Inkjet printing method

Abstract

An inkjet printing method for forming a print image on a print medium, the print image including a dark image forming part and a light image forming part, wherein the printing duty of ink containing a coloring agent for the dark image forming part is greater than the printing duty of ink containing a coloring agent for the light image forming part, the method comprising: step 1 for obtaining a print medium having a preprocessing liquid application part by applying a preprocessing liquid to an outer edge portion of an area to be the dark image forming part; and step 2 for applying, to an area of a surface having the pretreatment liquid application part of the print medium obtained in step 1 that is to be the dark image forming part, an ink containing a coloring agent by a line head-type inkjet system.

Description

Inkjet printing method

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

[0002] Inkjet printing has many advantages, such as not requiring plate making, being easily adaptable to variable information, and not contacting the print medium during printing. In addition to being used in offices and homes, inkjet printing has recently been expanded to commercial printing applications, which require significantly larger print runs. In commercial printing applications, there is a demand for improved image quality when printing on non-liquid-absorbent print media such as resin films, in addition to low-liquid-absorbent print media such as printing paper. Accordingly, various proposals have been made.

[0003] For example, Japanese Patent Laid-Open No. 2018-126972 (Patent Document 1) discloses an image forming apparatus that can obtain an image with high image density while suppressing bleeding between an image portion and a non-image portion, and the apparatus includes a recording medium, an ink containing a colorant, an organic solvent, and water, a liquid containing the organic solvent and water but not the colorant, a means for applying the ink onto the recording medium to form an image portion, and a means for applying the liquid to non-image portions other than the image portion on the recording medium, and the static surface tension γ of the ink at 25° C. A and the static surface tension γ of the liquid at 25°C B Furthermore, Japanese Patent Laid-Open No. 2009-196274 (Patent Document 2) describes an inkjet recording method for performing recording on a recording medium using color inks containing color materials, with the aim of preventing bleeding of the color inks regardless of the type of recording medium used, such as a recording medium with excellent ink absorption capacity or a recording medium with poor ink absorption capacity, and for the purpose of preventing bleeding of the color inks, the inkjet recording method includes recording on the edge of a recording area recorded with the color inks using a clear ink that does not contain color materials and that has a static surface tension and a dynamic surface tension at a lifetime of 100 milliseconds lower than those of the color inks.

[0004] The present invention relates to an inkjet printing method for forming a print image on a print medium, the print image including a dark image forming unit and a light image forming unit, wherein the print duty of ink containing a colorant in the dark image forming unit is higher than the print duty of ink containing a colorant in the light image forming unit, the inkjet printing method comprising: Step 1: applying a pretreatment liquid to an outer edge of a portion that will become the dark image forming unit, to obtain a print medium having a pretreatment liquid application unit; and Step 2: applying ink containing a colorant by a line head inkjet system to a portion that will become the dark image forming unit on the surface of the print medium obtained in Step 1 that has the pretreatment liquid application unit.

[0005] Commercial printing applications require high productivity, necessitating high-speed printing. To accommodate this demand, linehead printheads have been developed. While conventional serial-head printheads print by operating the head (nozzles) multiple times, linehead printheads are equipped with a head capable of inkjet printing across a width equal to or greater than the length of the print medium in the direction perpendicular to its transport direction. This allows high-speed printing by scanning the print medium while keeping the printhead stationary. However, unlike serial-head printheads, linehead inkjet printing cannot print by moving the head back and forth across the print area multiple times. This makes it difficult to compensate for misalignment of ink droplets due to misaligned ink droplets, resulting in the problem of streaks. Furthermore, when forming a print image containing a dark image formation area and a light image formation area on a low-liquid-absorbent print medium, bleeding occurs at the boundary between the dark and light image formation areas, resulting in unclear printed images. However, the techniques of Patent Documents 1 and 2 are not fully satisfactory in addressing these problems, and there is a need for the development of a technique that can suppress the occurrence of streaks while providing excellent clarity in printed images including dark image forming sections and light image forming sections, particularly in sharpness of printed images of outline characters, even when printing by a line head inkjet method using a low liquid-absorbent printing medium, specifically a resin film. The present invention relates to an inkjet printing method that can suppress the occurrence of streaks in the resulting print, while providing excellent clarity in printed images including dark image forming sections and light image forming sections.

[0006] The present inventors have discovered that the above-mentioned problems can be solved by an inkjet printing method for forming a print image including a dark image forming portion and a light image forming portion on a print medium, the method comprising the steps of: applying a pretreatment liquid to the outer edge of an area that will become the dark image forming portion, to obtain a print medium having a pretreatment liquid application portion; and applying an ink containing a colorant by a line head inkjet system to an area that will become the dark image forming portion on the surface of the print medium obtained in the above step that has the pretreatment liquid application portion.

[0007] That is, the present invention provides an inkjet printing method for forming a print image on a print medium, which includes a dark image forming section and a light image forming section, and in which the printing duty of ink containing a colorant in the dark image forming section is higher than the printing duty of ink containing a colorant in the light image forming section, the inkjet printing method comprising: Step 1: applying a pretreatment liquid to the outer edge of an area that will become the dark image forming section, to obtain a print medium having a pretreatment liquid application section; and Step 2: applying ink containing a colorant by a line head inkjet system to an area that will become the dark image forming section on the surface of the printing medium obtained in Step 1 that has the pretreatment liquid application section.

[0008] The present invention can provide an inkjet printing method that suppresses the occurrence of streaks in the resulting printed matter, even when printing using a line head inkjet method that uses a low-liquid-absorbency printing medium, and that provides excellent clarity in printed images that include a dark image forming section and a light image forming section.

[0009]

[0033] FIG. 1 shows an example of a schematic diagram of a printed image including a dark image forming section and a light image forming section. In the figure, the solid line indicates the boundary between the dark image forming section and the light image forming section, the area surrounded by the solid line indicates the light image forming section, and the area surrounded by the solid and dotted lines indicates the outer edge of the area that will become the dark image forming section.

[0034] FIG. 1 shows an example of a schematic diagram of a printed image including a dark image forming section and a light image forming section. In the figure, the solid line indicates the boundary between the dark image forming section and the light image forming section, the area surrounded by the solid line indicates the light image forming section, the area surrounded by the solid and dotted lines indicates the outer edge of the area that will become the dark image forming section, and the area surrounded by the solid and dashed lines indicates the inner edge of the area that will become the dark image forming section.

[0035] FIG. 1 shows a schematic diagram of a printed image of a hollow character formed in Examples 1 to 8, 10 to 12, and Comparative Examples 1 and 2, consisting of a light image forming section (i) (printing duty of ink containing a colorant: 0%) and a dark image forming section (ii) (printing duty of ink containing a colorant: 100%). FIG. 1 is an explanatory diagram showing an area where a pretreatment liquid is applied in step 1 in Examples 1 to 10 and 12. FIG. 2 is an explanatory diagram showing an area where a pretreatment liquid is applied in step 1 in Example 11. FIG. 3 is an explanatory diagram showing an area where an ink containing a colorant is applied in step 2 in Examples 1 to 12 and Comparative Examples 1 and 2. FIG. 4 is a photograph of a printed image of cut-out characters obtained in Example 1. FIG. 5 is a photograph of a printed image of cut-out characters obtained in Comparative Example 2. FIG. 6 is a schematic diagram of a printed image of a barcode formed in Example 13, comprising a light image forming portion (i) (printing duty of ink containing a colorant: 0%) and a dark image forming portion (ii) (printing duty of ink containing a colorant: 100%). FIG. 7 is an explanatory diagram showing an area where a pretreatment liquid is applied in step 1 in Example 13. FIG. 8 is a photograph of a printed image of a barcode obtained in Example 13.

[0010] [Inkjet Printing Method] The inkjet printing method of the present invention (hereinafter also referred to as "the printing method of the present invention") is an inkjet printing method for forming a print image on a print medium, which includes a dark image forming portion and a light image forming portion, and in which the printing duty of the ink containing a colorant in the dark image forming portion (hereinafter also referred to as "colorant-containing ink") is higher than the printing duty of the colorant-containing ink in the light image forming portion, and includes: Step 1: applying a pretreatment liquid to the outer edge of the portion that will become the dark image forming portion to obtain a print medium having a pretreatment liquid application portion; and Step 2: applying the colorant-containing ink by a line head inkjet system to the portion that will become the dark image forming portion on the surface of the print medium obtained in Step 1 that has the pretreatment liquid application portion. Note that in the present invention, "printing" is a concept that includes printing to record characters or images and printing letters.

[0011] The printing method of the present invention, even when printing by a linehead inkjet method using a low-liquid-absorbency printing medium, suppresses the occurrence of streaks in the resulting print and provides excellent clarity of a printed image including a dark image forming portion and a light image forming portion. The reason for this is unclear, but is thought to be as follows: In the printing method of the present invention, a printed image including a dark image forming portion and a light image forming portion is formed on the printing medium, and the printing duty of the colorant-containing ink in the dark image forming portion is higher than the printing duty of the colorant-containing ink in the light image forming portion. The method includes, as step 1, applying a pretreatment liquid to the outer edge of a region that will become a dark image forming region to obtain a printing medium having a pretreatment liquid application region, and as step 2, applying a colorant-containing ink using a line head inkjet system to the region that will become a dark image forming region on the surface of the printing medium obtained in step 1 that has the pretreatment liquid application region. This prevents the pretreatment liquid and the colorant-containing ink from contacting each other at the boundary between the outer edge of the dark image forming region to which the pretreatment liquid is applied and the dark image forming region to which the colorant-containing ink is applied, thereby suppressing ink wetting and spreading, thereby suppressing ink bleeding at the boundary between the light image forming region and the dark image forming region, and improving the clarity of the printed image that includes the dark image forming region and the light image forming region. On the other hand, in the present invention, the pretreatment liquid is not applied to the entire surface of the printing medium. When the pretreatment liquid is applied to the entire surface of the printing medium, the dark image forming region and the light image forming region are printed using a line head inkjet system with a colorant-containing ink. This suppresses the wetting and spreading of the pretreatment liquid that has been applied to the dark image forming region and the light image forming region, making the aforementioned streaks more noticeable. However, in the present invention, since the pretreatment liquid is not applied to most of the dark image forming section and the light image forming section, the occurrence of streaks is unlikely to occur, and the effect of the pretreatment liquid can be effectively exerted at the boundary between the dark image forming section and the light image forming section, which is thought to result in both suppression of streaks and improvement of the clarity of the printed image including the dark image forming section and the light image forming section.

[0012] The present invention relates to an inkjet printing method that includes a dark image forming unit and a light image forming unit, and forms a print image on a printing medium in which the printing duty of the colorant-containing ink in the dark image forming unit is higher than the printing duty of the colorant-containing ink in the light image forming unit. In the present invention, the "colorant-containing ink printing duty" refers to the proportion of the area occupied by the colorant-containing ink within a predetermined area on the printing medium, i.e., the proportion of the cumulative area to which the colorant-containing ink is applied. For example, in the present invention, a "colorant-containing ink printing duty of 100%" refers to applying ink droplets in a square grid pattern without thinning out the application area of ​​the colorant-containing ink, such that the inter-dot distance between adjacent ink dots spread in a circle on the printing medium is such that the ends of the adjacent ink dots contact each other at the circumferential position. For example, a dark image forming unit with a "colorant-containing ink printing duty" of 100% refers to a solid printing unit. On the other hand, in the present invention, "printing duty of colorant-containing ink is 0%" means that no ink is applied within a specified area on the printing medium, and for example, a light image forming area where the "printing duty of colorant-containing ink" is 0% means a non-printing area.

[0013] The printing duty of the colorant-containing ink in the dark image forming portion 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 forming a high-quality printed image by clearly defining the contours of the dark image forming portion. The printing duty of the colorant-containing ink in the dark image forming portion is preferably 100% from the viewpoint of obtaining a printed image of outline characters. The printing duty of the colorant-containing ink in the light image forming portion is 0% or more, from the viewpoint of forming a high-quality printed image by clearly defining the contours of the dark image forming portion, and is preferably 50% or less, more preferably 30% or less, and even more preferably 10% or less. The printing duty of the colorant-containing ink in the light image forming portion is preferably 0%, from the viewpoint of obtaining a printed image of outline characters. The difference between the printing duty of the colorant-containing ink in the dark image forming portion and the printing duty of the colorant-containing ink in the light image forming portion is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more, from the viewpoint of forming a high-quality printed image by clearly defining the contours of the dark image forming portion. The difference between the printing duty of the colorant-containing ink in the dark image forming portion and the printing duty of the colorant-containing ink in the light image forming portion is preferably 100% from the viewpoint of obtaining a printed image of outline characters.

[0014] In the present invention, the printed image formed may be an image of hollow characters, one-dimensional codes such as barcodes, two-dimensional codes of matrix or stack type, or extremely small characters. In the present invention, a "hollow character image" refers to an image in which characters are recognizable through light image areas of colors other than the first color against a background of dark image areas inkjet-printed in a first color. In this case, the first color and the colors other than the first color may be primary colors such as yellow, magenta, cyan, and black, respectively, or may be a mixture of these primary colors, i.e., a secondary color. Among these printed images, a hollow character image is preferred as the printed image formed from the viewpoint of improving the clarity of the printed image while suppressing the occurrence of streaks in the resulting print.

[0015] <Step 1> Step 1 is a step of applying a pretreatment liquid to the outer edge of a region that will become a dark image forming region to obtain a print medium having a pretreatment liquid application region. In the present invention, the outer edge of the region that will become a dark image forming region belongs to a light image forming region in the resulting printed image, as shown in FIG. 1 . From the perspective of practicality, taking into account ejection misalignment and print medium transport misalignment, and from the perspective of improving the clarity of the printed image while suppressing the occurrence of streaks in the resulting print, the outer edge of the region that will become a dark image forming region 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, calculated from the boundary between the dark image forming region and the light image forming region, on the side away from the dark image forming region. The pretreatment liquid application in step 1 may be applied to at least the outer edge of the region that will become a dark image forming region of the printed image, or may be applied to the entire light image forming region, including the outer edge of the region that will become a dark image forming region. In the printing method of the present invention, the pretreatment liquid is preferably applied in step 1 only to the outer edge of the area that will become the dark image forming area. When the printing duty of the colorant-containing ink in the light image forming area is 0%, the pretreatment liquid is more preferably applied in step 1 only to the outer edge of the area that will become the dark image forming area. When the printing duty of the colorant-containing ink in the light image forming area is greater than 0%, the pretreatment liquid may be applied not only to the outer edge of the area that will become the dark image forming area, but also to areas in the area that will become the light image forming area where the colorant-containing ink is not applied. In this case, in step 2 described below, the colorant-containing ink is applied by a line head inkjet method to areas in the area that will become the light image forming area on the surface of the printing medium obtained in step 1 that has the pretreatment liquid application area. Note that when the printing duty of the colorant-containing ink in the light image forming area is greater than 0%, the "areas where the colorant-containing ink is not applied" refers to non-output areas in the raster image data used for colorant-containing ink output.For example, when the printing duty of the colorant-containing ink in the light image forming section is 40%, the "area where the colorant-containing ink is not applied" means the non-output area of ​​the colorant-containing ink, which accounts for 60% of the raster image used to output the colorant-containing ink in the light image forming section.

[0016] In step 1, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, it is preferable that (1) the pretreatment liquid is not applied to the area that will become the dark image forming area, or (2) if the pretreatment liquid is applied to the area that will become the dark image forming area, the pretreatment liquid is further applied to the inner edge of the area that will become the dark image forming area, and the pretreatment liquid is not applied to the dark image forming area other than the inner edge of the area that will become the dark image forming area. Among these, the case (2) is more preferable because it can suppress misalignment between the area where the pretreatment liquid is applied in step 1 and the area where the colorant-containing ink is landed in step 2, thereby improving the clarity of the printed image even if it is a fine printed image. In the present invention, the inner edge of the area that will become the dark image forming area belongs to the dark image forming area in the formed printed image, as shown in Figure 2. From the viewpoint of practicality taking into account ejection misalignment and misalignment in the transport of the printing medium, and from the viewpoint of suppressing misalignment of the landing position of the colorant-containing ink to further improve the clarity of the printed image, the inner edge portion of the area that will become the dark image forming portion is preferably 0.01 mm or more, more preferably 0.1 mm or more, even more preferably 0.2 mm or more, calculated from the boundary line between the dark image forming portion and the light image forming portion, on the side away from the light image forming portion, and is preferably 1 mm or less, more preferably 0.7 mm or less, even more preferably 0.4 mm or less.

[0017] (Printing Medium) As the printing medium used in the present invention, either a low-absorbency printing medium or a high-absorbency printing medium can be used, but from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter and from the viewpoint of the clarity of the printed image, a low-absorbency printing medium is preferred. In the present invention, whether a printing medium is low-absorbency or high-absorbency is determined by the amount of water absorbed by the printing medium when the printing medium is in contact with pure water for 100 ms. The amount of water absorption can be measured as the amount of transfer of pure water when the printing medium is in contact with pure water for 100 ms under conditions of 23°C and a relative humidity of 50% using an automatic scanning liquid absorption meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.). In the present invention, "low-absorbency" is a concept that includes low-absorbency and non-absorbency, and is defined as a printing medium having a water absorption of 0 g / m 2 7g / m or more 2 "Highly absorbent" means that the water absorption amount is 7 g / m or less. 2 This means that the print quality exceeds the print quality limit. Examples of low-absorbency print media include low-absorbency coated paper and non-absorbency resin film. Examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper. The resin film is preferably at least one selected from the group consisting of polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film, and more preferably polyester film. These resin films may be surface-treated, such as by corona treatment. Examples of highly absorbent print media include highly absorbent plain paper. When using a resin film as a low-absorbency print medium, step 1 may be performed by determining the dark image formation area and the light image formation area based on a mirror image obtained by inverting the desired print image so that the desired image appears when viewed from the opposite side of the print image-forming surface of the non-absorbency film.

[0018] (Pretreatment Liquid) <Component (A) for Suppressing Wet Spreading> The pretreatment liquid according to the present invention preferably contains a component (A) that suppresses the wetting and spreading of the colorant-containing ink used in step 2 on a printing medium (hereinafter also referred to simply as "component (A) for suppressing wetting and spreading"). Since the pretreatment liquid according to the present invention contains the component (A) that suppresses wetting and spreading, at the boundary between the outer edge of the dark image forming section to which the pretreatment liquid is applied and the dark image forming section to which the colorant-containing ink is applied, the component (A) that suppresses wetting and spreading prevents the colorant-containing ink from penetrating into the light image forming section, thereby suppressing ink bleeding at the boundary between the light image forming section and the dark image forming section, and improving the clarity of the printed image including the dark image forming section and the light image forming section. In the present invention, the component (A) that suppresses wetting and spreading is preferably one or more compounds selected from the group consisting of aggregating compounds (A1) and hydrophobic compounds (A2). That is, the pretreatment liquid according to the present invention preferably contains one or more compounds selected from the group consisting of aggregating compounds (A1) and hydrophobic compounds (A2). These will be explained below.

[0019] [Aggregating Compound (A1)] In the present invention, the term "aggregating compound (A1)" refers to a component that, when applied to a printing medium, causes aggregation due to a decrease in the dispersibility of dispersoids present in the colorant-containing ink or a decrease in the solubility of solutes, thereby causing thickening or precipitation of the ink and preventing the ink from penetrating into light image forming areas. In the present invention, the dispersoids present in the colorant-containing ink refer to ink components such as pigments that are currently dispersed in the ink in a solid state. Furthermore, the solutes present in the colorant-containing ink refer to components that are dissolved in the ink but lose their solubility upon contact with a printing medium treated with a pretreatment liquid, causing thickening or precipitation. Specific examples of components (solutes) that are dissolved in the colorant-containing ink but lose their solubility upon contact with a printing medium treated with a pretreatment liquid, causing thickening or precipitation include dyes and water-soluble resins. Preferred examples of the aggregating compound (A1) include metal salts, acids or their salts, and cationic compounds. The aggregating compound (A1) may be used alone or in combination of two or more. Examples of metal salts include monovalent metal salts and divalent or higher metal salts. Examples of acids include organic acids and inorganic acids. Examples of cationic compounds include cationic resins and cationic surfactants. Among these, the aggregating compound (A1) is more preferably at least one selected from the group consisting of metal salts, acids or salts thereof, and cationic resins.

[0020] (Metal Salt) The metal salt used as the aggregating compound (A1) is preferably a polyvalent metal salt from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image. Any polyvalent metal salt can be used as long as it is composed of a divalent or higher polyvalent metal ion and an anion (a counterion of the polyvalent metal ion). Examples of divalent or higher polyvalent metal ions include ions of calcium, magnesium, copper, nickel, zinc, barium, aluminum, titanium, strontium, chromium, cobalt, and iron. Among these, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, divalent or trivalent metal ions are preferred, and divalent metal ions are more preferred. Examples of divalent metal ions include ions of elements belonging to Group 2 of the periodic table of elements, and specific examples thereof include 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 suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, more preferred are one or more selected from the group consisting of magnesium ions, calcium ions, and aluminum ions, even more preferred are one or more selected from the group consisting of magnesium ions and calcium ions, and even more preferred are calcium ions. Examples of the anion of the polyvalent metal salt 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 nitrate ions.

[0021] From the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, the polyvalent metal salt is preferably at least one selected from the group consisting of magnesium nitrate, magnesium sulfate, calcium nitrate, and aluminum nitrate, more preferably at least one selected from the group consisting of magnesium nitrate, calcium nitrate, and aluminum nitrate, even more preferably at least one selected from the group consisting of magnesium nitrate and calcium nitrate, and still more preferably calcium nitrate. The polyvalent metal salt may have water of hydration in the form of a raw material. The polyvalent metal salt may be used alone or in combination of two or more.

[0022] (Acid) The acid used as the aggregating compound (A1) may be one or more selected from the group consisting of organic acids and inorganic acids. Examples of organic acids include aliphatic carboxylic acids, aliphatic dicarboxylic acids, hydroxycarboxylic acids, heterocyclic carboxylic acids, derivatives of these compounds, and salts thereof. Examples of aliphatic carboxylic acids include formic acid and acetic acid. Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, and fumaric acid. Examples of hydroxycarboxylic acids include glycolic acid, lactic acid, malic acid, tartaric acid, and citric acid. Examples of heterocyclic carboxylic acids include ascorbic acid, pyrrolidone carboxylic acid, pyrrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, and nicotinic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Among these, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, the acid is preferably an organic acid or a salt thereof, more preferably an aliphatic dicarboxylic acid or a salt thereof, even more preferably one or more selected from the group consisting of oxalic acid, malonic acid, and succinic acid, and even more preferably malonic acid. The acid may be used alone or in combination of two or more. These acids may form salts, and when the acid forms a metal salt, it is included in the above-mentioned metal salt.

[0023] (Cationic Resin) Examples of the cationic compound used as the aggregating compound (A1) include cationic resins and cationic surfactants. The cationic resin preferably has a cationic group. In the present invention, the term "cationic group" refers to a cationic group or a group that can be ionized to become a cationic group. Examples of the cationic group include basic groups such as a primary amino group (-NH), a secondary amino group (-NHR, ═NH (imino group)), a tertiary amino group (-NRR′), a quaternary ammonium group, and a hydrazino group. Among these, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, the cationic resin preferably has one or more groups selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium group, and more preferably has a quaternary ammonium group. The basic group includes those neutralized with acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, maleic acid, fumaric acid, citric acid, tartaric acid, adipic acid, lactic acid, etc. The cationic resins may be used alone or in combination of two or more.

[0024] The cationic resin has a cationic degree of preferably 0.5 meq / g or more, more preferably 3.0 meq / g or more, and preferably 10 meq / g or less, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter and improving the clarity of the printed image. The cationic degree of the cationic resin can be determined by colloid titration using a potassium polyvinyl sulfate reagent. Examples of cationic resins include cationic vinyl resins, cationic olefin resins, cationic urethane resins, and cationic amine resins.

[0025] Examples of cationic vinyl resins include vinyl resins containing structural units derived from vinyl monomers having a cationic group. Suitable examples of vinyl monomers having a cationic group include alkyl(meth)acrylate-based quaternary ammonium salts, alkyl(meth)acryloylamide-based quaternary ammonium salts, (meth)acrylic acid esters having a dialkylamino group, (meth)acrylamides having a dialkylamino group, styrenes having a dialkylamino group, amino group-containing heterocyclic vinyl monomers, and allylamine compounds. Examples of alkyl(meth)acrylate-based quaternary ammonium salts include (meth)acryloyloxyethyl trimethylammonium chloride, (meth)acryloyloxyethyl triethylammonium chloride, (meth)acryloyloxyethyl dimethylbenzylammonium chloride, (meth)acryloyloxyethyl methylmorpholino ammonium chloride, and 2-hydroxy-3-(meth)acryloyloxypropyl trimethylammonium chloride. Examples of alkyl(meth)acryloylamide-based quaternary ammonium salts include (meth)acryloylaminoethyl triethylammonium chloride, (meth)acryloylaminoethyl dimethylbenzylammonium chloride, etc. Examples of (meth)acrylic acid esters having a dialkylamino group include trimethyl[(vinylphenyl)methyl]ammonium chloride, dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, dipropylaminoethyl(meth)acrylate, diisopropylaminoethyl(meth)acrylate, dibutylaminoethyl(meth)acrylate, diisobutylaminoethyl(meth)acrylate, di-t-butylaminoethyl(meth)acrylate, etc. Examples of (meth)acrylamides having a dialkylamino group include dimethylaminopropyl(meth)acrylamide, diethylaminopropyl(meth)acrylamide, dipropylaminopropyl(meth)acrylamide, diisopropylaminopropyl(meth)acrylamide, dibutylaminopropyl(meth)acrylamide, diisobutylaminopropyl(meth)acrylamide, and di-t-butylaminopropyl(meth)acrylamide.Examples of styrenes having a dialkylamino group include dimethylaminostyrene, dimethylaminomethylstyrene, etc. Examples of amino group-containing heterocyclic vinyl monomers include N-vinylpyrrolidine, N-vinylpyrrolidone, N-vinylcarbazole, etc. Examples of allylamine compounds include allylamine, dimethylallylamine, diallylamine, methyldiallylamine, etc.

[0026] The cationic vinyl resin may contain structural units derived from monomers other than vinyl monomers having cationic groups. Examples of such other monomers include alkyl group-containing (meth)acrylic monomers, alkylene oxide chain-containing (meth)acrylic monomers, alkylene oxide chain-containing (meth)acrylic monomers, and aromatic ring-containing (meth)acrylic monomers. Examples of styrene-based monomers include styrene and α-methylstyrene. Examples of alkyl group-containing (meth)acrylic monomers include methyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. Examples of alkylene oxide chain-containing (meth)acrylic monomers include (poly)ethylene glycol mono(meth)acrylate, (poly)propylene glycol mono(meth)acrylate, and (poly)(ethylene glycol-propylene glycol) mono(meth)acrylate. Examples of aromatic ring-containing (meth)acrylic monomers include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

[0027] Among these, the cationic vinyl resin is preferably a polyallylamine resin having a structure derived from an allylamine compound in the main skeleton, from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter and improving the clarity of the printed image. Examples of the polyallylamine resin include homopolymers and copolymers of the above-mentioned allylamine compounds. Specific examples of polyallylamine resins include polyallylamine hydrochloride, polyallylamine amidosulfate, 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 amidosulfate, 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, diallyldimethylammonium chloride / acrylamide copolymer, and the like.

[0028] The cationic vinyl resin may be synthesized by a known method or may be a commercially available product, such as a diallyldimethylammonium chloride polymer such as PAS-H-1L (trade name, manufactured by Nittobo Medical Co., Ltd.).

[0029] The cationic olefin resin has a structural unit derived from an olefin such as ethylene or propylene as a basic skeleton, and known resins can be appropriately selected and used. The cationic olefin resin may also be used as an emulsion dispersed in a medium containing water, an organic solvent, or the like. Commercially available cationic olefin resins can be used. Examples of commercially available cationic olefin resins include Arrowbase CB-1200 and Arrowbase CD-1200 (both trade names manufactured by Unitika Ltd.).

[0030] Examples of cationic urethane resins include those obtained by reacting the isocyanate groups of a urethane pre-resin obtained by polyaddition reaction of an organic compound (polyol) having two or more alcoholic hydroxyl groups per molecule with a polyisocyanate with an active hydrogen compound for introducing cationic hydrophilic groups. In the polyaddition reaction, a chain extender or a reaction terminator may be used in combination as needed. The use of a chain extender can further increase the molecular weight. Examples of chain extenders include polyols and polyamines, and examples of reaction terminators include monoalcohols and monoamines. The cationic urethane resin is preferably used as an emulsion, and the emulsion may contain a dispersant such as a surfactant as needed. Examples of 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. Commercially available cationic urethane resins include Hydran CP-7010, CP-7020, CP-7030, CP-7040, CP-7050, CP-7060, and CP-7610 (all manufactured by DIC Corporation under trade names); Superflex 600, 610, 620, 630, 640, and 650 (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. under trade names); and Urethane Emulsion WBR-2120C and WBR-2122C (all manufactured by Taisei Fine Chemical Co., Ltd. under trade names).

[0031] Examples of cationic amine resins include polyamine resins and polyamide resins. Polyamine resins are resins that have amino groups in the main skeleton 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.

[0032] Commercially available cationic amine resins include Unisense KHE103L (hexamethylenediamine / epichlorohydrin condensate) and Unisense KHE104L (dimethylamine / epichlorohydrin condensate, aqueous solution with a solids concentration of 20% by mass) (all of which are product names of Senka Corporation); FL-14 (product name of SNF); Arafix 100, Arafix 251S, Arafix 255, and Arafix 255LOX (all of which are product names of Arakawa Chemical Co., Ltd.); and DK modified polyamine resins such as DK6810, DK6853, and DK6885; polyamide epichlorohydrin resins or polyamine epichlorohydrin resins such as WS4010, WS4011, WS4020, WS4024, WS4027, and WS4030 (all of which are product names manufactured by Seiko PMC Corporation); dimethylamine / ammonia / epichlorohydrin condensates such as Papiogen P-105 (product name manufactured by Senka Corporation); Sumirez Examples of suitable epoxy resins include polyamide epoxy resins such as Resin 650(30), Resin 675A, Resin 6615, and Resin SLX-1 (all manufactured by Taoka Chemical Co., Ltd., trade names); Catiomaster PD-1, Catiomaster PD-7 (dimethylamine / epichlorohydrin condensate), Catiomaster PD-30, Catiomaster A, Catiomaster PDT-2, Catiomaster PE-10, Catiomaster PE-30 (dimethylamine / ethylenediamine / epichlorohydrin condensate), DT-EH, EPA-SK01 (polyamidepolyamine / epichlorohydrin condensate), and TMHMDA-E (all manufactured by Yokkaichi Synthetic Co., Ltd., trade names); and Jetfix 36N, Jetfix 38A, and Jetfix 5052 (all manufactured by Satoda Chemical Co., Ltd., trade names).

[0033] (Cationic Surfactant) Examples of the cationic compound used as the aggregating compound (A1) include cationic surfactants. In the present invention, the term "cationic surfactant" refers to a compound having a hydrophobic group and a cationic group as a hydrophilic group, and not having a repeating structure derived from a monomer. Preferred examples of the hydrophobic group of the cationic surfactant include alkyl groups having 10 to 22 carbon atoms. Examples of the cationic surfactant include alkylamine salts and alkyl quaternary ammonium salts. Examples of the alkylamine salt include alkylamine acetates such as laurylamine acetate and stearylamine acetate. Examples of the alkyl quaternary ammonium salt include alkyltrimethylammonium salts, dialkyldialkylammonium salts, and alkylbenzyldimethylammonium salts. Among these, the cationic surfactant is preferably an alkyl quaternary ammonium salt, and more preferably alkyltrimethylammonium chloride having an alkyl group having 10 to 22 carbon atoms.

[0034] [Hydrophobic Compound (A2)] In the present invention, the "hydrophobic compound (A2)" is a compound containing a hydrophobic structure, which does not cause thickening or precipitation of the colorant-containing ink, but which, at the boundary between the outer edge of the dark image forming area to which the pretreatment liquid is applied and the dark image forming area to which the colorant-containing ink is applied, has low affinity for the ink due to the hydrophobic structure, and thus prevents the ink from penetrating into the light image forming area. The hydrophobic compound (A2) is preferably at least one selected from the group consisting of anionic resins and hydrophobic surfactants.

[0035] (Anionic Resin) The "anionic resin" used as the hydrophobic compound (A2) refers to an anionic resin that, when dried at 105°C for 2 hours to reach a constant weight, dissolves in 100 g of water at 25°C until saturation is reached, yields a dissolution amount of 10 g or less. Furthermore, when the anionic resin has an anionic group and the anionic group is neutralized with a neutralizer, the dissolution amount is determined by measuring the dissolution amount in the presence of a neutralizer such that the mass ratio of the anionic resin to the neutralizer is the same as that in the pretreatment liquid. From the viewpoints of blendability into the pretreatment liquid and dispersion stability in the pretreatment liquid, the anionic resin is preferably a resin having an anionic group. In the present invention, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxyl group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-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 carboxy group as the anionic group, and M is preferably ammonium. Examples of the anionic resin include anionic vinyl resins, anionic urethane resins, and anionic silicone resins. The anionic resins may be used alone or in combination of two or more.

[0036] The anionic vinyl resin is preferably a vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group. The vinyl monomer having an anionic group is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably at least one selected from the group consisting of acrylic acid and methacrylic acid, and even more preferably acrylic acid.

[0037] The anionic vinyl resin may be either a homopolymer or a copolymer, but is preferably a vinyl resin containing a structural unit derived from a hydrophobic vinyl monomer in addition to a structural unit derived from a vinyl monomer having an anionic group. Preferred examples of the hydrophobic vinyl monomer 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-based monomers. Preferred examples of alkyl(meth)acrylates having an alkyl group having 1 to 22 carbon atoms include 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. Preferred examples of the aryl group-containing (meth)acrylate having an aryl group having from 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. Preferred examples of the styrene-based monomer include one or more selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene.Among these, the hydrophobic vinyl monomer is more preferably at least one selected from the group consisting of alkyl(meth)acrylates having a linear or branched alkyl group having from 1 to 8 carbon atoms, cycloalkyl(meth)acrylates, and styrene-based monomers, and even more preferably at least one 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.

[0038] The content of vinyl monomers having an anionic group in the raw material monomers constituting the anionic vinyl resin or the content of structural units derived from vinyl monomers having an anionic group 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, 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 structural 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, even more preferably 85% by mass or less.

[0039] The anionic vinyl resin preferably has a crosslinked structure from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image. From the same viewpoint as above, the anionic vinyl resin having a crosslinked structure is preferably one obtained by reacting an anionic vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group and a structural unit derived from a hydrophobic vinyl monomer 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 structural unit derived from the vinyl monomer having an anionic group and the structural unit derived from the hydrophobic vinyl monomer. From the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, the crosslinking agent is preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, 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.

[0040] The crosslinking rate of the 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, even more preferably 60 mol% or less. When the anionic vinyl resin having a crosslinked structure is obtained by reacting an anionic vinyl resin containing a structural unit derived from a vinyl monomer having an anionic group and a structural unit derived from a hydrophobic vinyl monomer with a crosslinking agent, the crosslinking rate is calculated from the equivalent of the anionic group in the anionic vinyl resin before crosslinking and the equivalent of the crosslinkable functional group in the crosslinking agent, and is expressed as "the number of molar equivalents of the crosslinkable functional group in the crosslinking agent / the number of molar equivalents of the anionic group in the anionic vinyl resin before crosslinking."

[0041] The anionic vinyl resin may be synthesized appropriately or may be a commercially available product. The anionic vinyl resin may be produced by copolymerizing raw material monomers by a known polymerization method. The anionic vinyl resin is preferably used as a dispersion.

[0042] The acid value of the anionic vinyl resin is preferably 40 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, even more preferably 120 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 240 mgKOH / g or less, and even more preferably 200 mgKOH / 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, 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. When the anionic vinyl resin has a crosslinked structure, the acid value of the anionic vinyl resin can also be calculated from the mass ratio of the constituent monomers and crosslinking agent.

[0043] The anionic urethane resin is a resin having a structural unit derived from an organic compound (polyol) having two or more alcoholic hydroxyl groups per molecule, a structural unit derived from a polyisocyanate, and a structural unit derived from a dialkanolcarboxylic acid. The anionic urethane resin is obtained by polyaddition reaction of a polyol, a polyisocyanate, and a dialkanolcarboxylic acid.

[0044] 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, and is preferably a polycarbonate polyol, a polyester polyol, or a polyether polyol, more preferably a polycarbonate polyol or a polyester polyol. That is, the anionic urethane resin is preferably a polycarbonate polyurethane or a polyester polyurethane.

[0045] Polycarbonate polyols are compounds obtainable by reacting a carbonate compound with a diol, i.e., diols having 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 that 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.

[0046] Polyester polyols are compounds obtainable 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 diols having 2 to 6 carbon atoms, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and 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 brassylic 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.

[0047] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0048] Examples of polyisocyanates constituting the anionic urethane resin include chain-like aliphatic diisocyanates, aliphatic diisocyanates having a cyclic structure, aliphatic diisocyanates having an aromatic ring, aliphatic diisocyanates having an aromatic ring, aromatic diisocyanates, and modified products of these diisocyanates (carbodiimide, uretdione, uretoimine-containing modified products, etc.). Examples of chain-like aliphatic diisocyanates include tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. Examples of aliphatic diisocyanates having a cyclic structure include isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate. Examples of aliphatic diisocyanates having an aromatic ring include xylylene diisocyanate, tetramethylxylylene diisocyanate, etc. Examples of aromatic diisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, etc. Among these, one or more selected from the group consisting of aliphatic diisocyanates and aromatic diisocyanates are preferred.

[0049] Examples of dialkanolcarboxylic acids constituting the anionic urethane resin include dimethylolbutanoic acid, dimethylolpropionic acid, and salts thereof.

[0050] The anionic urethane resin may be used in combination with a chain extender or a reaction terminator, if necessary. The use of a chain extender can further increase the molecular weight. Examples of chain extenders include polyols and polyamines, and examples of reaction terminators include monoalcohols and monoamines. The anionic urethane resin is preferably used as an emulsion, and the emulsion may contain a dispersant such as a surfactant, if necessary.

[0051] The acid value of the anionic urethane resin is preferably 3 mgKOH / g or more, more preferably 5 mgKOH / g or more, even more preferably 7 mgKOH / g or more, and is preferably 50 mgKOH / g or less, more preferably 40 mgKOH / g or less, even more preferably 35 mgKOH / g or less.

[0052] An anionic silicone resin is a resin having a silicone structure and an anionic group within its resin structure. The silicone structure may be present in the main chain structure of the resin, or may be present as a side chain of the resin. In the present invention, when 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 blended), acid value: 2.2 mg KOH / g), all manufactured by Nissin Chemical Industry Co., Ltd.

[0053] The acid value of the anionic silicone resin is preferably 2 mgKOH / g or more, more preferably 4 mgKOH / g or more, even more preferably 6 mgKOH / g or more, and is preferably 20 mgKOH / g or less, more preferably 10 mgKOH / g or less, even more preferably 5 mgKOH / g or less.

[0054] (Hydrophobic Surfactant) The "hydrophobic surfactant" used as the hydrophobic compound (A2) refers to a surfactant that does not form a single phase when mixed with ion-exchanged water at a mass ratio of 1:1 at 25°C. Cationic surfactants that satisfy this condition are not included in the hydrophobic surfactants. The hydrophobic surfactant used as the hydrophobic compound (A2) is preferably nonionic. Preferred examples of nonionic hydrophobic surfactants include one or more surfactants selected from the group consisting of acetylene glycol surfactants and silicone surfactants. The acetylene glycol surfactant is a diol having a carbon-carbon triple bond in the center of its structure and a hydroxyl group on each carbon atom adjacent to the carbon-carbon triple bond, or an ethylene oxide (hereinafter also referred to as "EO") adduct of the diol. Acetylene glycol surfactants can be synthesized by reacting acetylene with a ketone or aldehyde corresponding to the desired acetylene glycol, and can be obtained, for example, by the method described in Takehiko Fujimoto, revised edition, "New Introduction to Surfactants" (published by Sanyo Chemical Industries, Ltd., 1992), pages 94 to 107. The HLB value of the acetylene glycol surfactant is preferably 8 or less. Here, the HLB (hydrophile-lipophile balance) value indicates the affinity of the surfactant for water and oil, and the HLB value of the acetylene glycol surfactant can be calculated using the Griffin method using the following formula: HLB value = 20 × [(sum of formula weights 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 examples of the acetylene glycol surfactant include one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and EO adducts thereof.Among these, one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and EO adducts thereof are more preferred, one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and adducts thereof having an average EO addition mole 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-decyne-4,7-diol, an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol having an average 1.3 mols, and an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol having an average 3 mols. Commercially available acetylene glycol surfactants include Surfynol 104PG-50 (2,4,7,9-tetramethyl-5-decyne-4,7-diol, a 50% propylene glycol solution with an average number of moles of EO added: 0, an HLB value of 3.0 (calculation formula: 20×(34 / 226))) and Surfynol 420 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with an average of 1.3 moles of EO added, an HLB value of 6.4 (calculation formula: 20×((34+44×1.3) / (226+44×1.3)))) available from Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals.

[0055] Silicone surfactants have a silicone structure and a structure exhibiting hydrophilicity, and the hydrophilic structure can be a polyether group. The HLB value of the silicone surfactant is preferably 7 or less. Here, the HLB value of the silicone surfactant can be the value listed in the catalog. Preferred commercially available silicone 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-co-modified type), HLB value: 3.0 (catalog value)), and KF-6048 (polyether-modified silicone (linear type, alkyl-modified type), HLB value: 3.5 (catalog value)).

[0056] Among these, from the viewpoint of improving the clarity of the printed image while suppressing the occurrence of streaks in the resulting printed matter, the pretreatment liquid according to the present invention preferably contains, as the component (A) that suppresses wetting and spreading, one or more selected from the group consisting of metal salts, organic acids or salts thereof, cationic resins, anionic resins, and hydrophobic surfactants, more preferably one or more selected from the group consisting of metal salts, organic acids or salts thereof, cationic resins, and anionic resins, and even more preferably one or more selected from the group consisting of metal salts, organic acids or salts thereof, cationic resins, and anionic resins having a crosslinked structure.

[0057] <Organic Solvent (B)> The pretreatment liquid according to the present invention preferably further contains an organic solvent (B) from the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image. The organic solvent (B) may be used singly or in combination of two or more. From the viewpoint of suppressing the occurrence of streaks in the resulting printed matter while improving the clarity of the printed image, the static surface tension of the organic solvent (B) measured at 25°C is preferably 40 mN / m or less, more preferably 38 mN / m or less, and preferably 18 mN / m or more, more preferably 20 mN / m or more, even more preferably 22 mN / m or more, and still more preferably 24 mN / m or more. The static surface tension of the organic solvent (B) at 25°C is measured by the method described in the Examples. When two or more organic solvents are used as the organic solvent (B), the static surface tension of the organic solvent (B) is a weighted average value weighted by the content (mass%) of each organic solvent.

[0058] The boiling point of the organic solvent (B) under 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 evaporation from the printing medium, suppressing the occurrence of streaks in the resulting printed matter, and improving the clarity of the printed image, and is preferably 140°C or higher, more preferably 160°C or higher, and even more preferably 180°C or higher, from the viewpoint of suppressing excessive acceleration of the evaporation rate, suppressing uneven distribution of the component that suppresses wetting and spreading, suppressing the occurrence of streaks in the resulting printed matter, and improving the clarity of the printed image. When two or more organic solvents are used as the organic solvent (B), the boiling point of the organic solvent (B) is a weighted average value weighted by the content (mass%) of each organic solvent.

[0059] Examples of the organic solvent (B) include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, and polyhydric alcohol aralkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. Among these, one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.

[0060] 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.

[0061] 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. An example of the polyhydric alcohol aralkyl ether is ethylene glycol monobenzyl ether.

[0062] 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. Examples of organic solvents other than those mentioned above include propylene carbonate and ethylene carbonate.

[0063] [Water] The pretreatment liquid according to the present invention preferably further contains water. The pretreatment liquid according to the present invention is preferably aqueous. The pretreatment liquid according to the present invention being "aqueous" means that water accounts for the largest proportion by mass of the liquid components contained in the pretreatment liquid. The water is preferably pure water or ultrapure water, such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, from which ionic impurities have been removed as much as possible.

[0064] The pretreatment liquid according to the present invention may further contain other components, as necessary, such as surfactants other than the cationic surfactants and hydrophobic surfactants described above, pH adjusters, fixing aids, colorants, defoamers, antiseptics and antifungals, and rust inhibitors.

[0065] The pretreatment liquid according to the present invention preferably further contains a surfactant other than the cationic surfactant and hydrophobic surfactant described above. The surfactant other than the cationic surfactant and hydrophobic surfactant described above is preferably a hydrophilic nonionic surfactant. In the present invention, the term "hydrophilic nonionic surfactant" refers to a surfactant that forms a single phase when mixed with ion-exchanged water at a mass ratio of 1:1 at 25°C. Examples of hydrophilic nonionic surfactants include hydrophilic polyoxyalkylene alkyl ether surfactants, hydrophilic acetylene surfactants, hydrophilic polyhydric alcohol surfactants, hydrophilic fatty acid alkanolamides, hydrophilic silicone surfactants, and hydrophilic fluorine-containing surfactants. Among these, one or more surfactants selected from the group consisting of hydrophilic acetylene surfactants and hydrophilic silicone surfactants are preferred. The HLB value of the hydrophilic acetylene surfactant is preferably greater than 8. The HLB value of the hydrophilic acetylene surfactant can be determined from the above formula using the Griffin method. Examples of hydrophilic acetylene surfactants include one or more ethylene oxide (EO) adducts selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-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 (n) of the EO adducts is preferably more than 8 and preferably 20 or less, more preferably 10 or less. Preferred hydrophilic silicone surfactants are polyether-modified silicone surfactants. Suitable examples of the polyether group in the polyether-modified silicone surfactant include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups (trimethyleneoxy groups or propane-1,2-diyloxy groups) are added in block or random fashion. Compounds in which polyether groups are grafted onto a silicone main chain and compounds in which polyether groups are bonded in block fashion to both ends of a silicone main chain can also be used. The HLB value of the hydrophilic silicone surfactant is preferably greater than 8.Here, the HLB value of the hydrophilic silicone surfactant can be the value listed in the catalog. Commercially available examples of hydrophilic nonionic surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, and the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd. One type of hydrophilic nonionic surfactant can be used alone, or two or more types can be used in combination. Among these, from the viewpoint of improving the clarity of printed images while suppressing the occurrence of streaks in the resulting printed matter, it is preferable to use a hydrophilic acetylene glycol surfactant and a hydrophilic silicone surfactant in combination.

[0066] The pretreatment liquid according to the present invention may contain a pH adjuster. The pH adjuster is an agent that suppresses pH fluctuations due to environmental changes and maintains the pH of the pretreatment liquid constant. Any known pH adjuster can be selected depending on the pH of the pretreatment liquid according to the present invention.

[0067] The pretreatment liquid according to the present invention may contain a colorant to the extent that the effects of the present invention are not impaired. Examples of such colorants include those used in the colorant-containing inks described below. When the pretreatment liquid according to the present invention contains a colorant, the colorant is preferably a pigment or a hydrophobic dye from the viewpoint of water resistance, and preferably a pigment from the viewpoint of achieving high weather resistance. From the viewpoint of improving the sharpness of printed images, the content of the colorant in the pretreatment liquid is preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, still more preferably 0.01% by mass or less, and even more preferably no colorant is contained.

[0068] [Composition of Pretreatment Liquid] The content of the component (A) that suppresses wetting and spreading in the pretreatment liquid 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 viewpoints of suppressing the occurrence of streaks in the resulting printed matter and improving the clarity of the printed image, and from the same viewpoints as above, is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0069] The content of the organic solvent (B) in the pretreatment liquid 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 still more preferably 25% by mass or more, from the viewpoints of suppressing the occurrence of streaks in the resulting printed matter and improving the clarity of the printed image, and from the same viewpoints as above, is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and still more preferably 35% by mass or less.

[0070] The mass ratio of the content of the component (A) that inhibits wetting and spreading to the content of the organic solvent (B) in the pretreatment liquid according to the present invention [component (A) that inhibits wetting and spreading / organic solvent (B)] is preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.05 or more, and still more preferably 0.07 or more, from the viewpoints of suppressing the occurrence of streaks in the obtained printed matter and improving the sharpness of the printed image, and is also preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.3 or less, from the same viewpoints as above.

[0071] 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 is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and still more preferably 70% by mass or less. When the polyvalent metal salt is used as a raw material in the form of a hydrate having water of hydration, the water content in the pretreatment solution according to the present invention means the amount including the water content from the hydrate of the polyvalent metal salt.

[0072] When the pre-treatment liquid according to the present invention contains a hydrophilic nonionic surfactant, the content of the hydrophilic nonionic surfactant in the pre-treatment liquid 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, even more preferably 1% by mass or less. The content of the colorant in the pre-treatment liquid 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, still more preferably 0.1% by mass or less, and still more preferably 0% by mass.

[0073] The pre-treatment liquid according to the present invention is preferably prepared by appropriately mixing the component (A) that suppresses wetting and spreading, the organic solvent (B), and, if necessary, water and the other components described above. The pH of the pre-treatment liquid can be appropriately adjusted with the pH adjuster described above.

[0074] In order to improve the clarity of the printed image, the pretreatment liquid according to the present invention is preferably applied to the printing medium in a solid state, i.e., so that the printing duty of the pretreatment liquid is 100%. Here, the "printing duty of the pretreatment liquid" refers to the proportion of the area occupied by the pretreatment liquid within a predetermined area on the printing medium, i.e., the proportion of the cumulative area to which the pretreatment liquid is applied. Preferred methods for applying the pretreatment liquid to the printing medium include, for example, spraying, brushing, and inkjet printing. Among these, application of the pretreatment liquid by inkjet printing is more preferred from the viewpoints of ease of adjusting the application position of the pretreatment liquid and of improving the clarity of the printed image while suppressing the occurrence of streaks in the resulting print. From the viewpoint of being able to perform step 1 and step 2 continuously, the device used to apply the pretreatment liquid to the printing medium is preferably one in which a means for applying the pretreatment liquid used in step 1 and a means for applying the colorant-containing ink used in step 2 are integrated, and more preferably one that uses a line head inkjet system as the means for applying the pretreatment liquid used in step 1 and the means for applying the colorant-containing ink used in step 2.

[0075] The amount of the pretreatment liquid applied to the printing medium is preferably 0.003 g / m from the viewpoint of suppressing the occurrence of streaks in the printed matter and improving the clarity of the printed image. 2 More preferably, 0.01 g / m 2 More preferably, 0.1 g / m 2 From the same viewpoint as above, it is preferably 10 g / m 2 Less than 5 g / m, more preferably 2 More preferably, 1 g / m or less 2 More preferably, 0.5 g / m or less 2The amount of the component (A) contained in the pretreatment liquid that suppresses wetting and spreading to be applied to the printing medium is preferably 0.0001 g / m from the viewpoint of suppressing the occurrence of streaks in the printed matter and improving the clarity of the printed image. 2 More preferably, 0.0005 g / m 2 More preferably, 0.001 g / m 2 From the same viewpoint as above, it is preferably 0.1 g / m 2 or less, more preferably 0.01 g / m 2 More preferably, 0.001 g / m or less 2 The following is the result.

[0076] The printing method of the present invention preferably includes, in step 1, a step of applying a pretreatment liquid to the printing medium and then holding the printing medium to which the pretreatment liquid has been applied at 25°C or higher. This step has the effect of removing volatile components in the pretreatment liquid from the printing medium to which the pretreatment liquid has been applied, thereby drying the printing medium (hereinafter, the step of holding the printing medium to which the pretreatment liquid has been applied at 25°C or higher in step 1 is also referred to as the "drying step of step 1"). The printing method of the present invention also preferably includes, in step 1, a step of drying the printing medium to which the pretreatment liquid has been applied. The printing method of the present invention also preferably includes, in step 1, a step of fixing the area to which the pretreatment liquid has been applied. That is, the drying step of step 1 is preferably a step of holding the printing medium to which the pretreatment liquid has been applied at 25°C or higher and drying the printing medium to which the pretreatment liquid has been applied, and more preferably a step of holding the printing medium to which the pretreatment liquid has been applied at 25°C or higher and drying the printing medium to which the pretreatment liquid has been applied, and fixing the area to which the pretreatment liquid has been applied. This further improves the clarity of the printed image. In step 1, preferred methods for maintaining the printing medium to which the pretreatment liquid has been applied at 25°C or higher include leaving it to stand, blowing air, heating, reducing pressure, and the like. 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 1 of the present invention. The temperature at which the printing medium is maintained in the drying step of step 1 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. Furthermore, from the viewpoint of drying in a short period of time and further improving the clarity of the printed image, the temperature is preferably 25°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher. The time at which the maintenance temperature is maintained (maintenance time) in the drying step of step 1 is preferably 0.5 seconds or longer, more preferably 1 second or longer, even more preferably 1.5 seconds or longer, and preferably 30 minutes or shorter, more preferably 20 minutes or shorter, even more preferably 10 minutes or shorter, and still more preferably 1 minute or shorter.

[0077] From the viewpoint of improving the clarity, and particularly the sharpness, of printed images, the drying rate of the pretreatment liquid in the drying step of step 1, i.e., the rate at which volatile components in the pretreatment liquid are removed, 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. In the present invention, the "drying rate of the pretreatment liquid" is the percentage ratio of the total mass of components contained in the pretreatment liquid that can be removed by the drying step of step 1 to the total mass of components that are actually removed by the drying step, and is calculated using the following formula, where M0 is the mass of the printing medium, M1 is the mass of the printing medium immediately after applying the pretreatment liquid in step 1, M2 is the mass of the printing medium after the step of maintaining the printing medium at 25°C or higher, and X% by mass is the proportion of the total mass of components in the pretreatment liquid that can be removed by the drying step of step 1. Drying rate (mass %)=(M1−M2) / [(M1−M0)×X / 100]×100 In the present invention, the proportion X (mass %) of the total mass of components in the pretreatment liquid that can be removed by the drying step in step 1 is preferably the water content (mass %) in the pretreatment liquid.

[0078] <Step 2> Step 2 is a step of applying a colorant-containing ink by a line head inkjet method to a portion of the surface of the printing medium obtained in step 1 that has a pretreatment liquid application portion, where the dark image formation portion will be formed. If the print duty of the colorant-containing ink in the light image formation portion is 0%, it is preferable that the colorant-containing ink is not applied to the light image formation portion in step 2. That is, in this case, step 2 is preferably step 2-1 below. Step 2-1: A step of applying a colorant-containing ink by a line head inkjet method only to a portion of the surface of the printing medium obtained in step 1 that has a pretreatment liquid application portion, where the dark image formation portion will be formed.

[0079] Furthermore, when the printing duty of the colorant-containing ink in the light image forming portion exceeds 0%, in step 2, the colorant-containing ink is applied not only to the portion that will become the dark image forming portion on the surface of the printing medium obtained in step 1 having the pretreatment liquid application portion, but also to the portion of the portion that will become the light image forming portion to which the colorant-containing ink is applied. That is, in this case, step 2 becomes step 2-2 below. Step 2-2: A step of applying the colorant-containing ink by a line head inkjet method to the portion that will become the dark image forming portion on the surface of the printing medium obtained in step 1 having the pretreatment liquid application portion, and to the portion of the portion that will become the light image forming portion to which the colorant-containing ink is applied.

[0080] (Colorant-Containing Ink) The ink containing the colorant according to the present invention (colorant-containing ink) is described below. The colorant-containing ink according to the present invention is preferably one or more inks selected from the group consisting of black inks and chromatic inks.

[0081] [Colorant] The colorant used in the colorant-containing ink of the present invention can be either a dye or a pigment. Among these, it is preferable to use a pigment as the colorant from the viewpoint of water resistance, light resistance, weather resistance, gas resistance, etc. The pigment can be either a known organic pigment or an inorganic pigment. One type of pigment may be used alone, or two or more types may be used in combination, or a mixed crystal may be used. Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Examples of polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of dye chelates include basic dye-type chelates and acid dye-type chelates. Specific examples of pigments for black inks include carbons, metals, and organic pigments. Examples of carbons include lamp black (C.I. Pigment Black 6), carbon black (C.I. Pigment Black 7) such as furnace black, acetylene black, and channel black. Examples of metals include copper-chromium oxide (C.I. Pigment Black 28), iron oxide (C.I. Pigment Black 11), and titanium oxide (C.I. Pigment Black 35). Examples of organic pigments include aniline black (C.I. Pigment Black 1). Specific examples of pigments for chromatic inks include C.I. Pigment Yellow, C.I. Pigment Orange, C.I. Pigment Red, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green.

[0082] The dye is not particularly limited, and examples thereof include acid dyes, basic dyes, direct dyes, reactive dyes, etc. The dyes may be used alone or in combination of two or more. Examples of the dye include C.I. Acid Yellow, C.I. Acid Red, C.I. Acid Blue, C.I. Acid Black, C.I. Food Black, C.I. Direct Yellow, C.I. Direct Red, C.I. Direct Blue, C.I. Direct Black, C.I. Reactive Red, and C.I. Reactive Black.

[0083] When a colorant-containing ink contains a pigment, the pigment is dispersed in a medium within the ink. Examples of the form of the pigment in the colorant-containing ink include a form in which the pigment is dispersed using a resin (hereinafter also referred to as a "pigment-dispersing resin") or a surfactant as a dispersant, and a form in which the pigment is self-dispersed without using a dispersing agent. Among these, a form in which the pigment is dispersed using a pigment-dispersing resin is preferred for the colorant-containing ink. The pigment-dispersing resin may be either a water-soluble resin or a water-insoluble resin. Regarding the "water-soluble" and "water-insoluble" nature of a resin, when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, the resin is deemed "water-soluble" if the dissolved amount exceeds 10 g, and "water-insoluble" if the dissolved amount is 10 g or less. Furthermore, as described below, when the resin has an anionic group, the dissolved amount is the amount measured in the presence of a neutralizer under conditions where the mass ratio of the resin to the neutralizer is the same as that in the colorant-containing ink.

[0084] Specific examples of the form of the pigment in the colorant-containing ink, from the viewpoint of improving the dispersion stability of the pigment, include (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 in which a hydrophilic functional group is chemically or physically introduced onto the surface of the pigment and the pigment is dispersed without using a pigment dispersing resin or a surfactant, and (d) a form in which the pigment is coated with a water-insoluble resin.

[0085] The pigments having the aforementioned forms (a) to (d) preferably have anionic properties. In form (a), the water-soluble resin preferably has an anionic group; in form (b), the water-soluble surfactant or water-dispersible surfactant preferably has an anionic group; in form (c), the hydrophilic functional group introduced onto the pigment surface preferably has an anionic group; and in form (d), the water-insoluble resin preferably has an anionic group. Examples of anionic groups are as defined for the anionic resin of hydrophobic compound (A2). Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Among these, the anionic resin preferably has a carboxy group as the anionic group, and M is preferably an alkali metal.

[0086] Among these, when the component (A) contained in the pretreatment liquid that suppresses wetting and spreading is an aggregating compound (A1), the pigment in the colorant-containing ink can reduce the dispersibility of dispersoids present in the ink, thereby efficiently exhibiting the aggregation effect. Furthermore, when the component (A) contained in the pretreatment liquid that suppresses wetting and spreading is a hydrophobic compound (A2), excessive wetting and spreading of the ink can be prevented. This increases the efficiency of wetting and spreading prevention, thereby suppressing the occurrence of streaks in the resulting printed matter and improving the clarity of the printed image. From this perspective, the pigment is preferably one or more forms selected from the group consisting of form (c) and form (d), and more preferably form (d). When the pigment in the colorant-containing ink is form (d), examples of the form in which the pigment is coated with a water-insoluble resin include 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 to the pigment. When the pigment in the colorant-containing ink is in the form (d), the pigment is preferably 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, the water-insoluble resin preferably has a structure containing a polymer component having a linear two-dimensional structure, which may have branched chains, and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure, which may have branched chains, being converted into a three-dimensional structure by the component derived from the crosslinking agent.

[0087] [Pigment Dispersion Resin] When the colorant-containing ink is in the form (d), the type of water-insoluble resin used as the pigment dispersing resin for dispersing the pigment in 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 pigment in the colorant-containing ink is in the form (d) and the pigment is coated with a water-insoluble resin having a crosslinked structure, the constituent component of the polymer having a linear two-dimensional structure that may have a branched chain is preferably one or more selected from the group consisting of (meth)acrylic resins, styrene / (meth)acrylic resins, urethane resins, and polyester resins, from the viewpoint of forming high-quality printed images, 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 a known method, or a commercially available product may be used. The water-insoluble resin may be used alone or in combination of two or more.

[0088] The number-average molecular weight of 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, even more preferably 30,000 or less. The number-average molecular weight of the pigment dispersion resin is measured by the method described in the Examples. When the colorant-containing ink is in the form (d) in which the pigment is coated with a water-insoluble resin having a crosslinked structure, the number-average molecular weight of the constituent component of the polymer having a linear two-dimensional structure, which may have a branched chain, of the water-insoluble resin used to disperse 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, even more preferably 30,000 or less. The acid value of the pigment dispersion resin is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 70 mgKOH / g or more, and even more preferably 90 mgKOH / g or more, and is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, and even more preferably 300 mgKOH / 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. When 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 crosslinker.

[0089] [Fixing Resin] From the viewpoint of forming a high-quality printed image, the colorant-containing ink may contain a resin (hereinafter also referred to as "fixing resin") that functions as a fixing aid. 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 a pigment. The fixing resin is not particularly limited and can be appropriately selected depending on the purpose. Specific examples of fixing resins include urethane resins, polyester resins, acrylic resins, vinyl acetate resins, styrene resins, butadiene resins, styrene / butadiene resins, vinyl chloride resins, styrene / acrylic resins, and acrylic silicone resins. An ink can be obtained by mixing a particulate fixing resin with a colorant, water, an organic solvent, etc. The fixing resin may be synthesized or commercially available. One fixing resin may be used alone, or two or more fixing resins may be used in combination.

[0090] [Wax] The colorant-containing ink may contain wax from the viewpoint of forming a high-quality printed image. In this specification, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid when heated. Here, "semi-solid wax" means that the wax deforms and flows when force is applied to it, but can maintain a certain shape when no force is applied to it. The temperature at which the wax becomes liquid when heated, i.e., the melting point of the wax, is in the temperature range of 45°C or higher. The wax may be either natural or synthetic. 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 synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax; silicone-based waxes; and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. Among these, polyolefin waxes primarily composed of olefin-based monomers are preferred. The waxes can be used alone or in combination of two or more.

[0091] The colorant-containing ink preferably contains wax as a dispersion (hereinafter also referred to as "wax dispersion"). The wax dispersion is not particularly limited, and examples thereof include those prepared by emulsifying wax with a known surfactant. Examples of the surfactant that can be used include nonionic surfactants and anionic surfactants. 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, and the like. Among these, from the viewpoint of improving the ink ejection stability and the image fastness of printed matter, nonionic wax dispersions prepared by emulsifying wax with a nonionic surfactant are preferred, and nonionic polyolefin wax dispersions are more preferred. Suitable examples of commercially available wax dispersions include the "Hi-Tec E" series manufactured by Toho Chemical Industry Co., Ltd., the "AQUACER" series manufactured by BYK Corporation, the "Cellosol" series manufactured by Chukyo Yushi Co., Ltd., and the "Chemipearl" series manufactured by Mitsui Chemicals, Inc.

[0092] [Water] The medium of the colorant-containing ink is preferably an aqueous medium. That is, the colorant-containing ink is preferably an aqueous ink containing water. Here, "aqueous" means that water accounts for the largest proportion by mass of the medium of the colorant-containing ink. As the water contained in the colorant-containing ink, ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water is preferably used.

[0093] [Water-soluble organic solvent] The colorant-containing ink may further contain a water-soluble organic solvent as the aqueous medium. Examples of the water-soluble organic solvent contained in the ink include polyhydric alcohols; ethers such as polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, and polyhydric alcohol aralkyl ethers; nitrogen-containing heterocyclic compounds; amides; amines; and sulfur-containing compounds. From the viewpoint of environmental friendliness, the content of water 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 still more preferably 65% ​​by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and still more preferably 80% by mass or less.

[0094] The colorant-containing ink may contain surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, pH adjusters, and the like, as required.

[0095] [Composition of Colorant-Containing Ink] The content of the 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, from the viewpoint of improving the image density of the printed matter. When the colorant-containing ink contains a pigment as a colorant, the content of the pigment 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 matter. When the colorant-containing ink contains a pigment dispersing resin, the content of the 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 matter. When the colorant-containing ink contains a pigment dispersion resin, the mass ratio of the pigment content to the pigment dispersion resin content in the ink [pigment / pigment dispersion resin] is preferably 0.30 or more, more preferably 0.50 or more, and even more preferably 0.70 or more, from the viewpoint of improving the image density of printed matter, and is preferably 1.00 or less, more preferably 0.90 or less, and even more preferably 0.80 or less, from the viewpoint of pigment dispersion stability and forming high-quality printed images. When the colorant-containing ink contains a fixer resin, the content of the fixer 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 high-quality printed images, and is preferably 10% by mass or less, more preferably 7% by mass or less, from the viewpoint of improving the image density of printed matter. When the colorant-containing ink contains a wax, the content of the wax 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, from the viewpoint of forming a high-quality printed image, and is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less.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, from the viewpoint of forming a high-quality printed image, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and still more preferably 20% by mass or less. From the viewpoint of environmental friendliness, the content of water in the colorant-containing ink is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and is preferably 85% by mass or less, more preferably 80% by mass or less, and still more preferably 75% by mass or less.

[0096] (Linehead type inkjet method) The inkjet method used in the printing method of the present invention is carried out using a linehead type print head. A linehead type print head is equipped with a head that can perform inkjet printing over a width equal to or greater than the length in the direction perpendicular to the transport direction of the print medium, and therefore high-speed printing is possible because the print head is left fixed and only the print medium is scanned. A linehead type print head may be one in which multiple individual heads are arranged in a line. It is preferable to provide a linehead type print head for each color of colorant-containing ink.

[0097] From the viewpoint of forming high-quality printed images, the nozzle spacing in a linehead 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 600 npi or more, and from the same viewpoint as above, 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 the present invention, the unit "npi" indicating the nozzle spacing in a linehead print head refers to the number of nozzles per inch in the longitudinal direction of the nozzle row of the print head.

[0098] There are various types of print head ejection systems, but the printing method of the present invention may use either a piezo system using a piezoelectric element or a thermal system using a thermal element. Of these, the piezo system is preferred as the print head ejection system from the viewpoint of forming high-quality printed images.

[0099] 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 matter, and is 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 a high-quality printed image.

[0100] In the present invention, the amount of ink droplets ejected containing a colorant is preferably 1 pL or more, more preferably 1.5 pL or more, even more preferably 2 pL or more, from the viewpoint of forming a high-quality printed image, and is 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. Here, "pL (picoliter)" is 10 times "L (liter)". -12 The amount of ink droplets ejected containing the colorant can be set by an inkjet head control device.

[0101] In the present invention, the resolution in the direction parallel to the transport direction of the printing medium, i.e., the density of ink dots 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 viewpoints as above, is 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, i.e., the density of ink dots 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 viewpoints as above, is 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 unit "dpi" indicating resolution means the number of ink dots per inch in the direction parallel or perpendicular to the transport direction of the printing medium. When the resolution differs for each ink color, the highest resolution is regarded as the resolution in the present invention.

[0102] In the present invention, the diameter of the ink dots that have landed on the printing medium (hereinafter 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, is 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 the ink dots that have landed on the printing medium can be determined by observing 10 ink dots under a microscope after applying ink by inkjet printing, and taking the average value of the observed values.

[0103] The amount of the colorant-containing ink applied to the area where the dark image is to be formed in step 2 is preferably 1 g / m from the viewpoint of improving the clarity of the printed image while suppressing the occurrence of streaks in the resulting printed matter. 2 More preferably, 3 g / m 2 More preferably, 4.5 g / m 2From the same viewpoint as above, it is preferably 10 g / m 2 More preferably, 7 g / m or less 2 More preferably 5 g / m or less 2 The following is the result.

[0104] <Step 3> In the present invention, from the viewpoint of forming a high-quality printed image by clearly defining the contours of the dark image formation portion, it is preferable to further include step 3, in which a white ink containing a white pigment (hereinafter also simply referred to as "white ink") is applied to the printing medium or the surface of the printing medium to which the colorant-containing ink has been applied, before step 1 or after step 2. When step 3 is further included, it is preferable to apply the white ink to the surface of the printing medium opposite to the surface to which the colorant-containing ink has been applied (i.e., the printing medium) or the surface to which the colorant-containing ink has been applied after step 2. When a resin film is used as the low-liquid-absorbent printing medium, and a mirror image of the desired printed image is formed on the printing medium so that it appears as the intended image when viewed from the opposite side of the printed image forming surface of the non-liquid-absorbent film, it is preferable that step 3 be applied to the entire surface of the printing medium to which the colorant-containing ink has been applied.

[0105] Examples of pigments for white inks include white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, antimony oxide, and zirconium oxide. From the viewpoint of increasing whiteness and improving the sharpness of cut-out characters, one or more selected from the group consisting of titanium oxide and zinc oxide are preferred, and titanium oxide (C.I. Pigment White 6) is more preferred. While untreated titanium oxide can be used, surface-treated titanium oxide is preferred from the viewpoint of obtaining good dispersibility. Examples of surface treatments for titanium oxide include surface treatment with an inorganic substance and surface treatment with an organic substance such as a titanium coupling agent, a silane coupling agent, or silicone oil, and surface treatment with an inorganic substance is preferred.

[0106] In the present invention, the white pigment in the white ink is dispersed in a medium. The form of the white pigment in the white ink may be a form in which the white pigment is dispersed using the aforementioned pigment dispersion resin or surfactant as a dispersant, or a form of a self-dispersed pigment in which the white pigment is dispersed without using a dispersant. Among these, the form in which the white pigment is dispersed using a pigment dispersion resin is preferred. The pigment dispersion resin is preferably the same as the resin exemplified for the colorant-containing ink. The white ink may further contain the aforementioned fixing resin.

[0107] The medium for the white ink is preferably an aqueous medium. That is, the white ink is preferably an aqueous ink containing water. Here, "aqueous" means that water accounts for the largest proportion by mass of the white ink medium. The water contained in the white ink is preferably ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water. The white ink may also contain wax, water-soluble organic solvents, surfactants, defoamers, antiseptics / fungicides, rust inhibitors, pH adjusters, and the like, as needed. The preferred ranges for the content of each component, such as the white pigment, in the white ink are the same as the preferred ranges for the content of each component, such as the colorant, in the colorant-containing ink described above.

[0108] Examples of methods for applying the white ink in step 3 include roller application, spray application, brush application, and inkjet application. Among these, from the viewpoint of applying the white ink simply and uniformly, one selected from the group consisting of roller application and inkjet application is preferred. Specific examples of rollers used for roller application 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. Specific examples of inkjet application are preferably those using a line inkjet system. Furthermore, from the viewpoint of being able to perform steps 1, 2, and 3 continuously, the device for applying the white ink to the printing medium or the print image forming surface in step 3 is preferably one that is integrated with a means for applying the pretreatment liquid used in step 1 and a means for applying the colorant-containing ink used in step 2. In this case, for example, the inkjet printing device may be one in which a white ink application means such as a roller applicator is incorporated, or one in which an inkjet head that applies white ink is incorporated.

[0109] In order to form a high-quality printed image, the amount of white ink applied to the printing medium in step 3 is preferably 1 g / m 2 More preferably 5 g / m 2 More preferably, 10 g / m 2 From the same viewpoint as above, it is preferably 50 g / m 2 or less, more preferably 30 g / m 2 More preferably 15 g / m or less 2 The following is the result.

[0110] When the printing method of the present invention includes step 3, from the viewpoint of forming a high-quality printed image, step 3 preferably includes a step of applying a white ink to a printing medium or the surface of the printing medium to which a colorant-containing ink has been applied, and then holding the printing medium to which the white ink has been applied at 25°C or higher. This step has the effect of removing volatile components in the white ink from the printing medium or printed matter to which the white ink has been applied, and can dry the printing medium or printed matter (hereinafter, the step of holding the printing medium to which the white ink has been applied at 25°C or higher in step 3 is also referred to as the "drying step of step 3"). Methods for holding the printing medium to which the white ink has been applied at 25°C or higher in step 3 include leaving it to stand, blowing air, heating, reducing pressure, etc. In the printing method of the present invention, the drying step of step 3 of the present invention does not include application of active energy rays such as ultraviolet light or radiation. The temperature at which the print medium is held in the drying step of step 3 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 print medium, and is preferably 25° C. or higher, more preferably 30° C. or higher, from the viewpoint of drying in a short time. The time at which the holding temperature is maintained (holding time) in the drying step of step 3 is preferably 0.5 seconds or longer, more preferably 1 second or longer, even more preferably 3 seconds or longer, still more preferably 5 seconds or longer, and preferably 30 minutes or shorter, more preferably 20 minutes or shorter, even more preferably 10 minutes or shorter, and even more preferably 1 minute or shorter.

[0111] The inkjet printing apparatus of the present invention is an inkjet printing apparatus used in the inkjet printing method of the present invention, and includes an inkjet head filled with a pretreatment liquid and an inkjet head filled with an ink containing a colorant. In the inkjet printing apparatus of the present invention, the pretreatment liquid and the ink containing a colorant are synonymous with the pretreatment liquid and the ink containing a colorant used in the printing method of the present invention. In the inkjet printing apparatus of the present invention, the inkjet head filled with the ink containing a colorant may be one inkjet head or multiple inkjet heads. However, from the viewpoint of using inks containing multiple colorants, multiple inkjet heads are preferred. Furthermore, the inkjet printing apparatus of the present invention preferably includes, in addition to the inkjet head filled with the pretreatment liquid and the inkjet head filled with the ink containing a colorant, an inkjet head filled with a white ink containing a white pigment. That is, the inkjet printing apparatus of the present invention preferably includes an inkjet head filled with a pretreatment liquid, an inkjet head filled with an ink containing a colorant, and an inkjet head filled with a white ink containing a white pigment. It is more preferred that the inkjet printing apparatus of the present invention includes an inkjet head filled with a pretreatment liquid, multiple inkjet heads filled with ink containing a colorant, and an inkjet head filled with the white ink containing a white pigment. The inkjet printing apparatus of the present invention can be preferably used in the printing method of the present invention described above or the method of producing a printed matter of the present invention described below.

[0112] The inkjet printing ink set of the present invention is an inkjet printing ink set used in the inkjet printing method of the present invention, and includes a pretreatment liquid and an ink containing a colorant. In the inkjet printing ink set of the present invention, the ink containing a pretreatment liquid and a colorant has the same meaning as the ink containing a pretreatment liquid and a colorant used in the printing method of the present invention described above. In the inkjet printing ink set of the present invention, the number of inks containing a colorant may be one or more, but preferably multiple. Furthermore, the inkjet printing ink set of the present invention preferably further includes a white ink containing a white pigment in addition to the ink containing a pretreatment liquid and a colorant. That is, the inkjet printing ink set of the present invention preferably includes a pretreatment liquid, an ink containing a colorant, and a white ink containing a white pigment, and more preferably includes a pretreatment liquid, an ink containing multiple colorants, and a white ink containing a white pigment. The inkjet printing ink set of the present invention can be preferably used in the printing method of the present invention described above or the method for producing a printed matter of the present invention described below.

[0113] [Method for Producing Printed Material] The printed material according to the present invention can be obtained by the printing method of the present invention described above. That is, the method for producing a printed material according to the present invention is a method for producing a printed material in which a print image including a dark image forming portion and a light image forming portion is formed on a printing medium, the print image including a dark image forming portion and a light image forming portion, and the print duty of the ink containing a colorant in the dark image forming portion is higher than the print duty of the ink containing a colorant in the light image forming portion, and includes the following steps: Step 1: applying a pretreatment liquid to the outer edge of the portion that will become the dark image forming portion, to obtain a printing medium having a pretreatment liquid application portion; and Step 2: applying an ink containing a colorant by a line head inkjet system to the portion that will become the dark image forming portion on the surface of the printing medium obtained in Step 1 that has the pretreatment liquid application portion.

[0114] In the method for producing a printed matter of the present invention, steps 1 and 2 are synonymous with steps 1 and 2 of the printing method of the present invention described above. Furthermore, the method for producing a printed matter of the present invention preferably further includes step 3, before step 1 or after step 2, of applying a white ink to the printing medium or to the surface of the printing medium to which the colorant-containing ink has been applied. In the method for producing a printed matter of the present invention, step 3 is synonymous with step 3 of the printing method of the present invention described above. Because the method for producing a printed matter of the present invention has the above-described characteristics, the resulting printed matter exhibits excellent clarity of a printed image including a dark image forming portion and a light image forming portion while suppressing the occurrence of streaks.

[0115] The present invention further includes the following aspects: <1> An inkjet printing method for forming a print image on a print medium, the print image including a dark image forming unit and a light image forming unit, wherein the print duty of ink containing a colorant in the dark image forming unit is higher than the print duty of ink containing a colorant in the light image forming unit, the inkjet printing method comprising: Step 1: applying a pretreatment liquid to an outer edge of a portion that will become the dark image forming unit, to obtain a print medium having a pretreatment liquid application unit; and Step 2: applying ink containing a colorant to a portion that will become the dark image forming unit on the surface of the print medium obtained in Step 1 that has the pretreatment liquid application unit, by a line head inkjet system. <2> An inkjet printing method for forming a print image on a print medium, the print image including a dark image forming unit and a light image forming unit, wherein the print duty of ink containing a colorant in the dark image forming unit is higher than the print duty of ink containing a colorant in the light image forming unit, the inkjet printing method comprising: step 1: applying a pretreatment liquid to an outer edge of a portion that will become the dark image forming unit, and maintaining the print medium to which the pretreatment liquid has been applied at 25°C or higher to obtain a print medium having a pretreatment liquid application unit; and step 2: applying ink containing a colorant by a line head inkjet system to a portion that will become the dark image forming unit on the surface of the print medium obtained in step 1 that has the pretreatment liquid application unit. <3> An inkjet printing method for forming a print image on a print medium, the print image including a dark image forming unit and a light image forming unit, wherein the print duty of ink containing a colorant in the dark image forming unit is higher than the print duty of ink containing a colorant in the light image forming unit, the inkjet printing method comprising: step 1: applying a pretreatment liquid to an outer edge of a portion that will become the dark image forming unit, and drying the print medium to which the pretreatment liquid has been applied, to obtain a print medium having a pretreatment liquid application unit; and step 2: applying ink containing a colorant by a line head inkjet system to a portion that will become the dark image forming unit on the surface of the print medium obtained in step 1 that has the pretreatment liquid application unit.<4> An inkjet printing method for forming a print image on a print medium, the print image including a dark image forming section and a light image forming section, wherein the print duty of ink containing a colorant in the dark image forming section is higher than the print duty of ink containing a colorant in the light image forming section, the inkjet printing method comprising: Step 1: applying a pretreatment liquid to an outer edge of a region that will become the dark image forming section to fix the pretreatment liquid application section, thereby obtaining a print medium having the pretreatment liquid application section; and Step 2: applying ink containing a colorant by a line head inkjet system to a region that will become the dark image forming section on the surface of the print medium obtained in Step 1 that has the pretreatment liquid application section. <5> The inkjet printing method according to any one of <1> to <4>, wherein the print medium is a low liquid-absorbent print medium. <6> The inkjet printing method according to <5>, wherein the non-liquid-absorbent print medium is a resin film. <7> The inkjet printing method according to <6>, wherein the resin film is a polyester film. <8> The inkjet printing method according to any one of <1> and <3> to <7>, comprising, in Step 1, a step of holding the printing medium to which the pretreatment liquid has been applied at 25°C or higher. <9> The inkjet printing method according to any one of <1>, <2> and <4> to <7>, comprising, in Step 1, a step of drying the printing medium to which the pretreatment liquid has been applied. <10> The inkjet printing method according to any one of <1> to <3> and <5> to <7>, comprising, in Step 1, a step of fixing the pretreatment liquid application unit. <11> The inkjet printing method according to any one of <1> to <10>, comprising, in Step 1, a step of holding the printing medium to which the pretreatment liquid has been applied at 40°C or higher and 100°C or lower for 1.5 seconds to 1 minute, to dry the pretreatment liquid and fix the pretreatment liquid. <12> The inkjet printing method according to any one of <1> to <11>, wherein the pretreatment liquid contains one or more compounds selected from the group consisting of an aggregating compound (A1) and a hydrophobic compound (A2). <13> The inkjet printing method according to <12>, wherein the aggregating compound (A1) is one or more compounds selected from the group consisting of a metal salt, an organic acid or a salt thereof, and a cationic resin.<14> The inkjet printing method according to <13>, wherein the aggregating compound (A1) is calcium nitrate. <15> The inkjet printing method according to <13>, wherein the aggregating compound (A1) is malonic acid. <16> The inkjet printing method according to <13>, wherein the aggregating compound (A1) is a diallyldimethylammonium chloride polymer. <17> The inkjet printing method according to <12>, wherein the hydrophobic compound (A2) is one or more compounds selected from the group consisting of anionic resins and hydrophobic surfactants. <18> The inkjet printing method according to <13>, wherein the anionic resin is one or more compounds selected from the group consisting of anionic vinyl resins, anionic urethane resins, and anionic silicone resins. <19> The inkjet printing method according to <12>, wherein the hydrophobic compound (A2) is a crosslinked acrylic acid / styrene resin. <20> The inkjet printing method according to any one of <1> to <19>, wherein an outer edge of the region that will become the dark image forming region is an area of ​​0.01 mm to 1 mm, calculated from the boundary between the dark image forming region and the light image forming region, on a side away from the dark image forming region. <21> The inkjet printing method according to <20>, wherein the outer edge is an area of ​​0.1 mm to 0.4 mm, calculated from the boundary between the dark image forming region and the light image forming region, on a side away from the dark image forming region. <22> The inkjet printing method according to any one of <1> to <21>, wherein in step 1, the pretreatment liquid is further applied to an inner edge of the region that will become the dark image forming region. <23> The inkjet printing method according to any one of <1> to <22>, wherein the inner edge of the region that will become the dark image forming region is an area of ​​0.01 mm to 1 mm, calculated from the boundary between the dark image forming region and the light image forming region, on a side away from the light image forming region. <24> The inkjet printing method according to <23>, wherein the inner edge portion is an area of ​​0.2 mm to 0.4 mm from the boundary line between the dark image forming portion and the light image forming portion on the side away from the light image forming portion.<25> The inkjet printing method according to any one of <1> to <24>, wherein the difference between the printing duty of the ink containing a colorant in the dark image forming section and the printing duty of the ink containing a colorant in the light image forming section is 50% or more. <26> The inkjet printing method according to <25>, wherein the difference between the printing duty of the ink containing a colorant in the dark image forming section and the printing duty of the ink containing a colorant in the light image forming section is 90% or more. <27> The inkjet printing method according to <25>, wherein the difference between the printing duty of the ink containing a colorant in the dark image forming section and the printing duty of the ink containing a colorant in the light image forming section is 100%. <28> The inkjet printing method according to any one of <1> to <27>, wherein the printing duty of the ink containing a colorant in the light image forming section is 0%. <29> The inkjet printing method according to any one of <1> to <28>, wherein the printed image is a hollow character image. <30> The inkjet printing method according to any one of <1> to <29>, further comprising step 3 of applying a white ink containing a white pigment to the printing medium or to a surface of the printing medium to which the ink containing a colorant has been applied, before step 1 or after step 2. <31> The inkjet printing method according to any one of <1> to <30>, wherein the print duty of the ink containing a colorant in the light image forming portion is greater than 0%, and the pretreatment liquid in step 1 is applied not only to the outer edge of the portion that will become the dark image forming portion, but also to a portion of the portion that will become the light image forming portion to which the ink containing a colorant has not been applied. <32> An inkjet printing apparatus used in the inkjet printing method according to any one of <1> to <31>, the inkjet printing apparatus having an inkjet head filled with the pretreatment liquid and an inkjet head filled with the ink containing the colorant. <33> An inkjet printing ink set used in the inkjet printing method according to any one of <1> to <32>, the inkjet printing ink set comprising the pretreatment liquid and the ink containing the colorant.<34> A method for producing a printed matter, which includes a dark image forming unit and a light image forming unit, and forms a print image on a printing medium, wherein the print duty of ink containing a colorant in the dark image forming unit is higher than the print duty of ink containing a colorant in the light image forming unit, the method comprising: Step 1: applying a pretreatment liquid to an outer edge of a portion that will become the dark image forming unit, to obtain a printing medium having a pretreatment liquid application unit; and Step 2: applying ink containing a colorant by a line head inkjet system to a portion that will become the dark image forming unit on a surface of the printing medium obtained in Step 1 that has the pretreatment liquid application unit.

[0116] In the following Preparation Examples, Production Examples, Examples, and Comparative Examples, "parts" and "%" mean "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring physical properties are as follows. Physical properties of resins and the like were measured by the following methods.

[0117] [Measurement of number average molecular weight and weight average molecular weight of resin] The number average molecular weight and weight average molecular weight were determined by gel permeation chromatography. The measurement conditions are as follows: GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation; Column: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation; Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60 mmol / L and 50 mmol / L, respectively; Flow rate: 0.5 mL / min; Standard: Monodisperse polystyrene kits with known molecular weights [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 calculated using this sample.

[0118] [Measurement of Resin Acid Value] Using an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), in the case of a resin without a crosslinked structure, the resin was dissolved in a titration solvent consisting of a mixture of toluene and acetone (2:1), or in the case of a resin with a crosslinked structure, the resin was dispersed in the titration solvent and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve being the endpoint. The acid value (mg KOH / g) was calculated from the titration amount of the potassium hydroxide solution up to the endpoint.

[0119] [Measurement of solid content concentration] 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm), and approximately 1.0 g of the sample was added thereto and mixed. The mixture was then accurately weighed, maintained at 105°C for 2 hours to remove volatiles, and left in the desiccator for 15 minutes, after which the mass was measured. The mass of the sample after volatiles removal was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration (%).

[0120] [Measurement of the average particle size of pigment-free resin particles and pigment-containing resin particles] Cumulant analysis was performed using a 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 pigment-free resin particles or pigment-containing resin particles. The measurement sample had a particle concentration of 5 × 10 -3 The dispersion was diluted with water to a mass % (solid content equivalent) and the measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion medium.

[0121] [Measurement of static surface tension of organic solvent (B) at 25°C] A platinum plate was immersed in a cylindrical polyethylene container (diameter 3.6 cm x depth 1.2 cm) containing 5 g of a sample adjusted to 25°C, and the static surface tension at 25°C was measured by the Wilhelmy method using a surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., "CBVP-Z").

[0122] Production Example 1 (Production of Acrylic Acid / Styrene Resin) A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. A reaction vessel was charged with 10 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, and the mixture was thoroughly purged with nitrogen gas. Meanwhile, a dropping funnel was charged with a mixture of the remainder of the 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. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C with stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours had passed at 65°C from the end of the dropwise addition, a solution prepared by dissolving 0.1 part of the polymerization initiator in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and at 70°C for 2 hours, followed by drying under reduced pressure to obtain an acrylic acid / styrene resin (number average molecular weight: 19,000, acid value: 240 mgKOH / g).

[0123] Production Example 2 (Production of Aqueous Dispersion of Crosslinked Acrylic Acid / Styrene Resin) 15.3 parts of the acrylic acid / styrene resin obtained in Production Example 1 was mixed with 63.5 parts of ion-exchanged water, and 1.8 parts of 25% aqueous ammonia was added to neutralize the mixture so that the ratio of the number of moles of ammonia to the number of moles of carboxyl groups in the acrylic acid / styrene resin was 40% (degree of neutralization: 40 mol%). This neutralized 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 the acrylic acid / styrene resin. 4.6 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321LT" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) was added as a crosslinking agent to the resulting dispersion of the acrylic acid / styrene resin, and the mixture was sealed and heated at 90°C for 1.5 hours while stirring with a stirrer. At this time, crosslinking treatment was carried out with an amount of crosslinking agent of an epoxy amount capable of reacting with 50% of the total number of carboxyl groups contained in the acrylic acid / styrene resin (crosslinking rate: 50%). Thereafter, the dispersion was cooled to room temperature (25°C) and filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a membrane filter ("Minisart" manufactured by Sartorius, material: cellulose acetate) with a pore size of 5 μm. Ion-exchanged water was added to adjust the solid content concentration to 20%, and an aqueous dispersion of crosslinked acrylic acid / styrene resin (acid value: 120 mg KOH / g) was obtained.

[0124] Preparation Examples 1 to 8 The components of the pretreatment liquid were added to a container equipped with a stirrer in the formulation shown in Table 1, mixed at 25°C for 1 hour, and then filtered using the membrane filter with a pore size of 5 μm and the needleless syringe to obtain each pretreatment liquid. The components shown in Table 1 are as follows. <Component (A) for suppressing wetting and spreading> [Aggregating compound (A1)] (cationic resin) Cationic vinyl resin A1-1: "PAS-H-1L" (diallyldimethylammonium chloride polymer) manufactured by Nittobo Medical Co., Ltd. (metal salt) Calcium nitrate: calcium nitrate tetrahydrate (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) The amount of calcium nitrate shown in Table 1 is the amount added as an anhydrous form. (Organic Acid) Malonic acid: (Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) [Hydrophobic Compound (A2)] (Anionic Resins) Anionic vinyl resin A2-1: Water dispersion (solid content concentration: 20%) of crosslinked acrylic acid / styrene resin (acid value: 120 mg KOH / g) obtained in Production Example 2. Anionic vinyl resin A2-2: "Joncryl 7100" manufactured by BASF (styrene / acrylic acid resin emulsion, acid value: 51 mg KOH / g, active content: 48%). Anionic urethane resin A2-3: "NeoRez R-600" manufactured by Covestro (aqueous dispersion of aliphatic urethane resin, acid value: 7 mg KOH / g, active content: 38%). Anionic silicone resin A2-4: "Chaline Ru-911" manufactured by Nissin Chemical Industry Co., Ltd. (blend type (urethane blended), form: aqueous emulsion, acid value: 2.2 mg KOH / g, active ingredient: 36%). The blending amounts of the anionic resins (A2-1 to A2-4) are the blending amounts of the active ingredients.(Hydrophobic surfactants) Surfynol 420: "Surfynol 420" manufactured by Nissin Chemical Industry Co., Ltd. (an adduct of 2,4,7,9-tetramethyl-5-decyne-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)))) <Organic solvent (B)> Diethylene glycol monobutyl ether: (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., static surface tension at 25°C: 26.2 mN / m) Propylene glycol: (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., static surface tension at 25°C: 36.0 mN / m) (Hydrophilic nonionic surfactants) Surfynol 465: "Surfynol 465" manufactured by Nissin Chemical Industry Co., Ltd. (an adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol with an average of 10 moles of EO, 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)).

[0125]

[0126] Production Example 3 (Production of an aqueous dispersion of crosslinked resin particles containing a black pigment) 100 parts of the acrylic acid / styrene resin obtained in Production Example 1 was mixed with 78.6 parts of MEK, and 41.2 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide content: 16.9%) was added as a neutralizing agent to neutralize (neutralization degree: 40 mol%). 800 parts of ion-exchanged water was then added, and 100 parts of a black pigment (CB, C.I. Pigment Black 7, "Monarch 717" manufactured by Cabot Chemical Co.) was added thereto. The mixture was stirred for 60 minutes at 20°C using a disperser ("Ultra Disperser" manufactured by Asada Iron Works Co., Ltd.) with the disperser blade rotating at 7000 rpm. The resulting mixture was then dispersed 10 times using a Microfluidizer (trade name, manufactured by Microfluidics Co., Ltd.) at a pressure of 200 MPa. Next, 250 parts of ion-exchanged water was added to the resulting dispersion and stirred. After stirring, MEK was removed under reduced pressure at 60°C, and then some of the water was removed to adjust the pigment concentration to 10%. 35.7 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) was added as a crosslinking agent to the dispersion, which was then sealed and heated at 70°C for 5 hours while stirring with a stirrer. The mixture was then cooled to room temperature (25°C) to obtain an aqueous dispersion of crosslinked resin particles containing a black pigment (crosslinking rate: 60 mol%) (solids concentration: 23.4%, pigment content: 9.7%, acid value: 96 mgKOH / g (calculated value)).

[0127] Production Example 4 (Production of Aqueous Dispersion of Pigment-Free Resin Particles) In a reaction vessel equipped with a dropping funnel, the monomers shown in the "Initial Charge 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 ion-exchanged water were mixed and purged with nitrogen gas to obtain an initial charge monomer solution. Furthermore, the monomers, surfactants, polymerization initiator, and ion-exchanged water shown in the "Monomer Solution to be Dropped" in Table 2 were mixed to obtain a monomer solution to be dropped, which was placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial charge monomer solution in the reaction vessel was heated from room temperature (25°C) to 80°C over 30 minutes while stirring, and while maintaining the temperature at 80°C, the monomers in the dropping funnel were gradually added dropwise into the reaction vessel over 3 hours. After completion of the dropwise addition, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. The resulting mixture was filtered through a 200 mesh filter to obtain a water dispersion of pigment-free resin particles (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.

[0128] Production Example 5 (Production of Black Ink Bk1) 33.0 parts of an aqueous dispersion of crosslinked resin particles containing the black pigment obtained in Production Example 3 (solid content: 23.4%, pigment content: 9.7%), 11.3 parts of an aqueous dispersion of pigment-free resin particles obtained in Production Example 4 (solid content: 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.), polyether-modified silicone surfactant ("Silface SAG005" manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 7 (catalog value), kinematic viscosity: 170 mm 2

[0047] A mixture containing 0.2 parts of an acetylene glycol surfactant ("Surfynol 104PG-50" manufactured by Nissin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient: 50%, HLB value: 3.0 (calculation formula: 20 × (34 / 226))), 1.0 parts of an acetylene glycol surfactant, and ion-exchanged water were added to bring the total amount to 100 parts. The resulting mixture was filtered using the membrane filter and needleless syringe, to obtain black ink Bk1.

[0129] Production Example 6 (Production of aqueous dispersion of resin particles containing a white pigment) 2500 g of polyacrylic acid ("Aron A-10SL" manufactured by Toa Gosei Co., Ltd., weight average molecular weight: 6,000, acid value: 735 mg KOH / g, solids concentration: 40%) and 3.57 g of ion-exchanged water were added to a 5 L plastic container, the container was cooled in an ice bath, and the solution was neutralized by slowly adding 1666.43 g of a 5 N aqueous sodium hydroxide solution while stirring at 100 rpm. Ion-exchanged water was added to the neutralized aqueous solution to adjust the solids concentration to 20%, thereby obtaining a neutralized aqueous solution of polyacrylic acid (degree of neutralization: 53 mol%, acid value: 735 mg KOH / g). Next, 33.0 g of a neutralized aqueous solution of polyacrylic acid (solids concentration: 20%), 300 g of titanium oxide (Ishihara Sangyo Kaisha, Ltd., "Tipake CR-80", C.I. 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 plastic container (Nikko Hansen J Bottle, round wide-mouth, natural). 1000 g of zirconia beads were added, and the mixture was dispersed for 8 hours using a benchtop pot mill stand (AS ONE Corporation). The zirconia beads were removed using a metal mesh, and the solids concentration was adjusted with ion-exchanged water to obtain an aqueous dispersion of resin particles containing a white pigment (solids concentration: 51%, pigment content: 50%, polyacrylic acid content: 1%, average particle size: 280 nm, pH: 7.6).

[0130] Production Example 7 (Production of White Ink W2) 20.0 g of the aqueous dispersion (solid content: 51%) of resin particles containing the white pigment obtained in Production Example 6, styrene / acrylic acid resin emulsion ("Joncryl" manufactured by BASF)

[0049] A mixture of 10.4 g of "7100", acid value: 51 mg KOH / g, solids content: 48%), 3.0 g of diethylene glycol monoisobutyl ether (manufactured by Nippon Nyukazai Co., Ltd.), 30.0 g of propylene glycol, 3.0 g of an acetylene glycol surfactant ("Surfynol 104PG-50" manufactured by Nissin Chemical Industry Co., Ltd., a propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient: 50%, HLB value: 3.0 (calculated value)), 0.8 g of a silicone surfactant ("KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd., HLB value: 14.5 (catalog value)), 2.4 g of a 1N aqueous sodium hydroxide solution, and ion-exchanged water added to bring the total amount to 100 g, was filtered using the membrane filter and needleless syringe to obtain a white ink W2.

[0131] Examples 1 to 12 and Comparative Examples 1 and 2 Inkjet printing was performed as described below using the combinations of printing medium, pretreatment liquid, application area of ​​the pretreatment liquid, and whether or not a drying process of the pretreatment liquid on the printing medium was performed, as shown in Table 3, and the evaluations described below were performed. (Step 1) In an environment of a temperature of 25±1°C and a relative humidity of 30±5%, a printing evaluation device (manufactured by Tritec Corporation) equipped with multiple inkjet heads (Kyocera Corporation's "KJ4B-HD06MHG-STDV," piezo type) was filled with each of the pretreatment liquids shown in Table 3 and the black ink Bk1 obtained in Production Example 5 as a colorant-containing ink. The settings were: head voltage 26 V, frequency 26 kHz, head temperature 32°C, resolution 1200 dpi, number of pre-ejection flushes 200, and negative pressure -4.0 kPa. The printing medium was fixed to a conveying table under reduced pressure, with the longitudinal direction of the printing medium aligned with the conveying direction. At this time, the printing medium was a non-absorbent film, PET film FE2001 (manufactured by Futamura Chemical Co., Ltd., water absorption: 0 g / m 2 ) or coated paper, such as OK topcoat paper (Oji Paper Co., Ltd., water absorption: 4.9 g / m 2) was used. In Examples 1 to 8, and 10, step 1 was performed using a mirror image obtained by inverting the cut-out characters shown in FIG. 4-a so that a printed image of cut-out characters with a character size of 12 was formed, consisting of a light image forming portion (i) (printing duty of the colorant-containing ink: 0%) and a dark image forming portion (ii) (printing duty of the colorant-containing ink: 100%) shown in FIG. 3, when viewed from the opposite side of the printed image forming surface of the non-liquid-absorbing film. Similarly, in Example 9, a mirror image obtained by inverting the cut-out characters shown in FIG. 4-a was used, and therefore the printed image formed in Example 9 was an inverted image of the printed image formed in Examples 1 to 8, and 10. In step 1 of Examples 1 to 10, the pretreatment liquid was applied to the printing medium in a solid state (printing duty of the pretreatment liquid: 100%) at an ejection droplet volume of 1.5 pL to the outer edge portion (iii) of the portion (ii') that would become the dark image forming portion in FIG. 4-a. The outer edge portion (iii) of the region (ii') that will become the dark image forming region in FIG. 4-a corresponds to the outer edge portion of the dark image forming region (ii) in FIG. 3 and belongs to the light image forming region (i) in FIG. 3. The outer edge portion (iii) of the region (ii') that will become the dark image forming region in FIG. 4-a was an area within 0.3 mm from the boundary between the dark image forming region and the light image forming region, on the side away from the dark image forming region. The region (i') that will become the light image forming region in FIG. 4-a corresponds to the light image forming region (i) in FIG. 3. In Example 11, the printed image was the outline character printed image shown in FIG. 3 formed in Examples 1 to 8 and 10, with a character size of Class 8. The pretreatment liquid was applied to the printing medium in a solid state (printing duty of the pretreatment liquid: 100%) on both the outer edge portion (iii) and the inner edge portion (iv) of the region (ii') that will become the dark image forming region in FIG. 4-b. The outer edge portion (iii) of the region (ii') that will become the dark image forming region in Figure 4-b corresponds to the outer edge portion of the dark image forming region (ii) in Figure 3, and belongs to the light image forming region (i) in Figure 3. The outer edge portion (iii) of the region (ii') that will become the dark image forming region in Figure 4-b was an area within 0.3 mm on the side away from the dark image forming region, calculated from the boundary line between the dark image forming region and the light image forming region. The region (i') that will become the light image forming region in Figure 4-b corresponds to the light image forming region (i) in Figure 3.Furthermore, the inner edge portion (iv) of the region (ii') that becomes the dark image forming region in Figure 4-b corresponds to the inner edge portion of the dark image forming region (ii) in Figure 3, and belongs to the dark image forming region (ii) in Figure 3. The inner edge portion (iv) of the region (ii') that becomes the dark image forming region in Figure 4-b was an area within 0.3 mm on the side away from the light image forming region, calculated from the boundary line between the dark image forming region and the light image forming region. Furthermore, in Example 12, the printed image had a character size of Class 8 for the outline characters shown in Figure 3 formed in Examples 1 to 8 and 10, the area to which the pretreatment liquid was applied and the amount of ejected droplets were the same as in Examples 1 to 10, and the pretreatment liquid was applied solidly (printing duty of the pretreatment liquid: 100%) to the printing medium. In Comparative Example 1, the pretreatment liquid was applied in a solid state (printing duty of the pretreatment liquid: 100%) to the entire surface of the printing medium with an ejection droplet volume of 1.5 pL, while in Comparative Example 2, the pretreatment liquid was not applied to the printing medium. After the pretreatment liquid was applied, a drying step was performed in which the temperature of the surface of the printing medium to which the pretreatment liquid had been applied was maintained at 100°C for 1.5 seconds using hot air to dry the pretreatment liquid. At this time, the temperature of the printing medium was confirmed with a non-contact thermometer. In Example 10, after the pretreatment liquid was applied, the above-mentioned drying step was not performed, and the printing medium was left to stand for 3 seconds in an environment at a temperature of 25±1°C and a relative humidity of 30±5%.

[0132] (Step 2) On the surface of the printing medium obtained in step 1 having the pretreatment liquid application portion, using an inkjet head filled with the black ink Bk1 obtained in Production Example 5 of the device used in step 1, the black ink was applied to a portion (ii") that would become a dark image formation portion at a discharge droplet volume of 2 pL and a print duty of 100%, so that the portion (i") that would become a light image formation portion in FIG. 5 would correspond to the portion (i') that would become a light image formation portion in FIG. 4-a or FIG. 4-b used in step 1. In Comparative Example 2, the black ink was applied to the printing medium at a discharge droplet volume of 2 pL and a print duty of 100% to the portion (ii") that would become a dark image formation portion in FIG. 5. The portion (ii") that would become a dark image formation portion to which the colorant-containing ink is applied in FIG. 5 corresponds to the dark image formation portion (ii) in FIG. 3. (Step 3) A printing device similar to that used in Step 1 was filled with the white ink W2 obtained in Production Example 7, and the white ink was applied to the entire surface of the printing medium to which the black ink obtained in Step 2 had been applied, with a droplet volume of 5 pL and a print duty of 100%. Note that Step 3 was not performed in Example 9, and no white ink was applied. Photographs of the printed images of the cut-out characters obtained in Example 1 and Comparative Example 2 are shown in Figures 6 and 7, respectively. Note that Figures 6 and 7 are photographs taken from the opposite side of the non-absorbent film from the side on which the printed image was formed.

[0133] Example 13 Printing was performed in the same manner as in Example 1, except that the printed image was changed to a barcode. In Example 13, step 1 was performed using a mirror image of the barcode shown in FIG. 9 , so that when viewed from the opposite side of the printed image-forming surface of the non-liquid-absorbent film, a barcode printed image consisting of a light image forming portion (i) (printing duty of the colorant-containing ink: 0%) and a dark image forming portion (ii) (printing duty of the colorant-containing ink: 100%) shown in FIG. 8 was formed. In step 1, the pretreatment liquid was applied to the printing medium in a solid state (printing duty of the pretreatment liquid: 100%) at an ejected droplet volume of 1.5 pL to the portion shown in FIG. 9 , which is the outer edge portion (iii) of the portion (ii') that will become the dark image forming portion. In the drying step, the temperature of the surface of the printing medium to which the pretreatment liquid was applied was maintained at 100°C for 1.5 seconds using hot air to dry the pretreatment liquid. At this time, the temperature of the printing medium was confirmed with a non-contact thermometer. Next, in step 2, the black ink was applied to the surface of the printing medium obtained in step 1 having the pretreatment liquid application portion using an inkjet head filled with the black ink Bk1 obtained in Production Example 5 of the device used in step 1, at a discharge droplet volume of 2 pL and a print duty of 100% to a region (ii'') (not shown) that would become a dark image formation region, so that the region (i'') (not shown) that would become a light image formation region would correspond to the region (i') that would become the light image formation region in Figure 9 used in step 1. Further, in step 3, the same printing device as in step 1 was filled with the white ink W2 obtained in Production Example 7, and the white ink was applied to the entire surface of the printing medium to which the black ink obtained in step 2 had been applied, at a discharge droplet volume of 5 pL and a print duty of 100%. In Figure 9, the outer edge portion (iii) of the region (ii') that would become a dark image formation region corresponds to the outer edge portion of the dark image formation region (ii) in Figure 8, and belongs to the light image formation region (i) in Figure 8. A photograph of the printed image of the bar code obtained in Example 13 is shown in Figure 10. Note that Figure 10 is a photograph taken from the side opposite to the printed image-forming surface of the non-liquid-absorbent film.

[0134] <Evaluation of streak occurrence> The black ink portion of the obtained print was observed, and streaks were evaluated visually. (Evaluation criteria) 4: No streaks, uniform and good. 3: Slight streaks are observed. 2: Streaks are observed, but not to a level that is problematic for practical use. 1: Streaks are clearly observed, and are problematic for practical use. For practical use, a rating of 2 or higher on the above evaluation criteria is sufficient.

[0135] <Evaluation of Clarity of Printed Image (Sharpness of Cutout Characters and Sharpness of Barcode Edges)> The cutout characters or barcode portions of the obtained prints were observed, and the clarity of the printed image (sharpness of cutout characters and sharpness of barcode edges) was evaluated visually. (Evaluation Criteria) 4: Cutout characters or barcode are clearly distinguishable. 3: Cutout characters or barcode are blurred, but the cutout characters or barcode are distinguishable. 2: Cutout characters or barcode are blurred and difficult to distinguish, but not to a level that is problematic in practical use. 1: Cutout characters or barcode are concealed by black ink, making the cutout characters or barcode unrecognizable. In practical use, a rating of 2 or higher on the above evaluation criteria is sufficient.

[0136]

[0137] From Table 3, it can be seen that the printed matter obtained in the examples has excellent clarity of the printed image (sharpness of cut-out characters or barcodes) while suppressing the occurrence of streaks compared to the comparative examples.

[0138] According to the present invention, even when printing using a line head inkjet method that uses a low-liquid-absorbency printing medium, it is possible to obtain printed matter that has excellent clarity of printed images including dark image forming areas and light image forming areas while suppressing the occurrence of streaks.

[0139] (i) Light image forming section (ii) Dark image forming section (i') Section to become light image forming section (ii') Section to become dark image forming section (iii) Outer edge of section (ii') to become dark image forming section (iv) Inner edge of section (ii') to become dark image forming section (i'') Section to become light image forming section (ii'') Section to become dark image forming section

Claims

1. An inkjet printing method for forming a print image on a printing medium, the print image including a dark image forming section and a light image forming section, the print duty of the ink containing a colorant in the dark image forming section being higher than the print duty of the ink containing a colorant in the light image forming section, the inkjet printing method comprising: step 1: applying a pretreatment liquid to the outer edge of the area that will become the dark image forming section to obtain a printing medium having a pretreatment liquid application section; and step 2: applying ink containing a colorant to the area that will become the dark image forming section on the surface of the printing medium obtained in step 1 that has the pretreatment liquid application section, by a line head type inkjet method.

2. The ink jet printing method of claim 1, wherein the print medium is a low liquid absorbent print medium.

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

4. The inkjet printing method according to any one of claims 1 to 3, further comprising a step of drying the printing medium to which the pretreatment liquid has been applied in step 1.

5. The inkjet printing method according to any one of claims 1 to 4, further comprising a step of fixing the portion to which the pretreatment liquid is applied in step 1.

6. The inkjet printing method according to any one of claims 1 to 5, wherein the pretreatment liquid contains at least one compound selected from the group consisting of an aggregating compound (A1) and a hydrophobic compound (A2).

7. The ink-jet printing method according to claim 6, wherein the aggregating compound (A1) is at least one member selected from the group consisting of metal salts, organic acids or salts thereof, and cationic resins.

8. The ink-jet printing method according to claim 6, wherein the hydrophobic compound (A2) is at least one member selected from the group consisting of anionic resins and hydrophobic surfactants.

9. An inkjet printing method according to any one of claims 1 to 8, wherein the outer edge of the part that becomes the dark image forming part is an area of ​​0.01 mm to 1 mm away from the boundary line between the dark image forming part and the light image forming part.

10. The inkjet printing method according to any one of claims 1 to 9, wherein in step 1, the pretreatment liquid is further applied to an inner edge portion of a portion that will become a dark image forming portion.

11. The inkjet printing method according to claim 10, wherein the inner edge of the area that becomes the dark image forming area is an area that is 0.01 mm or more and 1 mm or less away from the light image forming area, calculated from the boundary line between the dark image forming area and the light image forming area.

12. The inkjet printing method according to any one of claims 1 to 11, wherein the difference between the printing duty of the ink containing the colorant in the dark image forming portion and the printing duty of the ink containing the colorant in the light image forming portion is 50% or more.

13. The inkjet printing method according to any one of claims 1 to 12, wherein the printing duty of the ink containing the colorant in the light image forming portion is 0%.

14. The inkjet printing method according to any one of claims 1 to 13, wherein the printed image is an image of cut-out characters.

15. The inkjet printing method according to any one of claims 1 to 14, further comprising a step 3, before step 1 or after step 2, of applying a white ink containing a white pigment to the printing medium or to the surface of the printing medium to which the ink containing a colorant has been applied.

16. An inkjet printing method according to any one of claims 1 to 15, wherein the printing duty of the ink containing the colorant in the light image forming portion exceeds 0%, and the pretreatment liquid in step 1 is applied not only to the outer edge of the portion that will become the dark image forming portion, but also to a portion of the portion that will become the light image forming portion to which the ink containing the colorant is not applied.

17. An inkjet printing device used in the inkjet printing method according to any one of claims 1 to 16, comprising an inkjet head filled with the pretreatment liquid, and an inkjet head filled with ink containing the colorant.

18. An ink set for ink jet printing used in the ink jet printing method according to any one of claims 1 to 16, comprising the pretreatment liquid and an ink containing the colorant.

19. A method for producing a printed matter, which includes a dark image forming section and a light image forming section, and forms a print image on a printing medium, in which the printing duty of the ink containing a colorant in the dark image forming section is higher than the printing duty of the ink containing a colorant in the light image forming section, comprising: step 1: applying a pretreatment liquid to the outer edge of the section that will become the dark image forming section to obtain a printing medium having a pretreatment liquid application section; and step 2: applying ink containing a colorant by a line head type inkjet method to the section that will become the dark image forming section on the surface of the printing medium obtained in step 1 that has the pretreatment liquid application section.

Images