JP2013216819A - Ink set for inkjet, recording method, and recorded matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set with which an image with a wide color representation area is recorded when ink containing a pH color change type pigment is used, a recording method using the same, and recorded matter obtained by the same.SOLUTION: An ink set for inkjet includes a plurality of ink, and includes: first ink containing a pH color change type pigment and an acidic substance or a basic substance with a normal boiling point of 370°C or lower; and second ink having a hue of which the hue angle is different from a hue of the first ink by 70° or more.

Description

  The present invention relates to an ink jet ink set, a recording method, and a recorded matter.

  2. Description of the Related Art Conventionally, as a method for recording characters and images on a recording medium, an ink jet recording method for recording images and characters on a recording medium with minute ink droplets ejected from nozzles is known. In recent years, since the ink jet recording method is used in various fields, the functions required for the ink used are also diverse. For example, Patent Literature 1 describes that the color of an image recorded using an ink containing a pH indicator disappears due to a change in pH.

JP-A 63-286481

  However, when an ink containing a pH indicator as described above was used, the recorded image could not express a color other than the color based on the pH-changing dye. Therefore, the ink containing the pH indicator as described above cannot express a color that can be expressed by using a normal ink for inkjet recording, and can reproduce only a limited color expression region.

  Some embodiments according to the present invention solve at least a part of the above-described problems, whereby an ink set capable of recording an image having a wide color expression region when using an ink containing a pH-changing colorant. Another object of the present invention is to provide a recording method using the same, and a recorded matter obtained thereby.

  The present invention can be realized as the following aspects or application examples.

[Application Example 1]
One aspect of the ink set for inkjet according to the present invention is as follows:
An inkjet ink set comprising a plurality of inks,
a first ink containing a pH color-changing dye and an acidic substance or basic substance having a standard boiling point of 370 ° C. or lower;
A second ink having a hue different from the hue of the first ink by a hue angle of 70 ° or more;
Is provided.

  According to the aspect described in Application Example 1, it is possible to record an image having a wide color expression area.

[Application Example 2]
In application example 1,
The second ink may contain a colorant that is not a pH-changing colorant.

[Application Example 3]
In application example 1,
The second ink may contain a pH color-changing dye and an acidic substance or a basic substance having a standard boiling point of 370 ° C. or lower.

[Application Example 4]
In any one of Application Examples 1 to 3,
Three or more inks of cyan ink, magenta ink, and yellow ink can be provided.

[Application Example 5]
One aspect of the recording method according to the present invention is:
A mixed color image is formed using the inkjet ink set described in any one of Application Examples 1 to 4.

  According to the recording method described in Application Example 5, the color expression range of the recorded image can be expanded.

[Application Example 6]
In application example 5,
The mixed color image may be an achromatic color.

[Application Example 7]
One aspect of the recorded matter of the present invention is:
It is obtained by the recording method described in Application Example 5 or Application Example 6.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

1. Ink set for ink jet recording An ink set for ink jet according to an embodiment of the present invention is an ink set for ink jet comprising a plurality of inks, and a pH discoloring dye and an acidic substance or base having a standard boiling point of 370 ° C. or lower And a second ink having a hue angle different from the hue of the first ink by 70 ° or more.

  Hereinafter, each ink constituting the inkjet ink set according to the present embodiment (hereinafter also simply referred to as “ink set”) will be described in detail.

1.1. 1st ink The 1st ink which concerns on this embodiment contains pH discoloration type | mold pigment | dye and the acidic substance or basic substance whose standard boiling point is 370 degrees C or less.

  The pH of an image recorded using the first ink changes with the volatilization of an acidic substance or basic substance (described later) having a standard boiling point of 370 ° C. or lower. For this reason, the image recorded using the first ink changes to a color different from the original recorded color due to the action of the pH-changing dye.

1.1.1. pH color-changing dye The pH color-changing dye has a function of changing color due to pH change. Examples of pH color-changing dyes include those having a color change range near acidity, those having a color change range near neutrality, those having a color change range near alkalinity, and those having two or more color change ranges, etc. Those having a color change range in the pH value of can be used. In the present specification, the color change range refers to a pH range in which a color change occurs.

  The color-changing mode of the pH color-changing dye is not particularly limited, and examples thereof include those that change from colored to colored, those that change from colored to colorless (decolored), and those that change from colorless to colored. It is done.

  The pH-changing dye is not particularly limited as long as it has the above functions. For example, macalite green, methyl violet, o-cresol red, thymol blue, 2,4-dinitrophenol, methyl yellow, and congo red , Bromophenol blue, methyl orange, bromocresol green, methyl red, litmus, methyl purple, p-nitrophenol, bromocresol purple, chlorophenol red, bromothymol blue, neutral red, phenol red, p-naphtholphthalein, cresol Red, α-naphtholphthalein, curcumin, m-cresol purple, ethylbis (2,4-dinitrophenyl) acetate, phenolphthalein, p-naphtholbenzein, p-ki Les Nord Blue, o- cresol phthalein, thymol phthalein, alpha-naphtholbenzein in, alizarin yellow GG, alizarin yellow R, 1,3,5-trinitrobenzene, and the like. The pH color-changing dyes may be used alone or in combination of two or more.

  Table 1 shows the color change range of typical pH color changing dyes.

  The content of the pH color-changing dye can be appropriately set depending on the application and is not particularly limited. However, for example, the content may be 0.1% by mass or more and 5% by mass or less based on the total mass of the first ink. Preferably, it is 0.5 mass% or more and 3 mass% or less. When the content of the pH color-changing dye is within the above range, particularly not less than 0.1% by mass, the recorded image tends to be highly visible. Further, when the content of the pH color-changing dye is within the above range, particularly not exceeding 5% by mass, the solubility of the pH color-changing dye in the first ink is improved, and the ejection stability of the first ink is improved. Tend to improve.

  As the pH color-changing dye, one previously dissolved in a solvent or the like can be used. By doing so, there may be a case where unevenness in the density of the image can be suppressed. The solvent for dissolving the pH color-changing dye is not particularly limited, and for example, a known organic solvent can be used. Specific examples of the organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, dimethylformamide, N-methyl-2-pyrrolidone, dioxane, tetrahydrofuran, dimethyl sulfoxide, methyl alcohol, ethanol, isopropyl alcohol and the like.

  When the pH color-changing dye is dissolved in a solvent in advance, an amount of the solvent capable of dissolving the pH color-changing dye may be added. For example, 1 part by mass or more with respect to 1 part by mass of the pH color-changing dye What is necessary is just to use 40 mass parts or less of solvent.

1.1.2. Acidic substance and basic substance The first ink according to the present embodiment contains an acidic substance having a standard boiling point of 370 ° C. or lower, or a basic substance having a standard boiling point of 370 ° C. or lower.

  Since the pH immediately after the preparation of the first ink can be adjusted by adding the acidic substance or the basic substance to the first ink, the color immediately after the preparation of the first ink can be easily set.

  Further, since the acidic substance and the basic substance have a volatile property, they volatilize when the image recorded with the first ink is left or heated. In this way, the pH of the image recorded using the first ink changes due to the volatilization of the acidic substance or the basic substance, so that the color of the image changes.

  The standard boiling points of the acidic substance and the basic substance contained in the first ink according to this embodiment are both 370 ° C. or lower, preferably 100 ° C. or higher and 250 ° C. or lower. By using an acidic substance and a basic substance having a standard boiling point within the above range, the substance is easily volatilized, so that the color of the image can be changed over time.

  The acidic substance is not particularly limited as long as it can make the pH of the first ink acidic and has a normal boiling point of 370 ° C. or lower (that is, a substance having volatility). Examples include acids. Examples of inorganic acids include nitric acid, hydrochloric acid, phosphoric acid and the like. Examples of the organic acid include formic acid, acetic acid, propionic acid, acrylic acid, methacrylic acid, adipic acid, citric acid, and succinic acid. Among these, it is preferable to use an organic acid from the viewpoint of safety and the like. Citric acid is an organic acid that decomposes at about 175 ° C., but is included in “an acidic substance having a normal boiling point of 370 ° C. or lower”. That is, any substance that can change the pH of the image can be used in this embodiment.

  The basic substance is not particularly limited as long as the pH of the first ink can be made basic and the standard boiling point is 370 ° C. or lower (that is, volatile). Inorganic amines and organic amines may be mentioned. Examples of inorganic amines include ammonia and hydrazine. Examples of organic amines include alkanolamines such as triethanolamine, diethanolamine, monoethanolamine, N-methylethanolamine, tri-iso-propanolamine, pentadecylamine, cetylamine, tetradecylamine, tridecylamine, dodecyl. Examples thereof include aliphatic amines such as amine, octylamine, diamylamine, dibutylamine, tributylamine, tripropylamine, triallylamine and cyclohexylamine, and aromatic amines such as dibenzylamine, naphthylamine and benzylamine. Among these, it is preferable to use an organic amine from the viewpoint of safety and the like.

  The content of the acidic substance or basic substance is not particularly limited as long as the initial pH of the first ink can be set to a desired value, but for example, 0.1 mass with respect to the total mass of the first ink. % To 15% by mass, more preferably 0.1% to 10% by mass. The content of the substance is within the above range, particularly not less than 0.1% by mass, and the pH color-changing dye may work well as a color former. In addition, when the content of the substance is within the above range, particularly not exceeding 10% by mass, the change in the molecular structure of the pH-changing dye can be suppressed, and the ink ejection stability can be improved. There is.

1.1.3. Other ingredients (water)
The first ink according to the present embodiment may be a water-based ink in which the main solvent (for example, a solvent contained in an amount of 50% by mass or more with respect to the total mass of the ink) is water, or an organic solvent. A certain non-aqueous (solvent) ink may be used.

  When the first ink according to the present embodiment is a water-based ink, the reactivity to a piezoelectric element that may be used in a recording head or an organic binder included in a recording medium is weak. In some cases, corrosion can be reduced. In addition, the water-based ink may be able to form an image having excellent drying properties as compared with a non-water-based ink containing a large amount of a solvent having a high boiling point and a low viscosity. Further, the water-based ink has an advantage that it is good for the environment because 50% or more of the composition is water.

(Wetting agent)
The first ink according to this embodiment may contain a wetting agent. Thereby, clogging in the vicinity of the nozzle portion of the ink discharge head can be effectively reduced.

  As the wetting agent, for example, glycerin, 1,2,6-hexanetriol, trimethylolpropane, pentamethylene glycol, trimethylene glycol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, number Polyethylene glycol having an average molecular weight of 2000 or less, dipropylene glycol, tripropylene glycol, isobutylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol Polyhydric alcohols such as mesoerythritol and pentaerythritol, as well as glucose, mannose, fructose, ribose, xylose, arabinose, galactose, Sugars such as ludonic acid, glucitol (sorbit), maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose, so-called solid wetting agents such as sugar alcohols, hyaluronic acids, and ureas, and ethanol, methanol, butanol, C1-C4 alkyl alcohols such as propanol and isopropanol, and 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, Examples include sorbitan, acetin, diacetin, triacetin, and sulfolane, and one or more of these can be used in combination.

(Penetration enhancer)
The first ink according to this embodiment may contain a penetration enhancer. The penetration enhancer has a function of further improving the wettability of the ink with respect to the recording medium and applying it uniformly. As a result, it is possible to further reduce the density unevenness and bleeding of the ink of the recorded image, and to further improve the color density of the image.

  Examples of such penetration enhancers include alkyl alcohol alkyl ethers (also referred to as glycol ethers), 1,2-alkyl diols, and the like.

  Examples of the alkyl ether of polyhydric alcohol include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono Isopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, Lopylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether , Dipropylene glycol monoisopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and the like. Examples of the 1,2-alkyldiol include 1,2-pentanediol and 1,2-hexanediol. In addition to these, straight-line such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol. Examples thereof include diols of chain hydrocarbons, and one or more of these can be used in combination.

(Surfactant)
The first ink according to this embodiment may contain a surfactant. The surfactant is not particularly limited, and any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant can be used.

  Among these, it is preferable to use a surfactant having high wettability of ink, and specific examples include acetylene glycol surfactants and silicon surfactants.

  The acetylene glycol surfactant is a nonionic surfactant having an acetylene group in the center and a symmetrical structure, and is applied to aqueous materials in various directions as a wetting agent that hardly foams. The acetylene glycol surfactant is excellent in functions such as wetting, defoaming, and dispersion. The glycol has a very stable molecular structure, has a small molecular weight, and has the effect of lowering the surface tension of water. Therefore, the permeability and bleeding of the ink to the recording medium can be controlled appropriately, and the fixing property of the ink to the recording medium can be controlled. Can be increased.

  Specific examples of the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, , 5-dimethyl-1-hexyn-3-ol and the like. Commercially available acetylene glycol surfactants include, for example, Surfinol 104 (series), 420, 440, 465, 485 (trade name, manufactured by Air Products), Olphine STG, PD-001, SPC, E1004, E1010. PD-002W (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), acetylenol E00, E40, E100, LH (trade name, manufactured by Kawaken Fine Chemical Co., Ltd.) and the like.

  The silicon-based surfactant can appropriately control the wettability to the surface of the recording medium, the permeability to the recording medium and the bleeding, and can improve the fixing property of the ink to the recording medium.

  As the silicon-based surfactant, a polysiloxane compound or the like is preferably used, and examples thereof include polyether-modified organosiloxane. More specifically, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (above trade names, manufactured by Big Chemie Japan Co., Ltd.), KF-351A, KF- 352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF- 6012, KF-6015, KF-6017 (above trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) and the like.

(resin)
The first ink according to the present embodiment may contain a resin. One of the functions of the resin is to improve image fixability and abrasion resistance on the recording medium.

  Examples of the resin include acrylic resin, urethane resin, polyolefin resin, ester resin, rosin modified resin, terpene resin, polyamide resin, epoxy resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer Known resins such as coalescence, ethylene vinyl acetate resin, fluorene resin, polyolefin wax and the like can be mentioned.

(Preservatives and fungicides)
The first ink according to this embodiment may contain a preservative and a fungicide. Examples of antiseptics and fungicides include sodium benzoate, sodium pentachlorophenol, 2-pyridinethiol-1-oxide sodium, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazoline-3-one Etc. Examples of commercially available products include Proxel XL2, Proxel GXL (above trade name, manufactured by Avicia), Denside CSA, NS-500W (above trade name, manufactured by Nagase ChemteX Corporation), and the like.

  Examples of the rust inhibitor include benzotriazole.

  Examples of the chelating agent include ethylenediaminetetraacetic acid and salts thereof (such as ethylenediaminetetraacetic acid dihydrogen disodium salt).

1.1.4. Method for Preparing First Ink The first ink according to the present embodiment is obtained by mixing the components described above in an arbitrary order and removing impurities by filtering or the like as necessary. As a method for mixing the components, a method in which materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirred and mixed is suitably used. As a filtration method, centrifugal filtration, filter filtration, or the like can be performed as necessary.

1.1.5. Physical Properties of First Ink The first ink according to the present embodiment preferably has a surface tension at 20 ° C. of 20 mN / m or more and 50 mN / m from the viewpoint of a balance between recording quality and reliability as an ink jet ink. 25 mN / m or more and 40 mN / m or less is more preferable. The surface tension is measured by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) by confirming the surface tension when the platinum plate is wetted with ink in an environment of 20 ° C. be able to.

  From the same viewpoint, the viscosity of the first ink according to this embodiment at 20 ° C. is preferably 2 mPa · s or more and 15 mPa · s or less, and more preferably 2 mPa · s or more and 10 mPa · s or less. . The viscosity is measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), increasing the Shear Rate to 10 to 1000 in an environment of 20 ° C., and reading the viscosity at Shear Rate 200. Can be measured.

1.2. Second Ink The second ink according to this embodiment has a hue angle of 70 ° or more different from the hue of the first ink. For this reason, the ink set according to the present embodiment can form a mixed color image using the first ink and the second ink. Therefore, a color that cannot be expressed when using only an ink containing a conventional pH-changing colorant is used. An image with a wide expression area can be recorded.

  In particular, when two or more colors of ink are used, an achromatic color such as composite black may be formed on the recording medium. Composite black is a black color formed by mixing two or more inks. In the case of forming composite black using two colors of ink, it can be obtained, for example, by using a green ink and a magenta ink and mixing each ink in an appropriate ratio on a recording medium. In addition, when forming composite black using three colors of ink, for example, cyan ink, magenta ink, and yellow ink are used to mix each ink at an appropriate ratio on a recording medium.

  In the present invention, the term “mixed color” refers to a mixture of different ink droplets (dots) mixed with each other, as well as a mixture of both dots that are adjacent to or in contact with different ink droplets. Including those capable of expressing the same color as.

In the present invention, an achromatic color means a color having a saturation C ^* defined by the CIELAB color space of 15 or less. The black color means a color having a lightness L * defined in the CIELAB color space of 50 or less and a saturation C * of 15 or less.

The CIELAB color space is an approximate uniform color space recommended by the International Commission on Illumination (CIIE) in 1976, and this committee has designated CIE 1976 (L ^* a ^* B ^* ).

The hue angle in the present invention refers to a hue angle (h °) defined in the CIELAB color space, and is a value calculated from the values of a ^* and b ^* using the following formula. Specifically, the hue angle h ° is h ° = tan ⁻¹ (b ^* / a ^* ), a ^* ≦ 0, and a ^* ≧ 0 and b ^* ≧ 0 (first quadrant). In the case of b ^* ≧ 0 (second quadrant), h ° = 180 + tan ⁻¹ (b ^* / a ^* ), and in the case of a ^* ≦ 0 and b ^* ≦ 0 (third quadrant), h ° = 180 + tan ⁻¹ (b ^* / a ^* ), a ^* ≧ 0, and b ^* ≦ 0 (fourth quadrant), the calculation is performed using the equation h ° = 360 + tan ⁻¹ (b ^* / a ^* ). .

In the present invention, the hue angle (h °) of the ink was measured using a colorimeter Gretag Spectrolino (trade name, manufactured by Gretag) when an ink image was recorded on neutral paper of pH 7. It refers to the hue angle (h °) of the image. Therefore, the ink B having a hue angle (h °) different from that of the ink A means that the hue angle (h °) of the ink A and the hue angle (h °) of the ink B show different values. In this case, as the neutral paper of pH 7, paper having a range of 70 ≦ L ^* ≦ 100, −4.5 ≦ a ^* ≦ 2, −6 ≦ b ^* ≦ 2.5 is used.

  The hue angle h ° differs depending on the hue of the ink. For example, when an image is formed on neutral paper of pH 7 using each ink, the hue angle h ° of the image made of yellow ink is 80 ° to 110 °. The hue angle h ° of the image made of magenta ink is 330 ° to 360 °, the hue angle h ° of the image made of cyan ink is 230 ° to 260 °, and the hue angle h of the image made of red ink is ° is 0 ° to 80 °, and the hue angle h ° of an image made of blue ink is 260 ° to 330 °.

1.2.1. Colorant The second ink according to the present embodiment may contain a colorant that is not a pH-changing colorant (described above). In this case, the second ink does not contain a pH color-changing dye as a colorant.

  When a color-mixed image is formed by mixing a second ink containing a colorant that is not a pH-color-changing dye and the first ink on a recording medium, the pH-changing dye derived from the first ink changes in pH. Since the color changes depending on the color, various color expressions are possible.

  Examples of the colorant that is not a pH-changing colorant include pigments (for example, organic pigments and inorganic pigments) and dyes.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone. Polycyclic pigments such as pigments, dye chelates (for example, basic dye type chelates, acidic dye type chelates), dyeing lakes (basic dye type lakes, acid dye type lakes), nitro pigments, nitroso pigments, aniline black, A daylight fluorescent pigment is mentioned. The said pigment may be used individually by 1 type, and may use 2 or more types together.

  More specifically, examples of the inorganic pigment used for black include, for example, the following carbon black, for example, No. manufactured by Mitsubishi Chemical. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, or No2200B, etc .; Columbia-made Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc .; 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc .; or Color Black FW1, Color Black FW2, Clk Black FW2C, Decksa's Color Black FW2 FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, and Special Black 5S.

  Although it does not specifically limit as a yellow organic pigment, For example, C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180, 185, 213 and the like.

  Although it does not specifically limit as a magenta organic pigment, For example, C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, 254, 264 or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50 and the like.

  Although it does not specifically limit as a cyan organic pigment, For example, C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 15:34, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60 and the like.

  The organic pigments other than magenta, cyan and yellow are not particularly limited. I. Pigment green 7, 10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, and the like.

  As the dye, for example, various dyes that are usually used for inkjet recording such as direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, and reactive disperse dyes are used. can do.

  Although it does not specifically limit as a yellow dye, For example, C.I. I. Acid Yellow 1, 3, 11, 17, 19, 23, 25, 29, 36, 38, 40, 42, 44, 49, 59, 61, 70, 72, 75, 76, 78, 79, 98, 99, 110, 111, 127, 131, 135, 142, 162, 164, 165, C.I. I. Direct Yellow 1, 8, 11, 12, 24, 26, 27, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 110, 132, 142, 144, C.I. I. Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37, 42, C.I. I. Food Yellow 3, 4, C.I. I. Solvent yellow 15, 19, 21, 30, 109 etc. are mentioned.

  The magenta dye is not particularly limited. I. Acid Red 1, 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 37, 42, 51, 52, 57, 75, 77, 80, 82, 85, 87, 88, 89, 92, 94, 97, 106, 111, 114, 115, 117, 118, 119, 129, 130, 131, 133, 134, 138, 143, 145, 154, 155, 158, 168, 180, 183, 184, 186, 194, 198, 209, 211, 215, 219, 249, 252, 254, 262, 265, 274, 282, 289, 303, 317, 320, 321, 322, C.I. I. Direct Red 1, 2, 4, 9, 11, 13, 17, 20, 23, 24, 28, 31, 33, 37, 39, 44, 46, 62, 63, 75, 79, 80, 81, 83, 84, 89, 95, 99, 113, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229, 230, 231, C.I. I. Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 49, 50, 58, 59, 63, 64, C.I. I. Sorbize red 1, C.I. I. Food red 7, 9, 14 etc. are mentioned.

  Although it does not specifically limit as a cyan dye, For example, C.I. I. Acid Blue 1, 7, 9, 15, 22, 23, 25, 27, 29, 40, 41, 43, 45, 54, 59, 60, 62, 72, 74, 78, 80, 82, 83, 90, 92, 93, 100, 102, 103, 104, 112, 113, 117, 120, 126, 127, 129, 130, 131, 138, 140, 142, 143, 151, 154, 158, 161, 166, 167, 168, 170, 171, 182, 183, 184, 187, 192, 199, 203, 204, 205, 229, 234, 236, 249, C.I. I. Direct Blue 1, 2, 6, 15, 22, 25, 41, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 120, 123, 158, 160, 163, 165, 168, 192, 193, 194, 195, 196, 199, 200, 201, 202, 203, 207, 225, 226, 236, 237, 246, 248, 249, C.I. I. Reactive Blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33 , 34, 37, 38, 39, 40, 41, 43, 44, 46, C.I. I. Solvize Bat Blue 1, 5, 41, C.I. I. Bat Blue 4, 29, 60, C.I. I. Food Blue 1, 2, C.I. I. Basic blue 9, 25, 28, 29, 44 etc. are mentioned.

  The dyes other than magenta, cyan and yellow are not particularly limited. I. Acid Green 7, 12, 25, 27, 35, 36, 40, 43, 44, 65, 79, C.I. I. Direct Green 1, 6, 8, 26, 28, 30, 31, 37, 59, 63, 64, C.I. I. Reactive Green 6, 7, C.I. I. Acid Violet 15, 43, 66, 78, 106, C.I. I. Direct violet 2, 48, 63, 90, C.I. I. Reactive violet 1, 5, 9, 10, C.I. I. Direct black 154 etc. are mentioned.

  When the second ink contains the colorant, the content thereof can be appropriately set depending on the application and is not particularly limited. For example, the content is 0.1% by mass or more and 10% by mass with respect to the total mass of the second ink. % Or less, more preferably 0.5% by mass or more and 5% by mass or less.

1.2.2. pH discoloring dye The second ink according to the present embodiment may contain a pH discoloring dye. In this case, the second ink does not contain the colorant.

  When a color-mixed image is formed by mixing the second ink containing a pH-changing colorant and the first ink on a recording medium, the pH-coloring colorant derived from the first ink and the pH derived from the second ink Since the color-changing dye changes color due to a change in pH, various color expressions are possible.

  In particular, if the color change areas of the pH color change pigments contained in the first ink and the second ink are different, the color change of the mixed color image to be recorded can be further diversified. When the color changes become diverse as described above, the time lapse, the heat history, and the like can be shown in more detail.

  Specific examples and functions of the pH color-changing dye are the same as those described in the first ink, and thus the description thereof is omitted.

  When the second ink contains a pH-changing colorant, the content thereof can be appropriately set according to the application and is not particularly limited. It is preferable that it is mass% or less, and it is more preferable that it is 0.5 mass% or more and 3 mass% or less.

  Further, when the second ink contains a pH-changing dye, an acidic substance and a basic substance having a standard boiling point of 370 ° C. or less may be contained. Specific examples and functions of the acidic substance and basic substance having a standard boiling point of 370 ° C. or lower are the same as the contents described in the first ink, and thus the description thereof is omitted.

  When the second ink contains the above acidic substance or basic substance, the content is not particularly limited as long as the initial pH of the second ink can be set to a desired value. It is preferable that it is 0.1 to 15 mass% with respect to the total mass, for example, and it is more preferable that it is 0.1 to 10 mass%.

1.2.3. Other Components The second ink according to the present embodiment contains components such as water, a wetting agent, a penetration accelerator, a surfactant, a resin, a preservative and an antifungal agent, for the purpose of further improving the performance of the ink. May be. Specific examples and functions of these components are the same as the contents described in the first ink, and thus description thereof is omitted.

1.2.4. Method for Preparing Second Ink The second ink according to the present embodiment is obtained by mixing the components described above in an arbitrary order and removing impurities by filtering or the like as necessary. As a method for mixing the components, a method in which materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirred and mixed is suitably used. As a filtration method, centrifugal filtration, filter filtration, or the like can be performed as necessary.

1.2.5. Physical Properties of Second Ink The second ink according to the present embodiment preferably has a surface tension at 20 ° C. of 20 mN / m or more and 50 mN / m from the viewpoint of the balance between recording quality and reliability as an inkjet ink. 25 mN / m or more and 40 mN / m or less is more preferable. Since the surface tension of the second ink can be measured in the same manner as the first ink, the description thereof is omitted.

  From the same viewpoint, the viscosity of the second ink according to this embodiment at 20 ° C. is preferably 2 mPa · s or more and 15 mPa · s or less, and more preferably 2 mPa · s or more and 10 mPa · s or less. . Since the viscosity of the second ink can be measured in the same manner as the first ink, the description thereof is omitted.

1.3. Others The ink set according to the present embodiment may further include one or more inks in addition to the first ink and the second ink. This makes it possible to express a wider variety of colors.

  In the case where the ink set according to the present embodiment includes, for example, a third ink in addition to the first ink and the second ink, the third ink has a hue angle from the hue of the first ink and the second ink described above. Are preferably different by 70 ° or more. As a result, a variety of color expressions may be possible.

  In addition, the ink (third ink) other than the first ink and the second ink can contain a pH color changing dye or a colorant other than the pH color changing dye. Since the color-changing dye and the colorant other than the pH-changing dye are the same as those described in the first ink and the second ink, description thereof is omitted.

  The ink set according to the present embodiment preferably includes three or more types of inks, cyan ink, magenta ink, and yellow ink. As described above, by using an ink set including three or more kinds of inks of cyan ink, magenta ink, and yellow ink, composite black can be easily formed or a color expression area may be widened.

  When used as an ink set including three or more inks of cyan ink, magenta ink, and yellow ink, at least one of the three colors of cyan ink, magenta ink, and yellow ink is the first ink, and at least one of them One type may be the second ink, and the third ink may be appropriately used. For example, it can be obtained by preparing the first ink, the second ink, and the third ink (inks other than the first ink and the second ink) described above for each color.

In the present invention, the cyan ink refers to an ink that exhibits a cyan color when an image made of the ink is recorded on neutral paper of pH 7. The cyan color means a color defined in the CIELAB color space having a lightness L ^* of 50 to 85, a saturation C ^* of 40 to 80, and a hue angle h of 230 ° to 260 °.

In the present invention, magenta ink refers to ink that exhibits a magenta color when an image made of the ink is recorded on neutral paper of pH 7. The magenta color refers to a color defined in the CIELAB color space having a lightness L ^* of 40 to 70, a saturation C ^* of 60 to 100, and a hue angle h of 330 ° to 360 °.

In the present invention, the yellow ink refers to an ink that exhibits a yellow color when an image made of the ink is recorded on neutral paper of pH 7. The yellow color means a color defined in the CIELAB color space having a lightness L ^* of 70 to 100, a saturation C ^* of 55 to 90, and a hue angle h of 80 ° to 110 °.

The brightness L ^* , saturation C ^* , and hue angle h of an image made of each ink can be measured using a colorimeter Gretag Spectrolino (trade name, manufactured by Gretag).

2. Recording Method A recording method according to an embodiment of the present invention forms a mixed-color image using the inkjet ink set.

  The recording method according to the present embodiment can be performed using an ink jet recording apparatus. Examples of the ink jet recording apparatus include a known ink jet printer (hereinafter also simply referred to as “printer”). Hereinafter, the recording method according to the present embodiment will be described by taking a case where a printer is used as an example. In addition, this invention is not limited to the following aspects.

  First, the first ink droplets are ejected from the nozzles of the recording head of the printer to adhere the first ink droplets onto the recording medium. Next, the second ink droplet is ejected from the nozzle of the recording head of the printer, and the second ink droplet is brought into contact with or adjacent to the first ink droplet on the recording medium. Thereby, it is possible to obtain a recorded matter in which a mixed color image composed of the droplets of the first ink and the second ink is recorded on the recording medium.

  Here, the recording method in which the second ink is ejected after the first ink is ejected first is shown, but the present invention is not limited to this, and the first ink and the second ink may be ejected simultaneously. The first ink may be ejected after the second ink is ejected first.

  The first ink droplet (dot) and the second ink droplet (dot) may be mixed on the recording medium, or may be in contact with each other or adjacent to each other.

  The recording method according to the present embodiment can express a color change due to the color change of the first ink, and can also record a mixed color image of at least two types of inks. Therefore, compared with the case where each ink is used alone. Can expand the color expression area.

  The recording method according to the present embodiment can form a black mixed color image (composite black). In this case, an ink set having a combination of colors that can form a composite black by selecting a pH-changing colorant or a colorant contained in each ink may be used. A composite black can be formed by setting the ejection ratio of each ink in advance.

  In the case of using the third ink described above in addition to the first ink and the second ink, the mixed color image can be formed by the same method as the method of forming the mixed color image by using the first ink and the second ink. it can.

  As a recording medium used in the recording method according to the present embodiment, any recording medium may be used as desired. For example, in addition to paper such as plain paper, special paper having an ink receiving layer, etc., for example, ink The region including the surface to which is applied is various plastics, ceramics, glass, metal, or a substrate composed of these composite materials.

  Among such recording media, when a recording medium having acidic properties (for example, acidic paper) is used, if an image is recorded using the first ink containing a basic substance, the recorded image The pH tends to tilt to the acidic side. Thereby, the change in the color of the recorded image can be promoted.

3. Examples Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the present embodiments are not limited to these examples.

3.1. Preparation of ink Inks 1 to 7 were prepared by mixing and stirring the components shown in Table 2. The pH-changing colorant contained in inks 1 to 5 was used after being dissolved in ethanol in advance. Among the components described in Table 2, the components described by abbreviations or trade names are as follows. Table 2 also shows the pH immediately after the preparation of each ink. A commercially available pH meter was used to measure the pH of each ink.
・ D. Y. 132 (C.I. Direct Yellow 132, Yellow Dye)
・ D. B. 199 (CI Direct Blue 199, cyan dye)
・ Orphine PD-002W (trade name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol surfactant)

3.2. Ink set Each ink prepared as described above was filled into a dedicated cartridge of an ink jet printer PM-A750 (trade name, manufactured by Seiko Epson Corporation), and inks of combinations described in Examples 1 to 5 in Table 3 Set.

  For each ink constituting the ink set, when an image is printed on the recording medium P paper (trade name, manufactured by Fuji Xerox Co., Ltd., pH 7 neutral paper) under the same conditions, the hue of each image immediately after printing The angles differed from each other by more than 70 °.

3.3. Evaluation Test Each ink constituting the ink set was ejected from the nozzle of the printer to form a mixed color image on a recording medium. At this time, the ink was discharged so that the dots of each ink were in contact with each other. Table 3 shows the ejection amount ratio of each ink used for forming the mixed color image and the type of the recording medium used. In Table 3, neutral paper is P paper (trade name, manufactured by Fuji Xerox Co., Ltd., pH 7), and acidic paper is photographic paper <gloss> (trade name, manufactured by Seiko Epson Corp., pH 5).

  The mixed color image thus obtained was left in an environment of 20 ° C. and 65% RH, and the color of the mixed color image immediately after printing, 5 days, 10 days, 15 days, and 30 days later was visually confirmed.

3.4. Evaluation results The results of the evaluation tests are also shown in Table 3 above.

  As shown in Examples 1 to 5, an ink containing a pH-changing dye and an acidic substance or basic substance having a standard boiling point of 370 ° C. or less, and the hue of the ink has a hue angle of 70 ° or more. It has been shown that various color images can be formed using inks having different hues.

  In particular, it was shown that when the ink sets used in Examples 1, 2 and 5 were used, composite black could be formed.

  Further, the evaluation results of Example 5 showed that discoloration of the mixed color image can be promoted by using acidic paper as the recording medium.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (7)

An inkjet ink set comprising a plurality of inks,
a first ink containing a pH color-changing dye and an acidic substance or basic substance having a standard boiling point of 370 ° C. or lower;
A second ink having a hue different from the hue of the first ink by a hue angle of 70 ° or more;
An inkjet ink set comprising: In claim 1,
The ink-jet ink set, wherein the second ink contains a colorant that is not a pH-changing colorant. In claim 1,
The second ink is an ink-jet ink set containing a pH-changing colorant and an acidic substance or a basic substance having a standard boiling point of 370 ° C. or lower. In any one of Claims 1 thru | or 3,
An ink jet ink set comprising three or more inks of cyan ink, magenta ink, and yellow ink.   A recording method for forming a mixed-color image using the inkjet ink set according to any one of claims 1 to 4. In claim 5,
The recording method, wherein the mixed color image is an achromatic color.   A recorded matter obtained by the recording method according to claim 5.