JP7734864B2 - Temperature indicator and method for manufacturing the same - Google Patents

Description

The present invention relates to a temperature indicator for checking the temperature history of a temperature detection object and a method for manufacturing a temperature indicator.

Fresh foods, frozen foods, vaccines, biopharmaceuticals, and other low-temperature-storage pharmaceuticals require a cold chain that maintains them at uninterrupted low temperatures throughout the production, transportation, and consumption distribution process. In practice, to constantly measure and record temperatures during distribution, shipping containers are often equipped with data loggers that can continuously record time and temperature, making it possible to determine who is responsible if a product is damaged.

When managing the quality of individual products, one method is to use a temperature indicator instead of a data logger. Although temperature indicators do not have the same recording accuracy as data loggers, they can be attached to individual products and their surface will become stained if the temperature exceeds or falls below a preset temperature, making it possible to detect changes in the temperature environment.

In particular, when managing the quality of products whose deterioration is dependent on temperature and time, such as fresh foods and biopharmaceuticals, TTIs (Time-Temperature Indicators), which change color as the time and temperature accumulate, are used.

Patent document 1 discloses a temperature-indicating material that irreversibly changes color at ambient temperatures and undergoes crystalline-amorphous or phase-separated-non-phase-separated transitions.

Patent document 2 discloses a temperature sensing material that can detect temperature increases and decreases and whose function can be initialized.

Japanese Patent Application Laid-Open No. 2000-131152 Japanese Patent Application Laid-Open No. 2018-179826

Although temperature indicators themselves are relatively inexpensive, they have the property of irreversibly changing color when the temperature exceeds or falls below a preset temperature. This means that temperature control is required before using the temperature indicator for product management, for example, when storing or transporting the temperature indicator, which can make it difficult to use the temperature indicator conveniently.

Meanwhile, the degree of irreversibility required of a temperature indicator varies depending on the product to which it is attached. In the case of expensive pharmaceuticals, there is also a need to prevent counterfeiting, and once the temperature exceeds the set temperature and the color changes, the temperature indicator must be completely irreversible, maintaining that color thereafter. However, for the quality control of inexpensive pharmaceuticals and food, it is sufficient if irreversibility is maintained throughout the distribution process, which takes place at or below ambient temperature. In fact, it is expected that the use of temperature indicators will be promoted by reducing the effort and cost involved in managing them.

As mentioned above, in order to apply this to the quality control of fresh foods and biopharmaceuticals, a temperature indicator that changes color as a function of time and temperature is required. One example of such a temperature indicator is one in which ink, whose viscosity changes with temperature, changes color as it penetrates a penetrating material. However, this type of temperature indicator has the drawback of being structurally complex and difficult to reduce in price, as the ink alone does not function as a temperature indicator. Furthermore, it is difficult to reuse temperature indicators such as those mentioned above.

Therefore, materials containing at least a leuco dye, a color developer, and a decolorizer may be applicable as temperature sensing materials and temperature indicators, due to the phenomenon in which amorphous or supercooled materials change from a decolorized state to a colored state upon crystallization. These materials can be initialized by melting them at temperatures above their melting point, returning them to a decolorized state even when in a colored state. Furthermore, the phenomenon in which amorphous or supercooled liquids change to a colored state upon crystallization occurs as a result of the accumulation of time and temperature, making them applicable as TTIs.

When applying TTI to the quality control of fresh foods and biopharmaceuticals, it is necessary to ensure that the relationship between the time and temperature at which TTI discolors and the time and temperature at which fresh foods and biopharmaceuticals deteriorate are consistent. When evaluating the quality of food and pharmaceuticals, reaction kinetic analysis, such as the Arrhenius law, is widely used. According to this, the rate of quality deterioration increases exponentially with increasing temperature. When using TTI, which develops its color by crystallizing from an amorphous state, the crystallization rate increases exponentially with increasing temperature within a certain temperature range. In other words, the rate of TTI discoloration increases exponentially with increasing temperature. Therefore, it is possible to ensure consistency between the relationship between the time and temperature at which TTI discolors and the relationship between the time and temperature at which food and pharmaceuticals deteriorate.

On the other hand, it is known that the crystallization rate has a maximum value in a certain temperature range, and the rate decreases above that temperature. Therefore, in a temperature range near the maximum value or higher, the discoloration rate decreases with increasing temperature. In other words, in this temperature range, the consistency between the relationship between the time and temperature at which TTI discolors and the relationship between the time and temperature at which food and pharmaceutical quality deteriorates is lost.

The temperature-indicating material disclosed in Patent Document 1 changes color between crystalline and amorphous states, so it is expected that the rate of color change will decrease with increasing temperature in a temperature range above the maximum value of the crystallization rate.

The temperature-sensing material disclosed in Patent Document 2 is capable of adjusting the color change rate by using two types of temperature-indicating materials that change color through crystallization. However, it is expected that the color change rate will decrease with increasing temperature in temperature ranges above the maximum value of the crystallization rate of one of the temperature-indicating materials.

The invention was made to solve the above-mentioned problems. That is, one of the objects of the present invention is to provide a temperature indicator and a method for manufacturing a temperature indicator that changes color due to the crystallization phenomenon of amorphous material, and that, in addition to the mechanism of this change, can detect abnormal heating by a sudden change in color in the high temperature range.

To solve the above problem, the temperature indicator of the present invention includes a first temperature sensing material that changes color due to the amorphous crystallization phenomenon, and a second temperature sensing material that changes color irreversibly within a temperature range higher than the glass transition point of the first temperature sensing material and lower than the melting point of the first temperature sensing material.

The temperature indicator manufacturing method of the present invention is a method for manufacturing a temperature indicator including a first temperature sensing material that changes color due to the amorphous crystallization phenomenon, and a second temperature sensing material that changes color irreversibly within a temperature range higher than the glass transition point of the first temperature sensing material and lower than the melting point of the first temperature sensing material, in which after initializing the color of the first temperature sensing material, and before the first temperature sensing material begins to change color, the second temperature sensing material is applied to a position close to the first temperature sensing material.

According to the present invention, temperature can be detected within a certain temperature range by the color changing as a function of time and temperature, and abnormal heating can be detected by the color changing abruptly at temperatures above that temperature range.

FIG. 1 is a diagram showing a differential scanning calorimetry curve of a temperature indicator. FIG. 2A is a diagram showing the temperature and time dependence of the crystallinity of a temperature indicating material. FIG. 2B is a graph showing the temperature dependence of the crystallization rate. FIG. 4 is a diagram showing a change in color density of the first temperature detecting material. FIG. 4A is a diagram schematically illustrating the first temperature detection material in a decolored state. FIG. 4B is a diagram schematically illustrating the color-developed state of the first temperature detection material. FIG. 5A is an optical microscope photograph of the phase-separated structure in a decolorized state. FIG. 5B is an optical microscope photograph of the phase-separated structure in a developed state. FIG. 6A is a graph showing the temperature dependence of the color change rate of the second temperature detecting material. FIG. 6B is a graph showing the temperature dependence of the color change rate of the first temperature detection material and the second temperature detection material. FIG. 7A is a graph showing the relationship between the color density of the second temperature detecting material and temperature. FIG. 7B is a graph showing the relationship between the color density of the first temperature detection material and the second temperature detection material and the temperature. FIG. 8 is a schematic diagram showing the configuration of the temperature indicator. FIG. 9 is a schematic diagram showing the configuration of the temperature indicator. FIG. 10 is a schematic diagram showing the configuration of the temperature indicator. FIG. 11A is a photograph showing the color density versus the time elapsed since the temperature deviation in the temperature indicator of the example. FIG. 11B is a photograph showing the color density versus the time elapsed since the temperature deviation in the temperature indicator of the example. FIG. 12 is a graph showing the time dependence of the color density of the temperature indicator of the embodiment. FIG. 13A is a photograph showing the temperature dependence of color density in the temperature indicator of the example. FIG. 13B is a photograph showing the temperature dependence of color density in the temperature indicator of the example. FIG. 14 is a graph showing the temperature dependency of the color density of the temperature indicator of the example. FIG. 15A is a photograph showing the change over time in color density of the first temperature detection material of the temperature indicator of the example. FIG. 15B is a photograph showing the change over time in color density of the second temperature detecting material of the temperature indicator of the example.

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, common parts are designated by the same reference numerals and duplicated explanations will be omitted.
<<Embodiment>>
A temperature indicator according to an embodiment of the present invention will now be described. The temperature indicator according to an embodiment of the present invention includes a first temperature sensing material and a second temperature sensing material.
<First temperature sensing material>
The first temperature detection material includes a temperature indicator. The configuration of the temperature indicator used in the first temperature detection material will be described below with reference to Figs. 1, 2A and 2B.
<Temperature indicating material>
The temperature indicator is a material whose color density changes reversibly with temperature change (heating up/down). The temperature indicator contains a leuco dye, which is an electron-donating compound, a developer, which is an electron-accepting compound, and a decolorizer for controlling the temperature range of the color change.

Figure 1 shows the differential scanning calorimetry (DSC) curve of a temperature indicator. A temperature indicator is a material that solidifies in an amorphous state without crystallizing when rapidly cooled after melting.

In Figure 1, crystallization does not occur during the temperature drop process (left-pointing arrow (←) in the figure), so no exothermic peak due to crystallization is observed. On the other hand, an exothermic peak due to crystallization is observed during the temperature rise process (right-pointing arrow (→) in the figure). At the temperature and time when this exothermic peak appears, crystallization progresses and the discoloration of the temperature indicator progresses. Tg is the glass transition point, and Tm is the melting point.

The temperature at which the exothermic peak appears depends on the heating rate and the elapsed time. This is because the crystallization phenomenon occurs as a result of the accumulation of temperature and time. If the temperature is raised slowly, the peak appears at a low temperature, and if the temperature is raised quickly, the peak appears at a high temperature, or does not appear at all and the material melts at the melting point Tm.

The crystallization rate at each temperature can be determined by measuring the change in crystallinity over time when the temperature is raised from an amorphous state below Tg and then placed at a constant temperature below the melting point Tm. Figure 2A shows the temperature and time dependence of the crystallinity of a temperature indicator. As shown in Figure 2A, crystallization does not progress even over a long period of time near Tg, but at temperatures higher than Tg, it progresses in a short period of time, depending on the temperature.

Specific methods for determining the crystallization rate are not particularly limited. For example, it can be calculated by measuring the temperature and time dependence of crystallinity using a differential scanning calorimeter (DSC). To determine the temperature and time dependence of crystallinity, a temperature indicator is melted at a temperature above its melting point (Tm) and then rapidly cooled to a predetermined temperature below its glass transition point (Tg) at a rate of, for example, -2000°C/s. The temperature is then rapidly increased to the predetermined temperature at a rate of, for example, 2000°C/s and held at that temperature for a certain period of time. During this holding period, the amorphous phase crystallizes, resulting in the detection of an exothermic peak due to crystallization. If the integrated value of the heat flux of this exothermic peak is considered the crystallinity, the time dependence of crystallinity at a predetermined temperature can be calculated, as shown in Figure 2A. If the time required for the crystallinity to reach, for example, half its value is considered the time required for crystallization, the reciprocal of this time can be calculated as a measure of the rate of crystallization (crystallization rate). Using this method, the temperature dependence of the crystallization rate shown in Figure 2B can be determined.

From Figure 2A, we can derive the time it takes for the degree of crystallinity to reach a constant value, and by using the inverse of this time as a measure of speed (crystallization rate), we can calculate the relationship between crystallization rate and temperature at each temperature, as shown in Figure 2B. Figure 2B shows that the crystallization rate has a maximum value T1 at a certain temperature.

Since color develops when crystallization occurs, the crystallization rate is set according to the detection temperature and detection time requirements as a temperature indicator. For example, if a temperature indicator begins to crystallize after one hour at a certain temperature, it can be used as a material to detect when one hour has passed at that temperature.

The specific method for determining the color development speed of a temperature sensing material is not particularly limited. For example, measurements can be made using a Peltier cooling and heating stage as a temperature controller and a camera or fiber-optic colorimeter as a color detection method. To determine the temperature and time dependence of color density, the temperature sensing material is melted at a temperature above its melting point (Tm) and then rapidly cooled to a predetermined temperature below its glass transition point (Tg) at a rate of, for example, -30°C/min. The temperature is then rapidly increased to the predetermined temperature at a rate of, for example, 30°C/min and maintained at that temperature for a certain period of time. While maintained at that temperature, the color change process of the temperature sensing material is observed using a camera or colorimeter. The method for calculating color density is also not particularly limited. It is possible to evaluate the color in RGB or Lab color space using a camera or colorimeter, and calculate the color density based on the color difference from a specific color, such as white. This allows the time dependence of color density at each temperature to be measured as a graph like that shown in Figure 2A. If the time required for the color density to reach, say, half of its original value is considered to be the time required for the color to change, the reciprocal of this time can be calculated as a measure of the speed required for the color to change (the color change rate). Using this method, it is possible to obtain the temperature dependence of the color change rate as a graph like that shown in Figure 2B. The temperature dependence of this color change rate has almost the same relationship as the temperature dependence of the crystallization rate.

Below, we will describe a temperature-sensing material whose color changes depending on the cumulative effect of time and temperature, and whose color can be initialized by heating at high temperatures.

Figure 3 is a diagram showing the change in color density of the temperature indicator of the first temperature indicator of the embodiment. In Figure 3, the vertical axis represents color density and the horizontal axis represents temperature.

Figure 3 shows the relationship between the color density of a temperature indicator and temperature. Temperature indicators have a hysteresis characteristic in the change in color density. If a material that does not easily crystallize is used as the temperature indicator or decolorizer, when the temperature indicator is rapidly cooled from a molten state P above the decolorization initiation temperature Td of the temperature indicator to below the color development initiation temperature Ta, the decolorizer forms an amorphous state while incorporating the color developer, maintaining the decolorized state. If the temperature is raised from this state to above the color development initiation temperature Ta during the temperature rise process, the decolorizer crystallizes and develops color. Therefore, by using a temperature indicator containing a temperature indicator, when temperature is controlled below the color development initiation temperature Ta, it is possible to detect whether the temperature has deviated from the control range and reached a temperature above Ta.

When a temperature indicator is used to manage the temperature of goods such as merchandise during distribution, it is required that the color does not change. Even if the temperature rises and the color changes during distribution, if the temperature drops again during the distribution process and the color returns to normal, it will be impossible to determine whether the temperature has changed or not. However, the temperature indicator of this embodiment does not change color unless heated above the color-disappearing temperature Td, making it possible to detect changes in the temperature environment.

The color development start temperature Ta of the temperature indicator is close to Tg, and the color disappearance start temperature Td is close to Tm, so Tg and Tm are set according to the required specifications as a temperature indicator.

Next, the leuco dye, color developer, and decolorizer that constitute the temperature indicating material will be described.
(Leuco dye)
The leuco dye is an electron-donating compound, and may be any of those conventionally known as dyes for pressure-sensitive copying paper or thermal recording paper, such as triphenylmethanephthalide-based dyes, fluorans-based dyes, phenothiazine-based dyes, indolylphthalide-based dyes, leucoauramine-based dyes, spiropyran-based dyes, rhodamine lactam-based dyes, triphenylmethane-based dyes, triazenes-based dyes, spirophthalane xanthene-based dyes, naphtholactam-based dyes, and azomethine-based dyes. Specific examples of leuco dyes include 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-diethylaminophenyl)-6-dimethylaminophthalide, 2′-anilino-6 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].

The temperature indicating material may be a combination of two or more leuco dyes.
(Developer)
The color developer changes the structure of the leuco dye upon contact with the electron-donating leuco dye, causing the leuco dye to change color. Known color developers used in thermal recording paper, pressure-sensitive copying paper, and the like can be used. Specific examples of such color developers include phenols such as benzyl 4-hydroxybenzoate, 2,2'-biphenol, 1,1-bis(3-cyclohexyl-4-hydroxyphenyl)cyclohexane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, bisphenol A, bisphenol F, bis(4-hydroxyphenyl)sulfide, parahydroxybenzoic acid esters, and gallic acid esters. 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. Furthermore, metal salts of carboxylic acid derivatives, salicylic acid and metal salicylate salts, sulfonic acids, sulfonate salts, phosphoric acids, metal phosphate salts, acidic phosphate esters, metal salts of acidic phosphate esters, phosphorous acids, metal phosphites, etc. may also be used.

However, the color density at which the developer can develop the leuco dye varies depending on the material used in the decolorizer. The decolorizer forms an amorphous state while incorporating the developer, while the decolorizer crystallizes, bonding the leuco dye and developer. The color density of each state depends on the combination and ratio of the developer and decolorizer. Therefore, when combining a leuco dye with the ester compound or steroid compound described below as a decolorizer, it is necessary to select a developer that will exhibit both a decolorized state (decolorization) with a sufficiently low color density and a developed state (development) with a sufficiently high color density.

In addition, when initializing the color or marking with a thermal marking device, the temperature sensing material or the thermosensitive material used in the temperature sensing ink is heated above its melting point, so heat resistance is required to prevent discoloration during this heating. Specifically, the ink must not fade significantly when heated to high temperatures of around 120 to 180°C. When used with a thermal marking device, the ink must maintain the appropriate viscosity in a liquid state for an extended period of time, so it must not fade significantly even when exposed to temperatures of around 120 to 180°C for several hours to several tens of hours.

In addition, light resistance is required so that the ink and indicator do not fade even when exposed to indoor or outdoor light for long periods of time. Of the materials used in temperature sensing materials and temperature sensing inks, leuco dyes and color developers are the materials most susceptible to photodegradation. Because leuco dyes affect the color of the ink, the more selectivity available to meet customer requirements, the better, and the present invention does not limit this. On the other hand, as long as other properties are equivalent, it is preferable for the color developer to be a material that increases the light resistance of the temperature indicator.

For the above reasons, there is a demand for developers that exhibit high decolorization and color development properties in relation to various ester compounds and steroid compounds used as decolorizers, and that also have high heat and light resistance. Specific examples of such developers include 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)diphenol, bisphenol A, bisphenol M, and 4,4'-thiodiphenol. Bisphenol compounds such as 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 4-hydroxyphenyl(4'-n-propoxyphenyl)sulfone can be preferably used.

The temperature indicator may be one of these color developers or a combination of two or more of them. By combining color developers, it is possible to adjust the color density of the leuco dye when it develops color. The amount of the color developer used is selected depending on the desired color density. For example, it is usually selected within the range of about 0.1 to 100 parts by weight per 1 part by weight of the leuco dye.
(Decolorizing agent)
A decolorizer is a compound capable of dissociating the bond between a leuco dye and a color developer, and is a compound capable of controlling the color development temperature of the leuco dye and the color developer. Generally, in the temperature range in which the leuco dye is in a colored state, the decolorizer is solidified in a phase-separated state. Furthermore, in the temperature range in which the leuco dye is in a decolorized state, the decolorizer is melted or in an amorphous state, and is in a state in which it has the function of dissociating the bond between the leuco dye and the color developer. Therefore, the state transition temperature of the decolorizer is important for temperature control of the temperature indicator.

A wide range of materials capable of dissociating the bond between the leuco dye and the developer can be used as the decolorizer. Various materials can be used as decolorizers as long as they have low polarity, do not exhibit color development properties for the leuco dye, and are sufficiently polar enough to dissolve the leuco dye and the developer. Representative examples of such organic compounds include hydroxy compounds, ester compounds, peroxy compounds, carbonyl compounds, aromatic compounds, aliphatic compounds, halogen compounds, amino compounds, imino compounds, N-oxide compounds, hydroxyamine compounds, nitro compounds, azo compounds, diazo compounds, azide compounds, ether compounds, oils and fats, sugar compounds, peptide compounds, nucleic acid compounds, alkaloid compounds, and steroid compounds. Specifically, tricaprin, isopropyl myristate, acetic acid, etc. m-Tolyl, diethyl sebacate, dimethyl adipate, 1,4-diacetoxybutane, decyl decanoate, diethyl phenylmalonate, diisobutyl phthalate, triethyl citrate, benzyl butyl phthalate, butylphthalyl butyl glycolate, methyl N-methylanthranilate, ethyl anthranilate, 2-hydroxyethyl salicylate, methyl nicotinate, butyl 4-aminobenzoate, methyl p-toluate, ethyl 4-nitrobenzoate, 2-phenylethyl phenylacetate, benzyl cinnamate, methyl acetoacetate, geranyl acetate, dimethyl succinate, dimethyl sebacate, diethyl oxalacetate, monoolein, butyl palmitate, ethyl stearate, methyl palmitate, methyl stearate, linalyl acetate, di-n-octyl phthalate, benzyl benzoate, diethylene glycol dibenzoate, methyl p-anisate, acetic acid m-Tolyl, cinnamyl cinnamate, 2-phenylethyl propionate, butyl stearate, ethyl myristate, methyl myristate, methyl anthranilate, neryl acetate, isopropyl palmitate, ethyl 4-fluorobenzoate, cyclandelate (Isomers), Butopyronoxyl, Ethyl 2-Bromopropionate, Tricaprylin, Ethyl Levulinate, Hexadecyl Palmitate, Tert-Butyl Acetate, 1,1-Ethanediol Diacetate, Dimethyl Oxalate, Tristearin, Methyl Acetylsalicylate, Benzal Diacetate, Methyl 2-Benzoylbenzoate, Ethyl 2,3-Dibromobutyrate, Ethyl 2-Furoate, Ethyl Acetopyruvic Acid, Ethyl Vanillate, Dimethyl Itaconate, Methyl 3-Bromobenzoate, Monoethyl Adipate, Dimethyl Adipate, 1,4-Diacetoxybutane, Diethylene Glycol Diacetate, Ethyl Palmitate, Diethyl Terephthalate, Phenyl Propionate, Phenyl Stearate, 1-Naphthyl Acetate, Methyl Behenate, Methyl Arachidate methyl 4-chlorobenzoate, methyl sorbate, ethyl isonicotinate, dimethyl dodecanedioate, methyl heptadecanoate, ethyl α-cyanocinnamate, ethyl N-phenylglycine, diethyl itaconate, methyl picolinate, methyl isonicotinate, methyl DL-mandelate, methyl 3-aminobenzoate, methyl 4-methylsalicylate, diethyl benzylidenemalonate, isoamyl DL-mandelate, triethyl methanetricarboxylate, diethyl formaminomalonate, 1,2-bis(chloroacetoxy)ethane, methyl pentadecanoate, ethyl arachidate, ethyl 6-bromohexanoate, monoethyl pimelate, hexadecyl lactate, ethyl benzilate, mefenpyr-diethyl, procaine, dicyclohexyl phthalate, 4-tert-butyl salicylate t-Butylphenyl, isobutyl 4-aminobenzoate, butyl 4-hydroxybenzoate, tripalmitin, 1,2-diacetoxybenzene, dimethyl isophthalate, monoethyl fumarate, methyl vanillate, methyl 3-amino-2-thiophenecarboxylate, etomidate, cloquintocet-mexyl, methyl benzilate, diphenyl phthalate, phenyl benzoate, propyl 4-aminobenzoate, ethylene glycol dibenzoate, triacetin, ethyl pentafluoropropionate, methyl 3-nitrobenzoate, 4-nitrophenyl acetate, methyl 3-hydroxy-2-naphthoate, trimethyl citrate, ethyl 3-hydroxybenzoate, methyl 3-hydroxybenzoate, trimebutine, 4-methoxybenzyl acetate, pentaerythritol tetraacetate ester, methyl 4-bromobenzoate, 1-naphthalene ethyl acetate, 5-nitro-2-furaldehyde diacetate, ethyl 4-aminobenzoate, propylparaben, 1,2,4-triacetoxybenzene, methyl 4-nitrobenzoate, diethyl acetamidomalonate, valethamate bromide, 2-naphthyl benzoate, dimethyl fumarate, adiphenine hydrochloride, benzyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, vinyl butyrate, vitamin K4, methyl 4-iodobenzoate, methyl 3,3-dimethylacrylate, propyl gallate, 1,4-diacetoxybenzene, diethyl mesooxalate, dimethyl 1,4-cyclohexanedicarboxylate (cis-, trans-mixture), triethyl 1,1,2-ethanetricarboxylate, hexafluoroglutaric acid Dimethyl benzoate, amyl benzoate, ethyl 3-bromobenzoate, ethyl 5-bromo-2-chlorobenzoate, bis(2-ethylhexyl) phthalate, diethyl allylmalonate, diethyl bromomalonate, diethyl ethoxymethylenemalonate, diethyl ethylmalonate, diethyl fumarate, diethyl maleate, diethyl malonate, diethyl phthalate, dimethyl 1,3-acetonedicarboxylate, dimethyl phthalate, ethyl 3-aminobenzoate, ethyl benzoate, ethyl 4-(dimethylamino)benzoate, ethyl nicotinate, ethyl phenylpropiolate, ethyl pyridine-2-carboxylate, ethyl 2-pyridylacetate, ethyl 3-pyridylacetate, methyl benzoate, ethyl phenylacetate, amyl 4-hydroxybenzoate, 2,5-diacetoxytoluene, 4-oxazo Ethyl methyl ester, trimethyl 1,3,5-cyclohexanetricarboxylate (cis- and trans-mixture), methyl 3-(chlorosulfonyl)-2-thiophenecarboxylate, pentaerythritol distearate, benzyl laurate, diethyl acetylenedicarboxylate, phenyl methacrylate, benzyl acetate, dimethyl glutarate, ethyl 2-oxocyclohexanecarboxylate, ethyl phenylcyanoacetate, ethyl 1-piperazinecarboxylate, methyl benzoylformate, methyl phenylacetate, phenyl acetate, diethyl succinate, tributyrin, diethyl methylmalonate, dimethyl oxalate, diethyl 1,1-cyclopropanedicarboxylate, dibenzyl malonate, methyl 4-tert-butylbenzoate, ethyl 2-oxocyclopentanecarboxylate , methyl cyclohexanecarboxylate, ethyl 4-methoxyphenylacetate, methyl 4-fluorobenzoylacetate, dimethyl maleate, methyl terephthalaldehyde, ethyl 4-bromobenzoate, methyl 2-bromobenzoate, methyl 2-iodobenzoate, ethyl 3-iodobenzoate, ethyl 3-furancarboxylate, diallyl phthalate, benzyl bromoacetate, dimethyl bromomalonate, methyl m-toluate, diethyl 1,3-acetonedicarboxylate, methyl phenylpropiolate, 1-naphthyl butyrate, ethyl o-toluate, methyl 2-oxocyclopentanecarboxylate, isobutyl benzoate, ethyl 3-phenylpropionate, di-tert-butyl malonate, dibutyl sebacate, diethyl adipate, diethyl terephthalate, dipropyl phthalate, 1,1-ethanediol diacetate, diisopropyl adipate, diisopropyl fumarate, ethyl cinnamate, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate, neopentyl glycol diacrylate, triolein, ethyl benzoylacetate, ethyl p-anisate, diethyl suberate, sorbitan tristearate, sorbitan monostearate, stearic acid amide, glycerol monostearate, glycerol distearate, 3-(tert-butoxycarbonyl)phenylboronic acid, racecadotril, 4-[(6-acryloyloxy)hexyloxy]-4'-cyanobiphenyl, 2-(dimethylamino)vinyl 3-pyridyl ketone, stearyl acrylate, ethyl 4-bromophenylacetate, dibenzyl phthalate, 3,5 methyl dimethoxybenzoate, eugenol acetate, didodecyl 3,3'-thiodipropionate, vanillin acetate, diphenyl carbonate, ethyl oxanilate, methyl terephthalaldehyde, dimethyl 4-nitrophthalate, ethyl (4-nitrobenzoyl)acetate, dimethyl nitroterephthalate, methyl 2-methoxy-5-(methylsulfonyl)benzoate, methyl 3-methyl-4-nitrobenzoate, dimethyl 2,3-naphthalenedicarboxylate, bis(2-ethylhexyl) adipate, 4'-acetoxyacetophenone, ethyl trans-3-benzoylacrylate, ethyl coumarin-3-carboxylate, BAPTA tetraethyl ester, methyl 2,6-dimethoxybenzoate, di-tert-butyl iminodicarboxylate, benzyl p-benzyloxybenzoate, Methyl 3,4,5-trimethoxybenzoate, methyl 3-amino-4-methoxybenzoate, diethylene glycol distearate, ditetradecyl 3,3'-thiodipropionate, ethyl 4-nitrophenylacetate, methyl 4-chloro-3-nitrobenzoate, 1,4-dipropionyloxybenzene, dimethyl terephthalate, ethyl 4-nitrocinnamate, dimethyl 5-nitroisophthalate, triethyl 1,3,5-benzenetricarboxylate, diethyl N-(4-aminobenzoyl)-L-glutamate, 2-methyl-1-naphthyl acetate, 7-acetoxy-4-methylcoumarin, methyl 4-amino-2-methoxybenzoate, 4,4'-diacetoxybiphenyl, dimethyl 5-aminoisophthalate, 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylic acid Diethyl 4,4'-biphenyldicarboxylate, dimethyl 4-benzyloxyphenylethyl octanoate, 4-benzyloxyphenylethyl nonanoate, 4-benzyloxyphenylethyl decanoate, 4-benzyloxyphenylethyl undecanoate, 4-benzyloxyphenylethyl dodecanoate, 4-benzyloxyphenylethyl tridecanoate, 4-benzyloxyphenylethyl tetradecanoate, 4-benzyloxyphenylethyl pentadecanoate, 4-benzyloxyphenylethyl hexadecanoate, 4-benzyloxyphenylethyl heptadecanoate, 4-benzyloxyphenylethyl octadecanoate, 1,1-diphenylmethyl octanoate, 1,1-diphenylmethyl nonanoate, 1,1-diphenyl decanoate Ester compounds such as 1,1-diphenylmethyl undecanoate, 1,1-diphenylmethyl dodecanoate, 1,1-diphenylmethyl tridecanoate, 1,1-diphenylmethyl tetradecanoate, 1,1-diphenylmethyl pentadecanoate, 1,1-diphenylmethyl hexadecanoate, 1,1-diphenylmethyl heptadecanoate, and 1,1-diphenylmethyl octadecanoate, as well as cholesterol, cholesteryl bromide, β-estradiol, methylandrostenediol, pregnenolone, cholesterol benzoate, cholesterol acetate, cholesterol linoleate, cholesterol palmitate, cholesterol stearate, cholesterol n-octanoate, cholesterol oleate, 3-chlorocholestene, and cholesterol trans-cinnamate. terol, cholesterol decanoate, cholesterol hydrocinnamate, cholesterol laurate, cholesterol butyrate, cholesterol formate, cholesterol heptanoate, cholesterol hexanoate, cholesterol hydrogen succinate, cholesterol myristate, cholesterol propionate, cholesterol valerate, cholesterol hydrogen phthalate, cholesterol phenylacetate, cholesterol chloroformate, cholesterol 2,4-dichlorobenzoate, cholesterol pelargonate, cholesterol nonyl carbonate, cholesterol heptyl carbonate, cholesterol oleyl carbonate, cholesterol methyl carbonate, cholesterol ethyl carbonate, cholesterol isopropyl carbonate, cholesterol butyl carbonate nate, cholesterol isobutyl carbonate, cholesterol amyl carbonate, cholesterol n-octyl carbonate, cholesterol hexyl carbonate, allylestrenol, altrenogest, 9(10)-dehydronandrolone, estrone, ethinyl estradiol, estriol, estradiol benzoate, β-estradiol 17-cypionate, β-estradiol 17-valerate, α-estradiol, β-estradiol 17-heptanoate, gestrinone, mestranol, 2-methoxy-β-estradiol, nandrolone, (-)-norgestrel, quinestrol, trenbolone, tibolone, stanolone, androsterone, abiraterone, abiraterone acetate, dehydroepiandrosterone, Dehydroepiandrosterone acetate, ethisterone, epiandrosterone, 17β-hydroxy-17-methylandrosta-1,4-dien-3-one, methylandrostenediol, methyltestosterone, Δ9(11)-methyltestosterone, 1α-methylandrostan-17β-ol-3-one, 17α-methylandrostan-17β-ol-3-one, stanozolol, testosterone, testosterone propionate, altrenogest, 16-dehydropregnenolone acetate, 16,17-epoxypregnenolone acetate, 11α-hydroxyprogesterone, 17α-hydroxyprogesterone caproate, 17α-hydroxyprogesterone, pregnenolone acetate, 17α-hydroxyprogesterone acetate Examples of suitable steroid compounds include steroid compounds such as methacrylate, megestrol acetate, medroxyprogesterone acetate, pregnenolone acetate, 5β-pregnane-3α,20α-diol, budesonide, corticosterone, cortisone acetate, cortisone, cortexolone, deoxycorticosterone acetate, deflazacort, hydrocortisone acetate, hydrocortisone, hydrocortisone-17-butyrate, 6α-methylprednisolone, prednisolone, prednisone, prednisolone acetate, sodium deoxycholate, sodium cholate, methyl cholate, methyl hyodeoxycholate, β-cholestanol, cholesterol-5α,6α-epoxide, diosgenin, ergosterol, β-sitosterol, stigmasterol, and β-sitosterol acetate. From the viewpoint of compatibility with the leuco dye and the developer, it is preferable to contain these compounds. Of course, the present invention is not limited to these compounds, and any material that can dissociate the bond between the leuco dye and the developer may be used.

You can also use one or more of these decolorizing agents in combination. By combining decolorizing agents, it is possible to adjust the freezing point, crystallization rate, melting point, and glass transition point.

The decolorizer used in the temperature indicator must not crystallize during rapid cooling from the melting point, but must become amorphous near the glass transition point. Therefore, a material that is difficult to crystallize is preferred. While most materials will become amorphous if cooled very quickly, considering practicality, it is preferable for the material to be difficult to crystallize, so that it will become amorphous when cooled rapidly using a general-purpose cooling device. Most preferable materials are difficult to crystallize, so that they will become amorphous when cooled naturally from a molten state above their melting point. For this condition, decolorizers that become amorphous when cooled from their melting point to their glass transition point at a rate of at least 20°C/min or less are preferred, and decolorizers that become amorphous when cooled from their melting point to their glass transition point at a rate of 1°C/min or less are most preferable.

To initialize the color of a temperature indicator, the temperature must be raised above the melting point of the decolorizer in the temperature indicator. The color initialization temperature needs to be high enough that it is unlikely to occur near the control temperature, but for practicality, it is desirable that it be in a temperature range that can be heated using a general-purpose heating device. Furthermore, since matrix materials and microcapsules are used in temperature detection materials to protect the temperature indicator, the heat resistance of these must also be taken into consideration. Specifically, a temperature between 40°C and 250°C is preferred, and between 60°C and 150°C is most preferred.

The temperature-indicating material contains at least the above-mentioned leuco dye, color developer, and color eraser. However, if the material contains a material that has color-developing and color-decoloring properties in one molecule, the color developer and color eraser may not be necessary. Furthermore, as long as the ability to change color upon crystallization is maintained, materials other than leuco dye, color developer, and color eraser can also be included. For example, by including dyes or pigments other than leuco dyes, it is possible to change the color when decolorizing and when developing.

When applying a temperature indicator to the first temperature detection material, a technique for coating and dispersing the temperature indicator is required. Specifically, the first temperature detection material includes at least a phase-separated structure formed by mixing the above-mentioned combination of temperature indicator and matrix material, or at least a microencapsulated temperature indicator. Examples of such forms are shown below.
(matrix material)
The matrix material must be a material that does not impair the color-developing and color-decoloring properties of the temperature indicator when mixed with the temperature indicator. Therefore, it is preferable that the matrix material itself does not exhibit color development. As such a material, a non-polar material that is not an electron acceptor can be used.

In addition, in order to form a phase-separated structure in which the temperature indicator is dispersed within the matrix material, the matrix material must meet the following two conditions: it must be in a solid state at the operating temperature of the temperature indicator, and it must be a material that has low compatibility with the leuco dye, decolorant, and developer. This is because if the leuco dye, developer, or decolorant is in a solid state with the matrix material, the temperature detection function will be impaired. Furthermore, using a matrix material that is in a solid state at the operating temperature makes the temperature detection material easier to handle.

Matrix materials that satisfy the above conditions are preferably those in which the energy due to intermolecular dipole interactions δp and the energy due to intermolecular hydrogen bonds δh, as predicted by the Hansen solubility parameters, are each 3 or less. Specifically, materials that do not have polar groups and materials composed only of hydrocarbons are preferably used. Specific examples include waxes such as paraffin, microcrystalline, olefin, polypropylene, and polyethylene, as well as low-molecular-weight and high-molecular-weight materials with many skeletons such as propylene, ethylene, styrene, cycloolefin, siloxane, and terpene, and copolymers of these.

Among these, materials that become a low-viscosity molten liquid above their melting point and easily solidify below their melting point are easy to handle. Materials that dissolve in organic solvents and solidify as the organic solvent evaporates are also easy to handle. Specific examples include paraffin wax, microcrystalline wax, polyolefin, polyethylene, polypropylene, cycloolefin, polystyrene, terpene resin, styrene resin, silicone resin, and silicone oil.

Examples of polyolefins include low-molecular-weight polyethylene and low-molecular-weight polypropylene. There are no particular restrictions on the molecular weight of the polyolefin or its viscosity in liquid form, but a low viscosity in liquid form results in fewer air bubbles and better moldability. Specifically, a molecular weight of 50,000 or less and a viscosity of 5 to 50,000 mPa·s near the melting point are preferred, and a molecular weight of 10,000 or less and a viscosity of 10 to 10,000 mPa·s near the melting point are even more preferred.

It is also possible to use multiple types of these matrix materials in combination.

Furthermore, even materials that are in a liquid state at the operating temperature can be used as a matrix material if they exhibit a phase-separated structure with the temperature indicator. If the matrix material is a highly viscous liquid, it is as easy to handle as a solid matrix material. However, even if the matrix material is highly viscous, sedimentation and aggregation of the temperature indicator in the matrix material cannot be avoided over long-term use, and the material will eventually separate into two phases. This reduces the long-term stability of the material as a temperature-sensing material.
<Phase separation structure>
4A and 4B are schematic diagrams showing the phase-separated structure of the first temperature detection material, with Fig. 4A showing the phase-separated structure in a decolorized state and Fig. 4B showing the phase-separated structure in a developed state. The phase-separated structure 1 (first temperature detection material 1) forms a structure in which a temperature indicator 2 is dispersed in a matrix material 3.

Figures 5A and 5B are optical microscope photographs of the first temperature detection material, with Figure 5A showing the material in a decolorized state and Figure 5B showing the material in a developed state. From the optical microscope photographs, it can be seen that the phase-separated structure 1 forms a structure in which the temperature indicator 2 is dispersed in the matrix material 3.

The phase separation structure 1 uses a matrix material 3 whose melting point is close to that of the temperature indicator 2. The color development start temperature of the temperature indicator 2 is close to the glass transition point of the temperature indicator 2, and since the matrix material 3 does not melt at that temperature, the temperature sensing material remains in a solid state during the color change process of the temperature indicator 2. On the other hand, when the temperature indicator 2 changes state from solid to liquid above its melting point and color initialization occurs, the matrix material 3 also melts. Therefore, when applied to a heating marking device, the temperature sensing material can be melted along with the color initialization of the temperature indicator 2, and the temperature sensing material can be ejected and marked by heating to a temperature slightly higher than the initialization temperature.

On the other hand, there is no problem if the melting point of the matrix material 3 is different from that of the temperature-indicating material 2. For example, if the melting point of the matrix material 3 is higher than that of the temperature-indicating material 2, when the temperature-indicating material 2 changes state from solid to liquid and color initialization occurs, the matrix material 3 does not melt, and the temperature-sensing material can maintain its solid state.

In addition, since the matrix material 3 and the temperature indicator 2 are phase-separated and the matrix material 3 does not affect the color change of the temperature indicator, the temperature detection function of the temperature indicator 2 can be maintained as is.

While the concentration of the temperature indicator 2 contained in the matrix material 3 is not particularly limited, it is preferable to include 0.1 to 100 parts by weight of the matrix material 3 per 1 part by weight of the temperature indicator 2. A concentration of 100 parts by weight or less of the matrix material 3 per 1 part by weight of the temperature indicator 2 can prevent a decrease in visibility as a temperature sensing material. Furthermore, by ensuring that the concentration of the matrix material 3 is equal to or greater than the concentration of the temperature indicator 2, it is possible to prevent the matrix material 3 and the temperature indicator 2 from forming a structure in which they are interconnected (hereinafter referred to as a co-continuous structure). Even in a co-continuous structure, the matrix material 3 and the temperature indicator 2 are phase-separated, so their functionality as a temperature sensing material is not impaired. However, there is a risk of leakage of the temperature indicator 2 from within the matrix material 3, which may impair long-term stability. Furthermore, when the temperature indicator 2 crystallizes, crystal growth may progress between adjacent temperature indicators 2, potentially reducing the reproducibility of color development time and increasing the risk of color unevenness. Therefore, it is more preferable that the matrix material 3 is 1 part by weight or more and 10 parts by weight or less per 1 part by weight of the temperature indicator 2.

The major axis of the phase consisting of the temperature indicator 2 dispersed in the matrix material 3 is preferably 100 nm or more and 1 mm or less, and more preferably 100 nm or more and 100 μm or less. The size of the phase consisting of the temperature indicator 2 is not particularly limited, but by making it 100 nm or more, the influence of the interface between the temperature indicator 2 and the matrix material 3 on the detected temperature can be suppressed. Furthermore, by making it 1 mm or less, it becomes difficult to visually distinguish between the temperature indicator 2 and the matrix material 3, thereby suppressing color unevenness in the temperature detection material. The size of the phase consisting of the temperature indicator 2 can be reduced by adding a surfactant or by cooling while stirring during the cooling process. The major axis of the phase consisting of the temperature indicator 2 is the major axis of the approximate ellipse when the phase consisting of the temperature indicator 2 is approximated as an ellipse.

One method for dispersing the temperature-indicating material 2 in a temperature-sensing material that satisfies the above conditions is to microencapsulate the temperature-indicating material 2 and disperse the microcapsules in a dispersion medium. It is also possible to use the microencapsulated temperature-indicating material 2 as is, with the microcapsule membrane considered to be the dispersion medium.

The temperature sensing material can also contain materials other than leuco dyes, color developers, and decolorizers, as long as the ability to change color upon crystallization is maintained. For example, microcapsules can be included in the phase-separated structure 1. This makes it possible to include two or more types of temperature indicators 2 in the temperature sensing material, making it possible to create a material that can detect two or more types of temperature changes.

By microencapsulating the temperature indicator 2, the temperature indicator 2's environmental resistance to light, humidity, etc. is improved, and storage stability and color change characteristics can be stabilized. Microencapsulation also makes it possible to suppress the effects of other resins, additives, and other compounds on the leuco dye, developer, and decolorant when preparing the ink.

Various known methods can be used for microencapsulation. Examples include, but are not limited to, emulsion polymerization, suspension polymerization, coacervation, interfacial polymerization, and spray drying. Two or more different methods may also be combined.

Resin coatings used for microcapsules include, but are not limited to, urea resin coatings made from polyamines and carbonyl compounds; melamine resin coatings made from melamine-formaldehyde prepolymers, methylol melamine prepolymers, and methylated melamine prepolymers; urethane resin coatings made from polyisocyanates and polyol compounds; amide resin coatings made from polybasic acid chlorides and polyamines; and vinyl resin coatings made from various monomers such as vinyl acetate, styrene, (meth)acrylic acid esters, acrylonitrile, and vinyl chloride. Furthermore, additional treatments can be performed on the surface of the formed resin coating to adjust the surface energy when making it into ink or paint, thereby improving the dispersion stability of the microcapsules.

In addition, since storage stability and other issues are important, the diameter of the microcapsules is preferably in the range of approximately 0.1 to 100 μm, and more preferably in the range of 0.1 to 10 μm.

The phase-separated structure 1 can also be crushed in a mortar or other container to form a powder, which allows it to be handled in the same way as microcapsules.

The phase-separated structure 1 and the microcapsules can also be mixed with a solvent, a resin material, or the like to form a solvent ink. In this case, surface treatments such as silane coupling treatment, surface grafting, and corona treatment may be performed to stabilize the dispersion for forming the ink, improve resistance to the solvent, and improve environmental resistance to light, humidity, etc. The phase-separated structure 1 and the microcapsules can also be further coated with a matrix material 3 or microcapsules.
<Method of producing a phase-separated structure>
The first temperature sensing material (phase-separated structure 1) can be produced, for example, by the following method. The method for producing a temperature sensing material includes a mixing step of heating and mixing a leuco dye, a color developer, a decolorizer, and a matrix material to a temperature equal to or higher than the melting point of the matrix material, and a cooling step of cooling the mixture obtained in the mixing step to a temperature equal to or lower than the freezing point of the matrix material. In the cooling step, the matrix material and the temperature indicating material rapidly phase-separate to form a phase-separated structure in which a phase consisting of the leuco dye, the color developer, and the decolorizer is dispersed in the matrix material.

When the matrix material is heated above its melting point and brought to a liquid state, depending on the compatibility between the two materials, the temperature indicator and matrix material may be compatible (the temperature indicator will be finely dispersed and appear to be compatible to the naked eye) or incompatible (the temperature indicator and matrix material will separate into two phases). In this case, compatibility is preferable from the perspective of ease of handling. The temperature indicator and matrix material must phase separate at the operating temperature when the matrix material is in a solid state, but this is not the case when the matrix material is in a liquid state under heating. To ensure that the temperature indicator and matrix material phase separate at the operating temperature and are compatible under heating, it is desirable for the polarity of the decolorizing agent, especially when present in large amounts, to be within a certain range. If the polarity of the decolorizing agent is too low, it will be compatible with the matrix material at the operating temperature, while if the polarity is too high, it will separate from the matrix material under heating. As a specific method for calculating polarity, a material in which the energy δp due to intermolecular dipole interactions and the energy δh due to intermolecular hydrogen bonds predicted by the Hansen solubility parameter are each between 1 and 10 can be preferably used. However, even in materials in which the polarity of the decolorizing agent is high and the temperature indicator and matrix material are not compatible even when heated, it is possible to form a phase-separated structure by cooling with stirring. Furthermore, a surfactant may be added to cause compatibility.

When the temperature indicator is cooled below the freezing point of the matrix material to form a phase-separated structure, the size of the dispersion structure of the temperature indicator varies depending on the compatibility between the temperature indicator and the matrix material. In particular, when the decolorizing agent and matrix material are present in a large amount, good compatibility results in fine dispersion, while poor compatibility results in large dispersion. The size of the dispersion structure is not particularly limited, but if it is less than 100 nm, the interface between the temperature indicator and the matrix material may be affected, thereby affecting the detection temperature. Furthermore, if it exceeds 1 mm, the temperature indicator and the matrix material may be visually distinguishable, resulting in increased color unevenness in the temperature detector. Therefore, the size of the dispersion structure is preferably 100 nm or more and 1 mm or less, and most preferably 100 nm or more and 100 μm or less. To achieve this dispersion structure, a decolorizing agent whose intermolecular dipole interaction energy δp and intermolecular hydrogen bond energy δh, predicted by the Hansen solubility parameter as a specific polarity calculation method, are each between 1 and 10, is preferably used. In the cooling step, the size of the dispersed structure can be reduced by cooling with stirring or by adding a surfactant.
<Heated marking device>
The first temperature sensing material can be applied to various thermal marking devices. Thermal marking devices are devices that heat a material to a low viscosity and then eject and print the material. Examples include thermal inkjet printers, heated dispensers, and glue guns. A temperature sensing material made of a phase-separated structure becomes a low-viscosity liquid when heated above the melting points of the matrix material and the temperature indicator, making it possible to print using a thermal marking device without turning it into ink. Furthermore, since the color can be initialized by heating during printing, temperature control using the temperature sensing material is possible immediately after printing. This means that a separate heating device for initializing the temperature sensing material is not required, which is useful from the perspective of equipment costs. Possible timings for printing using a thermal marking device include printing the temperature sensing material on a temperature-controlled target object at a controlled temperature, or printing the temperature sensing material on the target object at room temperature and then moving the target object to a controlled temperature range before the temperature sensing material develops its color.
<Ink>
A temperature-sensing ink can be produced by preparing a phase-separated structure in which a temperature indicator is dispersed in a matrix material or a microencapsulated first temperature-sensing material in advance and mixing it with a solvent. The temperature-sensing ink can be used in inks for pens, stamps, crayons, inkjet printers, and other applications, as well as in paints for printing.

The temperature sensing ink has a form in which the first temperature sensing material is dispersed in a solvent. To achieve this, it is necessary to use a solvent that has low compatibility with the matrix material and microcapsules that contain the temperature sensing material.

When a phase-separated structure using a matrix material is used as a temperature sensing material, it is preferable to use a highly polar solvent. Examples of highly polar solvents that can be used include water, glycerin, and alcohols such as methanol, ethanol, and propanol. Other examples include ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate; and ethers such as dimethyl ether and tetrahydrofuran.

When using microencapsulated temperature sensing materials, it is preferable to use a solvent that the microcapsule material is resistant to. When using a highly polar microcapsule material, it is better to use a less polar organic solvent. Specifically, nonpolar solvents such as hexane, benzene, and toluene, and oils such as petroleum, mineral oil, and silicone oil are particularly preferred. Other examples include ketones such as acetone, methyl ethyl ketone, and cyclohexanone, esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate, and ethers such as dimethyl ether and tetrahydrofuran.

When a low-polarity material is used as the microcapsule material, it is better to use a high-polarity solvent. Specifically, water, glycerin, and alcohols such as methanol, ethanol, and propanol are preferably used. Other solvents that can be used include ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate; and ethers such as dimethyl ether and tetrahydrofuran.

These temperature-sensing inks have temperature and time detection capabilities even in their liquid state. Furthermore, when they are printed, written, or stamped on an object, the solvent evaporates, leaving only the temperature-sensing material remaining as the printed matter. This printed matter can be used as a temperature indicator.

The temperature-sensing ink may contain additives in the form of organic solvents or water, as long as they do not affect the temperature and time detection functions. For example, by adding a pigment, it is possible to change the color when the ink is erased or developed.

Temperature-sensing ink can be made with a variety of additives and solvents. Its viscosity can also be adjusted by changing the amount of temperature-sensing material or additives. This makes it suitable for use in a variety of printing devices, including offset printing, gravure printing, flexographic printing, label printers, and thermal printers.
<Inkjet ink>
If the resistance of the ink solution is high, the ink droplets will not fly straight but will tend to curve when ejected from the ink ejection section of the charge-controlled inkjet printer. Therefore, the resistance of the ink solution needs to be approximately 2000 Ωcm or less.

The resins and organic solvents contained in the ink (especially methyl ethyl ketone, ethanol, etc., which are commonly used as organic solvents in inkjet printer inks) have low conductivity, so the resistance of the ink solution is high, ranging from 5,000 to tens of thousands of Ωcm. High resistance makes it difficult to achieve the desired printing with a charge-controlled inkjet printer. Therefore, to reduce the resistance of the ink solution, it is necessary to add a conductive agent to the ink.

It is preferable to use a complex as the conductive agent. The conductive agent must be soluble in the solvent used, and it is also important that it does not affect the color tone. Furthermore, conductive agents generally have a salt structure. This has an imbalance of charge within the molecule, and is thought to enable high conductivity.

After considering the above points, it was found that the conductive agent should have a salt structure and the cation should have a tetraalkylammonium ion structure. The alkyl chain can be either straight or branched, and the higher the carbon number, the better the solubility in the solvent. However, the lower the carbon number, the lower the resistance can be with a small addition rate. A practical number of carbon atoms for use in ink is around 2 to 8.

Anions such as hexafluorophosphate ions and tetrafluoroborate ions are preferred because they have high solubility in solvents.

Although perchlorate ions are highly soluble, they are explosive, making their use in ink impractical. Other examples include chlorine, bromine, and iodine ions, but these are undesirable as they tend to corrode metals such as iron and stainless steel when they come into contact with them.

In view of the above, preferred conductive agents include 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.
<Second Temperature Sensing Material>
As shown in Figure 2B, the first temperature sensing material included in the temperature indicator according to this embodiment has the problem that the color change rate decreases in a temperature range higher than near T1. In contrast, the temperature indicator according to this embodiment further includes a second temperature sensing material in addition to the first temperature sensing material, and is therefore able to indicate that a temperature range higher than near T1 has been reached by a color change of the second temperature sensing material.

Figure 6A shows the temperature dependence of the color change rate of the second temperature detection material. When simulating quality deterioration of food or pharmaceuticals, the purpose is to complement the function by using a second temperature detection material with a fast color change rate in a temperature range where the color change rate of the first temperature detection material slows. Therefore, a material that begins to change color abruptly at a certain temperature (color change onset temperature T2) is preferred, and a material whose color change rate increases rapidly above a certain temperature is also preferred. T2 is sometimes referred to as the "color change onset temperature."

Figure 6B shows the temperature dependence of the discoloration rate of the first and second temperature detection materials. The first temperature detection material is required to be a material that changes color slowly near the control temperature when the temperature of food or medicine deviates from the control temperature, while the second temperature detection material is required to be a material that changes color very quickly at high temperatures in order to detect abnormal heating when food or medicine is exposed to very high temperatures. Therefore, it is preferable that the discoloration rate of the second temperature detection material be faster than that of the first temperature detection material.

The second temperature sensing material irreversibly changes color within a temperature range higher than the glass transition temperature Tg of the first temperature sensing material (temperature indicator) and lower than the melting point Tm of the first temperature sensing material (temperature indicator). Furthermore, the color change onset temperature T2 (color change onset temperature) of the second temperature sensing material is preferably near the maximum value T1 of the color change rate of the first temperature sensing material. This allows the second temperature sensing material to quickly change color in a temperature range where the color change rate of the first temperature sensing material slows, enabling the temperature indicator to indicate an abnormal temperature condition. If the color change onset temperature T2 of the second temperature sensing material is lower than the color development onset temperature Ta of the first temperature sensing material or the glass transition temperature Tg of the temperature indicator, the second temperature sensing material will change color at a temperature lower than the temperature at which the color change rate of the first temperature sensing material increases with increasing temperature, resulting in the loss of its function as a TTI. Furthermore, if the color change onset temperature T2 of the second temperature detection material is higher than the color loss onset temperature Td of the first temperature detection material or the melting point Tm of the thermochromic material, when the food or medicine is exposed to extremely high temperatures, a temperature range will be created where neither the first nor second temperature detection material will develop color, making the inclusion of the second temperature detection material less meaningful.The maximum color change rate T1 of the first temperature detection material is sometimes referred to as the "maximum color change rate temperature."

The crystallization rate of the first temperature sensing material is graphed as shown in Figure 2B. However, depending on the type of temperature sensing material, there may be a temperature range where the crystals form a metastable phase (crystals with disordered orientation) and a temperature range where they form a stable phase. For this reason, the crystallization rate may not be a single peak as shown in Figure 2B, but may be split into multiple peaks or appear broad (with a gradual rate of change from the maximum value). In particular, at temperatures above the temperature T1 where the crystallization rate reaches its maximum, the rate often peaks and gradually decreases. The same is true for the discoloration rate. Therefore, it is advisable to adjust the discoloration onset temperature T2 of the second temperature sensing material to an appropriate temperature, appropriate for the type of first temperature sensing material, near the maximum value T1 of the discoloration rate of the first temperature sensing material.

Regarding the specific discoloration temperature of the first temperature detection material, assuming application to the quality control of foods and pharmaceuticals, it is preferable that the glass transition point Tg, which is related to the discoloration onset temperature, is between -40°C and 60°C, and the melting point Tm, which is related to the initialization temperature, is between 60°C and 150°C, and the temperature difference between Tg and Tm is between 100°C and 150°C. Given this temperature relationship, it is preferable to adjust the discoloration onset temperature T2 of the second temperature detection material to the range of between -20°C and 60°C, which is the maximum value T1 of the discoloration rate.

Figure 7A shows the relationship between the color density and temperature of the second temperature detection material. The second temperature detection material changes color when the temperature rises above the color change onset temperature T2 during the temperature rise process. At this time, it is required that the color does not return to its original state even if the temperature drops again. This is because if the color returns to its original state, it will be impossible to determine whether the temperature has changed or not. In other words, it is preferable to use an irreversible temperature indicator that does not return to its original color once it has changed.

Figure 7B shows the relationship between color density and temperature of the first and second temperature detection materials. The second temperature detection material's color change onset temperature T2 is higher than the color development onset temperature Ta of the first temperature detection material and lower than the color loss onset temperature Td.

Furthermore, while the first temperature detection material has the characteristic of being able to initialize its color by heating it above its decolorization temperature Td, the second temperature detection material is not required to have this function. The color change onset temperature of the first temperature detection material is often near the management temperature for food and pharmaceuticals, i.e., in the low temperature range such as freezing or refrigeration, and without an initialization function, the temperature detection material itself would be difficult to store and use. In contrast, the second temperature detection material is intended to detect abnormal heating, and can often be stored and used at room temperature even without an initialization function. Of course, it is possible to use a material with an initialization function, but since there are many commonly available irreversible temperature indicators that undergo a steep color change at a certain temperature, using these can reduce the cost of the temperature indicator.

The second temperature detection material can be a wide variety of irreversible temperature indicators that undergo a rapid color change at temperatures near the maximum value T1 of the color change rate of the first temperature detection material. For example, general-purpose temperature indicators such as heat-sensitive material, heat-sensitive paper, heat-sensitive sheet, heat-sensitive paint, heat-sensitive ink, and heat-sensitive microcapsules can be selected according to the structure of the temperature indicator.
<Temperature indicator configuration>
The temperature indicator according to this embodiment may include a substrate that directly or indirectly supports the first and second temperature sensing materials in addition to the first and second temperature sensing materials. The temperature indicator according to this embodiment may have various configurations as long as it includes at least the substrate and the first and second temperature sensing materials. The first and second temperature sensing materials may be in contact with each other or may be separated within the substrate. Furthermore, by including microcapsules of the first and second temperature sensing materials in the ink, the ink may be treated as a single type of temperature sensing material.

Temperature indicators are not limited to the following forms, but examples are shown below.

Figure 8 is a schematic diagram showing an example of the simplest temperature indicator. The temperature indicator 4 has a substrate 5, a first temperature sensing material 1, and a second temperature sensing material 6, with the first temperature sensing material 1 and the second temperature sensing material 6 each disposed on one main surface of the substrate 5. Alternatively, the first temperature sensing material may be disposed on one main surface of the substrate 5, and the second temperature sensing material 6 may be disposed on the other main surface of the substrate 5.

One or both of the first temperature detection material 1 and the second temperature detection material 6 may be covered with a transparent substrate or a transparent adhesive to prevent the temperature detection material from peeling off from the substrate. In this temperature indicator, if the color of the first temperature detection material 1 changes, it can be detected that the food or medicine has deviated from the controlled temperature and is beginning to deteriorate. If the color of the second temperature detection material 6 changes, it can be detected that the food or medicine has been exposed to a temperature significantly higher than the controlled temperature.

In the temperature indicator 4 of Figure 8, the first temperature detection material 1 can be initialized by heating. Therefore, the temperature indicator 4 can be initialized by selectively heating only the first temperature detection material 1. If a material that cannot be initialized is used for the second temperature detection material 6, placing the first temperature detection material 1 and the second temperature detection material 6 in close proximity (so that they are close to each other) makes it difficult to selectively initialize the first temperature detection material 1. On the other hand, it is possible to prevent easy initialization by a third party (to detect initialization by a third party). In this case, too, the temperature indicator can be initialized by using a heating method that is difficult for a third party to handle, such as fine heating using laser heating.

Note that "close" includes a state in which the two are in contact with each other, and refers to a state in which the distance between the two is close when there is zero distance between them (i.e., a contact state) or when there is a distance between them. For example, the distance between the two can be said to be close when it is difficult to selectively heat only one of them using a heating method other than the above-mentioned fine heating. For example, the distance between the two can be said to be close when it is 40 mm or less.
(Base material)
In this embodiment, the substrate material can be freely selected depending on the functionality required for the temperature indicator. The initialization temperature of the temperature sensing material is most preferably between 60°C and 150°C. Therefore, when the temperature indicator is to be initialized, any substrate that can withstand heat above this temperature can be used. For example, organic materials such as paper and plastic, inorganic materials such as ceramics and metals, and composites thereof can be freely selected. The material is selected based on the characteristics required for the temperature indicator, such as high strength, heat resistance, weather resistance, chemical resistance, insulation, and conductivity. A sticker can be used to attach the material to the object to be detected (label it). Transparency is also not particularly limited. The change process of the temperature sensing material can be observed from the side that is not in contact with the substrate. The change process can also be observed when the temperature sensing material is covered with a transparent substrate or transparent adhesive. On the other hand, even if the adhesive is not transparent, the color change process of the temperature sensing material can be observed from the outside of the substrate if the substrate is transparent.

The design of the substrate is not limited. It is possible to print information other than the color-changing characteristics of the temperature-sensing material, or to print a color that is useful for inspecting the color of the temperature-sensing material.

The substrate may be formed into a layered structure using several types of materials. For example, as shown in Figure 9, the substrate 5 may be formed to surround the temperature detection material 1. This increases the smoothness of the temperature detection material 1 relative to the substrate 5, thereby reducing the variation in color density of the first temperature detection material 1.

In the example shown in Figure 9, the top of the first temperature detection material 1 is covered with a transparent substrate. By incorporating an ultraviolet-blocking material into this transparent substrate and the transparent adhesive 7, it is possible to suppress photo-fading of the temperature detection material 1. It is also possible to give the temperature indicator functions other than the color-changing properties of the temperature detection material, such as by providing a material that loses its transparency upon detecting ultraviolet rays, humidity, oxygen, etc.

In the example shown in Figure 9, the second temperature detection material 6 is placed at the top. In this structure, the second temperature detection material covers the surface of the first temperature detection material where the color is visible, so the second temperature detection material must be transparent in its initial state. In this case, a transparent heat-sensitive sticker, for example, can be preferably used. As shown in the example shown in Figure 10, if the position of the second temperature detection material is shifted and the color of the first temperature detection material is visible, the second temperature detection material can be a non-transparent heat-sensitive sticker.

In the example shown in Figure 9, for example, practical use can be made easier by varying the timing at which the first temperature detection material and the second temperature detection material are applied to the temperature indicator. Since the temperature indicator can be initialized before the second temperature detection material is applied, by initializing the temperature indicator by heating it immediately before applying it to food or medicine, and then applying the second temperature detection material, it can be treated as a temperature indicator that cannot be initialized by third parties thereafter.

Next, the present invention will be explained in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples.

(Preparation of first temperature detection material)
The materials used were 1 part by weight of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (CVL manufactured by Yamada Chemical Co., Ltd.) as the leuco dye, 1 part by weight of octyl gallate manufactured by Tokyo Chemical Industry Co., Ltd. as the developer, 100 parts by weight of Vitamin K4 manufactured by Tokyo Chemical Industry Co., Ltd. as the decolorizer, and 100 parts by weight of Hiwax 200P manufactured by Mitsui Chemicals Co., Ltd. as the matrix material. These materials were melted and mixed at 150°C, which is above the melting points of the decolorizer and matrix material, and then allowed to solidify by natural cooling, to produce a temperature sensing material with a phase-separated structure.
(Application of first temperature detecting material)
The prepared first temperature detecting material was heated to 150° C. using a jet dispenser AeroJet manufactured by Musashi Engineering Co., Ltd. to turn it into a liquid state, and then discharged onto a substrate, which was a general-purpose coated paper.
(Application of second temperature sensing material and preparation of temperature indicator)
The second temperature detecting material was a clear thermal label manufactured by Toshiba Tec Corporation. A temperature indicator was produced by attaching the second temperature detecting material to a position adjacent to the first temperature detecting material ejected onto the substrate.
(Evaluation of discoloration properties)
Within one minute of preparation, the temperature indicator was held at 0°C, which is below the glass transition point of the temperature indicator (approximately 5°C), for five minutes, assuming the temperature to be the product's control temperature. The temperature was then raised at 30°C/min to 25°C, above the glass transition point of the temperature indicator. The change in color density of the temperature indicator over time was observed. The results are shown in Figures 11A, 11B, and 12. Note that Figure 11A is a black-and-white image due to the specifications of the application drawings; if it were a color image, the black would appear as a shade of blue corresponding to the density (similar to Figures 13A and 15A). Figure 11B is a black-and-white image due to the specifications of the application drawings; if it were a color image, the black would appear as a shade of gray-brown corresponding to the density (similar to Figures 13B and 15B).

From the images in Figures 11A and 11B and the color density data in Figure 12, it was confirmed that at a temperature of 25°C, the first temperature detection material in Figure 11A developed color (turning blue) over time. This is because 25°C is above the glass transition point of the decolorizer, causing the temperature indicator to crystallize. On the other hand, the second temperature detection material in Figure 11B did not change color at all. This confirmed the process by which the first temperature detection material changes color as a result of the accumulation of temperature and time at temperatures above the control temperature.

Next, after preparing the temperature indicator again, the temperature was maintained at 0°C, below the glass transition point of the temperature indicator, for 5 minutes within one minute, assuming the product's control temperature. The temperature was then raised at 30°C/min to 150°C, above the melting point of the temperature indicator (approximately 110°C). The temperature dependence of the color density of the temperature indicator during this process was observed. The results are shown in Figures 13A, 13B, and 14. From the images in Figures 13A and 13B and the color density data in Figure 14, it was observed that the first temperature sensing material in Figure 13A began to change color around 25°C. While maintaining its color-developed state, the second temperature sensing material began to change color around 80°C. The first temperature sensing material then lost color around 110°C, the melting point of the temperature indicator, and its color was initialized. This confirmed the process by which the second temperature sensing material changed color due to high-temperature heating before the first temperature sensing material was initialized.

Next, after preparing the temperature indicators, they were again held at 0°C, below the glass transition point of the temperature indicator, for 5 minutes within one minute, assuming the product's intended temperature. Then, they were immediately placed on hot plates at temperatures of 15°C, 25°C, 35°C, 45°C, 55°C, 65°C, 75°C, 85°C, 95°C, 105°C, and 115°C. The color density of the temperature indicator was observed over time. The results are shown in Figures 15A and 15B. The color change rate of the first temperature sensing material in Figure 15A was fastest at 55°C, while the color change onset of the second temperature sensing material in Figure 15B was observed above 85°C. In other words, the maximum color change rate (T1) of the first temperature sensing material was near 55°C, and the color change onset temperature (T2) of the second temperature sensing material was found to be between 75°C and 85°C. This confirmed the relationship T1≦T2, with T2 being approximately 20-30°C higher than T1.

From the above, it was confirmed that the temperature indicator of this embodiment can detect temperature in a certain temperature range by changing color as a result of the accumulation of time and temperature, and can detect abnormal heating by changing color abruptly at temperatures above that temperature range.
<<Modifications>>
The present invention is not limited to the above-described embodiments and examples, and various modifications can be adopted within the scope of the present invention. For example, in the above-described embodiments, the plurality of first temperature sensing materials and the plurality of second temperature sensing materials may be arranged on a substrate. In this case, in order to prevent easy initialization by a third party, one or more pairs of adjacent first temperature sensing materials and second temperature sensing materials may be present, and it is preferable that all of the first temperature sensing materials are adjacent to at least one second temperature sensing material. For example, in the above-described embodiments, the second temperature sensing material may have a color change onset temperature, at which the color change of the second temperature sensing material begins, within a temperature range equal to or greater than an intermediate temperature midway between the glass transition point of the first temperature sensing material and the melting point of the first temperature sensing material and equal to or less than the melting point of the first temperature sensing material.

1...First temperature detection material, 2...Temperature indicating material, 3...Matrix material, 4...Temperature indicator, 5...Substrate, 6...Second temperature detection material, 7...Transparent substrate and transparent adhesive

Claims (14)

a first temperature detection material that changes color due to an amorphous crystallization phenomenon;
a second temperature sensing material that irreversibly changes color within a temperature range higher than the glass transition point of the first temperature sensing material and lower than the melting point of the first temperature sensing material;
Including ,
The first temperature sensing material is
a color change rate maximum temperature at which the color change rate reaches a maximum value within a temperature range higher than the glass transition point of the first temperature detection material and lower than the melting point of the first temperature detection material;
Temperature indicator. 2. The temperature indicator according to claim 1,
The second temperature sensing material is
a color change initiation temperature, which is the temperature at which the color change of the second temperature detection material starts, within a temperature range that is higher than the glass transition point of the first temperature detection material and lower than the melting point of the first temperature detection material;
Temperature indicator. 2. The temperature indicator according to claim 1 ,
The second temperature sensing material is
a color change initiation temperature at which a color change of the second temperature detection material starts, within a temperature range that is higher than the glass transition point of the first temperature detection material and lower than the melting point of the first temperature detection material;
The color change rate maximum temperature of the first temperature sensing material is equal to or lower than the color change initiation temperature of the second temperature sensing material.
Temperature indicator. 2. The temperature indicator according to claim 1 ,
The second temperature sensing material is
a color change initiation temperature at which a color change of the second temperature detection material starts, within a temperature range that is higher than the glass transition point of the first temperature detection material and lower than the melting point of the first temperature detection material;
The color change initiation temperature of the second temperature detecting material is
The temperature range is equal to or higher than a first temperature that is 20°C lower than the maximum color change rate temperature of the first temperature sensing material and equal to or lower than a second temperature that is 60°C higher than the maximum color change rate temperature of the first temperature sensing material.
Temperature indicator. 5. The temperature indicator according to claim 4 ,
the glass transition point of the first temperature detection material is −40° C. or higher and 60° C. or lower, the melting point of the first temperature detection material is 60° C. or higher and 150° C. or lower, and the temperature difference between the glass transition point and the melting point is 100° C. or higher and 150° C. or lower;
Temperature indicator. 2. The temperature indicator according to claim 1,
The color change starting temperature, which is the temperature at which the color change of the second temperature detecting material starts, is
the temperature is within a temperature range that is equal to or higher than an intermediate temperature that is a middle temperature between the glass transition point of the first temperature detection material and the melting point of the first temperature detection material, and is equal to or lower than the melting point of the first temperature detection material;
Temperature indicator. 2. The temperature indicator according to claim 1,
The first temperature detection material includes a temperature indicator including a leuco dye, a color developer, and a decolorizer.
Temperature indicator. 8. The temperature indicator of claim 7 ,
the first temperature sensing material includes a matrix material;
Temperature indicator. 9. The temperature indicator of claim 8 ,
The first temperature detection material has a phase-separated structure in which the temperature indicating material is dispersed in the matrix material.
Temperature indicator. 2. The temperature indicator according to claim 1,
a substrate that directly or indirectly supports the first temperature sensing material and the second temperature sensing material;
Temperature indicator. 2. The temperature indicator according to claim 1,
the second temperature sensing material is a heat sensitive material;
Temperature indicator. 12. The temperature indicator of claim 11 ,
The heat-sensitive material is heat-sensitive paper, heat-sensitive sheet, heat-sensitive paint, heat-sensitive ink, or heat-sensitive microcapsules.
Temperature indicator. 2. The temperature indicator according to claim 1,
The first temperature sensing material and the second temperature sensing material are in close proximity to each other.
Temperature indicator. a first temperature detection material that changes color due to an amorphous crystallization phenomenon, the first temperature detection material having a color change rate maximum temperature at which the color change rate reaches a maximum value within a temperature range that is higher than the glass transition point of the first temperature detection material and lower than the melting point of the first temperature detection material;
a second temperature sensing material that irreversibly changes color within a temperature range higher than the glass transition point of the first temperature sensing material and lower than the melting point of the first temperature sensing material;
A method for manufacturing a temperature indicator, comprising:
applying the second temperature sensing material to a position adjacent to the first temperature sensing material after initializing the color of the first temperature sensing material and before the first temperature sensing material starts to change color;
Temperature indicator manufacturing method.