Inkjet recording method

Abstract

To provide an inkjet recording method capable of suppressing a phenomenon of an ink droplet applied later sinking into an ink droplet applied prior thereto, and capable of recording a clear image with highly developed colors.SOLUTION: An inkjet recording method includes: a corona discharge treatment step of imparting a corona discharge treatment to a recording medium; and an ink application step of applying an ink containing an anionic pigment onto a surface of the recording medium with the corona discharge treatment imparted. A discharge amount at the corona discharge treatment is 3400 W min / m2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method. [Background technology]

[0002] In inkjet recording methods, images are formed by directly or indirectly applying a liquid composition containing colorants (ink) onto a recording medium such as paper. If the time interval between adjacent ink dots applied by the inkjet recording head is short, subsequent adjacent dots may be applied before the previously deposited ink droplets have penetrated, dried, and fixed onto the recording medium, potentially causing problems such as beading and bleeding. Furthermore, in multi-color image formation, if the primary color applied first is a solid image, and the previously applied ink has not penetrated, dried, and fixed onto the recording medium, subsequent ink droplets may become embedded within the previously applied ink droplets, resulting in reduced color vibrancy of the resulting image. These problems become more pronounced when the ink has low or no penetration into the recording medium. Conventional technologies to solve problems such as beading and bleeding include methods that improve ink dot roundness and suppress the migration of pigments, as well as methods that suppress beading, by treating the surface of the recording medium with a plasma treatment means to change the wettability, pH value, and permeability of the recording medium (Patent Document 1). In addition, as a method for obtaining sharp images by surface treatment of recording media, a method has been proposed in which the surface of the recording media is treated by a corona treatment means to improve the wettability of the recording media (Patent Document 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-138384 [Patent Document 2] Japanese Patent Publication No. 2019-130869 [Overview of the project]

Problems to be Solved by the Invention

[0004] Although the problems of bleeding and bleeding are improved by the methods of Patent Documents 1 and 2, it is insufficient to suppress the phenomenon that the later-applied ink droplets are buried in the previously-applied ink droplets and the color development property of the image is deteriorated.

Means for Solving the Problems

[0005] The present invention includes a corona discharge treatment step of subjecting a recording medium to corona discharge treatment, an ink application step of applying an ink containing an anionic pigment to the surface of the recording medium that has been subjected to the corona discharge treatment, and has an inkjet recording method characterized in that the discharge amount of the corona discharge treatment is 3400 W·min / m 2 or more.

Effects of the Invention

[0006] According to the present invention, it is possible to provide an inkjet recording method capable of suppressing the phenomenon that later-applied ink droplets are buried in previously-applied ink droplets and recording a clear and highly color-developed image.

Brief Description of the Drawings

[0007] [Figure 1] It is a schematic diagram showing an example of the configuration of an inkjet recording apparatus used in the inkjet recording method according to an embodiment of the present invention. [Figure 2] It is a diagram showing the relationship between the power, processing speed, and discharge amount of corona discharge treatment. [Figure 3] It is a diagram showing the relationship between the processing speed and the generator output when the discharge amount is 3400 W·min / m2 or more. [Figure 4] It is a block diagram showing the control system of the entire apparatus in the inkjet recording apparatus shown in FIG. 1. [Figure 5]It is a block diagram of a printer control unit in an inkjet recording apparatus shown in FIG. 1. [Figure 6] It is a photograph of each image when ink is applied onto a recording medium that has been subjected to corona discharge treatment and plasma treatment to form an image. [Figure 7] It is a diagram showing the relationship between the discharge amount of corona discharge treatment and the brightness of an image.

Mode for Carrying Out the Invention

[0008] The inkjet recording method according to this embodiment includes a corona discharge treatment step of subjecting a recording medium to corona discharge treatment, and an ink application step of applying ink containing an anionic pigment onto the surface of the recording medium that has been subjected to the corona discharge treatment, and is characterized in that the discharge amount of the corona discharge treatment is 3400 W·min / m 2 or more.

[0009] Normally, the hydrophilicity of the surface of the recording medium is enhanced by corona discharge treatment, and the contact angle between water and the recording medium becomes smaller, so water spreads. On the other hand, when using anionic pigment ink containing an anionic pigment, the inventors have found that the anionic pigment in the ink can aggregate and be fixed by the protons generated on the surface of the recording medium by corona discharge treatment. Particularly, when the discharge amount of corona discharge treatment is 3400 W·min / m 2 or more, the effect is remarkable, and the inventors have found that it is easier to obtain the effect by corona discharge treatment than by plasma treatment. Also, the discharge amount of corona discharge treatment is preferably 4200 W·min / m 2 or more and 25000 W·min / m 2 or less, more preferably 4520 W·min / m 2 or more and 25000 W·min / m 2 or less, and even more preferably 5700 W·min / m 2 or more and 25000 W·min / m 2 or less. The aggregation of anionic pigments by corona discharge treatment of the recording medium is due to the generation of oxonium ions (H3O) on the surface of the recording medium. + However, the inventors speculate that this is because it destroys the dispersion state of the anionic pigment. Although the discharge amount is larger in plasma treatment (Figure 6(d)), the mechanism for why ink aggregation does not occur as in corona discharge treatment (Figure 6(c)) is unknown, but plasma treatment ultimately generates more H3O + This is likely because the number is small.

[0010] The present invention will be described in detail below with reference to preferred embodiments, but the present invention is not limited to the following embodiments. An inkjet recording apparatus used in an inkjet recording method according to an embodiment of the present invention will be described below with reference to the drawings.

[0011] Figure 1 is a schematic diagram showing an example of the general configuration of an inkjet recording apparatus 100 used in the inkjet recording method of this embodiment. In this apparatus, a recording medium 102, which is a continuous paper formed in a roll shape, is unwound from an unwinding unit 101a and wound up by a take-up unit 101b. The recording medium 102 unwound from the unwinding unit 101a passes at a position facing the corona electrode portion 103d of the corona discharge processing unit 103, thereby undergoing corona discharge processing. The distance (shortest distance) between the corona electrode portion 103d of the corona discharge processing unit 103 and the recording medium 102 is preferably 0.01 mm or more and 1 mm or less. After that, it passes through inkjet recording heads 104a to 104d, and ink of each color is applied. The inkjet recording heads are recording heads that eject cyan ink (104a), magenta ink (104b), yellow ink (104c), and black ink (104d).

[0012] <Recording medium> The recording medium used in the present invention may be either a sheet of paper or a roll of paper, but from the viewpoint of productivity, a roll-shaped recording medium is preferred. As recording media, absorbent recording media that can absorb liquid components in ink, and non-absorbent recording media that do not absorb liquid components are used.

[0013] Examples of non-absorbent recording media include resin films. These include polyester films, polyvinyl chloride films, polypropylene films, polyethylene films, and nylon films. Examples of commercially available resin films include Lumirror T60 (manufactured by Toray Industries, Inc., polyethylene terephthalate), Taiko FE2001 (manufactured by Futamura Chemical Co., Ltd., corona-treated polyethylene terephthalate), PVC80B P (manufactured by Lintec Corporation, polyvinyl chloride), Kainas KEE70CA (manufactured by Lintec Corporation, polyethylene), Yupo SG90 PAT1 (manufactured by Lintec Corporation, polypropylene), Bonil RX (manufactured by Kojin Film & Chemicals Co., Ltd., nylon), and PET(50) PAT1 8LK (manufactured by Lintec Corporation, PET).

[0014] Examples of absorbent recording media include art paper and high-quality paper. Examples of commercially available absorbent recording media include 55PW8K (manufactured by Lintec Corporation, high-quality paper) and Art E PW 8K (manufactured by Lintec Corporation, coated paper).

[0015] <Storage configuration for transporting recording media> The recording medium has a Y-direction length of 330 mm, and its transport speed is controlled by the rotational speed of the unwinding unit 101a and the winding unit 101b. The unwinding unit 101a and the winding unit 101b are connected to a drive motor and control means (not shown) to control their rotational speed. The transport speed of the recording medium is preferably between 1.5 m / min and 4 m / min.

[0016] <Corona discharge treatment unit> The corona electrode section 103d of the corona discharge treatment unit 103 has a length of 350 mm in the Y direction and is connected to a generator (not shown) to supply power used for corona discharge treatment. The recording medium 102 is suspended from the idler rollers 103a and 103c and the grounded electrode-facing roller 103b of the corona discharge treatment unit. Corona discharge is generated as the recording medium 102 passes between the corona electrode portion 103d and the electrode-facing roller 103b, thereby performing corona discharge treatment on the surface of the recording medium 102. The discharge amount Q [W·min / m] of the corona discharge treatment. 2 This can be controlled by the relationship shown in equation (1) from the generator power E [W], electrode width D [m], and transport speed V [m / min] of the recording medium 102. Q=E / (D×V) Equation (1)

[0017] Figure 2 shows the relationship between generator output and recording medium transport speed and the discharge amount of the corona discharge process. To achieve a discharge amount greater than the target value, it is effective to either increase the generator output or decrease the processing speed.

[0018] Figure 3 shows the discharge rate of 3400 W·min / m in Figure 2. 2 This is the relationship between the generator output and processing speed required to achieve this. By performing corona discharge processing under the conditions in the region indicated by the arrow in Figure 3, the discharge rate is 3400 W·min / m 2 The above corona discharge treatment is possible.

[0019] In this way, the amount of corona discharge can be adjusted by changing the output of the corona discharge process and the transport speed of the recording medium. It is preferable that the output of the corona discharge process (power supplied by the generator) be between 3000W and 5000W.

[0020] <Ink dispenser> In this embodiment, an inkjet recording head is used as the ink dispensing device. Examples of inkjet recording heads include those that eject ink by generating film boiling in the ink using an electro-thermal converter and forming bubbles, those that eject ink using an electro-mechanical converter, and those that eject ink using static electricity. In this embodiment, known inkjet recording heads can be used. Among these, those using an electro-thermal converter are particularly preferred from the viewpoint of performing high-speed and high-density printing. Image recording on the recording medium is performed by receiving an image signal and applying the required amount of ink to each position.

[0021] In this embodiment, the inkjet recording head is a full-line recording head extending in the Y direction, and nozzles are arranged to cover the width of the image recording area of ​​the largest usable recording medium. The inkjet recording head has an ink ejection surface on its lower surface (the recording medium 102 side) where the nozzles open, and the ink ejection surface faces the surface of the recording medium 102 with a small gap (about a few millimeters) between them.

[0022] The amount of ink applied to the recording medium can be expressed by the density value of the image data or the ink thickness, but in this embodiment, the average value obtained by multiplying the mass of each ink dot (ink droplet) by the number of dots applied and dividing by the printing area is used to determine the amount of ink applied (g / m²). 2 ) was defined as follows. Furthermore, the maximum ink application amount in the image area is defined as at least 5 mm within the area used as information on the recording medium, from the viewpoint of removing the liquid component in the ink. 2 This indicates the amount of ink applied to the area.

[0023] The inkjet recording heads (104a to 104d) may have multiple inkjet recording heads to dispense each color ink onto the recording medium. For example, when forming color images using yellow ink, magenta ink, cyan ink, and black ink, the ink dispenser will have four inkjet recording heads, each ejecting one of the four types of ink onto the recording medium, and these will be arranged in a line in the X direction.

[0024] <ink> The following describes in detail each component of the ink used in this embodiment, including the colorant, resin, aqueous medium, and additives.

[0025] (Colorants) Anionic pigments are used as the colorants. The colorant content in the ink is preferably 0.5% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. Specific examples of anionic pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine.

[0026] As for the dispersion method of the pigment, resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with resin or the like can be used.

[0027] As a resin dispersant for dispersing pigments in an aqueous medium, it is preferable to use one that can disperse pigments in the aqueous medium through the action of anionic groups. Preferably, as the resin dispersant, a resin as described later can be used, and more preferably, a water-soluble resin can be used. The pigment content (mass%) is preferably 0.3 times or more and 10.0 times or less in mass ratio (pigment / resin dispersant) to the resin dispersant content.

[0028] Self-dispersing pigments can be those in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded directly to the surface of the pigment particles or via other atomic groups (-R-). The anionic group may be either acidic or salt-type, and if it is salt-type, it may be in a partially dissociated state or a fully dissociated state. Examples of cations that become counterions when the anionic group is salt-type include alkali metal cations, ammonium, and organic ammonium. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups with 1 to 12 carbon atoms, arylene groups such as phenylene and naphthylene groups, carbonyl groups, imino groups, amide groups, sulfonyl groups, ester groups, and ether groups. Combinations of these groups may also be used.

[0029] Additionally, dyes may be used along with pigments as needed. It is preferable to use dyes that have anionic groups. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone.

[0030] (resin) The ink may contain resin. The resin content (by mass) in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0031] Resins can be added to ink for reasons such as (i) stabilizing the dispersion state of pigments, i.e., as the resin dispersant or its auxiliary, and (ii) improving various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be dissolved in an aqueous medium as a water-soluble resin, or dispersed in an aqueous medium as resin particles. The resin particles do not need to contain colorants. Furthermore, the resin is preferably anionic resin particles.

[0032] In this invention, a resin is considered water-soluble if, when neutralized with an equivalent amount of alkali to its acid value, it does not form particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid containing the resin (resin solids content: 10% by mass) is prepared, neutralized with an alkali equivalent to its acid value (such as sodium hydroxide or potassium hydroxide). Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles with a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions can be set, for example, as follows: SetZero: 30 seconds, Number of measurements: 3 times, Measurement time: 180 seconds. As the particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above.

[0033] The acid value of the resin is preferably 100 mg KOH / g or more and 250 mg KOH / g or less for water-soluble resins, and preferably 5 mg KOH / g or more and 100 mg KOH / g or less for resin particles. The weight-average molecular weight of the resin is preferably 3,000 or more and 15,000 or less for water-soluble resins, and preferably 1,000 or more and 2,000,000 or less for resin particles. The volume-average particle diameter of the resin particles, measured by dynamic light scattering (measurement conditions are the same as above), is preferably 100 nm or more and 500 nm or less.

[0034] Examples of resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred. As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. Among these, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer of styrene and α-methylstyrene are preferred. Because these resins readily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments. In this invention, (meth)acrylic acid means acrylic acid or methacrylic acid.

[0035] Hydrophilic units are units that have hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers that have hydrophilic groups. Specific examples of hydrophilic monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Cations that constitute salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. Hydrophobic units are units that do not have hydrophilic groups, such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups, such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers, such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0036] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0037] (aqueous medium) The ink may contain an aqueous medium, which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the aqueous ink is preferably 50.0% to 95.0% by mass, based on the total weight of the ink. Furthermore, the water-soluble organic solvent content (mass%) in the aqueous ink is preferably 3.0% to 50.0% by mass, based on the total weight of the ink. As the water-soluble organic solvent, any solvent suitable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

[0038] (Other additives) In addition to the components listed above, the ink may also contain various additives as needed, such as defoamers, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, fungicides, antioxidants, and reduction inhibitors.

[0039] <Control System> The inkjet recording apparatus used in the inkjet recording method of this embodiment has a control system that controls each device. Figure 4 is a block diagram showing the overall control system of the transfer-type inkjet recording apparatus shown in Figure 1.

[0040] In Figure 4, 401 is a data generation unit such as an external print server, 402 is an operation control unit such as an operation panel, 403 is a printer control unit for carrying out the recording process, 404 is a recording medium transport control unit for transporting the recording medium, and 405 is an inkjet device for printing.

[0041] Figure 5 is a block diagram of the printer control unit shown in Figure 4 in the inkjet recording device shown in Figure 1. 501 is the CPU that controls the entire printer, 502 is ROM for storing the control program for CPU 501, and 503 is RAM for executing the program. 504 is an Application Specific Integrated Circuit (ASIC) that incorporates a network controller, serial IF controller, recording head data generation controller, motor controller, etc. 509 is the recording head control unit, which generates the final ejection data and drive voltage for the inkjet device 405. [Examples]

[0042] The present invention will be described in further detail below using examples and comparative examples. The present invention is not limited in any way by the following examples unless it exceeds the scope of the invention.

[0043] Figure 6 is a photograph of an image formed on a recording medium that has undergone corona discharge or plasma treatment. PET media was used as the recording medium. The ink is an aqueous pigment ink containing anionic pigment and water, with cyan ink at 9 ng / m². 2 I printed solid text and then added yellow ink with 1 dot and 5 spaces on top.

[0044] For corona discharge treatment, a Corona Master PS-1M (manufactured by Shinko Electric Instrumentation Co., Ltd., corona discharge power 300W, treatment width 200mm) was used. With a treatment speed of 1.8m / min and 6 treatment scans, the discharge volume was 8333W·min / m 2 The processing, with a processing speed of 7.2 m / min and 6 processing scans, resulted in a discharge output of 2083 W·min / m 2 The following process was performed.

[0045] For plasma processing, we used the AP-T02-L150 (manufactured by Sekisui Chemical Co., Ltd., plasma generation power 355.5W, processing width 30mm). A mixture of oxygen and nitrogen gas (3% oxygen) was flowed through the plasma generation section, and with a processing speed of 0.11m / min and one processing scan, the discharge rate was 110,000 W·min / m 2 The following process was performed.

[0046] When an unprocessed recording medium is used, the subsequent yellow ink droplets are embedded in the cyan ink that forms a solid image first, and the yellow dots are further elongated due to advection caused by the drying of the cyan ink (Figure 6(a)).

[0047] Next, when the recording medium was subjected to corona treatment, the corona discharge rate was 8333 W·min / m². 2 In this case, the cyan ink aggregates, making it less likely for the subsequent yellow ink to be buried, and the advection in the cyan ink is suppressed, resulting in higher roundness of the yellow dot (Figure 6(c)). Discharge rate: 2083 W·min / m 2 In Figure 6(b), some effect was observed, but not as much as in Figure 6(c), indicating that the degree of ink aggregation depends on the amount of corona discharge. On the other hand, when the recording medium was subjected to plasma treatment (Figure 6(d)), the discharge amount was 110,000 W·min / m 2 Despite this, no coagulation effect was observed from the preceding cyan ink, the subsequent yellow ink was buried, and the dots became elongated due to the advection of the cyan ink.

[0048] Furthermore, these trends described above are also reflected in the brightness of the image. Figure 7 shows cyan ink at 6.8 ng / m². 2 This shows the amount of discharge and the brightness of the cyan image when a solid print image is subjected to corona discharge treatment. Increasing the discharge amount decreases the brightness. 2 Saturation was reached at this point. Considering this together with the result in Figure 6(a), we get 8333 W·min / m in Figure 6(c). 2 In this case, the preceding ink has sufficiently aggregated, resolving the problem of the following ink being buried, and the brightness has also decreased sufficiently. Figure 6(b) 2083 W·min / m 2 In this case, the aggregation of the preceding ink was insufficient, and the brightness did not decrease sufficiently. Based on these results, it is thought that the amount of corona discharge that can solve the problem of the subsequent ink being buried and sufficiently reduce the brightness can be determined from the change in brightness shown in Figure 7. The brightness shown in Figure 7 changes exponentially with respect to the discharge amount and could be approximated by equation (2). L=(46-36)×exp(-Q / τ)+36 Equation (2) L is brightness, Q is the discharge amount during corona discharge treatment, and τ (= 1129 W·min / m) 2 ) is the attenuation coefficient. From this relationship, if the discharge amount is τ, the brightness decreases by 63% from the initial level, similarly, if the discharge amount is 2τ, the brightness decreases by 86%, and similarly, if the discharge amount is 3τ, the brightness decreases by 95%. In Figure 6(b), where the discharge amount was approximately the same as 2τ, the aggregation effect of the preceding ink was insufficient, but 3τ = 3386 W·min / m 2 It was found that this method solves the problem of ink embedding in subsequent lines and sufficiently reduces brightness. More preferably, 4τ = 4520W·min / m 2 By doing the above, the coagulation effect of the preceding ink can be obtained more reliably.

[0049] Therefore, in order to induce ink coagulation, corona treatment must be used and the discharge rate set to 3400 W·min / m 2 The above approach proved effective. However, there was concern that the surface of the recording medium might be damaged by corona discharge, so the surface of the recording medium after corona discharge treatment was evaluated.

[0050] The recording media used were PET(50) PAT1 8LK (Lintec Corporation, PET) and Art E PW 8E (Lintec Corporation), with a discharge rate of 25,000 W·min / m². 2 The evaluation was conducted up to this point. A comparison of the state before and after processing revealed no change in the color or transparency of the recording medium, nor was any change observed in the surface shape (Sa). Specifically, the discharge rate was 25,000 W·min / m². 2 Up to this point, it was found that the surface of the recording medium was not damaged by corona discharge. Therefore, in order to achieve the ink coagulation effect and avoid damage to the recording medium due to corona discharge, a discharge rate of 4520 W·min / m is preferable. 2 More than 25000W min / m 2 The following is recommended.

[0051] (Example 1) In this embodiment 1, the inkjet recording device shown in Figure 1 was used. The recording medium 102 was PET(50) PAT1 8LK (Lintec Corporation, PET). The corona discharge processing unit 103 is connected to a generator (not shown) and can supply a maximum power of 5000W. In this embodiment, the power supplied by the generator was set to 3000W, and printing was performed with the transport speed of the recording medium 102 set to 2.5m / min. The corona discharge amount at this time was 3430W·min / m 2 The discharge amount was sufficient to agglomerate the preceding ink, avoiding the problem of the following ink being buried, and resulting in a highly colored image.

[0052] (Example 2) This embodiment is basically under the same conditions as Embodiment 1, with only the transport speed of the recording medium 102 and the power supply conditions of the generator connected to the corona discharge processing unit 103 being different. In this embodiment, after performing print job 1 with a power supply of 3000W from the generator and a transport speed of 2.5m / min for the recording medium 102, print job 2 was performed by changing the transport speed of the recording medium 102 to 4m / min in order to improve printing productivity. At this time, in order to meet the discharge amount conditions for corona discharge processing, the power supply from the generator was changed to 5000W. As a result, the discharge amount due to corona discharge processing was 3570W·min / m 2 This results in a corona discharge rate of 3400 W·min / m², which is the condition necessary for sufficient aggregation of the preceding ink. 2 While maintaining the above, we were able to increase printing productivity.

[0053] (Example 3) The conditions for this third embodiment were the same as in the first embodiment, with a power supply of 3000W from the generator and a transport speed of 1.5m / min for the recording medium 102. The corona discharge amount at this time was 5710W·min / m 2 This resulted in a discharge amount sufficient to agglomerate the preceding ink more effectively than in Example 1, eliminating the problem of subsequent ink embedding and allowing for the acquisition of highly colored images.

[0054] (Example 4) This embodiment is basically under the same conditions as Embodiment 3, with only the transport speed of the recording medium 102 and the power supply conditions of the generator connected to the corona discharge processing unit 103 being different. In this embodiment, after performing print job 1 with a power supply of 3000W from the generator and a transport speed of 1.5m / min for the recording medium 102, print job 2 was performed by changing the transport speed of the recording medium 102 to 2.5m / min in order to improve printing productivity. At this time, in order to meet the discharge amount conditions for corona discharge processing, the power supply from the generator was changed to 5000W. As a result, the discharge amount due to corona discharge processing was 5710W·min / m 2 Therefore, similar to Example 3, the corona discharge amount condition required for sufficient aggregation of the preceding ink is 5710 W·min / m². 2 While maintaining the above, we were able to increase printing productivity.

[0055] (Comparative Example 1) The conditions for this comparative example were the same as in Example 1, but corona discharge treatment was not performed, and printing was carried out with the transport speed of the recording medium 102 set to 1.5 m / min. In the absence of corona discharge treatment, the coagulation effect of the preceding ink did not work, resulting in an image with low color development.

[0056] (Comparative Example 2) In this comparative example, printing was performed in the same manner as in Example 1, except that the corona discharge treatment unit 103 was replaced with a plasma treatment unit. The plasma treatment discharge rate was 110,000 W·min / m². 2 Although processing was performed, the prior ink did not aggregate sufficiently, resulting in an image with poor color development.

[0057] Furthermore, the disclosure of this embodiment includes the following methods. (Method 1) A corona discharge treatment step in which the recording medium is subjected to corona discharge treatment, An ink application step of applying an ink containing an anionic pigment to the surface of the recording medium that has undergone corona discharge treatment, It has, The discharge rate of the corona discharge treatment described above was 3400 W·min / m 2 An inkjet recording method characterized by the above. (Method 2) The discharge rate is 4200 W·min / m 2 More than 25000W min / m 2 The inkjet recording method described in Method 1 below. (Method 3) The discharge rate is 5700 W·min / m 2 More than 25000W min / m 2 The inkjet recording method described in Method 1 or 2 below. (Method 4) An inkjet recording method according to any one of methods 1 to 3, wherein the amount of discharge in the corona discharge process is adjusted by changing the output of the corona discharge process and the transport speed of the recording medium. (Method 5) An inkjet recording method according to any one of Methods 1 to 4, wherein the transport speed of the recording medium is 1.5 m / min or more and 4 m / min or less. (Method 6) An inkjet recording method according to any one of Methods 1 to 5, wherein the output of the corona discharge treatment is 3000W or more and 5000W or less. (Method 7) The ink is an inkjet recording method according to any one of Methods 1 to 6, wherein the ink comprises anionic resin particles. (Method 8) An inkjet recording method according to any one of Methods 1 to 7, wherein the ink contains water, and the amount of water in the ink is 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink. [Explanation of Symbols]

[0058] 100 Inkjet Recording Devices 101a Unwinding Unit 101b Winding Unit 102 Recording media 103 Corona treatment unit 103a, c Idlerola 103b Electrode Opposing Roller 103d Corona electrode section 104a inkjet recording head 104b Inkjet Recording Head 104c inkjet recording head 104d inkjet recording head

Claims

1. A corona discharge treatment step of subjecting a recording medium to corona discharge treatment; An ink application step of applying ink containing an anionic pigment to the surface of the recording medium that has been subjected to the corona discharge treatment; characterized by comprising; The discharge amount of the corona discharge treatment is 3400 W·min / m ２ or more, and an inkjet recording method characterized by this.

2. The anionic pigment is (i) a resin-dispersed pigment dispersed by a resin dispersant having an anionic group, or (ii) a self-dispersing pigment that is particles having an anionic group directly or indirectly bonded through another atomic group on the surface. The inkjet recording method according to claim 1.

3. The discharge amount is 4200 W·min / m ２ or more and 25000 W·min / m ２ or less, and the inkjet recording method according to claim 1 or 2.

4. The discharge amount is 5,700 W·min / m ２ or more and 25,000 W·min / m ２ or less. The inkjet recording method according to claim 1 or 2

5. The inkjet recording method according to claim 1 or 2, wherein the discharge amount of the corona discharge treatment is adjusted by changing the output of the corona discharge treatment and the conveyance speed of the recording medium.

6. The inkjet recording method according to claim 1 or 2, wherein the conveyance speed of the recording medium is 1.5 m / min or more and 4 m / min or less.

7. The inkjet recording method according to claim 1 or 2, wherein the output of the corona discharge treatment is 3000 W or more and 5000 W or less.

8. The inkjet recording method according to claim 1 or 2, wherein the ink contains anionic resin particles.

9. The inkjet recording method according to claim 1 or 2, wherein the ink contains water, and the content of the water in the ink is 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

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