Ink for ink jet recording and ink jet recording apparatus

Abstract

The invention provides an ink for ink jet recording and an ink jet recording apparatus. The ink for inkjet recording includes a pigment, binder resin particles, and an aqueous medium. The aqueous medium includes a glycol ether, a specific organic solvent, and water. The specific organic solvent is a diol compound having 3-6 carbon atoms (inclusive). The content ratio of the specific organic solvent is from 27.5% by mass to 35.5% by mass (inclusive). The shear viscosity of the ink jet recording ink measured at a temperature of 32 DEG C and a shear rate of 105 s <-1 > is 5.5 mPa * s to 7.0 mPa * s (inclusive). The drying rate of the ink for inkjet recording is from 20% to 40% (inclusive).

Description

Technical Field

[0001] The present invention relates to an ink for inkjet recording and an inkjet recording device. Background Art

[0002] Inkjet recording devices sometimes have a circulating type recording head as a recording head. The inkjet recording ink used in the inkjet recording device having the circulating type recording head is required to have excellent performance (jetting stability) of maintaining jetting accuracy even during continuous printing. In response to this requirement, for example, it has been proposed to use a high-viscosity inkjet recording ink in the inkjet recording device having the circulating type recording head (Japanese Patent Laid-Open No. 2005-178246). Summary of the invention

[0003] However, even the ink for inkjet recording described in Japanese Patent Laid-Open No. 2005-178246 cannot fully satisfy ejection stability.

[0004] In view of the above problems, an object of the present invention is to provide an inkjet recording ink having excellent ejection stability, and an inkjet recording apparatus using the inkjet recording ink.

[0005] The ink for inkjet recording of the present invention comprises a pigment, a binder resin particle and an aqueous medium, wherein the aqueous medium comprises a glycol ether, a specific organic solvent and water, wherein the specific organic solvent is a glycol compound having 3 to 6 carbon atoms, wherein the content ratio of the specific organic solvent is 27.5 mass % to 35.5 mass %, and the ink is heated to 32° C. and the shear rate is 10 5 s -1 The measured shear viscosity of the inkjet recording ink is not less than 5.5 mPa·s and not more than 7.0 mPa·s, and the drying rate of the inkjet recording ink is not less than 20% and not more than 40%. The drying rate is calculated by the following formula (1) based on the volume V0 of the ink droplet just after contact and the volume V1 of the ink droplet 500 milliseconds after contact when an ink droplet of not less than 100 pL and not more than 400 pL of the inkjet recording ink is ejected onto a measuring table at a temperature of 25°C.

[0006] Drying rate = 100 × (volume V0 - volume V1) / volume V0 ... (1).

[0007] The inkjet recording device of the present invention comprises: ink; and a circulation type recording head for ejecting the ink, wherein the ink is the ink for inkjet recording described above.

[0008] The ink for inkjet recording of the present invention is excellent in ejection stability. The ink for inkjet recording of the inkjet recording apparatus of the present invention is excellent in ejection stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram showing a main part of an example of an inkjet recording apparatus according to a second embodiment.

[0010] Figure 2 is shown with Figure 1 A diagram of components related to ink circulation of an inkjet recording apparatus. DETAILED DESCRIPTION

[0011] Hereinafter, the embodiments of the present invention will be described. 50 ) is a value measured using a dynamic light scattering particle size distribution measuring device (e.g., "Zeta Sizernano ZS" manufactured by Malvern). Shear viscosity is a value measured using an image analysis viscometer (e.g., "FLUIDI CAM RHEO" manufactured by Formula). Drying rate is a value measured using the method described in the Examples or a method based thereon. In this specification, acryl and methacryl are sometimes collectively referred to as "(meth)acryl".

[0012] <First Embodiment: Inkjet Recording Device>

[0013] The first embodiment of the present invention relates to an ink for inkjet recording (hereinafter, sometimes referred to as ink). The ink of this embodiment contains a pigment, a binder resin particle 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 a carbon number of 3 or more and 6 or less. The content ratio of the specific organic solvent is 27.5 mass % or more and 35.5 mass % or less. 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 at 50°C (hereinafter, sometimes 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.

[0014] The drying rate is calculated by the following formula (1) based on the volume V0 of the ink droplet just after contact and the volume V1 of the ink droplet 500 milliseconds after contact when an ink droplet of 100 pL or more and 400 pL or less of the ink of this embodiment is ejected onto a measuring table at a temperature of 25°C.

[0015] Drying rate = 100 × (volume V0 - volume V1) / volume V0 ... (1)

[0016] Since the ink of the present embodiment has the above-mentioned structure, it has excellent jetting stability. The reason is presumed to be as follows. The ink of the present embodiment contains glycol ether and a certain amount of specific organic solvent as an aqueous medium. Due to such components, the ink of the present embodiment has a shear viscosity of 5.5 mPa·s or more and 7.0 mPa·s or less, and a dryness of 20% or more and 40% or less. Since the viscosity of the ink of the present embodiment is moderately high (shear viscosity is 5.5 mPa·s or more), the ink droplets can be moderately concentrated when ejected. In addition, since the viscosity of the ink of the present embodiment is not too high (shear viscosity is 7.0 mPa·s or less), it can be properly supplied to the nozzle of the recording head of the inkjet recording device. As a result, the basic jetting accuracy of the ink of the present embodiment is excellent.

[0017] Here, in the known ink, from the viewpoint of suppressing the clogging of the nozzle of the recording head of the inkjet recording device, it is preferred that the drying rate is low. However, in the known ink, if the drying rate is reduced, there is a tendency that the shear viscosity becomes too high. Since the ink of this embodiment has a moderately low drying rate (20% or more and 40% or less), it is possible to suppress the shear viscosity from becoming too high and suppress the occurrence of nozzle clogging. As a result, the ink of this embodiment has excellent jetting stability.

[0018] The use of the ink of this embodiment is not particularly limited, and for example, it can be used to form an image on a permeable recording medium or a non-permeable recording medium. The ink of this embodiment has excellent permeability to permeable recording media. Examples of permeable recording media include printing paper and media made of fibers (such as cloth). Examples of printing paper include plain paper, copy paper, recycled paper, thin paper, thick paper, and glossy paper.

[0019] The ink of this embodiment has poor permeability to non-permeable recording media compared to permeable recording media. The absorption of the aqueous medium in the non-permeable recording medium is, for example, 1.0 g / m 2 As follows. Examples of non-permeable recording media include: resin recording media, metal recording media and glass recording media. Examples of resin recording media include: resin sheets and resin films. The resin contained in the resin recording medium is preferably a thermoplastic resin. Specific resins include: polyethylene, polypropylene, polyvinyl chloride and polyethylene terephthalate (PET). Examples of resin recording media include oriented polypropylene (OPP) films. When an image is formed on a resin recording medium using the ink of this embodiment, the surface (printing surface) of the recording medium may be subjected to corona treatment.

[0020] Since the ink of the present embodiment contains binder resin particles, an image having excellent abrasion resistance can be formed even on an impermeable recording medium.

[0021] (Drying rate)

[0022] The drying rate of the ink of this embodiment is 20% or more and 40% or less, preferably 25% or more and 35% or less. By setting the drying rate of the ink of this embodiment to 20% or more, it is possible to prevent the shear viscosity from becoming too high. By setting the drying rate of the ink of this embodiment to 40% or less, it is possible to prevent the occurrence of nozzle clogging.

[0023] (Shear viscosity)

[0024] The shear viscosity of the ink of this embodiment is 5.5 mPa·s to 7.0 mPa·s, preferably 6.0 mPa·s to 6.5 mPa·s. By setting the shear viscosity of the ink of this embodiment to 5.5 mPa·s to 7.0 mPa·s, the ejection stability can be optimized.

[0025] (pigment)

[0026] In the ink of the present embodiment, the pigment, for example, together with the pigment coating resin, constitutes a pigment particle. The pigment particle, for example, includes: a core containing a pigment, and a pigment coating resin coating the core. The pigment coating resin is, for example, dispersed in a solvent. From the viewpoint of optimizing the color concentration, hue, or stability of the ink of the present embodiment, the volume median diameter of the pigment particle is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0027] Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, violet 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 violet pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0028] In the ink of the present embodiment, the content of the pigment 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 setting the content of the pigment to 0.5% by mass or more, the ink of the present embodiment can form an image with a desired image density. In addition, by setting the content of the pigment to 10.0% by mass or less, the fluidity of the ink of the present embodiment can be ensured.

[0029] (Pigment coated resin)

[0030] The pigment coating resin is a resin soluble in an aqueous medium. A portion of the pigment coating resin is present on the surface of the pigment particles, for example, to optimize the dispersibility of the pigment particles. Another portion of the pigment coating resin is present in a state of being dissolved in the aqueous medium, for example.

[0031] 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 of a (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.

[0032] In the ink of the present embodiment, the content of the pigment coating resin is preferably 0.1% by mass or more and 4.0% by mass or less, and more preferably 0.4% by mass or more and 1.2% by mass or less. By setting the content of the pigment coating resin to 0.1% by mass or more and 4.0% by mass or less, the ejection stability of the ink of the present embodiment can be further optimized.

[0033] In the ink of the present embodiment, the content of the pigment coating resin is preferably 10 parts by mass or more and 60 parts by mass or less, and more preferably 20 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the pigment. By setting the content of the pigment coating resin to 10 parts by mass or more and 60 parts by mass or less, the ejection stability of the ink of the present embodiment can be further optimized.

[0034] (Binder resin particles)

[0035] The binder resin particles exist in a state dispersed in an aqueous medium. The binder resin particles contain a binder resin. Examples of the binder resin include polyurethane resins, (meth) acrylic resins, styrene-(meth) acrylic resins, (meth) acrylic-polyurethane resins, polyester resins, and modified polyolefin resins. The binder resin particles preferably contain a polyurethane resin as a binder resin. The content of the binder resin in the binder resin particles is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0036] The polyurethane resin is, for example, a copolymer of: a diol compound or a bisphenol compound; and polyisocyanate.

[0037] The volume median diameter of the binder resin particles (D 50 ) is preferably greater than 5 nm and less than 100 nm, and more preferably greater than 20 nm and less than 65 nm.

[0038] The content ratio of the binder resin particles in the ink of the present embodiment is preferably 1.0 mass % or more and 10.0 mass % or less, and more preferably 2.0 mass % or more and 6.0 mass % or less. By setting the content ratio of the binder resin particles to 1.0 mass % or more, the ink of the present embodiment can optimize the abrasion resistance of the formed image and the adhesion to the recording medium. By setting the content ratio of the binder resin particles to 10.0 mass % or less, the jetting stability of the ink of the present embodiment can be further optimized.

[0039] (Surfactant)

[0040] The surfactant optimizes the compatibility and dispersion stability of the components contained in the ink of this embodiment. In addition, the surfactant optimizes the permeability (wettability) of the ink of this embodiment to the recording medium. Examples of the surfactant include nonionic surfactants.

[0041] Examples of nonionic surfactants include acetylene glycol surfactants (surfactants including acetylene glycol compounds), silicone surfactants (surfactants including silicone compounds), and fluorine surfactants (surfactants including fluorine resins or fluorine-containing compounds). Examples of acetylene glycol surfactants include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. The ink of this embodiment preferably contains an acetylene glycol surfactant as a surfactant.

[0042] The content ratio of the surfactant in the ink of the present embodiment is preferably 0.05% by mass or more and 2.0% by mass or less, and more preferably 0.3% by mass or more and 0.7% by mass or less.

[0043] (Aqueous medium)

[0044] The aqueous medium comprises glycol ether, a specific organic solvent and water. The aqueous medium can function as a solvent or as a dispersion medium. In the aqueous medium, the total content of glycol ether, the specific organic solvent and water is preferably 90% by mass or more, more preferably 100% by mass.

[0045] In the ink of the present embodiment, the content ratio of the aqueous medium is preferably 80.0% by mass or more and 97.0% by mass or less, and more preferably 90.0% by mass or more and 96.0% by mass or less.

[0046] (water)

[0047] In the ink of this embodiment, the content of water is preferably 30.0 mass % or more and 70.0 mass % or less, more preferably 42.0 mass % or more and 50.0 mass % or less, and particularly preferably 45.0 mass % or more and 48.0 mass % or less.

[0048] (glycol ether)

[0049] 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. The glycol ether is preferably triethylene glycol monobutyl ether or dipropylene glycol monomethyl ether.

[0050] In the ink of the present embodiment, the content of glycol ether is preferably 10.0 mass % or more and 20.0 mass % or less, and more preferably 14.0 mass % or more and 16.0 mass % or less. The higher the content of glycol ether, the greater the shear viscosity of the ink of the present embodiment and the lower the drying rate. By setting the content of glycol ether to 10.0 mass % or more and 20.0 mass % or less, it is easy to adjust the shear viscosity and drying rate of the ink of the present embodiment to the above range.

[0051] (Specific organic solvents)

[0052] The specific organic solvent is a diol compound having a carbon number of 3 or more and 6 or less. Examples of the specific organic solvent include 1,2-propylene glycol, 3-methyl-1,3-butylene glycol, 1,2-pentanediol, 2-methyl-1,3-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. The specific organic solvent is preferably 1,2-propylene glycol or 1,3-propylene glycol.

[0053] In the ink of the present embodiment, the content ratio of the specific organic solvent is 27.5 mass % or more and 35.5 mass % or less, preferably 29.0 mass % or more and 33.0 mass % or less. The greater the content ratio of the specific organic solvent, the greater the shear viscosity of the ink of the present embodiment and the lower the drying rate. By setting the content ratio of the specific organic solvent to 27.5 mass % or more and 35.5 mass % or less, it is easy to adjust the shear viscosity and drying rate of the ink of the present embodiment to the above range.

[0054] The aqueous medium may further contain a water-soluble organic solvent other than glycol ethers and specific organic solvents (hereinafter sometimes referred to as other water-soluble organic solvents). 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, glycerol, and dimethyl sulfoxide.

[0055] (Other ingredients)

[0056] The ink of the present embodiment may further contain known additives (for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity adjuster, a pH adjuster, and an antifungal agent) as necessary.

[0057] (Method for producing ink)

[0058] The ink of the present embodiment can be manufactured, for example, by using a stirrer to uniformly mix a pigment dispersion containing a pigment, a resin emulsion containing binding resin particles, an aqueous medium, and other components (such as a surfactant) prepared as needed. In the manufacture of the ink of the present embodiment, after uniformly mixing the components, a filter (such as a filter with a pore size of 5 μm or less) can be used to remove foreign matter and coarse particles.

[0059] (Preferred ingredients)

[0060] The ink of this embodiment preferably has any one of the components (i-1) to (i-8) shown in Table 1. In addition, in Table 1, the numerical range represents the content ratio of each component. For example, "2.5-3.5" in the pigment column of component (i-1) means that the content ratio of the pigment is 2.5 mass% or more and 3.5 mass% or less. The following are the abbreviations used in Table 1.

[0061] wt%: mass%

[0062] TEGMBE: triethylene glycol monobutyl ether

[0063] DPGMME: Dipropylene glycol monomethyl ether

[0064] 1,2-PD: 1,2-propylene glycol

[0065] 1,3-PD: 1,3-propylene glycol

[0066] [Table 1]

[0067]

[0068] <Second Embodiment: Inkjet Recording Device>

[0069] The second embodiment of the present invention relates to an inkjet recording device. The inkjet recording device of this embodiment has ink and a circulation type recording head for ejecting the ink. The ink is the ink of the first embodiment. Since the inkjet recording device of this embodiment has the ink of the first embodiment, the ejection stability of the ink is excellent.

[0070] The inkjet recording device of this embodiment may have only one ink or may have multiple inks (e.g., yellow ink, cyan ink, magenta ink, and black ink). When the inkjet recording device of this embodiment has multiple inks, at least one ink may be the ink of the first embodiment, but preferably all inks are the inks of the first embodiment.

[0071] The following is a detailed description of the structure of the inkjet recording device of the present embodiment with reference to the accompanying drawings. In addition, for ease of understanding, the accompanying drawings are schematic representations of the components, and for the convenience of drawing, the size, number, etc. of the components illustrated are sometimes different from the actual ones.

[0072] Figure 1 1 is a diagram showing the main parts of an inkjet recording device 100, which is an example of an inkjet recording device according to the present embodiment. Figure 1 As shown, the inkjet recording device 100 mainly includes a conveying section 1 and four recording heads 11 (circulation type recording heads) as circulating type linear recording heads. The inkjet recording device 100 also includes: a paper supply tray 2, a paper supply roller 3, a paper supply driven roller 4, a conveyor 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 conveyor belt 5, the belt driving roller 6 and the belt driven roller 7 constitute a part of the conveying section 1. The paper supply tray 2 is provided at the left end of the inkjet recording device 100 in the figure. The paper supply tray 2 accommodates recording media M (such as recording sheets or printing paper). The paper supply roller 3 and the paper supply driven roller 4 are provided at one end of the paper supply tray 2. The paper supply roller 3 takes out the accommodated recording media M one by one from the recording medium M at the uppermost position, and conveys them to the conveyor belt 5 for paper supply. The paper supply driven roller 4 is pressed against the paper supply roller 3 and rotates drivenly.

[0073] On the downstream side of the paper feed roller 3 and the paper feed driven roller 4 in the paper conveying direction ( Figure 1 The conveyor belt 5 is provided with a freely rotatable conveyor belt 5 (right side in the figure). The conveyor belt 5 is mounted on a belt drive roller 6 and a belt driven roller 7. The belt drive roller 6 is arranged on the downstream side in the paper conveying direction. The belt drive roller 6 drives the conveyor belt 5. The belt driven roller 7 is arranged on the upstream side in the paper conveying direction. The belt driven roller 7 rotates with the belt drive roller 6 via the conveyor belt 5. By driving the belt drive roller 6 to rotate in the clockwise direction, the recording medium M is conveyed along the conveying direction X indicated by the arrow.

[0074] In addition, a discharge roller 8 and a discharge driven roller 9 are provided on the downstream side of the conveying direction of the conveyor belt 5. The discharge roller 8 is driven in the clockwise direction in the figure to discharge the recording medium M with the image formed thereon to the outside of the device housing. The discharge driven roller 9 is pressed against the upper part of the discharge roller 8 and is driven to rotate. A discharge tray 10 is provided on the downstream side of the discharge roller 8 and the discharge driven roller 9. The recording medium M discharged to the outside of the device housing is loaded on the discharge tray 10.

[0075] 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 sequence at approximately equal intervals from the upstream side to the downstream side in the conveying direction X of the recording medium M. The four recording heads 11 are respectively supported at a height of a predetermined length from the upper surface of the conveyor belt 5. The four recording heads 11 respectively record images on the recording medium M conveyed by the conveyor belt 5. The four recording heads 11 respectively supply different four-color (cyan, magenta, yellow, and black) inks (first ink, second ink, third ink, and fourth ink). The four recording heads 11 respectively spray ink on the recording medium M in a predetermined order. Thus, a color image is formed on the recording medium M. The four recording heads 11 are driven, for example, by a piezoelectric method.

[0076] Next, refer to Figure 2 The inkjet recording apparatus 100 will be further described. Figure 2 This is a diagram showing components related to ink circulation in the inkjet recording apparatus 100 .

[0077] like Figure 2 As shown, the inkjet recording device 100 includes: a recording head 11 (specifically Figure 1 The ink supply unit 15 supplies ink to the ink sac member 16. The ink sac 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. In addition, the control unit 101 also controls the recording head 11.

[0078] Although not shown in the figure, the inkjet recording device 100 includes a total of four sets of supply tubular members 13a to 13c, an ink supply unit 15, an ink bag member 16, and four recording heads 11 ( Figure 1 The first recording head 11C, the second recording head 11M, the third recording head 11Y, and the fourth recording head 11K correspond to the first recording head 11C, the second recording head 11M, the third recording head 11Y, and the fourth recording head 11K.

[0079] The ink supply unit 15 includes: an ink tank 151, a sub-tank pump 152, a sub-tank 153 (ink storage unit), 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 discharge valve 170 and a discharge pipe 171.

[0080] The ink tank 151 contains ink I. The ink tank 151 is connected to the sub-tank 153 via the first pipe 161. The first pipe 161 allows the ink I to flow from the ink tank 151 to the sub-tank 153. The sub-tank 153 stores the ink I supplied from the ink tank 151.

[0081] The sub-tank pump 152 is disposed on the first pipe 161. The sub-tank pump 152 supplies the ink I stored in the ink tank 151 to the sub-tank 153 according to a command from the control unit 101, for example, when the liquid level of the ink I in the sub-tank 153 is lower than a predetermined value.

[0082] In the inkjet recording device 100, the ink I is supplied from the sub-tank 153 to the recording head 11 via the ink bag member 16. The recording head 11 ejects at least a portion of the ink I supplied by the ink bag member 16 onto the recording medium M, and discharges the rest of the ink I (the ink not ejected) to the ink supply unit 15. Specifically, the ink I discharged from the recording head 11 returns to the sub-tank 153. That is, the ink circulates mainly between the sub-tank 153, the ink bag member 16, and the recording head 11.

[0083] The sub-tank 153 is connected to the diaphragm pump 154 ​​via the second pipe 162. The second pipe 162 allows the ink I to flow from the sub-tank 153 to the diaphragm pump 154. The diaphragm pump 154 ​​is connected to the ink bag member 16 via the third pipe 163. The third pipe 163 allows the ink I to flow from the diaphragm pump 154 ​​to the ink bag member 16.

[0084] 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.

[0085] The piston is inserted in the cylinder. The piston moves in a direction away from the bottom of the cylinder according to the command of the control unit 101. In addition, the piston moves in a direction close to the bottom of the cylinder according to the command of the control unit 101.

[0086] 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 sub-tank 153 into the second pipe 162 , and the ink I flows into the cylinder through the second pipe 162 .

[0087] 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 ink bag member 16 through the third pipe 163 .

[0088] The first valve 162a is arranged on the second pipe 162. The second valve 163a is arranged on the third pipe 163. The first valve 162a and the second valve 163a are opened and closed according to the command of the control unit 101. Specifically, during the period when the piston moves in the direction away from the bottom of the cylinder, the first valve 162a is in the open state and the second valve 163a is in the closed state. During the period when the piston moves in the direction close to the bottom of the cylinder, the first valve 162a is in the closed state and the second valve 163a is in the open state.

[0089] The ink bag member 16 supplies the ink I to the recording head 11 via the supply tubular members 13a to 13c. The ink bag member 16 has a function of alleviating the pressure change of the ink I supplied to the recording head 11. The ink bag member 16 has at least an ink passage portion through which the ink I passes. The ink bag member 16 may further have an ink storage chamber for temporarily storing the ink I. In the ink bag member 16, for example, a part of the member constituting the ink passage portion and the ink storage chamber is an elastic member (for example, a resin film). Thus, in the ink bag member 16, when the pressure of the ink I inside (the ink passage portion or the ink storage chamber) increases or decreases, the elastic member is deformed, and the pressure change of the ink I can be alleviated. As a result, the pressure change of the ink I supplied to the recording head 11 is alleviated.

[0090] The circulation pipe 164 allows the recording head 11 and the sub-tank 153 to communicate with each other. The third valve 164a is disposed on the circulation pipe 164. The third valve 164a is opened and closed according to the command of the control unit 101. The control unit 101 controls the third valve 164a to be in an open state when the inkjet recording device 100 forms an image, and controls the third valve 164a to be in a closed state when the inkjet recording device 100 does not form an image. The third valve 164a is, for example, a backflow prevention valve, which is used to prevent the ink I from flowing back when the inkjet recording device 100 does not form an image.

[0091] The circulation pump 164b is disposed on the circulation pipe 164. The circulation pump 164b delivers the ink I in the circulation pipe 164 to the sub-tank 153, for example. As a result, the internal pressure of the circulation pipe 164 is lower than the internal pressure of the recording head 11. As a result, the ink I is discharged from the recording head 11 to the sub-tank 153 through the circulation pipe 164.

[0092] 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, for example, semiconductor memories such as random access memory (RAM) and 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, for example, a processor such as a central processing unit (CPU) or a microprocessor (MPU). The processing device 103 controls the operation of each part of the inkjet recording device 100 according to the program stored in the storage device 102.

[0093] The discharge valve 170 is arranged on the third pipe 163. The discharge pipe 171 connects the second pipe 162 and the third pipe 163 through the discharge valve 170. The discharge valve 170 and the discharge pipe 171 constitute a discharge mechanism. That is, the ink supply unit 15 has a discharge mechanism. The discharge valve 170 is, for example, an independent component that is not controlled by the control unit 101. The discharge valve 170 is usually kept in a closed state due to, for example, a spring force, and becomes an open state when the pressure of the ink I in the third pipe 163 reaches a predetermined value or more. Therefore, when the pressure of the ink I in the third pipe 163 reaches a predetermined value or more, the discharge mechanism discharges the ink I in the third pipe 163 into the second pipe 162 through the discharge pipe 171. As a result, the discharge mechanism adjusts the pressure of the ink I in the third pipe 163 (that is, the pressure of the ink I supplied to the ink bag member 16) to not be above the predetermined value.

[0094] The pressure of the ink I circulating between the sub-tank 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. As a result, for example, the pressure of the circulating ink I decreases. 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. As a result, the pressure of the circulating ink I also increases. Although the pressure change of the circulating ink I is alleviated to some extent by adjusting the piston running speed of the diaphragm pump 154, it is not enough. In known inkjet recording devices, a sharp increase or decrease in ink pressure (especially a sharp increase in ink pressure) can cause ink coagulation. In response to this, the inkjet recording device 100 can suppress the rapid increase or decrease in ink I pressure by having a discharge mechanism and an ink bag member 16. As a result, the inkjet recording device 100 can effectively suppress the occurrence of ink coagulation.

[0095] The circulation flow rate of the recording head 11 (circulation type recording head) is preferably 40 mL / min or more and 70 mL / min or less, and more preferably 45 mL / min or more and 55 mL / min or less. By setting the circulation flow rate of the recording head 11 to 40 mL / min or more, it is possible to suppress the drying of the ink near the nozzle and suppress the occurrence of 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.

[0096] An example of the inkjet recording device of the present embodiment has been described above, but the inkjet recording device of the present embodiment is not limited to the Figures 1 to 2 shown.

[0097] Figures 1 to 2 In the embodiment, the inkjet recording device 100 is used as an example for description, and the inkjet recording device 100 has four recording heads 11 corresponding to four colors of ink. However, the number of recording heads of the inkjet recording device of this embodiment is not particularly limited, and can be set to, for example, more than 1 and less than 10, preferably more than 3 and less than 5. In addition, the inkjet recording device 100 ejects the four colors of cyan, magenta, yellow and black in sequence, but in the inkjet recording device of this embodiment, the ink types, combinations and ejection order are not limited thereto.

[0098] Furthermore, the inkjet recording device of this embodiment requires only ink and a circulation type recording head. Furthermore, the inkjet recording device of this embodiment may be a multifunction machine having the functions of a scanner, a copier, a printer, or a facsimile machine.

[0099] [Example]

[0100] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0101] (Measurement of volume median diameter)

[0102] In the examples, the volume median diameter of the resin particles was measured using a dynamic light scattering particle size distribution measuring apparatus (“Zetascope (Japanese registered trademark) Nano ZS” manufactured by Malvern Corporation).

[0103] (Measurement of shear viscosity)

[0104] 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. The number of plots was set to 5. During the measurement, the shear rate was automatically changed from 100,000 s to 100,000 s.-1 Start measuring, and measure the shear rate to 10000s -1 Other conditions are as follows.

[0105] (Other conditions)

[0106] Microchip: "Glass chip for viscosity measurement" manufactured by Formulaaction

[0107] Standard fluid: "5 cP aqueous viscosity standard fluid" manufactured by Formulaaction

[0108] (Measurement of drying rate)

[0109] In the measurement of the drying rate of ink, first, fill the ink to be measured in an inkjet droplet observation device ("DropMeasure (Japanese registered trademark)-100" manufactured by Microjet Co., Ltd.). A drop of the ink to be measured is ejected from the head (piezoelectric) of the above-mentioned observation device so that it contacts the measurement table. At this time, the volume of the ejected droplet is greater than 100 pL and less than 400 pL (about 250 pL), and the ejection speed is greater than 6 m / s and less than 8 m / s (about 7 m / s). Next, use a high-speed camera ("FASTCAM (Japanese registered trademark) SA-X2" manufactured by Foster Co., Ltd.) to observe the change in the volume of the ink droplet contacting the measurement table over time. Thus, the volume V0 of the ink droplet just after contact and the volume V1 of the ink droplet 500 milliseconds after the start of contact are measured. Next, the drying rate of the ink of the measurement object is calculated according to formula (1).

[0110] Drying rate = 100 × (volume V0 - volume V1) / volume V0 ... (1)

[0111] In addition, the drying rate measurement was repeated multiple times for each measurement object, and even if the volume of the ejected droplets changed, as long as it was within the range of 100 pL to 400 pL, the drying rate was the same value. Similarly, the drying rate measurement was repeated multiple times for each measurement object, and even if the ejection speed changed, as long as it was within the range of 6 m / s to 8 m / s, the drying rate was the same value.

[0112] [Preparation of Pigment Dispersion]

[0113] A pigment dispersion (C) containing a cyan pigment, a pigment dispersion (Y) containing a yellow pigment, a pigment dispersion (M) containing a magenta pigment, and a pigment dispersion (K) containing a black pigment were prepared by the following method.

[0114] (Pigment dispersion (C))

[0115] 15 parts by mass of a cyan pigment ("HELIOGEN (Japanese registered trademark) BLUE D 7088" manufactured by BASF (ビーエーエスエフ), CI Pigment Blue (Pigment Blue) 15:3), 10 parts by mass of a dispersion containing a pigment-coated resin ("DIS PERBYK (Japanese registered trademark) 190" manufactured by Bic Chemi, non-volatile component: 40%, active ingredient: acrylic resin), and 75 parts by mass of water were mixed and pre-dispersed using a disperser to obtain a mixed solution.

[0116] Next, the mixed solution was dispersed using a 0.6 L bead mill ("Dignomil" manufactured by Willy A. Bachofen (WAB), which was filled with 1800 g of zirconia beads with a diameter of 0.1 mm as a dispersion medium). Thus, a pigment dispersion (C) (pigment concentration: 15% by mass, pigment coating resin concentration: 4% by mass) was obtained.

[0117] (Pigment dispersion (Y), pigment dispersion (M) and pigment dispersion (B))

[0118] Pigment dispersions (Y), (M) and (B) were prepared in the same manner as in the preparation of the pigment dispersion (C), except that the yellow pigment, magenta pigment and black pigment shown below were used instead of the cyan pigment.

[0119] Yellow pigment: "FAST YELLOW 7413" manufactured by Sanyo Pigment Co., Ltd., CI Pigment Yellow 74

[0120] Magenta pigment: "Red No. 63" manufactured by Dainichi Seika Industries, Ltd.

[0121] Black pigment: "Printex (Japanese registered trademark) 85" manufactured by Ariel Electronics Co., Ltd., carbon black

[0122] [Polyurethane emulsion]

[0123] As a polyurethane emulsion containing polyurethane resin particles, "Superflex (Japanese registered trademark) 870" (non-volatile content: 30% by mass, volume median diameter of polyurethane resin particles: 0.03 μm) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was used.

[0124] <Ink Preparation>

[0125] Inks (C1) to (C13), (B1), (Y1), and (M1) were prepared using the following method.

[0126] [Ink (C 1)]

[0127] In a beaker, ion exchange water, 20.0 parts by mass of a 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-propylene glycol, 13.3 parts by mass of a polyurethane emulsion ("Superflex (Japanese registered trademark) 870" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (polyurethane resin particles: 4.0 parts by mass), and 0.5 parts by mass of a surfactant ("Surfinol (Japanese registered trademark) 440" manufactured by Nissin Chemical Co., Ltd., ethylene oxide adduct of acetylene glycol) were added. The amount of ion exchange water added was set to 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 ("Slider Model BL-600" manufactured by Shinto Scientific Co., Ltd.) to obtain a mixed solution. The mixed solution was filtered using a filter (pore size of 5 μm) to remove foreign matter and coarse particles contained in the mixed solution. In this way, ink (C1) was obtained.

[0128] [Inks (C2) to (C13), (B1), (Y1) and (M1)]

[0129] Inks (C2) to (C13), (B1), (Y1) and (M1) were prepared by the same method as that for ink (C1), except that the types and amounts of the components were changed as shown in Tables 2 to 3. Inks (C1) to (C13), (B1), (Y1) and (M1) are shown in Tables 2 to 3 and are the inks of Examples 1 to 11 and Comparative Examples 1 to 5.

[0130] In addition, the abbreviations used in Tables 2 and 3 and Table 4 described later are shown below.

[0131] wt%: mass%

[0132] TEGMBE: triethylene glycol monobutyl ether

[0133] DPGMME: Dipropylene glycol monomethyl ether

[0134] 1,2-PD: 1,2-propylene glycol

[0135] 1,3-PD: 1,3-propylene glycol

[0136] Example 1 to Example 11: Example 1 to Example 11

[0137] Comparison 1 to Comparison 5: Comparison Example 1 to Comparison Example 5 [Table 2]

[0138]

[0139] [Table 3]

[0140]

[0141] <Evaluation>

[0142] The ejection stability of the inks of Examples 1 to 11 and Comparative Examples 1 to 5 was evaluated by the following method. The evaluation results are shown in Table 4. Unless otherwise specified, the evaluation was performed at a temperature of 25° C. and a humidity of 60% RH.

[0143] An evaluation machine (a test machine manufactured by Kyocera Document Solutions Co., Ltd.) having at least a circulation type recording head and an ink circulation pump ("circulation pump CIMS" manufactured by Megnaj et Co.) was prepared. The ink circulation pump corresponds to the ink supply unit of the second embodiment and is set to supply the ink of the evaluation object to the circulation type recording head. The circulation type recording head is set as follows: at least a part of the ink supplied by the ink circulation pump is ejected onto the recording medium as required, and the rest of the supplied ink is returned to the ink circulation pump. In addition, the circulation type recording head is set as follows: in a state where it is not necessary to eject the ink (a state where image formation is not performed), the entire amount of the ink supplied by the ink circulation pump is returned to the ink circulation pump. The circulation flow rate of the circulation pump is set as shown in Table 4 below.

[0144] As the recording medium, A4-size matte paper for inkjet ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used.

[0145] Using the evaluation machine, a solid image of 150 mm × 200 mm is continuously printed on 5,000 sheets of recording medium. Next, the ink of the evaluation object is removed from the circulating recording head of the evaluation machine. Next, the ink ejection surface of the circulating recording head of the evaluation machine is wiped to clean the circulating recording head. Next, a stripe image formed by a plurality of parallel thin lines is formed on the recording medium using the evaluation machine. In the formation of the stripe image, the line width of the thin line is set to 1 pixel, and the interval (line spacing) between adjacent thin lines is set to 3 pixels.

[0146] Next, a microscope is used to read the stripe image formed on the recording medium. Specifically, the interval A between specific thin lines a and b is measured at 204 locations, and thin line b is located 16 pixels away from thin line a. In addition, there are 3 other thin lines between thin line a and thin line b. Using image processing software (manufactured by Kyocera Document Solutions, Ltd.), the deviation (3σ, unit: μm) of the measured interval A is calculated. The calculated deviation (3σ) of the interval A is used as the evaluation value of the injection stability. The injection stability is judged according to the following criteria.

[0147] (Benchmark for jet stability)

[0148] A (good): 3σ is less than 20.

[0149] B (bad): 3σ is 20 or more.

[0150] C (particularly bad): Nozzles that did not eject ink occurred due to nozzle clogging, and 3σ analysis could not be performed.

[0151] [Table 4]

[0152]

[0153] 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 contain a pigment, a binder resin particle and an aqueous medium. The aqueous medium contains a glycol ether, a specific organic solvent and water. The content ratio of the specific organic solvent is 27.5% by mass or more and 35.5% by mass or less. The shear viscosity of each ink of the examples is 5.5 mPa·s or more and 7.0 mPa·s or less. The drying rate of each ink of the examples is 20% or more and 40% or less. The jetting stability of each ink of the examples is excellent.

[0154] On the other hand, the content ratio of the specific organic solvent in the ink (C1) of Comparative Example 1 and the ink (C9) of Comparative Example 3 was insufficient. Therefore, the shear viscosity of the ink (C1) and the ink (C9) was too low and the drying rate was too high. As a result, the ejection stability of the ink (C1) and the ink (C9) was poor.

[0155] In the ink (C5) of Comparative Example 2 and the ink (C12) of Comparative Example 4, the content ratio of the specific organic solvent was excessive. Therefore, the shear viscosity of the ink (C5) and the ink (C12) was too high and the drying rate was too low. As a result, the ejection stability of the ink (C5) and the ink (C12) was poor.

[0156] The ink (C13) of Comparative Example 5 does not contain glycol ether. Therefore, the shear viscosity of the ink (C13) is too low and the drying rate is too high. As a result, the ejection stability of the ink (C13) is poor.

Claims

1. An ink for inkjet recording, comprising a pigment, a binder resin particle and an aqueous medium, The aqueous medium comprises glycol ether, a specific organic solvent and water, The specific organic solvent is a diol compound having 3 to 6 carbon atoms, The content ratio of the specific organic solvent is 27.5 mass % or more and 35.5 mass % or less, At a temperature of 32°C and a shear rate of 10 5 s -1 The measured shear viscosity of the ink for inkjet recording is 5.5 mPa·s or more and 7.0 mPa·s or less, The inkjet recording ink has a drying rate of 20% to 40%. The drying rate is obtained by the following formula (1) based on the volume V0 of the ink droplet immediately after contact and the volume V1 of the ink droplet 500 milliseconds after contact when a droplet of 100 pL or more and 400 pL or less of the inkjet recording ink is ejected onto a measuring table at a temperature of 25°C: Drying rate = 100 × (volume V0 - volume V1) / volume V0 ... (1).

2. The ink for inkjet recording according to claim 1, characterized in that The specific organic solvent includes at least one of 1,2-propylene glycol, 3-methyl-1,3-butylene glycol, 1,2-pentanediol, 2-methyl-1,3-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol.

3. The ink for inkjet recording according to claim 2, characterized in that The specific organic solvent includes at least one of 1,2-propylene glycol and 1,3-propylene glycol.

4. The ink for inkjet recording according to claim 1 or 2, characterized in that The glycol ether includes at least one of triethylene glycol monobutyl ether and dipropylene glycol monomethyl ether.

5. The ink for inkjet recording according to claim 1 or 2, characterized in that The binder resin particles contain a polyurethane resin.

6. The ink for inkjet recording according to claim 1 or 2, characterized in that The content ratio of the glycol ether is 10.0 mass % or more and 20.0 mass % or less.

7. The ink for inkjet recording according to claim 1 or 2, characterized in that The content ratio of the binder resin particles is 2.0 mass % or more and 6.0 mass % or less.

8. The ink for inkjet recording according to claim 1 or 2, characterized in that The water content is 42.0 mass % or more and 50.0 mass % or less.

9. An inkjet recording device comprising: Ink; as well as a circulation type recording head for ejecting the ink, The ink is the ink for inkjet recording according to claim 1 or 2.

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

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