Recording head filling liquid, ink set, and recording head inspection method

Abstract

The invention provides a recording head filling liquid, an ink set, and a recording head inspection method. The recording head filling liquid contains a specific humectant, a monovalent alkali, and water. The specific humectant is a compound represented by general formula (1). The content ratio of the specific humectant is from 19.00% by mass to 42.00% by mass (inclusive). The recording head filling liquid has a static surface tension at 25 DEG C of from 20.0 mN / m to 29.0 mN / m (inclusive). # imgabs0 # (In general formula (1), a, b, and c independently represent an integer of 1 or more, and a + b + c is 4-20 (inclusive).

Description

Technical Field

[0001] The present invention relates to a recording head filling liquid, 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] As for the recording head filling liquid, for example, a recording head filling liquid containing silicone oil has been proposed. Summary of the invention

[0007] However, the above-mentioned recording head filling liquid cannot satisfy the above-mentioned requirements.

[0008] The present invention is made in view of the above problems, and its object is to provide a recording head filling liquid that can be easily introduced 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 be stably flushed out. Another object of the present invention is to provide an ink set and a recording head inspection method using the above recording head filling liquid.

[0009] The recording head filling liquid involved in the present invention contains a specific moisturizing agent, a monovalent base and water. The specific moisturizing agent is a compound represented by the following general formula (1). The content ratio of the specific moisturizing agent is 19.00 mass % or more and 42.00 mass % or less. The static surface tension of the recording head filling liquid at 25°C is 20.0 mN / m or more and 29.0 mN / m or less.

[0010]

[0011] In the general formula (1), a, b and c are independent of each other and represent an integer greater than or equal to 1, and a+b+c is greater than or equal to 4 and less than or equal to 20.

[0012] The ink set according to the present invention comprises an inkjet ink and the above-mentioned recording head filling liquid.

[0013] The recording head inspection method according to 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 filling liquid into the recording head after the inspection step. In the inspection step, the ejection performance of the recording head is inspected by ejecting the inkjet ink using the recording head.

[0014] [Effects of the Invention]

[0015] According to the recording head filling liquid and ink set involved in the present invention, the recording head filling liquid can be easily introduced into the ink flow path in the recording head, the pigment component in the inkjet ink can be effectively suppressed from agglomerating in the recording head, and the recording head filling liquid can be stably flushed out. According to the recording head inspection method involved in the present invention, the occurrence of ejection failure in the recording head after inspection can be suppressed. DETAILED DESCRIPTION

[0016] 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 (“Zetasizer (registered trademark in Japan) Nano ZS” manufactured by Malvern).

[0017] 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.

[0018] Hereinafter, unless otherwise specified, the measured value of static surface tension is a value measured at 25° C. using a surface tensiometer (eg, “Automatic Surface Tensiometer DY-300” manufactured by Kyowa Interface Science Co., Ltd.) based on the Wilhelmy method (plate method).

[0019] Hereinafter, unless otherwise specified, the measured values ​​of viscosity are values ​​measured at 25° C. using a falling ball viscometer (“Lovis 2000” manufactured by Anton Paar).

[0020] Hereinafter, unless otherwise specified, the measured value of pH is a value measured at 25° C. using a pH meter (for example, “D-51” manufactured by Horiba, Ltd.).

[0021] In this specification, acryl and methacryl are sometimes collectively referred to as "(meth)acryl". Each component described in this specification may be used alone or in combination of two or more. "At least one of A and B" means "A and / or B".

[0022] [First Embodiment: Recording Head Filling Liquid]

[0023] The following is a description of the recording head filling liquid (hereinafter sometimes referred to as the filling liquid) involved in the first embodiment of the present invention. The filling liquid involved in this embodiment contains a specific moisturizing agent, a monovalent base and water. The specific moisturizing agent is a compound represented by the following general formula (1). The content ratio of the specific moisturizing agent is not less than 19.00 mass % and not more than 42.00 mass %. The static surface tension of the filling liquid involved in this embodiment at 25°C is not less than 20.0 mN / m and not more than 29.0 mN / m.

[0024]

[0025] In the general formula (1), a, b and c are each independently an integer greater than or equal to 1, and a+b+c is greater than or equal to 4 and less than or equal to 20.

[0026] The filling liquid involved in this embodiment is used to fill the recording head in which inkjet ink (hereinafter, sometimes simply referred to as ink) remains. Specifically, the filling liquid involved in this embodiment 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 filling liquid involved in this embodiment is preferably used as the filling liquid used in the ink set involved in the second embodiment or the recording head inspection method involved in the third embodiment.

[0027] The filling liquid of this embodiment can be easily introduced into the ink flow path in the recording head by having the above structure, and can effectively suppress the aggregation of the pigment component in the ink in the recording head and can be flushed out stably. The reason why the filling liquid of this embodiment produces the above effect is speculated as follows.

[0028] The filling liquid involved in this embodiment contains a specific wetting agent, a monovalent base and water. The filling liquid involved in this embodiment enters the ink flow path of the recording head to dilute the ink remaining in the ink flow path. As a result, the solid components of the ink remaining in the ink flow path become difficult to agglomerate. In particular, the filling liquid involved in this embodiment contains a specific wetting agent represented by the general formula (1). The viscosity of the specific wetting agent in which a+b+c in the general formula (1) is 4 or more is low, and the pressure (flushing pressure) of the recording head when flushing the filling liquid involved in this embodiment does not increase. Therefore, the filling liquid involved in this embodiment can be stably flushed out of the recording head even after the recording head is placed. In addition, although the reason is not clear, according to the research of the inventor of this application, the wetting agent in which a+b+c in the general formula (1) exceeds 20 cannot fully inhibit the aggregation of the pigment component in the ink in the recording head. The filling liquid according to the present embodiment contains a specific moisturizing agent in which a+b+c in the general formula (1) is 4 or more and 20 or less, thereby being able to sufficiently suppress the aggregation of the pigment components in the ink in the recording head and being able to be flushed out stably. In particular, the filling liquid according to the present embodiment contains the specific moisturizing agent represented by the general formula (1) in a ratio of 19.00 mass % or more and 42.00 mass % or less, thereby being able to effectively suppress the aggregation of the pigment components in the ink in the recording head.

[0029] Furthermore, the filling liquid involved in this embodiment can effectively suppress the aggregation of the pigment components in the ink by containing a monovalent base, and can maintain high dispersion stability of the pigment components. According to the research of the inventors of this application, fillers without alkali cannot fully suppress the aggregation of the pigment components in the ink in the recording head. Furthermore, when the filling liquid contains a divalent base instead of a monovalent base, the filling liquid cannot ensure the dispersion stability of the pigment components and cannot fully suppress the aggregation of the pigment components in the ink in the recording head.

[0030] The filling liquid of the present embodiment has a static surface tension of 20.0 mN / m or more and 29.0 mN / m or less at 25° C. The filling liquid of the present embodiment has a low static surface tension and is easily introduced into the ink flow path in the recording head. The filling liquid of the present embodiment is described in more detail below.

[0031] The static surface tension of the filling liquid according to the present embodiment at 25° C. may be 20.0 mN / m to 29.0 mN / m, preferably 27.0 mN / m to 29.0 mN / m, and more preferably 28.0 mN / m to 29.0 mN / m. When the static surface tension of the filling liquid according to the present embodiment at 25° C. is 27.0 mN / m to 29.0 mN / m, the filling liquid according to the present embodiment can be reliably introduced into the ink flow path in the recording head.

[0032] The pH value of the filling liquid according to the present embodiment is preferably 7 to 10, more preferably 8 to 9. By setting the pH value of the filling liquid according to the present embodiment to 7 to 10, the filling liquid according to the present embodiment can more effectively suppress the aggregation of the pigment component in the ink in the recording head.

[0033] (Specific moisturizer)

[0034] The specific moisturizing agent involved in this embodiment is a compound represented by the above-mentioned general formula (1). In the general formula (1), a+b+c can be an integer of 4 to 20, preferably an integer of 6 to 18, more preferably an integer of 6 to 15, and even more preferably an integer of 6 to 9. The filling liquid involved in this embodiment contains a specific moisturizing agent with low viscosity (for example, a specific moisturizing agent with a viscosity of 450 mPa·s or less at 25°C), so that the filling liquid involved in this embodiment can be stably flushed out from the recording head even after the recording head is left. In addition, when a+b+c in the general formula (1) is an integer of 4 to 20, the high dispersion stability of the pigment component in the ink can be maintained, and the aggregation of the pigment component in the ink in the recording head can be effectively suppressed. In addition, by making a+b+c in the general formula (1) be 6 to 18, the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0035] The viscosity of the specific moisturizing agent at 25° C. is preferably 260 mPa·s to 450 mPa·s, and more preferably 330 mPa·s to 450 mPa·s. By setting the viscosity of the specific moisturizing agent to 260 mPa·s to 450 mPa·s, it is possible to effectively suppress the aggregation of the pigment component in the ink in the recording head. In addition, after the recording head is placed, the filling liquid involved in this embodiment can be stably flushed out from the recording head.

[0036] The content ratio of the specific moisturizing agent in the filling liquid involved in the present embodiment can be 19.00 mass% or more and 42.00 mass% or less, preferably 27.00 mass% or more and 38.00 mass% or less, and more preferably 27.00 mass% or more and 33.00 mass% or less. By making the content ratio of the specific moisturizing agent in the filling liquid involved in the present embodiment 19.00 mass% or more and 42.00 mass% or less, it is possible to effectively suppress the aggregation of the pigment components in the ink in the recording head. In addition, by making the content ratio of the specific moisturizing agent in the filling liquid involved in the present embodiment 27.00 mass% or more and 38.00 mass% or less, it is possible to more effectively suppress the aggregation of the pigment components in the ink in the recording head.

[0037] (monovalent alkali)

[0038] Examples of monovalent bases include sodium compounds, potassium compounds, lithium compounds, cesium compounds, and rubidium compounds. Examples of these monovalent bases include hydroxides, carbonates, and bicarbonates with alkali metal ions as cations. Examples of sodium compounds include sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and sodium bicarbonate (NaHCO3). Examples of potassium compounds include potassium hydroxide (KOH), potassium carbonate (K2CO3), and potassium bicarbonate (KHCO3). Examples of lithium compounds include lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium bicarbonate (LiHCO3). Examples of cesium compounds include cesium hydroxide (CsOH), cesium carbonate (Cs2CO3), and cesium bicarbonate (CsHCO3). Examples of rubidium compounds include rubidium hydroxide (RbOH), rubidium carbonate (Rb2CO3), and rubidium bicarbonate (RbHCO3). The monovalent base is dissolved in water, ionized into alkali metal ions and counter ions, and exhibits alkalinity (pH value ≥ 7). The monovalent base is preferably a hydroxide, and sodium hydroxide is particularly preferred.

[0039] The filling liquid according to the present embodiment can effectively suppress the aggregation of the pigment component in the ink in the recording head by containing a monovalent base, and can maintain high dispersion stability of the pigment component. In particular, the filling liquid according to the present embodiment contains the above-mentioned specific moisturizing agent as a moisturizing agent, so that the pigment component in the ink has high dispersion stability. Therefore, the filling liquid according to the present embodiment has a high degree of freedom in selecting anions that can be used as counter ions of alkali metal ions.

[0040] (water)

[0041] Water is the main solvent of the filling solution according to the present embodiment. The content of water in the filling solution according to the present embodiment is, for example, preferably 45.00 mass % or more and 80.00 mass % or less, and more preferably 60.00 mass % or more and 75.00 mass % or less.

[0042] (Surfactant)

[0043] The filling liquid involved in the present embodiment preferably also contains a surfactant. The surfactant reduces the static surface tension of the filler involved in the present embodiment at 25°C, so that the filling liquid involved in the present embodiment can be easily introduced into the ink flow path in the recording head. The surfactant in the filler involved in the present embodiment is preferably a nonionic surfactant. The nonionic surfactant contained in the filling liquid involved in the present embodiment is preferably an acetylene glycol type surfactant. The acetylene glycol type surfactant has the effect of optimizing the wettability of the filling liquid involved in the present embodiment to the stainless steel material, and the material of the recording head flow path is usually made of stainless steel. Therefore, the filling liquid involved in the present embodiment contains an acetylene glycol type surfactant, so that it can be easily introduced into the ink flow path in the recording head. The acetylene glycol surfactant contained in the filling liquid involved in the present embodiment can be cited as: "OLFINE (Japanese registered trademark) E1010" (manufactured by Nissin Chemical Industry Co., Ltd., ethylene oxide adduct of acetylene glycol).

[0044] The content ratio of the surfactant in the filling liquid involved in the present embodiment is preferably 0.05 mass % or more and 0.10 mass % or less, and more preferably 0.05 mass % or more and 0.07 mass % or less. By making the content ratio of the surfactant in the filling liquid involved in the present embodiment 0.05 mass % or more, the filling liquid involved in the present embodiment is more easily introduced into the ink flow path in the recording head, and can more effectively suppress the aggregation of the pigment components in the ink in the recording head. On the other hand, a large amount of surfactant sometimes reduces the dispersion stability of the pigment components in the ink. Therefore, by making the content ratio of the surfactant in the filling liquid involved in the present embodiment 0.10 mass % or less, the filling liquid involved in the present embodiment can more effectively suppress the aggregation of the pigment components in the ink in the recording head.

[0045] (Other ingredients)

[0046] The filling liquid according to the present embodiment may further contain well-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.

[0047] (Preferred components)

[0048] The filling liquid involved in this embodiment preferably has one of the components 1 to 13 in Table 1 below. In addition, in Table 1 below, "ratio" represents a numerical range of a preferred content ratio [mass %]. For example, the ratio of the specific moisturizer in component 1 "27.00-33.00" means that the specific moisturizer is contained in a ratio of 27.00 mass % to 33.00 mass %. The types of specific moisturizers "M-2", "M-3", "M-4" and "M-5" respectively represent the specific moisturizers (M-2), (M-3), (M-4) and (M-5) used in the examples.

[0049]

Table 1

[0050]

[0051] (Method for producing filling liquid)

[0052] For example, the filling solution according to the present embodiment can be produced by mixing a specific moisturizing agent, a monovalent base, water, and other components (eg, a surfactant) added as needed. The specific moisturizing agent can be produced by reacting polyethylene glycol and glycerol at 180 to 220°C for etherification.

[0053] [Second embodiment: ink set]

[0054] Hereinafter, an ink set according to a second embodiment of the present invention will be described. The ink set according to this embodiment includes ink and the filling liquid according to the first embodiment. Detailed information on the filling liquid has been described in the first embodiment and is therefore omitted.

[0055] The ink set according to this embodiment uses the filling liquid according to the first embodiment, so 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.

[0056] [Ink]

[0057] The ink preferably contains a pigment, a pigment-encapsulating resin, and water. In the ink, the pigment, for example, forms pigment particles together with the pigment-encapsulating resin. The pigment particles are dispersed in a solvent. Based on the viewpoint of optimizing the color concentration, hue, or stability of the ink, the D 50 The diameter is preferably from 30 nm to 250 nm, and more preferably from 70 nm to 130 nm.

[0058] (pigment)

[0059] 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).

[0060] The content of the pigment in the ink is preferably 2.00% by mass or more and 15.00% by mass or less, and more preferably 5.00% by mass or more and 10.00% by mass or less. By setting the content of the pigment to 2.00% by mass or more, it is easy to form an image with a desired image density. In addition, by setting the content of the pigment to 15.00% by mass or less, the fluidity of the ink can be ensured.

[0061] (Pigment coated resin)

[0062] 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 make the pigment particles dispersible. A portion of the pigment coating resin exists in a state of being dissolved in the ink, for example.

[0063] Examples of the pigment coating resin include copolymers of at least one monomer selected from the group consisting of (meth)acrylic acid alkyl ester, styrene and vinylnaphthalene, and at least one monomer selected from the group consisting of (meth)acrylic acid and maleic acid.

[0064] The pigment coating resin is preferably a styrene-(meth)acrylic resin. The styrene-(meth)acrylic resin has repeating units from at least one monomer of a (meth)acrylic acid alkyl ester and (meth)acrylic acid, and also has a styrene unit. Examples of (meth)acrylic acid alkyl esters include: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. The styrene-(meth)acrylic resin is preferably a copolymer (X) copolymerized by 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 and sodium hydroxide).

[0065] Among all the repeating units possessed by the copolymer (X), the content ratio of the repeating units derived from styrene is preferably 10.00 mass % or more and 20.00 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 10.00 mass % or more and 20.00 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 35.00 mass % or more and 45.00 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 25.00 mass % or more and 35.00 mass % or less.

[0066] The content of the pigment coating resin in the ink is preferably 0.70 mass % to 6.00 mass %, more preferably 2.00 mass % to 4.00 mass %. By setting the content of the pigment coating resin to 0.70 mass % to 6.00 mass %, clogging of the nozzle by the ink can be suppressed.

[0067] The acid value of the pigment coating resin is preferably 30 mgKOH / g to 300 mgKOH / g, more preferably 50 mgKOH / g to 150 KOH / g. By making the acid value of the pigment coating resin 30 mgKOH / g to 300 mgKOH / g, the dispersibility of the pigment particles (pigment component) can be optimized and the storage stability of the ink can be optimized.

[0068] The acid value of the pigment-coated resin can be adjusted by changing the amount of monomers used in the synthesis process of the pigment-coated resin. For example, in the synthesis process of the pigment-coated resin, the acid value of the pigment-coated resin can be increased by using monomers having acidic functional groups (e.g., carboxyl groups) (more specifically, acrylic acid, methacrylic acid, etc.).

[0069] The Mw of the pigment coating resin is, for example, 10000 to 50000. By setting the Mw of the pigment coating resin to 10000 to 50000, the viscosity of the ink can be suppressed from increasing and the image density of an image formed by the ink can be made to reach a desired value.

[0070] 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.).

[0071] In the polymerization of the pigment-coated resin, the amount of the polymerization initiator used is preferably 0.001 mol to 5 mol, more preferably 0.01 mol to 2 mol, relative to 1 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 hours to 24 hours. In addition, the pigment-coated resin after polymerization can be used directly as a raw material for ink, or it can be used as a raw material for ink after being neutralized in equal amounts using an alkaline compound. The alkaline compound is preferably a hydroxide of an alkali metal ion (e.g., NaOH).

[0072] (Aqueous medium)

[0073] The aqueous medium contained in the ink refers to a medium containing water. The aqueous medium can be used as a solvent or a dispersion medium. Specific examples of the aqueous medium include aqueous media containing water and a water-soluble organic solvent.

[0074] The content ratio of the aqueous medium in the ink is preferably 30.00 mass % or more and 95.00 mass % or less, and more preferably 70.00 mass % or more and 95.00 mass % or less.

[0075] (water)

[0076] Water is the main solvent of the ink. The content of water in the ink is, for example, preferably from 20.00 mass % to 90.00 mass %, and more preferably from 50.00 mass % to 80.00 mass %.

[0077] (Water-soluble organic solvent)

[0078] 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, glycerol, and dimethyl sulfoxide.

[0079] 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-1,3-butanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0080] 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.

[0081] Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0082] Examples of the nitrogen-containing compound include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0083] As an example of the acetate compound, diethylene glycol monoethyl ether acetate can be mentioned.

[0084] The water-soluble organic solvent in the ink is preferably triethylene glycol monobutyl ether, 2-pyrrolidone or glycerol.

[0085] The content of the water-soluble organic solvent in the ink is preferably 10.00 mass % to 80.00 mass %, more preferably 20.00 mass % to 40.00 mass %. By setting the content of the water-soluble organic solvent to 10.00 mass % to 80.00 mass %, the ejection stability of the ink can be optimized.

[0086] (Surfactant)

[0087] The ink preferably further contains a surfactant. The surfactant optimizes the compatibility and dispersion stability of the components contained in the ink. In addition, the surfactant makes the ink wettable with respect to the recording medium. The surfactant in the ink is preferably a nonionic surfactant.

[0088] Examples of nonionic surfactants in ink include acetylene glycol type surfactants (surfactants containing acetylene glycol compounds), silicone type surfactants (surfactants containing silicone compounds), and fluorine type surfactants (surfactants containing fluorine resins or fluorine-containing compounds). Examples of acetylene glycol type surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol.

[0089] When the ink contains a surfactant, the content ratio of the surfactant in the ink is preferably 0.10 mass % to 1.00 mass %, and more preferably 0.20 mass % to 0.40 mass %.

[0090] (additive)

[0091] The ink may further contain well-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.

[0092] (Preferred components)

[0093] The ink preferably has the composition shown in Table 2 below. In addition, the pigment ratio "5.40-6.60" of component 1 in Table 2 below means that the pigment is contained in a ratio of 5.40 mass % to 6.60 mass %. The descriptions of other columns are the same. "Resin" means a pigment coating resin. "TGBE" means triethylene glycol mono-n-butyl ether.

[0094]

Table 2

[0095]

[0096] (Method for producing ink)

[0097] For example, ink can be produced by mixing a pigment dispersion containing a pigment, an aqueous medium, and components added as needed (e.g., a surfactant). The pigment dispersion contains a pigment, a pigment-coated resin, and water. For example, an alkali-soluble resin is neutralized in equal amounts by an alkaline compound (e.g., sodium hydroxide), thereby preparing the pigment-coated resin. After the pigment is added to an aqueous solution containing the pigment-coated resin, a dispersion treatment is performed, thereby preparing the pigment dispersion. An example of the device used in the dispersion treatment is a bead mill. In the manufacture of ink, after the dispersion treatment, foreign matter and coarse particles can also be removed by a filter (e.g., a filter with a pore size of 5 μm or less).

[0098] [Third Embodiment: Recording Head Inspection Method]

[0099] Hereinafter, a recording head inspection method according to a third 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 second embodiment, and includes an inspection process for inspecting the ejection performance of the recording head and a filling process for filling the recording head after the inspection process with the filling liquid according to the first embodiment. In the inspection process, the ejection performance of the recording head is inspected by ejecting ink for inkjet using the recording head. The ink set used in the recording head inspection method according to this embodiment may be the same as the ink set described in the second embodiment. Furthermore, the filling liquid used in the recording head inspection method according to this embodiment may be the same as the filling liquid described in the first embodiment. Therefore, repeated descriptions are omitted.

[0100] The recording head inspection method according to the present embodiment uses the ink set according to the second embodiment, and thus can suppress ejection failures of the recording head after inspection. The recording head inspection method according to the present embodiment is performed, for example, before the recording head manufacturer ships the recording head. The recording head inspected using the recording head inspection method according to the present embodiment is not particularly limited, and examples include piezoelectric recording heads and thermal recording heads. The recording head may also be, for example, a line recording head.

[0101] [Inspection process]

[0102] In this step, the ejection performance of the recording head is inspected. Specifically, in this step, the ejection performance of the recording head is inspected by ejecting ink using the recording head. In the recording head inspected in this step, ink remains in the ink flow path.

[0103] In this process, the recording head after the inspection process may also be cleaned. The method of cleaning the recording head is not particularly limited, and an example of this is a method of filling the recording head with a cleaning liquid and then ejecting the cleaning liquid from the recording head. The cleaning liquid may be, for example, a cleaning liquid containing water or a water-soluble organic solvent. In this process, even if the recording head is cleaned, it is difficult to completely remove the ink in the ink flow path.

[0104] [Filling process]

[0105] In this process, the filling liquid involved in the first embodiment is filled into the recording head. After this process, the recording head is stored for shipment, or transported for shipment. After the recording head is delivered to the user, the filling liquid involved in the first embodiment can be discharged from the recording head by ejecting the filling liquid involved in the first embodiment from the recording head.

[0106] [Example]

[0107] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0108] 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 created 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. The pH value of the filling liquid is a value measured at 25°C using a pH detector (e.g., "D-51" manufactured by Horiba, Ltd.).

[0109] (Measurement conditions of weight average molecular weight)

[0110] ·Chromatographic column: "TSKgel SuperMultipore HZ-H" manufactured by Tosoh Corporation (semi-micro column of 4.6 mm I.D. × 15 cm)

[0111] Number of columns: 3

[0112] Eluent: Tetrahydrofuran

[0113] Flow rate: 0.35mL / min

[0114] Sample injection volume: 10μL

[0115] Measurement temperature: 40℃

[0116] Detector: IR detector

[0117] [Study 1: Types of moisturizers in fillers]

[0118] First, the types of moisturizers used in the filling solution are examined. The following describes the preparation methods of each raw material used in the production of the ink.

[0119] [Preparation of Pigment Dispersion]

[0120] A pigment dispersion (D-1) used in the preparation of the ink was prepared. In the preparation of the pigment dispersion (D-1), first, a pigment coating resin solution containing the pigment coating resin (R) and water was prepared.

[0121] (Preparation of Pigment-Coated Resin Solution)

[0122] 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 is mixed with an aqueous sodium hydroxide solution (neutralization treatment). Through the neutralization treatment, the alkali-soluble resin is neutralized with sodium hydroxide (NaOH). In the neutralization treatment, the amount of the aqueous sodium hydroxide solution used is 1.05 times the theoretical value of the amount of the aqueous sodium hydroxide solution required to neutralize the alkali-soluble resin. Thus, the alkali-soluble resin is neutralized with an equal amount (strictly speaking, 105% of the amount) of sodium hydroxide. Thus, a pigment coating resin solution containing the pigment coating resin (R) (neutralized alkali-soluble resin) and water is obtained.

[0123] (Distributed Processing)

[0124] As shown in the following Table 3, magenta pigment (CI Pigment Red 122), the above-mentioned pigment coating resin solution containing the pigment coating resin (R), surfactant A and ion exchange water are put into the vessel of a medium-type wet disperser ("DYNO (Japanese registered trademark) MILL" manufactured by Willy A. Bachofen (WAB)).

[0125] 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 generated by the neutralization reaction of the alkali-soluble resin and sodium hydroxide). In addition, the surfactant A is "OLFINE (Japanese registered trademark) E1010" (ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd. as an acetylene glycol surfactant (nonionic surfactant).

[0126]

Table 3

[0127] Pigment dispersion (D-1) Content ratio [mass %] Magenta pigment 15.00 Pigment coating resin (R) (NaOH neutralization) 6.00 Surfactant A 0.50 water 78.50 total 100.00

[0128] Then, the contents of the vessel 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 vessel capacity. The dispersion conditions were a temperature of 10° C. and a rotation speed of 8 m / sec. Thus, a pigment dispersion was obtained.

[0129] 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 ("Zetasizer (Japanese registered trademark) Nano ZS" manufactured by Malvern). 50 Measure the D of the pigment particles in the sample. 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 taken as the D 50 The D of the pigment particles contained in the pigment dispersion (D-1) 50 It is 100nm.

[0130] [Preparation of ink]

[0131] [Preparation of ink (I-1)]

[0132] In a flask equipped with a stirrer ("THREE-ONE MOTOR (Japanese registered trademark) BL-600" manufactured by Shinto Science Co., Ltd.), ion exchange water is placed. While the contents are stirred using the above-mentioned stirrer (stirring speed: 400 rpm), the pigment dispersion (D-1), surfactant B, triethylene glycol mono-n-butyl ether, 2-pyrrolidone, and glycerol are added in sequence. The input amount ratio of each raw material is shown in the following Table 4. In addition, surfactant B represents "SURFYNOL (Japanese registered trademark) 420" (ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd. as an acetylene glycol surfactant (nonionic surfactant).

[0133]

Table 4

[0134] Ink(I-1) Input amount [mass %] Pigment dispersion (D-1) 40.00 Surfactant B 0.30 Triethylene glycol mono-n-butyl ether 4.00 2-Pyrrolidone 5.00 Glycerol 20.00 water margin total 100.00

[0135] [Preparation of filling solution]

[0136] Filling solutions (F-1) to (F-12) were prepared according to the following method. First, the moisturizing agents (M-1) to (M-6) used in the preparation of filling solutions (F-1) to (F-6) and (F-8) to (F-12) are specifically as follows.

[0137] [Moisturizing agent (M-1) to (M-6)]

[0138] The compounds shown in Table 5 were prepared as humectants (M-1) to (M-6) according to the following method. The viscosity of humectants (M-1) to (M-6) is a value measured at 25°C using a falling ball viscometer ("Lovis 2000" manufactured by Anton Paar).

[0139] [Preparation of moisturizing agents (M-2) to (M-6)]

[0140] Polyethylene glycol and glycerol were reacted and etherified at 200°C. Thus, compounds as moisturizers (M-2) to (M-6) in Table 5 were synthesized. By high performance liquid chromatography (HPLC), it was confirmed that the peak values ​​of glycerol and polyethylene glycol in the obtained compounds were 99% or more. Specifically, acetonitrile and water were added to the obtained compounds and mixed, and quantitative analysis was performed by HPLC under the following conditions. In addition, moisturizers (M-2) to (M-6) are specific moisturizers.

[0141] HPLC apparatus: "HITACHID-7000" manufactured by Hitachi High-Tech Science Corporation

[0142] Flow rate: 1.0mL / min

[0143] Detector: ESA Biosciences' Corona CAD Detector

[0144] (Analysis conditions of glycerol)

[0145] Chromatographic column: "TSK-GEL Amide-80" manufactured by Tosoh Corporation (5 μm, 4.6 × 250 mm)

[0146] Solution: 50% by volume acetonitrile / water (distilled water)

[0147] (Analysis conditions for polyethylene glycol)

[0148] ·Chromatographic column: "Inertsil C8-3" manufactured by GL Science (5μm, 4.6×150mm)

[0149] Solution: acetonitrile / water (distilled water)

[0150] 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 %.

[0151] [Preparation of moisturizing agent (M-1)]

[0152] The compound as the humectant (M-1) in Table 5 was synthesized according to the method of humectants (M-2) to (M-6), except that ethylene glycol was used instead of polyethylene glycol. According to the method of humectants (M-2) to (M-6), it was confirmed that the peak values ​​of glycerol and ethylene glycol in the obtained compound were 99% or more.

[0153]

Table 5

[0154] Moisturizer M-1 M-2 M-3 M-4 M-5 M-6 a+b+c 3 6 9 15 18 21 Viscosity [mPa·s] 480 410 350 310 280 250

[0155] [Preparation of filling solution (F-1)]

[0156] 30.00 parts by mass of moisturizing agent (M-1), 0.06 parts by mass of surfactant C, sodium hydroxide and ion exchange water are mixed to obtain a mixed solution. The amount of sodium hydroxide added is an amount (trace amount) such that the pH value of the mixed solution reaches 8 to 9. The amount of ion exchange water added is an amount such that the total amount of the mixed solution is 100.00 parts by mass. The mixed solution is used as a filling solution (F-1). In addition, surfactant C represents "OLFINE (Japanese registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd. as an acetylene glycol surfactant (nonionic surfactant).

[0157] [Preparation of filling solutions (F-2) to (F-12)]

[0158] Filling solutions (F-2) to (F-12) were prepared according to the method for preparing the filling solution (F-1), except that the types and amounts of the components were changed as shown in Tables 6 to 7.

[0159] The static surface tension of the filling liquids (F-1) to (F-12) is a value measured at 25° C. using a surface tensiometer (e.g., “Automatic Surface Tensiometer DY-300” manufactured by Kyowa Interface Science Co., Ltd.) based on the Wilhelmy method (plate method). The measurement results are shown together in Tables 6 and 7 below.

[0160]

Table 6

[0161]

[0162]

Table 7

[0163]

[0164] [Ink set preparation]

[0165] As shown in the following Tables 8 to 9, the ink (I-1) was combined with each of the filling liquids (F-1) to (F-12), thereby preparing ink sets of Examples 1 to 6 and Comparative Examples 1 to 6.

[0166] [Evaluation 1]

[0167] The ink sets of Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated for their ink aggregation suppression performance (performance of suppressing aggregation of pigment components in the ink) in an open system (with evaporation) and a sealed system (without evaporation), flushing performance of the filling liquid (whether the filling liquid can be flushed after being left standing), and introduction performance of the filling liquid (performance of easily introducing the filling liquid into the ink flow path in the recording head) according to the following methods. The evaluation results are shown in Tables 8 to 9 below.

[0168] (Agglutination inhibition performance (open system))

[0169] 1.00 parts by mass of the ink (ink (I-1) in Study 1) included in the ink set to be evaluated and 50.00 parts by mass of the filling liquid (one of the filling liquids (F-1) to (F-12)) were mixed in a beaker. Next, the beaker containing the mixed liquid was stored in a thermostatic chamber at 40°C for 1 month without being sealed (storage treatment). The mixed liquid after the 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).

[0170] In addition, when filling the recording head with filling liquid after the recording head has been inspected, residual ink and filling liquid are mixed inside the recording head. The mixing ratio of residual ink and filling liquid (amount of ink / amount of filling liquid) varies depending on the part of the recording head, and it is assumed that the maximum is about 1 / 50. Therefore, the mixing ratio of ink and filling liquid is 1.00 parts by mass of ink: 50.00 parts by mass 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, thereby causing ink ejection failure. Therefore, whether agglomerates with a particle size of 3μm or more are generated after the storage process is used as a criterion for judging whether ink agglomeration can be suppressed.

[0171] (Agglutination inhibition performance (sealed system))

[0172] The "aggregation inhibition performance (sealed system)" was evaluated according to the evaluation method of the "aggregation inhibition performance (open system)" described above, except for the following changes. In the evaluation of the "aggregation inhibition performance (sealed system)", the beaker was sealed with a film during the storage treatment to prevent evaporation. The "aggregation inhibition performance (closed system)" does not cause the concentration of pigment components due to the evaporation of the solvent, so it is evaluated under milder conditions than the "aggregation inhibition performance (open system)".

[0173] (Criteria for judging the agglutination inhibition performance)

[0174] A (pass): No aggregates with a particle size of 3 μm or more were generated after storage in either the open system or the sealed system.

[0175] B (failure): Agglomerates with a particle size of 3 μm or more were generated after storage in at least one of the open system and the sealed system.

[0176] (Flushing)

[0177] When flushing out the filling liquid from a recording head that has been left in a high temperature environment, the water-soluble organic solvent or water in the filling liquid inside the recording head evaporates, so the viscosity of the filling liquid around the nozzle increases. When the viscosity of the filling liquid 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 inventor of the present application, when the viscosity of the moisturizing agent at 25°C is 450mPa·s or less, the filling liquid can be flushed out without any problem without increasing the flushing pressure, and there is no risk of damaging the recording head. Therefore, whether the viscosity of the moisturizing agent 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 left).

[0178] (Criteria for judging flushability)

[0179] A (pass): The viscosity of the moisturizer at 25°C is 450 mPa·s or less

[0180] B (failure): The viscosity of the moisturizer at 25°C exceeds 450 mPa·s

[0181] (Introduction)

[0182] First, fill the ink into an unused recording head ("KJ4B-QA" manufactured by Kyocera Corporation, with a total of 2656 nozzles) and spray it. As for the ink, ink (I-1) is used. Then, the recording head is cleaned with pure water and then dried thoroughly. Next, 25 mL of the filling liquid (each of the filling liquids (F-1) to (F-12)) provided in the ink set to be evaluated is filled into the recording head. Then, the filling liquid is discharged from the recording head by spraying it from the recording head. This operation is performed 10 times in total (a total of 250 mL is filled). 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 the glass plate. Thus, a nozzle check pattern is formed on the glass plate using the filling liquid. Next, the above-mentioned glass plate is read using a scanner, and the number of ejection nozzles (the number of ejection nozzles) from which the filling liquid has been ejected is counted. 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.

[0183] Introduction rate = 100 × number of ejection nozzles / total number of nozzles

[0184] (Criteria for determining whether it is suitable for adoption)

[0185] A (qualified): introduction rate is more than 90%

[0186] B (Unqualified): Import rate is less than 90%

[0187]

Table 8

[0188]

[0189]

Table 9

[0190]

[0191] As shown in Tables 3 to 9, when a+b+c in the general formula (1) of the moisturizing agent is less than 4, the flushing property of the filling liquid is unacceptable. On the other hand, when a+b+c in the general formula (1) of the moisturizing agent exceeds 20, sufficient ink aggregation inhibition performance cannot be obtained. Therefore, it is understood that a+b+c in the general formula (1) of the moisturizing agent is preferably 4 or more and 20 or less.

[0192] Furthermore, as shown in Tables 3 to 9, when the content of the specific moisturizing agent in the filling liquid is less than 19.00 mass % or exceeds 42.00 mass %, sufficient ink aggregation inhibition performance cannot be obtained. Therefore, it is known that the content of the specific moisturizing agent in the filling liquid is preferably 19.00 mass % or more and 42.00 mass % or less.

[0193] Furthermore, as shown in Tables 5 and 7, it can be seen that when the filling liquid does not contain an alkali, sufficient ink aggregation inhibition performance cannot be obtained.

[0194] [Study 2: Type of alkali in the filling solution]

[0195] Next, the type of alkali contained in the filling solution was examined.

[0196] [Preparation of filling solutions (F-13) to (F-18)]

[0197] Filling liquids (F-13) to (F-18) were prepared according to the preparation method of filling liquid (F-1), except that the types and amounts of each component were changed as shown in Tables 10 to 11. The static surface tension of filling liquids (F-13) to (F-18) was measured using the same measurement method as the static surface tension measurement method of filling liquids (F-1) to (F-12). The measurement results are shown together in the following Tables 10 to 11.

[0198]

Table 10

[0199]

[0200]

Table 11

[0201]

[0202] [Ink set preparation]

[0203] As shown in the following Table 12, the ink (I-1) was combined with each of the filling liquids (F-13) to (F-18). Thus, ink sets of Examples 7 to 11 and Comparative Example 7 were prepared.

[0204] [Evaluation 2]

[0205] The ink sets of Examples 7 to 11 and Comparative Example 7 were evaluated for ink aggregation inhibition performance, filling liquid flushing properties, and filling liquid introduction properties according to the method described in [Evaluation 1]. The evaluation results are shown in Table 12 below.

[0206]

Table 12

[0207]

[0208] As shown in Tables 10 to 12, by making the filling liquids (F-13) to (F-17) contain a monovalent base, no agglomerates with a particle size of 3 μm or more were generated after the storage treatment of the mixed solution of the ink (I-1) and the filling liquids (F-13) to (F-17). On the other hand, since the filling liquid (F-18) contained a divalent base, the dispersion stability of the pigment component could not be ensured, and the generation of agglomerates with a particle size of 3 μm or more after the storage treatment could not be suppressed. Therefore, it can be seen that by making the filling liquid contain a monovalent base, the aggregation of the pigment component in the ink can be effectively suppressed, and the high dispersion stability of the pigment component can be maintained.

[0209] [Study 3: Static surface tension of filling fluid]

[0210] Next, the static surface tension of the filling fluid was investigated.

[0211] [Preparation of filling solutions (F-19) to (F-23)]

[0212] Filling liquids (F-19) to (F-23) were prepared according to the preparation method of filling liquid (F-1), except that the types and amounts of each component were changed as shown in Table 13. The static surface tension of filling liquids (F-19) to (F-23) was measured using the same measurement method as the static surface tension measurement method of filling liquids (F-1) to (F-18). The measurement results are shown together in the following Table 13.

[0213]

Table 13

[0214]

[0215] [Ink set preparation]

[0216] As shown in the following Table 14, the ink (I-1) was combined with each of the filling liquids (F-19) to (F-23), thereby preparing ink sets of Examples 12 to 13 and Comparative Examples 8 to 10.

[0217] [Evaluation 3]

[0218] The ink sets of Examples 12 to 13 and Comparative Examples 8 to 10 were evaluated for ink aggregation inhibition performance, filling liquid flushing properties, and filling liquid introduction properties according to the method described in [Evaluation 1]. The evaluation results are shown in Table 14 below.

[0219]

Table 14

[0220]

[0221] As shown in Tables 13 and 14, the static surface tension of the filling liquids (F-22) to (F-23) used in Examples 12 to 13 at 25°C was 20.0 mN / m or more and 29.0 mN / m or less. The filling liquids of the ink sets of Examples 12 to 13 were easily introduced into the ink flow path in the recording head. On the other hand, the static surface tension of the filling liquids (F-19) to (F-21) used in Comparative Examples 8 to 10 at 25°C exceeded 29.0 mN / m. As a result, the filling liquids of the ink sets of Comparative Examples 8 to 10 were difficult to introduce into the ink flow path in the recording head. Therefore, it can be seen that by making the static surface tension of the filling liquid at 25°C be 20.0 mN / m or more and 29.0 mN / m or less, the filling liquid can have excellent introduction properties.

[0222] In addition, as shown in Tables 13 and 14, the static surface tension of the filling liquid at 25°C can be adjusted by changing the content ratio of the nonionic surfactant (surfactant C in Study 3). The nonionic surfactant reduces the static surface tension of the filling liquid at 25°C, so that the filling liquid is easily introduced into the ink flow path in the recording head. As shown in Table 13, when the content ratio of the nonionic surfactant in the filling liquid is 0.05 mass% or more and 0.10 mass% or less, the static surface tension of the filling liquid can be easily adjusted to a range of 20.0 mN / m or more and 29.0 mN / m or less.

Claims

1. A recording head filling liquid, Contains specific moisturizers, monovalent alkali and water. The specific moisturizing agent is a compound represented by the following general formula (1): The content ratio of the specific moisturizing agent is 19.00 mass % or more and 42.00 mass % or less, The static surface tension of the recording head filling liquid at 25° C. is 20.0 mN / m or more and 29.0 mN / m or less, In the general formula (1), a, b and c are independent of each other and represent an integer greater than or equal to 1, and a+b+c is greater than or equal to 4 and less than or equal to 20.

2. The recording head filling liquid according to claim 1, characterized in that: The specific moisturizing agent has a viscosity of 260 mPa·s or more and 450 mPa·s or less at 25°C.

3. The recording head filling liquid according to claim 1 or 2, characterized in that: The monovalent base contains at least one of a sodium compound, a potassium compound, a lithium compound, a cesium compound, and a rubidium compound.

4. The recording head filling liquid according to claim 1 or 2, characterized in that: In the general formula (1), a+b+c is 6 or more and 18 or less.

5. The recording head filling liquid according to claim 1 or 2, characterized in that: It also contains non-ionic surfactants. The nonionic surfactant contains an acetylene glycol type surfactant.

6. The recording head filling liquid according to claim 5, characterized in that: The content ratio of the nonionic surfactant is 0.05 mass % or more and 0.10 mass % or less.

7. The recording head filling liquid according to claim 1 or 2, characterized in that: The pH value is above 7 and below 10.

8. The recording head filling liquid according to claim 1 or 2, characterized in that: The recording head filling liquid is used to fill the recording head in which the inkjet ink remains.

9. An ink set, The invention comprises an inkjet ink and the recording head filling liquid according to any one of claims 1 to 8.

10. A recording head inspection method, Using the ink set according to claim 9, The recording head inspection method 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 inkjet ink is ejected using the recording head, thereby inspecting the ejection performance of the recording head.

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