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 pigment-coated resin, an aqueous medium, a polymeric nonionic surfactant, and a specific glycol ether. The specific glycol ether is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether. The weight-average molecular weight of the polymer nonionic surfactant is from 6500 to 10500 (inclusive). The recording head filling liquid contains a specific humectant and water. The specific humectant is a compound represented by general formula (1). # 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] 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 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 pigment coating resin, an aqueous medium, a polymer nonionic surfactant and a specific glycol ether. The specific glycol ether is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether. The weight average molecular weight of the polymer nonionic surfactant is greater than or equal to 6500 and less than or equal to 10500. The recording head filling liquid contains a specific moisturizing agent and water. The specific moisturizing agent is a compound represented by the following general formula (1).

[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 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.

[0013] [Effects of the Invention]

[0014] 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

[0015] 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).

[0016] 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.

[0017] 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."

[0018] <First embodiment: ink set>

[0019] Hereinafter, an ink set according to a first embodiment of the present invention will be described. The ink set according to this embodiment comprises 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 pigment coating resin, an aqueous medium, a polymer nonionic surfactant, and a specific glycol ether. The specific glycol ether is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether. The weight average molecular weight of the polymer nonionic surfactant is 6500 or more and 10500 or less. The filling liquid contains a specific moisturizing agent and water. The specific moisturizing agent is a compound represented by the following general formula (1).

[0020]

[0021] 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.

[0022] 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.

[0023] The ink set of this 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 aggregating in the recording head. In addition, even if the filling liquid is flushed out from the recording head after the recording head is placed, the filling liquid can be flushed out stably. The reason is presumed to be as follows. The ink set of this embodiment includes ink and filling liquid. The filling liquid 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 ink set of this embodiment contains a specific moisturizing agent with low viscosity in the filling liquid. By making the filling liquid contain a specific moisturizing agent, even if the water in the filling liquid evaporates, it is possible to prevent the filling liquid from becoming viscous. As a result, the filling liquid can effectively suppress the pigment components (pigment and pigment coating resin) in the ink from aggregating in the recording head. In addition, the pressure (flushing pressure) of the recording head when flushing the filling liquid does not become high, and the filling liquid can be flushed out from the recording head stably after the recording head is placed. In addition, the ink set of the present embodiment contains a polymer nonionic surfactant in the ink. The polymer nonionic surfactant can effectively suppress the aggregation of the pigment components (pigment and pigment coating resin) in the ink. In particular, with respect to the ink set of the present embodiment, when the ink is mixed with the filling liquid, the aggregation of the pigment components in the ink can be effectively suppressed, and the filling liquid can be made to have importability. In addition, the ink set of the present embodiment contains a specific glycol ether in the ink. The specific glycol ether has high hydrophobicity and good wettability, and therefore, when the ink is mixed with the filling liquid, the filling liquid can be made to have importability.

[0024] The ink set of the present embodiment will be described in more detail below. In addition, each component described below may be used alone or in combination of two or more.

[0025] [Ink]

[0026] The ink contains a pigment, a pigment coating resin, an aqueous medium, a polymer nonionic surfactant, and a specific glycol ether. In the ink, the pigment forms pigment particles together with the pigment coating resin. The pigment particles are dispersed in the aqueous medium. 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 200 nm, and more preferably from 70 nm to 130 nm.

[0027] (pigment)

[0028] 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).

[0029] The content of the pigment in the ink 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 setting the content of the pigment to 2.0% 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 15.0% by mass or less, the fluidity of the ink can be ensured.

[0030] (Pigment coated resin)

[0031] 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.

[0032] 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 also has a styrene unit. Examples of alkyl (meth)acrylates 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 with styrene, methyl methacrylate, methacrylic acid, and butyl acrylate. In addition, the copolymer (X) is preferably neutralized in equal amounts using a basic compound (e.g., potassium hydroxide and sodium hydroxide).

[0033] 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.

[0034] 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 ejection stability of the ink can be optimized.

[0035] The acid value of the pigment coating resin is preferably 30 mgKOH / g to 300 mgKOH / g, more preferably 80 mgKOH / g to 180 mgKOH / g. By setting the acid value of the pigment coating resin to 30 mgKOH / g to 300 mgKOH / g, the dispersibility of the pigment and the storage stability of the ink can be optimized.

[0036] 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.).

[0037] 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, the viscosity of the ink can be suppressed from increasing, and the image density of the formed image and the ejection stability of the ink can be optimized.

[0038] 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.).

[0039] 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 is preferably neutralized with an equal amount of an alkaline compound before being used as a raw material for ink. The alkaline compound is preferably a hydroxide of an alkali metal ion (for example, potassium hydroxide or sodium hydroxide).

[0040] (Aqueous medium)

[0041] 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.

[0042] The content ratio of the aqueous medium in the ink is preferably 70.0 mass % or more and 96.0 mass % or less, and more preferably 80.0 mass % or more and 92.0 mass % or less.

[0043] (water)

[0044] Water is the main solvent of the ink. The content of water in the ink is, for example, preferably from 20.0% by mass to 93.0% by mass, and more preferably from 50.0% by mass to 87.0% by mass.

[0045] (Water-soluble organic solvent)

[0046] 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 other than specific glycol ethers, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerol, and dimethyl sulfoxide.

[0047] 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.

[0048] Examples of the glycol ether compounds other than the specific glycol ethers 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, and propylene glycol monomethyl ether.

[0049] Examples of the lactam compound include 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0050] Examples of the nitrogen-containing compound include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0051] As an example of the acetate compound, diethylene glycol monoethyl ether acetate can be mentioned.

[0052] The water-soluble organic solvent in the ink is preferably 2-pyrrolidone or glycerol.

[0053] The content of the water-soluble organic solvent in the ink is preferably 8.0% by mass to 60.0% by mass, and more preferably 20.0% by mass to 45.0% by mass. By setting the content of the water-soluble organic solvent to 8.0% by mass to 60.0% by mass, the ejection stability of the ink can be optimized.

[0054] When the ink contains 2-pyrrolidone as a water-soluble organic solvent, the content ratio of 2-pyrrolidone in the ink is preferably 1.5 mass % to 12.5 mass %, and more preferably 4.0 mass % to 9.0 mass %.

[0055] When the ink contains glycerol as a water-soluble organic solvent, the content ratio of glycerol in the ink is preferably 6.0 mass % to 50.0 mass %, and more preferably 16.0 mass % to 36.0 mass %.

[0056] (Polymer nonionic surfactant)

[0057] The weight average molecular weight of the polymer nonionic surfactant is 6500 to 10500, preferably 7000 to 9000. By making the weight average molecular weight of the polymer nonionic surfactant 6500 to 10500, the aggregation of the pigment components (pigment and pigment coating resin) in the ink can be effectively suppressed (in other words, the aggregation suppression performance can be optimized).

[0058] Examples of the polymer nonionic surfactant include copolymers having repeating units derived from (meth)acrylic acid polyalkylene glycol alkyl ether and repeating units derived from (meth)acrylic acid alkyl ester (hereinafter, sometimes referred to as copolymers (α)).

[0059] Examples of (meth)acrylic acid polyalkylene glycol alkyl ethers include (meth)acrylic acid polyethylene glycol methyl ether and (meth)acrylic acid polypropylene glycol methyl ether. In (meth)acrylic acid polyethylene glycol methyl ether, the molecular weight of the polyethylene glycol portion is, for example, 100 to 300. In (meth)acrylic acid polypropylene glycol methyl ether, the molecular weight of the polypropylene portion is, for example, 80 to 150. (Meth)acrylic acid polyalkylene glycol alkyl ethers are preferably acrylate polyethylene glycol methyl ether (PEGA) or acrylate polypropylene glycol methyl ether (PPGA).

[0060] The content ratio of the repeating units derived from the (meth)acrylic acid polyalkylene glycol alkyl ether is preferably 50.0 mass % to 90.0 mass %, more preferably 60.0 mass % to 80.0 mass %, based on all the repeating units in the copolymer (α).

[0061] Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and lauryl (meth)acrylate. The alkyl (meth)acrylate is preferably methyl methacrylate (MMA), lauryl acrylate (LA), butyl acrylate (BA), ethyl acrylate (EA), or lauryl methacrylate (LMA).

[0062] The content ratio of the repeating unit derived from the alkyl (meth)acrylate is preferably 10.0 mass % to 50.0 mass %, and more preferably 20.0 mass % to 40.0 mass %, based on all the repeating units in the copolymer (α).

[0063] The copolymer (α) is preferably a copolymer having repeating units derived from monomers of the following combination (1) or a copolymer having repeating units of monomers of the following combination (2).

[0064] Combination (1): PEGA, BA, PPGA, LA and MMA

[0065] Combination (2): PEGA, EA, PPGA, LMA and MMA

[0066] The copolymer (α) is preferably one of the combinations 1 to 2 having repeating units derived from the monomers in Table 1 below. In Table 1 below, "ratio" represents the numerical range of the preferred content ratio [mass %] of the repeating units derived from each monomer. For example, the ratio "50.0-70.0" of "PEGA" in combination 1 means that PEGA is contained in an amount of 50.0 mass % or more and 70.0 mass % or less.

[0067]

Table 1

[0068]

[0069] The content of the polymer nonionic surfactant in the ink is preferably 0.2% by mass to 0.9% by mass, and more preferably 0.2% by mass to 0.4% by mass. By setting the content of the polymer nonionic surfactant to 0.2% by mass to 0.9% by mass, the aggregation inhibition performance can be further improved.

[0070] (Specific glycol ethers)

[0071] The specific glycol ether contained in the ink is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether.

[0072] Specific glycol ethers have high hydrophobicity and good wettability, and thus can make the filling liquid more absorbent when the ink and the filling liquid are mixed.

[0073] The content of the specific glycol ether in the ink is preferably 1.0% by mass to 6.0% by mass, and more preferably 3.0% by mass to 5.0% by mass. By making the content of the specific glycol ether 1.0% by mass to 6.0% by mass, the introduction of the filling liquid when the ink and the filling liquid are mixed can be optimized.

[0074] (Low molecular surfactant)

[0075] In the ink, the surfactant may contain only a high molecular weight nonionic surfactant, or may further contain a surfactant having a molecular weight smaller than that of the high molecular weight nonionic surfactant (hereinafter referred to as a low molecular weight surfactant). The content ratio of the high molecular weight nonionic surfactant in the surfactant is preferably 40.0% by mass or more, and more preferably 50.0% by mass or more.

[0076] Examples of low molecular surfactants include nonionic surfactants such as acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds), and fluorine surfactants (surfactants containing fluorine resins or fluorine-containing compounds). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. More specifically, examples of acetylene glycol surfactants include: "OLFINE (Japanese registered trademark) E1010" (manufactured by Nissin Chemical Industry Co., Ltd., ethylene oxide adduct of acetylene glycol).

[0077] When the ink contains a low-molecular-weight surfactant, the content ratio of the low-molecular-weight surfactant in the ink is preferably 0.1 mass % to 0.5 mass %, and more preferably 0.1 mass % to 0.3 mass %.

[0078] (Other ingredients)

[0079] 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.

[0080] (Preferred components)

[0081] The ink preferably has one of the components 1 to 7 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 pigment in component 1 "5.0-7.0" means that the pigment is contained in a ratio of 5.0 mass % to 7.0 mass %. The types of polymer nonionic surfactants "S-1", "S-3", "S-4" and "S-6" respectively represent the surfactants (S-1), (S-3), (S-4) and (S-6) used in the examples. In addition, BTG is triethylene glycol mono-n-butyl ether, and BDG is diethylene glycol mono-n-butyl ether.

[0082]

Table 2

[0083]

[0084] In addition, among the components 1 to 7 in Table 2, the water-soluble organic solvent preferably has the composition shown in the following Table 3. In addition, in the following Table 3, "ratio" indicates the numerical range of the preferred content ratio [mass %]. For example, the ratio of 2-pyrrolidone "3.0-7.0" means that 2-pyrrolidone is contained in a ratio of 3.0 mass % or more and 7.0 mass % or less.

[0085]

Table 3

[0086]

[0087] (Method for producing ink)

[0088] For example, a pigment dispersion containing a pigment, an aqueous medium, a high molecular nonionic surfactant, and a specific glycol ether are uniformly mixed by a stirrer, thereby producing an ink. In the manufacture of the ink, after the components are uniformly mixed, foreign matter and coarse particles can also be removed by a filter (for example, a filter with a pore size of 5 μm or less). The pigment dispersion contains a pigment, a pigment-coated resin, and an aqueous medium. The pigment dispersion may further contain a low molecular surfactant. For example, an alkali-soluble resin is neutralized in equal amounts by an alkaline compound (for example, potassium hydroxide or sodium hydroxide), thereby preparing a pigment-coated resin. After the pigment is added to an aqueous solution containing the pigment-coated resin, a dispersion treatment is performed, thereby producing a pigment dispersion. An example of the device used in the dispersion treatment is a bead mill. In the manufacture of the ink, after the dispersion treatment, foreign matter and coarse particles can also be removed by a filter (for example, a filter with a pore size of 5 μm or less).

[0089] [Filling fluid]

[0090] The filling liquid contains a specific moisturizing agent and water. In addition, the filling liquid may further contain a surfactant.

[0091] (Specific moisturizer)

[0092] The specific moisturizing agent is a compound represented by the above-mentioned general formula (1). In the general formula (1), a+b+c is 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. By making the filling liquid contain 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), even if the water in the filling liquid evaporates, it is possible to prevent the filling liquid from becoming viscous. As a result, the filling liquid can effectively suppress the aggregation of the pigment components (pigment and pigment coating resin) in the ink in the recording head. In addition, after the recording head is placed, the filling liquid can be stably flushed out of the recording head. However, when the viscosity of the specific moisturizing agent is too low, the filling liquid sometimes reduces the dispersibility of the pigment components in the recording head. In the general formula (1), when a+b+c is 4 to 20, the aggregation of the pigment components in the ink can be effectively suppressed in the recording head. In the general formula (1), by setting a+b+c to be 6 or more and 18 or less, it is possible to more effectively suppress the aggregation of the pigment component in the ink in the recording head.

[0093] The viscosity of the specific moisturizing agent at 25°C is preferably 260 mPa·s to 450 mPa·s, more preferably 330 mPa·s to 450 mPa·s, and further preferably 380 mPa·s to 440 mPa·s. By making the viscosity of the specific moisturizing agent 260 mPa·s to 450 mPa·s, the aggregation of the pigment component in the ink can be effectively suppressed in the recording head. In addition, the filling liquid can be flushed out of the recording head stably after the recording head is placed. The measured value of the viscosity of the specific moisturizing agent is a value measured at 25°C using a falling ball viscometer (for example, "Lovis2000" manufactured by Anton Paar).

[0094] The content ratio of the specific moisturizing agent in the filling liquid is preferably 16.0 mass % or more and 41.0 mass % or less, and more preferably 25.0 mass % or more and 35.0 mass % or less. By setting the content ratio of the specific moisturizing agent in the filling liquid to 16.0 mass % or more and 41.0 mass % or less, the aggregation of the pigment component in the ink can be effectively suppressed in the recording head. In addition, after the recording head is placed, the filling liquid can be flushed out from the recording head stably.

[0095] (Surfactant)

[0096] The surfactant contained in the filling liquid can include the same substances as the surfactants exemplified as the low molecular surfactants in the ink. The surfactant contained in the filling liquid is preferably an acetylene glycol type surfactant. The acetylene glycol type surfactant has the effect of improving the wettability of the filling liquid to the stainless steel material, and the material of the recording head flow path is usually made of stainless steel. Therefore, the filling liquid contains an acetylene glycol type surfactant, which makes it easier to introduce the ink flow path in the recording head. For example, the acetylene glycol surfactant contained in the filling liquid can be: "SURFYNOL (Japanese registered trademark) 420" (manufactured by Nissin Chemical Industry Co., Ltd.).

[0097] The content ratio of the surfactant in the filling liquid is preferably 0.1 mass % or more and 0.5 mass % or less, and more preferably 0.1 mass % or more and 0.3 mass % or less. By setting the content ratio of the surfactant in the filling liquid to 0.1 mass % or more, it becomes easier to introduce the filling liquid into the ink flow path in the recording head, and it is possible to more effectively suppress the aggregation of the pigment component in the ink in the recording head. On the other hand, a large amount of surfactant sometimes reduces the dispersibility of the pigment component. Therefore, by setting the content ratio of the surfactant in the filling liquid to 0.5 mass % or less, the filling liquid can more effectively suppress the aggregation of the pigment component in the ink in the recording head.

[0098] (water)

[0099] Water is the main solvent of the filling liquid. The content of water in the filling liquid is, for example, preferably 45.0 mass % to 95.0 mass %, and more preferably 65.0 mass % to 85.0 mass %.

[0100] (Other ingredients)

[0101] The filling liquid may further contain well-known additives (for example, a dissolution stabilizer, an anti-desiccation agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an antifungal agent) as necessary.

[0102] (Preferred components)

[0103] The filling liquid preferably has one of the components 1 to 7 shown in Table 4 below. In Table 4 below, "ratio" indicates a numerical range of a preferred content ratio [mass %]. For example, the ratio of the specific moisturizer in component 1 "27.0-33.0" indicates that the specific moisturizer is contained in a ratio of 27.0 mass % to 33.0 mass %. The types of specific moisturizers "M-2", "M-3", "M-4" and "M-5" respectively indicate the specific moisturizers (M-2), (M-3), (M-4) and (M-5) used in the examples.

[0104]

Table 4

[0105]

[0106] (Method for producing filling liquid)

[0107] For example, the filling solution can be produced by mixing a specific moisturizing agent, water, and other components (eg, surfactant) added as needed. The specific moisturizing agent can be produced by reacting polyethylene glycol and glycerol at 180 to 220°C for etherification.

[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 filling liquid after the inspection step. In the inspection step, the ejection performance of the recording head is inspected by ejecting ink for inkjet using the recording head.

[0110] The recording head inspection method of this embodiment uses the ink set involved in the first embodiment, so it is possible to suppress ejection failure of 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 there are, for example, piezoelectric recording heads and thermal recording heads. The recording head may also be, for example, a line recording head.

[0111] [Inspection process]

[0112] 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.

[0113] 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.

[0114] [Filling process]

[0115] In this process, the recording head is filled with filling liquid. 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 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 high molecular nonionic 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.

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

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

[0121] Number of 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: Types of moisturizers in fillers]

[0128] 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.

[0129] [Preparation of Pigment Dispersion]

[0130] 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.

[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 is mixed with an aqueous sodium hydroxide solution (neutralization treatment). The alkali-soluble resin is neutralized with NaOH through the neutralization treatment. 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 NaOH. Thus, a pigment coating resin solution containing the pigment coating resin (R) (neutralized alkali-soluble resin) and water is obtained.

[0133] (Distributed Processing)

[0134] As shown in the following Table 5, 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)).

[0135] In addition, the content ratio of "water" in the following Table 5 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.

[0136]

Table 5

[0137] Pigment dispersion (D-1) Content ratio [mass %] Magenta pigment 15.0 Pigment coating resin (R) (NaOH neutralization) 6.0 Surfactant A 0.5 water 78.5 total 100.0

[0138] 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.

[0139] The volume median diameter (D 50Specifically, 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.

[0140] [Preparation of polymer nonionic surfactant]

[0141] A polymer nonionic surfactant (S-1) used in the preparation of ink was prepared. A copolymer (weight average molecular weight (Mw) 8000) having repeating units (PEGA units) derived from polyethylene glycol methyl ether acrylate (molecular weight of polyethylene glycol part: 200), repeating units (BA units) derived from butyl acrylate, repeating units (PPGA units) derived from polypropylene glycol methyl ether acrylate (molecular weight of polypropylene glycol part: 100), repeating units (LA units) derived from lauryl acrylate, and repeating units (MMA units) derived from methyl methacrylate was prepared. This copolymer was used as a polymer nonionic surfactant (S-1). The mass ratio of each repeating unit in the polymer nonionic surfactant (S-1) was "PEGA unit: BA unit: PPGA unit: LA unit: MMA unit = 60:10:10:12:8". The polymer nonionic surfactant (S-1) is soluble in water.

[0142] [Preparation of ink]

[0143] [Preparation of ink (I-1)]

[0144] Ion exchange water was placed in a flask equipped with a stirrer ("THREE-ONE MOTOR (Japanese registered trademark) BL-600" manufactured by Shinto Scientific Co., Ltd.). While the contents were stirred using the stirrer (stirring speed: 400 rpm), the pigment dispersion (D-1), polymer nonionic surfactant (S-1), triethylene glycol mono-n-butyl ether, 2-pyrrolidone, and glycerol were added in sequence. The input amount ratio of each raw material is shown in Table 6 below.

[0145]

Table 6

[0146] Ink(I-1) Input amount [mass %] Pigment dispersion (D-1) 40.0 High molecular weight nonionic surfactant (S-1) 0.3 Triethylene glycol mono-n-butyl ether 4.0 2-Pyrrolidone 5.0 Glycerol 20.0 water margin total 100.0

[0147] [Preparation of filling solution]

[0148] Filling solutions (F-1) to (F-6) were prepared by the following method. First, the moisturizing agents (M-1) to (M-6) used in the preparation of the filling solutions are specifically as follows.

[0149] [Moisturizing agent (M-1) to (M-6)]

[0150] The compounds shown in Table 7 were prepared as follows and designated as humectants (M-1) to (M-6). The viscosity of the humectant is a value measured at 25° C. using a falling ball viscometer (“Lovis 2000” manufactured by Anton Paar).

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

[0152] Polyethylene glycol and glycerol were reacted and etherified at 200°C. Thus, compounds as moisturizers (M-2) to (M-6) in Table 7 were synthesized. The peaks of glycerol and polyethylene glycol in the obtained compounds were confirmed to be 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 Corporation

[0154] Flow rate: 1.0mL / min

[0155] Detector: ESA Biosciences' Corona CAD Detector

[0156] (Analysis conditions of glycerol)

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

[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 compound as the humectant (M-1) in Table 7 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.

[0165]

Table 7

[0166] 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

[0167] [Preparation of filling solution (F-1)]

[0168] 30.0 parts by mass of the moisturizing agent (M-1), 0.2 parts by mass of "SURFYNOL (Japanese registered trademark) 420" (ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd. as an acetylene glycol surfactant, and ion exchange water were mixed to obtain a mixed solution. The amount of ion exchange water added was such that the total amount of the mixed solution was 100.0 parts by mass. The mixed solution was used as the filling solution (F-1).

[0169] [Preparation of filling solutions (F-2) to (F-6)]

[0170] Filling solutions (F-2) to (F-6) were prepared according to the preparation method of filling solution (F-1), except that the types and amounts of each component were changed as shown in Table 8. In addition, the surfactant B in the following Table 8 represents the above-mentioned "SURFYNOL (Japanese registered trademark) 420".

[0171]

Table 8

[0172]

[0173] [Ink set preparation]

[0174] As shown in the following Table 9, the ink (I-1) was combined with each of the filling liquids (F-1) to (F-6). Thus, ink sets of Examples 1 to 4 and Comparative Examples 1 and 2 were prepared.

[0175] [Evaluation 1]

[0176] The ink sets of Examples 1 to 4 and Comparative Examples 1 to 2 were evaluated for 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 easy introduction of the filling liquid into the ink flow path in the recording head) in the following method. The evaluation results are shown in Table 9 below.

[0177] (Agglutination inhibition performance (open system))

[0178] 1.0 parts by mass of the ink (ink (I-1) in Study 1) included in the ink set to be evaluated and 50.0 parts by mass of the filling liquid (one of the filling liquids (F-1) to (F-6)) 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).

[0179] 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 1.0 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, 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.

[0180] (Agglomeration inhibition performance (sealed system))

[0181] 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)".

[0182] (Criteria for judging the agglutination inhibition performance)

[0183] 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.

[0184] 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.

[0185] (Flushing)

[0186] 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).

[0187] (Criteria for judging flushability)

[0188] A (pass): The viscosity of the moisturizer at 25°C is 450 mPa·s or less

[0189] B (failure): The viscosity of the moisturizer at 25°C exceeds 450 mPa·s

[0190] (Introduction)

[0191] First, fill the ink into an unused recording head ("KJ4B-QA" manufactured by Kyocera Corporation, with a total of 2656 nozzles) and spray it. For the ink, use the cyan ink for the inkjet color printer "TASKalfa Pro 15000c" manufactured by Kyocera Document Systems, Ltd. Then, clean the recording head with pure water and then dry it thoroughly. Next, fill the recording head with 25 mL of the filling liquid (each of the filling liquids (F-1) to (F-6)) provided in the ink set to be evaluated. Then, discharge the filling liquid from the recording head by spraying the filling liquid from the recording head. This operation is performed 10 times in total (a total of 250 mL is filled). Then, fill the recording head with the filling liquid again. Then, use the recording head filled with the filling liquid to print the nozzle check pattern on the 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 to count 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 is calculated using the following formula. The introducibility of the filling liquid is determined according to the following criteria.

[0192] Introduction rate = 100 × number of ejection nozzles / total number of nozzles

[0193] (Criteria for determining whether it is suitable for adoption)

[0194] A (qualified): introduction rate is more than 90%

[0195] B (Unqualified): Import rate is less than 90%

[0196]

Table 9

[0197]

[0198] As shown in Tables 1 to 9, it was found that a+b+c in the general formula (1) of the moisturizing agent is preferably 4 or more and 20 or less.

[0199] [Study 2: Weight average molecular weight of polymer nonionic surfactants]

[0200] Next, the weight average molecular weight of the polymer nonionic surfactant was examined. The following is a method for preparing each raw material used in the production of the ink.

[0201] (Polymer nonionic surfactants (S-2) to (S-6))

[0202] As shown in Table 10 below, copolymers having repeating units and weight average molecular weights different from those of the polymer nonionic surfactant (S-1) were prepared as polymer nonionic surfactants (S-2) to (S-6). All polymer nonionic surfactants (S-2) to (S-6) are soluble in water. In addition, in Table 10 below, the item of repeating units indicates repeating units derived from the monomers (polyethylene glycol methyl ether acrylate (PEGA), butyl acrylate (BA), polypropylene glycol methyl ether acrylate (PPGA), lauryl acrylate (LA), methyl methacrylate (MMA), ethyl acrylate (EA) and lauryl methacrylate (LMA)). In addition, in Table 10 below, regarding the mass ratio of each repeating unit in the polymer nonionic surfactant, for example, in the case of the polymer nonionic surfactant (S-1), by mass ratio, the repeating unit derived from PEGA is 60%, the repeating unit derived from BA is 10%, the repeating unit derived from PPGA is 10%, the repeating unit derived from LA is 12%, and the repeating unit derived from MMA is 8%.

[0203]

Table 10

[0204]

[0205] [Preparation of inks (I-2) to (I-8)]

[0206] Inks (I-2) to (I-8) were prepared according to the method for preparing ink (I-1) except that the types and amounts of each raw material were changed as shown in Table 11. In Table 11, BTG represents triethylene glycol mono-n-butyl ether.

[0207]

Table 11

[0208]

[0209] [Preparation of filling solution (F-7)]

[0210] A filling solution (F-7) was prepared in the same manner as the filling solutions (F-1) to (F-6), except that the type of the moisturizer and the amounts of the moisturizer and water were changed as shown in Table 12.

[0211]

Table 12

[0212] Filling fluid (F-7) Content ratio [mass %] Moisturizer (M-2) 35.0 Surfactant B 0.2 water margin total 100.0

[0213] [Ink set preparation]

[0214] As shown in the following Table 13, each of the inks (I-1) to (I-8) was combined with the filling liquid (F-7), thereby preparing ink sets of Examples 5 to 9 and Comparative Examples 3 to 5.

[0215] [Evaluation 2]

[0216] The ink sets of Examples 5 to 9 and Comparative Examples 3 to 5 were evaluated for ink aggregation inhibition performance, flushing properties of the filling liquid, and filler liquid introduction properties according to the method described in [Evaluation 1]. The evaluation results are shown in Table 13 below.

[0217]

Table 13

[0218]

[0219] As shown in Tables 10 to 13, by making the ink contain a polymer nonionic surfactant, when the ink is mixed with the filling liquid, the aggregation of the pigment component in the ink can be effectively suppressed, and the filling liquid can be introduced. In addition, as shown in Tables 10 to 13, when the weight average molecular weight of the polymer nonionic surfactant is less than 6500 or exceeds 10500, the dispersion stability cannot be ensured, and agglomerates with a particle size of 3μm or more are generated after the storage treatment. On the other hand, it was found that when the weight average molecular weight of the polymer nonionic surfactant is within the range of 6500 to 10500, no agglomerates with a particle size of 3μm or more are generated after the storage treatment.

[0220] [Study 3: Types of glycol ethers]

[0221] Next, the types of glycol ethers were studied.

[0222] [Preparation of inks (I-9) to (I-13)]

[0223] Inks (I-9) to (I-13) were prepared according to the preparation method of inks (I-1) to (I-8), except that the types and amounts of each raw material were changed as shown in Table 14 below. In Table 14 below, BTG is triethylene glycol mono-n-butyl ether, BDG is diethylene glycol mono-n-butyl ether, BEG is ethylene glycol mono-n-butyl ether, and iPDG is diethylene glycol isopropyl ether.

[0224]

Table 14

[0225]

[0226] [Ink set preparation]

[0227] As shown in the following Table 15, each of the inks (I-9) to (I-12) was combined with the filling liquid (F-7), thereby preparing ink sets of Examples 10 to 12 and Comparative Examples 4 to 6.

[0228] [Evaluation 3]

[0229] The ink sets of Examples 10 to 12 and Comparative Examples 4 to 6 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 15 below.

[0230]

Table 15

[0231]

[0232] As shown in Tables 14 to 15, triethylene glycol mono-n-butyl ether and diethylene glycol mono-n-butyl ether can make the filling liquid have good importability. It can be considered that this is because the specific glycol ether has high hydrophobicity and good wettability. On the other hand, compared with the specific glycol ether, ethylene glycol mono-n-butyl ether has fewer ether bonds (-O-) than the specific glycol ether, and therefore exhibits higher hydrophilicity than the specific glycol ether. In addition, compared with the specific glycol ether, diethylene glycol isopropyl ether has a shorter alkyl chain length than the specific glycol ether, and therefore exhibits higher hydrophilicity than the specific glycol ether. Therefore, these ethylene glycol mono-n-butyl ether and diethylene glycol isopropyl ether have insufficient wettability and fail to make the filling liquid have sufficient importability.

[0233] [Study 4: Moisturizer content of filler fluid]

[0234] Next, the content of moisturizer used in the filling fluid was studied.

[0235] [Preparation of filling solutions (F-8) to (F-9)]

[0236] Filling solutions (F-8) to (F-9) were prepared according to the preparation method of filling solutions (F-1) to (F-6), except that the types and amounts of each component were changed as shown in Table 16. In addition, the surfactant B in the following Table 16 is the above-mentioned "SURFYNOL (Japanese registered trademark) 420".

[0237]

Table 16

[0238]

[0239] [Ink set preparation]

[0240] As shown in the following Table 17, the ink (I-1) was combined with each of the filling liquids (F-8) to (F-9). Thus, the ink sets of Examples 13 and 14 were prepared.

[0241] [Evaluation 4]

[0242] The ink sets of Examples 13 and 14 were evaluated for their ink aggregation suppression performance, filler liquid flushing performance, and filler liquid introduction performance according to the method described in [Evaluation 1]. The evaluation results are shown in Table 17 below. Table 17 below also shows the evaluation results of the ink set of Example 1 for reference.

[0243]

Table 17

[0244]

[0245] As shown in Tables 16 and 17, regardless of whether the content of the specific moisturizing agent in the filling liquid was 20.0 mass % or 40.0 mass %, similar to Example 1, the results of the ink aggregation inhibition performance, the filling liquid flushing property, and the filling liquid introduction property were all good.

Claims

1. An ink set comprising inkjet ink and recording head filling liquid, characterized in that: The inkjet ink contains a pigment, a pigment-coating resin, an aqueous medium, a polymer nonionic surfactant and a specific glycol ether. The specific glycol ether is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether, The weight average molecular weight of the polymer nonionic surfactant is 6500 or more and 10500 or less. The recording head filling liquid contains a specific moisturizing agent and water, The specific moisturizing agent is a compound represented by the following general formula (1): 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 ink set according to claim 1, characterized in that: In the inkjet ink, the content ratio of the polymer nonionic surfactant is 0.2 mass % or more and 0.9 mass % or less.

3. The ink set according to claim 1 or 2, characterized in that: In the inkjet ink, the content ratio of the specific glycol ether is 1.0 mass % or more and 6.0 mass % or less.

4. The ink set according to claim 1 or 2, characterized in that: The recording head filling liquid may contain the specific moisturizing agent in an amount of 16.0 mass % to 41.0 mass %.

5. The ink set according to claim 1 or 2, 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.

6. The ink set according to claim 1 or 2, characterized in that: The polymer nonionic surfactant is a copolymer having repeating units derived from (meth)acrylic acid polyalkylene glycol alkyl ether and repeating units derived from (meth)acrylic acid alkyl ester.

7. The ink set according to claim 6, characterized in that: The polymer nonionic surfactant is a copolymer having repeating units derived from polyethylene glycol methyl ether of acrylate, repeating units derived from butyl acrylate, repeating units derived from polypropylene glycol methyl ether of acrylate, repeating units derived from lauryl acrylate and repeating units derived from methyl methacrylate. Or it is a copolymer having repeating units derived from polyethylene glycol methyl ether acrylate, repeating units derived from ethyl acrylate, repeating units derived from polypropylene glycol methyl ether acrylate, repeating units derived from lauryl methacrylate and repeating units derived from methyl methacrylate.

8. The ink set 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.

9. The ink set 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.

10. A recording head inspection method, Use of the ink set according to any one of claims 1 to 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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