Nonaqueous inkjet ink set

Abstract

The present invention relates to a nonaqueous inkjet ink set that comprises at least a pair of variable-density inks, composed of a dark-colored ink and a light-colored ink, said nonaqueous inkjet ink set being characterized in that: the dark-colored ink and the light-colored ink each include at least a solvent, a pigment, a pigment dispersant, and a resin; the pigment quantity included in the light-colored ink, the resin quantity included in the light-colored ink, the pigment dispersant quantity included in the light-colored ink, the pigment quantity included in the dark-colored ink, the resin quantity included in the dark-colored ink, and the pigment dispersant quantity included in the dark-colored ink satisfy a specified relational expression; and the viscosity of the dark-colored ink and the light-colored ink at 25°C is 2.5 mPa・s or greater and less than 7.0 mPa・s.

Description

Non-aqueous inkjet ink set

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

[0002] In recent years, ink sets comprising at least one pair of dark and light inks have been developed as a means of forming high-quality color images. Such ink sets achieve color by varying the amount of colorant that lands on a recording medium per unit area, thereby enabling a greater range of gradation and a greater number of colors to be expressed.

[0003] Japanese Patent Laid-Open Publication No. 2008-19409 (Patent Document 1) describes an invention aimed at providing a non-aqueous inkjet ink set that provides stable ejection performance even in high-speed printing and has good printability (abrasion resistance, gloss, and drying properties) on polyvinyl chloride. Specifically, the invention describes a non-aqueous inkjet ink set that is composed of one or more inks that are made of at least a mixed solvent, a pigment, and a resin, at least one of the inks being composed of a light-colored ink and a dark-colored ink with different pigment concentrations, wherein 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. Furthermore, Patent Document 1 describes that in a non-aqueous inkjet ink set (hereinafter also simply referred to as ink), it is preferable to adjust the viscosity of each ink to a value that is as close as possible to the respective inks in the set to enable stable ejection of ink droplets, and that by using a method of reducing the difference in viscosity between light-colored ink and dark-colored ink by using a high-viscosity solvent, it is possible to suppress bending of ejected ink droplets and enable stable ejection.

[0004] Japanese Patent Laid-Open Publication No. 2022-191658 (Patent Document 2) describes an invention aimed at providing an ink set that can effectively suppress bleeding of prints, even when the ink set is made up of a plurality of ink compositions including dark color inks and light color inks. Specifically, the invention describes an ink set that contains a plurality of non-aqueous ink compositions that contain a colorant and an organic solvent and are ejected by an inkjet method, the ink set including dark color inks and light color inks that have a lower content of colorant than the dark color inks, and at least one non-aqueous ink composition of the plurality of non-aqueous ink compositions included in the ink set contains at least one of a specific alkyd amide solvent (a1) and a specific cyclic amide solvent (a2). Furthermore, Patent Document 2 describes that light-colored inks have a lower content of coloring material than dark-colored inks, and therefore have a relatively higher content of organic solvent, which in turn increases the content of organic solvent ejected onto the substrate (recording medium), making print bleeding more likely to occur, and that the above-mentioned object can be achieved with an ink set that includes a non-aqueous ink composition that contains at least one of a specific alkyd amide solvent (a1) and a specific cyclic amide solvent (a2).

[0005] JP 2008-19409 A JP 2022-191658 A

[0006] Although Patent Documents 1 and 2 describe non-aqueous inkjet ink sets comprising at least one pair of dark and light inks, there is room for improvement in the ejection stability of such ink sets. Specifically, printing with an inkjet printer may require a series of printing operations to be stopped and then resumed after a certain period of time. Therefore, it is important for an inkjet ink set to have the property of being able to eject ink satisfactorily even in such cases (re-ejectability). However, light-colored inks tend to dry out easily in the inkjet printer head, which may prevent re-ejectability. While ink drying in the head is hardly a problem when the head is cleaned with a cleaning liquid, if the head is not cleaned when printing is interrupted (for example, when a paper jam occurs, printing is interrupted but the head cannot be cleaned immediately, and the ink remaining in the head may dry and harden), clogging of the head can result in reduced productivity and image quality, or the head must be replaced if recovery of the head is not expected.

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a non-aqueous inkjet ink set that is excellent in re-ejection properties and continuous ejection stability.

[0008] If ink dries in the head when printing is interrupted, the pigment and resin contained in the ink may remain in the head and solidify. Resuming printing in this state will result in poor ejection and poor re-ejectability. A pair of dark and light inks often uses the same pigment and resin in the dark and light inks, and adjusting their amounts can result in two different inks (dark and light inks). Relatively, light inks contain less pigment and more resin, while dark inks contain more pigment and less resin. The inventors' investigations revealed that some light inks lack sufficient re-ejectability, suggesting that re-ejectability is particularly influenced by resin. In particular, in inkjet printers that heat the head and platen while printing, the ink ejection head, particularly the area around the nozzles, is heated as it passes above the platen. This heats light inks, particularly those with a high resin content, and they are prone to thickening and drying due to solvent evaporation, leading to nozzle blockage caused by the ink drying out.

[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 when printing is interrupted, dissolving in the ink used when printing is resumed or in the cleaning liquid used when cleaning the nozzles. Highly re-solubilizable inks are easily dissolved or softened even after solidification, making them removable. Solvent-based inks can generally be divided into lacquer-type and reactive-type inks. Lacquer-type solvent-based inks form a film upon drying, and the increase in solid content and viscosity due to solvent evaporation can cause the ink to dry out and become solid, potentially leading to nozzle clogging. However, it was confirmed that highly re-solubilizable inks are less likely to cause nozzle clogging, and even if clogging does occur, the blocked portion can be dissolved or softened and removed by cleaning the nozzles.

[0010] Furthermore, as mentioned above, a pair of dark and light inks often uses the same pigment and resin in both the dark and light inks. Therefore, the inventors investigated other components contained in the ink to improve the resolubility of the ink, focusing on pigment dispersants. Because the amount of pigment dispersant is typically determined based on the amount of pigment contained in the ink, light inks with low pigment amounts generally contain a small amount of pigment dispersant. Therefore, the inventors formulated a light ink containing a larger amount of pigment dispersant than conventional light inks. They found that this had a beneficial effect on the resolubility and softening of the resin that had dried up due to the evaporation of the ink, tending to improve the resolubility of the ink. Furthermore, increasing the amount of pigment dispersant can suppress the increase in viscosity of the ink when heated compared to increasing the amount of resin, and has less impact on the thickening and drying of the ink in the head. For these reasons, the inventors discovered that a light ink with excellent re-ejection properties could be obtained, leading to the completion of 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 dark and light inks, wherein the pair of dark and light inks consists of a dark ink and a light ink, the dark ink is any one of cyan ink, magenta ink, yellow ink and black ink, and the light ink is any 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 any combination of 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 contain at least a solvent, a pigment, a pigment dispersant and a resin, the amount of pigment (% by mass) contained in the light color ink is P1, the amount of resin (% by mass) contained in the light color ink is R1, the amount of pigment dispersant (% by mass) contained in the light color ink is D1, the amount of pigment (% by mass) contained in the dark color ink is P2, the amount of resin (% by mass) contained in the dark color ink is R2, and the amount of pigment dispersant (% by mass) contained in the dark color ink is D2, the pair of dark and light inks satisfy the relationships shown in the following formulas (1) to (4): Formula (1): P1 < P2 Formula (2): 0.6 ≦ D1 / P1 ≦ 25.0 Formula (3): P1 + R1 + D1 ≧ 4 mass% Formula (4): P2 + R2 + D2 ≧ 4 mass% The dark color ink and the light color ink have a viscosity at 25°C that is in the range of 2.5 mPa·s or more and less than 7.0 mPa·s.

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

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

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

[0015] In another preferred embodiment of the non-aqueous inkjet ink set of the present invention, the light color ink satisfies the relationship shown in the following formula (6): 0.5≦R1 / (P1+D1)≦5.0.

[0016] The non-aqueous inkjet ink set of the present invention can provide a non-aqueous inkjet ink set that is excellent in re-ejection property and continuous ejection stability.

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

[0018] In this specification, a non-aqueous ink set refers to an ink set containing a plurality of non-aqueous inks. Non-aqueous inks refer to inks that do not contain water as a solvent, but also include inks that contain trace amounts of water that may be contained in raw materials or that unavoidably become mixed into the ink during the manufacturing process or storage.

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

[0020] The ink set of the present invention comprises at least a pair of dark and light inks. That is, the ink set of the present invention may comprise a pair of dark and light inks, or may comprise two or more pairs of dark and light inks (in other words, two or more sets of dark and light inks). In this specification, a pair of dark and light inks refers to a set of inks consisting of a dark ink and a light ink. The dark ink is the dark ink of the pair of dark and light inks, and the light ink is the light ink of the pair of dark and light inks. Because the ink set of the present invention comprises at least a pair of dark and light 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 any one of cyan ink, magenta ink, yellow ink, and black ink, and the light ink is any 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 and light inks is composed of any combination of cyan ink and light cyan ink, magenta ink and light magenta ink, yellow ink and light yellow ink, or black ink and light black ink. In other words, when the dark ink constituting a pair of dark and light inks is cyan ink, the light ink is light cyan ink. The ink set of the present invention may contain additional inks, such as orange ink and white ink.

[0022] In the ink set of the present invention, the dark ink and the light ink 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 are 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 color ink is P1, the amount of resin (mass%) contained in the light color ink is R1, the amount of pigment dispersant (mass%) contained in the light color ink is D1, the amount of pigment (mass%) contained in the dark color ink is P2, the amount of resin (mass%) contained in the dark color ink is R2, and the amount of pigment dispersant (mass%) contained in the dark color ink is D2, the pair of dark and light inks satisfy the relationships shown in the following formulas (1) to (4): Formula (1): P1 < P2 Formula (2): 0.6 ≦ D1 / P1 ≦ 25.0 Formula (3): P1 + R1 + D1 ≧ 4 mass% Formula (4): P2 + R2 + D2 ≧ 4 mass%

[0024] The light-colored ink is an ink that exhibits a lighter color than the 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. When the ink contains multiple pigments, the amount of pigments refers to the total amount of pigments.

[0025] Light-colored inks have a high ratio of the amount of pigment dispersant to the amount of pigment (D1 / P1), with D1 / P1 being 0.6 or greater, preferably 0.8 or greater, more preferably 1.0 or greater, and particularly preferably 1.2 or greater. Light-colored inks with such a high D1 / P1 value have high resolubility, thereby improving the re-ejection properties of non-aqueous inkjet ink sets. Furthermore, D1 / P1 is 25.0 or less, preferably 22.0 or less, and particularly preferably 20.0 or less. A D1 / P1 value of more than 25.0 may reduce the abrasion resistance of printed matter.

[0026] The amount of resin (R1) contained in the light color ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 10% by mass. When 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 the light color ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 5% by mass. When the ink contains multiple pigment dispersants, the amount of pigment dispersant is the total amount of the pigment dispersants.

[0028] In the light-colored ink, the total amount of pigment, resin, and pigment dispersant (P1 + R1 + D1) is 4% by mass or more, preferably 4.5% by mass or more, and particularly preferably 5.0% by mass or more. A high total amount of pigment, resin, and pigment dispersant provides high continuous ejection stability and enables rapid fixation of the ink on the substrate (the substrate to which the ink is applied during printing), which is preferable from the perspective 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 color ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 5% by mass. When the ink contains multiple resins, the resin amount is the total amount of the resins.

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

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

[0032] In the dark color ink, the total amount of pigment, resin, and pigment dispersant (P2 + R2 + D2) is 4% by mass or more, preferably 4.5% by mass or more, and particularly preferably 5.0% by mass or more. A high total amount of pigment, resin, and pigment dispersant provides high continuous ejection stability and enables the ink to be quickly fixed on the substrate (the substrate to which the ink is applied during printing), which is preferable from the perspective of forming high-resolution color images. Furthermore, the total amount of pigment, resin, and pigment dispersant (P2 + R2 + D2) 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 preferably satisfy the relationship shown in the following formula (5): 0.3 < (P1 + R1 + D1) / (P2 + R2 + D2) < 3.0. The total amount of pigment, resin, and pigment dispersant in the light color ink (P1 + R1 + D1) is preferably approximately the same as the total amount of pigment, resin, and pigment dispersant in the dark color ink (P2 + R2 + D2). The value of (P1 + R1 + D1) / (P2 + R2 + D2) is more preferably 0.4 to 2.5, particularly preferably 0.5 to 1.7, and most preferably 1.0. By making the total amounts of pigment, resin, and pigment dispersant in the light color ink and the dark color ink approximately the same, printed matter with excellent sharpness is more likely to be obtained.

[0034] In the ink set of the present invention, the light-colored ink preferably satisfies the relationship shown in the following formula (6): Formula (6): 0.5 ≦ R1 / (P1+D1) ≦ 5.0. The lower the ratio of the resin amount to the sum of the pigment amount and the pigment dispersant amount [R1 / (P1+D1)], the more improved the resolubility of the ink. The R1 / (P1+D1) value is preferably 4.5 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less. The R1 / (P1+D1) value is also preferably 0.5 or more, more preferably 0.6 or more, and particularly preferably 0.7 or more. If the R1 / (P1+D1) value is below 0.5, the abrasion resistance of the image may decrease.

[0035] In the ink set of the present invention, the dark ink preferably satisfies the relationship shown in the following formula (6'): 0.3 ≦ R2 / (P2+D2) ≦ 4.0. While dark inks generally do not present problems with resolubility or re-ejection, from the viewpoint of re-ejection, dark inks with high resolubility are preferred. The lower the ratio of the resin amount to the sum of the pigment amount and the pigment dispersant amount [R2 / (P2+D2)], the more improved the ink resolubility can be. The R2 / (P2+D2) value is preferably 4.0 or less, more preferably 3.0 or less, and particularly preferably 2.5 or less. 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 is less than 0.3, the abrasion resistance of the image may be reduced.

[0036] The amount of solids contained in the 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. The pigment, resin, and pigment dispersant preferably constitute the majority (e.g., 95% by mass or more) of the solids contained in the light-colored ink, and in some cases the solids contained in the light-colored ink may consist solely 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. The pigment, resin, and pigment dispersant preferably constitute the majority (e.g., 95% by mass or more) of the solids contained in the dark ink, and in some cases the solids contained in the dark ink may consist solely of the pigment, resin, and pigment dispersant.

[0038] In this specification, the solid content of the ink refers to the components excluding volatile components such as the solvent, and is the component that will ultimately form the printed matter. In the present invention, the solid content is defined as the components that remain when the ink is dried 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 or more but 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 preferred viscosities have high continuous ejection stability, good drainage when ejected from a printer, and are capable of forming clean dots, making them suitable from the perspective of forming high-quality color images. In addition, in order to form high-quality color images, it is also preferable that the viscosities of the dark ink and the light ink are approximately the same. The difference in viscosity between the dark ink and 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 at 25°C is the same as that of the light ink at 25°C.

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

[0041] In the ink set of the present invention, the dark ink and the light ink preferably have a surface tension at 25°C of 25 to 30 mN / m, 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 at 25°C and the surface tension of the light ink at 25°C is preferably 2.0 mN / m or less, and it is particularly preferable that the surface tension of the dark ink at 25°C and the surface tension of 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 color ink and / or the light color 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 resins and vinyl chloride / vinyl acetate copolymer resins (in other words, has excellent resin solubility).

[0044] The solvent contained in the dark color ink and / or the light color ink preferably contains: (A-1) a glycol ether solvent having a boiling point of less than 200°C; and (A-2) an amide bond or urea bond-containing compound, such that 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 the (A-2) amide bond or urea bond-containing compound has a pH of 7.0 or higher.

[0045] In this specification, the "glycol ether-based solvent having a boiling point of less than 200°C" is referred to as component (A-1), and as described above, is also referred to as "(A-1) glycol ether-based solvent having a boiling point of less than 200°C." Furthermore, the "amide bond- or urea bond-containing compound, which makes a mixed solution 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 have a pH of 7.0 or higher" is referred to as component (A-2), and as described above, is also referred to as "(A-2) amide bond- or urea bond-containing compound."

[0046] The glycol ether solvent of component (A-1) is an organic solvent that has low viscosity, a relatively high tag closed-cell flash point, and good drying properties, and is preferably used as the main solvent for the ink. The glycol ether solvent of component (A-1) preferably has a flash point of 50°C or higher and 75°C or lower. In this specification, the flash point is the flash point measured by the tag closed-cell method.

[0047] In this specification, glycol ether solvents refer to compounds having an alkyl ether structure based on glycol such as ethylene glycol, propylene glycol, etc. Glycol ether solvents include those in which both terminals of the molecule are hydroxyl groups, and those in which the hydrogen atoms of the hydroxyl groups at one or both terminals of the molecule are substituted with a substituent such as an alkyl group or an acyl group.

[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, the boiling point refers to the boiling point at 1 atmosphere. When the glycol ether solvent of component (A-1) has a boiling point of less than 200°C, the drying properties of the ink are improved, making it easier to obtain printed matter with excellent blocking resistance.

[0049] The glycol ether solvent of component (A-1) preferably contains a glycol ether solvent represented by the following general formula (I): R1-(OR2)n-O-R3 (I) In formula (I), n is an integer of 1 to 4, R1 is an alkyl group having 1 to 8 carbon atoms which may be branched or an acyl group having 1 to 4 carbon atoms, R2 is an alkylene group having 1 to 4 carbon atoms which may be branched, and R3 is hydrogen, an alkyl group having 1 to 4 carbon atoms which may be branched, 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 within a range of 60 to 95% by mass, and more preferably within a range of 75 to 95% by mass. The 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) is an organic solvent that does not corrode the head because a mixed solution 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 (A-2) has a pH of 7.0 or higher, which is not in the acidic range, and has a high ability to dissolve resins such as vinyl chloride resins and vinyl chloride / vinyl acetate copolymer resins (in other words, has excellent resin solubility). Using component (A-2) as a solvent provides the effect of allowing the ink on the substrate to penetrate without spreading. Therefore, when used in combination with the glycol ether-based solvent of component (A-1), the amide bond- or urea bond-containing compound of component (A-2) can provide printed materials that are resistant to image bleeding and to media blocking when printed on and wound up on roll media. 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 the compound containing an amide bond or a urea bond to 7.0 or higher is based on the idea that the head can be protected from corrosion by not making the pH of the ink acidic. Diethylene glycol ethyl methyl ether is a glycol ether-based solvent of component (A-1), and it is considered important that the pH of an aqueous solution containing this glycol ether (A-1), water, and the compound containing an amide bond or a urea bond of component (A-2) does not fall into a strongly acidic range. Therefore, the pH of the aqueous solution at a specific mixing ratio that approximates the blending ratio of an actual ink is specified as 7.0 or higher.

[0053] When a mixed liquid containing 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 of the component (A-2) is prepared, the pH of the mixed liquid is 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 the component (A-2) preferably contains at least one solvent 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, etc. Specific examples of cyclic amide solvents include 2-pyrrolidone and ε-caprolactam, etc. Specific examples of aromatic amide solvents include benzamide, etc. Specific examples of alkylurea solvents include N-methylurea, etc. Specific examples of cyclic urea solvents include 1,3-dimethyl-2-imidazolidinone, etc.

[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 most preferred.

[0057] The amount of component (A-2) in the solvent is preferably within a range of 4.0 to 30% by mass, more preferably within a range of 5 to 30% by mass, and even more preferably within a range of 5 to 15% by mass. The component (A-2) may be used alone or in combination of two or more. 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 the component (A-1) in the solvent to the amount of the 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 the component (A-1) in the solvent to the amount of the component (A-2) in the solvent may be expressed as "(A-1) / (A-2)." Here, the ratio of the amount of the component (A-1) in the solvent to the amount of the component (A-2) in the solvent is based on mass.

[0059] The solvent contained in the dark ink and / or the light ink preferably contains (A-3) a glycol or glycol ether solvent having a boiling point of 220° C. or higher but lower than 300° C. From the viewpoint of safety, it is particularly preferred that component (A-3) be a glycol having a boiling point of 220° C. or higher but lower than 300° C. and having hydroxyl groups at both ends.

[0060] In this specification, the "glycol or glycol ether-based solvent having a boiling point of 220°C or higher and lower than 300°C" is referred to as component (A-3), and is also referred to as "(A-3) glycol or glycol ether-based solvent having a boiling point of 220°C or higher and lower 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 head portion, further improving re-ejection properties, and also contributes to improving the gloss of the printed matter.

[0062] Examples of the component (A-3) include diethylene glycol, triethylene glycol, tripropylene 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, diethylene glycol dibutyl ether, etc. The component (A-3) preferably has excellent compatibility with the components (A-1) and (A-2).

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

[0064] The solvent contained in the dark ink and / or the light ink may include (A-4) an organic solvent having a boiling point of less than 150° C. and not corresponding to component (A-1) or component (A-2).

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

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

[0067] Examples of the component (A-4) include propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, cyclopentanone, etc. The component (A-4) preferably has excellent compatibility with the components (A-1) and (A-2).

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

[0069] The dark ink and / or the light ink preferably does not contain γ-butyrolactone.

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

[0071] The resin contained in the dark ink and / or the light ink is a resin used as a binder, and is also referred to as a binder resin. The binder resin is usually solid at 40°C. Furthermore, the binder resin is preferably a resin that does not dissolve when diethylene glycol ethyl methyl ether and the resin are mixed at 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. By using a resin with an Mw of 20,000 or more, the weather resistance of printed matter can be improved. In addition, from the viewpoint of the solubility of the resin, the Mw of the resin is preferably 90,000 or less.

[0073] 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. From the viewpoint of abrasion resistance and weather resistance of printed matter, Mw / Mn is preferably 2.0 or more. From the viewpoint of solubility in solvents, Mw / Mn is preferably 8.0 or less.

[0074] In this specification, the weight average molecular weight and number average molecular weight of a resin are values ​​measured by gel filtration chromatography, using polystyrene 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 glass transition temperature of plastics). Specifically, about 10 mg of a resin piece is collected in an aluminum pan for measurement, and DSC measurement is performed under the following measurement conditions. (Measurement temperature conditions) 1st temperature rise: -80°C to 220°C (20°C / min) Temperature drop condition: 220°C to -80°C (50°C / min) 2nd temperature rise: -80°C to 220°C (10°C / 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, fluorine resin, epoxy resin, polyester resin, ketone resin, phenolic resin, polyvinyl alcohol, polyvinyl alcohol derivatives (anion-modified polyvinyl alcohol, etc.), cellulose, cellulose derivatives (hydroxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate, etc.), rosin resin, oil-based resin, petroleum resin, alkyd resin, alginic acid, alginic acid derivatives (propylene glycol alginate, etc.), etc. Modified products of these resins are also included, for example, modifications such as hydroxyalkyl etherification modifications and carboxylic acid modifications are mentioned. Of these, from the viewpoint of adhesion to the substrate and durability of the printed matter, acrylic resins, vinyl chloride resins, and vinyl chloride / vinyl acetate copolymer resins are preferred, with vinyl chloride / vinyl acetate copolymer resins being particularly preferred.

[0078] The resin contained in the dark ink and / or the light ink preferably includes a vinyl chloride / vinyl acetate copolymer resin, which has high adhesiveness and durability, as well as high solubility in glycol ether solvents and solvents of compounds containing amide bonds or urea bonds.

[0079] In the vinyl chloride / vinyl acetate copolymer resin, the mass ratio (a / b) of vinyl chloride units (a) to vinyl acetate units (b) is preferably 70 / 30 to 95 / 5, and more preferably 80 / 20 to 90 / 10. The vinyl chloride units are monomer units derived from vinyl chloride, and the vinyl acetate units are monomer units derived from vinyl acetate. By ensuring that the proportion of vinyl chloride units in the total monomer units constituting the resin is 70% by mass or more, high weather resistance and bleeding-free printed matter can be easily obtained. On the other hand, if the proportion of vinyl chloride units exceeds 90% by mass, solubility in solvents may decrease.

[0080] The amount of vinyl chloride / vinyl acetate copolymer resin contained in the light color ink is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and particularly preferably 1 to 10% by mass, while the amount of vinyl chloride / vinyl acetate copolymer resin contained in the dark color 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 pigment contained in the dark color ink and / or the light color ink may be an organic pigment or an inorganic pigment. Specific examples of the pigment include C.I. Pigment 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, 17 1, 172, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 187, 188, 1 90, 193, 194, 200, 202, 206, 207, 208, 209, 210, 211, 213, 214, 216, 220, 2 20, 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. C.I. Pigment Brown 5, 6, 23, 24, 25, 32, 41, 42, C.I. Pigment Black 1, 6, 7, 9, 10, 11, 20, 26, 28, 31, 32, 34, C.I. Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28, and the like.

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

[0083] The pigment dispersant contained in the dark and / or light inks is a dispersant component that helps break down the pigment into small particles and suspend it in the dispersant. Furthermore, since the pigment dispersant is a substance that dissolves in the solvent and is compatible with the resin, it is believed to contribute to improving the resolubility of the ink. While the pigment dispersant also includes polymers, pigment dispersants are distinguished from the resin (binder resin) described above. Pigment dispersants are typically liquid at 40°C. Furthermore, when diethylene glycol ethyl methyl ether and the pigment dispersant are mixed at a mass ratio of 1:2 at 40°C, the pigment dispersant is completely dissolved. The pigment dispersant's liquid nature at 40°C and its excellent solubility in the solvent are believed to contribute to improving the resolubility of the ink.

[0084] When the pigment dispersant is a polymer, the weight average molecular weight (Mw) of the pigment dispersant is, for example, 50,000 or less, and preferably 1,000 to 45,000. Furthermore, when the pigment dispersant is a polymer, the glass transition temperature (Tg) of the pigment dispersant is, for example, less than 50° C., and preferably −30° C. to 30° C. The weight average molecular weight and glass transition temperature of a polymer pigment dispersant are values ​​obtained by the same methods as those for the weight average molecular weight and glass transition temperature of the resin described above.

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

[0086] In this specification, the term "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. The term "amine value" refers to the number of milligrams of potassium hydroxide (unit: mgKOH / g) equivalent to the amount of hydrochloric acid or perchloric acid 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 BYK Japan), 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, Solsperse 41000, Solsperse 54000, Solsperse 55000, Solsperse 56000, Solsperse 71000, Solsperse 76500, Solsperse X300 (all manufactured by Lubrizol Corporation), Disparlon DA-7301, Disparlon DA-325, Disparlon DA-375, Disparlon DA-234 (all manufactured by Kusumoto Chemicals Co., Ltd.), FLOWLEN AF-1000, FLOWLEN DOPA-15B, FLOWLEN DOPA-15BHFS, FLOWLEN DOPA-17HF, FLOWLEN DOPA-22, FLOWLEN DOPA-33, FLOWLEN G-600, FLOWLEN G-700, FLOWLEN G-700AMP, FLOWLEN G-700DMEA, FLOWLEN G-820, FLOWLEN G-900, FLOWLEN GW-1500, FLOWLEN KDG-2400, FLOWLEN NC-500, FLOWLEN WK-13E (all manufactured by Kyoeisha Chemical Co., Ltd.), TEGO Dispers 610, TEGO Dispers 610S, TEGO Dispers 630, TEGO Dispers 650, TEGO Dispers652, TEGO Dispers655, TEGO Dispers662C, TEGO Dispers670, TEGO Dispers685, TEGO Dispers700, TEGO Dispers710, TEGO Dispers740W, LIPOTIN A, LIPOTIN BL, LIPOTIN DB, LIPOTIN SB (manufactured by Evonik Degussa),Examples of the suitable acrylic acid surfactant include Ajisper PB821, PB822, PB824, PB827, PB831, PB881, PN411, and PA111 (manufactured by Ajinomoto Fine-Techno Co., Inc.), Texahole 963, Texahole 964, Texahole 987, Texahole P60, Texahole P61, Texahole P63, Texahole 3250, Texahole SF71, Texahole UV20, and Texahole UV21 (manufactured by Cognis), and BorchiGen SN88 and BorchiGen 0451 (manufactured by Borchias).

[0088] The dark ink and / or the light ink may contain a synergist. A synergist is a substance used to improve the dispersion stability and color development of a pigment. A synergist is a compound in which a specific substituent, such as a sulfate group, a sulfonamide group, a sulfonic acid group and its salt, a phthalimide group, a phthalimidemethyl group, an amino group, or a triazine group, is introduced into an organic pigment, and is also called a pigment derivative. Azo-based, phthalocyanine-based, quinacridone-based, and other pigment derivatives (synergists) are known. In this specification, synergists are distinguished from pigments.

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

[0090] The dark color ink and the light color ink may contain, as other components, additives such as ultraviolet absorbers, radical scavengers, surface conditioners, antioxidants, plasticizers, rust inhibitors, solvents, fillers, defoamers, charge control agents, stress relaxation agents, penetrating agents, light-guiding materials, lustrous materials, magnetic materials, fluorescent materials, antibacterial agents, antiviral agents, and anti-algae agents, as needed.

[0091] The dark ink and the light ink can be prepared by mixing various components appropriately selected as needed, and, if necessary, filtering the resulting mixture using a filter having a pore size of about 1 / 10 or less of the nozzle diameter of the inkjet printhead to be used.

[0092] Printing using the ink set of the present invention is carried out by inkjet printing. Various inkjet printers can be used for inkjet printing. Examples of inkjet printers include inkjet printers that eject ink using a charge control system or a piezoelectric system. Large-format inkjet printers, specifically inkjet printers designed for printing on products produced on industrial lines, can also be suitably used.

[0093] The printing substrate (substrate to which ink is applied during printing) is not particularly limited, but suitable examples include substrates used in industrial lines. The substrate may be in the form of, for example, a film, a sheet, or a plate. Examples of the substrate material include plastics such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, and acrylic resin, particularly 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 vinyl chloride sheets, tarpaulin, plastic cardboard, acrylic boards, flexible boards, calcium silicate boards, gypsum slag barite boards, calcium carbonate boards, wood chip cement boards, precast concrete boards, lightweight foamed concrete (ALC) boards, gypsum boards, tiles, and glass boards. Among these, polyvinyl chloride substrates and tarpaulin substrates are preferred.

[0094] 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 in any way.

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

[0096] The pigments used are as follows: Black pigment (C.B.): Monarch 1000 (carbon black manufactured by Cabot Corporation) Cyan pigment (P.B. 15:4): Chromofine Blue A-220JC (pigment blue 15:4 manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) Magenta pigment (P.R. 122): Fastogen Super Magenta RG (pigment red 122 manufactured by DIC Corporation) Yellow pigment (P.Y. 150): Comalix Yellow 150 (pigment yellow 150 manufactured by Zeya Chemicals) The solvents used are as follows. The abbreviation and boiling point 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 as follows: Resin 1: VINNOL H15 / 42 (vinyl chloride-vinyl acetate copolymer resin, solids content 100%, manufactured by Wacker Chemie) Resin 2: Solvine C (vinyl chloride-vinyl acetate copolymer resin, solids content 100%, manufactured by Nissin Chemical Industry Co., Ltd.) The pigment dispersants used are as follows: 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 Corporation) Pigment dispersant 2: Solsperse 32000 (polycaprolactone polymer dispersant, acid value: 15.5 mg KOH / g, amine value: 31.2 mg KOH / g, solids content: 100%, manufactured by Lubrizol Corporation)

[0097] <Continuous Discharge Stability> For each ink prepared in <Preparation of Non-Aqueous Inks> above, a nozzle check pattern image was printed using a large format inkjet printer (platen temperature 45°C), and then a 100% solid image was printed for 1000 m. After printing 1000 m, a nozzle check pattern was printed again, and continuous discharge stability was evaluated according to the following criteria. The results are shown in Tables 1 to 4. Inks with an evaluation result of "◎", "◯", or "△" are non-aqueous inks with excellent continuous discharge stability. (Criteria) ◎: Missing or disturbance in the nozzle check pattern is less than 1%. ○: Missing or disturbance in the nozzle check pattern is less than 5%. △: Missing or disturbance in the nozzle check pattern is 5% to 10%. ×: Missing or disturbance in the nozzle check pattern is more than 10%.

[0098] <Re-ejection Property> For each ink prepared in <Preparation of Non-Aqueous Ink> above, 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 for 30 minutes without maintenance or printing, and the same image was printed again. If any nozzles were non-ejecting, they were cleaned and the same image was printed again. The appearance of the print was visually evaluated for re-ejection property according to the following criteria. The results are shown in Tables 1 to 4. Inks with an evaluation result of "◎", "◯", or "△" are non-aqueous inks with excellent re-ejection property. (Criteria) ◎: When printing after being left alone, ink was ejected from all nozzles without cleaning. ○: When printing after being left alone, ink was ejected from all nozzles after one cleaning. △: When printing after being left alone, ink was ejected from all nozzles after three cleanings. ×: When printing after being left alone, ink was non-ejected from 20% or more of the nozzles even after three or more cleanings.

[0099] <Evaluation of Printed Matter: Abrasion Resistance> Each of the dark and light inks prepared in <Preparation of Non-Aqueous Inks> above 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 dark and light inks are shown in Tables 1 to 4. After application, the coated surface was rubbed with an ethanol-soaked cotton swab, and the printed matter was evaluated according to the following criteria. The results are shown in Tables 1 to 4. Dark and light inks that were evaluated as "Good" or "Good" are non-aqueous inks that can produce printed matter with excellent abrasion resistance. (Criteria) Good: No abrasion marks were left on both the coating films formed from the light and dark inks, and the cotton swab was not discolored. Fair: No abrasion marks were left on both the coating films formed from the light and dark inks, but the coating formed from the light ink was discolored. Bad: Of the coating films formed from the light and dark inks, the coating formed from the light ink was left with a scratch mark and the cotton swab was discolored.

[0100]

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[0103]

Claims

1. A non-aqueous inkjet ink set comprising at least one pair of dark and light inks, wherein the pair of dark and light inks comprises a dark ink and a light ink, the dark ink being any one of cyan ink, magenta ink, yellow ink and black ink, and the light ink being any one of light cyan ink, light magenta ink, light yellow ink and light black ink, provided that the pair of dark and light inks comprises any one of a combination of 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 containing at least a solvent, a pigment, a pigment dispersant and a resin, 1. A non-aqueous inkjet ink set comprising: a pair of dark and light inks each having a viscosity of 2.5 mPa·s or more and less than 7.0 mPa·s at 25°C; a light ink having a viscosity of 2.5 mPa·s or more and less than 7.0 mPa·s at 25°C; a dark ink having a viscosity of 2.5 mPa·s or more and less than 7.0 mPa·s at 25°C; a resin having a viscosity of 2.5 mPa·s or more and less than 7.0 mPa·s at 25°C; a resin having a viscosity of 2.5 mPa·s or more and less than 4.0 mPa·s at 25°C; a dark ink ...

2. The non-aqueous inkjet ink set according to claim 1, wherein the pair of dark and light inks satisfy the relationship shown in the following formula (5): 0.3 < (P1 + R1 + D1) / (P2 + R2 + D2) < 3.

0.

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

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

5. The non-aqueous inkjet ink set according to claim 1 or 2, wherein the light color ink satisfies the relationship shown in the following formula (6): 0.5≦R1 / (P1+D1)≦5.0.

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