Irreversible heat sensitive color developing ink and printing device using the same

Abstract

To provide an irreversible thermosensitive color development ink which can be used in printing on a charging control type ink jet printer, and which can be discolored to a chromatic color by integration of a temperature and time when a temperature of a printing dot formed by printing becomes equal to or greater than a prescribed temperature, and provide a printer using the same.SOLUTION: An irreversible thermosensitive color development ink according to the present invention includes, a leuco dye, a developer, a decoloring agent and a solvent. At least one of the leuco dye, the developer and the decoloring agent is not microencapsulated. In the irreversible thermosensitive color development ink, volatility satisfies a relationship of the solvent>the decoloring agent>the leuco dye and the developer. By volatilization of the decoloring agent, the ink is developed to a chromatic color.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an irreversible thermosensitive color developing ink and a printing device using the same. [Background technology]

[0002] Due to the need for quality control of foods, medicines, etc., there is a demand for uninterrupted temperature control throughout the distribution process of production, transportation, and consumption. For example, at the production stage of foods, medicines, etc., temperature control is performed to determine whether necessary heating treatment (e.g., heat treatment at around 60°C) and sterilization treatment (e.g., sterilization treatment at around 110°C) are being performed appropriately. In addition, at the stages of transportation and consumption, temperature control is performed, for example, to keep products at low temperatures without interruption (cold chain).

[0003] In order to constantly measure and record the temperature during production and transportation, data loggers that can continuously record time and temperature are often installed. This makes it possible to clarify where responsibility lies if necessary heating or sterilization processes are not performed, or if the product is damaged. However, data loggers are not suitable for managing individual products due to their price and size.

[0004] When managing the quality of individual products, relatively inexpensive temperature indicators may be used instead of data loggers. Although temperature indicators do not have the same recording accuracy as data loggers, they can be attached to individual products, and the surface becomes dyed when the temperature exceeds or falls below a preset temperature, making it possible to know changes in the temperature environment. However, temperature indicators are often unsuitable for use in mass-produced products in terms of cost and attachment speed.

[0005] Meanwhile, charge-controlled inkjet printers are used in a wide range of fields, such as food and electronic components, to print expiration dates, use-by dates, serial numbers, etc. If a charge-controlled inkjet printer could print ink that irreversibly changes color in response to temperature changes, it would be more suitable for temperature control of mass-produced products than a temperature indicator in terms of cost and printing speed.

[0006] Patent Document 1 discloses an erasable inkjet ink that can form a high-density image and can be erased to a sufficiently invisible state. Specifically, Patent Document 1 discloses an erasable inkjet ink that contains a leuco dye, a water-insoluble developer, and a solvent containing alcohol and water, and the amount of the water is 7% by mass or more and 25% by mass or less of the solvent.

[0007] Patent Document 2 discloses a heat-sensitive recording material that utilizes a color-developing reaction between a leuco dye and a color developer, and is characterized by using a benzoic anhydride derivative represented by a specific general formula as a sensitivity enhancer. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2012-224789 A [Patent Document 2] Publication No. 2729253 Summary of the Invention [Problem to be solved by the invention]

[0009] In order for a charge-controlled inkjet printer to print ink that irreversibly changes color in response to temperature changes on mass-produced products at high speed, it is necessary to solve several problems, such as the following. For example, the ink printed by the inkjet must be able to dry quickly and form printed dots. In addition, the printed dots must have high adhesion to the mass-produced products. Furthermore, in order for the inkjet printer to print with high resolution, it is necessary to be able to eject ink from inkjet nozzles with a small aperture.

[0010] In order to use the printed dots as a temperature indicator, it is preferable that the color change caused by the temperature change be clearly visible, so the ink color must be one that changes from colored to colored in an easily noticeable way, or from colorless to colored.

[0011] In addition, when managing products whose quality deteriorates depending on temperature and time, such as fresh foods and biopharmaceuticals, time-temperature indicators that change color as a cumulative result of time and temperature are used. In order to use printed dots as such time-temperature indicators, the ink must change color as a cumulative result of time and temperature in response to temperature changes.

[0012] Under such circumstances, the erasable inkjet ink disclosed in Patent Document 1 is mainly composed of a solvent containing water. Therefore, it is expected that this erasable inkjet ink will not dry fast enough when printing at high speed, and will not have high adhesion to plastics and the like that are often used in mass-produced products. In addition, this erasable inkjet ink is an ink that changes color from colored to colorless when heated, making it difficult to use as a temperature indicator. Furthermore, this erasable inkjet ink is also difficult to use as a time-temperature indicator, since it does not take into account the color change due to the accumulation of time and temperature.

[0013] The thermal recording material disclosed in Patent Document 2 contains a solid material that is not completely dissolved in the solvent component. Therefore, when this thermal recording material is applied to a charge-control type inkjet printer, it is expected that it will be difficult to stably eject ink from a small-diameter inkjet nozzle. In addition, this thermal recording material is characterized by a high color development speed, making it difficult to use it as a time-temperature indicator that changes color with the accumulation of time and temperature.

[0014] The present invention has been made in consideration of the above problems, and it is an object of the present invention to provide an irreversible thermosensitive color-developing ink that can be printed by a charge-controlled inkjet printer and that changes color to a color depending on the cumulative effect of temperature and time when the printed dots reach a predetermined temperature or higher, and a printing device that uses the same. [Means for solving the problem]

[0015] In order to solve the above problems, the irreversible thermosensitive color developing ink according to the present invention includes a leuco dye, a color developer, a decolorizer, and a solvent, at least one of the leuco dye, the color developer, and the decolorizer is not microencapsulated, and the volatility of the ink satisfies the relationship of the solvent>the decolorizer>the leuco dye and the color developer, the decolorizing agent is a compound dissolved in the solvent to dissociate a bond between the leuco dye and the developer and to bring the leuco dye into a decolorized state; The print dots formed by printing with an inkjet printer are configured to develop color when the temperature reaches a temperature at which the decolorizing agent volatilizes. Effect of the Invention

[0016] According to the present invention, it is possible to provide an irreversible thermosensitive color-developing ink that can be printed by a charge-controlled inkjet printer and that changes color to a color depending on the cumulative effect of temperature and time when the printed dots formed by printing reach or exceed a predetermined temperature, and a printing device using the same. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic diagram showing an inkjet head of a charge control type inkjet printer. [Figure 2A]FIG. 2 is a schematic cross-sectional view of a printed dot formed by printing the irreversible thermosensitive color developing ink according to the present embodiment using a charge-controlled inkjet printer in an environment at or below a predetermined temperature. [Figure 2B] FIG. 2 is a schematic cross-sectional view of a printed dot formed by printing the irreversible thermosensitive color developing ink according to the present embodiment using a charge-controlled inkjet printer in an environment exceeding a predetermined temperature. [Diagram 3] FIG. 1 is a schematic diagram illustrating an example of a printing device using an irreversible thermosensitive color developing ink according to an embodiment of the present invention. [Figure 4] FIG. 13 is a schematic diagram illustrating another example of a printing device using the irreversible thermosensitive color developing ink according to the present embodiment. [Diagram 5] FIG. 13 is a schematic diagram illustrating another example of a printing device using the irreversible thermosensitive color developing ink according to the present embodiment. [Figure 6] FIG. 13 is a schematic diagram illustrating another example of a printing device using the irreversible thermosensitive color developing ink according to the present embodiment. [Figure 7] FIG. 2 is a schematic diagram illustrating an example of a writing device using the irreversible thermosensitive color developing ink according to the present embodiment. [Figure 8] 11 is a schematic diagram illustrating another example of a writing device using the irreversible thermosensitive color developing ink according to the present embodiment. FIG. [Figure 9A] 1 is a photograph showing the time-temperature dependency of printed dots using the irreversible thermosensitive color developing ink of Example 1. The figure shows the state after 1 minute at 110° C. under normal pressure. [Figure 9B] FIG. 9B is a schematic diagram of FIG. 9A. [Figure 9C] 1 is a photograph showing the time-temperature dependency of printed dots using the irreversible thermosensitive color developing ink of Example 1. The figure shows the state after 10 minutes at 110° C. under normal pressure. [Figure 9D] FIG. 9C is a schematic diagram. [Figure 10A] 5 is a photograph showing the time-temperature dependency of printed dots using the irreversible thermosensitive color developing ink of Example 2. The figure shows the state after 2 minutes at 110° C. under normal pressure. [Figure 10B]FIG. 10B is a schematic diagram of FIG. 10A. [Figure 10C] 5 is a photograph showing the time-temperature dependency of printed dots using the irreversible thermosensitive color developing ink of Example 2. The figure shows the state after 20 minutes at 110° C. under normal pressure. [Figure 10D] FIG. 10C is a schematic diagram. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as an "embodiment") will be described in detail with reference to the drawings as appropriate. In each drawing, the same reference numerals are given to common parts, and duplicated explanations will be omitted.

[0019] <Irreversible heat sensitive color developing ink> An irreversible thermosensitive color developing ink (hereinafter, sometimes simply referred to as "ink") according to one embodiment of the present invention contains a leuco dye, a color developer, a decolorizing agent, and a solvent. In addition, in the ink according to this embodiment, at least one of the leuco dye, the color developer, and the decolorizing agent is not microencapsulated. Furthermore, the ink according to this embodiment satisfies the relationship of volatility: solvent>decolorizing agent>leuco dye and color developer. The ink according to this embodiment develops a color as the decolorizing agent volatilizes. First, the leuco dye, color developer, decolorizing agent, and solvent in the ink according to this embodiment will be described.

[0020] <Leuco dye> Leuco dyes are electron donating compounds. Leuco dyes can be those known as dyes for pressure sensitive copying paper or dyes for thermal recording paper. Leuco dyes can be, for example, triphenylmethanephthalide, fluoran, phenothiazine, indolylphthalide, leucoauramine, spiropyran, rhodamine lactam, triphenylmethane, triazene, spirophthalane xanthene, naphtholactam, azomethine, etc. Specific examples of leuco dyes include 2'-methyl-6'-(Np-tolyl-N-ethylamino)spiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one, 9-(N-ethyl-N-isopentylamino)spiro[benzo[a]xanthene-12,3'-phthalide], 2-methyl-6-(Np-tolyl-N-ethylamino)-fluoran 6-(diethylamino)-2-[(3-trifluoromethyl)anilino]xanthene-9-spiro-3'-phthalide, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, and 3,3-bis(p-diethylaminophenyl)-6-diphenylphthalide. Methylaminophthalide, 2'-anilino-6'-(dibutylamino)-3'-methylspiro[phthalide-3,9'-xanthene], 3-(4-diethylamino-2-methylphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 1-ethyl-8-[N-ethyl-N-(4-methylphenyl)amino]-2,2,4-trimethyl-1,2-dihydrospiro[11H-chromeno[2,3-g]quinoline-11,3'-phthalide], 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylamino-2-methylphenyl)-4-azaphthalide, and the like. The leuco dye may be any one selected from the above-exemplified compounds, or may be a combination of two or more.

[0021] <Developer> The color developer changes the structure of the leuco dye by contacting with the electron-donating leuco dye to cause the leuco dye to develop a color. The color developer may be a known one used in thermal recording paper or pressure-sensitive copying paper. Specific examples of the color developer include phenols such as 4-hydroxybenzoate benzyl, 2,2'-biphenol, 1,1-bis(3-cyclohexyl-4-hydroxyphenyl)cyclohexane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)cyclohexane, α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene, bisphenol A, bisphenol F, bis(4-hydroxyphenyl)sulfide, paraoxybenzoic acid esters, and gallic acid esters (e.g., octyl gallate). The color developer is not limited to these, and any compound that is an electron acceptor and can change the color of the leuco dye can be used. In addition, the color developer can be metal salts of carboxylic acid derivatives, salicylic acid and metal salts of salicylic acid, sulfonic acids, sulfonates, phosphoric acids, metal salts of phosphoric acids, acidic phosphates, metal salts of acidic phosphates, phosphorous acids, metal phosphorous acids, and the like.In particular, the developer is preferably one that is highly compatible with the leuco dye and the decolorizing agent described later, and examples of such developers include 4-hydroxybenzoate benzyl, 2,2'-bisphenol, 4,4'-cyclohexylidenebis(2-cyclohexylphenol), 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(2-hydroxy-5-biphenylyl)propane, 4,4'-cyclohexylidenebis(o-cresol), 2,2-bis(4-hydroxy-3-methylphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, bisphenol P, 4,4'-(9-fluorenylidene)diphenyl ether, and the like. Organic developers such as phenol, bisphenol A, bisphenol M, 4,4'-thiodiphenol, bisphenol S, 4,4'-biphenol, 4,4'-oxydiphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-(1,3-dimethylbutylidene)diphenol, 4,4'-(2-ethylhexylidene)diphenol, 4,4'-ethylidenebisphenol (bisphenol E), 4,4'-(2-hydroxybenzylidene)bis(2,3,6-trimethylphenol), 1,1'-methylenebis(2-naphthol), tetrabromobisphenol A, and gallic acid esters are preferred. The developer may be any one selected from the above-mentioned exemplary compounds, or may be a combination of two or more. The developer may be a combination of two or more, which allows the color density of the leuco dye to be adjusted. The amount of developer used is selected according to the desired color density. The amount of developer used may be selected, for example, within the range of about 0.1 to 100 parts by mass per part by mass of the leuco dye.

[0022] <Decolorizing agent> The decolorizing agent is a compound capable of dissociating the bond between the leuco dye and the color developer, and is a compound capable of controlling the color development temperature and time between the leuco dye and the color developer. In the temperature range in which the leuco dye is in a decolorized state immediately after the formation of the printed dot, the function of dissociating the bond between the leuco dye and the color developer is exerted. On the other hand, for example, when the printed dot formed by printing the ink with a printing device such as an inkjet printer is exposed to a certain temperature or higher or heated to a temperature at which the decolorizing agent volatilizes (evaporates), the decolorizing agent volatilizes and disappears from the printed dot, and the leuco dye shows a colored state (develops into a color). This makes it possible to know that the control temperature has been exceeded. Therefore, the state change temperature of the decolorizing agent is important for the temperature control of the printed dot. In this specification, "develops into a color" refers to, for example, changing from a colorless and transparent state to a color in the visible light region, and changing from a specific colored state to another colored state in the visible light region. Here, the inkjet printer is preferably a charge-controlled inkjet printer, as described below. In this manner, when a charge-controlled inkjet printer is used, a temperature indicator that is suitable for temperature control of mass-produced products can be realized from the standpoint of cost and printing speed.

[0023] For example, when the ink according to the present embodiment is used for quality control of a product that is considered normal at or below the controlled temperature and is considered abnormal when exposed to a temperature exceeding the controlled temperature for a certain period of time, the printed dots formed using the ink according to the present embodiment must not develop color for a long period of time at or below the controlled temperature. In such a case, the decolorizing agent in the printed dots must not volatilize for a long period of time at or below the controlled temperature, but must volatilize for a certain period of time at a temperature exceeding the controlled temperature. When the temperature is below the controlled temperature, the decolorizing agent contained in the ink according to the present embodiment must not volatilize even in the printing device before the printed dots are formed. Therefore, it is preferable that the decolorizing agent used in the present embodiment has a high boiling point so that it hardly evaporates at a temperature of about room temperature under a normal pressure (for example, about 101 kPa). Although it depends on the usage environment and the controlled temperature of the target product, the color development temperature, that is, the temperature at which the decolorizing agent volatilizes from the printed dots, is, for example, about 40 to 180° C. at normal pressure. More specifically, it is preferable that the color development time is about several hours to several days at 40° C. at normal pressure, and about several minutes to several hours at 100° C. at normal pressure. As a decolorizing agent that can realize these color development temperatures and color development times, it is preferable to use one that has a boiling point of about 80 to 370° C. at normal pressure. In this way, for example, in the production stage of foods, medicines, etc., it is possible to know whether necessary heating treatment (for example, heat treatment at about 60° C.) or sterilization treatment (for example, sterilization treatment at about 110° C.) is being properly performed.

[0024] If the volatilization of the decolorizing agent in the ink before printing can be suppressed, a decolorizing agent having a boiling point of about 40 to 80°C at normal pressure can be used, and the color development temperature of the ink can be lowered. Therefore, the ink according to this embodiment can be used for temperature control of products with low control temperatures. The volatilization of the decolorizing agent in the ink before printing can be suppressed, for example, by providing a cooling mechanism adjacent to a holding part that holds an ink tank (ink container / ink cartridge) of a printing device such as an inkjet printer, or by providing a mechanism for mixing the decolorizing agent with a mixed liquid containing a leuco dye, a color developer, and a solvent immediately before printing. These aspects will be described later.

[0025] A wide variety of materials can be used as decolorants as long as they can dissociate the bond between the leuco dye and the developer. Various materials can be used as decolorants as long as they have low polarity, do not exhibit color development to the leuco dye, and have high polarity to the extent that they can dissolve the leuco dye and the developer. Representative examples of decolorants that can be used include various organic compounds such as hydroxy compounds, ester compounds, peroxy compounds, carbonyl compounds, aromatic compounds, aliphatic compounds, halogen compounds, amino compounds, imino compounds, N-oxide compounds, aliphatic amine compounds, hydroxylamine compounds, nitro compounds, azo compounds, diazo compounds, azide compounds, ether compounds, oils and fats compounds, sugar compounds, peptide compounds, nucleic acid compounds, alkaloid compounds, and steroid compounds. Of these, the decolorizing agent preferably has a boiling point of about 80 to 370° C. at normal pressure and is highly volatile. Specific examples of the decolorizing agent include aliphatic amine compounds such as ethylamine, dibutylamine, triethylamine, tripropylamine, 3-aminopropyldiethoxymethylsilane, 3-aminopropyldimethoxymethylsilane, bis(hexamethylene)triamine, bis(2-methoxyethyl)amine, 1,4-butanediolbis(3-aminopropyl)ether, didecylmethylamine, N,N-didodecylmethylamine, di-n-octylamine, isophoronediamine, and dibenzylamine, and hydroxylamine compounds such as ethanolamine, N,N-diethylethanolamine, N-ethyldiethanolamine, triethanolamine, and N-butyldiethanolamine. From the viewpoint of compatibility with the leuco dye and the developer, the decolorizing agent preferably contains these compounds. Of course, the decolorizing agent is not limited to these compounds, and any material that can dissociate the bond between the leuco dye and the color developer may be used. The decolorizing agent may be any one selected from the above-mentioned exemplary compounds, or may be a combination of two or more. By combining decolorizing agents, the volatilization speed, the color development temperature, and the color development time can be adjusted.

[0026] <Solvent> The ink according to the present embodiment is applied to an electrostatically controlled inkjet printer and is assumed to be used for printing on mass-produced products, so it is preferable to use a solvent with a high drying speed. In addition, the ink used in the electrostatically controlled inkjet printer must have a viscosity of about several mPa·s. Furthermore, the ink according to the present embodiment must contain at least a leuco dye, a color developer, and a decolorizer, and must dissolve these materials. Examples of solvents that satisfy these requirements at the same time include alcohols such as methanol, ethanol, and propanol, ketones such as acetone, methyl ethyl ketone, isopropyl methyl ketone, and cyclohexanone, esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate, and ethers such as dimethyl ether and tetrahydrofuran.

[0027] In addition, in order to provide high adhesion to general-purpose plastics such as polypropylene, polyethylene, and polyethylene terephthalate, which are widely used in mass-produced products, a resin (binder material) with low polarity may be dissolved in the ink. In this case, an organic solvent with low polarity is preferable as the solvent. Examples of such organic solvents include alcohols such as butanol and pentanol, ketones such as acetone, methyl ethyl ketone, isopropyl methyl ketone, and cyclohexanone, esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate, and ethers such as dimethyl ether and tetrahydrofuran.

[0028] As described above, in the ink according to the present embodiment, at least one of the leuco dye, the color developer, and the decolorizer is not microencapsulated. When the particles are microencapsulated, the particle size becomes larger. Therefore, the more microencapsulated particles the ink contains, the more difficult it becomes for the particles to fly as intended in a charge-controlled inkjet printer that prints by applying an electric charge to ink droplets, and the more difficult it tends to be to print high-definition characters. In the ink according to the present embodiment, at least one of the leuco dye, the color developer, and the decolorizer is not microencapsulated, so that high-definition characters can be printed when printed by a charge-controlled inkjet printer, compared to when all of these are microencapsulated. From the viewpoint of printing even higher-definition characters with a charge-controlled inkjet printer, it is preferable that all of the leuco dye, the color developer, and the decolorizer are not microencapsulated.

[0029] Even if one or two of the leuco dye, developer, and decolorizer contained in the ink according to the present embodiment are microencapsulated, for example, when the ink is used in a DOD (Drop On Demand) type inkjet printer, high-definition characters can be printed. A DOD type inkjet printer controls the ejection and stopping of ink droplets by changing the volume of a piezoelectric element (piezoelectric element) provided in the nozzle when energized, or by opening and closing a solenoid valve provided in the nozzle when energized, to perform printing. In other words, a DOD type inkjet printer can print without applying an electric charge to ink droplets. Therefore, as described above, a DOD type inkjet printer can print high-definition characters even if one or two of the leuco dye, developer, and decolorizer are microencapsulated.

[0030] As described above, the ink according to the present embodiment satisfies the following relationship in terms of volatility: solvent>decolorizer>leuco dye and developer. In this way, since the solvent has the highest volatility, the solvent can volatilize quickly to form printed dots after the ink is printed on a target product by a printing device such as a charge-controlled inkjet printer. Since the volatility of the decolorizer is higher than that of the leuco dye and developer, when the printed dot is exposed to a certain temperature or higher or heated, the decolorizer volatilizes before the leuco dye and developer and disappears from the printed dot. Therefore, the leuco dye and developer remaining in the printed dot cause the printed dot to develop a color due to the accumulation of temperature and time. The color development of the printed dot will be described in detail later.

[0031] <Pigments and dyes> As described above, the ink according to this embodiment contains at least a leuco dye, a color developer, a decolorizer, and a solvent, but may contain materials other than these as long as the color developing properties of the ink are not impaired. For example, the ink according to this embodiment may contain a pigment or dye to the extent that the color development characteristics of the ink are not impaired. By containing a pigment or dye, the color of the ink before development (the color of the printed dots) and the color of the ink after development (the color of the printed dots) can be changed as desired. Any pigment or dye that is used in printing inks can be used, but when used in inkjet printers, those with a finer particle size are preferable. The size of the pigment is preferably 500 nm or less, more preferably 100 nm or less. The size of the dye is preferably 50 nm or less, more preferably 10 nm or less.

[0032] <Binder material> The ink according to the present embodiment may contain a binder material, which can improve the adhesion of the print dots when the print target is general-purpose plastic, metal, glass, film, or the like. The binder material can be any resin that is soluble in a solvent commonly used in the fields of ink, paint, adhesives, etc., within a range that does not impair the color development characteristics of the ink. In the case of this embodiment, for example, in order to impart high adhesion to general-purpose plastics that are widely used as mass-produced products, it is preferable to use a resin with low polarity as the main material of the binder material. Examples of such low polarity resins include styrene resin, styrene-acrylic resin, acrylic resin, end-blocked epoxy resin, vinyl chloride-vinyl acetate copolymer resin, butyral resin, various rosin-modified resins, phenolic resin, novolac resin, polyamide resin, polyester resin, xylene resin, maleic acid resin, various cellulose resins, etc. As the binder material, the above-mentioned resins can be used alone or in combination of two or more types so that the viscosity of the ink according to this embodiment is within a few mPa·s. In addition, the ink according to this embodiment can be applied to various printing objects such as nonwoven fabrics and papers in addition to general-purpose plastics, metals, glass, and films. The ink according to this embodiment can be used by appropriately selecting a binder material having high adhesion to each printing object.

[0033] When the ink according to the present embodiment contains a binder material, it is preferable that the volatility satisfy the following relationship: solvent > decolorizing agent > leuco dye and color developer > binder material. In this way, the binder material has the lowest volatility and remains to the end, preventing the printing dots from being removed.

[0034] <Measurement of Volatility> In this specification, the volatility of each of the solvent, the decolorizing agent, the leuco dye, the color developer, and the binder material can be measured by, for example, a method of measuring the vapor pressure using a pressure gauge or the like, a method of measuring the boiling point using an ebullometer or a differential scanning calorimeter, or a method of measuring the evaporation amount using a heat-drying type moisture meter or the like, but is not limited to these.

[0035] <Additives> When the ink according to the present embodiment is used as ink for a charge-controlled inkjet printer, if a leuco dye and a developer having high electrical conductivity can be used, a conductive agent is not necessary. On the other hand, if the leuco dye and the developer cannot provide sufficient electrical conductivity to the ink, electrical conductivity can be provided by adding a conductive agent. It is preferable to use a complex as the conductive agent. It is necessary for the conductive agent to be soluble in a solvent, and it is also important that the conductive agent does not affect the color tone. Furthermore, conductive agents having a salt structure are generally used. It is presumed that this is because the charge is biased within the molecule, and therefore high electrical conductivity can be achieved.

[0036] As a result of consideration from the above viewpoints, it is preferable that the conductive agent has a salt structure. The conductive agent with a salt structure is preferably one in which the cation has a tetraalkylammonium ion structure. The alkyl chain may be either linear or branched, and the larger the carbon number, the better the solubility in the solvent. However, the smaller the carbon number, the lower the resistance can be with a small addition rate. The practical number of carbons for use in ink is about 2 to 8. The conductive agent having a salt structure is preferably one in which the anion is a hexafluorophosphate ion, a tetrafluoroborate ion, or the like, because it has high solubility in a solvent.

[0037] Preferred conductive agents include, for example, tetraethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, tetrapentylammonium hexafluorophosphate, tetrahexylammonium hexafluorophosphate, tetraoctylammonium hexafluorophosphate, tetraethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetrapentylammonium tetrafluoroborate, tetrahexylammonium tetrafluoroborate, and tetraoctylammonium tetrafluoroborate.

[0038] In addition, the surface of the printed dots after the solvent has dried may not be smooth, and the color development state of the printed characters or marks may not exhibit a uniform color density. In such cases, a leveling agent can be suitably used as an additive. The leveling agent is effective in forming flat and small printed dots by flattening the printed dots or preventing the dots from spreading. As the leveling agent, for example, commonly used surfactants, lubricants, modifier flow, etc. can be used. As the leveling agent, for example, silicone oil and its modified derivatives, fluorine-based lubricants, lanolin, palm oil, carnauba wax, etc. can be used.

[0039] In addition, the ink according to this embodiment may further contain plasticizers, surfactants, lubricants, various adhesives, pressure sensitive adhesives, softeners, etc., to compensate for the color development speed of the printing dots and adhesion to the substrate, within a range that does not impair the color development properties of the ink. As described above, the ink according to the present embodiment is intended for use as ink for charge-control inkjet printers, but it can also be used as ink for pens, stamps, etc., or as paint for printing such as screen printing.

[0040] <Ink for charge-control inkjet printers> As described above, one of the assumptions is that the ink according to the present embodiment will be applied to a charge-controlled inkjet printer, i.e., the ink according to the present embodiment is used as ink for a charge-controlled inkjet printer. FIG. 1 is a schematic diagram showing an inkjet head 11 of a charge control type inkjet printer 10. As shown in FIG. As shown in Fig. 1, an inkjet head 11 of a charge-controlled inkjet printer 10 includes a nozzle 12, a charging electrode 13, a deflection electrode 14, and a gutter 15. The nozzle 12 is a device that ejects an ink solution as minute ink droplets 16 by changing the volume of a piezoelectric element when electricity is applied. The charging electrode 13 is an electrode that imparts an electric charge to the ejected ink droplets 16. The deflection electrode 14 is an electrode that controls the flight direction of the charged ink droplets 16 to land them on a print target 17.

[0041] When the ink according to this embodiment is used as ink for a charge-controlled inkjet printer, if the resistivity in solution is high, the ink droplets 16 tend to curve rather than fly straight in the inkjet head 11 of the charge-controlled inkjet printer 10. For this reason, it is preferable that the ink for a charge-controlled inkjet printer has a resistivity in solution of approximately 2 kΩ cm or less.

[0042] Furthermore, in order for the print dots 2 after the ink droplets 16 land to represent characters or codes, it is necessary to regularly eject the ink droplets 16 from the nozzles 12 with an aperture diameter of about 40 to 100 μm. In this case, if solid materials with a diameter of about several μm such as impurities are present in the ink, the ink droplets 16 will not fly straight, making it difficult to print high-definition characters. For this reason, it is preferable that the materials in the ink are uniformly dissolved in the solvent. If the ink contains a pigment, it is preferable to use a pigment with as small a diameter as possible. As mentioned above, the size of the pigment is preferably 500 nm or less.

[0043] <Print dots> The ink of this embodiment is printed on a print target 17 by an inkjet printer (particularly, a charge-controlled inkjet printer) to form print dots 2, and then develops a color as a result of the accumulation of temperature and time when the temperature reaches or exceeds a predetermined temperature at which the decolorizing agent 5 (see Figures 2A and 2B) volatilizes.

[0044] Fig. 2A is a schematic cross-sectional view of a printed dot 2 formed by printing the ink according to this embodiment using the charge-controlled inkjet printer 10 in an environment below a predetermined temperature (control temperature). Fig. 2B is a schematic cross-sectional view of a printed dot 2 formed by printing the ink according to this embodiment using the charge-controlled inkjet printer 10 in an environment above a predetermined temperature (control temperature).

[0045] As shown in Fig. 2A, the ink (not shown) according to this embodiment is printed on a substrate 1 (subject to be printed 17) by a charge-controlled inkjet printer 10, and then the main component, a solvent (not shown), evaporates to form a printed dot 2. The formed printed dot 2 contains a leuco dye 3, a color developer 4, and a decolorizer 5. Note that, if the ink according to this embodiment contains a binder material, the binder material (not shown) is also contained in the printed dot 2. By containing a resin as a binder material, the printed dot 2 can adhere highly to the substrate 1, such as plastic.

[0046] The print dots 2 contain a leuco dye 3, which is an electron donating compound, and a developer 4, which is an electron accepting compound, and thus develop a color due to the structure of the leuco dye 3. On the other hand, the print dots 2 have the characteristic of being decolorized when they contain a certain amount of a decolorizing agent 5, which is a compound capable of dissociating the bond between the leuco dye 3 and the developer 4.

[0047] As shown in FIG. 2A, when the printed dot 2 is placed in an environment below a specified temperature (controlled temperature), it contains a certain amount of decolorizing agent 5, so that the bond between the leuco dye 3 and the developer 4 is dissociated and the dot is in a decolorized state. From this state, if the printing dot 2 is placed in an environment that exceeds a specified temperature (control temperature) at which the decolorizing agent 5 volatilizes, the decolorizing agent 5 begins to volatilize, and after a certain amount of time has passed at that temperature, the leuco dye 3 and the developer 4 combine, as shown in Figure 2B, and the color resulting from the structure of the leuco dye 3 is developed.

[0048] At this time, if the leuco dye 3, developer 4, and decolorant 5 contained in the print dot 2 are colorless or white materials (if a binder material is included, the binder material is also colorless or white), the print dot 2 formed by inkjet is colorless or white immediately after printing. Then, when the temperature reaches a predetermined temperature or higher at which the decolorant 5 volatilizes due to heating or the like, the print dot 2 develops a color that depends on the leuco dye 3. In this way, the print dot 2 formed using the ink according to this embodiment can exhibit a function of irreversibly changing color from colorless to color in response to a change in temperature, like a temperature indicator.

[0049] Furthermore, if at least one of the leuco dye 3, developer 4, and decolorizer 5 contained in the print dot 2 is a colored material (if a binder is included, the binder is a colored material), or if a colored material such as a dye is added to the ink, the print dot 2 immediately after formation will be colored. When the temperature reaches a predetermined level at which the decolorizer 5 volatilizes due to heating or the like, the color will be developed according to the leuco dye 3, and the colored print dot 2 can be changed to another color.

[0050] The temperature and time at which the printed dots 2 develop color depend on the volatilization temperature and speed of the decolorizing agent 5. Since the volatilization speed of the decolorizing agent 5 increases as the temperature increases, the printed dots 2 can be used as a time-temperature indicator that changes color as a function of the cumulative time and temperature.

[0051] The volatilization temperature of the decolorant 5 in the print dot 2 is also affected by the leuco dye 3 and the developer 4 (and also by the binder if a binder is included). The volatilization temperature of the decolorant 5 in the print dot 2 is also greatly dependent on the boiling point and saturated vapor pressure of the decolorant 5. For this reason, by using a decolorant 5 with a boiling point and saturated vapor pressure suitable for the temperature and time conditions suitable for quality control of the print target 17, it is possible to adjust the temperature and speed at which the print dot 2 develops.

[0052] <Printing device> The ink according to this embodiment can be applied to any general printing device used for offset printing, gravure printing, flexographic printing, letterpress printing, screen printing, on-demand printing, and the like. However, as described above, the ink according to the present embodiment develops its color by volatilizing the decolorizing agent. In order to prevent unnecessary color development and to appropriately monitor the control temperature, it is preferable that a printing device using the ink according to the present embodiment adopts a configuration that prevents the decolorizing agent from volatilizing from the ink inside the device before printing. A printing device that prints using the ink according to this embodiment will now be described with reference to Fig. 3 to Fig. 6. Fig. 3 to Fig. 6 are all schematic diagrams illustrating an example of a printing device that uses the ink according to this embodiment. Fig. 3 to Fig. 6 all show printing devices that employ a configuration that prevents the decolorizing agent from volatilizing. Note that the same reference numerals are used to designate configurations that are common to each aspect, and detailed descriptions thereof will be omitted.

[0053] <First Aspect of Printing Device> 3, a printing device 30 according to a first embodiment is a charge-controlled inkjet printer 10 equipped with a first container holding unit 31 and a cooling unit 32. The first container holding unit 31 and the cooling unit 32 are provided in a printing device main body 33. The first container holding unit 31 holds an ink container A that contains the ink according to this embodiment. The cooling unit 32 is provided adjacent to the first container holding unit 31 and cools the first container holding unit 31.

[0054] The printing device body 33 includes a main container 34 that mixes the inks and supplies the inks to the nozzles 12, and a solvent container 35 that contains a solvent. The main container 34 and the ink container A held in the first container holding portion 31 are connected by an ink supply path 36, so that the ink in the ink container A can be replenished to the main container 34 through the ink supply path 36. Furthermore, the main container 34 and the gutter 15 in the inkjet head 11 are connected by a recovery path 37, so that the ink droplets 16 recovered in the gutter 15 can be supplied to the main container 34 through the recovery path 37. Furthermore, the main container 34 and the solvent container 35 are connected by a solvent supply line 38, so that the solvent in the solvent container 35 can be supplied to the main container 34 through the solvent supply line 38. The ink in the main container 34 is controlled in terms of concentration, viscosity, etc., and ink is replenished from the ink container A and solvent is supplied from the solvent container 35 as appropriate so that the concentration and viscosity are within the respective prescribed ranges. The main container 34 and the nozzles 12 are connected by an ink supply passage 39, so that the ink in the main container 34 can be supplied to the nozzles 12 through the ink supply passage 39. The nozzles 12 supplied with ink eject ink droplets 16 from their ejection openings.

[0055] As described above, the printing device 30 is provided with the cooling unit 32 that cools the first container holding unit 31, and therefore the ink in the ink container A held in the first container holding unit 31 can be cooled by cooling the first container holding unit 31 with the cooling unit 32. Therefore, the volatilization of the solvent and decolorizing agent in the ink container A can be prevented. It is more preferable that the printing device 30 is provided with a cooling device (not shown) for cooling the main container 34. In this way, the ink is more suitably cooled, and the volatilization of the solvent and decolorizing agent can be further prevented.

[0056] <Second embodiment of the printing device> 4, a printing device 40 according to the second embodiment is a charge-controlled inkjet printer 10 equipped with a second container holding unit 41, a third container holding unit 42, and a main container 34. The second container holding unit 41, the third container holding unit 42, and the main container 34 are provided within a printing device body 33. The second container holder 41 holds a mixed liquid container B that contains a mixed liquid containing a leuco dye, a developer, and a solvent. The third container holder 42 holds a decolorant container C that contains a decolorant. The main container 34 is a container that mixes the mixed liquid supplied from the mixed liquid container B and the decolorant supplied from the decolorant container C to produce the ink according to this embodiment.

[0057] The main container 34 and the mixed liquid container B held in the second container holding portion 41 are connected by a mixed liquid supply path 43, so that the mixed liquid in the mixed liquid container B can be replenished to the main container 34 through the mixed liquid supply path 43. In addition, the main container 34 and the decolorant container C held in the third container holding portion 42 are connected by a decolorant supply path 44, so that the decolorant in the decolorant container C can be replenished to the main container 34 through the decolorant supply path 44.

[0058] As described above, the printing device 40 mixes the mixed liquid supplied from the mixed liquid container B and the decolorant supplied from the decolorant container C in the main container 34. In this way, the printing device 40 mixes the mixed liquid and the decolorant immediately before supplying ink to the nozzles 12, and therefore can prevent the decolorant in the main container 34 from volatilizing.

[0059] <Third aspect of the printing device> 5, the printing device 50 according to the third embodiment differs from the printing device 30 according to the first embodiment in that the charge-controlled inkjet printer 10 of the printing device 30 is replaced with a DOD inkjet printer 51. More specifically, the printing device 50 differs from the printing device 30 according to the first embodiment in that the inkjet head 11 of the printing device 30 according to the first embodiment is replaced with a DOD inkjet head 52. Other than that, the printing device 50 and the printing device 30 have the same configuration.

[0060] The DOD inkjet head 52 performs printing by controlling the ejection and stopping of ink droplets 16 by changing the volume of a piezoelectric element provided in the nozzle 12 when energized, or by opening and closing a solenoid valve provided in the nozzle 12 when energized. In other words, the DOD inkjet printer 51 performs printing without applying an electric charge to the ink droplets 16.

[0061] The printing device 50 also includes a cooling unit 32 that cools the first container holding unit 31, and therefore the ink in the ink container A held in the first container holding unit 31 can be cooled by cooling the first container holding unit 31 with the cooling unit 32. Therefore, the printing device 50 can prevent the solvent and decolorizing agent in the ink container A from volatilizing. It is more preferable that the printing device 50 also includes a cooling device (not shown) for cooling the main container 34. In this way, the ink is more suitably cooled, and the volatilization of the solvent and decolorizing agent can be further prevented.

[0062] <Fourth aspect of the printing device> 6, the printing device 60 according to the fourth embodiment differs from the printing device 40 in that the charge-controlled inkjet printer 10 of the printing device 40 according to the second embodiment is replaced by a DOD inkjet printer 51. More specifically, the printing device 60 differs from the printing device 40 in that the inkjet head 11 of the printing device 40 according to the second embodiment is replaced by a DOD inkjet head 52. Other than that, the printing device 60 and the printing device 40 have the same configuration.

[0063] The printing device 60 also mixes the mixed liquid supplied from the mixed liquid container B and the decolorant supplied from the decolorant container C in the main container 34. In this way, the printing device 60 also mixes the mixed liquid and the decolorant just before supplying ink to the nozzles 12, so that the volatilization of the decolorant in the main container 34 can be prevented.

[0064] In this way, the ink according to this embodiment can be printed by the charge control type ink jet printer 10, but can also be printed by the DOD type ink jet printer 51. Moreover, the ink container A, the mixed liquid container B and the decolorizing agent container C described in the first to fourth embodiments of the printing device can be of a replaceable cartridge type.

[0065] <Writing device> Next, a writing device capable of writing with the ink according to this embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 and Fig. 8 are both schematic diagrams for explaining an example of a writing device using the ink according to this embodiment. As described above, the ink according to this embodiment develops its color by volatilizing the decolorizing agent. In order to prevent unnecessary color development and to properly monitor the controlled temperature, it is preferable that a writing device using the ink according to this embodiment adopts a configuration that prevents the decolorizing agent from volatilizing from the ink inside the device before printing. Both Fig. 7 and Fig. 8 show writing devices that adopt a configuration that prevents the decolorizing agent from volatilizing. Note that the same symbols are used for configurations that are common to each aspect, and detailed explanations are omitted.

[0066] <First embodiment of the writing device> As shown in FIG. 7, a writing device 70 according to a first embodiment includes an ink case 72 and a writing device cooling section 73 inside a substantially cylindrical outer case 71. The ink case 72 contains the ink according to this embodiment. The writing device cooling section 73 is provided inside the outer case 71 so as to cover the outer periphery of the ink case 72, and cools the ink case 72. As the writing device cooling section 73, for example, a coolant (refrigerant) that has been cooled or frozen in advance can be used. The outer case 71 and the ink case 72 may be formed from any resin.

[0067] The ink case 72 is connected to the pen tip portion 74 so that the ink in the ink case 72 can be supplied to the pen tip portion 74. An observation window 75 can be provided in the outer case 71. In this way, if the ink case 72 is made of a transparent material, the amount of ink remaining in the ink case 72 can be checked.

[0068] As described above, the writing device 70 is provided with the writing device cooling unit 73 that cools the ink case 72, and therefore the ink in the ink case 72 can be cooled by cooling the ink case 72 with the writing device cooling unit 73. Therefore, the writing device 70 can prevent the volatilization of the solvent and decolorizing agent in the ink case 72.

[0069] <Second embodiment of the writing device> As shown in FIG. 8, a writing device 80 according to the second embodiment includes a mixed liquid case 81, a decolorizing agent case 82, and a main case 83 inside a substantially cylindrical outer case 71. The mixed liquid case 81 contains a mixed liquid containing a leuco dye, a developer, and a solvent. The decolorizer case 82 contains a mixed liquid containing a decolorizer. The main case 83 is connected to the mixed liquid case 81 and the decolorizer case 82. The main case 83 mixes the mixed liquid supplied from the mixed liquid case 81 with the decolorizer supplied from the decolorizer case 82 to form the ink according to this embodiment, and supplies the ink to the pen tip portion 74. The mixed liquid case 81, the decolorizing agent case 82 and the main case 83 may all be made of any resin.

[0070] The writing device 80 mixes the mixed liquid supplied from the mixed liquid case 81 and the decolorant supplied from the decolorant case 82 in the main case 83. In this way, the writing device 80 mixes the mixed liquid and the decolorant just before supplying ink to the pen tip portion 74, and therefore can prevent the decolorant in the main case 83 from volatilizing.

[0071] Next, the irreversible thermosensitive color developing ink will be described in more detail with reference to examples and comparative examples, although the present invention is not limited to these examples. EXAMPLES

[0072] <Preparation of irreversible heat-sensitive color-developing ink> The leuco dye used was 4 parts by weight of 2'-methyl-6'-(Np-tolyl-N-ethylamino)spiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one (RED520 manufactured by Yamada Chemical Industry Co., Ltd.), the developer was 8 parts by weight of octyl gallate manufactured by Tokyo Chemical Industry Co., Ltd., the decolorizer was 8 parts by weight of N,N-diethylethanolamine with a boiling point of 162°C, the binder was 10 parts by weight of a copolymer of polyvinyl alcohol and polyvinyl acetate with a number average molecular weight (Mn) of 10,000 (repeating number of polyvinyl alcohol units:repeating number of polyvinyl acetate units ≒ 36:64, hydroxyl value is 285), and the solvent was 70 parts by weight of methyl ethyl ketone. The irreversible heat-sensitive color-developing ink was prepared by mixing these materials for about 1 hour.

[0073] The volatility of the solvent, decolorizer, leuco dye and developer, and binder material was verified by measuring the amount of evaporation when 1 g of each material was heated at 110°C for 1 minute using a heat-dry moisture meter MS-70. As a result, the volatility of the solvent was 99%, that of the decolorizer was 20%, that of the leuco dye and developer was 0.01 wt%, and that of the binder was 0 wt%. It was confirmed that the relationship of volatility is solvent > decolorizer > leuco dye and developer > binder material.

[0074] <Evaluation of temperature and time detection functions> The ink thus prepared was filled into a UX-type inkjet printer manufactured by Hitachi Industrial Equipment Systems Co., Ltd., and used to print on a white polypropylene substrate. The dots printed on the substrate were initially colorless. After leaving the solution at 20°C for one week, it was confirmed that the solution remained colorless. When the substrate on which the dots were printed was left in an environment of 110°C under normal pressure, it was confirmed that the red color started to develop gradually after 1 minute (see Figs. 9A and 9B), and the red color was completely developed after 10 minutes (see Figs. 9C and 9D). It is considered that this color development occurred due to the volatilization of the decolorizing agent. Fig. 9A is a photograph showing the time-temperature dependence of the dots printed using the irreversible thermosensitive color developing ink according to Example 1. The figure shows the state after 1 minute at 110°C under normal pressure. Fig. 9B is a schematic diagram of Fig. 9A. Fig. 9C is a photograph showing the time-temperature dependence of the dots printed using the irreversible thermosensitive color developing ink according to Example 1. The figure shows the state after 10 minutes at 110°C under normal pressure. Fig. 9D is a schematic diagram of Fig. 9C. Thereafter, the substrate on which the dots were printed was again placed in an environment of 20°C, and it was confirmed that the dots that had once developed a red color did not return to their original colorless state and retained their red color. On the other hand, as described above, when the substrate on which the print dots were printed was left to stand in an environment of normal pressure and 60°C, it was confirmed that the substrate began to gradually develop a red color after one day, and the red color was completely developed after one week (not shown).

[0075] From the above, it was confirmed that the irreversible thermosensitive color developing ink according to Example 1 can be printed on a substrate using a charge-controlled inkjet printer. It was also confirmed that the printed dots formed by printing in this manner can change color by integrating temperature and time when the temperature reaches a predetermined temperature or higher. Furthermore, it was confirmed that the color change of the printed dots that have changed color once is irreversible. EXAMPLES

[0076] <Preparation of irreversible heat-sensitive color-developing ink> The leuco dye used was 4 parts by weight of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (CVL manufactured by Yamada Chemical Industry Co., Ltd.), the developer was 8 parts by weight of octyl gallate manufactured by Tokyo Chemical Industry Co., Ltd., the decolorizer was 8 parts by weight of triethanolamine with a boiling point of 335°C, the binder was 10 parts by weight of a copolymer of polyvinyl alcohol and polyvinyl acetate with a number average molecular weight (Mn) of 10,000 (repeating number of polyvinyl alcohol units:repeating number of polyvinyl acetate units ≒ 36:64, hydroxyl value 285), and the solvent was 70 parts by weight of methyl ethyl ketone. The irreversible heat-sensitive color developer ink was produced by mixing these materials for about an hour.

[0077] As in Example 1, the volatility of the solvent, the volatility of the decolorizer, the volatility of the leuco dye and the color developer, and the volatility of the binder material were verified by measuring the amount of evaporation when 1 g of each material was heated at 110°C for 1 minute using a heat-dry moisture meter MS-70. As a result, the volatility of the solvent was 99%, that of the decolorizer was 10%, that of the leuco dye and developer was 0.01 wt%, and that of the binder was 0 wt%. It was confirmed that the relationship of volatility is solvent > decolorizer > leuco dye and developer > binder material.

[0078] <Evaluation of temperature and time detection functions> The ink thus prepared was filled into a UX-type inkjet printer manufactured by Hitachi Industrial Equipment Systems Co., Ltd., and used to print on a white polypropylene substrate. The dots printed on the substrate were initially colorless. After leaving the solution at 20°C for one week, it was confirmed that the solution remained colorless. When the substrate on which the dots were printed was left in an environment of 110°C under normal pressure, it was confirmed that the blue color started to develop gradually after 2 minutes (see Figs. 10A and 10B), and the blue color was completely developed after 20 minutes (see Figs. 10C and 10D). It is considered that this color development occurred due to the volatilization of the decolorizing agent. Fig. 10A is a photograph showing the time-temperature dependence of the dots printed using the irreversible thermosensitive color developing ink according to Example 2. The figure shows the state after 2 minutes at 110°C under normal pressure. Fig. 10B is a schematic diagram of Fig. 10A. Fig. 10C is a photograph showing the time-temperature dependence of the dots printed using the irreversible thermosensitive color developing ink according to Example 2. The figure shows the state after 20 minutes at 110°C under normal pressure. Fig. 10D is a schematic diagram of Fig. 10C. Thereafter, the substrate on which the printed dots were printed was again placed in an environment of 20°C, and it was confirmed that the printed dots that had once turned blue did not return to their original colorless state and retained their blue color. On the other hand, when the substrate on which the dots were printed was left to stand in an environment of 60°C under normal pressure as described above, it was confirmed that the substrate began to gradually turn blue after three days, and the blue color was completely developed after two weeks (not shown).

[0079] From the above, it was confirmed that the irreversible thermosensitive color developing ink according to Example 2 can also be printed on a substrate using a charge-controlled inkjet printer. It was also confirmed that the printed dots formed by printing in this manner can change color by integrating temperature and time when the temperature reaches a predetermined temperature or higher. Furthermore, it was confirmed that the color change of the printed dots that have once changed color is irreversible. In addition, from the results of Example 2 and Example 1, it was confirmed that by using decolorizing agents with different boiling points in the irreversible thermosensitive color developing ink, it is possible to adjust the discoloration temperature and time of the printed dots formed by the charge-controlled inkjet printer. EXAMPLES

[0080] <Preparation of irreversible heat-sensitive color-developing ink> The leuco dye used was 4 parts by weight of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (CVL manufactured by Yamada Chemical Industry Co., Ltd.), the developer was 8 parts by weight of octyl gallate manufactured by Tokyo Chemical Industry Co., Ltd., the decolorizer was 8 parts by weight of triethanolamine with a boiling point of 335°C, and the solvent was 80 parts by weight of methyl ethyl ketone. These materials were mixed for about 1 hour to prepare an irreversible heat-sensitive color-developing ink. As with Example 2, the relationship of volatility is solvent>decolorizer>leuco dye and developer.

[0081] <Evaluation of temperature and time detection functions> The ink thus prepared was filled into a UX-type inkjet printer manufactured by Hitachi Industrial Equipment Systems Co., Ltd., and used to print on a white polypropylene substrate. The dots printed on the substrate were initially colorless. After leaving the solution at 20°C for one week, it was confirmed that the solution remained colorless. When the substrate with the printed dots was left in an environment of 110°C under normal pressure, it was confirmed that the blue color began to develop gradually after 2 minutes, and the blue color developed completely after 20 minutes (the photographs and schematic diagrams were the same as those in Figures 10A to 10D). This color development is thought to have occurred due to the volatilization of the decolorizing agent. After that, the substrate with the printed dots was left in an environment of 20°C again, and it was confirmed that the printed dots that had once developed a blue color did not return to their original colorless state, but retained their blue color. On the other hand, when the substrate on which the dots were printed was left to stand in an environment of 60°C under normal pressure as described above, it was confirmed that the substrate began to gradually turn blue after three days, and the blue color was completely developed after two weeks (not shown). From the above, it was confirmed that even with ink that does not contain a binder material, the performance of printed dots developing color is dependent on temperature and time.

[0082] The irreversible thermosensitive color developing ink and the printing device using the same according to the present invention have been described in detail above through embodiments and examples, but the gist of the present invention is not limited to these and includes various modified examples. For example, the above-mentioned embodiments have been described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0083] 1 Base material 2 Print dots 3 Leuco dyes 4. Developer 5. Decolorizer 6 Binder material 10. Charge-controlled inkjet printer 11 Inkjet head 12 Nozzles 13 Charged electrode 14 Deflection electrode 15 Gutter 16 Ink Drops 17 Printing target 30, 40, 50, 60 printing equipment 31 First container holding part 32 Cooling section 33 Printing device body 34 Main Container 35 Solvent container 41 Second container holding part 42 Third container holding part

Claims

1. Contains a leuco dye, a developer, a decolorizer and a solvent, At least one of the leuco dye, the developer, and the decolorizer is not microencapsulated; The volatility satisfies the relationship of the solvent>the decolorizing agent>the leuco dye and the color developer, the decolorizing agent is a compound dissolved in the solvent to dissociate a bond between the leuco dye and the developer and to bring the leuco dye into a decolorized state; The dots printed by the inkjet printer become colored when the temperature reaches a level at which the decolorizing agent volatilizes. An irreversible heat-sensitive color developing ink.

2. In claim 1, Further comprising a binder material, The volatility satisfies the relationship of the solvent>the decolorizing agent>the leuco dye and the color developer>the binder material. An irreversible heat-sensitive color developing ink.

3. In claim 1, The irreversible heat-sensitive color developing ink is characterized in that the ink-jet printer is a charge-control type ink-jet printer.

4. In claim 1, The irreversible thermosensitive color developing ink, wherein the decolorizing agent is an amine compound.

5. In claim 1, The irreversible thermosensitive color developing ink is characterized in that the boiling point of the decolorizing agent is 80 to 370°C.

6. In claim 1, 1. An irreversible thermosensitive color developing ink, wherein the solvent contains at least one of alcohols, ketones, esters, and ethers.

7. In claim 1, An irreversible heat-sensitive color developing ink comprising at least one of a conductive agent, a leveling agent, and a plasticizer.

8. A printing device that prints using the irreversible thermosensitive color developing ink according to any one of claims 1 to 7, a first container holder for holding an ink container containing the irreversible thermosensitive color developing ink; A cooling unit provided adjacent to the first container holding unit and configured to cool the first container holding unit; A printing device comprising:

9. A printing device that prints using the irreversible thermosensitive color developing ink according to any one of claims 1 to 7, a second container holder for holding a mixed liquid container containing a mixed liquid including the leuco dye, the color developer, and the solvent; a third container holder that holds a decolorant container containing the decolorant; a main container for mixing the mixed liquid supplied from the mixed liquid container and the decolorant supplied from the decolorant container to produce the irreversible thermosensitive color developing ink; A printing device comprising:

10. Contains a leuco dye, a developer, a decolorizer and a solvent, At least one of the leuco dye, the developer, and the decolorizer is not microencapsulated; The volatility satisfies the relationship of the solvent>the decolorizing agent>the leuco dye and the color developer, the decolorizing agent is a compound dissolved in the solvent to dissociate a bond between the leuco dye and the developer and to bring the leuco dye into a decolorized state; A printing device that prints using an irreversible thermosensitive color developing ink that develops a color when the decolorizing agent volatilizes, a first container holder for holding an ink container containing the irreversible thermosensitive color developing ink; A cooling unit provided adjacent to the first container holding unit and configured to cool the first container holding unit; A printing device comprising:

11. Contains a leuco dye, a developer, a decolorizer and a solvent, At least one of the leuco dye, the developer, and the decolorizer is not microencapsulated; The volatility satisfies the relationship of the solvent>the decolorizing agent>the leuco dye and the color developer, the decolorizing agent is a compound dissolved in the solvent to dissociate a bond between the leuco dye and the developer and to bring the leuco dye into a decolorized state; A printing device that prints using an irreversible thermosensitive color developing ink that develops a color when the decolorizing agent volatilizes, a second container holder for holding a mixed liquid container containing a mixed liquid including the leuco dye, the color developer, and the solvent; a third container holder that holds a decolorant container containing the decolorant; a main container for mixing the mixed liquid supplied from the mixed liquid container and the decolorant supplied from the decolorant container to produce the irreversible thermosensitive color developing ink; A printing device comprising:

Images