Ink jet recording method and recording apparatus

Abstract

To provide an ink jet recording method excellent in clogging recoverability, color development and storage stability.SOLUTION: An ink jet recording method includes a transporting step of transporting a recording medium by transport means, and an adhesion step of ejecting an ink composition from an ink jet head to cause the ink composition to adhere to the recording medium being transported, wherein the ink jet head is a line head having a length equal to or longer than a recording area of the recording medium in a direction crossing a direction of transportation, the recording medium is an absorbent recording medium, the ink composition is a red-based aqueous ink containing a pigment, the pigment contains an azo-based pigment, and a viscosity η1 of a mixed liquid when 10 pts.mass of the ink composition and 1 pt.mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L are mixed together is less than 2.0 times a viscosity η0 of the ink composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method and a recording apparatus. [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. In the process, various studies have been conducted on the ability to recover from clogging. For example, Patent Document 1 discloses an ink composition containing a specific amine compound for the purpose of suppressing nozzle clogs and clogging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-006556 Summary of the Invention [Problem to be solved by the invention]

[0004] When high-speed recording is performed on an absorbent recording medium using a recording apparatus having a line head, there are problems such as poor color development, poor ejection stability, and poor recovery from clogging. [Means for solving the problem]

[0005] The inkjet recording method of the present invention includes a transporting step of transporting a recording medium by a transport means, and a depositing step of ejecting an ink composition from an inkjet head and depositing the ink composition on the recording medium being transported in the transporting step, wherein the inkjet head is a line head having a length equal to or greater than the length of a recording area of ​​the recording medium in a direction intersecting the transport direction, the recording medium is an absorbent recording medium, the ink composition is a reddish water-based ink containing a pigment, the pigment contains an azo-based pigment, and when 10 parts by mass of the ink composition and 1 part by mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L are mixed, the viscosity η1 of the mixture 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 matter by the inkjet recording method described above, and comprises the ink composition, the inkjet head, and the transport means. [Brief explanation of the drawings]

[0007] [Figure 1] Table 1 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 2] Table 2 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 3] Table 3 shows the compositions of ink compositions used in the examples and the evaluation results thereof. [Figure 4] FIG. 2 is a diagram illustrating an example of an ink supply mechanism of a recording apparatus used in the recording method of the present embodiment. [Figure 5] FIG. 2 is a diagram illustrating an example of a recording apparatus used in the recording method of the present 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 recording method The inkjet recording method according to this embodiment (hereinafter also simply referred to as "the recording method") includes a deposition step of ejecting an ink composition from an inkjet head and depositing the ink composition on the recording medium being transported, wherein the inkjet head is a line head having a length equal to or greater than the recording area of ​​the recording medium in a direction intersecting the transport direction, the recording medium is an absorbent recording medium, the ink composition is a reddish water-based ink containing a pigment, the pigment contains an azo-based pigment, and when 10 parts by mass of the ink composition and 1 part by mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L are mixed, the viscosity η1 of the mixture is less than 2.0 times the viscosity η0 of the ink composition.

[0010] In an absorbent recording medium 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 a calcium salt component, or the recording medium may have a layer containing a calcium salt component. For example, the layer containing a calcium salt component may be formed by coating the recording medium with a layer containing a calcium salt component. Such recording media tend to have enhanced color development due to the calcium salt components contained in the recording media. For example, it is thought that the pigment contained in the ink that adheres to the recording media reacts with the calcium salt, causing the pigment to aggregate and making it difficult for the pigment to penetrate the recording media, thereby enhancing color development.

[0011] Furthermore, when printing at high speed using a line printer, a large amount of paper dust containing calcium salts originating from the recording medium is generated within the recording device. The dust adhering to the nozzles reacts with the ink, increasing its viscosity, or the ink aggregates and dries and solidifies within the nozzles, resulting in problems that cannot be resolved by cleaning the nozzles. It has also been found that this type of problem is more likely to occur when printing continuously for long periods of time with a line printer. Therefore, there is a need for an ink composition that is low in reactivity and can suppress viscosity increases even when mixed with calcium salts. Furthermore, in line printers, the recording medium is transported at high speed, which can lead to misfeeds and the recording medium coming into contact with the nozzles. In this case, the ink can aggregate and dry out in the nozzles, causing similar problems.

[0012] On the other hand, if the reactivity with calcium salts is suppressed, the ink will be more likely to penetrate deep into the recording medium when it lands on it, resulting in poor color development. While it is conceivable that increasing the pigment concentration would improve color development, this would increase the viscosity, raising concerns that it could reduce the ink's ejection stability. In particular, when printing at high speed with a line printer, a large amount of ink is supplied to the line head. Therefore, if the ink viscosity is high, the ink's ability to be supplied to the line head will be reduced, leading to insufficient supply and reduced ejection stability. Therefore, the pigment concentration in the ink cannot be increased significantly.

[0013] In contrast, the recording method of this embodiment uses a reddish azo pigment that exhibits excellent color development while suppressing reactivity with calcium salts. By using such a pigment, the reactivity of the ink composition with calcium salts is reduced, thereby suppressing clogging and maintaining color development. This makes it possible to provide an inkjet recording method that exhibits excellent color development, ejection stability, and clogging recovery.

[0014] The ink compositions used in each step of the recording method will be described in detail below.

[0015] This recording method includes a transport step of transporting a recording medium by a transport means, and an adhesion step of ejecting an ink composition from an inkjet head and adhering it to the recording medium being transported, wherein the inkjet head is a line head having a length equal to or greater than the recording area of ​​the recording medium in a direction intersecting the transport direction.

[0016] In a line system using a line head, the head is fixed and the recording medium is moved in the sub-scanning direction (the vertical direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, thereby recording an image on the recording medium. In a line system recording method using a line head, the head is fixed and (almost) does not move, and recording is performed in one pass (single pass), making it suitable for large-volume, high-speed printing. On the other hand, since the recording medium transport speed is fast and the number of recording media transported is large, there is a large amount of paper dust generated and there are many recording medium transport errors, making this embodiment particularly useful.

[0017] The line head has cavities that eject the stored ink composition from nozzles, an ejection drive unit provided for each cavity that applies an ejection driving force to the ink, and a nozzle provided for each cavity that ejects the ink composition out of the head. A single head may have a plurality of cavities, ejection drive units, and nozzles provided for each cavity, each independent of one another. The ejection drive unit may be formed using an electromechanical conversion element such as a piezoelectric element that changes the volume of the cavity by mechanical deformation, or an electrothermal conversion element that generates heat to generate bubbles in the ink and eject it.

[0018] 2. Ink composition In this recording method, the ink composition is a red water-based ink containing a pigment, the pigment including an azo pigment, and when 10 parts by mass of the ink composition is mixed with 1 part by mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L, the viscosity η1 of the mixture is less than 2.0 times the viscosity η0 of the ink composition. This reduces the reactivity of the ink composition with the calcium salt, suppressing clogging and maintaining color development, even in situations where paper dust is likely to accumulate in the nozzles during long periods of high-speed printing using a line printer, for example.

[0019] Furthermore, the viscosity η1 is preferably 1.7 times or less, more preferably 1.5 times or less, the viscosity η0. When the ratio η1 / η0, which indicates the rate of change in viscosity, is within the above range, the present invention is excellent in clogging recovery, color development, and ejection stability. There is no lower limit to the viscosity change, but it is preferably 1 time or more, and more preferably 1.3 times or more. Note that η1 and η0 are values ​​measured after the above-mentioned mixing, stirring, and leaving at 60°C for 24 hours. The viscosity measurements are values ​​measured at 25°C. When measuring viscosity, the mixed liquid is stirred to use a sample with even components. Calcium propionate may be used, for example, in the form of pentahydrate. The value of viscosity η1 relative to viscosity η0 may be adjusted by adjusting the type of pigment or the content of the pigment.

[0020] 2.1.Pigments The ink composition contains an azo pigment as a pigment. By including the azo pigment, excellent color development can be achieved even when the reactivity of the ink with calcium salts is suppressed. The ink may contain other pigments in addition to the aso pigment. Examples of other pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, and azomethine pigments.

[0021] 2.1.1. Azo pigments The ink composition of this embodiment contains an azo pigment. Examples of the azo pigment include a monoazo pigment, a disazo pigment, a condensed disazo pigment, and a benzimidazolone pigment. Among the azo pigments, a pigment capable of producing a red color is used.

[0022] The ink composition of this embodiment is a reddish ink. Reddish inks are inks that are primarily used to express red when printing is performed to reproduce secondary or higher colors using multiple color inks. For example, the ink composition is a magenta ink, a red ink, or an ink similar thereto. The red ink is preferably magenta ink. Here, magenta ink generally refers to an ink used as an ink set together with cyan ink, yellow ink, and, if necessary, black ink. For example, it includes ink generally named magenta ink in commercially available ink cartridges and all inks that are reminiscent of magenta ink. Red refers to a color whose hue angle falls within a predetermined 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 inks are inks that are primarily used when printing red. Preferably, the ink is capable of expressing the red color on its own.

[0023] The recording method of this embodiment may further use cyan ink, yellow ink, and, if necessary, black ink.

[0024] Red inks are used to print red images, and red images are required to have particularly high visibility. Furthermore, there are many types of pigments that can be used in red inks. Therefore, this embodiment is particularly useful when using red inks.

[0025] The azo pigment may be any azo pigment that can produce a red ink in the inkjet ink composition, such as an azo pigment designated as CI Pigment Red. 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.

[0026] The ink composition preferably contains, as the 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. By using the above compounds as the azo pigment, the effects of the present invention on clogging recovery, color development, and ejection stability tend to be further improved.

[0027] Furthermore, from the viewpoint of obtaining images with even better color development, the azo pigment is preferably a compound represented by the following formula (I) or a solid solution thereof, wherein A represents a hydrogen atom or an aromatic group.

[0028] [ka]

[0029] Here, the aromatic group is a group having an aromatic ring such as a benzene ring or a naphthalene ring, and the aromatic ring can 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 is, for example, an organic group or an inorganic group, and the number of substituents can also be selected arbitrarily. The substituent is not limited, but examples thereof include an alkyl group, a halo group, an alkoxy group, a hydroxyl group, a carboxyl group, an amino group, and a nitro group.

[0030] The azo pigment may be a resin-dispersed pigment dispersed in a resin, or may be a self-dispersed pigment in which a functional group is introduced by treating the pigment surface, and the resin-dispersed pigment is preferred.

[0031] 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 measuring device. Examples of particle size distribution measuring devices include particle size distribution meters that use dynamic light scattering as their measurement principle (e.g., the "Nanotrack Series" manufactured by Microtrackbell). 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.

[0032] The solid content of the azo pigment is preferably 0.3% by mass or more, and preferably 10% by mass or less, based on the total amount of the ink composition. It is further 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. It is also preferably 5% by mass or more. This tends to further improve the effects of clogging recovery, color development, and ejection stability.

[0033] The solid content of the azo pigment is preferably 15% by mass or more and 100% by mass or less, 25% by mass or more and 100% by mass or less, 45% by mass or more and 100% by mass or less, 65% by mass or more and 100% by mass or less, or 85% by mass or more and 100% by mass or less, based on the total amount of pigment. On the other hand, it is also preferable that the amount of the pigment is 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, and even more preferably 30% by mass or less, based on the total amount of pigments. These tend to further improve the effects of clogging recovery, color development, and ejection stability.

[0034] The ink composition of this embodiment is preferably a magenta ink, and the recording method of the present invention is particularly effective when using magenta ink.

[0035] The ink composition preferably further contains a quinacridone pigment as another pigment. By further containing a quinacridone pigment, the lightfastness is further improved, and the recorded material can be used outdoors. Examples of quinacridone pigments include CI Pigment Violet 19 and CI Pigment Red 122, with CI Pigment Violet 19 being preferred.

[0036] When other pigments are contained, the solid content of the other pigments relative to the total amount of the ink composition is preferably 0.1% by mass to 1.6% by mass, 0.2% by mass to 1.2% by mass, or 0.3% by mass to 1.0% by mass, which tends to further improve lightfastness.

[0037] When other pigments are contained, the content of the solid content of the other pigments relative to the total amount of 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, which tends to further improve lightfastness. Among other pigments, the content of quinacridone pigments may be set within the above range, which is preferred.

[0038] The total content of the pigment solids, relative to the total mass of the ink composition, is preferably 0.3% by mass to 10% by mass, 0.5% by mass to 10% by mass, 0.6% by mass to 9% by mass, 0.7% by mass to 8% by mass, or 0.8% by mass to 7% by mass. 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. It is also preferably 5% by mass or more. By setting the pigment content within the above range, color development, ejection stability, and clogging recovery properties tend to be even more excellent.

[0039] The ink composition may contain a resin dispersant that disperses the pigment. A preferred example of the resin dispersant is a resin-dispersed pigment in which a resin is adsorbed onto the surface of 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, even more preferably 180 mgKOH / g or less, and particularly preferably 150 mgKOH / g or less. By setting the acid value of the resin dispersant to the above range or less, the reactivity with the calcium salt of the ink tends to be reduced, and the effects of clogging recovery and ejection stability tend to be further improved. On the other hand, the lower limit of the acid value of the resin dispersant is preferably 30 mgKOH / g or more, more preferably 50 mgKOH / g, even more preferably 100 mgKOH / g, and even more preferably 150 mgKOH / g or more. By setting the acid value of the resin dispersant within the above range, color development is more excellent. In addition, an acid value above the above range is preferable in terms of excellent suppression of phase separation of the acetylene glycol surfactant described below.

[0040] The acid value of the resin dispersant can be adjusted, for example, by adjusting the ratio of the amount of a monomer having an acidic group added when used in the synthesis of the resin. Examples of the acidic group include a carboxyl group.

[0041] Examples of resins that can be used for the resin dispersant include acrylic resins, urethane resins, and maleic resins, with acrylic resins and maleic resins being preferred.

[0042] When a resin dispersant is used, the mass ratio of the amount of resin dispersant used to the amount of pigment used (resin dispersant / pigment) is preferably from 1 to 20, from 2 to 10, or from 3 to 8. By setting the mass ratio of the amount of resin dispersant used to the amount of pigment used within the above ranges, the effects of the present invention on clogging recovery, color development, and ejection stability tend to be further improved.

[0043] The pigment may be a self-dispersing pigment. A self-dispersing pigment is one in which hydrophilic functional groups are introduced onto the pigment surface through a chemical reaction, thereby imparting dispersion stability to the pigment and dispersing it. Examples of hydrophilic functional groups include phosphorus-containing groups such as carboxyl groups and phosphonic acid groups, and acidic groups such as sulfo groups.

[0044] When the pigment is a self-dispersing pigment, the ink viscosity ratio can be adjusted by adjusting the amount of hydrophilic functional groups introduced onto the pigment surface. Note that resin-dispersed pigments are preferred because they can easily achieve pigment dispersion stability even when the ink viscosity ratio is less than 2 times.

[0045] 2.2.Surfactants The ink composition may contain a surfactant. Examples of surfactants include acetylene glycol surfactants, silicone surfactants, and fluorine surfactants. Among these, it is preferable that the ink composition contains an acetylene glycol surfactant. By including an acetylene glycol surfactant, the surface tension of the ink is reduced, the wettability to the recording medium is improved, and clogging recovery and ejection stability tend to be further improved. Note that one type of surfactant may be used alone, or two or more types may be used in combination.

[0046] From the viewpoint of further improving the effects of the present invention, it is preferable that the ink composition contains an acetylene glycol surfactant with an HLB value of 5 or less. In this case, compared to those with an HLB value of more than 5, they are relatively superior in the above respects, but on the other hand, they tend to have low solubility in water, are prone to phase separation in the ink, and tend to have reduced ejection stability, etc.

[0047] The lower limit of the HLB value is 0 or more, preferably 1 or more. It is preferable to include both 5 or less and more than 5, more preferably 5 or less and 7 or more, and even more preferably 5 or less and 10 or more. In this case, wettability, clogging recovery, ejection stability, etc. are more excellent, and phase separation is also more excellently suppressed, which is preferable. The upper limit of the HLB is 20 or less, preferably 15 or less.

[0048] In this specification, the term "HLB value (hydrophilic lipophilic balance)" refers to a value calculated by the Griffin method. Specifically, the HLB value of a surfactant can be calculated according to the following formula (H): HLB value = 20 × (mass % of hydrophilic groups) (H)

[0049] Commercially available acetylene glycol surfactants include, for example, Surfynol 104PG50 (HLB value=4), Surfynol 104, Surfynol 420, Surfynol 82, Surfynol DF110D, Surfynol 104S, Surfynol 420, Surfynol 82, and Surfynol MD-20 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), and Olfine E1010 (trade name, HLB value: 13 to 14, manufactured by Air Products Co., Ltd.). From the viewpoint of more effectively and reliably achieving the effects of the present invention, it is preferable for the ink composition to contain at least one of Surfynol 104PG50 and Olfine E1010, and it is more preferable for the ink composition to contain Surfynol 104PG50 and Olfine E1010.

[0050] The content of the surfactant is preferably 0.05% by mass or more and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.2% by mass or more and 2.0% by mass or less, relative to the total amount of the ink composition. By setting the content of the surfactant within the above ranges, clogging recovery, color development, and ejection stability tend to be further improved. From the same viewpoint, the content of the acetylene glycol surfactant is preferably 0.05% by mass or more and 5.0% by mass or less, 0.1% by mass or more and 3.0% by mass or less, or 0.2% by mass or more and 2.0% by mass or less, relative to the total amount of the ink composition. A range of 0.5 to 1.0% by mass is even more preferable.

[0051] The content of the acetylene glycol surfactant having an HLB value of 5 or less may be within the above range, which is preferable from the above viewpoint, and is more preferably 0.2% by mass or more and 0.8% by mass or less, more preferably 0.3% by mass or more and 0.7% by mass or less, and even more preferably 0.4% by mass or more and 0.6% by mass or less.

[0052] 2.3. Lactam compounds The ink composition preferably contains a lactam compound. A lactam compound has a structure in which a carboxy group and an amino group in a 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 viewpoint, 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 lactam compound having a 4- or 5-membered lactam ring is also preferred.

[0053] The lactam compounds may be used alone or in combination of two or more. It is also preferred to use a lactam having a 4- or 5-membered lactam ring in combination with a lactam having a 6- or 8-membered lactam ring.

[0054] Specific examples of lactam compounds include ε-caprolactam, N-hydroxyethylpyrrolidone (HEP), δ-valerolactam, and 5-(methylamino)pentanoic acid lactam, and it is preferable to include ε-caprolactam, N-hydroxyethylpyrrolidone (HEP), 2-pyrrolidone, etc. By including these compounds, clogging recovery, color development, and ejection stability tend to be further improved.

[0055] The content of the lactam compound is preferably from 0.1 to 15% by mass, and more preferably from 0.5 to 10% by mass, more preferably from 1 to 8% by mass, and even more preferably from 2 to 7% by mass, relative to the total mass of the ink composition. The content of lactams having a 6- to 8-membered lactam ring may be within the above range, more preferably 1 to 5 mass %, and even more preferably 2 to 4 mass %. By setting the content of the lactam compound within the above range, clogging recovery, color development, and ejection stability tend to be further improved.

[0056] 2.4. Water-soluble organic solvents The ink composition preferably contains a water-soluble organic solvent as a solvent component. By containing a water-soluble organic solvent, the ink composition tends to have excellent clogging recovery properties and ejection stability. Examples of water-soluble organic solvents include polyhydric alcohols, glycol ethers, nitrogen-containing solvents, esters, and cyclic esters. Among these, it is preferable to contain polyhydric alcohols as the water-soluble organic solvent.

[0057] Polyhydric alcohols have two or more hydroxyl groups in the molecule, and examples thereof include alkanediols such as 1,2-hexanediol or 1,2-butanediol, and polyols.

[0058] 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 preferred from the viewpoint of further improving clogging recovery and ejection stability. Alkanediols having 5 or more carbon atoms are preferred, and alkanediols having 5 to 8 carbon atoms are more preferred. 1,2-alkanediols are preferred.

[0059] Specific examples of polyol compounds include ethylene glycol, propylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, dipropylene glycol, trimethylolpropane, and glycerin. Examples include those having three or more hydroxyl groups in the molecule, those having an ether group in the skeleton (an intermolecular condensation product of alkanediol), and alkanediols having four or less carbon atoms. Glycol ethers are those in which one of the hydroxyl groups of the above polyhydric alcohols has been etherified. The etherification is preferably alkyl etherification. Examples include diethers and monoethers, with monoethers being preferred. Examples include, but are not limited to, triethylene glycol monobutyl ether. Among these, from the viewpoint of further improving clogging recovery and ejection stability, it is preferable to use glycerin, triethylene glycol, or triethylene glycol monobutyl ether.

[0060] The content of the water-soluble organic solvent is preferably 5.0% by mass to 40% by mass, 10% by mass to 30% by mass, or 12% by mass to 25% by mass, more preferably 15 to 20% by mass, relative to the total amount of the ink composition. By setting the content of the water-soluble organic solvent within the above range, the effects of the present invention tend to be more effectively and reliably exhibited.

[0061] The content of the alkanediols is preferably from 0.5% to 7.0% by mass, and more preferably from 1.0% to 5.0% by mass, relative to the total amount of the ink composition. By being within such a range, the effects of the present invention tend to be more effectively and reliably achieved. The content of the alkanediol having 5 or more carbon atoms may be set within the above range, and is preferred.

[0062] The content of the polyols is preferably from 5.0% to 30% by mass, and more preferably from 10% to 20% by mass, relative to the total amount of the ink composition. By being within such a range, the effects of the present invention tend to be more effectively and reliably achieved.

[0063] The content of the polyol having a normal boiling point of 280° C. or higher in the ink is preferably from 1 to 15% by mass, more preferably from 3 to 10% by mass, and even more preferably from 5 to 9% by mass. The content of polyhydric alcohols, including polyols having a normal boiling point of 280° C. or higher, in the ink may be within the above range.

[0064] 2.5.Resin particles The ink composition may contain resin particles. Examples of resin particles include resin particles made of urethane-based resins, acrylic-based resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, vinyl chloride-based resins, and the like. Among these, urethane-based resins are preferred from the viewpoint of more effectively and reliably achieving the effects of the present invention. These resin particles are often handled in the form of an emulsion, but may also be in the form of a powder. Note that one type of resin particle may be used alone, or two or more types may be used in combination.

[0065] Examples of urethane-based resin particles include urethane resin emulsions. The urethane resin emulsions are not particularly limited as long as they are resin emulsions having urethane bonds in the molecules, and examples include polyether-type urethane resins having ether bonds in the main chain, polyester-type urethane resins having ester bonds in the main chain, and polycarbonate-type urethane resins having carbonate bonds in the main chain. Among these, cationic or anionic urethane resin particles are preferred.

[0066] Commercially available urethane resin particles include, for example, Superflex 420, 600, 610, and 620 (trade names, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Hydran CP-7010, CP-7020, and CP-7030 (trade names, manufactured by Dainippon Ink and Chemicals, Inc.), and Urethane Emulsion WBR-2120C and WBR-2122C (trade names, manufactured by Taisei Fine Chemical Co., Ltd.). Of these, Superflex 420 is preferred from the viewpoint of more effectively and reliably achieving the effects of the present invention.

[0067] Examples of acrylic resin particles include acrylic resin emulsions. The acrylic resin emulsions are not particularly limited, but examples include those obtained by polymerizing (meth)acrylic monomers such as (meth)acrylic acid and (meth)acrylic acid esters, and those obtained by copolymerizing (meth)acrylic monomers with other monomers.

[0068] The content of the resin particles is from 0.05% to 3.0% by mass, from 0.1% to 2.0% by mass, or from 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 range, the effects of the present invention can be more effectively and reliably achieved.

[0069] 2.6.Water The ink of this embodiment is a water-based ink, which contains water as a solvent component. It is preferable that the water be one from which ionic impurities have been removed as much as possible. Examples of such water include, but are not limited to, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, as well as ultrapure water.

[0070] The water content is preferably 30% by mass or more and 99% by mass or less, more preferably 35% by mass or more and 90% by mass or less, and even more preferably 40% by mass or more and 80% by mass or less, based on the total amount of the ink composition.

[0071] 2.7.Other Ingredients The ink composition of this embodiment may contain components other than those described above, as necessary. Examples of such components include a pH adjuster, a chelating agent, and a rust inhibitor.

[0072] 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 (triethanolamine, diethanolamine, monoethanolamine, tripropanolamine), organic acids (e.g., adipic acid, citric acid, succinic acid, etc.), etc. From the viewpoint of more effectively and reliably achieving the effects of the present invention, triethanolamine is preferred.

[0073] The content of the pH adjuster is preferably 0.05% by mass to 3.0% by mass, 0.1% by mass to 2.0% by mass, or 0.2% by mass to 1.0% by mass, relative to the total amount of the ink composition. By keeping the content of the pH adjuster within the above ranges, the effects of the present invention tend to be more effectively and reliably achieved.

[0074] 3. Recording Media In this embodiment, an absorbent recording medium is used as the recording medium. The recording surface of the absorbent recording medium is made of paper such as plain paper or inkjet paper, cloth, or an organic or inorganic material that has the property of absorbing ink. Paper such as plain paper or inkjet paper is preferred. From the viewpoint of more effectively and reliably achieving the effects of the present invention, it is preferable that the calcium salt be contained in a portion of the recording medium that absorbs the ink composition even without water, such as the entire recording medium or a layer that absorbs the ink composition. Examples of calcium salts include water-soluble calcium salts and poorly water-soluble calcium salts. Water-soluble calcium salts are preferred in terms of further enhancing the color development of the ink, but poorly water-soluble calcium salts are also acceptable. Examples of poorly water-soluble calcium salts include calcium carbonate. Examples of water-soluble calcium salts include calcium chloride.

[0075] In this embodiment, the term "absorbent recording medium" refers to a recording medium that has a water absorption rate of 10 mL / m2 or more within 30 msec from the start of contact in the Bristow method. 2This 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."

[0076] The recording speed of this recording method is preferably 35 pages / minute (ppm) or more, more preferably 40 pages / minute or more, and even more preferably 50 pages / minute (ppm) or more, converted into the conveying speed of the recording medium. A speed of 60 ppm or more is particularly preferable. Since clogging is likely to occur when recording at such speeds, the effects of the present invention are even more effective. The above page count is preferably based on A4 paper.

[0077] Although there is no upper limit to the printing speed, it is preferably 100 pages / minute or less, and more preferably 80 pages / minute or less. When printing on one side of a recording medium, pages / minute = sheets / minute, and when printing on both sides of a recording medium, pages / minute = sheets / minute x 2.

[0078] When the speed is above the above range, recording is performed quickly and is useful, but on the other hand, the generation of paper dust and the amount of ink supplied tend to increase, and the effect of the present invention is more effective. Furthermore, when double-sided printing is performed, the generation of paper dust and the amount of ink supplied tend to increase, making the effects of the present invention even more effective.

[0079] It is preferable that the recording medium be A4 size, but the size of the recording medium is not limited because recording one sheet requires the recording medium to be fed from the paper feed tray and then discharged to the paper discharge tray once, which may result in the generation of paper dust, etc.

[0080] 4. Inkjet recording device The inkjet recording apparatus of this embodiment is for obtaining a recorded matter by the inkjet recording method described above, and includes the ink composition described above, the inkjet head described above, and the transport means described above.

[0081] FIG. 4 shows one embodiment of an ink supply mechanism for an inkjet recording device. More specifically, FIG. 4 is a schematic perspective view showing the arrangement of ink containers and pressure adjustment valves in the ink supply mechanism. As shown in FIG. 4, the ink supply mechanism 100 includes, for example, an ink container 4 and a pressure adjustment valve 8. It also includes a transparent cylindrical container 3 and a pressure sensor 5 associated with the ink container 4. The pipe 7a connecting the ink container 4 to the on-off valve 6, the pipe 7b connecting the on-off valve 6 to the pressure adjustment valve 8, and the pipe 7c connecting the pressure adjustment valve 8 to the droplet ejection head set 2 are all flexible tubes made of, for example, polyethylene terephthalate. Ink is supplied from an ink cartridge (not shown) or the like to the container 3 of the ink container 4 via the IN port.

[0082] The droplet ejection head set 2 is an inkjet head that is a line head and has multiple heads arranged in a row in the left-right direction of the figure. Each head has a nozzle row (not shown), and the nozzle row has multiple nozzles arranged in a row in the left-right direction of the figure. From the perspective of head productivity, it is common to use a line head in which multiple heads are combined, as in the droplet ejection head set 2, rather than a single long line head. During printing, a large ink flow rate is required in a short period of time because ink is supplied to the ejection sections of the multiple heads in the droplet ejection head set 2 by the pressure adjustment valve 8. The recording method of this embodiment is suitable for line-type recording devices that require a large ink flow rate in a short period of time.

[0083] Next, another embodiment of the inkjet recording apparatus is shown in Fig. 5. Fig. 5 is an overall view of the inkjet recording apparatus, including the configuration related to the transport of the recording medium.

[0084] The inkjet recording apparatus according to this embodiment will be described in further detail with reference to Fig. 5. In the XYZ coordinate system shown in Fig. 5, 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 apparatus, and the Z direction indicates the height direction of the apparatus.

[0085] 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 8, an Fd (face-down) discharge unit 20 as an "discharge unit," an Fd (face-down) placement unit 22 as a "placement unit," a reversing path unit 24 as a "reversing conveyance mechanism," an Fu (face-up) discharge unit 26, and an Fu (face-up) placement unit 28.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] The recording unit 8 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. The inkjet head 48 is arranged such that the Y-axis direction in the figure is the direction in which the nozzles of the nozzle row of the line head are lined up, and for example, the ink droplet ejection head set 2 of Figure 4 may be arranged such that the Y-axis direction is the direction in which the nozzles of the nozzle row are lined up. Note that the inkjet recording device of Figure 5 may also have an ink supply mechanism such as an ink container, but this is omitted from the figure.

[0091] The inkjet head 48 is a line head having a length equal to or greater than the recording area of ​​the recording medium in a direction intersecting the direction of conveyance of the recording medium (the Y direction in the figure). Here, the length of the line head is the length of the nozzle row of the line head, which is the length 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 in the Y direction of the recording medium that can be recorded on.

[0092] Furthermore, if the recording unit 8 is configured as an inkjet head mounted on a carriage that moves back and forth in the Y-axis direction, and one of the heads in FIG. 4 is configured as an inkjet head with the direction in which the nozzles of the nozzle row are arranged in the X-direction in FIG. 5, then a serial-type inkjet recording device will be obtained.

[0093] The inkjet head 48 is disposed so as to face the upper section 42a of the endless belt 42 supported by the support body 44. When the recording medium P is transported in the upper section 42a of the endless belt 42, the inkjet head 48 ejects ink toward the recording medium P to perform recording. The recording medium P is transported downstream of the transport path 11 by the belt transport unit 16 while recording is being performed.

[0094] 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, which 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, which reverses the recorded side of the recording medium P and conveys the recording medium P again to the recording unit 8. Note that the recording medium P switched to the reversing path 52 by the first branch section 50 is reversible in the conveying process on the reversing path 52, and is conveyed again to the recording unit 8 so that the side opposite to the first recorded side faces the inkjet head 48. In this way, double-sided printing is performed. When double-sided printing is performed, the conveying path tends to be longer and paper dust tends to be generated more, making the recording method of this embodiment particularly useful.

[0095] 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.

[0096] 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. [Example]

[0097] 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.

[0098] 1. Preparation of Ink Composition 1 to 3, Tables 1 to 3 show the compositions of the ink compositions used in the examples and comparative examples and the evaluation results thereof. Each component was placed in a mixing tank so as to obtain the composition shown in Tables 1 to 3, mixed and stirred, and then filtered through a membrane filter to obtain an inkjet ink composition for each example. The numerical values ​​for each component shown in each example in the tables represent mass % unless otherwise specified. Furthermore, the numerical values ​​for inorganic oxide particles, resin particles, and pigment dispersions represent mass % of the solid content of the inorganic oxide particles, resin particles, and pigment, respectively. All of the resulting inks were magenta inks.

[0099] Details of the abbreviations and product ingredients used in Tables 1 to 3 are as follows, and the numbers to the right of the solvent abbreviations indicate the SP values ​​of the solvents. [Pigment] Pigment dispersions A to F were prepared as follows. Dispersion A: 20% by mass of the azo pigment CI Pigment Red 150 (PR150), 5% by mass of a resin dispersant (a styrene-acrylic acid copolymer neutralized with sodium hydroxide, acid value 150 mg KOH / g, molecular weight 10,000), and 75% by mass of pure water were mixed and stirred to obtain a mixture. This mixture was placed in 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 3.0 μm pore cellulose acetate filter to obtain a pigment dispersion.

[0100] Dispersion B: Dispersion B was obtained in the same manner as Dispersion A, except that the acid value of the resin dispersant was changed to 260 mgKOH / g.

[0101] Dispersion C: Dispersion C was prepared in the same manner as Dispersion A, except that CI Pigment Red 150 (PR150) was replaced with CI Pigment Violet 19 (PV19), a quinacridone pigment.

[0102] Dispersion D: Dispersion D was prepared in the same manner as Dispersion A, except that CI Pigment Red 150 (PR150) was replaced with CI Pigment Violet 19 (PV19), a quinacridone pigment, and the acid value of the resin dispersant was changed to 260 mg KOH / g.

[0103] Dispersion E: Dispersion E was obtained in the same manner as Dispersion A, except that the acid value of the resin dispersant was changed to 200 mg KOH / g.

[0104] Dispersion F: Dispersion F was obtained in the same manner as Dispersion A, except that CI Pigment Red 17 (PR17), an azo pigment, was used instead of CI Pigment Red 150 (PR150).

[0105] [Lactam compounds] HEP ε-caprolactam [Water-soluble organic solvent] 1,2-Hexanediol 1,2-Butanediol Glycerin TEG (triethylene glycol) TEGmBE (triethylene glycol monobutyl ether) [Surfactants] Olfine E1010 (product name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.) Surfynol 104 (trade name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.) [resin] Superflex 420 (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) [pH adjuster] TEA (triethylamine)

[0106] 2. Evaluation Method 2.1. Thickening rate Each ink composition obtained above was mixed with an aqueous calcium solution (Ca concentration: 0.3 mol / L) at a ratio of 10:1, and the mixture was left to stand at 60°C for 24 hours. The viscosity η1 of the ink composition after standing and the viscosity η0 of the ink composition in its initial state were calculated as the viscosity increase rate as shown below, and evaluation was performed. Viscosity increase rate = ink viscosity after standing η1 / initial ink viscosity η0 (Evaluation criteria) A: The viscosity increase rate is 1.5 or less. B: The viscosity increase rate is more than 1.5 and 2.0 or less. C: The viscosity ratio is over 2.0.

[0107] 2.2.Color development The ink application amount was 5.0 mg / inch using a modified recording device, PX-S840 (product name, manufactured by Seiko Epson Corporation). 2 A magenta monochrome test pattern was recorded on plain paper (manufactured by Navigator) so that the OD value was measured using a colorimeter (manufactured by Xrite, Xrite i1), and evaluated according to the following criteria. (Evaluation criteria) A:OD value is 0.85 or more B:OD value is 0.75 or more and less than 0.85 C:OD value is 0.65 or more but less than 0.75 D:OD value is less than 0.65

[0108] 2.3.Redispersibility The resulting ink composition and an aqueous calcium solution (Ca concentration: 0.3 mol / L) were mixed at a ratio of 10:1, and five 2 μl drops of the mixed liquid were placed on a glass slide and dried for 24 hours at 60° C. The dried slide was immersed in a sample bottle containing only the ink composition before mixing and left for 3 minutes. After being turned upside down five times, the slide was removed and the remaining mixed liquid in the glass and the degree of re-dissolution were visually evaluated according to the following criteria. (Evaluation criteria) A: All solids have redissolved and are no longer visible B: The solids have become smaller, but some residue is still visible. C: The solids did not become smaller and most of them remained. D: The ink composition that received a C rating was tested again under the same conditions except that the drying temperature was changed to 40°C. As a result, as with drying at 60°C, the solids did not become smaller and most of them remained.

[0109] 2.4.Lightfastness The recorded matter obtained during the evaluation of color development was subjected to a lightfastness test in accordance with JEITA CP-3901B, and evaluated according to the following criteria based on the calculated lifespan. (Evaluation criteria) A: More than 50 years B: 30 years or more but less than 50 years C: 10 years or more but less than 30 years D: Less than 10 years

[0110] 2.5.Compatibility The ink composition obtained above was placed in a glass screw tube, which was then capped and left to stand for 24 hours in a thermostatic chamber at 60° C. The screw tube was then removed from the thermostatic chamber, and it was confirmed whether the surfactant had separated due to phase separation on the ink surface, and the result was evaluated according to the following criteria. (Evaluation criteria) A: No separation of surfactant was observed B: The surfactant separated and floated on the liquid surface. C: The surfactant separated into two layers.

[0111] 3. Recording Test The ink composition obtained above was filled into the following two types of recording devices, and continuous printing was carried out on plain paper (manufactured by Navigator). A modified line-type recording device (LX-10050MF, manufactured by Seiko Epson Corporation). It is a line-type recording device as shown in Figure 5, and is equipped with a line head and ink supply mechanism as shown in Figure 4. A modified serial recording device (PX-M886FL, manufactured by Seiko Epson Corporation). The line recording device was converted into a serial recording device as described above.

[0112] 3.1.Discharge stability After filtering and degassing, the ink was filled into the recording device and test patterns were continuously printed. With the line-type recording device, 100 sheets of A4 paper (Navigator paper (plain paper)) were continuously printed at a speed of 60 pages per minute (ppm). Printing was performed on one side. The test pattern consisted of a 1 x 1 cm solid pattern arranged in a checkerboard pattern in the recordable area.

[0113] With the serial recording device, 100 sheets were printed continuously at a speed of 30 pages per minute, single-sided. The rest of the test was carried out in the same manner. In addition, with the serial recording device, flushing was carried out at a position where the head was separated from the recording medium after each pass (one main scan).

[0114] After printing, a nozzle check pattern was printed to check the number of nozzles that had print deviations or non-ejection, and the results were evaluated according to the following criteria. Nozzles with a landing position deviation of more than half the distance between adjacent nozzles were considered to have print deviations. Note that ejection stability is also affected by factors such as the viscosity of the ink (initial viscosity) and whether the amount of ink supplied to the inkjet head can keep up. (Evaluation criteria) A: No misprinting or non-ejecting nozzles occurred B: Printing deviation or non-ejecting nozzles occurred in less than 50% of the nozzles. C: Printing irregularities or non-ejecting nozzles occurred in 50% or more but less than 70% of the nozzles D: Printing deviation or non-ejecting nozzles occurred in 70% or more of the nozzles.

[0115] 3.2.Clogging recovery Continuous printing was carried out in the same manner as in the above-mentioned ejection stability test, except that it was carried out continuously for 10 minutes.

[0116] The inkjet head was then left uncapped, misaligned from the printer's cap, in an environment with a temperature of 40°C and humidity of 20% for 7 days. After leaving the inkjet head, the ink was cleaned by suctioning ink from the nozzles, counting the number of nozzles that could not eject ink, and repeating the cleaning operation until all nozzles were restored. Evaluation was then performed based on the number of cleanings required until all nozzles were restored, using the following evaluation criteria. Note that clogging recovery is affected by the degree of dried ink solidification in the nozzles and the composition of the dried solidification. (Evaluation criteria) A: All nozzles recovered within two cleanings. B: All nozzles recovered after 3 or 4 cleanings C: All nozzles recovered after 5 or 6 cleanings D: Nozzles were found to be unrecovered even after six cleanings

[0117] 4. Evaluation Results The compositions of the inks used in each example and the evaluation results are shown in Tables 1 to 3. Tables 1 to 3 show that excellent ejection stability and clogging recovery are achieved when recording is performed using an inkjet recording method that includes a transport step of transporting a recording medium by a transport means and a deposition step of ejecting an ink composition from an inkjet head and depositing it on the transported recording medium, wherein the inkjet head is a line head having a length equal to or greater than the recording area of ​​the recording medium in a direction intersecting the transport direction, the recording medium is an absorbent recording medium, the ink composition is a reddish water-based ink containing a pigment, the pigment includes an azo-based pigment, and when 10 parts by mass of the ink composition is mixed with 1 part by mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L, the viscosity η1 of the mixture is less than 2.0 times the viscosity η0 of the ink composition.

[0118] Although not shown in the table, when the same procedure was carried out in Example 1 for clogging recovery using the above-mentioned line-type recording device, except that continuous printing was performed using double-sided printing, the evaluation result was B. This shows that double-sided printing increases the generation of paper dust in the process of reversing the recording medium, which affects clogging recovery, but with this embodiment, excellent clogging recovery was obtained. [Explanation of symbols]

[0119] 100...carriage, 2...droplet ejection head set, 3...container, 4...ink container, 5...pressure sensor, 6...opening / closing valve, 7a, 7b, 7c...piping, 8...pressure adjustment valve, 10...recording device, 11...conveyance path, 12...feed section, 14...conveyance section, 16...belt conveyance section, 18...recording section, 20...Fd discharge section, 22...Fd placement section, 24...reversal path section, 26...Fu discharge section, 28...Fu placement section, 30...feed tray, 32...feed roller, 34...conveyance 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 portion, 52...reverse path, 54...second branch portion, 56...discharge roller pair, 64...discharge drive roller, 68...drive shaft, 76...placing surface, 78...convex portion, 80...first urging member, 82...second urging member, 84, 86...support shaft, P...recording medium.

Claims

1. a conveying step of conveying the recording medium by a conveying means; a deposition step of ejecting an ink composition from an inkjet head and depositing the ink composition onto the recording medium being transported in the transport step, the inkjet head is a line head having a length equal to or greater than the length of a recording area of ​​the recording medium in a direction intersecting the transport direction, the recording medium is an absorbent recording medium; the ink composition is a red water-based ink containing a pigment, The pigment includes an azo pigment, a viscosity η1 of a mixture obtained by mixing 10 parts by mass of the ink composition with 1 part by mass of an aqueous calcium propionate solution having a Ca element concentration of 0.3 mol / L is less than 2.0 times the viscosity η0 of the ink composition; Inkjet recording method.

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

3. The pigment further comprises a quinacridone pigment. The inkjet recording method according to claim 1 .

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

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

6. The ink composition contains an acetylene glycol surfactant. The inkjet recording method according to claim 1 .

7. The acetylene glycol surfactant has an HLB value of 5 or less. The inkjet recording method according to claim 6.

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

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

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

11. the ink composition contains a resin dispersant that disperses the pigment, The acid value of the resin dispersant is 250 mg KOH / g or less. The inkjet recording method according to claim 1 .

12. The recording speed is 50 pages / minute or more. The inkjet recording method according to claim 1 .

13. An inkjet recording apparatus for obtaining a recorded matter by the inkjet recording method according to any one of claims 1 to 12, comprising: an ink jet head including the ink composition, the ink jet head, and the conveying means; Inkjet recording device.

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