JP2013216836A - 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 displaying the lapse of time and an experienced heat history is recorded.SOLUTION: An ink set for inkjet includes a plurality of ink, and includes: first ink containing an acidic substance or a basic substance with a normal boiling point of 370°C or lower; and second ink containing a pH color change type pigment, wherein the acidic substance is exemplified by an organic acid, and the basic substance is exemplified by an organic amine.

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, it has been impossible to know the elapsed time, the history of heat received, and the like from the recorded image.

  Some aspects according to the present invention provide an ink set that can record an image that displays a history of time or received heat by solving at least a part of the above-described problems, a recording method using the ink set, and the ink set It is to provide a recorded matter obtained by.

  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 acidic substance or a basic substance having a standard boiling point of 370 ° C. or lower;
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 passage of time and the heat history. Specifically, an image recorded using the first ink and the second ink changes color due to volatilization of an acidic substance or a basic substance with the passage of time or heating. By doing so, it is possible to easily know the passage of time and the heat history.

[Application Example 2]
In application example 1,
The acidic substance may be an organic acid.

[Application Example 3]
In application example 1,
The basic substance may be an organic amine.

[Application Example 4]
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 3,
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 the application example 4, it is possible to record an image that displays the passage of time and the heat history.

[Application Example 5]
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 3,
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 acidic substance or the basic substance and the content (W2) of the pH color-changing dye is different for each image.

  According to the aspect described in the application example 5, it is possible to record an image that displays the passage of time and the heat history in detail.

[Application Example 6]
One aspect of the recorded matter of the present invention is:
The recording method described in Application Example 4 or Application Example 5 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.

  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 jet ink set according to an embodiment of the present invention includes a plurality of inks, and includes a first ink containing an acidic substance or a basic substance having a standard boiling point of 370 ° C. or lower, and a pH color-changing dye. Second ink.

  The pH of an image obtained by bringing the first ink and the second ink (described later) into contact with each other on the recording medium gradually increases as the acidic or basic substance having a standard boiling point of 370 ° C. or less contained in the first ink volatilizes. To change. For this reason, an image recorded using the first ink and the second ink becomes a color different from the original recorded color due to the action of the pH-changing dye contained in the second ink.

  Thus, when the inkjet ink set according to the present embodiment is used, it is possible to easily obtain an image capable of displaying a time lapse, a heating history, and the like.

  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. First ink 1.1.1. 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 acidic substance and the basic substance have volatile properties, they volatilize when the image made of the first ink is left or heated. Since the pH of the image recorded using the first ink changes due to the volatilization of the substance, the color of the image composed of the second ink formed in contact with the first ink 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 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 will be described later. It is preferable to set in consideration of the value and the like. As specific content, it can be set as 0.1 to 15 mass% with respect to the total mass of 1st ink, for example. When the content of the substance is within the above range, particularly not less than 0.1% 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 is within the above range, particularly not exceeding 15% by mass, the corrosion of the head member may be suppressed.

1.1.2. 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 may 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. 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 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.

(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 according to the application and is not particularly limited. However, for example, the content of the pH-changing dye is 0.1% by mass or more and 5% by mass or less with respect to the total mass of the second ink. Preferably, it is 0.1 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.

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.

  Other inks of the first ink and the second ink include, for example, the third ink containing the above acidic substance or basic substance, the fourth ink containing the above colorant, and the above pH discoloration type dye. 5th ink etc. are mentioned.

  When the ink set according to the present embodiment includes the third ink, the third ink may contain the acidic substance or the basic substance so as to have a pH different from that of the first ink. For example, when the first ink contains the acidic substance, the third ink contains a basic substance, and when the first ink contains the basic substance, the third ink contains an acidic substance. May be contained. By doing so, images with different discoloration patterns 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 there may be a case where an image showing more detailed information such as the passage of time and the heat history 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 first recording method changes color with the passage of time or volatilization of the acidic substance or basic substance by heating. That is, information such as the passage of time and heat history can be easily confirmed from the image. Therefore, the image (recorded material) obtained by the recording method can be used as an indicator that indicates the passage of time, thermal history, or the like.

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 the acidic substance or the base The ratio (W1 / W2) between the content (W1) of the active substance 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, and a plurality of first substances having different contents of the acidic substance or the basic substance are respectively contained in a plurality of regions having the same area. An image is formed (see FIG. 1). The method for varying the content of the acidic substance or basic substance for each region is not particularly limited, and examples thereof include a method of recording under a condition where the duty values are 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.

  Thus, on the recording medium, the ratio (W1 / W2) of the content (W1) of the acidic substance or the basic substance and the content (W2) of the pH color-changing dye is mutually different. A plurality of different images are 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.

  According to the second recording method, the rate of change in the pH of the image can be freely adjusted by adjusting the ratio (W1 / W2). Specifically, among the obtained images, an image having a large value of the ratio (W1 / W2) has a slow color change of the image, and an image having a small value of the ratio (W1 / W2) is The color change of the image becomes faster. That is, by forming a plurality of images, it is possible to confirm (view) a thermal history or an intermediate point in time. Therefore, a plurality of images (recorded materials) obtained by the recording method can be used as indicators that show in detail the passage of time, the history of heating, 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 time lapse 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.

  Among such recording media, when a recording medium having an acidic property (for example, acidic paper) is used, an image is recorded using a first ink containing a basic substance and a second ink. The pH of the recorded image tends to be inclined toward 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 The first ink A and the first ink B were prepared by mixing and stirring the components shown in Table 2.

  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 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.
・ 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 the inks of combinations described in Examples 1 to 3 in Table 3 Set.

3.3. Evaluation Test First, a first ink droplet was ejected from the nozzle of the printer, and a plurality of first images having different duty values of the first ink were formed in each of a plurality of regions having the same area ( (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.

  In this way, a plurality of images in which the first image and the second image were stacked were formed on the recording medium. The recording medium is neutral paper (trade name “P paper”, manufactured by Fuji Xerox Co., Ltd., pH 7), or acidic paper (trade name “photo paper <gloss>”, manufactured by Seiko Epson Corporation, pH 5). Using.

  The obtained image was allowed to stand in an environment of 20 ° C. and 65% RH, and the color change of the image after 20 days was visually confirmed.

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, and FIG. 5A schematically illustrate color changes when an image recorded using the ink set according to each of Examples 1 to 3 is left for 10 days. FIG.

  FIGS. 3B, 4B, and 5B schematically illustrate color changes when an image recorded using the ink set according to each of Examples 1 to 3 is left for 20 days. FIG.

  From the evaluation results of Examples 1 to 3, it was shown that the recorded images discolored over time. Further, the evaluation result of Example 3 showed that discoloration of the image can be promoted by using acidic paper as the recording medium.

  Further, as shown in FIGS. 3 to 5, by recording a plurality of images in which the ratio of the content of the acidic substance or basic substance and the content of the pH-changing dye is different from each other, one image can be recorded. It was shown that detailed information (here, the passage of time) that cannot be displayed when recorded is 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 (6)

An inkjet ink set comprising a plurality of inks,
A first ink containing an acidic substance or a basic substance having a standard boiling point of 370 ° C. or lower;
a second ink containing a pH color-changing dye;
An inkjet ink set comprising: In claim 1,
The inkjet ink set, wherein the acidic substance is an organic acid. In claim 1,
The ink jet ink set, wherein the basic substance is an organic amine. A recording method using the inkjet ink set according to any one of claims 1 to 3,
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 3,
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) between the content (W1) of the acidic substance or the basic substance 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 4 or 5.