Inkjet ink composition and recording method

Abstract

To provide an inkjet ink composition that prevents curling of a medium and has excellent discharge stability.SOLUTION: An ink jet ink composition includes: a self-dispersible pigment; an alcohol having four carbon atoms or less; an asymmetric alkyl ether; and water. The content of the alcohol is 0.5 to 15 mass% relative to the total amount of the ink jet ink composition, and the content of the water is 10 to 40 mass% relative to the total amount of the ink jet ink composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink-jet ink composition and a recording method. [Background technology]

[0002] Inkjet recording methods are capable of recording high-resolution images using relatively simple equipment and have been rapidly developing in various fields. Various studies have been conducted on curl suppression, ejection stability, and the like. For example, Patent Document 1 discloses an ink that uses water and a specified organic solvent while keeping the surface tension and viscosity within specified ranges, with the aim of providing an inkjet ink that has improved ejection properties and decap suitability during printing, and that is excellent in strike-through resistance, character quality, and curl resistance when printed on plain paper. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-220296 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, self-dispersing pigments have been favorably used in inkjet ink compositions for printing on plain paper. However, it has been found that when a self-dispersing pigment is used as a colorant in the ink composition described in Patent Document 1, the dispersion stability of the pigment decreases, causing ejection defects. [Means for solving the problem]

[0005] The present invention provides an inkjet ink composition comprising a self-dispersing pigment, an alcohol having 4 or less carbon atoms, an asymmetric alkyl ether, and water, wherein the content of the alcohol is 0.5 to 15 mass % relative to the total amount of the inkjet ink composition, and the content of the water is 10 to 40 mass % relative to the total amount of the inkjet ink composition.

[0006] The present invention also provides a recording method comprising a step of ejecting the ink-jet ink composition onto a recording medium by an ink-jet method. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a recording apparatus according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0009] 1. Inkjet ink composition The inkjet ink composition of this embodiment (hereinafter also simply referred to as "ink composition") contains a self-dispersing pigment, an alcohol having 4 or less carbon atoms, an asymmetric alkyl ether, and water, wherein the content of the alcohol is 0.5 to 15 mass % relative to the total amount of the inkjet ink composition, and the content of the water is 10 to 40 mass % relative to the total amount of the inkjet ink composition.

[0010]

[0003] Conventionally, curling has been an issue when an aqueous ink composition containing water as a main solvent component is applied to an absorbent recording medium such as plain paper. This curling occurs when the water contained in the ink composition penetrates into the recording medium, and therefore, reducing the water content of the ink composition is considered to reduce curling. However, reducing the water content can reduce the dispersion stability of the pigment, which can lead to another problem of poor ejection.

[0011] Therefore, in this embodiment, the water content is adjusted to suppress curling, and by using an alcohol having 4 or less carbon atoms in combination with an asymmetric alkyl ether, the dispersibility of the self-dispersion pigment is stabilized even when the water content is relatively low, thereby making it possible to suppress curling and maintain ejection stability.

[0012] The reason why the dispersibility of the self-dispersing pigment is stabilized by using an alcohol having 4 or fewer carbon atoms in combination with an asymmetric alkyl ether is not particularly limited, but it is thought that, for example, the alcohol having 4 or fewer carbon atoms and the asymmetric alkyl ether softly adsorb to the surface of the self-dispersing pigment, thereby increasing the electrostatic repulsion and repulsion due to steric hindrance on the self-dispersing pigment. In addition to this, it is also assumed that the alcohol having 4 or fewer carbon atoms and the asymmetric alkyl ether interact with each other, thereby stabilizing each other. Note that the mechanism of dispersion stabilization is not limited to the above. Below, each component of the ink composition of this embodiment will be described in detail.

[0013] 1.1.Self-dispersing pigments A self-dispersing pigment is a pigment that can be dispersed in an aqueous medium due to hydrophilic groups on its surface, even without the use of a dispersant. The use of such a self-dispersing pigment provides advantages in handling, such as suppressing an increase in the viscosity of the ink composition due to the dispersant.

[0014] The content (solid content) of the self-dispersing pigment is preferably 1.0 to 10 mass %, more preferably 2.0 to 8.0 mass %, and even more preferably 3.0 to 6.0 mass %, relative to the total amount of the ink composition.

[0015] 1.2. Alcohols with 4 or fewer carbon atoms Examples of alcohols having 4 or less carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, t-butanol, and isobutanol. These may be used alone or in combination of two or more.

[0016] Among these, alcohols having 1 to 3 carbon atoms are preferred, and alcohols having 1 to 2 carbon atoms are more preferred. By using such alcohols, the dispersion stability of the self-dispersion pigment tends to be further improved, and the ejection stability tends to be further improved.

[0017] The content of the alcohol having 4 or less carbon atoms is 0.5 to 15% by mass, preferably 1.0 to 12.5% ​​by mass, more preferably 2.5 to 10% by mass, and even more preferably 2.5 to 7.5% by mass, relative to the total amount of the ink composition. When the content of the alcohol having 4 or less carbon atoms is within the above range, the amount of water is relatively reduced, which makes curling less likely to occur and also tends to further improve ejection stability.

[0018] The content of the alcohol having 4 or less carbon atoms is preferably 0.1 to 2.5 parts by mass, more preferably 0.2 to 2.0 parts by mass, and even more preferably 0.5 to 1.5 parts by mass, relative to 1 part by mass of the self-dispersion pigment. When the content of the alcohol having 4 or less carbon atoms relative to the self-dispersion pigment is within the above range, ejection stability tends to be further improved.

[0019] 1.3. Asymmetric alkyl ethers Asymmetric alkyl ether refers to an alkyl ether in which both ends are asymmetric functional groups. Such asymmetric alkyl ethers are not particularly limited, but examples thereof include compounds represented by the following formula (1). The asymmetric alkyl ethers may be used alone or in combination of two or more. R 1 O-(R 3 O) n -R 2 ···(1) (R 1 and R 2 each independently represents a hydroxyl group, an alkyl group, an alkyl group having a hydroxyl group, or an acyl group; R 1 and R 2 are different groups, and R 3 represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 1 to 4.

[0020] R 1 and R 2 The alkyl group represented by the formula (I) is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group.

[0021] The alkyl group having a hydroxyl group is not particularly limited, but examples thereof include alkyl groups in which one or more hydrogen atoms have been substituted with a hydroxyl group.

[0022] R 1 and R 2 The acyl group represented by the formula (I) is not particularly limited, but examples thereof include a formyl group, an acetyl group, a propanoyl group, and a butanoyl group.

[0023] R 1 and R 2 The total number of carbon atoms in is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. Furthermore, n is preferably 1 to 4, more preferably 1 to 3, and even more preferably 2 or 3.

[0024] R1 and R 2 The total number of carbon atoms in R is preferably 1.5 or less, more preferably 0.2 to 1.5, and even more preferably 0.3 to 1.4, relative to n. 1 and R 2 When the ratio of the total number of carbon atoms to n is within the above range, the dispersion stability of the self-dispersion pigment tends to be further improved, and the ejection stability tends to be further improved.

[0025] The asymmetric alkyl ether represented by the formula (1) is not particularly limited, and examples thereof include one or more selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, and diethylene glycol monoethyl ether acetate. Among these, one or more selected from the group consisting of triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, and diethylene glycol monoethyl ether acetate are preferred. By using such an asymmetric alkyl ether, the dispersion stability of the self-dispersion pigment is further improved, and the ejection stability tends to be further improved.

[0026] The content of the asymmetric alkyl ether is preferably 30 to 60% by mass, more preferably 30 to 55% by mass, and even more preferably 35 to 55% by mass, relative to the total amount of the ink composition. When the content of the asymmetric alkyl ether is within the above range, the amount of water is relatively reduced, making curling less likely to occur, and the dispersion stability of the self-dispersion pigment is improved, which tends to further improve ejection stability.

[0027] The content of the asymmetric alkyl ether is preferably 2.5 to 16 parts by mass, more preferably 5.0 to 14 parts by mass, and even more preferably 7.5 to 12 parts by mass, relative to 1 part by mass of the self-dispersion pigment. When the content of the asymmetric alkyl ether relative to the self-dispersion pigment is within the above range, ejection stability tends to be further improved.

[0028] Furthermore, the content of the asymmetric alkyl ether is preferably 1.0 to 100 parts by mass, more preferably 2.5 to 50 parts by mass, and even more preferably 5.0 to 20 parts by mass, relative to 1 part by mass of the alcohol having 4 or fewer carbon atoms. When the content of the asymmetric alkyl ether relative to the alcohol having 4 or fewer carbon atoms is within the above range, ejection stability tends to be further improved.

[0029] 1.4.Water The water content is 10 to 40% by mass, preferably 15 to 40% by mass, and more preferably 20 to 40% by mass, relative to the total amount of the ink composition. A water content of 40% by mass or less suppresses curling of the resulting recorded matter. Furthermore, a water content of 10% by mass or more further improves ejection stability, further improves the color development of the resulting recorded matter, and suppresses strike-through.

[0030] 1.5.Other Ingredients The ink composition of this embodiment may further contain an aprotic solvent, a humectant, a surfactant, and other additives, as needed.

[0031] 1.5. Aprotic Solvents The aprotic solvent is not particularly limited, but examples thereof include 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylimidazolidinone, N,N-diethylacetamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylcaprolactam, N-methyl-pyrrolidone, N-methylpropionamide, β-butyllactone, γ-butyllactone, acetonitrile, dimethyl sulfoxide, sulfolane, tetrahydrofuran, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate, and ethylene carbonate. These may be used alone or in combination of two or more.

[0032] Among these, it is preferable to include at least one selected from the group consisting of N-methyl-2-pyrrolidone, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, γ-butyrolactone, propylene carbonate, and ethylene carbonate, and it is more preferable to include at least one selected from the group consisting of 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, γ-butyrolactone, propylene carbonate, and ethylene carbonate. Such aprotic solvents are highly polarizable, and even when used in place of water, the decrease in dielectric constant is small. Therefore, the ejection stability tends to be further improved.

[0033] The content of the aprotic solvent is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and even more preferably 15 to 30% by mass, relative to the total amount of the ink composition. When the content of the aprotic solvent is within the above range, the amount of water is relatively reduced, making curling less likely to occur, and the ejection stability and color development of the resulting recorded matter tend to be further improved.

[0034] Moisturizers The moisturizing agent is not particularly limited, but examples thereof include solvents with relatively high boiling points such as glycerin, propylene glycol, and diethylene glycol. These may be used alone or in combination of two or more. The normal boiling point of the moisturizing agent is preferably 180°C or higher, more preferably 200°C or higher.

[0035] The content of the humectant is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass, relative to the total amount of the ink composition. When the content of the humectant is within the above range, ejection stability tends to be further improved.

[0036] Surfactants The surfactant is not particularly limited, but examples thereof include acetylene glycol surfactants, fluorine-based surfactants, and silicone-based surfactants. Among these, it is preferable to use an acetylene glycol surfactant and a silicone-based surfactant in combination.

[0037] The acetylene glycol surfactant is not particularly limited, but is preferably at least one selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol.

[0038] The fluorine-based surfactant is not particularly limited, but examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds.

[0039] Examples of silicone surfactants include polysiloxane compounds and polyether-modified organosiloxanes.

[0040] The content of the surfactant is preferably 0.1 to 2.0% by mass, more preferably 0.3 to 1.5% by mass, and even more preferably 0.5 to 1.0% by mass, relative to the total amount of the ink composition.

[0041] 2. Recording method The recording method of this embodiment includes a discharge step of discharging the ink composition onto a recording medium by an inkjet method, and may also include a drying step, etc., as necessary.

[0042] 2.1.Discharge process In the ejection process, ink is ejected from the inkjet head and deposited on the recording medium. More specifically, a pressure generating means provided in the inkjet head is driven to eject ink filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called the inkjet method.

[0043] Inkjet heads used in the ejection step include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0044] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the recording device. The recording medium is then moved in the sub-scanning direction (the direction in which the recording medium is transported), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to record an image on the recording medium.

[0045] In the serial method using a serial head, for example, the inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved in the main scanning direction (the width direction of the recording medium), and ink droplets are ejected from the nozzles of the head in conjunction with this movement to record an image on the recording medium.

[0046] 2.2. Recording Media The recording medium used in this embodiment is not particularly limited, but examples thereof include absorbent and non-absorbent recording media. Among these, the present invention is particularly effective for absorbent recording media, which are prone to problems such as curling.

[0047] Absorbent recording media include, but are not limited to, plain paper such as electrophotographic paper, which has high ink permeability, inkjet paper (paper specifically for inkjet printing, which has an ink absorbing layer made of silica particles or alumina particles, or an ink absorbing layer made of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), art paper, coated paper, cast paper, and the like, which are used in general offset printing and have relatively low ink permeability.

[0048] Of these, plain paper is preferred as the recording medium, and the present invention is effective for plain paper, since it is prone to problems such as curling.

[0049] Here, the "absorbent recording medium" is defined as a recording medium having a water absorption rate of 10 mL / m2 within 30 msec from the start of contact in the Bristow method. 2 This refers to a recording medium that exceeds the specified limit. The Bristow method is the most widely used method for measuring liquid absorption in a short period of time, and is also adopted by the Japan Pulp and Paper Technical Association (JAPAN TAPPI). Details of the test method are described in Standard No. 51 "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method" of the "JAPAN TAPPI Paper and Pulp Test Method 2000 Edition."

[0050] 3. Recording device The recording apparatus of this embodiment includes an inkjet head having nozzles for ejecting inkjet ink onto a recording medium, and a transport unit for transporting the recording medium. The inkjet head includes pressure chambers to which ink is supplied and nozzles for ejecting the ink. The transport unit is composed of a transport roller and a transport belt provided within the recording apparatus.

[0051] The recording device according to this embodiment will be described below with reference to Fig. 1. In the XYZ coordinate system shown in Fig. 1, the X direction indicates the length direction of the recording medium, the Y direction indicates the width direction of the recording medium on the transport path within the recording device, and the Z direction indicates the height direction of the device.

[0052] As an example, the recording device 10 is a line-type inkjet printer capable of high-speed, high-density printing. The recording device 10 includes a feed unit 12 that stores recording media P such as paper, a conveyance unit 14, a belt conveyance unit 16, a recording unit 18, an Fd (face-down) discharge unit 20 as an "discharge unit," an Fd (face-down) loading unit 22 as a "loading unit," a reversing path unit 24 as a "reversing conveyance mechanism," an Fu (face-up) discharge unit 26, and an Fu (face-up) loading unit 28.

[0053] The feeding unit 12 is disposed at the bottom of the recording device 10. The feeding unit 12 includes a feeding tray 30 that stores recording media P, and a feeding roller 32 that sends the recording media P stored in the feeding tray 30 to the transport path 11.

[0054] The recording medium P stored in the feed tray 30 is fed by a feed roller 32 along the conveying path 11 to the conveying unit 14. The conveying unit 14 includes a conveying drive roller 34 and a conveying driven roller 36. The conveying drive roller 34 is driven to rotate by a drive source (not shown). In the conveying unit 14, the recording medium P is nipped between the conveying drive roller 34 and the conveying driven roller 36 and conveyed to the belt conveying unit 16 located downstream of the conveying path 11.

[0055] The belt conveying section 16 includes a first roller 38 located upstream on the conveying path 11, a second roller 40 located downstream, an endless belt 42 rotatably attached to the first roller 38 and the second roller 40, and a support 44 that supports the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0056] The endless belt 42 is driven by the first roller 38 or the second roller 40, which is driven by a drive source (not shown), so as to move from the +X direction to the −X direction in the upper section 42a. Therefore, the recording medium P conveyed from the conveying unit 14 is further conveyed downstream of the conveying path 11 in the belt conveying unit 16.

[0057] The recording unit 18 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. The recording unit 18 may also be a serial type in which the inkjet head is mounted on a carriage that moves back and forth in the Y-axis direction. The inkjet head 48 is disposed to face the upper section 42a of the endless belt 42 supported by the support body 44. The inkjet head 48 ejects ink toward the recording medium P as the recording medium P is transported in the upper section 42a of the endless belt 42, thereby performing recording. The recording medium P is transported downstream of the transport path 11 by the belt transport unit 16 while recording is being performed.

[0058] A line-type inkjet head is a head that is used in a recording device in which the nozzle area formed in a direction intersecting the transport direction of the recording medium P is arranged so as to be able to cover the entire intersecting direction of the recording medium P, and which forms an image by fixing one of the head or the recording medium P and moving the other. The nozzle area in the intersecting direction of the line head does not have to be able to cover the entire intersecting direction of all recording media P that the recording device supports.

[0059] Furthermore, a first branch section 50 is provided downstream of the conveying path 11 of the belt conveying unit 16. The first branch section 50 is configured to be switchable between the conveying path 11 that conveys the recording medium P to the Fd discharge unit 20 or the Fu discharge unit 26 and a reversing path 52 of the reversing path section 24 that reverses the recorded side of the recording medium P and conveys the recording medium P again to the recording unit 18. Note that the recording medium P that is switched to the reversing path 52 by the first branch section 50 and conveyed has its recorded side reversed during the conveying process on the reversing path 52, and is conveyed again to the recording unit 18 so that the side opposite to the initially recorded side faces the inkjet head 48.

[0060] A second branch section 54 is further provided downstream of the first branch section 50 along the conveying path 11. The second branch section 54 is configured to be able to switch the conveying direction of the recording medium P so that the recording medium P is conveyed toward the Fd discharge section 20 or the recording medium P is conveyed toward the Fu discharge section 26.

[0061] The recording medium P transported from the second branching section 54 toward the Fd discharge section 20 is discharged from the Fd discharge section 20 and placed on the Fd placement section 22. At this time, the recording medium P is placed so that the recorded surface faces the Fd placement section 22. Also, the recording medium P transported from the second branching section 54 toward the Fu discharge section 26 is discharged from the Fu discharge section 26 and placed on the Fu placement section 28. At this time, the recording medium P is placed so that the recorded surface faces away from the Fu placement section 28.

[0062] In recording devices using the inkjet method, liquid ink is applied to a recording medium, which can cause problems such as curling of the recording medium, particularly absorbent recording media such as plain paper and inkjet paper. In contrast, in this embodiment, the water content can be made relatively low, which can suppress curling.

[0063] Although the above description is of an example in which a line-type inkjet head is used, the recording device according to this embodiment may also be a printer that uses a serial-type inkjet head (serial printer). In a serial printer, printing is performed by transporting the recording medium in the transport direction while moving the inkjet head in a direction intersecting the transport direction. [Example]

[0064] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0065] 1. Ink Preparation The inkjet ink compositions of each example were obtained by placing the components in a mixing tank, mixing and stirring, and filtering through a 5 μm membrane filter so as to obtain the compositions shown in Tables 1 and 2. The numerical values ​​for each component shown in each example in the tables represent % by mass unless otherwise specified. Furthermore, the numerical values ​​for pigments in the tables represent % by mass of the solid content.

[0066] [Table 1]

[0067] [Table 2]

[0068] The abbreviations and product ingredients used in Tables 1 and 2 are as follows: [Self-dispersing pigment] Aqua-Black 162 (Tokai Carbon Co., Ltd.) [Alcohols with 4 or fewer carbon atoms] ethanol [Aprotic Solvent] N-methyl-pyrrolidone 2-pyrrolidone 1-(2-hydroxyethyl)-2-pyrrolidone gamma-butyrolactone Propylene Carbonate Ethylene carbonate [Asymmetric alkyl ether] DEGmBE (Diethylene glycol monobutyl ether) TEGmME (triethylene glycol monomethyl ether) TEGmBE (triethylene glycol monobutyl ether) EDGAC (Diethylene glycol monoethyl ether acetate) [Symmetric alkyl ether] triethylene glycol [Moisturizer] glycerin [Surfactant] E1010 (acetylene glycol surfactant, manufactured by Air Products, Olfine E1010) BYK307 (silicone surfactant, manufactured by BYK Japan)

[0069] 2. Evaluation Method 2.1.Curl evaluation The ink prepared as described above was filled into an EPSON M105 printer, and a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m) was used. 2 A solid pattern with 100% duty was printed on a sheet of paper (88μm thick) at a temperature of 25℃ and humidity of 50%, and then the sheet was placed face up on the floor to check the amount of lift at the point where the gap between the floor and the printed surface was maximum. Based on the amount of lift obtained, curl was evaluated according to the following evaluation criteria. [Evaluation criteria] A: Floating amount less than 5mm B: Floating amount: 5mm or more but less than 10mm C: Floating amount: 10mm or more but less than 20mm D: Floating amount 20mm or more

[0070] 2.2. Discharge stability (immediately after ink filling) The ink prepared as described above was filled into an EPSON M105 printer, and a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m) was used. 2 The nozzle check pattern was checked after printing 20 consecutive pages of Microsoft Word documents (font size 11, standard, MSP Gothic) at a rate of 700 characters per page on a sheet of paper (88 μm thick) at a temperature of 25°C and humidity of 50%. [Evaluation criteria] A: 0 missing nozzles B: 1-2 missing nozzles C: 3 to 5 missing nozzles D: 6 or more nozzles missing

[0071] 2.3. Discharge stability (1 week after ink refill) The ink prepared as described above was filled into an Epson M105 printer and left for one week in an environment of 25°C temperature and 50% humidity. After that, the ink was printed on a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m). 2The nozzle check pattern was checked after printing 20 consecutive pages of Microsoft Word documents (font size 11, standard, MSP Gothic) at a rate of 700 characters per page on a sheet of paper (88 μm thick) at a temperature of 25°C and humidity of 50%. [Evaluation criteria] AA: 1 to 2 missing nozzles A: 3 to 5 missing nozzles B: 6 to 15 missing nozzles C: 16 to 24 missing nozzles D: 25 or more nozzles missing

[0072] 2.3. Color development and bleed-through The ink prepared as described above was filled into an EPSON M105 printer, and a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m) was used. 2 A solid pattern was printed with 100% duty on a printing area of ​​204mm x 291mm on a sheet of paper (88μm thick) at a temperature of 25°C and humidity of 50%. The optical density (OD value) of the printed surface and back surface of the resulting recorded matter was measured using a colorimeter "Xrite i1" (product name, manufactured by Xrite Corporation). Of the obtained measurements, the color development was evaluated from the measurement value of the printed surface, and the bleed-through was evaluated from the measurement value of the back surface. [Evaluation criteria (coloring)] A:OD value is 1.2 or more B: OD value is 1.1 or more but less than 1.2 C:OD value is less than 1.1 [Evaluation criteria (bleed-through)] A:OD value is less than 0.25 B: OD value is 0.25 or more and less than 0.35 C:OD value is 0.35 or more

[0073] 3. Evaluation Results The ink compositions and evaluation results used in each example are shown in Tables 1 and 2. Tables 1 and 2 show that by keeping the water content within a specified range and using an alcohol having four or fewer carbon atoms in combination with an asymmetric alkyl ether, curling of the resulting printed matter can be suppressed and ejection stability is excellent. [Explanation of symbols]

[0074] 10 recording device, 11 transport path, 12 feeding section, 14 transport section, 16 belt transport section, 18 recording section, 20 Fd discharge section, 22 Fd placement section, 24 reversing path section, 26 Fu discharge section, 28 Fu placement section, 30 feeding tray, 32 feeding roller, 34 transport drive roller, 36 transport driven roller, 38 first roller, 40 second roller, 42 endless belt, 42a upper section of endless belt, 44 support, 46 head holder, 48 inkjet head, 50 first branch section, 52 reversing path, 54 second branch section, 56 discharge roller pair, 64 discharge drive roller, 68 drive shaft, 76 placement surface, 78 convex portion, 80 first urging member, 82 second urging member, 84, 86 support shaft, P recording medium

Claims

1. a self-dispersing pigment, an alcohol having 4 or less carbon atoms, an asymmetric alkyl ether, and water; the content of the alcohol is 0.5 to 15% by mass relative to the total amount of the inkjet ink composition; the content of the water is 10 to 40% by mass relative to the total amount of the inkjet ink composition; the content of the asymmetric alkyl ether is 30 to 60% by mass relative to the total amount of the inkjet ink composition; Inkjet ink composition.

2. the content of the self-dispersion pigment is 1.0 to 10% by mass relative to the total amount of the inkjet ink composition; The ink-jet ink composition of claim 1 .

3. the content of the alcohol is 0.1 to 2.5 parts by mass relative to 1 part by mass of the self-dispersion pigment; The ink-jet ink composition according to claim 1 or 2.

4. The asymmetric alkyl ether includes a compound represented by the following formula (1): The ink-jet ink composition according to any one of claims 1 to 3. R 1 O-(R 3 O) n -R 2 ・・・(1) (R 1 and R 2 each independently represents a hydroxyl group, an alkyl group, an alkyl group having a hydroxyl group, or an acyl group; R 1 and R 2 are different groups, and R 3 represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 1 to 4.

5. In formula (1), R 1 and R 2 the total number of carbon atoms in the formula (I) is 1.5 or less relative to n; The ink-jet ink composition of claim 4.

6. The asymmetric alkyl ether includes at least one selected from the group consisting of triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, and diethylene glycol monoethyl ether acetate. The ink-jet ink composition according to any one of claims 1 to 5.

7. containing aprotic solvents, The ink-jet ink composition according to any one of claims 1 to 6.

8. the aprotic solvent comprises at least one selected from the group consisting of 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, γ-butyrolactone, propylene carbonate, and ethylene carbonate; The ink-jet ink composition of claim 7.

9. the content of the aprotic solvent is 10 to 40% by mass relative to the total amount of the inkjet ink composition; The ink-jet ink composition according to claim 7 or 8.

10. a step of ejecting the inkjet ink composition according to any one of claims 1 to 9 onto a recording medium by an inkjet method; Recording method.

11. The recording medium is plain paper. The recording method according to claim 10.

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