Ink set and method of inspecting recording head

Abstract

To provide a recording head filling liquid that is easily introduced into an ink flow path in a recording head, can effectively inhibit aggregation of a pigment component in an inkjet ink in the recording head, and can be stably purged.SOLUTION: An ink set comprises: an inkjet ink that contains a pigment, a first surfactant, and an aqueous medium; and a recording head filling liquid that contains a specific moisturizing agent represented by formula (1), a second surfactant, and water. The first surfactant and the second surfactant are each independently a compound represented by formula (2).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. Generally, the recording head is thoroughly inspected for ejection performance before being shipped. To inspect the ejection performance of the recording head, an ejection test is performed by actually filling the recording head with inkjet ink.

[0003] However, if the recording head is shipped with ink-jet ink remaining in the ink flow path, the solvent of the ink-jet ink may evaporate during transportation or storage, causing the solids (particularly the pigment components) of the ink-jet ink to aggregate and produce aggregates. The above-mentioned aggregates may cause ejection defects in the recording head after shipment.

[0004] Therefore, in some cases, recording head manufacturers ship recording heads filled with a solution that does not contain pigment components (hereinafter, sometimes referred to as recording head filling fluid). The recording head filling fluid is required to be able to be purged from a recording head that has been left unused for a while.

[0005] Furthermore, the print head filler fluid enters the ink flow paths of the print head and dilutes the ink-jet ink remaining in the ink flow paths, so the print head filler fluid is required to be easily introduced into the ink flow paths in the print head.

[0006] As the recording head filling liquid, for example, a recording head filling liquid containing silicone oil has been proposed (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2010-227729 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, Patent Document 1 cannot meet the above-mentioned requirements.

[0009] 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 which allows the print head filler liquid to be easily introduced into the ink flow paths in the print head, effectively prevents the pigment components in the inkjet ink from coagulating in the print head, and enables the print head filler liquid to be stably purged. Another object of the present invention is to provide a method for inspecting a print head using the above ink set. [Means for solving the problem]

[0010] 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 first surfactant, and an aqueous medium. The recording head filling liquid contains a specific humectant, a second surfactant, and water. The specific humectant is a compound represented by the following general formula (1). The first surfactant and the second surfactant are each independently a compound represented by the following general formula (2).

[0011] [ka]

[0012] In the general formula (1), a, b, and c each independently represent an integer of 1 or more, and a+b+c is 5 or more and 20 or less.

[0013] [ka]

[0014] In the general formula (2), m and n are each independently a number between 0.0 and 12.0. m+n is a number between 8.0 and 12.0. x is a number between 1.0 and 20.0. y is a number between 2.0 and 10.0.

[0015] 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

[0016] According to the ink set of the present invention, the print head filler liquid can be easily introduced into the ink flow path in the print head, the pigment components in the inkjet ink can be effectively prevented from coagulating in the print head, and the print head filler liquid can be stably purged. According to the print head inspection method of the present invention, the occurrence of ejection defects in the inspected print head can be prevented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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 (for example, Zetasizer (registered trademark) Nano ZS manufactured by Malvern Instruments) unless otherwise specified.

[0018] 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.

[0019] In the following, unless otherwise specified, the measured value of dynamic surface tension is the dynamic surface tension with a surface life of 10 milliseconds, measured at 25°C by the maximum bubble pressure method using a bubble pressure type dynamic surface tensiometer (e.g., KRUSS "BP100", capillary diameter 0.4 mm).

[0020] In the following, unless otherwise specified, the measured viscosity values ​​are values ​​measured at 25°C using a falling ball viscometer (for example, "Lovis2000" manufactured by Anton Paar).

[0021] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Additionally, "at least one of A and B" means "A and / or B."

[0022] [First embodiment: ink set] An ink set according to a first embodiment of the present invention will be described below. The ink set according to this embodiment 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 first surfactant, and an aqueous medium. The filling liquid contains a specific humectant, a second surfactant, and water. The specific humectant is a compound represented by the following general formula (1). The first surfactant and the second surfactant are each independently a compound represented by the following general formula (2).

[0023] [ka]

[0024] In the general formula (1), a, b, and c each independently represent an integer of 1 or more, and a+b+c is 5 or more and 20 or less.

[0025] [ka]

[0026] In the general formula (2), m and n each independently represent a number between 0.0 and 12.0. m+n is between 8.0 and 12.0. x represents a number between 1.0 and 20.0. y represents a number between 2.0 and 10.0.

[0027] In the ink set according to this embodiment, the filler liquid may contain multiple types of compounds represented by general formula (1). In this case, in general formula (1), a, b, and c respectively represent the number average values ​​of a, b, and c in the multiple types of compounds represented by general formula (1).

[0028] In the ink set according to the present embodiment, the ink may contain multiple types of compounds represented by general formula (2). The filling liquid may contain multiple types of compounds represented by general formula (2). In these cases, in general formula (2), m, n, x, and y respectively represent the number average values ​​of m, n, x, and y in the multiple types of compounds represented by general formula (2).

[0029] In the ink set according to this embodiment, the filling liquid is used by filling a recording head in which ink remains. For example, when the recording head is left unused for a while for some reason after ink is ejected by the recording head, the filling liquid is filled into the recording head for use. Specifically, the filling liquid is filled into the recording head for use when the recording head is shipped, stored for a long period of time, or transported. The ink set according to this embodiment is suitable as an ink set for use in the recording head inspection method according to the second embodiment.

[0030] The ink set according to the present embodiment has the above-mentioned configuration, so that the filling liquid can be easily introduced into the ink flow path in the recording head, the pigment components (pigment and pigment-coated resin) in the ink can be effectively suppressed from agglomerating in the recording head, and the filling liquid can be stably purged. The reason is presumed to be as follows. The ink set according to the present embodiment includes ink and a filling liquid. The filling liquid enters the ink flow path of the recording head and dilutes the ink remaining in the ink flow path. As a result, the solid content of the ink remaining in the ink flow path is less likely to aggregate. In particular, the ink set according to the present embodiment contains a specific moisturizing agent represented by general formula (1) in the filling liquid. In general formula (1), a, b, and c represent integers of 1 or more, and a+b+c is 5 or more. The specific moisturizing agent has a low viscosity, and the pressure (purge pressure) of the recording head when purging the filling liquid does not increase. Therefore, the ink set according to the present embodiment can stably purge the filling liquid from the recording head even after the recording head is left standing. Furthermore, although the reason is unclear, according to the study of the present inventors, aggregation of the pigment components in the ink within the recording head cannot be sufficiently suppressed with a humectant in which a+b+c in general formula (1) exceeds 20. The ink set according to this embodiment contains a specific humectant in which a, b, and c in general formula (1) represent integers of 1 or more, and a+b+c is 5 or more and 20 or less, thereby making it possible to sufficiently suppress aggregation of the pigment components in the ink within the recording head and stably purge the filler liquid.

[0031] The ink set according to the present embodiment contains a compound represented by general formula (2) in the ink as a first surfactant. The ink set according to the present embodiment contains a compound represented by general formula (2) in the filling liquid as a second surfactant. When the ink contains a compound represented by general formula (2), the dynamic surface tension of the ink can be reduced. When the filling liquid contains a compound represented by general formula (2), the dynamic surface tension of the filling liquid can be reduced. Moreover, the compound represented by general formula (2) has a hydrophobic alkyl chain and has a structure in which a propylene oxide group, which is more hydrophobic than an ethylene oxide group, is bonded to an ethylene oxide group ether-bonded to the alkyl chain. Therefore, the compound represented by general formula (2) has high hydrophobicity and good wettability. For these reasons, in the ink set according to the present embodiment, when the ink and the filling liquid are mixed, the filling liquid is easily introduced into the ink flow path in the recording head. The ink set according to the present embodiment will be described in more detail below. Note that each component described below may be used alone or in combination of two or more.

[0032] [ink] The ink contains a pigment, a first surfactant, and an aqueous medium. In the ink, the pigment forms pigment particles together with, for example, a pigment-coated resin. For this reason, it is preferable that the ink contains a pigment, a pigment-coated resin, a first surfactant, and an aqueous medium. The pigment particles are present in a dispersed state in a solvent. From the viewpoint of optimizing the color density, hue, or stability of the ink, it is preferable to adjust the D of the pigment particles. 50 The thickness is preferably 30 nm or more and 300 nm or less, and more preferably 50 nm or more and 150 nm or less.

[0033] (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).

[0034] In the ink, the pigment content is preferably 2.0% by mass or more and 15.0% by mass or less, and more preferably 5.0% by mass or more and 10.0% by mass or less. By making the pigment content 2.0% by mass or more, it becomes easier to form an image having a desired image density. In addition, by making the pigment content 15.0% by mass or less, the fluidity of the ink can be ensured.

[0035] (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 to impart dispersibility to the pigment particle. A part of the pigment coating resin is present, for example, in a dissolved state in the ink.

[0036] 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.

[0037] As the pigment coating resin, styrene-(meth)acrylic resin is preferred. The styrene-(meth)acrylic resin has a repeating unit derived from at least one monomer selected from among (meth)acrylic acid alkyl esters and (meth)acrylic acid, and a styrene unit. As the (meth)acrylic acid alkyl esters, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate are listed. As the styrene-(meth)acrylic resin, a copolymer (X) of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate is preferred. The copolymer (X) is preferably neutralized with an equal amount of a basic compound (e.g., potassium hydroxide or sodium hydroxide).

[0038] In the total repeating units contained in the copolymer (X), the content of repeating units derived from styrene is preferably 10.0% by mass or more and 20.0% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from methyl methacrylate is preferably 10.0% by mass or more and 20.0% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from methacrylic acid is preferably 35.0% by mass or more and 45.0% by mass or less. In the total repeating units contained in the copolymer (X), the content of repeating units derived from butyl acrylate is preferably 25.0% by mass or more and 35.0% by mass or less.

[0039] In the ink, the content of the pigment coating resin is preferably 0.7% by mass to 6.0% by mass, and more preferably 2.0% by mass to 4.0% by mass. By setting the content of the pigment coating resin to 0.7% by mass to 6.0% by mass, it is possible to prevent the ink from clogging the nozzles.

[0040] The acid value of the pigment coating resin is preferably from 30 mgKOH / g to 300 mgKOH / g, and more preferably from 50 mgKOH / g to 150 mgKOH / g. By setting the acid value of the pigment coating resin to be from 30 mgKOH / g to 300 mgKOH / g, it is possible to optimize the storage stability of the ink while optimizing the dispersibility of the pigment.

[0041] 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.

[0042] The Mw of the pigment coating resin is preferably from 10,000 to 50,000, and more preferably from 15,000 to 25,000. By setting the Mw of the pigment coating resin to from 10,000 to 50,000, it is possible to optimize the image density of an image formed by the ink while suppressing an increase in the viscosity of the ink.

[0043] 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.).

[0044] In the polymerization of the pigment-coated resin, the amount of the polymerization initiator used is preferably 0.001 to 5.0 mol, more preferably 0.01 to 2.0 mol, per mol of the monomer mixture. In the polymerization of the pigment-coated resin, for example, the polymerization temperature can be 50° C. to 70° C., and the polymerization time can be 10 to 24 hours. The polymerized pigment-coated resin is preferably neutralized with an equal amount of a basic compound before being used as a raw material for the ink. The basic compound is preferably a hydroxide of an alkali metal ion (e.g., potassium hydroxide or sodium hydroxide).

[0045] (First Surfactant) The first surfactant is a compound represented by the above general formula (2). In the general formula (2), m and n are each independently a number between 0.0 and 12.0. m+n is 8.0 or more and 12.0 or less. In the general formula (2), m and n are each independently preferably a number between 0.0 and 11.0, and m+n is preferably 9.0 or more and 11.0 or less. In the general formula (2), x is a number between 1.0 and 20.0. y is a number between 2.0 and 10.0. x is preferably a number between 6.0 and 16.0, and more preferably a number between 6.0 and 8.0. y is preferably a number between 2.0 and 3.0. In the general formula (2), x is more preferably a number between 6.0 and 8.0, and y is even more preferably a number between 2.0 and 3.0.

[0046] The compound represented by the general formula (2) is a nonionic surfactant having a polyoxyalkylene alkyl ether as a main skeleton, and has an ether bond (-O-) in the molecule that does not dissociate into ions even when dissolved in water. The compound represented by the general formula (2) has a hydrophobic alkyl chain in which m+n in the general formula (2) is 8.0 or more and 12.0 or less. The compound represented by the general formula (2) has a structure in which a propylene oxide group (-[CH2CH2O]-), which is more hydrophobic than an ethylene oxide group, is bonded to an ethylene oxide group (-[CH2CH(CH3)O]-) that is ether-bonded to the above-mentioned alkyl chain. Therefore, the compound represented by the general formula (2) has high hydrophobicity and good wettability.

[0047] Commercially available products of the compound represented by general formula (2) include, for example, "SOFTANOL (registered trademark) EP5035", "SOFTANOL (registered trademark) EP7025", "SOFTANOL (registered trademark) EP7045", "SOFTANOL (registered trademark) EP7085", "SOFTANOL (registered trademark) EP9050", and "SOFTANOL (registered trademark) EP12030" manufactured by Nippon Shokubai Co., Ltd.

[0048] In the ink, the content of the first surfactant (in other words, the compound represented by general formula (2)) is preferably 0.1% by mass or more and 2.5% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less. By setting the content of the first surfactant to 0.1% by mass or more and 2.5% by mass or less, the filling liquid can be more reliably introduced into the ink flow path in the recording head. Therefore, it is possible to reliably obtain an ink set in which the filling liquid is easily introduced into the ink flow path in the recording head, the pigment components in the ink can be effectively prevented from coagulating in the recording head, and the filling liquid can be stably purged.

[0049] (Other surfactants) The ink may contain only the first surfactant as a surfactant, or may further contain a surfactant other than the first surfactant (hereinafter, referred to as another surfactant). The content of the first surfactant in the surfactant is preferably 60.0% by mass or more, and more preferably 80.0% by mass or more.

[0050] Examples of other surfactants include surfactants in which y is 1.0 or less in general formula (2), acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds), and fluorine surfactants (surfactants containing fluorine resins or fluorine-containing compounds). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol.

[0051] The content of other surfactants in the ink is preferably from 0.1% by mass to 0.5% by mass, and more preferably from 0.1% by mass to 0.3% by mass.

[0052] (aqueous medium) The aqueous medium contained in the ink is a medium containing water. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include aqueous media containing water and a water-soluble organic solvent.

[0053] The content of the aqueous medium in the ink is preferably from 30.0% by mass to 95.0% by mass, and more preferably from 70.0% by mass to 95.0% by mass.

[0054] (water) Water is the main solvent of the ink. The content of water in the ink is, for example, preferably from 20.0% by mass to 80.0% by mass, and more preferably from 50.0% by mass to 70.0% by mass.

[0055] (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.

[0056] 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.

[0057] 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.

[0058] Lactam compounds include, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

[0059] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0060] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0061] The water-soluble organic solvent in the ink is preferably triethylene glycol monobutyl ether, 2-pyrrolidone or glycerin.

[0062] The content of the water-soluble organic solvent in the ink is preferably from 10.0% to 80.0% by mass, and more preferably from 20.0% to 40.0% by mass. By setting the content of the water-soluble organic solvent to be from 10.0% to 80.0% by mass, the ink can be ejected from the recording head more stably.

[0063] (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.

[0064] (Preferred composition) The ink preferably has any one of compositions 1 to 6 shown in Table 1 below. In Table 1 below, "ratio" indicates a numerical range of a preferable content ratio [mass %]. For example, "5.4-6.6" which is the pigment ratio of composition 1 in Table 1 indicates that the pigment is contained in an amount of 5.4 mass % or more and 6.6 mass % or less. The same applies to the notations in the other columns. "S-1", "S-3", "S-4", and "S-5" for the type of the first surfactant respectively indicate the surfactants (S-1), (S-3), (S-4), and (S-5) used in the examples. "Resin" indicates a pigment-coated resin. "TGBE" indicates triethylene glycol mono-n-butyl ether.

[0065] [Table 1]

[0066] (Ink manufacturing method) The ink can be produced, for example, by mixing a pigment dispersion containing a pigment, a first surfactant, an aqueous medium, and components added as necessary (for example, other surfactants, additives). The first surfactant can be produced, for example, by mixing a branched alcohol with KOH, dehydrating the mixture at 90°C to 130°C and 1.1 kPa to 1.5 kPa for 15 to 45 minutes, adding ethylene oxide, and reacting at 135°C to 175°C for 15 to 45 minutes. By confirming that no raw material components remain by gas chromatography analysis of the reaction liquid, it can be confirmed that the target substance represented by general formula (2) is obtained. 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, sodium hydroxide). 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 an apparatus used for the dispersion treatment is a bead mill. In the production of 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.

[0067] [Filling liquid] The filling liquid contains a specific moisturizing agent, a second surfactant, and water.

[0068] (Specific moisturizer) The specific moisturizing agent is a compound represented by the above-mentioned general formula (1). In the general formula (1), a, b, and c each independently represent an integer of 1 or more. a+b+c is 5 or more and 20 or less. a+b+c preferably represents an integer of 6 or more and 18 or less, more preferably represents an integer of 6 or more and 15 or less, and even more preferably represents an integer of 6 or more and 9 or less. When a+b+c is small, the pressure (purge pressure) of the recording head when purging the filling liquid increases. On the other hand, when a+b+c is large, the aggregation of the pigment component in the ink cannot be sufficiently suppressed. In the general formula (1), the specific moisturizing agent in which a+b+c is an integer of 5 or more and 20 or less has a low viscosity (for example, a viscosity at 25°C of 450 mPa·s or less), and the pressure (purge pressure) of the recording head when purging the filling liquid does not increase. In addition, in the general formula (1), a specific moisturizing agent in which a+b+c is an integer of 5 or more and 20 or less can maintain high dispersion stability of the pigment component in the ink and can effectively suppress aggregation of the pigment component in the ink in the recording head. In addition, by setting a+b+c in the general formula (1) to, for example, 6 or more and 18 or less, aggregation of the pigment component in the ink in the recording head can be more effectively suppressed.

[0069] In general formula (1), a, b, and c may be the same or different. In general formula (1), a, b, and c can be changed in various ways by adjusting reaction conditions such as the reaction temperature and reaction time of glycerin and polyethylene glycol. Therefore, in general formula (1), a, b, and c may be a=b=c, a=c≠b, or a≠b≠c. Only one of a and c may be the same as b.

[0070] As described above, in the general formula (1), a, b, and c can be set independently of each other, but in the general formula (1), a, b, and c are preferably a=b=c or a=c≠b. By using these specific humectants, it is possible to more effectively suppress the aggregation of the pigment components in the ink in the recording head, and to more stably purge the filling liquid. In addition, when a, b, and c in the general formula (1) are a=b=c, a+b+c can be freely set within the range of a multiple of 3 from 6 to 18.

[0071] Furthermore, in general formula (1), when a, b, and c satisfy a=c≠b, a, c, and b can be freely set within the range of a+b+c being 5 or more and 20 or less (however, as described above, a, b, and c each independently represent an integer of 1 or more). However, in general formula (1), when a, b, and c satisfy a=c≠b, b is preferably a+1 or a+2. In this case, aggregation of the pigment components in the ink in the recording head can be more effectively suppressed, and the filler liquid can be purged more stably.

[0072] The viscosity of the specific moisturizing agent at 25°C is preferably 230 mPa·s or more and 450 mPa·s or less, more preferably 270 mPa·s or more and 450 mPa·s or less, even more preferably 300 mPa·s or more and 450 mPa·s or less, and even more preferably 340 mPa·s or more and 410 mPa·s or less. By having the viscosity of the specific moisturizing agent be 230 mPa·s or more and 450 mPa·s or less, aggregation of the pigment components in the ink in the recording head can be effectively suppressed. In addition, the filling liquid can be stably purged from the recording head after the recording head is left standing.

[0073] The content of the specific moisturizing agent in the filling liquid is preferably 10.0% by mass or more and 50.0% by mass or less, and more preferably 25.0% by mass or more and 40.0% by mass or less. By making the content of the specific moisturizing agent in the filling liquid 10.0% by mass or more and 50.0% by mass or less, it is possible to effectively suppress the aggregation of the pigment component in the ink in the recording head. In addition, the filling liquid can be stably purged from the recording head after the recording head is left standing. In addition, by making the content of the specific moisturizing agent in the filling liquid 25.0% by mass or more and 40.0% by mass or less, it is possible to more effectively suppress the aggregation of the pigment component in the ink in the recording head.

[0074] (Second Surfactant) Like the first surfactant, the second surfactant is also a compound represented by the above general formula (2). The compound represented by general formula (2) used in the second surfactant can be, for example, the same as the compound represented by general formula (2) used in the first surfactant. Therefore, a duplicated description will be omitted. The first surfactant and the second surfactant may be the same compound or different compounds, but are preferably the same compound.

[0075] In the filling liquid, the content of the second surfactant (in other words, the compound represented by the general formula (2)) is preferably 0.1% by mass or more and 2.5% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less. By setting the content of the second surfactant to 0.1% by mass or more and 2.5% by mass or less, the filling liquid can be more reliably introduced into the ink flow path in the recording head when the ink and the filling liquid are mixed. Therefore, the filling liquid is easily introduced into the ink flow path in the recording head, the aggregation of the pigment components in the ink in the recording head can be effectively suppressed, and an ink set that can stably purge the filling liquid can be reliably obtained.

[0076] (water) Water is the main solvent of the filling liquid. The content of water in the filling liquid is, for example, preferably 35.0% by mass or more and 95.0% by mass or less, and more preferably 45.0% by mass or more and 85.0% by mass or less.

[0077] (Other ingredients) 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.

[0078] (Preferred composition) The filling liquid preferably has any one of compositions 1 to 18 shown in Table 2 below. In Table 2 below, "ratio" indicates a numerical range of a preferred content ratio [mass %]. For example, "27.0-33.0", which is the ratio of a specific moisturizing agent in composition 1, indicates that the specific moisturizing agent is contained in an amount of 27.0 mass % or more and 33.0 mass % or less. The same applies to the notations in other columns. "M-2", "M-3", "M-4", "M-5", "M-8", "M-9", "M-10", and "M-11" for the types of specific moisturizing agents indicate moisturizing agents (M-2), (M-3), (M-4), (M-5), (M-8), (M-9), (M-10), and (M-11) used in the examples, respectively. The types of second surfactants "S-1," "S-3," "S-4," and "S-5" respectively indicate the surfactants (S-1), (S-3), (S-4), and (S-5) used in the examples.

[0079] [Table 2]

[0080] The combination of the specific moisturizing agent and the second surfactant is not particularly limited, and various combinations are possible within the scope of the above description. However, as a combination of the specific moisturizing agent and the second surfactant, for example, the specific moisturizing agent is moisturizing agent (M-2), (M-3), or (M-8), and the second surfactant is surfactant (S-1) is preferable. Therefore, in the ink set according to this embodiment, the specific moisturizing agent is preferably a compound in which a+b+c in general formula (1) is 6 or more and 10 or less, and the second surfactant is preferably a compound in general formula (2) in which x represents a number of 6.0 or more and 8.0 or less, and y represents a number of 2.0 or more and 3.0 or less. Also, as described above, it is preferable that the first surfactant and the second surfactant are the same compound. Therefore, in the ink set according to this embodiment, it is more preferable that the specific humectant is a compound in which a+b+c in general formula (1) is 6 or greater and 10 or less, and the first surfactant and the second surfactant are compounds in general formula (2) in which x is a number that is 6.0 or greater and 8.0 or less, and y is a number that is 2.0 or greater and 3.0 or less.

[0081] (Method of manufacturing the filling liquid) The filling liquid can be produced, for example, by mixing a specific moisturizing agent, a second surfactant, water, and a component (for example, an additive) that is added as necessary. In the general formula (1), a, b, and c are a=b=c, and the specific moisturizing agent can be produced by reacting polyethylene glycol with glycerin at, for example, 180 to 220°C to etherify. In the general formula (1), a, b, and c are a=c≠b, and the specific moisturizing agent can also be produced by reacting polyethylene glycol with glycerin to etherify. However, in the production of a specific moisturizing agent in the general formula (1), a, b, and c are a=c≠b, first, polyethylene glycol and glycerin are reacted at, for example, 140 to 180°C to complete the reaction of the two α-position hydroxyl groups bonded to the primary carbon of glycerin. This forms an intermediate. Next, this intermediate is reacted with polyethylene glycol at, for example, 200 to 240°C to complete the reaction of the β-position hydroxyl group bonded to the secondary carbon of glycerin. This produces a specific moisturizing agent in which a, b, and c in general formula (1) satisfy a=c≠b. The method for producing the second surfactant can be, for example, the same as that for the first surfactant.

[0082] [Dynamic surface tension] As described above, the ink set according to the present embodiment can reduce the dynamic surface tension of the ink by containing a compound represented by general formula (2) as a first surfactant in the ink. In addition, the ink set according to the present embodiment can reduce the dynamic surface tension of the filling liquid by containing a compound represented by general formula (2) as a second surfactant in the filling liquid. It is preferable that the dynamic surface tension of the ink and the dynamic surface tension of the filling liquid are both 35.0 mN / m or less at a surface life of 10 milliseconds at 25°C. If the dynamic surface tension of the ink and the dynamic surface tension of the filling liquid are 35.0 mN / m or less at a surface life of 10 milliseconds at 25°C, the ink and the filling liquid spread out in the recording head in a short time. As a result, when the ink and the filling liquid are mixed, it becomes easier to introduce the filling liquid into the ink flow path in the recording head. Furthermore, if the dynamic surface tension of the ink and the dynamic surface tension of the filler liquid with a surface life of 10 milliseconds at 25°C are 25.0 mN / m or more and 35.0 mN / m or less, the filler liquid can be more reliably introduced into the ink flow path in the recording head when the ink and the filler liquid are mixed.

[0083] [Second embodiment: recording head inspection method] A method for inspecting a printhead according to a second embodiment of the present invention will be described below. The method for inspecting a printhead according to the present invention is a method for inspecting a printhead using the ink set according to the first embodiment, and includes an inspection step for inspecting the ejection performance of the printhead, and a filling step for filling the printhead with filler liquid after the inspection step. In the inspection step, the ejection performance of the printhead is inspected by ejecting ink using the printhead. The ink set used in the method for inspecting a printhead according to this embodiment can be the same as the ink set described in the first embodiment. Therefore, a duplicated description will be omitted.

[0084] The printhead inspection method according to the present embodiment 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 according to the present embodiment is performed, for example, before a printhead manufacturer ships the printhead. The printhead inspected by the printhead inspection method according to the present embodiment is not particularly limited, and examples thereof include a piezoelectric printhead and a thermal printhead. The printhead may be, for example, a line printhead.

[0085] [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.

[0086] 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.

[0087] [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

[0088] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0089] In the examples, the Mw of the alkali-soluble resin and the surfactant were measured under the following conditions using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation). Calibration curves were 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.

[0090] (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

[0091] [Study 1: Type and amount of moisturizer in filling fluid] First, the type and amount of humectant used in the filling liquid was examined. The preparation methods of each raw material used in the production of the ink are shown below.

[0092] [Preparation of pigment dispersion] A pigment dispersion (D-1) for use in preparing an ink was prepared. In preparing the pigment dispersion (D-1), first, a pigment coating resin solution containing the pigment coating resin (R-1) and water was prepared.

[0093] (Preparation of pigment coated resin solution) 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 (neutralization treatment). The alkali-soluble resin was neutralized with sodium hydroxide (NaOH) by the neutralization treatment. In the neutralization treatment, the amount of the aqueous sodium hydroxide solution used was 1.05 times the theoretical amount of the aqueous sodium hydroxide solution required to neutralize the alkali-soluble resin. In this way, the alkali-soluble resin was neutralized with an equal amount (strictly speaking, 105% amount) of sodium hydroxide, thereby obtaining a pigment-coated resin solution containing a pigment-coated resin (R-1) (neutralized alkali-soluble resin) and water.

[0094] (Distributed Processing) The above-mentioned pigment-coated resin solution containing a magenta pigment (CI Pigment Red 122) and a pigment-coated resin (R-1), surfactant A, and ion-exchanged water were added to the vessel of a media-type wet disperser (DYNO (registered trademark)-MILL manufactured by WAB) so as to obtain the composition shown in Table 3 below.

[0095] The "water" content in Table 3 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). Surfactant A indicates "Olfine (registered trademark) E1010" (ethylene oxide adduct of acetylene glycol), an acetylene glycol surfactant (nonionic surfactant) manufactured by Nissin Chemical Industry Co., Ltd.

[0096] [Table 3]

[0097] Next, the contents of the vessel were wet-dispersed. Zirconia beads (particle diameter 1.0 mm) were used as media. The amount of media put in 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 was obtained.

[0098] The volume median diameter (D 50 ) was measured. Specifically, the obtained pigment dispersion (D-1) was diluted 300 times with ion-exchanged water, and this was used as 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 ("Zetasizer (registered trademark) Nano ZS" manufactured by Malvern Instruments). 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 measurement was carried out 10 times, and the average of the measurement results was taken as the D of the pigment particles. 50 The D of the pigment particles contained in the pigment dispersion (D-1) was adopted. 50 was 100 nm.

[0099] [Ink preparation] [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 above-mentioned stirrer (stirring speed: 400 rpm), pigment dispersion liquid (D-1) (6.0 parts by mass of pigment, 2.4 parts by mass of pigment-coated resin (R-1)), surfactant (S-1) shown in Table 4 below, triethylene glycol mono-n-butyl ether, 2-pyrrolidone, and glycerin were added in this order. Details of the surfactant (S-1) used in the preparation of ink (I-1) are shown in Table 4 below. In Table 4 below, m+n, x, and y represent the values ​​of m+n, x, and y in the general formula (2) of the surfactant. In Table 4 below, "(R)" represents a registered trademark. The ratio of the amount of each raw material added was as shown in Table 5 below.

[0100] [Table 4]

[0101] [Table 5]

[0102] [Preparation of filling solution] Filling solutions (F-1) to (F-14) were prepared by the following method. First, the details of the moisturizers (M-1) to (M-12) used in the preparation of filling solutions (F-1) to (F-14) are shown below.

[0103] [Moisturizers (M-1)~(M-12)] The compounds shown in Tables 6 and 7 were prepared by the method described below, and these were designated as moisturizers (M-1) to (M-12). The viscosity of moisturizers (M-1) to (M-12) was measured at 25°C using a falling-ball viscometer ("Lovis2000" manufactured by Anton Paar). The moisturizers (M-2) to (M-5) and (M-8) to (M-11) were specific moisturizers. The moisturizers (M-2) to (M-5) were compounds in which a, b, and c in the general formula (1) were a=b=c, and a+b+c was a multiple of 3 between 6 and 18. The moisturizers (M-8) to (M-12) were compounds in which a, b, and c in the general formula (1) were a=c≠b. Furthermore, the moisturizers (M-8) to (M-12) were compounds in which in the general formula (1), b was a+1 or a+2.

[0104] [Preparation of moisturizers (M-2) to (M-6)] Polyethylene glycol and glycerin were reacted at 200°C for etherification. In this way, compounds as moisturizers (M-2) to (M-6) shown in Table 6 were synthesized. It was confirmed by high performance liquid chromatography (HPLC) that the peaks of glycerin and polyethylene glycol of the obtained compounds were 99% or more. In detail, acetonitrile and water were added to the obtained compounds and mixed, and quantitative analysis was performed by HPLC under the following conditions. - HPLC equipment: Hitachi High-Tech Science Corporation "HITACHI D-7000" ·Flow rate: 1.0mL / min Detector: ESA Biosciences "Corona CAD Detector"

[0105] (Glycerin analysis conditions) Column: Tosoh Corporation "TSK-GEL Amide-80" (5 μm, 4.6 × 250 mm) Solution: 50% by volume acetonitrile / water (distilled water)

[0106] (Polyethylene glycol analysis conditions) Column: GL Science "Inertsil C8-3" (5 μm, 4.6 × 150 mm) Solution: Acetonitrile / water (distilled water) The volume ratio of acetonitrile in the solution was kept at 45% by volume for 3 minutes, and then a linear gradient was run for 9 minutes from 45% by volume to 98% by volume, after which the volume ratio of acetonitrile was kept at 98% by volume.

[0107] [Preparation of moisturizer (M-1)] A compound as moisturizer (M-1) shown in Table 6 was synthesized in the same manner as moisturizers (M-2) to (M-6), except that ethylene glycol was used instead of polyethylene glycol. The obtained compound was confirmed to have glycerin and ethylene glycol peaks of 99% or more by the same method as moisturizers (M-2) to (M-6).

[0108] [Preparation of moisturizers (M-7) to (M-12)] The compounds as moisturizers (M-7) to (M-12) shown in Table 7 were synthesized by the same method as moisturizers (M-2) to (M-6), except for the following changes. In the synthesis of the compounds as moisturizers (M-7) to (M-12), first, polyethylene glycol and glycerin were reacted at 160°C to complete the reaction of the two α-position hydroxyl groups bonded to the primary carbon of glycerin. After this, an intermediate was formed, and then this intermediate was reacted with polyethylene glycol at 220°C to complete the reaction of the β-position hydroxyl group bonded to the secondary carbon of glycerin. In this way, the compounds as moisturizers (M-7) to (M-12) shown in Table 7 were synthesized. It was confirmed that the peaks of glycerin and polyethylene glycol of the obtained compounds were 99% or more by the same method as moisturizers (M-1) to (M-6).

[0109] [Table 6]

[0110] [Table 7]

[0111] [Preparation of filling solution (F-1)] A mixture was obtained by mixing 30.0 parts by mass of the moisturizing agent (M-1), 0.2 parts by mass of the above-mentioned surfactant (S-1), and ion-exchanged water. The amount of ion-exchanged water added was such that the total amount of the mixture was 100.0 parts by mass. This mixture was used as the filling liquid (F-1).

[0112] [Preparation of filling solutions (F-2) to (F-14)] Filling solutions (F-2) to (F-14) were prepared in the same manner as filling solution (F-1), except that the types and amounts of each component were changed as shown in Tables 8 to 10.

[0113] [Table 8]

[0114] [Table 9]

[0115] [Table 10]

[0116] [Ink set preparation] As shown in the following Tables 11 to 13, the ink (I-1) was combined with any one of the filling liquids (F-1) to (F-14), thereby preparing the ink sets of Examples 1 to 10 and Comparative Examples 1 to 4.

[0117] [Rating 1] The ink sets of Examples 1 to 10 and Comparative Examples 1 to 4 were evaluated by the following methods for the ink aggregation suppression performance (ability to suppress aggregation of pigment components in the ink) in an open system (with evaporation) and a closed system (without evaporation), the purging property of the filling liquid (whether the filling liquid can be purged after being left as it is) and the introductory property of the filling liquid (the tendency of the filling liquid to be easily introduced into the ink flow path in the recording head). The evaluation results are shown in Tables 11 to 13 below.

[0118] (Aggregation suppression performance (open system)) 1.0 part by mass of the ink (ink (I-1) in study 1) included in the ink set to be evaluated and 50.0 parts by mass of the filling liquid (any of filling liquids (F-1) to (F-14) in study 1) were mixed in a beaker. Next, the beaker containing the mixed liquid was stored in a thermostatic bath at 40°C without sealing for one month (storage treatment). 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").

[0119] 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 is set to 1.0 part by mass of ink: 50.0 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 is used as the criterion for determining whether or not ink aggregation can be suppressed.

[0120] (Agglomeration suppression performance (closed system)) "Flocculation inhibition performance (closed system)" was evaluated in the same manner as the evaluation of "Flocculation inhibition performance (open system)" above, except for the following changes. When evaluating "Flocculation inhibition performance (closed system)", the beaker was sealed with parafilm during storage processing to prevent evaporation. "Flocculation inhibition performance (closed system)" is evaluated under milder conditions than "Flocculation inhibition performance (open system)" because there is no concentration of pigment components due to evaporation of the solvent.

[0121] (Criteria for evaluating aggregation inhibition performance) A (Pass): In both open and closed systems, no aggregates with particle diameters of 3 μm or more were generated after storage and processing. B (Fail): Aggregates with particle diameters of 3 μm or more were generated in at least one of the open and closed systems after storage treatment.

[0122] (Purgeability) When filling liquid is purged from a recording head that has been left in a high-temperature environment, the water-soluble organic solvent and moisture in the filling liquid inside the recording head evaporate, causing the viscosity of the filling liquid around the nozzles to increase. If the viscosity of the filling liquid increases, the pressure (purge pressure) of the recording head when purging the filling liquid increases, destroying the recording head. According to the study by the present inventors, if the viscosity of the moisturizing agent at 25°C is 450 mPa·s or less, the filling liquid can be purged without problems without increasing the purge pressure, and there is no risk of destroying the recording head. Therefore, whether the viscosity of the moisturizing agent at 25°C is 450 mPa·s or less is used as a criterion for purging the filling liquid (whether the filling liquid can be purged after being left alone).

[0123] (Purgeability criteria) A (Pass): Viscosity of moisturizer at 25°C is 450 mPa s or less B (Fail): Viscosity of moisturizer at 25°C exceeds 450 mPa s

[0124] (Easy to introduce) First, an unused recording head (Kyocera Corporation's "KJ4B-QA", total number of nozzles: 2656) was filled with 100 cc of the ink (ink (I-1) in study 1) included in the ink set to be evaluated, and discharged. Next, the recording head was washed with pure water and then thoroughly dried. Next, the recording head was filled with 300 cc of the filling liquid (any of filling liquids (F-1) to (F-14) in study 1) included in the ink set to be evaluated, and discharged. This operation was performed a total of 10 times. After that, the recording head was filled with the filling liquid again. 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 was formed on the glass plate using the filling liquid. Next, the above-mentioned glass plate was read with a scanner to count the number of discharge nozzles that could discharge the filling liquid (number of discharge nozzles). The ratio [%] (introduction rate) of the number of discharge nozzles to the total number of nozzles (2656) of the recording head was calculated using the following formula. The introduceability of the filling liquid was evaluated according to the following criteria. Adoption rate = 100 x number of discharge nozzles / total number of nozzles

[0125] (Criteria for determining introductory properties) A (Pass): Adoption rate is 90% or higher B (Fail): Adoption rate is less than 90%

[0126] [Dynamic surface tension] In addition, the dynamic surface tension of the ink of each Example and Comparative Example at a surface life of 10 milliseconds and the dynamic surface tension of the filling liquid of each Example and Comparative Example at a surface life of 10 milliseconds were measured by the maximum bubble pressure method using a bubble pressure type dynamic surface tensiometer (KRUSS "BP100", capillary diameter 0.4 mm) at 25° C. The measurement results are shown in Tables 11 to 13 below.

[0127] [Table 11]

[0128] [Table 12]

[0129] [Table 13]

[0130] In Tables 11 to 13, "Type of surfactant" indicates the type of surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling fluid. "Surfactant proportion" indicates the content [mass %] of the surfactant (first surfactant) contained in the ink or the surfactant (second surfactant) contained in the filling fluid. "Type of humectant" indicates the type of humectant contained in the filling fluid. "Humectant proportion" indicates the content [mass %] of the humectant in the filling fluid.

[0131] As shown in Tables 3 to 13, the ink of each Example contained a pigment, a first surfactant, and an aqueous medium, and the filling liquid contained a specific humectant, a second surfactant, and water. The specific humectant was a compound represented by general formula (1), and the first surfactant and the second surfactant were each compounds represented by general formula (2).

[0132] As shown in Tables 3 to 13, if a+b+c in the general formula (1) of the moisturizer is less than 5, the purging property of the filling liquid will be unacceptable. On the other hand, if a+b+c in the general formula (1) of the moisturizer is more than 20, sufficient ink aggregation suppression performance will not be obtained. For this reason, it was found that a+b+c in the general formula (1) of the moisturizer is favorable when it is 5 or more and 20 or less.

[0133] Furthermore, as shown in Tables 3 to 13, when the content of the specific moisturizer in the filling liquid was 10.0% by mass or more and 50.0% by mass or less, the evaluation results were good. This shows that when the content of the specific moisturizer in the filling liquid is within the above-mentioned range, the filling liquid is easily introduced into the ink flow path in the recording head, aggregation of the pigment components in the ink in the recording head can be effectively suppressed, and an ink set that can stably purge the filling liquid can be reliably obtained.

[0134] [Study 2: Type and amount of surfactant] Next, the type and amount of the surfactant contained in the filling liquid and the ink were examined.

[0135] [Preparation of surfactants (S-2) to (S-7)] As the surfactants, the above-mentioned surfactant (S-1) and surfactants (S-2) to (S-7) shown in Table 14 below were prepared. In the product names in Table 14 below, "(R)" indicates a registered trademark. Among the surfactants (S-1) to (S-7), surfactants (S-1) and (S-3) to (S-5) were compounds represented by general formula (2). Surfactant (S-2) was a surfactant in which y = 0.0 in the general formula (2). Surfactant (S-6) was a surfactant in which y = 1.0 in the general formula (2). In Table 14 below, m + n, x, and y represent the numerical values ​​of m + n, x, and y in the general formula (2) of the surfactant.

[0136] [Table 14]

[0137] [Preparation of surfactant] The compounds shown in Table 14 were prepared by the method described below, and these were designated as surfactants (S-2) to (S-6).

[0138] [Preparation of surfactant (S-2)] A mixture was obtained by mixing 197 g (1 mole equivalent) of a branched alcohol corresponding to m+n=10.0 in the general formula (2) with 3 g of KOH. This mixture was dehydrated for 30 minutes while reacting at 110°C and 1.3 kPa using an autoclave equipped with a stirrer, a temperature control device, and an automatic introduction device. This removed some of the water in the mixture. After dehydration of the mixture, nitrogen replacement was performed and the autoclave was heated to 155°C. Then, 314 g of ethylene oxide (1 mole equivalent, corresponding to x in the general formula (2)) was added to the mixture in the autoclave using the automatic introduction device. After the addition of ethylene oxide, the autoclave was kept at 155°C and the reaction was carried out for 30 minutes. It was confirmed by gas chromatography analysis of the reaction liquid that no raw material components remained, and it was determined that the compound obtained by this reaction was the target substance having the m+n value, x value, and y value shown in Table 14. The compound obtained by this reaction was designated as surfactant (S-2).

[0139] [Preparation of Surfactants (S-3) to (S-6)] The surfactants (S-3) to (S-6) shown in Table 14 were synthesized by the same method as for preparing surfactant (S-2), except that the type and amount of raw materials used and the reaction time were changed so that the values ​​of m+n, x, and y in general formula (2) were the values ​​shown in Table 14. Branched alcohols react preferentially with the ethylene oxide moiety, not with the propylene oxide moiety. Therefore, by changing the type and amount of raw materials used and the reaction time, the surfactants (S-3) to (S-6) shown in Table 14 can be prepared.

[0140] [Preparation of Inks (I-2) to (I-10)] Inks (I-2) to (I-10) were prepared in the same manner as for the preparation of ink (I-1), except that the types and amounts of each raw material were changed as shown in the following Tables 15 and 16. In addition, "TGBE" in Tables 15 and 16 stands for triethylene glycol mono-n-butyl ether.

[0141] [Table 15]

[0142] [Table 16]

[0143] [Preparation of filling solutions (F-15) to (F-23)] Filling solutions (F-15) to (F-23) were prepared in the same manner as filling solution (F-1), except that the type and amount of each component was changed as shown in Table 17 or Table 18.

[0144] [Table 17]

[0145] [Table 18]

[0146] [Ink set preparation] As shown in the following Tables 19 to 21, any one of the inks (I-1) to (I-10) was combined with any one of the filling liquids (F-2) and (F-15) to (F-23), thereby preparing the ink sets of Examples 11 to 18 and Comparative Examples 5 to 10.

[0147] [Rating 2] The ink sets of Examples 11 to 18 and Comparative Examples 5 to 10 were evaluated for the ink aggregation suppression performance, the purging property of the filling liquid, and the introduction property of the filling liquid by the same method as that described in [Evaluation 1]. However, in [Evaluation 2], as described above, any of the inks (I-1) to (I-10) was used as the inks included in the ink sets to be evaluated. Also, any of the filling liquids (F-2) and (F-15) to (F-23) was used as the filling liquids included in the ink sets to be evaluated. The evaluation results are shown in Tables 19 to 21 below. Also, the dynamic surface tensions of the inks of each Example and Comparative Example at a surface life of 10 milliseconds and the dynamic surface tensions of the filling liquids of each Example and Comparative Example at a surface life of 10 milliseconds were measured by the method described in [Study 1: Type of humectant in the filling liquid]. The measurement results are shown in Tables 19 to 21 below.

[0148] [Table 19]

[0149] [Table 20]

[0150] [Table 21]

[0151] In Tables 19 to 21, "Type of surfactant" indicates the type of surfactant (first surfactant) contained in the ink or the type of surfactant (second surfactant) contained in the filling fluid. "Surfactant proportion" indicates the content proportion [mass %] of the surfactant (first surfactant) contained in the ink or the surfactant (second surfactant) contained in the filling fluid. "Type of humectant" indicates the type of humectant contained in the filling fluid. "Humectant proportion" indicates the content proportion [mass %] of the humectant in the filling fluid.

[0152] As shown in Tables 14 to 21, the ink of each Example contained a pigment, a first surfactant, and an aqueous medium, and the filling liquid contained a specific humectant, a second surfactant, and water. The specific humectant was a compound represented by general formula (1), and the first surfactant and the second surfactant were each compounds represented by general formula (2).

[0153] As shown in Tables 14 to 21, when the first surfactant and the second surfactant are each a compound represented by general formula (2), the filler liquid is easily introduced into the ink flow path in the recording head.

[0154] However, as shown in Comparative Example 7, if the ink and filler liquid do not contain a surfactant, the dynamic surface tension of the ink and filler is high, making it difficult for the filler liquid to be introduced into the ink flow path in the recording head. If the ink and filler liquid do not contain a surfactant, the dynamic surface tension of the ink and filler liquid at 25°C with a surface life of 10 milliseconds becomes 35 mN / m or more.

[0155] In addition, when a compound having y=0.0 in general formula (2) that does not have a propylene oxide group is used as the surfactant of the ink as in Comparative Example 5, the dynamic surface tension of the ink increases, and as a result, it becomes difficult for the filler liquid to be introduced into the ink flow path in the recording head. In this case, the dynamic surface tension of the ink at 25°C with a surface life of 10 milliseconds becomes 35 mN / m or more.

[0156] Furthermore, when a compound having y=0.0 in general formula (2) that does not have a propylene oxide group is used as the surfactant of the filling liquid as in Comparative Example 6, the dynamic surface tension of the filling liquid becomes high, making it difficult for the filling liquid to be introduced into the ink flow path in the recording head. In this case, the dynamic surface tension of the filling liquid at 25°C with a surface life of 10 milliseconds becomes 35 mN / m or more.

[0157] Furthermore, when a compound in which y=1.0 in general formula (2) is used as the surfactant for the ink and the surfactant for the filler liquid as in Comparative Example 8, the dynamic surface tension of the ink and the filler increases, making it difficult for the filler liquid to be introduced into the ink flow path in the recording head. When a compound in which y=1.0 in general formula (2) is used as the first surfactant and the second surfactant, the dynamic surface tension of the ink and the filler liquid at 25° C. with a surface life of 10 milliseconds becomes 35 mN / m or more.

[0158] Furthermore, as shown in Tables 14 to 21, it has been found that the first surfactant and the second surfactant are preferably the same compound, but may be different compounds, provided that they are each independently a compound represented by general formula (2).

[0159] Furthermore, as shown in Tables 14 to 21, when the content of the first surfactant in the ink was 0.1% by mass or more and 2.5% by mass or less, the evaluation results were good. This shows that when the content of the first surfactant in the ink is within the above-mentioned range, it is possible to reliably obtain an ink set in which the filler liquid is easily introduced into the ink flow path in the recording head, aggregation of the pigment component in the ink in the recording head can be effectively suppressed, and the filler liquid can be stably purged.

[0160] Furthermore, as shown in Tables 14 to 21, when the content of the second surfactant in the filling liquid was 0.1% by mass or more and 2.5% by mass or less, the evaluation results were good. This shows that when the content of the second surfactant in the filling liquid is within the above-mentioned range, the filling liquid is easily introduced into the ink flow path in the recording head, aggregation of the pigment components in the ink in the recording head can be effectively suppressed, and an ink set that can stably purge the filling liquid can be reliably obtained. [Industrial Applicability]

[0161] 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 first surfactant, and an aqueous medium, the recording head filling liquid contains a specific humectant, a second surfactant, and water; The specific moisturizing agent is a compound represented by the following general formula (1): the first surfactant and the second surfactant are each independently a compound represented by the following general formula (2): 【Chemistry 1】 (In the general formula (1), a, b, and c each independently represent an integer of 1 or more, and a+b+c is 5 or more and 20 or less.) 【Chemistry 2】 (In the general formula (2), m and n each independently represent a number of 0.0 or more and 12.0 or less, m+n is a number of 8.0 or more and 12.0 or less, x represents a number of 1.0 or more and 20.0 or less, and y represents a number of 2.0 or more and 10.0 or less.)

2. 2. The ink set according to claim 1, wherein the viscosity of the specific humectant at 25° C. is from 230 mPa·s to 450 mPa·s.

3. 3. The ink set according to claim 1, wherein the content of the specific humectant in the recording head filling liquid is 10.0% by mass or more and 50.0% by mass or less.

4. The ink set according to claim 1 , wherein the content of the first surfactant in the inkjet ink is from 0.1% by mass to 2.5% by mass.

5. 3. The ink set according to claim 1, wherein the content of the second surfactant in the recording head filling liquid is from 0.1% by mass to 2.5% by mass.

6. The ink set according to claim 1 , wherein the first surfactant and the second surfactant are the same compound.

7. 3. The ink set according to claim 1, wherein in the general formula (1), a, b, and c satisfy a=b=c, and a+b+c is a multiple of 3 that is 6 or more and 18 or less.

8. 3. The ink set according to claim 1, wherein in the general formula (1), a, b, and c satisfy a=c≠b.

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

10. 3. The ink set according to claim 1, wherein in the general formula (2), x represents a number of 6.0 or more and 8.0 or less, and y represents a number of 2.0 or more and 3.0 or less.

11. In the general formula (1), a+b+c is 6 or more and 10 or less, 3. The ink set according to claim 1, wherein in the general formula (2), x represents a number of 6.0 or more and 8.0 or less, and y represents a number of 2.0 or more and 3.0 or less.

12. 3. A method for inspecting a recording head using the ink set according to claim 1, 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.

13. 13. The method of inspecting a recording head according to claim 12, wherein the recording head is a line type recording head.

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