JP6747187B2 - Ink set, recording method, and recording apparatus - Google Patents

Description

The present invention relates to an ink set, a recording method, and a recording device.

The inkjet recording method is widely used because it has the advantages that the process is simpler than other recording methods, full-colorization is easy, and high-resolution images can be obtained even with a device with a simple structure. I'm doing it.

Generally, when printing is performed using a white ink and a chromatic color ink as one of methods for forming a reflection image on a transparent recording medium (base material), first, a white background is formed on the transparent base material with the white ink. After that, an image is formed with chromatic color inks such as yellow, magenta, cyan, and black, and the final image is viewed from the printed surface "front printing", and an image is formed with chromatic color inks on the transparent substrate and then white. There is a method called "reverse printing" in which ink is overlaid and the final image is viewed from the back side through a transparent substrate.

Even in the inkjet recording method, these images can be similarly created by using a white ink and various chromatic color inks. The white ink used in the inkjet recording method is a transparent recording medium or a recording having a low lightness. It has good visibility with respect to the medium, and in particular, when used in combination with chromatic color ink, it is possible to obtain a clear full-color image similar to that when recording on a white medium, which is one of the effective methods. ..

Therefore, for example, for inkjet, the hollow resin particles have an outer diameter of 0.1 μm or more and 1 μm or less, an inner diameter of 0.05 μm or more and 0.8 μm, are insoluble in a water-soluble solvent, and do not chemically react with the binder resin component. White ink has been proposed (for example, see Patent Document 1).
Further, Patent Document 2 describes that the surface tension of white ink is lower than the surface tension of color ink.

An object of the present invention is to provide an ink set that can suppress collapse of hollow resin particles in the white ink (decrease in lightness L ^* ) in an ink set containing a white ink and that can obtain a high gloss image.

The ink set of the present invention as a means for solving the above problems, water, hollow resin particles, and a white first ink containing an organic solvent,
A second ink that contains water, and an organic solvent, and is formed on the first image formed using the first ink to form a second image, and an ink set comprising:
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A-B) is 1 μm or more and 3 μm or less.

According to the present invention, in an ink set containing a white ink, it is possible to provide a high-gloss image in which the hollow resin particles in the white ink can be prevented from being crushed (the brightness L ^* is lowered).

FIG. 1 is a perspective explanatory view showing an example of an inkjet recording apparatus. FIG. 2 is a perspective explanatory view showing an example of a main tank in the inkjet recording apparatus.

(Ink set)
The ink set of the present invention is a white first ink containing water, hollow resin particles, and an organic solvent,
Water, and a second ink containing an organic solvent, a second ink is formed on the first image formed using the first ink to form a second image, and
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A-B) is 1 μm or more and 3 μm or less.

In the ink set of the present invention, in the related art, the outer shell resin of the hollow resin particles is dissolved by contacting the hollow resin particles with an organic solvent having a value close to the SP value of the outer shell resin, This is based on the finding that the particles are crushed (the lightness L ^* is lowered).
In the present invention, the average thickness (A) of the first image before the second ink is applied and the average of the white areas in the first image after the second image is formed. It is necessary that the average thickness difference (AB) from the thickness (B) is 1 μm or more and 3 μm or less.
By the ink formulation and recording method described below, the average thickness difference (AB) of the average thickness of the white area in the first image when the first ink and the second ink are in contact with each other is 1 μm. It is possible to set the thickness to 3 μm or less, and the white first image can be maintained as a white image even when the first ink and the second ink come into contact with each other.
By setting the average thickness difference (AB) to 1 μm or more, the first image surface becomes smooth when the first ink and the second ink come into contact with each other, and as a result, the image gloss is increased. be able to. On the other hand, by setting the average thickness difference (A−B) to 3 μm or less, the white first image can be maintained as a white image.
The average thickness (A) of the first image and the average thickness (B) of the white area in the first image after the second image is formed are 3 cm square solid images formed in a dot pattern. The cross section of the image sample of No. 2 is cut with a cutter, the cross section is observed by SEM (JSL-6510A, manufactured by JEOL Ltd.), the thickness at any 5 positions can be measured, and the average thickness can be obtained.

In the present invention, the first image formed by the first ink having a lightness (L ^* ) of 20 or more is defined as white.
For the lightness (L ^* ), for example, a spectrophotometer (manufactured by X-Rite, 939) is used for an image sample of a solid image of 3 cm square formed by a dot pattern in which only the first ink is printed. Can be measured.
The average thickness reduction (the average thickness difference (A−B) is 1 μm or more) in the white region that occurs when the first ink and the second ink are in contact is unique to the hollow resin particles as the white coloring material. This problem does not occur when a non-hollow white pigment such as titanium oxide is used, or even if it occurs, the average thickness difference (AB) is less than 1 μm.
Regarding the ink set design in which the average thickness difference (A−B) is 1 μm or more and 3 μm or less, the resin SP value of the hollow resin particles and the SP value of the organic solvent in the ink, which will be described later, are one of the important achievement means. ..

The average thickness (A) of the first image before the application of the second ink is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 30 μm or less.
By setting the average thickness (A) of the first image to 5 μm or more, the first image formed using the white first ink can be maintained as a white image. On the other hand, by setting the average thickness (A) of the first image to 50 μm or less, the productivity during image formation can be improved. When forming the first image, if the average thickness (A) of the first image is within the numerical range, before the white first ink is applied to the second ink. May be recorded multiple times.

In the present invention, the second image is formed by the second ink on the first image formed by using the white first ink. In this case, the wettability of the second ink with respect to the first image is important. If the wettability is high, adjacent dots of the second ink will coalesce, and an image called beading will be blurred. On the other hand, if the wettability is insufficient, the dots of the second ink do not spread, and the desired color tone cannot be obtained.
Therefore, in the present invention, the wettability is expressed by a characteristic called a contact angle, and the contact angle of the second ink with respect to the first image is preferably 15 degrees or more and 30 degrees or less, and 20 degrees or more and 30 degrees or less. More preferable.
By setting the contact angle to 15 degrees or more and 30 degrees or less, it is possible to prevent the occurrence of beading in which the dots of the second ink coalesce, it is possible to widen the dots of the second ink, and it is possible to achieve the desired color tone. Image is obtained.

In the present invention, the solubility parameter of the mixed solution of the organic solvent and water contained in the first ink (Solubility Parameter, sometimes referred to as “SP value” hereinafter) (X), and the second ink are contained. The SP value (Y) of the mixed solution of the organic solvent and water is preferably 17.0 (cal/cm ³ ) ^0.5 or more and 20.2 (cal/cm ³ ) ^0.5 or less.
When the SP value of the mixed solution of the organic solvent and water is 17.0 (cal/cm ³ ) ^0.5 or more, collapse of the hollow resin particles can be suppressed. On the other hand, when the SP value of the mixed solution of the organic solvent and water is 20.2 (cal/cm ³ ) ^0.5 or less, it is possible to suppress deterioration of fixing property due to poor drying.
The SP value of the mixed solution of two or more kinds of organic solvents contained in the first ink and the second ink is 11.0 (cal/cm ³ ) ^0.5 or more and 17.4 (cal/cm ³ ). It is preferably ^0.5 or less.
When the SP value of the mixed solution of the two or more kinds of organic solvents is 11.0 (cal/cm ³ ) ^0.5 or more, collapse of the hollow resin particles can be suppressed. On the other hand, when the SP value of the mixed solution is 17.4 (cal/cm ³ ) ^0.5 or less, it is possible to suppress deterioration of fixing property due to poor drying.

The SP value of the mixed solution of the organic solvent and water contained in the ink can be calculated by the following formula.
SP value (cal/cm ³ ) ^0.5 in mixed solution of organic solvent and water in ink
= [SP value of organic solvent A x volume fraction of organic solvent A] + [SP value of organic solvent B x volume fraction of organic solvent B] + ... + [SP value of water x volume fraction of water] ]

The SP value is a numerical value indicating how easily each SP melts. The SP value is represented by a force of attraction between molecules, that is, a square root of cohesive energy density CED (Cohesive Energy Density). The CED is the amount of energy required to evaporate 1 mL.

The SP value can be calculated using the following formula (B) by the Fedors method.
SP value (dissolution parameter) = (CED value) ^1/2 = (E/V) ^1/2 ... formula (B)
In the above formula (B), E is a molecular cohesive energy (cal/mol), V is a molecular volume (cm ³ /mol), and when the evaporation energy of the atomic group is Δei and the molar volume is Δvi, the following formula ( C) and the formula (D).
E=ΣΔei Equation (C)
V=ΣΔvi Equation (D)
Although there are various theories regarding the method for calculating the SP value, the Fedors method that is generally used in the present invention was used.

As the data of the calculation method, the evaporation energy Δei and the molar volume Δvi of each atomic group, the data described in “Basic Theory of Adhesion” (Minori Imoto, published by Kobunshi Kogakukai, Chapter 5) can be used. it can.
Further, regarding those in which a —CF ₃ group or the like is not shown, R. F. Fedors, Polym. Eng. Sci. 14, 147 (1974).
For reference, when converting the SP value represented by the formula (B) into (J/cm ³ ) ^1/2 , convert 2.046 into SI unit (J/m ³ ) ^1/2 . To do so, multiply by 2,046.

In the present invention, the organic solvents include those which are functionally classified as penetrants, foam suppressors, and the like. Further, in the present invention, only the organic solvent contained in an amount of 3% by mass or more based on the total amount of ink is considered in the calculation of the SP value.

The SP value (X) of the mixed solution of the organic solvent and water contained in the first ink and the SP value of the mixed solution of the mixed solution of the organic solvent and water contained in the second ink (X) The difference (X-Y) in the mixed SP value with Y) is preferably -1 or more and 3 or less.
When the difference (X−Y) in the mixed SP value is −1 or more, the average thickness of the first image is reduced by the organic solvent of itself even when the white first ink is recorded a plurality of times. Never. Further, since the difference (X−Y) in the mixed SP value is 3 or less, the average thickness of the first image formed by the white first ink is not reduced by the second ink.

SP value (C) of the organic solvent having the highest content other than water contained in the first ink, and SP value (D) of the organic solvent having the highest content other than water contained in the second ink. It is preferable that the SP value difference (C-D) between and is 3 or more and 3 or less.
By setting the SP value difference (CD) to -3 or more and 3 or less, dissolution of the hollow resin particles by the organic solvent can be suppressed.

In the present invention, the absolute value of the difference in dynamic surface tension between the first ink and the second ink at a life time of 1,500 msec according to the maximum bubble pressure method is preferably 0 mN/m or more and 12 mN/m or less. It is more preferably 5 mN/m or more and 10 mN/m or less.
When the absolute value of the difference in the dynamic surface tension is 0 mN/m or more and 12 mN/m or less, the wettability of the second ink with the first ink is good, and the dot formation and the first The average thickness of the white area of the image can be realized.
The dynamic surface tension is a value measured at 25° C. by the maximum bubble pressure method, and can be measured using, for example, a dynamic surface tension meter SITA DynoTester (manufactured by SITA Mestechnik).
The "life time" is the life of the bubbles generated in the maximum bubble pressure method, also referred to as "bubble life time", and the maximum bubble pressure from the time when a new interface is formed in the probe tip of the dynamic surface tension meter. Refers to the time until.
The dynamic surface tension of the first ink and the second ink at a life time of 1,500 msec according to the maximum bubble pressure method is preferably 20 mN/m or more and 35 mN/m or less.
In the preferable numerical value range, the ink is appropriately leveled on the recording medium, and the drying time of the ink can be shortened.

<First ink>
The first ink is a white ink, contains water, hollow resin particles, and an organic solvent, preferably contains a wax, and further contains other components as necessary.

<Hollow resin particles>
The hollow resin particles have an inner layer that is hollow and an outer layer that is covered with resin. The outer diameter (volume average particle diameter) of the particles is preferably 0.1 μm or more and 1 μm or less, and the inner diameter is 0.05 μm or more and 0.1 μm or less. It is preferably 8 μm or less.
Examples of the measurement of the volume average particle diameter include a method using a laser scattering/diffraction type particle diameter measuring device.
Since the inner layer of the hollow resin particles is hollow, the specific gravity of the ink is around 1, and it does not settle out over time like titanium dioxide.
From the viewpoint of avoiding sedimentation over time, the average thickness of the outer layer of the hollow resin particles is preferably 10% or more and 20% or less with respect to the entire size of the hollow resin particles.
The hollow resin particles are white and have excellent opacity due to light scattering due to the difference in refractive index between the air layer inside the particles after drying and the polymer layer of the shell.

The hollow rate of the hollow resin particles is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 20% to 80%, more preferably 35% to 70%. When the hollow ratio is 20% or more, the whiteness of the printed image can be improved, and when the hollow ratio is 80% or less, the particle diameter of the hollow resin particles can be suppressed to be small. It is possible to suppress sedimentation inside.
Examples of the measurement of the hollow ratio include a method using a scanning electron microscope (SEM). The hollow ratio is a volume ratio when the outer diameter and the inner diameter (diameter of the hollow portion) of the hollow resin particles are approximated to a sphere, and can be expressed by the following formula (1).
Hollow ratio (%)=(internal volume of hollow resin particles/volume of hollow resin particles)×100...Equation (1)
Internal volume of hollow resin particles=4π/3×(inner diameter of hollow resin particles) ³
Volume of hollow resin particles=4π/3×(outer diameter of hollow resin particles) ³

When the SP value of the outer shell resin of the hollow resin particles is close to the SP value of the organic solvent contained in the first ink, the outer shell resin of the hollow resin particles is formed by the organic solvent contained in the first ink. Is easily dissolved, the difference between the SP value of the outer shell resin of the hollow resin particles and the SP value of the organic solvent contained in the first ink (SP value of the mixed solvent in the case of two or more kinds) is The absolute value of the difference in SP value is preferably 1 or more and 10 or less.

The outer shell resin of the hollow resin particles preferably contains a styrene-acrylic copolymer resin or a methyl methacrylate resin from the viewpoint of the refractive index with the inner air layer. In addition, it may be changed to a thermoplastic resin in consideration of the drying property by heat.

As the hollow resin particles, appropriately synthesized particles may be used, or commercially available products may be used.
The method for synthesizing the hollow resin particles is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a vinyl monomer, a surfactant, a polymerization initiator, and an aqueous dispersion medium are heated under a nitrogen atmosphere. A so-called emulsion polymerization method, in which a hollow resin particle emulsion is formed by stirring while stirring, is suitable.
Examples of the vinyl monomer include a nonionic monofunctional ethylenically unsaturated monomer and a bifunctional vinyl monomer.
Examples of the nonionic monofunctional ethylenically unsaturated monomer include styrene, vinyltoluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, (meth)acrylamide, and (meth)acrylic acid ester. These may be used alone or in combination of two or more. Among these, (meth)acrylic acid ester is preferable.
Examples of the (meth)acrylic acid ester include methyl acrylate, methyl methacrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl methacrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, Examples thereof include lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.
Examples of the bifunctional vinyl monomer include divinylbenzene, allyl methacrylate, ethylene glycol dimethacrylate, 1,5-butanediol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate.
By copolymerizing the nonionic monofunctional ethylenically unsaturated monomer and the difunctional vinyl monomer and crosslinking them to a high degree, not only light scattering characteristics but also heat resistance, solvent resistance, solvent dispersibility and other characteristics. Hollow resin particles provided with can be obtained.

The surfactant may be one that forms a molecular assembly such as a micelle in water, and for example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant, etc. Is mentioned.
As the polymerization initiator, known compounds that can be used in water can be used, and examples thereof include hydrogen peroxide and potassium persulfate.
Examples of the aqueous dispersion medium include water and water containing a hydrophilic organic solvent.

As a commercial product of the hollow resin particles, for example, in the case of styrene-acrylic copolymer resin, trade name: Ropaek OP-62 (volume average particle diameter: 450 nm, hollow ratio: 33%), trade name: Ropaik OP-84J( Volume average particle size: 550 nm, hollow ratio: 20%), trade name: Ropaik OP-91, trade name: Ropaik HP-1055 (volume average particle size: 1000 nm, hollow ratio: 55%), trade name: Ropaik HP- 91 (volume average particle diameter: 1000 nm, hollow ratio: 50%), trade name: Ropaque ULTRA (volume average particle diameter: 380 nm, hollow ratio: 45%) (above, manufactured by Rohm and Haas); cross-linked styrene-acrylic In the copolymer resin, trade name: SX-863(A), trade name: SX-864(B), trade name: SX-866(A), trade name: SX-866(B) (volume average particle diameter: 300 nm, hollow ratio: 30%), trade name: SX-868 (volume average particle size: 500 nm) (above, manufactured by JSR Corporation), trade name: ROPAYK ULTRA E (volume average particle size: 380 nm, hollow ratio: 45) %), trade name: Lowpaque ULTRA DUAL (volume average particle size: 380 nm, hollow ratio: 45%) (above, manufactured by Rohm and Haas Co.); modified styrene-acrylic copolymer resin, trade name: Nipol MH5055 (volume average) Particle size: 500 nm), trade name: Nipol MH8101 (average particle size: 1 μm) (above, manufactured by Nippon Zeon Co., Ltd.) and the like. These may be used alone or in combination of two or more.

The content of the hollow resin particles is not particularly limited and may be appropriately selected depending on the purpose, but is preferably 5% by mass or more and 12.5% by mass or less with respect to the total amount of the first ink, and 8. It is more preferably 5% by mass or more and 10% by mass or less.
When the content is 5% by mass or more and 12.5% by mass or less, the brightness of the first image formed from the first ink is improved.

<Organic solvent>
Examples of the organic solvent include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amine Louis, and sulfur-containing compounds.
Examples of the organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2, 3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4 -Pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1, 2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3- Polyhydric alcohols such as pentanediol and petriol, and polyhydric alcohols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether and propylene glycol monoethyl ether. Polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3 Nitrogen-containing heterocyclic compounds such as dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, Examples thereof include amides such as 3-butoxy-N,N-dimethylpropionamide, amines such as monoethanolamine, diethanolamine and triethylamine, sulfur-containing compounds such as dimethyl sulfoxide, sulfolane and thiodiethanol, propylene carbonate and ethylene carbonate. ..

It is preferable to use an organic solvent having a boiling point of 250° C. or less because it not only functions as a wetting agent but also obtains good drying properties.
When an organic solvent having a hydrogen bond term of 3 (cal/cm ³ ) ^0.5 or more and 6.8 (cal/cm ³ ) ^0.5 or less and a boiling point of 150° C. or more and 300° C. or less is used, It is more preferable because the fixing property becomes good.
The hydrogen bond term can be obtained by using the atomic group summation method in which an organic molecule proposed by Krevelen is treated as an atomic group (see Krevelen, Properties of Polymer 2nd Edition, New York, 154 (1976)).
Examples of the organic solvent satisfying the above conditions include glycerin, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, isoprene glycol, and oxetane compounds. ..

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

The polyol compound having 8 or more carbon atoms and the glycol ether compound can improve the ink permeability when paper is used as the recording medium.

The content of the organic solvent in the ink is not particularly limited and can be appropriately selected according to the purpose, but from the viewpoint of the drying property of the ink and the ejection reliability, 10% by mass or more and 60% by mass or less is preferable, 20 mass% or more and 60 mass% or less are more preferable.

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

<Wax>
It is preferable that wax is added to the ink in order to impart slipperiness to the image area.
The wax is not particularly limited and may be appropriately selected depending on the intended purpose. From the viewpoint of film-forming property and slipperiness when the ink is applied to the image forming portion, polyethylene wax and carnauba wax are preferable. preferable.
As the polyethylene wax, a commercially available product can be used, and examples of the commercially available product include Hitech series manufactured by Toho Chemical Industry Co., Ltd. and AQUACER series manufactured by BYK.
As the carnauba wax, a commercially available product can be used, and examples of the commercially available product include Cerosol 524 and Trasol CN manufactured by Chukyo Yushi Co., Ltd.

The melting point of the wax is appropriately selected depending on the intended purpose without any limitation, but it is preferably 80°C or higher and 140°C or lower, more preferably 100°C or higher and 140°C or lower. By setting the melting point to 80° C. or higher, the wax is less likely to be excessively melted or solidified even in a room temperature environment, and the storage stability of the ink can be maintained. On the other hand, by setting the melting point to 140° C. or lower, the wax is sufficiently melted even in a room temperature environment, and it becomes possible to impart slipperiness to the ink.
The volume average particle diameter of the wax is appropriately selected depending on the intended purpose without any limitation, but it is preferably 0.01 μm or more, more preferably 0.01 μm or more and 0.1 μm or less. When the volume average particle diameter is 0.01 μm or more, the wax particles are easily oriented on the ink surface, and the ink can be made slippery.
The content of the wax is preferably 1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, based on the total amount of the first ink.
When the content is 1% by mass or more and 10% by mass or less, the slipperiness in the image area becomes good.

<Resin>
The type of resin contained in the ink is not particularly limited and may be appropriately selected depending on the purpose. Examples thereof include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, and butadiene resin. Examples thereof include resins, styrene-butadiene resins, vinyl chloride resins, acrylic styrene resins, and acrylic silicone resins. You may use the resin particle which consists of these resins. Ink can be obtained by mixing resin particles in the state of a resin emulsion in which water is used as a dispersion medium with a material such as a coloring material or an organic solvent. As the resin particles, those synthesized appropriately may be used, or commercially available products may be used. 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 purpose, but is preferably 10 nm or more and 1,000 nm or less from the viewpoint of obtaining good fixability and high image hardness. It is more preferably 200 nm or more and more preferably 10 nm or more and 100 nm or less.
The volume average particle size can be measured using, for example, a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell KK).

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

The average particle diameter of the solid content in the ink is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of enhancing image quality such as ejection stability and image density, the maximum number converted is the maximum. The frequency is preferably 20 nm or more and 1,000 nm or less, and more preferably 20 nm or more and 800 nm or less. The solid content includes resin particles and pigment particles. The average particle size can be measured using, for example, a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell KK).

<Additive>
If necessary, a surfactant, an antifoaming agent, an antiseptic/antifungal agent, an anticorrosive agent, a pH adjusting agent, etc. may be added to the ink.

<Surfactant>
As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
The silicone surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferable, and examples thereof include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and side-chain both-end modified polydimethylsiloxane. Those having an oxyethylene group or 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 having a polyalkylene oxide structure introduced into the side chain of the Si moiety of dimethylsiloxane.
Examples of the fluorinated surfactant include a perfluoroalkyl sulfonic acid compound, a perfluoroalkyl carboxylic acid compound, a perfluoroalkyl phosphoric acid ester 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 sulfonate. Examples of the perfluoroalkylcarboxylic acid compound include perfluoroalkylcarboxylic acid and perfluoroalkylcarboxylic acid salts. Examples of the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in its side chain include a sulfuric acid ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in its side chain and a perfluoroalkyl ether group in its side chain. Examples thereof include salts of polyoxyalkylene ether polymers. As counter ions of salts in these fluorine-based surfactants, 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) are used. ₃ etc. are mentioned.
Examples of the amphoteric surfactant include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan. Examples thereof include fatty acid esters and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, and salt of polyoxyethylene alkyl ether sulfate.
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. Examples thereof include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and side-modified. Examples thereof include polydimethyl siloxane modified at both chain ends, and a polyether modified silicone surfactant having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group exhibits excellent properties as an aqueous surfactant. preferable.
As such a surfactant, those synthesized appropriately may be used, or commercially available products may be used. Commercially available products can be obtained from, for example, BIC Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nippon Emulsion Co., Ltd., Kyoeisha Kagaku Co., Ltd.
The above 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 represented by dimethylpolyethylene. Examples thereof include those introduced into the side chain of the Si portion of siloxane.
[General Formula (S-1)]
(However, in the general formula (S-1), m, n, a, and b represent an integer. R and R′ represent an alkyl group or an alkylene group.)
As the above polyether-modified silicone-based surfactant, commercially available products can be used, and examples thereof include KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-. 1906EX (Japan 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.), etc. are mentioned.

As the fluorine-based surfactant, a fluorine-substituted compound having 2 to 16 carbon atoms is preferable, and a fluorine-substituted compound having 4 to 16 carbon atoms is more preferable.
Examples of the fluorine-based surfactant include a perfluoroalkyl phosphate ester compound, a perfluoroalkylethylene oxide adduct, and a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in its side chain.
Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferable because they have a low foaming property, and the fluorine-based compounds represented by the general formula (F-1) and the general formula (F-2) are particularly preferable. 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 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. An integer or CpH _2p+1 and p is an integer of 1 to 19. a is an integer of 4-14.
A commercial item 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, S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullrad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F-470, F -1405, F-474 (all manufactured by DIC Corporation); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR (all manufactured by DuPont) ); FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF. -154, PF-159 (manufactured by OMNOVA Co., Ltd.), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.) and the like. From the point that the dyeability is remarkably improved, FS-300 manufactured by DuPont, FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW manufactured by Neos Co., Ltd. Polyfox PF-151N and Unidyne DSN-403N manufactured by Daikin Industries, Ltd. are particularly preferable.

The content of the surfactant in the ink is appropriately selected depending on the intended purpose without any limitation, but it is 0.001 mass% from the viewpoint of excellent wettability and ejection stability and improving image quality. % Or more and 5 mass% or less is preferable, and 0.05 mass% or more and 5 mass% or less is more preferable.

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

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

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

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

<Second ink>
The second ink contains water, an organic solvent, preferably a coloring material and a wax, and further contains other components as necessary.
The second ink includes all inks other than white ink, and examples thereof include chromatic ink containing a color material and clear ink containing no color material.

As the water, the organic solvent, the wax, and the other components, those similar to the second ink can be used.

<Color material>
The color material is not particularly limited, and pigments and dyes can be used.
An inorganic pigment or an organic pigment can be used as the pigment. These may be used alone or in combination of two or more. Also, mixed crystals may be used.
Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, luster color pigments such as gold and silver, and metallic pigments.
As an inorganic pigment, in addition to titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method. Can be used.
Further, as the organic pigment, an azo pigment, a polycyclic pigment (for example, a phthalocyanine pigment, a perylene pigment, a perinone pigment, an anthraquinone pigment, a quinacridone pigment, a dioxazine pigment, an indigo pigment, a thioindigo pigment, an isoindolinone pigment, a quinofuraron pigment, etc.) , Dye chelates (for example, basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Among these pigments, those having a good affinity with the solvent are preferably used. In addition, hollow resin particles and hollow inorganic particles can also be used.
Specific examples of the pigment include carbon blacks (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, or copper and iron (CI pigment black 11) for black. , Metal oxides such as titanium oxide, and organic pigments such as aniline black (CI Pigment Black 1).
Further, for color, 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, 138, 150, 153, 155, 180, 185, 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 Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (Bengara), 104, 105, 106, 108 ( Cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. 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, 15:4 (phthalocyanine blue), 16, 17:1, 56, 60, 63, C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, and the like.
The dye is not particularly limited, and an acid dye, a direct dye, a reactive dye, and a basic dye can be used, and one kind may be used alone, or two or more kinds may be used in combination.
Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52,80,82,249,254,289, C.I. I. Acid Blue 9,45,249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Dilectd Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive Black 3, 4, 35 can be mentioned.

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 the image density, good fixing property and ejection stability. It is the following.

To disperse the pigment in the ink, a method of introducing a hydrophilic functional group into the pigment to form a self-dispersing pigment, a method of coating the surface of the pigment with a resin to disperse, a method of dispersing using a dispersant, And so on.
Examples of a method for introducing a hydrophilic functional group into a pigment to give a self-dispersing pigment include, for example, a self-dispersing pigment that is dispersible in water by adding a functional group such as a sulfone group or a carboxyl group to a pigment (for example, carbon). Can be used.
As a method for coating the surface of the pigment with a resin to disperse the pigment, a method in which the pigment is contained in microcapsules and can be dispersed in water can be used. This can be rephrased as a resin-coated pigment. In this case, it is not necessary for all the pigments mixed in the ink to be coated with the resin, and as long as the effect of the present invention is not impaired, uncoated pigments and partially coated pigments are dispersed in the ink. May be.
Examples of the method of dispersing using a dispersant include a method of dispersing using a known low molecular type dispersant or polymer type dispersant represented by a surfactant.
As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant or the like can be used depending on the pigment.
Takemoto Yushi Co., Ltd.'s RT-100 (nonionic surfactant) and naphthalenesulfonic acid Na formalin condensate can also be suitably used as the dispersant.
The dispersants may be used alone or in combination of two or more.

<Pigment dispersion>
It is possible to obtain an ink by mixing a pigment with a material such as water or an organic solvent. Further, it is also possible to manufacture an ink by mixing a pigment and other materials such as water and a dispersant to form a pigment dispersion, and mixing materials such as water and an organic solvent.
The pigment dispersion is obtained by dispersing water, a pigment, a pigment dispersant, and other components as necessary, and adjusting the particle size. A disperser may be used for dispersion.
There is no particular limitation on the particle size of the pigment in the pigment dispersion, but since the dispersion stability of the pigment is good and the image quality such as ejection stability and image density is also high, the maximum frequency is 20 nm or more when converted to the maximum number. It is preferably 500 nm or less, more preferably 20 nm or more and 150 nm or less. The particle size of the pigment can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell KK).
The content of the pigment in the pigment dispersion is not particularly limited and may be appropriately selected depending on the purpose, but from the viewpoint of obtaining good ejection stability and increasing the image density, it is 0.1 mass. % Or more and 50% by mass or less is preferable, and 0.1% by mass or more and 30% by mass or less is more preferable.
The pigment dispersion is preferably degassed by filtering coarse particles with a filter, a centrifugal separator or the like, if necessary.

<Physical properties of ink>
The physical properties of the first and second inks are not particularly limited and may be appropriately selected depending on the 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, from the viewpoint that the image density and character quality are improved and good ejection properties are obtained, and the viscosity is 5 mPa·s or more and 25 mPa·s or less. Is more preferable.
Here, as the viscosity, for example, a rotary viscometer (manufactured by Toki Sangyo Co., Ltd., RE-80L) can be used. The measurement conditions are 25° C., standard corn rotor (1°34′×R24), sample liquid amount 1.2 mL, rotation speed 50 rpm, 3 minutes. The pH of the ink is in contact with the liquid. From the viewpoint of preventing corrosion of the metal member, 7 or more and 12 or less are preferable, and 8 or more and 11 or less are more preferable.

(White ink)
The white ink of the present invention is used together with a second ink that is applied onto a first image to form a second image, and is a white ink that forms the first image,
The white ink contains water, hollow resin particles, and an organic solvent,
The second ink contains water and an organic solvent,
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A-B) is 1 μm or more and 3 μm or less.
The white ink of the present invention is the same as the first ink in the ink set of the present invention.

(ink)
The ink of the present invention is used together with a white first ink forming a first image on which a second image is formed, which is an ink forming the second image,
The first ink contains water, hollow resin particles, and an organic solvent,
The ink forming the second image contains water, and an organic solvent,
Average thickness (A) of the first image before the ink forming the second image is applied, and average thickness of the white area in the first image after the second image is formed The average thickness difference (AB) from (B) is 1 μm or more and 3 μm or less.
The ink forming the second image of the present invention is the same as the second ink in the ink set of the present invention.

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

<Post-treatment liquid>
The post-treatment liquid is not particularly limited as long as it can form a transparent layer. The post-treatment liquid is obtained by selecting and mixing an organic solvent, water, a resin, a surfactant, an antifoaming agent, a pH adjusting agent, an antiseptic/antifungal agent, an anticorrosive agent, etc., if necessary. Further, the post-treatment liquid may be applied to the entire recording area formed on the recording medium, or may be applied only to the area where the ink image is formed.

<Recording medium>
The recording medium is not particularly limited, and plain paper, glossy paper, special paper, cloth, and the like can be used, but good image formation can be performed using a non-permeable substrate.
The non-permeable base material is a base material having a surface with low water permeability and low absorbability, and includes a material that does not open to the outside even if there are many cavities inside, and more quantitatively. , Bristow method refers to a substrate having a water absorption amount of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 .
As the non-permeable substrate, for example, a plastic film such as a vinyl chloride resin film, a polyethylene terephthalate (PET) film, polypropylene, polyethylene, a polycarbonate film can be preferably used.

<Recording device, recording method>
The ink set of the present invention can be suitably used for various recording devices using an inkjet recording method, such as a printer, a facsimile device, a copying device, a printer/fax/copier compound machine, and a three-dimensional modeling device.
In the present invention, the recording device and the recording method are a device capable of ejecting ink, various treatment liquids, and the like onto a recording medium, and a method of recording using the device. The recording medium means a medium to which ink or various treatment liquids can be attached even temporarily.
The recording apparatus may include not only a head portion for ejecting ink, but also means for feeding, conveying, and discharging a recording medium, and other devices such as a pre-processing device and a post-processing device. ..
The recording device and the recording method may include a heating unit used in the heating process and a drying unit used in the drying process. The heating means and the drying means include, for example, means for heating and drying the printing surface or the back surface of the recording medium. The heating means and the drying means are not particularly limited, but, for example, a warm air heater or an infrared heater can be used. Heating and drying can be performed before printing, during printing, after printing, and the like.

The recording method of the present invention, water, hollow resin particles, and a white first ink containing an organic solvent,
An image forming method using an ink set having water, and a second ink formed on the first image formed by using the first ink containing an organic solvent to form a second image. There
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A-B) is 1 μm or more and 3 μm or less.

The recording apparatus of the present invention is an image forming unit that ejects the first ink and the second ink in the ink set of the present invention,
A heating unit for heating the first image formed by the first ink and the second image formed by the second ink, and further includes other units as necessary.

Furthermore, a first heating step of heating the first image after applying the first ink and before applying the second ink,
And a second heating step of heating the second image after applying the second ink.
The heating temperature in the second heating step is preferably 70°C or higher and 150°C or lower, and more preferably 70°C or higher and 100°C or lower. The heating temperature in the second heating step is preferably the same as or higher than the heating temperature in the first heating step.
The heating time in the second heating step is preferably 5 seconds or longer and 60 seconds or shorter, and more preferably 5 seconds or longer and 30 seconds or shorter. The heating time of the second heating step is preferably the same as or longer than the heating time of the first heating step.

The recording device and the recording method are not limited to those in which a significant image such as a character or a figure is visualized by ink. For example, it also includes one that forms a pattern such as a geometric pattern and one that models a three-dimensional image.
Further, the recording apparatus includes both a serial type apparatus that moves the ejection head and a line type apparatus that does not move the ejection head, unless otherwise limited.
Further, the recording device is not limited to a desktop type, and can be a wide recording device capable of printing on an A0 size recording medium, or a continuous paper wound in a roll can be used as the recording medium. It also includes a continuous form printer.

Here, an example of the recording device will be described with reference to FIGS. FIG. 1 is a perspective explanatory view of the device. FIG. 2 is a perspective 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 section 420 is provided inside the exterior 401 of the image forming apparatus 400. Each ink storage portion 411 of the main tank 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is, for example: aluminum laminated film or the like. It is formed by the packaging member. The ink container 411 is housed in a container case 414 made of plastics, for example. 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 on the inner side of the opening when the cover 401c of the apparatus body is opened. The main tank 410 is detachably attached to the cartridge holder 404. As a result, the ink discharge ports 413 of the main tank 410 communicate with the ejection heads 434 for each color via the supply tubes 436 for each color, and ink can be ejected from the ejection head 434 to the recording medium.

This recording device can include not only a portion for ejecting ink, but also a device called a pre-processing device, a post-processing device, or the like.
As one mode of the pretreatment device and the posttreatment device, as in the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y), a pretreatment liquid and a posttreatment liquid are included. There is a mode in which a liquid storage section and a liquid ejection head are added and a pretreatment liquid and a posttreatment liquid are ejected by an inkjet recording method.
As another aspect of the pretreatment apparatus and the posttreatment apparatus, there is an aspect in which a pretreatment apparatus and a posttreatment apparatus other than the ink jet recording method are provided, for example, by a blade coating method, a roll coating method, a spray coating method.

The method of using the ink is not limited to the ink jet recording method and can be widely used. In addition to the inkjet recording method, for example, a blade coating method, a gravure coating method, a bar coating method, a roll coating method, a dip coating method, a curtain coating method, a slide coating method, a die coating method, a spray coating method and the like can be mentioned.

The use of the ink of the present invention is not particularly limited and can be appropriately selected according to the purpose. For example, the ink can be applied to printed matter, paints, coating materials, substrates and the like. Furthermore, it can be used not only for forming two-dimensional characters and images using ink, but also as a three-dimensional modeling material for forming a three-dimensional three-dimensional image (three-dimensional model).
As a three-dimensional modeling device for modeling a three-dimensional molded object, a known one can be used and is not particularly limited. For example, a device provided with an ink containing means, a supplying means, a discharging means, a drying means, etc. is used. be able to. The three-dimensional molded item includes a three-dimensional molded item obtained by overcoating with ink. Further, it also includes a molded product obtained by processing a structure to which ink is applied on a substrate such as a recording medium. The molded product is, for example, a recording product or a structure formed in a sheet shape or a film shape, which has been subjected to molding processing such as heat drawing and punching processing. -It is suitable for applications such as electronic devices, meters for cameras, panels for operation parts, etc., where the surface is molded after decoration.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Production Example 1 of hollow resin particles)
-Preparation of hollow resin particles A-
A four-neck separable flask equipped with a stirrer, a thermometer, a condenser, and a dropping funnel was charged with ion-exchanged water (726 g), methyl methacrylate (5 g), and methacrylic acid (0.1 g) and heated while stirring. did. Then, when the internal temperature in the separable flask reached 70° C., a 10 mass% ammonium persulfate solution (1 g) was added, and the mixture was heated at 80° C. for 20 minutes. On the other hand, methyl methacrylate (141 g), methacrylic acid (94.9 g), and sodium alkylbenzenesulfonate (5 g: manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen SF-20) and ion-exchanged water (120 g) as anionic emulsifiers. ) Was emulsified with a homodisper to prepare a pre-emulsion and then added to a dropping funnel.
Next, while maintaining the internal temperature in the separable flask at 80° C., the pre-emulsion obtained above was uniformly added dropwise over 3 hours, and at the same time, a 10 mass% ammonium persulfate solution (10 g) was added over 3 hours. And evenly dripped. After the completion of dropping, the mixture was aged at 80° C. for 3 hours, cooled, and filtered through a 120-mesh filter to obtain a seed particle emulsion.
Next, a separable flask was charged with ion-exchanged water (188.2 g), the seed particle emulsion (66 g) obtained above was added, and the mixture was heated to 80° C. with stirring. On the other hand, butyl acrylate (2.4 g), butyl methacrylate (1.1 g), methyl methacrylate (19.5 g), methacrylic acid (0.7 g), sodium alkylbenzenesulfonate (0.1 g: Daiichi Kogyo Seiyaku Co., Ltd.) Manufactured by Neogen SF-20) and ion-exchanged water (55.3 g) were emulsified with a homodisper to prepare pre-emulsion 1 and then added to a dropping funnel. Then, while maintaining the internal temperature in the separable flask at 80° C., the pre-emulsion 1 obtained above was uniformly added dropwise over 30 minutes, and at the same time, a 10 mass% sodium persulfate solution (1.2 g) was added. It dripped uniformly over 30 minutes.
Next, styrene (128.3 g), sodium alkylbenzene sulfonate (0.6 g: manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen SF-20), and ion-exchanged water (51.8 g) were emulsified with a homodisper to give a pre After the emulsion 2 was prepared, it was put into a dropping funnel. Then, while maintaining the internal temperature in the separable flask at 80° C., 1 hour after the dropping of the pre-emulsion 1 was completed, the pre-emulsion 2 obtained above was dropped uniformly over 60 minutes. At the same time, a 10 mass% sodium persulfate solution (3.5 g) was uniformly added dropwise over 60 minutes. After the dropping of the pre-emulsion 2 was completed, it was aged at 80° C. for 1 hour. After cooling, the mixture was filtered through a 120-mesh filter to obtain a styrene-acrylic copolymer resin emulsion (hollow resin particles A).
The volume average particle diameter of the obtained hollow resin particles A was 530 nm.
The volume average particle size was measured using a laser scattering/diffraction type particle size measuring device (NanoTrac Wave EX150, manufactured by Microtrac Bell).

(Production Example 2 of hollow resin particles)
-Preparation of hollow resin particles B-
A methyl methacrylate resin emulsion (hollow resin particle B) was obtained in the same manner as in the hollow resin particle production example 1 except that styrene was replaced with methyl methacrylate.
The volume average particle diameter of the obtained hollow resin particles B was measured in the same manner as in Production Example 1 of hollow resin particles, and it was 530 nm.

(Examples 1 to 16 and Comparative Examples 1 to 5)
<Preparation of first ink (white ink)>
First, the organic solvent, the surfactant, the defoaming agent, the pH adjusting agent, the antibacterial agent, and the ion-exchanged water shown in Tables 1 to 5 were stirred for 1 hour and uniformly mixed.
Next, the resin and the polyethylene wax emulsion were added and stirred for an additional 1 hour to uniformly mix, and then the hollow resin particles A or B were added and stirred for an additional 1 hour to uniformly mix. The mixture was pressure-filtered with a polyvinylidene fluoride membrane filter having an average pore size of 5 μm to remove coarse particles and dust, and thus each first ink used in Examples 1 to 16 and Comparative Examples 1 to 5 was obtained.

<Preparation of second ink (chromatic ink)>
-Preparation of water-soluble polymer aqueous solution A-
[alpha]-Olefin-maleic anhydride copolymer (manufactured by Seikou PMC Co., Ltd., T-YP112) 10% by mass, 1N LiOH aqueous solution 17.34% by mass, and ion-exchanged water 72.56% by mass were mixed with a stirrer. After heating and stirring, a trace amount of insoluble matter was filtered with a filter having an average pore size of 5 μm to prepare a water-soluble polymer aqueous solution A.

-Cyan pigment surfactant dispersion-
10% by mass of polyoxyethylene styrene phenyl ether (nonionic surfactant, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Neugen EA-177) was dissolved in ion-exchanged water, and a phthalocyanine pigment (CI Pigment Blue 15:3, (Manufactured by Dainichi Seika Kogyo Co., Ltd.) When 30% by mass was mixed and sufficiently moistened, a wet disperser (Dyno Mill KDL A type, manufactured by WAB Co.) was filled with zirconia beads having a diameter of 0.5 mm, and 2,000 rpm was applied to 2 Time dispersion was performed to obtain a primary pigment dispersion.
Next, 7.51% by mass of the water-soluble polymer aqueous solution A and 2.51% by mass of a water-soluble polyester resin (Nichigo Polyester W-0030, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) were added to the primary pigment dispersion. Then, the mixture was thoroughly stirred to obtain a cyan pigment surfactant dispersion liquid. The average particle diameter (D ₅₀ ) of the pigment in the resulting cyan pigment surfactant dispersion was 78 nm. The average particle diameter (D ₅₀ ) was measured using a particle size distribution measuring device (Nanotrack UPA-EX150, manufactured by Nikkiso Co., Ltd.).

-Preparation of chromatic ink-
First, the organic solvent, the surfactant, the defoaming agent, the pH adjuster, the antibacterial agent, and the ion-exchanged water shown in Examples 1 to 15 and Comparative Examples 1 to 5 of Tables 1 to 5 are stirred for 1 hour to be uniform Mixed.
Next, the resin and the cyan pigment surfactant dispersion liquid were added, and the mixture was further stirred for 1 hour and uniformly mixed. This mixture is pressure-filtered with a polyvinylidene fluoride membrane filter having an average pore size of 0.8 μm to remove coarse particles and dust, and thus each second ink used in Examples 1 to 15 and Comparative Examples 1 to 5 is obtained. It was
In the chromatic color ink, the coloring material is added in such a proportion that the solid content of the coloring material in the cyan pigment surfactant dispersion is 5% by mass.
The average particle size of the coloring material used in the present invention is 0 when the solid content concentration (mass concentration) in the measurement sample is 0 using a particle size distribution measuring device (Nanotrack UPA-EX150 manufactured by Nikkiso Co., Ltd.). It was 120 nm as a result of measurement using a sample diluted with pure water so as to be 0.01% by mass. The average particle diameter referred to here means a 50% average particle diameter (D ₅₀ ).

<Preparation of second ink (clear ink)>
First, the organic solvent, the surfactant, the defoaming agent, the pH adjuster, the antibacterial agent, and the ion-exchanged water shown in Example 16 of Table 5 were stirred for 1 hour and uniformly mixed.
Next, the resin and the wax were added, and the mixture was stirred for another hour and mixed uniformly. The mixture was pressure-filtered with a polyvinylidene fluoride membrane filter having an average pore size of 0.8 μm to remove coarse particles and dust, and thus a second ink (clear ink) used in Example 16 was obtained.

<Image formation>
First, 1.2 mg/cm ² of the first ink shown in Tables 1 to 5 was attached to a recording medium (Lumina Color Black 127 gsm, manufactured by Takeo Co., Ltd.) using a liquid ejection device (IPSiO GXe5500, manufactured by Ricoh Co., Ltd.). After being discharged in an amount, it was heated at the heating temperature and heating time shown in Table 1 to Table 5. When recording the first ink a plurality of times, the recording and heating steps shown in Tables 1 to 5 were repeated.
Next, the second inks shown in Tables 1 to 5 were recorded on the first ink by a liquid ejection device (IPSiO GXe5500, manufactured by Ricoh Co., Ltd.) (Lumina Color Black 127gsm, manufactured by Takeo Co., Ltd.). After being discharged at a deposition amount of 0.8 mg/cm ^2, the coating was dried at the heating temperature and the heating time shown in Tables 1 to 5.
The image chart used was a solid image of 3 cm square formed in a dot pattern. This is an image sample.
Next, various characteristics of an image sample of a solid image of 3 cm square formed in a dot pattern were evaluated by the following methods. The results are shown in Tables 1 to 5.

<Average thickness of the first image and average thickness of the white area in the first image after the second image is formed>
A cross section of a printed sample of a solid image of 3 cm square formed in a dot pattern is cut with a cutter, and the cross section is observed with an SEM (JSL-6510A manufactured by JEOL Ltd.) to measure the thickness at any 5 positions. , And the average thickness was determined.

<Contact angle>
A contact angle meter (PCA-1 manufactured by Kyowa Interface Science Co., Ltd.) filled with the second ink was added to an image sample of a solid image of 3 cm square formed by a dot pattern in which only the first ink was printed. Was used to measure the contact angle of the second ink with respect to the first image formed with the first ink.

<Dynamic surface tension>
Using the first ink and the second ink, a dynamic surface tension meter (Sita Messtechnik's bubbling pressure tensiometer) was used to measure the dynamic surface tension at a life time of 1,500 msec by the maximum bubble pressure method to 25. The measurement was carried out at 0° C., and the absolute value of the difference in dynamic surface tension between the first ink and the second ink was obtained.

<Lightness of first image sample (L ^* )>
For a first image sample of a solid image of 3 cm square formed by a dot pattern in which only the first ink was printed, a lightness (L ^* was measured using a spectrocolorimeter (X-Rite 939, manufactured by X-Rite) ^. ) Was measured. The larger the lightness value, the higher the whiteness and the better. It should be noted that the lightness (L ^* ) of 20 or more is a practically acceptable level.

<Glossiness of the first image sample>
The first image sample of a solid image of 3 cm square formed with a dot pattern in which only the first ink was printed was measured with a gloss meter (manufactured by BYK, Microgloss 60) at an incident angle of 60°. ° Gloss was measured. The larger the value of glossiness, the better the glossiness of the image. The 60° gloss value of 5 or more is a practically acceptable level.

Details of the compositions of the first ink and the second ink in Tables 1 to 5 are as follows.
<Organic solvent>
-Organic solvent A: glycerin, SP value=17.4 (cal/cm ³ ) ^0.5
Organic solvent B: 1,2-propanediol, SP value ^{= 14.3 (cal / cm 3)} 0.5
-Organic solvent C: 1,2-butanediol, SP value=13.1 (cal/cm ³ ) ^0.5
Organic solvent D: 3- ethyl-3-hydroxymethyl oxetane, SP value ^{= 11.0 (cal / cm 3)} 0.5
Organic solvent E: 3- methoxy -N, N-dimethyl propoxy amide, SP value ^{= 9.2 (cal / cm 3)} 0.5

<Surfactant>
・Silicone type surfactant (KF-6011 manufactured by Shin-Etsu Chemical Co., Ltd.)
<Antifoam>
・KF-615A manufactured by Shin-Etsu Chemical Co., Ltd.
<Resin>
-Acrylic-silicone resin (manufactured by Toyochem, RKP-02, solid content concentration 40 mass%)
<Wax>
-Polyethylene wax emulsion: manufactured by BYK Japan KK, trade name: AQUACER-515, solid content concentration: 35% by mass
<Antibacterial agent>
・Proxel LV (S) (manufactured by Avicia)
<pH adjuster>
・2-Amino-2-ethyl-1,3-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.)
<Water>
・Ion-exchanged water (SP value=23.3 (cal/cm ³ ) ^0.5 )

(Test Examples 1 to 6)
-Evaluation of heating time and influence of heating time in the first heating step and the second heating step-
Example 1 except that the same first ink and second ink as in Example 1 were used and the heating time and heating time in the first heating step and the second heating step were changed as shown in Table 6. The difference in average thickness (AB), lightness (L ^* ), and glossiness were evaluated in the same manner as in. The results are shown in Table 6. In addition, Test Example 1 is the same as Example 1 described above, and Test Example 5 is the same as Comparative Example 5 described above, and are described for comparison.

From the results of Table 6, in Test Examples 1, 3 and 4, the heating temperature and the heating time in the first heating step and the second heating step were appropriate, and the brightness and glossiness were good.
In Test Example 2, it was found that the heating temperature in the first heating step and the second heating step was too low and the heating time was long, so that the glossiness was inferior.
In Test Example 5, it was found that the heating temperature in the first heating step and the second heating step was too high, and thus the brightness was inferior.
In Test Example 6, the heating temperature of the second heating step is lower than that of the first heating step, and the heating time of the second heating step is shorter than that of the first heating step. Turned out to be inferior.

Aspects of the present invention are as follows, for example.
<1> A white first ink containing water, hollow resin particles, and an organic solvent,
A second ink that contains water and an organic solvent, and is formed on the first image formed using the first ink to form a second image, and an ink set comprising:
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A−B) is 1 μm or more and 3 μm or less.
<2> The ink set according to <1>, wherein the average thickness (A) of the first image is 5 μm or more and 50 μm or less.
<3> The ink set according to any one of <1> to <2>, wherein a contact angle of the second ink with respect to the first image is 15 degrees or more and 30 degrees or less.
<4> The dissolution parameter (X) of the mixed solution of the organic solvent and water contained in the first ink and the dissolution parameter (Y) of the mixed solution of the organic solvent and water contained in the second ink are 17. The ink set according to any one of <1> to <3>, which is 0 (cal/cm ³ ) ^0.5 or more and 20.2 (cal/cm ³ ) ^0.5 or less.
<5> The ink set according to <4>, wherein a solubility parameter difference (X−Y) between the solubility parameter (X) and the solubility parameter (Y) is −1 or more and 3 or less.
<6> The solubility parameter (C) of the organic solvent having the highest content other than water contained in the first ink, and the solubility parameter of the organic solvent having the highest content other than water contained in the second ink. The ink set according to any one of the items <1> to <5>, in which the solubility parameter difference (C-D) from (D) is -3 or more and 3 or less.
<7> The absolute value of the difference in dynamic surface tension between the first ink and the second ink at a life time of 1,500 msec according to the maximum bubble pressure method is 0 mN/m or more and 12 mN/m or less. The ink set according to any one of 1> to <6>.
<8> The ink set according to any one of <1> to <7>, in which the outer shell resin of the hollow resin particles contains any of a styrene-acrylic copolymer resin and a methyl methacrylate resin.
<9> The ink set according to any one of <1> to <7>, wherein the content of the hollow resin particles is 5% by mass or more and 12.5% by mass or less with respect to the total amount of the first ink. is there.
<10> A white first ink containing water, hollow resin particles, and an organic solvent,
An image forming method using an ink set having water, and a second ink formed on the first image formed by using the first ink containing an organic solvent to form a second image. There
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A−B) is 1 μm or more and 3 μm or less.
<11> Further, a first heating step of heating the first image after applying the first ink and before applying the second ink,
A second heating step of heating the second image after applying the second ink,
The recording method according to <10>, wherein the heating temperature in the second heating step is 70° C. or higher and 150° C. or lower, and is the heating temperature in the first heating step or higher.
<12> The recording method according to <11>, wherein the heating time in the second heating step is 5 seconds or more and 60 seconds or less, and is the heating time in the first heating step or more.
<13> The recording method according to any one of <10> to <12>, wherein the average thickness (A) of the first image is 5 μm or more and 50 μm or less.
<14> The recording method according to any one of <10> to <13>, wherein a contact angle of the second ink with respect to the first image is 15 degrees or more and 30 degrees or less.
<15> The dissolution parameter (X) of the mixed solution of the organic solvent and water contained in the first ink and the dissolution parameter (Y) of the mixed solution of the organic solvent and water contained in the second ink are 17. The recording method according to any one of <10> to <14>, which is 0 (cal/cm ³ ) ^0.5 or more and 20.2 (cal/cm ³ ) ^0.5 or less.
<16> The recording method according to <15>, wherein the solubility parameter difference (X−Y) between the solubility parameter (X) and the solubility parameter (Y) is −1 or more and 3 or less.
<17> A solubility parameter (C) of an organic solvent having the highest content other than water contained in the first ink, and a solubility parameter of an organic solvent having the highest content other than water contained in the second ink. The ink set according to any one of <10> to <16>, in which a solubility parameter difference (C-D) from (D) is -3 or more and 3 or less.
<18> The absolute value of the difference in dynamic surface tension between the first ink and the second ink at a life time of 1,500 msec according to the maximum bubble pressure method is 0 mN/m or more and 12 mN/m or less. The recording method according to any one of <10> to <17>.
<19> The recording method according to any one of <10> to <18>, in which the outer shell of the hollow resin particles contains either a styrene-acrylic copolymer resin or a methyl methacrylate resin.
<20> The recording method according to any one of <10> to <19>, wherein the content of the hollow resin particles is 5% by mass or more and 12.5% by mass or less with respect to the total amount of the first ink. is there.
<21> An image forming unit that ejects the first ink and the second ink in the ink set according to any one of <1> to <9>,
A recording device comprising: a heating unit configured to heat a first image formed by the first ink and a second image formed by the second ink.
<22> A white ink that is used together with a second ink that is applied on the first image to form a second image, and that forms the first image,
The white ink contains water, hollow resin particles, and an organic solvent,
The second ink contains water and an organic solvent,
An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The average thickness difference (A−B) is 1 μm or more and 3 μm or less, which is a white ink.
<23> An ink for forming a second image, which is used together with a white first ink forming a first image on which a second image is formed,
The first ink contains water, hollow resin particles, and an organic solvent,
The ink forming the second image contains water, and an organic solvent,
Average thickness (A) of the first image before the ink forming the second image is applied, and average thickness of the white area in the first image after the second image is formed The ink is characterized in that the average thickness difference (AB) from (B) is 1 μm or more and 3 μm or less.

The ink set according to any one of the items <1> to <9>, the recording method according to any one of the items <10> to <20>, the recording device according to the item <21>, and the item <22>. The white ink and the ink described in <23> can solve the problems in the related art and achieve the object of the invention.

400 image forming apparatus 401 exterior of image forming apparatus 401c cover of apparatus body 404 cartridge holder 410 main tanks 410k, 410c, 410m, 410y for each color of black (K), cyan (C), magenta (M) and yellow (Y) Main tank 411 Ink storage unit 413 Ink discharge port 414 Storage container case 420 Mechanism unit 434 Discharge head 436 Supply tube

Japanese Patent No. 3562754 Japanese Patent No. 4877224

Claims (17)

Water, hollow resin particles, and a white first ink containing an organic solvent,
A second ink that contains water, and an organic solvent, and is formed on the first image formed using the first ink to form a second image, and an ink set comprising:
The solubility parameter (X) of the mixed solution of the organic solvent and water contained in the first ink is 18.30 (cal/cm ³ ) ^0.5 or more and 20.25 (cal/cm ³ ) ^0.5 or less. ,
The solubility parameter (Y) of the mixed solution of the organic solvent and water contained in the second ink is 17.02 (cal/cm ³ ) ^0.5 or more and 19.80 (cal/cm ³ ) ^0.5 or less. An ink set that is characterized. An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The ink set according to claim 1, wherein the average thickness difference (AB) is 1 μm or more and 3 μm or less. The ink set according to claim 2, wherein the average thickness (A) of the first image is 5 μm or more and 50 μm or less. The ink set according to claim 1, wherein a contact angle of the second ink with respect to the first image is 15 degrees or more and 30 degrees or less. The ink set according to claim 1, wherein a solubility parameter difference (X−Y) between the solubility parameter (X) and the solubility parameter (Y) is −1 or more and 3 or less. The solubility parameter (C) of the organic solvent having the highest content other than water contained in the first ink and the solubility parameter (D) of the organic solvent having the highest content other than water contained in the second ink. The ink set according to any one of claims 1 to 5, wherein a difference in solubility parameter (C-D) from -3 is -3 or more and 3 or less. 7. The absolute value of the difference in dynamic surface tension between the first ink and the second ink at a life time of 1,500 msec according to the maximum bubble pressure method is 0 mN/m or more and 12 mN/m or less. The ink set according to any one of 1. The ink set according to claim 1, wherein the outer shell resin of the hollow resin particles contains one of a styrene-acrylic copolymer resin and a methyl methacrylate resin. Water, hollow resin particles, and a white first ink containing an organic solvent,
A recording method using an ink set, comprising: a second ink that is applied onto a first image formed using the first ink containing water and an organic solvent to form a second image. hand,
The solubility parameter (X) of the mixed solution of the organic solvent and water contained in the first ink is 18.30 (cal/cm ³ ) ^0.5 or more and 20.25 (cal/cm ³ ) ^0.5 or less. ,
The solubility parameter (Y) of the mixed solution of the organic solvent and water contained in the second ink is 17.02 (cal/cm ³ ) ^0.5 or more and 19.80 (cal/cm ³ ) ^0.5 or less. A recording method characterized by the above. An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The recording method according to claim 9, wherein the average thickness difference (A-B) is 1 μm or more and 3 μm or less. Furthermore, a first heating step of heating the first image after applying the first ink and before applying the second ink,
A second heating step of heating the second image after applying the second ink,
The recording method according to claim 9, wherein the heating temperature in the second heating step is 70° C. or higher and 150° C. or lower, and is the heating temperature in the first heating step or higher. The recording method according to claim 11, wherein the heating time in the second heating step is 5 seconds or more and 60 seconds or less, and is the heating time or more in the first heating step. An image forming unit for ejecting the first ink and the second ink in the ink set according to claim 1.
A recording device, comprising: a heating unit configured to heat a first image formed by the first ink and a second image formed by the second ink. A white ink used in conjunction with a second ink applied on a first image to form a second image, the white ink forming the first image,
The white ink contains water, hollow resin particles, and an organic solvent,
The second ink contains water and an organic solvent,
The solubility parameter (X) of the mixed solution of the organic solvent and water contained in the white ink is 18.30 (cal/cm). ^Three ) ^0.5 20.25 (cal/cm ^Three ) ^0.5 Is
The solubility parameter (Y) of the mixed solution of the organic solvent and water contained in the second ink is 17.02 (cal/cm). ^Three ) ^0.5 Above 19.80 (cal/cm ^Three ) ^0.5 A white ink characterized in that: An average thickness (A) of the first image before the second ink is applied, and an average thickness (B) of a white area in the first image after the second image is formed. The color ink according to claim 14, wherein the average thickness difference (A-B) is 1 μm or more and 3 μm or less. A second image is used with a white first ink forming a first image on which a second image is formed, the ink forming the second image,
The first ink contains water, hollow resin particles, and an organic solvent,
The ink forming the second image contains water, and an organic solvent,
The solubility parameter (X) of the mixed solution of the organic solvent and water contained in the first ink is 18.30 (cal/cm). ^Three ) ^0.5 20.25 (cal/cm ^Three ) ^0.5 Is
The solubility parameter (Y) of the mixed solution of the organic solvent and water contained in the ink forming the second image is 17.02 (cal/cm). ^Three ) ^0.5 Above 19.80 (cal/cm ^Three ) ^0.5 An ink characterized in that: Average thickness (A) of the first image before the ink forming the second image is applied, and average thickness of the white area in the first image after the second image is formed The ink according to claim 16, wherein an average thickness difference (AB) from (B) is 1 μm or more and 3 μm or less.