JP7631946B2 - Ink, ink container and printed matter - Google Patents

Description

The present invention relates to ink, ink containers, and printed matter.

Inkjet printers have the advantages of being quiet, having low running costs, and being easy to print in color, so they are widely used in ordinary households as a device for outputting digital signals. In recent years, they have been used not only for home use, but also for industrial purposes such as displays, posters, and bulletin boards.

However, for industrial use, recording media are not limited to paper, and can range from transparent to colored. When expressing white on these media or coloring them with color inks, it is necessary to conceal the transparency of the recording media with ink, or to sufficiently conceal the color of the recording media with ink. Therefore, white ink is used to make such transparent or colored media white. Also, when using color inks, white ink is printed on the recording media as a base for the color inks to improve color development, so that they can be used in common with the color inks used for general images.

Titanium dioxide, a white pigment with excellent hiding power and coloring power, is widely used as a pigment for white ink. In order to obtain high hiding power using titanium dioxide, it is necessary to disperse the particles in a particle size range of approximately 200 to 300 nm in order to scatter visible light. However, titanium dioxide has a high specific gravity compared to the ink medium, so it tends to settle, and the settling rate is faster in low-viscosity inks such as water-based inks and solvent-based inks. In addition, once titanium dioxide settles, it forms a close-packed structure, making it difficult to disperse it again.

In response to these issues, inks using hollow particles have been reported. In the ink, the ink medium is present in the pores of hollow particles, so the apparent specific gravity is low and they are less likely to settle. In addition, the hiding power of hollow particles is achieved by utilizing the difference in refractive index between the hollow shell after the coating is dried and the pores emptied of the ink components.
For example, Patent Document 1 discloses a white inkjet ink having excellent ejection stability, the inkjet ink containing white hollow particles having a porosity of 40% or more and 80% or less, a number average particle diameter of 50 nm or more and 200 nm or less, and a ratio of particles having a particle diameter of 1 μm or more of 1000 ppm or less.

The present invention aims to provide an ink that improves the white hiding power of printed images.

The ink of the present invention as a means for solving the above problems has the following composition.
The ink contains hollow particles, and the hollow particle diameter distribution has two or more dispersion peaks in the range of 300 nm to 900 nm, and the ratio of the particle content at the peak position with the largest hollow diameter among the two or more dispersion peaks to the particle content at the peak position with the smallest hollow diameter is 6:4 to 7:3.

The present invention provides an ink that can produce printed matter with high white hiding power.

FIG. 1 is a diagram showing an example of an image forming apparatus using the ink of the present invention. FIG. 2 is a perspective view of a main tank that contains the ink of the present invention. FIG. 3 is a diagram showing how to determine the diameter of the hollow hole portion of a hollow particle. FIG. 4 is a diagram showing how to determine the content of hollow particles having a hollow diameter R. FIG. 5 is a diagram showing an example of the distribution of hollow diameters of hollow particles.

The present invention relates to an inkjet ink as shown in (1) below, but embodiments of the invention include the following (2) to (10).

The present invention relates to the following ink (1), but also includes the following embodiments (2) to (10):
(1) An ink containing hollow particles,
The hollow particle has a hollow diameter distribution having two or more dispersion peaks in the range of 300 nm or more and 900 nm or less,
the ratio of the hollow particle content at the peak position with the largest hollow particle diameter among the two or more dispersion peaks to the hollow particle content at the peak position with the smallest hollow particle diameter is 6:4 to 7:3;
An ink characterized by:
(2) The ink according to (1) above, wherein the content of hollow particles having a diameter of 300 nm or more and 900 nm or less contained in the ink is 80% or more of the total content of hollow particles in the ink.
(3) The ink according to (2) above, wherein the content of hollow particles having a diameter of 300 nm or more and 900 nm or less contained in the ink is 95% or more of the total content of hollow particles in the ink.
(4) The ink according to any one of (1) to (3) above, wherein the hollow particles contained in the ink consist of only hollow resin particles, or consist of only hollow inorganic particles, or consist of a mixture of hollow resin particles and hollow inorganic particles.
(5) The ink according to any one of (1) to (4) above, containing hollow particles in which the value obtained by dividing the shell thickness of the hollow particles by the primary particle diameter of the hollow particles is 0.01 or more and 0.1 or less.
(6) The ink according to any one of (1) to (5) above, which is a white ink.
(7) An ink container comprising the ink according to any one of (1) to (6) above contained therein.
(8) A printed matter having a substrate and a printing layer, characterized in that the distribution of hollow diameters of hollow particles calculated from a cross-sectional observation image of the printing layer has two or more dispersion peaks in the range of 300 nm or more and 900 nm or less.
(9) The printed matter according to (8) above, characterized in that the ratio of the hollow particle content at the peak position of the largest hollow particle diameter among the dispersion peaks of 300 nm or more and 900 nm or less in the distribution of hollow particle diameters of hollow particles calculated from a cross-sectional observation image of the printing layer to the hollow particle content at the peak position of the smallest hollow particle diameter is 6:4 to 7:3.
(10) The printed matter according to (8) or (9) above, wherein the content of hollow particles having a hollow diameter of 300 nm or more and 900 nm or less is 80% or more of the total content of hollow particles in the ink.

The ink of the present invention contains "hollow particles" such as hollow resin particles or hollow inorganic particles.
A hollow particle is composed of a shell layer and a void (hollow portion) surrounded by the shell layer.
In the present invention, the hollow diameter of the hollow particles refers to the diameter of the hollow portion.
In the present invention, the "distribution of hollow diameters" refers to a curve (distribution curve) obtained by plotting hollow diameters on the horizontal axis and the number of particles having the hollow diameters or the equivalent on the vertical axis.
In the present invention, the "dispersion peak of a hollow system" refers to the peak position (position of the hollow diameter at which the peak occurs) in the "distribution of hollow diameters."
Furthermore, "having two or more dispersion peaks in the range of 300 nm or more and 900 nm or less" means that there are two or more "peak positions (positions of the hollow diameter at which the peaks occur)" within the range of 300 nm or more and 900 nm or less.

<Definition of Various Parameters Used in the Present Invention>
<Hollow diameter R>
In the present invention, the hollow diameter refers to the diameter of the hollow hole of a hollow particle, that is, the length obtained by subtracting the shell thickness from the primary particle diameter as shown in Figure 3 (1).
In the present invention, the hollow diameter is measured using TEM images of particles in the ink observed with a transmission electron microscope (JEM-2100F, manufactured by JEOL Ltd.) and SEM images of the printed layer of the printed matter observed with a heated cathode field scanning microscope (Schottky, FE-SEM, ULTRA55, manufactured by Carl Zeiss). Since these observation images are two-dimensional images, the spherical hollow hole portion is observed as a circle. In this case, as shown in FIG. 3(1), the hollow diameter is the diameter of the observed circle. Also, as shown in FIG. 3(2) and FIG. 3(3), the observed hollow hole portion may not be a perfect circle but may be an ellipse or other shape that deviates from the circle shape. In such a case, the maximum diameter of the shape is defined as the hollow diameter R.

なお、中空径４００ｎｍの場合の例を図４に示してあり、Ｘ（４００ｎｍ）ｏｒＹ（４００ｎｍ）＝［Ｓ（４００ｎｍ）／Ｓ（ｔｏｔａｌ）］×１００で算出される。 <Content of hollow particles with diameter R>
In the present invention, the content of hollow particles having a hollow diameter R in the ink or printed matter is calculated from TEM images of particles in the ink or SEM images of the printed layer, in the same manner as in the measurement of the hollow diameter. The content of hollow particles having a hollow diameter R is calculated as X(R) from the TEM image of the ink, and as Y(R) from the SEM image of the printed layer. X(R) and Y(R) are defined by the following formula (1).

An example in which the hollow diameter is 400 nm is shown in FIG. 4, and the calculation is made by X(400 nm) or Y(400 nm)=[S(400 nm)/S(total)]×100.

<Methods of measuring and calculating various factors>
The above-mentioned "hollow diameter R" and "total area S(R) occupied by the hollow hole parts of hollow particles having a hollow diameter R" can be calculated by processing TEM observation images or cross-sectional SEM images using image processing software (e.g., Image-Pro, manufactured by Hakuto Co., Ltd.).
For example, when an observation image as shown in FIG. 4 is obtained, and particle A with a hollow diameter of 400 nm and particle B with a hollow diameter of 710 nm are observed in the image, the area of the hollow hole portion of each particle size is calculated by image processing software. Here, the sum of the areas of all particles with a hollow diameter of 400 nm is S (400 nm). S (710 nm) can be calculated in the same manner. And, when there are no particles other than 400 nm and 710 nm in FIG. 4, S (total) = S (400 nm) + S (710 nm). Furthermore, by using these factors obtained by calculation, X (400 nm), X (710 nm), Y (400 nm), and Y (710 nm) can be obtained by definition formula (1).
In the present invention, the hollow diameter R [nm] is counted in increments of 10 nm. The range in which a particle is counted as having a hollow diameter R [nm] is from R-5 nm to less than R+5 nm. For example, a particle with a hollow diameter of 395 nm is counted as having R=400 nm, and a particle with a hollow diameter of 405 nm is counted as having R=410 nm.

<Distribution of Hollow Particle Hollow Diameter>
In the present invention, the "distribution of hollow diameters" refers to a distribution in which the horizontal axis is the "hollow diameter R" of hollow particles and the vertical axis is the "content X(R) or Y(R) of particles having hollow diameter R." The peak position in the distribution is called the "dispersion peak of the distribution of hollow diameters." Furthermore, "having two or more dispersion peaks in the range of 400 nm to 1000 nm" means that the maximum point, which is the peak position of the dispersion peak, is in the range of 400 nm to 1000 nm. An example of the "distribution of hollow diameters" is shown in FIG. 5. Example 1 of FIG. 5 shows a case in which there are three dispersion peaks in the range of 300 nm to 900 nm, and Example 2 shows a case in which there are two dispersion peaks in the range of 300 nm to 900 nm.

<Ratio of particle content of hollow particles with different hollow diameters>
For example, in the case of an observation image containing a hollow particle 1 with a hollow diameter R1 and a hollow particle 2 with a hollow diameter R2, the ratio of the particle contents of these two particles is equal to the ratio of the respective contents X(R1) and X(R2) (or Y(R1) and Y(R2)), and therefore, this ratio can be calculated.
When the distribution in FIG. 5 is obtained, the ratio of the particle content at the peak position of the largest hollow diameter to the particle content at the peak position of the smallest hollow diameter is 14:11 in Example 1 and 2:3 in Example 2.

<Calculation method for shell thickness/primary particle size>
When the distribution peaks at hollow diameter R1, the shell thickness and primary particle diameter are measured for hollow particles counted as having a hollow diameter at peak position R1 (i.e., hollow particles having a hollow diameter of R1-5 nm or more and less than R1+5 nm), and the average shell thickness L1 and average primary particle diameter D1 are calculated.
In the present invention, "the value obtained by dividing the shell thickness of the hollow particles by the primary particle diameter of the hollow particles" refers to "the value obtained by dividing the average shell thickness L1 by the average primary particle diameter D1".
This value is preferably 0.01 or more and 0.1 or less.
In addition, in the case of an ink or printing layer having multiple hollow diameter peaks, it is preferable that the "value obtained by dividing the average shell thickness by the average primary particle diameter" is calculated for each peak position, and that the values at these multiple peaks are all within the range of 0.01 or more and 0.1 or less.

<Resin>
The resin contained in the ink of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyurethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, acrylic silicone resin, etc. These may be used alone or in combination of two or more. Among these, from the viewpoint of obtaining excellent abrasion resistance, polyurethane resin, polyester resin, acrylic resin, and vinyl chloride resin are preferable.

The resin is preferably resin particles that can be dispersed in water in the form of an aqueous emulsion, and is more preferably added to the ink in the form of a resin emulsion in which the resin particles are dispersed.
Here, the "resin particles dispersible in water in the form of an aqueous emulsion" refers to a form in which a substantially water-insoluble resin is dispersed in water in the form of particles, and the resin emulsion in the present invention includes those generally called emulsions, dispersions, latexes, or suspensions.
As the resin particles, appropriately synthesized ones or commercially available ones may be used.

The 50% cumulative volume particle size (D50) of the resin particles is preferably 10 nm or more and 350 nm or less from the viewpoint of storage stability and ejection stability when made into an ink.
The content of the resin particles is preferably 2.0% by mass or more and 7.5% by mass or less, and more preferably 3.0% by mass or more and 7.0% by mass or less, based on the total amount of the ink. When the content is 2.0% by mass or more, the hiding power is improved as described above. Also, when the content is 7.5% by mass or less, the resin particles can be stably maintained in the ink.

The other components in the ink of the present invention are not particularly limited and can be appropriately selected from known components, and examples thereof include the various components shown below.

<Volatile Solvent>
The volatile solvent used in the present invention is not particularly limited, and a water-soluble organic solvent can be used. When the volatile solvent is water, or water and a water-soluble organic solvent, the ink can be used as a water-based ink, and when the volatile solvent is an organic solvent, the ink can be used as a solvent ink.
In recent years, the issue of VOCs (volatile organic compounds) has been much discussed, and water-based inks capable of reducing the amount of VOCs emitted are widely desired. VOCs are a general term for organic compounds that easily volatilize into the atmosphere at normal temperature and pressure, but in the present invention, the volatile solvent means a solvent that is required to volatilize when heated on a recording medium and has a boiling point of 300° C. or less.

- Volatile solvents in water-based inks -
Examples of water used in the aqueous ink include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, and ultrapure water.
Examples of the water-soluble organic solvent used in the aqueous ink include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
The water-solubility of the water-soluble organic solvent means that the organic solvent is soluble in water at a rate of 30 mass % or more.

The water-soluble organic solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 1,5-pentanediol. , 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and polyhydric alcohols such as petriol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; polyhydric alcohol alkyl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; polyhydric alcohol aryl ethers such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and ε-caprolactam; nitrogen-containing heterocyclic compounds such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methylformamide, and dimethylformamide; Examples of the amines include amides such as 3-butoxy-N,N-dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane and thiodiethanol; propylene carbonate, ethylene carbonate, 3-methoxy-3-methyl-1-butanol, N,N-dimethyl-β-butoxypropionamide (Equamide B100, manufactured by Idemitsu Kosan Co., Ltd.), and N,N-dimethyl-β-methoxypropionamide (Equamide M100, manufactured by Idemitsu Kosan Co., Ltd.). These may be used alone or in combination of two or more.
It is preferable to use a water-soluble organic solvent having a boiling point of 260° C. or less, since this not only functions as a wetting agent but also provides good drying properties.

Among these, polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.
Specific examples of glycol ether compounds include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether. These may be used alone or in combination of two or more.

The content of the water-soluble organic solvent in the aqueous ink is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of the drying property and ejection reliability of the ink, it is preferably from 10% by mass to 60% by mass, and more preferably from 20% by mass to 60% by mass.

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

- Volatile solvent in solvent ink -
The organic solvent used in the solvent ink is not particularly limited and can be appropriately selected depending on the purpose. For example, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, ethylene glycol monomethyl ether propionate, ethylene glycol monoethyl ether propionate, ethylene glycol monobutyl ether propionate, diethylene glycol monomethyl ether propionate, diethylene glycol monoethyl ether propionate, diethylene glycol monobutyl ether propionate, glycol monoacetates such as ethylene glycol monomethyl ether butyrate, propylene glycol monomethyl ether propionate, dipropylene glycol monomethyl ether propionate, ethylene glycol monomethyl ether butyrate, ethylene glycol monoethyl ether butyrate, ethylene glycol monobutyl ether butyrate, diethylene glycol monomethyl ether butyrate, diethylene glycol monoethyl ether butyrate, diethylene glycol monobutyl ether butyrate, propylene glycol monomethyl ether butyrate, and dipropylene glycol monomethyl ether butyrate; ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, ethylene glycol propionate butyrate, ethylene Glycol diacetates such as ethylene glycol dipropionate, ethylene glycol acetate dibutyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, diethylene glycol propionate butyrate, diethylene glycol dipropionate, diethylene glycol acetate dibutyrate, propylene glycol acetate propionate, propylene glycol acetate butyrate, propylene glycol propionate butyrate, propylene glycol dipropionate, propylene glycol acetate dibutyrate, dipropylene glycol acetate propionate, dipropylene glycol acetate butyrate, dipropylene glycol propionate butyrate, dipropylene glycol dipropionate, and dipropylene glycol acetate dibutyrate; ethylene glycol, diethylene glycol, triethylene glycol glycols such as glycol, propylene glycol, dipropylene glycol, etc.; glycol ethers such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, propylene glycol monopropyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, triethylene glycol diethyl ether, etc.; lactic acid esters such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, etc., γ-butyrolactone, etc. These may be used alone or in combination of two or more.
Solvent ink may also be prepared by using a water-soluble organic solvent used in water-based ink.

The content of the organic solvent in the solvent ink is preferably 30% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 90% by mass or less, and even more preferably 39% by mass or more and 82% by mass or less, based on the total amount of ink.

The solvent ink preferably does not contain water. By not containing water, it is possible to improve the stability of the pigment dispersion, suppress hydrolysis of the solvent, and suppress corrosion of the head. Therefore, it is more preferable that the water content in the solvent ink is 0.5 mass% or less, which is the normal moisture absorption amount.

<Additives>
If necessary, surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, pH adjusters, and the like 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.
Silicone surfactants are not particularly limited and can be appropriately selected according to purpose. Among them, those that do not decompose even at high pH are preferred, such as side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having polyoxyethylene group or polyoxyethylene polyoxypropylene group as modified group are particularly preferred because they show good properties as aqueous surfactants. In addition, polyether modified silicone surfactants can also be used as the silicone surfactant, such as a compound in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane.
As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compound, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate compound, perfluoroalkyl ethylene oxide adduct, and polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain are particularly preferred because they have low foaming properties. As the perfluoroalkyl sulfonic acid compound, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. are included. As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. are included. As the polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain, for example, sulfate ester salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, etc. are included. Examples of counter ions of the salts in these fluorosurfactants include _Li , Na, K, _NH4 , _NH3CH2CH2OH , _NH2 ( _{CH2CH2OH ) 2} , and _NH ( _CH2CH2OH ) _{3 .}
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

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

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

上記一般式（Ｆ－１）で表される化合物において、水溶性を付与するためにｍは０～１０の整数が好ましく、ｎは０～４０の整数が好ましい。
一般式（Ｆ-２）
Ｃ_ｎＦ_{２ｎ＋１－}ＣＨ_２ＣＨ（ＯＨ）ＣＨ_２－Ｏ－（ＣＨ_２ＣＨ_２Ｏ）_ａ－Ｙ
上記一般式（Ｆ-２）で表される化合物において、ＹはＨ、又はＣｍＦ_２ｍ＋１でｍは１～６の整数、又はＣＨ_２ＣＨ（ＯＨ）ＣＨ_２－ＣｍＦ_２ｍ＋１でｍは４～６の整数、又はＣｐＨ_２ｐ＋１でｐは１～１９の整数である。ｎは１～６の整数である。ａは４～１４の整数である。
上記のフッ素系界面活性剤としては市販品を使用してもよい。 この市販品としては、例えば、サーフロンＳ－１１１、Ｓ－１１２、Ｓ－１１３、Ｓ－１２１、Ｓ－１３１、Ｓ－１３２、Ｓ－１４１、Ｓ－１４５（いずれも、旭硝子株式会社製）；フルラードＦＣ－９３、ＦＣ－９５、ＦＣ－９８、ＦＣ－１２９、ＦＣ－１３５、ＦＣ－１７０Ｃ、ＦＣ－４３０、ＦＣ－４３１（いずれも、住友スリーエム株式会社製）；メガファックＦ－４７０、Ｆ－１４０５、Ｆ－４７４（いずれも、大日本インキ化学工業株式会社製）；ゾニール（Ｚｏｎｙｌ）ＴＢＳ、ＦＳＰ、ＦＳＡ、ＦＳＮ－１００、ＦＳＮ、ＦＳＯ－１００、ＦＳＯ、ＦＳ－３００、ＵＲ、キャプストーンＦＳ－３０、ＦＳ－３１、ＦＳ－３１００、ＦＳ－３４、ＦＳ－３５（いずれも、Ｃｈｅｍｏｕｒｓ社製）；ＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ（いずれも、株式会社ネオス社製）、ポリフォックスＰＦ－１３６Ａ，ＰＦ－１５６Ａ、ＰＦ－１５１Ｎ、ＰＦ－１５４、ＰＦ－１５９（オムノバ社製）、ユニダインＤＳＮ-４０３Ｎ（ダイキン工業株式会社製）などが挙げられ、これらの中でも、良好な印字品質、特に発色性、紙に対する浸透性、濡れ性、均染性が著しく向上する点から、Ｃｈｅｍｏｕｒｓ社製のＦＳ－３１００、ＦＳ－３４、ＦＳ－３００、株式会社ネオス製のＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ、オムノバ社製のポリフォックスＰＦ－１５１Ｎ及びダイキン工業株式会社製のユニダインＤＳＮ-４０３Ｎが特に好ましい。 The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
The fluorine-based surfactant may include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains, etc. Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains are preferred because they have low foaming properties, and the fluorine-based surfactants represented by general formula (F-1) and general formula (F-2) are particularly preferred.

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

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

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

<Anti-septic and anti-fungal agents>
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

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

<pH Adjuster>
There are no particular limitations on the pH adjuster, so long as it is capable of adjusting the pH to 7 or higher, and examples of the pH adjuster include amines such as diethanolamine and triethanolamine.

<Coloring material>
As the coloring material, hollow resin particles or hollow inorganic particles, or both, are used.
<<Hollow resin particles>>
As the hollow resin particles, appropriately synthesized ones or commercially available ones may be used.
The method for synthesizing the hollow resin particles is not particularly limited and can be appropriately selected depending on the purpose. For example, a so-called emulsion polymerization method is preferred in which a vinyl monomer, a surfactant, a polymerization initiator, and an aqueous dispersion medium are heated and stirred under a nitrogen atmosphere to form a hollow resin particle emulsion.

Examples of the vinyl monomer include nonionic monofunctional ethylenically unsaturated monomers, bifunctional vinyl monomers, trifunctional or higher vinyl monomers, etc. These may be used alone or in combination of two or more.

Examples of the nonionic monofunctional ethylenically unsaturated monomer include styrene, vinyl toluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, (meth)acrylamide, and (meth)acrylic acid esters. These may be used alone or in combination of two or more. Among these, (meth)acrylic acid esters are preferred.

Examples of the (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

Examples of the bifunctional vinyl monomer include divinylbenzene, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,5-butanediol di(meth)acrylate, and diethylene glycol di(meth)acrylate.

Examples of the trifunctional or higher vinyl monomer include trimethylolpropane tri(meth)acrylate.

By copolymerizing the nonionic monofunctional ethylenically unsaturated monomer with at least one of the bifunctional vinyl monomer and the trifunctional or higher vinyl monomer and crosslinking to a high degree, hollow resin particles can be obtained that have not only light scattering properties but also properties such as heat resistance, solvent resistance, and solvent dispersibility.

The surfactant may be any surfactant that forms molecular aggregates such as micelles in water, and examples of such surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. These surfactants may be used alone or in combination of two or more.

As the polymerization initiator, a known compound that is soluble in water can be used, such as hydrogen peroxide and potassium persulfate. These can be used alone or in combination of two or more types.

Examples of the aqueous dispersion medium include water and water containing a hydrophilic organic solvent.

Commercially available hollow resin particles include, for example, ROPAQUE HT1432, ROPAQUE ULTRA E, DUAL, and OP-62 manufactured by The Dow Chemical Company, the Cybinol series manufactured by Saiden Chemical Industry Co., Ltd., and the SX series manufactured by JSR Corporation. These may be used alone or in combination of two or more types.

The content of the hollow resin particles is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 3.0% by mass or more and 14.0% by mass or less, and more preferably 5.0% by mass or more and 12.5% by mass or less, based on the total amount of ink. If the content is 5.0% by mass or more, whiteness can be ensured even on recording media such as fine paper. If the content is 12.5% by mass or less, the degree of settling and ejection stability are excellent.

<<Hollow inorganic particles>>
The hollow inorganic particles are not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include oxides, nitrides, and oxynitrides of titanium, silicon, aluminum, zirconium, strontium, etc. Among these, titanium oxide is preferred from the viewpoint of hiding power.
In addition, silicon oxide can be used as the hollow inorganic particles because it can obtain scattering from the shell corresponding to the outer shell of the hollow particles and the internal pores in addition to scattering from the particle surface. Also, from the viewpoint of sedimentation in the ink, it is preferable to use silicon oxide, which has a small specific gravity, as the hollow inorganic particles.

When the hollow inorganic particles are made of titanium dioxide (hereinafter, sometimes referred to as "titanium hollow particles"), there are no particular limitations on the manufacturing method, and any known manufacturing method can be used, such as the method described in JP 2014-051401 A.

The content of the hollow inorganic particles is preferably 3% by mass or more and 10% by mass or less, and more preferably 5% by mass or more and 9% by mass or less, based on the total amount of the ink. If the content is 3% by mass or more, sufficient hiding power can be obtained, and if the content is 10% by mass or less, sufficient coating film density can be obtained, and good ejection stability can be obtained.

A dispersant may be added to enhance the dispersion stability of the hollow inorganic particles in the ink.
The dispersant is not particularly limited and can be appropriately selected depending on the purpose, but a dispersant polymer is suitable. Examples of the dispersant polymer include α-olefin-maleic anhydride copolymer, styrene-(meth)acrylic copolymer, acrylic block copolymer, water-soluble polyurethane resin, water-soluble polyester resin, etc. These may be used alone or in combination of two or more.

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

<Hollow diameter dispersion peak>
In the ink of the present invention, the hollow particle diameter distribution has two or more dispersion peaks in the range of 300 nm to 900 nm, which enables the hollow particles to scatter light in a plurality of visible light regions, thereby increasing the whiteness even if the film thickness is small. Furthermore, in the present invention, the ratio of the hollow particle content at the peak position with the largest hollow particle diameter among the two or more dispersion peaks to the hollow particle content at the peak position with the smallest hollow particle diameter is 6:4 to 7:3.
This ratio improves the balance of the scattering degree between the long wavelength region and the short wavelength region, making it possible to improve the whiteness. This balance also overcomes the problems of settling and ejection properties. Note that the "content" here refers to the "number of hollow particles."

In the ink of the present invention, the content of hollow particles having a hollow diameter of 300 nm or more and 900 nm or less is preferably 80% or more, and more preferably 95% or more, of the total content of hollow particles in the ink. By making the content of hollow particles having a hollow diameter of 300 nm or more and 900 nm or less 80% or more, there will be fewer hollow particles (impurities) having a diameter of less than 300 nm or more than 900 nm, which will further improve whiteness and low sedimentation.

The hollow particles contained in the ink may consist of only hollow resin particles or only hollow inorganic particles. The hollow particles contained in the ink may also consist of a mixture of hollow resin particles and hollow inorganic particles.

The hollow particles preferably have a shell thickness divided by the primary particle diameter of the hollow particles of 0.01 or more and 0.1 or less. This allows the hollow particles to maintain low settling while also maintaining high Hunter whiteness.

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

The coloring material used in the present invention can be not only a white pigment such as the hollow resin particles or the hollow inorganic particles, but also other types of coloring materials. In this way, a white ink is produced when a white pigment is used alone, but by using other coloring materials (colored coloring materials) in combination, it is possible to produce an image that has the color of the coloring material used while having the desired hiding power.
Coloring materials other than the white pigment are not particularly limited, and pigments and dyes can be used.
As the pigment, inorganic pigments or organic pigments can be used. These pigments can be used alone or in combination of two or more. Mixed crystals can also be used.

Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy pigments such as gold and silver pigments, and metallic pigments.
As inorganic pigments, titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, as well as carbon black produced by known methods such as the contact method, furnace method, and thermal method can be used.
As organic pigments, azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Among these pigments, those having good affinity with the solvent are preferably used. In addition, hollow resin particles and hollow inorganic particles can also be used.
Specific examples of pigments for black colors include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black; metals such as copper, iron (C.I. Pigment Black 11), and titanium oxide; and organic pigments such as aniline black (C.I. Pigment Black 1).
Further, for color, C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C.I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (Red ochre), 1 04, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38, C.I. Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63, C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.
The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. One type of dye may be used alone, or two or more types may be used in combination.
Examples of the dyes include C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35.

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

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

The inks of the present invention can be used as ink-jet inks.
The amount of ink attached by the inkjet recording method is preferably 1.5 g/m2 or ^more and 25 g/m2 or ^less . When the amount of ink attached is 1.5 g/m2 or ^more , sufficient image density can be obtained, and when the amount is ²⁵ g/m2 or less, sufficient fixability can be obtained.

(Ink storage container)
The ink container of the present invention contains the ink of the present invention in a container, and further contains other members appropriately selected as necessary.
The container is not particularly limited, and its shape, structure, size, material, etc. can be appropriately selected depending on the purpose. For example, a container having at least an ink bag formed of an aluminum laminate film, a resin film, etc. is preferably used.

<Ink cartridge>
The ink cartridge contains the ink of the present invention in a container, and further contains other members appropriately selected as necessary.
The container is not particularly limited, and its shape, structure, size, material, etc. can be appropriately selected depending on the purpose. For example, a container having at least an ink bag formed of an aluminum laminate film, a resin film, etc. is preferably used.

<Recording media>
There are no particular limitations on the recording medium, and although plain paper, glossy paper, special paper, cloth, etc. can be used, good image formation is also possible using a non-permeable substrate.
The non-permeable substrate is a substrate having a surface with low water permeability and absorbency, and includes materials that have many cavities inside but are not open to the outside. More quantitatively, the non-permeable substrate is a substrate having a water absorption amount of 10 mL/m2 or ^less from the start of contact to 30 msec ^1/2 in the Bristow method.
As the non-permeable substrate, for example, a plastic film such as a polyvinyl chloride resin film, a polyethylene terephthalate (PET) film, a polypropylene film, a polyethylene film, or a polycarbonate film can be suitably used.
The recording medium is not limited to those generally used as recording media, and may be wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc. By adjusting the configuration of the path for conveying the recording medium, ceramics, glass, metal, etc. may also be used.

For example, a polyethylene terephthalate (PET) film with a thickness of 100 μm has a total light transmittance of 80% or more.

<Recording device and recording method>
The ink of the present invention can be suitably used in various recording devices using the ink jet recording method, such as printers, facsimile machines, copying machines, printer/fax/copier combination machines, and three-dimensional modeling devices.
In the present invention, the recording apparatus and recording method refer to an apparatus capable of ejecting ink, various treatment liquids, etc. onto a recording medium, and a method of recording using the apparatus. The recording medium refers to an object onto which ink or various treatment liquids can be attached even temporarily.
This recording device can include not only a head portion that ejects ink, but also means related to feeding, transporting, and discharging the recording medium, as well as other devices called pre-processing devices and post-processing devices.
The recording apparatus and the recording method may have a heating means used in the heating step and a drying means used in the drying step. The heating means and the drying means include, for example, a means for heating and drying the printed surface and the back surface of the recording medium. The heating means and the drying means are not particularly limited, but for example, a hot air heater and an infrared heater can be used. Heating and drying can be performed before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, those that form patterns such as geometric designs and those that form three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move.
Furthermore, this recording device includes not only desktop types, but also wide-width recording devices capable of printing on A0-sized recording media, and continuous-feed printers that can use continuous paper wound into a roll as a recording medium.
An example of a recording apparatus will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of the apparatus. FIG. 2 is a perspective view of a main tank. An image forming apparatus 400 as an example of a recording apparatus is a serial type image forming apparatus. A mechanism section 420 is provided in an exterior 401 of the image forming apparatus 400. Each ink storage section 411 of the main tanks 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is formed of a packaging material such as an aluminum laminate film. The ink storage section 411 is stored in a storage container case 414 made of plastic, for example. As a result, the main tanks 410 are used as ink cartridges for each color.
On the other hand, a cartridge holder 404 is provided at the rear of the opening when the cover 401c of the apparatus body is opened. A main tank 410 is detachably attached to the cartridge holder 404. This allows each ink outlet 413 of the main tank 410 to communicate with an ejection head 434 for each color via a supply tube 436 for each color, making it possible to eject ink from the ejection head 434 onto a recording medium.

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

The temperature in the drying step after the ink of the present invention is recorded on a recording medium by the inkjet method is preferably from 50° C. to 200° C. Within this temperature range, the recording medium is less susceptible to heat effects.
It is more preferable that the temperature is from 50° C. to 70° C. Within this temperature range, even when hollow resin particles are used, the hollow structure of the hollow resin particles will not be destroyed by heat.

The ink of the present invention has a Hunter whiteness of W when a 50 mm x 50 mm solid image formed on a polyethylene terephthalate (PET) film is dried for 1 hour in a 50°C thermostatic chamber.

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

In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous.

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

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

<Examples of hollow particles>
In the examples and comparative examples shown in Tables 3 and 4, the following hollow resin particles and hollow inorganic particles were used.
Hollow resin particles A: SX-866(B) manufactured by Rohm and Haas
Hollow resin particles B: Rohm and Haas Company's ROPAQUE ULTRA E
Hollow resin particles C: Rohm and Haas Ropeake OP-62
Hollow resin particles D: A synthetic product obtained by the method described in JP 2019-155847 A. Hollow resin particles E: Saibinol X-213-913E-43 manufactured by Saiden Chemical Industry Co., Ltd.
Hollow resin particles F: Rohm and Haas Ropeake HP-1055
Hollow inorganic particle G: Silica hollow particle described in the Preparation Examples. Hollow inorganic particle H: Silica hollow particle described in the Preparation Examples. Table 1 shows the properties of hollow resin particles A to F and hollow inorganic particles G and H.

<Preparation of Hollow Resin Particles D>
Hollow resin particles D were prepared by the same method as that described in JP-A-2019-155847.
(1) Synthesis of seed particle emulsion Deionized water (726.0 parts), methyl methacrylate (5.0 parts), and methacrylic acid (0.1 parts) were charged into a four-necked separable flask equipped with a stirrer, a thermometer, a cooler, and a dropping funnel, and heated with stirring. Then, when the internal temperature of the separable flask reached 70°C, a 10% aqueous ammonium persulfate solution (1.0 parts) was added, and the mixture was heated at 80°C for 20 minutes. Meanwhile, methyl methacrylate (141.0 parts), methacrylic acid (94.9 parts), sodium alkylbenzenesulfonate (5.0 parts: Neogen SF-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an anionic emulsifier, and deionized water (120.0 parts) were emulsified with a homodisper to form a pre-emulsion, and then charged into the dropping funnel.
Next, while maintaining the internal temperature of the separable flask at 80° C., the pre-emulsion obtained above was uniformly dropped over 3 hours, and at the same time, a 10% aqueous solution of ammonium persulfate (10.0 parts) was uniformly dropped over 3 hours. After completion of the dropwise addition, the mixture was aged at 80° C. for 3 hours, cooled, and then filtered using a 120 mesh filter cloth to obtain a seed particle emulsion.

(2) Synthesis of hollow resin particles (first-stage polymerization)
A four-necked separable flask equipped with a stirrer, a thermometer, a cooler, and a dropping funnel was charged with deionized water (188.2 parts), the seed particle emulsion (66.0 parts) obtained above was dropped, and the mixture was heated to 80 ° C. while stirring. Meanwhile, butyl acrylate (2.4 parts), butyl methacrylate (1.1 parts), methyl methacrylate (19.5 parts), methacrylic acid (0.7 parts), sodium alkylbenzene sulfonate (5.0 parts: Neogen SF-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and deionized water (55.3 parts) were emulsified with a homodisper to obtain pre-emulsion 1, which was then poured into the dropping funnel. Then, while maintaining the internal temperature of the separable flask at 80 ° C., the pre-emulsion 1 obtained above was uniformly dropped over 30 minutes, and at the same time, a 10% aqueous sodium persulfate solution (1.2 parts) was uniformly dropped over 30 minutes.

(Second stage polymerization)
Styrene (75.0 parts), sodium alkylbenzenesulfonate (5.0 parts: Neogen SF-20 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and deionized water (51.8 parts) were emulsified with a homodisper to obtain pre-emulsion 2, which was then charged into a dropping funnel. Then, while maintaining the internal temperature of the separable flask at 80° C., one hour after the completion of the dropping of pre-emulsion 1, the pre-emulsion 2 obtained above was dropped uniformly over 60 minutes, and at the same time, a 10% aqueous sodium persulfate solution (3.5 parts) was dropped uniformly over 60 minutes. After the completion of the dropping of pre-emulsion 2, 28% aqueous ammonia (7.5 parts) was dropped to swell and dissolve the seed particles, and the mixture was aged at 80° C. for one hour. After cooling, the mixture was filtered using a 120-mesh filter cloth to obtain hollow resin particles D.

<Preparation of hollow inorganic particles G and H>
Hollow inorganic particles G and H were prepared by the same method as that described in JP 2020-121528 A.
The reaction components and reaction conditions for producing hollow inorganic particles G and H are shown in Table 2.
(Production of hollow inorganic particles G)
- Preparation of silica-coated particles -
1.3 parts by mass of non-crosslinked styrene acrylic resin particle water dispersion FS201E (manufactured by Nippon Paint Co., Ltd.) and 98.7 parts by mass of water were thoroughly dispersed using an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., US-300T, tip diameter 7 mm, 100 μA, 10 minutes). Thereafter, the mixture was transferred to a plastic container and stirred, and several drops of 1N aqueous sodium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) were added to adjust the pH to 10.5. Thereafter, 1.0 part by mass of 3-aminopropylethoxysilane: (APTES, manufactured by Tokyo Chemical Industry Co., Ltd.) and 1.2 parts by mass of tetraethoxysilane: (TEOS, manufactured by Tokyo Chemical Industry Co., Ltd.) were slowly added in this order, and the mixture was allowed to react at 25° C. for 20 hours, forming a silica shell on the surface of the resin particles using a sol-gel reaction, and silica-coated particles were obtained.
--Preparation of 18% by mass aqueous phase of hollow inorganic particles G--
Next, the obtained silica-coated particles were washed with water and centrifuged to obtain a wet cake of silica-coated particles. Further, tetrahydrofuron was added to dissolve the resin particles of the core material, and the mixture was stirred for 1 hour, washed with water, and dispersed in water again, followed by concentration to obtain [18% by mass aqueous phase of hollow inorganic particles G].
In any of the washing steps, the silica-coated particles or hollow inorganic particles were subjected to liquid-liquid replacement since there was a risk of aggregation if the particles were dried.

(Production of hollow inorganic particles H)
[Hollow inorganic particles H (18% by mass in water phase)] was obtained in the same manner as in the production of hollow inorganic particles G, except that the composition and reaction conditions were changed to those shown in Table 2 in the production of hollow inorganic particles G.

Details of the materials in Table 2 are as follows:
- Core material (resin particles) -
FS201E: (non-crosslinked styrene acrylic resin particle water dispersion, solid content 27% by mass, negatively charged, manufactured by Nippon Paint Co., Ltd.)
FS301E: (non-crosslinked styrene acrylic resin particle water dispersion, solid content 27% by mass, negatively charged, manufactured by Nippon Paint Co., Ltd.)
- Core material (calcium carbonate) -

-Silicon alkoxide-
3-Aminopropylmethoxysilane: (APTMS, manufactured by Tokyo Chemical Industry Co., Ltd.)
3-Aminopropylethoxysilane: (APTES, manufactured by Tokyo Chemical Industry Co., Ltd.)
Tetramethoxysilane: (TMOS, manufactured by Tokyo Chemical Industry Co., Ltd.)
Tetraethoxysilane: (TEOS, manufactured by Tokyo Chemical Industry Co., Ltd.)

(Preparation Example 1)
--Preparation of hollow inorganic particle dispersion G--
To 100 parts by mass of the [18% by mass aqueous phase of hollow inorganic particles G], 6 parts by mass of an amino group-containing copolymer (dispersant, manufactured by BYK Japan, product name "Disperbyk-190" (active ingredient 100% by mass)) and 12 parts by mass of water were added and thoroughly stirred, and then dispersed using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., US-300T, tip diameter 7 mm, 100 μA, 30 minutes). Coarse particles in the obtained dispersion were removed using centrifugation (4000 rpm, 1 minute), and further filtration was performed using a membrane filter (cellulose acetate membrane) having an average pore size of 5 μm to prepare [hollow inorganic particle dispersion G] (hollow inorganic particle concentration: 15% by mass).

(Preparation Example 2)
--Preparation of hollow inorganic particle dispersion H--
[Hollow inorganic particle dispersion H] was prepared in the same manner as in Preparation Example 1 of hollow inorganic particle dispersion, except that in Preparation Example 1 of hollow inorganic particle dispersion, [18 mass % aqueous phase of hollow inorganic particles G] was changed to [18 mass % aqueous phase of hollow inorganic particles H].

Example 1
<Ink Preparation>
11.5 mass% of 1,2-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.5 mass% of 3-methoxy-3-methylbutanol (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.3 mass% of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), 8.0 mass% of a urethane resin emulsion (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Superflex 210, 35 mass%) as a resin, 0.4 mass% of a silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-640) as a surfactant, 0.1 mass% of 2-amino-2-ethyl-1,3-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) as a pH adjuster, and 23.9 mass% of ion-exchanged water were stirred for 1 hour to uniformly mix. Next, 2.4 mass% of hollow resin particles A (manufactured by Rohm and Haas, product name: SX-866(A), hollow diameter: 201 nm) as a pigment solid content, 2.2 mass% of hollow resin particles C (manufactured by Rohm and Haas, Ropeake OP-62, hollow diameter: 311 nm) as a pigment solid content, and further 3.4 mass% of hollow resin particles E (manufactured by Saiden Chemical Industry, Saibinol X-213-913E-43, hollow diameter: 500 nm) as a pigment solid content were added and further stirred for 1 hour to mix uniformly. This mixture was pressure filtered through a membrane filter (cellulose acetate membrane) with an average particle size of 5 μm to remove coarse particles and dust, thereby preparing the ink of Example 1.
The pigment solid content in Tables 2 and 3 is the amount as the pigment solid content, and the resin emulsion content in Tables 2 and 3 is the amount of the entire resin emulsion.

(Examples 2 to 9 and Comparative Examples 1 to 4)
Inks of Examples 2 to 9 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, except that the compositions in Example 1 were changed as shown in Tables 3 and 4 below.

Next, the "difference in settling degree" and "Hunter brightness" were evaluated as follows. The results are shown in Tables 3 and 4 below.

<Difference in sedimentation rate before and after standing>
Approximately 5 g of each of the obtained inks was placed in a 25 g glass tube (product name: screw-top test tube, manufactured by AS ONE Corporation) and allowed to stand for 168 hours in an environment at 25° C. The sedimentation degree of the ink before and after standing for 168 hours was measured using a sedimentation degree measuring device (device name: Turbiscan Classic MA2000, manufactured by Eiko Seiki Co., Ltd.). The difference in sedimentation degree was calculated by subtracting the sedimentation degree of the ink before standing from the sedimentation degree of the ink after standing for 168 hours. Note that a difference in sedimentation degree of -2 or more is a feasible level.
[Evaluation Criteria]
S: The difference in the degree of settling after 168 hours from the start of the evaluation is -0.5 or more. A: The difference in the degree of settling after 168 hours from the start of the evaluation is -1.0 or more and less than -0.5. B: The difference in the degree of settling after 168 hours from the start of the evaluation is -4.0 or more and less than -1.0. C: The difference in the degree of settling after 168 hours from the start of the evaluation is -5.0 or more and less than -4.0. D: The difference in the degree of settling after 168 hours from the start of the evaluation is less than -5.0.

<Printing conditions>
The exterior of an inkjet printer (IPSiOGXe5500 manufactured by Ricoh) was removed, a rear multi-manual feeder was attached, and pure water was passed through the ink supply path including the print head to clean it. The cleaning liquid was passed through sufficiently until it was no longer colored, and then the cleaning liquid was completely drained from the device to prepare a printing device for evaluation.
The prepared ink was stirred for 30 minutes under reduced pressure conditions of 5 to 10 Pa to remove the gas in the ink for evaluation, and then filled into an ink cartridge to prepare an ink cartridge for evaluation. A filling operation was performed to confirm that all nozzles were filled with the ink for evaluation and that no abnormal images were produced, and after selecting the glossy paper clean mode in the driver attached to the printer, the printing mode was set to color matching off in the user settings. In this mode, the ejection amount was adjusted by changing the head drive voltage so that the amount of ink attached to the media for a solid image was 9.6 g/ ^m2 .

<Hunter Whiteness>
White hiding power was evaluated by measuring Hunter Whiteness.
The inks prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were filled into an inkjet printer (IPSiOGXe5500, manufactured by Ricoh), and a 50 cm x 50 cm solid image created using Microsoft Word 2003 was printed on a transparent PET film (Ester Film E5100, manufactured by Toyobo) fixed with double-sided tape on My Paper (PPC plain paper, manufactured by Ricoh), and then the image was dried in a thermostatic chamber at 50°C for 1 hour to obtain a solid image.
With a commercially available black paper placed underneath the printed PET film, the L ^* , a ^* , and b ^* of the printed image were measured using a spectrophotometric densitometer (device name: X-Rite 939, manufactured by X-Rite Corporation), and the Hunter whiteness was calculated using the following formula (2).
Hunter whiteness = 100 - [(100 - L ^* )2 + (a ^*2 + b ^*2 )] ^0.5 ... formula (2)
The evaluation was based on the following criteria.
[Evaluation Criteria]
S: Hunter whiteness is 80 or more A: Hunter whiteness is 70 or more and less than 80 B: Hunter whiteness is 65 or more and less than 70 C: Hunter whiteness is 60 or more and less than 65 D: Hunter whiteness is less than 60 For reference, the Hunter whiteness measured with an unprinted PET film placed on black paper was 26.

<Measurement of the diameter of hollow particles in pigment dispersions and inks>
Observation was performed at a magnification of 30,000 using a transmission electron microscope (manufactured by JEOL Ltd., "JEM-2100F") to obtain a TEM image. The hollow diameter of the obtained TEM image was measured using the hollow diameter measurement method described above.

<Hollow diameter measurement in the cross section of the printed matter>
A cross section was prepared for a printed matter produced by an inkjet printer or the like using an ion milling device (IM4000, manufactured by Hitachi High-Technologies Corporation), and the obtained cross section was observed with a scanning electron microscope such as a heated cathode field scanning microscope (Schottky, FE-SEM, ULTRA55 manufactured by Carl Zeiss) to obtain an SEM image of the printed layer of the printed matter. The hollow diameter of the obtained SEM image was measured using the hollow diameter measurement method described above.

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

JP 2014-122310 A

Claims (10)

An ink containing hollow particles,
The hollow particle has a hollow diameter distribution having two or more dispersion peaks in the range of 300 nm or more and 900 nm or less,
the ratio of the hollow particle content at the peak position with the largest hollow particle diameter among the two or more dispersion peaks to the hollow particle content at the peak position with the smallest hollow particle diameter is 6:4 to 7:3;
An ink characterized by: The ink according to claim 1, wherein the content of hollow particles having a diameter of 300 nm or more and 900 nm or less contained in the ink is 80% or more of the total content of hollow particles in the ink. The ink according to claim 2, wherein the content of hollow particles having a diameter of 300 nm or more and 900 nm or less contained in the ink is 95% or more of the total content of hollow particles in the ink. The ink according to any one of claims 1 to 3, wherein the hollow particles contained in the ink consist of only hollow resin particles, only hollow inorganic particles, or a mixture of hollow resin particles and hollow inorganic particles. The ink according to any one of claims 1 to 4, which contains hollow particles in which the shell thickness of the hollow particles divided by the primary particle diameter of the hollow particles is 0.01 or more and 0.1 or less. The ink according to any one of claims 1 to 5, which is a white ink. An ink container comprising the ink according to any one of claims 1 to 6. A printed matter having a substrate and a printing layer, characterized in that the distribution of hollow particle diameters calculated from a cross-sectional observation image of the printing layer has two or more dispersion peaks in the range of 300 nm to 900 nm. The printed matter according to claim 8, characterized in that the ratio of the hollow particle content at the peak position with the largest hollow particle diameter and the hollow particle content at the peak position with the smallest hollow particle diameter among the dispersion peaks of 300 nm to 900 nm inclusive in the distribution of hollow particle diameters calculated from the cross-sectional observation image of the print layer is 6:4 to 7:3. 10. The printed matter according to claim 8, wherein a content of hollow particles having a hollow diameter of 300 nm or more and 900 nm or less is 80% or more of a content of all hollow particles in the ink.

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