Inkjet recording apparatus

Abstract

To provide an inkjet recording device capable of suppressing repelling and bleeding of ink when forming an image by using aqueous ink.SOLUTION: The inkjet recording apparatus includes a conveying unit, a recording unit, a coating unit, and a control unit. The conveying unit conveys a recording medium. The recording section includes a recording head configured to eject an aqueous ink onto the recording medium conveyed by the conveying section. The application unit is disposed on the upstream side of the recording unit in the conveyance direction of the recording medium, and applies the pretreatment liquid to the recording medium. The control unit controls application of the pretreatment liquid to the recording medium by the application unit. The pretreatment liquid contains at least a polyester resin, a surfactant, a water-soluble organic solvent, and water. The control part changes the application amount of the pretreatment liquid by the application part according to the surface tension of the recording medium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording apparatus that records an image by ejecting ink onto a recording medium. [Background technology]

[0002] 2. Description of the Related Art Inkjet recording devices that eject ink to record images are widely used as recording devices such as facsimiles, copying machines, and printers because they are capable of forming high-definition images.

[0003] In such inkjet recording devices, aqueous pigment inks that use pigments with excellent weather resistance as coloring materials have become mainstream. However, aqueous pigment inks have the problem of being prone to ink repellency and bleeding when ejected onto recording media with low wettability, such as plastic sheets.

[0004] Therefore, various methods have been proposed for adjusting 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 unit that applies a pretreatment liquid to the surface of the recording medium before forming an image, and a posttreatment unit that ejects a pretreatment liquid different from the pretreatment liquid onto the recording medium after forming the image. The pretreatment unit applies the pretreatment liquid in an application amount determined based on at least the type of ink, and the posttreatment unit ejects the pretreatment liquid in an ejection amount determined based on at least the type of ink, and ejects 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 device in which, when a pre-treatment section that forms dots of treatment liquid and then ink dots is mixed on a recording medium, and a post-treatment section that forms dots of ink and then treatment liquid dots, the amount of ink ejected per unit area of ​​the post-treatment section is made smaller than the amount of ink ejected per unit area of ​​the pre-treatment section. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-172218 [Patent Document 2] Japanese Patent Application Publication No. 10-226055 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method of Patent Document 1, the amount of pretreatment liquid to be applied is determined based on the amount of ink adhered per unit area, which can lead to problems such as insufficient wetting tension (surface tension) of the printing substrate, causing the ink to be repelled, or too high wetting tension, causing the ink to bleed.

[0008] Furthermore, even in the method of Patent Document 2, when a plastic film such as polyethylene terephthalate (PET) or polypropylene is used as the recording medium, there is a problem that the wetting tension is insufficient, causing ink repellency and bleeding.

[0009] SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an inkjet recording apparatus that can suppress ink repellency and bleeding when forming an image using aqueous ink. [Means for solving the problem]

[0010] In order to achieve the above object, a first aspect of the present invention is an inkjet recording apparatus including a transport unit, a recording unit, an application unit, and a control unit. 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 application unit is disposed upstream of the recording unit in the recording medium transport direction and applies a pretreatment liquid to the recording medium. The control unit controls application of the pretreatment liquid to the recording medium by the application unit. The pretreatment liquid contains at least a polyester resin, a surfactant, a water-soluble organic solvent, and water. The control unit changes the amount of pretreatment liquid applied by the application unit depending on the surface tension of the recording medium. [Effects of the Invention]

[0011] According to a first aspect of the present invention, an inkjet recording apparatus applies a pretreatment liquid containing a polyester resin to a recording medium before forming an image with aqueous ink, thereby increasing the wettability (wetting tension) of the recording medium and suppressing the repellency and bleeding of the aqueous ink, thereby improving image quality. Furthermore, by varying the amount of pretreatment liquid applied depending on the surface tension of the recording medium, it is possible to adjust the wettability of the recording medium within an optimal range, and since the application process of the pretreatment liquid is not performed when the wetting tension of the recording medium is high, unnecessary consumption of the pretreatment liquid can also be suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagram showing the structure of an inkjet recording apparatus 100 [Figure 2] Enlarged view of the coating section 2 and recording section 9 in FIG. [Figure 3] A diagram showing an image obtained when a single dot line is printed at 600 dpi using water-based ink without applying a pretreatment liquid to sheet S. [Figure 4] A diagram showing an image obtained when a pretreatment liquid is applied to sheet S and one dot line is printed at 600 dpi using water-based ink. [Figure 5] 10A and 10B are diagrams showing the state of an ink droplet Id1 immediately after it lands and after it dries when no pretreatment liquid is applied to a sheet S; [Figure 6] 10A and 10B are diagrams showing the state of an ink droplet Id1 immediately after it lands and after it dries when a pretreatment liquid is applied to a sheet S; DETAILED DESCRIPTION OF THE INVENTION

[0013] [1. Pretreatment liquid] The pretreatment liquid used in the inkjet recording apparatus of the present invention adjusts the wettability of a plastic sheet, which is a recording medium, to suppress ink repellency and bleeding when forming an image with the 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 contains at least a polyester resin, a surfactant, a water-soluble organic solvent, and water. The pretreatment liquid used in the inkjet recording apparatus of the present invention will be described in detail below.

[0014] (polyester resin) The polyester resin is added to impart wettability to the recording medium with the pretreatment liquid, thereby suppressing ink droplet repellency that occurs when the surface tension of the recording medium is low.

[0015] The polyester resin to be blended in the pretreatment liquid is not particularly limited and can be appropriately selected depending on the purpose. The polyester resin can be obtained by condensation polymerization or co-condensation polymerization of a divalent or trivalent or higher alcohol component and a divalent or trivalent or higher carboxylic acid component. The components used in synthesizing the polyester resin include the following alcohol components and carboxylic acid components.

[0016] Specific examples of the dihydric or trihydric or higher alcohol component 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 bisphenols such as hydroxypropylated bisphenol A and polyoxypropylated bisphenol A; and trihydric 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.

[0017] Specific examples of the divalent or trivalent or higher carboxylic acid component include divalent carboxylic acids such as maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or 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-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic 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 trimer acid. These divalent 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" refers to an alkyl group having 1 to 6 carbon atoms.

[0018] The content (blending amount) of the polyester resin in the pretreatment liquid is preferably 5% by mass or more, and more preferably 5% by mass or more and 20% by mass or less. If the content of the polyester resin is less than 5% by mass, the ink will not spread sufficiently when the wetting tension of the recording medium is low. (surfactant) The surfactant is added to improve the wettability of the pretreatment liquid to the recording medium. The amount of surfactant added is preferably 0.001 to 5% by mass, more preferably 0.05 to 2% by mass, of the total treatment liquid. If the amount is 0.001% by mass or more, the effect of adding the surfactant can be obtained. On the other hand, if the amount is added in excess of 5% by mass, no additional effect can be expected.

[0019] As the surfactant, various surfactants such as silicone surfactants, nonionic surfactants, anionic surfactants, cationic surfactants, and betaine surfactants can be used, but nonionic surfactants are preferred. As the nonionic surfactant, acetylene glycol surfactants, which have an acetylene group at the center and a symmetrical structure, are preferred because they are less likely to foam and can impart wettability. These surfactants may be used alone or in combination of two or more.

[0020] (Water-soluble organic solvent) The water-soluble organic solvent is added to enhance compatibility with the polyester resin and to maintain the moisture content of the pretreatment liquid, thereby preventing an increase in viscosity of the pretreatment liquid even if the moisture in the pretreatment liquid evaporates in the nozzle or coating device for the pretreatment liquid, and preventing nozzle clogging, deflected discharge, and other problems when the pretreatment liquid is applied by an inkjet method, thereby maintaining discharge stability.

[0021] 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 thereof 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 the polyester resin without causing it to aggregate.

[0022] 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.

[0023] The amount of the water-soluble organic solvent added is not particularly limited, but is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, of the total pretreatment liquid. If the amount is 5 to 40% by mass, the moisture in the pretreatment liquid can be sufficiently maintained, and the viscosity is not too high, so that the pretreatment liquid can be effectively applied to the recording medium.

[0024] (water) The pretreatment liquid used in the present invention is aqueous and contains water as an essential component. The water contained in the pretreatment liquid is not particularly limited as long as it does not impair the object of the present invention, and water of the desired purity, such as purified water or ion-exchanged water, can be appropriately selected and used. The content of water in the pretreatment liquid is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately changed depending on the amount of other components used, as described below. The content of water in the pretreatment liquid is preferably 50 to 90% by mass based on the total mass of the pretreatment liquid.

[0025] The pretreatment solution used in the present invention may also contain, if necessary, materials used in known treatment solutions, such as a foam inhibitor, a pH adjuster, an antiseptic / fungal agent, and an antirust agent.

[0026] (foam suppressor) A foam inhibitor is added to suppress foaming in the pretreatment liquid. Generally, liquids with high surface tension, such as water, are less likely to foam due to the action of forces that minimize the surface area of ​​the liquid. However, liquids with low surface tension and high viscosity are more likely to foam, and the generated foam is difficult to eliminate. When the pretreatment liquid of the present invention contains a polyester resin, a water-soluble organic solvent, a surfactant, etc., the surface tension decreases and the viscosity increases, making foaming more likely. Therefore, it is preferable to add a foam inhibitor. The amount of foam inhibitor added is preferably 0.01 to 10% by mass, more preferably 0.02 to 5% by mass. A content of 0.01% by mass or more provides a sufficient foam suppression effect. Furthermore, a content of 10% by mass or less ensures that the foam inhibitor does not become insoluble in the pretreatment liquid.

[0027] (pH adjuster) The pH adjuster is not particularly limited and can be appropriately selected depending on the purpose, as long as it can adjust the pH to 6 to 10 without adversely affecting the pretreatment liquid. If the pH is 6 or higher, corrosion of transport members such as transport rollers that come into contact with the pretreatment liquid is unlikely to occur.

[0028] Preferred pH adjusters include alcohol amines, alkali metal hydroxides, ammonium hydroxides, phosphonium hydroxides, and alkali metal carbonates. Examples of alcohol amines 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 hydroxides. Examples of phosphonium hydroxides include quaternary phosphonium hydroxides. Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate.

[0029] (preservative and fungicide) Suitable antiseptic and antifungal agents include, for example, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol, and sodium 1,2-benzisothiazolin-3-one.

[0030] (rust inhibitor) Suitable examples of the rust inhibitor include acidic sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, dicyclohexylammonium nitrite, pentaerythritol tetranitrate, and 1,2,3-benzotriazole.

[0031] The pretreatment liquid of the present invention obtained as described above is applied to a recording medium before recording with a water-based ink (pigment ink) by an inkjet method, thereby improving the wettability (wetting tension) of the surface of the recording medium, thereby suppressing the repelling and bleeding of the water-based ink ejected onto the recording medium.

[0032] There is no particular limit to the amount of pretreatment liquid to be applied, but the amount to be applied is 1 g / m 2 If the amount is less than 20 g / m, the wettability (wetting tension) of the surface of the recording medium cannot be sufficiently improved, and the effect of suppressing the repellency and bleeding of the water-based ink is insufficient. 2 If the amount of pretreatment liquid applied exceeds 1 g / m, the wettability of the surface of the recording medium will become too high, and the pretreatment liquid may not dry in time, causing bleeding of the water-based ink. 2 More than 20g / m 2 It is preferable that the density is 5 g / m or less. 2 More than 10g / m 2 It is more preferable to set the following:

[0033] [2. Image recording method] Next, an image recording method using an inkjet recording apparatus will be described. The inkjet recording apparatus used in the image recording method of the present invention is not particularly limited, and a serial head type or line head type inkjet recording apparatus can be used. In particular, inkjet recording apparatuses using aqueous pigment inks are prone to ink repellency and bleeding when a plastic sheet is used as the recording medium, but the image recording method of the present invention is less likely to cause these problems.

[0034] Fig. 1 is a schematic diagram showing the structure of an inkjet recording apparatus 100 according to one embodiment of the present invention. Fig. 2 is an enlarged view of the periphery of a recording unit 2 and a coating unit 3 in Fig. 1. As shown in Fig. 1, the inkjet recording apparatus 100 includes a sheet feeding unit 1, the recording unit 2, the coating unit 3, a conveying plate 4, a heating drum 6, a sheet winding unit 7, a control unit 10, and an operation panel 11.

[0035] Sheet S, a long printing substrate (here, a plastic sheet), is placed in sheet feeding unit 1, which is provided on the upstream side of recording unit 2 in the transport direction (left side in Figure 1). Sheet feeding unit 1 includes a rotating shaft on which rolled sheet S is attached, and a motor (neither shown) that rotates the rotating shaft in a predetermined rotation direction. When the motor is driven, sheet S is fed downstream in the transport direction (right side in Figure 1) as the rotating shaft rotates.

[0036] The recording unit 2 includes recording heads 2a, 2b, 2c, and 2d (see FIG. 2). Four colors of ink (yellow, magenta, cyan, and black) stored in ink tanks (not shown) are supplied to the recording heads 2a to 2d. The recording unit 2 records an image on the sheet S fed out from the sheet feeding unit 1 using the recording heads 2a to 2d.

[0037] The coating unit 3 is disposed upstream of the recording unit 2 in the sheet conveyance direction (on the left side in FIG. 1). The coating unit 3 includes a pretreatment liquid ejection head 3a. The pretreatment liquid ejection head 3a has the same structure as the recording heads 2a to 2d, and ejects the pretreatment liquid onto the sheet S fed from the sheet feeding unit 1 by an inkjet method.

[0038] A conveying plate 4 is disposed below the recording unit 2 and the coating unit 3. The sheet S fed from the sheet feeding unit 1 is supported by the conveying plate 4 at a predetermined distance from the recording unit 2 and the coating unit 3. A heater 4a is disposed on the back side of the conveying plate 4 (the side opposite the recording unit 2 and the coating unit 3). The sheet S is heated from the back side by the heater 4a as it is conveyed along the conveying plate 4. This dries the pretreatment liquid ejected onto the sheet S in the coating unit 3 before ink is ejected by the recording unit 2. The heater 4a may be any type, such as a halogen heater, ceramic heater, high-frequency induction heating (IH), or hot water heater.

[0039] After passing through the recording unit 3, the sheet S is conveyed to the heating drum 6 after its conveying direction is changed by the guide roller 5a. When the sheet S comes into contact with the heating drum 6, the ink is dried and fixed to the sheet S. After the conveying direction of the sheet S with the fixed ink is changed by the guide roller 5b, the sheet S is wound into a roll in the sheet winding unit 7. Note that, although the ink is dried using the heating drum 6 in this embodiment, other drying devices such as an infrared dryer or a hot air dryer may also be used.

[0040] The control unit 10 controls the ejection of ink in the recording unit 2 in accordance with image data received from an external computer. The control unit 10 also determines whether or not the pretreatment liquid needs to be ejected in the application unit 3, and the amount of the pretreatment liquid to be ejected, as will be described later.

[0041] The operation panel 11 functions as a touch panel for the user to perform various settings and inputs for the inkjet recording apparatus 100, and also displays the status of the inkjet recording apparatus 100, the image recording status, the number of prints, and the like.

[0042] Fig. 3 is a diagram showing an image obtained when a 1-dot line is printed at 600 dpi using aqueous ink without applying a pretreatment liquid to a sheet S. Fig. 4 is a diagram showing an image obtained when a 1-dot line is printed at 600 dpi using aqueous ink after applying a pretreatment liquid to a sheet S.

[0043] As shown in Figure 3, when the pretreatment liquid was not applied to the sheet S, the line width was uneven, sometimes thicker and sometimes thinner. On the other hand, as shown in Figure 4, when the pretreatment liquid was applied to the sheet S, the line width was uniform.

[0044] 5 and 6 are diagrams that schematically show the states of ink droplets immediately after landing and after drying when a pretreatment liquid is applied and not applied to a sheet S, respectively. As shown in FIG. 5, when a pretreatment liquid is not applied to the sheet S and the wetting tension of the sheet S is low, ink droplets Id1 that are ejected closely are attracted to each other and coalesce into a single large ink droplet Id2 in some areas. This results in non-uniform ink droplet sizes, and non-uniform line widths as shown in FIG. 3.

[0045] On the other hand, as shown in Figure 6, when the pretreatment liquid is applied to the sheet S, the wetting tension of the sheet S increases, so the ink droplets Id1 do not coalesce and the size of the ink droplets does not change, resulting in a uniform line width as shown in Figure 4.

[0046] Furthermore, the control unit 10 determines whether or not the application of the pretreatment liquid in the application unit 3 is necessary, and the amount of application, based on the wetting tension of the sheet S. Specifically, a table that associates the type of sheet S with the surface tension (wetting tension) is stored in advance in a storage unit (not shown). Then, at the start of printing, the type of sheet S to be used is input from the operation panel 11 of the inkjet recording apparatus 100. The control unit 10 reads out the surface tension corresponding to the input type of sheet S from the table stored in the storage unit, and determines whether or not the application of the pretreatment liquid in the application unit 3 is necessary, and the amount of application, based on the read surface tension.

[0047] This makes it possible to adjust the wetting tension of the sheet S within an optimal range, thereby suppressing ink bleeding and repelling and obtaining a good image. Furthermore, when the wetting tension of the sheet S is high, the pretreatment liquid application process is not performed, which also makes it possible to suppress unnecessary consumption of the pretreatment liquid.

[0048] When the surface tension of the sheet S is 45 mN / m or less, it is preferable to apply the pretreatment liquid to the sheet S in the application unit 3. Furthermore, it is preferable to increase the amount of pretreatment liquid applied as the surface tension of the sheet S decreases.

[0049] According to the image recording method described above, a pretreatment liquid containing a polyester resin is applied to a sheet before an image is formed using aqueous pigment ink using the inkjet recording apparatus 100. This increases the wettability (wetting tension) of the sheet, suppressing the repellency and bleeding of the aqueous ink and improving image quality. Therefore, the image recording method of the present invention can be suitably used in various inkjet recording apparatuses that use aqueous ink.

[0050] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. For example, although the inkjet recording apparatus 100 shown in Fig. 1 ejects ink from a long, rolled sheet at a predetermined speed, the present invention can also be applied to an inkjet recording apparatus that ejects ink onto a sheet cut to a predetermined shape.

[0051] In the above embodiment, the pretreatment liquid is ejected by the pretreatment liquid ejection head 20 using an inkjet method. However, the method is not limited to the inkjet method, and the pretreatment liquid may also be applied by, for example, a spray method, as long as the pretreatment liquid can be applied uniformly to the sheet S.

[0052] Furthermore, the material of the recording medium is not limited to plastic film, and various recording media can be used, such as paper such as plain paper or coated paper, and fabrics such as woven fabrics, knitted fabrics, or nonwoven fabrics made of natural or synthetic fibers. The effects of the present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. [Example]

[0053] [Manufacturing Example 1] (Preparation of pigment dispersion) 75 g of pigment dispersion resin (DISPERBYK-190, manufactured by BYK Japan, non-volatile content: 40% by mass, dispersion medium: water) was diluted with 775 g of ion-exchanged water, and 150 g of pigment (Pigment Blue 15:03) was added. This was then premixed for 1 hour using a Homodisper at a rotation speed of 5000 rpm. This was then dispersed using a bead mill (manufactured by Nippon Coke Corporation) to obtain a pigment dispersion. Zirconia beads (0.2 mm diameter) were filled into the vessel at a filling rate of 80% of the capacity. The dispersed particle size was Z-ave. 101 nm.

[0054] [Manufacturing Example 2] (Ink Preparation) Pigment ink I-1 was prepared by mixing 5 parts by mass of the pigment dispersion obtained in Production Example 1, 3 parts by mass of a binder resin (HA560, manufactured by Nicca Chemical Co., Ltd.), 0.04 parts by mass of a surfactant (SAG-502A, manufactured by Nissin Chemical Industry Co., Ltd.), 25 parts by mass of propylene glycol, 8 parts by mass of butyl triglycol, and 58.96 parts by mass of water.

[0055] Ink I-2 was prepared in the same manner as Ink I-1, except that the binder resin was changed to Superflex 130 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0056] [Manufacturing Example 3] [Preparation of pretreatment solution] Pretreatment solution 1 was prepared by stirring 10 mass% of polyester resin A (Pesresin A-640, manufactured by Takamatsu Oil & Fat Co., Ltd., number average molecular weight: 17,000, glass transition point: 64°C, solids content: 25 mass%, viscosity: less than 50 mPa s), 0.04 mass% of surfactant (Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.), 25 mass% of propylene glycol, and 64.96 mass% of ion-exchanged water using a stirrer.

[0057] Pretreatment solution 2 was prepared in the same manner as pretreatment solution 1, except that polyester resin B (Elitel KA-5034, manufactured by Unitika Ltd., number average molecular weight: 9,000, glass transition point: 67°C, solid content: 30% by mass, viscosity: 10 to 100 mPa s) was used instead of polyester resin A. Pretreatment solutions 3 to 5 were prepared in the same manner as pretreatment solution 1, except that the blending amount of polyester resin A was changed.

[0058] In addition, instead of polyester resin A, an acrylic resin (Movinyl 6820, manufactured by Japan Coating Resin Co., Ltd., glass transition temperature: 71°C, solid content: 50% by mass, viscosity: 50 Pretreatment solution 6 was prepared in the same manner as pretreatment solution 1, except that a 1,3-propanediol (up to 1000 mPa·s) was used. Pretreatment solution 7 was prepared in the same manner as pretreatment solution 1, except that 1,3-propanediol was used instead of propylene glycol. The compositions of pretreatment solutions 1 to 7 are shown in Table 1.

[0059] [Table 1]

[0060] [Evaluation of line width uniformity] The uniformity of line width was evaluated when images were formed using the pigment inks (cyan inks) I-1 and I-2 obtained in Production Example 2 and the pretreatment liquids 1 to 7 obtained in Production Example 3. The testing machine used for the evaluation was equipped with one inkjet head (KJ4B-YH, manufactured by Kyocera Corporation) that ejects the pigment ink and the pretreatment liquid, and a transport table for transporting the printing substrate (sheet) was installed below each inkjet head. The transport table could be heated to a specified temperature.

[0061] <Evaluation method> Using the above-mentioned tester, printing was performed under the following conditions: head applied voltage 21 V, drive frequency 20 kHz, ejection liquid volume 3 pL, print head temperature 32°C, print head resolution 600 dpi, and pre-ejection flushing count 1,000 times. The print medium transport table was preheated to 40°C. The print medium transport speed was 30 m / min. Then, a single dot line was printed at 600 dpi on the printing substrate coated with the pretreatment liquid under preset conditions (system conditions). The print was then dried for 120 seconds in a hot air dryer at 80°C to obtain a printed product. The resulting print was visually evaluated for line width uniformity using the following criteria. (Evaluation criteria) ◯: The line width is uniform. ×: The line width is non-uniform.

[0062] The system conditions and printing substrates used are shown in Tables 2 and 3, respectively. The evaluation results for line width uniformity are also shown in Tables 4 and 5, along with the types and application amounts of the printing substrates, inks, and pretreatment liquids used.

[0063] [Table 2]

[0064] [Table 3] *1: Biaxially oriented polypropylene *2: Polyethylene terephthalate

[0065] [Table 4]

[0066] [Table 5]

[0067] As is clear from Table 4, when a single dot line was printed at 600 dpi using ink I-1 or I-2 on a printing substrate coated with any of pretreatment liquids 1 to 4, or 7 under system condition 1 (present inventions 1 to 6), the line width was uniform in the evaluation of line width uniformity when the amount of pretreatment liquid applied was 10 g, and the pretreatment liquid increased the surface tension (wetting tension) of printing substrates 1 to 4. Furthermore, when the amount applied was 5 g, present invention 4, which used pretreatment liquid 4 with a low polyester resin blend amount of 5 mass%, produced nonuniform line widths on printing substrates 1 and 2, whereas present inventions 1 to 3, 5, and 6 produced uniform line widths.

[0068] In contrast, in Comparative Example 1, which used pretreatment liquid 5 containing 3% by mass of polyester resin, and Comparative Example 2, which used pretreatment liquid 6 containing acrylic resin instead of polyester resin, the line widths on the printing substrates 1 and 2 were non-uniform regardless of the amount of pretreatment liquid 5 or 6 applied. The reason for this is thought to be that in Comparative Example 1, the amount of polyester resin in pretreatment liquid 5 did not reach the specified amount, and in Comparative Example 2, the resin component of pretreatment liquid 6 was not polyester resin, so in both cases the ink did not wet and spread sufficiently on the printing substrates 1 and 2, which have low surface tension.

[0069] Furthermore, in Comparative Example 3, in which printing was performed under system condition 2, the line width on printing substrate 2 was non-uniform, and in Comparative Example 4, in which printing was performed under system condition 3 without applying pretreatment liquid 1, the line width on printing substrates 1 and 2 was non-uniform. The reason for this is thought to be that in Comparative Example 3, pretreatment liquid 1 was not applied to printing substrate 2, which has a surface tension of 35 mN / m or more, and therefore the ink did not wet and spread sufficiently on printing substrate 2. Also, in Comparative Example 4, pretreatment liquid 1 was not applied to either printing substrate 1 or 2, which has a low surface tension, and therefore the ink did not wet and spread sufficiently on printing substrates 1 and 2.

[0070] The results of Inventions 1 to 6 and Comparative Examples 1 to 4 confirmed that applying a pretreatment liquid containing 5% by mass or more of polyester resin to a printing substrate having a surface tension of 45 mN / m or less can effectively suppress ink droplet repellency and bleeding when printing with aqueous ink. [Industrial Applicability]

[0071] The present invention can be applied to an inkjet recording apparatus that ejects ink onto a recording medium, and by using the present invention, it is possible to provide an inkjet recording apparatus that can suppress ink repellency and bleeding when forming an image using aqueous ink. [Explanation of symbols]

[0072] 1 Sheet feeding section (conveying section) 2 Recording section 2a~2d recording head 3. Application section 3a Pre-treatment liquid ejection head 4 Transport plate 4a heater 6 heating drums 7 Sheet winding section (transport section) 10 Control Unit 11 Operation panel 100 Inkjet recording device S sheet (recording medium)

Claims

1. a conveying unit that conveys the recording medium; a recording unit having a recording head that ejects water-based ink onto the recording medium transported by the transport unit; an application unit that is disposed upstream of the recording unit in a conveyance direction of the recording medium and applies a pretreatment liquid to the recording medium; a control unit that controls application of the pretreatment liquid to the recording medium by the application unit; Equipped with the pretreatment liquid contains at least a polyester resin, a surfactant, a water-soluble organic solvent, and water; The inkjet recording apparatus is characterized in that the control unit changes the amount of the pretreatment liquid applied by the application unit in accordance with the surface tension of the recording medium.

2. 2. The inkjet recording apparatus according to claim 1, wherein the pretreatment liquid contains the polyester resin in an amount of 5% by mass or more.

3. 2. The inkjet recording apparatus according to claim 1, wherein the control unit causes the application unit to apply the pretreatment liquid when the surface tension of the recording medium is 45 mN / m or less.

4. 2. The inkjet recording apparatus according to claim 1, wherein the coating unit is a pretreatment liquid ejection head that ejects the pretreatment liquid by an inkjet method.

5. 2. The inkjet recording apparatus according to claim 1, further comprising a heating section for heating the recording medium passing through the coating section and the recording section.

6. The heating unit is a conveying plate that supports a surface of the recording medium opposite to the application unit and the recording unit; a heater for heating the conveying plate; 6. The inkjet recording apparatus according to claim 5, further comprising:

7. 7. The inkjet recording apparatus according to claim 1, wherein the recording medium is a plastic film.

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