JPS6365944A - Preparation of microcapsule - Google Patents

Abstract

PURPOSE:To enhance the holdability of a core substance, by forming a microcapsule by encapsulating the hydrophobic core substance by a melamine- formaldehyde polycondensation resin wall film in the presence of a vinyl toluenesulfonic acid type polymer. CONSTITUTION:A microcapsule is formed by encapsulating a hydrophobic core substance by a melamine-formaldehyde polycondensation resin wall film in the presence of an anionic polymer electrolyte being a vinyl toluenesulfonic acid type polymer. As the vinyl toluenesulfonic acid type polymer, polyvinyl toluenesulfonic acid is pref. and made water-soluble by converting a part or whole of the sulfone group thereof to a sodium salt however, one with MW of about 10,000-2,000,000 is pref. The resin wall film is formed of a hydrophobic melamine-formaldehyde resin initial condensate.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing microcapsules containing a hydrophobic core substance, and in particular a method for extremely easily manufacturing capsules that have excellent core substance retention properties. It is related to.

"Prior Art" In recent years, microencapsulation technology has made remarkable progress, and the fields of use of encapsulated products are extremely wide and diverse, including pressure-sensitive copying paper.

Various methods are known for producing microcapsules, such as coacervation, interfacial polymerization, and 1n-situ polymerization. Since gelatin is mainly used as the membrane material in the coacervation method, it is expensive, it is difficult to obtain a highly concentrated capsule liquid, and it is easily attacked by microorganisms.
It has disadvantages such as poor water resistance, and also has the disadvantage that the encapsulation process is complicated.

In addition, the interfacial polymerization method is a method in which a hydrophobic upper layer and a hydrophilic monomer are polymerized at the interface of a core material to form a wall film. Highly sexual,
Moreover, since a toxic substance is used, there are restrictions on handling, for example, a core material containing active hydrogen cannot be used.

Another disadvantage is that the materials are expensive.

The in-5-itu polymerization method includes a method in which a wall film is formed by polymerizing monomers from inside the core material, and a method in which a wall film is formed from the outside of the core material. In the former method, since isocyanate or the like is used as a hydrophobic polymer, there are restrictions on the use of a core material, similar to the interfacial polymerization method. On the other hand, in the latter method, amino resins such as urea-formaldehyde resins and melamine-formaldehyde resins are generally used as wall membrane materials.

Capsules whose wall material is melamine-formaldehyde resin have excellent hydrophobicity and solvent resistance, and many encapsulation methods have been proposed. JP-A-55-15660, JP-A-55-47139, regarding a method of depositing an initial condensate around a hydrophobic core substance,
JP-A-55-51431, JP-A-56-51238, JP-A-56-58536, JP-A-56-10062
No. 9, JP-A-56-121628, JP-A-57-10
No. 3891, JP-A-58-14942, JP-A-58-
112041, JP 59-177129, JP 60-28819, JP 60-190227, JP 61-25635, etc. have been proposed.

"Problems to be Solved by the Invention" However, despite the fact that many encapsulation methods have been developed and proposed, these methods are still subject to improvement because they have one of the following disadvantages: The need remains.

■ Agglomeration of capsule particles and increase in viscosity of capsule liquid are likely to occur during the reaction.

(2) In order to avoid the phenomenon (2), it is necessary to manufacture capsules at a low concentration and at a low temperature, which results in a long reaction time.

(2) It is difficult to obtain minute capsules because the emulsifying power of the emulsifier is insufficient, and when this is applied to pressure-sensitive copying paper, the copying paper becomes extremely smudged.

■ Due to the poor emulsification stability of the emulsifier, giant oil droplets are likely to occur, and when this is applied to pressure-sensitive copying paper, spot stains occur.

■ The deposition efficiency of the wall film material on the surface of the core material is poor, and the ability of the capsule to retain the core material is reduced.

In view of the current situation, the present inventors conducted intensive research on a method for manufacturing microcapsules having melamine-formaldehyde resin as a wall film, and found that melamine-formaldehyde resin is polycondensed in the presence of a specific anionic polymer electrolyte. The present inventors have discovered that, by doing so, the deposition of the polycondensation resin on the surface of the core material becomes extremely efficient, resulting in the formation of a capsule wall film with extremely excellent properties, and the present invention has been completed.

"Means for Solving the Problems" The present invention proposes that melamine-
A method for producing microcapsules in which a hydrophobic core material is covered with a formaldehyde polycondensation resin wall film, characterized in that a vinyltoluenesulfonic acid-based polymer is used as the anionic polymer electrolyte. .

"Function" As the vinyltoluenesulfonic acid polymer used in the method of the present invention, polyvinyltoluenesulfonic acid is preferably used, but examples include maleic anhydride, maleic ester, acrylic acid, acrylic ester, acrylamide, acrylonitrile, Methacrylic acid, methacrylic acid ester, methacrylamide, methacrylonitrile, ethylene, propylene, styrene, styrene sulfonic acid, α-methylstyrene, vinyltoluene, vinylsulfonic acid, 2-acrylamido-2methylpropanesulfonic acid, vinylpyrrolidone, etc. It may also be a copolymer with a monomer.

Vinyltoluenesulfonic acid-based polymers can be made water-soluble by converting some or all of the sulfonic groups into salts such as sodium salts, potassium salts, ammonium salts, etc., and can be dissolved in an aqueous medium, but sodium salts are particularly preferred. used. In addition, the molecular weight is 10,000 to 2,000,0
A polymer with a molecular weight of about 00 is preferable, more preferably a polymer with a molecular weight of about 200
, 000 to 1,000,000. Polymers with a molecular weight of less than 10,000 cannot provide sufficient emulsifying and dispersing power;
If it exceeds 000, handling of the polymer becomes difficult.

In the method of the present invention, such a vinyltoluenesulfonic acid-based polymer is contained in a hydrophilic medium for manufacturing capsules. 0.3% by weight
As mentioned above, it is more preferable to contain 1% by weight or more. The upper limit of the content is generally determined by the viscosity of the system, the capsule preparation device used, etc., but it is desirable to keep it below 20%.

In the method of the present invention, a melamine-formaldehyde polycondensation resin wall film is formed in a hydrophilic medium containing a vinyltoluenesulfonic acid polymer as described above, but such a resin wall film is generally made of hydrophilic melamine- Formed by formaldehyde resin initial condensate. In addition, methylated products of resin initial condensates, other amines, phenols, aldehydes, anions, cations,
Partially modified materials such as nonionic modifiers are also used.

Examples of amines include urea, thiourea, alkyl urea, ethylene urea, acetoguanamine, benzoguanamine, melamine, guanidine, dicinediamide, biuret, cyanamide, etc.; examples of phenols include phenol, cresol, xylenol, resorcinol, and hydroquinone. , pyrocatechol, pyrogallol, etc.;
Examples of aldehydes include formaldehyde, acetaldehyde, paraformaldehyde, hexamethylenetetramine, geltaraldehyde, glyoxal,
Furfural, etc.; Examples of anion modifiers include sulamic acid, sulanilic acid, glycolic acid, glycine, acidic sulfite, phenol sulfonate, taurine, etc.;
Examples of cationic modifiers include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminoethanol, and the like; further examples of nonionic modifiers include ethylene glycol, diethylene glycol, and the like.

As the hydrophilic melamine-formaldehyde resin initial condensate, various products such as those mentioned above can be used, but among them, the melamine-formaldehyde resin initial condensate and its methylated product are most preferably used because a dense film can be obtained. .

The blending amount of the hydrophilic melamine-formaldehyde resin initial condensate is adjusted as appropriate depending on the type of hydrophobic core material used, the use of the capsule, etc., but generally 100% of the hydrophobic core material is used.
The amount is 2 to 40 parts by weight, more preferably 6 to 20 parts by weight in terms of melamine.

In the capsule manufacturing system of the present invention, -a has a pH of 4 to 7.
The polycondensation reaction of the melamine-formaldehyde resin is carried out by adjusting the pH to a pH range of 5 to 6, preferably 5 to 6. At that time, in order to maintain the capsule manufacturing system acidic,
For example, so-called acid catalysts commonly used in the field of producing aminoaldehyde resins such as formic acid, acetic acid, citric acid, oxalic acid, para-toluenesulfonic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, ammonium chloride, ammonium sulfate, etc. are used.

The polycondensation reaction of melamine-formaldehyde resin is accelerated by heating the system, and as a result, capsules with stable quality are formed in a relatively short time. Preferably, it is desirable to heat to 80°C or higher.

In the method of the present invention, there is no need to overly carefully manipulate the capsule preparation conditions, and the polycondensation resin is efficiently deposited on the surface of the hydrophobic core material by simply mixing the capsule-forming materials and providing simple polycondensation conditions. , capsules having extremely excellent properties in terms of capsule quality such as core material retention can be easily formed.

The hydrophobic core substance contained in the capsule is not particularly limited, and includes, for example, animal oils such as fish oil and lard oil, vegetable oils such as olive oil, peanut oil, linseed oil, soybean oil, and castor oil, petroleum, kerosene, xylene, Mineral oils such as toluene, alkyl-substituted diphenylalkanes, alkyl-substituted naphthalenes, biphenylethanes, methyl salicylate,
Diethyl adipate, di-n-propyl adipate, di-n-butyl adipate, dimethyl phthalate, diethyl phthalate, di-n-propyl phthalate, di-n phthalate
- Synthetic oils such as butyl, di-n-octyl fuculate, etc. (liquids that are insoluble or substantially insoluble in water, and the synthetic oils that contain electron-donating color formers, electron-accepting color developers, and ligands) Solutions of compounds, organic metal salts, etc., water-insoluble metal oxides and EAR, fiber-like substances such as cellulose and asbestos, water-insoluble synthetic polymer substances, minerals, pigments, glasses, fragrances. Examples include flavoring agents, fungicidal compositions, physiological compositions, fertilizer compositions, flame retardants, temperature indicating materials, liquid crystals, toner materials, and the like.

"Example" In order to more specifically explain the method of the present invention, examples will be described below regarding the case where the method is applied to the field of pressure-sensitive copying paper, but of course the present invention is not limited thereto. Further, unless otherwise specified, parts and % in the examples represent parts by weight and % by weight, respectively.

Example 1 Partial sodium salt of polyvinyltoluenesulfonic acid (manufactured by National Starch and Chemical Co., Ltd., VERS
150 parts of a 3.3% aqueous solution of A-Tl6O00) was added to 20
The pH was adjusted to 4.5 with a % acetic acid solution to provide a hydrophilic medium for capsule production.

Separately, 4 parts of crystal violet lactone was added as a capsule core material to alkylnaphthalene (manufactured by Kureha Chemical Co., Ltd., K
MC-113) was heated and dissolved in 100 parts of MC-113), and this was emulsified and dispersed in the above-mentioned hydrophilic medium for capsule production so that the average particle size was 3.5 μm.

Next, a melamine-formaldehyde initial condensate aqueous solution prepared by heating and stirring 10 parts of melamine and 30 parts of a 37% formaldehyde aqueous solution at 60°C for 10 minutes was added to the above emulsion, and while stirring, a 20% aqueous sodium hydroxide solution was added. Adjust the pH of the system to 6.0, raise the liquid temperature to 90°C, and
Stirring was continued for hours to obtain a capsule dispersion.

Comparative Example 1 As a hydrophilic medium for capsule production, an ethylene-maleic anhydride copolymer (manufactured by Monsanto) adjusted to pH 4.5 with a 20% aqueous sodium hydroxide solution.

A capsule dispersion was obtained in the same manner as in Example 1, except that 150 parts of a 3.3% aqueous solution of EMA31) was used.

Comparative Example 2 A styrene-maleic anhydride copolymer (manufactured by Monsando) adjusted to pH 4.5 with a 20% aqueous sodium hydroxide solution was used as a hydrophilic medium for capsule production.

The encapsulation reaction was carried out in the same manner as in Example 1, except that 150 parts of a 3.3% aqueous solution of Suflipset 520) was used, but there was significant foaming during the reaction, making capsule preparation quite difficult.

Comparative Example 3 Partial sodium salt of polyvinylhenzenesulfonic acid (manufactured by National Starch and Chemical Co., Ltd., VERSA-Tl2) adjusted to H4,5 with 20% aqueous sodium hydroxide solution as a hydrophilic medium for capsule production.
A capsule dispersion was obtained in the same manner as in Example 1 except that 150 parts of a 3.3% aqueous solution of O3) was used, but the capsules were giant capsules having a particle size of 50 μm or more due to coalescence of oil droplets.

In order to test the performance of the four types of capsule dispersions thus obtained, the following comparative tests were conducted.

That is, 65 parts of aluminum hydroxide, 20 parts of zinc oxide, 3
, 5-di(α-methylbenzyl)salicylate zinc and α-
A dispersion obtained by grinding 15 parts of a mixed melt with methylstyrene-styrene copolymer (melt ratio 80/20), 5 parts of polyvinyl alcohol aqueous solution (solid content) and 300 parts of water in a ball mill for 24 hours, A developer coating solution prepared by adding 20 parts (solid content) of carboxy-modified styrene-butadiene copolymer latex was applied to 40 g/rd base paper to a dry weight of 5 g/rd.
A base paper for pressure-sensitive copying paper was prepared by applying the following coating to give the following properties.

The four types of capsule dispersions obtained in Examples and Comparative Examples were applied to the developer-coated surface of the obtained pressure-sensitive copying paper bottom paper, each with a dry weight of 5 g/n? Apply it so that it becomes 120
It was dried at ℃ for 30 seconds to prepare a comparative test paper.

The whiteness of the coated surface of the comparative test paper was measured according to JIS l'8123 and is listed in Table 1. Also, 6 at 120℃
The whiteness of the coated surface of the comparative test paper after heat treatment for 0 minutes was measured in the same manner and is listed in Table 1.

Table 1 "Effects" As is clear from the results in Table 1, the microcapsules obtained by the method of the present invention had extremely excellent core substance retention.

Claims (1)

[Claims] In a method for producing microcapsules in which a hydrophobic core substance is covered with a melamine-formaldehyde polycondensed resin wall film in the presence of an anionic polymer electrolyte, a vinyltoluenesulfonic acid-based polymer is used as the anionic polymer electrolyte. A method for producing microcapsules characterized by: