Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide an aqueous ink that enables recording of an image having excellent scratch resistance and beading resistance.SOLUTION: An aqueous ink contains: a pigment; a compound (A) represented by the general formula (1); and a compound (B) represented by the general formula (2). A weight average molecular weight of the compound (A) is 1,500 or more and 7,500 or less. A ratio of a content A (mass%) of the compound (A) based on the total mass of the aqueous ink to the sum of the content A (mass%) of the compound (A) and the content B (mass%) of the compound (B) based on the total mass of the aqueous ink is 0.40 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method. [Background technology]

[0002] In recent years, inkjet recording methods have been used not only for printing documents at home or in the office, but also for commercial and industrial printing. In particular, large-format inkjet recording devices suitable for printing posters and large-format advertisements have become widespread. Such recording devices require increased recording speed, improved throughput, and higher image quality. To meet these demands, various inkjet recording devices have been developed.

[0003] In recording devices with increased recording speeds, the time it takes for recording media to overlap on the stacking tray or output basket of an inkjet recording device is reduced. As a result, the recording media rub against each other immediately after recording, making them more susceptible to scratches, and scratch resistance is often a challenge.

[0004] Furthermore, for posters and advertising applications, printing with a wide color gamut and high color reproduction is required. As a means of recording such images, a method is sometimes employed that increases the amount of ink applied, thereby increasing the amount of colorant on the recording medium. While this method improves the color gamut and color reproduction of the resulting image, it creates the problem of unevenness in solid areas. This is a phenomenon called "beading," in which ink dots that the recording medium could not fully absorb coalesce locally and fix unevenly, and it is more likely to occur when the recording medium has low ink absorption.

[0005] To solve the above problems, various proposals have been made so far. For example, there is a proposal to improve the rubbing resistance of an image by including a specific resin and a specific polyether-modified organosiloxane in the ink (Patent Documents 1 to 4). Also, as a method for suppressing beading, inks containing a glycol ether compound, a silicone-based surfactant, and a fluorine-based surfactant, and inks containing a plurality of types of surfactants have been proposed (Patent Documents 4 and 5).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] When the present inventors recorded an image with the inks proposed in Patent Documents 1 and 3, a certain effect was obtained with respect to the rubbing resistance. However, it was found that since high molecular weight silicone oil and resin block the pores of the recording medium, the ink permeability decreases, and it is difficult to achieve both good anti-beading properties.

[0008] In addition, when recording was performed using the ink containing a silicone-based surfactant proposed in Patent Document 2, the abrasion resistance of the image was insufficient in areas with a low recording duty. This is presumably because the silicone-based surfactant added as a slip agent penetrated in the thickness direction of the recording medium together with the aqueous medium, and the amount remaining in the pigment layer formed by the ink decreased. Also, since the silicone-based surfactant decreased the surface energy of the ink dots present in a liquid state on the recording medium, the subsequently applied ink was repelled, resulting in uneven shading in the recorded image.

[0009] In Patent Document 4, an ink has been proposed that reduces the tack of the ink film with a silicone-based surfactant to provide abrasion resistance, while increasing the ink permeability with a fluorine-based surfactant to enhance the anti-beading property. However, when recording was performed using the ink proposed in Patent Document 4, in areas with a low recording duty, the abrasion resistance of the image was insufficient because the silicone-based surfactant did not remain in the pigment layer.

[0010] Also, in the method described in Patent Document 4, the recorded image is dried at a temperature of 100°C to promote gelation of the ink, thereby obtaining good anti-beading properties. However, when drying was performed at room temperature, the anti-beading property decreased. This is considered to be because a large amount of a silicone-based surfactant and a fluorine-based surfactant with a high ability to lower the surface tension to increase the ink permeability are used. Furthermore, in the ink containing a plurality of types of silicone-based surfactants with different HLB values proposed in Patent Document 5, uneven shading was observed in the image because the silicone-based surfactant decreased the surface energy of the dots, and the anti-beading property was insufficient.

[0011] Therefore, an object of the present invention is to provide an aqueous ink capable of recording an image excellent in abrasion resistance and anti-beading property. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Means for Solving the Problems

[0012] In other words, the present invention provides an aqueous ink containing a pigment, a compound (A) represented by the following general formula (1), and a compound (B) represented by the following general formula (2), wherein the weight-average molecular weight of compound (A) is 1,500 or more and 7,500 or less, the content A (mass%) of compound (A) based on the total mass of the aqueous ink is 0.40 or less in ratio to the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B), and the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B) based on the total mass of the aqueous ink is 1.00 mass% or less.

[0013] TIFF2023088852000001.tif33170 (In the above general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R2 represents an alkylene group having 1 to 20 carbon atoms, a represents an integer between 1 and 170, and p represents an integer between 1 and 120.)

[0014] TIFF2023088852000002.tif31170 (In the above general formula (2), m and n each independently represent integers between 0 and 15, inclusive.) [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an aqueous ink capable of recording images with excellent scratch resistance and beading resistance. Furthermore, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. [Figure 2]This figure schematically shows an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. [Modes for carrying out the invention]

[0017] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based ink for inkjet printers may be simply referred to as "ink." Unless otherwise specified, the physical properties are values ​​at room temperature (25°C).

[0018] The inventors first investigated the composition of an aqueous inkjet ink capable of recording images with excellent scratch resistance. To improve the scratch resistance of the image, it is preferable to lower the surface energy of the pigment layer to make it slippery. Therefore, they decided to include a silicone-based surfactant in the ink as a material to lower the surface energy of the pigment layer.

[0019] Silicone-based surfactants are surfactants in which hydrophilic substituents are introduced into a polyorganosiloxane, which has a main skeleton of siloxane bonds (SiO) in which silicon (Si) and oxygen (O) atoms are alternately linked. The siloxane skeleton has a helical structure in which six SiO bonds make one turn, with the highly hydrophilic siloxane bonds facing the inside of the helix and the highly hydrophobic organic groups facing the outside of the helix. Due to this characteristic structure, the organic groups with weak intermolecular interactions are located on the outside of the molecule, resulting in a low surface energy. Silicone-based surfactants with such a structure were expected to function as lubricants.

[0020] However, the scratch resistance of images recorded using inks containing silicone-based surfactants was unsatisfactory. Specifically, in areas with low recording duty cycles, the images were easily scratched immediately after recording, resulting in a lack of scratch resistance.

[0021] In areas with low recording duty cycles, the amount of ink applied per unit area is small, and the penetration of the aqueous medium in the ink into the recording medium is completed in a short time. Silicone-based surfactants, which have a relatively slow orientation speed at the gas-liquid interface, penetrate into the thickness direction of the recording medium along with the aqueous medium without being able to sufficiently orient themselves at the gas-liquid interface. Therefore, it is thought that the amount of surfactant remaining in the pigment layer was insufficient, and the effect of improving abrasion resistance was not achieved.

[0022] Next, the inventors considered increasing the amount of silicone-based surfactant present in the pigment layer. Specifically, they increased the amount of silicone-based surfactant contained in the ink. As a result, the scratch resistance of the image improved slightly, but not sufficiently. Furthermore, unevenness in shading was observed in the recorded images, and beading occurred.

[0023] The slight improvement in image abrasion resistance resulting from increasing the amount of silicone-based surfactant in the ink is thought to be because the increased amount of silicone-based surfactant remaining in the pigment layer lowered its surface energy, making it more slippery. However, lowering the surface energy of the pigment layer also reduces the wettability of the dot surface. Ink droplets applied to overlapping dot surfaces that have become less wettable due to the silicone-based surfactant are repelled without mixing, resulting in uneven fixation on the recording medium, which is thought to have caused unevenness in density.

[0024] From the above, it was found that simply including a component that reduces surface energy in the ink and adjusting its content makes it difficult to achieve both scratch resistance and beading resistance in the image.

[0025] The inventors further investigated the composition of an aqueous inkjet ink capable of recording images that achieve a high level of both abrasion resistance and beading resistance. As a result, they found that the following conditions [1] to [5] must be met for the aqueous ink to satisfy both performance requirements. [1] The aqueous ink contains compound (A) represented by the general formula (1). [2] The aqueous ink contains compound (B) represented by the general formula (2) above. [3] The weight-average molecular weight of compound (A) is 1,500 or more and 7,500 or less. [4] The content A (mass%) of compound (A) based on the total mass of the water-based ink is 0.40 or less as a ratio to the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B). [5] The sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B) based on the total mass of the water-based ink is 1.00% by mass or less.

[0026] Based on the above configuration, the inventors hypothesize the following mechanism enables both abrasion resistance and beading resistance.

[0027] First, the ink of the present invention contains compound (A), represented by the general formula (1), which is a silicone-based surfactant, and compound (B), represented by the general formula (2), which is an acetylene glycol-based surfactant. When an image is recorded using an ink containing both of these surfactants, the two surfactants compete to orient themselves at the gas-liquid interface of the dots ejected from the recording head and attached to the recording medium. Compound (B), which is an acetylene glycol-based surfactant, orients at the gas-liquid interface faster than compound (A), which is a silicone-based surfactant. Therefore, it is thought that compound (B), which is an acetylene glycol-based surfactant, orients at the interface more frequently in the short time elapsed after the ink is applied to the recording medium. At this time, compound (B) that is orienting at the gas-liquid interface forms loose aggregates with other molecules through hydrophobic interactions.

[0028] On the other hand, compound (A), a silicone-based surfactant, has a relatively slow orientation rate. As mentioned earlier, due to its slow orientation rate, when silicone-based surfactants were included in the ink alone, they penetrated the recording medium before orientation could occur, resulting in a lack of abrasion resistance. However, when compound (B), an acetylene glycol-based surfactant, was included together, the penetration of compound (A), the silicone-based surfactant, into the recording medium was suppressed, allowing more of it to remain in the pigment layer. This is thought to be because the hydrophobic portion of compound (A), the silicone-based surfactant, interacted with the hydrophobic portion of the aggregate of compound (B), the acetylene glycol-based surfactant, which had already oriented at the gas-liquid interface, making it easier for it to orient at the interface.

[0029] Compound (B), an acetylene glycol-based surfactant, has branched hydrophobic groups. It is presumed that this bulky structure acts as steric hindrance, delaying the timing at which compound (A), a silicone-based surfactant, orients onto the ink droplet surface, thereby improving beading resistance.

[0030] When ink is applied to a recording medium, compound (B), an acetylene glycol-based surfactant, first orients on the surface of the ink droplet. Due to this steric hindrance, the orientation of compound (A), a silicone-based surfactant, is delayed, so a decrease in surface energy immediately after dot formation is unlikely to occur. As a result, ink droplets applied on top of these dots are less likely to be repelled and are fixed to the recording medium in a mixed state, which is thought to eliminate unevenness in density.

[0031] Compound (A), a silicone-based surfactant with a slow orientation rate, gradually migrates to the dot surface over time, reducing the surface energy. As a result, the slipperiness of the formed pigment layer is improved, and the image's scratch resistance is enhanced.

[0032] As described above, compound (B), an acetylene glycol-based surfactant, suppresses the penetration of compound (A), a silicone-based surfactant, into the recording medium, allowing compound (A) to efficiently remain in the pigment layer and thus improving abrasion resistance. Furthermore, compound (B) acts as a steric hinder, delaying the orientation of compound (A), thus enabling a balance with beading resistance.

[0033] However, simply including these surfactants in the ink did not always yield the effects of the present invention. In addition to the above, the interaction of the two surfactants functions to produce the effects of the present invention only when the conditions [1], [3] to [5] described above are met. The details are described below.

[0034] First, in order to obtain images with the high level of abrasion resistance that is the aim of this invention, it is necessary to use compound (A) represented by general formula (1), that is, a silicone-based surfactant modified with ethylene oxide groups at both ends. As mentioned above, the siloxane skeleton has a helical structure that makes one turn with six SiO bonds, with hydrophilic SiO bonds facing the inside of the helix and hydrophobic organic groups facing the outside of the helix. The low surface energy of silicone compounds is due to their characteristic molecular structure covered with methyl groups, which have weak intermolecular forces. Compound (A) represented by general formula (1) has ethylene oxide groups introduced at both ends of the molecule, and the parts other than the ends are covered with methyl groups. Therefore, it is thought that the effect of lowering the surface energy due to the continuous methyl groups can be efficiently obtained.

[0035] In addition to the structure represented by general formula (1), silicone-based surfactants include those in which the side chains are modified with ethylene oxide groups, such as the compound represented by general formula (3) below. Furthermore, there are also compounds with a block structure of polydimethylsiloxane and ethylene oxide, such as the compound represented by general formula (4). In silicone-based surfactants having these structures, some of the methyl groups covering the outside of the siloxane skeleton are modified with hydrophilic ethylene oxide groups, resulting in fewer consecutive methyl groups, which is thought to reduce the effect of lowering the surface energy.

[0036] TIFF2023088852000003.tif33170 (In general formula (3), R3 represents a hydrogen atom or an alkyl group, R4 represents an alkylene group, and b, q, and r represent integers.)

[0037] TIFF2023088852000004.tif32170 (In general formula (4), R5 represents a hydrogen atom or an alkyl group, R6 represents an alkylene group, and c, s, and t represent integers.)

[0038] Furthermore, compound (A), represented by general formula (1), which is a silicone-based surfactant, has an optimal structure for interaction with compound (B), represented by general formula (2), which is an acetylene glycol-based surfactant, from the standpoint of improving beading resistance.

[0039] Compound (A), represented by general formula (1), has hydrophilic groups introduced at both ends of the molecule, and the hydrophobic parts are located in a concentrated position within the molecule, so the hydrophobic interactions between molecules are considered to be relatively large. In contrast, compounds represented by general formulas (3) and (4) have a structure in which hydrophilic parts are sandwiched between hydrophobic parts, so the hydrophobic interactions between molecules are considered to be small. Compound (A), represented by general formula (1), is more likely to form large aggregates due to intermolecular interactions. Therefore, it is thought that compound (A) can be sterically hindered by compound (B), represented by general formula (2), which is an acetylene glycol-based surfactant, and can be oriented at the gas-liquid interface over time, thereby achieving excellent beading resistance.

[0040] Furthermore, the weight-average molecular weight (Mw) of compound (A), represented by general formula (1), which is a silicone-based surfactant, must be between 1,500 and 7,500. If the weight-average molecular weight of compound (A) is less than 1,500, the number of repeating methyl groups, which are the structure that reduces surface energy and exhibits slipperiness, decreases, and therefore abrasion resistance cannot be obtained. Specifically, if the weight-average molecular weight of compound (A) is less than 1,500, regardless of the values ​​or substituents of a, R1, and R2 in general formula (1), the number of repeating methyl groups decreases, and abrasion resistance cannot be obtained.

[0041] When the weight-average molecular weight of compound (A), a silicone-based surfactant, exceeds 7,500, beading resistance cannot be obtained. For example, when the commercially available silicone-based surfactant "BYK-333" (weight-average molecular weight 8,000, manufactured by Bic Chemie) was used, beading resistance could not be obtained. The orientation of most silicone-based surfactant compounds (A) to the dot surface is delayed by the steric hindrance of compound (B), an acetylene glycol-based surfactant. However, some compounds (A) can overcome the steric hindrance and orient themselves to the dot surface due to fluctuations in the association of compound (B). Compounds (A) with a weight-average molecular weight exceeding 7,500 have a high ability to reduce surface energy due to the many repeating methyl groups, and when oriented to the dot surface, they have a strong force to repel ink droplets, resulting in reduced beading resistance.

[0042] The content A (mass%) of compound (A), which is a silicone-based surfactant, relative to the total mass of the ink, is 0.40 or less as a ratio of the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B), which is an acetylene glycol-based surfactant. That is, it satisfies the following equation (5). A / (A+B)≦0.40 (5)

[0043] The value of A / (A+B) in equation (5) represents the ratio of the content of the silicone-based surfactant (compound (A)) to the total amount of the silicone-based surfactant (compound (B)) and acetylene glycol-based surfactant (compound (B)) in the ink. If this ratio exceeds 0.40, the proportion of compound (A) is too high and the proportion of compound (B) is too low, resulting in insufficient steric hindrance by compound (B), causing ink droplets to repel each other and reducing beading resistance.

[0044] Furthermore, the sum of the content A (mass%) of compound (A), which is a silicone-based surfactant, and the content B (mass%) of compound (B), which is an acetylene glycol-based surfactant, based on the total mass of the water-based ink, is 1.00 mass% or less. If the sum of the above contents exceeds 1.00 mass%, even if the ratio of compound (A) to compound (B) satisfies the above formula (5), the total amount of compound (A) contained in the ink will be large, making the ink more likely to be repelled on the dot surface and reducing beading resistance.

[0045] <ink> The following provides a detailed explanation of the components that make up the ink of this invention, as well as the physical properties of the ink.

[0046] (Compound (A) represented by general formula (1)) The ink contains a nonionic silicone-based surfactant, compound (A), represented by the following general formula (1). The ink may contain one or more of the compounds (A) represented by general formula (1). In this specification, compound (A) represented by general formula (1) may be simply referred to as "compound (A)". Compound (A) can be synthesized as a mixture of compounds with various molecular weights due to different polysiloxane polymerization degrees (p), but for convenience, it will be referred to as "compound," including when it is a mixture. Furthermore, since it can be synthesized as a mixture, a and p can also be considered as mass-weighted average values, in which case a and p may be decimals, but in this specification, they will be treated as integers rounded to the nearest whole number. In compound (A) represented by general formula (1), C2H4O represents an ethylene oxide unit.

[0047] TIFF2023088852000005.tif33170 (In general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R2 represents an alkylene group having 1 to 20 carbon atoms, a represents an integer between 1 and 170, and p represents an integer between 1 and 120.)

[0048] In general formula (1), R1 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom, a methyl group, an ethyl group, or a propyl group, and even more preferably a hydrogen atom. In general formula (1), R2 is preferably an alkylene group having 1 to 10 carbon atoms, more preferably an ethylene group, a propylene group, or a butylene group, and even more preferably a propylene group. In general formula (1), a is preferably an integer between 1 and 100, and even more preferably an integer between 1 and 50. In general formula (1), p is preferably an integer between 1 and 100, and even more preferably an integer between 1 and 50.

[0049] In compound (A) represented by general formula (1), the number of moles of ethylene oxide added to compound (A) is preferably 1.0 or more and 5.0 or less in ratio to the degree of polymerization of polysiloxane (degree of polymerization of polydimethylsiloxane) in compound (A). In other words, in compound (A), the total number of moles of ethylene oxide added represented by a in general formula (1) (2a) is preferably 1.0 or more and 10.0 or less in ratio (2a / p) to the degree of polymerization of polysiloxane represented by p in general formula (1) (p). That is, the relationship between the total number of moles of ethylene oxide added (2a) and the degree of polymerization of polysiloxane (p) preferably satisfies the following formula (6). 1.0 ≤ 2a / p ≤ 10.0 (6) (In equation (6), a and p are equivalent to a and p in general equation (1), respectively.)

[0050] In equation (6), the number of moles of ethylene oxide added, represented by 2a, is an indicator of the degree of hydrophilicity of compound (A), which is a silicone-based surfactant. The degree of polysiloxane polymerization, represented by p, is an indicator of the degree of hydrophobicity of compound (A), which is a silicone-based surfactant. A 2a / p value of 1.0 or higher results in moderately high hydrophilicity of compound (A), making it easier to improve beading resistance. On the other hand, a 2a / p value of 10.0 or lower results in moderate hydrophobicity of compound (A), making it easier to improve abrasion resistance. A 2a / p value between 2.0 and 5.0 is even more preferable.

[0051] The weight-average molecular weight (Mw) of compound (A), represented by general formula (1), which is a silicone-based surfactant, must be between 1,500 and 7,500, and more preferably between 2,000 and 5,000. The weight-average molecular weight (Mw) is the weight-average molecular weight on a polystyrene basis in the molecular weight distribution measured by gel permeation chromatography (GPC). Since compound (A), which is a silicone-based surfactant, is a mixture of molecules with various molecular weights, its molecular weight is determined as a weight-weighted average molecular weight.

[0052] As described above, the weight-average molecular weight (Mw) of compound (A), represented by general formula (1), which is a silicone-based surfactant, can be measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the mobile phase. The method for measuring the Mw of compound (A) is specifically as follows, and the Mw of each compound used in the examples described later was measured by the preferred measurement method described below. The measurement conditions, such as filters, columns, standard polystyrene samples and their molecular weights, are not limited to those described below.

[0053] First, the sample to be measured is placed in tetrahydrofuran (THF) and allowed to stand for several hours to dissolve, thereby preparing a solution. Then, the solution is filtered through a solvent-resistant membrane filter with a pore size of 0.2 μm to obtain the sample solution. The concentration of the sample in the sample solution is adjusted so that the content of compound (A) is between 0.1% by mass and 0.3% by mass. A Refractive Index Detector (RI) is used for GPC. Also, 10 3 ~2×10 6 To accurately measure the molecular weight range, it is preferable to combine multiple commercially available polystyrene gel columns. For example, four Shodex LF-804 columns (manufactured by Showa Denko) can be used in combination, or an equivalent can be used. THF is flowed as the mobile phase at a flow rate of 1 mL / min through a column stabilized in a heat chamber at 40.0°C, and approximately 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 with a standard polystyrene sample. The standard polystyrene sample has a molecular weight of 10 2 〜10 7 It is appropriate to use materials of a certain quality (for example, those manufactured by Polymer Laboratories) and to use at least 10 different standard polystyrene samples.

[0054] (Compound (B) represented by general formula (2)) The ink contains compound (A) represented by general formula (1) along with compound (B) represented by general formula (2), which is an acetylene glycol-based surfactant. Compound (B) represented by general formula (2) is a nonionic surfactant. The ink may contain one or more of the compounds (B) represented by general formula (2).

[0055] TIFF2023088852000006.tif31170 (In general formula (2), m and n each represent an independent integer between 0 and 15.)

[0056] In general formula (2), m and n represent a single bond when they are 0. In this case, the compound represented by general formula (2) means that a hydroxyl group is bonded to the carbon atom bonded to the acetylene group in general formula (2).

[0057] (Surfactant content) The content A (mass%) of compound (A) represented by general formula (1) in the ink is preferably 0.05% by mass or more and 0.80% by mass or less, and more preferably 0.10% by mass or more and 0.50% by mass or less, based on the total mass of the ink. When the above content A of compound (A) is 0.10% by mass or more, compound (A) is more likely to remain in the pigment layer, and an image with excellent scratch resistance is easily obtained. Furthermore, when the above content A of compound (A) is 0.50% by mass or less, an image with even better beading resistance is easily obtained.

[0058] The content B (mass%) of compound (B), represented by general formula (2), which is an acetylene glycol-based surfactant, is preferably 0.10% by mass or more and 0.80% by mass or less, based on the total mass of the ink, from the viewpoint of achieving both abrasion resistance and beading resistance. The above content B (mass%) of compound (B) is more preferably 0.20% by mass or more and 0.50% by mass or less.

[0059] The content A (mass%) of compound (A) relative to the total mass of ink is 0.40 or less as a ratio to the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B). That is, the relationship between the content A (mass%) of compound (A) represented by general formula (1) and the content B (mass%) of compound (B) represented by general formula (2) satisfies the following formula (5). A / (A+B)≦0.40 (5)

[0060] When A / (A+B) exceeds 0.40, there is a large amount of compound (A) represented by general formula (1), which is a silicone-based surfactant, causing ink droplets to repel each other and reducing beading resistance. A / (A+B) is preferably 0.20 or higher, more preferably 0.30 or higher, and preferably 0.35 or lower.

[0061] Furthermore, the sum (mass%) of the content A (mass%) of compound (A) represented by general formula (1) and the content B (mass%) of compound (B) represented by general formula (2), based on the total mass of the ink, is 1.00 mass% or less. If the sum of the content A of compound (A) and the content B of compound (B) exceeds 1.00 mass%, even if the ratio of compound (A) to compound (B) satisfies formula (5), the total amount of compound (A) in the ink increases, causing the dot surface to become slippery and reducing beading resistance. The sum of the content A of compound (A) and the content B of compound (B) is preferably 0.10 mass% or more, more preferably 0.20 mass% or more, and preferably 0.80 mass% or less.

[0062] (HLB value of surfactants) The HLB value, determined by the Griffin method, is a physical property that represents the degree of hydrophilicity or lipophilicity of nonionic surfactants, and it takes a value between 0 and 20. A smaller HLB value indicates higher lipophilicity, and a larger HLB value indicates higher hydrophilicity. The HLB value by the Griffin method can be calculated from the following formula (7). In the case of compound (A), represented by general formula (1), which is a silicone-based surfactant, and compound (B), represented by general formula (2), which is an acetylene glycol-based surfactant, the hydrophilic part in the following formula (7) is the ethylene oxide group. HLB value = 20 × sum of the molecular weights of the hydrophilic portion of the surfactant / molecular weight of the surfactant (7)

[0063] In one embodiment of the present invention, it is preferable that the absolute difference between the HLB value of compound (A), represented by general formula (1), which is a silicone-based surfactant, and the HLB value of compound (B), represented by general formula (2), which is an acetylene glycol-based surfactant, is within 10. By having this absolute difference in HLB values ​​within 10, that is, between 0 and 10, the compatibility between compound (A) and compound (B) is increased. In this case, compound (A), which is a silicone-based surfactant, mixes more easily with compound (B), which is an acetylene glycol-based surfactant that is oriented at the gas-liquid interface first, and compound (A) is more likely to remain in the pigment layer. Therefore, it becomes easier to obtain images with even better scratch resistance. When two or more compounds (A) are contained in the ink, the HLB value of compound (A) is the average value weighted by the mass of the HLB values ​​of the two or more compounds (A). Similarly, when two or more compounds (B) are contained in the ink, the HLB value of compound (B) is the average value weighted by the mass of the HLB values ​​of the two or more compounds (B).

[0064] The HLB value of compound (A) represented by general formula (1) is preferably 1 to 16, more preferably 5 to 15, and even more preferably 8 to 15. Similarly, the HLB value of compound (B) represented by general formula (2) is preferably 1 to 19, more preferably 5 to 19, and even more preferably 9 to 15. By setting the HLB value of the surfactant within the above range, interaction between compound (A), which is a silicone-based surfactant, and compound (B), which is an acetylene glycol-based surfactant, becomes easier. This makes it easier to obtain abrasion resistance.

[0065] (Pigment) The ink contains pigment as a coloring agent. From the viewpoint of achieving both color development and ejection stability, the pigment content (mass%) in the ink is preferably 0.10% to 15.00% by mass, and more preferably 1.00% to 10.00% by mass, based on the total mass of the ink.

[0066] Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, dioxazine, and perinone. Among these pigments, carbon black and organic pigments are preferred. The ink may contain one or more of these pigments.

[0067] As for pigments, when classified by dispersion method, resin-dispersed pigments using resin as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with resin can be used. Among these, it is preferable to use resin-dispersed pigments in which the resin used as a dispersant is physically adsorbed onto the surface of the pigment particles, rather than resin-bonded pigments or microcapsule pigments.

[0068] For dispersing pigments in an aqueous medium, it is preferable to use a resin dispersant that disperses the pigments in the aqueous medium through the action of anionic groups. A water-soluble resin can be used as the resin dispersant. The pigment content (mass%) in the ink is preferably 0.3 to 10.0 times the mass ratio of the resin dispersant content.

[0069] Self-dispersing pigments can be those in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded directly to the particle surface of the pigment or via other atomic groups (-R-). The anionic group may be either acidic or salt-type, and if it is salt-type, it may be in a partially dissociated state or a fully dissociated state. When the anionic group is salt-type, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups with 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Combinations of these groups may also be used.

[0070] (resin) The ink may contain one or more types of resin. From the viewpoint of image quality, the resin content (mass%) in the ink is preferably 0.10% to 20.00% by mass, and more preferably 0.50% to 15.00% by mass, based on the total mass of the ink.

[0071] Resins can be added to ink (i) to stabilize the dispersion of pigments, i.e., as a resin dispersant or its auxiliary. Resins can also be added to ink (ii) to improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that dissolves in an aqueous medium, or it may be resin particles dispersed in an aqueous medium. The resin particles do not need to contain colorants.

[0072] In this specification, "the resin is water-soluble" means that when the resin is neutralized with an amount of alkali equivalent to its acid value, the resin exists in an aqueous medium in a state in which no particles whose particle size can be measured by dynamic light scattering are formed.

[0073] Whether or not a resin is water-soluble can be determined by the following method. First, prepare a liquid containing the resin (resin solids content: 10% by mass) neutralized with an alkali of equivalent acid value (such as sodium hydroxide or potassium hydroxide). Next, prepare a sample solution by diluting the prepared liquid 10 times (by volume) with pure water. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles with a particle size are measured, the resin can be determined to be water-soluble. As a particle size analyzer for dynamic light scattering, a particle size analyzer (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used. The measurement conditions in this case can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds. Of course, the particle size analyzer and measurement conditions used are not limited to those described above.

[0074] Examples of resins include acrylic resins, urethane resins, olefin resins, and polyester resins. Among these, acrylic resins and urethane resins are preferred. In the following description, "(meth)acrylic acid" refers to "acrylic acid, methacrylic acid," and "(meth)acrylate" refers to "acrylate, methacrylate."

[0075] As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. Among these, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer of styrene and α-methylstyrene are preferred. Because these resins readily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0076] A hydrophilic unit is a unit having a hydrophilic group, such as an anionic group. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Cations that constitute salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

[0077] A hydrophobic unit is a unit that does not have hydrophilic groups such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The acid value of the acrylic resin is preferably 100 mg KOH / g or more and 250 mg KOH / g or less.

[0078] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting a chain extender. From the viewpoint of solubility in ink, the acid value of water-soluble urethane resins is preferably 45 mg KOH / g or more and 70 mg KOH / g or less. Examples of polyolefin resins include polyethylene and polypropylene. Polyester resins can be obtained, for example, by reacting a polyol with a polycarboxylic acid.

[0079] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may further contain a water-soluble organic solvent as an aqueous medium. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the ink is preferably 40.00% by mass or more and 95.00% by mass or less, based on the total mass of the ink. The above water content is more preferably 50.00% by mass or more and 95.00% by mass or less, and even more preferably 50.00% by mass or more and 90.00% by mass or less.

[0080] Furthermore, any of the water-soluble organic solvents commonly used in inks can be used. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. 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, based on the total mass of the ink. The above content of the water-soluble organic solvent is more preferably 7.00% by mass or more and 45.00% by mass or less, and even more preferably 10.00% by mass or more and 40.00% by mass or less. Since glycol ethers tend to excessively increase the permeability of the ink, if they are used, it is preferable to keep their content very low. Specifically, the content (mass%) of glycol ethers in the ink is preferably 0.10% by mass or less, and even more preferably 0.05% by mass or less, based on the total mass of the ink.

[0081] (Additives) In addition to the components described above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea. Furthermore, the ink may also contain, as necessary, various additives other than those described above, such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins. When using surfactants other than those described above, such as fluorinated surfactants and ionic surfactants, it is preferable to keep their content very low. Specifically, the content (mass%) of surfactants other than those described above in the ink is preferably 0.10% by mass or less, and more preferably 0.05% by mass or less, based on the total mass of the ink.

[0082] (Physical properties of ink) The static surface tension of ink is measured using a Wilhelmie-type surface tensimeter (e.g., product name "Automatic Surface Tensimeter CBVP-Z," manufactured by Kyowa Interface Science, etc.). The dynamic surface tension of ink is measured using a dynamic surface tensimeter using the maximum bubble pressure method (e.g., product name "BUBBLE PRESSURE TENSIOMETER BP-100," manufactured by KRUSS, etc.). The maximum bubble pressure method measures the maximum pressure required to release bubbles generated at the tip of a probe (a thin tube) immersed in the liquid being measured, and then determines the surface tension of the liquid from the measured maximum pressure. Specifically, the maximum pressure is measured while continuously generating bubbles at the tip of the probe. The time from the point when a new bubble surface is generated at the tip of the probe until the maximum bubble pressure (the point when the radius of curvature of the bubble is equal to the radius of the probe tip) is reached is called the "lifetime." In other words, the maximum bubble pressure method is a method for measuring the surface tension of a liquid in a moving state.

[0083] Static surface tension of ink at 25°C γ s It is preferable that the static surface tension of the ink is γ 32.0 mN / m or less. sBy being 32.0 mN / m or less, the ink's permeability to the recording medium increases, the ink is less likely to overflow on the recording medium, and it becomes easier to enhance the bead resistance. The static surface tension γ of the ink at 25 °C s is preferably 20.0 mN / m or more, and more preferably 25.0 mN / m or more. Also, the dynamic surface tension γ of the ink at 25 °C at the ink life time of 10 milliseconds 10 is preferably 30.0 mN / m or more and 50.0 mN / m or less, and more preferably 35.0 mN / m or more and 40.0 mN / m or less.

[0084] The dynamic surface tension γ of the ink at 25 °C at the ink life time of 10 milliseconds 10 and the above static surface tension γ s The absolute value of the difference |γ 10 -γ s | is preferably 4.0 mN / m or more and 10.0 mN / m or less. The absolute value of the difference between the dynamic surface tension γ and the static surface tension γ of the ink 10 and the static surface tension γ s |γ 10 -γ s | being 4.0 mN / m or more and 10.0 mN / m or less makes it easier to enhance the bead resistance. When |γ 10 -γ s | exceeds 10.0 mN / m, the surface tension of the ink immediately after being applied to the recording medium is high, and since it takes time for the ink to penetrate into the recording medium, the amount of compound (A), which is a silicone-based surfactant oriented on the surface of the ink droplet, increases. When |γ 10 -γ s | is less than 4.0 mN / m, the decrease in the surface tension of the ink after being applied to the recording medium is small, and since the penetration into the recording medium does not progress, the amount of compound (A), which is a silicone-based surfactant oriented on the surface of the ink droplet, increases. As a result, |γ 10 -γ sWhether | is greater than 10.0 mN / m or less than 4.0 mN / m, the amount of compound (A), a silicone-based surfactant, on the surface of the formed dots increases, and the surface energy tends to decrease. Therefore, ink droplets applied overlapping these dots are more likely to be repelled, and the beading resistance may decrease slightly within an acceptable level.

[0085] Static surface tension of ink γ s , and dynamic surface tension γ at a lifetime of 10 milliseconds 10 and static surface tension γ s The difference between |γ 10 -γ s By setting | to the above range, images with even better beading resistance can be obtained regardless of the type of recording medium. From this perspective, the static surface tension γ of the ink s It is more preferably 25.0 mN / m or more and 32.0 mN / m or less, and the dynamic surface tension γ at a lifetime of 10 milliseconds 10 It is preferable that the dynamic surface tension γ at a lifetime of 10 milliseconds is between 30.0 mN / m and 50.0 mN / m. 10 and static surface tension γ s The absolute value of the difference between |γ 10 -γ s It is even more preferable that the | value is between 5.0 mN / m and 9.0 mN / m.

[0086] The physical properties of the ink are preferably appropriately controlled for application in an inkjet system. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 5.0 mPa·s.

[0087] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the 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 consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0088] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin. In the present invention, it is sufficient to perform the step of applying the ink to the recording medium, and other processes (such as the step of applying a reaction solution that reacts with the ink, the step of curing the image by irradiation with active energy rays, the step of heating the image, etc.) do not need to be performed.

[0089] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32.

[0090] In this inkjet recording method, an inkjet recording device equipped with a recording head is used, and the recording head is scanned multiple times over a unit area of ​​the recording medium. This preferably allows for the application of ink used to record the image of the unit area to the unit area of ​​the recording medium in multiple passes. In other words, it is preferable to record the image of the unit area of ​​the recording medium by so-called "multi-pass recording," which involves recording the image by scanning the recording head multiple times. A "unit area" refers to a single pixel, an area obtained by dividing a pixel into any number of parts, a band, etc., and the unit area can be set as various areas as needed. A single pixel refers to a single pixel corresponding to the resolution, and a band refers to an area of ​​the image formed by one scan of the recording head.

[0091] When recording using so-called "single-pass recording," which records an image of a unit area of ​​the recording medium in a single scan of the recording head, the amount of ink applied to the unit area of ​​the recording medium in one scan is greater than in multi-pass recording. As a result, ink that cannot be absorbed by the recording medium may overflow, causing dots to merge and resulting in unevenness in density.

[0092] Furthermore, in the process of applying ink to a unit area of ​​the recording medium in multiple passes (multi-pass recording), the time interval between multiple scans for recording to the same unit area is preferably 1 second or more and 10 seconds or less. If the scanning time interval is shorter than 1 second, the N+1 scan is performed before the ink applied in the N scan has sufficiently penetrated the recording medium, and ink is applied to the same unit area of ​​the recording medium. As a result, ink that the recording medium cannot absorb overflows, and ink droplets may merge, causing unevenness in density. Also, if the scanning time interval exceeds 10 seconds, when ink is applied to the recording medium in the N+1 scan, the orientation of the silicone-based surfactant has progressed on the surface of the dots formed by the ink applied to the same unit area of ​​the recording medium in scans prior to the N scan. Therefore, the dot surface becomes slippery, and ink droplets repel each other, which may slightly reduce beading resistance.

[0093] Any recording medium may be used to record an image using the inkjet recording method of the present invention. In particular, it is preferable to use permeable paper, such as recording media without a coating layer, such as plain paper or uncoated paper, and recording media with a coating layer, such as glossy paper or art paper. Among these, it is more preferable to use a recording medium with a coating layer, and among these, it is particularly preferable to use glossy paper. [Examples]

[0094] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0095] <Preparing the resin> (Resin 1) As resin 1, a styrene / n-butyl acrylate / acrylic acid copolymer (copolymerization [mass] ratio: 57 / 29 / 14) synthesized by a conventional method was prepared. This resin 1 was dissolved in water containing potassium hydroxide equimolar to the acid value to prepare an aqueous solution of resin 1 with a resin 1 content of 10.00%.

[0096] (Resin 2) As resin 2, an acrylic resin (trade name "Joncryl 678", manufactured by BASF) with an acid value of 215 mg KOH / g and a weight-average molecular weight of 8,500 was prepared. This resin 2 was dissolved in water containing potassium hydroxide at a concentration of 0.95 times (molar ratio) of the acid value to prepare an aqueous solution of resin 2 with a resin 2 content of 10.00%.

[0097] (Resin 3) In a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet tube, and condenser, 39.3 g of polypropylene glycol (number average molecular weight 1,000), 44.5 g of isophorone diisocyanate, and 0.007 g of dibutyltin dilaurate were placed. The mixture was reacted at 100°C for 5 hours under a nitrogen gas atmosphere, and then cooled to below 65°C. 13.2 g of dimethylolpropionic acid, 3.0 g of neopentyl glycol, and 150.0 g of methyl ethyl ketone were added, and the mixture was reacted at 80°C. The mixture was then cooled to 40°C, and 20.0 g of methanol was added to stop the reaction. Next, an appropriate amount of deionized water was added, and while stirring with a homomixer, aqueous potassium hydroxide solution necessary to neutralize the resin was added. Subsequently, methyl ethyl ketone and unreacted methanol were removed by distillation under heating and reduced pressure to obtain an aqueous solution of resin 3, a water-soluble urethane resin, with a resin content of 10.00%. The acid value of resin 3 was 55 mgKOH / g, and the weight-average molecular weight was 15,000.

[0098] (Resin 4) As resin 4, an acrylic resin (trade name "Joncryl 683", manufactured by BASF) with an acid value of 160 mg KOH / g and a weight-average molecular weight of 8,000 was prepared. This resin 4 was dissolved in water containing potassium hydroxide equimolar to the acid value to prepare an aqueous solution of resin 4 with a resin content of 10.00%.

[0099] <Preparation of Pigment Dispersion> (Pigment dispersion 1) A pigment dispersion was prepared by mixing 10.0 parts of pigment (CI pigment blue 15:3), 50.0 parts of an aqueous solution of resin 1, and 40.0 parts of deionized water, and dispersing the mixture in a batch-type vertical sand mill for 3 hours. The resulting dispersion was pressure filtered through a 2.5 μm pore size filter (product name: HDCII; manufactured by Nippon Pall). Water was added to this dispersion to prepare pigment dispersion 1, which had a pigment content of 10.00% and a resin dispersant content of 5.00%.

[0100] (Pigment dispersion 2) A pigment dispersion was prepared by mixing 10.0 parts of pigment (CI Pigment Blue 15:3), 50.0 parts of an aqueous solution of resin 2, and 40.0 parts of deionized water, and dispersing the mixture for 3 hours in a batch-type vertical sand mill. The resulting dispersion was pressure filtered through a 2.5 μm pore size filter (product name: HDCII; manufactured by Nippon Pall). Water was added to this dispersion to prepare pigment dispersion 2, which had a pigment content of 10.00% and a resin dispersant content of 5.00%.

[0101] (Pigment dispersion 3) Referring to Patent Document 5, 10.0 parts of pigment (CI pigment blue 15:3) and 90.0 parts of deionized water were mixed and dispersed for 3 hours in a batch-type vertical sand mill to prepare a pigment dispersion. The obtained dispersion was pressure filtered through a pore size 2.5 μm filter (product name: HDCII; manufactured by Nippon Pall). Water was added to this dispersion to prepare pigment dispersion 3, which has a pigment content of 10.00%.

[0102] <Preparation of surfactants> Compounds A1-A11 and A13-A19, which are silicone-based surfactants, as well as compound A12, described below, were prepared as shown in Tables 1-3. In Tables 1-3, the "number of moles of ethylene oxide added / degree of polymerization of polysiloxane" for each compound is abbreviated as "ratio".

[0103] (Compounds represented by general formula (1)) A polysiloxane compound represented by formula (8) and a polyoxyethylene compound represented by formula (9) were placed in a glass container equipped with a thermometer and a stirring device. These were subjected to an addition reaction in the presence of a platinum catalyst to synthesize compounds A1-A11, A13, and A14 having the structure represented by general formula (1). The properties of each synthesized compound, such as the HLB value and weight-average molecular weight (Mw), are shown in Table 1. In Table 1, a, p, R1, and R2 correspond to a, p, R1, and R2 in general formula (1) representing the structure of each synthesized compound, and the ratios in the table correspond to the 2a / p values. Compound A12 is a silicone-based surfactant (trade name "BYK-333", manufactured by Bic Chemie, HLB value 10, weight-average molecular weight 8,000) having the structure represented by general formula (1).

[0104] TIFF2023088852000007.tif33170

[0105] TIFF2023088852000008.tif20170

[0106] TIFF2023088852000009.tif84170

[0107] (Compound represented by general formula (3)) A polysiloxane compound represented by formula (10) and a polyoxyethylene compound represented by formula (11) were placed in a glass container equipped with a thermometer and a stirring device. These were subjected to an addition reaction in the presence of a platinum catalyst to synthesize compounds A15 to A18 represented by general formula (3). The properties of each synthesized compound, such as the HLB value and weight-average molecular weight (Mw), are shown in Table 2. In Table 2, b, q, r, R3, and R4 correspond to b, q, r, R3, and R4 in general formula (3) representing the structure of each synthesized compound, and the ratios in the table correspond to the value of b × r / (q + r).

[0108] TIFF2023088852000010.tif31170

[0109] TIFF2023088852000011.tif20170

[0110] TIFF2023088852000012.tif41170

[0111] (Compounds represented by general formula (4)) A polysiloxane compound represented by formula (12) and a polyoxyethylene compound represented by formula (13) were placed in a glass container equipped with a thermometer and a stirring device. Compound A19, represented by general formula (4), was synthesized by addition reaction in the presence of a platinum catalyst. The properties of the synthesized compound A19, such as the HLB value and weight-average molecular weight (Mw), are shown in Table 3. In Table 3, c, s, t, R5, and R6 correspond to c, s, t, R5, and R6 in general formula (4) representing the structure of the synthesized compound A19, respectively, and the ratios in the table correspond to the value of (c + c × t) / s × t.

[0112] TIFF2023088852000013.tif32170

[0113] TIFF2023088852000014.tif20170

[0114] TIFF2023088852000015.tif29170

[0115] (Compounds represented by general formula (2), and other surfactants) Compounds B1-B4 and C1-C3, shown in Table 4, were prepared. In Table 4, "○" in the General Formula (2) column indicates a compound represented by General Formula (2) (acetylene glycol-based surfactant), and "×" indicates other surfactants that do not correspond to General Formula (2).

[0116] TIFF2023088852000016.tif83170

[0117] <Ink preparation> Each ink was prepared by mixing the components (in %) shown in the middle section of Table 5 (Tables 5-1 to 5-5), stirring thoroughly, and then pressure filtering through a polypropylene filter (Advantec) with a pore size of 1.0 μm. The lower section of Table 5 shows the content A (%) of silicone-based surfactants (compounds A1 to A19) and B (%) of acetylene glycol-based surfactants (compounds represented by general formula (2) in Table 4), as well as the values ​​of A / (A+B) and A+B, based on the total mass of the ink. Also shown in the lower section of Table 5 is γ s (mN / m) represents the static surface tension value for each ink, measured at 25°C using a Wilhelmy-type surface tensile meter (product name "Automatic Surface Tension Meter CBVP-Z", manufactured by Kyowa Interface Science). γ 10 (mN / m) represents the dynamic surface tension value at a lifetime of 10 milliseconds, measured for each ink using a dynamic surface tensimeter with the maximum bubble pressure method under conditions of 25°C. The dynamic surface tensimeter used was the "BUBBLE PRESSURE TENSIOMETER BP-100" (manufactured by KRUSS). The lower row of Table 5 shows |γ 10 -γ s The value in |(mN / m) is also shown. Furthermore, the "absolute difference in HLB values" shown in the lower part of Table 5 represents the absolute difference between the HLB values ​​of the silicone-based surfactants (compounds A1 to A19) used in each ink and the HLB values ​​of the acetylene glycol-based surfactants (compounds represented by general formula (2) in Table 4).

[0118] TIFF2023088852000017.tif161170

[0119] TIFF2023088852000018.tif161170

[0120] TIFF2023088852000019.tif157170

[0121] TIFF2023088852000020.tif160170

[0122] TIFF2023088852000021.tif156170

[0123] <Rating> Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "imagePROGRAF PRO-1000", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. In this embodiment, a solid image recorded by applying 30 ng of ink to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as having a "recording duty cycle of 100%". In this invention, "A", "B", and "B" are used in the evaluation criteria for each of the following items. - "A" was defined as an acceptable level, while "C" and "D" were deemed unacceptable levels. The evaluation conditions and results are shown in Table 7.

[0124] (Abrasion resistance) Using the inkjet recording device described above, a solid image with a recording duty cycle of 10% was recorded on a recording medium (product name "Canon Photo Paper Glossy Pro [Platinum Grade]", manufactured by Canon). Ink was applied to a unit area in one or four main scans (number of passes) of the recording head. When recording in four passes, a wait time was set at the point when the recording head's reciprocating motion switched so that the recording interval between each pass was a predetermined time (time interval). After leaving the image recorded under the above conditions for one minute, a sheet of lens tissue and a surface pressure of 300 g / cm² were placed on top of the image. 2 and 500g / cm³ 2 A weight was placed on top, and the recording material and the lens tissue were rubbed together. After that, the lens tissue and weight were removed, and the image and non-recorded areas were visually inspected for dirt, and the scratch resistance of the image was evaluated according to the evaluation criteria shown below. A: In all cases, no dirt was found on the non-recording area, and no image was erased. B: Surface pressure 300g / cm 2 When using this weight, there is no contamination of the non-recording area or abrasion of the image, and the surface pressure is 500 g / cm². 2 When using the weight, the image was scratched, but it was not abraded. B - Regardless of which weight was used, the image was scratched, but it was not abraded. C: In all cases where weights were used, there was dirt on the non-recording area and image abrasion, with the abraded area being less than half of the image. D: In all cases where weights were used, there was dirt on the non-recording area and image abrasion, with the abraded area exceeding half of the image.

[0125] (Beading resistance) Solid images with a recording duty cycle of 300% were recorded on the recording media shown in Table 6 using either a one-pass or four-pass method. These recording media differ in their ink permeability. When recording in four passes, a wait time was set at the point where the recording head's reciprocating motion switched, so that the recording interval between each pass was a predetermined time. The image immediately after recording was observed at a magnification of 25x, and the beading resistance of the image was evaluated according to the evaluation criteria shown below. A: No unevenness was observed on any recording medium, and beading was suppressed. B: No color unevenness was observed in 9 types of recording media, but color unevenness was observed in 8 types of recording media. C: No color inconsistencies were observed with 5 types of recording media, but color inconsistencies were observed with 12 types of recording media. D: Color unevenness was observed on all recording media.

[0126] TIFF2023088852000022.tif94170

[0127] TIFF2023088852000023.tif223170

[0128] Furthermore, the disclosure of this embodiment includes the following configurations and methods. (Composition 1) An aqueous ink containing a pigment, a compound (A) represented by the following general formula (1), and a compound (B) represented by the following general formula (2), The weight-average molecular weight of compound (A) is 1,500 or more and 7,500 or less. The content A (mass%) of compound (A), based on the total mass of the aqueous ink, is 0.40 or less in ratio to the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B). An aqueous ink characterized in that the sum of the content A (mass%) of compound (A) and the content B (mass%) of compound (B), based on the total mass of the aqueous ink, is 1.00% by mass or less.

[0129] TIFF2023088852000024.tif33170 (In the above general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R2 represents an alkylene group having 1 to 20 carbon atoms, a represents an integer between 1 and 170, and p represents an integer between 1 and 120.)

[0130] TIFF2023088852000025.tif31170 (In the above general formula (2), m and n each independently represent integers between 0 and 15, inclusive.)

[0131] (Configuration 2) Static surface tension γ of the aqueous ink at 25°C s The dynamic surface tension γ of the aqueous ink at 25°C during a lifetime of 10 milliseconds is 32.0 mN / m or less. 10 and the static surface tension γ s The absolute value of the difference between |γ 10 -γ s A water-based ink as described in Constituent 1, wherein the | value is between 4.0 mN / m and 10.0 mN / m. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the absolute value of the difference between the HLB value of compound (A) and the HLB value of compound (B) is 10 or less. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein in compound (A), the total number of ethylene oxide addition moles represented by a in the general formula (1) (2a) is 1.0 or more and 10.0 or less in ratio (2a / p) to the degree of polymerization of polysiloxane represented by p in the general formula (1) (p). (Configuration 5) An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is an aqueous ink as described in any one of items 1 to 4 of the configuration. (Method 1) An inkjet recording method in which ink is ejected from an inkjet recording head to record an image on a recording medium, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of the items 1 to 4 of the configuration. (Method 2) The inkjet recording method according to Method 1, further comprising the step of applying the aqueous ink used for recording an image of the unit area to the unit area of ​​the recording medium in multiple steps by scanning the recording head multiple times over a unit area of ​​the recording medium using an inkjet recording apparatus equipped with the recording head. (Method 3) The inkjet recording method according to Method 1 or 2, wherein in the step of applying the aqueous ink to the unit area of ​​the recording medium in multiple steps, the time interval between multiple scans in recording to the same unit area is 1 second or more and 10 seconds or less. (Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the recording medium is a recording medium having a coating layer.

Claims

1. An aqueous ink containing a pigment, a compound (A) represented by the following general formula (1), and a compound (B) represented by the following general formula (2), The weight average molecular weight of the compound (A) is 1,500 or more and 7,500 or less, the ratio of the content A (mass%) of the compound (A) to the sum of the content A (mass%) of the compound (A) and the content B (mass%) of the compound (B) based on the total mass of the water-based ink is 0.40 or less, the sum of the content A (mass%) of the compound (A) and the content B (mass%) of the compound (B) is 1.00 mass% or less, based on the total mass of the aqueous ink. (In the general formula (1), R １ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R ２ represents an alkylene group having 1 to 20 carbon atoms, a represents an integer of 1 to 170, and p represents an integer of 1 to 120. (In the general formula (2), m and n each independently represent an integer of 0 to 15.)

2. 2. The aqueous ink according to claim 1, wherein in the compound (A), the ratio (2a / p) of the total number of moles of ethylene oxide added (2a), represented by a in the general formula (1), to the degree of polysiloxane polymerization (p), represented by p in the general formula (1), is 1.0 or more and 10.0 or less.

3. An aqueous ink as described in claim 1, wherein the content A (mass %) of said compound (A) is 0.36 or less as a ratio to the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B).

4. An aqueous ink as described in claim 1, wherein the content A (mass %) of said compound (A) is 0.35 or less in ratio to the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B).

5. An aqueous ink as described in claim 1, wherein the content A (mass %) of said compound (A) is 0.20 or more in ratio to the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B).

6. An aqueous ink as described in claim 1, wherein the content A (mass %) of said compound (A) is 0.30 or more in ratio to the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B).

7. An aqueous ink as described in claim 1, wherein the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B) is 0.10 mass % or more.

8. An aqueous ink as described in claim 1, wherein the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B) is 0.20 mass % or more.

9. An aqueous ink as described in claim 1, wherein the sum of the content A (mass %) of said compound (A) and the content B (mass %) of said compound (B) is 0.80 mass % or less.

10. An aqueous ink as described in claim 1, wherein the content A (mass %) of the compound (A) is 0.05 mass % or more and 0.80 mass % or less, based on the total mass of the ink.

11. An aqueous ink as described in claim 1, wherein the content A (mass %) of the compound (A) is 0.10 mass % or more and 0.50 mass % or less, based on the total mass of the ink.

12. An aqueous ink as described in claim 1, wherein the content B (mass %) of the compound (B) is 0.10 mass % or more and 0.80 mass % or less, based on the total mass of the ink.

13. An aqueous ink as described in claim 1, wherein the content B (mass %) of the compound (B) is 0.20 mass % or more and 0.50 mass % or less, based on the total mass of the ink.

14. The static surface tension γ of the water-based ink at 25°C ｓ The dynamic surface tension γ of the aqueous ink at 25° C. during a life time of 10 milliseconds is 32.0 mN / m or less. １０ and the static surface tension γ ｓ Absolute value of the difference between |γ １０ -γ ｓ The aqueous ink according to claim 1, wherein | is 4.0 mN / m or more and 10.0 mN / m or less.

15. The aqueous ink according to claim 14, wherein the absolute value of the difference between the dynamic surface tension γ 10 and the static surface tension γ s , |γ 10 - γ s |, is 5.0 mN / m or more and 9.0 mN / m or less.

16. The aqueous ink according to claim 14, wherein the static surface tension γ s is 25.0 mN / m or more.

17. The aqueous ink according to claim 14, wherein the dynamic surface tension γ 10 is 30.0 mN / m or more and 50.0 mN / m or less.

18. 2. The aqueous ink according to claim 1, wherein the absolute value of the difference between the HLB value of the compound (A) and the HLB value of the compound (B) is 10 or less.

19. An aqueous ink as described in claim 18, wherein the HLB value of the compound (A) is 9 or more and 16 or less.

20. An aqueous ink as described in claim 18, wherein the HLB value of the compound (B) is 9 or more and 15 or less.

21. An ink cartridge comprising ink and an ink storage section for storing the ink, 21. An ink cartridge, wherein the ink is a water-based ink according to claim 1.

22. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, 21. An ink-jet recording method, wherein the ink is the aqueous ink according to claim 1.

23. 23. The inkjet recording method according to claim 22, further comprising a step of applying the water-based ink used to record an image in the unit area to the unit area of ​​the recording medium in multiple batches by using an inkjet recording device equipped with the recording head and scanning the recording head multiple times over the unit area of ​​the recording medium.

24. 24. The inkjet recording method according to claim 23, wherein in the step of applying the aqueous ink to the unit area of ​​the recording medium in a plurality of separate scans, the time interval between the plurality of scans in recording on the same unit area is 1 second or more and 10 seconds or less.

25. 23. The ink jet recording method according to claim 22, wherein the recording medium has a coating layer.

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