Ink set and inkjet recording method

Abstract

To provide an ink set capable of enhancing color saturation of a red region of orange to high brightness and a red region of low brightness and capable of recording an image of which color reproducibility is improved, in a*>0,b*>0 region on a L*a*b* color space.SOLUTION: It is an ink set that has a combination of a first ink and a second ink. The hue angle of the first dilution obtained by diluting the first ink with water is between 330° and 345°, and the hue angle of the second dilution obtained by diluting the second ink with water is between 40°and 80°. An absolute value of the difference between the short wavelength peak absorption wavelength λ1 (nm) of the first dilution, which has two peak absorption wavelengths in the wavelength range of 380 nm to 780 nm, and the maximum absorption wavelength λ2 (nm) of the second dilution in the wavelength range of 380 nm to 780 nm is between 0 and 10. Additionally, the absolute value of the difference between an integral value of absorbance of the first dilution and the integral value of absorbance of the second dilution in the wavelength range of 560 nm to 580 nm is 11.0 or greater.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ink set and an inkjet recording method.

Background Art

[0002] In the fields of posters and photography where images are printed using large-format inkjet printers, ink sets that combine basic colors with special colors are widely used to expand the color reproduction range of images. By using a number of special inks such as red, orange, green, and blue, together with basic color inks such as cyan, magenta, yellow, and black, a high level of color reproducibility required can be achieved. However, as the number of colors of the inks used increases, problems such as an increase in the size of the inkjet recording apparatus and an increase in the load on the system are likely to occur. For this reason, various technical developments have been carried out to record an image with an expanded color reproduction range even when the number of special inks is reduced.

[0003] In recent years, especially in the field of posters, in order to enhance the impression of printed materials, the vivid color reproduction range in the region where a * a * b * > 0 and b * > 0 in the color space has attracted attention, and various techniques for expanding this color reproduction range have been proposed. * > 0 in the color space has attracted attention, and various techniques for expanding this color reproduction range have been proposed.

[0004] Various methods for expanding color reproducibility by using a combination of basic color inks and special inks have been proposed so far. For example, an ink set has been proposed in which orange ink with a special feature is added to magenta ink, yellow ink, and black ink to expand the color reproduction range (Patent Document 1). Also, an ink set has been proposed in which light cyan ink, light magenta ink, orange ink with a special feature, and green ink with a special feature are added to cyan ink, magenta ink, and yellow ink (Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to achieve the color reproduction range required in recent years, the present inventors used the ink sets proposed in Patent Documents 1 and 2 to reproduce the region where a * a * b * on the L*a*b* color space is greater than 0 and b * is greater than 0. As a result, it was found that for the high-brightness regions in the region where a * is greater than 0 and b * a * b * on the L*a*b* color space is greater than 0 and b * is greater than 0, the required color reproduction range can be achieved. However, it was found that for the low-brightness regions in the region where a * is greater than 0 and b * a * b * on the L*a*b* color space is greater than 0 and b * is greater than 0, the required color reproduction range cannot be achieved. As a result of detailed examination, it was found that the chroma C * in the orange to high-brightness red region is large, while the chroma C * in the low-brightness red region (dark red region) becomes small, making it difficult to achieve the required color reproduction range. * becomes small, making it difficult to achieve the required color reproduction range.

[0007] Therefore, an object of the present invention is to provide a method for reproducing a color reproduction range on the L*a*b* color space where a * a * b * is greater than 0 and b * is greater than 0 and b *In the >0 region, it is an object to provide an ink set capable of recording an image with improved color reproducibility by enhancing the saturation of the orange to high-brightness red region and the low-brightness red region. Another object of the present invention is to provide an inkjet recording method using this ink set.

Means for Solving the Problems

[0008] That is, according to the present invention, there is provided an ink set having a combination of a first ink and a second ink, wherein the first ink contains a first pigment, the second ink contains a second pigment, and the hue angle of a first diluent obtained by diluting the first ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 330° or more and 345° or less, and the hue angle of a second diluent obtained by diluting the second ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 40° or more and 80° or less, and the absolute value of the difference between the short-wavelength side maximum absorption wavelength λ1 (nm) of the two maximum absorption wavelengths of the first diluent in the wavelength range of 380 nm to 780 nm and the maximum absorption wavelength λ2 (nm) of the second diluent in the wavelength range of 380 nm to 780 nm is 0 or more and 10 or less, and the absolute value of the difference between the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm and the integral value of the absorbance of the second diluent in the wavelength range of 560 nm to 580 nm is 11.0 or more. An ink set is provided.

Effects of the Invention

[0009] According to the present invention, L * a * b * On the a * >0, b * >0 region, it is possible to provide an ink set capable of recording an image with improved color reproducibility by enhancing the saturation of the orange to high-brightness red region and the low-brightness red region. Further, according to the present invention, it is possible to provide an inkjet recording method using this ink set.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments will be given to explain the present invention in more detail. In the description of this specification, "C.I." means an abbreviation of "Color Index". An aqueous ink for inkjet may be simply described as "ink". Further, when the compound is a salt, in the aqueous ink, the salt is dissociated into ions and exists, but for convenience, it is expressed as "containing a salt". Physical property values are values at normal temperature (25 ° C), normal pressure (1 atmospheric pressure = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified.

[0012] FIG. 1 is a schematic diagram showing a color space region. In FIG. 1, the region (1) is an orange to high-brightness red region, and the region (2) is a low-brightness red region. The inventors of the present invention, L * a * b * a on the color space * > 0, b *In the >0 region, the configuration of an ink set capable of improving the color reproducibility of the orange to high-brightness red region and the low-brightness red region (hereinafter also referred to as the "dark red region") was examined. As a result, it was found that the correlation between the optical properties of the magenta ink and the optical properties of the orange ink is important for enhancing the color reproducibility of these regions. The secondary color formed by combining a magenta ink with a hue angle of 330° or more and 345° or less and an orange ink with a hue angle of 40° or more and 80° or less was able to reproduce a certain region of the orange region and the red region. For this region, the maximum absorption wavelength in the absorption spectrum of the magenta ink and the maximum absorption wavelength in the absorption spectrum of the orange ink were overlapped to absorb light in the green color region (515 nm to 545 nm), which is the complementary color of the red color. As a result, it was found that the chroma of the red region in the secondary color could be further expanded.

[0013] As a result of further investigation, the present inventors found that it is necessary to expand the expressible range from the bright region to the dark region in order to further expand the color gamut. Specifically, the difference between the absorbance of the orange ink and the absorbance of the magenta ink in the wavelength range contributing to lightness (560 nm to 580 nm) is increased, that is, the absorption width in the wavelength range contributing to lightness is increased. Thereby, the color reproduction region from the bright region to the dark region can be expanded.

[0014] And the present inventors found that by satisfying the following requirements (i) to (v), a * >0, b * >0 region, it is possible to increase the chroma of the orange to high-brightness red region and the low-brightness red region, and to record an image with improved color reproducibility, thus arriving at the present invention. (i) The first ink (magenta ink) contains a first pigment, and the second ink (orange ink) contains a second pigment. (ii) The hue angle of the first diluent obtained by diluting the first ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 330° or more and 345° or less. (iii) The hue angle of the second dilution obtained by diluting the second ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 40° or more and 80° or less. (iv) The absolute value of the difference between the short-wavelength side maximum absorption wavelength λ1 (nm) of the two maximum absorption wavelengths of the first dilution in the wavelength range of 380 nm to 780 nm and the maximum absorption wavelength λ2 (nm) of the second dilution in the wavelength range of 380 nm to 780 nm is 0 or more and 10 or less. (v) The absolute value of the difference between the integrated value of the absorbance of the first dilution in the wavelength range of 560 nm to 580 nm and the integrated value of the absorbance of the second dilution in the wavelength range of 560 nm to 580 nm is 11.0 or more.

[0015] <Ink set> The ink set of the present invention has a combination of a first ink and a second ink. Further, the ink set of the present invention may further have an ink other than the first ink and the second ink. Also, both the first ink and the second ink are preferably aqueous inks. Furthermore, the ink set of the present invention is particularly suitable as an ink set for inkjet. As the form of the ink set of the present invention, there are (i) a set of a plurality of ink cartridges each independently containing each ink, and (ii) an ink cartridge integrally configured by combining a plurality of ink containing portions each independently containing each ink. However, the ink set of the present invention is not limited to the forms (i) and (ii) above as long as it is configured so that the first ink and the second ink can be used in combination. Hereinafter, the components contained in each ink constituting the ink set of the present invention and the physical properties of the ink will be described in detail.

[0016] (Colorant) [Colorant of the first ink] The first ink contains a pigment (first pigment) as a coloring material. The content (mass %) of the first pigment in the first ink is preferably 0.5 mass % or more and 15.0 mass % or less, more preferably 0.5 mass % or more and 10.0 mass % or less, based on the total mass of the ink. The hue angle of the first diluted liquid obtained by diluting the first ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm becomes 1 is 330° or more and 345° or less, preferably 330° or more and 340° or less. That is, the first ink contains the first pigment such that the hue angle of the first diluted liquid is within the above range. If the hue angle of the first diluted liquid is outside the above range, the chroma in the orange to high-brightness red region and the low-brightness red region (hereinafter, also referred to as "predetermined color reproduction region") cannot be increased.

[0017] The hue angle of the first diluted liquid can be obtained according to the following procedure. First, the first ink is diluted with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm becomes 1 to obtain a first diluted liquid. Next, the obtained first diluted liquid is put into a quartz glass cell with an optical path length of 10 mm, and an absorption spectrum in the wavelength range of 200 nm to 800 nm is measured using a spectrophotometer (for example, trade name "Spectophotometer U-3900H", manufactured by HITACHI). The peak detection conditions during the absorption spectrum measurement are: sampling interval: 0.5 nm, threshold value: 0.01, sensitivity: 1, and pure water is used as a reference. From the measured absorption spectrum, under the conditions of light source: C, field of view: 2°, L * a * b * is calculated. And from the formula: h = tan -1 (b * / a * ), the hue angle h in the L * C * h color system can be obtained.

[0018] Also, among the two maximum absorption wavelengths in the wavelength range of 380 nm to 780 nm of the absorption spectrum of the first diluent, the maximum absorption wavelength on the short wavelength side is defined as "λ1 (nm)". When there are three or more maximum absorption wavelengths, among the two maximum absorption wavelengths with high absorbance, the maximum absorption wavelength on the short wavelength side is defined as "λ1 (nm)".

[0019] Furthermore, the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm can be calculated according to the following procedure. That is, the absorption spectrum of the first diluent in the wavelength range of 560 nm to 580 nm is measured at a wavelength interval (sampling interval) of 0.5 nm, and the obtained absorbances are integrated. Then, by multiplying the integrated value by "0.5", which is the sampling interval, the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm can be calculated.

[0020] The first pigment is preferably a solid solution of C.I. Pigment Red 122 and C.I. Pigment Violet 19. Due to the appropriate crystal growth of this solid solution, the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm increases. As a result, the absolute value of the difference between the integral value of the absorbance of the first diluent and the integral value of the absorbance of the second diluent becomes larger, and a predetermined color reproduction region in monochromatic and secondary colors can be expanded more outward. On the other hand, when the first pigment is a solid solution of C.I. Pigment Red 202 and C.I. Pigment Violet 19, the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm tends to be small. Therefore, it is difficult to adjust the absolute value of the difference between the integral value of the absorbance of the first diluent and the integral value of the absorbance of the second diluent to 11.0 or more. Examples of the solid solution of C.I. Pigment Red 202 and C.I. Pigment Violet 19 include CROMOPHTAL Jet Magenta 2BC (manufactured by Ciba Japan).

[0021] In the above solid solution, the content (% by mass) of C.I. Pigment Red 122 is preferably 1.5 times or more and 9.0 times or less, more preferably 2.0 times or more and 6.0 times or less, in terms of mass ratio with respect to the content (% by mass) of C.I. Pigment Violet 19. By setting the above mass ratio, the integrated value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm increases. As a result, the absolute value of the difference between the integrated value of the absorbance of the first diluent and the integrated value of the absorbance of the second diluent can be made larger.

[0022] [Colorant of the second ink] The second ink contains a pigment (second pigment) as a colorant. The content (% by mass) of the second pigment in the second ink is preferably 0.5% by mass or more and 15.0% by mass or less, more preferably 0.5% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The hue angle of the second diluent obtained by diluting the second ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 40° or more and 80° or less, preferably 45° or more and 72° or less. That is, the second ink contains a second pigment such that the hue angle of the second diluent is within the above range. If the hue angle of the second diluent is outside the above range, the chroma in a predetermined color reproduction region cannot be increased.

[0023] The hue angle of the second diluent can be determined according to the same procedure as in the case of the hue angle of the first diluent described above. Also, let the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm of the absorption spectrum of the second diluent be "λ2 (nm)". Furthermore, the integrated value of the absorbance of the second diluent in the wavelength range of 560 nm to 580 nm can be calculated according to the same procedure as in the case of the integrated value of the absorbance of the first diluent described above.

[0024] The second pigment is preferably C.I. Pigment Orange 43. The maximum absorption wavelength (λ2) of the second diluent obtained using the second ink containing C.I. Pigment Orange 43 is likely to overlap with the maximum absorption wavelength on the short wavelength side of the first diluent. Therefore, by using C.I. Pigment Orange 43 as the second pigment, a predetermined color reproduction region can be further expanded.

[0025] [Color materials of inks other than the first ink and the second ink] As the color material to be contained in the inks other than the first ink and the second ink (other inks), it is preferable to use a pigment. The content (mass%) of the pigment in the other inks is preferably 0.5 mass% or more and 15.0 mass% or less, more preferably 0.5 mass% or more and 10.0 mass% or less, based on the total mass of the ink.

[0026] Specific examples of the pigment include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine; and the like.

[0027] [Dispersion method of pigment] Examples of the pigment dispersion method include resin-dispersed pigments using a resin as a dispersant, self-dispersed pigments in which a hydrophilic group is bonded to the particle surface of the pigment, and the like. In addition, resin-bonded pigments in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, microcapsule pigments in which the surface of the pigment particles is coated or encapsulated with a resin, and the like can be used. It is also possible to use pigments with different dispersion methods in combination.

[0028] As the resin (resin dispersant) for dispersing the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of an anionic group. As the resin dispersant, a resin as described below, particularly a water-soluble resin, can be used. The content (mass%) of the pigment in the ink is preferably 0.3 times or more and 10.0 times or less in terms of the mass ratio to the content (mass%) of the resin dispersant.

[0029] As the self-dispersing pigment, those in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded directly to the particle surface of the pigment or via another atomic group (-R-) can be used. The anionic group may be either in the acid form or the salt form, and in the case of the salt form, it may be in either a partially dissociated state or a completely dissociated state. When the anionic group is in the salt form, examples of the cation serving as the counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene groups and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; ether groups; and the like. Further, a group formed by combining these groups may also be used.

[0030] (Urethane resin) Preferably, the first ink and the second ink each contain a urethane resin. The weight average molecular weight of the urethane resin is preferably 10,000 or more, and more preferably 10,000 or more and 30,000 or less. Since the urethane resin having a weight average molecular weight of 10,000 or more has a large proportion of urethane bond sites with high surface energy, the dots of the first ink and the second ink are likely to wet each other and are likely to overlap uniformly. As a result, the overlap between the maximum absorption wavelength on the short wavelength side of the first diluent and the maximum absorption wavelength (λ2) of the second diluent, and the difference in absorbance at 560 nm to 580 nm, which is the wavelength range contributing to lightness, can be made larger, and a predetermined color reproduction region can be further expanded.

[0031] The urethane resin can be obtained, for example, by reacting a polyisocyanate and a polyol. Further, it may be a product obtained by further reacting a polyamine, a crosslinking agent, a chain extender, and the like.

[0032] [Polyisocyanate] Polyisocyanate is a compound having two or more isocyanate groups in its molecule. Examples of polyisocyanates include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; and the like.

[0033] Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0034] [Polyol] Polyol is a compound having two or more hydroxyl groups in its molecule. Examples of polyols include polyols having no acid groups such as polyether polyols, polyester polyols, and polycarbonate polyols; polyols having acid groups; and the like.

[0035] Examples of the polyether polyol include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycols; and the like. Examples of the polyester polyol include acid esters and the like. Examples of the polycarbonate polyol include alkane diol-based polycarbonate diols and the like. The number average molecular weight of the polyol having no acid group is preferably 450 or more and 4,000 or less.

[0036] Examples of the polyol having an acid group include polyols containing acid groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups in the molecule. In particular, in addition to the polyol having no acid group, it is preferable to use a urethane resin synthesized by further using a polyol having an acid group such as dimethylolpropionic acid or dimethylolbutanoic acid, and it is more preferable to use a water-soluble urethane resin. The acid group may be in the form of a salt. Examples of the cation constituting the salt include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. When the water-soluble urethane resin has an acid group, it usually becomes water-soluble by being neutralized with a neutralizing agent such as a hydroxide of an alkali metal (such as lithium, sodium, potassium) or aqueous ammonia.

[0037] [Polyamine] Examples of the polyamine include monoamines having a plurality of hydroxyl groups such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; trifunctional or higher polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide polyamine, and polyethylene polyimine; and the like. For convenience, a compound having a plurality of hydroxyl groups and one "amino group or imino group" is also listed as a "polyamine".

[0038] [Crosslinking agent, chain extender] The urethane resin may have units derived from a crosslinking agent or a chain extender. The crosslinking agent is usually used when synthesizing a prepolymer. The chain extender is usually used when chain-extending a prepolymer synthesized in advance. As the crosslinking agent and the chain extender, water, the aforementioned polyisocyanate, polyol, polyamine, etc. can be appropriately selected and used according to applications such as crosslinking and chain extension. As the chain extender, one that can crosslink the urethane resin can also be used.

[0039] (Aqueous medium) Each ink constituting the ink set of the present invention can contain water or an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent. Each ink is preferably an aqueous ink containing at least water as the aqueous medium. Deionized water (ion-exchanged water) is preferably used as the water. The content (mass%) of water in the ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inks for inkjet such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00 mass% or more and 50.00 mass% or less based on the total mass of the ink.

[0040] (Other additives) Each ink constituting the ink set of the present invention may contain, in addition to the above components, polyhydric alcohols such as trimethylolpropane and trimethylolethane; water-soluble organic compounds that are solid at room temperature such as urea and its derivatives, if necessary. Further, each ink constituting the ink set of the present invention may contain various additives such as a surfactant, a pH adjuster, a rust inhibitor, a preservative, a fungicide, an antioxidant, a reduction inhibitor, an evaporation accelerator, a chelating agent, and a water-soluble resin, if necessary.

[0041] The surface tension of the ink can be adjusted, for example, using a surfactant. Examples of surfactants include hydrocarbon surfactants such as polyoxyethylene alkyl ethers and ethylene oxide adducts of acetylene glycol; fluorosurfactants such as perfluoroalkyl ethylene oxide adducts; silicone surfactants such as polyether-modified siloxane compounds; and the like.

[0042] (Physical properties of the ink) The cumulative 50% particle diameter D2 (nm) on a volume basis of the second pigment and the cumulative 50% particle diameter D1 (nm) of the volume distribution of the first pigment preferably satisfy the relationship of the following formula (1). |D2 - D1| ≦ 40 ···(1)

[0043] When the cumulative 50% particle diameter D1 of the volume distribution of the first pigment is large, the integrated value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm becomes large. Also, when the cumulative 50% particle diameter D2 of the volume distribution of the second pigment is small, the integrated value of the absorbance of the second diluent in the wavelength range of 560 nm to 580 nm becomes small. Therefore, by D2 and D2 satisfying the relationship of the above formula (1), a predetermined color reproduction region can be further expanded. On the other hand, when the value of "|D2 - D1|" exceeds 40, one pigment with a large particle size may conceal the other pigment, and the effect of expanding the predetermined color reproduction region may easily decrease.

[0044] The cumulative 50% particle diameter D1 (nm) on a volume basis of the first pigment and the cumulative 50% particle diameter D2 (nm) of the volume distribution of the second pigment are each preferably 30 nm or more and 180 nm or less, and more preferably 50 nm or more and 160 nm or less. When D1 and D2 are each outside the above ranges, one pigment with a large particle size may conceal the other pigment, and the effect of expanding the predetermined color reproduction region may easily decrease.

[0045] Each ink constituting the ink set of the present invention is an ink applicable to an inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. When the ink is an aqueous ink, the static surface tension of the first ink at 25°C measured by the plate method is preferably 25.0 mN or more. More preferably, it is 25.0 mN / m or more and 60.0 mN / m or less, and even more preferably, it is 30.0 mN / m or more and 45.0 mN / m or less. Further, the static surface tension of the second ink at 25°C is preferably 25.0 mN or more, more preferably 25.0 mN / m or more and 60.0 mN / m or less, and even more preferably 30.0 mN / m or more and 45.0 mN / m or less. When the static surface tension of the ink is less than 25 m.0 N / m, the penetration rate into the recording medium becomes high, and the first ink and the second ink may be less likely to mix. The absolute value of the difference between the static surface tension of the first ink and the static surface tension of the second ink is preferably 0.1 mN / m or more. When the absolute value of the difference in static surface tension is less than 0.1 mN / m, the driving force for mixing the first ink and the second ink becomes small, and the first ink and the second ink may be less likely to mix. When the first ink and the second ink are less likely to mix, it becomes difficult to form secondary colors. As a result, the overlap between the maximum absorption wavelength on the short wavelength side of the first diluent and the maximum absorption wavelength (λ2) of the second diluent, and the difference from the absorbance at 560 nm to 580 nm, which is the wavelength range contributing to lightness, become large. For this reason, the effect of expanding a predetermined color reproduction region may be slightly reduced.

[0046] When the ink is an aqueous ink, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, and more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. Further, the pH of the ink at 25°C is preferably 7.0 or more and 10.0 or less.

[0047] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting each ink constituting the ink set of the present invention described above from a recording head of an inkjet system. Examples of the method of ejecting the ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is preferable to adopt a method of applying thermal energy to the ink to eject the ink. Except for using each ink constituting the ink set of the present invention, the steps of the inkjet recording method and the configuration of the inkjet recording apparatus may be those known in the art.

[0048] FIG. 3 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention. (a) is a perspective view of a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40 and is configured such that an ink cartridge 42 can be set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by the conveying means (not shown).

Examples

[0049] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Regarding the amounts of components, “parts” and “%” are based on mass unless otherwise specified.

[0050] <Preparation of Quinacridone Solid Solution> (Quinacridone Solid Solution) C.I. Pigment Red 122 (PR122), C.I. Pigment Violet 19 (PV19), and C.I. Pigment Red 202 (PR202) were prepared. Then, the prepared pigments were combined at the ratios (%) shown in Table 1 to form a press cake, which was milled and then treated with an organic solvent according to a conventional method to be pigmented, and quinacridone solid solutions 1 to 8 were obtained.

[0051] TIFF2025102728000001.tif76170

[0052] <Method for Measuring Cumulative 50% Particle Size of Pigment Volume Distribution> The pigment dispersion was diluted with pure water to prepare a sample for measurement. Then, a particle size analyzer by the dynamic light scattering method (trade name "Microtrac WAVE", manufactured by Microtrac·BEL) was used to measure the cumulative 50% particle size (D (nm)) based on volume of the pigment in the sample. The measurement conditions were SetZero: 30 seconds, number of measurements: 3 times, measurement time: 120 seconds, shape: true spherical, refractive index: 1.59.

[0053] <Preparation of Pigment Dispersion> (Pigment Dispersion 1) 12.0 parts of quinacridone solid solution 1, 24.0 parts of an aqueous solution of a resin dispersant, and 64.0 parts of ion-exchanged water were mixed to obtain a mixture. As the aqueous solution of the resin dispersant, an aqueous solution having a resin (solid content) content of 20.0% obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 250 mgKOH / g and a weight average molecular weight of 8,000 with a 10.0% aqueous sodium hydroxide solution was used. The obtained mixture was charged into a batch vertical sand mill (manufactured by IMAX), filled with 85 parts of 0.3 mm zirconia beads, and subjected to a dispersion treatment for 3 hours while cooling with water. After removing non-dispersed matter containing coarse particles by centrifugation, it was pressure-filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to obtain Pigment Dispersion 1 having a pigment content (solid content) of 10.0%. The cumulative 50% particle size of the pigment volume distribution in the obtained Pigment Dispersion 1 was 100 nm.

[0054] (Pigment Dispersion 2 to 7) Except for changing the time of the dispersion treatment, pigment dispersions 2 to 7 with a pigment content (solid content) of 10.0% were obtained in the same manner as in the case of the aforementioned pigment dispersion 1. Specifically, the time of the dispersion treatment was set to be more than 3 hours, and pigment dispersions 2 to 4 with a cumulative 50% particle size of the volume distribution of the pigment being 75 nm, 90 nm, and 95 nm, respectively, were obtained. Also, the time of the dispersion treatment was set to be less than 3 hours, and pigment dispersions 5 to 7 with a cumulative 50% particle size of the volume distribution of the pigment being 115 nm, 120 nm, and 125 nm, respectively, were obtained.

[0055] (Pigment dispersion 8) Except for using quinacridone solid solution 2 instead of quinacridone solid solution 1, a pigment dispersion 8 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion 8 was 100 nm.

[0056] (Pigment dispersion 9) Except for using quinacridone solid solution 3 instead of quinacridone solid solution 1, a pigment dispersion 9 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion 9 was 100 nm.

[0057] (Pigment dispersion 10) Except for using quinacridone solid solution 4 instead of quinacridone solid solution 1, a pigment dispersion 10 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion 10 was 100 nm.

[0058] (Pigment dispersion 11) Except for using quinacridone solid solution 5 instead of quinacridone solid solution 1, a pigment dispersion 11 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion 11 was 100 nm.

[0059] (Pigment dispersion liquid 12) A pigment dispersion liquid 12 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that the dispersion treatment time was less than 3 hours. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 12 was 125 nm.

[0060] (Pigment dispersion liquid 13) A pigment dispersion liquid 13 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that quinacridone solid solution 7 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 13 was 100 nm.

[0061] (Pigment dispersion liquid 14) A pigment dispersion liquid 14 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that quinacridone solid solution 6 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 14 was 100 nm.

[0062] (Pigment dispersion liquid 15) A pigment dispersion liquid 15 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that C.I. Pigment Red 122 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 15 was 100 nm.

[0063] (Pigment dispersion liquid 16) A pigment dispersion liquid 16 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that C.I. Pigment Violet 19 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 16 was 100 nm.

[0064] (Pigment dispersion liquid 17) A pigment dispersion liquid 17 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that quinacridone solid solution 8 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 17 was 100 nm.

[0065] (Pigment dispersion liquid 18) A pigment dispersion liquid 18 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that C.I. Pigment Orange 43 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 18 was 135 nm.

[0066] (Pigment dispersion liquids 19 - 23) Pigment dispersion liquids 19 - 23 with a pigment content (solid content) of 10.0% were obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 18, except that the dispersion treatment time was changed. Specifically, the dispersion treatment time was less than 3 hours, and pigment dispersion liquids 19 and 20 with cumulative 50% particle sizes of the volume distribution of the pigment of 160 nm and 165 nm, respectively, were obtained. Also, the dispersion treatment time was more than 3 hours, and pigment dispersion liquids 21 - 23 with cumulative 50% particle sizes of the volume distribution of the pigment of 80 nm, 35 nm, and 40 nm, respectively, were obtained.

[0067] (Pigment dispersion liquid 24) A pigment dispersion liquid 24 with a pigment content (solid content) of 10.0% was obtained in the same manner as in the case of the aforementioned pigment dispersion liquid 1, except that C.I. Pigment Orange 71 was used instead of quinacridone solid solution 1. The cumulative 50% particle size of the volume distribution of the pigment in the obtained pigment dispersion liquid 24 was 135 nm.

[0068] <Manufacture of urethane resin> Into a four-necked flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a cooling tube, 39.3 g of polypropylene glycol, 44.5 g of isophorone diisocyanate, and 0.007 g of dibutyltin dilaurate were added. The reaction was carried out at a temperature of 100 °C for 5 hours under a nitrogen atmosphere. After cooling to a temperature of 65 °C or lower, 13.2 g of dimethylolpropionic acid, 3.0 g of neopentyl glycol, and 150.0 g of methyl ethyl ketone were added, and the reaction was carried out at a temperature of 80 °C for a predetermined time. After cooling to a temperature of 40 °C, 20.0 g of methanol was added to stop the reaction. An appropriate amount of ion-exchanged water was added, and while stirring with a homomixer, an aqueous potassium hydroxide solution in an amount necessary to neutralize the resin was added. Then, methyl ethyl ketone and unreacted methanol were distilled off under heating and reduced pressure to obtain aqueous solutions of water-soluble urethane resins 1 to 4 having a resin (solid content) content of 10.0% respectively. The weight-average molecular weights in terms of polystyrene of the obtained urethane resins 1 to 4 are shown in Table 2. The weight-average molecular weight of the urethane resin was measured by gel permeation chromatography. The weight-average molecular weight of the urethane resin was controlled by appropriately adjusting the time when reacting at a temperature of 80 °C.

[0069] TIFF2025102728000002.tif42170

[0070] <Preparation of Ink> The components shown in the middle rows of Tables 3-1 to 3-3 (unit: %) were mixed and stirred well, and then pressure filtered through a polypropylene filter with a pore size of 1.0 μm (manufactured by Pall) to prepare the first ink. Also, the components shown in the middle rows of Tables 4-1 and 4-2 (unit: %) were mixed and stirred well, and then pressure filtered through a polypropylene filter with a pore size of 1.0 μm (manufactured by Pall) to prepare the second ink. In Tables 3-1 to 3-3, 4-1, and 4-2, "Acetylenol E100" is the trade name of a nonionic surfactant (manufactured by Kawaken Fine Chemicals). The characteristics of each obtained ink are shown in the lower rows of Tables 3-1 to 3-3, 4-1, and 4-2. Note that for Inks 1-20, 1-25, and 1-26, a mixture of Pigment Dispersions 15 and 16 was used. For Ink 1-20, they were mixed so that PR122 was 80% and PV19 was 20% based on the total pigment mass. For Ink 1-25, they were mixed so that PR122 was 90% and PV19 was 10% based on the total pigment mass. For Ink 1-26, they were mixed so that PR122 was 40% and PV19 was 60% based on the total pigment mass.

[0071] TIFF2025102728000003.tif149170

[0072] TIFF2025102728000004.tif149170

[0073] TIFF2025102728000005.tif149170

[0074] TIFF2025102728000006.tif149170

[0075] TIFF2025102728000007.tif150170

[0076] <Evaluation> Each ink (the first ink and the second ink) of the combinations shown in the evaluation conditions of Table 5 was filled into an ink cartridge, and the inkjet recording apparatus equipped with a recording head that discharges the ink by thermal energy was set. As the inkjet recording apparatus, a modified machine of the product name "PIXUS PRO-10S" (manufactured by Canon) was used. The first ink was set in the position of the magenta ink, and the second ink was set in the position of the red ink. In this example, the resolution was 600 dpi × 600 dpi, and the recording duty of the solid image recorded under the condition of applying 8 ink droplets of 4.0 ng per droplet to a unit area of 1 / 600 inch × 1 / 600 inch was defined as 100%. In the present invention, according to the evaluation criteria of each item shown below, "AA" and "A" were set as acceptable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Table 5. Further, the absorption spectra of the first ink 1 and the second ink 1 constituting the ink set of Example 1 are shown in FIG. 2.

[0077] (Chroma in the orange to high-brightness red region) The solid images of the secondary colors (a total of 361 images) obtained by overlapping the recording duties of the first ink and the second ink, each changed in 5% increments from 10% to 100%, were recorded on a recording medium under the conditions of a temperature of 23°C and a relative humidity of 55%. As the recording medium, the product name "Canon Photo Paper, Glossy Gold GL-101" (manufactured by Canon) was used. The recorded solid images were dried for one day in an environment of a temperature of 23°C and a relative humidity of 55%. Next, using a spectrophotometer (product name "Spectorolino", manufactured by Gretag Macbeth), the hue angle measured under the conditions of a light source: D50 and a field of view: 2° was 55°, and the L * The solid image of the secondary color closest to 70 was selected. Since the hue angle of 55° is a representative angle that can express the orange to high-brightness red region with good sensitivity, the hue angle of 55° was selected. Also, the "closest secondary color" was defined as the secondary color for which the sum of "(hue angle of the solid image of the secondary color) / 55°" and "(L * of the solid image of the secondary color) / 70" was minimized. The chroma C * of the solid image selected using the above spectrophotometer was measured, and the chroma in the orange to high-brightness red region was evaluated according to the evaluation criteria shown below. AA: Chroma C * was 90 or more. A: Chroma C * was 80 or more and less than 90. C: Chroma C * was less than 80.

[0078] (Chroma of the shadow red area) The solid images (total 361 images) of secondary colors obtained by overlapping the recording duties of the first ink and the second ink while changing them in 5% increments from 10% to 100% were recorded on a recording medium under the conditions of a temperature of 23°C and a relative humidity of 55%. As the recording medium, the product named "Canon Photo Paper, Glossy Gold GL-101" (manufactured by Canon) was used. The recorded solid images were dried for one day in an environment of a temperature of 23°C and a relative humidity of 55%. Next, using a spectrophotometer (product name "Spectorolino", manufactured by Gretag Macbeth), the hue angle measured under the conditions of a light source: D50 and a field of view: 2° was 35°, and L * The solid image of the secondary color that was closest to 45 for L was selected. Since the hue angle of 35° is a representative angle that can express the shadow red area with good sensitivity, the hue angle of 35° was selected. Also, the "closest secondary color" was defined as the secondary color for which the sum of "(hue angle of the solid image of the secondary color) / 35°" and "(L * of the solid image of the secondary color)) / 45" was minimized. The chroma C * of the solid image selected using the above spectrophotometer was measured, and the chroma of the shadow red area was evaluated according to the evaluation criteria shown below. AA: Chroma C * was 75 or more. A: Chroma C * was 70 or more and less than 75. C: Chroma C * was less than 70.

[0079] TIFF2025102728000008.tif255165

Claims

1. An ink set having a combination of a first ink and a second ink, wherein the first ink contains a first pigment and the second ink contains a second pigment, the hue angle of a first diluent obtained by diluting the first ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 330° or more and 345° or less, the hue angle of a second diluent obtained by diluting the second ink with water so that the absorbance at the maximum absorption wavelength in the wavelength range of 380 nm to 780 nm is 1 is 40° or more and 80° or less, the absolute value of the difference between the shorter-wavelength maximum absorption wavelength λ1 (nm) of the two maximum absorption wavelengths of the first diluent in the wavelength range of 380 nm to 780 nm and the maximum absorption wavelength λ2 (nm) of the second diluent in the wavelength range of 380 nm to 780 nm is 0 or more and 10 or less, An ink set, characterized in that the absolute value of the difference between the integral value of the absorbance of the first diluent in the wavelength range of 560 nm to 580 nm and the integral value of the absorbance of the second diluent in the wavelength range of 560 nm to 580 nm is 11.0 or more.

2. The ink set according to claim 1, wherein the hue angle of the second diluent is 45° or more and 72° or less.

3. The ink set according to claim 1, wherein the cumulative 50% particle diameter D2 (nm) of the second pigment based on volume and the cumulative 50% particle diameter D1 (nm) of the volume distribution of the first pigment satisfy the relationship of the following formula (1). |D2 - D1| ≤ 40... (1)

4. The ink set according to claim 1, wherein the static surface tension of the first ink is 25.0 mN / m or more, and the static surface tension of the second ink is 25.0 mN / m or more.

5. The ink set according to claim 1, wherein the absolute value of the difference between the static surface tension (mN / m) of the first ink and the static surface tension (mN / m) of the second ink is 0.1 mN / m or more.

6. The ink set according to claim 1, wherein the first ink and the second ink each contain a urethane resin having a weight average molecular weight of 10,000 or more.

7. The ink set according to claim 1, wherein the second pigment is C.I. Pigment Orange 43.

8. The ink set according to claim 1, wherein the first pigment is a solid solution of C.I. Pigment Red 122 and C.I. Pigment Violet 19.

9. In the solid solution, the content (mass %) of the C.I. Pigment Red 122 is 1.5 times or more and 9.0 times or less in terms of mass ratio with respect to the content (mass %) of the C.I. Pigment Violet 19. The ink set according to claim 8.

10. The ink set according to any one of claims 1 to 9, wherein both the first ink and the second ink are aqueous inks.

11. The ink set according to any one of claims 1 to 9, which is for an inkjet.

12. An inkjet recording method of ejecting ink from a recording head of an inkjet system to record an image on a recording medium, wherein the ink is each ink constituting the ink set according to claim 11. An inkjet recording method characterized by this.

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