JPS5815174B2 - Manufacturing method of microcapsules - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method for producing microcapsules, in particular a method in which a core material is used to encapsulate a substance that is water-insoluble in neutral or alkaline conditions but becomes water-soluble in acidic conditions. This paper relates to a method for producing microcapsules.

Conventionally, as a method for producing microcapsules containing a water-insoluble core material, a complex coacervation method as described in, for example, US Pat. No. 2,800,457 is well known.

In such a complex coacervation method, a water-insoluble core substance is emulsified and dispersed in an aqueous solution containing two types of hydrophilic colloid substances, such as gelatin and gum arabic, to form a system in which gelatin is made into a polycation and gum arabic, which is a polyanion, is emulsified and dispersed. In order to cause complex coacervation with rubber, the pH of the system is set to 3.0 to 4.
．． It is adjusted to an acidic region such as 5.

Then, the water-insoluble core substance is covered and encapsulated by the produced coacervate.

In this microencapsulation method, as mentioned above, the pH of the system is adjusted to an acidic range of 3.0 to 4.5, so a hydrophobic core substance or a neutral or Core substances that are water-insoluble in acidic conditions can be encapsulated, but core substances that are water-insoluble in neutral or alkaline conditions but become water-soluble in acidic conditions, or core substances that are unstable to acids, can be encapsulated. It has the disadvantage that it cannot be encapsulated.

In order to improve these drawbacks, a method has been proposed in which gelatin is coacervated in an alkaline region of pH 7 or higher by using a cationic surfactant such as dodecyltrimethylammonium or cetyltrimethylammonium (Japanese Patent Laid-Open No. 115083/1983). has been done.

However, improvements come with new drawbacks, and therefore satisfactory results have not always been obtained.

That is, surfactants have a strong tendency to make hydrophobic substances, which are capsule core substances, hydrophilic, and in particular, in the case of liquid hydrophobic substances, they form micelles and partially solubilize the hydrophobic substances in water.

Therefore, it is not possible to efficiently encapsulate all the hydrophobic substances, and the adverse effects of the hydrophobic substances left outside the capsule cannot be avoided.

Furthermore, the foaming properties of the capsule dispersion obtained due to the influence of the surfactant are increased, so that the operability in the capsule coating liquid preparation or coating process is significantly reduced.

In addition, a method (Japanese Patent Publication No. 48-4717) has been proposed in which coacervation is caused at a pH of approximately 8.0 using an initial condensate of gelatin and a self-polymerizable synthetic resin. Strict control of reactivity is required as it is significantly affected by the reactivity of the initial condensate of the synthetic resin.For example, if the reactivity is high, the properties of the coacervate will change significantly due to curing shrinkage, resulting in insufficient envelopment of the core material. This sometimes causes the wall membrane material to fall off from the capsule surface.

Furthermore, if the reactivity is low, the hardening of the capsule wall will be insufficient, and harsh conditions must be applied to the system for hardening, sometimes resulting in degeneration of the system.

Furthermore, in such a method, it is essential that the synthetic resin initial condensate essentially has curing ability under the capsule preparation conditions. The condensate also hardens and the generation of unnecessary capsule aggregates is unavoidable.

In view of the current situation, the present inventors conducted intensive research on the material of the wall material, the encapsulation process, etc. in the complex coacervation method using at least gelatin as the wall material, and as a result, they achieved the present invention.

The main purpose of the present invention is to improve the drawbacks of the prior art and to provide a core material that is water-insoluble in neutral or alkaline conditions but becomes water-soluble in an acidic region, or a core material that is unstable to acids. The object of the present invention is to provide a new method for producing microcapsules that can be completely and easily encapsulated without increasing the foamability of the system.

An object of the present invention is to use anionic gelatin and a cationic synthetic polymer electrolyte as hydrophilic colloid substances in a method for producing microcapsules containing a water-insoluble core material by a complex coacervation method, and to This is achieved by coacervation while maintaining the value of 7 or higher.

Examples of anionic gelatin used in the present invention include acid-treated gelatin with an isoelectric point of 9.2 or less, which is extracted with hot water after treating collagen with an inorganic acid for several days, or acid-treated gelatin obtained by coal-pickling treatment. Examples include alkali-treated gelatin whose isoelectric point is relatively lower than that of acid-treated gelatin, but acid-treated gelatin is preferably used because it has excellent retention of the core substance in the capsule wall membrane.

As the cationic synthetic polymer electrolyte used in combination with gelatin, at least one type of polymer electrolyte having an ammonium salt, sulfonium salt, or phosphonium salt as a functional group is preferably used.

Specifically, polyethyleneimine hydrochloride, poly(N-methyl-4-vinylpyridinium chloride)
, poly(2-methacryloyloxyethyltrimethylnanmonium chloride), poly(2-hydroxy-3-
(methacryloyloxypropyltrimethylammonium chloride), poly(N-acrylamidopropyl-3
-trimethylammonium chloride), poly(N.

Ammonium salts such as N-,; methyl-3,5-methylenepiperidium chloride), polyvinyltrimethylammonium chloride, polyallyltrimethylammonium chloride, polyvinylbenzyltrimethylammonium chloride, poly(2-acryloxyethyldimethylsulfonium chloride), etc. Sulfonium salt of poly(
Examples include phosphonium salts such as glycidyltributylphosphonium chloride).

Among these polymer electrolytes, those having an ammonium salt, particularly a quaternary ammonium salt as a functional group, are more preferably used.

Although the average molecular weight of these polymer electrolytes is not necessarily limited, it is generally in the range of 2,000 to 100,000, more preferably 3,000 to 50,000, considering the characteristics of the capsule wall formed. is used.

In the method of the present invention, it is preferable that anionic gelatin and cationic synthetic polymer electrolyte be used together in such a manner that the relative ratio of cationic synthetic polymer electrolyte to gelatin is in the range of 10 to 10%.

In the method of the present invention, the important points are not only the selection of the gelatin and cationic synthetic polyelectrolyte as hydrophilic colloid substances forming the capsule wall, but also the pH range that causes complex coacervation. It is.

As mentioned above, in the conventionally known general method, when complex coacervation is caused with various anionic colloid substances using gelatin, the pH range is 3.0.
The pH of the system was adjusted to an acidic range of 4.5 to 4.5, but in the present invention, coacervation is caused while maintaining the pH of the system at 7 or higher.

In particular, it is preferable to cause coacervation by adjusting the pH range to a range of 9.0 to 11.0 because microcapsules with excellent retention of the capsule core substance can be obtained.

As mentioned above, the method of the present invention has important features in that a specific material is selected as the hydrophilic colloid substance forming the capsule wall and coacervation occurs in a specific pH range, and the encapsulation step There are no particular limitations on this, and it is carried out according to the usual complex coacervation method.

For example, after emulsifying or dispersing the core substance in an aqueous solution of gelatin that is kept at a temperature above the gelatin point and whose pH is in the alkaline range, an aqueous solution of a cationic synthetic polymer electrolyte is added to this system and stirred. Coacervation is caused and coacervate is fixed around the core substance.

Next, the coacervate is cooled to below the gelling point of gelatin to gel, and then hardened with a suitable hardening agent such as formaldehyde, glyoxal, geltaraldehyde, etc. to obtain microcapsules.

As the core substance contained in the capsule, any commonly used oily substances, solid substances, etc. that are substantially water-insoluble and dispersible in water can be used.

In particular, according to the method of the present invention, core substances that are water-insoluble in neutral to alkaline conditions but water-soluble in acidic conditions, or core substances that are unstable to acids, such as N, N-
4,4' which is an intermediate for basic substances such as amines such as dimethylaniline, α-methylbenzyldimethylamine, and 2-undecylimidazole, or basic dyes;

4"-trisaminotriphenylcarbisol, 4
．． 4'-bis-dimethyl-triphenylcarbinol,
4.4',4"-tris-dimethylamino-triphenylcarbinol, 4-dimethylamine-4',4"-bis-ethylbenzylamino-triphenylcarbinol, 4.4',4"-tris- α-Naphthylamino-triphenylcarbinol, 4°4', 4"-trianilino-3-methyl-triphenylcarbinol, 4.4',
Carbinol dyes such as 4"-tris-diphenylamine-triphenylcarbinol can be easily encapsulated without any problems either directly or by dissolving them in a water-insoluble oily substance.

Carbinol dyes include, for example, crystal violet lactone, benzoylleucomethylene blue, malachite green lactone, rhodamine-B-lactam, 3-dialkylamino-7-dialkylaminofluoran, and other bases commonly used in pressure-sensitive copying paper and thermal copying paper. Carbinol dyes have long been considered for application in this field because they are inexpensive compared to colorless dyes and have excellent water resistance and moisture resistance of colored images, but carbinol dyes are very weak acids and cannot be colored. Because of this, microcapsules cannot be created using normal methods, and in fact, application to such fields has been impossible.

However, according to the method of the present invention, the carbinol dye can be encapsulated without changing the pH of the system to an acidic range, and therefore, it is possible to apply such carbinol dyes to pressure-sensitive copying paper and the like very effectively.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples.

In addition, unless otherwise specified, "part" and "%" in the examples
indicate "parts by weight" and "% by weight", respectively.

Example 1 200 parts of a 5% aqueous solution of acid-treated gelatin having an isoelectric point of 8.0 and a gel point of 21°C, whose pH was adjusted to 9.5 with a 5% aqueous solution of NaOH, was added while maintaining the system temperature at 55°C. While 4.4
60 parts of a 2% isopropylnaphthalene solution of ',4''-tris-dimethylamine-triphenylcarbinol was added and emulsified using a homomixer so that the average particle size of emulsified oil droplets was 8 μm.

Poly(N-methyl-4
-vinylpyridinium chloride) [Merck PC-
Add 100 parts of a 1% aqueous solution of
00 parts was added to deposit coacervate around the emulsified oil droplets.

After cooling the system temperature to 10℃ while continuing stirring,
% formaldehyde aqueous solution was added dropwise to harden the capsule wall film to obtain a microcapsule dispersion.

The resulting dispersion was aged for 7 hours, but the system was hardly colored and almost no bubbles were observed.

In order to confirm the degree of coloring of the obtained dispersion, the absorbance of the dispersion at 450 mμ was measured using a spectrophotometer, and the results are listed in Table 1.

Example 2 In Example 1, poly(2-methacryloyloxy-ethyl-
A microcapsule dispersion was obtained in the same manner as in Example 1, except that trimethylammonium chloride (ET-68, manufactured by Dainippon Shikizai Kogyo Co., Ltd.) was used.

The resulting dispersion was aged in the same manner as in Example 1, but the system was hardly colored and almost no bubbles were observed.

Example 3 The same procedure as in Example 1 was carried out except that polyvinylbenzyltrimethylammonium chloride (ECR-34 manufactured by Dow Chemical Company) was used instead of poly(N-methyl-4-vinylpyridinium chloride) as the cationic synthetic polymer electrolyte. A microcapsule dispersion was obtained in the same manner as in Example 1.

The resulting dispersion was aged in the same manner as in Example 1, but the system was hardly colored and no bubbles were observed.

Example 4 In Example 1, acid-treated gelatin with an isoelectric point of 9.0 and a gelation temperature of 25° C. was used as the gelatin, and 4,4′,4″-tridiphenylamino-triphenylcarbinol was used as the colorless dye. A microcapsule dispersion liquid was obtained in the same manner as in Example 1 except that .

The resulting dispersion was aged in the same manner as in Example 1, but the system was hardly colored and no bubbles were observed.

Comparative Example 1 200 parts of a 5% aqueous solution of acid-treated gelatin having an isoelectric point of 8.0 and a gelation point of 21°C was added with 4.
．． Add 60 parts of a 2% solution of 4',4''-tris-dimethylamino-triphenylcarbinol in isopropylnaphthalene, and mix with a homomixer until the average particle size of emulsified oil droplets is 8μ.
It was emulsified to become

Add 10% of gum arabic to this emulsion while continuing to stir.
100 parts of aqueous solution and 100 parts of dilution water were added.

The pH of the system was then adjusted to 4.2 with a 15% aqueous acetic acid solution to deposit coacervate around the emulsified oil droplets.

After cooling the system temperature to 10℃ while continuing stirring,
% formaldehyde aqueous solution was added dropwise, and an additional 5%
The pH of the system was adjusted to 10.0 with an aqueous NaOH solution to harden the capsule wall film to obtain a microcapsule dispersion, and the resulting dispersion was further aged for 7 hours.

In addition, when the pH of the system was adjusted to 4.2 in the encapsulation step, the carbinol dye dissolved in the oil droplets was dissolved in the water, and the entire system was colored purple.

The degree of coloring at this point was measured using a spectrophotometer in the same manner as in Example 1 and is listed in Table 1.

The coloring of this remarkable system became lighter when the pH was adjusted to 10.0, and became pale yellow after ripening, but the carbinol dye in the oil droplets was dissolved in the water during coloring, so it remained in the microcapsules. contained almost no carbinol dye, and the resulting capsules were unsuitable for their original purpose and could not be used for applications such as pressure-sensitive copying paper.

Comparative Example 2 While maintaining the system temperature at 55°C, 4.4',4"-tris-dimethylamino- 2% isopropylnaphthalene solution of triphenyl carbinol 6
0 part was added and emulsified using a homomixer so that the average particle size of emulsified oil droplets was 8 μm.

100 parts of a 10% aqueous solution of cetyltrimethylammonium bromide was added to this emulsion while stirring,
The pH of the system was adjusted to 12 by dropwise addition of 5% NaOH aqueous solution to deposit coacervate around the oil droplets.

After cooling the system temperature to 10°C while continuing stirring, 1
14 parts of a 0% formaldehyde aqueous solution was dropped to harden the capsule wall film to obtain a microcapsule dispersion, and the dispersion was further aged for 7 hours.

Although the system was not colored during the encapsulation process, the entire system foamed significantly from the time cetyltrimethylammonium bromide was added, and after cooling it became ice cream-like, making it extremely difficult to apply as a capsule dispersion. Only a dispersion was obtained.

Furthermore, the surface pH of the paper used as the base paper for pressure-sensitive copying paper is
When the obtained capsule dispersion was applied to the high-quality paper of 4 and 5, the capsule-coated paper was uniformly coated because the oil droplets that had been solubilized in water by trimethylammonium bromide remained in the system without being encapsulated. It was colored and could not be used as pressure-sensitive copying paper.

The degree of coloring of the capsule-coated paper was measured using a reflection type absorptiophotometer at 450 mμ and found to be 0.68.

Claims (1)

[Scope of Claims] 1. A method for producing microcapsules containing a water-insoluble core substance by a complex coacervation method, using anionic gelatin and a cationic synthetic polymer electrolyte as hydrophilic colloid substances, and pH to 7
A method for producing microcapsules characterized by coacervation while maintaining the above. 2. The microcapsule according to claim 1, wherein the cationic synthetic polymer electrolyte is at least one selected from ammonium salts, sulfonium salts, and polymer electrolytes having phosphonium salts as a functional group. Manufacturing method. 3. The method for producing microcapsules according to claim 2, wherein the cationic synthetic polymer electrolyte is a polymer electrolyte having a quaternary ammonium salt as a functional group. 4. The method for producing microcapsules according to claim 1, wherein coacervation is caused in a pH range of 9.0 to 11.0. 5. The method for producing microcapsules according to claim 1, wherein the water-insoluble core substance contains a carbisol dye.