Method for manufacturing printed matter

Abstract

To provide a method for manufacturing a printed matter which can manufacture a printed matter having improved image density and scratch resistance.SOLUTION: A method for manufacturing a printed matter includes the steps of: applying oily inkjet ink onto a base material by an inkjet method; and applying aqueous clear ink onto the base material applied with the oily inkjet ink. The oily inkjet ink contains a pigment, a pigment dispersant, and a non-water soluble organic solvent, and the aqueous clear ink contains a water-dispersible resin, a surface-active agent, and water. When a film obtained by drying the aqueous clear ink is immersed in the oily inkjet ink, and is left at 70°C for one week, a change rate of the mass of the film after having been taken out from the oily inkjet ink to the mass of the film before being immersed in the oily inkjet ink exceeds 0%, the glass transition point of the water-dispersible resin of the aqueous clear ink is 5°C or more and less than 50°C, and a content of the surface-active agent to the total amount of the aqueous clear ink with respect to the content of the pigment to the total amount of the oily inkjet ink of 1 is 0.5 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a method for producing a printed matter. [Background technology]

[0002] Inkjet recording, in which highly fluid inkjet ink is ejected as droplets from minute nozzles to record an image on a substrate placed opposite the nozzle, has rapidly become popular in recent years due to its low-noise, high-speed printing capabilities. Inks used in inkjet recording include aqueous inks containing water as the primary solvent, ultraviolet-curable inks (UV inks) containing a high content of polymerizable monomers as the primary component, and hot-melt inks (solid inks) containing a high content of wax as the primary component, as well as so-called non-aqueous inks containing a non-aqueous solvent as the primary solvent. Non-aqueous inks can be classified into solvent-based inks, which contain a volatile organic solvent as the primary solvent, and oil-based inks, which contain a low-volatility or non-volatile organic solvent as the primary solvent. Solvent inks dry on the recording medium primarily through the evaporation of the organic solvent, whereas oil-based inks dry primarily through penetration into the recording medium.

[0003] Non-aqueous inks dry quickly and are excellent in printability. On the other hand, when oil-based inks are used, the solvent in the ink penetrates into the substrate when the ink is ejected onto the substrate, and the pigment penetrates into the substrate together with the solvent, which can result in a decrease in image density.

[0004] Patent Document 1 proposes a printing method that involves printing a non-aqueous ink onto a recording medium and then treating the recording medium with a post-treatment agent containing a resin and / or wax in order to reduce strike-through and obtain high print density. Patent Document 2 proposes a method that involves applying a clear ink to a recording medium after applying a water-based ink containing a pigment to the recording medium in order to improve the color development of the image.

[0005] Patent Document 3 describes a method for improving the scratch resistance of an image, which includes a step of applying a clear ink onto an ink layer containing a coloring material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-166453 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-043559 [Patent Document 3] Patent Publication No. 2021-95552 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of an embodiment of the present invention is to provide a method for producing a printed matter that can produce a printed matter with improved image density and abrasion resistance. [Means for solving the problem]

[0008] An embodiment of the present invention relates to a method for producing a printed matter, the method comprising: applying an oil-based inkjet ink to a substrate by an inkjet method; and applying an aqueous clear ink to the substrate to which the oil-based inkjet ink has been applied, wherein the oil-based inkjet ink contains a pigment, a pigment dispersant, and a water-insoluble organic solvent; and the aqueous clear ink contains a water-dispersible resin, a surfactant, and water; when a film obtained by drying the aqueous clear ink is immersed in the oil-based inkjet ink and left at 70°C for one week, the rate of change in mass of the film after removal from the oil-based inkjet ink relative to the mass of the film before immersion in the oil-based inkjet ink exceeds 0%; the glass transition point of the water-dispersible resin of the aqueous clear ink is 5°C or higher and lower than 50°C; and the ratio of the content of the pigment to the total amount of the oil-based inkjet ink is 1 to 0.5. [Effects of the Invention]

[0009] According to an embodiment of the present invention, it is possible to provide a method for producing a printed matter that can produce a printed matter with improved image density and abrasion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0011] a water-based clear ink (hereinafter simply referred to as clear ink) to the substrate to which the oil-based inkjet ink has been applied, the water-based clear ink comprising a pigment, a pigment dispersant, and a water-insoluble organic solvent; and a water-based clear ink comprising a water-dispersible resin, a surfactant, and water; the water-based clear ink is dried to form a film, which is then immersed in the oil-based inkjet ink and left at 70°C for one week; the mass of the film after removal from the oil-based inkjet ink is greater than 0% compared to the mass of the film before immersion in the oil-based inkjet ink; the glass transition point of the water-dispersible resin in the water-based clear ink is greater than or equal to 5°C and less than 50°C; and the pigment content relative to the total amount of the oil-based inkjet ink is 1:1, and the surfactant content relative to the total amount of the water-based clear ink is 0.5 or more.

[0012] When oil-based inks are used, the pigments penetrate into the substrate together with the solvent, which can reduce image density. In addition, the solvent tends to remain between the fibers and on the surface of the substrate without evaporating, which can cause abrasion stains after printing. When the method for producing a printed matter of the present invention is used, a printed matter with improved image density and abrasion resistance can be produced. The mechanism behind this is not clear, but is presumed as follows. The present invention is not bound by the mechanism presumed below.

[0013] By applying a clear ink containing a water-dispersible resin to a substrate to which an oil-based ink has been applied as a post-treatment agent, the particulate resin remains on the substrate surface and fuses, smoothing the surface with a resin coating. This reduces diffuse reflection and improves image density. On the other hand, when a water-soluble resin is used, the resin penetrates into the substrate, which tends to reduce the effect of improving density through surface smoothing. Furthermore, the surface condition of printed materials using a substrate made of fibers such as paper can be affected by the unevenness of the substrate fibers themselves, as well as the presence of pigments on the fibers, which can result in fine unevenness when viewed as a whole, resulting in diffuse reflection of light and a decrease in image density. By applying a clear ink containing a water-dispersible resin, the substrate surface is covered with a resin film, smoothing the surface, reducing diffuse reflection and improving image density.

[0014] However, when a water-based clear ink is applied to a substrate to which an oil-based ink has been applied, the difference in polarity can make it difficult for the resin in the clear ink to wet and spread evenly over the substrate wetted with the solvent. Therefore, by using a resin in the water-based clear ink that has an affinity for the solvent in the oil-based ink, it is possible to make the resin wet and spread more easily. In the aqueous clear ink and oil-based inkjet ink used in the method for producing printed matter of the embodiment, when a film obtained by drying the aqueous clear ink is immersed in oil-based inkjet ink and left at 70°C for one week, the mass change ratio of the film after removal from the oil-based inkjet ink to the mass of the film before immersion (hereinafter also referred to as "mass change ratio R") exceeds 0%. Here, when the weight mass change ratio R exceeds 0%, the resin has absorbed the solvent. This is thought to be due to the high affinity between the resin and the solvent. The higher the affinity, the easier it is for the resin film to spread on a substrate wetted with the solvent, and the smoothness of the resin film tends to improve. Therefore, when the mass change ratio R exceeds 0%, the concentration improvement effect is thought to be large. On the other hand, if the mass change rate R is less than 0%, the resin dissolves in the solvent. This is thought to be due to the even higher affinity between the resin and the solvent. In this case, the resin film wets and spreads, but it dissolves in the remaining solvent and the resin penetrates into the substrate, so sufficient smoothness of the resin film cannot be obtained. Also, if the mass change rate R is 0%, the resin does not change in response to the solvent. As a result, the resin film does not wet and spread sufficiently on the substrate, and smoothness cannot be obtained. Therefore, if the mass change rate R is 0% or less, it is thought that the concentration improvement effect is small.

[0015] In this way, when a water-dispersible resin with a mass change rate R of more than 0% is used in a water-based clear ink, the affinity between the resin and the solvent becomes moderately high, making it easier to achieve an improved image density.

[0016] Furthermore, the surface of the substrate to which the oil-based ink has been applied (printed surface) contains a solvent and is generally low polar, but clear ink tends to be water-based and highly polar, and when clear ink is applied to the surface of the substrate to which the oil-based ink has been applied (printed surface), the clear ink may be repelled. When the clear ink contains a surfactant, the clear ink spreads more evenly over the surface of the substrate, and the resin film is more easily formed more evenly, which makes it easier to improve image density.

[0017] Furthermore, image density can be further improved by ensuring that the surfactant content relative to the total amount of aqueous clear ink is 0.5 or more relative to the pigment content relative to the total amount of oil-based inkjet ink. It is believed that when clear ink is applied to a substrate to which ink has already been applied, the surfactant is adsorbed to the ink pigment, resulting in less surfactant oriented at the air-liquid interface. Therefore, when the surfactant content is low, the clear ink does not wet and spread easily, resulting in little effect in improving density. Therefore, by increasing the surfactant content so that the surfactant content relative to the total amount of aqueous clear ink is 0.5 or more relative to the pigment content relative to the total amount of oil-based inkjet ink, the amount of surfactant oriented at the air-liquid interface can be increased, making it easier for the clear ink to wet and spread, and further improving image density.

[0018] Furthermore, the abrasion resistance of the image can be improved by the aqueous clear ink containing a water-dispersible resin with a glass transition temperature (Tg) of 5°C or higher but lower than 50°C. It is believed that the use of a water-dispersible resin makes it easier for particulate resin to remain on the surface of the substrate surface, facilitating fusion between resins and improving abrasion resistance. Furthermore, resins with high glass transition temperatures are generally hard. When such resins are used, the surface is slippery even when the area where the clear ink is applied is rubbed, the resin film does not peel off, and staining is unlikely to occur. On the other hand, resins with even higher glass transition temperatures tend to produce hard and brittle resin films. When such resins are used, the resin film is easily peeled off when the area where the clear ink is applied is rubbed, and staining is likely to occur. When the glass transition temperature (Tg) of the water-dispersible resin of the aqueous clear ink is 5°C or higher but lower than 50°C, the surface is slippery even when the area where the clear ink is applied is rubbed, the resin film does not peel off, and staining is unlikely to occur.

[0019] <Base material> In the present embodiment, the substrate is not particularly limited, and examples thereof include printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheet, film, OHP sheet, and adhesive sheet having an adhesive layer on the back surface of the substrate, etc. Among these, printing paper such as plain paper and coated paper can be preferably used from the viewpoint of ink permeability.

[0020] Here, plain paper refers to ordinary paper on which no ink-receiving layer or film layer is formed. Examples of plain paper include fine paper, medium-quality paper, PPC paper, wood paper, recycled paper, etc.

[0021] Furthermore, as the coated paper, inkjet coated paper such as matte paper, glossy paper, and semi-glossy paper, as well as so-called coated printing paper, can be preferably used. Here, coated printing paper refers to printing paper that has traditionally been used in letterpress printing, offset printing, gravure printing, and the like, and is printing paper in which a coating layer is provided on the surface of fine or medium-quality paper using a paint containing an inorganic pigment such as clay or calcium carbonate and a binder such as starch. Coated printing paper is classified into lightly coated paper, fine lightweight coated paper, medium lightweight coated paper, fine coated paper, medium coated paper, art paper, cast coated paper, and the like, depending on the amount of paint applied and the coating method.

[0022] <Oil-based inkjet ink> Oil-based inkjet inks can contain pigments.

[0023] Pigments can be used in the present invention, including organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and dye lake pigments, as well as inorganic pigments such as carbon black and metal oxides. Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. Examples of polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrroles (DPPs). Examples of carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of metal oxides include titanium oxide and zinc oxide. These pigments can be used alone or in combination.

[0024] From the viewpoints of ejection stability and storage stability, the average particle size of the pigment particles in the ink is preferably 300 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less, as the volume-based average value in the particle size distribution measured by dynamic light scattering.

[0025] From the viewpoint of print density and ink viscosity, the pigment content is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 5 to 10% by mass, based on the total amount of the oil-based inkjet ink.

[0026] From the viewpoint of improving image density, it is preferable that the content of the surfactant in the aqueous clear ink relative to the total amount of the aqueous clear ink described below is 0.5 or more relative to the content of the pigment relative to the total amount of the oil-based inkjet ink of 1.

[0027] In order to stably disperse the pigment in the oil-based ink, a pigment dispersant can be used together with the pigment. The pigment dispersant is not particularly limited as long as it can stably disperse the pigment in a non-aqueous solvent, but for example, hydroxyl group-containing carboxylic acid ester, salt of long-chain polyaminoamide and high molecular weight acid ester, salt of high molecular weight polycarboxylic acid, salt of long-chain polyaminoamide and polar acid ester, high molecular weight unsaturated acid ester, copolymer of vinylpyrrolidone and long-chain alkene, modified polyurethane, modified polyacrylate, polyether ester-type anionic surfactant, polyoxyethylene alkyl phosphate ester, polyester polyamine, etc. are preferably used.

[0028] Examples of commercially available pigment dispersants include "Antaron V216 (vinylpyrrolidone-hexadecene copolymer)" and "V220 (vinylpyrrolidone-eicosene copolymer)" (all trade names) manufactured by Ashland Japan Co., Ltd., "Solsperse 13940 (polyester amine type), 16000, 17000, 18000 (fatty acid amine type), 11200, 24000, 28000" (all trade names) manufactured by Lubrizol Japan Co., Ltd., and "Efka 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 4800" (all trade names) manufactured by BASF Japan Co., Ltd. Examples of such polyurethanes include "8, 49, 4010, 4055 (modified polyurethane)" (all trade names), "Disparlon KS-860, KS-873N (amine salt of polyester)" (all trade names) manufactured by Kusumoto Chemicals Co., Ltd., "Discol 202, 206, OA-202, OA-600 (multi-chain polymer nonionic)" (all trade names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "DISPERBYK2155, BYK9077" (all trade names) manufactured by BYK Japan KK, and "Hypermer KD2, KD3, KD11, KD12" (all trade names) manufactured by Croda Japan Co., Ltd.

[0029] The pigment dispersant is preferably contained in a mass ratio of 0.2 to 1.0 per pigment 1. The content of the pigment dispersant in the total amount of ink is preferably 0.5 to 15 mass%, and more preferably 1 to 10 mass%.

[0030] Oil-based inks may contain water-insoluble organic solvents. As the water-insoluble organic solvent, either a non-polar organic solvent or a polar organic solvent can be used. These can be used alone or in combination. In the present invention, it is preferable to use a water-insoluble organic solvent that is not uniformly miscible with the same volume of water at 20°C under 1 atmosphere.

[0031] Preferred examples of the non-polar organic solvent include petroleum-based hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and silicone solvents.

[0032] Preferred examples of polar organic solvents include fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents.

[0033] These non-water-soluble organic solvents may be used alone or in combination of two or more kinds as long as they form a single phase.

[0034] In addition to the above components, the oil-based ink may contain various additives, such as surfactants and antioxidants.

[0035] The method for producing an oil-based ink is not particularly limited, and the ink can be produced, for example, by mixing and stirring the components all at once or in portions. Specifically, the ink can be produced by dispersing all the components in a dispersing machine such as a bead mill, either all at once or in portions, and then passing the mixture through a filtering machine such as a membrane filter, if desired.

[0036] The viscosity of an oil-based inkjet ink varies depending on the nozzle diameter of the ejection head of the inkjet recording system, the ejection environment, and other factors, but in general, it is preferably 5 to 30 mPa·s, and more preferably 5 to 15 mPa·s at 23°C.

[0037] <Water-based clear ink> The water-based clear ink may contain a water-dispersible resin. There are no particular limitations on the water-dispersible resin. Specific examples of water-dispersible resins that can be used include acrylic resins, urethane resins, ester resins, olefin resins, and fluorene resins. The water-dispersible resin can be blended in the form of a resin emulsion into the water-based clear ink.

[0038] These water-dispersible resins may be used alone or in combination of two or more. The content (solid content) of the water-dispersible resin in the ink may be, for example, 0.5 to 30% by mass.

[0039] From the viewpoint of abrasion resistance, the glass transition point (Tg) of the water-dispersible resin is preferably 5°C or higher. From the viewpoint of abrasion resistance, the glass transition point (Tg) of the water-dispersible resin is preferably lower than 50°C. From the viewpoint of abrasion resistance, the glass transition point of the water-dispersible resin is preferably 5°C or higher and lower than 50°C.

[0040] The glass transition point (Tg) of the water-dispersible resin is a value measured by differential scanning calorimetry (DSC).

[0041] Considering the film-forming properties of the resin and its application to inkjet ejection, the average particle size of the water-dispersible resin is preferably 500 nm or less.

[0042] The water-based clear ink may contain a surfactant. As the surfactant, it is preferable to use a nonionic surfactant from the viewpoint of preventing aggregation of the water-dispersible resin.Specific examples of the nonionic surfactant include acetylene glycol surfactants, polyether-modified silicone surfactants, and polyoxyethylene alkyl ether surfactants. The surfactants may be used alone or in combination of two or more.

[0043] From the viewpoint of improving image density, the amount of surfactant in the aqueous clear ink is preferably such that the pigment content in the total amount of oil-based inkjet ink is 1, and the surfactant content in the aqueous clear ink relative to the total amount of aqueous clear ink is 0.5 or more.

[0044] The water-based clear ink preferably contains water as a solvent. The water is not particularly limited, but it is preferable that it contains as few ionic components as possible. In particular, from the viewpoint of pigment dispersion stability of the ink, it is preferable that the content of polyvalent metal ions such as calcium is low. As the water, for example, ion-exchanged water, distilled water, ultrapure water, etc. can be used. From the viewpoint of adjusting the ink viscosity, the amount of water may be, for example, 40 to 90% by mass, or 50 to 80% by mass, relative to the total amount of the aqueous clear ink.

[0045] The water-based clear ink may contain a water-soluble organic solvent as a humectant, such as glycerin, diethylene glycol, or 1,3-propanediol.

[0046] The water-soluble organic solvent may be used alone or in combination with two or more solvents as long as they form a single phase with water. The content of the water-soluble organic solvent in the water-based clear ink may be, for example, 1 to 10% by mass.

[0047] In addition to the above components, the water-based clear ink may contain various additives, such as antioxidants.

[0048] In the aqueous clear ink and oil-based inkjet ink used in the method for producing printed matter of the embodiment, when a film obtained by drying the aqueous clear ink is immersed in oil-based inkjet ink and left at 70°C for one week, it is preferable that the rate of change in mass of the film after being removed from the oil-based inkjet ink relative to the mass of the film before being immersed in the oil-based inkjet ink ("mass change rate R") exceeds 0%.

[0049] Specifically, the mass change rate R can be determined as follows. A 4cm diameter plastic dish is filled with water-based clear ink so that the resin amount is 0.4g, and the resulting dried film is then dried at room temperature for one day. Then, the resulting film is cut into 2cm squares. The resulting film is then immersed in oil-based ink and left at 70°C for one week. The film is then removed from the ink, the ink on the surface is wiped off, and the mass of the film is measured. The mass of the film before immersion in the oil-based ink is A (g), and the mass of the film after removal from the oil-based ink is B (g), and the mass change rate R is calculated using the following formula:

[0050] Mass change rate R (%) = (BA) ÷ A × 100

[0051] The method for producing the aqueous clear ink is not particularly limited, but the ink can be produced, for example, by mixing and stirring the components all at once or in portions. Specifically, the ink can be produced by adding all the components all at once or in portions to a disperser such as a bead mill, dispersing them, and, if desired, passing the mixture through a filter such as a membrane filter.

[0052] <Manufacturing method for printed matter> A method for producing a printed matter according to one embodiment includes applying an oil-based inkjet ink to a substrate by an inkjet method, and applying a water-based clear ink to the substrate to which the oil-based inkjet ink has been applied. The substrate, the oil-based inkjet ink, and the water-based clear ink are as described above.

[0053] The inkjet method is not particularly limited, and may be any method such as a piezoelectric method, an electrostatic method, a thermal method, etc. When an inkjet recording apparatus is used, it is preferable to eject the ink according to one embodiment from an inkjet head based on a digital signal, and to cause the ejected ink droplets to land on a recording medium.

[0054] The method for applying the aqueous clear ink to the substrate is not particularly limited. Specifically, coating methods such as roll coating, blade coating, gravure coating, and bar coating, or printing methods such as gravure printing, screen printing, offset printing, and inkjet printing (inkjet method) can be used.

[0055] The area to which the water-based clear ink is applied may be an area having the same shape as the image formed by the oil-based inkjet ink, or may be a wider area including the shape of the image formed by the oil-based inkjet ink, or may be the entire surface of the substrate. It is preferable that the area where the oil-based inkjet ink is applied and the area where the water-based clear ink is applied at least partially overlap each other.

[0056] The method for producing a printed product may include other steps. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] <Preparing clear ink> Table 1 shows the formulations of clear inks 1 to 12. The amount of each material listed in Table 1 is in mass %. Inks 1 to 5 are clear inks of examples, and inks 6 to 12 are clear inks of comparative examples. Resin emulsion or water-soluble resin, surfactant, solvent and water were mixed in the proportions shown in Table 1, and the resulting mixture was filtered through a membrane filter (3 μm) to obtain a water-based clear ink.

[0059] Details of the materials listed in Table 1 are shown below. In addition, the amounts of active ingredients and the like for the resin emulsions and surfactants listed in Table 1 are shown in Tables 2 and 3.

[0060] (resin emulsion) Takelac W-6061 (product name): manufactured by Mitsui Chemicals, Inc. Mowinyl 742A (product name): manufactured by Japan Coating Resin Co., Ltd. NeoCryl A-1127 (product name): manufactured by Covestro Coating Resins Superflex 150 (product name): manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Movinyl 743N (product name): manufactured by Japan Coating Resin Co., Ltd. Superflex E4800 (product name): manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Superflex E2000 (product name): manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0061] (Water-soluble resin) Polyacrylic acid: Fujifilm Wako Pure Chemical Industries, Ltd. (surfactant) Silface SAG002 (product name): manufactured by Nissin Scientific Industry Co., Ltd. Emulgen 108 (product name): manufactured by Kao Corporation Olfin EXP4001 (product name): manufactured by Nissin Scientific Industry Co., Ltd. (Water-soluble organic solvent) Glycerin: Fujifilm Wako Pure Chemical Industries, Ltd.

[0062] <Preparation of oil-based ink> Table 4 shows the formulation of K ink, which is an oil-based ink. The amount of each material listed in the table is in mass %. K ink was prepared based on the formulation shown in Table 4.

[0063] Details of the materials listed in Table 4 are given below. SUNBLACK X55 (product name): manufactured by Asahi Carbon Co., Ltd. Solsperse 13940 (product name): manufactured by Lubrizol Japan Co., Ltd. 2-Ethylhexyl isononanoate: manufactured by Kokyu Alcohol Kogyo Co., Ltd. Exxor D110 (product name): Exxon Mobil

[0064] <Mass change rate R> The mass change rates R (%) shown in Table 1 were determined as follows using each clear ink and ink K, an oil-based ink. Clear ink was added to a 4cm diameter plastic dish so that the resin amount was 0.4g, and the resulting dried film was then cut into 2cm squares. The film thus obtained was immersed in oil-based ink and left at 70°C for 1 week. The film was then removed from the oil-based ink, the ink on the film surface was wiped off, and the mass of the film was measured. The mass change rate R was calculated using the following formula, where A (g) is the mass of the film before immersion in oil-based ink and B (g) is the mass of the film after removal from the oil-based ink. Mass change rate R (%) = (BA) ÷ A × 100

[0065] <Evaluation method> A line-type inkjet printer "Comphis GD9630" (manufactured by Riso Kagaku Corporation) was loaded with the K ink shown in Table 4 and the clear ink shown in Table 1, and a K ink solid chart (600 x 600 dpi, 8 pl / dot) and a clear ink solid chart (600 x 600 dpi, 8 pl / dot) were printed in that order on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation) to obtain a print. The obtained print was left at room temperature for one day and then evaluated as follows.

[0066] (Image density) The print density of the printed surface (front side) and non-printed surface (back side) of the printed material was measured using an Xrite eXact (manufactured by X-Rite), and the OD value of the printed surface (front OD value) was evaluated according to the following criteria. The results are shown in Table 2. Image density (OD value) S: Table OD value 1.20 or more A: Table OD value 1.18 or more and less than 1.20 B: Table OD value 1.16 or more and less than 1.18 C: Table OD value less than 1.16

[0067] (Abrasion resistance) The solid chart area of ​​the print was rubbed five times with a white cotton cloth using a Crockmeter "CM-1" (manufactured by Atlas Electric Devices), and the stained areas on the paper and cloth were evaluated according to the following criteria. The results are shown in Table 2. S: Almost no dirt is visible A: Slight dirt is visible B: Dirt is visible C: Significant dirt is visible

[0068] A printed matter was prepared in the same manner as above, except that no clear ink was used, on which a K ink solid chart was printed. The image density and abrasion resistance were evaluated in the same manner as above. The results are shown in Table 4.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] [Table 4]

[0073] Combinations of inks 1 to 5 of the examples with K ink, an oil-based ink, result in a mass change rate R of more than 0%. Inks 1 to 5 are clear inks that use a water-dispersible resin with a glass transition point (Tg) of 5°C or higher and lower than 50°C. When inks 1 to 5 are applied as clear inks after applying K ink, the image density and scratch resistance are improved compared to the results when no clear ink is applied (evaluation results for K ink only in Table 4). This is thought to be because the water-dispersible resin in the clear ink forms a film, smoothing the surface of the printed material and improving image density. Also, because the resin's Tg is between 5°C and 50°C, the resin film is hard and the surface is slippery even when the post-treated area is rubbed, resulting in good abrasion resistance.

[0074] Comparative example inks 6 to 7 and 9 are clear inks that, when combined with K ink, an oil-based ink, result in a mass change rate R of less than 0%. When inks 6 to 7 and 9 are applied after K ink is applied, the effect of improving image density is smaller than when inks 1 to 3 are used. This is thought to be because the resin dissolves in the ink solvent, making it impossible to maintain surface smoothness. Comparative example inks 8 and 9 are clear inks that use a water-dispersible resin with a glass transition temperature (Tg) of less than 5°C. When inks 8 and 9 are applied after the K ink is applied, the scratch resistance is lower than when inks 1 to 3 are used. This is thought to be because resins with low glass transition temperatures are soft, and when the area where the clear ink is applied is rubbed, the resin film is easily deformed and peeled off. Comparative examples Inks 10 and 11 are clear inks with reduced amounts of surfactant. When these clear inks are used, the density improvement effect is reduced compared to when ink 1 is used. This is thought to be because when the amount of surfactant is small, the water-based clear ink does not wet and spread sufficiently on the printed material that is wet with solvent. Comparative example Ink 12 is a clear ink that uses a water-soluble resin instead of a water-dispersible resin. When post-processing is performed with this clear ink, the image density and scratch resistance decrease compared to when inks 1 to 3 are used. This is thought to be because the resin penetrates into the substrate, reducing the smoothing effect and resin film formation on the paper surface.

Claims

[Claim 1] applying an oil-based inkjet ink to a substrate by an inkjet method; applying a water-based clear ink to the substrate to which the oil-based inkjet ink has been applied, The oil-based inkjet ink contains a pigment, a pigment dispersant, and a non-water-soluble organic solvent, the water-based clear ink contains a water-dispersible resin, a surfactant, and water; when the film obtained by drying the aqueous clear ink is immersed in the oil-based inkjet ink and left to stand at 70°C for one week, the rate of change in mass of the film after being removed from the oil-based inkjet ink relative to the mass of the film before being immersed in the oil-based inkjet ink exceeds 0%, the glass transition temperature of the water-dispersible resin of the aqueous clear ink is 5°C or higher and lower than 50°C; a content of the surfactant relative to the total amount of the water-based clear ink being 0.5 or more relative to a content of the pigment relative to the total amount of the oil-based inkjet ink being 1;

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