Inkjet ink

Abstract

To provide an inkjet ink which can form an image having excellent abrasion resistance and has excellent flying properties.SOLUTION: There is provided an inkjet ink which contains a pigment, a first surfactant, a second surfactant and an aqueous medium. The first surfactant is a compound represented by the following general formula (I). The second surfactant is a compound represented by the following general formula (II). The aqueous medium contains water and a specific organic solvent. The octanol / water partition coefficient LogKow of the specific organic solvent is -1.80 or more and -1.00 or less. The content ratio of the first surfactant is 0.03 mass% or more and 0.35 mass% or less. The content ratio of the second surfactant is 0.03 mass% or more and 0.30 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to ink-jet inks. [Background technology]

[0002] Some inkjet recording devices use aqueous inkjet inks containing a pigment and an aqueous medium. In order to form clear images, inkjet inks are required to have excellent flight properties. Here, the flight properties of inkjet inks refer to the ability of ink droplets to remain together as one droplet without splitting until they land on a recording medium when ejected from a recording head of an inkjet recording device. Inkjet inks with low flight properties split ink droplets in the air before landing on a recording medium, and split into a main ink droplet (main droplet) and minute ink droplets (satellite droplets). Then, while the main droplet lands on the desired position on the recording medium, the satellite droplets scatter around the main droplet and land. Therefore, images formed with inkjet inks with low flight properties have poor clarity.

[0003] In addition, inkjet inks are required to be capable of forming images with excellent abrasion resistance (durability of the printed inkjet ink against abrasion). However, there is a trade-off between flying performance and abrasion resistance, and it is difficult to achieve both.

[0004] For example, as an aqueous inkjet ink capable of forming a clear image, an inkjet ink has been proposed that contains a pigment, an organic solvent, a surfactant, and water, and the surfactant contains polyoxyethylene (poly)styrenated phenyl ether sulfate and one or more compounds selected from acetylene glycol and alkylene oxide adducts of acetylene glycol (Patent Document 1). This inkjet ink is said to be capable of achieving excellent print quality and high print density. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6897949 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inkjet ink described in Patent Document 1 is unable to provide satisfactory flying properties and abrasion resistance of the formed image.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet ink that is capable of forming an image having excellent abrasion resistance and also has excellent flying properties. [Means for solving the problem]

[0008] The inkjet ink according to the present invention contains a pigment, a first surfactant, a second surfactant, and an aqueous medium. The first surfactant is a compound represented by the following general formula (I). The second surfactant is a compound represented by the following general formula (II). The aqueous medium contains water and a specific organic solvent. The octanol / water partition coefficient LogK of the specific organic solvent is ow is -1.80 or more and -1.00 or less. The content ratio of the first surfactant is 0.03 mass % or more and 0.35 mass % or less. The content ratio of the second surfactant is 0.03 mass % or more and 0.30 mass % or less.

[0009] [ka]

[0010] In the general formula (I), m and n each independently represent a number between 0.0 and 11.0. m+n is between 9.0 and 11.0. x represents a number between 1.0 and 20.0. y represents a number between 1.0 and 10.0.

[0011] [ka]

[0012] In the general formula (II), a and c each independently represent a number of 0 or more and 25 or less. a+c is a number of 13 or more and 25 or less. b represents a number of 15 or more and 27 or less. Effect of the Invention

[0013] The inkjet ink according to the present invention can form an image having excellent abrasion resistance and also has excellent flying properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described. In the following, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer (for example, Zetasizer (registered trademark) Nano ZS manufactured by Malvern Instruments) unless otherwise specified.

[0015] Unless otherwise specified, the measured acid value is a value measured in accordance with "JIS (Japanese Industrial Standards) K0070-1992".

[0016] Unless otherwise specified, the measured value of the weight average molecular weight (Mw) is a value measured using gel permeation chromatography (for example, "HLC-8020GPC" manufactured by Tosoh Corporation).

[0017] Unless otherwise specified, the measured value of dynamic surface tension is a value measured at 25°C by the maximum bubble pressure method (bubble pressure method) using a bubble pressure type dynamic surface tensiometer (e.g., "BP100" manufactured by KRUSS, capillary diameter 0.4 mm).

[0018] Octanol / water partition coefficient LogK ow If no specification is given, the literature value can be used as a reference. owmay be calculated using various calculation software (for example, "Hansen Solubility Parameter in Practice (HSPiP) Ver. 5.2.06" (developed by Prof. Steven Abbott et al.)).

[0019] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Additionally, "at least one of A and B" means "A and / or B."

[0020] [ink] An inkjet ink (hereinafter, sometimes simply referred to as ink) according to an embodiment of the present invention will be described below. The ink according to this embodiment contains a pigment, a first surfactant, a second surfactant, and an aqueous medium. The first surfactant is a compound represented by the following general formula (I). The second surfactant is a compound represented by the following general formula (II). The aqueous medium contains water and a specific organic solvent. The octanol / water partition coefficient LogK of the specific organic solvent ow (Hereafter, simply LogK ow The viscosity coefficient (may be described as "mass %") is -1.80 or more and -1.00 or less. The content of the first surfactant is 0.03% by mass or more and 0.35% by mass or less. The content of the second surfactant is 0.03% by mass or more and 0.30% by mass or less.

[0021] [ka]

[0022] In the general formula (I), m and n each independently represent a number between 0.0 and 11.0. m+n is between 9.0 and 11.0. x represents a number between 1.0 and 20.0. y represents a number between 1.0 and 10.0.

[0023] [ka]

[0024] In the general formula (II), a and c each independently represent a number of 0 or more and 25 or less. a+c is a number of 13 or more and 25 or less. b represents a number of 15 or more and 27 or less.

[0025] The ink according to this embodiment may contain multiple types of compounds represented by general formula (I). In this case, in general formula (1), m, n, x, and y respectively represent the number average values ​​of m, n, x, and y in the multiple types of compounds represented by general formula (I).

[0026] The ink according to this embodiment may contain multiple types of compounds represented by general formula (II), in which case a, b, and c in general formula (II) represent the number average values ​​of a, b, and c, respectively, in the multiple types of compounds represented by general formula (II).

[0027] The ink according to the present embodiment, having the above-mentioned configuration, can form an image with excellent abrasion resistance and has excellent flight properties. The reason for this is presumed to be as follows. The surface tension of the ink is extremely important for flight properties. In particular, ink droplets with high surface tension immediately after being ejected from the recording head can continue to remain together as a single droplet. For this reason, increasing the surface tension (dynamic surface tension) of the ink immediately after being ejected from the recording head improves the flight properties of the ink.

[0028] On the other hand, the permeability of the ink into the recording medium is very important for the durability of the printed ink against rubbing (abrasion resistance). The permeability of the ink into the recording medium is related to the surface tension of the ink when the ink permeates into the recording medium (in other words, the surface tension of the ink after the ink droplets land on the recording medium (dynamic surface tension)).

[0029] As a method for increasing the surface tension (dynamic surface tension) of the ink, there is a method of adding a highly hydrophobic organic solvent to an aqueous medium. A known ink containing a highly hydrophobic organic solvent forms ink droplets having a high surface tension when ejected from a recording head. Therefore, a known ink containing a highly hydrophobic organic solvent has excellent flying properties. On the other hand, the ink droplets maintain a high surface tension even after landing on the recording medium, do not penetrate into the recording medium, and continue to remain on the surface of the recording medium. As a result, a known ink containing a highly hydrophobic organic solvent forms an image with insufficient abrasion resistance. Thus, in a known ink, there is a trade-off between flying properties and abrasion resistance of the image formed.

[0030] In contrast, the ink according to this embodiment uses an organic solvent (LogK ow The ink according to this embodiment contains a specific organic solvent having a LogK owThe ink according to the present embodiment uses a specific organic solvent having a relatively high hydrophobicity, contains a first surfactant at a ratio of 0.03% by mass to 0.35% by mass, and contains a second surfactant at a ratio of 0.03% by mass to 0.30% by mass, and the specific organic solvent moderately inhibits the surface-active function of the first surfactant and the second surfactant. Therefore, when the ink according to the present embodiment is ejected from the recording head, the specific organic solvent inhibits the surface-active function of the first surfactant and the second surfactant, and forms ink droplets having high surface tension. As a result, the ink according to the present embodiment has excellent flying properties. On the other hand, the ink according to the present embodiment contains a first surfactant at a ratio of 0.03% by mass to 0.35% by mass, and contains a second surfactant at a ratio of 0.03% by mass to 0.30% by mass, and therefore, after the ink droplets land on the recording medium, the surface tension is sufficiently reduced by the action of the first surfactant and the second surfactant. As a result, the ink according to the present embodiment can penetrate into the inside of the recording medium and form an image with excellent abrasion resistance. For this reason, the ink according to this embodiment can achieve both good flying properties and good abrasion resistance of the formed image.

[0031] The ink according to this embodiment will be described in more detail below. Each component described below may be used alone or in combination of two or more. First, the surface tension (dynamic surface tension) of the ink according to this embodiment will be described below.

[0032] [Dynamic surface tension] The dynamic surface tension of the ink according to the present embodiment with a surface life of 10 milliseconds is preferably 38 mN / m or more and 50 mN / m or less, and more preferably 42 mN / m or more and 48 mN / m or less. The dynamic surface tension of the ink according to the present embodiment with a surface life of 10 milliseconds corresponds to the surface tension immediately after it is ejected as an ink droplet from a recording head. By setting the dynamic surface tension at 38 mN / m or more at a surface life of 10 milliseconds, the flying properties of the ink according to the present embodiment can be optimized. By setting the dynamic surface tension at 50 mN / m or less at a surface life of 10 milliseconds, the ink according to the present embodiment can form an image with even better abrasion resistance.

[0033] The dynamic surface tension of the ink according to this embodiment with a surface life of 1000 milliseconds is preferably 30 mN / m or more and 38 mN / m or less, and more preferably 32 mN / m or more and 38 mN / m or less. The dynamic surface tension of the ink according to this embodiment with a surface life of 1000 milliseconds corresponds to the surface tension at the stage after the ink droplets land on the recording medium. By setting the dynamic surface tension with a surface life of 1000 milliseconds to 30 mN / m or more and 38 mN / m or less, the ink according to this embodiment can form an image with even better abrasion resistance.

[0034] [composition] As described above, the ink according to this embodiment contains a pigment, a first surfactant, a second surfactant, and an aqueous medium. It is preferable that the ink according to this embodiment further contains at least one of a pigment coating resin and a surfactant.

[0035] (Pigments) In the ink according to this embodiment, the pigment constitutes a pigment particle together with, for example, a pigment coating resin. The pigment particle is constituted, for example, by a core containing the pigment and a pigment coating resin that coats the core. The pigment coating resin exists, for example, in a state of being dispersed in a solvent. From the viewpoint of optimizing the color density, hue, or stability of the ink according to this embodiment, the volume median diameter (D 50 ) is preferably 30 nm or more and 250 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0036] Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, purple pigments, and black pigments. Examples of yellow pigments include CI Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include CI Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include CI Pigment Red (122 and 202). Examples of blue pigments include CI Pigment Blue (15, more specifically 15:3). Examples of purple pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0037] In the ink according to the present embodiment, the pigment content is preferably 1.00% by mass or more and 10.00% by mass or less, and more preferably 4.00% by mass or more and 8.00% by mass or less. By making the pigment content 1.00% by mass or more, the ink according to the present embodiment can easily form an image having a desired image density. In addition, by making the pigment content 15.00% by mass or less, the fluidity of the ink according to the present embodiment can be ensured.

[0038] [Pigment-coated resin] The pigment coating resin is a resin that is soluble in the aqueous medium of the ink according to this embodiment. A portion of the pigment coating resin, for example, adheres to the surface of the pigment to optimize the dispersion stability of the pigment in the aqueous medium. Note that a portion of the pigment coating resin may be free in the aqueous medium without adhering to the surface of the pigment.

[0039] As the pigment coating resin, styrene-(meth)acrylic resin is preferred. The styrene-(meth)acrylic resin has a repeating unit derived from at least one monomer selected from among (meth)acrylic acid alkyl esters and (meth)acrylic acid, and a styrene unit. As the (meth)acrylic acid alkyl esters, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate can be mentioned. As the styrene-(meth)acrylic resin, a copolymer (X) of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate is preferred. The copolymer (X) is preferably neutralized with an equal amount of a base (e.g., potassium hydroxide and sodium hydroxide).

[0040] In the total repeating units contained in the copolymer (X), the content of repeating units derived from styrene is preferably 10.00% by mass or more and 20.00% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from methyl methacrylate is preferably 10.00% by mass or more and 20.00% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from methacrylic acid is preferably 35.00% by mass or more and 45.00% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from butyl acrylate is preferably 25.00% by mass or more and 35.00% by mass or less.

[0041] In the ink according to this embodiment, the content of the pigment coating resin is preferably from 0.50% to 6.00% by mass, and more preferably from 1.50% to 4.00% by mass. By setting the content of the pigment coating resin to be from 0.50% to 6.00% by mass, the ejection stability of the ink according to this embodiment can be optimized.

[0042] The acid value of the pigment coating resin is preferably from 30 mgKOH / g to 200 mgKOH / g, and more preferably from 70 mgKOH / g to 130 mgKOH / g. By setting the acid value of the pigment coating resin to be from 30 mgKOH / g to 200 mgKOH / g, the dispersibility of the pigment can be further improved while optimizing the storage stability of the ink according to this embodiment.

[0043] The acid value of the pigment coating resin can be adjusted by changing the amount of monomer used in synthesizing the pigment coating resin. For example, the acid value of the pigment coating resin can be increased by using a monomer (more specifically, acrylic acid, methacrylic acid, etc.) having an acidic functional group (e.g., a carboxyl group) in synthesizing the pigment coating resin.

[0044] The Mw of the pigment coating resin is preferably from 10,000 to 50,000, and more preferably from 15,000 to 25,000. By setting the Mw of the pigment coating resin to be from 10,000 to 50,000, it is possible to optimize the image density of the formed image while suppressing an increase in the viscosity of the ink according to this embodiment.

[0045] The Mw of the pigment coating resin can be adjusted by changing the polymerization conditions for the pigment coating resin (more specifically, the amount of polymerization initiator used, polymerization temperature, polymerization time, etc.).

[0046] In the polymerization of the pigment-coated resin, the amount of the polymerization initiator used is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture. In the polymerization of the pigment-coated resin, for example, the polymerization temperature can be 50° C. to 70° C., and the polymerization time can be 10 to 24 hours. The polymerized pigment-coated resin is preferably neutralized with an equal amount of a basic compound before being used as a raw material for the ink according to this embodiment. The basic compound is preferably a hydroxide of an alkali metal ion (e.g., NaOH or KOH).

[0047] [First Surfactant] The first surfactant is a compound represented by the above general formula (I). As described above, in general formula (I), m and n are each independently a number between 0.0 and 11.0. m+n is between 9.0 and 11.0. x is a number between 1.0 and 20.0. x is preferably a number between 6.0 and 13.0, more preferably a number between 6.0 and 8.0, or more preferably a number between 11.0 and 13.0. y is a number between 1.0 and 10.0. y is preferably a number between 1.5 and 6.0, more preferably a number between 1.5 and 4.0.

[0048] The first surfactant is a nonionic surfactant having a polyoxyalkylene alkyl ether as the main skeleton. Examples of commercially available products of the first surfactant include "Softanol (registered trademark) 30", "Softanol (registered trademark) 50", "Softanol (registered trademark) 70", "Softanol (registered trademark) 90", and "Softanol (registered trademark) 120" (all "Softanol (registered trademark) M series") manufactured by Nippon Shokubai Co., Ltd. Examples of commercially available products of the first surfactant include "Softanol (registered trademark) EP5035", "Softanol (registered trademark) EP7025", "Softanol (registered trademark) EP7045", "Softanol (registered trademark) EP7085", "Softanol (registered trademark) EP9050", "Softanol (registered trademark) EP90150", and "Softanol (registered trademark) EP12030" (all "Softanol (registered trademark) EP series") manufactured by Nippon Shokubai Co., Ltd.

[0049] In the ink according to the present embodiment, the content ratio of the first surfactant is 0.03% by mass or more and 0.35% by mass or less, and preferably 0.05% by mass or more and 0.15% by mass or less. By setting the content ratio of the first surfactant to 0.03% by mass or more, it is possible to sufficiently reduce the surface tension of the ink at the stage after the ink droplets land on the recording medium. As a result, it is possible to form an image with excellent abrasion resistance. In addition, by setting the content ratio of the first surfactant to 0.35% by mass or less, it is possible to form ink droplets having high surface tension when the ink according to the present embodiment is ejected from the recording head. As a result, it is possible to provide an ink with excellent flying properties.

[0050] [Second surfactant] The second surfactant is a compound represented by the above general formula (II). As described above, in general formula (II), a and c each independently represent a number between 0 and 25. a+c is between 13 and 25. a+c is preferably between 16 and 22. b is preferably between 15 and 27. b is preferably between 18 and 24.

[0051] The second surfactant is a nonionic surfactant having a polyoxyethylene polyoxypropylene glycol skeleton. Commercially available products of the second surfactant include, for example, "Epane (registered trademark) 450" and "Epane (registered trademark) 710" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0052] In the ink according to the present embodiment, the content ratio of the second surfactant is 0.03% by mass or more and 0.30% by mass or less, and preferably 0.05% by mass or more and 0.15% by mass or less. By making the content ratio of the second surfactant 0.03% by mass or more, it is possible to sufficiently reduce the surface tension of the ink at the stage after the ink droplets land on the recording medium. As a result, it is possible to form an image with excellent abrasion resistance. In addition, by making the content ratio of the second surfactant 0.30% by mass or less, it is possible to form ink droplets having high surface tension when the ink according to the present embodiment is ejected from the recording head. As a result, it is possible to provide an ink with excellent flying properties.

[0053] In the ink according to the present embodiment, the total content ratio of the first surfactant and the second surfactant is preferably 0.06% by mass or more and 0.40% by mass or less, more preferably 0.10% by mass or more and 0.33% by mass or less, and even more preferably 0.15% by mass or more and 0.25% by mass or less. By making the total content ratio of the first surfactant and the second surfactant 0.06% by mass or more, the surface tension of the ink at the stage after the ink droplets land on the recording medium can be optimized. As a result, an image with excellent abrasion resistance can be reliably formed. In addition, by making the total content ratio of the first surfactant and the second surfactant 0.40% by mass or less, the surface tension of the ink droplets when the ink according to the present embodiment is ejected from the recording head can be optimized. As a result, an ink with better flying properties can be provided.

[0054] [Other surfactants] The ink according to this embodiment may contain only the first surfactant and the second surfactant as the surfactant, or may further contain a surfactant other than the first surfactant and the second surfactant (hereinafter, referred to as another surfactant). In the surfactant, the total content of the first surfactant and the second surfactant is preferably 50.00% by mass or more, and more preferably 60.00% by mass or more.

[0055] Other surfactants include, for example, acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds) and fluorine surfactants (surfactants containing fluorine resins or fluorine-containing compounds).Acetylene glycol surfactants include, for example, ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol.

[0056] In the ink according to this embodiment, the content of the other surfactant is preferably from 0.05% by mass to 0.35% by mass, and more preferably from 0.05% by mass to 0.25% by mass.

[0057] [Aqueous medium] The aqueous medium includes water and the specific organic solvent. The aqueous medium may function as a solvent or as a dispersion medium. The aqueous medium may include a water-soluble organic solvent (LogK ow The water-soluble organic solvent may further include a water-soluble organic solvent having a viscosity index less than -1.80 or more than -1.00 (hereinafter, sometimes referred to as other water-soluble organic solvent).

[0058] In the ink according to this embodiment, the content of the aqueous medium is preferably from 75.00% by mass to 98.00% by mass, and more preferably from 85.00% by mass to 95.00% by mass.

[0059] In the ink according to the present embodiment, the water content is preferably 40.00% by mass to 80.00% by mass, and more preferably 50.00% by mass to 70.00% by mass. By setting the water content to 40.00% by mass to 80.00% by mass, the surface tension of the ink according to the present embodiment (particularly the surface tension of the ink droplets when ejected from the recording head and the surface tension of the ink after the ink droplets land on the recording medium) can be optimized.

[0060] (Specific organic solvent) LogK of specific organic solvent ow is -1.80 or more and -1.00 or less. ow By setting the LogK of the specific organic solvent to -1.80 or more, the surface tension of the ink can be sufficiently reduced after the ink droplets land on the recording medium. As a result, an image with excellent abrasion resistance can be formed. ow By making the ratio of the surface tension of the ink droplets to the surface tension of the ink droplets is set to -1.00 or less, the ink droplets according to the present embodiment can be formed with high surface tension when the ink droplets are ejected from a recording head. As a result, the ink droplets can be provided with excellent flying properties.

[0061] Examples of the specific organic solvent include the organic solvents shown in the following Table 1. As the specific organic solvent, glycerin or 1,3-propanediol is preferable.

[0062] [Table 1]

[0063] In the ink according to this embodiment, the content of the specific organic solvent is preferably 15.00% by mass or more and 45.00% by mass or less, and more preferably 25.00% by mass or more and 35.00% by mass or less. By making the content of the specific organic solvent 15.00% by mass or more, the flying properties of the ink according to this embodiment can be optimized. By making the content of the specific organic solvent 40.00% by mass or less, the ink according to this embodiment can form an image with even better abrasion resistance.

[0064] (Other water-soluble organic solvents) Other water-soluble organic solvents include, for example, glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, and dimethylsulfoxide.

[0065] In the aqueous medium, the content of the other water-soluble organic solvent is preferably 10.00% by mass or less, more preferably 1.00% by mass or less, and even more preferably 0.00% by mass.

[0066] [Other ingredients] The ink according to this embodiment may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0067] [Preferred composition] The ink according to the present embodiment preferably has any one of compositions 1 to 10 shown in Tables 2 to 3 below. In Tables 2 to 3 below, "ratio" indicates a numerical range of a preferred content ratio [mass %]. For example, "5.10-6.30" which is the ratio of the pigment in composition 1 indicates that the pigment is contained in an amount of 5.10 mass % or more and 6.30 mass % or less. "A-1", "A-2", "A-3", and "A-4" of the types of the first surfactant respectively indicate the surfactants (A-1), (A-2), (A-3), and (A-4) used in the examples. "B-1" and "B-2" of the types of the second surfactant respectively indicate the surfactants (B-1) and (B-2) used in the examples. "GL" indicates glycerin. "1,3-PD" indicates 1,3-propanediol.

[0068] [Table 2]

[0069] [Table 3]

[0070] [Ink manufacturing method] The ink according to this embodiment can be produced, for example, by uniformly mixing a pigment dispersion liquid containing a pigment, a first surfactant, a second surfactant, and an aqueous medium with a stirrer. In producing the ink according to this embodiment, after the components are uniformly mixed, foreign matter and coarse particles may be removed with a filter (for example, a filter with a pore size of 5 μm or less).

[0071] (Pigment dispersion) The pigment dispersion is a dispersion containing a pigment. The pigment dispersion preferably further contains a pigment-coating resin. The dispersion medium of the pigment dispersion is preferably water.

[0072] The content of the pigment in the pigment dispersion is preferably from 5.00% to 30.00% by mass, more preferably from 10.00% to 20.00% by mass. The content of the pigment coating resin in the pigment dispersion is preferably from 2.00% to 10.00% by mass, more preferably from 5.00% to 7.00% by mass.

[0073] The pigment dispersion can be prepared by wet-dispersing the pigment, the pigment-coated resin, a dispersion medium (e.g., water), and optional components (e.g., other surfactants) using a media-type wet disperser. In the wet dispersion using a media-type wet disperser, small-particle-size beads (e.g., D 50 The material of the beads is not particularly limited, but hard materials (for example, glass and zirconia) are preferable. EXAMPLES

[0074] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0075] [Preparation of the first surfactant] As the first surfactant, surfactants (A-1) to (A-4) and (S-1) shown in Table 4 below were prepared. In the product names in Table 4 below, "(R)" indicates a registered trademark. Among surfactants (A-1) to (A-4) and (S-1), surfactants (A-1) to (A-4) were compounds represented by general formula (I). Surfactant (S-1) was an acetylene glycol surfactant. In Table 4 below, the values ​​of m+n, x and y in general formula (I) for surfactants (A-1) to (A-4) and (S-1) are shown.

[0076] [Table 4]

[0077] [Preparation of the second surfactant] As the second surfactant, surfactants (B-1) to (B-2) shown in Table 5 below and surfactant (S-1) shown in Table 4 were prepared. In the product names in Table 5 below, "(R)" indicates a registered trademark. Surfactants (B-1) to (B-2) were compounds represented by general formula (II). Table 5 below lists the values ​​of m+n and b in general formula (II) for surfactants (B-1) to (B-2).

[0078] [Table 5]

[0079] [Preparation of pigment dispersion] A pigment dispersion for use in preparing the ink was prepared. In preparing the pigment dispersion, first, a pigment coating resin solution containing the pigment coating resin (R-1) and water was prepared.

[0080] (Preparation of pigment coated resin solution) An alkali-soluble resin having a repeating unit derived from methacrylic acid (MAA unit), a repeating unit derived from methyl methacrylate (MMA unit), a repeating unit derived from butyl acrylate (BA unit), and a repeating unit derived from styrene (ST unit) was prepared. This alkali-soluble resin had a mass average molecular weight (Mw) of 20,000 and an acid value of 100 mgKOH / g. The mass ratio of each repeating unit in this alkali-soluble resin was "MAA unit: MMA unit: BA unit: ST unit = 40: 15: 30: 15". This alkali-soluble resin was mixed with an aqueous sodium hydroxide solution (neutralization treatment). The alkali-soluble resin was neutralized with NaOH by the neutralization treatment. In the neutralization treatment, the amount of the aqueous sodium hydroxide solution used was 1.05 times the theoretical amount of the aqueous sodium hydroxide solution required to neutralize the alkali-soluble resin. This gave a pigment-coated resin solution containing the pigment-coated resin (R-1) (neutralized alkali-soluble resin) and water.

[0081] The Mw of the above-mentioned alkali-soluble resin was measured under the following conditions using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation). A calibration curve was prepared using TSKgel standard polystyrenes "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", and "A-1000" manufactured by Tosoh Corporation, and n-propylbenzene.

[0082] (Conditions for measuring mass average molecular weight) Column: Tosoh Corporation's "TSKgel SuperMultiporeHZ-H" (4.6mm I.D. x 15cm semi-microcolumn) Number of columns: 3 Eluent: Tetrahydrofuran ·Flow rate: 0.35mL / min Sample injection volume: 10μL ·Measurement temperature: 40℃ Detector: IR detector

[0083] (Distributed Processing) The above-mentioned pigment-coated resin solution containing a magenta pigment (CI Pigment Red 122) and a pigment-coated resin (R-1), an acetylene glycol surfactant "Olfine (registered trademark) E1010" (an ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd., and ion-exchanged water were added to the vessel of a media-type wet disperser (DYNO (registered trademark)-MILL manufactured by Willy & Bachofen (WAB)) so as to obtain the composition shown in Table 6 below.

[0084] The content of "water" in Table 6 below indicates the total content of the ion-exchanged water charged into the vessel described above and the water contained in the pigment-coated resin solution (more specifically, the water contained in the aqueous sodium hydroxide solution used for neutralizing the alkali-soluble resin, and the water generated by the neutralization reaction of the alkali-soluble resin and sodium hydroxide).

[0085] [Table 6]

[0086] Next, the contents of the vessel were wet-dispersed. Zirconia beads (particle diameter 1.0 mm) were used as media. The amount of media put in was 70 volume % of the capacity of the vessel. The dispersion conditions were a temperature of 10°C and a peripheral speed of 8 m / sec. As a result, a pigment dispersion liquid was obtained.

[0087] The volume median diameter (D 50 Specifically, the obtained pigment dispersion was diluted 300 times with ion-exchanged water to prepare a measurement sample. The D of the pigment particles in the measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Zetasizer (registered trademark) Nano ZS manufactured by Malvern Instruments). 50 The D of the pigment particles in the measurement sample was 50 of pigment particles contained in the pigment dispersion liquid 50 The measurement was carried out 10 times, and the average of each measurement result was taken as the D of the pigment particles. 50 The D of the pigment particles contained in the pigment dispersion liquid was adopted. 50 was 100 nm.

[0088] <Ink Preparation> Inks of Examples 1 to 10 and Comparative Examples 1 to 11 having the compositions shown in Tables 7 to 10 below were prepared by the following method.

[0089] [Example 1] 38.10 parts by mass of the pigment dispersion (5.71 parts by mass of pigment, 2.29 parts by mass of pigment coating resin (R)), a first surfactant shown in Table 7 below (0.10 parts by mass of surfactant (A-1) in Example 1), a second surfactant shown in Table 7 below (0.10 parts by mass of surfactant (B-1) in Example 1), an organic solvent shown in Table 7 below (30.00 parts by mass of glycerin in Example 1), and ion-exchanged water were charged into a beaker. The amount of ion-exchanged water used was an amount that would make the amount of the contents of the beaker 100.00 parts by mass (31.70 parts by mass in Example 1). The contents of the beaker were mixed at a rotation speed of 400 rpm using a stirrer ("Three-One Motor BL-600" manufactured by Shinto Scientific Co., Ltd.) to obtain a mixed liquid. The mixed liquid was filtered using a filter (pore size 5 μm) to remove foreign matter and coarse particles contained in the mixed liquid. In this manner, the ink of Example 1 was obtained.

[0090] [Examples 2 to 10 and Comparative Examples 1 to 11] Inks of Examples 2 to 10 and Comparative Examples 1 to 11 were prepared in the same manner as in the preparation of the ink of Example 1, except that the type and amount of each component was changed as shown in Tables 7 to 10. In addition, in the following Tables 7 to 10, "GL" represents glycerin, "1,3-PD" represents 1,3-propanediol, "PG" represents propylene glycol, and "EBEE" represents ethylene glycol butyl ethyl ether.

[0091] [Table 7]

[0092] [Table 8]

[0093] [Table 9]

[0094] [Table 10]

[0095] [Dynamic surface tension measurement] At 25° C., the dynamic surface tension of the ink of each of the Examples and Comparative Examples at a surface life of 10 ms and at a surface life of 1000 ms was measured by the maximum bubble pressure method (bubble pressure method) using a bubble pressure type dynamic surface tensiometer (KRUSS "BP100", capillary diameter 0.4 mm). The measurement results are shown in Table 11 below.

[0096] [evaluation] The ink jetting properties (ease of ink droplets to gather when ejected) and the scratch resistance of the formed images were evaluated for each of the examples and comparative examples by the following methods. The evaluation results are shown in Table 11 below. The evaluations were performed at a temperature of 25° C. and a humidity of 15% RH unless otherwise specified.

[0097] [Evaluation machine] A line head type inkjet recording device (a tester manufactured by Kyocera Document Solutions Inc.) was used as the evaluation machine. The evaluation machine was equipped with a piezoelectric type recording head. The recording head was set to a head temperature of 32° C. and an ink ejection speed of 8 m / sec. The recording head was filled with the ink to be evaluated (specifically, any of the inks of the examples and comparative examples).

[0098] [Flightability] In the evaluation of flight performance, the ink to be evaluated was ejected from the recording head of the evaluation machine. A high-speed camera (Shimadzu Corporation's "Hyper Vision HPV-X2") was used to photograph the ink droplets as they were ejected. The length of the tail of the photographed ink droplet was calculated from the length from the rear end of the main droplet to the rear end of the tail. Ink droplets with long tails are prone to generating satellite droplets when the tail breaks off during flight. Therefore, the length of the tail serves as a guide to the flight performance of the ink. The flight performance of the ink was judged according to the following criteria based on the length of the tail.

[0099] (Evaluation criteria for flight ability) A (Good): The tail length is less than 0.31 mm. B (bad): The tail length is 0.31 mm or more.

[0100] [Abrasion resistance] In the evaluation of abrasion resistance, copy paper ("CC90" manufactured by Mondi) was used as a recording medium. In the evaluation of abrasion resistance, the volume of one drop of ink ejected from the recording head of the evaluation machine was set to 11.5 pL (11.5 pL of ink volume per pixel). A solid image (size: 5 cm x 4 cm) was formed on the recording medium using the evaluation machine. Next, an unused recording medium (evaluation paper) was placed on top of the recording medium on which the solid image was formed. Next, a 1 kg weight with a base area of ​​5 cm x 4 cm was placed on the evaluation paper. At this time, the weight was placed so that the center of gravity of the weight was located at the center of the solid image. Next, both ends of the evaluation paper were held with the weight placed (load of 1 kg), and the evaluation paper was moved back and forth horizontally five times to rub the solid image with the evaluation paper.

[0101] Next, the image density of the stain image transferred from the solid image to the evaluation paper was measured with a reflection densitometer ("FD-9" manufactured by Konica Minolta, Inc.) (observation light source: D50 light source, lighting conditions: M2, field of view: 2°, density status: I). In detail, the image density of 10 randomly selected points in the stain image was measured with a reflection densitometer, and the arithmetic mean value (ID value) of the image densities of the 10 points was calculated. Next, instead of the evaluation paper, the image density of unused copy paper ("CC90" manufactured by Mondi) was measured in the same manner as the ID value, and the obtained value was defined as the "background value". The value obtained by subtracting the background value from the ID value was defined as the evaluation value (FD value) of the abrasion resistance (FD value = ID value - background value). The abrasion resistance was judged according to the following criteria.

[0102] (Abrasion resistance standard) Good (A): FD value is less than 0.020. Poor (B): FD value is 0.020 or more.

[0103] [Table 11]

[0104] As shown in Tables 4 to 11, the inks of the respective examples contained a pigment, a first surfactant, a second surfactant, and an aqueous medium. The first surfactant was a compound represented by general formula (I). The second surfactant was a compound represented by general formula (II). The aqueous medium contained water and a specific organic solvent. The octanol / water partition coefficient LogK of the specific organic solvent ow was -1.80 or more and -1.00 or less. In the inks of each Example, the content ratio of the first surfactant was 0.03 mass% or more and 0.35 mass% or less, and the content ratio of the second surfactant was 0.03 mass% or more and 0.30 mass% or less. The inks of each Example were good in the evaluation results of flying performance and abrasion resistance of the formed images.

[0105] On the other hand, the inks of Comparative Examples 1 and 3 do not contain a specific organic solvent, but instead have an octanol / water partition coefficient LogK ow The inks of Comparative Examples 1 and 3 had an excessively low dynamic surface tension at a surface life of 10 milliseconds due to the influence of propylene glycol. As a result, the inks of Comparative Examples 1 and 3 had poor evaluation results for flying performance.

[0106] The inks of Comparative Examples 2 and 4 did not contain a specific organic solvent, but instead had an octanol / water partition coefficient LogK ow The inks of Comparative Examples 2 and 4 had an excessively high dynamic surface tension at a surface life of 1000 milliseconds due to the influence of ethylene glycol butyl ethyl ether. As a result, the inks of Comparative Examples 2 and 4 had poor evaluation results for the abrasion resistance of the images formed.

[0107] The inks of Comparative Examples 5 to 7 did not contain at least one of the compounds represented by general formula (I) and general formula (II) as a surfactant, but contained an acetylene glycol surfactant instead. Although the inks of Comparative Examples 5 to 7 contained a surfactant, the dynamic surface tension at a surface life of 1000 milliseconds could not be reduced to a desired range. As a result, the inks of Comparative Examples 5 to 7 had poor evaluation results for the scratch resistance of the images formed.

[0108] The inks of Comparative Examples 8 and 9 contained a compound represented by general formula (I) and a compound represented by general formula (II) as surfactants. However, the inks of Comparative Examples 8 and 9 contained an excessively high proportion of the compound represented by general formula (I) or the compound represented by general formula (II). As a result, the inks of Comparative Examples 8 and 9 had poor evaluation results for flying performance.

[0109] The inks of Comparative Examples 10 and 11 used only one type of surfactant, and contained only one of the compounds represented by general formula (I) and the compounds represented by general formula (II) as the surfactant. Therefore, the inks of Comparative Examples 10 and 11 could not reduce the dynamic surface tension at a surface life of 1000 milliseconds to a desired range. As a result, the inks of Comparative Examples 10 and 11 had poor evaluation results for the scratch resistance of the images formed. [Industrial Applicability]

[0110] The inks of the present embodiments can be used to form images.

Claims

1. The ink composition includes a pigment, a first surfactant, a second surfactant, and an aqueous medium, The first surfactant is a compound represented by the following general formula (I): The second surfactant is a compound represented by the following general formula (II): The aqueous medium contains water and a specific organic solvent, Octanol / water partition coefficient LogK of the specific organic solvent ow is equal to or greater than -1.80 and equal to or less than -1.00, The content ratio of the first surfactant is 0.03% by mass or more and 0.35% by mass or less, The content of the second surfactant is from 0.03% by mass to 0.30% by mass. 【Chemistry 1】 (In the general formula (I), m and n each independently represent a number of 0.0 or more and 11.0 or less, m+n is 9.0 or more and 11.0 or less, x represents a number of 1.0 or more and 20.0 or less, and y represents a number of 1.0 or more and 10.0 or less.) 【Chemistry 2】 (In the general formula (II), a and c each independently represent a number of 0 to 25, a+c represents a number of 13 to 25, and b represents a number of 15 to 27.)

2. At a temperature of 25° C. The dynamic surface tension at a surface life of 10 milliseconds is 38 mN / m or more and 50 mN / m or less, 2. The ink-jet ink according to claim 1, wherein the dynamic surface tension at a surface life of 1000 milliseconds is 30 mN / m or more and 38 mN / m or less.

3. The ink-jet ink according to claim 1 or 2, wherein a content of the specific organic solvent is from 15.00% by mass to 45.00% by mass.

4. In the general formula (I), x represents a number of 6.0 or more and 13.0 or less; The ink-jet ink according to claim 1 or 2, wherein y represents a number of 1.5 or more and 6.0 or less.

5. In the general formula (II), 3. The ink-jet ink according to claim 1, wherein a+c is 16 or more and 22 or less, and b is a number 18 or more and 24 or less.

6. 3. The ink-jet ink according to claim 1, wherein the specific organic solvent includes at least one of glycerin and 1,3-propanediol.

Images