Pretreatment liquid, ink set, inkjet recording apparatus, and inkjet recording method

Abstract

Provided is a pretreatment liquid for pretreating an impermeable medium for image recording using an aqueous ink, the impermeable medium having a polar term of surface free energy of 20 mJ / m or less, the pretreatment liquid containing core-shell particles having 2-ethylhexyl acrylate as a core and benzyl methacrylate as a shell.

Description

Technical Field

[0001] This invention relates to a pretreatment liquid, an ink assembly, an inkjet recording device, and an inkjet recording method. Background Technology

[0002] Japanese Patent Application Publication Nos. 2003-313468 and 2024-062760 disclose water-based inks that form images on a medium using an inkjet recording device. In such water-based inks, high adhesion to non-permeable media with low water permeability is essential when forming images. To achieve this, the water-based ink described in Patent Document 2 adds polyurethane resin microparticles as a binder. Summary of the Invention

[0003] The problem the invention aims to solve

[0004] For water-based inks used in applications where images are formed on the observer-facing side of a non-permeable medium, high abrasion resistance is required for the image formed in the non-permeable medium. However, water-based inks containing polyurethane resin particles tend to result in insufficient abrasion resistance for images formed in non-permeable media. Furthermore, water-based inks containing binders also present the problem of difficulty in achieving ejection stability.

[0005] In view of the above, the object of the present invention is to provide a technique that can form highly adhesive images in non-permeable media using water-based inks.

[0006] Solution for solving the problem

[0007] To achieve the above objectives, one embodiment of the pretreatment solution of the present invention is used for pretreatment of non-permeable media used for image recording with water-based inks. The polar term of the surface free energy of the aforementioned non-permeable media is 20 mJ / m. 2 The pretreatment solution described above contains core-shell particles with 2-ethylhexyl acrylate as the core and benzyl methacrylate as the shell.

[0008] In this pretreatment solution, by using 2-ethylhexyl acrylate as the core of the binder, which enhances adhesion to low-polarity surfaces, high adhesion of water-based inks to low-polarity, non-permeable media can be achieved. Furthermore, by using benzyl methacrylate, which has a high glass transition temperature and high hardness, as the shell of the binder core-shell particles in this pretreatment solution, high ejection stability can be ensured.

[0009] One embodiment of the ink assembly of the present invention comprises the above-mentioned pretreatment liquid and water-based ink.

[0010] The aforementioned water-based ink contains pigments, polyurethane microparticles, water-soluble solvents, and water.

[0011] The glass transition temperature of the aforementioned polyurethane microparticles is above 40°C and below 110°C, and the elongation at break at 25°C is below 50%.

[0012] The boiling point of the above-mentioned water-soluble solvent is above 200°C, and the SP value is above 19.5 and below 25.5.

[0013] The content of the polyurethane microparticles in the above-mentioned water-based ink is more than 3% by mass and less than 8% by mass, based on the solid content.

[0014] The content of the water-soluble solvent in the above-mentioned water-based ink is 0.5% by mass or more and less than 2% by mass.

[0015] In this water-based ink, by using rigid polyurethane microparticles with a high glass transition temperature and an elongation at break of less than 50% after film formation as a binder, the effect of the binder on improving the adhesion of the image to the non-permeable medium can be suppressed, and the abrasion resistance of the image formed on the non-permeable medium can be improved. To this end, by adding a water-soluble solvent with a boiling point of 200°C or higher and an SP value of 19.5 or higher and 25.5 or lower, and further pretreating the non-permeable medium with the aforementioned pretreatment solution, high adhesion of the image to the non-permeable medium can be obtained. Therefore, according to this ink assembly, an image with both good adhesion and abrasion resistance can be formed on a non-permeable medium.

[0016] The D50 of the aforementioned polyurethane microparticles can be above 10 nm and below 100 nm.

[0017] The aforementioned water-based inks may also contain organosilicon surfactants.

[0018] One aspect of the inkjet recording apparatus of the present invention records images on a recording surface of a non-permeable medium.

[0019] The inkjet recording device described above has a preprocessing unit, a recording head, and a control unit.

[0020] The pretreatment unit applies the pretreatment solution to the recording surface.

[0021] The aforementioned recording head ejects the aforementioned water-based ink onto the aforementioned recording surface.

[0022] When the non-permeable medium includes at least one of polypropylene and polyethylene, the control unit controls the process by having the pretreatment unit apply the pretreatment liquid to the recording surface and then having the recording head eject the water-based ink onto the recording surface.

[0023] The inkjet recording device described above may also include a discrimination unit that determines whether the non-permeable medium contains at least one of polypropylene and polyethylene.

[0024] In this case, if the discrimination unit determines that the non-permeable medium contains at least one of polypropylene and polyethylene, the control unit controls the process by having the pretreatment unit apply the pretreatment liquid to the recording surface and the recording head eject the water-based ink onto the recording surface.

[0025] The above record header can be a circular row header.

[0026] The inkjet recording apparatus described above can be used to produce printed materials in which the recording surface of the non-permeable medium is visible to the outside and no processing for protecting the image is applied.

[0027] In one embodiment of the inkjet recording method of the present invention, image recording is performed on the recording surface of a non-permeable medium.

[0028] In the above inkjet recording method, after the pretreatment liquid is applied to the recording surface, the water-based ink is sprayed onto the recording surface.

[0029] Invention Effects

[0030] As described above, the present invention provides a technique for forming highly adhesive images in a non-permeable medium using water-based inks. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating an embodiment of the inkjet recording method of the present invention.

[0032] Figure 2 This is a block diagram illustrating the schematic configuration of an inkjet recording apparatus according to one embodiment of the present invention.

[0033] Figure 3 This is a diagram showing the evaluation criteria for abrasion resistance. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below.

[0035] [The Composition of the Ink Set]

[0036] One embodiment of the present invention provides an ink assembly comprising a pretreatment liquid and an aqueous ink (hereinafter also simply referred to as "ink"). The recording medium used in this embodiment to form an image with the ink assembly is a non-permeable medium having a low-polarity recording surface with low ink permeability and difficulty in achieving ink adhesion. Specifically, the polarity term of the surface free energy of this non-permeable medium is 20 mJ / m. 2Examples of such non-permeable media include polypropylene membranes and polyethylene membranes. Furthermore, the surface free energy of non-permeable media can be measured using commercially available surface free energy measuring devices, such as the "Handy Contact Angle Meter MSA Flex" manufactured by Sanyo Trading Co., Ltd.

[0037] In the ink assembly of this embodiment, a pretreatment liquid is applied to the recording surface of the non-permeable medium, and then an image is formed using ink. The ink assembly of this embodiment, described in detail later, is configured to form an image that combines adhesion to the non-permeable medium with abrasion resistance. Therefore, the ink assembly of this embodiment forms an image on the outward-facing side of the non-permeable medium, for example, in the case of surface printing on transparent non-permeable media. Because of its configuration that forms an image that combines adhesion and abrasion resistance, the image is less prone to peeling or wear even without processing such as lamination to protect the image. Therefore, the ink assembly of this embodiment is particularly suitable for producing printed materials where the recording surface of the non-permeable medium is viewed from the outward-facing side and no processing to protect the image is applied. However, the ink assembly of this embodiment is not limited to the above applications and can also be used, for example, for reverse printing on transparent non-permeable media.

[0038] [Pretreatment solution]

[0039] (Brief Structure)

[0040] The pretreatment solution of this embodiment contains adhesive X and water. By applying the pretreatment solution of this embodiment to the recording surface of a non-permeable medium and drying it, a pretreatment layer can be formed in the non-permeable medium.

[0041] (Adhesive X)

[0042] The pretreatment solution of this embodiment contains an adhesive X to improve the adhesion of the ink-formed image to non-permeable media. In this embodiment's pretreatment solution, core-shell particles are used as adhesive X, these particles having a core of 2-ethylhexyl acrylate and a shell of benzyl methacrylate. By using 2-ethylhexyl acrylate, which improves adhesion to low-polarity surfaces, as the core of the core-shell particles in this embodiment's pretreatment solution, the adhesion of the ink-formed image to low-polarity non-permeable media can be improved.

[0043] Furthermore, in the pretreatment solution of this embodiment, by using benzyl acrylate, which has a high glass transition temperature and high hardness, as the shell of the core-shell particles constituting binder X, the ejection stability of the recording head can be improved. Therefore, through ejection from the recording head, the pretreatment solution of this embodiment can be accurately applied to the image formation position on the recording surface of the non-permeable medium. Thus, the pretreatment solution of this embodiment can control the amount used and improve the drying properties of the printed matter.

[0044] Therefore, the pretreatment liquid of this embodiment, by having the core and shell of the core-shell particles constituting the binder X having different functions, can ensure ejection stability and achieve high adhesion of the image formed by the ink to low-polarity, non-permeable media. This effect of the pretreatment liquid of this embodiment is even more pronounced when combined with the inks of the ink group of this embodiment. However, this effect of the pretreatment liquid of this embodiment can be effectively obtained not only with the ink group of this embodiment, but also when combined with water-based inks other than those of the ink group of this embodiment.

[0045] In the pretreatment solution of this embodiment, in order to fully obtain the effect of the adhesive X, the content of adhesive X, based on the solid components, is preferably 5% by mass or more. Furthermore, in the pretreatment solution of this embodiment, in order to avoid poor spraying caused by increased viscosity and thickening, the content of adhesive X, based on the solid components, is preferably 25% by mass or less.

[0046] (water)

[0047] In the pretreatment solution of this embodiment, water such as ion-exchanged water, purified water, or distilled water can be used. From the viewpoint of dryness and spray reliability, the water content in the pretreatment solution of this embodiment is preferably 40% by mass or more and 80% by mass or less.

[0048] (Other ingredients)

[0049] In the pretreatment solution of this embodiment, components other than those described above may be added as needed. For example, a water-soluble organic solvent may be added to the pretreatment solution of this embodiment. The choice of water-soluble organic solvent added to the pretreatment solution of this embodiment is not particularly limited, as long as it is compatible with other components. The drying properties of the pretreatment solution of this embodiment can be adjusted using a water-soluble organic solvent. Examples of water-soluble organic solvents that can be used in the pretreatment solution of this embodiment include, for example, methanol, ethanol, 1-propanol, 2-propanol, propylene glycol, acetone, tetrahydrofuran, and acetonitrile.

[0050] Furthermore, a surfactant can be added to the pretreatment solution of this embodiment. The pretreatment solution of this embodiment can improve the compatibility and dispersion stability of each component through the surfactant. Furthermore, the pretreatment solution of this embodiment can improve the wettability to the recording medium through the surfactant. As the surfactant added to the pretreatment solution of this embodiment, a nonionic surfactant is preferred.

[0051] Furthermore, in addition to water-soluble organic solvents and surfactants, various additives such as solubility stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH modifiers, and fungicides can be added to the pretreatment solution of this embodiment as needed.

[0052] [Water-based Ink]

[0053] (Summary Structure)

[0054] The water-based ink of this embodiment contains pigment a, binder b, water-soluble solvent c, and water. The ink of this embodiment is ejected from the recording head of an inkjet recording device onto the recording surface of a non-permeable medium, thereby forming an image on the recording surface of the non-permeable medium. The ink of this embodiment, by using a binder b with a specific composition and a water-soluble solvent c with a specific composition, can form an image in a non-permeable medium that possesses both adhesion and abrasion resistance. Hereinafter, the components of the ink of this embodiment will be described in detail.

[0055] (pigment a)

[0056] The ink of this embodiment contains pigment a as a colorant, from the viewpoint of improving the color mixing prevention and water resistance of images recorded on the recording medium. Pigment a can be either inorganic or organic pigments. Furthermore, pigment a can be used in combination with extender pigments as needed.

[0057] Specific examples of inorganic pigments that can be used in the ink of this embodiment include carbon black, metal oxides, etc., with carbon black being particularly preferred in black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0058] Specific examples of organic pigments that can be used in the ink of this embodiment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, diazine pigments, perylene pigments, perylene ketone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0059] The ink of this embodiment does not particularly limit the hue and can use any of the colored pigments such as yellow, magenta, cyan, blue, red, orange, and green. Preferred examples of colored pigments include CI pigment yellow, CI pigment red, CI pigment orange, CI pigment violet, CI pigment blue, and CI pigment green. The ink of this embodiment can use one or more of these colored pigments as pigment a.

[0060] (Adhesive b)

[0061] In this embodiment, an adhesive b is added to improve the adhesion of the image to non-permeable media. The ink of this embodiment uses polyurethane microparticles, which are microparticles formed from polyurethane, as adhesive b. The polyurethane microparticles used as adhesive b have a high glass transition temperature, above 40°C and below 110°C, and an elongation at break of less than 50% after film formation, making them rigid. Therefore, the ink of this embodiment can achieve high abrasion resistance to images formed in non-permeable media.

[0062] The ink of this embodiment uses rigid polyurethane microparticles as binder b. Compared to the composition using conventional polyurethane microparticles, binder b has a weaker effect on improving the adhesion of the image to the non-permeable medium. To address this, the ink of this embodiment compensates for the poor adhesion of the image to the non-permeable medium by using a water-soluble solvent c, and pre-treats the non-permeable medium with the aforementioned pretreatment solution, thereby obtaining sufficient adhesion of the image to the non-permeable medium.

[0063] In order to fully utilize the effect of the binder b described above, the ink of this embodiment has a binder b content of 3% by mass or more based on the solid content. Furthermore, to avoid poor ejection due to contamination and thickening of the nozzle surface of the recording head, the ink of this embodiment has a binder b content of 8% by mass or less based on the solid content. Moreover, to more effectively utilize the effect of the binder b described above, the particle size (D50) of the binder b is preferably 10 nm or more and 100 nm or less.

[0064] (Water-soluble solvent c)

[0065] In the ink of this embodiment, the boiling point of the water-soluble solvent c is 200°C or higher, and the SP value (solubility parameter) is 19.5 or higher and 25.5 or lower. Therefore, the ink of this embodiment improves film uniformity and achieves high image adhesion to non-permeable media. Examples of water-soluble solvent c that can be used in the ink of this embodiment include, for example, diethylene glycol monobutyl ether, tripropylene glycol, and 3-methyl-1,3-butanediol.

[0066] In order to fully utilize the effect of the water-soluble solvent c described above, the ink of this embodiment contains 0.5% by mass or more of the water-soluble solvent c. Furthermore, since the water-soluble solvent c in the ink of this embodiment is a high-boiling-point solvent, in order to ensure the drying properties of the non-permeable medium, the content of the water-soluble solvent c is 2% by mass or less.

[0067] (water)

[0068] In the ink of this embodiment, water such as ion-exchanged water, purified water, or distilled water can be used. From the viewpoint of dryness and spray reliability, the water content of the ink of this embodiment is preferably 40% by mass or more and 80% by mass or less.

[0069] (Other ingredients)

[0070] Other components besides those described above can be added to the ink of this embodiment as needed. For example, a surfactant is preferably added to the ink of this embodiment. As the surfactant added to the ink of this embodiment, an organosilicone surfactant is preferred. By adding an organosilicone surfactant to the ink of this embodiment, the wetting and spreading properties of the layer formed by the pretreatment liquid on the surface of a non-permeable medium can be improved. Organosilicone surfactants are surfactants that have siloxane bonds within their molecules. Commercially available organosilicone surfactants include, for example, SILFACE (registered trademark) SAG002 and SILFACE SAG503A manufactured by Nissin Chemical Industries, Ltd.

[0071] Furthermore, a dispersant that improves the dispersibility of pigment a in the solvent can be added to the ink of this embodiment. Pigment dispersion resins, etc., can be used as dispersants. Pigment dispersion resins are water-soluble resin particles that inhibit the aggregation of pigment a by adhering to the surface of pigment a. Examples of pigment dispersion resins include copolymers of at least one monomer selected from (meth)acrylate, styrene, and vinylnaphthalene with at least one monomer selected from (meth)acrylic acid and maleic acid.

[0072] As a pigment dispersion resin, a resin having repeating units from (meth)acrylic acid ((meth)acrylic acid unit), repeating units from (meth)acrylate ((meth)acrylate alkyl ester) ((meth)acrylate alkyl ester) and styrene units is preferred. In this case, the proportion of (meth)acrylic acid units among all repeating units of the pigment dispersion resin is preferably 4.5% by mass or more and 8.0% by mass or less. The proportion of (meth)acrylate alkyl ester units among all repeating units of the pigment dispersion resin is preferably 35% by mass or more and 70% by mass or less. The proportion of styrene units among all repeating units of the pigment dispersion resin is preferably 27% by mass or more and 60% by mass or less. As a pigment dispersion resin, a resin having repeating units from methacrylic acid, repeating units from methyl methacrylate, repeating units from butyl acrylate, and styrene units is more preferred.

[0073] In the ink of this embodiment, the content of pigment dispersion resin is preferably 0.5% by mass or more and 8.0% by mass or less, more preferably 1.5% by mass or more and 4.0% by mass or less. By making the content of pigment dispersion resin 0.5% by mass or more, the aggregation of pigment a can be suppressed more effectively. By making the content of pigment dispersion resin 8.0% by mass or less, the occurrence of nozzle clogging of the recording head can be suppressed.

[0074] In addition to surfactants and pigment dispersion resins, various additives such as solubilizers, antioxidants, viscosity modifiers, pH adjusters, and neutralizers can be added to the ink of this embodiment as needed.

[0075] [Inkjet Recording Method]

[0076] The inkjet recording method of this embodiment uses the ink group of this embodiment described above. Figure 1 This is a flowchart illustrating the inkjet recording method of this embodiment. In step S01, the polar term of the surface free energy is set to 20 mJ / m. 2 The following non-permeable medium is placed in a designated position. In step S02, a pretreatment liquid is applied to the recording surface of the non-permeable medium. In step S03, an image is formed by ejecting ink from the recording surface of the non-permeable medium after the pretreatment liquid has been applied.

[0077] [Inkjet recording device]

[0078] The inkjet recording apparatus 1 of this embodiment is configured to perform the inkjet recording method of this embodiment described above. Figure 2 This is a block diagram showing the general structure of the inkjet recording apparatus 1. The inkjet recording apparatus 1 includes a preprocessing unit 2, a recording head 3, a discrimination unit 4, and a control unit 5.

[0079] The pretreatment unit 2 performs pretreatment by applying a pretreatment liquid to the recording surface of the non-permeable medium. The pretreatment unit 2, for example, has a recording head different from the recording head 3, and can be configured to spray the pretreatment liquid onto the recording surface of the non-permeable medium at the position for image formation. As described above, due to the high spraying stability of the pretreatment liquid in this embodiment, the pretreatment unit 2 can spray the pretreatment liquid at an accurate position on the recording surface of the non-permeable medium. The recording head that sprays the pretreatment liquid is preferably a circulating line head. In a circulating line head, the pretreatment liquid present near the nozzle surface is continuously circulated, making it less likely for spray defects caused by increased drying viscosity to occur. Alternatively, the pretreatment unit 2 may not be configured with a recording head; for example, it may be configured to use a roller to apply the pretreatment liquid to the entire area of ​​the recording surface of the non-permeable medium.

[0080] The recording head 3 forms an image by ejecting ink from the recording surface of the non-permeable medium at the position where the image is formed. As described above, due to the high ink ejection stability of this embodiment, the recording head 3 can eject ink at an accurate position on the recording surface of the non-permeable medium. The recording head 3 is preferably a circulating line head. In a circulating line head, the ink present near the nozzle surface also circulates continuously, making it less likely for ejection defects caused by increased drying viscosity to occur.

[0081] The discrimination unit 4 determines whether the non-permeable medium is a non-permeable medium that requires pretreatment by applying a pretreatment solution. For example, the discrimination unit 4 determines whether the polar term of the surface free energy of the non-permeable medium is 20 mJ / m. 2 The following applies. Specifically, when the discrimination unit 4 determines that the polarity term of the surface free energy of the non-permeable medium is 20 mJ / m... 2 The following conditions indicate that the medium is a non-permeable medium requiring pretreatment. Furthermore, when the discrimination unit 4 determines that the polar term of the surface free energy of the non-permeable medium is not 20 mJ / m... 2 In the following cases, it can be determined that it is a non-permeable medium that does not require pretreatment.

[0082] Furthermore, the discrimination unit 4 can also determine whether the non-permeable medium contains at least one of polypropylene and polyethylene. That is, when the discrimination unit 4 determines that the non-permeable medium contains at least one of polypropylene and polyethylene, it is determined that it is a non-permeable medium that requires pretreatment. Furthermore, when the discrimination unit 4 determines that the non-permeable medium does not contain either polypropylene or polyethylene, it is determined that it is a non-permeable medium that does not require pretreatment.

[0083] When the discrimination unit 4 determines that the medium is a non-permeable medium requiring pretreatment, the control unit 5 controls the process by applying a pretreatment solution to the recording surface of the non-permeable medium using the pretreatment unit 2, and then using the recording head 3 to eject ink from the recording surface of the non-permeable medium coated with the pretreatment solution. On the other hand, when the discrimination unit 4 determines that the medium is a non-permeable medium that does not require pretreatment, the control unit 5 controls the process by not applying the pretreatment solution to the recording surface of the non-permeable medium using the pretreatment unit 2, and then using the recording head 3 to eject ink from the recording surface of the non-permeable medium coated with the pretreatment solution.

[0084] Furthermore, the inkjet recording device 1 is not limited to the above configuration and can be modified as needed. For example, the inkjet recording device 1 may not have a discrimination unit 4. In this case, the inkjet recording device 1 may, for example, have an input operation unit for receiving input from the user regarding whether the medium is a non-permeable medium requiring pretreatment with a pretreatment solution.

[0085] [Examples and Comparative Examples]

[0086] As embodiments and comparative examples of the present invention, the preparation and evaluation of pretreatment liquid and ink were carried out.

[0087] (Preparation of pretreatment solution)

[0088] In the pretreatment solution of this example, binder X1 as shown in Table 1 was used as binder X. Binder X1 was prepared by emulsion polymerization of a mixture of 2-ethylhexyl acrylate (core) and benzyl methacrylate (shell) in a 7:3 ratio to form an aqueous emulsion dispersion. The pretreatment solution of this example was prepared with the following composition: 20% by mass of solids, 20% by mass of propylene glycol, and the remainder being deionized water.

[0089] In the pretreatment solution of the comparative example, one of the binders X2 to X4 shown in Table 1 was used as binder X. Binders X2 to X4 were also prepared as dispersions of an aqueous emulsion in the same manner as binder X1. The pretreatment solution of the comparative example was prepared by making the aqueous emulsion contain 20% by mass of solids, 20% by mass of propylene glycol, and the remainder being ion-exchanged water.

[0090] [Table 1]

[0091]

[0092] (Ink preparation)

[0093] First, a pigment dispersion of pigment a in water is prepared. The pigment dispersion is prepared by wet dispersion of pigment a, pigment dispersion resin, and water using a medium-type wet disperser. In wet dispersion using a medium-type wet disperser, small-diameter beads (e.g., beads with a D50 of 0.5 mm or more and 1.0 mm or less) can be used as the medium. The material of the medium is not particularly limited, but a hard material (e.g., glass and zirconium oxide) is preferred.

[0094] In both the examples and comparative examples, carbon black was used as pigment a, styrene-acrylic resin was used as the pigment dispersion resin, and deionized water was used as water. Furthermore, in the inks of both examples and comparative examples, the content of pigment a was 3% by mass, the content of the pigment dispersion resin was 1.5% by mass, and the remainder was water.

[0095] Next, the inks of the Examples and Comparative Examples were prepared. In the inks of the Examples and Comparative Examples, one of the binders b1 and b2 shown in Table 2 was used as binder b, and one of the water-soluble solvents c1 and c2 shown in Table 3 was used as water-soluble solvent c. The inks of the Examples and Comparative Examples were prepared by adding binder b, water-soluble solvent c, pigment dispersion, propylene glycol, triethylene glycol monobutyl ether, SILFACE SAG503A, and water. Ion-exchanged water was used as water in both the Examples and Comparative Examples.

[0096] [Table 2]

[0097]

[0098] [Table 3]

[0099]

[0100] (Evaluation of Pretreatment Liquid and Ink)

[0101] Evaluations were made on the image adhesion, image rubbing resistance, and ejection stability of the pretreatment liquid and ink for the examples and comparative examples.

[0102] · Method for Evaluating Image Adhesion

[0103] In the evaluation of image adhesion, first, a solid image was formed by ejecting ink after applying the pretreatment liquid onto a non-permeable medium. As the non-permeable medium, a corona-treated biaxially stretched polypropylene (OPP) film manufactured by Nimura Chemical Co., Ltd. was used. A tape (manufactured by Nichiban Co., Ltd., Cellotape (registered trademark), 18 mm wide, CT-18S) was attached to the solid image formed on the non-permeable medium, and the surface state of the solid image after peeling was observed. The ratio of the area of the region where the image peeled off in the solid image to the area of the entire region where the tape was attached was measured. For the image adhesion, the obtained measured value was used as the evaluation value. Regarding the evaluation value of the image adhesion, evaluations were made according to the following criteria A to C. Regarding the image adhesion, a solid image evaluated as A was considered qualified, and solid images evaluated as B and C were considered unqualified.

[0104] A: 0%

[0105] B: Less than 50% <​​​​​​​​​​​​​​​​​

[0111] C: More than 10 stripes were observed. (Reference) Figure 3 Photo C)

[0112] • Ejection stability

[0113] The ejection stability of the pretreatment liquid and ink is evaluated by the degree of offset of the non-printing area. That is, the lower the ejection stability of the pretreatment liquid and ink, the more likely the tail of the ejected droplet is to develop ripples, resulting in offset of the non-printing area. Therefore, the greater the offset of the non-printing area, the lower the ejection stability.

[0114] To evaluate the degree of offset in the non-printing section, the evaluation was conducted under normal temperature and high humidity conditions (25°C and 80% RH) to suppress the effect of nozzle drying in the line printhead. An inkjet recording device (a prototype manufactured by Kyocera Office Information Systems Co., Ltd., 600 dpi) was used as the evaluation machine. For this evaluation machine, pretreatment liquid or ink was removed from the line printhead and the line printhead was wiped (cleaning and wiping treatment). After 1 minute of cleaning and wiping treatment, a horizontal line (along the main scanning direction) was formed on A4 glossy paper (Seiko Epson Co., Ltd.'s "Ultra-fine Paper") using the evaluation machine. At this time, the line width of the horizontal line was set to 1 point (1 drop of pretreatment liquid or ink). The volume of each point of pretreatment liquid or ink ejected from each nozzle of the line printhead (the volume of each drop) was set to 3 pL.

[0115] Next, the offset of the horizontal lines was determined using an optical microscope (Nikon MM-800, manufactured by Nikon Corporation). Specifically, the maximum distance (offset) in the sub-scanning direction of each point constituting the horizontal lines was measured using the application accompanying the optical microscope. The larger the offset, the more severe the distortion of the horizontal lines due to bending of the non-printing parts. Regarding ejection stability, the offset obtained with each pretreatment liquid or ink was used as the evaluation value. The evaluation value of the ejection stability of each pretreatment liquid or ink was evaluated according to the following criteria A and B. Regarding image density, pretreatment liquids or inks rated A were considered acceptable, while those rated B were considered unacceptable.

[0116] A: Below 20μm

[0117] B: Greater than 20μm

[0118] (Examples 1-6)

[0119] Examples 1-6 all used a pretreatment solution containing binder X1. Furthermore, Examples 1-6 used inks with the compositions shown in Table 4. Table 5 shows the evaluation results for image adhesion, image abrasion resistance, and ejection stability of the pretreatment solution and ink in Examples 1-6. As shown in Table 5, in Examples 1-6, the image adhesion, image abrasion resistance, and ejection stability of the pretreatment solution and ink all met the requirements.

[0120] [Table 4]

[0121]

[0122] [Table 5]

[0123]

[0124] (Comparative Examples 1-8)

[0125] Comparative Examples 1-5 used a pretreatment solution containing binder X2, Comparative Examples 6 and 7 used a pretreatment solution containing binder X3, and Comparative Example 8 used a pretreatment solution containing binder X4. Furthermore, Comparative Examples 1-8 used inks with the compositions shown in Table 6. Table 7 shows the evaluation results of image adhesion, image abrasion resistance, and ejection stability of the pretreatment solution and ink in Comparative Examples 1-8.

[0126] As shown in Table 7, the image adhesion in Comparative Examples 6 and 7 failed. This is believed to be because Comparative Examples 6 and 7 used adhesive X3 without 2-ethylhexyl acrylate in the pretreatment solution, thus failing to fully utilize the effect of the pretreatment solution in improving image adhesion. Furthermore, the image abrasion resistance in Comparative Examples 1 to 8 all failed. It is believed that while the pretreatment solution containing adhesive X2 in Comparative Examples 1 to 5 improved image adhesion, its insufficient hardness led to easy peeling from non-permeable media. Furthermore, it is believed that the pretreatment solution containing adhesive X3 in Comparative Examples 6 and 7 failed to fully improve image adhesion. Moreover, it is believed that while the pretreatment solution containing adhesive X4 in Comparative Example 8 improved image adhesion, its insufficient hardness led to easy peeling from non-permeable media. The ejection stability of the pretreatment solution in Comparative Examples 1 to 5 and 8 failed. It is believed that in the pretreatment solutions of Comparative Examples 1 to 5 and 8, the emulsion state of the binders X2 and X4, which have soft properties, is disrupted by the shear stress applied during spraying, resulting in poor dispersion, which in turn increases viscosity and adheres to the nozzle surface, causing poor spraying.

[0127] [Table 6]

[0128]

[0129] [Table 7]

[0130]

[0131] [Explanation of reference numerals in the attached figures]

[0132] 1: Inkjet recording device; 2: Pre-processing unit; 3: Recording head; 4: Judgment unit; 5: Control unit.

Claims

1. A pretreatment liquid for a non-penetrative medium on which image recording is performed using an aqueous ink, a polar term of a surface free energy of the non-penetrative medium is 20 mJ / m2 or less, the pretreatment liquid contains core-shell particles having 2-ethylhexyl acrylate as a core and benzyl methacrylate as a shell.

2. An ink set having an aqueous ink and the pretreatment liquid according to claim 1, the aqueous ink contains a pigment, polyurethane fine particles, a water-soluble solvent, and water, the polyurethane fine particles have a glass transition temperature of 40°C or higher and 110°C or lower and an elongation at break at 25°C of 50% or less, the water-soluble solvent has a boiling point of 200°C or higher and an SP value of 19.5 or higher and 25.5 or lower, a content of the polyurethane fine particles in the aqueous ink is 3% by mass or more and 8% by mass or less based on a solid content, a content of the water-soluble solvent in the aqueous ink is 0.5% by mass or more and less than 2% by mass.

3. The ink set of claim 2, wherein, a D50 of the polyurethane fine particles is 10 nm or more and 100 nm or less.

4. The ink set according to claim 2 or 3, wherein, the aqueous ink further contains a silicone-based surfactant.

5. An inkjet recording apparatus that performs image recording on a recording surface of a non-penetrative medium, the inkjet recording apparatus has: a pretreatment section that applies the pretreatment liquid according to claim 1 to the recording surface; a recording head that ejects the aqueous ink contained in the ink set according to claim 2 to the recording surface; and a control section that controls, in a case where the non-penetrative medium contains at least one of polypropylene and polyethylene, the pretreatment section to apply the pretreatment liquid to the recording surface and the recording head to eject the aqueous ink to the recording surface after the pretreatment section applies the pretreatment liquid to the recording surface.

6. The inkjet recording apparatus according to claim 5, wherein the inkjet recording apparatus further has a discrimination section that discriminates whether the non-penetrative medium contains at least one of polypropylene and polyethylene, the control section controls, in a case where the non-penetrative medium is judged by the discrimination section to contain at least one of polypropylene and polyethylene, the pretreatment section to apply the pretreatment liquid to the recording surface and the recording head to eject the aqueous ink to the recording surface after the pretreatment section applies the pretreatment liquid to the recording surface.

7. The inkjet recording apparatus according to claim 5 or 6, wherein the recording head is a cyclical line head.

8. The inkjet recording apparatus according to claim 5 or 6, wherein the inkjet recording apparatus is used to produce a printout in which the recording surface of the non-penetrative medium is visible from the outside and no treatment for protecting the image is applied.

9. An inkjet recording method that is an inkjet recording method of performing image recording on a recording surface of a non-penetrative medium, the pretreatment liquid according to claim 1 is applied to the recording surface and the aqueous ink contained in the ink set according to claim 2 is ejected to the recording surface.

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