Recording method and recording apparatus

Abstract

To provide a recording method capable of reducing color difference stripes even when using a recording device having parts with different impact time differences.SOLUTION: And an ink attaching step of ejecting the ink composition from an ink jet head and attaching the ink composition to the recording medium transported by the transport step, in which the ink jet head is a line head having a length equal to or longer than a recording region of the recording medium in a direction intersecting a transport direction, the ink composition includes a first ink which contains an azo-based pigment and is a red-based ink and a second ink which contains a pigment and is a chromatic color ink other than the red-based ink, the first ink and the second ink are water-based inks, in the line head, a plurality of first nozzles which discharge the first ink are disposed in a direction intersecting a transport direction, and a plurality of second nozzles which discharge the second ink are disposed in the direction intersecting the transport direction, wherein the line head has a portion in which a time difference between landing of the first ink and landing of the second ink on the recording medium is different between portions of the line head in a direction intersecting the transport direction, and at least one of the first ink and the second ink has a viscosity increase rate of less than 2.0 times when an ink and a calcium propionate aqueous solution having a Ca concentration of 0.3 mol / L are mixed at a mass ratio of 10:1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a 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. For example, Patent Document 1 discloses a recording device equipped with a line head. The recording device in Patent Document 1 has a specific head arrangement, which can cause color unevenness in printed matter. To reduce this, Patent Document 1 discloses a recording method that uses an ink composition containing inorganic oxide particles to reduce color differences in the width direction, which intersects with the scanning direction, in the resulting recorded matter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-135219 Summary of the Invention [Problem to be solved by the invention]

[0004] A recording device having a line head is suitable for high-speed printing. In a recording method using a recording device having a line head, there are problems in suppressing the appearance of areas with color differences in an image and achieving excellent color development in red images. [Means for solving the problem]

[0005] One aspect of the recording method according to the present invention is to a conveying step of conveying the recording medium; an ink deposition step of ejecting an ink composition from an inkjet head and depositing the ink composition on the recording medium transported in the transport step; and 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 ink composition includes a first ink that is a reddish ink containing an azo pigment, and a second ink that is a chromatic color ink other than a reddish ink that contains a pigment, the first ink and the second ink are water-based inks, the line head has a plurality of first nozzles that eject the first ink arranged in a direction intersecting the transport direction, and a plurality of second nozzles that eject the second ink arranged in a direction intersecting the transport direction, the line head has a portion in which a time difference between landing of the first ink and landing of the second ink on the recording medium differs between portions of the line head in a direction intersecting the transport direction, At least one of the first ink and the second ink has a viscosity increase rate of less than 2.0 times when the ink is mixed with an aqueous calcium propionate solution having a Ca concentration of 0.3 mol / L at a mass ratio of 10:1.

[0006] One aspect of the recording device according to the present invention is A recording device that performs the above-mentioned recording method, the ink composition; a transport mechanism that performs the transport step; The inkjet head. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a recording apparatus that can be used in a recording method according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram of an example of an inkjet head having portions with different inter-nozzle distances. [Figure 3] FIG. 10 is a schematic diagram of another example of an inkjet head. [Figure 4] Table 1 shows the compositions of inks used in the examples and the evaluation results. [Figure 5]Table 2 shows the compositions and evaluation results of the inks used in the examples, comparative examples, and reference examples. [Figure 6] Table 3 shows the conditions and evaluation results of the examples. [Figure 7] Table 4 shows the conditions and evaluation results of the examples. [Figure 8] Table 5 shows the conditions and evaluation results for Examples, Comparative Examples, and Reference Examples. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following describes embodiments of the present invention. The embodiments described below are examples of the present invention. The present invention is not limited to the following embodiments, and includes various modified forms that are implemented within the scope of the present invention. Note that not all of the configurations described below are necessarily essential configurations of the present invention.

[0009] 1. Recording method The recording method according to this embodiment includes a transporting step of transporting a recording medium, and an ink depositing step of ejecting an ink composition from an inkjet head and depositing it onto the recording medium transported in the transporting step.

[0010] Recording devices with line heads are suitable for high-speed printing. Line heads often have multiple unit heads arranged side by side. This type of line head is particularly useful when using multiple color inks and shortening the length of the line head in the transport direction to create a space-saving line printer.

[0011] However, depending on the configuration and arrangement of the unit heads, there may be portions in the line head where the distance between the nozzles of the first ink and the nozzles of the second ink in the transport direction (scanning direction) of the recording medium differs, resulting in portions where the time difference between the landing of the first ink and the landing of the second ink on the same portion of the recording medium differs.

[0012] With such a line head, when the line head is viewed in the recording medium transport direction (scanning direction), the resulting image has areas in the width direction, which intersects with the transport direction, where the color tone differs between areas with different landing time differences, and this can cause areas with color differences in the image to appear as bands or streaks. Such color differences are called color difference streaks.

[0013] According to this embodiment, it is possible to reduce color difference streaks and obtain an image with excellent color development. The ink composition, recording medium, steps of the recording method, and recording aspects will be described below, and an overview of the recording device such as an inkjet head will be described later.

[0014] 1.1. Ink composition The ink composition used in the recording method of this embodiment includes a first ink, which is a reddish ink containing an azo pigment, and a second ink, which is a chromatic color ink other than a reddish ink, containing a pigment. The first ink and the second ink are water-based inks.

[0015] 1.1.1. First ink The first ink is a red-based ink containing an azo-based pigment. Red-based inks are primarily used to express red when printing is performed using multiple ink colors to reproduce secondary or higher colors. For example, magenta ink, red ink, or inks similar to these may be used. It is an ink that does this.

[0016] 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.

[0017] Red is the L standardized by the CIE (International Commission on Illumination). * a * b *It refers to a color whose hue angle is within a predetermined range in a color system. The hue angle of red is preferably 5° to 60°, 15° to 50°, or 25° to 40°. Red-based inks are inks that are primarily used when printing red. Preferably, they are inks that can express the red color by themselves.

[0018] (1) Azo pigments The first ink contains an azo pigment. Examples of azo pigments include monoazo pigments, disazo pigments, condensed disazo pigments, and benzimidazolone pigments. The azo pigment contained in the first ink is an azo pigment that makes the first ink a reddish ink, and is a reddish azo pigment. For example, when the azo pigment is the only colorant contained in the ink, the ink becomes a reddish ink.

[0019] The azo pigment may be a pigment that can produce a red ink. Specific examples of the azo pigment 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 114, CI Pigment Red 146, CI Pigment Red 185, 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.

[0020] Of the above examples, the azo pigment is preferably selected from CI Pigment Red 150, CI Pigment Red 269, CI Pigment Red 17, and solid solutions thereof, since images with better color development can be obtained.

[0021] Furthermore, examples of azo pigments include pigments having a chemical structure represented by the following formula (I), which are preferred.

[0022] [ka]

[0023] (In formula (I), A represents a hydrogen atom or an aromatic group.)

[0024] 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.

[0025] By selecting the azo pigment from among pigments having the chemical structure represented by the above formula (I) and solid solutions thereof, it is possible to obtain images with even better color development.

[0026] The azo pigment may be a resin-dispersed pigment dispersed in a resin as described below, or may be a self-dispersed pigment in which a functional group is introduced by treating the pigment surface, and a resin-dispersed pigment is preferred.

[0027] 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.

[0028] The volume average particle size of the azo pigment is preferably 10 nm or more and 110 nm or less, more preferably 50 nm or more and 110 nm or less, even more preferably 80 nm or more and 110 nm or less, even more preferably 80 nm or more and less than 110 nm, and particularly preferably 80 nm or more and 100 nm or less.

[0029] By setting the volume average particle size of the azo pigment within the above range, the dispersion stability of the pigment is good, color development is improved, and settling of the components during storage is further suppressed.

[0030] The content of the azo pigment is preferably 1% by mass or more relative to the total mass of the composition, more preferably 1 to 10% by mass, preferably 3% by mass or more to 8% by mass or less, more preferably 3% by mass or more to 7% by mass or less, even more preferably 3% by mass or more to 7% by mass or less, even more preferably 5 ....5% by mass or more to 7% by mass or less. When the content of the azo pigment is within this range, images with even better color development can be obtained.

[0031] (2) Other ingredients Pigments other than azo pigments The first ink may contain a magenta pigment other than an azo pigment, so long as it can be a magenta ink, red ink, or inks similar thereto (i.e., red-based inks). Examples of such pigments include CI Pigment Red 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 18, 19, 21, 23, 30, 32, 37, 38, 40, 41, 42, 88, 112, 122, 123, 144, 149, 166, 168, 171, 175, 176, 177, 178, 179, 187, 202, 209, 219, and 224, and CI Pigment Violet 19, 23, 32, 33, 36, 38, 43, and 50. As the pigment other than the azo pigment, a quinacridone pigment is preferred.

[0032] When the first ink contains these pigments, the content of the azo pigment relative to the total mass of the pigments contained in the first ink is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. It is preferable. The upper limit is 100% by mass or less, and although not limited thereto, it may be 90% by mass or less, or 85% by mass or less. When it is above the above range, the color development is more excellent, which is preferable. When it is below the above range, it is preferable in terms of the degree of freedom in ink design and low cost.

[0033] By including an azo pigment in the first ink, the color development of the first ink can be further enhanced. For example, if the first ink has low reactivity with calcium ions, the ink will easily penetrate the recording medium and will not easily remain on the surface of the recording medium, resulting in low color development of the ink. There are various types of pigments suitable for red inks, and among these, azo pigments tend to have excellent color development. By using an azo pigment in the first ink, it is possible to create a red ink with high color development, even if the first ink has low reactivity with calcium ions.

[0034] The color of the first ink is not limited, but the first ink may be, for example, a magenta ink, a process color ink. Particularly in business applications, high visibility of red marks on recorded materials, such as confidentiality markings and printed seals, is required, and the magenta ink used for this color is required to have high color development. Furthermore, because red is a highly visible color, color difference streaks are easily noticeable. Therefore, when recording colors using magenta ink, it is required to be possible to reduce color difference streaks, and the present invention provides excellent effects in this regard.

[0035] ·water The first ink is a water-based red ink (e.g., magenta ink). Water-based means that it contains water as one of its main solvent components. This reduces the environmental impact and enables recording with less odor.

[0036] Water is contained as the main solvent component of the ink and is a component that evaporates and dissipates upon drying. The water is preferably pure water or ultrapure water, such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, from which ionic impurities have been removed as much as possible. Furthermore, using water that has been sterilized by ultraviolet irradiation or the addition of hydrogen peroxide is preferable, as this can prevent the growth of mold and bacteria when the ink is stored for a long period of time.

[0037] The water content of the ink is preferably 45% by mass or more, more preferably 50% by mass to 98% by mass, and even more preferably 55% by mass to 95% by mass. It is further preferably 65% ​​by mass to 90% by mass, and even more preferably 70% by mass to 85% by mass. A water content of at least this range is preferred because it provides excellent ink drying properties and prevents the image on the recorded product from being rubbed off and becoming dirty.

[0038] Organic solvents The first ink may contain an organic solvent. Such an organic solvent is preferably water-soluble. One of the functions of the organic solvent is to improve the ink's wettability with respect to the recording medium and to increase the ink's moisture retention.

[0039] Examples of organic solvents include polyhydric alcohols, esters, alkylene glycol ethers, cyclic esters, nitrogen-containing solvents, and polyhydric alcohols. Examples of nitrogen-containing solvents include cyclic amides and non-cyclic amides. Examples of non-cyclic amides include alkoxyalkylamides.

[0040] Examples of esters include glycol monoacetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and ethylene glycol monobutyl ether acetate, and glycol diesters such as ethylene glycol diacetate, diethylene glycol diacetate, and propylene glycol diacetate. Examples include:

[0041] The alkylene glycol ethers may be monoethers or diethers of alkylene glycol, and alkyl ethers are preferred. Specific examples include alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether, and alkylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and triethylene glycol diethyl ether.

[0042] Examples of cyclic esters include cyclic esters (lactones) such as β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and β-butyrolactone, as well as compounds in which the hydrogen atom of the methylene group adjacent to the carbonyl group of these cyclic esters is substituted with an alkyl group having 1 to 4 carbon atoms.

[0043] Examples of alkoxyalkylamides include 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-N,N-diethylpropionamide, 3-methoxy-N,N-methylethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-diethylpropionamide, 3-ethoxy-N,N-methylethylpropionamide, 3-n-butoxy-N,N-dimethylpropionamide, 3-n-butoxy-N,N-diethylpropionamide, and 3-n-butoxy-N,N-methylethylpropionamide.

[0044] Examples of cyclic amides include lactams, such as pyrrolidones such as 2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, 1-propyl-2-pyrrolidone, and 1-butyl-2-pyrrolidone.

[0045] Examples of polyhydric alcohols include 1,2-alkanediols and other polyhydric alcohols (polyols) (for example, diethylene glycol, triethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol (also known as 1,3-butylene glycol), 1,5-pentanediol, 1,6-hexanediol, 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, 2-methylpentane-2,4-diol, trimethylolpropane, and glycerin).

[0046] Among polyhydric alcohols, alkanediols are preferred. Among alkanediols, those that are particularly suitable for increasing ink penetration are preferred. Examples of such alkanediols include 1,2-alkanediol.

[0047] Examples of 1,2-alkanediols include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and 1,2-octanediol, each of which has 4 to 8 carbon atoms. These may have a branched alkane moiety, but a straight chain is preferred. 1,2-alkanediols are more preferred because they function well as penetrating agents.

[0048] Examples of polyhydric alcohols include alkanediols of alkanes having 4 or less carbon atoms, and intermolecular condensation products of hydroxyl groups of alkanediols of alkanes having 4 or less carbon atoms. Here, the number of carbon atoms in the alkane is preferably 2 to 3. In the case of the above intermolecular condensation products, the number of intermolecular condensations is 2 or more, preferably 4 or less, and more preferably 3 or less. Examples of polyhydric alcohols also include triol or higher polyhydric alcohols. The number of hydroxyl groups in the polyhydric alcohol molecule is 2 or more, preferably 5 or less, and more preferably 3 or less. These polyhydric alcohols are particularly preferred because of their excellent moisturizing properties. The polyhydric alcohols can be used alone or in combination of two or more.

[0049] When the ink contains an organic solvent, the organic solvent may be used alone or in combination of two or more. The total content of the organic solvent relative to the total mass of the ink is, for example, 5% by mass to 50% by mass, preferably 10% by mass to 45% by mass, more preferably 15% by mass to 40% by mass, and even more preferably 16% by mass to 40% by mass. It is further preferably 17 to 30% by mass, and more preferably 18 to 25% by mass.

[0050] When the content of the organic solvent is within the above range, the balance between the wetting and spreading properties and the drying properties is better, and it is easier to form a higher quality image.

[0051] Lacrum The first ink more preferably contains a lactam (a lactam-based compound). The lactam may be the organic solvent described above, or may not be an organic solvent. It may also be the cyclic amide described above.

[0052] Lactam compounds have a structure in which a carboxyl group and an amino group in the molecule form a ring through a dehydration condensation reaction. When lactams are included, they tend to have better redispersibility, suppression of phase separation, discharge stability, and clogging recovery. This is presumably due to the particularly excellent moisturizing properties of lactams.

[0053] Furthermore, the inclusion of a lactam compound tends to further improve the compatibility of surfactants, particularly acetylene glycol surfactants, with the ink composition. From these perspectives, 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, compounds having a 4- or 5-membered lactam ring are also preferred.

[0054] From these viewpoints, the molecular weight of lactams is preferably 80 or more, more preferably 100 or more, even more preferably 100 to 300, and even more preferably 110 to 200.

[0055] 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.

[0056] Specific examples of lactam compounds include, in addition to the above-mentioned cyclic amides, epsilon-caprolactam (CPL), N-hydroxyethylpyrrolidone (HEP), delta-valerolactam, and 5-(methylamino)pentanoic acid lactam, and it is preferable to include epsilon-caprolactam (CPL), N-hydroxyethylpyrrolidone (HEP), etc. By including these compounds, clogging recovery, color development, and ejection stability tend to be further improved.

[0057] When a lactam compound is contained, the content thereof is preferably 100% by mass relative to the total mass of the ink. The content is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less, and even more preferably 1 to 8% by mass, and even more preferably 2 to 7% by mass.

[0058] The content of lactams having a 6- to 8-membered lactam ring may be within the above range, preferably 1 to 5% by mass, and more preferably 2 to 4% by mass. By setting the content of lactam compounds within the above range, clogging recovery, color development, and ejection stability tend to be further improved.

[0059] Line printers print large volumes of material continuously at high speeds, generating a lot of paper dust, which can fill the interior of the printer. This paper dust adheres to the nozzles, thickening the nozzles and causing problems with ejection stability and clogging recovery. This tendency is particularly pronounced when the ink is highly reactive with calcium, but it also applies to inks with low reactivity. Inks with low reactivity with calcium offer excellent ejection stability and clogging recovery. When paper dust generated during printing comes into contact with the ink in the nozzles, the pigment in highly reactive inks can become foreign matter due to the paper dust. This can lead to poor ejection stability and clogging recovery. This can be prevented with low-reactivity inks.

[0060] According to this recording method, the moisturizing effect of lactams prevents the mixture of paper powder and ink in the nozzle from drying out, and even if the mixture begins to dry out, the redispersibility of the dried material can be improved, resulting in good ejection stability and good recovery from clogging. Furthermore, this effect is more effective when the molecular weight is above a certain level.

[0061] Furthermore, when the ink contains an acetylene glycol-based surfactant, the acetylene glycol-based surfactant has low solubility in water, which can lead to phase separation, especially when the ink dries in the nozzle. Furthermore, while low-HLB acetylene glycol-based surfactants have particularly excellent penetration, they have low solubility in water and are prone to phase separation. In such cases, lactams can easily prevent the acetylene glycol-based surfactant from dissolving in water and causing phase separation. Among lactams, 1-(2-hydroxyethyl)-2-pyrrolidone (HEP) and ε-caprolactam (HEP) have the most pronounced effects. In particular, HEP tends to prevent the ink from becoming too viscous when contained in the ink, making it easier to control the ink ejection volume and ensuring stable ejection. Furthermore, CPL in particular exhibits the above-mentioned redispersibility effect.

[0062] Surfactants The ink may contain a surfactant. The surfactant adjusts the surface tension of the ink and, for example, adjusts the wettability of the ink with a recording medium. Among surfactants, for example, acetylene glycol surfactants, silicone surfactants, and fluorine surfactants can be preferably used.

[0063] The acetylene glycol surfactant is not particularly limited, but examples thereof include Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 104S, 420, 440, 465, 485, SE, SE-F, 504, 61, DF37, CT111, CT121, CT131, CT136, TG, GA, and DF110D (all trade names, manufactured by Air Products & Chemicals Co.). , Olfine B, Y, P, A, STG, SPC, E1004, E1010, PD-001, PD-002W, PD-003, PD-004, EXP.4001, EXP.4036, EXP.4051, AF-103, AF-104, AK-02, SK-14, AE-3 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), Acetylenol E00, E00P, E40, E100 (all trade names, manufactured by Kawaken Fine Chemicals Co., Ltd.).

[0064] Acetylene glycol surfactants improve ink penetration into recording media (especially plain paper). It has a high ink-repelling effect and is less likely to foam, making it particularly useful for printing on plain paper. When printing on plain paper with a high-speed line printer, slow ink penetration into the recording medium can cause transfer smearing. After the ink adheres to the recording medium, it is immediately transported, and the rollers come into contact with the recording surface, or the ink is piled up in the paper output tray, resulting in transfer smearing. However, the use of an acetylene glycol-based surfactant can increase ink penetration into the recording medium and suppress transfer smearing.

[0065] Acetylene glycol surfactants are preferred because they have superior permeability into recording media, but they tend to have low solubility in water, are prone to phase separation in ink, and tend to have particularly poor compatibility with ink compositions.

[0066] This tendency is particularly pronounced among acetylene glycol surfactants with an HLB value of 6 or less. When an ink composition contains an acetylene glycol surfactant, particularly an acetylene glycol surfactant with an HLB value of 6 or less, it is preferable that the ink contains the aforementioned lactams. The lower limit of the HLB value is 0 or more, preferably 1 or more, and more preferably 2 or more. Also, 5 or less is more preferable.

[0067] Furthermore, among acetylene glycol surfactants, those with an HLB value of more than 6 tend to be slightly more soluble in water than those with an HLB value of 6 or less. For this reason, it is preferable to include those with an HLB value of 6 or less and those with an HLB value of more than 6, more preferably those with an HLB value of 5 or less and those with an HLB value of 7 or more, and even more preferably those with an HLB value of 5 or less and those with an HLB value of 10 or more. In this case, wettability, clogging recovery, discharge stability, etc. are better, and suppression of phase separation is also better, which is preferable. The upper limit of the HLB is 20 or less, and preferably 15 or less.

[0068] The "HLB value (hydrophilic lipophilic balance)" is a value calculated by the Griffin method.

[0069] The silicone surfactant is not particularly limited, but a polysiloxane compound is preferred. The polysiloxane compound is not particularly limited, but for example, a polyether-modified organosiloxane is exemplified. Commercially available products of the polyether-modified organosiloxane include, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (all trade names, manufactured by BYK-Chemie Japan), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF- 615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), Silface SAG002, 005, 503A, 008 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), and the like.

[0070] As the fluorine-based surfactant, it is preferable to use a fluorine-modified polymer, and specific examples include BYK-3440 (manufactured by BYK Japan), Surflon S-241, S-242, S-243 (all trade names, manufactured by AGC Seimi Chemical Co., Ltd.), and Futergent 215M (manufactured by Neos Corporation).

[0071] When the ink contains a surfactant, multiple types may be contained. When the ink contains a surfactant, the content of the surfactant may be 0.1% by mass or more and 2% by mass or less, preferably 0.4% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 1.0% by mass or less, based on the total mass of the ink.

[0072] ·Resins The ink may contain resins such as a resin dispersant and a fixing resin. (Resin dispersant) It is preferable that the azo pigment can be stably dispersed in the dispersion medium, and for this purpose, a dispersant may be used for dispersion. Examples of the dispersant include resin dispersants, and the dispersant is selected from those that can improve the dispersion stability of the azo pigment.

[0073] Examples of resin dispersants (dispersant resins) include (meth)acrylic resins and salts thereof such as poly(meth)acrylic acid, (meth)acrylic acid-acrylonitrile copolymer, (meth)acrylic acid-(meth)acrylic acid ester copolymer, vinyl acetate-(meth)acrylic acid ester copolymer, vinyl acetate-(meth)acrylic acid copolymer, and vinylnaphthalene-(meth)acrylic acid copolymer; styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, styrene-α-methylstyrene-(meth)acrylic acid copolymer, and styrene-α-methylstyrene-(meth)acrylic acid copolymer. Examples of suitable water-soluble resins include styrene-based resins such as acrylic acid-(meth)acrylic acid ester copolymers, styrene-maleic acid copolymers, and styrene-maleic anhydride copolymers, and salts thereof; urethane-based resins and salts thereof, which are polymeric compounds (resins) containing urethane bonds formed by the reaction of an isocyanate group and a hydroxyl group and may be linear and / or branched, and may have a crosslinked structure; polyvinyl alcohols; vinyl naphthalene-maleic acid copolymers and salts thereof; vinyl acetate-maleic acid ester copolymers and salts thereof; and vinyl acetate-crotonic acid copolymers and salts thereof. Among these, preferred are copolymers of a monomer having a hydrophobic functional group and a monomer having a hydrophilic functional group, and polymers composed of a monomer having both a hydrophobic and a hydrophilic functional group. The copolymers may be random copolymers, block copolymers, alternating copolymers, or graft copolymers.

[0074] Commercially available styrene resin dispersants include, for example, X-200, X-1, X-205, X-220, and X-228 (manufactured by Seiko PMC Co., Ltd.), Nopcosperse (registered trademark) 6100 and 6110 (manufactured by San Nopco Ltd.), Joncryl 67, 586, 611, 678, 680, 682, and 819 (manufactured by BASF), DISPERBYK-190 (manufactured by BYK Japan KK), N-EA137, N-EA157, N-EA167, N-EA177, N-EA197D, N-EA207D, and E-EN10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0075] Commercially available acrylic resin dispersants include BYK-187, BYK-190, BYK-191, BYK-194N, and BYK-199 (manufactured by BYK-Chemie Co., Ltd.), Aron A-210, A6114, AS-1100, AS-1800, A-30SL, A-7250, and CL-2 (manufactured by Toagosei Co., Ltd.).

[0076] Furthermore, commercially available urethane resin dispersants include BYK-182, BYK-183, BYK-184, and BYK-185 (manufactured by BYK-Chemie Co., Ltd.), TEGO Disperse 710 (manufactured by Evonic Tego Chemi), and Borchi (registered trademark) Gen 1350 (manufactured by OMG Borschers).

[0077] The resin dispersants may be used alone or in combination of two or more. The total content of the dispersants is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 25 parts by mass, even more preferably 1 to 20 parts by mass, and even more preferably 1.5 to 15 parts by mass, per 50 parts by mass of the pigment. By using a dispersant content of 0.1 parts by mass or more per 50 parts by mass of the pigment, the dispersion stability of the pigment can be further improved. Furthermore, by using a dispersant content of 30 parts by mass or less per 50 parts by mass of the pigment, the viscosity of the resulting dispersion can be kept low.

[0078] The resin dispersant is preferably a resin that adsorbs and disperses the resin on the surface of the pigment particles. Examples of suitable resin dispersants include dispersed pigments. 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.

[0079] If the first ink contains a dispersant resin for dispersing the azo pigment, and the acid value of the dispersant resin is particularly 200 mgKOH / g or less, the color development of the first ink can be further improved.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] When the pigment is a self-dispersing pigment, the ink viscosity 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 is less than doubled.

[0086] (fixing resin) The first ink may contain a fixing resin. The fixing resin is a resin that is not a resin dispersant, that is, a resin that is not attached to or adsorbed on the pigment, and that is dispersed or dissolved as a resin alone in the solvent component of the ink.

[0087] The fixing resin can further improve the adhesion of the image formed by the first ink adhered to the recording medium. Furthermore, the inclusion of the fixing resin makes it easier to suppress transfer after printing. If the fixing resin is reactive with calcium, it also affects the reactivity of the ink with calcium. To create an ink with low reactivity with calcium, a resin with low reactivity is preferred. The reactivity of the ink can be adjusted by adjusting the reactivity of the resin together with the pigment.

[0088] Examples of fixing resins include fixing resins made of urethane-based resins, acrylic-based resins (including styrene-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, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate-based resins, etc. Among these, urethane-based resins, acrylic-based resins, polyolefin-based resins, and polyester-based resins are preferred.

[0089] These fixing resins include resin particles and water-soluble resins. Resin particles are often handled in the form of an emulsion, but may also be in the form of a powder. Water-soluble resins are resins that can be dissolved in water, and are dissolved in a solvent component containing water as the main component in the ink. The fixing resins can be used alone or in combination of two or more.

[0090] Urethane resin is a general term for resins having urethane bonds. In addition to urethane bonds, the urethane resin may be a polyether urethane resin containing ether bonds in the main chain, a polyester urethane resin containing ester bonds in the main chain, or a polycarbonate urethane resin containing carbonate bonds in the main chain. Furthermore, commercially available products may be used as the urethane resin, and examples thereof include Superflex 420, 460, 460s, 840, and E-4000 (trade names, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Rezamin D-1060, D-2020, D-4080, D-4200, D-6300, and D-6455 (trade names, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), Takelac WS-6021 and W-512-A-6 (trade names, manufactured by Mitsui Chemicals Polyurethanes Inc.), Sancure 2710 (trade name, manufactured by Lubrizol), and Permarin UA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.).

[0091] Acrylic resin is a general term for polymers obtained by polymerizing at least an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester as one component. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers with other monomers. Examples include acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers. Another example of a vinyl monomer is styrene.

[0092] Examples of acrylic monomers that can be used include acrylamide and acrylonitrile. Commercially available products may be used for the resin emulsion made from an acrylic resin, such as FK-854 (trade name, manufactured by Chuo Rika Kogyo Co., Ltd.), Movinyl 952B and 718A (trade names, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and Nipol LX852 and LX874 (trade names, manufactured by Nippon Zeon Co., Ltd.).

[0093] In this specification, the acrylic resin may be a styrene-acrylic resin, which will be described later. In addition, in this specification, the term "(meth)acrylic" means at least one of acrylic and methacrylic.

[0094] Styrene-acrylic resins are copolymers obtained from styrene monomer and (meth)acrylic monomer, and examples include styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, and styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer. As the styrene-acrylic resin, commercially available products may be used, such as JONCRYL 62J, 7100, 390, 678, 711, 511, 7001, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, and 7610 (trade names, manufactured by BASF), and Mowinyl 966A and 975N (trade names, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.). , Vinyblan 2586 (manufactured by Nissin Chemical Industry Co., Ltd.), etc. may also be used.

[0095] The polyolefin resin has an olefin such as ethylene, propylene, or butylene in its structural skeleton, and known polyolefin resins can be appropriately selected and used. As the olefin resin, commercially available products can be used, such as Arrowbase CB-1200 and CD-1200 (trade names, manufactured by Unitika Ltd.).

[0096] The resin particles may also be supplied in the form of an emulsion. Examples of commercially available resin emulsions include Microgel E-1002 and E-5002 (trade names of Nippon Paint Co., Ltd., styrene-acrylic resin emulsions), Boncoat 4001 (trade name of DIC Corporation, acrylic resin emulsion), Boncoat 5454 (trade name of DIC Corporation, styrene-acrylic resin emulsion), Polysol AM-710, AM-920, AM-2300, AP-4735, AT-860, PSASE-4210E (acrylic resin emulsion), Polysol Polysol AP-7020 (styrene-acrylic resin emulsion), Polysol SH-502 (vinyl acetate resin emulsion), Polysol AD-13, AD-2, AD-10, AD-96, AD-17, AD-70 (ethylene-vinyl acetate resin emulsion), Polysol PSASE-6010 (ethylene-vinyl acetate resin emulsion) (trade name, manufactured by Showa Denko K.K.), Polysol SAE1014 (trade name, styrene-acrylic resin emulsion, manufactured by Nippon Zeon Co., Ltd.), Saivinol SK-200 (trade name, acrylic resin emulsion, manufactured by Saiden Chemical Co., Ltd.), A E-120A (trade name of JSR Corporation, acrylic resin emulsion), AE373D (trade name of E-Tech Corporation, carboxy-modified styrene-acrylic resin emulsion), Seikadyne 1900W (trade name of Dainichiseika Color & Chemicals Mfg. Co., Ltd., ethylene-vinyl acetate resin emulsion), Vinyblan 2682 (acrylic resin emulsion), Vinyblan 2886 (vinyl acetate-acrylic resin emulsion), Vinyblan 5202 (acetic acid acrylic resin emulsion) (trade name of Nissin Chemical Industry Co., Ltd.), Elitel KA-5071S, KT-8803, KT-9204, KT-8701, K T-8904, KT-0507 (trade names of Unitika Ltd., polyester resin emulsion), Hi-Tec SN-2002 (trade name of Toho Chemical Co., Ltd., polyester resin emulsion), Takelac W-6020, W-635, W-6061, W-605, W-635, W-6021 (trade names of Mitsui Chemicals Polyurethanes, urethane resin emulsion), Superflex 420, 870, 800, 150, 420, 460, 470, 610, 700 (trade names of Daiichi Kogyo Seiyaku Co., Ltd., urethane resin emulsion), Parmarin UA-150 (trade name of Sanyo Chemical Industries, Ltd.,Urethane resin emulsion), Sancure 2710 (manufactured by Lubrizol Japan, urethane resin emulsion), NeoRez R-9660, R-9637, R-940 (manufactured by Kusumoto Chemicals Co., Ltd., urethane resin emulsion), Adeka Bontitor HUX-380, 290K (manufactured by ADEKA Corporation, urethane resin emulsion), Mowinyl 966A, Mowinyl 7320 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Joncryl 7100, 390, 711, 511, 7001, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7 The binder may be selected from 630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (all manufactured by BASF), NK Binder R-5HN (manufactured by Shin-Nakamura Chemical Co., Ltd.), Hydran WLS-210 (non-crosslinked polyurethane: manufactured by DIC Corporation), Joncryl 7610 (manufactured by BASF), and the like.

[0097] The volume average particle diameter of the resin particles is preferably 10 nm or more and 300 nm or less, more preferably 30 nm or more and 300 nm or less, even more preferably 30 nm or more and 250 nm or less, and particularly preferably 40 nm or more and 220 nm or less. The volume average particle diameter can be measured by the method described above.

[0098] When the first ink contains or does not contain a fixing resin, the content thereof is preferably 10% by mass or less in terms of solid content relative to the total mass of the first ink. The content is more preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, even more preferably 0.1% by mass or more and 1% by mass or less, and still more preferably 0.1% by mass or more and 0.5% by mass or less. In the case where the fixing resin is a reactive resin, a smaller content is preferable in terms of lowering the reactivity of the ink, while a larger content is preferable in terms of suppressing transfer.

[0099] Additives The first ink may contain additives such as ureas, amines, sugars, etc. Examples of ureas include urea, ethylene urea, tetramethyl urea, thiourea, 1,3-dimethyl-2-imidazolidinone, etc., and betaines (trimethylglycine, triethylglycine, tripropylglycine, triisopropylglycine, N,N,N-trimethylalanine, N,N,N-triethylalanine, N,N,N-triisopropylalanine, N,N,N-trimethylmethylalanine, carnitine, acetylcarnitine, etc.).

[0100] Examples of amines include diethanolamine, triethanolamine, triisopropanolamine, etc. Ureas and amines may function as pH adjusters or alkaline agents.

[0101] Examples of sugars include glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol (sorbitol), maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose.

[0102] Furthermore, the first ink may contain components such as preservatives, antifungals, rust inhibitors, chelating agents, viscosity modifiers, antioxidants, anti-mold agents, waxes, etc. Furthermore, the first ink according to this embodiment may contain coloring materials other than azo pigments, as long as the effects described below are not impaired.

[0103] 1.1.2. Second ink The second ink is a chromatic ink other than a red ink that contains a pigment, and is a water-based ink.

[0104] (1) Pigments The pigment is preferably a color pigment such as cyan, yellow, or black. The pigment may be a white pigment or a special color pigment. The pigment has excellent storage stability such as light resistance, weather resistance, and gas resistance, and from this viewpoint, it is preferable that the pigment is an organic pigment.

[0105] Specifically, examples of pigments that can be used include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates, dye lakes, nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments, and carbon black. These pigments can be used alone or in combination. Furthermore, a luster pigment can be used as a non-white colorant.

[0106] Specific examples of pigments include, but are not limited to, the following:

[0107] Examples of black pigments include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, and No. 22. 00B etc. (all manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700 etc. (all manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 etc. (manufactured by CABOT JAPAN KK), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4 (all manufactured by Degussa).

[0108] Examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, and 180.

[0109] Examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66, and CI Vat Blue 4 and 60.

[0110] Furthermore, pigments other than magenta, cyan, and yellow are not particularly limited, but examples thereof include CI Pigment Green 7, 10, CI Pigment Brown 3, 5, 25, 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0111] The pearl pigment is not particularly limited, but examples thereof include pigments having pearlescent or interference luster, such as titanium dioxide-coated mica, fish scale foil, and bismuth oxychloride.

[0112] The metallic pigment is not particularly limited, but examples thereof include particles of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, copper, and the like, either alone or as an alloy.

[0113] The pigment is preferably capable of being stably dispersed or dissolved in the dispersion medium, and may be dispersed using a dispersant as needed. Examples of dispersants include the same dispersants used to improve the dispersibility of the pigment in the first ink described above.

[0114] The pigment may be dispersed using a dispersant. The dispersant is preferably a dispersant resin. The acid value of the dispersant resin for the pigment may be the same as the acid value of the dispersant resin for the white colorant described above.

[0115] The pigment content of the second ink is preferably from 0.3 to 20% by mass, more preferably from 0.5 to 15% by mass, even more preferably from 1 to 10% by mass, and even more preferably from 2 to 7% by mass.

[0116] The pigment content of the second ink is preferably less than that of the first ink, and more preferably at least 0.5% by mass less, which can prevent deterioration of the redispersibility, ejection stability, and clogging recovery properties of the second ink.

[0117] In particular, with yellow inks that use yellow pigments, increasing the pigment content does not tend to improve color visibility to the same extent, so there is little need to increase the pigment content beyond that of the first ink.

[0118] (2) Other ingredients The second ink contains water. The water is the same as that described above for the first ink. The second ink may also contain organic solvents, lactams, surfactants, resins, additives, etc. These components are the same as those described above for the first ink. The components of the second ink other than the pigment may be the same as those of the first ink.

[0119] 1.1.3. Thickening rate At least one of the first ink and the second ink has a viscosity increase rate of less than 2.0 times when the ink is mixed with an aqueous calcium propionate solution with a Ca concentration of 0.3 mol / L in a mass ratio of 10:1 (ink composition: aqueous calcium propionate solution).

[0120] The viscosity increase rate is defined as follows: The ink and an aqueous calcium propionate solution (Ca concentration: 0.3 mol / L) were mixed in a ratio of 10:1 (ink:aqueous calcium propionate solution) and left to stand for 24 hours at 60°C. Each ink was mixed with an aqueous calcium propionate solution to form a mixture, and the mixture was left to stand as described above.

[0121] This allows the ink components to react sufficiently with calcium propionate. The viscosity of the ink in its initial state (before mixing) and the ink (mixture) after standing is measured. Measurements are performed at 25°C, and the sample is thoroughly stirred before measurement. Viscosity can be measured using, for example, a rotational viscometer. The viscosity η1 of the ink after standing and the viscosity η0 of the ink in the initial state are calculated as the viscosity increase rate according to the following formula. Viscosity increase rate (times) = ink viscosity after standing η1 / initial ink viscosity η0

[0122] The viscosity increase ratio of at least one of the first ink and the second ink is less than 2.0 times. Furthermore, the viscosity increase ratio of the ink is more preferably less than 1.8 times, and even more preferably less than 1.6 times. Less than 1.5 times is even more preferable. This results in a better reduction in color difference. Furthermore, the redispersibility of the ink is also excellent.

[0123] On the other hand, the lower limit of the viscosity increase rate of the ink is not particularly limited, but is preferably 1.0 times or more, more preferably 1.2 times or more, and even more preferably 1.5 times or more. This is preferable as it results in better color development of the ink.

[0124] In terms of excellent reduction in color difference in reddish images obtained using the first ink, it is preferable that the viscosity increase rate of the first ink is less than 2.0 times.

[0125] On the other hand, as long as the viscosity increase rate of at least one of the first ink and the second ink is less than 2.0 times, the first ink or the second ink may be present in a state where the viscosity increase rate is not less than 2.0 times. In other words, the viscosity increase rate of the other of the first ink and the second ink may be 2.0 times or more. This can also sufficiently reduce color difference streaks. Furthermore, the color development of the other ink is excellent, which is preferable.

[0126] 1.1.4. Color combinations of the first and second inks The first ink may be a magenta ink, and the second ink may be a yellow ink or a cyan ink. By using an azo pigment-based magenta ink with low reactivity with calcium, the second ink can be an ink with high reactivity with calcium, thereby increasing design flexibility. Furthermore, for example, using a yellow ink with high reactivity with calcium improves the visibility of yellow, which is more preferable. For warm-color images where color difference streaks are easily noticeable, using a yellow ink with high reactivity with calcium and a magenta ink with low reactivity with calcium allows for the recording of images using yellow and magenta inks with high visibility and reduced color difference streaks. This embodiment is particularly useful for recording secondary colors using yellow and magenta inks.

[0127] The reactivity of the ink with calcium ions can be adjusted by adjusting the reactivity of the components contained in the ink with calcium ions. For example, in the case of a resin-dispersed pigment, the reactivity can be reduced by lowering the acid value of the pigment dispersant resin. In the case of a self-dispersed pigment, the reactivity can be reduced by reducing the amount of acidic groups introduced into the pigment.

[0128] Furthermore, when the second ink is cyan ink, it is also preferable that it has high reactivity. Cyan ink is often used to generate a secondary color (blue) with magenta ink (first ink), and the low reactivity of magenta ink can further reduce blue color difference streaks.

[0129] Furthermore, the problem of color difference streaks tends to become more pronounced between inks used to generate secondary colors (two inks with adjacent hue angles). If the reactivity of magenta ink is low, the reactivity of yellow and cyan inks can be increased when printing secondary colors (red and blue) with magenta ink. Furthermore, high color development is particularly useful in red-based images, where color difference can be reduced, which is preferable.

[0130] 1.2. Recording Media The recording medium is not particularly limited, but examples thereof include absorbent recording media, low-absorbent recording media, and non-absorbent recording media. Among these, absorbent recording media and low-absorbent recording media are preferred, and absorbent recording media are more preferred. The present invention is particularly useful because the higher the absorbency, the more likely it is that differences in penetration due to differences in nozzle distance will occur. In other words, using an absorbent recording medium that does not easily leave pigment on the surface will more significantly reduce color difference streaks and improve color development on the surface, which is the effect of the recording method of this embodiment.

[0131] Here, a "low-absorbency recording medium" or a "non-absorbency recording medium" is defined as a medium having a water absorption of 10 mL / m2 or less within 30 msec from the start of contact in the Bristow method. 2 This refers to a recording medium that is as follows: 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."

[0132] The low-absorbency recording medium has a water absorption capacity of 5 mL / m 2 More than 10mL / m 2 On the other hand, an absorbent recording medium is a recording medium having a water absorption rate of 10 mL / m or less. 2 This refers to a recording medium that is super-

[0133] The absorbent recording medium is not particularly limited, but examples thereof include plain paper such as electrophotographic paper that has high ink composition permeability, inkjet paper (an ink absorbing layer made of silica particles or alumina particles, or an ink absorbing layer made of polyvinyl alcohol (PVA) or polyvinylpyrrolidone), and the like. Examples of suitable inkjet paper include inkjet paper with an ink absorbing layer made of a hydrophilic polymer such as PVP.

[0134] The low-absorbency recording medium is not particularly limited, but examples thereof include coated paper having a coating layer on the surface for receiving oil-based ink, and examples of coated paper include, but are not particularly limited to, printing paper such as art paper, coated paper, and matte paper.

[0135] Non-absorbent recording media are not particularly limited, but examples include films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc.; plates of metals such as iron, silver, copper, aluminum, etc.; metal plates and plastic films manufactured by vapor deposition of these various metals, and alloy plates such as stainless steel and brass; and recording media in which a plastic film such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, polyurethane, etc. is adhered (coated) to a paper substrate.

[0136] 1.3.Transportation process The recording method of this embodiment includes a transport step. In the transport step, the recording medium is transported in a predetermined direction within the recording device. More specifically, the recording medium is transported from a paper feed section to a paper discharge section of the recording device using a transport roller or a transport belt provided within the recording device. During this transport process, ink ejected from an inkjet head adheres to the recording medium, forming a recorded product. Transport may be performed continuously or intermittently.

[0137] 1.4.Ink application process The ejection step is a step in which the first ink and the second ink are ejected from a line head having a length equal to or greater than the recording width of the recording medium, and are deposited on the recording medium. Figure 1 shows a schematic cross-sectional view of a recording apparatus that can be used in the recording method of the present invention.

[0138] The line head 10 has a length equal to or greater than the recording width of the recording medium, and is a means for ejecting an ink composition to deposit it on the recording medium M. The inkjet head 10 has a nozzle surface 11 facing the recording medium M, and has a plurality of unit heads 12 (see FIG. 2) in the recording width direction of the recording medium. Each unit head 12 has a plurality of nozzles that eject the ink composition. The plurality of nozzles in each unit head 12 are arranged at different positions from each other in the recording width direction, and are also called "nozzle groups." The nozzles of a nozzle group may be arranged side by side, for example, in a row. A group of nozzles arranged in a row is also called a "nozzle row." The recording medium M is supported by a belt B and conveyed in the conveying direction D1. The belt B is moved in the conveying direction D1 by a belt roller 20. The recording device may also be equipped with a paper feed tray, a paper discharge tray, and the like, which are not shown.

[0139] The unit head 12 has such a nozzle group, and there are no limitations on its structure other than the fact that it has a nozzle group. The nozzle group is, for example, a nozzle row, but it will do as long as it is a nozzle group. The part of the line head 10 where one nozzle group exists is one unit head 12. It can also be said that a nozzle group is a unit head 12.

[0140] In this embodiment, the line head 10 has a portion where the distance between the first nozzles ejecting the first ink and the second nozzles ejecting the second ink in the scanning direction differs in the recording width direction, which causes color differences and makes the present invention particularly useful.

[0141] In the line method using a line head, for example, an ink jet head having a width equal to or greater than the recording width of the recording medium is used. An inkjet head is fixed to the recording device, and the recording medium is moved in the scanning direction (the longitudinal direction of the recording medium, the transport direction), and an image is recorded on the recording medium by performing a scan in which ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement.

[0142] Alternatively, the recording medium is fixed to the recording device. An inkjet head having a width equal to or greater than the recording width of the recording medium is moved along a scanning direction, and an image is recorded on the recording medium by ejecting ink droplets from the nozzles of the inkjet head in conjunction with this movement. The scanning direction is the direction of scanning.

[0143] In such a line method using a line head, printing can be performed by scanning the line head and recording medium once, and therefore printing speed can be improved.

[0144] An example of the nozzle surface of an inkjet head having portions with different inter-nozzle distances is shown in Figure 2. In this embodiment, a unit head equipped with first nozzles that eject a first ink is referred to as a first unit head 12a, and a unit head equipped with second nozzles that eject a second ink is referred to as a second unit head 12b; when there is no need to distinguish between the two, they are simply referred to as unit heads 12.

[0145] In the following, an example will be given in which the first unit head 12a ejects the first ink and the second unit head 12b ejects the second ink, but this is merely one example. That is, the present invention may also include an example in which one unit head includes nozzles that eject the first ink and nozzles that eject the second ink, regardless of whether it is the first unit head or the second unit head. More specifically, when a unit head includes multiple nozzle rows, each nozzle row may be capable of ejecting a different ink composition.

[0146] For example, the first unit head 12a and the second unit head 12b may not be separate entities but may be integrated. Also, the multiple first unit heads 12a aligned in the width direction and the multiple second unit heads 12b aligned in the width direction may not be separate entities but may be integrated. The multiple unit heads 12 constituting the line head may not be separate entities but may be integrated.

[0147] In this case as well, the portion where one nozzle row that ejects the first ink exists is the first unit head 12a, and the portion where one nozzle row that ejects the second ink exists is the second unit head 12b. In other words, the unit head 12 also refers to the nozzle row.

[0148] In addition, in the figure, one first unit head 12a has two nozzle rows in the scanning direction, but the number of nozzle rows may be one or more, as long as at least one of the nozzle rows ejects the first ink. The same is true for the second unit head 12b.

[0149] In the example of Fig. 2, a first unit head 12a and a second unit head 12b are aligned in the longitudinal direction to form one unit 12, and the units 12 are arranged in the width direction D2 so that the longitudinal direction of the unit 12 diagonally intersects with the width direction D2 of the line head. In Fig. 2, there is a gap between adjacent units 12 that are aligned diagonally, but instead, adjacent units 12 may be arranged adjacent to each other without a gap therebetween.

[0150] 2, a first nozzle group consisting of a plurality of first nozzles that eject a first ink and a second nozzle group consisting of a plurality of second nozzles that eject a second ink are arranged obliquely with respect to the direction of the recording width, which makes it possible to adjust the apparent nozzle density in the width direction of the entire line head and the number of unit heads required to configure a line head having a predetermined distance in the width direction.

[0151] Comparing the case where the nozzles are arranged diagonally with respect to the width direction D2 as in the example of FIG. 2 with the case where the nozzles are arranged parallel to the width direction D2, even when first unit heads 12a and second unit heads 12b having the same nozzle density are used, the nozzle density in the width direction of the entire line head is higher when the nozzles are arranged diagonally with respect to the width direction D2 as in the example of FIG. 2. In other words, the nozzle density is improved when the nozzles are arranged diagonally with respect to the width direction D2. This results in higher recording resolution and superior image quality, which is preferable. In this case, the distance between nozzles in the scanning direction is further increased, making the present invention particularly useful.

[0152] In the example shown in Fig. 2, there may be portions where the distance between the first unit head 12a and the second unit head 12b is different in the scanning direction, or portions where the first unit head 12a or the second unit head 12b overlap. As shown in Fig. 2, these portions are given names and symbols in this specification. That is, in the example shown in Fig. 2, there are a straddling portion A, an overlapping portion B1, an overlapping portion B2, and a normal portion C.

[0153] In the normal portion C, the first unit head 12a and the second unit head 12b each scan the recording medium once. In the overlapping portion B1, the first unit head 12a scans the recording medium twice and the second unit head 12b scans the recording medium once. In the overlapping portion B2, the first unit head 12a scans the recording medium once and the second unit head 12b scans the recording medium twice. In the straddling portion A, the first unit head 12a scans the recording medium once and the second unit head 12b scans the recording medium once.

[0154] If the time difference between the impact of the first ink and the impact of the second ink on the recording medium in the normal portion C is used as a reference, the time difference is approximately twice as long in the crossover portion A. The time difference between the impact of the first ink and the impact of the second ink on the recording medium is the time difference between the impact of the first ink and the impact of the second ink at a certain point on the recording medium. In other words, it is the time difference between the impact of the first ink and the impact of the second ink at the same point on the recording medium.

[0155] On the other hand, in the overlapping portions B1 and B2, the time difference can be changed by selecting the unit head to be used, and the time difference is the same as or about twice as long as that in the normal portion C. Even when the straddling portion A is used as the reference, in the overlapping portions B1 and B2, the time difference can be changed by selecting the unit head to be used, and the time difference is the same as that in the straddling portion A or about half as long.

[0156] However, in the example of Figure 2, the landing time difference will be different between the straddling portion A and the normal portion C. Furthermore, even if the selection of unit heads to be used is adjusted, the landing time difference between the overlapping portion B1 and the overlapping portion B2 will be different for either the straddling portion A or the normal portion C. This makes it difficult to land the first ink and the second ink with the same landing time difference across the entire width direction D2 of the line head. In other words, differences will occur between parts of the line head in the direction D2 that intersects with the transport direction D1 of the recording medium.

[0157] Furthermore, if the impact time difference is expressed in terms of the distance between nozzles, in the example of Figure 2, the first nozzles that eject the first ink and the second nozzles that eject the second ink are arranged such that the distance between the first nozzles that eject the first ink and the second nozzles that eject the second ink is different during recording.

[0158] The difference in the distance between nozzles and the difference in landing time can be changed by setting the inclination and density of the nozzle group relative to the direction of the printing width and by changing the conveyance speed of the printing medium. The effect of the printing method of this embodiment can be fully obtained if the difference in landing time is 1.1 times or more for the long part relative to the short part. Furthermore, it is preferable if the difference in landing time is 1.2 times or more, preferably 1.5 times or more, more preferably 2 times or more, and even more preferably 2.5 times or more. The impact time difference is preferably 4 times or less, and more preferably 3 times or less.

[0159] Furthermore, the faster the scanning speed of the recording medium, the shorter the difference in landing time between the first ink and the second ink, which tends to reduce color difference, but this can lead to other problems such as misalignment of the landing positions.Furthermore, the slower the scanning speed of the recording medium, the more likely color difference unevenness occurs, making the present invention more useful.

[0160] The nozzle density of the nozzle row in the unit head 12 is preferably 50 npi, and is preferably 1000 npi or less, more preferably 100 to 800 npi, even more preferably 200 to 600 npi, and still more preferably 300 to 500 npi.

[0161] Furthermore, the nozzle density in the width direction of the recording device may be the same as the above range, and is preferable. The nozzle density in the width direction of the recording device is the apparent nozzle density in the width direction when the head is arranged diagonally with respect to the width direction D2 as in the example of Figure 2. The nozzle density is also the nozzle density of one nozzle row that ejects ink.

[0162] The inkjet head is not limited to being arranged diagonally with respect to the width direction D2 as in the example of Figure 2, but may be arranged parallel to the width direction D2 as in Figures 2A and 2B of Japanese Patent Application Laid-Open No. 2023-135219. Even in this case, there will be areas where the landing time difference between the first ink and the second ink differs between parts of the line head in the direction D2 intersecting the conveyance direction D1 of the recording medium, making this embodiment necessary.

[0163] Methods for ejecting the ink composition from the nozzle include a method in which a pressure generating means is driven to eject the composition filled in the pressure generating chamber of an inkjet head from the nozzle, and a method in which thermal energy is applied to eject the composition. Such ejection methods are also called inkjet methods. Methods for applying pressure to the ink composition in the nozzle are not particularly limited, but examples include a piezoelectric method in which a piezoelectric element is used to eject droplets of the ink composition, and a thermal method in which heat is used to eject droplets.

[0164] Figure 3 shows another example of an inkjet head. In the example shown in Figure 3, the distance in the D1 direction between the first unit head 12a and the second unit head 12b is longer than in the example of Figure 2. Therefore, there is no spanning portion A shown in Figure 2. By adjusting the selection of unit heads to be used, the overlapping portion 13 can make the distance L in the D1 direction between the nozzles of the first unit head 12a and the nozzles of the second unit head 12b the same as in the normal portion.

[0165] As a result, there is no difference in the landing time difference between the first ink and the second ink in the recording width direction D2. However, in the example of Figure 3, a considerable gap 14 must be provided to prevent there from being any difference in the distance between the nozzles. As a result, it becomes impossible to achieve a compact head. Also, compared to the example of Figure 2, there is a larger overlapping portion 13, resulting in a lot of wasted head space.

[0166] 1.5. Mode of attachment The printing method of this embodiment is performed by a printing apparatus having a line head such as the one exemplified above. That is, the printing method of this embodiment is performed using a line head having portions in which the time difference between the landing of the first ink and the landing of the second ink at a certain point on the printing medium varies between portions of the line head in a direction intersecting the direction of conveyance of the printing medium.

[0167] The order in which the first ink and the second ink are deposited can be set arbitrarily by appropriately selecting the nozzle group to be used. However, for example, the first ink may be deposited after the second ink. In this case, based on the example of FIG. 2, the first unit head 12a ejects the second ink, and the second unit head 12b ejects the first ink.

[0168] In this way, the first ink (magenta) is applied later, which means that the first ink is more likely to be present at the top of the ink layer formed after application, which tends to enhance reddish color development, making it more preferable for recording reddish images.

[0169] Furthermore, the line head may have a portion where the inter-nozzle distance between the first nozzles and the second nozzles in the transport direction differs between portions in a direction intersecting the transport direction, and the difference in the inter-nozzle distance may be a portion where the difference in landing time between the first ink and the second ink is different. This makes it possible to reduce color difference streaks even in situations where color difference streaks are more likely to occur by using a line head having a portion where the difference in landing time between the first ink and the second ink is different.

[0170] 1.6. Effects, etc. Recording media such as plain paper contain calcium salts. When ink is highly reactive with calcium ions, the ink adhered to the recording medium reacts with the calcium ions in the recording medium, causing the ink's solid components to separate from the water and form a solid mass. This solid mass tends to solidify over time, forming a layer on top of the ink, making it difficult for later-applied ink to penetrate. Furthermore, the solid mass that has reacted with calcium ions also makes it difficult for previously applied ink to penetrate.

[0171] On the other hand, ink with low reactivity with calcium ions remains dispersed without separating from the water, so the ink layer is less likely to solidify even after time has passed since application, and subsequent inks applied on top of it easily penetrate. The ink itself also easily penetrates.

[0172] If the ink deposited first is highly reactive with calcium ions, the solidification of the ink will progress in areas of the image where there is a large difference in landing time between the ink deposited first and the ink deposited later, making it difficult for the ink to penetrate. Furthermore, if the ink deposited later is also highly reactive with calcium ions, the ink will react and the solid content will become aggregates, making it difficult for the ink to penetrate. In addition, the ink deposited later will be more likely to be repelled by the ink deposited earlier.

[0173] In this way, the ink that was deposited first and the ink that was deposited later do not mix, and the boundary between the deposited inks becomes clear. On the other hand, in areas of the image where the difference in landing time is small, the ink that was deposited first has not yet solidified, so the ink that is deposited later easily penetrates and mixes with the ink that was deposited earlier.

[0174] As a result, the appearance of the ink deposited earlier and the ink deposited later differs between areas where the difference in landing time between the first and second deposited inks is large and small, resulting in different colors in the image. This is how color difference streaks occur.

[0175] Furthermore, even in areas where the previously deposited ink has solidified and become difficult for ink to penetrate, unreacted calcium remains in the solidified material, and it is thought that the later-deposited ink reacts with the calcium on the previously deposited ink.

[0176] On the other hand, if the ink that is applied later has low reactivity with calcium ions, the ink that is applied later will easily penetrate. This will blur the ink boundary, and color difference streaks will be reduced. Alternatively, if the ink that is applied first has low reactivity with calcium ions, the ink solids will be less likely to solidify, and the ink that is applied later will easily penetrate. This will blur the ink boundary, and color difference streaks will be reduced.

[0177] In this way, if at least one of the inks has low reactivity with calcium ions, color difference streaks can be reduced. Ink having low reactivity such as the above may also be used.

[0178] 2. Recording device The recording apparatus of the present embodiment is a recording apparatus that performs the above-described recording method, and includes the above-described ink composition and an inkjet head that ejects the above-described ink composition and deposits it on a recording medium transported in a transport step.

[0179] 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, and the line head has a plurality of first nozzles arranged side by side in a direction intersecting the transport direction, each ejecting a first ink, and a plurality of second nozzles arranged side by side in a direction intersecting the transport direction.

[0180] The recording apparatus of this embodiment may further include a transport unit (transport mechanism) for transporting the recording medium. The transport unit is configured, for example, by a transport roller or a transport belt provided within the recording apparatus.

[0181] According to the recording apparatus of this embodiment, at least one of the ink compositions has low reactivity with calcium ions, so that color difference streaks can be reduced.

[0182] 3. Examples and Comparative Examples The present invention will be specifically described below using examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" are based on mass unless otherwise specified. Evaluations were conducted in an environment of 25°C and 40.0% relative humidity unless otherwise specified.

[0183] 3.1. Preparation of ink composition 3 and 4, Tables 1 and 2 showing the compositions of the ink compositions of Examples and Comparative Examples and the evaluation results thereof are provided. Each component was placed in a mixing tank so as to obtain the composition shown in Tables 1 and 2, mixed and stirred, and then filtered through a membrane filter to obtain the inkjet ink composition of 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. The resulting M inks were all magenta inks, and the Y inks were all yellow inks.

[0184] Details of the abbreviations and product ingredients used in Tables 1 and 2 are as follows, and the numbers written to the right of the solvent abbreviations indicate the SP values ​​of the solvents. [Pigment] Pigment dispersions A to F are prepared as follows. Dispersion A: 20% by weight of CI Pigment Red 150 (PR150), an azo pigment; 5% by weight 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 weight 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. Styrene-acrylic acid copolymer is a water-soluble polymer commonly used as a pigment dispersant. The volume average particle diameter D50 of Dispersion A measured using a particle size distribution analyzer was 100 nm. The resin dispersant had a low acid value (less reactive with calcium ions). The viscosity increase ratio was A. The viscosity increase ratio will be described later.

[0185] Dispersion B: Same as Dispersion A except that the acid value of the resin dispersant is 260 mgKOH / g. To obtain dispersion B, the acid value of the resin dispersant is high (it easily reacts with calcium ions), and the viscosity increase rate is C.

[0186] Dispersion C: Dispersion C is obtained in the same manner as Dispersion A, except that the acid value of the resin dispersant is 200 mg KOH / g. : The acid value of the resin dispersant is medium (does not react well with calcium ions) and the viscosity increase rate is B.

[0187] Dispersion D: Dispersion C is obtained in the same manner as Dispersion A, except that CI Pigment Yellow 74 (PY74), a yellow azo pigment, is used instead of CI Pigment Red 150 (PR150). The acid value of the resin dispersant is low (it is less likely to react with calcium ions). The viscosity increase rate is A.

[0188] Dispersion E: Dispersion E is obtained in the same manner as Dispersion D, except that the acid value of the resin dispersant is 260 mg KOH / g. : The acid value of the resin dispersant is high (it reacts easily with calcium ions). Thickening rate = C.

[0189] Dispersion F: Dispersion F is obtained in the same manner as Dispersion D, except that the acid value of the resin dispersant is 200 mg KOH / g. : The acid value of the resin dispersant is medium (does not react well with calcium ions). Thickening rate = B.

[0190] Dispersion G: Dispersion G is obtained in the same manner as Dispersion A, except that CI Pigment Violet 19 (PV19), a quinacridone pigment, is used instead of CI Pigment Red 150 (PR150). The acid value of the resin dispersant is low (it is less likely to react with calcium ions). The thickening ratio is A.

[0191] Dispersion H: Dispersion H is obtained in the same manner as dispersion G, except that the acid value of the resin dispersant is 260 mg KOH / g. : The acid value of the resin dispersant is high (it reacts easily with calcium ions). Thickening rate = C.

[0192] Dispersion I: Dispersion I is obtained in the same manner as Dispersion A, except that CI Pigment Red 17 (PR17), an azo pigment, is used instead of CI Pigment Red 150 (PR150). : The acid value of the resin dispersant is low (it is less likely to react with calcium ions). Thickening ratio = A.

[0193] [Lactam compounds] HEP: 1-(2-hydroxyethyl)-2-pyrrolidone CPL: ε-caprolactam [Water-soluble organic solvent (penetrating agent)] 1,2-Hexanediol [Other solvents] Gly: Glycerin TEG: Triethylene glycol) [Surfactants] Olfine E1010 (trade name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd., HLB value = 13-14) Surfynol 104 (trade name, acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd., HLB value = 4) [resin] Movinyl 6820 (product name, manufactured by Japan Coating Resin Co., Ltd.) [pH adjuster] TEA: Triethylamine

[0194] 3.2.Evaluation Method 3.2.1. Thickening rate The ink composition of each example was mixed with an aqueous calcium propionate solution (Ca concentration: 0.3 mol / L) at a ratio of 10:1 (ink:aqueous calcium propionate solution) and left to stand for 24 hours at 60°C. The viscosity η1 of the ink after standing and the viscosity η0 of the ink in its initial state were measured as described above, and the viscosity increase rate was calculated according to the following formula. Viscosity increase rate (times) = ink viscosity after standing η1 / initial ink viscosity η0

[0195] (Evaluation criteria) A: Viscosity increase rate is 1.0 or more and less than 1.5 B: Viscosity increase rate is 1.5 or more and less than 2.0 C: Viscosity increase rate is 2.0 or more

[0196] 3.2.2. Mixed liquid redispersibility The ink composition of each example was mixed with an aqueous calcium propionate solution (Ca concentration: 0.3 mol / L) at a ratio of 10:1 (ink:aqueous calcium propionate solution), and five 2 μl drops of the mixture were placed on a glass slide and dried for 24 hours at 60° C. After drying, the slide was immersed in a sample bottle containing only the ink composition before mixing and left for three minutes. After being turned upside down five times, the slide was removed and the amount of mixture remaining on the glass and the degree of redissolution were visually evaluated according to the following criteria. (Evaluation criteria) A: All ink droplets are redissolved. B: The ink droplets redissolve, but some residue is visible on the slide. C: The ink droplets do not redissolve and remain solid. 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, and it remained in a solid state, just as when dried at 60°C.

[0197] 3.2.3. Phase separation in ink The ink composition of each example 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 is observed. B: The surfactant separates and floats on the liquid surface. C: The surfactant separates into two layers.

[0198] 3.2.4. Recording test A modified LX-10050MF (Seiko Epson Corporation, line-type inkjet printer) was used. The head used was either H1, which has a difference in ink landing time, or H2, which has no difference in ink landing time. The two inks listed in Tables 3 to 5 were filled in the order listed so that they could be ejected.

[0199] The two inks were then printed on top of each other on Copyplus paper (plain paper, manufactured by Hammermill). The ink droplet mass was set to 12.5 ng / dot, and the basic resolution was set to 600 x 600 dpi. The dot density was adjusted by adjusting the number of ink droplets per pixel so that the deposition amount (application amount) in the solid pattern was that value. The print medium was transported at a speed of 600 mm / s.

[0200] The line heads H1 and H2 have the following configuration. Line head H1: A line head having the nozzle surface 11 shown in Fig. 2. The apparent nozzle density in the width direction is 600 npi. Line head H2: A line head in which the unit heads are arranged so as not to have the straddling portion shown in Figure 3. The apparent nozzle density in the width direction is 600 npi.

[0201] The head on the upstream side in the conveyance direction of the recording medium is filled with the ink that is first in the order, and the head on the downstream side is filled with the ink that is second in the order. One unit head has two nozzle rows and can use two inks, but only one of the nozzle rows is used.

[0202] 3.2.5.Color development The ink application amount on the recording device is 5.0 mg / inch 2 A test pattern for each ink alone is recorded on Copy+ paper (plain paper) so that the OD value is measured using a colorimeter (Xrite i1, manufactured by Xrite) 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 and less than 0.75 D:OD value is less than 0.65

[0203] 3.2.6.Discharge stability The ink application amount on the recording device is 5.0 mg / inch 2 Print 100 test patterns for each ink individually on Copy+ paper (plain A4 size) at the printing speeds listed in Tables 3 to 5 so that the print quality is as shown in Table 1. Print on one side only. After printing, print a nozzle check pattern and check for any print distortion or omissions after the continuous printing. (Evaluation criteria) A: There is no misprinting or missing prints. B: Printing deviation or omission occurs in less than 50% of the nozzles. C: Printing irregularities or omissions occur in 50% or more but less than 70% of the nozzles. D: Printing deviation or omission occurs in 70% or more of the nozzles.

[0204] 3.2.7.Clogging recovery As in the above-mentioned ejection stability test, 100 sheets are printed continuously at the recording speed indicated in the table. The inkjet head is then displaced from the cap position on the printer, and left uncapped for 7 days in an environment with a temperature of 40°C and humidity of 20%. After leaving the inkjet head, the ink is cleaned by suctioning ink from the nozzles, counting the number of nozzles that are unable to eject ink, and repeating the cleaning operation until all nozzles are restored. Evaluation is then performed according to the following criteria based on the number of cleanings required until all nozzles are restored. 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 three or four cleanings. C: All nozzles recovered after 5 or 6 cleanings. D: Even after six cleanings, some nozzles remained unrecovered.

[0205] 3.2.8. Visibility of Color Difference Streaks 7mg / inch with the above recording device 2 A solid pattern is printed on the entire printable area of ​​Copy+ paper (plain paper) with the same amount of ink applied. The first ink and the second ink are applied in equal amounts. The visibility of the color difference banding that occurs in the area where the secondary color is printed (how the color difference banding appears when visually inspected) is measured as follows: The evaluation is based on the following criteria: Color difference streaks are a phenomenon in which areas with different colors appear as streaks, and tend to occur with heads (H1) that have straddling sections. A: No color difference streaks are visible even when approaching the recorded material within 30 cm. B: Color difference lines are visible when approaching the recorded material within 30 cm. C: Color difference streaks are visible on the recorded material even when standing more than 30 cm away.

[0206] 3.2.9. Transferability (printed material, media transport path) The recording device and recording medium are placed in an environment (15°C, 80% RH) (low temperature and high humidity) where transfer is likely to occur, and allowed to acclimate for at least 12 hours. After confirming that the ink is ejecting normally, a nozzle check pattern is printed on 500 sheets using double-sided printing. Then, the presence or absence of transfer between printed items and the presence or absence of contamination on the transport path (transfer during transport) are visually checked. A: It does not transfer. B: There is transfer of dirt from the transport path. C: There is transfer of dirt between printed materials and on the transport path.

[0207] 3.3.Evaluation Results Tables 1 to 5 show that in the following examples, 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 direction of transport of the recording medium, a plurality of first nozzles ejecting a first ink are arranged in a row in a direction intersecting the direction of transport, a plurality of second nozzles ejecting a second ink are arranged in a row in a direction intersecting the direction of transport, and the time difference between the impact of the first ink and the impact of the second ink at a certain point on the recording medium varies between parts of the line head in the direction intersecting the direction of transport; the ink composition includes a first ink that is a reddish ink containing an azo pigment, and a second ink that is a chromatic color ink other than a reddish ink that contains a pigment, and the first ink and the second ink are water-based inks, and at least one of the first ink and the second ink has a viscosity increase rate of less than 2.0 times when the ink composition is mixed with an aqueous calcium propionate solution having a Ca concentration of 0.3 mol / L at a mass ratio of 10:1.

[0208] Furthermore, it can be seen that, according to the present invention, even when a head that causes a difference in landing time is used, color difference streaks can be reduced by setting the ink viscosity increase rate to less than 2.0 times. In other words, according to the present invention, color difference streaks can be reduced without changing the head design.

[0209] Although not shown in the table, when recording is performed using a serial printer (PX-M886L manufactured by Seiko Epson, modified model) instead of a line printer, less paper dust is generated than with a line printer, and the ejection stability and clogging recovery are generally higher, but the recording speed is slow and it is not a useful recording device.

[0210] Furthermore, when evaluated in the same manner as for M1 except that HEP and CPL of ink M1 were replaced with 2-pyrrolidone, the redispersibility of the mixed liquid and phase separation were reduced.

[0211] Furthermore, when evaluated in the same manner as the Y1 ink except for reducing the pigment content of the Y1 ink, the ink redispersibility improves, as does the ejection stability, etc. Even in such cases, the excellent color development of the M ink means that excellent color development can be obtained when recording secondary color images using yellow ink and magenta ink.

[0212] The present invention includes configurations that are substantially the same as the configurations described in the embodiments, for example, configurations with the same functions, methods, and results, or configurations with the same purpose and effects. The present invention also includes configurations that replace non-essential parts of the configurations described in the embodiments. The present invention also includes configurations that have the same operational effects as the configurations described in the embodiments or that can achieve the same purpose. The present invention also includes a configuration in which publicly known technology is added to the configurations described in the embodiments.

[0213] The following can be derived from the above-described embodiment and modifications.

[0214] The recording method is a conveying step of conveying the recording medium; an ink deposition step of ejecting an ink composition from an inkjet head and depositing the ink composition on the recording medium transported in the transport step; and 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 ink composition includes a first ink that is a reddish ink containing an azo pigment, and a second ink that is a chromatic color ink other than a reddish ink that contains a pigment, the first ink and the second ink are water-based inks, the line head includes a plurality of first nozzles that eject the first ink and are arranged in a direction intersecting the transport direction, and a plurality of second nozzles that eject the second ink and are arranged in a direction intersecting the transport direction; the line head has a portion in which a time difference between landing of the first ink and landing of the second ink on the recording medium differs between portions of the line head in a direction intersecting the transport direction, At least one of the first ink and the second ink has a viscosity increase rate of less than 2.0 times when the ink is mixed with an aqueous calcium propionate solution having a Ca concentration of 0.3 mol / L at a mass ratio of 10:1.

[0215] This recording method can produce a recorded product in which the occurrence of streaks due to differences in color development is suppressed. Furthermore, this recording method can provide an image with excellent color development, at least using the first ink.

[0216] Recording media such as plain paper contain calcium salts. When ink is highly reactive with calcium ions, the ink adhered to the recording medium reacts with the calcium ions in the recording medium, causing the ink's solid components to separate from the water and form a solid mass. This solid mass tends to solidify over time, forming a layer on top of the ink, making it difficult for later-applied ink to penetrate. Furthermore, the solid mass that has reacted with calcium ions also makes it difficult for previously applied ink to penetrate.

[0217] On the other hand, ink with low reactivity with calcium ions remains dispersed without separating from the water, so the ink layer is less likely to solidify even after time has passed since application, and subsequent inks applied on top of it easily penetrate. The ink itself also easily penetrates.

[0218] If the ink deposited first is highly reactive with calcium ions, the solidification of the ink will progress in areas of the image where there is a large difference in landing time between the ink deposited first and the ink deposited later, making it difficult for the ink to penetrate. Furthermore, if the ink deposited later is also highly reactive with calcium ions, the ink will react and the solid content will become aggregates, making it difficult for the ink to penetrate. In addition, the ink deposited later will be more likely to be repelled by the ink deposited earlier.

[0219] In this way, the ink that was deposited first and the ink that was deposited later do not mix, and the boundary between the deposited inks becomes clear. On the other hand, in areas of the image where the difference in landing time is small, the ink that was deposited first has not yet solidified, so the ink that is deposited later easily penetrates and mixes with the ink that was deposited earlier.

[0220] As a result, the appearance of the ink deposited earlier and the ink deposited later differs between areas where the difference in landing time between the first and second deposited inks is large and small, resulting in different colors in the image. This is how color difference streaks occur.

[0221] Furthermore, even in areas where the previously deposited ink has solidified and become difficult for ink to penetrate, unreacted calcium remains in the solidified material, and it is thought that the later-deposited ink reacts with the calcium on the previously deposited ink.

[0222] On the other hand, if the ink that is applied later has low reactivity with calcium ions, the ink that is applied later will easily penetrate. This will blur the ink boundary, and color difference streaks will be reduced. Alternatively, if the ink that is applied first has low reactivity with calcium ions, the ink solids will be less likely to solidify, and the ink that is applied later will easily penetrate. This will blur the ink boundary, and color difference streaks will be reduced.

[0223] In this way, color difference streaks can be reduced if at least one of the inks has low reactivity with calcium ions. From the viewpoint of reducing color difference streaks, both inks may have low reactivity with calcium ions.

[0224] In the above recording method, The content of the azo pigment relative to the total mass of the pigments contained in the first ink may be 30 mass % or more.

[0225] This recording method can further enhance the color development of the first ink. For example, if the first ink has low reactivity with calcium ions, the ink will easily penetrate the recording medium and will not easily remain on the surface of the recording medium, resulting in low color development of the ink. However, if the first ink is, for example, magenta ink, various pigments can be used, and by using an azo pigment with particularly high color development, a magenta ink with high color development can be obtained, even if the first ink has low reactivity with calcium ions.

[0226] The color of the first ink is not limited, but the first ink may be, for example, a magenta ink, a process color ink. Particularly in business applications, high visibility of red marks on recorded materials, such as confidentiality markings and printed seals, is required, and the magenta ink used for this color is required to have high color development. Furthermore, because red is a highly visible color, color difference streaks are easily noticeable. Therefore, when recording colors using magenta ink, it is required to be possible to reduce color difference streaks, and the present invention provides excellent effects in this regard.

[0227] In the above recording method, The first ink may have a viscosity increase rate of less than 2.0 times.

[0228] According to this recording method, the color development of the first ink can be further improved.

[0229] In the above recording method, The first ink may contain a dispersant resin for dispersing the azo pigment, and the acid value of the dispersant resin may be 200 mgKOH / g or less.

[0230] According to this recording method, the color development of the first ink can be further improved.

[0231] In the above recording method, The first ink and the second ink each contain lactams having a molecular weight of 100 or more. You may do so.

[0232] Line printers print large volumes of material continuously at high speeds, generating a lot of paper dust, which can fill the interior of the printer. This paper dust adheres to the nozzles, thickening them and making ejection stability and clogging recovery difficult. This tendency is particularly pronounced when the ink is highly reactive with calcium. This tendency also exists for inks with low reactivity. Inks with low reactivity with calcium offer excellent ejection stability and clogging recovery. When paper dust generated during printing comes into contact with the ink in the nozzles, highly reactive inks can cause the pigment to turn into foreign matter due to the paper dust. This can lead to poor ejection stability and clogging recovery. This can be prevented with inks with low reactivity.

[0233] According to this recording method, the moisturizing effect of lactams prevents the mixture of paper powder and ink in the nozzle from drying out. Even if the mixture begins to dry, the dried material can be redispersed more easily, resulting in better ejection stability and clogging recovery. This effect is more pronounced when lactams have a molecular weight equal to or greater than a certain level. Furthermore, particularly when the ink contains an acetylene glycol surfactant, lactams tend to prevent the acetylene glycol surfactant from becoming insoluble in water and undergoing phase separation. Among lactams, 1-(2-hydroxyethyl)-2-pyrrolidone (HEP) and ε-caprolactam (CPL) have the most pronounced effects. In particular, HEP tends to prevent the ink from becoming too viscous when contained in the ink, making it easier to control the ink ejection volume and ensuring stable ejection. Furthermore, CPL, in particular, exhibits the above-mentioned redispersibility effect.

[0234] In the above recording method, The viscosity increase rate of the other of the first ink and the second ink may be 2.0 times or more.

[0235] According to this recording method, color difference streaks can be further reduced.

[0236] In the above recording method, The first ink may be a magenta ink and the second ink may be a yellow ink or a cyan ink.

[0237] According to this recording method, by using an azo pigment-based magenta ink with low reactivity with calcium, the second ink can be made to have high reactivity with calcium, thereby increasing the degree of freedom in design. Furthermore, for example, by using a yellow ink with high reactivity with calcium, the visibility of yellow can be improved, which is more preferable. In images with warm colors, where color difference streaks are easily noticeable, using a yellow ink with high reactivity with calcium and a magenta ink with low reactivity with calcium makes it possible to record images with high visibility and reduced color difference streaks.

[0238] Furthermore, when the second ink is cyan ink, it is also preferable that it has high reactivity. Cyan ink is often used to generate a secondary color (blue) with magenta ink (first ink), and the low reactivity of magenta ink can further reduce blue color difference streaks.

[0239] Furthermore, the problem of color difference streaks tends to become more pronounced between inks used to generate secondary colors (two inks with adjacent hue angles). If the reactivity of magenta ink is low, the reactivity of yellow and cyan inks can be increased when printing secondary colors (reds and blues) with magenta ink.

[0240] In the above recording method, The first ink may be deposited after the second ink is deposited.

[0241] According to this recording method, the first ink (magenta) is applied later, which means that the first ink is often present at the top of the ink layer formed after application, which tends to enhance reddish color development and is more preferable for recording reddish images.

[0242] In the above recording method, The recording medium may be an absorbent recording medium.

[0243] According to this recording method, a recording medium on the surface of which pigment is less likely to remain is used, so the effect of the recording method of improving color development on the surface becomes more pronounced.

[0244] In the above recording method, the line head has a portion in which the inter-nozzle distance between the first nozzles and the second nozzles in the transport direction varies between portions in a direction intersecting the transport direction, The landing time difference may be different in the portion where the inter-nozzle distance is different.

[0245] According to this recording method, a line head having portions where the landing time difference between the first ink and the second ink is different is used, and color difference streaks can be reduced even in situations where color difference streaks are more likely to occur.

[0246] The recording device A recording device that performs any one of the above recording methods, the ink composition; an inkjet head that ejects the ink composition and deposits it on the recording medium that has been transported in the transporting step; Equipped with.

[0247] According to this recording apparatus, at least one of the inks has low reactivity with calcium ions, so that color difference streaks can be reduced. [Explanation of symbols]

[0248] 10...line head, 11...nozzle surface, 12...unit head, 12a...first unit head, 12b...second unit head, 13...overlapping portion, 14...gap, 100...recording device, B...belt, D1...scanning direction, D2...width direction, M...recording medium, A...straddling portion, B1...overlapping portion, B2...overlapping portion, C...normal portion

Claims

1. a conveying step of conveying the recording medium; an ink deposition step of ejecting an ink composition from an inkjet head and depositing the ink composition on the recording medium transported in the transport step; and 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 ink composition includes a first ink that is a reddish ink containing an azo pigment, and a second ink that is a chromatic color ink other than a reddish ink that contains a pigment, the first ink and the second ink are water-based inks, the line head has a plurality of first nozzles that eject the first ink arranged in a direction intersecting the transport direction, and a plurality of second nozzles that eject the second ink arranged in a direction intersecting the transport direction; the line head has a portion in which a time difference between landing of the first ink and landing of the second ink on the recording medium differs between portions of the line head in a direction intersecting the transport direction, a viscosity increase rate of at least one of the first ink and the second ink when the ink is mixed with an aqueous calcium propionate solution having a Ca concentration of 0.3 mol / L at a mass ratio of 10:1, the viscosity increase rate being less than 2.0 times;

2. In claim 1, A recording method, wherein the content of the azo pigment relative to the total mass of the pigments contained in the first ink is 30 mass % or more.

3. In claim 1, A recording method, wherein the viscosity increase rate of the first ink is less than 2.0 times.

4. In claim 3, A recording method, wherein the first ink contains a dispersant resin for dispersing the azo pigment, and the acid value of the dispersant resin is 200 mgKOH / g or less.

5. In claim 1, A recording method, wherein the first ink and the second ink each contain a lactam having a molecular weight of 100 or more.

6. In claim 1, The other of the first ink and the second ink has a viscosity increase rate of 2.0 times or more.

7. In claim 1, A recording method, wherein the first ink is a magenta ink, and the second ink is a yellow ink or a cyan ink.

8. In claim 1, A recording method in which the first ink is deposited after the second ink is deposited.

9. In claim 1, The recording method, wherein the recording medium is an absorbent recording medium.

10. In claim 1, the line head has a portion in which the inter-nozzle distance between the first nozzles and the second nozzles in the transport direction varies between portions in a direction intersecting the transport direction, A recording method, wherein the impact time difference is different in the portion where the inter-nozzle distance is different.

11. A recording apparatus for performing the recording method according to any one of claims 1 to 10, the ink composition; a transport mechanism that performs the transport step; A recording device having the inkjet head.

Images