KR20210032918A - Thermochromic Microcapsule and Freeze Indicator Using the Same - Google Patents

Abstract

The present invention relates to a thermochromic microcapsule which comprises: a core part including a thermochromic composition having a color-changing temperature control agent, a leuco dye, and a developer, wherein the thermochromic composition is provided in the form of fine particles; and a shell part including a polymer resin enclosing the core part. The thermochromic microcapsule exhibits hysteresis characteristics with respect to a color saturation-temperature curve, and thus can start to develop a color when a temperature reaches a temperature (t_2) in a process of decreasing the temperature in a color-disappearing state, and fully develop a color at a temperature (t_1) lower than the temperature (t_2). In a process of increasing the temperature in the color development state, the color begins to disappear when the temperature reaches a temperature (t_3) higher than the temperature (t_2), and the color completely disappears at a temperature (t_4) higher than the temperature (t_3). In a temperature range between the temperature (t_2) and the temperature (t_3), the color development state or the color-disappearing state appears alternatively. The color development start temperature (t_2) is from -6 to -2°C, the thermochromic microcapsule has an average particle size of 1.0 to 1.4 μm, D10 is 0.5 to 0.8 μm, and D90 is 2.5 to 3.0 μm. According to the present invention, a freeze indicator can be manufacture in the form of a thin film.

Description

Thermochromic Microcapsule and Freeze Indicator Using the Same}

The present invention relates to a thermochromic microcapsule and a freezing indicator using the same, and specifically, to a freezing indicator that displays the freezing history of a product using a thermochromic microcapsule having a large hysteresis.

The thermochromic composition is a substance containing a leuco dye, a developer, and a color change temperature control agent, and since it reversibly develops and discolors depending on temperature, the thermochromic microcapsules containing the thermochromic composition are printed materials, It is used for ink, paint, packaging materials, writing instruments, and various types of plastic injection products.

The thermochromic microcapsules show reversible color change according to temperature and can be applied to products in various fields by using this. Looking at the reversible color change, in order for the color fading state to return to the color development state according to the temperature change, the temperature must be slightly lower than the existing temperature, and this difference is called hysteresis.

The thermochromic microcapsules with high hysteresis have a reversible color change, but can display a kind of temperature memory or temperature history that maintains the changed color within a temperature range showing hysteresis.

Based on this temperature memory or temperature history, whether a product that was previously stored at room temperature has been placed in a high-temperature environment is displayed as a color at room temperature and a high-temperature environment, and then returned to room temperature, but maintains the discoloration state. In addition, it was limited to displaying overheating history or erasing handwriting by writing instruments through the delay of color development due to hysteresis after high-temperature discoloration.

However, there have been few examples of conventional thermochromic microcapsules used to display their freezing history whether they have been placed in a low-temperature environment.

As an example, according to the Food Code of the Ministry of Food and Drug Safety <Notification No. 2019-57, 2019.7.3>, refrigerated products of meat, packaged meat and processed meat products are -2 to 10℃ (however, poultry meat, poultry packaged meat, pulverized Meat and crushed meat products should be preserved and distributed at -2 ~ 5℃), so refrigerated products should not be lower than -2℃. Therefore, the basis for judging that there is a history of exposure to a temperature environment lower than -2°C when the freezing indicator containing a specific thermochromic microcapsule is colorless in the refrigeration temperature range, that is, -2 to 10°C and then displays a designated color. Can be, so it can be used to check the freezing history of the product.

<Prior literature>

Japanese Patent No. 5599679

An object of the present invention is to solve the problems of the prior art and technical problems that have been requested from the past.

An object of the present invention is to provide a thermochromic microcapsule that exhibits a delay in discoloration due to hysteresis after low temperature color development.

Another object of the present invention is to provide a freezing indicator that displays the freezing history of a product using such a thermochromic microcapsule.

The present invention.

A core portion including a thermochromic composition including a color change temperature control agent, a leuco dye and a developer in the form of fine particles; And a shell portion including a polymer resin surrounding the core portion; and a thermochromic microcapsule comprising,

The thermochromic microcapsules exhibit hysteresis characteristics with respect to the color density-temperature curve, and in the process of decreasing the temperature in the discoloration state, color _{development begins when the temperature (t 2} ) is reached, and is lower than the _{temperature (t 2 ).} Color completely develops at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, it begins to fade when it reaches a _{temperature (t 3 ) higher than the temperature (t 2} ), and a temperature higher than the _{temperature (t 3)} Color completely disappears at (t ₄ ), and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a color disappearance state alternatively appears,

The color development start temperature (t2) is -6°C or more and less than -2°C,

The thermochromic microcapsule has an average particle size of 1.0 to 1.4 µm, D10 is 0.5 to 0.8 µm, and D90 is 2.5 to 3.0 µm.

The color change temperature control agent may include at least one of the compounds represented by the following Chemical Formulas 1 to 4.

<Formula 1>

<Formula 2>

<Formula 3>

<Formula 4>

Based on the total weight of the thermochromic composition, the color change temperature control agent may be 1 to 99 parts by weight, the leuco dye may be 1 to 15 parts by weight, and the developer may be 1 to 40 parts by weight.

The leuco dye and the developer may be 1:1 to 1:5 based on the weight ratio.

The thermochromic composition may be 6 to 98 parts by weight based on the total weight of the thermochromic microcapsules.

The weight ratio of the shell portion to the core portion may be 0.1 to 0.8.

The complete color development temperature (t ₁ ) may be -23 to -18°C, the color start temperature (t ₃ ) may be 41 to 45°C, and the complete color disappearance temperature (t ₄ ) may be 56 to 60°C.

If the temperature is lowered at an _{irreversible temperature (t 5} ) equal to or higher than the temperature (t _{4 ), discoloration is maintained until the temperature (t 2} ) is reached, and the irreversible temperature (t ₅ ) may be 59°C or higher. have.

The thermochromic microcapsules may have a hysteresis width of 63 to 66°C based on a difference between a color intensity-temperature curve and a color fading start temperature (t ₂ ) and an irreversible temperature (t _{5 ).}

The present invention provides a freezing indicator that displays the freezing history of a refrigerated product by color change using the thermochromic microcapsule.

When the freezing indicator is in a discolored state at a refrigerating temperature, in the process of decreasing the temperature in the discolored state, color begins to develop at -6°C or more and less than -2°C, and in the process of increasing the temperature in the color developing state, the refrigeration temperature Even if it reaches, the color is maintained and the freezing history can be displayed.

The freezing indicator may be in the form of a film or a sticker.

The thermochromic microcapsule according to the present invention includes a predetermined thermochromic composition and exhibits a delay in color fading due to hysteresis after low-temperature color development, so the freezing history of the product can be displayed as a color change at a simple and low cost by using this. Freeze indicator can be provided.

Since the thermochromic microcapsule according to the present invention has a specific average particle size and particle size distribution, it is possible to provide a freezing indicator of excellent characteristics that accurately judges the conformity of preservation and distribution standards for products requiring refrigerated storage. .

Since the freeze indicator according to the present invention can be manufactured in the form of a thin film such as a film or a sticker, the volume can be minimized, and thus it can be used simply and easily.

1 is a schematic diagram of a cross-section of a thermochromic microcapsule 10 according to an embodiment of the present invention;
2 is a color density-temperature curve of a thermochromic microcapsule according to an embodiment of the present invention; And
3 is a result showing a change in color detected in a specimen according to a temperature change in Experimental Example 1 of the present invention.

Thermochromic composition

The present invention,

A core portion including a thermochromic composition including a color change temperature control agent, a leuco dye and a developer in the form of fine particles; And a shell portion including a polymer resin surrounding the core portion; and a thermochromic microcapsule comprising,

The thermochromic microcapsules exhibit hysteresis characteristics with respect to the color density-temperature curve, and in the process of decreasing the temperature in the discoloration state, color begins to develop when the _{temperature (t 2} ) is reached, and is lower than the _{temperature (t 2 ).} Color completely develops at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, it begins to fade when it reaches a _{temperature (t 3 ) higher than the temperature (t 2} ), and a temperature higher than the _{temperature (t 3)} Color completely disappears at (t ₄ ), and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a color disappearance state alternatively appears,

The color development start temperature (t ₂ ) is more than -6℃ and less than -2℃,

The thermochromic microcapsule has an average particle size of 1.0 to 1.4 µm, D10 is 0.5 to 0.8 µm, and D90 is 2.5 to 3.0 µm.

In the present invention, "discoloration" is a change in at least one of hue, saturation, and brightness of a color, and includes the concept of colorlessness, that is, disappearance and erasure. At this time, "disappearance" and "erasing" include not only colorlessness in which the color is not recognized at all, but also making the color not dark or close to colorlessness.

In the present invention, the "color change temperature control agent" is a substance that controls the color reaction temperature of the leuco dye and the developer, and determines the color change temperature of the thermochromic composition.

Other terms may be interpreted as meaning commonly understood in the field to which the present invention belongs.

(a) color change temperature control agent

The thermochromic composition according to the present invention includes a color change temperature control agent to reversibly color development and discoloration according to a heating-cooling cycle, and discolors through the reaction of a color change temperature control agent, a leuco dye, and a developer.

Specifically, the color change temperature control agent exists in a crystalline phase, that is, a solid phase at room temperature, and when heated, the phase transitions to a liquid phase, and when the temperature is lowered to a low temperature, the phase transitions to a solid phase. When the discoloration temperature control agent of the present invention is mixed with a leuco dye and a developer at room temperature in a solid state, the leuco dye develops color by color reaction with the developer, and when the discoloration temperature control agent of the present invention melts, the leuco dye and the developer Since the color reaction of is blocked by the color change temperature control agent, the leuco dye is discolored.

Specifically, the color change temperature control agent in the present invention may include at least one of the compounds represented by the following Chemical Formulas 1 to 4 and develop color at a low temperature of -6°C or more and less than -2°C.

<Formula 1>

<Formula 2>

<Formula 3>

<Formula 4>

Accordingly, when a color change temperature control agent is mixed with a leuco dye and a developer in a solid phase of Tc (crystallization temperature), the leuco dye is color-reacted by a color reaction with the developer. In addition, when the color change temperature control agent of Formula 1 is melted at Tm (melting temperature), the color reaction between the leuco dye and the developer is blocked by the color change temperature control agent, so that the leuco dye disappears.

In the thermochromic composition of the present invention, the content of the color change temperature control agent may be, for example, about 1 to 99 parts by weight based on the total amount of the thermochromic composition. When the content of the thermochromic composition is in the above-described range, the color change property is improved without lowering the color development concentration, thereby improving color development efficiency.

(b) leuco dye

In the thermochromic composition of the present invention, the leuco dye is an electron-donating compound and exhibits colorless or pale white color in nature. It develops color. These leuco dyes develop color-disappear according to the physical state of the color change temperature control agent. That is, in the thermochromic composition, the leuco dye develops color at room temperature, then fades when the color change temperature control agent melts, and when the color change temperature control agent solidifies, the leuco dye develops color again.

The leuco dye usable in the present invention is not particularly limited as long as it is generally known in the art, and for example, a fluorane-based leuco dye, a pulloene-based leuco dye, a diphenylmethane phthalide-based leuco dye, an indolyl phthalide-based leuco dye, Spiropyran-based leuco dyes, rhodamine lactam-based leuco dyes, and azaphthalide-based leuco dyes.

Specifically, the leuco dye is 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3,3- bis(1-n-butyl-2-methylindol-3-yl)phthalide, 3,3-bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-[2-ethoxy-4-(N-ethylanilino )phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3,6-diphenylaminofluoran, 3,6-dimethoxyfluoran, 3,6-di-n-butoxyfluoran, 2-methyl- 6-(N-ethyl-Np-tolylamino)fluoran, 3-chloro-6-cyclohexylaminofluoran, 2-methyl-6-cyclohexylaminofluoran, 2-(2-chloroamino)-6-dibutylaminofluoran, 2-(2-chloroanilino)-6 -di-n-butylaminofluoran, 2-(3-trifluoromethylanilino)-6-diethylaminofluoran, 2-(N-methylanilino)-6-(N-ethyl-Np-tolylamino)fluoran, 1,3-dimethyl-6-diethylaminofluoran, 2-chloro-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6-di-n-butylaminofluoran, 2-xylidino-3-methyl-6- diethylaminofluoran, 1,2-benz-6-diethylaminofluoran, 1,2-benz-6-(N-ethyl-N-isobutylamino)fluoran, 1,2-benz-6- (N-ethyl-N-isoamylamino)fluoran, 2-(3-methoxy-4-dodecoxystyryl)quinoline, spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1'(3'H) isobenzofuran]-3'-one, 2-(diethylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1'(3'H) isobenzofuran]-3-one, 2-(di-n-butylamino)-8-(di-n-butylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5, 1'(3'H)isobenzofuran]-3-one, 2-(di-n-butylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine -5,1'(3'H)isobenzofuran]-3-one, 2-(di-n-butylamino)-8-(N-ethyl-Ni-amylamino)-4-methyl-spiro[5H-(1) benzopyrano(2,3-g)pyrimidine-5,1'(3'H)isobenzofuran]-3-one, 2-(dibutylamino)-8-(dipentylamino)-4-methyl-spiro[5H-(1)benzopyrano (2,3-g)pyrimidine-5,1'(3'H)-isobenzofuran]-3-one, 3-(2-methoxy-4-dimethylaminophenyl)-3-(1-butyl-2-methylindol-3 -yl)-4,5,6,7-tetrachlorophthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4,5,6,7- tetrachlorophthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-pentyl-2-methylindol-3-y l)-4,5,6,7-tetrachlorophthalide, 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H- indol-3-yl)-1(3H)-isobenzofuranone, 3',6'-bis[phenyl(2-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3 -one, 3',6'-bis[phenyl(3-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3-one, 3',6'-bis[ phenyl(3-ethylphenyl)amino]-spiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3-one, 4-[2,6-bis(2-ethoxyphenyl)-4-pyridinyl]- N,N-dimethylbenzenamine, 2-(4'-dimethylaminophenyl)-4-methoxy-quinazoline, 4,4'-(ethylenedioxy)-bis[2-(4-diethylaminophenyl) quinazoline], and the like, but are not limited thereto. These may be used alone or in combination of two or more.

In the thermochromic composition of the present invention, the content of the leuco dye is not particularly limited, and may be, for example, 1 to 15 parts by weight based on the total amount of the thermochromic composition. When the content of the leuco dye is within the above-described range, discoloration properties are improved without lowering the color development concentration, thereby improving color development efficiency.

(c) developer

In the thermochromic composition of the present invention, the developer is an electron-accepting compound, and develops color (discolors) through an oxidation-reduction reaction with a leuco dye.

The developer usable in the present invention is not particularly limited as long as it is generally known in the art. For example, there are triazole-based, phenol-based, bisphenol-based, aromatic carboxylic acid-based, aliphatic carboxylic acid-based, thiourea-based, phosphoric acid-based, or esters, ethers, and metal salts thereof.

Specifically, bisphenol S or a derivative thereof, p-phenyl phenol, dodecylphenol, o-bromo phenol, phenol resin, phthalic acid, acetic acid, propionic acid, benzoic acid, butyl acid phosphate, 2-ethylhexyl-acid phosphate, dodecyl acid Phosphite, 1,2,3-triazole, 1,2,3-benzotriazole, diphenylthiourea, di-o-toluylurea, 2,2,2-trichloroethanol, 1,1,1 -Tribromo-2-methyl-2-propanol, N-3-pyridyl-N'-(1-hydroxy-2,2,2-trichloroethyl) urea; 2-mercapto benzene thiazole, 2-(4'-morpholino dithio) benzothiazole, and the like, and metal salts thereof, but are not limited thereto. These may be used alone, or two or more may be mixed and used.

In the thermochromic composition of the present invention, the content of the developer is not particularly limited, and may be, for example, about 1 to 40 parts by weight based on the total amount of the thermochromic composition. If the content of the developer is within the above-described range, discoloration properties may be improved without lowering the color development concentration, thereby improving color development efficiency.

In addition, the ratio of the content of the developer to the content of the leuco dye is not particularly limited, but if the content of the developer is too high compared to the leuco dye, the color density is dark during color development, but the color may not become transparent and may remain after color when fading. . Therefore, it is appropriate that the mixing ratio of the leuco dye and the developer (leuco dye: the developer) is 1:1 to 5 by weight.

(d) other additives

The thermochromic composition according to the present invention may optionally further include additives known in the art within a range that does not harm the intrinsic properties of the composition in addition to the above-described discoloration temperature control agent, leuco dye, and developer.

Non-limiting examples of additives that can be used in the present invention include ultraviolet absorbers, infrared absorbers, antioxidants, non-thermochromic pigments, fluorescent whitening agents, surfactants, antifoaming agents, leveling agents, solvents (e.g., water-soluble organic solvents). , Thickeners, and the like, and these may be used alone or in combination of two or more. These additives may be appropriately added within the content range known in the art, and for example, may be about 0 to 30% by weight, specifically about 0.01 to 15% by weight, based on the total amount of the thermochromic composition.

The thermochromic composition of the present invention can be prepared by a method known in the art, for example, a color change temperature control agent, a leuco dye and a developer, and, if necessary, an additive to be added to a mixer to be prepared by uniformly mixing. I can. At this time, it can be mixed while heating. The heating temperature is not limited, and may be, for example, about 120 to 180°C.

Thermochromic microcapsule

It will be described below with reference to the drawings.

1 is a schematic diagram of a cross-section of a thermochromic microcapsule 10 according to an embodiment of the present invention.

Referring to FIG. 1, the thermochromic microcapsule 10 includes a core 11 including the thermochromic composition in the form of fine particles; And a shell portion 12 including a polymer resin surrounding the core portion.

The thermochromic microcapsule 10 is a thermochromic composition encapsulated in the form of fine particles independently closed by the shell portion 12, and is subjected to temperature sensitivity to resin molded articles, printed materials, ink, paints, packaging materials, fibers, recording materials, etc. It can impart discoloration and can also be used as a colorant. In addition, even if the thermochromic microcapsule of the present invention is applied in a paint, ink or synthetic resin, since the thermochromic composition is encapsulated and protected by the shell portion, other components in the paint, ink or synthetic resin, such as organic solvents, It is possible to minimize the effect of surfactants and additives on the discoloration function of the thermochromic composition.

In the thermochromic microcapsule of the present invention, the core portion 11 contains fine particles made of a thermochromic composition. In this case, there may be one or a plurality of fine particles.

The fine particles are formed by emulsifying particles of the thermochromic composition in an aqueous solvent, and the average particle size thereof is not particularly limited, but may be, for example, about 0.1 to 21 µm.

The content of the thermochromic composition is not particularly limited, and may be, for example, about 6 to 98% by weight, specifically about 60 to 95% by weight, based on the total weight of the thermochromic microcapsule. If the content of the thermochromic composition is too small outside the above range, it is difficult to exhibit the color change function intended by the present invention, and when the content of the thermochromic composition is too large, it is difficult to uniformly and stably disperse in the form of emulsified particles in the emulsion, which is not preferable. .

In addition, the core portion may further include an emulsifier layer disposed (formed) on the surface of the fine particles. Here, when the core part contains one fine particle, the emulsifier layer exists at the interface between the fine particles and the shell part. On the other hand, when the core portion includes a plurality of fine particles, the emulsifier layer is present not only at the interface between the fine particles and the shell portion but also at the interface between the fine particles and the fine particles.

This emulsifier layer is a layer made of an emulsifier. The emulsifier is arranged on the surface of the thermochromic composition when preparing an oil-in-water type (O/W type, oil-in-water type) emulsion to form micelles, which are stable emulsifying particles, so the thermochromic composition is It can be uniformly and stably dispersed in the form of emulsified particles in the emulsion. In addition, the emulsifier pulls the components constituting the shell portion with an electrostatic attraction when manufacturing the thermochromic microcapsule so that the shell portion is formed on the outside of the emulsified particles.

To this end, the present invention includes an amphiphilic substance such as a water-soluble natural polymer, a water-soluble synthetic polymer, a surfactant, and inorganic fine particles as an emulsifier. Polysaccharides, such as, for example, Aribia gum; Proteins such as gelatin and casein; Ethylene-maleic anhydride copolymer, polyvinyl alcohol, styrene-maleic anhydride copolymer (SMA), methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, monostearate sorbitan, polyoxyethylene stearyl ether And the like, but are not limited thereto. These are used alone or in combination of two or more.

Here, the emulsifier can be appropriately selected depending on the components constituting the shell portion. For example, when the component of the shell part is an epoxy resin, a polysaccharide such as Aribia gum or a protein such as gelatin or casein may be used as an emulsifier. In addition, for example, when the component of the shell portion is a melamine-formaldehyde resin, an ethylene-maleic anhydride copolymer may be used as an emulsifier. In addition, for example, when the component of the shell portion is a urethane resin or an isocyanate compound, gelatin or polyvinyl alcohol may be used.

According to an example, a styrene maleic anhydride copolymer (SMA) may be used as an emulsifier. In this case, the styrene-maleic anhydride copolymer has a weight average molecular weight of about 300,000 to 400,000 g/mol.

In the core portion of the present invention, the content of the emulsifier is not particularly limited, and may be, for example, about 0.2 to 30 parts by weight based on 100 parts by weight of the thermochromic composition. If the content of the emulsifier is within the above-described range, the thermochromic composition may be dispersed into emulsified particles by the emulsifier when the microcapsules are manufactured, and at this time, the shell portion is formed by the emulsifier on the outer surface of the emulsified particles, so that about 1.0 A thermochromic microcapsule having an average particle size of from 1.4 μm may be formed.

In the thermochromic microcapsule of the present invention, the shell portion 12 may use, without limitation, various polymer resins widely used in the field of beads or microcapsules. For example, epoxy resin, polyamide resin, acrylonitrile resin, polyurethane resin, polyurea resin, melamine resin, phenol resin, urea-formaldehyde copolymer, melamine-formaldehyde, melamine-urea copolymer, melamine-phenol copolymer There are coalescence, benzoguanamine resin, butylated melamine resin, butylated urea resin, melamine-urea-formaldehyde copolymer resin, and the like, but are not limited thereto. These may be used alone or in combination of two or more. According to an example, the shell portion may be a melamine-urea-formaldehyde copolymer resin.

The thermochromic microcapsules of the present invention can be prepared by microencapsulation methods generally known in the art, and examples of microencapsulation methods include interfacial polymerization (polycondensation, addition polymerization), in situ polymerization, coacervation. There are methods, liquid-in-liquid drying methods, and spray drying methods.

For example, a thermochromic composition is added to an emulsifier aqueous solution (emulsifier concentration: about 0.1 to 15% by weight, specifically about 1 to 10% by weight) to form an O/W type emulsion. At this time, the average particle size of the droplets (emulsified particles) in the emulsion may be about 0.1 to 20 μm. Separately, in the presence or absence of a solvent (eg, water), the monomer(s) of a polymer resin constituting the shell portion and a crosslinking agent are polymerized to form a prepolymer for the shell portion. Thereafter, when the prepolymer for the shell portion is added and reacted to the O/W-type emulsion, a slurry containing a thermochromic microcapsule can be obtained. Thereafter, if necessary, the thermochromic microcapsules may be recovered as solids according to a solid-liquid separation method commonly known in the art, such as filtration and centrifugation, and the thermochromic microcapsules may be washed if necessary.

The shell portion 12 may be about 2 to 94% by weight, specifically about 5 to 40% by weight, based on the total weight of the thermochromic microcapsule.

As described above, the thermochromic microcapsules of the present invention may have an average particle size of 1.0 to 1.4 μm.

At this time, the content ratio of the core portion and the shell portion in the thermochromic microcapsule is not particularly limited. However, when the ratio of use of the shell portion to the core portion (content of the cell portion/content of the core portion) is about 0.1 to 0.8 weight ratio, color density, temperature discoloration reactivity, durability against pressure or heat, and workability are excellent.

In addition, the cross-sectional shape of the thermochromic microcapsule is not particularly limited, and may be, for example, a circular cross-section, an elliptical cross-section, or a non-circular cross-section.

The thermochromic microcapsule according to the present invention starts to develop color in a temperature range of -6°C or more and less than -2°C, and the freezing history of the refrigerated product can be displayed as a color change, but is not limited thereto. , Solvent volatile dry ink, two-component curable epoxy resin ink, printing paste, UV curable ink, etc. can impart temperature-sensitive discoloration. In addition, the thermochromic microcapsule of the present invention can be used not only to impart thermochromic discoloration to resin molded articles such as polyolefin, prints, paints, packaging materials, fibers, recording materials, etc., but also drawing materials such as writing instruments and crayons. It can also be used as a colorant for.

Meanwhile, FIG. 2 is a color density-temperature curve of a thermochromic microcapsule according to an embodiment of the present invention.

Referring to FIG. 2, the thermochromic microcapsule exhibits a hysteresis characteristic with respect to a color density-temperature curve, and in the process of decreasing the temperature in a color fading state, it begins to develop color when it reaches the _{temperature t 2, and the temperature} Color completely develops at a temperature lower than (t _{2 ) (t 1} ), and in the process of increasing the temperature in the color developing state, color begins to fade when it reaches a _{temperature (t 3 ) higher than the temperature (t 2 ), and the temperature (} t _3), and more fully bleached at a temperature (t _4), the temperature range between the temperature (t ₂₎ and the temperature (t ₃₎ color development state or decolorizing state are shown in the alternative.

Specifically, the change in color density according to the temperature change proceeds according to the arrow. Here, A is the color density at the _{temperature (t 2} ) at which color development starts, and B is the color density at the _{temperature (t 1) at which the color development state is reached.} C is the color density at the temperature (t ₃ ) at which the color disappears, and D is the color density at the _{temperature (t 4) at which the color disappears is reached.}

The color change temperature range is a temperature difference between the color development start temperature (t ₂ ) and the color disappearance start temperature (t ₃ ), and both states of the coloration state and the color disappearance state may coexist. In addition, the length of the line segment EF is a measure representing the contrast of color change, and the length of the line segment GH passing through the midpoint of the line segment EF is the temperature width (ΔH) representing the degree of hysteresis. When this temperature width ΔH is large, it becomes easy to maintain each state before and after discoloration.

Specifically, the complete color development temperature (t ₁ ) is -23 to -18°C, the color start temperature (t ₂ ) is more than -6°C and less than -2°C, and the discoloration start temperature (t ₃ ) is 41 to 45°C And may be a complete discoloration temperature (t ₄ ) 56 to 60°C. More specifically, the complete color development temperature (t ₁ ) is -21 to -20°C, the color start temperature (t ₂ ) is -6°C or more and -3°C or less, and the discoloration start temperature (t ₃ ) is 42 to 44 ℃, and complete discoloration temperature (t ₄ ) may be 57 to 59 ℃.

In the present invention, the complete _{discoloration temperature (t 4} ) is a temperature reaching complete discoloration, but when the temperature _{starts to decrease at the complete discoloration temperature (t 4} ), color development may proceed immediately. On the other hand, the inventors of the present invention the full predetermined color temperature (t ₄₎ in the case of even reach full decolorizing equal to the full predetermined color temperature (t ₄₎ or to reach a higher irreversible temperature (t _5), even if the temperature is lowered color development starting temperature It was confirmed that the discoloration can be maintained until reaching (t _{2 ).} The irreversible temperature (t ₅ ) may be 59°C or higher, and in detail, may be 59 to 62°C.

Accordingly, the thermochromic microcapsules may exhibit a hysteresis width of 63 to 66° C. based on a difference between a color intensity-temperature curve and a color fading start temperature (t ₂ ) and an irreversible temperature (t _{5 ).}

The temperature range defined above is a unique value of the thermochromic microcapsules having a specific average particle size and particle size distribution according to the present invention, as can be seen below.

Meanwhile, the thermochromic discoloration characteristics of the thermochromic microcapsules may be affected by the average particle size and particle size distribution of the microcapsules.

The "particle size" may be the particle diameter (particle diameter) when the microcapsules are spherical, but when the microcapsules are not perfectly spherical, the average diameter (average value of lengths in two or more directions) or equivalent diameter (a polyhedron is referred to as a simple shape). It can be expressed as an arbitrary average representative length such as (assuming that it is a representative length).

The particle size distribution can be determined by measuring the minimum size, maximum size, average value, etc. of the microcapsules using a particle size analyzer. For example, since it is not possible to accurately determine the particle size distribution only with the average value of the particle size, the particle size values corresponding to 10% and 90% for the largest particle size in the cumulative distribution of particle size are expressed as D10 and D90, respectively, and the above By defining the particle size distribution curve based on the value, the particle size distribution of the microcapsule can be accurately expressed.

Specifically, even if the thermochromic microcapsules have the same average particle size, if the particle size distribution is different, the color development start temperature and the complete color development temperature may be affected. For example, if a large number of microcapsules larger than the average particle size are distributed, microcapsules with a smaller particle size are distributed. In this case, microcapsules with a larger particle size develop color at a higher temperature than the average particle size, and microcapsules with a smaller particle size are Color development occurs at a temperature lower than the average particle size. That is, even if the average particle size is the same, if the area of the particle size distribution is wide, the color start temperature increases accordingly, and the complete color development temperature decreases, thereby widening the range of the color development temperature (the range between the color development start temperature and the complete color development temperature).

The average particle size and particle size distribution of these microcapsules can be adjusted by controlling the type and concentration of the emulsifier used in capsule manufacturing, the emulsification rpm and emulsification time of a homomixer used to proceed with the emulsification. In general, it is possible to increase or decrease the average particle size by adjusting the concentration of the emulsifier and the emulsification rpm of the homomixer, and the particle size distribution of the emulsion droplets can be adjusted by additionally adjusting the emulsification time.

In the present invention, the average particle size of the thermochromic microcapsul is 1.0 to 1.4 µm, D10 is 0.5 to 0.8 µm, D90 may be 2.5 to 3.0 µm, and the particle size distribution (D10 to D90) is 0.5 to 3.0 µm. I can. Specifically, D10 may be 0.5 to 0.6 µm, D90 may be 2.5 to 2.7 µm, and the particle size distribution (D10 to D90) may be 0.5 to 3.0 µm.

Here, sizes less than D10 and more than D90 are not considered because the amount is usually too small or not easy to classify, and the effect on the degree of color development is insignificant due to the limit of color change perceived by humans.

The average particle size or particle size distribution range of these thermochromic microcapsules is the optimal range that can be used as a freeze indicator by allowing the freezing history of refrigerated products to be displayed as a color change using the thermochromic microcapsules. If the average particle size or particle size distribution of the microcapsules is out of the above-defined range, the intended effect of the present invention cannot be obtained, which is not preferable.

Freeze indicator

The present invention provides a freezing indicator capable of displaying the freezing history of a refrigerated product by color change using the thermochromic microcapsule.

As described above, according to the Food Code of the Ministry of Food and Drug Safety <Notification No. 2019-57, 2019.7.3>, refrigerated products of meat, packaged meat and processed meat products are -2 to 10°C (however, poultry meat, poultry packaged meat, Since crushed meat and crushed meat products must be stored and distributed at -2 ~ 5℃), refrigerated products should not be lower than -2℃. Therefore, if the freezing indicator, which was colorless in the refrigeration temperature range, that is, from -2 to 10°C, exhibits a designated color, it may be a basis for determining that there is a history of exposure to a temperature environment lower than -2°C.

On the other hand, considering the limit of color change perceived by humans, it can be used as a freezing indicator to display the freezing history even if the color starts to develop below -2°C. In winter, the color may develop due to the cold outside during the loading and unloading process of the product, so it may be necessary to develop color at a slightly lower temperature as a safety device for this. In addition, in the case of intentionally freezing refrigerated meat, the temperature of the freezing chamber is lower than -18°C on average, so even if the color is developed at about -6°C, it is practically not unreasonable to display the freezing history of the refrigerated meat.

The freezing indicator according to the present invention begins to develop color at -6°C or more and 3°C, specifically, -6°C or more and less than -2°C, in the process of lowering the temperature in the color-disappearance state when the color disappears at the refrigeration temperature, In the process of increasing the temperature in the color development state, the color development is maintained even when the refrigeration temperature is reached, and the freezing history is displayed to provide a criterion for determining conformity to the preservation and distribution standards for products requiring refrigeration.

The color development start temperature (t ₂ ) range is an optimal value for exerting the function of the product by reflecting the realistic part of the consumer's demand and distribution, and it is not preferable because the intended effect of the present invention cannot be obtained if it deviates from it.

Since the freeze indicator can be manufactured in the form of a thin film such as a film or a sticker, the volume can be minimized and thus can be used conveniently and easily.

Hereinafter, an embodiment of the present invention will be described in detail. However, the following examples are only illustrative of the present invention, and the contents of the present invention are not limited to the following examples.

<Example 1>

1-1. Preparation of thermochromic composition

To prepare 500 g of thermochromic microcapsules having a solid content of 33% by weight, a color change temperature control agent (4-benzyloxyphenylethyl caprate, CAS No. 848484-93-5) (102.94 g), a leuco dye (7.36 g) and a developer (14.71 g) g) was mixed, followed by heating and stirring at 140° C. to prepare 125 g of a thermochromic composition.

1 -2. Preparation of thermochromic microcapsules

250 g of 5% SMA aqueous solution was prepared as an emulsifier. Here, SMA is a styrene-maleic anhydride copolymer (SMA). Thereafter, the SMA aqueous solution was heated to 90°C, and 125 g of the thermochromic composition prepared in Example 1-1 was added thereto, and then mixed and emulsified at 13,000 rpm for 15 minutes using a homomixer. /W type emulsion (average particle size of droplets: 0.8 µm) was prepared.

Melamine (31.85g), urea (5.2g), and formalin (39.94g) as a crosslinking agent were added to water (79.88g) and heated and stirred to prepare 156.87g of a melamine-urea copolymer prepolymer for the shell part.

Thereafter, the emulsion was transferred to an overhead stirrer, and then 156.87 g of the prepolymer for the shell portion was added thereto, allowed to react for 8 hours, and when the reaction was completed, the reaction was terminated by cooling while stirring to room temperature. , According to the amount of evaporated water, for multiple batches, the average particle size is 1.0 to 1.4 ㎛, the particle size distribution (D10 to D90) is 0.5 to 3.0 ㎛, D10 is 0.5 ㎛, D90 is 3.0 ㎛, thermochromic microcapsules 500 g of this dispersed slurry was prepared.

<Example 2>

In the same manner as in Example 1, except for mixing and emulsifying at 13,000 rpm for 30 minutes using a homomixer in Example 1, the average particle size was 1.0 to 1.4 µm, and the particle size distribution (D10 to D90) was A slurry 500g in which a thermochromic microcapsule having a D10 of 0.8 µm and a D90 of 2.5 µm was dispersed in a range of 0.8 to 2.5 µm was prepared.

<Comparative Example 1>

In the same manner as in Example 1, except for mixing and emulsifying at 10,000 rpm for 15 minutes using a homomixer in Example 1, the average particle size was 1.5 to 2.2 µm, and the particle size distribution (D ₁₀ to D ₉₀ ) Was 0.5 to 4.0 µm, D10 was 0.5 µm, D90 was 4.0 µm, and 500 g of a slurry in which thermochromic microcapsules were dispersed was prepared.

<Comparative Example 2>

In the same manner as in Example 1, except that 4% SMA aqueous solution was used as an emulsifier in Example 1 in the same amount, and mixed and emulsified at 15,000 rpm for 8 minutes using a homomixer, the average particle size was A slurry 500g in which thermochromic microcapsules of 1.0 to 1.4 μm, particle size distribution (D ₁₀ to D ₉₀ ) of 0.1 to 7.0 μm, D10 of 0.1 μm and D90 of 7.0 μm were dispersed was prepared.

<Experimental Example 1>

The slurries prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, were coated on paper using a #12 bar coator, and then cut into a size of 10mm*50mm, and then a thin film (OPP, oriented polypropylene) to prepare a specimen. The prepared specimen is discolored. After immersing this in water at room temperature, the temperature at which color development begins and the temperature at which color develops completely are measured by lowering the temperature using a chiller, and then, the temperature at which coloration begins and the temperature at which color disappears completely by raising the temperature are measured. It is shown in 1. In addition, the change in color detected in the specimen according to the temperature change is observed and shown in FIG. 3. 3 shows the color changes of Example 2 and Comparative Examples 1 and 2 at the corresponding temperatures based on the color development start temperature, complete color development temperature, color disappearance start temperature, and complete color disappearance temperature of Example 1. FIG.

Color start temperature
(℃) Complete color development temperature
(℃) Discoloration start temperature
(℃) Complete discoloration temperature
(℃) Irreversible temperature
(℃) Example 1 -3.0 -21.0 43.0 58.0 60.0 Example 2 -6.0 -20.0 43.0 58.0 60.0 Comparative Example 1 12.5 -16.0 45.0 57.0 60.0 Comparative Example 2 12.5 -25.0 45.0 58.0 60.0

Referring to Tables 1 and 3, the microcapsules of Example 1 and the microcapsules of Example 2 have the same average particle size, but Example 1 has a wider particle size distribution than that of Example 2, so that the color development temperature range (at the starting temperature of color development) As the section between the complete color development temperature) widens, it can be seen that the color starting temperature is higher and the complete color development temperature is lower.

The storage temperature of refrigerated products is -2 to 10°C (however, -2 to 5°C for poultry meat, poultry packaged meat, ground meat, and processed meat products), but -3°C when considering the limit of color change perceived by humans. The specimen according to Example 1, which starts color development at, can be sufficiently used as a freezing indicator indicating the freezing history.

On the other hand, in winter, colors may develop due to external cold temperatures in the process of loading and unloading products, so color development may be required at a slightly lower temperature as a safety device for this. In addition, in the case of intentionally freezing refrigerated meat, the temperature of the freezing chamber is below -18°C on average, so even if the color develops at -6°C, it is not too difficult to display the freezing history of the refrigerated meat. That is, reflecting the consumer's demand and the realistic part of the distribution, the specimen according to Example 2, which starts color development at -6° C. in some cases, may also be used as a freezing indicator.

On the other hand, the specimens according to Comparative Examples 1 and 2 cannot be used as a freezing indicator because they start to develop color at room temperature.

Claims (12)

A core portion including a thermochromic composition including a color change temperature control agent, a leuco dye and a developer in the form of fine particles; And a shell portion including a polymer resin surrounding the core portion; and a thermochromic microcapsule comprising,
The thermochromic microcapsules exhibit hysteresis characteristics with respect to the color density-temperature curve, and in the process of decreasing the temperature in the discoloration state, color begins to develop when the _{temperature (t 2} ) is reached, and is lower than the _{temperature (t 2 ).} Color completely develops at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, it begins to fade when it reaches a _{temperature (t 3 ) higher than the temperature (t 2} ), and a temperature higher than the _{temperature (t 3)} Color completely disappears at (t ₄ ), and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a color disappearance state alternatively appears,
The color development start temperature (t ₂ ) is more than -6℃ and less than -2℃,
The thermochromic microcapsule has an average particle size of 1.0 to 1.4 µm, D10 is 0.5 to 0.8 µm, and D90 is 2.5 to 3.0 µm. The thermochromic microcapsule of claim 1, wherein the color change temperature control agent comprises at least one of the compounds represented by the following Chemical Formulas 1 to 4:
<Formula 1>

<Formula 2>

<Formula 3>

<Formula 4>

The method of claim 1, wherein based on the total weight of the thermochromic composition, the color change temperature control agent is 1 to 99 parts by weight, the leuco dye is 1 to 15 parts by weight, and the developer is 1 to 40 parts by weight. Thermochromic microcapsules. The thermochromic microcapsule according to claim 1, wherein the leuco dye and the developer are 1:1 to 1:5 based on a weight ratio. The thermochromic microcapsule according to claim 1, wherein the thermochromic composition is 6 to 98 parts by weight based on the total weight of the thermochromic microcapsule. The thermochromic microcapsule according to claim 1, wherein the weight ratio of the shell part to the core part is 0.1 to 0.8. The method of claim 1,
The complete color development temperature (t ₁ ) is -23 to -18°C, the discoloration start temperature (t ₃ ) is 41 to 45°C, and the complete color _{discoloration temperature (t 4} ) is 56 to 60°C. Micro capsules. The method of claim 1,
If the temperature is lowered at an _{irreversible temperature (t 5} ) equal to or higher than the complete disappearance temperature (t _{4 ), the color disappears until the color development start temperature (t 2} ) is reached, and the irreversible temperature (t ₅ ) is 59 Temperature-sensitive discoloration microcapsules, characterized in that the temperature or more. The method of claim 1,
The thermochromic microcapsules are thermochromic, characterized in that they have a hysteresis width of 63 to 66°C based on the difference between the _{color intensity-temperature curve and the difference between the discoloration start temperature (t 2} ) and the irreversible temperature (t _{5 ).} Micro capsules. A freezing indicator, characterized in that, using the thermochromic microcapsule according to claim 1, the freezing history of the refrigerated product is displayed in color change. The method of claim 10,
When the freezing indicator is in a discolored state at a refrigerating temperature, in the process of decreasing the temperature in the discolored state, color begins to develop at -6°C or more and less than -2°C, and in the process of increasing the temperature in the color developing state, the refrigeration temperature A freezing indicator, characterized in that the color development is maintained even when reaching to to display the freezing history. The freeze indicator according to claim 10, wherein the freeze indicator is in the form of a film or a sticker.

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