Inkjet inks and inkjet recording devices

Abstract

To provide inkjet ink which can suppress occurrence of discharge deflection of ink from a recording head.SOLUTION: Inkjet ink contains a quinacridone pigment, a resin, and an aqueous medium. The resin contains an adsorbed resin adsorbed on the quinacridone pigment, and a non-adsorbed resin which is not adsorbed on the quinacridone pigment. A ratio of the non-adsorbed resin in the resin is more than 0 mass% and 40 mass% or less. The aqueous medium contains a first organic solvent having a boiling point of 180°C or higher and 280°C or lower. In the ultraviolet visible light absorption spectrum of 25 times dilution liquid of a supernatant obtained by subjecting the inkjet ink at 1,050,000 G for 3 hours to centrifugal treatment, absorbance of a predetermined peak is 0.15 or less. The predetermined peak is a maximum peak in a wavelength range of 400 nm or more and 490 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to inkjet ink and inkjet recording apparatus. [Background technology]

[0002] Inkjet inks require that the pigment be dispersed. The pigment dispersion composition described in Patent Document 1 disperses the pigment using at least one selected from the group consisting of pigment derivatives, pigment intermediates, dye derivatives, and dye intermediates, and a carbodiimide compound having at least one carbodiimide group. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2004 / 003085 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the pigment dispersion composition described in Patent Document 1 contains a pigment intermediate. The pigment intermediate can cause ejection irregularities when ink is ejected from the recording head of an inkjet recording device.

[0005] The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an inkjet ink that can suppress the occurrence of ejection distortion from the recording head, and an inkjet recording apparatus using this inkjet ink. [Means for solving the problem]

[0006] The inkjet ink according to the present invention contains a quinacridone pigment, a resin, and an aqueous medium. The resin includes an adsorbed resin adsorbed by the quinacridone pigment and an unadsorbed resin not adsorbed by the quinacridone pigment. The proportion of the unadsorbed resin in the total resin is greater than 0% by mass and 40% by mass or less. The aqueous medium contains a first organic solvent having a boiling point of 180°C or higher and 280°C or lower. In the ultraviolet-visible light absorption spectrum of a 25-fold diluted supernatant obtained by centrifuging the inkjet ink at 1,050,000 G for 3 hours, the absorbance of a predetermined peak is 0.15 or less. The predetermined peak is the maximum peak in the wavelength range of 400 nm to 490 nm.

[0007] The inkjet recording apparatus according to the present invention comprises a transport unit for transporting a recording medium and a recording head for ejecting ink onto the recording medium. The ink is the inkjet ink described above. [Effects of the Invention]

[0008] The inkjet ink and inkjet recording apparatus according to the present invention can suppress the occurrence of uneven ejection of inkjet ink from the recording head. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the ultraviolet-visible light absorption spectrum of a 25-fold dilution of the supernatant liquid. [Figure 2] This figure shows an example of an inkjet recording apparatus according to a second embodiment of the present invention. [Figure 3] This figure shows the underside of the recording head shown in Figure 2. [Figure 4] This diagram illustrates the operation of supplying the cleaning fluid. [Figure 5] This diagram illustrates the purging and wiping operations. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described. First, the terms used in this specification will be explained. The volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution measuring device ("Zetasizer Nano ZS" manufactured by Malvern) unless otherwise specified. The acid value is a value measured in accordance with "JIS (Japanese Industrial Standard) K0070: 1992" unless otherwise specified. The mass average molecular weight (Mw) is a value measured using gel permeation chromatography unless otherwise specified. In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". "Independently of each other" in the description of the formula means that the same group or different groups may be represented. Each component described in this specification may be used alone or in combination of two or more.

[0011] [First Embodiment: Ink for Inkjet] Hereinafter, the ink for inkjet of the first embodiment of the present invention (hereinafter, may be simply referred to as ink) will be described.

[0012] The ink of the first embodiment contains a quinacridone pigment, a resin, and an aqueous medium. The resin includes an adsorbed resin adsorbed on the quinacridone pigment and an unadsorbed resin not adsorbed on the quinacridone pigment. The proportion of the unadsorbed resin in the resin is more than 0% by mass and 40% by mass or less. The aqueous medium contains a first organic solvent having a boiling point of 180°C or higher and 280°C or lower. In the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant obtained by centrifuging the ink at 1,050,000 G for 3 hours, the absorbance of a predetermined peak is 0.15 or less. The predetermined peak is the maximum peak in the range of a wavelength of 400 nm or more and 490 nm or less.

[0013] Hereinafter, the "proportion of unadsorbed resin in the resin" may be referred to as the "unadsorbed resin ratio". The "first organic solvent" may be referred to as the "first solvent". The "supernatant obtained by centrifuging the ink at 1,050,000 G for 3 hours" may simply be referred to as the "supernatant". The "absorbance of a predetermined peak in the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant obtained by centrifuging the ink at 1,050,000 G for 3 hours" may be referred to as the "predetermined absorbance". In this specification, the "predetermined peak" is defined as the "maximum peak in the range of wavelengths from 400 nm to 490 nm in the ultraviolet-visible light absorption spectrum".

[0014] By having the above-described configuration, the ink of the first embodiment can suppress the occurrence of ink ejection unevenness from the recording head. The reason is presumed as follows.

[0015] First, to aid understanding, an outline of the method for synthesizing the quinacridone pigment will be described. The quinacridone pigment is, for example, a compound represented by formula (D). The quinacridone pigment is synthesized, for example, by carrying out the reactions represented by reaction formulas (r-a), (r-b), and (r-c).

[0016] [Chemical formula]

[0017] In formulas (A), (B), (C), and (D), R A , R B , R 1 , and R 2 each independently represents a monovalent group. Hereinafter, the "reactions represented by reaction formulas (r-a), (r-b), and (r-c)" may each be referred to as "reactions (r-a), (r-b), and (r-c)". Also, the "compounds represented by formulas (A), (B), (C), and (D)" may each be referred to as "compounds (A), (B), (C), and (D)". R 1 and R 2When it represents a methyl group, compound (D) becomes C.I. Pigment Red 122. R 1 and R 2 When they represent a hydrogen atom, compound (D) becomes C.I. Pigment Violet 19.

[0018] In the process of carrying out reactions (r-a), (r-b), and (r-c), intermediates, namely compounds (B) and (C), are formed. The above is an explanation of the outline of the method for synthesizing quinacridone pigments.

[0019] Intermediates (more specifically, compounds (B) and (C)) formed in the process of carrying out reactions (r-a), (r-b), and (r-c) may remain in the quinacridone pigment as impurities. When such a quinacridone pigment is contained in the ink, the ink also contains the intermediate. The polarity of the intermediate is relatively high. Therefore, when forming an image using an ink containing a quinacridone pigment, the intermediate may electrostatically adhere to the ejection surface of the recording head and the inner wall of the nozzle holes. The adhered intermediate is one of the causes of ink ejection irregularities from the recording head. Also, when the ink adhering to the ejection surface dries and thickens, aggregation of ink components may be caused by the intermediate contained in the ink, and aggregates may occur. The generated aggregates are also one of the causes of ink ejection irregularities from the recording head. Therefore, in the ink of the first embodiment, the predetermined absorbance of the 25-fold dilution of the supernatant is set to 0.15 or less. The predetermined peak is, for example, a peak derived from an intermediate (more specifically, compounds (B) and (C), etc.) for synthesizing a quinacridone pigment. If the predetermined absorbance of the 25-fold dilution of the supernatant is 0.15 or less, since there are relatively few intermediates that are impurities, the occurrence of ink ejection irregularities from the recording head can be suppressed.

[0020] Furthermore, a resin is contained in the ink to disperse the quinacridone pigment in the aqueous medium. The resin includes adsorbed resin that is adsorbed by the quinacridone pigment and unadsorbed resin that is not adsorbed by the quinacridone pigment. Unadsorbed resin may electrostatically adhere to the ejection surface of the recording head and the inner wall of the nozzle hole. The adsorbed unadsorbed resin, like the intermediate, contributes to uneven ink ejection from the recording head. Also, when the ink adhering to the ejection surface dries and thickens, the unadsorbed resin contained in the ink may cause aggregation of ink components, resulting in the formation of aggregates. These aggregates also contribute to uneven ink ejection from the recording head. Therefore, in the ink of the first embodiment, the ratio of unadsorbed resin is set to be greater than 0% by mass and 40% by mass or less. Ink with an unadsorbed resin ratio of greater than 0% by mass and 40% by mass or less has a relatively small amount of unadsorbed resin, and thus can suppress the occurrence of uneven ink ejection from the recording head.

[0021] Furthermore, in the ink of the first embodiment, the aqueous medium contains a first solvent having a boiling point of 180°C to 280°C. The boiling point of the first solvent is relatively high. Therefore, the ink adhering to the ejection surface of the recording head is less likely to dry or thicken. As a result, aggregation of ink components caused by intermediates and unadsorbed resins contained in the ink is suppressed, and the generation of aggregates can be suppressed. Consequently, the occurrence of uneven ink ejection from the recording head can be suppressed.

[0022] The above explains why the ink of the first embodiment can suppress the occurrence of ink ejection irregularities from the recording head. The ink of the first embodiment will now be described in more detail.

[0023] <Predetermined absorbance> The predetermined absorbance will be explained below with reference to Figure 1. Figure 1 shows the ultraviolet-visible light absorption spectrum of a 25-fold diluted supernatant obtained by centrifuging the reference ink at 1,050,000 G for 3 hours. Note that the reference ink is different from the inks in the examples and comparative examples described later, but is shown as an example to explain how to determine the predetermined absorbance. Each reference ink contains at least quinacridone pigment (CI Pigment Red 122), resin (resin (RA) described later), and an aqueous medium. The vertical axis of Figure 1 shows absorbance, and the horizontal axis shows wavelength (unit: nm). The ultraviolet-visible light absorption spectrum of a 25-fold diluted supernatant obtained from the reference ink was measured using the method described later in the examples, and the obtained spectrum is shown in Figure 1.

[0024] In Figure 1, the predetermined peak P is the maximum peak in the wavelength range of 400 nm to 490 nm. The maximum peak refers to the peak (i.e., the vertex) in the convex curve of the spectrum appearing in the predetermined wavelength range that has the highest absorbance.

[0025] In the example shown in Figure 1, among the spectral peaks appearing in the wavelength range of 400 nm to 490 nm, the peak with the maximum absorbance is observed at a wavelength of 429 nm. Therefore, the peak at wavelength 429 nm is the predetermined peak P. The predetermined absorbance can be determined by reading the absorbance of the predetermined peak P from the ultraviolet-visible light absorption spectrum. The method for determining the predetermined absorbance of a 25-fold diluted supernatant has been explained above with reference to Figure 1. The predetermined absorbance of a 25-fold diluted supernatant will be explained further below.

[0026] As already mentioned, the predetermined absorbance of a 25-fold diluted supernatant is 0.15 or less. To suppress the occurrence of ink ejection irregularities from the recording head, it is preferable that the predetermined absorbance of a 25-fold diluted supernatant is 0.10 or less. The lower limit of the predetermined absorbance of a 25-fold diluted supernatant is not particularly limited, but for example, it is 0.05 or more. For example, the predetermined peak is a peak derived from an intermediate for synthesizing quinacridone pigment contained in the ink. More specifically, the predetermined peak is a peak derived from intermediate compounds (B) and (C) contained in the ink. Therefore, the predetermined absorbance can be adjusted by changing the amount of intermediate in the pigment dispersion and the amount of intermediate in the ink containing the pigment dispersion. The amount of intermediate can be changed, for example, by changing the number of passes of the activated carbon treatment of the pigment dispersion, which will be described later in the examples. The more times the pigment dispersion is treated with activated carbon, the more likely it is that at least a portion of the intermediate will be removed, resulting in a lower predetermined absorbance for a 25-fold diluted supernatant. Furthermore, the amount of intermediate can be altered, for example, by washing the pigment dispersion with a filter press and changing the number of washes.

[0027] <Quinacridone pigment> Examples of quinacridone pigments contained in the ink include CI Pigment Violet (19 and 42), CI Pigment Red (122, 202, 206, 207, and 209), and CI Pigment Orange (48 and 49).

[0028] Examples of commercially available quinacridone pigments that can be used include "TRM-11" from Dainichi Seika Kogyo Co., Ltd., "Cinquasia® Magenta D4550" and "Cinquasia® Pink D4450" from BASF, "Inkjet Magenta ES" from Clariant, "HOSTAPERM PINK E 02" from Clariant, "HOSTAPERM RED E3B" from Clariant, and "HOSTAPERM RED E5B 02" from Clariant.

[0029] The quinacridone pigment content in the ink is preferably 1% by mass or more and 12% by mass or less, and more preferably 4% by mass or more and 8% by mass or less. If the quinacridone pigment content is 1% by mass or more, the image density of the image formed by the ink can be optimized. Furthermore, if the quinacridone pigment content is 12% by mass or less, the fluidity of the ink can be optimized. The ink may contain only quinacridone pigment as the pigment. In addition, to adjust the hue of the ink, the ink may further contain other pigments in addition to quinacridone pigment as the pigment.

[0030] Although an overview of the quinacridone pigment synthesis method has already been described, the following will explain the quinacridone pigment synthesis method in more detail.

[0031] In the above equations (A), (B), and (C), R A and R B Examples of monovalent groups represented by R include alkyl groups and aryl groups. A and R B The monovalent group represented is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably an ethyl group.

[0032] In the above equations (C) and (D), R 1 and R 2 Examples of monovalent groups represented by R include hydrogen atoms, alkyl groups, and halogen atoms. 1 and R 2 A chlorine atom is preferred as the halogen atom represented by R. 1 and R 2 The alkyl group represented is preferably an alkyl group having 1 to 6 carbon atoms, and a methyl group is more preferred.

[0033] In reaction (ra), compound (B) is obtained from compound (A). Then, in reaction (rb), 1 molar equivalent of compound (B) is reacted with 2 molar equivalents of an aniline derivative to obtain 1 molar equivalent of compound (C). Then, in reaction (rc), compound (C) is oxidized to obtain an oxide of compound (C). Then, in reaction (rc), the oxide of compound (C) is hydrolyzed to obtain a hydrolysate. Then, in reaction (rc), the hydrolysate is subjected to a dehydration and cyclization reaction using a catalyst to obtain compound (D). The reaction temperature for the dehydration and cyclization reaction is, for example, 90°C to 120°C. The reaction time for the dehydration and cyclization reaction is, for example, 1 hour to 2 hours.

[0034] After carrying out the above reaction (rc), the quinacridone pigment may be subjected to, for example, a solvent treatment step (hereinafter sometimes referred to as step A) and a post-treatment step (hereinafter sometimes referred to as step B).

[0035] (Process A) In step A, the quinacridone pigment is treated with a solvent. Before step A is performed, the quinacridone pigment is also called crude and consists of aggregated particles with a low degree of crystallinity. The quinacridone pigment before step A does not have sufficient coloring properties. Therefore, by performing step A, crystal growth of the quinacridone pigment and the micronization of the quinacridone pigment are promoted. By promoting the micronization of the quinacridone pigment, the coloring properties and saturation of the quinacridone pigment are optimized. As a method for treating the quinacridone pigment, for example, one method is to knead the quinacridone pigment and solvent using a kneader (e.g., a salt milling kneader). The temperature and time for treating the quinacridone pigment are not particularly limited and should be set appropriately to achieve the desired particle size and particle size distribution of the quinacridone pigment. In addition, in step A, an inorganic base (more specifically, sodium hydroxide and potassium hydroxide, etc.) may be added as a grinding aid as needed. The quinacridone pigment mixture obtained in step A is washed with water or a solvent as needed, to form a wet cake-like substance, for example.

[0036] (Process B) In step B, the quinacridone pigment mixture obtained in step A is post-treated. By performing step B, aggregation of the finely particulated quinacridone pigment is suppressed. Post-treatment methods include, for example, removing the solvent from the quinacridone pigment mixture to separate the quinacridone pigment. Methods for separating the quinacridone pigment include, for example, filtration, drying, and solvent removal using a rotary evaporator. When the solvent is removed by distillation, the temperature of the solvent distillation is, for example, above the boiling point of the solvent.

[0037] After step B is performed, the separated quinacridone pigment is washed (e.g., by filter pressing), dried, and pulverized as needed. However, intermediates may remain in the quinacridone pigment even after washing. Therefore, it is preferable to remove at least a portion of the intermediates by treating the pigment dispersion with activated carbon or the like. This can suppress the occurrence of ink ejection irregularities from the recording head.

[0038] <Resin> Some of the resin contained in the ink is adsorbed onto, for example, the quinacridone pigment. Because the resin is hydrophilic, the adsorbed resin on the surface of the quinacridone pigment disperses the quinacridone pigment in the aqueous medium. Such resins are also called pigment-dispersing resins.

[0039] The resin comprises an adsorbent resin and an unadsorbed resin. That is, the ink contains an adsorbent resin and an unadsorbed resin as the resin. The adsorbent resin is adsorbed onto the quinacridone pigment. The adsorbent resin, for example, together with the quinacridone pigment constitutes a pigment particle. The pigment particle has, for example, a core and a coating layer covering the core. The core of the pigment particle contains the quinacridone pigment. The coating layer of the pigment particle contains the resin. On the other hand, the unadsorbed resin is not adsorbed onto the quinacridone pigment. The unadsorbed resin is free in the aqueous medium.

[0040] As already mentioned, the unadsorbed resin ratio is greater than 0% by mass and 40% by mass or less. As already mentioned, if the unadsorbed resin ratio is greater than 0% by mass and 40% by mass or less, the occurrence of ink ejection irregularities from the recording head can be suppressed. Preferably, the unadsorbed resin ratio is 10% by mass or more and 40% by mass or less. If the unadsorbed resin ratio is 10% by mass or more, the resolubility of the ink is improved. In this specification, ink resolubility means the property that dried ink adhering to the ejection surface of the recording head and drying out is easily dissolved in either or both of the cleaning liquid and / or the purge ink.

[0041] The unadsorbed resin ratio can be measured by centrifuging the ink using a centrifuge. The unadsorbed resin ratio can be calculated using the formula: "Unadsorbed resin ratio = 100 × Mass of unadsorbed resin / Total mass of resin = 100 × Mass of unadsorbed resin / (Mass of unadsorbed resin + Mass of adsorbed resin)". For example, in the pigment dispersion preparation process described later, the unadsorbed resin ratio tends to decrease as the discharge rate of the wet disperser decreases.

[0042] Examples of resins include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid resin, and urethane resin. From the viewpoint of stably dispersing the quinacridone pigment, styrene-(meth)acrylic resin is preferred as the resin.

[0043] The styrene-(meth)acrylic resin has at least repeating units derived from at least one styrene and its derivatives, and at least one repeating unit derived from at least one (meth)acrylic acid. Preferably, the styrene-(meth)acrylic resin further has repeating units derived from at least one (meth)acrylic acid ester.

[0044] Examples of first monomers capable of forming repeating units derived from styrene or its derivatives include styrene, α-methylstyrene, and vinyltoluene. Styrene is preferred as the first monomer. The content of repeating units derived from styrene or its derivatives relative to the total repeating units of the resin is preferably 25.0% by mass or more and 60.0% by mass or less.

[0045] Examples of secondary monomers capable of forming repeating units derived from (meth)acrylic acid include acrylic acid and methacrylic acid. Methacrylic acid is preferred as the secondary monomer. The content ratio of repeating units derived from (meth)acrylic acid to the total repeating units of the resin is preferably 4.5% by mass or more and 15.0% by mass or less, and more preferably 8.0% by mass or more and 11.0% by mass or less. When the resin has repeating units derived from both acrylic acid and methacrylic acid, the content ratio of repeating units derived from (meth)acrylic acid is the total content ratio of repeating units derived from acrylic acid and methacrylic acid.

[0046] Examples of third monomers capable of forming repeating units derived from (meth)acrylic acid esters include alkyl (meth)acrylates. Preferably, alkyl (meth)acrylates have an alkyl alkyl group with 1 to 8 carbon atoms in the alkyl group; more preferably, alkyl (meth)acrylates have an alkyl group with 1 to 4 carbon atoms; even more preferably, methyl (meth)acrylate and butyl (meth)acrylate; and particularly preferably, methyl methacrylate and butyl acrylate. The content of repeating units derived from (meth)acrylic acid esters relative to the total repeating units of the resin is preferably 35.0% by mass or more and 70.0% by mass or less, and more preferably 40.0% by mass or more and 70.0% by mass or less. If the resin has repeating units derived from two or more (meth)acrylic acid esters, the content of repeating units derived from (meth)acrylic acid esters is the total content of repeating units derived from the two or more (meth)acrylic acid esters.

[0047] The resin preferably has repeating units derived from at least one type of (meth)acrylic acid, repeating units derived from at least one type of alkyl (meth)acrylate, and repeating units derived from styrene. More preferably the resin has repeating units derived from one type of (meth)acrylic acid, repeating units derived from one or two types of alkyl (meth)acrylate, and repeating units derived from styrene. It is particularly preferable that the resin has repeating units derived from methacrylic acid, repeating units derived from methyl methacrylate, repeating units derived from butyl acrylate, and repeating units derived from styrene. The content of repeating units derived from at least one type of (meth)acrylic acid (preferably the content of repeating units derived from one type of (meth)acrylic acid, more preferably the content of repeating units derived from methacrylic acid) is preferably 8.0% by mass or more and 11.0% by mass or less of the total repeating units of the resin.

[0048] The acid value of the resin is preferably 60 mg KOH / g or more and 300 mg KOH / g or less, more preferably 80 mg KOH / g or more and 150 mg KOH / g or less, and even more preferably 100 mg KOH / g or more and 130 mg KOH / g or less. If the acid value of the resin is 60 mg KOH / g or more, the pigment particles are suitably dispersed in the aqueous medium, and the color development and coloring power of the ink are optimized. On the other hand, if the acid value of the resin is 300 mg KOH / g or less, the storage stability of the ink is optimized.

[0049] The mass-average molecular weight of the resin is preferably between 10,000 and 50,000, and more preferably between 15,000 and 30,000. A mass-average molecular weight of 10,000 to 50,000 of the resin optimizes the viscosity of the ink.

[0050] To suppress the occurrence of ink ejection irregularities from the recording head and to appropriately disperse pigment particles in an aqueous medium, the ratio of the mass of pigment to the mass of resin (hereinafter sometimes referred to as the pigment / resin ratio) is preferably 5.0 or less, more preferably 0.1 to 2.5, and even more preferably 0.5 to 2.5. The pigment / resin ratio can be calculated using the formula "pigment / resin ratio = mass of pigment / mass of resin".

[0051] The resin content in the ink is preferably 0.5% by mass or more and 8.0% by mass or less, and more preferably 1.5% by mass or more and 4.0% by mass or less. If the resin content is 0.5% by mass or more, aggregation of quinacridone pigment can be suitably suppressed. If the resin content is 8.0% by mass or less, nozzle clogging of the recording head can be suitably suppressed.

[0052] <Aqueous medium> The aqueous medium contained in the ink is a medium containing water. The aqueous medium may function as a solvent or as a dispersion medium. Examples of aqueous mediums include those containing water and organic solvents. To enhance compatibility with water, the organic solvent contained in the aqueous medium is preferably a water-soluble organic solvent. A water-soluble organic solvent is an organic solvent that is uniformly miscible with water in any proportion.

[0053] Examples of water-soluble organic solvents include glycol compounds, triol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, γ-butyrolactone, thiodiglycol, and dimethyl sulfoxide.

[0054] Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,2-pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, 2-ethyl-1,2-hexanediol, and thiodiglycol. Preferably, the glycol compound is propylene glycol, 1,5-pentanediol, triethylene glycol, or tetraethylene glycol.

[0055] Examples of triol compounds include glycerin, 1,2,3-butanetriol, and 1,2,6-hexanetriol. Glycerin is preferred as the triol compound.

[0056] Examples of glycol ether compounds include diethylene glycol diethyl ether, diethylene glycol monoethyl 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. Triethylene glycol monobutyl ether is preferred as the glycol ether compound.

[0057] Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0058] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0059] Examples of acetate compounds include diethylene glycol monoethyl ether acetate.

[0060] As already mentioned, the aqueous medium contains a first solvent. The boiling point of the first solvent is between 180°C and 280°C. If the boiling point of the first solvent is between 180°C and 280°C, the occurrence of ink ejection irregularities from the recording head can be suppressed. Also, if the boiling point of the first solvent is 280°C or lower, the image formed by the ink dries easily, and an image with excellent scratch resistance can be formed. In order to suppress the occurrence of ink ejection irregularities from the recording head, the boiling point of the first solvent is preferably 188°C or higher, more preferably 190°C or higher, even more preferably 239°C or higher, and even more preferably 250°C or higher. In order for the image formed by the ink to dry easily and for an image with excellent scratch resistance to be formed, the boiling point of the first solvent is preferably 278°C or lower.

[0061] Examples of the first solvent include solvents among the water-soluble organic solvents mentioned above, having a boiling point of 180°C to 280°C. Preferred examples of the first solvent include triethylene glycol monobutyl ether, propylene glycol, and 1,5-pentanediol. The content of the first solvent is preferably 5% by mass or more and 20% by mass or less relative to the mass of the ink. If the content of the first solvent is 5% by mass or more relative to the mass of the ink, the occurrence of ink ejection irregularities from the recording head can be further suppressed. If the content of the first solvent is 20% by mass or less relative to the mass of the ink, the image formed by the ink dries easily, and an image with excellent scratch resistance can be formed.

[0062] To suppress the occurrence of ink ejection irregularities from the recording head, the aqueous medium preferably further contains a second organic solvent having a boiling point higher than 280°C. Hereinafter, "second organic solvent" may be referred to as "second solvent." The boiling point of the second solvent is preferably higher than 280°C and 350°C or lower, and more preferably between 285°C and 320°C.

[0063] To improve compatibility with water, the second solvent is preferably a water-soluble organic solvent. Examples of the second solvent include those water-soluble organic solvents with a boiling point higher than 280°C. Suitable examples of the second solvent include tetraethylene glycol, triethylene glycol, and glycerin. To further suppress the occurrence of ink ejection irregularities from the recording head, the content of the second solvent is preferably 1% by mass or more relative to the mass of the ink. To allow the image formed by the ink to dry easily and to form an image with excellent scratch resistance, the content of the second solvent is preferably 10% by mass or less relative to the mass of the ink.

[0064] The ratio M1 / M2 of the mass of the first solvent to the mass M2 of the second solvent is preferably 1.0 or more and 4.0 or less. If the ratio M1 / M2 is 1.0 or more, the occurrence of ink ejection irregularities from the recording head can be further suppressed. If the ratio M1 / M2 is 4.0 or less, the image formed by the ink dries easily, and an image with excellent scratch resistance can be formed.

[0065] To suppress the occurrence of uneven ink ejection from the recording head, it is preferable that the ink does not contain water-soluble organic solvents with a boiling point of less than 180°C.

[0066] As the aqueous medium, a mixed solvent consisting of any combination of (i) to (v) below is preferred. Combination (i): Water, triethylene glycol monobutyl ether, and glycerin Combination (ii): Water, propylene glycol, and glycerin Combination (iii): Water, 1,5-pentanediol, and glycerin Combination (iv): Water, triethylene glycol monobutyl ether, and tetraethylene glycol Combination (v): Water, triethylene glycol monobutyl ether, and triethylene glycol

[0067] The water-based medium content in the ink is preferably 30% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 95% by mass or less.

[0068] <Surfactants> The ink preferably further contains a surfactant. The surfactant optimizes the compatibility and dispersion stability of each component contained in the ink. Furthermore, the surfactant optimizes the penetration of the ink into the recording medium. A nonionic surfactant is preferred as the surfactant.

[0069] Examples of nonionic surfactants include acetylenediol and ethylene oxide adducts of acetylenediol. Examples of acetylenediols include 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol. Preferred nonionic surfactants are ethylene oxide adducts of acetylenediol and ethylene oxide adducts of acetylene glycol. The HLB value of the nonionic surfactant is preferably 4 to 14, more preferably 4 to 8 or 10 to 14. If the ink contains a surfactant, the surfactant content in the ink is preferably 0.01% by mass or more and 1.0% by mass or less.

[0070] <Other ingredients> The ink may further contain known additives as needed (more specifically, dissolving stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents, etc.).

[0071] <Ink manufacturing method> The ink manufacturing method of the first embodiment includes, for example, a step of preparing a pigment dispersion and a mixing step. Furthermore, if necessary, the ink manufacturing method preferably further includes an activated carbon treatment step. The activated carbon treatment step is preferably performed after the pigment dispersion preparation step and before the mixing step.

[0072] (Preparation process of pigment dispersion) In the preparation of the pigment dispersion, quinacridone pigment, resin, and aqueous medium are mixed to obtain the pigment dispersion. To ensure sufficient dispersion of the pigment particles, the pigment dispersion may further contain a surfactant. In the pigment dispersion, the median diameter (D) of the pigment particles composed of quinacridone pigment and resin is... 50 ) Preferably, the wavelength is between 70 nm and 130 nm.

[0073] The quinacridone pigment content in the pigment dispersion is preferably 5% to 25% by mass, and more preferably 10% to 20% by mass. The resin content in the pigment dispersion is preferably 2% to 10% by mass, and more preferably 4% to 8% by mass. If the pigment dispersion contains a surfactant, the surfactant content in the pigment dispersion is preferably 0.1% to 2% by mass, and more preferably 0.3% to 1% by mass.

[0074] Pigment dispersions can be prepared by wet-dispersing the components contained in the aforementioned pigment dispersion using a media-type wet-disperser. Examples of media-type wet-dispersers include bead mills (more specifically, the "NanoGlen Mill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries Co., Ltd., and the "Dino® Mill" manufactured by Willy E. Bakkofen).

[0075] In wet dispersion using a media-type wet disperser, small-particle beads (e.g., beads with a diameter of 0.5 mm to 1.0 mm) are used as the media. By changing the diameter of the beads, it is possible to change, for example, the degree of dispersion of pigment particles and the ratio of unadsorbed resin in the supernatant. The smaller the diameter of the beads, the more the pigment particles are dispersed.50 The ratio tends to decrease. The smaller the diameter of the beads, the easier it is for the core containing the quinacridone pigment to be coated with resin, and the ratio of unadsorbed resin in the supernatant tends to decrease. The material of the beads is not particularly limited, but hard materials (e.g., glass and zirconia) are preferred. The discharge rate of the media-type wet disperser is, for example, 200 g / min to 600 g / min. The lower the discharge rate of the media-type wet disperser, the lower the ratio of unadsorbed resin tends to be.

[0076] (Activated carbon treatment process) In the activated carbon treatment process, the pigment dispersion is treated with activated carbon. The activated carbon treatment removes unadsorbed resin and at least a portion of the intermediates. By including such a pigment dispersion in the ink, the predetermined absorbance of a 25-fold diluted supernatant obtained from the ink can be easily adjusted to a value within the desired range. The activated carbon treatment is carried out, for example, by circulating the pigment dispersion through an activated carbon filter. The flow rate of the circulating pigment dispersion is, for example, 100 g / min to 300 g / min. The circulation time of the pigment dispersion is, for example, 5 minutes to 30 minutes. If one pass is defined as 1000 g of pigment dispersion passing through the activated carbon filter, the number of passes in the activated carbon treatment is, for example, 5 times or less.

[0077] (Mixing process) In the mixing process, the pigment dispersion after activated carbon treatment and any additional components (e.g., further added aqueous media and surfactants) are mixed using a stirrer. After mixing the ink components, foreign matter and coarse particles may be removed using a filter (e.g., a filter with a pore size of 5 μm or less).

[0078] The proportion of pigment dispersion in the total raw materials of the ink is, for example, 25% by mass or more and 60% by mass or less. The ink of the first embodiment can be suitably used, for example, in an inkjet recording device described later.

[0079] [Second Embodiment: Inkjet Recording Device] Next, an inkjet recording apparatus according to a second embodiment of the present invention will be described. The inkjet recording apparatus of the second embodiment comprises a transport unit for transporting a recording medium and a recording head. The recording head ejects the ink of the first embodiment described above onto the recording medium. The details of the inkjet recording apparatus of the second embodiment will be described below with reference to the drawings. Note that the drawings shown are schematic representations mainly of each component for ease of understanding, and the size, number, etc. of each component shown may differ from the actual dimensions.

[0080] Figure 2 shows the configuration of the inkjet recording apparatus 1 according to the second embodiment. The X, Y, and Z axes shown in Figure 2 and Figures 3 to 5 described later are orthogonal to each other.

[0081] The inkjet recording device 1 shown in Figure 2 comprises a paper feed unit 3, a first recording head 4C, a second recording head 4M, a third recording head 4Y, a fourth recording head 4K, a liquid storage unit 5, a first transport unit 6, a second transport unit 7, an ejection unit 8, and a maintenance unit 9. Hereafter, when it is not necessary to distinguish between the first recording head 4C to the fourth recording head 4K, they may simply be referred to as "recording head 4".

[0082] The paper feeding unit 3 comprises a plurality of paper feeding cassettes 31, a plurality of pickup rollers 32, a plurality of transport rollers 33, and a pair of registration rollers 34. Recording media S are stacked and stored in the paper feeding cassettes 31. The pickup rollers 32 pick up the recording media S stored in the paper feeding cassettes 31 one by one. The transport rollers 33 transport the recording media S picked up by the pickup rollers 32. The pair of registration rollers 34 temporarily hold the recording media S transported by the transport rollers 33 and then supply them to the first transport unit 6 at a predetermined timing.

[0083] The recording head 4 is positioned above the first transport belt 63. The first to fourth recording heads 4C to 4K are arranged in this order in the transport direction D of the recording medium S. Each of the first to fourth recording heads 4C to 4K is positioned at the same height. The first to fourth recording heads 4C to 4K are each filled with four different colors of ink (for example, cyan, magenta, yellow, and black). The ink filled in the second recording head 4M is the magenta ink of the first embodiment. Each of the recording heads 4 ejects ink onto the recording medium S. Of the recording heads 4, the second recording head 4M ejects the magenta ink of the first embodiment onto the recording medium S. As a result, an image (for example, a color image) is formed on the recording medium S transported by the first transport belt 63.

[0084] Because the ink of the first embodiment is used, the inkjet recording apparatus 1 of the second embodiment can suppress the occurrence of ink ejection irregularities from the second recording head 4M for the same reasons as described in the first embodiment.

[0085] The liquid storage unit 5 comprises a first ink tank 51C, a second ink tank 51M, a third ink tank 51Y, a fourth ink tank 51K, and a cleaning fluid tank 52. Hereinafter, when it is not necessary to distinguish between the first ink tank 51C to the fourth ink tank 51K, they may simply be referred to as "ink tank 51". The first ink tanks 51C to the fourth ink tanks 51K each contain four different colors of ink (for example, cyan, magenta, yellow, and black). The ink contained in the second ink tank 51M is the magenta ink of the first embodiment. The first ink tanks 51C to the fourth ink tanks 51K each supply ink to the first recording heads 4C to the fourth recording heads 4K. The cleaning fluid tank 52 supplies cleaning fluid to the liquid-impregnated body 91.

[0086] The first transport unit 6 is located downstream of the paper feeding unit 3 in the transport direction D of the recording medium S. The first transport unit 6 comprises a first driven roller 61, a first drive roller 62, and a first transport belt 63. The first drive roller 62 is located downstream of the first driven roller 61 in the transport direction D of the recording medium S. The first transport belt 63 is an endless belt stretched between the first driven roller 61 and the first drive roller 62. The first drive roller 62 is driven to rotate counterclockwise in Figure 2. This causes the first drive roller 62 to drive the first transport belt 63. As a result, the first transport belt 63 transports the recording medium S fed from the paper feeding unit 3 to the second transport unit 7 in the transport direction D. The first driven roller 61 rotates driven by the first drive roller 62 via the first transport belt 63.

[0087] The second transport unit 7 is located downstream of the first transport unit 6 in the transport direction D of the recording medium S. The second transport unit 7 comprises a second driven roller 71, a second drive roller 72, and a second transport belt 73. The second drive roller 72 is located downstream of the second driven roller 71 in the transport direction D of the recording medium S. The second transport belt 73 is an endless belt stretched between the second driven roller 71 and the second drive roller 72. The second drive roller 72 is driven to rotate counterclockwise in Figure 2. This causes the second drive roller 72 to drive the second transport belt 73. As a result, the second transport belt 73 transports the recording medium S transported from the first transport unit 6 to the discharge unit 8 in the transport direction D. The second driven roller 71 rotates driven by the second drive roller 72 via the second transport belt 73.

[0088] The discharge unit 8 is located downstream of the second transport unit 7 in the transport direction D of the recording medium S. The discharge unit 8 comprises a discharge tray 81, a discharge drive roller 82, and a discharge driven roller 83. The discharge drive roller 82 and the discharge driven roller 83 are pressed against each other at opposing positions. The discharge drive roller 82 is driven to rotate counterclockwise in Figure 2. The discharge driven roller 83 rotates in accordance with the rotation of the discharge drive roller 82. As a result, the discharge drive roller 82 and the discharge driven roller 83 discharge the recording medium S transported from the second transport unit 7 to the discharge tray 81. The discharged recording medium S is placed on the discharge tray 81.

[0089] The maintenance unit 9 comprises a liquid-impregnated body 91 and a cleaning member 92. The liquid-impregnated body 91 is impregnated with cleaning liquid. The liquid-impregnated body 91 contacts the ejection surface 42 (see Figure 3) of the recording head 4 and supplies cleaning liquid to the ejection surface 42. The liquid-impregnated body 91 is, for example, a sponge, nonwoven fabric, or absorbent sheet. The cleaning member 92 wipes the ejection surface 42 of the recording head 4. This cleans the ink adhering to the ejection surface 42. The cleaning member 92 is, for example, a rubber wiper.

[0090] Examples of cleaning solutions include water, polyhydric alcohol, triethylene glycol monobutyl ether, lactam, and a mixture of polyhydric alcohols. In the cleaning solution, the water content, polyhydric alcohol content, triethylene glycol monobutyl ether content, lactam content, and polyhydric alcohol content are preferably 60% to 70% by mass, 10% to 15% by mass, 5% to 10% by mass, 5% to 10% by mass, and 1% to 5% by mass, respectively. An example of a cleaning solution having such a composition is the head cleaning solution for the TASKalfa Pro 15000c manufactured by Kyocera Document Solutions Inc.

[0091] Next, the recording head 4 will be further described with reference to Figure 3. Figure 3 shows the bottom surface of the recording head 4 shown in Figure 2.

[0092] As shown in Figure 3, the recording head 4 comprises a first nozzle row N1, a second nozzle row N2, and an ejection surface 42. For ease of understanding, in Figure 3, the first nozzle row N1 and the second nozzle row N2 are each enclosed by dashed lines. Each of the first nozzle row N1 and the second nozzle row N2 contains a plurality of nozzles 41. The nozzles 41 eject ink onto the recording medium S. The nozzles 41 open onto the ejection surface 42. The first nozzle row N1 and the second nozzle row N2 are arranged side by side in the transport direction D of the recording medium S. In each of the first nozzle row N1 and the second nozzle row N2, the plurality of nozzles 41 are spaced apart in a direction perpendicular to the transport direction D of the recording medium S. The recording head 4 is, for example, a line head.

[0093] The width 41w of each of the first nozzle row N1 and the second nozzle row N2 (i.e., the width of the area that can be recorded by the recording head 4) is equal to or wider than the width of the recording medium S. Therefore, the recording head 4 can record an image on the recording medium S being transported on the first transport belt 63 while remaining fixed. In other words, the inkjet recording device 1 employs a single-pass method, which does not involve shuttle motion. Because the inkjet recording device 1 of the second embodiment is equipped with such a recording head 4, it can print at a higher speed compared to an inkjet recording device equipped with a serial head.

[0094] Next, the cleaning operation by the maintenance unit 9 will be described with reference to Figures 4 and 5. The cleaning operation includes the supply of cleaning fluid, the purging operation, and the wiping operation. Figure 4 is a diagram illustrating the supply of cleaning fluid. Figure 5 is a diagram illustrating the purging operation and the wiping operation. Although the nozzle 41 is not visible in the side view of the recording head 4, its position is indicated by a dashed line in Figures 4 and 5 for ease of understanding.

[0095] As shown in Figure 4, the recording head 4 is further equipped with an ink inlet 43 and an ink outlet 44. Ink flows from the ink tank 51 through the ink inlet 43 to the recording head 4 and flows out of the recording head 4 through the ink outlet 44.

[0096] As shown in Figure 2, the liquid-impregnated body 91 of the maintenance unit 9 is positioned below the second conveyor belt 73. The cleaning member 92 of the maintenance unit 9 is positioned below the liquid-impregnated body 91. The liquid-impregnated body 91 and the cleaning member 92 are each movable between a position facing the second conveyor unit 7 and a position facing the ejection surface 42 of the recording head 4. Furthermore, as shown in Figure 4, the liquid-impregnated body 91 is movable in both the upward direction D1 and the downward direction D2. As shown in Figure 5, the cleaning member 92 is movable in both the upward direction D1, the downward direction D2, and the wiping direction D3. The "upward direction D1" is the direction approaching the ejection surface 42 in the Z-axis direction. The "downward direction D2" is the direction away from the ejection surface 42 in the Z-axis direction. The "wiping direction D3" is the direction along the ejection surface 42. The liquid-impregnated body 91 and the cleaning member 92 are each moved by a known drive mechanism (not shown).

[0097] At this point, ink adhering to the ejection surface 42 may dry and harden. A cleaning operation is performed to clean off this dried ink.

[0098] First, the cleaning liquid supply operation of the cleaning process will be explained. The cleaning liquid is impregnated into the liquid-impregnated body 91. Next, as shown in Figure 4, the liquid-impregnated body 91 moves to a position facing the discharge surface 42, and then moves upward in the direction D1. Then, the liquid-impregnated body 91 is pressed against the discharge surface 42. In this way, the cleaning liquid impregnated into the liquid-impregnated body 91 adheres to the discharge surface 42. It is preferable that the state in which the liquid-impregnated body 91 is pressed against the discharge surface 42 is maintained for a predetermined time. The predetermined time is preferably 1 second or more and 5 minutes or less. After the predetermined time has elapsed, the liquid-impregnated body 91 moves downward in the direction D2. Then, the state in which the liquid-impregnated body 91 is pressed against the discharge surface 42 is released.

[0099] Next, the purging operation will be explained. As shown in Figure 5, ink is purged from the recording head 4. In Figure 5, the purged ink (purged ink) is indicated by the label "Nf". Specifically, the ink is forcibly discharged from the nozzle 41 by pressurizing the recording head 4. This clears any clogging of the nozzle 41, and the purged ink Nf adheres to the discharge surface 42 of the recording head 4.

[0100] Next, the wiping operation will be described. The cleaning member 92 moves to a position facing the ejection surface 42 (the position shown in Figure 5), and then moves in the upward direction D1. The cleaning member 92 is then pressed against the ejection surface 42. While the state in which the cleaning member 92 is pressed against the ejection surface 42 is maintained, the cleaning member 92 moves in a direction along the ejection surface 42 (the wiping direction D3 shown in Figure 5). As a result, the cleaning member 92 wipes the ejection surface 42. Consequently, ink (e.g., dried ink and purge ink Nf) and cleaning fluid adhering to the ejection surface 42 are removed. This cleans the ejection surface 42 of the recording head 4. Next, the cleaning member 92 moves in the downward direction D2. The state in which the cleaning member 92 is pressed against the ejection surface 42 is then released.

[0101] If the ink of the first embodiment has excellent resolubility in addition to suppressing the occurrence of ejection distortion from the recording head 4, then even if the ink adheres to the ejection surface 42 of the recording head 4 and dries, the dried ink will easily dissolve in either or both of the purge ink Nf and the cleaning liquid. If the dried ink dissolves easily, the ejection surface 42 of the recording head 4 can be easily cleaned. Furthermore, if the ink of the first embodiment can form an image with excellent scratch resistance in addition to suppressing the occurrence of ejection distortion from the recording head 4, then the inkjet recording apparatus 1 of the second embodiment can form an image with excellent scratch resistance.

[0102] The above describes an inkjet recording device 1, which is an example of an inkjet recording device according to the second embodiment. However, the inkjet recording device of the second embodiment is not limited to the inkjet recording device 1. The inkjet recording device of the second embodiment may employ a multi-pass method. In addition, the number of nozzles 41, the spacing between nozzles 41, and the positional relationship of the nozzles 41 in the first recording head 4C to the fourth recording head 4K can be appropriately set according to the specifications of the device. In addition, the cleaning fluid supply operation may be discharge of cleaning fluid by the inkjet method, application of cleaning fluid using a roller, or spraying of cleaning fluid. Furthermore, the cleaning fluid supply operation, purging operation, and wiping operation may each be repeated. Furthermore, the order in which the cleaning fluid supply operation and purging operation are performed is not limited. In addition, the cleaning member 92 may move back and forth in the direction along the discharge surface 42. For example, while the cleaning member 92 is maintained in contact with the discharge surface 42, it may move in a first direction along the discharge surface 42 (wiping direction D3 shown in Figure 5), and then move in a second direction opposite to the first direction along the discharge surface 42 (the direction opposite to the wiping direction D3 shown in Figure 5). [Examples]

[0103] The following describes embodiments of the present invention. However, the present invention is not limited to the following embodiments. In the following embodiments, ion-exchanged water will be simply referred to as water.

[0104] [Preparing the resin] First, resins (RA) and (RB) used in the preparation of the ink were prepared. Table 1 shows the types and percentages of repeating units present in resins (RA) and (RB), their mass-average molecular weight, and their acid value.

[0105] [Table 1]

[0106] The terms used in Table 1 are as follows: "MAA" indicates repeating units derived from methacrylic acid. "MMA" indicates repeating units derived from methyl methacrylate. "BA" indicates repeating units derived from butyl acrylate. "ST" indicates repeating units derived from styrene. "Percentage" indicates the proportion of each repeating unit relative to the total mass of repeating units in the resin.

[0107] <Measurement of the acid value of resins> The acid value of each resin was measured in accordance with "JIS (Japanese Industrial Standards) K0070:1992".

[0108] <Measurement of mass-average molecular weight of resin> The mass-average molecular weight of each resin was measured using gel permeation chromatography (HLC-8020GPC, manufactured by Tosoh Corporation) under the following measurement conditions. Calibration curves were created using TSKgel standard polystyrenes F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000, manufactured by Tosoh Corporation, and n-propylbenzene.

[0109] (Measurement conditions for mass-average molecular weight) • Column: TSKgel SuperMultiporeHZ-H manufactured by Tosoh Corporation (semi-micro column with 4.6mm I.D. x 15cm) • Number of columns: 3 • Eluent: Tetrahydrofuran ·Flow rate: 0.35mL / min • Sample injection volume: 10 μL ·Measurement temperature: 40℃ • Detector: RI (refractive index) detector

[0110] [Consideration 1: Ratio of unadsorbed resin] The ratio of unadsorbed resin was investigated. The inks (A-1) to (A-7) used in the investigation were prepared by the following method.

[0111] <Preparation of ink (A-1)> (Preparation of pigment dispersion) Pigment dispersions were prepared to match the formulations shown in Table 2.

[0112] [Table 2]

[0113] The terms used in Table 2, and in Tables 5, 14, and 16 described later, are as follows: "Pigment (PR-122)" refers to quinacridone pigment (CI Pigment Red 122, "TRM-11" manufactured by Dainichi Seika Kogyo Co., Ltd.). "Orphine E1010" refers to nonionic surfactant ("Orphine (registered trademark) E1010" manufactured by Nisshin Chemical Industry Co., Ltd., contents: ethylene oxide adduct of acetylenediol, active ingredient concentration: 100% by mass, HLB value: 13.5±0.5).

[0114] First, 6.0 parts by mass of resin (RA) was mixed with an aqueous sodium hydroxide solution. The aqueous sodium hydroxide solution contained a predetermined amount of sodium hydroxide. The "determined amount" of sodium hydroxide added, shown in Table 2, represents 1.05 times the amount required for equivolent neutralization of resin (RA). In this way, resin (RA) was neutralized with an equal amount (strictly speaking, 105% equivalent) of sodium hydroxide to obtain aqueous solution I containing resin (RA).

[0115] The entire volume of the obtained aqueous solution I, along with 15.0 parts by mass of quinacridone pigment (CI Pigment Red 122), 0.5 parts by mass of nonionic surfactant (Orphine® E1010, manufactured by Nisshin Chemical Industry Co., Ltd.), and the remaining water were placed into a vessel. The contents of the vessel were mixed using a media-type wet disperser (DYNO®-MILL, manufactured by Willy E. Bakkofen (WAB)) to obtain mixed solution II.

[0116] Note that the "remaining amount" of water added in Table 2 refers to the amount that makes Mixture II 100.0 parts by mass. The remaining amount of water shown in Table 2 is the total amount of water added to the vessel as described above, plus the water contained in Aqueous Solution I (specifically, the water contained in the sodium hydroxide aqueous solution used to neutralize the resin, and the water produced by the neutralization reaction between the resin and sodium hydroxide).

[0117] Next, the contents of the vessel described above were dispersed using zirconia beads (particle size 0.5 mm) as a media and a bead mill ("Nanograin Mill" manufactured by Asada Iron Works Co., Ltd.). The dispersion conditions using the bead mill were a temperature of 10°C, a peripheral speed of 8 m / sec, and a discharge rate of 220 g / min. This yielded pigment dispersion III before activated carbon treatment.

[0118] It was confirmed that pigment particles with a median volume diameter in the range of 70 nm to 130 nm were dispersed in pigment dispersion III. The median volume diameter of the pigment particles was measured using a dynamic light scattering particle size distribution analyzer (ZetaSizer Nano ZS, manufactured by Spectris Co., Ltd.) with a diluted solution of pigment dispersion III diluted 300 times with water as the measurement sample.

[0119] (Activated carbon treatment) The obtained pigment dispersion III was treated with activated carbon. Specifically, 1800g of pigment dispersion III was passed through an activated carbon filter (YCC-1L, manufactured by Nippon Filter Co., Ltd.; type of activated carbon: coconut shell granular activated carbon) while circulating the pigment dispersion III at a flow rate of 190g / min. Hereafter, the passage of 1000g of pigment dispersion III through the activated carbon filter will be referred to as one pass. Since the flow rate was 190g / min, the time required for one pass was 5 minutes and 15 seconds (=(1000g) / (190g / min)). After two passes, the circulation of pigment dispersion III was stopped to obtain pigment dispersion IV after activated carbon treatment. Therefore, the number of passes in the activated carbon treatment was 2.

[0120] (Ink preparation) Ink (A-1) was prepared to match the formulation ia shown in Table 3.

[0121] [Table 3]

[0122] The terms used in Table 3, and in Tables 8, 10, and 12 described later, are as follows: "Surfinol 420" refers to a nonionic surfactant (Surfinol® 420, manufactured by Nisshin Chemical Industry Co., Ltd., content: ethylene oxide adduct of acetylene glycol, active ingredient concentration: 100% by mass, HLB value: 4). The boiling point of the solvent is indicated in parentheses next to the solvent.

[0123] First, water was added to a flask equipped with a stirrer ("Three One Motor® BL-600" manufactured by Shinto Kagaku Co., Ltd.). While stirring the contents of the flask at a stirring speed of 400 rpm using the stirrer, the pigment dispersion IV obtained from the "activated carbon treatment" described above, a nonionic surfactant ("Surfinol® 420" manufactured by Nisshin Chemical Industry Co., Ltd.), triethylene glycol monobutyl ether, and glycerin were added to obtain a mixture V. The amount of each raw material added is as shown in Table 3. The "residual amount," which is the amount of water added in Table 3, is the amount that makes the mixture V 100.0 parts by mass. The mixture V was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles from the mixture V. This yielded ink (A-1).

[0124] <Preparation of inks (A-2) to (A-7)> Inks (A-2) to (A-7) were prepared in the same manner as ink (A-1), except that the discharge volume of the dispersion process was changed as shown in Table 4 below.

[0125] <Measurement> The samples to be measured (each of the inks (A-1) to (A-7)) were centrifuged using the following method. The predetermined absorbance and the percentage of unadsorbed resin were then measured for each supernatant liquid. The measurement results are shown in Table 4.

[0126] Under conditions of 23°C, a 2g sample of the material, sealed in a container, was centrifuged for 3 hours using an ultracentrifuge (Eppendorf Himac Technologies Ltd. "himac® CS150FNX", rotor: S140AT) at a rotation speed of 140,000 rpm (equivalent to a centrifugal force of 1,050,000 G). This caused the pigment particles contained in the sample to precipitate.

[0127] <Measurement of predetermined absorbance> The entire volume of the supernatant liquid contained in the sample after centrifugation was collected using a syringe. The collected supernatant liquid was diluted 25 times with water and used as the measurement sample. The measurement sample placed in a cell was measured using a spectrophotometer (Hitachi High-Tech Science Co., Ltd. "U-3000") under the following conditions to obtain the ultraviolet-visible light absorption spectrum of the measurement sample (i.e., the 25-fold diluted supernatant liquid). The predetermined absorbance of the 25-fold diluted supernatant liquid was determined from the ultraviolet-visible light absorption spectrum.

[0128] (Measurement conditions for absorbance) • Measurement wavelength range: 200 nm to 800 nm • Scan speed: 300nm / min • Sampling interval: 1.00 nm • Slit width: 1nm • Cell: Quartz glass cell ·Optical path length: 10mm • Beam system: Double beam • Baseline measurement: Yes • Reference: Ion-exchanged water

[0129] <Measurement of unadsorbed resin ratio> The entire supernatant liquid contained in the sample after centrifugation was collected. Next, the entire collected supernatant liquid was placed in a disposable cup and dried under reduced pressure at 60°C for 24 hours to obtain the residue. The mass (WA) of the residue was measured. The mass (WA) of the residue was considered to be the mass of unadsorbed resin.

[0130] Based on the resin (RA) content B (=6.0 mass%) in the pigment dispersion, which can be read from Table 2, and the pigment dispersion content C (=40.0 mass%) in the ink, which can be read from Table 3, the mass of resin (WD) contained in 2g of the sample was calculated according to the following formula. WD = 2 × (C / 100) × (B / 100)

[0131] Then, the unadsorbed resin ratio was calculated from the mass of the residue (WA) obtained from 2g of the sample and the mass of the resin (WD) contained in 2g of the sample, according to the following formula. Unadsorbed resin ratio [mass%]=100×WA / WD

[0132] <Evaluation of discharge turbulence> For each of the inks (A-1) to (A-7), the presence or absence of ink ejection irregularities from the recording head was evaluated using the following method. The evaluation results are shown in Table 4.

[0133] For the evaluation, an inkjet recording device (a prototype manufactured by Kyocera Document Solutions Inc.) was used. This evaluation device was equipped with a piezo-type line head with nozzles (aperture radius: 10 μm) and a wiper as the recording head. The target ink (any of the inks (A-1) to (A-7)) was set in the magenta ink recording head of the evaluation device. Plain paper (Fuji Xerox Co., Ltd. "C2", A4 size PPC paper) was used as the paper.

[0134] The recording head temperature was set to 40°C. The ink ejection rate per pixel was set to 3.5 pL. Using the evaluation machine, an image (20.5 mm x 29.0 mm) with image processing settings that ejected ink from all nozzles of the recording head was printed continuously on paper for one hour. The first image printed during continuous printing (initial image) and the last image printed during continuous printing (end-printed image) were observed with the naked eye. The presence or absence of white streaks in the initial image and end-printed image was checked. White streaks are image defects caused by uneven ink ejection from the recording head. The unevenness of ink ejection from the recording head was judged according to the following criteria.

[0135] (Criteria for discharge swirl) Good (A): In the print-saturated image, white streaks are less prevalent than in the initial image. Defect (B): In the print-saturated image, white streaks are more prevalent than in the initial image.

[0136] [Table 4]

[0137] The terms used in Table 4, and in Tables 6, 7, 9, 11, 13, 15, and 17 described later, are as follows: "Discharge volume" refers to the discharge volume of the dispersion treatment in "Preparation of Pigment Dispersion" described above. "Number of passes" refers to the number of passes in "Activated Carbon Treatment" described above. "Skipping" refers to the evaluation of ink ejection skipping from the recording head.

[0138] For all inks prepared in Study 1 through Study 8 (described later), the predetermined peak was confirmed at a wavelength of 429 nm.

[0139] As shown in Table 4, the unadsorbed resin ratio of ink (A-6) was over 40% by mass. When ink (A-6) was used, ink ejection irregularities occurred from the recording head.

[0140] On the other hand, the unadsorbed resin ratio for inks (A-1) to (A-5) and (A-7) was greater than 0% by mass and less than or equal to 40% by mass. When using inks (A-1) to (A-5) and (A-7), the occurrence of ink ejection irregularities from the recording head was suppressed.

[0141] [Consideration 2: Types of quinacridone pigments] Next, we examined the types of quinacridone pigments. Inks (B-1) to (B-4) were prepared using the same method as for ink (A-1), except for the following changes. In the "Preparation of Pigment Dispersion" described above, formulation da was changed to formulation db shown in Table 5. The ink formulation remained unchanged from formulation ia. The pigments shown in Table 5 were the pigments shown in Table 6.

[0142] For inks (B-1) to (B-4), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 6.

[0143] [Table 5]

[0144] [Table 6]

[0145] The terms used in Table 6 are as follows: "PR122(A)" refers to CI Pigment Red 122 (Clariant's "HOSTAPERM PINK E 02"). "PR122(B)" refers to CI Pigment Red 122 (BASF's "Cinquasia® Pink D4450"). "PV19(C)" refers to CI Pigment Violet 19 (Clariant's "HOSTAPERM RED E3B"). "PV19(D)" refers to CI Pigment Violet 19 (Clariant's "HOSTAPERM RED E5B 02").

[0146] As shown in Table 6, inks (B-1) to (B-4), although differing in the type of quinacridone pigment, all had the following composition. Specifically, the unadsorbed resin ratio of these inks was greater than 0% by mass and less than or equal to 40% by mass. The aqueous medium of these inks contained a first solvent with a boiling point between 180°C and 280°C. The predetermined absorbance of these inks was 0.15 or less. When inks (B-1) to (B-4) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0147] [Consideration 3: Predetermined absorbance] Next, the predetermined absorbance was examined. Inks (C-1) to (C-4) were prepared in the same manner as ink (A-1), except for the following changes. In the "Preparation of Pigment Dispersion" described above, the discharge volume for the dispersion treatment was set as shown in Table 7. In the "Activated Carbon Treatment" described above, the number of passes was set as shown in Table 7. The formulation of the pigment dispersion was left unchanged at formulation da, and the formulation of the ink was left unchanged at formulation ia.

[0148] For inks (C-1) to (C-4), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 7.

[0149] [Table 7]

[0150] As shown in Table 7, the predetermined absorbance of a 25-fold diluted supernatant obtained from ink (C-4) was greater than 0.15. When ink (C-4) was used, ink ejection irregularities occurred from the recording head.

[0151] On the other hand, the predetermined absorbance of a 25-fold diluted supernatant obtained from inks (C-1) to (C-3) was 0.15 or less. When inks (C-1) to (C-3) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0152] [Consideration 4: Boiling point of the first solvent] Next, the boiling point of the first solvent was investigated. Inks (D-1) to (D-4) were prepared in the same manner as the preparation of ink (C-1), except for the following changes. In the "Preparation of Inks" described above, formulation ia was changed to formulation ib shown in Table 8. The formulation of the pigment dispersion remained unchanged from formulation da. As the first solvent shown in Table 8, the first solvent shown in Table 9 was used.

[0153] For inks (D-1) to (D-4), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 9.

[0154] [Table 8]

[0155] [Table 9]

[0156] As shown in Table 9, the boiling point of the first solvent contained in the aqueous medium of ink (D-4) was less than 180°C. When ink (D-4) was used, ink ejection irregularities occurred from the recording head.

[0157] On the other hand, the boiling point of the first solvent contained in the aqueous media of inks (D-1) to (D-3) was between 180°C and 280°C. When inks (D-1) to (D-3) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0158] [Consideration 5: Content of the first solvent] Next, the content of the first solvent relative to the mass of the ink was examined. Inks (E-1) to (E-4) were prepared in the same manner as the preparation of ink (C-1), except for the following changes. In the "Preparation of Ink" described above, formulation ia was changed to formulation ic shown in Table 10. The formulation of the pigment dispersion remained unchanged from formulation da. The amount of triethylene glycol monobutyl ether shown in Table 10 was set to the amount of the first solvent shown in Table 11.

[0159] For inks (E-1) to (E-4), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 11.

[0160] [Table 10]

[0161] [Table 11]

[0162] Since the total amount of ink components is 100.0 parts by mass, the amount of the first solvent relative to the mass of ink (in parts by mass) shown in Table 11 and Table 19 described later corresponds to the content of the first solvent relative to the mass of ink (in %).

[0163] As shown in Table 11, inks (E-1) to (E-4) all had the following composition, although they differed in the content of the first solvent. Specifically, the unadsorbed resin ratio of these inks was greater than 0% by mass and less than or equal to 40% by mass. These inks contained a first solvent with a boiling point between 180°C and 280°C. The predetermined absorbance of these inks was 0.15 or less. When inks (E-1) to (E-4) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0164] [Consideration 6: Type of second solvent] Next, the type of second solvent was examined. Inks (F-1) to (F-2) were prepared in the same manner as ink (C-1), except for the following changes. In the "Ink Preparation" described above, formulation ia was changed to formulation id shown in Table 12. The formulation of the pigment dispersion remained unchanged from formulation da. As the second solvent shown in Table 12, the second solvent shown in Table 13 was used.

[0165] For inks (F-1) to (F-2), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 13.

[0166] [Table 12]

[0167] [Table 13]

[0168] The terms used in Table 13 are as follows: "TetraEG" refers to tetraethylene glycol. "TriEG" refers to triethylene glycol.

[0169] As shown in Table 13, inks (F-1) to (F-2), although differing in the type of second solvent, all had the following composition. Specifically, the unadsorbed resin ratio of these inks was greater than 0% by mass and less than or equal to 40% by mass. These inks contained a first solvent with a boiling point between 180°C and 280°C. The predetermined absorbance of these inks was 0.15 or less. Therefore, when inks (F-1) to (F-2) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0170] [Consideration 7: Types of resins] Next, the type of resin was examined. Ink (G-1) was prepared using the same method as ink (C-1), except for the following changes. In the "Preparation of Pigment Dispersion" described above, formulation da was changed to formulation dc shown in Table 14. The ink formulation remained unchanged from formulation ia.

[0171] For ink (G-1), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 15.

[0172] [Table 14]

[0173] [Table 15]

[0174] As shown in Table 15, although the type of resin differed, all inks (G-1) had the following composition. Specifically, the unadsorbed resin ratio of these inks was greater than 0% by mass and less than or equal to 40% by mass. These inks contained a first solvent with a boiling point between 180°C and 280°C. The predetermined absorbance of this ink was 0.15 or less. Therefore, when using ink (G-1), the occurrence of ink ejection irregularities from the recording head could be suppressed.

[0175] [Consideration 8: Pigment / Resin Ratio] Next, the pigment / resin ratio was examined. Inks (H-1) to (H-2) were prepared using the same method as for ink (C-1), except for the following changes. In the "Preparation of Pigment Dispersion" described above, formulation da was changed to formulation dd shown in Table 16. The amounts of resin and pigment shown in Table 16 are as shown in the "Pigment / Resin" column of Table 17. The formulation of ink ia remained unchanged.

[0176] For inks (H-1) to (H-2), the predetermined absorbance and the ratio of unadsorbed resin were measured using the same method as in "Study 1" described above, and the presence or absence of ink ejection irregularities from the recording head was evaluated. The measurement results and evaluation results are shown in Table 17.

[0177] [Table 16]

[0178] [Table 17]

[0179] The meanings of the terms in Table 17 are as follows: "7.0 / 14.0" indicates that 7.0 parts by mass of pigment and 14.0 parts by mass of resin were added in the preparation of the pigment dispersion. "10.0 / 11.0" indicates that 10.0 parts by mass of pigment and 11.0 parts by mass of resin were added in the preparation of the pigment dispersion.

[0180] As shown in Table 17, inks (H-1) to (H-2), although having different pigment / resin ratios, all had the following composition. Specifically, the unadsorbed resin ratio of these inks was greater than 0% by mass and less than or equal to 40% by mass. These inks contained a first solvent with a boiling point between 180°C and 280°C. The predetermined absorbance of these inks was 0.15 or less. Therefore, when inks (H-1) to (H-2) were used, the occurrence of ink ejection irregularities from the recording head was suppressed.

[0181] Based on the above considerations 1 to 8, it is determined that the ink of the present invention can suppress the occurrence of ink ejection irregularities from the recording head. Furthermore, it is determined that the inkjet recording apparatus of the present invention using such ink can suppress the occurrence of ink ejection irregularities from the recording head.

[0182] [Evaluation of resolubility] Of the inks mentioned above, the resolubility of inks (A-1) to (A-7) and (B-1) to (B-4) was evaluated using the following method. The evaluation results are shown in Table 18.

[0183] The same evaluation machine used for evaluating the ejection irregularity described above was used to evaluate the resolubility. 0.3 mL of ink was placed on the tip of the wiper equipped with the evaluation machine and left for 10 minutes in an environment of 25°C and 60% RH. Next, the ejection surface of the recording head was wiped in the forward direction (opposite to the wiping direction D3 in Figure 5) using the ink-covered wiper, spreading the ink across the ejection surface. The spread ink was dried at 45°C for 4 days to form dried ink on the ejection surface.

[0184] After the dry ink had formed, a cleaning operation was performed using the evaluation machine. Specifically, a nonwoven fabric impregnated with 3g of cleaning solution was pressed against the ejection surface of the recording head for 30 seconds (corresponding to the cleaning solution supply operation). As the cleaning solution, the head cleaning solution for the inkjet color production printer "TASKalfa Pro 15000c" manufactured by Kyocera Document Solutions Inc. was used. As the nonwoven fabric, a cut piece of "Bencott® M-3II" manufactured by Asahi Kasei Corporation was used. Next, the nonwoven fabric was separated from the ejection surface of the recording head. Next, 0.3 mL of ink was forcibly discharged (purged) from the recording head (corresponding to the purging operation). Next, the ejection surface of the recording head was wiped in the return direction (wiping direction D3 in Figure 5) using a wiper (corresponding to the wiping operation). This removed the dry ink adhering to the ejection surface of the recording head, along with the cleaning solution and purged ink. The details of the cleaning operation performed in this test are generally the same as the cleaning operation described with reference to Figures 4 and 5. Next, the ejection surface of the recording head was visually inspected to check for any remaining dried ink that could not be cleaned. Note that the more easily the dried ink dissolves in the cleaning solution and purge ink, the easier it is to remove the dried ink adhering to the ejection surface of the recording head. The resolubility of the ink was determined according to the following evaluation criteria.

[0185] (Criteria for resolubility) Good (A): No dried ink is observed on the ejection surface of the recording head. Normal (N): A small amount of dried ink is visible on the ejection surface of the recording head, but it does not affect actual use.

[0186] [Table 18]

[0187] As shown in Table 18, if the unadsorbed resin ratio is 10% by mass or more, the resolubility of the ink can be improved. As shown in Table 4, if the unadsorbed resin ratio exceeds 40% by mass, the occurrence of ink ejection irregularities from the recording head cannot be suppressed. Therefore, it is judged that if the unadsorbed resin ratio is between 10% by mass and 40% by mass, the occurrence of ink ejection irregularities from the recording head can be suppressed, and the resolubility of the ink can be improved.

[0188] [Evaluation of abrasion resistance] Of the inks mentioned above, the scratch resistance of images formed using inks (D-1) to (D-4) and (E-1) to (E-4) was evaluated using the following method. The evaluation results are shown in Table 19.

[0189] For the evaluation of abrasion resistance, the same evaluation machine and paper as for the evaluation of ejection wrinkling described above were used. The evaluation of abrasion resistance was conducted in an environment with a temperature of 25°C and a humidity of 60%RH. The ink ejection amount per pixel was set to 11 pL. Using the evaluation machine, a solid image (4 cm x 5 cm) was printed on one sheet of paper (hereinafter sometimes referred to as Paper A). Next, the abrasion test described below was performed. In the abrasion test, an unused sheet of paper (hereinafter sometimes referred to as Paper B) was placed on top of the solid image printed on Paper A. Next, a 1 kg weight was placed on Paper B. Then, by moving Paper B and the weight together so that only the weight of the weight itself was applied, Paper B was rubbed back and forth five times against the solid image. After the abrasion test, the image density of areas on Paper A where no solid image was formed was measured at three locations using a reflectance densitometer (X-Rite "RD-19"). The highest image density among the measured image densities was taken as the evaluation value. If the evaluation value is 0.030 or less, the image is judged to have sufficient scratch resistance for practical use. Furthermore, a smaller evaluation value indicates less color transfer due to rubbing and superior scratch resistance.

[0190] [Table 19]

[0191] As shown in Table 19, if the content of the first solvent is 20% by mass or less relative to the mass of the ink, the scratch resistance of the image formed using the ink can be improved. As shown in Table 9, if the boiling point of the first solvent is less than 180°C, the occurrence of ink ejection distortion from the recording head cannot be suppressed. Therefore, if the boiling point of the first solvent is 180°C or higher and 280°C or lower, and the content of the first solvent is 5% by mass or higher and 20% by mass or less relative to the mass of the ink, it is judged that the occurrence of ink ejection distortion from the recording head can be suppressed, and the scratch resistance of the image formed using the ink can be improved. [Industrial applicability]

[0192] The ink and inkjet recording apparatus of the present invention can be used to form an image. [Explanation of symbols]

[0193] 1: Inkjet recording device 4: Recording head 6: First Conveyor Unit 41: Nozzle 42:Discharge surface 92: Cleaning parts S: Recording medium

Claims

1. An inkjet ink comprising a quinacridone pigment, a resin, and an aqueous medium, The resin comprises an adsorbed resin that is adsorbed onto the quinacridone pigment and an unadsorbed resin that is not adsorbed onto the quinacridone pigment. The proportion of the unadsorbed resin in the supernatant liquid obtained by centrifuging the inkjet ink at 1,050,000 G for 3 hours is 10% by mass or more and 40% by mass or less. The aqueous medium comprises a first organic solvent having a boiling point of 180°C or higher and 280°C or lower. In the ultraviolet-visible light absorption spectrum of a 25-fold diluted supernatant obtained by centrifuging the inkjet ink at 1,050,000 G for 3 hours, the absorbance of a predetermined peak is 0.15 or less, and the predetermined peak is the maximum peak in the wavelength range of 400 nm to 490 nm.

2. The inkjet ink according to claim 1, wherein the first organic solvent is triethylene glycol monobutyl ether, propylene glycol, or 1,5-pentanediol.

3. The inkjet ink according to claim 1 or 2, wherein the content of the first organic solvent is 5% by mass or more and 20% by mass or less, relative to the mass of the inkjet ink.

4. The aqueous medium further comprises a second organic solvent having a boiling point higher than 280°C. The inkjet ink according to claim 1 or 2, wherein the ratio of the mass of the first organic solvent to the mass of the second organic solvent is 1.0 or more and 4.0 or less.

5. The inkjet ink according to claim 1 or 2, wherein the predetermined peak is a peak derived from an intermediate for synthesizing the quinacridone pigment.

6. A transport unit that transports the recording medium, It comprises a recording head that ejects ink onto the recording medium, An inkjet recording apparatus wherein the ink is the inkjet ink described in claim 1 or 2.

7. The inkjet recording apparatus according to claim 6, wherein the recording head is a line head.

8. The recording head has an ejection surface through which the nozzle for ejecting the ink opens. The inkjet recording apparatus according to claim 6, further comprising a cleaning member for wiping the discharge surface.

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