JPH0781089B2 - Thermoreversible discoloration microcapsules and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a microcapsule that reversibly changes color with a rise and fall of temperature at a specific temperature and a method for producing the same. Specifically, it has excellent thermoreversible discoloration performance that can change color sharply and reversibly according to temperature changes, and it can be stored (leaved) in a hot and humid atmosphere or in a water system for a long time.
Even if it relates to a microcapsule which retains and develops a good and sharp thermoreversible discoloration performance and can develop a clear and deep good color tone at the time of color development, and an industrially advantageous production method thereof.
In the present invention, discoloration means decolorization, color development, color density,
A concept that includes a wide range of color changes such as color changes.

(Prior Art) Conventionally, color is developed at a certain temperature as is known, but when a predetermined temperature is reached, the color changes (discolors), and when the temperature decreases, the color returns to the original color. A specific composition consisting of an agent and a desensitizer, or a leuco dye that develops color (color) when the temperature drops to a predetermined temperature but becomes colorless again when the temperature rises, and a color developer and a reducing agent. A specific composition comprising a sensitizer, that is, a specific composition that develops a thermochromism phenomenon, is used to prepare a printing ink, a paint, or the like, and the composition is applied to, for example, paper, cloth, or the specific composition. It is used in applications that require temperature-sensitive display, such as when mixed with synthetic resin moldings.

Such a specific substance is called a thermoreversible color-changing coloring material (hereinafter referred to as a thermoreversible color-changing material), and was used in the form of a simple substance or a composition. In many cases, the thermoreversible discoloration performance is deteriorated or lost. Therefore, in order to protect the thermoreversible color-changing material, a microcapsule-like material whose surface is covered with a capsule wall made of a polymer such as a synthetic resin has also been proposed. As one of the examples, in Production Example 6 of Japanese Patent Publication No. 51-44708, a hydrophobic (oil-based) substance is added to an aqueous solution of urea formalin initial condensate.
A heat-reversible color-changing material A (a mixture of leuco dye crystal violet lactone, bisphenol A as a color developer, and cetyl alcohol as a desensitizer) heated to 80 ° C Was added dropwise and stirred to form fine oil droplets, citric acid was added and the pH was lowered to 4 and kept at 40 to 50 ° C for 5 hours (long time), the colorant A and water-insoluble polymerization It is described that a product is produced, which is coated with the colorant A to obtain a capsule containing the colorant A therein.

However, in this production method, the hydrophobic (oil-based) colorant A is made into fine droplets only by the stirring force without using an emulsifier, but as is well known, the stirring force alone necessarily causes a large particle diameter. In order to generate uneven and unstable oil droplet particles, the capsule coated with the polymer has a large particle size, and the coating state is also uneven, and moisture or water easily intrudes from the portion. Moreover, the polymer urea-
Formaldehyde polycondensate (urea resin) has low water resistance and non-uniform coating, resulting in extremely poor moisture resistance and slurry storage stability, as described below, as well as color density, heat resistance, and thermoreversible discoloration performance. As a result, the thermoreversible color-changing microcapsules having an insufficient commercial value are produced. Further, the above polycondensation reaction requires a long time (5 hours), and the reaction does not proceed smoothly.

(Problems to be Solved by the Invention) The present inventor has conducted diligent research as a solution to the problems in the production of microcapsules having such a urea-formaldehyde polycondensate as a capsule wall and the production thereof. Presence of a specific bisphenol compound in the water phase of an oil-in-water emulsion in which a hydrophobic composition having thermoreversible discoloration performance is emulsified and dispersed as at least one emulsifier selected from salts When the polycondensation reaction of urea and formaldehyde is performed below, (1) the polycondensation reaction proceeds quickly and smoothly, and urea-containing a bisphenol compound and bound around the uniformly fine oil droplets To produce a microcapsule having a stable and dense capsule wall made of a formaldehyde-based polycondensate.

(2) The microcapsules are good even when stored in an atmosphere of high temperature and high humidity or in a water system for a long time, and retain and develop a sharp thermoreversible discoloration performance, and when they are colored, they develop a clear and deep color tone. And has excellent temperature display function.

(3) The microcapsule slurry as a reaction product mixture (liquid) containing the microcapsules dispersed therein is an interaction between a specific bisphenol compound and at least one selected from residual coexisting polystyrenesulfonic acid and its salt. By maintaining the appropriate viscosity and viscosity, the coating work on the adherend (paper, cloth, etc.) can be facilitated.

Based on such findings, the present invention has been completed.

Therefore, the first object of the present invention is to provide a capsule wall having excellent moisture resistance, water resistance, and heat resistance, which is always improved and is capable of exhibiting a sharp thermoreversible discoloration performance and a temperature-sensitive display function. To provide microcapsules.

A second object is to provide a fine capsule slurry that contains the above-mentioned good fine capsules in a dispersed state and is excellent in storage stability, usability, and coatability. A third object is to provide a production method capable of producing the above-mentioned excellent microcapsule slurry smoothly, easily and industrially advantageously.

(Means for Solving the Problem) The above object of the present invention is a hydrophobic composition having a thermoreversible discoloration performance in which a hydrophobic core substance comprises a leuco dye, a developer, and a desensitizer. In the aqueous phase of an oil-in-water (O / W) emulsion in which the organic composition is emulsified and dispersed in water using at least one selected from polystyrene sulfonic acid and its salt as an emulsifier, urea is added in the presence of a bisphenol compound. By carrying out a polycondensation reaction of the formaldehyde with formaldehyde, it is clathrated by a capsule wall composed of a urea-formaldehyde polycondensate in which the bifphenol compound is bound to the surface of the hydrophobic composition having thermoreversible discoloration performance. The hydrophobic composition having thermoreversible discoloration performance composed of a microcapsule and a coil dye, a color developer, and a desensitizer is polystyrene. Polycondensation of urea and formaldehyde in the aqueous phase of an oil-in-water type (O / W type) emulsion in which at least one selected from sulfonic acid and its salts is emulsified and dispersed in water as an emulsifier in the presence of a bisphenol compound. The reaction is performed to form a capsule wall made of a urea-formaldehyde polycondensate having the bisphenol compound bonded to the surface of the hydrophobic composition having thermoreversible discoloration performance. This is achieved by the method of manufacturing capsules.

The microcapsules of the present invention are bound to the urea-formaldehyde-based polycondensate that constitutes the capsule wall of the microcapsules of the present invention. The bisphenol-based compound is a bisphenol-based compound soluble in an aqueous formaldehyde solution (generally does not have a substituted alkyl group in the phenol nucleus). What is shown by the following general formula (1) is used.

General formula (1) B-A-B ... (1) (In the above formula, A is R is an alkyl group having 1 to 4 carbon atoms) Most preferably, 1,1-ethylidene-bisphenol,
Examples are 2,2-propylidene-bisphenol-bisphenol S, methyl-isobutyl-methylidene-bisphenol, methyl-phenyl, methylidene-bisphenol and the like.

The content of at least one of the bisphenol compounds is 0.1 wt% to 2 wt% based on the weight of the capsule wall.
It is 0% by weight, preferably 0.5% by weight to 10% by weight. If the content is out of this range, the object of the present invention cannot be sufficiently achieved. The content of the capsule wall constituting the microcapsule is 2 based on the weight of the microcapsule.
˜15% by weight, preferably 5-12% by weight, and the content of said hydrophobic composition, which is the hydrophobic core substance, is 85-98%.
%, Preferably 88 to 95% by weight.

The specific bisphenol compound-bonded urea-formaldehyde-based polycondensation capsule wall,
It has excellent moisture resistance, water resistance, and heat resistance, is extremely dense, is strong, and does not easily break under internal or external pressure even when exposed to relatively high temperatures. Since the capsule wall has a translucent appearance,
When the color of the hydrophobic composition is developed, it gives a clear and deep and good color tone, and the color change at the time of erasing or discoloring can be sensitively and clearly perceived. Further, the specific bisphenol compound bound to the urea-formaldehyde polycondensate of the capsule wall contributes to the improvement of the physical properties of the capsule wall and the thermoreversible discoloration performance of the hydrophobic composition as the core substance. Is an excellent moisture resistance, water resistance, heat resistance, slurry storage stability, and high color density not found in microcapsules containing the urea-formaldehyde polycondensate in which the bisphenol compound is not present. , The color tone and thermo-reversible discoloration are manifested.

The hydrophobic composition, which is the hydrophobic core substance, is a homogeneous melt mixture of a substantially water-insoluble leuco dye, a developer and a desensitizer, and usually contains 0.1 to 10% by weight of the leuco dye.
It contains 0.1 to 20% by weight of a color developer and 70 to 99.8% by weight of a desensitizer.

The leuco dye is not particularly limited, but examples of commonly used leuco dyes are as follows.

I. Triphenylmethanephthalides …… Crystal violet lactone, malachite green lactone, etc.

II. Fluoranes ... 3,6-diethoxyfluorane, 3-
Dimethoxyamino-6-methyl-7-chlorofluorane, 1,2-benz-6-diethylaminofluorane, 3
-Diethiamino-7-methoxyfluorane and the like.

III. Phenothiazines ... Benzoyl leuco methylene blue, methyl leuco methylene blue, ethyl leuco methylene blue, methoxybenzoyl leuco methylene blue, etc.

IV. Indolylphthalides: 2- (phenyliminotanylidene) 3,3-dimethylindoline, etc.

V. Spiropyrans: 1,3,3-trimethyl-indolino-7-chloro-β-naphthospiropyran, di-β-naphthospiropyran, benzo-β-naphthospiropyran, xantho-β-naphthospiropyran and the like.

VI. Leuco auramines, N-acetyl auramine, N
-Phenyl auramine etc.

VII. Rhodamine lactams: Rhodamine B lactams, etc.

The color developer is a compound that reacts with the leuco dye to develop or change color, and as a suitable color developer,
For example, dodecylphenol, phenyl salicylate, dodecylphenol gallate, phenolic resin, 4-tert-butylphenol, 4-oxydiphenyl ether, α-naphthol, β-naphthol, n-butyl p-oxybenzoate, p-oxyacetophenone, 2 , 2 ′
-Methylenepis (4-methyl-6-tert-isobutylphenol), p-phenylphenol, 4,4'-
Isopropylidene diphenol, 2,2'-methylenebis (4-chlorophenol), hydroquinone, 2-oxy-1-naphthoic acid, 2-oxy-p-toluic acid, salicylic acid, m-oxybenzoic acid, 4-oxyphthalic acid , Froglucin carboxylic acid, gallic acid, propyl gallate,
In addition to phthalic acid, compounds having a phenolic hydroxyl group described in JP-B-52-30372, metal salts of compounds having a phenolic hydroxyl group, carboxylic acids and metal salts thereof, sulfonic acids and metal salts thereof, phosphorus Acid esters and the like, further described in JP-A-57-76072 1,
Examples thereof include 2,3 triazole compounds, but are not limited thereto.

Further, the desensitizer has a function of suppressing the discoloration by suppressing the reaction between the leuco dye and the developer outside the predetermined temperature, and having a function of rapidly discoloring when reaching the predetermined temperature, and discoloring ( Compounds that impart sensitivity to decolorization and color development) are not particularly limited, but representative ones are as follows.

I. Alcohols ... n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, n-lauryl alcohol, n-myristyl alcohol, n-cetyl alcohol, n-stearyl alcohol, n-icosyl alcohol, n-doco Syl alcohol, oleyl alcohol, cyclohexanol, benzyl alcohol, etc.

II. Esters: lauryl caproate, octyl caprate, butyl laurate, dodecyl laurate, hexyl myristate, myristyl myristate, octyl palmitate, stearyl palmitate, butyl stearate, cetyl stearate, lauryl behenate, Cetyl oleate, butyl benzoate, phenyl benzoate, dibutyl sebacate, etc.

III. Ketones ...... cyclohexanone, acetophenone,
Benzophenone, dimyristyl ketone, etc.

IV. Fatty acids: caproic acid, caprylic acid, capric acid, uraric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid,
Cerotic acid, partleic acid, oleic acid, ricinoleic acid, linolenic acid, eleostearic acid, erucic acid, etc.

V. Acid amides ... Capric acid amide, caprylic acid amide, uraric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide,
Oleic acid amide, benzamide, etc.

VI. Hydrocarbons: Aliphatic hydrocarbons such as decane, dodecane, undecane, etc .; Aromatic hydrocarbons such as naphthalene, anthracene, diphenylmethane, etc .; Decalin, pinene,
Alicyclic hydrocarbons such as bicyclohexyl; mixtures of hydrocarbons marketed as light oil and kerosene.

The leuco dye, the developer, and the desensitizer in the hydrophobic composition constituting the hydrophobic core substance are respectively contained in one kind or in a combination of two or more kinds, and the composition is melted. A mixed homogeneous system is formed.

The microcapsules of the present invention have an average particle size of 20μ or less (preferably 10μ or less), and with a uniform particle size,
The capsule wall composed of a urea-formaldehyde polycondensate in which a specific bisphenol compound is present forms a dense, strong and uniform coating structure. Therefore, the microcapsules of the present invention have extremely high humidity resistance, water resistance, heat resistance, and slurry storage stability, and are sensitive to temperature changes even when stored in a high temperature and high humidity atmosphere or in an aqueous system for a long time. It retains reversible thermochromic performance sensitive to heat and can reproduce a clear and deep good color tone at the time of color development. Therefore, a thermoreversible color-changing ink or its composition, such as printing ink or paint, is prepared. However, it can be applied to paper, cloth or the like, or by mixing the microcapsules of the present invention into a synthetic resin molded product or the like to be utilized in various applications requiring temperature-sensitive display, and the commercial value thereof is extremely high.

According to the present invention, the microcapsules having the above-mentioned excellent features and the microcapsule slurry containing the microcapsules can be easily and industrially produced by the production method described above.
The manufacturing method will be described in detail below.

At least one selected from polystyrene sulfonic acid and salts thereof in the present invention, as an emulsifier for emulsifying a hydrophobic composition having thermoreversible discoloration performance which is the hydrophobic core substance in water, and in the polycondensation reaction. Used as a promoter.

The salt of polystyrene sulfonic acid is obtained by neutralizing some or all of the acid groups of polystyrene sulfonic acid,
Examples of the neutralizing base include alkali metal hydroxides or carbonates, ammonia, organic amines and the like.

Polystyrene sulfonic acid and its salts have
It is about 5,000 to 2,000,000, preferably 10,000 to 1,500,000, and most preferably about 100,000 to 1,000,000, and the amount used is 0.5 to 20% by weight, preferably 1% by weight based on the total amount of the hydrophobic composition. ~ 10% by weight.

If this amount is too small, the emulsification becomes unstable and it becomes difficult to uniformly carry out the polycondensation reaction around the hydrophobic composition, and the urea-formaldehyde polycondensate in which a dense and strong bisphenol compound is bound. It becomes difficult to form a capsule wall made of On the other hand, if this amount is too large, the viscosity of the reaction system may increase, which may make stirring difficult and may produce the capsules having nonuniform particle size.

At least one selected from polystyrene sulfonic acid and its salt is present in the aqueous phase in the form of an aqueous solution, and the hydrophobic composition is emulsified and dispersed in water as fine oil droplets to cause polycondensation reaction (encapsulation). It forms and holds a stable oil-in-water emulsion until completion, facilitates the polycondensation reaction smoothly, and forms a dense and stable capsule wall composed of a urea-formaldehyde polycondensate bound with a bisphenol compound. It is also one of the features of the present invention that uniform and fine microcapsules can be obtained. At least one selected from polystyrene sulfonic acid and its salts is dissolved in water and then dissolved by adding urea under stirring, or without it, a molten mixture of the hydrophobic composition (usually about
(50-120 ° C) is gradually added to an aqueous system (about 40-70 ° C) to emulsify it. O / W type in which oil droplets with a hydrophobic composition particle size of about 1-10μ are dispersed in water. It becomes an emulsion.
Note that urea may be added to and dissolved in the emulsion after the emulsion is formed, and then reacted with formaldehyde.

The amount of urea used is usually 2 to 13% by weight, based on the total amount of the hydrophobic composition.

The hydrophobic composition is prepared by using a leuco dye, a color developer, and a desensitizer in the above-mentioned weight ratios, and usually by heating to about 50 to 120 ° C. and melt-mixing. If necessary, add an acid or alkali to this emulsion to obtain PH
To about 2.0 to 5.0 (preferably 2.4 to 4.0), and then formaldehyde aqueous solution and the solution of the bisphenol compound are gradually added in the desired order or at about the same time, or the bisphenol compound is added. Add the formaldehyde aqueous solution in which the compound is dissolved gradually,
Carry out polycondensation reaction of urea and formaldehyde. In addition,
Most preferred is a method of adding an aqueous formaldehyde solution in which a bisphenol compound is dissolved.

The polycondensation reaction is usually carried out at 40 to 70 ° C, but is not limited to this temperature. Although the reaction time is not limited,
Usually, the polycondensation reaction is substantially completed in a short time of 1 to 3 hours.

The required amount of formaldehyde is 1 for 1 mol of urea.
It is preferably within the range of 1 to 3 mol.

The bisphenol compounds may be used alone or in combination of two or more.

The amount of the bisphenol compound used is 1 based on the total weight of polystyrene sulfonic acid and / or its salt.
˜400 wt%, preferably 10-200 wt%.

When the amount of the bisphenol compound used is too small, it is difficult to form the aforementioned dense and strong capsules having excellent durability, and when the amount is too large, the emulsification becomes unstable, and the capsule is uniformly distributed around the hydrophobic composition. It may be difficult to carry out the polycondensation reaction. The bisphenol compound is incorporated into the activated polycondensation system of urea-formaldehyde by polystyrene sulfonic acid which coexists and dissociates in the acidic aqueous phase, and a part of the bisphenol compound is copolycondensed and chemically bound. A part of the polycondensate is formed as a solid solution inside and outside of the polycondensate, which physically binds to the polycondensate, strengthens the capsule wall densely, and significantly improves the durability, which is the most important feature of the present invention.

However, with diphenols and trivalent phenols such as resorcinol and pyrogallol having a phenolic nucleus having a phenolic hydroxyl group and a small molecular volume, as described below,
Moisture resistance, heat resistance, slurry storage stability, etc. cannot be improved.

When a small amount of dihydric phenol and its derivative such as resorcinol, catechol, hydroquinone and orcin, and trihydric phenol and its derivative such as pyrogallol, phloroglysin and gallic acid are used together with the bisphenol compound, the durability is further improved. In some cases, it can be used within a range that does not impair the effects of the present invention.

After the polycondensation reaction was substantially completed, when cooled to room temperature with stirring, the particle size was uniform, the dense, and strong capsule walls uniformly covered the hydrophobic composition as the core substance, It is obtained as a slurry in which fine capsules having good durability are dispersed.

This slurry is composed of the above-mentioned excellent microcapsules and an aqueous solution containing at least one selected from polystyrenesulfonic acid and its salts, formaldehyde, a bisphenol compound, and urea as main components.

Usually, the content of these components is, based on the total amount of the microcapsule slurry, 20 to 60% by weight of microcapsules, 0.5 to 5% by weight of at least one selected from polystyrenesulfonic acid and salts thereof, and 0.01 to 2 of formaldehyde. % By weight, 0.01 to 2% by weight of urea, and 0.01 to 5% by weight of bisphenol compound.

(Example) Hereinafter, an example will be described.

The parts shown in the examples mean parts by weight, and% related to weight means% by weight. In addition, the color density, moisture resistance, and
The test methods for heat resistance and slurry storage stability are as follows.

(1) Color density The capsule slurry was printed on white ketone paper by silk-screening and air-dried, and the chromaticity (L ₁ *, a ₁ *, b ₁ *) at the time of color development of the resulting printed film, and the disappearance Chromaticity at color (L ₂ *, a
₂ *, b ₂ *) is measured using a color chromaticity meter. Then
The color difference ΔE (L * a * b *) between the two was calculated using the following formula.

L *: Lightness index a *, b *: Chromaticity index relating to hue and saturation (2) Moisture resistance After leaving the printing paper obtained in (1) above in 70 ° C, 90% relative humidity atmosphere for 3 days , Take out and dry, (1)
Similar to the item above, the chromaticity L *, a at the time of coloring and erasing of the printed film
*, B * are measured to obtain the color difference ΔE, and then the ΔE (hereinafter referred to as ΔE ₂ ) obtained above is based on the ΔE (hereinafter referred to as ΔE ₁ ) obtained in the above item (1). In contrast, the color difference retention rate was determined using the following formula.

Color difference retention rate (%): (ΔE ₂ / ΔE ₁ ) × 100 (3) Heat resistance After leaving the printing paper of (1) above for 20 minutes in a 140 ° C. constant temperature bath, take it out, and similarly print a coating film. Color difference ΔE (hereinafter Δ
E ₃ ), and then Δ calculated in the above (1)
The E ₁ compared as a reference to determine the retention of the color difference using the following formula.

Color difference retention rate (%): (ΔE ₃ / ΔE ₁ ) × 100 (4) Slurry storage stability After leaving the capsule slurry in a constant temperature bath at 50 ° C. for 7 days, it was taken out and treated in the same manner as in the above (1). The chromaticity of the printed film obtained after printing on ketone paper and natural drying was measured and the color difference ΔE
(Hereinafter referred to as ΔE ₄ ), and then compared with ΔE ₁ obtained in the item (1) as a reference, and the color difference retention rate was calculated using the following formula.

Color difference retention rate (%): (ΔE ₄ / ΔE ₁ ) × 100 (5) Visual judgment criteria Color density evaluation point Visual feeling 5 Very dark color at the time of color development 4 〃 Very dark color 3 〃 Light color 2 〃 Almost no color 1 No color Appearance Water resistance, Heat resistance, Slurry storage stability Evaluation point Visual sense 5 Colors are not abnormal, very good 4 Colors are almost abnormal, good 3 Decolored and bad 2 Almost decolorized and bad 1 Completely decolorized and extremely bad Example 1 (1) Production and performance of microcapsules 3 g of potistyrenesulfonic acid (molecular weight = 500,000) in 97 g of water
And 6 g of urea are added and dissolved by stirring at 20 ° C to form a solution (A
solution).

Lauric acid 45 parts, myristic acid 25 parts, palmitic acid 30 parts, 3-diethylamino-6-methyl-7-chlorofluorane (leuco dye) 1.5 parts and methyl paraoxybenzoate (developer) 3 parts at 80 ° C. Heat and melt to form a solution (B
liquid).

To 15.6 g of 37% aqueous formaldehyde solution, 0.9 g of 2,2-propylidene-bisphenol (hereinafter abbreviated as PBP) is heated at 50 ° C to form a solution. (Solution C) Next, while keeping Solution A at 50 ° C., 90 g of Solution B was added with stirring with a homomixer,
The mixture was stirred for 5 minutes and dispersed and emulsified. The pH of the liquid was 2.0. Then add 1 g of 20% aqueous sodium hydroxide to this emulsion.
PH was adjusted to 3.2, C solution was added and stirred for 1 minute, and then polycondensation reaction was carried out at 60 ° C. for 3 hours. Then, the liquid was gradually cooled to obtain a fine capsule slurry. After the obtained microcapsule slurry was applied to white Kent paper and naturally dried, the thermoreversible discoloration property of the microcapsules in this coating film was examined. As a result, the color changed from red to colorless above 30 ° C, and returned to red below 30 ° C, and its thermoreversible discoloration was extremely sharp. The color tone at the time of color development was deep and clear red.

Next, the average particle size of the microcapsules obtained by filtering and drying this microcapsule slurry was about 8 μm, and the particle size was uniform. Also, the performance test of this microcapsule was carried out as described above, and the measured value of the color density was 58.1, the visual judgment was 5, and the color at the time of coloring was deep and very good, the measured value of water resistance was 97%, and the visual judgment was 5 is extremely good, and the measured value of heat resistance is
95%, the visual judgment was 5, which was very good. The measured value of the storage stability of the slurry was 92%, and the visual judgment was 5, which was very good.

(2) Detection and content of PBP in the capsule wall In order to remove the hydrophobic core substance in the microcapsules obtained in this Example, a pressure of 10 kg / cm ² was applied by a press machine to the microcapsules. After breaking, the broken pieces were refluxed in cyclohexane for 3 hours to extract the hydrophobic core substance. In order to separate the PBP in the broken capsule wall pieces remaining as a residue, after further finely grinding the broken capsule wall pieces,
Reflux for 3 hours in chloroform and extract.

When the chloroform extract was subjected to high performance liquid chromatography for quantitative analysis of PBP, about 3.5% of PBP was detected based on the weight of the capsule wall. Converting this result into the production scale of Example 1 (1), it is bound in the capsule wall of the microcapsules obtained in (1).
The total amount of PBP was found to be about 0.27 g.

In the same manner, quantitative analysis of PBP remaining in the aqueous phase of the microcapsule slurry obtained in the above (1) was carried out, and the total amount was about 0.58 g.
The total of the amount of BP (0.27 g) and the amount of PBP in the aqueous phase (0.58 g) was 0.85 g, which was approximately similar to the amount of PBP added at the time of production of 0.9 g.

Comparative Example 1 (when PBP is not used as a capsule wall component) The same procedure as in Example 1 was performed except that PBP was not used and only the 37% aqueous formaldehyde solution was used as the C liquid.

The obtained microcapsules changed color from red to colorless above 30 ° C and returned to red below 30 ° C, but the thermoreversible discoloration was lacking in sharpness.

As a result of the performance test of the microcapsules, the measured value of color density was 40.6, the visual judgment was 3 and the color was fairly light, the water resistance was 60%, the visual judgment was 2 and the color was almost decolored and was poor in heat resistance. Is 43%, the visual judgment is 1 and the color is completely decolorized, which is extremely bad. The slurry storage stability is 67% and the visual judgment is 3
It was so bad that it was decolorized. Thus, when PBP is not used as the capsule wall component, microcapsules with insufficient moisture resistance, slurry storage stability, and heat resistance are produced.

Comparative Example 2 (when PBP is used as the developer of the core substance and not as the capsule wall component) PBP is used in place of the methyl paraoxybenzoate as the developer of the B liquid, and PBP is used in the C liquid. Without using
The same procedure as in Example 1 was repeated except that only 37% aqueous formaldehyde solution was used. As a result, the measured color density is
45.5, the visual judgment is 3, the color is light, and the measured value of moisture resistance is 74
%, The visual judgment was bad at 2, the heat resistance measurement value was 68%, the visual judgment was bad at 3, the slurry storage stability measurement value was 71%, the visual judgment was bad at 3, and the color tone after both water resistance tests was It was also unclear and had no depth.

Thus, even if PBP is used as the color developer in the core substance, if PBP is not used as the capsule wall component, as in the case of Comparative Example 1, the water resistance such as moisture resistance and slurry storage stability, Microcapsules with good heat resistance cannot be obtained.

This fact is also clear from the results of Comparative Examples 3 to 6 described later.

Examples 2 to 3 and Comparative Examples 3 to 6 The same procedure as in Example 1 was carried out except that the color developer in the liquid B and / or the PBP in the liquid C was replaced with the compounds shown in Appendix 1. The results are shown in the table.

From the results of the attached table 1, in the liquid C (as a capsule wall component)
When the compound of the present invention is used as the bisphenol compound, the color density is high even when the developer is changed, and the durability is excellent (Examples 2 to 6). When the bisphenol compound of the present invention is not used for the capsule wall component (in the liquid C), the color density is low and the durability is poor. It is clear that when the bisphenol compound of the present invention (for example, PBP) is used as both the capsule wall component and the color developer, the color density is synergistically increased and the slurry storage stability is further improved. .

The microcapsules of Examples 2 to 3 have a uniform viscosity and are fine with an average particle size of about 2 to 7μ, and change from red to colorless when the temperature exceeds 30 ° C, and return to red when the temperature is lower than 30 ° C. In addition, the thermoreversible discoloration was extremely sharp and the color tone at the time of color development was clear and deep, which was preferable.

Comparative Example 7 The same procedure as in Example 1 was performed except that PBP in solution C (capsule wall component) was not used and resorcin was used in solution A (capsule wall component) (coexisting with urea). The color density of the obtained microcapsules was 45.1, the humidity resistance was 48%, the heat resistance was 38%, the slurry storage stability was 41%, and the durability was poor.

Comparative Example 8 The procedure of Example 1 was repeated except that PBP in the C liquid (capsule wall component) was not used and resorcin was used instead.

The color density of the obtained microcapsules was 45.7, the moisture resistance was 45%, the heat resistance was 32%, the slurry storage stability was 29%, and the durability was poor.

As is clear from the results of Comparative Examples 7 and 8, even when resorcin coexists in the capsule wall component (aqueous phase) and polycondensation reaction is performed, it is possible to obtain microcapsules having high color density and good durability. Can not.

Comparative Example 9 (Additional Test of Production Example 6 of Japanese Patent Publication No. 51-44708) For comparison, Production Example 6 of Japanese Patent Publication No. 51-44708 (No. 1)
Column 0) "Colorant A is crystal violet lactone (leuco dye) and bisphenol A described in column 8
(Developer) and cetyl alcohol (desensitizer) are used ”to produce microcapsules. As a result, the polycondensation reaction of the urea formalin initial condensate did not proceed smoothly, took 5 hours, and the particle size was uneven, the average particle size was 30μ, the color density was 40.5, and the moisture resistance was 21.8%. 25.1%, slurry storage stability was 23%, which was poor, durability was poor, and thermoreversible discoloration was also lacking in sharpness.

Example 7 Example 1 was repeated except that 100 parts of cetyl alcohol was used in place of 100 parts of the higher fatty acid mixture in the liquid B.

The resulting microcapsules have a uniform particle size and an average particle size of 8
In μ, the color density was 56.5, the measured value of moisture resistance was 96%, the heat resistance was 97%, and the storage stability of the slurry was 91%.

The thermo-reversible discoloration was also sharp, becoming colorless above 48 ° C and returning to red at temperatures below 48 ° C.

Example 8 Example 1 was repeated except that 100 parts of methyl stearate was used instead of 100 parts of the higher fatty acid mixture in the liquid B.

The particle size of the obtained microcapsules is uniform and the average particle size is 9
The color development density was 57.5, the humidity resistance was 95%, the heat resistance was 93%, and the slurry storage stability was 91%, which was good.

The thermo-reversible discoloration was also sharp, becoming colorless above 30 ° C and returning to red at temperatures below 30 ° C.

Example 9 Example 1 was repeated except that 50 parts of stearic acid amide and 50 parts of ularyl alcohol were used in place of 100 parts of the higher fatty acid mixture in the liquid B.

The resulting microcapsules have a uniform particle size and an average particle size of 7
In μ, the color density was 55.6, the measured moisture resistance was 96%, the heat resistance was 92%, and the slurry storage stability was 93%.

The thermo-reversible discoloration was also sharp, becoming colorless above 23 ° C and returning to red at temperatures below 23 ° C.

Example 10 Example 1 was repeated except that 100 parts of myristic acid was used in place of 100 parts of the higher fatty acid mixture in the solution B.

The resulting microcapsules have a uniform particle size and an average particle size of 4
In μ, the color density was 59.6, the measured moisture resistance was 97%, the heat resistance was 96%, the storage stability was 93%, and the durability was excellent.

The thermoreversible discoloration was sharp, and became colorless when the temperature exceeded 50 ° C, and returned to red when the temperature was lower than 50 ° C. When the color was developed, it had a clear and deep good color tone.

Further, the microcapsule slurry in which the microcapsules are dispersed is similar to the microcapsule slurries obtained in Examples 1 to 9 above, at a relatively high temperature (50 ° C.) for a long time (15 days).
Even when stored, it does not increase in viscosity like an anionic polyelectrolyte aqueous solution and does not change viscosity (structural viscosity, thixotropic property), is stable, and has a relatively low viscosity of 100 to 500 cps. Was confirmed. It was also found that such a unique and good effect is due to the interaction between the residual bisphenol compound coexisting in the microcapsule slurry and polystyrene sulfonic acid.

(Effect) The present invention comprises (1) emulsifying and dispersing in a water phase fine oil droplets of a hydrophobic composition having thermoreversible discoloration performance, using at least one selected from polystyrene sulfonic acid and salts thereof as an emulsifier. In the aqueous phase of the emulsion, the polycondensation reaction of urea and formaldehyde is carried out in the coexistence of a bisphenol compound and at least one selected from the polystyrene sulfonic acid and its salts, thereby reacting around the hydrophobic composition. Rapidly progresses smoothly and easily, and the surface of the hydrophobic composition is easily covered with a dense and strong capsule wall (urea-formaldehyde polycondensate to which a bisphenol compound is bound) to obtain a microcapsule having a uniform particle size. Can be obtained.

(2) The microcapsules are stable even when stored in a high-temperature, high-humidity atmosphere or in a water system for a long time, and have a reversible thermochromic property that is extremely sensitive to temperature changes. However, at the time of color development, it produces a good color tone with a clear depth.
Each application (printing ink, paint,
It is useful for fabric processing).

(3) The resulting capsule slurry in which the microcapsules are dispersed retains a low viscosity, and even when stored under relatively high temperature conditions, the viscosity is unlikely to change and the capsules do not deteriorate, which is stable and has good coating properties. Is.

The useful and remarkable actions and effects of the above are peculiar to the thermoreversible color-changing microcapsules and the production method thereof in the prior art, and their industrial significance is extremely large.

Claims (8)

[Claims] 1. A hydrophobic core substance comprising a leuco dye, a color developer and a desensitizer, which is a hydrophobic composition having thermoreversible discoloration performance, wherein the hydrophobic composition is selected from polystyrene sulfonic acid and salts thereof. In an aqueous phase of an oil-in-water type (O / W type) emulsion that is emulsified and dispersed in water using at least one of the above-mentioned compounds, by performing a polycondensation reaction of urea and formaldehyde in the presence of a bisphenol compound, A thermoreversible discolorable microparticle characterized by being covered with a capsule wall composed of a urea-formaldehyde polycondensate in which the bisphenol compound is bound to the surface of a hydrophobic composition having thermoreversible discoloration performance. capsule. 2. The thermoreversible color-changing microcapsule according to claim 1, wherein the bisphenol compound is 0.1 to 20% by weight based on the weight of the capsule wall. 3. The thermoreversible color-changing microcapsules according to claim 1, wherein the bisphenol compound is at least one compound represented by the following general formula (1). General formula (1) B-A-B ... (1) (In the above formula, A is B is The above R is an alkyl group having 1 to 4 carbon atoms) 4. A hydrophobic composition having a thermoreversible discoloration performance, which comprises a leuco dye, a developer and a desensitizer, is emulsified and dispersed in water using at least one selected from polystyrenesulfonic acid and its salts as an emulsifier. Oil-in-water type (O / W type)
In the water phase of the emulsion, urea-formaldehyde is bound to the surface of the hydrophobic composition having thermoreversible discoloration performance by performing a polycondensation reaction of urea and formaldehyde in the presence of a bisphenol compound. A method for producing thermoreversible color-changing microcapsules, which comprises forming a capsule wall made of a formaldehyde-based polycondensate. 5. The polycondensation reaction of urea and formaldehyde in the coexistence of the bisphenol compound is carried out in an aqueous solution containing at least one selected from polystyrene sulfonic acid and its salt and urea, and a leuco dye and a microscope. A colorant, and a hydrophobic composition having a thermoreversible discoloration performance composed of a molten mixture of a desensitizer was added with stirring to emulsify, and then PH was adjusted to 2.0 to 5.0, and then the bisphenol compound was A polycondensation reaction is carried out by adding a dissolved formaldehyde aqueous solution. Claim (4)
A method for producing the thermoreversible color-changing microcapsule according to the item. 6. A polycondensation reaction of urea and formaldehyde in the coexistence of the bisphenol compound is added to a solution containing a leuco dye, a color developer, and a leuco dye in an aqueous solution containing at least one selected from polystyrenesulfonic acid and salts thereof. And a hydrophobic composition having a thermoreversible discoloration performance composed of a molten mixture of a desensitizer is added under stirring to emulsify, urea is added and dissolved, and then PH is adjusted to 2.0 to 5.0, and then the bisphenol system is added. The method for producing thermoreversible color-changing microcapsules according to claim (4), wherein a polycondensation reaction is carried out by adding an aqueous formaldehyde solution in which the compound is dissolved. 7. The method according to claim 4, wherein after forming the capsule wall on the surface of the hydrophobic substance, the produced microcapsules are separated and obtained from the slurry. A method for producing thermoreversible color-changing microcapsules. 8. The bisphenol compound is used by being dissolved in an aqueous formaldehyde solution in an amount of 1 to 400% by weight, based on the total weight of polystyrenesulfonic acid and / or its salt in the aqueous solution. The method for producing thermoreversible color-changing microcapsules according to any one of items (4) to (6).