Inkjet printing method

Abstract

This invention provides an inkjet printing method that can produce printed materials with excellent image quality regardless of the type of non-absorbent printing medium used, even when printing with a line-head type inkjet system using a non-absorbent printing medium. [Solution] An inkjet printing method for forming a printed image on a non-absorbent printing medium, comprising a dark image forming section and a light image forming section, wherein the printing duty of the ink containing a colorant in the dark image forming section is greater than the printing duty of the ink containing a colorant in the light image forming section, comprising: step 1: a step of performing corona treatment on the printing medium; step 2: a step of applying a pretreatment liquid to the outer edge portion of the portion that will become the dark image forming section of the printing medium obtained in step 1 to obtain a printing medium having a pretreatment liquid application section; and step 3: a step of applying ink containing a colorant to the portion that will become the dark image forming section of the surface of the printing medium obtained in step 2 having the pretreatment liquid application section, using a line head type inkjet method.

Description

[Technical Field]

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

[0002] Inkjet printing offers many advantages, including the elimination of the need for platemaking, ease of handling variable information, and non-contact printing on the medium. As a result, it is increasingly being used not only for office and home applications, but also for commercial printing applications with significantly larger print volumes.

[0003] For example, Patent Document 1 describes an inkjet recording method that prevents bleeding of color inks regardless of the recording medium used, such as a recording medium with excellent ink absorption capacity or a recording medium with poor ink absorption capacity. This method involves recording on a recording medium using color ink containing a colorant, characterized in that a clear ink that does not contain a colorant has a lower static surface tension and a lower dynamic surface tension with a lifespan of 100 milliseconds than the color ink, at the edge of the recording area recorded by the color ink. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-196274 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] High productivity is required for commercial printing applications, necessitating high-speed printing. To accommodate this high-speed printing, line-head type print heads have been developed. While conventional serial-head type print heads print by moving the head (nozzle) multiple times, line-head type print heads are equipped with a head that can inkjet print over a width equal to or greater than the length perpendicular to the transport direction of the printing medium. Therefore, high-speed printing is possible by scanning only the printing medium while keeping the print head fixed. On the other hand, in line-head type inkjet printing, when forming a print image that includes both dark and light image forming areas on a low-liquid absorption printing medium, bleeding occurs at the boundary between the dark and light image forming areas, resulting in a problem that degrades the image quality of the resulting print image. Furthermore, in commercial printing applications, there is a demand not only for low-absorbency printing media such as printing paper, but also for printing on non-absorbent printing media such as resin films. In response to these demands, Patent Document 1 considers not only paper but also a wide range of ink-receiving materials such as cloth, plastic film, metal plate, glass, ceramics, wood, and leather as recording media. However, in its examples, it only verifies the effectiveness using paper such as Water Resistant High Glossy Paper (manufactured by Canon Europe) and Pro Photo Paper (manufactured by Canon). Therefore, there is a need for the development of a technology that enables printing without compromising image quality even on various low-liquid-absorbent printing media, specifically when printing with resin films. Furthermore, while it is known that surface treatments such as corona treatment on printing media can improve the wettability of low-absorbent printing media and promote ink adhesion, even if corona treatment eliminates streaks and improves solid color filling, the image quality of the characters sometimes differed depending on the type of printing media.

[0006] The present invention aims to provide an inkjet printing method that can produce printed materials with excellent image quality regardless of the type of non-absorbent printing medium, even when using a line-head type inkjet system with a non-absorbent printing medium.

Means for Solving the Problem

[0007] The inventor has found that, in an inkjet printing method for forming a printed image including a dark image forming portion and a light image forming portion on a non-absorbent printing medium, a step of performing corona treatment on the printing medium, a step of obtaining a printing medium having a pretreatment liquid application portion by applying a pretreatment liquid to an outer edge portion of a portion that becomes the dark image forming portion of the printing medium obtained in this step, and a step of applying ink containing a colorant to a portion that becomes the dark image forming portion of the surface of the printing medium having the pretreatment liquid application portion obtained in this step by a line head type inkjet method can solve the above problems.

[0008] That is, the present invention is an inkjet printing method for forming a printed image including a dark image forming portion and a light image forming portion, wherein the printing duty of the ink containing a colorant in the dark image forming portion is larger than the printing duty of the ink containing a colorant in the light image forming portion on a non-absorbent printing medium, and Step 1: A step of performing corona treatment on the printing medium, Step 2: A step of obtaining a printing medium having a pretreatment liquid application portion by applying a pretreatment liquid to an outer edge portion of a portion that becomes the dark image forming portion of the printing medium obtained in Step 1, and Step 3: A step of applying ink containing a colorant to a portion that becomes the dark image forming portion of the surface of the printing medium having the pretreatment liquid application portion obtained in Step 2 by a line head type inkjet method. An inkjet printing method including the above steps is provided.

Advantages of the Invention

[0009] The present invention can provide an inkjet printing method capable of obtaining a printed matter with excellent image quality regardless of the type of non-absorbent printing medium even in printing by a line head type inkjet method using a non-absorbent printing medium.

Brief Description of the Drawings

[0010] [Figure 1]An example of a schematic diagram of a printed image including a dark image forming area and a light image forming area is shown. In the diagram, the solid line is the boundary line between the dark image forming area and the light image forming area. The area enclosed by the solid line represents the light image forming area, and the area enclosed by the solid line and the dotted line represents the outer edge of the dark image forming area. [Figure 2] An example of a schematic diagram of a printed image including a dark image forming area and a light image forming area is shown. In the diagram, the solid line is the boundary line between the dark image forming area and the light image forming area. The area enclosed by the solid line represents the light image forming area, the area enclosed by the solid line and the dotted line represents the outer edge of the dark image forming area, and the area enclosed by the solid line and the dashed line represents the inner edge of the dark image forming area. [Figure 3] This is a schematic diagram of a printed image consisting of a light image forming area (i) (printing duty 10% of ink containing a colorant) and a dark image forming area (ii) (printing duty 100% of ink containing a colorant) formed in Examples 1-5 and Comparative Examples 1-2. [Figure 4a] This is an explanatory diagram showing the area to which the pretreatment solution is applied in step 2 of Examples 1-4 and Comparative Example 1. [Figure 4-b] This is an explanatory diagram showing the area to which the pretreatment solution is applied in step 2 of Example 5. [Figure 5] This is an explanatory diagram showing the area to which the ink containing the coloring agent is applied in step 3 of Examples 1-5 and Comparative Examples 1-2. [Modes for carrying out the invention]

[0011] [Inkjet printing method] The present invention provides an inkjet printing method (hereinafter also referred to as "the printing method of the present invention") which includes a dark image forming section and a light image forming section, wherein the printing duty of the ink containing a colorant in the dark image forming section (hereinafter also referred to as "colorant-containing ink") is greater than the printing duty of the colorant-containing ink in the light image forming section, and the inkjet printing method provides an inkjet printing method for forming a printed image on a non-absorbent printing medium, Step 1: A step of performing corona treatment on the printing medium, Step 2: A step of applying a pretreatment solution to the outer edge portion of the area that will become the dense image forming portion of the printing medium obtained in Step 1 to obtain a printing medium having a pretreatment solution application portion, and Step 3: A step of applying a coloring agent-containing ink to the portion of the surface of the printing medium obtained in Step 2 that will become the dark image forming portion, using a line head type inkjet method. This is an inkjet printing method that includes [specific features / techniques]. In this invention, "printing" is a concept that includes printing and inscription that record characters and images. In this invention, whether or not a printing medium is non-absorbent is determined by the amount of water absorbed by the printing medium during a contact time of 100 milliseconds with pure water. This amount of water absorbed can be measured using an automatic scanning liquid absorber (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23°C and 50% relative humidity, as the amount of transfer during a contact time of 100 milliseconds with pure water. In this invention, "non-absorbent" means that the water absorption amount is 0 g / m². 2 More than 1g / m 2 This means that the following is true, and "low liquid absorption" means that the amount of water absorbed is 1 g / m². 2 Over 7g / m 2 This means the following:

[0012] The printing method of the present invention allows for the production of printed materials with excellent image quality, regardless of the type of printing medium, even when using a line-head type inkjet system with a non-absorbent printing medium. The reason for this is not entirely clear, but it is thought to be as follows. The printing method of the present invention includes a dark image forming section and a light image forming section, and a printed image is formed on a non-absorbent printing medium in which the printing duty of the colorant-containing ink in the dark image forming section is greater than the printing duty of the colorant-containing ink in the light image forming section. Step 1 includes a corona treatment process on a non-absorbent printing medium, thereby improving the wettability of the printing medium. Step 2 includes applying a pretreatment solution to the outer edge of the area that will become the dark image area of ​​the printing medium obtained in Step 1 to obtain a printing medium having a pretreatment solution application area, and Step 3 includes applying a colorant-containing ink to the dark image area of ​​the surface of the printing medium obtained in Step 2 that will become the dark image area using a line-head type inkjet method. By including contact between the pretreatment solution and the colorant-containing ink at the boundary between the outer edge of the dark image area to which the pretreatment solution is applied and the dark image area to which the colorant-containing ink is applied, the wetting spread of the ink is suppressed, and ink bleeding at the boundary between the light image area and the dark image area can be suppressed, resulting in a printed material with superior image quality. Thus, regardless of the type of printing medium, it is possible to improve wettability by corona treatment and suppress bleeding by applying a pretreatment solution, resulting in a printed material with superior image quality and increased versatility of the printing medium.

[0013] The present invention is an inkjet printing method comprising a dark image forming section and a light image forming section, wherein the printing duty cycle of the colorant-containing ink in the dark image forming section is greater than the printing duty cycle of the colorant-containing ink in the light image forming section, and a printed image is formed on a printing medium. In the present invention, "printing duty of colorant-containing ink" means the ratio of the area occupied by colorant-containing ink within a predetermined area on the printing medium, that is, the ratio of the cumulative area to which colorant-containing ink is applied. For example, in the present invention, "printing duty of colorant-containing ink 100%" means that when ink droplets are applied in a square grid pattern without thinning out the areas to which colorant-containing ink is applied, the distance between dots is such that the edges of adjacent ink dots that spread out in a circular shape on the printing medium touch at the circumferential position. For example, a dark image-forming area where "printing duty of colorant-containing ink" is 100% means a solid print area. On the other hand, in the present invention, "printing duty of colorant-containing ink 0%" means that no ink is applied at all within a predetermined area on the printing medium. For example, a light image-forming area where "printing duty of colorant-containing ink" is 0% means a non-printed area.

[0014] The printing duty of the colorant-containing ink in the dark image-forming area is preferably more than 50%, more preferably 70% or more, even more preferably 90% or more, and even more preferably 100%, from the viewpoint of clearly defining the contour of the dark image-forming area and forming a high-quality printed image. The printing duty of the colorant-containing ink in the faint image-forming area is 0% or more, preferably 50% or less, more preferably 30% or less, and even more preferably 10% or less, from the viewpoint of clearly defining the contours of the dark image-forming area and forming a high-quality printed image. The printing duty of the faint image-forming area may be set to 0% in order to obtain a printed image of cut-out characters. The difference between the printing duty cycle of the colorant-containing ink in the dark image-forming area and the printing duty cycle of the colorant-containing ink in the light image-forming area is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more, from the viewpoint of clearly defining the contour of the dark image-forming area and forming a high-quality printed image.

[0015] In the present invention, the printed images that are formed include cut-out letters, one-dimensional codes such as barcodes, matrix-type and stack-type two-dimensional codes, and images such as extremely small characters. In the present invention, the "image of missing characters" means an image in which a character can be recognized by a light image forming portion of a color other than the first color, with a dark image forming portion printed by inkjet printing with the first color as the background. At this time, the first color and the colors other than the first color may each be primary colors of yellow, magenta, cyan, and black, or may be a mixture of these primary colors, that is, secondary colors.

[0016] <Step 1> Step 1 is a step of performing corona treatment on a non-absorbent printing medium. As the corona treatment (also referred to as corona discharge treatment), there is a method of applying a high voltage of several thousand volts between a grounded metal roll and a wire-shaped electrode placed at a distance of several millimeters therefrom to generate corona discharge. By disposing the printing medium between the electrode and the roll during this corona discharge and discharging, the wettability of the image surface of the printing medium is improved. The corona treatment can be performed using a commercially available corona treatment apparatus. Examples of commercially available corona treatment apparatuses include, for example, the corona treatment apparatus (trade name: CTW-0212) manufactured by Wedge Co., Ltd. The amount of discharge treatment when performing corona treatment is the integrated irradiation power amount, and from the viewpoints of productivity and image quality, it is preferably 0.1 kW·min / m 2 or more, more preferably 0.3 kW·min / m 2 or more, still more preferably 0.5 kW·min / m 2 or more, and preferably 3.0 kW·min / m 2 or less, more preferably 2.0 kW·min / m 2 or less, still more preferably 1.5 kW·min / m 2 or less, even more preferably 1.0 kW·min / m 2 or less.

[0017] <Step 2> Step 2 is a step of obtaining a printing medium having a pretreatment liquid application portion by applying a pretreatment liquid to the outer edge portion of the portion that will become the dark image forming portion of the printing medium obtained in Step 1. In this invention, the outer edge portion of the area that forms the dark image-forming portion belongs to the light image-forming portion in the resulting printed image, as shown in Figure 1. From the viewpoint of improving the print quality of the resulting printed material, the outer edge portion of the area that forms the dark image formation area is preferably 0.01 mm or more, more preferably 0.1 mm or more, even more preferably 0.2 mm or more, and preferably 1 mm or less, more preferably 0.7 mm or less, and even more preferably 0.4 mm or less, on the side away from the dark image formation area, calculated from the boundary line between the dark image formation area and the light image formation area. The application of the pretreatment solution in step 2 is sufficient if it is applied to at least the outer edge portion of the area that will become the dark image forming portion of the printed image, or it may be applied to the entire light image forming portion including the outer edge portion of the area that will become the dark image forming portion. In the printing method of the present invention, the application of the pretreatment solution in the light image forming portion in step 2 is preferably limited to the outer edge portion of the area that will become the dark image forming portion, and more preferably limited to the outer edge portion of the area that will become the dark image forming portion if the printing duty of the colorant-containing ink in the light image forming portion is 0%. In step 2, if the printing duty of the colorant-containing ink in the faint image-forming area is greater than 0%, the pretreatment solution may be applied not only to the outer edge of the area that will become the dark image-forming area, but also to the area in the faint image-forming area where the colorant-containing ink is not applied. In this case, in step 3, which will be described later, the colorant-containing ink is applied to the area in the faint image-forming area of ​​the surface of the printing medium obtained in step 2 that has the pretreatment solution applied, using a line head type inkjet method. Furthermore, when the printing duty cycle of the colorant-containing ink in the faint image forming area is greater than 0%, the "area where colorant-containing ink is not applied" refers to the non-output area in the raster image data used for colorant-containing ink output. For example, when the printing duty cycle of the colorant-containing ink in the faint image forming area is 40%, the "area where colorant-containing ink is not applied" refers to the non-output area of ​​the colorant-containing ink that accounts for 60% of the raster image used for colorant-containing ink output in the faint image forming area.

[0018] In step 2, from the viewpoint of improving the image quality of the resulting printed material, it is preferable that (1) the pretreatment solution is not applied to the areas that will form a dense image, or (2) if it is applied to the areas that will form a dense image, the pretreatment solution is further applied to the inner edge portion of the areas that will form a dense image, and not applied to the areas that will form a dense image other than the inner edge portion. Among these, case (2) is more preferable because it can suppress misalignment between the area to which the pretreatment solution is applied in step 2 and the area to which the colorant-containing ink is deposited in step 3, thereby improving the image quality even for fine printed images. In the present invention, the inner edge portion of the area that forms the dense image forming portion belongs to the dense image forming portion in the formed printed image, as shown in Figure 2. In step 2, from the viewpoint of improving image quality, it is even more preferable to apply the pretreatment solution to both the outer edge portion and the inner edge portion of the area that will become the dense image forming area. From the viewpoint of further improving image quality, the inner edge portion of the area that forms the dark image is preferably 0.01 mm or more, more preferably 0.1 mm or more, even more preferably 0.2 mm or more, and preferably 1 mm or less, more preferably 0.7 mm or less, and even more preferably 0.4 mm or less, on the side away from the light image forming portion, calculated from the boundary line between the dark image forming portion and the light image forming portion.

[0019] (print media) Various non-absorbent printing media can be used as the printing medium in this invention. In this invention, the definition of "non-absorbent" is as described above. Examples of non-absorbent printing media include resin films. Specifically, these include polyester films such as polyethylene terephthalate (PET) film; polyamide films such as nylon (NY) film; polyvinyl chloride film; polypropylene (PP) film; and polyethylene (PE) film. The resin film may also be a stretched film, such as a stretched polyester film, a stretched nylon (ONY) film, or a stretched polypropylene (OPP) film. In addition, a stretched polypropylene (anti-fog OPP) film with an anti-fog agent coated on the film surface may be used as the resin film. The surface condition of anti-fog OPP film is different from that of ordinary OPP film, and even if the film material is the same, the wettability (print quality) may change significantly, similar to films of different materials. However, according to the printing method of the present invention, printed materials with excellent image quality similar to ordinary OPP film can be obtained. Preferably, it is at least one selected from the group consisting of polyester film, polyamide film, polyvinyl chloride film, polypropylene film, and polyethylene film, and more preferably, it is at least one selected from the group consisting of polyester film, polyamide film, and polypropylene film. As a printed image, the areas that will form a dark image and the areas that will form a light image may be determined based on a mirror image obtained by inverting the desired printed image, so that the desired image is formed when viewed from the opposite side of the printed image-forming surface of the non-absorbent film, and then step 2 may be performed.

[0020] (Pretreatment solution) <Ingredient (A) that suppresses the spreading of wetting> The pretreatment solution according to the present invention preferably contains a component (A) that suppresses the wetting and spreading of the colorant-containing ink used in step 3 on the printing medium (hereinafter also simply referred to as "component (A) that suppresses wetting and spreading"). The pretreatment solution according to the present invention contains a component (A) that suppresses wetting spread. Therefore, at the boundary between the outer edge of the dark image forming section to which the pretreatment solution is applied and the dark image forming section to which the colorant-containing ink is applied, the component (A) that suppresses wetting spread prevents the colorant-containing ink from entering the light image forming section. This suppresses ink bleeding at the boundary between the light image forming section and the dark image forming section, and is considered to improve the image quality including both the dark and light image forming sections. In the present invention, the component (A) that suppresses wetting is preferably one or more selected from the group consisting of cohesive compounds (A1) and hydrophobic compounds (A2). That is, the pretreatment liquid according to the present invention preferably contains one or more selected from the group consisting of cohesive compounds (A1) and hydrophobic compounds (A2). These will be explained below.

[0021] [Agglutinating compound (A1)] In the present invention, "aggregating compound (A1)" is a component that, when applied to a printing medium, causes aggregation due to a decrease in the dispersibility of the dispersed phase present in the colorant-containing ink, or a decrease in the solubility of the solute, thereby causing the ink to thicken or precipitate, and inhibiting the ink from entering the faint image-forming area. In the present invention, the dispersed phase present in the colorant-containing ink refers to ink components such as pigments that are currently dispersed in a solid state in the ink. The solute present in the colorant-containing ink refers to a component that is dissolved in the ink, but whose solubility is impaired when it comes into contact with a printing medium that has been treated with a pretreatment solution, causing it to thicken or precipitate. Specific examples of components (solutes) that are dissolved in the colorant-containing ink, but whose solubility is impaired when it comes into contact with a printing medium that has been treated with a pretreatment solution, causing it to thicken or precipitate, include dyes and water-soluble resins. Preferred examples of the cohesive compound (A1) include metal salts, acids or their salts, and cationic compounds. The cohesive compound (A1) may be used individually or in combination of two or more types. Examples of metal salts include monovalent metal salts and metal salts with two or more valents. Examples of acids include organic acids and inorganic acids. Examples of cationic compounds include cationic resins and cationic surfactants. Among these, the cohesive compound (A1) is more preferably one or more selected from the group consisting of metal salts, acids or salts thereof, and cationic resins.

[0022] (Metal salts) The metal salt used as the cohesive compound (A1) is preferably a polyvalent metal salt from the viewpoint of improving the image quality of the resulting printed material. Any polyvalent metal salt can be used as long as it is composed of a polyvalent metal ion with a valency of 2 or higher and an anion (counterion of the polyvalent metal ion). Examples of polyvalent metal ions with a valency of 2 or higher include calcium, magnesium, copper, nickel, zinc, barium, aluminum, titanium, strontium, chromium, cobalt, and iron. Among these, from the viewpoint of improving the image quality of the resulting printed material, a divalent or trivalent metal ion is preferred, and a divalent metal ion is more preferred. Examples of divalent metal ions include ions of elements belonging to group 2 of the periodic table, specifically magnesium ions, calcium ions, and iron(II) ions. Examples of trivalent metal ions include aluminum ions and iron(III) ions. Among these, from the viewpoint of improving the image quality of the resulting printed material, one or more selected from the group consisting of magnesium ions, calcium ions, and aluminum ions is even more preferred, one or more selected from the group consisting of magnesium ions and calcium ions is even more preferred, and calcium ions are even more preferred. Examples of anions in polyvalent metal salts include inorganic ions and organic ions. Examples of inorganic ions include monovalent anions such as nitrate ions and halide ions, and divalent anions such as sulfate ions. Examples of organic ions include organic acid ions such as carboxylate ions. Among these, the anion is preferably an inorganic ion, more preferably one or more selected from the group consisting of nitrate ions and sulfate ions, and even more preferably a nitrate ion.

[0023] The polyvalent metal salt is preferably one or more selected from the group consisting of magnesium nitrate, magnesium sulfate, calcium nitrate, and aluminum nitrate, more preferably one or more selected from the group consisting of magnesium nitrate, calcium nitrate, and aluminum nitrate, even more preferably one or more selected from the group consisting of magnesium nitrate and calcium nitrate, and even more preferably calcium nitrate. Polyvalent metal salts may have water of hydration in their raw material form. Polyvalent metal salts may be used individually or in combination of two or more types.

[0024] (acid) The acid used as the cohesive compound (A1) may be one or more selected from the group consisting of organic acids and inorganic acids. Examples of preferred organic acids include formic acid, acetic acid, glycolic acid, oxalic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, pyrrolidone carboxylic acid, pyrrone carboxylic acid, pyrrole carboxylic acid, furanic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, or derivatives of these compounds, or salts thereof. Preferred inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Among these, organic acids or their salts are preferred as acids. Acids may be used individually or in combination of two or more types. These acids may form salts, but if an acid forms a metal salt, it shall be included in the above list of metal salts.

[0025] (cationic resin) Cationic compounds used as the cohesive compound (A1) include cationic resins. It is preferable that the cationic resin has cationic groups. In the present invention, "cationic group" refers to a cationic group or a group that can be ionized to become a cationic group. Examples of cationic groups include basic groups such as primary amino groups (-NH2), secondary amino groups (-NHR, =NH (imino group)), tertiary amino groups (-NRR'), quaternary ammonium groups, and hydrazino groups. Among these, the cationic resin preferably has one or more selected from the group consisting of primary amino groups, secondary amino groups, tertiary amino groups, and quaternary ammonium groups, and more preferably has a quaternary ammonium group, from the viewpoint of improving the image quality of the resulting printed material. The basic group includes those neutralized by acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, maleic acid, fumaric acid, citric acid, tartaric acid, adipic acid, and lactic acid. Cationic resins may be used individually or in combination of two or more types.

[0026] From the viewpoint of improving the image quality of the resulting printed material, the cationicity of the cationic resin is preferably 0.5 meq / g or more, more preferably 3.0 meq / g or more, and preferably 10 meq / g or less. The cationicity of the cationic resin can be determined by colloidal titration using potassium polyvinyl sulfate reagent. Examples of cationic resins include cationic vinyl resins, cationic olefin resins, cationic urethane resins, and cationic amine resins.

[0027] Cationic vinyl resins include vinyl resins that contain constituent units derived from vinyl monomers having cationic groups. Suitable examples of vinyl monomers having cationic groups include alkyl (meth)acrylate quaternary ammonium salts such as (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxyethyltriethylammonium chloride, (meth)acryloyloxyethyldimethylbenzylammonium chloride, (meth)acryloyloxyethylmethylmorpholinoammonium chloride, and 2-hydroxy-3-(meth)acryloyloxypropyltrimethylammonium chloride; alkyl (meth)acryloylamide quaternary ammonium salts such as (meth)acryloylaminoethyltriethylammonium chloride and (meth)acryloylaminoethyldimethylbenzylammonium chloride; trimethyl[(vinylphenyl)methyl]ammonium chloride, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dipropylaminoethyl (meth)acrylate, and diisopropylaminoethyl (meth)acrylate. Examples include (meth)acrylic acid esters having a dialkylamino group, such as dibutylaminoethyl (meth)acrylate, diisobutylaminoethyl (meth)acrylate, and di-t-butylaminoethyl (meth)acrylate; (meth)acrylamides having a dialkylamino group, such as dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, dipropylaminopropyl (meth)acrylamide, diisopropylaminopropyl (meth)acrylamide, dibutylaminopropyl (meth)acrylamide, diisobutylaminopropyl (meth)acrylamide, and di-t-butylaminopropyl (meth)acrylamide; styrenes having a dialkylamino group, such as dimethylaminostyrene and dimethylaminomethylstyrene; amino group-containing heterocyclic vinyl monomers, such as N-vinylpyrrolidine, N-vinylpyrrolidone, and N-vinylcarbazole; and allylamine compounds, such as allylamine, dimethylallylamine, diallylamine, and methyldiallylamine.

[0028] Cationic vinyl resins may contain constituent units derived from monomers other than vinyl monomers having cationic groups. Examples of such other monomers include styrene monomers such as styrene and α-methylstyrene; alkyl group-containing (meth)acrylic monomers such as methyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; alkylene oxide chain-containing (meth)acrylic monomers such as (poly)ethylene glycol mono(meth)acrylate, (poly)propylene glycol mono(meth)acrylate, and (poly)(ethylene glycol-propylene glycol) mono(meth)acrylate; and aromatic ring-containing (meth)acrylic monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

[0029] Among these, the cationic vinyl resin is preferably a polyallylamine resin having a structure derived from an allylamine compound in its main skeleton. Examples of polyallylamine resins include homopolymers or copolymers of the allylamine compounds mentioned above. Specific examples of polyallylamine resins include polyallylamine hydrochloride, polyallylamine amide sulfate, allylamine hydrochloride / diallylamine hydrochloride copolymer, allylamine acetate / diallylamine acetate copolymer, allylamine acetate / diallylamine acetate copolymer, allylamine hydrochloride / dimethylallylamine hydrochloride copolymer, allylamine / dimethylallylamine copolymer, polydiallylamine hydrochloride, polymethyldiallylamine hydrochloride, polymethyldiallylamine amide sulfate, polymethyldiallylamine acetate, polydiallyldimethylammonium chloride, diallylamine acetate / sulfur dioxide copolymer, diallylmethylethylammonium ethyl sulfate / sulfur dioxide copolymer, methyldiallylamine hydrochloride / sulfur dioxide copolymer, diallyldimethylammonium chloride / sulfur dioxide copolymer, and diallyldimethylammonium chloride / acrylamide copolymer.

[0030] The cationic vinyl resin may be synthesized by known methods or may be a commercially available product. Examples of commercially available cationic vinyl resins include diallyldimethylammonium chloride polymers such as PAS-H-1L (manufactured by Nitto Boseki Medical Co., Ltd., trade name).

[0031] Cationic olefin resins have a basic framework of olefin-derived structural units such as ethylene and propylene, and known ones can be appropriately selected and used. Cationic olefin resins may also be used as emulsions dispersed in a medium containing water or organic solvents. Commercially available cationic olefin resins can be used. Examples of commercially available cationic olefin resins include Arrowbase CB-1200 and Arrowbase CD-1200 (both manufactured by Unitika Ltd., trade names).

[0032] Cationic urethane resins include those obtained by reacting the isocyanate groups of a urethane pre-resin, which is produced by a polyaddition reaction between an organic compound (polyol) having two or more alcoholic hydroxyl groups in one molecule and a polyisocyanate, with an active hydrogen compound for introducing cationic hydrophilic groups. In the aforementioned polyaddition reaction, chain extenders and reaction stoppers may be used in combination as needed. The molecular weight can be further increased by using chain extenders. Examples of chain extenders include polyols and polyamines, and examples of reaction stoppers include monoalcohols and monoamines. The cationic urethane resin is preferably used as an emulsion, and the emulsion may optionally contain a dispersant such as a surfactant. Preferred cationic urethane resins include cationic polycarbonate polyol-based urethane resins, cationic polyester polyol-based urethane resins, and cationic polyether polyol-based urethane resins. Commercially available cationic urethane resins can be used. Examples of commercially available cationic urethane resins that can be used include Hydran CP-7010, CP-7020, CP-7030, CP-7040, CP-7050, CP-7060, and CP-7610 (all manufactured by DIC Corporation, product names); Superflex 600, 610, 620, 630, 640, and 650 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product names); and Urethane Emulsion WBR-2120C and WBR-2122C (both manufactured by Taisei Fine Chemical Co., Ltd., product names).

[0033] Examples of cationic amine resins include polyamine resins and polyamide resins. Polyamine resins are resins that have amino groups in the main backbone of the resin. Examples of polyamine resins include polyalkyleneimines, polyethylene polyamines, condensates of alkylamines and epihalohydrins, and alkylamine / ammonia / epihalohydrin condensates. Polyamide resins are resins that have amide groups in the main skeleton of the resin.

[0034] Commercially available cationic amine resins can be used. Commercially available cationic amine resins include Unisense KHE103L (hexamethylenediamine / epichlorohydrin condensate), KHE104L (dimethylamine / epichlorohydrin condensate, aqueous solution with a solid content of 20% by mass) (both manufactured by Senka Co., Ltd., trade names); FL-14 (trade name manufactured by SNF Co., Ltd.); Arafix 100, 251S, 255, 255LOX (all manufactured by Arakawa Chemical Corporation, trade names); DK Modified polyamine resins such as 6810, DK6853, DK6885, polyamide epichlorohydrin resins or polyamine epichlorohydrin resins such as WS4010, WS4011, WS4020, WS4024, WS4027, WS4030 (all manufactured by Seikou PMC Co., Ltd., trade names); dimethylamine / ammonia / epichlorohydrin condensates such as Papiogen P-105 (manufactured by Senka Co., Ltd., trade name); Sumirez Examples include polyamide epoxy resins such as Resin650(30), 675A, 6615, and SLX-1 (all manufactured by Taoka Chemical Industry Co., Ltd., trade names); Catiomaster PD-1, PD-7 (dimethylamine / epichlorohydrin condensate), PD-30, PD-A, PDT-2, PE-10, PE-30 (dimethylamine / ethylenediamine / epichlorohydrin condensate), DT-EH, EPA-SK01 (polyamide polyamine / epichlorohydrin condensate), and TMHMDA-E (all manufactured by Yokkaichi Synthetic Co., Ltd., trade names); and Jetfix 36N, 38A, and 5052 (all manufactured by Satoda Chemical Co., Ltd., trade names).

[0035] (cationic surfactant) Cationic compounds used as the cohesive compound (A1) include cationic surfactants. In the present invention, "cationic surfactant" refers to a substance that has a hydrophobic group and a cationic group as a hydrophilic group, and does not have a repeating structure derived from a monomer. Preferred examples of the hydrophobic group of a cationic surfactant include alkyl groups having 10 to 22 carbon atoms. Examples of cationic surfactants include alkylamine salts and alkyl quaternary ammonium salts. Examples of alkylamine salts include alkylamine acetates such as laurylamine acetate and stearylamine acetate. Examples of alkyl quaternary ammonium salts include alkyltrimethylammonium salts, dialkyldialkylammonium salts, and alkylbenzyldimethylammonium salts. Among these, the cationic surfactant is preferably an alkyl quaternary ammonium salt, and more preferably an alkyltrimethylammonium chloride having an alkyl group with 10 to 22 carbon atoms.

[0036] [Hydrophobic compounds (A2)] In the present invention, "hydrophobic compound (A2)" refers to a compound containing a hydrophobic structure that does not cause thickening or precipitation of the colorant-containing ink, but at the boundary between the outer edge of the dark image-forming area to which the pretreatment solution is applied and the dark image-forming area to which the colorant-containing ink is applied, it is a component that suppresses the entry of the ink into the light image-forming area due to the low affinity for the ink caused by the hydrophobic structure. The hydrophobic compound (A2) is preferably one or more selected from the group consisting of anionic resins and hydrophobic surfactants.

[0037] (Anionic resin) The "anionic resin" used as the hydrophobic compound (A2) refers to an anionic resin that has been dried at 105°C for 2 hours to reach a constant weight, and when dissolved in 100g of water at 25°C until saturated, the amount dissolved is 10g or less. Furthermore, if the anionic resin has anionic groups and these anionic groups are neutralized by a neutralizing agent, the amount dissolved is determined by measuring the amount of the neutralizing agent in the presence of the neutralizing agent under conditions where the mass ratio of the anionic resin to the neutralizing agent is the same as that in the pretreatment solution. From the viewpoint of compatibility with the pretreatment solution and dispersion stability in the pretreatment solution, the anionic resin is preferably a resin having anionic groups. In the present invention, "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include carboxyl groups (-COOM), sulfonic acid groups (-SO3M), and phosphate groups (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, the anionic resin preferably has a carboxyl group as the anionic group, and M is preferably ammonium. Examples of anionic resins include anionic vinyl resins, anionic urethane resins, and anionic silicone resins. Anionic resins may be used individually or in combination of two or more types.

[0038] The anionic vinyl resin is preferably a vinyl resin that contains constituent units derived from vinyl monomers having anionic groups. Preferably, the vinyl monomer having anionic groups is one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid, and even more preferably acrylic acid.

[0039] The anionic vinyl resin may be either a homopolymer or a copolymer, but it is preferable that the vinyl resin further contains structural units derived from hydrophobic vinyl monomers in addition to structural units derived from vinyl monomers having anionic groups. Preferably, hydrophobic vinyl monomers include one or more selected from the group consisting of alkyl (meth)acrylates having a linear, branched, or cyclic alkyl group with 1 to 22 carbon atoms, aryl group-containing (meth)acrylates having an aryl group with 6 to 22 carbon atoms, and styrene monomers. Examples of alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms include, for example, alkyl (meth)acrylates having one or more linear or branched alkyl groups selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; and one or more cycloalkyl (meth)acrylates selected from the group consisting of cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate. Examples of preferred aryl group-containing (meth)acrylates having aryl groups with 6 to 22 carbon atoms include one or more selected from the group consisting of phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate. Preferably, the styrene monomer is one or more selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene. Among these, the hydrophobic vinyl monomer is more preferably one or more selected from the group consisting of alkyl (meth)acrylates, cycloalkyl (meth)acrylates, and styrene monomers having a linear or branched alkyl group with 1 to 8 carbon atoms, and even more preferably one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, cyclohexyl (meth)acrylate, styrene, and α-methylstyrene.

[0040] The content of vinyl monomers having anionic groups in the raw material monomers constituting the anionic vinyl resin, or the content of constituent units derived from vinyl monomers having anionic groups in the anionic vinyl resin, is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 36% by mass or less, and even more preferably 32% by mass or less. The content of hydrophobic vinyl monomers in the raw material monomers constituting the anionic vinyl resin, or the content of constituent units derived from hydrophobic vinyl monomers in the anionic vinyl resin, is preferably 60% by mass or more, more preferably 64% by mass or more, even more preferably 68% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0041] From the viewpoint of improving the image quality of the resulting printed material, anionic vinyl resins having a crosslinked structure are preferred. From the same viewpoint as above, as an anionic vinyl resin having a crosslinked structure, it is preferred to be obtained by reacting an anionic vinyl resin containing constituent units derived from vinyl monomers having anionic groups and constituent units derived from hydrophobic vinyl monomers with a crosslinking agent. In this case, the anionic vinyl resin having a crosslinked structure has a structure derived from the crosslinking agent in addition to the constituent units derived from vinyl monomers having anionic groups and constituent units derived from hydrophobic vinyl monomers. As a crosslinking agent, from the viewpoint of improving the image quality of the resulting printed material, polyglycidyl ether compounds of polyhydric alcohols having hydrocarbon groups with 3 to 8 carbon atoms are preferred, more preferably one or more selected from the group consisting of pentaerythritol polyglycidyl ether and trimethylolpropane polyglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether.

[0042] The crosslinking ratio of an anionic vinyl resin having a crosslinked structure is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 60 mol% or less. When an anionic vinyl resin having a crosslinked structure is obtained by reacting an anionic vinyl resin containing constituent units derived from vinyl monomers having anionic groups and constituent units derived from hydrophobic vinyl monomers with a crosslinking agent, the crosslinking ratio is calculated from the equivalent amount of anionic groups in the anionic vinyl resin before crosslinking and the equivalent amount of crosslinkable functional groups in the crosslinking agent, and is expressed as "molar equivalents of crosslinkable functional groups of the crosslinking agent / molar equivalents of anionic groups in the anionic vinyl resin before crosslinking".

[0043] The anionic vinyl resin may be synthesized as appropriate, or a commercially available product may be used. The anionic vinyl resin can be produced by copolymerizing the raw material monomers using a known polymerization method. Anionic vinyl resin is preferably used as a dispersion.

[0044] The acid value of the anionic vinyl resin is preferably 40 mg KOH / g or more, more preferably 80 mg KOH / g or more, even more preferably 100 mg KOH / g or more, even more preferably 120 mg KOH / g or more, and preferably 320 mg KOH / g or less, more preferably 280 mg KOH / g or less, even more preferably 240 mg KOH / g or less, and even more preferably 200 mg KOH / g or less. The weight-average molecular weight of the anionic vinyl resin is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and preferably 3,000,000 or less, more preferably 1,000,000 or less, and even more preferably 200,000 or less. The acid value and weight-average molecular weight of the anionic vinyl resin are measured by the method described in the examples. The acid value of the anionic vinyl resin can also be calculated from the mass ratio of the constituent monomers. If the anionic vinyl resin has a cross-linked structure, the acid value of the anionic vinyl resin can also be calculated from the mass ratio of the constituent monomers and the cross-linking agent.

[0045] Anionic urethane resin is a resin having structural units derived from organic compounds (polyols) having two or more alcoholic hydroxyl groups in one molecule, structural units derived from polyisocyanates, and structural units derived from dialkanolcarboxylic acids. Anionic urethane resin is obtained by polyaddition reactions of polyols, polyisocyanates, and dialkanolcarboxylic acids.

[0046] The polyol constituting the anionic urethane resin is not particularly limited as long as it is a compound having two or more alcoholic hydroxyl groups in one molecule. Polycarbonate polyols, polyester polyols, and polyether polyols are preferred, and polycarbonate polyols and polyester polyols are more preferred. In other words, the anionic urethane resin is preferably a polycarbonate-based polyurethane or a polyester-based polyurethane.

[0047] Polycarbonate polyols are compounds that can be obtained by reacting a carbonate compound with a diol; in other words, they are diols that have a carbonate structure. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, and diethylene carbonate. Examples of diols include aliphatic diols which may be substituted with lower alcohols; alicyclic diols such as cyclohexanediol and hydrogenated xylylene glycol; and aromatic diols such as xylylene glycol. Among these, aliphatic diols are preferred, and aliphatic diols with a carbon chain length of 4 to 9, such as 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, heptanediol, octanediol, and nonanediol, are more preferred.

[0048] Polyester polyols are compounds that can be obtained by condensing a low-molecular-weight diol with a dicarboxylic acid, i.e., diols having an ester structure. Examples of low molecular weight diols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and diols with 2 to 6 carbon atoms, such as 1,4-butanediol. Among these, ethylene glycol, propylene glycol, and 1,4-butanediol are preferred. Examples of dicarboxylic acids include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and brassic acid; and aromatic dibasic acids such as isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Among these, aliphatic dibasic acids are preferred, and dibasic acids with a methylene chain length of 4 to 8, such as adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, are more preferred.

[0049] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0050] Examples of polyisocyanates constituting anionic urethane resins include: chain-like aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; cyclic aliphatic diisocyanates such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aliphatic diisocyanates having aromatic rings such as xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic diisocyanates such as tolylene diisoanate and diphenylmethane diisocyanate; and modified products of these diisocyanates (modified products containing carbodiimide, uretodione, uretoimine, etc.). Among these, one or more selected from the group consisting of aliphatic diisocyanates and aromatic diisocyanates are preferred.

[0051] Examples of dialkanolcarboxylic acids that constitute anionic urethane resins include methylolbutanoic acid, methylolpropionic acid, and their salts.

[0052] Anionic urethane resins may be used in combination with chain extenders and reaction inhibitors as needed. The molecular weight can be further increased by using chain extenders. Examples of chain extenders include polyols and polyamines, while examples of reaction inhibitors include monoalcohols and monoamines. The anionic urethane resin is preferably used as an emulsion, and the emulsion may optionally contain a dispersant such as a surfactant.

[0053] The acid value of the anionic urethane resin is preferably 3 mg KOH / g or more, more preferably 5 mg KOH / g or more, even more preferably 7 mg KOH / g or more, and preferably 50 mg KOH / g or less, more preferably 40 mg KOH / g or less, and even more preferably 35 mg KOH / g or less.

[0054] Anionic silicone resin is a resin having a silicone structure and anionic groups in its resin structure. The silicone structure may be present in the main chain structure of the resin, or it may be present as a side chain of the resin. In the present invention, if an anionic resin has a polyurethane structure or a vinyl structure in addition to a silicone structure, it is classified as an anionic silicone resin if it has a silicone structure within its resin structure. Examples of commercially available anionic silicone resins include Charine FE-230N (silicone / acrylic graft polymerization type aqueous emulsion, acid value: 7.7 mg KOH / g), Charine FE-502 (silicone / acrylic graft polymerization type aqueous emulsion, acid value: 17.3 mg KOH / g), and Charine RU-911 (blend type (urethane compounded), acid value: 2.2 mg KOH / g), all manufactured by Nisshin Chemical Industry Co., Ltd.

[0055] The acid value of the anionic silicone resin is preferably 2 mg KOH / g or more, more preferably 4 mg KOH / g or more, even more preferably 6 mg KOH / g or more, and preferably 20 mg KOH / g or less, more preferably 10 mg KOH / g or less, and even more preferably 5 mg KOH / g or less.

[0056] (Hydrophobic surfactant) A "hydrophobic surfactant" used as a hydrophobic compound (A2) refers to a surfactant that does not form a single phase when mixed with ion-exchanged water in a mass ratio of 1:1 at 25°C. As the hydrophobic compound (A2), a nonionic hydrophobic surfactant is preferred. Preferably, one or more nonionic hydrophobic surfactants are selected from the group consisting of acetylene glycol-based surfactants and silicone-based surfactants. Acetylene glycol surfactants are diols or ethylene oxide (hereinafter also referred to as "EO") adducts of such diols, having a carbon-carbon triple bond in the center of their structure and hydroxyl groups on each carbon atom adjacent to the carbon-carbon triple bond. Acetylene glycol surfactants can be synthesized by reacting acetylene with a ketone or aldehyde corresponding to the desired acetylene glycol, for example, by the method described on pages 94-107 of "New Introduction to Surfactants" (revised edition) by Takehiko Fujimoto (published by Sanyo Chemical Industries, Ltd., 1992). The HLB value of the acetylene glycol-based surfactant is preferably 8 or less. Here, the HLB (Hydrophile-Lipophile Balance) value is a value that indicates the affinity of the surfactant for water and oil, and the HLB value of the acetylene glycol-based surfactant can be determined by the Griffin method using the following formula. HLB value = 20 × [(Total formula weight of hydrophilic groups contained in the surfactant) / (Molecular weight of the surfactant)] Examples of hydrophilic groups contained in surfactants include hydroxyl groups and ethyleneoxy groups. Preferred acetylene glycol-based surfactants include one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 2,5-dimethyl-3-hexyn-2,5-diol, and their EO adducts. Among these, one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol and its EO adducts are more preferred, one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol and those with an average EO addition number of 6 or less are even more preferred, and one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol, an EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol with an average of 1.3 moles, and an EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol with an average of 3 moles is even more preferred. Commercially available acetylene glycol-based surfactants include Surfinol 104PG-50 (2,4,7,9-tetramethyl-5-decine-4,7-diol, 50% propylene glycol solution with an average number of added moles of EO of 0, HLB value: 3.0 (calculation formula: 20 × (34 / 226))) and Surfinol 420 (an adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol with an average of 1.3 moles of EO, HLB value: 6.4 (calculation formula: 20 × ((34 + 44 × 1.3) / (226 + 44 × 1.3)))) from Nisshin Chemical Industry Co., Ltd. and Air Products & Chemicals.

[0057] Silicone-based surfactants have both a silicone structure and a hydrophilic structure, and a polyether group is an example of a hydrophilic structure. The HLB value of the silicone-based surfactant is preferably 7 or less. Here, the HLB value of the silicone-based surfactant can be the value listed in the catalog. Preferred commercially available silicone-based surfactants include KF-6015 (polyether-modified silicone (linear type), HLB value: 4.5 (catalog value)), KF-6017 (polyether-modified silicone (linear type), HLB value: 4.5 (catalog value)), KF-6028 (polyether-modified silicone (branched type), HLB value: 4.0 (catalog value)), KF-6038 (polyether-modified silicone (branched type, alkyl-comodified type), HLB value: 3.0 (catalog value)), and KF-6048 (polyether-modified silicone (linear type, alkyl-modified type), HLB value: 3.5 (catalog value)).

[0058] Among these, the pretreatment solution according to the present invention preferably contains one or more selected from the group consisting of metal salts, organic acids or their salts, cationic resins, anionic resins, and hydrophobic surfactants as a component (A) that suppresses wetting spread, more preferably contains one or more selected from the group consisting of metal salts, organic acids or their salts, cationic resins, and anionic resins, and even more preferably contains one or more selected from the group consisting of metal salts, organic acids or their salts, cationic resins, and anionic resins having a crosslinked structure.

[0059] <Organic solvent (B)> The pretreatment solution according to the present invention preferably further contains an organic solvent (B) from the viewpoint of improving the image quality of the resulting printed material. Organic solvent (B) can be used individually or in combination of two or more types. The static surface tension of organic solvent (B), measured at 25°C, is preferably 40 mN / m or less, more preferably 38 mN / m or less, and more preferably 18 mN / m or more, more preferably 20 mN / m or more, even more preferably 22 mN / m or more, and even more preferably 24 mN / m or more, from the viewpoint of improving the image quality of the resulting printed material. The static surface tension of organic solvent (B) at 25°C is measured by the method described in the examples. When two or more organic solvents are used as organic solvent (B), the static surface tension of organic solvent (B) is the weighted average value, weighted by the content (mass%) of each organic solvent.

[0060] The boiling point of the organic solvent (B) at atmospheric pressure is preferably 280°C or lower, more preferably 260°C or lower, and even more preferably 240°C or lower, from the viewpoint of promoting volatilization from the printing medium and improving the image quality of the resulting printed material. Furthermore, from the viewpoint of suppressing excessive acceleration of the volatilization rate and preventing the uneven distribution of components that suppress wetting, thereby improving the image quality of the resulting printed material, the boiling point is preferably 140°C or higher, more preferably 160°C or higher, and even more preferably 180°C or higher. When two or more organic solvents are used as organic solvent (B), the boiling point of organic solvent (B) is the weighted average value, weighted by the content (mass%) of each organic solvent.

[0061] Examples of organic solvents (B) include polyhydric alcohols; ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers; nitrogen-containing heterocyclic compounds; amides; amines; and sulfur-containing compounds. Among these, one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.

[0062] Examples of polyhydric alcohols include diols such as ethylene glycol, diethylene glycol, propylene glycol (1,2-propanediol), 1,3-propylene glycol, dipropylene glycol (isomer mixture), 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, triethylene glycol, polyethylene glycol, and polypropylene glycol.

[0063] Examples of polyhydric alcohol alkyl ethers include (poly)alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol dimethyl ether. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0064] Examples of nitrogen-containing heterocyclic compounds include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and ε-caprolactam. Examples of amides include formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide. Examples of amines include monoethanolamine, diethanolamine, triethanolamine, and triethylamine. Examples of sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol. Other organic solvents besides those mentioned above include, for example, propylene carbonate and ethylene carbonate.

[0065] 〔water〕 The pretreatment solution according to the present invention preferably further contains water. The pretreatment solution according to the present invention is preferably aqueous. The pretreatment solution according to the present invention is "aqueous" in the sense that water accounts for the largest proportion by mass of the liquid components contained in the pretreatment solution. The water should preferably be pure water or ultrapure water from which ionic impurities have been removed as much as possible, such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water.

[0066] The pretreatment solution according to the present invention may further contain other components as needed, such as surfactants other than the cationic surfactant and hydrophobic surfactant described above, pH adjusters, fixing aids, colorants, defoamers, antiseptics and antifungal agents, and rust inhibitors.

[0067] The pretreatment solution according to the present invention preferably further contains surfactants other than the cationic surfactant and hydrophobic surfactant described above. Other than the cationic and hydrophobic surfactants mentioned above, hydrophilic nonionic surfactants are preferred. In the present invention, "hydrophilic nonionic surfactant" refers to a surfactant that forms a single phase when mixed with ion-exchanged water in a mass ratio of 1:1 at 25°C. Examples of hydrophilic nonionic surfactants include hydrophilic polyoxyalkylene alkyl ether type surfactants, hydrophilic acetylene-based surfactants, hydrophilic polyhydric alcohol type surfactants, hydrophilic fatty acid alkanolamide type surfactants, hydrophilic silicone-based surfactants, and hydrophilic fluorine-based surfactants. Among these, one or more are preferably selected from the group consisting of hydrophilic acetylene-based surfactants and hydrophilic silicone-based surfactants. The HLB value of the hydrophilic acetylene-based surfactant is preferably greater than 8. Here, the HLB value of the hydrophilic acetylene-based surfactant can be determined from the above formula by the Griffin method. Examples of hydrophilic acetylene-based surfactants include one or more ethylene oxide (EO) adducts selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol. The average number of moles of EO added to the EO adduct (n) is preferably greater than 8, preferably 20 or less, and more preferably 10 or less. As hydrophilic silicone-based surfactants, polyether-modified silicone-based surfactants are preferred. Suitable polyether groups in polyether-modified silicone-based surfactants include, for example, polyethylene oxy groups, polypropylene oxy groups, and polyalkylene oxy groups in which ethylene oxy groups and propylene oxy groups (trimethylene oxy groups or propane-1,2-diyl oxy groups) are added in a block-like or random manner. Compounds in which polyether groups are grafted onto a silicone main chain, and compounds in which polyether groups are bonded in a block-like manner to both ends of a silicone main chain can be used. The HLB value of the hydrophilic silicone-based surfactant is preferably greater than 8. Here, the HLB value of the hydrophilic silicone-based surfactant can be the value listed in the catalog. Examples of commercially available hydrophilic nonionic surfactants include the "Surfinol" series from Nisshin Chemical Industry Co., Ltd. and Air Products & Chemicals, and the "KF" series from Shin-Etsu Chemical Co., Ltd. Hydrophilic nonionic surfactants can be used individually or in combination of two or more. Among these, it is preferable to use a hydrophilic acetyl glycol-based surfactant and a hydrophilic silicone-based surfactant in combination from the viewpoint of improving the image quality of the resulting printed material.

[0068] The pretreatment solution according to the present invention may contain a pH adjusting agent. A pH adjusting agent refers to an agent that suppresses pH fluctuations due to environmental changes and maintains a constant pH in the pretreatment solution. The pH adjusting agent can be arbitrarily selected from known agents depending on the pH of the pretreatment solution according to the present invention.

[0069] The pretreatment solution according to the present invention may contain a colorant, to the extent that it does not impair the effects of the present invention. Examples of such colorants include those used in the colorant-containing inks described later. When the pretreatment solution according to the present invention contains a colorant, from the viewpoint of water resistance, pigments and hydrophobic dyes are preferred as the colorant, and from the viewpoint of exhibiting high weather resistance, pigments are preferred.

[0070] [Composition of pretreatment solution] The content of component (A) that suppresses wetting in the pretreatment solution according to the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the image quality of the resulting printed material, and from the same viewpoint as above, preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0071] The content of the organic solvent (B) in the pretreatment solution according to the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more, from the viewpoint of improving the image quality of the resulting printed material, and also preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the same viewpoint as above.

[0072] The mass ratio of the content of the component that suppresses wetting spread (A) to the content of the organic solvent (B) in the pretreatment liquid according to the present invention [component that suppresses wetting spread (A) / organic solvent (B)] is preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.05 or more, and even more preferably 0.07 or more, from the viewpoint of improving the image quality of the resulting printed material, and also preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.3 or less, from the same viewpoint as above.

[0073] The water content in the pretreatment solution according to the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and even more preferably 70% by mass or less. Furthermore, when the polyvalent metal salt is used as a raw material in the form of a hydrate containing water of hydration, the water content in the pretreatment solution according to the present invention refers to the amount including the water content from the hydrate of the polyvalent metal salt.

[0074] When the pretreatment solution according to the present invention contains a hydrophilic nonionic surfactant, the content of the hydrophilic nonionic surfactant in the pretreatment solution is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The coloring agent content in the pretreatment solution according to the present invention is preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0% by mass.

[0075] The pretreatment solution according to the present invention is preferably prepared by appropriately mixing a component (A) that suppresses wetting spread, an organic solvent (B), and, if necessary, water or other components mentioned above. The pH of the pretreatment solution can be appropriately adjusted with the pH adjusting agent mentioned above.

[0076] From the viewpoint of improving the image quality of the resulting printed material, it is preferable to apply the pretreatment solution to the printing medium in a solid form, that is, to apply it so that the printing duty of the pretreatment solution becomes 100%. Here, "printing duty of pretreatment solution" refers to the ratio of the area occupied by the pretreatment solution within a predetermined area on the printing medium, that is, the ratio of the total area to which the pretreatment solution is applied. Preferred methods for applying the pretreatment solution to the printing medium include, for example, spraying, brushing, or using an inkjet method. Among these, the inkjet method is more preferred from the viewpoint of ease of adjusting the application position of the pretreatment solution and from the viewpoint of improving the image quality of the resulting printed material. As for the apparatus used to apply the pretreatment solution to the printing medium, from the viewpoint of being able to perform steps 2 and 3 continuously, it is preferable that the means for applying the pretreatment solution used in step 2 and the means for applying the colorant-containing ink used in step 3 are integrated, and it is even more preferable that a line head type inkjet system is used for both the means for applying the pretreatment solution used in step 2 and the means for applying the colorant-containing ink used in step 3.

[0077] From the viewpoint of improving the image quality of the printed material, the amount of the pretreatment solution applied to the printing medium is preferably 0.003 g / m². 2 In summary, a comfortable 0.01 g / m 2 More preferably 0.1 g / m 2Therefore, and from the same viewpoint as above, preferably 10 g / m 2 More preferably 5g / m 2 More preferably 1 g / m 2 More preferably, 0.5 g / m 2 The following applies: The amount of component (A) that suppresses wetting spread contained in the pretreatment solution applied to the printing medium is preferably 0.0001 g / m² from the viewpoint of improving the image quality of the printed material. 2 More precisely, 0.0005 g / m² 2 More preferably 0.001 g / m 2 Therefore, and from the same viewpoint as above, preferably 0.1 g / m 2 More preferably, 0.01 g / m 2 More preferably, 0.001 g / m 2 The following applies:

[0078] The printing method of the present invention preferably includes a step in step 2 in which a pretreatment solution is applied to the printing medium, and then the printing medium to which the pretreatment solution has been applied is kept at 25°C or higher. This step has the effect of removing volatile components in the pretreatment solution from the printing medium to which the pretreatment solution has been applied, and allows the printing medium to be dried (hereinafter, the step in step 2 in which the printing medium to which the pretreatment solution has been applied is kept at 25°C or higher will also be referred to as the "drying step of step 2"). This makes it possible to further improve the clarity of the printed image. In step 2, preferred methods for maintaining the printing medium to which the pretreatment solution has been applied at 25°C or higher include standing, blowing air, heating, and reducing pressure. In the printing method of the present invention, the application of active energy rays such as ultraviolet rays or radiation is not included in the drying step of step 2 of the present invention. The holding temperature of the printing medium in the drying step of step 2 is preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower, from the viewpoint of suppressing deformation of the printing medium, and preferably 25°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher, from the viewpoint of drying in a short time and further improving image quality. The duration for maintaining the holding temperature in the drying step of step 2 (holding time) is preferably 0.5 seconds or more, more preferably 1 second or more, even more preferably 1.5 seconds or more, and preferably 30 minutes or less, more preferably 20 minutes or less, even more preferably 10 minutes or less, and even more preferably 1 minute or less.

[0079] The drying rate of the pretreatment solution in the drying step of step 2, that is, the removal rate of volatile components in the pretreatment solution, is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 80% by mass or more, from the viewpoint of improving image quality. In the present invention, the "drying rate of the pretreatment solution" is the percentage of the ratio of the total mass of components actually removed by the drying process in step 2 to the total mass of components that can be removed by the drying process in step 2 contained in the pretreatment solution. It is calculated by the following formula, where M0 is the mass of the printing medium, M1 is the mass of the printing medium immediately after the pretreatment solution is applied in step 2, M2 is the mass of the printing medium after the step of holding the printing medium at 25°C or higher, and X is the percentage of the total mass of components that can be removed by the drying process in step 2 in the pretreatment solution. Drying rate (mass%) = (M1-M2) / [(M1-M0)×X / 100]×100 In the present invention, the percentage by mass of the total components that can be removed by the drying step of step 2 in the pretreatment solution is preferably the water content (mass%) in the pretreatment solution.

[0080] <Process 3> Step 3 is a step in which a coloring agent-containing ink is applied to the portion of the surface of the printing medium obtained in Step 2 that will become the dark image forming portion, using a line head type inkjet method. If the printing duty of the colorant-containing ink in the faint image forming area is 0%, it is preferable not to apply the colorant-containing ink to the faint image forming area in step 3. In other words, in this case, step 3 is preferably step 3-1 as described below. Step 3-1: A process in which a colorant-containing ink is applied using a line-head type inkjet method only to the areas that will form a dense image on the surface of the printing medium obtained in Step 2 that has a pre-treatment liquid applied area.

[0081] Furthermore, if the printing duty of the colorant-containing ink in the faint image-forming area is greater than 0%, in step 3, in addition to the area that will become the dark image-forming area on the surface of the printing medium obtained in step 2 that has the pretreatment liquid applied, the colorant-containing ink is also applied to the area that will become the faint image-forming area where the colorant-containing ink is applied. In other words, in this case, step 3 becomes step 3-2 as described below. Step 3-2: A step in which colorant-containing ink is applied to the areas of the surface of the printing medium obtained in Step 2 that will form a dark image and areas that will form a light image, using a line head type inkjet method.

[0082] (Ink containing colorants) The present invention describes an ink containing a coloring agent (coloring agent-containing ink). The colorant-containing ink according to the present invention is preferably one or more selected from the group consisting of black ink and chromatic ink.

[0083] [Coloring agents] In the colorant-containing ink according to the present invention, either dyes or pigments can be used as the colorant. Among these, it is preferable to use pigments as the colorant from the viewpoint of having water resistance, light resistance, weather resistance, gas resistance, etc. Any known organic or inorganic pigment can be used as the pigment. The pigment may be used individually or in combination of two or more types, or a mixed crystal may be used. Examples of inorganic pigments include titanium dioxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chromium yellow, and carbon black. Examples of organic pigments include azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinoflarone pigments, etc.), dye chelates (e.g., basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, and aniline black. Specific examples of pigments for black ink include carbon compounds such as lamp black (CI Pigment Black 6), furnace black, acetylene black, and channel black (CI Pigment Black 7); metals such as copper-chromium oxide (CI Pigment Black 28), iron oxide (CI Pigment Black 11), and titanium dioxide (CI Pigment Black 35); and organic pigments such as aniline black (CI Pigment Black 1). Specific examples of pigments for chromatic inks include, for example, one or more products for each product number selected from the group consisting of CI Pigment Yellow, CI Pigment Orange, CI Pigment Red, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green.

[0084] Examples of dyes, without particular limitations, include acid dyes, basic dyes, direct dyes, and reactive dyes. Dyes may be used individually or in combination of two or more types. Examples of the aforementioned dyes include each product number selected from the group consisting of CI Acid Yellow, CI Acid Red, CI Acid Blue, CI Acid Black, CI Food Black, CI Direct Yellow, CI Direct Red, CI Direct Blue, CI Direct Black, CI Reactive Red, and CI Reactive Black.

[0085] When a colorant-containing ink contains a pigment, the pigment is dispersed in a medium within the ink. Possible forms of the pigment in a colorant-containing ink include being dispersed with a resin (hereinafter also referred to as "pigment dispersion resin") or a surfactant as a dispersant, or being a self-dispersing pigment dispersed without the use of a dispersant. Among these, the form of the pigment in a colorant-containing ink dispersed with a pigment dispersion resin is preferred. The pigment dispersion resin may be either a water-soluble resin or a water-insoluble resin. Here, the "water-soluble" and "water-insoluble" properties of a resin are determined as follows: when a resin that has been dried at 105°C for 2 hours to reach a constant weight is dissolved in 100g of water at 25°C until saturation is reached, if the amount dissolved exceeds 10g, it is judged to be "water-soluble," and if it is 10g or less, it is judged to be "water-insoluble." Furthermore, as will be described later, if the resin has anionic groups, the amount dissolved is the amount measured when the neutralizing agent is present under conditions where the mass ratio of the resin to the neutralizing agent is the same as that of the colorant-containing ink.

[0086] Specifically, preferred forms of pigments in colorant-containing inks include, from the viewpoint of improving the dispersion stability of the pigment, (a) a form in which a water-soluble resin is adsorbed onto the surface of the pigment, (b) a form in which a water-soluble surfactant or a water-dispersible surfactant is adsorbed onto the surface of the pigment, (c) a form of self-dispersing pigment in which hydrophilic functional groups are chemically or physically introduced onto the surface of the pigment and dispersed without the use of pigment dispersion resin and surfactant, and (d) a form in which the pigment is coated with a water-insoluble resin.

[0087] The pigments having the forms (a) to (d) described above are preferably anionic. In form (a), the water-soluble resin preferably has anionic groups; in form (b), the water-soluble surfactant or water-dispersible surfactant preferably has anionic groups; in form (c), the hydrophilic functional group introduced on the pigment surface preferably has anionic groups; and in form (d), the water-insoluble resin preferably has anionic groups. The anionic group is defined as described for the anionic resin of the hydrophobic compound (A2). Examples of anionic groups include carboxyl groups (-COOM), sulfonic acid groups (-SO3M), and phosphate groups (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, the anionic resin preferably has a carboxyl group as the anionic group, and M is preferably an alkali metal.

[0088] Among these, the form of the pigment in the colorant-containing ink is preferably one or more forms selected from the group consisting of forms (c) and (d), and more preferably form (d), because if the component (A) containing the pretreatment solution that suppresses wetting spread is an agglomerating compound (A1), the dispersibility of the dispersed phase present in the ink can be reduced, thereby efficiently exhibiting an agglomerating effect, and if the component (A) containing the pretreatment solution that suppresses wetting spread is a hydrophobic compound (A2), the viscosity can be rapidly increased when the flow of the ink stops. From the viewpoint of improving the efficiency of preventing wetting spread and improving the image quality of the resulting printed material, it is preferable that the pigment is in one or more forms selected from the group consisting of forms (c) and (d). When the form of the pigment in the colorant-containing ink is form (d), the form in which the pigment is coated with a water-insoluble resin includes a form in which the water-insoluble resin encapsulates the pigment, a form in which the pigment is uniformly dispersed in the water-insoluble resin, a form in which the pigment is exposed from the surface of the water-insoluble resin particles, and a form in which the water-insoluble resin is adsorbed onto the pigment. When the pigment in the colorant-containing ink is in the form of (d), it is preferable that the pigment is coated with a water-insoluble resin having a crosslinked structure. In the form in which the pigment is coated with a water-insoluble resin having a crosslinked structure, it is preferable that the water-insoluble resin has a structure that includes a polymer component having a linear two-dimensional structure which may have branched chains, and a component derived from the crosslinking agent. In such a crosslinked structure, it is thought that the polymer having a linear two-dimensional structure which may have branched chains has a three-dimensional structure due to the component derived from the crosslinking agent.

[0089] [Pigment-dispersing resin] When the colorant-containing ink is in the form of (d), the type of water-insoluble resin used to disperse the pigment as the pigment dispersion resin of the colorant-containing ink is not particularly limited. Specific examples of water-insoluble resins include (meth)acrylic resins, styrene / (meth)acrylic resins, maleic acid resins, styrene / maleic acid resins, urethane resins, and polyester resins. Furthermore, when the form of the pigment in the colorant-containing ink is form (d) and the pigment is coated with a water-insoluble resin having a crosslinked structure, the constituent components of the polymer having a linear two-dimensional structure which may have branched chains are preferably one or more selected from the group consisting of (meth)acrylic resins, styrene / (meth)acrylic resins, urethane resins, and polyester resins, and more preferably one or more selected from the group consisting of (meth)acrylic resins and styrene / (meth)acrylic resins. The water-insoluble resin may be synthesized by known methods or a commercially available product may be used. The water-insoluble resin may be used alone or in combination of two or more types.

[0090] The number-average molecular weight of the pigment-dispersed resin is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The number-average molecular weight of the pigment-dispersed resin is measured by the method described in the examples. In the case where the colorant-containing ink is in the form of (d) and the pigment is coated with a water-insoluble resin having a crosslinked structure, the number-average molecular weight of the constituent components of the polymer having a linear two-dimensional structure which may have the aforementioned branched chains, of the water-insoluble resin used for dispersing the pigment as the pigment dispersion resin is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The acid value of the pigment dispersion resin is preferably 5 mg KOH / g or more, more preferably 50 mg KOH / g or more, even more preferably 70 mg KOH / g or more, and even more preferably 90 mg KOH / g or more, and preferably 800 mg KOH / g or less, more preferably 500 mg KOH / g or less, and even more preferably 300 mg KOH / g or less. The acid value of the pigment dispersion resin can be determined by the method described in the examples, but it can also be calculated from the mass ratio of the constituent monomers. If the pigment dispersion resin has a crosslinked structure, the acid value of the pigment dispersion resin can also be calculated from the mass ratio of the constituent monomers and the crosslinking agent.

[0091] [Fixing resin] Ink containing a colorant may contain a resin that functions as a fixing aid (hereinafter also referred to as "fixing resin") from the viewpoint of forming a high-quality printed image. The fixing resin in the colorant-containing ink is preferably in the form of a resin that does not coat the pigment, and more preferably in the form of resin particles that do not contain pigment. There are no particular restrictions on the fixing resin, and it can be appropriately selected according to the purpose. Specific examples of fixing resins include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene / butadiene resin, vinyl chloride resin, styrene / acrylic resin, and acrylic silicone resin. An ink can be obtained by mixing a resin in the form of particles, used as a fixing resin, with a colorant, water, an organic solvent, etc. The fixing resin may be a synthesized one or a commercially available one. The fixing resin may be used individually or in combination of two or more types.

[0092] 〔wax〕 Ink containing colorants may also contain wax from the viewpoint of forming high-quality printed images. In this specification, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid upon heating. Here, "semi-solid wax" means that the wax deforms and flows when force is applied, but can maintain a certain shape when no force is applied. Furthermore, the temperature at which wax becomes liquid upon heating, the so-called melting point of wax, is in the temperature range of 45°C or higher. The wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; plant-based waxes such as carnauba wax, candelilla wax, and rice wax; and animal-based waxes such as lanolin and beeswax. Examples of synthetic waxes include polyolefin waxes, synthetic hydrocarbon waxes such as Fischer-Tropsch waxes, silicone waxes, and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. Among these, polyolefin waxes, which mainly consist of olefin monomers, are preferred. Waxes can be used individually or in combination of two or more types.

[0093] Ink containing a colorant preferably contains wax as a dispersion (hereinafter also referred to as "wax dispersion"). There are no particular restrictions on the wax dispersion; for example, one may be obtained by emulsifying wax with a known surfactant. As the surfactant, nonionic surfactants, anionic surfactants, etc., can be used. Examples of nonionic surfactants include ethylene oxide adducts of higher alcohols and ethylene oxide adducts of alkylated phenols. Examples of anionic surfactants include sulfate ester salts and phosphate ester salts based on ethylene oxide adducts of higher alcohols; alkylated benzenesulfonates, etc. Among these, a nonionic wax dispersion obtained by emulsifying wax with a nonionic surfactant is preferred, and a nonionic polyolefin wax dispersion is more preferred, from the viewpoint of improving ink ejection stability and image fastness of printed materials. Suitable examples of commercially available wax dispersions include the "Hi-Tec E" series from Toho Chemical Industry Co., Ltd., the "AQUACER" series from BYK Corporation, the "Cerosol" series from Chukyo Oil & Fat Co., Ltd., and the "Chemipearl" series from Mitsui Chemicals, Inc.

[0094] 〔water〕 The medium for the colorant-containing ink is preferably an aqueous medium. That is, the colorant-containing ink is preferably an aqueous ink containing water. Here, "water-based" means that in the medium of the colorant-containing ink, water accounts for the largest proportion by mass. The water contained in the colorant-containing ink is preferably deionized water, ultrafiltered water, reverse osmosis water, or distilled water.

[0095] [Water-soluble organic solvents] The colorant-containing ink may further contain a water-soluble organic solvent as an aqueous medium. Examples of water-soluble organic solvents contained in the ink include polyhydric alcohols; ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers; nitrogen-containing heterocyclic compounds; amides; amines; sulfur-containing compounds, etc. Furthermore, from an environmental viewpoint, the water content in the aqueous medium of the colorant-containing ink is preferably 51% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0096] The colorant-containing ink may also contain surfactants, defoamers, preservatives, fungicides, rust inhibitors, pH adjusters, etc., as needed.

[0097] [Composition of ink containing colorants] From the viewpoint of improving the image density of printed materials, the amount of colorant in the colorant-containing ink is preferably 2% by mass or more, more preferably 3% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When a colorant-containing ink contains a pigment as a colorant, the pigment content in the ink is preferably 2% by mass or more, more preferably 3% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving the image density of the printed material. When a colorant-containing ink contains a pigment-dispersing resin, the amount of pigment-dispersing resin in the ink is preferably 2% by mass or more, more preferably 4% by mass or more, from the viewpoint of pigment dispersion stability and forming a high-quality printed image, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving the image density of the printed material. When a colorant-containing ink contains a pigment-dispersing resin, the mass ratio of the pigment content to the pigment-dispersing resin content in the ink [pigment / pigment-dispersing resin] is preferably 0.30 or higher, more preferably 0.50 or higher, and even more preferably 0.70 or higher, from the viewpoint of improving the image density of the printed material, and preferably 1.00 or lower, more preferably 0.90 or lower, and even more preferably 0.80 or lower, from the viewpoint of the dispersion stability of the pigment and the formation of a high-quality printed image. When a colorant-containing ink contains a fixing resin, the content of the fixing resin in the ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of forming a high-quality printed image, and preferably 10% by mass or less, and more preferably 7% by mass or less, from the viewpoint of improving the image density of the printed material. When a colorant-containing ink contains wax, the wax content in the ink is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, and preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of forming a high-quality printed image. When the colorant-containing ink contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the ink is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of forming a high-quality printed image. From an environmental standpoint, the water content in the colorant-containing ink is preferably 30% by mass or more, more preferably 33% by mass or more, even more preferably 35% by mass or more, and even more preferably 37% by mass or more, and preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less.

[0098] (Line head type inkjet method) The inkjet method used in the printing method of the present invention is performed using a line head type print head. Line head type print heads are equipped with a head that can inkjet print on a width equal to or greater than the length perpendicular to the transport direction of the printing medium. Therefore, high-speed printing is possible because only the printing medium is scanned while the print head remains fixed. A line-head type print head may consist of multiple individual heads arranged in a line. Preferably, a line-head type print head is provided for each color of the colorant-containing ink.

[0099] From the viewpoint of forming a high-quality printed image, the nozzle spacing of a line-head type print head is preferably 120 npi or more, more preferably 180 npi or more, even more preferably 300 npi or more, and even more preferably 800 npi or more. From the same viewpoint, it is preferably 6000 npi or less, more preferably 3600 npi or less, even more preferably 2400 npi or less, and even more preferably 1600 npi or less. In this invention, the unit "npi" which indicates the spacing between nozzles of a line-head type print head means the number of nozzles per inch in the longitudinal direction of the nozzle row of the print head.

[0100] There are various methods for ejecting print heads, but in the printing method of the present invention, either a piezoelectric method using a piezoelectric element or a thermal method using a heat element may be used. Among these, the piezoelectric method is preferred from the viewpoint of forming a high-quality printed image.

[0101] In the present invention, the transport speed of the printing medium is preferably 10 m / min or more, more preferably 15 m / min or more, and even more preferably 20 m / min or more, from the viewpoint of efficiently obtaining printed materials, and preferably 100 m / min or less, more preferably 80 m / min or less, and even more preferably 60 m / min or less, from the viewpoint of forming high-quality printed images.

[0102] In the present invention, the amount of colorant-containing ink droplets dispensed is preferably 1 pL or more, more preferably 1.5 pL or more, even more preferably 2 pL or more, and preferably 15 pL or less, more preferably 10 pL or less, even more preferably 7.5 pL or less, and even more preferably 5 pL or less, from the viewpoint of forming a high-quality printed image. Here, "pL (picoliters)" is 10 times "L (liters)". -12 It means... The amount of ink droplets containing colorants ejected can be set using the inkjet head control device.

[0103] In the present invention, the resolution in the direction parallel to the transport direction of the printing medium, so-called ink dot density on the printing medium, is preferably 600 dpi or more, more preferably 800 dpi or more, even more preferably 1000 dpi or more, and, from the same viewpoint as above, preferably 3600 dpi or less, more preferably 2400 dpi or less, even more preferably 1800 dpi or less, and even more preferably 1200 dpi or less. In the present invention, the resolution in the direction perpendicular to the transport direction of the printing medium, so-called ink dot density on the printing medium, is preferably 600 dpi or more, more preferably 800 dpi or more, even more preferably 1000 dpi or more, and, from the same viewpoint as above, preferably 3600 dpi or less, more preferably 2400 dpi or less, even more preferably 1800 dpi or less, and even more preferably 1200 dpi or less. In this invention, the unit "dpi" indicating resolution means the number of ink dots per inch in a direction parallel or perpendicular to the transport direction of the printing medium. If the resolution differs for each ink color, the resolution with the highest resolution will be considered the resolution in this invention.

[0104] In the present invention, the diameter of the ink dots that land on the printing medium (hereinafter also simply referred to as "ink dot diameter") is preferably 20 μm or more, more preferably 23 μm or more, and even more preferably 25 μm or more, from the viewpoint of forming a high-quality printed image, and from the same viewpoint as above, preferably 60 μm or less, more preferably 55 μm or less, and even more preferably 50 μm or less. As described in the examples, the diameter of an ink dot that lands on a printing medium can be determined by observing 10 ink dots on the printing medium after ink has been applied by inkjet printing under a microscope and taking the average value as the diameter of the ink dot.

[0105] In step 3, the amount of colorant-containing ink applied to the area that will form a dense image is preferably 1 g / m², from the viewpoint of improving the image quality of the resulting printed material. 2Above, a comfortable 3g / m 2 More preferably 4.5 g / m 2 Therefore, and from the same viewpoint as above, preferably 10 g / m 2 More preferably 7 g / m 2 More preferably 5 g / m 2 The following applies:

[0106] <Step 4> In the present invention, from the viewpoint of clarifying the contour of the dark image forming area and forming a high-quality printed image, it is preferable to further include step 4, which involves applying a white ink containing a white pigment (hereinafter also simply referred to as "white ink") to a printing medium or to a surface of the printing medium to which a colorant-containing ink has been applied, either before step 2 or after step 3. If step 4 is further included, it is preferable to apply white ink to the side of the printing medium opposite to the side to which the colorant-containing ink has been applied (i.e., the printing medium) or to the side of the printing medium to which the colorant-containing ink has been applied, after step 3. When a resin film is used as a non-absorbent printing medium, and the desired printed image is to be a mirror image of the printed image, inverted from the printed image-forming surface of the non-absorbent film, it is preferable to apply step 4 to the entire surface of the printed medium to which the colorant-containing ink has been applied.

[0107] Examples of white inorganic pigments for white ink include titanium dioxide, zinc oxide, zinc sulfide, antimony oxide, and zirconium oxide. However, from the viewpoint of increasing whiteness and improving the sharpness of cut-out letters, one or more selected from the group consisting of titanium dioxide and zinc oxide are preferred, and titanium dioxide (CI Pigment White 6) is more preferred. While untreated titanium dioxide can be used, surface-treated titanium dioxide is preferred from the viewpoint of obtaining good dispersibility. Surface treatments for titanium dioxide include surface treatment with inorganic substances, or surface treatment with organic substances such as titanium coupling agents, silane coupling agents, and silicone oil, but surface treatment with inorganic substances is preferred.

[0108] In the present invention, the white pigment is dispersed in a medium in the white ink. The form of the white pigment in the white ink may be a form in which it is dispersed with the aforementioned pigment dispersion resin or surfactant as a dispersant, or a form of a self-dispersing pigment dispersed without the use of a dispersant. Among these, the form in which the pigment is dispersed with a pigment dispersion resin is preferred. The pigment dispersion resin is preferably the same as the resin exemplified in the aforementioned colorant-containing ink. The white ink may also further contain the aforementioned fixing resin.

[0109] The medium for the white ink is preferably an aqueous medium. That is, the white ink is preferably an aqueous ink containing water. Here, "water-based" means that water makes up the largest proportion by mass in the white ink medium. The water contained in the white ink is preferably deionized water, ultrafiltered water, reverse osmosis water, or distilled water. Furthermore, white ink may also contain, as necessary, wax, water-soluble organic solvents, surfactants, defoamers, preservatives and antifungal agents, rust inhibitors, pH adjusters, etc. Furthermore, the preferred range for the content of each component, such as white pigment, in the white ink is the same as the preferred range for the content of each component, such as colorants, in the colorant-containing ink mentioned above.

[0110] Methods for applying white ink in step 4 include, for example, application by roller, application by spray, application by brush, and application by inkjet method. Among these, from the viewpoint of being able to apply white ink simply and uniformly, one selected from the group consisting of roller coating and inkjet coating is preferred. Specific examples of rollers used for coating with rollers include offset gravure coaters, gravure coaters, doctor coaters, bar coaters, blade coaters, flexo coaters, and roll coaters. Among these, one or more selected from the group consisting of doctor coaters, bar coaters, and roll coaters are preferred. As a specific example of coating using an inkjet method, a line-type inkjet method is preferred. Furthermore, from the viewpoint of enabling steps 2, 3, and 4 to be carried out continuously, it is preferable that the apparatus for applying white ink to the printing medium or printed image forming surface in step 4 is integrated with the means for applying the pretreatment liquid used in step 2 and the means for applying the colorant-containing ink used in step 3. In this case, for example, the inkjet printing apparatus may have a means for applying white ink, such as a roller applicator, incorporated into it, or the inkjet printing apparatus may have an inkjet head for applying white ink incorporated into it.

[0111] In step 4, the amount of white ink applied to the printing medium is preferably 1 g / m², from the viewpoint of forming a high-quality printed image. 2 Above, a comfortable 5g / m 2 More preferably 10 g / m 2 Therefore, and from the same viewpoint as above, preferably 50 g / m 2 More preferably 30g / m 2 More preferably, 15 g / m 2 The following applies:

[0112] If the printing method of the present invention includes step 4, it is preferable that step 4 includes a step of applying white ink to a printing medium or a surface of the printing medium coated with a colorant-containing ink, and then holding the printing medium coated with the white ink at 25°C or higher, from the viewpoint of forming a high-quality printed image. This step has the effect of removing volatile components in the white ink from the printing medium or printed material to which the white ink has been applied, and can dry the printing medium or printed material (hereinafter, the step of holding the printing medium coated with white ink at 25°C or higher in step 4 is also referred to as the "drying step of step 4"). In step 4, methods for maintaining the printing medium coated with white ink at 25°C or higher include standing, blowing air, heating, and reducing pressure. In the printing method of the present invention, the application of active energy rays such as ultraviolet rays or radiation is not included in the drying step of step 4 of the present invention. The holding temperature of the printing medium in the drying step of step 4 is preferably 120°C or lower, more preferably 100°C or lower, even more preferably 90°C or lower, and even more preferably 80°C or lower, from the viewpoint of suppressing deformation of the printing medium, and preferably 25°C or higher, more preferably 30°C or higher, from the viewpoint of drying in a short time. The duration for maintaining the holding temperature in the drying step of step 4 (holding time) is preferably 0.5 seconds or more, more preferably 1 second or more, even more preferably 3 seconds or more, and even more preferably 5 seconds or more, and preferably 30 minutes or less, more preferably 20 minutes or less, even more preferably 10 minutes or less, and even more preferably 1 minute or less. [Examples]

[0113] In the following preparation examples, manufacturing examples, examples, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement methods for each physical property are as follows. The physical properties of resins and other materials were measured using the following method.

[0114] [Measurement of number-average molecular weight and weight-average molecular weight of resins] The results were obtained by gel permeation chromatography. The measurement conditions are shown below. GPC device: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation. Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of resin was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter "DISMIC-13HP" (PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.). The number-average molecular weight or weight-average molecular weight of the resin was then calculated.

[0115] [Measurement of the acid value of resins] Using a potentiometric automatic titrator (manufactured by Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), for resins without a cross-linked structure, the resin was dissolved in a titration solvent of toluene and acetone (2:1). For resins with a cross-linked structure, the resin was dispersed in the titration solvent and titrated with a 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the endpoint. The acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution titrated to the endpoint.

[0116] [Measurement of solid content concentration] 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm). Approximately 1.0 g of the sample was added and mixed, then accurately weighed and maintained at 105°C for 2 hours to remove volatile components. After standing in the desiccator for another 15 minutes, the mass was measured. The mass of the sample after removal of volatile components was taken as the solid content, and the solid content concentration (%) was obtained by dividing it by the mass of the added sample.

[0117] [Measurement of average particle size of resin particles without pigment and resin particles containing pigment] Cumulant analysis was performed using the laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was taken as the average particle size of resin particles without pigment or resin particles containing pigment. The measurement sample had a particle concentration of 5 × 10⁻⁶ -3 A dispersion solution diluted with water to a concentration of % (converted to solid content) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion medium.

[0118] [Measurement of static surface tension of organic solvent (B) at 25°C] A platinum plate was immersed in a cylindrical polyethylene container (3.6 cm in diameter x 1.2 cm in depth) containing 5 g of sample adjusted to 25°C, and the static surface tension at 25°C was measured using the Wilhelmi method with a surface tensimeter (Kyowa Interface Chemical Co., Ltd., "CBVP-Z").

[0119] Manufacturing Example 1 (Manufacturing of Acrylic Acid / Styrene Resin) A monomer mixture was prepared by mixing 31 parts acrylic acid and 69 parts styrene. Ten parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.2 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the monomer mixture were added to the reaction vessel and mixed, and the vessel was thoroughly purged with nitrogen gas. Meanwhile, a mixture of the remaining monomer mixture (90% of the monomer mixture), 0.13 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo radical polymerization initiator was placed in a dropping funnel. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C following the completion of the dropwise addition, a solution of 0.1 parts of the polymerization initiator dissolved in 2 parts of MEK was added, and the mixture was aged for a further 2 hours at 65°C and 2 hours at 70°C before being dried under reduced pressure to obtain acrylic acid / styrene resin (number average molecular weight: 19,000, acid value: 240 mg KOH / g).

[0120] Manufacturing Example 2 (Production of aqueous dispersion of cross-linked acrylic acid / styrene resin) 15.3 parts of the acrylic acid / styrene resin obtained in Production Example 1 were mixed with 63.5 parts of deionized water, and then 1.8 parts of 25% aqueous ammonia were added to neutralize the mixture so that the ratio of moles of ammonia to moles of carboxyl groups in the acrylic acid / styrene resin was 40% (degree of neutralization: 40 mol%). The mixture was heated to 90°C using a warm bath and stirred for 1 hour to disperse the acrylic acid / styrene resin in water, and then cooled to room temperature (25°C) to obtain a dispersion of acrylic acid / styrene resin. To the obtained acrylic acid / styrene resin dispersion, 4.6 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321LT, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) was added as a crosslinking agent, the container was sealed, and the mixture was heated at 90°C for 1.5 hours while stirring with a stirrer. At this time, the crosslinking treatment was performed using an amount of crosslinking agent that could react with 50% of the total number of carboxyl groups contained in the acrylic acid / styrene resin (crosslinking rate: 50%). After that, the dispersion was cooled to room temperature (25°C), filtered using a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a 5 μm pore size membrane filter (Minisart, manufactured by Sartorius, material: cellulose acetate), and deionized water was added to adjust the solid content concentration to 20% to obtain an aqueous dispersion of crosslinked acrylic acid / styrene resin (acid value: 120 mg KOH / g).

[0121] Preparation Examples 1-4 Each component of the pretreatment solution was added to a container equipped with a stirrer according to the formulation shown in Table 1, mixed at 25°C for 1 hour, and then filtered using a 5 μm pore size membrane filter and a needleless syringe to obtain each pretreatment solution. The components shown in Table 1 are as follows: <Ingredient (A) that suppresses the spreading of wetting> [Agglutinating compound (A1)] (cationic resin) Cationic vinyl resin A1-1: Aqueous solution of polydiallyldimethylammonium chloride (solid content 28% by mass), manufactured by Nitto Boseki Medical Co., Ltd., product name "PAS-H-1L", weight-average molecular weight: 8,500 (catalog value) (Metal salts) Calcium nitrate: Calcium nitrate tetrahydrate (Reagent manufactured by Tokyo Chemical Industry Co., Ltd.) Note that the amounts of calcium nitrate shown in Table 1 are for the anhydrous form. (organic acid) Malonic acid: (Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0122] [Hydrophobic compounds (A2)] (Anionic resin) Anionic vinyl resin A2-1: Aqueous dispersion of crosslinked acrylic acid / styrene resin (acid value: 120 mg KOH / g) obtained in Production Example 2 (solids content concentration: 20%)

[0123] <Organic solvent (B)> Diethylene glycol monobutyl ether: (Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., static surface tension at 25°C: 26.2 mN / m) Propylene glycol: (Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., static surface tension at 25°C: 36.0 mN / m) (Hydrophilic nonionic surfactant) Surfinol 465: Manufactured by Nisshin Chemical Industry Co., Ltd. "Surfinol 465" (an average of 10 moles of EO adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol, HLB value: 14.2 (calculation formula: 20 × ((34 + 44 × 10) / (226 + 44 × 10)))) KF-6011: "KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd. (PEG-11 methyl ether dimethicone (side-chain polyether modified linear silicone), HLB value: 14.5 (catalog value))

[0124] [Table 1]

[0125] Manufacturing Example 3 (Production of an aqueous dispersion of cross-linked resin particles containing black pigment) 100 parts of the acrylic acid / styrene resin obtained in Production Example 1 were mixed with 78.6 parts of MEK, and then 41.2 parts of a 5N sodium hydroxide aqueous solution (sodium hydroxide content: 16.9%) were added as a neutralizing agent to neutralize the mixture (degree of neutralization: 40 mol%). 800 parts of deionized water were then added, and 100 parts of black pigment (CB, CI Pigment Black 7, Cabot Chemicals "Monarch 717") were added to the mixture. The mixture was then stirred for 60 minutes at 20°C with the disperser blades rotating at 7000 rpm using a disperser (Asada Iron Works Co., Ltd. "Ultra Disperser"). The resulting mixture was then dispersed in 10 passes at a pressure of 200 MPa using a microfluidizer (Microfluidics, trade name). Next, 250 parts of deionized water were added to the obtained dispersion, and after stirring, MEK was removed under reduced pressure at 60°C. Further removal of some water until the pigment concentration was 10%, then 35.7 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) were added as a crosslinking agent, the container was sealed, and heated at 70°C for 5 hours while stirring with a stirrer. After cooling to room temperature (25°C), an aqueous dispersion of crosslinked resin particles containing black pigment (crosslinking rate: 60 mol%) was obtained (solid content concentration: 23.4%, pigment content: 9.7%, acid value: 96 mg KOH / g (calculated value)).

[0126] Manufacturing Example 4 (Production of an aqueous dispersion of resin particles without pigments) In a reaction vessel equipped with a dropping funnel, the monomers shown in "Initial Monomer Solution" in Table 2, sodium polyoxyethylene alkyl ether sulfate (Latemul E-118B, manufactured by Kao Corporation) as a surfactant (hereinafter referred to as "Latemul E-118B"), potassium persulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and deionized water were added and mixed, and the mixture was purged with nitrogen gas to obtain the initial monomer solution. In addition, the monomers, surfactant, polymerization initiator, and deionized water shown in "Dropping Monomer Solution" in Table 2 were mixed to obtain the dropping monomer solution, which was then placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was heated from room temperature (25°C) to 80°C over 30 minutes while stirring. While maintaining the temperature at 80°C, the monomer from the dropping funnel was gradually added to the reaction vessel over 3 hours. After the addition was complete, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. The mixture was then filtered through a 200-mesh filter to obtain an aqueous dispersion of resin particles without pigment (solid content: 44.1%, average particle size: 94 nm). The weight-average molecular weight of the resin constituting the pigment-free resin particles was 750,000, and the acid value was 16 mgKOH / g.

[0127] [Table 2]

[0128] Manufacturing Example 5 (Manufacturing of Black Ink Bk1) 33.0 parts of an aqueous dispersion of cross-linked resin particles containing the black pigment obtained in Production Example 3 (solids concentration: 23.4%, pigment content: 9.7%), 11.3 parts of an aqueous dispersion of resin particles without pigment obtained in Production Example 4 (solids concentration: 44.1%), 11.5 parts of propylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 3.5 parts of diethylene glycol monoisobutyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and a polyether-modified silicone surfactant ("Sylface SAG005" manufactured by Nisshin Chemical Industry Co., Ltd., HLB value: 7 (catalog value), kinematic viscosity: 170 mmHg). 2 0.2 parts of (25℃) and 1.0 part of acetylene glycol surfactant (Surfinol 104PG-50 manufactured by Nisshin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol, effective content: 50%, HLB value: 3.0 (calculation formula: 20 × (34 / 226))) were added to deionized water to a total volume of 100 parts. The resulting mixture was filtered using the membrane filter and a needleless syringe to obtain black ink Bk1.

[0129] Manufacturing Example 6 (Production of an aqueous dispersion of resin particles containing a white pigment) 2500g of polyacrylic acid (Aron A-10SL, manufactured by Toagosei Co., Ltd., weight-average molecular weight: 6,000, acid value: 735 mgKOH / g, solid content concentration: 40%) and 3.57g of deionized water were added to a 5L plastic container. The container was cooled in an ice bath, and 1666.43g of 5N sodium hydroxide aqueous solution was slowly added while stirring the solution at 100 rpm to neutralize it. Deionized water was added to the neutralized aqueous solution to adjust the solid content concentration to 20% to obtain a neutralized aqueous solution of polyacrylic acid (degree of neutralization: 53 mol%, acid value: 735 mgKOH / g). Next, 33.0 g of a neutralized aqueous solution of polyacrylic acid (solid content concentration: 20%), 300 g of titanium dioxide (Ishihara Sangyo Co., Ltd. "Typake CR-80", CI Pigment White 6, rutile type, Al-Si treated, average particle size: 250 nm (catalog value)) as a white pigment, and 300 g of water were added to a 2 L poly container (Nikko Hansen J Bottle Round Wide Mouth Natural). Then, 1000 g of zirconia beads were added, and the mixture was dispersed for 8 hours on a tabletop pot mill stand (AS ONE Corporation). The zirconia beads were removed using a metal mesh, and the solid content concentration was adjusted with deionized water to obtain an aqueous dispersion of resin particles containing white pigment (solid content concentration: 51%, pigment content: 50%, polyacrylic acid content: 1%, average particle size: 280 nm, pH: 7.6).

[0130] Manufacturing Example 7 (Manufacturing of White Ink W2) 20.0 g of an aqueous dispersion of resin particles containing the white pigment obtained in Production Example 6 (solid content concentration: 51%), and styrene / acrylic resin emulsion (BASF's "Joncryl") 10.4g of 7100 (acid value: 51 mg KOH / g, solid content 48%), 3.0g of diethylene glycol monoisobutyl ether (manufactured by Nippon Emulsifier Co., Ltd.), 30.0g of propylene glycol, 3.0g of acetylene glycol surfactant ("Surfinol 104PG-50" manufactured by Nisshin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol, effective content: 50%, HLB value: 3.0 (calculated value)), 0.8g of silicone surfactant ("KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd., HLB value: 14.5 (catalog value)), 2.4g of 1N sodium hydroxide aqueous solution, and ion-exchanged water to make a total volume of 100g. The resulting mixture was filtered using the membrane filter and a needleless syringe to obtain white ink W2.

[0131] Examples 1-5 and Comparative Examples 1-2 Inkjet printing was performed using the combinations shown in Tables 3-5, including the type of printing medium, presence or absence of corona treatment, type of pretreatment solution, area where the pretreatment solution was applied, presence or absence of a drying step for the pretreatment solution on the printing medium, type of colored ink, area where the colored ink was applied, presence or absence of white ink application, and type of white ink, and the evaluations described below were performed.

[0132] (Process 1) As non-absorbent films for printing media, OPP film, PET film, ONY film, or anti-fog OPP film were treated with a corona treatment device (CTW-0212, manufactured by Wedge Co., Ltd.) at an output of 0.75 kW. Further details regarding PET film, OPP film, PET film, ONY film, and anti-fog OPP film are as follows. • The OPP film is P2161 (manufactured by Toyobo Co., Ltd., water absorption capacity: 0g / m²). 2 ) and is indicated as "OPP" in Tables 3-5. • The PET film is PET film FE2001 (manufactured by Futamura Chemical Co., Ltd., water absorption: 0g / m²). 2 ) and is indicated as "PET" in Tables 3-5. • ONY film is N1102 (manufactured by Toyobo Co., Ltd., water absorption: 0g / m²) 2 ) and is indicated as "ONY" in Tables 3-5. • The anti-fog OPP film is AF-642 (manufactured by Futamura Chemical Co., Ltd., water absorption: 0g / m²). 2 ) and is indicated as "Anti-fog OPP" in Tables 3-5.

[0133] (Process 2) In an environment with a temperature of 25±1℃ and a relative humidity of 30±5%, a printing evaluation device (manufactured by Trytech Co., Ltd.) equipped with multiple inkjet heads (Kyocera Corporation's "KJ4B-HD06MHG-STDV", piezo type) was filled with the pretreatment solutions shown in Tables 3 to 5, and the black ink Bk1 obtained in Manufacturing Example 5 as a colorant-containing ink. The head voltage was set to 26V, the frequency to 26kHz, the head temperature to 32℃, the resolution to 1200dpi, the number of pre-ejection flashes to 200, and the negative pressure to -4.0kPa. The printing medium was fixed to the transport table under reduced pressure, with the longitudinal direction of the printing medium being the same as the transport direction. The distance between the inkjet head and the printing substrate was set to 2.0mm in Example 5, and to 1.0mm in the other examples and comparative examples.

[0134] In Examples 1-4 and Comparative Examples 1-2, the printed image consisted of a light image-forming area (i) (print duty 10%) and a 5cm x 5cm square dark image-forming area (ii) (print duty 100%) as shown in Figure 3. In Example 5, the printed image consisted of a light image forming area (i) (print duty 10%) and a 3cm x 3cm square dark image forming area (ii) (print duty 100%) as shown in Figure 3.

[0135] In Step 2 of Examples 1-4 and Comparative Example 1, the pretreatment solution was applied to the outer edge portion (iii) of the area (ii') that will become the dense image forming area in Figure 4-a at a discharge droplet volume of 1.5 pL. The outer edge portion (iii) of the area (ii') that will become the dense image forming area in Figure 4-a corresponds to the outer edge portion of the dense image forming area (ii) in Figure 3, and belongs to the faint image forming area (i) in Figure 3. The outer edge portion (iii) of the area (ii') that will become the dense image forming area in Figure 4-a was defined as an area within 0.3 mm on the side away from the dense image forming area, calculated from the boundary line between the faint image forming area and the dense image forming area. The area (i') that will become the faint image forming area in Figure 4-a corresponds to the faint image forming area (i) in Figure 3.

[0136] In Example 5, the pretreatment solution was applied to both the outer edge (iii) and inner edge (iv) of the area (ii') that will become the dense image forming area in Figure 4-b, with a discharge droplet volume of 1.5 pL. The outer edge (iii) of the area (ii') that will become the dense image forming area in Figure 4-b corresponds to the outer edge of the dense image forming area (ii) in Figure 3, and belongs to the faint image forming area (i) in Figure 3. The outer edge (iii) of the area (ii') that will become the dense image forming area in Figure 4-b was defined as an area within 0.3 mm away from the dense image forming area, calculated from the boundary line between the faint image forming area and the dense image forming area. The area (i') that will become the faint image forming area in Figure 4-b corresponds to the faint image forming area (i) in Figure 3. Furthermore, the inner edge portion (iv) of the area (ii') that forms the dense image in Figure 4-b corresponds to the inner edge portion of the dense image forming area (ii) in Figure 3, and belongs to the dense image forming area (ii) in Figure 3. The inner edge portion (iv) of the area (ii') that forms the dense image in Figure 4-b is defined as an area within 0.3 mm on the side away from the faint image forming area, calculated from the boundary line between the faint image forming area and the dense image forming area. After applying the pretreatment solution, the pretreatment solution was dried in the drying process (the drying process of step 2) by holding the temperature of the surface of the printing medium to which the pretreatment solution had been applied at 40°C for 1.5 seconds using hot air. At this time, the temperature of the printing medium was confirmed with a non-contact thermometer. In Comparative Example 2, Step 2 was not performed, so each condition in the "Step 2" column of Table 5 is indicated with "-".

[0137] (Step 3) On the surface of the printing medium obtained in step 2, which has a pretreatment liquid application area, an inkjet head filled with black ink Bk1 obtained in manufacturing example 5 of the apparatus used in step 2 was used to apply black ink to the area that will become the light image forming area (i'') and the area that will become the dark image forming area (ii'') in Figure 5, with a discharge droplet volume of 2 pL according to the printing duty cycle shown in Tables 3 to 5, so that the area that will become the light image forming area (i'') in Figure 5 becomes the area that will become the light image forming area (i') in Figure 4-a or Figure 4-b used in step 2. In Comparative Example 2, black ink was applied to the printing medium at a droplet size of 2 pL and a printing duty cycle of 100% to the area (ii'') that would become the dense image-forming area in Figure 5. In Figure 5, the area (ii'') which is the dark image forming area to which the colorant-containing ink is applied corresponds to the dark image forming area (ii) in Figure 3.

[0138] (Step 4) On the surface of the printing medium to which the black ink obtained in step 3 was applied, the white ink W2 obtained in manufacturing example 7 was filled into a printing apparatus similar to that in step 2, and the white ink was applied to the entire surface of the printing medium at a discharge droplet volume of 5 pL.

[0139] <Evaluation of printed materials> [Evaluation of image quality by measuring the area of ​​dense image regions] The dark areas of the printed materials obtained from each printing medium were captured as 640 x 480 pixels using the portable magnifying camera "PIAS-II" (manufactured by QEA). The area difference between the different printing media was calculated using the image analysis software "Image-J," and the image quality (%) was calculated using the following formula. Image quality (%) = [[(Area of ​​densely formed image) / (5cm × 5cm)] - 1] × 100 In Example 5, the image quality (%) was calculated using the following formula. Image quality (%) = [[(Area of ​​densely formed image) / (3cm × 3cm)] - 1] × 100

[0140] (Evaluation Criteria) Image quality (%) is better when the absolute value is low. Furthermore, a smaller absolute value for image quality (%) across different print media indicates that the image quality of each medium is similar. The results are shown in Tables 3-5. Tables 3-5 also show the difference in the area of ​​the dark image between the print with the largest dark image area and the print with the smallest dark image area among four types of printed materials obtained using different printing media. The smaller the difference in the area of ​​the dark image area, the more versatile the printing medium is considered to be.

[0141] [Visual evaluation of characters] In Examples 1-5 and Comparative Examples 1-2, the printed image was the letter "A" with a font size of 8, except that steps 1 and 2 were carried out in the same manner to print the character. The text in the printed material was visually inspected, and the presence or absence of blurring or thinning of the lines was evaluated according to the following evaluation criteria. A: There are absolutely no areas where the letters are blurred or where the lines of the letters are thin. B: There are almost no areas where the letters are blurred or where the lines of the letters are thin. C: There are areas where the letters are blurred and areas where the lines of the letters are thin.

[0142] [Table 3]

[0143] [Table 4]

[0144] [Table 5]

[0145] Tables 3-5 show that the printed materials obtained in the examples have a smaller difference in the area of ​​the dark image compared to the comparative examples, indicating that the image quality of each printing medium is similar. Therefore, it can be seen that the printing method used in the examples offers high versatility for the printing medium. [Industrial applicability]

[0146] According to the present invention, even in line-head type inkjet printing using a non-absorbent printing medium, the versatility of the printing medium is high, and there are no restrictions on the type of printing medium. [Explanation of symbols]

[0147] (i) Faint image forming section (ii) Dense image forming section (i') Area that forms a faint image (ii') Area that forms a dense image (iii) Outer edge portion of the area that forms the dense image (ii') (iv) Inner edge portion of the area that forms the dense image (ii') (i'') Area that forms a faint image (ii'') Area that forms a dense image

Claims

1. An inkjet printing method comprising a dark image forming section and a light image forming section, wherein the printing duty cycle of the ink containing a colorant in the dark image forming section is greater than the printing duty cycle of the ink containing a colorant in the light image forming section, for forming a printed image on a non-absorbent printing medium, Step 1: A step of performing corona treatment on the printing medium, Step 2: A step of applying a pretreatment solution to the outer edge portion of the area that will become the dense image forming portion of the printing medium obtained in Step 1 to obtain a printing medium having a pretreatment solution application portion, and Step 3: A step of applying ink containing a coloring agent to the portion of the surface of the printing medium obtained in Step 2 that will become the dark image forming portion, using a line head type inkjet method. Inkjet printing methods, including those mentioned above.

2. The inkjet printing method according to claim 1, further comprising the step of maintaining the printing medium to which the pretreatment liquid has been applied at 25°C or higher in step 2.

3. The inkjet printing method according to claim 1 or 2, wherein the pretreatment solution contains one or more compounds selected from the group consisting of a coagulating compound (A1) and a hydrophobic compound (A2).

4. The inkjet printing method according to claim 3, wherein the agglomerating compound (A1) is one or more selected from the group consisting of metal salts, organic acids or salts thereof, and cationic resins.

5. The inkjet printing method according to claim 3, wherein the hydrophobic compound (A2) is one or more selected from the group consisting of anionic resins and hydrophobic surfactants.

6. The inkjet printing method according to claim 1 or 2, wherein the outer edge portion of the area that forms the dark image forming portion is a region of 0.01 mm to 1 mm away from the dark image forming portion, calculated from the boundary line between the dark image forming portion and the light image forming portion.

7. The inkjet printing method according to claim 1 or 2, wherein in step 2, the pretreatment solution is further applied to the inner edge portion of the area that will become the dense image forming portion.

8. The inkjet printing method according to claim 7, wherein the inner edge portion of the area that forms the dark image forming portion is a region of 0.01 mm to 1 mm away from the light image forming portion, calculated from the boundary line between the dark image forming portion and the light image forming portion.

9. The inkjet printing method according to claim 1 or 2, wherein the difference between the printing duty cycle of the ink containing the colorant in the dark image forming section and the printing duty cycle of the ink containing the colorant in the light image forming section is 50% or more.

10. The inkjet printing method according to claim 1 or 2, further comprising step 4, which involves applying a white ink containing a white pigment to a printing medium or to a surface of a printing medium coated with an ink containing a colorant, either before step 2 or after step 3.

11. The inkjet printing method according to claim 1 or 2, wherein the printing duty cycle of the ink containing the colorant in the light image forming area is greater than 0%, and the application of the pretreatment liquid in step 2 is applied not only to the outer edge portion of the portion that will become the dark image forming area, but also to the portion of the light image forming area to which the ink containing the colorant is not applied.

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