Non-aqueous inkjet ink set

Abstract

This invention provides a non-aqueous inkjet ink set that offers excellent re-ejectability and continuous ejection stability. [Solution] A non-aqueous inkjet ink set comprising at least one pair of dark and light inks, wherein the dark ink and the light ink each contain at least a solvent, a pigment, a pigment dispersant, and a resin, and the amount of pigment contained in the light ink, the amount of resin contained in the light ink, the amount of pigment dispersant contained in the light ink, the amount of pigment contained in the dark ink, the amount of resin contained in the dark ink, and the amount of pigment dispersant contained in the dark ink satisfy a specific relational expression, and the dark ink and the light ink each have a viscosity at 25°C in the range of 2.5 mPa·s or more and less than 7.0 mPa·s.

Description

Technical Field

[0001] The present invention relates to an ink set for non-aqueous inkjet.

Background Art

[0002] In recent years, as a means for forming high-quality color images, ink sets equipped with at least a pair of light and dark inks have been developed. Such an ink set performs coloration by changing the amount of colorant landing per unit area of the recording medium, thereby increasing the gradation and the number of colors that can be expressed.

[0003] Japanese Patent Application Laid-Open No. 2008-19409 (Patent Document 1) describes an invention aimed at providing an ink set for non-aqueous inkjet that can obtain stable ejection performance even in high-speed printing and has good printing suitability (rub resistance, gloss, drying property) for polyvinyl chloride. Specifically, it is composed of one or more colors of ink composed of at least a mixed solvent, a pigment, and a resin, and at least one color of the ink is composed of a light-colored ink and a dark-colored ink with different pigment concentrations. In the ink set for non-aqueous inkjet, the ratio (V1 / V2) of the viscosity (V1) of the mixed solvent contained in the light-colored ink to the viscosity (V2) of the mixed solvent contained in the dark-colored ink satisfies the condition of the formula: 1.1 < V1 / V2 < 2.5. Patent Document 1 also describes that in an ink set for non-aqueous inkjet (hereinafter, also simply referred to as ink), adjusting the viscosity of each ink to as close a value as possible is preferable from the viewpoint of stably ejecting ink droplets, and by using a method of reducing the viscosity difference between the light-colored ink and the dark-colored ink using a high-viscosity solvent, the bending of the ejected ink droplets can be suppressed and stable ejection becomes possible.

[0004] Japanese Patent Publication No. 2022-191658 (Patent Document 2) describes an invention that aims to provide an ink set that can effectively suppress printing bleeding even when the ink set consists of a plurality of ink compositions including dark ink and light ink. Specifically, it describes an ink set comprising a plurality of non-aqueous ink compositions containing a colorant and an organic solvent, which are ejected by an inkjet method, wherein the set includes a dark ink and a light ink having a lower colorant content than the dark ink, and at least one of the plurality of non-aqueous ink compositions included in the ink set contains at least one of a specific alkydamide solvent (a1) and a specific cyclic amide solvent (a2). Furthermore, Patent Document 2 states that since light-colored inks contain less colorant than dark-colored inks, they have a relatively higher content of organic solvents, which in turn increases the amount of organic solvent discharged onto the substrate (recording medium), making printing more prone to bleeding. It also states that the above objective can be achieved with an ink set containing a non-aqueous ink composition that includes at least one of a specific alkydamide solvent (a1) and a specific cyclic amide solvent (a2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-19409 [Patent Document 2] Japanese Patent Publication No. 2022-191658 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Patent documents 1 and 2 describe non-aqueous inkjet ink sets comprising at least one pair of light and dark inks, but there is room for improvement in the ejection stability of such ink sets. Specifically, when printing with an inkjet printer, the process may be stopped after a series of printing operations, and then resumed after a period of time. It is important that the inkjet ink set has the property (re-ejectability) to perform good ejection even in such cases. However, light-colored inks tend to dry out in the print head of an inkjet printer, so re-ejectability may not be achieved. While ink drying in the print head is hardly a problem when the print head is cleaned with a cleaning solution, if the print head is not cleaned when printing is interrupted (for example, when dealing with a paper jam, printing is interrupted, but the print head cannot be cleaned immediately, and the ink remaining in the print head may dry and harden), problems arise such as a decrease in productivity and image quality due to print head blockage, or the need to replace the print head if recovery of the print head is not expected.

[0007] Therefore, the object of the present invention is to provide a non-aqueous inkjet ink set that is excellent in re-ejectability and continuous ejection stability. [Means for solving the problem]

[0008] When printing is interrupted, if the ink dries in the print head, the pigments and resins contained in the ink may remain in the print head and solidify. Even if printing is resumed in this state, good ejection is not possible, and re-ejection performance cannot be obtained. In many cases, a pair of dark and light inks use the same pigments and resins for both the dark and light inks, and by adjusting the amounts of these, two different types of ink (dark and light inks) can be prepared. Relatively speaking, the light ink has less pigment and more resin, while the dark ink has more pigment and less resin. The inventors' investigations revealed that some light inks did not have sufficient re-ejection performance, suggesting that re-ejection performance is particularly influenced by the resin. In particular, in inkjet printers that heat the print head and platen during printing, the area around the nozzles of the ink ejection head passing over the platen is heated. Therefore, especially with light inks that have a high resin content, viscosity increases due to solvent evaporation, making them more prone to drying, and a phenomenon of nozzle blockage due to ink drying and solidification has been observed.

[0009] Therefore, the inventors conducted research to obtain an ink with excellent re-ejection properties, and found that improving the re-solubility of the ink contributes to re-ejection properties. Here, "re-solubility" refers to the property of ink that has solidified due to drying during a printing interruption to dissolve in the ink used when printing is resumed or in the cleaning fluid used during nozzle cleaning. If the ink has high re-solubility, it can be easily dissolved or softened even after solidification and removed. Solvent-based inks can generally be divided into lacquer type and reaction type. Lacquer-type solvent-based inks form a film upon drying, and the ink can dry out due to an increase in solid content and viscosity caused by the evaporation of the solvent, which can lead to nozzle blockage. However, if the ink has high re-solubility, nozzle blockage is less likely to occur, and even if blockage does occur, it has been confirmed that the blocked part can be dissolved or softened and removed by cleaning the nozzle.

[0010] Furthermore, as mentioned above, since a pair of dark and light inks often use the same pigment and resin for both the dark and light inks, we investigated how to improve the resolubility of the ink by adding other components to the ink, and focused on pigment dispersants. The amount of pigment dispersant is usually determined according to the amount of pigment contained in the ink, so it was generally the case that light inks with a small amount of pigment also contained a small amount of pigment dispersant. Therefore, the inventors found that when they incorporated a larger amount of pigment dispersant than in conventional light inks, they obtained a favorable effect on the resolubility and softening of the resin that had dried due to the evaporation of the ink, and it tended to improve the resolubility of the ink. Moreover, increasing the amount of pigment dispersant suppresses the increase in ink viscosity when heated compared to increasing the amount of resin, and has little effect on the thickening and drying of the ink in the print head. For these reasons, the inventors found that a light ink with excellent re-dispensing properties could be obtained, and thus completed the present invention.

[0011] Therefore, the non-aqueous inkjet ink set of the present invention is a non-aqueous inkjet ink set comprising at least one pair of light and dark inks, The pair of inks described above consists of a dark ink and a light ink. The dark ink is one of cyan ink, magenta ink, yellow ink, and black ink, and the light ink is one of light cyan ink, light magenta ink, light yellow ink, and light black ink, provided that the pair of dark and light inks consists of one of the following combinations: cyan ink and light cyan ink, magenta ink and light magenta ink, yellow ink and light yellow ink, and black ink and light black ink. The dark ink and the light ink each contain at least a solvent, a pigment, a pigment dispersant, and a resin. When the amount of pigment (mass%) contained in the light-colored ink is P1, the amount of resin (mass%) contained in the light-colored ink is R1, the amount of pigment dispersant (mass%) contained in the light-colored ink is D1, the amount of pigment (mass%) contained in the dark-colored ink is P2, the amount of resin (mass%) contained in the dark-colored ink is R2, and the amount of pigment dispersant (mass%) contained in the dark-colored ink is D2, the pair of light and dark inks are related by the following equations (1) to (4): Equation (1): P1 < P2 Equation (2): 0.6 ≦ D1 / P1 ≦ 25.0 Formula (3): P1+R1+D1 ≧ 4% by mass Formula (4): P2+R2+D2 ≧ 4% by mass Satisfying the conditions, The dark-colored ink and the light-colored ink are a non-aqueous inkjet ink set characterized in that their viscosity at 25°C is in the range of 2.5 mPa·s or more and less than 7.0 mPa·s.

[0012] In a preferred example of the non-aqueous inkjet ink set of the present invention, the pair of light and dark inks have the relationship shown in the following formula (5): Equation (5): 0.3 < (P1+R1+D1) / (P2+R2+D2) < 3.0 It satisfies the condition.

[0013] In another preferred example of the non-aqueous inkjet ink set of the present invention, the solvent comprises at least an amide bond or urea bond-containing compound.

[0014] In another preferred example of the non-aqueous inkjet ink set of the present invention, the resin comprises a vinyl chloride / vinyl acetate copolymer resin.

[0015] In another preferred example of the non-aqueous inkjet ink set of the present invention, the light-colored ink is related to the following formula (6): Equation (6): 0.5 ≦ R1 / (P1+D1) ≦ 5.0 It satisfies the condition. [Effects of the Invention]

[0016] According to the ink set for non-aqueous inkjet of the present invention, it is possible to provide a non-aqueous inkjet ink set excellent in redischargeability and continuous discharge stability.

Embodiments for Carrying Out the Invention

[0017] The present invention will be described in detail below. The present invention relates to an ink set for non-aqueous inkjet.

[0018] In this specification, a non-aqueous ink set is an ink set containing a plurality of non-aqueous inks. A non-aqueous ink means an ink that does not contain water as a solvent, but includes cases where it contains a trace amount of water that can be contained in the raw materials or a trace amount of water that cannot be avoided from being mixed into the ink during the manufacturing process or storage.

[0019] In this specification, an ink set for inkjet is an ink set containing a plurality of inks for inkjet. An ink for inkjet means an ink that can be used for printing with an inkjet printer. In this specification, the ink set for inkjet of the present invention is also referred to as "the ink set of the present invention".

[0020] The ink set of the present invention includes at least one pair of light and dark inks. That is, the ink set of the present invention may include one pair of light and dark inks, or may include two or more pairs of light and dark inks (in other words, two or more sets of light and dark inks). In this specification, a pair of light and dark inks means a set of inks consisting of a dark ink and a light ink. The dark ink is the ink that exhibits a darker color among the inks constituting the pair of light and dark inks, and the light ink is the ink that exhibits a lighter color among the inks constituting the pair of light and dark inks. Since the ink set of the present invention includes at least one pair of light and dark inks, it is suitable for forming high-quality color images. Unless otherwise specified, in this specification, the dark ink and the light ink are non-aqueous inks.

[0021] In the ink set of the present invention, the dark ink is one of cyan ink, magenta ink, yellow ink, and black ink, and the light ink is one of light cyan ink, light magenta ink, light yellow ink, and light black ink. However, in the ink set of the present invention, a pair of dark inks consists of one of the following combinations: cyan ink and light cyan ink, magenta ink and light magenta ink, yellow ink and light yellow ink, and black ink and light black ink. That is, if the dark ink constituting a pair of dark inks is cyan ink, the light ink is light cyan ink. The ink set of the present invention may also contain further inks, such as orange ink and white ink.

[0022] In the ink set of the present invention, the dark ink and the light ink each contain at least a solvent, a pigment, a pigment dispersant, and a resin. In this specification, the components such as the solvent, pigment, pigment dispersant, and resin contained in both the dark ink and the light ink may be the same or different between the dark ink and the light ink, but it is preferable that they be the same between the dark ink and the light ink.

[0023] In the ink set of the present invention, when the amount of pigment (mass%) contained in the light-colored ink is P1, the amount of resin (mass%) contained in the light-colored ink is R1, the amount of pigment dispersant (mass%) contained in the light-colored ink is D1, the amount of pigment (mass%) contained in the dark-colored ink is P2, the amount of resin (mass%) contained in the dark-colored ink is R2, and the amount of pigment dispersant (mass%) contained in the dark-colored ink is D2, the relationship between a pair of light and dark inks is shown in the following formulas (1) to (4): Equation (1): P1 < P2 Equation (2): 0.6 ≦ D1 / P1 ≦ 25.0 Formula (3): P1+R1+D1 ≧ 4% by mass Formula (4): P2+R2+D2 ≧ 4% by mass It satisfies the condition.

[0024] Light-colored ink is an ink that exhibits a lighter color than dark-colored ink, and preferably satisfies the relationship shown in formula (1). The amount of pigment (P1) contained in the light-colored ink is preferably 0.1 to 15% by mass, more preferably 0.1 to 10% by mass, and particularly preferably 0.1 to 5% by mass. The amount of pigment (P2) contained in the dark-colored ink is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, and particularly preferably 1 to 5% by mass. If the ink contains multiple pigments, the amount of pigment is the total amount of pigments.

[0025] Light-colored inks have a high ratio of pigment dispersant to pigment (D1 / P1), with a D1 / P1 of 0.6 or higher, preferably 0.8 or higher, more preferably 1.0 or higher, and particularly preferably 1.2 or higher. Light-colored inks with such high D1 / P1 values ​​have high resolubility, which can improve the re-ejection performance of non-aqueous inkjet ink sets. Furthermore, a D1 / P1 of 25.0 or lower is preferred, preferably 22.0 or lower, and particularly preferred to be 20.0 or lower. If the D1 / P1 value exceeds 25.0, it may reduce the abrasion resistance of the printed material.

[0026] The amount of resin (R1) contained in the light-colored ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 10% by mass. If the ink contains multiple resins, the amount of resin is the total amount of the resins.

[0027] The amount of pigment dispersant (D1) contained in light-colored ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 5% by mass. If the ink contains multiple pigment dispersants, the amount of pigment dispersant is the total amount of pigment dispersants.

[0028] For light-colored inks, the total amount of pigment, resin, and pigment dispersant (P1+R1+D1) is preferably 4% by mass or more, more preferably 4.5% by mass or more, and particularly preferably 5.0% by mass or more. A higher total amount of pigment, resin, and pigment dispersant results in higher continuous ejection stability, allows for rapid fixation of the ink on the substrate (the material to which the ink is applied during printing), and is preferable from the viewpoint of forming high-resolution color images. Furthermore, the total amount of pigment, resin, and pigment dispersant (P1+R1+D1) is preferably 35% by mass or less, more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

[0029] The amount of resin (R2) contained in the dark-colored ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 5% by mass. If the ink contains multiple resins, the amount of resin is the total amount of the resins.

[0030] The amount of pigment dispersant (D2) contained in dark-colored ink is preferably 1 to 20% by mass, more preferably 1 to 15% by mass, and particularly preferably 1 to 5% by mass. If the ink contains multiple pigment dispersants, the amount of pigment dispersant is the total amount of pigment dispersants.

[0031] For dark-colored inks, the ratio of pigment dispersant to pigment amount (D2 / P2) is preferably 0.2 to 10.0, more preferably 0.3 to 7.0, and particularly preferably 0.4 to 5.0. Furthermore, the D2 / P2 value is preferably smaller than the D1 / P1 value, more preferably 0.2 to 10 less than the D1 / P1 value, and particularly preferably 0.3 to 5 less than the D1 / P1 value.

[0032] The dark-colored ink has a total amount (P2+R2+D2) of pigment, resin, and pigment dispersant of 4% by mass or more, preferably 4.5% by mass or more, and particularly preferably 5.0% by mass or more. A higher total amount of pigment, resin, and pigment dispersant results in higher continuous ejection stability, allows for faster fixation of the ink on the substrate (the material to which the ink is applied during printing), and is preferable from the viewpoint of forming high-resolution color images. Furthermore, the total amount (P2+R2+D2) of pigment, resin, and pigment dispersant is preferably 35% by mass or less, more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

[0033] In the ink set of the present invention, a pair of dark and light inks have the relationship shown in formula (5) below: Equation (5): 0.3 < (P1+R1+D1) / (P2+R2+D2) < 3.0 It is preferable that the following conditions are met. It is preferable that the total amount of pigment, resin, and pigment dispersant in the light-colored ink (P1+R1+D1) and the total amount of pigment, resin, and pigment dispersant in the dark-colored ink (P2+R2+D2) are approximately the same. The (P1+R1+D1) / (P2+R2+D2) value is more preferably 0.4 to 2.5, particularly preferably 0.5 to 1.7, and most preferably 1.0. By making the total amount of pigment, resin, and pigment dispersant in the light-colored ink and the dark-colored ink approximately the same, it becomes easier to obtain printed materials with excellent sharpness.

[0034] In the ink set of the present invention, the light-colored inks are related by the following formula (6): Equation (6): 0.5 ≦ R1 / (P1+D1) ≦ 5.0 It is preferable that the following conditions are met. The lower the ratio of the amount of resin to the total amount of pigment and pigment dispersant [R1 / (P1+D1)], the better the resolubility of the ink can be. The R1 / (P1+D1) value is preferably 4.5 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less. Furthermore, the R1 / (P1+D1) value is preferably 0.5 or more, more preferably 0.6 or more, and particularly preferably 0.7 or more. If the R1 / (P1+D1) value falls below 0.5, the scratch resistance of the image may decrease.

[0035] In the ink set of the present invention, the dark colored inks have the relationship shown in the following formula (6'): Equation (6'): 0.3 ≦ R2 / (P2+D2) ≦ 4.0 It is preferable that the following conditions are met. Dark inks do not usually have problems with redissolvability or re-ejectability, but from the viewpoint of re-ejectability, it is preferable that dark inks have high redissolvability. The lower the ratio of the amount of resin to the total amount of pigment and pigment dispersant [R2 / (P2+D2)], the better the redissolvability of the ink can be improved. The R2 / (P2+D2) value is preferably 4.0 or less, more preferably 3.0 or less, and particularly preferably 2.5 or less. In addition, the R2 / (P2+D2) value is preferably 0.3 or more, more preferably 0.35 or more, and particularly preferably 0.4 or more. If the R2 / (P2+D2) value falls below 0.3, the scratch resistance of the image may decrease.

[0036] The amount of solids contained in light-colored ink is preferably 4 to 35% by mass, more preferably 4.5 to 30% by mass, and particularly preferably 5.0 to 25% by mass. It is preferable that the pigment, resin, and pigment dispersant constitute the majority of the solids contained in light-colored ink (for example, 95% by mass or more), although in some cases the solids contained in light-colored ink consist only of the pigment, resin, and pigment dispersant.

[0037] The amount of solids contained in the dark ink is preferably 4 to 35% by mass, more preferably 4.5 to 30% by mass, and particularly preferably 5.0 to 25% by mass. It is preferable that the pigment, resin, and pigment dispersant constitute the majority of the solids contained in the dark ink (for example, 95% by mass or more), although in some cases the solids contained in the dark ink consist only of the pigment, resin, and pigment dispersant.

[0038] In this specification, the solid content of ink refers to the components remaining after removing volatile components such as solvents, and which ultimately form the printed material. In this invention, the solid content is defined as the components remaining after drying the ink at 150°C for 60 minutes.

[0039] In the ink set of the present invention, the viscosity of the dark ink and the light ink at 25°C is preferably in the range of 2.5 mPa·s to less than 7.0 mPa·s, and particularly preferably in the range of 3.0 mPa·s to 5.0 mPa·s. Inks having such a preferred viscosity have high continuous ejection stability, good liquid cutoff when ejected from the printer, and can form clean dots, making them suitable from the viewpoint of forming high-quality color images. Furthermore, in order to form high-quality color images, it is also preferable that the viscosity of the dark ink and the light ink are about the same. The difference between the viscosity of the dark ink and the viscosity of the light ink at 25°C is preferably 1.0 mPa·s or less, and it is particularly preferable that the viscosity of the dark ink and the viscosity of the light ink at 25°C are the same.

[0040] In this specification, the viscosity of the ink is the viscosity measured using a cone-plate viscometer.

[0041] In the ink set of the present invention, the dark ink and the light ink preferably have a surface tension of 25 to 30 mN / m at 25°C, and particularly preferably 27 to 30 mN / m. From the viewpoint of forming high-quality color images, it is preferable that the surface tensions of the dark ink and the light ink are similar. The difference between the surface tension of the dark ink and the light ink at 25°C is preferably 2.0 mN / m or less, and it is particularly preferable that the surface tensions of the dark ink and the light ink at 25°C are the same.

[0042] In this specification, the surface tension of the ink is the surface tension measured by the plate method.

[0043] In the ink set of the present invention, the solvent contained in the dark ink and / or light ink preferably contains at least an amide bond or urea bond-containing compound. The amide bond or urea bond-containing compound used as a solvent is an organic solvent that has a high ability to dissolve resins such as vinyl chloride resin and vinyl chloride / vinyl acetate copolymer resin (in other words, has excellent resin solubility).

[0044] The solvents contained in dark-colored inks and / or light-colored inks are (A-1) Glycol ether solvents with a boiling point of less than 200°C, and (A-2) A compound containing an amide bond or urea bond, wherein the pH of a mixture consisting of 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of (A-2) the compound containing an amide bond or urea bond is 7.0 or higher. It is preferable that it includes.

[0045] In this specification, a glycol ether solvent with a boiling point of less than 200°C is referred to as component (A-1), and is also called "(A-1) glycol ether solvent with a boiling point of less than 200°C" as described above. Furthermore, a compound containing an amide bond or urea bond, which is a mixture of 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of an amide bond or urea bond-containing compound, has a pH of 7.0 or higher, is referred to as "(A-2) amide bond or urea bond-containing compound" as described above.

[0046] The glycol ether solvent of component (A-1) is an organic solvent with low viscosity, a relatively high Tag closure flash point, and good drying properties, and is preferable for use as the main solvent of the ink. The preferred flash point of the glycol ether solvent of component (A-1) is 50°C to 75°C. In this specification, the flash point is the flash point determined by the Tag closure method.

[0047] In this specification, glycol ether solvents mean compounds having an alkyl ether structure based on glycols, such as ethylene glycol and propylene glycol. Glycol ether solvents include those in which both ends of the molecule are hydroxyl groups, or in which the hydrogen atoms of one or both ends of the molecule's hydroxyl groups are substituted with substituents such as alkyl groups or acyl groups.

[0048] The glycol ether solvent of component (A-1) has a boiling point of less than 200°C, preferably 150 to 200°C, and more preferably 160 to 190°C. In this specification, boiling point refers to the boiling point at 1 atmosphere. The boiling point of the glycol ether solvent of component (A-1) being less than 200°C improves the drying properties of the ink, making it easier to obtain printed materials with excellent blocking resistance.

[0049] The glycol ether solvent of component (A-1) preferably includes a glycol ether solvent represented by the following general formula (I). R1-(OR2)nO-R3 (I) In equation (I), n is an integer between 1 and 4, R1 is a branched alkyl group having 1 to 8 carbon atoms or an acyl group having 1 to 4 carbon atoms. R2 is a branched alkylene group having 1 to 4 carbon atoms. R3 is hydrogen, or a branched alkyl group having 1 to 4 carbon atoms, or an acyl group having 1 to 4 carbon atoms.

[0050] The glycol ether solvent of component (A-1) preferably contains a dialkylene glycol dialkyl ether or a dialkylene glycol monoalkyl ether acetate, and more preferably contains at least one selected from diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, and propylene glycol monomethyl ether acetate.

[0051] The amount of component (A-1) in the solvent is preferably in the range of 60 to 95% by mass, and more preferably in the range of 75 to 95% by mass. Component (A-1) may be used alone or in combination of two or more types.

[0052] The amide bond or urea bond-containing compound of component (A-2) has a pH of 7.0 or higher when mixed with 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of the (A-2) amide bond or urea bond-containing compound, and is not in the acidic range, thus not corroding the print head. Furthermore, it is an organic solvent with high dissolving ability for resins such as vinyl chloride resin and vinyl chloride / vinyl acetate copolymer resin (in other words, excellent resin dissolving properties). When component (A-2) is used as a solvent, the effect of penetrating the ink on the substrate without spreading it is obtained. For this reason, by using the amide bond or urea bond-containing compound of component (A-2) in combination with the glycol ether-based solvent of component (A-1) described above, it is possible to provide printed materials in which the image is less prone to blurring and the media is less likely to block when printed on roll media and wound up. The reason for setting the pH of the mixture consisting of 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of an amide bond or urea bond-containing compound to 7.0 or higher is based on the idea that keeping the ink pH from becoming acidic would protect the print head from corrosion. Diethylene glycol ethyl methyl ether is a glycol ether solvent of component (A-1), and it is considered important that the pH of the aqueous solution containing this (A-1) glycol ether, water, and the amide bond or urea bond-containing compound of component (A-2) does not fall into the strongly acidic range. Therefore, the pH of the aqueous solution at a specific mixing ratio that approximates the actual ink formulation ratio was specified as 7.0 or higher.

[0053] (A-2) The amide bond or urea bond-containing compound of component (A-2) is such that when a mixture is prepared consisting of 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of the amide bond or urea bond-containing compound, the pH of the mixture will be 7.0 or higher, preferably 7.0 to 10.0, and more preferably 7.0 to 9.5.

[0054] The amide bond or urea bond-containing compound of component (A-2) preferably contains at least one selected from the group consisting of alkylamide solvents, cyclic amide solvents, aromatic amide solvents, alkylurea solvents, and cyclic urea solvents.

[0055] Specific examples of alkylamide solvents include 3-methoxy-N,N-dimethylpropanamide. Specific examples of cyclic amide solvents include 2-pyrrolidone and ε-caprolactam. Specific examples of aromatic amide solvents include benzamide. Examples of alkylurea solvents include N-methylurea. Examples of cyclic urea solvents include 1,3-dimethyl-2-imidazolidinone.

[0056] As the amide bond or urea bond-containing compound of component (A-2), cyclic urea solvents are preferred, imidazolidinone solvents are more preferred, and 1,3-dimethyl-2-imidazolidinone is the most preferred.

[0057] The amount of component (A-2) in the solvent is preferably in the range of 4.0 to 30% by mass, more preferably in the range of 5 to 30% by mass, and even more preferably in the range of 5 to 15% by mass. Component (A-2) may be used alone or in combination of two or more types. When the amount of component (A-2) in the solvent is 30% by mass or less, the glossiness of the image can be improved.

[0058] The ratio of the amount of component (A-1) in the solvent to the amount of component (A-2) in the solvent is preferably 2 to 10, and more preferably 4 to 8. In this specification, the ratio of the amount of component (A-1) in the solvent to the amount of component (A-2) in the solvent may be expressed as "(A-1) / (A-2)". Here, the ratio of the amount of component (A-1) in the solvent to the amount of component (A-2) in the solvent is on a mass basis.

[0059] The solvents contained in dark-colored inks and / or light-colored inks are (A-3) Glycol or glycol ether solvent with a boiling point of 220°C or higher and less than 300°C. It is preferable that it contains the following. In particular, from a safety standpoint, it is preferable that component (A-3) is a glycol with a boiling point of 220°C or higher and less than 300°C, and both ends being hydroxyl groups.

[0060] In this specification, "a glycol or glycol ether solvent having a boiling point of 220°C or higher and less than 300°C" is defined as component (A-3), and is also referred to as "(A-3) a glycol or glycol ether solvent having a boiling point of 220°C or higher and less than 300°C" as described above.

[0061] The glycol or glycol ether solvent of component (A-3) prevents the ink from drying out in the print head, further improving re-ejection performance, and also contributes to improving the glossiness of the printed material.

[0062] Examples of component (A-3) include diethylene glycol, triethylene glycol, tripylene glycol, polypropylene glycol, diethylene glycol-2-ethylhexyl ether, diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, dipropylene glycol, ethylene glycol monophenyl ether, triethylene glycol monomethyl ether, and diethylene glycol dibutyl ether. Component (A-3) is preferably highly compatible with components (A-1) and (A-2).

[0063] If the amount of component (A-3) is too high, the blocking resistance of the printed material may decrease. Therefore, the amount of component (A-3) in the solvent is preferably in the range of 0.1 to 5.0% by mass, more preferably 0.1 to 2.0% by mass, even more preferably 0.1 to 1.0% by mass, and most preferably in the range of 0.1 to 0.7% by mass. Component (A-3) may be used alone or in combination of two or more types.

[0064] The solvents contained in dark-colored inks and / or light-colored inks are (A-4) Organic solvents with a boiling point of less than 150°C that do not fall under component (A-1) or component (A-2). It can include...

[0065] In this specification, an organic solvent having a boiling point of less than 150°C and not belonging to either component (A-1) or component (A-2) is referred to as component (A-4), and is also referred to as "(A-4) an organic solvent having a boiling point of less than 150°C and not belonging to component (A-1) or component (A-2)" as described above.

[0066] The organic solvent in component (A-4) has a low boiling point, which can improve the drying properties of the ink.

[0067] Examples of component (A-4) include propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and cyclopentanone. Component (A-4) is preferably highly compatible with components (A-1) and (A-2).

[0068] The amount of component (A-4) in the solvent is preferably in the range of 0.5 to 2.0% by mass, and more preferably in the range of 0.5 to 1.0% by mass. Component (A-4) may be used alone or in combination of two or more types.

[0069] Dark-colored inks and / or light-colored inks are preferably free of γ-butyrolactone.

[0070] The amount of solvent (S1) contained in the light-colored ink is preferably 70-96% by mass, more preferably 75-96% by mass, and particularly preferably 80-95% by mass. Similarly, the amount of solvent (S2) contained in the dark-colored ink is preferably 70-96% by mass, more preferably 80-96% by mass, and particularly preferably 85-95% by mass. If the ink contains multiple solvents, the amount of solvent is the total amount of the solvents.

[0071] The resin contained in dark-colored inks and / or light-colored inks is a resin used as a binder, and is also called a binder resin. Binder resins are usually solid at 40°C. Furthermore, it is preferable that the binder resin does not dissolve when mixed with diethylene glycol ethyl methyl ether in a mass ratio of 1:2 at 40°C.

[0072] The resin preferably has a weight-average molecular weight (Mw) of 20,000 to 90,000, more preferably 30,000 to 80,000, and even more preferably 40,000 to 80,000. Using a resin with an Mw of 20,000 or more can improve the weather resistance of printed materials. Furthermore, in terms of resin solubility, it is preferable that the resin has an Mw of 90,000 or less.

[0073] Furthermore, the weight-average molecular weight / number-average molecular weight (Mw / Mn) of the resin is preferably 2.0 to 8.0, and more preferably 2.3 to 7.0. An Mw / Mn of 2.0 or higher is preferable in terms of the abrasion resistance and weather resistance of the printed material. Additionally, an Mw / Mn of 8.0 or lower is preferable in terms of solubility in the solvent.

[0074] In this specification, the weight-average molecular weight and number-average molecular weight of the resin are values ​​measured by gel filtration chromatography, with polystyrene used as the standard substance and tetrahydrofuran as the mobile phase.

[0075] The resin preferably has a glass transition temperature (Tg) of 40 to 90°C, more preferably 45 to 85°C, and particularly preferably 50 to 80°C.

[0076] In this specification, the glass transition temperature (Tg) of a resin can be determined by differential scanning calorimetry (DSC) in accordance with JIS K 7121:2012 (Method for measuring the transition temperature of plastics). Specifically, approximately 10 mg of resin is placed in an aluminum pan for measurement, and DSC measurement is performed under the following measurement conditions. (Measurement temperature conditions) 1st heating stage: -80℃ to 220℃ (20℃ / min) Temperature drop condition: 220℃~-80℃(50℃ / min) 2nd heating stage: -80℃ to 220℃ (10℃ / min)

[0077] Examples of resins include polyvinyl chloride (vinyl chloride resin), polyvinyl acetate, vinyl chloride-vinyl acetate copolymer (vinyl chloride / vinyl acetate copolymer resin), vinyl chloride resin, chlorinated rubber, chlorinated polyethylene resin, chlorinated polypropylene resin, chlorinated ethylene-vinyl acetate resin, acrylic resin, acrylic silicone resin, styrene-acrylic copolymer resin, polystyrene resin, polyamide resin, polyurethane resin, polyolefin resin, silicone resin, fluororesin, epoxy resin, polyester resin, ketone resin, phenolic resin, polyvinyl alcohol, polyvinyl alcohol derivatives (anionic modified polyvinyl alcohol, etc.), cellulose, cellulose derivatives (hydroxymethylcellulose, hydroxyethylcellulose, cellulose acetate, etc.), rosin-based resins, oily resins, petroleum resins, alkyd resins, alginic acid, alginic acid derivatives (propylene glycol alginate, etc.). Modified products of these resins are also included, such as hydroxyalkyl etherification modification and carboxylic acid modification. Of these, acrylic resin, vinyl chloride resin, and vinyl chloride / vinyl acetate copolymer resin are preferred from the viewpoint of adhesion to the substrate and durability of the printed material, with vinyl chloride / vinyl acetate copolymer resin being particularly preferred.

[0078] The resin contained in dark-colored inks and / or light-colored inks preferably contains a vinyl chloride / vinyl acetate copolymer resin. In addition to adhesion and durability, vinyl chloride / vinyl acetate copolymer resins have high solubility in glycol ether-based solvents and solvents containing amide or urea bonds.

[0079] The vinyl chloride / vinyl acetate copolymer resin preferably has a mass ratio (a / b) of vinyl chloride units (a) to vinyl acetate units (b) of 70 / 30 to 95 / 5, and more preferably 80 / 20 to 90 / 10. Note that vinyl chloride units are monomer units derived from vinyl chloride, and vinyl acetate units are monomer units derived from vinyl acetate. Here, by setting the proportion of vinyl chloride units to the total monomer units constituting the resin to 70% by mass or more, high weather resistance is more easily obtained, and printed materials without bleeding are more easily obtained. On the other hand, if the proportion of vinyl chloride units exceeds 90% by mass, solubility in the solvent may decrease.

[0080] The amount of vinyl chloride / vinyl acetate copolymer resin contained in the light-colored ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 10% by mass. Similarly, the amount of vinyl chloride / vinyl acetate copolymer resin contained in the dark-colored ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 5% by mass.

[0081] The pigments contained in dark and / or light inks may be organic or inorganic pigments. Specific examples of pigments include: CIPigment Yellow 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 24, 32, 34, 35, 36, 37, 41, 42, 43, 49, 53, 55, 60, 61, 62, 63, 65, 73, 74, 75, 77, 81, 83, 87, 93, 94, 95, 97, 98, 99, 100, 101, 104, 105, 106, 108, 109, 110, 111, 113, 114, 116, 117, 119, 120, 123, 124, 126, 127, 128, 129, 130, 133, 138, 139, 150, 151, 152, 153, 154, 155, 165, 167, 168, 169, 170, 172, 173, 174, 175, 176, 179, 180, 181, 182, 183, 184, 185, 191, 193, 194, 199, 205, 206, 209, 212, 213, 214, 215, 219, C.I.Pigment Orange 1、2、3、4、5、13、15、16、17、19、20、21、24、31、34、36、38、40、43、46、48、49、51、60、61、62、64、65、66、67、68、69、71、72、73、74、81、83、 C.I.Pigment Red 1、2、3、4、5、6、7、8、9、10、11、12、14、15、16、17、18、21、22、23、31、32、38、41、48、48:1、48:2、48:3、48:4、48:5、49、52、52:1、52:2、53:1、54、57:1、58、60:1、63、64:1、68、81:1、83、88、89、95、101、104、105、108、112、114、119、122、123、136、144、146、147、149、150、164、166、168、169、170、171、172、175、176、177、178、179、180、181、182、183、184、185、187、188、190、193、194、200、202、206、207、208、209、210、211、213、214、216、220、220、221、224、226、237、238、239、242、245、247、248、251、253、254、255、256、257、258、260、262、263、264、266、268、269、270、271、272、279、282、 C.I.Pigment Violet 1、2、3、3:1、3:3、5:1、13、15、16、17、19、23、25、27、29、31、32、36、37、38、42、50、 C.I.Pigment Blue 1、15、15:1、15:2、15:3、15:4、15:5、15:6、16、17:1、24、24:1、25、26、27、28、29、36、56、60、61、62、63、75、79、80、 C.I.Pigment Green 1、4、7、8、10、15、17、26、36、50、 C.I.Pigment Brown 5、6、23、24、25、32、41、42、 CIPigment Black 1, 6, 7, 9, 10, 11, 20, 26, 28, 31, 32, 34, CIPigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28, These are some examples.

[0082] Among these, from the perspective of weather resistance and color reproduction of printed materials, CIPigment Black 7, CIPigment Blue 15:3, 15:4, 28, CIPigment Red 101, 122, 202, 254, 282, CIPigment Violet 19, CIPigment Yellow 42, 120, 138, 139, 150, 151, 155, 213 and CIPigment Orange 43, 64, 71, 73, 83 are preferred.

[0083] Pigment dispersants contained in dark and / or light inks are substances that act as dispersion media components, helping to finely dissolve the pigment and suspend it in the dispersion medium. Furthermore, because pigment dispersants are soluble in solvents and also have compatibility with resins, they are thought to contribute to improved ink resolubility. While pigment dispersants also include polymers, they are distinguished from the aforementioned resins (binder resins). Pigment dispersants are typically liquid at 40°C. Additionally, at 40°C, pigment dispersants completely dissolve when mixed with diethylene glycol ethyl methyl ether in a 1:2 mass ratio. The fact that pigment dispersants are liquid at 40°C and have excellent solvent solubility is thought to improve ink resolubility.

[0084] When the pigment dispersant is a polymer, the weight-average molecular weight (Mw) of the pigment dispersant is preferably 50,000 or less, and more preferably between 1,000 and 45,000. Furthermore, when the pigment dispersant is a polymer, the glass transition temperature (Tg) of the pigment dispersant is preferably less than 50°C, and more preferably between -30°C and 30°C. The weight-average molecular weight and glass transition temperature of polymer pigment dispersants are obtained by the same method as described above for the weight-average molecular weight and glass transition temperature of resins.

[0085] The pigment dispersant preferably has an acid value and / or an amine value. A pigment dispersant having an acid value means a pigment dispersant with an acid value of 2 mg KOH / g or more. A pigment dispersant having an amine value means a pigment dispersant with an amine value of 2 mg KOH / g or more. Here, a pigment dispersant having both an acid value and an amine value refers to a pigment dispersant with an acid value of 2 mg KOH / g or more and an amine value of 2 mg KOH / g or more. The acid value of the pigment dispersant is preferably 5 to 20 mg KOH / g, and the amine value of the pigment dispersant is preferably 5 to 50 mg KOH / g.

[0086] In this specification, "acid value" refers to the number of milligrams of potassium hydroxide (unit: mgKOH / g) required to neutralize the acidic components present in 1 g of sample, and can be measured by the method specified in JIS K2501:2003. "Amine value" refers to the number of milligrams of potassium hydroxide equivalent to hydrochloric acid or perchloric acid (unit: mgKOH / g) required to neutralize the basic components contained in 1 g of sample, and can be measured by the method specified in JIS K2501:2003.

[0087] Specific examples of pigment dispersants include: ANTI-TERRA-U, ANTI-TERRA-U100, ANTI-TERRA-204, ANTI-TERRA-205, DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-108, DISPERBYK-109, DISPERBYK-110, DISPERBYK-111, DISPERBYK-112, DISPERBYK-116, DISPERBYK-130, DISPERBYK-140, DISPERBYK-142, DISPERBYK-145, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-180, DISPERBYK-182, DISPERBYK-183, DISPERBYK-184, DISPERBYK-185, DISPERBYK-2000, DISPERBYK-2001, DISPERBYK-2008, DISPERBYK-2009, DISPERBYK-2020, DISPERBYK-2025, DISPERBYK-2050, DISPERBYK-2070, DISPERBYK-2096, DISPERBYK-2150, DISPERBYK-2155, DISPERBYK-2163, DISPERBYK-2164, BYK-P104, BYK-P104S, BYK-P105, BYK-9076, BYK-9077, BYK-220S, BYKJET-9150, BYKJET-9151 (all manufactured by Big Chemie Japan Co., Ltd.) Solsperse3000, Solsperse5000, Solsperse9000, Solsperse11200, Solsperse13240, Solsperse13650, Solsperse13940, Solsperse16000, Solsperse17000, Solsperse18000, Solsperse20000, Solsperse21000, Solsperse24000SC, Solsperse24000GR, Solsperse26000, Solsperse27000, Solsperse28000, Solsperse32000, Solsperse32500, Solsperse32550, Solsperse32600, Solsperse33000, Solsperse34750, Solsperse35100, Solsperse35200, Solsperse36000, Solsperse36600, Solsperse37500, Solsperse38500, Solsperse39000, Solsperse41000, Solsperse54000, Solsperse55000, Solsperse56000, Solsperse71000, Solsperse76500, Solsperse X300 (manufactured by Lubrizol Corporation), Disparon DA-7301, Disparon DA-325, Disparon DA-375, Disparon DA-234 (all manufactured by Kusumoto Kasei Co., Ltd.) Floren AF-1000, Floren DOPA-15B, Floren DOPA-15BHFS, Floren DOPA-17HF, Floren DOPA-22, Floren DOPA-33, Floren G-600, Floren G-700, Floren G-700AMP, Floren G-700DMEA, Floren G-820, Floren G-900, Floren GW-1500, Floren KDG-2400, Floren NC-500, Floren WK-13E (all manufactured by Kyoeisha Chemical Co., Ltd.) TEGO Dispers610, TEGO Dispers610S, TEGO Dispers630, TEGO Dispers650, TEGO Dispers652, TEGO Dispers655, TEGO Dispers662C, TEGO Dispers670, TEGO Dispers685, TEGO Dispers700, TEGO Dispers710, TEGO Dispers740W, LIPOTIN A, LIPOTIN BL, LIPOTIN DB, LIPOTIN SB (both manufactured by Evonik Degussa), Ajisper PB821, PB822, PB824, PB827, PB831, PB881, PN411, PA111 (all manufactured by Ajinomoto Fine Techno Co., Ltd.) Texahole 963, Texahole 964, Texahole 987, Texahole P60, Texahole P61, Texahole P63, Texahole 3250, Texahole SF71, Texahole UV20, Texahole UV21 (all manufactured by Cognis), Examples include the BorchiGenSN88 and BorchiGen0451 (both manufactured by Borchis).

[0088] Dark and / or light inks may contain synergists. Synergists are substances used to improve the dispersion stability and color development of pigments. Synergists are compounds obtained by introducing specific substituents such as sulfate groups, sulfonamide groups, sulfonic acid groups and their salts, phthalimide groups, phthaloimidemethyl groups, amino groups, and triazine groups into organic pigments, and are also called pigment derivatives. Azo, phthalocyanine, and quinacridone pigment derivatives (synergists) are known. In this specification, synergists are distinguished from pigments.

[0089] The amount of synergist contained in dark and / or light inks is preferably in the range of 0.001% to 0.5% by mass, and more preferably in the range of 0.005% to 0.2% by mass. If the ink contains multiple synergists, the amount of synergist is the total amount of synergists.

[0090] Dark and light colored inks may also contain, as necessary, additives such as UV absorbers, radical scavengers, surface modifiers, antioxidants, plasticizers, rust inhibitors, solvents, fillers, defoamers, charge control agents, stress relievers, penetrating agents, light guides, brightening agents, magnetic materials, phosphors, antibacterial agents, antiviral agents, and anti-algal agents.

[0091] Dark and light-colored inks can be prepared by mixing various components as needed, and filtering the resulting mixture using a filter with a pore size of approximately 1 / 10 or less of the nozzle diameter of the inkjet print head used, if necessary.

[0092] Printing using the ink set of the present invention is performed by an inkjet printing method. Various inkjet printers can be used for inkjet printing. Examples of inkjet printers include inkjet printers that eject ink using a charged control method or a piezo method. In addition, large-format inkjet printers, specifically those intended for printing on articles produced on industrial lines, can also be suitably used.

[0093] The substrate to be printed on (the base material to which ink is applied during printing) is not particularly limited, but substrates used in industrial lines are preferred. The shape of the substrate can be, for example, film, sheet, or plate. Examples of materials for the substrate include epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, and especially plastics such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polypropylene (PP); metals such as iron, stainless steel, and aluminum; wood, cement, concrete, gypsum, calcium silicate, calcium carbonate, and glass. Specific examples of substrates include PVC sheets, tarpaulin, corrugated plastic sheets, acrylic sheets, flexible boards, calcium silicate boards, gypsum slag barlite boards, calcium carbonate boards, wood chip cement boards, precast concrete boards, lightweight foamed concrete (ALC) boards, gypsum boards, tiles, and glass plates. Among these, polyvinyl chloride substrates and tarpaulin substrates are preferred. [Examples]

[0094] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0095] <Preparation of non-aqueous inks> Mixtures containing each component in the amounts (parts by mass) shown in Tables 1-4 were kneaded in a bead mill for 3 hours to prepare the light-colored inks of Examples 1-30 and Comparative Examples 1-7, respectively.

[0096] The pigments used are listed below. • Black pigment (CB): Monarch 1000 (Cabot carbon black) • Cyan pigment (PB15:4): Chromofine Blue A-220JC (Dainichi Seika Kogyo Co., Ltd. Pigment Blue 15:4) • Magenta pigment (PR122): Fastogen Super Magenta RG (DIC Pigment Red 122) • Yellow pigment (PY150): Komarix Yellow 150 (Pigment Yellow 150 manufactured by Zeya Chemicals) The solvents used are listed below. The abbreviations and boiling points of each solvent are shown in parentheses. • Diethylene glycol ethyl methyl ether (MEDG, boiling point 176°C) • 1,3-Dimethylimidazolidinone (DMI, boiling point 220°C) • 2-Pyrrolidone (boiling point 250°C) The resins used are listed below. • Resin 1: VINNOL H15 / 42 (vinyl chloride-vinyl acetate copolymer resin, 100% solids content, manufactured by Wacker Chemie) • Resin 2: Solvine C (vinyl chloride-vinyl acetate copolymer resin, 100% solids content, manufactured by Nisshin Chemical Industry Co., Ltd.) The pigment dispersants used are listed below. • Pigment dispersant 1: DISPERBYK-2014 (Acrylic-modified polymer dispersant, Acid value: 8 mg KOH / g, Amine value: 18 mg KOH / g, Solids content: 100%, Manufactured by BYK) • Pigment dispersant 2: Solsperse 32000 (polycaprolactone-based polymer dispersant, acid value: 15.5 mg KOH / g, amine value: 31.2 mg KOH / g, solids content 100%, manufactured by Lubrizol)

[0097] <Continuous Dispensing Stability> For each ink prepared in the above <Preparation of Non-Aqueous Inks> section, a nozzle check pattern image was printed using a large-format inkjet printer (platen temperature 45°C), followed by printing a 100% solid image for 1000m. After printing 1000m, the nozzle check pattern was printed again, and the continuous ejection stability was evaluated according to the following criteria. The results are shown in Tables 1-4. Inks with an evaluation result of "◎", "○", or "△" are non-aqueous inks with excellent continuous ejection stability. (standard) ◎: Nozzle check pattern has less than 1% missing or irregular. ○: Less than 5% of nozzle check patterns are missing or distorted. △: 5% to 10% of nozzle check patterns are missing or distorted. ×: The nozzle check pattern shows more than 10% missing or distorted areas.

[0098] <Re-dischargeability> For each ink prepared in the above <Preparation of Non-Aqueous Inks>, a nozzle check pattern image was printed on copy paper using a large-format inkjet printer (platen temperature 45°C). The printer was then left idle for 30 minutes without maintenance or further printing, and the same image was printed again. If any nozzles failed to eject, cleaning was performed, and the same image was printed again. The print appearance was visually evaluated for re-ejection performance according to the following criteria. The results are shown in Tables 1-4. Inks with an evaluation result of "◎", "○", or "△" are non-aqueous inks with excellent re-ejection performance. (standard) ◎: When printing after being left idle, ink is ejected from all nozzles without cleaning. ○: When printing after a period of inactivity, performing a cleaning cycle once will ensure that ink is ejected from all nozzles. △: When printing after a period of inactivity, performing cleaning three times will ensure that ink is ejected from all nozzles. ×: In printing after being left idle, ink is not being ejected from more than 20% of the nozzles even after performing cleaning three or more times.

[0099] <Evaluation of printed materials: Abrasion resistance> Each of the light and dark inks prepared in the above <Preparation of Non-Aqueous Inks> section was applied to a glossy PVC sheet heated to 45°C using a bar coater #7. The combinations of light and dark inks that make up the light and dark inks are shown in Tables 1 to 4. After application, the applied surface was rubbed with an ethanol-impregnated cotton swab, and the printed material was evaluated according to the following criteria. The results are shown in Tables 1 to 4. Light and dark inks with an evaluation result of "○" or "△" are non-aqueous inks that can produce printed materials with excellent abrasion resistance. (standard) ○: No scratches or stains are left on the coating film formed from both light-colored and dark-colored inks, and the cotton swab does not become stained. △: No scratches are left on the coating film formed from either light-colored or dark-colored ink, but the cotton swab becomes stained when the coating film is formed from light-colored ink. ×: Of the coating films formed from light-colored and dark-colored inks, the coating film formed from light-colored ink will show scratches and the cotton swab will become discolored.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3]

[0103] [Table 4]

Claims

1. A non-aqueous inkjet ink set comprising at least one pair of dark inks, The pair of inks described above consists of a dark ink and a light ink. The dark ink is one of cyan ink, magenta ink, yellow ink, and black ink, and the light ink is one of light cyan ink, light magenta ink, light yellow ink, and light black ink, provided that the pair of dark and light inks consists of one of the following combinations: cyan ink and light cyan ink, magenta ink and light magenta ink, yellow ink and light yellow ink, and black ink and light black ink. The dark ink and the light ink each contain at least a solvent, a pigment, a pigment dispersant, and a resin. When the amount of pigment (mass%) contained in the light-colored ink is P1, the amount of resin (mass%) contained in the light-colored ink is R1, the amount of pigment dispersant (mass%) contained in the light-colored ink is D1, the amount of pigment (mass%) contained in the dark-colored ink is P2, the amount of resin (mass%) contained in the dark-colored ink is R2, and the amount of pigment dispersant (mass%) contained in the dark-colored ink is D2, the pair of light and dark inks are related by the following formulas (1) to (4): Formula (1): P1 < P2 Formula (2): 0.6≦D1 / P1≦25.0 Formula (3): P1+R1+D1 ≧ 4% by mass Formula (4): P2+R2+D2 ≧ 4% by mass Satisfying the conditions, A non-aqueous inkjet ink set characterized in that the dark ink and the light ink have a viscosity at 25°C in the range of 2.5 mPa·s or more and less than 7.0 mPa·s.

2. The pair of light and dark inks have the relationship shown in formula (5) below: Formula (5): 0.3 < (P1+R1+D1) / (P2+R2+D2) < 3.0 A non-aqueous inkjet ink set according to claim 1, satisfying the requirements.

3. The non-aqueous inkjet ink set according to claim 1 or 2, characterized in that the solvent contains at least an amide bond or a urea bond-containing compound.

4. The non-aqueous inkjet ink set according to claim 1 or 2, characterized in that the resin comprises a vinyl chloride / vinyl acetate copolymer resin.

5. The light-colored inks are related by the following formula (6): Formula (6): 0.5≦R1 / (P1+D1)≦5.0 A non-aqueous inkjet ink set according to claim 1 or 2, satisfying the requirements.

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