Inkjet recording method

Abstract

To provide an inkjet recording method which has discharge reliability, friction fastness, washing fastness and head durability, while maintaining cleaning performance of an inkjet head.SOLUTION: An inkjet recording method has an ink absorption member for making a wiping mechanism absorb an ink composition, wherein the ink absorption member wipes off a nozzle surface of an inkjet head by a wiping unit for holding a cleaning liquid. The ink composition contains a coloring material, an organic solvent containing a glycol-based solvent, a resin, and water. The content of the glycol-based solvent in the organic solvent is 50 mass% or more with respect to the total organic solvent. The glass transition point of the resin is within the range of -70 to 0°C. The content of the resin is within the range of 5 to 15 mass% with respect to the total ink composition.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method. [Background technology]

[0002] Conventionally, inkjet printers for fabric print patterns by ejecting ink droplets (liquid) from nozzles in a print head onto fabric (recording medium) placed on a platen. In the case of color printing, the print head has inkjet heads for ejecting each of the four primary colors, for example, cyan, magenta, yellow, and black (see, for example, Patent Document 1). Various colors and patterns are expressed by combining ink dots ejected from each inkjet head. The inkjet heads are configured to be cleaned by a maintenance device (see, for example, Patent Documents 2 and 3).

[0003] Patent Document 1 describes an inkjet textile printing ink. The inkjet textile printing ink described in Patent Document 1 contains water, a pigment, an organic solvent, and polycarbonate urethane resin particles. The inkjet textile printing ink is water-based, which improves ejection stability, and contains polycarbonate urethane resin particles, which improves the friction fastness of the printed textile.

[0004] Patent Document 2 describes a liquid ejection device having a head cleaning device including a cleaning roller containing a cleaning liquid. In the liquid ejection device described in Patent Document 1, the ink head is cleaned by the head cleaning device.

[0005] Patent Document 3 describes an inkjet printer equipped with a wiping mechanism that wipes the nozzle surface of the head. The water-based ink used in inkjet printers contains water, coloring material, binder resin, and water-soluble organic solvent. In the inkjet printer described in Patent Document 2, the ink adhering to the nozzle surface of the head is wiped off by the wiping mechanism.

[0006] In the head cleaning device of Patent Document 2 and the wiping mechanism of Patent Document 3, the durability of the head is increased by including a cleaning liquid. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-123235 A [Patent Document 2] JP 2005-161870 A [Patent Document 3] JP 2012-179825 A Summary of the Invention [Problem to be solved by the invention]

[0008] For example, when the inkjet textile printing ink described in Patent Document 1 is used in the liquid ejection device of Patent Document 2 or the inkjet printer of Patent Document 3, there is room for improvement in the durability of the inkjet head.

[0009] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an inkjet recording method which has ejection reliability, resistance to friction, and head durability while maintaining cleaning performance for the inkjet head. [Means for solving the problem]

[0010] An inkjet recording method according to an embodiment of the present invention is an inkjet recording method for forming an image on a recording medium using an ink composition and an inkjet recording device having a wiping mechanism, the wiping mechanism having an ink absorbing member for absorbing the ink composition, the ink absorbing member wiping a nozzle surface of an inkjet head with a wiper unit holding a cleaning liquid, the ink composition containing a colorant, an organic solvent including a glycol-based solvent, a resin, and water, the content of the glycol-based solvent in the organic solvent is 50% by mass or more with respect to the total organic solvent, the glass transition point of the resin is within a range of -70 to 0°C, and the content of the resin is within a range of 5 to 15% by mass with respect to the total ink composition. Effect of the Invention

[0011] According to the present invention, it is possible to provide an inkjet recording method that has ejection reliability, friction resistance, and head durability while maintaining head cleaning performance. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing a schematic configuration of an inkjet recording apparatus to which a wiping unit according to the present invention is applied. [Diagram 2] FIG. 2 is a perspective view for explaining a method of supplying the cleaning liquid to the wiping unit. [Diagram 3] FIG. 3 is a perspective view of a main part showing a state in which the wiping unit is pressed against the inkjet head. [Figure 4] 4A and 4B are cross-sectional views showing the fixed state of the sheet-shaped flexible member. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The inkjet recording method of the present embodiment is an inkjet recording method for forming an image on a recording medium using an ink composition and an inkjet recording device equipped with a wiping mechanism, the wiping mechanism having an ink absorbing member for absorbing the ink composition, the ink absorbing member wiping the nozzle surface of the inkjet head with a wiper unit holding a cleaning liquid, the ink composition containing a coloring material, a resin, an organic solvent, and water, the content of glycol-based solvent in the organic solvent is 50% by mass or more relative to the total organic solvent, the glass transition temperature of the resin is within the range of -70 to 0°C, and the content of the resin is within the range of 5 to 15% by mass relative to the total ink composition. In the following description, "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0014] [Ink composition] The ink composition used in the ink jet recording method of the present embodiment will be described below. The ink composition of the present embodiment contains a coloring material, an organic solvent, a resin, and water.

[0015] <Coloring material> The coloring material is not particularly limited, and examples of the coloring material include dyes and pigments.

[0016] (Pigments) Examples of pigments include organic or inorganic pigments having the following numbers as listed in the Color Index:

[0017] Examples of red or magenta pigments (magenta or red pigments) include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange Includes 13, 16, 20, and 36.

[0018] Examples of blue or cyan pigments (cyan or blue pigments) include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, 60.

[0019] Examples of green pigments include Pigment Green 7, 26, 36, and 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193.

[0020] Examples of black pigments include Pigment Black 7, 28, and 26.

[0021] Examples of white pigments include titanium dioxide.

[0022] From the viewpoint of improving dispersibility in the ink, the pigment is preferably further dispersed with a pigment dispersant, which will be described later.

[0023] The pigment may also be a self-dispersing pigment. A self-dispersing pigment is a pigment particle whose surface is modified with a group having a hydrophilic group, and has pigment particles and hydrophilic groups bonded to the surface of the pigment particles.

[0024] Examples of the hydrophilic group include a carboxyl group, a sulfonic acid group, and a phosphorus-containing group. Examples of the phosphorus-containing group include a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a phosphite group, and a phosphate group.

[0025] Commercially available examples of self-dispersing pigments include Cab-0-Jet® 200K, 250C, 260M, and 270V (sulfonic acid group-containing self-dispersing pigments), Cab-0-Jet® 300K (carboxylic acid group-containing self-dispersing pigments), and Cab-0-Jet® 400K, 450C, 465M, 470V, and 480V (phosphate group-containing self-dispersing pigments) (all manufactured by Cabot).

[0026] Commercially available examples of pigments include: Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, Chromofine Violet RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, CHROMO FINE GREEN 2GN, 2GO, 2G-550D, 5310, 5370, 6830, CHROMO FINE BLACK A-1103, SEIKA FAST YELLOW 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400(B), 2500, 2600, ZAY-260, 2700(B), 2770, Seika Fast Red 8040, C405(F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (Dainichi Seika Chemicals); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (manufactured by Dainippon Ink & Chemicals);Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex BrownB610N, Colortex Violet600, Pigment Red 122, Colortex Blue516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (Sanyo Pigment); Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (Toyo Ink Co., Ltd.); Toner Magenta E02, Permanent Rubin F6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapearm Blue B2G (Hoechst Industry); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant); Carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, #950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32, #30, #25, #20, #10, #5, #44, CF9 (manufactured by Mitsubishi Chemical).

[0027] (dye) The dye is not particularly limited as long as it is a solid dye, and the dye may be, for example, a disperse dye.

[0028] Examples of disperse dyes include CI Disperse Yellow: 3, 4, 5, 7, 9, 13, 23, 24, 30, 33, 34, 42, 44, 49, 50, 51, 54, 56, 58, 60, 63, 64, 66, 68, 71, 74, 76, 79, 82, 83, 85, 86, 88, 90, 91, 93, 98, 99, 100, 104, 108, 114, 116, 118, 1 19, 122, 124, 126, 135, 140, 141, 149, 160, 162, 163, 164, 165, 179, 180, 182, 183, 184 , 186, 192, 198, 199, 202, 204, 210, 211, 215, 216, 218, 224, 227, 231, 232;CIDisperse Orange:1, 3, 5, 7, 11, 13, 17, 20, 21, 25, 29, 30, 31, 32, 33, 37, 38, 42, 43, 44, 45, 46, 47, 48, 49, 50, 53, 5 4,55,56,57,58,59,61,66,71,73,76,78,80,89,90,91,93,96,97,119,127,130,139,142;CIDisperse Red:1, 4, 5, 7, 11, 12, 13, 15, 17, 27, 43, 44, 50, 52, 53, 54, 55, 56, 58, 59, 60, 65, 72, 73, 74, 75, 76, 78, 81, 82, 86, 88, 90, 91, 92, 9 3, 96, 103, 105, 106, 107, 108, 110, 111, 113, 117, 118, 121, 122, 126, 127, 128, 131, 132, 134, 135, 137, 143, 145, 146, 151, 152, 1 53, 154, 157, 159, 164, 167, 169, 177, 179, 181, 183, 184, 185, 188, 189, 190, 191, 192, 200, 201, 202, 203, 205, 206, 207, 210, 221 CIDisperse Violet:1, 4, 8, 23, 26, 27, 28, 31, 33, 35, 36, 38, 40, 43, 46, 48, 50, 51, 52, 56, 57, 59, 61, 63, 69, 77;CIDisperse Green9;CIDisperse Brown:1, 2, 4, 9, 13, 19;CIDisperse Blue:3, 7, 9, 14, 16, 19, 20, 26, 27, 35, 43, 44, 54, 55, 56, 58, 60, 62, 64, 71, 72, 73, 75, 77, 79, 79:1, 79:2, 81, 82, 83 , 87, 91, 93, 94, 95, 96, 102, 106, 108, 112, 113, 115, 118, 120, 122, 125, 128, 130, 139, 141, 142, 143, 146, 148, 149, 1 53, 154, 158, 165, 167, 171, 173, 174, 176, 181, 183, 185, 186, 187, 189, 197, 198, 200, 201, 205, 207, 211, 214, 224, 225, 257, 259, 267, 268, 270, 281, 284, 285, 287, 288, 291, 291:1, 293, 295, 297, 301, 315, 330, 333, 373; CI Disperse Black 1, 3, 10, 24.

[0029] Disperse dyes are preferred because they have good dispersibility in the components of the ink composition and excellent weather resistance.

[0030] The content of the coloring material is not particularly limited. The content of the coloring material is preferably within a range of 4 to 15% by mass with respect to the total amount of the ink composition. When the content of the coloring material is 4% by mass or more, not only the viscosity of the ink composition is appropriately increased, but also a high-density image is easily formed. When the content of the coloring material is 15% by mass or less, the viscosity of the ink does not become too high, so that nozzle clogging and the like are unlikely to occur. From the same viewpoint, the content of the coloring material is preferably within a range of 5 to 15% by mass with respect to the total amount of the ink composition, and more preferably within a range of 6.5 to 12% by mass.

[0031] <Resin> The ink composition contains a resin. The glass transition point (Tg) of the resin is within the range of -70 to 0°C. The glass transition point (Tg) of the resin is preferably within the range of -70 to -30°C. The glass transition point (Tg) of the resin was measured using a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation) in accordance with JIS K 7121. The glass transition point (Tg) can be measured using a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation).

[0032] Examples of resins having a glass transition point within the range of -70 to 0°C include urethane resins, butadiene resins, acrylic resins, polystyrene, styrene-acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate resins, and polyester resins. Examples of butadiene resins include styrene-butadiene copolymers and acrylonitrile-butadiene copolymers. Examples of acrylic resins include acrylic acid ester copolymers, styrene-acrylic copolymers, silicon-acrylic copolymers, and acrylic-modified fluororesins. Resins are preferred because they have a high degree of freedom in design and therefore are easy to obtain the desired film properties, i.e., the above-mentioned glass transition temperature and film elongation.

[0033] As the acrylic resin, a polymer of an acrylic monomer such as acrylic acid or an acrylic acid ester, or a copolymer of an acrylic monomer with another monomer, such as a vinyl monomer such as styrene, can be used. Commercially available examples of acrylic resins include Movinyl 6750, 6751D, 6940, 7525, and 6969D (all from The Nippon Synthetic Chemical Industry Co., Ltd.), Vinyblan 2682 (Nissin Chemical Industry Co., Ltd.), and Movinyl 6969D (The Nippon Synthetic Chemical Industry Co., Ltd.).

[0034] Examples of styrene-acrylic copolymers include styrene-(meth)acrylic acid copolymers and styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers. Examples of (meth)acrylic acid esters include benzyl (meth)acrylate, cyclohexyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylhexyl carbitol (meth)acrylate, phenol EO modified (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate.

[0035] The urethane resin is a polymer obtained by reacting a polyol with a polyisocyanate, and is not particularly limited as long as it has a urethane skeleton and is water dispersible. Examples of polyols include polypropylene glycol, polyethylene glycol, polytetramethylene glycol, poly(ethylene adipate), poly(diethylene adipate), poly(propylene adipate), poly(tetramethylene adipate), poly(hexamethylene adipate), poly-ε-caprolactone, poly(hexamethylene carbonate), and silicone polyol. Examples of isocyanates include tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, and tetramethylxylylene diisocyanate.

[0036] Examples of commercially available urethane resins include Superflex 300, 460, 460s, 470, 610, 170, and E4800 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Rezamin D-1060, D-2020, D-4080, D-4200, D-6300, and D-6455 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), Takelac W-6110 and WS-6021 (manufactured by Mitsui Chemicals Polyurethanes Inc.), Bontiter HUX-380 (manufactured by ADEKA Corporation), and U-coat UX-150 (manufactured by Sanyo Chemical Industries, Ltd.).

[0037] An example of a commercially available polyester resin is Aronmelt PES-2005 (manufactured by Toagosei Co., Ltd.).

[0038] In addition, as the urethane-based resin, polyether-based urethane resins containing ether bonds in the main chain, polyester-based urethane resins containing ester bonds in the main chain, polycarbonate-based urethane resins containing carbonate bonds in the main chain, etc. can be used in combination with a plurality of these urethane-based resins. It is preferable to use polycarbonate-based urethane resins in terms of good friction fastness.

[0039] The acid value of the resin according to the present invention is not particularly limited, but is preferably within the range of 15 to 100 mgKOH / g, more preferably within the range of 20 to 80 mgKOH / g, from the viewpoint of improving the resistance to rubbing, etc. The acid value can be measured in accordance with JIS K 0070.

[0040] The average particle size of the resin according to the present invention is not particularly limited, but from the viewpoint of preventing nozzle clogging of the inkjet head, it is preferably 300 nm or less, more preferably 130 nm or less. The average particle size of the resin can be measured by a laser diffraction / scattering type particle size distribution measurement.

[0041] The resin content is within the range of 5 to 20% by mass based on the total amount of the ink composition. The resin content is preferably within the range of 7 to 15% by mass based on the total amount of the ink composition. When the resin content is 5% by mass or more, the viscosity of the ink is easily increased appropriately, and not only can the ejection stability be further improved, but also the adhesion to the fabric and the abrasion resistance of the obtained image are easily improved. When the resin content is 15% by mass or less, the viscosity of the ink is not too high, and nozzle clogging is unlikely to occur. In addition, it is possible to impart friction fastness, washing fastness and flexibility to the printed matter in textile applications.

[0042] The strength of the resin-based coating is not particularly limited. The strength of the resin-based coating is preferably 50 MPa or less. The strength of the resin-based coating can be measured, for example, by the following method. Water-dispersible resin particles (resin particles) are applied onto a polytetrafluoroethylene sheet so that the average film thickness after drying is 500 μm, and the film is dried at room temperature (25° C.) for 15 hours, further dried at 80° C. for 6 hours, and then dried at 120° C. for 20 minutes, and then peeled off from the polytetrafluoroethylene sheet to obtain a water-dispersible resin film. The film strength of the obtained water-dispersible resin film was measured using a Tensilon universal testing machine (RTC-1225A; manufactured by Orientec Co., Ltd.) at a measurement temperature of 20° C. and a measurement speed of 200 mm / min. The film strength was defined as the strength at break. Thus, examples of commercially available resins having a film strength of 50 MPa or less are as shown below. Examples of commercially available polyester resins include Aronmelt PES-2005 (manufactured by Toa Gosei Co., Ltd.). Examples of commercially available urethane resins include Superflex 300, 460s, 470, and E4800 (all from Daiichi Kogyo Seiyaku Co., Ltd.), Bontitor HUX-380 (from ADEKA Corporation), and U-coat UX-150 (from Sanyo Chemical Industries, Ltd.). Examples of commercially available acrylic resins include Mowinyl 6969D (from Nippon Synthetic Chemical Industry Co., Ltd.).

[0043] <Organic solvent> The ink resin composition has an organic solvent. The organic solvent includes a glycol-based solvent. The type of the organic solvent is not particularly limited as long as it includes a glycol-based solvent. Examples of glycol-based solvents include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol; trihydric or higher alcohols such as glycerin, trimethylolpropane, and hexanetriol; and polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether).

[0044] Examples of other organic solvents include monohydric alcohols (e.g., methanol, ethanol, propanol, pentanol, hexanol, cyclohexanol, benzyl alcohol); amines (e.g., ethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine); amides (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide); heterocycles (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidine), sulfoxides (e.g., dimethyl sulfoxide); and sulfones (e.g., sulfolane).

[0045] The content of the glycol solvent in the organic solvent is 50% by mass or more based on the total amount of the organic solvent. If the content of the glycol solvent in the organic solvent is 50% by mass or more based on the total amount of the organic solvent, head durability and cleaning properties can be improved.

[0046] The organic solvent preferably has a standard boiling point (boiling point under 1 atmospheric pressure) of 250°C or higher. By using an organic solvent at 250°C or higher, it is possible to easily increase the viscosity of the ink composition to an appropriate level. In addition, it is possible to prevent the nozzle surface of the inkjet head from drying, prevent clogging, and improve ejection stability. Examples of organic solvents having a standard boiling point of 250°C or higher include glycerin, triethylene glycol, tripropylene glycol, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, 3-methyl-1,5-pentanediol, and trimethylolpropane.

[0047] The total content of organic solvents having a normal boiling point of 250° C. or higher is preferably within a range of 3 to 15% by mass with respect to the total amount of the ink composition. By setting the content of the organic solvent within the above range, the viscosity of the ink composition can be easily increased, nozzle clogging can be suppressed, and the ink composition can be stably ejected.

[0048] (water) Examples of water include ion-exchanged water, distilled water, pure water, etc. The content of water is preferably within a range of 30 to 85% by mass, and more preferably within a range of 40 to 70% by mass, based on the total amount of the ink composition.

[0049] <Other ingredients> The ink composition according to the present invention may further contain other components as necessary. Examples of the other components include polymer dispersants, solvents, surfactants, preservatives, antifungal agents, antirust agents, and pH adjusters.

[0050] (Polymer dispersant) The ink composition according to the present invention may further contain a polymer dispersant from the viewpoint of facilitating dispersion of the pigment.

[0051] The type of polymer dispersant is not particularly limited. Examples of polymer dispersants include block copolymers and random copolymers composed of two or more monomers selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, and fumaric acid derivatives, and salts thereof, polyoxyalkylene, and polyoxyalkylene alkyl ether.

[0052] When the polymer dispersant has an acidic group such as a carboxyl group, the acidic group is preferably neutralized with a neutralizing base. Examples of the neutralizing base include organic bases such as ammonia, monoethanolamine, diethanolamine, triethanolamine, and morpholine.

[0053] The content of the polymer dispersant is preferably 4% by mass or less, and more preferably 0.8 to 2% by mass, based on the total amount of the ink composition. If the content of the polymer dispersant is 0.8% by mass or more, the dispersibility of color materials such as pigments is easily increased sufficiently, and if it is 4% by mass or less, an excessive increase in viscosity is easily suppressed.

[0054] (Surfactant) The ink composition according to the present invention may further contain a surfactant in order to control the surface tension.

[0055] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Examples of anionic surfactants include fatty acid salts, alkyl sulfates, alkyl sulfate esters, alkylbenzene sulfonates, alkylnaphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate ester salts, alkylnaphthalene sulfonate-formaldehyde condensates, and polyoxyethylene alkyl sulfate ester salts. Examples of cationic surfactants include amine salts, tetraalkyl quaternary ammonium salts, trialkyl quaternary ammonium salts, alkylpyridinium salts, and alkylquinolinium salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylamines, ethylene oxide adducts of polypropylene glycol, acetylene glycol, and ethylene oxide adducts of acetylene glycol.

[0056] (Preservatives, antifungal agents) Examples of preservatives or antifungals include aromatic halogen compounds (e.g., Preventol CMK; manufactured by Lanxess), methylene dithiocyanate, halogen-containing nitrogen-sulfur compounds, and 1,2-benzisothiazolin-3-one (e.g., PROXEL (registered trademark) GXL; manufactured by Lonza).

[0057] (pH adjuster) Examples of pH adjusters include known acids, bases and buffers, including ammonia, citric acid, sodium citrate, hydrochloric acid, sodium hydroxide, and the like.

[0058] [Inkjet recording device] Next, an inkjet recording apparatus used in the inkjet recording method of the present invention will be described. The inkjet recording apparatus in this embodiment has an inkjet head. The inkjet head may be of an on-demand type or a continuous type. The ejection method of the inkjet recording apparatus may be any ejection method such as an electro-mechanical conversion type (e.g., single cavity type, double cavity type, bender type, piston type, share mode type, shared wall type, etc.) or an electro-thermal conversion type (e.g., thermal inkjet type, bubble jet (registered trademark) type, etc.).

[0059] The inkjet recording apparatus has a wiping mechanism having an ink absorbing member for absorbing the ink composition, and the ink absorbing member wipes the nozzle surface of the inkjet head with a wipe unit that holds a cleaning liquid.

[0060] The following describes an inkjet recording apparatus applicable to the inkjet recording method of the present embodiment, and a wiping mechanism of the inkjet recording apparatus, etc. Note that the embodiment is not limited to the one exemplified here, as long as the nozzle surface of the inkjet head can be wiped with an ink absorbing member that holds the cleaning liquid and the stability of ejection can be maintained.

[0061] FIG. 1 is a perspective view showing a schematic configuration of an inkjet recording apparatus 1 to which a wiping unit according to the present invention is applied.

[0062] 1, in the inkjet recording device 1, a platen 2 that supports a recording medium P from below is arranged horizontally. A carriage 5 is provided above the platen 2. The carriage 5 scans a plurality of inkjet heads 4 in a main scanning direction B that is perpendicular to a sub-scanning direction A, which is the transport direction of the recording medium P, along a guide rail (not shown) that extends horizontally.

[0063] The carriage 5 is connected to a timing belt that is stretched between a drive pulley and an idler pulley (not shown). The drive pulley is joined to a rotating shaft of a scanning motor. Therefore, when the scanning motor is driven, the carriage 5 moves in the main scanning direction B.

[0064] The inkjet heads 4 eject ink compositions of each color used in the inkjet recording device 1 toward the recording medium P. Inside each inkjet head 4, a number of nozzles for ejecting the ink composition are arranged in a row along the sub-scanning direction A. The surface of the inkjet head 4 facing the recording medium P is the nozzle surface on which these nozzles are formed. It is preferable that the nozzle surface is subjected to an ink-repellent treatment, such as a fluorine treatment using FEP (fluorinated ethylene propylene resin) or a silicone treatment, so that ink does not easily adhere to the nozzle surface.

[0065] A plurality of ink tanks 6 storing ink of each color, for example, yellow (Y), magenta (M), cyan (C), and black (K), are connected to these inkjet heads 4. The ink composition of this embodiment is used for each of these ink compositions. The ink tanks 6 are connected to the inkjet heads 4 via ink flow paths 7 that guide the ink compositions.

[0066] Furthermore, although not shown, for example, a discharge energy generating means and a driving circuit thereof are integrally built into each of the inkjet heads 4. The discharge energy generating means is, for example, a piezoelectric element that causes the nozzles of each inkjet head 4 to discharge ink.

[0067] In addition, a wiping unit 13 and a suction unit 14 that perform maintenance on the inkjet head 4 are provided on the sides of the platen 2. The wiping unit 13 and the suction unit 14 are configured to be movable vertically and horizontally in synchronization with each other.

[0068] In addition, the wiping unit 13 includes an ink absorbing member 50 and a sheet-like flexible member 51 in a box-shaped housing 52. The ink absorbing member 50 extends upward in a convex shape. The sheet-like flexible member 51 supports the ink absorbing member 50. The wiping unit 13 itself is moved upward by a driving source such as a motor (not shown), and then the inkjet head 4 is moved in the B direction. As a result, the ink absorbing member 50 rubs against the nozzle surface 41 of the inkjet head 4 while in contact with the nozzle surface 41. Then, the ink composition, cleaning liquid, and the like attached to the entire nozzle surface 41 are removed. When the wiping operation is completed, the wiping unit 13 is lowered to release the contact state between the ink absorbing member 50 and the nozzle surface 41.

[0069] The suction unit 14, which sucks the ink composition in the nozzles of the inkjet head 4, is provided with a cap 15 that is brought into contact with and separated from the nozzle surface 41 of the inkjet head 4 as the suction unit 14 ascends and descends. When sucking the ink composition in the nozzles, the cap 15 is brought into close contact with the nozzle surface 41 as the suction unit 14 ascends. The cap 15 covers all the nozzles in the nozzle surface 41. When the suction is completed, the cap 15 is moved away from the nozzle surface 41 as the suction unit 14 descends. A pump P1 is connected to the cap 15 for sucking the space formed between the recess of the cap 15 and the nozzle surface 41 when the cap 15 is brought into close contact with the nozzle surface 41. The cap 15 and the pump P1 are connected via a waste liquid flow path 17.

[0070] The waste liquid flow path 17 is formed, for example, by a resin tube. A so-called tube pump is preferably used as the pump P1. The pump P1 is a pump that sandwiches the resin tube that constitutes the waste liquid flow path 17 between rollers and moves the rollers along the tube to exhaust air and the like from the tube from the end of the tube.

[0071] The wiping unit 13 according to the present invention will be described in further detail with reference to FIGS.

[0072] The wiping unit 13 according to the present invention has a box-shaped housing 52. An opening is formed in the center of the upper surface of the housing 52.

[0073] FIG. 3 is a perspective view of the main part, showing a state in which the wiping unit is pressed against the inkjet head 4. As shown in FIG.

[0074] 3, a feed-out shaft 54 ​​that feeds out the ink absorbing member 50 is provided at one end in the main scanning direction B inside the housing 52. A take-up shaft 55 that takes up the ink absorbing member 50 is provided at the other end in the main scanning direction B inside the housing 52. A motor (not shown) is provided below the take-up shaft 55 as a drive source that drives the take-up shaft 55 to rotate.

[0075] A long sheet-like ink absorbing member 50 is wound in a roll around the delivery shaft 54. The ink absorbing member 50 is stretched between the delivery shaft 54 ​​and the take-up shaft 55 while maintaining a certain tension, and a part of the ink absorbing member 50 is exposed from the opening. As shown in FIG. 1, the ink absorbing member 50 exposed from the opening faces the nozzle surface 41 of the inkjet head 4 during wiping operation. The ink absorbing member 50 is delivered from the delivery shaft 54 ​​as the take-up shaft 55 rotates. Then, the ink absorbing member 50 is guided by the sheet-like flexible member 51 that supports the ink absorbing member 50 from the side opposite to the side that contacts the nozzle surface 41, and is taken up by the take-up shaft 55.

[0076] When the ink composition adheres to the ink absorbing member 50 as a result of the wiping operation, the ink absorbing member 50 is appropriately wound up around the winding shaft 55, and an unused portion is exposed from the opening. The ink absorbing member 50 may be wound up around the winding shaft 55 every time the wiping operation of one inkjet head 4 is performed. Alternatively, the ink absorbing member 50 may be wound up every time the wiping operation of a plurality of inkjet heads 4 is performed, or when the wiping operation of all inkjet heads 4 is completed. In this way, by reducing the number of times the ink absorbing member 50 is wound up, the consumption of the ink absorbing member 50 can be reduced.

[0077] In addition, the ink absorbing member 50 is removable from inside the housing 52. When the ink absorbing member 50 is completely used up (when there is no unused portion), it can be removed from inside the housing 52 and replaced with a new ink absorbing member 50.

[0078] For example, cloth or sponge can be used for the ink absorbing member 50. Cloth and sponge tend to absorb anything that comes into contact with their surface, and can enhance the action of absorbing and removing ink adhering to the nozzle surface of the inkjet head 4.

[0079] The ink absorbing member 50 may be any member capable of absorbing at least the ink composition, and the material thereof is not limited to those exemplified here.

[0080] The size of the ink absorbing member 50 is not particularly limited. However, in order to perform maintenance operations such as wiping the nozzle surface 41 evenly, the ink absorbing member 50 is formed to a size that can at least cover the entire nozzle surface that is the target of the maintenance operation. In other words, the ink absorbing member 50 is formed to have a width dimension that is larger than the width dimension (length in the sub-scanning direction A) of the nozzle surface 41.

[0081] Inside the housing 52, between the delivery shaft 54 ​​and the winding shaft 55, a sheet-like flexible member 51 is positioned below the ink absorbing member 50 so as to face the nozzle surface. In addition, the sheet-like flexible member 51 is stretched between the delivery shaft 54 ​​and the winding shaft 55.

[0082] Both ends of the sheet-shaped flexible member 51 are attached to a first supporting member 56 and a second supporting member 57 that support the sheet-shaped flexible member 51 in a bent state so as to be convex toward the nozzle surface 41. The first supporting member 56 and the second supporting member 57 are substantially cylindrical.

[0083] The first support member 56 and the second support member 57 are disposed at both ends in a direction perpendicular to the extension direction (sub-scanning direction A) of the convex portions of the sheet-like flexible member 51. The first support member 56 and the second support member 57 are attached to the housing 52 in a state in which they can rotate about an axis along the extension direction (sub-scanning direction A) of the convex portions by a driving source such as a motor (not shown).

[0084] 4A and 4B show a fixed state of the sheet-shaped flexible member 51. Fig. 4A is a cross-sectional view showing a state where the pressing force is low, and Fig. 4B is a cross-sectional view showing a state where the pressing force is high.

[0085] The first support member 56 and the second support member 57 have fixing portions (support positions) for fixing the ends of the sheet-like flexible member 51 arranged in flat regions of their outer circumferential surfaces. Fixing holes are formed in the fixing portions. As shown in Fig. 4, the sheet-like flexible member 51 is fixed onto the fixing portions of the first support member 56 and the second support member 57 by screws 58, 59 that are inserted into the fixing holes.

[0086] There is no particular limitation on the shape, arrangement, and number of the support members 56 and 57. In addition, the configuration for fixing the sheet-shaped flexible member 51 to the support members 56 and 57 is not limited to that shown in the drawings, and other configurations can be applied.

[0087] The sheet-like flexible member 51 presses the ink absorbing member 50 from the side opposite to the side that contacts the nozzle face 41 during the wiping operation, thereby contacting the nozzle face. For this reason, the sheet-like flexible member 51 is formed with a width dimension larger than the width dimension (dimension in the sub-scanning direction A) of the nozzle face 41 of the inkjet head 4, which is the area that is the target of the wiping operation.

[0088] The surface of the sheet-like flexible member 51 that comes into contact with the ink absorbing member 50 is formed into a curved surface. The shape of the sheet-like flexible member 51 is not particularly limited as long as it is convex toward the nozzle surface 41, but it is preferable that the sheet-like flexible member 51 is fixed so that the surface that comes into contact with the ink absorbing member 50 has a substantially curved surface.

[0089] The sheet-like flexible member 51 is a flexible rubber sheet, metal sheet, or resin sheet.

[0090] <How to supply cleaning liquid to the wipe unit> Next, a method of supplying cleaning liquid to the wiping unit 13 according to the present invention will be described.

[0091] In the ink jet recording method of the present invention, an ink absorbing member that absorbs the ink composition is used, and the ink absorbing member holds a cleaning liquid.

[0092] FIG. 2 is a perspective view for explaining a method of supplying cleaning liquid to the wiping unit 13. As shown in FIG.

[0093] A cleaning liquid tank 3, a liquid delivery path 11, and a cleaning liquid supply valve (not shown) are arranged on the side of the platen 2 shown in Fig. 1. The cleaning liquid tank 3 can store cleaning liquid. The liquid delivery path 11 communicates between the cleaning liquid tank 3 and a part where cleaning liquid is supplied to the wiping unit 13. The cleaning liquid supply valve is arranged midway along the liquid delivery path 11.

[0094] A liquid feed path 11 for supplying cleaning liquid to the ink absorbing member 50, and a cleaning liquid supply valve V3 are disposed between the cleaning liquid tank 3 and the wiping unit 13. The cleaning liquid supply valve V3 is disposed midway along the liquid feed path 11.

[0095] The cleaning liquid supply valve V3 and the air leak valve (not shown) are valves whose open / closed states can be electrically controlled. The cleaning liquid supply valve V3 and the air leak valve (not shown) are, for example, electromagnetic valves.

[0096] The liquid supply path 11 is a passage through which the cleaning liquid flows in response to the operation of the cleaning liquid supply valve V3. The liquid supply path 11 is, for example, a resin tube.

[0097] The cleaning liquid tank 3 is disposed at a position higher than the position of the wiping unit 13 (the position of the ink absorbing member 50) and the position of the cap 15. Therefore, the cleaning liquid can be easily supplied to the ink absorbing member 50 by the head difference.

[0098] The cleaning liquid supply valve V3 controls the communication state of the liquid feed path 11. That is, when the cleaning liquid supply valve V3 is open, the inside of the cleaning liquid tank 3 and the ink absorbing member 50 of the wiping unit 13 communicate with each other through the liquid feed path 11. Therefore, when the cleaning liquid supply valve V3 is appropriately opened, the cleaning liquid is supplied to the ink absorbing member 50. On the other hand, when the cleaning liquid supply valve V3 is closed, the liquid feed path 11 is blocked at the position of the cleaning liquid supply valve V3. Therefore, the inside of the cleaning liquid tank 3 and the ink absorbing member 50 are also blocked.

[0099] In this embodiment, the cleaning liquid tank 3, the liquid transfer path 11, and the cleaning liquid supply valve V3 function as a cleaning liquid supplying means.

[0100] 2, specifically, a cleaning liquid ejection port 53 is provided at the tip of the liquid feed path 11 on the ink absorbing member 50 side. The liquid feed path 11 near the cleaning liquid ejection port 53 is configured to be reciprocable in the direction of the arrow (sub-scanning direction A) by a driving source (not shown).

[0101] An area retracted from above the ink absorbing member 50 is defined as an evacuation area, and when the cleaning liquid is not supplied to the ink absorbing member 50, the liquid sending path 11 is located in the evacuation area.

[0102] When supplying the cleaning liquid, the liquid feed path 11 moves from the retreat area to one end above the ink absorbing member 50. Thereafter, it moves to the other end while opening the cleaning liquid supply valve V3. As a result, the cleaning liquid dropped from the cleaning liquid ejection port 53 is supplied over the entire surface of the ink absorbing member 50 in contact with the nozzle face 41 in the sub-scanning direction A.

[0103] <Image formation: Heat treatment> In the inkjet ink recording method of the present embodiment, it is preferable to heat the recording surface side of the recording medium for recording. By heating the recording surface side of the recording medium for recording, a high-quality image with high image durability can be formed, and printing can be achieved at a higher speed. By heating the recording medium in advance when printing, the drying property and viscosity increasing speed of the ink can be improved after the ink is applied to the recording medium, and as a result, bleeding can be prevented and high image quality can be obtained.

[0104] The surface temperature of the recording surface of the recording medium is preferably in the range of 35 to 90° C., more preferably in the range of 40 to 60° C. By controlling and heating the surface temperature of the recording surface of the recording medium so that it is within the above range, high image quality and sufficient image durability can be easily obtained. Furthermore, by keeping the surface temperature of the recording surface of the recording medium within the above range, the drying time can be shortened, and stable printing can be achieved without significantly affecting the ejection properties of the ink composition.

[0105] Examples of heating methods include a method in which a heater is incorporated in the recording medium transport system or platen member to heat the recording medium from below in a contact manner, and a method in which radiant heat from a lamp or the like is used to heat the recording medium from below or above in a non-contact manner.

[0106] Furthermore, if necessary, a drying process may be performed after ejecting the ink composition onto a recording medium in order to remove unnecessary organic solvents, etc. The method for drying the ink composition is not particularly limited. Examples of the method for drying the ink composition include a method of drying the back side of the recording medium by contacting it with a heating roller or flat heater, a method of blowing hot air onto the recording surface by a dryer, or a method of removing volatile components by a reduced pressure treatment, which can be appropriately selected or combined.

[0107] The mechanism of expression or action of the effects of the present invention is not clear, but is presumed to be as follows. An ink composition containing a resin with a low glass transition point is likely to solidify, and when it dries and adheres to the nozzle surface, it becomes a film-like ink deposit. In order to remove the film-like ink deposit using a wiping unit holding a cleaning liquid, it is necessary to increase the roller pressure to wipe the nozzle surface. In this case, cleaning using a wiping unit is likely to damage the nozzle surface, making it difficult to obtain head durability. For this reason, resins with low glass transition points have not been actively used in ink compositions used in inkjet recording devices including a wiping unit holding a cleaning liquid.

[0108] However, when a glycol-based solvent is contained in the ink composition at 50 wt % or more of the total organic solvent amount together with a resin having a low glass transition point, the glycols having high polarity and hydroxyl groups are oriented by hydrogen bonding around the resin having a low glass transition point, which is easily dried and formed into a film, and a complete film is not formed, but a semi-film in which the solvent surrounds the resin particles. When cleaning is performed using a wipe unit holding a cleaning liquid, the semi-film formed in this state quickly swells when maintenance liquid is applied to the semi-film from the ink absorbing member, and becomes a more flexible semi-film.

[0109] Such a flexible semi-coating film can easily follow the roller of the wiping unit holding the cleaning liquid, so that the head surface can be cleaned with a smaller roller pressure. As a result, it is presumed that the head durability can be improved. In addition, in this embodiment, at least a resin having a glass transition point in the range of -70 to 0°C is included. Therefore, the resin interacts with the coloring material and the substrate in the ink composition, and the fixation of the image to the substrate can be improved. As a result, it is presumed that the friction fastness is excellent. EXAMPLES

[0110] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the following examples, unless otherwise specified, the operations were performed at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0111] [Constituents of ink composition] The components used in the preparation of the ink composition are as follows. <Resin> Urethane resin (U-coat UX-150, Tg: -70°C; Sanyo Chemical Industries, Ltd.) Urethane resin (U-coat UX-310, Tg: -25°C; Sanyo Chemical Industries, Ltd.) Urethane resin (U-coat DA-100, Tg: -80°C; Sanyo Chemical Industries, Ltd.) Urethane resin (Takelac WS-6110, Tg: -20℃; Mitsui Chemicals) Urethane resin (Takelac WS-6021, Tg: -60℃; Mitsui Chemicals) Urethane resin (Bontitor HUX-380, Tg: -5℃; manufactured by Adeka Corporation) Urethane resin (Superflex 150, Tg: 40℃; Daiichi Kogyo Co., Ltd.) Urethane resin (Superflex 300, Tg: -42°C; Daiichi Kogyo Co., Ltd.) Urethane resin (Superflex 460S, Tg: -21°C; Daiichi Kogyo Co., Ltd.) Urethane resin (Superflex 470, Tg: -31℃; Daiichi Kogyo Co., Ltd.) Urethane resin (Superflex 840, Tg: 5°C; Daiichi Kogyo Co., Ltd.) Urethane resin (Superflex E-4800, Tg: -65℃; Daiichi Kogyo Co., Ltd.) Acrylic resin (Movinyl 6969D, Tg: -50 to -30°C; manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) Acrylic resin synthetic a (B53683, Tg: -50~-31℃) Polyester resin (Aronmelt PES-2005, Tg: 0°C; manufactured by Toagosei Co., Ltd.)

[0112] <Preparation of acrylic resin synthesis a> A surfactant solution prepared by dissolving 2.52 g of anionic surfactant (sodium dodecylbenzenesulfonate: SDS) and 0.58 g of sodium carbonate in 553 g of ion-exchanged water was added to a separable flask equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, and the internal temperature was raised to 80°C while stirring at a stirring speed of 330 rpm under a nitrogen stream. On the other hand, a monomer solution was prepared by dissolving 156 g of n-butyl acrylate (BA), 44 g of methyl methacrylate (MMA), 15.4 g of methacrylic acid, and 11 g of diacetone acrylamide. Next, a solution was prepared by dissolving 0.07 g of a polymerization initiator (potassium persulfate: KPS) in 2.66 g of ion-exchanged water, and the solution was heated at 80° C. The monomer solution prepared above was added dropwise to this solution over 60 minutes and stirred to prepare a dispersion of resin particles. After the dropwise addition was completed, the mixture was heated and stirred for 120 minutes, and then a solution of 0.07 g of a polymerization initiator (potassium persulfate: KPS) dissolved in 2.66 g of ion-exchanged water was further added, and the mixture was stirred for 60 minutes and then cooled to 40°C to obtain acrylic resin synthesis a.

[0113] <Organic solvent> Ethylene glycol (normal boiling point: 197°C) Propylene glycol (normal boiling point: 187°C) Triethylene glycol (normal boiling point: 287.4°C) Glycerin (normal boiling point: 290℃) 1,2-Hexanediol (normal boiling point: 170℃) 3-Methoxy-1-butanol (normal boiling point: 161°C) Diethylene glycol monobutyl ether (normal boiling point: 231°C) Amino acids (tryptophan, molecular weight 204.1)

[0114] <Surfactant> Acetylene surfactant (Olfine E-1010; manufactured by Nissin Chemical Industry Co., Ltd.)

[0115] <Pigment dispersion> As the pigment dispersions, the following pigment dispersions 1 and 2 were prepared. ·Pigment dispersion 1 (contains Pigment Black 7) (Preparation of Pigment Dispersion 1) As a pigment dispersant, 13.5 parts by mass of DISPERBYK190 (BYK-Chemie) was added to 20 parts by mass of ethylene glycol and 48.5 parts by mass of ion-exchanged water. To this solution, 18.0 parts by mass of Pigment Black 7 was added as a black pigment and premixed. Then, the mixture was dispersed using a sand grinder filled with 0.5 mm zirconia beads at a volume ratio of 50%, to prepare Black Pigment Dispersion 1 with a pigment solid content of 18.0% by mass. Pigment dispersion 2: Cab-o-jet 400 (self-dispersing pigment, Cabot, black water-based pigment dispersion)

[0116] <Water> Ion-exchanged water

[0117] [Preparation of sample (ink composition)] <Preparation of Sample 1> The urethane resin, ethylene glycol, propylene glycol, sorbitol, acetylene surfactant, pigment dispersion 1 (Pigment Black 7), and ion-exchanged water were mixed so as to obtain the contents (parts by mass) shown in Table 1. The mixture was then filtered through a 0.8 μm filter to prepare sample (ink composition) 1.

[0118] <Preparation of Samples 2 to 24> Samples 2 to 24 were prepared in the same manner as Sample 1, except that the components of each sample were changed to have the compositions shown in Tables 1 to 3 below.

[0119] [Image formation] The above-prepared samples 1 to 24 were loaded onto a piezo-type inkjet head having a nozzle diameter of 28 μm, a driving frequency of 10 kHz, a number of nozzles of 512, a minimum droplet volume of 14 pl, and a nozzle density of 180 dpi. A driving pulse with a pulse width of 5 μsec was applied to the electrodes of the inkjet head at a voltage adjusted so that the flying speed of the ink droplets was 6 m / sec. Then, the inkjet head was driven for three cycles (every two ink channels). As a result, a solid image was continuously printed for 30 minutes on a polyvinyl chloride resin sheet IJ180-10 (manufactured by Sumitomo 3M Limited) according to wiping operations a to c listed in Table 4. The external environment at this time was 25° C. and 50% RH.

[0120] The conditions for the wiping operation shown in Table 4 below are as follows: Operation a: Wiping operation using a roller to which a cleaning liquid has been applied Specifically, the nozzle surface of the inkjet head was wiped with a polyester cloth pressed against a polyethylene terephthalate film of a wiping unit. The polyester cloth was soaked in the cleaning liquid described below, and the nozzle surface of the piezo-type inkjet head was rubbed against the polyester cloth at a speed of 5 mm / sec.

[0121] Operation b: Wiping operation using a roller that does not apply cleaning liquid Specifically, the nozzle surface of the inkjet head was wiped by rubbing the nozzle surface of the piezo-type inkjet head against the polyester cloth at a speed of 5 mm / sec with a polyester cloth pressed against a polyethylene terephthalate film of a wiping unit.

[0122] Operation c: After applying cleaning liquid to the nozzle surface, wipe with a rubber blade Specifically, the nozzle surface of the inkjet head was wiped by rubbing the nozzle surface of the piezo-type inkjet head with a polybutadiene rubber blade at a speed of 5 mm / sec.

[0123] (cleaning fluid) The cleaning liquid used in operations a and c was a 20% aqueous solution of diethylene glycol adjusted to pH 8.2 with sodium bicarbonate at a temperature of 25°C.

[0124] [Table 1]

[0125] [Table 2]

[0126] [Table 3]

[0127] [evaluation] <Head durability> After printing a solid image continuously for 30 minutes, the nozzle surface was cleaned by wiping (either operation a, b, or c) 10 times (operation 1). (i) After operation 1, the nozzle surface was observed with a microscope digital camera (DS-Fi3; manufactured by Nikon Corporation). (ii) The contact angle of pure water on the nozzle surface before and after operation 1 was compared. Then, (i) and (ii) were carried out and judged according to the following criteria. In the following criteria, "AAA", "AA", and "A" were deemed to be acceptable for practical use. (standard) AAA: No scratches were observed on the nozzle surface, and there was no change in the contact angle of the nozzle surface before and after operation 1. AA: No scratches were observed on the nozzle surface, and there was a change in the contact angle of the nozzle surface before and after operation 1. A: A few scratches were observed on the nozzle surface, and there was a change in the contact angle on the nozzle surface before and after operation 1. B: Numerous scratches are observed on the nozzle surface, and there is also a change in the contact angle on the nozzle surface before and after operation 1.

[0128] <Cleaning ability> Thirty minutes after the start of printing, a wiping operation (operation a, b, or c) was performed on the nozzle surface of the inkjet head to create a solid image. The uniformity of the solid image was visually observed for any nozzle bending or missing nozzles (nozzle clogging). Next, after removing the inkjet head, the nozzle surface of the inkjet head was observed and the cleaning ability was evaluated according to the following criteria. In the following criteria, "AAA", "AA", and "A" were deemed to be acceptable for practical use. (standard) AAA: No residue of the ink composition is observed on the nozzle surface, and no white streaks or density unevenness are observed in the solid image. AA: No residue of ink composition is observed on the nozzle surface, but slight white streaks and uneven density are observed in the solid image. A: Residue of the ink composition is found on the nozzle surface, and white streaks and uneven density are found in solid images. B: Residue of the ink composition was observed on the nozzle surface, and the occurrence of obvious density unevenness was observed in the solid image.

[0129] <Friction resistance> A washing fastness test was conducted on the printed fabric obtained under conditions of 25°C and 50% RH in accordance with the A-2 method of JIS L 0844 (test method for color fastness to washing). Specifically, after washing, rinsing, spin-drying, and drying, the discoloration of the printed part of the test piece was judged. Discoloration was evaluated based on the degree of fading according to the JIS L0804:2004 (ISO 105-A02:1993) discoloration gray scale and the following criteria. In the following criteria, "AAA", "AA" and "A" were deemed to be acceptable for practical use. (standard) AAA: Abrasion fastness is grade 4 or higher. AA: Abrasion fastness is grade 3 or higher but less than grade 4. A: The friction fastness is between grade 2 and grade 3. B: The friction fastness is less than grade 2.

[0130] <Discharge reliability> The printed surface of the printed matter obtained under conditions of 25°C and 50% RH was visually observed and evaluated based on the following criteria, where "AAA", "AA" and "A" were deemed to be acceptable for practical use. (standard) AAA: No missing dots or misalignment of landing positions were observed. Excellent ejection reliability. AA: There was some misalignment in the impact position, but it recovered naturally. Discharge reliability was good. A: There is some deviation in the impact position. B: Missing pixels occurred.

[0131] Table 4 shows the wiping operation, head durability, cleaning performance, friction fastness and ejection reliability.

[0132] [Table 4]

[0133] As shown in Table 4, in Samples 1 to 15 (Examples), in which the content of the glycol solvent in the organic solvent was 50 mass % or more relative to the total organic solvent, the glass transition point of the resin was within the range of -70 to 0°C, and the content of the resin was within the range of 5 to 15 mass % relative to the total ink composition, all of the head durability, cleaning performance, friction fastness, and ejection reliability were feasible. In particular, when using samples 3 to 15 (Examples) in which the resin coating strength was 50 MPa or less, head durability improved. This was thought to be because the coating strength was low, so the nozzle surface could be wiped without being damaged by the wiping operation. Furthermore, when Samples 5 to 15, which contain an acrylic resin or a urethane resin as the resin, were used, and when Samples 8 to 15, which have a resin glass transition point in the range of −70 to −30° C., were used, the cleaning property or the friction fastness was improved. In addition, in the case of Samples 12 to 15, in which the normal boiling point of the organic solvent was 250°C or higher and the content was within the range of 3 to 15 mass% of the total ink composition, head durability and ejection reliability were improved. This was thought to be because the inkjet head was prevented from drying out and the viscosity of the ink composition was easily increased appropriately.

[0134] On the other hand, in the case of Samples 17 and 18 (Comparative Examples) in which the wiping operation was not wet wiping, the head durability and cleaning performance were poor. This is thought to be because the inkjet head was worn down by dry wiping, and the coating of the ink composition was fixed to the nozzle surface. Moreover, in Samples 18, 19, and 20 (comparative examples) in which the glass transition point of the resin was not within the range of −70 to 0° C., any one of head durability, cleaning performance, friction fastness, and ejection reliability was poor. In addition, when Samples 22 and 23 (Comparative Examples) were used, in which the content of glycol-based solvent was less than 50% by mass relative to the total organic solvent, the head durability and cleaning performance were poor. This is thought to be because the amount of glycol-based solvent was so small that the inkjet head wore out and the coating of the ink composition became fixed on the nozzle surface. Moreover, in Samples 23 and 24 (comparative examples) in which the resin content was not within the range of 5 to 15% by mass relative to the total ink composition, either the friction fastness or the ejection reliability was poor. [Explanation of symbols]

[0135] 1. Inkjet printer 3 Cleaning fluid tank 4 Inkjet head 6 Ink Tank 13 Wipe unit 15 Cap 50 Ink absorbing material 51 Sheet-like flexible member 56 First support member 57 Second support member

Claims

1. An inkjet recording method for forming an image on a recording medium by using an ink composition and an inkjet recording apparatus having a wiping mechanism, comprising the steps of: the wiping mechanism has an ink absorbing member for absorbing the ink composition, and the ink absorbing member wipes the nozzle surface of the inkjet head with a wipe unit that holds a cleaning liquid; The ink composition includes a colorant, an organic solvent including a glycol-based solvent, a resin, and water, The content of the glycol solvent in the organic solvent is 50% by mass or more based on the total amount of the organic solvent, The glass transition point of the resin is within the range of −70 to 0° C. The content of the resin is within a range of 5 to 15% by mass based on the total mass of the ink composition. Inkjet recording method.

2. The ink jet recording method according to claim 1, wherein the resin has a coating strength of 50 MPa or less.

3. The ink jet recording method according to claim 1 , wherein the resin is urethane resin particles or acrylic resin particles.

4. 2. The ink jet recording method according to claim 1, wherein the glass transition point of the resin is within a range of -70 to -30°C.

5. The organic solvent has a normal boiling point of 250° C. or higher, the content of the organic solvent having a normal boiling point of 250° C. or higher is within a range of 3 to 15% by mass with respect to the entire ink composition; The ink-jet recording method according to claim 1 .

Images