Ink set and recording head inspection method

Abstract

The invention provides an ink set and a recording head inspection method. The ink set includes an inkjet ink and a recording head filling liquid. The inkjet ink contains a pigment, a first surfactant, and an aqueous medium. The recording head filling liquid contains a specific humectant, a second surfactant, and water. The specific humectant is a compound represented by general formula (1). The first surfactant and the second surfactant are independent of each other and are compounds represented by general formula (2). # imgabs0 #

Description

Technical Field

[0001] The present invention relates to an ink set and a recording head inspection method. Background Art

[0002] The inkjet recording device has a recording head for ejecting ink for inkjet. Generally, the ejection performance of the recording head is fully inspected before shipment. In the inspection of the ejection performance of the recording head, the inkjet ink is actually filled into the recording head and an ejection test is performed.

[0003] However, if the recording head is shipped with inkjet ink still remaining in the ink flow path, the solvent in the inkjet ink may evaporate during transportation and storage, and the solid components (especially pigment components) in the inkjet ink may aggregate to form aggregates. The above-mentioned aggregates may cause ejection failures in the recording head after shipment.

[0004] Therefore, the recording head manufacturer sometimes ships the recording head with a solution containing no pigment component (hereinafter sometimes referred to as recording head filling liquid) filled in the recording head. Even when the recording head is temporarily not used and is placed aside, it is necessary to be able to flush out the recording head filling liquid from the placed recording head.

[0005] Furthermore, the recording head filling liquid enters the ink flow path of the recording head to dilute the inkjet ink remaining in the ink flow path. Therefore, it is required that the recording head filling liquid can be easily introduced into the ink flow path in the recording head.

[0006] Regarding the recording head filling liquid, for example, a recording head filling liquid containing silicone oil has been proposed (Japanese Patent Application Laid-Open No. 2010-227729). Summary of the invention

[0007] However, Japanese Patent Application Laid-Open No. 2010-227729 cannot satisfy the above requirements.

[0008] The present invention has been made in view of the above problems, and its object is to provide an ink set that can easily introduce a recording head filling liquid into the ink flow path in the recording head, can effectively suppress the aggregation of pigment components in the inkjet ink in the recording head, and can stably flush out the recording head filling liquid. Another object of the present invention is to provide a recording head inspection method using the above ink set.

[0009] The ink set of the present invention comprises an inkjet ink and a recording head filling liquid. The inkjet ink contains a pigment, a first surfactant and an aqueous medium. The recording head filling liquid contains a specific moisturizing agent, a second surfactant and water. The specific moisturizing agent is a compound represented by the following general formula (1). The first surfactant and the second surfactant are independent of each other and are compounds represented by the following general formula (2).

[0010] [Chemistry 1]

[0011]

[0012] In the general formula (1), a, b and c are each independently an integer greater than 1, and a+b+c is 5 to 20.

[0013] [Chemistry 2]

[0014]

[0015] In the general formula (2), m and n are independent of each other and represent a number of 0.0 to 12.0, m+n is 8.0 to 12.0, x represents a number of 1.0 to 20.0, and y represents a number of 2.0 to 10.0.

[0016] The recording head inspection method of the present invention uses the above-mentioned ink set, and comprises: an inspection step of inspecting the ejection performance of the recording head; and a filling step of filling the recording head with the recording head filling liquid after the inspection step. In the inspection step, the ejection performance of the recording head is inspected by ejecting the inkjet ink from the recording head.

[0017] According to the ink set of the present invention, the recording head filling liquid can be easily introduced into the ink flow path in the recording head, the aggregation of the pigment component in the inkjet ink in the recording head can be effectively suppressed, and the recording head filling liquid can be stably flushed out. According to the recording head inspection method of the present invention, the occurrence of ejection failure in the recording head after inspection can be suppressed. DETAILED DESCRIPTION

[0018] Hereinafter, embodiments of the present invention will be described. In the following description, unless otherwise specified, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution measuring apparatus (“Zeta Size Nano ZS” manufactured by Malvern Corporation (registered trademark in Japan)).

[0019] Hereinafter, unless otherwise specified, the measured values ​​of the acid value are values ​​measured in accordance with "JIS (Japanese Industrial Standards) K0070-1992". Furthermore, unless otherwise specified, the measured values ​​of the weight average molecular weight (Mw) are values ​​measured using a gel permeation chromatograph.

[0020] Unless otherwise specified, the measured value of dynamic surface tension is a value obtained by measuring the dynamic surface tension at a surface life of 10 milliseconds at 25° C. using a bubble pressure type dynamic surface tension meter (e.g., “BP 100” manufactured by KRUSS Corporation, with a capillary diameter of 0.4 mm) by the maximum bubble pressure method.

[0021] Hereinafter, unless otherwise specified, the measured values ​​of viscosity are values ​​measured at 25° C. using a falling ball viscometer (for example, “Lovis 2000” manufactured by Antenna Pal Co., Ltd.).

[0022] In the present specification, an acryl group and a methacryl group may be collectively referred to as a "(meth)acryl group." Also, "at least one of A and B" means "A and / or B."

[0023] [First embodiment: ink set]

[0024] The following is an explanation of an ink set according to a first embodiment of the present invention. The ink set according to this embodiment includes an inkjet ink (hereinafter, sometimes referred to as ink) and a recording head filling liquid (hereinafter, sometimes referred to as filling liquid). The ink contains a pigment, a first surfactant, and an aqueous medium. The filling liquid contains a specific moisturizing agent, a second surfactant, and water. The specific moisturizing agent is a compound represented by the following general formula (1). The first surfactant and the second surfactant are independent of each other and are compounds represented by the following general formula (2).

[0025] [Chemistry 3]

[0026]

[0027] In the general formula (1), a, b and c are each independently an integer greater than 1. a+b+c is 5 or more and 20 or less.

[0028] [Chemistry 4]

[0029]

[0030] In the general formula (2), m and n are independent of each other and represent a number of 0.0 to 12.0. m+n is 8.0 to 12.0. x represents a number of 1.0 to 20.0. y represents a number of 2.0 to 10.0.

[0031] In the ink set of this embodiment, the filling liquid may contain a plurality of compounds represented by the general formula (1). In this case, in the general formula (1), a, b, and c represent the average of a, b, and c in the plurality of compounds represented by the general formula (1).

[0032] In the ink set of the present embodiment, the ink may contain a plurality of compounds represented by the general formula (2). In addition, the filling liquid may contain a plurality of compounds represented by the general formula (2). In these cases, in the general formula (2), m, n, x, and y respectively represent the average of m, n, x, and y in the plurality of compounds represented by the general formula (2).

[0033] In the ink set of the present invention, the filling liquid is used to fill the recording head in which the ink remains. For example, after the recording head ejects ink, when the recording head is temporarily not used for some reason, the filling liquid is filled into the recording head. Specifically, the filling liquid is used to fill the recording head when the recording head is shipped, the recording head is stored for a long time, or the recording head is transported. The ink set of this embodiment is preferably used as the ink set used in the recording head inspection method involved in the second embodiment.

[0034] The ink set of the present embodiment has the above-mentioned structure, so that the filling liquid can be easily introduced into the ink flow path in the recording head, and the pigment components (pigment and pigment coating resin) in the ink can be effectively suppressed from agglomerating in the recording head, and the filling liquid can be stably flushed out. The reason is presumed to be as follows. The ink set of the present embodiment includes ink and filling liquid. The filling liquid enters the ink flow path of the recording head and dilutes the ink remaining in the ink flow path. Therefore, the solid components of the ink remaining in the ink flow path are difficult to agglomerate. In particular, in the ink set of the present embodiment, a specific moisturizing agent represented by the general formula (1) is contained in the filling liquid. In the general formula (1), a, b and c represent integers greater than 1 and a+b+c is greater than 5. The viscosity of the specific moisturizing agent is low, and the pressure (flushing pressure) of the recording head does not increase when flushing the filling liquid. Therefore, the ink set of the present embodiment can also stably flush the filling liquid from the recording head after the recording head is placed. In addition, although the reason is not clear, according to the research of the inventors of the present application, it is believed that the use of a humectant in which a+b+c in the general formula (1) is greater than 20 cannot fully suppress the aggregation of the pigment component in the ink in the recording head. Since the ink set of this embodiment contains a specific humectant in which a, b and c in the general formula (1) are integers greater than 1 and a+b+c is 5 to 20, it is possible to fully suppress the aggregation of the pigment component in the ink in the recording head and to stably flush out the filling liquid.

[0035] In addition, the ink set of the present embodiment contains a compound represented by the general formula (2) as a first surfactant in the ink. In addition, the ink set of the present embodiment contains a compound represented by the general formula (2) as a second surfactant in the filling liquid. When the compound represented by the general formula (2) is contained in the ink, the dynamic surface tension of the ink can be reduced. In addition, when the compound represented by the general formula (2) is contained in the filling liquid, the dynamic surface tension of the filling liquid can be reduced. Moreover, the compound represented by the general formula (2) has a structure in which a propylene oxide group having a hydrophobic alkyl chain and forming an ether bond with the alkyl chain is bonded to an ethylene oxide group having a hydrophobic alkyl chain and forming an ether bond with the alkyl chain. Therefore, the compound represented by the general formula (2) has high hydrophobicity and good wettability. Based on these reasons, it is considered that the ink set of the present embodiment can easily introduce the filling liquid into the ink flow path in the recording head when the ink and the filling liquid are mixed. The ink set of the present embodiment is described in more detail below. Each component described below can be used alone or in combination of two or more.

[0036] [Ink]

[0037] The ink contains a pigment, a first surfactant, and an aqueous medium. In the ink, the pigment forms pigment particles together with, for example, a pigment-coating resin. Therefore, the ink preferably contains a pigment, a pigment-coating resin, a first surfactant, and an aqueous medium. The pigment particles are dispersed in a solvent. From the perspective of optimizing the color concentration, hue, or stability of the ink, the D 50 It is preferably from 30 nm to 300 nm, and more preferably from 50 nm to 150 nm.

[0038] (pigment)

[0039] Examples of pigments contained in the ink include yellow pigments, orange pigments, red pigments, blue pigments, violet 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 violet pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0040] In the ink, the content of the pigment is preferably 2.0% by mass or more and 15.0% by mass or less, and more preferably 5.0% by mass or more and 10.0% by mass or less. By making the content of the pigment 2.0% by mass or more, it is easy to form an image with a desired image density. In addition, by making the content of the pigment 15.0% by mass or less, the fluidity of the ink can be ensured.

[0041] (Pigment coated resin)

[0042] The pigment coating resin is a resin soluble in ink. A portion of the pigment coating resin exists on the surface of the pigment particles, for example, to impart dispersibility to the pigment particles. A portion of the pigment coating resin exists in a state of being dissolved in the ink, for example.

[0043] Examples of the pigment coating resin include copolymers of alkyl (meth)acrylates, at least one monomer selected from styrene and vinylnaphthalene, and at least one monomer selected from (meth)acrylic acid and maleic acid.

[0044] The pigment coating resin is preferably a styrene-(meth)acrylic resin. The styrene-(meth)acrylic resin has a repeating unit derived from at least one monomer of an alkyl (meth)acrylate and (meth)acrylic acid, and a styrene unit. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. The styrene-(meth)acrylic resin is preferably a copolymer (X) of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate. The copolymer (X) is preferably neutralized in equal amounts using a basic compound (e.g., potassium hydroxide or sodium hydroxide).

[0045] Among all the repeating units possessed by the copolymer (X), the content ratio of the repeating units derived from styrene is preferably 10.0 mass % or more and 20.0 mass % or less. Among all the repeating units possessed by the copolymer (X), the content ratio of the repeating units derived from methyl methacrylate is preferably 10.0 mass % or more and 20.0 mass % or less. Among all the repeating units possessed by the copolymer (X), the content ratio of the repeating units derived from methacrylic acid is preferably 35.0 mass % or more and 45.0 mass % or less. Among all the repeating units possessed by the copolymer (X), the content ratio of the repeating units derived from butyl acrylate is preferably 25.0 mass % or more and 35.0 mass % or less.

[0046] In the ink, the content of the pigment coating resin is preferably 0.7% to 6.0% by mass, more preferably 2.0% to 4.0% by mass. By setting the content of the pigment coating resin to 0.7% to 6.0% by mass, the occurrence of nozzle clogging by the ink can be suppressed.

[0047] The acid value of the pigment coating resin is preferably 30 mgKOH / g to 300 mgKOH / g, more preferably 50 mgKOH / g to 150 mgKOH / g. By making the acid value of the pigment coating resin 30 mgKOH / g to 300 mgKOH / g, the dispersibility of the pigment can be optimized and the storage stability of the ink can be optimized.

[0048] The acid value of the pigment coating resin can be adjusted by changing the amount of the monomer used when synthesizing the pigment coating resin. For example, when synthesizing the pigment coating resin, the acid value of the pigment coating resin can be increased by using a monomer having an acidic functional group (e.g., a carboxyl group) (more specifically, acrylic acid, methacrylic acid, etc.).

[0049] The Mw of the pigment coating resin is preferably 10000 to 50000, more preferably 15000 to 25000. By setting the Mw of the pigment coating resin to 10000 to 50000, an increase in ink viscosity can be suppressed, and the image density of an image formed by the ink can be optimized.

[0050] The Mw of the pigment coating resin can be adjusted by changing the polymerization conditions of the pigment coating resin (more specifically, the amount of the polymerization initiator used, the polymerization temperature, the polymerization time, etc.).

[0051] In the polymerization of the pigment-coated resin, the amount of the polymerization initiator used is preferably 0.001 mol to 5.0 mol, more preferably 0.01 mol to 2.0 mol, relative to 1 mol of the monomer mixture. In the polymerization of the pigment-coated resin, for example, the polymerization temperature can be set to 50° C. to 70° C., and the polymerization time can be set to 10 hours to 24 hours. In addition, the polymerized pigment-coated resin is preferably used as a raw material for ink after being neutralized in equal amounts with an alkaline compound. The alkaline compound is preferably a hydroxide of an alkali metal ion (such as potassium hydroxide or sodium hydroxide).

[0052] (First Surfactant)

[0053] The first surfactant is a compound represented by the above-mentioned general formula (2). In the general formula (2), m and n are independent of each other and represent a number greater than 0.0 and less than 12.0. m+n is greater than 8.0 and less than 12.0. In the general formula (2), m and n are preferably independent of each other and represent a number greater than 0.0 and less than 11.0, and m+n is preferably greater than 9.0 and less than 11.0. In addition, in the general formula (2), x represents a number greater than 1.0 and less than 20.0. y represents a number greater than 2.0 and less than 10.0. x preferably represents a number greater than 6.0 and less than 16.0, and more preferably represents a number greater than 6.0 and less than 8.0. y preferably represents a number greater than 2.0 and less than 3.0. In addition, in the general formula (2), it is more preferred that x represents a number greater than 6.0 and less than 8.0, and y represents a number greater than 2.0 and less than 3.0.

[0054] The compound represented by the general formula (2) is a nonionic surfactant with a polyoxyalkylene alkyl ether as the main skeleton, and has an ether bond (-O-) in the molecule that will not dissociate into ions even if dissolved in water. In addition, the compound represented by the general formula (2) has a hydrophobic alkyl chain in which m+n in the general formula (2) is greater than 8.0 and less than 12.0. In addition, the compound represented by the general formula (2) has the following structure: an ethylene oxide group (-[CH2CH2O]-) that forms an ether bond with the above-mentioned alkyl chain is bonded to a propylene oxide group (-[CH2CH(CH3)O]-) having a higher hydrophobicity than the ethylene oxide group. Therefore, the compound represented by the general formula (2) has high hydrophobicity and good wettability.

[0055] Examples of commercially available products of the compound represented by general formula (2) include “Softtanol (Japanese registered trademark) EP5035”, “Softtanol (Japanese registered trademark) EP7025”, “Softtanol (Japanese registered trademark) EP7045”, “Softtanol (Japanese registered trademark) EP7085”, “Softtanol (Japanese registered trademark) EP 9050” and “Softtanol (Japanese registered trademark) EP12030” manufactured by Nippon Shokubai Co., Ltd.

[0056] In the ink, the content of the first surfactant (in other words, the compound represented by the general formula (2)) is preferably 0.1% by mass or more and 2.5% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and particularly preferably 0.1% by mass or more and 0.5% by mass or less. By setting the content of the first surfactant to 0.1% by mass or more and 2.5% by mass or less, the filling liquid can be more reliably introduced into the ink flow path in the recording head. Therefore, an ink set having the following characteristics can be reliably obtained: the filling liquid can be easily introduced into the ink flow path in the recording head, the pigment component in the ink can be effectively suppressed from agglomerating in the recording head, and the filling liquid can be stably flushed out.

[0057] (Other surfactants)

[0058] The ink may contain only the first surfactant as a surfactant, or may further contain surfactants other than the first surfactant (hereinafter referred to as other surfactants). Among the surfactants, the first surfactant is preferably contained in an amount of 60.0% by mass or more, more preferably 80.0% by mass or more.

[0059] Examples of other surfactants include surfactants wherein y in the general formula (2) represents a number less than 1.0, acetylene glycol surfactants (including surfactants of acetylene glycol compounds), silicone surfactants (including surfactants of silicone compounds), and fluorine surfactants (including surfactants of fluorine resins or fluorine-containing compounds). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol.

[0060] The content ratio of other surfactants in the ink is preferably 0.1 mass % to 0.5 mass %, and more preferably 0.1 mass % to 0.3 mass %.

[0061] (Aqueous medium)

[0062] The aqueous medium contained in the ink is a medium containing water. The aqueous medium can function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include aqueous media containing water and a water-soluble organic solvent.

[0063] The content ratio of the aqueous medium in the ink is preferably 30.0 mass % or more and 95.0 mass % or less, and more preferably 70.0 mass % or more and 95.0 mass % or less.

[0064] (water)

[0065] Water is a main solvent of the ink. The content of water in the ink is, for example, preferably from 20.0% by mass to 80.0% by mass, and more preferably from 50.0% by mass to 70.0% by mass.

[0066] (Water-soluble organic solvent)

[0067] The ink preferably further contains a water-soluble organic solvent. Examples of the water-soluble organic solvent in the ink include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

[0068] Examples of the diol compound include ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0069] Examples of the glycol ether compound include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether and propylene glycol monomethyl ether.

[0070] Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0071] Examples of the nitrogen-containing compound include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0072] Examples of the acetate compound include diethylene glycol monoethyl ether acetate.

[0073] The water-soluble organic solvent in the ink is preferably triethylene glycol monobutyl ether, 2-pyrrolidone or glycerol.

[0074] The content of the water-soluble organic solvent in the ink is preferably 10.0% by mass to 80.0% by mass, more preferably 20.0% by mass to 40.0% by mass. By setting the content of the water-soluble organic solvent to 10.0% by mass to 80.0% by mass, the ink can be ejected more stably from the recording head.

[0075] (additive)

[0076] The ink may further contain known additives (for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an antifungal agent) as necessary.

[0077] (Preferred components)

[0078] The ink preferably has any one of components 1 to 6 shown in Table 1 below. In addition, in Table 1 below, "ratio" represents the numerical range of the preferred content ratio [mass %]. For example, the ratio of the pigment of component 1 in Table 1 "5.4-6.6" means that it contains 5.4 mass % or more and 6.6 mass % or less of the pigment. The representation in other columns is the same. The types of the first surfactant "S-1", "S-3", "S-4", and "S-5" respectively represent the surfactants (S-1), (S-3), (S-4), and (S-5) used in the examples. "Resin" represents a pigment-coated resin. "TGBE" represents triethylene glycol mono-n-butyl ether.

[0079] [Table 1]

[0080]

[0081] (Method for producing ink)

[0082] The ink can be manufactured, for example, by mixing the following components: a pigment dispersion containing a pigment, a first surfactant, an aqueous medium, and components added as needed (e.g., other surfactants, additives). The first surfactant can be manufactured, for example, by mixing a branched alcohol and KOH, reacting the mixture at 90°C to 130°C and 1.1 kPa to 1.5 kPa, dehydrating the mixture for 15 to 45 minutes, adding ethylene oxide, and reacting at 135°C to 175°C for 15 to 45 minutes. The reaction liquid is analyzed by gas chromatography to confirm that there is no residue of each raw material component, thereby confirming that it is the target substance represented by general formula (2). The pigment dispersion contains a pigment, a pigment-coated resin, and water. The pigment-coated resin is prepared, for example, by neutralizing an alkali-soluble resin in equal amounts using an alkaline compound (e.g., sodium hydroxide). The pigment dispersion can be prepared by adding a pigment to an aqueous solution containing the pigment-coated resin and then performing a dispersion treatment. The device used for the dispersion treatment can be, for example, a bead mill. In the production of the ink, after the dispersion treatment, foreign matter and coarse particles may be removed using a filter (eg, a filter having a pore size of 5 μm or less).

[0083] [Filling fluid]

[0084] The filler fluid contains a specific humectant, a second surfactant, and water.

[0085] (Specific moisturizer)

[0086] The specific moisturizing agent is a compound represented by the above-mentioned general formula (1). In the general formula (1), a, b and c are independent of each other and represent an integer greater than 1. a+b+c is greater than 5 and less than 20. a+b+c preferably represents an integer greater than 6 and less than 18, more preferably represents an integer greater than 6 and less than 15, and particularly preferably represents an integer greater than 6 and less than 9. If a+b+c is small, the pressure (flushing pressure) of the recording head when flushing the filling liquid will increase. On the other hand, if a+b+c becomes large, the aggregation of the pigment components in the ink cannot be fully suppressed. The specific moisturizing agent in which a+b+c is an integer greater than 5 and less than 20 in the general formula (1) has a low viscosity (for example, a viscosity of 450 mPa·s or less at 25°C), and the pressure (flushing pressure) of the recording head when flushing the filling liquid does not increase. In addition, the specific moisturizing agent in which a+b+c is an integer greater than 5 and less than 20 in the general formula (1) can highly maintain the dispersion stability of the pigment components in the ink and can effectively suppress the aggregation of the pigment components in the ink in the recording head. In addition, by setting a+b+c in the general formula (1) to, for example, 6 or more and 18 or less, aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0087] a, b and c in the general formula (1) may be the same or different. For example, by adjusting the reaction conditions such as the reaction temperature and reaction time of glycerol and polyethylene glycol, a, b and c in the general formula (1) may be changed in various ways. Therefore, a, b and c in the general formula (1) may be a=b=c, a=c≠b, or a≠b≠c. In addition, only one of a or c may be the same as b.

[0088] As described above, in the general formula (1), a, b and c can be set independently of each other. In the general formula (1), a, b and c are preferably a=b=c or a=c≠b. By using these specific moisturizers, the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed, and the filling liquid can be flushed out more stably. In addition, in the general formula (1), when a, b and c are a=b=c, a+b+c can be freely set within the range of 6 to 18 and a multiple of 3.

[0089] In the general formula (1), when a, b, and c are a=c≠b, a and c and b can be freely set within the range of a+b+c being 5 or more and 20 or less (however, as described above, a, b, and c are independent of each other and represent an integer greater than 1). However, in the general formula (1), when a, b, and c are a=c≠b, b is preferably a+1 or a+2. In this case, the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed, and the filling liquid can be flushed out more stably.

[0090] The viscosity of the specific moisturizing agent at 25°C is preferably 230 mPa·s or more and 450 mPa·s or less, more preferably 270 mPa·s or more and 450 mPa·s or less, particularly preferably 300 mPa·s or more and 450 mPa·s or less, and particularly preferably 340 mPa·s or more and 410 mPa·s or less. By setting the viscosity of the specific moisturizing agent to be 230 mPa·s or more and 450 mPa·s or less, the aggregation of the pigment component in the ink in the recording head can be effectively suppressed. In addition, the filling liquid can be stably flushed out of the recording head after the recording head is placed.

[0091] The content ratio of the specific moisturizing agent in the filling liquid is preferably 10.0 mass% or more and 50.0 mass% or less, and more preferably 25.0 mass% or more and 40.0 mass% or less. By making the content ratio of the specific moisturizing agent in the filling liquid 10.0 mass% or more and 50.0 mass% or less, the aggregation of the pigment component in the ink in the recording head can be effectively suppressed. In addition, the filling liquid can be stably flushed from the recording head after the recording head is placed. In addition, by making the content ratio of the specific moisturizing agent in the filling liquid 25.0 mass% or more and 40.0 mass% or less, the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0092] (Second Surfactant)

[0093] Like the first surfactant, the second surfactant is also a compound represented by the above-mentioned general formula (2). The compound represented by the general formula (2) used for the second surfactant can be, for example, the same as the compound represented by the general formula (2) used for the first surfactant. Therefore, repeated descriptions are omitted. The first surfactant and the second surfactant can be the same compound or different compounds, but are preferably the same compound.

[0094] In the filling liquid, the content ratio of the second surfactant (in other words, the compound represented by the general formula (2)) is preferably 0.1 mass % or more and 2.5 mass % or less, more preferably 0.1 mass % or more and 1.0 mass % or less, and particularly preferably 0.1 mass % or more and 0.5 mass % or less. By setting the content ratio of the second surfactant to 0.1 mass % or more and 2.5 mass % or less, the filling liquid can be more reliably introduced into the ink flow path in the recording head when the ink and the filling liquid are mixed. Therefore, an ink set having the following characteristics can be reliably obtained: the filling liquid can be easily introduced into the ink flow path in the recording head, the pigment component in the ink can be effectively suppressed from agglomerating in the recording head, and the filling liquid can be stably flushed.

[0095] (water)

[0096] Water is the main solvent of the filling liquid. The content of water in the filling liquid is, for example, preferably 35.0 mass % or more and 95.0 mass % or less, and more preferably 45.0 mass % or more and 85.0 mass % or less.

[0097] (Other ingredients)

[0098] The filling liquid may further contain known additives (eg, a dissolution stabilizer, an anti-desiccation agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an antifungal agent) as necessary.

[0099] (Preferred ingredients)

[0100] The filling liquid preferably has any one of the components 1 to 18 shown in Table 2 below. In addition, in Table 2 below, "ratio" represents the numerical range of the preferred content ratio [mass %]. For example, the ratio of the specific moisturizer of component 1 "27.0-33.0" means that the specific moisturizer is contained in an amount of 27.0 mass % or more and 33.0 mass % or less. The notation in other columns is the same. The types of specific moisturizers "M-2", "M-3", "M-4", "M-5", "M-8", "M-9", "M-10", and "M-11" respectively represent the moisturizers (M-2), (M-3), (M-4), (M-5), (M-8), (M-9), (M-10), and (M-11) used in the examples. The types of the second surfactants "S-1", "S-3", "S-4", and "S-5" respectively represent the surfactants (S-1), (S-3), (S-4), and (S-5) used in the examples.

[0101] [Table 2]

[0102]

[0103] The combination of the specific moisturizing agent and the second surfactant is not particularly limited, and various combinations can be made within the scope of the above description. However, the combination of the specific moisturizing agent and the second surfactant is preferably the following combination, for example: the specific moisturizing agent is a moisturizing agent (M-2), (M-3), or (M-8), and the second surfactant is a surfactant (S-1). Therefore, the ink set of this embodiment is preferably: the specific moisturizing agent is a compound in which a+b+c in the general formula (1) is 6 to 10, and the second surfactant is a compound in which x in the general formula (2) represents a number of 6.0 to 8.0, and y represents a number of 2.0 to 3.0. In addition, as described above, it is preferred that the first surfactant and the second surfactant are the same compound. Therefore, the ink set of this embodiment is more preferably: the specific moisturizing agent is a compound in which a+b+c in the general formula (1) is 6 to 10, and the first surfactant and the second surfactant are compounds in which x in the general formula (2) represents a number of 6.0 to 8.0, and y represents a number of 2.0 to 3.0.

[0104] (Method for producing filling liquid)

[0105] The filling liquid can be produced, for example, by mixing a specific moisturizing agent, a second surfactant, water, and components (such as additives) added as needed. A specific moisturizing agent in which a, b, and c in the general formula (1) are a=b=c can be produced by reacting polyethylene glycol and glycerol at, for example, 180°C to 220°C for etherification. A specific moisturizing agent in which a, b, and c in the general formula (1) are a=c≠b can also be produced by reacting polyethylene glycol and glycerol for etherification. However, in the production of a specific moisturizing agent in which a, b, and c in the general formula (1) are a=c≠b, first, polyethylene glycol and glycerol are reacted at, for example, 140°C to 180°C to complete the reaction of the two α-hydroxyl groups bonded to the primary carbon of glycerol. Thus, an intermediate is formed. Next, the intermediate is reacted with polyethylene glycol at, for example, 200°C to 240°C to complete the reaction of the β-hydroxyl groups bonded to the secondary carbon of glycerol. In this way, a specific moisturizing agent can be produced in which a, b, and c satisfy a=c≠b in the general formula (1). The production method of the second surfactant can be, for example, the same as that of the first surfactant.

[0106] [Dynamic surface tension]

[0107] As described above, the ink set of the present embodiment can reduce the dynamic surface tension of the ink by containing the compound represented by the general formula (2) as the first surfactant in the ink. In addition, the ink set of the present embodiment can reduce the dynamic surface tension of the filling liquid by containing the compound represented by the general formula (2) as the second surfactant in the filling liquid. The dynamic surface tension of the ink and the dynamic surface tension of the filling liquid at a surface life of 10 milliseconds at 25°C are preferably 35.0 mN / m or less. If the dynamic surface tension of the ink and the dynamic surface tension of the filling liquid at a surface life of 10 milliseconds at 25°C are 35.0 mN / m or less, the ink and the filling liquid will wet and spread in the recording head in a short time. As a result, when the ink and the filling liquid are mixed, the filling liquid can be easily introduced into the ink flow path in the recording head. In addition, when the dynamic surface tension of the ink and the dynamic surface tension of the filling liquid at a surface life of 10 milliseconds at 25°C are 25.0 mN / m or more and 35.0 mN / m or less, when the ink and the filling liquid are mixed, the filling liquid can be more reliably introduced into the ink flow path in the recording head.

[0108] [Second Embodiment: Recording Head Inspection Method]

[0109] Hereinafter, a recording head inspection method according to a second embodiment of the present invention will be described. The recording head inspection method according to the present invention uses the ink set according to the first embodiment, and includes an inspection step of inspecting the ejection performance of the recording head, and a filling step of filling the recording head with the filling liquid after the inspection step. In the inspection step, the ejection performance of the recording head is inspected by ejecting ink from the recording head. The ink set used in the recording head inspection method according to this embodiment can be the same as the ink set described in the first embodiment. Therefore, repeated descriptions are omitted.

[0110] The recording head inspection method of this embodiment uses the ink set of the first embodiment, so it is possible to suppress ejection defects in the recording head after inspection. The recording head inspection method of this embodiment is performed, for example, before the recording head manufacturer ships the recording head. The recording head inspected by the recording head inspection method of this embodiment is not particularly limited, and examples thereof include: a piezoelectric recording head and a thermal recording head. The recording head may also be, for example, a line recording head.

[0111] [Inspection steps]

[0112] In this step, the ejection performance of the recording head is checked. Specifically, in this step, the ejection performance of the recording head is checked by ejecting ink from the recording head. In the recording head checked in this step, ink may remain in the ink flow path.

[0113] In this step, the recording head after the inspection step may be cleaned. The method of cleaning the recording head is not particularly limited, and examples thereof include a method of filling the recording head with a cleaning liquid and then ejecting the cleaning liquid from the recording head. Examples of the cleaning liquid include a cleaning liquid containing water or a water-soluble organic solvent. In this step, even if the recording head is cleaned, it is difficult to completely remove the ink in the ink flow path.

[0114] [Filling steps]

[0115] In this step, the filling liquid is filled into the recording head. After this step, the recording head is stored for shipment or transported for shipment. After the recording head is delivered to the user, the filling liquid can be discharged from the recording head by ejecting the filling liquid from the recording head.

[0116] [Example]

[0117] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0118] In the examples, the Mw of the alkali-soluble resin and the surfactant were measured using a gel permeation chromatograph ("HLC-8020GPC" manufactured by Tosoh Corporation) under the following conditions. The 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.

[0119] (Measurement conditions of weight average molecular weight)

[0120] ·Chromatographic column: "TSKgel SuperMultiporeHZ-H" manufactured by Tosoh Corporation (4.6 mm I.D. × 15 cm semi-micro column)

[0121] Number of chromatographic columns: 3

[0122] Eluent: Tetrahydrofuran

[0123] Flow rate: 0.35mL / min

[0124] Sample injection volume: 10μL

[0125] Measurement temperature: 40℃

[0126] Detector: IR detector

[0127] [Study 1: Type and amount of moisturizer in filler solution]

[0128] First, the type and amount of the moisturizing agent used in the filling liquid were studied. The following is a method for preparing each raw material used in the production of the ink.

[0129] [Preparation of Pigment Dispersion]

[0130] A pigment dispersion (D-1) was prepared, and the pigment dispersion (D-1) was used for preparing ink. In the preparation of the pigment dispersion (D-1), a pigment coating resin solution containing a pigment coating resin (R-1) and water was first prepared.

[0131] (Preparation of Pigment-Coated Resin Solution)

[0132] Prepare an alkali-soluble resin having repeating units derived from methacrylic acid (MAA units), repeating units derived from methyl methacrylate (MMA units), repeating units derived from butyl acrylate (BA units), and repeating units derived from styrene (ST units). The weight average molecular weight (Mw) of the alkali-soluble resin is 20,000, and the acid value is 100 mgKOH / g. The mass ratio of each repeating unit in the alkali-soluble resin is "MAA unit: MMA unit: BA unit: ST unit = 40:15:30:15". The alkali-soluble resin and an aqueous solution of sodium hydroxide are mixed (neutralization treatment). Through the neutralization treatment, the alkali-soluble resin is neutralized using sodium hydroxide (NaOH). In the neutralization treatment, the amount of the aqueous solution of sodium hydroxide used is set to 1.05 times the theoretical value of the amount of the aqueous solution of sodium hydroxide required to neutralize the alkali-soluble resin. Thus, an equal amount (strictly speaking, 105% amount) of sodium hydroxide is used to neutralize the alkali-soluble resin. Thus, a pigment coating resin solution containing the pigment coating resin (R-1) (neutralized alkali-soluble resin) and water was obtained.

[0133] (Distributed Processing)

[0134] As shown in the following Table 3, magenta pigment (CI Pigment Red 122), the above-mentioned pigment coating resin solution containing pigment coating resin (R-1), surfactant A, and ion exchange water are put into the container of a medium-type wet disperser ("DYNO (Japanese registered trademark)-MILL") manufactured by Willy A. Bachofen, WAB).

[0135] In addition, the content ratio of "water" in the following Table 3 represents the total content ratio of the ion exchange water put into the above-mentioned container and the water contained in the pigment coating resin solution (specifically, the water contained in the sodium hydroxide aqueous solution used for neutralization of the alkali-soluble resin, and the water produced by the neutralization reaction of the alkali-soluble resin and sodium hydroxide). In addition, surfactant A represents an acetylene glycol surfactant (nonionic surfactant), i.e., "Olfin (Japanese registered trademark) E1010" (ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd.

[0136] [Table 3]

[0137] Pigment dispersion (D-1) Content ratio [mass%] Magenta pigment 15.0 Pigment-coated resin (R-1) (neutralized with NaOH) 6.0 Surfactant A 0.5 Water 78.5 Total 100.0

[0138] Next, the contents of the container were wet dispersed. Zirconia beads (particle size 1.0 mm) were used as the medium. The amount of the medium added was 70% by volume of the container capacity. The dispersion conditions were set at a temperature of 10° C. and a peripheral speed of 8 m / sec. Thus, a pigment dispersion was obtained.

[0139] The volume median diameter (D 50 Specifically, the obtained pigment dispersion (D-1) was diluted 300 times with ion exchange water and used as a measurement sample. The particle size distribution of the pigment particles in the measurement sample was measured using a dynamic light scattering particle size distribution measuring device ("Zetascope (Japanese registered trademark) NanoZ S" manufactured by Malvern). 50 The D of the pigment particles in the sample will be measured. 50 D as the pigment particles contained in the pigment dispersion (D-1) 50 In addition, the measurement was performed 10 times, and the average value of each measurement result was used as the D 50 The D of the pigment particles contained in the pigment dispersion (D-1) 50 is 100nm.

[0140] [Preparation of ink]

[0141] [Preparation of ink (I-1)]

[0142] Ion exchange water is added to a flask equipped with a stirrer ("Slyvan Model (Japanese registered trademark) BL-600" manufactured by Shinto Scientific Co., Ltd.). While stirring the contents using the above stirrer (stirring speed: 400 rpm), the pigment dispersion (D-1) (6.0 parts by mass of pigment, 2.4 parts by mass of pigment coating resin (R-1)), the surfactant (S-1) shown in Table 4 below, triethylene glycol mono-n-butyl ether, 2-pyrrolidone and glycerol are added in sequence. Table 4 below shows the details of the surfactant (S-1) used to prepare the ink (I-1). In addition, in Table 4 below, m+n, x and y represent the values ​​of m+n, x and y in the general formula (2) of the surfactant. In addition, in Table 4 below, "(R)" represents a registered trademark. The ratio of the input amount of each raw material is shown in Table 5 below.

[0143] [Table 4]

[0144] Surfactant m + n X Y Manufacturer Product name S-1 10.0 7.0 2.5 Nippon Shokubai Co., Ltd. Softanol (R) EP7025

[0145] [Table 5]

[0146] Ink (I-1) Input amount [mass%] Pigment dispersion (D-1) 40.0 Surfactant (S-1) 0.3 Triethylene glycol monobutyl ether 4.0 2-Pyrrolidone 5.0 Glycerol 20.0 Water Balance Total 100.0

[0147] [Preparation of filling solution]

[0148] Filling solutions (F-1) to (F-14) were prepared according to the method shown below. First, the details of moisturizers (M-1) to (M-12) used to prepare filling solutions (F-1) to (F-14) are as follows.

[0149] [Moisturizer (M-1) to (M-12)]

[0150] The compounds shown in Tables 6 and 7 below were prepared according to the method shown below and set as moisturizers (M-1) to (M-12). The viscosity of moisturizers (M-1) to (M-12) was measured at 25°C using a falling ball viscometer ("Lovis 2000" manufactured by Anton Paar). In addition, moisturizers (M-2) to (M-5) and (M-8) to (M-11) are specific moisturizers. In addition, moisturizers (M-2) to (M-5) are compounds in which a, b, and c are a=b=c in the general formula (1), and a+b+c is 6 to 18 and is a multiple of 3. In addition, moisturizers (M-8) to (M-12) are compounds in which a, b, and c are a=c≠b in the general formula (1). In addition, the moisturizing agents (M-8) to (M-12) are compounds of the general formula (1) wherein b is a+1 or a+2.

[0151] [Preparation of moisturizing agents (M-2) to (M-6)]

[0152] Polyethylene glycol and glycerol were reacted and etherified at 200°C. Thus, the compounds (M-2) to (M-6) shown in Table 6 were synthesized. The obtained compounds were confirmed to have peaks of glycerol and polyethylene glycol of 99% or more by high performance liquid chromatography (HPLC). Specifically, acetonitrile and water were added to the obtained compounds and mixed, and quantitative analysis was performed by HPLC under the following conditions.

[0153] HPLC apparatus: "HITACHID-7000" manufactured by Hitachi High-Tech Science Co., Ltd.

[0154] Flow rate: 1.0mL / min

[0155] Detector: Corona CAD Detector, manufactured by ESA Biosciences

[0156] (Analysis conditions for glycerol)

[0157] Chromatographic column: "TSK-GEL Amide-80" manufactured by Tosoh Corporation (5μm, 4.6×250mm)

[0158] Solution: 50% by volume acetonitrile / water (distilled water)

[0159] (Analysis conditions for polyethylene glycol)

[0160] ·Chromatographic column: "Inertsil C8-3" manufactured by GL Science (5μm, 4.6×150mm)

[0161] Solution: acetonitrile / water (distilled water)

[0162] After the volume ratio of acetonitrile in the solution was maintained at 45 volume % for 3 minutes, the volume ratio of acetonitrile was linearly changed from 45 volume % to 98 volume % over 9 minutes, and then the volume ratio of acetonitrile was maintained at 98 volume %.

[0163] [Preparation of moisturizing agent (M-1)]

[0164] The compounds as moisturizers (M-1) shown in Table 6 were synthesized by the same method as moisturizers (M-2) to (M-6), except that ethylene glycol was used instead of polyethylene glycol. The obtained compounds were confirmed to have peaks of glycerol and ethylene glycol of 99% or more by the same method as moisturizers (M-2) to (M-6).

[0165] [Preparation of moisturizing agents (M-7) to (M-12)]

[0166] The compounds as moisturizers (M-7) to (M-12) shown in Table 7 were synthesized by the same method as moisturizers (M-2) to (M-6) except that the following aspects were changed. In the synthesis of the compounds as moisturizers (M-7) to (M-12), first, polyethylene glycol and glycerol were reacted at 160°C to completely react the two α-hydroxyl groups bound to the primary carbon of glycerol. An intermediate was thus formed, and then the intermediate and polyethylene glycol were reacted at 220°C to completely react the β-hydroxyl groups bound to the secondary carbon of glycerol. Thus, the compounds as moisturizers (M-7) to (M-12) shown in Table 7 were synthesized. The obtained compounds were confirmed to have peak values ​​of glycerol and polyethylene glycol of 99% or more by the same method as moisturizers (M-1) to (M-6).

[0167] [Table 6]

[0168] Humectant M-1 M-2 M-3 M-4 M-5 M-6 a + b + c 3 6 9 15 18 21 A 1 2 3 5 6 7 B 1 2 3 5 6 7 C 1 2 3 5 6 7 Viscosity [mPa·s] 480 410 350 310 280 250

[0169] [Table 7]

[0170] Humectant M-7 M-8 M-9 M-10 M-11 M-12 a + b + c 4 8 11 17 19 23 a 1 2 3 5 6 7 b 2 4 5 7 7 9 c 1 2 3 5 6 7 Viscosity [mPa·s] 470 400 330 290 250 220

[0171] [Preparation of filling solution (F-1)]

[0172] 30.0 parts by mass of the moisturizer (M-1), 0.2 parts by mass of the surfactant (S-1) and ion exchange water were mixed to obtain a mixed solution. The amount of ion exchange water added was set to an amount that the total amount of the mixed solution was 100.0 parts by mass. This mixed solution was used as the filling solution (F-1).

[0173] [Preparation of filling solutions (F-2) to (F-14)]

[0174] Filling solutions (F-2) to (F-14) were prepared by the same method as that for the filling solution (F-1), except that the types and amounts of the components were changed as shown in Tables 8 to 10.

[0175] [Table 8]

[0176]

[0177] [Table 9]

[0178]

[0179] [Table 10]

[0180]

[0181]

[0182] [Ink set preparation]

[0183] The ink (I-1) and each of the filling liquids (F-1) to (F-14) were combined as shown in the following Tables 11 to 13. Ink sets of Examples 1 to 10 and Comparative Examples 1 to 4 were prepared in this manner.

[0184] [Evaluation 1]

[0185] The ink sets of Examples 1 to 10 and Comparative Examples 1 to 4 were evaluated by the following methods for the ink aggregation inhibition performance (performance of inhibiting the aggregation of the pigment components in the ink) in an open system (with evaporation) and a closed system (without evaporation), the flushing performance of the filling liquid (whether the filling liquid can be flushed after being left standing), and the introduction performance of the filling liquid (property of the filling liquid being easily introduced into the ink flow path in the recording head). The evaluation results are shown in Tables 11 to 13 below.

[0186] (Agglutination inhibition performance (open system))

[0187] 1.0 parts by mass of the ink (ink (I-1) in Study 1) in the ink set to be evaluated and 50.0 parts by mass of the filler (any of the fillers (F-1) to (F-14) in Study 1) were mixed in a beaker. Next, the beaker containing the mixed solution was not sealed and stored in a thermostatic chamber at 40°C for 1 month (storage treatment). The mixed solution after treatment was analyzed for the presence of aggregates with a particle size of 3 μm or more using a particle shape image analyzer ("FPIA (Japanese registered trademark)-3000" manufactured by Malvern Panalytical).

[0188] In addition, when filling the filling liquid into the recording head after the recording head is inspected, residual ink and the filling liquid are mixed inside the recording head. The mixing ratio of the residual ink and the filling liquid (amount of ink / amount of filling liquid) varies depending on the part of the recording head, and it is estimated that the maximum is about 1 / 50. Therefore, the mixing ratio of ink and the filling liquid is set to 1.0 mass parts of ink: 50.0 mass parts of filling liquid. In addition, agglomerates with a particle size of 3μm or more generated inside the recording head may clog the filter provided inside the recording head and cause poor ink ejection. Therefore, whether agglomerates with a particle size of 3μm or more are generated after the storage treatment is used as a criterion for determining whether ink agglomeration can be suppressed.

[0189] (Agglutination inhibition performance (closed system))

[0190] The "aggregation inhibition performance (closed system)" was evaluated by the same method as the evaluation of the "aggregation inhibition performance (open system)" described above, except that the following aspects were changed. In the evaluation of the "aggregation inhibition performance (closed system)", the beaker was sealed with a film during the storage treatment to prevent evaporation. Since the concentration of the pigment component due to solvent evaporation does not occur, the "aggregation inhibition performance (closed system)" is evaluated under mild conditions compared to the "aggregation inhibition performance (open system)".

[0191] (Judgment criteria for agglutination inhibition performance)

[0192] A (pass): No aggregates with a particle size of 3 μm or more were generated after storage in both the open system and the closed system

[0193] B (failure): Agglomerates with a particle size of 3 μm or more were generated in at least one of the open system and the closed system after storage treatment.

[0194] (Flushing)

[0195] When flushing the filling liquid from a recording head placed in a high temperature environment, the water-soluble organic solvent or water in the internal filling liquid in the placed recording head evaporates, so the filling liquid viscosity around the nozzle increases. When the filling liquid viscosity increases, the pressure (flushing pressure) of the recording head when flushing the filling liquid increases, which may damage the recording head. According to the research of the inventors of the present application, if the viscosity of the moisturizing agent at 25°C is 450mPa·s or less, the flushing pressure will not increase, and the filling liquid can be flushed smoothly without worrying about damaging the recording head. Therefore, whether the moisturizing agent viscosity at 25°C is 450mPa·s or less is used as a criterion for judging the flushability of the filling liquid (whether the filling liquid can be flushed after being placed).

[0196] (Criteria for judging flushability)

[0197] A (pass): Moisturizing agent viscosity at 25°C is 450 mPa·s or less

[0198] B (unqualified): The viscosity of the moisturizer at 25°C is greater than 450 mPa·s

[0199] (Introduction)

[0200] First, an unused recording head ("KJ4B-QA" manufactured by Kyocera Corporation, total number of nozzles: 2656) is filled with 100 ml of the ink contained in the ink set to be evaluated (ink (I-1) in Study 1) and ejected. Next, the recording head is cleaned with pure water and then dried thoroughly. Next, the recording head is filled with 300 ml of the filling liquid contained in the ink set to be evaluated (each of the filling liquids (F-1) to (F-14) in Study 1) and ejected. This operation is performed a total of 10 times. Then, the filling liquid is filled into the recording head again. Then, using the recording head filled with the filling liquid, a nozzle check pattern is printed on a glass plate. Thus, a nozzle check pattern is formed on the glass plate using the filling liquid. Next, the glass plate is read using a scanner, thereby counting the number of ejection nozzles that have ejected the filling liquid (the number of ejection nozzles). The ratio [%] (introduction rate) of the number of ejection nozzles to the total number of nozzles (2656) of the recording head was calculated using the following formula. The introducibility of the filling liquid was determined based on the following criteria.

[0201] Introduction rate = 100 × number of ejection nozzles / total number of nozzles

[0202] (Criteria for judging the importability)

[0203] A (qualified): introduction rate is more than 90%

[0204] B (Unqualified): Import rate is less than 90%

[0205] [Dynamic surface tension]

[0206] In addition, the dynamic surface tension of the ink of each Example and Comparative Example when the surface life is 10 milliseconds and the dynamic surface tension of the filling liquid of each Example and Comparative Example when the surface life is 10 milliseconds were measured by the maximum bubble pressure method at 25°C using a bubble pressure type dynamic surface tension meter ("BP 100" manufactured by KRUSS, capillary diameter: 0.4 mm). The measurement results are shown in the following Tables 11 to 13.

[0207] [Table 11]

[0208]

[0209] [Table 12]

[0210]

[0211] [Table 13]

[0212]

[0213]

[0214] In Tables 11 to 13, "Type of surfactant" indicates the type of surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling liquid. "Ratio of surfactant" indicates the content ratio [mass %] of the surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling liquid. "Type of moisturizer" indicates the type of moisturizer contained in the filling liquid. "Ratio of moisturizer" indicates the content ratio [mass %] of the moisturizer in the filling liquid.

[0215] As shown in Tables 3 to 13, the ink of each example contains a pigment, a first surfactant and an aqueous medium, and the filling liquid contains a specific moisturizing agent, a second surfactant and water. In addition, the specific moisturizing agent is a compound represented by the general formula (1), and the first surfactant and the second surfactant are compounds represented by the general formula (2).

[0216] As shown in Tables 3 to 13, when a+b+c in the moisturizing agent general formula (1) is less than 5, the flushing property of the filling liquid is unacceptable. On the other hand, when a+b+c in the moisturizing agent general formula (1) is greater than 20, sufficient ink aggregation inhibition performance cannot be obtained. Therefore, when a+b+c in the moisturizing agent general formula (1) is 5 or more and 20 or less, it is judged to be good.

[0217] In addition, as shown in Tables 3 to 13, when the content ratio of the specific moisturizing agent in the filling liquid is 10.0 mass % or more and 50.0 mass % or less, the evaluation result is good. It is understood that when the content ratio of the specific moisturizing agent in the filling liquid is within the above range, an ink set having the following characteristics can be reliably obtained: the filling liquid can be easily introduced into the ink flow path in the recording head, the aggregation of the pigment component in the ink in the recording head can be effectively suppressed, and the filling liquid can be stably flushed out.

[0218] [Study 2: Type and amount of surfactant]

[0219] Next, the type and amount of the surfactant contained in the filling liquid and the ink were examined.

[0220] [Preparation of surfactants (S-2) to (S-7)]

[0221] The above-mentioned surfactant (S-1) and surfactants (S-2) to (S-7) shown in the following Table 14 are prepared as surfactants. In the product names in the following Table 14, "(R)" represents a registered trademark. Among the surfactants (S-1) to (S-7), surfactants (S-1), (S-3) to (S-5) are compounds represented by the general formula (2). Surfactant (S-2) is a surfactant in which y=0.0 in the general formula (2) of the surfactant. Surfactant (S-6) is a surfactant in which y=1.0 in the general formula (2) of the surfactant. In the following Table 14, m+n, x and y represent the values ​​of m+n, x and y in the general formula (2) of the surfactant.

[0222] [Table 14]

[0223]

[0224] [Preparation of surfactant]

[0225] The compounds shown in Table 14 were prepared by the method shown below and were set as surfactants (S-2) to (S-6).

[0226] [Preparation of surfactant (S-2)]

[0227] 197 g (equivalent to 1 mole) of a branched alcohol satisfying the general formula (2) of m+n=10.0 and 3 g of KOH were mixed to obtain a mixed solution. Using an autoclave equipped with a stirring device, a temperature control device and an automatic introduction device, the mixed solution was reacted at 110°C and 1.3 kPa while being dehydrated for 30 minutes. In this way, part of the water in the mixed solution was removed. After the mixed solution was dehydrated, nitrogen was replaced and the autoclave was heated to 155°C. Then, 314 g (equivalent to 1 mole, equivalent to x in the general formula (2)) of ethylene oxide was added to the mixed solution in the autoclave by the automatic introduction device. After the addition of ethylene oxide, the autoclave was maintained at 155°C for 30 minutes. By gas chromatography analysis of the reaction solution, it was confirmed that there was no residue of each raw material component, and the compound obtained by the reaction was determined to be the target substance having the m+n value, x value and y value shown in Table 14. The compound obtained by the reaction was set as surfactant (S-2).

[0228] [Preparation of surfactants (S-3) to (S-6)]

[0229] The compounds of surfactants (S-3) to (S-6) shown in Table 14 were synthesized by the same method as for the preparation of surfactant (S-2), except that the types and amounts of the raw materials used and the reaction time were changed so that the values ​​of m+n, x and y in the general formula (2) became the values ​​shown in Table 14. Branched alcohols react preferentially with the ethylene oxide portion rather than the propylene oxide portion. Therefore, by changing the types and amounts of the raw materials used and the reaction time, surfactants (S-3) to (S-6) shown in Table 14 can be prepared.

[0230] [Preparation of inks (I-2) to (I-10)]

[0231] Inks (I-2) to (I-10) were prepared by the same method as that for ink (I-1), except that the types and input amounts of each raw material were changed as shown in Table 15 or Table 16. In addition, "TGBE" in Table 15 and Table 16 represents triethylene glycol mono-n-butyl ether.

[0232] [Table 15]

[0233]

[0234] [Table 16]

[0235]

[0236]

[0237] [Preparation of filling solutions (F-15) to (F-23)]

[0238] Filling solutions (F-15) to (F-23) were prepared by the same method as that for preparing the filling solution (F-1), except that the types and amounts of the components were changed as shown in Table 17 or Table 18.

[0239] [Table 17]

[0240]

[0241] [Table 18]

[0242]

[0243] [Ink set preparation]

[0244] As shown in Tables 19 to 21 below, any one of inks (I-1) to (I-10) and any one of filler liquids (F-2) and (F-15) to (F-23) were combined to prepare ink sets of Examples 11 to 18 and Comparative Examples 5 to 10.

[0245] [Evaluation 2]

[0246] The ink sets of Examples 11 to 18 and Comparative Examples 5 to 10 were evaluated for their agglomeration inhibition performance, flushing properties of the filling liquid, and inlet properties of the filling liquid by the same method as described in [Evaluation 1]. However, in [Evaluation 2], the ink of the ink set to be evaluated was any one of inks (I-1) to (I-10) as described above. In addition, the filling liquid of the ink set to be evaluated was any one of filling liquids (F-2) and (F-15) to (F-23). ​​The evaluation results are shown in Tables 19 to 21 below. In addition, the dynamic surface tension of the ink surface life of each Example and Comparative Example when it was 10 milliseconds, and the dynamic surface tension of the filling liquid surface life of each Example and Comparative Example when it was 10 milliseconds were measured by the method described in [Study 1: Type of filling liquid moisturizer]. The measurement results are shown in Tables 19 to 21 below.

[0247] [Table 19]

[0248]

[0249] [Table 20]

[0250]

[0251]

[0252] [Table 21]

[0253]

[0254] In Tables 19 to 21, "Type of surfactant" indicates the type of surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling liquid. "Ratio of surfactant" indicates the content ratio [mass %] of the surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling liquid. "Type of moisturizer" indicates the type of moisturizer contained in the filling liquid. "Ratio of moisturizer" indicates the content ratio [mass %] of the moisturizer in the filling liquid.

[0255] As shown in Tables 14 to 21, the ink of each example contains a pigment, a first surfactant and an aqueous medium, and the filling liquid contains a specific moisturizing agent, a second surfactant and water. In addition, the specific moisturizing agent is a compound represented by the general formula (1), and the first surfactant and the second surfactant are compounds represented by the general formula (2).

[0256] As shown in Tables 14 to 21, when the first surfactant and the second surfactant are compounds represented by the general formula (2), the filling liquid can be easily introduced into the ink flow path in the recording head.

[0257] However, as shown in Comparative Example 7, when the ink and the filling liquid do not contain a surfactant, the dynamic surface tension of the ink and the filling liquid is high, and it is difficult to introduce the filling liquid into the ink flow path in the recording head. When the ink and the filling liquid do not contain a surfactant, the dynamic surface tension of the ink and the filling liquid at 25° C. when the surface life is 10 milliseconds is 35 mN / m or more.

[0258] In addition, as shown in Comparative Example 5, when a compound containing no propylene oxide group and having y=0.0 in the general formula (2) is used as the surfactant of the ink, the dynamic surface tension of the ink increases, resulting in difficulty in introducing the filling liquid into the ink flow path in the recording head. In this case, the dynamic surface tension of the ink at 25°C when the surface life is 10 milliseconds is 35 mN / m or more.

[0259] In addition, as shown in Comparative Example 6, when a compound containing no propylene oxide group and having y=0.0 in the general formula (2) is used as the surfactant of the filling liquid, the dynamic surface tension of the filling liquid increases, and it is difficult to introduce the filling liquid into the ink flow path in the recording head. In this case, the dynamic surface tension of the filling liquid at 25° C. when the surface life is 10 milliseconds is 35 mN / m or more.

[0260] In addition, as shown in Comparative Example 8, when the compound of y=1.0 in the general formula (2) is used as the surfactant of the ink and the surfactant of the filling liquid, the dynamic surface tension of the ink and the filling liquid also increases, making it difficult to introduce the filling liquid into the ink flow path in the recording head. When the compound of y=1.0 in the general formula (2) is used as the first surfactant and the second surfactant, the dynamic surface tension of the ink and the filling liquid at 25° C. when the surface life is 10 milliseconds is 35 mN / m or more.

[0261] In addition, as shown in Tables 14 to 21, it can be seen that the first surfactant and the second surfactant are preferably the same compound, but they may also be different compounds as long as they are independent of each other and are compounds represented by general formula (2).

[0262] In addition, as shown in Tables 14 to 21, when the content ratio of the first surfactant in the ink is 0.1 mass % or more and 2.5 mass % or less, the evaluation result is good. It can be seen that when the content ratio of the first surfactant in the ink is within the above range, an ink set having the following characteristics can be reliably obtained: the filling liquid can be easily introduced into the ink flow path in the recording head, the aggregation of the pigment component in the ink in the recording head can be effectively suppressed, and the filling liquid can be stably flushed out.

[0263] In addition, as shown in Tables 14 to 21, when the content ratio of the second surfactant in the filling liquid is 0.1 mass % or more and 2.5 mass % or less, the evaluation result is good. It can be seen that when the content ratio of the second surfactant in the filling liquid is within the above range, an ink set having the following characteristics can be reliably obtained: the filling liquid can be easily introduced into the ink flow path in the recording head, the aggregation of the pigment component in the ink in the recording head can be effectively suppressed, and the filling liquid can be stably flushed.

Claims

1. An ink set comprising ink for inkjet and a recording head filling liquid, The inkjet ink contains a pigment, a first surfactant and an aqueous medium. The recording head filling liquid contains a specific moisturizing agent, a second surfactant and water, The specific moisturizing agent is a compound represented by the following general formula (1): The first surfactant and the second surfactant are independent of each other and are compounds represented by the following general formula (2): In the general formula (1), a, b and c are independent of each other and represent an integer greater than 1, and a+b+c is greater than or equal to 5 and less than or equal to 20. In the general formula (2), m and n are independent of each other and represent a number of 0.0 to 12.0, m+n is 8.0 to 12.0, x represents a number of 1.0 to 20.0, and y represents a number of 2.0 to 10.

0.

2. The ink set according to claim 1, characterized in that: The specific moisturizing agent has a viscosity of 230 mPa·s or more and 450 mPa·s or less at 25°C.

3. The ink set according to claim 1 or 2, characterized in that: The content ratio of the specific moisturizing agent in the recording head filling liquid is 10.0 mass % or more and 50.0 mass % or less.

4. The ink set according to claim 1 or 2, characterized in that: The content ratio of the first surfactant in the inkjet ink is 0.1 mass % or more and 2.5 mass % or less.

5. The ink set according to claim 1 or 2, characterized in that: The content ratio of the second surfactant in the recording head filling liquid is 0.1 mass % or more and 2.5 mass % or less.

6. The ink set according to claim 1 or 2, characterized in that: The first surfactant and the second surfactant are the same compound.

7. The ink set according to claim 1 or 2, characterized in that: In the general formula (1), a, b, and c are a=b=c, and a+b+c is 6 to 18 and is a multiple of 3.

8. The ink set according to claim 1 or 2, characterized in that: In the general formula (1), a, b, and c satisfy a=c≠b.

9. The ink set according to claim 8, characterized in that In the general formula (1), b is a+1 or a+2.

10. A recording head inspection method using the ink set according to claim 1 or 2, comprising: An inspection step of inspecting the ejection performance of the recording head; as well as a filling step of filling the recording head with the recording head filling liquid after the inspection step, In the inspection step, the ejection performance of the recording head is inspected by ejecting the inkjet ink from the recording head.

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