Inkjet recording ink and ink jet recording apparatus

Abstract

To provide inkjet recording ink having excellent ejection stability.SOLUTION: Inkjet recording ink contains pigment, binder resin particles and aqueous medium. The aqueous medium includes glycol ether, specific organic solvent and water. The specific organic solvent is a glycol compound having the number of carbon atoms of 3 or more and 6 or less. A content ratio of the specific organic solvent is 27.5 mass% or more and 35.5 mass% or less. Shear viscosity of the inkjet recording ink measured at the temperature 32°C and a shear rate 105s-1 is 5.5 mPa s or more and 7.0 mPa s or less. A drying rate of the inkjet recording ink is 20% or more and 40% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ink for ink-jet recording and an ink-jet recording apparatus. [Background technology]

[0002] Inkjet recording devices may be equipped with a circulating recording head as a recording head. Inkjet recording inks used in inkjet recording devices equipped with a circulating recording head are required to have excellent performance (ejection stability) that allows them to maintain ejection accuracy even during continuous printing. In response to such requirements, for example, it has been proposed to use high-viscosity inkjet recording inks in inkjet recording devices equipped with a circulating recording head (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-178246 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even the inkjet recording ink described in Patent Document 1 does not provide a fully satisfactory ejection stability.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink for ink-jet recording having excellent ejection stability, and an ink-jet recording apparatus using the ink for ink-jet recording. [Means for solving the problem]

[0006] The inkjet recording ink according to the present invention contains a pigment, binder resin particles, and an aqueous medium. The aqueous medium contains glycol ether, a specific organic solvent, and water. The specific organic solvent is a glycol compound having 3 to 6 carbon atoms. The content of the specific organic solvent is 27.5% by mass to 35.5% by mass. The inkjet recording ink according to the present invention is mixed at a temperature of 32° C. and a shear rate of 10 5 s -1 The shear viscosity of the inkjet recording ink measured by is 5.5 mPa·s or more and 7.0 mPa·s or less. The drying rate of the inkjet recording ink is 20% or more and 40% or less. The drying rate is determined by measuring the volume V of an ink droplet immediately after landing when 100 pL to 400 pL of the inkjet recording ink is discharged onto a measurement stage at a temperature of 25°C. 0 , and the volume V of the ink droplet 500 milliseconds after landing. 1 Based on this, it can be calculated using the following formula (1). Drying rate = 100 × (volume V 0 - volume V 1 ) / volume V 0 (1)

[0007] An inkjet recording apparatus according to the present invention includes an ink, and a circulation type recording head that ejects the ink. The ink is the ink for inkjet recording described above. Effect of the Invention

[0008] The ink for ink-jet recording according to the present invention has excellent ejection stability. The ink-jet recording apparatus according to the present invention has excellent ejection stability of the ink for ink-jet recording. [Brief description of the drawings]

[0009] [Figure 1] FIG. 11 is a diagram illustrating a main part of an example of an inkjet recording apparatus according to a second embodiment. [Diagram 2] 2 is a diagram showing members related to the circulation of ink in the inkjet recording apparatus of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described. In the following, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer (e.g., Malvern Instruments' Zetasizer Nano ZS), unless otherwise specified. The shear viscosity is a value measured using an image analysis viscometer (e.g., Formulaction's FLUIDICAM RHEO). The drying rate is a value measured by the method described in the Examples or a method based thereon. In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic".

[0011] <First embodiment: Inkjet recording apparatus> The first embodiment of the present invention relates to an ink for inkjet recording (hereinafter, may be referred to as ink). The ink of this embodiment contains a pigment, binder resin particles, and an aqueous medium. The aqueous medium contains glycol ether, a specific organic solvent, and water. The specific organic solvent is a glycol compound having 3 to 6 carbon atoms. The content of the specific organic solvent is 27.5% by mass to 35.5% by mass. The ink is then mixed at a temperature of 32° C. and a shear rate of 10 5 s -1 The shear viscosity of the ink of this embodiment measured by (hereinafter sometimes simply referred to as "shear viscosity") is 5.5 mPa s or more and 7.0 mPa s or less. The drying rate of the ink of this embodiment is 20% or more and 40% or less. The ink of this embodiment preferably further contains a pigment coating resin and a surfactant.

[0012] The drying rate is determined by measuring the volume V of the ink droplet immediately after landing when 100 pL to 400 pL of the ink of this embodiment is ejected onto the measurement stage at a temperature of 25° C. 0 , and the volume of the ink droplet 500 ms after landing V 1 Based on this, it can be calculated using the following formula (1). Drying rate = 100 × (volume V 0 - volume V 1 ) / volume V 0 (1)

[0013] The ink of the present embodiment has excellent ejection stability due to the above-mentioned configuration. The reason is presumed to be as follows. The ink of the present embodiment contains glycol ether and a certain amount of a specific organic solvent as an aqueous medium. With such a composition, the ink of the present embodiment has a shear viscosity of 5.5 mPa·s to 7.0 mPa·s and a dryness of 20% to 40%. Since the ink of the present embodiment has a moderately high viscosity (shear viscosity of 5.5 mPa·s or more), the ink droplets can be appropriately collected during ejection. In addition, since the ink of the present embodiment does not have an excessively high viscosity (shear viscosity of 7.0 mPa·s or less), the ink is appropriately supplied to the nozzles of the recording head of the inkjet recording device. As a result, the ink of the present embodiment has excellent basic ejection accuracy.

[0014] Here, with known inks, a low drying rate is preferable from the viewpoint of suppressing the occurrence of nozzle clogging in the recording head of an inkjet recording device. However, with known inks, when the drying rate is lowered, the shear viscosity tends to become excessively high. The ink of the present embodiment has an appropriately low drying rate (20% or more and 40% or less), so that it is possible to suppress the occurrence of nozzle clogging while suppressing the shear viscosity from becoming excessively high. As a result, the ink of the present embodiment has excellent ejection stability.

[0015] The application of the ink of the present embodiment is not particularly limited, but can be used, for example, for forming an image on a permeable recording medium or a non-permeable recording medium. The permeable recording medium has excellent permeability for the ink of the present embodiment. Examples of permeable recording media include printing paper and media made of fibers (e.g., fabric). Examples of printing paper include plain paper, copy paper, recycled paper, thin paper, thick paper, and glossy paper.

[0016] The ink of the present embodiment is less permeable to a non-permeable recording medium than to a permeable recording medium. In the non-permeable recording medium, the amount of absorption of the aqueous medium is, for example, 1.0 g / m2 or less. Examples of the non-permeable recording medium include a resin recording medium, a metal recording medium, and a glass recording medium. Examples of the resin recording medium include a resin sheet and a resin film. The resin contained in the resin recording medium is preferably a thermoplastic resin. Specific examples of the resin include polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate (PET). Examples of the resin recording medium include an OPP film. When an image is formed on a resin recording medium with the ink of the present embodiment, the surface (printing surface) of the recording medium may be subjected to a corona treatment.

[0017] The ink of this embodiment contains binder resin particles, and therefore can form an image with excellent abrasion resistance even on a non-permeable recording medium.

[0018] (drying rate) The ink drying rate of this embodiment is 20% or more and 40% or less, and preferably 25% or more and 35% or less. By setting the ink drying rate of this embodiment to 20% or more, it is possible to prevent the shear viscosity from becoming excessively high. By setting the ink drying rate of this embodiment to 40% or less, it is possible to prevent nozzle clogging.

[0019] (shear viscosity) The shear viscosity of the ink of this embodiment is from 5.5 mPa·s to 7.0 mPa·s, and preferably from 6.0 mPa·s to 6.5 mPa·s. By setting the shear viscosity of the ink of this embodiment to be from 5.5 mPa·s to 7.0 mPa·s, the ejection stability can be optimized.

[0020] (Pigments) In the ink of this embodiment, the pigment constitutes a pigment particle together with, for example, a pigment coating resin. The pigment particle is constituted, for example, by a core containing a pigment and a pigment coating resin coating the core. The pigment coating resin exists, for example, in a state of being dispersed in a solvent. From the viewpoint of optimizing the color density, hue, or stability of the ink of this embodiment, the volume median diameter of the pigment particles is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0021] 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).

[0022] In the ink of this embodiment, the pigment content is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.5% by mass or more and 4.5% by mass or less. By making the pigment content 0.5% by mass or more, the ink of this embodiment can form an image with a desired image density. In addition, by making the pigment content 10.0% by mass or less, the fluidity of the ink of this embodiment can be ensured.

[0023] (pigment coated resin) The pigment coating resin is a resin that is soluble in an aqueous medium. A part of the pigment coating resin is present, for example, on the surface of the pigment particle to optimize the dispersibility of the pigment particle. A part of the pigment coating resin is present, for example, in a dissolved state in the aqueous medium.

[0024] The pigment coating resin is preferably a styrene-(meth)acrylic resin. The styrene-(meth)acrylic resin has a repeating unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid alkyl ester and (meth)acrylic acid, and a styrene unit. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate.

[0025] In the ink of this embodiment, the content of the pigment coating resin is preferably 0.1% by mass to 4.0% by mass, and more preferably 0.4% by mass to 1.2% by mass. By setting the content of the pigment coating resin to 0.1% by mass to 4.0% by mass, the ejection stability of the ink of this embodiment can be further optimized.

[0026] In the ink of this embodiment, the content of the pigment coating resin relative to 100 parts by mass of the pigment is preferably from 10 to 60 parts by mass, and more preferably from 20 to 30 parts by mass. By setting the content of the pigment coating resin to be from 10 to 60 parts by mass, the ejection stability of the ink of this embodiment can be further optimized.

[0027] (Binder resin particles) The binder resin particles are present in a state of being dispersed in an aqueous medium. The binder resin particles contain a binder resin. Examples of the binder resin include urethane resin, (meth)acrylic resin, styrene-(meth)acrylic resin, (meth)acrylic-urethane resin, polyester resin, and modified polyolefin resin. The binder resin particles preferably contain a urethane resin as the binder resin. The content ratio of the binder resin in the binder resin particles is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

[0028] The urethane resin is, for example, a copolymer of a diol compound or a bisphenol compound with a polyisocyanate.

[0029] Volume median diameter of binder resin particles (D 50 ) is preferably 5 nm or more and 100 nm or less, and more preferably 20 nm or more and 65 nm or less.

[0030] The content of the binder resin particles in the ink of this embodiment is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 6.0% by mass or less. By making the content of the binder resin particles 1.0% by mass or more, the ink of this embodiment can optimize the scratch resistance of the formed image and the adhesion to the recording medium. By making the content of the binder resin particles 10.0% by mass or less, the ejection stability of the ink of this embodiment can be further optimized.

[0031] (Surfactant) The surfactant optimizes the compatibility and dispersion stability of each component contained in the ink of the present embodiment. The surfactant also optimizes the permeability (wettability) of the ink of the present embodiment to the recording medium. Examples of the surfactant include nonionic surfactants.

[0032] Examples of nonionic surfactants include acetylene glycol surfactants (surfactants containing an acetylene glycol compound), silicone surfactants (surfactants containing a silicone compound), and fluorine surfactants (surfactants containing a fluorine resin or a fluorine-containing compound). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. The ink of this embodiment preferably contains an acetylene glycol surfactant as a surfactant.

[0033] The content of the surfactant in the ink of this embodiment is preferably from 0.05% by mass to 2.0% by mass, and more preferably from 0.3% by mass to 0.7% by mass.

[0034] (aqueous medium) The aqueous medium contains glycol ether, a specific organic solvent, and water. The aqueous medium may function as a solvent or as a dispersion medium. In the aqueous medium, the total content of glycol ether, specific organic solvent, and water is preferably 90% by mass or more, more preferably 100% by mass.

[0035] In the ink of this embodiment, the content of the aqueous medium is preferably from 80.0% by mass to 97.0% by mass, and more preferably from 90.0% by mass to 96.0% by mass.

[0036] (water) In the ink of this embodiment, the water content is preferably from 30.0% to 70.0% by mass, more preferably from 42.0% to 50.0% by mass, and even more preferably from 45.0% to 48.0% by mass.

[0037] (Glycol Ether) Examples of glycol ethers 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, propylene glycol monomethyl ether and dipropylene glycol monomethyl ether. As the glycol ether, triethylene glycol monobutyl ether or dipropylene glycol monomethyl ether is preferred.

[0038] In the ink of this embodiment, the content of glycol ether is preferably 10.0% by mass or more and 20.0% by mass or less, and more preferably 14.0% by mass or more and 16.0% by mass or less. As the content of glycol ether increases, the shear viscosity of the ink of this embodiment tends to increase and the drying rate tends to decrease. By setting the content of glycol ether to 10.0% by mass or more and 20.0% by mass or less, it becomes easier to adjust the shear viscosity and drying rate of the ink of this embodiment to the above-mentioned ranges.

[0039] (Specific organic solvent) The specific organic solvent is a glycol compound having 3 to 6 carbon atoms. Examples of the specific organic solvent include 1,2-propanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, dipropylene glycol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. The specific organic solvent is preferably 1,2-propanediol or 1,3-propanediol.

[0040] In the ink of this embodiment, the content of the specific organic solvent is 27.5% by mass or more and 35.5% by mass or less, and preferably 29.0% by mass or more and 33.0% by mass or less. As the content of the specific organic solvent increases, the shear viscosity of the ink of this embodiment tends to increase and the drying rate tends to decrease. By setting the content of the specific organic solvent to 27.5% by mass or more and 35.5% by mass or less, it becomes easier to adjust the shear viscosity and drying rate of the ink of this embodiment to the above-mentioned ranges.

[0041] The aqueous medium may further contain a water-soluble organic solvent other than glycol ether and the specific organic solvent (hereinafter, may be referred to as other water-soluble organic solvent). Examples of other water-soluble organic solvents include glycol compounds having 2 or less carbon atoms, glycol compounds having 7 or more carbon atoms, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

[0042] (Other ingredients) The ink of this embodiment may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0043] (Ink manufacturing method) The ink of this embodiment can be produced, for example, by uniformly mixing a pigment dispersion containing a pigment, a resin emulsion containing binder resin particles, an aqueous medium, and other components (e.g., surfactants) that are blended as necessary, using a stirrer. In producing the ink of this embodiment, 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).

[0044] (Preferred composition) The ink of this embodiment preferably has any one of compositions (i-1) to (i-8) shown in Table 1. In Table 1, the numerical ranges indicate the content ratio of each component. For example, "2.5-3.5" in the pigment column for composition (i-1) indicates that the pigment content is 2.5% by mass or more and 3.5% by mass or less. The abbreviations used in Table 1 are as follows: wt%: mass% TEGMBE: Triethylene glycol monobutyl ether DPGMME: Dipropylene glycol monomethyl ether 1,2-PD: 1,2-propanediol 1,3-PD: 1,3-propanediol

[0045] [Table 1]

[0046] <Second embodiment: Inkjet recording apparatus> A second embodiment of the present invention relates to an inkjet recording apparatus. The inkjet recording apparatus of this embodiment includes an ink and a circulation type recording head that ejects the ink. The ink is the ink of the first embodiment. Since the inkjet recording apparatus of this embodiment includes the ink of the first embodiment, the inkjet recording apparatus has excellent ejection stability of the ink.

[0047] The inkjet recording apparatus of this embodiment may be provided with only one type of ink, or may be provided with multiple types of ink (for example, four types of ink: yellow ink, cyan ink, magenta ink, and black ink). When the inkjet recording apparatus of this embodiment is provided with multiple types of ink, it is sufficient that at least one of the inks is the ink of the first embodiment, but it is preferable that all of the inks are the inks of the first embodiment.

[0048] The configuration of the inkjet recording apparatus of this embodiment will be described in detail below with reference to the drawings. Note that the drawings are mainly and diagrammatically illustrated with respect to each component for ease of understanding, and the size, number, etc. of each component illustrated may differ from the actual size for the convenience of drawing.

[0049] FIG. 1 is a diagram showing a main part of an inkjet recording device 100, which is an example of an inkjet recording device of the present embodiment. As shown in FIG. 1, the inkjet recording device 100 mainly includes a conveying section 1 and four recording heads 11 (circulating recording heads) which are circulating line-type recording heads. The inkjet recording device 100 further includes a paper feed tray 2, a paper feed roller 3, a paper feed driven roller 4, a conveying belt 5, a belt driving roller 6, a belt driven roller 7, a discharge roller 8, a discharge driven roller 9, and a paper discharge tray 10. The conveying belt 5, the belt driving roller 6, and the belt driven roller 7 constitute a part of the conveying section 1. A paper feed tray 2 is provided at the left end of the inkjet recording device 100 in the figure. The paper feed tray 2 stores a recording medium M (for example, a recording sheet or a printing paper). A paper feed roller 3 and a paper feed driven roller 4 are provided at one end of the paper feed tray 2. The paper feed roller 3 takes out the stored recording media M one by one starting from the uppermost recording medium M, and conveys and feeds them onto the conveyor belt 5. The paper feed driven roller 4 is pressed against the paper feed roller 3 and is rotated by the paper feed roller 3.

[0050] A conveyor belt 5 is rotatably disposed downstream in the paper conveying direction of the paper feed roller 3 and the paper feed driven roller 4 (on the right side in FIG. 1). The conveyor belt 5 is stretched across a belt drive roller 6 and a belt driven roller 7. The belt drive roller 6 is disposed downstream in the paper conveying direction. The belt drive roller 6 drives the conveyor belt 5. The belt driven roller 7 is disposed upstream in the paper conveying direction. The belt driven roller 7 rotates following the belt drive roller 6 via the conveyor belt 5. As the belt drive roller 6 is driven to rotate clockwise, the recording medium M is conveyed in the conveying direction X indicated by the arrow.

[0051] Further, a discharge roller 8 and a discharge driven roller 9 are provided downstream in the conveying direction of the conveyor belt 5. The discharge roller 8 is driven in a clockwise direction in the figure, and discharges the recording medium M on which an image has been formed to the outside of the device housing. The discharge driven roller 9 is pressed against an upper portion of the discharge roller 8 and rotates in response. A paper discharge tray 10 is provided downstream of the discharge roller 8 and the discharge driven roller 9. The recording medium M discharged to the outside of the device housing is stacked on the paper discharge tray 10.

[0052] The four recording heads 11 include a first recording head 11C, a second recording head 11M, a third recording head 11Y, and a fourth recording head 11K. The first recording head 11C, the second recording head 11M, the third recording head 11Y, and the fourth recording head 11K are arranged above the conveyor belt 5 in this order from the upstream side to the downstream side in the conveying direction X of the recording medium M at approximately equal intervals. Each of the four recording heads 11 is supported at a height such that the distance from the upper surface of the conveyor belt 5 is a predetermined length. Each of the four recording heads 11 records an image on the recording medium M conveyed on the conveyor belt 5. Each of the four recording heads 11 is supplied with ink (first ink, second ink, third ink, and fourth ink) of four different colors (cyan, magenta, yellow, and black). Each of the four recording heads 11 performs inkjet ejection onto the recording medium M in a predetermined order. As a result, a color image is formed on the recording medium M. The four recording heads 11 are driven, for example, by a piezoelectric method.

[0053] Next, the inkjet recording apparatus 100 will be further described with reference to Fig. 2. Fig. 2 is a diagram showing members related to the circulation of ink in the inkjet recording apparatus 100.

[0054] As shown in FIG. 2, the inkjet recording device 100 includes a recording head 11 (more specifically, any one of the first recording head 11C, the second recording head 11M, the third recording head 11Y, and the fourth recording head 11K in FIG. 1), supply tubular members 13a to 13c, an ink supply unit 15, a damper member 16, and a control unit 101. The ink supply unit 15 supplies ink to the damper member 16. The damper member 16 supplies ink to the recording head 11 via the supply tubular members 13a to 13c. The control unit 101 controls the ink supply unit 15. The control unit 101 also controls the recording head 11.

[0055] Although omitted for illustrative purposes, the inkjet recording device 100 corresponds to the four recording heads 11 (the first recording head 11C, the second recording head 11M, the third recording head 11Y, and the fourth recording head 11K in FIG. 1) and is provided with a total of four sets of supply tubular members 13a-13c, ink supply units 15, and damper members 16.

[0056] The ink supply unit 15 includes an ink tank 151, a pump 152 for a sub tank, a sub tank 153 (ink storage section), a diaphragm pump 154 ​​(supply pump), a first pipe 161, a second pipe 162, a third pipe 163, a circulation pipe 164, a first valve 162a, a second valve 163a, a third valve 164a, a circulation pump 164b, a relief valve 170, and a relief pipe 171.

[0057] The ink tank 151 contains the ink I. The ink tank 151 is connected to the sub tank 153 via a first pipe 161. The first pipe 161 distributes the ink I from the ink tank 151 to the sub tank 153. The sub tank 153 stores the ink I supplied from the ink tank 151.

[0058] The sub-tank pump 152 is disposed in the first pipe 161. The sub-tank pump 152 supplies the ink I stored in the ink tank 151 to the sub-tank 153 in accordance with an instruction from the control unit 101, for example, when the liquid level of the ink I in the sub-tank 153 falls below a predetermined value.

[0059] In the inkjet recording apparatus 100, the ink I is supplied from the subtank 153 to the recording head 11 via the damper member 16. The recording head 11 then ejects at least a portion of the ink I supplied from the damper member 16 onto the recording medium M, and discharges the remainder of the ink I (ink that was not ejected) to the ink supply unit 15. Specifically, the ink I discharged from the recording head 11 is returned to the subtank 153. That is, the ink circulates mainly between the subtank 153, the damper member 16, and the recording head 11.

[0060] The sub tank 153 is connected to the diaphragm pump 154 ​​via a second pipe 162. The second pipe 162 distributes the ink I from the sub tank 153 to the diaphragm pump 154. The diaphragm pump 154 ​​is connected to the damper member 16 via a third pipe 163. The third pipe 163 distributes the ink I from the diaphragm pump 154 ​​to the damper member 16.

[0061] The diaphragm pump 154 ​​sucks the ink I stored in the sub tank 153 through the second pipe 162. The diaphragm pump 154 ​​discharges the ink I sucked from the sub tank 153 to the third pipe 163. Specifically, the diaphragm pump 154 ​​has a cylinder and a piston. The cylinder stores the ink I sucked from the sub tank 153. The cylinder is, for example, cylindrical. An inlet and an outlet are formed at the bottom of the cylinder. The inlet is connected to the second pipe 162. The outlet is connected to the third pipe 163.

[0062] The piston is inserted into the cylinder. The piston moves in a direction away from the bottom of the cylinder according to a command from the control unit 101. The piston also moves in a direction toward the bottom of the cylinder according to a command from the control unit 101.

[0063] When the piston moves in a direction away from the bottom of the cylinder, the ink I is sucked into the cylinder. Specifically, the ink I flows out from the subtank 153 to the second pipe 162, and the ink I flows into the cylinder via the second pipe 162.

[0064] When the piston moves in a direction approaching the bottom of the cylinder, the ink I flows out of the cylinder into the third pipe 163 , and the ink I is supplied to the damper member 16 via the third pipe 163 .

[0065] The first valve 162a is disposed in the second pipe 162. The second valve 163a is disposed in the third pipe 163. The first valve 162a and the second valve 163a open and close according to instructions from the control unit 101. Specifically, while the piston moves in a direction away from the bottom of the cylinder, the first valve 162a is in an open state and the second valve 163a is in a closed state. While the piston moves in a direction toward the bottom of the cylinder, the first valve 162a is in a closed state and the second valve 163a is in an open state.

[0066] The damper member 16 supplies the ink I to the recording head 11 via the supply tubular members 13a to 13c. The damper member 16 has a function of mitigating pressure changes in the ink I supplied to the recording head 11. The damper member 16 has at least an ink passing portion through which the ink I passes. The damper member 16 may further have an ink storage chamber that temporarily stores the ink I. In the damper member 16, for example, a part of the member that constitutes the ink passing portion and the ink storage chamber is an elastic member (for example, a resin film). Thereby, when the pressure of the ink I inside (the ink passing portion or the ink storage chamber) of the damper member 16 increases or decreases, the elastic member deforms, and the damper member 16 can mitigate the pressure change of the ink I. As a result, the pressure change of the ink I supplied to the recording head 11 is mitigated.

[0067] The circulation pipe 164 connects the recording head 11 and the subtank 153. The third valve 164a is disposed in the circulation pipe 164. The third valve 164a opens and closes according to instructions from the control unit 101. For example, the control unit 101 opens the third valve 164a when the inkjet recording apparatus 100 is forming an image, and closes the third valve 164a when the inkjet recording apparatus 100 is not forming an image. The third valve 164a is, for example, a backflow prevention valve for preventing the ink I from flowing backward when the inkjet recording apparatus 100 is not forming an image.

[0068] The circulation pump 164b is disposed in the circulation pipe 164. The circulation pump 164b, for example, pumps the ink I inside the circulation pipe 164 to the sub-tank 153. This makes the pressure inside the circulation pipe 164 lower than the pressure inside the recording head 11. As a result, the ink I is discharged from the recording head 11 to the sub-tank 153 via the circulation pipe 164.

[0069] The control unit 101 includes a storage device 102 and a processing device 103. The storage device 102 stores data and programs. The storage device 102 includes semiconductor memories such as a random access memory (RAM) and a read only memory (ROM). The storage device 102 may further include a storage device such as a hard disk drive (HDD). The processing device 103 includes a processor such as a central processing unit (CPU) or a micro processing unit (MPU). The processing device 103 controls the operation of each part of the inkjet recording apparatus 100 based on the programs stored in the storage device 102.

[0070] The relief valve 170 is disposed in the third pipe 163. The relief pipe 171 communicates the second pipe 162 and the third pipe 163 via the relief valve 170. The relief valve 170 and the relief pipe 171 constitute a relief mechanism. That is, the ink supply unit 15 has a relief mechanism. The relief valve 170 is, for example, an independent member that is not controlled by the control unit 101. The relief valve 170 is normally kept in a closed state by, for example, the force of a spring, and opens when the pressure of the ink I in the third pipe 163 becomes equal to or higher than a predetermined value. Thereby, when the pressure of the ink I in the third pipe 163 becomes equal to or higher than the predetermined value, the relief mechanism discharges the ink I in the third pipe 163 to the second pipe 162 via the relief pipe 171. As a result, the relief mechanism adjusts the pressure of the ink I in the third pipe 163 (i.e., the pressure of the ink I supplied to the damper member 16) so as not to become equal to or higher than a predetermined value.

[0071] The pressure of the ink I circulating between the subtank 153 and the recording head 11 varies depending on the type of image formed by the inkjet recording device 100. Specifically, when the inkjet recording device 100 forms an image with a high image density, the recording head 11 consumes a large amount of ink I. This, for example, causes the pressure of the circulating ink I to decrease. On the other hand, when the inkjet recording device 100 forms an image with a low image density, the recording head 11 does not consume much ink I. This also causes the pressure of the circulating ink I to increase. The pressure change of the circulating ink I is mitigated to some extent by adjusting the operating speed of the piston of the diaphragm pump 154, but this is not sufficient. In a known inkjet recording device, a sudden increase or decrease in the ink pressure (especially a sudden increase in the ink pressure) can cause the ink to aggregate. In response to this, the inkjet recording device 100 is provided with a relief mechanism and a damper member 16, thereby making it possible to suppress a sudden increase or decrease in the pressure of the ink I. As a result, the inkjet recording apparatus 100 can effectively suppress the occurrence of ink aggregation.

[0072] The circulation flow rate of the recording head 11 (circulation type recording head) is preferably 40 mL / min to 70 mL / min, more preferably 45 mL / min to 55 mL / min. By setting the circulation flow rate of the recording head 11 to 40 mL / min or more, the ink near the nozzles can be prevented from drying out and causing nozzle clogging. By setting the circulation flow rate of the recording head 11 to 70 mL / min or less, the ink ejection accuracy can be optimized.

[0073] Although an example of the inkjet recording apparatus of this embodiment has been described above, the inkjet recording apparatus of this embodiment is not limited to the one shown in FIGS.

[0074] 1 and 2, an inkjet recording apparatus 100 having four recording heads 11 corresponding to four colors of ink has been described as an example. However, the number of recording heads provided in the inkjet recording apparatus of this embodiment is not particularly limited, and can be, for example, 1 to 10, and preferably 3 to 5. In addition, the inkjet recording apparatus 100 ejects four colors of ink, cyan, magenta, yellow, and black, in that order, but the type, combination, and ejection order of the inks in the inkjet recording apparatus of this embodiment are not limited to this.

[0075] Furthermore, in the inkjet recording apparatus of the present embodiment, only the ink and the circulation type recording head are required. Furthermore, the inkjet recording apparatus of the present embodiment may be a multifunction machine further having the functions of a scanner, a copier, a printer, or a facsimile. EXAMPLES

[0076] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0077] (Volume Median Diameter Measurement) In the examples, the volume median diameter of the resin particles was measured using a dynamic light scattering particle size distribution measuring device ("Zetasizer (registered trademark) Nano ZS" manufactured by Malvern Instruments).

[0078] (Shear Viscosity Measurement) The shear viscosity of the ink was measured at a temperature of 32°C using an image analysis viscometer ("FLUIDICAM RHEO" manufactured by Formulaction) under the following measurement conditions. A glass chip for viscosity measurement (gap: 50 μm) was used as the chip. Five points were plotted. In the measurement, the shear rate was automatically changed and the shear rate was set to 100,000 s -1 Measurement started at a shear rate of 10,000 s -1 The other conditions were as follows.

[0079] (Other conditions) Microchip: "Viscosity measurement glass chip" manufactured by Formulaction Standard solution: Formulaction "5cP water-based viscosity standard solution"

[0080] (Measurement of drying rate) In measuring the drying rate of the ink, first, an inkjet type ink landing observation device (Microjet Corporation's "DropMeasure (registered trademark)-100") was filled with the ink to be measured. One ink droplet to be measured was ejected from a head (piezo type) equipped on the above-mentioned observation device, and landed on the measurement stage. At this time, the volume of the ejected droplet was 100 pL to 400 pL (approximately 250 pL), and the ejection speed was 6 m / sec to 8 m / sec (approximately 7 m / sec). Next, the change over time in the volume of the ink droplet that landed on the stage was observed with a high-speed camera (Photoron Corporation's "FASTCAM (registered trademark) SA-X2"). As a result, the volume V of the ink droplet immediately after landing was measured. 0 and the volume of the ink droplet 500 milliseconds after it hits the surface, V 1 Next, the drying rate of the ink to be measured was calculated based on formula (1). Drying rate = 100 × (volume V 0 - volume V 1 ) / volume V 0 (1)

[0081] The drying rate was measured multiple times for each measurement object, and even if the volume of the ejected droplets varied, the drying rate was the same as long as it was within the range of 100 pL to 400 pL. Similarly, the drying rate was measured multiple times for each measurement object, and even if the ejection speed varied, the drying rate was the same as long as it was within the range of 6 m / sec to 8 m / sec.

[0082] [Preparation of pigment dispersion] A pigment dispersion containing a cyan pigment (C), a pigment dispersion containing a yellow pigment (Y), a pigment dispersion containing a magenta pigment (M) and a pigment dispersion containing a black pigment (K) were prepared by the following method.

[0083] (Pigment dispersion (C)) 15 parts by mass of a cyan pigment ("HELIOGEN (registered trademark) BLUE D 7088" manufactured by BASF, CI Pigment Blue 15:3), 10 parts by mass of a pigment-coated resin-containing dispersion ("DISPERBYK (registered trademark) 190" manufactured by BYK-Chemie, non-volatile content: 40%, active ingredient: acrylic resin), and 75 parts by mass of water were mixed and pre-dispersed using a disper to obtain a mixed liquid.

[0084] Next, the mixture was dispersed using a 0.6 L bead mill (Dyno Mill, manufactured by Willy & Bachofen) filled with 1800 g of zirconia beads with a diameter of 0.1 mm as a dispersion medium, to obtain pigment dispersion (C) (pigment concentration: 15 mass %, pigment coating resin concentration: 4 mass %).

[0085] (Pigment Dispersion (Y), Pigment Dispersion (M) and Pigment Dispersion (B)) Pigment dispersion (Y), pigment dispersion (M) and pigment dispersion (B) were prepared in the same manner as in the preparation of pigment dispersion (C), except that the following yellow pigment, magenta pigment and black pigment were used instead of the cyan pigment. Yellow pigment: Sanyo Pigment Co., Ltd.'s "FAST YELLOW 7413", CI Pigment Yellow 74 Magenta pigment: "Red No. 63" manufactured by Dainichiseika Color & Chemicals Co., Ltd. Black pigment: Orion Engineered Carbon's "Printex® 85", carbon black

[0086] [Urethane emulsion] As the urethane emulsion containing urethane resin particles, "Superflex (registered trademark) 870" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (non-volatile content: 30 mass %, volume median diameter of urethane resin particles: 0.03 μm) was used.

[0087] <Ink Preparation> Inks (C1) to (C13), (B1), (Y1) and (M1) were prepared by the following method.

[0088] Ink (C1) Ion-exchanged water, 20.0 parts by mass of pigment dispersion (C) (black pigment: 3.0 parts by mass, pigment coating resin: 0.8 parts by mass), 15.0 parts by mass of triethylene glycol monobutyl ether, 27.0 parts by mass of 1,2-propanediol, 13.3 parts by mass of urethane emulsion (Dai-ichi Kogyo Seiyaku Co., Ltd.'s "Superflex (registered trademark) 870") (urethane resin particles: 4.0 parts by mass), and 0.5 parts by mass of surfactant (Nissin Chemical Co., Ltd.'s "Surfynol (registered trademark) 440", an ethylene oxide adduct of acetylene glycol) were placed in a beaker. The amount of ion-exchanged water added was an amount (24.2 parts by mass) such that the total amount of the mixture in the beaker was 100.0 parts by mass. The contents of the beaker were mixed at a rotation speed of 400 rpm using a stirrer (Shinto Scientific Co., Ltd.'s "Three-One Motor BL-600"). A mixed liquid was obtained. The mixture was filtered using a filter (pore size: 5 μm) to remove foreign matter and coarse particles contained in the mixture, thus obtaining ink (C1).

[0089] [Inks (C2) to (C13), (B1), (Y1) and (M1)] Inks (C2) to (C13), (B1), (Y1) and (M1) were prepared in the same manner as for the preparation of ink (I-1), except that the type and amount of each component was changed as shown in Tables 2 to 3. As shown in Tables 2 to 3, inks (C1) to (C13), (B1), (Y1) and (M1) were the inks of Examples 1 to 11 and Comparative Examples 1 to 5.

[0090] The abbreviations used in Tables 2 and 3 and Table 4 described later are as follows. wt%: mass% TEGMBE: Triethylene glycol monobutyl ether DPGMME: Dipropylene glycol monomethyl ether 1,2-PD: 1,2-propanediol 1,3-PD: 1,3-propanediol Example 1 to Example 11: Example 1 to Example 11 Ratio 1 to Ratio 5: Comparative Example 1 to Comparative Example 5

[0091] [Table 2]

[0092] [Table 3]

[0093] <Evaluation> The ink ejection stability was evaluated by the following method for the inks of Examples 1 to 11 and Comparative Examples 1 to 5. The evaluation results are shown in Table 4. The evaluation was performed at a temperature of 25° C. and a humidity of 60% RH, unless otherwise specified.

[0094] An evaluation machine (a test machine manufactured by Kyocera Document Solutions Inc.) including at least a circulation type recording head and an ink circulation pump ("Circulation Pump CIMS" manufactured by Megnajet) was prepared. The ink circulation pump corresponds to the ink supply unit of the second embodiment, and was set to supply the ink to be evaluated to the circulation type recording head. The circulation type recording head was set to eject at least a part of the ink supplied from the ink circulation pump onto a recording medium as necessary, and to return the remaining part of the ink supplied to the ink circulation pump. Note that the circulation type recording head was set to return the entire amount of the ink supplied from the ink circulation pump to the ink circulation pump in a state where it is not necessary to eject ink (a state where image formation is not being performed). The circulation flow rate of the circulation pump was set as shown in Table 4 below.

[0095] As a recording medium, A4-sized matte paper for inkjet printing ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used.

[0096] Using the evaluation machine, a 150 mm x 200 mm solid image was continuously printed on 5,000 sheets of recording medium. Next, the ink to be evaluated was purged from the circulating recording head of the evaluation machine. Next, the ink ejection surface of the circulating recording head of the evaluation machine was wiped to clean the circulating recording head. Next, using the evaluation machine, a stripe image formed of multiple parallel thin lines was formed on the recording medium. In forming the stripe image, the line width of the thin lines was set to 1 pixel, and the interval (line pitch) between adjacent thin lines was set to 3 pixels.

[0097] Next, the stripe image formed on the recording medium was read under a microscope. In detail, the interval A between a specific thin line a and a thin line b located 16 pixels away from the thin line a was measured at 204 points. Note that there were three other thin lines between the thin lines a and b. The variation (3σ [unit: μm]) of the measured interval A was calculated using image processing software (manufactured by Kyocera Document Solutions Inc.). The calculated variation (3σ) of the interval A was used as the evaluation value of the ejection stability. The ejection stability was judged according to the following criteria.

[0098] (Standard for discharge stability) A (good): 3σ is less than 20. B (bad): 3σ is 20 or more. C (particularly poor): Nozzles are clogged and ink is not ejected from some nozzles, making it impossible to analyze 3σ.

[0099] [Table 4]

[0100] As shown in Tables 2 to 4, the inks (C2) to (C4), (B1), (Y1), (M1), (C6) to (C8), and (C10) to (C11) of Examples 1 to 9 contained a pigment, binder resin particles, and an aqueous medium. The aqueous medium contained glycol ether, a specific organic solvent, and water. The content of the specific organic solvent was 27.5% by mass or more and 35.5% by mass or less. The shear viscosity of each ink of the Examples was 5.5 mPa s or more and 7.0 mPa s or less. The drying rate of each ink of the Examples was 20% or more and 40% or less. Each ink of the Examples had excellent ejection stability.

[0101] On the other hand, the ink (C1) of Comparative Example 1 and the ink (C9) of Comparative Example 3 had an insufficient content of the specific organic solvent. As a result, the shear viscosity of the ink (C1) and the ink (C9) were excessively low and the drying rate was excessively high. As a result, the ejection stability of the ink (C1) and the ink (C9) was poor.

[0102] The ink (C5) of Comparative Example 2 and the ink (C12) of Comparative Example 4 contained an excessive amount of the specific organic solvent. As a result, the shear viscosity of the ink (C5) and the ink (C12) were excessively high and the drying rate was excessively low. As a result, the ejection stability of the ink (C5) and the ink (C12) was poor.

[0103] The ink (C13) of Comparative Example 5 did not contain glycol ether. As a result, the shear viscosity of the ink (C13) was too low and the drying rate was too high. As a result, the ejection stability of the ink (C13) was poor. [Industrial Applicability]

[0104] The ink and inkjet recording apparatus according to this embodiment can be used to form an image.

Claims

1. An inkjet recording ink containing a pigment, binder resin particles, and an aqueous medium, The aqueous medium contains a glycol ether, a specific organic solvent, and water, the specific organic solvent is a glycol compound having 3 to 6 carbon atoms, The content of the specific organic solvent is 27.5% by mass or more and 35.5% by mass or less, Temperature 32°C and shear rate 10 5 s -1 the shear viscosity of the ink for ink-jet recording measured by is 5.5 mPa·s or more and 7.0 mPa·s or less, The drying rate of the ink for ink-jet recording is 20% or more and 40% or less, The drying rate is determined by measuring the volume V of an ink droplet immediately after landing when 100 pL to 400 pL of the ink for ink jet recording is discharged onto a measurement stage at a temperature of 25° C. 0 , and the volume V of the ink droplet 500 milliseconds after landing. 1 The ink for ink-jet recording is determined by the following formula (1) based on the above. Drying rate = 100 x (volume V 0 - Volume V 1 ) / volume V 0 ...(1)

2. 2. The inkjet recording ink according to claim 1, wherein the specific organic solvent contains at least one of 1,2-propanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, dipropylene glycol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol.

3. 3. The ink for ink-jet recording according to claim 2, wherein the specific organic solvent includes at least one of 1,2-propanediol and 1,3-propanediol.

4. The inkjet recording ink according to claim 1 or 2, wherein the glycol ether comprises at least one of triethylene glycol monobutyl ether and dipropylene glycol monomethyl ether.

5. The inkjet recording ink according to claim 1 , wherein the binder resin particles contain a urethane resin.

6. The inkjet recording ink according to claim 1 or 2, wherein a content of the glycol ether is from 10.0% by mass to 20.0% by mass.

7. The inkjet recording ink according to claim 1 or 2, wherein a content of the binder resin particles is from 2.0% by mass to 6.0% by mass.

8. The ink for ink-jet recording according to claim 1 or 2, wherein the content of the water is from 42.0% by mass to 50.0% by mass.

9. Ink and a circulation type recording head that ejects the ink, The inkjet recording apparatus according to claim 1 , wherein the ink is the inkjet recording ink according to claim 1 .

10. 10. The inkjet recording apparatus according to claim 9, wherein the circulation type recording head has a circulation flow rate of 40 mL / min or more and 70 mL / min or less.

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