Ink set, inkjet recording apparatus, and image forming method

Abstract

To provide an ink set in which a highly dryable inkjet ink is easily removed by washing.SOLUTION: The ink set includes an inkjet ink and a cleaning liquid. The inkjet ink contains a pigment and an aqueous medium. When the inkjet ink is allowed to stand at 40 °C for 24 hours, the drying rate is 87% by mass or more and 93% by mass or less. The cleaning liquid contains diethylene glycol butyl methyl ether and a polyhydric alcohol having three or more hydroxyl groups.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink set, an inkjet recording apparatus, and an image forming method. [Background technology]

[0002] In recent years, in order to increase printing speed, inkjet inks with high drying properties have been used to accelerate the fixation of inkjet inks. Inkjet inks with high volatile components and high drying properties adhere strongly to substrates upon drying. In particular, inkjet inks that use pigments remain solidified and do not redissolve once the water evaporates.

[0003] Therefore, when such inkjet ink adheres to the ink ejection surface (also called the nozzle surface) of the recording head and dries, the nozzles on the ink ejection surface become clogged, resulting in a problem of reduced ejection stability of the inkjet ink.

[0004] In particular, inkjet inks for offset coated paper and inkjet inks for label packaging contain binder resins to improve fixation to the substrate of the recording medium. When an inkjet ink that has high drying properties and contains a binder resin adheres to the ink ejection surface of a recording head and dries, it firmly adheres to the ink ejection surface and cannot be easily removed.

[0005] For this reason, ink sets and inkjet recording devices that include high-drying inkjet ink and cleaning liquid are required to be able to easily remove solidified material of the high-drying inkjet ink (specifically, solidified material of the high-drying inkjet ink that has adhered to the ink ejection surface of the recording head) by washing (cleaning).

[0006] As an example of an ink set that can prevent ink non-ejection due to clogging of the nozzles of a recording head and maintain stable ejection performance of the recording head, Patent Document 1 proposes an ink set that includes, for example, an ink (ink composition) containing water, a pigment, and polymer particles, and a cleaning liquid (maintenance liquid) containing propylene glycol monopropyl ether. Specifically, Patent Document 1 uses a cleaning liquid that is composed of propylene glycol monopropyl ether, a nonionic surfactant, and water. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5566741 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the cleaning liquid of the ink set described in Patent Document 1 has poor cleaning performance against solidified inkjet inks with high drying properties, and is unable to meet the above-mentioned requirements. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an ink set, an inkjet recording apparatus, and an image forming method that make it easy to remove solidified fast-drying inkjet ink by cleaning. [Means for solving the problem]

[0009] The ink set according to the present invention comprises an inkjet ink and a cleaning liquid. The inkjet ink contains a pigment and an aqueous medium. When the inkjet ink is left at 40°C for 24 hours, the drying rate is 87% by mass or more and 93% by mass or less. The cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

[0010] An inkjet recording apparatus according to the present invention comprises an inkjet ink, a cleaning liquid, and a recording head, the recording head having a recording section that ejects the inkjet ink onto an image formation area of ​​a recording medium, and a cleaning section that cleans the ink ejection surface of the recording section with the cleaning liquid, the inkjet ink having a drying rate of 87% by mass or more and 93% by mass or less when left to stand at 40°C for 24 hours, and the cleaning liquid containing diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

[0011] The image forming method according to the present invention includes a discharge step of discharging an inkjet ink from an ink discharge surface of a recording head onto a recording medium, and a cleaning step of cleaning the ink discharge surface with a cleaning liquid. The inkjet ink contains a pigment and an aqueous medium. When the inkjet ink is left at 40°C for 24 hours, the drying rate is 87% by mass or more and 93% by mass or less. The cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol. [Effects of the Invention]

[0012] According to the ink set, inkjet recording apparatus, and image forming method of the present invention, solidified material of fast-drying inkjet ink can be easily removed by washing (cleaning). [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a main part of an inkjet recording apparatus which is an example of an inkjet recording apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing the bottom surface of the recording head and head housing of FIG. 1; [Figure 3] FIG. 2 is a diagram showing a side view of the first recording head of FIG. [Figure 4] 1A to 1C are diagrams illustrating a series of cleaning steps in a cleaning operation performed by an inkjet recording apparatus. [Figure 5] 1A to 1C are diagrams illustrating a series of cleaning steps in a cleaning operation performed by an inkjet recording apparatus. [Figure 6]1A to 1C are diagrams illustrating a series of cleaning steps in a cleaning operation performed by an inkjet recording apparatus. [Figure 7] 1A to 1C are diagrams illustrating a series of cleaning steps in a cleaning operation performed by an inkjet recording apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The present invention can be modified in various ways within the scope of the object of the present invention, and embodiments obtained by appropriately combining the technical means described in different embodiments are also included in the technical scope of the present invention.

[0015] 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.

[0016] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Each component described in this specification may be used singly or in combination of two or more. Furthermore, in this specification, "at least one of A and B" means "A and / or B." "A and / or B" means "A or B, or A and B."

[0017] [First embodiment: ink set] An ink set according to a first embodiment of the present invention will now be described. The ink set according to this embodiment comprises inkjet ink (hereinafter sometimes simply referred to as ink) and a cleaning solution. The ink contains a pigment and an aqueous medium. When the ink is left to stand at 40°C for 24 hours, the drying rate is 87% by mass or more and 93% by mass or less. The cleaning solution contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

[0018] As described above, the ink provided in the ink set according to this embodiment is a high-drying ink that contains a pigment and an aqueous medium and has a drying rate of 87% to 93% by mass when left at 40°C for 24 hours. When the ink is left at 40°C for 24 hours, the drying rate of the ink becomes saturated. Therefore, the drying rate of the ink when left at 40°C for 24 hours refers to the drying rate of the ink when it has reached its upper limit. By virtue of the above-described configuration, the ink set according to this embodiment makes it easy to remove solidified material from the high-drying ink by washing (cleaning). The reason why the ink set according to this embodiment exhibits the above-described effects is presumed to be as follows.

[0019] The cleaning solution of the ink set according to this embodiment contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol. The combined use of diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol in the cleaning solution makes it easier for the diethylene glycol butyl methyl ether contained in the cleaning solution to be absorbed by the solidified ink. This can cause volumetric distortion in the solidified ink, weakening the adhesive strength of the solidified ink to the ink ejection surface of the recording head.

[0020] Furthermore, trihydric or higher polyhydric alcohols have the effect of destabilizing diethylene glycol butyl methyl ether in the cleaning solution. This destabilization of diethylene glycol butyl methyl ether in the cleaning solution means that the trihydric or higher polyhydric alcohol weakens the interaction between diethylene glycol butyl methyl ether and the hydrated water. By destabilizing diethylene glycol butyl methyl ether in the cleaning solution, the absorption of ink stains by diethylene glycol butyl methyl ether can be enhanced. This further enhances the cleaning power of diethylene glycol butyl methyl ether.

[0021] For the reasons described above, the ink set according to this embodiment makes it possible to easily peel off and remove solidified ink deposits, even if the solidified deposits are from highly drying inks that are difficult to dissolve or disperse in a solvent. Thus, a cleaning liquid containing diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol has excellent performance for removing solidified deposits from highly drying inks. Therefore, by combining the inks described above with the cleaning liquid described above, it is possible to provide an ink set that makes it easy to remove solidified deposits from highly drying inks by cleaning. The ink set according to this embodiment will be described in more detail below.

[0022] [ink] The inks included in the ink set according to this embodiment contain at least a pigment and an aqueous medium. The inks preferably further contain at least one of a pigment-coated resin, binder resin particles, and a surfactant.

[0023] (drying rate) The inks included in the ink set according to this embodiment are highly dry inks that have a drying rate of 87% to 93% by mass when left for 24 hours at 40° C. (hereinafter, sometimes simply referred to as the drying rate of the ink.) In this embodiment, the drying rate of the ink refers to the percentage of the ink mass that has been reduced as a result of vaporization of the volatile components in the ink and the ink drying after being left for 24 hours at 40° C.

[0024] Specifically, the drying rate of ink is calculated by the following formula (i), and represents the ratio of the mass of ink reduced by drying to the mass of ink before drying. Ink drying rate = 100 × (W0 - W1) / W0 (i)

[0025] In formula (i), W0 represents the mass of the ink before drying (before being left at 40°C for 24 hours), and W1 represents the mass of the ink after drying (after being left at 40°C for 24 hours). Ink is usually stored so that its composition does not change from the time of manufacture. Therefore, the proportion of volatile components in the ink does not change with the number of years since the ink was manufactured. In other words, the number of years since the ink was manufactured does not affect the drying rate of the ink. Therefore, the drying rate of the ink can be easily calculated by measuring the mass of the ink before and after drying. Specifically, the drying rate of the ink can be calculated using the method shown below.

[0026] First, ink from the ink set to be evaluated was applied to a thin stainless steel plate at 0.7 μL / cm 2 The ink is then spin-coated in an amount of 1000 W. The stainless steel sheet is then left at 40°C for 24 hours to dry the ink, forming a dry thin film on the stainless steel sheet. In this case, the mass of the ink before drying, represented by W0, specifically represents the mass of the ink applied to the stainless steel sheet. The mass of the ink after drying, represented by W1, specifically represents the mass of the ink after it has been applied to the stainless steel sheet and left at 40°C for 24 hours (in other words, the mass of the dry thin film of ink (i.e., solids) formed on the stainless steel sheet).

[0027] The ink contains vaporizable components. The vaporizable components include at least volatile components. The volatile components may be any volatile components used in the ink. The volatile components are those that are volatile at 40°C or less. Examples of volatile components include water and so-called volatile organic compounds (VOCs) with a boiling point in the range of 50°C to 260°C. However, volatile components are not limited to water and VOCs. The vaporizable components may include, for example, so-called highly volatile organic compounds (VVOCs) with a boiling point of 50°C or less, or semi-volatile organic compounds (SVOCs) with a boiling point of 260°C or more.

[0028] The content of volatile components in the ink is preferably 85% by mass or more and 93% by mass or less. By making the content of volatile components in the ink 85% by mass or more, an ink set can be obtained that includes ink with high drying properties that enable high-speed printing. On the other hand, by making the content of volatile components in the ink 93% by mass or less, an image with the desired image density can be formed. In addition, the ink can be reliably removed from the ink ejection surface of the recording head by the cleaning liquid. This allows the ejection stability of the ink in the inkjet recording device to be optimized. Note that examples of volatile components contained in the ink include aqueous media.

[0029] The vaporizable component may also contain a sublimable component. The sublimable component may contain, for example, a pigment, a pigment-coated resin, or a portion of binder resin particles. The ink composition is appropriately set so that the solid content in the ink that does not evaporate even after being left at 40°C for 24 hours is 7% by mass or more and 12% by mass or less. By ensuring that the solid content in the ink that does not evaporate even after being left at 40°C for 24 hours is 7% by mass or more, an image with a desired image density can be formed. Furthermore, the ink can be reliably removed from the ink ejection surface of the recording head using a cleaning liquid. This optimizes the ejection stability of the ink in an inkjet recording device. On the other hand, by ensuring that the solid content in the ink that does not evaporate even after being left at 40°C for 24 hours is 12% by mass or less, an ink set can be obtained that includes ink with high drying properties that enable high-speed printing.

[0030] (pigment) Examples of pigments 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).

[0031] The pigment content of the ink is preferably 2.00% by mass or more and 15.00% by mass or less, and more preferably 5.00% by mass or more and 10.00% by mass or less. By setting the pigment content to 2.00% by mass or more, it becomes easier to form an image with the desired image density. Furthermore, by setting the pigment content to 15.00% by mass or less, the ink can be reliably removed from the ink ejection surface of the recording head using a cleaning liquid. This allows for optimal ink ejection stability in inkjet recording devices.

[0032] In the ink, the pigment is dispersed in the aqueous medium as particles (hereinafter sometimes referred to as pigment particles). The pigment particles may contain only the pigment, or may contain the pigment and a pigment-coating resin that coats the surface of the pigment. When the pigment particles contain a pigment-coating resin, the pigment particles are composed of, for example, a core containing the pigment and the pigment-coating resin that coats the core.

[0033] (pigment coated resin) At least a portion of the pigment coating resin coats the core (pigment portion). The presence of the pigment coating resin on the surface of the pigment particle optimizes the dispersibility of the pigment particle. Note that a portion of the pigment coating resin may be dissolved or dispersed in the aqueous medium without coating the core.

[0034] The pigment coating resin is not particularly limited, but examples thereof include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid copolymer, vinylnaphthalene-(meth)acrylic acid copolymer, and vinylnaphthalene-maleic acid copolymer.

[0035] When the ink contains a pigment-coated resin, the content of the pigment-coated resin in the ink is preferably 0.5% by mass or more and 4.0% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less.

[0036] Furthermore, when the ink contains a pigment-coating resin, the content of the pigment-coating resin relative to 100.0 parts by mass of the pigment in the ink is preferably 10.0 parts by mass or more and 60.0 parts by mass or less, and more preferably 20.0 parts by mass or more and 30.0 parts by mass or less.

[0037] In order to optimize the color density, hue, or stability of the ink, the volume median diameter (D 50 ) is preferably 30 nm or more and 300 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0038] (binder resin particles) The binder resin particles function as a binder in an image formed by the ink. After the ink lands, the binder resin particles bond the pigment in the ink to the recording medium, improving the fixation of the pigment to the recording medium. The binder resin particles exist in a dispersed state in an aqueous medium. The binder resin particles are contained in the ink, for example, in the form of an emulsion (emulsified particles). Therefore, for example, emulsified particles composed of binder resin particles are dispersed in the ink.

[0039] Examples of the binder resin particles include particles of a urethane resin, a (meth)acrylic resin, a urethane-(meth)acrylic resin, a polyester resin, a styrene-(meth)acrylic resin, a styrene-maleic acid copolymer, a vinylnaphthalene-(meth)acrylic acid copolymer, and a vinylnaphthalene-maleic acid copolymer. As the binder resin particles, particles of a urethane resin or a urethane-(meth)acrylic resin are preferred.

[0040] The content of binder resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 3.0% by mass or more and 7.0% by mass or less. By making the content of binder resin particles 1.0% by mass or more, the fixation of the pigment to the recording medium can be improved. On the other hand, by making the content of binder resin particles 10.0% by mass or less, the ink can be more reliably removed from the ejection surface of the recording head by the cleaning liquid. This allows the ejection stability of the ink from the inkjet recording device to be optimized.

[0041] (surfactant) Surfactants optimize the compatibility and dispersion stability of the components contained in the ink. They also optimize the ink's permeability (wettability) to the recording medium. Examples of surfactants include nonionic surfactants.

[0042] Examples of nonionic surfactants include acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds), and fluorine surfactants (surfactants containing fluororesins or fluorine-containing compounds). Preferred nonionic surfactants are acetylene glycol surfactants. Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. Preferred acetylene glycol surfactants are ethylene oxide adducts of acetylene glycol.

[0043] When the ink contains a surfactant, the content of the surfactant in the ink is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.2% by mass or more and 0.6% by mass or less.

[0044] (aqueous medium) The aqueous medium contained in the ink is a medium containing water. The aqueous medium may function as a solvent or a dispersion medium. Specific examples of the aqueous medium include an aqueous medium containing water and a water-soluble organic solvent.

[0045] (water) Water is the main solvent of the ink, and the content of water in the ink is preferably, for example, 60.0% by mass or more and 90.0% by mass or less.

[0046] (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.

[0047] Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0048] 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.

[0049] Lactam compounds include, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

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

[0051] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0052] The water-soluble organic solvent is preferably a glycol compound or a glycol ether compound, more preferably propylene glycol and / or diethylene glycol monoethyl ether.

[0053] The content of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 30.0% by mass or less, and more preferably 5.0% by mass or more and 20.0% by mass or less.

[0054] The content of propylene glycol in the ink is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 8.0% by mass or less.

[0055] The content of diethylene glycol monoethyl ether in the ink is preferably 3.0% by mass or more and 20.0% by mass or less, and more preferably 5.0% by mass or more and 15.0% by mass or less.

[0056] In the aqueous medium, the total content of water, propylene glycol, and diethylene glycol monoethyl ether is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass.

[0057] (Other ingredients) The ink may further contain known additives (for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as needed.

[0058] [Ink manufacturing method] The ink can be produced, for example, by uniformly mixing a pigment dispersion containing pigment particles, a binder resin particle dispersion (e.g., a resin emulsion) containing a binder resin, an aqueous medium, and other components (e.g., a surfactant) that are added as needed, using a mixer. In producing the ink, after the components are uniformly mixed, foreign matter and coarse particles may be removed using a filter (e.g., a filter with a pore size of 5 μm or less).

[0059] (pigment dispersion) The pigment dispersion is a dispersion containing pigment particles. The pigment dispersion preferably further contains a pigment-coating resin. The dispersion medium of the pigment dispersion is preferably water.

[0060] The pigment content in the pigment dispersion is preferably 5.0% by mass or more and 25.0% by mass or less, and more preferably 150.0% by mass or more and 20.0% by mass or less. When the pigment particles contain a pigment-coating resin, the content of the pigment-coating resin in the pigment dispersion is preferably 1.0% by mass or more and 10.0% by mass or less.

[0061] The pigment dispersion can be prepared by wet-dispersing a pigment, a dispersion medium (e.g., water), and optional components (e.g., a pigment-coated resin and / or a surfactant) using a media-type wet disperser. Commercially available pigment dispersions may also be used as the pigment dispersion.

[0062] When a pigment dispersion is added in the production of ink, the ratio of the pigment dispersion to all the raw materials of the ink is, for example, 10.0% by mass or more and 40.0% by mass or less.

[0063] [Cleaning solution] The cleaning liquid of the ink set according to this embodiment contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol as organic solvents. The cleaning liquid preferably contains water as the main solvent.

[0064] (Diethylene glycol butyl methyl ether) Diethylene glycol butyl methyl ether is absorbed by ink deposits, thereby weakening their adhesive strength, thereby imparting excellent cleaning performance to the cleaning solution.

[0065] The content of diethylene glycol butyl methyl ether in the cleaning solution is preferably 1% by mass or more and 8% by mass or less, and more preferably 4% by mass or more and 8% by mass or less. By making the content of diethylene glycol butyl methyl ether in the cleaning solution 1% by mass or more, it is possible to impart even better cleaning performance to the cleaning solution. Furthermore, by making the content of diethylene glycol butyl methyl ether in the cleaning solution 8% by mass or less, it becomes easier to ensure the compatibility of diethylene glycol butyl methyl ether with other components (for example, water and polyhydric alcohols).

[0066] (Polyhydric alcohol) Examples of trihydric or higher polyhydric alcohols contained in the cleaning solution include sorbitol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-1,2,4-butanetriol, and 1,2,3,6-hexatetraol. The trihydric or higher polyhydric alcohol contained in the cleaning solution is preferably a trihydric or higher aliphatic alcohol, more preferably glycerin or sorbitol. As described above, the use of diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol in combination in the cleaning solution facilitates absorption of the diethylene glycol butyl methyl ether contained in the cleaning solution by ink deposits.

[0067] The content of the trihydric or higher polyhydric alcohol in the cleaning solution is preferably 1% by mass or more and 53% by mass or less. By making the content of the trihydric or higher polyhydric alcohol in the cleaning solution 1% by mass or more, the cleaning performance of the cleaning solution can be reliably improved. By making the content of the trihydric or higher polyhydric alcohol in the cleaning solution 53% by mass or less, compatibility with diethylene glycol butyl methyl ether can be easily ensured.

[0068] When the cleaning solution contains glycerin as the trihydric or higher polyhydric alcohol, the content ratio of diethylene glycol butyl methyl ether and the content ratio of glycerin in the cleaning solution preferably satisfy the following formula (1): In formula (1), A represents the content ratio (unit: mass %) of diethylene glycol butyl methyl ether in the cleaning solution, and B represents the content ratio (unit: mass %) of glycerin in the cleaning solution. -7×A+57≦B≦-7×A+60 (1)

[0069] For example, when the cleaning solution contains 8% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 1% by mass or more and 4% by mass or less of glycerin. Furthermore, when the cleaning solution contains 4% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 29% by mass or more and 32% by mass or less. When the cleaning solution contains 1% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 50% by mass or more and 53% by mass or less of glycerin.

[0070] The cleaning performance of the cleaning liquid can be optimized by ensuring that the content ratio of diethylene glycol butyl methyl ether and the content ratio of glycerin in the cleaning liquid satisfy formula (1), which in turn can more reliably weaken the adhesive force of ink deposits on the ink ejection surface of the print head, making it easier to peel off and remove the ink deposits.

[0071] Furthermore, when the cleaning solution contains sorbitol as the trihydric or higher polyhydric alcohol, the content ratio of diethylene glycol butyl methyl ether and the content ratio of sorbitol in the cleaning solution preferably satisfy the following formula (2): In formula (2), A represents the content ratio (unit: mass %) of diethylene glycol butyl methyl ether in the cleaning solution, and C represents the content ratio (unit: mass %) of sorbitol in the cleaning solution. -5×A+41≦C≦-5×A+45 (2)

[0072] For example, when the cleaning solution contains 8% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 1% by mass or more and 5% by mass or less of sorbitol. Furthermore, when the cleaning solution contains 4% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 21% by mass or more and 25% by mass or less. When the cleaning solution contains 1% by mass of diethylene glycol butyl methyl ether, the cleaning solution preferably contains 36% by mass or more and 40% by mass or less of sorbitol.

[0073] The cleaning performance of the cleaning liquid can be optimized by ensuring that the content ratio of diethylene glycol butyl methyl ether and the content ratio of sorbitol in the cleaning liquid satisfy formula (2), which in turn can more reliably weaken the adhesive force of ink deposits on the ink ejection surface of the print head, making it easier to peel off and remove the ink deposits.

[0074] The cleaning solution may contain an organic solvent other than diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol. However, the total content of diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol in the organic solvent in the cleaning solution is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass. In particular, the total content of diethylene glycol butyl methyl ether and glycerin or sorbitol in the organic solvent in the cleaning solution is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass.

[0075] (water) As described above, the cleaning liquid preferably contains water as a main solvent. The water content in the cleaning liquid is, for example, preferably 40% by mass or more and 95% by mass or less, and more preferably 60% by mass or more and 90% by mass or less.

[0076] (additives) The cleaning 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 needed.

[0077] [Cleaning solution manufacturing method] The cleaning liquid can be produced, for example, by mixing diethylene glycol butyl methyl ether, a trihydric or higher polyhydric alcohol, and components that are added as needed (for example, water). The ink set of the first embodiment has been described above.

[0078] [Second embodiment: inkjet recording apparatus] An inkjet recording apparatus according to a second embodiment of the present invention will now be described. The inkjet recording apparatus according to this embodiment comprises ink, a cleaning liquid, and a recording head. The recording head has a recording unit that ejects ink onto an image formation area of ​​a recording medium, and a cleaning unit that cleans the ink ejection surface of the recording unit with a cleaning liquid. The inkjet ink has a drying rate of 87% by mass or more and 93% by mass or less when left at 40°C for 24 hours. The cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

[0079] The ink and cleaning liquid provided in the inkjet recording apparatus according to this embodiment are the same as the ink and cleaning liquid provided in the ink set according to the first embodiment. Therefore, the inkjet recording apparatus according to this embodiment is an inkjet recording apparatus equipped with a print head that uses the ink set according to the first embodiment. Therefore, for the same reasons as those described in the first embodiment, the inkjet recording apparatus according to this embodiment is easy to remove solidified inkjet ink with high drying properties by cleaning. Details of the ink and cleaning liquid have already been described in the first embodiment, so they will be omitted here.

[0080] [Structure of inkjet recording device] The inkjet recording apparatus according to the present embodiment will be described below with reference to the drawings. The drawings are primarily intended to illustrate each component in a schematic manner for ease of understanding, and the size, number, etc. of each component shown may differ from the actual size and number of each component due to the convenience of creating the drawings. The size, number, etc. of each component shown may also be changed as appropriate.

[0081] FIG. 1 is a diagram showing the main components of an inkjet recording apparatus 1, which is an example of an inkjet recording apparatus according to the present embodiment. The inkjet recording apparatus 1 shown in FIG. 1 includes a recording head 2, a head housing 3 that holds the recording head 2, and a transport unit 4 that transports a recording medium (not shown). The recording head 2 includes a first recording head 2a, a second recording head 2b, a third recording head 2c, and a fourth recording head 2d. The transport unit 4 includes a pair of transport rollers, a first roller 4a and a second roller 4b, and a transport belt 4c that is stretched between the first roller 4a and the second roller 4b. The transport unit 4 transports the recording medium placed on the transport belt 4c in a specific direction (to the right as indicated by the arrow in FIG. 1). Hereinafter, the direction in which the recording medium is transported may be referred to as the transport direction X. When a recording medium is transported directly below the first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d eject ink to record an image (i.e., form an image).

[0082] The first recording head 2a, the second recording head 2b, the third recording head 2c, the fourth recording head 2d, and the conveying unit 4 are each supported at a height such that the distance from the upper surface of the conveying belt 4c is a predetermined length.

[0083] The first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d each record (form) an image on a recording medium transported on a transport belt 4c.

[0084] The first print head 2a, the second print head 2b, the third print head 2c, and the fourth print head 2d are each provided to be able to contain the ink and cleaning liquid described in the first embodiment. The first print head 2a, the second print head 2b, the third print head 2c, and the fourth print head 2d each include an ink tank (ink storage section) and a cleaning liquid tank (cleaning liquid storage section), both of which are not shown.

[0085] The ink tanks of the first print head 2a, the second print head 2b, the third print head 2c, and the fourth print head 2d each contain (reserve) ink (first ink, second ink, third ink, and fourth ink) of four different colors (black, cyan, magenta, and yellow). Using the fast-drying inks described in the first embodiment for these inks enables high-speed printing with these inks. In addition, the cleaning liquid tanks of the first print head 2a, the second print head 2b, the third print head 2c, and the fourth print head 2d each contain (reserve) the cleaning liquid described in the first embodiment.

[0086] The first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d ink-jet eject each color of ink stored in an ink tank (not shown) onto the recording medium through their respective nozzles. The first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d ink-jet eject each ink onto the recording medium in a predetermined order at regular intervals. This forms a color image on the recording medium.

[0087] Fig. 2 is a diagram showing the underside of the recording head 2 and head housing 3 in Fig. 1. The first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d each extend in a direction perpendicular to the transport direction X (hereinafter, sometimes referred to as the width direction A).

[0088] The first, second, third, and fourth print heads 2a, 2b, 2c, and 2d have substantially the same structure. Therefore, the following description of the print heads 2 will be given using the first print head 2a as an example. However, the same description also applies to the second, third, and fourth print heads 2b, 2c, and 2d.

[0089] Fig. 3 is a diagram showing a side view of the first recording head 2a in Fig. 1. As shown in Fig. 3, the first recording head 2a includes a recording unit 5 that ejects ink onto an image forming area of ​​a recording medium, and a cleaning unit 6 that cleans the ink ejection surface F1 of the recording unit 5 with cleaning liquid.

[0090] On the ink ejection surface F1 on the lower surface of the recording unit 5, a plurality of nozzles (not shown) that eject ink are arranged.

[0091] As shown in FIG. 3, the cleaning unit 6 has a cleaning liquid supply unit 6a disposed near the ink ejection surface F1 of the recording unit 5, and a wiper blade 6b. A cleaning liquid supply surface F2 below the cleaning liquid supply unit 6a is provided with a plurality of cleaning liquid ejection holes (not shown) for ejecting cleaning liquid. The cleaning liquid supply unit 6a supplies cleaning liquid stored in a cleaning liquid tank (not shown) to the cleaning liquid supply surface F2 through the cleaning liquid ejection holes. The wiper blade 6b has the function of wiping the ink ejection surface F1. The wiper blade 6b is, for example, a rubber wiper. The linear pressure of the wiper blade 6b is, for example, 5.0 N / m or more and 15.0 N / m or less.

[0092] 4 to 7 show a series of cleaning steps (supply step, wiping step) in the cleaning operation by the inkjet recording apparatus 1. As shown in FIG. 4, in the cleaning operation, first, a small amount of ink I is purged from the recording unit 5 (purging operation). This clears nozzle clogging and the like in the recording unit 5. The purged ink I adheres to the ink ejection surface F1 of the recording unit 5. In the cleaning operation, simultaneously with the purging operation, cleaning liquid C is supplied from the cleaning liquid supply unit 6a (cleaning liquid supplying operation). The supplied cleaning liquid C adheres to the vicinity of the ink ejection surface F1 of the recording unit 5 (cleaning liquid supply surface F2 below the cleaning liquid supply unit 6a).

[0093] Next, as shown in FIG. 5, the wiper blade 6b is pressed against the cleaning liquid supply surface F2 on the underside of the cleaning liquid supply unit 6a. Next, as shown in FIG. 6, the wiper blade 6b moves horizontally (to the left in FIG. 6). As a result, cleaning liquid C is supplied to the ink ejection surface F1. The wiper blade 6b wipes away the cleaning liquid C adhering to the cleaning liquid supply surface F2 and the ink I adhering to the ink ejection surface F1 (wiping operation). At this time, the cleaning liquid C mixes with the ink I. As a result, as shown in FIG. 7, the cleaning liquid C adhering to the cleaning liquid supply surface F2 and the ink I adhering to the ink ejection surface F1 are removed. In this way, the recording unit 5 is cleaned with the cleaning liquid C.

[0094] The above describes a series of steps in the cleaning operation performed by the inkjet recording apparatus 1. Similar to the first recording head 2a, the second recording head 2b, the third recording head 2c, and the fourth recording head 2d each have a recording unit 5 that ejects ink and a cleaning unit 6 that cleans the ink ejection surface F1 of the recording unit 5 with cleaning liquid. The cleaning unit 6 for the second recording head 2b, the third recording head 2c, and the fourth recording head 2d also has a cleaning liquid supply unit 6a disposed near the ink ejection surface F1 of the recording unit 5, and a wiper blade 6b.

[0095] An example of the inkjet recording apparatus according to this embodiment has been described above, but the inkjet recording apparatus according to this embodiment is not limited to the one shown in FIGS.

[0096] 1 to 7, an inkjet recording device 1 equipped with four line-type recording heads corresponding to four colors of ink has been described as an example of the recording heads. However, the number of recording heads equipped in the inkjet recording device according to this embodiment is not particularly limited, and can be, for example, 1 to 10, and preferably 3 to 5.

[0097] Furthermore, in the inkjet recording apparatus according to this embodiment, the types, combinations, and ejection order of inks are not particularly limited.

[0098] 1 to 7, the inkjet recording apparatus 1 has been described as an example in which the cleaning unit 6 includes a cleaning liquid supply unit 6a disposed near the ink ejection surface F1 of the recording unit 5, and a wiper blade 6b. However, the inkjet recording apparatus according to this embodiment may also be an inkjet recording apparatus that performs a wiping operation by applying a cleaning liquid directly to the wiper blade. The inkjet recording apparatus according to this embodiment may also be an inkjet recording apparatus that performs a wiping operation by directly supplying (for example, applying, scattering, or spraying) a cleaning liquid to the ink ejection surface F1 of the recording unit 5. The cleaning unit of the inkjet recording apparatus according to this embodiment may be any inkjet recording apparatus that can clean the ink ejection surface F1 of the recording unit 5 with a cleaning liquid.

[0099] Furthermore, the inkjet recording apparatus according to this embodiment may be a multifunction machine that also has the functions of a scanner, a copier, a printer, or a facsimile.

[0100] [Third embodiment: image forming method] An image forming method according to a third embodiment of the present invention will now be described. The image forming method according to this embodiment includes a discharge step of discharging ink from the ink discharge surface of a recording head onto a recording medium, and a cleaning step of cleaning the ink discharge surface with a cleaning liquid. The ink contains a pigment and an aqueous medium. When the ink is left at 40°C for 24 hours, the drying rate is 87% by mass or more and 93% by mass or less. The cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

[0101] The ink and cleaning liquid used in the image forming method according to this embodiment are the same as those included in the ink set according to the first embodiment. Therefore, for the same reasons as those described in the first embodiment, the image forming method according to this embodiment makes it easy to remove solidified inkjet ink with high drying properties by cleaning. Details of the ink and cleaning liquid have already been described in the first embodiment, so they will not be repeated here.

[0102] The image forming method according to this embodiment can be carried out using, for example, the ink set according to the first embodiment. In the cleaning process, inks provided in the ink set according to the first embodiment are ejected onto a recording medium from the ink ejection surface of a recording head in an inkjet recording apparatus. In the cleaning process, the ink ejection surface is cleaned with the cleaning liquid provided in the ink set according to the first embodiment. The image forming method according to the third embodiment has been described above. [Example]

[0103] Examples of the present invention will be described below. However, the present invention is not limited to the following examples. In the following description, water refers to ion-exchanged water.

[0104] [Ink preparation] Inks (I-1) to (I-3) were prepared by the following method.

[0105] (Ink (I-1)) 35.0 parts by weight of pigment dispersion (pigment: 35.0 × 20 / 100 = 7.0 parts by weight), 12.5 parts by weight of binder resin particle dispersion (binder resin particles: 12.5 × 40 / 100 = 5.0 parts by weight), 0.5 parts by weight of acetylene glycol surfactant ("Olfine® EXP.4300" manufactured by Nissin Chemical Industry Co., Ltd.), 10.0 parts by weight of diethylene glycol monoethyl ether, 3.0 parts by weight of propylene glycol, and 39.0 parts by weight of water were thoroughly mixed using a mixer ("Three-One Motor® BL-600" manufactured by Shinto Scientific Co., Ltd.). This resulted in the preparation of ink (I-1). The pigment dispersion used was "EMACOL SF BLACK AH2186F" manufactured by Sanyo Dye Co., Ltd. (pigment: CI Pigment Black 7, dispersion medium: water, pigment concentration: 20% by weight). As the binder particle dispersion, "Movinyl (registered trademark) 6763" (binder resin particle dispersion containing urethane-acrylic resin, resin concentration: 40% by mass) manufactured by Japan Coating Resins Co., Ltd. was used.

[0106] (Ink (I-2)) Ink (I-2) was prepared in the same manner as ink (I-1), except that 17.0 parts by mass of Superflex (registered trademark) 870 (urethane resin emulsion, dispersion medium: water, solids concentration: 30% by mass) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. (binder resin particles: 17.0 × 30 / 100 = 5.1 parts by mass) was used as the binder resin particle dispersion liquid instead of 12.5 parts by mass of Mowinyl (registered trademark) 6763, and the amount of water used was changed from 39.0 parts by mass to 34.5 parts by mass. That is, ink (I-2) was prepared by thoroughly mixing 35.0 parts by mass of "EMACOL SF BLACK AH2186F" (pigment: 7.0 parts by mass, water: 28.0 parts by mass), 17.0 parts by mass of "Superflex (registered trademark) 870" (binder resin particles: 5.1 parts by mass, water: 11.9 parts by mass), 0.5 parts by mass of "Olfine (registered trademark) EXP.4300", 10.0 parts by mass of diethylene glycol monoethyl ether, 3.0 parts by mass of propylene glycol, and 34.5 parts by mass of water using a mixer ("Three-One Motor (registered trademark) BL-600" manufactured by Shinto Scientific Co., Ltd.).

[0107] (Ink (I-3)) Ink (I-3) was prepared in the same manner as ink (I-2), except that the amount of propylene glycol used was changed from 3.0 parts by mass to 25.0 parts by mass and the amount of water used was changed from 34.5 parts by mass to 12.5 parts by mass. That is, 35.0 parts by mass of "EMACOL SF BLACK AH2186F" (pigment: 7.0 parts by mass, water: 28.0 parts by mass), 17.0 parts by mass of "Superflex (registered trademark) 870" (binder resin particles: 5.1 parts by mass, water: 11.9 parts by mass), 0.5 parts by mass of "Olfine (registered trademark) EXP.4300", 10.0 parts by mass of diethylene glycol monoethyl ether, 25.0 parts by mass of propylene glycol, and 12.5 parts by mass of water were thoroughly mixed using a mixer ("Three-One Motor (registered trademark) BL-600" manufactured by Shinto Scientific Co., Ltd.) to prepare ink (I-3).

[0108] [Preparation of cleaning solution] Cleaning solutions (C-1) to (C-9) and (c-1) to (c-12) were prepared by the following method.

[0109] (Cleaning solution (C-1)) 8.0 parts by mass of diethylene glycol butyl methyl ether, 4.0 parts by mass of glycerin, and 88.0 parts by mass of water were mixed with sufficient stirring to prepare a cleaning liquid (C-1).

[0110] (Cleaning solutions (C-2) to (C-9) and (c-1) to (c-12)) Cleaning solutions (C-2) to (C-9) and (c-1) to (c-12) were prepared in the same manner as cleaning solution (C-1), except that the types and amounts of raw materials used were changed as shown in Tables 1 to 4 below. In Tables 1 to 4 below, "DEGBME" refers to diethylene glycol butyl methyl ether. "PGMPE" refers to propylene glycol monopropyl ether. "EG" refers to ethylene glycol. "1,2-PG" refers to 1,2-propanediol. "1,3-PG" refers to 1,3-propanediol. "E1010" refers to a nonionic surfactant ("Olfine (registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd., an ethylene oxide adduct of acetylene diol). "Parts" refers to parts by mass. "-" indicates that the corresponding component was not used. Glycerin and sorbitol are trivalent or higher polyhydric alcohols.

[0111] [Ink set preparation] As shown in the following Tables 1 to 4, one of the inks (I-1) to (I-3) was combined with one of the cleaning solutions (C-1) to (C-9) and (c-1) to (c-12), thereby preparing the ink sets of Examples 1 to 11 and Comparative Examples 1 to 16.

[0112] [Preparation of sample plates] The sample plate used for the measurements to calculate the ink drying rate and ink removal rate was prepared by the following method. First, 2 mL of ink from the ink set to be evaluated was dropped onto a thin stainless steel plate (SUS304) fixed to a spin coater, and the plate was rotated at 2000 rpm for 3 seconds. In this way, the ink from the ink set to be evaluated, which was the subject of measurement, was applied to the thin stainless steel plate by spin coating (application amount 0.7 μL / cm 2 Next, this stainless steel thin plate was left at 40°C for 24 hours to dry the applied ink. In this way, a stainless steel thin plate on which a dry thin film of the ink to be measured was formed was obtained as a sample plate.

[0113] [Ink drying rate] The mass of the ink applied to the stainless steel thin plate to prepare the sample plate was defined as W0, and the mass of the dried thin film of ink formed on the sample plate was defined as W1. The drying rate of the ink after leaving it at 40°C for 24 hours was calculated using the above-mentioned formula (i). The drying rates of inks (I-1) to (I-3) calculated using the above-mentioned method are shown in Tables 1 to 4, along with the percentage of volatile components contained in inks (I-1) to (I-3). In Tables 1 to 4, the "percentage of volatile components" refers to the percentage of volatile components contained in inks (I-1) to (I-3). The drying rate of ink (I-3) was lower than that of inks (I-1) and (I-2) by increasing the amount of propylene glycol compared to inks (I-1) and (I-2).

[0114] [Ink removal rate] Using a pipetter, 0.1 mL of the cleaning solution for the ink set being evaluated was dropped onto the thin, dry ink film formed on the sample plate. Next, a rubber blade was used to wipe the thin, dry ink film on the sample plate at a linear pressure of 10 N / m. After wiping, the area x of the region where the rubber blade contacted the sample plate, where the thin, dry ink film had peeled off and the underlying stainless steel sheet was exposed (the region where the thin, dry ink film had been removed by the cleaning solution), was measured. The percentage of area x relative to the total area of ​​the portion of the sample plate where the rubber blade contacted was taken as the ink removal rate, which was used as an evaluation value for cleaning performance. The removal rates for inks (I-1) to (I-3) for each ink set, calculated using the above method, are shown in Tables 1 to 4.

[0115] [Table 1]

[0116] [Table 2]

[0117] [Table 3]

[0118] [Table 4]

[0119] As shown in Tables 1 to 4, inks (I-1) and (I-2) contain a pigment and an aqueous medium. They are fast-drying pigment inks that exhibit a drying rate of 88% by mass or more when left at 40°C for 24 hours. The ink sets of Examples 1 to 11 each comprised ink (I-1) or (I-2) and one of cleaning solutions (C-1) to (C-9). Cleaning solutions (C-1) to (C-9) contain diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol such as glycerin or sorbitol. Therefore, cleaning solutions (C-1) to (C-9) all exhibited ink removal rates of 80% or more, allowing the dried thin film of fast-drying pigment ink that had adhered to the sample plate to be easily peeled off and removed.

[0120] On the other hand, the cleaning solution (c-1) of the ink sets of Comparative Examples 1, 2, and 13 does not contain a polyhydric alcohol having a valence of 3 or more. Therefore, while the cleaning solution (c-1) exhibited sufficient cleaning performance for ink (I-3) having a low drying rate of 70% by mass when left at 40°C for 24 hours as in Comparative Example 13, it did not exhibit sufficient cleaning performance for inks having a high drying rate such as inks (I-1) and (I-2), and the ink removal rate after cleaning was lower than in the Examples. Similarly, the cleaning solution (c-2) of the ink set of Comparative Example 3 did not contain a polyhydric alcohol having a valence of 3 or more, and therefore its cleaning performance was inferior to that of the cleaning solution used in the Examples.

[0121] The cleaning solutions (c-3) to (c-6) of Comparative Examples 4 to 7 do not contain diethylene glycol butyl methyl ether, and therefore do not have the cleaning performance to remove inks with high drying rates such as inks (I-1) and (I-2), and were unable to peel off and remove the dried thin film.

[0122] The cleaning solution (c-7) of Comparative Example 8 did not contain a trihydric or higher polyhydric alcohol, and diethylene glycol butyl methyl ether was mixed into water in an amount exceeding its solubility in water. Therefore, in Comparative Example 8, the cleaning solution (c-7) separated, and the cleaning performance could not be evaluated.

[0123] In the cleaning solutions (c-8) to (c-11) of Comparative Examples 9 to 12, a dihydric alcohol was used instead of a trihydric or higher polyhydric alcohol. As a result, in Comparative Examples 9 to 12, not only was no improvement in cleaning performance achieved compared to the cleaning solution (c-1) of Comparative Example 1, which did not contain a polyhydric alcohol, but the cleaning performance actually deteriorated.

[0124] The cleaning solution (c-12) in Comparative Examples 14 to 16 is a cleaning solution described in Patent Document 1, consisting of propylene glycol monopropyl ether, a nonionic surfactant, and water. Cleaning solution (c-12) does not contain diethylene glycol butyl methyl ether or a trivalent or higher polyhydric alcohol. For this reason, while cleaning solution (c-12) exhibited sufficient cleaning performance for ink (I-3), which had a low drying rate of 70% by mass when left at 40°C for 24 hours as in Comparative Example 16, it was unable to clean inks with high drying rates such as inks (I-1) and (I-2). [Industrial Applicability]

[0125] The ink set and image forming method of the present invention can be used to form an image on a recording medium. [Explanation of symbols]

[0126] 1: Inkjet recording device 2: Recording head 2a: First recording head 2b: Second recording head 2c: Third recording head 2d: 4th recording head 3: Head housing 4: Transport unit 5: Recording section 6: Cleaning section 6a: Cleaning liquid supply unit 6b: Wipe blade I: Ink C: Cleaning solution F1: Ink ejection surface F2: Cleaning liquid supply surface

Claims

1. An ink set comprising an inkjet ink and a cleaning liquid, The inkjet ink contains a pigment and an aqueous medium, the inkjet ink has a drying rate of 87% by mass or more and 93% by mass or less when left to stand at 40°C for 24 hours; The cleaning solution contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

2. The inkjet ink further contains binder resin particles, and The ink set according to claim 1 , wherein the content of volatile components in the inkjet ink is 85% by mass or more and 93% by mass or less.

3. 3. The ink set according to claim 1, wherein the polyhydric alcohol is glycerin or sorbitol.

4. 3. The ink set according to claim 1, wherein the content of diethylene glycol butyl methyl ether in the cleaning liquid is 1% by mass or more and 8% by mass or less.

5. the polyhydric alcohol is glycerin or sorbitol; the content ratio of the diethylene glycol butyl methyl ether and the content ratio of the glycerin in the cleaning solution satisfy formula (1), or The ink set according to claim 4, wherein the content ratio of the diethylene glycol butyl methyl ether and the content ratio of the sorbitol in the cleaning solution satisfy formula (2). −7×A+57≦B≦−7×A+60 (1) (In the formula (1), A represents the content of the diethylene glycol butyl methyl ether in the cleaning solution, and B represents the content of the glycerin in the cleaning solution.) −5×A+41≦C≦−5×A+45 (2) (In the formula (2), A represents the content of the diethylene glycol butyl methyl ether in the cleaning solution, and C represents the content of the sorbitol in the cleaning solution.)

6. Inkjet ink, A cleaning solution, a recording head; The recording head includes: a recording unit that ejects the inkjet ink onto an image forming area of ​​a recording medium; a cleaning unit that cleans the ink ejection surface of the recording unit with the cleaning liquid, the inkjet ink has a drying rate of 87% by mass or more and 93% by mass or less when left to stand at 40°C for 24 hours; The inkjet recording apparatus, wherein the cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

7. a discharge step of discharging inkjet ink from an ink discharge surface of a recording head onto a recording medium; a cleaning step of cleaning the ink ejection surface with a cleaning liquid, The inkjet ink contains a pigment and an aqueous medium, the inkjet ink has a drying rate of 87% by mass or more and 93% by mass or less when left to stand at 40°C for 24 hours; The image forming method, wherein the cleaning liquid contains diethylene glycol butyl methyl ether and a trihydric or higher polyhydric alcohol.

8. The washing step includes: a supplying step of supplying the cleaning liquid to the ink ejection surface; The image forming method according to claim 7 , further comprising a wiping step of wiping the ink ejection surface with a wiper blade.

Images