JPH0118116B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to microcapsules made of a temperature-indicating material that reversibly changes color in response to temperature changes. Conventionally, as temperature-indicating materials, there are those using metal complex salt crystals and those using cholesteric liquid crystals. However, the former contains heavy metal salts, generally has a high discoloration temperature, and has the disadvantage of having a small hue, while the latter has short lifespan, relatively low temperature range, and high price. However, there are many restrictions and inconveniences in using it as a temperature-indicating material. Therefore, the color change temperature and hue can be freely selected, and the color changes rapidly.
It has been desired to develop a durable and inexpensive temperature-indicating material. Recently, temperature-indicating materials using electron-donating color-forming organic compounds have been proposed as temperature-indicating materials that take this point into consideration (for example, Japanese Patent Publication No. 44706/1983,
(Japanese Patent Application Laid-open No. 102284, etc.). All of these basically consist of an electron-donating color-forming organic compound, an acidic substance having a phenolic hydroxyl group or a carboxylic acid group that causes the organic compound to color, and alcohol, ether, ester, ketone, etc. It is composed of a three-component system, and the hue, density, and discoloration temperature can be freely changed depending on the type and combination of each component. However, printed matter or molded products using these temperature-indicating materials,
In general, they had poor light resistance, with noticeable fading or loss of color-changing ability after being exposed to direct sunlight for more than 10 hours, and there were few that could withstand practical use. As a result of intensive research aimed at solving the various problems mentioned above, the present inventors have already developed a new type of temperature-indicating material (Patent Application No. 162486 of 1972).
That is, this reversible temperature-indicating material (composition) comprises (A) an electron-accepting color-changing organic compound consisting of phthalein or fluorescein and derivatives thereof;
(B) an organic nitrogen compound that exhibits electron donating properties for the compound (A), and (C) a compound (B) for the above compound (A).
It is characterized by containing a compound that causes the discoloration effect of the color to disappear at a specific temperature. The temperature indicating material is
Various hues can be controlled depending on the type of compound (A), color density can be controlled depending on the amount of compound (B) or (C), and discoloration temperature can be controlled freely depending on the type of compound (C). Furthermore, it has extremely good physical properties including durability. The present invention relates to improvements in the usage of the above-mentioned reversible temperature indicating material. That is, the temperature-indicating property of the above-mentioned reversible temperature-indicating material is based on the color-changing effect of the electron-donating organic nitrogen compound (B) on the electron-accepting color-changing organic compound (A), and on the color-changing effect of the electron-donating organic nitrogen compound (B) on the electron-accepting color-changing organic compound (A). Alternatively, it can be obtained by deactivating the compound (C) having a phenolic hydroxyl group at a temperature above a specific temperature, and the boundary temperature, that is, the discoloration temperature, depends on the freezing point of the above-mentioned three-component mixture. In other words, the reversible temperature-indicating material exhibits a liquid-solid phase change when heated and cooled near the discoloration temperature, and becomes liquid in the high temperature range of discoloration, so the composition of the above three components changes and its discoloration function is affected. may cause abnormalities or become extremely difficult to handle. The present invention provides the above-mentioned reversible temperature indicating material (composition)
By encapsulating it in the capsule wall membrane to form microcapsules, it is stable and easy to handle.
The present invention provides a reversible temperature indicating material in an apparently stable solid form. The present invention will be explained in more detail below. In the following description, "%" and "part" are based on weight unless otherwise specified. The reversible temperature-indicating composition used as the capsule core material in the present invention has the above-mentioned three components, namely (A) an electron-accepting color-changing organic compound selected from phthaleins, fluoresceins, and derivatives thereof;
(B) an electron-donating organic nitrogen compound that acts on the compound (A) to cause it to change color; and (C) a compound that causes the color change effect of the compound (B) on the compound (A) to disappear at a specific temperature or higher. It includes. As the electron-accepting color-changing organic compound (A), phthaleins, fluoresceins, and their derivatives, those represented by the following general formula are preferably used, but the present invention is not limited thereto.

【formula】

【formula】

【formula】

【formula】

【formula】

[ _{Formula ]} Where, Represents a saturated or unsaturated carbon atomic group necessary to form a 5-membered or 6-membered ring with the central carbon, and this atomic group is fused with a benzene ring, a halogen-substituted benzene ring, a naphthalene ring, a cyclohexane ring, etc. Includes things that have been done. Specific examples of the electron-accepting color-changing organic compound (A) mentioned above include the following compounds. Namely, thymolphthalein, phenolphthalein, o-
Cresolphthalein, 1,4-dimethyl-5-
Hydroxybenzenesulfophthalein, thymolsulfophthalein, m-cresolsulfophthalein, α-naphtholphthalein, o-cresolsulfophthalein, phenolsulfophthalein, dibromothymolsulfophthalein, dibromophenol Tetrabromophenolsulfophthalein, dibromophenolsulfophthalein, dibromo-o-cresolsulfophthalein, dichlorophenolsulfophthalein, tetrabromo-m-cresolsulfophthalein, dibromodichlorophenolsulfophthalein, Tetrabromophenol tetrabromo sulfophthalein, tetrabromophenol sulfophthalein, dibromopyrogallol sulfophthalein, fluorescein, sulfofluorescein, tetrabromofluorescein,
These include tetrachlorofluorescein and tetrachlorotetrabromofluorescein. Next, the organic nitrogen compound (B) exhibiting electron-donating properties used in the present invention may be any compound as long as it exhibits a color-changing effect on the electron-accepting color-changing organic compound (A). Specifically, primary, secondary, and tertiary aliphatic amines in which the hydrogen atom of ammonia is substituted with an alkyl group, such as ethylamine, butylamine, octylamine, dodecylamine, stearylamine, dipropylamine, diamylamine, and tripropylamine. , tributylamine, allylamine, cyclohexylamine, etc.; primary, secondary, and tertiary aromatic amines substituted with aryl groups, such as dimethylaniline, p-toluidine, dibenzylamine, tribenzylamine,
β-naphthylamine, etc.; Hydrazine derivatives, such as dimethylhydrazine, diphenylhydrazine, etc.; Amide derivatives, such as carbamide, thiourea, etc.; Hydrazide derivatives, such as acetohydrazide,
Benzoyl hydrazide, phthalic acid hydrazide, etc.; Amidine derivatives, such as 1,3-diphenylguandine, di-o-tolylguanidine, etc.; Quaternary ammonium salts, such as tetraethylammonium chloride, trimethylbenzylammonium chloride, hexadecyltrimethylammonium chloride , hexyldibenzylammonium chloride, etc.; amino acid compounds such as glycine, alanine,
Cysteine, arginine, histidine, etc.; Nitrogen-containing heterocyclic compounds containing a nitrogen atom in the ring, such as pyridine, quinoline, piperidine, indole, thiazole, imidazole, acridine, pyrimidine, triazine derivatives, etc.; or the above nitrogen-containing heterocycles Examples include alkaloid compounds consisting of compounds such as quinine, thiobromine, and the like. Further, as the third component used in the present invention, a compound (C) is required that causes the coloring effect of the electron-donating organic nitrogen compound (B) on the electron-accepting color-changing organic compound (A) to disappear at a specific temperature. Compounds that have this effect include alcohol,
These include esters, ethers, ketones, carboxylic acids, thiols, acid amides, sulfides, disulfides, compounds having a phenolic hydroxyl group, and specifically include the following. (1) Alcohols: Alcohols include monohydric alcohols, polyhydric alcohols, and their derivatives. Specifically, for example, n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, n-lauryl alcohol, n-myristyl alcohol, n-cetyl alcohol, n-stearyl alcohol, n-icosyl alcohol, n-docosyl alcohol, n-mericyl alcohol,
Isocetyl alcohol, isostearyl alcohol, isodocosyl alcohol, oleyl alcohol, cyclohexanol, cyclopentanol, benzyl alcohol, cinnamyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, hexylene These include glycol, cyclohexane-1,4-diol, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol, sorbitol, mannitol, and the like. (2) Esters: Specifically, for example, amyl acetate, octyl acetate, butyl propionate, octyl propionate, phenyl propionate, ethyl caproate, amyl caproate, ethyl caprylate, amyl caprylate, ethyl caprate, caprin. amyl acid, octyl caprylate, methyl laurate, ethyl laurate, butyl laurate,
Hexyl laurate, octyl laurate, dodecyl laurate, myristyl laurate, cetyl laurate, stearyl laurate, methyl myristate, ethyl myristate, butyl myristate, hexyl myristate, octyl myristate, lauryl myristate, myristic acid myristyl, cetyl myristate, stearyl myristate, methyl palmitate,
Ethyl palmitate, butyl palmitate, hexyl palmitate, octyl palmitate,
Lauryl palmitate, myristyl palmitate, cetyl palmitate, stearyl palmitate, methyl stearate, ethyl stearate, butyl stearate, hexyl stearate, octyl stearate, lauryl stearate, myristyl stearate, cetyl stearate, stearic acid Stearyl, methyl behenate, ethyl behenate, propyl behenate, butyl behenate, ethyl benzoate, butyl benzoate, amyl benzoate, phenyl benzoate, ethyl acetoacetate, methyl oleate, butyl oleate, butyl acrylate, Diethyl oxalate, dibutyl oxalate, diethyl malonate, dibutyl malonate, dibutyl tartrate, dibutyl sebatate, dimethyl sebatate, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, dibutyl fumarate, diethyl maleate, dibutyl maleate , triethyl citrate, 12-hydroxystearic acid triglyceride, castor oil, dioxystearic acid methyl ester, 12-hydroxystearic acid methyl ester, etc. (3) Ethers: Specifically, for example, diethylene glycol dimethyl ether, diphenyl ether, distearyl ether, butyl ether, hexyl ether, diisopropyl benzyl ether, diphenyl ether, dioxane, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, ethylene glycol diethyl ether. , diethylene glycol diethyl ether, ethylene glycol diphenyl ether, ethylene glycol monophenyl ether, and the like. (4) Ketones: Specifically, for example, diphenyl ketone, distyryl ketone, diethyl ketone, ethyl butyl ketone, methylhexyl ketone, mesityl oxide, cyclohexanone, methylcyclohexanone, acetophenone, propiophenone, benzophenone, 2,4-pentane. These include dione, acetonylacetone, diacetone alcohol, ketone wax, etc. (5) Carboxylic acids: Carboxylic acids include monocarboxylic acids to polycarboxylic acids and their derivatives. Specifically, for example, acetic acid, propionic acid, butyric acid, caproic acid, cabrylic acid, cabric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, behenic acid, crotonic acid, oleic acid, elaidic acid, linoleic acid. , linolenic acid, monochloroacetic acid, monobromoacetic acid, monofluoroacetic acid, glycolic acid, hydroxypropionic acid, hydroxybutyric acid, ricinoleic acid, 12-
Hydroxystearic acid, lactic acid, pyruvic acid,
Oxalic acid, malonic acid, succinic acid, adipic acid,
Sebacic acid, malic acid, tartaric acid, chituchoic acid,
Maleic acid, fumaric acid, naphthenic acid, benzoic acid, toluic acid, phenyl acetic acid, p-tert-butylbenzoic acid, cinnamic acid, chlorbenzoic acid, bromobenzoic acid, ethoxybenzoic acid, mandelic acid, brotocatechuic acid, vanillic acid, These include resorcinic acid, dioxybenzoic acid, dioxychlorobenzoic acid, gallic acid, naphthoic acid, hydroxynaphthoic acid, phthalic acid, phthalic acid monoethyl ester, naphthalenedicarboxylic acid, naphthalenedicarboxylic acid monoethyl ester, trimellitic acid, pyromellitic acid, and the like. (6) Acid amides: Specifically, for example, acetamide, propionic acid amide, butyric acid amide, caproic acid amide,
Caprylic acid amide, capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, benzamide, caproic acid anilide, cabrylic acid anilide, capric acid anilide, Lauric acid anilide, myristic acid anilide, palmitic acid anilide, stearic acid anilide, behenic acid anilide, oleic acid anilide, erucic acid anilide, caproic acid anilide, caprylic acid anilide, capric acid anilide, lauric acid anilide Methylamide, myristic acid N-methylamide, palmitic acid N-methylamide, stearic acid N-methylamide, behenic acid N-methylamide, oleic acid N-methylamide, erucic acid N-methylamide, lauric acid N-ethylamide, myristic acid N-ethylamide, palmitic acid N-ethylamide,
Stearic acid N-ethylamide, oleic acid N
- Ethylamide, lauric acid N-butylamide, myristic acid N-butylamide, palmitic acid N-butylamide, stearic acid N-butylamide, oleic acid N-butylamide, lauric acid N-octylamide, myristic acid N-
Octylamide, palmitic acid N-octylamide, stearic acid N-octylamide, oleic acid N-octylamide, lauric acid N-dodecylamide, myristic acid N-dodecylamide, palmitic acid N-dodecylamide, stearic acid N-dodecylamide amide, oleic acid N-dodecylamide, distearic acid amide, dipalmitic acid amide, dimyristic acid amide, dilauric acid amide, dioleic acid amide, tristearic acid amide, tripalmitic acid amide,
Trimyristic acid amide, trilauric acid amide, trioleic acid amide, succinic acid amide,
Adipic acid amide, glutaric acid amide, malonic acid amide, azelaic acid amide, maleic acid amide, succinic acid N-methylamide, adipic acid N-methylamide, glutaric acid N-methylamide, malonic acid N-methylamide, azelaic acid N-methylamide, Succinic acid N-ethylamide, adipic acid N-ethylamide, glutaric acid N-ethylamide, malonic acid N-ethylamide, azefiic acid N-ethylamide, succinic acid N-butylamide, adipic acid N-butylamide, glutaric acid N-butylamide, malonic acid N
-butylamide, adipic acid N-octylamide, adipic acid N-dodecylamide, etc. (7) Compounds having a phenolic hydroxyl group: Specifically, for example, tertiary-butylphenol, nonylphenol, dodecylphenol, styrene tatephenol, 2,2'methylenebis(4-methyl-6-tertiarybutylphenol), α-naphthol, β-naphthol, hydroquinone monomethyl ether,
Guaiacol, eugenol, p-chlorphenol, p-bromophenol, o-chlorophenol, o-bromophenol, o-phenylphenol, p-phenylphenol, p-
(p-chlorophenyl)phenol, o-(o
-chlorophenyl) phenol, methyl p-oxybenzoate, ethyl p-oxybenzoate, p
-Propyl oxybenzoate, butyl p-oxybenzoate, octyl p-oxybenzoate, p-
Dodecyl oxybenzoate, 3-isopropylcatechol, p-tertiarybutylcatechol, 4,4'-methylene diphenyl, bisphenol A, 1,2-dioxynaphthalene, 2,3
-Dioxynaphthalene, chlorcatechol, bromocatechol, 2,4-dihydroxybenzophenone, phenolphthalein, o-cresolphthalein, methyl protocatechuate,
Ethyl protocatechuate, propyl protocatechuate, octyl protocatechuate, dodecyl protocatechuate, 2,4,6-trioxymethylbenzene, 2,3,4-trioxyethylbenzene, methyl gallate, gallic acid Ethyl acid, propyl gallate, butyl gallate,
These include hexyl gallate, octyl gallate, dodecyl gallate, cetyl gallate, stearyl gallate, 2,3,5-trioxynaphthalene, tannic acid, and phenolic resin. Components in the reversible temperature-indicating composition used in the present invention
An example of the discoloration mechanism that occurs between (A) and (B) is as follows. Example (A) Phenolphthalein (electron-accepting color-forming organic compound) + (B) Amine (electron-donating organic nitrogen compound) The above discoloration system is the basis of the present invention, but in order to make this discoloration reversible in response to temperature changes, it is necessary to use an electron-donating organic nitrogen for the electron-accepting discolored organic compound (A), as described above. A compound that causes the discoloration effect of compound (B) to disappear at a temperature above a certain temperature
The existence of (C) is essential. That is, at temperatures where compound (C) does not have a lapse effect, discoloration occurs due to the interaction between compounds (A) and (B), but at temperatures where compound (C) exhibits a lapse effect, no discoloration occurs. Almost the same color as the compound (A) itself (or, if the composition contains dyes or pigments that do not change color, these colors and the compound
A composition (color mixture with color (A)) is obtained. Note that the compound (C) generally does not exhibit a deactivation effect at low temperatures, that is, when it is solid, but when the temperature is increased, many exhibit a deactivation effect at the melting point of the compound. As will be described later, in the reversible thermostatic composition of the present invention, since the compound (C) usually accounts for a large proportion, the melting point of the compound (C) is not significantly different from the melting point of the composition. The blending ratio of each component in the reversible thermostatic composition is 0.1 to 100 parts of the electron-donating organic nitrogen compound (B) to 1 part (by weight, the same applies hereinafter) of the electron-accepting color-changing organic compound (A). It is particularly desirable to use 0.5 to 10 parts and 10 to 1000 parts of compound (C). Especially (B)
The ratio of the components varies depending on the combination of components; if it is too large, the color will be discolored from beginning to end, and if it is too small, the color will not change from beginning to end. In addition to the above-mentioned three components, non-discoloring dyes, pigments, plasticizers, ultraviolet absorbers, thickeners, leveling agents, etc. can be added to the reversible thermostatic composition as needed. In the present invention, the above-mentioned reversible temperature-indicating composition is encapsulated in a capsule wall to form microcapsules. Microencapsulation techniques include, for example, chemical methods such as interfacial polymerization, in situ polymerization, and in-liquid curing coating methods; physicochemical methods and phase separation methods (aqueous solution systems), in-liquid drying, and melting and dispersion. Cooling method;
As physical methods, air suspension coating methods, spray drying methods, and the like are known as known techniques, and the method is selected from these techniques in consideration of the properties of the core material, the final usage form, etc. The reversible thermostatic composition as the core material in the microcapsules of the present invention is chemically active,
Moreover, since it involves a phase change of solid←→liquid, there is a risk that it will lose its original function during the encapsulation operation. Therefore, when performing microencapsulation, it is important to select a method that does not cause such troubles. Furthermore, the microencapsulation of the present invention makes the core material, which can be in a liquid state, into a stable solid;
In addition, for the purpose of improving storage stability, it is desirable that the wall film be seamless and have appropriate strength. In addition, the capsule wall membrane is transparent enough to allow the color change of the contents to be confirmed through it, has appropriate heat resistance because handling involves thermal operations, and is suitable for general gravure, offset, flexo, etc. It is desirable to have durability against various solvents in consideration of dispersion and printing in various inks used in various printing methods such as screen printing. Considering the above points, the microencapsulation method to be adopted in the present invention is so-called in
It has been found that it is desirable to provide a capsule wall membrane consisting of a thermosetting resin, in particular an unsaturated polyester resin, by a method belonging to the in situ polymerization method. That is, the above-mentioned reversible thermostatic composition is mixed and adjusted in advance, and a prepolymer of preferably an unsaturated polyester resin and a polymerization initiation catalyst are mixed therein, and the mixture is preferably mixed with, for example, gum arabic, gelatin, A water-soluble resin such as casein or carboxymethyl cellulose is dissolved and finely dispersed in a protective colloid aqueous solution to which a surfactant such as an alkylbenzene sulfonate or funnel oil (sulfated oil) is added as necessary. An oil-in-water emulsion is obtained. Next, when the oil droplets reach an appropriate particle size, the system is heated,
The microcapsules of the present invention are obtained by cross-linking and polymerizing a prepolymer near the surface of an oil droplet, in which a reversible thermostat composition is encapsulated in a capsule wall membrane. The thermosetting resin prepolymer that can be used in the present invention is an initial condensation product of monomers containing radically polymerizable unsaturated bonds. Among them, a prepolymer of an unsaturated polyester resin, that is, a prepolymer of an unsaturated polyester resin, that is, an unsaturated polyester is preferably used. Here, unsaturated polyester refers to unsaturated polyester in the narrow sense, which is a polycondensation reaction product of unsaturated dicarboxylic acids such as maleic acid and fumaric acid and glycols such as ethylene glycol and diethylene glycol, as well as unsaturated polyesters such as phthalic acid. A condensation product of 1 mole of polycarboxylic acid and several moles of unsaturated alcohol such as allyl alcohol (typically a prepolymer of so-called allyl resin), glycol (or a condensation product of 2 moles of glycol and 1 mole of dicarboxylic acid)
This includes condensation products of (meth)acrylic acid and (meth)acrylic acid. Although these prepolymers are basically oil-soluble, they are suitable for each component in the reversible thermostatic composition, especially for compounds.
It is desirable that it is more hydrophilic than (C). Otherwise, the prepolymer may harden while being mixed with the resin, and a good capsule wall film may not be obtained. Unsaturated polyester has a suitable hydrophilic group (bond) in its molecule and is a preferable prepolymer in this sense as well. Further, the prepolymer preferably has a viscosity in the range of 40 to 2000 cps. These prepolymers are preferably used in a proportion of 0.05 to 1 part per 1 part of the reversible thermostat composition. Examples of the radical polymerization initiator include methyl ethyl ketone peroxide, benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, tert-butyl perbenzoate,
Bis(4-tert-butyl)cyclohexyl peroxydicarbonate and the like are used. In order to adjust the polymerization temperature, a curing accelerator such as cobalt naphthenate or dimethylaniline may be used in combination, if necessary. The reversible temperature-indicating microcapsules of the present invention thus obtained are, for example, mononuclear capsules with a particle size of 1 to 100μ and a wall thickness of 0.05 to 5μ, and may be used as an ink or paint while being dispersed in a protective colloid aqueous solution. However, it may be isolated as a powder through treatments such as filtration, centrifugation, and drying, or this powdered capsule may be dispersed and mixed into an ink or paint vehicle or a molded object such as a film, chip, or block. It can also be used. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 The following three components were heated and dissolved to obtain a reversible temperature-indicating composition. (A) Tetrachlortetrapromefluorescein
1 part (B) 2-aminobenzothiazole 1 part (C) Ethyl myristate 50 parts Unsaturated polyester resin (HA-900, manufactured by Nihon Reichhall Co., Ltd.)
10 parts and 0.1 part of bis(p-tert-butyl)cyclohexyl peroxydicarbonate (Perkadox 16, manufactured by Kayaku Nury Co., Ltd.) were mixed and dissolved.
This mixture was heated to 250 ml of 5% aqueous gum arabic solution at 20°C.
to prepare an O/W emulsion. When the particle size reached approximately 5 μm, the mixture was heated to approximately 85° C. while stirring. By maintaining this temperature for about 1 hour, microcapsules with a particle size of about 5 μm and a wall thickness of 0.25 μm were obtained. This microcapsule reversibly changed color from red when heated to colorless when cooled with a boundary temperature of about 4°C, similar to the above-mentioned temperature-indicating composition. Example 2 The following three components were heated and dissolved to obtain a reversible thermostat composition. (A) α-Naphtholphthalein 1 part (B) Di-o-tolylguanidine 2 parts (C) Ethyl oleylamide stearate 10 parts 40 parts Polyester-
25 parts of acrylate (Aronix-6100, manufactured by Toagosei Kagaku Co., Ltd.) and bis(p-tert-butyl)
0.5 part of cyclohexyl peroxidine carbonate (Perkadox 16, manufactured by Kayaku Nury Co., Ltd.) was mixed and dissolved. This mixture was dispersed in 250 parts of a 2% aqueous gelatin solution at 20°C to form an O/W emulsion.
When the particle size reached approximately 10 μm, the mixture was heated to approximately 95° C. while stirring. By maintaining this temperature for about 2 hours, microcapsules with a particle size of about 10 μm and a wall thickness of about 0.5 μm were obtained. This microcapsule reversibly changed color to blue-green upon heating and cooling to yellow with a boundary temperature of about 27°C, similar to the above-mentioned thermostatic composition.

Claims (1)

[Scope of Claims] 1 (A) an electron-accepting color-changing organic compound selected from phthaleins, fluoresceins, and their derivatives; (B) an electron-donating compound that acts on the compound (A) to change its color; a reversible thermostatic oil-based composition containing a chemical organic nitrogen compound and (C) a compound that causes the discoloration effect of compound (B) on the above compound (A) to disappear at a certain temperature or above, is encapsulated in the capsule wall membrane. Reversible temperature-indicating microcapsules. 2. The microcapsule according to item 1 above, wherein the compound (C) is at least one selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, acid amides, and compounds having a phenolic hydroxyl group. 3. Item 1 or 2 above, in which the capsule wall film is made of a thermosetting resin cross-linked and cured by radical polymerization.
Microcapsules of the term. 4. The microcapsule according to item 3 above, in which the capsule wall film is made of an unsaturated polyester resin. 5. The above-mentioned third method, which is obtained by dispersing a mixture of a reversible temperature-indicating oil composition and a prepolymer of a resin constituting the capsule wall as an oil-in-water emulsion, and crosslinking the prepolymer in the presence of a radical polymerization initiator.
Microcapsules according to item 1 or item 4.