Inkjet ink, inkjet head, and inkjet recording apparatus

Abstract

An inkjet ink according to one embodiment of the present invention contains first particles containing a pigment and a first resin, second particles containing a second resin, an ultraviolet absorber, and an aqueous medium. The average particle diameter of the second particles is smaller than the average particle diameter of the first particles.

Description

Technical Field

[0001] The present invention relates to an inkjet ink, an inkjet head, and an inkjet recording device. Background Art

[0002] In inkjet printing, ink containing a colorant is formed into droplets. These droplets are ejected toward a print medium in response to an image signal (print signal), causing them to impact the print medium, thereby forming an image on the print medium. Examples of inks used in this type of inkjet printing (inkjet inks) include aqueous inks in which a colorant such as a pigment is dispersed in an aqueous medium such as water. Aqueous inks are characterized by their high safety. After their droplets impact the print medium, the aqueous medium contained in the aqueous ink permeates the print medium or evaporates, thereby forming an image on the print medium. Examples of such aqueous inks include the inks described in Patent Document 1.

[0003] Patent Document 1 describes an ink comprising a colorant, an ultraviolet absorber, a resin, and an aqueous medium for emulsifying or suspending the resin. Patent Document 1 also describes a printing method for printing on a medium using an inkjet method. In this printing method, an inkjet head is used to eject the ink onto the medium, the ink adheres to the medium, an ultraviolet light source is used to irradiate the ink adhered to the medium with ultraviolet light, the temperature is raised to a temperature lower than the boiling point of the ink and which suppresses ink bleeding, and at least a portion of the aqueous medium contained in the ink is volatilized and removed. Patent Document 1 discloses the following principles: a printed material having sufficient gloss can be obtained by preventing matting of the surface, and ink bleeding can be more appropriately suppressed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-89300 Summary of the Invention

[0007] An inkjet ink according to one embodiment of the present invention includes first particles containing a pigment and a first resin, second particles containing a second resin, a UV absorber, and an aqueous medium. The second particles have an average particle size smaller than that of the first particles.

[0008] Another embodiment of the present invention provides an inkjet ink comprising first particles containing a pigment and a first resin, a UV absorber, and an aqueous medium, wherein the UV absorber has an average particle size equal to or smaller than the average particle size of the first particles.

[0009] An inkjet ink according to another embodiment of the present invention includes first particles containing a pigment and a first resin, a UV absorber, and an aqueous medium, wherein the UV absorber is present in an amount of 0.1% by mass to 1.6% by mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram showing the configuration of an example of an inkjet recording apparatus according to an embodiment of the present invention.

[0011] Figure 2 This is a schematic diagram for explaining the fixing of an image formed using the inkjet ink according to an embodiment of the present invention. DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present invention will be described; however, the present invention is not limited thereto.

[0013] [Inkjet ink]

[0014] An inkjet ink according to one embodiment of the present invention includes first particles containing a pigment and a first resin, second particles containing a second resin, a UV absorber, and an aqueous medium. The second particles have an average particle size smaller than that of the first particles.

[0015] After the inkjet ink is applied to a print medium (recording medium) serving as a printed object in response to an image signal (print signal) corresponding to the desired image, it is dried. The pigment contained in the inkjet ink remains on the print medium, forming an image (note that text is also a type of image) on the print medium. At this point, due to the melting of the second resin contained in the second particles, the second particles fuse together, fixing the image formed by the pigment contained in the inkjet ink. Furthermore, due to the melting of the first resin contained in the first particles, the first particles fuse with the second particles, and this fusion also contributes to improving the fixability of the image. Therefore, the first resin contained in the first particles also contributes to the fixing process, thereby improving the fixability of the image. Moreover, since the inkjet ink contains the first particles containing the pigment in addition to the first resin as described above, the dispersibility of the pigment can be improved, the occurrence of uneven distribution of the pigment in the formed image can be suppressed, and the fixability of the image can be improved. In addition, since the inkjet ink contains an ultraviolet absorber, the inkjet ink is heated by irradiation with ultraviolet rays, making it easier to remove the aqueous medium from the inkjet ink. In addition, in the inkjet ink, since the average particle size of the second particles is smaller than the average particle size of the first particles, it is easier to remove the aqueous medium from the inkjet ink, and the quick-drying property is improved. This is believed to be because the vaporized aqueous medium easily passes through the inkjet ink. In addition, in the inkjet ink, since the average particle size of the second particles is smaller than the average particle size of the first particles, the second particles are easier to disperse in the aqueous medium, and the fixability is improved. Based on the above reasons, the inkjet ink is an inkjet ink that is excellent in quick-drying properties and fixing properties.

[0016] As mentioned above, the inkjet ink is an ink containing an aqueous medium (aqueous ink). Aqueous inks are generally difficult to dry compared to inks containing organic solvents with a higher volatility than water, and tend to have poor quick-drying properties. In particular, when the printing medium is a medium such as a resin that is difficult for aqueous media to penetrate, such as a film, the quick-drying property is significantly reduced. Therefore, aqueous inks are required to have high quick-drying properties, that is, the aqueous medium such as water contained therein should be easily evaporated from the aqueous ink hitting the printing medium. In addition, inkjet inks such as aqueous inks are also required to have high fixability of the image formed on the above-mentioned printing medium. The inkjet ink is an ink that meets such requirements. That is, although the inkjet ink is an aqueous ink, it is an inkjet ink with excellent quick-drying properties and fixability.

[0017] (1st particle)

[0018] The first particles are, for example, a pigment dispersion in which the first resin is attached to the pigment, and the pigments are stably dispersed in an aqueous medium without agglomerating. The method for producing the first particles is not particularly limited; for example, a method includes polymerizing monomers (or a monomer mixture if two or more monomers are present) that serve as the raw materials for the first resin to obtain the first resin, and then dispersing the obtained first resin along with the pigment in a bead mill. The first particles may be so-called self-dispersible pigment particles or pigment-encapsulated resin particles.

[0019] The average particle size of the first particles can be adjusted, for example, by adjusting the conditions for the dispersion treatment using the bead mill. Furthermore, the average particle size of the first particles can also be adjusted, for example, by filtering using a filter. More specifically, it can be adjusted using the number of filtrations (number of passes) and the type of filter used. Furthermore, the average particle size of the first particles can be further adjusted by repeatedly performing a dispersion treatment using a bead mill and filtering using a filter. Examples of the bead mill include bead mills manufactured by Ashizawa Finetech Co., Ltd. Examples of the conditions for the dispersion treatment using the bead mill include bead diameter and rotor speed. Furthermore, the zeta potential of the first particles and the content of coarse particles contained in the first particles can also be adjusted using the same method as for adjusting the average particle size.

[0020] ·pigment

[0021] The pigments are not particularly limited as long as they can form the desired image (can reveal the colors that constitute the desired image), and examples thereof include well-known organic pigments and inorganic pigments. Examples of the organic pigments include azo pigments, polycyclic pigments, nitro pigments, nitroso pigments, and aniline black. Examples of the azo pigments include azo lake pigments, insoluble azo pigments, condensed azo pigments, and chelated azo pigments. Examples of the polycyclic pigments include phthalocyanine pigments, perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindole pigments, and quinophthalone pigments. Examples of the inorganic pigments include carbon blacks such as acetylene black and lamp black.

[0022] The pigments can also be classified according to color. For example, there can be mentioned pigments for black, pigments for magenta or red, pigments for orange or yellow, and pigments for green or cyan.

[0023] Examples of the black pigment include CI Pigment Black 7.

[0024] Examples of the pigment for magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 150, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 202, and CI Pigment Red 222.

[0025] Examples of the orange or yellow pigment include CI Pigment Orange 31, CI Pigment Orange 34, CI Pigment Orange 36, CI Pigment Orange 43, CI Pigment Orange 61, CI Pigment Orange 63, CI Pigment Orange 71, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 95, CI Pigment Yellow 109, CI Pigment Yellow 110, Pigment Yellow 120, CI Pigment Yellow 128, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 173, CI Pigment Yellow 180, CI Pigment Yellow 185, and CI Pigment Yellow 193.

[0026] Examples of the green or cyan pigment include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, and CI Pigment Green 7.

[0027] The above pigments may be used alone or in combination of two or more.

[0028] ·1st resin

[0029] Examples of the first resin include resins that adhere to the pigment and stably disperse the first particles in an aqueous medium (so-called dispersing polymers, dispersant polymers, and polymer dispersants). More specifically, examples include resins having a portion that adheres to the pigment (a hydrophobic portion) and a portion that promotes the dispersibility of the first particles (a hydrophilic portion). Examples of the first resin include styrene-based resins. Examples of styrene-based resins include copolymers of styrene and a carboxylic acid component such as a carboxylic acid or a carboxylic acid ester (e.g., at least one selected from acrylic acid, methacrylic acid, an acrylate, a methacrylate, and maleic acid). As the above-mentioned styrene resin, specifically, styrene-acrylic acid copolymer, styrene-acrylate copolymer, styrene-acrylic acid-acrylate copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid-methacrylic acid copolymer, styrene-methacrylate copolymer, styrene-methacrylate copolymer, styrene-methacrylic acid-methacrylic acid copolymer, styrene-acrylate-methacrylic acid copolymer, styrene-acrylate-methacrylic acid copolymer, styrene-acrylate-methacrylic acid copolymer, styrene-acrylate-methacrylic acid copolymer, styrene-acrylate-methacrylic acid copolymer, styrene-acrylate-methacrylic acid-methacrylic acid copolymer, styrene-maleic acid copolymer and styrene-maleic acid-acrylate copolymer etc. As the above-mentioned acrylate, for example, methyl acrylate, methyl acrylate, butyl acrylate and methoxy polyethylene glycol acrylate etc. can be mentioned. As the above-mentioned methacrylate, for example, methyl methacrylate, methyl methacrylate, butyl methacrylate and methoxy polyethylene glycol methacrylate etc. can be mentioned. In addition, the above-mentioned first resin can be used alone or in combination of two or more.

[0030] In consideration of factors such as the temperature of the inkjet head and the drying temperature of the inkjet ink, a resin having a predetermined glass transition temperature (Tg) is appropriately selected as the first resin. For example, the glass transition temperature (Tg) of the first resin can be 50°C or higher and less than 70°C. The glass transition temperature (Tg) is the temperature at which glass transition occurs, and examples thereof include a value (glass transition temperature) measured using differential scanning calorimetry (DSC).

[0031] In order to appropriately select a resin having a predetermined weight-average molecular weight as the first resin, taking into account the glass transition temperature of the second resin and the drying temperature of the inkjet ink, the weight-average molecular weight of the first resin can be, for example, 5,000 to 30,000. The weight-average molecular weight may be a value measured using a common molecular weight measurement method, specifically, a value measured using gel permeation chromatography (GPC).

[0032] (2nd particle)

[0033] The second particles may be particles containing the second resin as a main component, or particles formed from the second resin. Furthermore, the second particles are resin particles (so-called fixing polymer particles, fixer polymer particles, or polymer fixer particles) that can improve the fixability of an image formed by the pigment contained in the inkjet ink. The second resin is not particularly limited as long as it is a resin that improves the fixability (so-called fixing polymer, fixer polymer, or polymer fixer). Examples include thermoplastic resins and other resins that melt upon heating. If the second resin is such a heat-meltable resin, heating the inkjet ink melts the second resin contained in the second particles, causing the second particles to fuse together, thereby improving the fixability. In this case, the second particles exist in the inkjet ink as particles (solid) before being heated, such as before the inkjet ink is ejected. Therefore, the second particles have a low solubility in the aqueous medium contained in the inkjet ink (e.g., water solubility) and are dispersed in the aqueous medium. Furthermore, in the case of a resin that melts upon heating as described above, the glass transition temperature (Tg) of the second resin can be higher than the temperature of the inkjet ink before heating (e.g., room temperature) to improve the fixing properties. Specifically, it can be between 70°C and 120°C, or between 70°C and 110°C. Furthermore, the second resin can be a resin with different components from the first resin or a resin with the same components as the first resin. However, the first particles differ from the second particles in that they contain a pigment. In other words, the second particles can contain components other than the second resin but not a pigment.

[0034] Examples of the second resin include styrene resins, silicone resins, polyester resins, and polyurethane resins. The second resin may be used alone or in combination of two or more.

[0035] Examples of the styrene-based resins include copolymers of styrene with carboxylic acid and carboxylic acid components such as carboxylic acid esters (e.g., at least one selected from acrylic acid, methacrylic acid, acrylate, methacrylate, and maleic acid). Specific examples of the styrene-based resins include copolymers of styrene with at least one selected from acrylic acid, methacrylic acid, acrylate, and methacrylate. Specific examples of the styrene-based resins include styrene-acrylic acid copolymers, styrene-acrylate copolymers, styrene-acrylic acid-acrylate copolymers, styrene-methacrylic acid copolymers, styrene-acrylic acid-methacrylic acid copolymers, styrene-methacrylic acid-methacrylic acid copolymers, styrene-methacrylic acid-acrylate copolymers, styrene-acrylate-methacrylic acid ...-methacrylic acid copolymers, styrene-maleic acid copolymers, and styrene-maleic acid-acrylate copolymers. Examples of the acrylic acid ester include methyl acrylate, methyl acrylate, butyl acrylate, and methoxy polyethylene glycol acrylate. Examples of the methacrylic acid ester include methyl methacrylate, methyl methacrylate, butyl methacrylate, and methoxy polyethylene glycol methacrylate.

[0036] Examples of the silicone resin include side chain modified silicone oils, single-terminal modified silicone oils, dual-terminal modified silicone oils, and side chain dual-terminal modified silicone oils.

[0037] The polyester resin is a polymer formed by ester bonds between a divalent or higher carboxylic acid and a divalent or higher alcohol. Examples of the divalent carboxylic acid in the polyester resin include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, sulfoisophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, and dimer acid. Examples of the trivalent or higher carboxylic acid in the polyester resin include trimellitic acid and pyromellitic acid. Examples of the divalent alcohol in the polyester resin include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A.

[0038] The polyurethane resin is a polymer formed by urethane bonds between a divalent or higher alcohol (polyol) and a divalent or higher isocyanate (polyisocyanate). Examples of the polyol in the polyurethane resin include polypropylene glycol, polyethylene glycol, polybutylene glycol, poly(ethylene adipate), poly(diethylene glycol adipate), poly(propylene adipate), poly(butylene adipate), poly(hexylene adipate), poly-ε-caprolactone, poly(hexylene carbonate), and silicone polyols. Examples of the polyisocyanate in the polyurethane resin include toluene diisocyanate, 4,4-diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, and tetramethylxylylene diisocyanate.

[0039] The weight-average molecular weight of the second resin is not particularly limited. For example, from the perspective of improving the fluidity of the inkjet ink and reducing its ejection fluctuation, it can be 300,000 to 1,500,000. From the perspective of achieving a fluidity that is more suitable for reducing ejection fluctuation, it can be 400,000 to 1,000,000. It should be noted that the weight-average molecular weight here can be any value obtained by measuring the first resin using a general molecular weight measurement method, specifically, a value obtained by gel permeation chromatography (GPC). The weight-average molecular weight of the second resin can be obtained more specifically by freeze-drying an aqueous dispersion containing the second resin to obtain a powdered second resin, dissolving the obtained second resin in tetrahydrofuran (THF), and subjecting the resulting solution to GPC analysis.

[0040] The method for producing the second particles is not particularly limited. Examples include emulsion polymerization of monomers (or a monomer mixture when there are two or more monomers) that serve as the raw materials for the second resin. The average particle size of the second particles can be adjusted, for example, by adjusting the conditions for the emulsion polymerization. Examples of the conditions for the emulsion polymerization include stirring conditions for the monomers prior to emulsion polymerization using a stirrer and stirring conditions for the monomers during emulsion polymerization using a stirrer. Examples of stirring conditions include the rotational speed and treatment time of the blades provided in the stirrer. Examples of the stirrer include a batch high-speed stirrer. Examples of the batch high-speed stirrer include the Telecorta R manufactured by PRIMIX Co., Ltd. The average particle size of the second particles can also be adjusted by filtering using a filter. The zeta potential of the second particles can be adjusted using the same method as that used to adjust the average particle size.

[0041] (UV absorber)

[0042] The ultraviolet absorber is not particularly limited, and examples thereof include benzotriazole ultraviolet absorbers, triazine ultraviolet absorbers, benzophenone ultraviolet absorbers, benzoate ultraviolet absorbers, and benzimidazole ultraviolet absorbers. The ultraviolet absorber may also be in liquid form. Examples of the benzotriazole ultraviolet absorber include ultraviolet absorbers containing a benzotriazole structure, and more specifically, 2(2'-hydroxy-5'-methylphenyl)benzotriazole, 2(2'-hydroxy-5'-octylphenyl)benzotriazole, 2[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimide-methyl)-5-methylphenyl]benzotriazole, 2[2'-hydroxy-3

[0015] 2H-benzotriazole, 2(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, 2(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole, and 2(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole. Examples of the triazine-based UV absorbers include those containing a hydroxyphenyltriazine structure, and more specifically, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine and 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine. Examples of the benzophenone-based UV absorbers include dihydroxybenzophenone compounds such as 2,2'-dihydroxybenzophenone and 2-hydroxy-4-alkoxybenzophenone. Examples of the benzoate-based UV absorbers include resorcinol monobenzoate. Examples of the benzimidazole-based UV absorbers include phenylbenzimidazole sulfonic acid.

[0043] Furthermore, UV absorbers not only simply have a higher UV absorption capacity than typical substances, but also essentially convert UV light into heat. Furthermore, after essentially converting UV light into heat, UV absorbers return to their original state, capable of converting UV light into heat, repeatedly converting UV light into heat. UV polymerization initiators contained in UV-curable (polymerizable) inks, etc., have a certain degree of UV absorption capacity. However, the generation of free radicals, etc. that initiate polymerization, does not necessarily generate heat, and the reactions of the generated free radicals, etc., are not necessarily exothermic. Furthermore, free radicals, etc., generated by UV light are generated only once and do not undergo repeated reactions. Based on this perspective, it can be considered that UV polymerization initiators are not included in UV absorbers.

[0044] The above-mentioned ultraviolet absorbers may be used alone or in combination of two or more.

[0045] The average particle size of the ultraviolet absorber can be adjusted by, for example, pulverization. Examples of the pulverization include pulverization using a mixer. Examples of the mixer include a batch high-speed mixer. Examples of the batch high-speed mixer include the Telecorta R manufactured by PRIMIX Co., Ltd. The average particle size of the ultraviolet absorber can be adjusted by adjusting stirring conditions such as the rotational speed of the blades in the mixer and the processing time. Furthermore, the average particle size of the ultraviolet absorber can also be adjusted by filtering using a filter.

[0046] (Aqueous medium)

[0047] The aqueous medium is not particularly limited as long as it contains water. For example, it may be an aqueous medium containing water as a main component (e.g., 50% by mass or greater) or an aqueous medium consisting entirely of water. The water content in the aqueous medium may be 50% by mass or greater, 90% by mass or greater, or 100% by mass. Furthermore, the aqueous medium may contain water and further contain a water-soluble organic solvent. That is, the aqueous medium may be an aqueous medium containing both water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohol compounds, ketone compounds, glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerol, and dimethyl sulfoxide. Examples of the alcohol compound include methanol, ethanol, isopropyl alcohol, and butanol. Examples of the ketone compound include methyl ethyl ketone. Examples of the diol compound include ethylene glycol, 1,3-propylene glycol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Examples of the glycol ether compound include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and propylene glycol monomethyl ether. Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone. Examples of the nitrogen-containing compound include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide. Examples of the acetate compound include diethylene glycol monoethyl ether acetate. The water-soluble organic solvent may be used alone or in combination of two or more. The aqueous medium may function as either a solvent or a dispersion medium.

[0048] (content)

[0049] The inkjet ink comprises the first particles, the ultraviolet absorber, and the aqueous medium, and may further comprise the second particles. The content of the first particles is not particularly limited, but the content of the first particles may be 3.0 to 8.0 parts by mass relative to 100 parts by mass of the inkjet ink. Furthermore, the content of the second particles may be 1.0 to 15.0 parts by mass relative to 100 parts by mass of the inkjet ink.

[0050] Furthermore, the content of the ultraviolet absorber can be from 0.1 parts by mass to 1.6 parts by mass per 100 parts by mass of the inkjet ink. That is, the content of the ultraviolet absorber can be from 0.1% by mass to 1.6% by mass. When the inkjet ink attached to the print medium is irradiated with ultraviolet light to generate heat, as described later, by increasing the amount of the ultraviolet absorber to 0.1 parts by mass or more, the amount of heat generated within the inkjet ink can be increased. This promotes drying and improves fixability. When the inkjet ink contains secondary particles, the fusing of the secondary particles further improves fixability. Furthermore, in the inkjet ink attached to the print medium, if the absorption of ultraviolet light on the side of the ultraviolet radiation source increases, the amount of ultraviolet light transmitted to the side opposite the radiation source decreases, potentially reducing the amount of heat generated on the side opposite the radiation source. However, by decreasing the amount of the ultraviolet absorber to 1.6 parts by mass or less, this can be minimized. This promotes drying and improves fixability. In particular, when the printing medium is irradiated with ultraviolet light from the side to which the inkjet ink is attached, it is possible to promote drying of the printing medium side of the inkjet ink, which is difficult to dry. In addition, when the second particle is included, the fixing property is further improved due to the melting of the second particle.

[0051] Furthermore, the inkjet ink may contain components other than the first particles, the second particles, the ultraviolet absorber, and the aqueous medium, as long as the inkjet ink contains the first particles, the second particles, the ultraviolet absorber, and the aqueous medium. The remainder may be the aqueous medium.

[0052] (Average particle size)

[0053] In the inkjet ink, the average particle size of the second particles is smaller than the average particle size of the first particles. In other words, the ratio of the average particle size of the second particles to the average particle size of the first particles (average particle size of the second particles / average particle size of the first particles) is less than 1. This makes it easier to remove the aqueous medium from the inkjet ink, improving quick-drying properties. This is believed to be because the vaporized aqueous medium easily passes through the inkjet ink. Furthermore, this makes it easier for the second particles to disperse more evenly in the aqueous medium, improving fixability. The ratio (average particle size of the second particles / average particle size of the first particles) is less than 1, but can be between 0.6 and 0.9 to improve both quick-drying properties and fixability.

[0054] The average particle size of the first particles may be determined, for example, by performing cumulant analysis using a dynamic scattering method to determine the dynamic structure factor using a particle size distribution meter (ELSZneo, a Zeta Potential / Particle Size / Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source. The average particle size of the second particles may be determined by performing image analysis on the image obtained by observing the second particles with a scanning electron microscope (SEM) after drying and removing the aqueous medium.

[0055] The average particle size of the first particles is not particularly limited as long as it is larger than the average particle size of the second particles. However, from the perspective of improving the quality of the formed image, such as facilitating the achievement of a desired image density and improving color stability, the average particle size can be from 80 nm to 100 nm. From the perspective of further improving the above-mentioned image quality, the average particle size can be from 85 nm to 95 nm.

[0056] The above-mentioned first particles may be aggregated, and coarse particles may be inevitably mixed in. As the above-mentioned coarse particles, for example, coarse particles with a particle size of 2 μm or more can be cited, and coarse particles with a particle size of 2 μm or more and 10 μm or less can also be cited. The average particle size of the above-mentioned first particles is the average particle size excluding the above-mentioned coarse particles. That is, the inkjet ink of this embodiment contains the above-mentioned first particles, the above-mentioned second particles, the above-mentioned ultraviolet absorber, and the above-mentioned aqueous medium, the above-mentioned first particles contain coarse particles with a particle size of 2 μm or more, and the average particle size of the first particles other than the above-mentioned coarse particles is smaller than the average particle size of the above-mentioned second particles. It should be noted that in the above-mentioned inkjet ink, even if the average particle size of the above-mentioned first particles is grasped as the average particle size when the above-mentioned coarse particles are included, the average particle size of the above-mentioned first particles is smaller than the average particle size of the above-mentioned second particles.

[0057] If the amount of coarse particles mixed into the first particles is low, the fluidity of the inkjet ink is improved, and the ejection fluctuation of the inkjet ink can be reduced, thereby improving the accuracy of the inkjet ink. Based on this, for example, the number of coarse particles with a particle size of 2 μm or more and 10 μm or less in the first particles can be 70,000 or less per mL. To further improve the accuracy of the coarse particles, the number can also be 40,000 or less per mL. It should be noted that, with regard to the coarse particles, the less the amount mixed into the first particles, the better, but in practice, reducing it to approximately 30,000 per mL is the limit. Therefore, the number of coarse particles with a particle size of 2 μm or more and 10 μm or less in the first particles can be 30,000 or more per mL and 70,000 or less per mL. It should be noted that the above number refers to the number of coarse particles per 1 mL of the first particles. The number of coarse particles (the amount of contamination) can be measured using, for example, a number counting type particle size distribution analyzer (AccuSizer A700APS manufactured by Entegris).

[0058] The average particle size of the second particles is not particularly limited as long as it is smaller than the average particle size of the first particles. From the perspective of improving the quality of the formed image and the fixability, the average particle size may be, for example, 70 nm to 80 nm.

[0059] If the particle size fluctuation of the second particle is small, the ejection fluctuation of the inkjet ink can be reduced, and the hitting accuracy of the inkjet ink can be improved. From this point of view, the particle size fluctuation of the second particle can be, for example, less than 7 nm in terms of standard deviation σ, and can be less than 5 nm in terms of further improving the hitting accuracy. It should be noted that, with respect to the particle size fluctuation of the second particle, the smaller the better in terms of improving the hitting accuracy, however, in practice, reducing it to about 3 nm is the limit. Therefore, the particle size fluctuation of the second particle can be greater than 3 nm and less than 7 nm in terms of standard deviation σ. It should be noted that as the standard deviation σ, a value calculated based on the obtained particle size by observing with a scanning electron microscope (SEM) and measuring the particle size based on the obtained image can be cited. More specifically, the value can be obtained by applying the inkjet ink onto a film using a bar coater, drying at 40° C., observing the dried product using a SEM, measuring the particle size from the obtained image, and calculating based on the obtained particle size.

[0060] If the UV absorber is small, its dispersibility improves, and the weather resistance of the image (including the image formed by inkjet ink) fixed to the print medium is enhanced. To this end, the average particle size of the UV absorber can be less than or equal to the average particle size of the first particles. That is, the ratio of the average particle size of the UV absorber to the average particle size of the first particles (average particle size of the UV absorber / average particle size of the first particles) can be 1 or less. Furthermore, to further enhance weather resistance, the ratio (average particle size of the UV absorber / average particle size of the first particles) can be 0.6 to 1.0. Furthermore, to enhance weather resistance, the average particle size of the UV absorber can be 60 nm to 100 nm, and even 60 nm to 80 nm. Furthermore, the ratio of the average particle size of the ultraviolet absorber to the average particle size of the second particles (average particle size of the ultraviolet absorber / average particle size of the second particles) may be 0.75 or more and 1.25 or less in order to improve the weather resistance.

[0061] The average particle size of the ultraviolet absorber may be, for example, an average particle size obtained by performing cumulative analysis using a dynamic structure factor obtained by a dynamic scattering method using a particle size distribution analyzer (ELSZneo, a Zeta Potential / Particle Size / Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source.

[0062] (Zeta potential)

[0063] If the absolute value of the zeta potential of the second particles is large, the image fixability is improved. This is believed to be because a large absolute value of the zeta potential of the second particles improves the dispersibility of the second particles, thereby further enhancing the effect of the second particles in improving the image fixability. Based on this, the absolute value of the zeta potential of the second particles can be greater than the absolute value of the zeta potential of the first particles. In other words, the ratio of the absolute value of the zeta potential of the second particles to the absolute value of the zeta potential of the first particles (absolute value of the zeta potential of the second particles / absolute value of the zeta potential of the first particles) can be greater than 1. Furthermore, in order to further improve the dispersibility and fixability, the ratio (absolute value of the zeta potential of the second particles / absolute value of the zeta potential of the first particles) can be greater than 1.1 and less than 1.3. Furthermore, the absolute value of the zeta potential of the second particles can be 50 mV or greater to improve dispersibility and fixability, and can be 55 mV or greater and 60 mV or less to further improve dispersibility and fixability. Examples of the zeta potential include values measured using an electrophoretic light scattering method (laser Doppler method). Specifically, values measured using a zeta potential meter based on the electrophoretic light scattering method (laser Doppler method) using a solution obtained by diluting the particles (the first particles or the second particles) 5000 times with water. Examples of zeta potential meters include the ELSZneo Zeta Potential / Particle Size / Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd.

[0064] (Other ingredients)

[0065] The inkjet ink may further contain components other than the first particles, the second particles, the ultraviolet absorber, and the aqueous medium (other components). Examples of the other components include components added to the inkjet ink, such as penetrants, surfactants, pH adjusters, preservatives, mildew inhibitors, anti-desiccant (humectant), chelating agents, defoaming agents, deoxidizers, conductivity-imparting agents, infrared absorbers, and anti-curling agents.

[0066] (use)

[0067] The inkjet ink is used when forming images using an inkjet recording device. As mentioned above, the inkjet ink has excellent quick-drying and fixing properties. Therefore, using the inkjet ink when forming images using an inkjet recording device can produce images with high fixing properties while suppressing the occurrence of problems that may arise when the inkjet ink adheres to the printing medium. The printing medium for forming images using the inkjet ink is not particularly limited; examples include paper, film, and fabric. Examples of paper include plain paper, offset paper, matte paper, cast-coated paper, and photo paper. Examples of film include resins such as polyethylene terephthalate (PET) film. Examples of fabric include woven fabrics, knitted fabrics, and non-woven fabrics. Because the inkjet ink has excellent quick-drying properties, it can properly form images even on printing media with low ink permeability. For this reason, the printing medium may also be the film. That is, the inkjet ink can also be used when forming an image on a film using an inkjet recording apparatus.

[0068] [Inkjet Recording Device]

[0069] As long as the inkjet ink can be used to form an image, the inkjet recording device used to form the image is not particularly limited. As an example of the inkjet recording device, the following can be cited: Figure 1 The inkjet recording device shown in FIG. Figure 1 It is a schematic diagram showing a configuration of an example of an inkjet recording apparatus 10 according to an embodiment of the present invention.

[0070] like Figure 1 As shown, the inkjet recording device 10 includes a discharge unit 12 having at least one inkjet head 21; a transport unit 11 that transports a print medium (printed material) 101 to which inkjet ink discharged from the inkjet head 21 is applied; and an ultraviolet irradiation unit 14 that irradiates ultraviolet light onto the print medium 101 to which the inkjet ink is applied. The inkjet recording device 10 may further include a first heating unit 13 that heats the print medium 101 before the inkjet ink discharged from the discharge unit 12 is applied; and a second heating unit 15 that heats the print medium 101 after the inkjet ink discharged from the discharge unit 12 is applied. The inkjet recording device 10 also includes a control unit 16 that controls the transport unit 11, the discharge unit 12, the first heating unit 13, the ultraviolet irradiation unit 14, the second heating unit 15, and the like.

[0071] The transport unit 11 transports the print medium 101 from the supply roller 11A to the recovery roller 11B. The inkjet recording device 10 includes the ejection unit 12, the first heating unit 13, the ultraviolet irradiation unit 14, the second heating unit 15, and the like along a transport path for the print medium 101 by the transport unit 11. The supply roller 11A supplies the print medium 101, to which inkjet ink ejected from the inkjet head 21 is applied, to the ejection unit 12. The recovery roller 11B recovers the print medium 101 supplied to the ejection unit 12. The transport unit 11 may include rollers 19A to 19D for causing the print medium 101 to pass through a predetermined transport path when transporting the print medium 101 from the supply roller 11A to the recovery roller 11B. The supply roller 11A, the recovery roller 11B, and the rollers 19A to 19D may be driving rollers or driven rollers as long as they can convey the print medium 101 from the supply roller 11A to the recovery roller 11B.

[0072] Generally speaking, the faster the print medium is transported, the higher the printing speed. However, this results in incomplete drying of the inkjet ink deposited on the print medium, which can lead to reduced image quality and a tendency for jetting fluctuations to occur. The inkjet ink of this embodiment has excellent quick-drying properties, so using this inkjet ink can suppress degradation of the image quality even when the print medium is transported at a high speed. Furthermore, since the inkjet ink of this embodiment tends to reduce jetting fluctuations, using this inkjet ink, particularly an inkjet ink that reduces jetting fluctuations, can suppress jetting fluctuations even when the print medium is transported at a high speed. The transport speed of the above-mentioned printing medium 101 in the above-mentioned transport section 11 is not particularly limited. However, from the perspective of being able to suppress the reduction in image quality and the occurrence of ejection fluctuations of the formed image by using the inkjet ink of this embodiment as described above, it can be higher, for example, it can be greater than 80 m / min and less than 120 m / min, and more specifically, it can be 100 m / min.

[0073] The print medium 101 transported by the transport unit 11 may be in the form of a long strip or a sheet. If the print medium 101 is in the form of a sheet, the transport unit 11 may include a transport belt. In this case, the transport unit 11 can transport the print medium 101 by placing the print medium 101 on the transport belt and transporting the transport belt in this state. As mentioned above, the print medium 101 may be paper or cloth. However, since the inkjet ink of this embodiment has excellent quick-drying properties, it may also be a print medium with low permeability, specifically, a film.

[0074] The ejection unit 12 ejects droplets of inkjet ink toward the printing medium 101, so that the inkjet ink adheres to the printing medium 101. The ejection unit 12 includes at least one inkjet head 21 facing the printing medium 101 and directly responsible for ejecting the ink, and an ink cartridge 17 storing the inkjet ink supplied to the inkjet head 21. The inkjet head 21 ejects the inkjet ink supplied from the ink cartridge 17 toward the printing medium 101. The inkjet head 21 is held in a manner such that an ejection surface 21a for ejecting the inkjet ink corresponds to the printing medium 101. The inkjet head 21 is as shown in FIG. Figure 2 As shown, a plurality of ejection ports 21 b for ejecting inkjet ink onto the printing medium 101 are formed on the ejection surface 21 a .

[0075] Generally speaking, the smaller the inkjet head's ejection orifice, the smaller the ink droplets ejected. While this allows for high-definition images, it also tends to cause ejection fluctuations. Since the inkjet ink of this embodiment tends to reduce ejection fluctuations, using this embodiment, particularly an inkjet ink that reduces ejection fluctuations, can suppress ejection fluctuations even when the inkjet head has a small ejection orifice. The diameter R of the ejection orifice 21b is not particularly limited as long as it can eject the inkjet ink. However, to suppress ejection fluctuations as described above using the inkjet ink of this embodiment, the diameter R can be relatively small, for example, from 10 μm to 15 μm, and more specifically, 12 μm.

[0076] Generally speaking, a higher drive frequency (ejection frequency) for ejecting inkjet ink results in a higher printing speed. However, this can lead to incomplete drying of the inkjet ink deposited on the print medium, resulting in reduced image quality and a tendency for ejection fluctuations to occur. Since the inkjet ink of this embodiment has excellent quick-drying properties, using this inkjet ink can suppress degradation of the image quality even at high drive frequencies. Furthermore, since the inkjet ink of this embodiment tends to reduce ejection fluctuations, using this inkjet ink, particularly one that reduces ejection fluctuations, can suppress the occurrence of ejection fluctuations even at high drive frequencies. The drive frequency at which the ejection unit 12 ejects the inkjet ink is not particularly limited; however, to suppress degradation of the image quality and the occurrence of ejection fluctuations as described above, the drive frequency can be relatively high, for example, from 60 kHz to 100 kHz.

[0077] It should be noted that the image can be divided into multiple sections (e.g., in a grid pattern), and printing can be performed in each section depending on whether pixels (dots) are formed. Alternatively, printing can be performed by forming pixels of varying sizes in stages. One or more droplets are ejected from the ejection orifice 21b to form one pixel. The reciprocal of the period during which droplets forming one pixel are ejected from the ejection orifice 21b is the driving frequency.

[0078] The first heating unit 13 heats the print medium 101 to promote evaporation of the aqueous medium contained in the inkjet ink adhered to the print medium 101. The first heating unit 13 may include a first heating roller 13A that contacts the print medium 101 and directly heats the print medium 101. The first heating roller 13A heats the print medium 101 and also functions as a roller in the transport unit 11. Alternatively, the first heating unit 13 may heat the print medium 101 by blowing hot air toward the print medium 101, instead of or in addition to the heating by the first heating roller 13A. The heating of the print medium 101 by the first heating unit 13 may be performed before, after, or both. That is, the first heating unit 13 may be provided on the upstream side of the ejection unit 12 in the conveyance direction of the printing medium 101 , on the downstream side, or both.

[0079] The ultraviolet irradiation unit 14 irradiates the inkjet ink adhered to the print medium 101 with ultraviolet rays (UV), heating the inkjet ink. The inkjet ink of this embodiment contains not only the pigment but also the ultraviolet absorber, making it easily heated. This heating melts the first resin contained in the first particles and the second resin contained in the second particles in the inkjet ink. The melted resins then solidify, fixing the image formed by the pigment in the inkjet ink on the print medium 101. Furthermore, the ultraviolet irradiation unit 14 includes at least a light source 14A for irradiating ultraviolet rays. Since the ultraviolet irradiation unit 14 irradiates the inkjet ink adhered to the print medium 101 with ultraviolet rays, the ultraviolet irradiation unit 14 irradiates the inkjet ink adhered to the print medium 101 after the inkjet ink adheres to the print medium 101. That is, the ultraviolet irradiation unit 14 is provided on the downstream side of the ejection unit 12 in the conveyance direction of the printing medium 101 .

[0080] The second heating unit 15 heats the inkjet ink adhered to the print medium 101 by heating the print medium 101. The heating by the second heating unit 15 assists in melting the first and second resins by the ultraviolet irradiation unit 14. Because the second heating unit 15 assists in melting the first and second resins by the ultraviolet irradiation unit 14, it is located near the ultraviolet irradiation unit 14. For example, the second heating unit 15 is located on the side of the print medium 101 opposite the ultraviolet irradiation unit 14. The second heating unit 15 may include a second heating roller 15A that contacts the print medium 101 and directly heats it. The second heating roller 15A not only heats the print medium 101 but also functions as a roller in the transport unit 11. Alternatively, the second heating unit 15 may heat the print medium 101 by blowing hot air onto the print medium 101, instead of, or in addition to, heating by the second heating roller 15A.

[0081] The control unit 16 controls the transport unit 11, the ejection unit 12, the first heating unit 13, the ultraviolet irradiation unit 14, the second heating unit 15, and the like. Specifically, the control unit 16 also controls the transport speed of the print medium 101 in the transport unit 11 and the drive frequency of the inkjet ink ejected by the ejection unit 12. The control unit 16 includes a computer. Although not specifically shown, the control unit 16 includes, for example, a CPU (central processing unit), ROM (read only memory), RAM (random access memory), and an external storage device.

[0082] The inkjet recording device is not particularly limited as long as it can form an image using the inkjet ink as described above. Figure 1 The inkjet recording device shown can fix a high-quality image on the above-mentioned printing medium using the above-mentioned inkjet ink. Specifically, it can be as follows Figure 2 The image is fixed as shown. Figure 2 This is a schematic diagram for explaining the fixing of an image formed using the inkjet ink according to an embodiment of the present invention. Specifically, the fixing is explained by giving the first state S1 to the fifth state S5. Figure 2 This is a schematic diagram showing that the number and size of components constituting inkjet ink are different from the actual ones.

[0083] First, the first state S1 is the state of the inkjet ink 103 while being held by the inkjet head 21 (i.e., before being ejected). The inkjet ink 103 comprises the first particles 105, the second particles 106, and the ultraviolet absorber 107 dispersed in the aqueous medium 104. Specifically, the inkjet ink 103 includes the first particles 105, the second particles 106, the ultraviolet absorber 107, and the aqueous medium 104. Furthermore, the first particles 105 include the pigment 108 and the first resin 109. More specifically, the first particles 105 are preferably a pigment dispersion in which the first resin 109 adheres to the surface of the pigment 108, and the pigments 108 are prevented from agglomerating.

[0084] The second state S2 is the state (state of the droplets) of the inkjet ink 103 as it flies from the inkjet head 21 toward the print medium 101 (i.e., after being ejected and before impacting). The inkjet ink in the second state S2 (such as the composition ratio and composition state) is essentially the same as that in the first state S1.

[0085] The third state S3 is the state of the inkjet ink 103 after a certain period of time has passed since it was attached to the print medium 101. In this state, the aqueous medium 104 gradually evaporates. Since the print medium 101 is heated by the first heating unit 13, the heat is transferred to the inkjet ink 103, thereby promoting the evaporation of the aqueous medium 104.

[0086] The fourth state S4 is the state of the inkjet ink 103 immediately before being irradiated with ultraviolet light by the ultraviolet irradiation unit 14. In this state, the evaporation of the aqueous medium 104 has advanced compared to the third state S3. For example, the evaporation of the aqueous medium 104 may be complete. When the evaporation of the aqueous medium 104 is complete, components other than the aqueous medium 104 in the inkjet ink 103 remain on the print medium 101. Specifically, the first particles 105, the second particles 106, and the ultraviolet absorber 107 remain.

[0087] The fifth state S5 is the state of the inkjet ink 103 when irradiated with ultraviolet light by the ultraviolet irradiation unit 14. In this state, the pigment 108 and the ultraviolet absorber 107 absorb ultraviolet light and generate heat. This heat melts the first resin contained in the first particles 105 and the second resin contained in the second particles 106. When the ultraviolet irradiation ends, the temperature of the inkjet ink 103 drops, and the first resin contained in the first particles 105 and the second resin contained in the second particles 106 solidify. The solidified resin 110 fixes the image formed by the pigment 108. At this point, the pigment 108 is primarily covered by the second resin.

[0088] While this specification discloses various types of technologies as described above, the main technologies are summarized below.

[0089] The inkjet ink of the first embodiment includes first particles containing a pigment and a first resin, second particles containing a second resin, an ultraviolet absorber, and an aqueous medium. The average particle size of the second particles is smaller than that of the first particles.

[0090] Regarding the inkjet ink of the second embodiment, in the inkjet ink of the first embodiment, the particle size fluctuation of the second particles is 7 nm or less in terms of standard deviation σ.

[0091] Regarding the inkjet ink of the third embodiment, in the inkjet ink of the first or second embodiment, the weight average molecular weight of the second resin is 300,000 or more and 1,500,000 or less.

[0092] The inkjet ink of a fourth embodiment is the inkjet ink of any one of the first to third embodiments, wherein the concentration of coarse particles of the first particles having a particle size of 2 μm to 10 μm is 70,000 particles / mL or less.

[0093] Regarding the inkjet ink of a fifth aspect, in the inkjet ink of any one of the first to fourth aspects, the absolute value of the zeta potential of the second particles is larger than the absolute value of the zeta potential of the first particles.

[0094] Regarding the inkjet ink of a sixth aspect, in the inkjet ink of any one of the first to fifth aspects, the absolute value of the zeta potential of the second particles is 50 mV or more.

[0095] In the inkjet ink according to a seventh aspect, in the inkjet ink according to any one of the first to sixth aspects, an average particle size of the ultraviolet absorber is equal to or smaller than an average particle size of the first particles.

[0096] An inkjet ink according to an eighth aspect is an inkjet ink comprising first particles containing a pigment and a first resin, a UV absorber, and an aqueous medium, wherein the average particle size of the UV absorber is equal to or smaller than the average particle size of the first particles.

[0097] The inkjet ink of a ninth aspect is the inkjet ink of the eighth aspect, further comprising second particles containing a second resin.

[0098] The inkjet ink according to a tenth aspect is the inkjet ink according to any one of the first to ninth aspects, wherein the content of the ultraviolet absorber is 0.1% by mass or more and 1.6% by mass or less.

[0099] An eleventh embodiment of the inkjet ink is an inkjet ink comprising first particles containing a pigment and a first resin, a UV absorber, and an aqueous medium, wherein the UV absorber content is 0.1% by mass or more and 1.6% by mass or less.

[0100] The inkjet ink according to the twelfth aspect is the inkjet ink according to the eleventh aspect, further comprising second particles containing a second resin.

[0101] An inkjet head according to a thirteenth aspect includes a plurality of ejection orifices for ejecting the inkjet ink according to any one of the first to twelfth aspects onto a printing medium, wherein the diameter of the ejection orifices is 10 to 15 μm.

[0102] The inkjet recording device of the 14th method includes: a discharge section having at least one inkjet head for discharging inkjet ink of any one of the 1st to 12th methods onto a printing medium; a transport section for transporting a printing medium to which the inkjet ink discharged from the above-mentioned inkjet head is attached; and an ultraviolet irradiation section for irradiating ultraviolet rays to the printing medium to which the above-mentioned inkjet ink is attached.

[0103] The inkjet recording apparatus according to a fifteenth aspect is the inkjet recording apparatus according to the fourteenth aspect, wherein a transport speed of the printing medium is 80 m / min or more and 120 m / min or less.

[0104] The inkjet recording apparatus according to a sixteenth aspect is the inkjet recording apparatus according to the fourteenth or fifteenth aspect, wherein a driving frequency for ejecting the inkjet ink is 60 kHz or more and 100 kHz or less.

[0105] The inkjet recording apparatus according to a seventeenth aspect is the inkjet recording apparatus according to any one of the fourteenth to sixteenth aspects, wherein the transport unit transports a film as the printing medium.

[0106] According to the present invention, an inkjet ink having excellent quick-drying properties and fixing properties can be provided. In addition, according to the present invention, an inkjet head and an inkjet recording apparatus using the inkjet ink can be provided.

[0107] Hereinafter, the present invention will be described in more detail with reference to Examples; however, the scope of the present invention is not limited to these Examples.

[0108] Example

[0109] [Production Example 1: Synthesis of First Resin]

[0110] The first resin used in this example was synthesized. Specifically, the first resin was synthesized by the following method.

[0111] Styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), butyl acrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), methacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and methoxy polyethylene glycol methacrylate (BLEMMER PME-200 manufactured by NOF Corporation) were mixed at a mass ratio of 65:20:5:10 to prepare 115 parts by mass of a monomer mixture liquid.

[0112] 10% (11.5 parts by mass) of the monomer mixture, 18 parts (2-mercaptoethanol) as a chain transfer agent, and 0.03 parts (2-mercaptoethanol) as a chain transfer agent were added to a reaction vessel, mixed, and thoroughly purged with nitrogen. Separately, a mixture of the remaining 90% (103.5 parts) of the monomer mixture, 0.27 parts (2,4-dimethylvaleronitrile) as a polymerization initiator, 42 parts (2,2-azobis(2,4-dimethylvaleronitrile)) (Fujifilm Wako Pure Chemical Industries, Ltd.)) as a polymerization initiator was added to a dropping funnel. The mixture in the reaction vessel was then heated to 75°C while stirring under a nitrogen atmosphere. The mixture in the dropping funnel was then added dropwise to the reaction vessel over 3 hours. After 2 hours at 75°C from the completion of the dropwise addition, a solution consisting of 3 parts (2,4-dimethylvaleronitrile) dissolved in 5 parts (2,2-azobis(2,4-dimethylvaleronitrile)) was added to the reaction vessel. Then, the mixture was aged at 75° C. for 2 hours and at 80° C. for 2 hours. Thereafter, 50 parts by mass of methyl ethyl ketone was added to the reaction container.

[0113] In this manner, a solution of the first resin used in this example was obtained. The weight-average molecular weight of the obtained first resin was measured by GPC analysis, and the result was that the weight-average molecular weight of the first resin was approximately 15,000. Furthermore, the glass transition temperature (Tg) of the first resin was measured by DSC analysis, and the result was that the glass transition temperature (Tg) of the first resin was approximately 60°C. The solid content concentration in the first resin solution was approximately 45% by mass.

[0114] [Production Example 2: Production of First Particles]

[0115] The first particles used in this example were produced. Specifically, the first particles were produced by the following method.

[0116] 95.2 parts by mass of the first resin solution obtained in Production Example 1 were dissolved in 53.9 parts by mass of methyl ethyl ketone. 15.0 parts by mass of a 5N aqueous sodium hydroxide solution and 0.5 parts by mass of a 25% by mass ammonia solution were added as neutralizers, followed by 341.3 parts by mass of ion-exchanged water. To the resulting liquid, 100 parts by mass of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) was further added as a carbon black pigment to produce a pigment mixture. The degree of neutralization was approximately 79 mol%.

[0117] The pigment mixture was mixed for 1 hour using a disperser blade at 7000 rpm and 20° C. The dispersion was dispersed using a bead mill (LMZ015 manufactured by Ashizawa Finetech Co., Ltd.) with 15 passes using a bead mill with a diameter of 0.3 mm and a rotor speed of 3000 rpm.

[0118] Methyl ethyl ketone was removed from the resulting dispersion under reduced pressure at 60°C, and water was further removed. The dispersion from which the methyl ethyl ketone and water had been removed was then centrifuged, and the liquid layer was filtered through a filter (microsyringe filter manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion containing the black pigment and the first resin.

[0119] To 100 parts by mass of the obtained aqueous dispersion were added 0.45 parts by mass of an epoxy crosslinking agent (trimethylolpropane polyglycidyl ether, DENACOL EX321L manufactured by Nagase ChemteX Co., Ltd., epoxy equivalent: 130) and 15.23 parts by mass of ion-exchanged water, and the mixture was heated at 70° C. for 3 hours while stirring.

[0120] After the heat-treated aqueous dispersion was cooled to room temperature, the liquid layer was filtered through a filter (microsyringe filter manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion in which the first particles containing the black pigment and the first resin were dispersed.

[0121] The resulting aqueous dispersion (in which the first particles containing the black pigment and the first resin are dispersed) had a solids concentration of 22% by weight. The pigment incorporation rate was 68.76% by mass. The contents of the black pigment, first resin, epoxy crosslinking agent, and ion-exchanged water in the aqueous dispersion were 15.13 parts by mass, 6.48 parts by mass, 0.39 parts by mass, and 78.00 parts by mass, respectively, per 100 parts by mass of the aqueous dispersion. The average particle size of the first particles was determined by dynamic scattering analysis using a particle size distribution analyzer (ELSZneo, Zeta Potential / Particle Size / Molecular Weight Measurement System, manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source, and the dynamic structure factor was determined by cumulative analysis. The result was 100 nm. The aqueous dispersion had a viscosity of 4.8 mPa·s and a pH of 9.7.

[0122] [Production Example 3: Production of Aqueous Dispersion Containing Second Particles]

[0123] Styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), butyl acrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), methacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and methoxy polyethylene glycol methacrylate (BLEMMER PME-200, manufactured by NOF Corporation) were mixed in a 1000 mL separable flask at a mass ratio of 80:5:10:5 to prepare 200 parts by mass of a monomer mixture. To this monomer mixture were added 18.5 parts by mass of an emulsifier (LATEMUL E118B, manufactured by Kao Corporation, 26% active ingredient), 96 parts by mass of ion-exchanged water, and potassium persulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the mixture was stirred with a stirring blade (300 rpm) to obtain a monomer emulsion.

[0124] 4.6 parts by mass of LATEMUL E118B, 186 parts by mass of ion-exchanged water, and 0.08 parts by mass of potassium persulfate were added to a reaction vessel and the atmosphere was purged with nitrogen. The liquid in the reaction vessel was heated to 80°C while stirring with a stirring blade (200 rpm) under a nitrogen atmosphere. The monomer emulsion was then added dropwise to the reaction vessel using a dropping funnel over 3 hours and allowed to react. This procedure yielded an aqueous dispersion containing dispersed second particles containing the second resin.

[0125] The resulting aqueous dispersion (aqueous dispersion in which second particles containing the second resin were dispersed) had a solids concentration of approximately 42% by weight. The average particle size of the second particles, determined by image analysis of an image obtained by observing the second particles, after drying and removing the aqueous medium, using a scanning electron microscope (SEM), was 100 nm.

[0126] [Manufacturing Example 4: Manufacturing of Inkjet Ink]

[0127] 508.9 g of the aqueous dispersion (solid content: 22.0 mass %) of the first particles obtained in Production Example 2, in which the black pigment and the first resin were dispersed, 48.3 g of the aqueous dispersion (solid content: 41.6 mass %) of the second particles obtained in Production Example 3, 44.0 g of diethylene glycol monoisobutyl ether (boiling point: 230° C.), 286.0 g of propylene glycol (boiling point: 188° C.), 5.5 g of a silicone surfactant (polyether-modified silicone, KF-6011 manufactured by Shin-Etsu Chemical Co., Ltd., HLB: 14.5), 50.9 g of a benzotriazole-based UV absorber (2(2'-hydroxy-5'-methylphenyl)benzotriazole, Tinuvin P manufactured by BASF) as a UV absorber, and 207.3 g of ion-exchanged water were mixed. The resulting mixed liquid was filtered through a filter (microsyringe filter manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to obtain a black inkjet ink. The average particle size of the ultraviolet absorber was determined by cumulant analysis using a dynamic scattering method using a particle size distribution analyzer (ELSZneo Zeta Potential / Particle Size / Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source to determine the dynamic structure factor. The result was 60 nm.

[0128] The resulting inkjet ink contained 508.9 parts by mass of the aqueous dispersion containing the first particles, 48.3 parts by mass of the aqueous dispersion containing the second particles, 286.0 parts by mass of diethylene glycol monoisobutyl ether, 5.5 parts by mass of a silicone surfactant, and 50.9 parts by mass of a benzotriazole ultraviolet absorber, respectively. The average particle size of the particles in the inkjet ink was 98.8 nm. The inkjet ink had a viscosity of 5.2 mPa·s at 32°C, a dynamic surface tension of 28.9 mN / m, and a pH of 9.1.

[0129] [Relationship between the average particle size of the first particles and the average particle size of the second particles]

[0130] Then, the relationship between the average particle size of the first particles and the average particle size of the second particles was studied. Specifically, except that the first particles having the average particle size shown in Table 1 and the second particles having the average particle size shown in Table 1 were used, an inkjet ink was produced in the same manner as in the above-mentioned Production Example 4. In addition, the aqueous dispersion dispersed with the first particles produced in the above-mentioned Production Example 2 was treated with the above-mentioned bead mill, and its treatment conditions were adjusted, or the number of passes through the above-mentioned filter was adjusted, thereby preparing the first particles having the respective average particle sizes shown in Table 1. In addition, when producing the aqueous dispersion dispersed with the second particles produced in the above-mentioned Production Example 3, the stirring conditions of the stirring blades were adjusted, or the number of passes through the above-mentioned filter was adjusted, thereby preparing the second particles having the respective average particle sizes shown in Table 1. The zeta potentials of the first particles having an average particle size of 100 μm and the second particles having an average particle size of 80 μm were measured using a zeta potential meter (Zeta Potential / Particle Size / Molecular Weight Measurement System ELSZneo manufactured by Otsuka Electronics Co., Ltd.) and were -45 mV and -60 mV, respectively.

[0131] Each inkjet ink obtained in this manner was evaluated as follows.

[0132] (Weight change due to heating)

[0133] Each inkjet ink was applied to a film using a bar coater, and the weight of the inkjet ink applied to the film was measured (weight before heating). The film coated with the inkjet ink was then dried in a drier at 40°C for 40 minutes, and the weight of the dried inkjet ink was measured (weight after heating). The weight change rate was calculated based on the weight before heating and the weight after heating. A greater weight change rate indicates better quick-drying properties of the inkjet ink. For example, a value of 54% or greater was rated "○," while a value of less than 54% was rated "×."

[0134] (Tape peeling)

[0135] Each inkjet ink was applied to a film using a bar coater to form a black image. The resulting black image was subjected to a cross-cut test (according to JIS K5600-5-6). The less the image peeled during the cross-cut test, the better the image's fixability. For example, 25 print media printed with an image were subjected to the cross-cut test. If two or fewer sheets peeled (i.e., "2 / 25" or less), the result was rated "○," while if three or more sheets peeled (i.e., "3 / 25" or more), the result was rated "X."

[0136] If both "weight change due to heating" and "tape peeling" are "○", then even if Figure 1The inkjet recording device medium shown in the figure has an inkjet head with a nozzle diameter of 12 μm. Using the above-mentioned inkjet inks, a black image with excellent fixability can be appropriately printed under the conditions of a printing medium transport speed of 100 m / min and a driving frequency (ejection frequency) for ejecting the inkjet ink of 78.74 kHz.

[0137] Table 1 shows the results.

[0138]

[0139] As shown in Table 1, when the average particle size of the second particles is smaller than that of the first particles, an inkjet ink having excellent quick-drying and fixing properties can be obtained compared to a situation where the average particle size of the first particles is greater than or equal to that of the first particles. Furthermore, when the first particles having an absolute value of 45 mV of zeta potential and the second particles having an absolute value of 60 mV of zeta potential are used, an inkjet ink having excellent quick-drying and fixing properties can also be obtained. As shown in the results, an absolute value of the zeta potential of the second particles greater than that of the first particles and an absolute value of 50 mV of the zeta potential of the second particles contribute to an improvement in quick-drying and fixing properties.

[0140] [Content of Coarse Particles in the First Particle Size, Particle Size Fluctuation σ of the Second Particles, and Weight Average Molecular Weight of the Second Resin]

[0141] Next, the effects of the coarse particle content in the first particle size, the particle size fluctuation σ of the second particles, and the weight-average molecular weight of the second resin were examined for first particles having an average particle size of 100 nm and second particles having an average particle size of 80 nm. Specifically, inkjet inks were produced in the same manner as in Production Example 4, except that the first and second particles having the coarse particle content in the first particle size, the particle size fluctuation σ of the second particles, and the weight-average molecular weight of the second resin shown in Table 2 were used. Furthermore, the aqueous dispersion containing the first particles produced in Production Example 2 was treated using the bead mill described above, and the treatment conditions or the number of passes through the filter were adjusted to prepare first particles having the coarse particle content shown in Table 2. It should be noted that the coarse particles herein are those having a particle size of 2 μm or greater and 10 μm or less. Furthermore, when preparing the aqueous dispersion containing the second particles prepared in Production Example 3, the stirring conditions using the stirring blade or the number of passes through the filter were adjusted to prepare second particles having the various particle size fluctuations σ shown in Table 2. Subsequently, the synthesis conditions for the second resin in Production Example 3 were adjusted to prepare second particles containing the second resin having the weight-average molecular weight shown in Table 2. It should be noted that in this study example, since first particles having an average particle size of 100 nm and second particles having an average particle size of 80 nm were used, quick-drying properties and fixing properties were excellent.

[0142] Each inkjet ink obtained in this manner was evaluated as follows.

[0143] (Fluctuation of ejection velocity)

[0144] Each inkjet ink was ejected from a 1200 dpi printhead manufactured by Kyocera Corporation. The ejected droplets were observed using an inkjet droplet observation device (JetXpert manufactured by imageXpert Corporation). The fluctuation (standard deviation σ) of the droplet ejection velocity was measured. If the fluctuation (ejection fluctuation) was 0.6 m / s or less, it was evaluated as "○", and if it was greater than 0.6 m / s, it was evaluated as "×". If the ejection fluctuation is small, a suitable image can be formed even at high-speed printing. For example, if the above evaluation is "○", even if Figure 1 The inkjet recording device medium shown in the figure has an inkjet head with a nozzle diameter of 12 μm, and can also print black images using the above-mentioned inkjet inks under the conditions of a printing medium conveying speed of 100 m / min and a driving frequency (ejection frequency) for ejecting the inkjet ink of 78.74 kHz.

[0145] The average ejection velocity of the droplets is about 9 m / s. Alternatively, the ejection velocity may be 6 m / s to 15 m / s.

[0146] Table 2 shows the results.

[0147]

[0148] Table 2 shows that when the particle size fluctuation of the second particles, as measured by standard deviation σ, is 7 nm or less, discharge fluctuation is reduced compared to when the particle size exceeds 7 nm. Furthermore, when the weight-average molecular weight of the second resin is 300,000 to 1,500,000, discharge fluctuation is reduced compared to when the molecular weight exceeds this range. It is also shown that when the coarse particles with a particle size of 2 μm to 10 μm in the first particles are 70,000 or less / mL, discharge fluctuation is reduced compared to when the particle size exceeds this value.

[0149] [Average particle size of UV absorber]

[0150] Next, the effect of the average particle size of a UV absorber on an inkjet ink containing first particles having an average particle size of 100 nm and second particles having an average particle size of 80 nm was studied. Specifically, a UV absorber having the average particle size shown in Table 3 was prepared, and an inkjet ink was produced in the same manner as in Production Example 4, except that this UV absorber, first particles having the average particle size shown in Table 3, and second particles having the average particle size shown in Table 3 were used. It should be noted that in this research example, the use of first particles having an average particle size of 100 nm and second particles having an average particle size of 80 nm resulted in excellent quick-drying properties and fixing properties.

[0151] Each inkjet ink obtained in this manner was evaluated as follows.

[0152] (Weather resistance)

[0153] Each inkjet ink was applied to OK-coated paper, serving as the printing medium, using a bar coater to form a black image. The optical density (OD) of the resulting black image was measured using an X-Rite spectrodensitometer. The black image was then subjected to a xenon lamp accelerated weathering tester (Q-SUN Xe-3, manufactured by Q-Lab) at an illumination of 100,000 Lux / hour for four days. The optical density of the black image after the xenon lamp irradiation test was measured using a spectrodensitometer to determine its rate of change. This rate of change represents the rate of change in hue. The smaller the absolute value, the higher the weather resistance. For example, an absolute value of 6% or less (e.g., -6% or greater) is evaluated as "○," while an absolute value exceeding 6% (e.g., less than -6%) is evaluated as "×."

[0154] The results are shown in Table 3.

[0155]

[0156] As shown in Table 3, when the average particle size of the ultraviolet absorber is less than or equal to the average particle size of the first particles, an image with excellent weather resistance can be formed compared to when the average particle size of the first particles is larger. In other words, it can be seen that an image with excellent quick-drying properties, excellent fixability, and excellent weather resistance can be formed.

[0157] The above embodiment is an example of using the above-mentioned first particles obtained in the above-mentioned Manufacturing Example 2, which contain the above-mentioned black pigment and the above-mentioned first resin, as the above-mentioned first particles. Below, the case of using pigments other than black pigment (pigment for cyan, pigment for magenta, and pigment for yellow) instead of the above-mentioned black pigment is also studied.

[0158] [blue]

[0159] The same procedure as in the example using the first particles containing the black pigment and the first resin was performed except that the first particles containing a cyan pigment and the first resin manufactured as shown below were used instead of the first particles containing the black pigment and the first resin.

[0160] (First Particles: Production of First Particles Containing a Cyan Pigment and the First Resin)

[0161] First particles containing the cyan pigment and the first resin were produced by the same method as in Production Example 2 (Production of First Particles), except that CI Pigment Blue 15:3 (PB15:3 manufactured by DIC Corporation) was used as the cyan pigment instead of the black pigment.

[0162] The solids concentration of the aqueous dispersion containing the first particles containing the cyan pigment and the first resin was 22% by weight. The pigment incorporation rate was 68.52% by mass. The contents of the cyan pigment, the first resin, the epoxy crosslinking agent, and the ion-exchanged water in the aqueous dispersion were 15.08 parts by mass, 6.46 parts by mass, 0.46 parts by mass, and 78.00 parts by mass, respectively, per 100 parts by mass of the aqueous dispersion. The average particle size of the first particles was determined by dynamic scattering analysis using a particle size distribution meter (ELSZneo, Zeta Potential / Particle Size / Molecular Weight Measurement System, manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source, and the dynamic structure factor was determined by cumulative analysis. The result was 100 nm. The viscosity of the aqueous dispersion was 4.2 mPa·s, and the pH was 9.6.

[0163] [Magenta]

[0164] The same procedure as in the example using the first particles containing the black pigment and the first resin was performed except that the first particles containing the magenta pigment and the first resin manufactured as shown below were used as the first particles instead of the first particles containing the black pigment and the first resin.

[0165] (First Particles: Production of First Particles Containing a Magenta Pigment and the First Resin)

[0166] First particles containing the magenta pigment and the first resin were produced by the same method as in Production Example 2 (Production of First Particles), except that CI Pigment Red 150 (PR150 manufactured by Fuji Pigments Co., Ltd.) was used as the magenta pigment instead of the black pigment.

[0167] The solids concentration of the aqueous dispersion containing the first particles containing the magenta pigment and the first resin was 22% by weight. The pigment incorporation rate was 68.52% by mass. The contents of the magenta pigment, the first resin, the epoxy crosslinking agent, and the ion-exchanged water in the aqueous dispersion were 15.08 parts by mass, 6.46 parts by mass, 0.46 parts by mass, and 78.00 parts by mass, respectively, per 100 parts by mass of the aqueous dispersion. The average particle size of the first particles was determined by dynamic scattering analysis using a particle size distribution meter (ELSZneo, Zeta Potential / Particle Size / Molecular Weight Measurement System, manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source, and the dynamic structure factor was determined by cumulative analysis. The result was 100 nm. The viscosity of the aqueous dispersion was 4.6 mPa·s, and the pH was 9.8.

[0168] [yellow]

[0169] The same procedure as in the example using the first particles containing the black pigment and the first resin was performed except that the first particles containing a yellow pigment and the first resin, produced as shown below, were used as the first particles instead of the first particles containing the black pigment and the first resin.

[0170] (First Particles: Production of First Particles Containing a Yellow Pigment and the First Resin)

[0171] First particles containing the yellow pigment and the first resin were produced by the same method as in Production Example 2 (Production of First Particles), except that CI Pigment Yellow 74 (PY74 manufactured by Dainichi Seika Industries, Ltd.) was used as the yellow pigment instead of the black pigment.

[0172] The solids concentration of the aqueous dispersion containing the first particles containing the yellow pigment and the first resin was 22% by weight. The pigment incorporation rate was 68.52% by mass. The yellow pigment, first resin, epoxy crosslinking agent, and ion-exchanged water in the aqueous dispersion were 15.08 parts by mass, 6.46 parts by mass, 0.46 parts by mass, and 78.00 parts by mass, respectively, per 100 parts by mass of the aqueous dispersion. The average particle size of the first particles was determined by dynamic scattering analysis using a particle size distribution meter (ELSZneo, Zeta Potential / Particle Size / Molecular Weight Measurement System, manufactured by Otsuka Electronics Co., Ltd.) using a helium-neon (HeNe) laser as a light source, and the dynamic structure factor was 100 nm. The viscosity of the aqueous dispersion was 4.5 mPa·s, and the pH was 9.6.

[0173] The above examples examined the use of first particles containing pigments other than black pigment (cyan, magenta, and yellow) and the first resin, instead of the first particles containing the black pigment and the first resin obtained in Production Example 2. The results showed that in all cases, the same results as in the example using the first particles containing the black pigment and the first resin were achieved. In other words, even when using cyan, magenta, and yellow pigments, the same results as when using black pigment were achieved. These results demonstrate that if the average particle size of the second particles is smaller than that of the first particles, an inkjet ink with excellent quick-drying and fixing properties can be obtained, regardless of the color of the pigment.

[0174] This application is based on Japanese patent application No. 2023-003921 filed on January 13, 2023, the contents of which are incorporated into this application.

[0175] To illustrate the present invention, the present invention has been appropriately and fully described above through the embodiments. However, those skilled in the art will recognize that the above embodiments can be easily modified and / or improved. Therefore, as long as the modifications or improvements implemented by those skilled in the art do not depart from the scope of the claims set forth in the claims, such modifications or improvements shall be construed as being included within the scope of the claims.

[0176] Industrial applicability

[0177] According to the present invention, an inkjet ink having excellent quick-drying properties and fixing properties can be provided. In addition, according to the present invention, an inkjet head and an inkjet recording apparatus using the inkjet ink can be provided.

[0178] Description of Reference Numerals

[0179] 10 Inkjet recording device, 11 Transport unit, 11A Supply roller, 11B Recovery roller, 12 Discharge unit, 13 First heating unit, 13A First heating roller, 14 Ultraviolet irradiation unit, 14A Light source, 15 Second heating unit, 15A Second heating roller, 16 Control unit, 17 Ink cartridge, 21 Inkjet head, 21a Discharge surface, 21b Discharge port, 101 Printing medium, 103 Inkjet ink, 104 Aqueous medium, 105 First particles, 106 Second particles, 107 Ultraviolet absorber, 108 Pigment, 109 First resin, 110 Resin.

Claims

1. An inkjet ink comprising first particles containing a pigment and a first resin, second particles containing a second resin, an ultraviolet absorber, and an aqueous medium. The average particle size of the second particles is smaller than the average particle size of the first particles.

2. The inkjet ink according to claim 1, wherein The particle size fluctuation of the second particles is 7 nm or less in terms of standard deviation σ.

3. The inkjet ink according to claim 1 or 2, wherein The second resin has a weight average molecular weight of 300,000 or more and 1,500,000 or less.

4. The inkjet ink according to any one of claims 1 to 3, wherein The first particles have a coarse particle size of 2 μm or more and 10 μm or less at a concentration of 70,000 particles / mL or less.

5. The inkjet ink according to any one of claims 1 to 4, wherein The absolute value of the zeta potential of the second particles is greater than the absolute value of the zeta potential of the first particles.

6. The inkjet ink according to any one of claims 1 to 5, wherein The absolute value of the zeta potential of the second particles is 50 mV or more.

7. The inkjet ink according to any one of claims 1 to 6, wherein The average particle size of the ultraviolet absorber is equal to or smaller than the average particle size of the first particles.

8. An inkjet ink comprising first particles containing a pigment and a first resin, an ultraviolet absorber, and an aqueous medium. The average particle size of the ultraviolet absorber is equal to or smaller than the average particle size of the first particles. 9 . The inkjet ink according to claim 8 , comprising second particles containing a second resin.

10. The inkjet ink according to any one of claims 1 to 9, wherein The content of the ultraviolet absorber is 0.1% by mass or more and 1.6% by mass or less.

11. An inkjet ink comprising first particles containing a pigment and a first resin, an ultraviolet absorber, and an aqueous medium. The content of the ultraviolet absorber is 0.1% by mass or more and 1.6% by mass or less. 12 . The inkjet ink according to claim 11 , comprising second particles containing a second resin.

13. An inkjet head comprising a plurality of ejection ports for ejecting the inkjet ink according to any one of claims 1 to 12 onto a printing medium. The diameter of the ejection port is 10 μm or more and 15 μm or less.

14. An inkjet recording device comprising: A discharge unit comprising at least one inkjet head for discharging the inkjet ink according to any one of claims 1 to 12 onto a printing medium; a transport unit that transports a printing medium to which the inkjet ink ejected from the inkjet head adheres; and The ultraviolet irradiation unit irradiates the printing medium to which the inkjet ink is attached with ultraviolet rays.

15. The inkjet recording apparatus according to claim 14, wherein The transport speed of the printing medium is 80 m / min or more and 120 m / min or less.

16. The inkjet recording apparatus according to claim 14 or 15, wherein The driving frequency for ejecting the inkjet ink is 60 kHz or more and 100 kHz or less.

17. The inkjet recording device according to any one of claims 14 to 16, wherein The transport unit transports a film as the printing medium.

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