JP2013221111A - Ink set for inkjet, recording method and recorded material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an ink set capable of recording an image displaying the history of photoirradiation or heating, or the like; a recording method of recording using the ink set; and a recorded material obtained by the recording method.SOLUTION: An ink set for inkjet is provided with a plurality of inks and is provided with a first ink and a second ink, wherein the first ink contains an acid generator, the second ink contains a pH discoloring type pigment and the acid generator contained in the first ink is a heat acid generator or a photoacid generator.

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 Document 1 describes using a colorless and transparent ink containing a non-volatile acid or base and an ink containing a pH coloring indicator. According to this, it is described that the color of the portion to which the ink containing the pH coloring indicator is attached changes by attaching the ink containing the pH coloring indicator on the image formed of the colorless and transparent ink. .

JP 2000-127358 A

  When an image was formed by attaching an ink containing a pH coloring indicator on a colorless and transparent ink containing a non-volatile acid or base as described above, the image became a color corresponding to the pH of the colorless and transparent ink. Later, there was no color change. That is, the color change of the image occurs only immediately after the ink containing the pH coloring indicator is attached. For this reason, after recording an image, it was impossible to know the effect that the image received (for example, that the image was energized by being heated or irradiated with light).

  Some embodiments according to the present invention provide an ink set that can record an image that displays the received action by solving at least a part of the above-described problems, a recording method using the ink set, and a recorded matter obtained thereby. Is to provide.

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

[Application Example 1]
One aspect of the inkjet ink set of the present invention is:
An inkjet ink set comprising a plurality of inks,
A first ink containing an acid generator;
a second ink containing a pH color-changing dye;
Is provided.

  According to the aspect described in Application Example 1, it is possible to record an image that displays the received action. Specifically, when an image recorded using the first ink and the second ink is energized by heating, light irradiation, or the like, the pH of the image is inclined to the acid side by the action of the acid generator. . Then, since the color of the image changes, it can be easily known that the image has been affected.

[Application Example 2]
In application example 1,
The acid generator may be a thermal acid generator or a photoacid generator.

[Application Example 3]
In application example 2,
The thermal acid generator can generate an acid in a temperature range of 40 ° C. or higher and 200 ° C. or lower.

[Application Example 4]
In application example 2 or application example 3,
The thermal acid generator may be at least one selected from a sulfonium salt, a monosulfone compound, and a sulfonate ester.

[Application Example 5]
In application example 2,
The photoacid generator is selected from at least one selected from iodonium salts, sulfonium salts, triazine compounds, sulfonate esters, monosulfone compounds, diazodisulfone compounds, imide sulfonates, oxime sulfonates, and nitrobenzyl sulfonates. Can be at least one.

[Application Example 6]
One aspect of the recording method of the present invention is:
A recording method using the inkjet ink set according to any one of Application Examples 1 to 5,
A step of bringing the first ink and the second ink into contact with each other on a recording medium to form an image.

  According to the aspect described in Application Example 6, it is possible to form an image that can display the received action.

[Application Example 7]
One aspect of the recording method of the present invention is:
A recording method using the inkjet ink set according to any one of Application Examples 1 to 5,
Forming a plurality of images by bringing the first ink and the second ink into contact with each other on a recording medium;
The ratio (W1 / W2) of the content (W1) of the acid generator and the content (W2) of the pH color-changing dye is different for each image.

  According to the aspect described in Application Example 7, it is possible to form an image that can display the received action in detail.

[Application Example 8]
One aspect of the recorded matter of the present invention is:
The recording method described in Application Example 6 or Application Example 7 is used.

Schematic which shows the some image formed using the 1st ink which concerns on this embodiment. Schematic which shows the several image formed using the 1st ink and 2nd ink which concern on this embodiment. FIG. 3 is a schematic diagram illustrating color changes of a plurality of images formed using the ink set according to the first embodiment. FIG. 10 is a schematic diagram illustrating color changes of a plurality of images formed using the ink set according to the second embodiment. FIG. 10 is a schematic diagram illustrating color changes of a plurality of images formed using an ink set according to Example 3. FIG. 10 is a schematic diagram illustrating color changes of a plurality of images formed using an ink set according to Example 4. FIG. 10 is a schematic diagram illustrating color changes of a plurality of images formed using an ink set according to Example 5.

  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 An ink set for inkjet according to an embodiment of the present invention includes a plurality of inks, and includes a first ink containing an acid generator and a second ink containing a pH-changing colorant.

  An image obtained by bringing the first ink and the second ink (described later) into contact with each other on a recording medium is subjected to an action such as light irradiation or heating, so that an acid is generated from the acid generator contained in the first ink. The pH gradually leans toward the acidic side. Therefore, the image becomes a color different from the original recorded color due to the color change of the pH color change type dye contained in the second ink.

  Thus, when the inkjet ink set according to the present embodiment is used, an image capable of displaying light irradiation, heating history, and the like can be easily obtained.

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

1.1. First ink 1.1.1. Acid generator The 1st ink which concerns on this embodiment contains an acid generator. The acid generator has a function of generating an acid when given energy. Therefore, when energy is applied to the image made of the first ink, the pH of the image made of the first ink gradually inclines to the acidic side, so that the color of the image made of the second ink formed in contact with the first ink is changed. Change.

  The acid generator is not particularly limited as long as it is a substance that generates acid by applying energy. For example, a photoacid generator that generates acid by light irradiation, or a thermal acid generator that generates acid by heating. Etc.

  The photoacid generator is not particularly limited as long as it generates an acid by at least light irradiation. For example, onium salts such as diazonium salts, phosphonium salts, iodonium salts and sulfonium salts, triazine compounds, sulfonic acid esters, mono Nonionic acid generators such as sulfone compounds, diazodisulfone compounds, imide sulfonates, oxime sulfonates and nitrobenzyl sulfonates can be mentioned. These compounds may be used alone or in combination of two or more.

  Specific examples of the iodonium salt include diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, bis (4-t-butylphenyl) iodonium-p-toluenesulfonate, and the like.

  Specific examples of the sulfonium salt include triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, diphenyl (p-toluenyl) trifluoromethanesulfonate, diphenyl (2,4,6-trimethylphenyl) Nonafluorobutanesulfonate, diphenyl (2,4,6-trimethylphenyl) -p-toluenesulfonate, and the like can be given.

  Specific examples of the triazine compound include 2,4-ditriiodomethyl-6- (p-methoxyphenyl) triazine, 2,4-ditriiodomethyl-6- (m, p-dimethoxystyryl) triazine, 2- (4- And methoxyphenyl) -4,6-bis (trichloromethyl) -1,3,5-triazine.

  Specific examples of the sulfonic acid ester include 2-phenyl-2- (p-toluenesulfonyloxy) acetophenone, 1- (p-toluenesulfonyloxy) -3,3-dimethylbicyclo [2,2,1] heptane-2- ON etc. are mentioned.

  Specific examples of the monosulfone compound include 2-pyridyl (tribromomethyl) sulfone, phenyl (tribromomethyl) sulfone, p-tolyl (dibromomethyl) sulfone, and top-tolyl (trichloromethyl) sulfone.

  Specific examples of the diazodisulfone compound include bis (t-butylsulfonyl) diazomethane, bis (p-toluenesulfonyl) diazomethane, bis (cyclohexanesulfonyl) diazomethane, and the like.

  Specific examples of the imide sulfonate include N-methanesulfonyloxyphthalimide, N- (p-toluenesulfonyloxy) phthalimide and the like.

  Specific examples of oxime sulfonate include 2- [2- (4-methylphenylsulfonyloxyimino) thiophene-3 (2H) -ylidene] -2- (2-methylphenyl) acetonitrile.

  Specific examples of nitrobenzyl disulfonate include 4-nitrobenzyl p-toluenesulfonate, 4-nitrobenzyl 4-methoxybenzenesulfonate, and the like.

  The thermal acid generator is not particularly limited as long as it generates an acid at least by heating. For example, nonionic acid generators such as onium salts such as sulfonium salts and iodonium salts, monosulfone compounds and sulfonate esters, etc. Is mentioned. These compounds may be used alone or in combination of two or more.

  The thermal acid generator is not particularly limited, but preferably generates an acid in a temperature range of 40 ° C. or higher and 200 ° C. or lower, and more preferably generates heat in a temperature range of 50 ° C. or higher and 100 ° C. or lower. . An ink having good storage stability can be obtained when the temperature range in which the acid is generated is within the above-mentioned range, particularly not below the lower limit.

  Specific examples of the sulfonium salt include 4-acetoxyphenyldimethylsulfonium hexafluoroantimonate and 4-hydroxyphenylbenzylmethylsulfonium hexafluoroantimonate.

  Specific examples of the monosulfone compound include 4-methylphenyl (cyclohexyl) sulfone, 4-methylphenyl (1H-imidazol-1-yl) sulfone, and the like.

  Specific examples of the sulfonic acid ester include n-hexyl methanesulfonate, 2-nitrobenzyl p-toluenesulfonate, n-octyl p-toluenesulfonate, cyclohexyl p-toluenesulfonate, and the like.

  The above-mentioned photoacid generator or thermal acid generator is not particularly limited, but may be added to ink that has been previously dissolved in a solvent or the like. The solvent that can be used in this case is not particularly limited, and for example, glycol ethers and glyceryl ethers described later can be used.

  Note that the photoacid generator may generate an acid not only by light but also by heat. Similarly, the thermal acid generator may generate an acid not only by heat but also by light.

  The content of the acid generator contained in the first ink may be set so that the color change of the image obtained by the first ink and the second ink can be adjusted to a desired speed, and the duty value described later is taken into consideration. Is preferably set. As specific content, it can be set as 0.25 mass% or more and 10 mass% or less, for example with respect to the total mass of 1st ink. When the content of the substance is within the above range, particularly not less than 0.25% by mass, the pH color-changing dye contained in the second ink may work well as a color former. When the content of the substance does not particularly exceed 10% by mass, corrosion of the head member may be suppressed.

1.1.2. Other ingredients (sensitizer)
The first ink according to the present embodiment may contain a sensitizer together with the acid generator. By including the sensitizer, the energy (light, heat, etc.) necessary for generating the acid can be adjusted. As the sensitizer, a commercially available one may be used, or it may be synthesized by a known synthesis method. For example, examples of the sensitizer that can be used together with the photoacid generator include those having an absorption wavelength of 450 nm or less, and polynuclear aromatics, xanthenes, cyanines, merocyanines, thiazines, acridines. , Anthraquinones, squalium, coumarins and the like.

(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 nozzles of the ink discharge head may be 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. Thereby, the density unevenness and the blur of the ink of the recorded image can be further reduced, and the color density of the image can be further improved.

  Examples of such penetration enhancers include glycol ethers, glyceryl ethers, and 1,2-alkyl diols.

  Examples of glycol ethers 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 monoisopropyl 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, propylene group Coal 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, Examples include dipropylene glycol monoisopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monobutyl ether. Examples of glyceryl ethers include polyoxyethylene glyceryl ether and polyoxypropylene glyceryl ether. 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.

(Coloring agent)
The 1st ink which concerns on this embodiment may contain the coloring agent which is not a pH color-change type pigment | dye (after-mentioned).

  When the first ink contains a colorant, the first ink and the second ink have different hue angles (preferably, the hue angle difference is 70 ° or more). It is preferred to select a colorant. This is because the color change of the image recorded using the first ink and the second ink can be easily confirmed even if the first ink contains a colorant.

The hue angle in the present invention refers to a hue angle (h °) defined in the CIELAB color space. The hue angle (h °) of the ink is the image measured using a colorimeter Gretag Spectrolino (trade name, manufactured by Gretag) when an image made of ink is recorded on neutral paper of pH 7. The hue angle (h °). 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 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 ^* ).

(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).

1.1.3. 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.

1.1.4. 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 1.2.1. pH color-changing dye The second ink according to this embodiment contains a pH color-changing dye.

  The pH color-changing dye has a function of changing color when the pH changes. 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 mode of color change 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 (that is, those that decolor), and those that change from colorless to colored. Can be mentioned.

  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 second ink is improved, and the ejection stability of the second 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.

1.2.2. 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.

  In addition, the second ink according to the present embodiment may contain a pH adjusting agent for the purpose of setting the pH of the ink immediately after adjustment to a desired value. Although it does not specifically limit as a pH adjuster, For example, inorganic acids (for example, sulfuric acid, hydrochloric acid, nitric acid, etc.), inorganic bases (for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), organic bases ( Triethanolamine, diethanolamine, monoethanolamine, tri-iso-propanolamine), organic acids (for example, adipic acid, citric acid, succinic acid, etc.) and the like.

1.2.3. 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.

1.2.4. 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.

  As other inks of the first ink and the second ink, for example, a third ink containing the above acid generator, a fourth ink containing the above colorant, and a fifth ink containing the above pH discoloration type dye. Etc.

  When the ink set according to the present embodiment includes the third ink, the third ink may contain an acid generator that generates an acid by a different energy amount or a different acid generation path than the first ink. That's fine. For example, when the first ink contains an acid generator that generates an acid at a heating temperature of 50 ° C., the third ink may contain an acid generator that generates an acid at a heating temperature of 100 ° C. . Alternatively, when the first ink contains a thermal acid generator, the third ink may contain a photoacid generator. As a result, images with different color change timings can be recorded.

  When the ink set according to the present embodiment includes the fourth ink, the hue angles of the second ink and the fourth ink are different (preferably, the difference of hue angles is 70 ° or more). It is preferable to select a colorant for the fourth ink. By doing so, it may be easy to visually recognize the discolored state of the recorded image.

  When the ink set according to this embodiment includes the fifth ink, the hue angles of the second ink and the fifth ink are different (preferably, the difference in hue angle is 70 ° or more), and the second ink In addition, it is preferable to select the pH color-changing dye contained in the fifth ink so that the color-changing regions of the pH color-changing dye contained in the fifth ink do not completely match. By doing so, the discoloration pattern of the recorded image can be further diversified, so that an image showing in more detail the history of light irradiation and heating applied to the image may be formed.

2. Recording Method A recording method according to an embodiment of the present invention includes a step of forming an image using the ink jet 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”).

  In addition, as an ink jet recording method, any method such as a method using a piezoelectric element or a method of rapidly expanding the volume of ink by the action of thermal energy can be used, but the change in ink characteristics due to heat can be reduced. From the viewpoint, a method using a piezoelectric element is preferable.

  Hereinafter, the recording method according to the present embodiment will be described in detail.

2.1. First Recording Method The first recording method according to the present embodiment includes a step of recording an image by bringing the first ink and the second ink into contact with each other on a recording medium.

  The first recording method according to this embodiment will be specifically described. Note that the first recording method according to the present embodiment is not limited to the following mode.

  First, the first ink droplets are ejected from the nozzles of the recording head of the printer to attach 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 the first ink droplet on the recording medium. In this way, it is possible to obtain a recorded matter in which an image composed 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 image obtained by the recording method according to the present embodiment changes color with a change in pH caused by the acid generated from the acid generator when heated or irradiated with light. That is, information such as light irradiation and heating history can be easily confirmed from the image. Therefore, an image (recorded material) obtained by the recording method can be used as an indicator that indicates a history of light irradiation or heating.

2.2. Second Recording Method The second recording method according to the present embodiment includes a step of bringing the first ink and the second ink into contact with each other on a recording medium to form a plurality of images, and containing the acid generator The ratio (W1 / W2) between the amount (W1) and the content (W2) of the pH color-changing dye is different for each image.

  Hereinafter, the second recording method according to the present embodiment will be specifically described with reference to FIGS. 1 and 2. Note that the second recording method according to the present embodiment is not limited to the following mode.

  FIG. 1 is a schematic view showing a plurality of images formed using the first ink. FIG. 2 is a schematic diagram showing a plurality of images formed using the first ink and the second ink.

  First, a first ink droplet is ejected from a nozzle of a recording head of a printer to form a plurality of first images having different contents of the acid generator in each of a plurality of regions having the same area. (See FIG. 1). The method for making the content of the acid generator different for each region is not particularly limited, and for example, a method for recording under a condition where the Duty value is different for each of the plurality of first images.

  In this specification, the “Duty value” is a value calculated by the following equation.

Duty (%) = number of actual ejection dots / (vertical resolution × horizontal resolution) × 100
(In the formula, “number of actual ejection dots” is the number of actual ejection dots per unit area, and “vertical resolution” and “horizontal resolution” are resolutions per unit area.)

  Next, droplets of the second ink are ejected from the nozzles of the recording head of the printer, and the droplets of the second ink are brought into contact with each of the plurality of first images. A plurality of second images composed of two inks are formed (see FIG. 2). A method for making the content of the pH color-changing dyes equal among the images is not particularly limited, and examples thereof include a method of recording each of the plurality of second images under an equal duty value.

  In this way, on the recording medium, a plurality of images in which the ratio (W1 / W2) of the content (W1) of the acid generator and the content (W2) of the pH-changing dye is different from each other. Is formed.

  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.

  Among the obtained images, an image with a large value of the ratio (W1 / W2) has a faster color change due to heating or light irradiation, and an image with a small value of the ratio (W1 / W2) has a heating effect. And the color change of the image accompanying light irradiation becomes slow. That is, by forming a plurality of images, it is possible to confirm (view) the intermediate point in time of light irradiation or heating history. Therefore, by forming a plurality of images by the recording method, information such as light irradiation and heating history can be known in more detail. Therefore, an image (recorded material) obtained by the recording method can be used as an indicator that shows details of light irradiation, heating history, and the like.

  Thus, by forming a plurality of images by the second recording method, it is possible to obtain more detailed information such as light irradiation and heating history than when forming a single image by the first recording method. it can.

2.3. Recording medium As the 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 and dedicated paper having an ink receiving layer, for example, The region including the surface to which the ink is applied is made of various plastics, ceramics, glass, metal, or the substrate made of these composite materials.

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 Each component shown in Table 2 was mixed and stirred to prepare a first ink A, a first ink B, and a first ink C. The photoacid generator used for the first ink A and the first ink B was used by dissolving in advance with trioxypropylene glyceryl ether (Newpol GP-250).

  In addition, the second ink A and the second ink B were prepared by mixing and stirring the components shown in Table 3. In addition, the pH color-changing dye contained in the second ink A and the second ink B was used after being dissolved in ethanol in advance.

Among the components described in Table 2 and Table 3, the components described by abbreviations and trade names are as follows. Tables 2 and 3 also show the pH immediately after the preparation of each ink. A commercially available pH meter was used to measure the pH of each ink.
Photoacid generator 1 (2- (4-methoxyphenyl) -4,6-bis (trichloromethyl) -1,3,5-triazine)
Photoacid generator 2 (2-pyridyl (tribromomethyl) sulfone)
-Thermal acid generator (4-hydroxyphenylbenzylmethylsulfonium hexafluoroantimonate)
・ New Pole GP-250 (trade name, manufactured by Sanyo Chemical Industries, polyoxypropylene glyceryl ether)
・ 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.

3.3. Evaluation Test (1) Preparation of Evaluation Sample First, a first ink droplet is ejected from the nozzle of the printer, and a plurality of areas having the same area have a plurality of different duty values of the first ink. A first image was formed (see FIG. 1). The duty value at the time of forming each image was set to 40% to 130% duty as shown in FIG.

  Next, the second ink droplet is ejected from the nozzle of the printer, the second ink droplet is brought into contact with each of the plurality of first images, and the plurality of second images having the same duty value of the second ink. (Consisting of the second ink) was formed (see FIG. 2). The duty value when forming each image was set to 40% duty as shown in FIG. As a result, a plurality of images in which the first image and the second image were stacked were formed on the recording medium.

  Thus, the evaluation sample which concerns on Example 1- Example 5 was obtained. As the recording medium, 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 Co., Ltd., pH 5). It was.

(2) Evaluation method About the evaluation sample which concerns on Example 1- Example 3 among the obtained evaluation samples, an integrated light quantity is 200 mJ / cm < ² > using ultraviolet irradiation device Fusion UV Systems Japan F450 series. Ultraviolet rays were irradiated so that On the other hand, the evaluation samples according to Example 4 and Example 5 were left in an environment of 60 ° C. for 10 hours. Then, the color change of each image was confirmed visually.

3.4. Evaluation results The results of the evaluation tests are also shown in Table 4 above. Moreover, the color change of each image is typically shown in FIGS.

  3A, FIG. 4A, FIG. 5A, FIG. 6A, and FIG. 7A were recorded using the ink sets according to Examples 1 to 5, respectively. It is a figure which shows typically the image before a color change (immediately after evaluation sample preparation).

  3 (B), 4 (B), 5 (B), 6 (B), and 7 (B) were recorded using the ink sets according to Examples 1 to 5, respectively. It is a figure which shows typically the discoloration state immediately after the evaluation test of an image.

  From the evaluation results of Examples 1 to 3, it was shown that the image irradiated with light was discolored by the action of the photoacid generator and the pH color-changing dye. In addition, the evaluation results of Example 4 and Example 5 showed that the heated image changes color due to the action of the thermal acid generator and the pH color-changing dye.

  Moreover, as shown in FIGS. 3 to 7, it is shown when one image is recorded by recording a plurality of images in which the ratio of the content of the acid generator and the content of the pH-changing dye is different from each other. It was confirmed that detailed information (heating time, light irradiation amount, etc.) that cannot be displayed can be displayed.

  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 (8)

An inkjet ink set comprising a plurality of inks,
A first ink containing an acid generator;
a second ink containing a pH color-changing dye;
An inkjet ink set comprising: In claim 1,
An inkjet ink set, wherein the acid generator is a thermal acid generator or a photoacid generator. In claim 2,
The thermal acid generator is an ink jet ink set that generates an acid in a temperature range of 40 ° C. or higher and 200 ° C. or lower. In claim 2 or claim 3,
An inkjet ink set, wherein the thermal acid generator is at least one selected from a sulfonium salt, a monosulfone compound, and a sulfonate ester. In claim 2,
The photo acid generator is at least one selected from iodonium salts, sulfonium salts, triazine compounds, sulfonic acid esters, monosulfone compounds, diazodisulfone compounds, imide sulfonates, oxime sulfonates, and nitrobenzodisulfsulfonates. Ink set. A recording method using the inkjet ink set according to any one of claims 1 to 5,
A recording method comprising a step of bringing the first ink and the second ink into contact on a recording medium to form an image. A recording method using the inkjet ink set according to any one of claims 1 to 5,
Forming a plurality of images by bringing the first ink and the second ink into contact with each other on a recording medium;
The recording method, wherein a ratio (W1 / W2) of the content (W1) of the acid generator and the content (W2) of the pH color-changing dye is different for each image.   A recorded matter obtained by using the recording method according to claim 6.