Ink set and recording head inspection method

Abstract

To provide an ink set which allows a recording head filling liquid to be easily introduced into an ink flow passage in a recording head, and can effectively suppress aggregation of a pigment component in ink for inkjet in the recording head.SOLUTION: An ink set includes ink for ink jet, and a recording head filling liquid. The ink for ink jet contains a pigment, 1,2-alkane diol having 7 or 8 carbon atoms, and water. The recording head filling liquid contains a specific alcohol compound having 10 or more and 12 or less carbon atoms, a specific surface active agent, and water. An HLB value of the specific surface active agent is 5.0 or less. A content ratio of the specific alcohol compound in the recording head filling liquid is 0.1 ppm or more and 1.0 ppm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink set and a method for inspecting a recording head. [Background technology]

[0002] An inkjet recording device is equipped with a recording head that ejects inkjet ink. The recording head is a precision instrument that requires extremely high accuracy. Therefore, after manufacturing the recording head, the recording head manufacturer generally thoroughly inspects the ejection performance and other aspects before shipping the recording head.

[0003] In testing the ejection performance of a recording head, an ejection test is performed by actually filling the recording head with inkjet ink. After the test, inkjet ink inevitably remains in the ink flow paths of the recording head. Because the ink flow paths of a recording head are very fine, it is difficult to completely remove the inkjet ink remaining in the ink flow paths even if the recording head is washed. If a recording head is shipped with inkjet ink remaining in the ink flow paths, the solvent of the inkjet ink may evaporate during transportation and storage, causing the solid components of the inkjet ink (particularly the pigment components) to aggregate and generate aggregates. The above-mentioned aggregates may cause ejection defects in the recording head after shipment.

[0004] Therefore, some recording head manufacturers ship recording heads filled with a solution that does not contain pigment components (hereinafter, sometimes referred to as recording head filling liquid). The recording head filling liquid enters the ink flow path of the recording head and dilutes the inkjet ink remaining in the ink flow path. This makes it difficult for the solid content of the inkjet ink remaining in the ink flow path to aggregate. Such a recording head filling liquid is required to be easily introduced into the ink flow path in the recording head and to be able to suppress the aggregation of the solid content of the inkjet ink in the recording head. For example, a recording head filling liquid containing silicone oil has been proposed as a recording head filling liquid to be filled in the recording head (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-227729 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the print head filling liquid described in Patent Document 1 cannot sufficiently suppress aggregation of the pigment components in the inkjet ink in the print head in harsh environments such as high temperature environments. Also, the print head filling liquid described in Patent Document 1 is difficult to introduce into the ink flow path in the print head.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink set that allows the filler liquid for a recording head to be easily introduced into the ink flow passages in the recording head, and that can effectively prevent the pigment components in the inkjet ink from coagulating in the recording head. Another object of the present invention is to provide a method for inspecting a recording head using the above-mentioned ink set. [Means for solving the problem]

[0008] The ink set according to the present invention comprises an inkjet ink and a recording head filling liquid. The inkjet ink contains a pigment, a 1,2-alkanediol having 7 or 8 carbon atoms, and water. The recording head filling liquid contains a specific alcohol compound having 10 to 12 carbon atoms, a specific surfactant, and water. The specific surfactant has an HLB value of 5.0 or less. The content of the specific alcohol compound in the recording head filling liquid is 0.1 ppm or more and 1.0 ppm or less.

[0009] The method for inspecting a recording head according to the present invention is a method for inspecting a recording head using the ink set described above, and includes an inspection step of inspecting the ejection performance of the recording head, and a filling step of filling the recording head with the recording head filler liquid after the inspection step. In the inspection step, the ejection performance of the recording head is inspected by ejecting the inkjet ink from the recording head. Effect of the Invention

[0010] According to the ink set of the present invention, the filler liquid for the recording head can be easily introduced into the ink flow path in the recording head, and the aggregation of the pigment component in the inkjet ink in the recording head can be effectively suppressed. According to the method for inspecting a recording head of the present invention, the occurrence of ejection defects in the recording head after inspection can be suppressed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described. In the following, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer ("Zetasizer Nano ZS" manufactured by Malvern Instruments, unless otherwise specified.

[0012] In the following, unless otherwise specified, the measured acid value is a value measured according to "JIS (Japanese Industrial Standards) K0070-1992". Furthermore, unless otherwise specified, the measured mass average molecular weight (Mw) is a value measured using gel permeation chromatography.

[0013] In this specification, acrylic and methacrylic may be collectively referred to as “(meth)acrylic.” “1 ppm” indicates 0.0001% by mass.

[0014] <First embodiment: Ink set> An ink set according to a first embodiment of the present invention will be described below. The ink set of the present invention comprises an inkjet ink (hereinafter sometimes simply referred to as ink) and a recording head filling liquid (hereinafter sometimes simply referred to as filling liquid). The ink contains a pigment, a 1,2-alkanediol having 7 or 8 carbon atoms, and water. The filling liquid contains a specific alcohol compound having 10 to 12 carbon atoms, a specific surfactant, and water. The HLB value of the specific surfactant is 5.0 or less. The content of the specific alcohol compound in the filling liquid is 0.1 ppm or more and 1.0 ppm or less.

[0015] In the ink set of the present invention, the filling liquid is used by filling a recording head in which ink remains. For example, when the recording head is not used for a while for some reason after ink is ejected by the recording head, the filling liquid is filled into the recording head. Specifically, the filling liquid is filled into the recording head when the recording head is shipped, stored for a long period of time, or transported. The ink set of the present invention is suitable as an ink set used in the recording head inspection method according to the second embodiment.

[0016] The ink set of the present invention has the above-mentioned configuration, so that the filling liquid is easily introduced into the ink flow path in the recording head, and the pigment components in the ink (for example, the pigment and the pigment coating resin described later) can be effectively suppressed from coagulating in the recording head. The reason for this is presumed to be as follows. The filling liquid contains a specific surfactant (relatively highly hydrophobic surfactant) with an HLB value of 5.0 or less. The specific surfactant effectively reduces the surface activity of the filling liquid. In addition, the ink contains a 1,2-alkanediol having 7 or 8 carbon atoms. Such a long-chain 1,2-alkanediol has a highly hydrophilic region and a highly hydrophobic region in the molecule, and the hydrophobicity of the molecule as a whole is relatively high. Therefore, the 1,2-alkanediol reduces the surface activity of the ink. As a result, when the filling liquid is filled into a recording head in which ink remains, the ink in the ink set of the present invention is easily diffused into the filling liquid. From the above, the ink set of the present invention makes it easy for the filling liquid to be introduced into the ink flow path in the recording head.

[0017] On the other hand, when the ink and the filler liquid are mixed, the specific surfactant tends to have difficulty forming micelles by itself to disperse the pigment in the ink. In contrast, in the ink set of the present invention, the filler liquid contains a specific amount of a specific alcohol compound having 10 to 12 carbon atoms. Such a specific alcohol compound promotes the formation of micelles by the specific surfactant. As a result, when the ink and the filler liquid are mixed, the ink set of the present invention allows the specific surfactant to form micelles to disperse the pigment in the ink. From the above, the ink set of the present invention can suppress aggregation of the pigment component in the ink in the recording head.

[0018] The ink set of the present invention will be described in more detail below. Each of the components described below may be used alone or in combination of two or more.

[0019] [ink] The ink contains a pigment, a 1,2-alkanediol having 7 or 8 carbon atoms, and water. The ink preferably further contains a pigment-coating resin. In the ink, the pigment forms pigment particles together with the pigment-coating resin, for example. The pigment particles are present in a dispersed state in a solvent. From the viewpoint of improving the color density, hue, or stability of the ink, the D of the pigment particles is preferably selected from the group consisting of 1,2-alkanediol, ... 50 The thickness is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0020] (Pigments) Examples of pigments contained in the ink include yellow pigments, orange pigments, red pigments, blue pigments, purple pigments, and black pigments. Examples of yellow pigments include CI Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include CI Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include CI Pigment Red (122 and 202). Examples of blue pigments include CI Pigment Blue (15, more specifically 15:3). Examples of purple pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0021] In the ink, the pigment content is preferably 1.0% by mass or more and 12.0% by mass or less, and more preferably 4.0% by mass or more and 8.0% by mass or less. By making the pigment content 1.0% by mass or more, the image density of the image formed by the ink can be made to a desired value. In addition, by making the pigment content 12.0% by mass or less, the fluidity of the ink can be improved.

[0022] (pigment coated resin) The pigment coating resin is a resin that is soluble in the ink. A part of the pigment coating resin is present, for example, on the surface of the pigment particle, and improves the dispersibility of the pigment particle. A part of the pigment coating resin is present, for example, in a dissolved state in the ink.

[0023] The pigment coating resin is preferably a styrene-acrylic resin. The styrene-acrylic resin is a copolymer of at least one monomer selected from the group consisting of an alkyl (meth)acrylate ester and (meth)acrylic acid, and styrene. The styrene-acrylic resin preferably has a repeating unit derived from (meth)acrylic acid ((meth)acrylic acid unit), a repeating unit derived from an alkyl (meth)acrylate ester ((meth)acrylic acid alkyl ester unit), and a styrene unit.

[0024] Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate. The (meth)acrylic acid alkyl ester is preferably methyl methacrylate or butyl acrylate.

[0025] Of all the repeating units contained in the pigment coating resin, the proportion of (meth)acrylic acid units is preferably 20% by mass or more and 60% by mass or less. Of all the repeating units contained in the pigment coating resin, the proportion of (meth)acrylic acid alkyl ester units is preferably 30% by mass or more and 65% by mass or less. Of all the repeating units contained in the pigment coating resin, the proportion of styrene units is preferably 5% by mass or more and 25% by mass or less. As the pigment coating resin, a resin having a repeating unit derived from methacrylic acid, a repeating unit derived from methyl methacrylate, a repeating unit derived from butyl acrylate, and a styrene unit is more preferable.

[0026] In the ink, the content of the pigment coating resin is preferably 0.5% by mass or more and 8.0% by mass or less, and more preferably 1.5% by mass or more and 4.0% by mass or less. By making the content of the pigment coating resin 0.5% by mass or more, the dispersibility of the pigment component can be further improved. By making the content of the pigment coating resin 8.0% by mass or less, the occurrence of nozzle clogging by the ink can be suppressed.

[0027] The acid value of the pigment coating resin is, for example, 50 mgKOH / g or more and 150 mgKOH / g or less. By setting the acid value of the pigment coating resin to 50 mgKOH / g or more and 150 mgKOH / g or less, the dispersibility of the pigment component can be further improved while improving the storage stability of the ink.

[0028] The acid value of the pigment coating resin can be adjusted by changing the amount of monomer used in synthesizing the pigment coating resin. For example, the acid value of the pigment coating resin can be increased by using a monomer (more specifically, acrylic acid, methacrylic acid, etc.) having an acidic functional group (e.g., a carboxyl group) in synthesizing the pigment coating resin.

[0029] The Mw of the pigment coating resin is, for example, from 10,000 to 50,000. By setting the Mw of the pigment coating resin to from 10,000 to 50,000, it is possible to suppress an increase in the viscosity of the ink while achieving a desired image density of the image formed by the ink.

[0030] The Mw of the pigment coating resin can be adjusted by changing the polymerization conditions for the pigment coating resin (more specifically, the amount of polymerization initiator used, polymerization temperature, polymerization time, etc.).

[0031] In the polymerization of the pigment-coated resin, the amount of the polymerization initiator used is preferably 0.001 to 5 moles, more preferably 0.01 to 2 moles, per mole of the monomer mixture. In the polymerization of the pigment-coated resin, for example, the polymerization temperature can be 50° C. to 70° C., and the polymerization time can be 10 to 24 hours. The polymerized pigment-coated resin may be used as it is as a raw material for the ink, or may be neutralized with an equivalent amount of a basic compound before use as a raw material for the ink. The basic compound is preferably a hydroxide of an alkali metal ion (e.g., NaOH).

[0032] (1,2-Alkanediol) The number of carbon atoms in the 1,2-alkanediols is 7 or 8. Examples of the 1,2-alkanediols include 1,2-heptanediol and 1,2-octanediol.

[0033] In the ink, the content of 1,2-alkanediol is preferably 0.2% by mass or more and 2.0% by mass or less, and more preferably 0.7% by mass or more and 1.5% by mass or less. By making the content of 1,2-alkanediol 0.2% by mass or more, the filler liquid can be more easily introduced into the ink flow path in the recording head. By making the content of 1,2-alkanediol 2.0% by mass or less, the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0034] (water) Water is the main solvent of the ink. The content of water in the ink is, for example, 40.0% by mass to 75.0% by mass.

[0035] (Other water-soluble organic solvents) The ink preferably further contains a water-soluble organic solvent other than the 1,2-alkanediol, such as a glycol compound, a glycol ether compound, a lactam compound, a nitrogen-containing compound, an acetate compound, thiodiglycol, glycerin, or dimethyl sulfoxide.

[0036] Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0037] Examples of glycol ether compounds 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.

[0038] Lactam compounds include, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0039] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0040] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0041] Other water-soluble organic solvents in the ink are preferably triethylene glycol monobutyl ether, 2-pyrrolidone or glycerin.

[0042] The content of the other water-soluble organic solvent in the ink is preferably from 10.0% to 45.0% by mass, and more preferably from 25.0% to 35.0% by mass. By setting the content of the other water-soluble organic solvent to be from 10.0% to 45.0% by mass, the ejection stability of the ink can be improved.

[0043] (Surfactant) The ink preferably further contains a surfactant. The surfactant improves the compatibility and dispersion stability of each component contained in the ink. The surfactant also improves the permeability (wettability) of the ink to the recording medium. The surfactant in the ink is preferably a nonionic surfactant.

[0044] Examples of the nonionic surfactant in the ink include acetylene glycol surfactants (surfactants containing an acetylene glycol compound), silicone surfactants (surfactants containing a silicone compound), and fluorine surfactants (surfactants containing a fluorine resin or a fluorine-containing compound). Examples of the acetylene glycol surfactant include an ethylene oxide adduct of acetylene glycol and a propylene oxide adduct of acetylene glycol.

[0045] When the ink contains a surfactant, the content of the surfactant in the ink is preferably from 0.1% by mass to 2.0% by mass, and more preferably from 0.2% by mass to 0.6% by mass.

[0046] (Additives) The ink may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0047] (Ink manufacturing method) The ink can be produced, for example, by mixing water, a pigment dispersion, and components added as necessary (for example, other water-soluble organic solvents and surfactants). The pigment dispersion contains a pigment, a pigment-coated resin, and water. The pigment-coated resin is prepared, for example, by neutralizing an equal amount of an alkali-soluble resin with a basic compound (for example, NaOH). The pigment dispersion can be prepared by adding a pigment to an aqueous solution containing a pigment-coated resin, and then performing a dispersion treatment. An example of the device used for the dispersion treatment is a bead mill. In the production of the ink, foreign matter and coarse particles may be removed by a filter (for example, a filter with a pore size of 5 μm or less) after the mixing treatment.

[0048] [Filling liquid] The filling liquid contains a specific alcohol compound having 10 to 12 carbon atoms, a specific surfactant, and water.

[0049] (Specific alcohol compounds) Examples of the specific alcohol compound include n-decyl alcohol, 2-propyl-1-heptanol, n-undecyl alcohol, n-dodecyl alcohol, and 2-butyl-1-octanol. As the specific alcohol compound, n-decyl alcohol or n-dodecyl alcohol is preferred.

[0050] In the filling solution, the content of the specific alcohol compound is 0.1 ppm or more and 1.0 ppm or less, and preferably 0.3 ppm or more and 0.7 ppm or less. By setting the content of the specific alcohol compound to 0.1 ppm or more and 1.0 ppm or less, the ink set of the present invention can effectively suppress aggregation of the pigment component in the ink in the recording head.

[0051] (Specific surfactant) The specific surfactant has an HLB value of 5.0 or less. The specific surfactant has an HLB value of preferably 2.0 or more and 5.0 or less, more preferably 3.5 or more and 4.5 or less. By making the HLB value of the specific surfactant 5.0 or less, in the ink set of the present invention, the filler liquid can be easily introduced into the ink flow path in the recording head.

[0052] The "HLB value" is a value indicating the degree of affinity of a surfactant for water or oil, and is calculated by the following formula based on the Griffin method. Specifically, the closer the HLB value is to 0, the higher the lipophilicity of the surfactant. Also, the closer the HLB value is to 20, the higher the hydrophilicity of the surfactant. HLB value = 20 × (sum of formula weights of hydrophilic parts) / molecular weight

[0053] The specific surfactant is preferably a nonionic surfactant, and more preferably an acetylene glycol surfactant or a sorbitan fatty acid ester.

[0054] Commercially available acetylene glycol surfactants include, for example, the "Olfine (registered trademark) series" manufactured by Nissin Chemical Industry Co., Ltd. (e.g., "D-10A", "D-10PG", and "Exp4300") and the "Surfynol (registered trademark) series" manufactured by Nissin Chemical Industry Co., Ltd. (e.g., "104", "420", and "DF110D").

[0055] Sorbitan fatty acid esters include, for example, sorbitan stearyl esters (eg, sorbitan monostearate, sorbitan distearate, and sorbitan tristearate) and sorbitan oleyl esters (eg, sorbitan monooleate and sorbitan trioleate).

[0056] Commercially available sorbitan fatty acid esters include, for example, the "ADEKA Esthole (registered trademark) series" manufactured by ADEKA Corporation (e.g., "S-60" and "S-80") and the "LEODOR (registered trademark) series" manufactured by Kao Corporation (e.g., "SP-S10V", "SP-S20", "SP-S30V", "SP-O10V", "SP-O30V", "AS-10V", "AO-10V", and "AO-15V").

[0057] The content of the specific surfactant in the filling liquid is preferably 0.03% by mass or more and 0.30% by mass or less, and more preferably 0.07% by mass or more and 0.20% by mass or less. By setting the content of the specific surfactant to 0.03% by mass or more and 0.30% by mass or less, the filling liquid can be more easily introduced into the ink flow path in the recording head, and the aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0058] (Polyhydric alcohol compounds) The filling liquid preferably further contains a polyhydric alcohol compound, such as a diol compound (glycol compound), a triol compound, or a sugar alcohol.

[0059] Examples of polyhydric alcohol compounds include polyethylene glycol (e.g., polyethylene glycol having a molecular weight of 150 to 400), ethylene glycol, 1,3-propanediol, propylene glycol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, glycerin, trimethylolethane, trimethylolpropane, and sorbitol. Polyhydric alcohol compounds are preferably polyethylene glycol, tetraethylene glycol, or glycerin.

[0060] The content of the polyhydric alcohol compound in the filling liquid is preferably 20.0% by mass to 60.0% by mass, more preferably 30.0% by mass to 50.0% by mass. By setting the content of the polyhydric alcohol compound to 20.0% by mass to 60.0% by mass, aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0061] (water) Water is a main solvent of the filling liquid, and the content of water in the filling liquid is, for example, 40.0% by mass or more and 70.0% by mass or less.

[0062] (Additives) The filling liquid may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0063] The filling liquid preferably further contains a pH adjuster. Examples of the pH adjuster include basic compounds. Examples of the basic compounds are hydroxides of alkali metal ions (e.g., NaOH). The pH of the filling liquid is preferably from pH 7 to pH 10.

[0064] (Method of manufacturing the filling liquid) The filling liquid can be produced, for example, by mixing a specific alcohol compound, a specific surfactant, water, and other components (for example, a polyhydric alcohol compound and additives) that are used as necessary.

[0065] <Second embodiment: Recording head inspection method> A method for inspecting a print head according to a second embodiment of the present invention will be described below. The method for inspecting a print head according to the present invention is a method for inspecting a print head using the ink set according to the first embodiment, and includes an inspection step for inspecting the ejection performance of the print head, and a filling step for filling the print head with a filling liquid after the inspection step. In the inspection step, the ejection performance of the print head is inspected by ejecting ink from the print head.

[0066] The printhead inspection method of the present invention uses the ink set according to the first embodiment, and therefore can suppress ejection defects from occurring in the printhead after inspection. The printhead inspection method of the present invention is carried out, for example, by a printhead manufacturer before the printhead is shipped. The printhead inspected by the printhead inspection method of the present invention is not particularly limited, but examples thereof include a piezoelectric printhead and a thermal printhead.

[0067] [Inspection process] In this process, the ejection performance of the print head is inspected. Specifically, in this process, the ejection performance of the print head is inspected by ejecting ink from the print head. In the print head inspected in this process, ink remains in the ink flow path.

[0068] In this step, the recording head after the inspection step may be washed. The method for washing the recording head is not particularly limited, but for example, a method of filling the recording head with a cleaning liquid and then discharging the cleaning liquid from the recording head can be mentioned. For example, the cleaning liquid can be a cleaning liquid containing water or a water-soluble organic solvent. In this step, even if the recording head is washed, it is difficult to completely remove the ink in the ink flow path.

[0069] [Filling process] In this process, the recording head is filled with the filling liquid. After this process, the recording head is, for example, stored in preparation 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. EXAMPLES

[0070] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0071] <Study A: Surfactants in filling fluid> In the examples, first, the surfactant used in the filling liquid was examined.

[0072] [Preparation of pigment-coated resin (R)] An alkali-soluble resin having a repeating unit derived from methacrylic acid (MAA unit), a repeating unit derived from methyl methacrylate (MMA unit), a repeating unit derived from butyl acrylate (BA unit), and a repeating unit derived from styrene (ST unit) was prepared. This alkali-soluble resin had a mass average molecular weight (Mw) of 20,000 and an acid value of 100 mgKOH / g. The mass ratio of each repeating unit in this alkali-soluble resin was "MAA unit: MMA unit: BA unit: ST unit = 40: 15: 30: 15". This alkali-soluble resin was mixed with an aqueous sodium hydroxide solution containing sodium hydroxide (neutralization treatment). By the neutralization treatment, the alkali-soluble resin was neutralized with an equal amount (strictly speaking, 105% amount) of NaOH. As a result, a pigment-coated resin solution containing a pigment-coated resin (R) and water was obtained.

[0073] The Mw of the above-mentioned alkali-soluble resin was measured under the following conditions using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation). A calibration curve was prepared using TSKgel standard polystyrenes F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 manufactured by Tosoh Corporation and n-propylbenzene.

[0074] (Conditions for measuring mass average molecular weight) Column: Tosoh Corporation's "TSKgel SuperMultiporeHZ-H" (4.6mm I.D. x 15cm semi-microcolumn) Number of columns: 3 Eluent: Tetrahydrofuran ·Flow rate: 0.35mL / min Sample injection volume: 10μL ·Measurement temperature: 40℃ Detector: IR detector

[0075] [Preparation of pigment dispersion (D)] In order to obtain the composition shown in Table 1 below, a pigment ("Lionol (registered trademark) Blue FG-7330" manufactured by Toyo Color Co., Ltd., component: copper phthalocyanine, color index: pigment blue 15:3), the above-mentioned pigment-coated resin solution containing the pigment-coated resin (R), an acetylene glycol-based surfactant "Olfine (registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd. (ethylene oxide adduct of acetylene glycol), and ion-exchanged water were added to the vessel of a media-type wet disperser ("DYNO (registered trademark)-MILL" manufactured by Willy & Bachofen (WAB)).

[0076] The "water" content in Table 1 below indicates the total content of the ion-exchanged water charged into the vessel and the water contained in the pigment-coated resin solution (more specifically, the water contained in the aqueous sodium hydroxide solution used to neutralize the alkali-soluble resin, and the water generated by the neutralization reaction of the alkali-soluble resin and sodium hydroxide).

[0077] [Table 1]

[0078] Next, the contents of the vessel were wet-dispersed. Zirconia beads (particle diameter 1.0 mm) were used as media. The amount of media added was 70 volume % of the capacity of the vessel. The dispersion conditions were a temperature of 10°C and a peripheral speed of 8 m / sec. As a result, a pigment dispersion liquid (D) was obtained.

[0079] The volume median diameter (D 50 Specifically, the obtained pigment dispersion (D) was diluted 300 times with ion-exchanged water to prepare a measurement sample. The D of the pigment particles in the measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Malvern Zetasizer Nano ZS). 50 The D of the pigment particles in the measurement sample was 50 of pigment particles contained in the pigment dispersion (D) 50 The D of the pigment particles contained in the pigment dispersion (D) 50 was 100 nm.

[0080] [Preparation of Ink (I-1)] Ion-exchanged water was added to a flask equipped with a stirrer (Three-One Motor (registered trademark) BL-600, manufactured by Shinto Scientific Co., Ltd.). While stirring the contents with the stirrer (stirring speed: 400 rpm), the pigment dispersion liquid (D), an acetylene glycol surfactant (Surfynol (registered trademark) 420, manufactured by Nissin Chemical Industry Co., Ltd.), triethylene glycol monobutyl ether, 2-pyrrolidone, glycerin, 1,2-octanediol, and ion-exchanged water were added in this order. The ratio of the amounts of each raw material added was as shown in Table 2 below. In Table 2 below, "(R)" indicates a registered trademark.

[0081] [Table 2]

[0082] In order to remove foreign matter and coarse particles from the resulting mixture, the mixture was filtered using a filter with a pore size of 5 μm, thereby obtaining an ink (I-1).

[0083] [Preparation of filling solutions (F-1) to (F-7)] Filling solutions (F-1) to (F-7) were prepared by the methods described below. First, the surfactants (S-1) to (S-7) used in the preparation of filling solutions (F-1) to (F-7) are shown in Table 1 below. In Table 3 below, "(R)" indicates a registered trademark. "EO adduct" indicates an ethylene oxide adduct.

[0084] [Table 3]

[0085] [Preparation of filling solution (F-1)] A mixed liquid was obtained by mixing 30.0 parts by mass of tetraethylene glycol (TEG), 0.10 parts by mass of surfactant (S-1) ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd., an acetylene glycol-based surfactant), 7.0 parts by mass of glycerin, sodium hydroxide, 0.00005 parts by mass (0.5 ppm) of n-decyl alcohol, and water. The amount of sodium hydroxide added was an amount (trace amount) that made the pH of the mixed liquid 8.0 to 9.0. The amount of water added was an amount that made the total amount of the mixed liquid 100 parts by mass. This mixed liquid was used as the filling liquid (F-1).

[0086] [Preparation of filling solutions (F-2) to (F-7)] Filling solutions (F-2) to (F-7) were prepared in the same manner as in the preparation of filling solution (F-1), except that the amount of each component added was changed as shown in Table 4 below.

[0087] [Preparation of ink sets (IS-1) to (IS-7)] As shown in Table 4 below, the ink (I-1) was combined with one of the filling liquids (F-1) to (F-7), thereby preparing the ink sets (IS-1) to (IS-7).

[0088] [evaluation] The ink sets (IS-1) to (IS-7) were measured for their ability to suppress ink aggregation and for their introductory properties (the ability of the introductory liquid to be easily introduced into the ink flow path in the recording head) using the following method. The measurement results are shown in Table 4 below.

[0089] (Suppression of aggregation) One part by mass of the ink (ink (I-1) in Study A) included in the ink set to be evaluated and 50 parts by mass of the filling liquid (any of filling liquids (F-1) to (F-7) in Study A) were mixed in a beaker. Next, the beaker containing the mixed liquid was stored in a thermostatic bath at 40°C for one month (storage treatment). The volume of the mixed liquid after the treatment had decreased by about 50% due to evaporation. The mixed liquid after the treatment was analyzed for the presence or absence of aggregates with a particle diameter of 3 μm or more using a particle shape image analyzer (Malvern Panatical's "FPIA (registered trademark)-3000"). The inhibition of ink aggregation was evaluated as "A (pass)" when no aggregates with a particle diameter of 3 μm or more were generated after the storage treatment, and "B (fail)" when they were generated.

[0090] In addition, when the recording head is filled with filling liquid after inspecting the recording head, the residual ink and filling liquid are mixed inside the recording head. The mixing ratio of the residual ink and filling liquid (amount of ink / amount of filling liquid) varies depending on the part of the recording head, but is expected to be about 1 / 50 at most. Therefore, the mixing ratio of the ink and filling liquid was set to 1 part by mass of ink: 50 parts by mass of filling liquid. In addition, aggregates with a particle diameter of 3 μm or more generated inside the recording head may clog the filter arranged inside the recording head and cause ink discharge failure. Therefore, whether or not aggregates with a particle diameter of 3 μm or more are generated after the storage process was used as the criterion for determining whether or not ink aggregation can be suppressed.

[0091] (Easy to introduce) An unused recording head (Kyocera Corporation's "KJ4B-QA", total number of nozzles: 2656) was washed with pure water and then thoroughly dried. The recording head was filled with 25 mL of the filling liquid (in Study A, any of filling liquids (F-1) to (F-7)) included in the ink set to be evaluated. Then, the filling liquid was discharged from the recording head by ejecting the filling liquid from the recording head. This operation was performed a total of 10 times (a total of 250 mL was filled). Then, the recording head was filled again with the filling liquid. Then, a nozzle check pattern was printed on a glass plate using the recording head filled with the filling liquid. As a result, a nozzle check pattern containing the filling liquid was formed on the glass plate. Next, the above-mentioned glass plate was read with a scanner to count the number of ejection nozzles that were able to eject the filling liquid (number of ejection nozzles). The ratio [%] (introduction rate) of the number of ejection nozzles to the total number of nozzles (2656) of the recording head was calculated using the following formula. The introductory property of the filling liquid was judged according to the following criteria. Adoption rate = 100 x number of discharge nozzles / total number of nozzles

[0092] (Criteria for determining introductory properties) A (Pass): Adoption rate is 90% or higher B (Fail): Adoption rate is less than 90%

[0093] [Table 4]

[0094] As shown in Tables 1 to 4, the filling solutions (F-1) to (F-5) included in the ink sets (IS-1) to (IS-5) contained specific surfactants with HLB values ​​of 5.0 or less. In the ink sets (IS-1) to (IS-5), the filling solutions were easily introduced into the ink flow paths in the recording head, and the pigment components in the ink were effectively prevented from coagulating in the recording head.

[0095] On the other hand, the filling liquids (F-6) to (F-7) provided in the ink sets (IS-6) to (IS-7) contained surfactants with HLB values ​​exceeding 5.0. It is determined that surfactants with HLB values ​​exceeding 5.0 are unable to sufficiently reduce the interfacial activity of the filling liquid. As a result, the ink sets (IS-6) to (IS-7) had insufficient introducibility of the filling liquid.

[0096] <Study B: Alcohol compounds in filling fluid> Next, the alcohol compound used in the filling liquid was examined.

[0097] [Preparation of filling solutions (F-8) to (F-15)] Filling solutions (F-8) to (F-15) were prepared in the same manner as in the preparation of filling solution (F-1), except that the amounts of each component added were changed as shown in Tables 5 to 6 below.

[0098] [Preparation of ink sets (IS-8) to (IS-15)] As shown in the following Tables 5 and 6, the ink (I-1) was combined with one of the filling liquids (F-8) to (F-15), thereby preparing the ink sets (IS-8) to (IS-15).

[0099] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-8) to (IS-15) were evaluated for their ability to suppress ink aggregation and for the introduceability of the filler liquid. The evaluation results are shown in Tables 5 to 6 below.

[0100] The explanations for Tables 5 and 6 are as follows: PEG-200: Polyethylene glycol ("PEG-200" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 200 Nonyl Alc: Nonyl alcohol, 9 carbon atoms Decyl Alc: n-Decyl alcohol, 10 carbon atoms Dodecyl Alc: n-dodecyl alcohol, carbon number 12 Myristyl Alc: Myristyl alcohol, 14 carbon atoms

[0101] [Table 5]

[0102] [Table 6]

[0103] As shown in Tables 5 and 6, the filling liquids (F-9), (F-10), (F-13) and (F-14) included in the ink sets (IS-9), (IS-10), (IS-13) and (IS-14) contained a specific alcohol compound having 10 to 12 carbon atoms. In (F-9), (F-10), (F-13) and (F-14), the content of the specific alcohol compound was 0.1 ppm or more and 1.0 ppm or less. In the ink sets (IS-9), (IS-10), (IS-13) and (IS-14), the filling liquid was easily introduced into the ink flow path in the recording head, and the aggregation of the pigment components in the ink in the recording head was effectively suppressed.

[0104] On the other hand, the filling liquids (F-8) and (IS-11) provided in the ink sets (IS-8) and (IS-11) contained alcohol compounds having less than 10 carbon atoms or alcohol compounds having more than 12 carbon atoms. It is determined that alcohol compounds having less than 10 carbon atoms are relatively highly hydrophilic and cannot sufficiently promote the micellization of the specific surfactant. It is determined that alcohol compounds having more than 12 carbon atoms are relatively highly hydrophobic and the alcohol compounds themselves form micelles and therefore cannot sufficiently promote the micellization of the specific surfactant. As a result, the ink sets (IS-8) and (IS-11) were unable to sufficiently suppress the aggregation of the pigment components in the ink in the recording head.

[0105] The filling liquid (F-12) included in the ink set (IS-12) contained less than 0.1 ppm of specific alcohol compounds. It is determined that the filling liquid (F-12) does not adequately promote the micellization of the specific surfactant due to a lack of specific alcohol compounds. As a result, the ink set (IS-12) was unable to adequately suppress the aggregation of the pigment components in the ink inside the recording head.

[0106] The filling liquid (F-15) included in the ink set (IS-15) contained a specific alcohol compound at a content rate exceeding 1.0 ppm. It was determined that the filling liquid (F-15) contained an excessive amount of the specific alcohol compound, which inhibited the dispersion of the pigment particles. As a result, the ink set (IS-15) was unable to sufficiently suppress the aggregation of the pigment components in the ink inside the recording head.

[0107] <Study C: Alkanediols> Next, 1,2-alkanediols in inks were examined.

[0108] [Preparation of Inks (I-2) to (I-9)] Inks (I-2) to (I-9) were prepared in the same manner as ink (I-1), except that the amounts of each component added were changed as shown in Tables 7 to 9 below.

[0109] [Preparation of ink sets (IS-16) to (IS-23)] As shown in Tables 5 and 6 below, one of the inks (I-2) to (I-9) was combined with the filling liquid (F-2), thereby preparing the ink sets (IS-16) to (IS-23).

[0110] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-16) to (IS-23) were evaluated for their ability to suppress ink aggregation and for the introductory properties of the filler liquid. The evaluation results are shown in Tables 8 to 9 below.

[0111] The explanations for Tables 8 to 9 are as follows: 1,2-Hex: 1,2-hexanediol, 6 carbon atoms 1,2-Hep: 1,2-heptanediol, 7 carbon atoms 1,2-Oct: 1,2-octanediol, 8 carbon atoms 1,2-Non: 1,2-nonanediol, 9 carbon atoms

[0112] [Table 7]

[0113] [Table 8]

[0114] [Table 9]

[0115] As shown in Table 8, the inks (I-3), (I-4), (I-6) and (I-7) included in the ink sets (IS-17), (IS-18), (IS-20) and (IS-21) contained 1,2-alkanediol having 7 or 8 carbon atoms. In the ink sets (IS-17), (IS-18), (IS-20) and (IS-21), the filler liquid was easily introduced into the ink flow path in the recording head, and the pigment components in the ink were effectively prevented from coagulating in the recording head.

[0116] On the other hand, the inks (I-2), (I-8) and (I-9) included in the ink sets (IS-16), (IS-22) and (IS-23) did not contain a 1,2-alkanediol having 7 or 8 carbon atoms. It is considered that the inks (I-2), (I-8) and (I-9) did not mix sufficiently with the filler liquid because they did not contain a 1,2-alkanediol having 7 or 8 carbon atoms. As a result, the ink sets (IS-16), (IS-22) and (IS-23) were unable to sufficiently suppress aggregation of the pigment components in the inks in the recording head.

[0117] The ink (I-5) included in the ink set (IS-19) contained a 1,2-alkanediol with nine carbon atoms. The 1,2-alkanediol with nine carbon atoms is highly hydrophobic and is considered to reduce the dispersibility of the pigment. As a result, the ink set (IS-19) was unable to sufficiently prevent the pigment components in the ink from coagulating inside the recording head. [Industrial Applicability]

[0118] The ink set and recording head inspection method of the present invention can be used in the manufacture of recording heads.

Claims

1. An ink set comprising an inkjet ink and a recording head filling liquid, The ink-jet ink contains a pigment, a 1,2-alkanediol having 7 or 8 carbon atoms, and water; the recording head filling liquid contains a specific alcohol compound having 10 to 12 carbon atoms, a specific surfactant, and water; The specific surfactant has an HLB value of 5.0 or less, The ink set, wherein the content of the specific alcohol compound in the recording head filling liquid is 0.1 ppm or more and 1.0 ppm or less.

2. The ink set according to claim 1 , wherein the specific surfactant comprises an acetylene glycol surfactant or a sorbitan fatty acid ester.

3. 3. The ink set according to claim 1, wherein the content of the specific surfactant in the recording head filling liquid is 0.03% by mass or more and 0.30% by mass or less.

4. The ink set according to any one of claims 1 to 3, wherein the specific alcohol compound includes n-decyl alcohol or n-dodecyl alcohol.

5. 5. The ink set according to claim 1, wherein the content of the 1,2-alkanediol in the ink-jet ink is from 0.2% by mass to 2.0% by mass.

6. 6. The ink set according to claim 1, wherein the recording head filling liquid is used by filling a recording head in which the ink-jet ink remains.

7. A method for inspecting a recording head using the ink set according to any one of claims 1 to 6, comprising the steps of: an inspection step of inspecting the ejection performance of the recording head; a filling step of filling the recording head with the recording head filler liquid after the inspection step, In the inspection step, the ejection performance of the recording head is inspected by ejecting the inkjet ink from the recording head.

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