JP4301163B2 - Aqueous ink set for inkjet recording and inkjet recording method - Google Patents

Description

  The present invention relates to a water-based ink set for ink-jet recording suitable for reducing graininess in a low-density print area and expanding a color reproduction range, and an ink-jet recording method using the water-based ink set for ink-jet recording.

  When a color image is expressed by an inkjet recording method, generally, an ink set composed of three colors of yellow ink (Y), magenta ink (M), and cyan ink (C), or further black ink (K) An ink set composed of four color inks with the above added is used.

  In the ink jet recording method, generally, the gradation of an image is controlled by the density of dots formed on a recording material by ejecting ink. However, when the gradation is controlled by such a method, the dot density is reduced in the low density printed portion, so that individual dots are relatively easy to be visually recognized, and as a result, the image has a graininess. Occurs.

  For this, with respect to cyan ink, two or more inks having different dye concentrations are used, and the types of these dyes are made different. For dark ink, a dye that is inferior in light resistance but excellent in sharpness is used. It has been proposed to select a dye which is inferior in sharpness but excellent in light resistance as a light-colored ink (Patent Document 1), and a similar proposal has been made for magenta ink (Patent Document). 2). However, according to these methods, although the graininess is improved, there is a problem that the color reproduction range cannot be expanded.

  In general, in an ink set composed of three colors of yellow ink, magenta ink, and cyan ink, or an ink set composed of four colors of ink including black ink, the green color is cyan ink. In this way, when using two types of ink to express the green color, there is a problem that it is difficult to obtain sharp print quality and vivid color development due to the landing error of overstrike. .

JP-A-1-95093 JP-A-2-127482

  The present invention has been made to solve the above-described problems.In the ink jet recording method, (i) the color reproduction range in the green direction and the cyan direction in the high density print portion is not reduced, and an ink set is formed. The purpose is to reduce the graininess in the low-density print area including cyan, while minimizing the number of inks that make up, and (ii) to expand the color reproduction range in the green direction and improve the clarity. .

Inventors of the present invention have a color index of lightness (L ^* ), hue angle (h) and saturation (C ^* ) according to the L ^* a ^* b ^* color system of the ink constituting the water base ink set for ink jet recording. As a result of earnest research under the hypothesis that there is a close relationship between the reduction of graininess and the expansion of the color reproduction range in the low-density print area of an image, cyan ink is used in an aqueous ink set for inkjet recording with cyan ink. As described above, by using a light cyan ink having a lightness index (L ^* ) of a specific value or more and using a green ink instead of the normal cyan ink used in the conventional ink set, the above-mentioned purpose (i) And (ii) have been found, and the present invention has been completed.

In other words, the present invention includes a cyan ink and a green ink, and the inkjet recording does not have a normal cyan ink having a lightness index (L ^* ) of L ^* <60 in the L ^* a ^* b ^* color system. A water-based ink set for inkjet recording, wherein the cyan ink is a light cyan ink having a lightness index (L ^* ) of L ^* a ^* b ^* color system of L ^* ≧ 60. provide.

  The present invention also provides an ink jet recording method using the above-described aqueous ink set for ink jet recording.

  Since the water-based ink set for ink jet recording of the present invention includes a light cyan ink having a low colorant concentration as a cyan ink, by performing ink jet recording using this ink set, the granularity of a low density print portion containing cyan is obtained. The feeling can be reduced. In addition, since the ink set of the present invention includes the green ink together with the light cyan ink, the color reproduction range in the cyan direction in the high density print portion is not reduced, and the color reproduction range in the green direction is remarkably enlarged. Improves color clarity. The improvement in the clearness of the green color is because the green color can be expressed by the green ink alone, regardless of the color mixture of the cyan ink and the yellow ink.

  Further, according to the ink set of the present invention, the graininess of the low density print portion including cyan is reduced, the color reproduction range in the cyan high density print portion is prevented from being reduced, and the color reproduction range in the green direction is remarkable. The effect of enlarging and improving the clarity of the green color can be achieved with two types of inks, light cyan ink and green ink.

  Therefore, according to the ink set of the present invention, color reproducibility and print quality of a color image formed by the ink jet recording method can be improved.

  Further, the green color is generally used for text printing, and according to the present invention, this green text printing is printed with a single green ink without using two types of ink overprinting. Therefore, it is possible to realize sharp print quality with reduced feathering and vivid color development.

  Hereinafter, the present invention will be described in detail.

In the present invention, the lightness index (L ^* ), hue angle (h), and saturation (C ^* ) are in the L ^* a ^* b ^* color system standardized by the International Commission on Illumination (CIE) in 1976. Is based. The Japanese Industrial Standard (JIS) is defined in JIS Z 8729.

In the present invention, the lightness index (L ^* ) is a value measured by using a spectrocolorimeter or the like on a glossy paper obtained by printing each ink with 1200 × 1200 dpi, and the hue angle (h) And saturation (C ^* ), for the same solid print, first, the perceptual chromaticity index (a ^* , b ^* ) is measured using a spectrocolorimeter or the like, and the measured a ^* and b ^* are measured. It is a value calculated using the following formulas (1) and (2).

The “glossy paper” used in the measurement of L ^* , a ^* and b ^* refers to a paper provided with a coat layer capable of obtaining surface smoothness on a base paper (base paper). Specifically, Image (registered trademark) glossy finish (Fuji Photo Film Co., Ltd.), inkjet printer paper (glossy paper) (Kokuyo Co., Ltd.), thick glossy paper (Kodak Co., Ltd.), and the like. “Resolution 1200 × 1200 dpi solid print” means printing so that an area of resolution 1200 × 1200 dpi is covered 100%. Examples of the ink jet printer that can be used for printing include a digital multifunction device MFC-5200J equipped with an ink jet printer manufactured by Brother Industries, Ltd., and Spectrolino manufactured by Gretag Macbeth can be used as a spectrocolorimeter. The color measurement conditions were a light source: D ₆₅ and a viewing angle: 2 °.

The water-based ink set for ink jet recording according to the present invention includes at least a cyan ink and a green ink, and the cyan ink is a light cyan ink with L ^* ≧ 60. Therefore, normal cyan ink with L ^* <60 does not constitute the ink set of the present invention. If a normal cyan ink of L ^* <60 is used as the cyan ink, it is not preferable because the graininess is noticeable in the low density print portion including cyan.

L ^* of the light cyan ink constituting the ink set of the present invention is preferably 60 ≦ L ^* ≦ 85. If L ^{* of} light cyan ink exceeds 85, it is difficult to reproduce the original cyan color, which is not preferable.

  Further, h of light cyan ink is preferably adjusted so that 215 ° ≦ h ≦ 255 °. If h is not within this range, it will be difficult to sufficiently express cyan.

Furthermore, it is preferable to adjust C ^* of the light cyan ink so that 40 ≦ C ^* ≦ 70. By setting C ^* within this range, it becomes possible to reproduce a vivid cyan color.

On the other hand, the green ink constituting the ink set of the present invention preferably has L ^* ≦ 60. If the L ^{* of the} green ink exceeds 60, it is difficult to reproduce the original green color, which is not preferable. A more preferable range of L ^* of the green ink is 35 ≦ L ^* ≦ 60. By setting L ^* of the green ink within this range, it is possible to reproduce green and cyan colors with sufficient density.

  The h of the green ink is preferably adjusted so that 175 ° ≦ h ≦ 215 °. By adjusting h within this range, the green color can be sufficiently expressed.

Further, it is preferable to adjust the C ^* of the green ink so that 60 ≦ C ^* ≦ 80. By adjusting C ^* within this range, it becomes possible to reproduce a vivid green color.

The ink set of the present invention can include any ink in addition to the light cyan ink and green ink described above, and can include, for example, a blue ink. This is preferable because the color reproduction range can be remarkably expanded in the blue direction and the sharpness of the blue color can be improved. The blue ink preferably has L ^* ≦ 45. If the blue ink has L ^* > 45, it is difficult to reproduce the original blue color. A more preferable range of L ^* of the blue ink is 35 ≦ L ^* ≦ 45. By setting L ^* of the blue ink within this range, it is possible to reproduce a blue color having a sufficient density.

  The h of the blue ink is preferably adjusted so that 270 ° ≦ h ≦ 285 °. By adjusting h within this range, a blue color can be sufficiently expressed.

Further, the C ^* of the blue ink is preferably adjusted so as to satisfy 70 ≦ C ^* ≦ 80. By adjusting C ^* within this range, it is possible to reproduce a vivid blue color.

  In addition, the ink set of the present invention can include yellow ink and / or magenta ink. You may provide black ink as needed. In addition to the light cyan ink and the green ink, a yellow ink, a magenta ink, and, if necessary, a black ink can be provided to reproduce a full color image.

When magenta ink is provided in the ink set of the present invention, normal magenta ink used in a known ink set can be used as the magenta ink. However, instead of normal magenta ink, L ^* ≧ 50 It is preferable to use light magenta ink and further use red ink. In this case, normal magenta ink with L ^* <50 is unnecessary. By using a light magenta ink of L ^* ≧ 50 as the magenta ink, it is possible to reduce the graininess in the low density print portion including the magenta color. The preferred L ^* of light magenta ink is 50 ≦ L ^* ≦ 65. If L ^{* of} light magenta ink exceeds 65, it is difficult to reproduce the original magenta color, which is not preferable.

  Further, h of light magenta ink is preferably adjusted so that 335 ° ≦ h ≦ 360 ° or 0 ° ≦ h ≦ 5 °. If h is not within this range, it becomes difficult to sufficiently express magenta color.

Further, it is preferable to adjust C ^{* of} light magenta ink so that 80 ≦ C ^* ≦ 90. By setting C ^* within this range, it becomes possible to reproduce a vivid magenta color.

The red ink used with the light magenta ink preferably has L ^* ≦ 50. If the red ink has L ^* > 50, it is difficult to obtain a sufficient color reproduction range in the red direction. A more preferable range for L ^* of the red ink is 25 ≦ L ^* ≦ 50. By setting the L ^* of the red ink within this range, it is possible to reproduce red and magenta colors with sufficient density.

  The h of the red ink is preferably adjusted so as to satisfy 20 ° ≦ h ≦ 35 °. By adjusting h within this range, the red color can be sufficiently expressed.

Further, the C ^* of the red ink is preferably adjusted so that 80 ≦ C ^* ≦ 90. By making C ^* within this range, vivid red color can be reproduced.

  When the ink set of the present invention includes yellow ink and black ink, those used in known ink sets can be used. For example, as yellow ink, normal yellow ink having h of 70 to 140 ° can be used.

Each ink constituting the ink set of the present invention contains a colorant, water, and a water-soluble organic solvent so as to have the above-mentioned predetermined L ^* , h, and C ^* , respectively.

  Examples of the colorant contained in each ink include water-soluble dyes and / or pigments, and the desired ink color is adjusted by using these in appropriate combinations.

  That is, as the water-soluble dye, water-soluble dyes represented by direct dyes, acid dyes, basic dyes, reactive dyes and the like are used. The structure of the water-soluble dye includes azo dye, metal complex dye, naphthol dye, anthraquinone dye, indigo dye, carbonium dye, quinoneimine dye, xanthene dye, aniline dye, quinoline dye, nitro dye, nitroso dye, benzoquinone dye, Naphthoquinone dyes, phthalocyanine dyes, metal phthalocyanine dyes and the like are preferable. In particular, water-soluble dyes that are suitable as inks for ink jet recording systems and that satisfy the required performance such as sharpness, water-solubility, stability, light resistance, and the like include C.I. I. Direct yellow 12, 24, 26, 27, 28, 33, 39, 58, 86, 98, 100, 132 and 142, C.I. I. Direct Red 4, 17, 28, 37, 63, 75, 79, 80, 81, 83 and 254, C.I. I. Direct violet 47, 48, 51, 90 and 94, C.I. I. Direct Blue 1, 6, 8, 15, 22, 25, 71, 76, 80, 86, 87, 90, 106, 108, 123, 163, 165, 199 and 226, C.I. I. Direct dyes such as direct green 1,26, 28, 59, 80 and 85; C.I. I. Acid Yellow 3, 11, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 71 and 72, C.I. I. Acid Red 1, 6, 8, 18, 32, 35, 37, 42, 52, 85, 88, 115, 133, 134, 154, 186, 249, 289 and 407, C.I. I. Acid Violet 10, 34, 49 and 75, C.I. I. Acid Blue 9, 22, 29, 40, 59, 62, 93, 102, 104, 112, 113, 117, 120, 167, 175, 183, 229 and 234, C.I. I. Acid dyes such as Acid Green 3, 5, 9, 12, 15, 16, 19, 25, 27, 28, 36, 40, 41, 43, 44, 56, 73, 81, 84, 104, 108 and 109; C. I. Basic Yellow 40, C.I. I. Basic Red 9, 12, and 13, C.I. I. Basic Violet 7, 14, and 27, C.I. I. Basic Blue 1, 3, 5, 7, 9, 24, 25, 26, 28 and 29, C.I. I. Basic dyes such as basic green 1 and 4; C.I. I. Reactive Yellow 2, C.I. I. Reactive Red 4, 23, 24, 31 and 56, C.I. I. Reactive Blue 7, 13, and 49, C.I. I. Reactive dyes such as Reactive Green 5, 6, 7, 8, 12, 15, 19 and 21 are listed.

  Examples of the pigment include C.I. I. Pigment Yellow 1, 2, 3, 13, 16, 74, 83, 93, 128, 134 and 144, C.I. I. Pigment Red 5, 7, 12, 23, 48 (Mn), 57 (Ca), 112, 122, 144, 170, 177, 221, 254 and 264, C.I. I. Pigment violet 19 and 48 (Ca), C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 5, 15: 6, 16, 17: 1, 22, 27, 28, 29, 36 and 60, C.I. I. And CI Pigment Green 7.

  Examples of the colorant for the black ink include water-soluble dyes and / or pigments, which may be used in appropriate combination. Examples of water-soluble dyes include C.I. I. Direct dyes such as direct black 17, 19, 32, 51, 71, 108, 146, 154 and 168; I. Acid dyes such as Acid Black 2, 7, 24, 26, 31, 52, 63, 112 and 118; I. Basic dyes such as basic black 2; C.I. I. Food black 1 and 2 etc. are mentioned. As the pigment, for example, carbon black such as MA8, MA100 (manufactured by Mitsubishi Kasei Co., Ltd.), color black FW200 (manufactured by Degussa) and the like can be used. As the carbon black, a self-dispersing type that can be dispersed in water without using a dispersant may be used. The self-dispersing carbon black can be obtained by treating the surface with at least one hydrophilic group such as carbonyl group, carboxyl group, hydroxyl group or sulfone group or a salt thereof. Specific examples of this surface treatment include the methods described in JP-A-8-3498 and JP-T 2000-513396. Further, as the self-dispersing black pigment, for example, commercially available products such as CAB-O-JET (registered trademark) 200 and 300 (manufactured by Cabot), Bonjet (registered trademark) CW1 (manufactured by Orient Chemical Industry Co., Ltd.) and the like are used. It is also possible to do.

  The content of the water-soluble dye in each ink varies depending on the desired print density and color, but if it is too small, the color on the recording material is insufficient, and if it is too large, the nozzles of the inkjet head are likely to be clogged. Therefore, it is preferably 0.1 to 15% by weight, more preferably 0.3 to 10% by weight, particularly preferably 0.5 to 5.0% by weight based on the total amount of each ink.

  The pigment content in each ink varies depending on the desired print density and color. However, if the amount is too small, the color on the recording material is insufficient, and if it is too large, the nozzles of the inkjet head are likely to be clogged. Preferably, it is in the range of 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of each ink.

  On the other hand, the water used for each ink is preferably deionized water. The water content is determined according to the type of water-soluble organic solvent, the ink composition, and the desired ink characteristics. However, if the amount is too small, the viscosity of the ink will increase, making it difficult to eject from the nozzle of the inkjet head. If the amount is too large, the evaporation of water causes colorant precipitation, aggregation and the like, and the nozzles of the inkjet head are likely to be clogged. Therefore, it is preferably 10 to 95% by weight, more preferably 10 to 95% by weight based on the total weight of each ink. It is in the range of 70% by weight, particularly preferably 20 to 70% by weight.

The water-soluble organic solvent used in each ink is roughly classified into a wetting agent and a penetrating agent.
A wetting agent is added to the ink to prevent clogging of the nozzles of the inkjet head. Specific examples of the wetting agent include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, and the like. Of water-soluble glycol. If the content of the water-soluble organic solvent as the wetting agent is too small, it is insufficient to prevent clogging of the nozzles of the ink jet head, and if it is too large, the viscosity of the ink increases and ejection becomes difficult. The range is preferably 5 to 50% by weight, more preferably 5 to 40% by weight, and particularly preferably 5 to 35% by weight based on the total weight of each ink.

  The penetrant is added to the ink so that the ink quickly penetrates into the paper when printed. Specific examples of the penetrant include glycol ethers typified by ethylene glycol and propylene glycol alkyl ethers. Specific examples of the ethylene glycol alkyl ether include ethylene glycol methyl ether, ethylene glycol-n-ethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-n-butyl ether, ethylene glycol isobutyl ether, diethylene glycol methyl ether, diethylene glycol- n-ethyl ether, diethylene glycol-n-propyl ether, diethylene glycol-n-butyl ether, diethylene glycol isobutyl ether, triethylene glycol methyl ether, triethylene glycol-n-ethyl ether, triethylene glycol-n-propyl ether, triethylene glycol- n-butyl ether, triethylene glycol isobutyl ether, etc. Specific examples of the propylene glycol alkyl ether include propylene glycol methyl ether, propylene glycol-n-ethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene Glycol-n-ethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol-n-ethyl ether, tripropylene glycol-n-propyl ether, tripropylene Examples include glycol-n-butyl ether.

  As the content of the water-soluble organic solvent as the penetrating agent, if the amount is too small, the penetrability is insufficient.If the amount is too large, bleeding such as feathering is likely to occur due to excessive penetrability. It is 0.1 to 10 weight% with respect to a weight, More preferably, it is the range of 0.1 to 5 weight%.

  In addition to the above-mentioned wetting agent and penetrating agent, each ink constituting the ink set of the present invention prevents the ink from drying at the tip of the ink jet head, increases the print density, and gives a vivid color. Water-soluble organic solvent. Examples of such water-soluble organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide, dimethylacetamide Amides such as acetone, diacetone alcohol, etc .; ethers such as tetrahydrofuran, dioxane; glycerin; 2-pyrrolidone, N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone, etc. Can be mentioned.

  Each ink constituting the ink set of the present invention may further include a conventionally known surfactant; a viscosity adjusting agent such as polyvinyl alcohol, cellulose, or a water-soluble resin; a surface tension adjusting agent; Can be added.

  The inkjet recording method of the present invention performs inkjet recording using the ink set of the present invention. There is no particular limitation on the ink jet recording method, and examples thereof include an electrostatic attraction method, a method using a piezoelectric element, and a thermal method.

  Below, based on an Example and a comparative example, this invention is demonstrated concretely. In this example, “%” represents “% by weight” unless otherwise specified.

Examples 1-5, Comparative Examples 1-3
(1) Preparation of ink A light cyan ink 1 having the ink composition shown in Table 1 was prepared as follows.

  First, 69 parts by weight of water, 27 parts by weight of glycerin, and 2 parts by weight of dipropylene glycol-n-propyl ether were mixed to prepare 98 parts by weight of an ink solvent. Next, 2 parts by weight of a cyan water-soluble dye (CI Direct Blue 199) was added to 98 parts by weight of the ink solvent being stirred, and the mixture was further stirred for 30 minutes and filtered through a membrane filter having a pore size of 1 μm. Obtained.

  A light cyan ink 2, 3, normal cyan ink, green ink 1, 2, and yellow ink were prepared by repeating the same operation as the light cyan ink 1 except that the composition was changed as shown in Table 1.

(2) Acquisition of L ^* , a ^* , b ^* , C ^* , and h Each ink is filled into a predetermined ink cartridge and mounted on a digital multifunction machine equipped with an ink jet printer (manufactured by Brother Industries, Ltd .; MFC-5200J). A 1200 × 1200 dpi solid print is printed on glossy paper (Fuji Photo Film Co., Ltd .; Image (registered trademark) glossy finish), and L ^* , a ^* and b ^* of the solid print are manufactured by Gretag Macbeth. It was measured by Spectrolino (light source: D ₆₅ ; field of view: 2 °).

Moreover, C ^* and h were calculated | required using following Formula (1) and (2) based on the obtained measured value. These results are shown in Table 1.

(3) Configuration of Ink Set A water-based ink set for ink jet recording was configured by combining the inks shown in Table 1 as shown in Table 2. Comparative example 1 corresponds to a conventional ink set.

(4) Evaluation of ink set For each ink set shown in Table 2, the ink constituting the ink set was filled in a predetermined ink cartridge, and a digital multifunction machine equipped with an ink jet printer (manufactured by Brother Industries, Ltd .; MFC-5200J) ), Printed on glossy paper (Fuji Photo Film Co., Ltd .; Image (registered trademark) glossy finish) with gradation samples of light cyan ink and normal cyan ink for graininess evaluation, green and cyan For evaluation of color reproduction, print pattern samples including patches of various hues were printed by changing the mixing ratio of cyan ink (light cyan ink, normal cyan ink), green ink, and yellow ink.

About the obtained patch of each sample, a ^* , b ^* and L ^* are measured in the same manner as described above, and (a) cyan color granularity evaluation, (b) green color reproduction evaluation, (c) cyan color reproduction evaluation, And (d) Comprehensive evaluation was performed as follows.

(a) Cyan color graininess evaluation In the above gradation sample, the cyan graininess was visually evaluated based on the following evaluation criteria with respect to the patch of L ^* = 90. The evaluation results are shown in Table 2.
◎… No graininess is noticed ○… The graininess is almost inconspicuous ×… The graininess is noticeable, and there is a problem in practical use

(b) Green color reproduction evaluation
(b-1) Visual Evaluation From the above-mentioned print pattern sample, a green color patch corresponding to h = 200 ° ± 10 ° is selected, and whether or not the green color is sufficiently expressed by visual observation is evaluated as follows. Evaluation was based on criteria. The evaluation results are shown in Table 2.
◎… High density green color can be expressed sufficiently ○… High density green color can be expressed ×… High density green color expression is insufficient

(b-2) Saturation (C ^* ) and saturation difference (A)
From the above-mentioned print pattern sample, a patch having h corresponding to a green color of 200 ° ± 10 ° and L ^* of 55 ± 3 was selected, and C ^* was calculated for each patch by the above-described equation (1). .

Further, by using the C ^* ₁ of Comparative Example 1 patch (h = 196 °) as comparison reference, the following equation (3), and C ^* ₁ of the patch of Comparative Example 1 and C ^* ₂ of each patch above Was determined as a saturation difference (A). Here, the greater the saturation difference (A), the better the high density green color reproducibility. The results are shown in Table 2.

(c) Cyan color reproduction evaluation
(c-1) Visual Evaluation A patch of h = 234 ° ± 5 ° corresponding to the cyan color is selected from the above-mentioned print pattern sample, and whether or not the cyan color is sufficiently expressed by visual observation is as follows. Evaluation was performed based on the evaluation criteria. The evaluation results are shown in Table 2.
◎… High density cyan color can be expressed sufficiently ○… Color close to high density cyan color can be expressed ×… High density cyan color expression is insufficient

(c-2) Saturation (C ^* ) and brightness difference (B)
From the above-mentioned print pattern sample, the patch of Comparative Example 1 that exhibits a cyan color when h is 215 ° ≦ h ≦ 255 ° that is recognized as belonging to the cyan category and is printed with a conventional ink set ( h = 234 °, L ^* = 54) and the patch with the closest L ^* and h was selected, and C ^* was calculated for each patch by the above-described equation (1).

  Further, the brightness difference (B) between each patch and the patch of Comparative Example 1 was obtained by the following equation (4). Here, the brightness difference (B) indicates that the higher the value is, the more highly cyan color cannot be expressed.

(d) Overall evaluation
From the results of (a) cyan color graininess evaluation, (b) green color reproduction evaluation, and (c) cyan color reproduction evaluation, comprehensive evaluation was performed according to the following evaluation criteria. The results are shown in Table 2.
○… All evaluation results are ◎ or ○ ×: There is × in any of the evaluation results

As shown in Table 2, in Examples 1 and 4, since the light cyan ink with L ^* ≧ 60 was used, the graininess was hardly noticeable in the cyan low density print portion (L ^* = 90). . In Examples 1 and 4, since green ink of L ^* ≦ 60 is used, the green color reproduction range is widened (A value is large) compared to the conventional ink set (Comparative Example 1). A high density cyan color comparable to the cyan color that can be expressed by the conventional ink set (Comparative Example 1) was also expressed. In addition, since the green color can be expressed by a single green ink, there is no landing error due to overstrike for green printing, and sharp printing can be obtained.

In Examples 2, 3 and 5, since a light cyan ink having a higher L ^* than the light cyan ink used in Examples 1 and 4 was used, cyan graininess was not recognized. Also in this case, since green ink with L ^* ≦ 60 is used, a high density green color can be sufficiently expressed, and is comparable to the cyan color that can be expressed in the conventional ink set (Comparative Example 1). The high density of cyan was also expressed.

Since Comparative Examples 2 and 3 use light cyan ink with a high L ^* , cyan color graininess is reduced as compared with the conventional ink set (Comparative Example 1), but since green ink is not used, it is clearly high. The density green color cannot be expressed, and the expression of the high density cyan color is insufficient.

Example 6 and Comparative Example 4
(1) Preparation of ink and composition of ink set With the ink composition shown in Table 3, yellow ink, light magenta ink, red ink, light cyan ink 1, blue ink and green ink 1 were prepared in the same manner as in Example 1. From these, the ink set of Example 6 was constructed.

In addition, as an ink set of Comparative Example 4, a yellow ink (LC600Y), a magenta ink (LC600M), and a cyan ink (LC600C) for a commercially available digital multifunction machine MFC-5200J (manufactured by Brother Industries, Ltd.) An ink set consisting of various types of inks was prepared.

(2) Acquisition of L ^* , C ^* , and h For each ink, L ^* , a ^* , and b ^* were measured in the same manner as in Example 1, and C ^* and h were calculated. These results are shown in Table 3.

(3) Evaluation of Ink Set Similar to the evaluation of the ink set in Example 1, using the ink sets of Example 6 and Comparative Example 4, print pattern samples for color reproduction evaluation including patches of various hues were prepared. Printed.

In this case, since the number of ink cartridges that can be mounted in the ink jet printer used for printing is four, when printing the print pattern sample of the ink set of Example 6, first, six types of ink are filled in the ink cartridge, For convenience, the following two sets were divided and printed twice.
First set: red ink, yellow ink, green ink 1, light cyan ink 1
Second set: light cyan ink 1, blue ink, light magenta ink, red ink

  In this ink grouping method, among the six types of ink, four types of ink are selected in ascending order of the hue angle to make the first set, and then the largest hue angle of the first set is obtained. The second set is composed of ink, two types of ink having a hue angle larger than that of the ink, and an ink having the smallest hue angle among the first set of inks.

  In printing, a printer driver capable of printing patch patterns including various hues was created and used.

The a ^* and b ^* of the obtained print pattern samples were measured in the same manner as described above, and the color reproduction areas at L ^* = 40, 50, 60, 70 and 80 were obtained.

The ratio of the color reproduction area of Example 6 to the color reproduction area of Comparative Example 4 at the same L ^* value was determined, and the results obtained were evaluated based on the following evaluation criteria. The results are shown in Table 4. Moreover, what plotted the color reproduction range of Example 6 and Comparative Example 4 about each L ^* value is shown in FIGS.
◎… Over 110% ○… Over 105%, 110% or less △… Over 90%, 105% or less ×… 90% or less

  From the results in Table 4, it can be seen that the color reproduction area of the ink set of Example 6 is significantly increased as compared with the ink set of Comparative Example 4.

  The water-based ink set for ink-jet recording of the present invention realizes reduction of graininess and expansion of a color reproduction range in a low-density print portion, and is useful when reproducing a color image with a printer for ink-jet recording.

10 is a graph of a color reproduction range in Example 6 and Comparative Example 4 at L ^* = 40. 10 is a graph of a color reproduction range in Example 6 and Comparative Example 4 when L ^* = 50. 10 is a graph of a color reproduction range in Example 6 and Comparative Example 4 at L ^* = 60. 10 is a graph of a color reproduction range in Example 6 and Comparative Example 4 at L ^* = 70. 10 is a graph of a color reproduction range in Example 6 and Comparative Example 4 at L ^* = 80.

Claims (10)

This is a water-based ink set for ink jet recording that has cyan ink and green ink, and has no normal cyan ink with a lightness index (L ^* ) of L ^* a ^* b ^* color system L ^* <60. A water-based ink set for ink-jet recording, wherein the cyan ink is a light cyan ink having a lightness index (L ^* ) of L ^* a ^* b ^* color system of L ^* ≧ 60. Light cyan ink in the L ^* a ^* b ^* lightness color system (L ^*) is 60 ≦ L ^* ≦ 85 a is claim 1 Symbol mounting of the ink jet recording water-based ink set. The water-based ink set for inkjet recording according to claim 1 or 2 , wherein a hue angle (h) of the light cyan ink according to the L ^* a ^* b ^* color system is 215 ° ≦ h ≦ 255 °. Light cyan ink L ^* a ^* b ^* color saturation by color system (C ^*) is 40 ≦ C ^* ≦ 70 a based ink set for ink-jet recording according to any one of claims 1 to 3. The water-based ink set for inkjet recording according to any one of claims 1 to 4 , wherein the lightness index (L ^* ) of the L ^* a ^* b ^* color system of the green ink is L ^* ≤60. The water-based ink set for ink-jet recording according to any one of claims 1 to 5 , wherein the lightness index (L ^* ) according to the L ^* a ^* b ^* color system of the green ink is 35≤L ^* ≤60. The water-based ink set for ink-jet recording according to any one of claims 1 to 6 , wherein a hue angle (h) according to the L ^* a ^* b ^* color system of the green ink is 175 ° ≦ h ≦ 215 °. The water-based ink set for inkjet recording according to any one of claims 1 to 7 , wherein the saturation (C ^* ) of the green ink according to the L ^* a ^* b ^* color system is 60 ≦ C ^* ≦ 80. The aqueous ink set for inkjet recording according to any one of claims 1 to 8 , further comprising yellow ink and / or magenta ink. An ink jet recording method using the water-based ink set for ink jet recording according to any one of claims 1 to 9 .

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