Inkjet recording device

Abstract

The present invention provides an inkjet recording device that can suppress ink repellency and bleeding when forming images using water-based ink, and can also suppress the blurring of characters. [Solution] The inkjet recording device comprises a transport unit, a recording unit, and a pre-treatment liquid ejection head. The transport unit transports the recording medium. The recording unit has a recording head that ejects aqueous ink onto the recording medium transported by the transport unit. The pre-treatment liquid ejection head is positioned upstream of the recording unit with respect to the transport direction of the recording medium and ejects pre-treatment liquid onto the recording medium using an inkjet method. The pre-treatment liquid contains at least a binder resin and water. When the resolution of the pre-treatment liquid ejection head is A [dpi] and the resolution of the recording head is B [dpi], A

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus that discharges ink onto a recording medium to record an image.

Background Art

[0002] As a recording apparatus such as a facsimile machine, a copying machine, or a printer, an inkjet recording apparatus that discharges ink to record an image is widely used because it can form a high-definition image.

[0003] In such an inkjet recording apparatus, water-based pigment ink using a pigment excellent in weather resistance as a coloring material has become mainstream. However, water-based pigment ink has a problem that when discharged onto a recording medium with low wettability such as a plastic sheet, ink splashing and bleeding are likely to occur.

[0004] Therefore, various methods have been proposed for adjusting the wettability by applying a pretreatment liquid to a recording medium on which an image is formed by an inkjet recording apparatus. For example, Patent Document 1 discloses an image forming apparatus having a pretreatment means for applying a pretreatment liquid to the surface of a recording medium before forming an image, and a post-treatment means for discharging a post-treatment liquid different from the pretreatment liquid onto the recording medium after forming the image. The pretreatment means applies the pretreatment liquid with an application amount determined based on at least the type of ink, and the post-treatment means discharges the post-treatment liquid with a discharge amount determined based on at least the type of ink, and discharges the ink onto the recording medium to form an image on the surface of the recording medium.

[0005] Patent Document 2 discloses an inkjet recording apparatus in which when a pretreatment portion for forming dots of a treatment liquid and then forming dots of ink and a post-treatment portion for forming dots of the treatment liquid after forming dots of ink are mixed on a recording medium, the ink discharge amount per unit area of the post-treatment portion is made less than the ink discharge amount per unit area of the pretreatment portion.

[0006] Patent Document 3 discloses an inkjet recording apparatus comprising: a first inkjet head that ejects inkjet recording ink containing pigment-dispersed fine particles onto a recording medium to form an image; and a second inkjet head comprising a processing liquid coating means that applies an inkjet recording processing liquid to the portion on the recording medium where an image has been formed, the processing liquid containing identification fine particles having a mark on its surface that includes at least one selected from the group consisting of characters, symbols, and figures. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2014-172218 [Patent Document 2] Japanese Patent Application Publication No. 10-226055 [Patent Document 3] Japanese Patent Publication No. 2013-241619 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the method described in Patent Document 1, the amount of pretreatment solution to be applied is determined based on the amount of ink deposited per unit area. As a result, depending on the printing substrate, the amount of pretreatment solution applied may be too large, requiring a long drying time and resulting in decreased productivity.

[0009] In the method described in Patent Document 2, when using plastic films such as polyethylene terephthalate (PET) or polypropylene as recording media, there was a problem that it took a long time to dry the pretreatment solution.

[0010] In the method of Patent Document 3, when applying an inkjet recording ink and an inkjet recording treatment liquid containing labeling fine particles, the resolution of each inkjet head is set to 600 dpi, the application amount of the inkjet recording treatment liquid is set to 10 to 40 pL / pixel, and the shape of the identification fine particles is set to a flat plate shape with a thickness of 2 to 30 μm, whereby it is described that the visibility of the label on the surface of the identification fine particles can be improved. However, there was a problem that the resolution of the inkjet recording ink was poor and the characters were smeared when printing complex characters such as "轰" in small fonts.

[0011] In view of the above problems, an object of the present invention is to provide an inkjet recording apparatus capable of suppressing ink splashing and bleeding when forming an image using an aqueous ink and also suppressing character smearing.

Means for Solving the Problems

[0012] In order to achieve the above object, a first configuration of the present invention is an inkjet recording apparatus including a conveyance unit, a recording unit, and a pretreatment liquid discharge head. The conveyance unit conveys a recording medium. The recording unit has a recording head that discharges an aqueous ink onto the recording medium conveyed by the conveyance unit. The pretreatment liquid discharge head is disposed upstream of the recording unit with respect to the conveyance direction of the recording medium and discharges the pretreatment liquid onto the recording medium by an inkjet method. The pretreatment liquid contains at least a binder resin and water. When the resolution of the pretreatment liquid discharge head is A [dpi] and the resolution of the recording head is B [dpi], A <B is satisfied.

Effects of the Invention

[0013] According to the first configuration of the present invention, by making the resolution A of the pretreatment liquid discharge head that applies the pretreatment liquid smaller than the resolution B of the recording head that discharges ink, it is possible to discharge a high-concentration (high-viscosity) pretreatment liquid with a small amount of moisture. As a result, the time required for drying the pretreatment liquid can be shortened, and it becomes possible to achieve both productivity and good images. Further, by reducing the resolution A, clogging of nozzles when using a high-concentration pretreatment liquid can be suppressed. Further, by increasing the resolution B, a high-resolution clear image can be formed.

Brief Description of the Drawings

[0014] [Figure 1] Schematic diagram showing the structure of the inkjet recording apparatus 100 [Figure 2] Enlarged view of the periphery of the coating unit 2 and the recording unit 9 in FIG. 1 [Figure 3] Figure showing an image when printing a 1-dot line at 600 dpi using aqueous ink without applying a pretreatment liquid to the sheet S [Figure 4] Figure showing an image when printing a 1-dot line at 600 dpi using aqueous ink after applying a pretreatment liquid to the sheet S [Figure 5] Figure schematically showing the state immediately after landing and after drying of the ink droplet Id1 when no pretreatment liquid is applied to the sheet S [Figure 6] Figure schematically showing the state immediately after landing and after drying of the ink droplet Id1 when a pretreatment liquid is applied to the sheet S [Figure 7] Figure showing a missing pin confirmation chart when there is no missing pin [Figure 8] Figure showing a missing pin confirmation chart when there is a missing pin

Embodiments for Carrying Out the Invention

[0015] [1. Pretreatment Liquid] When forming an image by an inkjet recording apparatus using an aqueous ink containing a pigment dispersion containing a pigment and a resin, an organic solvent, and water, the pretreatment liquid used in the inkjet recording apparatus of the present invention adjusts the wettability of a plastic sheet as a recording medium to suppress ink splashing and bleeding. The pretreatment liquid contains at least a binder resin and water. Further, it may contain a surfactant and a water-soluble organic solvent as necessary. Hereinafter, the pretreatment liquid used in the inkjet recording apparatus of the present invention will be described in detail.

[0016] (Binder resin) The binder resin is added for the purpose of imparting wettability to the recording medium with the pretreatment liquid. Thereby, it is possible to suppress the splashing of ink droplets that occurs when the surface tension of the recording medium is low. As the binder resin, a urethane resin and a polyester resin are preferable. There are no particular restrictions on the urethane resin and polyester resin incorporated in the pretreatment liquid, and they can be appropriately selected according to the purpose.

[0017] The urethane resin is, for example, a copolymer of a diol compound or a bisphenol compound and a polyisocyanate.

[0018] Examples of the diol compound include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4-diol, 1,5-pentanediol, 2-pentene-1,5-diol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, 1,4-benzenediol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0019] Examples of bisphenol compounds include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adducts (e.g., polyoxyethylene (2,2)-2,2-bis(4-hydroxyphenyl)propane), and bisphenol A propylene oxide adducts.

[0020] Examples of polyisocyanates include diisocyanates. Examples of diisocyanates include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

[0021] Examples of aliphatic diisocyanates include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate.

[0022] Examples of alicyclic diisocyanates include hydrogenated 4,4'-diphenylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

[0023] Examples of aromatic diisocyanates include 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, toluene diisocyanate, and naphthalene diisocyanate.

[0024] Polyester resins can be obtained by condensation polymerization or copolymerization of a divalent or trivalent or higher alcohol component with a divalent or trivalent or higher carboxylic acid component. The following alcohol and carboxylic acid components are examples of components used in the synthesis of polyester resins.

[0025] Specific examples of divalent or trivalent or higher alcohol components include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, and polyoxyethylene Examples include bisphenols such as bisphenol A and polyoxypropylene bisphenol A; and trivalent or higher alcohols such as sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0026] Specific examples of divalent or trivalent or higher carboxylic acid components include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebatic acid, azelaic acid, malonic acid, or divalent alkyl or alkenyl succinic acids such as n-butylsuccinic acid, n-butenylsuccinic acid, isobutylsuccinic acid, isobutenylsuccinic acid, n-octylsuccinic acid, n-octenylsuccinic acid, n-dodecylsuccinic acid, n-dodecenylsuccinic acid, isododecylsuccinic acid, and isododecenylsuccinic acid. Carboxylic acids include trivalent or higher carboxylic acids such as 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimeric acid. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, "lower alkyl" means an alkyl group having 1 to 6 carbon atoms.

[0027] The binder resin content (amount blended) in the pretreatment solution is preferably 5% by mass or more, and more preferably 5% by mass or more and 20% by mass or less. If the polyester resin content is less than 5% by mass, the ink will not spread sufficiently when the wetting tension of the recording medium is low.

[0028] (Surfactants) Surfactants are added to improve the wettability of the pretreatment solution to the recording medium. The amount of surfactant added is preferably 0.001 to 5% by mass of the total treatment solution, and more preferably 0.05 to 2% by mass. An effect of adding surfactant can be obtained with an amount of 0.001% by mass or more. On the other hand, no further improvement can be expected by adding more than 5% by mass.

[0029] Various surfactants can be used, including silicone-based surfactants, nonionic surfactants, anionic surfactants, cationic surfactants, and betaine-based surfactants, but nonionic surfactants are preferred. Among nonionic surfactants, acetylene glycol-based surfactants, which have an acetylene group in the center and a symmetrical structure, are preferred because they do not easily produce foam and can impart wettability. These surfactants may be used individually or in combination of two or more.

[0030] (Water-soluble organic solvent) Water-soluble organic solvents are added to improve compatibility with the binder resin and to retain moisture in the pretreatment solution. This suppresses the increase in viscosity of the pretreatment solution even if moisture evaporates in the nozzle or coating device, and maintains discharge stability by suppressing nozzle sticking and ejection deviations when the pretreatment solution is applied by inkjet method.

[0031] Examples of water-soluble organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, propylene carbonate, and ethylene carbonate. Among these, those with an equilibrium water content of 30% by mass or more are preferred, and those with an equilibrium water content of 40% by mass or more are more preferred. Polyhydric alcohols are particularly preferred, and examples include ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, hexylene glycol, 1,6-hexanediol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol, glycerin, diglycerin, 1,2,3-butanetriol, and 1,2,4-butanetriol. Among these, propylene glycol and 1,3-butanediol are particularly preferred because they have low viscosity when they contain water, and can stably hold polyester resin without causing aggregation when polyester resin is used as a binder.

[0032] Specific examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether, and propylene glycol monoethyl ether. Specific examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether. Specific examples of nitrogen-containing heterocyclic compounds include 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone.

[0033] The amount of water-soluble organic solvent added is not particularly limited, but 5 to 40% by mass of the total pretreatment solution is preferred, and 10 to 30% by mass is more preferred. If the amount added is 5 to 40% by mass, it is possible to sufficiently retain moisture in the pretreatment solution and the viscosity is not too high, so it can be effectively coated onto the recording medium.

[0034] (water) The pretreatment solution used in the present invention is aqueous and contains water as an essential component. The water contained in the pretreatment solution is not particularly limited as long as it does not hinder the objective of the present invention, and water of a desired purity, such as purified water or ion-exchanged water, can be appropriately selected and used. The water content in the pretreatment solution is not particularly limited as long as it does not hinder the objective of the present invention, and can be appropriately changed according to the amount of other components used, as described later. The water content in the pretreatment solution is preferably 50 to 90% by mass relative to the total mass of the pretreatment solution.

[0035] Furthermore, the pretreatment solution used in the present invention may contain, as necessary, materials used in known pretreatment solutions, such as antifoaming agents, pH adjusters, antiseptics and antifungal agents, and rust inhibitors.

[0036] (Foam suppressant) A foam inhibitor is added to suppress foaming of the pretreatment solution. Generally, liquids with high surface tension, such as water, are less likely to foam because a force acts to minimize the surface area of ​​the liquid. However, liquids with low surface tension and high viscosity foam easily, and the foam that is generated is difficult to extinguish. In the pretreatment solution of the present invention, if the pretreatment solution contains a binder resin, a water-soluble organic solvent, a surfactant, etc., the surface tension decreases and the viscosity increases, making it more prone to foaming, so it is preferable to add a foam inhibitor. The amount of foam inhibitor to add is preferably 0.01 to 10% by mass, and more preferably 0.02 to 5% by mass. If the amount is 0.01% by mass or more, a sufficient foam-suppressing effect can be obtained. Also, if the amount is 10% by mass or less, the foam inhibitor will not become unsoluble in the pretreatment solution.

[0037] (pH adjuster) There are no particular restrictions on the pH adjusting agent, as long as it can adjust the pH to 6-10 without adversely affecting the pretreatment solution; it can be selected appropriately depending on the purpose. If the pH is 6 or higher, corrosion of conveying components such as conveying rollers that come into contact with the pretreatment solution is less likely to occur.

[0038] Preferred pH adjusters include alcoholamines, alkali metal hydroxides, ammonium hydroxides, phosphonium hydroxides, and alkali metal carbonates. Examples of alcoholamines include diethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of ammonium hydroxides include ammonium hydroxide and quaternary ammonium hydroxide. Examples of phosphonium hydroxides include quaternary phosphonium hydroxide. Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate.

[0039] (preservative and fungicide) Suitable preservatives and fungicides include, for example, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol, and sodium 1,2-benzoisothiazoline-3-one.

[0040] (Rust inhibitor) Suitable rust inhibitors include, for example, acidic sulfites, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, dicyclohexylammonium nitrite, pentaerythritol tetranitrate, and 1,2,3-benzotriazole.

[0041] By applying the pretreatment solution obtained as described above to a recording medium before recording with water-based ink (pigment ink) using an inkjet method, the wettability (wetting tension) of the recording medium surface is improved. This makes it possible to suppress the repulsion and bleeding of the water-based ink ejected onto the recording medium.

[0042] There are no particular restrictions on the amount of pretreatment solution to be applied, but the application rate is 1 g / m². 2 If the amount is less than this, the wettability (wetting tension) of the recording medium surface cannot be sufficiently improved, and the effect of suppressing water-based ink repellency and bleeding will be insufficient. On the other hand, if the amount is 20 g / m² 2 If the amount exceeds this, the wettability of the recording medium surface will become too high, and the pretreatment solution may not dry in time, potentially causing bleeding of the water-based ink. Therefore, the application amount of the pretreatment solution should be 1 g / m². 2 More than 20g / m 2 Preferably, it should be 5 g / m 2 More than 10g / m 2 The following is more preferable.

[0043] [2. Image Recording Method] Next, an image recording method using an inkjet recording device will be described. The inkjet recording device used in the image recording method of the present invention is not particularly limited, and serial head type or line head type inkjet recording devices can be used. In particular, with inkjet recording devices using aqueous pigment ink, ink repellency and bleeding tend to occur when a plastic sheet is used as the recording medium, but these problems are less likely to occur with the image recording method of the present invention.

[0044] Figure 1 is a schematic diagram showing the structure of an inkjet recording apparatus 100 according to one embodiment of the present invention. Figure 2 is an enlarged view of the area around the recording unit 2 and coating unit 3 in Figure 1. As shown in Figure 1, the inkjet recording apparatus 100 includes a sheet feeding unit 1, a recording unit 2, a coating unit 3, a transport plate 4, a heating drum 6, a sheet winding unit 7, a control unit 10, an operation panel 11, and an input unit 12.

[0045] The sheet S, which is a long, rectangular printing substrate (in this case, a plastic sheet), is installed in the sheet feeding unit 1, which is located upstream of the recording unit 2 in the transport direction (left side in Figure 1). The sheet feeding unit 1 includes a rotating shaft on which the roll-shaped sheet S is mounted, and a motor (neither shown) that rotates the rotating shaft in a predetermined direction. The sheet S is fed out downstream in the transport direction (right side in Figure 1) as the rotating shaft rotates due to the motor's operation.

[0046] The recording unit 2 is equipped with recording heads 2a, 2b, 2c, and 2d (see Figure 2). Each of the recording heads 2a to 2d is supplied with four colors of ink (yellow, magenta, cyan, and black) stored in ink tanks (not shown). The recording unit 2 uses the recording heads 2a to 2d to record an image on the sheet S fed from the sheet feeding unit 1.

[0047] The coating unit 3 is located upstream of the recording unit 2 (left side in Figure 1) in the sheet transport direction. The coating unit 3 is equipped with a pre-treatment liquid ejection head 3a. The pre-treatment liquid ejection head 3a has the same structure as the recording heads 2a to 2d and ejects the aforementioned pre-treatment liquid onto the sheet S fed from the sheet feeding unit 1 using an inkjet method.

[0048] A transport plate 4 is positioned below the recording unit 2 and the coating unit 3. The sheet S, fed from the sheet dispensing unit 1, is supported by the transport plate 4 at a predetermined distance from the recording unit 2 and the coating unit 3. A heater 4a is positioned on the back side of the transport plate 4 (opposite the recording unit 2 and the coating unit 3). As the sheet S is transported along the transport plate 4, it is heated from the back side by the heater 4a. This dries the pretreatment liquid dispensed onto the sheet S by the coating unit 3 before the ink is dispensed by the recording unit 2. The heater 4a may be of any type, such as a halogen heater, ceramic heater, high-frequency induction heating (IH), or hot water heater.

[0049] After passing through the recording unit 2, the sheet S is conveyed to the heating drum 6 after its conveyance direction is changed by the guide roller 5a. The ink is dried and fixed to the sheet S by contact with the heating drum 6. After the ink has been fixed to the sheet S, its conveyance direction is changed by the guide roller 5b and it is wound into a roll in the sheet winding unit 7. In this embodiment, the ink is dried using the heating drum 6, but other drying devices such as an infrared dryer or a hot air dryer may be used.

[0050] The control unit 10 controls the ink ejection in the recording unit 2 according to the image data received from an external computer. The control unit 10 also determines the ejection area of ​​the pretreatment liquid in the coating unit 3 according to the image data, as will be described later.

[0051] The control panel 11 functions as a touch panel for the user to make various settings and inputs for the inkjet recording device 100, and also displays the status of the inkjet recording device 100, image recording status, number of printed pages, etc.

[0052] The input unit 12 receives image data from an external device such as a personal computer. The control unit 10 controls the ink ejection by the recording unit 2 onto the sheet S based on the image data received by the input unit 12, and records a predetermined image on the sheet S. If the inkjet recording device 100 has an image reading function (scanner function), the image reading unit also functions as the input unit 12.

[0053] Figure 3 shows an image printed at 600 dpi using water-based ink without applying a pretreatment solution to sheet S. Figure 4 shows an image printed at 600 dpi using water-based ink after applying a pretreatment solution to sheet S.

[0054] As shown in Figure 3, when the pretreatment solution was not applied to sheet S, color mixing occurred at the color boundaries, resulting in unclear boundaries. On the other hand, as shown in Figure 4, when the pretreatment solution was applied to sheet S, no color mixing occurred, and the boundaries were clear.

[0055] FIG. 5 and FIG. 6 are diagrams schematically showing the states of ink droplets immediately after landing and after drying, respectively, when the pretreatment liquid is not applied to the sheet S and when it is applied. As shown in FIG. 5, when the pretreatment liquid is not applied to the sheet S and the wetting tension of the sheet S is low, the ink droplets Id1 ejected in proximity are attracted to each other, and a portion where they become (merge into) one large ink droplet Id2 occurs. Therefore, the size of the ink droplets becomes non-uniform, color mixing occurs as shown in FIG. 3, and the color boundary becomes unclear.

[0056] On the other hand, as shown in FIG. 6, when the pretreatment liquid is applied to the sheet S, the wetting tension of the sheet S increases, so the merging of the ink droplets Id1 does not occur and the size of the ink droplets does not change. Therefore, as shown in FIG. 4, color mixing does not occur and the color boundary becomes clear. When the sheet S is the plastic sheet as described above, by applying the pretreatment liquid, the wetting tension of the sheet S can be adjusted to an optimal range to suppress ink bleeding and repelling, and the printability can be improved.

[0057] When the pretreatment liquid is applied to the sheet S, there is a problem that it takes time for the pretreatment liquid to dry. Also, when a high-concentration pretreatment liquid with a reduced moisture content is applied to shorten the drying time, there is a problem that nozzle clogging of the pretreatment liquid ejection head 3a is likely to occur.

[0058] Therefore, in the inkjet recording apparatus 100 of the present embodiment, when the resolution of the pretreatment liquid ejection head 3a that applies the pretreatment liquid is A [dpi] and the resolution of the recording heads 2a to 2d that eject ink is B [dpi], A <B is set. Thus, by making the resolution A of the pretreatment liquid ejection head 3a that applies the pretreatment liquid smaller than the resolution B of the recording heads 2a to 2d that eject ink, a high-concentration (high-viscosity) pretreatment liquid with a small amount of moisture can be ejected. As a result, the time required for drying the pretreatment liquid can be shortened, and both productivity and good image quality can be achieved.

[0059] Also, by reducing the resolution A of the pretreatment liquid discharge head 3a, the nozzle diameter for discharging the pretreatment liquid becomes larger. As a result, clogging of the nozzles when using a high-concentration pretreatment liquid can be suppressed. Further, by increasing the resolution B of the recording heads 2a to 2d, a high-resolution and clear image can be formed. As a result, blurring of characters when printing complex characters such as "轟" in a small font can be suppressed.

[0060] The resolution of a generally used inkjet head is any one of 300 dpi, 600 dpi, and 1200 dpi. Therefore, as combinations of the resolutions A and B in the inkjet recording apparatus 100 of the present embodiment, there are three possible combinations: a combination where the resolution A is 300 dpi and the resolution B is 600 dpi, a combination where the resolution A is 300 dpi and the resolution B is 1200 dpi, and a combination where the resolution A is 600 dpi and the resolution B is 1200 dpi.

[0061] When the resolution A decreases, the nozzle diameter of the pretreatment liquid discharge head 3a becomes larger, so clogging of the nozzles of the pretreatment liquid discharge head 3a is less likely to occur, but the droplets of the pretreatment liquid become larger. As a result, the time required for the pretreatment liquid to dry becomes longer. On the other hand, when the resolution B decreases, the nozzle diameter of the recording heads 2a to 2d becomes larger, so the ink droplets become larger. As a result, blurring of small-font characters is more likely to occur.

[0062] From the above viewpoints, the resolution B is preferably 1200 dpi. Further, as a combination of the resolutions A and B, a combination where the resolution A is 600 dpi and the resolution B is 1200 dpi is particularly preferable.

[0063] The viscosity of the pretreatment solution is preferably between 6.0 [mPa·s] and 7.0 [mPa·s]. If the viscosity of the pretreatment solution is less than 6.0 [mPa·s], clogging of the nozzle of the pretreatment solution discharge head 3a is less likely to occur, but the drying time of the pretreatment solution will be longer due to the increased water content. On the other hand, if the viscosity of the pretreatment solution exceeds 7.0 [mPa·s], the drying time of the pretreatment solution is shortened due to the reduced water content, but the margin of the nozzle of the pretreatment solution discharge head 3a for drying the pretreatment solution is eliminated, making nozzle clogging more likely. In addition, the pretreatment solution is more likely to react with the ink mist and harden.

[0064] Furthermore, the control unit 10 detects the printing area (ink ejection area) on the sheet S based on the image data received by the input unit 12 from an external computer. The control unit 10 ejects the pre-treatment liquid only to the printing area on the sheet S detected using the pre-treatment liquid ejection head 3a. By limiting the ejection area of ​​the pre-treatment liquid to only the printing area in this way, ejection to non-printing areas where pre-treatment liquid is not needed is suppressed, thereby reducing the consumption of pre-treatment liquid. As a result, the running costs of the inkjet recording device 100 can be reduced.

[0065] According to the image recording method described above, a pretreatment solution containing a binder resin is applied to the sheet before image formation using aqueous pigment ink with the inkjet recording device 100. This increases the wettability (wetting tension) of the sheet, suppressing repulsion and bleeding of the aqueous ink, and improving image quality. For this reason, the image recording method of the present invention can be suitably used in various inkjet recording devices that use aqueous ink.

[0066] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. For example, although Figure 1 describes an inkjet recording device 100 that feeds out a long sheet wound in a roll at a predetermined speed and ejects ink, the present invention is similarly applicable to an inkjet recording device that ejects ink onto a sheet cut into a predetermined shape.

[0067] Furthermore, the material of the recording medium is not limited to plastic film; various recording media can be used, such as plain paper, coated paper, natural fibers, synthetic fiber fabrics, knitted fabrics, or nonwoven fabrics. The effects of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0068] [Manufacturing Example 1] (Preparation of pigment dispersions) 75 g of pigment dispersion resin (DISPERBYK-190, manufactured by BIC Chemie Japan, non-volatile content: 40% by mass, dispersion medium: water) was diluted with 775 g of deionized water, and 150 g of pigment (pigment blue 15:03) was added. Pre-mixing was then performed using a homodisper at a rotation speed of 5000 rpm for 1 hour. Subsequently, dispersion treatment was performed using a bead mill (manufactured by Nippon Coke Co., Ltd.) to obtain a pigment dispersion. Zirconia beads (0.2 mmφ) were packed into the vessel at a packing density of 80% of the volume. The dispersion particle size was Z-ave. 101 nm.

[0069] [Manufacturing Example 2] (Ink preparation) A pigment ink was prepared by mixing 5% by mass of the pigment dispersion obtained in Production Example 1 with 3% by mass of urethane resin (HA560, manufactured by Nikka Chemical Co., Ltd.), 0.05% by mass of surfactant (SAG-502A, manufactured by Nisshin Chemical Industry Co., Ltd.), 25% by mass of propylene glycol, 8% by mass of butyl triglyceride, and 58.95% by mass of water.

[0070] [Manufacturing Example 3] [Preparation of pretreatment solution] Pretreatment solution 1 was prepared by stirring 8% by mass of urethane resin (HA560, manufactured by Nikka Chemical Co., Ltd.), 0.05% by mass of surfactant (Surfinol 440, manufactured by Nisshin Chemical Industry Co., Ltd.), 25% by mass of propylene glycol, 8% by mass of butyl triglyceride, and 58.95% by mass of water in a stirrer.

[0071] Pretreatment solutions 2-4 were prepared using the same method as pretreatment solution 1, except for changing the amount of urethane resin used. The viscosity and composition of the pigment ink and pretreatment solutions 1-4 are shown in Table 1.

[0072] [Table 1]

[0073] [Evaluation of nozzle clogging, drying time, and blurring of small font characters] Using the pigment ink (cyan ink) obtained in Manufacturing Example 2 and the pretreatment solutions 1-4 obtained in Manufacturing Example 3, we evaluated nozzle clogging of the pretreatment solution ejection head, drying time of the pretreatment solution, and blurring of small font characters when printing. The test machine used for evaluation is equipped with one inkjet head (KJ4B-YH, manufactured by Kyocera Corporation) each for ejecting pigment ink and pretreatment solution, and a transport table for transporting the printing substrate (sheet) is provided below each inkjet head. The transport table can be heated to a predetermined temperature. In addition, a drying section is provided downstream of each inkjet head. The drying section dries the pretreatment solution and ink by applying hot air to the printing substrate.

[0074] The system conditions were: head applied voltage 21V, drive frequency 20kHz, appropriate discharge liquid volume 3pl, pre-treatment liquid discharge head and recording head temperature 32°C, pre-discharge flushing 1000 times, and the transport table for the printing substrate was preheated to 40°C. The transport speed of the printing substrate was set to 30m / min. A plastic sheet was used as the printing substrate.

[0075] <Nozzle clogging> The pretreatment solution was supplied to the pretreatment solution discharge head and left for one hour. After one hour, the pretreatment solution was discharged from all nozzles onto thermal paper, and a pin-loosening confirmation chart was printed. The thermal paper from which the pretreatment solution was discharged turned black due to a reaction with the alcohols contained in the pretreatment solution as a water-soluble organic solvent. The white areas on the thermal paper were then visually inspected to confirm the occurrence of pin-loosening (non-discharging nozzles).

[0076] Figures 7 and 8 are diagrams showing a missing pin confirmation chart, showing the case where there is no missing pin and the case where there is a missing pin, respectively. The missing pin confirmation chart is composed of a horizontal strip solid image on the upper side of the paper and a grid image composed of vertical and horizontal lines formed adjacent to the lower side of the solid image.

[0077] When there is no missing pin, as shown in Figure 7, there are no white streaks in the solid image, and the lines of the grid image are also formed at equal intervals. On the other hand, when there is a missing pin, as shown in Figure 8, there are white streaks in the solid image, and a break can be seen in the vertical lines of the grid image.

[0078] When a missing pin was confirmed, after performing the purge (extrusion) operation of the pretreatment liquid, ejection was performed again, and the missing pin was confirmed. Then, it was evaluated according to the following evaluation criteria. (Evaluation Criteria) ○: No occurrence of missing pins is observed without purging the pretreatment liquid. △: Missing pins occurred when ejecting without purging the pretreatment liquid, but no occurrence of missing pins is observed after purging the pretreatment liquid. ×: Missing pins occurred even after purging the pretreatment liquid.

[0079] <Drying Time> Hot air at 80 °C was applied to the printed medium on which the pretreatment liquid was ejected, and the drying time of the pretreatment liquid was measured. Then, it was evaluated according to the following evaluation criteria. (Evaluation Criteria) ○: Dried within 10 seconds. △: Dried within 15 seconds. ×: The drying time exceeded 15 seconds.

[0080] <Crushing of Small Font Characters> Using the above test machine, the resolution of the pretreatment liquid ejection head and the recording head was changed to print the character "轰" of font 3. Regarding the obtained printed matter, the crushing of the characters was visually evaluated according to the following evaluation criteria. (Evaluation Criteria) 〇: The characters are not crushed. ×: The characters are crushed.

[0081] Table 2 shows the evaluation results for nozzle clogging, drying time, and distortion of small font characters, along with the resolution of the inkjet head that ejects the pretreatment solution and ink, and the viscosity of the pretreatment solution.

[0082] [Table 2]

[0083] As is clear from Table 2, when the resolution of the inkjet head ejecting the pretreatment solution was 600 dpi and the resolution of the inkjet head ejecting the ink was 1200 dpi (Invention 1-4), in all cases, no pin loss was observed without purging the pretreatment solution, or no pin loss was observed after purging the pretreatment solution. Furthermore, the drying time of the pretreatment solution was within 15 seconds, and no blurring of small font characters was observed.

[0084] In particular, in Invention 1 and 2, where the viscosity of the pretreatment solution is 6.0 [mPa·s] or more and 7.0 [mPa·s] or less, no pin detachment was observed without purging the pretreatment solution, and the drying time of the pretreatment solution was within 10 seconds.

[0085] In contrast, in Comparative Example 1, where both the pretreatment solution and the inkjet head ejecting the ink had a resolution of 600 dpi, small font characters became distorted. This is thought to be because the resolution of the image formed by ejecting the ink was insufficient.

[0086] Furthermore, in Comparative Example 2, where the resolution of both the pretreatment solution and the inkjet head ejecting the ink was set to 1200 dpi, no blurring of small font characters occurred, but nozzle clogging did occur. This is thought to be because the high-viscosity pretreatment solution is more likely to clog the nozzles when the nozzle diameter for ejecting the pretreatment solution is reduced.

[0087] From the results of Invention 1 to 4 and Comparative Examples 1 and 2, it was confirmed that by making the resolution of the inkjet head that ejects the pretreatment liquid smaller than the resolution of the inkjet head that ejects the ink, clogging of the nozzle of the inkjet head that ejects the pretreatment liquid can be suppressed, the drying time can be shortened, and the blurring of small font characters can be effectively suppressed. [Industrial applicability]

[0088] The present invention is applicable to inkjet recording devices that eject ink onto a recording medium. By using the present invention, it is possible to provide an inkjet recording device that can suppress ink repellency and bleeding when forming images using water-based ink, and can also suppress the blurring of characters. [Explanation of symbols]

[0089] 1. Sheet dispensing unit (conveying unit) 2. Records Section 2a~2d Recording head 3. Application area 3a Pretreatment liquid discharge head 4. Conveyor board 4a Heater (heating section) 6. Heating drum 7. Sheet winding section (conveying section) 10 Control Unit 11. Control Panel 100 Inkjet Recording Devices S Sheet (Recording medium)

Claims

1. A transport unit that transports the recording medium, A recording unit having a recording head that ejects aqueous ink onto the recording medium transported by the transport unit, A pre-treatment liquid ejection head is positioned upstream of the recording unit in the transport direction of the recording medium and ejects a pre-treatment liquid onto the recording medium using an inkjet method. Equipped with, The aforementioned pretreatment liquid contains at least a binder resin and water, An inkjet recording apparatus characterized in that, when the resolution of the pre-treatment liquid ejection head is A [dpi] and the resolution of the recording head is B [dpi], A < B.

2. The inkjet recording apparatus according to claim 1, characterized in that the viscosity of the pretreatment liquid is 6.0 [mPa·s] or more and 7.0 [mPa·s] or less.

3. The inkjet recording apparatus according to claim 1, characterized in that the resolution B of the recording head is 1200 dpi.

4. The inkjet recording apparatus according to claim 3, characterized in that the resolution A of the pre-treatment liquid ejection head is 600 dpi.

5. An input section into which image data is input, The system includes a control unit that controls the ejection of the ink onto the recording medium by the recording unit based on the image data input to the input unit, and controls the ejection of the pre-treatment liquid onto the recording medium by the pre-treatment liquid ejection head, The inkjet recording apparatus according to claim 1, characterized in that the control unit detects a printing area on the recording medium from which the ink is ejected by the recording unit based on the image data, and ejects the pre-treatment liquid only to the printing area using the pre-treatment liquid ejection head.

6. The inkjet recording apparatus according to claim 1, characterized in that it has a heating unit for heating the recording medium that passes through the coating unit and the recording unit.

7. The heating section is A transport plate that supports the surface of the recording medium opposite to the coating portion and the recording portion, A heater for heating the transport plate, The inkjet recording apparatus according to claim 6, characterized by comprising the following features.

8. The inkjet recording apparatus according to any one of claims 1 to 7, characterized in that the recording medium is a plastic film.

Images