an ink used for printing in which the brightness of an image changes due to the application of a liquid.

It is a perspective explanatory view of the inkjet recording apparatus. It is a perspective explanatory view of a main tank. It is a figure for demonstrating the cartridge of this invention. It is a figure for demonstrating the cartridge of this invention. It is a figure for demonstrating the printing method of this invention. It is a figure for demonstrating the printing method of this invention. It is a figure for demonstrating the printing method of this invention. It is a figure for demonstrating the printing method of this invention. It is a figure for demonstrating the printing pattern used in an Example.

Hereinafter, embodiments of the present invention will be described in more detail.
The present invention is characterized in that, in an ink used for printing in which the brightness of an image changes due to the application of a liquid, the ink contains a solvent and hollow inorganic particles. When water or a volatile solvent is applied to the formed image, the ink of the present invention emerges, and becomes white when dry and transparent when wet.

<Hollow inorganic particles>
The hollow inorganic particles used in the present invention are not particularly limited, and for example, oxides such as titanium, silicon, aluminum, zirconium, and strontium, nitrides, and oxide nitrides can be used. Titanium oxide is preferable from the viewpoint of white hiding property of the coating film because of its lack of coloring and high refractive index. Since scattering at the interface with and is also obtained, other materials such as silica (silicon dioxide) can also be used. Further, from the viewpoint of sedimentation in ink, it is preferable to use silica having a small specific gravity as the hollow inorganic particles, and it is compared that silica controls the shell thickness (shell thickness) and pore diameter of the hollow inorganic particles. Easy to target. Silica can be freely particle-designed using an organosilicon compound such as tetraethoxysilane or tetramethoxysilane or an inorganic silicon compound such as silicate as a starting material.

The hollow inorganic particles preferably have a specific gravity close to the specific gravity of the ink liquid in order to suppress precipitation, floating or separation in the ink, and therefore the shell thickness of the hollow inorganic particles is preferably 4 nm or more and 20 nm or less, preferably 6 nm. It is more preferably 18 nm or less. When the shell thickness is 4 nm or more, the collapse of the hollow structure due to the energy applied in the dispersion step is prevented, high concealment is obtained, and sedimentation in the ink is also prevented. When the shell thickness is 20 nm or less, the specific gravity of the hollow inorganic particles can be kept small, and sedimentation in the ink is prevented. Further, it is preferable that the ratio (inner diameter / outer diameter) of the inner diameter (pore diameter) and the outer diameter (primary particle diameter) of the hollow inorganic particles is 0.75 or more and 0.95 or less. When the ratio is 0.75 or more, sufficient scattering between the hollow shell and the internal vacancies is obtained, high concealment is obtained, and further, the internal vacancies make it difficult to settle, and when the ratio is 0.95 or less. , The strength of the hollow shell can be obtained, the structure can be maintained even under the energy load at the time of dispersion, and high concealment property and high dispersion stability which is hard to settle can be obtained.

The number of hollow inorganic particles The average primary particle diameter is preferably 20 nm or more and less than 200 nm. When the number average primary particles are 20 nm or more, the hiding property of the coating film can be ensured by scattering between the hollow shell and the internal pores, and when the number is less than 200 nm, it is difficult to settle in the ink and high dispersion stability is achieved. Can be expected. As the number of primary average particle diameters and the shell thickness, a transmission electron microscope (manufactured by JEOL Ltd., "JEM-2100F") is used to determine the primary particles of 200 or more and 500 or less primary particles in a 30,000-fold field. It is possible to measure the constant direction diameter at the distance between two parallel lines in a certain direction sandwiching a particle and obtain it from the average value of the cumulative distribution.

The 50% cumulative volume particle size (D50) of the hollow inorganic particles in the ink is preferably 200 nm or more and 500 nm or less. When the 50% cumulative volume particle diameter (D50) is 200 nm or more, the hiding property of the coating film can be enhanced, and when it is 500 nm or less, the apparent specific gravity due to the binding solvent between the particles due to the secondary agglutination increases. It can be suppressed, it is difficult to settle, and high dispersion stability can be obtained. The 50% cumulative volume grain size (D50) of the ink composition described here is the secondary particle size in the ink.

The cumulative 10% particle diameter (D10), cumulative 50% particle diameter (D50), and cumulative 90% particle diameter (D90) of the hollow inorganic particles are measured to determine the diameter and the number of hollow inorganic particles, and the results are obtained. From the particle size addition curve obtained by statistical processing, the cumulative particle diameter when it becomes 10% of the total mass is the cumulative 10% particle diameter (D10), and the particle diameter when it becomes 50% of the total mass. It is a value in which the cumulative 50% particle diameter (D50) and the particle diameter when the total mass is 90% are the cumulative 90% particle diameter (D90). The diameter of the hollow inorganic particles may be the diameter of the hollow inorganic particles themselves, or may be the diameter of the particle colloid when the hollow inorganic particles are dispersed in a colloidal form.
The diameter of the hollow inorganic particles can be determined, for example, by using a particle size distribution measuring device based on a dynamic light scattering method if it is in a dispersed state in a solvent. Examples of the particle size distribution measuring device by the dynamic light scattering method include Nanotrack Wave-UT151 (manufactured by Microtrack Bell Co., Ltd.), Nanotrack Wave-EX150 (manufactured by Nikkiso Co., Ltd.), ELSZ-2, and DLS-8000. (The above is manufactured by Otsuka Electronics Co., Ltd.), LB-550 (manufactured by HORIBA, Ltd.) and the like.
In addition to these, measurement can be performed by electron microscopy. A photograph of the hollow inorganic particles is obtained by the electron microscope, and the diameter of the hollow inorganic particles can be determined by performing image processing and measuring the photograph. As an example, the areas of 50 or more hollow inorganic particles in a photograph are randomly obtained from a photograph, and the diameters of equivalent circles are calculated to obtain the particle size. Then, the particle size addition curve can be obtained from the obtained particle size.

The 90% cumulative volume particle size (D90) of the hollow inorganic particles in the ink is preferably 1 μm or less. Further, it is more preferably 600 nm or less. When the 90% cumulative volume particle diameter (D90) is 1 μm or less, even if the particles are agglomerated due to drying of the ink or foreign matter in the ink, the agglomeration does not exceed the nozzle diameter and the nozzle is not clogged. Further, when D90 is 600 nm or less, the size of the agglomerates is sufficiently small with respect to the flow path in the head and the nozzle, so that stable discharge can be performed. The 90% cumulative volume grain size (D90) of the ink described here is the secondary particle size in the ink.

The content of the hollow inorganic particles in the ink is preferably 3% by mass or more and 12% by mass or less, and more preferably 4.5% by mass or more and 10% by mass or less. When it is 3% by mass or more, sufficient hiding property and scratch resistance can be obtained, and when it is 12% by mass or less, a sufficient coating film concentration can be obtained and good ejection stability can be obtained.

When the hollow inorganic particles are made of silica (hereinafter, may be referred to as hollow silica particles), the production method thereof is not particularly limited, but a known production method can be used. For example, as described in Japanese Patent No. 4654428 and Japanese Patent No. 5810362, calcium carbonate is used as a core material, and alkoxysilane is formed on the surface of calcium carbonate in the presence of a basic catalyst to obtain silica. Then, hollow silica particles can be obtained by a method of dissolving calcium carbonate by adding an acid.

When hollow silica particles are used in the ink of the present invention, it is desirable to use a dispersion liquid of hollow silica particles generated in the process of producing the hollow silica particles rather than powder-dried hollow silica particles. By using a dispersion liquid of hollow silica particles, it is possible to prevent strong interparticle aggregation during drying, and it is possible to disperse in the ink while maintaining the hollow structure.

When dispersing the hollow inorganic particles in the ink, it is desirable to add a dispersant polymer. Examples of the dispersant polymer include α-olefin-maleic anhydride copolymer, styrene- (meth) acrylic copolymer, water-soluble polyurethane resin and water-soluble polyester resin. These may be used alone or in combination of two or more. When the dispersant polymer is used, the steric repulsion effect associated with the adsorption of the dispersant can be improved, and high dispersion stability can be obtained. The dispersant polymer means a polymer having a weight average molecular weight of 1,000 or more.
The content of the dispersant polymer is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 50% by mass or less, based on the hollow inorganic particles. When the content is 10% by mass or more, dispersibility can be ensured by the steric repulsion effect of the dispersant polymer adsorbed on the hollow inorganic particles, and when it is 60% by mass or less, the dispersion is not adsorbed on the hollow inorganic particles. The amount of the agent polymer is small, and it is possible to reduce the viscosity of the ink. Further, since the amount of the dispersant polymer that is not adsorbed is small, the increase in the tincture property of the ink is suppressed, and the filtration liquid permeability and the ejection property are improved.

<Solvent>
The ink of the present invention contains a solvent, typically a volatile solvent. The volatile solvent is preferably a non-polymerizable solvent having no polymerizable functional group, and more preferably one that does not remain in the hollow inorganic particles when the coating film is dried. When the volatile solvent is water or a water-soluble organic solvent, it can be used as a water-based ink, and when the volatile solvent is an organic solvent, it can be used as a solvent ink. However, in recent years, many VOC (volatile organic compound) problems have been taken up, and there is a background in which water-based inks capable of reducing the amount of VOC generated are widely desired. VOC is a general term for organic compounds that easily volatilize in the atmosphere at normal temperature and pressure. The volatile solvent described in the present invention is required to volatilize when heated on a recording medium, and has a boiling point of 300. It means the one below ℃.
As described above, the ink of the present invention can obtain concealment property by utilizing scattering between the shell of hollow inorganic particles and internal pores in addition to scattering on the particle surface. Therefore, if the ink component remains in the hollow inorganic particles after the coating film is dried, the hiding property of the coating film is lowered. From the above points, the volatile solvent preferably has a boiling point of 260 ° C. or lower.

<< Water-soluble organic solvent for water-based ink >>
Examples of the water-soluble organic solvent for water-based inks include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and propylene carbonate. , Ethylene carbonate.
The content of the water-soluble organic solvent is preferably 20% by mass or more, more preferably 30% by mass to 70% by mass, based on the total amount of the ink.
When the content is less than 20% by mass, the moisturizing power of the ink is reduced, so that the ink is easily dried, and the head meniscus portion causes precipitation of dissolved components in the ink and aggregation of dispersed components due to drying, resulting in ejection. It may be defective.
Examples of such water-soluble organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, cyclic ethers, amines, amides, sulfur-containing compounds, propylene carbonate, and carbonic acid. Examples include ethylene.

Examples of the polyhydric alcohols include 1,2-propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-butanediol, 3-methyl-1,3-butanediol, and 1,5-. Pentandiol, 2-methyl-2,4-pentanediol, hexylene glycol, 1,6-hexanediol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 3-methyl-1,3- Examples thereof include hexanediol and propylpropylene diglycol.
Examples of the polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether, and propylene glycol monoethyl ether. , Triethylene glycol dimethyl ether, and the like.
Examples of the polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.
Examples of the cyclic ethers include epoxies, oxetane, tetrahydrofurans, tetrahydropyrans, crown ethers and the like. Among these, oxetane and tetrahydrofuran are preferable, and oxetane is more preferable from the viewpoint of water solubility.
Examples of the sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiglycol.
Examples of the amines include monoethanolamine, diethanolamine, triethanolamine, N, N-dimethylmonoethanolamine, N-methyldiethanolamine, N-methylethanolamine, N-phenylethanolamine, 3-aminopropyldiethylamine and the like. Can be mentioned.
Examples of the amide compounds include 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, β-methoxy-N, N-dimethyl. Examples thereof include propionamide, β-butoxy-N, N-dimethylpropionamide and the like. Among these, the water-soluble amide compound described below is preferable.
The water-soluble amide compound is a polar solvent capable of dissolving many organic compounds and inorganic salts, and can be widely mixed from water to an organic solvent. Therefore, the effect of improving the wettability and solubility in the recording medium and the miscibility of other components can be obtained.

Further, an amide compound represented by the following structural formula, which is a kind of acyclic amide compound, is also included.

The amide compound having the structural formula has different hydrophilicity depending on the length of the alkyl group, and has different miscibility with water or an organic solvent.

<Water>
The content of water in the ink is not particularly limited and may be appropriately selected depending on the intended purpose, but from the viewpoint of ink drying property and ejection reliability, it is preferably 10% by mass or more and 90% by mass or less, and 20% by mass. % To 60% by mass is more preferable.

<< Organic solvent for solvent-based ink >>
As the organic solvent for solvent-based inks, volatile organic solvents used in ordinary solvent-based inks can be used.
Examples of the organic solvent include alcohols, glycols, glycol ethers, esters, ketones, aromatic compounds, nitrogen-containing compounds and the like.
Examples of the alcohols include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, tridecyl alcohol, cyclohexyl alcohol, 2-methylcyclohexyl alcohol and the like.
Examples of the glycols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and the like.
Examples of the esters include ethyl acetate, isopropylene acetate, n-butyl acetate, methyl lactate, ethyl lactate, butyl lactate and the like.
Examples of the ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, diacetone alcohol and the like.
Examples of the aromatic compound include toluene, xylene and the like.
Examples of the nitrogen-containing compound include acetonitrile, γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and the like.
Various solvents are selected from the viewpoints of compatibility with the characteristics of the head nozzle at the time of printing, safety, and dryness, and a plurality of solvents can be mixed and used as necessary.

It is preferable that the solvent-based ink contains glycol ethers as an organic solvent from the viewpoints of wettability to a recording medium, permeability, and appropriate drying property.
Examples of the glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and diethylene glycol ethyl methyl ether. Examples thereof include diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate.

In the solvent-based ink, the content of the organic solvent is preferably 85% by mass or more, more preferably 85% by mass to 95% by mass, based on the total amount of the ink.

The ink of the present invention is used for spectroscopic measurement of an image printed on a polyethylene terephthalate film with black paper laid under the polyethylene terephthalate film before and after being immersed in pure water for 1 minute. When the lightness is measured using a color densitometer, it is preferable that the lightness difference | ΔL * | obtained by the following formula 1 is 13 or more. When the brightness difference | ΔL * | is 13 or more, the change in brightness can be confirmed satisfactorily.
Equation 1 | ΔL * | = (L * initial)-(L * after immersion)
(In Equation 1, the initial L * is L * before the image is immersed in pure water, and the term after L * immersion is L * after the image is immersed in pure water for 1 minute.)
The brightness difference | ΔL * | can be measured by a known method, for example, using a spectrophotometric densitometer X-Rite 939.

Further, the ink of the present invention is an image printed on a polyethylene terephthalate film with black paper laid under the polyethylene terephthalate film before being immersed in an organic solvent and after being immersed for 1 minute and dried. It is preferable that the brightness difference | ΔL * | obtained by the following formula 2 is 13 or less when the brightness is measured by using the spectrophotometric densitometer of the above. When the brightness difference | ΔL * | is 13 or less, the solvent resistance is excellent.
Equation 2 | ΔL * | = (L * initial)-(L * after immersion and drying in organic solvent)
(In the formula 2, the initial L * is L * before the image is immersed in the organic solvent, and after the L * organic solvent immersion drying is after the image is immersed in the organic solvent for 1 minute and dried. L *)

<Ink set>
The ink set of the present invention includes a first ink containing hollow inorganic particles and a second ink containing solid inorganic particles. The second ink is preferably one in which the image does not change due to the application of the liquid. The ink set of the present invention preferably contains the first ink, which is the above ink containing a solvent and hollow inorganic particles, and more preferably the first ink and the second ink. The ink is a white ink, and particularly preferably, the first ink, which is the above-mentioned ink containing a solvent and hollow inorganic particles, and the second ink, which contains solid inorganic particles and whose image is not changed by the application of a liquid. Ink and, including.
When forming a printed matter in which the image changes due to the application of a liquid, for example, the image emerges, the hollow inorganic particles in the first ink become white when dried and become transparent when wet, thereby causing the image to appear. Since the brightness of the solid inorganic particles in the second ink does not change due to the application of the liquid, it is possible to increase the contrast of the image by using both inks. In addition, since the ink set contains hollow inorganic particles and solid inorganic particles, respectively, the heat resistance and solvent resistance are excellent, and since the hollow inorganic particles are used, the coating film is coated even if the coating film is repeatedly exposed to the solvent. Since the hollow shape inside is not broken, the white hiding property can be restored every time the coating film is dried.

The ink set of the present invention may contain known inks in addition to the first ink and the second ink. For example, process color inks such as black ink, cyan ink, magenta ink, and yellow ink, special color inks such as red ink, orange ink, blue ink, green ink, and metallic ink, gray ink, light cyan ink, and light magenta ink. Light color ink and the like can be used together.

The second ink or the ink that can be used in combination can be a photocurable ink, a thermosetting ink, or a hot melt ink that does not contain a volatile solvent, but from the viewpoint of matching the coating thickness, the ink set. Is preferably available in inks containing volatile solvents. Further, since the apparatus can be miniaturized by using a single drying fixing process, it is preferable to perform drying fixing with an ink containing a volatile solvent.
Further, in order to suppress feathering and bleeding between inks, it is desirable to control the ink addition component to suppress the surface tension difference between inks to 5 mN / m or less, preferably 2 mN / m.

<Solid inorganic particles>
Unlike hollow particles, the solid inorganic particles are filled with a solid component inside the particles, and the particles themselves are composed of a single component or a plurality of components. Since the solid occupies the inside of the particle, the solid inside the particle does not change when the ink dries, and a cavity due to gas is not formed inside the particle.
The solid inorganic particles are not particularly limited, and for example, oxides such as titanium, silicon, aluminum, zirconium, and strontium, nitrides, and oxide nitrides can be used. It is preferable to contain an inorganic white pigment from the viewpoint of matching the color with the hollow inorganic particles, weather resistance, and heat resistance. Barium sulfate, white lead, zinc oxide, titanium oxide, etc. are raised in such solid inorganic pigments due to their lack of coloring and high refractive index, and silica, aluminum oxide, zirconium oxide, and carbon dioxide are used to adjust the whiteness. It is also possible to use calcium and the like together. Among these, it is preferable to use titanium dioxide for the solid inorganic particles from the viewpoint of white hiding property.

As the crystal system of titanium dioxide particles, among amorphous, rutile type and anatase type, the rutile type having a high refractive index and easily increasing the whiteness is preferable. Further, when the average primary particle size of the titanium dioxide particles is 100 to 400 nm, the whiteness is high, and from the viewpoint of the scattering characteristics of visible light, the whiteness is high at 200 to 300 nm, particularly at 210 to 250 nm, which is preferable. Examples of the method for producing such titanium oxide particles include a sulfuric acid method and a chlorine method, but the method is not particularly limited.
The surface treatment of the titanium dioxide particles is also not particularly limited, but in order to suppress the high photocatalytic activity of the titanium dioxide particles and suppress the decomposition of additives adhering to the particle surface, the particle surface is made of aluminum, silicon, zirconia, etc. Those treated with oxide are preferable.
In the above, the white pigment is exemplified as the solid inorganic particles, but other inorganic pigments can also be used. Examples of other inorganic pigments include iron oxide, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, titanium yellow, carbon black and the like.

The 50% cumulative volume particle size (D50) of the solid inorganic particles in the second ink is preferably 50 nm or more and 350 nm or less, and more preferably 150 nm or more and 302 nm or less. When the 50% cumulative volume particle diameter (D50) is 50 nm or more, the hiding property of the coating film can be obtained, and when it is 350 nm or less, the apparent specific gravity due to the binding solvent between the particles due to the secondary agglutination increases. It can be suppressed, it is difficult to settle, and high dispersion stability can be obtained. The 50% cumulative volume grain size (D50) of the ink described here is the secondary particle size in the ink.
The cumulative 10% particle diameter (D10), cumulative 50% particle diameter (D50), and cumulative 90% particle diameter (D90) of the solid inorganic particles can be calculated by measuring in the same manner as for hollow inorganic particles. .. The diameter of the solid inorganic particles may be the diameter of the solid inorganic particles themselves, or may be the diameter of the particle colloid when the solid inorganic particles are dispersed in a colloidal form.
The diameter of the solid inorganic particles can be determined, for example, by using a particle size distribution measuring device based on a dynamic light scattering method if it is in a dispersed state in a solvent. It can also be measured by electron microscopy in the same way as hollow inorganic particles.

The 90% cumulative volume grain size (D90) of the solid inorganic particles in the second ink is preferably 1 μm or less. Further, it is more preferably 600 nm or less. When the 90% cumulative volume particle diameter (D90) is 1 μm or less, even if the particles are agglomerated due to drying of the ink or foreign matter in the ink, the agglomeration does not exceed the nozzle diameter and the nozzle is not clogged. Further, when D90 is 600 nm or less, the size of the agglomerates is sufficiently small with respect to the flow path in the head and the nozzle, so that stable discharge can be performed.

The content of the solid inorganic particles in the second ink is preferably 3% by mass or more and 12% by mass or less, and more preferably 4.5% by mass or more and 10% by mass or less. When it is 3% by mass or more, sufficient hiding property and scratch resistance can be obtained, and when it is 12% by mass or less, a sufficient coating film concentration can be obtained and good ejection stability can be obtained.

<Color material>
In the present invention, the first ink and the second ink are preferably white inks, but these inks can also be used as colored inks. As the coloring material, both pigments and dyes can be used, but pigments are preferable from the viewpoint of light fading because titanium dioxide has strong photoactivity and high decomposability.

Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelate, nitro pigments, nitroso pigments, aniline black and the like. Among these, azo pigments, polycyclic pigments and the like are more preferable.
Examples of the azo pigment include azo lakes, poorly soluble azo pigments, condensed azo pigments, chelate azo pigments and the like. Examples of the polycyclic pigment include phthalocyanine pigment, perylene pigment, perinone pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, indigo pigment, thioindigo pigment, isoindolinone pigment, quinophthalone pigment and the like. Examples of the dye chelate include a basic dye type chelate and an acid dye type chelate.
The color of the color material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a color material for black and a color material for color.
These may be used alone or in combination of two or more.

Examples of the color material for black include carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black, and channel black, copper, iron (CI pigment black 11), and the like. Metals, organic pigments such as aniline black (CI pigment black 1) and the like can be mentioned.
Examples of the coloring material for the color include C.I. 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, 128, 138, 150, 151, 153, 155, 183, 213, C.I. I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48: 2, 48: 2 (Permanent Red 2B (Ca)), 48: 3, 48: 4, 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Cadmium 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81, 83, 88, 101 (Magenta), 104, 105, 106, 108 Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, C.I. I. Pigment Violet 1 (Rhodamine Lake), 3, 5: 1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15: 1, 15: 2, 15: 3 (phthalocyanine blue), 15: 4 (phthalocyanine blue), 16, 17: 1, 56, 60, 63; C.I. I. Pigment Greens 1, 4, 7, 8, 10, 17, 18, 36 and the like.
Other suitable color pigments include those described in The Color Index, Third Edition (The Society of Dyers and Colorists, 1982).
It is preferable to add such a pigment as necessary for toning the ink, and the color is not transparent due to the influence of the hiding power of the inorganic particles.

The content of the coloring material in the ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass, from the viewpoint of improving image density, good fixability and ejection stability. It is as follows.

<Dispersion method>
As a method for dispersing the hollow inorganic particles and the solid inorganic particles, a dispersion device using a recording medium such as a ball mill, a sand mill or a bead mill, or a recording medium-less dispersion device may be used. Since the hollow structure of the hollow inorganic particles is destroyed when a strong force is applied to the particles during dispersion, it is preferable to use a recording medium-less dispersion device in order to maintain the hollow structure.
The recording medium-less device can disperse the hollow inorganic particles while maintaining the hollow structure by avoiding the collision of the recording medium with the particles. Further, since contamination derived from the recording medium does not occur, it is possible to suppress the generation of fine powder and coarse powder in the system. Further, since the uniformity of the particle size distribution can be improved, good ink ejection property can be obtained. Examples of the recording medium-less dispersion device include a dispersion device that utilizes a high-speed shearing force such as a collision dispersion type and an ultrasonic dispersion type, a dispersion device that utilizes high-speed stirring, an ultrasonic dispersion device, and the like. Examples of the disperser using the high-speed shearing force include a device name: NanoVita Series Lab Machine C-ES008 (manufactured by Yoshida Kikai Kogyo Co., Ltd.). Examples of the ultrasonic dispersion device include a device name: ultrasonic homogenizer US-150E (manufactured by Nissei Tokyo Office Co., Ltd.).
The temperature of the dispersion liquid at the time of dispersion is preferably 5 ° C. or higher and 60 ° C. or lower, and more preferably 5 ° C. or higher and 50 ° C. or lower.
As the dispersed recording medium in the dispersion device using the recording medium, it is necessary to set mild conditions by appropriately selecting the recording medium specific gravity and the recording medium diameter so that the hollow structure of the hollow inorganic particles can be maintained.

Hereinafter, other components that can be used for the first ink and / or the second ink (hereinafter, may be simply referred to as ink) will be described.

<Resin>
The type of resin contained in the ink is not particularly limited and may be appropriately selected depending on the intended purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, etc. Examples thereof include resins, styrene-butadiene resins, vinyl chloride resins, acrylic styrene resins, and acrylic silicone resins.
Resin particles made of these resins may be used. It is possible to obtain ink by mixing resin particles with a material such as a coloring material or an organic solvent in the state of a resin emulsion in which water is dispersed as a dispersion medium. As the resin particles, those synthesized as appropriate may be used, or commercially available products may be used. Further, these may be used alone or in combination of two or more kinds of resin particles.

The volume average particle diameter of the resin particles is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of obtaining good fixability and high image hardness, 10 nm or more and 1,000 nm or less are preferable. More than 200 nm is more preferable, and 10 nm or more and 100 nm or less is particularly preferable.
The volume average particle size can be measured using, for example, a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell Co., Ltd.).

The content of the resin is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of fixability and storage stability of the ink, 1% by mass or more and 30% by mass or less with respect to the total amount of the ink. Is preferable, and 5% by mass or more and 20% by mass or less is more preferable.

The particle size of the solid content in the ink is not particularly limited and can be appropriately selected according to the purpose, but from the viewpoint of improving image quality such as ejection stability and image density, the maximum frequency in terms of the maximum number of inks. Is preferably 20 nm or more and 1000 nm or less, and more preferably 20 nm or more and 150 nm or less. The solid content includes resin particles, pigment particles, and the like. The particle size can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell Co., Ltd.).

<Additives>
If necessary, a surfactant, a defoaming agent, an antiseptic / antifungal agent, a rust preventive, a pH adjuster, or the like may be added to the ink.

<Surfactant>
As the surfactant, any of a silicone-based surfactant, a fluorine-based surfactant, an amphoteric surfactant, a nonionic surfactant, and an anionic surfactant can be used.
The silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. Among them, those that do not decompose even at high pH are preferable, and examples thereof include side chain modified polydimethylsiloxane, double-ended modified polydimethylsiloxane, single-ended modified polydimethylsiloxane, side chain double-ended modified polydimethylsiloxane, and the like. Those having an oxyethylene group and a polyoxyethylene polyoxypropylene group are particularly preferable because they exhibit good properties as an aqueous surfactant. Further, as the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used, and examples thereof include a compound in which a polyalkylene oxide structure is introduced into the Si portion side chain of dimethylsiloxane.
Examples of the fluorine-based surfactant include a perfluoroalkyl sulfonic acid compound, a perfluoroalkyl carboxylic acid compound, a perfluoroalkyl phosphate compound, a perfluoroalkyl ethylene oxide adduct, and a perfluoroalkyl ether group in the side chain. A polyoxyalkylene ether polymer compound is particularly preferable because it has a low foaming property. Examples of the perfluoroalkyl sulfonic acid compound include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonic acid salt. Examples of the perfluoroalkylcarboxylic acid compound include perfluoroalkylcarboxylic acid and perfluoroalkylcarboxylic acid salt. The polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain includes a sulfate ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain and a perfluoroalkyl ether group in the side chain. Examples thereof include salts of polyoxyalkylene ether polymers. The counterions of the salts in these fluorine-based surfactants are Li, Na, K, NH ₄ , NH ₃ CH ₂ CH ₂ OH, NH ₂ (CH ₂ CH ₂ OH) ₂ , NH (CH ₂ CH ₂ OH). ₃ etc. can be mentioned.
Examples of the amphoteric tenside agent include laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, and lauryldihydroxyethylbetaine.
Examples of the nonionic surfactant include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkyl amine, polyoxyethylene alkyl amide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, and polyoxyethylene sorbitan. Examples thereof include a fatty acid ester and an ethylene oxide adduct of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, and polyoxyethylene alkyl ether sulfate salt.
These may be used alone or in combination of two or more.

The silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, side chain-modified polydimethylsiloxane, double-ended modified polydimethylsiloxane, one-ended modified polydimethylsiloxane, side. Examples thereof include polydimethylsiloxane modified at both ends of the chain, and a polyether-modified silicone-based surfactant having a polyoxyethylene group and a polyoxyethylene polyoxypropylene group as modifying groups exhibits good properties as an aqueous surfactant, and is particularly effective. preferable.
As such a surfactant, an appropriately synthesized one may be used, or a commercially available product may be used. As commercially available products, for example, they can be obtained from Big Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nippon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd., and the like.
The above-mentioned polyether-modified silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the polyalkylene oxide structure represented by the general formula (S-1) is dimethylpoly. Examples thereof include those introduced into the Si part side chain of siloxane.

General formula (S-1)
(However, 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.)
Commercially available products can be used as the above-mentioned polyether-modified silicone-based surfactant, for example, KF-618, KF-642, KF-643 (Shinetsu Chemical Industry Co., Ltd.), EMALEX-SS-5602, SS- 1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Toray Dow Corning Silicone Co., Ltd.), BYK-33, BYK-387 (Big Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.) and the like can be mentioned.

As the fluorine-based surfactant, a compound having 2 to 16 carbon atoms substituted with fluorine is preferable, and a compound having 4 to 16 carbon atoms substituted with fluorine is more preferable.
Examples of the fluorine-based surfactant include a perfluoroalkyl phosphate compound, a perfluoroalkylethylene oxide adduct, and a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain. Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferable because they have low foaming property, and are particularly fluorine-based compounds represented by the general formulas (F-1) and (F-2). Surfactants are preferred.

General formula (F-1)
In the compound represented by the 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 CnF _{2n + 1} and n is an integer of 1 to 6, or CH ₂ CH (OH) CH _2- CnF _{2n + 1} and n is 4 to 6. It is an integer, or CpH _{2p + 1} and p is an integer of 1-19. a is an integer of 4 to 14.
Commercially available products may be used as the above-mentioned fluorine-based surfactant. Examples of this commercially available product 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.); Full Lard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Co., Ltd.); Megafuck F-470, F -1405, F-474 (all manufactured by Dainippon Ink and Chemicals Co., Ltd.); 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 The Chemours Company); 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 Omniova), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.) Among these, FS-3100, FS-34, FS- of The Chemours Co., Ltd., from the viewpoint of remarkably improving good print quality, particularly color development, penetrability to paper, wettability, and leveling property. 300, FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omninova, and Unidyne DSN-manufactured by Daikin Industries, Ltd. 403N is particularly preferable.

The content of the surfactant in the ink is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of excellent wettability and ejection stability and improvement in image quality, 0.001 mass is used. % Or more and 5% by mass or less are preferable, and 0.05% by mass or more and 5% by mass or less are more preferable.

<Defoamer>
The defoaming agent is not particularly limited, and examples thereof include a silicone-based defoaming agent, a polyether-based defoaming agent, and a fatty acid ester-based defoaming agent. These may be used alone or in combination of two or more. Among these, a silicone-based defoaming agent is preferable because it has an excellent defoaming effect.

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

<Rust inhibitor>
The rust preventive is not particularly limited, and examples thereof include acidic sulfites and sodium thiosulfate.

<pH adjuster>
The pH adjusting agent is not particularly limited as long as the pH can be adjusted to 7 or more, and examples thereof include amines such as diethanolamine and triethanolamine.

The physical characteristics of the ink are not particularly limited and may be appropriately selected depending on the intended purpose. For example, the viscosity, surface tension, pH and the like are preferably in the following ranges.
The viscosity of the ink at 25 ° C. is preferably 5 mPa · s or more and 30 mPa · s or less, preferably 5 mPa · s or more and 25 mPa · s or less, from the viewpoint of improving the print density and character quality and obtaining good ejection properties. More preferred. Here, for the viscosity, for example, a rotary viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used. As the measurement conditions, it is possible to measure at 25 ° C. with a standard cone rotor (1 ° 34'× R24), a sample liquid volume 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, more preferably 32 mN / m or less at 25 ° C. from the viewpoint that the ink is preferably leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably 7 to 12, more preferably 8 to 11, from the viewpoint of preventing corrosion of the metal member in contact with the liquid.

<Pretreatment liquid>
The pretreatment liquid contains a coagulant, an organic solvent, and water, and may contain a surfactant, an antifoaming agent, a pH adjuster, an antiseptic / antifungal agent, an anticorrosive agent, and the like, if necessary.
As the organic solvent, surfactant, defoaming agent, pH adjuster, antiseptic / antifungal agent, and rust preventive, the same materials as those used for ink can be used, and other materials used for known treatment liquids can be used. ..
The type of coagulant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, and polyvalent metal salts.

<Post-treatment liquid>
The post-treatment liquid is not particularly limited as long as it is possible to form a transparent layer. The post-treatment liquid is obtained by selecting and mixing organic solvents, water, resins, surfactants, antifoaming agents, pH adjusters, antiseptic and antifungal agents, rust preventives and the like, if necessary. Further, the post-treatment liquid may be applied to the entire area of the recording area formed on the recording medium, or may be applied only to the area where the ink image is formed.

<Ink cartridge>
The ink cartridge of the present invention comprises containing the first ink and / or the second ink in the ink set in a container, respectively, and further includes other members and the like appropriately selected as necessary.
The container is not particularly limited, and its shape, structure, size, material, etc. can be appropriately selected according to the purpose. For example, at least an ink bag made of an aluminum laminate film, a resin film, or the like can be selected. Those having, etc. are preferably mentioned.
Next, the ink cartridge will be described with reference to FIGS. 3 and 4.
Here, FIG. 3 is a schematic view showing the ink cartridge, and FIG. 4 is a schematic view showing a modified example of the ink cartridge of FIG.
As shown in FIG. 3, in the ink cartridge 201, the ink of the present invention is filled in the ink bag 241 from the ink injection port 242 and exhausted, and then the ink injection port 242 is closed by fusion. At the time of use, for example, a needle of an inkjet recording device is pierced into an ink discharge port 243 made of a rubber member and supplied to the inkjet recording device.
The ink bag 241 is formed of a packaging member such as an aluminum laminate film having low air permeability. As shown in FIG. 4, the ink bag 241 is usually housed in a cartridge case 244 made of plastics, and is detachably attached to, for example, various inkjet recording devices for use.
The ink cartridge 201 contains the ink of the present invention and can be detachably attached to, for example, various inkjet recording devices, and is particularly preferably attached to and detachably attached to an inkjet recording apparatus described later. ..

<Recording medium>
The recording medium is not particularly limited, and plain paper, glossy paper, special paper, cloth, etc. can be used, but according to the ink of the present invention, good image formation can be achieved even if a poorly water-absorbent recording medium is used. Is. Such a recording medium may be a transparent medium having no concealment property, the recording medium may be colored, and an image composed of photographs, illustrations, patterns, characters, or the like may be formed. ..
The poorly water-absorbent recording medium is a recording medium having a surface having low water permeability and low absorbency, and includes a material that does not open to the outside even if there are many cavities inside, and more quantitatively. Is the standard No. of "JAPAN TAPPI Pulp and Paper Test Method 2000 Edition". 51 In the Bristow method described in "Paper and Paperboard-Liquid Absorption Test Method-Bristow Method", a recording medium having a water absorption amount of 10 mL / m ^{2 or less from the start of contact to 30 msec 1/2 is used.} Say.
Examples of the poorly water-absorbent recording medium include vinyl chloride resin film, polyethylene terephthalate (PET) film, polypropylene film, polyethylene film, plastic film such as polycarbonate film, coated paper for printing, and art paper. These may be used alone or in combination of two or more. Among these, vinyl chloride resin film and coated paper for printing are preferable.
The ink of the present invention has sufficient performance not only for poorly water-absorbent recording media but also for conventionally used porous media such as porous media such as plain paper and inkjet paper and inorganic coated porous media. Shown.
The ink of the present invention can print high image quality on the poorly water-absorbent recording medium, but can also be used for forming an image with higher image quality and higher abrasion resistance and adhesiveness, and for high-speed printing conditions. It is more preferable to heat the recording medium after printing.

The printing method of the present invention includes an ink applying step of applying the ink of the present invention (first ink) to the printed matter and a drying step of drying the printed matter to which the ink is applied.
In addition, another printing method of the present invention uses the ink set of the present invention, a first ink applying step of applying the first ink to a printed matter, and a second applying the second ink. The ink applying step includes a drying step of drying the printed matter to which the first ink and the second ink are applied.
A new image can be formed by adding water or a volatile solvent to the image printed by these printing methods.
Further, the printing apparatus of the present invention has a means for ejecting ink and the ink of the present invention (first ink).
Further, another printing apparatus of the present invention has a means for ejecting ink and an ink set of the present invention.
In addition, image formation, recording, printing, printing, etc. in the terms of the present invention are all synonymous.

<Recorded material>
The ink recording material of the present invention comprises an image formed by using the ink of the present invention on a recording medium.
It can be recorded by an inkjet recording device and an inkjet recording method to obtain a recorded material.

<Recording device, recording method>
The ink of the present invention can be suitably used for various recording devices by an inkjet recording method, for example, a printer, a facsimile device, a copying device, a printer / fax / copier multifunction device, a three-dimensional modeling device, and the like.
In the present invention, the recording device and the recording method are devices capable of ejecting ink, various processing liquids, and the like to a recording medium, and a method of recording using the device. The recording medium means a medium to which ink and various treatment liquids can adhere even temporarily.
This recording device can include not only a head portion for ejecting ink, but also means related to feeding, transporting, and discharging paper of a recording medium, and other devices called pretreatment devices and posttreatment devices. ..
The recording device and recording method may include 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, means for heating and drying the print 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 and an infrared heater can be used. Heating and drying can be performed before printing, during printing, after printing, and the like.
Further, the recording device and the recording method are not limited to those in which significant images such as characters and figures are visualized by ink. For example, those that form patterns such as geometric patterns and those that form a three-dimensional image are also included.
Further, the recording device includes both a serial type device that moves the discharge head and a line type device that does not move the discharge head, unless otherwise specified.
Further, as this recording device, it is possible to use not only a desktop type but also a wide recording device capable of printing on an A0 size recording medium, or, for example, continuous paper wound in a roll shape as a recording medium. A continuous line printer is also included.
An example of the recording device will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective explanatory view of the device. FIG. 2 is a perspective explanatory view of the main tank. The image forming apparatus 400 as an example of the recording apparatus is a serial type image forming apparatus. A mechanical unit 420 is provided in the exterior 401 of the image forming apparatus 400. Each ink container 411 of the main tank 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is packaged with, for example, an aluminum laminate film. It is formed of members. The ink container 411 is housed in, for example, a plastic container case 414. As a result, the main tank 410 is used as an ink cartridge for each color.
On the other hand, a cartridge holder 404 is provided behind the opening when the cover 401c of the apparatus main body is opened. A main tank 410 is detachably attached to the cartridge holder 404. As a result, each ink ejection port 413 of the main tank 410 and the ejection head 434 for each color communicate with each other via the supply tube 436 for each color, and ink can be ejected from the ejection head 434 to the recording medium.

Although the general inkjet recording apparatus has been described above, the main tank 410 contains the ink or ink set of the present invention.

This recording device can include not only a portion that ejects ink, but also a device called a pretreatment device, a posttreatment device, and the like.
As one aspect of the pretreatment apparatus and the posttreatment apparatus, it has a pretreatment liquid and a posttreatment liquid as in the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y). There is an embodiment in which a liquid accommodating portion and a liquid discharge head are added, and a pretreatment liquid or a posttreatment liquid is discharged by an inkjet recording method.
As another aspect of the pretreatment device and the posttreatment device, there is a mode in which a pretreatment device and a posttreatment device by, for example, a blade coating method, a roll coating method, and a spray coating method are provided other than the inkjet recording method.

In the recording method using the ink set in the present invention, a first ink coating portion composed of hollow inorganic particles and a second ink coating portion composed of solid inorganic particles are formed as an image pattern on a recording medium. To do. The ink coating method is not particularly limited, but in addition to the injet recording method as described above, plate printing such as stencil printing, letterpress printing, intaglio printing, lithographic printing, and plateless printing such as electrophotographic method. Either printing is available. Among them, the inkjet recording method is preferable because the ink can be adhered in an arbitrary pattern in a non-contact manner regardless of the shape of the recording medium.
When both the first ink and the second ink are dried, they exhibit a hiding property due to light scattering derived from hollow inorganic particles. The first ink contains hollow inorganic particles, and since the coating film has fine pores derived from the hollow inorganic particles, a liquid such as water or a solvent is sucked into the coating film, and the fine pores change from air to liquid. Can be replaced. As a result of the replacement with a liquid, a liquid having a refractive index higher than that of air fills the pores, so that the difference in refractive index is reduced, and the light scattering of the coating film is reduced, so that the hiding property is lowered.
Since the second ink contains a solid inorganic pigment, there are no minute pores in the coating film and the liquid is not sucked into the coating film. Therefore, the difference in hiding power between the two types of ink is larger when the coating film is wet than when it is dried, so that the hiding power of the coated portion of the first ink is reduced and the image pattern becomes conspicuous.

When the recording medium on which printing is performed is a coloring medium, the hiding power of the first ink coating film wet with the liquid is reduced, so that the color of the recording medium becomes visible and the pattern is conspicuous. When the recording medium is a transparent medium, when the hiding power is reduced, the light transmitted through the recording medium can be seen, so that the scenery beyond the recording medium can be seen when it gets wet.
When the coating film is wetted with a liquid colored with a dye or the like, the colored liquid in the coating film of the first ink permeates into minute pores together with the dye, so that the coating film is colored. Does not penetrate and is not colored. The image pattern can be made apparent by the ease of coloring.

The printing order of the first ink and the second ink is not particularly limited, and it is sufficient that the coating film can be formed regardless of whether the images are formed at the same time or the images are formed in order. Further, the first ink and the second ink may not clearly separate the printed portion, and may form a gradation and continuously change from the first ink to the second ink.
When the gradation part gets wet with a liquid, the part having more hollow inorganic particles becomes transparent, and the part having more solid inorganic particles changes less, so that the transparency can also show a gradation.

The temperature of the drying step after recording the ink of the present invention on a recording medium by an inkjet method is preferably 50 ° C. or higher and 200 ° C. or lower. According to this temperature range, the influence of heat on the recording medium is unlikely to occur.
As described above, the ink of the present invention can obtain concealment property by utilizing scattering between the shell of hollow inorganic particles and internal pores in addition to scattering on the particle surface. Therefore, if a component such as a water-soluble organic solvent remains in the hollow inorganic particles after the coating film is dried, the hiding property of the coating film is lowered. However, in the ink of the present invention, the hollow particles are formed of the inorganic material. Since it has higher solvent resistance even during high-temperature drying as compared with resin hollow particles, it can be dried at high speed in a high-temperature environment.

Further, in the ink of the present invention, a solid image of 50 mm × 50 mm formed on a polyethylene terephthalate (PET) film is dried in a constant temperature bath at 50 ° C. for 1 hour, and the brightness is L * 50 ° C. for 1 hour in a constant temperature bath at 100 ° C. When the lightness when dried is L * 100 ° C., the absolute value of the lightness difference ΔL * represented by the following formula 3 can be 10 or less. That is, the ink of the present invention is excellent in image stability (for example, whiteness).
| ΔL * | = (L * 50 ° C)-(L * 100 ° C) ... Equation 3

The recording method (printing method) of the present invention will be illustrated below with reference to FIGS. 5 to 8.
A first ink 51 containing a solvent and hollow inorganic particles, a second ink 52 containing solid inorganic particles, and an ejection device capable of printing these inks are used. First, a recording medium 54 such as a transparent PET film is conveyed to the print area, and the first ink 51 is ejected onto the recording medium 54 to form an image (FIG. 5A). After that, the second ink 52 is printed (FIG. 5B), the recording medium 54 is conveyed, the recording medium 54 is heated by the heater 55, and the first ink 51 and the second ink 52 are dried. Let and fix (Fig. 5 (c)).
When water or a solvent is applied to the image recorded in this way, the water or solvent permeates the hollow inorganic particles, and the scattering property of the ink coating film changes.
In the dry state, there are small holes made of air in the hollow inorganic particles, and the difference in refractive index between the shell part of the hollow inorganic particles and the part made of other solids of ink such as binder resin and the air part becomes large and scattered. And appear white (Fig. 6 (a) dry state). In the wet state, water or solvent enters the air portion and the difference in refractive index becomes small, so that scattering is reduced and transmitted light is increased (FIG. 6 (b) wet state).
In the dry state (FIG. 7A), the printing unit 511 composed of the first ink 51 and the printing unit 521 composed of the second ink 52 both show white on the recording medium 54, so that the paper 56 with the image is displayed. No change occurs in the recording medium 54 even when the images are stacked on top of each other (FIG. 7 (c)).
In the wet state (FIG. 7B), the printing portion 511 made of the first ink 51 becomes transparent on the recording medium 54, so that there is a difference from the printing portion 521 made of the second ink 52, and the paper with the image has an image. When overlapped, the image drawn on the paper can be seen through the transparent printing unit 511 (FIG. 7 (d)).
Similarly, for example, when a recording medium 54 having the colored layer 57 in the transparent PET is used, even if the colored layer 57 is on the printing portion 511 side composed of the first ink 51 (FIG. 8A), the colored layer 57 is Even if it is on the opposite side of the printing portion 511 composed of the first ink 51 (FIG. 8 (b)), the printing portion 511 becomes transparent in a wet state, and the colored layer 57 is transparent to develop an image (FIG. 8 (c)). )).

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

<< Preparation of dispersion >>
The hollow inorganic particles in the present invention can be produced by a known method as described above.
<Adjustment Example 1: Preparation of Hollow Inorganic Particle Dispersion Liquid 1>
In a beaker, 18.15 parts by mass of calcium carbonate (manufactured by Shiraishi Kogyo, product name "Homocal-D", particle shape: cubic, surface treatment agent: logonic acid, primary particle size: 80 nm) was added to 151.54 parts by mass of methanol (xida). It was sufficiently dispersed in a homogenizer (manufactured by Hitachi Koki, HG30, C20 cutter, 8000 rpm, 30 minutes). Then, while sufficiently stirring so as to maintain the dispersed state of calcium carbonate, 14.52 parts by mass of tetraethoxysilane (TEOS, manufactured by Shinetsu Chemical Industries, Ltd., product name "KBE-04"), 28% aqueous ammonia 14.61% by mass. Parts (NH ₄ OH, manufactured by Wako Pure Chemical Industries, Ltd.) and 71.17 parts by mass of water are mixed and reacted at 25 ° C. for 2 hours to form a silica shell on the surface of calcium carbonate using a sol-gel reaction. A silica-coated particle dispersion was obtained.
Next, the obtained silica-coated particles were precipitated with a centrifuge at 4000 rpm × 1 hour, and after discarding the supernatant, pure water was added and dispersed in water. In addition, 10-fold diluted acetic acid was added to dissolve the core particles of calcium carbonate. The pH after the addition of acetic acid was 4.0. After that, in order to desalt the generated calcium acetate out of the system, the generated hollow particles are precipitated with a centrifuge at 4000 rpm × 1 hour, the supernatant is discarded, and then pure water is added to disperse the particles in water. This was carried out three times and concentrated to obtain a solid 18% by mass hollow inorganic particle solution.
In 100 parts by mass of this hollow inorganic particle solution, an amine group-containing acrylic block copolymer (dispersant, manufactured by Big Chemie Japan, product name "BYKJET-9151", acid value: 8 mgKOH / g, amine value: 18 mgKOH / g, effective (100% by mass of component) 6 parts by mass and 14 parts by mass of water are added and sufficiently stirred, and then a recording medium-less disperser (manufactured by Yoshida Kikai Kogyo, NVC-ES008, 150 μm collision type nozzle, discharge pressure 50 MPa, number of passes, 10 times) Dispersion was performed at. The obtained dispersion was filtered through a 5 μm cellulose acetate membrane filter (trade name: Minisalt 17594K, manufactured by Sartorius) to obtain a hollow inorganic particle dispersion 1 having a particle concentration of 15% by mass. The volume average particle size (D50) was 310 nm.

<Adjustment example 2: Preparation of hollow inorganic particle dispersion liquid 2>
The calcium carbonate used in Adjustment Example 1 was changed to "Shiraishi Hana DD" (manufactured by Shiraishi Kogyo, particle shape: cubic, surface treatment agent: rosin acid, primary particle size: 50 nm) to obtain a dispersion liquid. Centrifugation of the dispersion was performed, and the volume average particle diameter (D50) was measured while sampling the supernatant in a timely manner to obtain a hollow inorganic particle dispersion 2 having a volume average particle diameter (D50) of 200 nm and a particle concentration of 15% by mass. It was.

<Adjustment example 3: Preparation of hollow inorganic particle dispersion liquid 3>
In a beaker, 18.15 parts by mass of calcium carbonate (manufactured by Shiraishi Kogyo, product name "Homogenizer DD", particle shape: cubic, surface treatment agent: logonic acid, primary particle size: 50 nm) was added to 151.54 parts by mass of methanol (Kishida Chemical). Disperse in a homogenizer (Hitachi Koki, HG30, C20 cutter, 8000 rpm, 30 minutes), and disperse the dispersion with an ultrasonic homogenizer (trade name: US-300T, manufactured by Nippon Seiki Seisakusho Co., Ltd., chip: φ26). ) Was treated at 200 μA for 1 hour to sufficiently disperse. Then, while sufficiently stirring so as to maintain the dispersed state of calcium carbonate, 14.52 parts by mass of tetraethoxysilane (TEOS, manufactured by Shinetsu Chemical Industries, Ltd., product name "KBE-04"), 28% aqueous ammonia 14.61% by mass. Parts (NH ₄ OH, manufactured by Wako Pure Chemical Industries, Ltd.) and 71.17 parts by mass of water are mixed and reacted at 25 ° C. for 2 hours to form a silica shell on the surface of calcium carbonate using a sol-gel reaction. A silica-coated particle dispersion was obtained.
By hollowing out and dispersing in the same manner, a hollow inorganic particle dispersion liquid 3 having a particle concentration of 15% by mass was obtained. The volume average particle size (D50) was 94 nm.

<Adjustment Example 4: Preparation of Hollow Inorganic Particle Dispersion Liquid 4>
Calcium carbonate used in Adjustment Example 1 was changed to "Brillant 1500" (manufactured by Shiraishi Kogyo, particle shape: cubic, surface treatment agent: none, primary particle size: 150 nm), and a hollow inorganic particle dispersion having a particle concentration of 15% by mass was changed. I got 4. The volume average particle size (D50) was 690 nm.

<Adjustment Example 5: Preparation of Hollow Inorganic Particle Dispersion Liquid 5>
The hollow inorganic particle dispersion liquid 4 obtained in Adjustment Example 4 was centrifuged, and the volume average particle diameter (D50) was measured while sampling the supernatant in a timely manner. The volume average particle diameter (D50) was 500 nm and the particle concentration was 15 mass. % Hollow inorganic particle dispersion liquid 5 was obtained.

<Adjustment Example 6: Preparation of Hollow Inorganic Particle Dispersion Solution 6>
Titanium isopropoxide (0.1 mol) and orthophthalic acid (0.5 mol) were mixed with 10 L of methanol and stirred overnight. 3.5 mL of this mixture was transferred to a SUS316 reaction tube having a volume of 10 mL, and the temperature was raised to 300 ° C. at a heating rate of 6.0 ° C./min to obtain supercritical methanol, which was reacted for 10 minutes to obtain anatase-type titanium oxide hollow particles.
Next, the generated hollow particles are precipitated with a centrifuge at 4000 rpm × 1 hour, the supernatant is discarded, and then a washing operation of adding pure water and dispersing in water is performed three times and concentrated to produce 18% by mass of solids. Hollow inorganic particle solution was obtained.
In a dispersion container, put 66.7 parts by mass of the hollow inorganic particle liquid and 1.2 parts by mass of the dispersant (trade name: DISPERBYK-190, manufactured by Big Chemie Japan Co., Ltd.), stir lightly to make it uniform, and then cool with water. However, it was treated with an ultrasonic homogenizer (trade name: US-300T, manufactured by Nippon Seiki Seisakusho Co., Ltd., chip: φ26) at 200 μA for 1 hour, and filtered through a 5 μm cellulose acetate membrane filter (trade name: Minisalt 17594K, manufactured by Sartorius). The solid content was adjusted to obtain a solid inorganic particle dispersion liquid 6 having a solid content of 15% by mass. The volume average particle size (D50) was 630 nm.

<Adjustment Example 7: Preparation of Solid Inorganic Particle Dispersion Liquid 1>
Put 30.8 parts by mass of high pure water and 1.2 parts by mass of a dispersant (trade name: DISPERBYK-190, manufactured by Big Chemie Japan Co., Ltd.) in a dispersion container, and lightly stir to make them uniform, and then titanium dioxide (trade name). : JR-405, manufactured by Teika Co., Ltd., primary particle size: 210 nm, crystal form: rutile type, Al surface-treated product) Add 12.0 parts by mass, and while cooling with water, ultrasonic homogenizer (trade name: US-300T, stock) Manufactured by Nippon Seiki Seisakusho Co., Ltd., chip: φ26) for 1 hour at 200 μA, filtered through a 5 μm cellulose acetate membrane filter (trade name: Minisalt 17594K, manufactured by Sartorius) to disperse solid inorganic particles with a solid content of 30% by mass. Liquid 1 was obtained. The volume average particle size (D50) was 302 nm.

<Adjustment Example 8: Preparation of Solid Inorganic Particle Dispersion Liquid 2>
The titanium dioxide used in Adjustment Example 7 was changed to "MT-900HD" (manufactured by TAYCA Corporation, primary particle size: 110 nm, crystal form: rutile type, Al, Zr surface-treated product), and the particle concentration was 15% by mass. A solid inorganic particle dispersion 2 was obtained. The volume average particle size (D50) was 150 nm.

<Adjustment Example 9: Preparation of Solid Inorganic Particle Dispersion Liquid 3>
The titanium dioxide used in Adjustment Example 7 was changed to "MT-700HD" (manufactured by TAYCA Corporation, primary particle size: 50 nm, crystal form: rutile type, Al, Zr surface-treated product), and the particle concentration was 15% by mass. A solid inorganic particle dispersion 3 was obtained. The volume average particle size (D50) was 92 nm.

<Adjustment example 10: Preparation of solid inorganic particle dispersion liquid 4>
A zirconium oxide dispersion "Nanouse ZR-40BL" (manufactured by Nissan Chemical Industries, Ltd., solid 40% by mass, primary particle size: 90 nm, pH 9.6) was used as the solid inorganic particle dispersion 4.

<Adjustment example 11: Preparation of solid inorganic particle dispersion liquid 5>
A silica dispersion "Snowtex MP-4540M" (manufactured by Nissan Chemical Industries, Ltd., solid 40% by mass, primary particle size: 440 nm, pH 8.5) was used as the solid inorganic particle dispersion 5.

<Adjustment example 12: Preparation of urethane resin fine particles>
1,500 parts by mass of polycarbonate diol, 2,2-dimethylol, which is a reaction product of 1,6-hexanediol and dimethyl carbonate in a reaction vessel containing a stirrer, a reflux condenser, and a thermometer. 220 parts by mass of propionic acid (DMPA) and 1,347 parts by mass of N-methylpyrrolidone (NMP) were charged under a nitrogen stream and heated to 60 ° C. to dissolve 2,2-dimethylolpropionic acid.
Next, 1,445 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 2.6 parts by mass of dibutyltin dilaurylate (catalyst) were added and heated to 90 ° C., and a urethanization reaction was carried out over 5 hours to carry out a urethanization reaction at the isocyanate terminal. Urethane prepolymer solution 1 was obtained.
Next, the isocyanate-terminated urethane prepolymer solution 1 was cooled to 80 ° C., 149 parts by mass of triethylamine was added, 4,340 parts by mass was extracted from the mixed mixture, and 5,400 parts by mass of water was vigorously stirred. , And 15 parts by mass of triethylamine was added to the mixed solution.
Next, 1,500 parts by mass of ice was added, and 626 parts by mass of a 35% by mass 2-methyl-1,5-pentanediamine aqueous solution was added to carry out a chain extension reaction so that the solid content concentration became 30% by mass. The solvent was distilled off to obtain a urethane resin emulsion (resin dispersion).

<Adjustment example 13: Preparation of water-insoluble polymer solution>
17.6 parts by mass of styrene, 12.0 parts by mass of AS-6 (S) (manufactured by Toa Synthetic Co., Ltd., styrene macromer, effective component concentration 50% by mass,) in a reaction vessel provided with two dropping funnels 1 and 2. Number average molecular weight 6000), NK ester M-40G 10.0 parts by mass (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., methoxypolyethylene glycol monomethacrylate, average number of moles of ethylene oxide added: 4, terminal: methoxy group), methyl ethyl ketone 6.0 mass A part, 0.08 part by mass of 2-mercaptoethanol was added, and the temperature was raised to 77 ° C. with stirring while substituting with nitrogen gas.
51.2 parts by mass of methacrylic acid, 140.8 parts by mass of styrene, 108.0 parts by mass of AS-6 (S) (manufactured by Toa Synthetic Co., Ltd., styrene macromer, effective content concentration 50% by mass, number average molecular weight 6000), NK ester M-40G 80.0 parts by mass (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., methoxypolyethylene glycol monomethacrylate, average number of moles of ethylene oxide added: 4, terminal: methoxy group), 66.0 parts by mass of methyl ethyl ketone, V65 3.2 A mass portion (manufactured by Wako Pure Chemical Industries, Ltd. 2,2'-azobis (2,4-dimethylvaleronitrile)) and 0.56 parts by mass of 2-mercaptoethanol were added and stirred, and the mixture was added to the dropping funnel 1. It was put in and replaced with nitrogen gas.
Similarly, 12.8 parts by mass of methacrylic acid, 17.6 parts by mass of styrene, 10.0 parts by mass of NK ester M-40G (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., methoxypolyethylene glycol monomethacrylate, average number of moles of ethylene oxide added: 4) , Terminal: methoxy group), methyl ethyl ketone 48.0 parts by mass, V65 0.8 parts by mass (manufactured by Wako Pure Chemical Industries, Ltd. 2,2'-azobis (2,4-dimethylvaleronitrile)), 2-mercaptoethanol After adding 0.16 parts by mass and stirring, the mixture was placed in the dropping funnel 2 and replaced with nitrogen gas.
The dropping monomer solution 1 in the dropping funnel 1 was gradually dropped into the reaction vessel over 3 hours while stirring while maintaining the temperature at 80 ° C. in a nitrogen atmosphere. Then, the dropping monomer solution 2 in the dropping funnel 2 was gradually dropped into the reaction vessel over 2 hours. After completion of the dropping, the mixed solution in the reaction vessel was stirred at 80 ° C. for 0.5 hour.
Next, 0.6 parts by mass of V-65 and 27.0 parts by mass of methyl ethyl ketone were stirred and a uniformly dissolved solution was added into the reaction vessel, and the mixture was stirred at 80 ° C. for 1 hour to carry out an aging reaction. The same aging reaction operation was repeated 5 times to continue the reaction for 5 hours, after which the reaction solution in the reaction vessel was maintained at 85 ° C. for 1 hour, methyl ethyl ketone was added, and a solution of a water-insoluble polymer (solid content concentration: 40%). ) Was obtained.

<Adjustment example 14: Preparation of black pigment dispersion liquid>
160.8 parts by mass of a water-insoluble polymer solution (solid content concentration 40%) is mixed with 60.4 parts by mass of methyl ethyl ketone, and while stirring at 1400 rpm with a disper, 448.3 parts by mass of pure water and 5N sodium hydroxide 19.5 parts by mass of the aqueous solution was added, and the mixture was stirred at 1400 rpm for 15 minutes while cooling in a water bath at 0 ° C.
Next, 150 parts by mass of a carbon black pigment (trade name: Monarch800, manufactured by Cabot Corporation) was added, and the mixture was stirred at 7000 rpm for 3 hours. The obtained pigment mixture was dispersed by a recording medium-less dispersion device (manufactured by Nanomizer, desktop ultrafine granulation tester NM2-2000AR, 100 μm collision type nozzle, discharge pressure 200 MPa, number of passes, 20 times), and the obtained dispersion treatment was performed. I got something. 400 g of ion-exchanged water was added to this dispersion-treated product, the organic solvent was removed by a rotary evaporator, and the concentration was further increased to a solid content concentration of 25.0% by mass. The concentrate was treated with a centrifuge at 4000 rpm for 60 minutes, and the liquid layer portion was filtered through a 5 μm membrane filter “Minisart” (manufactured by Sartorius).
Ion-exchanged water was added to the filtrate so that the solid content concentration was 15.0% by mass to obtain a black content dispersion.

<Adjustment example 15: Preparation of cyan pigment dispersion liquid>
In the preparation of the black pigment dispersion, a cyan pigment dispersion having a solid content concentration of 15% by mass was obtained in the same manner as in the preparation of the black pigment dispersion except that the carbon black pigment was changed to Pigment Blue 15: 4. ..

<Adjustment example 16: Preparation of magenta pigment dispersion liquid>
In the preparation of the black pigment dispersion, a magenta pigment dispersion having a solid content concentration of 15% by mass was obtained in the same manner as in the preparation of the black pigment dispersion except that the carbon black pigment was changed to Pigment Red 122.

<Adjustment example 17: Preparation of yellow pigment dispersion liquid>
In the preparation of the black pigment dispersion, a yellow pigment dispersion having a solid content concentration of 15% by mass was obtained in the same manner as in the preparation of the black pigment dispersion except that the carbon black pigment was changed to Pigment Yellow 74.

<< Ink preparation >>
To prepare the ink, add an organic solvent, surfactant, antifoaming agent, antiseptic fungicide, and high pure water to the beaker according to the mass ratio shown in Table 1 below, and stir for 30 minutes with a stirrer to mix uniformly. did. To this mixed solution, the resin dispersion prepared in the above adjustment example is added and stirred for 15 minutes, then a coloring material is added and stirred for 30 minutes, and a syringe filter unit of a cellulose acetate membrane filter having an average pore size of 5.0 μm (commodity). Name: Mini-Salt 17594K, manufactured by Sartorius), filtered under pressure to obtain evaluation ink. The volume average particle size of the obtained ink was measured using a particle size analyzer (Nanotrac Wave-EX150, manufactured by Nikkiso Co., Ltd.) to evaluate the particle size.

The following evaluations were performed on each of the obtained inks.
<Printing conditions>
Remove the exterior of the inkjet printer (IPSiO GXe5500 manufactured by Ricoh), attach the multi-manual feed feeder on the back, and pass pure water through the ink supply path including the print head to clean it. Then, the cleaning liquid was drained from the device to make an evaluation printing device.
Further, the prepared ink was stirred under a reduced pressure condition of 5 to 10 Pa for 30 minutes to degas the gas in the evaluation ink and filled in the ink cartridge to prepare an evaluation ink cartridge. After performing the filling operation and confirming that the evaluation ink was filled in all the nozzles and no abnormal image was displayed, the glossy paper clean mode was selected by the driver attached to the printer, and then the color matching off was set to the print mode by the user setting. In this mode, the ejection amount was adjusted by changing the drive voltage of the head so that the amount of ink adhering to the recording medium of the solid image was 20 g / m ^2.

<< Brightness evaluation of printed image >>
The prepared ink was filled in an inkjet printer (Ricoh: IPSiO GXe5500) in the same manner as above, and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. On the other hand, a solid image of 50 cm × 50 cm prepared by Microsoft Word 2013 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.
The printed portion was measured for brightness using a spectrophotometric densitometer X-Rite 939 to measure L *.
[Evaluation criteria]
A: L * value is 70 or more B: L * value is 60 or more and less than 70 C: L * value is less than 60

<< Evaluation of discharge stability >>
The prepared ink is filled in an inkjet printer (manufactured by Ricoh: IPSiO GXe5500) having a covering means in the same manner as the above printing conditions, left with the head covered at a temperature of 10 ° C. and a humidity of 15% RH for 1 week, and then marketed. A nozzle check pattern was printed on the black paper of Nozzle, and the presence or absence of non-ejection and injection turbulence was evaluated by visual observation according to the following criteria.
〔Evaluation criteria〕
A: There is no non-ejection or injection turbulence.
B: Some injection turbulence is observed.
C: There is a nozzle in which non-ejection is recognized.

<< Evaluation of whiteness when the printed image is wet >>
The prepared ink was filled in an inkjet printer (Ricoh: IPSiO GXe5500) in the same manner as above, and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. On the other hand, a solid image of 50 cm × 50 cm prepared by Microsoft Word 2013 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.
The printed part was measured for brightness using a spectrophotometric densitometer X-Rite939 to set it to L ^* initial, soak the printed recording medium in pure water for 1 minute, remove it from the liquid, and then remove the water on the surface with filter paper. After that, the printed portion was measured for brightness using a spectrophotometric densitometer X-Rite 939 to obtain L ^* immersion. The difference in brightness | ΔL ^* | = (L ^* initial)-(L ^* immersion) was calculated and evaluated.
The brightness was measured by laying a commercially available black paper under the printed PET film and measuring the printed portion using a spectrophotometric densitometer X-Rite939, and evaluated according to the following criteria.
[Evaluation criteria]
A: | ΔL * | value is 30 or more B: | ΔL * | value is 13 or more and less than 30 C: | ΔL * | value is less than 13

<< Evaluation of solvent resistance recovery of printed images >>
The prepared ink was filled in an inkjet printer (Ricoh: IPSiO GXe5500) in the same manner as above, and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. On the other hand, a solid image of 50 cm × 50 cm prepared by Microsoft Word 2013 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour. With a commercially available black paper laid under the PET film on which the obtained solid image was printed, the printed portion was measured for brightness using a spectrophotometric densitometer X-Rite 939 and set to the L ^* initial stage.
The printed recording medium is immersed in acetone for 1 minute, taken out of the liquid, the solvent on the surface is removed with a filter paper, and the printed part is dried until the surface is no longer tacked. The brightness was measured using −Rite939 and used as L ^* immersion. Then, the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour, and the printed portion was measured for brightness using a spectrophotometric densitometer X-Rite 939 in the same manner as described above to obtain L ^* drying. Based on the measured brightness, the following brightness difference was calculated.
The difference in brightness | ΔL * wet | = (L * dry)-(L * immersion) was calculated and evaluated.
The difference in brightness | ΔL * drying | = (L * initial)-(L * drying) was calculated and evaluated.
The measured values were evaluated according to the following criteria.
[Evaluation criteria]
A: | ΔL * wet | value is 30 or more and | ΔL * dry | value is 13 or less B: | ΔL * wet | value is 13 or more and less than 30 and | ΔL * dry | value is 13 or less C: | ΔL * Wet | value less than 13, or | ΔL * dry | value greater than 13

<< Evaluation of durability of printed images >>
The prepared ink was filled in an inkjet printer (Ricoh: IPSiO GXe5500) in the same manner as above, and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. On the other hand, a solid image of 50 cm × 50 cm prepared by Microsoft Word 2013 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.
The printed part was measured for brightness using a spectrophotometric densitometer X-Rite939 to set the L * initial stage, the printed recording medium was immersed in pure water for 1 minute, taken out of the liquid, and then the water on the surface was removed with a filter paper. After that, it is placed in a constant temperature bath at 60 ° C. and dried for 1 hour. After repeating this operation 20 times, the printed portion was measured for brightness using a spectrophotometric densitometer X-Rite 939 to obtain L * durability.
Brightness difference | ΔL * | = (L * initial)-(L * durability) was calculated and evaluated.
The brightness was measured by laying a commercially available black paper under the printed PET film and measuring the printed portion using a spectrophotometric densitometer X-Rite939, and evaluated according to the following criteria.
[Evaluation criteria]
A: | ΔL * | value is 13 or less B: | ΔL * | value is larger than 13, 30 or less C: | ΔL * | value is greater than 30 The evaluation results of the water-based ink are shown below.

<Ink set evaluation>
The prepared inks were combined as shown in Table 3, and the ink sets of each example were prepared and filled in a cartridge of an inkjet printer (manufactured by Ricoh: IPSiO GXe5500).

<Printing conditions>
Remove the exterior of the inkjet printer (IPSiO GXe5500 manufactured by Ricoh), attach the multi-manual feed feeder on the back, and pass pure water through the ink supply path including the print head to clean it. Then, the cleaning liquid was drained from the device to make an evaluation printing device.
Further, the prepared ink was stirred under a reduced pressure condition of 5 to 10 Pa for 30 minutes to degas the gas in the evaluation ink and filled in the ink cartridge to prepare an evaluation ink cartridge. After performing the filling operation and confirming that the evaluation ink was filled in all the nozzles and no abnormal image was displayed, the glossy paper clean mode was selected by the driver attached to the printer, and then the color matching off was set to the print mode by the user setting. In this mode, the ejection amount was adjusted by changing the drive voltage of the head so that the amount of ink adhering to the recording medium of the solid image was 20 g / m ^2.

<< Evaluation of discharge stability >>
The prepared ink is filled in an inkjet printer (manufactured by Ricoh: IPSiO GXe5500) having a covering means in the same manner as the above printing conditions, left with the head covered at a temperature of 10 ° C. and a humidity of 15% RH for 1 week, and then marketed. A nozzle check pattern was printed on the black paper of Nozzle, and the presence or absence of non-ejection and injection turbulence was evaluated by visual observation according to the following criteria.
〔Evaluation criteria〕
A: There is no non-ejection or injection turbulence.
B: Some injection turbulence is observed.
C: There is a nozzle in which non-ejection is recognized.

<< Evaluation of pattern confirmation when the printed image is wet >>
Using this cartridge, an inkjet printer (Ricoh: IPSiO GXe5500) was filled with ink in the same manner as the above printing conditions, and a transparent PET film (Toyo Boseki ester) fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. A checkered pattern image (FIG. 9 (a)) in which one square of ink 1 and ink 2 having a size of 4 cm × 4 cm created by Microsoft Word 2013 is printed on the film E5100), and the recording medium is placed in a constant temperature bath at 50 ° C. It was put in and dried for 1 hour.
For the image formed on the printed recording medium, soak the printed recording medium in water for 1 minute, remove it from the liquid, remove the solvent on the surface with a filter paper, and place a commercially available black paper under the PET film. The checkered pattern was observed and evaluated in the laid state.
[Evaluation criteria]
A: The checkered pattern can be clearly seen (Fig. 9 (d)).
B: The checkered pattern cannot be understood without staring at it.

<< Evaluation of pattern confirmation during solvent resistance recovery of printed images >>
Using this cartridge, an inkjet printer (Ricoh: IPSiO GXe5500) was filled with ink in the same manner as the above printing conditions, and a transparent PET film (Toyo Boseki ester) fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. A checkered pattern image consisting of ink 1 and ink 2 having a size of 4 cm × 4 cm, which was created by Microsoft Word 2013, was printed on the film E5100), and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.
For the white checkered pattern formed on the printed recording medium, soak the printed recording medium in acetone for 1 minute, remove it from the liquid, remove the solvent on the surface with filter paper, and dry it until the surface tack is eliminated. After that, the checkered pattern was observed and evaluated with a commercially available black paper laid under the PET film.
[Evaluation criteria]
A: The checkered pattern cannot be understood without staring at it. B: The checkered pattern can be clearly understood.

<< Pattern confirmation evaluation when printed images are used repeatedly >>
Using this cartridge, an inkjet printer (Ricoh: IPSiO GXe5500) was filled with ink in the same manner as the above printing conditions, and a transparent PET film (Toyo Boseki ester) fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. A checkered pattern image consisting of ink 1 and ink 2 having a size of 4 cm × 4 cm, which was created by Microsoft Word 2013, was printed on the film E5100), and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.
For the white checkered pattern formed on the printed recording medium, soak the printed recording medium in pure water for 1 minute, remove it from the liquid, remove the water on the surface with a filter paper, and then use a constant temperature bath at 60 ° C. Place in and dry for 1 hour. After repeating this operation 20 times, a checkered pattern was observed and evaluated with a commercially available black paper laid under the PET film.
[Evaluation criteria]
A: The checkered pattern cannot be understood without staring at it. B: The checkered pattern can be clearly understood.

<< Evaluation of pattern confirmation when wet when white ink is printed on the image surface >>
The process color inks of black, cyan, magenta, and yellow shown in Preparation Examples 30 to 33 are filled in cartridges of each color of an inkjet printer (manufactured by Ricoh: IPSiO GXe5500), and the same as the above printing conditions, the inkjet printer (manufactured by Ricoh). : IPSiO GXe5500) is filled with ink and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape on a transparent PET film (Toyo Boseki Ester Film E5100) with Microsoft Word 2013 test pattern 1 (Fig. 9). (B)) was printed in glossy paper-clean mode, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour. After drying, it was cooled to room temperature to form a test pattern 1 on a transparent PET film.

Further, as shown in Table 3, the prepared ink is filled in a cartridge of each color of an inkjet printer (manufactured by Ricoh: IPSiO GXe5500), and using this cartridge, an inkjet printer (manufactured by Ricoh: IPSiO GXe5500) is used in the same manner as in the above printing conditions. ) Is filled with ink, and the transparent PET film (fixed with double-sided tape on My Paper) on which the test pattern 1 produced above is printed, one square created by Microsoft Word 2013 is 4 cm x 4 cm. A checkered pattern image consisting of Ink 1 and Ink 2 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.

(Image hiding property)
The printed recording medium was observed from the printing surface, and the concealed state of the J6 image was observed and evaluated for the white checkered pattern formed on the surface of the medium.
[Evaluation criteria]
AA: Test pattern 1 is sufficiently concealed A: Test pattern 1 is slightly transparent B: Test pattern 1 is transparent (FIG. 9 (c))

(Pattern expression)
Further, the printed recording medium was immersed in water for 1 minute, taken out of the liquid, the solvent on the surface was removed with a filter paper, and the PET film was observed from the printed surface for evaluation.
[Evaluation criteria]
A: Test pattern 1 can be clearly seen from a part of the checkered pattern when wet (Fig. 9 (c)).
B: The appearance of test pattern 1 does not change when wet

≪Evaluation of pattern confirmation when wet when white ink is printed on the back side of the image≫
The process color inks of black, cyan, magenta, and yellow shown in Preparation Examples 30 to 33 are filled in cartridges of each color of an inkjet printer (manufactured by Ricoh: IPSiO GXe5500), and the same as the above printing conditions, the inkjet printer (manufactured by Ricoh). : IPSiO GXe5500) is filled with ink and fixed on My Paper (Ricoh PPC plain paper) with double-sided tape. For a transparent PET film (Toyo Boseki Ester Film E5100), test pattern 1 is applied to glossy paper with Microsoft Word 2013. -Printing was performed in clean mode, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour. After drying, it was cooled to room temperature to form a test pattern 1 on a transparent PET film.

Further, as shown in Table 3, the prepared ink is filled into a cartridge of each color of an inkjet printer (manufactured by Ricoh: IPSiO GXe5500), and using this cartridge, an inkjet printer (manufactured by Ricoh: IPSiO GXe5500) is used in the same manner as in the above printing conditions. ) Is filled with ink, and the back side of the transparent PET film on which the test pattern 1 produced above is printed (the printed side is inverted and fixed on My Paper with double-sided tape), Microsoft Word 2013 A checkered pattern image in which one square of 4 cm × 4 cm was composed of ink 1 and ink 2 was printed, and the recording medium was placed in a constant temperature bath at 50 ° C. and dried for 1 hour.

(Image sharpness)
The printed recording medium was observed from the printing surface of the test pattern 1 with a commercially available black paper laid, and the sharpness of the test pattern 1 formed on the surface of the medium was observed and evaluated.
[Evaluation criteria]
AA: The back side of test pattern 1 is white and looks very clear. A: The white side of the back side is slightly transparent, but it looks clear. B: The white side of the back side is transparent and black paper is visible. A little less sharp

(Pattern expression)
Further, the printed recording medium was immersed in water for 1 minute, taken out of the liquid, the solvent on the surface was removed with a filter paper, and the PET film was observed from the printed surface of Test Pattern 1 for evaluation.
[Evaluation criteria]
A: Part of the back surface becomes transparent when wet, and test pattern 1 becomes translucent. B: The appearance of test pattern 1 does not change even when wet. Table 4 shows the above evaluation results of the water-based ink set.

In an ink set consisting of a first ink containing a solvent and hollow inorganic particles and a second ink containing solid inorganic particles and whose image does not change due to the application of a liquid, as in Examples 1 to 7. , An image can be obtained that has excellent pattern expression when wet and has excellent durability when used in a solvent or repeatedly.
On the other hand, as in Comparative Example 1, an ink set including an ink containing hollow resin particles has pattern development when the image is wet, but is not durable when used with a solvent or repeatedly, resulting in low practicality. It became.
Further, as in Comparative Examples 2 and 3, in the ink set composed of only the second ink or only the first ink, the pattern expression at the time of image wetting is not exhibited and the function cannot be exhibited.

51 First ink 52 Second ink 53 Discharge device 54 Recording medium 55 Heater 56 Paper with image 57 Colored layer 201 Ink cartridge 241 Ink bag 242 Ink inlet 243 Ink outlet 244 Cartridge case 400 Image forming device 401 Image Exterior of forming device 401c Device body cover 404 Cartridge holder 410 Main tank 410k, 410c, 410m, 410y Black (K), Cyan (C), Magenta (M), Yellow (Y) Main tank 411 Ink storage Part 413 Ink discharge port 414 Storage container case 420 Mechanism part 434 Discharge head 436 Supply tube 511 Printing part consisting of first ink 51 521 Printing part consisting of second ink 52

Japanese Unexamined Patent Publication No. 2014-122310 Japanese Unexamined Patent Publication No. 2011-170064

Claims (13)

The first white ink containing hollow inorganic particles,
An ink set comprising a second white ink containing solid inorganic particles. The first white ink is used for printing in which an image is changed by applying a liquid, contains a solvent, and the change in the image is a change in the brightness of the image . Ink set. The ink set according to claim 1 or 2, wherein the hollow inorganic particles are silica. The ink set according to any one of claims 1 to 3, wherein the shell thickness of the hollow inorganic particles is 4 nm or more and 20 nm or less. The ink set according to any one of claims 1 to 4, wherein the ratio of the inner diameter to the outer diameter of the hollow inorganic particles is 0.75 or more and 0.95 or less. The ink set according to any one of claims 1 to 5, wherein the number average primary particle diameter of the hollow inorganic particles is 20 nm or more and less than 200 nm. The ink set according to any one of claims 1 to 6, wherein the 50% cumulative volume particle diameter (D50) of the hollow inorganic particles is 200 nm or more and 500 nm or less. The ink set according to any one of claims 1 to 7, wherein the content of the hollow inorganic particles in the first white ink is 3% by mass or more and 12% by mass or less. The ink set according to any one of claims 1 to 8, wherein the first white ink contains a solvent having a boiling point of 300 ° C. or lower. Ink cartridge, characterized by comprising housing the first white ink and the second white ink in the ink set according to each container to any one of claims 1 to 9. Using the ink set according to any of claims 1 to 9, the first ink application step of applying the first white ink to the substrate, the second to impart the second white ink A printing method comprising an ink applying step and a drying step of drying a printed matter to which the first white ink and the second white ink are applied. A printing method comprising adding water or a volatile solvent to an image printed by the printing method according to claim 11 to form a new image. A printing apparatus comprising the means for ejecting ink and the ink set according to any one of claims 1 to 9.

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