Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide aqueous ink that is capable of recording an image with satisfactory color development and light resistance, and has satisfactory intermittent discharge stability.SOLUTION: Aqueous ink for inkjet contains pigment, urethane resin, and silicone-based surfactant. The pigment includes first pigment and second pigment. The first pigment is naphthol AS-based azo pigment, and the second pigment is quinacridone-based pigment. The urethane resin is water-soluble urethane resin having a unit derived from polyisocyanate, polyol having no acid group, and polyol having an acid group severally. The silicone-based surfactant has a specific structure, a weight-average molecular weight of 800 or more and 10,000 or less, and an HLB value of 4 or more by Griffin method.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink, an ink cartridge, and an ink-jet recording method. [Background technology]

[0002] In recent years, inkjet recording methods have made it possible to record high-definition images with excellent color development, similar to those achieved by silver halide photography and offset recording. Coloring materials used in inks include dyes and pigments. Among these, pigments are widely used from the viewpoint of being able to record images with excellent fastness (resistance to light, ozone gas, water, etc.).

[0003] However, pigment inks in which coloring materials are dispersed in the form of particles in an aqueous medium may have inferior image clarity and color development compared to dye inks in which coloring materials are dissolved in the aqueous medium. For this reason, even when pigment inks are used, it is necessary to achieve color reproducibility comparable to that of dye inks. To meet such requirements, it is effective to improve the color development characteristics of the coloring materials of each color of ink used for recording or to increase the content of the coloring materials.

[0004] Traditionally, quinacridone pigments, which have excellent fastness, have been widely used as pigments for magenta inks (hereinafter sometimes referred to as "magenta pigments"). However, quinacridone pigments have a drawback in that they have low coloring power, and even if the pigment content is increased, it has been difficult to achieve the high level of color reproducibility that is currently required.

[0005] On the other hand, azo pigments are known as magenta pigments that have high color development and vividness and a wide color reproduction range. Among them, naphthol AS-based azo pigments have excellent coloring power. An ink has been proposed that can record images with improved saturation and density in the magenta to red color range by using naphthol AS-based azo pigments in combination with quinacridone solid solution pigments (Patent Document 1).

[0006] Meanwhile, there is an increasing demand for inks capable of recording images with excellent light resistance. Inks containing ultraviolet absorbents and light stabilizers have been proposed (Patent Document 2). However, ultraviolet absorbents and light stabilizers may affect the ejection properties of the ink. An ink capable of recording images with improved light resistance by adding a urethane resin without using ultraviolet absorbents or light stabilizers has been proposed (Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-014535 [Patent Document 2] JP 2016-006150 A [Patent Document 3] JP 2021-008563 A Summary of the Invention [Problem to be solved by the invention]

[0008] Through the study of the present inventors, it was found that an image with excellent color development could be recorded by using the ink described in Patent Document 1, which uses a combination of a naphthol AS azo pigment and a quinacridone pigment. However, it was found that the naphthol AS azo pigment has low light resistance, and therefore the image fades when exposed to light for a long period of time. In order to solve this problem, the present inventors have studied an ink containing a urethane resin with reference to Patent Document 3. As a result, although the light resistance has improved somewhat, it does not satisfy the level required in recent years. In addition, when an image is recorded under the conditions that the recovery operation of the recording head is not performed during or after recording of an image, and the ink is not discharged for a certain period of time, and then recording is resumed, another problem occurs in that the ink discharge accuracy decreases and the image is disturbed. The performance of being able to maintain good ink discharge accuracy when image recording is resumed from the above-mentioned state is called "intermittent discharge stability".

[0009] It is therefore an object of the present invention to provide an aqueous ink capable of recording images with good color development and light resistance, and having good intermittent ejection stability. It is also an object of the present invention to provide an ink cartridge and an ink-jet recording method using the aqueous ink. [Means for solving the problem]

[0010] The above object can be achieved by the present invention, which is described below. That is, according to the present invention, there is provided an aqueous inkjet ink containing a pigment, a urethane resin, and a silicone surfactant, the pigment including a first pigment and a second pigment, the first pigment being a naphthol AS-based azo pigment, the second pigment being a quinacridone-based pigment, the urethane resin being a water-soluble urethane resin having units derived from a polyisocyanate, a polyol having no acid group, and a polyol having an acid group, the silicone surfactant being at least one selected from the group consisting of compounds represented by each of the following general formulas (1) to (3), and the aqueous ink having a weight average molecular weight of 800 to 10,000 and an HLB value of 4 or more as measured by the Griffin method.

[0011] TIFF2024023140000001.tif31170 (In the general formula (1), R1 represents an alkylene group, R2 represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, and a and b each independently represent an integer of 0 or more, but are not 0 at the same time.)

[0012] TIFF2024023140000002.tif29170 (In the general formula (2), R3 represents an alkylene group, R4 represents a hydrogen atom or an alkyl group, p represents an integer of 1 or more, and c and d each independently represent an integer of 0 or more, but are not 0 at the same time.)

[0013] TIFF2024023140000003.tif30170 (In the general formula (3), R5 represents an alkylene group, R6 represents a hydrogen atom or an alkyl group, q and r each independently represent an integer of 1 or more, and e and f each independently represent an integer of 0 or more, but are not 0 at the same time.) Effect of the Invention

[0014] According to the present invention, it is possible to provide a water-based ink capable of recording images with good color development and light resistance, and having good intermittent ejection stability. Furthermore, according to the present invention, it is possible to provide an ink cartridge and an ink-jet recording method using the water-based ink. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view illustrating an embodiment of an ink cartridge of the present invention. [Diagram 2] 1A and 1B are diagrams illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0017] The present inventors have investigated inks containing naphthol AS azo pigments, quinacridone pigments, and urethane resins in order to record images with excellent color development and light resistance. As a result of the investigation, it was found that when images are recorded under certain conditions, the ink ejection accuracy decreases, causing image distortion.

[0018] When the surface of the recording head on which the ejection ports are formed is exposed to the atmosphere, liquid components (mainly water) evaporate from the ink at the tip (ejection port) of the nozzle from which the ink is ejected. When an image is recorded, if the recording head is not restored and ink is not ejected for a certain period of time, the liquid components evaporate from the ejection port, the ink becomes concentrated, and the ink may become viscous or the ejection port may become clogged, preventing normal ejection. The ability to maintain good ink ejection accuracy when image recording is resumed even in the above-mentioned state is called "intermittent ejection stability." It has been found that this intermittent ejection stability is easily reduced in inks containing naphthol AS-based azo pigments, quinacridone-based pigments, and urethane resins.

[0019] The present inventors have investigated the cause of the deterioration of intermittent ejection stability in inks containing naphthol AS azo pigments, quinacridone pigments, and urethane resins. First, when observing a recording head with a deterioration of intermittent ejection stability, it was found that aggregates had accumulated in the ink flow path. It is believed that such accumulated aggregates hinder normal ejection of the ink and cause a deterioration in ejection accuracy. As a result of further investigation, it was found that the above-mentioned aggregates do not occur in inks that do not contain at least one of the three components of naphthol AS azo pigments, quinacridone pigments, and urethane resins, but occur specifically when the three components coexist in the ink. The present inventors speculate as follows about the cause of the occurrence of the aggregates.

[0020] Quinacridone pigments have a specific high affinity for urethane resins due to two interactions: hydrophobic interaction and hydrogen bonding. Therefore, it is thought that urethane resins are easily adsorbed onto quinacridone pigments.

[0021] First, quinacridone pigments are prone to adsorption of urethane resins due to hydrophobic interactions. Urethane resins are usually composed of hard segments that provide strength and soft segments that provide flexibility. The hard segments are composed of units derived from polyisocyanates, acid group-containing components, chain extenders, etc. The soft segments are composed of units derived from polyols, etc. In general, hard segments are hydrophobic sites, and soft segments are hydrophilic sites. Quinacridone pigments have multiple aromatic rings and are highly hydrophobic, so they strongly interact with the hard segments of urethane resins.

[0022] Furthermore, quinacridone pigments are also prone to adsorption of urethane resins through hydrogen bonds. Quinacridone pigments, which are composed of molecules with highly planar structures, have a crystal structure that stacks perpendicularly to the molecular plane due to π-π stacking of aromatic rings. At this time, it is believed that a crystal plane in which structures such as amino groups and carbonyl groups of the quinacridone skeleton are densely packed exists in the direction perpendicular to the stacking direction. This crystal plane is rich in amino groups that act as proton donors and carbonyl groups that act as proton acceptors. Meanwhile, urethane bonds and urea bonds exist at the bond between the hard segment and soft segment of the urethane resin. These bonds also have structures that can act as both proton donors and acceptors, so it is believed that quinacridone pigments can form very strong hydrogen bonds.

[0023] Magenta pigments with skeletons other than quinacridone, such as anthrapyridone and dioxazine pigments, have molecular skeletons with linked aromatic rings and are highly hydrophobic. However, these pigments have a carbonyl group that acts as a proton acceptor, but do not have a structure that acts as a proton donor, so their interaction with urethane resins is weaker than that of quinacridone pigments. Diketopyrrolopyrrole has both a carbonyl group that acts as a proton acceptor and an amino group that acts as a proton donor, but has low hydrophobicity and therefore does not have as high an affinity for urethane resins as quinacridone pigments. Quinacridone pigments, which are highly hydrophobic and have substituents that easily form hydrogen bonds densely present in a certain direction of the crystal, are thought to be specifically prone to interact with urethane resins.

[0024] On the other hand, among magenta pigments, naphthol AS azo pigments are thought to have particularly weak interactions with urethane resins. Naphthol AS azo pigments have hydrophilic groups such as carbamoyl and hydroxyl groups, making the pigment particle surface highly hydrophilic and less likely to adsorb urethane resins. In addition, they are less likely to form crystal faces with densely packed substituents capable of forming hydrogen bonds, as with quinacridone pigments, and are therefore thought to have a particularly low affinity with urethane resins.

[0025] In this way, when pigments with a particularly high affinity for urethane resin and pigments with a low affinity coexist in the ink with the urethane resin, and the ink becomes further concentrated, the distance between the two pigments decreases, making them more susceptible to interaction, it is speculated that the following phenomenon will occur.

[0026] When the ink is concentrated, most of the urethane resin adsorbed to the naphthol AS azo pigment is detached from the surface of the naphthol AS azo pigment particles and is adsorbed to the surface of the quinacridone pigment particles with which it has a stronger interaction. At this time, the detachment of the urethane resin destabilizes the dispersion state of the naphthol AS azo pigment. The destabilized naphthol AS azo pigment forms associations with the naphthol AS azo pigments themselves and with the quinacridone pigment. Furthermore, the urethane resin strongly interacts with the quinacridone pigments contained in the associations, bridging the molecules of the associations to form aggregates with strong binding power. These aggregates are difficult to redisperse due to the ink flow that occurs in the ink flow path, because the three components of the naphthol AS azo pigment, the quinacridone pigment, and the urethane resin strongly interact with each other through hydrophobic interactions and hydrogen bonds, and are intricately entangled. Therefore, it is thought that the recording head cannot be restored by recovery operations such as preliminary ejection, and the aggregates gradually accumulate in the ink flow path, causing the intermittent ejection stability to decrease.

[0027] When the ink contains a quinacridone pigment and a urethane resin but does not contain a naphthol AS azo pigment, or when the ink contains a naphthol AS azo pigment and a urethane resin but does not contain a quinacridone pigment, the problem of decreased intermittent ejection stability does not occur. This is because the ink does not contain either a quinacridone pigment or a naphthol AS azo pigment, and therefore the adsorption and desorption of the urethane resin between the two pigments described above does not occur, and the dispersion state of the pigment is less likely to become unstable. Also, when the ink contains a naphthol AS azo pigment and a quinacridone pigment but does not contain a urethane resin, the dispersion state may become unstable due to the closeness of the pigments to each other, and an association may be formed. However, in this case, since no crosslinking by the urethane resin occurs, the binding force between the pigments is weak. The association is redispersed by the flow of ink in the ink flow path and does not accumulate in the ink flow path, so the intermittent ejection stability does not decrease. In this case, however, since the ink does not contain a urethane resin, the light resistance is reduced, and it is not possible to simultaneously satisfy all of color development, light resistance, and intermittent ejection stability. Even if an acrylic resin or other resin other than the urethane resin is contained, no aggregates are generated, but it is difficult to achieve both the ink and light resistance.

[0028] The present inventors have studied the composition of an aqueous ink that achieves both image coloring and light resistance, as well as intermittent ejection stability. As a result, they have found that by adding a specific silicone surfactant to an ink containing a naphthol AS azo pigment, a quinacridone pigment, and a urethane resin, an image with good coloring and light resistance can be recorded, and an ink with good intermittent ejection stability can be obtained. Since this ink has good intermittent ejection stability, it has good ejection accuracy and the recorded image is less likely to be disturbed.

[0029] The present inventors speculate that the reason why the above-mentioned effects are obtained is as follows. The compounds represented by the general formulas (1) to (3) described below, which can be used as the specific silicone surfactant, each have an ethylene oxide group and / or a propylene oxide group. The oxygen atom of the ethylene oxide group and / or the propylene oxide group in this silicone surfactant has an unshared electron pair, which acts as an electron donor and can form a hydrogen bond with a polarized hydrogen atom. At this time, since the degree of polarization of the ethylene oxide group and / or the propylene oxide group is small, the electron donating property is small, and it is considered that the hydrogen bond formed by the silicone surfactant is relatively weak.

[0030] When a silicone surfactant represented by general formula (1), (2), or (3) is added to an ink containing a naphthol AS azo pigment, a quinacridone pigment, and a urethane resin, the silicone surfactant is adsorbed to the quinacridone pigment and the urethane resin. As a result, some of the strong hydrogen bonds formed between the quinacridone pigment and the urethane resin are replaced with weak hydrogen bonds formed by the silicone surfactant. This weakens the interaction between the quinacridone pigment and the urethane resin, making it difficult for the quinacridone pigment to take away the urethane resin adsorbed to the naphthol AS azo pigment, and the dispersion state of the naphthol AS azo pigment is maintained stably.

[0031] Furthermore, a small amount of silicone surfactant is adsorbed to the particle surface of the naphthol AS azo pigment. This allows the ethylene oxide group and / or propylene oxide group of the silicone surfactant to be present in the vicinity of the naphthol AS azo pigment. This hydrogen bond site facilitates interaction with the urethane resin, so the dispersion state of the naphthol AS azo pigment is maintained more stably.

[0032] The silicone surfactant also weakens the hydrogen bonds between the quinacridone pigment and the urethane resin, making it less likely that the three components will aggregate together with strong forces, thereby improving intermittent ejection stability.

[0033] Other surfactants having an ethylene oxide group and / or a propylene oxide group, such as acetylene glycol surfactants, fluorine surfactants, and polyoxyalkylene alkyl ether surfactants, did not improve the intermittent ejection stability. The inventors speculate that the reason why the effect was obtained only when a silicone surfactant was used is as follows.

[0034] Silicone surfactants are compounds whose main structure is a siloxane bond, which is an alternating chain of silicon and oxygen atoms. Siloxane bonds are characterized by a long bond distance between atoms and a large bond angle. Due to this characteristic, siloxane bonds are highly flexible and have a high degree of freedom in bonding.

[0035] Hydrogen bonds are directional and can only be bonded in a specific direction. Silicone surfactants, which have a high degree of freedom in the arrangement of the main skeleton, are considered to be able to adopt a molecular arrangement in which the ethylene oxide group and / or propylene oxide group, which are hydrogen bond sites, can efficiently interact with the hydrogen bond sites of the quinacridone pigment and the urethane resin. As a result, the silicone surfactant is considered to be able to weaken the hydrogen bond between the quinacridone pigment and the urethane resin. On the other hand, carbon-fluorine bonds and carbon-carbon bonds have shorter interatomic distances than siloxane bonds and have a lower degree of freedom. Therefore, it is considered difficult for fluorosurfactants and polyoxyalkylene alkyl ether surfactants, which have these as their main skeletons, to arrange the hydrogen bond sites at appropriate positions where they can form hydrogen bonds with the quinacridone pigment and the urethane resin. Therefore, it is considered that the intermittent ejection stability was not improved because the fluorosurfactants and polyoxyalkylene alkyl ether surfactants cannot loosen the hydrogen bonds between the quinacridone pigment and the urethane resin.

[0036] In addition, it is considered that the acetylene glycol surfactant did not improve the intermittent ejection stability because the orientation to the gas-liquid interface was too fast. If the orientation to the gas-liquid interface is too fast, the surfactant is quickly adsorbed to the ink flow path and is lost from the vicinity of the pigment and the urethane resin. If the recording is stopped for a long period of time, most of the surfactant is detached from the pigment and the urethane resin, so the hydrogen bond between the quinacridone pigment and the urethane resin cannot be loosened, and the intermittent ejection stability is reduced. The silicone surfactant is slower to orient to the gas-liquid interface than other surfactants. Therefore, even if the recording is stopped for a long period of time, the silicone surfactant is less likely to be adsorbed to the ink flow path and a large amount of the silicone surfactant remains in the vicinity of the pigment and the urethane resin. Therefore, the silicone surfactant can loosen the hydrogen bond between the quinacridone pigment and the urethane resin, and the intermittent ejection stability is improved.

[0037] In order to obtain the above-mentioned effect, the silicone surfactant contained in the ink needs to have a weight-average molecular weight of 800 or more and 10,000 or less. If the weight-average molecular weight of the silicone surfactant exceeds 10,000, the molecular size becomes large and it becomes difficult to exist in the vicinity of the urethane resin or the quinacridone pigment due to steric hindrance. Then, the hydrogen bond between the urethane resin and the quinacridone pigment cannot be loosened, and the effect of improving the intermittent ejection stability cannot be obtained. On the other hand, if the weight-average molecular weight of the silicone surfactant is less than 800, the number of units of the ethylene oxide group and / or propylene oxide group is inevitably small. If the number of units capable of forming these hydrogen bonds is small, the hydrogen bond is formed in place of the urethane resin and the quinacridone pigment, and the effect of loosening the interaction between the urethane resin and the quinacridone pigment becomes too weak, so the effect of improving the intermittent ejection stability cannot be obtained.

[0038] Furthermore, the silicone surfactant must have an HLB value, as determined by the Griffin method, of at least 4. If the HLB value is less than 4, the silicone surfactant cannot dissolve in the ink, and the effect of improving intermittent ejection stability cannot be obtained.

[0039] Furthermore, when an ink containing a silicone surfactant was used, not only was the intermittent ejection stability improved, but the lightfastness of the image was further improved. The present inventors speculate that the reason for this is as follows. Images recorded with an ink containing a naphthol AS azo pigment, a quinacridone pigment, and a urethane resin, but not containing a silicone surfactant, were observed under an electron microscope. As a result, it was confirmed that the amorphous substance thought to be the urethane resin did not uniformly cover the entire surface of the pigment particles, but was unevenly distributed. As described above, strong hydrogen bonds act between the quinacridone pigment and the urethane resin. Therefore, it is speculated that a large amount of the urethane resin is adsorbed to the quinacridone pigment in the ink, and the amount of the urethane resin adsorbed to the naphthol AS azo pigment is reduced, so that the particle surface of the naphthol AS azo pigment is exposed. It is considered that the naphthol AS azo pigment that is not sufficiently covered with the urethane resin is not protected from light and is directly exposed to direct sunlight or fluorescent light, resulting in a decrease in lightfastness.

[0040] Here, when the ink contains a silicone surfactant, as described above, the silicone surfactant acts on the quinacridone pigment and the urethane resin, weakening the specifically strong hydrogen bond between them. In other words, the unevenness of the amount of urethane resin adsorbed to the naphthol AS azo pigment and the quinacridone pigment can be eliminated. When an image is recorded using such an ink, the uneven distribution of the urethane resin on the pigment layer is eliminated, and the naphthol AS azo pigment and the quinacridone pigment tend to be evenly coated. It is considered that the lightfastness of the image is improved because the naphthol AS azo pigment, which has low lightfastness, tends to be protected from light.

[0041] Furthermore, the silicone surfactant in the ink increases the uniformity of the urethane resin film that is formed. The ethylene oxide group and / or propylene oxide group of the silicone surfactant loosens the hydrogen bonds between the urethane resins, suppressing the aggregation of the urethane resins when they form a film in the pigment layer. As a result, it is believed that the pigment is more easily covered with the urethane resin, resulting in improved light resistance.

[0042] In addition, in order to obtain the above effect, the urethane resin must be water-soluble. If the urethane resin is water-dispersible, it is difficult to thicken when the liquid component evaporates, and when a recording medium into which the ink easily penetrates is used, the urethane resin does not remain in the pigment layer, and an image with excellent light resistance cannot be recorded. Also, even when the ink does not contain a quinacridone pigment, the urethane resin penetrates into the recording medium and cannot be efficiently left in the pigment layer of the image, and light resistance is not improved. From this, it is considered that the quinacridone pigment has an interaction with the urethane resin and has an effect of retaining the urethane resin in the pigment layer, although the specific interaction with the urethane resin is weakened.

[0043] <Ink> As described above, the ink of the present invention is an aqueous ink for inkjet printing that contains a specific pigment, a urethane resin, and a silicone surfactant. The ink of the present invention does not need to be a so-called "curable ink". Therefore, the ink of the present invention does not need to contain a compound such as a polymerizable monomer that can be polymerized by the addition of external energy. Each component constituting the ink will be described in detail below.

[0044] (Pigments) The ink contains at least a naphthol AS azo pigment as a first pigment and a quinacridone pigment as a second pigment, and may contain one or more types of the first pigment and one or more types of the second pigment.

[0045] [First pigment] The first pigment is a naphthol AS-based azo pigment. Azo pigments are pigments formed by a compound having a structure in which a diazo component, which is an aromatic amine diazotized, is coupled with a coupler component. Naphthol AS-based azo pigments are obtained by using naphthol AS-type pigments as the coupler component. Naphthol AS is 3-hydroxy-2-carboxynaphthalene anilide, and naphthol AS-type pigments are a general term for compounds with different substitution positions of the hydroxyl group and carboxynaphthalene anilide.

[0046] Specific examples of naphthol AS azo pigments include CI Pigment Red: 2, 5, 17, 22, 31, 112, 146, 147, 150, 170, 176, 185, 266, 269; CI Pigment Orange 22; and CI Pigment Violet 50. Among the naphthol AS azo pigments, CI Pigment Red: 31, 146, 147, 150, 269 is preferred, and CI Pigment Red 150 is more preferred. In CI Pigment Red: 31, 146, 147, 150, 269, a compound represented by the following general formula (4) is used as a coupler component. A naphthol AS azo pigment obtained by using a coupler component having such a structure is likely to form a hydrogen bond with a urethane resin, and therefore the light resistance of an image is likely to be improved. In addition, the dispersion state of the first pigment in the concentrated ink is likely to be stably maintained, and therefore the intermittent ejection stability of the ink is likely to be improved.

[0047] The use of CI Pigment Red 150 is preferable because it can further improve lightfastness. In CI Pigment Red 150, a compound represented by the following general formula (4) in which R7 is a hydrogen atom is used as a coupler component. By using this coupler component, CI Pigment Red 150 having such a structure can form a hydrogen bond between the two hydrogen atoms bonded to the nitrogen atom of the CONH2 group. Therefore, CI Pigment Red 150 is more likely to interact with the urethane resin, which makes it easier to improve the lightfastness of the image and the intermittent ejection stability of the ink.

[0048] TIFF2024023140000004.tif53170 (In general formula (4), R7 represents a hydrogen atom or a group represented by the following general formula (5).)

[0049] TIFF2024023140000005.tif42170 (In the general formula (5), R8, R9, and R 10 represents any one of the following (5-1) to (5-4), and * represents a bond to the nitrogen atom to which R7 in general formula (4) is bonded. (5-1) R and R are hydrogen atoms and R 10 is a nitro group. (5-2) R8 and R 10 is a methoxy group and R9 is a chlorine atom. (5-3) R8 is a methyl group, R9 is a hydrogen atom, R 10 is a chlorine atom. (5-4) R8 is a methoxy group, R9 is a hydrogen atom, R 10 is a chlorine atom.)

[0050] [Second pigment] The second pigment is a quinacridone pigment. The quinacridone pigment is a pigment formed of quinacridone (5,12-dihydro-quino[2,3-b]acridine-7,14-dione) or a quinacridone derivative.

[0051] Specific examples of quinacridone pigments include CI Pigment Red: 122, 192, 202, 206, 207, 209; CI Pigment Violet 19, etc. A solid solution of two or more quinacridone pigments may be used. A solid solution is also called a mixed crystal, and is a solid solution in which two or more pigments are mutually dissolved to form a uniform solid phase as a whole, and is different from a simple mixture of two or more pigments. Commercially available solid solutions of two or more quinacridone pigments include the following trade names: "CROMOPHTAL Jet 2BC" (manufactured by Chiba Specialty Chemicals), "Cinquasia Magenta D 4500 J", "Cinquasia Magenta D 4400" (all manufactured by BASF), "Inkjet Magenta E 02", "Inkjet Magenta E7B LV 3958", "Inkjet Magenta E7B 02 VP 3958" (all manufactured by Clariant), and "FASTOGEN Super Magenta JM2120" (manufactured by DIC).

[0052] Among the above quinacridone pigments, a solid solution pigment containing CI Pigment Red 122 and CI Pigment Violet 19 is more preferable. In the solid solution of quinacridone, the arrangement is distorted during the crystal formation process, and the amino group of the quinacridone skeleton appears on the crystal surface more frequently than in a pigment consisting of one type of quinacridone. Therefore, it is easy to form hydrogen bonds with urethane resin. On the other hand, if the quinacridone pigment constituting the solid solution has a bulky substituent, the hydrogen bond surface is disturbed due to the steric hindrance of the substituent, making it difficult for the urethane resin to be adsorbed. In the solid solution pigment containing CI Pigment Red 122 substituted with a methyl group and CI Pigment Violet 19, which is an unmodified quinacridone, the size of the substituent is small. Therefore, the hydrogen bond surface of the solid solution is less likely to be disturbed, and the amount of adsorption of the urethane resin increases, making it easy to improve light resistance.

[0053] In addition to the above pigments, the ink may contain other pigments as necessary. Examples of other pigments include inorganic pigments such as carbon black and organic pigments known in the art. The ratio of the total content (mass%) of the first pigment and the second pigment to the total content (mass%) of the pigments in the aqueous ink is preferably 95.0% by mass or more, and may be 100.0% by mass.

[0054] [Pigment dispersion method] Examples of the pigment dispersion method include resin-dispersed pigments using a resin dispersant, pigments dispersed with a surfactant, and microencapsulated pigments in which at least a part of the pigment particle surface is coated with a resin or the like. In addition, self-dispersed pigments in which a functional group containing a hydrophilic group such as an anionic group is bonded to the pigment particle surface, and pigments in which an organic group containing a polymer is chemically bonded to the pigment particle surface (resin-bonded self-dispersed pigments) can be used. Pigments of any dispersion method can be used in the ink. Furthermore, pigments of different dispersion methods can be used in combination. Among them, a method in which the pigment is dispersed by the action of a resin dispersant physically adsorbed on the particle surface (resin-dispersed pigment) is preferred.

[0055] [Pigment content] The content (mass%) of the pigment (total of the first pigment and the second pigment) in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink. The content (mass%) of the first pigment (naphthol AS-based azo pigment) in the ink is preferably 0.02% by mass or more and 3.00% by mass or less, and more preferably 0.20% by mass or more and 2.00% by mass or less, based on the total mass of the ink. The content (mass%) of the second pigment (quinacridone-based pigment) in the ink is preferably 0.08% by mass or more and 12.00% by mass or less, and more preferably 0.80% by mass or more and 8.00% by mass or less, based on the total mass of the ink. The content (mass%) of the first pigment (naphthol AS-based azo pigment) in the ink is preferably smaller than the content (mass%) of the second pigment (quinacridone-based pigment).

[0056] The pigment content (mass %) in the ink is preferably 1.00 times or more, and more preferably 25.00 times or less, and even more preferably 6.00 times or less, in terms of mass ratio to the urethane resin content (mass %). By making the mass ratio 1.00 times or more, the proportion of urethane resin in the pigment layer of the image is reduced, the surface smoothness of the pigment layer is increased, and scattering is less likely to occur, which makes it easier to improve the color development of the image. On the other hand, by making the mass ratio 25.00 times or less, the pigment is sufficiently covered with the urethane resin, making it easier to obtain an effect of improving the light resistance of the image.

[0057] The content (mass%) of the second pigment (quinacridone pigment) in the ink is preferably 0.80 times or more, more preferably 0.95 times or less, and even more preferably 0.94 times or less, in terms of the mass ratio to the pigment content (mass%). When the mass ratio is 0.80 times or more, the mass ratio of the quinacridone pigment, which has a property of easily adsorbing urethane resin, is high, so that the amount of urethane resin present in the pigment layer becomes sufficient, and the effect of improving the light resistance of the image is easily obtained. On the other hand, when the mass ratio is 0.95 times or less, the content of the naphthol AS-based azo pigment, which has excellent color development efficiency, can be secured, and the color development of the image is easily improved. In addition, the content (mass%) of the first pigment (naphthol AS-based azo pigment) in the ink is preferably 0.01 times or more and 0.20 times or less, in terms of the mass ratio to the pigment content (mass%). The content (mass %) of the first pigment (naphthol AS-based azo pigment) in the ink is, in mass %, preferably 0.01 to 0.50 times, and more preferably 0.01 to 0.40 times, the mass ratio of the content (mass %) of the second pigment (quinacridone-based pigment).

[0058] (urethane resin) The urethane resin has units derived from polyisocyanate, polyol without acid group, and polyol with acid group. One or more of the urethane resins having these units can be contained in the ink. In this specification, the "unit" of the resin means a repeating unit derived from one monomer.

[0059] The content (mass%) of the urethane resin in the ink is preferably 0.10% by mass or more and 10.00% by mass or less, and more preferably 0.10% by mass or more and 6.00% by mass or less, based on the total mass of the ink. By having the content (mass%) of the urethane resin be 0.10% by mass or more, it is easy to obtain an effect of improving the light resistance of the image. By having the content (mass%) of the urethane resin be 10.00% by mass or less, an increase in the viscosity of the ink is suppressed, and it is easy to maintain the ejection stability of the ink.

[0060] [Polyisocyanate] Polyisocyanate is a compound having two or more isocyanate groups in its molecular structure. Examples of polyisocyanate include aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic polyisocyanate, and aromatic aliphatic polyisocyanate. These polyisocyanates can be used alone or in combination of two or more. The proportion (mass%) of units derived from polyisocyanate in the urethane resin is preferably 10.0 mass% or more and 80.0 mass% or less.

[0061] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate. Examples of the alicyclic polyisocyanate include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0062] Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Examples of aromatic aliphatic polyisocyanates include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0063] Among the above polyisocyanates, isophorone diisocyanate is preferred. In the structure of the polyurethane resin, the unit derived from the polyisocyanate exists as a hydrophobic site. Among the polyisocyanates, isophorone diisocyanate has two methyl groups on the carbon at the 3rd position of the cyclohexane ring, and is therefore particularly hydrophobic. Therefore, when a polyurethane resin having a unit derived from isophorone diisocyanate is used, the silicone surfactant is easily adsorbed due to hydrophobic interaction. When a large amount of the silicone surfactant is adsorbed, the effect of weakening the hydrogen bond between the urethane resin and the quinacridone pigment becomes stronger, and the intermittent ejection stability and light resistance are easily improved.

[0064] [Polyols not Having Acid Groups] Examples of the polyol having no acid group include polyester polyol, polyether polyol, polycarbonate polyol, polyhydroxy polyacetal, polyhydroxy polyacrylate, polyhydroxy polyester amide, polyhydroxy polythioether, etc. These polyols having no acid group can be used alone or in combination of two or more.

[0065] The number average molecular weight of the polyol having no acid group is preferably 1,500 or more and 4,000 or less. When the number average molecular weight of the polyol having no acid group is 1,500 or more, the chain length of the polyol, which is the soft segment in the urethane resin, is long, so that the mobility of the urethane molecular chain increases, and it becomes difficult to form hydrogen bonds between the hard segments of the urethane resin. As a result, the urethane resin has more sites that can form hydrogen bonds with the pigment, and the amount of urethane resin remaining on the pigment layer increases, so that the effect of improving the light resistance of the image is easily obtained. On the other hand, when the number average molecular weight of the polyol having no acid group is 4,000 or less, it is easy to make the urethane resin moderately hydrophilic, and the amount of the silicone surfactant adsorbed is increased. Therefore, it is easy to weaken the hydrogen bond with the quinacridone pigment, and it is easy to obtain the effect of improving the intermittent ejection stability and the light resistance of the image.

[0066] Examples of polyester polyols include esters of an acid component and a polyalkylene glycol, a dihydric alcohol, or a trihydric or higher polyhydric alcohol. Examples of acid components include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and aliphatic dicarboxylic acids. Examples of aromatic dicarboxylic acids include isophthalic acid, terephthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyl dicarboxylic acid, and tetrahydrophthalic acid. Examples of alicyclic dicarboxylic acids include hydrogenated products of the above aromatic dicarboxylic acids. Examples of aliphatic dicarboxylic acids include malonic acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkyl succinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid. Reactive derivatives of these acid components, such as acid anhydrides, alkyl esters, or acid halides, can also be used as the acid components constituting polyester polyols. These acid components may be used alone or in combination of two or more.

[0067] Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene glycol-propylene glycol copolymers. Examples of dihydric alcohols include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4-dihydroxyphenylpropane, and 4,4-dihydroxyphenylmethane. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, and pentaerythritol. These polyester polyols can be used alone or in combination of two or more.

[0068] Examples of polyether polyols include polyalkylene glycols, addition polymers of alkylene oxides with dihydric alcohols or polyhydric alcohols having 3 or more hydric groups. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and α-olefin oxide. Examples of polyalkylene glycols, dihydric alcohols, and polyhydric alcohols having 3 or more hydric groups include those exemplified as components constituting the polyester polyols. These polyether polyols can be used alone or in combination of two or more types.

[0069] The polycarbonate polyol may be a polycarbonate diol produced by a known method. For example, polyhexamethylene carbonate, which is a hexanediol-based polycarbonate diol, may be used. In addition, polycarbonate diols obtained by reacting carbonates such as alkylene carbonate, diaryl carbonate, and dialkyl carbonate with phosgene and an aliphatic diol may be used. These polycarbonate diols may be used alone or in combination of two or more.

[0070] Among the above-mentioned polyols not having an acid group, it is more preferable to use a polyether polyol, and even more preferable to use a polypropylene glycol. In a urethane resin containing a unit derived from a polyether polyol such as polypropylene glycol, the branched chain of the polyether polyol such as polypropylene glycol becomes a steric hindrance, and the formation of hydrogen bonds between the urethane resins is suppressed. By suppressing the hydrogen bonds between the urethane resins, the number of hydrogen bond sites that can form hydrogen bonds with the pigment increases, so the amount of urethane resin remaining in the pigment layer increases, and the effect of improving light resistance is more easily obtained.

[0071] [Polyol having an acid group] Examples of the polyol having an acid group include polyols having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. The acid group is preferably a carboxylic acid group. Examples of the polyol having a carboxylic acid group include dimethylol acetic acid, dimethylol propionic acid, and dimethylol butanoic acid. The acid group of the polyol having an acid group may be in the form of a salt. Examples of the cation forming the salt include ions of alkali metals such as lithium, sodium, and potassium; ammonium ions, and cations of organic amines such as dimethylamine. The polyol having an acid group may be used alone or in combination of two or more.

[0072] [Polyamine] The urethane resin may be further reacted with a polyamine. Examples of polyamines include monoamines having multiple hydroxyl groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; and trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine. These polyamines may be used alone or in combination of two or more. For convenience, compounds having multiple hydroxyl groups and one "amino group, imino group" are also listed as "polyamines" above.

[0073] [Cross-linking agents, chain extenders] When synthesizing a urethane resin, a crosslinking agent or a chain extender can be used. Usually, a crosslinking agent is used when synthesizing a prepolymer, and a chain extender is used when carrying out a chain extension reaction on a prepolymer that has been synthesized in advance. Basically, the crosslinking agent or the chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. according to the purpose of crosslinking or chain extension. As the chain extender, one that can crosslink the urethane resin can also be used.

[0074] [Ratio of units derived from polyol having an acid group at the molecular terminal] In addition, the urethane resin preferably has a ratio of units derived from polyol having an acid group at the molecular end to the total units derived from polyol having an acid group of 30.0 mol% or less. By making the ratio 30.0 mol% or less, the urethane resin is more likely to remain near the surface of the recording medium, and the light resistance of the image is more likely to be improved. The ratio is preferably 0.0 mol% or more.

[0075] [Verification method] The ratio of units derived from polyol having an acid group present at the molecular end to the total units derived from polyol having an acid group in the urethane resin can be verified by the method shown below. The urethane resin to be verified can be a urethane resin prepared for the preparation of the ink or a urethane resin appropriately extracted from the ink. First, the urethane resin is analyzed by pyrolysis gas chromatography to identify the types of polyisocyanate, polyol without an acid group, and polyol with an acid group. Next, the reaction product of the identified polyisocyanate and polyol with an acid group is dissolved in deuterated dimethyl sulfoxide (deuterated DMSO) and analyzed by carbon nuclear magnetic resonance spectroscopy ( 13 The compound is analyzed by C-NMR. This confirms the chemical shift of the carbonyl carbon (lower magnetic field side) in the unit derived from the polyol having an acid group at the molecular end. In addition, the chemical shift of the carbonyl carbon (higher magnetic field side) in the unit derived from the polyol having an acid group inside the molecule is confirmed.

[0076] Next, the ratio of the peak integrated value of the carbonyl carbon in the unit derived from the polyol having an acid group present at the molecular end to the total of the peak integrated values ​​of the carbonyl carbon in the unit derived from the polyol having an acid group is calculated. This makes it possible to obtain the ratio of the unit derived from the polyol having an acid group present at the molecular end to the total units derived from the polyol having an acid group in the urethane resin. For example, when dimethylolpropionic acid (DMPA) is used, the peak of the carbonyl carbon in the unit derived from the polyol having an acid group present at the molecular end is detected at about 176 ppm, although there is some deviation depending on the measurement conditions. In addition, the peak of the carbonyl carbon in the unit derived from the polyol having an acid group present inside the molecule is detected at about 175 ppm. Furthermore, when dimethylolbutanoic acid (DMBA) is used, the peak of the carbonyl carbon in the unit derived from the polyol having an acid group present at the molecular end is detected at about 175 ppm. And the peak of the carbonyl carbon in the unit derived from the polyol having an acid group present inside the molecule is detected at about 174 ppm. In addition, 13 By analyzing by C-NMR, the number of repeating units derived from polyol can be determined, and the number average molecular weight can be calculated.

[0077] (Silicone surfactant) The ink contains at least one silicone surfactant selected from the group consisting of compounds represented by each of the following general formulas (1) to (3). In the general formulas (1) to (3), (C2H4O) represents an ethylene oxide group, and (C3H6O) represents a propylene oxide group. Each silicone surfactant has at least one of an ethylene oxide group and a propylene oxide group. In each silicone surfactant, the ethylene oxide group and the propylene oxide group may be present in any state in the structure, such as a random state or a block state. Here, the fact that each group exists in a random state means that the ethylene oxide group and the propylene oxide group are irregularly arranged in units of "groups (units)". In addition, the fact that each group exists in a block state means that each block is composed of several of the above "groups (units)" as units, and is arranged in units of blocks thus composed.

[0078] TIFF2024023140000006.tif31170

[0079] TIFF2024023140000007.tif29170

[0080] TIFF2024023140000008.tif30170

[0081] In the general formulas (1), (2), and (3), R1, R3, and R5 represent an alkylene group, and R2, R4, and R6 represent a hydrogen atom or an alkyl group. m and n are each independently, and q and r are each independently, and m, n, p, q, and r represent integers of 1 or more. a and b, c and d, and e and f are each independently, and a, b, c, d, e, and f represent integers of 0 or more. However, a and b, c and d, and e and f cannot be 0 at the same time.

[0082] In the silicone surfactant, the alkylene group represented by R1 in general formula (1), R3 in general formula (2), and R5 in general formula (3) is preferably an alkylene group having from 2 to 6 carbon atoms. As this alkylene group, an ethylene group or a propylene group is more preferable, and a propylene group is even more preferable.

[0083] In the silicone surfactant, the alkyl group that can be R2 in the general formula (1), R4 in the general formula (2), and R6 in the general formula (3) is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group, or a propyl group. Among them, in the silicone surfactant, R2, R4, or R6 in the general formulas (1) to (3) is more preferably a methyl group. The methyl group has a low cohesive force and a small interaction with the target object. When the terminal of the ethylene oxide group and / or propylene oxide group of the silicone surfactant is a methyl group, the methyl group weakens the interaction between the urethane resins, and the cohesion becomes gentle. As a result, the uniformity of the urethane resin film formed on the pigment layer is increased, and the light resistance of the image is easily improved.

[0084] The compound represented by the general formula (1) is obtained, for example, by an addition reaction between a compound represented by the following general formula (A) and a compound represented by the following general formula (B). The compound represented by the general formula (2) is obtained, for example, by an addition reaction between a compound represented by the following general formula (C) and a compound represented by the following general formula (D). The compound represented by the general formula (3) is obtained, for example, by an addition reaction between a compound represented by the following general formula (E) and a compound represented by the following general formula (F). The compound represented by the general formula (A) is a polysiloxane compound having n hydrogen atoms bonded to n Si in the general formula (A). The compound represented by the general formula (C) and the compound represented by the general formula (E) are polysiloxane compounds having hydrogen atoms at both ends. The compound represented by the general formula (B), the compound represented by the general formula (D), and the compound represented by the general formula (F) are polyoxyalkylene compounds having an ethylene oxide group and / or a propylene oxide group.

[0085] TIFF2024023140000009.tif30170 (m and n in general formula (A) are defined as m and n in general formula (1), respectively.)

[0086] TIFF2024023140000010.tif18170 (R in general formula (B) 11 represents an alkenyl group, and R2, a, and b have the same meanings as R2, a, and b in general formula (1), respectively.

[0087] TIFF2024023140000011.tif31170 (p in general formula (C) has the same meaning as p in general formula (2).)

[0088] TIFF2024023140000012.tif16170 (R in general formula (D) 31 represents an alkenyl group, and R4, c, and d have the same meanings as R4, c, and d in general formula (2), respectively.

[0089] TIFF2024023140000013.tif29170 (q in general formula (E) has the same meaning as q in general formula (3).)

[0090] TIFF2024023140000014.tif19170 (R in general formula (F) 51 and R 61 each independently represents an alkenyl group, and e and f have the same meanings as e and f in formula (3).

[0091] R in general formula (B) 11 is a group that becomes R1 in general formula (1) by addition reaction between a compound represented by general formula (A) and a compound represented by general formula (B). R in general formula (D) 31 is a group that becomes R3 in general formula (2) by addition reaction between a compound represented by general formula (C) and a compound represented by general formula (D). R in general formula (F) 51 and R 61are groups which become R5 and R6 in general formula (3) by addition reaction between a compound represented by general formula (E) and a compound represented by general formula (F), respectively. R in general formula (B) 11 R in general formula (D) 31 and R in general formula (F) 51 and R 61 The alkenyl group represented by the following formula (I) is preferably an alkenyl group having from 2 to 6 carbon atoms, and more preferably an allyl group.

[0092] The weight average molecular weight (Mw) of the silicone surfactant is 800 or more and 10,000 or less. The weight average molecular weight (Mw) is the weight average molecular weight in terms of polystyrene in the molecular weight distribution measured by gel permeation chromatography (GPC). Since the silicone surfactants represented by each of the general formulas (1) to (3) are mixtures of those having various molecular weights, the molecular weight is calculated as the average molecular weight.

[0093] [Measurement of weight average molecular weight of silicone surfactant] The weight average molecular weight (Mw) of the silicone surfactant can be measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the mobile phase. The specific method for measuring the Mw of the silicone surfactant is as follows, and the Mw of surfactants 1 to 13 used in the examples described below was measured by the preferred measurement method described below. Note that the measurement conditions such as the filter, column, standard polystyrene sample and its molecular weight are not limited to those described below.

[0094] First, the sample to be measured is placed in tetrahydrofuran (THF) and left to stand for several hours to dissolve, preparing a solution. The solution is then filtered through a solvent-resistant membrane filter with a pore size of 0.2 μm to obtain a sample solution. The concentration of the sample in the sample solution is adjusted so that the content of the silicone surfactant is 0.1% by mass to 0.3% by mass. An RI detector (Refractive Index Detector) is used for GPC. In addition, 10 3 ~2×106 In order to accurately measure the molecular weight range, it is preferable to combine multiple commercially available polystyrene gel columns. For example, four Shodex LF-804 (Showa Denko) columns can be combined or an equivalent can be used. THF is passed through the column stabilized in a heat chamber at 40.0°C as the mobile phase at a flow rate of 1 mL / min, and about 0.1 mL of the above sample solution is injected. The weight-average molecular weight of the sample is determined using a molecular weight calibration curve prepared using standard polystyrene samples. The standard polystyrene samples are used for a molecular weight of 10 2 〜10 7 It is appropriate to use a standard polystyrene standard (eg, manufactured by Polymer Laboratories) and to use at least about 10 types of standard polystyrene samples.

[0095] [HLB value of silicone surfactants] The HLB value determined by the Griffin method is a physical property value that indicates the degree of hydrophilicity or lipophilicity of a nonionic surfactant, and takes a value of 0 or more and 20 or less. The smaller the HLB value, the higher the lipophilicity, and the larger the HLB value, the higher the hydrophilicity. The HLB value according to the Griffin method can be calculated from the following formula (6). In the case of the above silicone-based surfactant, the hydrophilic part in the following formula (6) is an ethylene oxide group and / or a propylene oxide group. HLB value = 20 × sum of the formula weights of the hydrophilic parts of the surfactant / molecular weight of the surfactant (6)

[0096] The HLB value of the silicone surfactant according to the Griffin method is equal to or greater than 4. Furthermore, the HLB value is preferably equal to or less than 18. When two or more types of silicone surfactants are contained in the ink, the HLB value of the silicone surfactant is taken as the average value of the HLB values ​​of the two or more types of silicone surfactants (preferably an average value weighted by the content on a mass basis).

[0097] The content (mass%) of the silicone surfactant in the ink is preferably 0.01% by mass or more and 1.00% by mass or less, and more preferably 0.05% by mass or more and 0.50% by mass or less, based on the total mass of the ink. The content (mass%) of the first pigment in the ink is preferably 1.00 times or more and 15.00 times or less, in terms of the mass ratio to the content (mass%) of the silicone surfactant. The content (mass%) of the second pigment in the ink is preferably 40.00 times or more and 55.00 times or less, in terms of the mass ratio to the content (mass%) of the silicone surfactant. The content (mass%) of the water-soluble urethane resin in the ink is preferably 1.00 times or more and 60.00 times or less, and more preferably 5.00 times or more and 20.00 times or less, in terms of the mass ratio to the content (mass%) of the silicone surfactant.

[0098] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. As the water, deionized water (ion-exchanged water) is preferably used. The content (mass%) of water in the ink is preferably 10.00% by mass or more and 90.00% by mass or less, and more preferably 50.00% by mass or more and 90.00% by mass or less, based on the total mass of the ink.

[0099] The aqueous medium may further contain a water-soluble organic solvent. Examples of the water-soluble organic solvent include monohydric alcohols, polyhydric alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing polar solvents, and sulfur-containing polar solvents. One or more water-soluble organic solvents can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, and more preferably 3.00% by mass or more and 30.00% by mass or less, based on the total mass of the ink.

[0100] (Other additives) In addition to the above-mentioned components, the ink may contain, as necessary, water-soluble organic compounds that are solid at room temperature (25° C.), such as polyhydric alcohols, such as trimethylolpropane and trimethylolethane, and urea derivatives, such as urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives, such as other resins, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, chelating agents, and water-soluble resins.

[0101] (Ink properties) The viscosity of the ink at 25°C is preferably from 1.0 mPa·s to 10.0 mPa·s, more preferably from 1.0 mPa·s to 5.0 mPa·s, and particularly preferably from 1.0 mPa·s to 3.0 mPa·s. The surface tension (static surface tension) of the ink at 25°C is preferably from 10.0 mN / m to 60.0 mN / m, more preferably from 20.0 mN / m to 60.0 mN / m, and particularly preferably from 30.0 mN / m to 50.0 mN / m. The pH of the ink at 25°C is preferably from 5.0 to 10.0, and more preferably from 7.0 to 9.5.

[0102] <Ink cartridges> The ink cartridge of the present invention includes ink and an ink storage section that stores the ink. The ink stored in the ink storage section is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view that shows a schematic diagram of an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to a recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are communicated with each other via a communication port 18. The absorber storage chamber 16 is also communicated with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, and may be in a form in which the entire amount of ink stored is held by the absorber. The ink storage section may also be in a form in which the entire amount of ink stored is stored in a liquid state, without having an absorber. Furthermore, the ink cartridge may be configured to have an ink container and a recording head.

[0103] <Inkjet recording method> The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods of ejecting ink include a method of imparting mechanical energy to the ink and a method of imparting thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting ink by imparting thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be publicly known. In the present invention, it is sufficient to carry out a step of applying ink to a recording medium, and it is not necessary to carry out other treatments (such as a step of applying a reaction liquid that reacts with the ink, a step of curing an image by irradiation with active energy rays, or a step of heating an image).

[0104] FIG. 2 is a diagram showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. The inkjet recording device is provided with a conveying means (not shown) for conveying a recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured so that an ink cartridge 42 is set thereon. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown).

[0105] Any recording medium may be used as the target for recording using the ink of the present invention, but it is preferable to use a recording medium having ink permeability, such as plain paper or a recording medium having a coating layer (glossy paper or art paper). In particular, it is preferable to use a recording medium having a coating layer that allows at least a part of the pigment particles in the ink to be present on the surface of the recording medium or in its vicinity. Such a recording medium can be selected depending on the purpose of use of the recorded matter on which the image is recorded. For example, glossy paper suitable for obtaining an image having a glossy feel of photographic quality, and art paper that makes use of the texture of the base material (drawing paper, canvas, Japanese paper, etc.) to express paintings, photographs, and graphic images according to preference, etc., can be mentioned. Among them, it is particularly preferable to use so-called glossy paper, in which the surface of the coating layer has glossiness. EXAMPLES

[0106] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0107] <Preparing the pigment> The following solid solution pigments were prepared: (Solid solution pigment 1) 23.4 parts of 3-amino-4-methoxybenzanilide was added to 364.4 parts of water, and the mixture was thoroughly stirred to prepare a suspension. Then, ice was added to adjust the liquid temperature to 5°C to obtain a suspension. 39.7 parts of 35% hydrochloric acid was added to this suspension, and the mixture was stirred for 1 hour. Then, an aqueous solution of 7.1 parts of sodium nitrite dissolved in 22.0 parts of water was added, and the mixture was stirred for 1 hour to diazotize 3-amino-4-methoxybenzanilide and obtain a reaction solution. 1.0 part of sulfamic acid was added to the obtained reaction solution to eliminate nitrous acid, and then an aqueous solution of 20.7 parts of sodium acetate, 1.8 parts of acetic acid, and 165.0 parts of water was added to obtain a diazonium aqueous solution. 15.0 parts of 3-hydroxy-2-naphthamide and 5.0 parts of 3-hydroxy-3'-nitro-2-naphthanilide were added to 31.8 parts of 25% aqueous sodium hydroxide solution and 414.0 parts of water, and the mixture was thoroughly stirred to prepare an aqueous coupler solution. The aqueous coupler solution was then added to the aqueous diazonium solution prepared above, and the mixture was stirred for 1 hour to complete the reaction. The mixture slurry was then heated to 70°C, filtered, and washed with water to obtain a press cake of a solid solution pigment of naphthol AS azo pigment. The press cake was then dried at 90°C for 18 hours, and then pulverized to obtain a solid solution pigment 1 of CI Pigment Red 150 and CI Pigment Red 31.

[0108] (Solid solution pigment 2) A commercially available pigment (product name "Inkjet Magenta E7B 02 VP 3958", manufactured by Clariant) which is a solid solution pigment of CI Pigment Red 122, CI Pigment Violet 19, and CI Pigment Red 202 was used as solid solution pigment 2.

[0109] (Solid solution pigment 3) A commercially available pigment (product name "Inkjet Magenta E 02", manufactured by Clariant) which is a solid solution pigment of CI Pigment Red 122 and CI Pigment Violet 19 was used as solid solution pigment 3.

[0110] (Solid solution pigment 4) A commercially available pigment (trade name "FASTOGEN Super Magenta JM2120", manufactured by DIC) which is a solid solution pigment of CI Pigment Red 202 and CI Pigment Violet 19 was used as solid solution pigment 4.

[0111] <Preparation of pigment dispersion> By a conventional method, 80.7 parts of styrene and 19.3 parts of acrylic acid were copolymerized to synthesize acrylic resin 1, which is a water-soluble resin having an acid value of 150 mgKOH / g and a weight average molecular weight of 8,000. The obtained acrylic resin 1 was dissolved in ion-exchanged water by adding potassium hydroxide in an amount equimolar to the acid value, to prepare an aqueous solution of acrylic resin 1 with an acrylic resin 1 content of 20.00%.

[0112] A mixture of 10.0 parts of the pigment type shown in Table 1, 20.0 parts of an aqueous solution of acrylic resin 1, and 70.0 parts of ion-exchanged water was placed in a sand grinder and subjected to a dispersion treatment for 1 hour. Then, a centrifugation treatment was performed to remove coarse particles, and pressure filtration was performed using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. An appropriate amount of ion-exchanged water was added to obtain pigment dispersions with a pigment content of 10.00% and an acrylic resin 1 content of 4.00%.

[0113] TIFF2024023140000015.tif110170

[0114] <Synthesis of urethane resin> (Urethane resin 1-14) A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was prepared. Into this four-neck flask, polyisocyanate, polyol having no acid group, a part of dimethylolpropionic acid (amount used a), and 200.0 parts of methyl ethyl ketone, the types and amounts of which are shown in Table 2, were placed. Then, the mixture was reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Next, a part of dimethylolpropionic acid (amount used b), a chain extender, a terminator, and 100.0 parts of methyl ethyl ketone, the types and amounts of which are shown in Table 2, were added. The residual rate of the isocyanate group was confirmed by FT-IR, and the reaction was carried out at 80°C until the desired residual rate was reached, to obtain a reaction liquid. The obtained reaction liquid was cooled to 40°C, and then ion-exchanged water was added. While stirring at high speed with a homomixer, an appropriate amount of ion-exchanged water and potassium hydroxide equivalent in moles to the acid value of the synthesized resin were added to obtain a liquid. Methyl ethyl ketone was distilled off from the obtained liquid by heating under reduced pressure, and liquids containing water-soluble urethane resins 1 to 14 with a urethane resin content of 20.00% were obtained. The obtained urethane resins 1 to 14 were all water-soluble. The abbreviations in Table 2 are IPDI: isophorone diisocyanate, HDI: hexamethylene diisocyanate, PPG: polypropylene glycol, PTMG: polytetramethylene glycol, EDA: ethylenediamine, NPG: neopentyl glycol, and MeOH: methanol, and the numbers attached to PPG and PTMG represent number average molecular weights.

[0115] (Proportion of units derived from polyols having acid groups at the molecular terminals) Hydrochloric acid was added to the liquid containing the urethane resin to precipitate the urethane resin. The dried resin was dissolved in deuterated DMSO to prepare a measurement sample. 13The prepared sample was analyzed by C-NMR (apparatus name "Avance500", manufactured by BRUKER Bio Spin). The ratio of the peak integrated value of the carbonyl carbon in the unit derived from the polyol having an acid group at the molecular end to the total peak integrated value of the carbonyl carbon in the unit derived from the polyol having an acid group was calculated. The value (ratio) calculated in this way was taken as the "ratio of the unit derived from the polyol having an acid group at the molecular end". For example, when dimethylolpropionic acid is used, the peak of the carbonyl carbon in the unit derived from the polyol having an acid group at the molecular end is detected at about 176 ppm, although there is some deviation depending on the measurement conditions. In addition, the peak of the carbonyl carbon in the unit derived from the polyol having an acid group inside the molecule is detected at about 175 ppm. The results are shown in Table 2 as "Ratio of terminal acid groups (mol%)".

[0116] TIFF2024023140000016.tif103170

[0117] (Urethane Resin 15) A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was prepared. 43.5 parts of polypropylene glycol (number average molecular weight 1,000), 44.5 parts of isophorone diisocyanate, and 0.007 parts of dibutyltin dilaurate were placed in this four-neck flask. Then, the mixture was reacted at 100°C for 5 hours under a nitrogen gas atmosphere. After the reaction system was cooled to about 60°C, 150.0 parts of methyl ethyl ketone, 9.0 parts of dimethylolpropionic acid, and 3.0 parts of neopentyl glycol were added, and the inside of the reaction vessel was heated to 80°C, followed by polymerization reaction. After that, the reaction system was cooled to room temperature, and 20.0 parts of methanol were added to stop the reaction. Next, water was added, and further an aqueous potassium hydroxide solution was added with stirring to neutralize. The mixed solution was then heated under reduced pressure to distill off methyl ethyl ketone and unreacted methanol, yielding an aqueous solution of urethane resin 15 with a water-soluble urethane resin content of 20.00%. The proportion of terminal acid groups in urethane resin 15 was 50.0 mol%.

[0118] (Urethane Resin 16) A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was prepared. 39.7 parts of polytetramethylene glycol (number average molecular weight 2,000), 44.2 parts of isophorone diisocyanate, and 0.007 parts of dibutyltin dilaurate were placed in this four-neck flask. Then, the mixture was reacted at 100°C for 5 hours under a nitrogen gas atmosphere. After the reaction system was cooled to about 60°C, 150.0 parts of methyl ethyl ketone, 13.1 parts of dimethylolpropionic acid, and 3.0 parts of neopentyl glycol were added, and the inside of the reaction vessel was heated to 80°C, followed by polymerization reaction. After that, the reaction system was cooled to room temperature, and 20.0 parts of methanol were added to stop the reaction. Next, water was added, and further an aqueous potassium hydroxide solution was added while stirring to neutralize. The mixed solution was then heated under reduced pressure to distill off methyl ethyl ketone and unreacted methanol, yielding an aqueous solution of urethane resin 16 with a water-soluble urethane resin content of 20.00%. The proportion of terminal acid groups in urethane resin 16 was 50.0 mol%.

[0119] (Synthesis of urethane resin particles) 26.0 parts of neopentyl glycol, 20.0 parts of 1,4-butanediol, 54.0 parts of adipic acid, and 0.003 parts of an esterification catalyst (tetraisopropyl titanate) were placed in a flask. After heating to 120°C to melt, the mixture was heated to 220°C over 3 to 4 hours while stirring, and then maintained for 10 hours. The mixture was cooled to 100°C to obtain a polyester polyol having a number average molecular weight of 2,000. 60.0 parts of the polyester polyol, 36.0 parts of isophorone diisocyanate, 4.0 parts of dimethylolpropionic acid, and 60.1 parts of methyl ethyl ketone were placed in a flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube, and reacted for 5 hours. A 50% aqueous potassium hydroxide solution was added to neutralize the carboxylic acid group, and then water was added and thoroughly stirred. The mixture was then heated under reduced pressure to remove the solvent, and an aqueous dispersion of urethane resin particles with a resin particle content of 20.00% was obtained.

[0120] <Synthesis of acrylic resin 2> A four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube was prepared. 200.0 parts of ethylene glycol monobutyl ether was placed in this four-neck flask, and the mixture was stirred under a nitrogen gas atmosphere and heated to 130°C. As monomers, 65.0 parts of styrene, 20.0 parts of butyl acrylate, 15.0 parts of acrylic acid, and 4.0 parts of t-butyl peroxide as a polymerization initiator were dropped over 3 hours. After aging for 2 hours, ethylene glycol monobutyl ether was distilled off under reduced pressure to obtain a resin. To the obtained resin, potassium hydroxide in an amount equimolar to the acid value of the resin and an appropriate amount of ion-exchanged water were added, and the resin was dissolved by heating to 80°C. As a result, an aqueous solution containing acrylic resin 2 with an acrylic resin content of 20.00% was obtained.

[0121] <Preparation of surfactant> (Surfactants 1-10) The polysiloxane compound and polyoxyalkylene compound described below were placed in a glass vessel equipped with a thermometer and a stirring means, and an addition reaction was carried out in the presence of a platinum catalyst to synthesize surfactants 1 to 10. The polysiloxane compound used was a compound represented by the above-mentioned general formula (A) and in which m and n in general formula (A) are the numbers shown in Table 3. The polyoxyalkylene compound used was a compound represented by the above-mentioned general formula (B) and in which a, b, R in general formula (B) are the numbers shown in Table 3. 11 The compounds used were those in which R1 and R2 are the numbers or structures shown in Table 3. The surfactants obtained by the above synthesis are compounds represented by the above-mentioned general formula (1), and in which R1 in general formula (1) is the structure shown in Table 3. m, n, a, b, and R2 in general formula (1) correspond to m, n, a, b, and R2 in general formulas (A) and (B) which represent the structures of the compounds used in the synthesis, respectively. Table 3 also shows the weight average molecular weight (Mw) and HLB value of each of the obtained surfactants.

[0122] TIFF2024023140000017.tif88170

[0123] (Surfactants 11 and 12) The polysiloxane compound and polyoxyalkylene compound described below were placed in a glass vessel equipped with a thermometer and stirring means, and an addition reaction was carried out in the presence of a platinum catalyst to synthesize surfactants 11 and 12. The polysiloxane compound used was the compound represented by the above-mentioned general formula (C) and in general formula (C), where p is a number shown in Table 4. The polyoxyalkylene compound used was the compound represented by the above-mentioned general formula (D) and in general formula (D), where c, d, R 31 The compounds used were those in which R3, R4, and R5 are the numbers or structures shown in Table 4. The surfactants obtained by the above synthesis are compounds represented by the above general formula (2) and the structure in which R3 in general formula (2) is shown in Table 4. p, c, d, and R4 in general formula (2) correspond to p, c, d, and R4 in general formulas (C) and (D) which represent the structures of the compounds used in the synthesis, respectively. Table 4 also shows the weight average molecular weight (Mw) and HLB value of each of the obtained surfactants.

[0124] TIFF2024023140000018.tif36170

[0125] (Surfactant 13) A polysiloxane compound and a polyoxyalkylene compound described below were placed in a glass vessel equipped with a thermometer and a stirring means, and an addition reaction was carried out in the presence of a platinum catalyst to synthesize surfactant 13. The polysiloxane compound used was a compound in which q in the above-mentioned general formula (E) is represented by a number shown in Table 5. The polyoxyalkylene compound used was a compound in which e, f, R in the above-mentioned general formula (F) are represented by a number shown in Table 5. 51 and R 61 The surfactant obtained by the above synthesis is a compound represented by the above general formula (3) and the structure in which R5 and R6 in general formula (3) are shown in Table 5. q, e, f, R5, and R6 in general formula (3) correspond to q, e, f, R5, and R6 in general formula (E) and (F) which represent the structure of each compound used in the synthesis, respectively. In addition, r in general formula (3) corresponds to r shown in Table 5. Table 5 also shows the weight average molecular weight (Mw) and HLB value of the obtained surfactant.

[0126] TIFF2024023140000019.tif29170

[0127] (Surfactants 14-19) The following commercially available surfactants 14 to 19 were used. Surfactants 14 Product name: "Acetylenol E100" (Kawaken Fine Chemicals), acetylene glycol surfactant Surfactants 15 Product name: Captone FS3100 (manufactured by DuPont), fluorosurfactant Surfactants 16 Product name: "NIKKOL BC-20" (manufactured by Nikko Chemicals), polyoxyethylene alkyl ether surfactant Surfactants 17 Product name: Surfynol 440 (manufactured by Nissin Chemical Industry Co., Ltd.), acetylene glycol surfactant Surfactants 18 Product name: Sannol NL1430 (manufactured by Lion), polyoxyethylene alkyl ether surfactant Surfactants 19 Product name: Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd.), acetylene glycol surfactant

[0128] <Ink Preparation> Each component (unit: %) shown in the middle of Table 6 (Tables 6-1 to 6-8) was mixed, thoroughly stirred, and then pressure-filtered with a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare each ink. The types (numbers) shown in the upper part of Table 6 were used for the "pigment dispersion I", "pigment dispersion II", "aqueous solution of urethane resin", and "surfactant" shown in the middle of Table 6. However, "-" in the upper part of Table 6 indicates that no surfactant was used. "Proxel GXL" in the middle of Table 6 is the trade name of a preservative manufactured by Arch Chemicals. The lower part of Table 6 shows the characteristics of the ink. That is, the content A (%) of the first pigment (pigment in pigment dispersions I-1 to I-8), the content Q (%) of the second pigment (pigment in pigment dispersions II-1 to II-5), the content P (%) of the pigment, the content U (%) of the urethane resin, and the content S (%) of the silicone surfactant in the ink are shown. Similarly, the P / U value (fold), A / P value (fold), Q / P value (fold), A / Q value (fold), A / S value (fold), Q / S value (fold), and U / S value (fold) are shown.

[0129] TIFF2024023140000020.tif146170

[0130] TIFF2024023140000021.tif147170

[0131] TIFF2024023140000022.tif149170

[0132] TIFF2024023140000023.tif149170

[0133] TIFF2024023140000024.tif150170

[0134] TIFF2024023140000025.tif147170

[0135] TIFF2024023140000026.tif150170

[0136] TIFF2024023140000027.tif145170

[0137] Comparative Example 22 The components shown below were mixed and thoroughly stirred, and then pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare an ink of Comparative Example 22. This ink does not contain a second pigment. Pigment dispersion I-7: 40.00% Aqueous solution of urethane resin 15: 25.00% Surfactant 10: 1.00% 1,2-Pentanediol: 15.00% Proxel GXL: 0.05% -Ion-exchanged water: 18.95%

[0138] (Comparative Example 23) The components shown below were mixed and thoroughly stirred, and then pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare an ink of Comparative Example 23. This ink does not contain a water-soluble urethane resin or a surfactant represented by each of the general formulas (1) to (3). Pigment dispersion I-1: 24.00% Pigment dispersion II-3: 56.00% Surfactant 17: 0.40% Surfactant 18: 0.40% Glycerin: 8.00% Polyethylene glycol with number average molecular weight of 200: 3.00% Triethylene glycol: 5.00% Triethylene glycol-n-butyl ether: 2.00% Ion-exchanged water: 1.20%

[0139] Comparative Example 24 The components shown below were mixed and thoroughly stirred, and then pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare the ink of Comparative Example 24. This ink does not contain a water-soluble urethane resin. Pigment dispersion I-1: 15.60% Pigment dispersion II-2: 34.51% Surfactant 6: 0.50% Glycerin: 10.00% Butyl diglycol: 20.00% Ion-exchanged water 19.39%

[0140] Comparative Example 25 The components shown below were mixed and thoroughly stirred, and then pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare an ink of Comparative Example 25. This ink does not contain any of the surfactants represented by the general formulas (1) to (3). Pigment dispersion I-8: 25.00% Pigment dispersion II-4: 15.00% Aqueous solution of urethane resin 16: 25.00% Surfactant 19: 1.00% 1,2-Pentanediol: 15.00% Ion-exchanged water: 19.00%

[0141] <Evaluation> The prepared inks were used to carry out the following evaluations. In this embodiment, in the evaluation criteria for each evaluation item shown below, "AA", "A" and "B" were set as acceptable levels, and "C" and "D" were set as unacceptable levels. For the evaluation, an inkjet recording device (product name "PIXUS PRO-10") equipped with a recording head that ejects ink by thermal energy was used. In this embodiment, an image recorded under the condition that 35 ng of ink is applied to a unit area of ​​1 / 600 inch x 1 / 600 inch was defined as having a recording duty of 100%. The evaluation environment was a temperature of 25°C and a relative humidity of 55%. The evaluation results are shown in Table 7.

[0142] (Color development) Each ink prepared was filled into an ink cartridge and set in the inkjet recording device. A solid image with a recording duty of 50% was recorded on a recording medium (glossy paper, product name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon), and dried for one day in an environment of 25°C. A spectrophotometer (product name "FD-7", manufactured by Konica Minolta) was used to measure the color of the ink using a light source D. 50 The optical density of the solid image was measured under the condition of 2° visual field. Of the obtained optical densities, the optical density of the magenta component was evaluated according to the following evaluation criteria. A: The optical density was 2.0 or more. B: The optical density was 1.8 or more and less than 2.0. C: The optical density was 1.6 or more and less than 1.8.

[0143] (Lightfastness) Each ink prepared was filled into an ink cartridge and set in the inkjet recording device. A solid image with a recording duty of 5% was recorded on a recording medium (matte paper, product name "Canon Photo Paper Premium Matte PM-101", manufactured by Canon) and dried for one day in an environment of 25°C. The optical density of the recorded solid image was measured using a spectrophotometer (product name "FD-7", manufactured by Konica Minolta) (optical density before lightfastness test). Then, the solid image was put into a xenon light test device (low-temperature cycle xenon weather meter XL-75C: manufactured by Suga Test Instruments). Then, the xenon light was irradiated until the integrated irradiance reached 33,400 klx·hr, with an illuminance of 50 klx, an air temperature in the chamber of 23°C, a relative humidity of 50%, and a black panel temperature of 23°C. Then, the optical density of the solid image was measured (optical density after lightfastness test). From the optical density values ​​obtained before and after the light fastness test, the residual optical density rate (%) (= (optical density after light fastness test / optical density before light fastness test) × 100) was calculated, and the light fastness of the image was evaluated according to the evaluation criteria shown below. AA: The remaining optical density was 90% or more. A: The remaining optical density was 80% or more and less than 90%. B: The remaining optical density was 75% or more and less than 80%. C: The remaining optical density was 70% or more and less than 75%. D: The remaining optical density was less than 70%.

[0144] (Intermittent ejection stability) Each prepared ink was filled into an ink cartridge and set in the inkjet recording device. After recording one solid image with a recording duty of 50% on a recording medium (glossy paper, product name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon), the inkjet recording device was paused for a predetermined time. Then, ink was ejected only once from each ejection port. When the ink was ejected normally, a vertical line with approximately the same width as the ejection port row was recorded. The recorded lines were visually observed, and the intermittent ejection stability was evaluated according to the following evaluation criteria. AA: After a 10-minute pause, ink was being ejected normally from 90% or more of the ejection ports. A: The downtime was less than 10 minutes and more than 5 minutes, and ink was ejected normally from 90% or more of the nozzles. B: The downtime was less than 5 minutes but 1 minute or more, and ink was ejected normally from 90% or more of the total ejection ports. C: The pause time was less than 1 minute (15 seconds or more), and ink was ejected normally from 90% or more of all ejection ports. D: When the rest time was 15 seconds or more, ink was not ejected normally from 90% or more of the total ejection ports, and ink was distorted or not ejected at all.

[0145] TIFF2024023140000028.tif167170

[0146] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) A water-based inkjet ink containing a pigment, a urethane resin, and a silicone surfactant, the pigment includes a first pigment and a second pigment, the first pigment is a naphthol AS-based azo pigment, and the second pigment is a quinacridone-based pigment; the urethane resin is a water-soluble urethane resin having units derived from a polyisocyanate, a polyol having no acid group, and a polyol having an acid group, The silicone surfactant is at least one selected from the group consisting of compounds represented by each of the following general formulas (1) to (3), and has a weight average molecular weight of 800 or more and 10,000 or less and an HLB value of 4 or more as measured by the Griffin method.

[0147] TIFF2024023140000029.tif31170 (In the general formula (1), R1 represents an alkylene group, R2 represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, and a and b each independently represent an integer of 0 or more, but are not both 0.)

[0148] TIFF2024023140000030.tif29170 (In the general formula (2), R3 represents an alkylene group, R4 represents a hydrogen atom or an alkyl group, p represents an integer of 1 or more, and c and d each independently represent an integer of 0 or more, but are not 0 at the same time.)

[0149] TIFF2024023140000031.tif30170 (In the general formula (3), R5 represents an alkylene group, R6 represents a hydrogen atom or an alkyl group, q and r each independently represent an integer of 1 or more, and e and f each independently represent an integer of 0 or more, but are not 0 at the same time.)

[0150] (Configuration 2) The aqueous ink according to configuration 1, wherein the content (mass %) of the pigment in the aqueous ink is at least 1.00 times the content (mass %) of the urethane resin in the aqueous ink. (Configuration 3) The aqueous ink according to configuration 1 or 2, wherein the content (mass %) of the second pigment in the aqueous ink is 0.80 times or more the mass ratio of the content (mass %) of the pigment. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the first pigment is at least one selected from the group consisting of CI Pigment Red: 31, 146, 147, 150, and 269. (Arrangement 5) The aqueous ink according to any one of Arrangements 1 to 3, wherein the first pigment is CI Pigment Red 150. (Arrangement 6) The aqueous ink according to any one of Arrangements 1 to 5, wherein the second pigment is a solid solution pigment containing CI Pigment Red 122 and CI Pigment Violet 19. (Configuration 7) The aqueous ink according to any one of Configurations 1 to 6, wherein, in the silicone surfactant, R2 in general formula (1), R4 in general formula (2), or R6 in general formula (3) is a methyl group. (Configuration 8) The aqueous ink according to any one of Configurations 1 to 7, wherein the polyisocyanate comprises isophorone diisocyanate. (Configuration 9) The aqueous ink according to any one of Configurations 1 to 8, wherein the polyol having no acid group has a number average molecular weight of 1,500 or more and 4,000 or less. (Configuration 10) The aqueous ink according to any one of configurations 1 to 9, wherein the polyol having no acid group is polypropylene glycol. (Structure 11) The aqueous ink according to any one of Structures 1 to 10, wherein the proportion of units derived from the polyol having an acid group present at a molecular terminal in the urethane resin is 30.0 mol % or less of all units derived from the polyol having an acid group. (Configuration 12) An ink cartridge including an ink and an ink storage section for storing the ink, 12. An ink cartridge, wherein the ink is the aqueous ink described in any one of configurations 1 to 11. (Method 1) An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, 12. An ink-jet recording method, wherein the ink is the aqueous ink described in any one of configurations 1 to 11.

Claims

1. An aqueous inkjet ink containing a pigment, a urethane resin, and a silicone-based surfactant, The aforementioned pigment comprises a first pigment and a second pigment, wherein the first pigment is a naphthol AS-based azo pigment, and the second pigment is a quinacridone-based pigment. The urethane resin is a water-soluble urethane resin having units derived from polyisocyanate, polyol without acid groups, and polyol having acid groups, respectively. The aqueous ink is characterized in that the silicone-based surfactant is at least one selected from the group consisting of compounds represented by each of the following general formulas (1) to (3), and has a weight-average molecular weight of 800 or more and 10,000 or less, and an HLB value of 4 or more according to the Griffin method. (In the above general formula (1), R １ represents an alkylene group, R ２ represents a hydrogen atom or an alkyl group. m and n each independently represent an integer of 1 or greater, and a and b each independently represent an integer of 0 or greater, but they cannot be simultaneously 0. (In the above general formula (2), R ３ represents an alkylene group, R ４ (where p represents a hydrogen atom or alkyl group, and c and d represent integers of 0 or greater independently, but cannot be 0 simultaneously.) (In the above general formula (3), R ５ represents an alkylene group, R ６ represents a hydrogen atom or an alkyl group. q and r each independently represent an integer greater than or equal to 1, and e and f each independently represent an integer greater than or equal to 0, but they cannot be both 0.

2. The aqueous ink according to claim 1, wherein the content (mass%) of the pigment in the aqueous ink is 1.00 times or more by mass ratio to the content (mass%) of the urethane resin.

3. The aqueous ink according to claim 1, wherein the content (mass%) of the second pigment in the aqueous ink is 0.80 times or more by mass ratio to the content (mass%) of the pigment.

4. The aqueous ink according to claim 1, wherein the first pigment is at least one selected from the group consisting of C.I. Pigment Red: 31, 146, 147, 150, and 269.

5. The aqueous ink according to claim 1, wherein the first pigment is C.I. Pigment Red 150.

6. The aqueous ink according to claim 1, wherein the second pigment is a solid solution pigment containing C.I. Pigment Red 122 and C.I. Pigment Violet 19.

7. In the silicone surfactant, R in the general formula (1) ２ , R in the general formula (2) ４ , or R in the general formula (3) ６ is a methyl group, and the aqueous ink according to claim

8. The aqueous ink according to claim 1, wherein the polyisocyanate comprises isophorone diisocyanate.

9. The aqueous ink according to claim 1, wherein the number average molecular weight of the polyol without acid groups is 1,500 or more and 4,000 or less.

10. The aqueous ink according to claim 1, wherein the polyol that does not have an acid group is polypropylene glycol.

11. The aqueous ink according to claim 1, wherein the proportion of units derived from the polyol having acid groups located at the molecular terminals of the urethane resin to the total number of units derived from the polyol having acid groups is 30.0 mol% or less.

12. The aqueous ink according to claim 1, wherein the content (mass%) of the first pigment in the aqueous ink is 1.00 times or more and 15.00 times or less by mass ratio to the content (mass%) of the silicone-based surfactant, and the content (mass%) of the second pigment is 40.00 times or more and 55.00 times or less by mass ratio to the content (mass%) of the silicone-based surfactant.

13. The aqueous ink according to claim 1, wherein the content (by mass) of the first pigment in the aqueous ink is 0.02% by mass or more and 3.00% by mass or less, based on the total mass of the ink.

14. The aqueous ink according to claim 1, wherein the content (by mass) of the second pigment in the aqueous ink is 0.08% by mass or more and 12.00% by mass or less, based on the total mass of the ink.

15. The aqueous ink according to claim 1, wherein the content (by mass) of the pigment in the aqueous ink is 0.10% by mass or more and 15.00% by mass or less, based on the total mass of the ink.

16. The aqueous ink according to claim 1, wherein the content (by mass) of the urethane resin in the aqueous ink is 0.10% by mass or more and 10.00% by mass or less, based on the total mass of the ink.

17. The aqueous ink according to claim 1, wherein the content (by mass) of the silicone-based surfactant in the aqueous ink is 0.01% by mass or more and 1.00% by mass or less, based on the total mass of the ink.

18. The aqueous ink according to claim 1, wherein the content (mass%) of the first pigment in the aqueous ink is 0.01 times or more and 0.20 times or less in mass ratio to the content (mass%) of the pigment.

19. The aqueous ink according to claim 1, wherein the content (mass%) of the first pigment in the aqueous ink is 0.01 times or more and 0.50 times or less by mass ratio to the content (mass%) of the second pigment.

20. The aqueous ink according to claim 1, wherein the content (mass%) of the urethane resin in the aqueous ink is 1.00 times or more and 60.00 times or less by mass ratio to the content (mass%) of the silicone-based surfactant.

21. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in any one of claims 1 to 20.

22. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of claims 1 to 20.

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