Ink set and recording head inspection method

Abstract

To provide an ink set which is likely to introduce a recording head filling liquid into an ink flow channel 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 inkjet, and a recording head filling liquid. The ink for inkjet contains a pigment, a pigment coating resin, first alkali metal ions, and water. The recording head filling liquid contains polyethylene glycol, second alkali metal ions, a surface active agent, and water. A mass average molecular weight of the polyethylene glycol is 180 or more and 800 or less. A content ratio of the surface active agent in the recording head filling liquid is more than 0.00 mass% and 0.10 mass% or less. Each of the first alkali metal ions and the second alkali metal ions contains at least one of Li+, Na+ and K+.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. For this reason, after manufacturing the recording head, the recording head manufacturer generally thoroughly inspects the ejection performance and other aspects before shipping the 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, some 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 the 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 produce 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] In recent years, inkjet inks containing a pigment and a pigment-coated resin have come to be used. Such inkjet inks are not very compatible with the recording head filling liquid described in Patent Document 1. In particular, when the recording head filling liquid described in Patent Document 1 is used in combination with the above-mentioned inkjet ink, the pigment component in the inkjet ink cannot be sufficiently prevented from aggregating in the recording 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 pigment coating resin, a first alkali metal ion, and water. The recording head filling liquid contains polyethylene glycol, a second alkali metal ion, a surfactant, and water. The mass average molecular weight of the polyethylene glycol is 180 or more and 800 or less. The content of the surfactant in the recording head filling liquid is more than 0.00 mass % and 0.10 mass % or less. The first alkali metal ion and the second alkali metal ion are each Li+ , Na + and K + The filler liquid for the recording head contains at least one of the following: The first alkali metal ion and the second alkali metal ion are identical to each other. The pH of the filler liquid for the recording head is 7.0 or more and 11.5 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".

[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 pigment-coated resin, a first alkali metal ion, and water. The filling liquid contains polyethylene glycol, a second alkali metal ion, a surfactant, and water. The mass average molecular weight of the polyethylene glycol is 180 or more and 800 or less. The content of the surfactant in the filling liquid is more than 0.00 mass % and 0.10 mass % or less. The first alkali metal ion and the second alkali metal ion are each Li + , Na + and K + The filling solution contains at least one of the following: The first alkali metal ion and the second alkali metal ion are the same as each other. The pH of the filling solution is 7.0 or more and 11.5 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 discharged by the recording head, the filling liquid is filled into the recording head and used. 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, having the above-mentioned configuration, makes it easy for the filler liquid to be introduced into the ink flow path in the recording head, and effectively prevents the pigment components in the ink (pigment and pigment-coating resin) from coagulating in the recording head. The reason for this is presumed to be as follows. The ink contains Li + , Na + and K +The ink contains a first alkali metal ion containing at least one of the following: The first alkali metal ion contained in the ink is a monovalent cation and has high ionic strength, so it functions as an excellent counter ion for the pigment coating resin and contributes to improving the dispersibility of the pigment component. Thus, the first alkali metal ion is an essential component for stably dispersing the pigment component in the ink.

[0017] Here, if the filling liquid does not contain an alkali metal ion, or if the alkali metal ion contained in the filling liquid is different from the alkali metal ion contained in the ink, the dispersibility of the pigment component becomes unstable when the ink and the filling liquid are mixed. In contrast, the filling liquid contains a second alkali metal ion. The first alkali metal ion and the second alkali metal ion are the same. Therefore, the ink set of the present invention can suppress the dispersibility of the pigment component from becoming unstable when the ink and the filling liquid are mixed. Furthermore, the pigment component tends to be stably dispersed in a neutral to weakly alkaline solution. Since the filling liquid is neutral to weakly alkaline, the dispersibility of the pigment component can be maintained when mixed with the ink. Furthermore, the filling liquid contains a surfactant. The surfactant improves the dispersibility of the pigment component and makes it easier for the filling liquid to be introduced into the ink flow path in the recording head. However, a large amount of surfactant rather reduces the dispersibility of the pigment component. Therefore, the content of the surfactant in the filling liquid is very small.

[0018] Furthermore, the ink flow path in the recording head is connected to the outside air through an opening (for example, a nozzle hole). Therefore, the water in the filling liquid filled in the recording head gradually evaporates, and other components are concentrated. For this reason, the filling liquid is required to maintain the dissolved state of the surfactant even when the water evaporates. In contrast, the filling liquid contains polyethylene glycol. Polyethylene glycol is a component that easily dissolves surfactants (especially highly hydrophobic surfactants) and is difficult to volatilize. By containing polyethylene glycol, the filling liquid can maintain the dissolved state of the surfactant even if the water evaporates after the filling liquid is filled in the recording head. For this reason, the ink set of the present invention can effectively suppress the aggregation of the pigment components in the ink in the recording head. Furthermore, the polyethylene glycol contained in the filling liquid is a relatively low molecular weight with a mass average molecular weight of 180 to 800, and has a low viscosity. For this reason, 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.

[0019] 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.

[0020] [ink] The ink contains a pigment, a pigment-coated resin, a first alkali metal ion, and water.

[0021] In the ink, the pigment forms pigment particles together with, for example, a pigment-coated resin. The pigment particles are dispersed in a solvent. From the viewpoint of improving the color density, hue, or stability of the ink, the D of the pigment particles is 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.

[0022] (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).

[0023] 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.

[0024] (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.

[0025] Examples of pigment coating resins include copolymers of at least one monomer selected from the group consisting of (meth)acrylic acid alkyl esters, styrene, and vinyl naphthalene, and at least one monomer selected from the group consisting of (meth)acrylic acid and maleic acid.

[0026] The pigment coating resin is preferably a resin having 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. In this case, the proportion of the (meth)acrylic acid unit among all the repeating units contained in the pigment coating resin is preferably 20% by mass or more and 60% by mass or less. The proportion of the (meth)acrylic acid alkyl ester unit among all the repeating units contained in the pigment coating resin is preferably 30% by mass or more and 65% by mass or less. The proportion of the styrene unit among all the repeating units contained in the pigment coating resin is preferably 5% by mass or more and 25% by mass or less. The pigment coating resin is more preferably 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.).

[0032] 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 a first alkali metal ion.

[0033] (First alkali metal ion) The first alkali metal ion functions as a counter ion of the pigment coating resin. The first alkali metal ion is Li + , Na + and K + The first alkali metal ion is Li + , Na + and K + It is preferred to include only one of the above.

[0034] The first alkali metal ion is added to the ink, for example, as a salt, in particular as a hydroxide, i.e. the ink contains, for example, lithium hydroxide, sodium hydroxide or potassium hydroxide.

[0035] The amount of the first alkali metal ion in the ink is, for example, an amount sufficient to neutralize an equivalent amount of the pigment coating resin (more specifically, 90% by mass or more and 120% by mass or less of the amount sufficient to neutralize an equivalent amount of the pigment coating resin).

[0036] (water) Water is the main solvent of the ink. The content of water in the ink is, for example, 30.0% by mass to 60.0% by mass.

[0037] (Water-soluble organic solvent) The ink preferably further contains a water-soluble organic solvent, such as a glycol compound, a glycol ether compound, a lactam compound, a nitrogen-containing compound, an acetate compound, thiodiglycol, glycerin, or dimethyl sulfoxide.

[0038] 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.

[0039] 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.

[0040] Lactam compounds include, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0041] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0042] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0043] The water-soluble organic solvent in the ink is preferably triethylene glycol monobutyl ether, 2-pyrrolidone or glycerin.

[0044] The content of the 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 water-soluble organic solvent to be from 10.0% to 45.0% by mass, the ejection stability of the ink can be improved.

[0045] (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.

[0046] 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.

[0047] When the ink contains a nonionic surfactant, the content of the nonionic surfactant in the ink is preferably from 0.1% to 2.0% by mass, and more preferably from 0.2% to 0.6% by mass.

[0048] (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.

[0049] (Ink manufacturing method) The ink can be produced, for example, by mixing water, a pigment dispersion, and components added as necessary (for example, a water-soluble organic solvent and a nonionic surfactant). The pigment dispersion contains a pigment, a pigment-coated resin, and a first alkali metal ion. The pigment-coated resin is prepared, for example, by neutralizing an equal amount of an alkali-soluble resin with a salt (for example, a hydroxide) containing a first alkali metal ion. 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 using a filter (for example, a filter with a pore size of 5 μm or less) after the dispersion treatment.

[0050] [Filling liquid] The filling liquid contains polyethylene glycol, a second alkali metal ion, a surfactant, and water.

[0051] The pH of the filling liquid is from 7.0 to 11.5, and preferably from 7.5 to 9.0. By setting the pH of the filling liquid to from 7.0 to 11.5, the ink set of the present invention can effectively suppress aggregation of the pigment components in the ink within the recording head.

[0052] The contact angle of the filler liquid with respect to the stainless steel plate is preferably 60° or less. Here, the ink flow paths of the recording head are often made of stainless steel. By making the contact angle of the filler liquid with respect to the stainless steel plate 60° or less, the filler liquid can be more easily introduced into the ink flow paths in the recording head.

[0053] The static surface tension of the filling liquid at 20° C. is preferably 20 mN / m or more and 30 mN / m or less. By setting the static surface tension of the filling liquid to 20 mN / m or more and 30 mN / m or less, the filling liquid becomes more easily introduced into the ink flow path in the recording head.

[0054] (Polyethylene glycol) The mass average molecular weight (Mw) of the polyethylene glycol is 180 or more and 800 or less, and preferably 250 or more and 500 or less. By making the mass average molecular weight of the polyethylene glycol 180 or more, it is possible to suppress the polyethylene glycol from volatilizing in the recording head after the filling liquid is filled in the recording head. By making the mass average molecular weight of the polyethylene glycol 800 or less, it is possible to appropriately reduce the viscosity of the filling liquid. As a result, the filling liquid is easily introduced into the ink flow path in the recording head.

[0055] The content of polyethylene glycol in the filling liquid is preferably 3.0% by mass or more and 60.0% by mass or less, and more preferably 15.0% by mass or more and 60.0% by mass or less. By making the content of polyethylene glycol in the filling liquid 3.0% by mass or more, it is possible to more effectively suppress aggregation of the pigment components in the ink in the recording head. By making the content of polyethylene glycol in the filling liquid 60.0% by mass or less, it is possible to appropriately lower the viscosity of the filling liquid. As a result, the filling liquid becomes more easily introduced into the ink flow path in the recording head.

[0056] (Secondary alkali metal ion) The second alkali metal ion is Li + , Na + and K + The second alkali metal ion is the same as the first alkali metal ion contained in the ink. The second alkali metal ion is Li + , Na + and K + It is preferred to include only one of the above.

[0057] The second alkali metal ion is added to the filling liquid, for example, as a salt (e.g., hydroxide). That is, the filling liquid contains, for example, lithium hydroxide, sodium hydroxide, or potassium hydroxide. The second alkali metal ion imparts weak alkalinity to the filling liquid.

[0058] (Surfactant) The surfactant contained in the filling liquid is preferably a nonionic surfactant. Examples of the nonionic surfactant contained in the filling liquid include the same surfactants as those exemplified as the nonionic surfactant in the ink.

[0059] The surfactant content in the filling liquid is more than 0.00% by mass and not more than 0.10% by mass, and preferably 0.01% by mass or more and not more than 0.06% by mass. By making the surfactant content in the filling liquid more than 0.00% by mass, the filling liquid is easily introduced into the ink flow path in the recording head, and can effectively prevent the pigment components in the ink from aggregating in the recording head. By making the surfactant content in the filling liquid not more than 0.10% by mass, the filling liquid can effectively prevent the pigment components in the ink from aggregating in the recording head.

[0060] (water) Water is a main solvent of the filling liquid, and the content of water in the filling liquid is, for example, 30.0% by mass or more and 60.0% by mass or less.

[0061] (Water-soluble organic solvent) The filling liquid preferably further contains a water-soluble organic solvent. When the filling liquid contains a water-soluble organic solvent, the filling liquid can be easily discharged from the recording head. As a result, when it becomes necessary to discharge the filling liquid from the recording head filled with the filling liquid, the filling liquid can be easily discharged by discharging the filling liquid from the recording head. Examples of the water-soluble organic solvent in the filling liquid include the same water-soluble organic solvents as those exemplified as the water-soluble organic solvent in the ink. The water-soluble organic solvent in the filling liquid is preferably glycerin or propylene glycol.

[0062] The content of the water-soluble organic solvent in the filling liquid is preferably 1.0% by mass or more and 30.0% by mass or less, and more preferably 10.0% by mass or more and 20.0% by mass or less. By setting the content of the water-soluble organic solvent in the filling liquid to 1.0% by mass or more and 30.0% by mass or less, the filling liquid becomes easier to eject from the recording head.

[0063] (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.

[0064] (Method of manufacturing the filling liquid) The filling liquid can be prepared, for example, by mixing polyethylene glycol, a surfactant, and water, and then adding a salt containing a second alkali metal ion to adjust the pH.

[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: Mass average molecular weight of polyethylene glycol> In the examples, the weight average molecular weight of the polyethylene glycol used in the filling liquid was examined. The preparation methods of each raw material used in the production of the ink are described below.

[0072] [Preparation of pigment-coated resin (R-1)] 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-1) 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-1)] 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-1), 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 charged into a vessel having a capacity of 0.6 L. The contents of the vessel were then wet-dispersed using 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 dispersed using zirconia beads (particle diameter 0.5 mm) as media and a wet disperser ("Nanograin Mill" manufactured by Asada Iron Works Co., Ltd.). The dispersion conditions were a temperature of 10°C and a peripheral speed of 8 m / sec. As a result, a pigment dispersion (D-1) was obtained.

[0079] The volume median diameter (D 50 Specifically, the obtained pigment dispersion (D-1) 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 the pigment particles contained in the pigment dispersion (D-1)50 The D of the pigment particles contained in the pigment dispersion (D-1) 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 (D-1), an acetylene glycol surfactant (Surfynol (registered trademark) 420, manufactured by Nissin Chemical Industry Co., Ltd.), triethylene glycol monobutyl ether, 2-pyrrolidone, glycerin, and water were added in this order. The ratio of the amounts of each raw material added was as shown in Table 2 below.

[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 following method. First, the polyethylene glycol (PEG), triethylene glycol (TEG), and polypropylene glycol (PPG) used in the preparation of filling solutions (F-1) to (F-7) are shown below.

[0084] TEG: Triethylene glycol (Maruzen Oil Co., Ltd.), molecular weight 150 PEG-200: Polyethylene glycol ("PEG-200" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 200 PEG-300: Polyethylene glycol ("PEG-300" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 300 PEG-400: Polyethylene glycol ("PEG-400" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 400 PEG-600: Polyethylene glycol ("PEG-600" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 600 PEG-1000: Polyethylene glycol ("PEG-1000" manufactured by Sanyo Chemical Industries, Ltd.), weight average molecular weight 1000 PPG-400: Polypropylene glycol ("Polypropylene glycol 400" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), mass average molecular weight 400

[0085] (Preparation of Filling Solution (F-1)) A mixed liquid was obtained by mixing 30.0 parts by mass of triethylene glycol, 0.04 parts by mass of surfactant (S-1) ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd., an acetylene glycol-based surfactant), 15.0 parts by mass of glycerin, 1N aqueous sodium hydroxide solution, and water. The amount of 1N aqueous sodium hydroxide solution added was an amount (about 0.03 to 0.04 parts by mass) that would make the pH of the mixed liquid 8.0. The amount of water added was an amount that would make 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 3 below.

[0087] [Table 3]

[0088] [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).

[0089] [evaluation] Using the following method, the ink sets (IS-1) to (IS-7) were measured for their ability to suppress ink aggregation, their filler liquid introduction properties (the ability of the filler liquid to easily be introduced into the ink flow path in the recording head), and their filler liquid contact angles. The measurement results are shown in Table 4 below.

[0090] (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.

[0091] 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.

[0092] (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

[0093] (Criteria for determining introductory properties) A (Pass): Adoption rate is 90% or higher B (Fail): Adoption rate is less than 90%

[0094] (contact angle) The filling liquid (in Study A, any of filling liquids (F-1) to (F-7)) included in the ink set to be evaluated was dropped onto a stainless steel plate (SUS plate 304), and the static contact angle was measured. The contact angle was measured at a temperature of 23°C using a contact angle measuring device ("OCA40" manufactured by Eiko Precision Machinery Co., Ltd.).

[0095] [Table 4]

[0096] As shown in Tables 1 to 4, the filling liquids (F-2) to (F-5) included in the ink sets (IS-2) to (IS-5) contained polyethylene glycol with a mass average molecular weight of 180 or more and 800 or less. In the ink sets (IS-2) to (IS-5), the filling liquid was easily introduced into the ink flow path in the recording head, and aggregation of the pigment components in the ink in the recording head was effectively suppressed.

[0097] On the other hand, the filling liquid (F-1) included in the ink set (IS-1) contained tetraethylene glycol instead of polyethylene glycol. Tetraethylene glycol has a small mass average molecular weight, so it is considered that it cannot sufficiently ensure the solubility of the surfactant. As a result, the ink set (IS-1) was unable to suppress the aggregation of the pigment components in the ink inside the recording head.

[0098] The filling liquid (F-6) included in the ink set (IS-6) contained polyethylene glycol with a mass average molecular weight of more than 800. It was determined that the filling liquid (F-6) had a high viscosity because it contained polyethylene glycol with an excessively large mass average molecular weight. As a result, the filling liquid (F-6) included in the ink set (IS-6) was difficult to introduce into the ink flow path in the recording head.

[0099] The filling liquid (F-7) included in the ink set (IS-7) contained polypropylene glycol. Polypropylene glycol is highly hydrophobic, and is therefore believed to reduce the dispersibility of the pigment components. As a result, the ink set (IS-7) was unable to prevent the pigment components in the ink from coagulating inside the recording head.

[0100] <Study B: Type and amount of surfactant> Next, the type and amount of the surfactant used in the filling solution was examined.

[0101] [Preparation of filling solutions (F-8) to (F-15)] Filling solutions (F-8) to (F-15) were prepared by the following method. First, the surfactants used in the preparation of filling solutions (F-8) to (F-15) are shown below.

[0102] S-1: Acetylene glycol surfactant ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd.) S-2: Acetylene glycol surfactant ("Surfynol (registered trademark) 104" manufactured by Nissin Chemical Industry Co., Ltd.) S-3: Silicone surfactant (BYK Japan "BYK (registered trademark) 345") S-4: Fluorine-based surfactant (AGC Seimi Chemical Co., Ltd. "Surflon (registered trademark) S242")

[0103] 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.

[0104] [Table 5]

[0105] [Table 6]

[0106] [Preparation of ink sets (IS-8) to (IS-15)] As shown in Table 7 below, 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).

[0107] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-8) to (IS-15) were measured for their ability to suppress ink aggregation, their introduceability of the filler liquid, and their contact angle with the filler liquid. The measurement results are shown in Table 7 below.

[0108] [Table 7]

[0109] As shown in Tables 5 to 7, the filling liquids (F-8) to (F-12) and (F-14) included in the ink sets (IS-8) to (IS-12) and (IS-14) contained an acetylene glycol surfactant, a silicone surfactant or a fluorine surfactant as a surfactant. The surfactant content in the filling liquids (F-8) to (F-12) and (F-14) was more than 0.00% by mass and 0.10% by mass or less. In the ink sets (IS-8) to (IS-12) 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.

[0110] On the other hand, the filler fluids (F-13) and (F-15) included in the ink sets (IS-13) and (IS-15) contained surfactants in amounts exceeding 0.10% by mass. It is believed that the filler fluids in the ink sets (IS-13) and (IS-15) contained a large amount of surfactant, which interacted with the pigment-coating resin, causing the pigment components to aggregate. As a result, the ink sets (IS-13) and (IS-15) were unable to prevent the pigment components in the ink from aggregating inside the recording head.

[0111] <Study C: Types of alkali metal ions> Next, the types of alkali metal ions contained in the ink and the filling liquid were examined.

[0112] [Preparation of pigment-coated resins (R-2) to (R-5)] Pigment-coated resins (R-2) to (R-5) were prepared in the same manner as in the preparation of pigment-coated resin (R-1), except for the following changes. In the preparation of pigment-coated resins (R-2) to (R-5), a lithium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a cesium hydroxide aqueous solution, or a magnesium hydroxide aqueous solution was used instead of a sodium hydroxide aqueous solution in the neutralization treatment of the alkali-soluble resin. In other words, the alkali-soluble resin was neutralized with an equal amount (strictly speaking, 105% amount) of LiOH, KOH, CsOH, or Mg(OH)2. In this way, a pigment-coated resin solution containing any one of pigment-coated resins (R-2) to (R-5) and water was obtained.

[0113] [Preparation of pigment dispersions (D-2) to (D-5)] Pigment dispersions (D-2) to (D-5) were prepared in the same manner as in the preparation of pigment dispersion (D-1), except for the following changes: In preparing pigment dispersions (D-2) to (D-5), a pigment coating resin solution containing any one of the above-mentioned pigment coating resins (R-2) to (R-5) was used so as to have the composition shown in Table 8 below.

[0114] [Table 8]

[0115] [Preparation of Inks (I-2) to (I-5)] As shown in Table 9 below, inks (I-2) to (I-5) were prepared in the same manner as ink (I-1), except that pigment dispersions (D-2) to (D-5) were used instead of pigment dispersion (D-1).

[0116] [Table 9]

[0117] [Preparation of filling solutions (F-16) to (F-20)] A mixed liquid was obtained by mixing 35.0 parts by mass of the above-mentioned "PEG-400", 0.04 parts by mass of a surfactant (S-1) ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd., an acetylene glycol-based surfactant), 10.0 parts by mass of glycerin, an alkali component shown in Table 10 below, and water. The amount of the alkali component added was an amount (trace amount) that would give a pH of the mixed liquid of 8.0 to 9.0. The amount of water added was an amount that would give a total amount of the mixed liquid of 100 parts by mass. The obtained mixed liquids were used as filling liquids (F-16) to (F-20).

[0118] The concentrations of the aqueous sodium hydroxide (NaOH) solution, the aqueous potassium hydroxide (KOH) solution, and the aqueous lithium hydroxide (LiOH) solution shown in Table 10 below were each 1N.

[0119] [Table 10]

[0120] [Preparation of ink sets (IS-16) to (IS-23)] As shown in Table 11 below, one of the inks (I-1) to (I-5) was combined with one of the filling liquids (F-16) to (F-20). In this way, ink sets (IS-16) to (IS-23) were prepared. Table 11 below also shows the ions (alkali metal ions) contained in each ink or filling liquid.

[0121] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-16) to (IS-23) were measured for their ability to suppress ink aggregation, their introduceability of the filler liquid, and their contact angle with the filler liquid. The measurement results are shown in Table 11 below.

[0122] [Table 11]

[0123] As shown in Tables 8 to 11, the inks and filler solutions of the ink sets (IS-16) to (IS-18) contained the same alkali metal ions. The alkali metal ions were Li + , Na + and K + In the ink sets (IS-16) to (IS-18), the filler 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.

[0124] On the other hand, the ink sets (IS-19) and (IS-20) are inks and filler liquids that are Cs + or Mg 2+ It contained Cs + It is considered that the pigment component could not be stably dispersed in the water due to the low ionic strength. 2+ Since is a divalent cation, it is considered that it aggregated the pigment components. As a result, the ink sets (IS-19) and (IS-20) were unable to suppress the aggregation of the pigment components in the ink inside the recording head.

[0125] Ink sets (I-21) to (I-23) are inks and filler liquids each containing different alkali metal ions (Li + , Na + Or K + ) was contained. It is believed that if the type of alkali metal ion contained in the filler liquid is different from the type of alkali metal ion contained in the ink, the dispersibility of the pigment component decreases when the filler liquid and the ink are mixed. As a result, the ink sets (IS-21) to (IS-23) were unable to suppress the aggregation of the pigment component in the ink inside the recording head.

[0126] <Study D: pH of filling solution> [Preparation of filling solutions (F-21) to (F-24)] A mixed liquid was obtained by mixing 35.0 parts by mass of the above-mentioned "PEG-400", 0.04 parts by mass of a surfactant (S-1) ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd., an acetylene glycol-based surfactant), 10.0 parts by mass of glycerin, 1N aqueous sodium hydroxide solution, and water. The amount of the 1N aqueous sodium hydroxide solution added was an amount (trace amount) that made the pH of the mixed liquid 8.0 to 12.0, as shown in Table 12 below. The amount of water added was an amount that made the total amount of the mixed liquid 100 parts by mass. The obtained mixed liquids were used as filling liquids (F-21) to (F-24).

[0127] [Table 12]

[0128] [Preparation of ink sets (IS-24) to (IS-27)] As shown in Table 13 below, the ink (I-1) was combined with one of the filling liquids (F-21) to (F-24), thereby preparing the ink sets (IS-24) to (IS-27).

[0129] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-24) to (IS-27) were measured for the ability to suppress ink aggregation, the introduceability of the filler liquid, and the contact angle of the filler liquid. The measurement results are shown in Table 13 below.

[0130] [Table 13]

[0131] As shown in Tables 12 and 13, the pH of the filler solutions (F-21) to (F-23) in the ink sets (IS-24) to (IS-26) was 7.0 or more and 11.5 or less. In the ink sets (IS-24) to (IS-26), the filler solution was easily introduced into the ink flow path in the recording head, and aggregation of the pigment components in the ink in the recording head was effectively suppressed.

[0132] On the other hand, the pH of the filler fluid (F-24) included in the ink set (IS-27) was over 11.5. It is believed that if the pH of the filler fluid is too high, the dispersibility of the pigment component decreases. As a result, the ink set (IS-27) was unable to suppress the aggregation of the pigment component in the ink inside the recording head.

[0133] <Study E: Amount of polyethylene glycol> [Preparation of filling solutions (F-25) to (F-26)] The above-mentioned "PEG-300", 0.04 parts by mass of a surfactant (S-1) ("Olfine (registered trademark) Exp4300" manufactured by Nissin Chemical Industry Co., Ltd., an acetylene glycol surfactant), 10.0 parts by mass of glycerin, 1N aqueous sodium hydroxide solution, and water were mixed to obtain a mixed liquid. The amount of "PEG-300" added was as shown in Table 14 below. The amount of 1N aqueous sodium hydroxide added was an amount (trace amount) that made the pH of the mixed liquid 8.0. The amount of water added was an amount that made the total amount of the mixed liquid 100 parts by mass. The obtained mixed liquids were used as filling liquids (F-25) to (F-26).

[0134] [Table 14]

[0135] [Preparation of ink sets (IS-28)~(IS-29)] As shown in Table 15 below, the ink (I-1) was combined with one of the filling liquids (F-25) to (F-26), thereby preparing the ink sets (IS-28) to (IS-29).

[0136] [evaluation] Using the same method as for the ink sets (IS-1) to (IS-7), the ink sets (IS-28) to (IS-29) were measured for their ability to suppress ink aggregation, their introduceability of the filler liquid, and their contact angle with the filler liquid. The measurement results are shown in Table 15 below.

[0137] [Table 15]

[0138] As shown in Tables 14 and 15, the polyethylene glycol content in the filling liquids (F-25) to (F-26) of the ink sets (IS-28) to (IS-29) was 3.0% by mass or more and 60.0% by mass or less. In the ink sets (IS-28) to (IS-29), the filling liquid was easily introduced into the ink flow path in the recording head, and aggregation of the pigment components in the ink in the recording head was effectively suppressed. [Industrial Applicability]

[0139] 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 pigment-coated resin, a first alkali metal ion, and water, The recording head filling fluid contains polyethylene glycol, a second alkali metal ion, a surfactant, and water; The mass average molecular weight of the polyethylene glycol is 180 or more and 800 or less, a content ratio of the surfactant in the recording head filling fluid is more than 0.00% by mass and not more than 0.10% by mass, a content ratio of the polyethylene glycol in the recording head filling fluid is 3.0% by mass or more and 60.0% by mass or less, The first alkali metal ion and the second alkali metal ion each include at least one of Li+, Na+, and K+; the first alkali metal ion and the second alkali metal ion are identical to each other; The ink set, wherein the pH of the recording head filling liquid is 7.0 or more and 11.5 or less.

2. The ink set according to claim 1 , wherein the surfactant comprises at least one of an acetylene glycol surfactant, a silicone surfactant, and a fluorine-based surfactant.

3. 3. 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.

4. A method for inspecting a recording head using the ink set according to any one of claims 1 to 3, 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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