JPH01174591A - Heat reversible, color changeable microcapsule and production thereof - Google Patents

Abstract

PURPOSE:To form capsule walls to cover a hydrophilic core substance such as leuco dye, developer or desensitizer, having excellent water-vapor resistance, water resistance and heat resistance, comprising a urea-formaldehyde polycondensate to which a bisphenol compound is bonded. CONSTITUTION:The aimed capsule wall consists of a urea-formaldehyde polycondensate to which 0.1-20wt.% (preferably 0.5-10wt.%) based on weight of the capsule wall of one or more bisphenol compounds preferably shown by formula B-A-B' [A is -CH2- or group shown by formula I-IX (R is 1-4C alkyl); B is group X]. 1,1-Ethylidene-bisphenol, bisphenol S, methyl-isobutyl- methylidene-bisphenol, etc., may be cited as the optimum example of the bisphenol compound.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to microcapsules that reversibly change color as the temperature rises and falls below a specific temperature, and a method for producing the same. Specifically, it has excellent thermoreversible color change performance that allows it to change color sharply and reversibly in response to temperature changes, and can be stored (left) for long periods of time in high temperature and high humidity environments or in water systems.
The present invention relates to microcapsules that maintain and exhibit good and sharp thermoreversible color change performance even when the color is developed, and can develop a clear, deep, and good color tone when coloring, and an industrially advantageous manufacturing method thereof. In the present invention, the term "discoloration" refers to a concept that includes a wide range of color changes, such as decolorization, color development, color density, and color change.

(Prior art) As is well known, leuco dyes and color developers develop color at a certain temperature, but change color (discolor) when a predetermined temperature is reached, and restore the original color when the temperature drops. A specific composition consisting of a desensitizing agent and a desensitizing agent, or a leuco dye, a color developer, and a desensitizing agent that is colorless at room temperature but develops color when the temperature drops to a certain temperature, and becomes colorless again when the temperature rises. A printing ink, paint, etc. is prepared using a specific composition consisting of a sensitizing agent, that is, a specific composition that exhibits a thermochromism phenomenon, and is applied to paper, fabric, etc., or the specific composition is applied to paper, fabric, etc. It is used in applications that require temperature-sensitive display, such as by being mixed into synthetic resin molded products.

Such specific substances are called thermoreversible coloring materials (hereinafter referred to as thermoreversible coloring materials), and have been used alone or in the form of compositions, but when they come into contact with moisture or water, they change color. In many cases, thermoreversible color change performance deteriorates or is lost.Therefore, in order to protect the thermoreversible color change material, its surface is covered with a capsule wall made of a polymer such as synthetic resin, which is shaped like a microcapsule. is also proposed. As one example, in Production Example 6 of Japanese Patent Publication No. 51-44708, hydrophobic (
Coloring agent A (a mixture consisting of crystal violet lactone, a leuco dye, bisphenol A as a color developer, and cetyl alcohol as a desensitizer), which is an oil-based thermoreversible color-changing material, was heated to 80°C. Add the molten mixture dropwise, stir to form fine oil droplets, add citric acid, lower the pH to 4, and keep it at 40-50℃ for 5 hours (long time). It is described that a polymer is formed, which coats the coloring agent A, thereby obtaining a capsule containing the coloring agent A.

However, in this production method, the hydrophobic (oil-based) coloring agent A is made into microdroplets using only stirring force without using an emulsifier, but as is well known, stirring force alone inevitably results in large particle size. In order to produce non-uniform and unstable oil droplet particles, the capsules coated with the polymer have a large particle size, and the state of the coating is also non-uniform, making it easy for moisture and water to infiltrate from those areas. Moreover, the polymer urea-
Formaldehyde polycondensates (urea resins) have low water resistance and the resulting coating is uneven, resulting in extremely poor moisture resistance and slurry storage stability as described below, as well as poor color density, heat resistance, and thermoreversible color change performance. etc., resulting in the production of thermoreversible color-changing microcapsules with insufficient commercial value. Further, there are problems in industrial implementation, such as the polycondensation reaction takes a long time (5 hours) and the reaction does not proceed smoothly.

(Problems to be Solved by the Invention) As a result of intensive research aimed at solving the problems in microcapsules having capsule walls made of such urea-formaldehyde polycondensates and their production, the present inventors have found that polystyrene sulfonic acid and its Presence of a specific bisphenol compound in the aqueous phase of an oil-in-ice emulsion in which a hydrophobic composition with thermoreversible color-changing properties is emulsified and dispersed as oil droplets using at least one selected from salts as an emulsifier. When performing a polycondensation reaction between urea and formaldehyde, (1) the polycondensation reaction proceeds quickly and smoothly, and the bisphenol-based compound is incorporated around the uniformly fine oil droplets and the bonded urea- To produce microcapsules with stable and dense capsule walls made of formaldehyde-based polycondensates.

(2) This microcapsule maintains and exhibits sensitive thermoreversible color change performance even when stored for long periods in high temperature and high humidity environments or in aqueous systems, and when colored, it develops a clear and deep color tone. and has an excellent temperature-sensitive display function.

(3) The microcapsule slurry as a reaction product mixture (liquid) containing the microcapsules dispersedly contains the interaction between at least one selected from residual coexisting polystyrene sulfonic acid and its salts and a specific bisphenol compound. By maintaining appropriate viscosity and viscosity, the adherend (
To facilitate coating work on paper, fabric, etc.).

Based on these findings, the present invention was completed.

Therefore, the first object of the present invention is to provide an improved capsule wall that has excellent moisture resistance, water resistance, and heat resistance, and can maintain and exhibit good and sensitive thermoreversible color change performance and temperature-sensitive display function at all times. The purpose of the present invention is to provide microcapsules that are

The second object is to provide a microcapsule slurry containing the above-mentioned favorable microcapsules dispersed therein and having excellent storage stability, usability, and coating properties.

A third object is to provide a manufacturing method that allows the above-mentioned excellent microcapsule slurry to be manufactured smoothly, easily, and industrially advantageously.

(Means for Solving the Problems) The above-mentioned object of the present invention is to provide a hydrophobic composition having a thermoreversible color changing property in which the hydrophobic core substance is composed of a leuco dye, a color developer, and a desensitizer; The capsule wall surrounding the microcapsules is characterized by being formed of a urea-formaldehyde polycondensate to which a bisphenol compound is bonded, and a heat absorbent consisting of a leuco dye, a color developer, and a desensitizer. In the aqueous phase of an oil-in-water (O/W type) emulsilon, a hydrophobic composition having reversible color change performance is emulsified and dispersed in water using at least one selected from polystyrene sulfonic acid and its salts as an emulsifier. Consisting of a urea-formaldehyde polycondensate in which the bisphenol compound is bonded to the surface of the hydrophobic composition having thermoreversible color change performance by performing a polycondensation reaction of urea and formaldehyde in the presence of a compound. This is achieved by a method for manufacturing microcapsules, which is characterized by forming a capsule wall.

It is bonded to the urea-formaldehyde polycondensate constituting the capsule wall of the microcapsule of the present invention (bonded here means incorporated into the Isi & condensate, and is physically and chemically The bisphenol compound is a bisphenol compound that is soluble in an aqueous formaldehyde solution (generally does not have a substituted alkyl group on the phenol nucleus), and is preferably The compound represented by the following general formula (1) is used.

General formula (1) % formula % (1) (A in the above formula is CI, -C-C1) 5 groups.

Most preferred examples include 1,1-ethylidene-bisphenol, 2,2-propylidene-bisphenol, bisphenol S1 methyl-isobutyl-methylidene-bisphenol, and methyl-phenyl-methylidene-bisphenol.

The content of at least one bisphenol compound is 0.1% by weight based on the weight of the capsule wall.
-20% by weight, preferably 0.5% - 10% by weight. If the content is outside this range, the object of the present invention cannot be fully achieved.

The content of the capsule wall constituting the microcapsule is 2 to 15% by weight, preferably 5 to 12% by weight, based on the weight of the microcapsule, and the hydrophobic composition as a hydrophobic core substance is The content of the product is 85-98% by weight, preferably 88-95% by weight.

The capsule wall is made of a urea-formaldehyde polycondensate to which the specific bisphenol compound is bound,
It has good moisture resistance, water resistance, and heat resistance, and is extremely dense and strong (and is not easily destroyed by internal or external pressure even when exposed to relatively high temperatures.The capsule wall has a translucent appearance, When the hydrophobic composition is colored, it gives a clear, deep, elegant, and good color tone, and the color change when it fades or changes color can be sensitively and clearly sensed.Furthermore, it binds to the urea-formaldehyde polycondensate on the capsule wall. The fact that the specific bisphenol-based compound contributes to the improvement of the physical properties of the capsule wall and the thermoreversible color change performance of the hydrophobic composition that is the core material is that the urea in which the bisphenol-based compound is absent −
Excellent moisture resistance, water resistance, heat resistance, and
This is obvious from the fact that it exhibits slurry storage stability, high color density, color tone, and thermoreversible color change.

The hydrophobic composition, which is the hydrophobic core material, is a homogeneous molten mixture consisting of a substantially water-insoluble leuco dye, a color developer, and a desensitizer, and usually contains 0.1 to 10% of the leuco dye by weight. %, color developer 0.1-20% by weight, desensitizer 70-99%
．． It contains 81% by weight.

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

1.) Riphenylmethane phthalides 100. Crystal violet lactone, malachite green lactone, etc.

■, Fluoranes, 3.6-dinitoxyfluoran, 3-dimethoxyamino-6-methyl-7-chlorofluoran, 1.2-benz-6-dinithylaminofluoran, 3-diethylamino- 7-methoxyfluorane etc.

■, Phenothiazines 1) 0. Benzoyl leucomethylene blue, methyl leucomethylene blue, ethyl leucomethylene blue, methoxybenzoyl leucomethylene blue, etc.

■, indolylphthalide, 2-(phenyliminoethanedylidene) 3,3-dimethylindoline, etc.

■, spiropyrans, 1.3.3-trimethyl-
Indolino-7-chloro-β-naphthospiropyran, di-β-naphthospiropyran, benzo-β-naphthospiropyran, xantho-β-naphthospiropyran, and the like.

■, Leuco auramines, N-acetyl auramine, N
-Phenyluramine etc.

■, rhodamine lactams 001. Rhodamine B-lactam etc.

The color developer is a compound that develops or changes color by reacting with the leuco dye, and suitable color developers include:
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-tertiary isobutylphenol), p-phenylphenol, 4.4
' -isopropylidene diphenol.

2.21-methylenebis(4-chlorophenol), hydroquinone, 2-oxy-1-naphthoic acid, 2-oxy-p-)ruylic acid, salicylic acid.

In addition to m-oxybenzoic acid, 4-oxyphthalic acid, phloroglucincarboxylic acid, gallic acid, propyl gallate, and phthalic acid, phenol, a compound having a phenolic hydroxyl group described in Japanese Patent Publication No. 52-30372 metal salts of compounds having a hydroxyl group, carboxylic acids and their metal salts, sulfonic acids and their metal salts, phosphoric acid esters, etc., as well as 1, 2.3) described in JP-A-57-76072. Examples include, but are not limited to, lyazole compounds i.

Furthermore, a desensitizer has the function of inhibiting the reaction between the leuco dye and the color developer to inhibit discoloration at temperatures outside of a predetermined temperature, and rapidly discoloring when the predetermined temperature is reached. Compounds that provide the sensitivity of (color erasure, one color development) are not particularly limited, but typical examples thereof are as follows.

■, alcohol ll,..., n-octyl alcohol,
n-nonyl alcohol, n-decyl alcohol, -l, n-
lauryl alcohol, n-myristyl alcohol, cetyl alcohol, n-stearyl alcohol, le-icosyl alcohol, n-tocosyl alcohol, oleyl alcohol, cyclohexanol, benzyl alcohol, and the like.

■, Esters 1) 0. 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 sepatate, etc.

■, Ketones 905. Cyclohexanone, acetophenone, benzophenone, dimethyl listil ketone, etc.

■, fatty acids 008. Caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, araxic acid, behenic acid, lignoceric acid, cerotic acid, partoleic acid, oleic acid, ricinoleic acid, lilunic acid, eleostearic acid , erucic acid etc.

■, acid amides 000. Capric acid amide, caprylic acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, benzamide, etc.

■, Hydrocarbons 100. Aliphatic hydrocarbons such as decane, dodecane, undecane; aromatic hydrocarbons such as naphthalene, anthracene, diphenylmethane; alicyclic hydrocarbons such as decalin, pinene, bicyclohexyl; carbonized commercially available as light oil and kerosene Water S cheek mixture.

The leuco dye, color developer, and desensitizer in the hydrophobic composition constituting the hydrophobic core substance are each contained in one type or in combination of two or more types, and the composition includes: A homogeneous mixed system is formed by melt-mixing.

The microcapsules of the present invention have an average particle size of 20 μm or less (preferably 10 μm or less), are uniform in particle size, and have capsule walls made 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 for long periods in a high temperature and humidity atmosphere or in an aqueous system. Since it maintains and exhibits reversible thermochromic performance and can reproduce clear, deep, and good color tones during color development, thermoreversible thermochromic inks or their compositions can be used as printing inks,
Its commercial value is extremely high, as it can be used in various applications requiring temperature-sensitive display by mixing paints, etc. and coating it on paper, fabric, etc., or by mixing the microcapsules of the present invention into synthetic resin molded products, etc. .

According to the present invention, the microcapsules having the above-described excellent features and the microcapsule slurry containing the same can be easily and industrially advantageously produced by the above-described production method.

The manufacturing method will be described in detail below.

At least one selected from polystyrene sulfonic acid and its salts in the present invention is used as an emulsifier for emulsifying the hydrophobic core material, the hydrophobic composition having thermoreversible color change performance, in water, and also as an emulsifier for emulsifying the hydrophobic composition having thermoreversible color change performance as the hydrophobic core material, and used as a promoter.

The salt of polystyrene sulfonic acid is one in which some or all of the acid groups of polystyrene sulfonic acid are neutralized, and the neutralizing base includes alkali metal hydroxides or carbonates, ammonia, organic amines, etc. An example is a base.

Polystyrene sulfonic acid and its salts have a molecular weight of about s,ooo to 2,000,000, preferably 10,000 to 1,500,000, and most preferably about 100,000 to 1,000,000.
The amount used is 0.00% based on the total amount of the hydrophobic composition.
It is 5 to 20% by weight, preferably 1 to 10% by weight.

If this amount is too small, the emulsification will become unstable and it will be difficult to carry out the polycondensation reaction uniformly around the hydrophobic composition. It becomes difficult to form a capsule wall consisting of

Furthermore, if the amount is too large, the viscosity of the reaction system may increase, making stirring difficult or producing capsules with non-uniform particle sizes.

At least one selected from polystyrene sulfonic acid and its salts 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 a polycondensation reaction (encapsulation). Forms and maintains a stable oil-in-water emulsilone until completion to smoothly promote the polycondensation reaction, and forms a dense and stable capsule wall made of a urea-formaldehyde polycondensate bound to a bisphenol compound. Another feature of the present invention is that uniformly fine microcapsules can be obtained.

At least one selected from polystyrene sulfonic acid and soya salt is dissolved in water, and then urea is added and dissolved while stirring, or the molten mixture of the hydrophobic composition (
When a hydrophobic composition (usually about 50 to 120°C) is gradually added to an aqueous system (at about 40 to 70°C) and emulsified, oil droplets of the hydrophobic composition with a particle size of about 1 to 10μ are dispersed in water. /W-type emulsion.

Note that urea may be added and dissolved in emulsilone after this emulsilone is generated, 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 desensitizing agent in the above-mentioned weight ratios, and melt-mixing them by heating to usually 50 to 120°C. This emulsilon can be adjusted to a pH of about 2.0 to 5.0 (preferably 2.4 to 4.0) by adding acid or alkali to it as needed.
), and then add therein an aqueous formaldehyde solution and a solution of the bisphenol compound in the desired order.
Alternatively, the polycondensation reaction between urea and formaldehyde is carried out by gradually adding them at about the same time, or by gradually adding an aqueous formaldehyde solution in which the bisphenol compound is dissolved. The most preferred method is to add 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, the polycondensation reaction is generally completed in a short time of 1 to 3 hours.

The required amount of formaldehyde is 1 mole of urea.
The amount is preferably within the range of 1 to 3 moles.

Further, the bisphenol compounds may be used alone or in combination of two or more.

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

If the amount of bisphenol compound used is too small, it will be difficult to form the dense, strong, and durable capsules mentioned above, and if it is too large, emulsification will become unstable and it will not be possible to form a uniform capsule around the hydrophobic composition. It may be difficult to carry out the polycondensation reaction.

The bisphenol compound is incorporated into the activated urea-formaldehyde polycondensation reaction system by polystyrene sulfonic acid coexisting and dissociated in the acidic aqueous phase.
Some of it is chemically bonded through copolycondensation, and some of it is physically bonded to the inside and outside of the resulting polycondensate as a solid solution, densely strengthening the capsule wall and significantly improving its durability. This is the most distinctive feature of the present invention.

However, in dihydric phenols and trihydric phenols such as resorcinol and pyrogallol, which have a phenolic nucleus with a phenolic hydroxyl group and a small molecular volume, as described below,
Moisture resistance, heat resistance, slurry storage stability, etc. cannot be improved.

Furthermore, if a small amount of dihydric phenol and its derivatives such as resorcinol, catechol, hydroquinone, and orcine, and trihydric phenol and its derivatives such as pyrogallol, phloroglycin, and gallic acid are used in combination with the above bisphenol compound, the durability will be further improved. Therefore, it can be used within a range that does not impede the effects of the present invention.

After the polycondensation reaction is substantially completed, the capsule is cooled to room temperature with stirring, and the hydrophobic composition as the core material is uniformly encapsulated by a dense and strong capsule wall with uniform particle size. It is obtained as a slurry in which durable microcapsules are dispersed.

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

Usually, the content of these components is 20 to 60% by weight of microcapsules, 0.5 to 5% by weight of at least one selected from polystyrene sulfonic acid and its salts, and 0% of formaldehyde, based on the total amount of microcapsule slurry. ．．
The amount of urea is 0.01 to 2% by weight, the amount of urea is 0.01 to 2% by weight, and the amount of bisphenol compound is 0.01 to 5% by weight.

(Example) Examples will be described below.

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

(1) Color development density Capsule slurry was silk screen printed on white Kent paper and dried naturally, and the chromaticity (LI*, aI*, bI*) of the resulting printed coating film was determined when it was developed and the color when it was erased. degrees (L2
"*a**, b1L*) is measured using a colorimeter.Then, the color difference Δ between the two is calculated using the following formula.
B (L* a* b*) was calculated L*: Lightness index B*, b*: Fromatilty roughness index related to hue and saturation (2) Moisture resistance The printing paper obtained in the above (1) was After leaving it in an atmosphere of 90% relative humidity at ℃ for 3 days, take it out and dry it.
As in item 1), the chromaticity L of the printed coating film during color development and decolorization
*, a*, b*t are measured, the color difference ΔE is determined, and then,
The ΔB (hereinafter referred to as ΔE2) determined above was compared with the ΔE (hereinafter referred to as ΔE1) determined in the above item (1) as a reference, and the retention rate of color difference was determined using the following formula.

Color difference retention rate (%): (ΔE2/ΔL) x 100 (
3) Heat resistance After leaving the printing paper of item (1) above in a constant temperature bath at 140°C for 20 minutes, take it out and determine the color difference ΔE (hereinafter referred to as ΔE3) of the printed coating film in the same manner. Comparison was made using ΔB+ determined in section 1) as a reference, and the retention rate of color difference was determined using the following formula.

Color difference retention rate (%): (ΔHz/ΔB,) x 100 (
4) Slurry storage stability After leaving the capsule slurry in a 50°C constant temperature bath for 7 days,
Take it out and print it on Kent paper in the same way as in item (1) above,
The chromaticity of the printed coating film obtained after air drying was measured, and the color difference Δ
E (hereinafter referred to as ΔE4) was determined, and then compared using ΔB1 determined in section (1) as a reference, the retention rate of color difference was determined using the following formula.

Color difference retention rate (%): (Δε number/ΔE1) x 100 (5)
Visual Judgment Criteria ■ Color density evaluation score Visual impression 5 Very dark color when developed 4 〃 Very dark color 3 〃 Light color 2 〃 Hardly any color 1 〃 No color appears ■ Water resistance, heat resistance Visual impression 5 No abnormality in color, very good 4 Almost no abnormality in color, good 3 Considerably bleached, poor 2 Mostly bleached, poor 1 Completely bleached, extremely poor Examples 1 (1) Production and performance of microcapsules To 97 g of water, 3 g of polystyrene sulfonic acid (molecular quantum: 500,000) and 6 g of urea are added and dissolved with stirring at 20° C. to form a solution (solution A).

45 parts of lauric acid, 25 parts of myristic acid, 30 parts of palmitic acid, 1.5 parts of 3-diethylamino-6-methyl-7-chlorofluoran (leuco dye>), and 3 parts of methyl paraoxybenzoate (color developer) to 80 parts Heat and melt at ℃ to make a solution (solution B).

2.2-propylidene-bisphenol (hereinafter abbreviated as PBP) 0 to 15.6 g of 37% formaldehyde aqueous solution
．． 9g was heated at 50°C to form a solution. (Liquid C) Next,
While maintaining Solution A at 50° C., 90 g of Solution B was added while stirring with a homomixer, and the mixture was stirred for 5 minutes to disperse and emulsify. The pH of the liquid was 2.0.
After adding 1 g of % aqueous sodium hydroxide solution to adjust the pH to 3.2, adding liquid C and stirring for 1 minute, a polycondensation reaction was carried out at 60° C. over a period of 3 hours.

Thereafter, the liquid was slowly cooled to obtain a microcapsule slurry.

The resulting microcapsule slurry was applied to white Kent paper and air-dried, and then the thermoreversible color change of the microcapsules in this coating was examined. As a result, when the temperature exceeds 30 degrees, the color changes from red to colorless, and when the temperature drops below 30 degrees, the color returns to red.
Its thermoreversible color change was extremely sharp. The color tone at the time of color development was a deep and vivid red.

Next, this microcapsule slurry was filtered and dried, and the resulting microcapsules had an average particle diameter of about 8 μm and were uniform in particle size. Further, as a result of performing the performance test of this microcapsule as described above, the measured color density was 5B, 1. Visual judgment is 5, the color is deep when developed, very good, water resistance constant value is 97%, visual judgment is 5, very good, heat resistance measurement value is 95%, visual judgment is 5, very good, slurry The measured value of storage stability was 92%, and the visual judgment was 5, which was extremely 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/cd was applied with a press machine to destroy the microcapsules. After that, the broken pieces were refluxed in cyclohexane for 3 hours to extract the hydrophobic core material. In order to separate the PBP in the broken capsule wall pieces remaining as a residue, the broken capsule wall pieces were further ground finely and then refluxed in chloroform for 3 hours and extracted.

When the chloroform extract was subjected to high performance liquid chromatography for quantitative analysis of PBP, approximately 3.5% PBP was detected based on the weight of the capsule wall. When this result is converted to the manufacturing scale of Example 1, Section (1), the total amount of PBP bound in the capsule wall of the microcapsules obtained in Section (1) is approximately 0.27 g. There was found.

Similarly, quantitative analysis of PBP remaining in the aqueous phase of the microcapsule slurry obtained in item (1) above was conducted, and the total amount was approximately 0.58 g. The amount of PBP (O, 27 g) and the amount of PBP in the aqueous phase (O
, 58g), the amount of PBP added during manufacturing is 0.
．． It was 0.85g, which is almost similar to 9g.

Comparative Example 1, (When PBP is not used as a capsule wall component) PB
The same procedure as in Example 1 was carried out, except that P was not used and only a 37% formaldehyde aqueous solution was used as liquid C.

The obtained microcapsules turned from red to colorless when the temperature exceeded 30°C, and returned to red when the temperature dropped below 30°C, but the thermoreversible color change property lacked sharpness.

In addition, as a result of the performance test of the microcapsules, the measured color density was 40.6, the visual judgment was 3, and the color was quite pale, and the measured water resistance was 60%, and the visual judgment was 2, which was mostly bleached and bad.
The measured value of heat resistance was 43%, and the visual evaluation was 1, indicating complete decolorization, which was extremely poor.The measured value of slurry storage stability was 67%, and the visual evaluation was 3, indicating that the slurry was considerably decolored. Thus, when PBP is not used as a capsule wall component, microcapsules are produced that have insufficient moisture resistance, slurry storage stability, and heat resistance.

Comparative Example 2 (When PBP is used as a color developer for the core substance and not used as a capsule wall component) PBP is used instead of methyl hydroxybenzoate as a color developer in liquid B, and PBP is used in liquid C. Other than using only 37% formaldehyde aqueous solution without using
The same procedure as in Example 1 was carried out.

As a result, the measured color density was 45.5, the visual judgment was 3, and the color was pale, and the measured value of moisture resistance was 74%, and the visual judgment was 2.
The measured value of heat resistance was 68% and the visual judgment was 3, which was poor, and the measured value of slurry storage stability was 71% and the visual judgment was 3.
The color tone after both water resistance tests was unclear and lacked depth.

In this way, even if PBP is used as a color developer in the core material, if PBP is not used as a capsule wall component,
Similar to Comparative Example 1, microcapsules with good water resistance and heat resistance such as humidity resistance and slurry storage stability 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 conducted except that the developer in Solution B and/or PBP in Solution C was replaced with the compound shown in Attached Table 1. The results are shown in the same table.

From the results in Attached Table 1, in liquid C (as a capsule wall component)
When using the above-mentioned compound of the present invention as a bisphenol compound, it is important to have high color density and excellent durability even when the color developer is changed (Examples 2 to 6), and the capsule wall component (C If the bisphenol compound of the present invention is not used in the liquid (in liquid), the color density will be low and the durability will be poor. It is clear that the color density is significantly increased synergistically and the storage stability of the slurry is further improved.

In addition, the microcapsules of Examples 2 and 3 have uniform particle size, are fine with an average particle size of about 2 to 7μ, and turn from red to colorless when the temperature exceeds 30°C, and turn back to red when the temperature drops below 30°C. Moreover, the thermoreversible color change property was extremely sharp, and the color tone when developed was clear and deep, which was desirable.

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

Comparative Example 8 The same procedure as in Example 1 was conducted except that PBP in liquid C (capsule wall component) was not used and resorcinol was used instead.

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

As is clear from the results of Comparative Example 7.8, even if the polycondensation reaction is performed in the presence of resorcinol in the capsule wall component (aqueous phase), microcapsules with high color density and good durability can be obtained. Can not.

Comparative Example 9 (Supplementary test of Production Example 6 of Japanese Patent Publication No. 51-44708) For comparison, Production Example 6 of Japanese Patent Publication No. 51-44708
(Column 10): “Coloring agent A is crystal violet lactone (leuco dye), bisphenol A (lli coloring agent), and cetyl alcohol (desensitizer) as described in column 8.
Microcapsules were produced by following the instructions in "Using a Chinese Name". As a result, the polycondensation reaction of the urea-formalin initial condensate did not proceed smoothly and took 5 hours, and the particle size was non-uniform, with an average particle diameter of 30μ, a color density of 40.5, and a moisture resistance of 21.8. % heat resistance was 25.1%, slurry storage stability was poor at 23%, the durability was also poor, and the thermoreversible color change property also lacked sharpness.

Example 7 The same procedure as in Example 1 was carried out except that 100 parts of cetyl alcohol was used instead of 100 parts of the higher fatty acid mixture in liquid B.

The particle size of the obtained microcapsules was uniform, with an average particle size of 8.
μ, color density is 56.5, moisture resistance measurement is 96%,
Heat resistance is 97%, slurry storage stability is 91%, good ÷
there were.

The thermoreversible color change property was also sharp; it became colorless when the temperature exceeded 48°C, and returned to red when the temperature dropped below 48°C.

Example 8 The same procedure as in Example 1 was carried out except that 100 parts of methyl stearate was used instead of 100 parts of the higher fatty acid mixture in liquid B.

The particle size of the obtained microcapsules was uniform, with an average particle size of 9.
μ, color density is 57.5, moisture resistance measurement is 95%
The heat resistance was 93%, and the slurry storage stability was 91%, which were good.

The thermoreversible color change property was also sharp; it became colorless when the temperature exceeded 30°C, and the color returned to red when the temperature dropped below 30°C.

Example 9 Instead of 100 parts of the higher fatty acid mixture in liquid B, 50 parts of stearic acid amide and 5 parts of lauryl alcohol
The same procedure as in Example 1 was carried out except that 0 part was used.

The particle size of the obtained microcapsules was uniform, with an average particle size of 7.
2 chromogenicity in μ is 55.6, moisture resistance measurement is 96%,
The heat resistance was 92%, and the slurry storage stability was 93%, which were good.

The thermoreversible color change property was also sharp; it became colorless when the temperature exceeded 23°C, and the color returned to red when the temperature dropped below 23°C.

Example 1O The same procedure as in Example 1 was carried out except that 100 parts of myristic acid was used instead of 100 parts of the higher fatty acid mixture in liquid B.

The particle size of the obtained microcapsules was uniform, with an average particle size of 4
μ, color density is 59.6, moisture resistance measurement is 97%,
The heat resistance was 96%, the slurry storage stability was 93%, and the durability was also excellent.

The thermoreversible color change property was sharp; it became colorless when the temperature exceeded 50°C, and the color returned to red when the temperature fell below 50°C, and when the color developed, it had a clear and deep good color tone.

Furthermore, similar to the microcapsule slurries obtained in Examples 1 to 9, the microcapsule slurry in which these microcapsules are dispersed can be stored for a long time (15 days) at a relatively high temperature (50°C). It has been confirmed that it is stable and has a relatively low viscosity of 100 to 500 cps, without increasing viscosity or changing viscosity (structural viscosity, thixotropy) like anionic polymer electrolyte aqueous solutions. It was also found that this unique and good effect was due to the interaction between the residual bisphenol compound coexisting in the microcapsule slurry and polystyrene sulfonic acid.

(Effects) The present invention has the following features: (1) At least one selected from polystyrene sulfonic acid and its salts is used as an emulsifier to emulsify and disperse fine oil droplets of a hydrophobic composition having thermoreversible discoloration performance in an aqueous phase. By carrying out a polycondensation reaction of urea and formaldehyde in the aqueous phase of Emulsilon in the presence of a bisphenol compound and at least one selected from the polystyrene sulfonic acid and its salts, the reaction occurs around the hydrophobic composition. The process proceeds quickly and smoothly, and the surface of the hydrophobic composition is easily encapsulated by a dense and strong capsule wall (urea-formaldehyde polycondensate bound to a bisphenol compound) to form microcapsules of uniform particle size. can be obtained.

(2) These microcapsules are stable even when stored for long periods of time in high-temperature, high-humidity environments or in aqueous systems, and have reversible thermochromic properties that are extremely sensitive to temperature changes. When the color develops, it develops into a good color tone with clear depth,
Applications that require aesthetics or temperature-sensitive display (printing inks, paints,
It is useful for fabric processing, etc.).

(3) The capsule slurry produced by dispersing microcapsules maintains a low viscosity, and even when stored under relatively high temperature conditions, viscosity change and capsule deterioration are unlikely to occur, and it is stable and has good coating properties. It is.

These useful and remarkable actions and effects are unique and cannot be seen in conventional thermoreversible color-changing microcapsules and methods for producing the same, and their industrial significance is extremely great.

Claims (8)

[Claims] (1) A hydrophobic composition in which the hydrophobic core substance has a thermoreversible color change property consisting of a leuco dye, a color developer, and a desensitizer,
A thermoreversible color-changing microcapsule characterized in that the capsule wall surrounding the microcapsule is formed of a urea-formaldehyde polycondensate to which a bisphenol compound is bonded. (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 bisphenol compound has the following general formula (1
) The thermoreversible color-changing microcapsule according to claim (1), which is at least one of the compounds shown in (1). General formula (1) B-A-B'・・・・・・・・・・・・(1) (In the above formula, A can be ▲ mathematical formula, chemical formula, table, etc. ▼ group, ▲ mathematical formula, chemical formula , tables, etc. ▼, ▲mathematical formulas, chemical formulas,
There are tables, etc. ▼ groups, -CH_2 groups, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ groups,
▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Groups, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Groups, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Groups, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Groups, ▲ Mathematical formulas , chemical formula, table, etc. ▼ group, B is ▲ mathematical formula, chemical formula, table, etc. ▼ group, R above is an alkyl group having 1 to 4 carbon atoms) (4) Oil-in-water in which a hydrophobic composition having thermoreversible color change properties consisting of a leuco dye, a color developer, and a desensitizer is emulsified and dispersed in water using at least one selected from polystyrene sulfonic acid and its salts as an emulsifier. By carrying out a polycondensation reaction of urea and formaldehyde in the presence of a bisphenol compound in the aqueous phase of the droplet type (O/W type) emulsion, the bisphenol compound is applied to the surface of the hydrophobic composition having thermoreversible color changing performance. A method for producing thermoreversibly color-changing microcapsules, which comprises forming a capsule wall made of a urea-formaldehyde polycondensate to which a compound is bonded. (5) The polycondensation reaction of urea and formaldehyde in the coexistence of the bisphenol compound with at least one selected from polystyrene sulfonic acid and its salts;
In the aqueous solution containing urea, leuco dye, color developer,
A hydrophobic composition having thermoreversible color changing properties consisting of a molten mixture of P and a desensitizer is added under stirring and emulsified.
H is adjusted to 2.0 to 5.0, and then an aqueous formaldehyde solution in which the bisphenol compound is dissolved is added to carry out a polycondensation reaction.
) The method for producing thermoreversibly color-changing microcapsules according to item 1. (6) The polycondensation reaction of urea and formaldehyde in the coexistence of the bisphenol compound causes a leuco dye, a color developer, and a color reducer to be added to an aqueous solution containing at least one selected from polystyrene sulfonic acid and a salt thereof. A hydrophobic composition having thermoreversible color change properties consisting of a molten mixture of a sensitizing agent is added under stirring to emulsify it, urea is added and dissolved, and the pH is adjusted to 2.0 to 5.0. The method for producing thermoreversibly color-changing microcapsules according to claim (4), wherein a polycondensation reaction is performed by adding an aqueous formaldehyde solution in which a bisphenol compound is dissolved. (7) Claims (4) to (6), wherein after forming the capsule wall on the surface of the hydrophobic substance, the formed microcapsules are separated and obtained from the slurry.
A method for producing thermoreversibly color-changing microcapsules as described in . (8) The bisphenol compound is used after being dissolved in the formaldehyde aqueous solution in an amount of 1 to 400% by weight based on the total weight of polystyrene sulfonic acid and/or its salt in the aqueous solution. No. (4th
) to (6).