Ink for inkjet, and inkjet recording device

Abstract

To provide ink for inkjet which is excellent in discharge stability, dispersion stability and re-melting property, and enables formation of an image excellent in scratch resistance.SOLUTION: Ink for inkjet contains a quinacridone pigment, a pigment coating resin, and an aqueous medium. The pigment coating resin contains an adsorption resin which is adsorbed to the quinacridone pigment, and a non-adsorption resin which is not adsorbed to the quinacridone resin. A ratio of the non-adsorption resin to the pigment coating resin is 18 mass% or more and 52 mass% or less. Phosphorus concentration in a supernatant liquid obtained by subjecting ink for inkjet to centrifugal treatment at 1,050,000 G for 3 hours is 1.0 ppm or more and 12.5 ppm or less. Sulfur concentration in the supernatant liquid is 1.0 ppm or more and 12.5 ppm or less. In an ultraviolet visible light absorption spectrum on 25 times dilution liquid of the supernatant liquid, absorbance of a first peak is 0.010 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inkjet ink and an inkjet recording apparatus. [Background technology]

[0002] An inkjet recording apparatus ejects inkjet ink from a recording head. The inkjet ink is required to have excellent dispersion stability and ejection stability, and to be capable of forming an image having excellent abrasion resistance. In addition, when an inkjet recording apparatus is used, the inkjet ink attached to the ejection surface of the recording head may dry, and the pigment may adhere to the ejection surface of the recording head. For this reason, the inkjet recording apparatus may be provided with a cleaning member. The cleaning member wipes the pigment adhered to the ejection surface of the recording head together with, for example, a cleaning liquid or inkjet ink purged from the recording head (hereinafter, sometimes referred to as purged ink). From the viewpoint of reliably cleaning the ejection surface of the recording head with the cleaning member, the inkjet ink is also required to have the performance that the pigment that has dried and adhered to the ejection surface of the recording head can be easily dissolved in the cleaning liquid or purged ink (hereinafter, sometimes referred to as resolubility).

[0003] In response to such demands, for example, an inkjet recording liquid containing an aqueous pigment dispersion has been proposed (Patent Document 1). This aqueous pigment dispersion contains an aqueous liquid, a quinacridone pigment dispersed in the aqueous liquid, a water-soluble quinacridone derivative adsorbed to the surface of the quinacridone pigment, and an unadsorbed water-soluble quinacridone derivative. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-273383 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the inkjet recording liquid described in Patent Document 1 is insufficient in at least one of ejection stability, dispersion stability, resolubility, and scratch resistance of the formed image.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet ink that is excellent in ejection stability, dispersion stability and resolubility, and is capable of forming an image that is excellent in abrasion resistance, and an inkjet recording device that uses this inkjet ink. [Means for solving the problem]

[0007] The inkjet ink according to the present invention contains a quinacridone pigment, a pigment-coated resin, and an aqueous medium. The pigment-coated resin contains an adsorbed resin adsorbed to the quinacridone pigment and an unadsorbed resin not adsorbed to the quinacridone pigment. The proportion of the unadsorbed resin in the pigment-coated resin is 18% by mass or more and 52% by mass or less. The phosphorus concentration in the supernatant obtained by centrifuging the inkjet ink according to the present invention at 1,050,000 G for 3 hours is 1.0 ppm or more and 12.5 ppm or less. The sulfur concentration in the supernatant is 1.0 ppm or more and 12.5 ppm or less. In the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant, the absorbance of the first peak is 0.010 or less. The first peak is the maximum peak in the wavelength range of 400 nm or more and 450 nm or less.

[0008] An inkjet recording apparatus according to the present invention includes a transport unit that transports a recording medium, and a recording head that ejects ink onto the recording medium, the ink being the inkjet ink described above. Effect of the Invention

[0009] The inkjet ink according to the present invention is excellent in ejection stability, dispersion stability and resolubility, and can form an image with excellent abrasion resistance. The inkjet recording apparatus according to the present invention is provided with the inkjet ink with excellent ejection stability, dispersion stability and resolubility, and can form an image with excellent abrasion resistance. [Brief description of the drawings]

[0010] [Figure 1] FIG. 13 is a diagram illustrating an example of an inkjet recording apparatus according to a second embodiment. [Diagram 2] FIG. 2 is a diagram showing the bottom surface of the recording head shown in FIG. [Diagram 3] 5A to 5C are diagrams illustrating a supply operation of a cleaning liquid. [Figure 4] 11A and 11B are diagrams illustrating a purge operation and a wipe operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described. First, the terms used in this specification will be described. 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer (for example, Zetasizer Nano ZS manufactured by Malvern Instruments) unless otherwise specified. The acid value is a value measured according to JIS (Japanese Industrial Standards) K0070:1992 unless otherwise specified. The mass average molecular weight (Mw) is a value measured using gel permeation chromatography unless otherwise specified. The viscosity is a value measured in an environment of 25°C according to the method described in JIS (Japanese Industrial Standards) Z 8803:2011 Viscosity Measurement Method for Liquids unless otherwise specified. In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". In the explanation of the formula, "independently" means that they may represent the same group or different groups. Each component described in this specification may be used alone or in combination of two or more types.

[0012] [First embodiment: Inkjet ink] The first embodiment of the present invention relates to an inkjet ink (hereinafter, sometimes simply referred to as ink). The ink of this embodiment contains a quinacridone pigment, a pigment-coated resin, and an aqueous medium. The pigment-coated resin contains an adsorbed resin adsorbed to the quinacridone pigment and an unadsorbed resin not adsorbed to the quinacridone pigment. The ratio of the unadsorbed resin to the pigment-coated resin is 18% by mass or more and 52% by mass or less. The phosphorus concentration in the supernatant obtained by centrifuging the ink of this embodiment at 1,050,000 G for 3 hours is 1.0 ppm or more and 12.5 ppm or less. The sulfur concentration in the supernatant is 1.0 ppm or more and 12.5 ppm or less. In the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant, the absorbance of the first peak (hereinafter, sometimes referred to as the first absorbance) is 0.010 or less. The first peak is the maximum peak in the wavelength range of 400 nm or more and 450 nm or less.

[0013] Hereinafter, the "proportion of unadsorbed resin in the pigment-coated resin" may be referred to as the "proportion of unadsorbed resin." Also, the "sulfur concentration in the supernatant obtained by centrifuging the ink at 1,050,000G for 3 hours" may be referred to as the "predetermined sulfur concentration." Also, the "phosphorus concentration in the supernatant obtained by centrifuging the ink at 1,050,000G for 3 hours" may be referred to as the "predetermined phosphorus concentration."

[0014] The ink of the present embodiment, having the above-described composition, is capable of forming images that are excellent in ejection stability, dispersion stability, and resolubility, as well as excellent abrasion resistance. The reason for this is believed to be as follows.

[0015] First, to facilitate understanding, an outline of a method for synthesizing a quinacridone pigment will be described. A quinacridone pigment is, for example, a compound represented by formula (2). A quinacridone pigment is synthesized, for example, by carrying out reactions represented by reaction formulas (ra), (rb), (rc), and (r-1).

[0016] [ka]

[0017] In formulas (A), (B), (C), (1), and (2), R A , R B , R 1 , and R 2 Each independently represents a monovalent group. Hereinafter, "reactions represented by reaction formulas (ra), (rb), (rc), and (r-1)" may be referred to as "reactions (ra), (rb), (rc), and (r-1)", respectively. In addition, "compounds represented by formulas (A), (B), (C), (1), and (2)" may be referred to as "compounds (A), (B), (C), (1), and (2)", respectively. R 1 and R 2 When R represents a methyl group, compound (2) is CI Pigment Red 122. 1 and R 2 When represents a hydrogen atom, compound (2) is CI Pigment Violet 19.

[0018] In the process of carrying out the reactions (ra), (rb), and (rc), the intermediate compounds (B), (C), and (1) are sequentially produced using the compound (A) as a raw material. In addition, in the reaction (r-1), the compound (1) is reacted in the presence of a catalyst to obtain the compound (2). The catalyst used in the reaction (r-1) includes, for example, a phosphorus-containing catalyst. The outline of the synthesis method for the quinacridone pigment has been described above.

[0019] Intermediates (more specifically, compounds (B) and (C)) produced during the processes of carrying out reactions (ra), (rb), and (rc), as well as the phosphorus-containing catalyst used in reaction (r-1) may remain as impurities in the quinacridone pigment. For this reason, known inks containing quinacridone pigments may also contain the intermediates and the phosphorus-containing catalyst.

[0020] In addition, quinacridone pigments are difficult to disperse in aqueous media. Therefore, sulfur compounds (e.g., derivatives of quinacridone pigments having sulfur atoms) may be added to quinacridone pigments as dispersants. Hereinafter, the "derivatives of quinacridone pigments having sulfur atoms" may be referred to as "sulfur-containing pigment derivatives." For this reason, known inks containing quinacridone pigments may unavoidably contain sulfur compounds.

[0021] Furthermore, known inks contain, for example, a pigment-coating resin together with the quinacridone pigment in order to disperse the quinacridone pigment in an aqueous medium. The pigment-coating resin contained in known inks is present in a state in which only a portion is adsorbed to the quinacridone pigment, and the remainder is not adsorbed to the quinacridone pigment. Hereinafter, the pigment-coating resin adsorbed to the quinacridone pigment may be referred to as an adsorbed resin. The quinacridone pigment is dispersed in an aqueous medium by the adsorbed resin. The pigment-coating resin not adsorbed to the quinacridone pigment may be referred to as an unadsorbed resin. The unadsorbed resin is, for example, free in the aqueous medium.

[0022] The polarity of the phosphorus-containing catalyst and the unadsorbed resin is relatively high. Therefore, when forming an image using a known ink containing a quinacridone pigment, the phosphorus-containing catalyst and the unadsorbed resin may electrostatically adhere to the ejection surface of the recording head and the inner wall of the nozzle hole. The phosphorus-containing catalyst and the unadsorbed resin adhered to the ejection surface of the recording head and the inner wall of the nozzle hole suppress the known ink from being ejected stably from the recording head (decreases the ejection stability of the known ink).

[0023] In contrast, the ink of this embodiment contains a relatively small amount of phosphorus-containing catalyst, which is an impurity (predetermined phosphorus concentration is 12.5 ppm or less). Therefore, the ink of this embodiment can suppress the decrease in ejection stability caused by the phosphorus-containing catalyst. On the other hand, the ink of this embodiment contains, for example, a very small amount of a phosphorus compound (e.g., a phosphorus-containing catalyst) (predetermined phosphorus concentration is 1.0 ppm or more). Quinacridone pigments that contain a small amount of a phosphorus compound (especially a phosphorus-containing catalyst) tend to be easily redissolved in cleaning liquid or purged ink when they are fixed to the ejection surface of a recording head. Therefore, the ink of this embodiment can exhibit excellent resolubility by containing the above-mentioned very small amount of phosphorus compound.

[0024] In addition, the ink of this embodiment has a predetermined sulfur concentration of 1.0 ppm or more. The predetermined sulfur concentration is derived from, for example, a sulfur compound. The sulfur compound functions as a dispersant that reduces the diameter of pigment particles containing quinacridone pigments in the production of the ink of this embodiment. The sulfur compound used in the production of the ink of this embodiment is, for example, contained in the pigment particles. If a large amount of sulfur compound is used in the production of the ink of this embodiment, the pigment particles are reduced in diameter and the pigment particles are less likely to settle. Therefore, in the ink of this embodiment, the predetermined sulfur concentration is set to 1.0 ppm or more, so that the dispersion stability can be optimized. However, images containing pigment particles with excessively small particle diameters tend to have low abrasion resistance. Therefore, in the ink of this embodiment, the predetermined sulfur concentration is set to 12.5 ppm or less to suppress excessive reduction in the diameter of the pigment particles. As a result, the ink of this embodiment can optimize the abrasion resistance of the image formed.

[0025] Furthermore, the ink of this embodiment has an unadsorbed resin ratio of 52% by mass or less. Known inks that contain a large amount of unadsorbed resin tend to have a tendency to have reduced ejection stability. The ink of this embodiment has a relatively small amount of unadsorbed resin, and therefore can exhibit excellent ejection stability. Meanwhile, the unadsorbed resin also has the property of promoting the binding between the quinacridone pigment and the recording medium. Therefore, the ink of this embodiment contains a certain amount of unadsorbed resin (unadsorbed resin ratio of 18% by mass or more). This allows the ink of this embodiment to promote the binding between the quinacridone pigment and the recording medium, and further optimize the abrasion resistance of the formed image.

[0026] Furthermore, in the ink of this embodiment, the first absorbance is 0.010 or less in the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant. The first peak is, for example, a peak derived from an intermediate for synthesizing a quinacridone pigment (more specifically, compounds (B) and (C), etc.). In the ink of this embodiment, the first absorbance of the supernatant is 0.010 or less, and the content of the intermediate as an impurity is relatively small, so that a decrease in ejection stability caused by the intermediate can be suppressed.

[0027] As described above, the ink of the present embodiment has an optimized amount of unadsorbed resin, sulfur compound, phosphorus compound, intermediate, etc., and therefore has excellent ejection stability, dispersion stability, and resolubility, and can form an image with excellent abrasion resistance. The ink of the present embodiment will be described in more detail below.

[0028] <Specified phosphorus concentration> First, the predetermined phosphorus concentration of the ink of this embodiment will be described. As already mentioned, the predetermined phosphorus concentration is 1.0 ppm or more and 12.5 ppm or less, preferably 1.5 ppm or more and 10.0 ppm or less, more preferably 3.5 ppm or more and 8.5 ppm or less, and even more preferably 5.5 ppm or more and 7.0 ppm or less. By setting the predetermined phosphorus concentration to 1.0 ppm or more, the ink of this embodiment can exhibit excellent resolubility. By setting the predetermined phosphorus concentration to 12.5 ppm or less, the ink of this embodiment can exhibit excellent ejection stability.

[0029] The predetermined phosphorus concentration is, for example, the concentration of phosphorus atoms derived from a phosphorus-containing catalyst for synthesizing the quinacridone pigment. That is, the ink of the present embodiment contains, for example, a phosphorus-containing catalyst. In this case, the predetermined phosphorus concentration is, for example, the concentration of phosphorus atoms possessed by the phosphorus-containing catalyst contained in the supernatant.

[0030] The phosphorus-containing catalyst is, for example, at least one selected from the group consisting of polyphosphoric acid and polyphosphoric acid derivatives. Therefore, the predetermined phosphorus concentration is, more specifically, the concentration of phosphorus atoms contained in at least one selected from the group consisting of polyphosphoric acid and polyphosphoric acid derivatives. Hereinafter, "at least one selected from the group consisting of polyphosphoric acid and polyphosphoric acid derivatives" may be referred to as "polyphosphoric acids".

[0031] The polyphosphoric acid derivative may be, for example, a polyphosphate ester, more specifically, a polyphosphate alkyl ester. The polyphosphate alkyl ester is preferably a polyphosphate methyl ester. The catalyst used in the above reaction (r-1) may further contain a metal catalyst such as tin in addition to the phosphorus-containing catalyst.

[0032] The predetermined phosphorus concentration is reduced by removing at least a portion of the phosphorus-containing catalyst remaining in the quinacridone pigment, for example, by ultrafiltration. For example, the predetermined phosphorus concentration can be adjusted by changing the circulation time of the pigment dispersion when ultrafiltering the pigment dispersion. The longer the circulation time of the pigment dispersion, the lower the predetermined phosphorus concentration tends to be. The predetermined phosphorus concentration is measured, for example, by the method described in the examples. The predetermined phosphorus concentration of the ink of this embodiment has been described above.

[0033] Next, the components contained in the ink of this embodiment will be described. The ink of this embodiment contains at least a quinacridone pigment, a pigment-coated resin, and an aqueous medium. The ink of this embodiment further contains, for example, a sulfur compound. In the ink of this embodiment, the sulfur compound, for example, together with the quinacridone pigment, constitutes a pigment composition. The ink of this embodiment may further contain a surfactant and other components as necessary. Below, the pigment composition, the pigment-coated resin, the aqueous medium, the surfactant, and other components will be described.

[0034] <Pigment composition> The pigment composition contains a quinacridone pigment and a sulfur compound. The quinacridone pigment and the sulfur compound will be described below.

[0035] (Quinacridone pigments) Quinacridone pigments include, for example, CI Pigment Violet (19 and 42), CI Pigment Red (122, 202, 206, 207, and 209), and CI Pigment Orange (48 and 49).

[0036] Examples of commercially available quinacridone pigments that can be used include "TRM-11" manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., "Cinquasia (registered trademark) Magenta D4550" manufactured by BASF, "Cinquasia (registered trademark) Pink D4450" manufactured by BASF, "Inkjet Magenta ES" manufactured by Clariant, "HOSTAPERM PINK E 02" manufactured by Clariant, "HOSTAPERM RED E3B" manufactured by Clariant, and "HOSTAPERM RED E5B 02" manufactured by Clariant.

[0037] The content of the quinacridone pigment in the ink of the present embodiment is preferably 1.0% by mass or more and 12.0% by mass or less, and more preferably 4.0% by mass or more and 8.0% by mass or less. By making the content of the quinacridone pigment 1.0% by mass or more, an image having a desired image density can be formed using the ink of the present embodiment. By making the content of the quinacridone pigment 12.0% by mass or less, the fluidity of the ink of the present embodiment can be optimized. The ink of the present embodiment may contain only the quinacridone pigment as a pigment. In addition, in order to adjust the hue of the ink of the present embodiment, the ink of the present embodiment may further contain a pigment other than the quinacridone pigment in addition to the quinacridone pigment as a pigment. The content of the quinacridone pigment in the pigment is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0038] (Sulfur compounds) The sulfur compound is adsorbed to the quinacridone pigment, thereby dispersing the quinacridone pigment in the aqueous medium. The predetermined sulfur concentration is, for example, the concentration of sulfur atoms contained in the sulfur compound (for example, a sulfur-containing pigment derivative, more specifically, a sulfur compound represented by the formula (1) described later).

[0039] As already mentioned, the predetermined sulfur concentration is 1.0 ppm or more and 12.5 ppm or less, preferably 1.0 ppm or more and 10.0 ppm or less, more preferably 1.2 ppm or more and 5.0 ppm or less, and even more preferably 1.2 ppm or more and 2.5 ppm or less. By setting the predetermined sulfur concentration to 1.0 ppm or more, the ink of the present embodiment can exhibit excellent resolubility. By setting the predetermined sulfur concentration to 12.5 ppm or less, the ink of the present embodiment can form an image with excellent abrasion resistance.

[0040] For example, the predetermined sulfur concentration can be adjusted by changing the content of the sulfur compound relative to the total mass of the quinacridone pigment and the sulfur compound. The lower the content of the sulfur compound relative to the total mass of the quinacridone pigment and the sulfur compound, the lower the predetermined sulfur concentration tends to be. The content of the sulfur compound relative to the total mass of the quinacridone pigment and the sulfur compound is preferably within the same range as the content of the sulfur-containing pigment derivative (1) relative to the total mass of the quinacridone pigment and the sulfur-containing pigment derivative (1) described later. The predetermined sulfur concentration is measured, for example, by the method described in the Examples.

[0041] The sulfur compound is, for example, a sulfur-containing pigment derivative. The sulfur-containing pigment derivative has, for example, a sulfur-containing group. Examples of the sulfur-containing group include a sulfo group, a sulfino group, a sulfeno group, a thiocarboxy group, a dithiocarboxy group, and a sulfide group. The sulfur-containing pigment derivative is, for example, a compound in which a hydrogen atom contained in the quinacridone pigment exemplified above is replaced with a sulfur-containing group.

[0042] The sulfur-containing pigment derivative is preferably a metal salt. When the sulfur-containing pigment derivative is a metal salt, the affinity of the sulfur-containing pigment derivative to the aqueous medium is increased. As a result, the quinacridone pigment having the sulfur-containing pigment derivative adsorbed thereon is well dispersed in the aqueous medium. As the sulfur-containing pigment derivative that is a metal salt, a sulfur compound represented by formula (1) (hereinafter, sometimes referred to as sulfur-containing pigment derivative (1)) is preferred. That is, the ink of the present embodiment preferably contains the sulfur-containing pigment derivative (1).

[0043] [ka]

[0044] In formula (1), n ​​represents an integer of 1 or more and 3 or less, m represents an integer of 1 or more and 3 or less, and X represents a metal ion.

[0045] In formula (1), n ​​preferably represents 2 or 3. m preferably represents 1. In formula (1), X preferably represents a monovalent or more and trivalent or less metal ion, more preferably a divalent or trivalent metal ion, and is preferably Al. 3+ or Mg 2+ It is even more preferred that

[0046] Examples of the sulfur-containing pigment derivative (1) include sulfur compounds represented by formulas (1-1) and (1-2) (hereinafter, these may be referred to as sulfur-containing pigment derivatives (1-1) and (1-2), respectively). Note that although m in formulas (1-1) and (1-2) represents 1, this is omitted here.

[0047] [ka]

[0048] The content of the sulfur-containing pigment derivative (1) relative to the total mass of the quinacridone pigment and the sulfur-containing pigment derivative (1) is preferably 4% by mass or more and 12% by mass or less, more preferably 4% by mass or more and 6% by mass or less. Hereinafter, the "content of the sulfur-containing pigment derivative relative to the total mass of the quinacridone pigment and the sulfur-containing pigment derivative" may be referred to as the "derivative content". When the derivative content is 4% by mass or more and 12% by mass or less, the predetermined sulfur concentration can be easily adjusted to a value in the desired range. The lower the derivative content, the lower the predetermined sulfur concentration tends to be.

[0049] The content of the sulfur-containing pigment derivative in the ink of this embodiment is preferably from 0.03% by mass to 0.60% by mass, and more preferably from 0.12% by mass to 0.40% by mass.

[0050] <Pigment-coated resin> The pigment-coating resin includes an adsorbed resin and an unadsorbed resin. The adsorbed resin is adsorbed to the quinacridone pigment. The quinacridone pigment, for example, constitutes a pigment particle together with the adsorbed resin. The pigment particle has, for example, a core containing the quinacridone pigment and a coating layer that coats the core. The coating layer is composed of the adsorbed resin. Since the pigment-coating resin is hydrophilic, the quinacridone pigment is dispersed in the aqueous medium by the adsorbed resin adsorbed to the surface of the quinacridone pigment. On the other hand, the unadsorbed resin is not adsorbed to the quinacridone pigment. The unadsorbed resin is free in the aqueous medium.

[0051] As already mentioned, the unadsorbed resin ratio is 18% by mass or more and 52% by mass or less, preferably 25% by mass or more and 45% by mass or less, and more preferably 25% by mass or more and 35% by mass or less. By making the unadsorbed resin ratio 18% by mass or more, the ink of this embodiment can form an image with excellent abrasion resistance. By making the unadsorbed resin ratio 52% by mass or less, the ink of this embodiment can exhibit excellent ejection stability.

[0052] The proportion of unadsorbed resin can be measured by centrifuging the ink of this embodiment using a centrifuge. The proportion of unadsorbed resin can be calculated from the formula "proportion of unadsorbed resin = 100 x mass of unadsorbed resin / total mass of pigment-coated resin = 100 x mass of unadsorbed resin / (mass of unadsorbed resin + mass of adsorbed resin)". For example, the proportion of unadsorbed resin tends to increase as the discharge amount of the wet disperser increases in the pigment dispersion preparation process described below.

[0053] In the ink of this embodiment, the first absorbance is 0.010 or less, preferably 0.005 or less, and more preferably 0.002 or less. The first absorbance is, for example, 0.001 or more. By setting the first absorbance to 0.010 or less, the ink of this embodiment can exhibit excellent ejection stability.

[0054] In the ultraviolet-visible light absorption spectrum of the supernatant obtained by centrifuging the ink of this embodiment at 1,050,000 G for three hours, the absorbance of the second peak is preferably 0.15 or more and 0.40 or less. In this specification, the second peak is the maximum peak in the wavelength range of 300 nm or more and 350 nm or less. Hereinafter, "the absorbance of the second peak in the ultraviolet-visible light absorption spectrum of the supernatant obtained by centrifuging the ink of this embodiment at 1,050,000 G for three hours" may be referred to as "second absorbance".

[0055] The second peak is, for example, a peak derived from unadsorbed resin. If the second absorbance is 0.15 or more and 0.40 or less, the proportion of unadsorbed resin can be easily adjusted to a value within a desired range. As a result, the ink of this embodiment can further optimize the abrasion resistance of the formed image while further optimizing the ejection stability. In particular, if the second absorbance is 0.15 or more, the ink of this embodiment can form an image with even better abrasion resistance. If the second absorbance is 0.40 or less, the ejection stability of the ink of this embodiment can be further optimized. The second absorbance is more preferably 0.18 or more and 0.32 or less, and even more preferably 0.18 or more and 0.25 or less.

[0056] For example, the second absorbance can be adjusted by changing the proportion of unadsorbed resin. The higher the proportion of unadsorbed resin, the higher the second absorbance tends to be. The second peak appears, for example, at a wavelength of 320 nm. The second absorbance can be measured, for example, by the method described in the Examples.

[0057] In order to further optimize the ejection stability and dispersion stability of the ink of this embodiment, the ratio of the mass of the pigment-coated resin to the mass of the quinacridone pigment (hereinafter sometimes referred to as the "resin / pigment ratio") is preferably 0.30 or more and 0.50 or less, and more preferably 0.35 or more and 0.42 or less. The resin / pigment ratio can be calculated from the formula "resin / pigment ratio = mass of pigment-coated resin / mass of pigment". The mass of the pigment-coated resin is the total mass of the adsorbed resin and unadsorbed resin.

[0058] In order to further optimize the ejection stability of the ink of this embodiment, the acid value of the pigment coating resin is preferably 60 mgKOH / g or more and 300 mgKOH / g or less, more preferably 80 mgKOH / g or more and 120 mgKOH / g or less, and even more preferably 90 mgKOH / g or more and 110 mgKOH / g or less. If the acid value of the pigment coating resin is 60 mgKOH / g or more, the pigment particles are well dispersed in the aqueous medium, and an image with excellent color development and coloring power can be formed. On the other hand, if the acid value of the pigment coating resin is 300 mgKOH / g or less, the storage stability of the ink of this embodiment can be optimized.

[0059] In order to optimize the viscosity of the ink of this embodiment, the mass average molecular weight of the pigment coating resin is preferably 10,000 or more and 50,000 or less, and more preferably 15,000 or more and 30,000 or less.

[0060] Examples of the pigment coating resin include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid resin, and urethane resin. From the viewpoint of stably dispersing the quinacridone pigment, the pigment coating resin is preferably a styrene-(meth)acrylic resin.

[0061] The styrene-(meth)acrylic resin has, as repeating units, at least a first repeating unit derived from a styrene monomer, and at least one of a second repeating unit derived from (meth)acrylic acid, and a third repeating unit derived from a (meth)acrylic acid ester.

[0062] The styrene monomer is styrene or a derivative thereof. Examples of the styrene monomer include styrene, α-methylstyrene, and vinyltoluene. The styrene monomer is preferably styrene. The content ratio of the first repeating unit to the total repeating units contained in the pigment coating resin is preferably 25.0% by mass or more and 60.0% by mass or less, and more preferably 25.0% by mass or more and 30.0% by mass or less.

[0063] Examples of the (meth)acrylic acid monomer include acrylic acid and methacrylic acid. The (meth)acrylic acid monomer preferably contains methacrylic acid. The content of the second repeating unit in all repeating units contained in the pigment coating resin is preferably 4.5% by mass or more and 10.0% by mass or less, and more preferably 7.0% by mass or more and 9.0% by mass or less.

[0064] Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters. As (meth)acrylic acid alkyl esters, (meth)acrylic acid alkyl esters having an alkyl group with 1 to 8 carbon atoms are preferred, (meth)acrylic acid alkyl esters having an alkyl group with 1 to 4 carbon atoms are more preferred, methyl (meth)acrylate or butyl (meth)acrylate are even more preferred, and methyl methacrylate or butyl acrylate are particularly preferred. Of all the repeating units contained in the pigment coating resin, the content ratio of the third repeating unit is preferably 35.0% by mass or more and 70.0% by mass or less, and more preferably 50.0% by mass or more and 70.0% by mass or less. When the pigment coating resin has two or more types of third repeating units, the content ratio of the third repeating unit is the total content ratio of the two or more types of third repeating units.

[0065] The pigment-coated resin is preferably a resin having at least one type of second repeating unit, at least one type of third repeating unit, and a first repeating unit. The pigment-coated resin is more preferably a resin having a repeating unit derived from (meth)acrylic acid, a repeating unit derived from methyl (meth)acrylate, a repeating unit derived from butyl (meth)acrylate, and a repeating unit derived from styrene. The pigment-coated resin is further preferably a resin having a repeating unit derived from methacrylic acid, a repeating unit derived from methyl methacrylate, a repeating unit derived from butyl acrylate, and a repeating unit derived from styrene. The pigment-coated resin may have only these repeating units as repeating units, or may further have repeating units other than these repeating units.

[0066] The content of the pigment coating resin in the ink of this embodiment 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. By making the content of the pigment coating resin 0.5% by mass or more, it is possible to effectively suppress the aggregation of the quinacridone pigment. By making the content of the pigment coating resin 8.0% by mass or less, it is possible to effectively suppress the occurrence of nozzle clogging of the recording head.

[0067] <Aqueous medium> The aqueous medium contained in the ink of this embodiment is a medium containing water. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include aqueous media containing water and a water-soluble organic solvent.

[0068] Examples of the water-soluble organic solvent include glycol compounds, triol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, γ-butyrolactone, thiodiglycol, and dimethylsulfoxide.

[0069] 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. As the glycol compound, 3-methyl-1,5-pentanediol is preferred.

[0070] Examples of triol compounds include glycerin, 1,2,3-butanetriol, and 1,2,6-hexanetriol. As the triol compound, glycerin is preferred.

[0071] Examples of the glycol ether compound include alkylene glycol alkyl ethers, more specifically, 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. As the glycol ether compound, triethylene glycol monobutyl ether is preferred.

[0072] Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone. As the lactam compound, 2-pyrrolidone is preferred.

[0073] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0074] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0075] The water-soluble organic solvent is preferably a glycol ether compound, a glycol compound, or glycerin.The aqueous medium is preferably a mixed solvent of water, triethylene glycol monobutyl ether, 3-methyl-1,5-pentanediol, and glycerin.

[0076] The content of the aqueous medium in the ink of this embodiment is preferably 60.0% by mass or more and 95.0% by mass or less, and more preferably 80.0% by mass or more and 95.0% by mass or less. The content of water in the ink of this embodiment is preferably 40.0% by mass or more and 80.0% by mass or less, and more preferably 55.0% by mass or more and 70.0% by mass or less. The content of the glycol ether compound in the ink of this embodiment is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 3.0% by mass or more and 5.0% by mass or less. The content of the glycol compound in the ink of this embodiment is preferably 5.0% by mass or more and 35.0% by mass or less, and more preferably 15.0% by mass or more and 25.0% by mass or less. The content of glycerin in the ink of this embodiment is preferably 2.0% by mass or more and 11.0% by mass or less, and more preferably 4.0% by mass or more and 6.0% by mass or less.

[0077] <Surfactant> The surfactant optimizes the compatibility and dispersion stability of the components contained in the ink of the present embodiment. The surfactant also optimizes the penetrability of the ink of the present embodiment into a recording medium. The surfactant is preferably a nonionic surfactant.

[0078] Examples of the nonionic surfactant include acetylenic diol and ethylene oxide adducts of acetylenic diol. Examples of the acetylenic diol include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, and 2,4-dimethyl-5-hexyne-3-ol. Examples of the nonionic surfactant include ethylene oxide adducts of acetylenic diol 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. The content of the surfactant in the ink of this embodiment is preferably 0.01% by mass to 1.0% by mass, more preferably 0.1% by mass to 0.5% by mass.

[0079] <Other ingredients> The ink of the present embodiment may contain known additives (more specifically, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, a neutralizing agent, an anti-mold agent, etc.) as necessary. Note that the ink of the present embodiment does not necessarily need to contain known additives.

[0080] <Preferred composition> A preferred composition of the ink of this embodiment is shown below. In the following, the pigment composition is preferably a mixture of a quinacridone pigment and a sulfur-containing pigment derivative (1), more preferably a mixture of a quinacridone pigment and a sulfur-containing pigment derivative (1-1), or more preferably a mixture of a quinacridone pigment and a sulfur-containing pigment derivative (1-2). Pigment composition: 5.0% by mass or more and 7.0% by mass or less Pigment-coated resin: 2.0% by mass or more and 3.0% by mass or less Triethylene glycol monobutyl ether: 3.0% by mass or more and 5.0% by mass or less 3-Methyl-1,5-pentanediol: 19.0% by mass or more and 21.0% by mass or less Glycerin: 4.0% by mass or more and 6.0% by mass or less Surfactant: 0.3% by mass or more and 0.7% by mass or less Water: Remaining

[0081] <Method of synthesizing quinacridone pigments> Although the outline of the synthesis method of the quinacridone pigment has already been described, an example of the synthesis method of the quinacridone pigment will be described in more detail below. In the synthesis method of the quinacridone pigment, it is preferable to thoroughly wash each tool used in the synthesis in advance. This can remove residues (especially phosphorus-containing catalyst) remaining on each tool, and reduce the amount of phosphorus-containing catalyst remaining in the quinacridone pigment obtained by synthesis.

[0082] In the above formulas (A), (B), and (C), R A and R B Examples of the monovalent group represented by R include an alkyl group and an aryl group. A and RB The monovalent group represented by is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably an ethyl group.

[0083] In the above formulas (C), (1), and (2), R 1 and R 2 Examples of the monovalent group represented by R include a hydrogen atom, an alkyl group, and a halogen atom. 1 and R 2 The halogen atom represented by R is preferably a chlorine atom. 1 and R 2 The alkyl group represented by is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group.

[0084] 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, compound (1) is obtained by hydrolyzing the oxide of compound (C).

[0085] Then, in reaction (r-1), compound (1) is reacted in the presence of a catalyst to obtain compound (2). The catalytic reaction (r-1) is a dehydration ring-closing reaction. For example, in reaction (r-1), compound (1) is compressed and heated at a first predetermined temperature for a predetermined time in the presence of a catalyst (e.g., a phosphorus-containing catalyst, more specifically, polyphosphoric acid, etc.). The first predetermined temperature is, for example, 85°C or higher and 200°C or lower. The predetermined time is, for example, 1 hour or higher and 3 hours or lower. In reaction (r-1), an organic solvent such as acetone may be further used in addition to compound (1) and the catalyst. Also, instead of compound (1), an alkali salt obtained by saponifying compound (1) may be used in reaction (r-1). Also, instead of compound (1), an oxide of the above-mentioned compound (C) may be used in reaction (r-1).

[0086] After the reaction (r-1), if necessary, the compound (2) can be subjected to an alkali treatment to obtain a β-type quinacridone pigment. The alkali treatment can be carried out, for example, by heating a wet cake of the compound (2) and an alkali at a second predetermined temperature using an autoclave. The second predetermined temperature is, for example, 120°C or higher and 200°C or lower. An organic solvent may be further used in the alkali treatment. Examples of organic solvents that can be used in the alkali treatment include N,N-dimethylformamide and glycol.

[0087] In contrast to a synthesis method using an acid having a sulfonic acid group as a ring-closing agent, the method of synthesizing a quinacridone pigment by reaction (r-1) does not require the use of sulfuric acid to remove the sulfonic acid group or sulfonyl chloride group remaining in the generated quinacridone pigment, and therefore the method of synthesizing a quinacridone pigment by reaction (r-1) can be easily carried out.

[0088] <Method of preparing pigment composition> An example of a method for preparing a pigment composition will be described below. The method for preparing a pigment composition includes, 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). The sulfur-containing pigment derivative is added in step B. If necessary, the sulfur-containing pigment derivative may be added in step A in addition to step B.

[0089] (Step A in the process of preparing the pigment composition) In step A, the quinacridone pigment is treated with a solvent. For example, a method of treating the quinacridone pigment includes kneading the quinacridone pigment with a solvent using a kneader (e.g., a salt milling kneader). In step A, crystal growth of the quinacridone pigment and microparticulation of the quinacridone pigment are promoted. By promoting microparticulation of the quinacridone pigment, the coloring property and chroma of the quinacridone pigment are optimized. The temperature and time for treating the quinacridone pigment are not particularly limited, and may be appropriately set so as to obtain the desired particle size and particle size distribution of the quinacridone pigment. In step A, a sulfur-containing pigment derivative may be added as necessary. In addition, in step A, an inorganic base (more specifically, sodium hydroxide, potassium hydroxide, etc.) may be added as a grinding aid as necessary. The kneaded product of the quinacridone pigment obtained in step A is washed with water or a solvent as necessary, and becomes, for example, a wet cake.

[0090] (Step B in the process of preparing the pigment composition) In step B, the kneaded product of the quinacridone pigment obtained in step A is post-treated. As a method of post-treatment, for example, a method of removing the solvent from the kneaded product of the quinacridone pigment to separate a pigment composition can be mentioned. As a method of separating the pigment composition, for example, filtration, drying, and distillation of the solvent using a rotary evaporator can be mentioned. When the solvent is distilled off, the temperature of the solvent distillation is, for example, a temperature equal to or higher than the boiling point of the solvent. The separated pigment composition may be pulverized as necessary.

[0091] In step B, a sulfur-containing pigment derivative is added. In step B, the aggregation of the quinacridone pigment is suppressed, and the dispersibility and storage stability of the quinacridone pigment can be achieved at the same time. The sulfur-containing pigment derivative may be added when the process of separating the pigment composition from the kneaded product is started, or may be added during the separation process. The mass of the sulfur-containing pigment derivative added in step B (when the sulfur-containing pigment derivative is added in step A in addition to step B, the total mass of the sulfur-containing pigment derivative added in step A and step B) is preferably 0.5 parts by mass or more and 15 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, even more preferably 3 parts by mass or more and 6 parts by mass or less, and even more preferably 3 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the quinacridone pigment. When the mass of the sulfur-containing pigment derivative is 0.5 parts by mass or more and 15 parts by mass or less relative to 100 parts by mass of the quinacridone pigment, the hue of the quinacridone pigment is optimized. When the mass of the sulfur-containing pigment derivative is 3 parts by mass or more and 6 parts by mass or less relative to 100 parts by mass of the quinacridone pigment, the predetermined sulfur concentration can be easily adjusted to a value within the desired range.

[0092] When a sulfur-containing pigment derivative is added in step A in addition to step B, the type of the sulfur-containing pigment derivative added in step B may be the same as or different from the type of the sulfur-containing pigment derivative added in step A. Furthermore, when a sulfur-containing pigment derivative is added in step A in addition to step B, from the viewpoint of optimizing the coloring properties of the quinacridone pigment, it is preferable that the mass of the sulfur-containing pigment derivative added in step B is equal to or greater than the mass of the sulfur-containing pigment derivative added in step A.

[0093] <Ink manufacturing method> An example of a method for producing the ink of this embodiment will be described below. The method for producing the ink of this embodiment includes, for example, a pigment dispersion preparation step, an ultrafiltration step, and a mixing step.

[0094] (Pigment dispersion preparation process) In the pigment dispersion preparation step, a pigment composition containing a quinacridone pigment, a pigment-coated resin, and an aqueous medium are mixed to obtain a pigment dispersion. In order to thoroughly disperse the pigment particles, the pigment dispersion may further contain a surfactant. In the pigment dispersion, the D of the pigment particles composed of the quinacridone pigment and the pigment-coated resin is 50 The thickness is preferably 70 nm or more and less than 135 nm, and more preferably 110 nm or more and less than 135 nm.

[0095] The content of the quinacridone pigment in the pigment dispersion is preferably 5.0% by mass or more and 25.0% by mass or less, and more preferably 10.0% by mass or more and 20.0% by mass or less. The content of the pigment coating resin in the pigment dispersion is preferably 2.0% by mass or more and 10.0% by mass or less, and more preferably 4.0% by mass or more and 8.0% by mass or less. When the pigment dispersion contains a surfactant, the content of the surfactant in the pigment dispersion is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.3% by mass or more and 1.0% by mass or less.

[0096] The pigment dispersion can be prepared by wet-dispersing the components contained in the pigment dispersion using a media-type wet disperser. Examples of media-type wet dispersers include bead mills (more specifically, "Nanograin Mill" manufactured by Asada Iron Works Co., Ltd., "MSC Mill" manufactured by Nippon Coke & Engineering Co., Ltd., and "Dyno (registered trademark) Mill" manufactured by Willy & Bachofen Co., Ltd.).

[0097] In wet dispersion using a media type wet disperser, for example, small particle size beads (for example, beads with a diameter of 0.5 mm to 1.0 mm) are used as media. By changing the diameter of the beads, for example, the degree of dispersion of the pigment and the proportion of unadsorbed resin can be changed. The smaller the diameter of the beads, the greater the D of the pigment particles. 50The smaller the diameter of the beads, the easier it becomes for the core containing the quinacridone pigment to be covered with the pigment-coating resin, and the lower the proportion of unadsorbed resin tends to be. 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 or more and 600 g / min or less. The higher the discharge rate of the media-type wet disperser, the higher the proportion of unadsorbed resin tends to be.

[0098] (Activated carbon treatment process) In the activated carbon treatment step, the pigment dispersion is treated with activated carbon. The activated carbon treatment removes at least a portion of the unadsorbed resin and the intermediate. By using such a pigment dispersion, the first absorbance and the second absorbance of the ink of the present embodiment are easily adjusted to values ​​within a desired range. The activated carbon treatment is performed, for example, by circulating the pigment dispersion while passing the pigment dispersion through an activated carbon filter. The flow rate of the circulated pigment dispersion is, for example, 100 g / min or more and 300 g / min or less. The time for circulating the pigment dispersion is, for example, 5 minutes or more and 30 minutes or less. When the total amount of the pigment dispersion passes through the activated carbon filter, one pass is defined as the number of passes (number of passes) in the activated carbon treatment is, for example, 5 times or less.

[0099] (Ultrafiltration process) In the ultrafiltration step, the pigment dispersion is ultrafiltered. At least a part of the phosphorus-containing catalyst is removed by ultrafiltration, and the phosphorus concentration of the pigment dispersion is reduced. By using such a pigment dispersion, the predetermined phosphorus concentration of the ink of the present embodiment to be manufactured is easily adjusted to a value within a desired range. In order to remove at least a part of the phosphorus-containing catalyst, it is preferable to select a molecular weight cutoff of the ultrafiltration membrane used for ultrafiltration that filters at least a part of the phosphorus-containing catalyst and does not filter other components of the pigment dispersion. In addition, it is preferable that the molecular weight cutoff of the ultrafiltration membrane used for ultrafiltration is equal to or greater than the molecular weight of the phosphorus-containing catalyst and equal to or less than the molecular weight of the pigment-coating resin. In order to adjust the predetermined phosphorus concentration to a value within a desired range, it is preferable that the circulation time of ultrafiltration is 0.4 hours or more. In order to reduce the manufacturing cost, it is preferable that the circulation time of ultrafiltration is 2.0 hours or less. By ultrafiltration, the liquid containing the phosphorus-containing catalyst is discharged as a filtrate, and the liquid containing the components of the pigment dispersion other than the phosphorus-containing catalyst is circulated again as a recovered liquid. By adding water in an amount equal to the amount of the discharged filtrate to the recovered liquid, the solid content concentration of the pigment dispersion can be maintained constant.

[0100] (Mixing process) In the mixing step, the pigment dispersion after ultrafiltration and components that are blended as necessary (for example, an aqueous medium and a surfactant that are further added) are mixed using a stirrer. After mixing the ink components, foreign matter and coarse particles may be removed using a filter (for example, a filter with a pore size of 5 μm or less).

[0101] In the ink production method of this embodiment, the ratio of the pigment dispersion liquid to all raw materials is, for example, 25% by mass or more and 60% by mass or less. The ink of this embodiment can be suitably used, for example, in an inkjet recording device described later.

[0102] [Second embodiment: Inkjet recording apparatus] Next, an inkjet recording apparatus according to a second embodiment of the present invention will be described. The inkjet recording apparatus according to this embodiment includes a transport unit that transports a recording medium, and a recording head. The recording head ejects the ink of the first embodiment onto the recording medium. Therefore, for the same reasons as those described in the first embodiment, the inkjet recording apparatus according to this embodiment includes ink that is excellent in ejection stability, dispersion stability, and resolubility, and can form an image that is excellent in abrasion resistance.

[0103] Hereinafter, an inkjet recording apparatus 1, which is an example of an inkjet recording apparatus according to the present embodiment, will be described with reference to the drawings. Note that the drawings referred to are mainly schematic illustrations of the respective components for ease of understanding, and the size, number, etc. of the respective components illustrated may differ from the actual ones. Also, the X-axis, Y-axis, and Z-axis shown in Figs. 1 to 4 are mutually orthogonal.

[0104] 1 includes a paper feed section 3, a first recording head 4C, a second recording head 4M, a third recording head 4Y, a fourth recording head 4K, a liquid storage section 5, a first transport section 6, a second transport section 7, a discharge section 8, and a maintenance section 9. Hereinafter, when there is no need to distinguish between the first recording head 4C to the fourth recording head 4K, they may be simply referred to as "recording heads 4."

[0105] The paper feed section 3 includes a plurality of paper feed cassettes 31, a plurality of pickup rollers 32, a plurality of transport rollers 33, and a registration roller pair 34. The paper feed cassette 31 contains a stack of recording media S. The pickup roller 32 picks up the recording media S contained in the paper feed cassette 31 one by one. The transport roller 33 transports the recording media S picked up by the pickup roller 32. The registration roller pair 34 temporarily holds the recording media S transported by the transport roller 33, and then supplies the recording media S to the first transport section 6 at a predetermined timing.

[0106] The recording heads 4 are disposed above the first conveying section 6. The first recording head 4C to the fourth recording head 4K are arranged in this order in the conveying direction D of the recording medium S. The first recording head 4C to the fourth recording head 4K are disposed at the same height. The first recording head 4C to the fourth recording head 4K are filled with ink of four different colors (for example, cyan, magenta, yellow, and black). The ink filled in the second recording head 4M is the magenta ink of the first embodiment. The recording heads 4 each eject 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 conveyed by the first conveying belt 63.

[0107] The liquid storage section 5 includes a first ink tank 51C, a second ink tank 51M, a third ink tank 51Y, a fourth ink tank 51K, and a cleaning liquid tank 52. Hereinafter, when it is not necessary to distinguish between the first ink tank 51C to the fourth ink tank 51K, they may be simply referred to as "ink tanks 51". The first ink tank 51C to the fourth ink tank 51K each contain ink of four different colors (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 tank 51C to the fourth ink tank 51K supply ink to the first recording head 4C to the fourth recording head 4K, respectively. The cleaning liquid tank 52 supplies cleaning liquid to the liquid impregnated body 91.

[0108] The first conveying section 6 is disposed downstream of the paper feed section 3 in the conveying direction D of the recording medium S. The first conveying section 6 includes a first driven roller 61, a first driving roller 62, and a first conveying belt 63. The first driving roller 62 is disposed downstream of the first driven roller 61 in the conveying direction D of the recording medium S. The first conveying belt 63 is an endless belt stretched around the first driven roller 61 and the first driving roller 62. The first driving roller 62 is driven to rotate in a counterclockwise direction in FIG. 1. As a result, the first driving roller 62 drives the first conveying belt 63. As a result, the first conveying belt 63 conveys the recording medium S fed from the paper feed section 3 to the second conveying section 7 in the conveying direction D. In this way, the first conveying section 6 conveys the recording medium S. The first driven roller 61 rotates by following the first driving roller 62 via the first conveying belt 63.

[0109] The second conveying section 7 is disposed downstream of the first conveying section 6 in the conveying direction D of the recording medium S. The second conveying section 7 includes a second driven roller 71, a second driving roller 72, and a second conveying belt 73. The second driving roller 72 is disposed downstream of the second driven roller 71 in the conveying direction D of the recording medium S. The second conveying belt 73 is an endless belt stretched over the second driven roller 71 and the second driving roller 72. The second driving roller 72 is driven to rotate in a counterclockwise direction in FIG. 1. As a result, the second driving roller 72 drives the second conveying belt 73. As a result, the second conveying belt 73 conveys the recording medium S conveyed from the first conveying section 6 to the discharge section 8 in the conveying direction D. In this way, the second conveying section 7 conveys the recording medium S. The second driven roller 71 rotates by following the second driving roller 72 via the second conveying belt 73.

[0110] The discharge section 8 is disposed downstream of the second transport section 7 in the transport direction D of the recording medium S. The discharge section 8 includes 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 in pressure contact with each other at positions facing each other. The discharge drive roller 82 is driven to rotate in a counterclockwise direction in FIG. 1. The discharge driven roller 83 rotates following 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 section 7 to the discharge tray 81. The discharged recording medium S is placed on the discharge tray 81.

[0111] The maintenance unit 9 includes 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 comes into contact with the ejection surface 42 (see FIG. 2) of the recording head 4 to supply the cleaning liquid to the ejection surface 42. The liquid-impregnated body 91 is, for example, a sponge, a nonwoven fabric, or a water-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.

[0112] Next, the recording head 4 will be further described with reference to Fig. 2. Fig. 2 is a diagram showing the bottom surface of the recording head 4 shown in Fig. 1.

[0113] As shown in FIG. 2, the recording head 4 includes a first nozzle row N1, a second nozzle row N2, and an ejection surface 42. For ease of understanding, in FIG. 2, the first nozzle row N1 and the second nozzle row N2 are each surrounded by a dashed line. Each of the first nozzle row N1 and the second nozzle row N2 includes 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 in parallel 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 provided at intervals in a direction perpendicular to the transport direction D of the recording medium S. The recording head 4 is, for example, a line head.

[0114] The width 41w of each of the first nozzle row N1 and the second nozzle row N2 (i.e., the width of the area recordable 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 transported on the first transport belt 63 while remaining fixed. That is, the inkjet recording device 1 employs a single-pass method that does not involve shuttle motion. Since the inkjet recording device 1 is equipped with such a recording head 4, it can print at higher speeds than an inkjet recording device equipped with a serial head.

[0115] Next, the cleaning operation by the maintenance unit 9 will be described with reference to Figs. 3 and 4. The cleaning operation includes a cleaning liquid supply operation, a purging operation, and a wiping operation. Fig. 3 is a diagram for explaining the cleaning liquid supply operation. Fig. 4 is a diagram for explaining the purging operation and the wiping operation. Although the nozzles 41 cannot be confirmed in a side view of the recording head 4, the positions of the nozzles 41 are indicated by dashed lines in Figs. 3 and 4 to facilitate understanding.

[0116] 3, the recording head 4 has an ink inlet 43 and an ink outlet 44. Ink flows from an ink tank 51 into the recording head 4 through the ink inlet 43 and flows out of the recording head 4 through the ink outlet 44.

[0117] As shown in FIG. 1, the liquid-impregnated body 91 of the maintenance unit 9 is disposed below the second conveying unit 7. The cleaning member 92 of the maintenance unit 9 is disposed 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 conveying unit 7 and a position facing the ejection surface 42 of the recording head 4. Furthermore, as shown in FIG. 3, the liquid-impregnated body 91 is movable in each of the upward direction D1 and the downward direction D2. As shown in FIG. 4, the cleaning member 92 is movable in each of the upward direction D1, the downward direction D2, and the wiping direction D3. The "upward direction D1" is a direction approaching the ejection surface 42 in the Z-axis direction. Moreover, the "downward direction D2" is a direction moving away from the ejection surface 42 in the Z-axis direction. Moreover, the "wiping direction D3" is a direction along the ejection surface 42. The liquid impregnated body 91 and the cleaning member 92 are each moved by a known driving mechanism (not shown).

[0118] Here, the ink adhering to the ejection surface 42 may dry and become solidified. In order to remove such solidified ink, a cleaning operation is carried out.

[0119] First, the supply operation of the cleaning liquid in the cleaning operation will be described. The liquid impregnated body 91 is impregnated with the cleaning liquid. Next, as shown in FIG. 3, the liquid impregnated body 91 moves to a position facing the discharge surface 42, and then moves in an upward direction D1. Then, the liquid impregnated body 91 is pressed against the discharge surface 42. In this way, the cleaning liquid impregnated in 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 in a downward direction D2. Then, the state in which the liquid impregnated body 91 is pressed against the discharge surface 42 is released.

[0120] Next, the purge operation will be described. As shown in Fig. 4, ink is purged from the recording head 4. In Fig. 4, the purged ink (purged ink) is indicated with "Nf". Specifically, ink is forcibly discharged from the nozzles 41 by pressurizing the recording head 4. This clears any clogging in the nozzles 41, and the purged ink Nf adheres to the ejection surface 42 of the recording head 4.

[0121] Next, the wiping operation will be described. After the cleaning member 92 moves to a position facing the ejection surface 42 (position shown in FIG. 4), it moves in an upward direction D1. Then, the cleaning member 92 is pressed against the ejection surface 42. While the cleaning member 92 is kept pressed against the ejection surface 42, the cleaning member 92 moves in a direction along the ejection surface 42 (wiping direction D3 shown in FIG. 4). This causes the cleaning member 92 to wipe the ejection surface 42. As a result, the ink (for example, the fixed ink and the purged ink Nf) and the cleaning liquid adhering to the ejection surface 42 are removed. Then, the ejection surface 42 of the recording head 4 is cleaned. Next, the cleaning member 92 moves in a downward direction D2. Then, the state in which the cleaning member 92 is pressed against the ejection surface 42 is released.

[0122] The inkjet recording device 1, which is an example of the inkjet recording device of the present embodiment, has been described above. However, the inkjet recording device of the present embodiment is not limited to the inkjet recording device 1. The inkjet recording device of the present embodiment may adopt a multi-pass system. In addition, in the first recording head 4C to the fourth recording head 4K, the number of nozzles 41, the interval between the nozzles 41, and the positional relationship of the nozzles 41 can be appropriately set according to the specifications of the device. In addition, the supplying operation of the cleaning liquid may be ejection of the cleaning liquid by an inkjet method, application of the cleaning liquid using a roller, or spraying of the cleaning liquid. In addition, the supplying operation of the cleaning liquid, the purging operation, and the wiping operation may each be repeated. In addition, the order in which the supplying operation of the cleaning liquid and the purging operation are performed is not limited. In addition, the cleaning member 92 may reciprocate in a direction along the ejection surface 42. For example, while the cleaning member 92 is maintained pressed against the ejection surface 42, the cleaning member 92 may move in a first direction along the ejection surface 42 (wiping direction D3 shown in FIG. 4), and then move in a second direction opposite to the first direction along the ejection surface 42 (the direction opposite to the wiping direction D3 shown in FIG. 4). EXAMPLES

[0123] Examples of the present invention will be described below. However, the present invention is not limited to the following examples. In the following examples, ion-exchanged water will be simply referred to as water.

[0124] [Preparation of pigment-coated resin] First, pigment coating resins (RA) and (RB) shown in Table 1 were prepared as pigment coating resins used in preparing the inks. The pigment coating resins (RA) and (RB) each had a repeating unit derived from methacrylic acid (MAA unit), a repeating unit derived from methyl methacrylate (MMA unit), a repeating unit derived from butyl acrylate (BA unit), and a repeating unit derived from styrene (ST unit). The content ratio of each repeating unit relative to the total repeating units contained in the pigment coating resins (RA) and (RB), the mass average molecular weight (Mw), and the acid value are shown in Table 1.

[0125] (Acid value measurement) The acid value was measured in accordance with JIS (Japanese Industrial Standards) K0070:1992.

[0126] (Measurement of mass average molecular weight) The mass average molecular weight was measured under the following measurement conditions using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation). A calibration curve was prepared 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.

[0127] The conditions for measuring the weight average molecular weight were as follows. Column: Tosoh Corporation's "TSKgel SuperMultiporeHZ-H" (4.6mm I.D. x 15cm semi-microcolumn) Number of columns: 3 Eluent: Tetrahydrofuran ·Flow rate: 0.35mL / min Sample injection volume: 10μL ·Measurement temperature: 40℃ Detector: RI (refractive index) detector

[0128] [Table 1]

[0129] <Preparation of Ink (A-1)> (Preparation of Pigment Composition (P1)) A wet cake of quinacridone pigment (CI Pigment Red 122) with a solid content of 95 parts by mass was mixed with 5 parts by mass of methanol to obtain a mixture A. The entire amount of mixture A was mixed with 5 parts by mass of sulfur-containing pigment derivative (1-1) to obtain a mixture B. Methanol was distilled off from mixture B under reduced pressure at 80°C to obtain a residue. The residue was filtered using water and dried at 80°C to obtain a dried product. The dried product was pulverized using a counter jet mill (registered trademark) (manufactured by Hosokawa Micron Corporation) to obtain a pigment composition (P1). The content of the pigment derivative in the pigment composition (P1) was 5% by mass.

[0130] (Preparation of Pigment Dispersion) 6.0 parts by mass of the pigment-coated resin (RA) was mixed with an aqueous sodium hydroxide solution. The aqueous sodium hydroxide solution contained a predetermined amount of sodium hydroxide. The "predetermined amount" of sodium hydroxide added shown in Table 2 indicates 1.05 times the amount required for equal neutralization of the pigment-coated resin (RA). In this way, the pigment-coated resin (RA) was neutralized with an equal amount (strictly speaking, 105% equal amount) of sodium hydroxide, and an aqueous solution C containing the pigment-coated resin (RA) was obtained.

[0131] The entire amount of the obtained aqueous solution C, 15.0 parts by mass of the pigment composition (P1), 0.5 parts by mass of a nonionic surfactant, and water were added to the vessel. As a result, a mixed solution D having the composition X-1 shown in Table 2 was obtained. The amount of water added to the vessel was set so that the total amount of the mixed solution D (contents of the vessel) was 100.0 parts by mass. As the nonionic surfactant, "Olfine (registered trademark) E1010" (ethylene oxide adduct of acetylene diol, active ingredient concentration: 100 mass%, HLB value: 13.5 ± 0.5) manufactured by Nissin Chemical Industry Co., Ltd. was used. The contents of the vessel were mixed using a media-type wet disperser ("DYNO (registered trademark)-MILL" manufactured by Willy & Bachofen (WAB) Co., Ltd.) to obtain a mixed solution E.

[0132] In Table 2, the "remaining amount" which is the amount of water to be added means the amount that makes the mixed solution D 100.0 parts by mass. In Table 2, the "predetermined amount" which is the amount of sodium hydroxide to be added means 1.05 times the amount required for equal neutralization of the pigment coating resin (RA). The remaining amount of water shown in Table 2 is the total mass of the water charged into the vessel and the water contained in the aqueous solution C (more specifically, the water contained in the aqueous sodium hydroxide solution used to neutralize the pigment coating resin (RA), and the water generated by the neutralization reaction between the pigment coating resin (RA) and sodium hydroxide).

[0133] Mixture E was dispersed using zirconia beads (particle diameter 0.5 mm) as media and a bead mill (Nanograin Mill manufactured by Asada Iron Works Co., Ltd.). Dispersion using the bead mill was carried out at a temperature of 10°C and a peripheral speed of 8 m / sec. In the dispersion process, the discharge rate of the bead mill (hereinafter sometimes referred to as "discharge rate m") was set to 300 g / min. As a result, pigment dispersion F was obtained.

[0134] (Activated carbon treatment) The obtained pigment dispersion F was treated with activated carbon. Specifically, 1800 g of pigment dispersion F was circulated at a flow rate of 190 g / min while passing through an activated carbon filter ("YCC-1L" manufactured by Nippon Filter Co., Ltd., type of activated carbon: coconut shell granular activated carbon). Hereinafter, passing 1800 g of pigment dispersion F through the activated carbon filter is referred to as one pass. After five passes, the circulation of pigment dispersion F was stopped, and pigment dispersion G after activated carbon treatment was obtained. Therefore, the number of passes (number of passes) in the activated carbon treatment was five.

[0135] (Ultrafiltration process) The pigment dispersion G after the activated carbon treatment was filtered by vibration ultrafiltration. More specifically, an ultrafiltration membrane was used, and 480 g of the pigment dispersion G was circulated at a flow rate of 390 g / min under the condition that the internal pressure on the ultrafiltration membrane was 50 kPa. The circulation time (hereinafter, sometimes referred to as "circulation time t") was 30 minutes. As the ultrafiltration membrane, "UF Bensil Type Module AHP-0013D" manufactured by Asahi Kasei Corporation (hollow fiber membrane material: polyacrylonitrile, membrane inner diameter: 0.8 mm, effective membrane area: 170 cm) was used. 2 ) was used. The details of ultrafiltration will be described. By ultrafiltration, pigment dispersion G was separated into a filtrate and a component other than the filtrate (recovered liquid). The filtrate contained at least a part of the phosphorus-containing catalyst contained in pigment dispersion G. Of the filtrate and recovered liquid separated by filtration, the filtrate was discharged outside the system, and the recovered liquid was recycled. When the recovered liquid was recycled, water in an amount equal to the amount of the discharged filtrate was added to the recovered liquid. This made the solid concentration of the recovered liquid coincide with the solid concentration of pigment dispersion G. In this way, pigment dispersion H after ultrafiltration was obtained. The composition of pigment dispersion H was composition X-1 in Table 2.

[0136] [Table 2]

[0137] (Ink Preparation) An ink (A-1) was prepared so as to have the composition ia shown in Table 3.

[0138] [Table 3]

[0139] Water was added to a flask equipped with a stirrer ("Three-One Motor (registered trademark) BL-600" manufactured by Shinto Scientific Co., Ltd.). While stirring the contents of the flask at a stirring speed of 400 rpm using the stirrer, the pigment dispersion G obtained by the ultrafiltration process, a nonionic surfactant, triethylene glycol monobutyl ether, 3-methyl-1,5-pentanediol, and glycerin were added to obtain a mixed liquid I. As the nonionic surfactant, "Surfynol (registered trademark) 420" manufactured by Nissin Chemical Industry Co., Ltd. (ethylene oxide adduct of acetylene glycol, active ingredient concentration: 100% by mass, HLB value: 4) was used. The amount of each raw material added was as shown in Table 3. The "remaining amount" which is the amount of water added in Table 3 is the amount that makes the mixed liquid I 100.0 parts by mass. The mixed liquid I was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles from the mixed liquid I. In this way, an ink (A-1) was obtained.

[0140] [measurement] The ink to be measured (specifically, ink (A-1)) was centrifuged by the following method. The obtained supernatant was then measured for the specified phosphorus concentration, specified sulfur concentration, unadsorbed resin ratio, first absorbance, and second absorbance. The measurement results are shown in Table 4.

[0141] <Centrifugation> In an environment of 23°C, 2 g of ink sealed in a container was centrifuged for 3 hours at 140,000 rpm (corresponding to a centrifugal force of 1,050,000 G) using an ultracentrifuge (Eppendorf Himac Technologies Co., Ltd. "himac (registered trademark) CS150FNX", rotor: S140AT). The centrifugation caused the solids (mainly pigment particles) contained in the ink to settle, and the other components became the supernatant. The supernatant was collected from the container using a syringe.

[0142] <Specified phosphorus concentration and specified sulfur concentration> 1 mL of the supernatant was diluted 50 times with water and used as the measurement sample. The phosphorus concentration and sulfur concentration in the measurement sample were measured using an ICP (inductively coupled plasma) mass spectrometer ("iCAP PRO ICP-OES Duo" manufactured by Thermo Fisher Scientific). The phosphorus concentration (unit: ppm) and sulfur concentration (unit: ppm) in the measurement sample (50 times diluted solution of the supernatant) were multiplied by 50, respectively, to calculate the phosphorus concentration (unit: ppm) and sulfur concentration (unit: ppm) in the supernatant. The phosphorus concentration and sulfur concentration in the supernatant were set as the predetermined phosphorus concentration (unit: ppm) and the predetermined sulfur concentration (unit: ppm). When determining the phosphorus concentration in the measurement sample, a calibration curve prepared using a sample with a known phosphorus concentration was used. When determining the sulfur concentration in the measurement sample, a calibration curve prepared using a sample with a known sulfur concentration was used.

[0143] <Volume median diameter of pigment particles> The ink was diluted 100 times with water and used as the measurement sample. The volume median diameter of the pigment particles in the measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Malvern Instruments' Zetasizer Nano ZS). The volume median diameter of the pigment particles in the measurement sample was calculated as the volume median diameter of the pigment particles contained in the ink (D 50 ) was deemed to be

[0144] <Unadsorbed resin ratio> Centrifugation was performed under the above conditions on 2 g of ink sealed in a container. The entire supernatant obtained by the centrifugation was collected. Next, the entire collected supernatant was dried under reduced pressure (drying temperature: 60°C, drying time: 24 hours) to completely remove moisture. The mass (WA) of the residue (solid content) after drying under reduced pressure was regarded as the mass of unadsorbed resin.

[0145] From the content B (= 6.0 mass%) of the pigment coating resin in composition X-1 in Table 2 and the content C (= 40.0 mass%) of the pigment dispersion in the ink in Table 3, the mass (WD) of the pigment coating resin contained in 2 g of ink was calculated according to the following formula. WD = 2 × (C / 100) × (B / 100)

[0146] Then, the proportion of unadsorbed resin was calculated from the mass (WA) of the residue obtained from 2 g of ink and the mass (WD) of the pigment-coated resin contained in 2 g of ink according to the following formula. Unadsorbed resin ratio [mass%] = 100 × WA / WD

[0147] <First absorbance and second absorbance> Centrifugation was performed under the above-mentioned conditions on 2 g of ink sealed in a container. The entire amount of the supernatant obtained after centrifugation was collected using a syringe. The collected supernatant was diluted 25 times with water, and this was used as a measurement sample. Using a spectrophotometer ("U-3000" manufactured by Hitachi High-Tech Science Corporation), the measurement sample placed in a cell was measured under the following conditions, and the ultraviolet-visible light absorption spectrum of the measurement sample (i.e., a 25-fold diluted solution of the supernatant) was obtained. From the ultraviolet-visible light absorption spectrum, the first absorbance and second absorbance of the 25-fold diluted solution of the supernatant were obtained.

[0148] (Conditions for measuring absorbance) Measurement wavelength range: 200nm to 800nm Scan speed: 300nm / min Sampling interval: 1nm Slit width: 1 nm Cell: Quartz glass cell ·Optical path length: 10mm Beam type: Double beam Baseline measurement: Yes Reference: Water

[0149] <Preparation of Inks (A-2) to (A-12) and (B-1) to (B-7)> Except for the following changes, inks (A-2) to (A-12) and (B-1) to (B-7) were prepared in the same manner as ink (A-1), and various physical properties were measured. In the preparation of inks (A-2) to (A-12) and (B-1) to (B-7), various conditions were changed as shown in Tables 4 to 6. Specifically, in the preparation of the pigment composition, the type of quinacridone pigment, the type of sulfur-containing pigment derivative, and the content ratio of the sulfur-containing pigment derivative in the pigment composition were changed. In the preparation of the pigment composition, the total amount of the quinacridone pigment and the sulfur-containing pigment derivative used was not changed in the preparation of each ink, but was kept constant (100 parts by mass). In addition, the type of pigment-coated resin used in the preparation of the pigment dispersion was changed. In addition, the discharge amount m of the bead mill in the dispersion treatment performed in the preparation of the pigment dispersion, the number of passes in the activated carbon treatment, and the circulation time t in the ultrafiltration treatment were changed.

[0150] In the measurements of the first absorbance and the second absorbance of each ink, the first peak appeared at a wavelength of 320 nm, and the second peak appeared at a wavelength of 429 nm.

[0151] In Tables 4 to 6, "Actual" indicates an Example. "Ratio" indicates a Comparative Example. "Pigment" indicates a quinacridone pigment. "Derivative" indicates a sulfur-containing pigment derivative. "wt%" indicates the content ratio of the quinacridone pigment or the sulfur-containing pigment derivative in the pigment composition. "PR" indicates CI Pigment Red 122. "PV" indicates CI Pigment Violet 19. "Unadsorbed resin" indicates the proportion of unadsorbed resin in the pigment-coated resin. "1-1" and "1-2" in the derivative types indicate compounds represented by formulas (1-1) and (1-2), respectively.

[0152] [Table 4]

[0153] [Table 5]

[0154] [Table 6]

[0155] The CI Pigment Red 122 used in Examples 1 to 10, Example 12, and Comparative Examples 1 to 7 were different lots. The amounts of intermediates, sulfur compounds, and phosphorus compounds in each CI Pigment Red 122 were different due to the lot differences. In addition, in the preparation of each ink, it was confirmed that the longer the circulation time t in the ultrafiltration treatment, the lower the predetermined phosphorus concentration. It was confirmed that the higher the content ratio of the sulfur-containing pigment derivative in the pigment composition, the higher the predetermined sulfur concentration. The higher the discharge amount m of the bead mill, the more the ratio of unadsorbed resin was changed. The first absorbance was changed by changing the number of passes of the activated carbon treatment.

[0156] [evaluation] The inks (A-1) to (A-12) and (B-1) to (B-7) were each evaluated for ejection stability, resolubility, dispersion stability, and scratch resistance of the formed images by the following methods. In the following explanation of the evaluation methods, the inks (A-1) to (A-12) and (B-1) to (B-7) may be simply referred to as "ink". The evaluation results are shown in Tables 7 to 9 below.

[0157] <Evaluation machine, etc.> An inkjet recording device (a prototype manufactured by Kyocera Document Solutions Co., Ltd.) was used as the evaluation device. The evaluation device was equipped with a piezo-type line head having nozzles (opening radius: 10 μm) as the recording head. 2 ” (A4 size plain paper) was used.

[0158] <Discharge stability> The evaluation of the ink ejection stability from the recording head was performed in an environment with a temperature of 25°C and a humidity of 60% RH. The ink was set in the magenta ink recording head of the evaluation machine. The temperature of the recording head was set to 40°C. The amount of ink ejected per pixel was set to 3.5 pL.

[0159] Using an evaluation machine, an image (20.5 mm x 29.0 mm) was printed on paper continuously for one hour using an image processing setting in which ink was ejected from all nozzles of the recording head. The first image printed in the continuous printing (initial image) and the last image printed in the continuous printing (print-resistant image) were observed with the naked eye. The initial image and the print-resistant image were then checked for the presence or absence of white streaks. White streaks are image defects caused by ink ejection distortion (ejection failure) from the recording head. The ink ejection stability was judged according to the following criteria.

[0160] (Standard for discharge stability) Good (A): White streaks are not as numerous in the printed image as in the initial image. Poor (B): White streaks are more prevalent in the printed image than in the initial image.

[0161] <Abrasion resistance> The evaluation of the abrasion resistance was performed under an environment with a temperature of 25°C and a humidity of 60% RH. The ink discharge amount per pixel was set to 11 pL. A solid image (4 cm x 5 cm) was printed on one sheet of paper (hereinafter, sometimes referred to as Paper A) using an evaluation machine. Next, a rubbing test described below was performed. In the rubbing 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, Paper B and the weight were moved together so that only the weight of the weight was applied, and Paper B was rubbed back and forth against the solid image on Paper A five times. After the rubbing test, a reflection densitometer (X-Rite "RD-19") was used to measure the image density of 224 points in the area where no solid image was formed on Paper A (the outer margin of the solid image). The highest value of the measured image densities was taken as the evaluation value (ID MAX ) Evaluation value (IDMAX The lower the value of the abrasion resistance index, the less color transfer due to rubbing, and the more excellent the abrasion resistance of the image. The abrasion resistance of the image formed using the ink was judged according to the following criteria.

[0162] (Abrasion resistance standard) A (Good): Evaluation value (ID MAX ) is less than 0.020. B (bad): Evaluation value (ID MAX ) is greater than or equal to 0.020.

[0163] <Resolubility> 0.3 mL of ink was placed on the tip of the wiper of the evaluation machine and left for 10 minutes in an environment with a temperature of 25°C and a humidity of 60%RH. Next, the wiper with the ink on it was used to wipe the ejection surface of the recording head in the forward direction (the direction opposite to the wiping direction D3 in Figure 4), spreading the ink on the ejection surface. The spread ink was dried at 45°C for 4 days, forming dried ink on the ejection surface.

[0164] After the formation of the dried ink, a cleaning operation was performed using an evaluation machine. More specifically, a nonwoven fabric impregnated with 3 g of cleaning liquid was brought into contact with the ejection surface of the recording head for 30 seconds (corresponding to the supplying operation of the cleaning liquid). As the cleaning liquid, a cleaning liquid for cleaning the head for the inkjet color production printer "TASKalfa Pro 15000c" manufactured by Kyocera Document Solutions Inc. was used. As the nonwoven fabric, a cut product of "Bencotto (registered trademark) 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 FIG. 4) using a wiper (corresponding to the wiping operation). As a result, the dried ink attached to the ejection surface of the recording head was removed together with the cleaning liquid and the purged ink. The details of the cleaning operation performed in this test are generally the same as the cleaning operation described with reference to FIG. 3 and FIG. 4. Next, the ejection surface of the recording head was visually observed to check for the presence or absence of dried ink that could not be cleaned and remained. Note that the more easily the dried ink dissolves in the cleaning liquid and purged ink, the more easily the dried ink adhering to the ejection surface of the recording head tends to be removed. The resolubility of the ink was judged according to the following criteria.

[0165] (Criteria for resolubility) A (good): No dried ink was observed on the ejection surface of the recording head. B (Fail): A small amount of dried ink was observed on the ejection surface of the recording head. C (particularly poor): Dried ink is clearly visible on the ejection surface of the recording head.

[0166] <Dispersion stability> The volume median diameter (D 50 ) was used as an evaluation value and the dispersion stability of the ink was evaluated according to the following criteria.

[0167] (Criteria for Dispersion Stability) Good (A): The volume median diameter of the pigment particles is less than 135 nm. Poor (B): The volume median diameter of the pigment particles is 135 nm or more.

[0168] [Table 7]

[0169] [Table 8]

[0170] [Table 9]

[0171] As shown in Tables 7 to 9, the proportion of unadsorbed resin in ink (B-1) exceeded 52% by mass. The ejection stability of ink (B-1) was evaluated as poor.

[0172] The proportion of unadsorbed resin in the ink (B-2) was less than 18% by mass. The abrasion resistance of the ink (B-2) was evaluated as poor.

[0173] The ink (B-3) had a predetermined sulfur concentration of less than 1.0 ppm. The dispersion stability of the ink (B-3) was evaluated as poor.

[0174] Ink (B-4) had a specified sulfur concentration of more than 12.5 ppm. Ink (B-7) had a specified phosphorus concentration of more than 12.5 ppm. The dispersion stability of inks (B-4) and (B-7) was rated as poor.

[0175] The first absorbance of the ink (B-5) was more than 0.010. The ejection stability of the ink (B-5) was evaluated as poor.

[0176] The ink (B-6) had a phosphorus concentration of less than 1.0 ppm. The resolubility of the ink (B-6) was evaluated as poor.

[0177] The inks (A-1) to (A-12) each had the following composition. The unadsorbed resin ratio was 18% by mass or more and 52% by mass or less. The predetermined phosphorus concentration was 1.0 ppm or more and 12.5 ppm or less. The predetermined sulfur concentration was 1.0 ppm or more and 12.5 ppm or less. The first absorbance was 0.010 or less. The inks (A-1) to (A-12) were all good in ejection stability, abrasion resistance, resolubility, and dispersion stability.

[0178] From the above, it is considered that an ink satisfying the above-mentioned constitution has excellent ejection stability, can form an image having excellent abrasion resistance, has excellent resolubility, and has excellent dispersion stability of the quinacridone pigment. [Industrial Applicability]

[0179] The ink and inkjet recording apparatus of the present invention can be used to form images. [Explanation of symbols]

[0180] 1: Inkjet recording device 4: Recording head 6: First conveying section Nf: Purge ink S: Recording medium

Claims

1. An inkjet ink containing a quinacridone pigment, a pigment-coated resin, and an aqueous medium, the pigment-coated resin includes an adsorbed resin adsorbed to the quinacridone pigment and an unadsorbed resin not adsorbed to the quinacridone pigment, A ratio of the unadsorbed resin in the pigment-coated resin is 18% by mass or more and 52% by mass or less, the phosphorus concentration in a supernatant obtained by centrifuging the ink-jet ink at 1,050,000 G for 3 hours is 1.0 ppm or more and 12.5 ppm or less; The sulfur concentration in the supernatant is 1.0 ppm or more and 12.5 ppm or less, In the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of the supernatant, the absorbance of a first peak is 0.010 or less; The first peak is a maximum peak in a wavelength range of 400 nm or more and 450 nm or less.

2. The ink-jet ink according to claim 1 , comprising a sulfur compound represented by the following formula (1): 【Chemistry 1】 (In formula (1), n ​​represents an integer of 1 or more and 3 or less, m represents an integer of 1 or more and 3 or less, and X represents a metal ion.)

3. In the formula (1), X is Al. 3+ Or Mg 2+ 3. The ink-jet ink of claim 2, wherein

4. The ink-jet ink according to claim 2 , wherein a ratio of a mass of the sulfur compound to a total mass of the quinacridone pigment and the sulfur compound is 4 mass % or more and 12 mass % or less.

5. 3. The ink-jet ink according to claim 1, further comprising a phosphorus-containing catalyst.

6. The ink-jet ink of claim 5 , wherein the phosphorus-containing catalyst comprises at least one of polyphosphoric acid and a polyphosphoric acid derivative.

7. 3. The ink-jet ink according to claim 1, wherein the pigment coating resin has a repeating unit derived from (meth)acrylic acid, a repeating unit derived from a (meth)acrylic acid alkyl ester, and a repeating unit derived from styrene.

8. In the ultraviolet-visible light absorption spectrum of the supernatant, the absorbance of the second peak is 0.15 or more and 0.40 or less; The ink-jet ink according to claim 1 or 2, wherein the second peak is a maximum peak in a wavelength range of 300 nm or more and 350 nm or less.

9. A conveying unit that conveys the recording medium; a recording head that ejects ink onto the recording medium; The inkjet recording apparatus according to claim 1 , wherein the ink is the inkjet ink according to claim 1 .

10. The inkjet recording apparatus according to claim 9, wherein the recording head is a line head.

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