Inkjet ink and inkjet recording device

Abstract

To provide an inkjet ink that is capable of forming an image with desired image density and is be readily removed by cleaning.SOLUTION: An inkjet ink contains a pigment, an aqueous medium, and an amine compound. The aqueous medium contains water and a specific organic solvent. The specific organic solvent has an octanol / water partition coefficient LogP of 0.10 or more and 2.00 or less. The specific organic solvent has a viscosity at 25°C of 2.0 mPa s or more and 350.0 mPa s or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Inkjet recording apparatuses are required to be able to form images having a desired image density. As a method for forming an image having a desired image density with an inkjet recording apparatus, for example, a method using inkjet ink that dries quickly and thickens after landing on a recording medium has been proposed (for example, Patent Document 1).

[0003] However, if the viscosity of the inkjet ink when dried is too high, the inkjet ink adhering to the ink ejection surface of a recording head, for example, may dry and thicken, resulting in insufficient ejection stability of the inkjet ink.

[0004] For this reason, inkjet inks are required to be capable of forming images having a desired image density and to be easily removed by cleaning, and inkjet recording apparatuses are required to be capable of forming images having a desired image density and to be easily removed by cleaning. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-175951 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 cannot meet the above-mentioned requirements.

[0007] The present invention has been made in view of the above problems, and has as its object to provide an inkjet ink that can form an image having a desired image density and can be easily removed by cleaning. Another object of the present invention is to provide an inkjet recording apparatus that can form an image having a desired image density and can easily remove the inkjet ink by cleaning. [Means for solving the problem]

[0008] The inkjet ink according to the present invention contains a pigment, an aqueous medium, and an amine compound. The aqueous medium contains water and a specific organic solvent. The specific organic solvent has an octanol / water partition coefficient LogP of 0.10 or more and 2.00 or less. The specific organic solvent has a viscosity at 25°C of 2.0 mPa s or more and 350.0 mPa s or less.

[0009] The inkjet recording apparatus according to the present invention includes an inkjet ink, a recording head, and a wiper blade. The recording head has nozzles and performs a discharge operation for discharging the inkjet ink from the nozzles onto a recording medium, and a vibration operation for vibrating a meniscus of the inkjet ink in the nozzles. The wiper blade performs a wiping operation for wiping the ink discharge surface of the recording head. The inkjet ink is the inkjet ink described above. Effect of the Invention

[0010] The inkjet ink according to the present invention is capable of forming an image having a desired image density and is easily removed by cleaning. The inkjet recording apparatus according to the present invention is capable of forming an image having a desired image density and is easily removed by cleaning. [Brief description of the drawings]

[0011] [Figure 1] FIG. 11 is a diagram illustrating an example of an inkjet recording apparatus according to a second embodiment. [Diagram 2] FIG. 2 is a bottom view of the first line recording head. [Diagram 3] 3 is an enlarged view of a main part of cross section II in FIG. 2. [Figure 4] 2 is a diagram showing a side surface of the first line recording head in FIG. 1 and its vicinity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described. In the following, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer (for example, Zetasizer (registered trademark) Nano ZS manufactured by Malvern Instruments) unless otherwise specified.

[0013] For organic solvents with literature values, the literature value can be used as the octanol / water partition coefficient LogP. For organic solvents with no literature values, a value calculated using calculation software (for example, "ChemDraw" manufactured by PerkinElmer) can be used.

[0014] The viscosity is a value measured at 25° C. using a rotational viscometer (for example, “TV-100EL” manufactured by Toki Sangyo Co., Ltd.).

[0015] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". Each component described in this specification may be used alone or in combination of two or more. "At least one of A and B" means "A and / or B".

[0016] [First embodiment: Ink] An inkjet ink (hereinafter sometimes simply referred to as ink) according to a first embodiment of the present invention will be described below. The ink according to this embodiment contains a pigment, an aqueous medium, and an amine compound. The aqueous medium contains water and a specific organic solvent. The specific organic solvent has an octanol / water partition coefficient LogP (hereinafter sometimes simply referred to as LogP) of 0.10 or more and 2.00 or less. The viscosity of the specific organic solvent at 25°C is 2.0 mPa·s or more and 350.0 mPa·s or less.

[0017] The ink according to the present embodiment, having the above-mentioned configuration, can form an image having a desired image density and is easy to remove by cleaning. The reason why the ink according to the present embodiment exhibits the above-mentioned effects is presumed to be as follows.

[0018] The ink according to the present embodiment contains a specific organic solvent (LogP is 0.10 or more and 2.00 or less) having relatively high hydrophobicity as an organic solvent. The ink according to the present embodiment contains a specific organic solvent, and therefore exhibits high hydrophobicity when it is dried and the moisture content is reduced. When the ink according to the present embodiment becomes highly hydrophobic, the pigment contained in the ink according to the present embodiment aggregates, and the ink according to the present embodiment thickens. For this reason, when the ink according to the present embodiment dries and loses moisture, the pigment easily aggregates and thickens. The ink according to the present embodiment, which is easily thickened by drying, quickly thickens after landing on the recording medium, and the pigment is retained near the surface of the recording medium to form an image with a high image density. As a result, the ink according to the present embodiment can form an image with a desired image density.

[0019] Furthermore, the viscosity of the specific organic solvent at 25°C is 2.0 mPa·s or more and 350.0 mPa·s or less. Therefore, the nozzles of an inkjet recording device equipped with the ink according to this embodiment do not become clogged, and the ejection stability of the ink according to this embodiment by the inkjet recording device can be optimized. Furthermore, since the viscosity of the specific organic solvent at 25°C is 2.0 mPa·s or more and 350.0 mPa·s or less, the ink according to this embodiment can be easily removed by cleaning.

[0020] In addition, the ink according to the present embodiment contains an amine compound. The amine compound neutralizes a part of the acidic groups on the pigment surface. As a result, the charge repulsion action due to the ions generated after neutralization becomes large, and it is possible to suppress the ink according to the present embodiment from thickening or the pigment contained in the ink according to the present embodiment from flocculating during storage of the ink according to the present embodiment. In addition, since the ink according to the present embodiment contains an amine compound, the pigment contained in the ink according to the present embodiment that has dried (thickened) is easily redispersed in an aqueous medium. As a result, the ink according to the present embodiment that has dried (thickened) is easily removed by cleaning. The ink according to the present embodiment is easily removed by cleaning, for example, without using a cleaning liquid. Therefore, according to the present embodiment, the ejection stability of the ink according to the present embodiment by the inkjet recording device can be optimized.

[0021] The viscosity of the ink according to this embodiment after drying treatment at 25° C. is preferably from 100.0 mPa·s to 8200.0 mPa·s, more preferably from 100.0 mPa·s to 5000.0 mPa·s, and even more preferably from 2000.0 mPa·s to 5000.0 mPa·s. By setting the viscosity of the ink according to this embodiment after drying treatment at 25° C. to be from 100.0 mPa·s to 8200.0 mPa·s, it becomes easier to form an image having a desired image density.

[0022] The drying process is a process of heating the ink according to this embodiment at 40° C. until the mass of the ink according to this embodiment is reduced by 30.00 mass %. For details of the heating process, the method described in the examples or a method based thereon can be used.

[0023] The viscosity of the ink according to this embodiment at 25° C. is preferably from 2.0 mPa·s to 25.0 mPa·s, and more preferably from 7.5 mPa·s to 9.5 mPa·s. By setting the viscosity of the ink according to this embodiment at 25° C. to be from 2.0 mPa·s to 25.0 mPa·s, it is possible to optimize the ejection stability of the ink according to this embodiment when used in an inkjet recording apparatus.

[0024] (Pigments) In the ink according to this embodiment, the pigment constitutes a pigment particle together with, for example, a pigment-coated resin. The pigment particle is constituted, for example, by a core containing a pigment and a pigment-coated resin that coats the core. The pigment-coated resin exists, for example, in a dispersed state in an aqueous medium. From the viewpoint of optimizing the color density, hue, or stability of the ink according to this embodiment, the volume median diameter of the pigment particle is preferably 30 nm or more and 300 nm or less, and more preferably 90 nm or more and 130 nm or less.

[0025] 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).

[0026] In the ink according to the present embodiment, the pigment content is preferably 1.00% by mass or more and 15.00% by mass or less, and more preferably 5.00% by mass or more and 8.00% by mass or less. By setting the pigment content to 1.00% by mass or more, the ink according to the present embodiment can easily form an image having a desired image density. Furthermore, by setting the pigment content in the ink according to the present embodiment to 15.00% by mass or less, the ejection stability of the ink according to the present embodiment by an inkjet recording device can be optimized.

[0027] (pigment coated resin) The pigment coating resin adheres to the surface of the pigment to optimize the dispersion stability of the pigment in the aqueous medium. A part of the pigment coating resin may be free in the aqueous medium without adhering to the surface of the pigment. Examples of the pigment coating resin include polyether resin, (meth)acrylic resin, styrene-(meth)acrylic resin, and styrene-maleic acid resin. Examples of commercially available pigment coating resins include "DISPERBYK (registered trademark)-190" (manufactured by BYK Japan Co., Ltd.).

[0028] In the ink according to the present embodiment, the content of the pigment coating resin is preferably 0.30% by mass or more and 3.50% by mass or less, and more preferably 1.00% by mass or more and 2.00% by mass or less. By making the content of the pigment coating resin 0.30% by mass or more, it becomes easier to form an image having a desired image density. By making the content of the pigment coating resin 3.50% by mass or less, it is possible to further optimize the ejection stability of the ink according to the present embodiment by an inkjet recording device.

[0029] (aqueous medium) The aqueous medium is a medium containing water and a specific organic solvent. The aqueous medium may function as a solvent or as a dispersion medium. In addition to water and the specific organic solvent, the aqueous medium may further contain a water-soluble organic solvent other than the specific organic solvent (hereinafter, sometimes referred to as other water-soluble organic solvent).

[0030] In the ink according to this embodiment, the content of the aqueous medium is preferably from 60.00% to 98.00% by mass, and more preferably from 70.00% to 95.00% by mass. By setting the content of the aqueous medium to from 60.00% to 98.00% by mass, the ejection stability of the ink according to this embodiment when used with an inkjet recording device can be optimized.

[0031] (water) In the ink according to this embodiment, the water content is preferably 50.00% by mass to 90.00% by mass, and more preferably 55.00% by mass to 65.00% by mass. By setting the water content to 50.00% by mass to 90.00% by mass, the ejection stability of the ink according to this embodiment by the inkjet recording device can be optimized.

[0032] (Specific organic solvent) The LogP of the specific organic solvent is 0.10 to 2.00, preferably 0.20 to 0.60, and more preferably 0.20 to 0.40. By making the LogP of the specific organic solvent 0.10 to 2.00, the ink according to the present embodiment exhibits high hydrophobicity when dried and the moisture content is reduced. Therefore, the ink according to the present embodiment can easily form an image having a desired image density.

[0033] The viscosity of the specific organic solvent at 25°C is 2.0 mPa·s or more and 350.0 mPa·s or less, preferably 6.0 mPa·s or more and 150.0 mPa·s or less, and more preferably 10.0 mPa·s or more and 150.0 mPa·s or less. By setting the viscosity of the specific organic solvent at 25°C to 2.0 mPa·s or more and 350.0 mPa·s or less, the ejection stability of the ink according to this embodiment by the inkjet recording device can be optimized. Furthermore, by setting the viscosity of the specific organic solvent at 25°C to 2.0 mPa·s or more and 350.0 mPa·s or less, the ink according to this embodiment can be easily removed by cleaning.

[0034] Examples of the specific organic solvent include 3-methyl-1,5-pentanediol (LogP: 0.35) and triethylene glycol monobutyl ether (LogP: 0.44).

[0035] In the ink according to this embodiment, the content of the specific organic solvent is preferably from 5.00% to 40.00% by mass, and more preferably from 15.00% to 25.00% by mass. By setting the content of the specific organic solvent to from 5.00% to 40.00% by mass, it becomes easier to adjust the viscosity of the ink according to this embodiment at 25°C after drying treatment to within the above range.

[0036] (Other water-soluble organic solvents) The other water-soluble organic solvent is a water-soluble organic solvent having a LogP of less than 0.10 or more than 2.00. Examples of the other water-soluble organic solvent include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

[0037] Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, triethylene glycol, and tetraethylene glycol.

[0038] As the other water-soluble organic solvent, a glycol compound is preferable, and 1,3-propanediol is more preferable.

[0039] The content of the other water-soluble organic solvent in the ink according to this embodiment is preferably from 3.00% by mass to 25.00% by mass, and more preferably from 5.00% by mass to 15.00% by mass.

[0040] The total content of the specific organic solvent and other water-soluble organic solvents in the ink according to this embodiment is preferably from 8.00% to 65.00% by mass, and more preferably from 25.00% to 35.00% by mass.

[0041] The aqueous medium preferably contains only water, the specific organic solvent, and 1,3-propanediol. The total content of water, the specific organic solvent, and 1,3-propanediol in the aqueous medium is preferably 90.00% by mass or more, more preferably 99.00% by mass or more, and even more preferably 100.00% by mass.

[0042] (Amine compounds) In the ink according to the present embodiment, the content of the amine compound is preferably 0.05% by mass or more and 1.00% by mass or less, and more preferably 0.05% by mass or more and 0.30% by mass or less. By setting the content of the amine compound to 0.05% by mass or more and 1.00% by mass or less, the ink according to the present embodiment can be more reliably removed by cleaning. Furthermore, by setting the content of the amine compound to 1.00% by mass or less, the increase in the viscosity of the ink according to the present embodiment at 25° C. can be reliably suppressed, and the viscosity of the ink according to the present embodiment at 25° C. can be easily adjusted to the above-mentioned range. Furthermore, by setting the content of the amine compound to 1.00% by mass or less, the pH of the ink according to the present embodiment can be prevented from becoming too high.

[0043] Examples of the amine compound include ethanolamine, diethanolamine, triethanolamine, propanolamine, methylaminoethanol, dimethylaminomethanol, diethylaminoethanol, and dimethylaminoethanol. As the amine compound, triethanolamine and diethylaminoethanol are preferred.

[0044] (Surfactant) The surfactant optimizes the compatibility and dispersion stability of each component contained in the ink according to this embodiment. The surfactant also imparts wettability to the recording medium to the ink according to this embodiment. The surfactant in the ink according to this embodiment is preferably a nonionic surfactant.

[0045] Examples of the nonionic surfactant in the ink according to the present embodiment 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 the acetylene glycol surfactant include an ethylene oxide adduct of acetylene glycol and a propylene oxide adduct of acetylene glycol. The ink according to the present embodiment preferably contains an acetylene glycol surfactant.

[0046] The content of the surfactant in the ink according to this embodiment is preferably from 0.10% by mass to 1.50% by mass, and more preferably from 0.30% by mass to 0.60% by mass.

[0047] (Other Ingredients) The ink according to this embodiment may further contain known additives (more specifically, for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0048] (Preferred composition) The ink according to the present embodiment preferably has any one of compositions 1 to 6 shown in Tables 1 and 2 below. Tables 1 and 2 each show a part of compositions 1 to 6. For example, the components of composition 1 shown in Table 2 show the components of composition 1 shown in Table 1 other than the components shown in Table 1. In addition, in Tables 1 and 2 below, "ratio" shows a numerical range of a preferable content ratio [mass %]. For example, "5.70-6.90" which is the ratio of the pigment in composition 1 in Table 1 indicates that the pigment is contained in an amount of 5.70 mass % or more and 6.90 mass % or less. The same applies to the notations in the other columns. "Resin" indicates a pigment-coated resin. "MPD", "1,3PD", and "BTG" respectively indicate 3-methyl-1,5-pentanediol, 1,3-propanediol, and triethylene glycol monobutyl ether. "DMAE" and "TEA" respectively indicate dimethylaminoethanol and triethanolamine.

[0049] [Table 1]

[0050] [Table 2]

[0051] (Ink manufacturing method according to this embodiment) The ink according to this embodiment can be produced, for example, by mixing a pigment dispersion liquid containing a pigment, an aqueous medium, an amine compound, and other components (for example, a surfactant) that are added as necessary. In producing the ink according to this embodiment, after the components are mixed uniformly, foreign matter and coarse particles may be removed using a filter (for example, a filter with a pore size of 5 μm or less).

[0052] [Second embodiment: Inkjet recording apparatus] An inkjet recording apparatus according to a second embodiment of the present invention will now be described. The inkjet recording apparatus according to this embodiment comprises inkjet ink, a recording head, and a wiper blade. The recording head has nozzles, and performs an ejection operation for ejecting inkjet ink from the nozzles onto a recording medium, and an oscillation operation for oscillating the meniscus of the inkjet ink in the nozzles. The wiper blade performs a wiping operation for wiping the ink ejection surface of the recording head. The inkjet ink is the inkjet ink according to the first embodiment (hereinafter may be simply referred to as ink).

[0053] The inkjet recording apparatus according to the present embodiment, having the above-mentioned configuration, can form an image having a desired image density, and can easily remove ink by cleaning. The reason why the inkjet recording apparatus according to the present embodiment exhibits the above-mentioned effects is presumed to be as follows.

[0054] The inkjet recording apparatus according to this embodiment uses the ink according to the first embodiment, and therefore can form an image having a desired image density, and can easily remove the ink by cleaning.

[0055] Moreover, the recording head of the inkjet recording apparatus according to this embodiment performs a swinging operation to swing the meniscus of the ink in the nozzle, in addition to a discharge operation to discharge ink from the nozzle onto the recording medium. The recording head promotes the diffusion of the ink in the nozzle by the above-mentioned swinging operation, and can suppress thickening of the ink filled near the discharge port. Therefore, even if the ink according to the first embodiment becomes thickened, the swinging operation can eliminate the thickening of the ink according to the first embodiment. Therefore, the inkjet recording apparatus according to this embodiment is suitable as an inkjet recording apparatus for the ink according to the first embodiment.

[0056] The inkjet recording apparatus according to the present embodiment also includes a wiper blade. The wiper blade performs a wiping operation to wipe the ink ejection surface of the recording head. In general, if ink adheres to the ink ejection surface of the recording head, non-ejection or misaligned ejection of ink from the nozzles of the recording head occurs. However, the ink according to the first embodiment is easily removed by cleaning even without using a cleaning liquid. The inkjet recording apparatus according to the present embodiment performs a wiping operation using the wiper blade, so that the ink according to the first embodiment that has adhered to the ink ejection surface of the recording head can be easily removed by cleaning. Therefore, the inkjet recording apparatus according to the present embodiment has excellent ejection stability of the ink according to the first embodiment.

[0057] [Structure of inkjet recording device] The inkjet recording apparatus according to the present embodiment will be described 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.

[0058] FIG. 1 is a diagram showing a main part of an inkjet recording device 100, which is an example of an inkjet recording device according to the present embodiment. FIG. 1 is a diagram showing a main part of the inkjet recording device 100. As shown in FIG. 1, the inkjet recording device 100 mainly includes a conveying section 1, four line-type recording heads 11 (recording heads), and four wipe blades (not shown). 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 recording paper P (recording medium). 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 paper P one by one starting from the topmost recording paper P, and conveys and feeds the paper 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.

[0059] 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 paper P is conveyed in the conveying direction X indicated by the arrow.

[0060] 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 paper P on which an image has been formed to the outside of the device housing. The discharge driven roller 9 is pressed against an upper part of the discharge roller 8 and rotates in response. A paper output tray 10 is provided downstream of the discharge roller 8 and the discharge driven roller 9. The recording paper P discharged to the outside of the device housing is stacked on the paper output tray 10.

[0061] The four line-type recording heads 11 include a first line-type recording head 11C, a second line-type recording head 11M, a third line-type recording head 11Y, and a fourth line-type recording head 11K. The first line-type recording head 11C, the second line-type recording head 11M, the third line-type recording head 11Y, and the fourth line-type recording head 11K each extend in a direction (width direction A) perpendicular to the conveying direction X. The first line-type recording head 11C, the second line-type recording head 11M, the third line-type recording head 11Y, and the fourth line-type recording head 11K are disposed above the conveying belt 5 at approximately equal intervals from the upstream side to the downstream side in the conveying direction X of the recording paper P. Each of the four line-type recording heads 11 is supported at a height such that the distance from the upper surface of the conveying belt 5 is a predetermined length. Each of the four line-type recording heads 11 records an image on the recording paper P conveyed on the conveying belt 5. The four line-type recording heads 11 each contain ink (first ink, second ink, third ink, and fourth ink) of four different colors (cyan, magenta, yellow, and black). Each of the four line-type recording heads 11 ejects ink onto the recording paper P in a predetermined order at a fixed ejection interval T. As a result, a color image is formed on the recording paper P.

[0062] The line-type recording head 11 will be described in detail below with reference to Figures 2 and 3. The first line-type recording head 11C, the second line-type recording head 11M, the third line-type recording head 11Y, and the fourth line-type recording head 11K have almost the same structure. Therefore, in the following description, the first line-type recording head 11C will be used as a representative, but the same description also applies to the second line-type recording head 11M, the third line-type recording head 11Y, and the fourth line-type recording head 11K.

[0063] Fig. 2 is a bottom view of the first line-type recording head 11C of the inkjet recording apparatus 100. Fig. 3 is an enlarged view of a main part of the II cross section of Fig. 2.

[0064] The bottom surface of the first line-type recording head 11C is an ink ejection surface (hereinafter, sometimes simply referred to as the ejection surface) that ejects ink. As shown in Fig. 2, a plurality of ejection ports 224 are opened in an ejection surface 223 of the first line-type recording head 11C. The plurality of ejection ports 224 are arranged in a staggered pattern on the ejection surface 223 so that no blank spaces are formed between adjacent recording dots formed by ejecting ink droplets onto the recording paper P. The plurality of ejection ports 224 are also provided in the longitudinal direction of the ejection surface 223 across the maximum width of the maximum paper on which an image can be formed by the inkjet recording device 100.

[0065] As shown in FIG. 3, the first line-type recording head 11C includes a plurality of nozzles 222 (only one is shown in FIG. 3), a water-repellent film 225, a plurality of ink storage chambers 226 (only one is shown in FIG. 3), an ink tank (not shown), a common flow path 227, a supply hole 228, a nozzle flow path 229, a vibration plate 230, a common electrode 231, a piezoelectric element 232, and an individual electrode 233.

[0066] Each of the plurality of nozzles 222 opens to a discharge surface 223 of the first line-type recording head 11C to form a discharge port 224 (see FIG. 2). The plurality of nozzles 222 are arranged in a plurality of rows along the longitudinal direction of the first line-type recording head 11C.

[0067] The water-repellent film 225 is formed so as to cover the ejection surface 223 except for the ejection ports 224 .

[0068] The ink containing chambers 226 are provided in correspondence with the plurality of ejection ports 224, one for each.

[0069] The ink tanks store ink. The ink tank of the first line recording head 11C communicates with a cyan ink cartridge (not shown) and stores cyan ink supplied from the connected ink cartridge. The ink tanks of the second line recording head 11M, the third line recording head 11Y, and the fourth line recording head 11K communicate with a magenta ink cartridge, a yellow ink cartridge, or a black ink cartridge (none of which are shown), respectively, and store magenta ink, yellow ink, or black ink supplied from the connected ink cartridge.

[0070] The common flow channel 227 supplies ink from an ink tank to each of the plurality of ink containing chambers 226. The plurality of ink containing chambers 226 and the common flow channel 227 are in communication with each other via a supply hole 228.

[0071] The nozzle flow path 229 connects the nozzle 222 with the ink containing chamber 226 .

[0072] The vibration plate 230 constitutes one of the walls of the ink containing chamber 226 on the opposite side to the ejection surface 223. The vibration plate 230 is formed continuously across the multiple ink containing chambers 226.

[0073] The common electrode 231 is formed continuously on the diaphragm 230 across the ink containing chambers 226 .

[0074] The piezoelectric elements 232 are provided on the common electrode 231 in correspondence with each of the ink storage chambers 226 .

[0075] The individual electrodes 233 are provided corresponding to the plurality of ink containing chambers 226 so as to sandwich the piezoelectric elements 232 between the individual electrodes 233 and the common electrode 231 .

[0076] By application of an ejection drive pulse, which will be described later, one dot of ink droplets is ejected from the ejection port 224 onto the recording paper P. Note that even when no ink droplets are being ejected, the nozzle 222 remains filled with ink, and the ink forms a meniscus M within the nozzle 222.

[0077] A control mechanism (not shown) of the inkjet recording device 100 applies an ejection drive pulse to the individual electrode 233, thereby deforming the piezoelectric element 232. The deformation of the piezoelectric element 232 is transmitted to the vibration plate 230, and the ink storage chamber 226 is compressed by the deformation of the vibration plate 230. As a result, pressure is applied to the ink in the nozzle 222, and the ink that has passed through the nozzle 222 is ejected from the ejection port 224 onto the recording paper P as ink droplets.

[0078] The ejection drive pulse is set so that the pulse width is close to half the natural vibration period of the head flow path. Here, the "head flow path" refers to a flow path that includes the nozzle 222, the nozzle flow path 229, the ink storage chamber 226, and the supply hole 228. Thus, the pulse width of the drive voltage applied to the piezoelectric element 232 is also close to half the natural vibration period of the head flow path. With such a drive pulse, one ink droplet is ejected from the ejection port 224. As a result, the first line-type recording head 11C performs an ejection operation in which ink is ejected from the nozzle 222 at a predetermined position onto the recording medium.

[0079] A control mechanism (not shown) of the inkjet recording device 100 applies a driving pulse for oscillation to the individual electrode 233, thereby deforming the piezoelectric element 232. The driving pulse for oscillation is set so that a pulse having a width smaller than the pulse width of the driving pulse for ejection is applied repeatedly multiple times. The pulse width of each driving pulse for oscillation is set shorter than the natural vibration period of the head flow path. Thus, the pulse width of the driving voltage applied to the piezoelectric element 232 is also shorter than the natural vibration period of the head flow path. When such short pulses are successively applied, the flow speed of the ink in the nozzle 222 becomes a value at which the meniscus M is oscillated but ink droplets are not ejected. As a result, the first line-type recording head 11C performs an oscillation operation that oscillates the meniscus M of the ink in the nozzle 222.

[0080] As described above, the ejection operation or the oscillation operation is performed by applying pressure to the ink by the piezoelectric element 232 provided in each of the ink storage chambers 226. Note that the oscillation operation is an operation that oscillates the meniscus M of the ink in the nozzle 222 but does not eject ink droplets from the nozzle 222.

[0081] For example, the first line-type recording head 11C performs a discharge operation immediately after a swinging operation. When performing a plurality of discharge operations in a short period of time, the first line-type recording head 11C may perform the discharge operations continuously without performing a swinging operation between a specific discharge operation and the next discharge operation.

[0082] 4 is a diagram showing a side surface of the first line-type recording head 11C in FIG. 1 and its vicinity. A wiper blade 22 provided in the inkjet recording device 100 is disposed near the first line-type recording head 11C. The wiper blade 22 has a function of wiping the discharge surface 223 in a predetermined direction (leftward in FIG. 4; hereinafter, referred to as the wiping direction W). In this way, the wiper blade 22 performs a wiping operation to wipe the discharge surface 223 of the first line-type recording head 11C. The wiper blade 22 is, for example, a rubber wiper. The linear pressure of the wiper blade 22 is, for example, 5.0 N / m or more and 13.0 N / m or less.

[0083] Further, other wipe blades 22 provided in the inkjet recording apparatus 100 are disposed near the second line type recording head 11M, the third line type recording head 11Y, and the fourth line type recording head 11K.

[0084] Although an example of the inkjet recording apparatus according to the present embodiment has been described above, the inkjet recording apparatus according to the present embodiment is not limited to the one shown in FIGS.

[0085] 1 to 4, an inkjet recording device 100 equipped with four line-type recording heads 11 corresponding to four colors of ink has been described as an example. However, the number of recording heads equipped in the inkjet recording device according to this embodiment is not particularly limited, and can be, for example, 1 to 10, and preferably 3 to 5.

[0086] Furthermore, the inkjet recording apparatus 100 ejects ink of four colors, cyan, magenta, yellow, and black, in that order, but in the inkjet recording apparatus according to this embodiment, the types, combinations, and ejection order of the inks are not limited to this.

[0087] Furthermore, the inkjet recording apparatus 100 oscillates the meniscus M of the ink in the nozzle 222 by applying an oscillation drive pulse to the piezoelectric element 232. However, the inkjet recording apparatus according to this embodiment may oscillate the meniscus of the ink in the nozzle by another mechanism (for example, oscillation of the recording head itself). Therefore, the recording head may be a thermal type recording head.

[0088] Furthermore, the inkjet recording apparatus according to this embodiment may be a multifunction machine that also has the functions of a scanner, a copier, a printer, or a facsimile.

[0089] The recording medium on which the inkjet recording apparatus according to the present embodiment forms an image is preferably a permeable recording medium (e.g., plain paper). When a known inkjet recording apparatus (especially a known inkjet recording apparatus equipped with a line-type recording head) forms an image on plain paper, the image density tends to be insufficient. In contrast, the inkjet recording apparatus according to the present embodiment can form an image having a desired image density even when forming an image on plain paper. EXAMPLES

[0090] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0091] [Viscosity measurement] In the examples, the viscosity of the organic solvent and the ink was measured at a temperature of 25° C. using a torque balance servo type rotational viscometer (TV-100EL, manufactured by Toki Sangyo Co., Ltd.).

[0092] Details of the organic solvents used in the examples are shown in the following Table 3. Note that 3-methyl-1,5-pentanediol and triethylene glycol monobutyl ether were specific organic solvents.

[0093] [Table 3]

[0094] [Ink preparation] Inks (A) to (I) used in the inkjet recording devices of the Examples and Comparative Examples were prepared by the following method. The composition of each ink is shown in Table 4 below.

[0095] (Preparation of Pigment Dispersion) 18.00 parts by mass of carbon black ("Black Pearls (registered trademark) 800" manufactured by Cabot Corporation) as a black pigment, 4.00 parts by mass of a pigment coating resin ("DISPERBYK (registered trademark)-190" manufactured by BYK Japan K.K.), and 78.00 parts by mass of ion-exchanged water were mixed using a disperser. The resulting mixture was subjected to a dispersion treatment using a beads mill to obtain a black pigment dispersion (D of pigment particles) as a pigment dispersion. 50 : 110 nm).

[0096] (Preparation of Ink (A)) A mixed liquid was obtained by mixing 35.00 parts by mass of a black pigment dispersion (6.30 parts by mass of black pigment, 1.40 parts by mass of pigment coating resin, and 27.30 parts by mass of ion-exchanged water), 20.00 parts by mass of 3-methyl-1,5-pentanediol, 10.00 parts by mass of 1,3-propanediol, 0.50 parts by mass of a surfactant (Surfynol (registered trademark) 420 manufactured by Nissin Chemical Industry Co., Ltd., an acetylene surfactant), 0.10 parts by mass of dimethylaminoethanol, and 34.40 parts by mass of ion-exchanged water.

[0097] The above mixture was stirred at 400 rpm using a stirrer ("Three-One Motor BL-600" manufactured by Shinto Scientific Co., Ltd.). Next, the stirred mixture was filtered using a filter with a pore size of 5 μm to remove foreign matter and coarse particles. As a result, ink (A) was obtained.

[0098] (Preparation of Inks (B) to (I)) Inks (B) to (I) were prepared in the same manner as ink (A), except that the types and amounts of raw materials used were changed as shown in Table 4 below. The numbers in Table 4 below indicate the parts by mass of each component. "Resin" indicates pigment-coated resin. "MPD", "1,3PD", and "BTG" indicate 3-methyl-1,5-pentanediol, 1,3-propanediol, and triethylene glycol monobutyl ether, respectively. "DMAE" and "TEA" indicate dimethylaminoethanol and triethanolamine, respectively.

[0099] [Table 4]

[0100] [Ink viscosity measurement] Using the method described above, the viscosities of the inks (A) to (I) were measured at 25° C. The measurement results are shown in Table 5 below.

[0101] [Ink viscosity measurement after drying process] 100.00 parts by mass of the ink to be measured (specifically, any of inks (A) to (I)) was placed in a petri dish. The petri dish was placed in an oven at 40°C and a drying process was carried out. During the drying process, the mass of the measurement object in the petri dish was measured over time. Then, when the mass of the measurement object in the petri dish had decreased to 70.00 parts by mass (the mass of the measurement object had decreased by 30.00% by mass), the drying process was terminated. The viscosity of the measurement object after the drying process at 25°C was measured using the method described above. The measurement results (dry viscosity) are shown in Table 5 below.

[0102] [evaluation] A printing test machine (manufactured by Kyocera Document Solutions Inc.) equipped with a line-type recording head that ejects ink using a piezoelectric method and a wipe blade (linear pressure: 8.0 N / m) was used as the evaluation machine (inkjet recording device). The above-mentioned recording head was capable of performing an ejection operation that ejects ink from the nozzle onto the recording medium (ejected droplet volume: 10 pL, resolution 600 dpi), and an oscillation operation that oscillates the meniscus of the ink in the nozzle. During the oscillation operation, the recording head applied a weak pressure to the nozzle that was not strong enough to eject ink, thereby oscillating the meniscus of the ink in the nozzle. The recording medium used was A4-sized plain paper (Mondi's "Color Copy (registered trademark)", basis weight 90 g / m 2 The conveying speed of the recording medium was set to 350 mm / sec.

[0103] The recording head of the evaluation machine was filled with the ink shown in Table 5 below (specifically, any of inks (A) to (I)), and used as the inkjet recording devices of Examples 1 to 6 and Comparative Examples 1 to 3. The inkjet recording devices of Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated for the image density of the images formed and the cleanability. Cleanability refers to the ease with which the ink can be removed by cleaning using the inkjet recording device. The evaluation results are shown in Table 5 below. The evaluation was performed in an environment of a temperature of 25°C and a humidity of 50% RH, unless otherwise specified.

[0104] [Image Density] A solid image was formed on a recording medium using the evaluation machine. The image density (ID value) of the formed solid image was measured using a fluorescent spectrodensitometer ("FD-5" manufactured by Konica Minolta, Inc.). The image density was judged according to the following criteria.

[0105] (Image density standard) A (Good): ID value is 1.20 or higher. B (bad): ID value is less than 1.20.

[0106] [Cleaning ability] The cleaning performance of the ejection surface of the recording head was evaluated under a normal temperature and humidity environment (an environment with a temperature of 25° C. and a humidity of 60% RH). Using the evaluation machine, solid images (printing rate of 100%, A4 size) were continuously printed on 5,000 sheets of recording media. After printing, a purging process was performed to purge the ink from the recording head of the evaluation machine. Next, a wiping process was performed to wipe the ejection surface of the recording head of the evaluation machine with a wiper blade. This removed the ink adhering to the ejection surface of the recording head. Next, the ejection surface was observed using a microscope to confirm the presence or absence of ink that could not be cleaned and remained. The cleaning performance was judged according to the following criteria.

[0107] (Criteria for evaluating cleaning ability) A (particularly good): No ink was attached to the ejection surface. B (Good): A small amount of ink is attached to the ejection surface. C (poor): Ink is clearly attached to the ejection surface.

[0108] [Table 5]

[0109] As shown in Tables 3 to 5, the inkjet recording apparatus of Examples 1 to 6 included an ink, a recording head, and a wiper blade. The recording head had a nozzle, and performed a discharge operation for discharging ink from the nozzle onto a recording medium, and a vibration operation for vibrating the meniscus of the ink in the nozzle. The wiper blade performed a wiping operation for wiping the ink discharge surface of the recording head. The ink contained a pigment, an aqueous medium, and an amine compound. The aqueous medium contained water and a specific organic solvent. The octanol / water partition coefficient LogP of the specific organic solvent was 0.10 or more and 2.00 or less. The viscosity of the specific organic solvent at 25°C was 2.0 mPa·s or more and 350.0 mPa·s or less.

[0110] The inkjet recording apparatus of Examples 1 to 6 were capable of forming images having the desired image density and were also excellent in cleanability. The inks (A) to (D) and (G) to (H) of Examples 1 to 6 were capable of forming images having the desired image density and were also easily removed by cleaning.

[0111] More specifically, the inks (A) to (D) and (G) to (H) of Examples 1 to 6 have a LogP of 0.10 or more and 2.00 or less, and contain a specific organic solvent with a viscosity at 25°C of 2.0 mPa·s or more and 350.0 mPa·s or less, so that the inks thicken quickly and images with the desired image density can be formed. The viscosity at 25°C of the inks (A) to (D) and (G) to (H) after the drying process in Examples 1 to 6 was 100.0 mPa·s or more and 8200.0 mPa·s or less. The drying process was a process in which the ink was heated at 40°C until the mass of the ink was reduced by 30.00 mass%. Usually, thickened ink for high image density is difficult to remove by cleaning only by wiping the ejection surface of the recording head with a blade wipe without using a cleaning liquid. However, the inks (A) to (D) and (G) to (H) of Examples 1 to 6 contained an amine compound and a specific organic solvent having a viscosity of 2.0 mPa s or more and 350.0 mPa s or less at 25°C, and therefore were easily removed by cleaning without the use of a cleaning liquid.

[0112] On the other hand, the inks (E) and (F) used in the inkjet recording devices of Comparative Examples 1 and 2 contained a specific organic solvent, which enabled the formation of images with the desired image density even on plain paper, but did not contain an amine compound and was therefore difficult to remove by cleaning. The ink (I) used in the inkjet recording device of Comparative Example 3 contained an amine compound and was therefore easy to remove by cleaning, but because an organic solvent was used instead of the specific organic solvent that did not satisfy the condition of a LogP of 0.10 to 2.00 even if the viscosity at 25°C was 2.0 mPa·s to 350.0 mPa·s, the image density of the formed image was poor. [Industrial Applicability]

[0113] The ink and inkjet recording apparatus of the present embodiments can be used to form images. [Explanation of symbols]

[0114] 11: Line type recording head 11C: First line recording head 11M: 2nd line recording head 11Y: 3rd line recording head 11K: 4th line recording head 22: Wipe Blade 100: Inkjet recording device 222: Nozzle 223: Discharge surface (ink discharge surface) M: Meniscus P: Recording paper (recording medium)

Claims

1. The ink contains a pigment, an aqueous medium, and an amine compound, The aqueous medium contains water and a specific organic solvent, The specific organic solvent has an octanol / water partition coefficient Log P of 0.10 or more and 2.00 or less, The specific organic solvent has a viscosity at 25° C. of 2.0 mPa·s or more and 350.0 mPa·s or less.

2. the viscosity of the ink-jet ink after drying treatment is 100.0 mPa·s or more and 8200.0 mPa·s or less at 25° C.; The ink-jet ink according to claim 1 , wherein the drying treatment is a treatment of heating the ink-jet ink at 40° C. until the mass of the ink-jet ink is reduced by 30.00% by mass.

3. The ink-jet ink according to claim 1 , wherein the amine compound comprises at least one of triethanolamine and diethylaminoethanol.

4. The ink-jet ink according to claim 1 or 2, wherein the content of the amine compound is from 0.05% by mass to 1.00% by mass.

5. 3. The ink-jet ink according to claim 1, wherein the specific organic solvent comprises at least one of 3-methyl-1,5-pentanediol and triethylene glycol monobutyl ether.

6. The ink-jet ink according to claim 1 or 2, wherein a content of the specific organic solvent is from 5.00% by mass to 40.00% by mass.

7. The ink-jet ink according to claim 1 or 2, wherein the content of the water is 50.00% by mass or more and 90.00% by mass or less.

8. An inkjet recording apparatus comprising an inkjet ink, a recording head, and a wiper blade, the recording head has nozzles, and performs a discharge operation of discharging the ink-jet ink from the nozzles onto a recording medium, and a vibration operation of vibrating a meniscus of the ink-jet ink in the nozzles; the wiper blade performs a wiping action to wipe the ink ejection surface of the recording head; The inkjet ink according to claim 1 or 2, wherein the inkjet ink is an inkjet ink.

Images