KR102506072B1 - Thermochromic Microcapsule and Freeze Indicator Using the Same - Google Patents

Abstract

a core part including a thermochromic color-changing composition including a color change temperature controller, a leuco dye, and a color developer in the form of fine particles; and a shell portion including a polymer resin surrounding the core portion;
The thermally discolored microcapsules exhibit hysteresis characteristics with respect to the color concentration-temperature curve, and in the process of decreasing the temperature in the discoloration state, when the temperature (t ₂ ) is reached, the color starts to develop, and the temperature (t 2 ) is lower than the temperature (t ₂ ). The color is completely developed at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, when the temperature (t ₂ ) is reached at a temperature (t 3 ) higher than the temperature (t ₃ ), the color starts to disappear, and the temperature (t ₃ ) is higher than the temperature. (t ₄ ) completely disappears, and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a discoloration state appears alternatively,
The color development start temperature (t ₂ ) is -6 ° C or more and less than -2 ° C
The thermally discoloring microcapsules have an average particle size of 1.0 to 1.4 μm, a D10 of 0.5 to 0.8 μm, and a D90 of 2.5 to 3.0 μm, and a freezing indicator using the same.

Description

Thermochromic Microcapsule and Freeze Indicator Using the same {Thermochromic Microcapsule and Freeze Indicator Using the Same}

The present invention relates to a thermochromic microcapsule and a freezing indicator using the same, and more specifically, to a freezing indicator displaying the freezing history of a product using a thermochromic color-changing microcapsule having a large hysteresis.

Since the thermochromic color-changing composition is a material containing a leuco dye, a color developer, and a color-changing temperature regulator, and reversibly develops and disappears depending on temperature, the thermochromic color-changeable microcapsules containing the thermochromic color-changing composition are printed materials, It is used in inks, paints, packaging materials, writing instruments, and various types of plastic injection products.

Thermochromic microcapsules show reversible color change according to temperature and can be applied to products in various fields. Looking at the reversible color change, in order for the discolored state to return to the colored state according to the temperature change, the temperature must be slightly lower than the existing temperature, and this difference is called hysteresis.

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

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

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

As an example, according to the Ministry of Food and Drug Safety’s Food Code <Notice 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 meat packaging meat, ground Meat and ground meat products must be stored and distributed at -2 ~ 5℃), so refrigerated products must not be lower than -2℃. Therefore, if the freezing indicator containing a specific thermochromic microcapsule is colorless in the refrigeration temperature range, that is, -2 to 10 ° C and then shows a specific color, the basis for determining that there is a history of exposure to a temperature environment lower than -2 ° C , it can be used to check the freezing history of the product.

<Preceding Literature>

Japanese Patent Registration No. 5599679

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

It is an object of the present invention to provide thermochromic color-changing microcapsules in which discoloration is delayed by hysteresis after low-temperature color development.

Another object of the present invention is to provide a freezing indicator displaying the freezing history of a product using such thermochromic microcapsules.

the present invention.

a core part including a thermochromic color-changing composition including a color change temperature controller, a leuco dye, and a color developer in the form of fine particles; and a shell portion including a polymer resin surrounding the core portion;

The thermally discolored microcapsules exhibit hysteresis characteristics with respect to the color concentration-temperature curve, and in the process of decreasing the temperature in the discoloration state, when the temperature (t ₂ ) is reached, the color starts to develop, and the temperature (t 2 ) is lower than the temperature (t ₂ ). The color is completely developed at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, when the temperature (t ₂ ) is reached at a temperature (t 3 ) higher than the temperature (t ₃ ), the color starts to disappear, and the temperature (t ₃ ) is higher than the temperature. (t ₄ ) completely disappears, and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a discoloration state appears alternatively,

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

The thermally discoloring microcapsules have an average particle size of 1.0 to 1.4 μm, a D10 of 0.5 to 0.8 μm, and a D90 of 2.5 to 3.0 μm.

The discoloration temperature regulator may include at least one of the compounds represented by Chemical Formulas 1 to 4 below.

<Formula 1>

<Formula 2>

<Formula 3>

<Formula 4>

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

The leuco dye and the developer may be in a weight ratio of 1:1 to 1:5.

Based on the total weight of the thermochromic microcapsules, the thermochromic color-changing composition may be 6 to 98 parts by weight.

A weight ratio of the shell part to the core part may be 0.1 to 0.8.

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

When the temperature is lowered from the irreversible temperature (t ₅ ) equal to or higher than the temperature (t ₄ ), the discoloration is maintained until the temperature (t ₂ ) is reached, and the irreversible temperature (t ₅ ) may be 59° C. or higher. there is.

The thermochromic color-changing microcapsules may have a hysteresis width of 63 to 66° C. based on the difference between the color fading start temperature (t ₂ ) and the irreversible temperature (t ₅ ) in the color concentration-temperature curve.

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

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

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

The thermally discoloring microcapsule according to the present invention includes a predetermined thermally discoloring composition and shows a delay in discoloration due to hysteresis after low-temperature color development. A freezing indicator can be provided.

Since the thermochromic microcapsules according to the present invention have a specific average particle size and particle size distribution, they can be used to provide a freezing indicator with excellent characteristics that accurately determines the compliance with preservation and distribution standards for products requiring refrigerated storage. .

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

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

Thermochromic composition

The present invention,

a core part including a thermochromic color-changing composition including a color change temperature controller, a leuco dye, and a color developer in the form of fine particles; and a shell portion including a polymer resin surrounding the core portion;

The thermally discolored microcapsules exhibit hysteresis characteristics with respect to the color concentration-temperature curve, and in the process of decreasing the temperature in the discoloration state, when the temperature (t ₂ ) is reached, the color starts to develop, and the temperature (t 2 ) is lower than the temperature (t ₂ ). The color is completely developed at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, when the temperature (t ₂ ) is reached at a temperature (t 3 ) higher than the temperature (t ₃ ), the color starts to disappear, and the temperature (t ₃ ) is higher than the temperature. (t ₄ ) completely disappears, and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a discoloration state appears alternatively,

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

The thermally discoloring microcapsules have an average particle size of 1.0 to 1.4 μm, a D10 of 0.5 to 0.8 μm, and a D90 of 2.5 to 3.0 μm.

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

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

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

(a) discoloration temperature control agent

The thermochromic color changeable composition according to the present invention includes a color change temperature regulator, and can reversibly develop color-discoloration according to a heating-cooling cycle, and is discolored through the reaction of the color change temperature regulator, leuco dye, and color developer.

Specifically, the discoloration temperature regulator exists in a crystalline phase, that is, a solid phase at room temperature, phase transitions to a liquid phase when heated, and phase transitions to a solid phase when lowering the temperature to a low temperature. When the discoloration temperature regulator of the present invention is mixed with the leuco dye and the developer at room temperature in a solid state, the leuco dye reacts with the color developer to develop color, and when the color change temperature controller of the present invention is melted, the leuco dye and the developer Since the color reaction of the dye is blocked by the color change temperature regulator, the leuco dye is discolored.

Specifically, in the present invention, the discoloration temperature controller includes at least one of the compounds represented by Formulas 1 to 4 below, and can 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 the discoloration temperature regulator is mixed with the leuco dye and the color developer in the solid phase of Tc (crystallization temperature), the leuco dye reacts with the color developer to develop color. In addition, when the discoloration temperature controller of Chemical 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 controller, so the leuco dye is discolored.

In the thermally color-changing composition of the present invention, the content of the color-changing temperature regulator may be, for example, about 1 to 99 parts by weight based on the total amount of the thermally color-changing composition. When the content of the thermochromic color-changing composition is within the above-described range, color changeability may be improved without a decrease in color concentration, and color development efficiency may be improved.

(b) leuco dye

In the thermally discoloring composition of the present invention, leuco dye is an electron-donating compound and shows colorless or light white color in its natural state, but when it reacts with a color developer by oxidation-reduction, it becomes a complete dye and gives its own color. to color These leuco dyes develop color-discoloration depending on the physical state of the color change temperature controller. That is, in the thermochromic color changeable composition, the leuco dye develops color at room temperature, then disappears when the color change temperature controller melts, and when the color change temperature controller 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, for example, fluorane-based leuco dyes, fluorene-based leuco dyes, diphenylmethane phthalide-based leuco dyes, indolyl phthalide-based leuco dyes, There are 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-N-p-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-N-p-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-N-i-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 thermally color-changing 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 thermal color-changing composition. When the content of the leuco dye is within the above-described range, color changeability may be improved without a decrease in color concentration, and thus color development efficiency may be improved.

(c) color developer

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

The color 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 its derivatives, p-phenyl phenol, dodecylphenol, o-bromophenol, phenolic resin, phthalic acid, acetic acid, propionic acid, benzoic acid, butyric acid phosphate, 2-ethylhexyl-acid phosphate, dodecyl acid Phosphite, 1,2,3-triazole, 1,2,3-benzotriazole, diphenyl thiourea, di-o-toluyl urea, 2,2,2-trichloroethanol, 1,1,1 -tribromo-2-methyl-2-propanol, N-3-pyridyl-N'-(1-hydroxy-2,2,2-trichloroethyl) urea; 2-mercaptobenzene thiazole, 2-(4'-morpholino dithio) benzothiazole, and the like, and metal salts thereof, but are not limited thereto. These may be used alone or in combination of two or more.

In the thermally color-changing composition of the present invention, the content of the color developer is not particularly limited, and may be, for example, about 1 to 40 parts by weight based on the total weight of the thermally color-changing composition. If the content of the color developer is within the above-mentioned range, the color changeability may be improved without decreasing the color concentration, and thus the color development efficiency may be improved.

In addition, the ratio of the content of the developer to the content of the leuco dye is not particularly limited. However, if the amount of the developer used is too large compared to the content of the leuco dye, the color density is thick when developed, but the residual color may remain without becoming transparent when the color is extinguished. . Therefore, it is appropriate that the mixing ratio of leuco dye and developer (leuco dye: developer) is 1:1 to 5 weight ratio.

(d) other additives

The thermally color-changing composition according to the present invention may optionally further include additives known in the art within a range that does not impair the inherent characteristics of the composition, in addition to the above-described color-changing temperature controller, leuco dye, and color developer.

Non-limiting examples of additives usable in the present invention include ultraviolet absorbers, infrared absorbers, antioxidants, non-thermal color changing pigments, optical whitening agents, surfactants, antifoaming agents, leveling agents, solvents (eg, water-soluble organic solvents) , thickeners, etc., which may be used alone or in combination of two or more. These additives may be appropriately added within a content range known in the art, for example, about 0 to 30% by weight, specifically about 0.01 to 15% by weight based on the total amount of the thermochromic color changeable composition.

The thermochromic color-changeable composition of the present invention can be prepared by a method known in the art, for example, by introducing a color change temperature controller, a leuco dye, and a color developer and, if necessary, additives into a mixer and mixing them uniformly. can At this time, it may be mixed while heating. The heating temperature is not limited, and may be, for example, about 120 to 180°C.

Thermochromic Microcapsules

It will be described with reference to the drawings below.

1 is a schematic diagram of a cross section of a thermally discolorable microcapsule 10 according to one embodiment of the present invention.

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

These thermochromic color-changing microcapsules 10 are encapsulated in the form of microparticles in which the thermochromic color-changing composition is independently closed by the shell part 12, such as resin moldings, printed materials, inks, paints, packaging materials, fibers, recording materials, etc. It can impart discoloration and can also be used as a colorant. In addition, even if the thermally color-changing microcapsules of the present invention are applied in paints, inks or synthetic resins, since the thermally color-changing composition is encapsulated and protected by the shell part, other components in the paints, inks or synthetic resins, such as organic solvents, It is possible to minimize the effect of surfactants, additives, etc. on the color changing function of the thermochromic color changeable composition.

In the thermally color-changing microcapsule of the present invention, the core portion 11 includes microparticles made of a thermally color-changing composition. At this time, the fine particles may be one or a plurality.

The microparticles are formed by emulsifying a thermochromic composition in an aqueous solvent, and their average particle size is not particularly limited, but may be, for example, about 0.1 to 21 μm.

The amount of the thermally color-changing 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 thermally color-changing microcapsule. If the content of the thermochromic color-changing composition is too small outside the above range, it is difficult to exhibit the color-changing function intended by the present invention, and if the content of the thermochromic color-change 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 part may further include an emulsifier layer disposed (formed) on the surface of the microparticles. Here, when the core portion includes one particle, the emulsifier layer is present at the interface between the particle and the shell portion. Meanwhile, 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. Since the emulsifier is arranged on the surface of the thermally discolorable composition during preparation of an oil-in-water emulsion (O/W type, oil-in-water type) to form micelles, which are stable emulsified particles, the thermally discolorable composition is It can be dispersed uniformly and stably in the form of emulsified particles in emulsion. In addition, the emulsifier pulls components constituting the shell part by electrostatic attraction during the production of the thermochromic microcapsule so that the shell part is formed on the outside of the emulsified particles.

To this end, in the present invention, amphiphilic substances such as water-soluble natural polymers, water-soluble synthetic polymers, surfactants, and inorganic fine particles are included as emulsifiers. polysaccharides such as gum arabic; proteins such as gelatin and casein; Ethylene-maleic anhydride copolymer, polyvinyl alcohol, styrene-maleic anhydride copolymer (SMA), methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, sorbitan monostearate, polyoxyethylene stearyl ether etc., but is not limited thereto. These are used alone or in combination of two or more.

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

According to one 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 part 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 color changeable composition. If the content of the emulsifier is within the above-mentioned range, the thermochromic color changeable composition may be dispersed into the emulsified particles by the emulsifier during preparation of the microcapsules, and at this time, the emulsifier forms a shell portion on the outer surface of the emulsified particles, so that about 1.0 Thermally discolorable microcapsules having an average particle size of 1.4 μm to 1.4 μm may be formed.

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

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

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

The amount of the shell portion 12 may be about 2 to 94 wt %, specifically about 5 to 40 wt %, 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 part and the shell part in the thermochromic microcapsule is not particularly limited. However, when the use ratio of the shell part to the core part (the content of the shell part/the content of the core part) is about 0.1 to 0.8 weight ratio, the color density, temperature discoloration reactivity, durability against pressure or heat, processability, etc. 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 color changeable microcapsules according to the present invention start to develop color in the temperature range of -6 ° C or more and less than -2 ° C, so that the freezing history of refrigerated products can be displayed as a color change, but is not limited thereto, and aqueous emulsion ink It can be applied to solvent volatile dry ink, two-component curable epoxy resin ink, printing paste, and UV curable ink to impart thermal discoloration. In addition, the thermochromic color-changeable microcapsules of the present invention can be used to impart thermochromic color-changeability to resin moldings such as polyolefin, prints, paints, packaging materials, fibers, and recording materials, as well as drawing materials such as writing instruments and crayons. It can also be used as a colorant for

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

Referring to FIG. 2, the thermally discoloring microcapsules exhibit hysteresis characteristics with respect to the color concentration-temperature curve, and in the process of decreasing the temperature in the decoloring state, when the temperature (t ₂ ) is reached, they start to develop color, and the temperature (t ₂ ) Completely develops color at a temperature (t ₁ ) lower than, and in the process of increasing the temperature in the color development state, when the temperature (t ₂ ) is reached at a temperature (t ₃ ) higher than the temperature (t 2 ), the color starts to disappear, and the temperature ( The color disappears completely at a temperature (t ₄ ) higher than t ₃ ), and in a temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a discoloration state appears alternatively.

Specifically, a change in color density according to a change in temperature proceeds along an arrow. Here, A is the color density at the temperature at which color development starts (t ₂ ), and B is the color density at the temperature at which color development is reached (t ₁ ). C is the color density at the temperature at which color quenching is initiated (t ₃ ), and D is the color density at the temperature (t ₄ ) at which the complete color quenching state is reached.

The color change temperature range is the temperature difference between the color development start temperature (t ₂ ) and the color fading start temperature (t ₃ ), and both states of the colored state and the extinguished state may coexist. In addition, the length of the line segment EF is a scale representing the contrast of discoloration, and the length of the line segment GH passing through the midpoint of the line segment EF is the temperature range ΔH representing the degree of hysteresis. When this temperature range (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 onset temperature (t ₂ ) is -6 ° C or more and less than -2 ° C, and the color fading start temperature (t ₃ ) is 41 to 45 ° C And, the complete decolorization temperature (t ₄ ) may be 56 to 60°C. More specifically, the complete color development temperature (t ₁ ) is -21 to -20 ° C, the color development start temperature (t ₂ ) is -6 ° C or more -3 ° C or less, and the color fading start temperature (t ₃ ) is 42 to 44 ° C °C, and the complete decolorization temperature (t ₄ ) may be 57 to 59 °C.

In the present invention, the complete quenching temperature (t ₄ ) is a temperature at which complete quenching is reached, but when the temperature starts to decrease from the complete quenching temperature (t ₄ ), color development may proceed immediately. On the other hand, the inventors of the present invention, even if complete discoloration is reached at the complete discoloration temperature (t ₄ ), when the same or higher irreversible temperature (t ₅ ) is reached than the complete discoloration temperature (t ₄ ), even if the temperature is lowered, the color development start temperature It was confirmed that the discoloration could be maintained until reaching (t ₂ ). The irreversible temperature (t ₅ ) may be greater than or equal to 59°C, and specifically may be 59 to 62°C.

Accordingly, the thermochromic color changeable microcapsules may exhibit a hysteresis width of 63 to 66° C. based on the difference between the discoloration start temperature (t ₂ ) and the irreversible temperature (t ₅ ) in the color concentration-temperature curve.

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 thermal discoloration characteristics of the thermochromic microcapsules may be influenced by the average particle size and particle size distribution of the microcapsules.

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

The distribution of the particle size can be measured by measuring the minimum size, maximum size, average value, etc. of the microcapsule using a particle size analyzer. For example, since the particle size distribution cannot be accurately determined only with the average value of the particle size, the particle size values corresponding to 10% and 90% of the particle size of the largest value in the cumulative distribution of particle sizes are expressed as D10 and D90, respectively. If the particle size distribution curve is defined based on the value, the particle size distribution of the microcapsule can be accurately expressed.

Specifically, even if the thermochromic color changeable microcapsules have the same average particle size, if the particle size distribution is different, the color development start temperature and complete color development temperature may be affected. For example, if a large number of microcapsules with a larger than average particle size are distributed, microcapsules with a smaller particle size will be distributed accordingly. It develops color at a temperature lower than the average particle size. That is, even if the average particle size is the same, if the region of the particle size distribution is wide, the color onset temperature increases accordingly and the complete color development temperature decreases, so that the range of color development temperature (interval between the color onset temperature and the complete color development temperature) widens.

The average particle size and particle size distribution of these microcapsules can be controlled by controlling the type and concentration of the emulsifier used in capsule manufacturing, and the emulsification rpm and emulsification time of a homomixer used for emulsification. In general, the average particle size can be increased or decreased 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 controlled by additionally adjusting the emulsification time.

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

Here, sizes smaller than D10 and larger than D90 are usually not considered because the amount is 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 an optimal range that can be used as a freezing indicator by using the thermochromic microcapsules to display the freezing history of refrigerated products as a color change. If the average particle size or particle size distribution of the sex microcapsules is out of the range defined above, 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 as a color change using the thermochromic color changing microcapsule.

As described above, according to the Ministry of Food and Drug Safety's Food Code <Notice No. 2019-57, 2019.7.3>, refrigerated products of meat, packaged meat, and processed meat are -2 to 10 ° C (however, poultry meat, poultry meat packaging, Ground meat and ground processed meat products must be stored and distributed at -2 ~ 5℃), so refrigerated products must not be lower than -2℃. Therefore, if the freezing indicator, which was colorless in the refrigeration temperature range, that is, -2 to 10 ° C, shows a designated color, it can 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 that displays the freezing history even if color development starts at less than -2 ° C. In the case of winter, the color may develop due to the cold temperature outside in the process of loading and unloading the product, so it may be necessary to develop the color at a slightly lower temperature as a safety device. In addition, when intentionally freezing refrigerated meat, since the temperature of the freezing chamber is below -18 ° C on average, there is practically no difficulty in displaying the freezing history of refrigerated meat even if the color develops at about -6 ° C.

When the freezing indicator according to the present invention is in a discolored state at a refrigeration temperature, in the process of decreasing the temperature in the discolored state, it starts to develop color at -6 ° C or more and less than -2 ° C, in detail, at -6 ° C or more and 3 ° C, 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 preservation and distribution standards for products requiring refrigeration storage.

The color development start temperature (t ₂ ) range is an optimal value for demonstrating the function of the product by reflecting consumer demands and realistic parts of distribution.

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

Hereinafter, examples of the present invention will be described in detail. However, the following examples are only to illustrate the present invention, and the content of the present invention is not limited to the following examples.

<Example 1>

1-1. Preparation of thermochromic composition

To prepare 500 g of thermochromic microcapsules with a solid content of 33% by weight, a color change temperature controller (4-benzyloxyphenylethyl caprate, CAS No. 848484-93-5) (102.94 g), a leuco dye (7.36 g) and a color developer (14.71 g) g) was mixed, followed by heating and stirring at 140° C. to prepare 125 g of the thermochromic color changeable 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 (Styrene-maleic anhydride copolymer, SMA). Thereafter, the SMA aqueous solution was heated to 90 ° C, 125 g of the thermochromic color changeable composition prepared in Example 1-1 was added thereto, and then mixed and emulsified for 15 minutes at 13,000 rpm using a homomixer to O /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 shell parts.

Thereafter, the emulsion was transferred to an overhead stirrer for low viscosity, and then 156.87 g of the prepolymer for the shell portion was added thereto, reacted 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, the average particle size for a number of batches is 1.0 to 1.4 μm, and the particle size distribution (D10 to D90) is 0.5 to 3.0 μm, with a D10 of 0.5 μm and a D90 of 3.0 μm. 500 g of this dispersed slurry was prepared.

<Example 2>

In Example 1, the average particle size was 1.0 to 1.4 μm and the particle size distribution (D10 to D90) was the same as in Example 1, except that mixing and emulsification was performed at 13,000 rpm for 30 minutes using a homomixer. 500 g of a slurry in which thermochromic color-changing microcapsules having a size of 0.8 to 2.5 μm, with a D10 of 0.8 μm and a D90 of 2.5 μm were dispersed, was prepared.

<Comparative Example 1>

In Example 1, the average particle size was 1.5 to 2.2 μm and the particle size distribution (D ₁₀ ~ D ₉₀ ) was 0.5 to 4.0 μm, and 500 g of a slurry in which thermochromic color-changing microcapsules having a D10 of 0.5 μm and a D90 of 4.0 μm were dispersed was prepared.

<Comparative Example 2>

In Example 1, the average particle size was obtained in the same manner as in Example 1, except that the same amount of 4% SMA aqueous solution was used as an emulsifier and mixed and emulsified at 15,000 rpm for 8 minutes using a homomixer. 1.0 to 1.4 μm and a particle size distribution (D ₁₀ to D ₉₀ ) of 0.1 to 7.0 μm, with a D10 of 0.1 μm and a D90 of 7.0 μm, 500 g of slurry in which thermochromic microcapsules 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 coater, and then cut into a size of 10 mm * 50 mm, and then a thin film (OPP, Specimens were prepared by coating with oriented polypropylene). The prepared specimen is in a discolored state. After immersing it in room temperature water, the temperature was lowered using a chiller to measure the temperature at which color development started and the temperature at which color development was completely developed. 1. In addition, the color change detected in the specimen according to the temperature change was observed and shown in FIG. 3 . FIG. 3 shows the respective color changes of Example 2 and Comparative Examples 1 and 2 at corresponding temperatures based on the color development start temperature, complete color development temperature, color fading start temperature, and complete color quench temperature of Example 1. FIG.

color start temperature
(℃) full color temperature
(℃) discoloration start temperature
(℃) complete decolorization 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 Table 1 and FIG. 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 Example 2, so that the color development temperature range (from the color development start temperature) As the interval between the complete color development temperatures) widens, it can be confirmed that the color development start 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 meat packaging, ground meat, and ground processed meat products), but considering the limit of color change perceived by humans, -3 ° C The specimen according to Example 1, which starts to develop color at , can be sufficiently used as a freezing indicator displaying the freezing history.

On the other hand, in the case of winter, the color may develop due to the cold temperature outside in the process of loading and unloading the product, so it may be necessary to develop the color at a slightly lower temperature as a safety device. In addition, when refrigerated meat is intentionally frozen, since the temperature of the freezer is below -18 ° C on average, there is no great difficulty in displaying the freezing history of refrigerated meat even if the color develops at -6 ° C. That is, in some cases, the specimen according to Example 2, which starts to develop color at -6 ° C, can be used as a freezing indicator, reflecting consumer demand and realistic parts of distribution.

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

Claims (12)

A freezing indicator characterized in that the freezing history of refrigerated products is displayed by color change using thermochromic microcapsules,
The thermally color-changing microcapsules contain 1 to 99 parts by weight of a color change temperature controller represented by Formula 1 below, 1 to 15 parts by weight of a leuco dye, and 1 to 40 parts by weight of a color developer based on the total weight of the thermochromic color-changing composition. a core portion comprising a thermochromic color-changing composition in the form of fine particles; And a shell portion including a polymer resin surrounding the core portion; including,
The thermally discolored microcapsules exhibit hysteresis characteristics with respect to the color concentration-temperature curve, and in the process of decreasing the temperature in the discoloration state, when the temperature (t ₂ ) is reached, the color starts to develop, and the temperature (t 2 ) is lower than the temperature (t ₂ ). The color is completely developed at the temperature (t ₁ ), and in the process of increasing the temperature in the color development state, when the temperature (t ₂ ) is reached at a temperature (t 3 ) higher than the temperature (t ₃ ), the color starts to disappear, and the temperature (t ₃ ) is higher than the temperature. (t ₄ ) completely disappears, and in the temperature range between the temperature (t ₂ ) and the temperature (t ₃ ), a color development state or a discoloration state appears alternatively,
The color development start temperature (t ₂ ) is -6 ° C or more and -3 ° C or less,
The thermally discoloring microcapsules have an average particle size of 1.0 to 1.4 μm, D10 of 0.5 to 0.8 μm, D90 of 2.5 to 3.0 μm,
When the freezing indicator is in the discoloration state at the refrigeration temperature, in the process of decreasing the temperature in the discoloration state, the color starts to develop at -6 ° C or more and below -3 ° C. A freezing indicator characterized in that the color development is maintained even after reaching the freezing history to display the freezing history.
<Formula 1>

delete delete The freezing indicator according to claim 1, wherein the leuco dye and the developer have a weight ratio of 1:1 to 1:5. The freeze indicator according to claim 1, wherein the amount of the thermochromic color-changing composition is 6 to 98 parts by weight based on the total weight of the thermochromic microcapsules. The freezing indicator according to claim 1, wherein a weight ratio of the shell part to the core part ranges from 0.1 to 0.8. According to 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 discoloration temperature (t ₄ ) is 56 to 60 ° C. Frozen indicator. According to claim 1,
When the temperature is lowered at an irreversible temperature (t ₅ ) equal to or higher than the complete discoloration temperature (t ₄ ), the color is maintained until the color development start temperature (t ₂ ) is reached, and the irreversible temperature (t ₅ ) is 59 A freezing indicator, characterized in that more than ℃. According to claim 1,
The freezing indicator, characterized in that it has a hysteresis width of 63 to 66 ℃ based on the difference between the discoloration start temperature (t ₂ ) and the irreversible temperature (t ₅ ) with respect to the color concentration-temperature curve Freezing indicator. delete delete The freezing indicator according to claim 1, wherein the freezing indicator is in the form of a film or a sticker.

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