JPH02258053A - Preparation of single nucleus hydrated microcapsule - Google Patents

Abstract

PURPOSE:To permit an effective preparation of a single nucleus hydrated microcapsule by preparing a microcapsule enclosing an org. substance, after which this substance is removed therefrom and an aq. substance is filled in this membraned substance. CONSTITUTION:O/W emulsion is prepd. by suspending and dispersing an org. substance to be capsulized, in an aq. solvent such as low aliph. hydrocarbon, e.g. n-hexane, a radically polymerizable monomer and a radical polymn. initiator. This preparation is then subjected to radical polymn. to obtain a microcapsule enclosing the org. substance. This microcapsule is thereafter dried by heating to remove the org. substance through the polymer membrane. The subsequent suspension and dispersion thereof in an aq. solvent leads to an effective preparation of a single nucleus hydrated microcapsule enclosing an aq. substance and, due to its cool and heat reserving effect, this microcapsule affords an extensive application.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for effectively producing mononuclear water-containing microcapsules having water as a core material.

(Prior art and its problems) Conventionally, water-containing microcapsules with water as the core material have been used in heat exchangers and the like as a medium for storing cold heat by utilizing the latent heat of water (for example, Japanese Patent Publication No. 60-23279 Publication No.).

The method for producing this water-containing microcapsule includes, for example: (1) Forming a W10 emulsion, and performing interfacial polycondensation in this system to form a polymer film of polyamide or the like around the water droplets; (2) Forming a [W10]/W emulsion. (2) Form a W10 emulsion, use this emulsion system to perform coacervation in the organic phase, and form a polymeric film around the water droplets. There are known methods such as forming .

However, in the conventional method as described above, there is a problem in that it is difficult to obtain mononuclear microcapsules due to the fact that a polymeric film is formed around the water droplets.

That is, there is a tendency for a polymeric film to be continuously formed around a large number of water droplets to form multinuclear microcapsules, and as a result, such microcapsules have an unsatisfactory cold storage heat effect. There is.

(Means for Solving the Problems) The present invention employs a method of preparing microcapsules having an organic substance as the 8 substance X (core) in advance, and then replacing the core substance with an aqueous substance such as wood. As a result, we succeeded in effectively producing mononuclear water-containing microcapsules.

That is, according to the present invention, a step of preparing a microcapsule having a core material made of an organic substance permeable to a membrane material, a step of removing the core material, and a step of filling an aqueous substance into the membrane material. Provided is a method for producing mononuclear water-containing microcapsules, characterized by comprising the steps of:

(Function) The present invention provides that, in the case of microcapsules whose core material is an organic substance, mononuclear ones can be easily and effectively produced, and that the membrane material in such microcapsules usually has pores. It takes advantage of the permeability of the core material.

That is, according to the present invention, mononuclear microcapsules having an organic substance as a core material are manufactured in the first step.

Next, after completely removing the core material by thoroughly drying the mononuclear microcapsules, the remaining membrane material is removed by suspending the mononuclear microcapsules in water. is filled with water to produce mononuclear water-containing microcapsules.

(Preferred Embodiment of the Invention) Manufacturing of microcapsules having a substance as a core In the present invention, mononuclear microcapsules having an organic material as a core material can be produced by using an organic material that is permeable to the membrane material. Otherwise, this is carried out by methods known per se.

For example, any method can be employed, such as a method using interfacial polycondensation, a method using in 5 in situ polymerization, a method using coacervation, and the like.

Incidentally, the membrane material formed in this step is naturally water-insoluble.

An example of a case where in-5-itu polymerization is adopted will be explained below.

First, a radically polymerizable monomer, a radical polymerization initiator, and an organic substance serving as a core substance are suspended and dispersed in an aqueous medium.
/W form emulsion.

Radical polymerizable monomers are those that form water-insoluble polymer films, and include, for example, styrene monomers such as styrene and alkylstyrene, acrylic monomers such as acrylic acid and methacrylic acid esters, and vinyl acetate. Vinyl monomers such as these are used singly or in combination of two or more.

As the radical polymerization initiator, those that can be dissolved in the above-mentioned radically polymerizable monomers are used, such as organic peroxides such as lacryl peroxide and azo compounds such as azobisisobutyronitrile. Those known per se are used as appropriate depending on the type of vehicle body used.

The amount of the radical polymerization initiator used may be a so-called catalytic amount, and is generally 1.0 to 20 parts by weight per 100 parts by weight of the monomer.
It is used in proportions of 5 to 15 parts by weight, especially 5 to 15 parts by weight.

Furthermore, as the organic substance to be used as the core substance, one is used that is soluble in the monomer but insoluble in the formed polymer, easily permeates through the formed polymer film, and can be removed. .

As such an organic substance, lower aliphatic hydrocarbon solvents such as hexane are generally suitable, and these are usually used in an amount of 10 to 50 parts by weight, particularly 20 parts by weight, per 100 parts by weight of monomer.
It is preferably used in a proportion of 30 to 30 parts by weight.

Furthermore, in addition to the above-mentioned components, a crosslinking agent such as divinylbenzene may be added, for example, in order to impart strength to the formed polymer film. These crosslinking agents are generally used in an amount of 1 to 20 parts by weight per 100 parts by weight of the monomer.

Further, when suspending and dispersing these in an aqueous medium to form a 0/W emulsion, an organic or inorganic dispersion stabilizer is used.

Examples of organic dispersants include gelatin, starch, water-soluble starch conductors, water-soluble cellulose conductors such as carboxymethyl cellulose and etocel, water-soluble polymers such as polyvinyl alcohol, water-soluble acrylic resins, vinyl ether-maleic acid copolymers, etc. , anionic, nonionic, cationic or amphoteric surfactants.

Examples of the inorganic dispersant include poorly soluble inorganic fine particles such as various clays such as calcium carbonate, magnesium carbonate, magnesium phosphate, barium sulfate, silica, alumina, talc, and bentonite, diatomaceous clay, and the like.

These inorganic or organic dispersants can be used alone or in combination of two or more.

In the case of the present invention, if desired, although generally not necessary,
In addition to the above-mentioned dispersants, water-soluble salts such as NaCl, KCI, Na2SO4, etc. can also be used for the purpose of adjusting the specific gravity, surface tension, viscosity, etc. of the medium.

When forming a 0/W emulsion, the above-mentioned dispersion stabilizer may be mixed with other components and added to the aqueous medium, or only the dispersion stabilizer may be added in advance to the aqueous medium such as water. The above-mentioned components may be added to the mixed mixture.

In addition, the amount of dispersion stabilizer used, stirring conditions, etc. are adjusted as appropriate depending on the capsule diameter of the target microcapsules.
For example, in order to obtain small-diameter microcapsules, the amount of dispersion stabilizer used is relatively large and the stirring conditions are harsh so that an O/W emulsion with a small emulsion particle size is formed.

In addition, when trying to obtain microcapsules with relatively large diameters, contrary to the above, the amount of dispersion stabilizer used is relatively small and the stirring conditions are gentle, so that the emulsion particle size is What is necessary is to form a W emulsion.

After forming the O/W emulsion in this manner, radical polymerization is performed to obtain microcapsules having the above-mentioned organic substance as a core.

This radical polymerization may be carried out under conditions known per se, but it is preferably carried out at a temperature such that the organic substance serving as the core substance does not evaporate or escape.

After the polymerization reaction is completed, mononuclear microcapsules having an organic substance such as n-hexane as a core material are obtained by performing solid-liquid separation such as filtration.

In the method of the present invention, the core substance of the mononuclear microcapsules described above is replaced with an aqueous substance such as water.

This exchange operation is performed, for example, in the following steps.

First, the mononuclear microcapsules mentioned above are thoroughly dried by heating.

In this case, as mentioned above, pores are generally formed in the polymer membrane that forms the microcapsules, and as a result, lower hydrocarbons such as n-hexitine are volatilized by heating and drying. It is removed by passing through the polymer membrane.

Therefore, it will be understood that the organic substance that is the core substance is removed by heating and drying as described above.

This heat drying is carried out at a temperature above the boiling point of the organic substance serving as the core material, but particularly needs to be carried out at a temperature lower than the softening point or melting point of the polymer membrane constituting the membrane.

That is, if heat drying is performed at a temperature higher than the above range,
This causes fusion of the polymer membranes between the capsules, making it difficult to achieve the objective of the present invention, which is to produce mononuclear microcapsules.

After heating and drying has been carried out sufficiently to completely remove the organic substance of the core substance, by suspending and dispersing it in an aqueous medium, the aqueous substance such as water permeates through each polymer membrane, and the core substance is removed. Mononuclear water-containing microcapsules, which are aqueous substances, are obtained.

The above suspension dispersion is carried out to fill the aqueous substance into the polymer film, so there is no need to use a special dispersant or dispersion stabilizer such as a surfactant, and the aqueous substance is The amount of aqueous substance used and stirring should be such that sufficient pressure is applied to permeate the polymer membrane.

The water-containing microcapsules thus formed are subjected to a solid-liquid separation operation such as filtration, and then made into a final product.

In the present invention, the mononuclear water-containing microcapsules obtained as described above may be further subjected to membrane formation to obtain mononuclear water-containing microcapsules having a double membrane structure.

Such mononuclear water-containing microcapsules with a double membrane structure have an advantage of extremely high retention capacity for an aqueous core material.

The above-mentioned film formation can be easily performed, for example, by a per se known coacervation method.

That is, the obtained single-film mononuclear water-containing microcapsules are suspended and dispersed in an aqueous solution of a water-soluble polymer having film-forming ability. At this time, an inorganic dispersion stabilizer such as the above-mentioned calcium phosphate or an organic dispersion stabilizer such as a surfactant may be appropriately used.

A nonsolvent of the water-soluble polymer or another polymer aqueous solution or salt is added to this suspension dispersion to reduce the solubility of the water-soluble polymer, and the water-soluble polymer is coated on a single layer of microcapsules. form a film.

For example, to explain the case where gelatin is used as the water-soluble polymer, single-film water-containing microcapsules are suspended and dispersed in water, and an aqueous gelatin solution of an appropriate concentration and a dispersion stabilizer are added to this suspended dispersion. Add.

When a dilute acid aqueous solution is added to the system in which the single membrane water-containing microcapsules are suspended and dispersed to shift pt+ to the acidic side, gelatin is precipitated on the capsules.

In this case, gelatin will harden by adding formalin aqueous solution at a temperature below 20°C and then adding dilute alkali aqueous solution to shift the pH to the alkaline side, and then leaving the system in a heated state. , a hardened gelatin film is formed on the outermost layer, which is separated into solid and liquid and then washed.
It may be dried and used as a final product.

(Effects of the Invention) According to the present invention, mononuclear water-containing microcapsules can be effectively obtained.

The water-containing microcapsules obtained by the present invention have a sufficient cold storage effect due to their mononuclear nature, and can be effectively used as cold storage microcapsules in applications such as heat exchangers. .

Furthermore, by using a water-based ink as the core material, it can be used for applications such as pressure-sensitive copying paper.

The invention is illustrated by the following example.

(Example) Example】.

The organic phase contained 78.4 ml of hexane as a core material and 20.4 g (0.0 ml) of styrene monomer as a film-forming material.
, 2 mol), acrylonitrile 4.2 g (0.08 mol), divinylbenzene 1.3 g (0.01 mol), azobisdimethylvaleronitrile 1.95 g (7.8x
The above organic phase was added to 480 ml of a 2% by weight aqueous gum arabic solution as a continuous phase, and stirred with a homogenizer to prepare an O/w emulsion. Then, this emulsion was polymerized at 55° C. for 6 hours, and after the polymerization reaction was completed, the polymerization product was filtered to obtain mononuclear microcapsules having hexane as a core material.

Next, the microcapsules obtained above were dried at 70° C. until the core material, n-hexane, was completely volatilized.

When these microcapsules were suspended in water,
Water penetrated into the capsule through the pores of the polymer membrane, filling the microcapsule with water. Then, the microcapsules were taken out from the water through an oven and air-dried to obtain mononuclear water-containing microcapsules.

Example 2 Microcapsules filled with n-hexane were prepared in the same manner as in Example 1, and after filtration, they were sufficiently dried to obtain microcapsules from which n-hexane had been removed.

Next, after suspending and dispersing the microcapsules in water and filling the capsules with water, 30 g of a 3% by weight gelatin aqueous solution and 30g of a 3% by weight aqueous gum arabic solution were added to this dispersion, and an additional 10% Aqueous acetic acid solution was added dropwise to make the dispersion on the acidic side of pH 4 for 8 times, and then cooled to 5°C.

Then, 1 ml of formalin was added to the dispersion prepared in 8 rows on the acidic side, and then an aqueous sodium hydroxide solution was gradually added to make the system alkaline to pH 9. After that, the system was set at 50°C and left for 24 hours. A hardened gelatin film was formed on the outermost layer of the capsule. Microcapsules were taken out from the dispersion, washed and dried to obtain mononuclear water-containing microcapsules consisting of a double membrane. The obtained microcapsules had excellent water retention ability.

Claims (4)

[Claims] (1) Consisting of a step of preparing a microcapsule having a core material of an organic substance permeable to the membrane material, a step of removing the core material, and a step of filling the membrane material with an aqueous substance. A method for producing mononuclear water-containing microcapsules, characterized by: (2) The manufacturing method according to claim (1), wherein the core substance is a lower hydrocarbon that is normally liquid. (3) Claim (1) in which the core substance is removed by heating and drying.
) manufacturing method described. (4) Claim (1) wherein the filling of the aqueous substance is carried out by suspending and dispersing the membrane material from which the core substance has been removed in an aqueous medium.
) manufacturing method described.