Inkjet recording method and recording apparatus

Abstract

The invention provides an ink jet recording method and a recording apparatus. The ink jet recording method is excellent in clogging restorability, color rendering property and storage stability. The inkjet recording method includes: a transport step of transporting a recording medium by a transport unit; and an attachment step of ejecting an ink composition from an inkjet head, which is a line head having a length equal to or greater than a recording region of the recording medium in a direction intersecting the direction of conveyance, and attaching the ink composition to the recording medium being an absorbent recording medium, the ink composition is a red water-based ink containing a pigment, the pigment contains an azo pigment, and when 10 parts by mass of the ink composition and 1 part by mass of a calcium propionate aqueous solution having a Ca element concentration of 0.3 mol / L are mixed, the viscosity [eta] 1 of a mixed solution is less than 2.0 times the viscosity [eta] 0 of the ink composition.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method and a recording apparatus. Background Art

[0002] Inkjet recording methods, capable of recording high-definition images using relatively simple equipment, have seen rapid development in various areas. Among these, various studies have focused on issues such as clogging recovery. For example, Patent Document 1 discloses an ink composition containing a specific amine compound for the purpose of suppressing nozzle dropout and clogging.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-006556

[0004] When high-speed recording is performed on an absorptive recording medium using a recording device having a line head, there are problems such as poor color development, poor discharge stability, and poor clogging recovery. Summary of the Invention

[0005] The inkjet recording method of the present invention comprises: a conveying step of conveying a recording medium by a conveying unit; and an attaching step of ejecting an ink composition from an inkjet head and attaching the ink composition to the recording medium conveyed by the conveying step, wherein the inkjet head is a line head having a length greater than a recording area of ​​the recording medium in a direction intersecting the conveying direction, the recording medium is an absorptive recording medium, the ink composition is a red aqueous ink containing a pigment, the pigment contains an azo pigment, and the viscosity η1 of a mixed solution obtained by mixing 10 parts by mass of the ink composition and 1 part by mass of a calcium propionate aqueous solution having a Ca element concentration of 0.3 mol / L is less than 2.0 times the viscosity η0 of the ink composition.

[0006] The recording apparatus of the present invention is an inkjet recording apparatus for obtaining a recorded object by the above-mentioned inkjet recording method, and the inkjet recording apparatus includes the above-mentioned ink composition, the above-mentioned inkjet head, and the above-mentioned transport unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Table 1 shows the compositions of the ink compositions used in Examples and the evaluation results thereof.

[0008] Figure 2 Table 2 shows the compositions of the ink compositions used in Examples and the evaluation results thereof.

[0009] Figure 3 Table 3 shows the compositions of the ink compositions used in Examples and the evaluation results thereof.

[0010] Figure 4This is a diagram showing an example of an ink supply mechanism of a recording device used in the recording method of this embodiment.

[0011] Figure 5 This is a diagram showing an example of a recording device used in the recording method of this embodiment.

[0012] Description of Reference Numerals

[0013] 100: carriage; 2: droplet ejection head group; 3: container; 4: ink container; 5: pressure sensor; 6: on / off valve; 7a, 7b, 7c: piping; 8: pressure regulating valve; 10: recording device; 11: conveying path; 12: feed section; 14: conveying section; 16: belt conveying section; 18: recording section; 20: Fd discharge section; 22: Fd loading section; 24: reversing path section; 26: Fu discharge section; 28: Fu loading section; 30: feed tray; 32: feed roller; 34: conveying Driving roller; 36: Conveying driven roller; 38: First roller; 40: Second roller; 42: Endless belt; 42a: Upper section of the endless belt; 44: Support body; 46: Head bracket; 48: Inkjet head; 50: First branch portion; 52: Reversing path; 54: Second branch portion; 56: Discharge roller pair; 64: Discharge driving roller; 68: Driving shaft; 76: Loading surface; 78: Convex portion; 80: First force applying member; 82: Second force applying member; 84, 86: Support shafts; P: Recording medium. DETAILED DESCRIPTION

[0014] Below, an embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described in detail with reference to the accompanying drawings as needed. However, the present invention is not limited thereto and various modifications are possible without departing from the spirit and scope of the present invention. In the drawings, identical elements are denoted by the same reference numerals, and duplicate descriptions are omitted. Furthermore, positional relationships, such as up and down, left and right, are based on those shown in the drawings unless otherwise specified. Furthermore, dimensional ratios in the drawings are not limited to those shown.

[0015] 1. Inkjet recording method

[0016] The inkjet recording method involved in this embodiment (hereinafter also referred to as "the present recording method") includes an attachment step of ejecting an ink composition from an inkjet head and attaching the ink composition to the above-mentioned recording medium being transported, the above-mentioned inkjet head is a line head having a length greater than the recording area of ​​the above-mentioned recording medium in a direction intersecting the above-mentioned transport direction, the above-mentioned recording medium is an absorptive recording medium, the above-mentioned ink composition is a red-based aqueous ink containing a pigment, the above-mentioned pigment includes an azo pigment, and the viscosity η1 of the mixed liquid when 10 parts by mass of the above-mentioned ink composition and 1 part by mass of a calcium propionate aqueous solution having a Ca element concentration of 0.3 mol / L is mixed is less than 2.0 times the viscosity η0 of the above-mentioned ink composition.

[0017] In absorbent recording media such as plain paper, the recording medium may contain a calcium salt component. For example, at least the surface of the recording medium may contain the calcium salt component, or the recording medium may include a layer containing the calcium salt component. For example, the recording medium may also be coated with a layer containing the calcium salt component.

[0018] Such recording media tend to have enhanced ink color development due to the calcium salt component contained in the recording medium. For example, it is believed that the pigment contained in the ink that adheres to the recording medium reacts with the calcium salt, causing the pigment to aggregate and become less likely to penetrate the recording medium, thereby improving color development.

[0019] In addition, when using a line printer to print at high speed, a large amount of dust from the paper containing calcium salts of the recording medium is generated in the recording device. The dust attached to the nozzle reacts with the ink and the viscosity increases, or the ink condenses and then dries and solidifies in the nozzle, resulting in the problem that the blockage cannot be restored even if the nozzle is cleaned. In addition, it is known that such a problem is easy to occur when a line printer is used for long-term continuous printing. Therefore, it is required that the composition of the ink with low reactivity and the ability to suppress the viscosity increase is low even when mixed with calcium salts.

[0020] In addition, in line printers, because the recording medium is transported at high speed, there is a tendency for the recording medium to be transported incorrectly or easily contacted with the nozzle. In this case, the ink also aggregates and dries and solidifies at the nozzle, causing the same problem.

[0021] On the other hand, when the reactivity with calcium salts is suppressed, the ink easily penetrates the interior of the recording medium when it lands on it, resulting in poor color rendering. Conversely, increasing the pigment concentration to improve color rendering is considered, but this further raises concerns about increased viscosity and reduced ink jetting stability. Especially when printing at high speed using a line printer, the amount of ink supplied to the line head is high. Therefore, if the ink viscosity is high, the ink supply to the line head is reduced, preventing it from being delivered in time, leading to reduced jetting stability. Therefore, it is difficult to increase the pigment concentration in the ink.

[0022] In contrast, the recording method of this embodiment uses azo pigments that suppress reactivity with calcium salts and contain red-based pigments with excellent color development. Using such pigments reduces the reactivity of the ink composition with calcium salts, suppresses clogging, and maintains color development. This provides an inkjet recording method with excellent color development, ejection stability, and clogging recovery.

[0023] The following describes in detail the ink composition used in the recording method in each step included in the present recording method.

[0024] The recording method includes: a conveying step of conveying a recording medium by a conveying unit; and an attaching step of ejecting an ink composition from an inkjet head and attaching the ink composition to the conveyed recording medium, wherein the inkjet head is a line head having a length greater than the recording area of ​​the recording medium in a direction intersecting the conveying direction.

[0025] In a line-type printing method using a line head, the head is fixed while the recording medium moves in the secondary scanning direction (the longitudinal direction of the recording medium, or the conveying direction). In conjunction with this movement, ink droplets are ejected from the head's nozzle openings, thereby recording an image on the recording medium. In line-type printing methods using a line head, the head is fixed (almost) without movement, and recording is performed in a single stroke (single pass). This makes it suitable for high-volume, high-speed printing. However, due to the high speed of recording medium conveyance and the large amount of recording medium conveyed, this method is particularly useful, as it generates a large amount of paper dust and is prone to errors in recording medium conveyance.

[0026] A line head comprises a cavity that ejects the contained ink composition from a nozzle; an ejection drive unit, provided for each cavity, that applies a driving force to eject the ink; and a nozzle, provided for each cavity, that ejects the ink composition toward the exterior of the head. Multiple cavities, ejection drive units, and nozzles provided for each cavity can be independently provided in a single head. The ejection drive unit can be formed using an electromechanical transducer such as a piezoelectric element that changes the cavity volume through mechanical deformation, or an electrothermal transducer that generates bubbles in the ink by generating heat for ejection.

[0027] 2. Ink composition

[0028] In this recording method, the ink composition is a red aqueous ink containing a pigment, the pigment includes an azo pigment, and the viscosity η1 of the mixed liquid when 10 parts by mass of the above ink composition and 1 part by mass of a calcium propionate aqueous solution having a Ca element concentration of 0.3 mol / L is less than 2.0 times the viscosity η0 of the above ink composition.

[0029] This can reduce the reactivity of the ink composition with the calcium salt, suppress clogging, and maintain color development, even in a situation where paper dust easily accumulates in the nozzles during high-speed, long-term printing using a line printer.

[0030] Furthermore, the viscosity η1 is preferably 1.7 times or less, more preferably 1.5 times or less, relative to the viscosity η0. When the ratio η1 / η0, which represents the rate of change in viscosity, is within the above range, the present invention exhibits excellent clogging recovery, color development, and discharge stability.

[0031] The lower limit of the viscosity change is not particularly limited, but is preferably 1 time or more, and more preferably 1.3 times or more.

[0032] Note that η1 and η0 are values ​​obtained after the mixture is mixed and stirred, then left at 60°C for 24 hours. Viscosity measurements are based on the viscosity at 25°C. When measuring viscosity, the mixed solution is stirred, and a sample with uniform composition is used. For example, calcium propionate pentahydrate can be used.

[0033] The value of the viscosity η1 relative to the viscosity η0 can also be adjusted by adjusting the type of pigment and the content of the pigment.

[0034] Pigments

[0035] The ink composition contains an azo pigment as a pigment. By containing the azo pigment, excellent color development can be obtained even when the reactivity of the ink with the calcium salt is suppressed.

[0036] The ink may contain other pigments in addition to the azo pigment.

[0037] Examples of other pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthraquinone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, and azomethine pigments.

[0038] 2.1.1. Azo pigments

[0039] The ink composition of this embodiment includes an azo pigment. Examples of azo pigments include monoazo pigments, disazo pigments, condensed disazo pigments, and benzimidazolone pigments. Among azo pigments, a pigment capable of coloring a red color is used.

[0040] The ink composition of this embodiment is a red-based ink. Red-based inks are primarily used to express red when printing with multiple inks to reproduce secondary or higher colors. Examples include magenta ink, red ink, and similar inks.

[0041] The red ink is preferably magenta ink. Magenta ink is an ink typically used as an ink set along with cyan ink, yellow ink, and, if necessary, black ink. For example, commercially available ink cartridges typically include inks labeled "magenta ink" and all inks reminiscent of magenta ink.

[0042] Red refers to a color with a hue angle within the specified range in the L*a*b* color system standardized by the CIE (International Commission on Illumination). The hue angle of red is preferably 5° to 60°, 15° to 50°, or 25° to 40°. Red-based inks are primarily used for printing red. Inks that can independently express this red color are preferred.

[0043] The recording method of this embodiment can also be performed using cyan ink, yellow ink, and, if necessary, black ink.

[0044] Red inks are used to record red images, and red images are particularly required to have high visibility. Furthermore, red inks come in a wide variety of pigments. Therefore, this embodiment is particularly useful in the case of red inks.

[0045] Azo pigments are azo pigments, and any pigment that can make the inkjet ink composition function as a red ink can be used. For example, azo pigments numbered CI Pigment Red can be used.

[0046] Specific examples of such azo pigments include CI Pigment Red 5, CI Pigment Red 17, CI Pigment Red 22, CI Pigment Red 31, CI Pigment Red 48:1, CI Pigment Red 48:2, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 146, CI Pigment Red 150, CI Pigment Red 185, CI Pigment Red 114, CI Pigment Red 146, CI Pigment Red 150, CI Pigment Red 170, CI Pigment Red 184, CI Pigment Red 185, CI Pigment Red 208, CI Pigment Red 245, CI Pigment Red 268, CI Pigment Red 269, and solid solutions thereof.

[0047] The ink composition preferably contains, as an azo pigment, one or more compounds selected from the group consisting of CI Pigment Red 150, CI Pigment Red 269, and CI Pigment Red 17. The use of such compounds as azo pigments tends to further enhance the clogging recovery, color development, and ejection stability effects of the present invention.

[0048] Furthermore, from the viewpoint of obtaining an image with more excellent color development, azo pigments are preferably compounds represented by the following formula (I) and solid solutions thereof: In formula (I), A represents a hydrogen atom or an aromatic group.

[0049]

[0050] Here, the aromatic group refers to a group having an aromatic ring such as a benzene ring or a naphthalene ring, and the aromatic ring may be substituted or unsubstituted. In addition, the aromatic ring is directly bonded to the nitrogen atom to which the aromatic group is bonded. Furthermore, when the aromatic ring has a substituent, the substituent is not particularly limited, and may be, for example, an organic group or an inorganic group, and the number of substituents can be arbitrarily selected. The substituent is not limited, and examples thereof include alkyl, halide, alkoxy, hydroxyl, carboxyl, amino, and nitro groups.

[0051] The azo pigment may be a resin-dispersed pigment dispersed in a resin, or a self-dispersed pigment in which a functional group is introduced by treating the pigment surface. Resin-dispersed pigments are preferred.

[0052] The volume average particle diameter D50 of the azo pigment is preferably 110 nm or less. The volume average particle diameter D50 of the azo pigment can be measured using a particle size distribution analyzer. Examples of particle size distribution analyzers include particle size distribution meters based on dynamic light scattering (e.g., the "Nanotrac series" manufactured by Microtrac BEL). The volume average particle diameter is the D50 value. Furthermore, the volume average particle diameter is preferably 10 nm or more and 110 nm or less, more preferably 50 nm or more and 110 nm or less, and even more preferably 80 nm or more and 110 nm or less.

[0053] The solid content of the azo pigment is preferably 0.3% by mass or greater relative to the total amount of the ink composition. Furthermore, it is preferably 10% by mass or less. Furthermore, it is preferably 1% to 9% by mass, more preferably 2% to 8% by mass, even more preferably 3% to 7% by mass, and particularly preferably 4% to 6% by mass. Furthermore, it is preferably 5% by mass or greater.

[0054] This tends to further enhance the effects of clogging recovery, color development, and discharge stability.

[0055] The solid content of the azo pigment is preferably 15% by mass to 100% by mass, 25% by mass to 100% by mass, 45% by mass to 100% by mass, 65% by mass to 100% by mass, or 85% by mass to 100% by mass, relative to the total amount of the pigment.

[0056] On the other hand, the solid content of the azo pigment is preferably 90% by mass or less, more preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less, relative to the total amount of the pigment.

[0057] This tends to further enhance the effects of clogging recovery, color development, and discharge stability.

[0058] The ink composition of this embodiment is preferably a magenta ink. The recording method of the present invention is particularly effective when using a magenta ink.

[0059] The ink composition preferably further includes a quinacridone pigment as an additional pigment. The inclusion of a quinacridone pigment further enhances lightfastness, making it suitable for outdoor use of recorded materials. Examples of quinacridone pigments include CI Pigment Violet 19 and CI Pigment Red 122, with CI Pigment Violet 19 being preferred.

[0060] When other pigments are included, the solid content of the other pigments is preferably 0.1% to 1.6% by mass, 0.2% to 1.2% by mass, or 0.3% to 1.0% by mass relative to the total amount of the ink composition. This tends to further improve light resistance.

[0061] When other pigments are included, the solid content of the other pigments is preferably 1% by mass to 85% by mass, 1% by mass to 65% by mass, 1% by mass to 45% by mass, or 1% by mass to 25% by mass relative to the total amount of the pigments. This tends to further improve light resistance.

[0062] Among other pigments, the content of the quinacridone pigment can also be adjusted to fall within the above range, which is preferred.

[0063] The total solid content of the pigments is preferably 0.3% to 10% by mass, 0.5% to 10% by mass, 0.6% to 9% by mass, 0.7% to 8% by mass, or 0.8% to 7% by mass, relative to the total mass of the ink composition. Furthermore, it is more preferably 2 to 8% by mass, even more preferably 3 to 7% by mass, and particularly preferably 4 to 6% by mass. Furthermore, it is preferably 5% or more by mass.

[0064] When the content of the pigment is within the above range, color development, discharge stability, and clogging recovery tend to be more excellent.

[0065] The ink composition may also contain a resin dispersant for dispersing the pigment. Preferred resin dispersants include resin-dispersed pigments in which a resin is adsorbed onto the surface of the pigment particles and dispersed. Examples of such resin dispersants include anionic resins. The acid value of the resin dispersant is, for example, 300 mgKOH / g or less, preferably 250 mgKOH / g or less, more preferably 200 mgKOH / g or less, further preferably 180 mgKOH / g or less, and particularly preferably 150 mgKOH / g or less. By setting the acid value of the resin dispersant below the above range, the reactivity of the ink with the calcium salt tends to decrease, further improving clogging recovery and ejection stability.

[0066] On the other hand, the lower limit of the acid value of the resin dispersant is preferably 30 mgKOH / g or greater, more preferably 50 mgKOH / g. It is further preferably 100 mgKOH / g. Even more preferably, it is 150 mgKOH / g or greater. By setting the acid value of the resin dispersant within this range, color development is further improved. Furthermore, from the perspective of excellent suppression of phase separation of the acetylene glycol-based surfactant described later, an acid value above this range is preferred.

[0067] The acid value of the resin dispersant can be adjusted by, for example, the ratio of the amount of monomers having an acidic group to be charged when synthesizing the resin. Examples of the acidic group include a carboxyl group and the like.

[0068] As the resin of the resin dispersant, for example, acrylic resin, polyurethane resin, maleic resin, etc. can be used, and acrylic resin and maleic resin are preferred.

[0069] When a resin dispersant is used, the mass ratio of the amount of the resin dispersant used to the amount of the pigment used (resin dispersant / pigment) is preferably 1 to 20, 2 to 10, or 3 to 8. When the mass ratio of the amount of the resin dispersant used to the amount of the pigment used is within the above range, the effects of the present invention on clogging recovery, color development, and discharge stability tend to be further enhanced.

[0070] The pigment may also be a self-dispersing pigment. Self-dispersing pigments are pigments that are dispersed by introducing hydrophilic functional groups onto the pigment surface through a chemical reaction, thereby imparting dispersion stability to the pigment. Examples of hydrophilic functional groups include phosphorus-containing groups such as carboxyl groups and phosphonic acid groups, and acidic groups such as sulfonic groups.

[0071] In the case of a self-dispersible pigment, the viscosity increase ratio of the ink can be adjusted by adjusting the amount of hydrophilic functional groups introduced into the pigment surface. Furthermore, even when the viscosity increase ratio of the ink is less than 2 times, resin-dispersed pigments are preferred from the perspective of easily achieving pigment dispersion stability.

[0072] Surfactants

[0073] The ink composition may also contain a surfactant. Examples of surfactants include acetylene glycol surfactants, silicone surfactants, and fluorine-based surfactants. Among these, the ink composition preferably contains an acetylene glycol surfactant. The inclusion of an acetylene glycol surfactant not only reduces the surface tension of the ink and improves its wettability to the recording medium, but also tends to further improve clogging recovery and ejection stability. Surfactants may be used singly or in combination of two or more.

[0074] From the viewpoint of further enhancing the effects of the present invention, it is preferred that the ink composition contain an acetylene glycol-based surfactant having an HLB value of 5 or less.

[0075] In this case, compared with a case where the HLB value exceeds 5, the above-mentioned aspects are relatively superior, but the solubility in water tends to be low, and phase separation in the ink tends to be easy, and the ejection stability tends to be reduced.

[0076] The lower limit of the HLB value is 0 or greater, preferably 1 or greater. Furthermore, it is preferred to include both values ​​of 5 or less and values ​​exceeding 5, more preferably values ​​of 5 or less and values ​​exceeding 7, and even more preferably values ​​of 5 or less and values ​​exceeding 10. In this case, wettability, clogging recovery, and ejection stability are improved, and phase separation is also suppressed, which is preferred. The upper limit of the HLB value is preferably 20 or less and 15 or less.

[0077] In this specification, the “HLB value (hydrophilic lipophilic balance)” is a value calculated by the Griffin method. Specifically, the HLB value of a surfactant can be calculated according to the following formula (H).

[0078] HLB value = 20 × (mass % of hydrophilic group) … (H)

[0079] Examples of commercially available acetylene glycol surfactants include Surfynol 104PG50 (HLB value = 4), Surfynol 104, Surfynol 420, Surfynol 82, Surfynol DF110D, Surfynol 104S, and Surfynol MD-20 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), and Olfine E1010 (trade name, HLB value: 13-14, manufactured by Air Products). To more effectively and reliably exhibit the effects of the present invention, the ink composition preferably contains at least one of Surfynol 104PG50 or Olfine E1010, and more preferably contains both Surfynol 104PG50 and Olfine E1010.

[0080] The surfactant content is preferably 0.05% to 5.0% by mass, 0.1% to 3.0% by mass, or 0.2% to 2.0% by mass, relative to the total amount of the ink composition. By adjusting the surfactant content within this range, clogging recovery, color development, and ejection stability tend to be further improved. From a similar perspective, the acetylene glycol surfactant content is preferably 0.05% to 5.0% by mass, 0.1% to 3.0% by mass, or 0.2% to 2.0% by mass, relative to the total amount of the ink composition. More preferably, it is 0.5 to 1.0% by mass.

[0081] The content of the acetylene glycol surfactant having an HLB value of 5 or less may also be within the above range. From the above viewpoint, it is preferably from 0.2% by mass to 0.8% by mass, more preferably from 0.3% by mass to 0.7% by mass, and even more preferably from 0.4% by mass to 0.6% by mass.

[0082] 2.3. Lactam compounds

[0083] The ink composition preferably contains a lactam compound. Lactam compounds have a structure in which a carboxyl group and an amino group within the molecule form a ring through a dehydration condensation reaction. The inclusion of a lactam compound tends to further improve the compatibility of surfactants, particularly acetylene glycol surfactants, with the ink composition. From the same perspective, the lactam compound preferably has a 4- to 8-membered lactam ring, more preferably a 5- to 8-membered lactam ring, and even more preferably a 6- to 8-membered lactam ring. Alternatively, a 4- to 5-membered lactam ring is also preferred.

[0084] The lactam compound may be used alone or in combination of two or more. It is also preferred to use a lactam having a 4- to 5-membered lactam ring and a lactam having a 6- to 8-membered lactam ring in combination.

[0085] Specific examples of lactam compounds include ε-caprolactam, N-hydroxyethylpyrrolidone (HEP), δ-valerolactam, and 5-(methylamino)valerolactam. Preferably, ε-caprolactam, N-hydroxyethylpyrrolidone (HEP), and 2-pyrrolidone are included. The inclusion of these compounds tends to further improve clogging recovery, color development, and discharge stability.

[0086] The content of the lactam compound is preferably 0.1% to 15% by mass, or 0.5% to 10% by mass, relative to the total mass of the ink composition, more preferably 1 to 8% by mass, and even more preferably 2 to 7% by mass.

[0087] Furthermore, the content of lactams having a 6- to 8-membered lactam ring may be within the above-mentioned range, more preferably 1 to 5% by mass, and even more preferably 2 to 4% by mass.

[0088] When the content of the lactam compound is within the above range, clogging recovery properties, color development properties, and discharge stability tend to be further improved.

[0089] 2.4. Water-soluble organic solvents

[0090] The ink composition preferably contains a water-soluble organic solvent as a solvent component. The inclusion of a water-soluble organic solvent tends to improve clogging recovery and ejection stability. Examples of water-soluble organic solvents include polyols, glycol ethers, nitrogen-containing solvents, ethers, and cyclic esters. Among these, polyols are preferably included as the water-soluble organic solvent.

[0091] The polyols have two or more hydroxyl groups in the molecule, and examples thereof include alkanediols such as 1,2-hexanediol and 1,2-butanediol, and polyols.

[0092] Specific examples of alkanediol compounds include 1,2-hexanediol, 1,2-pentanediol, 1,2-octanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, 3-methyl-1,5-pentanediol, and 2-methylpentane-2,4-diol. Among these, 1,2-hexanediol is preferably included from the perspective of further improving clogging recovery and discharge stability. Alkanediols having 5 or more carbon atoms are preferred, and those having 5 to 8 carbon atoms are more preferred. 1,2-alkanediol is preferred.

[0093] Specific examples of the polyol compounds include ethylene glycol, propylene glycol, 1,2-propylene glycol, 1,2-butylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, trimethylolpropane, and glycerin.

[0094] Examples thereof include alkanediols having three or more hydroxyl groups in the molecule, alkanediols having an ether group in the skeleton (intermolecular condensation products of alkanediols), and alkanediols having 4 or less carbon atoms.

[0095] Glycol ethers are obtained by etherifying one of the hydroxyl groups of the aforementioned polyols. Alkyl etherification is preferred. Examples include diethers and monoethers, with monoethers being preferred. Examples include, but are not limited to, triethylene glycol monobutyl ether.

[0096] Among them, from the viewpoint of further improving clogging recovery and discharge stability, glycerin, triethylene glycol, or triethylene glycol monobutyl ether is preferably used.

[0097] The content of the water-soluble organic solvent is preferably 5.0% to 40% by mass, 10% to 30% by mass, or 12% to 25% by mass, and more preferably 15 to 20% by mass, relative to the total amount of the ink composition.

[0098] When the content of the water-soluble organic solvent is within the above range, the effects of the present invention tend to be more effectively and reliably exhibited.

[0099] The content of the alkanediols is preferably 0.5% to 7.0% by mass, or 1.0% to 5.0% by mass, relative to the total amount of the ink composition. Within these ranges, the effects of the present invention tend to be more effectively and reliably exhibited.

[0100] It is preferable to adjust the content of the alkanediol having 5 or more carbon atoms to be within the above range.

[0101] The content of the polyol is preferably 5.0% to 30% by mass, or 10% to 20% by mass, relative to the total amount of the ink composition. Within such a range, the effects of the present invention tend to be more effectively and reliably exhibited.

[0102] The content of the polyol having a normal boiling point of 280° C. or higher in the ink is preferably 1 to 15% by mass, more preferably 3 to 10% by mass, and even more preferably 5 to 9% by mass.

[0103] The content of the polyols in the ink containing a polyol having a normal boiling point of 280° C. or higher may be within the above range.

[0104] 2.5. Resin particles

[0105] The ink composition may also contain resin particles. Examples of the resin particles include those composed of polyurethane resins, acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, and vinyl chloride resins. Of these, polyurethane resins are preferred for more effectively and reliably achieving the effects of the present invention. These resin particles are often processed in the form of an emulsion, but may also be in the form of a powder. Furthermore, the resin particles may be used singly or in combination of two or more.

[0106] Examples of polyurethane resin particles include polyurethane resin emulsions. The polyurethane resin emulsion is not particularly limited as long as it contains a urethane bond in the molecule. Examples include polyether polyurethane resins containing ether bonds in the main chain, polyester polyurethane resins containing ester bonds in the main chain, and polycarbonate polyurethane resins containing carbonate bonds in the main chain. Among these, cationic or anionic polyurethane resin particles are preferred.

[0107] Commercially available polyurethane resin particles include, for example, Superflex 420, 600, 610, and 620 (trade names, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Hydran CP-7010, CP-7020, and CP-7030 (trade names, manufactured by Dainippon Ink & Chemicals Co., Ltd.), and polyurethane emulsions WBR-2120C and WBR-2122C (trade names, manufactured by Daisei Fine Chemicals Co., Ltd.). Among these, Superflex 420 is preferred from the perspective of more effectively and reliably exhibiting the effects of the present invention.

[0108] Examples of acrylic resin particles include acrylic resin emulsions. Examples of acrylic resin emulsions include, but are not particularly limited to, emulsions obtained by polymerizing (meth)acrylic acid monomers such as (meth)acrylic acid and (meth)acrylate esters, and emulsions obtained by copolymerizing (meth)acrylic acid monomers with other monomers.

[0109] The content of the resin particles is 0.05% to 3.0% by mass, 0.1% to 2.0% by mass, or 0.2% to 1.0% by mass, relative to the total amount of the ink composition. By setting the content of the resin particles within the above ranges, the effects of the present invention can be more effectively and reliably achieved.

[0110] 2.6. Water

[0111] The ink of this embodiment is a water-based ink. A water-based ink is an ink containing water as a solvent component contained in the ink.

[0112] As the water, water from which ionic impurities have been removed as much as possible is preferred. Such water is not particularly limited, and examples thereof include pure water and ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water.

[0113] The water content is preferably 30% by mass to 99% by mass, 35% by mass to 90% by mass, and more preferably 40% by mass to 80% by mass, relative to the total amount of the ink composition.

[0114] 2.7. Other ingredients

[0115] The ink composition of this embodiment may contain components other than the above components as needed. Examples of such components include a pH adjuster, a chelating agent, and a rust inhibitor.

[0116] Examples of pH adjusters include inorganic acids (e.g., sulfuric acid, hydrochloric acid, nitric acid, etc.), inorganic bases (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), organic bases (e.g., triethanolamine, diethanolamine, monoethanolamine, tripropanolamine), and organic acids (e.g., adipic acid, citric acid, succinic acid, etc.). Triethanolamine is preferred from the viewpoint of more effectively and reliably exhibiting the effects of the present invention.

[0117] The pH adjuster content is preferably 0.05% to 3.0% by mass, 0.1% to 2.0% by mass, or 0.2% to 1.0% by mass, relative to the total amount of the ink composition. By keeping the pH adjuster content within this range, the effects of the present invention tend to be more effectively and reliably exhibited.

[0118] 3. Recording medium

[0119] This embodiment uses an absorptive recording medium as the recording medium. An absorptive recording medium is a recording medium whose recording surface is made of paper such as plain paper or inkjet paper, cloth, or an organic or inorganic material that absorbs ink. Plain paper or inkjet paper is preferred.

[0120] From the viewpoint of more effectively and reliably exhibiting the effects of the present invention, the portion of the recording medium that absorbs the ink composition even in the absence of water preferably contains a calcium salt, for example, the entire recording medium or the layer that absorbs the ink composition.

[0121] Examples of calcium salts include water-soluble calcium salts and sparingly water-soluble calcium salts. From the perspective of further improving the color development properties of the ink, water-soluble calcium salts are preferred, but sparingly water-soluble calcium salts may also be used. Examples of sparingly water-soluble calcium salts include calcium carbonate. Examples of water-soluble calcium salts include calcium chloride.

[0122] In this embodiment, the "absorptive recording medium" refers to a medium that absorbs water in excess of 10 mL / m² from the start of contact to 30 msec according to the Bristow method. 2 The Bristow method is the most popular method for measuring liquid absorption over a short period of time and is also adopted by the Japan Pulp and Paper Technology Association (JAPAN TAPPI). Details of the test method are described in "JAPAN TAPPI Pulp Test Methods 2000 Edition," Standard No. 51, "Paper and Board - Liquid Absorption Test Method - Bristow Method."

[0123] The recording speed of this recording method is preferably 35 pages per minute (ppm) or higher, more preferably 40 pages per minute (ppm) or higher, and even more preferably 50 pages per minute (ppm) or higher, based on the conveyance speed of the recording medium. Furthermore, a speed of 60 ppm or higher is particularly preferred. Recording at such speeds is prone to clogging, making the present invention more effective. The aforementioned pages are preferably based on A4 paper.

[0124] The upper limit of the recording speed is not limited, but is preferably 100 pages / minute or less, and more preferably 80 pages / minute or less. When printing on one side of a recording medium, the page / minute is equal to the sheet / minute; when printing on both sides of a recording medium, the page / minute is equal to the sheet / minute × 2.

[0125] When the speed is above the above range, recording is performed quickly, which is useful. However, on the contrary, the generation of paper dust and the amount of ink supplied tend to increase, and the effect of the present invention is more effective.

[0126] Furthermore, when double-sided printing is performed, the generation of paper dust and the amount of ink supplied tend to increase, and thus the effects of the present invention are more effective.

[0127] The recording medium is preferably A4-sized. During recording of one sheet, paper is fed from the recording medium feed tray and discharged to the recording medium feed tray once, which may generate paper dust. Therefore, the size of the recording medium is not limited.

[0128] 4. Inkjet recording device

[0129] The inkjet recording apparatus of this embodiment is an apparatus for obtaining a recorded object by the above-mentioned inkjet recording method, and includes the above-mentioned ink composition, the above-mentioned inkjet head, and the above-mentioned transport unit.

[0130] Figure 4 One embodiment of an ink supply mechanism of an inkjet recording device is shown. More specifically, Figure 4 1 is a schematic perspective view showing the arrangement of the ink container and the pressure regulating valve in the ink supply mechanism. Figure 4 As shown, for example, the ink supply mechanism 100 includes an ink container 4 and a pressure regulating valve 8. Furthermore, it includes a transparent cylindrical container 3 attached to the ink container 4 and a pressure sensor 5. The pipe 7a connecting the ink container 4 and the on-off valve 6, the pipe 7b connecting the on-off valve 6 and the pressure regulating valve 8, and the pipe 7c connecting the pressure regulating valve 8 and the droplet ejection head group 2 all use flexible tubing, such as polyethylene terephthalate. Ink is supplied from an ink cartridge (not shown) or the like from the inlet (IN) to the container 3 of the ink container 4.

[0131] The droplet ejection head group 2 is configured with multiple heads, which are inkjet heads serving as line heads. The droplet ejection head group 2 is formed by arranging multiple heads in the horizontal direction of the figure. Each head has a nozzle array (not shown), which has multiple nozzles arranged in the horizontal direction of the figure.

[0132] From the perspective of head productivity, a line head is often used, as opposed to a single, long row of line heads, by combining multiple heads, as in the droplet ejection head group 2. During printing, ink is supplied to the ejection portions of the multiple heads in the droplet ejection head group 2 via the pressure regulating valve 8, requiring a high ink flow rate within a short period of time. The recording method of this embodiment is suitable for such line-type recording devices, which require a high ink flow rate within a short period of time.

[0133] then, Figure 5 Another embodiment of the inkjet recording apparatus is shown. Figure 5 This is an overall view of an inkjet recording apparatus including structures related to conveyance of a recording medium.

[0134] Reference Figure 5 The inkjet recording device according to this embodiment will be described in detail. Figure 5In the XYZ coordinate system shown, the X direction indicates the longitudinal direction of the recording medium, the Y direction indicates the width direction of the recording medium in the conveyance path in the recording apparatus, and the Z direction indicates the apparatus height direction.

[0135] As an example, the recording device 10 is a line inkjet printer capable of high-speed and high-density printing. The recording device 10 includes a feed unit 12 for storing recording media P, such as paper, a conveyor unit 14, a belt conveyor unit 16, a recording unit 8, an Fd (face down) discharge unit 20 as a "discharge unit," an Fd (face down) placement unit 22 as a "placement unit," a reversing path unit 24 as a "reversing conveying mechanism," a Fu (face up) discharge unit 26, and a Fu (face up) placement unit 28.

[0136] The feed unit 12 is disposed at the lower portion of the recording apparatus 10 . The feed unit 12 includes a feed tray 30 for storing recording media P and a feed roller 32 for feeding the recording media P stored in the feed tray 30 toward the transport path 11 .

[0137] Recording medium P stored in the feed tray 30 is fed along the conveyance path 11 to the conveyor unit 14 by the feed roller 32. The conveyor unit 14 includes a conveyance drive roller 34 and a conveyance driven roller 36. The conveyance drive roller 34 is rotationally driven by a drive source (not shown). In the conveyor unit 14, the recording medium P is sandwiched (held between) the conveyance drive roller 34 and the conveyance driven roller 36 and conveyed to the belt conveyor unit 16 located downstream of the conveyance path 11.

[0138] The belt conveying section 16 includes: a first roller 38, which is located on the upstream side of the conveying path 11; a second roller 40, which is located on the downstream side; an endless belt 42, which is rotatably mounted on the first roller 38 and the second roller 40; and a support body 44, which supports the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0139] The endless belt 42 is driven by the first roller 38 or the second roller 40, which is driven by a driving 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 section 14 is further conveyed to the downstream side of the conveyance path 11 by the belt conveying section 16.

[0140] The recording unit 8 includes a line-type inkjet head 48 and a head holder 46 for holding the inkjet head 48. The inkjet head 48 is arranged so that the Y-axis direction of the figure is the arrangement direction of the nozzles of the line-type head. Figure 4 The droplet ejection head group 2 is configured so that the Y-axis direction is the arrangement direction of the nozzles. Figure 5 The inkjet recording device may also have an ink supply mechanism such as an ink container, but it is omitted in the figure.

[0141] The inkjet head 48 is a line head that has a length, in a direction intersecting the direction in which the recording medium is transported (the Y direction in the figure), that is greater than the recording area of ​​the recording medium. Here, the length of the line head refers to the length of the nozzle array of the line head, measured from one end to the other in the Y direction. The length of the recording area of ​​the recording medium is the length from one end to the other of the recording medium in the Y direction, where recording can be performed.

[0142] In addition, if an inkjet head is provided on a carriage that reciprocates the recording unit 8 in the Y-axis direction, the nozzle arrangement direction of the nozzle array is set as Figure 5 In the X direction, Figure 4 If one of the heads is an inkjet head, it is called a serial inkjet recording device.

[0143] The inkjet head 48 is disposed opposite the upper section 42a of the endless belt 42 supported by the support body 44. The inkjet head 48 ejects ink onto the recording medium P to perform recording while the recording medium P is being conveyed in the upper section 42a of the endless belt 42. While recording is being performed on the recording medium P, the recording medium P is conveyed to the downstream side of the conveyance path 11 by the belt conveyor 16.

[0144] A first branching portion 50 is provided downstream of the conveying path 11 of the belt conveying portion 16. The first branching portion 50 is configured to be able to switch between the conveying path 11 for conveying the recording medium P to the Fd discharge portion 20 or the Fu discharge portion 26 and the reversing path 52 of the reversing path portion 24 for reversing the recording surface of the recording medium P and conveying the recording medium P to the recording portion 8 again. Furthermore, the recording medium P conveyed by switching to the reversing path 52 by the first branching portion 50 has its recording surface reversed during the conveyance process in the reversing path 52, and is conveyed to the recording portion 8 again in such a manner that the surface opposite to the original recording surface faces the inkjet head 48. This performs double-sided printing. When performing double-sided printing, there is a tendency for the conveying path to become longer, resulting in an increase in the generation of paper dust. The recording method of this embodiment is particularly useful.

[0145] A second branching portion 54 is provided downstream of the first branching portion 50 along the conveying path 11 . The second branching portion 54 is configured to switch the conveying direction of the recording medium P to convey the recording medium P to the Fd discharge portion 20 or to convey the recording medium P to the Fu discharge portion 26 .

[0146] In the second branching portion 54, the recording medium P conveyed to the Fd discharge portion 20 is discharged from the Fd discharge portion 20 and placed on the Fd placement portion 22. At this time, the recording surface of the recording medium P is placed opposite the Fd placement portion 22. Furthermore, in the second branching portion 54, the recording medium P conveyed to the Fu discharge portion 26 is discharged from the Fu discharge portion 26 and placed on the Fu placement portion 28. At this time, the recording surface of the recording medium P is placed facing the side opposite to the Fu placement portion 28.

[0147] Example

[0148] Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. However, the present invention is not limited to the following Examples.

[0149] 1. Preparation of ink composition

[0150] exist Figures 1 to 3 In the figures, Tables 1 to 3 showing the compositions of the ink compositions used in Examples and Comparative Examples and the evaluation results thereof are described.

[0151] The components were added to a mixing tank to form the compositions listed in Tables 1 to 3, mixed and stirred, and then filtered through a membrane filter to obtain the respective inkjet ink compositions. The numerical values ​​for each component in each example in the tables represent mass % unless otherwise specified. Furthermore, the numerical values ​​for inorganic oxide particles, resin particles, and pigment dispersion in the tables represent the mass % of the solids content of the inorganic oxide particles, resin particles, and pigment, respectively. All the resulting inks were magenta inks.

[0152] The abbreviations used in Tables 1 to 3 and the details of the product components are as follows. The numbers written to the right of the solvent abbreviations represent the SP values ​​of the solvents.

[0153] pigment

[0154] Pigment dispersions A to F were prepared as follows.

[0155] Dispersion A: A mixture was prepared by mixing and stirring 20% ​​by mass of CI Pigment Red 150 (PR150), an azo pigment, 5% by mass of a resin dispersant (acid value 150 mgKOH / g, molecular weight 10,000), a sodium hydroxide-neutralized product of a styrene-acrylic acid copolymer, and 75% by mass of pure water. This mixture was added to a wet sand mill filled with 0.3 mm diameter zirconia beads and dispersed for 6 hours. The zirconia beads were then removed using a separator, and the mixture was filtered through a cellulose acetate filter with a pore size of 3.0 μm to obtain a pigment dispersion.

[0156] Dispersion liquid B: Dispersion liquid B was obtained in the same manner as dispersion liquid A except that the acid value of the resin dispersant was set to 260 mgKOH / g.

[0157] Dispersion C: Dispersion C was obtained in the same manner as in Dispersion A except that CI Pigment Violet 19 (PV19), a quinacridone pigment, was used instead of CI Pigment Red 150 (PR150).

[0158] Dispersion D: Dispersion D was obtained in the same manner as Dispersion A except that CI Pigment Violet 19 (PV19) as a quinacridone pigment was used instead of CI Pigment Red 150 (PR150) and the acid value of the resin dispersant was set to 260 mgKOH / g.

[0159] Dispersion E: Dispersion E was obtained in the same manner as in Dispersion A except that the acid value of the resin dispersant was set to 200 mgKOH / g.

[0160] Dispersion liquid F: Dispersion liquid F was obtained in the same manner as in dispersion liquid A except that CI Pigment Red 17 (PR17) as an azo pigment was used instead of CI Pigment Red 150 (PR150).

[0161] lactam compounds

[0162] ·HEP

[0163] ·ε-caprolactam

[0164] Water-soluble organic solvents

[0165] 1,2-Hexanediol

[0166] 1,2-Butanediol

[0167] ·glycerin

[0168] ·TEG (triethylene glycol)

[0169] ·TEGmBE (triethylene glycol monobutyl ether)

[0170] surfactants

[0171] Olfine E1010 (trade name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)

[0172] Surfynol 104 (trade name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.)

[0173] resin

[0174] Superflex 420 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0175] pH adjusters

[0176] ·TEA (triethylamine)

[0177] 2. Evaluation Method

[0178] 2.1. Viscosity increase rate

[0179] Each ink composition obtained above was mixed with a calcium aqueous solution (Ca concentration: 0.3 mol / L) at a ratio of 10:1 and allowed to stand at 60°C for 24 hours. The viscosity η1 of the ink composition after standing and the initial viscosity η0 of the ink composition were calculated as the viscosity increase rate and evaluated as follows.

[0180] Thickening rate = ink viscosity after placement η1 / initial ink viscosity η0

[0181] Evaluation Benchmarks

[0182] A: Thickening rate is less than 1.5

[0183] B: The viscosity increase ratio is more than 1.5 and less than 2.0

[0184] C: Thickening rate exceeds 2.0

[0185] 2.2. Color rendering

[0186] The ink application amount was set to 5.0 mg / inch using a modified recording device PX-S840 (product name, manufactured by Seiko Epson Corporation). 2 A magenta single-color test pattern was recorded on plain paper (manufactured by Navigator Co., Ltd.) using a colorimeter (manufactured by Xrite Co., Ltd., Xrite i1) to measure the OD value and evaluate the results according to the following criteria.

[0187] Evaluation Benchmarks

[0188] A: OD value is 0.85 or above

[0189] B: OD value is 0.75 or more and less than 0.85

[0190] C: OD value is 0.65 or more and less than 0.75

[0191] D: OD value is less than 0.65

[0192] 2.3. Redispersibility

[0193] The resulting ink composition and a calcium aqueous solution (Ca concentration: 0.3 mol / L) were mixed at a ratio of 10:1. Five drops of 2 μl of the mixture were added to a glass slide and dried at 60°C for 24 hours. The dried slide was then immersed in a sample vial containing only the pre-mixed ink composition. After standing for 3 minutes, the slide was inverted five times, removed, and visually inspected for residual glassy mixed solution and any redissolution according to the following criteria.

[0194] Evaluation Benchmarks

[0195] A: The solid material completely redissolves without being observed

[0196] B: The solid matter becomes smaller, but some residue is observed

[0197] C: The solid matter has not become smaller and most of it remains

[0198] D: The ink composition evaluated as C was tested again under the same conditions except that the drying temperature was changed to 40°C. The results were the same as those obtained at 60°C. The solid matter did not decrease in size, and most of the solid matter remained.

[0199] 2.4.Lightfastness

[0200] The recorded material obtained in the evaluation of the color development properties was subjected to a light fastness test in accordance with JEITA CP-3901B, and the light fastness was evaluated based on the calculated lifespan according to the following criteria.

[0201] Evaluation Benchmarks

[0202] A: More than 50 years

[0203] B: More than 30 years and less than 50 years

[0204] C: More than 10 years and less than 30 years

[0205] D: less than 10 years

[0206] 2.5. Compatibility

[0207] The ink composition obtained above was placed in a glass spiral tube, capped, and placed in a thermostatic bath at 60°C for 24 hours. The spiral tube was then removed from the thermostatic bath, and the presence of a surfactant separated by phase separation on the ink surface was confirmed and evaluated according to the following criteria.

[0208] Evaluation Benchmarks

[0209] A: No separation of surfactant was observed

[0210] B: Surfactant separation, observed floating on the liquid surface

[0211] C: Surfactant separates and forms two layers

[0212] 3. Recording Test

[0213] The ink composition obtained above was filled in the following two recording apparatuses, and continuous printing was performed on plain paper (manufactured by Navigator Co., Ltd.).

[0214] ・This is a modified machine for a line recording device (LX-10050MF, manufactured by Seiko Epson Corporation). Figure 5 Such a line-type recording device has Figure 4 Such a line head and ink supply mechanism.

[0215] · Modified machine of serial recording device (PX-M886FL, manufactured by Seiko Epson Corporation): The above-mentioned line recording device was replaced with the aforementioned serial recording device.

[0216] 3.1. Ejection stability

[0217] After filtration and degassing, the recording device was filled with ink and a test pattern was continuously printed. 100 sheets of A4 paper (Navigator paper (plain paper)) were printed continuously at a speed of 60 pages per minute (ppm) using a line-type recording device. Printing was performed on one side of the paper. The test pattern consisted of a 1 x 1 cm solid pattern arranged in a checkered pattern within the recordable area.

[0218] In a serial recording device, 100 sheets were printed continuously at a speed of 30 pages per minute, single-sided. The same process was repeated thereafter. Furthermore, in a serial recording device, flushing is performed at the position where the head is separated from the recording medium for each pass (one main scan).

[0219] After printing, a nozzle check pattern is printed to identify nozzles with print distortion and non-discharging, and evaluation is performed based on the following criteria. Nozzles with a landing position deviation of at least half the distance between adjacent nozzles are considered print distortion. Discharge stability is also affected by factors such as ink viscosity (initial viscosity) and the adequacy of ink supply to the inkjet head.

[0220] Evaluation Benchmarks

[0221] A: No printing distortion occurs and the nozzle does not eject.

[0222] B: Print distortion or non-ejection occurs in less than 50% of the nozzles

[0223] C: Print distortion or non-discharging occurs in 50% or more and less than 70% of the nozzles

[0224] D: Print distortion or non-ejection occurs in more than 70% of the nozzles

[0225] 3.2. Blockage recovery

[0226] Continuous printing was performed in the same manner as in the above-mentioned ejection stability test, but for 10 minutes.

[0227] The inkjet head was then removed from the printer's cap and left uncapped for seven days in an environment with a temperature of 40°C and a humidity of 20%. After this period, the inkjet head was cleaned by counting the number of nozzles that failed to eject ink each time the ink within the nozzles was aspirated. This cleaning cycle was repeated until all nozzles were restored. The number of cleanings required to restore all nozzles was then evaluated according to the following criteria. Clogging recovery performance is also affected by factors such as the presence and composition of dried, solidified ink in the nozzles.

[0228] Evaluation Benchmarks

[0229] A: All nozzles are restored after cleaning within two times

[0230] B: After three or four cleanings, all nozzles are restored

[0231] C: After five or six cleanings, all nozzles are restored

[0232] D: Nozzles that did not recover were observed even after six cleanings

[0233] 4. Evaluation results

[0234] Tables 1 to 3 show the composition and evaluation results of the inks used in each example. As shown in Tables 1 to 3, the inkjet recording method comprises a transport step in which a recording medium is transported by a transport unit; and an attachment step in which an ink composition is ejected from an inkjet head and attached to the transported recording medium. The inkjet head is a line head having a length extending in a direction intersecting the transport direction, greater than the recording area of ​​the recording medium. The recording medium is an absorptive recording medium. The ink composition is a red aqueous ink containing a pigment, the pigment including an azo pigment. The viscosity η1 of the mixture obtained by mixing 10 parts by mass of the ink composition with 1 part by mass of a calcium propionate aqueous solution having a Ca concentration of 0.3 mol / L is less than 2.0 times the viscosity η0 of the ink composition. When recording is performed using this inkjet recording method, excellent ejection stability and clogging recovery are achieved.

[0235] Although not listed in the table, the jam recovery performance of the line-type recording device described above was evaluated in the same manner as in Example 1 except that continuous printing was performed using duplex printing. The evaluation result was B in Example 1. This indicates that duplex printing increases the generation of paper dust during the process of reversing the recording medium, which affects jam recovery performance. However, this embodiment achieves excellent jam recovery performance.

Claims

1. An inkjet recording method, characterized in that The inkjet ink recording method has: a conveying step of conveying the recording medium by the conveying unit; and an attachment step of ejecting an ink composition from an inkjet head and attaching the ink composition to the recording medium transported in the transport step, The inkjet head is a line head having a length greater than the recording area of ​​the recording medium in a direction intersecting the conveying direction. The recording medium is an absorptive recording medium, The ink composition is a red water-based ink containing a pigment, The pigment comprises an azo pigment, When 10 parts by mass of the ink composition and 1 part by mass of a calcium propionate aqueous solution having a Ca element concentration of 0.3 mol / L are mixed, the viscosity η1 of the mixed solution is less than 2.0 times the viscosity η0 of the ink composition.

2. The inkjet recording method according to claim 1, wherein The solid content of the pigment is 0.5% by mass or more and 10% by mass or less relative to the total mass of the ink composition.

3. The inkjet recording method according to claim 1, wherein The pigments also include quinacridone pigments.

4. The inkjet recording method according to claim 1, wherein The viscosity η1 is less than 1.5 times the viscosity η0.

5. The inkjet recording method according to claim 1, wherein The ink composition comprises a lactam compound, The content of the lactam compound is 0.5% by mass or more and 6.0% by mass or less relative to the total mass of the ink composition.

6. The inkjet recording method according to claim 1, wherein The ink composition includes an acetylene glycol-based surfactant.

7. The inkjet recording method according to claim 6, wherein The HLB value of the acetylene glycol-based surfactant is 5 or less.

8. The inkjet recording method according to claim 1, wherein The ink composition is a magenta ink.

9. The inkjet recording method according to claim 1, wherein The azo pigment includes one or more selected from the group consisting of CI Pigment Red 150, CI Pigment Red 269, and CI Pigment Red 17.

10. The inkjet recording method according to claim 1, wherein In the recording medium, the layer that absorbs the ink composition contains a calcium salt.

11. The inkjet recording method according to claim 1, wherein The ink composition comprises a resin dispersant for dispersing the pigment, The acid value of the resin dispersant is 250 mgKOH / g or less.

12. The inkjet recording method according to claim 1, wherein The recording speed is over 50 pages per minute.

13. An inkjet recording device, characterized in that: The inkjet recording apparatus is used to obtain a recorded object by the inkjet recording method according to any one of claims 1 to 12, The inkjet recording apparatus includes the ink composition, the inkjet head, and the transport unit.

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