Ink set, inkjet recording method, and printed matter

Abstract

To provide an ink set that makes it possible to obtain printed matter having excellent weather resistance and color reproducibility and improved graininess, metamerism and beading, and provide an ink jet recording method, and printed matter.SOLUTION: The ink set for single-pass printing at least includes a cyan ink, a magenta ink, a yellow ink, and a grey ink. The magenta ink satisfies specific conditions regarding spectral reflectance. The grey ink has a spectral reflectance of 20-70% at a wavelength of 500 nm and satisfies the specific conditions regarding the spectral reflectance.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink set, an inkjet recording method, and a printed matter which have excellent weather resistance and color reproducibility and which are improved in graininess and metamerism. [Background technology]

[0002] Traditionally, various methods have been used as a recording method for forming an image on a recording medium such as paper based on image data signals. Among these, the inkjet method, in which tiny droplets of ink are ejected and landed from an inkjet head to form an image or character, is an inexpensive device, and since ink is ejected only to the required image area to form an image directly on the recording medium, it is efficient and has low running costs. Furthermore, the inkjet method is quiet and excellent as a recording method, and has been developed not only for printing documents for home or office use, but also for commercial and industrial printing. In particular, multi-pass wide-format (large format) inkjet printers suitable for printing large advertisements to be pasted on show windows and walls of buildings have rapidly spread in popularity. Multi-pass is a method in which the inkjet head is moved back and forth multiple times (two or more times) in the side-view direction against the recording medium transported in the main view direction. Since large-format advertisements are mainly used outdoors, inks with excellent light resistance and coating resistance have been developed.

[0003] On the other hand, in recent years, the inkjet method has come to be used not only for outdoor applications, but also for indoor printing, cardboard printing, sticker labels, etc., replacing the offset method, gravure method, and flexo method. Therefore, inks are required to have high image quality in addition to light resistance and coating resistance.

[0004] In general, inkjet printers use cyan ink (C), magenta ink (M), yellow ink (Y), and black ink (K), which are ejected from an inkjet head to reproduce any color. In the case of gray, it is reproduced using only K, or using three colors of CMY or four colors of CMYK. When it is reproduced using only K, ink dots are formed in isolation in image areas with a small amount of ink, so roughness, or graininess of the image, becomes a problem. In addition, when it is reproduced using three colors of CMY or four colors of CMYK, the amount of ink is two to three times that when it is used using only K. In general, the graininess of an image is more noticeable when the number of ink dots is smaller, so from the viewpoint of graininess, it is preferable to reproduce using three colors of CMY or four colors of CMYK.

[0005] However, when reproducing using the three colors of CMY, a phenomenon known as metamerism occurs, where colors appear different depending on the lighting or viewing angle. Metamerism occurs because each of the CMY colors has a different distribution of spectral reflectance curves, and the spectral reflectance of the gray color obtained by mixing these is not flat but has considerable irregularities. Reducing the amount of the three colors of CMY and increasing the amount of K improves metamerism slightly, but is still not satisfactory, and graininess becomes an additional problem. For this reason, there is a demand for inks that achieve both graininess and metamerism.

[0006] In addition, because conventional multi-pass wide-format inkjet printers have low productivity, there is a demand for inks and recording methods suitable for single-pass inkjet printers, which are capable of faster printing. Single-pass is a method in which the inkjet head remains fixed and printing is performed in one go on the transported recording medium.

[0007] As an effort to improve metamerism, for example, Patent Document 1 discloses a method for detecting cyan and magenta. A metamerism-improving ink is prepared, which has a color equivalent to a specific tertiary color obtained by mixing three primary color inks including yellow and yellow, and has a flatter spectral reflectance than the spectral reflectance characteristics of the tertiary color. At least one color in a color image is then reproduced using the metamerism-improving ink and at least one of the three primary color inks, thereby making the spectral reflectance characteristics of the reproduced color flatter than those reproduced by mixing the three primary color inks.

[0008] Furthermore, for example, Patent Document 2 discloses an ink set including a magenta ink having a Z value of 83 or less when the Y value is 55 in the XYZ display system defined by the CIE, calculated from the ultraviolet-visible transmission spectrum of an aqueous solution diluted with ink having a colorant concentration of 0.01% by mass or less, and an L* value of 70 or less in the L*a*b* display system defined by the CIE, when the aqueous solution is diluted 1000 times by mass; a yellow ink having an L* value of 95 or less in the L*a*b* display system defined by the CIE, when the aqueous solution is diluted 1000 times by mass; and a cyan ink having an L* value of 70 or less in the L*a*b* display system defined by the CIE, when the aqueous solution is diluted 1000 times by mass; and further an ink set including a black ink having a different pigment concentration.

[0009] As an effort to develop inks suitable for single-pass inkjet printers, for example, Patent Document 3 discloses an active energy beam-curable inkjet ink set in which the amount of surface tension modifier blended in each ink is 1.0 to 5 mass % relative to the total amount of ink, and the difference between the amounts of surface tension modifier for each color according to the printing order is within a maximum and minimum of 2 mass %. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2002-225317 A [Patent Document 2] International Publication No. 2004 / 039899 [Patent Document 3] JP 2013-216784 A Summary of the Invention [Problem to be solved by the invention]

[0011] However, the metamerism improving ink of the above Patent Document 1 does not have a flat spectral reflectance characteristic at 420 to 570 nm, and metamerism is not improved sufficiently. In addition, depending on the type of colorant used in the cyan ink, magenta ink, and yellow ink, the use of the metamerism improving ink does not improve the color. Furthermore, the above Patent Document 1 is an approach using a multi-pass inkjet method, and in a single-pass inkjet method, the metamerism improving ink does not spread sufficiently on the cyan ink, magenta ink, and yellow ink, and metamerism is not improved sufficiently. In addition, in the above Patent Document 2, the weather resistance is not sufficient, and the improvement of metamerism is not sufficient. In addition, in a single-pass inkjet method, the metamerism improving ink does not spread sufficiently on the cyan ink, magenta ink, and yellow ink, and metamerism is not improved sufficiently. In addition, in the above Patent Document 3, the suppression of beading is not sufficient. Beading is a phenomenon in which ink droplets coalesce before the ink hardens and dries, and can cause banding in the printing direction and color mixing between inks.

[0012] The present invention has been made to solve the above-mentioned problems, and provides an ink set, an inkjet recording method, and a printed matter that can give a printed matter having excellent weather resistance and color reproducibility and improved graininess, metamerism, and beading. [Means for solving the problem]

[0013] As a result of intensive research aimed at solving the above problems, the present inventors have discovered the following ink set: The present invention has been completed based on the discovery that the above problems can be solved by the above method.

[0014] That is, the present invention provides at least cyan ink, magenta ink, yellow ink, Black ink, and a gray ink, The spectral reflectance of the magenta ink satisfies the following formulas (1) to (3), The gray ink has a spectral reflectance of 20 to 70% at a wavelength of 500 nm and satisfies the following formulas (4) and (5): death, All of the inks constituting the ink set are water-based inks containing water, a water-soluble organic solvent, and a surface tension modifier. The present invention relates to an ink set for single pass printing. (Spectral reflectance at 420 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 40 Formula (1) (Spectral reflectance at 500 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 10 Formula (2) (Spectral reflectance at 570 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 20 Formula (3) 80≦(Spectral reflectance at 420 nm) ÷ (Spectral reflectance at 500 nm) × 100≦110 Formula (4) 80≦(Spectral reflectance at 570 nm) ÷ (Spectral reflectance at 500 nm) × 100≦110 Formula (5)

[0015] In addition, in the present invention, when the hue angle defined in the CIELAB color space is H°, The hue angle H° of the cyan ink is 200 to 290°, The hue angle H° of the magenta ink is 0 to 45°, The present invention relates to the above ink set for single pass printing, wherein the yellow ink has a hue angle H° of 80 to 110°.

[0016] Further, the present invention is characterized in that the static surface tension of the gray ink at 25° C. is greater than the static surface tension of each of the cyan ink, the magenta ink, and the yellow ink at 25° C. 1mN / m or more The ink set for single pass printing is characterized in that the ink jet print density is low.

[0019] The present invention also relates to the above-mentioned ink set for single pass printing, wherein the water-soluble organic solvents in all of the inks constituting the ink set contain at least one selected from the group consisting of diols of glycol compounds (excluding alkanediol compounds), monoalkyl ethers of glycol compounds, and alkanediol compounds, and the total content of water-soluble organic solvents having a boiling point of 100 to 280°C is 50 mass% or more based on the total content of water-soluble organic solvents contained in the inks.

[0020] The present invention also provides a recording method using the ink set for single pass printing, comprising the steps of: After the step of printing the cyan ink, the magenta ink, and the yellow ink, A step of printing the gray ink is carried out. stomach, The method includes a step of printing the black ink after the step of printing the gray ink. The present invention relates to a recording method.

[0021] In addition, the present invention provides a method for printing the cyan ink, the magenta ink, and the yellow ink, and a method for printing the gray ink, the method comprising the steps of: semi-drying the printed inks; Dryness The present invention relates to the above recording method, which comprises the step of:

[0023] The present invention also relates to a printed matter obtained by printing the ink set for single pass printing on a substrate.

[0024] The present invention also relates to a printed matter printed by the above recording method. Effect of the Invention

[0025] The present invention provides an ink set, an inkjet recording method, and a printed matter which have excellent weather resistance and color reproducibility and are improved in graininess, metamerism, and beading. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

[0027] <Ink set for single pass printing> The ink set for single pass printing of the present invention is an ink set for single pass printing including at least a cyan ink, a magenta ink, a yellow ink, and a gray ink, characterized in that the spectral reflectance of the magenta ink satisfies formulas (1) to (3), and the spectral reflectance of the gray ink is 20 to 70% at a wavelength of 500 nm and satisfies formulas (4) and (5). (Spectral reflectance at 420 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 40 Formula (1) (Spectral reflectance at 500 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 10 Formula (2) (Spectral reflectance at 570 nm) ÷ (Spectral reflectance at 700 nm) × 100 ≦ 20 Formula (3) 80≦(Spectral reflectance at 420 nm) ÷ (Spectral reflectance at 500 nm) × 100≦110 Formula (4) 80≦(Spectral reflectance at 570 nm) ÷ (Spectral reflectance at 500 nm) × 100≦110 Formula (5)

[0028] The ink set for single-pass printing of the present invention improves metamerism compared to when gray is reproduced using only three inks, cyan, magenta, and yellow, without using gray ink, and improves graininess compared to when gray is reproduced using only black ink.

[0029] <Spectral reflectance> In the ink set for single-pass printing of the present invention, the spectral reflectance of the magenta ink satisfies the above formulas (1) to (3), and the spectral reflectance of the gray ink is 20 to 70% at a wavelength of 500 nm and satisfies the above formulas (4) and (5). When the magenta ink and the gray ink satisfy the above-mentioned relationship of spectral reflectance, the spectral reflectance curve of the gray color reproduced by the cyan ink, magenta ink, yellow ink, and gray ink can be flattened, and metamerism can be effectively improved.

[0030] In particular, from the viewpoint of improving metamerism, it is more preferable that the spectral reflectance ratio represented by formula (1) is 25 or less, and it is more preferable that the spectral reflectance ratio represented by formula (3) is 10 or less.

[0031] From the viewpoint of color reproducibility, the spectral reflectance of the magenta ink at a wavelength of 700 nm is preferably 60% or more, and from the viewpoint of improving metamerism, the spectral reflectance of the gray ink at a wavelength of 500 nm is preferably 30 to 60%.

[0032] As described later, the magenta ink and gray ink constituting the ink set for single-pass printing of the present invention may be any conventionally known pigment, or may be a combination of two or more pigments. Here, as a method for obtaining an ink set whose spectral reflectance and its ratio satisfy the above formulas (1) to (5), in addition to optimizing the type or combination of pigments used in the magenta ink and gray ink constituting the ink set, the particle size distribution of the pigments may be controlled within a suitable range. Regarding the latter, for example, it is preferable to reduce the effect of Mie scattering caused by coarse pigment particles. Specifically, the median diameter (D50) of the magenta ink and gray ink is preferably 400 nm or less, more preferably 300 nm or less. Furthermore, the 90% diameter (D90) is preferably 700 nm or less, more preferably 500 nm or less. The median diameter and 90% diameter are volume-based values ​​measured by dynamic light scattering, and can be measured, for example, using Nanotrac UPA-EX150 manufactured by Microtrack-Bell.

[0033] In order to keep the median diameter and 90% diameter of the pigment within the above range, it is preferable to use a pigment with a small primary particle diameter. Specifically, the average value of the primary particle diameter of the pigment used is preferably 10 to 200 nm, and more preferably 20 to 150 nm. The primary particle diameter of the pigment can be measured using a transmission electron microscope (TEM). Specifically, the average values ​​of the minor axis diameter and major axis diameter are calculated from the TEM image for 100 arbitrarily selected pigment particles, and the average value of the two average values ​​(minor axis diameter and major axis diameter) obtained is taken as the primary particle diameter of the pigment.

[0034] In order to simultaneously satisfy the above formulas (1) to (3), in the magenta ink constituting the ink set for single pass printing of the present invention, the value obtained by dividing the 90% diameter by the primary particle diameter of the pigment is preferably 2 to 20, and more preferably 3 to 12. In addition, in order to satisfy the above formulas (4) and (5), in the gray ink constituting the ink set for single pass printing of the present invention, the value obtained by dividing the 90% diameter by the primary particle diameter of the pigment is preferably 2 to 30, and more preferably 3 to 15.

[0035] However, compared to pigments of other colors, pigments generally used in magenta inks have primary particles that are tightly aggregated together, making it difficult to achieve the above-mentioned suitable median diameter and 90% diameter. Therefore, when producing the magenta ink constituting the ink set for single-pass printing of the present invention, it is preferable to optimize the dispersion conditions.

[0036] Specifically, it is preferable to use a media stirring type disperser such as a bead mill, and to use zirconia beads having a diameter of 0.3 to 1.5 mm as the media.The diameter of the zirconia beads is more preferably 0.3 to 1.0 mm.

[0037] Generally, the smaller the media size, the higher the dispersion efficiency, but it becomes more difficult to break down strong agglomerates. Zirconia beads have a high specific gravity and have sufficient kinetic energy even though they are small in size, so they can fully and efficiently break down even strongly agglomerated pigments.

[0038] Generally, the properties of zirconia beads can be adjusted by adding compounds such as calcium oxide, yttrium oxide, aluminum oxide (alumina) to zirconia. The zirconia beads preferably used in the present invention have a Vickers hardness of 1,100 to 1,350 Hv.

[0039] By dispersing the pigment using zirconia beads having the above Vickers hardness, deterioration of dispersion efficiency due to insufficient hardness of the zirconia beads can be suppressed, and mixing of worn zirconia beads can be prevented, so that the pigment can be efficiently loosened. As a result, a printed matter having excellent color reproducibility and improved metamerism can be obtained, and when the ink set for single pass printing of the present invention is a set of active energy ray-curable inks described below, the curability and storage stability of the inks are also improved.

[0040] In addition, when dispersing with a media-agitation type disperser, it is very important to control the peripheral speed of the agitation blade. The optimum peripheral speed of the agitation blade for producing a magenta ink that simultaneously satisfies the above formulas (1) to (3) is 8 to 13 m / s, and more preferably 9 to 12 m / s. By controlling in this way, the pigment can be sufficiently finely divided in a relatively short time, and a magenta ink that simultaneously satisfies the above formulas (1) to (3) can be obtained. Furthermore, it is possible to obtain a magenta ink that does not become overdispersed and has good weather resistance, color reproducibility, ejection stability, and storage stability.

[0041] In this specification, the "spectral reflectance" is a value calculated by forming an image with a dot area ratio of 100% (corresponding to a wet film thickness of 8 μm), measuring the reflectance at a wavelength of 400 to 700 nm under the CIE color system with a viewing angle of 2° and a light source of D65. The measuring device used is the X-Rite 500 series manufactured by X-Rite, Inc.

[0042] The dot area ratio means the ratio of the area of ​​dots to a unit area expressed as a percentage.

[0043] <Hue angle H°> In the ink set for single pass printing of the present invention, it is preferable that the hue angle H° defined in the CIELAB color space satisfies the relationship that the hue angle H° of the cyan ink is 200 to 290°, the hue angle H° of the magenta ink is 0 to 45°, and the hue angle H° of the yellow ink is 80 to 110°. More preferably, the hue angle H° of the cyan ink is 200 to 270°, the hue angle H° of the magenta ink is 10 to 40°, and the hue angle H° of the yellow ink is 90 to 110°. When the hue angles are within the above ranges, an image with high color reproducibility can be obtained.

[0044] In this specification, the term "hue angle H°" refers to a correlation amount calculated in accordance with JIS Z 8781-4:2013. The hue angle H° is expressed as follows: H°=tan -1 (b* / a*)+180(if a*<0), or H°=tan -1 It is calculated by (b* / a*)+360 (when a*>0). Note that "a*" and "b*" in the above formula are values ​​in the CIE1976L*a*b* color space when an image with a dot area rate of 100% is formed. The measurement device used is the X-Rite 500 series manufactured by X-Rite, Inc.

[0045] Hereinafter, the components that are or can be contained in the cyan ink, magenta ink, yellow ink, and gray ink that constitute the ink set for single pass printing of the present invention will be described.

[0046] The cyan ink, magenta ink, yellow ink, and gray ink each contain at least a pigment.

[0047] <Pigments in cyan ink> The pigment that can be used in the cyan ink of the present invention is not particularly limited, and any known pigment can be used. The pigment can be either an inorganic pigment or an organic pigment. Pigments that are generally used in printing and coating applications can be used, and an appropriate pigment can be selected from these pigments depending on the application requiring color reproducibility, weather resistance, and the like.

[0048] Specifically, in terms of the CI Color Index, examples of pigments exhibiting a cyan color include CI Pigment Blue 1, 2, 14, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 60, and 62. Among these, CI Pigment Blue 15:3 and 15:4 are preferred from the viewpoint of color reproducibility. In the present invention, the above-mentioned pigments exhibiting a cyan color may be used alone or in combination of two or more kinds.

[0049] The content of the pigment that exhibits cyan color in the cyan ink is preferably 0.1 to 10 mass %, and more preferably 1 to 10 mass %, based on the total mass of the cyan ink.

[0050] <Pigments in magenta ink> The pigment that can be used in the magenta ink of the present invention is not particularly limited, and any known pigment can be used, so long as it can provide a magenta ink whose spectral reflectance satisfies the above-mentioned relationship. Both inorganic and organic pigments can be used as the pigment. Pigments that are generally used in printing and coating applications may be used, and an appropriate pigment can be selected from these pigments depending on the application requiring color reproducibility, weather resistance, and the like.

[0051] Examples of pigments that exhibit a magenta color and that can easily produce a magenta ink whose spectral reflectance satisfies the above-mentioned relationship include, in terms of the CI Color Index, CI Pigment RED 48:1, 112, 146, 166, 177, 179, 202, 237, 242, 254, 255, 264, 282, and CI Pigment Violet 19. Among these, CI Pigment RED 112, 146, 166, 177, 179, 202, 237, 254, 255, and 264 are preferred, and by using these pigments, it is easy to produce a magenta ink that simultaneously satisfies formulas (1) to (3) without optimizing the dispersion conditions as described above.

[0052] In the present invention, the above magenta pigments may be used alone or in combination of two or more. Also, as long as the spectral reflectance of the magenta ink satisfies the above-mentioned relationship, the magenta pigments may be used in combination with other magenta pigments.

[0053] By mixing pigments such as CI Pigment RED 146, 166, and 254, which have particularly high color reproducibility in the red region, with pigments such as CI Pigment RED 122 and CI Pigment Violet 19, which have high color reproducibility in the blue region, it is possible to reproduce a good gamut in the red and blue regions while improving metamerism.

[0054] The content of the pigment that exhibits magenta color in the magenta ink is preferably 0.1 to 10 mass %, and more preferably 2 to 10 mass %, based on the total mass of the magenta ink.

[0055] <Pigments in Yellow Ink> The pigment that can be used in the yellow ink of the present invention is not particularly limited, and any known pigment can be used. The pigment can be either an inorganic pigment or an organic pigment. Pigments that are generally used in printing and coating applications can be used, and an appropriate pigment can be selected from these pigments depending on the application requiring color reproducibility, weather resistance, and the like.

[0056] Specifically, in terms of the CI color index, examples of pigments exhibiting a yellow color include CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 18, 24, 73, 74, 75, 83, 93, 95, 97, 98, 100, 108, 109, 110, 114, 120, 128, 129, 138, 139, 174, 150, 151, 154, 155, 167, 180, 185, and 213. Among these, pigments whose spectral reflectance gradually increases from a wavelength of about 450 nm and has a high spectral reflectance at wavelengths of 550 to 600 nm are preferred, and by using a yellow pigment having such a spectral reflectance, the spectral reflectance of a printed matter using cyan ink and yellow ink can be made flatter, and metamerism can be improved. From the viewpoint of optimal spectral reflectance for improving metamerism, CI Pigment Yellow 150, 184, and 185 are preferred, and from the viewpoint of weather resistance and color reproducibility, CI Pigment Yellow 150 is more preferred. In the present invention, the above yellow pigments may be used alone or in combination of two or more.

[0057] The content of the yellow pigment in the yellow ink is preferably 0.1 to 10 mass %, and more preferably 1 to 10 mass %, based on the total mass of the yellow ink.

[0058] <Pigments in gray ink> Pigments that can be used in the gray ink of the present invention are pigments whose spectral reflectance satisfies the above-mentioned relationship. As long as the pigment satisfies the above requirements, it is not particularly limited, and any known pigment can be used. The pigment may be either an inorganic pigment or an organic pigment. Pigments that are generally used for printing and coating applications may be used, and an appropriate pigment can be selected from these pigments depending on the application requiring color reproducibility, weather resistance, and the like.

[0059] Specifically, in terms of the CI Color Index, examples include CI Pigment Black 1, 6, 7, 9, 10, 11, 28, 26, and 31. Of these, CI Pigment Black 7 is preferred. In the present invention, the above pigments may be used alone or in combination of two or more.

[0060] The content of the pigment in the gray ink is preferably 0.2 to 1 mass % relative to the total mass of the gray ink, and more preferably 0.35 to 0.9 mass %.

[0061] Furthermore, from the viewpoint of improving metamerism, the gray ink may contain a pigment that exhibits a cyan color and / or a pigment that exhibits a magenta color.

[0062] The ink set for single pass printing of the present invention may contain inks other than the cyan ink, magenta ink, yellow ink, and gray ink. Examples of the ink set include black ink, white ink, green ink, violet ink, orange ink, etc. Among these, it is preferable to contain a black ink from the viewpoint of improving metamerism.

[0063] Examples of the pigment that exhibits the black color include CI Pigment Black 1, 6, 7, 9, 10, 11, 28, 26, and 31. Of these, CI Pigment Black 7 is preferable. In the present invention, the pigment that exhibits the black color may be used alone or in combination of two or more kinds.

[0064] The content of the pigment that exhibits black color in the black ink is preferably more than 1 mass % and not more than 10 mass %, and more preferably 2 to 10 mass %, relative to the total mass of the black ink.

[0065] In the present invention, it is more preferable that the pigments used for the gray ink and the black ink have the same CI color index, and it is particularly preferable to use CI Pigment Black 7 for the black ink and gray ink.

[0066] Furthermore, from the viewpoint of forming excellent image quality, the pigment content in the gray ink is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, of the pigment content in the black ink. When the pigment contents of the gray ink and the black ink satisfy the above range, metamerism can be effectively improved and high image quality can be obtained.

[0067] Examples of the pigment that exhibits the above-mentioned white color include CI Pigment White 5, 6, 7, 12, 28, and the like.

[0068] Examples of the pigment that exhibits the above green color include CI Pigment Green 1, 2, 3, 4, 7, 8, 10, 15, 17, 26, 36, 45, 50, and the like.

[0069] Examples of the violet pigment include CI Pigment Violet 1, 2, 3, 4, 5:1, 12, 13, 15, 16, 17, 19, 23, 25, 29, 31, 32, 36, 37, 39, and 42. Examples of pigments that exhibit the above orange color include CI Pigment Orange 13, 16, 20, 34, 36, 38, 39, 43, 51, 61, 63, 64, and 74. Can be obtained.

[0070] The components other than the pigment are not particularly limited as long as the spectral reflectance of the magenta ink and the gray ink can satisfy the above-mentioned relationship, and for example, in the case of an aqueous ink, examples thereof include a pigment dispersant, water, a water-soluble organic solvent, a resin, a surface tension modifier, and an antifoaming agent, and in the case of an active energy ray curable ink, examples thereof include a pigment dispersant, a polymerizable compound, a polymerization initiator, an organic solvent, a surface tension modifier, an antifoaming agent, an antioxidant, a resin, and water. Among these, from the viewpoint of coating film resistance and productivity, an active energy ray curable ink containing a polymerizable compound and a polymerization initiator is preferable. On the other hand, from the viewpoint of improving the graininess and metamerism of the printed matter, an aqueous ink containing water, a water-soluble organic solvent, and a surface tension modifier is preferable.

[0071] Hereinafter, when the ink set for single pass printing of the present invention is a set of active energy ray-curable inks, components other than pigments that can be used in the active energy ray-curable inks will be described in detail.

[0072] <Polymerizable compound> In this specification and the like, unless otherwise specified, the terms "(meth)acryloyl", "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyloxy" respectively mean "acryloyl and / or methacryloyl", "acrylic acid and / or methacrylic acid", "acrylate and / or methacrylate", and "acryloyloxy and / or methacryloyloxy". In addition, "PO" stands for "propylene oxide" and "EO" stands for "ethylene oxide".

[0073] The polymerizable compound that can be used in the active energy ray curable ink of the present invention is not particularly limited, and known polymerizable or crosslinkable materials such as radical polymerization reaction, cationic polymerization reaction, and dimerization reaction can be used. Among them, from the viewpoint of coating film resistance, adhesion, and curability, radical polymerizable compounds are preferable, and addition polymerizable compounds having at least one ethylenically unsaturated double bond are more preferable. Specifically, polymerizable compounds having a (meth)acryloyl group, an allyl group, a vinyl group, a vinyl ether group, or an internal double bond group (maleic acid, etc.) in the molecule are preferable. Among them, from the viewpoint of curability, polymerizable compounds having a (meth)acryloyl group (other than polymerizable compounds having a (meth)acryloyl group and a vinyl ether group), polymerizable compounds having a vinyl group, and polymerizable compounds having a (meth)acryloyl group and a vinyl ether group are more preferable. In the active energy ray curable ink of the present invention, the above polymerizable compounds may be used alone or in combination of two or more kinds.

[0074] Specific examples of the polymerizable compound having a (meth)acryloyl group include 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, β-carboxyethyl (meth)acrylate, 4-t-butylcyclohexanol (meth)acrylate, tetrahydrofurfuryl acrylate, alkoxylated tetrahydrofurfuryl acrylate, caprolactone (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isoamyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, isodecyl (meth)acrylate, and 3,3,5-trimethylcyclohexanol (meth)acrylate. , cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (oxyethyl) (meth)acrylate, 1,4-cyclohexanedimethanol (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, benzyl (meth)acrylate, EO modified nonylphenol acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, acryloyl morpholine, (poly)ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-Decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, (neopentyl glycol modified) trimethylolpropane di(meth)acrylate, tripropylene glycol di(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, EO adduct di(meth)acrylate of bisphenol A, EO adduct di(meth)acrylate of bisphenol F, PO adduct di(meth)acrylate of bisphenol A, cyclohexanedimethanol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, dicyclopentane Examples of the isocyanuric acid tri(meth)acrylate include pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ε-caprolactone modified tris-(2-acryloxyethyl)isocyanurate, ethoxylated isocyanuric acid tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated (3) trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0075] Specific examples of the polymerizable compound having a vinyl group include N-vinylcarbazole, 1-vinylimidazole, N-vinyl-2-pyrrolidone, N-vinylcaprolactam, and N-vinylformamide.

[0076] Specific examples of the polymerizable compound having a (meth)acryloyl group and a vinyl ether group include 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(1-vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, and 2-(vinyloxyethoxy)propyl (meth)acrylate.

[0077] The polymerizable compound may contain a polymerizable oligomer. The polymerizable oligomer preferably has a (meth)acryloyl group as an ethylenically unsaturated bond in the molecule. The number of ethylenically unsaturated bonds contained in the oligomer is preferably 1 to 15 per molecule, more preferably 2 to 6, further preferably 2 to 4, and particularly preferably 2, from the viewpoint of the balance between flexibility and curability. The weight average molecular weight of the oligomer is preferably 400 to 10,000, more preferably 500 to 5,000. Here, the "weight average molecular weight" can be determined as a styrene-equivalent molecular weight by general gel permeation chromatography (hereinafter, GPC).

[0078] Examples of the polymerizable oligomer include urethane acrylate oligomers such as aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers, acrylic ester oligomers, polyester acrylate oligomers, and epoxy acrylate oligomers. From the viewpoint of stretchability, aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers are preferred. The polymerizable oligomers may be used alone or in combination of two or more.

[0079] When the magenta ink constituting the ink set for single-pass printing of the present invention is an active energy ray curable ink, it is preferable that the polymerizable compound contains at least a polymerizable compound having a (meth)acryloyl group and a vinyl ether group. In particular, when used in combination with one or more pigments selected from the group consisting of the above-mentioned CI Pigment RED 112, 146, 166, 177, 179, 202, 237, 254, 255, and 264, the pigment reaggregation can be suppressed, although the details are unclear, and as a result, it is possible to produce a printed matter having excellent weather resistance and color reproducibility over a long period of time and improved metamerism.

[0080] Although details are unclear, by setting the blending amount of the addition polymerizable compound having only one ethylenically unsaturated double bond to 50% by mass or less of the total amount of polymerizable compounds contained in the ink, the ink has improved metamerism and coating resistance of printed matter, as well as improved curability. The blending amount of the addition polymerizable compound having only one ethylenically unsaturated double bond is more preferably 25% by mass or less of the total amount of polymerizable compounds contained in the ink.

[0081] Furthermore, by making the blending amount of the polymerizable compound having the above-mentioned vinyl group 15% by mass or less of the total amount of the ink, re-aggregation of the pigment is suppressed, and a printed matter with improved metamerism is obtained. The blending amount of the polymerizable compound having the vinyl group is more preferably 10% by mass or less of the total amount of the ink.

[0082] <Polymerization initiator> The polymerization initiator that can be used in the active energy ray curable ink of the present invention is not particularly limited, and known polymerization initiators can be used. The polymerization initiator may be used alone or in combination of two or more. The polymerization initiator includes not only a compound that absorbs external energy such as active energy rays to generate a polymerization initiation species, but also a compound (so-called sensitizer) that absorbs specific active energy rays to promote decomposition of the polymerization initiator.

[0083] Specific examples of the polymerization initiator include acylphosphine oxide compounds such as diphenylacylphenylphosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone. Examples of α-aminoalkylphenone compounds include 2-methyl-1-[4-(methoxythio)-phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, and 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone. Benzophenone compounds include benzophenone, 4-phenylbenzophenone, isophthalphenone, and 4-benzoyl-4'-methyl-diphenyl sulfide. Examples of the α-hydroxyalkylphenone compounds include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone). Examples of the amine compounds include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N,N-dimethylbenzylamine, ethyl-4-dimethylaminobenzoate, 4,4'-bis(diethylamino)benzophenone, and ethylhexyl-4-dimethylaminobenzoate. In the present invention, the above polymerization initiators may be used alone or in combination of two or more.

[0084] The content of the polymerization initiator is preferably from 5 to 20% by mass, and more preferably from 5 to 15% by mass, based on the total mass of the polymerizable compound.

[0085] The hue and metamerism of the ink coating film change depending on the polymerization initiator used in active energy ray curable inks. Furthermore, in order to cure the ink, strong active energy rays are irradiated. This causes the polymerization initiator to decompose, which also changes the hue and metamerism of the ink coating film. This is particularly noticeable in image areas with a small amount of ink and in light colors such as gray ink.

[0086] Among polymerization initiators, thioxanthone compounds cause the ink film to turn yellowish and shift the hue in light colors such as gray inks, and α-aminoalkylphenone compounds cause metamerism because they emit fluorescence at a wavelength of around 385 nm.

[0087] Therefore, in the present invention, from the viewpoints of hue and metamerism, the total amount of the thioxanthone compound and the α-aminoalkylphenone compound in the gray ink is preferably less than 3 mass % relative to the total mass of the ink, and more preferably 2 mass % or less. In particular, in the case of the active energy ray-curable ink of the present invention, from the viewpoint of curability, it is more preferable that the amount of the α-aminoalkylphenone compound is less than the amount of the thioxanthone compound.

[0088] In the present invention, from the viewpoint of curability, the cyan ink, the magenta ink, and the yellow ink preferably contain a total amount of the thioxanthone compound and the α-aminoalkylphenone compound of less than 7% by mass relative to the total mass of the ink. More preferably, it is 5% by mass or less. In particular, in the case of the present invention, from the viewpoint of curability, it is more preferable that the amount of the α-aminoalkylphenone compound is less than the amount of the thioxanthone compound.

[0089] <Surface tension adjuster (for active energy ray curable inks)> In this specification and the like, the term "surface tension modifier" refers to a substance that reduces the surface tension of the ink when added. Examples of surface tension modifiers include silicone-based surface tension modifiers, fluorine-based surface tension modifiers, acrylic-based surface tension modifiers, and acetylene glycol-based surface tension modifiers. From the viewpoint of the ability to reduce surface tension, it is preferable to use a silicone-based surface tension modifier.

[0090] Specific examples of silicone-based surface tension modifiers include modified dimethylsiloxane skeletons. Among them, polyether-modified siloxane-based surface tension modifiers are preferred. The polyether may be, for example, polyethylene oxide and / or polypropylene oxide. In the ink of the present invention, commercially available polyether-modified silicone-based surfactants can be used. Representative examples of products that can be preferably used include BYK (registered trademark)-331, 333, 348, 349, 378, UV3500, and UV3510 from BYK-Chemie Co., Ltd. In addition, TEGO (registered trademark) GLIDE 450, 440, 435, 432, 410, 406, 130, 110, and 100 from Evonik Degussa Co., Ltd. Among these, from the viewpoint of improving image quality, BYK-331, 333, 348, 378, UV3510, TEGO GLIDE 450, 440, 432, and 410 are preferred.

[0091] The content of the silicone-based surface tension modifier is preferably 0.1 to 2.0% by mass for the gray ink, and 0.01 to 0.3% by mass for the cyan ink, the magenta ink, and the yellow ink, relative to the total mass of the ink.

[0092] <Other ingredients> The active energy ray-curable ink may contain, in addition to the above-mentioned components, pigment dispersants, polymerization inhibitors, organic solvents, defoamers, antioxidants, resins, water, and the like, as necessary.

[0093] <Pigment dispersant (for active energy ray curable inks)> In order to improve the dispersibility of the pigment and the storage stability of the ink, it is preferable to use a pigment dispersant in the active energy ray curable ink. There is no particular limitation on the pigment dispersant that can be used in the present invention, and any known pigment dispersant can be used. Among them, a resin-type pigment dispersant having a basic functional group is preferable, and examples of the basic functional group include a primary, secondary, or tertiary amino group, and nitrogen-containing heterocycles such as pyridine, pyrimidine, and pyrazine.

[0094] Further, as the skeleton constituting the resin-type pigment dispersant, a fatty acid amine skeleton and / or a urethane skeleton are more preferable since a pigment dispersion having good storage stability can be easily obtained.

[0095] The pigment dispersant preferably has a weight average molecular weight of 5,000 to 50,000, an acid value (mgKOH / g) of 5 to 20, and an amine value (mgKOH / g) of 20 to 50. The "acid value" refers to the acid value per 1 g of dispersant solid content, and can be determined by potentiometric titration in accordance with JIS K 0070. The "amine value" refers to the amine value per 1 g of dispersant solid content, and can be determined by a method conforming to JIS K 7237, for example, by using a 0.1 N hydrochloric acid aqueous solution, determining the amount of the hydrochloric acid aqueous solution used for neutralization by potentiometric titration, and then converting the amount into the equivalent amount of potassium hydroxide.

[0096] Specific examples of the pigment dispersant include Solsperse 32000, 76400, 76500, J100, and J180, and Disperbyk-161, 162, 163, 164, 165, 166, 167, 168, and 190, all of which are manufactured by Lubrizol Corporation.

[0097] The content of the pigment dispersant is selected arbitrarily to ensure the desired stability. For example, the ink has excellent flow properties when the pigment dispersant is used in an amount of 25 to 150 parts by mass per 100 parts by mass of pigment. When the pigment dispersant is used within the above range, the ink has good dispersion stability and tends to show the same quality as the initial one even after a long period of time, which is preferable.

[0098] <Polymerization inhibitor> A polymerization inhibitor can be used to improve the storage stability of the ink. As the polymerization inhibitor, a hindered phenol compound, a phenothiazine compound, a hindered amine compound, and a phosphorus compound are particularly preferably used. Specific examples include 4-methoxyphenol, hydroquinone, methylhydroquinone, t-butylhydroquinone, 2,6-di-t-butyl-4-methylphenol, phenothiazine, and an aluminum salt of N-nitrosophenylhydroxylamine. Among these, it is preferable to contain a hindered phenol compound and / or a phenothiazine compound, and it is more preferable to contain 2,6-di-t-butyl-4-methylphenol and phenothiazine.

[0099] From the viewpoint of maintaining the curability while improving the stability over time, the content of the polymerization inhibitor is preferably 0.01 to 2% by mass relative to the total mass of the ink.

[0100] <Organic solvent> In order to lower the viscosity of the ink and improve the wettability to the recording medium, an organic solvent may be added to the active energy ray curable ink. The boiling point of the organic solvent is preferably 120 to 300°C, more preferably 140 to 270°C, and even more preferably 160 to 260°C.

[0101] Examples of the organic solvent include monoacetates, diacetates, diols, monoalkyl ethers, dialkyl ethers, and lactates of glycol compounds. Among them, monoacetates, monoalkyl ethers, and dialkyl ethers of glycol compounds are preferred. More specifically, tetraethylene glycol dialkyl ether, ethylene glycol monobutyl ether acetate, and diethylene glycol diethyl ether are preferred.

[0102] The content of the organic solvent is preferably 0.1 to 10% by mass relative to the total mass of the ink. By setting the content within the above range, it becomes easy to obtain good results in terms of each of the properties of curability, ejection stability, and adhesion. From the viewpoint of curability, the content of the organic solvent is more preferably 0.2 to 5% by mass relative to the total mass of the ink. Furthermore, from the viewpoint of ejection stability, it is preferably 0.5 to 4% by mass.

[0103] Next, when the ink set for single pass printing of the present invention is a set of water-based inks, components other than pigments that can be used in the water-based inks will be described in detail below.

[0104] <Water-soluble organic solvent> Any known water-soluble organic solvent can be used for the water-based ink, but one or more selected from the group consisting of diols of glycol compounds (excluding alkanediol compounds), monoalkyl ethers of glycol compounds, and alkanediol compounds, and having a boiling point of 100 to 280° C. can be preferably used. The boiling point is more preferably 120 to 250° C., and particularly preferably 170 to 215° C. In a preferred embodiment, a water-soluble organic solvent having a boiling point of 170 to 215° C. and a water-soluble organic solvent having a boiling point of more than 100° C. but less than 170° C. are used in combination, which is suitable from the viewpoint of obtaining a printed matter with improved color reproducibility, graininess, metamerism, and beading.

[0105] Specific examples of diols of glycol compounds include diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol #200, polyethylene glycol #400, dipropylene glycol, and tripropylene glycol.

[0106] Specific examples of monoalkyl ethers of glycol compounds include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.

[0107] Specific examples of the alkanediol compound include 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-heptanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methylpentane-2,4-diol, and 2-ethyl-1,3-hexanediol.

[0108] The content of the water-soluble organic solvent is preferably 5 to 40% by mass relative to the total mass of the ink. By setting the content within the above range, it becomes easy to obtain good results in terms of the graininess, metamerism, beading, and ejection stability of the printed matter. From the viewpoint of the graininess, beading, and ejection stability of the printed matter, the content of the water-soluble organic solvent is more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass, relative to the total mass of the ink.

[0109] Furthermore, from the viewpoint of particularly improving the graininess, metamerism, beading, and color reproducibility of printed matter, as well as the ejection stability and storage stability of the ink, the total content of water-soluble organic solvents having a boiling point of 100 to 280°C (preferably water-soluble organic solvents having a boiling point of 150 to 215°C), which are one or more types selected from the group consisting of diols of glycol compounds, monoalkyl ethers of glycol compounds, and alkanediol compounds, is preferably 50 mass% or more, and particularly preferably 70 mass% or more, of the total content of water-soluble organic solvents contained in the ink.

[0110] <Surface tension adjuster (for water-based inks)> Examples of surface tension modifiers that can be used in water-based inks include silicone-based surface tension modifiers, fluorine-based surface tension modifiers, polyoxyalkylene alkyl ether-based surface tension modifiers, acetylene glycol-based surface tension modifiers, etc. From the viewpoint of the ability to reduce surface tension, it is preferable to use an acetylene glycol-based surface tension modifier and / or a silicone-based surface tension modifier.

[0111] Specific examples of acetylene glycol surface tension adjusters that can be preferably used include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, and their ethylene oxide and / or propylene oxide adducts. In the present invention, commercially available acetylene glycol surface tension adjusters can also be used, examples of which include Surfynol (registered trademark) 104, DF-110, 420, 440, 465, 485, Olfine (registered trademark) E1004, E1010, etc., manufactured by Nissin Chemical Industry Co., Ltd., and Acetylenol (registered trademark) E00, E13, E40, E60, E80, E100, and E200, etc., manufactured by Kawaken Fine Chemical Co., Ltd.

[0112] Details of the silicone-based surface tension regulator that can be used in the water-based ink are the same as those in the case of the active energy ray-curable ink described above, and commercially available polyether-modified siloxane-based surfactants may also be used. Representative examples of products that can be preferably used include BYK (registered trademark)-331, 333, 348, 349, and 378 from BYK-Chemie Co., Ltd. In addition, TEGO (registered trademark) Glide 450, 440, 435, 432, 410, 406, 130, 110, and 100 from Evonik Degussa Corporation, as well as TEGO Wet 280, 270, 260, 250, and 240. Among these, BYK-331, 333, 348, 349, TEGO Glide 450, 440, 432, TEGO Wet 280, 270, and 240 are preferred from the viewpoint of improving image quality.

[0113] The total content of the surface tension modifier is preferably 1 to 5.5 mass %, more preferably 1.5 to 5 mass %, and particularly preferably 1.8 to 4.5 mass %, for the gray ink, relative to the total mass of the ink, and is preferably 0.8 to 5 mass %, more preferably 1.2 to 4.5 mass %, and particularly preferably 1.5 to 4.0 mass %, for the cyan ink, the magenta ink, and the yellow ink.

[0114] <Water> The water used in the water-based ink is preferably ion-exchanged water (deionized water) rather than ordinary water containing various ions, and its content is preferably within the range of 20 to 90% by mass of the total mass of the ink.

[0115] <Other ingredients> In addition to the above components, the water-based ink may contain pigment dispersants, resins, defoamers, preservatives, and the like, as necessary.

[0116] <Pigment dispersant (for water-based inks)> In order to improve the dispersibility of the pigment and the storage stability of the ink, it is preferable to use a pigment dispersant in the water-based ink. There is no particular limitation on the pigment dispersant that can be used in the water-based ink, and any known pigment dispersant can be used. Among them, a resin-type pigment dispersant having an acidic functional group is preferable, and examples of the acidic functional group include a phenolic hydroxyl group, a carboxyl group, a sulfo group, and a phosphate group.

[0117] From the viewpoint of improving the adsorption ability to the pigment, ensuring dispersion stability, and further improving the color reproducibility of the printed matter, it is preferable that the pigment dispersant contains an aromatic group in addition to the above-mentioned acidic functional group. Examples of the aromatic group include a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, and an anisyl group, and among these, a phenyl group and a tolyl group are preferable.

[0118] As the skeleton constituting the resin-type pigment dispersant, a (meth)acrylic skeleton, a styrene / olefin-maleic anhydride skeleton, and / or a urethane skeleton are more preferable since a pigment dispersion having good storage stability can be easily obtained. In this specification and the like, the expression "styrene / olefin-maleic (anhydride) skeleton" means "any of a styrene-maleic acid skeleton, a styrene-maleic anhydride skeleton, an olefin-maleic acid skeleton, and an olefin-maleic anhydride skeleton."

[0119] The acid value (mgKOH / g) of the pigment dispersant is preferably 100 to 450, more preferably 120 to 400, and particularly preferably 150 to 350. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment, and it is also possible to maintain the ejection stability from the inkjet head. Furthermore, it is preferable in that the solubility of the pigment dispersant in water can be ensured and the color reproducibility of the printed matter can be improved. The acid value can be determined in the same manner as in the case of the pigment dispersant that can be used in the above-mentioned active energy ray curable ink.

[0120] The pigment dispersant preferably has a weight average molecular weight of 5,000 to 50,000, more preferably 5,000 to 40,000, even more preferably 10,000 to 35,000, and particularly preferably 15,000 to 30,000. By having the weight average molecular weight in the above range, the pigment dispersant is more strongly adsorbed to the pigment, and the dispersion stability is improved, and the storage stability is also improved, so that a printed matter having excellent color reproducibility can be obtained for a long period of time. The weight average molecular weight can be determined in the same manner as in the case of the polymerizable oligomer described above.

[0121] The content of the pigment dispersant is selected arbitrarily so as to ensure the desired dispersion stability, storage stability, and ejection stability of the aqueous ink. For example, the content of the pigment dispersant is preferably 2 to 100 parts by mass, and more preferably 4 to 50 parts by mass, per 100 parts by mass of the pigment.

[0122] <Resin> Resins (binder resins) can be used from the viewpoint of improving the weather resistance and coating resistance of printed matter and improving beading. Usable types of resins include acrylic, styrene acrylic, urethane, styrene butadiene, vinyl chloride, polyolefin, etc. Among them, from the viewpoint of suitably exerting the above-mentioned effects, one or more resins selected from the group consisting of acrylic, styrene acrylic, and polyolefin are preferably used.

[0123] Resins used in water-based inks are generally water-soluble resins or resin particles, either of which may be used in the present invention. When the resin is a copolymer, the polymerization form may be any of random, block, star, and star.

[0124] From the viewpoint of suitably exerting the above-mentioned effects, when a resin is used, the acid value (mgKOH / g) is preferably from 10 to 80, more preferably from 20 to 60, and particularly preferably from 20 to 45. The method for measuring the acid value is the same as that for the pigment dispersant described above.

[0125] Furthermore, from the viewpoint of achieving both the above-mentioned effects and ejection stability, the resin content (converted into solid content) is preferably 1 to 15 mass % and more preferably 2 to 12 mass % relative to the total mass of the ink.

[0126] <Ink properties> <Static surface tension> Regardless of whether the ink set for single-pass printing of the present invention is a set of active energy ray-curable inks or a set of water-based inks, it is preferable that the static surface tension of the gray ink at 25° C. is lower than each of the static surface tensions of the cyan ink, the magenta ink, and the yellow ink at 25° C. Specifically, from the viewpoint of improving metamerism, it is more preferable that the static surface tension of the gray ink at 25° C. is lower by 1 mN / m or more than each of the static surface tensions of the cyan ink, the magenta ink, and the yellow ink at 25° C. When the static surface tensions satisfy the above relationship, the gray ink wets and spreads over the image formed by the cyan ink, the magenta ink, and the yellow ink, thereby effectively improving metamerism.

[0127] Furthermore, in the present invention, the static surface tension of the ink is preferably 20 to 32 mN / m, more preferably 21 to 26 mN / m for the gray ink, and 22 to 28 mN / m for the cyan ink, magenta ink, and yellow ink. When the static surface tension satisfies the above range, the gray ink wets and spreads over the image formed by the cyan ink, magenta ink, and yellow ink, thereby effectively improving metamerism and providing good dischargeability in inkjet printing.

[0128] <Viscosity> From the viewpoint of printing by an inkjet system, the cyan ink, the magenta ink, the yellow ink, and the gray ink constituting the single pass printing ink set of the present invention preferably have a viscosity of 40 mPa·s or less at 25°C. When the single pass printing ink set of the present invention is a set of active energy ray curable inks, the viscosity is more preferably 5 to 40 mPa·s, and even more preferably 7 to 30 mPa·s. On the other hand, when the single pass printing ink set of the present invention is a set of water-based inks, the viscosity is more preferably 3 to 30 mPa·s, and even more preferably 5 to 20 mPa·s.

[0129] <Recording method> The recording method of the present invention includes a step of printing the cyan ink, the magenta ink, and the yellow ink contained in the single-pass printing ink set (hereinafter also referred to as the "ink printing step"), and then a step of printing the gray ink (hereinafter also referred to as the "gray ink printing step"). By forming an image using the gray ink on top of an image formed using the cyan ink, magenta ink, and yellow ink, the spectral reflectance characteristics of the printed matter become flat, making it possible to effectively improve metamerism.

[0130] <Ink printing process> In the present invention, from the viewpoint of productivity, the ink printing step is preferably performed by a single-pass inkjet method, and the printing speed is preferably 35 m / min or more, more preferably 50 m / min or more, and particularly preferably 75 m / min or more.

[0131] In the step of printing the cyan ink, the magenta ink, and the yellow ink, it is not necessary to print all three colors of ink, and it is not necessary to print the cyan ink, the magenta ink, and the yellow ink in that order. The order can be appropriately selected depending on the desired image.

[0132] In the present invention, the amount of ink ejected from one nozzle of the inkjet head is preferably 0.1 to 100 pL / drop, more preferably 0.5 to 75 pL / drop, and even more preferably 1 to 40 pL / drop.

[0133] In the present invention, the nozzle density of the inkjet head is preferably 180 dpi or more, more preferably 300 dpi or more, and even more preferably 600 dpi or more.

[0134] <Semi-curing or semi-drying process> The recording method of the present invention preferably includes a semi-curing or semi-drying step after the step of printing the cyan ink, the magenta ink, and the yellow ink contained in the ink set for single pass printing of the present invention and before the step of printing the gray ink.

[0135] In the present invention, "semi-cured" means partially cured, and refers to a state in which the cyan, magenta, and yellow inks are partially cured but not completely cured. Specifically, after the completion of semi-curing, plain paper is pressed against the ink to determine whether the ink has been transferred. In other words, if the ink has been transferred, the ink is said to be in a semi-cured state. By semi-curing, the gray ink becomes easier to spread, and metamerism can be effectively improved. In addition, the cyan, magenta, and yellow inks are partially cured, and the ink is not completely cured. It suppresses the mixing of Zenith ink, yellow ink dots and gray ink dots (known as beading), resulting in high-quality images.

[0136] The method for semi-curing is not particularly limited, and includes known methods such as a method of irradiating active energy rays. The active energy rays may be energy rays such as electron beams, ultraviolet rays, and infrared rays that affect the electron orbit of the irradiated object and induce polymerization reactions such as radicals, cations, and anions, and are not limited thereto. Among them, electron beams and ultraviolet rays are preferred, and ultraviolet rays are more preferred.

[0137] The light source is not particularly limited, and known light sources can be used. Specific examples include mercury lamps, xenon lamps, metal hydride lamps, UV-LEDs, LEDs (light-emitting diodes) such as ultraviolet laser diodes (UV-LDs), gas and solid-state lasers, etc. Among these, it is preferable to use UV-LEDs.

[0138] When using a UV-LED, the peak wavelength is preferably 380 to 420 nm, more preferably 380 to 410 nm, from the viewpoint of curability. When it is 380 nm or more, it is excellent in safety. Also, when it is 420 nm or less, it is preferable because it is excellent in curability.

[0139] The amount of energy required for semi-curing varies depending on the type and content of the polymerization initiator, but is generally between 1 and 500 mJ / cm 2 is preferred.

[0140] In the present invention, "semi-dry" means partial drying, and refers to a state in which the cyan ink, magenta ink, and yellow ink are partially dried but not completely dried. Specifically, it refers to a state in which the total amount of volatile components (water and water-soluble organic solvent) present in the ink after semi-drying is 10 to 80 mass % of the total amount of volatile components present in the ink before semi-drying. By semi-drying, the gray ink becomes easier to spread, and metamerism can be effectively improved.

[0141] The method for semi-drying is not particularly limited, and examples thereof include heat drying, hot air drying, infrared drying, microwave drying, and drum drying. The above drying methods may be used alone or in combination. For example, by using heat drying and hot air drying in combination, the ink can be dried more quickly than when each method is used alone.

[0142] The specific conditions for the semi-drying process vary depending on the polymerizable compound, water-soluble organic solvent, and water content. For example, in the case of infrared drying, the maximum absorption wavelength is 1500 to 2500 nm, and the energy density is 20 to 200 kW / m 2 The semi-dry state can be achieved by drying the material for about 0.5 to 5 seconds using a carbon heater.

[0143] <Black ink printing process> When the ink set for single-pass printing of the present invention contains a black ink, the step of printing the black ink (hereinafter also referred to as the "black ink printing step") may be carried out before the ink printing step described above, or after the ink printing step and before the gray ink printing step described below, or after the gray ink printing step. Among these, from the viewpoint of improving metamerism, it is preferable to carry out the black ink printing step after the step of printing the gray ink.

[0144] In addition, when the black ink printing step is not the last printing step, the black ink printing step may be followed by a semi-curing step or a semi-drying step, the details of which are as described above.

[0145] <Gray ink printing process> In the present invention, from the viewpoint of improving metamerism, it is preferable to print using an image that has been processed and created so that the printing rate of gray ink is 50% or more. As an example of a method for processing and creating the image, an ICC profile for the ink set used in the recording method of the present invention is created using Profile maker manufactured by X-rite. Next, image data separated into the colors of each ink constituting the ink set can be created using the ICC profile and Photoshop (registered trademark) manufactured by Adobe.

[0146] <Main curing or drying process> The recording method of the present invention includes a step of full curing or full drying after carrying out all of the above-mentioned steps.

[0147] In the present invention, "main curing" refers to a state in which the inside and surface of the ink are completely cured. Specifically, after the main curing is completed, press a plain paper against the ink and check whether the ink is transferred. In other words, if there is no transfer at all, it is said to be in a completely cured state.

[0148] The method for full curing can be the same as the semi-curing method described above. The amount of energy required for full curing varies depending on the type and content of the polymerization initiator, but is generally in the range of 100 to 10,000 mJ / cm 2 is preferred.

[0149] In the present invention, "mainly dried" refers to a state in which the inside and surface of the ink are completely dry. Specifically, after the completion of the main drying, a plain paper is pressed against the ink, and it can be judged whether the ink transfers or not. In other words, if there is no transfer at all, it is said to be in a completely dried state.

[0150] The main drying method can be the same as the semi-drying method described above. EXAMPLES

[0151] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these. In the examples and comparative examples, "parts" and "%" respectively represent "parts by mass" and "% by mass".

[0152] <Preparation of pigment dispersion> 20 parts of LIONOL BLUE FG-7919 was added as a pigment, 10 parts of Solsperse 32000 as a pigment dispersant, and 70 parts of SR508 as a polymerizable compound, and the mixture was stirred in a high-speed mixer until uniform, and then dispersed in a horizontal sand mill for about 1 hour to prepare pigment dispersion CM1. The horizontal sand mill used was a DYNO-MILL (Multi-Lab type, manufactured by Shinmaru Enterprises) with a volume of 0.6 L and filled with 1,800 g of zirconia beads (Vickers hardness 1,200 Hv) with a diameter of 1 mm. The peripheral speed of the stirring blade during dispersion was 10 m / s.

[0153] In addition, the pigment dispersions shown in Table 1 were prepared in the same manner as above, except that the raw materials used were changed. The values ​​in Table 1 represent "parts by mass" unless otherwise specified, and blank spaces indicate that no ingredients were added.

[0154] [Table 1]

[0155] [Table 1]

[0156] [Table 1]

[0157] [Table 1]

[0158] [Table 1]

[0159] In addition, pigment dispersions MM14-1, MM14-2, and MM14-3 were each produced in the same manner as pigment dispersion MM14, except that zirconia beads with a diameter of 1.5 mm (Vickers hardness 1,200 Hv), alumina beads with a diameter of 1 mm (Vickers hardness 1,500 Hv), or alumina-zirconia beads with a diameter of 1 mm (Vickers hardness 1,000 Hv) were used as the media filled in the horizontal sand mill.

[0160] <Ink Creation> In a mixing vessel equipped with a stirrer, 17.5 parts of pigment dispersion CM1, 27.4 parts of SR508 as a polymerizable compound, 35 parts of VEEA, 10 parts of SR454, 6 parts of Omnirad TPO, 2 parts of Omnirad 379, 2 parts of Omnirad ITX as a polymerization initiator, and 0.1 parts of BYK-3510 as a surface tension modifier were added, and the contents were heated to 50°C. After stirring for 2 hours with a high-speed mixer while maintaining the temperature in the mixing vessel, it was confirmed that no solid components remained dissolved, and then filtered with a membrane filter with a pore size of 1 μm to prepare cyan ink C1.

[0161] In addition, the inks shown in Table 2 were prepared in the same manner as above, except for changing the raw materials used. Note that the values ​​in Table 2 represent "parts by mass" unless otherwise specified, and blank spaces indicate that no ingredients were blended.

[0162] [Table 2]

[0163] [Table 2]

[0164] [Table 2]

[0165] [Table 2]

[0166] [Table 2]

[0167] Details of each component shown in Tables 1 and 2 and above are as follows. LIONOL BLUE FG-7919: Toyo Color Co., Ltd., CI Pigment Blue 15:3 LIONOL BLUE FG-7400G: Toyo Color Co., Ltd., CI Pigment Blue 15:4 LIONOL BLUE E: Toyo Color Co., Ltd., CI Paint Blue 15:6 ·PIGMENT YELLOW IRC: Sanyo Pigment Co., Ltd., CI Pigment Yellow 83 ·Paliotol Yellow D 1819: Manufactured by BASF, CIPigment Yellow 139 BAYSCRIPT YELLOW 4GF: LANXESS, CI Pigment Yellow 150 ·Sicopal Yellow L 1100: Manufactured by BASF, CIPigm ent Yellow 184 ·Paliotol Yellow D 1155: Manufactured by BASF, CIPigment Yellow 185 · FASTOGEN Super Red 7100Y: DIC, CIPigment Violet 19 Irgalite Red D 3865: BASF, CI Pigment Red 112 · FASTOGEN Super Magenta RG: DIC, CIPigment Red 122 Pigment Pink 4602: Sanyo Pigment Co., Ltd., CI Pigment Red 146 ·Cromophtal Scarlet D 3540: Manufactured by BASF, CI Pigment Red 166 Paliogen Red L 4039: BASF, CI Pigment Red 177 PERRINDO Maroon 179: DIC, CI Pigment Red 179 ·Cinquasia Magenta L 4530: Manufactured by BASF, CIP igment Red 202 Pigment Scarlet BL: Sanyo Pigment Co., Ltd., CI Pigment Red 237 Irgazin Red L 3670 HD: BASF, CI Pigment Red 254 Irgazin Scarlet L3550 HD: BASF, CIP stain Red 255 IrgazinRubine L 4020: BASF, CI Pigment Red 264 ·Cinquasia Magenta L 4400: Manufactured by BASF, CIP igment Red 282 Hostaperm Scarlet GO: CLARIANT, CIP igment Red 168 Special Black 350: Evonik Degussa, CI Pigment Black 7 Solspers 32000: Lubrizol resin-based pigment dispersant BYK-190: BYK-Chemie, a resin-type pigment dispersant with a styrene-maleic acid structure Acrylic resin 1: A resin-type pigment dispersant polymerized with a weight ratio of acrylic acid / methyl methacrylate / lauryl methacrylate = 30 / 40 / 30. Acrylic resin 2: A resin-type pigment dispersant polymerized with a weight ratio of acrylic acid / styrene / lauryl methacrylate = 30 / 40 / 30. SR508: Dipropylene glycol diacrylate, manufactured by Arkema Corporation VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd. SR454: Arkema Corporation, ethoxylated (3) trimethylolpropane triacrylate Omnirad TPO: 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, manufactured by iGM RESINS Omnirad 379: GM RESINS, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone Omnirad ITX: 2-isopropylthiophene manufactured by iGM RESINS BYK-UV3510: BYK-Chemie, polyether modified polydimethylsiloxane BYK-333: BYK-Chemie, polyether-modified polydimethylsiloxane JONCRYL819: BASF acrylic resin 1,2PG: 1,2-propylene glycol

[0168] <Ink evaluation> Using a Trytec One Pass JET equipped with a Kyocera inkjet head (resolution 600 dpi x 600 dpi), the inks were filled, and a solid image with a dot area ratio of 100% (equivalent to a film thickness of 8 μm) was printed on Oji Paper OK Topcoat+ for each ink. The ink amount was 14 pL and the printing speed was 50 m / min. After printing, except for C5, Y7-12, M21-36, Gr15-17, and K2, the solid image was cured using a 160 W / cm metal hydride lamp (365 nm) manufactured by Harrison Toshiba Lighting Co., Ltd. to obtain a solid print. In addition, for C5, Y7-12, M21-36, Gr15-17, and K2, which are water-based inks, after printing under the above conditions, they were dried for 3 minutes in an air oven at 70°C to obtain a solid print.

[0169] <Measurement of static surface tension of ink> The static surface tension of the prepared ink was measured at 25°C using a Kyowa Interface Science Co., Ltd. DY-300.

[0170] <Measurement of hue angle H°> The solid prints produced by the above method were measured for hue angle H° using the X-Rite 500 series manufactured by X-Rite, Inc. However, the hue angle H° was not measured for the gray ink and black ink.

[0171] <Light resistance evaluation> The solid print produced by the above method was exposed for 400 hours under the conditions of a black panel temperature of 63°C and an exposure dose of 70,000 Lux using a xenon weather meter XL75 manufactured by Suga Test Instruments Co., Ltd. After exposure, the OD value of the solid print was measured using an X-Rite 500 series manufactured by X-Rite, Inc. under the conditions of a viewing angle of 2°, a light source of D65, and a filter T. The OD value of the solid print before exposure was used as a reference to determine the reduction rate of the OD value of the solid print after exposure, and the lightfastness was evaluated based on the following evaluation criteria. In addition, a score of 3 or more on the following evaluation criteria was determined to be at a level that is acceptable for practical use. 5: OD value reduction rate < 10% 4: 10% or less OD value reduction rate < 15% 3: 15% or less OD value reduction rate < 20% 2:20% or less OD value reduction rate < 30% 1: OD value reduction rate ≧ 30%

[0172] <Spectral reflectance measurement> The spectral reflectance of the solid prints of magenta ink and gray ink produced by the above method was measured at 420 nm, 500 nm, 570 nm, and 700 nm using an X-Rite 500 series manufactured by X-Rite, Inc., with a viewing angle of 2°, light source D65, and CIE color system. However, the spectral reflectance at 700 nm was measured only for the magenta ink.

[0173] The evaluation results of the hue angle H°, static surface tension, and light fastness are shown in Table 2, and the evaluation results of the spectral reflectance are shown in Tables 3 and 4.

[0174] [Table 3]

[0175] [Table 4]

[0176] [Examples 1 to 63, Comparative Examples 1 to 12] <Ink set evaluation> Using a One Pass JET manufactured by Tritec Corporation equipped with an inkjet head (resolution 600 dpi x 600 dpi) manufactured by Kyocera Corporation, the ink combinations described in Examples 1 to 63 and Comparative Examples 1 to 12 in Table 5 were filled as ink sets, and then color chart prints were produced in the same manner as the above solid prints. Then, each patch of the color chart image was measured with a measuring device (X-rite's X-Rite 500 series), and based on the results, an optimal ICC profile was created for each ink set. Note that Profile maker manufactured by X-rite was used for the creation. Using this ICC profile, the RGB data of the evaluation image, Pantone Warm Gray 4 (a gray single color image), was color converted to CMYK color space data to obtain evaluation image data. Note that Adobe's Photoshop (registered trademark) was used for the conversion. Next, using the created evaluation image data, an image was printed on OK Topcoat+ manufactured by Oji Paper Co., Ltd. using the same device as for the color chart printout. The ink amount was 14 pL and the printing speed was 50 m / min. In addition, among the ink sets that are semi-cured or semi-dried "Yes" in Table 5, for the ink sets other than those in Examples 42 to 63 and Comparative Example 12, 0.2 seconds after printing the third color, a Phoseon LED lamp (395 nm, 4 W / cm 2 In the ink sets of Examples 42 to 63 and Comparative Example 12, hot air at 120° C. was blown onto the ink 0.2 seconds after the third color was printed. After printing the fourth or fifth color, the ink was cured using a GEW 240 W / cm metal halide lamp (except for Examples 42 to 63 and Comparative Example 12) or a Heraeus IR lamp (maximum output wavelength 2000 nm, 80 kW / m 2 ) for 2 seconds and then completely dried (Examples 42 to 63, Comparative Example 12), thereby obtaining evaluation image prints.

[0177] <Metamerism evaluation> The hue of the evaluation image print obtained by the above method and the hue of Pantone Warm Gray 4 (PANTONE [registered trademark] Plus SERIES), a color sample manufactured by Pantone, were measured using X-Rite 500 series manufactured by X-Rite, Inc., at a viewing angle of 2°, light source D65, and CIE color system, and the color difference (referred to as ΔED65*) between the evaluation image print and the color sample was obtained. In addition, the color difference (referred to as ΔETL84*) was obtained in the same manner as above, except that the measurement was performed using TL84 as the light source. Then, the color difference (referred to as ΔE*) between the two types of light sources was calculated using the following formula, and metamerism was evaluated. ΔE*={(ΔED65*) 2 -(ΔETL84*) 2} 1 / 2 The evaluation criteria were as follows, with a rating of 3 or higher being considered to be at a level that presents no practical problems. 5: ΔE*<0.5 4:0.5≦ΔE*<1 3:1≦ΔE*<2 2:2≦ΔE*<3 1:3≦ΔE*

[0178] <Granularity evaluation> The graininess of the print image obtained by the above method was visually evaluated according to the following criteria, with a score of 3 or higher being considered to be at a level that presents no practical problems. 5: There is no graininess in the image. 4: The image has a slight roughness (similar to the graininess of the evaluation image print produced using the ink set of Comparative Example 1) 3: The image is slightly grainy. 2: The image has a rough texture (similar to the graininess of the evaluation image print produced using the ink set of Comparative Example 4). 1: The image is quite grainy.

[0179] <Beading evaluation> The beading of the evaluation image print obtained by the above method was evaluated by visual inspection and an optical microscope at a magnification of 50. The evaluation criteria were as follows, with 3 or more being considered to be at a level that is not problematic in practical use. 5: No beading was observed even when examined under a microscope. 4: When examined under a microscope, there was very little beading, but almost no beading was observed with the naked eye (similar to the beading of the evaluation image print produced using the ink set of Example 2). 3: When visually inspected, there was very little beading. 2: When visually inspected, there was some beading and the colors were clearly mixed (similar to the beading of the evaluation image print produced using the ink set of Comparative Example 2). 1: Upon visual inspection, there was clear beading.

[0180] <Color reproducibility evaluation> Using the resulting ink, secondary color step charts of green, red, orange, and blue were printed as shown below, and color reproducibility was evaluated by comparing them with Pantone color samples. The evaluation criteria were as follows, with a score of 3 or higher being considered to be at a level that is acceptable for practical use. In particular, a chart with small differences from the color samples for all green, red, and blue was evaluated as having particularly excellent color reproducibility. 5:ΔE<5 4:5≦ΔE<7 3:7≦ΔE<9 2:9≦ΔE<11 1: ΔE≧11

[0181] <Green color reproducibility evaluation> A green secondary color step chart print was produced in the same manner as the above solid print, using the cyan ink and yellow ink constituting each ink set except for Comparative Examples 3 to 5. The green secondary color step chart print is an image having patches in which the printing rate of the two colors of ink, cyan ink and yellow ink, was changed by 10% between 0 and 200% (however, the printing rate of the cyan ink and the yellow ink was the same). Next, the hue (L*, a*, b*) of each patch constituting the obtained green secondary color step chart print was measured using an X-Rite 500 series manufactured by X-Rite, Inc., at a viewing angle of 2°, a light source of D65, and the CIE color system. Then, the difference (ΔE) between the hue of each patch and the hue of Pantone (registered trademark) HEXACHROME Green, a color sample manufactured by Pantone, was calculated using the following formula. ΔE={(LL*) 2 +(aa*) 2 +(bb*) 2} 1 / 2 In the above formula, L, a, and b are the hue values ​​of the color sample, and L*, a*, and b* are the hue values ​​of the secondary color step chart printout. The calculation of ΔE was performed for each patch, and the patch with the smallest ΔE was evaluated based on the above evaluation criteria.

[0182] <Red color reproducibility evaluation> A red secondary color step chart print was produced in the same manner as the above solid print using the yellow ink and magenta ink constituting each ink set except for Comparative Examples 3 to 5. Then, the hue of each patch was measured in the same manner as the above green color reproducibility evaluation, and the difference (ΔE) between the hue of each patch and the hue of Pantone [registered trademark] WARM RED, a color sample made by Pantone, was calculated using the above formula. Then, the ΔE was calculated for each patch, and the patch with the smallest ΔE was evaluated based on the above evaluation criteria.

[0183] <Blue color reproducibility evaluation> A blue secondary color step chart print was produced in the same manner as the above solid print using the cyan ink and magenta ink constituting each ink set except for Comparative Examples 3 to 5. Then, the hue of each patch was measured in the same manner as the above green color reproducibility evaluation, and the difference (ΔE) between the hue of each patch and the hue of Pantone [registered trademark] Reflex Blue, a color sample made by Pantone, was calculated using the above formula. Then, the above ΔE was calculated for each patch, and the patch with the smallest ΔE was evaluated based on the above evaluation criteria.

[0184] <Paint film resistance evaluation> The evaluation image print obtained by the above method was rubbed 10 times with a cotton swab soaked in 50% ethanol under a load of about 100g, and the coating resistance of each ink set was evaluated based on the state of color transfer between the surface of the print and the cotton swab. The evaluation criteria were as follows, with a score of 3 or higher being considered to be at a level that is acceptable for practical use. 5: There were no marks from rubbing on the surface of the printed matter, and no color transfer to the cotton swab. 4: There were no marks from rubbing on the surface of the print, but there was slight color transfer to the cotton swab. 3: There were slight scratches on the surface of the print, and color transfer to the cotton swab was observed. 2: There were large scuff marks on the surface of the print, and the color transferred significantly to the cotton swab. 1: The ink peeled off from the surface of the printed matter, and the surface of the recording medium was visible.

[0185] <Curing evaluation> The cured film surface of the evaluation image print obtained by the above method was rubbed with a fingernail, and the tackiness of the print surface was evaluated to confirm the curability. The evaluation criteria were as follows, with 3 or more being considered to be at a level that is not problematic for practical use. 5: The cured film did not peel off even when rubbed hard with a fingernail, and the surface had no tacky feel. 4: When rubbed hard with a fingernail, part of the cured film peeled off, but there was no tacky feeling on the surface. 3: When rubbed with a fingernail, part of the cured film peeled off, but there was no tacky feeling on the surface. 2: When rubbed with a fingernail, part of the cured film peeled off and the surface felt a bit tacky. 1: When I put my fingernail on it, the hardened film came off easily and there was a tacky feeling on the surface.

[0186] [Table 5]

[0187] [Table 5]

[0188] [Table 5]

[0189] [Table 5]

[0190] [Table 5]

[0191] [Table 5]

[0192] [Table 5]

[0193] According to the present invention, it has been found that an ink set for single-pass printing including at least a cyan ink, a magenta ink, a yellow ink, and a gray ink can be obtained, which has excellent weather resistance and color reproducibility, and is improved in graininess and metamerism.

[0194] Next, in the case where the ink set for single pass printing was a set of water-based inks, the effect of the water-soluble organic solvent used in the water-based ink on the quality was evaluated.

[0195] The inks shown in Table 6 were prepared in the same manner as above, except for changing the raw materials used. Note that the values ​​in Table 6 represent "parts by mass" unless otherwise specified, and blank spaces indicate that no ingredients were blended.

[0196] [Table 6]

[0197] [Table 6]

[0198] [Table 6]

[0199] [Table 6]

[0200] [Table 6]

[0201] Among the components listed in Table 6, details of those not listed in Tables 1 and 2 above are as follows. 1,3PG: 1,3-propanediol 2e-1,3HeD: 2-ethyl-1,3-hexanediol EG: Ethylene glycol ·DEG: Diethylene glycol TEG: Triethylene glycol ·PGM: Propylene glycol monomethyl ether ·DPGP: Dipropylene glycol monopropyl ether ·TEGE: Triethylene glycol monoethyl ether

[0202] [Examples 64 to 76] Using a One Pass JET manufactured by Tritec Corporation equipped with an inkjet head (resolution 600 dpi x 600 dpi) manufactured by Kyocera Corporation, the ink combinations shown in Table 6 were filled as ink sets, and then evaluation image prints were obtained in the same manner as in Example 42. Then, for the obtained evaluation image prints, metamerism evaluation, granularity evaluation, beading evaluation, color reproducibility evaluation, and color reproducibility evaluation (green, red, blue) were performed using the methods described above.

[0203] The evaluation results of metamerism, granularity, beading, color reproducibility, and color reproducibility (green, red, and blue) for the ink set shown in Table 6 are as shown in Table 7.

[0204] [Table 7]

Claims

1. 1. An ink set for single pass printing comprising at least a cyan ink, a magenta ink, a yellow ink, a black ink, and a gray ink, The magenta ink comprises one or more selected from the group consisting of C.I. Pigment Red 112, 146, 166, 177, 179, 202, 237, 254, 255, and 282; The gray ink comprises C.I. Pigment Black 7; The spectral reflectance of the magenta ink satisfies the following formulas (1) to (3), The gray ink has a spectral reflectance of 20 to 70% at a wavelength of 500 nm and satisfies the following formulas (4) and (5): All of the inks constituting the ink set are aqueous inks containing water, a water-soluble organic solvent, and a surface tension modifier; An ink set for single pass printing, characterized in that all of the inks constituting the ink set are selected from the group consisting of diols of glycol compounds, monoalkyl ethers of glycol compounds, and alkanediol compounds, and contain a water-soluble organic solvent having a boiling point of 150 to 215°C in an amount of 50 mass% or more based on the total content of the water-soluble organic solvents contained in the inks. (Spectral reflectance at 420 nm)÷(Spectral reflectance at 700 nm)×100≦40 Formula (1) (Spectral reflectance at 500 nm)÷(Spectral reflectance at 700 nm)×100≦10 Formula (2) (Spectral reflectance at 570 nm)÷(Spectral reflectance at 700 nm)×100≦20 Formula (3) 80≦(spectral reflectance at 420 nm)÷(spectral reflectance at 500 nm)×100≦110 Formula (4) 80≦(spectral reflectance at 570 nm)÷(spectral reflectance at 500 nm)×100≦110 Formula (5)

2. When the hue angle defined in the CIELAB color space is H°, The hue angle H° of the cyan ink is 200 to 290°, The hue angle H° of the magenta ink is 0 to 45°, 2. The ink set for single pass printing according to claim 1, wherein the yellow ink has a hue angle H° of 80 to 110°.

3. 3. The ink set for single pass printing according to claim 1, wherein the static surface tension of the gray ink at 25°C is lower by 1 mN / m or more than each of the static surface tensions of the cyan ink, the magenta ink, and the yellow ink at 25°C.

4. The cyan ink comprises one or more selected from the group consisting of C.I. Pigment Blue 15:3 and 15:4; The yellow ink comprises one or more selected from the group consisting of C.I. Pigment Yellow 150, 184, and 185; The ink set for single pass printing according to any one of claims 1 to 3, characterized in that the black ink comprises C.I. Pigment Black 7.

5. A recording method using the ink set for single-pass printing according to any one of claims 1 to 4, comprising the steps of: After the step of printing the cyan ink, the magenta ink, and the yellow ink, A step of printing the gray ink is carried out, a step of printing the black ink after the step of printing the gray ink.

6. 6. The recording method according to claim 5, further comprising a step of semi-drying the printed inks between the step of printing the cyan ink, the magenta ink, and the yellow ink and the step of printing the gray ink.

7. A printed matter obtained by printing the ink set for single pass printing according to any one of claims 1 to 4 on a substrate.

8. A printed matter printed by the recording method according to claim 5 or 6.

Images